Cobalt and Nickel-Based Organometallic Chemistry of the [N]Phenylenes

by

Robin Padilla

A dissertation submitted in partial satisfaction of the

requirements for the degree of

Doctor of Philosophy

in

Chemistry

in the

Graduate Division

of the

University of California Berkeley

Committee in Charge

Professor K Peter C Vollhardt Chair Professor Jonathan A Ellman

Professor Yuri Suzuki

Spring 2010

Cobalt and Nickel-Based Organometallic Chemistry of the [N]Phenylenes

copy 2010

by Robin Padilla

- 1 -

Abstract

Cobalt and Nickel-Based Organometallic Chemistry of the [N]Phenylenes

by

Robin Padilla

Doctor of Philosophy in Chemistry

University of California Berkeley

Professor K Peter C Vollhardt Chair

This dissertation explores the synthesis and study of linear [N]phenylene cobalt complexes and the reactions of angular [N]phenylenes with nickel catalysts Chapter 1 contains a general introduction to the properties of the [N]phenylenes as well as a brief overview of earlier organometallic [N]phenylene chemistry with an emphasis on work directly related to that presented in the subsequent chapters Chapter 2 presents studies regarding first ever examples of photo-induced thermally reversible haptotropic shifts in linear [3]phenylene cyclopentadienyl cobalt (CpCo) complexes In these reactions the CpCo fragment migrates from one cyclobutadiene ring to another upon exposure to UV irradiation Heating the photoisomer complexes causes the metal fragment to return to its original position Aside from the novelty of an η4η4 cyclobutadiene migration the photo-induced thermally reversible nature of these systems makes them attractive as candidates for photostorage devices andor molecular switches The syntheses and structural studies of the linear phenylene(CpCo) complexes are discussed In addition to the experimental work computational studies on the haptotropic shift are also included Closely related work such as the observation of an intermediate haptotropic species at low temperature and the preparation of a linear [3]phenylene complex containing two CpCo units bound to the ligand is also discussed Chapter 3 describes nickel-catalyzed insertion reactions with angular phenylenes as a method for preparing derivatives of [N]phenacenes a class of polycyclic aromatic hydrocarbons that are of interest in organic electronic applications Previous work regarding nickel insertion reactions with biphenylene is mentioned Nickel-catalyzed insertion reactions with angular [3]- and [4]phenylene are then described Mechanistic studies both experimental and computational are discussed The results from these studies were used to optimize the reaction to produce [N]phenacenes as the major products of these insertion reactions Chapter 4 contains experimental details relating to chapters two and three General experimental considerations synthetic procedures crystallographic and computation data are presented Relevant references are also included in this chapter

i

Table of Contents

CHAPTER ONE PROPERTIES OF THE [N]PHENYLENES AND THEIR ORGANOMETALLIC CHEMISTRY 1

11)General Discussion of [N]Phenylene Properties 1 12)Overview of Phenylene Organometallic Chemistry 6 13)Direction of Work 10

CHAPTER TWO PHOTOndashTHERMAL HAPTOTROPISM IN CYCLOPENTADIENYLCOBALT COMPLEXES OF LINEAR PHENYLENES INTERCYCLOBUTADIENE METAL MIGRATION 12

21)Introduction 12 22)Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes 16 23)Structural Studies on the Linear [3]Phenylene(CpCo) Complexes 22 24)Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift 30 25)Low Temperature Photolytic Studies on the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes 41 26)Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 56 27)Summary and Outlook 62

CHAPTER THREE NICKEL-CATALYZED INSERTION REACTIONS FOR THE PREPARATION OF [N]PHENACENE DERIVATIVES 63

31)Introduction 63 32)Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene 67 33)Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene 75 34)Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions 81 35)Summary and Outlook 87

CHAPTER FOUR EXPERIMENTAL AND COMPUTATIONAL DETAILS 88

41)General Considerations 88 42)Experimental Section for Chapter Two 88 43)Computational Details for Chapter Two 129 44)NMR Data for Chapter Two 154 45)Experimental Information for Chapter Three 162 46)Computational Details for Chapter Three 168 47)References 169

ii

Acknowledgements

ldquoWhere would I find leather enough to cover the surface of the earth The Earth is covered over merely with the leather of my sandalsrdquo

-Shāntideva in the Bodhicaryāvatārah Ch 4 v13 Five years ago I arrived in Berkeley with a rather clear objective get (or rather survive) a PhD Though the goal never changed the all paths (scientific personal professional and spiritual) I traversed were often quite unlike anything I could have anticipated I have had the great fortune to stand on the shoulders of many giants during these past few years and it is to them that I owe my deepest gratitude First and foremost I would like to thank my advisor Peter Vollhardt for all of his support and patience The things I have learned from him are far too numerous to list but certainly the two most important are clarity and rigor two qualities that extend far beyond the chemical realm Working with so many different people was another interesting challenging and ultimately highly rewarding experience I am particularly indebted to ldquoThe Old Gangrdquo consisting in part of Phil Leonard and Ken Windler These two gentlemanly pyromaniacal firearms enthusiasts aside from showing me the ins and outs when I was a new arrival (and teaching me more than I will ever need to know about guns and explosives) soon became good and close friends No mention of The Gang would be complete without Jordan Rose Figura Despite being a chemical biologist and not actually a member of the Vollhardt Group she nonetheless (somehow) managed to fit in perfectly My life has been forever changed by her introducing me to ldquoDoctor Whordquo Many others also deserve special mention Sabine Amslinger has and will continue to provide a near endless amount of legendary stories that often border on mythological Tom Gadek was just plain awesome Vince Gandon aside from being one the best experimentalists Irsquove seen also happened to have a rather fine taste in films and music Dominik Hager excelled at getting me out of the lab for an occasional weekend of fun The elegant and refined chocolate cakes of Aude Hubaud were a rare yet very welcome occurrence Her sassy chic comments on all aspects of life however were quite copious Greg Boursalian performed an excellent job of filling the ldquocool undergradrdquo spot and I wish him the best for his own graduate school journey Steve Meier managed the Herculean task of (legally) disposing of all those old empty gas cylinders It is my great hope that Prof Sgt Meier will share many (but certainly not all) of his Berkeley experiences with the next generation of chemists that he will educate Explaining the strange and quirky aspects of American culture and the English language to Kerstin Weiszlig made for a fair number of humorous conversations Learning the stranger and quirkier aspects of German language and culture made for many more Similarly much time was spent meticulously examining the lyrics and slang expressions of assorted hip-hop songs with Sander Oldenhof Practicing kindergarten level German while sharing a fairly constant supply of Ritter Sport bars with Verena Engelhardt was another fine example of cultural exchange Despite his best efforts Kasper Moth-Poulsen has yet to convince me that Volvo is the greatest vehicle manufacturer in the known universe My cultural exposure was not limited to European interactions however and I managed to learn a little Chinese as well Apparently ldquoHao Shenrdquo

iii

means ldquoMacGyverrdquo in Mandarin I would also like to thank the rest of my co-workers past and present for all of their support They are in rough chronological order Thomas Carl Miles Carter Kaspar Schaumlrer Ingo Janser Romy Michiels Elisa Paredes Thilo Heckrodt Nicholas Cheron Alex Lee Anais Geny Samer Al-Gharabli Nicole Franssen Vladislav Kulikov Alexandra Romek Isaac Ho Zhenhua Gu Florian Montermini Nikolai Vinokurov Robert Zitterbart and Cedric Ghellamallah Bonnie Kirk skillfully handled the various arcane administrative procedures but also provided many interesting and memorable early morning conversations The finer points of NMR spectroscopy were taught to me by the indomitable Rudi Nunlist His wry humor and outlook on life were often the perfect supplement to the rigors of graduate school life Working with Chris Canlas Rudirsquos able successor has also been a pleasure I was encouraged when he was so quick to remind me that I have the same name as a bad-boy Filipino action-movie star Teaching while always quite time consuming proved to be an invaluable experience Teaching under the direction of Peter the man who wrote the book on organic chemistry was quite an adventure His passion and talent for teaching are immediately obvious and inspiring even without flipping through the Basque translation of his textbook Jon Ellmanrsquos ability to write exams that are easy to grade but difficult for students to take is similarly awe inspiring There is no doubt in my mind that Heino Nitsche has taken teaching of general chemistry to new levels of eccentricity and excitement Jean Freacutechetrsquos impressive aptitude for lecturing is perhaps surpassed only by the impressiveness of his wine collection Looking down the academic chain I have to acknowledge many of the brilliant and wonderful students that made teaching such a fantastic experience Special thanks goes to Steve Seyedin Nellie Ekmejian Jessie Zhang Yao Yue Ashley Johnson Brent Jellen Zarina Khan and Mojgan Rastegar all of whom were extraordinary students that I hope will do their part to save the world No acknowledgement could be complete without recognizing the love and support of my family in particular my mother Her love though always tough was always there My various housemates also provided me with some great times Chris Trinh my first housemate in Berkeley was a superb fellow to live with and I will always fondly remember our conversations on life love and quantum gravity Cory McLitus when he wasnrsquot slaving away in the architecture studio also became a good friend I feel no need to apologize for getting him hopelessly addicted to ldquoThe Big Bang Theoryrdquo The awesome Samra Kasim was always ready for chai good food and hearty discussions on Bollywood and all things South Asian The housemates of 1505 Oxford St are also great people Though we rarely cross paths Vicky Zhuangrsquos highly entertaining biology lab adventures are much appreciated Vannamaria Kalafonos always has something wonderful going on in the kitchen and I aspire to learn the Greek specialty of cooking for a zillion people from her The cats Pink Tuffy and especially Floyd are nice companions even though they sleep a combined 60 hours per day Many kalyānamitras helped me get through the toughest times and to them I am especially grateful A large number of my Saturday evenings were spent in the calm environs of the Berkeley Monastery where Rev Heng Surersquos Avataṃsaka Sūtra

iv

lectures gave me much to think about The monthly lectures by Ajahn Amaro Ajahn Passano and the Abhayagiri Sangha were also a wonderful learning experience Chats about long-dead ancient languages and obscure texts with Sean Kerr a fellow survivor of Dagmar Theisonrsquos German class will also be fondly remembered The NY Sangha though far away always supported me and welcomed me warmly whenever I returned home Frank Yao Hai-Dee Lee Sheila Sussman Fred Ng Martin Applebaum Josephine Verceles Tiffany Taulton Phung Tran and especially Aaron Vederman repeatedly reminded me to ldquosmile breath deep and go slowlyrdquo The many visits to Bodhi Monastery were always the high points of my summers Michael Roehm Bhikkhu Bodhi Jane Berry Henry and Lily Teoh Marcie Barth Mahendra Sagar the dearly departed Felicia Miller Ven Guo Jun Susan Chastain and the polygot Bhikkhu Analayo made every visit an unforgettable experience and never failed to remind me why I get out of bed in the morning

- 1 -

Chapter One

Properties of the [N]Phenylenes and Their Organometallic Chemistry

11 General Discussion of [N]Phenylene Properties Polycyclic aromatic hydrocarbons (PAHs) are a class of molecules that have occupied the minds of chemists for generations1 Their essential feature aromaticity is the unusual stabilization that arises from having a 4n+2 number of π-electrons in a cyclical array This seemingly simple definition obscures the fact that aromaticity continues to be one of the most scrutinized topics in modern organic chemistry2 and more rigorous definitions3 have remained elusive Much of the early work4 with PAHs was aimed at investigating theoretical issues surrounding aromaticity There has been renewed interest in these systems in recent years because they are increasingly attractive as functional materials in organic-based electronics5 Of the many different kinds of PAHs known eg 1ndash6 (Figure 11) one subclass is of particular interest the [N]phenylenes6

Anthracene Coronene Phenanthrene

Chrysene Triphenylene Pyrene

1 2 3

4 5 6

Figure 11 Some examples of polycyclic aromatic hydrocarbons The [N]phenylenes (where N = the number of benzene rings) are PAHs in which benzene and cyclobutadiene rings are fused in an alternating manner The cyclobutadiene ring imparts very unusual structural and electronic properties as seen in the simplest molecule in the series biphenylene (7) It can be described by several resonance forms (Figure 12 andashe) in which the major contributor 7c avoids formation of the highly destabilizing antiaromatic cyclobutadiene (7a 7e) and benzocyclobutadiene circuit (7b 7d) This preference is manifest in the significant bond alternation7 seen in

- 2 -

the crystal structure of biphenylene (Figure 12) which shows a clear difference in bond lengths between the formal single bonds (~143 Aring) and the shorter formal double bonds (~137 Aring)

1423

1372

Figure 12 Biphenylene bond lengths (top Aring) and resonance contributors (bottom)

An extreme example of [N]phenylene π-bond localization is triangular [4]phenylene (8) (Scheme 11) in which the three-fold peripheral fusion imparts complete cyclohexatriene character on the central ring89a This property is reflected in the reactivity of the system eg catalytic hydrogenation (9)8b epoxidation (10)8c and cyclopropanation (11)8c Scheme 11 Reactions Illustrating the Fully Bond Localized Character of the Central Benzene

Ring in Triangular [4]Phenylene 8 Bond lengths are in Aring

- 3 -

Phenylenes exhibit another interesting structural feature in contrast to other PAHs sizable deviations from planarity (Figure 13)9ab The flexibility of the phenylene framework arises from the combined effect of π- and σ-strain9ab By adopting a nonplanar geometry overlap between the π-orbitals is diminished and in turn leads to a decrease in destabilizing antiaromatic character Pyramidalization of the four-membered ring carbons also reduces σ-strain9ab a phenomenon observed in highly strained alkene systems9c

Figure 13 Crystal structures showing deviations from planarity in (a) helical [6]phenylene (12)10 (b) dimethyl triangular [4]phenylene-23-dicarboxylate (13)9a and (c) 23-bis(tri-

methylsilyl) linear [3]phenylene (14)9a

The fusion of aromatic benzene rings with antiaromatic cyclobutadiene units in the same molecule has prompted numerous experimental and theoretical discussions6 regarding the magnetic and electronic properties of the phenylenes 1H-NMR spectroscopy is one typical measure of aromaticity Protons on the exterior of aromatic rings (eg 15) show relatively low field resonances while their interior counterparts resonate at relatively high field due to the presence of a diamagnetic ring current Conversely antiaromatic rings with 4n π-electrons are paratropic and reveal the opposite disposition of the two respective types of protons (eg 16) The interplay between aromatic and antiaromatic character in the phenylenes is evident in their chemical shifts which tend to show weakly aromatic resonances (Figure 15) relative to benzene (736 ppm)

(a) (b) (c)

12 13 14

- 4 -

Figure 14 Observed 1H-NMR resonances in (a) the aromatic [18]annulene (15)11 and (b) the antiaromatic 5-bromo-19-bisdehydro-[12]annulene (16)12

Aside from NMR spectroscopy nucleus independent chemical shift (NICS)13 calculations have also proven to be useful measures of aromaticity The NICS technique works by calculating the magnetic shielding of a ldquoghost nucleusrdquo that can be positioned anywhere around a molecule For probing aromaticity the calculated point is in the center of the π-electron circuit to be examined Calculations placing the ghost nucleus 1 Aring above the plane of the molecule are often used to minimize local anisotropy and are referred to as NICS(1)14 NICS data are given in ppm and are thus comparable to experimental 1H-NMR measurements Negative NICS values indicate aromatic character while positive values suggest antiaromatic character For example the NICS(1) of benzene15 is ndash125 ppm whereas for cyclobutadiene15 it is 151 ppm NICS calculations for various phenylenes have been carried out6 and are shown in Figure 15 alongside the experimentally measured 1H-NMR chemical shifts The attenuated aromatic character of the benzene and the relatively weak antiaromatic character of the cyclobutadiene rings in phenylenes such as biphenylene (7) triangular [4]phenylene (8) and angular [4]phenylene (17) are apparent from both sets of data

Figure 15 1H-NMR (blue) and NICS(1) (green) data for selected phenylene topologies (ppm)6

The phenylenes possess multiple modes of reactivity7 as illustrated by biphenylene (7) in Scheme 12 It can undergo electrophilic aromatic substitution like other PAHs but does so selectively at the 2-position to avoid the formation of intermediates with antiaromatic character Biphenylene does not readily undergo Diels-

- 5 -

Alder reactions but was shown to react with electron-deficient benzynes to give the corresponding cycloadducts16 Opening of the highly strained four-membered ring is another prominent aspect of phenylene reactivity

Scheme 12 Illustrative Reaction Pathways of Biphenylene6

Early work17 showed that it was possible to cleave the aryl-aryl C-C bonds via thermolysis in the neat state Rupture of the four-membered ring is a key step in the rearrangement of phenylenes into other PAHs and has been observed typically under flash vacuum pyrolytic conditions18 (eg 10ndash3ndash10ndash6 torr 800ndash1000 degC) Strained ring opening on exposure to metal complexes to give metallacycles19 is discussed in further detail in Section 12 12 Overview of Phenylene Organometallic Chemistry

As mentioned above the weakly aromatic character of the phenylenes dominates their structure and reactivity In the linear phenylenes the antiaromatic contribution to structure and reactivity becomes increasingly significant A simple yet instructive explanation for this phenomenon can be seen in the various resonance structures of linear [3]phenylene (18) a selection of which is depicted in Figure 16 Even the most favorable forms a and b feature double bonds in the four-membered rings The cumulative increase in cyclobutadienoid circuits should therefore lead to an increase in antiaromatic character The relative augmentation in

- 6 -

cyclobutadienoidantiaromatic character of the linear phenylenes was confirmed6 by NMR NICS calculations and HOMO-LUMO measurements20

Figure 16

Resonance contributors to linear [3]phenylene

Cyclobutadiene is often invoked as the typical example of a highly destabilized antiaromatic system Indeed the difficulties21 in preparing and isolating it confirm theoretical predictions regarding its instability22 Attachment of a metal however is known to produce aromatic organometallic molecules of high stability23 The increased antiaromatic character of the linear phenylenes thus makes them amenable to metal complexation Cyclopentadienylcobalt cyclobutadiene complexes of linear [3]- (19)24 linear [4]- (20)25 and linear [5]phenylene (21)26 have been prepared using the well-developed cobalt-based [2+2+2] alkyne cyclotrimerization methods (Scheme 13)27

Compounds 19ndash21 constitute the only linear CpCo phenylene systems known so far

Scheme 13 Synthesis of Linear Phenylene(CpCo) Cyclobutadiene Complexes

In the metallated linear [4]- and [5]phenylene 20 and 21 respectively the CpCo unit is located on the inner cyclobutadiene ring This is curious as one would have expected the metal fragment to be bound to its outside counterpart close to the center of reactivity during the cyclotrimerization step The position of the CpCo unit was established by NMR spectroscopy2628 In addition a crystal structure of a tetrahexyl

TMS

TMS

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMSTMS

TMS

Co

CpCo(CO)2BTMSA

h

Co

Co

CpCo(CO)2BTMSA

h

CpCo(CO)2BTMSA

h

19

20

21

- 7 -

substituted linear [5]phenylene28 (Figure 17) clearly reveals the inside position of the metal fragment Difficulties in obtaining high quality crystals however precluded a detailed bond analysis of the complex The unexpected location of the CpCo unit in 20 and 21 suggested the occurrence of CpCo migration under the conditions of their preparation Detailed experiments verifying this hypothesis will be the subject of Chapter 2

Figure 17 Disordered crystal structure for the 23910-tetrakis(trimethylsilyl)-571214-

tetrahexyl linear [5]phenylene(CpCo)

In contrast to the linear phenylenes their angular relatives undergo π-metallation at the cyclohexatrienoid moieties (Figure 18) For example angular [3]phenylene (22) reacts with CpCo(C2H4)2 to form the η4-CpCo complex 2329 Similar treatment with Cr(CO)3(NH3)3 yields the η6-Cr(CO)3 analog 2430

Figure 18 η

4-CpCo (23) and η6-Cr(CO)3 (24) complexes of angular [3]phenylene (22)

In addition to 24 related chromium complexes of the triangular [4]phenylene frame eg 25 have been prepared (Scheme 14)31 Interestingly regioisomer 26 generated at relatively lower temperatures is the kinetic product of monocomplexation and rearranges thermally to 27 Double metallation is possible as illustrated in the conversion of 27 to 28 with added (naphthalene)Cr(CO)3

- 8 -

Scheme 14 Synthesis and Reactions of Triangular [4]Phenylene(Cr(CO)3) Complexes

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3(NH3)3dioxane 100 oC

14 h

(naphthalene)Cr(CO)3THF Et2O 60 oC 14 h

90 oC

(naphthalene)Cr(CO)3THF Et2O 60 oC

14 h

25

27

26

28

57 43

89

In contrast to CpCo which attaches itself exclusively to the four-membered ring in the linear phenylenes including the linear [3]phenylene frame as in 19 (Scheme 13) Fe2(CO)9 gives a plethora of complexes with the tetrasilyl derivative 29 among which the iron tricarbonyl cyclobutadiene complex 30 is only minor (Scheme 15)27 Instead other organometallic molecules such as arene complex 31 were isolated This compound contains two Fe(CO)3 units coordinated to the central benzene ring An iron-iron bond was proposed for this molecule (31a) although the spectral data are also consistent with a structure in which the Fe(CO)3 fragments are located on opposite faces (31b) Because a crystal structure could not be obtained the structural identity of 31 remains ambiguous The major products of this reaction 32 and 33 illustrate another important aspect of phenylene reactivity metal insertion into the strained ring

- 9 -

in this case involving the dinuclear Fe2(CO)6 unit Complex 33 probably originating from 32 contains an additional Fe(CO)3 moiety coordinated to the terminal benzene ring closest to the Fe2(CO)6 fragment

Scheme 15 Reaction of Linear [3]Phenylene with Fe2(CO)9

While as yet absent in the linear series a cobalt insertion product analogous to iron compounds 32 and 33 was isolated when angular phenylene 22 was exposed to excess CpCo(ethene)2 (Figure 19)32 In this case double insertion of two (CpCo)2

Figure 19 Tetranuclear CpCo-terphenylene complex 34 and its crystal structure

34

- 10 -

fragments occurred to give 34 in 71 yield Notably neither 23 nor analogs of the type 31 were detected As alluded to in Scheme 12 biphenylene (7) itself also undergoes metal insertions into the four-membered ring This type of reactivity has been observed with a range of transition metals including Co19 Mechanistically best delineated is the attack of Ni and Pt species Thus Ni(PEt3)4

33a and Ni(COD)(PMe3)233b begin with insertion of

the nickel fragment into the four-membered ring to give a metallacycle of the type 35 (Scheme 16) Subsequent dimerization assembles 36 from which Ni is extruded to furnish tetraphenylene 37 as the final product A similar reaction pathway was proposed for Pt(PEt)4

19 but proceeding via 38 to a monometallacycle 40 possibly through the intermediacy of 39 In summary the σ- and π-activation of the phenylenes endows them with rich organometallic chemical potential The synthetic and mechanistic exploration of one aspect of it namely the Ni-catalyzed cycloaddition of alkynes to the four-membered rings in angular phenylenes will be discussed in Chapter 3

Scheme 16 Reaction of Biphenylene with Nickel and Platinum Complexes

13 Direction of Work The discussions in Sections 11 and 12 have provided a brief overview of phenylene properties and their previously studied organometallic chemistry

- 11 -

respectively The aim of this thesis was to advance two aspects of prior investigations The first area examines the chemistry of the linear phenylene(CpCo) complexes In particular experiments are presented addressing the question of a possible migration of the CpCo fragment along their framework The revocable movement of a metal fragment between cyclobutadiene rings is a highly noteworthy discovery as this process has never before been reported On a practical level this mode of reactivity places linear phenylene(CpCo) complexes in the increasingly appealing class of organometallic arrays that can serve as the basis for various molecular electronic systems The reversible isomerizations described in the second chapter can potentially be employed in molecular machines and switches data storage and as will be detailed photostorage devices Experimental work in the form of detailed solid state and spectroscopic analyses is provided Computational studies are also employed to further scrutinize the novel chemistry of the abovementioned Co-based molecules The second topic of this thesis examines nickel-catalyzed insertions into the four- membered rings of angular phenylene systems Specifically the application of this reactivity to the synthesis of a class of PAHs known as [N]phenacenes is discussed Phenacenes (polyphenanthrenes) have recently shown great promise as organic transistors and conductors but advancement of this field has been hampered due to few practical syntheses The insolubility of these molecules has also been a substantial barrier to the development of phenacene-based applications The content of the third chapter explores the preparation of soluble phenacene derivatives using a tandem Ni-insertion alkyne cycloaddition reaction This new process provides an efficient widely applicable and practical synthesis of larger phenacenes using correspondingly larger angular phenylene systems Detailed mechanistic studies of this reaction are presented Experimental data are used in conjunction with computational studies to gain further insight with the optimization of the reaction by reduction of side product formation being a crucial milestone

- 12 -

Chapter Two

PhotondashThermal Haptotropism in Cyclopentadienylcobalt Complexes of Linear Phenylenes Intercyclobutadiene Metal Migration

21 Introduction As previewed in Section 12 the unexpected position of the metallic unit in the linear [4]- and [5]phenylene(CpCo) systems 20 and 21 constituted the background for the studies presented in this chapter Specifically it was hypothesized that its origin was due to the migration of the metal fragment from one cyclobutadiene ring to another a process that would constitute an unprecedented type of haptotropic shift34-36 However a prerequisite for studying such a rearrangement would be the generation of the haptoisomers of 20 and 21 (Scheme 13) bearing the CpCo appendage at the respective terminal four-membered rings a possibility obviated by their thermal method of synthesis The following describes the history that led to the discovery of photochemical conditions that circumvented this thermodynamic problem The story begins with a prior attempt to stabilize the linear phenylene frame by alkyl substitution the ultimate aim being the synthesis of members of the series with Ngt5 Such substitution was also hoped to improve solubility a facet exploited in the corresponding zigzag series37 The synthetic strategy followed that used in the preparation of the largest known linear phenylene 41 namely the CpCo-catalyzed cyclization to 21 followed by careful oxidative demetallation as shown in Scheme 21 The initial target chosen was the tetrahexyl system 43 approached via the synthesis of complex 42 (Scheme 22)28 Demetallation was thought to be facile to provide the free ligand but this anticipation proved to be erroneous

Scheme 21 Oxidative Decomplexation of Linear [5]Phenylene Complex 21

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMS

41

CoCp

21

40

CuCl2middot2H2ODME NEt3 H2O

Scheme 22 Preparation of Tetrahexyl Linear [5]Phenylene Complex 42

- 13 -

TMS

TMS

TMS

TMS

Hex

Hex

Hex

Hex

CoCp

42

CpCo(CO)2 BTMSAm-xylene ∆ hν

27

Hex Hex

HexHex

TMS

TMS

TMS

TMS

Hex Hex

HexHex

ndashCpCo

43

The demetallation of 42 under numerous conditions was unattainable However in one of these attempts an NMR sample of 42 was exposed to UV-irradiation leading to the evolution of new signals eventually assigned to originate from rearranged compound 45 (Scheme 23)28 This molecule is also a linear [5]phenylene(CpCo) complex but now has the metal fragment bound to the outer cyclobutadiene ring an arrangement that was suspected to be the initial product of the preparation of 42 (Scheme 22) That this conjecture was correct was established by heating which caused photoisomer 45 to revert to 42 An indication of the generality of this phenomenon was gleaned from 21 which underwent the same photoinduced thermally reversible haptotropic migration (Scheme 23)38 A detailed discussion of the spectral properties of these haptomers is provided in Sections 23 and 24 Scheme 23 Photoinduced Thermally Reversible Haptotropic Migration of the CpCo Fragment

in Linear [5]Phenylene(CpCo) Complexes

This discovery was deemed significant for two reasons 1 it constitutes the first observation of intercyclobutadiene metallohaptotropism and 2 there are only two previously known examples of mononuclear39 additive-free40 photothermal reversible haptotropic shifts both of which are based on Mo(PMe3)3 complexes (Scheme 24)41 Systems capable of undergoing this type of reaction are of much practical importance because of their potential employment as photostorage devices andor molecular switches42 The development and application of functional organometallic materials43 has proceeded at a relatively slow pace when compared to their non-metallated counterparts5c Thus the great prospects for discovery and advancement make this area of study particularly attractive

- 14 -

Scheme 24 Photothermal Reversible Metallohaptotropism in (a) Molybendum-Indole41a and (b) Molybendum-Isoquinoline Complexes41b

Having confirmed that an η4η4 cyclobutadiene haptotropic migration was indeed occurring mechanistic investigations2838 were begun Interestingly full conversion of the inner bound CpCo complexes to their photoisomers was never achieved The maximum ratio obtained for 2144 and 4245 was 8812 Variations of solvent (eg benzene THF CHCl3) and temperature (0ndash30degC) had no effect on this ratio Added ligands such as 15-cyclooctadiene CO and phosphines were also inconsequential Of further significance was the robustness of the photothermal cycle which could be run multiple times without decomposition Kinetic experiments were carried out to determine the activation parameters for the thermal reversal of 44 and 45 to 21 and 42 respectively These data are shown in Table 21 The isomerizations are cleanly first order a finding that was unaffected by changes in concentration22 The enthalpy of activation (∆Hne) increased only slightly with hexyl substitution (44 vs 45) The near zero entropy of activation values (∆Sne) was consistent with the occurrence of an intramolecular process

Table 21 Activation Parameters for the Conversion of Outer to Inner CpCo Complexes Under

Thermal Conditions ∆Sne Values are in Entropy Units (1 eu = calmolsdotK)

Reaction Solvent ∆H

ne (kcalmol) ∆Sne (eu)

44 to 21 C6D6 259 plusmn 04 16 plusmn 14 44 to 21 THF-d8 256 plusmn 09 01 plusmn 30 45 to 42 THF-d8 276 plusmn 08 77 plusmn 27

Consideration of the relative facility of the above haptotropic shifts made it likely that migration was occurring along the entire phenylene frame including the ldquohoppingrdquo across the central six-membered ring (Scheme 25) This degenerate equilibration should be detectable by NMR spectroscopy44 if it were sufficiently fast Unfortunately but perhaps not surprisingly considering the data in Table 21 coalescence of the spectrum of 21 could not be achieved even at temperatures as high as 120 degC Spin saturation transfer experiments (eg EXSY) also failed44 These data allowed an estimate of the lower limit for the activation energy of the internal shift of ∆Gne ge 22 kcalmol28

Scheme 25 Proposed Internal η4η4 Cyclobutadiene CpCo Migration

- 15 -

The failure of the above experiments inspired a different approach based on the following arguments The antiaromatic character of the linear phenylenes has been shown by theory and experiment to increase with size645 Consequently the effect of metalloaromatization46 makes linear [5]phenylene a better (and hence more strongly bound) ligand for CpCo than a smaller system (eg linear [3]phenylene) Indeed the enthalpy of the homodesmotic in Scheme 26 was computed by DFT methods to be Scheme 26 Calculated Homodesmotic Reaction Showing Preferential Binding of CpCo to

Linear [5]Phenylene

113 kcalmol47 If the barrier to intercyclobutadiene hopping were related to the binding energy of the metal one would expect a more loosely bound metal fragment to migrate faster The hope was therefore that the degenerate haptotropism in Scheme 27 would be observable by VT NMR methods Unfortunately these efforts failed again38 either because the anticipated acceleration was not sufficient to be observable by NMR or because the argument above (which rests solely on ground state considerations) is flawed

Scheme 27 Proposed Degenerate Haptotropic Shift in Linear [3]Phenylene Complex 19

- 16 -

The preceding discussion summarizes some of the quantitative aspects of this new type of haptotropic shift Many fundamental questions however remained to be answered Is it possible to observe the photothermal shift in other systems such as linear [3]- and [4]phenylene What is the exact mechanism of metal migration between cyclobutadiene rings In what way if any does attachment of CpCo alter the structure of the phenylene scaffold Related to these questions was the long-standing quest for an accurate crystal structure of any linear phenylene(CpCo) complex The answers are addressed in the following sections 22 Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes As recounted in Section 21 the degenerate internal haptotropic shift could not be seen by NMR in the symmetrical 19 Therefore recourse had to be taken to chemical methods involving an isomerization of the sort shown in Scheme 28

Scheme 28 Isomerization of a Desymmetrized Linear [3]Phenylene(CpCo) Complex

Initial efforts focused on attempts to desymmetrize compound 19 directly by selective electrophilic desilylation specifically protodesilylation Earlier studies48 had shown that such selectivity was possible in the reactions of bis(trimethylsilyl)benzocycloalkenes such as the benzocyclobutene depicted in Scheme 29 In this case loss of the first TMS group is approximately forty times faster than that of the second Along these lines it was thought that exposing 19 to acidic conditions would selectively remove one (or perhaps two) TMS groups before attacking the remaining silylarene positions In the event treating compound 19 with trifluoroacetic acid in carbon tetrachloride did induce protodesilylation but with no selectivity A mixture of products was obtained and its separation proved impossible (Scheme 210) In light of this setback a new synthetic scheme had to be considered that would generate a desymmetrized system directly in the CpCo-catalyzed cyclization step

- 17 -

Scheme 29 Selective Desymmetrizing Reactions of 12-Bis(trimethylsilyl)benzocyclobutene with Electrophiles

Scheme 210 Attempted Selective Protodesilylation of 19

Fortunately such a strategy had already been executed successfully in the creation of 23-bis(trimethylsilyl) linear [3]phenylene (46) and employed the iterative Scheme 211 Iterative Cyclotrimerization Route in the Synthesis of Linear [3]Phenylene 46

cyclization depicted in Scheme 21127 Its specific execution (Scheme 212) started with a Sonogashira reaction between trimethylsilylacetylene (TMSA) and 12-diiodobenzene (47) to give diyne 48 in high yield Deprotection of 48 with K2CO3 immediately followed by standard CpCo(CO)2-catalyzed alkyne cyclotrimerization649 with bis(trimethylsilyl)acetylene (BTMSA) afforded 23-bis(trimethylsilyl)biphenylene (49) Iododesilylation was then performed using pure ICl to give 23-diiodobiphenylene (50) A Sonogashira coupling between TMSA and 50 produced diyne 51 in good yield The use of a slightly modified cyclization procedure provided the new 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52) in 57 yield This protocol employed THF as a cosolvent to BTMSA thus reducing the reaction temperature in turn allowing for the CpCo to remain attached in the final product and preventing catalytic turnover252638

TMS

TMS46

+

TMS

TMS

+

TMS

TMS

+

TMS

R

TMS

dilute

[X+]

X = H D Br

TMS

TMS

[X+]

TMS

X = H D Br

X

- 18 -

Scheme 212 Synthesis of Asymmetric Linear [3]Phenylene(CpCo) 52

High dilution conditions also helped to suppress formation of cyclobutadiene(CpCo) complexes a well known side reaction in alkyne cyclization chemistry

Compound 52 like its tetrasilylated analogue 19 is a black air-sensitive solid Although it can be handled in air for brief periods of time complete decomposition occurs within 24 hours if left exposed to the ambient atmosphere Purification must always be done with neutral activity III alumina as lower activities (and silica gel) cause decomplexation to give the deep red ligand 46 as the only isolable product Critically exposing molecule 52 to UV irradiation induced the desired haptotropic shift giving its photoisomer 53 (Scheme 213) Heating 53 converted it back to 52 thus completing the photothermal cycle Interestingly close inspection of the NMR spectra of this experiment revealed that a small amount of 53 (2) always remained even on prolonged heating That this observation signaled a thermodynamic equilibrium was confirmed by dissolution of pure crystalline 52 and NMR analysis From the equilibrium constant the ∆Gdeg298 was calculated to be 23 kcalmol in favor of 52 The reasons for this energetic preference and a discussion of the NMR spectral properties of these and related complexes are presented in Section 23

Scheme 213 The Photoinduced Thermally Reversible Haptropic Shift in Linear

- 19 -

[3]Phenylene-(CpCo) 52 to Give Photoisomer Complex 53 The investigations of the equilibration depicted in Scheme 213 were all carried out in sealed Pyrex NMR tubes (J-Young or flame-sealed) using benzene-d6 andor toluene-d8 as the solvent As for the linear [5]phenylene(CpCo) system the cycle could be run multiple times without decomposition and was unaffected by changes in solvent and temperature The maximum ratio of 5352 that could be obtained on irradiation was 11 after ten hours This value is larger than that observed for its linear [5] analogs 2144 and 4245 Photoisomerization also occurs with sunlight leading to the photostationary equilibrium of 5253 = 105 Consequently care must be taken to shield 52 from direct andor indirect sunlight Indoor fluorescent lighting however did not induce CpCo migration Attempts to monitor the photoisomerization and its thermal reverse by UV-Vis spectroscopy failed because of minimal changes in the absorptions due to 52 during these processes This finding implies that the absorption spectra of 52 and 53 are not unexpectedly very similar and offers a possible explanation for the maximum photostationary ratio of 11 The activation parameters for the thermal reversal reaction (53 to 52) in Scheme 213 were obtained in the manner described in Section 21 and are shown in Table 22 The relatively high activation barriers (with respect to the NMR time scale) explain why the degenerate isomerization in 19 could not be verified by NMR experiments Qualitatively the ∆Hne values agree with the hypothesis that the more loosely bound CpCo unit in the linear [3]phenylene is relatively more mobile they are approximately 3 kcalmol lower than those of the [5]phenylene system On the other hand the ∆Sne values especially in C6D6 are positive and relatively high although still within the range acceptable for intramolecular reactions Nevertheless a crossover experiment was devised to provide a definite answer

Table 22 Activation Parameters for the Thermal Conversion of Complex 53 to 52

Solvent ∆H

ne (kcalmol) ∆Sne (eu)

C6D6 204 plusmn 14 158 plusmn 22 Toluene-d8 231 plusmn 07 60 plusmn 13

For this purpose two new linear [3]phenylene(CpCo) derivatives were required One would carry a marker on the Cp ring while the other would be labeled at the phenylene frame Execution of Scheme 213 would involve an equimolar mixture of both compounds An intramolecular mechanism would retain the integrity of the labeling while a dissociative path would lead to label scrambling The outcome of this experiment should be ascertainable by NMR spectroscopy and more rigorously by

CoTMS

TMS

CoTMS

TMS

310 365 nmsunlight

30ndash50oC52 53

- 20 -

Scheme 214 Preparation of MeCp- (54) and Deuterium Labeled (55) [3]Phenylene Complexes

mass spectrometry To this end methyl-Cp complex 54 and dideuterio compound 55 were targeted for synthesis (Scheme 214) Compound 54 was prepared by carrying out the modified cyclotrimerization reaction with MeCpCo(CO)2

50 while 55 was made using methanol-OD in the desilylation of 51 The amount of deuterium incorporation in 55 was found to be 63 as gleaned from its proton NMR spectrum Scheme 215 Crossover Experiment with Labeled Linear [3]Phenylene(CpCo) Complexes

- 21 -

Co

TMS

TMS

TMS

TMS

Co

h CoTMS

TMS

Co

D

D

TMS

TMSD

D

TMS

TMS

Co

Co

TMS

TMSD

DCo

TMS

TMS

Co

TMS

TMSD

D

+

+

+

+

mz = 510

mz = 494

56mz = 508

57mz = 496

54mz = 508

55mz = 496

58 59

53 52

Not observed

Six distinct products are possible in the crossover experiment using 54 and 55 (Scheme 215) Compounds 56 and 5 would arise as a consequence of an intramolecular shift Molecules 53 and 58 and their photoisomers 52 and 59 respectively would be the result of metal fragment dissociation Mass spectrometry would readily verify the occurrence of crossover as the masses (given in mz in Scheme 215) of the products with scrambled labels (52 53 58 59) are distinct from the masses of the starting materials (54 55) and their photoisomers (56 57) In the first part of the experiment equal amounts of 54 and 55 were mixed (shielded from light) and allowed to stand for 2 hours at room temperature The resulting 1H-NMR spectrum consisted of only the signals for 54 and 55 Similarly the mass spectrum showed molecular ion peaks matching the masses of 55 and 56 (Figure 21) The second step was irradiation Analysis of the photolyzed mixture showed new peaks due to complex 56 (the resonances of which had been obtained in a separate photothermal experiment with pure 54) with the expected integration ratio and a second set assigned to 57 identical with the spectrum of 53 but with the expected attenuated absorption for the silyl bearing arene hydrogens The relative integrations for all compounds observed were consistent with a mixture of 5455 and 5657 Mass spectral analysis of the irradiated mixture showed a pattern that was identical to that collected before irradiation (Figure 21) Finally the thermal reversal reaction was carried out by heating the photolyzed mixture at 80 degC After 30 hours the resulting

- 22 -

NMR spectrum matched that of the initial mixture of 54 and 56 in particular confirming the full protonation of 54 and the unchanged level of deuterium incorporation in the silyl

Figure 21 Molecular ion peaks for 5456 (mz = 508) and 5557 (mz = 496)

bearing arene ring of 55 The corresponding mass spectrum contained no evidence for the presence of scrambled products To conclude The haptotropic shift is non-dissociative The exact manner in which the metal traverses from one cyclobutadiene ring to the other will be examined in greater detail in Section 24

23 X-Ray Structural and Comparative NMR Analysis of Linear [3]Phenylene(CpCo) Complexes The results described in Sections 21 and 22 pose some fundamental questions beyond those concerned with the immediate details of the observed haptotropism and addressing the basic novelty of the complexes involved What actually happens to the phenylene ligand when it is ligated via a cyclobutadienoid ring This section will address this question from a structural and (NMR) magnetic point of view Only one crystal structure of a linear phenylene(CpCo) complex was known at the outset of this work namely that of [5]phenylene(CpCo) 42 (Figure 17) and its acquisition required extensive efforts at crystallization28 Unfortunately extensive disorder obviated a detailed analysis It was hoped that some of the complexes employed in the chemistry disclosed in Section 22 would be more forthcoming in this respect The challenge lay in finding the right conditions for crystal growth We began with tetrasilyl linear [3]phenylene(CpCo) 19 which had been crystallized previously by slow cooling in acetone38 These conditions and numerous others (Table 23) did not provide material suitable for X-ray diffraction Success entailed slow cooling a solution of 19 to ndash10 degC in a mixture of methanol-diethyl ether (41) The ensuing sample allowed the determination of the first high quality crystal structure of a linear phenylene (CpCo) complex obtained in collaboration with the group of Professor Tatiana Timofeeva of New Mexico Highlands University (Figure 22)

Table 23 Trial Crystallization Conditions for Linear [3]Phenylene(CpCo)19

Solvent (Ratio) Conditions Result

Acetone Slow Cooling Heterocrystalline Solid Acetone-Pentane (31) Slow Cooling Heterocrystalline Solid

Pentane-Acetone (101) Solvent Diffusion Amorphous Solid Chlorobenzene Slow Cooling Amorphous Solid

- 23 -

Acetone-Methanol (110 Slow Cooling Amorphous Solid Diethyl Ether-Methanol Slow Cooling Small Needles

Acetonitrile Slow Cooling Powder Ethyl Acetate Slow Cooling No Crystals

Ethyl Acetate-Methanol (11) Slow Cooling Amorphous Solid Methanol-Diethyl Ether (41) Slow Cooling Large Fine Needles

Figure 22 X-ray crystal structure of 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) (19) Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are

omitted for clarity Expectedly the CpCo unit is bound in an η4 fashion to the cyclobutadiene ring Also prominent is the deviation from planarity (Section 11) in the linear [3]phenylene a facet typical of the phenylenes themselves (Section 11)9a Of greater importance than these general observations however is the effect of metal complexation on the linear [3] framework The bond lengths for 19 are shown in Figure 23 and as is typical for the phenylenes6 show a certain degree of bond π-localization with measurable differences between single and double bonds However the extent of this phenomenon and its direction varies significantly when compared to the free ligand 60 A quantitative

- 24 -

comparison of the structural data for 19 with those of its ligand 60 is shown in Figure 2327

In 60 the terminal rings adopt bond alternation similar to that in biphenylene (Section 11) and the central benzene takes on a ldquobis-allylrdquo configuration both ostensibly to minimize electron density (and therefore antiaromaticity) in the four-membered rings As dictated by symmetry the two bonds spanning the central ring are of equal length (1385 Aring) Ligation by CpCo alters this picture profoundly in as much as bond alternation across the entire phenylene frame including the four-membered rings is strongly reduced (Figure 23) Generally all relatively long bonds in 60 shorten in 19 while all short bonds lengthen Some residual but attenuated biphenylene type

Co

1512(2)

1513(2)

1407(2)

1385(2)

1385(2)

1397(2)

1356(2)

1359(2)1436(2)

1397(2)

1441(2)

1411(3)(0052)

1384(3)(-0052)

1474(3)(0077)

1384(3)(-0057)

1408(3)(0052)

1448(3)(0051)

1480(3)(-0032)

1468(3)(-0045)

1437(3)(0052)

1465(3)( 0058)

1434(3)( 0049)

1352(3)(-0033)

1351(3)(-0034)

1476(3)(0069)

1495(3)(-0017)

1372(3)( 0016)

1405(3)(0008)

1376(3)(0017)

1413(3)(-0023)

1427(3)(0030)

1488(3)(-0025)

1423(3)(-0018)

(x) = (19) - (60)increasedecrease

60

19

1907(1)

1891(1)

1886(3)

1889(3)

1889(2)

1901(3)

1669

1725

Si

Si

Si

Si

Me

MeMe

Me

Me

Me

Me

MeMe

MeMe

Me

Si

Si

Me

MeMe

MeMe

Me

Si

Me

MeMe

Si

Me

MeMe

- 25 -

Figure 23 Comparison of bond lengths (in Aring) between linear [3]phenylene(CpCo)complex 19 and 2378-tetrakis(trimethylsilyl) linear [3]phenylene (60) The bond distances in 19 are shown in blue Increases in bond length in going from 60 to 19 are marked in green decreases in red

ldquobond fixationrdquo (Figure 12) remains in the vicinity of the uncomplexed cyclobutadiene Compound 19 thus provides a prime demonstration of the powerful effect of metalloaromatization46 in which the bonds of a cyclobutadiene-metal system attempt to adopt the equalized bond lengths that are a classic hallmark of aromaticity2ndash4 Encouraged by the successful development of a procedure to obtain X-ray quality crystals of 19 these techniques were applied to bis(trimethylsilyl) linear [3]phenylene(CpCo) 52 Gratifyingly with acetone as the solvent the results depicted in Figure 24 were ultimately obtained Figure 24 X-ray crystal structure of 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52)

Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are omitted for clarity

A comparison of the bond lengths of 52 with those of its corresponding linear [3]phenylene ligand 469a is given in Figure 25 Comparison with Figure 23 reveals the same type of aromatization of the ligand on attachment of the metal With these structures in hand an attempt was made to rationalize structurally the

- 26 -

thermodynamic preference for 52 in which the CpCo is located proximal to the silylated terminus in its equilibrium with 53 in which the metal is located close to the unsilylated benzene ring Focusing on the desymmetrizing ortho-bis(trimethylsilyl) unit one notes that the SiCndashCSi bond in 52 is elongated by 005 Aring on attaching the metal in 46 thus providing steric relief On the other hand the symmetry equivalent remote C7ndashC8 distance is unchanged The same effect is seen in the tetrasilyl complex 19

Figure 25 Comparison of bond lengths (in Aring) between bis(trimethylsilyl) linear [3]phenylene(CpCo) complex 52 and 23-bis(trimethylsilyl) linear [3]phenylene (46) Bond lengths for 46 are the average of four molecules in the unit cell (standard deviation = plusmn002)

Increases in bond length going from 46 to 52 are marked in green decreases in red

The observed structural changes make sense in a simple resonance picture

Co

1413(10)(007)

1406(10)(-004)

1459(10)

( 005)

1370(11)(-007)

1418(10)( 005)

1443(10)(003)

1470(10)(-005)

1465(10)(-005)

1446(10)( 008)

1485(10)( 006)

1432(10)( 004)

1347(10)(-003)

1345(10)(-002)

1492(10)( 007)

1503(11)(-002)

1379(10)(001)

1391(11)(-001)

1409(10)(004)

1418(11)(-003)

1367(11)(001)

1478(10)(-002)

1408(11)(-001)

1891(8)

1890(13)

1670

1723

SiMe

MeMe

Si

Me

Me

Me

(x) = (53) - (62)increasedecrease

SiMe

MeMe

Si

Me

Me

Me

190

145134152

139138

150

137145

136

142 137

152137 137

152

141

137 144

189

141143142140

52

46

- 27 -

(Scheme 216) Metalloaromatization alters the dominant resonance forms during intercyclobutadiene hopping such that the essentially single SiCndashCSi bond in 52 transforms into an essential double bond in 53 increasing unfavorable repulsion between the TMS groups Scheme 216 A Resonance Picture Rationale for the Preference of 52 in its Equilibrium with 53 The aromatization effect of metal complexation on the phenylene nucleus described structurally in the preceding text can also be demonstrated powerfully through the measurement of ring currents with 1H-NMR spectroscopy both by experiment and computation (NICS13 see Section 11) A relevant simple example is depicted in Figure 26(a) featuring the changes occurring when 12-bis(trimethylsilyl)benzocyclobutadiene (61) is complexed by CpCo as in 6251 The paratropic antiaromatic 8π system 61 exhibiting relatively shielded six-membered ring hydrogens turns diatropic in 62 Equally importantly and focusing on the ring current contributions of the individual cycles the paratropism of the four-membered ring in 63 shields the adjacent hydrogens more than the remote ones Conversely aromatization of this ring and the ensuing diatropism inverts this order

Figure 26 The effect CpCo complexation (a) on benzocyclobutadiene 61 and (b) linear [3]phenylene 46 Chemicals shifts are in ppm

Co SiMe3

SiMe3

Co

SiMe3

SiMe352 53

∆Gdeg298 =23 kcalmol

- 28 -

Turning to a phenylene system comparison of the NMR data for complex 52 with those for ligand 46 (Figure 26(b)) reveals the same changes not only in the vicinity of the ligated ring but also in the remote parts of the molecule Thus the hydrogens closest to the metal fragment are shifted downfield by 125 ppm in 62 and 148068 ppm in 52 when compared with 61 and 46 respectively The observed relatively large chemical shifts of the arene hydrogens proximal to the metal unit are not due to its anisotropy since its value in this area of space is (if anything) shielding5152 In addition the remote hydrogens in 52 are deshielded by 055033 ppm relative to the corresponding nuclei in 46 clearly substantiating the aromatization of the overall system upon metal complexation that was seen by structural analysis These pronounced chemical shift changes are diagnostic and greatly aided the spectral interpretations of the photochemically induced haptotropic shift experiments described in Sections 21 and 22 as illustrated for the isomerization between 52 and 53 (Scheme 217)

Scheme 217 Chemical Shift Changes in the Isomerization of 52 to 53

These NMR measurements were augmented by NICS calculations carried out in collaboration with Professor Amnon Stanger at the Technion in Haifa NICS data have the advantage that they indicate the extent of (anti)aromaticity even in rings for which the molecule has no hydrogen probe in the classical NMR experiment in this case the cyclobutadienes Computational details are given in Chapter 4 The experimentally determined proton NMR data for the series of silylated linear phenylenes from [2] to [5] and their metallated analogues in addition to the corresponding NICS(1) values of the respective parent phenylenes are shown in Figure 27 All compounds in Figure 27 are known except for the hypothetical biphenylene(CpCo) 64 which is included for comparative purposes Metalloaromatization is pronounced as all rings of the phenylene exhibit diminished or more negative NICS numbers signaling increasing aromatic and decreasing antiaromatic character respectively Again the effect is most pronounced on the rings closest to the metal bound unit tapering off (but never disappearing) with distance Most illustrative in this respect is 44 in which the penultimate and ultimate rings away from the Co still show decreases in the NICS values of 06 and 05 ppm respectively Interestingly the sum of all NICS values of 44 (ldquototal NICSrdquo13c) ndash91 is less negative than that of 21 ndash132 suggesting that 21 is more aromatic hence more stable as observed experimentally This may be fortuitous and the issue is addressed further in Section 24 Finally a caveat regarding the unusually large negative NICS values associated with the CpCo-complexed cyclobutadiene rings As pointed out by Solagrave in connection with a related study of (benzene)Cr(CO)3 which produced similar numbers53 there are local ring currents associated with the extra electrons involved in the metal to π-ligand

CoTMS

TMS796675674

678

436 CoTMS

TMS747683724

662

444

310 365 nmsunlight

30ndash50oC

52 53

- 29 -

bonding that lead to an overestimation of aromaticity Therefore to corroborate the general conclusions of metalloaromatization of this (and all other rings) in Figure 27 Stangerrsquos NICS scan method was applied54 This procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (NICSXY) and out-of-plane components (NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their

Figure 27 Experimental 1H-NMR (C6D6 blue) and computed NICS(1) (green) values for linear phenylenes and their corresponding CpCo complexes The experimental data are for the silylated

derivatives shown The NICS data are for the parent systems interpretation The data presented in Chapter 4 confirm the conclusions of this section While not reflective of ring current effects the values of the 13C chemical shifts for the linear phenylene(CpCo)complexes do provide some insight into the nature of the

- 30 -

σ-framework Comparing complex 19 with parent ligand 60 one observes two general phenomena (Figure 28) The most apparent is the upfield values for the cobalt-bound cyclobutadiene carbons (~74ndash78 ppm) in 19 arising from the local anisotropic shielding effect of the metal (vide supra) Secondly the carbon atoms in the four-membered ring not bound to the metal exhibit large deshielded values (144ndash149 ppm) This effect also seen in ligand 60 arises from the rehybridization6 of the cyclobutadiene sp2 orbitals and is observed in all phenylene topologies A comparison of the 13C-NMR data for the linear [3]- [4]- and [5]phenylene(CpCo)complexes with their respective parent ligands is given in Chapter 4

Figure 28

13C-NMR data for complex 19 and parent silylated ligand 60 Values are in ppm 24 Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift How does the CpCo moiety migrate from one cyclobutadiene unit to the next Two extreme alternatives present themselves a least-motion movement across the intervening arene unit or a more circuitous pathway along the periphery The latter is prevalent in other computed haptotropic shifts56-57 in particular those occurring in (arene)Cr(CO)3 complexes all of which choose peripheral trails56 In these the metal typically moves straight to the edge to adopt an η4 (often described as η1) trimethylenemethane-like transition state on the way to a neighboring ring as illustrated for the η6-η6 hopping in naphthaleneCr(CO)3 summarized in Scheme 218 More relevant is the computed course of the η6-η6 interconversion of (biphenylene)Cr(CO)3 (Scheme 219)57 The metal slides from the (near)center of one benzene ring to the quaternary (four-membered) ring carbon to reach a distorted trimethylenemethane maximum and then proceeds to the edge of the bridging cyclobutadiene bond This species represents a minimum on the potential energy curve and adopts an η2-like complexed cyclobutadiene topology (ldquoquasi-η4rdquo) from which it continues by the microscopic reverse on to the other benzene nucleus The relevance of these findings with respect to the intercyclobutadiene hopping of CpCo along the phenylene frame was not clear at the outset of the work described in this section The CpCo fragment has a different electronic requirement from Cr(CO)3 and interring migration in arenes (and related systems) involves aromatic electron counts of all intervening circuits

Scheme 218 Migration of Cr(CO)3 Across Naphthalene

- 31 -

Scheme 219 Migration of Cr(CO)3 Across Biphenylene

DFT calculations were carried out in collaboration with Professor Thomas Albright at the University of Houston In these studies using B3LYP 3-21G (carbonhydrogen) and LANL2DZ (cobalt) basis sets the metal fragment was placed 18 Aring above the π system with energy minimizations carried out every 02 Aring along the frame of the parent linear phenylene in question When transition states and local minima were located their structures were refined with the B3LYP 6-31G (hydrogen) 6-113G (carbon) and LANL2DZ (with inclusion of cobalt f-orbitals) basis sets More computational details are given in Chapter 4 The resulting potential energy surface for the thermal rearrangement in the parent linear [3]phenylene(CpCo)system is shown in Figure 29 Figure 210 contains enlarged images of the transition states and intermediate structures The haptotropic shift begins with the (η4-cyclobutadiene)CpCo global minimum (labeled ground state GS) assigned a relative value of 000 kcalmol An η2-cyclobutadiene transition state (TS 1) 269 kcalmol higher in energy than GS is passed before reaching a local minimum (LM) that lies 109 kcalmol above GS LM features CpCo coordinated unsymmetrically η4 to the central benzene ring thus avoiding an unstable 20 electron η6-benzene configuration (not shown) which when explicitly calculated proved to lie 36 kcalmol above LM From LM a symmetry-related second η4 structure is reached via an η3-benzene transition state (TS 2 barrier 14 kcalmol) that symmetrizes the ldquoleftrdquo with the ldquorightrdquo half of the molecule LM is 249 kcalmol higher in energy than GS The shift is completed through the reverse of the initial two movements through LM and TS 1 on the other side of the ligand to reach the second cyclobutadiene ring Thus as for Cr(CO)3 (Scheme 219) CpCo migrates along the edge of the linear phenylene but because of its differing electronic needs through distinctly different intermediates and transition states Most obvious is the internal η2-cyclobutadiene TS 1 which for Cr changes to a peripheral η2-intermediate The calculated rate determining barrier of 269 kcalmol (GS to TS 1) is slightly higher than that measured for the reversal of 53 to 52 (~23 kcalmol) Part of this discrepancy may be due to ground state activation of 53 which is ~2 kcalmol less stable than 52 The LM structure has some resemblance to the isolated η4-CpCo angular [3]phenylene 23 (Section 12) Its location in an energetic well of ~14ndash16 kcalmol (TS 1 and TS 2) suggested that it may be observable at low temperature This investigation is detailed in Section 25

- 32 -

Figure 29 Calculated potential energy profile for the thermal η4η4 haptotropic shift in linear [3]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

0

5

10

15

20

25

30

1 2 3 4Reaction Path

Co

Co

C o

C o

GS η

4

LM η

4

TS1 η

2

TS 2 η

3

00

269

109

249

Key - Global MinimumGround State (GS)- Local Minimum (LM)

- Transition State (TS)

122

3 34 4

- 33 -

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 34 -

(d) Transition state 2 η3-benzene (249 kcalmol)

Figure 210 Optimized structures and relative energies for the linear [3]phenylene(CpCo) haptotropic shift Carbon atoms are shaded grey hydrogens light grey and cobalt blue Bond

lengths are in Aring The potential energy profile for the thermal shift in the linear [5]phenylene(CpCo) system was calculated in the same manner and is shown in Figure 211 Images of the intermediates and transition states are depicted in Figure 212 Placing the metal fragment on the inner cyclobutadiene ring resulted in the lowest energy structure and was therefore set as the global minimum (GS) Two distinct haptotropic migrations inner-to-inner and inner-to-outer cyclobutadiene are now possible (Section 21) Beginning at GS the metal can proceed in the direction of TS 2 or TS 3 respectively both of which are η2 with similar barrier heights (~36 kcalmol) The former pathway is degenerate and continues from TS 2 to η4-LM 1 and then via η3 central benzene TS 1 to the symmetry related corresponding LM 1 TS 2 and finally GS involving the opposite inner four-membered ring The rate determining barrier for this process is 359 kcalmol clearly too high to be measurable by NMR techniques as found for 212838 Interior-to-exterior shifting of the cobalt continues from TS 3 on to η4-benzene LM 2 The η3-TS 3 is traversed before the second η4η2

sequence (LM3 and TS 5 respectively) ultimately leading to LM 4 which is the outer

- 35 -

cyclobutadiene coordinated structure and represents the photoisomeric species observed experimentally in Scheme 23 The computed rate-determining barrier (TS 3) of 263 kcalmol for the reverse reaction of LM 4 to GS is close to the experimentally measured values of 256ndash276 kcalmol for the derivatives in Table 21

Figure 211 Calculated potential energy profile for the η4η4 haptotropic shift in linear [5]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

40

Reaction Path

263

0

5

10

15

20

25

30

35

C o

C o

C o

C o

Co

Co Co

C o

C o Co 360 370

359 357

367

97

203 190 196

1 2 3 4 5 6 7 8 9 10

TS 1 η

3

LM 1 η

4

TS 2 η

2

GS η

4 00

TS 3 η

2 TS 4 η

3 TS 5

η2

LM 2 η

4 LM 3 η

4

LM 4 η

4

Key- Global MinimumGround State (GS)

- Local Minimum (LM)

- Transition State (TS)

- 36 -

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 37 -

(d) Transition state 4 η3-benzene (367 kcalmol)

(e) Local minimum 3 η4-benzene (190 kcalmol)

- 38 -

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 39 -

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

(i) Local minimum 1 η4-benzene (190 kcalmol)

- 40 -

(j) Transition state 1 η3-cyclobutadiene (356 kcalmol)

Figure 212 Optimized structures and relative energies for the linear [5]phenylene(CpCo) haptotropic shift Structures for the inner-to-outer cyclobutadiene migration are given by (a)ndash(g)

Species (h)ndash(j) are involved in the interior-to-interior four-membered ring pathway Carbon atoms are shaded grey hydrogen atoms light grey and cobalt blue Bond lengths are in Aring

Why does CpCo prefer complexation to the internal cyclobutadiene that is GS (as represented by 21 and 42) over LM 4 (as represented by 44 and 45) Calculations show that the energies required to distort linear [5]phenylene to the geometries found in

- 41 -

the complexed isomers are very similar (16 versus 14 kcalmol) Hence the answer must rest on electronic grounds Indeed extended Huumlckel calculations reveal that the overlap populations between the frontier orbitals on the CpCo fragment and the HOMO and the LUMO of the π system are greater for GS (00793 and 00745 respectively) than for LM 4 (00556 and 00517 respectively) A didactically more instructive valence bond view recognizes that metalloaromatization of the inside four-membered ring allows the formulation of more resonance forms that avoid antiaromatic cyclobutadiene circuits A full list of these resonance forms as well as details of the EHMO calculations are given in Chapter 4 25 Low Temperature Photochemical Studies of the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes Of the various participating species in the mechanism for intercyclobutadiene migration (Section 24) specific attention was focused on the η4-benzene intermediates that occur in both the linear [3]- and [5]phenylene haptotropic shifts These structures are energetic local minima on the reaction profiles for both systems and were of considerable intrinsic interest not only as reactive intermediates in this manifold but also because of their relationship to the isolable angular [3]phenylene(CpCo) complex 2329 (Figure 213) Figure 213 (a) Calculated structure for the η4-benzene linear [3]phenylene(CpCo)intermediate

in the haptotropic migration (b) Crystal structure of η4 angular [3]phenylene (CpCo) 23

While rare a handful of other η4-benzene-metal complexes have been isolated (Figure 214) For example two related iridium based systems benzene(CpIr) 6658 and benzene triphos(Ir) 6759 are known As expected ligation causes significant shielding of the hydrogens in the η4 portion of the ligand especially the terminal positions The η4 intermediates in the haptotropic shift are situated in wells on the potential energy surface that are ~17 kcalmol deep for the linear [5]- and ~15 kcalmol for the linear [3]phenylene complexes These values are large enough that such species might be observable by NMR spectroscopy if irradiation of the starting materials were performed at low temperature and if the excited state would relax selectively to these intermediates As a suitable candidate with which to explore this possibility the partly symmetric tetrasilyl complex 19 was chosen The generation of anticipated desymmetrized 68 would be readily detected by the appearance of 11 new singlets in the 1H- and 23 new peaks in the 13C-NMR spectra (Scheme 220)

(a) (b)

- 42 -

Figure 214 Selected relevant examples of isolated η4-benzene complexes and their proton NMR chemical shifts (ppm)

Scheme 220 Low Temperature Irradiation Experiment Designed to Generate η4-Benzene Intermediate 68

Construction of a satisfactory setup to allow for the planned low temperature irradiation was not trivial An optimal experimental configuration however was devised utilizing three pieces of equipment each of which is shown in Figure 215 The first was a custom-made Pyrex Dewar flask small enough to adequately contain an NMR tube Cooling was achieved by means of a Neslab refrigerated circulating bath Thirdly a Rayonet Photochemical Reactor was used as the light source The sample was first placed inside of the Dewar flask and cooled to the required temperature inside of the Rayonet Once cold irradiation was carried out for the desired length of time When complete the sample was transported cold to the NMR laboratory and very quickly placed inside of a pre-cooled NMR probe for analysis A solution of complex 19 was irradiated at ndash65 degC as described and its 1H-NMR spectrum recorded at ndash30 degC revealing a dramatic change The signals for 19 had almost entirely vanished and a set of new peaks appeared The new aromatic resonances were comprised of two sharp singlets at δ = 708 and 644 ppm and a broad singlet at δ = 558 ppm all of which integrated for 2 hydrogens each Another broad

649

586

316

H H

Co544

66 67 23

Ir

P(Ph2)P(Ph2) P(Ph2)

H

H

H

625

594

350

Ir

H

H

H

- 43 -

Figure 215 Cold irradiation experimental setup consisting of (a) Pyrex Dewar flask (b)

refrigerated circulating bath (c) Rayonet Photochemical Reactor with Pyrex Dewar vessel placed inside

(a) η

4 (b) η

4 (c) η

4

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

New peaks

L L

- 44 -

Figure 216 Stacked plot of the aromatic 1H-NMR spectral region recorded after the cold irradiation of 19 in toluene-d8 Peaks for 19 are indicated by blue new peaks by red arrows

Impurities are marked with and traces of free ligand 60 with L The scale is in ppm

singlet at δ = 398 ppm (5 H) was assigned to a new Cp group (Figure 217) and two new TMS singlets (9 H each not shown) were also present The new broad Cp absorption displayed peculiar behavior gradually moving to higher field (∆δ ~ 08 ppm for Cp-H) on warming from ndash30 degC to 10 degC (Figure 217) The broadened singlet at δ = 558 ppm showed similar albeit much attenuated behavior At room temperature all new peaks had disappeared leading to regeneration of the original spectrum of 19

Figure 217 Stacked plot of the Cp spectral region in the cold irradiation of 19 in toluene-d8 Peaks for molecule 19 are indicated by blue the new peaks by red arrows The scale is in ppm

In addition to these NMR observations a remarkable change in color from the redmaroon of 19 to olive green took place during the course of this experiment (Figure 218) Indeed the UV-Vis spectrum of the low temperature species is strikingly different from that of 19 showing a large broad absorbance band centered in the visible region

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

19

THF

- 45 -

Figure 218 Color change during the low temperature irradiation of 19 (a) Before irradiation (b) After irradiation

Complex 19

Low Temperature Species

0

02

04

06

08

1

12

14

16

18

2

400 430 460 490 520 550 580 610 640 670 700

Wavelength (nm)

Ab

sorb

an

ce

Figure 219 UV-Vis spectra (toluene) of 19 (at rt) shown in blue and the new compound (at ~

ndash30 degC) shown in red

at 654 nm (Figure 219) Warming the sample to room temperature restored its original red color While the observation of a new species was gratifying the NMR data posed a puzzle as they were clearly incompatible with (a static) structure 68 Instead they pointed to a molecule exhibiting mirror (or ldquotop-downrdquo) symmetry along the long molecular axis as in 19 itself The two most obvious candidates 69 and 70 (Figure

(a) η

4 (b) η

4

- 46 -

220) were ruled out as the first could not be found during the computations underlying Figure 29 and the second actually constitutes the transition state TS 1 for the thermal reverse process

Figure 220 Possible (but unlikely) structures of correct symmetry for the low temperature

photoisomer of 19 In the hope to shed further light on the nature of purported 68 low temperature 13C in conjunction with 2-D NMR (HSQC HMBC) experiments were carried out These data led to the tentative assignments shown in Figure 221 Assuming the presence of top-down symmetry as surmised by the proton spectra one would have expected to observe nine phenylene carbon signals The actual spectrum however contains only six peaks The Cp line was broadened to the point of being barely visible and no crosspeaks for the absorption at δ = 556 ppm were seen by 2-D NMR spectroscopy

Figure 221 Partial assignments of 1H-(italicized) and 13C-NMR signals of 68 The ldquotop-downrdquo plane of symmetry is indicated by the dashed purple line HMBC δ = 643 ppm correlates with δ = 1461 and 1521 ppm δ = 708 ppm correlates with δ = 1477 and 1508 ppm δ = 033 ppm

correlates with δ = 1477 ppm and δ = 036 ppm correlates with δ = 1461 ppm HSQC δ = 643 ppm correlates with δ = 1121 ppm δ = 708 ppm correlates with δ = 1227 ppm and δ = 398

ppm correlates with δ = 85 ppm The connectivity of the CpCo to the central ring is left intentionally unspecified and the choice of positioning it to the left of the center hydrogens (blue)

SiMe3

SiMe3

H

Me3Si

Me3Si

H

Co

398 (br)

HH

1461

~85 (br)

708

H

556 (br)1508

= Unobserved 13C signals

H

H

Mirrorplane

6431477 1521

033036

11211227

- 47 -

arbitrary Similarly the assignments of the groups of ldquoleftrdquo and ldquorightrdquo benzene signals are tentative and might be inverted The carbons marked could not be observed

It is thus clear that we are dealing with an unusual species and if it is 68 the molecule must be partly (but not completely) fluxional around the central ring Returning to the computed energy profile in Figure 29 one notes that central η4η4-benzene fluxionality via TS 2 with a barrier of 140 kcalmol is presaged This process which causes ldquoleftrdquo-ldquorightrdquo but not ldquotoprdquo-ldquobottomrdquo symmetrization is unlikely to be responsible for the above data as it should have given rise to two 1H-NMR singlets for the central hydrogens However considering the expected relative closeness in the respective chemical shifts of the anticipated signals (see Figure 214) accidental isochronism could not be ruled out Consequently low temperature irradiation experiments were executed with 52 in which the ldquoleftrdquo-ldquorightrdquo option of symmetrization was obviated by the substitution pattern while leaving the ldquotoprdquo-ldquobottomrdquo option intact (Scheme 221) As Scheme 221 Low Temperature Irradiation of 52 and Possible Pathways for Fluxionality of

Intermediate 71

indicated in color the latter would provide a diagnostically simple proton spectrum of only four phenylene signals The former on the other hand should show eight such peaks A potential complication of this experiment was the possibility of two regioisomeric (and non-interconverting) cobalt species located on either side of the central six-membered ring (Scheme 222) In the event the spectra shown in Figure 222 were obtained At ndash60 degC in

HH

CoTMS

TMS

CoTMS

TMS

TMS

TMS

Co

TMS

TMS

CoTMS

TMS

Co

TMS

TMS

Co

Top-bottom

cold hν ∆

Lef t-right

52 53

∆

71

or

H

HH

H

H H

H HH

HH H H

H

- 48 -

addition to unreacted 52 and photoisomer 53 a new species formed the spectral features of which implicate 71 as a ldquotop-bottomrdquo symmetrizing species Specifically the

Scheme 222 The Two Possible Regioisomers of 71 ldquoLeftrdquo and ldquoRightrdquo

71

52

53 53

53

52

TMS

TMS

Co

TMS

TMS

Co

TMS

TMS

Co

71

TMS

TMS

Co

or

Right Lef t

ndash60 degC

ndash50 degC

ndash40 degC

ndash30 degC

53

- 49 -

Figure 222 Stacked plot of the aromatic spectral region in the cold irradiation of 52 in toluene-d8 Peaks for molecule 52 are marked by blue arrows 53 in red and 71 in green Trace amounts

of free ligand bis(trimethylsilyl) linear [3]phenylene] 46 are denoted with L The scale is in ppm

unsubstituted benzene terminus hydrogens exhibit an AArsquoBBrsquo pattern at δ = 647 ppm which integrate for 4 hydrogens The central ring hydrogens appear as a broad singlet at δ = 557 ppm (2H) and the silylated terminus as a singlet at δ = 632 ppm (2H) Warming the reaction mixture to 10 degC led to the gradual disappearance of 71 with a concomitant increase of the signals assigned to 52 and 53 This experiment confirms the conclusions drawn as a result of the low temperature irradiation of 19 namely that a ldquotop-bottomrdquo symmetrizing species is generated Remarkably in view of the possibility of two regioisomers (Scheme 222) only one set of peaks is observed indicating that the excited state of 53 relaxes to settle on only one side of the central ring Which side is a matter of speculation Figure 223 compares the 1H chemical shifts of 71 with those of 68 and for calibration 52 53 and free ligands 46 and 60 For the first pair it is clear that the two species are very similar with almost identical chemical shifts of the relevant hydrogens taking into account the considerable deshielding effect of TMS substitution on the unsubstituted terminus in 73 (~07 ppm cf 52 vs 53 46 vs 60) Arguably placing the CpCo moiety to the ldquoleftrdquo as depicted in 68 and 71 aromatizes the proximal benzene by η2-complexation of the adjacent four-membered ring leaving considerable benzocyclobutadiene character on the ldquorightrdquo consistent with the associated chemical shifts

- 50 -

CoTMS

TMS796675674

678

CoTMS

TMS747683724

662

Co

TMS

TMS

52

71

53

424

642

557 632652

436 444

Co

TMS

TMS

68

398

556 643708

TMSTMS

TMS

TMS684607619

645

46

assignmenttentative

TMS

TMS

TMS

TMS623 685

60

TMS

TMS

TMS

TMS

Co

691 795745

19

441

Figure 223 1H-NMR chemical shift comparison of 68 and 71 with other relevant species A plot of the changes in concentration of 52 53 and 71 with temperature is shown in Figure 224 Within (the considerable) error and considering the unusual magnetic behavior of 71 (vide infra) it appears that the latter converts mainly to 52 in the temperature regime in which 53 is stable with respect to its thermal reverse to 52 This observation may be interpreted as indicating a lower barrier for Co migration from the center ring to the more stable cyclobutadiene haptomer

- 51 -

0

1

2

3

4

5

6

7

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Inte

gra

tio

n v

s I

nte

ra

l S

tan

da

rd

52

53

71

Figure 224 Plot of the concentration changes of 52 53 and 71 with temperature measured by the relative integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively

The ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100)

Another plot this one showing the ratios of 52 53 and 71 with respect to each other is given in Figure 225 The disappearance of 71 with rising temperature is illustrated by the increase in the ratios of 5271 and 5371 As indicated by the steep slopes the conversion of 71 into 52 and 53 is particularly fast between ndash10 and 0 degC That complex 52 is preferentially formed is again confirmed by the escalating 5253 ratio While these data do not provide a definitive answer for the location of the CpCo they are consistent with the plots shown in Figure 224 and the above discussions

- 52 -

0

1

2

3

4

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Rel

ati

ve

Inte

gra

tio

n

5271

5371

5253

Figure 225 Plot of the ratios of 52 53 and 71 against each other with temperature measured by the integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively The

ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100) Having established the topological aspects of 68 and 71 attention was turned to their peculiar NMR characteristics in the vicinity of the metal ie the broad peaks for the central hydrogens and the CpHs the broad Cp-carbon line the inability to observe 13C signals for the central benzene ring and the temperature dependent drifting of (particularly) the Cp absorption A trivial (and ultimately unsatisfying) explanation for at least peak broadening was the presence of trace paramagnetic metallic impurities60 that might have been generated during the irradiation process Spin exchange preferentially Co-based might affect the center atoms in 68 and 71 more than the remainder of the molecule although it should also cause line broadening in the isomers 19 and 52 and 53 respectively Experimentally the presence of such species was made unlikely by executing the cold irradiation experiment of 19 in the presence of the radical trap 13-cyclohexadiene which produced spectra identical to those described earlier An attractive alternative that might explain the data and in addition provide a mechanism for ldquotop-downrdquo exchange is of the intervention of triplet state cobalt species The ability of metals to change their electronic spin state and the consequences of this phenomenon on organometallic structure and reactivity are well documented61

18-Electron CpCo complexes are ground state singlets but their 16-electron counterparts accessed typically by ligand dissociation have more stable triplet configurations62 A number of CpCo and related Co species have also been reported in

- 53 -

which singlets are in thermal equilibrium with paramagnetic triplets by intersystem crossing63 Such complexes display spectral behavior very similar to that seen for 68 and 71 For example 7263b exists as a mixed spin state system in which the singlet predominates at room temperature in solution (Figure 226) On heating the triplet becomes increasingly populated shifting and broadening its NMR signals Cooling the solution back to room temperature reverses these spectral changes In addition to complexes of cobalt analogous observations have been reported for other metals such those based on hafnium64 copper65 ruthenium66 and tungsten67

Figure 226 Temperature dependent chemical shifts in CpCo derivative 72 in toluene-d8

(marked as S on the plot) The scale is in ppm

Consideration of these examples would then suggest that 6871 undergo ldquotop-downrdquo equilibration through a triplet 16-electron intermediate or that 6871 themselves are triplets or have thermally accessible triplet states from which fluxionality might occur Since the relaxation times (T1) of paramagnetic systems60a are much shorter compared to their diamagnetic counterparts measurement of this property was thought to be informative The T1 values for the proton in 68 were determined via a standard inversion recovery experiment44 and are given in Table 24 (cf Figure 220) in comparison to p-terphenyl60b

Co

CoPMe3

72

- 54 -

Table 24 1H-NMR Relaxation Times in Intermediate 68 at ndash30 degC

Resonance (ppm) T1(s) 711 2309 646 0997 556 005 398 0108

In consonance with the associated line broadening the relaxation times of the Cp

(δ = 398 ppm 0108 s) and central ring hydrogens (556 ppm 005 s) are much smaller than those of the remaining phenylene ligand (711 and 646 ppm 2309 and 0997 s respectively) the latter in turn comparing well with the values in p-terphenyl With this corroborative evidence in hand the question whether the species is itself a triplet or is in thermal equilibrium with such was addressed The answer can be obtained by using a Curie-like graph68 in which chemical shifts are plotted as a function of temperature65 A linear relationship corresponds to the presence of a triplet compound while curved behavior is indicative of a singlet-triplet equilibrium Plotting the chemical shifts of the Cp hydrogen of 68 and 71 against the inverse of temperature (Figure 227) gave distinctly curved lines supporting the notion that these species are in thermal equilibrium with their triplets The exact nature of these species however remains to be determined

156

395404

345

p-Terphenyl

- 55 -

3

32

34

36

38

4

42

44

46

00036 00038 0004 00042 00044 00046 00048

1T (K -1

)

Ch

em

ica

l S

hif

t (p

pm

)

71

68

Figure 227 Plot of the Cp chemical shift (toluene-d8) of 68 and 71 versus the inverse of temperature

DFT calculations have commenced in an attempt to find a plausible structure for such a triplet cobalt species and with it possibly arrive at a mechanism for the fluxional behavior of 68 and 71 These studies are being carried out in collaboration with Professors Tom Albright of the University of Houston and Vincent Gandon of the Universiteacute Paris-Sud 11 Preliminary results at the B3LYP6-31G(dp) and BP866-31G(dp) levels suggest the η2-cyclobutadiene structure depicted in Figure 228 It is apparent that this species corresponds topologically to singlet TS 1 in Figure 29 and 70 in Figure 220 endowed with the symmetrical requirements dictated by the experiments

- 56 -

Figure 228 Calculated structure of a triplet η2-cyclobutadiene linear [3]phenylene(CpCo)

One can therefore envision fluxionality between the two ldquotoprdquo and ldquodownrdquo η4-benzene structures via the intermediacy of a triplet η2-cyclobutadiene (Scheme 223) Further Scheme 223 Conversion of ldquoTop-Downrdquo η4-Haptomers of 68 Via a Triplet η2-Cyclobutadiene

Intermediate

computations are required to pinpoint the minimum energy crossing points between the singlet η4 and triplet η2 structures and to explain why this triplet does not collapse to the CpCo cyclobutadiene isomer This work is in progress 26 Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 All of the linear phenylene(CpCo) complexes mentioned thus far share one common feature a single CpCo unit bound to the phenylene scaffold However since there are one or more additional cyclobutadienoid rings in the series the question arises whether it might be possible to bind more than one metal fragment to the ligand If so what would be the structural consequences Would be there further metalloaromatization Would such systems be capable of light-induced haptotropism and if so how would the metals move relative to the ligand and to each other Finally would such complexes mimic structurally the variety of arrays obtained in the reaction of 29 with Fe2(CO)9 (Scheme 15) Since the linear phenylenes become increasingly more antiaromatic with size the optimal candidates for preparing such multi-metallic systems should be the higher members of the series Indeed evidence for double CpCo attachment was obtained in the form of the minor by-products 73 and 74 (Scheme 224) obtained during the

Scheme 224 Side Products in the Preparation of Linear [4]- and [5]Phenylene(CpCo)

- 57 -

Complexes by Cobalt-Catalyzed Cyclization

preparation of 20 and 21 respectively (Scheme 13) These Diels-Alder type adducts of a third BTMSA molecule to the π-frame can be envisaged to be derived from 75 and 76 respectively in which the six-membered ring flanked by the two CpCo(cyclobutadiene) units would be expected to have an unusual (biradicaloid) electronic structure Evidence for the feasibility of such arrays rests on the unique black-red syn-bis(irontricarbonyl) compound 77 whose structure was determined by X-ray analysis69 With reasonable quantities of 19 in hand the possibility of ligating a second CpCo unit to it was explored This idea was further encouraged by the observation that crude samples of bis(trimethylsilyl) linear [3] phenylene(CpCo) complex 53 contained a very small (3 ) peak at mz = 618 an exact match for the mass of a doubly metallated analog Consequently 19 was treated with one equivalent of CpCo(C2H4)2 in benzene to afford a reddish black solid (Scheme 225) The mass spectrum data exhibited a

Scheme 225 Preparation of Complex 78 from Complex 19

TMS

TMSTMS

TMS

CoCpCo(C2H4)2

22h 70 oC C6H6Linear [3]TMS4(CoCp)2

5619 78

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

74

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

73

TMS

TMS

TMS

TMSCoCpCpCo

76

TMS

TMS

TMS

TMSCoCpCpCo

75

Ph

Ph

Ph

Ph

Fe(CO)3Fe(CO)3

77

- 58 -

molecular ion peak at mz 762 corresponding to 19(CpCo)2 The 1H-NMR spectrum (acetone-d6) revealed four sharp singlets integrating in the ratio 410236 indicative of a highly symmetrical structure The chemical shift of the benzene termini (736 ppm) suggested that these rings have significant aromatic character and is similar to the value of 745 ppm seen for the hydrogen positioned farthest away from the CpCo in 19 (Figure 27) Similarly the 13C signals of the terminal rings in 78 (1505 1454 and 1258 ppm) are analogous to those from the corresponding terminal ring in 19 (1484 1433 and 1256 ppm Figure 28) Detailed analysis of 78 with two-dimensional NMR techniques (HSQC and HMBC) allowed for a complete assignment of all peaks in the 1H and 13C spectra (Figure 229) The strongly shielded (relative to the free ligand) proton (481 ppm) and carbon (537 and 571 ppm) resonances assigned to the central benzene ring clearly showed that both cobalt fragments are coordinated to the phenylene ligand at this position Interestingly these data bear a very close resemblance to those of the corresponding diiron complex 31 (Scheme 15) and are compared in Figure 229 Its central 13C resonances (688 and 582 ppm) are shifted upfield in a manner akin to 78 although not quite as much reflecting the increased electron withdrawing ability of the Fe(CO)3 group relative to CpCo70 Complex 31 like 78 exhibits aromatized terminal benzene rings as indicated by its 1H (750 ppm) and 13C (1484 1446 and 1258 ppm) chemical shifts These spectral similarities make it likely that 78 and 31 are isostructural The only structural ambiguity pertains to the orientation of the two metal fragments with respect to the π ligand a problem that had been left undecided in the assignment of structure 31 ie 31a (syn) versus b (anti Scheme 15)27 These options for 78 are

- 59 -

CpCoTMSTMS

TMS TMS

H H039 (36)

537 1258822

270

1454571

1505

481 (2) 736 (4)489 (10)

TMS TMS

TMSTMS

H

(OC)3Fe

(OC)3Fe

CpCo

78

31a

750 (4)553 (2)

036 (36)H

220

1446

1258

1484

688582

2128

Figure 229 Comparison of 1H- and 13C-NMR assignments (ppm) for molecules 78 (acetone-d6) and 31 (1H acetone-d6

13C CDCl3) Proton chemical shifts are in red and carbon in blue Integrations for the proton resonances are in green HSQC for 78 δ = 039 ppm correlates with δ = 270 ppm δ = 481 ppm correlates with δ = 537 ppm δ = 489 ppm correlates with δ = 822 δ

= 736 ppm correlates with δ = 1258 ppm HMBC for 78 δ = 036 ppm correlates with δ = 1454 ppm δ = 481 ppm correlates with δ = 571 and 1505 ppm δ = 736 ppm correlates with δ = 571 1454 and 1505 ppm The placement of the cobalt atoms in 78 is tentative (see Figure

229)

Figure 230 Possible structures for 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

- 60 -

shown in Figure 230) Both equally exotic options are precedented in the literature and corroborated by X-ray structural analyses (Figure 231)71

Figure 231 Illustrative examples of complexes with two metal fragments coordinated to the same benzene ring

Bis(CpFe) complex 7972 and its rhodium analog 8073 contain [M2(syn-micro-arene)] units in which the metals are linked58 Molecule 79 consists of two CpFe units coordinated η4 to the boat-shaped benzene ring sharing ligating carbon atoms In contrast the CpRh fragments in 80 are bound in an allyl η3 manner and the arene also adopts a boat conformation On the other hand bis[tris(tert-butyl)]toluene(CpCo) complex 8174 and the related system 8275 both exhibit [M2(anti-micro-arene)] units in which η4 coordination between the benzene ring and each of the metal fragments takes place Here the metals share carbon atoms but now involving a sandwiched ligand The arene in 81 retains a planar aromatic geometry while the benzene moiety in 82 is bent into a highly distorted chair conformation Unfortunately model structures 79ndash82 do not exhibit diagnostic NMR properties that would provide a clear distinction between synanti and planarnon-planar topologies For example the 1H-NMR peaks for the toluene ligand in anti-complex 81 range from 400ndash380 ppm74 whereas the signals for the benzene moiety in syn-bis(CpRh) 80 appear at 400ndash330 ppm73 The 13C data are similarly inconclusive as illustrated by comparison of 78 (562ndash531 ppm for the benzene ring) with 79 (648ndash525 ppm)72b An interesting property of these bis(metal) arene complexes is fluxionality of the metal fragments by haptotropic shifts along the periphery of the aromatic ring as depicted in Scheme 226 In complex 79 the hexamethylbenzene ligand (bound η4η4

in the solid state) displays a single arene resonance at 588 ppm in its room temperature carbon NMR spectrum Cooling to ndash90 degC however produces two distinct arene peaks at 525 and 648 ppm (for the shared and single-metal-bound carbons respectively as shown in 79a in Scheme 227) Fluxionality was postulated to proceed through an η3η3 intermediate (79b) that is structurally similar to Rh complex 80 which is itself a fluxional species

Scheme 226 Examples of Fluxional Processes in Dinuclear Arene Complexes 79 and 80

82 81

80 (R = CH3)

79

- 61 -

Anti-bis(β-diiminate)Rh complex 83 shows similar mobility (Scheme 226)76 A mechanism for η4η4 migration of the anti-metal fragments was proposed using the lowest energy species found by DFT calculations In these compounds the anti-metal fragments convert between η4η4 (83a 83c 83e) structures by passing through η3η3

(83b) and η4η2 (83d) transition states The energy barrier for η4η4 migration in 83 was experimentally determined to be 6 kcalmol This value is in line with other experimentally measured syn and anti dinuclear ring slippage processes which are typically le ~10 kcalmol71-75 The possibility of fluxionality in 78 might be observable if asymmetric configurations such as 78c and 78d (Figure 231) represent the lowest energy forms since they entail NMR observable desymmmetrization of the ligand Unfortunately cooling 78 in the NMR probe to temperatures as low as ndash80 degC in toluene-d8 did not reveal any signs of signal decoalescence

- 62 -

Figure 232 Possible lowest energy forms of complex 78

Hoping that further light could be shed on the disposition of the CpCo moieties in 78 by chemical transformations a brief investigation of its reactivity was undertaken For example bis(metal) arene complexes have been shown to readily undergo arene exchange reactions71 In complex 81 for example the toluene ligand is displaced by benzene at room temperature74 However heating a sample of 78 to 120 degC in toluene-d8 did not lead to any changes in the NMR spectra Turning to potential photochemical activation 78 was irradiated at various wavelengths (300ndash365 nm) These conditions as well as ambient sunlight did not cause any changes in its 1H-NMR spectrum further documenting 78 as a rather inert species X-ray crystallographic analysis would appear to be the only method of resolving the identity of complex 78 Producing suitable crystals of this molecule however has proven extremely difficult and will be the subject of future investigations 27 Summary and Outlook The work presented in this chapter published as a communication77 has detailed the first examples of η4η4 intercyclobutadiene migration and detailed mechanistic studies of this unprecedented reaction The haptotropic shift was found to be an intramolecular process with the CpCo fragment undergoing various changes in hapticity for the thermal isomerization Low temperature photolytic studies have revealed the existence of a thermally unstable intermediate species the exact structure of which is uncertain These results point to what appear to be significant differences between the photo- and thermal haptotropic pathways Further work both experimental and computational will be required to elucidate the details of the photochemical reaction In addition to the studies of linear phenylene(CpCo) haptotropism a hitherto unknown complex containing two CpCo fragments bound to linear [3]phenylene was prepared and scrutinized in preliminary form Despite extensive characterization the structure of this complex with respect to the position of the metal centers remains elusive Future work will focus on the acquisition of a crystal structure

- 63 -

Chapter 3

Nickel-Catalyzed Insertion Reactions for the Preparation of [N]Phenacene Derivatives

31 Introduction Transformations involving metal insertion into the four-membered ring of the [N]phenylenes as discussed in Section 12 represent a significant mode of reactivity with a high potential for practical synthetic utility One specific application of this chemistry is the synthesis of the phenanthrene moiety via tandem metal insertion and alkyne cycloaddition to the four-membered ring (Scheme 31) Such a methodology Scheme 31 Potential Preparation of the Phenanthrene Group from the Alkyne Cycloaddition

with Biphenylene would be valuable for the preparation of PAHs possessing phenanthrene subunits but has remained fairly unexplored Only a few examples demonstrating this transformation have been detailed previously for biphenylene (7) (Scheme 32)

Scheme 32 Metal Catalyzed Alkyne Cycloaddition Reactions with Biphenylene

The first report of this process is by Eisch in 198533a who treated biphenylene with Ni(PEt3)4 and diphenylacetylene to produce 910-diphenylphenanthrene 84 Since then a number of metals have been shown to mediate this process19 Ni systems being most relevant to this chapter Thus for example 84 can also be made using an N-heterocyclic carbene-based Ni(0) catalyst78 Bis(diisopropylphosphino)ethane Ni(alkyne) species enable similar cycloadditions of fairly hindered (trimethylsilyl)alkynes sometimes involving more complex processes of silyl group migration79 while less hindered substrates lead to 84ndash8680a A mixed phosphinoaminoethane-chelated Ni species proved more reactive enabling cycloaddition of even the encumbered tert-butyl(phenyl)acetylene to furnish the corresponding phenanthrene80b With this background in mind our attention turned to applying this reaction to larger phenylene systems Of the various topologies of phenylenes at our disposal the angular version was

R1 R2

R2R1[M]

[M]

7 R R

R = Ph (84)

R = Me (85)

R = CH2OMe (86)

RR

[Ni]

- 64 -

particularly intriguing as it offered two extreme modes of alkyne addition (Scheme 33) In the first scenario exclusive attack at the outer periphery of the four-membered rings would produce the helical shaped PAHs known as helicenes (Scheme 33a)81

Scheme 33 Alkyne Cycloaddition with Angular Phenylenes to Produce (a) Helicenes or (b) Phenacenes

Reactions occurring only at the interior or ldquobayrdquo region (Scheme 33b) however would afford a class of compounds exhibiting a linear polyphenanthrene motif that are known as [N]phenacenes82 Unselective additions would result in mixed topologies Helicenes and their various derivatives constitute a well studied83 family of molecules and continue to be a popular area of research Phenacenes in contrast have been scrutinized much less in part because only four members of the parent series are known and because for N = 5 and 6 they are extremely insoluble84 Phenacene-based applications have been slow to develop but the first reports of the utilization of these molecules as functional organic materials suggest the beginning of a rich and promising field85 Thus in 2008 [5]phenacene (picene) was demonstrated to behave as stable high performance organic field effect transistor (FET)85b Currently the most common organic polycyclic benzenoid hydrocarbon-based FETs employ acenes which have a polyanthracene structure (Figure 31) The sensitivity

Figure 31 Linearly fused benzene topology of the acenes of these systems to air however has obstructed progress in this area86 For example pentacene a commonly used acene in FETs reacts readily with oxygen to form

+ RR

Helicenes

+ RR

Phenacenesn

R

R R R R

n

R

R

R

(a)

(b)

[N]Acenes

n

- 65 -

pentacenequinone a process that severely reduces device efficiency (Scheme 34)

Scheme 34 Degradation of Pentacene to Pentacenequinone Under Aerobic Conditions

Phenacenes on the other hand are much less prone to such decomposition pathways due to their higher HOMO-LUMO gap thus rendering them less reactive85b86a Their enhanced stability relative to acenes87 makes them better candidates for molecular electronic applications In a second seminal breakthrough [5]phenacene was very recently also found to behave as a superconductor at low temperature when doped with potassium85a This work paves the way for a new class of PAH-based superconducting materials in which phenacenes may play a key role

As this chemistry advances new synthetic methods for preparing derivatives of these molecules will be required in particular those bearing solubilizing andor otherwise functionally useful substituents The most general procedure for synthesizing phenacenes as developed by Mallory88 makes use of oxidative stilbene photocyclizations (Scheme 35)8388 In this transformation irradiation of the stilbene

Scheme 35 Generic Oxidative Stilbene Photocyclization Used to Prepare Phenacenes as Illustrated for Phenanthrene

moiety leads to conrotatory electrocyclic ring closure Trapping of the resulting intermediate with oxidizing reagents such as iodine or oxygen yields the desired phenanthrene subunit The requisite stilbenes are most generally accessible via the Wittig reaction as illustrated in the synthesis of [7]phenacene derivative 87 (Scheme 36) Although the yields for the photocyclization are typically reasonable (60ndash90 )85a the major drawback of this methodology is the numerous steps associated with preparing the functional groups required for the prerequisite Wittig reaction These

- 66 -

transformations serve to decrease the overall yield of the target molecule

Scheme 36 Synthesis of [7]Phenacene 87

While laborious Malloryrsquos method addresses successfully the problem of solubility As alluded to in Section 21 large PAHs become insoluble due to the increased π-π stacking forces that are experienced between aromatic rings The best solubilizing groups for the phenacenes were found to be sterically bulky groups located in the bay regions85a These modifications distort the phenacene framework from planarity thereby disrupting π-stacking and increasing solubility as demonstrated by the tert-butyl [7]phenacene 87 (Figure 32) This approach was applied to systems as large as [11]phenacene the current record in the series85a

Br

CH3t -Bu

1 BuLi2 DMF

Br

CH2

t-Bu

CHO

CH3t-Bu

PPh3

Br

+Wittig

t-Bu t-Bu

Br CH3 1 hν2 I2

t-Bu t -Bu

Br CH3

t-Bu t-Bu

Br H2C PPh3 Br

+

t-Bu t-Bu

OHC CH3

Wittig

t-Bu t-Bu

Br Br 1 hν2 I2

t-Bu t-Bu

Br CH3

t-Bu t -Bu

t-Bu t-Bu

87

1 NBS2 PPh3

- 67 -

Figure 32 Crystal structure of tetrakis(tert-butyl) [7]phenacene 87 Hydrogens are omitted for clarity

To test the viability of angular phenylenes as substrates in Ni catalyzed alkyne cycloadditions the simplest member 22 was chosen raising a number of questions First how many and what kind of products will be formed (AndashE in Scheme 37) Will there be inherent selectivity toward helicene C or phenacene E formation respectively If not can the reaction conditions be modified so as to induce such What will be the limitations with respect to the size of substituents especially in view of the crowded fjord and bay regions of D and E respectively The work presented in this chapter carried out in collaboration with Dr Zhenhua Gu89 explores these questions

Scheme 37 Possible Cycloaddition Products of Angular [3]Phenylene 22

22

[Ni]R R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

A B

C D E

32 Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene

Before embarking on the proposed chemistry the reactivity of 22 in the presence of nickel in the form of Ni(COD)(PMe3)2 in the absence of alkynes was queried Only starting material was recovered and there was no sign of dimerization (or oligomerization) to products of the type shown in Scheme 38 a mode of reactivity

- 68 -

readily attained by biphenylene and substituted derivatives33b

Scheme 38 Attempted Dimerization of Angular [3]Phenylene 22

In contrast exposing diphenylacetylene 88 to Ni(COD)(PMe3)2 and a small excess (109 equivalents) of angular phenylene 22 generated two products in the absence of any other (Figure 39) The first molecule 89 was the result of the cycloaddition of one diphenylacetylene at the bay region and the minor component The major product constituted tetraphenyl [5]phenacene 90 derived from 22 by double bay region attack The structures of both compounds were confirmed by X-ray analysis revealing highly distorted frames89 Scheme 39 Nickel Catalyzed Cycloaddition of Angular [3]Phenylene 22 to Diphenylacetylene

Yields Based on Diphenylacetylene

The outcome of this transformation was gratifying in its seeming simplicity and selectivity Thus it appeared that metal insertion occurred exclusively to bay region bonds heralding the discovery of a new phenacene synthesis The observation of relatively large amounts of 90 could be ascribed to increased reactivity of 89 relative to 22 possibly due to steric activation by the newly introduced bay region phenyl group To test this hypothesis 89 was subjected to the cycloaddition reaction conditions (Scheme 310) Surprisingly not only was this reaction slower than that of 22 but the expected phenacene 90 was only a minor product (6 ) Instead tetraphenylbenzo[c]chrysene 91 a regioisomer of 90 as confirmed by X-ray analysis89

+

+ +

Ni(COD)(PMe3)2

22

- 69 -

was isolated in 74 yield the result of non-bay alkyne cycloaddition to 89 Therefore 89 is not the precursor of 90 Rather there must be separate reaction pathways leading to each respective product

Scheme 310 Cycloaddition Reaction of 89 with Diphenylacetylene 88

A series of semi-quantitative experiments monitored by 1H-NMR spectroscopy was carried out to shed some light on this mechanistic problem First the reaction of angular [3]phenylene 22 with diphenylacetylene 88 in Scheme 39 was addressed Because dinuclear metallic activation of the strained C-C bond in biphenylenes has been implicated in a number of studies19 it was possible that the above mechanistic duality was caused by the presence of catalytic Ni2 species in addition to the ldquoregularrdquo mononuclear alternatives Alternatively double Ni insertion before cycloaddition might be responsible for one product whereas sequential ldquonormalrdquo activation might be the origin of the other Therefore the amount of initial Ni(COD)(PMe3)2 was gradually increased and the effect of this incremental change on rate and product ratios recorded As shown in Table 31 the speed with which 89 and 90 formed was roughly proportional to the amount of metal present while the product ratio stayed unchanged

Table 31 Variation of Catalyst Loading in the Reaction of Phenylene 22 with Diphenylacetylene 88 Reactions Were Carried Out with Equimolar Amounts of 22 and 88 in

THF-d8 at 40 degC

Run Ni(COD)(PMe3)2

(mol) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

Ratio of 8990

1 50 32 times 10ndash4 031 times 10ndash4 103 2 35 20 times 10ndash4 022 times 10ndash4 91 3 7 064 times 10ndash4 0064 times 10ndash4 100

Next the amount of diphenylacetylene 88 was gradually increased from 1 to 4 equivalents (Table 32) The outcome of this series of experiments was counterintuitive as it led to a larger preference for the production of monoadduct 89 suggesting a mechanistic bifurcation in which whatever Ni species is responsible for the eventual formation of 90 is sequestered by external ligand (in this case 88)

- 70 -

Table 32 Variation of Alkyne Equivalents in the Reaction of 22 (1 equiv) with Diphenylacetylene 88 in the Presence of 50 mol of Ni(COD)(PMe3)2 Experiments Were Run

in THF-d8 at 40 degC

Run 88 (equiv) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

8990

1 10 320 times 10ndash4 031 times 10ndash4 103 2 20 220 times 10ndash4 018 times 10ndash4 122 3 40 220 times 10ndash4 011 times 10ndash4 200

Following the reaction progress by NMR spectroscopy afforded additional insights Thus mixing the ingredients at room temperature left the phenylene component untouched Instead there was a near instantaneous displacement of COD by diphenylacetylene to produce Ni(PhCequivCPh)(PMe3)2 (92) and free COD in addition to the generation of Ni(PMe3)4

90 The speed with which this complex was formed implied that it might be the active catalyst precursor Consistent with this notion higher reaction rates were observed when the reaction in Scheme 38 was carried out with pure 9291 as the catalyst (50 mol) and 05 equivalent of 88 (Table 33 Run 2) In consonance with Table 32 the lesser concentration of available free alkyne increased the relative amount of 90 formed Conversely (Run 3) using Ni(COD)(PMe3)2 with an extra equivalent of PMe3 decreased the rates of formation of 89 and 90 and increased the ratio of 8990 consistent with ligand inhibition of the activation of 92 and the external ligand effect noted in Table 32 Table 33 Variation of Catalyst in the Reaction of 22 with Diphenylacetylene 88 and its Effect

on Reaction Rate Experiments Were Run in THF-d8 at 40 degC with 1 Equivalent of 22

Run Catalyst 88

(equiv)

Rate of formation of 89 (mol

Lmiddoth)

Rate of formation

of 90 (mol Lmiddoth)

8990

1 Ni(COD)(PMe3)2 10 320 times 10ndash4 031 times 10ndash4 103 2 Ni(PhCequivCPh)(PMe3)2 (92)

(05 equivalent) 05 1270 times 10ndash4 210 times 10ndash4 60

3 Ni(COD)(PMe3)2 (05 equivalent) + PMe3 (10 equiv)

10 088 times 10ndash4 005 times 10ndash4 163

Attention was then shifted to the reaction of monoadduct 89 with 88 as in Scheme 310 (Table 34) Here increasing the amount of alkyne and catalyst favors the formation of 91 consistent with an independent pathway At low concentration of alkyne it appears that 89 reenters the manifold of its generation and proceeds on to 90 Indeed following the change in the ratio of 9190 in Run 1 (Table 34) with time reveals a decrease from 47 to the eventual 22 as 88 is depleted

- 71 -

Table 34 Variation of Catalyst Loading and Alkyne Concentration in the Reaction of 90 with Diphenylacetylene 88 Reactions Were Run in THF-d8 at 40 degC

Run 88 (equiv) Ni(COD)(PMe3)2

(mol) 9190

1 10 50 2 2 30 50 15 3 30 10 25

The information obtained from these experiments allowed a narrowing of mechanistic possibilities For example dinuclear Ni activation only one possibility of which is shown in Scheme 311 was rendered unlikely by the absence of any observable changes in product distribution of the reaction in Scheme 39

Scheme 311 Generic Example of a Dual Mechanism Based on Mono- and Dimetallic Phenylene Activation

An alternative mechanism shown in Scheme 312 was in much better agreement with the results of the various control experiments The first step would be displacement of a phosphine in the initially dominant Ni-containing species 92 by angular [3]phenylene 22 inhibited by added PMe3 From 93 oxidative addition can take place to afford metallacycle 94 Why should bay region insertion be favored Arguably the regioselectivity of this step is controlled by the lesser steric hindrance in the resulting arene fragment or relative stabilization of the polarized Ni-C(α-

PhPh

Ph Ph Ph Ph

PhPh

NiL L

Ni(COD)(PMe3)2

NiNiL L L L

PhPh

2

Ph

Ph

Ph Ph Ph Ph Ph Ph

+

+22

89

90

91 90

- 72 -

biphenylene) bond in 94 by the electron withdrawing nature of the neighboring cyclobutadienoid ring This phenomenon in biphenylene is due to the rehybridization of the four-membered ring carbons to adopt relatively larger p character in the strained linkages hence larger s character (ie electron withdrawing) in the remaining bond and manifests itself most clearly in the relative acidity of the α-hydrogens7a This step is followed by migratory insertion and reductive elimination to produce molecule 96 the mechanistic bifurcation point One branch proceeds through presumably ligand-assisted metal dissociation to generate the relatively unreactive free 89 The second entails Ni migration92 and insertion into the bay region of the remaining four-membered ring (97) before the second cycloaddition occurs generating phenacene 90

Scheme 312 Possible Mechanism for the Alkyne Cycloaddition Reaction of Angular [3]Phenylene 22

The regioselective formation of 97 may again be sterically dictated or may involve anchimeric assistance by the bay-region phenyl group as sketched in Scheme 313 specifically 99

Scheme 313 Anchimeric Assistance on Route to [5]Phenacene 90

Ph Ph

PhPhPhPh

Ph

Ph

Ph PhNi

NiMe3P Ph

Ph

Ni

Me3P Ph

Ph

NiPMe3Me3P

Ligand exchangeOxidativeaddition

Migra toryinser tion

Reductiveelimination

Ph

Ph

Me3P

Ni migra tionOxidative addition

22

92

9394

96 89

9097

Ph Ph

Ni

Me3P

Ni(PMe3

Ph

Ph

minusNi(PMe3)

95

- 73 -

This type of metal coordination to the double bond of a proximal arene ligand is common and two examples are provided based on ruthenium94 and molybdenum95 (Figure 33)

Figure 33 Examples of complexes with phenyl groups coordinating to a nearby metal center Turning to the largely selective conversion of 89 to 91 (Scheme 310) requires the postulate of preferential insertion of the metal at the non-bay region and hence a different Ni species from that in 96 possibly a Ni(PMe3)(alkyne) moiety akin to that in 93 ie 100 (Scheme 314) Bay insertion would lead to metallacycle 101 and ultimately molecule 90 The expected large degree of steric repulsion between the phenyl groups in 101 should disfavor this reaction pathway On the other hand non-bay insertion to produce 102 should be relatively less impeded and would furnish 91 Another option for the generation of 90 from 89 would be reentering the pathway described in Scheme 312 facilitated at low concentrations of alkyne consistent with the data in Table 34

Scheme 314 Proposed Mechanism for the Alkyne Cycloaddition Reaction of 89

Ni

PhMe3P

PhPh

(Me3P)Ni

PhPh(Me3P)Ni

Ph

Ph

93 98

99

Ph Ph Ph Ph

90

+

Ph Ph

Ni

Me3P

97

- 74 -

While the above mechanistic perambulations appear plausible it should be stressed that they are speculative and may be restricted to diphenylacetylene 88 as the substrate Thus both 3-hexyne 103 and 14-dimethoxy-2-butyne 106 added to 22 less selectively than 88 to provide only the bay and non-bay monoadducts 104 and 105 and 107 and 108 respectively (Scheme 315)

Scheme 315 Reaction of Angular [3]Phenylene 22 with Other Alkynes

NiMe3P PMe3

Ph Ph+

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph

Ni(PMe)3

PhPh

Ni(PMe3)

Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

92 89

101

90

102

100

91

Ni

Ph Ph

PMe3

+

R

R

THF-d8 40 oCR

R22

Ni(COD)(PMe3)2

R

R

+

R = Et 104

R = CH2OMe 107

R = Et 103

R = CH2OMe 106 R = Et 105

R = CH2OMe 108

11 45 9 68

- 75 -

In view of these uncertainties recourse was taken to DFT computations delineated in the next section 33 Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene DFT studies were carried out in collaboration with Prof Vincent Gandon of the Universiteacute Paris-Sud 11 The B3LYP 6-31G(d) basis set was used for hydrogen and carbon atoms while LANL2DZ was used for nickel Before attempting to model the more complex alkyne cycloaddition reactions in Schemes 38 and 39 the basic Ni-catalyzed addition of the parent acetylene to biphenylene in the presence of PMe3 was studied (Scheme 316) The free energies

Scheme 316 Computational Modeling of Ni-catalyzed Addition of Acetylene to Biphenylene Free Energies (∆G KcalMol) are Relative to 109 Transition State Energies are Absolute Values

for This Step

NiMe3P PMe3

NiMe3P

NiMe3P

Ni

Ni

PMe3

PMe3

+

+ PMe3+

+ PMe3

+ 2 PMe3

+ 2

(00)

(281)(37)

(140)

(12)

NiMe3P PMe3

NiMe3P

NiNiPMe3Ni

PMe3

PMe3NiMe3P

PMe3

(727) (693) (476) (374) (394) (395)

Ni

Me3P

PMe3Ni

Me3P

Ni

Ni

Me3P

PMe3NiMe3P PMe3

(590) (532)

(157) (125) (150)

Most Accessible TS

+

7

114

110

113109

111 112

Ni

Me3P

(253)

Ni

PMe3

(242)

- 76 -

(∆G) of various possible catalyst structures consisting of an assortment of combinations of nickel PMe3 and acetylene as well as those of several possible transition states and the resulting products were calculated As is evident on inspection of the values in the first part of Scheme 316 a number of species were found to be very close in energy making it difficult to pinpoint a specific structure for the initial insertion step Bis(ethyne) nickel complex 109 was established as the lowest energy nickel species and was thus assigned a relative value of 0 kcalmol The most accessible transition state 110 features the oxidative addition of the Ni(PMe3)(C2H2) fragment 114 (+ 14 kcalmol) in which the alkyne is held exo to biphenylene The corresponding endo structure 111 was found to be just slightly higher in energy by 20 kcalmol as was the bisalkyne transition state 112 It is likely that biphenylene-NiL2 complexes (two of which were calculated at relative energies 242 and 253 kcalmol) lie on the way to these maxima93 Metallacycle 113 the structure ensuing from transition state 110 constituted the lowest energy product uphill from the starting 109 by 125 kcalmol but other alternatives are nearly isoenergetic Clearly however attack by Ni(PMe3)2 or Diels-Alder type cycloadditions are not likely From 113 the species proceeds smoothly by alkyne insertion-reductive elimination to the phenanthrene product a cascade associated with a large exergonic driving force Undaunted by the relatively complicated picture that emerged with biphenylene attention was turned to the original object of scrutiny the cycloaddition reaction between angular [3]phenylene 22 and diphenylacetylene 88 to produce [5]phenacene derivative 90 Modeled in the same manner as described above the metal insertion into the four-membered ring of 22 is shown in Scheme 317 The lowest energy nickel species

- 77 -

was found to be diphenylacetylene complex 92 gratifyingly corresponding to experiment and was set to a reference value of 00 kcalmol One notes again however an array of at least 10 species all of which must be in equilibrium in the initial reaction mixture Notably the Ni-π complexes to 22 are all more than 20 kcalmol higher in energy than 92 providing a computational rationale for the failure to observe such species by NMR The first step in the optimal reaction pathway is the coordination of Ni(PMe3) to the cyclobutadiene ring of 22 which results in formation of η2-like complex 114 Again in gratifying agreement with experiment bay region insertion through transition state 115 to give 116 is favored albeit by a bare 07 kcalmol relative to its non-bay region counterpart 117 Moreover there are at least six other structures that are energetically viable in silico although insertions of Ni(PhCequivCPh)(PMe3) appear less so possibly due to steric hindrance The same observation is made for the products of insertion although 116 emerges as the thermodynamically most stable possibility

Scheme 317 Calculated Structures and Reaction Pathway for the Insertion of Nickel into the Four-Membered Ring of Angular [3]Phenylene 22 Free Energies ∆G are in KcalMol Relative

to 92

The next step was to map out the first alkyne cycloaddition (Scheme 318) Coordination of diphenylacetylene to 116 is endothermic by 139 kcalmol and after migratory insertion produces 119 Interestingly a transition state to regioisomer 95

(328) (352)

NiMe3P PMe3

(364)

NiMe3P

NiMe3P PMe3

NiPMe3

(339)

Ni

PMe3

PMe3

NiMe3PPMe3

NiMe3P

NiPMe3

(16) (04) (108) (117)

NiMe3P PMe3 Ni

Me3PNi

Me3P Ni Ni

PMe3

PMe3

+ [3]+ DPA

+ PMe3+ [3]+ DPA

+ PMe3+ [3]

+ 2 PMe3+ [3]

+ [3]+ 2 DPA

Ph Ph Ph PhPh Ph

Ph

PhPh Ph

Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

Ph

(45) (96)

(00)

(89) (134)

Most AccessibleTS

NiPMe3

+ PMe3+ [3]+ 2 DPA

(314)

Ni

+ 2 PMe3+ [3]+ DPA

Ph Ph

(294)

1i(PMe3)

Ni

PhPh

(212)

(218)

(345)

Ni

PhPh(297)

Ni

Me3P

Ni

Ph

Ph

(350)

Ni

PMe3

(303)

Ni

Ni

(43) (41)

Ph

Ph

PhPh

Ni

PMe3

NiMe3P

(-10) (-22)

(Me3P)Ni

Ni(PMe3)

Ph Ph

Ph Ph(225) (256)

+ PMe3+ 2 DPA

+ 2 PMe3+ DPA

+ PMe3+ DPA

+ PMe3+ DPA

92114

115

116118

117

- 78 -

written (arbitrarily) in Scheme 312 could not be located

Scheme 318 Calculated Reaction Pathway for the Coordination of Diphenylacetylene Migratory Insertion and Nickel Migration Free Energies ∆G are in KcalMol Transition

State Energies are Absolute Values for This Step

Subsequent reductive elimination from 119 occurs to produce nickel coordinated arene species 120 From it free 89 is presumably readily obtained by demetallation in the presence of external ligands shown only for the formation of 92 in a very favorable process (ndash487 kcalmol) This step is sufficiently exothermic to tolerate the emergence of all the calculated species in the starting line up of Scheme 317 and is presumably the source of 89 in Scheme 39 However if not removed the Ni moiety in 120 can migrate along a shallow manifold across the π frame choosing the phenyl functionalized edge of the molecule (cf Section 24) until the remaining four-membered ring is reached (121) At this point two separate reaction pathways become possible Nickel insertion on the side proximal or opposite of the phenyl groups generates 99 or 122 respectively The barriers for these transformations are similar but show a noticeable preference for the formation of 99 In addition there is a significant energy difference (175 kcalmol) between 122 and 99 in favor of the bay region metallacycle The reason is the coordination of the neighboring phenyl ring to the nickel which serves to stabilize 103 vindicating the proposal made in Scheme 313 and providing a rationale for the exclusive observation of 90 in Scheme 39 From 99 as shown in Scheme 319 coordination of diphenylacetylene (123) is followed by migratory insertion to produce 124 Insertion occurs away from the bay region so as to reduce steric repulsion due to the phenyl group in the phenanthrene part of the molecule Finally reductive elimination ensues providing phenacene-Ni

NiMe3P

NiPMe3

Ni(PMe3)

Ni Ph

PhMe3P

Ph

Ph

PhPh

(117)

126

(44)

102

( 80)

01

( 412)

Ph PhNi(PMe3)

( 389)

Ph Ph

45

Ni(PMe3)

( 408)

Ph Ph

13

PhNi

PMe3

Ph Ph

Ni(PMe)3

133

( 488)

117

( 663)

NiMe3P

( 22)

PhPh+

95

116

119

120121 122

99

NiMe3P Ph

Ph

Ph Ph

( 899)

NiMe3P PMe3

Ph Ph+

92 89

- 79 -

complex 125 At this point the stage is set for exergonic nickel dissociation to 90 and catalyst turnover

Scheme 319 Calculated Reaction Pathway for the Second Diphenylacetylene Insertion All Relative Energies (in red) are in KcalMol Transition State Energies are Absolute Values for

This Step

In conclusion of this discussion the consideration of the combined computational and experimental data affords a mechanistic picture of the cycloaddition reaction of diphenylacetylene 88 to angular [3]phenylene 22 (Scheme 39) the essential features of which are summarized in Scheme 320 The crucial point is a mechanistic bifurcation in which 89 is either released early and (nearly) irreversibly from the metal or the metal stays attached so as to effect a second cycloaddition to give 90 This mechanism implies that 91 is formed by a different mechanism involving a different Ni species

PhNi

PMe3

( 663)

+

PhNi

Ph PMe3Ph

Ph

( 403) ( 403)

PhNi

PhPMe3

PhPh

( 519)

94

93

( 696)

PhNi

PhPMe3

Ph

Ph

96

( 817)

Ph Ph Ph Ph

(MeP)3Ni

99

123

124

125

PhPh

Ph PhPh Ph

+Ni

Me3P PMe3

( 1101)

PMe3

90

- 80 -

Scheme 320 Essential Mechanistic Features of the Formation of 89 and 90 in the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene 88 and Angular [3]Phenylene 22

Consequently the reaction of 89 with diphenylacetylene to give 91 (Scheme 310) was also modeled by DFT Of the various options probed that shown in Scheme 321 proved to be most plausible The reaction pathway entails coordination of alkyne-Ni phosphine 126 to molecule 89 which generates complex 127 in a process that is found to require 228 kcalmol of energy Insertion into the non-bay region of the four-membered ring has a barrier of 16 kcalmol and provides metallacycle 128 After the second cycloaddition event benzo[c]chrysene 91 is formed Interestingly the transition state leading to insertion of nickel complex 126 into the bay region of 89 structure 129 was found to be so high in energy relative to 128 that it could not be modeled This is not unexpected as the phenyl group closest to bay region effectively blocks the approach of any catalyst species This result is consistent with the high ratio of 91 to 90 formed in Scheme 310 and the increase in this ratio at higher initial diphenylacetylene concentration Why is any 90 formed and why does its relative proportion increase at lower diphenylacetylene concentration A possible explanation is that under these conditions the concentrations of 92 and 126 are sufficiently small that 89 reenters Scheme 318 competitively

PhPhNi(PMe3)

PhPh

Ni(PMe3)

Ph Ph Ph Ph

PhPh

Ni(PMe3)

Ni

PMe3

Ph Ph

NiPhMe3P

22 116

88

120

121

99

88

90

PhPh

89

Externalligand

assistedNi migration

Regioselectiveinsertion

Regioselectiveinsertion

Mechanistic bifurcation

- 81 -

Scheme 321 Calculated Reaction Mechanism for the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene and Compound 90 Relative Energies are in KcalMol Transition

State Energies are Absolute Values for This Step

Consideration of Scheme 320 suggests that phenacene formation might be maximized by keeping the concentration of external ligand low during the course of the reaction Experiments aimed at verifying this conjecture are the subject of Section 34 in addition to presenting extensions of the methodology to higher angular phenylenes

34 Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions The experimental and computational studies described in Section 33 suggested that the decisive factor for selective formation of phenacene 90 is suppression of metal dissociation in Ni complex 120 This scenario would be achievable by maintaining a low concentration of diphenylacetylene 88 (vide supra) Previously the alkyne cycloaddition was performed with all reagents mixed together at the start of the reaction invariably resulting in a high initial concentration of 88 To obviate this occurrence an alternative procedure was devised In this new arrangement the required stoichiometric amount (in this case two equivalents) of alkyne 88 was slowly introduced to a mixture of 22 and Ni(COD)(PMe3)2 by means of a syringe pump (Scheme 322) The results of varying addition and reaction times are shown in Table 35

Scheme 322 Modified Reaction Alkyne Cycloaddition Reaction Between 22 and 89

Ph Ph

Ni(PMe3)

Ph Ph Ph Ph

Ni(PMe)3

160

Ph

Ph

PhPh

(309)(317)

Ph Ph

Ph

Ph

NiMe3P

Ph Ph

(minus573)

89

126

127 128 91

Ph Ph Ph

Ni

Ph

PMe3

129

NiMe3P PMe3

Ph Ph

(00)

92

(89)

+

- 82 -

Table 35 Variation of Alkyne Addition and Total Reaction Time in the Scheme 322

Run Addition time of 88 (h)

Total run time (h)

Yield of 89 ()

Yield of 90 ()

1 4 16 44 55 2 6 22 23 77 3 5 41 24 76 4 12 69 17 73 5 13 19 13 87

The most immediate result of the modified protocol was the quantitative conversion of 22 to cycloadduct products 89 and 90 Turning to the product ratios a four hour addition time led to a slight preference for 90 Increasing the time to six hours dramatically influenced the product distribution and 90 was isolated in 77 yield as compared to the 23 for 89 In the optimal Run 5 87 of 90 was generated vs 13 of 90 Extending the run time after the addition of diphenylacetylene had a negligible effect The successful enhancement in phenacene selectivity under these conditions makes the reaction a practical method for synthesizing compound 90 and also provides further experimental support for the proposed mechanism shown in Scheme 320 Having reached a reasonable level of understanding both the mechanistic and experimental aspects of the reaction of angular [3]phenylene 22 with diphenylacetylene attention was shifted to a larger and more challenging substrate angular [4]phenylene (17) This system could conceivably afford 17 possible adducts one of which is hexaphenyl[7]phenacene 130 (Scheme 324) Would the mechanistic features of this triple cycloaddition be sufficiently similar to those of 22 to apply the same principles and enable selectivity toward 130

+THF reflux

Ph Ph Ph PhPh

Ph

+

Ph

Ph

2 equivslow addition

22 89 90

Ni(COD)(PMe3)2(10 mol)

88

- 83 -

Scheme 324 The Possible Cycloadducts of Diphenylacetylene 88 to Angular [4]Phenylene 17

+ Ph Ph

Ph Ph

Ph Ph

PhPh

Ph

Ph

Ph Ph Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph PhPhPh

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph Ph PhPhPh

Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

PhPh

Ph Ph Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

88

17

130

- 84 -

Encouragingly a first experiment under conditions comparable to those in Scheme 39 for 22 namely reaction of angular [4]phenylene (17) with one equivalent of diphenylacetylene in the absence of high dilution indeed engendered only five products two of which monoadducts 131 and 132 were minor (Scheme 325) The major components of the mixture were molecules 133 134 and most significantly 130

Scheme 325 Nickel Catalyzed Alkyne Cycloaddition with 17 and 88

Monitoring the course of the transformation by NMR revealed that 133 is the sole initial new compound followed by gradual appearance of the others Extrapolation of the insights gained with 22 it is tempting to propose that migration of the metal in Ni-complexed 133 is the source of 134 and ultimately 130 If true [7]phenacene 130 might be made selectively by application of the slow alkyne addition procedure of Scheme 322 Scheme 326 illustrates the proposed scenario It starts with doubly regioselective Ni insertion into the central ring and from the bay region to give 135 On the basis of the electron withdrawing effect of the adjacent cyclobutadienoid rings invoked earlier in the selective formation of 94 (Scheme 312) this metallacycle would seem the most stable Again this conjecture is tentative as the appearance of the minor products 131 and 132 would indicate Metallacycle 135 would then give rise to 136 (and hence 133 by demetallation) which would connect by Ni migration and insertion to 137 Alkyne cycloaddition would result in 138 (and hence 134 by demetallation) which would connect by Ni migration and insertion to 139 Alkyne cycloaddition would result in 140 (and hence 130 by demetallation)

+

Ph Ph

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2(10 mol)THF 75 degC

5 6

33

27 28

132131

133

134 130

17

88

- 85 -

Scheme 326 Proposed Reaction Pathway to Phenacene 130 from Angular [4]Phenylene 17 via Ni Migration

The successful preparation of [5]- and [7]phenacene from angular [3]- and [4]phenylene respectively prompted an attempt to prepare [13]phenacene derivative 141 from helical [7]phenylene 14210 (Scheme 327) This transformation would make use of six alkyne cycloadditions to produce the target molecule In addition to the possibility of preparing the largest known phenacene this reaction would also serve as an interesting test of the alkyne cycloaddition methodology

Scheme 327 Proposed Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Using the slow addition procedure phenylene 142 was subjected to the alkyne cycloaddition conditions (Scheme 329) All of the starting material was consumed but the reaction ultimately resulted in an intractable mixture of products Unfortunately no conclusive structural identifications for any of the ensuing compounds could be made from the 1H-NMR data A large assortment of peaks was seen in the region of 6ndash7

Ni

PMe3

Ph

NiPMe3

Ph Ph Ph PhNi

PMe3

Ph Ph Ph

NiMe3P

135

137

Ph Ph

Ph Ph

Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2

13617

88Ni

PMe3

Ph Ph88

138 139

Ph Ph88

Ni

PMe3

140

- 86 -

ppm suggesting the presence of phenylene subunits More informative was the absence of the highly diagnostic phenacene bay region proton signals that are typically found at ~8ndash9 ppm84 signaling the absence of any phenacene product(s)

Scheme 328 Attempted Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Nevertheless mass spectral analysis clearly indicated that multiple alkyne cycloaddition had occurred (Table 36) Peaks were observed at mz = 700 1056 1234 and 1412 which correspond to the presence of single triple quadruple and quintuple alkyne adducts in the reaction mixture No signal corresponding to the mass of 141 (mz = 1590) was detected however Although the structures of the resulting products remain to be established by follow-up experiments on a larger scale the fact that five cycloadditions occurred is encouraging in the basic scientific quest for large novel polycyclic aromatic hydrocarbons

Table 36 Mass Spectral Data (FAB) of the Product Mixture of the Cycloaddition Reaction of Phenylene 142 to Diphenylacetylene 88

mz Percentage Cycloaddition count 700 13 1

1056 11 3 1234 8 4 1412 7 5

Our disappointment in the apparent failure to generate 141 in this reaction may be the result of overambitious expectations on our part Thus we assumed in analogy to the reactivity of angular systems 17 and 22 that bay region cycloaddition to one of the inner cyclobutadiene rings would be preferred ideally producing an initial structure such as 143 (Figure 38) The corresponding non-bay adduct is illustrated by 144 It is evident on comparison that such bay region reactivity would lead to constructs devoid of the helical strain present in the starting material96 as well as non-bay structures like 144 The subsequent course of the reaction however may be marred by relatively non-selective cycloadditions as already indicated for 17 (Scheme 325) Therefore it will be prudent for future investigators to return to the latter optimize its outcome and then proceed along the series in the quest for large phenacene (or other) structures

- 87 -

Figure 38 Proposed representative initial bay (143) and non-bay (144) alkyne cycloaddition products of the reaction of [7]heliphene 141 with diphenylacetylene 88

35 Summary and Outlook The first alkyne cycloaddition studies were carried with angular phenylene systems Angular [3]phenylene 22 was successfully used as a precursor to a novel phenyl substituted [5]phenacene derivative 90 Similarly hexaphenyl [7]phenacene 131 was prepared from angular [4]phenylene 17 Extensive experiment and computational mechanistic studies suggested that the optimal conditions for preparing phenacene 90 from phenylene 22 were the maintenance of a low concentration of alkyne in the reaction mixture Future work will focus on applying these conditions to the synthesis of [7]phenacene 130 from angular [4]phenylene 17 An attempt to prepare a [13]phenacene 142 from helical [7]phenylene 141 proved unsuccessful for reasons that are not well understood Nevertheless cycloaddition was found to have occurred up to five times This observation is promising with respect to the further application of the methodology described in this chapter The development of an alkyne cycloaddition-based approach to synthesizing phenacenes should greatly facilitate the study of this emerging class of molecules Future work will focus on expanding the substrate scope of the reaction by examining various functionalized alkynes the application of metal systems that may allow the isolation of crucial intermediates and the expansion of the substrate scope to the higher angular phenylenes as well as other topologies

- 88 -

Chapter Four Experimental and Computational Details

41 General Considerations

All glassware was oven-dried (180 degC) prior to use Reagents were used as received from suppliers unless otherwise noted Flash chromatography97 was performed with Merck 60 230ndash400 mesh silica gel MP EcoChrom neutral alumina was deactivated to activity III by adding 6 water by mass followed by thorough mixing98 Air sensitive compounds were handled under argon with standard Schlenk techniques andor in a nitrogen atmosphere glovebox (Vacuum Atmospheres Model Nexus) Irradiation in CpCo(CO)2 reactions was carried out with a 120V 300W slide projection lamp (ELH) positioned 5 cm away from the reaction vessel UV-irradiation experiments were conducted in a Rayonet Photochemical Reactor (RPR-100) Bis(trimethylsilyl)- and trimethylsilylacetylene (BTMSA and TMSA respectively) were distilled from molecular sieves (4 Aring) prior to use TMSA was degassed with four freeze-pump-thaw cycles while BTMSA was degassed using a 20 min Ar purge BTMSA was recycled using from all CpCo(CO)2 reactions using the following procedure The BTMSA was first removed by vacuum transfer Residual cobalt was removed by dissolving the BTMSA in pentane and washing the pentaneBMTSA layer mixture with a dilute solution of ceric ammonium nitrate in acetonitrile in a separatory funnel The denser acetonitrile layer was drained off and the pentane removed by distillation at atmospheric pressure Vacuum distillation of the BTMSA from molecular sieves afforded a product pure enough for future use All solvents were distilled under N2

immediately before use from the appropriate drying agent triethylamine (KOH pellets) benzene toluene CH2Cl2 (CaH2) THF and diethylether (Nabenzophenone) acetonitrile (CaH2) Deoxygenation of solvents andor reaction mixtures was carried out by a 20 min Ar purge or four free-pump-thaw cycles for volatile (bp lt 70 degC) mixturessolvents Ni(COD)2 (Strem) was stored and manipulated in the glovebox 1H and proton decoupled 13C spectra were measured at 500 MHz and 125 MHz respectively unless otherwise noted 1H-NMR chemical shifts are reported in ppm units relative to the signal of the solvent (CDCl3ndash726 ppm C6D6ndash715 ppm acetone-d6ndash205 ppm CD2Cl2ndash532 ppm toluene-d8ndash209 ppm (for ndashCD3) Except where noted two-dimensional NMR experiments were run under temperature control at 300 K All spectral data were processed with Bruker TopSpin 21 software Melting points were recorded in open capillary tubes using a Thomas Hoover Unimelt apparatus and are uncorrected Melting points for air-sensitive samples were carried out in flame sealed capillary tubes Mass spectral measurements (Electron Impact Fast Atom Bombardment) and elemental analyses were supplied by the Micro-Mass Facility of the College of Chemistry University of California Berkeley UV-Vis spectra were recorded on Agilent 8453 and Perkin-Elmer Lambda 35 spectrophotometers with absorbance data reported in nm (log ε) IR spectra were taken on a Perkin-Elmer Spectrum 100 Where appropriate analysis by GCMS was done with an Agilent 5973 instrument

42 Experimental Section for Chapter Two

- 89 -

2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19

A mixture of KF2 H2O (700 mg 744 mmol) [18]crown-6 (100 mg 0378 mmol) and 2378-tetrakis[(triisopropylsilyl)ethynyl] linear [3]phenylene26 (370 mg 0800 mmol) in degassed THF (25 mL) was stirred for 70 min at RT The orange solution was filtered through a plug of silica gel (1 x 3 cm) eluting with degassed THF (15 mL) providing a light-yellow solution After adding CpCo(CO)2 (260 mg 144 mmol) the solution was protected from light and added via syringe pump over a period of 6 h to a boiling mixture of degassed BTMSA (50 mL) and THF (200 mL) which was irradiated with a projector lamp under nitrogen After additional heating and irradiation for 15 h the solvents were removed by vacuum transfer and the black residue filtered through a plug of neutral alumina activity III eluting with hexaneTHF (501) The volatiles were removed and the dark brown residue crystallized from degassed acetone yielding 19 (330 mg 65 ) as black needles mp 192ndash195 degC (decomp) 1H-NMR (400 MHz C6D6) δ = 794 (s 2 H) 744 (s 2 H) 690 (s 2 H) 441 (s 5 H) 035 (s 18 H) 031 (s 18 H) ppm 13C-NMR (100 MHz C6D6) δ = 1494 1484 1433 1394 1360 1256 1155 802 781 739

269 261 ppm IR (neat) ν~ = 2951 2898 1259 1248 1073 830 799 752 cmndash1 UV-VIS (ethanol) λmax (log ε) = 288 (486) 299 (500) 352 (445) 410 (439) 438 (449) end absorption to 550 nm MS (70 eV) mz () 638 (9) [M+] 514 (100) 499 (3) 387 (2) 73 (24) HRMS (FAB) calcd for C35H47CoSi4 6382087 found 6382095 Elemental analysis calcd for C35H47CoSi4 C 6578 H 741 found 6582 721

Crystallographic information for 19 (H atoms omitted)

Table 41 Crystal Data and Structure Refinement For 19

Empirical formula C35H47CoSi4 Formula weight 63902 cryst size (mm) 025 x 020 x 005 cryst syst Triclinic refl used for unit cell determination 6958

2 θ range (deg) 245ndash2900

a (Aring) 9497(3) b (Aring) 12321(4) c (Aring) 16469(5) α (deg) 74058(5)

β (deg) 82154(5)

Me3Si

Me3Si

CoSiMe3

SiMe3

- 90 -

γ (deg) 72276(5)

V (Aring3) 17620(10) space group Pndash1 Z 2

Dcalc gcm3 1762

F000 680 micro cmndash1 645 temp ordmC ndash173

Tmax Tmin 0858 0972 no of total rflns 24355

no of unique rflns 6958

no of obsd rflns 9209

no of variables 361

Reflection to Parameter Ratio 255

R 00503

Rw 01426

Rall 00734

GOF 1006

Max Peak in Final Diff Map (endash Aring3) 0867

Min Peak in Final Diff Map (endash Aring3) ndash0755

- 91 -

Figure 41 ORTEP representation of 19

- 92 -

Table 42 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 19 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y Z U (eq)

Co1 073881(4) ndash000927(3) 060643(2) 002551(10) Si1 077416(8) ndash019090(6) 094343(4) 002594(16) Si2 113437(8) ndash016706(7) 082404(5) 003023(17) Si3 040491(7) 062139(6) 020406(4) 002291(15) Si4 005088(7) 056545(6) 030946(4) 002144(14) C1 06709(3) ndash00385(2) 079440(16) 00239(5) C2 08019(3) ndash00967(2) 083428(16) 00241(5) C3 09418(3) ndash00743(2) 079331(16) 00233(5) C4 09428(3) 00098(2) 071779(15) 00225(5) C5 08094(2) 00691(2) 067735(15) 00207(4) C6 07282(2) 01574(2) 060605(15) 00207(4) C7 07303(2) 02531(2) 053306(15) 00211(4) C8 05938(2) 03094(2) 050431(15) 00205(4) C9 05057(2) 03981(2) 043438(15) 00207(4) C10 05076(2) 04760(2) 035695(15) 00227(5) C11 03734(2) 05293(2) 031459(15) 00215(4) C12 02408(2) 05011(2) 035315(15) 00205(4) C13 02432(2) 04196(2) 043269(15) 00215(4) C14 03751(2) 03698(2) 047171(15) 00208(4) C15 04564(2) 02794(2) 054277(15) 00211(4) C16 04487(2) 01908(2) 061161(15) 00224(5) C17 05916(3) 01278(2) 064393(15) 00221(5) C18 06734(2) 00417(2) 071473(15) 00215(5) C19 05795(3) ndash02027(3) 09572(2) 00446(8) C20 08892(4) ndash03470(2) 09642(2) 00387(7) C21 07986(4) ndash01192(3) 10246(2) 00419(7) C22 11685(4) ndash03077(3) 07914(3) 00584(10) C23 11726(3) ndash01969(3) 09372(2) 00426(7) C24 12742(4) ndash00933(4) 07624(3) 00640(12) C25 05777(3) 06657(3) 020261(18) 00348(6) C26 02610(3) 07629(2) 016564(17) 00292(5) C27 04355(3) 05272(3) 012760(18) 00347(6) C28 ndash00272(3) 07195(2) 03194(2) 00360(6) C29 00487(3) 05542(3) 019882(18) 00344(6) C30 ndash00786(3) 04816(2) 037272(18) 00278(5) C31 06994(4) ndash00612(3) 05062(2) 00432(7) C32 08520(4) ndash00698(3) 05033(2) 00407(7) C33 09085(3) ndash01473(3) 05788(2) 00407(7) C34 07922(4) ndash01879(3) 06277(2) 00424(7) C35 06647(4) ndash01370(3) 05833(2) 00403(7)

- 93 -

Table 43 Bond Lengths (Aring) for Complex 19

Atom1 Atom2 Length

Co1 C5 1993(3) Co1 C6 2023(3) Co1 C17 2022(2) Co1 C18 2009(3) Co1 C31 2042(4) Co1 C32 2075(3) Co1 C33 2062(3) Co1 C34 2042(4) Co1 C35 2048(4) Si1 C2 1886(2) Si1 C19 1877(3) Si1 C20 1863(2) Si1 C21 1865(4) Si2 C3 1889(3) Si2 C22 1876(5) Si2 C23 1862(3) Si2 C24 1865(4) Si3 C11 1901(2) Si3 C25 1876(4) Si3 C26 1867(2) Si3 C27 1875(4) Si4 C12 1889(2) Si4 C28 1860(3) Si4 C29 1868(3) Si4 C30 1870(3) C1 C2 1384(4) C1 C18 1411(3) C2 C3 1474(4) C3 C4 1384(3) C4 C5 1408(3) C5 C6 1480(3) C5 C18 1448(3) C6 C7 1437(3) C6 C17 1465(4) C7 C8 1351(3) C8 C9 1495(3) C8 C15 1476(3) C9 C10 1371(3) C9 C14 1405(3) C10 C11 1423(3) C11 C12 1427(3) C12 C13 1413(3) C13 C14 1376(3)

- 94 -

C14 C15 1488(3) C15 C16 1352(3) C16 C17 1434(3) C17 C18 1468(3) C31 C32 1416(6) C31 C35 1419(4) C32 C33 1401(4) C33 C34 1411(5) C34 C35 1386(5)

Table 44 Bond Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 4325(9) C5 Co1 C17 621(1) C5 Co1 C18 4240(9) C5 Co1 C31 1629(1) C5 Co1 C32 1271(1) C5 Co1 C33 1102(1) C5 Co1 C34 1223(1) C5 Co1 C35 1556(1) C6 Co1 C17 425(1) C6 Co1 C18 6191(9) C6 Co1 C31 1253(1) C6 Co1 C32 1164(1) C6 Co1 C33 1329(1) C6 Co1 C34 1651(1) C6 Co1 C35 1550(1) C17 Co1 C18 427(1) C17 Co1 C31 1204(1) C17 Co1 C32 1451(1) C17 Co1 C33 1722(1) C17 Co1 C34 1419(1) C17 Co1 C35 1194(1) C18 Co1 C31 1517(1) C18 Co1 C32 1676(1) C18 Co1 C33 1312(1) C18 Co1 C34 1112(1) C18 Co1 C35 1198(1) C31 Co1 C32 402(1) C31 Co1 C33 673(1) C31 Co1 C34 675(1) C31 Co1 C35 406(1) C32 Co1 C33 396(1) C32 Co1 C34 672(1)

- 95 -

C32 Co1 C35 675(1) C33 Co1 C34 402(1) C33 Co1 C35 671(1) C34 Co1 C35 396(1) C2 Si1 C19 1085(1) C2 Si1 C20 1157(1) C2 Si1 C21 1096(1) C19 Si1 C20 1035(1) C19 Si1 C21 1081(2) C20 Si1 C21 1110(2) C3 Si2 C22 1071(2) C3 Si2 C23 1162(1) C3 Si2 C24 1100(2) C22 Si2 C23 1110(2) C22 Si2 C24 1067(2) C23 Si2 C24 1056(2) C11 Si3 C25 1077(1) C11 Si3 C26 1177(1) C11 Si3 C27 1083(1) C25 Si3 C26 1045(1) C25 Si3 C27 1086(1) C26 Si3 C27 1097(1) C12 Si4 C28 1099(1) C12 Si4 C29 1132(1) C12 Si4 C30 1101(1) C28 Si4 C29 1119(1) C28 Si4 C30 1066(1) C29 Si4 C30 1048(1) C2 C1 C18 1193(2) Si1 C2 C1 1130(2) Si1 C2 C3 1270(2) C1 C2 C3 1198(2) Si2 C3 C2 1260(2) Si2 C3 C4 1124(2) C2 C3 C4 1208(2) C3 C4 C5 1192(2) Co1 C5 C4 1188(2) Co1 C5 C6 695(1) Co1 C5 C18 694(1) C4 C5 C6 1498(2) C4 C5 C18 1200(2) C6 C5 C18 902(2) Co1 C6 C5 673(1) Co1 C6 C7 1267(2) Co1 C6 C17 687(1) C5 C6 C7 1474(2)

- 96 -

C5 C6 C17 893(2) C7 C6 C17 1227(2) C6 C7 C8 1121(2) C7 C8 C9 1461(2) C7 C8 C15 1251(2) C9 C8 C15 885(2) C8 C9 C10 1471(2) C8 C9 C14 912(2) C10 C9 C14 1214(2) C9 C10 C11 1186(2) Si3 C11 C10 1116(2) Si3 C11 C12 1283(2) C10 C11 C12 1197(2) Si4 C12 C11 1264(2) Si4 C12 C13 1135(2) C11 C12 C13 1201(2) C12 C13 C14 1185(2) C9 C14 C13 1216(2) C9 C14 C15 915(2) C13 C14 C15 1465(2) C8 C15 C14 888(2) C8 C15 C16 1250(2) C14 C15 C16 1458(2) C15 C16 C17 1118(2) Co1 C17 C6 688(1) Co1 C17 C16 1265(2) Co1 C17 C18 682(1) C6 C17 C16 1233(2) C6 C17 C18 900(2) C16 C17 C18 1460(2) Co1 C18 C1 1229(2) Co1 C18 C5 682(1) Co1 C18 C17 691(1) C1 C18 C5 1206(2) C1 C18 C17 1487(2) C5 C18 C17 905(2) Co1 C31 C32 712(2) Co1 C31 C35 699(2) C32 C31 C35 1077(3) Co1 C32 C31 686(2) Co1 C32 C33 697(2) C31 C32 C33 1076(3) Co1 C33 C32 707(2) Co1 C33 C34 691(2) C32 C33 C34 1081(3) Co1 C34 C33 707(2)

- 97 -

Co1 C34 C35 704(2) C33 C34 C35 1086(3) Co1 C35 C31 695(2) Co1 C35 C34 700(2) C31 C35 C34 1079(3)

Table 44 Torsion Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 ndash1479(3) C6 Co1 C5 C18 983(2) C17 Co1 C5 C4 1630(2) C17 Co1 C5 C6 ndash491(1) C17 Co1 C5 C18 492(1) C18 Co1 C5 C4 1138(2) C18 Co1 C5 C6 ndash983(2) C31 Co1 C5 C4 ndash941(4) C31 Co1 C5 C6 538(4) C31 Co1 C5 C18 1522(4) C32 Co1 C5 C4 ndash573(2) C32 Co1 C5 C6 906(2) C32 Co1 C5 C18 ndash1710(2) C33 Co1 C5 C4 ndash160(2) C33 Co1 C5 C6 1319(1) C33 Co1 C5 C18 ndash1297(2) C34 Co1 C5 C4 271(2) C34 Co1 C5 C6 1750(2) C34 Co1 C5 C18 ndash866(2) C35 Co1 C5 C4 629(4) C35 Co1 C5 C6 ndash1492(3) C35 Co1 C5 C18 ndash509(3) C5 Co1 C6 C7 1458(3) C5 Co1 C6 C17 ndash986(2) C17 Co1 C6 C5 986(2) C17 Co1 C6 C7 ndash1156(3) C18 Co1 C6 C5 491(1) C18 Co1 C6 C7 ndash1650(2) C18 Co1 C6 C17 ndash494(1) C31 Co1 C6 C5 ndash1631(2) C31 Co1 C6 C7 ndash173(3) C31 Co1 C6 C17 983(2) C32 Co1 C6 C5 ndash1170(2) C32 Co1 C6 C7 288(2) C32 Co1 C6 C17 1444(2) C33 Co1 C6 C5 ndash725(2)

- 98 -

C33 Co1 C6 C7 734(3) C33 Co1 C6 C17 ndash1710(2) C34 Co1 C6 C5 ndash166(5) C34 Co1 C6 C7 1293(5) C34 Co1 C6 C17 ndash1151(5) C35 Co1 C6 C5 1499(3) C35 Co1 C6 C7 ndash642(4) C35 Co1 C6 C17 514(3) C5 Co1 C17 C6 501(1) C5 Co1 C17 C16 1666(3) C5 Co1 C17 C18 ndash489(1) C6 Co1 C17 C16 1165(3) C6 Co1 C17 C18 ndash989(2) C18 Co1 C17 C6 989(2) C18 Co1 C17 C16 ndash1446(3) C31 Co1 C17 C6 ndash1106(2) C31 Co1 C17 C16 59(3) C31 Co1 C17 C18 1505(2) C32 Co1 C17 C6 ndash656(3) C32 Co1 C17 C16 510(3) C32 Co1 C17 C18 ndash1645(2) C33 Co1 C17 C6 571(9) C33 Co1 C17 C16 1736(8) C33 Co1 C17 C18 ndash418(9) C34 Co1 C17 C6 1578(2) C34 Co1 C17 C16 ndash857(3) C34 Co1 C17 C18 589(2) C35 Co1 C17 C6 ndash1578(2) C35 Co1 C17 C16 ndash413(3) C35 Co1 C17 C18 1033(2) C5 Co1 C18 C1 ndash1133(3) C5 Co1 C18 C17 993(2) C6 Co1 C18 C1 ndash1635(2) C6 Co1 C18 C5 ndash502(1) C6 Co1 C18 C17 491(1) C17 Co1 C18 C1 1474(3) C17 Co1 C18 C5 ndash993(2) C31 Co1 C18 C1 836(3) C31 Co1 C18 C5 ndash1632(2) C31 Co1 C18 C17 ndash638(3) C32 Co1 C18 C1 ndash779(6) C32 Co1 C18 C5 353(6) C32 Co1 C18 C17 1346(5) C33 Co1 C18 C1 ndash395(3) C33 Co1 C18 C5 737(2) C33 Co1 C18 C17 1731(2)

- 99 -

C34 Co1 C18 C1 20(2) C34 Co1 C18 C5 1152(2) C34 Co1 C18 C17 ndash1455(2) C35 Co1 C18 C1 451(3) C35 Co1 C18 C5 1583(2) C35 Co1 C18 C17 ndash1023(2) C5 Co1 C31 C32 478(5) C5 Co1 C31 C35 1656(4) C6 Co1 C31 C32 904(2) C6 Co1 C31 C35 ndash1517(2) C17 Co1 C31 C32 1412(2) C17 Co1 C31 C35 ndash1010(2) C18 Co1 C31 C32 ndash1739(2) C18 Co1 C31 C35 ndash561(3) C32 Co1 C31 C35 1179(3) C33 Co1 C31 C32 ndash370(2) C33 Co1 C31 C35 808(2) C34 Co1 C31 C32 ndash808(2) C34 Co1 C31 C35 371(2) C35 Co1 C31 C32 ndash1179(3) C5 Co1 C32 C31 ndash1642(2) C5 Co1 C32 C33 764(2) C6 Co1 C32 C31 ndash1143(2) C6 Co1 C32 C33 1263(2) C17 Co1 C32 C31 ndash710(3) C17 Co1 C32 C33 1697(2) C18 Co1 C32 C31 1666(5) C18 Co1 C32 C33 472(6) C31 Co1 C32 C33 ndash1194(3) C33 Co1 C32 C31 1194(3) C34 Co1 C32 C31 816(2) C34 Co1 C32 C33 ndash377(2) C35 Co1 C32 C31 385(2) C35 Co1 C32 C33 ndash808(2) C5 Co1 C33 C32 ndash1243(2) C5 Co1 C33 C34 1166(2) C6 Co1 C33 C32 ndash802(2) C6 Co1 C33 C34 1607(2) C17 Co1 C33 C32 ndash1309(8) C17 Co1 C33 C34 1100(9) C18 Co1 C33 C32 ndash1679(2) C18 Co1 C33 C34 730(2) C31 Co1 C33 C32 376(2) C31 Co1 C33 C34 ndash815(2) C32 Co1 C33 C34 ndash1191(3) C34 Co1 C33 C32 1191(3)

- 100 -

C35 Co1 C33 C32 818(2) C35 Co1 C33 C34 ndash373(2) C5 Co1 C34 C33 ndash833(2) C5 Co1 C34 C35 1577(2) C6 Co1 C34 C33 ndash700(5) C6 Co1 C34 C35 1711(4) C17 Co1 C34 C33 ndash1681(2) C17 Co1 C34 C35 730(3) C18 Co1 C34 C33 ndash1295(2) C18 Co1 C34 C35 1115(2) C31 Co1 C34 C33 809(2) C31 Co1 C34 C35 ndash380(2) C32 Co1 C34 C33 372(2) C32 Co1 C34 C35 ndash818(2) C33 Co1 C34 C35 ndash1189(3) C35 Co1 C34 C33 1189(3) C5 Co1 C35 C31 ndash1699(3) C5 Co1 C35 C34 ndash508(4) C6 Co1 C35 C31 663(4) C6 Co1 C35 C34 ndash1746(2) C17 Co1 C35 C31 1036(2) C17 Co1 C35 C34 ndash1373(2) C18 Co1 C35 C31 1531(2) C18 Co1 C35 C34 ndash878(2) C31 Co1 C35 C34 1191(3) C32 Co1 C35 C31 ndash382(2) C32 Co1 C35 C34 809(2) C33 Co1 C35 C31 ndash812(2) C33 Co1 C35 C34 378(2) C34 Co1 C35 C31 ndash1191(3) C19 Si1 C2 C1 118(2) C19 Si1 C2 C3 ndash1731(2) C20 Si1 C2 C1 1275(2) C20 Si1 C2 C3 ndash574(3) C21 Si1 C2 C1 ndash1061(2) C21 Si1 C2 C3 690(3) C22 Si2 C3 C2 714(3) C22 Si2 C3 C4 ndash988(2) C23 Si2 C3 C2 ndash532(3) C23 Si2 C3 C4 1365(2) C24 Si2 C3 C2 ndash1731(3) C24 Si2 C3 C4 167(3) C25 Si3 C11 C10 ndash241(2) C25 Si3 C11 C12 1624(2) C26 Si3 C11 C10 ndash1417(2) C26 Si3 C11 C12 447(3)

- 101 -

C27 Si3 C11 C10 932(2) C27 Si3 C11 C12 ndash804(2) C28 Si4 C12 C11 ndash731(2) C28 Si4 C12 C13 1055(2) C29 Si4 C12 C11 529(2) C29 Si4 C12 C13 ndash1285(2) C30 Si4 C12 C11 1698(2) C30 Si4 C12 C13 ndash116(2) C18 C1 C2 Si1 1755(2) C18 C1 C2 C3 00(4) C2 C1 C18 Co1 784(3) C2 C1 C18 C5 ndash41(4) C2 C1 C18 C17 ndash1772(4) Si1 C2 C3 Si2 198(4) Si1 C2 C3 C4 ndash1707(2) C1 C2 C3 Si2 ndash1654(2) C1 C2 C3 C4 41(4) Si2 C3 C4 C5 1668(2) C2 C3 C4 C5 ndash40(4) C3 C4 C5 Co1 ndash816(3) C3 C4 C5 C6 1799(4) C3 C4 C5 C18 ndash01(4) Co1 C5 C6 C7 ndash1233(4) Co1 C5 C6 C17 671(1) C4 C5 C6 Co1 1122(4) C4 C5 C6 C7 ndash112(7) C4 C5 C6 C17 1793(4) C18 C5 C6 Co1 ndash678(1) C18 C5 C6 C7 1688(4) C18 C5 C6 C17 ndash07(2) Co1 C5 C18 C1 1164(2) Co1 C5 C18 C17 ndash672(1) C4 C5 C18 Co1 ndash1121(2) C4 C5 C18 C1 42(3) C4 C5 C18 C17 ndash1793(2) C6 C5 C18 Co1 679(1) C6 C5 C18 C1 ndash1757(2) C6 C5 C18 C17 07(2) Co1 C6 C7 C8 858(2) C5 C6 C7 C8 ndash1683(3) C17 C6 C7 C8 ndash08(3) Co1 C6 C17 C16 ndash1205(2) Co1 C6 C17 C18 665(1) C5 C6 C17 Co1 ndash658(1) C5 C6 C17 C16 1736(2) C5 C6 C17 C18 07(2)

- 102 -

C7 C6 C17 Co1 1209(2) C7 C6 C17 C16 03(4) C7 C6 C17 C18 ndash1726(2) C6 C7 C8 C9 ndash1697(3) C6 C7 C8 C15 09(3) C7 C8 C9 C10 05(7) C7 C8 C9 C14 1728(4) C15 C8 C9 C10 ndash1718(4) C15 C8 C9 C14 05(2) C7 C8 C15 C14 ndash1752(2) C7 C8 C15 C16 ndash06(4) C9 C8 C15 C14 ndash04(2) C9 C8 C15 C16 1742(2) C8 C9 C10 C11 1714(3) C14 C9 C10 C11 05(3) C8 C9 C14 C13 ndash1756(2) C8 C9 C14 C15 ndash05(2) C10 C9 C14 C13 ndash06(4) C10 C9 C14 C15 1746(2) C9 C10 C11 Si3 ndash1741(2) C9 C10 C11 C12 01(3) Si3 C11 C12 Si4 ndash90(3) Si3 C11 C12 C13 1725(2) C10 C11 C12 Si4 1779(2) C10 C11 C12 C13 ndash07(3) Si4 C12 C13 C14 ndash1781(2) C11 C12 C13 C14 06(3) C12 C13 C14 C9 ndash00(3) C12 C13 C14 C15 ndash1713(3) C9 C14 C15 C8 05(2) C9 C14 C15 C16 ndash1717(4) C13 C14 C15 C8 1730(4) C13 C14 C15 C16 09(7) C8 C15 C16 C17 00(3) C14 C15 C16 C17 1704(3) C15 C16 C17 Co1 ndash870(3) C15 C16 C17 C6 01(3) C15 C16 C17 C18 1674(4) Co1 C17 C18 C1 ndash1195(4) Co1 C17 C18 C5 664(1) C6 C17 C18 Co1 ndash671(1) C6 C17 C18 C1 1734(4) C6 C17 C18 C5 ndash07(2) C16 C17 C18 Co1 1235(4) C16 C17 C18 C1 40(7) C16 C17 C18 C5 ndash1701(4)

- 103 -

Co1 C31 C32 C33 590(2) C35 C31 C32 Co1 ndash607(2) C35 C31 C32 C33 ndash16(4) Co1 C31 C35 C34 ndash596(3) C32 C31 C35 Co1 615(3) C32 C31 C35 C34 18(4) Co1 C32 C33 C34 592(2) C31 C32 C33 Co1 ndash583(2) C31 C32 C33 C34 09(4) Co1 C33 C34 C35 605(3) C32 C33 C34 Co1 ndash602(2) C32 C33 C34 C35 03(4) Co1 C34 C35 C31 593(3) C33 C34 C35 Co1 ndash606(2) C33 C34 C35 C31 ndash13(4)

23-Bis(trimethylsilyl) linear [3]phenylene(CpCo) 52

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (029 g 085 mmol)27 in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (014 g 101 mmol) The mixture was stirred for 15 h and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the yellow residue dissolved in ether (30 mL) Aqueous workup with sat NaCl (2 x 20 mL) followed by drying over MgSO4 and concentration in vacuo provided a yellow solid This material was redissolved in THF (15 mL) degassed (Ar) and CpCo(CO)2 (0140 g 078 mmol) added The resulting solution (protected from light with foil) was injected (syringe pump) over 8 h into a boiling mixture of THF (200 mL) and BTMSA (50 mL) while irradiating with a slide projection lamp Once addition was complete heating and irradiation were continued for another 14 h The volatiles were removed via vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (4 x 4 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed in vacuo and the residue crystallized from acetone yielding 52 (024 g 57 ) as dark red crystals mp 198ndash202 degC (decomp) 1H-NMR (500 MHz C6D6) δ = 796 (s 2 H) 678 (AArsquom 2 H) 675 (s 2 H) 674 (BBrsquom 2 H) 436 (s 5 H) 037 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1426 1393

1360 1294 1194 1149 802 779 738 268 ppm IR (neat) ν~ = 2960 2923 2853 1461 1455 1378 1260 1093 1019 800 cmndash1 UV-VIS (hexane) λmax (log ε) = 255 (393) 282 (376) 293 (sh 378) 308 (389) 348 (390) 397 (sh 335) 436 (301) 511

CoSiMe3

SiMe3

- 104 -

(262) MS (70 eV) mz () 494 (100) [M+] 370 (14) HRMS (FAB) calcd for C29H31CoSi2 4941296 found 4941292 Elemental analysis calcd for C29H31CoSi2 C 7041 H 632 found 7048 628 Crystallographic information for 52 (H atoms omitted)

Table 45 Crystal Data and Structure Refinement For 52

Empirical formula C29H31CoSi2 Formula weight 49465 cryst size (mm) 030 x 020 x 005 cryst syst Monoclinic refl used for unit cell determination 2640 2 θ range (deg) 242ndash2503 a (Aring) 4391(3) b (Aring) 7472(4) c (Aring) 16869(11) α (deg)

β (deg) 111522(11) γ (deg) V (Aring3) 5149(6) space group C2c Z 8 Dcalc gcm

3 1276

F000 2080 micro cmndash1 774

temp ordmC ndash153

Tmax Tmin 0963 0800 no of total rflns 18401 no of unique rflns 2640 no of obsd rflns 4266 no of variables 271 Reflection to Parameter Ratio 974 R 00892 Rw 02042 Rall 01248 GOF 1008 Max Peak in Final Diff Map (endash Aring3) 1051 Min Peak in Final Diff Map (endash Aring3) ndash0707

- 105 -

Figure 42 ORTEP representation of 52

- 106 -

Table 46 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 52 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y z U(eq)

Co1 006961(2) 087577(12) 038136(6) 00200(3) Si1 018827(6) 08761(5) 063753(18) 00627(9) Si2 018540(5) 05425(3) 046900(16) 00410(6) C1 012151(19) 08410(10) 05589(5) 00310(17) C2 015018(13) 07767(11) 05552(4) 00343(18) C3 015002(14) 06417(10) 04926(5) 00324(17) C4 011985(17) 05770(9) 04357(4) 00247(16) C5 009030(17) 06465(9) 04383(4) 00220(14) C6 005450(16) 06378(9) 04077(4) 00216(14) C7 002537(17) 05420(9) 03591(4) 00224(15) C8 ndash000060(18) 05847(9) 03798(4) 00246(15) C9 ndash003560(17) 05555(10) 03644(4) 00256(16) C10 ndash006399(18) 04581(10) 03174(4) 00284(17) C11 ndash009208(19) 05019(12) 03360(5) 00344(18) C12 ndash009130(19) 06274(12) 03957(5) 00340(18) C13 ndash006300(17) 07256(11) 04422(5) 00294(17) C14 ndash003558(19) 06826(10) 04247(4) 00274(16) C15 000008(18) 07212(10) 04449(4) 00251(16) C16 002653(17) 08159(10) 04925(4) 00234(15) C17 005500(17) 07741(9) 04722(4) 00231(15) C18 009090(17) 07798(10) 05007(4) 00247(15) C19 01766(3) 10793(15) 06845(9) 0098(3) C20 02181(3) 0957(2) 05901(7) 0098(3) C21 02076(3) 07068(14) 07228(7) 0098(3) C22 01946(2) 06941(13) 03925(6) 00631(17) C23 01724(2) 03224(9) 04142(7) 00631(17) C24 022363(17) 04883(16) 05614(5) 00631(17) C25 007501(19) 09264(10) 02652(4) 00281(17) C26 004279(18) 09614(10) 02593(4) 00264(16) C27 004343(18) 10945(10) 03211(4) 00271(16) C28 007584(19) 11429(10) 03645(5) 00296(17) C29 00960(2) 10392(11) 03322(5) 00321(17)

Table 47 Bond Lengths (Aring) for Complex 52

Atom1 Atom2 Length

Co1 C5 2011(7) Co1 C6 2004(7) Co1 C17 2014(8) Co1 C18 2015(6) Co1 C25 2093(8)

- 107 -

Co1 C26 2063(6) Co1 C27 2042(7) Co1 C28 2049(8) Co1 C29 206(1) Si1 C2 1890(6) Si1 C19 187(1) Si1 C20 187(2) Si1 C21 187(1) Si2 C3 1891(8) Si2 C22 187(1) Si2 C23 1870(8) Si2 C24 1869(7) C1 C2 137(1) C1 C18 1418(9) C2 C3 146(1) C3 C4 1406(8) C4 C5 141(1) C5 C6 147(1) C5 C18 144(1) C6 C7 1432(9) C6 C17 148(1) C7 C8 135(1) C8 C9 148(1) C8 C15 149(1) C9 C10 1410(9) C9 C14 139(1) C10 C11 142(1) C11 C12 137(1) C12 C13 141(1) C13 C14 138(1) C14 C15 150(1) C15 C16 1345(9) C16 C17 145(1) C17 C18 147(1) C25 C26 141(1) C25 C29 144(1) C26 C27 143(1) C27 C28 139(1) C28 C29 143(1)

Table 48 Bond Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 428(3) C5 Co1 C17 619(3)

- 108 -

C5 Co1 C18 420(3) C5 Co1 C25 1145(3) C5 Co1 C26 1372(3) C5 Co1 C27 1733(3) C5 Co1 C28 1468(3) C5 Co1 C29 1184(3) C6 Co1 C17 434(3) C6 Co1 C18 621(3) C6 Co1 C25 1219(3) C6 Co1 C26 1125(3) C6 Co1 C27 1305(3) C6 Co1 C28 1653(3) C6 Co1 C29 1539(3) C17 Co1 C18 428(3) C17 Co1 C25 1632(3) C17 Co1 C26 1307(3) C17 Co1 C27 1137(3) C17 Co1 C28 1247(3) C17 Co1 C29 1562(3) C18 Co1 C25 1460(3) C18 Co1 C26 1733(3) C18 Co1 C27 1388(3) C18 Co1 C28 1167(3) C18 Co1 C29 1194(3) C25 Co1 C26 395(3) C25 Co1 C27 680(3) C25 Co1 C28 681(3) C25 Co1 C29 406(3) C26 Co1 C27 409(3) C26 Co1 C28 674(3) C26 Co1 C29 672(3) C27 Co1 C28 397(3) C27 Co1 C29 678(3) C28 Co1 C29 407(3) C2 Si1 C19 1089(5) C2 Si1 C20 1125(5) C2 Si1 C21 1092(4) C19 Si1 C20 1053(6) C19 Si1 C21 1100(6) C20 Si1 C21 1109(6) C3 Si2 C22 1081(4) C3 Si2 C23 1089(4) C3 Si2 C24 1177(4) C22 Si2 C23 1072(4) C22 Si2 C24 1106(4) C23 Si2 C24 1039(4)

- 109 -

C2 C1 C18 1206(7) Si1 C2 C1 1141(5) Si1 C2 C3 1249(5) C1 C2 C3 1210(7) Si2 C3 C2 1296(5) Si2 C3 C4 1113(5) C2 C3 C4 1190(6) C3 C4 C5 1199(6) Co1 C5 C4 1239(5) Co1 C5 C6 684(4) Co1 C5 C18 692(4) C4 C5 C6 1484(7) C4 C5 C18 1203(6) C6 C5 C18 910(6) Co1 C6 C5 688(4) Co1 C6 C7 1280(5) Co1 C6 C17 687(4) C5 C6 C7 1473(6) C5 C6 C17 892(5) C7 C6 C17 1222(6) C6 C7 C8 1133(6) C7 C8 C9 1475(7) C7 C8 C15 1242(7) C9 C8 C15 882(6) C8 C9 C10 1454(7) C8 C9 C14 928(6) C10 C9 C14 1218(7) C9 C10 C11 1147(7) C10 C11 C12 1222(8) C11 C12 C13 1231(8) C12 C13 C14 1149(7) C9 C14 C13 1233(7) C9 C14 C15 910(6) C13 C14 C15 1457(7) C8 C15 C14 879(6) C8 C15 C16 1254(7) C14 C15 C16 1467(7) C15 C16 C17 1121(6) Co1 C17 C6 679(4) Co1 C17 C16 1300(5) Co1 C17 C18 686(4) C6 C17 C16 1227(6) C6 C17 C18 892(5) C16 C17 C18 1464(7) Co1 C18 C1 1235(5) Co1 C18 C5 688(4)

- 110 -

Co1 C18 C17 686(4) C1 C18 C5 1191(7) C1 C18 C17 1500(7) C5 C18 C17 906(6) Co1 C25 C26 691(4) Co1 C25 C29 683(4) C26 C25 C29 1065(7) Co1 C26 C25 714(4) Co1 C26 C27 688(4) C25 C26 C27 1091(6) Co1 C27 C26 704(4) Co1 C27 C28 704(5) C26 C27 C28 1079(7) Co1 C28 C27 699(5) Co1 C28 C29 699(5) C27 C28 C29 1085(7) Co1 C29 C25 711(5) Co1 C29 C28 694(5) C25 C29 C28 1080(7)

Table 49 Torsion Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 1468(8) C6 Co1 C5 C18 ndash999(5) C17 Co1 C5 C4 ndash1627(7) C17 Co1 C5 C6 504(4) C17 Co1 C5 C18 ndash494(4) C18 Co1 C5 C4 ndash1133(8) C18 Co1 C5 C6 999(5) C25 Co1 C5 C4 356(7) C25 Co1 C5 C6 ndash1113(4) C25 Co1 C5 C18 1489(4) C26 Co1 C5 C4 765(7) C26 Co1 C5 C6 ndash703(5) C26 Co1 C5 C18 ndash1702(4) C27 Co1 C5 C4 146(2) C27 Co1 C5 C6 ndash1(3) C27 Co1 C5 C18 ndash101(2) C28 Co1 C5 C4 ndash515(9) C28 Co1 C5 C6 1617(5) C28 Co1 C5 C18 619(7) C29 Co1 C5 C4 ndash98(7) C29 Co1 C5 C6 ndash1567(4) C29 Co1 C5 C18 1035(5)

- 111 -

C5 Co1 C6 C7 ndash1474(8) C5 Co1 C6 C17 977(5) C17 Co1 C6 C5 ndash977(5) C17 Co1 C6 C7 1149(8) C18 Co1 C6 C5 ndash482(4) C18 Co1 C6 C7 1644(7) C18 Co1 C6 C17 495(4) C25 Co1 C6 C5 927(5) C25 Co1 C6 C7 ndash547(7) C25 Co1 C6 C17 ndash1696(4) C26 Co1 C6 C5 1362(4) C26 Co1 C6 C7 ndash112(7) C26 Co1 C6 C17 ndash1261(4) C27 Co1 C6 C5 1799(4) C27 Co1 C6 C7 325(8) C27 Co1 C6 C17 ndash824(5) C28 Co1 C6 C5 ndash137(1) C28 Co1 C6 C7 75(1) C28 Co1 C6 C17 ndash40(1) C29 Co1 C6 C5 523(8) C29 Co1 C6 C7 ndash951(9) C29 Co1 C6 C17 1501(7) C5 Co1 C17 C6 ndash497(4) C5 Co1 C17 C16 ndash1646(8) C5 Co1 C17 C18 484(4) C6 Co1 C17 C16 ndash1149(8) C6 Co1 C17 C18 981(5) C18 Co1 C17 C6 ndash981(5) C18 Co1 C17 C16 1470(9) C25 Co1 C17 C6 32(1) C25 Co1 C17 C16 ndash83(1) C25 Co1 C17 C18 130(1) C26 Co1 C17 C6 799(5) C26 Co1 C17 C16 ndash350(8) C26 Co1 C17 C18 1780(4) C27 Co1 C17 C6 1245(4) C27 Co1 C17 C16 97(8) C27 Co1 C17 C18 ndash1373(4) C28 Co1 C17 C6 1686(4) C28 Co1 C17 C16 538(8) C28 Co1 C17 C18 ndash932(5) C29 Co1 C17 C6 ndash1471(7) C29 Co1 C17 C16 98(1) C29 Co1 C17 C18 ndash489(9) C5 Co1 C18 C1 1117(8) C5 Co1 C18 C17 ndash995(5)

- 112 -

C6 Co1 C18 C1 1609(7) C6 Co1 C18 C5 492(4) C6 Co1 C18 C17 ndash502(4) C17 Co1 C18 C1 ndash1488(8) C17 Co1 C18 C5 995(5) C25 Co1 C18 C1 544(9) C25 Co1 C18 C5 ndash573(7) C25 Co1 C18 C17 ndash1568(5) C26 Co1 C18 C1 ndash162(2) C26 Co1 C18 C5 87(3) C26 Co1 C18 C17 ndash13(3) C27 Co1 C18 C1 ndash784(8) C27 Co1 C18 C5 1699(4) C27 Co1 C18 C17 705(6) C28 Co1 C18 C1 ndash356(7) C28 Co1 C18 C5 ndash1473(4) C28 Co1 C18 C17 1133(4) C29 Co1 C18 C1 107(8) C29 Co1 C18 C5 ndash1010(5) C29 Co1 C18 C17 1595(4) C5 Co1 C25 C26 1356(4) C5 Co1 C25 C29 ndash1058(5) C6 Co1 C25 C26 873(5) C6 Co1 C25 C29 ndash1540(5) C17 Co1 C25 C26 62(1) C17 Co1 C25 C29 ndash1796(9) C18 Co1 C25 C26 1738(5) C18 Co1 C25 C29 ndash675(7) C26 Co1 C25 C29 1187(6) C27 Co1 C25 C26 ndash376(4) C27 Co1 C25 C29 810(5) C28 Co1 C25 C26 ndash806(5) C28 Co1 C25 C29 381(5) C29 Co1 C25 C26 ndash1187(6) C5 Co1 C26 C25 ndash696(6) C5 Co1 C26 C27 1703(4) C6 Co1 C26 C25 ndash1134(5) C6 Co1 C26 C27 1265(4) C17 Co1 C26 C25 ndash1604(4) C17 Co1 C26 C27 795(5) C18 Co1 C26 C25 ndash149(2) C18 Co1 C26 C27 91(3) C25 Co1 C26 C27 ndash1201(6) C27 Co1 C26 C25 1201(6) C28 Co1 C26 C25 825(5) C28 Co1 C26 C27 ndash376(4)

- 113 -

C29 Co1 C26 C25 383(5) C29 Co1 C26 C27 ndash818(5) C5 Co1 C27 C26 ndash77(3) C5 Co1 C27 C28 165(2) C6 Co1 C27 C26 ndash774(5) C6 Co1 C27 C28 1644(5) C17 Co1 C27 C26 ndash1254(4) C17 Co1 C27 C28 1163(5) C18 Co1 C27 C26 ndash1698(5) C18 Co1 C27 C28 720(6) C25 Co1 C27 C26 364(4) C25 Co1 C27 C28 ndash818(5) C26 Co1 C27 C28 ndash1182(6) C28 Co1 C27 C26 1182(6) C29 Co1 C27 C26 804(5) C29 Co1 C27 C28 ndash378(5) C5 Co1 C28 C27 ndash1768(5) C5 Co1 C28 C29 637(7) C6 Co1 C28 C27 ndash54(1) C6 Co1 C28 C29 ndash173(1) C17 Co1 C28 C27 ndash861(5) C17 Co1 C28 C29 1544(5) C18 Co1 C28 C27 ndash1355(5) C18 Co1 C28 C29 1050(5) C25 Co1 C28 C27 815(5) C25 Co1 C28 C29 ndash380(5) C26 Co1 C28 C27 387(4) C26 Co1 C28 C29 ndash809(5) C27 Co1 C28 C29 ndash1195(7) C29 Co1 C28 C27 1195(7) C5 Co1 C29 C25 953(5) C5 Co1 C29 C28 ndash1461(5) C6 Co1 C29 C25 576(9) C6 Co1 C29 C28 1762(6) C17 Co1 C29 C25 1797(7) C17 Co1 C29 C28 ndash617(9) C18 Co1 C29 C25 1437(4) C18 Co1 C29 C28 ndash977(5) C25 Co1 C29 C28 1186(7) C26 Co1 C29 C25 ndash373(4) C26 Co1 C29 C28 813(5) C27 Co1 C29 C25 ndash817(5) C27 Co1 C29 C28 369(5) C28 Co1 C29 C25 ndash1186(7) C19 Si1 C2 C1 ndash144(8) C19 Si1 C2 C3 1663(7)

- 114 -

C20 Si1 C2 C1 ndash1307(7) C20 Si1 C2 C3 500(8) C21 Si1 C2 C1 1057(7) C21 Si1 C2 C3 ndash736(7) C22 Si2 C3 C2 ndash852(7) C22 Si2 C3 C4 908(6) C23 Si2 C3 C2 1587(7) C23 Si2 C3 C4 ndash253(7) C24 Si2 C3 C2 410(8) C24 Si2 C3 C4 ndash1431(6) C18 C1 C2 Si1 1795(6) C18 C1 C2 C3 ndash1(1) C2 C1 C18 Co1 ndash817(9) C2 C1 C18 C5 1(1) C2 C1 C18 C17 173(1) Si1 C2 C3 Si2 ndash5(1) Si1 C2 C3 C4 1790(5) C1 C2 C3 Si2 1755(6) C1 C2 C3 C4 ndash0(1) Si2 C3 C4 C5 ndash1747(5) C2 C3 C4 C5 2(1) C3 C4 C5 Co1 822(8) C3 C4 C5 C6 ndash174(1) C3 C4 C5 C18 ndash2(1) Co1 C5 C6 C7 128(1) Co1 C5 C6 C17 ndash674(4) C4 C5 C6 Co1 ndash120(1) C4 C5 C6 C7 8(2) C4 C5 C6 C17 173(1) C18 C5 C6 Co1 671(4) C18 C5 C6 C7 ndash165(1) C18 C5 C6 C17 ndash03(6) Co1 C5 C18 C1 ndash1175(7) Co1 C5 C18 C17 667(4) C4 C5 C18 Co1 1179(7) C4 C5 C18 C1 0(1) C4 C5 C18 C17 ndash1754(7) C6 C5 C18 Co1 ndash663(4) C6 C5 C18 C1 1762(7) C6 C5 C18 C17 04(6) Co1 C6 C7 C8 ndash887(8) C5 C6 C7 C8 160(1) C17 C6 C7 C8 ndash2(1) Co1 C6 C17 C16 1243(7) Co1 C6 C17 C18 ndash672(4) C5 C6 C17 Co1 675(4)

- 115 -

C5 C6 C17 C16 ndash1681(7) C5 C6 C17 C18 03(5) C7 C6 C17 Co1 ndash1223(7) C7 C6 C17 C16 2(1) C7 C6 C17 C18 1705(7) C6 C7 C8 C9 ndash180(1) C6 C7 C8 C15 2(1) C7 C8 C9 C10 2(2) C7 C8 C9 C14 ndash179(1) C15 C8 C9 C10 ndash179(1) C15 C8 C9 C14 01(6) C7 C8 C15 C14 1791(7) C7 C8 C15 C16 ndash2(1) C9 C8 C15 C14 ndash01(5) C9 C8 C15 C16 1792(8) C8 C9 C10 C11 ndash180(1) C14 C9 C10 C11 1(1) C8 C9 C14 C13 1791(7) C8 C9 C14 C15 ndash01(6) C10 C9 C14 C13 ndash1(1) C10 C9 C14 C15 1796(7) C9 C10 C11 C12 ndash1(1) C10 C11 C12 C13 1(1) C11 C12 C13 C14 ndash2(1) C12 C13 C14 C9 2(1) C12 C13 C14 C15 ndash180(1) C9 C14 C15 C8 01(6) C9 C14 C15 C16 ndash179(1) C13 C14 C15 C8 ndash179(1) C13 C14 C15 C16 2(2) C8 C15 C16 C17 1(1) C14 C15 C16 C17 ndash180(1) C15 C16 C17 Co1 858(8) C15 C16 C17 C6 ndash2(1) C15 C16 C17 C18 ndash161(1) Co1 C17 C18 C1 120(1) Co1 C17 C18 C5 ndash669(4) C6 C17 C18 Co1 666(4) C6 C17 C18 C1 ndash173(1) C6 C17 C18 C5 ndash03(5) C16 C17 C18 Co1 ndash131(1) C16 C17 C18 C1 ndash11(2) C16 C17 C18 C5 162(1) Co1 C25 C26 C27 586(5) C29 C25 C26 Co1 ndash583(5) C29 C25 C26 C27 03(9)

- 116 -

Co1 C25 C29 C28 ndash598(6) C26 C25 C29 Co1 588(5) C26 C25 C29 C28 ndash10(9) Co1 C26 C27 C28 607(5) C25 C26 C27 Co1 ndash602(5) C25 C26 C27 C28 05(9) Co1 C27 C28 C29 595(6) C26 C27 C28 Co1 ndash607(5) C26 C27 C28 C29 ndash12(9) Co1 C28 C29 C25 609(6) C27 C28 C29 Co1 ndash595(6) C27 C28 C29 C25 14(9)

Photo-thermal cycle between 52 and 53

An NMR tube containing a solution of 52 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 53 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 724 (AArsquom 2 H) 683 (s 2 H) 662 (BBrsquom 2 H) 444 (s 5 H) 032 (s 18 H) ppm 13C- NMR (100 MHz C6D6) δ = 1493 1482 1430 1276 1256 1241 1155 803 796 725 222 ppm Thermal reversal could be conveniently followed by VT-NMR

Kinetic studies of the thermal CoCp migration in 53 In the glovebox 23-[bis(trimethylsilyl)] linear[3]phenylene(CpCo) 52 dissolved in the solvent of choice (C6D6 or toluene-d8) was passed through an HPLC filter and then transfered via syringe into a thick-walled NMR tube connected to a vacuum line adapter The sample was then degassed by three freeze-pump-thaw cycles and flame-sealed under vacuum Prior to the kinetic runs the mixtures were irradiated for 10 h in a Rayonet Photochemical Reactor fitted with lamps emitting at 310 and 365 nm After this treatment care was taken to exclude ambient light as it causes some isomerization The irradiated samples were then placed in the NMR spectrometer at ndash65 degC (500 MHz) which was then warmed to the required temperature In the case of the 60 degC runs the magnet was prewarmed because of the fast reaction rate at this temperature After five min the spectra were recorded The Cp signal of the photoisomer was integrated relative to the solvent peak of C6D6 or the CD3 peak of toluene-d8 and monitored as a function of time The integral from the first scan was used as [A]o Since the equilibrium constant between the isomers was 50 the kinetic analysis treated the isomerization as a first-order non-reversible process Plotting the data accordingly

CoSiMe3

SiMe3

52

CoSiMe3

SiMe3

53

hν∆

- 117 -

yielded the reaction rate constants which were used in the Eyring plots to obtain the activation parameters Kinetic studies of the thermal haptotropic shift for complex 52 Kinetic runs were executed in C6D6 as the optimum solvent A sample of 52 in degassed C6D6 or toluene-d8 was subjected to UV light for 10 h leading to maximum enrichment of 53 The sample was kept at the specified temperature and the disappearance of 53 monitored by 1H-NMR spectroscopy The reaction proved to be first-order (eq 1) consistent with an intramolecular process

[ ] [ ]Akdt

Adminus=

(1)

[ ][ ] dtkA

Ad=minus

(2)

[ ][ ]

tkA

A=minus

0

ln (3)

The rate constant (k) at 30 40 50 and 60 degC was obtained from the slope of a plot of ndashln([A][A]0) versus time (t) following eq 2 and 3 The actual error in reproducibility was estimated by the calculation of one standard deviation (σ) for a triplicate run at 60 degC The percentage error was applied for k at 30 40 and 50 degC The rate constants and their errors are given in Tables 411 and 414 The values for k and their standard deviations were used to calculate the activation enthalpy (∆HDagger) and entropy (∆SH) of the haptotropic shift The basis for these calculations is the Eyring equation (eq 4) This expression (eq 4) was transformed to eq 5 and the activation enthalpy (∆HDagger) obtained from the slope of a plot of ndashln(kT) versus 1RT The intercept (ndashC) provides the activation entropy (∆SH) following eq 6 and 7

C

TR

H

R

S

h

k

TR

H

T

k B

minus∆

=

∆+minus

∆=minus

ne

nene

lnln

( 4)

R

S

h

kC B

ne∆+= ln

(5)

minus=∆ ne

h

kCRS Bln

(6)

- 118 -

The errors in ∆HDagger and ∆SDagger were calculated based on those in the rate constants leading to two additional least square fits in the Eyring plot These fits represent the two most extreme deviations from the original plot This provides a conservative error estimate and finally the values of 204plusmn14 kcalmol for ∆HH and 158plusmn22 eu (calmolmiddotK) for ∆SH in C6D6 In order to probe for solvent effects the kinetics were also repeated in toluene-d8 The preparation of the sample followed the described procedure and the rate constants (k) were obtained at 30 40 50 and 60 degC At 60 degC three measurements were carried out to estimate the errors in reproducibility for k and the activation parameters Error propagation was done as described for the kinetic experiments in C6D6 It is assumed that those rate constants (k) show the same relative error as the ones for the rearrangement of 53 to 52 in C6D6 The activation parameters in toluene-d8 were found to be 231plusmn07 kcalmol and 60plusmn13 eu

Table 410 Kinetic Data for the Conversion of 53 to 52 in C6D6

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09657 00349 1000 09419 00599 6000 09380 00640 2000 09018 01034 9000 09038 01012 3000 08557 01558 12000 08760 01324 4000 08176 02013 15000 08418 01723 5000 07796 02490 18000 08206 01978 6000 07555 02804 21000 08010 02219 7000 07255 03210 32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 400 09541 00470 30 09888 00113 800 09197 00837 60 09820 00181 1200 08910 01154 90 09708 00296 1600 08489 01638 120 09596 00413 2000 08298 01865 150 09506 00507 2400 07954 02289 180 09416 00602 2800 07591 02756 210 09348 00674 240 09281 00746 270 09213 00819 300 09124 00917 330 09034 01016 360 08966 01091

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

- 119 -

0 10000 00000 0 10000 00000 30 09950 00050 30 09909 00092 60 09900 00101 60 09854 00147 90 09800 00202 90 09762 00241 120 09750 00253 120 09671 00335 150 09700 00305 150 09634 00372 180 09625 00382 180 09543 00468 210 09575 00434 210 09433 00583 240 09475 00539 240 09397 00622 270 09400 00619 270 09287 00740 300 09350 00672 300 09232 00799 330 09300 00726 330 09177 00858 360 09250 00780 360 09086 00959

Table 411 The Rate Constants (k) in C6D6 Calculated From the Data in Table 410 and Their

Standard Deviations (σ)

Temp (K) k (1s) σσσσ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 10809Endash05 74258Endash07 09970 171494 00688

31315 45615Endash05 31338Endash06 09948 157420 00688

32315 95118Endash05 65346Endash06 09965 150385 00688

33315 (1) 27425Endash04 09965

33315 (2) 25714Endash04 09964

33315 (3) 30051Endash04 09990

33315 (avg) 26511Endash04 18841Endash05 140101 00688

Table 412 Activation Parameters for the Kinetic Experiments in C6D6

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 90990 85414 79291 Intercept ndash1789 ndash1674 ndash1559 R

2 09869 09869 09869

∆HDagger (Jmol) 90990 85414 79291

∆HDagger (kcalmol) 217 204 190

∆SDagger (JmolmiddotK) ndash569 ndash660 ndash751

∆SDagger (eu) ndash136 ndash158 ndash180

- 120 -

(323 15 K 50 degC) y = 95118E-05x + 44505E-03

R2 = 9965

(30315 K 30 degC) y = 10809E-05x + 20474E-03

R2 = 9970

(31315 K 40 degC) y = 45615E-05x + 11689E-02

R2 = 9948

(33315 K 60 degC) y = 263387E-04x + 390297E-04

R2 = 9992

000

005

010

015

020

025

030

035

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

Figure 43 Kinetic plots for the conversion of 53 to 52 in C6D6

Table 413 Kinetic Data for the Conversion of 53 to 52 in Toluene-d8

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09556 00454 1000 09488 00526 6000 09256 00773 2000 08931 01130 9000 08956 01103 3000 08545 01572 12000 08667 01430 4000 08143 02054 15000 08343 01811 5000 07818 02461 18000 08103 02103 6000 07559 02798 21000 07863 02404 7000 07179 03314

- 121 -

32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

000 10000 00000 0 10000 00000 40000 09470 00544 30 09887 00113 80000 08934 01127 60 09775 00228 120000 08594 01515 90 09691 00314 160000 08175 02015 120 09592 00416 200000 07861 02406 150 09473 00542 240000 07502 02875 180 09381 00639 280000 06991 03579 210 09262 00767 240 09149 00889 270 09086 00959 300 08973 01083 330 08868 01202 360 08762 01321

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 30 09945 00055 30 09910 00090 60 09795 00207 60 09828 00173 90 09700 00304 90 09716 00288 120 09645 00361 120 09559 00451 150 09479 00535 150 09440 00576 180 09464 00551 180 09313 00712 210 09314 00711 210 09238 00792 240 09188 00847 240 09156 00882 270 09101 00942 270 08992 01063 300 08991 01064 300 08932 01129 330 08896 01170 330 08872 01197 360 08801 01277 360 08686 01409

- 122 -

Table 414 The Rate Constants (k) in Toluene-d8 Calculated From the Data in Table 413 and Their Standard Deviations (σ)

Temp (K) k (1s) σ σ σ σ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 11314Endash05 37152Endash07 09976 17104 05610

31315 46470Endash05 15251Endash06 09948 15723 05157

32315 12214Endash04 401074Endash06 09957 14788 04851

33315 (1) 36441Endash04 09992

33315 (2) 36124Endash04 09951

33315 (3) 38855Endash04 09956

33315 (avg) 37140Endash04 14937Endash05 13707 04496

Table 415 Activation Parameters for the Kinetic Experiments in Toluene-d8

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 96590 93523 90455 Intercept ndash2073 ndash2007 ndash1941 R

2 09962 09962 09962

∆HDagger (Jmol) 96590 93523 90455

∆HDagger (kcalmol) 2309 2235 2162

∆SDagger (JmolmiddotK) ndash2521 ndash3068 ndash3615

∆SDagger (eu) ndash602 ndash733 ndash864

- 123 -

00000

00500

01000

01500

02000

02500

03000

03500

04000

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

(31315 K 40 degC) y = 46470E-05x + 10553E-02

R2 = 9948

(32315 K 50 degC) y = 12214E-04x + 47671E-03

R2 = 9957

(33315 K 60 degC)y = 371377E-04x - 208381E-03

R2 = 9992

(30315 K 30 degC) y = 11314E-05x + 71900E-03

R2 = 9976

Figure 44 Kinetic plots for the conversion of 53 to 52 in toluene-d8

- 124 -

(C6D6) y = 85141x - 16743

R2

= 09869

(toluene-d 8) y = 93523x - 2007

R2 = 09962

13600

14600

15600

16600

17600

36100E-04

36600E-04

37100E-04

37600E-04

38100E-04

38600E-04

39100E-04

39600E-04

40100E-04

1RT (Jmol)

-ln

(kT

)

Figure 45 Eyring plots for conversion of 53 to 52 MeCpCo(CO)2

Adapted from the literature procedure50 Co2(CO)8 (809 g 2366 mmol) was added to a round bottom flask in the glovebox The flask was capped with a septum and brought out of the glovebox A reflux condenser connected to the high vacuum line was quickly exchanged with the septum under a heavy purge of argon Degassed CH2Cl2 (30 mL) was added followed by freshly cracked deoxygenated methylcyclopentadiene (135 mL 123 mmol) The mixture evolved gas upon addition of the methylcyclopentadiene indicating CO liberation The entire setup was protected from light with foil and heated to a gentle reflux using a heating mantlevariac heat source After stirring at reflux for 26 h the mixture now dark crimson in color was cooled to rt The reflux condenser was quickly exchanged for a distillation head under an Ar purge and CH2Cl2 distilled off at atmospheric pressure under Ar Vacuum distillation at 002 Torr was performed and the forerun discarded The desired complex was obtained as a red liquid (7296 g 79) bp = 31 degC (002 Torr) stored at ndash10 degC and shielded from light Note A small

CoOC CO

- 125 -

amount of methylcyclopentadiene dimer (15 ) which could not be separated was present in the isolated product This was deemed harmless however and the obtained product was used in further experiments without further purification 85 pure 1H-NMR data match those reported in the literature 1H-NMR (C6D6) δ = 145 (s 3 H) 431 (br s 2 H) 451 (br s 2 H) 23-Bis(trimethylsilyl) linear [3]phenylene(MeCpCo) 54

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (0146 g 0424 mmol) in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (0101 g 0731 mmol) The mixture was stirred for 100 min and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the remaining yellow residue was dissolved in freshly distilled THF (15 mL) The green solution was separated from the solids via canula filtration and transferred into another Schlenk flask After a 20 min Ar purge MeCpCo(CO)2 (0092 g 0403 mmol) was added and the resulting solution (protected from light with foil) injected via syringe pump over 9 h into a boiling mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 15 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (201) The volatiles were again removed under high vacuum line and the residue crystallized from acetone yielding 55 (0125 g 61 ) as black crystals mp 163ndash165 degC 1H-NMR (500 MHz C6D6) δ = 783 (s 2 H) 676 (m 4 H) 675 (s 2 H) 442 (apparent t J = 21 Hz 2 H) 427 (apparent t J = 21 Hz 2 H) 134 (s 3 H) 038 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1423 1386 1354 1293 1193 1147 899 806 798 783 739 111 279 ppm IR (neat) ν~ = 2959 2923 2853 1462 1455 1378 1260 1093 1030 802 cmndash1 UV-VIS (hexane) λmax (log ε) = 256 (368) 281 (356) 293 (359) 310 (373) 350 (368) 386 (sh 321) 437 (sh 287) 499 (sh 247) end absorption to 550 nm MS (70 eV) mz () 508 (100) [M+] 370 (28) HRMS (FAB) calcd for C30H33CoSi2 5081453 found 5081442 Photo-thermal cycle between 54 and 56

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

54

CoSiMe3

SiMe3

56

hν∆

Me Me

- 126 -

An NMR tube containing a solution of 54 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 56 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 715 (AArsquom obscured by solvent peak) 680 (s 2 H) 664 (AArsquom 2 H) 447 (apparent t J = 21 Hz 2 H) 428 (apparent t J = 21 Hz 2 H) 148 (s 3 H) 032 (s 18 H) ppm Thermal reversal could be conveniently followed by VT-NMR

14-Deuterio-23-bis(trimethylsilyl) linear [3]phenylene cyclopentadienylcobalt 55

To 23-bis(trimethylsilylethynyl)biphenylene 52 (0144 g 0418 mmol) in CH3OD (10 mL) was added freshly distilled ether (20 mL) and K2CO3 (0083 g 0600 mmol) The mixture was stirred for 100 min and monitored by TLC (hexaneCH2Cl2 51) When the starting material had disappeared the solvents were removed and the remaining yellow residue very quickly dissolved in freshly distilled THF (10 mL) The green solution was separated from the solids using a filter cannula and transferred to another Schlenk flask After a 20 min Ar purge CpCo(CO)2 (0072 g 0400 mmol) was added and the resulting solution (protected from light with foil) was injected via syringe pump over 7 h into a refluxing mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 14 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed on the high vacuum line and the residue recrystallized from acetone yielding 8 (0085 g 41 ) as dark red crystals 1H-NMR spectroscopy showed 63 incorporation of deuterium as indicated by the diminution of the peak intensity of the signal at δ = 796 (s 074 H) ppm MS (FAB) mz () 496 (100) [M+] 372 (19)

CoSiMe3

SiMe3

D

D

- 127 -

Crossover experiment with 54 and 55

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

h

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

5455

5657

A solution of complex 55 (~2 mg) and 54 (~2 mg) in C6D6 (06 mL) rigorously protected from light was analyzed by 1H-NMR spectroscopy to reveal a 1861 mixture of 5554 The peak for 55 at δ = 796 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound A mass spectrum of an aliquot gave the appropriate composite of the two respective molecular ion patterns (Figure 46) The sample was then irradiated as described for above 13 h at RT The 1H-NMR spectrum of the irradiated mixture showed the presence of the respective photoisomers of 55 and 54 There were no unidentifiable peaks the signal at δ = 7470 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound and the clearly resolved peak for 56 at δ = 7473 (s 2 H) ppm revealed unattenuated intensity An aliquot was submitted for mass spectral analysis furnishing the same pattern as that depicted above The sample was then placed in an oil bath preheated to 80 degC for 30 h a treatment that regenerated the original NMR spectrum of the mixture of 55 and 54 including the relative integration ratios Similarly mass spectral analysis resulted in the same pattern as that depicted in Figure 46

- 128 -

Figure 46 Mass spectrum from the crossover experiment between 55 and 56

Low temperature photolyses of 19 and 52 A small amount (~5 mg) of linear[3]phenylene(CpCo) 19 or 52 dissolved in toluene-d8 was added to a J-Young NMR tube in the glovebox The sealed sample was then placed inside a Pyrex Dewar flask positioned in a Rayonet Photochemical Reactor outfitted with UV-lamps emitting at 310 and 350 nm (as shown in Figure 214) Cooling was achieved with the use of a Neslab Refrigerated Circulating bath employing isopropanol as the cooling medium The cold isopropanol was pumped into and out of the Pyrex Dewar using securely fastened Tygon tubes maintaining a temperature of ndash55 to ndash50 degC Once the sample was chilled irradiation was commenced The total irradiation time varied from 25 to 4 h When analysis was required the sample was transported in another Dewar flask containing dry iceisopropanol (ndash78 degC) while the NMR spectrometer was prepared for the low temperature experiment The spectrometer was cooled (ndash80 to ndash30 degC depending on the experiment) the sample wiped with a paper towel placed inside the spinner and very quickly lowered manually with a string into the cold magnet After allowing time for the temperature to equilibrate (10 min) a spectrum was recorded For VT experiments the temperature was slowly

- 129 -

raised from ndash80 degC in 10 degree increments to 10 degC Spectra were recorded at each interval For all other experiments spectra were recorded at ndash30 degC 2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

In the glovebox 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19 (0049 g 0133 mmol) and CpCo(C2H4)2 (0025 g 0139 mmol)99 were added to a Schlenk flask The flask was sealed brought out of the box connected to a vacuum manifold and freshly distilled degassed benzene (15 mL) added The mixture was heated to 70 degC on an oil bath for 23 h before being cooled to RT The solvent was removed in vacuo giving a black residue that was rapidly filtered through a plug of neutral alumina activity III (25 x 35 cm) eluting with a mixture of hexanes and THF (1001) under nitrogen and into a Schlenk flask The solvents were again removed in vacuo and the ensuing black residue recrystallized from acetone at ndash78 degC to give pure 78 (0057 g 56 ) as black crystals 1H-NMR (400 MHz acetone-d6) δ = 039 (s 36H) 481 (s 2H) 489 (m 4H) 736 (s 4H) ppm 13C-NMR (100 MHz acetone-d6) δ = 266 5372 5710 8284 12587 14542 15054 ppm UV-VIS (hexane) λmax (log ε) 197 (334) 221 (336 sh) 244 (344) 286 (363) 386 (279 sh) 439 (258) MS (FAB) 762 (M+ 100) HRMS calcd for C40H52Si4Co2 7621810 found 7621791 43 Computational Details for Chapter Two All calculations were performed using the GAUSSIAN03100 program GaussView 30101 and ChemCraft102 were employed to input structures as well as view output results Optimized geometries were obtained at the hybrid density functional theory (DFT) using Beckersquos three-parameter exchange-correlation functional103 containing the non-local gradient correction of Lee Yang and Parr104 (B3LYP) For optimization purposes a standard basis 3-21G105 was used for hydrogen and carbon atoms For cobalt the LANL2DZ106 basis set was applied with the outermost d function released yielding a triple-zeta d basis along with the effective core potentials (ECP) to describe the core electrons For the single point energy calculations the basis sets were increased to 6-31G107 for hydrogen 6-311G108 for carbon and the modified LANL2DZ basis as described above for cobalt with an added f-orbital coefficient109 The potential energy surfaces were mapped through a scan calculation a feature also available within the GAUSSIAN03 program Transition state structures were obtained in three different steps (i) determination of initial and final products or the minimum closest to a TS (ii) a linear QST2110 search for an initial guess of a TS and

- 130 -

(iii) input of the results from (ii) into a QST3 search Transition states and minima were confirmed by carrying out frequency calculations (using the same basis as that used for the optimizations)

Calculated structures for linear [3]phenylene(CpCo) (labels from Figures 29 and 210 in Section 24)

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

C 2878616000 ndash1675635000 ndash1461246000 C 3986441000 ndash2043582000 ndash0714088000 C 3986471000 ndash2043226000 0714700000 C 2878686000 ndash1674908000 1461732000 C 1740663000 ndash1265994000 0736724000 C 1740638000 ndash1266353000 ndash0736388000 H 2884721000 ndash1731772000 ndash2551997000 H 2884845000 ndash1730511000 2552509000 C 0311237000 ndash0833174000 0748280000 C 0311204000 ndash0833522000 ndash0748106000 C ndash0893980000 ndash0698348000 ndash1520584000 C ndash0893913000 ndash0697588000 1520749000 C ndash1996288000 ndash0532216000 0744771000 C ndash1996322000 ndash0532586000 ndash0744640000 C ndash3491040000 ndash0328769000 ndash0716524000 C ndash3490989000 ndash0328300000 0716632000 C ndash4645388000 ndash0172650000 ndash1448232000 C ndash4645276000 ndash0171672000 1448326000 C ndash5836534000 ndash0014205000 ndash0697760000

- 131 -

C ndash5836481000 ndash0013731000 0697841000 H ndash0905006000 ndash0741217000 ndash2609771000 H ndash0904887000 ndash0739873000 2609960000 H ndash4666353000 ndash0168153000 ndash2539086000 H ndash6785734000 0111682000 ndash1227959000 H ndash6785641000 0112502000 1228028000 H ndash4666162000 ndash0166493000 2539178000 Co 1455829000 0662094000 ndash0000295000 C 0672548000 2613322000 0000481000 C 1502831000 2459745000 1168426000 C 2819523000 2140942000 0722371000 C 2818808000 2141294000 ndash0723848000 C 1501651000 2460224000 ndash1168394000 H ndash0391329000 2836892000 0001070000 H 1172930000 2540112000 2200200000 H 3678957000 1932268000 1353707000 H 3677612000 1932967000 ndash1356152000 H 1170676000 2541059000 ndash2199789000 H 4894703000 ndash2369906000 1230670000 H 4894651000 ndash2370516000 ndash1229936000

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

C ndash3991583000 ndash2430244000 ndash0695300000 C ndash2895249000 ndash1923385000 ndash1446977000 C ndash1838331000 ndash1436925000 ndash0718218000 C ndash0460541000 ndash0772703000 ndash0748934000

- 132 -

C 0758545000 ndash0733408000 ndash1513161000 C 1871918000 ndash0586111000 ndash0739684000 C 3374782000 ndash0432509000 ndash0717168000 C 4533131000 ndash0322603000 ndash1448209000 C 5731498000 ndash0208370000 ndash0696796000 C 5731438000 ndash0207885000 0696952000 C 4533003000 ndash0321597000 1448333000 C 3374722000 ndash0432010000 0717261000 C 1871861000 ndash0585642000 0739747000 C 0758457000 ndash0732583000 1513259000 C ndash0460578000 ndash0772439000 0748991000 C ndash1838348000 ndash1436677000 0718485000 C ndash2895298000 ndash1922892000 1447371000 C ndash3991613000 ndash2429987000 0695830000 H ndash4853881000 ndash2841402000 ndash1229010000 H ndash2909366000 ndash1943431000 ndash2538196000 H 0770744000 ndash0814782000 ndash2600896000 H 4554949000 ndash0321315000 ndash2539049000 H 6684245000 ndash0118682000 ndash1227928000 H 6684140000 ndash0117859000 1228104000 H 4554722000 ndash0319567000 2539175000 H 0770611000 ndash0813312000 2601042000 H ndash2909450000 ndash1942588000 2538596000 H ndash4853932000 ndash2840954000 1229654000 Co ndash1032604000 1030206000 ndash0000179000 C ndash2903591000 1947430000 ndash0000175000 C ndash2211742000 2430689000 ndash1177143000 C ndash1026232000 3056089000 ndash0732194000 C ndash1026229000 3056139000 0731719000 C ndash2211730000 2430773000 1176747000 H ndash3829247000 1376180000 ndash0000150000 H ndash2513347000 2264399000 ndash2207387000 H ndash0243163000 3477094000 ndash1358586000 H ndash0243137000 3477190000 1358051000 H ndash2513304000 2264572000 2207015000

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 133 -

C 4829664000 ndash1220862000 0883782000 C 3649435000 ndash0895915000 1609183000 C 2478533000 ndash0900239000 0886069000 C 0985532000 ndash0699413000 0895282000 C ndash0207413000 ndash0351140000 1567281000 C ndash1295977000 ndash0355264000 0631690000 C ndash2799524000 ndash0368596000 0647705000 C ndash3950748000 0104186000 1252743000 C ndash5173877000 ndash0370408000 0725519000 C ndash5217559000 ndash1270006000 ndash0351644000 C ndash4043168000 ndash1754445000 ndash0967619000 C ndash2843350000 ndash1293792000 ndash0444950000 C ndash1365414000 ndash1319830000 ndash0538287000 C ndash0225558000 ndash1662005000 ndash1182029000 C 0928168000 ndash1009692000 ndash0554559000 C 2436156000 ndash1209374000 ndash0509824000 C 3575395000 ndash1530032000 ndash1215144000 C 4792344000 ndash1526592000 ndash0477473000 H 5781080000 ndash1237670000 1406156000 H 3693287000 ndash0679862000 2671420000 H ndash0279175000 ndash0037747000 2601166000 H ndash3939706000 0801901000 2083798000 H ndash6106757000 ndash0031072000 1165263000 H ndash6183419000 ndash1601741000 ndash0720200000 H ndash4097586000 ndash2453276000 ndash1795561000 H ndash0137803000 ndash2306368000 ndash2049380000 H 3570207000 ndash1781979000 ndash2270507000 H 5717527000 ndash1774506000 ndash0988963000 Co 0235674000 0924694000 ndash0006080000 C 1650242000 2605908000 ndash0261710000 C 0606451000 3071372000 0583798000

C ndash0633939000 2891762000 ndash0112192000 C ndash0354070000 2388098000 ndash1431110000 C 1060641000 2182627000 ndash1507942000 H 2701380000 2562827000 ndash0018620000 H 0717262000 3431891000 1595877000 H ndash1615358000 3123686000 0274491000 H ndash1077256000 2190401000 ndash2207047000

- 134 -

H 1601331000 1788686000 ndash2355167000

(d) Transition State 2 η3-benzene (249 kcalmol)

C 5059641000 ndash0675345000 0741440000 C 3868057000 ndash0242461000 1393542000 C 2691208000 ndash0611642000 0796692000 C 1164924000 ndash0568451000 0814993000 C 0001006000 ndash0193010000 1575722000 C ndash1162903000 ndash0569406000 0815406000 C ndash2689168000 ndash0613549000 0797134000 C ndash3866228000 ndash0245076000 1394017000 C ndash5057560000 ndash0678583000 0741882000 C ndash5030442000 ndash1430649000 ndash0426732000 C ndash3802288000 ndash1812828000 ndash1038342000 C ndash2662603000 ndash1392426000 ndash0404590000 C ndash1143695000 ndash1392940000 ndash0383227000 C 0001354000 ndash1885575000 ndash1010384000 C 1146183000 ndash1392203000 ndash0383465000 C 2665098000 ndash1390792000 ndash0404876000 C 3805017000 ndash1810598000 ndash1038596000 C 5032958000 ndash1427555000 ndash0427087000 H 6017043000 ndash0408623000 1174840000 H 3916675000 0338622000 2306082000 H 0001106000 0141040000 2603832000 H ndash3915179000 0335814000 2306664000 H ndash6015116000 ndash0412488000 1175329000

- 135 -

H ndash5963925000 ndash1737868000 ndash0883265000 H ndash3794877000 ndash2406462000 ndash1944276000 H 0001449000 ndash2505619000 ndash1894591000 H 3797948000 ndash2404400000 ndash1944423000 H 5966616000 ndash1734262000 ndash0883606000 Co ndash0000294000 1006304000 0016484000 C 1144150000 2811021000 ndash0317903000 C ndash0001831000 3236912000 0413780000 C ndash1150105000 2808519000 ndash0312717000 C ndash0712506000 2257800000 ndash1588662000 C 0702130000 2259464000 ndash1591918000 H 2174046000 2940434000 ndash0021226000 H ndash0000096000 3693787000 1391408000 H ndash2178919000 2935539000 ndash0011312000 H ndash1360790000 1903514000 ndash2375388000 H 1347563000 1907002000 ndash2381795000

Calculated structures for linear [5]phenylene CpCo (labels from Figures 211 and 212 in Section 24)

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

C ndash2147283000 ndash0385762000 ndash0741520000 C ndash2146881000 ndash0382747000 0740465000 C ndash0675330000 ndash0218887000 0741228000 C ndash0675503000 ndash0222208000 ndash0743565000 C 0535474000 ndash0309864000 ndash1519364000

- 136 -

C 1654024000 ndash0363787000 ndash0743565000 C 1653968000 ndash0359108000 0742223000 C 0535464000 ndash0301263000 1517648000 C 3146303000 ndash0437352000 0715394000 C 3146555000 ndash0442081000 ndash0715839000 H 0537903000 ndash0329735000 2601810000 H 0538062000 ndash0344229000 ndash2603354000 Co ndash1585768000 1444604000 ndash0004763000 C ndash2656365000 3118646000 0813641000 C ndash1264152000 3247968000 1115884000 C ndash0546296000 3292610000 ndash0128221000 C ndash1500173000 3225060000 ndash1199322000 C ndash2801883000 3099872000 ndash0616868000 H ndash3459184000 3033020000 1530368000 H ndash0824887000 3279284000 2101474000 H 0525240000 3366953000 ndash0237713000 H ndash1272392000 3239735000 ndash2254384000 H ndash3732669000 2998753000 ndash1154572000 C ndash3315848000 ndash0698077000 1516941000 C ndash3316515000 ndash0705270000 ndash1515890000 C ndash4404590000 ndash0970491000 0742487000 C ndash4404888000 ndash0974125000 ndash0739677000 H ndash3311463000 ndash0745189000 ndash2599679000 H ndash3310191000 ndash0733014000 2600900000 C ndash5857232000 ndash1346832000 ndash0713671000 C ndash5856902000 ndash1343302000 0718959000 C ndash6992149000 ndash1638138000 ndash1445564000 C ndash6991464000 ndash1630979000 1452826000 C 4314567000 ndash0501395000 ndash1493440000 C 4313844000 ndash0491124000 1494022000

C ndash8157130000 ndash1937355000 ndash0695553000 C ndash8156796000 ndash1933908000 0704865000 H ndash7013569000 ndash1630976000 2537309000 H ndash9075842000 ndash2169721000 1232475000 H ndash9076411000 ndash2175846000 ndash1221548000 H ndash7014707000 ndash1643790000 ndash2530023000 C 5464859000 ndash0553191000 0719930000 C 5465218000 ndash0558312000 ndash0718328000 C 6977989000 ndash0635007000 ndash0714777000 C 6977565000 ndash0629511000 0717833000 H 4313279000 ndash0484164000 2577745000 H 4314609000 ndash0502067000 ndash2577185000 C 8138196000 ndash0684071000 1451266000 C 8139115000 ndash0695400000 ndash1446980000 C 9348946000 ndash0746919000 0699256000 C 9349380000 ndash0752387000 ndash0693700000

- 137 -

H 8162380000 ndash0700716000 ndash2531270000 H 8160717000 ndash0680929000 2535584000 H 10294800000 ndash0791917000 1230058000 H 10295576000 ndash0801571000 ndash1223516000

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

C ndash8026536000 ndash2149127000 ndash0697047000 C ndash6872771000 ndash1801590000 ndash1447012000 C ndash5755909000 ndash1466198000 ndash0717983000 C ndash4305789000 ndash1041476000 ndash0739357000 C ndash3218268000 ndash0750848000 ndash1510952000 C ndash2077793000 ndash0315087000 ndash0749237000 C ndash0550342000 ndash0400850000 ndash0716361000 C 0616872000 ndash0404801000 ndash1489728000 C 1770640000 ndash0412395000 ndash0716060000 C 3300443000 ndash0457807000 ndash0715861000 C 4454767000 ndash0490291000 ndash1489427000 C 5616257000 ndash0520747000 ndash0712496000 C 5616269000 ndash0520699000 0712492000 C 4454793000 ndash0490190000 1489443000 C 3300455000 ndash0457762000 0715895000 C 1770651000 ndash0412347000 0716117000 C 0616894000 ndash0404700000 1489800000 C ndash0550335000 ndash0400796000 0716454000 C ndash2077818000 ndash0315060000 0749341000 C ndash3218306000 ndash0750915000 1510996000

- 138 -

C ndash4305781000 ndash1041534000 0739359000 C ndash5755900000 ndash1466256000 0717962000 C ndash6872758000 ndash1801708000 1446971000 C ndash8026533000 ndash2149171000 0696987000 H ndash6893447000 ndash1807486000 ndash2529846000 H ndash3199702000 ndash0827686000 ndash2591829000 H 0616147000 ndash0415875000 ndash2572166000 H 4455855000 ndash0492565000 ndash2571217000 H 4455901000 ndash0492389000 2571233000 H 0616188000 ndash0415693000 2572238000 H ndash3199790000 ndash0827916000 2591862000 H ndash6893430000 ndash1807681000 2529804000 Co ndash2237895000 1566525000 ndash0000035000 C ndash0770702000 3039808000 0000091000 C ndash1582333000 3276979000 1176306000 C ndash2906316000 3484053000 0731575000 C ndash2906172000 3484095000 ndash0731735000 C ndash1582100000 3277047000 ndash1176233000 H 0281094000 2798829000 0000215000 H ndash1247438000 3209109000 2198999000 H ndash3777291000 3625124000 1353071000 H ndash3777011000 3625160000 ndash1353424000 H ndash1246943000 3209260000 ndash2198847000 H ndash8933230000 ndash2423019000 ndash1224452000 H ndash8933222000 ndash2423113000 1224377000 C 7146943000 ndash0559737000 0717588000 C 7146931000 ndash0559786000 ndash0717614000 C 8302361000 ndash0588480000 1447040000 C 8302337000 ndash0588576000 ndash1447082000 C 9516918000 ndash0618789000 ndash0692883000 C 9516929000 ndash0618742000 0692823000 H 8324450000 ndash0589130000 2529610000 H 10461320000 ndash0642422000 1224406000 H 10461300000 ndash0642481000 ndash1224480000 H 8324409000 ndash0589299000 ndash2529653000

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 139 -

C ndash7810644000 ndash2064896000 ndash0088979000 C ndash6582065000 ndash2396690000 ndash0700394000 C ndash5469369000 ndash1694626000 ndash0259356000 C ndash4011414000 ndash1478684000 ndash0398743000 C ndash2839913000 ndash1679834000 ndash1045300000 C ndash1807973000 ndash0777407000 ndash0523048000 C ndash0288034000 ndash0728447000 ndash0497727000 C 0877200000 ndash0917515000 ndash1257428000 C 2033335000 ndash0625143000 ndash0541547000 C 3550975000 ndash0572504000 ndash0566638000 C 4702932000 ndash0775398000 ndash1323945000 C 5869717000 ndash0493099000 ndash0604711000 C 5877160000 ndash0049178000 0749672000 C 4719648000 0152978000 1509600000 C 3558389000 ndash0127834000 0791889000 C 2041313000 ndash0178303000 0818968000 C 0890228000 0010834000 1576182000

C ndash0275189000 ndash0290874000 0857465000 C ndash1777915000 ndash0332627000 0896504000 C ndash3000252000 ndash0144927000 1576583000 C ndash4087655000 ndash0414543000 0681649000 C ndash5565811000 ndash0681071000 0748878000 C ndash6769777000 ndash0358061000 1349731000 C ndash7902756000 ndash1078577000 0906205000 H ndash6531350000 ndash3165530000 ndash1463988000 H ndash2656944000 ndash2379915000 ndash1852763000

- 140 -

H 0873498000 ndash1259556000 ndash2286041000 H 4697058000 ndash1113491000 ndash2353481000 H 4726794000 0489146000 2539724000 H 0892018000 0335667000 2610226000 H ndash3107471000 0242268000 2582171000 H ndash6863567000 0403771000 2116786000 Co ndash2805901000 1045228000 ndash0126008000 C ndash1966955000 3131745000 ndash0137391000 C ndash3345106000 3172285000 0219040000 C ndash4105003000 2591218000 ndash0859559000 C ndash3194452000 2177424000 ndash1877135000 C ndash1861601000 2475718000 ndash1403791000 H ndash1139494000 3467521000 0469940000 H ndash3757304000 3575577000 1132204000 H ndash5178689000 2478840000 ndash0883920000 H ndash3449207000 1717975000 ndash2819531000 H ndash0944137000 2267497000 ndash1933863000 H ndash8711780000 ndash2586977000 ndash0395882000 H ndash8871888000 ndash0864282000 1346179000 C 7394568000 0005138000 0727783000

C 7387058000 ndash0441388000 ndash0634217000 C 8557433000 0273605000 1404315000

C 8542647000 ndash0629395000 ndash1349402000 C 9760631000 ndash0352464000 ndash0653366000 C 9767843000 0080954000 0667800000 H 8586089000 0612106000 2434348000 H 10716375000 0279405000 1157078000

H 10703753000 ndash0485281000 ndash1174332000 H 8560430000 ndash0966385000 ndash2380163000

(d) Transition state 4 η3-benzene (367 kcalmol)

- 141 -

C 7669717000 ndash2174926000 ndash0105923000 C 6450462000 ndash2458728000 0544003000 C 5349535000 ndash1733337000 0120322000 C 3893688000 ndash1505268000 0269179000 C 2708972000 ndash1942858000 0838638000 C 1596115000 ndash1239419000 0370186000 C 0149218000 ndash1103313000 0368184000 C ndash1061261000 ndash1583264000 0932639000 C ndash2167377000 ndash0965378000 0405284000 C ndash3686709000 ndash0866795000 0409630000 C ndash4872520000 ndash1347856000 0960688000 C ndash5997863000 ndash0728310000 0421450000 C ndash5941471000 0288854000 ndash0586107000 C ndash4758793000 0770529000 ndash1137452000 C ndash3629556000 0150846000 ndash0598044000 C ndash2119390000 0068600000 ndash0617626000 C ndash0945265000 0548559000 ndash1173832000 C 0191709000 ndash0072876000 ndash0643629000 C 1695402000 ndash0118964000 ndash0667389000 C 2835200000 0041396000 ndash1507494000 C 3981535000 ndash0415532000 ndash0796385000 C 5449049000 ndash0747489000 ndash0920326000 C 6638556000 ndash0473422000 ndash1556289000 C 7762417000 ndash1216205000 ndash1122513000 H 6396888000 ndash3209338000 1323030000 H 2647172000 ndash2772334000 1532449000 H ndash1099468000 ndash2356302000 1688990000 H ndash4914534000 ndash2116326000 1720908000 H ndash4717626000 1537921000 ndash1898781000 H ndash0906852000 1317204000 ndash1935050000 H 2849903000 0560387000 ndash2457942000 H 6730568000 0262385000 ndash2346085000 Co 3078365000 1106450000 0223118000 C 2432920000 3235925000 0352954000 C 3805628000 3232135000 ndash0000959000 C 4525686000 2519574000 1027488000 C 3591065000 2151422000 2051886000 C 2287258000 2550618000 1620273000

- 142 -

H 1625110000 3662123000 ndash0222202000 H 4237852000 3652387000 ndash0895767000 H 5588986000 2336674000 1044912000 H 3828106000 1629983000 2966790000 H 1363656000 2417646000 2161607000 H 8562189000 ndash2715853000 0187384000 H 8723754000 ndash1039126000 ndash1591154000 C ndash7467794000 0379383000 ndash0580257000 C ndash7522920000 ndash0639213000 0428535000 C ndash8594261000 0964602000 ndash1089561000 C ndash8706397000 ndash1090617000 0945872000 C ndash9887862000 ndash0485330000 0420145000 C ndash9834353000 0499744000 ndash0555359000 H ndash8574126000 1734202000 ndash1850912000 H ndash10757407000 0931123000 ndash0925119000 H ndash10851990000 ndash0807405000 0796463000 H ndash8770071000 ndash1858056000 1706995000

(e) Local minimum 3 η4-benzene (190 kcalmol)

C ndash7704806000 ndash1625445000 ndash0076324000 C ndash6491455000 ndash1789497000 ndash0801300000 C ndash5352262000 ndash1326936000 ndash0190371000 C ndash3836374000 ndash1127906000 ndash0291559000 C ndash2669014000 ndash1876939000 ndash0775878000 C ndash1540408000 ndash1361850000 ndash0248671000 C ndash0067088000 ndash1219487000 ndash0231176000 C 1147603000 ndash1746746000 ndash0723682000

- 143 -

C 2245517000 ndash1037457000 ndash0289605000 C 3767258000 ndash0910575000 ndash0313273000 C 4961694000 ndash1439625000 ndash0795996000 C 6075343000 ndash0726547000 ndash0354068000 C 5999362000 0418026000 0498208000 C 4804020000 0947684000 0980899000 C 3691158000 0235329000 0538756000 C 2171505000 0121554000 0570963000 C 0990404000 0649716000 1051234000

C ndash0139369000 ndash0066282000 0613306000 C ndash1640889000 ndash0139469000 0665899000 C ndash2708579000 0044357000 1607074000 C ndash3890300000 ndash0515482000 1069631000 C ndash5389479000 ndash0719093000 1106627000 C ndash6553177000 ndash0561696000 1815459000 C ndash7736166000 ndash1034716000 1182797000 H ndash6489929000 ndash2263627000 ndash1775522000 H ndash2743316000 ndash2692464000 ndash1483904000 H 1201969000 ndash2617287000 ndash1364047000 H 5019196000 ndash2306567000 ndash1440440000 H 4747029000 1814065000 1626168000 H 0933710000 1519855000 1692796000 H ndash2640951000 0605584000 2529735000 H ndash6590996000 ndash0122891000 2805220000 Co ndash3231943000 0870639000 ndash0218177000 C ndash2631117000 2925280000 ndash0475333000 C ndash4019450000 2955930000 ndash0137499000 C ndash4720042000 2167067000 ndash1095287000 C ndash3768150000 1717753000 ndash2089396000 C ndash2477085000 2188405000 ndash1710046000 H ndash1832546000 3399891000 0073720000 H ndash4448788000 3419647000 0737399000 H ndash5777018000 1951944000 ndash1095854000 H ndash3999907000 1119290000 ndash2956393000 H ndash1549894000 2013889000 ndash2232360000 H ndash8630326000 ndash1978241000 ndash0517433000 H ndash8683428000 ndash0939767000 1701100000 C 7524401000 0541032000 0473497000

C 7600630000 ndash0607844000 ndash0382149000 C 8637973000 1216338000 0890053000

C 8792152000 ndash1101412000 ndash0836674000 C 9961705000 ndash0402146000 ndash0407106000 C 9887895000 0708141000 0420266000 H 8602106000 2084773000 1535736000 H 10801526000 1207625000 0721410000

H 10931894000 ndash0752974000 ndash0739605000

- 144 -

H 8871661000 ndash1966753000 ndash1482602000

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

C 7143264000 ndash2348493000 0699665000 C 6037664000 ndash1857298000 1448523000 C 4969251000 ndash1391864000 0720257000 C 3582514000 ndash0743198000 0748195000 C 2358402000 ndash0737338000 1512136000 C 1240141000 ndash0634711000 0742222000 C ndash0262684000 ndash0516912000 0716494000 C ndash1428088000 ndash0430968000 1492584000 C ndash2574224000 ndash0346717000 0719319000 C ndash4098679000 ndash0233199000 0715866000 C ndash5251323000 ndash0147278000 1490294000 C ndash6408253000 ndash0063372000 0713741000 C ndash7934932000 0047490000 0717366000 C ndash9088044000 0130556000 1446914000 C ndash10299063000 0217080000 0692638000 C ndash10298939000 0215301000 ndash0693576000 C ndash9087782000 0126841000 ndash1447398000 C ndash7934811000 0045602000 ndash0717417000 C ndash6408180000 ndash0065400000 ndash0713264000 C ndash5251144000 ndash0151514000 ndash1489420000 C ndash4098619000 ndash0235099000 ndash0714599000 C ndash2574142000 ndash0348081000 ndash0717615000 C ndash1428022000 ndash0433439000 ndash1490677000

- 145 -

C ndash0262587000 ndash0517946000 ndash0714342000 C 1239930000 ndash0636111000 ndash0739947000 C 2357013000 ndash0742891000 ndash1511730000 C 3581891000 ndash0749703000 ndash0749006000 C 4968536000 ndash1397444000 ndash0717250000 C 6036190000 ndash1868351000 ndash1443314000 C 7142499000 ndash2353756000 ndash0691900000 H 8003789000 ndash2740125000 1230531000 H 6052031000 ndash1874231000 2531931000 H 2350726000 ndash0802237000 2593967000 H ndash1427931000 ndash0429806000 2574521000 H ndash5251989000 ndash0146640000 2572026000 H ndash9110076000 0132990000 2529448000 H ndash11241535000 0285430000 1223689000 H ndash11241318000 0282253000 ndash1224971000 H ndash9109613000 0126365000 ndash2529940000 H ndash5251637000 ndash0153720000 ndash2571150000 H ndash1427824000 ndash0434279000 ndash2572612000 H 2347832000 ndash0810535000 ndash2593375000 H 6049185000 ndash1893779000 ndash2526553000 H 8002469000 ndash2749449000 ndash1220666000 Co 4148367000 1055016000 ndash0009106000 C 5996101000 2006266000 0022069000 C 5276853000 2480887000 1185002000 C 4085420000 3079352000 0718350000 C 4110596000 3077077000 ndash0745160000 C 5316353000 2474554000 ndash1168669000 H 6921324000 1451094000 0038659000 H 5556549000 2314709000 2212960000 H 3287274000 3477873000 1325692000 H 3334253000 3474398000 ndash1380859000 H 5631980000 2304731000 ndash2185537000

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 146 -

C 4893664000 ndash1209972000 0735005000 C 4893573000 ndash1213475000 ndash0730870000 C 3475382000 ndash0763132000 ndash0743915000 C 3475432000 ndash0760320000 0747049000 C 2260316000 ndash0690973000 1520580000 C 1145205000 ndash0595973000 0744946000 C 1145156000 ndash0599246000 ndash0742744000 C 2260358000 ndash0697381000 ndash1517904000 C ndash0343192000 ndash0479177000 ndash0713609000 C ndash0343168000 ndash0476032000 0715380000 H 2252105000 ndash0735285000 ndash2601934000 H 2251901000 ndash0724154000 2604763000 Co 4601208000 0736083000 ndash0002055000 C 5960130000 2243618000 ndash0721946000 C 4640007000 2540538000 ndash1172530000 C 3804522000 2681992000 ndash0008876000 C 4632302000 2544967000 1160921000 C 5955467000 2247130000 0721276000 H 6816321000 2038808000 ndash1347044000 H 4312673000 2604006000 ndash2199136000 H 2745254000 2890841000 ndash0012873000 H 4298236000 2612143000 2185222000 H 6807361000 2044890000 1353015000 C 6022290000 ndash1649780000 1464200000 C 6022277000 ndash1656609000 ndash1457900000 C 7122289000 ndash2056771000 0719324000 C 7122311000 ndash2060028000 ndash0711126000 H 6027301000 ndash1702610000 2548102000 H 8011576000 ndash2407816000 1233935000 H 8011528000 ndash2413601000 ndash1224115000 H 6027432000 ndash1714310000 ndash2541551000 C ndash1512226000 ndash0382902000 1494684000 C ndash1512274000 ndash0389473000 ndash1493257000 C ndash2658093000 ndash0297761000 0720325000 C ndash2658103000 ndash0300923000 ndash0719236000 H ndash1511446000 ndash0379165000 2578406000

- 147 -

H ndash1511531000 ndash0390614000 ndash2576954000 C ndash4169046000 ndash0190131000 ndash0714237000 C ndash4169015000 ndash0186849000 0714915000 C ndash5325016000 ndash0103295000 1491764000 C ndash5325120000 ndash0110177000 ndash1491395000 C ndash6483203000 ndash0023670000 0713863000 C ndash6483258000 ndash0027061000 ndash0713749000 H ndash5325252000 ndash0101647000 2575308000 H ndash5325471000 ndash0113799000 ndash2574933000 C ndash7997403000 0080746000 0716440000 C ndash7997524000 0076500000 ndash0716680000 C ndash9155096000 0160872000 1448927000 C ndash9155379000 0152083000 ndash1449432000 C ndash10366775000 0240123000 0695134000 C ndash10366925000 0235844000 ndash0695874000 H ndash9178696000 0150122000 ndash2533721000 H ndash11311550000 0297904000 ndash1227155000 H ndash11311298000 0305233000 1226228000 H ndash9178228000 0165001000 2533216000

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

C 8266704000 ndash2005162000 0692734000 C 7088955000 ndash1708719000 1446000000 C 5966603000 ndash1428050000 0716466000

- 148 -

C 4483884000 ndash1054830000 0713802000 C 3355736000 ndash0795879000 1487813000 C 2219848000 ndash0542568000 0715155000 C 0748349000 ndash0122254000 0743952000 C ndash0460068000 ndash0300197000 1509394000 C ndash1583463000 ndash0354552000 0739667000 C ndash3088504000 ndash0455891000 0716671000 C ndash4249167000 ndash0553278000 1491353000 C ndash5399475000 ndash0634011000 0717623000 C ndash6922525000 ndash0754459000 0717051000 C ndash8076029000 ndash0852663000 1446746000 C ndash9285359000 ndash0940991000 0693505000 C ndash9286426000 ndash0927591000 ndash0694047000 C ndash8078221000 ndash0824629000 ndash1447252000 C ndash6923651000 ndash0740632000 ndash0717519000 C ndash5400498000 ndash0620402000 ndash0717994000 C ndash4251528000 ndash0525736000 ndash1491803000 C ndash3089431000 ndash0443610000 ndash0717063000 C ndash1585243000 ndash0344579000 ndash0740307000 C ndash0463450000 ndash0290395000 ndash1513612000 C 0748496000 ndash0127629000 ndash0751652000 C 2219455000 ndash0546002000 ndash0721683000 C 3355860000 ndash0802470000 ndash1493276000 C 4483583000 ndash1057975000 ndash0718022000 C 5966360000 ndash1431783000 ndash0719354000 C 7088265000 ndash1716549000 ndash1447876000 C 8266466000 ndash2008718000 ndash0693595000 H 9183427000 ndash2233531000 1224348000 H 7110060000 ndash1714392000 2528663000 H 3353411000 ndash0803478000 2570367000 H ndash0456292000 ndash0373454000 2590614000 H ndash4248665000 ndash0564171000 2573279000 H ndash8096828000 ndash0865292000 2529266000 H ndash10227269000 ndash1021159000 1223954000 H ndash10229127000 ndash0997490000 ndash1224546000 H ndash8100648000 ndash0816347000 ndash2529785000 H ndash4252664000 ndash0517117000 ndash2573754000 H ndash0464650000 ndash0354640000 ndash2595436000 H 3353541000 ndash0815213000 ndash2575752000 H 7108905000 ndash1727728000 ndash2530504000 H 9182976000 ndash2239822000 ndash1224379000 Co 1060170000 1739352000 ndash0013647000 C 0820599000 3762931000 0679296000 C 2023158000 3250849000 1217023000 C 2833506000 2814255000 0100512000 C 2185795000 3225276000 ndash1129991000

- 149 -

C 0924349000 3753677000 ndash0780133000 H ndash0033478000 4112410000 1239126000 H 2257663000 3114053000 2260457000 H 3791311000 2322414000 0171627000 H 2565428000 3065285000 ndash2126458000 H 0160713000 4098445000 ndash1460120000

(i) Local minimum 1 η4-benzene (190 kcalmol)

C 8767525000 ndash0664628000 0869444000 C 7569070000 ndash0364489000 1586360000 C 6400497000 ndash0535559000 0896308000 C 4872998000 ndash0456407000 0896648000 C 3729258000 ndash0166123000 1633430000 C 2558863000 ndash0367557000 0899969000 C 1050529000 ndash0274920000 0917771000 C ndash0154687000 0103769000 1545183000 C ndash1231288000 ndash0039565000 0606842000 C ndash2736221000 ndash0089835000 0603708000 C ndash3901526000 0467576000 1153370000 C ndash5054648000 ndash0104455000 0647800000 C ndash6579036000 ndash0120351000 0673091000 C ndash7732820000 0402806000 1194768000 C ndash8948594000 ndash0155119000 0702959000 C ndash8958839000 ndash1167887000 ndash0247745000 C ndash7753788000 ndash1707235000 ndash0785423000 C ndash6589806000 ndash1166201000 ndash0307896000

- 150 -

C ndash5063448000 ndash1158179000 ndash0339650000 C ndash3923750000 ndash1713712000 ndash0884954000 C ndash2743411000 ndash1141750000 ndash0370168000 C ndash1264100000 ndash1152263000 ndash0442985000 C ndash0114410000 ndash1509648000 ndash1047872000 C 1001557000 ndash0717865000 ndash0509678000 C 2529242000 ndash0815059000 ndash0456630000 C 3680301000 ndash1106705000 ndash1192448000 C 4847485000 ndash0909766000 ndash0461159000 C 6375435000 ndash0989198000 ndash0464503000 C 7517684000 ndash1280530000 ndash1157992000 C 8743181000 ndash1104009000 ndash0445669000 H 9720775000 ndash0544729000 1371431000 H 7610320000 ndash0024462000 2613574000 H 3742883000 0162901000 2664422000 H ndash0241422000 0534554000 2534230000 H ndash3894210000 1260341000 1890621000 H ndash7746436000 1191936000 1936109000 H ndash9890199000 0223840000 1083439000

H ndash9908180000 ndash1561665000 ndash0592194000 H ndash7783148000 ndash2497305000 ndash1525270000 H ndash3929534000 ndash2506814000 ndash1621099000 H 0005285000 ndash2235278000 ndash1842324000 H 3664139000 ndash1453900000 ndash2217556000 H 7520111000 ndash1625509000 ndash2184413000 H 9677483000 ndash1320445000 ndash0950825000 Co 0245526000 1194775000 ndash0183529000 C ndash0498660000 3223481000 ndash0207100000 C 0902667000 3310487000 0056983000 C 1591310000 2661311000 ndash1009417000 C 0610054000 2243094000 ndash1989593000 C ndash0681576000 2592200000 ndash1494981000 H ndash1289524000 3595536000 0425619000 H 1355880000 3721411000 0946130000 H 2657726000 2519341000 ndash1088515000 H 0823168000 1743521000 ndash2921425000 H ndash1626608000 2403559000 ndash1979282000

(j) Transition state 1 η3-benzene (356 kcalmol)

- 151 -

C ndash8901354000 ndash0223681000 ndash0743434000 C ndash7695103000 0220198000 ndash1360549000 C ndash6531343000 ndash0208573000 ndash0779115000 C ndash5007706000 ndash0207407000 ndash0796109000 C ndash3863247000 0247302000 ndash1433753000 C ndash2690760000 ndash0206508000 ndash0819013000 C ndash1184933000 ndash0153490000 ndash0843116000 C ndash0016095000 0217826000 ndash1588049000 C 1142075000 ndash0155798000 ndash0877497000 C 2665172000 ndash0195830000 ndash0859864000 C 3835813000 0283152000 ndash1437197000 C 4978920000 ndash0204857000 ndash0802474000 C 6505676000 ndash0216574000 ndash0771205000 C 7678527000 0226433000 ndash1319208000 C 8875127000 ndash0251684000 ndash0703235000 C 8845790000 ndash1112691000 0383544000 C 7616005000 ndash1570592000 0948642000 C 6475812000 ndash1107284000 0353147000 C 4945633000 ndash1092812000 0320013000 C 3774824000 ndash1565295000 0903163000 C 2628495000 ndash1080676000 0265289000 C 1119158000 ndash1093642000 0244670000 C ndash0052242000 ndash1637616000 0861793000 C ndash1193959000 ndash1109215000 0331010000 C ndash2676505000 ndash1073633000 0328062000 C ndash3841325000 ndash1514463000 0979035000 C ndash4995446000 ndash1053912000 0371366000 C ndash6522185000 ndash1052982000 0381089000 C ndash7676261000 ndash1483950000 0978498000 C ndash8892512000 ndash1041633000 0378747000

- 152 -

H ndash9850267000 0087677000 ndash1164894000 H ndash7723622000 0856176000 ndash2236504000 H ndash3873085000 0886115000 ndash2307512000 H ndash0031238000 0768624000 ndash2518870000 H 3857949000 0953892000 ndash2286176000 H 7723941000 0897606000 ndash2167700000 H 9831384000 0069893000 ndash1099633000 H 9779177000 ndash1450269000 0819087000 H 7614291000 ndash2243551000 1796930000 H 3751975000 ndash2237828000 1750478000 H ndash0016047000 ndash2343040000 1681308000 H ndash3832680000 ndash2159963000 1847727000 H ndash7691389000 ndash2121828000 1853393000 H ndash9834648000 ndash1354566000 0814012000 Co ndash0004249000 1140918000 0250383000 C 0931445000 3181201000 0326993000 C ndash0487068000 3279997000 0223542000 C ndash1069741000 2607436000 1368652000 C 0008159000 2107122000 2176577000 C 1235098000 2411215000 1492603000 H 1650004000 3565479000 ndash0380430000 H ndash1033454000 3774248000 ndash0564979000 H ndash2124544000 2537255000 1584462000 H ndash0094112000 1572170000 3107766000 H 2227446000 2134637000 1815486000

LUMO

HOMO

2887

239

00862

2496

1163

1382

1418

1312

0

3155

2767

0498

2588

1531

0831

Figure 47 Orbital coefficients of linear [5]phenylene

- 153 -

Figure 48 Top view of the contour plots of (a) the HOMO and (b) the LUMO of the [5]-phenylene ligand

- 154 -

Bad

Bad

Good Good

External cyclobutadiene coordination Internal cyclobutadiene coordination

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCpCoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

Figure 49 Resonance rationale for the increased stability of internal Co coordination in linear [5]phenylene

44 NMR Data for Chapter Two

- 155 -

Figure 410 1H-NMR data for the respective parent phenylene frames experimental (C6D6) and

calculated [NICS (1) B3LYP6-31+G] Assignments by NOESY DEPT HMBC and HSQC as applicable

- 156 -

Me3Si

Me3Si

SiMe3

SiMe3

1

23

4 56

7 89

10 1112

13 1415

16

17

18

Co

222

1490

1252

1450

1433

1151

744

730

11091121

14161504

11211109

1540

1499

1224

1486

217

801

SiMe3

SiMe3

Me3Si

Me3Si

Co

802

261

1484

1256

1433

1494

1155

739

781

1360

1394

269

SiMe3

SiMe3

Co

802

1294

1149

1426

1502

1194

738

779

1363

1393

268

SiMe3

SiMe3

1241

1276

8029

725

1155

1493

1430

1256

1482

222

Co

796

678674 675 796

436

037032662

724 683 747

444

TMS

TMS

TMS

TMS

213

1474

1211

1538

1499

1112

623 685

SiMe3

SiMe3Me3Si

Me3Si SiMe3

SiMe3Me3Si

Me3Si459 Co

589 681 672 745

2201204

15131096

1535

2221252

1480

1433

1149741

801

1501 1490

1475

Figure 411 Comparison of 1H-NMR (blue) and 13C-NMR assignments (C6D6)

NICS-Scan calculations Methods The free ligands were optimized at the B3LYP6-31G and the CpCo complexes at the B3LYPLANL2DZ computational levels Analytical frequency calculations were executed to ensure real minima (Nimag = 0) GIAO-B3LYP6-31+G was used to calculate NICS values The NICS-scan procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (ipc or NICSXY) and out-of-plane components (oopc or NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their interpretation

- 157 -

Since there are no published NICS-scan studies of transition metal complexed cyclic polyenes we benchmark the method with (C6H6)Cr(CO)3

53

Figure 412 NICS-scan of benzene (left) and (benzene)Cr(CO)3 (right)

The shape of the oopc curve suggests that the diamagnetic ring current in the ligand is diminished on complexation although still prevalent Thus at r = 0 Aring (ie at the benzene plane) the oopc value [NICSZZ(0)] of the complex is less negative than that of benzene and the minimum of the curve is less negative and occurs at a larger distance (ndash29911 vs ndash31910) A larger change is observed in the ipc (which is governed by the σ electrons) which shows far more negative values in the complex relative to benzene itself (eg ndash55400 vs ndash5900 and ndash13910 vs ndash0910) Therefore isotropic NICS values are misleading with respect to the diatropism in the complex because they originate largely from the diamagnetic effect of the σ framework NICS-scans for the four-membered ring B in linear [3]phenylene and its CpCo complex are shown below

00 05 10 15 20 25 30 35 40

-34-32-30-28-26-24-22-20-18-16-14-12-10

-8-6-4-202

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

oopc ipc isotropic

pp

m

r

- 158 -

Figure 413 NICS-scan above ring B of linear [3]phenylene (left) and its CpCo complex (right) Inspection of the shape and values of the oopc curve shows that the four-membered ring in the free ligand is strongly paratropic This picture changes on CpCo complexation At or close to the ring plane the values are much less positive (12100 vs 88000) become negative at greater distance and reach a minimum of -16112 Consequently the presence of the metal clearly reduces paratropic character The ipc curve is similar to that of (benzene)Cr(CO)3 Therefore again isotropic NICS values are misleading with respect to an assessment of the size of ring current effects The two isomeric CpCo complexes of linear [5]phenylene as depicted next behave in an analogous manner and engender the same conclusions as above

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

- 159 -

Figure 414 NICS-scans of linear [5]phenylene and its CpCo complexes Top left - ring B of the free ligand Top right - ring B complexed to CpCo Bottom left - ring D of the free ligand

Bottom right - ring D complexed to CpCo The effect of CpCo complexation is also reflected in the NICS-scan properties of the remaining rings To illustrate this point the NICS-scans of the central cyclohexatrienoid ring C of linear [3]phenylene are shown below first for the free ligand then for the cyclobutadiene complex

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

- 160 -

Figure 415 NICS-scans of ring C of linear [3]phenylene Left - as a free ligand Right as a

CpCo complex of the neighboring cyclobutadiene ring B The oopc curve clearly reveals a diminution of paratropism Thus at the ring plane the oopc values of the free ligand and of the complex are 177 and 110 ppm respectively Both plots show shallow and relatively distant minima at ndash3417 and ndash7316 respectively an indication of larger diamagnetic character of the latter While the ipc values also become more negative on complexation this effect is far smaller The tables that follow provide an overview of the NICS-scan results over all component rings in linear [3]- and [5]phenylene complexed and uncomplexed The diagnostic shape of the oopc curve is designated NM for no minimum indicating paratropism and M for minimum indicating diatropism Specific values are given at r = 0 Aring r = 10 Aring and the minimum (if diamagnetic) Table 416 NICS-scan Details of the oopc for Linear [3]Phenylene and its CpCo Complex at

Ring B

Ring Shape oopc00 oopc10 Minimum A M 71 ndash107 ndash11813 AndashCpCo M ndash65 ndash228 ndash22811 B NM 880 381 BndashCpCo M 121 ndash151 ndash16112 C M 177 ndash01 ndash3418 CndashCpCo M 116 ndash17 ndash9315 D NM 880 381 DndashCpCo NM 704 237 E M 71 ndash107 ndash11813 EndashCpCo M 15 ndash148 ndash15212

00 05 10 15 20 25 30 35 40

-8-6-4-202468

101214161820

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-14-12-10

-8-6-4-202468

1012

oopc ipc isotropic

pp

m

r

- 161 -

Table 417 NICS-Scan Details of the oopc for Linear [5]Phenylene and its CpCo Complex at Ring B

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M ndash62 ndash227 ndash22811 B NM 898 396 BndashCpCo M 137 ndash148 ndash15612 C M 176 00 ndash3317 CndashCpCo M 152 ndash09 ndash8415 D NM 846 357 DndashCpCo NM 668 223 E M 164 ndash12 ndash4116 EndashCpCo M 142 ndash17 ndash5315 F NM 846 357 FndashCpCo NM 807 340 G M 176 00 ndash3317 GndashCpCo M 161 ndash04 ndash3216 H NM 898 396 HndashCpCo NM 867 378 I M 83 ndash97 ndash10813 IndashCpCo M 64 ndash109 ndash12113

Table 418 NICS-scan Details of the oopc for Lnear [5]Phenylene and its CpCo Complex at

Ring D

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M 19 ndash150 ndash15912 B NM 898 396 BndashCpCo NM 717 256 C M 176 00 ndash3317 CndashCpCo M 110 ndash122 ndash12210 D NM 846 357 DndashCpCo M 151 ndash169 ndash17311 E M 164 ndash12 ndash4116 EndashCpCo M 151 ndash169 ndash17311 F NM 846 357 FndashCpCo NM 685 231 G M 176 00 ndash3317 GndashCpCo M 148 ndash15 ndash5415 H NM 898 396 HndashCpCo NM 850 370

I M 83 ndash97 ndash10813

- 162 -

The data clearly show that on CpCo complexation the paramagnetic ring current contributions decrease (or the diamagnetic ring current contributions increase) The strongest effect is on the complexed cycle but it occurs for all rings even the most remote (eg I in the linear [5]phenylene complexed at ring B) Thus upon complexation the paratropic (and by inference antiaromatic) character of the phenylenes decrease 45 Experimental Section for Chapter Three Angular [3]phenylene 2290 angular [4]phenylene 17111 and [7]heliphene10 were prepared according to the literature Ni(COD)(PMe3)2

112 To a solution of Ni(COD)2 (0275 g 10 mmol) in dry and vigorously degassed THF (10 mL) PMe3 (020 mL 0150 g 20 mmol) was added via syringe in a single portion After stirring at RT for 24 h the mixture was transferred using a canula and filtered under Ar to remove unreacted starting material The solvent was removed on the high vacuum line and the resulting product dried for 3 h It is extremely air sensitive and must be manipulated under an inert atmosphere at all times Yellow solid (0306 g 96 ) 1H-NMR (400 MHz C6D6) δ = 412 (d J = 112 Hz 4 H) 238 (br t J = 52 Hz 4 H) 225 (t J = 52 Hz 4 H) 102 (d J = 32 Hz 18 H) ppm 31P-NMR (162 MHz C6D6) δ = ndash946 (s) ppm Adducts of diphenylacetylene 88 to angular [3]phenylene 22 ndash compounds 89 and 90

In a glove box an Ace pressure tube was charged with angular [3]phenylene 22 (0014 g 006 mmol) diphenylacetylene 88 (0098 g 0055 mmol) THF (5 mL) and Ni(COD)(PMe3)2 (70 microL 008 M in THF 0006 mmol) The reaction vessel was tightly sealed removed from the glovebox and heated to 75ndash80 oC (oil bath) for 23 h After cooling to RT the solvent was removed by rotary evaporation and the residue purified by flash chromatography on silica gel using gradient elution (101 and then 81 hexaneCH2Cl2) After a small amount of angular [3]phenylene 22 (0001 g) the monoadduct 89 (0004 g 20 ) eluted to give a yellow solid mp 195ndash196 degC 1H-NMR (500 MHz CDCl3) δ = 853 (d J = 84 Hz 1 H) 831 (d J = 80 Hz 1 H) 755 (ddd J = 16 64 80 Hz 1 H) 740ndash732 (m 2 H) 725ndash715 (m 6 H) 715ndash711 (m 2 H) 708 (d J = 65 Hz 2 H) 704 (d J = 80 Hz 1 H) 648 (t J = 72 Hz 1 H) 643 (d J = 70 Hz 1 H) 624 (t J = 75 Hz 1 H) 401 (d J = 70 Hz 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1525 15101 15096 1495 1399 13883 13879 1342 1320 1312

- 163 -

13083 13075 1282 1280 1277 1276 1275 1268 1266 1265 1264 1250 1235 1223 1179 1164 1156 ppm one peak in the region δ = 128ndash126 ppm is

presumed to be accidentally isochronous IR (KBr) ν~ = 3060 1490 1481 1442 1415 1159 1072 755 734 698 cmndash1 UV-Vis (CH3CN) λmax (log ε) 233 (442) 265 (450) 278 (sh) 294 (sh) 306 (447) 318 (449) 329 (sh) 380 (344) 399 (366) 420 (366) nm MS (70 eV) mz () 405 [M++1] (35) 404 [M+] (100) 326 (13) HRMS (EI) calcd for C32H20 4041565 found 4041571 Elemental analysis calcd for C32H20 C 9502 H 498 found 9479 460 Subsequent elution furnished 5678-tetraphenylpicene (90) (0009 g 59 ) as a white solid mp 325ndash327 degC the molecule exhibits hindered rotation of the 67-phenyl groups on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 891 (s 2 H) 885 (d J = 84 Hz 2 H) 769 (ddd J = 28 52 80 Hz 2 H) 750ndash744 (m 4 H) 744ndash732 (m 4 H) 720 (tt J = 16 72 Hz 2 H) 696 (dt J = 08 76 Hz 2 H) 689 (tt J = 09 76 Hz 2 H) 662 (br s 4 H) 617 (d J = 76 Hz 2 H) 607 (br s 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1403 1401 1377 1367 1335 1325 1324 1306 1300 1295 1292

1283 1277 1269 1264 1263 1262 1256 1254 1228 1213 ppm IR (KBr) ν~ = 3051 2922 1599 1490 1467 1442 1263 1072 1027 758 702 630 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (461) 307 (474) 352 (417) 366 (414) nm MS (70 eV) mz () 583 [M++1] (52) 582 [M+] (100) 505 (24) 504 (9) 426 (7) HRMS (EI) calcd for C46H30 5822348 found 5822336 1278-Tetraphenylbenzo[c]chrysene (91)

In a glovebox an Ace pressure tube was charged with 88 (0020 g 0050 mmol) diphenylacetylene 88 (0026 mg 0148 mmol) Ni(COD)(PMe3)2 (62 microL of a 008 M solution in THF) and THF (5 mL) The reaction vessel was sealed removed from the glovebox and heated to 85 degC for 39 h After removal of the solvent the residue was purified by flash chromatography on silica gel (eluting with 81 hexaneCH2Cl2) producing a white solid (0023 g) which was found to consist of starting material (88 18 mg) 90 (0001 g 6 ) and 91 Further purification by chromatography afforded pure 91 (0017 g 74 ) as a white solid mp 273ndash274 degC the 12-phenyl groups of 91 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 869 (d J = 95 Hz 1 H) 830ndash822 (m 1 H) 801 (d J = 75 Hz 1 H) 780ndash747 (m 2 H) 770 (ddd J = 10 70 85 Hz 1 H) 762 (dt J = 15 75 Hz 1 H) 753 (ddd J = 15 70 85 Hz 1 H) 738ndash732 (m 2 H) 730 (td J = 15 75 Hz 1 H) 729ndash722 (m 6 H) 722ndash717 (m 2 H) 717ndash710 (m 2 H) 710ndash695 (m 3 H) 680ndash640 (m 3 H) 635 (d J = 70 Hz 1 H) 623ndash595 (br s 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1418 1400 1395 1394 1378 1377 1375 1357 1323 1322 1316 1314 13113 13107 1309 1308 1307 1305 1296 1295 1288 1282 1277 1275 1274 1273 1270 12653 12647 1264 1260 1256 1253 1252 1251

- 164 -

1243 1231 1208 ppm due to extensive signal overlap four peaks are presumed to be isochronous in the regions δ = 132ndash130 and 128ndash125 ppm IR (KBr) ν~ = 3058 1601 1489 1442 1263 1073 773 762 736 699 628 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 250 (487) 313 (511) 340 (sh) nm MS(EI) mz () 583 (M++1 72) 582 (M+ 100) 505 (24) 391 (13) HRMS (EI) calcd for C46H30 5822348 found 5822341 Elemental analysis calcd for C46H30 C 8933 H 500 found 8914 493 Ni(PhCequivCPh)(PMe3)2 (92)91

In a glove box PMe3 (203 microL 0152 g 20 mmol) was mixed with a suspension of Ni(COD)2 (0275 g 10 mmol) in hexane (15 mL) Diphenylacetylene 88 (0178 g 10 mmol) was then added in one portion resulting in an immediate color change from yellow to red The mixture was stirred at room temperature for 195 h during which the color gradually turning returning to yellow Upon concentration (to ~5 mL) a yellow precipitate formed collected by filtration under nitrogen The resulting powder 92 (0370 g 95 ) was dried under vacuum providing a yellow solid 1H-NMR (500 MHz C6D6) δ = 751 (d J = 75 Hz 4 H) 717 (t J = 75 Hz 4 H) 702 (t J = 75 Hz 2 H) 101 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1406 1287 1279 196 (d JC-P = 188 Hz) ppm 31P-NMR (162 MHz C6D6) δ = ndash1282 (br s) ppm Adducts of 3-hexyne to angular [3]phenylene 22 ndash compounds 104 and 105

In a glovebox 22 (0014 mg 0060 mmol) 3-hexyne 103 (57 microL 0004 g 0050 mmol) Ni(COD)(PMe3)2 (0002 g 0005 mmol) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 14 h Flash chromatography on silica gel gave a first fraction that was recrystallized from CH2Cl2 to provide pure 104 (70 mg 45 ) as a yellow solid mp 169ndash170 degC 1H-NMR (500 MHz CDCl3) δ = 843 (d J = 70 Hz 1 H) 821 (d J = 75 Hz 1 H) 795 (d J = 70 Hz 1 H) 752 (dt J = 10 70 Hz 1 H) 748 (dt J = 10 70 Hz 1 H) 697 (d J = 75 Hz 1 H) 673ndash662 (m 3 H) 655 (d J = 55 Hz 1 H) 307 (q J = 75 Hz 2 H) 299 (q J = 75 Hz 2 H) 133 (t J = 75 Hz 3 H) 130 (t J = 75 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1530 1516 1504 1471 1360 1330 13129 13127 1307 1282 1279 1267 1263 1259 1246 1239 1228 1179 1159 1156 232 214 164 149 ppm IR (KBr) ν~ = 3045 2960 1600 1481 1414 1261 1197 1159 758 740 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (463) 299 (sh) 309 (460) 320 (462) 331 (452) 380 (356) 399 (374) 419 (371) nm MS (70 eV) mz () 309 [M++1] (26) 308 [M+] (100) 293 [M+ndash15] (8) 278 [M+ndash30] (21) HRMS (EI) calcd for C24H20 3081565 found 3081666

- 165 -

A second fraction was 105 (0002 g 11 ) isolated as a yellow solid mp 120ndash122 degC 1H-NMR (400 MHz CDCl3) δ = 830 (d J = 72 Hz 1 H) 797 (d J = 76 Hz 1 H) 761 (d J = 80 Hz 1 H) 761ndash749 (m 2 H) 700 (d J = 80 Hz 1 H) 699 (d J = 72 Hz 1 H) 674 (quint J = 76 Hz 2 H) 658 (d J = 64 Hz 1 H) 307 (q J = 76 Hz 2 H) 302 (q J = 76 Hz 2 H) 132 (t J = 76 Hz 3 H) 131 (t J = 76 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1525 1519 1489 1472 1356 1345 1324 1318 1288 1283 1279 1273 1259 1252 1251 1250 1241 1179 1165 1160 2213 2205 149 146 ppm IR (KBr) ν~ = 3063 2958 2925 1490 1442 1417 1262 1147 1099 822 762 730 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 281 (434) 291 (448) 303 (460) 313 (sh) 369 (346) 389 (373) 410 (377) nm MS (70 eV) mz () 309 [M++1] (28) 308 [M+] (100) 293 [M+ndash15] (13) 278 [M+ndash30] (21) 226 (22) 149 (29) HRMS (EI) calcd for C24H20 3081565 found 3081664 Adducts of 14-dimethoxy-2-butyne to angular [3]phenylene 22 ndash compounds 107 and 108

In a glovebox 22 (0011 g 0050 mmol) 14-dimethoxybut-2-yne 106 (0034 g 030 mmol) Ni(COD)(PMe3)2 (63 microL of a 008 M solution in THF) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 165 h The 1H-NMR spectrum of the crude indicated the formation of 107 and 108 in the ratio of 61 Flash chromatography on silica gel gave first 107 (0012 g 68 ) as a yellow solid mp 150ndash151 degC 1H-NMR (400 MHz CDCl3) δ = 841 (dd J = 32 64 Hz 1 H) 819 (d J = 80 Hz 1 H) 810 (dd J = 36 64 Hz 1 H) 754 (dd J = 36 64 Hz 2 H) 700 (d J = 80 Hz 1 H) 676 (t J = 64 Hz 1 H) 674ndash665 (m 2 H) 656 (d J = 60 Hz 1 H) 493 (s 2 H) 488 (s 2 H) 353 (s 3 H) 345 (s 3 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1527 1513 1509 1484 1336 1318 1316 1309 1296 1283 1282 1272 1270 1259 1255 1238 1225 1183 1166 1161 677 675 584 575 ppm IR (KBr) ν~ = 3072 2927 1485 1446 1417 1376 1185 1097 956 898 821 743 730 cmndash1 MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (100) 308 [M+ndash38] (26) 293 (34) 280 (15) 265 (44) HRMS (EI) calcd for C24H20O2 3401463 found 3401466 Further elution provided 108 (0002 g 9 ) as a yellow solid mp 156ndash157 degC 1H-NMR (400 MHz CDCl3) δ = 831ndash824 (m 1 H) 813ndash806 (m 1 H) 775 (d J = 80 Hz 1 H) 763ndash756 (m 2 H) 702 (d J = 80 Hz 1 H) 699 (d J = 64 Hz 1 H) 681ndash670 (m 2 H) 660 (d J = 64 Hz 1 H) 493 (s 2 H) 487 (s 2 H) 353 (s 3 H) 351 (s 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1523 1517 1505 1470 1327 1322

- 166 -

1316 1315 1297 1285 1282 1276 1268 1266 12564 12555 1252 1181 1168 1165 6804 6801 5838 5835 ppm IR (KBr) ν~ = 2925 1498 1415 1379 1262 1187 1095 1061 940 930 814 750 734 717 cmndash1 UV-Vis (CH3CN) λmax (log ε) 237 (458) 287 (462) 298 (472) 314 (sh) 371 (357) 387 (380) 407 (386) nm MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (56) 308 [M+ndashMeOH] (8) 293 (27) 279 (17) 265 (24) HRMS (EI) calcd for C24H20O2 3401463 found 3401456 Optimized cycloaddition reaction between 22 and 88 In a glovebox a round bottom flask was charged with 22 (0058 g 0257 mmol) and Ni(COD)(PMe3)2 (0008 g 0034 mmol) Both reagents were then dissolved in THF (100 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0093 g 0521 mmol) in THF (20 mL) was taken up in a gas-tight syringe and slowly added over 13 h via syringe pump to the boiling mixture of 22Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 6 h After this time mixture was cooled to RT and the solvent removed by rotary evaporation to give a yellow residue The crude product was passed through a plug of silica gel eluting with a mixture of hexanesCH2Cl2 (101) to afford a yellow solid Analysis of the product by 1H-NMR (using the solvent peak of CDCl3 as the internal standard) revealed the presence of 89 and 90 in a 1387 ratio Adducts of diphenylacetylene 88 to angular [4]phenylene 17 ndash compounds 130ndash134 In a glovebox angular [4]phenylene 17 (0036 g 012 mmol) diphenylacetylene 88 (0018 g 010 mmol) and Ni(COD)(PMe3)2 (125 microL of a 008 M solution in THF) were added to an Ace pressure tube and dissolved in THF (6 mL) The reaction vessel was sealed removed from the glovebox and stirred at 75 degC for 5 h Flash chromatography

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph Ph PhPh Ph

132131

133 134

130

- 167 -

on silica gel gave starting material (0013 g of 17) as well as a yellow residue Further purification of the latter by preparative TLC afforded (in order of elution) 132 131 133 134 and 139 Compound 130 (0008 g 28 ) was obtained as a white solid mp 360ndash363 degC (decomp) the phenyl groups located on the central benzene ring of 130 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 904 (d J = 90 Hz 2 H) 895 (d J = 90 Hz 2 H) 881 (d J = 85 Hz 2 H) 765 (ddd J = 15 65 80 Hz 2 H) 742ndash736 (m 4 H) 734 (dd J = 10 85 Hz 2 H) 721 (tt J = 15 75 Hz 2 H) 716 (d J = 75 Hz 2 H) 698 (dd J = 05 80 Hz 2 H) 693 (tt J = 10 85 Hz 2 H) 681 (tt J = 10 70 Hz 2 H) 676 (t J = 75 Hz 4 H) 656 (t J = 70 Hz 4 H) 633 (d J = 70 Hz 4 H) 614 (d J = 75 Hz 2 H) 595 (d J = 70 Hz 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 14058 14057 1403 1394 1375 1374 1345 1341 1336 1327 1324 1309 1308 1301 1294 1292 1282 1276 1268 1263 12622 12619 1259 1257 1254 1250 1227 1214 1212 ppm IR (KBr) ν~ = 3052 2923 1600 1491 1440 1261 1076 1029 809 783 759 747 700 631 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 248 (498) 306 (sh) 329 (520) 388 (463) nm MS(FAB) mz () 836 [M++2] (18) 835 [M++1] (42) 834 [M+] (54) 757 (8) HRMS (FAB) calcd for C66H42 8343287 found 8343280 Compound 131 (0003g 6) was isolated as yellow solid mp 251ndash253 degC (decomp) 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 775 (dt J = 10 80 Hz 1 H) 752 (dt J = 10 80 Hz 1 H) 746 (d J = 80 Hz 1 H) 737 (d J = 65 Hz 1 H) 726ndash721 (m 5 H) 721ndash716 (m 2 H) 716ndash711 (m 5 H) 709 (t J = 75 Hz 1 H) 705 (d J = 80 Hz 1 H) 699 (d J = 70 Hz 1 H) 619 (d J = 60 Hz 1 H) 614 (d J = 60 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1502 1492 1491 1490 1485 1444 1394 1392 1382 1371 1367 1351 13271 13268 13092 13088 1299 12898 12896 1283 12764 12760 1274 12654 12652 1261 1253 1245 1195 1184 1172 1138 1129 ppm one peak is presumed to be accidentally isochronous in the region between δ = 130ndash124 ppm IR (KBr) ν~ = 3023 2921 1602 1478 1371 1262 1026 809 795 748 725 695 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 252 (473) 285 (456) 320 (453) 335 (462) 353 (437) 370 (432) 410 (376) 431 (372) nm MS (FAB) mz () 479 [M++1] (27) 478 [M+] (70) 300 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781718 Molecule 132 (0002 g 5 ) was acquired as a yellow solid 1H-NMR (500 MHz CDCl3) δ = 726ndash721 (m 2 H) 716ndash709 (m 6 H) 695ndash690 (m 2 H) 676 (d J = 80 Hz 2 H) 673 (d J = 75 Hz 2 H) 671 (t J = 75 Hz 2 H) 665 (t J = 70 Hz 2 H) 658 (d J = 65 Hz 2 H) 648 (d J = 65 Hz 2 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1516 1510 1497 1490 1391 1372 1310 1303 1283 1281 1277 1275 1273 1264 1216 1168 1163 ppm UV-Vis (CH2Cl2) λmax (log ε) 254 (476) 294 (sh) 300 (465) 322 (sh) 338 (392) 376 (400) nm MS (FAB) mz () 479 [M++1] (50) 478 [M+] (86) 391 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781723 Adduct 133 (0017 g 33 ) was isolated as a red crystalline solid mp 290ndash291 degC 1H-NMR (500 MHz CDCl3) δ = 800 (d J = 80 Hz 2 H) 720ndash713 (m 6 H) 708ndash702 (m 4 H) 690 (d J = 80 Hz 2 H) 648 (t J = 70 Hz 2 H) 642 (d J = 70 Hz 2 H) 623 (t J = 70 Hz 2 H) 393 (d J = 70 Hz 2 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1522 1509 1506 1496 1392 1359 1315 1309 1282 1278 1277 1266 1250 1232 1181 1166 1157 ppm IR (KBr) ν~ = 3057 1489 1441 1412 1273

- 168 -

1161 810 738 709 690 623 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 271 (474) 285 (469) 345 (460) 353 (454) 414 (483) 432 (381) 460 (363) nm MS (70 eV) mz () 479 [M++1] (46) 478 [M+] (100) 400 (10) HRMS (EI) calcd for C38H22 4781722 found 4781719 Compound 134 (0009 g 27 ) was obtained as a yellow solid mp 178ndash180 degC the phenyl groups of this molecule located at the bay regions of the phenanthrene subunit are static while the others exhibit hindered rotation on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 880 (d J = 88 Hz 1 H) 879 (d J = 88 Hz 1 H) 863 (d J = 92 Hz 1 H) 834 (d J = 80 Hz 1 H) 770ndash758 (m 1 H) 748ndash732 (m 4 H) 727ndash721 (m 2 H) 721ndash710 (m 2 H) 706 (d J = 80 Hz 1 H) 702ndash691 (m 3 H) 684 (t J = 74 Hz 1 H) 673 (br s 2 H) 655 (t J = 76 Hz 2 H) 650ndash638 (m 3 H) 630ndash610 (m 4 H) 590 (d J = 76 Hz 2 H) 410 (d J = 68 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1527 1510 1509 1494 1403 1400 1399 1396 1373 1371 1339 1335 1330 1325 1324 1317 1309 1306 1305 1304 1299 1295 1291 1283 1282 1281 1277 1275 1272 1269 1268 12632 12627 1261 12562 12556 1254 1253 1239 1226 1216 1209 1180 1162 1154 ppm three peaks are presumed to be accidentally isochronous in the region δ = 128ndash125 ppm IR (KBr) ν~ = 2964 1262 1096 1022 801 701 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 267 (501) 303 (497) 335 (489) 361 (sh) 379 (464) 427 (402) 456 (377) nm MS(FAB) mz () 658 [M++2] (22) 657 [M++2] (67) 656 [M+] 1(00) 579 (12) 502 (7) HRMS (FAB) calcd for C52H32 6562504 found 6562492 Cycloaddition reaction between [7]heliphene 142 and diphenylacetylene 88 In a glovebox a round bottom flask was charged with 142 (0008 g 0152 mmol) and Ni(COD)(PMe3)2 (0001 g 0003 mmol) The mixture was then dissolved in THF (25 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0016 g 300 mmol) in THF (10 mL) was taken up in a gas-tight syringe and slowly added over 12 h via syringe pump to the boiling mixture of 142Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 12 h After this time it was cooled to RT and the solvent removed by rotary evaporation to give an orange residue The crude product was chromatographed on silica gel (25 x 165 cm) eluting first with hexaneCH2Cl2 (101 then 51) The first product collected was diphenylacetylene 88 (0005 g) followed by a yellow band Analysis of the isolated yellow solid (0002 g) revealed a large mixture of products MS(FAB) mz () 532 (70) 664 (25) 700 (13) 732 (16) 911 (21) 1056 (11) 1234 (4) 1412 (5) 46 Computational Details for Chapter Three All geometries of intermediates and transition states were optimized fully without symmetry constraints using the Gaussian 03 program100 The DFT computations were carried out using the B3LYP functional as implemented in Gaussian The nickel atom was described by a double-zeta basis set (LANL2DZ)113 and the 6-31G(d) basis set114

- 169 -

was used for the other elements Frequency calculations were performed to confirm the nature of the stationary points and to obtain zero-point energies (ZPE) The connectivity between stationary points was established by intrinsic reaction coordinate calculations (IRC) The Chemcraft program102 was used to draw the calculated structures

47 References

1) Harvey R G Polycyclic Aromatic Hydrocarbons Wiley-VCH New York 1997 2) (a) Chem Rev 2001 101 1115ndash1566 Special Issue Aromaticity (b) Chem Rev

2005 105 3343ndash3397 Special Issue Delocalization-Pi and Sigma 3) (a) Cyranski M K Krygowski T M Katritzky A R Schleyer P von R J Org

Chem 2002 67 1333 (b) Stanger A Chem Commun 2009 1939 4) (a) Minkin V I Glukhovtsev M N Simkin B Ya Aromaticity and Antiaromaticity

Electronic and Structural Aspects Wiley New York 1994 pp 63ndash74 (b) Garratt P J Aromaticity Wiley New York 1986 pp 30ndash34 93ndash95

5) (a) Wu J Muumlllen K In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 3 pp 90ndash139 (b) Wu J Pisula W Muumlllen K Chem Rev 2007 107 718 (c) Handbook of Organic Electronics and Photonics Nalwa H S Ed American Scientific 2008

6) Miljanić O Š Vollhardt K P C In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 4 pp 140ndash197

7) (a) Shepherd M K Cyclobutarenes The Chemistry of Benzocyclobutene Biphenylene and Related Compounds Elsevier Amsterdam 1991 (b) Toda F Garratt P J Chem Rev 1992 92 1685

8) (a) Diercks R Vollhardt K P C J Am Chem Soc 1986 108 3150 (b) Mohler D L Vollhardt K P C Wolff S Angew Chem Int Ed Engl 1990 29 1151 (c) Mohler D L Vollhardt K P C Wolff S Angew Chem Int Ed Engl 1995 34 563

9) (a) Holmes D Kumaraswamy S Matzger A J Vollhardt K P C Chem Eur J 1999 5 3399 (b) Dosche C Kumke M U Ariese F Bader A N Gooijer C Dosa P I Han S Miljanic O Š Vollhardt K P C Puchta R van Eikema Hommes N J R Phys Chem Chem Phys 2003 5 4563 (c) Wagner H-U Szeimies G Chandrasekhar J Schleyer P von R Pople J A Binkley J S J Am Chem Soc 1978 100 1210

10) Han S Bond A D Disch R L Holmes D Schulman J M Teat S J Vollhardt K P C Whitener G D Angew Chem Int Ed 2002 41 3223

11) Jackman L M Sondheimer F Amiel Y Ben-Efraim D A Gaoni Y Wolovsky R Bothner-By A A J Am Chem Soc 1962 84 4307

12) Untch K G Wysocki D C J Am Chem Soc 1967 89 6386 13) (a) Chen Z Wannere S C Corminboeuf C Puchta R Schleyer P von R

Chem Rev 2005 105 3842 and the references therein (b) Steinmann S N Jana D F Wu J I-C Schleyer P v R Mo Y Corminboeuf C Angew Chem Int Ed 2009 48 9828

14) Schleyer P v R Manoharan M Wang Z-X Kiran B Jiao H Puchta R van Eikema Hommes N J R Org Lett 2001 3 2465

- 170 -

15) Schulman J M Disch R L Jiao H Schleyer P v R J Phys Chem A 1998 102 8051

16) Jeany H Mason K G Sketchley J M Tetrahedron Lett 1970 11 485 17) Brown F C Choi N Coulston K J Eastwood F W Wiersum U E

Jenneskens L W Tetrahedron Lett 1994 35 4405 18) (a) Linear [3]phenylene Dosa P I Schleifenbaum A Vollhardt K P C Org Lett

2001 3 1017 (b) Angular [3]phenylene Matzger A J Vollhardt K P C Chem Commun 1997 1415 (c) Angular [4]phenylene Dosa P I Gu Z Hager D Karney W L Vollhardt K P C Chem Commun 2009 1967

19) Perthuisot C Edelbach B L Zubris D L Simhai N Iverson C N Muumlller C Satoh T Jones W D J Mol Catal A 2002 189 157

20) Dosche C Loumlhmannsroumlben H-G Bieser A Dosa P I Han S Iwamoto M Schleifenbaum A Vollhardt K P C Phys Chem Chem Phys 2002 4 2156

21) (a) Deniz A A Peters K S Snyder G J Science 1999 286 1119 (b) Fattahi A Lis L Tian Z Kass P S Angew Chem Int Ed 2006 45 4984 (c) Bally T Angew Chem Int Ed 2006 45 6616

22) Anslyn E Dougherty D Modern Physical Organic Chemistry University Science Books Palo Alto 2006

23) Crabtree R H The Organometallic Chemistry of the Transition Metals 4th Ed Wiley-VCH New York 2005

24) Mestdagh H Postdoctoral Research Report University of California Berkeley 1986

25) Hirthammer M Vollhardt K P C J Am Chem Soc 1986 108 2481 26) Blanco L Helson H E Hirthammer M Mestdagh H Spyroudis S Vollhardt K

P C Angew Chem Int Ed Engl 1987 26 1246 27) Berris B C Hovakeemian G H Lai Y-H Mestdagh H Vollhardt K P C J

Am Chem Soc 1985 107 5670 28) Dosa P I The Chemistry of Angular and Linear [N]Phenylenes PhD Thesis

University of California Berkeley 2002 29) Diercks R Eaton B E Guumlrtzgen S Jalisatgi S Matzger A J Radde R H

Vollhardt K P C J Am Chem Soc 1998 120 8247 30) (a) Nambu M Siegel J S J Am Chem Soc 1988 110 3675 (b) Nambu M

Hardcastle K Baldridge K K Siegel J S J Am Chem Soc 1992 114 369 31) Nambu M Mohler D L Hardcastle K Baldridge K K Siegel J S J Am

Chem Soc 1993 115 6138 32) Kumaraswamy S Jalisatgi S S Matzger A J Miljanić O Š Vollhardt K P C

Angew Chem Int Ed 2004 43 3711 33) (a) Eisch J J Piotrowski A M Han K I Kruumlger C Tsay Y H Organometallics

1985 4 224 (b) Schwager H Spyroudis S Vollhardt K P C J Organometallic Chem 1990 382 191

34) Albright T A Hofmann P Hoffmann R Lillya C P Dobosh P A J Am Chem Soc 1983 105 3397

35) Doumltz K H Jahr H C Chem Rec 2005 4 61 36) Gridnev I D Coord Chem Rev 2008 252 1798 37) Eickmeier C Holmes D Junga H Matzger A J Scherhag F Shim M

Vollhardt K P C Angew Chem Int Ed Engl 1999 38 800

- 171 -

38) Groszligmann T N Haptotropism in Linear Phenylene Complexes Diplomarbeit Thesis University of California Berkeley 2004

39) Dinculear photothermal haptotropic systems Tsuchiya K Ideta K Mogi K Sunada Y Nagashima H Dalton Trans 2008 2708 and the references therein

40) Additive assisted photothermal haptotropic systems (a) Jahr H C Nieger M Doumltz H K Chem Eur J 2005 11 5333 d) Herbert D E Tanabe M Bourke S C Lough A J Manners I J Am Chem Soc 2008 130 4166 e) Ieong N S Manners I J Organomet Chem 2008 693 802 and references therein

41) (a) Zhu G Tanski T M Churchill D G Janak K E G Parkin G J Am Chem Soc 2002 124 13658 (b) Zhu G Pang G Parkin G J Am Chem Soc 2008 130 1564

42) Selected reviews of photobased devices and molecular switches (a) Balzani V Credi A Venturi M Chem Soc Rev 2009 38 1542 (b) Kay E R Leigh D A Zerbetto F Angew Chem Int Ed 2007 46 72 (c) Photochromism Molecules and Systems Duumlrr H Bouas-Laurent H Eds Elsevier Amsterdam 2003 (d) Feringa B Molecular Switches Wiley-VCH Weinheim 2001

43) (a) a) Photofunctional Transition Metal Complexes Yam V W W Ed Springer Berlin 2007 b) Coppens P Novozhilova I Kovalevsky A Chem Rev 2002 102 861 c) Guumltlich P Garcia Y Woike T Coord Chem Rev 2001 219ndash221 839

44) (a) Lambert J B Mazozola E P Nuclear Magnetic Resonance Spectroscopy An Introduction to Princples Applications and Experimental Methods Pearson Education Upper Saddle River 2004 (b) Berger S Braun S 200 and More NMR Experiments A Practical Course Wiley-VCH Weinheim 2004 (c) Friebolin H Basic One- and Two-Dimensional NMR Spectroscopy 4th edition Wiley-VCH Weinheim 2005

45) (a) Schulman J M Disch R L J Phys Chem A 2003 107 5223 (b) Schulman J M Disch R L J Am Chem Soc 1996 118 8470 and the references cited therein

46) (a) Bursten B E Fenske R F Inorg Chem 1979 18 1760 (b) Chinn J W Jr Hall M B Inorg Chem 1983 22 2759 (c) Datta A Pati S K J Am Chem Soc 2005 127 3496

47) Ooloba K Haptotropic Shifts in the Linear [N]-Phenylene (N=3 4 and 5) and Angular [3]-Phenylene Cyclopentadienylcobalt Complexes PhD Thesis University of Houston 2008

48) Hillard III R L Vollhardt K P C J Am Chem Soc 1977 99 4058 49) Berris B C Lai Y-H Vollhardt K P C J Chem Soc Chem Commun 1982

953 50) (a) Rausch M D Genetti R A J Org Chem 1970 35 3888 (b) Hart W P

Rausch D M J Organometallic Chem 1988 355 455 51) Duclos R I Vollhardt K P C Yee J L S J Organomet Chem 1979 174 109 52) (a) Myers A G Sogi M Lewis M A Arvedson S P J Org Chem 2004 69

2516 (b) Wolfart V Ramming M Gleiter R Nuber B Pritzkow H Rominger F Eur J Inorg Chem 1999 499 (c) Mitchell R H Chen Y Khalifa N Zhou P J Am Chem Soc 1998 120 1785 (d) McGlinchey M J Burns R C Hofer R Top S Jaouen G Organometallics 1986 5 104

53) Feixas F Jimeacutenez-Halla J O C Matito E Poater J Solagrave M Pol J Chem

- 172 -

2007 81 783 54) (a)Stanger A J Org Chem 2006 71 883 (b) Stanger A Chem Eur J 2006 12

2745 (c) Tsipis A C Phys Chem Chem Phys 2009 11 8244 (d) Stanger A Chem Commun 2009 1939

55) For very recent literature compilations of theoretical (and experimental) treatments of haptotropism in arene metal complexes see a) Joistgen O Pfletschinger A Ciupka J Dolg M Nieger M Schnakenburg G Froumlhlich R Kataeva O Doumltz K H Organometallics 2009 28 3473 b) Pfletschinger A Dolg N J Organomet Chem 2009 694 3338 c) Jimeacutenez-Halla J O C Robles J Solagrave M Organometallics 2008 27 5230 d) Kirillov E Kahlal S Roisnel T Georgelin T Saillard J-Y Carpentier J-F Organometallics 2008 27 387 and references therein

56) Jimeacutenez-Halla J O C Robles J Solagrave M J Phys Chem A 2008 112 1202 57) Oprunenko Y Gloriozov I Lyssenko K Malyugina S Mityuk D Mstislavsky

V Guumlnther H von Firks G Ebener M J Organomet Chem 2002 656 27 58) Muumlller J Gaede P E Qiao K J Organomet Chem 1994 480 213 59) Bianchini C Caulton K G Chardon C Doublet M L Eisenstein O Jackson

S A Johnson T J Meli A Peruzzini M Streib W E Vacca A Vizzat F Organometallics 1994 13 2010

60) (a) De Boer E Van Willigen H V Prog Nuc Mag Res Spec 1967 2 111 (b) Memory J D Wilson N K NMR of Aromatic Compounds Wiley-VCH New York 1982

61) (a) Poli R Chem Rev 1996 96 2135 and the references cited therein (b) Schroumlder D Shaik S Schwartz H Acc Chem Res 2000 33 139 (c) Harvey J N Poli R Smith K M Coord Chem Rev 2003 237 347 and the references cited therein

62) For computational examples of 16 electron triplet Cp cobalt species influencing cobalt-mediated reactions see (a) Siegbahn P E M J Am Chem Soc 1996 118 1487 (b) Poli R Smith K M Eur J Inorg Chem 1999 877 (c) Carreoacuten-Macedo J-L Harvey J N J Am Chem Soc 2004 126 5789 (d) Petit A Richard P Cacelli I Poli R Chem Eur J 2006 12 813 (e) Aubert C Betschmann P Eichberg M J Gandon V Geny A Heckrodt T J Lehmann J Malacria M Masjost B Paredes E Vollhardt K P C Whitener G D Chem Eur J 2007 13 7443 (f) Gandon V Agenet N Vollhardt K P C Malacria M Aubert C J Am Chem Soc 2009 131 3007

63) Illustrative examples (a) Olson W L Stacy A M Dahl L F J Am Chem Soc 1986 108 7646 (b) Wadepohl H Galm W Pritzkow H Wolf A Chem Eur J 1996 2 1453 (c) Knijnenburg W Hetterscheid D Kooistra T M Budzelaar P H M Eur J Inorg Chem 2004 1204

64) Benito-Garagorri D Bernskoetter W H Lobkovsky E Chirik P J Organometallics 2009 28 4807

65) Fox J P Ramdhanie B Zareba A A Czernuszewicz R S Goldberg D P Inorg Chem 2004 43 6600

66) Guennic B L Floyd T Galan B R Autschbach J Keister J B Inorg Chem 2009 48 5504

67) Cremer C Burger P J Am Chem Soc 2003 125 7664

- 173 -

68) Atkins P de Paula J P Physical Chemistry 8th Edition Oxford University Press Oxford 2006

69) Butters T Toda F Winters W Angew Chem Int Ed Engl 1980 19 926 70) Mann B E Taylor B F 13C Data for Organometallic Compounds Academic

London 1981 71) For a review on triple decker arene complexes and closely related syn dinuclear

systems see (a) Beck V OlsquoHare D J Organomet Chem 2004 698 3920 and the references therein For a review of trinuclear CpCo(arene) complexes see (b) Wadepohl H Angew Chem Int Ed Engl 1992 31 247 and the references therein

72) Jonas K Koepe G Schieferstein L Mynott R Kruumlger C Tsay Y-H Angew Chem Int Ed Engl 1983 22 620 Angew Chem Suppl 1983 920

73) Muumlller J Gaede P E Qiao K Angew Chem Int Ed Engl 1993 32 1697 74) Schneider J J Wolf D Janiak C Heinemann O Rust J Kruumlger C Chem

Eur J 1998 4 1982 75) Schneider J J Denninger U Heinemann O Kruumlger C Angew Chem Int Ed

Engl 1995 34 592 76) Budzelaar P H M Moonen N N P de Gelder R Smits J M M Gal A W

Chem Eur J 2000 6 2740 77) Albright T A Dosa P I Groszligmann T N Oluwakemi O Padilla R Paubelle

R Timofeeva T Vollhardt K P C Angew Chem Int Ed 2009 48 9853 78) Schaub T Radius U Chem Eur J 2005 11 5024 79) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4660 80) (a) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4040

(b) Muumlller C Lachicotte R J Jones W D Organometallics 2002 21 1975 81) Martin R H Angew Chem Int Ed Engl 1974 13 649 82) Mallory FB Butler K E Evans AC Mallory CW Tetrahedron Lett 1996 37

7176 83) Selected Reviews (a) Amemiya R Yamaguchi M Chem Rec 2008 8 116 (b)

Ruliacutešek L Exner O Cwiklik L Jungwirth P Staryacute I Pospiacutešil L Havlas Z J Phys Chem C 2007 111 14948 (c) Hopf H Classics in Hydrocarbon Chemistry Wiley-VCH Weinheim 2000 pp 321ndash330 (d) Voumlgtle F Fascinating Molecules in Organic Chemistry Wiley New York 1992 pp 156ndash180 (e) Meurer K P F Voumlgtle Top Curr Chem 1985 127 1 (f) Laarhoven W H Prinsen W J Top Curr Chem 1984 125 63

84) (a) Mallory FB Butler K E Mallory CW Beacuterubeacute A Luzik E D Brondyke E J Hiremath R Ngo P Carroll P J Tetrahedron 2001 57 3715 (b) Mallory F B Butler K E Evans A C Brondyke E J Mallory C W Yang C Ellenstein A J Am Chem Soc 1997 119 2119

85) (a) Mitsuhashi R Suzuki Y Yamanari Y Mitamura H Kambe T Ikeda N Okamoto H Fujiwara A Yamaji M Kawasaki N Maniwa Y Kubozono Y Nature 2010 464 74 (b) Okamoto H Kawasaki N Kaji Y Kubozono Y Fujiwara A Yamaji M J Am Chem Soc 2008 130 10470 (c) Tian Y H Park G Kertesz M Chem Mater 2008 20 3266

86) Recent reviews of acenes in electronic applications (a)Yamashita Y Sci Technol Adv Mater 2009 10 024313 (b) Wuumlrthner F Schmidt R ChemPhysChem

- 174 -

2006 7 793 (c) Bendikov M Wudl F Chem Rev 2004 104 4891 87) NICS-based comparison of phenacene and acene properties Portella G Poater

P Bofill J M Alemany P Solagrave M J Org Chem 2005 70 2509 and the references therein

88) Mallory F B Mallory C W Org React 1984 30 1 89) Gu Z Nickel-Catalyzed Cycloaddition Reaction of [N]Phenylenes and Alkynes

Postdoctoral Report University of California Berkeley 2008 90) Preferential displacement of COD by π ligands from Ni(COD)(PMe3)2 is well

documented See eg Karsch H H Leithe A W Reisky M Witt E Organometallics 1999 18 90

91) (a) Bochmann M Hawkins I Hursthouse M B Short R L J Chem Soc Dalton Trans 1990 1213 (b) Poerschke K R Mynott R Angermund K Kruumlger C Z Naturforsch 1990 40B 199 See also (c) Bartik T Happ B Iglewsky M Bandmann H Boese R Heimbach P Hoffmann T Wenschuh E Organometallics 1992 11 1235

92) For Ni-phosphine migrations along polycyclic benzenoid ligands see eg Stanger A Vollhardt K P C Organometallics 1992 11 317

93) Edelbach B L Vicic D A Lachicotte R J Jones W D Organometallics 1998 17 4784

94) (a) Feiken N Pregosin P S Trabesinger G Scalone M Organometallics 1997 16 537 (b) Feiken N Pregosin P S Trabesinger G Albinati A Evoli G L Organometallics 1997 16 5756 (c) Geldbach T J Pregosin P S Eur J Inorg Chem 2002 1907

95) Cheng T-Y Szalda D J Hanson J C Muckerman J T Bullock R M Organometallics 2008 27 3785

96) (a) Grimme S Harren J Sobanski A Voumlgtle F Eur J Org Chem 1998 8 1491 (b) Dias J J Chem Inf Model 2005 45 562

97) Still W C Mitra A Kahn M J Org Chem 1978 43 2923 98) (a) Leonard J Lygo B Procter G Advanced Practical Organic Chemistry 2nd

ed CRC Press Boca Raton 1998 (b) Errington R J Advanced Practical Inorganic Chemistry and Metalorganic Chemistry Chapman and Hill London 1997

99) Jonas K Deffense E Habermann D Angew Chem Int Ed Engl 1983 22 716 100) Gaussian 03 Revision B03 M J Frisch G W Trucks H B Schlegel G E

Scuseria M A Robb J R Cheeseman J A Montgomery Jr T Vreven K N Kudin J C Burant J M Millam S S Iyengar J Tomasi V Barone B Mennucci M Cossi G Scalmani N Rega G A Petersson H Nakatsuji M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida T Nakajima Y Honda O Kitao H Nakai M Klene X Li J E Knox H P Hratchian J B Cross C Adamo J Jaramillo R Gomperts R E Stratmann O Yazyev A J Austin R Cammi C Pomelli J W Ochterski P Y Ayala K Morokuma G A Voth P Salvador J J Dannenberg V G Zakrzewski S Dapprich A D Daniels M C Strain O Farkas D K Malick A D Rabuck K Raghavachari J B Foresman J V Ortiz Q Cui A G Baboul S Clifford J Cioslowski B B Stefanov G Liu A Liashenko P Piskorz I Komaromi R L Martin D J Fox T Keith M A Al-Laham C Y Peng A Nanayakkara M Challacombe P M W Gill B Johnson W Chen M W Wong C Gonzalez J A Pople Gaussian Inc Pittsburgh PA

- 175 -

2003 101) wwwgaussiancom 102) wwwchemcraftprogcom 103) Becke A D J Chem Phys 1993 98 5648 104) Lee C Yang W Parr G R Phys Rev B 1988 37 785 105) Binkley J S Pople J A Hehre W J J Am Chem Soc 1980 102 939 for

hydrogen and Gordon M S Binkley J S Pople J A Pietro W J Hehre W J J Am Chem Soc 1983 104 2797

106) Hay P J Wadt W R J Chem Phys 1985 82 270 107) Hehre W J Ditchfield R Pople J A J Chem Phys B 1972 56 2257 108) Curtiss L A McGrath M P Blaudeau J-P Davis N E Binning R C Jr

Radom L J Chem Phys 1995 103 6104 109) A W Ehlers M Boumlhme S Dapprich A Gobbi A Houmlllwarth V Jonas K F

Koumlhler R Stegmann A Veldkamp G Frenking Chem Phys Lett 1993 208 111

110) QST is a synchronous transit approach to the quadratic region around the transition state structure For details see (a) J B Foresman A Frisch in Exploring Chemistry with Electronic Structure Methods A Guide to Using Gaussian Gaussian Inc Pittsburgh PA USA 1996 (b) H B Schlegel in Ab Initio Methods in Quantum Chemistry Part I Wiley Chichester 1987

111) Gu Z The Improvement of Total Synthesis of Angular [4]Phenylene and Its Flash Vacuum Pyrolysis (FVP) Study Postdoctoral Report University of California Berkeley 2008

112) Schwager H Postdoctoral Research Report University of California Berkeley 1987

113) Kuumlchle W Dolg M Stoll H Preuss H Mol Phys 1991 74 1245 114) (a) Hariharan P C Pople J A Theor Chim Acta 1973 28 213 (b) Francl M

M Petro W J Hehre W J Binkley J S Gordon M S DeFrees D J Pople J A J Chem Phys 1982 77 3654 (c) Rassolov V Pople J A Ratner M Windus T L J Chem Phys 1998 109 1223

Cobalt and Nickel-Based Organometallic Chemistry of the [N]Phenylenes

copy 2010

by Robin Padilla

- 1 -

Abstract

Cobalt and Nickel-Based Organometallic Chemistry of the [N]Phenylenes

by

Robin Padilla

Doctor of Philosophy in Chemistry

University of California Berkeley

Professor K Peter C Vollhardt Chair

This dissertation explores the synthesis and study of linear [N]phenylene cobalt complexes and the reactions of angular [N]phenylenes with nickel catalysts Chapter 1 contains a general introduction to the properties of the [N]phenylenes as well as a brief overview of earlier organometallic [N]phenylene chemistry with an emphasis on work directly related to that presented in the subsequent chapters Chapter 2 presents studies regarding first ever examples of photo-induced thermally reversible haptotropic shifts in linear [3]phenylene cyclopentadienyl cobalt (CpCo) complexes In these reactions the CpCo fragment migrates from one cyclobutadiene ring to another upon exposure to UV irradiation Heating the photoisomer complexes causes the metal fragment to return to its original position Aside from the novelty of an η4η4 cyclobutadiene migration the photo-induced thermally reversible nature of these systems makes them attractive as candidates for photostorage devices andor molecular switches The syntheses and structural studies of the linear phenylene(CpCo) complexes are discussed In addition to the experimental work computational studies on the haptotropic shift are also included Closely related work such as the observation of an intermediate haptotropic species at low temperature and the preparation of a linear [3]phenylene complex containing two CpCo units bound to the ligand is also discussed Chapter 3 describes nickel-catalyzed insertion reactions with angular phenylenes as a method for preparing derivatives of [N]phenacenes a class of polycyclic aromatic hydrocarbons that are of interest in organic electronic applications Previous work regarding nickel insertion reactions with biphenylene is mentioned Nickel-catalyzed insertion reactions with angular [3]- and [4]phenylene are then described Mechanistic studies both experimental and computational are discussed The results from these studies were used to optimize the reaction to produce [N]phenacenes as the major products of these insertion reactions Chapter 4 contains experimental details relating to chapters two and three General experimental considerations synthetic procedures crystallographic and computation data are presented Relevant references are also included in this chapter

i

Table of Contents

CHAPTER ONE PROPERTIES OF THE [N]PHENYLENES AND THEIR ORGANOMETALLIC CHEMISTRY 1

11)General Discussion of [N]Phenylene Properties 1 12)Overview of Phenylene Organometallic Chemistry 6 13)Direction of Work 10

CHAPTER TWO PHOTOndashTHERMAL HAPTOTROPISM IN CYCLOPENTADIENYLCOBALT COMPLEXES OF LINEAR PHENYLENES INTERCYCLOBUTADIENE METAL MIGRATION 12

21)Introduction 12 22)Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes 16 23)Structural Studies on the Linear [3]Phenylene(CpCo) Complexes 22 24)Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift 30 25)Low Temperature Photolytic Studies on the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes 41 26)Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 56 27)Summary and Outlook 62

CHAPTER THREE NICKEL-CATALYZED INSERTION REACTIONS FOR THE PREPARATION OF [N]PHENACENE DERIVATIVES 63

31)Introduction 63 32)Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene 67 33)Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene 75 34)Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions 81 35)Summary and Outlook 87

CHAPTER FOUR EXPERIMENTAL AND COMPUTATIONAL DETAILS 88

41)General Considerations 88 42)Experimental Section for Chapter Two 88 43)Computational Details for Chapter Two 129 44)NMR Data for Chapter Two 154 45)Experimental Information for Chapter Three 162 46)Computational Details for Chapter Three 168 47)References 169

ii

Acknowledgements

ldquoWhere would I find leather enough to cover the surface of the earth The Earth is covered over merely with the leather of my sandalsrdquo

-Shāntideva in the Bodhicaryāvatārah Ch 4 v13 Five years ago I arrived in Berkeley with a rather clear objective get (or rather survive) a PhD Though the goal never changed the all paths (scientific personal professional and spiritual) I traversed were often quite unlike anything I could have anticipated I have had the great fortune to stand on the shoulders of many giants during these past few years and it is to them that I owe my deepest gratitude First and foremost I would like to thank my advisor Peter Vollhardt for all of his support and patience The things I have learned from him are far too numerous to list but certainly the two most important are clarity and rigor two qualities that extend far beyond the chemical realm Working with so many different people was another interesting challenging and ultimately highly rewarding experience I am particularly indebted to ldquoThe Old Gangrdquo consisting in part of Phil Leonard and Ken Windler These two gentlemanly pyromaniacal firearms enthusiasts aside from showing me the ins and outs when I was a new arrival (and teaching me more than I will ever need to know about guns and explosives) soon became good and close friends No mention of The Gang would be complete without Jordan Rose Figura Despite being a chemical biologist and not actually a member of the Vollhardt Group she nonetheless (somehow) managed to fit in perfectly My life has been forever changed by her introducing me to ldquoDoctor Whordquo Many others also deserve special mention Sabine Amslinger has and will continue to provide a near endless amount of legendary stories that often border on mythological Tom Gadek was just plain awesome Vince Gandon aside from being one the best experimentalists Irsquove seen also happened to have a rather fine taste in films and music Dominik Hager excelled at getting me out of the lab for an occasional weekend of fun The elegant and refined chocolate cakes of Aude Hubaud were a rare yet very welcome occurrence Her sassy chic comments on all aspects of life however were quite copious Greg Boursalian performed an excellent job of filling the ldquocool undergradrdquo spot and I wish him the best for his own graduate school journey Steve Meier managed the Herculean task of (legally) disposing of all those old empty gas cylinders It is my great hope that Prof Sgt Meier will share many (but certainly not all) of his Berkeley experiences with the next generation of chemists that he will educate Explaining the strange and quirky aspects of American culture and the English language to Kerstin Weiszlig made for a fair number of humorous conversations Learning the stranger and quirkier aspects of German language and culture made for many more Similarly much time was spent meticulously examining the lyrics and slang expressions of assorted hip-hop songs with Sander Oldenhof Practicing kindergarten level German while sharing a fairly constant supply of Ritter Sport bars with Verena Engelhardt was another fine example of cultural exchange Despite his best efforts Kasper Moth-Poulsen has yet to convince me that Volvo is the greatest vehicle manufacturer in the known universe My cultural exposure was not limited to European interactions however and I managed to learn a little Chinese as well Apparently ldquoHao Shenrdquo

iii

means ldquoMacGyverrdquo in Mandarin I would also like to thank the rest of my co-workers past and present for all of their support They are in rough chronological order Thomas Carl Miles Carter Kaspar Schaumlrer Ingo Janser Romy Michiels Elisa Paredes Thilo Heckrodt Nicholas Cheron Alex Lee Anais Geny Samer Al-Gharabli Nicole Franssen Vladislav Kulikov Alexandra Romek Isaac Ho Zhenhua Gu Florian Montermini Nikolai Vinokurov Robert Zitterbart and Cedric Ghellamallah Bonnie Kirk skillfully handled the various arcane administrative procedures but also provided many interesting and memorable early morning conversations The finer points of NMR spectroscopy were taught to me by the indomitable Rudi Nunlist His wry humor and outlook on life were often the perfect supplement to the rigors of graduate school life Working with Chris Canlas Rudirsquos able successor has also been a pleasure I was encouraged when he was so quick to remind me that I have the same name as a bad-boy Filipino action-movie star Teaching while always quite time consuming proved to be an invaluable experience Teaching under the direction of Peter the man who wrote the book on organic chemistry was quite an adventure His passion and talent for teaching are immediately obvious and inspiring even without flipping through the Basque translation of his textbook Jon Ellmanrsquos ability to write exams that are easy to grade but difficult for students to take is similarly awe inspiring There is no doubt in my mind that Heino Nitsche has taken teaching of general chemistry to new levels of eccentricity and excitement Jean Freacutechetrsquos impressive aptitude for lecturing is perhaps surpassed only by the impressiveness of his wine collection Looking down the academic chain I have to acknowledge many of the brilliant and wonderful students that made teaching such a fantastic experience Special thanks goes to Steve Seyedin Nellie Ekmejian Jessie Zhang Yao Yue Ashley Johnson Brent Jellen Zarina Khan and Mojgan Rastegar all of whom were extraordinary students that I hope will do their part to save the world No acknowledgement could be complete without recognizing the love and support of my family in particular my mother Her love though always tough was always there My various housemates also provided me with some great times Chris Trinh my first housemate in Berkeley was a superb fellow to live with and I will always fondly remember our conversations on life love and quantum gravity Cory McLitus when he wasnrsquot slaving away in the architecture studio also became a good friend I feel no need to apologize for getting him hopelessly addicted to ldquoThe Big Bang Theoryrdquo The awesome Samra Kasim was always ready for chai good food and hearty discussions on Bollywood and all things South Asian The housemates of 1505 Oxford St are also great people Though we rarely cross paths Vicky Zhuangrsquos highly entertaining biology lab adventures are much appreciated Vannamaria Kalafonos always has something wonderful going on in the kitchen and I aspire to learn the Greek specialty of cooking for a zillion people from her The cats Pink Tuffy and especially Floyd are nice companions even though they sleep a combined 60 hours per day Many kalyānamitras helped me get through the toughest times and to them I am especially grateful A large number of my Saturday evenings were spent in the calm environs of the Berkeley Monastery where Rev Heng Surersquos Avataṃsaka Sūtra

iv

lectures gave me much to think about The monthly lectures by Ajahn Amaro Ajahn Passano and the Abhayagiri Sangha were also a wonderful learning experience Chats about long-dead ancient languages and obscure texts with Sean Kerr a fellow survivor of Dagmar Theisonrsquos German class will also be fondly remembered The NY Sangha though far away always supported me and welcomed me warmly whenever I returned home Frank Yao Hai-Dee Lee Sheila Sussman Fred Ng Martin Applebaum Josephine Verceles Tiffany Taulton Phung Tran and especially Aaron Vederman repeatedly reminded me to ldquosmile breath deep and go slowlyrdquo The many visits to Bodhi Monastery were always the high points of my summers Michael Roehm Bhikkhu Bodhi Jane Berry Henry and Lily Teoh Marcie Barth Mahendra Sagar the dearly departed Felicia Miller Ven Guo Jun Susan Chastain and the polygot Bhikkhu Analayo made every visit an unforgettable experience and never failed to remind me why I get out of bed in the morning

- 1 -

Chapter One

Properties of the [N]Phenylenes and Their Organometallic Chemistry

11 General Discussion of [N]Phenylene Properties Polycyclic aromatic hydrocarbons (PAHs) are a class of molecules that have occupied the minds of chemists for generations1 Their essential feature aromaticity is the unusual stabilization that arises from having a 4n+2 number of π-electrons in a cyclical array This seemingly simple definition obscures the fact that aromaticity continues to be one of the most scrutinized topics in modern organic chemistry2 and more rigorous definitions3 have remained elusive Much of the early work4 with PAHs was aimed at investigating theoretical issues surrounding aromaticity There has been renewed interest in these systems in recent years because they are increasingly attractive as functional materials in organic-based electronics5 Of the many different kinds of PAHs known eg 1ndash6 (Figure 11) one subclass is of particular interest the [N]phenylenes6

Anthracene Coronene Phenanthrene

Chrysene Triphenylene Pyrene

1 2 3

4 5 6

Figure 11 Some examples of polycyclic aromatic hydrocarbons The [N]phenylenes (where N = the number of benzene rings) are PAHs in which benzene and cyclobutadiene rings are fused in an alternating manner The cyclobutadiene ring imparts very unusual structural and electronic properties as seen in the simplest molecule in the series biphenylene (7) It can be described by several resonance forms (Figure 12 andashe) in which the major contributor 7c avoids formation of the highly destabilizing antiaromatic cyclobutadiene (7a 7e) and benzocyclobutadiene circuit (7b 7d) This preference is manifest in the significant bond alternation7 seen in

- 2 -

the crystal structure of biphenylene (Figure 12) which shows a clear difference in bond lengths between the formal single bonds (~143 Aring) and the shorter formal double bonds (~137 Aring)

1423

1372

Figure 12 Biphenylene bond lengths (top Aring) and resonance contributors (bottom)

An extreme example of [N]phenylene π-bond localization is triangular [4]phenylene (8) (Scheme 11) in which the three-fold peripheral fusion imparts complete cyclohexatriene character on the central ring89a This property is reflected in the reactivity of the system eg catalytic hydrogenation (9)8b epoxidation (10)8c and cyclopropanation (11)8c Scheme 11 Reactions Illustrating the Fully Bond Localized Character of the Central Benzene

Ring in Triangular [4]Phenylene 8 Bond lengths are in Aring

- 3 -

Phenylenes exhibit another interesting structural feature in contrast to other PAHs sizable deviations from planarity (Figure 13)9ab The flexibility of the phenylene framework arises from the combined effect of π- and σ-strain9ab By adopting a nonplanar geometry overlap between the π-orbitals is diminished and in turn leads to a decrease in destabilizing antiaromatic character Pyramidalization of the four-membered ring carbons also reduces σ-strain9ab a phenomenon observed in highly strained alkene systems9c

Figure 13 Crystal structures showing deviations from planarity in (a) helical [6]phenylene (12)10 (b) dimethyl triangular [4]phenylene-23-dicarboxylate (13)9a and (c) 23-bis(tri-

methylsilyl) linear [3]phenylene (14)9a

The fusion of aromatic benzene rings with antiaromatic cyclobutadiene units in the same molecule has prompted numerous experimental and theoretical discussions6 regarding the magnetic and electronic properties of the phenylenes 1H-NMR spectroscopy is one typical measure of aromaticity Protons on the exterior of aromatic rings (eg 15) show relatively low field resonances while their interior counterparts resonate at relatively high field due to the presence of a diamagnetic ring current Conversely antiaromatic rings with 4n π-electrons are paratropic and reveal the opposite disposition of the two respective types of protons (eg 16) The interplay between aromatic and antiaromatic character in the phenylenes is evident in their chemical shifts which tend to show weakly aromatic resonances (Figure 15) relative to benzene (736 ppm)

(a) (b) (c)

12 13 14

- 4 -

Figure 14 Observed 1H-NMR resonances in (a) the aromatic [18]annulene (15)11 and (b) the antiaromatic 5-bromo-19-bisdehydro-[12]annulene (16)12

Aside from NMR spectroscopy nucleus independent chemical shift (NICS)13 calculations have also proven to be useful measures of aromaticity The NICS technique works by calculating the magnetic shielding of a ldquoghost nucleusrdquo that can be positioned anywhere around a molecule For probing aromaticity the calculated point is in the center of the π-electron circuit to be examined Calculations placing the ghost nucleus 1 Aring above the plane of the molecule are often used to minimize local anisotropy and are referred to as NICS(1)14 NICS data are given in ppm and are thus comparable to experimental 1H-NMR measurements Negative NICS values indicate aromatic character while positive values suggest antiaromatic character For example the NICS(1) of benzene15 is ndash125 ppm whereas for cyclobutadiene15 it is 151 ppm NICS calculations for various phenylenes have been carried out6 and are shown in Figure 15 alongside the experimentally measured 1H-NMR chemical shifts The attenuated aromatic character of the benzene and the relatively weak antiaromatic character of the cyclobutadiene rings in phenylenes such as biphenylene (7) triangular [4]phenylene (8) and angular [4]phenylene (17) are apparent from both sets of data

Figure 15 1H-NMR (blue) and NICS(1) (green) data for selected phenylene topologies (ppm)6

The phenylenes possess multiple modes of reactivity7 as illustrated by biphenylene (7) in Scheme 12 It can undergo electrophilic aromatic substitution like other PAHs but does so selectively at the 2-position to avoid the formation of intermediates with antiaromatic character Biphenylene does not readily undergo Diels-

- 5 -

Alder reactions but was shown to react with electron-deficient benzynes to give the corresponding cycloadducts16 Opening of the highly strained four-membered ring is another prominent aspect of phenylene reactivity

Scheme 12 Illustrative Reaction Pathways of Biphenylene6

Early work17 showed that it was possible to cleave the aryl-aryl C-C bonds via thermolysis in the neat state Rupture of the four-membered ring is a key step in the rearrangement of phenylenes into other PAHs and has been observed typically under flash vacuum pyrolytic conditions18 (eg 10ndash3ndash10ndash6 torr 800ndash1000 degC) Strained ring opening on exposure to metal complexes to give metallacycles19 is discussed in further detail in Section 12 12 Overview of Phenylene Organometallic Chemistry

As mentioned above the weakly aromatic character of the phenylenes dominates their structure and reactivity In the linear phenylenes the antiaromatic contribution to structure and reactivity becomes increasingly significant A simple yet instructive explanation for this phenomenon can be seen in the various resonance structures of linear [3]phenylene (18) a selection of which is depicted in Figure 16 Even the most favorable forms a and b feature double bonds in the four-membered rings The cumulative increase in cyclobutadienoid circuits should therefore lead to an increase in antiaromatic character The relative augmentation in

- 6 -

cyclobutadienoidantiaromatic character of the linear phenylenes was confirmed6 by NMR NICS calculations and HOMO-LUMO measurements20

Figure 16

Resonance contributors to linear [3]phenylene

Cyclobutadiene is often invoked as the typical example of a highly destabilized antiaromatic system Indeed the difficulties21 in preparing and isolating it confirm theoretical predictions regarding its instability22 Attachment of a metal however is known to produce aromatic organometallic molecules of high stability23 The increased antiaromatic character of the linear phenylenes thus makes them amenable to metal complexation Cyclopentadienylcobalt cyclobutadiene complexes of linear [3]- (19)24 linear [4]- (20)25 and linear [5]phenylene (21)26 have been prepared using the well-developed cobalt-based [2+2+2] alkyne cyclotrimerization methods (Scheme 13)27

Compounds 19ndash21 constitute the only linear CpCo phenylene systems known so far

Scheme 13 Synthesis of Linear Phenylene(CpCo) Cyclobutadiene Complexes

In the metallated linear [4]- and [5]phenylene 20 and 21 respectively the CpCo unit is located on the inner cyclobutadiene ring This is curious as one would have expected the metal fragment to be bound to its outside counterpart close to the center of reactivity during the cyclotrimerization step The position of the CpCo unit was established by NMR spectroscopy2628 In addition a crystal structure of a tetrahexyl

TMS

TMS

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMSTMS

TMS

Co

CpCo(CO)2BTMSA

h

Co

Co

CpCo(CO)2BTMSA

h

CpCo(CO)2BTMSA

h

19

20

21

- 7 -

substituted linear [5]phenylene28 (Figure 17) clearly reveals the inside position of the metal fragment Difficulties in obtaining high quality crystals however precluded a detailed bond analysis of the complex The unexpected location of the CpCo unit in 20 and 21 suggested the occurrence of CpCo migration under the conditions of their preparation Detailed experiments verifying this hypothesis will be the subject of Chapter 2

Figure 17 Disordered crystal structure for the 23910-tetrakis(trimethylsilyl)-571214-

tetrahexyl linear [5]phenylene(CpCo)

In contrast to the linear phenylenes their angular relatives undergo π-metallation at the cyclohexatrienoid moieties (Figure 18) For example angular [3]phenylene (22) reacts with CpCo(C2H4)2 to form the η4-CpCo complex 2329 Similar treatment with Cr(CO)3(NH3)3 yields the η6-Cr(CO)3 analog 2430

Figure 18 η

4-CpCo (23) and η6-Cr(CO)3 (24) complexes of angular [3]phenylene (22)

In addition to 24 related chromium complexes of the triangular [4]phenylene frame eg 25 have been prepared (Scheme 14)31 Interestingly regioisomer 26 generated at relatively lower temperatures is the kinetic product of monocomplexation and rearranges thermally to 27 Double metallation is possible as illustrated in the conversion of 27 to 28 with added (naphthalene)Cr(CO)3

- 8 -

Scheme 14 Synthesis and Reactions of Triangular [4]Phenylene(Cr(CO)3) Complexes

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3(NH3)3dioxane 100 oC

14 h

(naphthalene)Cr(CO)3THF Et2O 60 oC 14 h

90 oC

(naphthalene)Cr(CO)3THF Et2O 60 oC

14 h

25

27

26

28

57 43

89

In contrast to CpCo which attaches itself exclusively to the four-membered ring in the linear phenylenes including the linear [3]phenylene frame as in 19 (Scheme 13) Fe2(CO)9 gives a plethora of complexes with the tetrasilyl derivative 29 among which the iron tricarbonyl cyclobutadiene complex 30 is only minor (Scheme 15)27 Instead other organometallic molecules such as arene complex 31 were isolated This compound contains two Fe(CO)3 units coordinated to the central benzene ring An iron-iron bond was proposed for this molecule (31a) although the spectral data are also consistent with a structure in which the Fe(CO)3 fragments are located on opposite faces (31b) Because a crystal structure could not be obtained the structural identity of 31 remains ambiguous The major products of this reaction 32 and 33 illustrate another important aspect of phenylene reactivity metal insertion into the strained ring

- 9 -

in this case involving the dinuclear Fe2(CO)6 unit Complex 33 probably originating from 32 contains an additional Fe(CO)3 moiety coordinated to the terminal benzene ring closest to the Fe2(CO)6 fragment

Scheme 15 Reaction of Linear [3]Phenylene with Fe2(CO)9

While as yet absent in the linear series a cobalt insertion product analogous to iron compounds 32 and 33 was isolated when angular phenylene 22 was exposed to excess CpCo(ethene)2 (Figure 19)32 In this case double insertion of two (CpCo)2

Figure 19 Tetranuclear CpCo-terphenylene complex 34 and its crystal structure

34

- 10 -

fragments occurred to give 34 in 71 yield Notably neither 23 nor analogs of the type 31 were detected As alluded to in Scheme 12 biphenylene (7) itself also undergoes metal insertions into the four-membered ring This type of reactivity has been observed with a range of transition metals including Co19 Mechanistically best delineated is the attack of Ni and Pt species Thus Ni(PEt3)4

33a and Ni(COD)(PMe3)233b begin with insertion of

the nickel fragment into the four-membered ring to give a metallacycle of the type 35 (Scheme 16) Subsequent dimerization assembles 36 from which Ni is extruded to furnish tetraphenylene 37 as the final product A similar reaction pathway was proposed for Pt(PEt)4

19 but proceeding via 38 to a monometallacycle 40 possibly through the intermediacy of 39 In summary the σ- and π-activation of the phenylenes endows them with rich organometallic chemical potential The synthetic and mechanistic exploration of one aspect of it namely the Ni-catalyzed cycloaddition of alkynes to the four-membered rings in angular phenylenes will be discussed in Chapter 3

Scheme 16 Reaction of Biphenylene with Nickel and Platinum Complexes

13 Direction of Work The discussions in Sections 11 and 12 have provided a brief overview of phenylene properties and their previously studied organometallic chemistry

- 11 -

respectively The aim of this thesis was to advance two aspects of prior investigations The first area examines the chemistry of the linear phenylene(CpCo) complexes In particular experiments are presented addressing the question of a possible migration of the CpCo fragment along their framework The revocable movement of a metal fragment between cyclobutadiene rings is a highly noteworthy discovery as this process has never before been reported On a practical level this mode of reactivity places linear phenylene(CpCo) complexes in the increasingly appealing class of organometallic arrays that can serve as the basis for various molecular electronic systems The reversible isomerizations described in the second chapter can potentially be employed in molecular machines and switches data storage and as will be detailed photostorage devices Experimental work in the form of detailed solid state and spectroscopic analyses is provided Computational studies are also employed to further scrutinize the novel chemistry of the abovementioned Co-based molecules The second topic of this thesis examines nickel-catalyzed insertions into the four- membered rings of angular phenylene systems Specifically the application of this reactivity to the synthesis of a class of PAHs known as [N]phenacenes is discussed Phenacenes (polyphenanthrenes) have recently shown great promise as organic transistors and conductors but advancement of this field has been hampered due to few practical syntheses The insolubility of these molecules has also been a substantial barrier to the development of phenacene-based applications The content of the third chapter explores the preparation of soluble phenacene derivatives using a tandem Ni-insertion alkyne cycloaddition reaction This new process provides an efficient widely applicable and practical synthesis of larger phenacenes using correspondingly larger angular phenylene systems Detailed mechanistic studies of this reaction are presented Experimental data are used in conjunction with computational studies to gain further insight with the optimization of the reaction by reduction of side product formation being a crucial milestone

- 12 -

Chapter Two

PhotondashThermal Haptotropism in Cyclopentadienylcobalt Complexes of Linear Phenylenes Intercyclobutadiene Metal Migration

21 Introduction As previewed in Section 12 the unexpected position of the metallic unit in the linear [4]- and [5]phenylene(CpCo) systems 20 and 21 constituted the background for the studies presented in this chapter Specifically it was hypothesized that its origin was due to the migration of the metal fragment from one cyclobutadiene ring to another a process that would constitute an unprecedented type of haptotropic shift34-36 However a prerequisite for studying such a rearrangement would be the generation of the haptoisomers of 20 and 21 (Scheme 13) bearing the CpCo appendage at the respective terminal four-membered rings a possibility obviated by their thermal method of synthesis The following describes the history that led to the discovery of photochemical conditions that circumvented this thermodynamic problem The story begins with a prior attempt to stabilize the linear phenylene frame by alkyl substitution the ultimate aim being the synthesis of members of the series with Ngt5 Such substitution was also hoped to improve solubility a facet exploited in the corresponding zigzag series37 The synthetic strategy followed that used in the preparation of the largest known linear phenylene 41 namely the CpCo-catalyzed cyclization to 21 followed by careful oxidative demetallation as shown in Scheme 21 The initial target chosen was the tetrahexyl system 43 approached via the synthesis of complex 42 (Scheme 22)28 Demetallation was thought to be facile to provide the free ligand but this anticipation proved to be erroneous

Scheme 21 Oxidative Decomplexation of Linear [5]Phenylene Complex 21

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMS

41

CoCp

21

40

CuCl2middot2H2ODME NEt3 H2O

Scheme 22 Preparation of Tetrahexyl Linear [5]Phenylene Complex 42

- 13 -

TMS

TMS

TMS

TMS

Hex

Hex

Hex

Hex

CoCp

42

CpCo(CO)2 BTMSAm-xylene ∆ hν

27

Hex Hex

HexHex

TMS

TMS

TMS

TMS

Hex Hex

HexHex

ndashCpCo

43

The demetallation of 42 under numerous conditions was unattainable However in one of these attempts an NMR sample of 42 was exposed to UV-irradiation leading to the evolution of new signals eventually assigned to originate from rearranged compound 45 (Scheme 23)28 This molecule is also a linear [5]phenylene(CpCo) complex but now has the metal fragment bound to the outer cyclobutadiene ring an arrangement that was suspected to be the initial product of the preparation of 42 (Scheme 22) That this conjecture was correct was established by heating which caused photoisomer 45 to revert to 42 An indication of the generality of this phenomenon was gleaned from 21 which underwent the same photoinduced thermally reversible haptotropic migration (Scheme 23)38 A detailed discussion of the spectral properties of these haptomers is provided in Sections 23 and 24 Scheme 23 Photoinduced Thermally Reversible Haptotropic Migration of the CpCo Fragment

in Linear [5]Phenylene(CpCo) Complexes

This discovery was deemed significant for two reasons 1 it constitutes the first observation of intercyclobutadiene metallohaptotropism and 2 there are only two previously known examples of mononuclear39 additive-free40 photothermal reversible haptotropic shifts both of which are based on Mo(PMe3)3 complexes (Scheme 24)41 Systems capable of undergoing this type of reaction are of much practical importance because of their potential employment as photostorage devices andor molecular switches42 The development and application of functional organometallic materials43 has proceeded at a relatively slow pace when compared to their non-metallated counterparts5c Thus the great prospects for discovery and advancement make this area of study particularly attractive

- 14 -

Scheme 24 Photothermal Reversible Metallohaptotropism in (a) Molybendum-Indole41a and (b) Molybendum-Isoquinoline Complexes41b

Having confirmed that an η4η4 cyclobutadiene haptotropic migration was indeed occurring mechanistic investigations2838 were begun Interestingly full conversion of the inner bound CpCo complexes to their photoisomers was never achieved The maximum ratio obtained for 2144 and 4245 was 8812 Variations of solvent (eg benzene THF CHCl3) and temperature (0ndash30degC) had no effect on this ratio Added ligands such as 15-cyclooctadiene CO and phosphines were also inconsequential Of further significance was the robustness of the photothermal cycle which could be run multiple times without decomposition Kinetic experiments were carried out to determine the activation parameters for the thermal reversal of 44 and 45 to 21 and 42 respectively These data are shown in Table 21 The isomerizations are cleanly first order a finding that was unaffected by changes in concentration22 The enthalpy of activation (∆Hne) increased only slightly with hexyl substitution (44 vs 45) The near zero entropy of activation values (∆Sne) was consistent with the occurrence of an intramolecular process

Table 21 Activation Parameters for the Conversion of Outer to Inner CpCo Complexes Under

Thermal Conditions ∆Sne Values are in Entropy Units (1 eu = calmolsdotK)

Reaction Solvent ∆H

ne (kcalmol) ∆Sne (eu)

44 to 21 C6D6 259 plusmn 04 16 plusmn 14 44 to 21 THF-d8 256 plusmn 09 01 plusmn 30 45 to 42 THF-d8 276 plusmn 08 77 plusmn 27

Consideration of the relative facility of the above haptotropic shifts made it likely that migration was occurring along the entire phenylene frame including the ldquohoppingrdquo across the central six-membered ring (Scheme 25) This degenerate equilibration should be detectable by NMR spectroscopy44 if it were sufficiently fast Unfortunately but perhaps not surprisingly considering the data in Table 21 coalescence of the spectrum of 21 could not be achieved even at temperatures as high as 120 degC Spin saturation transfer experiments (eg EXSY) also failed44 These data allowed an estimate of the lower limit for the activation energy of the internal shift of ∆Gne ge 22 kcalmol28

Scheme 25 Proposed Internal η4η4 Cyclobutadiene CpCo Migration

- 15 -

The failure of the above experiments inspired a different approach based on the following arguments The antiaromatic character of the linear phenylenes has been shown by theory and experiment to increase with size645 Consequently the effect of metalloaromatization46 makes linear [5]phenylene a better (and hence more strongly bound) ligand for CpCo than a smaller system (eg linear [3]phenylene) Indeed the enthalpy of the homodesmotic in Scheme 26 was computed by DFT methods to be Scheme 26 Calculated Homodesmotic Reaction Showing Preferential Binding of CpCo to

Linear [5]Phenylene

113 kcalmol47 If the barrier to intercyclobutadiene hopping were related to the binding energy of the metal one would expect a more loosely bound metal fragment to migrate faster The hope was therefore that the degenerate haptotropism in Scheme 27 would be observable by VT NMR methods Unfortunately these efforts failed again38 either because the anticipated acceleration was not sufficient to be observable by NMR or because the argument above (which rests solely on ground state considerations) is flawed

Scheme 27 Proposed Degenerate Haptotropic Shift in Linear [3]Phenylene Complex 19

- 16 -

The preceding discussion summarizes some of the quantitative aspects of this new type of haptotropic shift Many fundamental questions however remained to be answered Is it possible to observe the photothermal shift in other systems such as linear [3]- and [4]phenylene What is the exact mechanism of metal migration between cyclobutadiene rings In what way if any does attachment of CpCo alter the structure of the phenylene scaffold Related to these questions was the long-standing quest for an accurate crystal structure of any linear phenylene(CpCo) complex The answers are addressed in the following sections 22 Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes As recounted in Section 21 the degenerate internal haptotropic shift could not be seen by NMR in the symmetrical 19 Therefore recourse had to be taken to chemical methods involving an isomerization of the sort shown in Scheme 28

Scheme 28 Isomerization of a Desymmetrized Linear [3]Phenylene(CpCo) Complex

Initial efforts focused on attempts to desymmetrize compound 19 directly by selective electrophilic desilylation specifically protodesilylation Earlier studies48 had shown that such selectivity was possible in the reactions of bis(trimethylsilyl)benzocycloalkenes such as the benzocyclobutene depicted in Scheme 29 In this case loss of the first TMS group is approximately forty times faster than that of the second Along these lines it was thought that exposing 19 to acidic conditions would selectively remove one (or perhaps two) TMS groups before attacking the remaining silylarene positions In the event treating compound 19 with trifluoroacetic acid in carbon tetrachloride did induce protodesilylation but with no selectivity A mixture of products was obtained and its separation proved impossible (Scheme 210) In light of this setback a new synthetic scheme had to be considered that would generate a desymmetrized system directly in the CpCo-catalyzed cyclization step

- 17 -

Scheme 29 Selective Desymmetrizing Reactions of 12-Bis(trimethylsilyl)benzocyclobutene with Electrophiles

Scheme 210 Attempted Selective Protodesilylation of 19

Fortunately such a strategy had already been executed successfully in the creation of 23-bis(trimethylsilyl) linear [3]phenylene (46) and employed the iterative Scheme 211 Iterative Cyclotrimerization Route in the Synthesis of Linear [3]Phenylene 46

cyclization depicted in Scheme 21127 Its specific execution (Scheme 212) started with a Sonogashira reaction between trimethylsilylacetylene (TMSA) and 12-diiodobenzene (47) to give diyne 48 in high yield Deprotection of 48 with K2CO3 immediately followed by standard CpCo(CO)2-catalyzed alkyne cyclotrimerization649 with bis(trimethylsilyl)acetylene (BTMSA) afforded 23-bis(trimethylsilyl)biphenylene (49) Iododesilylation was then performed using pure ICl to give 23-diiodobiphenylene (50) A Sonogashira coupling between TMSA and 50 produced diyne 51 in good yield The use of a slightly modified cyclization procedure provided the new 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52) in 57 yield This protocol employed THF as a cosolvent to BTMSA thus reducing the reaction temperature in turn allowing for the CpCo to remain attached in the final product and preventing catalytic turnover252638

TMS

TMS46

+

TMS

TMS

+

TMS

TMS

+

TMS

R

TMS

dilute

[X+]

X = H D Br

TMS

TMS

[X+]

TMS

X = H D Br

X

- 18 -

Scheme 212 Synthesis of Asymmetric Linear [3]Phenylene(CpCo) 52

High dilution conditions also helped to suppress formation of cyclobutadiene(CpCo) complexes a well known side reaction in alkyne cyclization chemistry

Compound 52 like its tetrasilylated analogue 19 is a black air-sensitive solid Although it can be handled in air for brief periods of time complete decomposition occurs within 24 hours if left exposed to the ambient atmosphere Purification must always be done with neutral activity III alumina as lower activities (and silica gel) cause decomplexation to give the deep red ligand 46 as the only isolable product Critically exposing molecule 52 to UV irradiation induced the desired haptotropic shift giving its photoisomer 53 (Scheme 213) Heating 53 converted it back to 52 thus completing the photothermal cycle Interestingly close inspection of the NMR spectra of this experiment revealed that a small amount of 53 (2) always remained even on prolonged heating That this observation signaled a thermodynamic equilibrium was confirmed by dissolution of pure crystalline 52 and NMR analysis From the equilibrium constant the ∆Gdeg298 was calculated to be 23 kcalmol in favor of 52 The reasons for this energetic preference and a discussion of the NMR spectral properties of these and related complexes are presented in Section 23

Scheme 213 The Photoinduced Thermally Reversible Haptropic Shift in Linear

- 19 -

[3]Phenylene-(CpCo) 52 to Give Photoisomer Complex 53 The investigations of the equilibration depicted in Scheme 213 were all carried out in sealed Pyrex NMR tubes (J-Young or flame-sealed) using benzene-d6 andor toluene-d8 as the solvent As for the linear [5]phenylene(CpCo) system the cycle could be run multiple times without decomposition and was unaffected by changes in solvent and temperature The maximum ratio of 5352 that could be obtained on irradiation was 11 after ten hours This value is larger than that observed for its linear [5] analogs 2144 and 4245 Photoisomerization also occurs with sunlight leading to the photostationary equilibrium of 5253 = 105 Consequently care must be taken to shield 52 from direct andor indirect sunlight Indoor fluorescent lighting however did not induce CpCo migration Attempts to monitor the photoisomerization and its thermal reverse by UV-Vis spectroscopy failed because of minimal changes in the absorptions due to 52 during these processes This finding implies that the absorption spectra of 52 and 53 are not unexpectedly very similar and offers a possible explanation for the maximum photostationary ratio of 11 The activation parameters for the thermal reversal reaction (53 to 52) in Scheme 213 were obtained in the manner described in Section 21 and are shown in Table 22 The relatively high activation barriers (with respect to the NMR time scale) explain why the degenerate isomerization in 19 could not be verified by NMR experiments Qualitatively the ∆Hne values agree with the hypothesis that the more loosely bound CpCo unit in the linear [3]phenylene is relatively more mobile they are approximately 3 kcalmol lower than those of the [5]phenylene system On the other hand the ∆Sne values especially in C6D6 are positive and relatively high although still within the range acceptable for intramolecular reactions Nevertheless a crossover experiment was devised to provide a definite answer

Table 22 Activation Parameters for the Thermal Conversion of Complex 53 to 52

Solvent ∆H

ne (kcalmol) ∆Sne (eu)

C6D6 204 plusmn 14 158 plusmn 22 Toluene-d8 231 plusmn 07 60 plusmn 13

For this purpose two new linear [3]phenylene(CpCo) derivatives were required One would carry a marker on the Cp ring while the other would be labeled at the phenylene frame Execution of Scheme 213 would involve an equimolar mixture of both compounds An intramolecular mechanism would retain the integrity of the labeling while a dissociative path would lead to label scrambling The outcome of this experiment should be ascertainable by NMR spectroscopy and more rigorously by

CoTMS

TMS

CoTMS

TMS

310 365 nmsunlight

30ndash50oC52 53

- 20 -

Scheme 214 Preparation of MeCp- (54) and Deuterium Labeled (55) [3]Phenylene Complexes

mass spectrometry To this end methyl-Cp complex 54 and dideuterio compound 55 were targeted for synthesis (Scheme 214) Compound 54 was prepared by carrying out the modified cyclotrimerization reaction with MeCpCo(CO)2

50 while 55 was made using methanol-OD in the desilylation of 51 The amount of deuterium incorporation in 55 was found to be 63 as gleaned from its proton NMR spectrum Scheme 215 Crossover Experiment with Labeled Linear [3]Phenylene(CpCo) Complexes

- 21 -

Co

TMS

TMS

TMS

TMS

Co

h CoTMS

TMS

Co

D

D

TMS

TMSD

D

TMS

TMS

Co

Co

TMS

TMSD

DCo

TMS

TMS

Co

TMS

TMSD

D

+

+

+

+

mz = 510

mz = 494

56mz = 508

57mz = 496

54mz = 508

55mz = 496

58 59

53 52

Not observed

Six distinct products are possible in the crossover experiment using 54 and 55 (Scheme 215) Compounds 56 and 5 would arise as a consequence of an intramolecular shift Molecules 53 and 58 and their photoisomers 52 and 59 respectively would be the result of metal fragment dissociation Mass spectrometry would readily verify the occurrence of crossover as the masses (given in mz in Scheme 215) of the products with scrambled labels (52 53 58 59) are distinct from the masses of the starting materials (54 55) and their photoisomers (56 57) In the first part of the experiment equal amounts of 54 and 55 were mixed (shielded from light) and allowed to stand for 2 hours at room temperature The resulting 1H-NMR spectrum consisted of only the signals for 54 and 55 Similarly the mass spectrum showed molecular ion peaks matching the masses of 55 and 56 (Figure 21) The second step was irradiation Analysis of the photolyzed mixture showed new peaks due to complex 56 (the resonances of which had been obtained in a separate photothermal experiment with pure 54) with the expected integration ratio and a second set assigned to 57 identical with the spectrum of 53 but with the expected attenuated absorption for the silyl bearing arene hydrogens The relative integrations for all compounds observed were consistent with a mixture of 5455 and 5657 Mass spectral analysis of the irradiated mixture showed a pattern that was identical to that collected before irradiation (Figure 21) Finally the thermal reversal reaction was carried out by heating the photolyzed mixture at 80 degC After 30 hours the resulting

- 22 -

NMR spectrum matched that of the initial mixture of 54 and 56 in particular confirming the full protonation of 54 and the unchanged level of deuterium incorporation in the silyl

Figure 21 Molecular ion peaks for 5456 (mz = 508) and 5557 (mz = 496)

bearing arene ring of 55 The corresponding mass spectrum contained no evidence for the presence of scrambled products To conclude The haptotropic shift is non-dissociative The exact manner in which the metal traverses from one cyclobutadiene ring to the other will be examined in greater detail in Section 24

23 X-Ray Structural and Comparative NMR Analysis of Linear [3]Phenylene(CpCo) Complexes The results described in Sections 21 and 22 pose some fundamental questions beyond those concerned with the immediate details of the observed haptotropism and addressing the basic novelty of the complexes involved What actually happens to the phenylene ligand when it is ligated via a cyclobutadienoid ring This section will address this question from a structural and (NMR) magnetic point of view Only one crystal structure of a linear phenylene(CpCo) complex was known at the outset of this work namely that of [5]phenylene(CpCo) 42 (Figure 17) and its acquisition required extensive efforts at crystallization28 Unfortunately extensive disorder obviated a detailed analysis It was hoped that some of the complexes employed in the chemistry disclosed in Section 22 would be more forthcoming in this respect The challenge lay in finding the right conditions for crystal growth We began with tetrasilyl linear [3]phenylene(CpCo) 19 which had been crystallized previously by slow cooling in acetone38 These conditions and numerous others (Table 23) did not provide material suitable for X-ray diffraction Success entailed slow cooling a solution of 19 to ndash10 degC in a mixture of methanol-diethyl ether (41) The ensuing sample allowed the determination of the first high quality crystal structure of a linear phenylene (CpCo) complex obtained in collaboration with the group of Professor Tatiana Timofeeva of New Mexico Highlands University (Figure 22)

Table 23 Trial Crystallization Conditions for Linear [3]Phenylene(CpCo)19

Solvent (Ratio) Conditions Result

Acetone Slow Cooling Heterocrystalline Solid Acetone-Pentane (31) Slow Cooling Heterocrystalline Solid

Pentane-Acetone (101) Solvent Diffusion Amorphous Solid Chlorobenzene Slow Cooling Amorphous Solid

- 23 -

Acetone-Methanol (110 Slow Cooling Amorphous Solid Diethyl Ether-Methanol Slow Cooling Small Needles

Acetonitrile Slow Cooling Powder Ethyl Acetate Slow Cooling No Crystals

Ethyl Acetate-Methanol (11) Slow Cooling Amorphous Solid Methanol-Diethyl Ether (41) Slow Cooling Large Fine Needles

Figure 22 X-ray crystal structure of 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) (19) Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are

omitted for clarity Expectedly the CpCo unit is bound in an η4 fashion to the cyclobutadiene ring Also prominent is the deviation from planarity (Section 11) in the linear [3]phenylene a facet typical of the phenylenes themselves (Section 11)9a Of greater importance than these general observations however is the effect of metal complexation on the linear [3] framework The bond lengths for 19 are shown in Figure 23 and as is typical for the phenylenes6 show a certain degree of bond π-localization with measurable differences between single and double bonds However the extent of this phenomenon and its direction varies significantly when compared to the free ligand 60 A quantitative

- 24 -

comparison of the structural data for 19 with those of its ligand 60 is shown in Figure 2327

In 60 the terminal rings adopt bond alternation similar to that in biphenylene (Section 11) and the central benzene takes on a ldquobis-allylrdquo configuration both ostensibly to minimize electron density (and therefore antiaromaticity) in the four-membered rings As dictated by symmetry the two bonds spanning the central ring are of equal length (1385 Aring) Ligation by CpCo alters this picture profoundly in as much as bond alternation across the entire phenylene frame including the four-membered rings is strongly reduced (Figure 23) Generally all relatively long bonds in 60 shorten in 19 while all short bonds lengthen Some residual but attenuated biphenylene type

Co

1512(2)

1513(2)

1407(2)

1385(2)

1385(2)

1397(2)

1356(2)

1359(2)1436(2)

1397(2)

1441(2)

1411(3)(0052)

1384(3)(-0052)

1474(3)(0077)

1384(3)(-0057)

1408(3)(0052)

1448(3)(0051)

1480(3)(-0032)

1468(3)(-0045)

1437(3)(0052)

1465(3)( 0058)

1434(3)( 0049)

1352(3)(-0033)

1351(3)(-0034)

1476(3)(0069)

1495(3)(-0017)

1372(3)( 0016)

1405(3)(0008)

1376(3)(0017)

1413(3)(-0023)

1427(3)(0030)

1488(3)(-0025)

1423(3)(-0018)

(x) = (19) - (60)increasedecrease

60

19

1907(1)

1891(1)

1886(3)

1889(3)

1889(2)

1901(3)

1669

1725

Si

Si

Si

Si

Me

MeMe

Me

Me

Me

Me

MeMe

MeMe

Me

Si

Si

Me

MeMe

MeMe

Me

Si

Me

MeMe

Si

Me

MeMe

- 25 -

Figure 23 Comparison of bond lengths (in Aring) between linear [3]phenylene(CpCo)complex 19 and 2378-tetrakis(trimethylsilyl) linear [3]phenylene (60) The bond distances in 19 are shown in blue Increases in bond length in going from 60 to 19 are marked in green decreases in red

ldquobond fixationrdquo (Figure 12) remains in the vicinity of the uncomplexed cyclobutadiene Compound 19 thus provides a prime demonstration of the powerful effect of metalloaromatization46 in which the bonds of a cyclobutadiene-metal system attempt to adopt the equalized bond lengths that are a classic hallmark of aromaticity2ndash4 Encouraged by the successful development of a procedure to obtain X-ray quality crystals of 19 these techniques were applied to bis(trimethylsilyl) linear [3]phenylene(CpCo) 52 Gratifyingly with acetone as the solvent the results depicted in Figure 24 were ultimately obtained Figure 24 X-ray crystal structure of 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52)

Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are omitted for clarity

A comparison of the bond lengths of 52 with those of its corresponding linear [3]phenylene ligand 469a is given in Figure 25 Comparison with Figure 23 reveals the same type of aromatization of the ligand on attachment of the metal With these structures in hand an attempt was made to rationalize structurally the

- 26 -

thermodynamic preference for 52 in which the CpCo is located proximal to the silylated terminus in its equilibrium with 53 in which the metal is located close to the unsilylated benzene ring Focusing on the desymmetrizing ortho-bis(trimethylsilyl) unit one notes that the SiCndashCSi bond in 52 is elongated by 005 Aring on attaching the metal in 46 thus providing steric relief On the other hand the symmetry equivalent remote C7ndashC8 distance is unchanged The same effect is seen in the tetrasilyl complex 19

Figure 25 Comparison of bond lengths (in Aring) between bis(trimethylsilyl) linear [3]phenylene(CpCo) complex 52 and 23-bis(trimethylsilyl) linear [3]phenylene (46) Bond lengths for 46 are the average of four molecules in the unit cell (standard deviation = plusmn002)

Increases in bond length going from 46 to 52 are marked in green decreases in red

The observed structural changes make sense in a simple resonance picture

Co

1413(10)(007)

1406(10)(-004)

1459(10)

( 005)

1370(11)(-007)

1418(10)( 005)

1443(10)(003)

1470(10)(-005)

1465(10)(-005)

1446(10)( 008)

1485(10)( 006)

1432(10)( 004)

1347(10)(-003)

1345(10)(-002)

1492(10)( 007)

1503(11)(-002)

1379(10)(001)

1391(11)(-001)

1409(10)(004)

1418(11)(-003)

1367(11)(001)

1478(10)(-002)

1408(11)(-001)

1891(8)

1890(13)

1670

1723

SiMe

MeMe

Si

Me

Me

Me

(x) = (53) - (62)increasedecrease

SiMe

MeMe

Si

Me

Me

Me

190

145134152

139138

150

137145

136

142 137

152137 137

152

141

137 144

189

141143142140

52

46

- 27 -

(Scheme 216) Metalloaromatization alters the dominant resonance forms during intercyclobutadiene hopping such that the essentially single SiCndashCSi bond in 52 transforms into an essential double bond in 53 increasing unfavorable repulsion between the TMS groups Scheme 216 A Resonance Picture Rationale for the Preference of 52 in its Equilibrium with 53 The aromatization effect of metal complexation on the phenylene nucleus described structurally in the preceding text can also be demonstrated powerfully through the measurement of ring currents with 1H-NMR spectroscopy both by experiment and computation (NICS13 see Section 11) A relevant simple example is depicted in Figure 26(a) featuring the changes occurring when 12-bis(trimethylsilyl)benzocyclobutadiene (61) is complexed by CpCo as in 6251 The paratropic antiaromatic 8π system 61 exhibiting relatively shielded six-membered ring hydrogens turns diatropic in 62 Equally importantly and focusing on the ring current contributions of the individual cycles the paratropism of the four-membered ring in 63 shields the adjacent hydrogens more than the remote ones Conversely aromatization of this ring and the ensuing diatropism inverts this order

Figure 26 The effect CpCo complexation (a) on benzocyclobutadiene 61 and (b) linear [3]phenylene 46 Chemicals shifts are in ppm

Co SiMe3

SiMe3

Co

SiMe3

SiMe352 53

∆Gdeg298 =23 kcalmol

- 28 -

Turning to a phenylene system comparison of the NMR data for complex 52 with those for ligand 46 (Figure 26(b)) reveals the same changes not only in the vicinity of the ligated ring but also in the remote parts of the molecule Thus the hydrogens closest to the metal fragment are shifted downfield by 125 ppm in 62 and 148068 ppm in 52 when compared with 61 and 46 respectively The observed relatively large chemical shifts of the arene hydrogens proximal to the metal unit are not due to its anisotropy since its value in this area of space is (if anything) shielding5152 In addition the remote hydrogens in 52 are deshielded by 055033 ppm relative to the corresponding nuclei in 46 clearly substantiating the aromatization of the overall system upon metal complexation that was seen by structural analysis These pronounced chemical shift changes are diagnostic and greatly aided the spectral interpretations of the photochemically induced haptotropic shift experiments described in Sections 21 and 22 as illustrated for the isomerization between 52 and 53 (Scheme 217)

Scheme 217 Chemical Shift Changes in the Isomerization of 52 to 53

These NMR measurements were augmented by NICS calculations carried out in collaboration with Professor Amnon Stanger at the Technion in Haifa NICS data have the advantage that they indicate the extent of (anti)aromaticity even in rings for which the molecule has no hydrogen probe in the classical NMR experiment in this case the cyclobutadienes Computational details are given in Chapter 4 The experimentally determined proton NMR data for the series of silylated linear phenylenes from [2] to [5] and their metallated analogues in addition to the corresponding NICS(1) values of the respective parent phenylenes are shown in Figure 27 All compounds in Figure 27 are known except for the hypothetical biphenylene(CpCo) 64 which is included for comparative purposes Metalloaromatization is pronounced as all rings of the phenylene exhibit diminished or more negative NICS numbers signaling increasing aromatic and decreasing antiaromatic character respectively Again the effect is most pronounced on the rings closest to the metal bound unit tapering off (but never disappearing) with distance Most illustrative in this respect is 44 in which the penultimate and ultimate rings away from the Co still show decreases in the NICS values of 06 and 05 ppm respectively Interestingly the sum of all NICS values of 44 (ldquototal NICSrdquo13c) ndash91 is less negative than that of 21 ndash132 suggesting that 21 is more aromatic hence more stable as observed experimentally This may be fortuitous and the issue is addressed further in Section 24 Finally a caveat regarding the unusually large negative NICS values associated with the CpCo-complexed cyclobutadiene rings As pointed out by Solagrave in connection with a related study of (benzene)Cr(CO)3 which produced similar numbers53 there are local ring currents associated with the extra electrons involved in the metal to π-ligand

CoTMS

TMS796675674

678

436 CoTMS

TMS747683724

662

444

310 365 nmsunlight

30ndash50oC

52 53

- 29 -

bonding that lead to an overestimation of aromaticity Therefore to corroborate the general conclusions of metalloaromatization of this (and all other rings) in Figure 27 Stangerrsquos NICS scan method was applied54 This procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (NICSXY) and out-of-plane components (NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their

Figure 27 Experimental 1H-NMR (C6D6 blue) and computed NICS(1) (green) values for linear phenylenes and their corresponding CpCo complexes The experimental data are for the silylated

derivatives shown The NICS data are for the parent systems interpretation The data presented in Chapter 4 confirm the conclusions of this section While not reflective of ring current effects the values of the 13C chemical shifts for the linear phenylene(CpCo)complexes do provide some insight into the nature of the

- 30 -

σ-framework Comparing complex 19 with parent ligand 60 one observes two general phenomena (Figure 28) The most apparent is the upfield values for the cobalt-bound cyclobutadiene carbons (~74ndash78 ppm) in 19 arising from the local anisotropic shielding effect of the metal (vide supra) Secondly the carbon atoms in the four-membered ring not bound to the metal exhibit large deshielded values (144ndash149 ppm) This effect also seen in ligand 60 arises from the rehybridization6 of the cyclobutadiene sp2 orbitals and is observed in all phenylene topologies A comparison of the 13C-NMR data for the linear [3]- [4]- and [5]phenylene(CpCo)complexes with their respective parent ligands is given in Chapter 4

Figure 28

13C-NMR data for complex 19 and parent silylated ligand 60 Values are in ppm 24 Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift How does the CpCo moiety migrate from one cyclobutadiene unit to the next Two extreme alternatives present themselves a least-motion movement across the intervening arene unit or a more circuitous pathway along the periphery The latter is prevalent in other computed haptotropic shifts56-57 in particular those occurring in (arene)Cr(CO)3 complexes all of which choose peripheral trails56 In these the metal typically moves straight to the edge to adopt an η4 (often described as η1) trimethylenemethane-like transition state on the way to a neighboring ring as illustrated for the η6-η6 hopping in naphthaleneCr(CO)3 summarized in Scheme 218 More relevant is the computed course of the η6-η6 interconversion of (biphenylene)Cr(CO)3 (Scheme 219)57 The metal slides from the (near)center of one benzene ring to the quaternary (four-membered) ring carbon to reach a distorted trimethylenemethane maximum and then proceeds to the edge of the bridging cyclobutadiene bond This species represents a minimum on the potential energy curve and adopts an η2-like complexed cyclobutadiene topology (ldquoquasi-η4rdquo) from which it continues by the microscopic reverse on to the other benzene nucleus The relevance of these findings with respect to the intercyclobutadiene hopping of CpCo along the phenylene frame was not clear at the outset of the work described in this section The CpCo fragment has a different electronic requirement from Cr(CO)3 and interring migration in arenes (and related systems) involves aromatic electron counts of all intervening circuits

Scheme 218 Migration of Cr(CO)3 Across Naphthalene

- 31 -

Scheme 219 Migration of Cr(CO)3 Across Biphenylene

DFT calculations were carried out in collaboration with Professor Thomas Albright at the University of Houston In these studies using B3LYP 3-21G (carbonhydrogen) and LANL2DZ (cobalt) basis sets the metal fragment was placed 18 Aring above the π system with energy minimizations carried out every 02 Aring along the frame of the parent linear phenylene in question When transition states and local minima were located their structures were refined with the B3LYP 6-31G (hydrogen) 6-113G (carbon) and LANL2DZ (with inclusion of cobalt f-orbitals) basis sets More computational details are given in Chapter 4 The resulting potential energy surface for the thermal rearrangement in the parent linear [3]phenylene(CpCo)system is shown in Figure 29 Figure 210 contains enlarged images of the transition states and intermediate structures The haptotropic shift begins with the (η4-cyclobutadiene)CpCo global minimum (labeled ground state GS) assigned a relative value of 000 kcalmol An η2-cyclobutadiene transition state (TS 1) 269 kcalmol higher in energy than GS is passed before reaching a local minimum (LM) that lies 109 kcalmol above GS LM features CpCo coordinated unsymmetrically η4 to the central benzene ring thus avoiding an unstable 20 electron η6-benzene configuration (not shown) which when explicitly calculated proved to lie 36 kcalmol above LM From LM a symmetry-related second η4 structure is reached via an η3-benzene transition state (TS 2 barrier 14 kcalmol) that symmetrizes the ldquoleftrdquo with the ldquorightrdquo half of the molecule LM is 249 kcalmol higher in energy than GS The shift is completed through the reverse of the initial two movements through LM and TS 1 on the other side of the ligand to reach the second cyclobutadiene ring Thus as for Cr(CO)3 (Scheme 219) CpCo migrates along the edge of the linear phenylene but because of its differing electronic needs through distinctly different intermediates and transition states Most obvious is the internal η2-cyclobutadiene TS 1 which for Cr changes to a peripheral η2-intermediate The calculated rate determining barrier of 269 kcalmol (GS to TS 1) is slightly higher than that measured for the reversal of 53 to 52 (~23 kcalmol) Part of this discrepancy may be due to ground state activation of 53 which is ~2 kcalmol less stable than 52 The LM structure has some resemblance to the isolated η4-CpCo angular [3]phenylene 23 (Section 12) Its location in an energetic well of ~14ndash16 kcalmol (TS 1 and TS 2) suggested that it may be observable at low temperature This investigation is detailed in Section 25

- 32 -

Figure 29 Calculated potential energy profile for the thermal η4η4 haptotropic shift in linear [3]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

0

5

10

15

20

25

30

1 2 3 4Reaction Path

Co

Co

C o

C o

GS η

4

LM η

4

TS1 η

2

TS 2 η

3

00

269

109

249

Key - Global MinimumGround State (GS)- Local Minimum (LM)

- Transition State (TS)

122

3 34 4

- 33 -

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 34 -

(d) Transition state 2 η3-benzene (249 kcalmol)

Figure 210 Optimized structures and relative energies for the linear [3]phenylene(CpCo) haptotropic shift Carbon atoms are shaded grey hydrogens light grey and cobalt blue Bond

lengths are in Aring The potential energy profile for the thermal shift in the linear [5]phenylene(CpCo) system was calculated in the same manner and is shown in Figure 211 Images of the intermediates and transition states are depicted in Figure 212 Placing the metal fragment on the inner cyclobutadiene ring resulted in the lowest energy structure and was therefore set as the global minimum (GS) Two distinct haptotropic migrations inner-to-inner and inner-to-outer cyclobutadiene are now possible (Section 21) Beginning at GS the metal can proceed in the direction of TS 2 or TS 3 respectively both of which are η2 with similar barrier heights (~36 kcalmol) The former pathway is degenerate and continues from TS 2 to η4-LM 1 and then via η3 central benzene TS 1 to the symmetry related corresponding LM 1 TS 2 and finally GS involving the opposite inner four-membered ring The rate determining barrier for this process is 359 kcalmol clearly too high to be measurable by NMR techniques as found for 212838 Interior-to-exterior shifting of the cobalt continues from TS 3 on to η4-benzene LM 2 The η3-TS 3 is traversed before the second η4η2

sequence (LM3 and TS 5 respectively) ultimately leading to LM 4 which is the outer

- 35 -

cyclobutadiene coordinated structure and represents the photoisomeric species observed experimentally in Scheme 23 The computed rate-determining barrier (TS 3) of 263 kcalmol for the reverse reaction of LM 4 to GS is close to the experimentally measured values of 256ndash276 kcalmol for the derivatives in Table 21

Figure 211 Calculated potential energy profile for the η4η4 haptotropic shift in linear [5]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

40

Reaction Path

263

0

5

10

15

20

25

30

35

C o

C o

C o

C o

Co

Co Co

C o

C o Co 360 370

359 357

367

97

203 190 196

1 2 3 4 5 6 7 8 9 10

TS 1 η

3

LM 1 η

4

TS 2 η

2

GS η

4 00

TS 3 η

2 TS 4 η

3 TS 5

η2

LM 2 η

4 LM 3 η

4

LM 4 η

4

Key- Global MinimumGround State (GS)

- Local Minimum (LM)

- Transition State (TS)

- 36 -

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 37 -

(d) Transition state 4 η3-benzene (367 kcalmol)

(e) Local minimum 3 η4-benzene (190 kcalmol)

- 38 -

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 39 -

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

(i) Local minimum 1 η4-benzene (190 kcalmol)

- 40 -

(j) Transition state 1 η3-cyclobutadiene (356 kcalmol)

Figure 212 Optimized structures and relative energies for the linear [5]phenylene(CpCo) haptotropic shift Structures for the inner-to-outer cyclobutadiene migration are given by (a)ndash(g)

Species (h)ndash(j) are involved in the interior-to-interior four-membered ring pathway Carbon atoms are shaded grey hydrogen atoms light grey and cobalt blue Bond lengths are in Aring

Why does CpCo prefer complexation to the internal cyclobutadiene that is GS (as represented by 21 and 42) over LM 4 (as represented by 44 and 45) Calculations show that the energies required to distort linear [5]phenylene to the geometries found in

- 41 -

the complexed isomers are very similar (16 versus 14 kcalmol) Hence the answer must rest on electronic grounds Indeed extended Huumlckel calculations reveal that the overlap populations between the frontier orbitals on the CpCo fragment and the HOMO and the LUMO of the π system are greater for GS (00793 and 00745 respectively) than for LM 4 (00556 and 00517 respectively) A didactically more instructive valence bond view recognizes that metalloaromatization of the inside four-membered ring allows the formulation of more resonance forms that avoid antiaromatic cyclobutadiene circuits A full list of these resonance forms as well as details of the EHMO calculations are given in Chapter 4 25 Low Temperature Photochemical Studies of the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes Of the various participating species in the mechanism for intercyclobutadiene migration (Section 24) specific attention was focused on the η4-benzene intermediates that occur in both the linear [3]- and [5]phenylene haptotropic shifts These structures are energetic local minima on the reaction profiles for both systems and were of considerable intrinsic interest not only as reactive intermediates in this manifold but also because of their relationship to the isolable angular [3]phenylene(CpCo) complex 2329 (Figure 213) Figure 213 (a) Calculated structure for the η4-benzene linear [3]phenylene(CpCo)intermediate

in the haptotropic migration (b) Crystal structure of η4 angular [3]phenylene (CpCo) 23

While rare a handful of other η4-benzene-metal complexes have been isolated (Figure 214) For example two related iridium based systems benzene(CpIr) 6658 and benzene triphos(Ir) 6759 are known As expected ligation causes significant shielding of the hydrogens in the η4 portion of the ligand especially the terminal positions The η4 intermediates in the haptotropic shift are situated in wells on the potential energy surface that are ~17 kcalmol deep for the linear [5]- and ~15 kcalmol for the linear [3]phenylene complexes These values are large enough that such species might be observable by NMR spectroscopy if irradiation of the starting materials were performed at low temperature and if the excited state would relax selectively to these intermediates As a suitable candidate with which to explore this possibility the partly symmetric tetrasilyl complex 19 was chosen The generation of anticipated desymmetrized 68 would be readily detected by the appearance of 11 new singlets in the 1H- and 23 new peaks in the 13C-NMR spectra (Scheme 220)

(a) (b)

- 42 -

Figure 214 Selected relevant examples of isolated η4-benzene complexes and their proton NMR chemical shifts (ppm)

Scheme 220 Low Temperature Irradiation Experiment Designed to Generate η4-Benzene Intermediate 68

Construction of a satisfactory setup to allow for the planned low temperature irradiation was not trivial An optimal experimental configuration however was devised utilizing three pieces of equipment each of which is shown in Figure 215 The first was a custom-made Pyrex Dewar flask small enough to adequately contain an NMR tube Cooling was achieved by means of a Neslab refrigerated circulating bath Thirdly a Rayonet Photochemical Reactor was used as the light source The sample was first placed inside of the Dewar flask and cooled to the required temperature inside of the Rayonet Once cold irradiation was carried out for the desired length of time When complete the sample was transported cold to the NMR laboratory and very quickly placed inside of a pre-cooled NMR probe for analysis A solution of complex 19 was irradiated at ndash65 degC as described and its 1H-NMR spectrum recorded at ndash30 degC revealing a dramatic change The signals for 19 had almost entirely vanished and a set of new peaks appeared The new aromatic resonances were comprised of two sharp singlets at δ = 708 and 644 ppm and a broad singlet at δ = 558 ppm all of which integrated for 2 hydrogens each Another broad

649

586

316

H H

Co544

66 67 23

Ir

P(Ph2)P(Ph2) P(Ph2)

H

H

H

625

594

350

Ir

H

H

H

- 43 -

Figure 215 Cold irradiation experimental setup consisting of (a) Pyrex Dewar flask (b)

refrigerated circulating bath (c) Rayonet Photochemical Reactor with Pyrex Dewar vessel placed inside

(a) η

4 (b) η

4 (c) η

4

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

New peaks

L L

- 44 -

Figure 216 Stacked plot of the aromatic 1H-NMR spectral region recorded after the cold irradiation of 19 in toluene-d8 Peaks for 19 are indicated by blue new peaks by red arrows

Impurities are marked with and traces of free ligand 60 with L The scale is in ppm

singlet at δ = 398 ppm (5 H) was assigned to a new Cp group (Figure 217) and two new TMS singlets (9 H each not shown) were also present The new broad Cp absorption displayed peculiar behavior gradually moving to higher field (∆δ ~ 08 ppm for Cp-H) on warming from ndash30 degC to 10 degC (Figure 217) The broadened singlet at δ = 558 ppm showed similar albeit much attenuated behavior At room temperature all new peaks had disappeared leading to regeneration of the original spectrum of 19

Figure 217 Stacked plot of the Cp spectral region in the cold irradiation of 19 in toluene-d8 Peaks for molecule 19 are indicated by blue the new peaks by red arrows The scale is in ppm

In addition to these NMR observations a remarkable change in color from the redmaroon of 19 to olive green took place during the course of this experiment (Figure 218) Indeed the UV-Vis spectrum of the low temperature species is strikingly different from that of 19 showing a large broad absorbance band centered in the visible region

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

19

THF

- 45 -

Figure 218 Color change during the low temperature irradiation of 19 (a) Before irradiation (b) After irradiation

Complex 19

Low Temperature Species

0

02

04

06

08

1

12

14

16

18

2

400 430 460 490 520 550 580 610 640 670 700

Wavelength (nm)

Ab

sorb

an

ce

Figure 219 UV-Vis spectra (toluene) of 19 (at rt) shown in blue and the new compound (at ~

ndash30 degC) shown in red

at 654 nm (Figure 219) Warming the sample to room temperature restored its original red color While the observation of a new species was gratifying the NMR data posed a puzzle as they were clearly incompatible with (a static) structure 68 Instead they pointed to a molecule exhibiting mirror (or ldquotop-downrdquo) symmetry along the long molecular axis as in 19 itself The two most obvious candidates 69 and 70 (Figure

(a) η

4 (b) η

4

- 46 -

220) were ruled out as the first could not be found during the computations underlying Figure 29 and the second actually constitutes the transition state TS 1 for the thermal reverse process

Figure 220 Possible (but unlikely) structures of correct symmetry for the low temperature

photoisomer of 19 In the hope to shed further light on the nature of purported 68 low temperature 13C in conjunction with 2-D NMR (HSQC HMBC) experiments were carried out These data led to the tentative assignments shown in Figure 221 Assuming the presence of top-down symmetry as surmised by the proton spectra one would have expected to observe nine phenylene carbon signals The actual spectrum however contains only six peaks The Cp line was broadened to the point of being barely visible and no crosspeaks for the absorption at δ = 556 ppm were seen by 2-D NMR spectroscopy

Figure 221 Partial assignments of 1H-(italicized) and 13C-NMR signals of 68 The ldquotop-downrdquo plane of symmetry is indicated by the dashed purple line HMBC δ = 643 ppm correlates with δ = 1461 and 1521 ppm δ = 708 ppm correlates with δ = 1477 and 1508 ppm δ = 033 ppm

correlates with δ = 1477 ppm and δ = 036 ppm correlates with δ = 1461 ppm HSQC δ = 643 ppm correlates with δ = 1121 ppm δ = 708 ppm correlates with δ = 1227 ppm and δ = 398

ppm correlates with δ = 85 ppm The connectivity of the CpCo to the central ring is left intentionally unspecified and the choice of positioning it to the left of the center hydrogens (blue)

SiMe3

SiMe3

H

Me3Si

Me3Si

H

Co

398 (br)

HH

1461

~85 (br)

708

H

556 (br)1508

= Unobserved 13C signals

H

H

Mirrorplane

6431477 1521

033036

11211227

- 47 -

arbitrary Similarly the assignments of the groups of ldquoleftrdquo and ldquorightrdquo benzene signals are tentative and might be inverted The carbons marked could not be observed

It is thus clear that we are dealing with an unusual species and if it is 68 the molecule must be partly (but not completely) fluxional around the central ring Returning to the computed energy profile in Figure 29 one notes that central η4η4-benzene fluxionality via TS 2 with a barrier of 140 kcalmol is presaged This process which causes ldquoleftrdquo-ldquorightrdquo but not ldquotoprdquo-ldquobottomrdquo symmetrization is unlikely to be responsible for the above data as it should have given rise to two 1H-NMR singlets for the central hydrogens However considering the expected relative closeness in the respective chemical shifts of the anticipated signals (see Figure 214) accidental isochronism could not be ruled out Consequently low temperature irradiation experiments were executed with 52 in which the ldquoleftrdquo-ldquorightrdquo option of symmetrization was obviated by the substitution pattern while leaving the ldquotoprdquo-ldquobottomrdquo option intact (Scheme 221) As Scheme 221 Low Temperature Irradiation of 52 and Possible Pathways for Fluxionality of

Intermediate 71

indicated in color the latter would provide a diagnostically simple proton spectrum of only four phenylene signals The former on the other hand should show eight such peaks A potential complication of this experiment was the possibility of two regioisomeric (and non-interconverting) cobalt species located on either side of the central six-membered ring (Scheme 222) In the event the spectra shown in Figure 222 were obtained At ndash60 degC in

HH

CoTMS

TMS

CoTMS

TMS

TMS

TMS

Co

TMS

TMS

CoTMS

TMS

Co

TMS

TMS

Co

Top-bottom

cold hν ∆

Lef t-right

52 53

∆

71

or

H

HH

H

H H

H HH

HH H H

H

- 48 -

addition to unreacted 52 and photoisomer 53 a new species formed the spectral features of which implicate 71 as a ldquotop-bottomrdquo symmetrizing species Specifically the

Scheme 222 The Two Possible Regioisomers of 71 ldquoLeftrdquo and ldquoRightrdquo

71

52

53 53

53

52

TMS

TMS

Co

TMS

TMS

Co

TMS

TMS

Co

71

TMS

TMS

Co

or

Right Lef t

ndash60 degC

ndash50 degC

ndash40 degC

ndash30 degC

53

- 49 -

Figure 222 Stacked plot of the aromatic spectral region in the cold irradiation of 52 in toluene-d8 Peaks for molecule 52 are marked by blue arrows 53 in red and 71 in green Trace amounts

of free ligand bis(trimethylsilyl) linear [3]phenylene] 46 are denoted with L The scale is in ppm

unsubstituted benzene terminus hydrogens exhibit an AArsquoBBrsquo pattern at δ = 647 ppm which integrate for 4 hydrogens The central ring hydrogens appear as a broad singlet at δ = 557 ppm (2H) and the silylated terminus as a singlet at δ = 632 ppm (2H) Warming the reaction mixture to 10 degC led to the gradual disappearance of 71 with a concomitant increase of the signals assigned to 52 and 53 This experiment confirms the conclusions drawn as a result of the low temperature irradiation of 19 namely that a ldquotop-bottomrdquo symmetrizing species is generated Remarkably in view of the possibility of two regioisomers (Scheme 222) only one set of peaks is observed indicating that the excited state of 53 relaxes to settle on only one side of the central ring Which side is a matter of speculation Figure 223 compares the 1H chemical shifts of 71 with those of 68 and for calibration 52 53 and free ligands 46 and 60 For the first pair it is clear that the two species are very similar with almost identical chemical shifts of the relevant hydrogens taking into account the considerable deshielding effect of TMS substitution on the unsubstituted terminus in 73 (~07 ppm cf 52 vs 53 46 vs 60) Arguably placing the CpCo moiety to the ldquoleftrdquo as depicted in 68 and 71 aromatizes the proximal benzene by η2-complexation of the adjacent four-membered ring leaving considerable benzocyclobutadiene character on the ldquorightrdquo consistent with the associated chemical shifts

- 50 -

CoTMS

TMS796675674

678

CoTMS

TMS747683724

662

Co

TMS

TMS

52

71

53

424

642

557 632652

436 444

Co

TMS

TMS

68

398

556 643708

TMSTMS

TMS

TMS684607619

645

46

assignmenttentative

TMS

TMS

TMS

TMS623 685

60

TMS

TMS

TMS

TMS

Co

691 795745

19

441

Figure 223 1H-NMR chemical shift comparison of 68 and 71 with other relevant species A plot of the changes in concentration of 52 53 and 71 with temperature is shown in Figure 224 Within (the considerable) error and considering the unusual magnetic behavior of 71 (vide infra) it appears that the latter converts mainly to 52 in the temperature regime in which 53 is stable with respect to its thermal reverse to 52 This observation may be interpreted as indicating a lower barrier for Co migration from the center ring to the more stable cyclobutadiene haptomer

- 51 -

0

1

2

3

4

5

6

7

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Inte

gra

tio

n v

s I

nte

ra

l S

tan

da

rd

52

53

71

Figure 224 Plot of the concentration changes of 52 53 and 71 with temperature measured by the relative integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively

The ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100)

Another plot this one showing the ratios of 52 53 and 71 with respect to each other is given in Figure 225 The disappearance of 71 with rising temperature is illustrated by the increase in the ratios of 5271 and 5371 As indicated by the steep slopes the conversion of 71 into 52 and 53 is particularly fast between ndash10 and 0 degC That complex 52 is preferentially formed is again confirmed by the escalating 5253 ratio While these data do not provide a definitive answer for the location of the CpCo they are consistent with the plots shown in Figure 224 and the above discussions

- 52 -

0

1

2

3

4

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Rel

ati

ve

Inte

gra

tio

n

5271

5371

5253

Figure 225 Plot of the ratios of 52 53 and 71 against each other with temperature measured by the integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively The

ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100) Having established the topological aspects of 68 and 71 attention was turned to their peculiar NMR characteristics in the vicinity of the metal ie the broad peaks for the central hydrogens and the CpHs the broad Cp-carbon line the inability to observe 13C signals for the central benzene ring and the temperature dependent drifting of (particularly) the Cp absorption A trivial (and ultimately unsatisfying) explanation for at least peak broadening was the presence of trace paramagnetic metallic impurities60 that might have been generated during the irradiation process Spin exchange preferentially Co-based might affect the center atoms in 68 and 71 more than the remainder of the molecule although it should also cause line broadening in the isomers 19 and 52 and 53 respectively Experimentally the presence of such species was made unlikely by executing the cold irradiation experiment of 19 in the presence of the radical trap 13-cyclohexadiene which produced spectra identical to those described earlier An attractive alternative that might explain the data and in addition provide a mechanism for ldquotop-downrdquo exchange is of the intervention of triplet state cobalt species The ability of metals to change their electronic spin state and the consequences of this phenomenon on organometallic structure and reactivity are well documented61

18-Electron CpCo complexes are ground state singlets but their 16-electron counterparts accessed typically by ligand dissociation have more stable triplet configurations62 A number of CpCo and related Co species have also been reported in

- 53 -

which singlets are in thermal equilibrium with paramagnetic triplets by intersystem crossing63 Such complexes display spectral behavior very similar to that seen for 68 and 71 For example 7263b exists as a mixed spin state system in which the singlet predominates at room temperature in solution (Figure 226) On heating the triplet becomes increasingly populated shifting and broadening its NMR signals Cooling the solution back to room temperature reverses these spectral changes In addition to complexes of cobalt analogous observations have been reported for other metals such those based on hafnium64 copper65 ruthenium66 and tungsten67

Figure 226 Temperature dependent chemical shifts in CpCo derivative 72 in toluene-d8

(marked as S on the plot) The scale is in ppm

Consideration of these examples would then suggest that 6871 undergo ldquotop-downrdquo equilibration through a triplet 16-electron intermediate or that 6871 themselves are triplets or have thermally accessible triplet states from which fluxionality might occur Since the relaxation times (T1) of paramagnetic systems60a are much shorter compared to their diamagnetic counterparts measurement of this property was thought to be informative The T1 values for the proton in 68 were determined via a standard inversion recovery experiment44 and are given in Table 24 (cf Figure 220) in comparison to p-terphenyl60b

Co

CoPMe3

72

- 54 -

Table 24 1H-NMR Relaxation Times in Intermediate 68 at ndash30 degC

Resonance (ppm) T1(s) 711 2309 646 0997 556 005 398 0108

In consonance with the associated line broadening the relaxation times of the Cp

(δ = 398 ppm 0108 s) and central ring hydrogens (556 ppm 005 s) are much smaller than those of the remaining phenylene ligand (711 and 646 ppm 2309 and 0997 s respectively) the latter in turn comparing well with the values in p-terphenyl With this corroborative evidence in hand the question whether the species is itself a triplet or is in thermal equilibrium with such was addressed The answer can be obtained by using a Curie-like graph68 in which chemical shifts are plotted as a function of temperature65 A linear relationship corresponds to the presence of a triplet compound while curved behavior is indicative of a singlet-triplet equilibrium Plotting the chemical shifts of the Cp hydrogen of 68 and 71 against the inverse of temperature (Figure 227) gave distinctly curved lines supporting the notion that these species are in thermal equilibrium with their triplets The exact nature of these species however remains to be determined

156

395404

345

p-Terphenyl

- 55 -

3

32

34

36

38

4

42

44

46

00036 00038 0004 00042 00044 00046 00048

1T (K -1

)

Ch

em

ica

l S

hif

t (p

pm

)

71

68

Figure 227 Plot of the Cp chemical shift (toluene-d8) of 68 and 71 versus the inverse of temperature

DFT calculations have commenced in an attempt to find a plausible structure for such a triplet cobalt species and with it possibly arrive at a mechanism for the fluxional behavior of 68 and 71 These studies are being carried out in collaboration with Professors Tom Albright of the University of Houston and Vincent Gandon of the Universiteacute Paris-Sud 11 Preliminary results at the B3LYP6-31G(dp) and BP866-31G(dp) levels suggest the η2-cyclobutadiene structure depicted in Figure 228 It is apparent that this species corresponds topologically to singlet TS 1 in Figure 29 and 70 in Figure 220 endowed with the symmetrical requirements dictated by the experiments

- 56 -

Figure 228 Calculated structure of a triplet η2-cyclobutadiene linear [3]phenylene(CpCo)

One can therefore envision fluxionality between the two ldquotoprdquo and ldquodownrdquo η4-benzene structures via the intermediacy of a triplet η2-cyclobutadiene (Scheme 223) Further Scheme 223 Conversion of ldquoTop-Downrdquo η4-Haptomers of 68 Via a Triplet η2-Cyclobutadiene

Intermediate

computations are required to pinpoint the minimum energy crossing points between the singlet η4 and triplet η2 structures and to explain why this triplet does not collapse to the CpCo cyclobutadiene isomer This work is in progress 26 Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 All of the linear phenylene(CpCo) complexes mentioned thus far share one common feature a single CpCo unit bound to the phenylene scaffold However since there are one or more additional cyclobutadienoid rings in the series the question arises whether it might be possible to bind more than one metal fragment to the ligand If so what would be the structural consequences Would be there further metalloaromatization Would such systems be capable of light-induced haptotropism and if so how would the metals move relative to the ligand and to each other Finally would such complexes mimic structurally the variety of arrays obtained in the reaction of 29 with Fe2(CO)9 (Scheme 15) Since the linear phenylenes become increasingly more antiaromatic with size the optimal candidates for preparing such multi-metallic systems should be the higher members of the series Indeed evidence for double CpCo attachment was obtained in the form of the minor by-products 73 and 74 (Scheme 224) obtained during the

Scheme 224 Side Products in the Preparation of Linear [4]- and [5]Phenylene(CpCo)

- 57 -

Complexes by Cobalt-Catalyzed Cyclization

preparation of 20 and 21 respectively (Scheme 13) These Diels-Alder type adducts of a third BTMSA molecule to the π-frame can be envisaged to be derived from 75 and 76 respectively in which the six-membered ring flanked by the two CpCo(cyclobutadiene) units would be expected to have an unusual (biradicaloid) electronic structure Evidence for the feasibility of such arrays rests on the unique black-red syn-bis(irontricarbonyl) compound 77 whose structure was determined by X-ray analysis69 With reasonable quantities of 19 in hand the possibility of ligating a second CpCo unit to it was explored This idea was further encouraged by the observation that crude samples of bis(trimethylsilyl) linear [3] phenylene(CpCo) complex 53 contained a very small (3 ) peak at mz = 618 an exact match for the mass of a doubly metallated analog Consequently 19 was treated with one equivalent of CpCo(C2H4)2 in benzene to afford a reddish black solid (Scheme 225) The mass spectrum data exhibited a

Scheme 225 Preparation of Complex 78 from Complex 19

TMS

TMSTMS

TMS

CoCpCo(C2H4)2

22h 70 oC C6H6Linear [3]TMS4(CoCp)2

5619 78

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

74

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

73

TMS

TMS

TMS

TMSCoCpCpCo

76

TMS

TMS

TMS

TMSCoCpCpCo

75

Ph

Ph

Ph

Ph

Fe(CO)3Fe(CO)3

77

- 58 -

molecular ion peak at mz 762 corresponding to 19(CpCo)2 The 1H-NMR spectrum (acetone-d6) revealed four sharp singlets integrating in the ratio 410236 indicative of a highly symmetrical structure The chemical shift of the benzene termini (736 ppm) suggested that these rings have significant aromatic character and is similar to the value of 745 ppm seen for the hydrogen positioned farthest away from the CpCo in 19 (Figure 27) Similarly the 13C signals of the terminal rings in 78 (1505 1454 and 1258 ppm) are analogous to those from the corresponding terminal ring in 19 (1484 1433 and 1256 ppm Figure 28) Detailed analysis of 78 with two-dimensional NMR techniques (HSQC and HMBC) allowed for a complete assignment of all peaks in the 1H and 13C spectra (Figure 229) The strongly shielded (relative to the free ligand) proton (481 ppm) and carbon (537 and 571 ppm) resonances assigned to the central benzene ring clearly showed that both cobalt fragments are coordinated to the phenylene ligand at this position Interestingly these data bear a very close resemblance to those of the corresponding diiron complex 31 (Scheme 15) and are compared in Figure 229 Its central 13C resonances (688 and 582 ppm) are shifted upfield in a manner akin to 78 although not quite as much reflecting the increased electron withdrawing ability of the Fe(CO)3 group relative to CpCo70 Complex 31 like 78 exhibits aromatized terminal benzene rings as indicated by its 1H (750 ppm) and 13C (1484 1446 and 1258 ppm) chemical shifts These spectral similarities make it likely that 78 and 31 are isostructural The only structural ambiguity pertains to the orientation of the two metal fragments with respect to the π ligand a problem that had been left undecided in the assignment of structure 31 ie 31a (syn) versus b (anti Scheme 15)27 These options for 78 are

- 59 -

CpCoTMSTMS

TMS TMS

H H039 (36)

537 1258822

270

1454571

1505

481 (2) 736 (4)489 (10)

TMS TMS

TMSTMS

H

(OC)3Fe

(OC)3Fe

CpCo

78

31a

750 (4)553 (2)

036 (36)H

220

1446

1258

1484

688582

2128

Figure 229 Comparison of 1H- and 13C-NMR assignments (ppm) for molecules 78 (acetone-d6) and 31 (1H acetone-d6

13C CDCl3) Proton chemical shifts are in red and carbon in blue Integrations for the proton resonances are in green HSQC for 78 δ = 039 ppm correlates with δ = 270 ppm δ = 481 ppm correlates with δ = 537 ppm δ = 489 ppm correlates with δ = 822 δ

= 736 ppm correlates with δ = 1258 ppm HMBC for 78 δ = 036 ppm correlates with δ = 1454 ppm δ = 481 ppm correlates with δ = 571 and 1505 ppm δ = 736 ppm correlates with δ = 571 1454 and 1505 ppm The placement of the cobalt atoms in 78 is tentative (see Figure

229)

Figure 230 Possible structures for 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

- 60 -

shown in Figure 230) Both equally exotic options are precedented in the literature and corroborated by X-ray structural analyses (Figure 231)71

Figure 231 Illustrative examples of complexes with two metal fragments coordinated to the same benzene ring

Bis(CpFe) complex 7972 and its rhodium analog 8073 contain [M2(syn-micro-arene)] units in which the metals are linked58 Molecule 79 consists of two CpFe units coordinated η4 to the boat-shaped benzene ring sharing ligating carbon atoms In contrast the CpRh fragments in 80 are bound in an allyl η3 manner and the arene also adopts a boat conformation On the other hand bis[tris(tert-butyl)]toluene(CpCo) complex 8174 and the related system 8275 both exhibit [M2(anti-micro-arene)] units in which η4 coordination between the benzene ring and each of the metal fragments takes place Here the metals share carbon atoms but now involving a sandwiched ligand The arene in 81 retains a planar aromatic geometry while the benzene moiety in 82 is bent into a highly distorted chair conformation Unfortunately model structures 79ndash82 do not exhibit diagnostic NMR properties that would provide a clear distinction between synanti and planarnon-planar topologies For example the 1H-NMR peaks for the toluene ligand in anti-complex 81 range from 400ndash380 ppm74 whereas the signals for the benzene moiety in syn-bis(CpRh) 80 appear at 400ndash330 ppm73 The 13C data are similarly inconclusive as illustrated by comparison of 78 (562ndash531 ppm for the benzene ring) with 79 (648ndash525 ppm)72b An interesting property of these bis(metal) arene complexes is fluxionality of the metal fragments by haptotropic shifts along the periphery of the aromatic ring as depicted in Scheme 226 In complex 79 the hexamethylbenzene ligand (bound η4η4

in the solid state) displays a single arene resonance at 588 ppm in its room temperature carbon NMR spectrum Cooling to ndash90 degC however produces two distinct arene peaks at 525 and 648 ppm (for the shared and single-metal-bound carbons respectively as shown in 79a in Scheme 227) Fluxionality was postulated to proceed through an η3η3 intermediate (79b) that is structurally similar to Rh complex 80 which is itself a fluxional species

Scheme 226 Examples of Fluxional Processes in Dinuclear Arene Complexes 79 and 80

82 81

80 (R = CH3)

79

- 61 -

Anti-bis(β-diiminate)Rh complex 83 shows similar mobility (Scheme 226)76 A mechanism for η4η4 migration of the anti-metal fragments was proposed using the lowest energy species found by DFT calculations In these compounds the anti-metal fragments convert between η4η4 (83a 83c 83e) structures by passing through η3η3

(83b) and η4η2 (83d) transition states The energy barrier for η4η4 migration in 83 was experimentally determined to be 6 kcalmol This value is in line with other experimentally measured syn and anti dinuclear ring slippage processes which are typically le ~10 kcalmol71-75 The possibility of fluxionality in 78 might be observable if asymmetric configurations such as 78c and 78d (Figure 231) represent the lowest energy forms since they entail NMR observable desymmmetrization of the ligand Unfortunately cooling 78 in the NMR probe to temperatures as low as ndash80 degC in toluene-d8 did not reveal any signs of signal decoalescence

- 62 -

Figure 232 Possible lowest energy forms of complex 78

Hoping that further light could be shed on the disposition of the CpCo moieties in 78 by chemical transformations a brief investigation of its reactivity was undertaken For example bis(metal) arene complexes have been shown to readily undergo arene exchange reactions71 In complex 81 for example the toluene ligand is displaced by benzene at room temperature74 However heating a sample of 78 to 120 degC in toluene-d8 did not lead to any changes in the NMR spectra Turning to potential photochemical activation 78 was irradiated at various wavelengths (300ndash365 nm) These conditions as well as ambient sunlight did not cause any changes in its 1H-NMR spectrum further documenting 78 as a rather inert species X-ray crystallographic analysis would appear to be the only method of resolving the identity of complex 78 Producing suitable crystals of this molecule however has proven extremely difficult and will be the subject of future investigations 27 Summary and Outlook The work presented in this chapter published as a communication77 has detailed the first examples of η4η4 intercyclobutadiene migration and detailed mechanistic studies of this unprecedented reaction The haptotropic shift was found to be an intramolecular process with the CpCo fragment undergoing various changes in hapticity for the thermal isomerization Low temperature photolytic studies have revealed the existence of a thermally unstable intermediate species the exact structure of which is uncertain These results point to what appear to be significant differences between the photo- and thermal haptotropic pathways Further work both experimental and computational will be required to elucidate the details of the photochemical reaction In addition to the studies of linear phenylene(CpCo) haptotropism a hitherto unknown complex containing two CpCo fragments bound to linear [3]phenylene was prepared and scrutinized in preliminary form Despite extensive characterization the structure of this complex with respect to the position of the metal centers remains elusive Future work will focus on the acquisition of a crystal structure

- 63 -

Chapter 3

Nickel-Catalyzed Insertion Reactions for the Preparation of [N]Phenacene Derivatives

31 Introduction Transformations involving metal insertion into the four-membered ring of the [N]phenylenes as discussed in Section 12 represent a significant mode of reactivity with a high potential for practical synthetic utility One specific application of this chemistry is the synthesis of the phenanthrene moiety via tandem metal insertion and alkyne cycloaddition to the four-membered ring (Scheme 31) Such a methodology Scheme 31 Potential Preparation of the Phenanthrene Group from the Alkyne Cycloaddition

with Biphenylene would be valuable for the preparation of PAHs possessing phenanthrene subunits but has remained fairly unexplored Only a few examples demonstrating this transformation have been detailed previously for biphenylene (7) (Scheme 32)

Scheme 32 Metal Catalyzed Alkyne Cycloaddition Reactions with Biphenylene

The first report of this process is by Eisch in 198533a who treated biphenylene with Ni(PEt3)4 and diphenylacetylene to produce 910-diphenylphenanthrene 84 Since then a number of metals have been shown to mediate this process19 Ni systems being most relevant to this chapter Thus for example 84 can also be made using an N-heterocyclic carbene-based Ni(0) catalyst78 Bis(diisopropylphosphino)ethane Ni(alkyne) species enable similar cycloadditions of fairly hindered (trimethylsilyl)alkynes sometimes involving more complex processes of silyl group migration79 while less hindered substrates lead to 84ndash8680a A mixed phosphinoaminoethane-chelated Ni species proved more reactive enabling cycloaddition of even the encumbered tert-butyl(phenyl)acetylene to furnish the corresponding phenanthrene80b With this background in mind our attention turned to applying this reaction to larger phenylene systems Of the various topologies of phenylenes at our disposal the angular version was

R1 R2

R2R1[M]

[M]

7 R R

R = Ph (84)

R = Me (85)

R = CH2OMe (86)

RR

[Ni]

- 64 -

particularly intriguing as it offered two extreme modes of alkyne addition (Scheme 33) In the first scenario exclusive attack at the outer periphery of the four-membered rings would produce the helical shaped PAHs known as helicenes (Scheme 33a)81

Scheme 33 Alkyne Cycloaddition with Angular Phenylenes to Produce (a) Helicenes or (b) Phenacenes

Reactions occurring only at the interior or ldquobayrdquo region (Scheme 33b) however would afford a class of compounds exhibiting a linear polyphenanthrene motif that are known as [N]phenacenes82 Unselective additions would result in mixed topologies Helicenes and their various derivatives constitute a well studied83 family of molecules and continue to be a popular area of research Phenacenes in contrast have been scrutinized much less in part because only four members of the parent series are known and because for N = 5 and 6 they are extremely insoluble84 Phenacene-based applications have been slow to develop but the first reports of the utilization of these molecules as functional organic materials suggest the beginning of a rich and promising field85 Thus in 2008 [5]phenacene (picene) was demonstrated to behave as stable high performance organic field effect transistor (FET)85b Currently the most common organic polycyclic benzenoid hydrocarbon-based FETs employ acenes which have a polyanthracene structure (Figure 31) The sensitivity

Figure 31 Linearly fused benzene topology of the acenes of these systems to air however has obstructed progress in this area86 For example pentacene a commonly used acene in FETs reacts readily with oxygen to form

+ RR

Helicenes

+ RR

Phenacenesn

R

R R R R

n

R

R

R

(a)

(b)

[N]Acenes

n

- 65 -

pentacenequinone a process that severely reduces device efficiency (Scheme 34)

Scheme 34 Degradation of Pentacene to Pentacenequinone Under Aerobic Conditions

Phenacenes on the other hand are much less prone to such decomposition pathways due to their higher HOMO-LUMO gap thus rendering them less reactive85b86a Their enhanced stability relative to acenes87 makes them better candidates for molecular electronic applications In a second seminal breakthrough [5]phenacene was very recently also found to behave as a superconductor at low temperature when doped with potassium85a This work paves the way for a new class of PAH-based superconducting materials in which phenacenes may play a key role

As this chemistry advances new synthetic methods for preparing derivatives of these molecules will be required in particular those bearing solubilizing andor otherwise functionally useful substituents The most general procedure for synthesizing phenacenes as developed by Mallory88 makes use of oxidative stilbene photocyclizations (Scheme 35)8388 In this transformation irradiation of the stilbene

Scheme 35 Generic Oxidative Stilbene Photocyclization Used to Prepare Phenacenes as Illustrated for Phenanthrene

moiety leads to conrotatory electrocyclic ring closure Trapping of the resulting intermediate with oxidizing reagents such as iodine or oxygen yields the desired phenanthrene subunit The requisite stilbenes are most generally accessible via the Wittig reaction as illustrated in the synthesis of [7]phenacene derivative 87 (Scheme 36) Although the yields for the photocyclization are typically reasonable (60ndash90 )85a the major drawback of this methodology is the numerous steps associated with preparing the functional groups required for the prerequisite Wittig reaction These

- 66 -

transformations serve to decrease the overall yield of the target molecule

Scheme 36 Synthesis of [7]Phenacene 87

While laborious Malloryrsquos method addresses successfully the problem of solubility As alluded to in Section 21 large PAHs become insoluble due to the increased π-π stacking forces that are experienced between aromatic rings The best solubilizing groups for the phenacenes were found to be sterically bulky groups located in the bay regions85a These modifications distort the phenacene framework from planarity thereby disrupting π-stacking and increasing solubility as demonstrated by the tert-butyl [7]phenacene 87 (Figure 32) This approach was applied to systems as large as [11]phenacene the current record in the series85a

Br

CH3t -Bu

1 BuLi2 DMF

Br

CH2

t-Bu

CHO

CH3t-Bu

PPh3

Br

+Wittig

t-Bu t-Bu

Br CH3 1 hν2 I2

t-Bu t -Bu

Br CH3

t-Bu t-Bu

Br H2C PPh3 Br

+

t-Bu t-Bu

OHC CH3

Wittig

t-Bu t-Bu

Br Br 1 hν2 I2

t-Bu t-Bu

Br CH3

t-Bu t -Bu

t-Bu t-Bu

87

1 NBS2 PPh3

- 67 -

Figure 32 Crystal structure of tetrakis(tert-butyl) [7]phenacene 87 Hydrogens are omitted for clarity

To test the viability of angular phenylenes as substrates in Ni catalyzed alkyne cycloadditions the simplest member 22 was chosen raising a number of questions First how many and what kind of products will be formed (AndashE in Scheme 37) Will there be inherent selectivity toward helicene C or phenacene E formation respectively If not can the reaction conditions be modified so as to induce such What will be the limitations with respect to the size of substituents especially in view of the crowded fjord and bay regions of D and E respectively The work presented in this chapter carried out in collaboration with Dr Zhenhua Gu89 explores these questions

Scheme 37 Possible Cycloaddition Products of Angular [3]Phenylene 22

22

[Ni]R R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

A B

C D E

32 Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene

Before embarking on the proposed chemistry the reactivity of 22 in the presence of nickel in the form of Ni(COD)(PMe3)2 in the absence of alkynes was queried Only starting material was recovered and there was no sign of dimerization (or oligomerization) to products of the type shown in Scheme 38 a mode of reactivity

- 68 -

readily attained by biphenylene and substituted derivatives33b

Scheme 38 Attempted Dimerization of Angular [3]Phenylene 22

In contrast exposing diphenylacetylene 88 to Ni(COD)(PMe3)2 and a small excess (109 equivalents) of angular phenylene 22 generated two products in the absence of any other (Figure 39) The first molecule 89 was the result of the cycloaddition of one diphenylacetylene at the bay region and the minor component The major product constituted tetraphenyl [5]phenacene 90 derived from 22 by double bay region attack The structures of both compounds were confirmed by X-ray analysis revealing highly distorted frames89 Scheme 39 Nickel Catalyzed Cycloaddition of Angular [3]Phenylene 22 to Diphenylacetylene

Yields Based on Diphenylacetylene

The outcome of this transformation was gratifying in its seeming simplicity and selectivity Thus it appeared that metal insertion occurred exclusively to bay region bonds heralding the discovery of a new phenacene synthesis The observation of relatively large amounts of 90 could be ascribed to increased reactivity of 89 relative to 22 possibly due to steric activation by the newly introduced bay region phenyl group To test this hypothesis 89 was subjected to the cycloaddition reaction conditions (Scheme 310) Surprisingly not only was this reaction slower than that of 22 but the expected phenacene 90 was only a minor product (6 ) Instead tetraphenylbenzo[c]chrysene 91 a regioisomer of 90 as confirmed by X-ray analysis89

+

+ +

Ni(COD)(PMe3)2

22

- 69 -

was isolated in 74 yield the result of non-bay alkyne cycloaddition to 89 Therefore 89 is not the precursor of 90 Rather there must be separate reaction pathways leading to each respective product

Scheme 310 Cycloaddition Reaction of 89 with Diphenylacetylene 88

A series of semi-quantitative experiments monitored by 1H-NMR spectroscopy was carried out to shed some light on this mechanistic problem First the reaction of angular [3]phenylene 22 with diphenylacetylene 88 in Scheme 39 was addressed Because dinuclear metallic activation of the strained C-C bond in biphenylenes has been implicated in a number of studies19 it was possible that the above mechanistic duality was caused by the presence of catalytic Ni2 species in addition to the ldquoregularrdquo mononuclear alternatives Alternatively double Ni insertion before cycloaddition might be responsible for one product whereas sequential ldquonormalrdquo activation might be the origin of the other Therefore the amount of initial Ni(COD)(PMe3)2 was gradually increased and the effect of this incremental change on rate and product ratios recorded As shown in Table 31 the speed with which 89 and 90 formed was roughly proportional to the amount of metal present while the product ratio stayed unchanged

Table 31 Variation of Catalyst Loading in the Reaction of Phenylene 22 with Diphenylacetylene 88 Reactions Were Carried Out with Equimolar Amounts of 22 and 88 in

THF-d8 at 40 degC

Run Ni(COD)(PMe3)2

(mol) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

Ratio of 8990

1 50 32 times 10ndash4 031 times 10ndash4 103 2 35 20 times 10ndash4 022 times 10ndash4 91 3 7 064 times 10ndash4 0064 times 10ndash4 100

Next the amount of diphenylacetylene 88 was gradually increased from 1 to 4 equivalents (Table 32) The outcome of this series of experiments was counterintuitive as it led to a larger preference for the production of monoadduct 89 suggesting a mechanistic bifurcation in which whatever Ni species is responsible for the eventual formation of 90 is sequestered by external ligand (in this case 88)

- 70 -

Table 32 Variation of Alkyne Equivalents in the Reaction of 22 (1 equiv) with Diphenylacetylene 88 in the Presence of 50 mol of Ni(COD)(PMe3)2 Experiments Were Run

in THF-d8 at 40 degC

Run 88 (equiv) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

8990

1 10 320 times 10ndash4 031 times 10ndash4 103 2 20 220 times 10ndash4 018 times 10ndash4 122 3 40 220 times 10ndash4 011 times 10ndash4 200

Following the reaction progress by NMR spectroscopy afforded additional insights Thus mixing the ingredients at room temperature left the phenylene component untouched Instead there was a near instantaneous displacement of COD by diphenylacetylene to produce Ni(PhCequivCPh)(PMe3)2 (92) and free COD in addition to the generation of Ni(PMe3)4

90 The speed with which this complex was formed implied that it might be the active catalyst precursor Consistent with this notion higher reaction rates were observed when the reaction in Scheme 38 was carried out with pure 9291 as the catalyst (50 mol) and 05 equivalent of 88 (Table 33 Run 2) In consonance with Table 32 the lesser concentration of available free alkyne increased the relative amount of 90 formed Conversely (Run 3) using Ni(COD)(PMe3)2 with an extra equivalent of PMe3 decreased the rates of formation of 89 and 90 and increased the ratio of 8990 consistent with ligand inhibition of the activation of 92 and the external ligand effect noted in Table 32 Table 33 Variation of Catalyst in the Reaction of 22 with Diphenylacetylene 88 and its Effect

on Reaction Rate Experiments Were Run in THF-d8 at 40 degC with 1 Equivalent of 22

Run Catalyst 88

(equiv)

Rate of formation of 89 (mol

Lmiddoth)

Rate of formation

of 90 (mol Lmiddoth)

8990

1 Ni(COD)(PMe3)2 10 320 times 10ndash4 031 times 10ndash4 103 2 Ni(PhCequivCPh)(PMe3)2 (92)

(05 equivalent) 05 1270 times 10ndash4 210 times 10ndash4 60

3 Ni(COD)(PMe3)2 (05 equivalent) + PMe3 (10 equiv)

10 088 times 10ndash4 005 times 10ndash4 163

Attention was then shifted to the reaction of monoadduct 89 with 88 as in Scheme 310 (Table 34) Here increasing the amount of alkyne and catalyst favors the formation of 91 consistent with an independent pathway At low concentration of alkyne it appears that 89 reenters the manifold of its generation and proceeds on to 90 Indeed following the change in the ratio of 9190 in Run 1 (Table 34) with time reveals a decrease from 47 to the eventual 22 as 88 is depleted

- 71 -

Table 34 Variation of Catalyst Loading and Alkyne Concentration in the Reaction of 90 with Diphenylacetylene 88 Reactions Were Run in THF-d8 at 40 degC

Run 88 (equiv) Ni(COD)(PMe3)2

(mol) 9190

1 10 50 2 2 30 50 15 3 30 10 25

The information obtained from these experiments allowed a narrowing of mechanistic possibilities For example dinuclear Ni activation only one possibility of which is shown in Scheme 311 was rendered unlikely by the absence of any observable changes in product distribution of the reaction in Scheme 39

Scheme 311 Generic Example of a Dual Mechanism Based on Mono- and Dimetallic Phenylene Activation

An alternative mechanism shown in Scheme 312 was in much better agreement with the results of the various control experiments The first step would be displacement of a phosphine in the initially dominant Ni-containing species 92 by angular [3]phenylene 22 inhibited by added PMe3 From 93 oxidative addition can take place to afford metallacycle 94 Why should bay region insertion be favored Arguably the regioselectivity of this step is controlled by the lesser steric hindrance in the resulting arene fragment or relative stabilization of the polarized Ni-C(α-

PhPh

Ph Ph Ph Ph

PhPh

NiL L

Ni(COD)(PMe3)2

NiNiL L L L

PhPh

2

Ph

Ph

Ph Ph Ph Ph Ph Ph

+

+22

89

90

91 90

- 72 -

biphenylene) bond in 94 by the electron withdrawing nature of the neighboring cyclobutadienoid ring This phenomenon in biphenylene is due to the rehybridization of the four-membered ring carbons to adopt relatively larger p character in the strained linkages hence larger s character (ie electron withdrawing) in the remaining bond and manifests itself most clearly in the relative acidity of the α-hydrogens7a This step is followed by migratory insertion and reductive elimination to produce molecule 96 the mechanistic bifurcation point One branch proceeds through presumably ligand-assisted metal dissociation to generate the relatively unreactive free 89 The second entails Ni migration92 and insertion into the bay region of the remaining four-membered ring (97) before the second cycloaddition occurs generating phenacene 90

Scheme 312 Possible Mechanism for the Alkyne Cycloaddition Reaction of Angular [3]Phenylene 22

The regioselective formation of 97 may again be sterically dictated or may involve anchimeric assistance by the bay-region phenyl group as sketched in Scheme 313 specifically 99

Scheme 313 Anchimeric Assistance on Route to [5]Phenacene 90

Ph Ph

PhPhPhPh

Ph

Ph

Ph PhNi

NiMe3P Ph

Ph

Ni

Me3P Ph

Ph

NiPMe3Me3P

Ligand exchangeOxidativeaddition

Migra toryinser tion

Reductiveelimination

Ph

Ph

Me3P

Ni migra tionOxidative addition

22

92

9394

96 89

9097

Ph Ph

Ni

Me3P

Ni(PMe3

Ph

Ph

minusNi(PMe3)

95

- 73 -

This type of metal coordination to the double bond of a proximal arene ligand is common and two examples are provided based on ruthenium94 and molybdenum95 (Figure 33)

Figure 33 Examples of complexes with phenyl groups coordinating to a nearby metal center Turning to the largely selective conversion of 89 to 91 (Scheme 310) requires the postulate of preferential insertion of the metal at the non-bay region and hence a different Ni species from that in 96 possibly a Ni(PMe3)(alkyne) moiety akin to that in 93 ie 100 (Scheme 314) Bay insertion would lead to metallacycle 101 and ultimately molecule 90 The expected large degree of steric repulsion between the phenyl groups in 101 should disfavor this reaction pathway On the other hand non-bay insertion to produce 102 should be relatively less impeded and would furnish 91 Another option for the generation of 90 from 89 would be reentering the pathway described in Scheme 312 facilitated at low concentrations of alkyne consistent with the data in Table 34

Scheme 314 Proposed Mechanism for the Alkyne Cycloaddition Reaction of 89

Ni

PhMe3P

PhPh

(Me3P)Ni

PhPh(Me3P)Ni

Ph

Ph

93 98

99

Ph Ph Ph Ph

90

+

Ph Ph

Ni

Me3P

97

- 74 -

While the above mechanistic perambulations appear plausible it should be stressed that they are speculative and may be restricted to diphenylacetylene 88 as the substrate Thus both 3-hexyne 103 and 14-dimethoxy-2-butyne 106 added to 22 less selectively than 88 to provide only the bay and non-bay monoadducts 104 and 105 and 107 and 108 respectively (Scheme 315)

Scheme 315 Reaction of Angular [3]Phenylene 22 with Other Alkynes

NiMe3P PMe3

Ph Ph+

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph

Ni(PMe)3

PhPh

Ni(PMe3)

Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

92 89

101

90

102

100

91

Ni

Ph Ph

PMe3

+

R

R

THF-d8 40 oCR

R22

Ni(COD)(PMe3)2

R

R

+

R = Et 104

R = CH2OMe 107

R = Et 103

R = CH2OMe 106 R = Et 105

R = CH2OMe 108

11 45 9 68

- 75 -

In view of these uncertainties recourse was taken to DFT computations delineated in the next section 33 Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene DFT studies were carried out in collaboration with Prof Vincent Gandon of the Universiteacute Paris-Sud 11 The B3LYP 6-31G(d) basis set was used for hydrogen and carbon atoms while LANL2DZ was used for nickel Before attempting to model the more complex alkyne cycloaddition reactions in Schemes 38 and 39 the basic Ni-catalyzed addition of the parent acetylene to biphenylene in the presence of PMe3 was studied (Scheme 316) The free energies

Scheme 316 Computational Modeling of Ni-catalyzed Addition of Acetylene to Biphenylene Free Energies (∆G KcalMol) are Relative to 109 Transition State Energies are Absolute Values

for This Step

NiMe3P PMe3

NiMe3P

NiMe3P

Ni

Ni

PMe3

PMe3

+

+ PMe3+

+ PMe3

+ 2 PMe3

+ 2

(00)

(281)(37)

(140)

(12)

NiMe3P PMe3

NiMe3P

NiNiPMe3Ni

PMe3

PMe3NiMe3P

PMe3

(727) (693) (476) (374) (394) (395)

Ni

Me3P

PMe3Ni

Me3P

Ni

Ni

Me3P

PMe3NiMe3P PMe3

(590) (532)

(157) (125) (150)

Most Accessible TS

+

7

114

110

113109

111 112

Ni

Me3P

(253)

Ni

PMe3

(242)

- 76 -

(∆G) of various possible catalyst structures consisting of an assortment of combinations of nickel PMe3 and acetylene as well as those of several possible transition states and the resulting products were calculated As is evident on inspection of the values in the first part of Scheme 316 a number of species were found to be very close in energy making it difficult to pinpoint a specific structure for the initial insertion step Bis(ethyne) nickel complex 109 was established as the lowest energy nickel species and was thus assigned a relative value of 0 kcalmol The most accessible transition state 110 features the oxidative addition of the Ni(PMe3)(C2H2) fragment 114 (+ 14 kcalmol) in which the alkyne is held exo to biphenylene The corresponding endo structure 111 was found to be just slightly higher in energy by 20 kcalmol as was the bisalkyne transition state 112 It is likely that biphenylene-NiL2 complexes (two of which were calculated at relative energies 242 and 253 kcalmol) lie on the way to these maxima93 Metallacycle 113 the structure ensuing from transition state 110 constituted the lowest energy product uphill from the starting 109 by 125 kcalmol but other alternatives are nearly isoenergetic Clearly however attack by Ni(PMe3)2 or Diels-Alder type cycloadditions are not likely From 113 the species proceeds smoothly by alkyne insertion-reductive elimination to the phenanthrene product a cascade associated with a large exergonic driving force Undaunted by the relatively complicated picture that emerged with biphenylene attention was turned to the original object of scrutiny the cycloaddition reaction between angular [3]phenylene 22 and diphenylacetylene 88 to produce [5]phenacene derivative 90 Modeled in the same manner as described above the metal insertion into the four-membered ring of 22 is shown in Scheme 317 The lowest energy nickel species

- 77 -

was found to be diphenylacetylene complex 92 gratifyingly corresponding to experiment and was set to a reference value of 00 kcalmol One notes again however an array of at least 10 species all of which must be in equilibrium in the initial reaction mixture Notably the Ni-π complexes to 22 are all more than 20 kcalmol higher in energy than 92 providing a computational rationale for the failure to observe such species by NMR The first step in the optimal reaction pathway is the coordination of Ni(PMe3) to the cyclobutadiene ring of 22 which results in formation of η2-like complex 114 Again in gratifying agreement with experiment bay region insertion through transition state 115 to give 116 is favored albeit by a bare 07 kcalmol relative to its non-bay region counterpart 117 Moreover there are at least six other structures that are energetically viable in silico although insertions of Ni(PhCequivCPh)(PMe3) appear less so possibly due to steric hindrance The same observation is made for the products of insertion although 116 emerges as the thermodynamically most stable possibility

Scheme 317 Calculated Structures and Reaction Pathway for the Insertion of Nickel into the Four-Membered Ring of Angular [3]Phenylene 22 Free Energies ∆G are in KcalMol Relative

to 92

The next step was to map out the first alkyne cycloaddition (Scheme 318) Coordination of diphenylacetylene to 116 is endothermic by 139 kcalmol and after migratory insertion produces 119 Interestingly a transition state to regioisomer 95

(328) (352)

NiMe3P PMe3

(364)

NiMe3P

NiMe3P PMe3

NiPMe3

(339)

Ni

PMe3

PMe3

NiMe3PPMe3

NiMe3P

NiPMe3

(16) (04) (108) (117)

NiMe3P PMe3 Ni

Me3PNi

Me3P Ni Ni

PMe3

PMe3

+ [3]+ DPA

+ PMe3+ [3]+ DPA

+ PMe3+ [3]

+ 2 PMe3+ [3]

+ [3]+ 2 DPA

Ph Ph Ph PhPh Ph

Ph

PhPh Ph

Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

Ph

(45) (96)

(00)

(89) (134)

Most AccessibleTS

NiPMe3

+ PMe3+ [3]+ 2 DPA

(314)

Ni

+ 2 PMe3+ [3]+ DPA

Ph Ph

(294)

1i(PMe3)

Ni

PhPh

(212)

(218)

(345)

Ni

PhPh(297)

Ni

Me3P

Ni

Ph

Ph

(350)

Ni

PMe3

(303)

Ni

Ni

(43) (41)

Ph

Ph

PhPh

Ni

PMe3

NiMe3P

(-10) (-22)

(Me3P)Ni

Ni(PMe3)

Ph Ph

Ph Ph(225) (256)

+ PMe3+ 2 DPA

+ 2 PMe3+ DPA

+ PMe3+ DPA

+ PMe3+ DPA

92114

115

116118

117

- 78 -

written (arbitrarily) in Scheme 312 could not be located

Scheme 318 Calculated Reaction Pathway for the Coordination of Diphenylacetylene Migratory Insertion and Nickel Migration Free Energies ∆G are in KcalMol Transition

State Energies are Absolute Values for This Step

Subsequent reductive elimination from 119 occurs to produce nickel coordinated arene species 120 From it free 89 is presumably readily obtained by demetallation in the presence of external ligands shown only for the formation of 92 in a very favorable process (ndash487 kcalmol) This step is sufficiently exothermic to tolerate the emergence of all the calculated species in the starting line up of Scheme 317 and is presumably the source of 89 in Scheme 39 However if not removed the Ni moiety in 120 can migrate along a shallow manifold across the π frame choosing the phenyl functionalized edge of the molecule (cf Section 24) until the remaining four-membered ring is reached (121) At this point two separate reaction pathways become possible Nickel insertion on the side proximal or opposite of the phenyl groups generates 99 or 122 respectively The barriers for these transformations are similar but show a noticeable preference for the formation of 99 In addition there is a significant energy difference (175 kcalmol) between 122 and 99 in favor of the bay region metallacycle The reason is the coordination of the neighboring phenyl ring to the nickel which serves to stabilize 103 vindicating the proposal made in Scheme 313 and providing a rationale for the exclusive observation of 90 in Scheme 39 From 99 as shown in Scheme 319 coordination of diphenylacetylene (123) is followed by migratory insertion to produce 124 Insertion occurs away from the bay region so as to reduce steric repulsion due to the phenyl group in the phenanthrene part of the molecule Finally reductive elimination ensues providing phenacene-Ni

NiMe3P

NiPMe3

Ni(PMe3)

Ni Ph

PhMe3P

Ph

Ph

PhPh

(117)

126

(44)

102

( 80)

01

( 412)

Ph PhNi(PMe3)

( 389)

Ph Ph

45

Ni(PMe3)

( 408)

Ph Ph

13

PhNi

PMe3

Ph Ph

Ni(PMe)3

133

( 488)

117

( 663)

NiMe3P

( 22)

PhPh+

95

116

119

120121 122

99

NiMe3P Ph

Ph

Ph Ph

( 899)

NiMe3P PMe3

Ph Ph+

92 89

- 79 -

complex 125 At this point the stage is set for exergonic nickel dissociation to 90 and catalyst turnover

Scheme 319 Calculated Reaction Pathway for the Second Diphenylacetylene Insertion All Relative Energies (in red) are in KcalMol Transition State Energies are Absolute Values for

This Step

In conclusion of this discussion the consideration of the combined computational and experimental data affords a mechanistic picture of the cycloaddition reaction of diphenylacetylene 88 to angular [3]phenylene 22 (Scheme 39) the essential features of which are summarized in Scheme 320 The crucial point is a mechanistic bifurcation in which 89 is either released early and (nearly) irreversibly from the metal or the metal stays attached so as to effect a second cycloaddition to give 90 This mechanism implies that 91 is formed by a different mechanism involving a different Ni species

PhNi

PMe3

( 663)

+

PhNi

Ph PMe3Ph

Ph

( 403) ( 403)

PhNi

PhPMe3

PhPh

( 519)

94

93

( 696)

PhNi

PhPMe3

Ph

Ph

96

( 817)

Ph Ph Ph Ph

(MeP)3Ni

99

123

124

125

PhPh

Ph PhPh Ph

+Ni

Me3P PMe3

( 1101)

PMe3

90

- 80 -

Scheme 320 Essential Mechanistic Features of the Formation of 89 and 90 in the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene 88 and Angular [3]Phenylene 22

Consequently the reaction of 89 with diphenylacetylene to give 91 (Scheme 310) was also modeled by DFT Of the various options probed that shown in Scheme 321 proved to be most plausible The reaction pathway entails coordination of alkyne-Ni phosphine 126 to molecule 89 which generates complex 127 in a process that is found to require 228 kcalmol of energy Insertion into the non-bay region of the four-membered ring has a barrier of 16 kcalmol and provides metallacycle 128 After the second cycloaddition event benzo[c]chrysene 91 is formed Interestingly the transition state leading to insertion of nickel complex 126 into the bay region of 89 structure 129 was found to be so high in energy relative to 128 that it could not be modeled This is not unexpected as the phenyl group closest to bay region effectively blocks the approach of any catalyst species This result is consistent with the high ratio of 91 to 90 formed in Scheme 310 and the increase in this ratio at higher initial diphenylacetylene concentration Why is any 90 formed and why does its relative proportion increase at lower diphenylacetylene concentration A possible explanation is that under these conditions the concentrations of 92 and 126 are sufficiently small that 89 reenters Scheme 318 competitively

PhPhNi(PMe3)

PhPh

Ni(PMe3)

Ph Ph Ph Ph

PhPh

Ni(PMe3)

Ni

PMe3

Ph Ph

NiPhMe3P

22 116

88

120

121

99

88

90

PhPh

89

Externalligand

assistedNi migration

Regioselectiveinsertion

Regioselectiveinsertion

Mechanistic bifurcation

- 81 -

Scheme 321 Calculated Reaction Mechanism for the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene and Compound 90 Relative Energies are in KcalMol Transition

State Energies are Absolute Values for This Step

Consideration of Scheme 320 suggests that phenacene formation might be maximized by keeping the concentration of external ligand low during the course of the reaction Experiments aimed at verifying this conjecture are the subject of Section 34 in addition to presenting extensions of the methodology to higher angular phenylenes

34 Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions The experimental and computational studies described in Section 33 suggested that the decisive factor for selective formation of phenacene 90 is suppression of metal dissociation in Ni complex 120 This scenario would be achievable by maintaining a low concentration of diphenylacetylene 88 (vide supra) Previously the alkyne cycloaddition was performed with all reagents mixed together at the start of the reaction invariably resulting in a high initial concentration of 88 To obviate this occurrence an alternative procedure was devised In this new arrangement the required stoichiometric amount (in this case two equivalents) of alkyne 88 was slowly introduced to a mixture of 22 and Ni(COD)(PMe3)2 by means of a syringe pump (Scheme 322) The results of varying addition and reaction times are shown in Table 35

Scheme 322 Modified Reaction Alkyne Cycloaddition Reaction Between 22 and 89

Ph Ph

Ni(PMe3)

Ph Ph Ph Ph

Ni(PMe)3

160

Ph

Ph

PhPh

(309)(317)

Ph Ph

Ph

Ph

NiMe3P

Ph Ph

(minus573)

89

126

127 128 91

Ph Ph Ph

Ni

Ph

PMe3

129

NiMe3P PMe3

Ph Ph

(00)

92

(89)

+

- 82 -

Table 35 Variation of Alkyne Addition and Total Reaction Time in the Scheme 322

Run Addition time of 88 (h)

Total run time (h)

Yield of 89 ()

Yield of 90 ()

1 4 16 44 55 2 6 22 23 77 3 5 41 24 76 4 12 69 17 73 5 13 19 13 87

The most immediate result of the modified protocol was the quantitative conversion of 22 to cycloadduct products 89 and 90 Turning to the product ratios a four hour addition time led to a slight preference for 90 Increasing the time to six hours dramatically influenced the product distribution and 90 was isolated in 77 yield as compared to the 23 for 89 In the optimal Run 5 87 of 90 was generated vs 13 of 90 Extending the run time after the addition of diphenylacetylene had a negligible effect The successful enhancement in phenacene selectivity under these conditions makes the reaction a practical method for synthesizing compound 90 and also provides further experimental support for the proposed mechanism shown in Scheme 320 Having reached a reasonable level of understanding both the mechanistic and experimental aspects of the reaction of angular [3]phenylene 22 with diphenylacetylene attention was shifted to a larger and more challenging substrate angular [4]phenylene (17) This system could conceivably afford 17 possible adducts one of which is hexaphenyl[7]phenacene 130 (Scheme 324) Would the mechanistic features of this triple cycloaddition be sufficiently similar to those of 22 to apply the same principles and enable selectivity toward 130

+THF reflux

Ph Ph Ph PhPh

Ph

+

Ph

Ph

2 equivslow addition

22 89 90

Ni(COD)(PMe3)2(10 mol)

88

- 83 -

Scheme 324 The Possible Cycloadducts of Diphenylacetylene 88 to Angular [4]Phenylene 17

+ Ph Ph

Ph Ph

Ph Ph

PhPh

Ph

Ph

Ph Ph Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph PhPhPh

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph Ph PhPhPh

Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

PhPh

Ph Ph Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

88

17

130

- 84 -

Encouragingly a first experiment under conditions comparable to those in Scheme 39 for 22 namely reaction of angular [4]phenylene (17) with one equivalent of diphenylacetylene in the absence of high dilution indeed engendered only five products two of which monoadducts 131 and 132 were minor (Scheme 325) The major components of the mixture were molecules 133 134 and most significantly 130

Scheme 325 Nickel Catalyzed Alkyne Cycloaddition with 17 and 88

Monitoring the course of the transformation by NMR revealed that 133 is the sole initial new compound followed by gradual appearance of the others Extrapolation of the insights gained with 22 it is tempting to propose that migration of the metal in Ni-complexed 133 is the source of 134 and ultimately 130 If true [7]phenacene 130 might be made selectively by application of the slow alkyne addition procedure of Scheme 322 Scheme 326 illustrates the proposed scenario It starts with doubly regioselective Ni insertion into the central ring and from the bay region to give 135 On the basis of the electron withdrawing effect of the adjacent cyclobutadienoid rings invoked earlier in the selective formation of 94 (Scheme 312) this metallacycle would seem the most stable Again this conjecture is tentative as the appearance of the minor products 131 and 132 would indicate Metallacycle 135 would then give rise to 136 (and hence 133 by demetallation) which would connect by Ni migration and insertion to 137 Alkyne cycloaddition would result in 138 (and hence 134 by demetallation) which would connect by Ni migration and insertion to 139 Alkyne cycloaddition would result in 140 (and hence 130 by demetallation)

+

Ph Ph

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2(10 mol)THF 75 degC

5 6

33

27 28

132131

133

134 130

17

88

- 85 -

Scheme 326 Proposed Reaction Pathway to Phenacene 130 from Angular [4]Phenylene 17 via Ni Migration

The successful preparation of [5]- and [7]phenacene from angular [3]- and [4]phenylene respectively prompted an attempt to prepare [13]phenacene derivative 141 from helical [7]phenylene 14210 (Scheme 327) This transformation would make use of six alkyne cycloadditions to produce the target molecule In addition to the possibility of preparing the largest known phenacene this reaction would also serve as an interesting test of the alkyne cycloaddition methodology

Scheme 327 Proposed Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Using the slow addition procedure phenylene 142 was subjected to the alkyne cycloaddition conditions (Scheme 329) All of the starting material was consumed but the reaction ultimately resulted in an intractable mixture of products Unfortunately no conclusive structural identifications for any of the ensuing compounds could be made from the 1H-NMR data A large assortment of peaks was seen in the region of 6ndash7

Ni

PMe3

Ph

NiPMe3

Ph Ph Ph PhNi

PMe3

Ph Ph Ph

NiMe3P

135

137

Ph Ph

Ph Ph

Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2

13617

88Ni

PMe3

Ph Ph88

138 139

Ph Ph88

Ni

PMe3

140

- 86 -

ppm suggesting the presence of phenylene subunits More informative was the absence of the highly diagnostic phenacene bay region proton signals that are typically found at ~8ndash9 ppm84 signaling the absence of any phenacene product(s)

Scheme 328 Attempted Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Nevertheless mass spectral analysis clearly indicated that multiple alkyne cycloaddition had occurred (Table 36) Peaks were observed at mz = 700 1056 1234 and 1412 which correspond to the presence of single triple quadruple and quintuple alkyne adducts in the reaction mixture No signal corresponding to the mass of 141 (mz = 1590) was detected however Although the structures of the resulting products remain to be established by follow-up experiments on a larger scale the fact that five cycloadditions occurred is encouraging in the basic scientific quest for large novel polycyclic aromatic hydrocarbons

Table 36 Mass Spectral Data (FAB) of the Product Mixture of the Cycloaddition Reaction of Phenylene 142 to Diphenylacetylene 88

mz Percentage Cycloaddition count 700 13 1

1056 11 3 1234 8 4 1412 7 5

Our disappointment in the apparent failure to generate 141 in this reaction may be the result of overambitious expectations on our part Thus we assumed in analogy to the reactivity of angular systems 17 and 22 that bay region cycloaddition to one of the inner cyclobutadiene rings would be preferred ideally producing an initial structure such as 143 (Figure 38) The corresponding non-bay adduct is illustrated by 144 It is evident on comparison that such bay region reactivity would lead to constructs devoid of the helical strain present in the starting material96 as well as non-bay structures like 144 The subsequent course of the reaction however may be marred by relatively non-selective cycloadditions as already indicated for 17 (Scheme 325) Therefore it will be prudent for future investigators to return to the latter optimize its outcome and then proceed along the series in the quest for large phenacene (or other) structures

- 87 -

Figure 38 Proposed representative initial bay (143) and non-bay (144) alkyne cycloaddition products of the reaction of [7]heliphene 141 with diphenylacetylene 88

35 Summary and Outlook The first alkyne cycloaddition studies were carried with angular phenylene systems Angular [3]phenylene 22 was successfully used as a precursor to a novel phenyl substituted [5]phenacene derivative 90 Similarly hexaphenyl [7]phenacene 131 was prepared from angular [4]phenylene 17 Extensive experiment and computational mechanistic studies suggested that the optimal conditions for preparing phenacene 90 from phenylene 22 were the maintenance of a low concentration of alkyne in the reaction mixture Future work will focus on applying these conditions to the synthesis of [7]phenacene 130 from angular [4]phenylene 17 An attempt to prepare a [13]phenacene 142 from helical [7]phenylene 141 proved unsuccessful for reasons that are not well understood Nevertheless cycloaddition was found to have occurred up to five times This observation is promising with respect to the further application of the methodology described in this chapter The development of an alkyne cycloaddition-based approach to synthesizing phenacenes should greatly facilitate the study of this emerging class of molecules Future work will focus on expanding the substrate scope of the reaction by examining various functionalized alkynes the application of metal systems that may allow the isolation of crucial intermediates and the expansion of the substrate scope to the higher angular phenylenes as well as other topologies

- 88 -

Chapter Four Experimental and Computational Details

41 General Considerations

All glassware was oven-dried (180 degC) prior to use Reagents were used as received from suppliers unless otherwise noted Flash chromatography97 was performed with Merck 60 230ndash400 mesh silica gel MP EcoChrom neutral alumina was deactivated to activity III by adding 6 water by mass followed by thorough mixing98 Air sensitive compounds were handled under argon with standard Schlenk techniques andor in a nitrogen atmosphere glovebox (Vacuum Atmospheres Model Nexus) Irradiation in CpCo(CO)2 reactions was carried out with a 120V 300W slide projection lamp (ELH) positioned 5 cm away from the reaction vessel UV-irradiation experiments were conducted in a Rayonet Photochemical Reactor (RPR-100) Bis(trimethylsilyl)- and trimethylsilylacetylene (BTMSA and TMSA respectively) were distilled from molecular sieves (4 Aring) prior to use TMSA was degassed with four freeze-pump-thaw cycles while BTMSA was degassed using a 20 min Ar purge BTMSA was recycled using from all CpCo(CO)2 reactions using the following procedure The BTMSA was first removed by vacuum transfer Residual cobalt was removed by dissolving the BTMSA in pentane and washing the pentaneBMTSA layer mixture with a dilute solution of ceric ammonium nitrate in acetonitrile in a separatory funnel The denser acetonitrile layer was drained off and the pentane removed by distillation at atmospheric pressure Vacuum distillation of the BTMSA from molecular sieves afforded a product pure enough for future use All solvents were distilled under N2

immediately before use from the appropriate drying agent triethylamine (KOH pellets) benzene toluene CH2Cl2 (CaH2) THF and diethylether (Nabenzophenone) acetonitrile (CaH2) Deoxygenation of solvents andor reaction mixtures was carried out by a 20 min Ar purge or four free-pump-thaw cycles for volatile (bp lt 70 degC) mixturessolvents Ni(COD)2 (Strem) was stored and manipulated in the glovebox 1H and proton decoupled 13C spectra were measured at 500 MHz and 125 MHz respectively unless otherwise noted 1H-NMR chemical shifts are reported in ppm units relative to the signal of the solvent (CDCl3ndash726 ppm C6D6ndash715 ppm acetone-d6ndash205 ppm CD2Cl2ndash532 ppm toluene-d8ndash209 ppm (for ndashCD3) Except where noted two-dimensional NMR experiments were run under temperature control at 300 K All spectral data were processed with Bruker TopSpin 21 software Melting points were recorded in open capillary tubes using a Thomas Hoover Unimelt apparatus and are uncorrected Melting points for air-sensitive samples were carried out in flame sealed capillary tubes Mass spectral measurements (Electron Impact Fast Atom Bombardment) and elemental analyses were supplied by the Micro-Mass Facility of the College of Chemistry University of California Berkeley UV-Vis spectra were recorded on Agilent 8453 and Perkin-Elmer Lambda 35 spectrophotometers with absorbance data reported in nm (log ε) IR spectra were taken on a Perkin-Elmer Spectrum 100 Where appropriate analysis by GCMS was done with an Agilent 5973 instrument

42 Experimental Section for Chapter Two

- 89 -

2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19

A mixture of KF2 H2O (700 mg 744 mmol) [18]crown-6 (100 mg 0378 mmol) and 2378-tetrakis[(triisopropylsilyl)ethynyl] linear [3]phenylene26 (370 mg 0800 mmol) in degassed THF (25 mL) was stirred for 70 min at RT The orange solution was filtered through a plug of silica gel (1 x 3 cm) eluting with degassed THF (15 mL) providing a light-yellow solution After adding CpCo(CO)2 (260 mg 144 mmol) the solution was protected from light and added via syringe pump over a period of 6 h to a boiling mixture of degassed BTMSA (50 mL) and THF (200 mL) which was irradiated with a projector lamp under nitrogen After additional heating and irradiation for 15 h the solvents were removed by vacuum transfer and the black residue filtered through a plug of neutral alumina activity III eluting with hexaneTHF (501) The volatiles were removed and the dark brown residue crystallized from degassed acetone yielding 19 (330 mg 65 ) as black needles mp 192ndash195 degC (decomp) 1H-NMR (400 MHz C6D6) δ = 794 (s 2 H) 744 (s 2 H) 690 (s 2 H) 441 (s 5 H) 035 (s 18 H) 031 (s 18 H) ppm 13C-NMR (100 MHz C6D6) δ = 1494 1484 1433 1394 1360 1256 1155 802 781 739

269 261 ppm IR (neat) ν~ = 2951 2898 1259 1248 1073 830 799 752 cmndash1 UV-VIS (ethanol) λmax (log ε) = 288 (486) 299 (500) 352 (445) 410 (439) 438 (449) end absorption to 550 nm MS (70 eV) mz () 638 (9) [M+] 514 (100) 499 (3) 387 (2) 73 (24) HRMS (FAB) calcd for C35H47CoSi4 6382087 found 6382095 Elemental analysis calcd for C35H47CoSi4 C 6578 H 741 found 6582 721

Crystallographic information for 19 (H atoms omitted)

Table 41 Crystal Data and Structure Refinement For 19

Empirical formula C35H47CoSi4 Formula weight 63902 cryst size (mm) 025 x 020 x 005 cryst syst Triclinic refl used for unit cell determination 6958

2 θ range (deg) 245ndash2900

a (Aring) 9497(3) b (Aring) 12321(4) c (Aring) 16469(5) α (deg) 74058(5)

β (deg) 82154(5)

Me3Si

Me3Si

CoSiMe3

SiMe3

- 90 -

γ (deg) 72276(5)

V (Aring3) 17620(10) space group Pndash1 Z 2

Dcalc gcm3 1762

F000 680 micro cmndash1 645 temp ordmC ndash173

Tmax Tmin 0858 0972 no of total rflns 24355

no of unique rflns 6958

no of obsd rflns 9209

no of variables 361

Reflection to Parameter Ratio 255

R 00503

Rw 01426

Rall 00734

GOF 1006

Max Peak in Final Diff Map (endash Aring3) 0867

Min Peak in Final Diff Map (endash Aring3) ndash0755

- 91 -

Figure 41 ORTEP representation of 19

- 92 -

Table 42 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 19 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y Z U (eq)

Co1 073881(4) ndash000927(3) 060643(2) 002551(10) Si1 077416(8) ndash019090(6) 094343(4) 002594(16) Si2 113437(8) ndash016706(7) 082404(5) 003023(17) Si3 040491(7) 062139(6) 020406(4) 002291(15) Si4 005088(7) 056545(6) 030946(4) 002144(14) C1 06709(3) ndash00385(2) 079440(16) 00239(5) C2 08019(3) ndash00967(2) 083428(16) 00241(5) C3 09418(3) ndash00743(2) 079331(16) 00233(5) C4 09428(3) 00098(2) 071779(15) 00225(5) C5 08094(2) 00691(2) 067735(15) 00207(4) C6 07282(2) 01574(2) 060605(15) 00207(4) C7 07303(2) 02531(2) 053306(15) 00211(4) C8 05938(2) 03094(2) 050431(15) 00205(4) C9 05057(2) 03981(2) 043438(15) 00207(4) C10 05076(2) 04760(2) 035695(15) 00227(5) C11 03734(2) 05293(2) 031459(15) 00215(4) C12 02408(2) 05011(2) 035315(15) 00205(4) C13 02432(2) 04196(2) 043269(15) 00215(4) C14 03751(2) 03698(2) 047171(15) 00208(4) C15 04564(2) 02794(2) 054277(15) 00211(4) C16 04487(2) 01908(2) 061161(15) 00224(5) C17 05916(3) 01278(2) 064393(15) 00221(5) C18 06734(2) 00417(2) 071473(15) 00215(5) C19 05795(3) ndash02027(3) 09572(2) 00446(8) C20 08892(4) ndash03470(2) 09642(2) 00387(7) C21 07986(4) ndash01192(3) 10246(2) 00419(7) C22 11685(4) ndash03077(3) 07914(3) 00584(10) C23 11726(3) ndash01969(3) 09372(2) 00426(7) C24 12742(4) ndash00933(4) 07624(3) 00640(12) C25 05777(3) 06657(3) 020261(18) 00348(6) C26 02610(3) 07629(2) 016564(17) 00292(5) C27 04355(3) 05272(3) 012760(18) 00347(6) C28 ndash00272(3) 07195(2) 03194(2) 00360(6) C29 00487(3) 05542(3) 019882(18) 00344(6) C30 ndash00786(3) 04816(2) 037272(18) 00278(5) C31 06994(4) ndash00612(3) 05062(2) 00432(7) C32 08520(4) ndash00698(3) 05033(2) 00407(7) C33 09085(3) ndash01473(3) 05788(2) 00407(7) C34 07922(4) ndash01879(3) 06277(2) 00424(7) C35 06647(4) ndash01370(3) 05833(2) 00403(7)

- 93 -

Table 43 Bond Lengths (Aring) for Complex 19

Atom1 Atom2 Length

Co1 C5 1993(3) Co1 C6 2023(3) Co1 C17 2022(2) Co1 C18 2009(3) Co1 C31 2042(4) Co1 C32 2075(3) Co1 C33 2062(3) Co1 C34 2042(4) Co1 C35 2048(4) Si1 C2 1886(2) Si1 C19 1877(3) Si1 C20 1863(2) Si1 C21 1865(4) Si2 C3 1889(3) Si2 C22 1876(5) Si2 C23 1862(3) Si2 C24 1865(4) Si3 C11 1901(2) Si3 C25 1876(4) Si3 C26 1867(2) Si3 C27 1875(4) Si4 C12 1889(2) Si4 C28 1860(3) Si4 C29 1868(3) Si4 C30 1870(3) C1 C2 1384(4) C1 C18 1411(3) C2 C3 1474(4) C3 C4 1384(3) C4 C5 1408(3) C5 C6 1480(3) C5 C18 1448(3) C6 C7 1437(3) C6 C17 1465(4) C7 C8 1351(3) C8 C9 1495(3) C8 C15 1476(3) C9 C10 1371(3) C9 C14 1405(3) C10 C11 1423(3) C11 C12 1427(3) C12 C13 1413(3) C13 C14 1376(3)

- 94 -

C14 C15 1488(3) C15 C16 1352(3) C16 C17 1434(3) C17 C18 1468(3) C31 C32 1416(6) C31 C35 1419(4) C32 C33 1401(4) C33 C34 1411(5) C34 C35 1386(5)

Table 44 Bond Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 4325(9) C5 Co1 C17 621(1) C5 Co1 C18 4240(9) C5 Co1 C31 1629(1) C5 Co1 C32 1271(1) C5 Co1 C33 1102(1) C5 Co1 C34 1223(1) C5 Co1 C35 1556(1) C6 Co1 C17 425(1) C6 Co1 C18 6191(9) C6 Co1 C31 1253(1) C6 Co1 C32 1164(1) C6 Co1 C33 1329(1) C6 Co1 C34 1651(1) C6 Co1 C35 1550(1) C17 Co1 C18 427(1) C17 Co1 C31 1204(1) C17 Co1 C32 1451(1) C17 Co1 C33 1722(1) C17 Co1 C34 1419(1) C17 Co1 C35 1194(1) C18 Co1 C31 1517(1) C18 Co1 C32 1676(1) C18 Co1 C33 1312(1) C18 Co1 C34 1112(1) C18 Co1 C35 1198(1) C31 Co1 C32 402(1) C31 Co1 C33 673(1) C31 Co1 C34 675(1) C31 Co1 C35 406(1) C32 Co1 C33 396(1) C32 Co1 C34 672(1)

- 95 -

C32 Co1 C35 675(1) C33 Co1 C34 402(1) C33 Co1 C35 671(1) C34 Co1 C35 396(1) C2 Si1 C19 1085(1) C2 Si1 C20 1157(1) C2 Si1 C21 1096(1) C19 Si1 C20 1035(1) C19 Si1 C21 1081(2) C20 Si1 C21 1110(2) C3 Si2 C22 1071(2) C3 Si2 C23 1162(1) C3 Si2 C24 1100(2) C22 Si2 C23 1110(2) C22 Si2 C24 1067(2) C23 Si2 C24 1056(2) C11 Si3 C25 1077(1) C11 Si3 C26 1177(1) C11 Si3 C27 1083(1) C25 Si3 C26 1045(1) C25 Si3 C27 1086(1) C26 Si3 C27 1097(1) C12 Si4 C28 1099(1) C12 Si4 C29 1132(1) C12 Si4 C30 1101(1) C28 Si4 C29 1119(1) C28 Si4 C30 1066(1) C29 Si4 C30 1048(1) C2 C1 C18 1193(2) Si1 C2 C1 1130(2) Si1 C2 C3 1270(2) C1 C2 C3 1198(2) Si2 C3 C2 1260(2) Si2 C3 C4 1124(2) C2 C3 C4 1208(2) C3 C4 C5 1192(2) Co1 C5 C4 1188(2) Co1 C5 C6 695(1) Co1 C5 C18 694(1) C4 C5 C6 1498(2) C4 C5 C18 1200(2) C6 C5 C18 902(2) Co1 C6 C5 673(1) Co1 C6 C7 1267(2) Co1 C6 C17 687(1) C5 C6 C7 1474(2)

- 96 -

C5 C6 C17 893(2) C7 C6 C17 1227(2) C6 C7 C8 1121(2) C7 C8 C9 1461(2) C7 C8 C15 1251(2) C9 C8 C15 885(2) C8 C9 C10 1471(2) C8 C9 C14 912(2) C10 C9 C14 1214(2) C9 C10 C11 1186(2) Si3 C11 C10 1116(2) Si3 C11 C12 1283(2) C10 C11 C12 1197(2) Si4 C12 C11 1264(2) Si4 C12 C13 1135(2) C11 C12 C13 1201(2) C12 C13 C14 1185(2) C9 C14 C13 1216(2) C9 C14 C15 915(2) C13 C14 C15 1465(2) C8 C15 C14 888(2) C8 C15 C16 1250(2) C14 C15 C16 1458(2) C15 C16 C17 1118(2) Co1 C17 C6 688(1) Co1 C17 C16 1265(2) Co1 C17 C18 682(1) C6 C17 C16 1233(2) C6 C17 C18 900(2) C16 C17 C18 1460(2) Co1 C18 C1 1229(2) Co1 C18 C5 682(1) Co1 C18 C17 691(1) C1 C18 C5 1206(2) C1 C18 C17 1487(2) C5 C18 C17 905(2) Co1 C31 C32 712(2) Co1 C31 C35 699(2) C32 C31 C35 1077(3) Co1 C32 C31 686(2) Co1 C32 C33 697(2) C31 C32 C33 1076(3) Co1 C33 C32 707(2) Co1 C33 C34 691(2) C32 C33 C34 1081(3) Co1 C34 C33 707(2)

- 97 -

Co1 C34 C35 704(2) C33 C34 C35 1086(3) Co1 C35 C31 695(2) Co1 C35 C34 700(2) C31 C35 C34 1079(3)

Table 44 Torsion Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 ndash1479(3) C6 Co1 C5 C18 983(2) C17 Co1 C5 C4 1630(2) C17 Co1 C5 C6 ndash491(1) C17 Co1 C5 C18 492(1) C18 Co1 C5 C4 1138(2) C18 Co1 C5 C6 ndash983(2) C31 Co1 C5 C4 ndash941(4) C31 Co1 C5 C6 538(4) C31 Co1 C5 C18 1522(4) C32 Co1 C5 C4 ndash573(2) C32 Co1 C5 C6 906(2) C32 Co1 C5 C18 ndash1710(2) C33 Co1 C5 C4 ndash160(2) C33 Co1 C5 C6 1319(1) C33 Co1 C5 C18 ndash1297(2) C34 Co1 C5 C4 271(2) C34 Co1 C5 C6 1750(2) C34 Co1 C5 C18 ndash866(2) C35 Co1 C5 C4 629(4) C35 Co1 C5 C6 ndash1492(3) C35 Co1 C5 C18 ndash509(3) C5 Co1 C6 C7 1458(3) C5 Co1 C6 C17 ndash986(2) C17 Co1 C6 C5 986(2) C17 Co1 C6 C7 ndash1156(3) C18 Co1 C6 C5 491(1) C18 Co1 C6 C7 ndash1650(2) C18 Co1 C6 C17 ndash494(1) C31 Co1 C6 C5 ndash1631(2) C31 Co1 C6 C7 ndash173(3) C31 Co1 C6 C17 983(2) C32 Co1 C6 C5 ndash1170(2) C32 Co1 C6 C7 288(2) C32 Co1 C6 C17 1444(2) C33 Co1 C6 C5 ndash725(2)

- 98 -

C33 Co1 C6 C7 734(3) C33 Co1 C6 C17 ndash1710(2) C34 Co1 C6 C5 ndash166(5) C34 Co1 C6 C7 1293(5) C34 Co1 C6 C17 ndash1151(5) C35 Co1 C6 C5 1499(3) C35 Co1 C6 C7 ndash642(4) C35 Co1 C6 C17 514(3) C5 Co1 C17 C6 501(1) C5 Co1 C17 C16 1666(3) C5 Co1 C17 C18 ndash489(1) C6 Co1 C17 C16 1165(3) C6 Co1 C17 C18 ndash989(2) C18 Co1 C17 C6 989(2) C18 Co1 C17 C16 ndash1446(3) C31 Co1 C17 C6 ndash1106(2) C31 Co1 C17 C16 59(3) C31 Co1 C17 C18 1505(2) C32 Co1 C17 C6 ndash656(3) C32 Co1 C17 C16 510(3) C32 Co1 C17 C18 ndash1645(2) C33 Co1 C17 C6 571(9) C33 Co1 C17 C16 1736(8) C33 Co1 C17 C18 ndash418(9) C34 Co1 C17 C6 1578(2) C34 Co1 C17 C16 ndash857(3) C34 Co1 C17 C18 589(2) C35 Co1 C17 C6 ndash1578(2) C35 Co1 C17 C16 ndash413(3) C35 Co1 C17 C18 1033(2) C5 Co1 C18 C1 ndash1133(3) C5 Co1 C18 C17 993(2) C6 Co1 C18 C1 ndash1635(2) C6 Co1 C18 C5 ndash502(1) C6 Co1 C18 C17 491(1) C17 Co1 C18 C1 1474(3) C17 Co1 C18 C5 ndash993(2) C31 Co1 C18 C1 836(3) C31 Co1 C18 C5 ndash1632(2) C31 Co1 C18 C17 ndash638(3) C32 Co1 C18 C1 ndash779(6) C32 Co1 C18 C5 353(6) C32 Co1 C18 C17 1346(5) C33 Co1 C18 C1 ndash395(3) C33 Co1 C18 C5 737(2) C33 Co1 C18 C17 1731(2)

- 99 -

C34 Co1 C18 C1 20(2) C34 Co1 C18 C5 1152(2) C34 Co1 C18 C17 ndash1455(2) C35 Co1 C18 C1 451(3) C35 Co1 C18 C5 1583(2) C35 Co1 C18 C17 ndash1023(2) C5 Co1 C31 C32 478(5) C5 Co1 C31 C35 1656(4) C6 Co1 C31 C32 904(2) C6 Co1 C31 C35 ndash1517(2) C17 Co1 C31 C32 1412(2) C17 Co1 C31 C35 ndash1010(2) C18 Co1 C31 C32 ndash1739(2) C18 Co1 C31 C35 ndash561(3) C32 Co1 C31 C35 1179(3) C33 Co1 C31 C32 ndash370(2) C33 Co1 C31 C35 808(2) C34 Co1 C31 C32 ndash808(2) C34 Co1 C31 C35 371(2) C35 Co1 C31 C32 ndash1179(3) C5 Co1 C32 C31 ndash1642(2) C5 Co1 C32 C33 764(2) C6 Co1 C32 C31 ndash1143(2) C6 Co1 C32 C33 1263(2) C17 Co1 C32 C31 ndash710(3) C17 Co1 C32 C33 1697(2) C18 Co1 C32 C31 1666(5) C18 Co1 C32 C33 472(6) C31 Co1 C32 C33 ndash1194(3) C33 Co1 C32 C31 1194(3) C34 Co1 C32 C31 816(2) C34 Co1 C32 C33 ndash377(2) C35 Co1 C32 C31 385(2) C35 Co1 C32 C33 ndash808(2) C5 Co1 C33 C32 ndash1243(2) C5 Co1 C33 C34 1166(2) C6 Co1 C33 C32 ndash802(2) C6 Co1 C33 C34 1607(2) C17 Co1 C33 C32 ndash1309(8) C17 Co1 C33 C34 1100(9) C18 Co1 C33 C32 ndash1679(2) C18 Co1 C33 C34 730(2) C31 Co1 C33 C32 376(2) C31 Co1 C33 C34 ndash815(2) C32 Co1 C33 C34 ndash1191(3) C34 Co1 C33 C32 1191(3)

- 100 -

C35 Co1 C33 C32 818(2) C35 Co1 C33 C34 ndash373(2) C5 Co1 C34 C33 ndash833(2) C5 Co1 C34 C35 1577(2) C6 Co1 C34 C33 ndash700(5) C6 Co1 C34 C35 1711(4) C17 Co1 C34 C33 ndash1681(2) C17 Co1 C34 C35 730(3) C18 Co1 C34 C33 ndash1295(2) C18 Co1 C34 C35 1115(2) C31 Co1 C34 C33 809(2) C31 Co1 C34 C35 ndash380(2) C32 Co1 C34 C33 372(2) C32 Co1 C34 C35 ndash818(2) C33 Co1 C34 C35 ndash1189(3) C35 Co1 C34 C33 1189(3) C5 Co1 C35 C31 ndash1699(3) C5 Co1 C35 C34 ndash508(4) C6 Co1 C35 C31 663(4) C6 Co1 C35 C34 ndash1746(2) C17 Co1 C35 C31 1036(2) C17 Co1 C35 C34 ndash1373(2) C18 Co1 C35 C31 1531(2) C18 Co1 C35 C34 ndash878(2) C31 Co1 C35 C34 1191(3) C32 Co1 C35 C31 ndash382(2) C32 Co1 C35 C34 809(2) C33 Co1 C35 C31 ndash812(2) C33 Co1 C35 C34 378(2) C34 Co1 C35 C31 ndash1191(3) C19 Si1 C2 C1 118(2) C19 Si1 C2 C3 ndash1731(2) C20 Si1 C2 C1 1275(2) C20 Si1 C2 C3 ndash574(3) C21 Si1 C2 C1 ndash1061(2) C21 Si1 C2 C3 690(3) C22 Si2 C3 C2 714(3) C22 Si2 C3 C4 ndash988(2) C23 Si2 C3 C2 ndash532(3) C23 Si2 C3 C4 1365(2) C24 Si2 C3 C2 ndash1731(3) C24 Si2 C3 C4 167(3) C25 Si3 C11 C10 ndash241(2) C25 Si3 C11 C12 1624(2) C26 Si3 C11 C10 ndash1417(2) C26 Si3 C11 C12 447(3)

- 101 -

C27 Si3 C11 C10 932(2) C27 Si3 C11 C12 ndash804(2) C28 Si4 C12 C11 ndash731(2) C28 Si4 C12 C13 1055(2) C29 Si4 C12 C11 529(2) C29 Si4 C12 C13 ndash1285(2) C30 Si4 C12 C11 1698(2) C30 Si4 C12 C13 ndash116(2) C18 C1 C2 Si1 1755(2) C18 C1 C2 C3 00(4) C2 C1 C18 Co1 784(3) C2 C1 C18 C5 ndash41(4) C2 C1 C18 C17 ndash1772(4) Si1 C2 C3 Si2 198(4) Si1 C2 C3 C4 ndash1707(2) C1 C2 C3 Si2 ndash1654(2) C1 C2 C3 C4 41(4) Si2 C3 C4 C5 1668(2) C2 C3 C4 C5 ndash40(4) C3 C4 C5 Co1 ndash816(3) C3 C4 C5 C6 1799(4) C3 C4 C5 C18 ndash01(4) Co1 C5 C6 C7 ndash1233(4) Co1 C5 C6 C17 671(1) C4 C5 C6 Co1 1122(4) C4 C5 C6 C7 ndash112(7) C4 C5 C6 C17 1793(4) C18 C5 C6 Co1 ndash678(1) C18 C5 C6 C7 1688(4) C18 C5 C6 C17 ndash07(2) Co1 C5 C18 C1 1164(2) Co1 C5 C18 C17 ndash672(1) C4 C5 C18 Co1 ndash1121(2) C4 C5 C18 C1 42(3) C4 C5 C18 C17 ndash1793(2) C6 C5 C18 Co1 679(1) C6 C5 C18 C1 ndash1757(2) C6 C5 C18 C17 07(2) Co1 C6 C7 C8 858(2) C5 C6 C7 C8 ndash1683(3) C17 C6 C7 C8 ndash08(3) Co1 C6 C17 C16 ndash1205(2) Co1 C6 C17 C18 665(1) C5 C6 C17 Co1 ndash658(1) C5 C6 C17 C16 1736(2) C5 C6 C17 C18 07(2)

- 102 -

C7 C6 C17 Co1 1209(2) C7 C6 C17 C16 03(4) C7 C6 C17 C18 ndash1726(2) C6 C7 C8 C9 ndash1697(3) C6 C7 C8 C15 09(3) C7 C8 C9 C10 05(7) C7 C8 C9 C14 1728(4) C15 C8 C9 C10 ndash1718(4) C15 C8 C9 C14 05(2) C7 C8 C15 C14 ndash1752(2) C7 C8 C15 C16 ndash06(4) C9 C8 C15 C14 ndash04(2) C9 C8 C15 C16 1742(2) C8 C9 C10 C11 1714(3) C14 C9 C10 C11 05(3) C8 C9 C14 C13 ndash1756(2) C8 C9 C14 C15 ndash05(2) C10 C9 C14 C13 ndash06(4) C10 C9 C14 C15 1746(2) C9 C10 C11 Si3 ndash1741(2) C9 C10 C11 C12 01(3) Si3 C11 C12 Si4 ndash90(3) Si3 C11 C12 C13 1725(2) C10 C11 C12 Si4 1779(2) C10 C11 C12 C13 ndash07(3) Si4 C12 C13 C14 ndash1781(2) C11 C12 C13 C14 06(3) C12 C13 C14 C9 ndash00(3) C12 C13 C14 C15 ndash1713(3) C9 C14 C15 C8 05(2) C9 C14 C15 C16 ndash1717(4) C13 C14 C15 C8 1730(4) C13 C14 C15 C16 09(7) C8 C15 C16 C17 00(3) C14 C15 C16 C17 1704(3) C15 C16 C17 Co1 ndash870(3) C15 C16 C17 C6 01(3) C15 C16 C17 C18 1674(4) Co1 C17 C18 C1 ndash1195(4) Co1 C17 C18 C5 664(1) C6 C17 C18 Co1 ndash671(1) C6 C17 C18 C1 1734(4) C6 C17 C18 C5 ndash07(2) C16 C17 C18 Co1 1235(4) C16 C17 C18 C1 40(7) C16 C17 C18 C5 ndash1701(4)

- 103 -

Co1 C31 C32 C33 590(2) C35 C31 C32 Co1 ndash607(2) C35 C31 C32 C33 ndash16(4) Co1 C31 C35 C34 ndash596(3) C32 C31 C35 Co1 615(3) C32 C31 C35 C34 18(4) Co1 C32 C33 C34 592(2) C31 C32 C33 Co1 ndash583(2) C31 C32 C33 C34 09(4) Co1 C33 C34 C35 605(3) C32 C33 C34 Co1 ndash602(2) C32 C33 C34 C35 03(4) Co1 C34 C35 C31 593(3) C33 C34 C35 Co1 ndash606(2) C33 C34 C35 C31 ndash13(4)

23-Bis(trimethylsilyl) linear [3]phenylene(CpCo) 52

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (029 g 085 mmol)27 in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (014 g 101 mmol) The mixture was stirred for 15 h and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the yellow residue dissolved in ether (30 mL) Aqueous workup with sat NaCl (2 x 20 mL) followed by drying over MgSO4 and concentration in vacuo provided a yellow solid This material was redissolved in THF (15 mL) degassed (Ar) and CpCo(CO)2 (0140 g 078 mmol) added The resulting solution (protected from light with foil) was injected (syringe pump) over 8 h into a boiling mixture of THF (200 mL) and BTMSA (50 mL) while irradiating with a slide projection lamp Once addition was complete heating and irradiation were continued for another 14 h The volatiles were removed via vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (4 x 4 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed in vacuo and the residue crystallized from acetone yielding 52 (024 g 57 ) as dark red crystals mp 198ndash202 degC (decomp) 1H-NMR (500 MHz C6D6) δ = 796 (s 2 H) 678 (AArsquom 2 H) 675 (s 2 H) 674 (BBrsquom 2 H) 436 (s 5 H) 037 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1426 1393

1360 1294 1194 1149 802 779 738 268 ppm IR (neat) ν~ = 2960 2923 2853 1461 1455 1378 1260 1093 1019 800 cmndash1 UV-VIS (hexane) λmax (log ε) = 255 (393) 282 (376) 293 (sh 378) 308 (389) 348 (390) 397 (sh 335) 436 (301) 511

CoSiMe3

SiMe3

- 104 -

(262) MS (70 eV) mz () 494 (100) [M+] 370 (14) HRMS (FAB) calcd for C29H31CoSi2 4941296 found 4941292 Elemental analysis calcd for C29H31CoSi2 C 7041 H 632 found 7048 628 Crystallographic information for 52 (H atoms omitted)

Table 45 Crystal Data and Structure Refinement For 52

Empirical formula C29H31CoSi2 Formula weight 49465 cryst size (mm) 030 x 020 x 005 cryst syst Monoclinic refl used for unit cell determination 2640 2 θ range (deg) 242ndash2503 a (Aring) 4391(3) b (Aring) 7472(4) c (Aring) 16869(11) α (deg)

β (deg) 111522(11) γ (deg) V (Aring3) 5149(6) space group C2c Z 8 Dcalc gcm

3 1276

F000 2080 micro cmndash1 774

temp ordmC ndash153

Tmax Tmin 0963 0800 no of total rflns 18401 no of unique rflns 2640 no of obsd rflns 4266 no of variables 271 Reflection to Parameter Ratio 974 R 00892 Rw 02042 Rall 01248 GOF 1008 Max Peak in Final Diff Map (endash Aring3) 1051 Min Peak in Final Diff Map (endash Aring3) ndash0707

- 105 -

Figure 42 ORTEP representation of 52

- 106 -

Table 46 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 52 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y z U(eq)

Co1 006961(2) 087577(12) 038136(6) 00200(3) Si1 018827(6) 08761(5) 063753(18) 00627(9) Si2 018540(5) 05425(3) 046900(16) 00410(6) C1 012151(19) 08410(10) 05589(5) 00310(17) C2 015018(13) 07767(11) 05552(4) 00343(18) C3 015002(14) 06417(10) 04926(5) 00324(17) C4 011985(17) 05770(9) 04357(4) 00247(16) C5 009030(17) 06465(9) 04383(4) 00220(14) C6 005450(16) 06378(9) 04077(4) 00216(14) C7 002537(17) 05420(9) 03591(4) 00224(15) C8 ndash000060(18) 05847(9) 03798(4) 00246(15) C9 ndash003560(17) 05555(10) 03644(4) 00256(16) C10 ndash006399(18) 04581(10) 03174(4) 00284(17) C11 ndash009208(19) 05019(12) 03360(5) 00344(18) C12 ndash009130(19) 06274(12) 03957(5) 00340(18) C13 ndash006300(17) 07256(11) 04422(5) 00294(17) C14 ndash003558(19) 06826(10) 04247(4) 00274(16) C15 000008(18) 07212(10) 04449(4) 00251(16) C16 002653(17) 08159(10) 04925(4) 00234(15) C17 005500(17) 07741(9) 04722(4) 00231(15) C18 009090(17) 07798(10) 05007(4) 00247(15) C19 01766(3) 10793(15) 06845(9) 0098(3) C20 02181(3) 0957(2) 05901(7) 0098(3) C21 02076(3) 07068(14) 07228(7) 0098(3) C22 01946(2) 06941(13) 03925(6) 00631(17) C23 01724(2) 03224(9) 04142(7) 00631(17) C24 022363(17) 04883(16) 05614(5) 00631(17) C25 007501(19) 09264(10) 02652(4) 00281(17) C26 004279(18) 09614(10) 02593(4) 00264(16) C27 004343(18) 10945(10) 03211(4) 00271(16) C28 007584(19) 11429(10) 03645(5) 00296(17) C29 00960(2) 10392(11) 03322(5) 00321(17)

Table 47 Bond Lengths (Aring) for Complex 52

Atom1 Atom2 Length

Co1 C5 2011(7) Co1 C6 2004(7) Co1 C17 2014(8) Co1 C18 2015(6) Co1 C25 2093(8)

- 107 -

Co1 C26 2063(6) Co1 C27 2042(7) Co1 C28 2049(8) Co1 C29 206(1) Si1 C2 1890(6) Si1 C19 187(1) Si1 C20 187(2) Si1 C21 187(1) Si2 C3 1891(8) Si2 C22 187(1) Si2 C23 1870(8) Si2 C24 1869(7) C1 C2 137(1) C1 C18 1418(9) C2 C3 146(1) C3 C4 1406(8) C4 C5 141(1) C5 C6 147(1) C5 C18 144(1) C6 C7 1432(9) C6 C17 148(1) C7 C8 135(1) C8 C9 148(1) C8 C15 149(1) C9 C10 1410(9) C9 C14 139(1) C10 C11 142(1) C11 C12 137(1) C12 C13 141(1) C13 C14 138(1) C14 C15 150(1) C15 C16 1345(9) C16 C17 145(1) C17 C18 147(1) C25 C26 141(1) C25 C29 144(1) C26 C27 143(1) C27 C28 139(1) C28 C29 143(1)

Table 48 Bond Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 428(3) C5 Co1 C17 619(3)

- 108 -

C5 Co1 C18 420(3) C5 Co1 C25 1145(3) C5 Co1 C26 1372(3) C5 Co1 C27 1733(3) C5 Co1 C28 1468(3) C5 Co1 C29 1184(3) C6 Co1 C17 434(3) C6 Co1 C18 621(3) C6 Co1 C25 1219(3) C6 Co1 C26 1125(3) C6 Co1 C27 1305(3) C6 Co1 C28 1653(3) C6 Co1 C29 1539(3) C17 Co1 C18 428(3) C17 Co1 C25 1632(3) C17 Co1 C26 1307(3) C17 Co1 C27 1137(3) C17 Co1 C28 1247(3) C17 Co1 C29 1562(3) C18 Co1 C25 1460(3) C18 Co1 C26 1733(3) C18 Co1 C27 1388(3) C18 Co1 C28 1167(3) C18 Co1 C29 1194(3) C25 Co1 C26 395(3) C25 Co1 C27 680(3) C25 Co1 C28 681(3) C25 Co1 C29 406(3) C26 Co1 C27 409(3) C26 Co1 C28 674(3) C26 Co1 C29 672(3) C27 Co1 C28 397(3) C27 Co1 C29 678(3) C28 Co1 C29 407(3) C2 Si1 C19 1089(5) C2 Si1 C20 1125(5) C2 Si1 C21 1092(4) C19 Si1 C20 1053(6) C19 Si1 C21 1100(6) C20 Si1 C21 1109(6) C3 Si2 C22 1081(4) C3 Si2 C23 1089(4) C3 Si2 C24 1177(4) C22 Si2 C23 1072(4) C22 Si2 C24 1106(4) C23 Si2 C24 1039(4)

- 109 -

C2 C1 C18 1206(7) Si1 C2 C1 1141(5) Si1 C2 C3 1249(5) C1 C2 C3 1210(7) Si2 C3 C2 1296(5) Si2 C3 C4 1113(5) C2 C3 C4 1190(6) C3 C4 C5 1199(6) Co1 C5 C4 1239(5) Co1 C5 C6 684(4) Co1 C5 C18 692(4) C4 C5 C6 1484(7) C4 C5 C18 1203(6) C6 C5 C18 910(6) Co1 C6 C5 688(4) Co1 C6 C7 1280(5) Co1 C6 C17 687(4) C5 C6 C7 1473(6) C5 C6 C17 892(5) C7 C6 C17 1222(6) C6 C7 C8 1133(6) C7 C8 C9 1475(7) C7 C8 C15 1242(7) C9 C8 C15 882(6) C8 C9 C10 1454(7) C8 C9 C14 928(6) C10 C9 C14 1218(7) C9 C10 C11 1147(7) C10 C11 C12 1222(8) C11 C12 C13 1231(8) C12 C13 C14 1149(7) C9 C14 C13 1233(7) C9 C14 C15 910(6) C13 C14 C15 1457(7) C8 C15 C14 879(6) C8 C15 C16 1254(7) C14 C15 C16 1467(7) C15 C16 C17 1121(6) Co1 C17 C6 679(4) Co1 C17 C16 1300(5) Co1 C17 C18 686(4) C6 C17 C16 1227(6) C6 C17 C18 892(5) C16 C17 C18 1464(7) Co1 C18 C1 1235(5) Co1 C18 C5 688(4)

- 110 -

Co1 C18 C17 686(4) C1 C18 C5 1191(7) C1 C18 C17 1500(7) C5 C18 C17 906(6) Co1 C25 C26 691(4) Co1 C25 C29 683(4) C26 C25 C29 1065(7) Co1 C26 C25 714(4) Co1 C26 C27 688(4) C25 C26 C27 1091(6) Co1 C27 C26 704(4) Co1 C27 C28 704(5) C26 C27 C28 1079(7) Co1 C28 C27 699(5) Co1 C28 C29 699(5) C27 C28 C29 1085(7) Co1 C29 C25 711(5) Co1 C29 C28 694(5) C25 C29 C28 1080(7)

Table 49 Torsion Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 1468(8) C6 Co1 C5 C18 ndash999(5) C17 Co1 C5 C4 ndash1627(7) C17 Co1 C5 C6 504(4) C17 Co1 C5 C18 ndash494(4) C18 Co1 C5 C4 ndash1133(8) C18 Co1 C5 C6 999(5) C25 Co1 C5 C4 356(7) C25 Co1 C5 C6 ndash1113(4) C25 Co1 C5 C18 1489(4) C26 Co1 C5 C4 765(7) C26 Co1 C5 C6 ndash703(5) C26 Co1 C5 C18 ndash1702(4) C27 Co1 C5 C4 146(2) C27 Co1 C5 C6 ndash1(3) C27 Co1 C5 C18 ndash101(2) C28 Co1 C5 C4 ndash515(9) C28 Co1 C5 C6 1617(5) C28 Co1 C5 C18 619(7) C29 Co1 C5 C4 ndash98(7) C29 Co1 C5 C6 ndash1567(4) C29 Co1 C5 C18 1035(5)

- 111 -

C5 Co1 C6 C7 ndash1474(8) C5 Co1 C6 C17 977(5) C17 Co1 C6 C5 ndash977(5) C17 Co1 C6 C7 1149(8) C18 Co1 C6 C5 ndash482(4) C18 Co1 C6 C7 1644(7) C18 Co1 C6 C17 495(4) C25 Co1 C6 C5 927(5) C25 Co1 C6 C7 ndash547(7) C25 Co1 C6 C17 ndash1696(4) C26 Co1 C6 C5 1362(4) C26 Co1 C6 C7 ndash112(7) C26 Co1 C6 C17 ndash1261(4) C27 Co1 C6 C5 1799(4) C27 Co1 C6 C7 325(8) C27 Co1 C6 C17 ndash824(5) C28 Co1 C6 C5 ndash137(1) C28 Co1 C6 C7 75(1) C28 Co1 C6 C17 ndash40(1) C29 Co1 C6 C5 523(8) C29 Co1 C6 C7 ndash951(9) C29 Co1 C6 C17 1501(7) C5 Co1 C17 C6 ndash497(4) C5 Co1 C17 C16 ndash1646(8) C5 Co1 C17 C18 484(4) C6 Co1 C17 C16 ndash1149(8) C6 Co1 C17 C18 981(5) C18 Co1 C17 C6 ndash981(5) C18 Co1 C17 C16 1470(9) C25 Co1 C17 C6 32(1) C25 Co1 C17 C16 ndash83(1) C25 Co1 C17 C18 130(1) C26 Co1 C17 C6 799(5) C26 Co1 C17 C16 ndash350(8) C26 Co1 C17 C18 1780(4) C27 Co1 C17 C6 1245(4) C27 Co1 C17 C16 97(8) C27 Co1 C17 C18 ndash1373(4) C28 Co1 C17 C6 1686(4) C28 Co1 C17 C16 538(8) C28 Co1 C17 C18 ndash932(5) C29 Co1 C17 C6 ndash1471(7) C29 Co1 C17 C16 98(1) C29 Co1 C17 C18 ndash489(9) C5 Co1 C18 C1 1117(8) C5 Co1 C18 C17 ndash995(5)

- 112 -

C6 Co1 C18 C1 1609(7) C6 Co1 C18 C5 492(4) C6 Co1 C18 C17 ndash502(4) C17 Co1 C18 C1 ndash1488(8) C17 Co1 C18 C5 995(5) C25 Co1 C18 C1 544(9) C25 Co1 C18 C5 ndash573(7) C25 Co1 C18 C17 ndash1568(5) C26 Co1 C18 C1 ndash162(2) C26 Co1 C18 C5 87(3) C26 Co1 C18 C17 ndash13(3) C27 Co1 C18 C1 ndash784(8) C27 Co1 C18 C5 1699(4) C27 Co1 C18 C17 705(6) C28 Co1 C18 C1 ndash356(7) C28 Co1 C18 C5 ndash1473(4) C28 Co1 C18 C17 1133(4) C29 Co1 C18 C1 107(8) C29 Co1 C18 C5 ndash1010(5) C29 Co1 C18 C17 1595(4) C5 Co1 C25 C26 1356(4) C5 Co1 C25 C29 ndash1058(5) C6 Co1 C25 C26 873(5) C6 Co1 C25 C29 ndash1540(5) C17 Co1 C25 C26 62(1) C17 Co1 C25 C29 ndash1796(9) C18 Co1 C25 C26 1738(5) C18 Co1 C25 C29 ndash675(7) C26 Co1 C25 C29 1187(6) C27 Co1 C25 C26 ndash376(4) C27 Co1 C25 C29 810(5) C28 Co1 C25 C26 ndash806(5) C28 Co1 C25 C29 381(5) C29 Co1 C25 C26 ndash1187(6) C5 Co1 C26 C25 ndash696(6) C5 Co1 C26 C27 1703(4) C6 Co1 C26 C25 ndash1134(5) C6 Co1 C26 C27 1265(4) C17 Co1 C26 C25 ndash1604(4) C17 Co1 C26 C27 795(5) C18 Co1 C26 C25 ndash149(2) C18 Co1 C26 C27 91(3) C25 Co1 C26 C27 ndash1201(6) C27 Co1 C26 C25 1201(6) C28 Co1 C26 C25 825(5) C28 Co1 C26 C27 ndash376(4)

- 113 -

C29 Co1 C26 C25 383(5) C29 Co1 C26 C27 ndash818(5) C5 Co1 C27 C26 ndash77(3) C5 Co1 C27 C28 165(2) C6 Co1 C27 C26 ndash774(5) C6 Co1 C27 C28 1644(5) C17 Co1 C27 C26 ndash1254(4) C17 Co1 C27 C28 1163(5) C18 Co1 C27 C26 ndash1698(5) C18 Co1 C27 C28 720(6) C25 Co1 C27 C26 364(4) C25 Co1 C27 C28 ndash818(5) C26 Co1 C27 C28 ndash1182(6) C28 Co1 C27 C26 1182(6) C29 Co1 C27 C26 804(5) C29 Co1 C27 C28 ndash378(5) C5 Co1 C28 C27 ndash1768(5) C5 Co1 C28 C29 637(7) C6 Co1 C28 C27 ndash54(1) C6 Co1 C28 C29 ndash173(1) C17 Co1 C28 C27 ndash861(5) C17 Co1 C28 C29 1544(5) C18 Co1 C28 C27 ndash1355(5) C18 Co1 C28 C29 1050(5) C25 Co1 C28 C27 815(5) C25 Co1 C28 C29 ndash380(5) C26 Co1 C28 C27 387(4) C26 Co1 C28 C29 ndash809(5) C27 Co1 C28 C29 ndash1195(7) C29 Co1 C28 C27 1195(7) C5 Co1 C29 C25 953(5) C5 Co1 C29 C28 ndash1461(5) C6 Co1 C29 C25 576(9) C6 Co1 C29 C28 1762(6) C17 Co1 C29 C25 1797(7) C17 Co1 C29 C28 ndash617(9) C18 Co1 C29 C25 1437(4) C18 Co1 C29 C28 ndash977(5) C25 Co1 C29 C28 1186(7) C26 Co1 C29 C25 ndash373(4) C26 Co1 C29 C28 813(5) C27 Co1 C29 C25 ndash817(5) C27 Co1 C29 C28 369(5) C28 Co1 C29 C25 ndash1186(7) C19 Si1 C2 C1 ndash144(8) C19 Si1 C2 C3 1663(7)

- 114 -

C20 Si1 C2 C1 ndash1307(7) C20 Si1 C2 C3 500(8) C21 Si1 C2 C1 1057(7) C21 Si1 C2 C3 ndash736(7) C22 Si2 C3 C2 ndash852(7) C22 Si2 C3 C4 908(6) C23 Si2 C3 C2 1587(7) C23 Si2 C3 C4 ndash253(7) C24 Si2 C3 C2 410(8) C24 Si2 C3 C4 ndash1431(6) C18 C1 C2 Si1 1795(6) C18 C1 C2 C3 ndash1(1) C2 C1 C18 Co1 ndash817(9) C2 C1 C18 C5 1(1) C2 C1 C18 C17 173(1) Si1 C2 C3 Si2 ndash5(1) Si1 C2 C3 C4 1790(5) C1 C2 C3 Si2 1755(6) C1 C2 C3 C4 ndash0(1) Si2 C3 C4 C5 ndash1747(5) C2 C3 C4 C5 2(1) C3 C4 C5 Co1 822(8) C3 C4 C5 C6 ndash174(1) C3 C4 C5 C18 ndash2(1) Co1 C5 C6 C7 128(1) Co1 C5 C6 C17 ndash674(4) C4 C5 C6 Co1 ndash120(1) C4 C5 C6 C7 8(2) C4 C5 C6 C17 173(1) C18 C5 C6 Co1 671(4) C18 C5 C6 C7 ndash165(1) C18 C5 C6 C17 ndash03(6) Co1 C5 C18 C1 ndash1175(7) Co1 C5 C18 C17 667(4) C4 C5 C18 Co1 1179(7) C4 C5 C18 C1 0(1) C4 C5 C18 C17 ndash1754(7) C6 C5 C18 Co1 ndash663(4) C6 C5 C18 C1 1762(7) C6 C5 C18 C17 04(6) Co1 C6 C7 C8 ndash887(8) C5 C6 C7 C8 160(1) C17 C6 C7 C8 ndash2(1) Co1 C6 C17 C16 1243(7) Co1 C6 C17 C18 ndash672(4) C5 C6 C17 Co1 675(4)

- 115 -

C5 C6 C17 C16 ndash1681(7) C5 C6 C17 C18 03(5) C7 C6 C17 Co1 ndash1223(7) C7 C6 C17 C16 2(1) C7 C6 C17 C18 1705(7) C6 C7 C8 C9 ndash180(1) C6 C7 C8 C15 2(1) C7 C8 C9 C10 2(2) C7 C8 C9 C14 ndash179(1) C15 C8 C9 C10 ndash179(1) C15 C8 C9 C14 01(6) C7 C8 C15 C14 1791(7) C7 C8 C15 C16 ndash2(1) C9 C8 C15 C14 ndash01(5) C9 C8 C15 C16 1792(8) C8 C9 C10 C11 ndash180(1) C14 C9 C10 C11 1(1) C8 C9 C14 C13 1791(7) C8 C9 C14 C15 ndash01(6) C10 C9 C14 C13 ndash1(1) C10 C9 C14 C15 1796(7) C9 C10 C11 C12 ndash1(1) C10 C11 C12 C13 1(1) C11 C12 C13 C14 ndash2(1) C12 C13 C14 C9 2(1) C12 C13 C14 C15 ndash180(1) C9 C14 C15 C8 01(6) C9 C14 C15 C16 ndash179(1) C13 C14 C15 C8 ndash179(1) C13 C14 C15 C16 2(2) C8 C15 C16 C17 1(1) C14 C15 C16 C17 ndash180(1) C15 C16 C17 Co1 858(8) C15 C16 C17 C6 ndash2(1) C15 C16 C17 C18 ndash161(1) Co1 C17 C18 C1 120(1) Co1 C17 C18 C5 ndash669(4) C6 C17 C18 Co1 666(4) C6 C17 C18 C1 ndash173(1) C6 C17 C18 C5 ndash03(5) C16 C17 C18 Co1 ndash131(1) C16 C17 C18 C1 ndash11(2) C16 C17 C18 C5 162(1) Co1 C25 C26 C27 586(5) C29 C25 C26 Co1 ndash583(5) C29 C25 C26 C27 03(9)

- 116 -

Co1 C25 C29 C28 ndash598(6) C26 C25 C29 Co1 588(5) C26 C25 C29 C28 ndash10(9) Co1 C26 C27 C28 607(5) C25 C26 C27 Co1 ndash602(5) C25 C26 C27 C28 05(9) Co1 C27 C28 C29 595(6) C26 C27 C28 Co1 ndash607(5) C26 C27 C28 C29 ndash12(9) Co1 C28 C29 C25 609(6) C27 C28 C29 Co1 ndash595(6) C27 C28 C29 C25 14(9)

Photo-thermal cycle between 52 and 53

An NMR tube containing a solution of 52 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 53 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 724 (AArsquom 2 H) 683 (s 2 H) 662 (BBrsquom 2 H) 444 (s 5 H) 032 (s 18 H) ppm 13C- NMR (100 MHz C6D6) δ = 1493 1482 1430 1276 1256 1241 1155 803 796 725 222 ppm Thermal reversal could be conveniently followed by VT-NMR

Kinetic studies of the thermal CoCp migration in 53 In the glovebox 23-[bis(trimethylsilyl)] linear[3]phenylene(CpCo) 52 dissolved in the solvent of choice (C6D6 or toluene-d8) was passed through an HPLC filter and then transfered via syringe into a thick-walled NMR tube connected to a vacuum line adapter The sample was then degassed by three freeze-pump-thaw cycles and flame-sealed under vacuum Prior to the kinetic runs the mixtures were irradiated for 10 h in a Rayonet Photochemical Reactor fitted with lamps emitting at 310 and 365 nm After this treatment care was taken to exclude ambient light as it causes some isomerization The irradiated samples were then placed in the NMR spectrometer at ndash65 degC (500 MHz) which was then warmed to the required temperature In the case of the 60 degC runs the magnet was prewarmed because of the fast reaction rate at this temperature After five min the spectra were recorded The Cp signal of the photoisomer was integrated relative to the solvent peak of C6D6 or the CD3 peak of toluene-d8 and monitored as a function of time The integral from the first scan was used as [A]o Since the equilibrium constant between the isomers was 50 the kinetic analysis treated the isomerization as a first-order non-reversible process Plotting the data accordingly

CoSiMe3

SiMe3

52

CoSiMe3

SiMe3

53

hν∆

- 117 -

yielded the reaction rate constants which were used in the Eyring plots to obtain the activation parameters Kinetic studies of the thermal haptotropic shift for complex 52 Kinetic runs were executed in C6D6 as the optimum solvent A sample of 52 in degassed C6D6 or toluene-d8 was subjected to UV light for 10 h leading to maximum enrichment of 53 The sample was kept at the specified temperature and the disappearance of 53 monitored by 1H-NMR spectroscopy The reaction proved to be first-order (eq 1) consistent with an intramolecular process

[ ] [ ]Akdt

Adminus=

(1)

[ ][ ] dtkA

Ad=minus

(2)

[ ][ ]

tkA

A=minus

0

ln (3)

The rate constant (k) at 30 40 50 and 60 degC was obtained from the slope of a plot of ndashln([A][A]0) versus time (t) following eq 2 and 3 The actual error in reproducibility was estimated by the calculation of one standard deviation (σ) for a triplicate run at 60 degC The percentage error was applied for k at 30 40 and 50 degC The rate constants and their errors are given in Tables 411 and 414 The values for k and their standard deviations were used to calculate the activation enthalpy (∆HDagger) and entropy (∆SH) of the haptotropic shift The basis for these calculations is the Eyring equation (eq 4) This expression (eq 4) was transformed to eq 5 and the activation enthalpy (∆HDagger) obtained from the slope of a plot of ndashln(kT) versus 1RT The intercept (ndashC) provides the activation entropy (∆SH) following eq 6 and 7

C

TR

H

R

S

h

k

TR

H

T

k B

minus∆

=

∆+minus

∆=minus

ne

nene

lnln

( 4)

R

S

h

kC B

ne∆+= ln

(5)

minus=∆ ne

h

kCRS Bln

(6)

- 118 -

The errors in ∆HDagger and ∆SDagger were calculated based on those in the rate constants leading to two additional least square fits in the Eyring plot These fits represent the two most extreme deviations from the original plot This provides a conservative error estimate and finally the values of 204plusmn14 kcalmol for ∆HH and 158plusmn22 eu (calmolmiddotK) for ∆SH in C6D6 In order to probe for solvent effects the kinetics were also repeated in toluene-d8 The preparation of the sample followed the described procedure and the rate constants (k) were obtained at 30 40 50 and 60 degC At 60 degC three measurements were carried out to estimate the errors in reproducibility for k and the activation parameters Error propagation was done as described for the kinetic experiments in C6D6 It is assumed that those rate constants (k) show the same relative error as the ones for the rearrangement of 53 to 52 in C6D6 The activation parameters in toluene-d8 were found to be 231plusmn07 kcalmol and 60plusmn13 eu

Table 410 Kinetic Data for the Conversion of 53 to 52 in C6D6

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09657 00349 1000 09419 00599 6000 09380 00640 2000 09018 01034 9000 09038 01012 3000 08557 01558 12000 08760 01324 4000 08176 02013 15000 08418 01723 5000 07796 02490 18000 08206 01978 6000 07555 02804 21000 08010 02219 7000 07255 03210 32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 400 09541 00470 30 09888 00113 800 09197 00837 60 09820 00181 1200 08910 01154 90 09708 00296 1600 08489 01638 120 09596 00413 2000 08298 01865 150 09506 00507 2400 07954 02289 180 09416 00602 2800 07591 02756 210 09348 00674 240 09281 00746 270 09213 00819 300 09124 00917 330 09034 01016 360 08966 01091

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

- 119 -

0 10000 00000 0 10000 00000 30 09950 00050 30 09909 00092 60 09900 00101 60 09854 00147 90 09800 00202 90 09762 00241 120 09750 00253 120 09671 00335 150 09700 00305 150 09634 00372 180 09625 00382 180 09543 00468 210 09575 00434 210 09433 00583 240 09475 00539 240 09397 00622 270 09400 00619 270 09287 00740 300 09350 00672 300 09232 00799 330 09300 00726 330 09177 00858 360 09250 00780 360 09086 00959

Table 411 The Rate Constants (k) in C6D6 Calculated From the Data in Table 410 and Their

Standard Deviations (σ)

Temp (K) k (1s) σσσσ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 10809Endash05 74258Endash07 09970 171494 00688

31315 45615Endash05 31338Endash06 09948 157420 00688

32315 95118Endash05 65346Endash06 09965 150385 00688

33315 (1) 27425Endash04 09965

33315 (2) 25714Endash04 09964

33315 (3) 30051Endash04 09990

33315 (avg) 26511Endash04 18841Endash05 140101 00688

Table 412 Activation Parameters for the Kinetic Experiments in C6D6

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 90990 85414 79291 Intercept ndash1789 ndash1674 ndash1559 R

2 09869 09869 09869

∆HDagger (Jmol) 90990 85414 79291

∆HDagger (kcalmol) 217 204 190

∆SDagger (JmolmiddotK) ndash569 ndash660 ndash751

∆SDagger (eu) ndash136 ndash158 ndash180

- 120 -

(323 15 K 50 degC) y = 95118E-05x + 44505E-03

R2 = 9965

(30315 K 30 degC) y = 10809E-05x + 20474E-03

R2 = 9970

(31315 K 40 degC) y = 45615E-05x + 11689E-02

R2 = 9948

(33315 K 60 degC) y = 263387E-04x + 390297E-04

R2 = 9992

000

005

010

015

020

025

030

035

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

Figure 43 Kinetic plots for the conversion of 53 to 52 in C6D6

Table 413 Kinetic Data for the Conversion of 53 to 52 in Toluene-d8

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09556 00454 1000 09488 00526 6000 09256 00773 2000 08931 01130 9000 08956 01103 3000 08545 01572 12000 08667 01430 4000 08143 02054 15000 08343 01811 5000 07818 02461 18000 08103 02103 6000 07559 02798 21000 07863 02404 7000 07179 03314

- 121 -

32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

000 10000 00000 0 10000 00000 40000 09470 00544 30 09887 00113 80000 08934 01127 60 09775 00228 120000 08594 01515 90 09691 00314 160000 08175 02015 120 09592 00416 200000 07861 02406 150 09473 00542 240000 07502 02875 180 09381 00639 280000 06991 03579 210 09262 00767 240 09149 00889 270 09086 00959 300 08973 01083 330 08868 01202 360 08762 01321

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 30 09945 00055 30 09910 00090 60 09795 00207 60 09828 00173 90 09700 00304 90 09716 00288 120 09645 00361 120 09559 00451 150 09479 00535 150 09440 00576 180 09464 00551 180 09313 00712 210 09314 00711 210 09238 00792 240 09188 00847 240 09156 00882 270 09101 00942 270 08992 01063 300 08991 01064 300 08932 01129 330 08896 01170 330 08872 01197 360 08801 01277 360 08686 01409

- 122 -

Table 414 The Rate Constants (k) in Toluene-d8 Calculated From the Data in Table 413 and Their Standard Deviations (σ)

Temp (K) k (1s) σ σ σ σ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 11314Endash05 37152Endash07 09976 17104 05610

31315 46470Endash05 15251Endash06 09948 15723 05157

32315 12214Endash04 401074Endash06 09957 14788 04851

33315 (1) 36441Endash04 09992

33315 (2) 36124Endash04 09951

33315 (3) 38855Endash04 09956

33315 (avg) 37140Endash04 14937Endash05 13707 04496

Table 415 Activation Parameters for the Kinetic Experiments in Toluene-d8

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 96590 93523 90455 Intercept ndash2073 ndash2007 ndash1941 R

2 09962 09962 09962

∆HDagger (Jmol) 96590 93523 90455

∆HDagger (kcalmol) 2309 2235 2162

∆SDagger (JmolmiddotK) ndash2521 ndash3068 ndash3615

∆SDagger (eu) ndash602 ndash733 ndash864

- 123 -

00000

00500

01000

01500

02000

02500

03000

03500

04000

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

(31315 K 40 degC) y = 46470E-05x + 10553E-02

R2 = 9948

(32315 K 50 degC) y = 12214E-04x + 47671E-03

R2 = 9957

(33315 K 60 degC)y = 371377E-04x - 208381E-03

R2 = 9992

(30315 K 30 degC) y = 11314E-05x + 71900E-03

R2 = 9976

Figure 44 Kinetic plots for the conversion of 53 to 52 in toluene-d8

- 124 -

(C6D6) y = 85141x - 16743

R2

= 09869

(toluene-d 8) y = 93523x - 2007

R2 = 09962

13600

14600

15600

16600

17600

36100E-04

36600E-04

37100E-04

37600E-04

38100E-04

38600E-04

39100E-04

39600E-04

40100E-04

1RT (Jmol)

-ln

(kT

)

Figure 45 Eyring plots for conversion of 53 to 52 MeCpCo(CO)2

Adapted from the literature procedure50 Co2(CO)8 (809 g 2366 mmol) was added to a round bottom flask in the glovebox The flask was capped with a septum and brought out of the glovebox A reflux condenser connected to the high vacuum line was quickly exchanged with the septum under a heavy purge of argon Degassed CH2Cl2 (30 mL) was added followed by freshly cracked deoxygenated methylcyclopentadiene (135 mL 123 mmol) The mixture evolved gas upon addition of the methylcyclopentadiene indicating CO liberation The entire setup was protected from light with foil and heated to a gentle reflux using a heating mantlevariac heat source After stirring at reflux for 26 h the mixture now dark crimson in color was cooled to rt The reflux condenser was quickly exchanged for a distillation head under an Ar purge and CH2Cl2 distilled off at atmospheric pressure under Ar Vacuum distillation at 002 Torr was performed and the forerun discarded The desired complex was obtained as a red liquid (7296 g 79) bp = 31 degC (002 Torr) stored at ndash10 degC and shielded from light Note A small

CoOC CO

- 125 -

amount of methylcyclopentadiene dimer (15 ) which could not be separated was present in the isolated product This was deemed harmless however and the obtained product was used in further experiments without further purification 85 pure 1H-NMR data match those reported in the literature 1H-NMR (C6D6) δ = 145 (s 3 H) 431 (br s 2 H) 451 (br s 2 H) 23-Bis(trimethylsilyl) linear [3]phenylene(MeCpCo) 54

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (0146 g 0424 mmol) in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (0101 g 0731 mmol) The mixture was stirred for 100 min and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the remaining yellow residue was dissolved in freshly distilled THF (15 mL) The green solution was separated from the solids via canula filtration and transferred into another Schlenk flask After a 20 min Ar purge MeCpCo(CO)2 (0092 g 0403 mmol) was added and the resulting solution (protected from light with foil) injected via syringe pump over 9 h into a boiling mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 15 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (201) The volatiles were again removed under high vacuum line and the residue crystallized from acetone yielding 55 (0125 g 61 ) as black crystals mp 163ndash165 degC 1H-NMR (500 MHz C6D6) δ = 783 (s 2 H) 676 (m 4 H) 675 (s 2 H) 442 (apparent t J = 21 Hz 2 H) 427 (apparent t J = 21 Hz 2 H) 134 (s 3 H) 038 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1423 1386 1354 1293 1193 1147 899 806 798 783 739 111 279 ppm IR (neat) ν~ = 2959 2923 2853 1462 1455 1378 1260 1093 1030 802 cmndash1 UV-VIS (hexane) λmax (log ε) = 256 (368) 281 (356) 293 (359) 310 (373) 350 (368) 386 (sh 321) 437 (sh 287) 499 (sh 247) end absorption to 550 nm MS (70 eV) mz () 508 (100) [M+] 370 (28) HRMS (FAB) calcd for C30H33CoSi2 5081453 found 5081442 Photo-thermal cycle between 54 and 56

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

54

CoSiMe3

SiMe3

56

hν∆

Me Me

- 126 -

An NMR tube containing a solution of 54 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 56 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 715 (AArsquom obscured by solvent peak) 680 (s 2 H) 664 (AArsquom 2 H) 447 (apparent t J = 21 Hz 2 H) 428 (apparent t J = 21 Hz 2 H) 148 (s 3 H) 032 (s 18 H) ppm Thermal reversal could be conveniently followed by VT-NMR

14-Deuterio-23-bis(trimethylsilyl) linear [3]phenylene cyclopentadienylcobalt 55

To 23-bis(trimethylsilylethynyl)biphenylene 52 (0144 g 0418 mmol) in CH3OD (10 mL) was added freshly distilled ether (20 mL) and K2CO3 (0083 g 0600 mmol) The mixture was stirred for 100 min and monitored by TLC (hexaneCH2Cl2 51) When the starting material had disappeared the solvents were removed and the remaining yellow residue very quickly dissolved in freshly distilled THF (10 mL) The green solution was separated from the solids using a filter cannula and transferred to another Schlenk flask After a 20 min Ar purge CpCo(CO)2 (0072 g 0400 mmol) was added and the resulting solution (protected from light with foil) was injected via syringe pump over 7 h into a refluxing mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 14 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed on the high vacuum line and the residue recrystallized from acetone yielding 8 (0085 g 41 ) as dark red crystals 1H-NMR spectroscopy showed 63 incorporation of deuterium as indicated by the diminution of the peak intensity of the signal at δ = 796 (s 074 H) ppm MS (FAB) mz () 496 (100) [M+] 372 (19)

CoSiMe3

SiMe3

D

D

- 127 -

Crossover experiment with 54 and 55

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

h

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

5455

5657

A solution of complex 55 (~2 mg) and 54 (~2 mg) in C6D6 (06 mL) rigorously protected from light was analyzed by 1H-NMR spectroscopy to reveal a 1861 mixture of 5554 The peak for 55 at δ = 796 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound A mass spectrum of an aliquot gave the appropriate composite of the two respective molecular ion patterns (Figure 46) The sample was then irradiated as described for above 13 h at RT The 1H-NMR spectrum of the irradiated mixture showed the presence of the respective photoisomers of 55 and 54 There were no unidentifiable peaks the signal at δ = 7470 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound and the clearly resolved peak for 56 at δ = 7473 (s 2 H) ppm revealed unattenuated intensity An aliquot was submitted for mass spectral analysis furnishing the same pattern as that depicted above The sample was then placed in an oil bath preheated to 80 degC for 30 h a treatment that regenerated the original NMR spectrum of the mixture of 55 and 54 including the relative integration ratios Similarly mass spectral analysis resulted in the same pattern as that depicted in Figure 46

- 128 -

Figure 46 Mass spectrum from the crossover experiment between 55 and 56

Low temperature photolyses of 19 and 52 A small amount (~5 mg) of linear[3]phenylene(CpCo) 19 or 52 dissolved in toluene-d8 was added to a J-Young NMR tube in the glovebox The sealed sample was then placed inside a Pyrex Dewar flask positioned in a Rayonet Photochemical Reactor outfitted with UV-lamps emitting at 310 and 350 nm (as shown in Figure 214) Cooling was achieved with the use of a Neslab Refrigerated Circulating bath employing isopropanol as the cooling medium The cold isopropanol was pumped into and out of the Pyrex Dewar using securely fastened Tygon tubes maintaining a temperature of ndash55 to ndash50 degC Once the sample was chilled irradiation was commenced The total irradiation time varied from 25 to 4 h When analysis was required the sample was transported in another Dewar flask containing dry iceisopropanol (ndash78 degC) while the NMR spectrometer was prepared for the low temperature experiment The spectrometer was cooled (ndash80 to ndash30 degC depending on the experiment) the sample wiped with a paper towel placed inside the spinner and very quickly lowered manually with a string into the cold magnet After allowing time for the temperature to equilibrate (10 min) a spectrum was recorded For VT experiments the temperature was slowly

- 129 -

raised from ndash80 degC in 10 degree increments to 10 degC Spectra were recorded at each interval For all other experiments spectra were recorded at ndash30 degC 2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

In the glovebox 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19 (0049 g 0133 mmol) and CpCo(C2H4)2 (0025 g 0139 mmol)99 were added to a Schlenk flask The flask was sealed brought out of the box connected to a vacuum manifold and freshly distilled degassed benzene (15 mL) added The mixture was heated to 70 degC on an oil bath for 23 h before being cooled to RT The solvent was removed in vacuo giving a black residue that was rapidly filtered through a plug of neutral alumina activity III (25 x 35 cm) eluting with a mixture of hexanes and THF (1001) under nitrogen and into a Schlenk flask The solvents were again removed in vacuo and the ensuing black residue recrystallized from acetone at ndash78 degC to give pure 78 (0057 g 56 ) as black crystals 1H-NMR (400 MHz acetone-d6) δ = 039 (s 36H) 481 (s 2H) 489 (m 4H) 736 (s 4H) ppm 13C-NMR (100 MHz acetone-d6) δ = 266 5372 5710 8284 12587 14542 15054 ppm UV-VIS (hexane) λmax (log ε) 197 (334) 221 (336 sh) 244 (344) 286 (363) 386 (279 sh) 439 (258) MS (FAB) 762 (M+ 100) HRMS calcd for C40H52Si4Co2 7621810 found 7621791 43 Computational Details for Chapter Two All calculations were performed using the GAUSSIAN03100 program GaussView 30101 and ChemCraft102 were employed to input structures as well as view output results Optimized geometries were obtained at the hybrid density functional theory (DFT) using Beckersquos three-parameter exchange-correlation functional103 containing the non-local gradient correction of Lee Yang and Parr104 (B3LYP) For optimization purposes a standard basis 3-21G105 was used for hydrogen and carbon atoms For cobalt the LANL2DZ106 basis set was applied with the outermost d function released yielding a triple-zeta d basis along with the effective core potentials (ECP) to describe the core electrons For the single point energy calculations the basis sets were increased to 6-31G107 for hydrogen 6-311G108 for carbon and the modified LANL2DZ basis as described above for cobalt with an added f-orbital coefficient109 The potential energy surfaces were mapped through a scan calculation a feature also available within the GAUSSIAN03 program Transition state structures were obtained in three different steps (i) determination of initial and final products or the minimum closest to a TS (ii) a linear QST2110 search for an initial guess of a TS and

- 130 -

(iii) input of the results from (ii) into a QST3 search Transition states and minima were confirmed by carrying out frequency calculations (using the same basis as that used for the optimizations)

Calculated structures for linear [3]phenylene(CpCo) (labels from Figures 29 and 210 in Section 24)

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

C 2878616000 ndash1675635000 ndash1461246000 C 3986441000 ndash2043582000 ndash0714088000 C 3986471000 ndash2043226000 0714700000 C 2878686000 ndash1674908000 1461732000 C 1740663000 ndash1265994000 0736724000 C 1740638000 ndash1266353000 ndash0736388000 H 2884721000 ndash1731772000 ndash2551997000 H 2884845000 ndash1730511000 2552509000 C 0311237000 ndash0833174000 0748280000 C 0311204000 ndash0833522000 ndash0748106000 C ndash0893980000 ndash0698348000 ndash1520584000 C ndash0893913000 ndash0697588000 1520749000 C ndash1996288000 ndash0532216000 0744771000 C ndash1996322000 ndash0532586000 ndash0744640000 C ndash3491040000 ndash0328769000 ndash0716524000 C ndash3490989000 ndash0328300000 0716632000 C ndash4645388000 ndash0172650000 ndash1448232000 C ndash4645276000 ndash0171672000 1448326000 C ndash5836534000 ndash0014205000 ndash0697760000

- 131 -

C ndash5836481000 ndash0013731000 0697841000 H ndash0905006000 ndash0741217000 ndash2609771000 H ndash0904887000 ndash0739873000 2609960000 H ndash4666353000 ndash0168153000 ndash2539086000 H ndash6785734000 0111682000 ndash1227959000 H ndash6785641000 0112502000 1228028000 H ndash4666162000 ndash0166493000 2539178000 Co 1455829000 0662094000 ndash0000295000 C 0672548000 2613322000 0000481000 C 1502831000 2459745000 1168426000 C 2819523000 2140942000 0722371000 C 2818808000 2141294000 ndash0723848000 C 1501651000 2460224000 ndash1168394000 H ndash0391329000 2836892000 0001070000 H 1172930000 2540112000 2200200000 H 3678957000 1932268000 1353707000 H 3677612000 1932967000 ndash1356152000 H 1170676000 2541059000 ndash2199789000 H 4894703000 ndash2369906000 1230670000 H 4894651000 ndash2370516000 ndash1229936000

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

C ndash3991583000 ndash2430244000 ndash0695300000 C ndash2895249000 ndash1923385000 ndash1446977000 C ndash1838331000 ndash1436925000 ndash0718218000 C ndash0460541000 ndash0772703000 ndash0748934000

- 132 -

C 0758545000 ndash0733408000 ndash1513161000 C 1871918000 ndash0586111000 ndash0739684000 C 3374782000 ndash0432509000 ndash0717168000 C 4533131000 ndash0322603000 ndash1448209000 C 5731498000 ndash0208370000 ndash0696796000 C 5731438000 ndash0207885000 0696952000 C 4533003000 ndash0321597000 1448333000 C 3374722000 ndash0432010000 0717261000 C 1871861000 ndash0585642000 0739747000 C 0758457000 ndash0732583000 1513259000 C ndash0460578000 ndash0772439000 0748991000 C ndash1838348000 ndash1436677000 0718485000 C ndash2895298000 ndash1922892000 1447371000 C ndash3991613000 ndash2429987000 0695830000 H ndash4853881000 ndash2841402000 ndash1229010000 H ndash2909366000 ndash1943431000 ndash2538196000 H 0770744000 ndash0814782000 ndash2600896000 H 4554949000 ndash0321315000 ndash2539049000 H 6684245000 ndash0118682000 ndash1227928000 H 6684140000 ndash0117859000 1228104000 H 4554722000 ndash0319567000 2539175000 H 0770611000 ndash0813312000 2601042000 H ndash2909450000 ndash1942588000 2538596000 H ndash4853932000 ndash2840954000 1229654000 Co ndash1032604000 1030206000 ndash0000179000 C ndash2903591000 1947430000 ndash0000175000 C ndash2211742000 2430689000 ndash1177143000 C ndash1026232000 3056089000 ndash0732194000 C ndash1026229000 3056139000 0731719000 C ndash2211730000 2430773000 1176747000 H ndash3829247000 1376180000 ndash0000150000 H ndash2513347000 2264399000 ndash2207387000 H ndash0243163000 3477094000 ndash1358586000 H ndash0243137000 3477190000 1358051000 H ndash2513304000 2264572000 2207015000

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 133 -

C 4829664000 ndash1220862000 0883782000 C 3649435000 ndash0895915000 1609183000 C 2478533000 ndash0900239000 0886069000 C 0985532000 ndash0699413000 0895282000 C ndash0207413000 ndash0351140000 1567281000 C ndash1295977000 ndash0355264000 0631690000 C ndash2799524000 ndash0368596000 0647705000 C ndash3950748000 0104186000 1252743000 C ndash5173877000 ndash0370408000 0725519000 C ndash5217559000 ndash1270006000 ndash0351644000 C ndash4043168000 ndash1754445000 ndash0967619000 C ndash2843350000 ndash1293792000 ndash0444950000 C ndash1365414000 ndash1319830000 ndash0538287000 C ndash0225558000 ndash1662005000 ndash1182029000 C 0928168000 ndash1009692000 ndash0554559000 C 2436156000 ndash1209374000 ndash0509824000 C 3575395000 ndash1530032000 ndash1215144000 C 4792344000 ndash1526592000 ndash0477473000 H 5781080000 ndash1237670000 1406156000 H 3693287000 ndash0679862000 2671420000 H ndash0279175000 ndash0037747000 2601166000 H ndash3939706000 0801901000 2083798000 H ndash6106757000 ndash0031072000 1165263000 H ndash6183419000 ndash1601741000 ndash0720200000 H ndash4097586000 ndash2453276000 ndash1795561000 H ndash0137803000 ndash2306368000 ndash2049380000 H 3570207000 ndash1781979000 ndash2270507000 H 5717527000 ndash1774506000 ndash0988963000 Co 0235674000 0924694000 ndash0006080000 C 1650242000 2605908000 ndash0261710000 C 0606451000 3071372000 0583798000

C ndash0633939000 2891762000 ndash0112192000 C ndash0354070000 2388098000 ndash1431110000 C 1060641000 2182627000 ndash1507942000 H 2701380000 2562827000 ndash0018620000 H 0717262000 3431891000 1595877000 H ndash1615358000 3123686000 0274491000 H ndash1077256000 2190401000 ndash2207047000

- 134 -

H 1601331000 1788686000 ndash2355167000

(d) Transition State 2 η3-benzene (249 kcalmol)

C 5059641000 ndash0675345000 0741440000 C 3868057000 ndash0242461000 1393542000 C 2691208000 ndash0611642000 0796692000 C 1164924000 ndash0568451000 0814993000 C 0001006000 ndash0193010000 1575722000 C ndash1162903000 ndash0569406000 0815406000 C ndash2689168000 ndash0613549000 0797134000 C ndash3866228000 ndash0245076000 1394017000 C ndash5057560000 ndash0678583000 0741882000 C ndash5030442000 ndash1430649000 ndash0426732000 C ndash3802288000 ndash1812828000 ndash1038342000 C ndash2662603000 ndash1392426000 ndash0404590000 C ndash1143695000 ndash1392940000 ndash0383227000 C 0001354000 ndash1885575000 ndash1010384000 C 1146183000 ndash1392203000 ndash0383465000 C 2665098000 ndash1390792000 ndash0404876000 C 3805017000 ndash1810598000 ndash1038596000 C 5032958000 ndash1427555000 ndash0427087000 H 6017043000 ndash0408623000 1174840000 H 3916675000 0338622000 2306082000 H 0001106000 0141040000 2603832000 H ndash3915179000 0335814000 2306664000 H ndash6015116000 ndash0412488000 1175329000

- 135 -

H ndash5963925000 ndash1737868000 ndash0883265000 H ndash3794877000 ndash2406462000 ndash1944276000 H 0001449000 ndash2505619000 ndash1894591000 H 3797948000 ndash2404400000 ndash1944423000 H 5966616000 ndash1734262000 ndash0883606000 Co ndash0000294000 1006304000 0016484000 C 1144150000 2811021000 ndash0317903000 C ndash0001831000 3236912000 0413780000 C ndash1150105000 2808519000 ndash0312717000 C ndash0712506000 2257800000 ndash1588662000 C 0702130000 2259464000 ndash1591918000 H 2174046000 2940434000 ndash0021226000 H ndash0000096000 3693787000 1391408000 H ndash2178919000 2935539000 ndash0011312000 H ndash1360790000 1903514000 ndash2375388000 H 1347563000 1907002000 ndash2381795000

Calculated structures for linear [5]phenylene CpCo (labels from Figures 211 and 212 in Section 24)

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

C ndash2147283000 ndash0385762000 ndash0741520000 C ndash2146881000 ndash0382747000 0740465000 C ndash0675330000 ndash0218887000 0741228000 C ndash0675503000 ndash0222208000 ndash0743565000 C 0535474000 ndash0309864000 ndash1519364000

- 136 -

C 1654024000 ndash0363787000 ndash0743565000 C 1653968000 ndash0359108000 0742223000 C 0535464000 ndash0301263000 1517648000 C 3146303000 ndash0437352000 0715394000 C 3146555000 ndash0442081000 ndash0715839000 H 0537903000 ndash0329735000 2601810000 H 0538062000 ndash0344229000 ndash2603354000 Co ndash1585768000 1444604000 ndash0004763000 C ndash2656365000 3118646000 0813641000 C ndash1264152000 3247968000 1115884000 C ndash0546296000 3292610000 ndash0128221000 C ndash1500173000 3225060000 ndash1199322000 C ndash2801883000 3099872000 ndash0616868000 H ndash3459184000 3033020000 1530368000 H ndash0824887000 3279284000 2101474000 H 0525240000 3366953000 ndash0237713000 H ndash1272392000 3239735000 ndash2254384000 H ndash3732669000 2998753000 ndash1154572000 C ndash3315848000 ndash0698077000 1516941000 C ndash3316515000 ndash0705270000 ndash1515890000 C ndash4404590000 ndash0970491000 0742487000 C ndash4404888000 ndash0974125000 ndash0739677000 H ndash3311463000 ndash0745189000 ndash2599679000 H ndash3310191000 ndash0733014000 2600900000 C ndash5857232000 ndash1346832000 ndash0713671000 C ndash5856902000 ndash1343302000 0718959000 C ndash6992149000 ndash1638138000 ndash1445564000 C ndash6991464000 ndash1630979000 1452826000 C 4314567000 ndash0501395000 ndash1493440000 C 4313844000 ndash0491124000 1494022000

C ndash8157130000 ndash1937355000 ndash0695553000 C ndash8156796000 ndash1933908000 0704865000 H ndash7013569000 ndash1630976000 2537309000 H ndash9075842000 ndash2169721000 1232475000 H ndash9076411000 ndash2175846000 ndash1221548000 H ndash7014707000 ndash1643790000 ndash2530023000 C 5464859000 ndash0553191000 0719930000 C 5465218000 ndash0558312000 ndash0718328000 C 6977989000 ndash0635007000 ndash0714777000 C 6977565000 ndash0629511000 0717833000 H 4313279000 ndash0484164000 2577745000 H 4314609000 ndash0502067000 ndash2577185000 C 8138196000 ndash0684071000 1451266000 C 8139115000 ndash0695400000 ndash1446980000 C 9348946000 ndash0746919000 0699256000 C 9349380000 ndash0752387000 ndash0693700000

- 137 -

H 8162380000 ndash0700716000 ndash2531270000 H 8160717000 ndash0680929000 2535584000 H 10294800000 ndash0791917000 1230058000 H 10295576000 ndash0801571000 ndash1223516000

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

C ndash8026536000 ndash2149127000 ndash0697047000 C ndash6872771000 ndash1801590000 ndash1447012000 C ndash5755909000 ndash1466198000 ndash0717983000 C ndash4305789000 ndash1041476000 ndash0739357000 C ndash3218268000 ndash0750848000 ndash1510952000 C ndash2077793000 ndash0315087000 ndash0749237000 C ndash0550342000 ndash0400850000 ndash0716361000 C 0616872000 ndash0404801000 ndash1489728000 C 1770640000 ndash0412395000 ndash0716060000 C 3300443000 ndash0457807000 ndash0715861000 C 4454767000 ndash0490291000 ndash1489427000 C 5616257000 ndash0520747000 ndash0712496000 C 5616269000 ndash0520699000 0712492000 C 4454793000 ndash0490190000 1489443000 C 3300455000 ndash0457762000 0715895000 C 1770651000 ndash0412347000 0716117000 C 0616894000 ndash0404700000 1489800000 C ndash0550335000 ndash0400796000 0716454000 C ndash2077818000 ndash0315060000 0749341000 C ndash3218306000 ndash0750915000 1510996000

- 138 -

C ndash4305781000 ndash1041534000 0739359000 C ndash5755900000 ndash1466256000 0717962000 C ndash6872758000 ndash1801708000 1446971000 C ndash8026533000 ndash2149171000 0696987000 H ndash6893447000 ndash1807486000 ndash2529846000 H ndash3199702000 ndash0827686000 ndash2591829000 H 0616147000 ndash0415875000 ndash2572166000 H 4455855000 ndash0492565000 ndash2571217000 H 4455901000 ndash0492389000 2571233000 H 0616188000 ndash0415693000 2572238000 H ndash3199790000 ndash0827916000 2591862000 H ndash6893430000 ndash1807681000 2529804000 Co ndash2237895000 1566525000 ndash0000035000 C ndash0770702000 3039808000 0000091000 C ndash1582333000 3276979000 1176306000 C ndash2906316000 3484053000 0731575000 C ndash2906172000 3484095000 ndash0731735000 C ndash1582100000 3277047000 ndash1176233000 H 0281094000 2798829000 0000215000 H ndash1247438000 3209109000 2198999000 H ndash3777291000 3625124000 1353071000 H ndash3777011000 3625160000 ndash1353424000 H ndash1246943000 3209260000 ndash2198847000 H ndash8933230000 ndash2423019000 ndash1224452000 H ndash8933222000 ndash2423113000 1224377000 C 7146943000 ndash0559737000 0717588000 C 7146931000 ndash0559786000 ndash0717614000 C 8302361000 ndash0588480000 1447040000 C 8302337000 ndash0588576000 ndash1447082000 C 9516918000 ndash0618789000 ndash0692883000 C 9516929000 ndash0618742000 0692823000 H 8324450000 ndash0589130000 2529610000 H 10461320000 ndash0642422000 1224406000 H 10461300000 ndash0642481000 ndash1224480000 H 8324409000 ndash0589299000 ndash2529653000

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 139 -

C ndash7810644000 ndash2064896000 ndash0088979000 C ndash6582065000 ndash2396690000 ndash0700394000 C ndash5469369000 ndash1694626000 ndash0259356000 C ndash4011414000 ndash1478684000 ndash0398743000 C ndash2839913000 ndash1679834000 ndash1045300000 C ndash1807973000 ndash0777407000 ndash0523048000 C ndash0288034000 ndash0728447000 ndash0497727000 C 0877200000 ndash0917515000 ndash1257428000 C 2033335000 ndash0625143000 ndash0541547000 C 3550975000 ndash0572504000 ndash0566638000 C 4702932000 ndash0775398000 ndash1323945000 C 5869717000 ndash0493099000 ndash0604711000 C 5877160000 ndash0049178000 0749672000 C 4719648000 0152978000 1509600000 C 3558389000 ndash0127834000 0791889000 C 2041313000 ndash0178303000 0818968000 C 0890228000 0010834000 1576182000

C ndash0275189000 ndash0290874000 0857465000 C ndash1777915000 ndash0332627000 0896504000 C ndash3000252000 ndash0144927000 1576583000 C ndash4087655000 ndash0414543000 0681649000 C ndash5565811000 ndash0681071000 0748878000 C ndash6769777000 ndash0358061000 1349731000 C ndash7902756000 ndash1078577000 0906205000 H ndash6531350000 ndash3165530000 ndash1463988000 H ndash2656944000 ndash2379915000 ndash1852763000

- 140 -

H 0873498000 ndash1259556000 ndash2286041000 H 4697058000 ndash1113491000 ndash2353481000 H 4726794000 0489146000 2539724000 H 0892018000 0335667000 2610226000 H ndash3107471000 0242268000 2582171000 H ndash6863567000 0403771000 2116786000 Co ndash2805901000 1045228000 ndash0126008000 C ndash1966955000 3131745000 ndash0137391000 C ndash3345106000 3172285000 0219040000 C ndash4105003000 2591218000 ndash0859559000 C ndash3194452000 2177424000 ndash1877135000 C ndash1861601000 2475718000 ndash1403791000 H ndash1139494000 3467521000 0469940000 H ndash3757304000 3575577000 1132204000 H ndash5178689000 2478840000 ndash0883920000 H ndash3449207000 1717975000 ndash2819531000 H ndash0944137000 2267497000 ndash1933863000 H ndash8711780000 ndash2586977000 ndash0395882000 H ndash8871888000 ndash0864282000 1346179000 C 7394568000 0005138000 0727783000

C 7387058000 ndash0441388000 ndash0634217000 C 8557433000 0273605000 1404315000

C 8542647000 ndash0629395000 ndash1349402000 C 9760631000 ndash0352464000 ndash0653366000 C 9767843000 0080954000 0667800000 H 8586089000 0612106000 2434348000 H 10716375000 0279405000 1157078000

H 10703753000 ndash0485281000 ndash1174332000 H 8560430000 ndash0966385000 ndash2380163000

(d) Transition state 4 η3-benzene (367 kcalmol)

- 141 -

C 7669717000 ndash2174926000 ndash0105923000 C 6450462000 ndash2458728000 0544003000 C 5349535000 ndash1733337000 0120322000 C 3893688000 ndash1505268000 0269179000 C 2708972000 ndash1942858000 0838638000 C 1596115000 ndash1239419000 0370186000 C 0149218000 ndash1103313000 0368184000 C ndash1061261000 ndash1583264000 0932639000 C ndash2167377000 ndash0965378000 0405284000 C ndash3686709000 ndash0866795000 0409630000 C ndash4872520000 ndash1347856000 0960688000 C ndash5997863000 ndash0728310000 0421450000 C ndash5941471000 0288854000 ndash0586107000 C ndash4758793000 0770529000 ndash1137452000 C ndash3629556000 0150846000 ndash0598044000 C ndash2119390000 0068600000 ndash0617626000 C ndash0945265000 0548559000 ndash1173832000 C 0191709000 ndash0072876000 ndash0643629000 C 1695402000 ndash0118964000 ndash0667389000 C 2835200000 0041396000 ndash1507494000 C 3981535000 ndash0415532000 ndash0796385000 C 5449049000 ndash0747489000 ndash0920326000 C 6638556000 ndash0473422000 ndash1556289000 C 7762417000 ndash1216205000 ndash1122513000 H 6396888000 ndash3209338000 1323030000 H 2647172000 ndash2772334000 1532449000 H ndash1099468000 ndash2356302000 1688990000 H ndash4914534000 ndash2116326000 1720908000 H ndash4717626000 1537921000 ndash1898781000 H ndash0906852000 1317204000 ndash1935050000 H 2849903000 0560387000 ndash2457942000 H 6730568000 0262385000 ndash2346085000 Co 3078365000 1106450000 0223118000 C 2432920000 3235925000 0352954000 C 3805628000 3232135000 ndash0000959000 C 4525686000 2519574000 1027488000 C 3591065000 2151422000 2051886000 C 2287258000 2550618000 1620273000

- 142 -

H 1625110000 3662123000 ndash0222202000 H 4237852000 3652387000 ndash0895767000 H 5588986000 2336674000 1044912000 H 3828106000 1629983000 2966790000 H 1363656000 2417646000 2161607000 H 8562189000 ndash2715853000 0187384000 H 8723754000 ndash1039126000 ndash1591154000 C ndash7467794000 0379383000 ndash0580257000 C ndash7522920000 ndash0639213000 0428535000 C ndash8594261000 0964602000 ndash1089561000 C ndash8706397000 ndash1090617000 0945872000 C ndash9887862000 ndash0485330000 0420145000 C ndash9834353000 0499744000 ndash0555359000 H ndash8574126000 1734202000 ndash1850912000 H ndash10757407000 0931123000 ndash0925119000 H ndash10851990000 ndash0807405000 0796463000 H ndash8770071000 ndash1858056000 1706995000

(e) Local minimum 3 η4-benzene (190 kcalmol)

C ndash7704806000 ndash1625445000 ndash0076324000 C ndash6491455000 ndash1789497000 ndash0801300000 C ndash5352262000 ndash1326936000 ndash0190371000 C ndash3836374000 ndash1127906000 ndash0291559000 C ndash2669014000 ndash1876939000 ndash0775878000 C ndash1540408000 ndash1361850000 ndash0248671000 C ndash0067088000 ndash1219487000 ndash0231176000 C 1147603000 ndash1746746000 ndash0723682000

- 143 -

C 2245517000 ndash1037457000 ndash0289605000 C 3767258000 ndash0910575000 ndash0313273000 C 4961694000 ndash1439625000 ndash0795996000 C 6075343000 ndash0726547000 ndash0354068000 C 5999362000 0418026000 0498208000 C 4804020000 0947684000 0980899000 C 3691158000 0235329000 0538756000 C 2171505000 0121554000 0570963000 C 0990404000 0649716000 1051234000

C ndash0139369000 ndash0066282000 0613306000 C ndash1640889000 ndash0139469000 0665899000 C ndash2708579000 0044357000 1607074000 C ndash3890300000 ndash0515482000 1069631000 C ndash5389479000 ndash0719093000 1106627000 C ndash6553177000 ndash0561696000 1815459000 C ndash7736166000 ndash1034716000 1182797000 H ndash6489929000 ndash2263627000 ndash1775522000 H ndash2743316000 ndash2692464000 ndash1483904000 H 1201969000 ndash2617287000 ndash1364047000 H 5019196000 ndash2306567000 ndash1440440000 H 4747029000 1814065000 1626168000 H 0933710000 1519855000 1692796000 H ndash2640951000 0605584000 2529735000 H ndash6590996000 ndash0122891000 2805220000 Co ndash3231943000 0870639000 ndash0218177000 C ndash2631117000 2925280000 ndash0475333000 C ndash4019450000 2955930000 ndash0137499000 C ndash4720042000 2167067000 ndash1095287000 C ndash3768150000 1717753000 ndash2089396000 C ndash2477085000 2188405000 ndash1710046000 H ndash1832546000 3399891000 0073720000 H ndash4448788000 3419647000 0737399000 H ndash5777018000 1951944000 ndash1095854000 H ndash3999907000 1119290000 ndash2956393000 H ndash1549894000 2013889000 ndash2232360000 H ndash8630326000 ndash1978241000 ndash0517433000 H ndash8683428000 ndash0939767000 1701100000 C 7524401000 0541032000 0473497000

C 7600630000 ndash0607844000 ndash0382149000 C 8637973000 1216338000 0890053000

C 8792152000 ndash1101412000 ndash0836674000 C 9961705000 ndash0402146000 ndash0407106000 C 9887895000 0708141000 0420266000 H 8602106000 2084773000 1535736000 H 10801526000 1207625000 0721410000

H 10931894000 ndash0752974000 ndash0739605000

- 144 -

H 8871661000 ndash1966753000 ndash1482602000

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

C 7143264000 ndash2348493000 0699665000 C 6037664000 ndash1857298000 1448523000 C 4969251000 ndash1391864000 0720257000 C 3582514000 ndash0743198000 0748195000 C 2358402000 ndash0737338000 1512136000 C 1240141000 ndash0634711000 0742222000 C ndash0262684000 ndash0516912000 0716494000 C ndash1428088000 ndash0430968000 1492584000 C ndash2574224000 ndash0346717000 0719319000 C ndash4098679000 ndash0233199000 0715866000 C ndash5251323000 ndash0147278000 1490294000 C ndash6408253000 ndash0063372000 0713741000 C ndash7934932000 0047490000 0717366000 C ndash9088044000 0130556000 1446914000 C ndash10299063000 0217080000 0692638000 C ndash10298939000 0215301000 ndash0693576000 C ndash9087782000 0126841000 ndash1447398000 C ndash7934811000 0045602000 ndash0717417000 C ndash6408180000 ndash0065400000 ndash0713264000 C ndash5251144000 ndash0151514000 ndash1489420000 C ndash4098619000 ndash0235099000 ndash0714599000 C ndash2574142000 ndash0348081000 ndash0717615000 C ndash1428022000 ndash0433439000 ndash1490677000

- 145 -

C ndash0262587000 ndash0517946000 ndash0714342000 C 1239930000 ndash0636111000 ndash0739947000 C 2357013000 ndash0742891000 ndash1511730000 C 3581891000 ndash0749703000 ndash0749006000 C 4968536000 ndash1397444000 ndash0717250000 C 6036190000 ndash1868351000 ndash1443314000 C 7142499000 ndash2353756000 ndash0691900000 H 8003789000 ndash2740125000 1230531000 H 6052031000 ndash1874231000 2531931000 H 2350726000 ndash0802237000 2593967000 H ndash1427931000 ndash0429806000 2574521000 H ndash5251989000 ndash0146640000 2572026000 H ndash9110076000 0132990000 2529448000 H ndash11241535000 0285430000 1223689000 H ndash11241318000 0282253000 ndash1224971000 H ndash9109613000 0126365000 ndash2529940000 H ndash5251637000 ndash0153720000 ndash2571150000 H ndash1427824000 ndash0434279000 ndash2572612000 H 2347832000 ndash0810535000 ndash2593375000 H 6049185000 ndash1893779000 ndash2526553000 H 8002469000 ndash2749449000 ndash1220666000 Co 4148367000 1055016000 ndash0009106000 C 5996101000 2006266000 0022069000 C 5276853000 2480887000 1185002000 C 4085420000 3079352000 0718350000 C 4110596000 3077077000 ndash0745160000 C 5316353000 2474554000 ndash1168669000 H 6921324000 1451094000 0038659000 H 5556549000 2314709000 2212960000 H 3287274000 3477873000 1325692000 H 3334253000 3474398000 ndash1380859000 H 5631980000 2304731000 ndash2185537000

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 146 -

C 4893664000 ndash1209972000 0735005000 C 4893573000 ndash1213475000 ndash0730870000 C 3475382000 ndash0763132000 ndash0743915000 C 3475432000 ndash0760320000 0747049000 C 2260316000 ndash0690973000 1520580000 C 1145205000 ndash0595973000 0744946000 C 1145156000 ndash0599246000 ndash0742744000 C 2260358000 ndash0697381000 ndash1517904000 C ndash0343192000 ndash0479177000 ndash0713609000 C ndash0343168000 ndash0476032000 0715380000 H 2252105000 ndash0735285000 ndash2601934000 H 2251901000 ndash0724154000 2604763000 Co 4601208000 0736083000 ndash0002055000 C 5960130000 2243618000 ndash0721946000 C 4640007000 2540538000 ndash1172530000 C 3804522000 2681992000 ndash0008876000 C 4632302000 2544967000 1160921000 C 5955467000 2247130000 0721276000 H 6816321000 2038808000 ndash1347044000 H 4312673000 2604006000 ndash2199136000 H 2745254000 2890841000 ndash0012873000 H 4298236000 2612143000 2185222000 H 6807361000 2044890000 1353015000 C 6022290000 ndash1649780000 1464200000 C 6022277000 ndash1656609000 ndash1457900000 C 7122289000 ndash2056771000 0719324000 C 7122311000 ndash2060028000 ndash0711126000 H 6027301000 ndash1702610000 2548102000 H 8011576000 ndash2407816000 1233935000 H 8011528000 ndash2413601000 ndash1224115000 H 6027432000 ndash1714310000 ndash2541551000 C ndash1512226000 ndash0382902000 1494684000 C ndash1512274000 ndash0389473000 ndash1493257000 C ndash2658093000 ndash0297761000 0720325000 C ndash2658103000 ndash0300923000 ndash0719236000 H ndash1511446000 ndash0379165000 2578406000

- 147 -

H ndash1511531000 ndash0390614000 ndash2576954000 C ndash4169046000 ndash0190131000 ndash0714237000 C ndash4169015000 ndash0186849000 0714915000 C ndash5325016000 ndash0103295000 1491764000 C ndash5325120000 ndash0110177000 ndash1491395000 C ndash6483203000 ndash0023670000 0713863000 C ndash6483258000 ndash0027061000 ndash0713749000 H ndash5325252000 ndash0101647000 2575308000 H ndash5325471000 ndash0113799000 ndash2574933000 C ndash7997403000 0080746000 0716440000 C ndash7997524000 0076500000 ndash0716680000 C ndash9155096000 0160872000 1448927000 C ndash9155379000 0152083000 ndash1449432000 C ndash10366775000 0240123000 0695134000 C ndash10366925000 0235844000 ndash0695874000 H ndash9178696000 0150122000 ndash2533721000 H ndash11311550000 0297904000 ndash1227155000 H ndash11311298000 0305233000 1226228000 H ndash9178228000 0165001000 2533216000

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

C 8266704000 ndash2005162000 0692734000 C 7088955000 ndash1708719000 1446000000 C 5966603000 ndash1428050000 0716466000

- 148 -

C 4483884000 ndash1054830000 0713802000 C 3355736000 ndash0795879000 1487813000 C 2219848000 ndash0542568000 0715155000 C 0748349000 ndash0122254000 0743952000 C ndash0460068000 ndash0300197000 1509394000 C ndash1583463000 ndash0354552000 0739667000 C ndash3088504000 ndash0455891000 0716671000 C ndash4249167000 ndash0553278000 1491353000 C ndash5399475000 ndash0634011000 0717623000 C ndash6922525000 ndash0754459000 0717051000 C ndash8076029000 ndash0852663000 1446746000 C ndash9285359000 ndash0940991000 0693505000 C ndash9286426000 ndash0927591000 ndash0694047000 C ndash8078221000 ndash0824629000 ndash1447252000 C ndash6923651000 ndash0740632000 ndash0717519000 C ndash5400498000 ndash0620402000 ndash0717994000 C ndash4251528000 ndash0525736000 ndash1491803000 C ndash3089431000 ndash0443610000 ndash0717063000 C ndash1585243000 ndash0344579000 ndash0740307000 C ndash0463450000 ndash0290395000 ndash1513612000 C 0748496000 ndash0127629000 ndash0751652000 C 2219455000 ndash0546002000 ndash0721683000 C 3355860000 ndash0802470000 ndash1493276000 C 4483583000 ndash1057975000 ndash0718022000 C 5966360000 ndash1431783000 ndash0719354000 C 7088265000 ndash1716549000 ndash1447876000 C 8266466000 ndash2008718000 ndash0693595000 H 9183427000 ndash2233531000 1224348000 H 7110060000 ndash1714392000 2528663000 H 3353411000 ndash0803478000 2570367000 H ndash0456292000 ndash0373454000 2590614000 H ndash4248665000 ndash0564171000 2573279000 H ndash8096828000 ndash0865292000 2529266000 H ndash10227269000 ndash1021159000 1223954000 H ndash10229127000 ndash0997490000 ndash1224546000 H ndash8100648000 ndash0816347000 ndash2529785000 H ndash4252664000 ndash0517117000 ndash2573754000 H ndash0464650000 ndash0354640000 ndash2595436000 H 3353541000 ndash0815213000 ndash2575752000 H 7108905000 ndash1727728000 ndash2530504000 H 9182976000 ndash2239822000 ndash1224379000 Co 1060170000 1739352000 ndash0013647000 C 0820599000 3762931000 0679296000 C 2023158000 3250849000 1217023000 C 2833506000 2814255000 0100512000 C 2185795000 3225276000 ndash1129991000

- 149 -

C 0924349000 3753677000 ndash0780133000 H ndash0033478000 4112410000 1239126000 H 2257663000 3114053000 2260457000 H 3791311000 2322414000 0171627000 H 2565428000 3065285000 ndash2126458000 H 0160713000 4098445000 ndash1460120000

(i) Local minimum 1 η4-benzene (190 kcalmol)

C 8767525000 ndash0664628000 0869444000 C 7569070000 ndash0364489000 1586360000 C 6400497000 ndash0535559000 0896308000 C 4872998000 ndash0456407000 0896648000 C 3729258000 ndash0166123000 1633430000 C 2558863000 ndash0367557000 0899969000 C 1050529000 ndash0274920000 0917771000 C ndash0154687000 0103769000 1545183000 C ndash1231288000 ndash0039565000 0606842000 C ndash2736221000 ndash0089835000 0603708000 C ndash3901526000 0467576000 1153370000 C ndash5054648000 ndash0104455000 0647800000 C ndash6579036000 ndash0120351000 0673091000 C ndash7732820000 0402806000 1194768000 C ndash8948594000 ndash0155119000 0702959000 C ndash8958839000 ndash1167887000 ndash0247745000 C ndash7753788000 ndash1707235000 ndash0785423000 C ndash6589806000 ndash1166201000 ndash0307896000

- 150 -

C ndash5063448000 ndash1158179000 ndash0339650000 C ndash3923750000 ndash1713712000 ndash0884954000 C ndash2743411000 ndash1141750000 ndash0370168000 C ndash1264100000 ndash1152263000 ndash0442985000 C ndash0114410000 ndash1509648000 ndash1047872000 C 1001557000 ndash0717865000 ndash0509678000 C 2529242000 ndash0815059000 ndash0456630000 C 3680301000 ndash1106705000 ndash1192448000 C 4847485000 ndash0909766000 ndash0461159000 C 6375435000 ndash0989198000 ndash0464503000 C 7517684000 ndash1280530000 ndash1157992000 C 8743181000 ndash1104009000 ndash0445669000 H 9720775000 ndash0544729000 1371431000 H 7610320000 ndash0024462000 2613574000 H 3742883000 0162901000 2664422000 H ndash0241422000 0534554000 2534230000 H ndash3894210000 1260341000 1890621000 H ndash7746436000 1191936000 1936109000 H ndash9890199000 0223840000 1083439000

H ndash9908180000 ndash1561665000 ndash0592194000 H ndash7783148000 ndash2497305000 ndash1525270000 H ndash3929534000 ndash2506814000 ndash1621099000 H 0005285000 ndash2235278000 ndash1842324000 H 3664139000 ndash1453900000 ndash2217556000 H 7520111000 ndash1625509000 ndash2184413000 H 9677483000 ndash1320445000 ndash0950825000 Co 0245526000 1194775000 ndash0183529000 C ndash0498660000 3223481000 ndash0207100000 C 0902667000 3310487000 0056983000 C 1591310000 2661311000 ndash1009417000 C 0610054000 2243094000 ndash1989593000 C ndash0681576000 2592200000 ndash1494981000 H ndash1289524000 3595536000 0425619000 H 1355880000 3721411000 0946130000 H 2657726000 2519341000 ndash1088515000 H 0823168000 1743521000 ndash2921425000 H ndash1626608000 2403559000 ndash1979282000

(j) Transition state 1 η3-benzene (356 kcalmol)

- 151 -

C ndash8901354000 ndash0223681000 ndash0743434000 C ndash7695103000 0220198000 ndash1360549000 C ndash6531343000 ndash0208573000 ndash0779115000 C ndash5007706000 ndash0207407000 ndash0796109000 C ndash3863247000 0247302000 ndash1433753000 C ndash2690760000 ndash0206508000 ndash0819013000 C ndash1184933000 ndash0153490000 ndash0843116000 C ndash0016095000 0217826000 ndash1588049000 C 1142075000 ndash0155798000 ndash0877497000 C 2665172000 ndash0195830000 ndash0859864000 C 3835813000 0283152000 ndash1437197000 C 4978920000 ndash0204857000 ndash0802474000 C 6505676000 ndash0216574000 ndash0771205000 C 7678527000 0226433000 ndash1319208000 C 8875127000 ndash0251684000 ndash0703235000 C 8845790000 ndash1112691000 0383544000 C 7616005000 ndash1570592000 0948642000 C 6475812000 ndash1107284000 0353147000 C 4945633000 ndash1092812000 0320013000 C 3774824000 ndash1565295000 0903163000 C 2628495000 ndash1080676000 0265289000 C 1119158000 ndash1093642000 0244670000 C ndash0052242000 ndash1637616000 0861793000 C ndash1193959000 ndash1109215000 0331010000 C ndash2676505000 ndash1073633000 0328062000 C ndash3841325000 ndash1514463000 0979035000 C ndash4995446000 ndash1053912000 0371366000 C ndash6522185000 ndash1052982000 0381089000 C ndash7676261000 ndash1483950000 0978498000 C ndash8892512000 ndash1041633000 0378747000

- 152 -

H ndash9850267000 0087677000 ndash1164894000 H ndash7723622000 0856176000 ndash2236504000 H ndash3873085000 0886115000 ndash2307512000 H ndash0031238000 0768624000 ndash2518870000 H 3857949000 0953892000 ndash2286176000 H 7723941000 0897606000 ndash2167700000 H 9831384000 0069893000 ndash1099633000 H 9779177000 ndash1450269000 0819087000 H 7614291000 ndash2243551000 1796930000 H 3751975000 ndash2237828000 1750478000 H ndash0016047000 ndash2343040000 1681308000 H ndash3832680000 ndash2159963000 1847727000 H ndash7691389000 ndash2121828000 1853393000 H ndash9834648000 ndash1354566000 0814012000 Co ndash0004249000 1140918000 0250383000 C 0931445000 3181201000 0326993000 C ndash0487068000 3279997000 0223542000 C ndash1069741000 2607436000 1368652000 C 0008159000 2107122000 2176577000 C 1235098000 2411215000 1492603000 H 1650004000 3565479000 ndash0380430000 H ndash1033454000 3774248000 ndash0564979000 H ndash2124544000 2537255000 1584462000 H ndash0094112000 1572170000 3107766000 H 2227446000 2134637000 1815486000

LUMO

HOMO

2887

239

00862

2496

1163

1382

1418

1312

0

3155

2767

0498

2588

1531

0831

Figure 47 Orbital coefficients of linear [5]phenylene

- 153 -

Figure 48 Top view of the contour plots of (a) the HOMO and (b) the LUMO of the [5]-phenylene ligand

- 154 -

Bad

Bad

Good Good

External cyclobutadiene coordination Internal cyclobutadiene coordination

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCpCoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

Figure 49 Resonance rationale for the increased stability of internal Co coordination in linear [5]phenylene

44 NMR Data for Chapter Two

- 155 -

Figure 410 1H-NMR data for the respective parent phenylene frames experimental (C6D6) and

calculated [NICS (1) B3LYP6-31+G] Assignments by NOESY DEPT HMBC and HSQC as applicable

- 156 -

Me3Si

Me3Si

SiMe3

SiMe3

1

23

4 56

7 89

10 1112

13 1415

16

17

18

Co

222

1490

1252

1450

1433

1151

744

730

11091121

14161504

11211109

1540

1499

1224

1486

217

801

SiMe3

SiMe3

Me3Si

Me3Si

Co

802

261

1484

1256

1433

1494

1155

739

781

1360

1394

269

SiMe3

SiMe3

Co

802

1294

1149

1426

1502

1194

738

779

1363

1393

268

SiMe3

SiMe3

1241

1276

8029

725

1155

1493

1430

1256

1482

222

Co

796

678674 675 796

436

037032662

724 683 747

444

TMS

TMS

TMS

TMS

213

1474

1211

1538

1499

1112

623 685

SiMe3

SiMe3Me3Si

Me3Si SiMe3

SiMe3Me3Si

Me3Si459 Co

589 681 672 745

2201204

15131096

1535

2221252

1480

1433

1149741

801

1501 1490

1475

Figure 411 Comparison of 1H-NMR (blue) and 13C-NMR assignments (C6D6)

NICS-Scan calculations Methods The free ligands were optimized at the B3LYP6-31G and the CpCo complexes at the B3LYPLANL2DZ computational levels Analytical frequency calculations were executed to ensure real minima (Nimag = 0) GIAO-B3LYP6-31+G was used to calculate NICS values The NICS-scan procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (ipc or NICSXY) and out-of-plane components (oopc or NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their interpretation

- 157 -

Since there are no published NICS-scan studies of transition metal complexed cyclic polyenes we benchmark the method with (C6H6)Cr(CO)3

53

Figure 412 NICS-scan of benzene (left) and (benzene)Cr(CO)3 (right)

The shape of the oopc curve suggests that the diamagnetic ring current in the ligand is diminished on complexation although still prevalent Thus at r = 0 Aring (ie at the benzene plane) the oopc value [NICSZZ(0)] of the complex is less negative than that of benzene and the minimum of the curve is less negative and occurs at a larger distance (ndash29911 vs ndash31910) A larger change is observed in the ipc (which is governed by the σ electrons) which shows far more negative values in the complex relative to benzene itself (eg ndash55400 vs ndash5900 and ndash13910 vs ndash0910) Therefore isotropic NICS values are misleading with respect to the diatropism in the complex because they originate largely from the diamagnetic effect of the σ framework NICS-scans for the four-membered ring B in linear [3]phenylene and its CpCo complex are shown below

00 05 10 15 20 25 30 35 40

-34-32-30-28-26-24-22-20-18-16-14-12-10

-8-6-4-202

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

oopc ipc isotropic

pp

m

r

- 158 -

Figure 413 NICS-scan above ring B of linear [3]phenylene (left) and its CpCo complex (right) Inspection of the shape and values of the oopc curve shows that the four-membered ring in the free ligand is strongly paratropic This picture changes on CpCo complexation At or close to the ring plane the values are much less positive (12100 vs 88000) become negative at greater distance and reach a minimum of -16112 Consequently the presence of the metal clearly reduces paratropic character The ipc curve is similar to that of (benzene)Cr(CO)3 Therefore again isotropic NICS values are misleading with respect to an assessment of the size of ring current effects The two isomeric CpCo complexes of linear [5]phenylene as depicted next behave in an analogous manner and engender the same conclusions as above

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

- 159 -

Figure 414 NICS-scans of linear [5]phenylene and its CpCo complexes Top left - ring B of the free ligand Top right - ring B complexed to CpCo Bottom left - ring D of the free ligand

Bottom right - ring D complexed to CpCo The effect of CpCo complexation is also reflected in the NICS-scan properties of the remaining rings To illustrate this point the NICS-scans of the central cyclohexatrienoid ring C of linear [3]phenylene are shown below first for the free ligand then for the cyclobutadiene complex

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

- 160 -

Figure 415 NICS-scans of ring C of linear [3]phenylene Left - as a free ligand Right as a

CpCo complex of the neighboring cyclobutadiene ring B The oopc curve clearly reveals a diminution of paratropism Thus at the ring plane the oopc values of the free ligand and of the complex are 177 and 110 ppm respectively Both plots show shallow and relatively distant minima at ndash3417 and ndash7316 respectively an indication of larger diamagnetic character of the latter While the ipc values also become more negative on complexation this effect is far smaller The tables that follow provide an overview of the NICS-scan results over all component rings in linear [3]- and [5]phenylene complexed and uncomplexed The diagnostic shape of the oopc curve is designated NM for no minimum indicating paratropism and M for minimum indicating diatropism Specific values are given at r = 0 Aring r = 10 Aring and the minimum (if diamagnetic) Table 416 NICS-scan Details of the oopc for Linear [3]Phenylene and its CpCo Complex at

Ring B

Ring Shape oopc00 oopc10 Minimum A M 71 ndash107 ndash11813 AndashCpCo M ndash65 ndash228 ndash22811 B NM 880 381 BndashCpCo M 121 ndash151 ndash16112 C M 177 ndash01 ndash3418 CndashCpCo M 116 ndash17 ndash9315 D NM 880 381 DndashCpCo NM 704 237 E M 71 ndash107 ndash11813 EndashCpCo M 15 ndash148 ndash15212

00 05 10 15 20 25 30 35 40

-8-6-4-202468

101214161820

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-14-12-10

-8-6-4-202468

1012

oopc ipc isotropic

pp

m

r

- 161 -

Table 417 NICS-Scan Details of the oopc for Linear [5]Phenylene and its CpCo Complex at Ring B

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M ndash62 ndash227 ndash22811 B NM 898 396 BndashCpCo M 137 ndash148 ndash15612 C M 176 00 ndash3317 CndashCpCo M 152 ndash09 ndash8415 D NM 846 357 DndashCpCo NM 668 223 E M 164 ndash12 ndash4116 EndashCpCo M 142 ndash17 ndash5315 F NM 846 357 FndashCpCo NM 807 340 G M 176 00 ndash3317 GndashCpCo M 161 ndash04 ndash3216 H NM 898 396 HndashCpCo NM 867 378 I M 83 ndash97 ndash10813 IndashCpCo M 64 ndash109 ndash12113

Table 418 NICS-scan Details of the oopc for Lnear [5]Phenylene and its CpCo Complex at

Ring D

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M 19 ndash150 ndash15912 B NM 898 396 BndashCpCo NM 717 256 C M 176 00 ndash3317 CndashCpCo M 110 ndash122 ndash12210 D NM 846 357 DndashCpCo M 151 ndash169 ndash17311 E M 164 ndash12 ndash4116 EndashCpCo M 151 ndash169 ndash17311 F NM 846 357 FndashCpCo NM 685 231 G M 176 00 ndash3317 GndashCpCo M 148 ndash15 ndash5415 H NM 898 396 HndashCpCo NM 850 370

I M 83 ndash97 ndash10813

- 162 -

The data clearly show that on CpCo complexation the paramagnetic ring current contributions decrease (or the diamagnetic ring current contributions increase) The strongest effect is on the complexed cycle but it occurs for all rings even the most remote (eg I in the linear [5]phenylene complexed at ring B) Thus upon complexation the paratropic (and by inference antiaromatic) character of the phenylenes decrease 45 Experimental Section for Chapter Three Angular [3]phenylene 2290 angular [4]phenylene 17111 and [7]heliphene10 were prepared according to the literature Ni(COD)(PMe3)2

112 To a solution of Ni(COD)2 (0275 g 10 mmol) in dry and vigorously degassed THF (10 mL) PMe3 (020 mL 0150 g 20 mmol) was added via syringe in a single portion After stirring at RT for 24 h the mixture was transferred using a canula and filtered under Ar to remove unreacted starting material The solvent was removed on the high vacuum line and the resulting product dried for 3 h It is extremely air sensitive and must be manipulated under an inert atmosphere at all times Yellow solid (0306 g 96 ) 1H-NMR (400 MHz C6D6) δ = 412 (d J = 112 Hz 4 H) 238 (br t J = 52 Hz 4 H) 225 (t J = 52 Hz 4 H) 102 (d J = 32 Hz 18 H) ppm 31P-NMR (162 MHz C6D6) δ = ndash946 (s) ppm Adducts of diphenylacetylene 88 to angular [3]phenylene 22 ndash compounds 89 and 90

In a glove box an Ace pressure tube was charged with angular [3]phenylene 22 (0014 g 006 mmol) diphenylacetylene 88 (0098 g 0055 mmol) THF (5 mL) and Ni(COD)(PMe3)2 (70 microL 008 M in THF 0006 mmol) The reaction vessel was tightly sealed removed from the glovebox and heated to 75ndash80 oC (oil bath) for 23 h After cooling to RT the solvent was removed by rotary evaporation and the residue purified by flash chromatography on silica gel using gradient elution (101 and then 81 hexaneCH2Cl2) After a small amount of angular [3]phenylene 22 (0001 g) the monoadduct 89 (0004 g 20 ) eluted to give a yellow solid mp 195ndash196 degC 1H-NMR (500 MHz CDCl3) δ = 853 (d J = 84 Hz 1 H) 831 (d J = 80 Hz 1 H) 755 (ddd J = 16 64 80 Hz 1 H) 740ndash732 (m 2 H) 725ndash715 (m 6 H) 715ndash711 (m 2 H) 708 (d J = 65 Hz 2 H) 704 (d J = 80 Hz 1 H) 648 (t J = 72 Hz 1 H) 643 (d J = 70 Hz 1 H) 624 (t J = 75 Hz 1 H) 401 (d J = 70 Hz 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1525 15101 15096 1495 1399 13883 13879 1342 1320 1312

- 163 -

13083 13075 1282 1280 1277 1276 1275 1268 1266 1265 1264 1250 1235 1223 1179 1164 1156 ppm one peak in the region δ = 128ndash126 ppm is

presumed to be accidentally isochronous IR (KBr) ν~ = 3060 1490 1481 1442 1415 1159 1072 755 734 698 cmndash1 UV-Vis (CH3CN) λmax (log ε) 233 (442) 265 (450) 278 (sh) 294 (sh) 306 (447) 318 (449) 329 (sh) 380 (344) 399 (366) 420 (366) nm MS (70 eV) mz () 405 [M++1] (35) 404 [M+] (100) 326 (13) HRMS (EI) calcd for C32H20 4041565 found 4041571 Elemental analysis calcd for C32H20 C 9502 H 498 found 9479 460 Subsequent elution furnished 5678-tetraphenylpicene (90) (0009 g 59 ) as a white solid mp 325ndash327 degC the molecule exhibits hindered rotation of the 67-phenyl groups on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 891 (s 2 H) 885 (d J = 84 Hz 2 H) 769 (ddd J = 28 52 80 Hz 2 H) 750ndash744 (m 4 H) 744ndash732 (m 4 H) 720 (tt J = 16 72 Hz 2 H) 696 (dt J = 08 76 Hz 2 H) 689 (tt J = 09 76 Hz 2 H) 662 (br s 4 H) 617 (d J = 76 Hz 2 H) 607 (br s 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1403 1401 1377 1367 1335 1325 1324 1306 1300 1295 1292

1283 1277 1269 1264 1263 1262 1256 1254 1228 1213 ppm IR (KBr) ν~ = 3051 2922 1599 1490 1467 1442 1263 1072 1027 758 702 630 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (461) 307 (474) 352 (417) 366 (414) nm MS (70 eV) mz () 583 [M++1] (52) 582 [M+] (100) 505 (24) 504 (9) 426 (7) HRMS (EI) calcd for C46H30 5822348 found 5822336 1278-Tetraphenylbenzo[c]chrysene (91)

In a glovebox an Ace pressure tube was charged with 88 (0020 g 0050 mmol) diphenylacetylene 88 (0026 mg 0148 mmol) Ni(COD)(PMe3)2 (62 microL of a 008 M solution in THF) and THF (5 mL) The reaction vessel was sealed removed from the glovebox and heated to 85 degC for 39 h After removal of the solvent the residue was purified by flash chromatography on silica gel (eluting with 81 hexaneCH2Cl2) producing a white solid (0023 g) which was found to consist of starting material (88 18 mg) 90 (0001 g 6 ) and 91 Further purification by chromatography afforded pure 91 (0017 g 74 ) as a white solid mp 273ndash274 degC the 12-phenyl groups of 91 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 869 (d J = 95 Hz 1 H) 830ndash822 (m 1 H) 801 (d J = 75 Hz 1 H) 780ndash747 (m 2 H) 770 (ddd J = 10 70 85 Hz 1 H) 762 (dt J = 15 75 Hz 1 H) 753 (ddd J = 15 70 85 Hz 1 H) 738ndash732 (m 2 H) 730 (td J = 15 75 Hz 1 H) 729ndash722 (m 6 H) 722ndash717 (m 2 H) 717ndash710 (m 2 H) 710ndash695 (m 3 H) 680ndash640 (m 3 H) 635 (d J = 70 Hz 1 H) 623ndash595 (br s 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1418 1400 1395 1394 1378 1377 1375 1357 1323 1322 1316 1314 13113 13107 1309 1308 1307 1305 1296 1295 1288 1282 1277 1275 1274 1273 1270 12653 12647 1264 1260 1256 1253 1252 1251

- 164 -

1243 1231 1208 ppm due to extensive signal overlap four peaks are presumed to be isochronous in the regions δ = 132ndash130 and 128ndash125 ppm IR (KBr) ν~ = 3058 1601 1489 1442 1263 1073 773 762 736 699 628 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 250 (487) 313 (511) 340 (sh) nm MS(EI) mz () 583 (M++1 72) 582 (M+ 100) 505 (24) 391 (13) HRMS (EI) calcd for C46H30 5822348 found 5822341 Elemental analysis calcd for C46H30 C 8933 H 500 found 8914 493 Ni(PhCequivCPh)(PMe3)2 (92)91

In a glove box PMe3 (203 microL 0152 g 20 mmol) was mixed with a suspension of Ni(COD)2 (0275 g 10 mmol) in hexane (15 mL) Diphenylacetylene 88 (0178 g 10 mmol) was then added in one portion resulting in an immediate color change from yellow to red The mixture was stirred at room temperature for 195 h during which the color gradually turning returning to yellow Upon concentration (to ~5 mL) a yellow precipitate formed collected by filtration under nitrogen The resulting powder 92 (0370 g 95 ) was dried under vacuum providing a yellow solid 1H-NMR (500 MHz C6D6) δ = 751 (d J = 75 Hz 4 H) 717 (t J = 75 Hz 4 H) 702 (t J = 75 Hz 2 H) 101 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1406 1287 1279 196 (d JC-P = 188 Hz) ppm 31P-NMR (162 MHz C6D6) δ = ndash1282 (br s) ppm Adducts of 3-hexyne to angular [3]phenylene 22 ndash compounds 104 and 105

In a glovebox 22 (0014 mg 0060 mmol) 3-hexyne 103 (57 microL 0004 g 0050 mmol) Ni(COD)(PMe3)2 (0002 g 0005 mmol) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 14 h Flash chromatography on silica gel gave a first fraction that was recrystallized from CH2Cl2 to provide pure 104 (70 mg 45 ) as a yellow solid mp 169ndash170 degC 1H-NMR (500 MHz CDCl3) δ = 843 (d J = 70 Hz 1 H) 821 (d J = 75 Hz 1 H) 795 (d J = 70 Hz 1 H) 752 (dt J = 10 70 Hz 1 H) 748 (dt J = 10 70 Hz 1 H) 697 (d J = 75 Hz 1 H) 673ndash662 (m 3 H) 655 (d J = 55 Hz 1 H) 307 (q J = 75 Hz 2 H) 299 (q J = 75 Hz 2 H) 133 (t J = 75 Hz 3 H) 130 (t J = 75 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1530 1516 1504 1471 1360 1330 13129 13127 1307 1282 1279 1267 1263 1259 1246 1239 1228 1179 1159 1156 232 214 164 149 ppm IR (KBr) ν~ = 3045 2960 1600 1481 1414 1261 1197 1159 758 740 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (463) 299 (sh) 309 (460) 320 (462) 331 (452) 380 (356) 399 (374) 419 (371) nm MS (70 eV) mz () 309 [M++1] (26) 308 [M+] (100) 293 [M+ndash15] (8) 278 [M+ndash30] (21) HRMS (EI) calcd for C24H20 3081565 found 3081666

- 165 -

A second fraction was 105 (0002 g 11 ) isolated as a yellow solid mp 120ndash122 degC 1H-NMR (400 MHz CDCl3) δ = 830 (d J = 72 Hz 1 H) 797 (d J = 76 Hz 1 H) 761 (d J = 80 Hz 1 H) 761ndash749 (m 2 H) 700 (d J = 80 Hz 1 H) 699 (d J = 72 Hz 1 H) 674 (quint J = 76 Hz 2 H) 658 (d J = 64 Hz 1 H) 307 (q J = 76 Hz 2 H) 302 (q J = 76 Hz 2 H) 132 (t J = 76 Hz 3 H) 131 (t J = 76 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1525 1519 1489 1472 1356 1345 1324 1318 1288 1283 1279 1273 1259 1252 1251 1250 1241 1179 1165 1160 2213 2205 149 146 ppm IR (KBr) ν~ = 3063 2958 2925 1490 1442 1417 1262 1147 1099 822 762 730 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 281 (434) 291 (448) 303 (460) 313 (sh) 369 (346) 389 (373) 410 (377) nm MS (70 eV) mz () 309 [M++1] (28) 308 [M+] (100) 293 [M+ndash15] (13) 278 [M+ndash30] (21) 226 (22) 149 (29) HRMS (EI) calcd for C24H20 3081565 found 3081664 Adducts of 14-dimethoxy-2-butyne to angular [3]phenylene 22 ndash compounds 107 and 108

In a glovebox 22 (0011 g 0050 mmol) 14-dimethoxybut-2-yne 106 (0034 g 030 mmol) Ni(COD)(PMe3)2 (63 microL of a 008 M solution in THF) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 165 h The 1H-NMR spectrum of the crude indicated the formation of 107 and 108 in the ratio of 61 Flash chromatography on silica gel gave first 107 (0012 g 68 ) as a yellow solid mp 150ndash151 degC 1H-NMR (400 MHz CDCl3) δ = 841 (dd J = 32 64 Hz 1 H) 819 (d J = 80 Hz 1 H) 810 (dd J = 36 64 Hz 1 H) 754 (dd J = 36 64 Hz 2 H) 700 (d J = 80 Hz 1 H) 676 (t J = 64 Hz 1 H) 674ndash665 (m 2 H) 656 (d J = 60 Hz 1 H) 493 (s 2 H) 488 (s 2 H) 353 (s 3 H) 345 (s 3 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1527 1513 1509 1484 1336 1318 1316 1309 1296 1283 1282 1272 1270 1259 1255 1238 1225 1183 1166 1161 677 675 584 575 ppm IR (KBr) ν~ = 3072 2927 1485 1446 1417 1376 1185 1097 956 898 821 743 730 cmndash1 MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (100) 308 [M+ndash38] (26) 293 (34) 280 (15) 265 (44) HRMS (EI) calcd for C24H20O2 3401463 found 3401466 Further elution provided 108 (0002 g 9 ) as a yellow solid mp 156ndash157 degC 1H-NMR (400 MHz CDCl3) δ = 831ndash824 (m 1 H) 813ndash806 (m 1 H) 775 (d J = 80 Hz 1 H) 763ndash756 (m 2 H) 702 (d J = 80 Hz 1 H) 699 (d J = 64 Hz 1 H) 681ndash670 (m 2 H) 660 (d J = 64 Hz 1 H) 493 (s 2 H) 487 (s 2 H) 353 (s 3 H) 351 (s 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1523 1517 1505 1470 1327 1322

- 166 -

1316 1315 1297 1285 1282 1276 1268 1266 12564 12555 1252 1181 1168 1165 6804 6801 5838 5835 ppm IR (KBr) ν~ = 2925 1498 1415 1379 1262 1187 1095 1061 940 930 814 750 734 717 cmndash1 UV-Vis (CH3CN) λmax (log ε) 237 (458) 287 (462) 298 (472) 314 (sh) 371 (357) 387 (380) 407 (386) nm MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (56) 308 [M+ndashMeOH] (8) 293 (27) 279 (17) 265 (24) HRMS (EI) calcd for C24H20O2 3401463 found 3401456 Optimized cycloaddition reaction between 22 and 88 In a glovebox a round bottom flask was charged with 22 (0058 g 0257 mmol) and Ni(COD)(PMe3)2 (0008 g 0034 mmol) Both reagents were then dissolved in THF (100 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0093 g 0521 mmol) in THF (20 mL) was taken up in a gas-tight syringe and slowly added over 13 h via syringe pump to the boiling mixture of 22Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 6 h After this time mixture was cooled to RT and the solvent removed by rotary evaporation to give a yellow residue The crude product was passed through a plug of silica gel eluting with a mixture of hexanesCH2Cl2 (101) to afford a yellow solid Analysis of the product by 1H-NMR (using the solvent peak of CDCl3 as the internal standard) revealed the presence of 89 and 90 in a 1387 ratio Adducts of diphenylacetylene 88 to angular [4]phenylene 17 ndash compounds 130ndash134 In a glovebox angular [4]phenylene 17 (0036 g 012 mmol) diphenylacetylene 88 (0018 g 010 mmol) and Ni(COD)(PMe3)2 (125 microL of a 008 M solution in THF) were added to an Ace pressure tube and dissolved in THF (6 mL) The reaction vessel was sealed removed from the glovebox and stirred at 75 degC for 5 h Flash chromatography

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph Ph PhPh Ph

132131

133 134

130

- 167 -

on silica gel gave starting material (0013 g of 17) as well as a yellow residue Further purification of the latter by preparative TLC afforded (in order of elution) 132 131 133 134 and 139 Compound 130 (0008 g 28 ) was obtained as a white solid mp 360ndash363 degC (decomp) the phenyl groups located on the central benzene ring of 130 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 904 (d J = 90 Hz 2 H) 895 (d J = 90 Hz 2 H) 881 (d J = 85 Hz 2 H) 765 (ddd J = 15 65 80 Hz 2 H) 742ndash736 (m 4 H) 734 (dd J = 10 85 Hz 2 H) 721 (tt J = 15 75 Hz 2 H) 716 (d J = 75 Hz 2 H) 698 (dd J = 05 80 Hz 2 H) 693 (tt J = 10 85 Hz 2 H) 681 (tt J = 10 70 Hz 2 H) 676 (t J = 75 Hz 4 H) 656 (t J = 70 Hz 4 H) 633 (d J = 70 Hz 4 H) 614 (d J = 75 Hz 2 H) 595 (d J = 70 Hz 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 14058 14057 1403 1394 1375 1374 1345 1341 1336 1327 1324 1309 1308 1301 1294 1292 1282 1276 1268 1263 12622 12619 1259 1257 1254 1250 1227 1214 1212 ppm IR (KBr) ν~ = 3052 2923 1600 1491 1440 1261 1076 1029 809 783 759 747 700 631 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 248 (498) 306 (sh) 329 (520) 388 (463) nm MS(FAB) mz () 836 [M++2] (18) 835 [M++1] (42) 834 [M+] (54) 757 (8) HRMS (FAB) calcd for C66H42 8343287 found 8343280 Compound 131 (0003g 6) was isolated as yellow solid mp 251ndash253 degC (decomp) 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 775 (dt J = 10 80 Hz 1 H) 752 (dt J = 10 80 Hz 1 H) 746 (d J = 80 Hz 1 H) 737 (d J = 65 Hz 1 H) 726ndash721 (m 5 H) 721ndash716 (m 2 H) 716ndash711 (m 5 H) 709 (t J = 75 Hz 1 H) 705 (d J = 80 Hz 1 H) 699 (d J = 70 Hz 1 H) 619 (d J = 60 Hz 1 H) 614 (d J = 60 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1502 1492 1491 1490 1485 1444 1394 1392 1382 1371 1367 1351 13271 13268 13092 13088 1299 12898 12896 1283 12764 12760 1274 12654 12652 1261 1253 1245 1195 1184 1172 1138 1129 ppm one peak is presumed to be accidentally isochronous in the region between δ = 130ndash124 ppm IR (KBr) ν~ = 3023 2921 1602 1478 1371 1262 1026 809 795 748 725 695 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 252 (473) 285 (456) 320 (453) 335 (462) 353 (437) 370 (432) 410 (376) 431 (372) nm MS (FAB) mz () 479 [M++1] (27) 478 [M+] (70) 300 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781718 Molecule 132 (0002 g 5 ) was acquired as a yellow solid 1H-NMR (500 MHz CDCl3) δ = 726ndash721 (m 2 H) 716ndash709 (m 6 H) 695ndash690 (m 2 H) 676 (d J = 80 Hz 2 H) 673 (d J = 75 Hz 2 H) 671 (t J = 75 Hz 2 H) 665 (t J = 70 Hz 2 H) 658 (d J = 65 Hz 2 H) 648 (d J = 65 Hz 2 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1516 1510 1497 1490 1391 1372 1310 1303 1283 1281 1277 1275 1273 1264 1216 1168 1163 ppm UV-Vis (CH2Cl2) λmax (log ε) 254 (476) 294 (sh) 300 (465) 322 (sh) 338 (392) 376 (400) nm MS (FAB) mz () 479 [M++1] (50) 478 [M+] (86) 391 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781723 Adduct 133 (0017 g 33 ) was isolated as a red crystalline solid mp 290ndash291 degC 1H-NMR (500 MHz CDCl3) δ = 800 (d J = 80 Hz 2 H) 720ndash713 (m 6 H) 708ndash702 (m 4 H) 690 (d J = 80 Hz 2 H) 648 (t J = 70 Hz 2 H) 642 (d J = 70 Hz 2 H) 623 (t J = 70 Hz 2 H) 393 (d J = 70 Hz 2 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1522 1509 1506 1496 1392 1359 1315 1309 1282 1278 1277 1266 1250 1232 1181 1166 1157 ppm IR (KBr) ν~ = 3057 1489 1441 1412 1273

- 168 -

1161 810 738 709 690 623 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 271 (474) 285 (469) 345 (460) 353 (454) 414 (483) 432 (381) 460 (363) nm MS (70 eV) mz () 479 [M++1] (46) 478 [M+] (100) 400 (10) HRMS (EI) calcd for C38H22 4781722 found 4781719 Compound 134 (0009 g 27 ) was obtained as a yellow solid mp 178ndash180 degC the phenyl groups of this molecule located at the bay regions of the phenanthrene subunit are static while the others exhibit hindered rotation on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 880 (d J = 88 Hz 1 H) 879 (d J = 88 Hz 1 H) 863 (d J = 92 Hz 1 H) 834 (d J = 80 Hz 1 H) 770ndash758 (m 1 H) 748ndash732 (m 4 H) 727ndash721 (m 2 H) 721ndash710 (m 2 H) 706 (d J = 80 Hz 1 H) 702ndash691 (m 3 H) 684 (t J = 74 Hz 1 H) 673 (br s 2 H) 655 (t J = 76 Hz 2 H) 650ndash638 (m 3 H) 630ndash610 (m 4 H) 590 (d J = 76 Hz 2 H) 410 (d J = 68 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1527 1510 1509 1494 1403 1400 1399 1396 1373 1371 1339 1335 1330 1325 1324 1317 1309 1306 1305 1304 1299 1295 1291 1283 1282 1281 1277 1275 1272 1269 1268 12632 12627 1261 12562 12556 1254 1253 1239 1226 1216 1209 1180 1162 1154 ppm three peaks are presumed to be accidentally isochronous in the region δ = 128ndash125 ppm IR (KBr) ν~ = 2964 1262 1096 1022 801 701 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 267 (501) 303 (497) 335 (489) 361 (sh) 379 (464) 427 (402) 456 (377) nm MS(FAB) mz () 658 [M++2] (22) 657 [M++2] (67) 656 [M+] 1(00) 579 (12) 502 (7) HRMS (FAB) calcd for C52H32 6562504 found 6562492 Cycloaddition reaction between [7]heliphene 142 and diphenylacetylene 88 In a glovebox a round bottom flask was charged with 142 (0008 g 0152 mmol) and Ni(COD)(PMe3)2 (0001 g 0003 mmol) The mixture was then dissolved in THF (25 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0016 g 300 mmol) in THF (10 mL) was taken up in a gas-tight syringe and slowly added over 12 h via syringe pump to the boiling mixture of 142Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 12 h After this time it was cooled to RT and the solvent removed by rotary evaporation to give an orange residue The crude product was chromatographed on silica gel (25 x 165 cm) eluting first with hexaneCH2Cl2 (101 then 51) The first product collected was diphenylacetylene 88 (0005 g) followed by a yellow band Analysis of the isolated yellow solid (0002 g) revealed a large mixture of products MS(FAB) mz () 532 (70) 664 (25) 700 (13) 732 (16) 911 (21) 1056 (11) 1234 (4) 1412 (5) 46 Computational Details for Chapter Three All geometries of intermediates and transition states were optimized fully without symmetry constraints using the Gaussian 03 program100 The DFT computations were carried out using the B3LYP functional as implemented in Gaussian The nickel atom was described by a double-zeta basis set (LANL2DZ)113 and the 6-31G(d) basis set114

- 169 -

was used for the other elements Frequency calculations were performed to confirm the nature of the stationary points and to obtain zero-point energies (ZPE) The connectivity between stationary points was established by intrinsic reaction coordinate calculations (IRC) The Chemcraft program102 was used to draw the calculated structures

47 References

1) Harvey R G Polycyclic Aromatic Hydrocarbons Wiley-VCH New York 1997 2) (a) Chem Rev 2001 101 1115ndash1566 Special Issue Aromaticity (b) Chem Rev

2005 105 3343ndash3397 Special Issue Delocalization-Pi and Sigma 3) (a) Cyranski M K Krygowski T M Katritzky A R Schleyer P von R J Org

Chem 2002 67 1333 (b) Stanger A Chem Commun 2009 1939 4) (a) Minkin V I Glukhovtsev M N Simkin B Ya Aromaticity and Antiaromaticity

Electronic and Structural Aspects Wiley New York 1994 pp 63ndash74 (b) Garratt P J Aromaticity Wiley New York 1986 pp 30ndash34 93ndash95

5) (a) Wu J Muumlllen K In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 3 pp 90ndash139 (b) Wu J Pisula W Muumlllen K Chem Rev 2007 107 718 (c) Handbook of Organic Electronics and Photonics Nalwa H S Ed American Scientific 2008

6) Miljanić O Š Vollhardt K P C In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 4 pp 140ndash197

7) (a) Shepherd M K Cyclobutarenes The Chemistry of Benzocyclobutene Biphenylene and Related Compounds Elsevier Amsterdam 1991 (b) Toda F Garratt P J Chem Rev 1992 92 1685

8) (a) Diercks R Vollhardt K P C J Am Chem Soc 1986 108 3150 (b) Mohler D L Vollhardt K P C Wolff S Angew Chem Int Ed Engl 1990 29 1151 (c) Mohler D L Vollhardt K P C Wolff S Angew Chem Int Ed Engl 1995 34 563

9) (a) Holmes D Kumaraswamy S Matzger A J Vollhardt K P C Chem Eur J 1999 5 3399 (b) Dosche C Kumke M U Ariese F Bader A N Gooijer C Dosa P I Han S Miljanic O Š Vollhardt K P C Puchta R van Eikema Hommes N J R Phys Chem Chem Phys 2003 5 4563 (c) Wagner H-U Szeimies G Chandrasekhar J Schleyer P von R Pople J A Binkley J S J Am Chem Soc 1978 100 1210

10) Han S Bond A D Disch R L Holmes D Schulman J M Teat S J Vollhardt K P C Whitener G D Angew Chem Int Ed 2002 41 3223

11) Jackman L M Sondheimer F Amiel Y Ben-Efraim D A Gaoni Y Wolovsky R Bothner-By A A J Am Chem Soc 1962 84 4307

12) Untch K G Wysocki D C J Am Chem Soc 1967 89 6386 13) (a) Chen Z Wannere S C Corminboeuf C Puchta R Schleyer P von R

Chem Rev 2005 105 3842 and the references therein (b) Steinmann S N Jana D F Wu J I-C Schleyer P v R Mo Y Corminboeuf C Angew Chem Int Ed 2009 48 9828

14) Schleyer P v R Manoharan M Wang Z-X Kiran B Jiao H Puchta R van Eikema Hommes N J R Org Lett 2001 3 2465

- 170 -

15) Schulman J M Disch R L Jiao H Schleyer P v R J Phys Chem A 1998 102 8051

16) Jeany H Mason K G Sketchley J M Tetrahedron Lett 1970 11 485 17) Brown F C Choi N Coulston K J Eastwood F W Wiersum U E

Jenneskens L W Tetrahedron Lett 1994 35 4405 18) (a) Linear [3]phenylene Dosa P I Schleifenbaum A Vollhardt K P C Org Lett

2001 3 1017 (b) Angular [3]phenylene Matzger A J Vollhardt K P C Chem Commun 1997 1415 (c) Angular [4]phenylene Dosa P I Gu Z Hager D Karney W L Vollhardt K P C Chem Commun 2009 1967

19) Perthuisot C Edelbach B L Zubris D L Simhai N Iverson C N Muumlller C Satoh T Jones W D J Mol Catal A 2002 189 157

20) Dosche C Loumlhmannsroumlben H-G Bieser A Dosa P I Han S Iwamoto M Schleifenbaum A Vollhardt K P C Phys Chem Chem Phys 2002 4 2156

21) (a) Deniz A A Peters K S Snyder G J Science 1999 286 1119 (b) Fattahi A Lis L Tian Z Kass P S Angew Chem Int Ed 2006 45 4984 (c) Bally T Angew Chem Int Ed 2006 45 6616

22) Anslyn E Dougherty D Modern Physical Organic Chemistry University Science Books Palo Alto 2006

23) Crabtree R H The Organometallic Chemistry of the Transition Metals 4th Ed Wiley-VCH New York 2005

24) Mestdagh H Postdoctoral Research Report University of California Berkeley 1986

25) Hirthammer M Vollhardt K P C J Am Chem Soc 1986 108 2481 26) Blanco L Helson H E Hirthammer M Mestdagh H Spyroudis S Vollhardt K

P C Angew Chem Int Ed Engl 1987 26 1246 27) Berris B C Hovakeemian G H Lai Y-H Mestdagh H Vollhardt K P C J

Am Chem Soc 1985 107 5670 28) Dosa P I The Chemistry of Angular and Linear [N]Phenylenes PhD Thesis

University of California Berkeley 2002 29) Diercks R Eaton B E Guumlrtzgen S Jalisatgi S Matzger A J Radde R H

Vollhardt K P C J Am Chem Soc 1998 120 8247 30) (a) Nambu M Siegel J S J Am Chem Soc 1988 110 3675 (b) Nambu M

Hardcastle K Baldridge K K Siegel J S J Am Chem Soc 1992 114 369 31) Nambu M Mohler D L Hardcastle K Baldridge K K Siegel J S J Am

Chem Soc 1993 115 6138 32) Kumaraswamy S Jalisatgi S S Matzger A J Miljanić O Š Vollhardt K P C

Angew Chem Int Ed 2004 43 3711 33) (a) Eisch J J Piotrowski A M Han K I Kruumlger C Tsay Y H Organometallics

1985 4 224 (b) Schwager H Spyroudis S Vollhardt K P C J Organometallic Chem 1990 382 191

34) Albright T A Hofmann P Hoffmann R Lillya C P Dobosh P A J Am Chem Soc 1983 105 3397

35) Doumltz K H Jahr H C Chem Rec 2005 4 61 36) Gridnev I D Coord Chem Rev 2008 252 1798 37) Eickmeier C Holmes D Junga H Matzger A J Scherhag F Shim M

Vollhardt K P C Angew Chem Int Ed Engl 1999 38 800

- 171 -

38) Groszligmann T N Haptotropism in Linear Phenylene Complexes Diplomarbeit Thesis University of California Berkeley 2004

39) Dinculear photothermal haptotropic systems Tsuchiya K Ideta K Mogi K Sunada Y Nagashima H Dalton Trans 2008 2708 and the references therein

40) Additive assisted photothermal haptotropic systems (a) Jahr H C Nieger M Doumltz H K Chem Eur J 2005 11 5333 d) Herbert D E Tanabe M Bourke S C Lough A J Manners I J Am Chem Soc 2008 130 4166 e) Ieong N S Manners I J Organomet Chem 2008 693 802 and references therein

41) (a) Zhu G Tanski T M Churchill D G Janak K E G Parkin G J Am Chem Soc 2002 124 13658 (b) Zhu G Pang G Parkin G J Am Chem Soc 2008 130 1564

42) Selected reviews of photobased devices and molecular switches (a) Balzani V Credi A Venturi M Chem Soc Rev 2009 38 1542 (b) Kay E R Leigh D A Zerbetto F Angew Chem Int Ed 2007 46 72 (c) Photochromism Molecules and Systems Duumlrr H Bouas-Laurent H Eds Elsevier Amsterdam 2003 (d) Feringa B Molecular Switches Wiley-VCH Weinheim 2001

43) (a) a) Photofunctional Transition Metal Complexes Yam V W W Ed Springer Berlin 2007 b) Coppens P Novozhilova I Kovalevsky A Chem Rev 2002 102 861 c) Guumltlich P Garcia Y Woike T Coord Chem Rev 2001 219ndash221 839

44) (a) Lambert J B Mazozola E P Nuclear Magnetic Resonance Spectroscopy An Introduction to Princples Applications and Experimental Methods Pearson Education Upper Saddle River 2004 (b) Berger S Braun S 200 and More NMR Experiments A Practical Course Wiley-VCH Weinheim 2004 (c) Friebolin H Basic One- and Two-Dimensional NMR Spectroscopy 4th edition Wiley-VCH Weinheim 2005

45) (a) Schulman J M Disch R L J Phys Chem A 2003 107 5223 (b) Schulman J M Disch R L J Am Chem Soc 1996 118 8470 and the references cited therein

46) (a) Bursten B E Fenske R F Inorg Chem 1979 18 1760 (b) Chinn J W Jr Hall M B Inorg Chem 1983 22 2759 (c) Datta A Pati S K J Am Chem Soc 2005 127 3496

47) Ooloba K Haptotropic Shifts in the Linear [N]-Phenylene (N=3 4 and 5) and Angular [3]-Phenylene Cyclopentadienylcobalt Complexes PhD Thesis University of Houston 2008

48) Hillard III R L Vollhardt K P C J Am Chem Soc 1977 99 4058 49) Berris B C Lai Y-H Vollhardt K P C J Chem Soc Chem Commun 1982

953 50) (a) Rausch M D Genetti R A J Org Chem 1970 35 3888 (b) Hart W P

Rausch D M J Organometallic Chem 1988 355 455 51) Duclos R I Vollhardt K P C Yee J L S J Organomet Chem 1979 174 109 52) (a) Myers A G Sogi M Lewis M A Arvedson S P J Org Chem 2004 69

2516 (b) Wolfart V Ramming M Gleiter R Nuber B Pritzkow H Rominger F Eur J Inorg Chem 1999 499 (c) Mitchell R H Chen Y Khalifa N Zhou P J Am Chem Soc 1998 120 1785 (d) McGlinchey M J Burns R C Hofer R Top S Jaouen G Organometallics 1986 5 104

53) Feixas F Jimeacutenez-Halla J O C Matito E Poater J Solagrave M Pol J Chem

- 172 -

2007 81 783 54) (a)Stanger A J Org Chem 2006 71 883 (b) Stanger A Chem Eur J 2006 12

2745 (c) Tsipis A C Phys Chem Chem Phys 2009 11 8244 (d) Stanger A Chem Commun 2009 1939

55) For very recent literature compilations of theoretical (and experimental) treatments of haptotropism in arene metal complexes see a) Joistgen O Pfletschinger A Ciupka J Dolg M Nieger M Schnakenburg G Froumlhlich R Kataeva O Doumltz K H Organometallics 2009 28 3473 b) Pfletschinger A Dolg N J Organomet Chem 2009 694 3338 c) Jimeacutenez-Halla J O C Robles J Solagrave M Organometallics 2008 27 5230 d) Kirillov E Kahlal S Roisnel T Georgelin T Saillard J-Y Carpentier J-F Organometallics 2008 27 387 and references therein

56) Jimeacutenez-Halla J O C Robles J Solagrave M J Phys Chem A 2008 112 1202 57) Oprunenko Y Gloriozov I Lyssenko K Malyugina S Mityuk D Mstislavsky

V Guumlnther H von Firks G Ebener M J Organomet Chem 2002 656 27 58) Muumlller J Gaede P E Qiao K J Organomet Chem 1994 480 213 59) Bianchini C Caulton K G Chardon C Doublet M L Eisenstein O Jackson

S A Johnson T J Meli A Peruzzini M Streib W E Vacca A Vizzat F Organometallics 1994 13 2010

60) (a) De Boer E Van Willigen H V Prog Nuc Mag Res Spec 1967 2 111 (b) Memory J D Wilson N K NMR of Aromatic Compounds Wiley-VCH New York 1982

61) (a) Poli R Chem Rev 1996 96 2135 and the references cited therein (b) Schroumlder D Shaik S Schwartz H Acc Chem Res 2000 33 139 (c) Harvey J N Poli R Smith K M Coord Chem Rev 2003 237 347 and the references cited therein

62) For computational examples of 16 electron triplet Cp cobalt species influencing cobalt-mediated reactions see (a) Siegbahn P E M J Am Chem Soc 1996 118 1487 (b) Poli R Smith K M Eur J Inorg Chem 1999 877 (c) Carreoacuten-Macedo J-L Harvey J N J Am Chem Soc 2004 126 5789 (d) Petit A Richard P Cacelli I Poli R Chem Eur J 2006 12 813 (e) Aubert C Betschmann P Eichberg M J Gandon V Geny A Heckrodt T J Lehmann J Malacria M Masjost B Paredes E Vollhardt K P C Whitener G D Chem Eur J 2007 13 7443 (f) Gandon V Agenet N Vollhardt K P C Malacria M Aubert C J Am Chem Soc 2009 131 3007

63) Illustrative examples (a) Olson W L Stacy A M Dahl L F J Am Chem Soc 1986 108 7646 (b) Wadepohl H Galm W Pritzkow H Wolf A Chem Eur J 1996 2 1453 (c) Knijnenburg W Hetterscheid D Kooistra T M Budzelaar P H M Eur J Inorg Chem 2004 1204

64) Benito-Garagorri D Bernskoetter W H Lobkovsky E Chirik P J Organometallics 2009 28 4807

65) Fox J P Ramdhanie B Zareba A A Czernuszewicz R S Goldberg D P Inorg Chem 2004 43 6600

66) Guennic B L Floyd T Galan B R Autschbach J Keister J B Inorg Chem 2009 48 5504

67) Cremer C Burger P J Am Chem Soc 2003 125 7664

- 173 -

68) Atkins P de Paula J P Physical Chemistry 8th Edition Oxford University Press Oxford 2006

69) Butters T Toda F Winters W Angew Chem Int Ed Engl 1980 19 926 70) Mann B E Taylor B F 13C Data for Organometallic Compounds Academic

London 1981 71) For a review on triple decker arene complexes and closely related syn dinuclear

systems see (a) Beck V OlsquoHare D J Organomet Chem 2004 698 3920 and the references therein For a review of trinuclear CpCo(arene) complexes see (b) Wadepohl H Angew Chem Int Ed Engl 1992 31 247 and the references therein

72) Jonas K Koepe G Schieferstein L Mynott R Kruumlger C Tsay Y-H Angew Chem Int Ed Engl 1983 22 620 Angew Chem Suppl 1983 920

73) Muumlller J Gaede P E Qiao K Angew Chem Int Ed Engl 1993 32 1697 74) Schneider J J Wolf D Janiak C Heinemann O Rust J Kruumlger C Chem

Eur J 1998 4 1982 75) Schneider J J Denninger U Heinemann O Kruumlger C Angew Chem Int Ed

Engl 1995 34 592 76) Budzelaar P H M Moonen N N P de Gelder R Smits J M M Gal A W

Chem Eur J 2000 6 2740 77) Albright T A Dosa P I Groszligmann T N Oluwakemi O Padilla R Paubelle

R Timofeeva T Vollhardt K P C Angew Chem Int Ed 2009 48 9853 78) Schaub T Radius U Chem Eur J 2005 11 5024 79) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4660 80) (a) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4040

(b) Muumlller C Lachicotte R J Jones W D Organometallics 2002 21 1975 81) Martin R H Angew Chem Int Ed Engl 1974 13 649 82) Mallory FB Butler K E Evans AC Mallory CW Tetrahedron Lett 1996 37

7176 83) Selected Reviews (a) Amemiya R Yamaguchi M Chem Rec 2008 8 116 (b)

Ruliacutešek L Exner O Cwiklik L Jungwirth P Staryacute I Pospiacutešil L Havlas Z J Phys Chem C 2007 111 14948 (c) Hopf H Classics in Hydrocarbon Chemistry Wiley-VCH Weinheim 2000 pp 321ndash330 (d) Voumlgtle F Fascinating Molecules in Organic Chemistry Wiley New York 1992 pp 156ndash180 (e) Meurer K P F Voumlgtle Top Curr Chem 1985 127 1 (f) Laarhoven W H Prinsen W J Top Curr Chem 1984 125 63

84) (a) Mallory FB Butler K E Mallory CW Beacuterubeacute A Luzik E D Brondyke E J Hiremath R Ngo P Carroll P J Tetrahedron 2001 57 3715 (b) Mallory F B Butler K E Evans A C Brondyke E J Mallory C W Yang C Ellenstein A J Am Chem Soc 1997 119 2119

85) (a) Mitsuhashi R Suzuki Y Yamanari Y Mitamura H Kambe T Ikeda N Okamoto H Fujiwara A Yamaji M Kawasaki N Maniwa Y Kubozono Y Nature 2010 464 74 (b) Okamoto H Kawasaki N Kaji Y Kubozono Y Fujiwara A Yamaji M J Am Chem Soc 2008 130 10470 (c) Tian Y H Park G Kertesz M Chem Mater 2008 20 3266

86) Recent reviews of acenes in electronic applications (a)Yamashita Y Sci Technol Adv Mater 2009 10 024313 (b) Wuumlrthner F Schmidt R ChemPhysChem

- 174 -

2006 7 793 (c) Bendikov M Wudl F Chem Rev 2004 104 4891 87) NICS-based comparison of phenacene and acene properties Portella G Poater

P Bofill J M Alemany P Solagrave M J Org Chem 2005 70 2509 and the references therein

88) Mallory F B Mallory C W Org React 1984 30 1 89) Gu Z Nickel-Catalyzed Cycloaddition Reaction of [N]Phenylenes and Alkynes

Postdoctoral Report University of California Berkeley 2008 90) Preferential displacement of COD by π ligands from Ni(COD)(PMe3)2 is well

documented See eg Karsch H H Leithe A W Reisky M Witt E Organometallics 1999 18 90

91) (a) Bochmann M Hawkins I Hursthouse M B Short R L J Chem Soc Dalton Trans 1990 1213 (b) Poerschke K R Mynott R Angermund K Kruumlger C Z Naturforsch 1990 40B 199 See also (c) Bartik T Happ B Iglewsky M Bandmann H Boese R Heimbach P Hoffmann T Wenschuh E Organometallics 1992 11 1235

92) For Ni-phosphine migrations along polycyclic benzenoid ligands see eg Stanger A Vollhardt K P C Organometallics 1992 11 317

93) Edelbach B L Vicic D A Lachicotte R J Jones W D Organometallics 1998 17 4784

94) (a) Feiken N Pregosin P S Trabesinger G Scalone M Organometallics 1997 16 537 (b) Feiken N Pregosin P S Trabesinger G Albinati A Evoli G L Organometallics 1997 16 5756 (c) Geldbach T J Pregosin P S Eur J Inorg Chem 2002 1907

95) Cheng T-Y Szalda D J Hanson J C Muckerman J T Bullock R M Organometallics 2008 27 3785

96) (a) Grimme S Harren J Sobanski A Voumlgtle F Eur J Org Chem 1998 8 1491 (b) Dias J J Chem Inf Model 2005 45 562

97) Still W C Mitra A Kahn M J Org Chem 1978 43 2923 98) (a) Leonard J Lygo B Procter G Advanced Practical Organic Chemistry 2nd

ed CRC Press Boca Raton 1998 (b) Errington R J Advanced Practical Inorganic Chemistry and Metalorganic Chemistry Chapman and Hill London 1997

99) Jonas K Deffense E Habermann D Angew Chem Int Ed Engl 1983 22 716 100) Gaussian 03 Revision B03 M J Frisch G W Trucks H B Schlegel G E

Scuseria M A Robb J R Cheeseman J A Montgomery Jr T Vreven K N Kudin J C Burant J M Millam S S Iyengar J Tomasi V Barone B Mennucci M Cossi G Scalmani N Rega G A Petersson H Nakatsuji M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida T Nakajima Y Honda O Kitao H Nakai M Klene X Li J E Knox H P Hratchian J B Cross C Adamo J Jaramillo R Gomperts R E Stratmann O Yazyev A J Austin R Cammi C Pomelli J W Ochterski P Y Ayala K Morokuma G A Voth P Salvador J J Dannenberg V G Zakrzewski S Dapprich A D Daniels M C Strain O Farkas D K Malick A D Rabuck K Raghavachari J B Foresman J V Ortiz Q Cui A G Baboul S Clifford J Cioslowski B B Stefanov G Liu A Liashenko P Piskorz I Komaromi R L Martin D J Fox T Keith M A Al-Laham C Y Peng A Nanayakkara M Challacombe P M W Gill B Johnson W Chen M W Wong C Gonzalez J A Pople Gaussian Inc Pittsburgh PA

- 175 -

2003 101) wwwgaussiancom 102) wwwchemcraftprogcom 103) Becke A D J Chem Phys 1993 98 5648 104) Lee C Yang W Parr G R Phys Rev B 1988 37 785 105) Binkley J S Pople J A Hehre W J J Am Chem Soc 1980 102 939 for

hydrogen and Gordon M S Binkley J S Pople J A Pietro W J Hehre W J J Am Chem Soc 1983 104 2797

106) Hay P J Wadt W R J Chem Phys 1985 82 270 107) Hehre W J Ditchfield R Pople J A J Chem Phys B 1972 56 2257 108) Curtiss L A McGrath M P Blaudeau J-P Davis N E Binning R C Jr

Radom L J Chem Phys 1995 103 6104 109) A W Ehlers M Boumlhme S Dapprich A Gobbi A Houmlllwarth V Jonas K F

Koumlhler R Stegmann A Veldkamp G Frenking Chem Phys Lett 1993 208 111

110) QST is a synchronous transit approach to the quadratic region around the transition state structure For details see (a) J B Foresman A Frisch in Exploring Chemistry with Electronic Structure Methods A Guide to Using Gaussian Gaussian Inc Pittsburgh PA USA 1996 (b) H B Schlegel in Ab Initio Methods in Quantum Chemistry Part I Wiley Chichester 1987

111) Gu Z The Improvement of Total Synthesis of Angular [4]Phenylene and Its Flash Vacuum Pyrolysis (FVP) Study Postdoctoral Report University of California Berkeley 2008

112) Schwager H Postdoctoral Research Report University of California Berkeley 1987

113) Kuumlchle W Dolg M Stoll H Preuss H Mol Phys 1991 74 1245 114) (a) Hariharan P C Pople J A Theor Chim Acta 1973 28 213 (b) Francl M

M Petro W J Hehre W J Binkley J S Gordon M S DeFrees D J Pople J A J Chem Phys 1982 77 3654 (c) Rassolov V Pople J A Ratner M Windus T L J Chem Phys 1998 109 1223

- 1 -

Abstract

Cobalt and Nickel-Based Organometallic Chemistry of the [N]Phenylenes

by

Robin Padilla

Doctor of Philosophy in Chemistry

University of California Berkeley

Professor K Peter C Vollhardt Chair

This dissertation explores the synthesis and study of linear [N]phenylene cobalt complexes and the reactions of angular [N]phenylenes with nickel catalysts Chapter 1 contains a general introduction to the properties of the [N]phenylenes as well as a brief overview of earlier organometallic [N]phenylene chemistry with an emphasis on work directly related to that presented in the subsequent chapters Chapter 2 presents studies regarding first ever examples of photo-induced thermally reversible haptotropic shifts in linear [3]phenylene cyclopentadienyl cobalt (CpCo) complexes In these reactions the CpCo fragment migrates from one cyclobutadiene ring to another upon exposure to UV irradiation Heating the photoisomer complexes causes the metal fragment to return to its original position Aside from the novelty of an η4η4 cyclobutadiene migration the photo-induced thermally reversible nature of these systems makes them attractive as candidates for photostorage devices andor molecular switches The syntheses and structural studies of the linear phenylene(CpCo) complexes are discussed In addition to the experimental work computational studies on the haptotropic shift are also included Closely related work such as the observation of an intermediate haptotropic species at low temperature and the preparation of a linear [3]phenylene complex containing two CpCo units bound to the ligand is also discussed Chapter 3 describes nickel-catalyzed insertion reactions with angular phenylenes as a method for preparing derivatives of [N]phenacenes a class of polycyclic aromatic hydrocarbons that are of interest in organic electronic applications Previous work regarding nickel insertion reactions with biphenylene is mentioned Nickel-catalyzed insertion reactions with angular [3]- and [4]phenylene are then described Mechanistic studies both experimental and computational are discussed The results from these studies were used to optimize the reaction to produce [N]phenacenes as the major products of these insertion reactions Chapter 4 contains experimental details relating to chapters two and three General experimental considerations synthetic procedures crystallographic and computation data are presented Relevant references are also included in this chapter

i

Table of Contents

CHAPTER ONE PROPERTIES OF THE [N]PHENYLENES AND THEIR ORGANOMETALLIC CHEMISTRY 1

11)General Discussion of [N]Phenylene Properties 1 12)Overview of Phenylene Organometallic Chemistry 6 13)Direction of Work 10

CHAPTER TWO PHOTOndashTHERMAL HAPTOTROPISM IN CYCLOPENTADIENYLCOBALT COMPLEXES OF LINEAR PHENYLENES INTERCYCLOBUTADIENE METAL MIGRATION 12

21)Introduction 12 22)Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes 16 23)Structural Studies on the Linear [3]Phenylene(CpCo) Complexes 22 24)Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift 30 25)Low Temperature Photolytic Studies on the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes 41 26)Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 56 27)Summary and Outlook 62

CHAPTER THREE NICKEL-CATALYZED INSERTION REACTIONS FOR THE PREPARATION OF [N]PHENACENE DERIVATIVES 63

31)Introduction 63 32)Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene 67 33)Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene 75 34)Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions 81 35)Summary and Outlook 87

CHAPTER FOUR EXPERIMENTAL AND COMPUTATIONAL DETAILS 88

41)General Considerations 88 42)Experimental Section for Chapter Two 88 43)Computational Details for Chapter Two 129 44)NMR Data for Chapter Two 154 45)Experimental Information for Chapter Three 162 46)Computational Details for Chapter Three 168 47)References 169

ii

Acknowledgements

ldquoWhere would I find leather enough to cover the surface of the earth The Earth is covered over merely with the leather of my sandalsrdquo

-Shāntideva in the Bodhicaryāvatārah Ch 4 v13 Five years ago I arrived in Berkeley with a rather clear objective get (or rather survive) a PhD Though the goal never changed the all paths (scientific personal professional and spiritual) I traversed were often quite unlike anything I could have anticipated I have had the great fortune to stand on the shoulders of many giants during these past few years and it is to them that I owe my deepest gratitude First and foremost I would like to thank my advisor Peter Vollhardt for all of his support and patience The things I have learned from him are far too numerous to list but certainly the two most important are clarity and rigor two qualities that extend far beyond the chemical realm Working with so many different people was another interesting challenging and ultimately highly rewarding experience I am particularly indebted to ldquoThe Old Gangrdquo consisting in part of Phil Leonard and Ken Windler These two gentlemanly pyromaniacal firearms enthusiasts aside from showing me the ins and outs when I was a new arrival (and teaching me more than I will ever need to know about guns and explosives) soon became good and close friends No mention of The Gang would be complete without Jordan Rose Figura Despite being a chemical biologist and not actually a member of the Vollhardt Group she nonetheless (somehow) managed to fit in perfectly My life has been forever changed by her introducing me to ldquoDoctor Whordquo Many others also deserve special mention Sabine Amslinger has and will continue to provide a near endless amount of legendary stories that often border on mythological Tom Gadek was just plain awesome Vince Gandon aside from being one the best experimentalists Irsquove seen also happened to have a rather fine taste in films and music Dominik Hager excelled at getting me out of the lab for an occasional weekend of fun The elegant and refined chocolate cakes of Aude Hubaud were a rare yet very welcome occurrence Her sassy chic comments on all aspects of life however were quite copious Greg Boursalian performed an excellent job of filling the ldquocool undergradrdquo spot and I wish him the best for his own graduate school journey Steve Meier managed the Herculean task of (legally) disposing of all those old empty gas cylinders It is my great hope that Prof Sgt Meier will share many (but certainly not all) of his Berkeley experiences with the next generation of chemists that he will educate Explaining the strange and quirky aspects of American culture and the English language to Kerstin Weiszlig made for a fair number of humorous conversations Learning the stranger and quirkier aspects of German language and culture made for many more Similarly much time was spent meticulously examining the lyrics and slang expressions of assorted hip-hop songs with Sander Oldenhof Practicing kindergarten level German while sharing a fairly constant supply of Ritter Sport bars with Verena Engelhardt was another fine example of cultural exchange Despite his best efforts Kasper Moth-Poulsen has yet to convince me that Volvo is the greatest vehicle manufacturer in the known universe My cultural exposure was not limited to European interactions however and I managed to learn a little Chinese as well Apparently ldquoHao Shenrdquo

iii

means ldquoMacGyverrdquo in Mandarin I would also like to thank the rest of my co-workers past and present for all of their support They are in rough chronological order Thomas Carl Miles Carter Kaspar Schaumlrer Ingo Janser Romy Michiels Elisa Paredes Thilo Heckrodt Nicholas Cheron Alex Lee Anais Geny Samer Al-Gharabli Nicole Franssen Vladislav Kulikov Alexandra Romek Isaac Ho Zhenhua Gu Florian Montermini Nikolai Vinokurov Robert Zitterbart and Cedric Ghellamallah Bonnie Kirk skillfully handled the various arcane administrative procedures but also provided many interesting and memorable early morning conversations The finer points of NMR spectroscopy were taught to me by the indomitable Rudi Nunlist His wry humor and outlook on life were often the perfect supplement to the rigors of graduate school life Working with Chris Canlas Rudirsquos able successor has also been a pleasure I was encouraged when he was so quick to remind me that I have the same name as a bad-boy Filipino action-movie star Teaching while always quite time consuming proved to be an invaluable experience Teaching under the direction of Peter the man who wrote the book on organic chemistry was quite an adventure His passion and talent for teaching are immediately obvious and inspiring even without flipping through the Basque translation of his textbook Jon Ellmanrsquos ability to write exams that are easy to grade but difficult for students to take is similarly awe inspiring There is no doubt in my mind that Heino Nitsche has taken teaching of general chemistry to new levels of eccentricity and excitement Jean Freacutechetrsquos impressive aptitude for lecturing is perhaps surpassed only by the impressiveness of his wine collection Looking down the academic chain I have to acknowledge many of the brilliant and wonderful students that made teaching such a fantastic experience Special thanks goes to Steve Seyedin Nellie Ekmejian Jessie Zhang Yao Yue Ashley Johnson Brent Jellen Zarina Khan and Mojgan Rastegar all of whom were extraordinary students that I hope will do their part to save the world No acknowledgement could be complete without recognizing the love and support of my family in particular my mother Her love though always tough was always there My various housemates also provided me with some great times Chris Trinh my first housemate in Berkeley was a superb fellow to live with and I will always fondly remember our conversations on life love and quantum gravity Cory McLitus when he wasnrsquot slaving away in the architecture studio also became a good friend I feel no need to apologize for getting him hopelessly addicted to ldquoThe Big Bang Theoryrdquo The awesome Samra Kasim was always ready for chai good food and hearty discussions on Bollywood and all things South Asian The housemates of 1505 Oxford St are also great people Though we rarely cross paths Vicky Zhuangrsquos highly entertaining biology lab adventures are much appreciated Vannamaria Kalafonos always has something wonderful going on in the kitchen and I aspire to learn the Greek specialty of cooking for a zillion people from her The cats Pink Tuffy and especially Floyd are nice companions even though they sleep a combined 60 hours per day Many kalyānamitras helped me get through the toughest times and to them I am especially grateful A large number of my Saturday evenings were spent in the calm environs of the Berkeley Monastery where Rev Heng Surersquos Avataṃsaka Sūtra

iv

lectures gave me much to think about The monthly lectures by Ajahn Amaro Ajahn Passano and the Abhayagiri Sangha were also a wonderful learning experience Chats about long-dead ancient languages and obscure texts with Sean Kerr a fellow survivor of Dagmar Theisonrsquos German class will also be fondly remembered The NY Sangha though far away always supported me and welcomed me warmly whenever I returned home Frank Yao Hai-Dee Lee Sheila Sussman Fred Ng Martin Applebaum Josephine Verceles Tiffany Taulton Phung Tran and especially Aaron Vederman repeatedly reminded me to ldquosmile breath deep and go slowlyrdquo The many visits to Bodhi Monastery were always the high points of my summers Michael Roehm Bhikkhu Bodhi Jane Berry Henry and Lily Teoh Marcie Barth Mahendra Sagar the dearly departed Felicia Miller Ven Guo Jun Susan Chastain and the polygot Bhikkhu Analayo made every visit an unforgettable experience and never failed to remind me why I get out of bed in the morning

- 1 -

Chapter One

Properties of the [N]Phenylenes and Their Organometallic Chemistry

11 General Discussion of [N]Phenylene Properties Polycyclic aromatic hydrocarbons (PAHs) are a class of molecules that have occupied the minds of chemists for generations1 Their essential feature aromaticity is the unusual stabilization that arises from having a 4n+2 number of π-electrons in a cyclical array This seemingly simple definition obscures the fact that aromaticity continues to be one of the most scrutinized topics in modern organic chemistry2 and more rigorous definitions3 have remained elusive Much of the early work4 with PAHs was aimed at investigating theoretical issues surrounding aromaticity There has been renewed interest in these systems in recent years because they are increasingly attractive as functional materials in organic-based electronics5 Of the many different kinds of PAHs known eg 1ndash6 (Figure 11) one subclass is of particular interest the [N]phenylenes6

Anthracene Coronene Phenanthrene

Chrysene Triphenylene Pyrene

1 2 3

4 5 6

Figure 11 Some examples of polycyclic aromatic hydrocarbons The [N]phenylenes (where N = the number of benzene rings) are PAHs in which benzene and cyclobutadiene rings are fused in an alternating manner The cyclobutadiene ring imparts very unusual structural and electronic properties as seen in the simplest molecule in the series biphenylene (7) It can be described by several resonance forms (Figure 12 andashe) in which the major contributor 7c avoids formation of the highly destabilizing antiaromatic cyclobutadiene (7a 7e) and benzocyclobutadiene circuit (7b 7d) This preference is manifest in the significant bond alternation7 seen in

- 2 -

the crystal structure of biphenylene (Figure 12) which shows a clear difference in bond lengths between the formal single bonds (~143 Aring) and the shorter formal double bonds (~137 Aring)

1423

1372

Figure 12 Biphenylene bond lengths (top Aring) and resonance contributors (bottom)

An extreme example of [N]phenylene π-bond localization is triangular [4]phenylene (8) (Scheme 11) in which the three-fold peripheral fusion imparts complete cyclohexatriene character on the central ring89a This property is reflected in the reactivity of the system eg catalytic hydrogenation (9)8b epoxidation (10)8c and cyclopropanation (11)8c Scheme 11 Reactions Illustrating the Fully Bond Localized Character of the Central Benzene

Ring in Triangular [4]Phenylene 8 Bond lengths are in Aring

- 3 -

Phenylenes exhibit another interesting structural feature in contrast to other PAHs sizable deviations from planarity (Figure 13)9ab The flexibility of the phenylene framework arises from the combined effect of π- and σ-strain9ab By adopting a nonplanar geometry overlap between the π-orbitals is diminished and in turn leads to a decrease in destabilizing antiaromatic character Pyramidalization of the four-membered ring carbons also reduces σ-strain9ab a phenomenon observed in highly strained alkene systems9c

Figure 13 Crystal structures showing deviations from planarity in (a) helical [6]phenylene (12)10 (b) dimethyl triangular [4]phenylene-23-dicarboxylate (13)9a and (c) 23-bis(tri-

methylsilyl) linear [3]phenylene (14)9a

The fusion of aromatic benzene rings with antiaromatic cyclobutadiene units in the same molecule has prompted numerous experimental and theoretical discussions6 regarding the magnetic and electronic properties of the phenylenes 1H-NMR spectroscopy is one typical measure of aromaticity Protons on the exterior of aromatic rings (eg 15) show relatively low field resonances while their interior counterparts resonate at relatively high field due to the presence of a diamagnetic ring current Conversely antiaromatic rings with 4n π-electrons are paratropic and reveal the opposite disposition of the two respective types of protons (eg 16) The interplay between aromatic and antiaromatic character in the phenylenes is evident in their chemical shifts which tend to show weakly aromatic resonances (Figure 15) relative to benzene (736 ppm)

(a) (b) (c)

12 13 14

- 4 -

Figure 14 Observed 1H-NMR resonances in (a) the aromatic [18]annulene (15)11 and (b) the antiaromatic 5-bromo-19-bisdehydro-[12]annulene (16)12

Aside from NMR spectroscopy nucleus independent chemical shift (NICS)13 calculations have also proven to be useful measures of aromaticity The NICS technique works by calculating the magnetic shielding of a ldquoghost nucleusrdquo that can be positioned anywhere around a molecule For probing aromaticity the calculated point is in the center of the π-electron circuit to be examined Calculations placing the ghost nucleus 1 Aring above the plane of the molecule are often used to minimize local anisotropy and are referred to as NICS(1)14 NICS data are given in ppm and are thus comparable to experimental 1H-NMR measurements Negative NICS values indicate aromatic character while positive values suggest antiaromatic character For example the NICS(1) of benzene15 is ndash125 ppm whereas for cyclobutadiene15 it is 151 ppm NICS calculations for various phenylenes have been carried out6 and are shown in Figure 15 alongside the experimentally measured 1H-NMR chemical shifts The attenuated aromatic character of the benzene and the relatively weak antiaromatic character of the cyclobutadiene rings in phenylenes such as biphenylene (7) triangular [4]phenylene (8) and angular [4]phenylene (17) are apparent from both sets of data

Figure 15 1H-NMR (blue) and NICS(1) (green) data for selected phenylene topologies (ppm)6

The phenylenes possess multiple modes of reactivity7 as illustrated by biphenylene (7) in Scheme 12 It can undergo electrophilic aromatic substitution like other PAHs but does so selectively at the 2-position to avoid the formation of intermediates with antiaromatic character Biphenylene does not readily undergo Diels-

- 5 -

Alder reactions but was shown to react with electron-deficient benzynes to give the corresponding cycloadducts16 Opening of the highly strained four-membered ring is another prominent aspect of phenylene reactivity

Scheme 12 Illustrative Reaction Pathways of Biphenylene6

Early work17 showed that it was possible to cleave the aryl-aryl C-C bonds via thermolysis in the neat state Rupture of the four-membered ring is a key step in the rearrangement of phenylenes into other PAHs and has been observed typically under flash vacuum pyrolytic conditions18 (eg 10ndash3ndash10ndash6 torr 800ndash1000 degC) Strained ring opening on exposure to metal complexes to give metallacycles19 is discussed in further detail in Section 12 12 Overview of Phenylene Organometallic Chemistry

As mentioned above the weakly aromatic character of the phenylenes dominates their structure and reactivity In the linear phenylenes the antiaromatic contribution to structure and reactivity becomes increasingly significant A simple yet instructive explanation for this phenomenon can be seen in the various resonance structures of linear [3]phenylene (18) a selection of which is depicted in Figure 16 Even the most favorable forms a and b feature double bonds in the four-membered rings The cumulative increase in cyclobutadienoid circuits should therefore lead to an increase in antiaromatic character The relative augmentation in

- 6 -

cyclobutadienoidantiaromatic character of the linear phenylenes was confirmed6 by NMR NICS calculations and HOMO-LUMO measurements20

Figure 16

Resonance contributors to linear [3]phenylene

Cyclobutadiene is often invoked as the typical example of a highly destabilized antiaromatic system Indeed the difficulties21 in preparing and isolating it confirm theoretical predictions regarding its instability22 Attachment of a metal however is known to produce aromatic organometallic molecules of high stability23 The increased antiaromatic character of the linear phenylenes thus makes them amenable to metal complexation Cyclopentadienylcobalt cyclobutadiene complexes of linear [3]- (19)24 linear [4]- (20)25 and linear [5]phenylene (21)26 have been prepared using the well-developed cobalt-based [2+2+2] alkyne cyclotrimerization methods (Scheme 13)27

Compounds 19ndash21 constitute the only linear CpCo phenylene systems known so far

Scheme 13 Synthesis of Linear Phenylene(CpCo) Cyclobutadiene Complexes

In the metallated linear [4]- and [5]phenylene 20 and 21 respectively the CpCo unit is located on the inner cyclobutadiene ring This is curious as one would have expected the metal fragment to be bound to its outside counterpart close to the center of reactivity during the cyclotrimerization step The position of the CpCo unit was established by NMR spectroscopy2628 In addition a crystal structure of a tetrahexyl

TMS

TMS

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMSTMS

TMS

Co

CpCo(CO)2BTMSA

h

Co

Co

CpCo(CO)2BTMSA

h

CpCo(CO)2BTMSA

h

19

20

21

- 7 -

substituted linear [5]phenylene28 (Figure 17) clearly reveals the inside position of the metal fragment Difficulties in obtaining high quality crystals however precluded a detailed bond analysis of the complex The unexpected location of the CpCo unit in 20 and 21 suggested the occurrence of CpCo migration under the conditions of their preparation Detailed experiments verifying this hypothesis will be the subject of Chapter 2

Figure 17 Disordered crystal structure for the 23910-tetrakis(trimethylsilyl)-571214-

tetrahexyl linear [5]phenylene(CpCo)

In contrast to the linear phenylenes their angular relatives undergo π-metallation at the cyclohexatrienoid moieties (Figure 18) For example angular [3]phenylene (22) reacts with CpCo(C2H4)2 to form the η4-CpCo complex 2329 Similar treatment with Cr(CO)3(NH3)3 yields the η6-Cr(CO)3 analog 2430

Figure 18 η

4-CpCo (23) and η6-Cr(CO)3 (24) complexes of angular [3]phenylene (22)

In addition to 24 related chromium complexes of the triangular [4]phenylene frame eg 25 have been prepared (Scheme 14)31 Interestingly regioisomer 26 generated at relatively lower temperatures is the kinetic product of monocomplexation and rearranges thermally to 27 Double metallation is possible as illustrated in the conversion of 27 to 28 with added (naphthalene)Cr(CO)3

- 8 -

Scheme 14 Synthesis and Reactions of Triangular [4]Phenylene(Cr(CO)3) Complexes

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3(NH3)3dioxane 100 oC

14 h

(naphthalene)Cr(CO)3THF Et2O 60 oC 14 h

90 oC

(naphthalene)Cr(CO)3THF Et2O 60 oC

14 h

25

27

26

28

57 43

89

In contrast to CpCo which attaches itself exclusively to the four-membered ring in the linear phenylenes including the linear [3]phenylene frame as in 19 (Scheme 13) Fe2(CO)9 gives a plethora of complexes with the tetrasilyl derivative 29 among which the iron tricarbonyl cyclobutadiene complex 30 is only minor (Scheme 15)27 Instead other organometallic molecules such as arene complex 31 were isolated This compound contains two Fe(CO)3 units coordinated to the central benzene ring An iron-iron bond was proposed for this molecule (31a) although the spectral data are also consistent with a structure in which the Fe(CO)3 fragments are located on opposite faces (31b) Because a crystal structure could not be obtained the structural identity of 31 remains ambiguous The major products of this reaction 32 and 33 illustrate another important aspect of phenylene reactivity metal insertion into the strained ring

- 9 -

in this case involving the dinuclear Fe2(CO)6 unit Complex 33 probably originating from 32 contains an additional Fe(CO)3 moiety coordinated to the terminal benzene ring closest to the Fe2(CO)6 fragment

Scheme 15 Reaction of Linear [3]Phenylene with Fe2(CO)9

While as yet absent in the linear series a cobalt insertion product analogous to iron compounds 32 and 33 was isolated when angular phenylene 22 was exposed to excess CpCo(ethene)2 (Figure 19)32 In this case double insertion of two (CpCo)2

Figure 19 Tetranuclear CpCo-terphenylene complex 34 and its crystal structure

34

- 10 -

fragments occurred to give 34 in 71 yield Notably neither 23 nor analogs of the type 31 were detected As alluded to in Scheme 12 biphenylene (7) itself also undergoes metal insertions into the four-membered ring This type of reactivity has been observed with a range of transition metals including Co19 Mechanistically best delineated is the attack of Ni and Pt species Thus Ni(PEt3)4

33a and Ni(COD)(PMe3)233b begin with insertion of

the nickel fragment into the four-membered ring to give a metallacycle of the type 35 (Scheme 16) Subsequent dimerization assembles 36 from which Ni is extruded to furnish tetraphenylene 37 as the final product A similar reaction pathway was proposed for Pt(PEt)4

19 but proceeding via 38 to a monometallacycle 40 possibly through the intermediacy of 39 In summary the σ- and π-activation of the phenylenes endows them with rich organometallic chemical potential The synthetic and mechanistic exploration of one aspect of it namely the Ni-catalyzed cycloaddition of alkynes to the four-membered rings in angular phenylenes will be discussed in Chapter 3

Scheme 16 Reaction of Biphenylene with Nickel and Platinum Complexes

13 Direction of Work The discussions in Sections 11 and 12 have provided a brief overview of phenylene properties and their previously studied organometallic chemistry

- 11 -

respectively The aim of this thesis was to advance two aspects of prior investigations The first area examines the chemistry of the linear phenylene(CpCo) complexes In particular experiments are presented addressing the question of a possible migration of the CpCo fragment along their framework The revocable movement of a metal fragment between cyclobutadiene rings is a highly noteworthy discovery as this process has never before been reported On a practical level this mode of reactivity places linear phenylene(CpCo) complexes in the increasingly appealing class of organometallic arrays that can serve as the basis for various molecular electronic systems The reversible isomerizations described in the second chapter can potentially be employed in molecular machines and switches data storage and as will be detailed photostorage devices Experimental work in the form of detailed solid state and spectroscopic analyses is provided Computational studies are also employed to further scrutinize the novel chemistry of the abovementioned Co-based molecules The second topic of this thesis examines nickel-catalyzed insertions into the four- membered rings of angular phenylene systems Specifically the application of this reactivity to the synthesis of a class of PAHs known as [N]phenacenes is discussed Phenacenes (polyphenanthrenes) have recently shown great promise as organic transistors and conductors but advancement of this field has been hampered due to few practical syntheses The insolubility of these molecules has also been a substantial barrier to the development of phenacene-based applications The content of the third chapter explores the preparation of soluble phenacene derivatives using a tandem Ni-insertion alkyne cycloaddition reaction This new process provides an efficient widely applicable and practical synthesis of larger phenacenes using correspondingly larger angular phenylene systems Detailed mechanistic studies of this reaction are presented Experimental data are used in conjunction with computational studies to gain further insight with the optimization of the reaction by reduction of side product formation being a crucial milestone

- 12 -

Chapter Two

PhotondashThermal Haptotropism in Cyclopentadienylcobalt Complexes of Linear Phenylenes Intercyclobutadiene Metal Migration

21 Introduction As previewed in Section 12 the unexpected position of the metallic unit in the linear [4]- and [5]phenylene(CpCo) systems 20 and 21 constituted the background for the studies presented in this chapter Specifically it was hypothesized that its origin was due to the migration of the metal fragment from one cyclobutadiene ring to another a process that would constitute an unprecedented type of haptotropic shift34-36 However a prerequisite for studying such a rearrangement would be the generation of the haptoisomers of 20 and 21 (Scheme 13) bearing the CpCo appendage at the respective terminal four-membered rings a possibility obviated by their thermal method of synthesis The following describes the history that led to the discovery of photochemical conditions that circumvented this thermodynamic problem The story begins with a prior attempt to stabilize the linear phenylene frame by alkyl substitution the ultimate aim being the synthesis of members of the series with Ngt5 Such substitution was also hoped to improve solubility a facet exploited in the corresponding zigzag series37 The synthetic strategy followed that used in the preparation of the largest known linear phenylene 41 namely the CpCo-catalyzed cyclization to 21 followed by careful oxidative demetallation as shown in Scheme 21 The initial target chosen was the tetrahexyl system 43 approached via the synthesis of complex 42 (Scheme 22)28 Demetallation was thought to be facile to provide the free ligand but this anticipation proved to be erroneous

Scheme 21 Oxidative Decomplexation of Linear [5]Phenylene Complex 21

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMS

41

CoCp

21

40

CuCl2middot2H2ODME NEt3 H2O

Scheme 22 Preparation of Tetrahexyl Linear [5]Phenylene Complex 42

- 13 -

TMS

TMS

TMS

TMS

Hex

Hex

Hex

Hex

CoCp

42

CpCo(CO)2 BTMSAm-xylene ∆ hν

27

Hex Hex

HexHex

TMS

TMS

TMS

TMS

Hex Hex

HexHex

ndashCpCo

43

The demetallation of 42 under numerous conditions was unattainable However in one of these attempts an NMR sample of 42 was exposed to UV-irradiation leading to the evolution of new signals eventually assigned to originate from rearranged compound 45 (Scheme 23)28 This molecule is also a linear [5]phenylene(CpCo) complex but now has the metal fragment bound to the outer cyclobutadiene ring an arrangement that was suspected to be the initial product of the preparation of 42 (Scheme 22) That this conjecture was correct was established by heating which caused photoisomer 45 to revert to 42 An indication of the generality of this phenomenon was gleaned from 21 which underwent the same photoinduced thermally reversible haptotropic migration (Scheme 23)38 A detailed discussion of the spectral properties of these haptomers is provided in Sections 23 and 24 Scheme 23 Photoinduced Thermally Reversible Haptotropic Migration of the CpCo Fragment

in Linear [5]Phenylene(CpCo) Complexes

This discovery was deemed significant for two reasons 1 it constitutes the first observation of intercyclobutadiene metallohaptotropism and 2 there are only two previously known examples of mononuclear39 additive-free40 photothermal reversible haptotropic shifts both of which are based on Mo(PMe3)3 complexes (Scheme 24)41 Systems capable of undergoing this type of reaction are of much practical importance because of their potential employment as photostorage devices andor molecular switches42 The development and application of functional organometallic materials43 has proceeded at a relatively slow pace when compared to their non-metallated counterparts5c Thus the great prospects for discovery and advancement make this area of study particularly attractive

- 14 -

Scheme 24 Photothermal Reversible Metallohaptotropism in (a) Molybendum-Indole41a and (b) Molybendum-Isoquinoline Complexes41b

Having confirmed that an η4η4 cyclobutadiene haptotropic migration was indeed occurring mechanistic investigations2838 were begun Interestingly full conversion of the inner bound CpCo complexes to their photoisomers was never achieved The maximum ratio obtained for 2144 and 4245 was 8812 Variations of solvent (eg benzene THF CHCl3) and temperature (0ndash30degC) had no effect on this ratio Added ligands such as 15-cyclooctadiene CO and phosphines were also inconsequential Of further significance was the robustness of the photothermal cycle which could be run multiple times without decomposition Kinetic experiments were carried out to determine the activation parameters for the thermal reversal of 44 and 45 to 21 and 42 respectively These data are shown in Table 21 The isomerizations are cleanly first order a finding that was unaffected by changes in concentration22 The enthalpy of activation (∆Hne) increased only slightly with hexyl substitution (44 vs 45) The near zero entropy of activation values (∆Sne) was consistent with the occurrence of an intramolecular process

Table 21 Activation Parameters for the Conversion of Outer to Inner CpCo Complexes Under

Thermal Conditions ∆Sne Values are in Entropy Units (1 eu = calmolsdotK)

Reaction Solvent ∆H

ne (kcalmol) ∆Sne (eu)

44 to 21 C6D6 259 plusmn 04 16 plusmn 14 44 to 21 THF-d8 256 plusmn 09 01 plusmn 30 45 to 42 THF-d8 276 plusmn 08 77 plusmn 27

Consideration of the relative facility of the above haptotropic shifts made it likely that migration was occurring along the entire phenylene frame including the ldquohoppingrdquo across the central six-membered ring (Scheme 25) This degenerate equilibration should be detectable by NMR spectroscopy44 if it were sufficiently fast Unfortunately but perhaps not surprisingly considering the data in Table 21 coalescence of the spectrum of 21 could not be achieved even at temperatures as high as 120 degC Spin saturation transfer experiments (eg EXSY) also failed44 These data allowed an estimate of the lower limit for the activation energy of the internal shift of ∆Gne ge 22 kcalmol28

Scheme 25 Proposed Internal η4η4 Cyclobutadiene CpCo Migration

- 15 -

The failure of the above experiments inspired a different approach based on the following arguments The antiaromatic character of the linear phenylenes has been shown by theory and experiment to increase with size645 Consequently the effect of metalloaromatization46 makes linear [5]phenylene a better (and hence more strongly bound) ligand for CpCo than a smaller system (eg linear [3]phenylene) Indeed the enthalpy of the homodesmotic in Scheme 26 was computed by DFT methods to be Scheme 26 Calculated Homodesmotic Reaction Showing Preferential Binding of CpCo to

Linear [5]Phenylene

113 kcalmol47 If the barrier to intercyclobutadiene hopping were related to the binding energy of the metal one would expect a more loosely bound metal fragment to migrate faster The hope was therefore that the degenerate haptotropism in Scheme 27 would be observable by VT NMR methods Unfortunately these efforts failed again38 either because the anticipated acceleration was not sufficient to be observable by NMR or because the argument above (which rests solely on ground state considerations) is flawed

Scheme 27 Proposed Degenerate Haptotropic Shift in Linear [3]Phenylene Complex 19

- 16 -

The preceding discussion summarizes some of the quantitative aspects of this new type of haptotropic shift Many fundamental questions however remained to be answered Is it possible to observe the photothermal shift in other systems such as linear [3]- and [4]phenylene What is the exact mechanism of metal migration between cyclobutadiene rings In what way if any does attachment of CpCo alter the structure of the phenylene scaffold Related to these questions was the long-standing quest for an accurate crystal structure of any linear phenylene(CpCo) complex The answers are addressed in the following sections 22 Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes As recounted in Section 21 the degenerate internal haptotropic shift could not be seen by NMR in the symmetrical 19 Therefore recourse had to be taken to chemical methods involving an isomerization of the sort shown in Scheme 28

Scheme 28 Isomerization of a Desymmetrized Linear [3]Phenylene(CpCo) Complex

Initial efforts focused on attempts to desymmetrize compound 19 directly by selective electrophilic desilylation specifically protodesilylation Earlier studies48 had shown that such selectivity was possible in the reactions of bis(trimethylsilyl)benzocycloalkenes such as the benzocyclobutene depicted in Scheme 29 In this case loss of the first TMS group is approximately forty times faster than that of the second Along these lines it was thought that exposing 19 to acidic conditions would selectively remove one (or perhaps two) TMS groups before attacking the remaining silylarene positions In the event treating compound 19 with trifluoroacetic acid in carbon tetrachloride did induce protodesilylation but with no selectivity A mixture of products was obtained and its separation proved impossible (Scheme 210) In light of this setback a new synthetic scheme had to be considered that would generate a desymmetrized system directly in the CpCo-catalyzed cyclization step

- 17 -

Scheme 29 Selective Desymmetrizing Reactions of 12-Bis(trimethylsilyl)benzocyclobutene with Electrophiles

Scheme 210 Attempted Selective Protodesilylation of 19

Fortunately such a strategy had already been executed successfully in the creation of 23-bis(trimethylsilyl) linear [3]phenylene (46) and employed the iterative Scheme 211 Iterative Cyclotrimerization Route in the Synthesis of Linear [3]Phenylene 46

cyclization depicted in Scheme 21127 Its specific execution (Scheme 212) started with a Sonogashira reaction between trimethylsilylacetylene (TMSA) and 12-diiodobenzene (47) to give diyne 48 in high yield Deprotection of 48 with K2CO3 immediately followed by standard CpCo(CO)2-catalyzed alkyne cyclotrimerization649 with bis(trimethylsilyl)acetylene (BTMSA) afforded 23-bis(trimethylsilyl)biphenylene (49) Iododesilylation was then performed using pure ICl to give 23-diiodobiphenylene (50) A Sonogashira coupling between TMSA and 50 produced diyne 51 in good yield The use of a slightly modified cyclization procedure provided the new 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52) in 57 yield This protocol employed THF as a cosolvent to BTMSA thus reducing the reaction temperature in turn allowing for the CpCo to remain attached in the final product and preventing catalytic turnover252638

TMS

TMS46

+

TMS

TMS

+

TMS

TMS

+

TMS

R

TMS

dilute

[X+]

X = H D Br

TMS

TMS

[X+]

TMS

X = H D Br

X

- 18 -

Scheme 212 Synthesis of Asymmetric Linear [3]Phenylene(CpCo) 52

High dilution conditions also helped to suppress formation of cyclobutadiene(CpCo) complexes a well known side reaction in alkyne cyclization chemistry

Compound 52 like its tetrasilylated analogue 19 is a black air-sensitive solid Although it can be handled in air for brief periods of time complete decomposition occurs within 24 hours if left exposed to the ambient atmosphere Purification must always be done with neutral activity III alumina as lower activities (and silica gel) cause decomplexation to give the deep red ligand 46 as the only isolable product Critically exposing molecule 52 to UV irradiation induced the desired haptotropic shift giving its photoisomer 53 (Scheme 213) Heating 53 converted it back to 52 thus completing the photothermal cycle Interestingly close inspection of the NMR spectra of this experiment revealed that a small amount of 53 (2) always remained even on prolonged heating That this observation signaled a thermodynamic equilibrium was confirmed by dissolution of pure crystalline 52 and NMR analysis From the equilibrium constant the ∆Gdeg298 was calculated to be 23 kcalmol in favor of 52 The reasons for this energetic preference and a discussion of the NMR spectral properties of these and related complexes are presented in Section 23

Scheme 213 The Photoinduced Thermally Reversible Haptropic Shift in Linear

- 19 -

[3]Phenylene-(CpCo) 52 to Give Photoisomer Complex 53 The investigations of the equilibration depicted in Scheme 213 were all carried out in sealed Pyrex NMR tubes (J-Young or flame-sealed) using benzene-d6 andor toluene-d8 as the solvent As for the linear [5]phenylene(CpCo) system the cycle could be run multiple times without decomposition and was unaffected by changes in solvent and temperature The maximum ratio of 5352 that could be obtained on irradiation was 11 after ten hours This value is larger than that observed for its linear [5] analogs 2144 and 4245 Photoisomerization also occurs with sunlight leading to the photostationary equilibrium of 5253 = 105 Consequently care must be taken to shield 52 from direct andor indirect sunlight Indoor fluorescent lighting however did not induce CpCo migration Attempts to monitor the photoisomerization and its thermal reverse by UV-Vis spectroscopy failed because of minimal changes in the absorptions due to 52 during these processes This finding implies that the absorption spectra of 52 and 53 are not unexpectedly very similar and offers a possible explanation for the maximum photostationary ratio of 11 The activation parameters for the thermal reversal reaction (53 to 52) in Scheme 213 were obtained in the manner described in Section 21 and are shown in Table 22 The relatively high activation barriers (with respect to the NMR time scale) explain why the degenerate isomerization in 19 could not be verified by NMR experiments Qualitatively the ∆Hne values agree with the hypothesis that the more loosely bound CpCo unit in the linear [3]phenylene is relatively more mobile they are approximately 3 kcalmol lower than those of the [5]phenylene system On the other hand the ∆Sne values especially in C6D6 are positive and relatively high although still within the range acceptable for intramolecular reactions Nevertheless a crossover experiment was devised to provide a definite answer

Table 22 Activation Parameters for the Thermal Conversion of Complex 53 to 52

Solvent ∆H

ne (kcalmol) ∆Sne (eu)

C6D6 204 plusmn 14 158 plusmn 22 Toluene-d8 231 plusmn 07 60 plusmn 13

For this purpose two new linear [3]phenylene(CpCo) derivatives were required One would carry a marker on the Cp ring while the other would be labeled at the phenylene frame Execution of Scheme 213 would involve an equimolar mixture of both compounds An intramolecular mechanism would retain the integrity of the labeling while a dissociative path would lead to label scrambling The outcome of this experiment should be ascertainable by NMR spectroscopy and more rigorously by

CoTMS

TMS

CoTMS

TMS

310 365 nmsunlight

30ndash50oC52 53

- 20 -

Scheme 214 Preparation of MeCp- (54) and Deuterium Labeled (55) [3]Phenylene Complexes

mass spectrometry To this end methyl-Cp complex 54 and dideuterio compound 55 were targeted for synthesis (Scheme 214) Compound 54 was prepared by carrying out the modified cyclotrimerization reaction with MeCpCo(CO)2

50 while 55 was made using methanol-OD in the desilylation of 51 The amount of deuterium incorporation in 55 was found to be 63 as gleaned from its proton NMR spectrum Scheme 215 Crossover Experiment with Labeled Linear [3]Phenylene(CpCo) Complexes

- 21 -

Co

TMS

TMS

TMS

TMS

Co

h CoTMS

TMS

Co

D

D

TMS

TMSD

D

TMS

TMS

Co

Co

TMS

TMSD

DCo

TMS

TMS

Co

TMS

TMSD

D

+

+

+

+

mz = 510

mz = 494

56mz = 508

57mz = 496

54mz = 508

55mz = 496

58 59

53 52

Not observed

Six distinct products are possible in the crossover experiment using 54 and 55 (Scheme 215) Compounds 56 and 5 would arise as a consequence of an intramolecular shift Molecules 53 and 58 and their photoisomers 52 and 59 respectively would be the result of metal fragment dissociation Mass spectrometry would readily verify the occurrence of crossover as the masses (given in mz in Scheme 215) of the products with scrambled labels (52 53 58 59) are distinct from the masses of the starting materials (54 55) and their photoisomers (56 57) In the first part of the experiment equal amounts of 54 and 55 were mixed (shielded from light) and allowed to stand for 2 hours at room temperature The resulting 1H-NMR spectrum consisted of only the signals for 54 and 55 Similarly the mass spectrum showed molecular ion peaks matching the masses of 55 and 56 (Figure 21) The second step was irradiation Analysis of the photolyzed mixture showed new peaks due to complex 56 (the resonances of which had been obtained in a separate photothermal experiment with pure 54) with the expected integration ratio and a second set assigned to 57 identical with the spectrum of 53 but with the expected attenuated absorption for the silyl bearing arene hydrogens The relative integrations for all compounds observed were consistent with a mixture of 5455 and 5657 Mass spectral analysis of the irradiated mixture showed a pattern that was identical to that collected before irradiation (Figure 21) Finally the thermal reversal reaction was carried out by heating the photolyzed mixture at 80 degC After 30 hours the resulting

- 22 -

NMR spectrum matched that of the initial mixture of 54 and 56 in particular confirming the full protonation of 54 and the unchanged level of deuterium incorporation in the silyl

Figure 21 Molecular ion peaks for 5456 (mz = 508) and 5557 (mz = 496)

bearing arene ring of 55 The corresponding mass spectrum contained no evidence for the presence of scrambled products To conclude The haptotropic shift is non-dissociative The exact manner in which the metal traverses from one cyclobutadiene ring to the other will be examined in greater detail in Section 24

23 X-Ray Structural and Comparative NMR Analysis of Linear [3]Phenylene(CpCo) Complexes The results described in Sections 21 and 22 pose some fundamental questions beyond those concerned with the immediate details of the observed haptotropism and addressing the basic novelty of the complexes involved What actually happens to the phenylene ligand when it is ligated via a cyclobutadienoid ring This section will address this question from a structural and (NMR) magnetic point of view Only one crystal structure of a linear phenylene(CpCo) complex was known at the outset of this work namely that of [5]phenylene(CpCo) 42 (Figure 17) and its acquisition required extensive efforts at crystallization28 Unfortunately extensive disorder obviated a detailed analysis It was hoped that some of the complexes employed in the chemistry disclosed in Section 22 would be more forthcoming in this respect The challenge lay in finding the right conditions for crystal growth We began with tetrasilyl linear [3]phenylene(CpCo) 19 which had been crystallized previously by slow cooling in acetone38 These conditions and numerous others (Table 23) did not provide material suitable for X-ray diffraction Success entailed slow cooling a solution of 19 to ndash10 degC in a mixture of methanol-diethyl ether (41) The ensuing sample allowed the determination of the first high quality crystal structure of a linear phenylene (CpCo) complex obtained in collaboration with the group of Professor Tatiana Timofeeva of New Mexico Highlands University (Figure 22)

Table 23 Trial Crystallization Conditions for Linear [3]Phenylene(CpCo)19

Solvent (Ratio) Conditions Result

Acetone Slow Cooling Heterocrystalline Solid Acetone-Pentane (31) Slow Cooling Heterocrystalline Solid

Pentane-Acetone (101) Solvent Diffusion Amorphous Solid Chlorobenzene Slow Cooling Amorphous Solid

- 23 -

Acetone-Methanol (110 Slow Cooling Amorphous Solid Diethyl Ether-Methanol Slow Cooling Small Needles

Acetonitrile Slow Cooling Powder Ethyl Acetate Slow Cooling No Crystals

Ethyl Acetate-Methanol (11) Slow Cooling Amorphous Solid Methanol-Diethyl Ether (41) Slow Cooling Large Fine Needles

Figure 22 X-ray crystal structure of 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) (19) Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are

omitted for clarity Expectedly the CpCo unit is bound in an η4 fashion to the cyclobutadiene ring Also prominent is the deviation from planarity (Section 11) in the linear [3]phenylene a facet typical of the phenylenes themselves (Section 11)9a Of greater importance than these general observations however is the effect of metal complexation on the linear [3] framework The bond lengths for 19 are shown in Figure 23 and as is typical for the phenylenes6 show a certain degree of bond π-localization with measurable differences between single and double bonds However the extent of this phenomenon and its direction varies significantly when compared to the free ligand 60 A quantitative

- 24 -

comparison of the structural data for 19 with those of its ligand 60 is shown in Figure 2327

In 60 the terminal rings adopt bond alternation similar to that in biphenylene (Section 11) and the central benzene takes on a ldquobis-allylrdquo configuration both ostensibly to minimize electron density (and therefore antiaromaticity) in the four-membered rings As dictated by symmetry the two bonds spanning the central ring are of equal length (1385 Aring) Ligation by CpCo alters this picture profoundly in as much as bond alternation across the entire phenylene frame including the four-membered rings is strongly reduced (Figure 23) Generally all relatively long bonds in 60 shorten in 19 while all short bonds lengthen Some residual but attenuated biphenylene type

Co

1512(2)

1513(2)

1407(2)

1385(2)

1385(2)

1397(2)

1356(2)

1359(2)1436(2)

1397(2)

1441(2)

1411(3)(0052)

1384(3)(-0052)

1474(3)(0077)

1384(3)(-0057)

1408(3)(0052)

1448(3)(0051)

1480(3)(-0032)

1468(3)(-0045)

1437(3)(0052)

1465(3)( 0058)

1434(3)( 0049)

1352(3)(-0033)

1351(3)(-0034)

1476(3)(0069)

1495(3)(-0017)

1372(3)( 0016)

1405(3)(0008)

1376(3)(0017)

1413(3)(-0023)

1427(3)(0030)

1488(3)(-0025)

1423(3)(-0018)

(x) = (19) - (60)increasedecrease

60

19

1907(1)

1891(1)

1886(3)

1889(3)

1889(2)

1901(3)

1669

1725

Si

Si

Si

Si

Me

MeMe

Me

Me

Me

Me

MeMe

MeMe

Me

Si

Si

Me

MeMe

MeMe

Me

Si

Me

MeMe

Si

Me

MeMe

- 25 -

Figure 23 Comparison of bond lengths (in Aring) between linear [3]phenylene(CpCo)complex 19 and 2378-tetrakis(trimethylsilyl) linear [3]phenylene (60) The bond distances in 19 are shown in blue Increases in bond length in going from 60 to 19 are marked in green decreases in red

ldquobond fixationrdquo (Figure 12) remains in the vicinity of the uncomplexed cyclobutadiene Compound 19 thus provides a prime demonstration of the powerful effect of metalloaromatization46 in which the bonds of a cyclobutadiene-metal system attempt to adopt the equalized bond lengths that are a classic hallmark of aromaticity2ndash4 Encouraged by the successful development of a procedure to obtain X-ray quality crystals of 19 these techniques were applied to bis(trimethylsilyl) linear [3]phenylene(CpCo) 52 Gratifyingly with acetone as the solvent the results depicted in Figure 24 were ultimately obtained Figure 24 X-ray crystal structure of 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52)

Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are omitted for clarity

A comparison of the bond lengths of 52 with those of its corresponding linear [3]phenylene ligand 469a is given in Figure 25 Comparison with Figure 23 reveals the same type of aromatization of the ligand on attachment of the metal With these structures in hand an attempt was made to rationalize structurally the

- 26 -

thermodynamic preference for 52 in which the CpCo is located proximal to the silylated terminus in its equilibrium with 53 in which the metal is located close to the unsilylated benzene ring Focusing on the desymmetrizing ortho-bis(trimethylsilyl) unit one notes that the SiCndashCSi bond in 52 is elongated by 005 Aring on attaching the metal in 46 thus providing steric relief On the other hand the symmetry equivalent remote C7ndashC8 distance is unchanged The same effect is seen in the tetrasilyl complex 19

Figure 25 Comparison of bond lengths (in Aring) between bis(trimethylsilyl) linear [3]phenylene(CpCo) complex 52 and 23-bis(trimethylsilyl) linear [3]phenylene (46) Bond lengths for 46 are the average of four molecules in the unit cell (standard deviation = plusmn002)

Increases in bond length going from 46 to 52 are marked in green decreases in red

The observed structural changes make sense in a simple resonance picture

Co

1413(10)(007)

1406(10)(-004)

1459(10)

( 005)

1370(11)(-007)

1418(10)( 005)

1443(10)(003)

1470(10)(-005)

1465(10)(-005)

1446(10)( 008)

1485(10)( 006)

1432(10)( 004)

1347(10)(-003)

1345(10)(-002)

1492(10)( 007)

1503(11)(-002)

1379(10)(001)

1391(11)(-001)

1409(10)(004)

1418(11)(-003)

1367(11)(001)

1478(10)(-002)

1408(11)(-001)

1891(8)

1890(13)

1670

1723

SiMe

MeMe

Si

Me

Me

Me

(x) = (53) - (62)increasedecrease

SiMe

MeMe

Si

Me

Me

Me

190

145134152

139138

150

137145

136

142 137

152137 137

152

141

137 144

189

141143142140

52

46

- 27 -

(Scheme 216) Metalloaromatization alters the dominant resonance forms during intercyclobutadiene hopping such that the essentially single SiCndashCSi bond in 52 transforms into an essential double bond in 53 increasing unfavorable repulsion between the TMS groups Scheme 216 A Resonance Picture Rationale for the Preference of 52 in its Equilibrium with 53 The aromatization effect of metal complexation on the phenylene nucleus described structurally in the preceding text can also be demonstrated powerfully through the measurement of ring currents with 1H-NMR spectroscopy both by experiment and computation (NICS13 see Section 11) A relevant simple example is depicted in Figure 26(a) featuring the changes occurring when 12-bis(trimethylsilyl)benzocyclobutadiene (61) is complexed by CpCo as in 6251 The paratropic antiaromatic 8π system 61 exhibiting relatively shielded six-membered ring hydrogens turns diatropic in 62 Equally importantly and focusing on the ring current contributions of the individual cycles the paratropism of the four-membered ring in 63 shields the adjacent hydrogens more than the remote ones Conversely aromatization of this ring and the ensuing diatropism inverts this order

Figure 26 The effect CpCo complexation (a) on benzocyclobutadiene 61 and (b) linear [3]phenylene 46 Chemicals shifts are in ppm

Co SiMe3

SiMe3

Co

SiMe3

SiMe352 53

∆Gdeg298 =23 kcalmol

- 28 -

Turning to a phenylene system comparison of the NMR data for complex 52 with those for ligand 46 (Figure 26(b)) reveals the same changes not only in the vicinity of the ligated ring but also in the remote parts of the molecule Thus the hydrogens closest to the metal fragment are shifted downfield by 125 ppm in 62 and 148068 ppm in 52 when compared with 61 and 46 respectively The observed relatively large chemical shifts of the arene hydrogens proximal to the metal unit are not due to its anisotropy since its value in this area of space is (if anything) shielding5152 In addition the remote hydrogens in 52 are deshielded by 055033 ppm relative to the corresponding nuclei in 46 clearly substantiating the aromatization of the overall system upon metal complexation that was seen by structural analysis These pronounced chemical shift changes are diagnostic and greatly aided the spectral interpretations of the photochemically induced haptotropic shift experiments described in Sections 21 and 22 as illustrated for the isomerization between 52 and 53 (Scheme 217)

Scheme 217 Chemical Shift Changes in the Isomerization of 52 to 53

These NMR measurements were augmented by NICS calculations carried out in collaboration with Professor Amnon Stanger at the Technion in Haifa NICS data have the advantage that they indicate the extent of (anti)aromaticity even in rings for which the molecule has no hydrogen probe in the classical NMR experiment in this case the cyclobutadienes Computational details are given in Chapter 4 The experimentally determined proton NMR data for the series of silylated linear phenylenes from [2] to [5] and their metallated analogues in addition to the corresponding NICS(1) values of the respective parent phenylenes are shown in Figure 27 All compounds in Figure 27 are known except for the hypothetical biphenylene(CpCo) 64 which is included for comparative purposes Metalloaromatization is pronounced as all rings of the phenylene exhibit diminished or more negative NICS numbers signaling increasing aromatic and decreasing antiaromatic character respectively Again the effect is most pronounced on the rings closest to the metal bound unit tapering off (but never disappearing) with distance Most illustrative in this respect is 44 in which the penultimate and ultimate rings away from the Co still show decreases in the NICS values of 06 and 05 ppm respectively Interestingly the sum of all NICS values of 44 (ldquototal NICSrdquo13c) ndash91 is less negative than that of 21 ndash132 suggesting that 21 is more aromatic hence more stable as observed experimentally This may be fortuitous and the issue is addressed further in Section 24 Finally a caveat regarding the unusually large negative NICS values associated with the CpCo-complexed cyclobutadiene rings As pointed out by Solagrave in connection with a related study of (benzene)Cr(CO)3 which produced similar numbers53 there are local ring currents associated with the extra electrons involved in the metal to π-ligand

CoTMS

TMS796675674

678

436 CoTMS

TMS747683724

662

444

310 365 nmsunlight

30ndash50oC

52 53

- 29 -

bonding that lead to an overestimation of aromaticity Therefore to corroborate the general conclusions of metalloaromatization of this (and all other rings) in Figure 27 Stangerrsquos NICS scan method was applied54 This procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (NICSXY) and out-of-plane components (NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their

Figure 27 Experimental 1H-NMR (C6D6 blue) and computed NICS(1) (green) values for linear phenylenes and their corresponding CpCo complexes The experimental data are for the silylated

derivatives shown The NICS data are for the parent systems interpretation The data presented in Chapter 4 confirm the conclusions of this section While not reflective of ring current effects the values of the 13C chemical shifts for the linear phenylene(CpCo)complexes do provide some insight into the nature of the

- 30 -

σ-framework Comparing complex 19 with parent ligand 60 one observes two general phenomena (Figure 28) The most apparent is the upfield values for the cobalt-bound cyclobutadiene carbons (~74ndash78 ppm) in 19 arising from the local anisotropic shielding effect of the metal (vide supra) Secondly the carbon atoms in the four-membered ring not bound to the metal exhibit large deshielded values (144ndash149 ppm) This effect also seen in ligand 60 arises from the rehybridization6 of the cyclobutadiene sp2 orbitals and is observed in all phenylene topologies A comparison of the 13C-NMR data for the linear [3]- [4]- and [5]phenylene(CpCo)complexes with their respective parent ligands is given in Chapter 4

Figure 28

13C-NMR data for complex 19 and parent silylated ligand 60 Values are in ppm 24 Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift How does the CpCo moiety migrate from one cyclobutadiene unit to the next Two extreme alternatives present themselves a least-motion movement across the intervening arene unit or a more circuitous pathway along the periphery The latter is prevalent in other computed haptotropic shifts56-57 in particular those occurring in (arene)Cr(CO)3 complexes all of which choose peripheral trails56 In these the metal typically moves straight to the edge to adopt an η4 (often described as η1) trimethylenemethane-like transition state on the way to a neighboring ring as illustrated for the η6-η6 hopping in naphthaleneCr(CO)3 summarized in Scheme 218 More relevant is the computed course of the η6-η6 interconversion of (biphenylene)Cr(CO)3 (Scheme 219)57 The metal slides from the (near)center of one benzene ring to the quaternary (four-membered) ring carbon to reach a distorted trimethylenemethane maximum and then proceeds to the edge of the bridging cyclobutadiene bond This species represents a minimum on the potential energy curve and adopts an η2-like complexed cyclobutadiene topology (ldquoquasi-η4rdquo) from which it continues by the microscopic reverse on to the other benzene nucleus The relevance of these findings with respect to the intercyclobutadiene hopping of CpCo along the phenylene frame was not clear at the outset of the work described in this section The CpCo fragment has a different electronic requirement from Cr(CO)3 and interring migration in arenes (and related systems) involves aromatic electron counts of all intervening circuits

Scheme 218 Migration of Cr(CO)3 Across Naphthalene

- 31 -

Scheme 219 Migration of Cr(CO)3 Across Biphenylene

DFT calculations were carried out in collaboration with Professor Thomas Albright at the University of Houston In these studies using B3LYP 3-21G (carbonhydrogen) and LANL2DZ (cobalt) basis sets the metal fragment was placed 18 Aring above the π system with energy minimizations carried out every 02 Aring along the frame of the parent linear phenylene in question When transition states and local minima were located their structures were refined with the B3LYP 6-31G (hydrogen) 6-113G (carbon) and LANL2DZ (with inclusion of cobalt f-orbitals) basis sets More computational details are given in Chapter 4 The resulting potential energy surface for the thermal rearrangement in the parent linear [3]phenylene(CpCo)system is shown in Figure 29 Figure 210 contains enlarged images of the transition states and intermediate structures The haptotropic shift begins with the (η4-cyclobutadiene)CpCo global minimum (labeled ground state GS) assigned a relative value of 000 kcalmol An η2-cyclobutadiene transition state (TS 1) 269 kcalmol higher in energy than GS is passed before reaching a local minimum (LM) that lies 109 kcalmol above GS LM features CpCo coordinated unsymmetrically η4 to the central benzene ring thus avoiding an unstable 20 electron η6-benzene configuration (not shown) which when explicitly calculated proved to lie 36 kcalmol above LM From LM a symmetry-related second η4 structure is reached via an η3-benzene transition state (TS 2 barrier 14 kcalmol) that symmetrizes the ldquoleftrdquo with the ldquorightrdquo half of the molecule LM is 249 kcalmol higher in energy than GS The shift is completed through the reverse of the initial two movements through LM and TS 1 on the other side of the ligand to reach the second cyclobutadiene ring Thus as for Cr(CO)3 (Scheme 219) CpCo migrates along the edge of the linear phenylene but because of its differing electronic needs through distinctly different intermediates and transition states Most obvious is the internal η2-cyclobutadiene TS 1 which for Cr changes to a peripheral η2-intermediate The calculated rate determining barrier of 269 kcalmol (GS to TS 1) is slightly higher than that measured for the reversal of 53 to 52 (~23 kcalmol) Part of this discrepancy may be due to ground state activation of 53 which is ~2 kcalmol less stable than 52 The LM structure has some resemblance to the isolated η4-CpCo angular [3]phenylene 23 (Section 12) Its location in an energetic well of ~14ndash16 kcalmol (TS 1 and TS 2) suggested that it may be observable at low temperature This investigation is detailed in Section 25

- 32 -

Figure 29 Calculated potential energy profile for the thermal η4η4 haptotropic shift in linear [3]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

0

5

10

15

20

25

30

1 2 3 4Reaction Path

Co

Co

C o

C o

GS η

4

LM η

4

TS1 η

2

TS 2 η

3

00

269

109

249

Key - Global MinimumGround State (GS)- Local Minimum (LM)

- Transition State (TS)

122

3 34 4

- 33 -

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 34 -

(d) Transition state 2 η3-benzene (249 kcalmol)

Figure 210 Optimized structures and relative energies for the linear [3]phenylene(CpCo) haptotropic shift Carbon atoms are shaded grey hydrogens light grey and cobalt blue Bond

lengths are in Aring The potential energy profile for the thermal shift in the linear [5]phenylene(CpCo) system was calculated in the same manner and is shown in Figure 211 Images of the intermediates and transition states are depicted in Figure 212 Placing the metal fragment on the inner cyclobutadiene ring resulted in the lowest energy structure and was therefore set as the global minimum (GS) Two distinct haptotropic migrations inner-to-inner and inner-to-outer cyclobutadiene are now possible (Section 21) Beginning at GS the metal can proceed in the direction of TS 2 or TS 3 respectively both of which are η2 with similar barrier heights (~36 kcalmol) The former pathway is degenerate and continues from TS 2 to η4-LM 1 and then via η3 central benzene TS 1 to the symmetry related corresponding LM 1 TS 2 and finally GS involving the opposite inner four-membered ring The rate determining barrier for this process is 359 kcalmol clearly too high to be measurable by NMR techniques as found for 212838 Interior-to-exterior shifting of the cobalt continues from TS 3 on to η4-benzene LM 2 The η3-TS 3 is traversed before the second η4η2

sequence (LM3 and TS 5 respectively) ultimately leading to LM 4 which is the outer

- 35 -

cyclobutadiene coordinated structure and represents the photoisomeric species observed experimentally in Scheme 23 The computed rate-determining barrier (TS 3) of 263 kcalmol for the reverse reaction of LM 4 to GS is close to the experimentally measured values of 256ndash276 kcalmol for the derivatives in Table 21

Figure 211 Calculated potential energy profile for the η4η4 haptotropic shift in linear [5]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

40

Reaction Path

263

0

5

10

15

20

25

30

35

C o

C o

C o

C o

Co

Co Co

C o

C o Co 360 370

359 357

367

97

203 190 196

1 2 3 4 5 6 7 8 9 10

TS 1 η

3

LM 1 η

4

TS 2 η

2

GS η

4 00

TS 3 η

2 TS 4 η

3 TS 5

η2

LM 2 η

4 LM 3 η

4

LM 4 η

4

Key- Global MinimumGround State (GS)

- Local Minimum (LM)

- Transition State (TS)

- 36 -

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 37 -

(d) Transition state 4 η3-benzene (367 kcalmol)

(e) Local minimum 3 η4-benzene (190 kcalmol)

- 38 -

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 39 -

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

(i) Local minimum 1 η4-benzene (190 kcalmol)

- 40 -

(j) Transition state 1 η3-cyclobutadiene (356 kcalmol)

Figure 212 Optimized structures and relative energies for the linear [5]phenylene(CpCo) haptotropic shift Structures for the inner-to-outer cyclobutadiene migration are given by (a)ndash(g)

Species (h)ndash(j) are involved in the interior-to-interior four-membered ring pathway Carbon atoms are shaded grey hydrogen atoms light grey and cobalt blue Bond lengths are in Aring

Why does CpCo prefer complexation to the internal cyclobutadiene that is GS (as represented by 21 and 42) over LM 4 (as represented by 44 and 45) Calculations show that the energies required to distort linear [5]phenylene to the geometries found in

- 41 -

the complexed isomers are very similar (16 versus 14 kcalmol) Hence the answer must rest on electronic grounds Indeed extended Huumlckel calculations reveal that the overlap populations between the frontier orbitals on the CpCo fragment and the HOMO and the LUMO of the π system are greater for GS (00793 and 00745 respectively) than for LM 4 (00556 and 00517 respectively) A didactically more instructive valence bond view recognizes that metalloaromatization of the inside four-membered ring allows the formulation of more resonance forms that avoid antiaromatic cyclobutadiene circuits A full list of these resonance forms as well as details of the EHMO calculations are given in Chapter 4 25 Low Temperature Photochemical Studies of the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes Of the various participating species in the mechanism for intercyclobutadiene migration (Section 24) specific attention was focused on the η4-benzene intermediates that occur in both the linear [3]- and [5]phenylene haptotropic shifts These structures are energetic local minima on the reaction profiles for both systems and were of considerable intrinsic interest not only as reactive intermediates in this manifold but also because of their relationship to the isolable angular [3]phenylene(CpCo) complex 2329 (Figure 213) Figure 213 (a) Calculated structure for the η4-benzene linear [3]phenylene(CpCo)intermediate

in the haptotropic migration (b) Crystal structure of η4 angular [3]phenylene (CpCo) 23

While rare a handful of other η4-benzene-metal complexes have been isolated (Figure 214) For example two related iridium based systems benzene(CpIr) 6658 and benzene triphos(Ir) 6759 are known As expected ligation causes significant shielding of the hydrogens in the η4 portion of the ligand especially the terminal positions The η4 intermediates in the haptotropic shift are situated in wells on the potential energy surface that are ~17 kcalmol deep for the linear [5]- and ~15 kcalmol for the linear [3]phenylene complexes These values are large enough that such species might be observable by NMR spectroscopy if irradiation of the starting materials were performed at low temperature and if the excited state would relax selectively to these intermediates As a suitable candidate with which to explore this possibility the partly symmetric tetrasilyl complex 19 was chosen The generation of anticipated desymmetrized 68 would be readily detected by the appearance of 11 new singlets in the 1H- and 23 new peaks in the 13C-NMR spectra (Scheme 220)

(a) (b)

- 42 -

Figure 214 Selected relevant examples of isolated η4-benzene complexes and their proton NMR chemical shifts (ppm)

Scheme 220 Low Temperature Irradiation Experiment Designed to Generate η4-Benzene Intermediate 68

Construction of a satisfactory setup to allow for the planned low temperature irradiation was not trivial An optimal experimental configuration however was devised utilizing three pieces of equipment each of which is shown in Figure 215 The first was a custom-made Pyrex Dewar flask small enough to adequately contain an NMR tube Cooling was achieved by means of a Neslab refrigerated circulating bath Thirdly a Rayonet Photochemical Reactor was used as the light source The sample was first placed inside of the Dewar flask and cooled to the required temperature inside of the Rayonet Once cold irradiation was carried out for the desired length of time When complete the sample was transported cold to the NMR laboratory and very quickly placed inside of a pre-cooled NMR probe for analysis A solution of complex 19 was irradiated at ndash65 degC as described and its 1H-NMR spectrum recorded at ndash30 degC revealing a dramatic change The signals for 19 had almost entirely vanished and a set of new peaks appeared The new aromatic resonances were comprised of two sharp singlets at δ = 708 and 644 ppm and a broad singlet at δ = 558 ppm all of which integrated for 2 hydrogens each Another broad

649

586

316

H H

Co544

66 67 23

Ir

P(Ph2)P(Ph2) P(Ph2)

H

H

H

625

594

350

Ir

H

H

H

- 43 -

Figure 215 Cold irradiation experimental setup consisting of (a) Pyrex Dewar flask (b)

refrigerated circulating bath (c) Rayonet Photochemical Reactor with Pyrex Dewar vessel placed inside

(a) η

4 (b) η

4 (c) η

4

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

New peaks

L L

- 44 -

Figure 216 Stacked plot of the aromatic 1H-NMR spectral region recorded after the cold irradiation of 19 in toluene-d8 Peaks for 19 are indicated by blue new peaks by red arrows

Impurities are marked with and traces of free ligand 60 with L The scale is in ppm

singlet at δ = 398 ppm (5 H) was assigned to a new Cp group (Figure 217) and two new TMS singlets (9 H each not shown) were also present The new broad Cp absorption displayed peculiar behavior gradually moving to higher field (∆δ ~ 08 ppm for Cp-H) on warming from ndash30 degC to 10 degC (Figure 217) The broadened singlet at δ = 558 ppm showed similar albeit much attenuated behavior At room temperature all new peaks had disappeared leading to regeneration of the original spectrum of 19

Figure 217 Stacked plot of the Cp spectral region in the cold irradiation of 19 in toluene-d8 Peaks for molecule 19 are indicated by blue the new peaks by red arrows The scale is in ppm

In addition to these NMR observations a remarkable change in color from the redmaroon of 19 to olive green took place during the course of this experiment (Figure 218) Indeed the UV-Vis spectrum of the low temperature species is strikingly different from that of 19 showing a large broad absorbance band centered in the visible region

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

19

THF

- 45 -

Figure 218 Color change during the low temperature irradiation of 19 (a) Before irradiation (b) After irradiation

Complex 19

Low Temperature Species

0

02

04

06

08

1

12

14

16

18

2

400 430 460 490 520 550 580 610 640 670 700

Wavelength (nm)

Ab

sorb

an

ce

Figure 219 UV-Vis spectra (toluene) of 19 (at rt) shown in blue and the new compound (at ~

ndash30 degC) shown in red

at 654 nm (Figure 219) Warming the sample to room temperature restored its original red color While the observation of a new species was gratifying the NMR data posed a puzzle as they were clearly incompatible with (a static) structure 68 Instead they pointed to a molecule exhibiting mirror (or ldquotop-downrdquo) symmetry along the long molecular axis as in 19 itself The two most obvious candidates 69 and 70 (Figure

(a) η

4 (b) η

4

- 46 -

220) were ruled out as the first could not be found during the computations underlying Figure 29 and the second actually constitutes the transition state TS 1 for the thermal reverse process

Figure 220 Possible (but unlikely) structures of correct symmetry for the low temperature

photoisomer of 19 In the hope to shed further light on the nature of purported 68 low temperature 13C in conjunction with 2-D NMR (HSQC HMBC) experiments were carried out These data led to the tentative assignments shown in Figure 221 Assuming the presence of top-down symmetry as surmised by the proton spectra one would have expected to observe nine phenylene carbon signals The actual spectrum however contains only six peaks The Cp line was broadened to the point of being barely visible and no crosspeaks for the absorption at δ = 556 ppm were seen by 2-D NMR spectroscopy

Figure 221 Partial assignments of 1H-(italicized) and 13C-NMR signals of 68 The ldquotop-downrdquo plane of symmetry is indicated by the dashed purple line HMBC δ = 643 ppm correlates with δ = 1461 and 1521 ppm δ = 708 ppm correlates with δ = 1477 and 1508 ppm δ = 033 ppm

correlates with δ = 1477 ppm and δ = 036 ppm correlates with δ = 1461 ppm HSQC δ = 643 ppm correlates with δ = 1121 ppm δ = 708 ppm correlates with δ = 1227 ppm and δ = 398

ppm correlates with δ = 85 ppm The connectivity of the CpCo to the central ring is left intentionally unspecified and the choice of positioning it to the left of the center hydrogens (blue)

SiMe3

SiMe3

H

Me3Si

Me3Si

H

Co

398 (br)

HH

1461

~85 (br)

708

H

556 (br)1508

= Unobserved 13C signals

H

H

Mirrorplane

6431477 1521

033036

11211227

- 47 -

arbitrary Similarly the assignments of the groups of ldquoleftrdquo and ldquorightrdquo benzene signals are tentative and might be inverted The carbons marked could not be observed

It is thus clear that we are dealing with an unusual species and if it is 68 the molecule must be partly (but not completely) fluxional around the central ring Returning to the computed energy profile in Figure 29 one notes that central η4η4-benzene fluxionality via TS 2 with a barrier of 140 kcalmol is presaged This process which causes ldquoleftrdquo-ldquorightrdquo but not ldquotoprdquo-ldquobottomrdquo symmetrization is unlikely to be responsible for the above data as it should have given rise to two 1H-NMR singlets for the central hydrogens However considering the expected relative closeness in the respective chemical shifts of the anticipated signals (see Figure 214) accidental isochronism could not be ruled out Consequently low temperature irradiation experiments were executed with 52 in which the ldquoleftrdquo-ldquorightrdquo option of symmetrization was obviated by the substitution pattern while leaving the ldquotoprdquo-ldquobottomrdquo option intact (Scheme 221) As Scheme 221 Low Temperature Irradiation of 52 and Possible Pathways for Fluxionality of

Intermediate 71

indicated in color the latter would provide a diagnostically simple proton spectrum of only four phenylene signals The former on the other hand should show eight such peaks A potential complication of this experiment was the possibility of two regioisomeric (and non-interconverting) cobalt species located on either side of the central six-membered ring (Scheme 222) In the event the spectra shown in Figure 222 were obtained At ndash60 degC in

HH

CoTMS

TMS

CoTMS

TMS

TMS

TMS

Co

TMS

TMS

CoTMS

TMS

Co

TMS

TMS

Co

Top-bottom

cold hν ∆

Lef t-right

52 53

∆

71

or

H

HH

H

H H

H HH

HH H H

H

- 48 -

addition to unreacted 52 and photoisomer 53 a new species formed the spectral features of which implicate 71 as a ldquotop-bottomrdquo symmetrizing species Specifically the

Scheme 222 The Two Possible Regioisomers of 71 ldquoLeftrdquo and ldquoRightrdquo

71

52

53 53

53

52

TMS

TMS

Co

TMS

TMS

Co

TMS

TMS

Co

71

TMS

TMS

Co

or

Right Lef t

ndash60 degC

ndash50 degC

ndash40 degC

ndash30 degC

53

- 49 -

Figure 222 Stacked plot of the aromatic spectral region in the cold irradiation of 52 in toluene-d8 Peaks for molecule 52 are marked by blue arrows 53 in red and 71 in green Trace amounts

of free ligand bis(trimethylsilyl) linear [3]phenylene] 46 are denoted with L The scale is in ppm

unsubstituted benzene terminus hydrogens exhibit an AArsquoBBrsquo pattern at δ = 647 ppm which integrate for 4 hydrogens The central ring hydrogens appear as a broad singlet at δ = 557 ppm (2H) and the silylated terminus as a singlet at δ = 632 ppm (2H) Warming the reaction mixture to 10 degC led to the gradual disappearance of 71 with a concomitant increase of the signals assigned to 52 and 53 This experiment confirms the conclusions drawn as a result of the low temperature irradiation of 19 namely that a ldquotop-bottomrdquo symmetrizing species is generated Remarkably in view of the possibility of two regioisomers (Scheme 222) only one set of peaks is observed indicating that the excited state of 53 relaxes to settle on only one side of the central ring Which side is a matter of speculation Figure 223 compares the 1H chemical shifts of 71 with those of 68 and for calibration 52 53 and free ligands 46 and 60 For the first pair it is clear that the two species are very similar with almost identical chemical shifts of the relevant hydrogens taking into account the considerable deshielding effect of TMS substitution on the unsubstituted terminus in 73 (~07 ppm cf 52 vs 53 46 vs 60) Arguably placing the CpCo moiety to the ldquoleftrdquo as depicted in 68 and 71 aromatizes the proximal benzene by η2-complexation of the adjacent four-membered ring leaving considerable benzocyclobutadiene character on the ldquorightrdquo consistent with the associated chemical shifts

- 50 -

CoTMS

TMS796675674

678

CoTMS

TMS747683724

662

Co

TMS

TMS

52

71

53

424

642

557 632652

436 444

Co

TMS

TMS

68

398

556 643708

TMSTMS

TMS

TMS684607619

645

46

assignmenttentative

TMS

TMS

TMS

TMS623 685

60

TMS

TMS

TMS

TMS

Co

691 795745

19

441

Figure 223 1H-NMR chemical shift comparison of 68 and 71 with other relevant species A plot of the changes in concentration of 52 53 and 71 with temperature is shown in Figure 224 Within (the considerable) error and considering the unusual magnetic behavior of 71 (vide infra) it appears that the latter converts mainly to 52 in the temperature regime in which 53 is stable with respect to its thermal reverse to 52 This observation may be interpreted as indicating a lower barrier for Co migration from the center ring to the more stable cyclobutadiene haptomer

- 51 -

0

1

2

3

4

5

6

7

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Inte

gra

tio

n v

s I

nte

ra

l S

tan

da

rd

52

53

71

Figure 224 Plot of the concentration changes of 52 53 and 71 with temperature measured by the relative integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively

The ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100)

Another plot this one showing the ratios of 52 53 and 71 with respect to each other is given in Figure 225 The disappearance of 71 with rising temperature is illustrated by the increase in the ratios of 5271 and 5371 As indicated by the steep slopes the conversion of 71 into 52 and 53 is particularly fast between ndash10 and 0 degC That complex 52 is preferentially formed is again confirmed by the escalating 5253 ratio While these data do not provide a definitive answer for the location of the CpCo they are consistent with the plots shown in Figure 224 and the above discussions

- 52 -

0

1

2

3

4

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Rel

ati

ve

Inte

gra

tio

n

5271

5371

5253

Figure 225 Plot of the ratios of 52 53 and 71 against each other with temperature measured by the integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively The

ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100) Having established the topological aspects of 68 and 71 attention was turned to their peculiar NMR characteristics in the vicinity of the metal ie the broad peaks for the central hydrogens and the CpHs the broad Cp-carbon line the inability to observe 13C signals for the central benzene ring and the temperature dependent drifting of (particularly) the Cp absorption A trivial (and ultimately unsatisfying) explanation for at least peak broadening was the presence of trace paramagnetic metallic impurities60 that might have been generated during the irradiation process Spin exchange preferentially Co-based might affect the center atoms in 68 and 71 more than the remainder of the molecule although it should also cause line broadening in the isomers 19 and 52 and 53 respectively Experimentally the presence of such species was made unlikely by executing the cold irradiation experiment of 19 in the presence of the radical trap 13-cyclohexadiene which produced spectra identical to those described earlier An attractive alternative that might explain the data and in addition provide a mechanism for ldquotop-downrdquo exchange is of the intervention of triplet state cobalt species The ability of metals to change their electronic spin state and the consequences of this phenomenon on organometallic structure and reactivity are well documented61

18-Electron CpCo complexes are ground state singlets but their 16-electron counterparts accessed typically by ligand dissociation have more stable triplet configurations62 A number of CpCo and related Co species have also been reported in

- 53 -

which singlets are in thermal equilibrium with paramagnetic triplets by intersystem crossing63 Such complexes display spectral behavior very similar to that seen for 68 and 71 For example 7263b exists as a mixed spin state system in which the singlet predominates at room temperature in solution (Figure 226) On heating the triplet becomes increasingly populated shifting and broadening its NMR signals Cooling the solution back to room temperature reverses these spectral changes In addition to complexes of cobalt analogous observations have been reported for other metals such those based on hafnium64 copper65 ruthenium66 and tungsten67

Figure 226 Temperature dependent chemical shifts in CpCo derivative 72 in toluene-d8

(marked as S on the plot) The scale is in ppm

Consideration of these examples would then suggest that 6871 undergo ldquotop-downrdquo equilibration through a triplet 16-electron intermediate or that 6871 themselves are triplets or have thermally accessible triplet states from which fluxionality might occur Since the relaxation times (T1) of paramagnetic systems60a are much shorter compared to their diamagnetic counterparts measurement of this property was thought to be informative The T1 values for the proton in 68 were determined via a standard inversion recovery experiment44 and are given in Table 24 (cf Figure 220) in comparison to p-terphenyl60b

Co

CoPMe3

72

- 54 -

Table 24 1H-NMR Relaxation Times in Intermediate 68 at ndash30 degC

Resonance (ppm) T1(s) 711 2309 646 0997 556 005 398 0108

In consonance with the associated line broadening the relaxation times of the Cp

(δ = 398 ppm 0108 s) and central ring hydrogens (556 ppm 005 s) are much smaller than those of the remaining phenylene ligand (711 and 646 ppm 2309 and 0997 s respectively) the latter in turn comparing well with the values in p-terphenyl With this corroborative evidence in hand the question whether the species is itself a triplet or is in thermal equilibrium with such was addressed The answer can be obtained by using a Curie-like graph68 in which chemical shifts are plotted as a function of temperature65 A linear relationship corresponds to the presence of a triplet compound while curved behavior is indicative of a singlet-triplet equilibrium Plotting the chemical shifts of the Cp hydrogen of 68 and 71 against the inverse of temperature (Figure 227) gave distinctly curved lines supporting the notion that these species are in thermal equilibrium with their triplets The exact nature of these species however remains to be determined

156

395404

345

p-Terphenyl

- 55 -

3

32

34

36

38

4

42

44

46

00036 00038 0004 00042 00044 00046 00048

1T (K -1

)

Ch

em

ica

l S

hif

t (p

pm

)

71

68

Figure 227 Plot of the Cp chemical shift (toluene-d8) of 68 and 71 versus the inverse of temperature

DFT calculations have commenced in an attempt to find a plausible structure for such a triplet cobalt species and with it possibly arrive at a mechanism for the fluxional behavior of 68 and 71 These studies are being carried out in collaboration with Professors Tom Albright of the University of Houston and Vincent Gandon of the Universiteacute Paris-Sud 11 Preliminary results at the B3LYP6-31G(dp) and BP866-31G(dp) levels suggest the η2-cyclobutadiene structure depicted in Figure 228 It is apparent that this species corresponds topologically to singlet TS 1 in Figure 29 and 70 in Figure 220 endowed with the symmetrical requirements dictated by the experiments

- 56 -

Figure 228 Calculated structure of a triplet η2-cyclobutadiene linear [3]phenylene(CpCo)

One can therefore envision fluxionality between the two ldquotoprdquo and ldquodownrdquo η4-benzene structures via the intermediacy of a triplet η2-cyclobutadiene (Scheme 223) Further Scheme 223 Conversion of ldquoTop-Downrdquo η4-Haptomers of 68 Via a Triplet η2-Cyclobutadiene

Intermediate

computations are required to pinpoint the minimum energy crossing points between the singlet η4 and triplet η2 structures and to explain why this triplet does not collapse to the CpCo cyclobutadiene isomer This work is in progress 26 Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 All of the linear phenylene(CpCo) complexes mentioned thus far share one common feature a single CpCo unit bound to the phenylene scaffold However since there are one or more additional cyclobutadienoid rings in the series the question arises whether it might be possible to bind more than one metal fragment to the ligand If so what would be the structural consequences Would be there further metalloaromatization Would such systems be capable of light-induced haptotropism and if so how would the metals move relative to the ligand and to each other Finally would such complexes mimic structurally the variety of arrays obtained in the reaction of 29 with Fe2(CO)9 (Scheme 15) Since the linear phenylenes become increasingly more antiaromatic with size the optimal candidates for preparing such multi-metallic systems should be the higher members of the series Indeed evidence for double CpCo attachment was obtained in the form of the minor by-products 73 and 74 (Scheme 224) obtained during the

Scheme 224 Side Products in the Preparation of Linear [4]- and [5]Phenylene(CpCo)

- 57 -

Complexes by Cobalt-Catalyzed Cyclization

preparation of 20 and 21 respectively (Scheme 13) These Diels-Alder type adducts of a third BTMSA molecule to the π-frame can be envisaged to be derived from 75 and 76 respectively in which the six-membered ring flanked by the two CpCo(cyclobutadiene) units would be expected to have an unusual (biradicaloid) electronic structure Evidence for the feasibility of such arrays rests on the unique black-red syn-bis(irontricarbonyl) compound 77 whose structure was determined by X-ray analysis69 With reasonable quantities of 19 in hand the possibility of ligating a second CpCo unit to it was explored This idea was further encouraged by the observation that crude samples of bis(trimethylsilyl) linear [3] phenylene(CpCo) complex 53 contained a very small (3 ) peak at mz = 618 an exact match for the mass of a doubly metallated analog Consequently 19 was treated with one equivalent of CpCo(C2H4)2 in benzene to afford a reddish black solid (Scheme 225) The mass spectrum data exhibited a

Scheme 225 Preparation of Complex 78 from Complex 19

TMS

TMSTMS

TMS

CoCpCo(C2H4)2

22h 70 oC C6H6Linear [3]TMS4(CoCp)2

5619 78

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

74

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

73

TMS

TMS

TMS

TMSCoCpCpCo

76

TMS

TMS

TMS

TMSCoCpCpCo

75

Ph

Ph

Ph

Ph

Fe(CO)3Fe(CO)3

77

- 58 -

molecular ion peak at mz 762 corresponding to 19(CpCo)2 The 1H-NMR spectrum (acetone-d6) revealed four sharp singlets integrating in the ratio 410236 indicative of a highly symmetrical structure The chemical shift of the benzene termini (736 ppm) suggested that these rings have significant aromatic character and is similar to the value of 745 ppm seen for the hydrogen positioned farthest away from the CpCo in 19 (Figure 27) Similarly the 13C signals of the terminal rings in 78 (1505 1454 and 1258 ppm) are analogous to those from the corresponding terminal ring in 19 (1484 1433 and 1256 ppm Figure 28) Detailed analysis of 78 with two-dimensional NMR techniques (HSQC and HMBC) allowed for a complete assignment of all peaks in the 1H and 13C spectra (Figure 229) The strongly shielded (relative to the free ligand) proton (481 ppm) and carbon (537 and 571 ppm) resonances assigned to the central benzene ring clearly showed that both cobalt fragments are coordinated to the phenylene ligand at this position Interestingly these data bear a very close resemblance to those of the corresponding diiron complex 31 (Scheme 15) and are compared in Figure 229 Its central 13C resonances (688 and 582 ppm) are shifted upfield in a manner akin to 78 although not quite as much reflecting the increased electron withdrawing ability of the Fe(CO)3 group relative to CpCo70 Complex 31 like 78 exhibits aromatized terminal benzene rings as indicated by its 1H (750 ppm) and 13C (1484 1446 and 1258 ppm) chemical shifts These spectral similarities make it likely that 78 and 31 are isostructural The only structural ambiguity pertains to the orientation of the two metal fragments with respect to the π ligand a problem that had been left undecided in the assignment of structure 31 ie 31a (syn) versus b (anti Scheme 15)27 These options for 78 are

- 59 -

CpCoTMSTMS

TMS TMS

H H039 (36)

537 1258822

270

1454571

1505

481 (2) 736 (4)489 (10)

TMS TMS

TMSTMS

H

(OC)3Fe

(OC)3Fe

CpCo

78

31a

750 (4)553 (2)

036 (36)H

220

1446

1258

1484

688582

2128

Figure 229 Comparison of 1H- and 13C-NMR assignments (ppm) for molecules 78 (acetone-d6) and 31 (1H acetone-d6

13C CDCl3) Proton chemical shifts are in red and carbon in blue Integrations for the proton resonances are in green HSQC for 78 δ = 039 ppm correlates with δ = 270 ppm δ = 481 ppm correlates with δ = 537 ppm δ = 489 ppm correlates with δ = 822 δ

= 736 ppm correlates with δ = 1258 ppm HMBC for 78 δ = 036 ppm correlates with δ = 1454 ppm δ = 481 ppm correlates with δ = 571 and 1505 ppm δ = 736 ppm correlates with δ = 571 1454 and 1505 ppm The placement of the cobalt atoms in 78 is tentative (see Figure

229)

Figure 230 Possible structures for 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

- 60 -

shown in Figure 230) Both equally exotic options are precedented in the literature and corroborated by X-ray structural analyses (Figure 231)71

Figure 231 Illustrative examples of complexes with two metal fragments coordinated to the same benzene ring

Bis(CpFe) complex 7972 and its rhodium analog 8073 contain [M2(syn-micro-arene)] units in which the metals are linked58 Molecule 79 consists of two CpFe units coordinated η4 to the boat-shaped benzene ring sharing ligating carbon atoms In contrast the CpRh fragments in 80 are bound in an allyl η3 manner and the arene also adopts a boat conformation On the other hand bis[tris(tert-butyl)]toluene(CpCo) complex 8174 and the related system 8275 both exhibit [M2(anti-micro-arene)] units in which η4 coordination between the benzene ring and each of the metal fragments takes place Here the metals share carbon atoms but now involving a sandwiched ligand The arene in 81 retains a planar aromatic geometry while the benzene moiety in 82 is bent into a highly distorted chair conformation Unfortunately model structures 79ndash82 do not exhibit diagnostic NMR properties that would provide a clear distinction between synanti and planarnon-planar topologies For example the 1H-NMR peaks for the toluene ligand in anti-complex 81 range from 400ndash380 ppm74 whereas the signals for the benzene moiety in syn-bis(CpRh) 80 appear at 400ndash330 ppm73 The 13C data are similarly inconclusive as illustrated by comparison of 78 (562ndash531 ppm for the benzene ring) with 79 (648ndash525 ppm)72b An interesting property of these bis(metal) arene complexes is fluxionality of the metal fragments by haptotropic shifts along the periphery of the aromatic ring as depicted in Scheme 226 In complex 79 the hexamethylbenzene ligand (bound η4η4

in the solid state) displays a single arene resonance at 588 ppm in its room temperature carbon NMR spectrum Cooling to ndash90 degC however produces two distinct arene peaks at 525 and 648 ppm (for the shared and single-metal-bound carbons respectively as shown in 79a in Scheme 227) Fluxionality was postulated to proceed through an η3η3 intermediate (79b) that is structurally similar to Rh complex 80 which is itself a fluxional species

Scheme 226 Examples of Fluxional Processes in Dinuclear Arene Complexes 79 and 80

82 81

80 (R = CH3)

79

- 61 -

Anti-bis(β-diiminate)Rh complex 83 shows similar mobility (Scheme 226)76 A mechanism for η4η4 migration of the anti-metal fragments was proposed using the lowest energy species found by DFT calculations In these compounds the anti-metal fragments convert between η4η4 (83a 83c 83e) structures by passing through η3η3

(83b) and η4η2 (83d) transition states The energy barrier for η4η4 migration in 83 was experimentally determined to be 6 kcalmol This value is in line with other experimentally measured syn and anti dinuclear ring slippage processes which are typically le ~10 kcalmol71-75 The possibility of fluxionality in 78 might be observable if asymmetric configurations such as 78c and 78d (Figure 231) represent the lowest energy forms since they entail NMR observable desymmmetrization of the ligand Unfortunately cooling 78 in the NMR probe to temperatures as low as ndash80 degC in toluene-d8 did not reveal any signs of signal decoalescence

- 62 -

Figure 232 Possible lowest energy forms of complex 78

Hoping that further light could be shed on the disposition of the CpCo moieties in 78 by chemical transformations a brief investigation of its reactivity was undertaken For example bis(metal) arene complexes have been shown to readily undergo arene exchange reactions71 In complex 81 for example the toluene ligand is displaced by benzene at room temperature74 However heating a sample of 78 to 120 degC in toluene-d8 did not lead to any changes in the NMR spectra Turning to potential photochemical activation 78 was irradiated at various wavelengths (300ndash365 nm) These conditions as well as ambient sunlight did not cause any changes in its 1H-NMR spectrum further documenting 78 as a rather inert species X-ray crystallographic analysis would appear to be the only method of resolving the identity of complex 78 Producing suitable crystals of this molecule however has proven extremely difficult and will be the subject of future investigations 27 Summary and Outlook The work presented in this chapter published as a communication77 has detailed the first examples of η4η4 intercyclobutadiene migration and detailed mechanistic studies of this unprecedented reaction The haptotropic shift was found to be an intramolecular process with the CpCo fragment undergoing various changes in hapticity for the thermal isomerization Low temperature photolytic studies have revealed the existence of a thermally unstable intermediate species the exact structure of which is uncertain These results point to what appear to be significant differences between the photo- and thermal haptotropic pathways Further work both experimental and computational will be required to elucidate the details of the photochemical reaction In addition to the studies of linear phenylene(CpCo) haptotropism a hitherto unknown complex containing two CpCo fragments bound to linear [3]phenylene was prepared and scrutinized in preliminary form Despite extensive characterization the structure of this complex with respect to the position of the metal centers remains elusive Future work will focus on the acquisition of a crystal structure

- 63 -

Chapter 3

Nickel-Catalyzed Insertion Reactions for the Preparation of [N]Phenacene Derivatives

31 Introduction Transformations involving metal insertion into the four-membered ring of the [N]phenylenes as discussed in Section 12 represent a significant mode of reactivity with a high potential for practical synthetic utility One specific application of this chemistry is the synthesis of the phenanthrene moiety via tandem metal insertion and alkyne cycloaddition to the four-membered ring (Scheme 31) Such a methodology Scheme 31 Potential Preparation of the Phenanthrene Group from the Alkyne Cycloaddition

with Biphenylene would be valuable for the preparation of PAHs possessing phenanthrene subunits but has remained fairly unexplored Only a few examples demonstrating this transformation have been detailed previously for biphenylene (7) (Scheme 32)

Scheme 32 Metal Catalyzed Alkyne Cycloaddition Reactions with Biphenylene

The first report of this process is by Eisch in 198533a who treated biphenylene with Ni(PEt3)4 and diphenylacetylene to produce 910-diphenylphenanthrene 84 Since then a number of metals have been shown to mediate this process19 Ni systems being most relevant to this chapter Thus for example 84 can also be made using an N-heterocyclic carbene-based Ni(0) catalyst78 Bis(diisopropylphosphino)ethane Ni(alkyne) species enable similar cycloadditions of fairly hindered (trimethylsilyl)alkynes sometimes involving more complex processes of silyl group migration79 while less hindered substrates lead to 84ndash8680a A mixed phosphinoaminoethane-chelated Ni species proved more reactive enabling cycloaddition of even the encumbered tert-butyl(phenyl)acetylene to furnish the corresponding phenanthrene80b With this background in mind our attention turned to applying this reaction to larger phenylene systems Of the various topologies of phenylenes at our disposal the angular version was

R1 R2

R2R1[M]

[M]

7 R R

R = Ph (84)

R = Me (85)

R = CH2OMe (86)

RR

[Ni]

- 64 -

particularly intriguing as it offered two extreme modes of alkyne addition (Scheme 33) In the first scenario exclusive attack at the outer periphery of the four-membered rings would produce the helical shaped PAHs known as helicenes (Scheme 33a)81

Scheme 33 Alkyne Cycloaddition with Angular Phenylenes to Produce (a) Helicenes or (b) Phenacenes

Reactions occurring only at the interior or ldquobayrdquo region (Scheme 33b) however would afford a class of compounds exhibiting a linear polyphenanthrene motif that are known as [N]phenacenes82 Unselective additions would result in mixed topologies Helicenes and their various derivatives constitute a well studied83 family of molecules and continue to be a popular area of research Phenacenes in contrast have been scrutinized much less in part because only four members of the parent series are known and because for N = 5 and 6 they are extremely insoluble84 Phenacene-based applications have been slow to develop but the first reports of the utilization of these molecules as functional organic materials suggest the beginning of a rich and promising field85 Thus in 2008 [5]phenacene (picene) was demonstrated to behave as stable high performance organic field effect transistor (FET)85b Currently the most common organic polycyclic benzenoid hydrocarbon-based FETs employ acenes which have a polyanthracene structure (Figure 31) The sensitivity

Figure 31 Linearly fused benzene topology of the acenes of these systems to air however has obstructed progress in this area86 For example pentacene a commonly used acene in FETs reacts readily with oxygen to form

+ RR

Helicenes

+ RR

Phenacenesn

R

R R R R

n

R

R

R

(a)

(b)

[N]Acenes

n

- 65 -

pentacenequinone a process that severely reduces device efficiency (Scheme 34)

Scheme 34 Degradation of Pentacene to Pentacenequinone Under Aerobic Conditions

Phenacenes on the other hand are much less prone to such decomposition pathways due to their higher HOMO-LUMO gap thus rendering them less reactive85b86a Their enhanced stability relative to acenes87 makes them better candidates for molecular electronic applications In a second seminal breakthrough [5]phenacene was very recently also found to behave as a superconductor at low temperature when doped with potassium85a This work paves the way for a new class of PAH-based superconducting materials in which phenacenes may play a key role

As this chemistry advances new synthetic methods for preparing derivatives of these molecules will be required in particular those bearing solubilizing andor otherwise functionally useful substituents The most general procedure for synthesizing phenacenes as developed by Mallory88 makes use of oxidative stilbene photocyclizations (Scheme 35)8388 In this transformation irradiation of the stilbene

Scheme 35 Generic Oxidative Stilbene Photocyclization Used to Prepare Phenacenes as Illustrated for Phenanthrene

moiety leads to conrotatory electrocyclic ring closure Trapping of the resulting intermediate with oxidizing reagents such as iodine or oxygen yields the desired phenanthrene subunit The requisite stilbenes are most generally accessible via the Wittig reaction as illustrated in the synthesis of [7]phenacene derivative 87 (Scheme 36) Although the yields for the photocyclization are typically reasonable (60ndash90 )85a the major drawback of this methodology is the numerous steps associated with preparing the functional groups required for the prerequisite Wittig reaction These

- 66 -

transformations serve to decrease the overall yield of the target molecule

Scheme 36 Synthesis of [7]Phenacene 87

While laborious Malloryrsquos method addresses successfully the problem of solubility As alluded to in Section 21 large PAHs become insoluble due to the increased π-π stacking forces that are experienced between aromatic rings The best solubilizing groups for the phenacenes were found to be sterically bulky groups located in the bay regions85a These modifications distort the phenacene framework from planarity thereby disrupting π-stacking and increasing solubility as demonstrated by the tert-butyl [7]phenacene 87 (Figure 32) This approach was applied to systems as large as [11]phenacene the current record in the series85a

Br

CH3t -Bu

1 BuLi2 DMF

Br

CH2

t-Bu

CHO

CH3t-Bu

PPh3

Br

+Wittig

t-Bu t-Bu

Br CH3 1 hν2 I2

t-Bu t -Bu

Br CH3

t-Bu t-Bu

Br H2C PPh3 Br

+

t-Bu t-Bu

OHC CH3

Wittig

t-Bu t-Bu

Br Br 1 hν2 I2

t-Bu t-Bu

Br CH3

t-Bu t -Bu

t-Bu t-Bu

87

1 NBS2 PPh3

- 67 -

Figure 32 Crystal structure of tetrakis(tert-butyl) [7]phenacene 87 Hydrogens are omitted for clarity

To test the viability of angular phenylenes as substrates in Ni catalyzed alkyne cycloadditions the simplest member 22 was chosen raising a number of questions First how many and what kind of products will be formed (AndashE in Scheme 37) Will there be inherent selectivity toward helicene C or phenacene E formation respectively If not can the reaction conditions be modified so as to induce such What will be the limitations with respect to the size of substituents especially in view of the crowded fjord and bay regions of D and E respectively The work presented in this chapter carried out in collaboration with Dr Zhenhua Gu89 explores these questions

Scheme 37 Possible Cycloaddition Products of Angular [3]Phenylene 22

22

[Ni]R R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

A B

C D E

32 Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene

Before embarking on the proposed chemistry the reactivity of 22 in the presence of nickel in the form of Ni(COD)(PMe3)2 in the absence of alkynes was queried Only starting material was recovered and there was no sign of dimerization (or oligomerization) to products of the type shown in Scheme 38 a mode of reactivity

- 68 -

readily attained by biphenylene and substituted derivatives33b

Scheme 38 Attempted Dimerization of Angular [3]Phenylene 22

In contrast exposing diphenylacetylene 88 to Ni(COD)(PMe3)2 and a small excess (109 equivalents) of angular phenylene 22 generated two products in the absence of any other (Figure 39) The first molecule 89 was the result of the cycloaddition of one diphenylacetylene at the bay region and the minor component The major product constituted tetraphenyl [5]phenacene 90 derived from 22 by double bay region attack The structures of both compounds were confirmed by X-ray analysis revealing highly distorted frames89 Scheme 39 Nickel Catalyzed Cycloaddition of Angular [3]Phenylene 22 to Diphenylacetylene

Yields Based on Diphenylacetylene

The outcome of this transformation was gratifying in its seeming simplicity and selectivity Thus it appeared that metal insertion occurred exclusively to bay region bonds heralding the discovery of a new phenacene synthesis The observation of relatively large amounts of 90 could be ascribed to increased reactivity of 89 relative to 22 possibly due to steric activation by the newly introduced bay region phenyl group To test this hypothesis 89 was subjected to the cycloaddition reaction conditions (Scheme 310) Surprisingly not only was this reaction slower than that of 22 but the expected phenacene 90 was only a minor product (6 ) Instead tetraphenylbenzo[c]chrysene 91 a regioisomer of 90 as confirmed by X-ray analysis89

+

+ +

Ni(COD)(PMe3)2

22

- 69 -

was isolated in 74 yield the result of non-bay alkyne cycloaddition to 89 Therefore 89 is not the precursor of 90 Rather there must be separate reaction pathways leading to each respective product

Scheme 310 Cycloaddition Reaction of 89 with Diphenylacetylene 88

A series of semi-quantitative experiments monitored by 1H-NMR spectroscopy was carried out to shed some light on this mechanistic problem First the reaction of angular [3]phenylene 22 with diphenylacetylene 88 in Scheme 39 was addressed Because dinuclear metallic activation of the strained C-C bond in biphenylenes has been implicated in a number of studies19 it was possible that the above mechanistic duality was caused by the presence of catalytic Ni2 species in addition to the ldquoregularrdquo mononuclear alternatives Alternatively double Ni insertion before cycloaddition might be responsible for one product whereas sequential ldquonormalrdquo activation might be the origin of the other Therefore the amount of initial Ni(COD)(PMe3)2 was gradually increased and the effect of this incremental change on rate and product ratios recorded As shown in Table 31 the speed with which 89 and 90 formed was roughly proportional to the amount of metal present while the product ratio stayed unchanged

Table 31 Variation of Catalyst Loading in the Reaction of Phenylene 22 with Diphenylacetylene 88 Reactions Were Carried Out with Equimolar Amounts of 22 and 88 in

THF-d8 at 40 degC

Run Ni(COD)(PMe3)2

(mol) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

Ratio of 8990

1 50 32 times 10ndash4 031 times 10ndash4 103 2 35 20 times 10ndash4 022 times 10ndash4 91 3 7 064 times 10ndash4 0064 times 10ndash4 100

Next the amount of diphenylacetylene 88 was gradually increased from 1 to 4 equivalents (Table 32) The outcome of this series of experiments was counterintuitive as it led to a larger preference for the production of monoadduct 89 suggesting a mechanistic bifurcation in which whatever Ni species is responsible for the eventual formation of 90 is sequestered by external ligand (in this case 88)

- 70 -

Table 32 Variation of Alkyne Equivalents in the Reaction of 22 (1 equiv) with Diphenylacetylene 88 in the Presence of 50 mol of Ni(COD)(PMe3)2 Experiments Were Run

in THF-d8 at 40 degC

Run 88 (equiv) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

8990

1 10 320 times 10ndash4 031 times 10ndash4 103 2 20 220 times 10ndash4 018 times 10ndash4 122 3 40 220 times 10ndash4 011 times 10ndash4 200

Following the reaction progress by NMR spectroscopy afforded additional insights Thus mixing the ingredients at room temperature left the phenylene component untouched Instead there was a near instantaneous displacement of COD by diphenylacetylene to produce Ni(PhCequivCPh)(PMe3)2 (92) and free COD in addition to the generation of Ni(PMe3)4

90 The speed with which this complex was formed implied that it might be the active catalyst precursor Consistent with this notion higher reaction rates were observed when the reaction in Scheme 38 was carried out with pure 9291 as the catalyst (50 mol) and 05 equivalent of 88 (Table 33 Run 2) In consonance with Table 32 the lesser concentration of available free alkyne increased the relative amount of 90 formed Conversely (Run 3) using Ni(COD)(PMe3)2 with an extra equivalent of PMe3 decreased the rates of formation of 89 and 90 and increased the ratio of 8990 consistent with ligand inhibition of the activation of 92 and the external ligand effect noted in Table 32 Table 33 Variation of Catalyst in the Reaction of 22 with Diphenylacetylene 88 and its Effect

on Reaction Rate Experiments Were Run in THF-d8 at 40 degC with 1 Equivalent of 22

Run Catalyst 88

(equiv)

Rate of formation of 89 (mol

Lmiddoth)

Rate of formation

of 90 (mol Lmiddoth)

8990

1 Ni(COD)(PMe3)2 10 320 times 10ndash4 031 times 10ndash4 103 2 Ni(PhCequivCPh)(PMe3)2 (92)

(05 equivalent) 05 1270 times 10ndash4 210 times 10ndash4 60

3 Ni(COD)(PMe3)2 (05 equivalent) + PMe3 (10 equiv)

10 088 times 10ndash4 005 times 10ndash4 163

Attention was then shifted to the reaction of monoadduct 89 with 88 as in Scheme 310 (Table 34) Here increasing the amount of alkyne and catalyst favors the formation of 91 consistent with an independent pathway At low concentration of alkyne it appears that 89 reenters the manifold of its generation and proceeds on to 90 Indeed following the change in the ratio of 9190 in Run 1 (Table 34) with time reveals a decrease from 47 to the eventual 22 as 88 is depleted

- 71 -

Table 34 Variation of Catalyst Loading and Alkyne Concentration in the Reaction of 90 with Diphenylacetylene 88 Reactions Were Run in THF-d8 at 40 degC

Run 88 (equiv) Ni(COD)(PMe3)2

(mol) 9190

1 10 50 2 2 30 50 15 3 30 10 25

The information obtained from these experiments allowed a narrowing of mechanistic possibilities For example dinuclear Ni activation only one possibility of which is shown in Scheme 311 was rendered unlikely by the absence of any observable changes in product distribution of the reaction in Scheme 39

Scheme 311 Generic Example of a Dual Mechanism Based on Mono- and Dimetallic Phenylene Activation

An alternative mechanism shown in Scheme 312 was in much better agreement with the results of the various control experiments The first step would be displacement of a phosphine in the initially dominant Ni-containing species 92 by angular [3]phenylene 22 inhibited by added PMe3 From 93 oxidative addition can take place to afford metallacycle 94 Why should bay region insertion be favored Arguably the regioselectivity of this step is controlled by the lesser steric hindrance in the resulting arene fragment or relative stabilization of the polarized Ni-C(α-

PhPh

Ph Ph Ph Ph

PhPh

NiL L

Ni(COD)(PMe3)2

NiNiL L L L

PhPh

2

Ph

Ph

Ph Ph Ph Ph Ph Ph

+

+22

89

90

91 90

- 72 -

biphenylene) bond in 94 by the electron withdrawing nature of the neighboring cyclobutadienoid ring This phenomenon in biphenylene is due to the rehybridization of the four-membered ring carbons to adopt relatively larger p character in the strained linkages hence larger s character (ie electron withdrawing) in the remaining bond and manifests itself most clearly in the relative acidity of the α-hydrogens7a This step is followed by migratory insertion and reductive elimination to produce molecule 96 the mechanistic bifurcation point One branch proceeds through presumably ligand-assisted metal dissociation to generate the relatively unreactive free 89 The second entails Ni migration92 and insertion into the bay region of the remaining four-membered ring (97) before the second cycloaddition occurs generating phenacene 90

Scheme 312 Possible Mechanism for the Alkyne Cycloaddition Reaction of Angular [3]Phenylene 22

The regioselective formation of 97 may again be sterically dictated or may involve anchimeric assistance by the bay-region phenyl group as sketched in Scheme 313 specifically 99

Scheme 313 Anchimeric Assistance on Route to [5]Phenacene 90

Ph Ph

PhPhPhPh

Ph

Ph

Ph PhNi

NiMe3P Ph

Ph

Ni

Me3P Ph

Ph

NiPMe3Me3P

Ligand exchangeOxidativeaddition

Migra toryinser tion

Reductiveelimination

Ph

Ph

Me3P

Ni migra tionOxidative addition

22

92

9394

96 89

9097

Ph Ph

Ni

Me3P

Ni(PMe3

Ph

Ph

minusNi(PMe3)

95

- 73 -

This type of metal coordination to the double bond of a proximal arene ligand is common and two examples are provided based on ruthenium94 and molybdenum95 (Figure 33)

Figure 33 Examples of complexes with phenyl groups coordinating to a nearby metal center Turning to the largely selective conversion of 89 to 91 (Scheme 310) requires the postulate of preferential insertion of the metal at the non-bay region and hence a different Ni species from that in 96 possibly a Ni(PMe3)(alkyne) moiety akin to that in 93 ie 100 (Scheme 314) Bay insertion would lead to metallacycle 101 and ultimately molecule 90 The expected large degree of steric repulsion between the phenyl groups in 101 should disfavor this reaction pathway On the other hand non-bay insertion to produce 102 should be relatively less impeded and would furnish 91 Another option for the generation of 90 from 89 would be reentering the pathway described in Scheme 312 facilitated at low concentrations of alkyne consistent with the data in Table 34

Scheme 314 Proposed Mechanism for the Alkyne Cycloaddition Reaction of 89

Ni

PhMe3P

PhPh

(Me3P)Ni

PhPh(Me3P)Ni

Ph

Ph

93 98

99

Ph Ph Ph Ph

90

+

Ph Ph

Ni

Me3P

97

- 74 -

While the above mechanistic perambulations appear plausible it should be stressed that they are speculative and may be restricted to diphenylacetylene 88 as the substrate Thus both 3-hexyne 103 and 14-dimethoxy-2-butyne 106 added to 22 less selectively than 88 to provide only the bay and non-bay monoadducts 104 and 105 and 107 and 108 respectively (Scheme 315)

Scheme 315 Reaction of Angular [3]Phenylene 22 with Other Alkynes

NiMe3P PMe3

Ph Ph+

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph

Ni(PMe)3

PhPh

Ni(PMe3)

Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

92 89

101

90

102

100

91

Ni

Ph Ph

PMe3

+

R

R

THF-d8 40 oCR

R22

Ni(COD)(PMe3)2

R

R

+

R = Et 104

R = CH2OMe 107

R = Et 103

R = CH2OMe 106 R = Et 105

R = CH2OMe 108

11 45 9 68

- 75 -

In view of these uncertainties recourse was taken to DFT computations delineated in the next section 33 Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene DFT studies were carried out in collaboration with Prof Vincent Gandon of the Universiteacute Paris-Sud 11 The B3LYP 6-31G(d) basis set was used for hydrogen and carbon atoms while LANL2DZ was used for nickel Before attempting to model the more complex alkyne cycloaddition reactions in Schemes 38 and 39 the basic Ni-catalyzed addition of the parent acetylene to biphenylene in the presence of PMe3 was studied (Scheme 316) The free energies

Scheme 316 Computational Modeling of Ni-catalyzed Addition of Acetylene to Biphenylene Free Energies (∆G KcalMol) are Relative to 109 Transition State Energies are Absolute Values

for This Step

NiMe3P PMe3

NiMe3P

NiMe3P

Ni

Ni

PMe3

PMe3

+

+ PMe3+

+ PMe3

+ 2 PMe3

+ 2

(00)

(281)(37)

(140)

(12)

NiMe3P PMe3

NiMe3P

NiNiPMe3Ni

PMe3

PMe3NiMe3P

PMe3

(727) (693) (476) (374) (394) (395)

Ni

Me3P

PMe3Ni

Me3P

Ni

Ni

Me3P

PMe3NiMe3P PMe3

(590) (532)

(157) (125) (150)

Most Accessible TS

+

7

114

110

113109

111 112

Ni

Me3P

(253)

Ni

PMe3

(242)

- 76 -

(∆G) of various possible catalyst structures consisting of an assortment of combinations of nickel PMe3 and acetylene as well as those of several possible transition states and the resulting products were calculated As is evident on inspection of the values in the first part of Scheme 316 a number of species were found to be very close in energy making it difficult to pinpoint a specific structure for the initial insertion step Bis(ethyne) nickel complex 109 was established as the lowest energy nickel species and was thus assigned a relative value of 0 kcalmol The most accessible transition state 110 features the oxidative addition of the Ni(PMe3)(C2H2) fragment 114 (+ 14 kcalmol) in which the alkyne is held exo to biphenylene The corresponding endo structure 111 was found to be just slightly higher in energy by 20 kcalmol as was the bisalkyne transition state 112 It is likely that biphenylene-NiL2 complexes (two of which were calculated at relative energies 242 and 253 kcalmol) lie on the way to these maxima93 Metallacycle 113 the structure ensuing from transition state 110 constituted the lowest energy product uphill from the starting 109 by 125 kcalmol but other alternatives are nearly isoenergetic Clearly however attack by Ni(PMe3)2 or Diels-Alder type cycloadditions are not likely From 113 the species proceeds smoothly by alkyne insertion-reductive elimination to the phenanthrene product a cascade associated with a large exergonic driving force Undaunted by the relatively complicated picture that emerged with biphenylene attention was turned to the original object of scrutiny the cycloaddition reaction between angular [3]phenylene 22 and diphenylacetylene 88 to produce [5]phenacene derivative 90 Modeled in the same manner as described above the metal insertion into the four-membered ring of 22 is shown in Scheme 317 The lowest energy nickel species

- 77 -

was found to be diphenylacetylene complex 92 gratifyingly corresponding to experiment and was set to a reference value of 00 kcalmol One notes again however an array of at least 10 species all of which must be in equilibrium in the initial reaction mixture Notably the Ni-π complexes to 22 are all more than 20 kcalmol higher in energy than 92 providing a computational rationale for the failure to observe such species by NMR The first step in the optimal reaction pathway is the coordination of Ni(PMe3) to the cyclobutadiene ring of 22 which results in formation of η2-like complex 114 Again in gratifying agreement with experiment bay region insertion through transition state 115 to give 116 is favored albeit by a bare 07 kcalmol relative to its non-bay region counterpart 117 Moreover there are at least six other structures that are energetically viable in silico although insertions of Ni(PhCequivCPh)(PMe3) appear less so possibly due to steric hindrance The same observation is made for the products of insertion although 116 emerges as the thermodynamically most stable possibility

Scheme 317 Calculated Structures and Reaction Pathway for the Insertion of Nickel into the Four-Membered Ring of Angular [3]Phenylene 22 Free Energies ∆G are in KcalMol Relative

to 92

The next step was to map out the first alkyne cycloaddition (Scheme 318) Coordination of diphenylacetylene to 116 is endothermic by 139 kcalmol and after migratory insertion produces 119 Interestingly a transition state to regioisomer 95

(328) (352)

NiMe3P PMe3

(364)

NiMe3P

NiMe3P PMe3

NiPMe3

(339)

Ni

PMe3

PMe3

NiMe3PPMe3

NiMe3P

NiPMe3

(16) (04) (108) (117)

NiMe3P PMe3 Ni

Me3PNi

Me3P Ni Ni

PMe3

PMe3

+ [3]+ DPA

+ PMe3+ [3]+ DPA

+ PMe3+ [3]

+ 2 PMe3+ [3]

+ [3]+ 2 DPA

Ph Ph Ph PhPh Ph

Ph

PhPh Ph

Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

Ph

(45) (96)

(00)

(89) (134)

Most AccessibleTS

NiPMe3

+ PMe3+ [3]+ 2 DPA

(314)

Ni

+ 2 PMe3+ [3]+ DPA

Ph Ph

(294)

1i(PMe3)

Ni

PhPh

(212)

(218)

(345)

Ni

PhPh(297)

Ni

Me3P

Ni

Ph

Ph

(350)

Ni

PMe3

(303)

Ni

Ni

(43) (41)

Ph

Ph

PhPh

Ni

PMe3

NiMe3P

(-10) (-22)

(Me3P)Ni

Ni(PMe3)

Ph Ph

Ph Ph(225) (256)

+ PMe3+ 2 DPA

+ 2 PMe3+ DPA

+ PMe3+ DPA

+ PMe3+ DPA

92114

115

116118

117

- 78 -

written (arbitrarily) in Scheme 312 could not be located

Scheme 318 Calculated Reaction Pathway for the Coordination of Diphenylacetylene Migratory Insertion and Nickel Migration Free Energies ∆G are in KcalMol Transition

State Energies are Absolute Values for This Step

Subsequent reductive elimination from 119 occurs to produce nickel coordinated arene species 120 From it free 89 is presumably readily obtained by demetallation in the presence of external ligands shown only for the formation of 92 in a very favorable process (ndash487 kcalmol) This step is sufficiently exothermic to tolerate the emergence of all the calculated species in the starting line up of Scheme 317 and is presumably the source of 89 in Scheme 39 However if not removed the Ni moiety in 120 can migrate along a shallow manifold across the π frame choosing the phenyl functionalized edge of the molecule (cf Section 24) until the remaining four-membered ring is reached (121) At this point two separate reaction pathways become possible Nickel insertion on the side proximal or opposite of the phenyl groups generates 99 or 122 respectively The barriers for these transformations are similar but show a noticeable preference for the formation of 99 In addition there is a significant energy difference (175 kcalmol) between 122 and 99 in favor of the bay region metallacycle The reason is the coordination of the neighboring phenyl ring to the nickel which serves to stabilize 103 vindicating the proposal made in Scheme 313 and providing a rationale for the exclusive observation of 90 in Scheme 39 From 99 as shown in Scheme 319 coordination of diphenylacetylene (123) is followed by migratory insertion to produce 124 Insertion occurs away from the bay region so as to reduce steric repulsion due to the phenyl group in the phenanthrene part of the molecule Finally reductive elimination ensues providing phenacene-Ni

NiMe3P

NiPMe3

Ni(PMe3)

Ni Ph

PhMe3P

Ph

Ph

PhPh

(117)

126

(44)

102

( 80)

01

( 412)

Ph PhNi(PMe3)

( 389)

Ph Ph

45

Ni(PMe3)

( 408)

Ph Ph

13

PhNi

PMe3

Ph Ph

Ni(PMe)3

133

( 488)

117

( 663)

NiMe3P

( 22)

PhPh+

95

116

119

120121 122

99

NiMe3P Ph

Ph

Ph Ph

( 899)

NiMe3P PMe3

Ph Ph+

92 89

- 79 -

complex 125 At this point the stage is set for exergonic nickel dissociation to 90 and catalyst turnover

Scheme 319 Calculated Reaction Pathway for the Second Diphenylacetylene Insertion All Relative Energies (in red) are in KcalMol Transition State Energies are Absolute Values for

This Step

In conclusion of this discussion the consideration of the combined computational and experimental data affords a mechanistic picture of the cycloaddition reaction of diphenylacetylene 88 to angular [3]phenylene 22 (Scheme 39) the essential features of which are summarized in Scheme 320 The crucial point is a mechanistic bifurcation in which 89 is either released early and (nearly) irreversibly from the metal or the metal stays attached so as to effect a second cycloaddition to give 90 This mechanism implies that 91 is formed by a different mechanism involving a different Ni species

PhNi

PMe3

( 663)

+

PhNi

Ph PMe3Ph

Ph

( 403) ( 403)

PhNi

PhPMe3

PhPh

( 519)

94

93

( 696)

PhNi

PhPMe3

Ph

Ph

96

( 817)

Ph Ph Ph Ph

(MeP)3Ni

99

123

124

125

PhPh

Ph PhPh Ph

+Ni

Me3P PMe3

( 1101)

PMe3

90

- 80 -

Scheme 320 Essential Mechanistic Features of the Formation of 89 and 90 in the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene 88 and Angular [3]Phenylene 22

Consequently the reaction of 89 with diphenylacetylene to give 91 (Scheme 310) was also modeled by DFT Of the various options probed that shown in Scheme 321 proved to be most plausible The reaction pathway entails coordination of alkyne-Ni phosphine 126 to molecule 89 which generates complex 127 in a process that is found to require 228 kcalmol of energy Insertion into the non-bay region of the four-membered ring has a barrier of 16 kcalmol and provides metallacycle 128 After the second cycloaddition event benzo[c]chrysene 91 is formed Interestingly the transition state leading to insertion of nickel complex 126 into the bay region of 89 structure 129 was found to be so high in energy relative to 128 that it could not be modeled This is not unexpected as the phenyl group closest to bay region effectively blocks the approach of any catalyst species This result is consistent with the high ratio of 91 to 90 formed in Scheme 310 and the increase in this ratio at higher initial diphenylacetylene concentration Why is any 90 formed and why does its relative proportion increase at lower diphenylacetylene concentration A possible explanation is that under these conditions the concentrations of 92 and 126 are sufficiently small that 89 reenters Scheme 318 competitively

PhPhNi(PMe3)

PhPh

Ni(PMe3)

Ph Ph Ph Ph

PhPh

Ni(PMe3)

Ni

PMe3

Ph Ph

NiPhMe3P

22 116

88

120

121

99

88

90

PhPh

89

Externalligand

assistedNi migration

Regioselectiveinsertion

Regioselectiveinsertion

Mechanistic bifurcation

- 81 -

Scheme 321 Calculated Reaction Mechanism for the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene and Compound 90 Relative Energies are in KcalMol Transition

State Energies are Absolute Values for This Step

Consideration of Scheme 320 suggests that phenacene formation might be maximized by keeping the concentration of external ligand low during the course of the reaction Experiments aimed at verifying this conjecture are the subject of Section 34 in addition to presenting extensions of the methodology to higher angular phenylenes

34 Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions The experimental and computational studies described in Section 33 suggested that the decisive factor for selective formation of phenacene 90 is suppression of metal dissociation in Ni complex 120 This scenario would be achievable by maintaining a low concentration of diphenylacetylene 88 (vide supra) Previously the alkyne cycloaddition was performed with all reagents mixed together at the start of the reaction invariably resulting in a high initial concentration of 88 To obviate this occurrence an alternative procedure was devised In this new arrangement the required stoichiometric amount (in this case two equivalents) of alkyne 88 was slowly introduced to a mixture of 22 and Ni(COD)(PMe3)2 by means of a syringe pump (Scheme 322) The results of varying addition and reaction times are shown in Table 35

Scheme 322 Modified Reaction Alkyne Cycloaddition Reaction Between 22 and 89

Ph Ph

Ni(PMe3)

Ph Ph Ph Ph

Ni(PMe)3

160

Ph

Ph

PhPh

(309)(317)

Ph Ph

Ph

Ph

NiMe3P

Ph Ph

(minus573)

89

126

127 128 91

Ph Ph Ph

Ni

Ph

PMe3

129

NiMe3P PMe3

Ph Ph

(00)

92

(89)

+

- 82 -

Table 35 Variation of Alkyne Addition and Total Reaction Time in the Scheme 322

Run Addition time of 88 (h)

Total run time (h)

Yield of 89 ()

Yield of 90 ()

1 4 16 44 55 2 6 22 23 77 3 5 41 24 76 4 12 69 17 73 5 13 19 13 87

The most immediate result of the modified protocol was the quantitative conversion of 22 to cycloadduct products 89 and 90 Turning to the product ratios a four hour addition time led to a slight preference for 90 Increasing the time to six hours dramatically influenced the product distribution and 90 was isolated in 77 yield as compared to the 23 for 89 In the optimal Run 5 87 of 90 was generated vs 13 of 90 Extending the run time after the addition of diphenylacetylene had a negligible effect The successful enhancement in phenacene selectivity under these conditions makes the reaction a practical method for synthesizing compound 90 and also provides further experimental support for the proposed mechanism shown in Scheme 320 Having reached a reasonable level of understanding both the mechanistic and experimental aspects of the reaction of angular [3]phenylene 22 with diphenylacetylene attention was shifted to a larger and more challenging substrate angular [4]phenylene (17) This system could conceivably afford 17 possible adducts one of which is hexaphenyl[7]phenacene 130 (Scheme 324) Would the mechanistic features of this triple cycloaddition be sufficiently similar to those of 22 to apply the same principles and enable selectivity toward 130

+THF reflux

Ph Ph Ph PhPh

Ph

+

Ph

Ph

2 equivslow addition

22 89 90

Ni(COD)(PMe3)2(10 mol)

88

- 83 -

Scheme 324 The Possible Cycloadducts of Diphenylacetylene 88 to Angular [4]Phenylene 17

+ Ph Ph

Ph Ph

Ph Ph

PhPh

Ph

Ph

Ph Ph Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph PhPhPh

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph Ph PhPhPh

Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

PhPh

Ph Ph Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

88

17

130

- 84 -

Encouragingly a first experiment under conditions comparable to those in Scheme 39 for 22 namely reaction of angular [4]phenylene (17) with one equivalent of diphenylacetylene in the absence of high dilution indeed engendered only five products two of which monoadducts 131 and 132 were minor (Scheme 325) The major components of the mixture were molecules 133 134 and most significantly 130

Scheme 325 Nickel Catalyzed Alkyne Cycloaddition with 17 and 88

Monitoring the course of the transformation by NMR revealed that 133 is the sole initial new compound followed by gradual appearance of the others Extrapolation of the insights gained with 22 it is tempting to propose that migration of the metal in Ni-complexed 133 is the source of 134 and ultimately 130 If true [7]phenacene 130 might be made selectively by application of the slow alkyne addition procedure of Scheme 322 Scheme 326 illustrates the proposed scenario It starts with doubly regioselective Ni insertion into the central ring and from the bay region to give 135 On the basis of the electron withdrawing effect of the adjacent cyclobutadienoid rings invoked earlier in the selective formation of 94 (Scheme 312) this metallacycle would seem the most stable Again this conjecture is tentative as the appearance of the minor products 131 and 132 would indicate Metallacycle 135 would then give rise to 136 (and hence 133 by demetallation) which would connect by Ni migration and insertion to 137 Alkyne cycloaddition would result in 138 (and hence 134 by demetallation) which would connect by Ni migration and insertion to 139 Alkyne cycloaddition would result in 140 (and hence 130 by demetallation)

+

Ph Ph

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2(10 mol)THF 75 degC

5 6

33

27 28

132131

133

134 130

17

88

- 85 -

Scheme 326 Proposed Reaction Pathway to Phenacene 130 from Angular [4]Phenylene 17 via Ni Migration

The successful preparation of [5]- and [7]phenacene from angular [3]- and [4]phenylene respectively prompted an attempt to prepare [13]phenacene derivative 141 from helical [7]phenylene 14210 (Scheme 327) This transformation would make use of six alkyne cycloadditions to produce the target molecule In addition to the possibility of preparing the largest known phenacene this reaction would also serve as an interesting test of the alkyne cycloaddition methodology

Scheme 327 Proposed Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Using the slow addition procedure phenylene 142 was subjected to the alkyne cycloaddition conditions (Scheme 329) All of the starting material was consumed but the reaction ultimately resulted in an intractable mixture of products Unfortunately no conclusive structural identifications for any of the ensuing compounds could be made from the 1H-NMR data A large assortment of peaks was seen in the region of 6ndash7

Ni

PMe3

Ph

NiPMe3

Ph Ph Ph PhNi

PMe3

Ph Ph Ph

NiMe3P

135

137

Ph Ph

Ph Ph

Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2

13617

88Ni

PMe3

Ph Ph88

138 139

Ph Ph88

Ni

PMe3

140

- 86 -

ppm suggesting the presence of phenylene subunits More informative was the absence of the highly diagnostic phenacene bay region proton signals that are typically found at ~8ndash9 ppm84 signaling the absence of any phenacene product(s)

Scheme 328 Attempted Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Nevertheless mass spectral analysis clearly indicated that multiple alkyne cycloaddition had occurred (Table 36) Peaks were observed at mz = 700 1056 1234 and 1412 which correspond to the presence of single triple quadruple and quintuple alkyne adducts in the reaction mixture No signal corresponding to the mass of 141 (mz = 1590) was detected however Although the structures of the resulting products remain to be established by follow-up experiments on a larger scale the fact that five cycloadditions occurred is encouraging in the basic scientific quest for large novel polycyclic aromatic hydrocarbons

Table 36 Mass Spectral Data (FAB) of the Product Mixture of the Cycloaddition Reaction of Phenylene 142 to Diphenylacetylene 88

mz Percentage Cycloaddition count 700 13 1

1056 11 3 1234 8 4 1412 7 5

Our disappointment in the apparent failure to generate 141 in this reaction may be the result of overambitious expectations on our part Thus we assumed in analogy to the reactivity of angular systems 17 and 22 that bay region cycloaddition to one of the inner cyclobutadiene rings would be preferred ideally producing an initial structure such as 143 (Figure 38) The corresponding non-bay adduct is illustrated by 144 It is evident on comparison that such bay region reactivity would lead to constructs devoid of the helical strain present in the starting material96 as well as non-bay structures like 144 The subsequent course of the reaction however may be marred by relatively non-selective cycloadditions as already indicated for 17 (Scheme 325) Therefore it will be prudent for future investigators to return to the latter optimize its outcome and then proceed along the series in the quest for large phenacene (or other) structures

- 87 -

Figure 38 Proposed representative initial bay (143) and non-bay (144) alkyne cycloaddition products of the reaction of [7]heliphene 141 with diphenylacetylene 88

35 Summary and Outlook The first alkyne cycloaddition studies were carried with angular phenylene systems Angular [3]phenylene 22 was successfully used as a precursor to a novel phenyl substituted [5]phenacene derivative 90 Similarly hexaphenyl [7]phenacene 131 was prepared from angular [4]phenylene 17 Extensive experiment and computational mechanistic studies suggested that the optimal conditions for preparing phenacene 90 from phenylene 22 were the maintenance of a low concentration of alkyne in the reaction mixture Future work will focus on applying these conditions to the synthesis of [7]phenacene 130 from angular [4]phenylene 17 An attempt to prepare a [13]phenacene 142 from helical [7]phenylene 141 proved unsuccessful for reasons that are not well understood Nevertheless cycloaddition was found to have occurred up to five times This observation is promising with respect to the further application of the methodology described in this chapter The development of an alkyne cycloaddition-based approach to synthesizing phenacenes should greatly facilitate the study of this emerging class of molecules Future work will focus on expanding the substrate scope of the reaction by examining various functionalized alkynes the application of metal systems that may allow the isolation of crucial intermediates and the expansion of the substrate scope to the higher angular phenylenes as well as other topologies

- 88 -

Chapter Four Experimental and Computational Details

41 General Considerations

All glassware was oven-dried (180 degC) prior to use Reagents were used as received from suppliers unless otherwise noted Flash chromatography97 was performed with Merck 60 230ndash400 mesh silica gel MP EcoChrom neutral alumina was deactivated to activity III by adding 6 water by mass followed by thorough mixing98 Air sensitive compounds were handled under argon with standard Schlenk techniques andor in a nitrogen atmosphere glovebox (Vacuum Atmospheres Model Nexus) Irradiation in CpCo(CO)2 reactions was carried out with a 120V 300W slide projection lamp (ELH) positioned 5 cm away from the reaction vessel UV-irradiation experiments were conducted in a Rayonet Photochemical Reactor (RPR-100) Bis(trimethylsilyl)- and trimethylsilylacetylene (BTMSA and TMSA respectively) were distilled from molecular sieves (4 Aring) prior to use TMSA was degassed with four freeze-pump-thaw cycles while BTMSA was degassed using a 20 min Ar purge BTMSA was recycled using from all CpCo(CO)2 reactions using the following procedure The BTMSA was first removed by vacuum transfer Residual cobalt was removed by dissolving the BTMSA in pentane and washing the pentaneBMTSA layer mixture with a dilute solution of ceric ammonium nitrate in acetonitrile in a separatory funnel The denser acetonitrile layer was drained off and the pentane removed by distillation at atmospheric pressure Vacuum distillation of the BTMSA from molecular sieves afforded a product pure enough for future use All solvents were distilled under N2

immediately before use from the appropriate drying agent triethylamine (KOH pellets) benzene toluene CH2Cl2 (CaH2) THF and diethylether (Nabenzophenone) acetonitrile (CaH2) Deoxygenation of solvents andor reaction mixtures was carried out by a 20 min Ar purge or four free-pump-thaw cycles for volatile (bp lt 70 degC) mixturessolvents Ni(COD)2 (Strem) was stored and manipulated in the glovebox 1H and proton decoupled 13C spectra were measured at 500 MHz and 125 MHz respectively unless otherwise noted 1H-NMR chemical shifts are reported in ppm units relative to the signal of the solvent (CDCl3ndash726 ppm C6D6ndash715 ppm acetone-d6ndash205 ppm CD2Cl2ndash532 ppm toluene-d8ndash209 ppm (for ndashCD3) Except where noted two-dimensional NMR experiments were run under temperature control at 300 K All spectral data were processed with Bruker TopSpin 21 software Melting points were recorded in open capillary tubes using a Thomas Hoover Unimelt apparatus and are uncorrected Melting points for air-sensitive samples were carried out in flame sealed capillary tubes Mass spectral measurements (Electron Impact Fast Atom Bombardment) and elemental analyses were supplied by the Micro-Mass Facility of the College of Chemistry University of California Berkeley UV-Vis spectra were recorded on Agilent 8453 and Perkin-Elmer Lambda 35 spectrophotometers with absorbance data reported in nm (log ε) IR spectra were taken on a Perkin-Elmer Spectrum 100 Where appropriate analysis by GCMS was done with an Agilent 5973 instrument

42 Experimental Section for Chapter Two

- 89 -

2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19

A mixture of KF2 H2O (700 mg 744 mmol) [18]crown-6 (100 mg 0378 mmol) and 2378-tetrakis[(triisopropylsilyl)ethynyl] linear [3]phenylene26 (370 mg 0800 mmol) in degassed THF (25 mL) was stirred for 70 min at RT The orange solution was filtered through a plug of silica gel (1 x 3 cm) eluting with degassed THF (15 mL) providing a light-yellow solution After adding CpCo(CO)2 (260 mg 144 mmol) the solution was protected from light and added via syringe pump over a period of 6 h to a boiling mixture of degassed BTMSA (50 mL) and THF (200 mL) which was irradiated with a projector lamp under nitrogen After additional heating and irradiation for 15 h the solvents were removed by vacuum transfer and the black residue filtered through a plug of neutral alumina activity III eluting with hexaneTHF (501) The volatiles were removed and the dark brown residue crystallized from degassed acetone yielding 19 (330 mg 65 ) as black needles mp 192ndash195 degC (decomp) 1H-NMR (400 MHz C6D6) δ = 794 (s 2 H) 744 (s 2 H) 690 (s 2 H) 441 (s 5 H) 035 (s 18 H) 031 (s 18 H) ppm 13C-NMR (100 MHz C6D6) δ = 1494 1484 1433 1394 1360 1256 1155 802 781 739

269 261 ppm IR (neat) ν~ = 2951 2898 1259 1248 1073 830 799 752 cmndash1 UV-VIS (ethanol) λmax (log ε) = 288 (486) 299 (500) 352 (445) 410 (439) 438 (449) end absorption to 550 nm MS (70 eV) mz () 638 (9) [M+] 514 (100) 499 (3) 387 (2) 73 (24) HRMS (FAB) calcd for C35H47CoSi4 6382087 found 6382095 Elemental analysis calcd for C35H47CoSi4 C 6578 H 741 found 6582 721

Crystallographic information for 19 (H atoms omitted)

Table 41 Crystal Data and Structure Refinement For 19

Empirical formula C35H47CoSi4 Formula weight 63902 cryst size (mm) 025 x 020 x 005 cryst syst Triclinic refl used for unit cell determination 6958

2 θ range (deg) 245ndash2900

a (Aring) 9497(3) b (Aring) 12321(4) c (Aring) 16469(5) α (deg) 74058(5)

β (deg) 82154(5)

Me3Si

Me3Si

CoSiMe3

SiMe3

- 90 -

γ (deg) 72276(5)

V (Aring3) 17620(10) space group Pndash1 Z 2

Dcalc gcm3 1762

F000 680 micro cmndash1 645 temp ordmC ndash173

Tmax Tmin 0858 0972 no of total rflns 24355

no of unique rflns 6958

no of obsd rflns 9209

no of variables 361

Reflection to Parameter Ratio 255

R 00503

Rw 01426

Rall 00734

GOF 1006

Max Peak in Final Diff Map (endash Aring3) 0867

Min Peak in Final Diff Map (endash Aring3) ndash0755

- 91 -

Figure 41 ORTEP representation of 19

- 92 -

Table 42 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 19 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y Z U (eq)

Co1 073881(4) ndash000927(3) 060643(2) 002551(10) Si1 077416(8) ndash019090(6) 094343(4) 002594(16) Si2 113437(8) ndash016706(7) 082404(5) 003023(17) Si3 040491(7) 062139(6) 020406(4) 002291(15) Si4 005088(7) 056545(6) 030946(4) 002144(14) C1 06709(3) ndash00385(2) 079440(16) 00239(5) C2 08019(3) ndash00967(2) 083428(16) 00241(5) C3 09418(3) ndash00743(2) 079331(16) 00233(5) C4 09428(3) 00098(2) 071779(15) 00225(5) C5 08094(2) 00691(2) 067735(15) 00207(4) C6 07282(2) 01574(2) 060605(15) 00207(4) C7 07303(2) 02531(2) 053306(15) 00211(4) C8 05938(2) 03094(2) 050431(15) 00205(4) C9 05057(2) 03981(2) 043438(15) 00207(4) C10 05076(2) 04760(2) 035695(15) 00227(5) C11 03734(2) 05293(2) 031459(15) 00215(4) C12 02408(2) 05011(2) 035315(15) 00205(4) C13 02432(2) 04196(2) 043269(15) 00215(4) C14 03751(2) 03698(2) 047171(15) 00208(4) C15 04564(2) 02794(2) 054277(15) 00211(4) C16 04487(2) 01908(2) 061161(15) 00224(5) C17 05916(3) 01278(2) 064393(15) 00221(5) C18 06734(2) 00417(2) 071473(15) 00215(5) C19 05795(3) ndash02027(3) 09572(2) 00446(8) C20 08892(4) ndash03470(2) 09642(2) 00387(7) C21 07986(4) ndash01192(3) 10246(2) 00419(7) C22 11685(4) ndash03077(3) 07914(3) 00584(10) C23 11726(3) ndash01969(3) 09372(2) 00426(7) C24 12742(4) ndash00933(4) 07624(3) 00640(12) C25 05777(3) 06657(3) 020261(18) 00348(6) C26 02610(3) 07629(2) 016564(17) 00292(5) C27 04355(3) 05272(3) 012760(18) 00347(6) C28 ndash00272(3) 07195(2) 03194(2) 00360(6) C29 00487(3) 05542(3) 019882(18) 00344(6) C30 ndash00786(3) 04816(2) 037272(18) 00278(5) C31 06994(4) ndash00612(3) 05062(2) 00432(7) C32 08520(4) ndash00698(3) 05033(2) 00407(7) C33 09085(3) ndash01473(3) 05788(2) 00407(7) C34 07922(4) ndash01879(3) 06277(2) 00424(7) C35 06647(4) ndash01370(3) 05833(2) 00403(7)

- 93 -

Table 43 Bond Lengths (Aring) for Complex 19

Atom1 Atom2 Length

Co1 C5 1993(3) Co1 C6 2023(3) Co1 C17 2022(2) Co1 C18 2009(3) Co1 C31 2042(4) Co1 C32 2075(3) Co1 C33 2062(3) Co1 C34 2042(4) Co1 C35 2048(4) Si1 C2 1886(2) Si1 C19 1877(3) Si1 C20 1863(2) Si1 C21 1865(4) Si2 C3 1889(3) Si2 C22 1876(5) Si2 C23 1862(3) Si2 C24 1865(4) Si3 C11 1901(2) Si3 C25 1876(4) Si3 C26 1867(2) Si3 C27 1875(4) Si4 C12 1889(2) Si4 C28 1860(3) Si4 C29 1868(3) Si4 C30 1870(3) C1 C2 1384(4) C1 C18 1411(3) C2 C3 1474(4) C3 C4 1384(3) C4 C5 1408(3) C5 C6 1480(3) C5 C18 1448(3) C6 C7 1437(3) C6 C17 1465(4) C7 C8 1351(3) C8 C9 1495(3) C8 C15 1476(3) C9 C10 1371(3) C9 C14 1405(3) C10 C11 1423(3) C11 C12 1427(3) C12 C13 1413(3) C13 C14 1376(3)

- 94 -

C14 C15 1488(3) C15 C16 1352(3) C16 C17 1434(3) C17 C18 1468(3) C31 C32 1416(6) C31 C35 1419(4) C32 C33 1401(4) C33 C34 1411(5) C34 C35 1386(5)

Table 44 Bond Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 4325(9) C5 Co1 C17 621(1) C5 Co1 C18 4240(9) C5 Co1 C31 1629(1) C5 Co1 C32 1271(1) C5 Co1 C33 1102(1) C5 Co1 C34 1223(1) C5 Co1 C35 1556(1) C6 Co1 C17 425(1) C6 Co1 C18 6191(9) C6 Co1 C31 1253(1) C6 Co1 C32 1164(1) C6 Co1 C33 1329(1) C6 Co1 C34 1651(1) C6 Co1 C35 1550(1) C17 Co1 C18 427(1) C17 Co1 C31 1204(1) C17 Co1 C32 1451(1) C17 Co1 C33 1722(1) C17 Co1 C34 1419(1) C17 Co1 C35 1194(1) C18 Co1 C31 1517(1) C18 Co1 C32 1676(1) C18 Co1 C33 1312(1) C18 Co1 C34 1112(1) C18 Co1 C35 1198(1) C31 Co1 C32 402(1) C31 Co1 C33 673(1) C31 Co1 C34 675(1) C31 Co1 C35 406(1) C32 Co1 C33 396(1) C32 Co1 C34 672(1)

- 95 -

C32 Co1 C35 675(1) C33 Co1 C34 402(1) C33 Co1 C35 671(1) C34 Co1 C35 396(1) C2 Si1 C19 1085(1) C2 Si1 C20 1157(1) C2 Si1 C21 1096(1) C19 Si1 C20 1035(1) C19 Si1 C21 1081(2) C20 Si1 C21 1110(2) C3 Si2 C22 1071(2) C3 Si2 C23 1162(1) C3 Si2 C24 1100(2) C22 Si2 C23 1110(2) C22 Si2 C24 1067(2) C23 Si2 C24 1056(2) C11 Si3 C25 1077(1) C11 Si3 C26 1177(1) C11 Si3 C27 1083(1) C25 Si3 C26 1045(1) C25 Si3 C27 1086(1) C26 Si3 C27 1097(1) C12 Si4 C28 1099(1) C12 Si4 C29 1132(1) C12 Si4 C30 1101(1) C28 Si4 C29 1119(1) C28 Si4 C30 1066(1) C29 Si4 C30 1048(1) C2 C1 C18 1193(2) Si1 C2 C1 1130(2) Si1 C2 C3 1270(2) C1 C2 C3 1198(2) Si2 C3 C2 1260(2) Si2 C3 C4 1124(2) C2 C3 C4 1208(2) C3 C4 C5 1192(2) Co1 C5 C4 1188(2) Co1 C5 C6 695(1) Co1 C5 C18 694(1) C4 C5 C6 1498(2) C4 C5 C18 1200(2) C6 C5 C18 902(2) Co1 C6 C5 673(1) Co1 C6 C7 1267(2) Co1 C6 C17 687(1) C5 C6 C7 1474(2)

- 96 -

C5 C6 C17 893(2) C7 C6 C17 1227(2) C6 C7 C8 1121(2) C7 C8 C9 1461(2) C7 C8 C15 1251(2) C9 C8 C15 885(2) C8 C9 C10 1471(2) C8 C9 C14 912(2) C10 C9 C14 1214(2) C9 C10 C11 1186(2) Si3 C11 C10 1116(2) Si3 C11 C12 1283(2) C10 C11 C12 1197(2) Si4 C12 C11 1264(2) Si4 C12 C13 1135(2) C11 C12 C13 1201(2) C12 C13 C14 1185(2) C9 C14 C13 1216(2) C9 C14 C15 915(2) C13 C14 C15 1465(2) C8 C15 C14 888(2) C8 C15 C16 1250(2) C14 C15 C16 1458(2) C15 C16 C17 1118(2) Co1 C17 C6 688(1) Co1 C17 C16 1265(2) Co1 C17 C18 682(1) C6 C17 C16 1233(2) C6 C17 C18 900(2) C16 C17 C18 1460(2) Co1 C18 C1 1229(2) Co1 C18 C5 682(1) Co1 C18 C17 691(1) C1 C18 C5 1206(2) C1 C18 C17 1487(2) C5 C18 C17 905(2) Co1 C31 C32 712(2) Co1 C31 C35 699(2) C32 C31 C35 1077(3) Co1 C32 C31 686(2) Co1 C32 C33 697(2) C31 C32 C33 1076(3) Co1 C33 C32 707(2) Co1 C33 C34 691(2) C32 C33 C34 1081(3) Co1 C34 C33 707(2)

- 97 -

Co1 C34 C35 704(2) C33 C34 C35 1086(3) Co1 C35 C31 695(2) Co1 C35 C34 700(2) C31 C35 C34 1079(3)

Table 44 Torsion Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 ndash1479(3) C6 Co1 C5 C18 983(2) C17 Co1 C5 C4 1630(2) C17 Co1 C5 C6 ndash491(1) C17 Co1 C5 C18 492(1) C18 Co1 C5 C4 1138(2) C18 Co1 C5 C6 ndash983(2) C31 Co1 C5 C4 ndash941(4) C31 Co1 C5 C6 538(4) C31 Co1 C5 C18 1522(4) C32 Co1 C5 C4 ndash573(2) C32 Co1 C5 C6 906(2) C32 Co1 C5 C18 ndash1710(2) C33 Co1 C5 C4 ndash160(2) C33 Co1 C5 C6 1319(1) C33 Co1 C5 C18 ndash1297(2) C34 Co1 C5 C4 271(2) C34 Co1 C5 C6 1750(2) C34 Co1 C5 C18 ndash866(2) C35 Co1 C5 C4 629(4) C35 Co1 C5 C6 ndash1492(3) C35 Co1 C5 C18 ndash509(3) C5 Co1 C6 C7 1458(3) C5 Co1 C6 C17 ndash986(2) C17 Co1 C6 C5 986(2) C17 Co1 C6 C7 ndash1156(3) C18 Co1 C6 C5 491(1) C18 Co1 C6 C7 ndash1650(2) C18 Co1 C6 C17 ndash494(1) C31 Co1 C6 C5 ndash1631(2) C31 Co1 C6 C7 ndash173(3) C31 Co1 C6 C17 983(2) C32 Co1 C6 C5 ndash1170(2) C32 Co1 C6 C7 288(2) C32 Co1 C6 C17 1444(2) C33 Co1 C6 C5 ndash725(2)

- 98 -

C33 Co1 C6 C7 734(3) C33 Co1 C6 C17 ndash1710(2) C34 Co1 C6 C5 ndash166(5) C34 Co1 C6 C7 1293(5) C34 Co1 C6 C17 ndash1151(5) C35 Co1 C6 C5 1499(3) C35 Co1 C6 C7 ndash642(4) C35 Co1 C6 C17 514(3) C5 Co1 C17 C6 501(1) C5 Co1 C17 C16 1666(3) C5 Co1 C17 C18 ndash489(1) C6 Co1 C17 C16 1165(3) C6 Co1 C17 C18 ndash989(2) C18 Co1 C17 C6 989(2) C18 Co1 C17 C16 ndash1446(3) C31 Co1 C17 C6 ndash1106(2) C31 Co1 C17 C16 59(3) C31 Co1 C17 C18 1505(2) C32 Co1 C17 C6 ndash656(3) C32 Co1 C17 C16 510(3) C32 Co1 C17 C18 ndash1645(2) C33 Co1 C17 C6 571(9) C33 Co1 C17 C16 1736(8) C33 Co1 C17 C18 ndash418(9) C34 Co1 C17 C6 1578(2) C34 Co1 C17 C16 ndash857(3) C34 Co1 C17 C18 589(2) C35 Co1 C17 C6 ndash1578(2) C35 Co1 C17 C16 ndash413(3) C35 Co1 C17 C18 1033(2) C5 Co1 C18 C1 ndash1133(3) C5 Co1 C18 C17 993(2) C6 Co1 C18 C1 ndash1635(2) C6 Co1 C18 C5 ndash502(1) C6 Co1 C18 C17 491(1) C17 Co1 C18 C1 1474(3) C17 Co1 C18 C5 ndash993(2) C31 Co1 C18 C1 836(3) C31 Co1 C18 C5 ndash1632(2) C31 Co1 C18 C17 ndash638(3) C32 Co1 C18 C1 ndash779(6) C32 Co1 C18 C5 353(6) C32 Co1 C18 C17 1346(5) C33 Co1 C18 C1 ndash395(3) C33 Co1 C18 C5 737(2) C33 Co1 C18 C17 1731(2)

- 99 -

C34 Co1 C18 C1 20(2) C34 Co1 C18 C5 1152(2) C34 Co1 C18 C17 ndash1455(2) C35 Co1 C18 C1 451(3) C35 Co1 C18 C5 1583(2) C35 Co1 C18 C17 ndash1023(2) C5 Co1 C31 C32 478(5) C5 Co1 C31 C35 1656(4) C6 Co1 C31 C32 904(2) C6 Co1 C31 C35 ndash1517(2) C17 Co1 C31 C32 1412(2) C17 Co1 C31 C35 ndash1010(2) C18 Co1 C31 C32 ndash1739(2) C18 Co1 C31 C35 ndash561(3) C32 Co1 C31 C35 1179(3) C33 Co1 C31 C32 ndash370(2) C33 Co1 C31 C35 808(2) C34 Co1 C31 C32 ndash808(2) C34 Co1 C31 C35 371(2) C35 Co1 C31 C32 ndash1179(3) C5 Co1 C32 C31 ndash1642(2) C5 Co1 C32 C33 764(2) C6 Co1 C32 C31 ndash1143(2) C6 Co1 C32 C33 1263(2) C17 Co1 C32 C31 ndash710(3) C17 Co1 C32 C33 1697(2) C18 Co1 C32 C31 1666(5) C18 Co1 C32 C33 472(6) C31 Co1 C32 C33 ndash1194(3) C33 Co1 C32 C31 1194(3) C34 Co1 C32 C31 816(2) C34 Co1 C32 C33 ndash377(2) C35 Co1 C32 C31 385(2) C35 Co1 C32 C33 ndash808(2) C5 Co1 C33 C32 ndash1243(2) C5 Co1 C33 C34 1166(2) C6 Co1 C33 C32 ndash802(2) C6 Co1 C33 C34 1607(2) C17 Co1 C33 C32 ndash1309(8) C17 Co1 C33 C34 1100(9) C18 Co1 C33 C32 ndash1679(2) C18 Co1 C33 C34 730(2) C31 Co1 C33 C32 376(2) C31 Co1 C33 C34 ndash815(2) C32 Co1 C33 C34 ndash1191(3) C34 Co1 C33 C32 1191(3)

- 100 -

C35 Co1 C33 C32 818(2) C35 Co1 C33 C34 ndash373(2) C5 Co1 C34 C33 ndash833(2) C5 Co1 C34 C35 1577(2) C6 Co1 C34 C33 ndash700(5) C6 Co1 C34 C35 1711(4) C17 Co1 C34 C33 ndash1681(2) C17 Co1 C34 C35 730(3) C18 Co1 C34 C33 ndash1295(2) C18 Co1 C34 C35 1115(2) C31 Co1 C34 C33 809(2) C31 Co1 C34 C35 ndash380(2) C32 Co1 C34 C33 372(2) C32 Co1 C34 C35 ndash818(2) C33 Co1 C34 C35 ndash1189(3) C35 Co1 C34 C33 1189(3) C5 Co1 C35 C31 ndash1699(3) C5 Co1 C35 C34 ndash508(4) C6 Co1 C35 C31 663(4) C6 Co1 C35 C34 ndash1746(2) C17 Co1 C35 C31 1036(2) C17 Co1 C35 C34 ndash1373(2) C18 Co1 C35 C31 1531(2) C18 Co1 C35 C34 ndash878(2) C31 Co1 C35 C34 1191(3) C32 Co1 C35 C31 ndash382(2) C32 Co1 C35 C34 809(2) C33 Co1 C35 C31 ndash812(2) C33 Co1 C35 C34 378(2) C34 Co1 C35 C31 ndash1191(3) C19 Si1 C2 C1 118(2) C19 Si1 C2 C3 ndash1731(2) C20 Si1 C2 C1 1275(2) C20 Si1 C2 C3 ndash574(3) C21 Si1 C2 C1 ndash1061(2) C21 Si1 C2 C3 690(3) C22 Si2 C3 C2 714(3) C22 Si2 C3 C4 ndash988(2) C23 Si2 C3 C2 ndash532(3) C23 Si2 C3 C4 1365(2) C24 Si2 C3 C2 ndash1731(3) C24 Si2 C3 C4 167(3) C25 Si3 C11 C10 ndash241(2) C25 Si3 C11 C12 1624(2) C26 Si3 C11 C10 ndash1417(2) C26 Si3 C11 C12 447(3)

- 101 -

C27 Si3 C11 C10 932(2) C27 Si3 C11 C12 ndash804(2) C28 Si4 C12 C11 ndash731(2) C28 Si4 C12 C13 1055(2) C29 Si4 C12 C11 529(2) C29 Si4 C12 C13 ndash1285(2) C30 Si4 C12 C11 1698(2) C30 Si4 C12 C13 ndash116(2) C18 C1 C2 Si1 1755(2) C18 C1 C2 C3 00(4) C2 C1 C18 Co1 784(3) C2 C1 C18 C5 ndash41(4) C2 C1 C18 C17 ndash1772(4) Si1 C2 C3 Si2 198(4) Si1 C2 C3 C4 ndash1707(2) C1 C2 C3 Si2 ndash1654(2) C1 C2 C3 C4 41(4) Si2 C3 C4 C5 1668(2) C2 C3 C4 C5 ndash40(4) C3 C4 C5 Co1 ndash816(3) C3 C4 C5 C6 1799(4) C3 C4 C5 C18 ndash01(4) Co1 C5 C6 C7 ndash1233(4) Co1 C5 C6 C17 671(1) C4 C5 C6 Co1 1122(4) C4 C5 C6 C7 ndash112(7) C4 C5 C6 C17 1793(4) C18 C5 C6 Co1 ndash678(1) C18 C5 C6 C7 1688(4) C18 C5 C6 C17 ndash07(2) Co1 C5 C18 C1 1164(2) Co1 C5 C18 C17 ndash672(1) C4 C5 C18 Co1 ndash1121(2) C4 C5 C18 C1 42(3) C4 C5 C18 C17 ndash1793(2) C6 C5 C18 Co1 679(1) C6 C5 C18 C1 ndash1757(2) C6 C5 C18 C17 07(2) Co1 C6 C7 C8 858(2) C5 C6 C7 C8 ndash1683(3) C17 C6 C7 C8 ndash08(3) Co1 C6 C17 C16 ndash1205(2) Co1 C6 C17 C18 665(1) C5 C6 C17 Co1 ndash658(1) C5 C6 C17 C16 1736(2) C5 C6 C17 C18 07(2)

- 102 -

C7 C6 C17 Co1 1209(2) C7 C6 C17 C16 03(4) C7 C6 C17 C18 ndash1726(2) C6 C7 C8 C9 ndash1697(3) C6 C7 C8 C15 09(3) C7 C8 C9 C10 05(7) C7 C8 C9 C14 1728(4) C15 C8 C9 C10 ndash1718(4) C15 C8 C9 C14 05(2) C7 C8 C15 C14 ndash1752(2) C7 C8 C15 C16 ndash06(4) C9 C8 C15 C14 ndash04(2) C9 C8 C15 C16 1742(2) C8 C9 C10 C11 1714(3) C14 C9 C10 C11 05(3) C8 C9 C14 C13 ndash1756(2) C8 C9 C14 C15 ndash05(2) C10 C9 C14 C13 ndash06(4) C10 C9 C14 C15 1746(2) C9 C10 C11 Si3 ndash1741(2) C9 C10 C11 C12 01(3) Si3 C11 C12 Si4 ndash90(3) Si3 C11 C12 C13 1725(2) C10 C11 C12 Si4 1779(2) C10 C11 C12 C13 ndash07(3) Si4 C12 C13 C14 ndash1781(2) C11 C12 C13 C14 06(3) C12 C13 C14 C9 ndash00(3) C12 C13 C14 C15 ndash1713(3) C9 C14 C15 C8 05(2) C9 C14 C15 C16 ndash1717(4) C13 C14 C15 C8 1730(4) C13 C14 C15 C16 09(7) C8 C15 C16 C17 00(3) C14 C15 C16 C17 1704(3) C15 C16 C17 Co1 ndash870(3) C15 C16 C17 C6 01(3) C15 C16 C17 C18 1674(4) Co1 C17 C18 C1 ndash1195(4) Co1 C17 C18 C5 664(1) C6 C17 C18 Co1 ndash671(1) C6 C17 C18 C1 1734(4) C6 C17 C18 C5 ndash07(2) C16 C17 C18 Co1 1235(4) C16 C17 C18 C1 40(7) C16 C17 C18 C5 ndash1701(4)

- 103 -

Co1 C31 C32 C33 590(2) C35 C31 C32 Co1 ndash607(2) C35 C31 C32 C33 ndash16(4) Co1 C31 C35 C34 ndash596(3) C32 C31 C35 Co1 615(3) C32 C31 C35 C34 18(4) Co1 C32 C33 C34 592(2) C31 C32 C33 Co1 ndash583(2) C31 C32 C33 C34 09(4) Co1 C33 C34 C35 605(3) C32 C33 C34 Co1 ndash602(2) C32 C33 C34 C35 03(4) Co1 C34 C35 C31 593(3) C33 C34 C35 Co1 ndash606(2) C33 C34 C35 C31 ndash13(4)

23-Bis(trimethylsilyl) linear [3]phenylene(CpCo) 52

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (029 g 085 mmol)27 in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (014 g 101 mmol) The mixture was stirred for 15 h and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the yellow residue dissolved in ether (30 mL) Aqueous workup with sat NaCl (2 x 20 mL) followed by drying over MgSO4 and concentration in vacuo provided a yellow solid This material was redissolved in THF (15 mL) degassed (Ar) and CpCo(CO)2 (0140 g 078 mmol) added The resulting solution (protected from light with foil) was injected (syringe pump) over 8 h into a boiling mixture of THF (200 mL) and BTMSA (50 mL) while irradiating with a slide projection lamp Once addition was complete heating and irradiation were continued for another 14 h The volatiles were removed via vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (4 x 4 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed in vacuo and the residue crystallized from acetone yielding 52 (024 g 57 ) as dark red crystals mp 198ndash202 degC (decomp) 1H-NMR (500 MHz C6D6) δ = 796 (s 2 H) 678 (AArsquom 2 H) 675 (s 2 H) 674 (BBrsquom 2 H) 436 (s 5 H) 037 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1426 1393

1360 1294 1194 1149 802 779 738 268 ppm IR (neat) ν~ = 2960 2923 2853 1461 1455 1378 1260 1093 1019 800 cmndash1 UV-VIS (hexane) λmax (log ε) = 255 (393) 282 (376) 293 (sh 378) 308 (389) 348 (390) 397 (sh 335) 436 (301) 511

CoSiMe3

SiMe3

- 104 -

(262) MS (70 eV) mz () 494 (100) [M+] 370 (14) HRMS (FAB) calcd for C29H31CoSi2 4941296 found 4941292 Elemental analysis calcd for C29H31CoSi2 C 7041 H 632 found 7048 628 Crystallographic information for 52 (H atoms omitted)

Table 45 Crystal Data and Structure Refinement For 52

Empirical formula C29H31CoSi2 Formula weight 49465 cryst size (mm) 030 x 020 x 005 cryst syst Monoclinic refl used for unit cell determination 2640 2 θ range (deg) 242ndash2503 a (Aring) 4391(3) b (Aring) 7472(4) c (Aring) 16869(11) α (deg)

β (deg) 111522(11) γ (deg) V (Aring3) 5149(6) space group C2c Z 8 Dcalc gcm

3 1276

F000 2080 micro cmndash1 774

temp ordmC ndash153

Tmax Tmin 0963 0800 no of total rflns 18401 no of unique rflns 2640 no of obsd rflns 4266 no of variables 271 Reflection to Parameter Ratio 974 R 00892 Rw 02042 Rall 01248 GOF 1008 Max Peak in Final Diff Map (endash Aring3) 1051 Min Peak in Final Diff Map (endash Aring3) ndash0707

- 105 -

Figure 42 ORTEP representation of 52

- 106 -

Table 46 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 52 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y z U(eq)

Co1 006961(2) 087577(12) 038136(6) 00200(3) Si1 018827(6) 08761(5) 063753(18) 00627(9) Si2 018540(5) 05425(3) 046900(16) 00410(6) C1 012151(19) 08410(10) 05589(5) 00310(17) C2 015018(13) 07767(11) 05552(4) 00343(18) C3 015002(14) 06417(10) 04926(5) 00324(17) C4 011985(17) 05770(9) 04357(4) 00247(16) C5 009030(17) 06465(9) 04383(4) 00220(14) C6 005450(16) 06378(9) 04077(4) 00216(14) C7 002537(17) 05420(9) 03591(4) 00224(15) C8 ndash000060(18) 05847(9) 03798(4) 00246(15) C9 ndash003560(17) 05555(10) 03644(4) 00256(16) C10 ndash006399(18) 04581(10) 03174(4) 00284(17) C11 ndash009208(19) 05019(12) 03360(5) 00344(18) C12 ndash009130(19) 06274(12) 03957(5) 00340(18) C13 ndash006300(17) 07256(11) 04422(5) 00294(17) C14 ndash003558(19) 06826(10) 04247(4) 00274(16) C15 000008(18) 07212(10) 04449(4) 00251(16) C16 002653(17) 08159(10) 04925(4) 00234(15) C17 005500(17) 07741(9) 04722(4) 00231(15) C18 009090(17) 07798(10) 05007(4) 00247(15) C19 01766(3) 10793(15) 06845(9) 0098(3) C20 02181(3) 0957(2) 05901(7) 0098(3) C21 02076(3) 07068(14) 07228(7) 0098(3) C22 01946(2) 06941(13) 03925(6) 00631(17) C23 01724(2) 03224(9) 04142(7) 00631(17) C24 022363(17) 04883(16) 05614(5) 00631(17) C25 007501(19) 09264(10) 02652(4) 00281(17) C26 004279(18) 09614(10) 02593(4) 00264(16) C27 004343(18) 10945(10) 03211(4) 00271(16) C28 007584(19) 11429(10) 03645(5) 00296(17) C29 00960(2) 10392(11) 03322(5) 00321(17)

Table 47 Bond Lengths (Aring) for Complex 52

Atom1 Atom2 Length

Co1 C5 2011(7) Co1 C6 2004(7) Co1 C17 2014(8) Co1 C18 2015(6) Co1 C25 2093(8)

- 107 -

Co1 C26 2063(6) Co1 C27 2042(7) Co1 C28 2049(8) Co1 C29 206(1) Si1 C2 1890(6) Si1 C19 187(1) Si1 C20 187(2) Si1 C21 187(1) Si2 C3 1891(8) Si2 C22 187(1) Si2 C23 1870(8) Si2 C24 1869(7) C1 C2 137(1) C1 C18 1418(9) C2 C3 146(1) C3 C4 1406(8) C4 C5 141(1) C5 C6 147(1) C5 C18 144(1) C6 C7 1432(9) C6 C17 148(1) C7 C8 135(1) C8 C9 148(1) C8 C15 149(1) C9 C10 1410(9) C9 C14 139(1) C10 C11 142(1) C11 C12 137(1) C12 C13 141(1) C13 C14 138(1) C14 C15 150(1) C15 C16 1345(9) C16 C17 145(1) C17 C18 147(1) C25 C26 141(1) C25 C29 144(1) C26 C27 143(1) C27 C28 139(1) C28 C29 143(1)

Table 48 Bond Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 428(3) C5 Co1 C17 619(3)

- 108 -

C5 Co1 C18 420(3) C5 Co1 C25 1145(3) C5 Co1 C26 1372(3) C5 Co1 C27 1733(3) C5 Co1 C28 1468(3) C5 Co1 C29 1184(3) C6 Co1 C17 434(3) C6 Co1 C18 621(3) C6 Co1 C25 1219(3) C6 Co1 C26 1125(3) C6 Co1 C27 1305(3) C6 Co1 C28 1653(3) C6 Co1 C29 1539(3) C17 Co1 C18 428(3) C17 Co1 C25 1632(3) C17 Co1 C26 1307(3) C17 Co1 C27 1137(3) C17 Co1 C28 1247(3) C17 Co1 C29 1562(3) C18 Co1 C25 1460(3) C18 Co1 C26 1733(3) C18 Co1 C27 1388(3) C18 Co1 C28 1167(3) C18 Co1 C29 1194(3) C25 Co1 C26 395(3) C25 Co1 C27 680(3) C25 Co1 C28 681(3) C25 Co1 C29 406(3) C26 Co1 C27 409(3) C26 Co1 C28 674(3) C26 Co1 C29 672(3) C27 Co1 C28 397(3) C27 Co1 C29 678(3) C28 Co1 C29 407(3) C2 Si1 C19 1089(5) C2 Si1 C20 1125(5) C2 Si1 C21 1092(4) C19 Si1 C20 1053(6) C19 Si1 C21 1100(6) C20 Si1 C21 1109(6) C3 Si2 C22 1081(4) C3 Si2 C23 1089(4) C3 Si2 C24 1177(4) C22 Si2 C23 1072(4) C22 Si2 C24 1106(4) C23 Si2 C24 1039(4)

- 109 -

C2 C1 C18 1206(7) Si1 C2 C1 1141(5) Si1 C2 C3 1249(5) C1 C2 C3 1210(7) Si2 C3 C2 1296(5) Si2 C3 C4 1113(5) C2 C3 C4 1190(6) C3 C4 C5 1199(6) Co1 C5 C4 1239(5) Co1 C5 C6 684(4) Co1 C5 C18 692(4) C4 C5 C6 1484(7) C4 C5 C18 1203(6) C6 C5 C18 910(6) Co1 C6 C5 688(4) Co1 C6 C7 1280(5) Co1 C6 C17 687(4) C5 C6 C7 1473(6) C5 C6 C17 892(5) C7 C6 C17 1222(6) C6 C7 C8 1133(6) C7 C8 C9 1475(7) C7 C8 C15 1242(7) C9 C8 C15 882(6) C8 C9 C10 1454(7) C8 C9 C14 928(6) C10 C9 C14 1218(7) C9 C10 C11 1147(7) C10 C11 C12 1222(8) C11 C12 C13 1231(8) C12 C13 C14 1149(7) C9 C14 C13 1233(7) C9 C14 C15 910(6) C13 C14 C15 1457(7) C8 C15 C14 879(6) C8 C15 C16 1254(7) C14 C15 C16 1467(7) C15 C16 C17 1121(6) Co1 C17 C6 679(4) Co1 C17 C16 1300(5) Co1 C17 C18 686(4) C6 C17 C16 1227(6) C6 C17 C18 892(5) C16 C17 C18 1464(7) Co1 C18 C1 1235(5) Co1 C18 C5 688(4)

- 110 -

Co1 C18 C17 686(4) C1 C18 C5 1191(7) C1 C18 C17 1500(7) C5 C18 C17 906(6) Co1 C25 C26 691(4) Co1 C25 C29 683(4) C26 C25 C29 1065(7) Co1 C26 C25 714(4) Co1 C26 C27 688(4) C25 C26 C27 1091(6) Co1 C27 C26 704(4) Co1 C27 C28 704(5) C26 C27 C28 1079(7) Co1 C28 C27 699(5) Co1 C28 C29 699(5) C27 C28 C29 1085(7) Co1 C29 C25 711(5) Co1 C29 C28 694(5) C25 C29 C28 1080(7)

Table 49 Torsion Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 1468(8) C6 Co1 C5 C18 ndash999(5) C17 Co1 C5 C4 ndash1627(7) C17 Co1 C5 C6 504(4) C17 Co1 C5 C18 ndash494(4) C18 Co1 C5 C4 ndash1133(8) C18 Co1 C5 C6 999(5) C25 Co1 C5 C4 356(7) C25 Co1 C5 C6 ndash1113(4) C25 Co1 C5 C18 1489(4) C26 Co1 C5 C4 765(7) C26 Co1 C5 C6 ndash703(5) C26 Co1 C5 C18 ndash1702(4) C27 Co1 C5 C4 146(2) C27 Co1 C5 C6 ndash1(3) C27 Co1 C5 C18 ndash101(2) C28 Co1 C5 C4 ndash515(9) C28 Co1 C5 C6 1617(5) C28 Co1 C5 C18 619(7) C29 Co1 C5 C4 ndash98(7) C29 Co1 C5 C6 ndash1567(4) C29 Co1 C5 C18 1035(5)

- 111 -

C5 Co1 C6 C7 ndash1474(8) C5 Co1 C6 C17 977(5) C17 Co1 C6 C5 ndash977(5) C17 Co1 C6 C7 1149(8) C18 Co1 C6 C5 ndash482(4) C18 Co1 C6 C7 1644(7) C18 Co1 C6 C17 495(4) C25 Co1 C6 C5 927(5) C25 Co1 C6 C7 ndash547(7) C25 Co1 C6 C17 ndash1696(4) C26 Co1 C6 C5 1362(4) C26 Co1 C6 C7 ndash112(7) C26 Co1 C6 C17 ndash1261(4) C27 Co1 C6 C5 1799(4) C27 Co1 C6 C7 325(8) C27 Co1 C6 C17 ndash824(5) C28 Co1 C6 C5 ndash137(1) C28 Co1 C6 C7 75(1) C28 Co1 C6 C17 ndash40(1) C29 Co1 C6 C5 523(8) C29 Co1 C6 C7 ndash951(9) C29 Co1 C6 C17 1501(7) C5 Co1 C17 C6 ndash497(4) C5 Co1 C17 C16 ndash1646(8) C5 Co1 C17 C18 484(4) C6 Co1 C17 C16 ndash1149(8) C6 Co1 C17 C18 981(5) C18 Co1 C17 C6 ndash981(5) C18 Co1 C17 C16 1470(9) C25 Co1 C17 C6 32(1) C25 Co1 C17 C16 ndash83(1) C25 Co1 C17 C18 130(1) C26 Co1 C17 C6 799(5) C26 Co1 C17 C16 ndash350(8) C26 Co1 C17 C18 1780(4) C27 Co1 C17 C6 1245(4) C27 Co1 C17 C16 97(8) C27 Co1 C17 C18 ndash1373(4) C28 Co1 C17 C6 1686(4) C28 Co1 C17 C16 538(8) C28 Co1 C17 C18 ndash932(5) C29 Co1 C17 C6 ndash1471(7) C29 Co1 C17 C16 98(1) C29 Co1 C17 C18 ndash489(9) C5 Co1 C18 C1 1117(8) C5 Co1 C18 C17 ndash995(5)

- 112 -

C6 Co1 C18 C1 1609(7) C6 Co1 C18 C5 492(4) C6 Co1 C18 C17 ndash502(4) C17 Co1 C18 C1 ndash1488(8) C17 Co1 C18 C5 995(5) C25 Co1 C18 C1 544(9) C25 Co1 C18 C5 ndash573(7) C25 Co1 C18 C17 ndash1568(5) C26 Co1 C18 C1 ndash162(2) C26 Co1 C18 C5 87(3) C26 Co1 C18 C17 ndash13(3) C27 Co1 C18 C1 ndash784(8) C27 Co1 C18 C5 1699(4) C27 Co1 C18 C17 705(6) C28 Co1 C18 C1 ndash356(7) C28 Co1 C18 C5 ndash1473(4) C28 Co1 C18 C17 1133(4) C29 Co1 C18 C1 107(8) C29 Co1 C18 C5 ndash1010(5) C29 Co1 C18 C17 1595(4) C5 Co1 C25 C26 1356(4) C5 Co1 C25 C29 ndash1058(5) C6 Co1 C25 C26 873(5) C6 Co1 C25 C29 ndash1540(5) C17 Co1 C25 C26 62(1) C17 Co1 C25 C29 ndash1796(9) C18 Co1 C25 C26 1738(5) C18 Co1 C25 C29 ndash675(7) C26 Co1 C25 C29 1187(6) C27 Co1 C25 C26 ndash376(4) C27 Co1 C25 C29 810(5) C28 Co1 C25 C26 ndash806(5) C28 Co1 C25 C29 381(5) C29 Co1 C25 C26 ndash1187(6) C5 Co1 C26 C25 ndash696(6) C5 Co1 C26 C27 1703(4) C6 Co1 C26 C25 ndash1134(5) C6 Co1 C26 C27 1265(4) C17 Co1 C26 C25 ndash1604(4) C17 Co1 C26 C27 795(5) C18 Co1 C26 C25 ndash149(2) C18 Co1 C26 C27 91(3) C25 Co1 C26 C27 ndash1201(6) C27 Co1 C26 C25 1201(6) C28 Co1 C26 C25 825(5) C28 Co1 C26 C27 ndash376(4)

- 113 -

C29 Co1 C26 C25 383(5) C29 Co1 C26 C27 ndash818(5) C5 Co1 C27 C26 ndash77(3) C5 Co1 C27 C28 165(2) C6 Co1 C27 C26 ndash774(5) C6 Co1 C27 C28 1644(5) C17 Co1 C27 C26 ndash1254(4) C17 Co1 C27 C28 1163(5) C18 Co1 C27 C26 ndash1698(5) C18 Co1 C27 C28 720(6) C25 Co1 C27 C26 364(4) C25 Co1 C27 C28 ndash818(5) C26 Co1 C27 C28 ndash1182(6) C28 Co1 C27 C26 1182(6) C29 Co1 C27 C26 804(5) C29 Co1 C27 C28 ndash378(5) C5 Co1 C28 C27 ndash1768(5) C5 Co1 C28 C29 637(7) C6 Co1 C28 C27 ndash54(1) C6 Co1 C28 C29 ndash173(1) C17 Co1 C28 C27 ndash861(5) C17 Co1 C28 C29 1544(5) C18 Co1 C28 C27 ndash1355(5) C18 Co1 C28 C29 1050(5) C25 Co1 C28 C27 815(5) C25 Co1 C28 C29 ndash380(5) C26 Co1 C28 C27 387(4) C26 Co1 C28 C29 ndash809(5) C27 Co1 C28 C29 ndash1195(7) C29 Co1 C28 C27 1195(7) C5 Co1 C29 C25 953(5) C5 Co1 C29 C28 ndash1461(5) C6 Co1 C29 C25 576(9) C6 Co1 C29 C28 1762(6) C17 Co1 C29 C25 1797(7) C17 Co1 C29 C28 ndash617(9) C18 Co1 C29 C25 1437(4) C18 Co1 C29 C28 ndash977(5) C25 Co1 C29 C28 1186(7) C26 Co1 C29 C25 ndash373(4) C26 Co1 C29 C28 813(5) C27 Co1 C29 C25 ndash817(5) C27 Co1 C29 C28 369(5) C28 Co1 C29 C25 ndash1186(7) C19 Si1 C2 C1 ndash144(8) C19 Si1 C2 C3 1663(7)

- 114 -

C20 Si1 C2 C1 ndash1307(7) C20 Si1 C2 C3 500(8) C21 Si1 C2 C1 1057(7) C21 Si1 C2 C3 ndash736(7) C22 Si2 C3 C2 ndash852(7) C22 Si2 C3 C4 908(6) C23 Si2 C3 C2 1587(7) C23 Si2 C3 C4 ndash253(7) C24 Si2 C3 C2 410(8) C24 Si2 C3 C4 ndash1431(6) C18 C1 C2 Si1 1795(6) C18 C1 C2 C3 ndash1(1) C2 C1 C18 Co1 ndash817(9) C2 C1 C18 C5 1(1) C2 C1 C18 C17 173(1) Si1 C2 C3 Si2 ndash5(1) Si1 C2 C3 C4 1790(5) C1 C2 C3 Si2 1755(6) C1 C2 C3 C4 ndash0(1) Si2 C3 C4 C5 ndash1747(5) C2 C3 C4 C5 2(1) C3 C4 C5 Co1 822(8) C3 C4 C5 C6 ndash174(1) C3 C4 C5 C18 ndash2(1) Co1 C5 C6 C7 128(1) Co1 C5 C6 C17 ndash674(4) C4 C5 C6 Co1 ndash120(1) C4 C5 C6 C7 8(2) C4 C5 C6 C17 173(1) C18 C5 C6 Co1 671(4) C18 C5 C6 C7 ndash165(1) C18 C5 C6 C17 ndash03(6) Co1 C5 C18 C1 ndash1175(7) Co1 C5 C18 C17 667(4) C4 C5 C18 Co1 1179(7) C4 C5 C18 C1 0(1) C4 C5 C18 C17 ndash1754(7) C6 C5 C18 Co1 ndash663(4) C6 C5 C18 C1 1762(7) C6 C5 C18 C17 04(6) Co1 C6 C7 C8 ndash887(8) C5 C6 C7 C8 160(1) C17 C6 C7 C8 ndash2(1) Co1 C6 C17 C16 1243(7) Co1 C6 C17 C18 ndash672(4) C5 C6 C17 Co1 675(4)

- 115 -

C5 C6 C17 C16 ndash1681(7) C5 C6 C17 C18 03(5) C7 C6 C17 Co1 ndash1223(7) C7 C6 C17 C16 2(1) C7 C6 C17 C18 1705(7) C6 C7 C8 C9 ndash180(1) C6 C7 C8 C15 2(1) C7 C8 C9 C10 2(2) C7 C8 C9 C14 ndash179(1) C15 C8 C9 C10 ndash179(1) C15 C8 C9 C14 01(6) C7 C8 C15 C14 1791(7) C7 C8 C15 C16 ndash2(1) C9 C8 C15 C14 ndash01(5) C9 C8 C15 C16 1792(8) C8 C9 C10 C11 ndash180(1) C14 C9 C10 C11 1(1) C8 C9 C14 C13 1791(7) C8 C9 C14 C15 ndash01(6) C10 C9 C14 C13 ndash1(1) C10 C9 C14 C15 1796(7) C9 C10 C11 C12 ndash1(1) C10 C11 C12 C13 1(1) C11 C12 C13 C14 ndash2(1) C12 C13 C14 C9 2(1) C12 C13 C14 C15 ndash180(1) C9 C14 C15 C8 01(6) C9 C14 C15 C16 ndash179(1) C13 C14 C15 C8 ndash179(1) C13 C14 C15 C16 2(2) C8 C15 C16 C17 1(1) C14 C15 C16 C17 ndash180(1) C15 C16 C17 Co1 858(8) C15 C16 C17 C6 ndash2(1) C15 C16 C17 C18 ndash161(1) Co1 C17 C18 C1 120(1) Co1 C17 C18 C5 ndash669(4) C6 C17 C18 Co1 666(4) C6 C17 C18 C1 ndash173(1) C6 C17 C18 C5 ndash03(5) C16 C17 C18 Co1 ndash131(1) C16 C17 C18 C1 ndash11(2) C16 C17 C18 C5 162(1) Co1 C25 C26 C27 586(5) C29 C25 C26 Co1 ndash583(5) C29 C25 C26 C27 03(9)

- 116 -

Co1 C25 C29 C28 ndash598(6) C26 C25 C29 Co1 588(5) C26 C25 C29 C28 ndash10(9) Co1 C26 C27 C28 607(5) C25 C26 C27 Co1 ndash602(5) C25 C26 C27 C28 05(9) Co1 C27 C28 C29 595(6) C26 C27 C28 Co1 ndash607(5) C26 C27 C28 C29 ndash12(9) Co1 C28 C29 C25 609(6) C27 C28 C29 Co1 ndash595(6) C27 C28 C29 C25 14(9)

Photo-thermal cycle between 52 and 53

An NMR tube containing a solution of 52 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 53 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 724 (AArsquom 2 H) 683 (s 2 H) 662 (BBrsquom 2 H) 444 (s 5 H) 032 (s 18 H) ppm 13C- NMR (100 MHz C6D6) δ = 1493 1482 1430 1276 1256 1241 1155 803 796 725 222 ppm Thermal reversal could be conveniently followed by VT-NMR

Kinetic studies of the thermal CoCp migration in 53 In the glovebox 23-[bis(trimethylsilyl)] linear[3]phenylene(CpCo) 52 dissolved in the solvent of choice (C6D6 or toluene-d8) was passed through an HPLC filter and then transfered via syringe into a thick-walled NMR tube connected to a vacuum line adapter The sample was then degassed by three freeze-pump-thaw cycles and flame-sealed under vacuum Prior to the kinetic runs the mixtures were irradiated for 10 h in a Rayonet Photochemical Reactor fitted with lamps emitting at 310 and 365 nm After this treatment care was taken to exclude ambient light as it causes some isomerization The irradiated samples were then placed in the NMR spectrometer at ndash65 degC (500 MHz) which was then warmed to the required temperature In the case of the 60 degC runs the magnet was prewarmed because of the fast reaction rate at this temperature After five min the spectra were recorded The Cp signal of the photoisomer was integrated relative to the solvent peak of C6D6 or the CD3 peak of toluene-d8 and monitored as a function of time The integral from the first scan was used as [A]o Since the equilibrium constant between the isomers was 50 the kinetic analysis treated the isomerization as a first-order non-reversible process Plotting the data accordingly

CoSiMe3

SiMe3

52

CoSiMe3

SiMe3

53

hν∆

- 117 -

yielded the reaction rate constants which were used in the Eyring plots to obtain the activation parameters Kinetic studies of the thermal haptotropic shift for complex 52 Kinetic runs were executed in C6D6 as the optimum solvent A sample of 52 in degassed C6D6 or toluene-d8 was subjected to UV light for 10 h leading to maximum enrichment of 53 The sample was kept at the specified temperature and the disappearance of 53 monitored by 1H-NMR spectroscopy The reaction proved to be first-order (eq 1) consistent with an intramolecular process

[ ] [ ]Akdt

Adminus=

(1)

[ ][ ] dtkA

Ad=minus

(2)

[ ][ ]

tkA

A=minus

0

ln (3)

The rate constant (k) at 30 40 50 and 60 degC was obtained from the slope of a plot of ndashln([A][A]0) versus time (t) following eq 2 and 3 The actual error in reproducibility was estimated by the calculation of one standard deviation (σ) for a triplicate run at 60 degC The percentage error was applied for k at 30 40 and 50 degC The rate constants and their errors are given in Tables 411 and 414 The values for k and their standard deviations were used to calculate the activation enthalpy (∆HDagger) and entropy (∆SH) of the haptotropic shift The basis for these calculations is the Eyring equation (eq 4) This expression (eq 4) was transformed to eq 5 and the activation enthalpy (∆HDagger) obtained from the slope of a plot of ndashln(kT) versus 1RT The intercept (ndashC) provides the activation entropy (∆SH) following eq 6 and 7

C

TR

H

R

S

h

k

TR

H

T

k B

minus∆

=

∆+minus

∆=minus

ne

nene

lnln

( 4)

R

S

h

kC B

ne∆+= ln

(5)

minus=∆ ne

h

kCRS Bln

(6)

- 118 -

The errors in ∆HDagger and ∆SDagger were calculated based on those in the rate constants leading to two additional least square fits in the Eyring plot These fits represent the two most extreme deviations from the original plot This provides a conservative error estimate and finally the values of 204plusmn14 kcalmol for ∆HH and 158plusmn22 eu (calmolmiddotK) for ∆SH in C6D6 In order to probe for solvent effects the kinetics were also repeated in toluene-d8 The preparation of the sample followed the described procedure and the rate constants (k) were obtained at 30 40 50 and 60 degC At 60 degC three measurements were carried out to estimate the errors in reproducibility for k and the activation parameters Error propagation was done as described for the kinetic experiments in C6D6 It is assumed that those rate constants (k) show the same relative error as the ones for the rearrangement of 53 to 52 in C6D6 The activation parameters in toluene-d8 were found to be 231plusmn07 kcalmol and 60plusmn13 eu

Table 410 Kinetic Data for the Conversion of 53 to 52 in C6D6

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09657 00349 1000 09419 00599 6000 09380 00640 2000 09018 01034 9000 09038 01012 3000 08557 01558 12000 08760 01324 4000 08176 02013 15000 08418 01723 5000 07796 02490 18000 08206 01978 6000 07555 02804 21000 08010 02219 7000 07255 03210 32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 400 09541 00470 30 09888 00113 800 09197 00837 60 09820 00181 1200 08910 01154 90 09708 00296 1600 08489 01638 120 09596 00413 2000 08298 01865 150 09506 00507 2400 07954 02289 180 09416 00602 2800 07591 02756 210 09348 00674 240 09281 00746 270 09213 00819 300 09124 00917 330 09034 01016 360 08966 01091

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

- 119 -

0 10000 00000 0 10000 00000 30 09950 00050 30 09909 00092 60 09900 00101 60 09854 00147 90 09800 00202 90 09762 00241 120 09750 00253 120 09671 00335 150 09700 00305 150 09634 00372 180 09625 00382 180 09543 00468 210 09575 00434 210 09433 00583 240 09475 00539 240 09397 00622 270 09400 00619 270 09287 00740 300 09350 00672 300 09232 00799 330 09300 00726 330 09177 00858 360 09250 00780 360 09086 00959

Table 411 The Rate Constants (k) in C6D6 Calculated From the Data in Table 410 and Their

Standard Deviations (σ)

Temp (K) k (1s) σσσσ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 10809Endash05 74258Endash07 09970 171494 00688

31315 45615Endash05 31338Endash06 09948 157420 00688

32315 95118Endash05 65346Endash06 09965 150385 00688

33315 (1) 27425Endash04 09965

33315 (2) 25714Endash04 09964

33315 (3) 30051Endash04 09990

33315 (avg) 26511Endash04 18841Endash05 140101 00688

Table 412 Activation Parameters for the Kinetic Experiments in C6D6

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 90990 85414 79291 Intercept ndash1789 ndash1674 ndash1559 R

2 09869 09869 09869

∆HDagger (Jmol) 90990 85414 79291

∆HDagger (kcalmol) 217 204 190

∆SDagger (JmolmiddotK) ndash569 ndash660 ndash751

∆SDagger (eu) ndash136 ndash158 ndash180

- 120 -

(323 15 K 50 degC) y = 95118E-05x + 44505E-03

R2 = 9965

(30315 K 30 degC) y = 10809E-05x + 20474E-03

R2 = 9970

(31315 K 40 degC) y = 45615E-05x + 11689E-02

R2 = 9948

(33315 K 60 degC) y = 263387E-04x + 390297E-04

R2 = 9992

000

005

010

015

020

025

030

035

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

Figure 43 Kinetic plots for the conversion of 53 to 52 in C6D6

Table 413 Kinetic Data for the Conversion of 53 to 52 in Toluene-d8

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09556 00454 1000 09488 00526 6000 09256 00773 2000 08931 01130 9000 08956 01103 3000 08545 01572 12000 08667 01430 4000 08143 02054 15000 08343 01811 5000 07818 02461 18000 08103 02103 6000 07559 02798 21000 07863 02404 7000 07179 03314

- 121 -

32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

000 10000 00000 0 10000 00000 40000 09470 00544 30 09887 00113 80000 08934 01127 60 09775 00228 120000 08594 01515 90 09691 00314 160000 08175 02015 120 09592 00416 200000 07861 02406 150 09473 00542 240000 07502 02875 180 09381 00639 280000 06991 03579 210 09262 00767 240 09149 00889 270 09086 00959 300 08973 01083 330 08868 01202 360 08762 01321

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 30 09945 00055 30 09910 00090 60 09795 00207 60 09828 00173 90 09700 00304 90 09716 00288 120 09645 00361 120 09559 00451 150 09479 00535 150 09440 00576 180 09464 00551 180 09313 00712 210 09314 00711 210 09238 00792 240 09188 00847 240 09156 00882 270 09101 00942 270 08992 01063 300 08991 01064 300 08932 01129 330 08896 01170 330 08872 01197 360 08801 01277 360 08686 01409

- 122 -

Table 414 The Rate Constants (k) in Toluene-d8 Calculated From the Data in Table 413 and Their Standard Deviations (σ)

Temp (K) k (1s) σ σ σ σ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 11314Endash05 37152Endash07 09976 17104 05610

31315 46470Endash05 15251Endash06 09948 15723 05157

32315 12214Endash04 401074Endash06 09957 14788 04851

33315 (1) 36441Endash04 09992

33315 (2) 36124Endash04 09951

33315 (3) 38855Endash04 09956

33315 (avg) 37140Endash04 14937Endash05 13707 04496

Table 415 Activation Parameters for the Kinetic Experiments in Toluene-d8

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 96590 93523 90455 Intercept ndash2073 ndash2007 ndash1941 R

2 09962 09962 09962

∆HDagger (Jmol) 96590 93523 90455

∆HDagger (kcalmol) 2309 2235 2162

∆SDagger (JmolmiddotK) ndash2521 ndash3068 ndash3615

∆SDagger (eu) ndash602 ndash733 ndash864

- 123 -

00000

00500

01000

01500

02000

02500

03000

03500

04000

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

(31315 K 40 degC) y = 46470E-05x + 10553E-02

R2 = 9948

(32315 K 50 degC) y = 12214E-04x + 47671E-03

R2 = 9957

(33315 K 60 degC)y = 371377E-04x - 208381E-03

R2 = 9992

(30315 K 30 degC) y = 11314E-05x + 71900E-03

R2 = 9976

Figure 44 Kinetic plots for the conversion of 53 to 52 in toluene-d8

- 124 -

(C6D6) y = 85141x - 16743

R2

= 09869

(toluene-d 8) y = 93523x - 2007

R2 = 09962

13600

14600

15600

16600

17600

36100E-04

36600E-04

37100E-04

37600E-04

38100E-04

38600E-04

39100E-04

39600E-04

40100E-04

1RT (Jmol)

-ln

(kT

)

Figure 45 Eyring plots for conversion of 53 to 52 MeCpCo(CO)2

Adapted from the literature procedure50 Co2(CO)8 (809 g 2366 mmol) was added to a round bottom flask in the glovebox The flask was capped with a septum and brought out of the glovebox A reflux condenser connected to the high vacuum line was quickly exchanged with the septum under a heavy purge of argon Degassed CH2Cl2 (30 mL) was added followed by freshly cracked deoxygenated methylcyclopentadiene (135 mL 123 mmol) The mixture evolved gas upon addition of the methylcyclopentadiene indicating CO liberation The entire setup was protected from light with foil and heated to a gentle reflux using a heating mantlevariac heat source After stirring at reflux for 26 h the mixture now dark crimson in color was cooled to rt The reflux condenser was quickly exchanged for a distillation head under an Ar purge and CH2Cl2 distilled off at atmospheric pressure under Ar Vacuum distillation at 002 Torr was performed and the forerun discarded The desired complex was obtained as a red liquid (7296 g 79) bp = 31 degC (002 Torr) stored at ndash10 degC and shielded from light Note A small

CoOC CO

- 125 -

amount of methylcyclopentadiene dimer (15 ) which could not be separated was present in the isolated product This was deemed harmless however and the obtained product was used in further experiments without further purification 85 pure 1H-NMR data match those reported in the literature 1H-NMR (C6D6) δ = 145 (s 3 H) 431 (br s 2 H) 451 (br s 2 H) 23-Bis(trimethylsilyl) linear [3]phenylene(MeCpCo) 54

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (0146 g 0424 mmol) in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (0101 g 0731 mmol) The mixture was stirred for 100 min and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the remaining yellow residue was dissolved in freshly distilled THF (15 mL) The green solution was separated from the solids via canula filtration and transferred into another Schlenk flask After a 20 min Ar purge MeCpCo(CO)2 (0092 g 0403 mmol) was added and the resulting solution (protected from light with foil) injected via syringe pump over 9 h into a boiling mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 15 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (201) The volatiles were again removed under high vacuum line and the residue crystallized from acetone yielding 55 (0125 g 61 ) as black crystals mp 163ndash165 degC 1H-NMR (500 MHz C6D6) δ = 783 (s 2 H) 676 (m 4 H) 675 (s 2 H) 442 (apparent t J = 21 Hz 2 H) 427 (apparent t J = 21 Hz 2 H) 134 (s 3 H) 038 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1423 1386 1354 1293 1193 1147 899 806 798 783 739 111 279 ppm IR (neat) ν~ = 2959 2923 2853 1462 1455 1378 1260 1093 1030 802 cmndash1 UV-VIS (hexane) λmax (log ε) = 256 (368) 281 (356) 293 (359) 310 (373) 350 (368) 386 (sh 321) 437 (sh 287) 499 (sh 247) end absorption to 550 nm MS (70 eV) mz () 508 (100) [M+] 370 (28) HRMS (FAB) calcd for C30H33CoSi2 5081453 found 5081442 Photo-thermal cycle between 54 and 56

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

54

CoSiMe3

SiMe3

56

hν∆

Me Me

- 126 -

An NMR tube containing a solution of 54 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 56 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 715 (AArsquom obscured by solvent peak) 680 (s 2 H) 664 (AArsquom 2 H) 447 (apparent t J = 21 Hz 2 H) 428 (apparent t J = 21 Hz 2 H) 148 (s 3 H) 032 (s 18 H) ppm Thermal reversal could be conveniently followed by VT-NMR

14-Deuterio-23-bis(trimethylsilyl) linear [3]phenylene cyclopentadienylcobalt 55

To 23-bis(trimethylsilylethynyl)biphenylene 52 (0144 g 0418 mmol) in CH3OD (10 mL) was added freshly distilled ether (20 mL) and K2CO3 (0083 g 0600 mmol) The mixture was stirred for 100 min and monitored by TLC (hexaneCH2Cl2 51) When the starting material had disappeared the solvents were removed and the remaining yellow residue very quickly dissolved in freshly distilled THF (10 mL) The green solution was separated from the solids using a filter cannula and transferred to another Schlenk flask After a 20 min Ar purge CpCo(CO)2 (0072 g 0400 mmol) was added and the resulting solution (protected from light with foil) was injected via syringe pump over 7 h into a refluxing mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 14 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed on the high vacuum line and the residue recrystallized from acetone yielding 8 (0085 g 41 ) as dark red crystals 1H-NMR spectroscopy showed 63 incorporation of deuterium as indicated by the diminution of the peak intensity of the signal at δ = 796 (s 074 H) ppm MS (FAB) mz () 496 (100) [M+] 372 (19)

CoSiMe3

SiMe3

D

D

- 127 -

Crossover experiment with 54 and 55

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

h

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

5455

5657

A solution of complex 55 (~2 mg) and 54 (~2 mg) in C6D6 (06 mL) rigorously protected from light was analyzed by 1H-NMR spectroscopy to reveal a 1861 mixture of 5554 The peak for 55 at δ = 796 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound A mass spectrum of an aliquot gave the appropriate composite of the two respective molecular ion patterns (Figure 46) The sample was then irradiated as described for above 13 h at RT The 1H-NMR spectrum of the irradiated mixture showed the presence of the respective photoisomers of 55 and 54 There were no unidentifiable peaks the signal at δ = 7470 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound and the clearly resolved peak for 56 at δ = 7473 (s 2 H) ppm revealed unattenuated intensity An aliquot was submitted for mass spectral analysis furnishing the same pattern as that depicted above The sample was then placed in an oil bath preheated to 80 degC for 30 h a treatment that regenerated the original NMR spectrum of the mixture of 55 and 54 including the relative integration ratios Similarly mass spectral analysis resulted in the same pattern as that depicted in Figure 46

- 128 -

Figure 46 Mass spectrum from the crossover experiment between 55 and 56

Low temperature photolyses of 19 and 52 A small amount (~5 mg) of linear[3]phenylene(CpCo) 19 or 52 dissolved in toluene-d8 was added to a J-Young NMR tube in the glovebox The sealed sample was then placed inside a Pyrex Dewar flask positioned in a Rayonet Photochemical Reactor outfitted with UV-lamps emitting at 310 and 350 nm (as shown in Figure 214) Cooling was achieved with the use of a Neslab Refrigerated Circulating bath employing isopropanol as the cooling medium The cold isopropanol was pumped into and out of the Pyrex Dewar using securely fastened Tygon tubes maintaining a temperature of ndash55 to ndash50 degC Once the sample was chilled irradiation was commenced The total irradiation time varied from 25 to 4 h When analysis was required the sample was transported in another Dewar flask containing dry iceisopropanol (ndash78 degC) while the NMR spectrometer was prepared for the low temperature experiment The spectrometer was cooled (ndash80 to ndash30 degC depending on the experiment) the sample wiped with a paper towel placed inside the spinner and very quickly lowered manually with a string into the cold magnet After allowing time for the temperature to equilibrate (10 min) a spectrum was recorded For VT experiments the temperature was slowly

- 129 -

raised from ndash80 degC in 10 degree increments to 10 degC Spectra were recorded at each interval For all other experiments spectra were recorded at ndash30 degC 2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

In the glovebox 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19 (0049 g 0133 mmol) and CpCo(C2H4)2 (0025 g 0139 mmol)99 were added to a Schlenk flask The flask was sealed brought out of the box connected to a vacuum manifold and freshly distilled degassed benzene (15 mL) added The mixture was heated to 70 degC on an oil bath for 23 h before being cooled to RT The solvent was removed in vacuo giving a black residue that was rapidly filtered through a plug of neutral alumina activity III (25 x 35 cm) eluting with a mixture of hexanes and THF (1001) under nitrogen and into a Schlenk flask The solvents were again removed in vacuo and the ensuing black residue recrystallized from acetone at ndash78 degC to give pure 78 (0057 g 56 ) as black crystals 1H-NMR (400 MHz acetone-d6) δ = 039 (s 36H) 481 (s 2H) 489 (m 4H) 736 (s 4H) ppm 13C-NMR (100 MHz acetone-d6) δ = 266 5372 5710 8284 12587 14542 15054 ppm UV-VIS (hexane) λmax (log ε) 197 (334) 221 (336 sh) 244 (344) 286 (363) 386 (279 sh) 439 (258) MS (FAB) 762 (M+ 100) HRMS calcd for C40H52Si4Co2 7621810 found 7621791 43 Computational Details for Chapter Two All calculations were performed using the GAUSSIAN03100 program GaussView 30101 and ChemCraft102 were employed to input structures as well as view output results Optimized geometries were obtained at the hybrid density functional theory (DFT) using Beckersquos three-parameter exchange-correlation functional103 containing the non-local gradient correction of Lee Yang and Parr104 (B3LYP) For optimization purposes a standard basis 3-21G105 was used for hydrogen and carbon atoms For cobalt the LANL2DZ106 basis set was applied with the outermost d function released yielding a triple-zeta d basis along with the effective core potentials (ECP) to describe the core electrons For the single point energy calculations the basis sets were increased to 6-31G107 for hydrogen 6-311G108 for carbon and the modified LANL2DZ basis as described above for cobalt with an added f-orbital coefficient109 The potential energy surfaces were mapped through a scan calculation a feature also available within the GAUSSIAN03 program Transition state structures were obtained in three different steps (i) determination of initial and final products or the minimum closest to a TS (ii) a linear QST2110 search for an initial guess of a TS and

- 130 -

(iii) input of the results from (ii) into a QST3 search Transition states and minima were confirmed by carrying out frequency calculations (using the same basis as that used for the optimizations)

Calculated structures for linear [3]phenylene(CpCo) (labels from Figures 29 and 210 in Section 24)

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

C 2878616000 ndash1675635000 ndash1461246000 C 3986441000 ndash2043582000 ndash0714088000 C 3986471000 ndash2043226000 0714700000 C 2878686000 ndash1674908000 1461732000 C 1740663000 ndash1265994000 0736724000 C 1740638000 ndash1266353000 ndash0736388000 H 2884721000 ndash1731772000 ndash2551997000 H 2884845000 ndash1730511000 2552509000 C 0311237000 ndash0833174000 0748280000 C 0311204000 ndash0833522000 ndash0748106000 C ndash0893980000 ndash0698348000 ndash1520584000 C ndash0893913000 ndash0697588000 1520749000 C ndash1996288000 ndash0532216000 0744771000 C ndash1996322000 ndash0532586000 ndash0744640000 C ndash3491040000 ndash0328769000 ndash0716524000 C ndash3490989000 ndash0328300000 0716632000 C ndash4645388000 ndash0172650000 ndash1448232000 C ndash4645276000 ndash0171672000 1448326000 C ndash5836534000 ndash0014205000 ndash0697760000

- 131 -

C ndash5836481000 ndash0013731000 0697841000 H ndash0905006000 ndash0741217000 ndash2609771000 H ndash0904887000 ndash0739873000 2609960000 H ndash4666353000 ndash0168153000 ndash2539086000 H ndash6785734000 0111682000 ndash1227959000 H ndash6785641000 0112502000 1228028000 H ndash4666162000 ndash0166493000 2539178000 Co 1455829000 0662094000 ndash0000295000 C 0672548000 2613322000 0000481000 C 1502831000 2459745000 1168426000 C 2819523000 2140942000 0722371000 C 2818808000 2141294000 ndash0723848000 C 1501651000 2460224000 ndash1168394000 H ndash0391329000 2836892000 0001070000 H 1172930000 2540112000 2200200000 H 3678957000 1932268000 1353707000 H 3677612000 1932967000 ndash1356152000 H 1170676000 2541059000 ndash2199789000 H 4894703000 ndash2369906000 1230670000 H 4894651000 ndash2370516000 ndash1229936000

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

C ndash3991583000 ndash2430244000 ndash0695300000 C ndash2895249000 ndash1923385000 ndash1446977000 C ndash1838331000 ndash1436925000 ndash0718218000 C ndash0460541000 ndash0772703000 ndash0748934000

- 132 -

C 0758545000 ndash0733408000 ndash1513161000 C 1871918000 ndash0586111000 ndash0739684000 C 3374782000 ndash0432509000 ndash0717168000 C 4533131000 ndash0322603000 ndash1448209000 C 5731498000 ndash0208370000 ndash0696796000 C 5731438000 ndash0207885000 0696952000 C 4533003000 ndash0321597000 1448333000 C 3374722000 ndash0432010000 0717261000 C 1871861000 ndash0585642000 0739747000 C 0758457000 ndash0732583000 1513259000 C ndash0460578000 ndash0772439000 0748991000 C ndash1838348000 ndash1436677000 0718485000 C ndash2895298000 ndash1922892000 1447371000 C ndash3991613000 ndash2429987000 0695830000 H ndash4853881000 ndash2841402000 ndash1229010000 H ndash2909366000 ndash1943431000 ndash2538196000 H 0770744000 ndash0814782000 ndash2600896000 H 4554949000 ndash0321315000 ndash2539049000 H 6684245000 ndash0118682000 ndash1227928000 H 6684140000 ndash0117859000 1228104000 H 4554722000 ndash0319567000 2539175000 H 0770611000 ndash0813312000 2601042000 H ndash2909450000 ndash1942588000 2538596000 H ndash4853932000 ndash2840954000 1229654000 Co ndash1032604000 1030206000 ndash0000179000 C ndash2903591000 1947430000 ndash0000175000 C ndash2211742000 2430689000 ndash1177143000 C ndash1026232000 3056089000 ndash0732194000 C ndash1026229000 3056139000 0731719000 C ndash2211730000 2430773000 1176747000 H ndash3829247000 1376180000 ndash0000150000 H ndash2513347000 2264399000 ndash2207387000 H ndash0243163000 3477094000 ndash1358586000 H ndash0243137000 3477190000 1358051000 H ndash2513304000 2264572000 2207015000

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 133 -

C 4829664000 ndash1220862000 0883782000 C 3649435000 ndash0895915000 1609183000 C 2478533000 ndash0900239000 0886069000 C 0985532000 ndash0699413000 0895282000 C ndash0207413000 ndash0351140000 1567281000 C ndash1295977000 ndash0355264000 0631690000 C ndash2799524000 ndash0368596000 0647705000 C ndash3950748000 0104186000 1252743000 C ndash5173877000 ndash0370408000 0725519000 C ndash5217559000 ndash1270006000 ndash0351644000 C ndash4043168000 ndash1754445000 ndash0967619000 C ndash2843350000 ndash1293792000 ndash0444950000 C ndash1365414000 ndash1319830000 ndash0538287000 C ndash0225558000 ndash1662005000 ndash1182029000 C 0928168000 ndash1009692000 ndash0554559000 C 2436156000 ndash1209374000 ndash0509824000 C 3575395000 ndash1530032000 ndash1215144000 C 4792344000 ndash1526592000 ndash0477473000 H 5781080000 ndash1237670000 1406156000 H 3693287000 ndash0679862000 2671420000 H ndash0279175000 ndash0037747000 2601166000 H ndash3939706000 0801901000 2083798000 H ndash6106757000 ndash0031072000 1165263000 H ndash6183419000 ndash1601741000 ndash0720200000 H ndash4097586000 ndash2453276000 ndash1795561000 H ndash0137803000 ndash2306368000 ndash2049380000 H 3570207000 ndash1781979000 ndash2270507000 H 5717527000 ndash1774506000 ndash0988963000 Co 0235674000 0924694000 ndash0006080000 C 1650242000 2605908000 ndash0261710000 C 0606451000 3071372000 0583798000

C ndash0633939000 2891762000 ndash0112192000 C ndash0354070000 2388098000 ndash1431110000 C 1060641000 2182627000 ndash1507942000 H 2701380000 2562827000 ndash0018620000 H 0717262000 3431891000 1595877000 H ndash1615358000 3123686000 0274491000 H ndash1077256000 2190401000 ndash2207047000

- 134 -

H 1601331000 1788686000 ndash2355167000

(d) Transition State 2 η3-benzene (249 kcalmol)

C 5059641000 ndash0675345000 0741440000 C 3868057000 ndash0242461000 1393542000 C 2691208000 ndash0611642000 0796692000 C 1164924000 ndash0568451000 0814993000 C 0001006000 ndash0193010000 1575722000 C ndash1162903000 ndash0569406000 0815406000 C ndash2689168000 ndash0613549000 0797134000 C ndash3866228000 ndash0245076000 1394017000 C ndash5057560000 ndash0678583000 0741882000 C ndash5030442000 ndash1430649000 ndash0426732000 C ndash3802288000 ndash1812828000 ndash1038342000 C ndash2662603000 ndash1392426000 ndash0404590000 C ndash1143695000 ndash1392940000 ndash0383227000 C 0001354000 ndash1885575000 ndash1010384000 C 1146183000 ndash1392203000 ndash0383465000 C 2665098000 ndash1390792000 ndash0404876000 C 3805017000 ndash1810598000 ndash1038596000 C 5032958000 ndash1427555000 ndash0427087000 H 6017043000 ndash0408623000 1174840000 H 3916675000 0338622000 2306082000 H 0001106000 0141040000 2603832000 H ndash3915179000 0335814000 2306664000 H ndash6015116000 ndash0412488000 1175329000

- 135 -

H ndash5963925000 ndash1737868000 ndash0883265000 H ndash3794877000 ndash2406462000 ndash1944276000 H 0001449000 ndash2505619000 ndash1894591000 H 3797948000 ndash2404400000 ndash1944423000 H 5966616000 ndash1734262000 ndash0883606000 Co ndash0000294000 1006304000 0016484000 C 1144150000 2811021000 ndash0317903000 C ndash0001831000 3236912000 0413780000 C ndash1150105000 2808519000 ndash0312717000 C ndash0712506000 2257800000 ndash1588662000 C 0702130000 2259464000 ndash1591918000 H 2174046000 2940434000 ndash0021226000 H ndash0000096000 3693787000 1391408000 H ndash2178919000 2935539000 ndash0011312000 H ndash1360790000 1903514000 ndash2375388000 H 1347563000 1907002000 ndash2381795000

Calculated structures for linear [5]phenylene CpCo (labels from Figures 211 and 212 in Section 24)

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

C ndash2147283000 ndash0385762000 ndash0741520000 C ndash2146881000 ndash0382747000 0740465000 C ndash0675330000 ndash0218887000 0741228000 C ndash0675503000 ndash0222208000 ndash0743565000 C 0535474000 ndash0309864000 ndash1519364000

- 136 -

C 1654024000 ndash0363787000 ndash0743565000 C 1653968000 ndash0359108000 0742223000 C 0535464000 ndash0301263000 1517648000 C 3146303000 ndash0437352000 0715394000 C 3146555000 ndash0442081000 ndash0715839000 H 0537903000 ndash0329735000 2601810000 H 0538062000 ndash0344229000 ndash2603354000 Co ndash1585768000 1444604000 ndash0004763000 C ndash2656365000 3118646000 0813641000 C ndash1264152000 3247968000 1115884000 C ndash0546296000 3292610000 ndash0128221000 C ndash1500173000 3225060000 ndash1199322000 C ndash2801883000 3099872000 ndash0616868000 H ndash3459184000 3033020000 1530368000 H ndash0824887000 3279284000 2101474000 H 0525240000 3366953000 ndash0237713000 H ndash1272392000 3239735000 ndash2254384000 H ndash3732669000 2998753000 ndash1154572000 C ndash3315848000 ndash0698077000 1516941000 C ndash3316515000 ndash0705270000 ndash1515890000 C ndash4404590000 ndash0970491000 0742487000 C ndash4404888000 ndash0974125000 ndash0739677000 H ndash3311463000 ndash0745189000 ndash2599679000 H ndash3310191000 ndash0733014000 2600900000 C ndash5857232000 ndash1346832000 ndash0713671000 C ndash5856902000 ndash1343302000 0718959000 C ndash6992149000 ndash1638138000 ndash1445564000 C ndash6991464000 ndash1630979000 1452826000 C 4314567000 ndash0501395000 ndash1493440000 C 4313844000 ndash0491124000 1494022000

C ndash8157130000 ndash1937355000 ndash0695553000 C ndash8156796000 ndash1933908000 0704865000 H ndash7013569000 ndash1630976000 2537309000 H ndash9075842000 ndash2169721000 1232475000 H ndash9076411000 ndash2175846000 ndash1221548000 H ndash7014707000 ndash1643790000 ndash2530023000 C 5464859000 ndash0553191000 0719930000 C 5465218000 ndash0558312000 ndash0718328000 C 6977989000 ndash0635007000 ndash0714777000 C 6977565000 ndash0629511000 0717833000 H 4313279000 ndash0484164000 2577745000 H 4314609000 ndash0502067000 ndash2577185000 C 8138196000 ndash0684071000 1451266000 C 8139115000 ndash0695400000 ndash1446980000 C 9348946000 ndash0746919000 0699256000 C 9349380000 ndash0752387000 ndash0693700000

- 137 -

H 8162380000 ndash0700716000 ndash2531270000 H 8160717000 ndash0680929000 2535584000 H 10294800000 ndash0791917000 1230058000 H 10295576000 ndash0801571000 ndash1223516000

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

C ndash8026536000 ndash2149127000 ndash0697047000 C ndash6872771000 ndash1801590000 ndash1447012000 C ndash5755909000 ndash1466198000 ndash0717983000 C ndash4305789000 ndash1041476000 ndash0739357000 C ndash3218268000 ndash0750848000 ndash1510952000 C ndash2077793000 ndash0315087000 ndash0749237000 C ndash0550342000 ndash0400850000 ndash0716361000 C 0616872000 ndash0404801000 ndash1489728000 C 1770640000 ndash0412395000 ndash0716060000 C 3300443000 ndash0457807000 ndash0715861000 C 4454767000 ndash0490291000 ndash1489427000 C 5616257000 ndash0520747000 ndash0712496000 C 5616269000 ndash0520699000 0712492000 C 4454793000 ndash0490190000 1489443000 C 3300455000 ndash0457762000 0715895000 C 1770651000 ndash0412347000 0716117000 C 0616894000 ndash0404700000 1489800000 C ndash0550335000 ndash0400796000 0716454000 C ndash2077818000 ndash0315060000 0749341000 C ndash3218306000 ndash0750915000 1510996000

- 138 -

C ndash4305781000 ndash1041534000 0739359000 C ndash5755900000 ndash1466256000 0717962000 C ndash6872758000 ndash1801708000 1446971000 C ndash8026533000 ndash2149171000 0696987000 H ndash6893447000 ndash1807486000 ndash2529846000 H ndash3199702000 ndash0827686000 ndash2591829000 H 0616147000 ndash0415875000 ndash2572166000 H 4455855000 ndash0492565000 ndash2571217000 H 4455901000 ndash0492389000 2571233000 H 0616188000 ndash0415693000 2572238000 H ndash3199790000 ndash0827916000 2591862000 H ndash6893430000 ndash1807681000 2529804000 Co ndash2237895000 1566525000 ndash0000035000 C ndash0770702000 3039808000 0000091000 C ndash1582333000 3276979000 1176306000 C ndash2906316000 3484053000 0731575000 C ndash2906172000 3484095000 ndash0731735000 C ndash1582100000 3277047000 ndash1176233000 H 0281094000 2798829000 0000215000 H ndash1247438000 3209109000 2198999000 H ndash3777291000 3625124000 1353071000 H ndash3777011000 3625160000 ndash1353424000 H ndash1246943000 3209260000 ndash2198847000 H ndash8933230000 ndash2423019000 ndash1224452000 H ndash8933222000 ndash2423113000 1224377000 C 7146943000 ndash0559737000 0717588000 C 7146931000 ndash0559786000 ndash0717614000 C 8302361000 ndash0588480000 1447040000 C 8302337000 ndash0588576000 ndash1447082000 C 9516918000 ndash0618789000 ndash0692883000 C 9516929000 ndash0618742000 0692823000 H 8324450000 ndash0589130000 2529610000 H 10461320000 ndash0642422000 1224406000 H 10461300000 ndash0642481000 ndash1224480000 H 8324409000 ndash0589299000 ndash2529653000

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 139 -

C ndash7810644000 ndash2064896000 ndash0088979000 C ndash6582065000 ndash2396690000 ndash0700394000 C ndash5469369000 ndash1694626000 ndash0259356000 C ndash4011414000 ndash1478684000 ndash0398743000 C ndash2839913000 ndash1679834000 ndash1045300000 C ndash1807973000 ndash0777407000 ndash0523048000 C ndash0288034000 ndash0728447000 ndash0497727000 C 0877200000 ndash0917515000 ndash1257428000 C 2033335000 ndash0625143000 ndash0541547000 C 3550975000 ndash0572504000 ndash0566638000 C 4702932000 ndash0775398000 ndash1323945000 C 5869717000 ndash0493099000 ndash0604711000 C 5877160000 ndash0049178000 0749672000 C 4719648000 0152978000 1509600000 C 3558389000 ndash0127834000 0791889000 C 2041313000 ndash0178303000 0818968000 C 0890228000 0010834000 1576182000

C ndash0275189000 ndash0290874000 0857465000 C ndash1777915000 ndash0332627000 0896504000 C ndash3000252000 ndash0144927000 1576583000 C ndash4087655000 ndash0414543000 0681649000 C ndash5565811000 ndash0681071000 0748878000 C ndash6769777000 ndash0358061000 1349731000 C ndash7902756000 ndash1078577000 0906205000 H ndash6531350000 ndash3165530000 ndash1463988000 H ndash2656944000 ndash2379915000 ndash1852763000

- 140 -

H 0873498000 ndash1259556000 ndash2286041000 H 4697058000 ndash1113491000 ndash2353481000 H 4726794000 0489146000 2539724000 H 0892018000 0335667000 2610226000 H ndash3107471000 0242268000 2582171000 H ndash6863567000 0403771000 2116786000 Co ndash2805901000 1045228000 ndash0126008000 C ndash1966955000 3131745000 ndash0137391000 C ndash3345106000 3172285000 0219040000 C ndash4105003000 2591218000 ndash0859559000 C ndash3194452000 2177424000 ndash1877135000 C ndash1861601000 2475718000 ndash1403791000 H ndash1139494000 3467521000 0469940000 H ndash3757304000 3575577000 1132204000 H ndash5178689000 2478840000 ndash0883920000 H ndash3449207000 1717975000 ndash2819531000 H ndash0944137000 2267497000 ndash1933863000 H ndash8711780000 ndash2586977000 ndash0395882000 H ndash8871888000 ndash0864282000 1346179000 C 7394568000 0005138000 0727783000

C 7387058000 ndash0441388000 ndash0634217000 C 8557433000 0273605000 1404315000

C 8542647000 ndash0629395000 ndash1349402000 C 9760631000 ndash0352464000 ndash0653366000 C 9767843000 0080954000 0667800000 H 8586089000 0612106000 2434348000 H 10716375000 0279405000 1157078000

H 10703753000 ndash0485281000 ndash1174332000 H 8560430000 ndash0966385000 ndash2380163000

(d) Transition state 4 η3-benzene (367 kcalmol)

- 141 -

C 7669717000 ndash2174926000 ndash0105923000 C 6450462000 ndash2458728000 0544003000 C 5349535000 ndash1733337000 0120322000 C 3893688000 ndash1505268000 0269179000 C 2708972000 ndash1942858000 0838638000 C 1596115000 ndash1239419000 0370186000 C 0149218000 ndash1103313000 0368184000 C ndash1061261000 ndash1583264000 0932639000 C ndash2167377000 ndash0965378000 0405284000 C ndash3686709000 ndash0866795000 0409630000 C ndash4872520000 ndash1347856000 0960688000 C ndash5997863000 ndash0728310000 0421450000 C ndash5941471000 0288854000 ndash0586107000 C ndash4758793000 0770529000 ndash1137452000 C ndash3629556000 0150846000 ndash0598044000 C ndash2119390000 0068600000 ndash0617626000 C ndash0945265000 0548559000 ndash1173832000 C 0191709000 ndash0072876000 ndash0643629000 C 1695402000 ndash0118964000 ndash0667389000 C 2835200000 0041396000 ndash1507494000 C 3981535000 ndash0415532000 ndash0796385000 C 5449049000 ndash0747489000 ndash0920326000 C 6638556000 ndash0473422000 ndash1556289000 C 7762417000 ndash1216205000 ndash1122513000 H 6396888000 ndash3209338000 1323030000 H 2647172000 ndash2772334000 1532449000 H ndash1099468000 ndash2356302000 1688990000 H ndash4914534000 ndash2116326000 1720908000 H ndash4717626000 1537921000 ndash1898781000 H ndash0906852000 1317204000 ndash1935050000 H 2849903000 0560387000 ndash2457942000 H 6730568000 0262385000 ndash2346085000 Co 3078365000 1106450000 0223118000 C 2432920000 3235925000 0352954000 C 3805628000 3232135000 ndash0000959000 C 4525686000 2519574000 1027488000 C 3591065000 2151422000 2051886000 C 2287258000 2550618000 1620273000

- 142 -

H 1625110000 3662123000 ndash0222202000 H 4237852000 3652387000 ndash0895767000 H 5588986000 2336674000 1044912000 H 3828106000 1629983000 2966790000 H 1363656000 2417646000 2161607000 H 8562189000 ndash2715853000 0187384000 H 8723754000 ndash1039126000 ndash1591154000 C ndash7467794000 0379383000 ndash0580257000 C ndash7522920000 ndash0639213000 0428535000 C ndash8594261000 0964602000 ndash1089561000 C ndash8706397000 ndash1090617000 0945872000 C ndash9887862000 ndash0485330000 0420145000 C ndash9834353000 0499744000 ndash0555359000 H ndash8574126000 1734202000 ndash1850912000 H ndash10757407000 0931123000 ndash0925119000 H ndash10851990000 ndash0807405000 0796463000 H ndash8770071000 ndash1858056000 1706995000

(e) Local minimum 3 η4-benzene (190 kcalmol)

C ndash7704806000 ndash1625445000 ndash0076324000 C ndash6491455000 ndash1789497000 ndash0801300000 C ndash5352262000 ndash1326936000 ndash0190371000 C ndash3836374000 ndash1127906000 ndash0291559000 C ndash2669014000 ndash1876939000 ndash0775878000 C ndash1540408000 ndash1361850000 ndash0248671000 C ndash0067088000 ndash1219487000 ndash0231176000 C 1147603000 ndash1746746000 ndash0723682000

- 143 -

C 2245517000 ndash1037457000 ndash0289605000 C 3767258000 ndash0910575000 ndash0313273000 C 4961694000 ndash1439625000 ndash0795996000 C 6075343000 ndash0726547000 ndash0354068000 C 5999362000 0418026000 0498208000 C 4804020000 0947684000 0980899000 C 3691158000 0235329000 0538756000 C 2171505000 0121554000 0570963000 C 0990404000 0649716000 1051234000

C ndash0139369000 ndash0066282000 0613306000 C ndash1640889000 ndash0139469000 0665899000 C ndash2708579000 0044357000 1607074000 C ndash3890300000 ndash0515482000 1069631000 C ndash5389479000 ndash0719093000 1106627000 C ndash6553177000 ndash0561696000 1815459000 C ndash7736166000 ndash1034716000 1182797000 H ndash6489929000 ndash2263627000 ndash1775522000 H ndash2743316000 ndash2692464000 ndash1483904000 H 1201969000 ndash2617287000 ndash1364047000 H 5019196000 ndash2306567000 ndash1440440000 H 4747029000 1814065000 1626168000 H 0933710000 1519855000 1692796000 H ndash2640951000 0605584000 2529735000 H ndash6590996000 ndash0122891000 2805220000 Co ndash3231943000 0870639000 ndash0218177000 C ndash2631117000 2925280000 ndash0475333000 C ndash4019450000 2955930000 ndash0137499000 C ndash4720042000 2167067000 ndash1095287000 C ndash3768150000 1717753000 ndash2089396000 C ndash2477085000 2188405000 ndash1710046000 H ndash1832546000 3399891000 0073720000 H ndash4448788000 3419647000 0737399000 H ndash5777018000 1951944000 ndash1095854000 H ndash3999907000 1119290000 ndash2956393000 H ndash1549894000 2013889000 ndash2232360000 H ndash8630326000 ndash1978241000 ndash0517433000 H ndash8683428000 ndash0939767000 1701100000 C 7524401000 0541032000 0473497000

C 7600630000 ndash0607844000 ndash0382149000 C 8637973000 1216338000 0890053000

C 8792152000 ndash1101412000 ndash0836674000 C 9961705000 ndash0402146000 ndash0407106000 C 9887895000 0708141000 0420266000 H 8602106000 2084773000 1535736000 H 10801526000 1207625000 0721410000

H 10931894000 ndash0752974000 ndash0739605000

- 144 -

H 8871661000 ndash1966753000 ndash1482602000

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

C 7143264000 ndash2348493000 0699665000 C 6037664000 ndash1857298000 1448523000 C 4969251000 ndash1391864000 0720257000 C 3582514000 ndash0743198000 0748195000 C 2358402000 ndash0737338000 1512136000 C 1240141000 ndash0634711000 0742222000 C ndash0262684000 ndash0516912000 0716494000 C ndash1428088000 ndash0430968000 1492584000 C ndash2574224000 ndash0346717000 0719319000 C ndash4098679000 ndash0233199000 0715866000 C ndash5251323000 ndash0147278000 1490294000 C ndash6408253000 ndash0063372000 0713741000 C ndash7934932000 0047490000 0717366000 C ndash9088044000 0130556000 1446914000 C ndash10299063000 0217080000 0692638000 C ndash10298939000 0215301000 ndash0693576000 C ndash9087782000 0126841000 ndash1447398000 C ndash7934811000 0045602000 ndash0717417000 C ndash6408180000 ndash0065400000 ndash0713264000 C ndash5251144000 ndash0151514000 ndash1489420000 C ndash4098619000 ndash0235099000 ndash0714599000 C ndash2574142000 ndash0348081000 ndash0717615000 C ndash1428022000 ndash0433439000 ndash1490677000

- 145 -

C ndash0262587000 ndash0517946000 ndash0714342000 C 1239930000 ndash0636111000 ndash0739947000 C 2357013000 ndash0742891000 ndash1511730000 C 3581891000 ndash0749703000 ndash0749006000 C 4968536000 ndash1397444000 ndash0717250000 C 6036190000 ndash1868351000 ndash1443314000 C 7142499000 ndash2353756000 ndash0691900000 H 8003789000 ndash2740125000 1230531000 H 6052031000 ndash1874231000 2531931000 H 2350726000 ndash0802237000 2593967000 H ndash1427931000 ndash0429806000 2574521000 H ndash5251989000 ndash0146640000 2572026000 H ndash9110076000 0132990000 2529448000 H ndash11241535000 0285430000 1223689000 H ndash11241318000 0282253000 ndash1224971000 H ndash9109613000 0126365000 ndash2529940000 H ndash5251637000 ndash0153720000 ndash2571150000 H ndash1427824000 ndash0434279000 ndash2572612000 H 2347832000 ndash0810535000 ndash2593375000 H 6049185000 ndash1893779000 ndash2526553000 H 8002469000 ndash2749449000 ndash1220666000 Co 4148367000 1055016000 ndash0009106000 C 5996101000 2006266000 0022069000 C 5276853000 2480887000 1185002000 C 4085420000 3079352000 0718350000 C 4110596000 3077077000 ndash0745160000 C 5316353000 2474554000 ndash1168669000 H 6921324000 1451094000 0038659000 H 5556549000 2314709000 2212960000 H 3287274000 3477873000 1325692000 H 3334253000 3474398000 ndash1380859000 H 5631980000 2304731000 ndash2185537000

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 146 -

C 4893664000 ndash1209972000 0735005000 C 4893573000 ndash1213475000 ndash0730870000 C 3475382000 ndash0763132000 ndash0743915000 C 3475432000 ndash0760320000 0747049000 C 2260316000 ndash0690973000 1520580000 C 1145205000 ndash0595973000 0744946000 C 1145156000 ndash0599246000 ndash0742744000 C 2260358000 ndash0697381000 ndash1517904000 C ndash0343192000 ndash0479177000 ndash0713609000 C ndash0343168000 ndash0476032000 0715380000 H 2252105000 ndash0735285000 ndash2601934000 H 2251901000 ndash0724154000 2604763000 Co 4601208000 0736083000 ndash0002055000 C 5960130000 2243618000 ndash0721946000 C 4640007000 2540538000 ndash1172530000 C 3804522000 2681992000 ndash0008876000 C 4632302000 2544967000 1160921000 C 5955467000 2247130000 0721276000 H 6816321000 2038808000 ndash1347044000 H 4312673000 2604006000 ndash2199136000 H 2745254000 2890841000 ndash0012873000 H 4298236000 2612143000 2185222000 H 6807361000 2044890000 1353015000 C 6022290000 ndash1649780000 1464200000 C 6022277000 ndash1656609000 ndash1457900000 C 7122289000 ndash2056771000 0719324000 C 7122311000 ndash2060028000 ndash0711126000 H 6027301000 ndash1702610000 2548102000 H 8011576000 ndash2407816000 1233935000 H 8011528000 ndash2413601000 ndash1224115000 H 6027432000 ndash1714310000 ndash2541551000 C ndash1512226000 ndash0382902000 1494684000 C ndash1512274000 ndash0389473000 ndash1493257000 C ndash2658093000 ndash0297761000 0720325000 C ndash2658103000 ndash0300923000 ndash0719236000 H ndash1511446000 ndash0379165000 2578406000

- 147 -

H ndash1511531000 ndash0390614000 ndash2576954000 C ndash4169046000 ndash0190131000 ndash0714237000 C ndash4169015000 ndash0186849000 0714915000 C ndash5325016000 ndash0103295000 1491764000 C ndash5325120000 ndash0110177000 ndash1491395000 C ndash6483203000 ndash0023670000 0713863000 C ndash6483258000 ndash0027061000 ndash0713749000 H ndash5325252000 ndash0101647000 2575308000 H ndash5325471000 ndash0113799000 ndash2574933000 C ndash7997403000 0080746000 0716440000 C ndash7997524000 0076500000 ndash0716680000 C ndash9155096000 0160872000 1448927000 C ndash9155379000 0152083000 ndash1449432000 C ndash10366775000 0240123000 0695134000 C ndash10366925000 0235844000 ndash0695874000 H ndash9178696000 0150122000 ndash2533721000 H ndash11311550000 0297904000 ndash1227155000 H ndash11311298000 0305233000 1226228000 H ndash9178228000 0165001000 2533216000

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

C 8266704000 ndash2005162000 0692734000 C 7088955000 ndash1708719000 1446000000 C 5966603000 ndash1428050000 0716466000

- 148 -

C 4483884000 ndash1054830000 0713802000 C 3355736000 ndash0795879000 1487813000 C 2219848000 ndash0542568000 0715155000 C 0748349000 ndash0122254000 0743952000 C ndash0460068000 ndash0300197000 1509394000 C ndash1583463000 ndash0354552000 0739667000 C ndash3088504000 ndash0455891000 0716671000 C ndash4249167000 ndash0553278000 1491353000 C ndash5399475000 ndash0634011000 0717623000 C ndash6922525000 ndash0754459000 0717051000 C ndash8076029000 ndash0852663000 1446746000 C ndash9285359000 ndash0940991000 0693505000 C ndash9286426000 ndash0927591000 ndash0694047000 C ndash8078221000 ndash0824629000 ndash1447252000 C ndash6923651000 ndash0740632000 ndash0717519000 C ndash5400498000 ndash0620402000 ndash0717994000 C ndash4251528000 ndash0525736000 ndash1491803000 C ndash3089431000 ndash0443610000 ndash0717063000 C ndash1585243000 ndash0344579000 ndash0740307000 C ndash0463450000 ndash0290395000 ndash1513612000 C 0748496000 ndash0127629000 ndash0751652000 C 2219455000 ndash0546002000 ndash0721683000 C 3355860000 ndash0802470000 ndash1493276000 C 4483583000 ndash1057975000 ndash0718022000 C 5966360000 ndash1431783000 ndash0719354000 C 7088265000 ndash1716549000 ndash1447876000 C 8266466000 ndash2008718000 ndash0693595000 H 9183427000 ndash2233531000 1224348000 H 7110060000 ndash1714392000 2528663000 H 3353411000 ndash0803478000 2570367000 H ndash0456292000 ndash0373454000 2590614000 H ndash4248665000 ndash0564171000 2573279000 H ndash8096828000 ndash0865292000 2529266000 H ndash10227269000 ndash1021159000 1223954000 H ndash10229127000 ndash0997490000 ndash1224546000 H ndash8100648000 ndash0816347000 ndash2529785000 H ndash4252664000 ndash0517117000 ndash2573754000 H ndash0464650000 ndash0354640000 ndash2595436000 H 3353541000 ndash0815213000 ndash2575752000 H 7108905000 ndash1727728000 ndash2530504000 H 9182976000 ndash2239822000 ndash1224379000 Co 1060170000 1739352000 ndash0013647000 C 0820599000 3762931000 0679296000 C 2023158000 3250849000 1217023000 C 2833506000 2814255000 0100512000 C 2185795000 3225276000 ndash1129991000

- 149 -

C 0924349000 3753677000 ndash0780133000 H ndash0033478000 4112410000 1239126000 H 2257663000 3114053000 2260457000 H 3791311000 2322414000 0171627000 H 2565428000 3065285000 ndash2126458000 H 0160713000 4098445000 ndash1460120000

(i) Local minimum 1 η4-benzene (190 kcalmol)

C 8767525000 ndash0664628000 0869444000 C 7569070000 ndash0364489000 1586360000 C 6400497000 ndash0535559000 0896308000 C 4872998000 ndash0456407000 0896648000 C 3729258000 ndash0166123000 1633430000 C 2558863000 ndash0367557000 0899969000 C 1050529000 ndash0274920000 0917771000 C ndash0154687000 0103769000 1545183000 C ndash1231288000 ndash0039565000 0606842000 C ndash2736221000 ndash0089835000 0603708000 C ndash3901526000 0467576000 1153370000 C ndash5054648000 ndash0104455000 0647800000 C ndash6579036000 ndash0120351000 0673091000 C ndash7732820000 0402806000 1194768000 C ndash8948594000 ndash0155119000 0702959000 C ndash8958839000 ndash1167887000 ndash0247745000 C ndash7753788000 ndash1707235000 ndash0785423000 C ndash6589806000 ndash1166201000 ndash0307896000

- 150 -

C ndash5063448000 ndash1158179000 ndash0339650000 C ndash3923750000 ndash1713712000 ndash0884954000 C ndash2743411000 ndash1141750000 ndash0370168000 C ndash1264100000 ndash1152263000 ndash0442985000 C ndash0114410000 ndash1509648000 ndash1047872000 C 1001557000 ndash0717865000 ndash0509678000 C 2529242000 ndash0815059000 ndash0456630000 C 3680301000 ndash1106705000 ndash1192448000 C 4847485000 ndash0909766000 ndash0461159000 C 6375435000 ndash0989198000 ndash0464503000 C 7517684000 ndash1280530000 ndash1157992000 C 8743181000 ndash1104009000 ndash0445669000 H 9720775000 ndash0544729000 1371431000 H 7610320000 ndash0024462000 2613574000 H 3742883000 0162901000 2664422000 H ndash0241422000 0534554000 2534230000 H ndash3894210000 1260341000 1890621000 H ndash7746436000 1191936000 1936109000 H ndash9890199000 0223840000 1083439000

H ndash9908180000 ndash1561665000 ndash0592194000 H ndash7783148000 ndash2497305000 ndash1525270000 H ndash3929534000 ndash2506814000 ndash1621099000 H 0005285000 ndash2235278000 ndash1842324000 H 3664139000 ndash1453900000 ndash2217556000 H 7520111000 ndash1625509000 ndash2184413000 H 9677483000 ndash1320445000 ndash0950825000 Co 0245526000 1194775000 ndash0183529000 C ndash0498660000 3223481000 ndash0207100000 C 0902667000 3310487000 0056983000 C 1591310000 2661311000 ndash1009417000 C 0610054000 2243094000 ndash1989593000 C ndash0681576000 2592200000 ndash1494981000 H ndash1289524000 3595536000 0425619000 H 1355880000 3721411000 0946130000 H 2657726000 2519341000 ndash1088515000 H 0823168000 1743521000 ndash2921425000 H ndash1626608000 2403559000 ndash1979282000

(j) Transition state 1 η3-benzene (356 kcalmol)

- 151 -

C ndash8901354000 ndash0223681000 ndash0743434000 C ndash7695103000 0220198000 ndash1360549000 C ndash6531343000 ndash0208573000 ndash0779115000 C ndash5007706000 ndash0207407000 ndash0796109000 C ndash3863247000 0247302000 ndash1433753000 C ndash2690760000 ndash0206508000 ndash0819013000 C ndash1184933000 ndash0153490000 ndash0843116000 C ndash0016095000 0217826000 ndash1588049000 C 1142075000 ndash0155798000 ndash0877497000 C 2665172000 ndash0195830000 ndash0859864000 C 3835813000 0283152000 ndash1437197000 C 4978920000 ndash0204857000 ndash0802474000 C 6505676000 ndash0216574000 ndash0771205000 C 7678527000 0226433000 ndash1319208000 C 8875127000 ndash0251684000 ndash0703235000 C 8845790000 ndash1112691000 0383544000 C 7616005000 ndash1570592000 0948642000 C 6475812000 ndash1107284000 0353147000 C 4945633000 ndash1092812000 0320013000 C 3774824000 ndash1565295000 0903163000 C 2628495000 ndash1080676000 0265289000 C 1119158000 ndash1093642000 0244670000 C ndash0052242000 ndash1637616000 0861793000 C ndash1193959000 ndash1109215000 0331010000 C ndash2676505000 ndash1073633000 0328062000 C ndash3841325000 ndash1514463000 0979035000 C ndash4995446000 ndash1053912000 0371366000 C ndash6522185000 ndash1052982000 0381089000 C ndash7676261000 ndash1483950000 0978498000 C ndash8892512000 ndash1041633000 0378747000

- 152 -

H ndash9850267000 0087677000 ndash1164894000 H ndash7723622000 0856176000 ndash2236504000 H ndash3873085000 0886115000 ndash2307512000 H ndash0031238000 0768624000 ndash2518870000 H 3857949000 0953892000 ndash2286176000 H 7723941000 0897606000 ndash2167700000 H 9831384000 0069893000 ndash1099633000 H 9779177000 ndash1450269000 0819087000 H 7614291000 ndash2243551000 1796930000 H 3751975000 ndash2237828000 1750478000 H ndash0016047000 ndash2343040000 1681308000 H ndash3832680000 ndash2159963000 1847727000 H ndash7691389000 ndash2121828000 1853393000 H ndash9834648000 ndash1354566000 0814012000 Co ndash0004249000 1140918000 0250383000 C 0931445000 3181201000 0326993000 C ndash0487068000 3279997000 0223542000 C ndash1069741000 2607436000 1368652000 C 0008159000 2107122000 2176577000 C 1235098000 2411215000 1492603000 H 1650004000 3565479000 ndash0380430000 H ndash1033454000 3774248000 ndash0564979000 H ndash2124544000 2537255000 1584462000 H ndash0094112000 1572170000 3107766000 H 2227446000 2134637000 1815486000

LUMO

HOMO

2887

239

00862

2496

1163

1382

1418

1312

0

3155

2767

0498

2588

1531

0831

Figure 47 Orbital coefficients of linear [5]phenylene

- 153 -

Figure 48 Top view of the contour plots of (a) the HOMO and (b) the LUMO of the [5]-phenylene ligand

- 154 -

Bad

Bad

Good Good

External cyclobutadiene coordination Internal cyclobutadiene coordination

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCpCoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

Figure 49 Resonance rationale for the increased stability of internal Co coordination in linear [5]phenylene

44 NMR Data for Chapter Two

- 155 -

Figure 410 1H-NMR data for the respective parent phenylene frames experimental (C6D6) and

calculated [NICS (1) B3LYP6-31+G] Assignments by NOESY DEPT HMBC and HSQC as applicable

- 156 -

Me3Si

Me3Si

SiMe3

SiMe3

1

23

4 56

7 89

10 1112

13 1415

16

17

18

Co

222

1490

1252

1450

1433

1151

744

730

11091121

14161504

11211109

1540

1499

1224

1486

217

801

SiMe3

SiMe3

Me3Si

Me3Si

Co

802

261

1484

1256

1433

1494

1155

739

781

1360

1394

269

SiMe3

SiMe3

Co

802

1294

1149

1426

1502

1194

738

779

1363

1393

268

SiMe3

SiMe3

1241

1276

8029

725

1155

1493

1430

1256

1482

222

Co

796

678674 675 796

436

037032662

724 683 747

444

TMS

TMS

TMS

TMS

213

1474

1211

1538

1499

1112

623 685

SiMe3

SiMe3Me3Si

Me3Si SiMe3

SiMe3Me3Si

Me3Si459 Co

589 681 672 745

2201204

15131096

1535

2221252

1480

1433

1149741

801

1501 1490

1475

Figure 411 Comparison of 1H-NMR (blue) and 13C-NMR assignments (C6D6)

NICS-Scan calculations Methods The free ligands were optimized at the B3LYP6-31G and the CpCo complexes at the B3LYPLANL2DZ computational levels Analytical frequency calculations were executed to ensure real minima (Nimag = 0) GIAO-B3LYP6-31+G was used to calculate NICS values The NICS-scan procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (ipc or NICSXY) and out-of-plane components (oopc or NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their interpretation

- 157 -

Since there are no published NICS-scan studies of transition metal complexed cyclic polyenes we benchmark the method with (C6H6)Cr(CO)3

53

Figure 412 NICS-scan of benzene (left) and (benzene)Cr(CO)3 (right)

The shape of the oopc curve suggests that the diamagnetic ring current in the ligand is diminished on complexation although still prevalent Thus at r = 0 Aring (ie at the benzene plane) the oopc value [NICSZZ(0)] of the complex is less negative than that of benzene and the minimum of the curve is less negative and occurs at a larger distance (ndash29911 vs ndash31910) A larger change is observed in the ipc (which is governed by the σ electrons) which shows far more negative values in the complex relative to benzene itself (eg ndash55400 vs ndash5900 and ndash13910 vs ndash0910) Therefore isotropic NICS values are misleading with respect to the diatropism in the complex because they originate largely from the diamagnetic effect of the σ framework NICS-scans for the four-membered ring B in linear [3]phenylene and its CpCo complex are shown below

00 05 10 15 20 25 30 35 40

-34-32-30-28-26-24-22-20-18-16-14-12-10

-8-6-4-202

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

oopc ipc isotropic

pp

m

r

- 158 -

Figure 413 NICS-scan above ring B of linear [3]phenylene (left) and its CpCo complex (right) Inspection of the shape and values of the oopc curve shows that the four-membered ring in the free ligand is strongly paratropic This picture changes on CpCo complexation At or close to the ring plane the values are much less positive (12100 vs 88000) become negative at greater distance and reach a minimum of -16112 Consequently the presence of the metal clearly reduces paratropic character The ipc curve is similar to that of (benzene)Cr(CO)3 Therefore again isotropic NICS values are misleading with respect to an assessment of the size of ring current effects The two isomeric CpCo complexes of linear [5]phenylene as depicted next behave in an analogous manner and engender the same conclusions as above

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

- 159 -

Figure 414 NICS-scans of linear [5]phenylene and its CpCo complexes Top left - ring B of the free ligand Top right - ring B complexed to CpCo Bottom left - ring D of the free ligand

Bottom right - ring D complexed to CpCo The effect of CpCo complexation is also reflected in the NICS-scan properties of the remaining rings To illustrate this point the NICS-scans of the central cyclohexatrienoid ring C of linear [3]phenylene are shown below first for the free ligand then for the cyclobutadiene complex

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

- 160 -

Figure 415 NICS-scans of ring C of linear [3]phenylene Left - as a free ligand Right as a

CpCo complex of the neighboring cyclobutadiene ring B The oopc curve clearly reveals a diminution of paratropism Thus at the ring plane the oopc values of the free ligand and of the complex are 177 and 110 ppm respectively Both plots show shallow and relatively distant minima at ndash3417 and ndash7316 respectively an indication of larger diamagnetic character of the latter While the ipc values also become more negative on complexation this effect is far smaller The tables that follow provide an overview of the NICS-scan results over all component rings in linear [3]- and [5]phenylene complexed and uncomplexed The diagnostic shape of the oopc curve is designated NM for no minimum indicating paratropism and M for minimum indicating diatropism Specific values are given at r = 0 Aring r = 10 Aring and the minimum (if diamagnetic) Table 416 NICS-scan Details of the oopc for Linear [3]Phenylene and its CpCo Complex at

Ring B

Ring Shape oopc00 oopc10 Minimum A M 71 ndash107 ndash11813 AndashCpCo M ndash65 ndash228 ndash22811 B NM 880 381 BndashCpCo M 121 ndash151 ndash16112 C M 177 ndash01 ndash3418 CndashCpCo M 116 ndash17 ndash9315 D NM 880 381 DndashCpCo NM 704 237 E M 71 ndash107 ndash11813 EndashCpCo M 15 ndash148 ndash15212

00 05 10 15 20 25 30 35 40

-8-6-4-202468

101214161820

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-14-12-10

-8-6-4-202468

1012

oopc ipc isotropic

pp

m

r

- 161 -

Table 417 NICS-Scan Details of the oopc for Linear [5]Phenylene and its CpCo Complex at Ring B

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M ndash62 ndash227 ndash22811 B NM 898 396 BndashCpCo M 137 ndash148 ndash15612 C M 176 00 ndash3317 CndashCpCo M 152 ndash09 ndash8415 D NM 846 357 DndashCpCo NM 668 223 E M 164 ndash12 ndash4116 EndashCpCo M 142 ndash17 ndash5315 F NM 846 357 FndashCpCo NM 807 340 G M 176 00 ndash3317 GndashCpCo M 161 ndash04 ndash3216 H NM 898 396 HndashCpCo NM 867 378 I M 83 ndash97 ndash10813 IndashCpCo M 64 ndash109 ndash12113

Table 418 NICS-scan Details of the oopc for Lnear [5]Phenylene and its CpCo Complex at

Ring D

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M 19 ndash150 ndash15912 B NM 898 396 BndashCpCo NM 717 256 C M 176 00 ndash3317 CndashCpCo M 110 ndash122 ndash12210 D NM 846 357 DndashCpCo M 151 ndash169 ndash17311 E M 164 ndash12 ndash4116 EndashCpCo M 151 ndash169 ndash17311 F NM 846 357 FndashCpCo NM 685 231 G M 176 00 ndash3317 GndashCpCo M 148 ndash15 ndash5415 H NM 898 396 HndashCpCo NM 850 370

I M 83 ndash97 ndash10813

- 162 -

The data clearly show that on CpCo complexation the paramagnetic ring current contributions decrease (or the diamagnetic ring current contributions increase) The strongest effect is on the complexed cycle but it occurs for all rings even the most remote (eg I in the linear [5]phenylene complexed at ring B) Thus upon complexation the paratropic (and by inference antiaromatic) character of the phenylenes decrease 45 Experimental Section for Chapter Three Angular [3]phenylene 2290 angular [4]phenylene 17111 and [7]heliphene10 were prepared according to the literature Ni(COD)(PMe3)2

112 To a solution of Ni(COD)2 (0275 g 10 mmol) in dry and vigorously degassed THF (10 mL) PMe3 (020 mL 0150 g 20 mmol) was added via syringe in a single portion After stirring at RT for 24 h the mixture was transferred using a canula and filtered under Ar to remove unreacted starting material The solvent was removed on the high vacuum line and the resulting product dried for 3 h It is extremely air sensitive and must be manipulated under an inert atmosphere at all times Yellow solid (0306 g 96 ) 1H-NMR (400 MHz C6D6) δ = 412 (d J = 112 Hz 4 H) 238 (br t J = 52 Hz 4 H) 225 (t J = 52 Hz 4 H) 102 (d J = 32 Hz 18 H) ppm 31P-NMR (162 MHz C6D6) δ = ndash946 (s) ppm Adducts of diphenylacetylene 88 to angular [3]phenylene 22 ndash compounds 89 and 90

In a glove box an Ace pressure tube was charged with angular [3]phenylene 22 (0014 g 006 mmol) diphenylacetylene 88 (0098 g 0055 mmol) THF (5 mL) and Ni(COD)(PMe3)2 (70 microL 008 M in THF 0006 mmol) The reaction vessel was tightly sealed removed from the glovebox and heated to 75ndash80 oC (oil bath) for 23 h After cooling to RT the solvent was removed by rotary evaporation and the residue purified by flash chromatography on silica gel using gradient elution (101 and then 81 hexaneCH2Cl2) After a small amount of angular [3]phenylene 22 (0001 g) the monoadduct 89 (0004 g 20 ) eluted to give a yellow solid mp 195ndash196 degC 1H-NMR (500 MHz CDCl3) δ = 853 (d J = 84 Hz 1 H) 831 (d J = 80 Hz 1 H) 755 (ddd J = 16 64 80 Hz 1 H) 740ndash732 (m 2 H) 725ndash715 (m 6 H) 715ndash711 (m 2 H) 708 (d J = 65 Hz 2 H) 704 (d J = 80 Hz 1 H) 648 (t J = 72 Hz 1 H) 643 (d J = 70 Hz 1 H) 624 (t J = 75 Hz 1 H) 401 (d J = 70 Hz 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1525 15101 15096 1495 1399 13883 13879 1342 1320 1312

- 163 -

13083 13075 1282 1280 1277 1276 1275 1268 1266 1265 1264 1250 1235 1223 1179 1164 1156 ppm one peak in the region δ = 128ndash126 ppm is

presumed to be accidentally isochronous IR (KBr) ν~ = 3060 1490 1481 1442 1415 1159 1072 755 734 698 cmndash1 UV-Vis (CH3CN) λmax (log ε) 233 (442) 265 (450) 278 (sh) 294 (sh) 306 (447) 318 (449) 329 (sh) 380 (344) 399 (366) 420 (366) nm MS (70 eV) mz () 405 [M++1] (35) 404 [M+] (100) 326 (13) HRMS (EI) calcd for C32H20 4041565 found 4041571 Elemental analysis calcd for C32H20 C 9502 H 498 found 9479 460 Subsequent elution furnished 5678-tetraphenylpicene (90) (0009 g 59 ) as a white solid mp 325ndash327 degC the molecule exhibits hindered rotation of the 67-phenyl groups on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 891 (s 2 H) 885 (d J = 84 Hz 2 H) 769 (ddd J = 28 52 80 Hz 2 H) 750ndash744 (m 4 H) 744ndash732 (m 4 H) 720 (tt J = 16 72 Hz 2 H) 696 (dt J = 08 76 Hz 2 H) 689 (tt J = 09 76 Hz 2 H) 662 (br s 4 H) 617 (d J = 76 Hz 2 H) 607 (br s 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1403 1401 1377 1367 1335 1325 1324 1306 1300 1295 1292

1283 1277 1269 1264 1263 1262 1256 1254 1228 1213 ppm IR (KBr) ν~ = 3051 2922 1599 1490 1467 1442 1263 1072 1027 758 702 630 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (461) 307 (474) 352 (417) 366 (414) nm MS (70 eV) mz () 583 [M++1] (52) 582 [M+] (100) 505 (24) 504 (9) 426 (7) HRMS (EI) calcd for C46H30 5822348 found 5822336 1278-Tetraphenylbenzo[c]chrysene (91)

In a glovebox an Ace pressure tube was charged with 88 (0020 g 0050 mmol) diphenylacetylene 88 (0026 mg 0148 mmol) Ni(COD)(PMe3)2 (62 microL of a 008 M solution in THF) and THF (5 mL) The reaction vessel was sealed removed from the glovebox and heated to 85 degC for 39 h After removal of the solvent the residue was purified by flash chromatography on silica gel (eluting with 81 hexaneCH2Cl2) producing a white solid (0023 g) which was found to consist of starting material (88 18 mg) 90 (0001 g 6 ) and 91 Further purification by chromatography afforded pure 91 (0017 g 74 ) as a white solid mp 273ndash274 degC the 12-phenyl groups of 91 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 869 (d J = 95 Hz 1 H) 830ndash822 (m 1 H) 801 (d J = 75 Hz 1 H) 780ndash747 (m 2 H) 770 (ddd J = 10 70 85 Hz 1 H) 762 (dt J = 15 75 Hz 1 H) 753 (ddd J = 15 70 85 Hz 1 H) 738ndash732 (m 2 H) 730 (td J = 15 75 Hz 1 H) 729ndash722 (m 6 H) 722ndash717 (m 2 H) 717ndash710 (m 2 H) 710ndash695 (m 3 H) 680ndash640 (m 3 H) 635 (d J = 70 Hz 1 H) 623ndash595 (br s 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1418 1400 1395 1394 1378 1377 1375 1357 1323 1322 1316 1314 13113 13107 1309 1308 1307 1305 1296 1295 1288 1282 1277 1275 1274 1273 1270 12653 12647 1264 1260 1256 1253 1252 1251

- 164 -

1243 1231 1208 ppm due to extensive signal overlap four peaks are presumed to be isochronous in the regions δ = 132ndash130 and 128ndash125 ppm IR (KBr) ν~ = 3058 1601 1489 1442 1263 1073 773 762 736 699 628 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 250 (487) 313 (511) 340 (sh) nm MS(EI) mz () 583 (M++1 72) 582 (M+ 100) 505 (24) 391 (13) HRMS (EI) calcd for C46H30 5822348 found 5822341 Elemental analysis calcd for C46H30 C 8933 H 500 found 8914 493 Ni(PhCequivCPh)(PMe3)2 (92)91

In a glove box PMe3 (203 microL 0152 g 20 mmol) was mixed with a suspension of Ni(COD)2 (0275 g 10 mmol) in hexane (15 mL) Diphenylacetylene 88 (0178 g 10 mmol) was then added in one portion resulting in an immediate color change from yellow to red The mixture was stirred at room temperature for 195 h during which the color gradually turning returning to yellow Upon concentration (to ~5 mL) a yellow precipitate formed collected by filtration under nitrogen The resulting powder 92 (0370 g 95 ) was dried under vacuum providing a yellow solid 1H-NMR (500 MHz C6D6) δ = 751 (d J = 75 Hz 4 H) 717 (t J = 75 Hz 4 H) 702 (t J = 75 Hz 2 H) 101 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1406 1287 1279 196 (d JC-P = 188 Hz) ppm 31P-NMR (162 MHz C6D6) δ = ndash1282 (br s) ppm Adducts of 3-hexyne to angular [3]phenylene 22 ndash compounds 104 and 105

In a glovebox 22 (0014 mg 0060 mmol) 3-hexyne 103 (57 microL 0004 g 0050 mmol) Ni(COD)(PMe3)2 (0002 g 0005 mmol) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 14 h Flash chromatography on silica gel gave a first fraction that was recrystallized from CH2Cl2 to provide pure 104 (70 mg 45 ) as a yellow solid mp 169ndash170 degC 1H-NMR (500 MHz CDCl3) δ = 843 (d J = 70 Hz 1 H) 821 (d J = 75 Hz 1 H) 795 (d J = 70 Hz 1 H) 752 (dt J = 10 70 Hz 1 H) 748 (dt J = 10 70 Hz 1 H) 697 (d J = 75 Hz 1 H) 673ndash662 (m 3 H) 655 (d J = 55 Hz 1 H) 307 (q J = 75 Hz 2 H) 299 (q J = 75 Hz 2 H) 133 (t J = 75 Hz 3 H) 130 (t J = 75 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1530 1516 1504 1471 1360 1330 13129 13127 1307 1282 1279 1267 1263 1259 1246 1239 1228 1179 1159 1156 232 214 164 149 ppm IR (KBr) ν~ = 3045 2960 1600 1481 1414 1261 1197 1159 758 740 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (463) 299 (sh) 309 (460) 320 (462) 331 (452) 380 (356) 399 (374) 419 (371) nm MS (70 eV) mz () 309 [M++1] (26) 308 [M+] (100) 293 [M+ndash15] (8) 278 [M+ndash30] (21) HRMS (EI) calcd for C24H20 3081565 found 3081666

- 165 -

A second fraction was 105 (0002 g 11 ) isolated as a yellow solid mp 120ndash122 degC 1H-NMR (400 MHz CDCl3) δ = 830 (d J = 72 Hz 1 H) 797 (d J = 76 Hz 1 H) 761 (d J = 80 Hz 1 H) 761ndash749 (m 2 H) 700 (d J = 80 Hz 1 H) 699 (d J = 72 Hz 1 H) 674 (quint J = 76 Hz 2 H) 658 (d J = 64 Hz 1 H) 307 (q J = 76 Hz 2 H) 302 (q J = 76 Hz 2 H) 132 (t J = 76 Hz 3 H) 131 (t J = 76 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1525 1519 1489 1472 1356 1345 1324 1318 1288 1283 1279 1273 1259 1252 1251 1250 1241 1179 1165 1160 2213 2205 149 146 ppm IR (KBr) ν~ = 3063 2958 2925 1490 1442 1417 1262 1147 1099 822 762 730 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 281 (434) 291 (448) 303 (460) 313 (sh) 369 (346) 389 (373) 410 (377) nm MS (70 eV) mz () 309 [M++1] (28) 308 [M+] (100) 293 [M+ndash15] (13) 278 [M+ndash30] (21) 226 (22) 149 (29) HRMS (EI) calcd for C24H20 3081565 found 3081664 Adducts of 14-dimethoxy-2-butyne to angular [3]phenylene 22 ndash compounds 107 and 108

In a glovebox 22 (0011 g 0050 mmol) 14-dimethoxybut-2-yne 106 (0034 g 030 mmol) Ni(COD)(PMe3)2 (63 microL of a 008 M solution in THF) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 165 h The 1H-NMR spectrum of the crude indicated the formation of 107 and 108 in the ratio of 61 Flash chromatography on silica gel gave first 107 (0012 g 68 ) as a yellow solid mp 150ndash151 degC 1H-NMR (400 MHz CDCl3) δ = 841 (dd J = 32 64 Hz 1 H) 819 (d J = 80 Hz 1 H) 810 (dd J = 36 64 Hz 1 H) 754 (dd J = 36 64 Hz 2 H) 700 (d J = 80 Hz 1 H) 676 (t J = 64 Hz 1 H) 674ndash665 (m 2 H) 656 (d J = 60 Hz 1 H) 493 (s 2 H) 488 (s 2 H) 353 (s 3 H) 345 (s 3 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1527 1513 1509 1484 1336 1318 1316 1309 1296 1283 1282 1272 1270 1259 1255 1238 1225 1183 1166 1161 677 675 584 575 ppm IR (KBr) ν~ = 3072 2927 1485 1446 1417 1376 1185 1097 956 898 821 743 730 cmndash1 MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (100) 308 [M+ndash38] (26) 293 (34) 280 (15) 265 (44) HRMS (EI) calcd for C24H20O2 3401463 found 3401466 Further elution provided 108 (0002 g 9 ) as a yellow solid mp 156ndash157 degC 1H-NMR (400 MHz CDCl3) δ = 831ndash824 (m 1 H) 813ndash806 (m 1 H) 775 (d J = 80 Hz 1 H) 763ndash756 (m 2 H) 702 (d J = 80 Hz 1 H) 699 (d J = 64 Hz 1 H) 681ndash670 (m 2 H) 660 (d J = 64 Hz 1 H) 493 (s 2 H) 487 (s 2 H) 353 (s 3 H) 351 (s 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1523 1517 1505 1470 1327 1322

- 166 -

1316 1315 1297 1285 1282 1276 1268 1266 12564 12555 1252 1181 1168 1165 6804 6801 5838 5835 ppm IR (KBr) ν~ = 2925 1498 1415 1379 1262 1187 1095 1061 940 930 814 750 734 717 cmndash1 UV-Vis (CH3CN) λmax (log ε) 237 (458) 287 (462) 298 (472) 314 (sh) 371 (357) 387 (380) 407 (386) nm MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (56) 308 [M+ndashMeOH] (8) 293 (27) 279 (17) 265 (24) HRMS (EI) calcd for C24H20O2 3401463 found 3401456 Optimized cycloaddition reaction between 22 and 88 In a glovebox a round bottom flask was charged with 22 (0058 g 0257 mmol) and Ni(COD)(PMe3)2 (0008 g 0034 mmol) Both reagents were then dissolved in THF (100 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0093 g 0521 mmol) in THF (20 mL) was taken up in a gas-tight syringe and slowly added over 13 h via syringe pump to the boiling mixture of 22Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 6 h After this time mixture was cooled to RT and the solvent removed by rotary evaporation to give a yellow residue The crude product was passed through a plug of silica gel eluting with a mixture of hexanesCH2Cl2 (101) to afford a yellow solid Analysis of the product by 1H-NMR (using the solvent peak of CDCl3 as the internal standard) revealed the presence of 89 and 90 in a 1387 ratio Adducts of diphenylacetylene 88 to angular [4]phenylene 17 ndash compounds 130ndash134 In a glovebox angular [4]phenylene 17 (0036 g 012 mmol) diphenylacetylene 88 (0018 g 010 mmol) and Ni(COD)(PMe3)2 (125 microL of a 008 M solution in THF) were added to an Ace pressure tube and dissolved in THF (6 mL) The reaction vessel was sealed removed from the glovebox and stirred at 75 degC for 5 h Flash chromatography

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph Ph PhPh Ph

132131

133 134

130

- 167 -

on silica gel gave starting material (0013 g of 17) as well as a yellow residue Further purification of the latter by preparative TLC afforded (in order of elution) 132 131 133 134 and 139 Compound 130 (0008 g 28 ) was obtained as a white solid mp 360ndash363 degC (decomp) the phenyl groups located on the central benzene ring of 130 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 904 (d J = 90 Hz 2 H) 895 (d J = 90 Hz 2 H) 881 (d J = 85 Hz 2 H) 765 (ddd J = 15 65 80 Hz 2 H) 742ndash736 (m 4 H) 734 (dd J = 10 85 Hz 2 H) 721 (tt J = 15 75 Hz 2 H) 716 (d J = 75 Hz 2 H) 698 (dd J = 05 80 Hz 2 H) 693 (tt J = 10 85 Hz 2 H) 681 (tt J = 10 70 Hz 2 H) 676 (t J = 75 Hz 4 H) 656 (t J = 70 Hz 4 H) 633 (d J = 70 Hz 4 H) 614 (d J = 75 Hz 2 H) 595 (d J = 70 Hz 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 14058 14057 1403 1394 1375 1374 1345 1341 1336 1327 1324 1309 1308 1301 1294 1292 1282 1276 1268 1263 12622 12619 1259 1257 1254 1250 1227 1214 1212 ppm IR (KBr) ν~ = 3052 2923 1600 1491 1440 1261 1076 1029 809 783 759 747 700 631 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 248 (498) 306 (sh) 329 (520) 388 (463) nm MS(FAB) mz () 836 [M++2] (18) 835 [M++1] (42) 834 [M+] (54) 757 (8) HRMS (FAB) calcd for C66H42 8343287 found 8343280 Compound 131 (0003g 6) was isolated as yellow solid mp 251ndash253 degC (decomp) 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 775 (dt J = 10 80 Hz 1 H) 752 (dt J = 10 80 Hz 1 H) 746 (d J = 80 Hz 1 H) 737 (d J = 65 Hz 1 H) 726ndash721 (m 5 H) 721ndash716 (m 2 H) 716ndash711 (m 5 H) 709 (t J = 75 Hz 1 H) 705 (d J = 80 Hz 1 H) 699 (d J = 70 Hz 1 H) 619 (d J = 60 Hz 1 H) 614 (d J = 60 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1502 1492 1491 1490 1485 1444 1394 1392 1382 1371 1367 1351 13271 13268 13092 13088 1299 12898 12896 1283 12764 12760 1274 12654 12652 1261 1253 1245 1195 1184 1172 1138 1129 ppm one peak is presumed to be accidentally isochronous in the region between δ = 130ndash124 ppm IR (KBr) ν~ = 3023 2921 1602 1478 1371 1262 1026 809 795 748 725 695 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 252 (473) 285 (456) 320 (453) 335 (462) 353 (437) 370 (432) 410 (376) 431 (372) nm MS (FAB) mz () 479 [M++1] (27) 478 [M+] (70) 300 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781718 Molecule 132 (0002 g 5 ) was acquired as a yellow solid 1H-NMR (500 MHz CDCl3) δ = 726ndash721 (m 2 H) 716ndash709 (m 6 H) 695ndash690 (m 2 H) 676 (d J = 80 Hz 2 H) 673 (d J = 75 Hz 2 H) 671 (t J = 75 Hz 2 H) 665 (t J = 70 Hz 2 H) 658 (d J = 65 Hz 2 H) 648 (d J = 65 Hz 2 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1516 1510 1497 1490 1391 1372 1310 1303 1283 1281 1277 1275 1273 1264 1216 1168 1163 ppm UV-Vis (CH2Cl2) λmax (log ε) 254 (476) 294 (sh) 300 (465) 322 (sh) 338 (392) 376 (400) nm MS (FAB) mz () 479 [M++1] (50) 478 [M+] (86) 391 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781723 Adduct 133 (0017 g 33 ) was isolated as a red crystalline solid mp 290ndash291 degC 1H-NMR (500 MHz CDCl3) δ = 800 (d J = 80 Hz 2 H) 720ndash713 (m 6 H) 708ndash702 (m 4 H) 690 (d J = 80 Hz 2 H) 648 (t J = 70 Hz 2 H) 642 (d J = 70 Hz 2 H) 623 (t J = 70 Hz 2 H) 393 (d J = 70 Hz 2 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1522 1509 1506 1496 1392 1359 1315 1309 1282 1278 1277 1266 1250 1232 1181 1166 1157 ppm IR (KBr) ν~ = 3057 1489 1441 1412 1273

- 168 -

1161 810 738 709 690 623 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 271 (474) 285 (469) 345 (460) 353 (454) 414 (483) 432 (381) 460 (363) nm MS (70 eV) mz () 479 [M++1] (46) 478 [M+] (100) 400 (10) HRMS (EI) calcd for C38H22 4781722 found 4781719 Compound 134 (0009 g 27 ) was obtained as a yellow solid mp 178ndash180 degC the phenyl groups of this molecule located at the bay regions of the phenanthrene subunit are static while the others exhibit hindered rotation on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 880 (d J = 88 Hz 1 H) 879 (d J = 88 Hz 1 H) 863 (d J = 92 Hz 1 H) 834 (d J = 80 Hz 1 H) 770ndash758 (m 1 H) 748ndash732 (m 4 H) 727ndash721 (m 2 H) 721ndash710 (m 2 H) 706 (d J = 80 Hz 1 H) 702ndash691 (m 3 H) 684 (t J = 74 Hz 1 H) 673 (br s 2 H) 655 (t J = 76 Hz 2 H) 650ndash638 (m 3 H) 630ndash610 (m 4 H) 590 (d J = 76 Hz 2 H) 410 (d J = 68 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1527 1510 1509 1494 1403 1400 1399 1396 1373 1371 1339 1335 1330 1325 1324 1317 1309 1306 1305 1304 1299 1295 1291 1283 1282 1281 1277 1275 1272 1269 1268 12632 12627 1261 12562 12556 1254 1253 1239 1226 1216 1209 1180 1162 1154 ppm three peaks are presumed to be accidentally isochronous in the region δ = 128ndash125 ppm IR (KBr) ν~ = 2964 1262 1096 1022 801 701 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 267 (501) 303 (497) 335 (489) 361 (sh) 379 (464) 427 (402) 456 (377) nm MS(FAB) mz () 658 [M++2] (22) 657 [M++2] (67) 656 [M+] 1(00) 579 (12) 502 (7) HRMS (FAB) calcd for C52H32 6562504 found 6562492 Cycloaddition reaction between [7]heliphene 142 and diphenylacetylene 88 In a glovebox a round bottom flask was charged with 142 (0008 g 0152 mmol) and Ni(COD)(PMe3)2 (0001 g 0003 mmol) The mixture was then dissolved in THF (25 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0016 g 300 mmol) in THF (10 mL) was taken up in a gas-tight syringe and slowly added over 12 h via syringe pump to the boiling mixture of 142Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 12 h After this time it was cooled to RT and the solvent removed by rotary evaporation to give an orange residue The crude product was chromatographed on silica gel (25 x 165 cm) eluting first with hexaneCH2Cl2 (101 then 51) The first product collected was diphenylacetylene 88 (0005 g) followed by a yellow band Analysis of the isolated yellow solid (0002 g) revealed a large mixture of products MS(FAB) mz () 532 (70) 664 (25) 700 (13) 732 (16) 911 (21) 1056 (11) 1234 (4) 1412 (5) 46 Computational Details for Chapter Three All geometries of intermediates and transition states were optimized fully without symmetry constraints using the Gaussian 03 program100 The DFT computations were carried out using the B3LYP functional as implemented in Gaussian The nickel atom was described by a double-zeta basis set (LANL2DZ)113 and the 6-31G(d) basis set114

- 169 -

was used for the other elements Frequency calculations were performed to confirm the nature of the stationary points and to obtain zero-point energies (ZPE) The connectivity between stationary points was established by intrinsic reaction coordinate calculations (IRC) The Chemcraft program102 was used to draw the calculated structures

47 References

1) Harvey R G Polycyclic Aromatic Hydrocarbons Wiley-VCH New York 1997 2) (a) Chem Rev 2001 101 1115ndash1566 Special Issue Aromaticity (b) Chem Rev

2005 105 3343ndash3397 Special Issue Delocalization-Pi and Sigma 3) (a) Cyranski M K Krygowski T M Katritzky A R Schleyer P von R J Org

Chem 2002 67 1333 (b) Stanger A Chem Commun 2009 1939 4) (a) Minkin V I Glukhovtsev M N Simkin B Ya Aromaticity and Antiaromaticity

Electronic and Structural Aspects Wiley New York 1994 pp 63ndash74 (b) Garratt P J Aromaticity Wiley New York 1986 pp 30ndash34 93ndash95

5) (a) Wu J Muumlllen K In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 3 pp 90ndash139 (b) Wu J Pisula W Muumlllen K Chem Rev 2007 107 718 (c) Handbook of Organic Electronics and Photonics Nalwa H S Ed American Scientific 2008

6) Miljanić O Š Vollhardt K P C In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 4 pp 140ndash197

7) (a) Shepherd M K Cyclobutarenes The Chemistry of Benzocyclobutene Biphenylene and Related Compounds Elsevier Amsterdam 1991 (b) Toda F Garratt P J Chem Rev 1992 92 1685

8) (a) Diercks R Vollhardt K P C J Am Chem Soc 1986 108 3150 (b) Mohler D L Vollhardt K P C Wolff S Angew Chem Int Ed Engl 1990 29 1151 (c) Mohler D L Vollhardt K P C Wolff S Angew Chem Int Ed Engl 1995 34 563

9) (a) Holmes D Kumaraswamy S Matzger A J Vollhardt K P C Chem Eur J 1999 5 3399 (b) Dosche C Kumke M U Ariese F Bader A N Gooijer C Dosa P I Han S Miljanic O Š Vollhardt K P C Puchta R van Eikema Hommes N J R Phys Chem Chem Phys 2003 5 4563 (c) Wagner H-U Szeimies G Chandrasekhar J Schleyer P von R Pople J A Binkley J S J Am Chem Soc 1978 100 1210

10) Han S Bond A D Disch R L Holmes D Schulman J M Teat S J Vollhardt K P C Whitener G D Angew Chem Int Ed 2002 41 3223

11) Jackman L M Sondheimer F Amiel Y Ben-Efraim D A Gaoni Y Wolovsky R Bothner-By A A J Am Chem Soc 1962 84 4307

12) Untch K G Wysocki D C J Am Chem Soc 1967 89 6386 13) (a) Chen Z Wannere S C Corminboeuf C Puchta R Schleyer P von R

Chem Rev 2005 105 3842 and the references therein (b) Steinmann S N Jana D F Wu J I-C Schleyer P v R Mo Y Corminboeuf C Angew Chem Int Ed 2009 48 9828

14) Schleyer P v R Manoharan M Wang Z-X Kiran B Jiao H Puchta R van Eikema Hommes N J R Org Lett 2001 3 2465

- 170 -

15) Schulman J M Disch R L Jiao H Schleyer P v R J Phys Chem A 1998 102 8051

16) Jeany H Mason K G Sketchley J M Tetrahedron Lett 1970 11 485 17) Brown F C Choi N Coulston K J Eastwood F W Wiersum U E

Jenneskens L W Tetrahedron Lett 1994 35 4405 18) (a) Linear [3]phenylene Dosa P I Schleifenbaum A Vollhardt K P C Org Lett

2001 3 1017 (b) Angular [3]phenylene Matzger A J Vollhardt K P C Chem Commun 1997 1415 (c) Angular [4]phenylene Dosa P I Gu Z Hager D Karney W L Vollhardt K P C Chem Commun 2009 1967

19) Perthuisot C Edelbach B L Zubris D L Simhai N Iverson C N Muumlller C Satoh T Jones W D J Mol Catal A 2002 189 157

20) Dosche C Loumlhmannsroumlben H-G Bieser A Dosa P I Han S Iwamoto M Schleifenbaum A Vollhardt K P C Phys Chem Chem Phys 2002 4 2156

21) (a) Deniz A A Peters K S Snyder G J Science 1999 286 1119 (b) Fattahi A Lis L Tian Z Kass P S Angew Chem Int Ed 2006 45 4984 (c) Bally T Angew Chem Int Ed 2006 45 6616

22) Anslyn E Dougherty D Modern Physical Organic Chemistry University Science Books Palo Alto 2006

23) Crabtree R H The Organometallic Chemistry of the Transition Metals 4th Ed Wiley-VCH New York 2005

24) Mestdagh H Postdoctoral Research Report University of California Berkeley 1986

25) Hirthammer M Vollhardt K P C J Am Chem Soc 1986 108 2481 26) Blanco L Helson H E Hirthammer M Mestdagh H Spyroudis S Vollhardt K

P C Angew Chem Int Ed Engl 1987 26 1246 27) Berris B C Hovakeemian G H Lai Y-H Mestdagh H Vollhardt K P C J

Am Chem Soc 1985 107 5670 28) Dosa P I The Chemistry of Angular and Linear [N]Phenylenes PhD Thesis

University of California Berkeley 2002 29) Diercks R Eaton B E Guumlrtzgen S Jalisatgi S Matzger A J Radde R H

Vollhardt K P C J Am Chem Soc 1998 120 8247 30) (a) Nambu M Siegel J S J Am Chem Soc 1988 110 3675 (b) Nambu M

Hardcastle K Baldridge K K Siegel J S J Am Chem Soc 1992 114 369 31) Nambu M Mohler D L Hardcastle K Baldridge K K Siegel J S J Am

Chem Soc 1993 115 6138 32) Kumaraswamy S Jalisatgi S S Matzger A J Miljanić O Š Vollhardt K P C

Angew Chem Int Ed 2004 43 3711 33) (a) Eisch J J Piotrowski A M Han K I Kruumlger C Tsay Y H Organometallics

1985 4 224 (b) Schwager H Spyroudis S Vollhardt K P C J Organometallic Chem 1990 382 191

34) Albright T A Hofmann P Hoffmann R Lillya C P Dobosh P A J Am Chem Soc 1983 105 3397

35) Doumltz K H Jahr H C Chem Rec 2005 4 61 36) Gridnev I D Coord Chem Rev 2008 252 1798 37) Eickmeier C Holmes D Junga H Matzger A J Scherhag F Shim M

Vollhardt K P C Angew Chem Int Ed Engl 1999 38 800

- 171 -

38) Groszligmann T N Haptotropism in Linear Phenylene Complexes Diplomarbeit Thesis University of California Berkeley 2004

39) Dinculear photothermal haptotropic systems Tsuchiya K Ideta K Mogi K Sunada Y Nagashima H Dalton Trans 2008 2708 and the references therein

40) Additive assisted photothermal haptotropic systems (a) Jahr H C Nieger M Doumltz H K Chem Eur J 2005 11 5333 d) Herbert D E Tanabe M Bourke S C Lough A J Manners I J Am Chem Soc 2008 130 4166 e) Ieong N S Manners I J Organomet Chem 2008 693 802 and references therein

41) (a) Zhu G Tanski T M Churchill D G Janak K E G Parkin G J Am Chem Soc 2002 124 13658 (b) Zhu G Pang G Parkin G J Am Chem Soc 2008 130 1564

42) Selected reviews of photobased devices and molecular switches (a) Balzani V Credi A Venturi M Chem Soc Rev 2009 38 1542 (b) Kay E R Leigh D A Zerbetto F Angew Chem Int Ed 2007 46 72 (c) Photochromism Molecules and Systems Duumlrr H Bouas-Laurent H Eds Elsevier Amsterdam 2003 (d) Feringa B Molecular Switches Wiley-VCH Weinheim 2001

43) (a) a) Photofunctional Transition Metal Complexes Yam V W W Ed Springer Berlin 2007 b) Coppens P Novozhilova I Kovalevsky A Chem Rev 2002 102 861 c) Guumltlich P Garcia Y Woike T Coord Chem Rev 2001 219ndash221 839

44) (a) Lambert J B Mazozola E P Nuclear Magnetic Resonance Spectroscopy An Introduction to Princples Applications and Experimental Methods Pearson Education Upper Saddle River 2004 (b) Berger S Braun S 200 and More NMR Experiments A Practical Course Wiley-VCH Weinheim 2004 (c) Friebolin H Basic One- and Two-Dimensional NMR Spectroscopy 4th edition Wiley-VCH Weinheim 2005

45) (a) Schulman J M Disch R L J Phys Chem A 2003 107 5223 (b) Schulman J M Disch R L J Am Chem Soc 1996 118 8470 and the references cited therein

46) (a) Bursten B E Fenske R F Inorg Chem 1979 18 1760 (b) Chinn J W Jr Hall M B Inorg Chem 1983 22 2759 (c) Datta A Pati S K J Am Chem Soc 2005 127 3496

47) Ooloba K Haptotropic Shifts in the Linear [N]-Phenylene (N=3 4 and 5) and Angular [3]-Phenylene Cyclopentadienylcobalt Complexes PhD Thesis University of Houston 2008

48) Hillard III R L Vollhardt K P C J Am Chem Soc 1977 99 4058 49) Berris B C Lai Y-H Vollhardt K P C J Chem Soc Chem Commun 1982

953 50) (a) Rausch M D Genetti R A J Org Chem 1970 35 3888 (b) Hart W P

Rausch D M J Organometallic Chem 1988 355 455 51) Duclos R I Vollhardt K P C Yee J L S J Organomet Chem 1979 174 109 52) (a) Myers A G Sogi M Lewis M A Arvedson S P J Org Chem 2004 69

2516 (b) Wolfart V Ramming M Gleiter R Nuber B Pritzkow H Rominger F Eur J Inorg Chem 1999 499 (c) Mitchell R H Chen Y Khalifa N Zhou P J Am Chem Soc 1998 120 1785 (d) McGlinchey M J Burns R C Hofer R Top S Jaouen G Organometallics 1986 5 104

53) Feixas F Jimeacutenez-Halla J O C Matito E Poater J Solagrave M Pol J Chem

- 172 -

2007 81 783 54) (a)Stanger A J Org Chem 2006 71 883 (b) Stanger A Chem Eur J 2006 12

2745 (c) Tsipis A C Phys Chem Chem Phys 2009 11 8244 (d) Stanger A Chem Commun 2009 1939

55) For very recent literature compilations of theoretical (and experimental) treatments of haptotropism in arene metal complexes see a) Joistgen O Pfletschinger A Ciupka J Dolg M Nieger M Schnakenburg G Froumlhlich R Kataeva O Doumltz K H Organometallics 2009 28 3473 b) Pfletschinger A Dolg N J Organomet Chem 2009 694 3338 c) Jimeacutenez-Halla J O C Robles J Solagrave M Organometallics 2008 27 5230 d) Kirillov E Kahlal S Roisnel T Georgelin T Saillard J-Y Carpentier J-F Organometallics 2008 27 387 and references therein

56) Jimeacutenez-Halla J O C Robles J Solagrave M J Phys Chem A 2008 112 1202 57) Oprunenko Y Gloriozov I Lyssenko K Malyugina S Mityuk D Mstislavsky

V Guumlnther H von Firks G Ebener M J Organomet Chem 2002 656 27 58) Muumlller J Gaede P E Qiao K J Organomet Chem 1994 480 213 59) Bianchini C Caulton K G Chardon C Doublet M L Eisenstein O Jackson

S A Johnson T J Meli A Peruzzini M Streib W E Vacca A Vizzat F Organometallics 1994 13 2010

60) (a) De Boer E Van Willigen H V Prog Nuc Mag Res Spec 1967 2 111 (b) Memory J D Wilson N K NMR of Aromatic Compounds Wiley-VCH New York 1982

61) (a) Poli R Chem Rev 1996 96 2135 and the references cited therein (b) Schroumlder D Shaik S Schwartz H Acc Chem Res 2000 33 139 (c) Harvey J N Poli R Smith K M Coord Chem Rev 2003 237 347 and the references cited therein

62) For computational examples of 16 electron triplet Cp cobalt species influencing cobalt-mediated reactions see (a) Siegbahn P E M J Am Chem Soc 1996 118 1487 (b) Poli R Smith K M Eur J Inorg Chem 1999 877 (c) Carreoacuten-Macedo J-L Harvey J N J Am Chem Soc 2004 126 5789 (d) Petit A Richard P Cacelli I Poli R Chem Eur J 2006 12 813 (e) Aubert C Betschmann P Eichberg M J Gandon V Geny A Heckrodt T J Lehmann J Malacria M Masjost B Paredes E Vollhardt K P C Whitener G D Chem Eur J 2007 13 7443 (f) Gandon V Agenet N Vollhardt K P C Malacria M Aubert C J Am Chem Soc 2009 131 3007

63) Illustrative examples (a) Olson W L Stacy A M Dahl L F J Am Chem Soc 1986 108 7646 (b) Wadepohl H Galm W Pritzkow H Wolf A Chem Eur J 1996 2 1453 (c) Knijnenburg W Hetterscheid D Kooistra T M Budzelaar P H M Eur J Inorg Chem 2004 1204

64) Benito-Garagorri D Bernskoetter W H Lobkovsky E Chirik P J Organometallics 2009 28 4807

65) Fox J P Ramdhanie B Zareba A A Czernuszewicz R S Goldberg D P Inorg Chem 2004 43 6600

66) Guennic B L Floyd T Galan B R Autschbach J Keister J B Inorg Chem 2009 48 5504

67) Cremer C Burger P J Am Chem Soc 2003 125 7664

- 173 -

68) Atkins P de Paula J P Physical Chemistry 8th Edition Oxford University Press Oxford 2006

69) Butters T Toda F Winters W Angew Chem Int Ed Engl 1980 19 926 70) Mann B E Taylor B F 13C Data for Organometallic Compounds Academic

London 1981 71) For a review on triple decker arene complexes and closely related syn dinuclear

systems see (a) Beck V OlsquoHare D J Organomet Chem 2004 698 3920 and the references therein For a review of trinuclear CpCo(arene) complexes see (b) Wadepohl H Angew Chem Int Ed Engl 1992 31 247 and the references therein

72) Jonas K Koepe G Schieferstein L Mynott R Kruumlger C Tsay Y-H Angew Chem Int Ed Engl 1983 22 620 Angew Chem Suppl 1983 920

73) Muumlller J Gaede P E Qiao K Angew Chem Int Ed Engl 1993 32 1697 74) Schneider J J Wolf D Janiak C Heinemann O Rust J Kruumlger C Chem

Eur J 1998 4 1982 75) Schneider J J Denninger U Heinemann O Kruumlger C Angew Chem Int Ed

Engl 1995 34 592 76) Budzelaar P H M Moonen N N P de Gelder R Smits J M M Gal A W

Chem Eur J 2000 6 2740 77) Albright T A Dosa P I Groszligmann T N Oluwakemi O Padilla R Paubelle

R Timofeeva T Vollhardt K P C Angew Chem Int Ed 2009 48 9853 78) Schaub T Radius U Chem Eur J 2005 11 5024 79) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4660 80) (a) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4040

(b) Muumlller C Lachicotte R J Jones W D Organometallics 2002 21 1975 81) Martin R H Angew Chem Int Ed Engl 1974 13 649 82) Mallory FB Butler K E Evans AC Mallory CW Tetrahedron Lett 1996 37

7176 83) Selected Reviews (a) Amemiya R Yamaguchi M Chem Rec 2008 8 116 (b)

Ruliacutešek L Exner O Cwiklik L Jungwirth P Staryacute I Pospiacutešil L Havlas Z J Phys Chem C 2007 111 14948 (c) Hopf H Classics in Hydrocarbon Chemistry Wiley-VCH Weinheim 2000 pp 321ndash330 (d) Voumlgtle F Fascinating Molecules in Organic Chemistry Wiley New York 1992 pp 156ndash180 (e) Meurer K P F Voumlgtle Top Curr Chem 1985 127 1 (f) Laarhoven W H Prinsen W J Top Curr Chem 1984 125 63

84) (a) Mallory FB Butler K E Mallory CW Beacuterubeacute A Luzik E D Brondyke E J Hiremath R Ngo P Carroll P J Tetrahedron 2001 57 3715 (b) Mallory F B Butler K E Evans A C Brondyke E J Mallory C W Yang C Ellenstein A J Am Chem Soc 1997 119 2119

85) (a) Mitsuhashi R Suzuki Y Yamanari Y Mitamura H Kambe T Ikeda N Okamoto H Fujiwara A Yamaji M Kawasaki N Maniwa Y Kubozono Y Nature 2010 464 74 (b) Okamoto H Kawasaki N Kaji Y Kubozono Y Fujiwara A Yamaji M J Am Chem Soc 2008 130 10470 (c) Tian Y H Park G Kertesz M Chem Mater 2008 20 3266

86) Recent reviews of acenes in electronic applications (a)Yamashita Y Sci Technol Adv Mater 2009 10 024313 (b) Wuumlrthner F Schmidt R ChemPhysChem

- 174 -

2006 7 793 (c) Bendikov M Wudl F Chem Rev 2004 104 4891 87) NICS-based comparison of phenacene and acene properties Portella G Poater

P Bofill J M Alemany P Solagrave M J Org Chem 2005 70 2509 and the references therein

88) Mallory F B Mallory C W Org React 1984 30 1 89) Gu Z Nickel-Catalyzed Cycloaddition Reaction of [N]Phenylenes and Alkynes

Postdoctoral Report University of California Berkeley 2008 90) Preferential displacement of COD by π ligands from Ni(COD)(PMe3)2 is well

documented See eg Karsch H H Leithe A W Reisky M Witt E Organometallics 1999 18 90

91) (a) Bochmann M Hawkins I Hursthouse M B Short R L J Chem Soc Dalton Trans 1990 1213 (b) Poerschke K R Mynott R Angermund K Kruumlger C Z Naturforsch 1990 40B 199 See also (c) Bartik T Happ B Iglewsky M Bandmann H Boese R Heimbach P Hoffmann T Wenschuh E Organometallics 1992 11 1235

92) For Ni-phosphine migrations along polycyclic benzenoid ligands see eg Stanger A Vollhardt K P C Organometallics 1992 11 317

93) Edelbach B L Vicic D A Lachicotte R J Jones W D Organometallics 1998 17 4784

94) (a) Feiken N Pregosin P S Trabesinger G Scalone M Organometallics 1997 16 537 (b) Feiken N Pregosin P S Trabesinger G Albinati A Evoli G L Organometallics 1997 16 5756 (c) Geldbach T J Pregosin P S Eur J Inorg Chem 2002 1907

95) Cheng T-Y Szalda D J Hanson J C Muckerman J T Bullock R M Organometallics 2008 27 3785

96) (a) Grimme S Harren J Sobanski A Voumlgtle F Eur J Org Chem 1998 8 1491 (b) Dias J J Chem Inf Model 2005 45 562

97) Still W C Mitra A Kahn M J Org Chem 1978 43 2923 98) (a) Leonard J Lygo B Procter G Advanced Practical Organic Chemistry 2nd

ed CRC Press Boca Raton 1998 (b) Errington R J Advanced Practical Inorganic Chemistry and Metalorganic Chemistry Chapman and Hill London 1997

99) Jonas K Deffense E Habermann D Angew Chem Int Ed Engl 1983 22 716 100) Gaussian 03 Revision B03 M J Frisch G W Trucks H B Schlegel G E

Scuseria M A Robb J R Cheeseman J A Montgomery Jr T Vreven K N Kudin J C Burant J M Millam S S Iyengar J Tomasi V Barone B Mennucci M Cossi G Scalmani N Rega G A Petersson H Nakatsuji M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida T Nakajima Y Honda O Kitao H Nakai M Klene X Li J E Knox H P Hratchian J B Cross C Adamo J Jaramillo R Gomperts R E Stratmann O Yazyev A J Austin R Cammi C Pomelli J W Ochterski P Y Ayala K Morokuma G A Voth P Salvador J J Dannenberg V G Zakrzewski S Dapprich A D Daniels M C Strain O Farkas D K Malick A D Rabuck K Raghavachari J B Foresman J V Ortiz Q Cui A G Baboul S Clifford J Cioslowski B B Stefanov G Liu A Liashenko P Piskorz I Komaromi R L Martin D J Fox T Keith M A Al-Laham C Y Peng A Nanayakkara M Challacombe P M W Gill B Johnson W Chen M W Wong C Gonzalez J A Pople Gaussian Inc Pittsburgh PA

- 175 -

2003 101) wwwgaussiancom 102) wwwchemcraftprogcom 103) Becke A D J Chem Phys 1993 98 5648 104) Lee C Yang W Parr G R Phys Rev B 1988 37 785 105) Binkley J S Pople J A Hehre W J J Am Chem Soc 1980 102 939 for

hydrogen and Gordon M S Binkley J S Pople J A Pietro W J Hehre W J J Am Chem Soc 1983 104 2797

106) Hay P J Wadt W R J Chem Phys 1985 82 270 107) Hehre W J Ditchfield R Pople J A J Chem Phys B 1972 56 2257 108) Curtiss L A McGrath M P Blaudeau J-P Davis N E Binning R C Jr

Radom L J Chem Phys 1995 103 6104 109) A W Ehlers M Boumlhme S Dapprich A Gobbi A Houmlllwarth V Jonas K F

Koumlhler R Stegmann A Veldkamp G Frenking Chem Phys Lett 1993 208 111

110) QST is a synchronous transit approach to the quadratic region around the transition state structure For details see (a) J B Foresman A Frisch in Exploring Chemistry with Electronic Structure Methods A Guide to Using Gaussian Gaussian Inc Pittsburgh PA USA 1996 (b) H B Schlegel in Ab Initio Methods in Quantum Chemistry Part I Wiley Chichester 1987

111) Gu Z The Improvement of Total Synthesis of Angular [4]Phenylene and Its Flash Vacuum Pyrolysis (FVP) Study Postdoctoral Report University of California Berkeley 2008

112) Schwager H Postdoctoral Research Report University of California Berkeley 1987

113) Kuumlchle W Dolg M Stoll H Preuss H Mol Phys 1991 74 1245 114) (a) Hariharan P C Pople J A Theor Chim Acta 1973 28 213 (b) Francl M

M Petro W J Hehre W J Binkley J S Gordon M S DeFrees D J Pople J A J Chem Phys 1982 77 3654 (c) Rassolov V Pople J A Ratner M Windus T L J Chem Phys 1998 109 1223

i

Table of Contents

CHAPTER ONE PROPERTIES OF THE [N]PHENYLENES AND THEIR ORGANOMETALLIC CHEMISTRY 1

11)General Discussion of [N]Phenylene Properties 1 12)Overview of Phenylene Organometallic Chemistry 6 13)Direction of Work 10

CHAPTER TWO PHOTOndashTHERMAL HAPTOTROPISM IN CYCLOPENTADIENYLCOBALT COMPLEXES OF LINEAR PHENYLENES INTERCYCLOBUTADIENE METAL MIGRATION 12

21)Introduction 12 22)Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes 16 23)Structural Studies on the Linear [3]Phenylene(CpCo) Complexes 22 24)Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift 30 25)Low Temperature Photolytic Studies on the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes 41 26)Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 56 27)Summary and Outlook 62

CHAPTER THREE NICKEL-CATALYZED INSERTION REACTIONS FOR THE PREPARATION OF [N]PHENACENE DERIVATIVES 63

31)Introduction 63 32)Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene 67 33)Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene 75 34)Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions 81 35)Summary and Outlook 87

CHAPTER FOUR EXPERIMENTAL AND COMPUTATIONAL DETAILS 88

41)General Considerations 88 42)Experimental Section for Chapter Two 88 43)Computational Details for Chapter Two 129 44)NMR Data for Chapter Two 154 45)Experimental Information for Chapter Three 162 46)Computational Details for Chapter Three 168 47)References 169

ii

Acknowledgements

ldquoWhere would I find leather enough to cover the surface of the earth The Earth is covered over merely with the leather of my sandalsrdquo

-Shāntideva in the Bodhicaryāvatārah Ch 4 v13 Five years ago I arrived in Berkeley with a rather clear objective get (or rather survive) a PhD Though the goal never changed the all paths (scientific personal professional and spiritual) I traversed were often quite unlike anything I could have anticipated I have had the great fortune to stand on the shoulders of many giants during these past few years and it is to them that I owe my deepest gratitude First and foremost I would like to thank my advisor Peter Vollhardt for all of his support and patience The things I have learned from him are far too numerous to list but certainly the two most important are clarity and rigor two qualities that extend far beyond the chemical realm Working with so many different people was another interesting challenging and ultimately highly rewarding experience I am particularly indebted to ldquoThe Old Gangrdquo consisting in part of Phil Leonard and Ken Windler These two gentlemanly pyromaniacal firearms enthusiasts aside from showing me the ins and outs when I was a new arrival (and teaching me more than I will ever need to know about guns and explosives) soon became good and close friends No mention of The Gang would be complete without Jordan Rose Figura Despite being a chemical biologist and not actually a member of the Vollhardt Group she nonetheless (somehow) managed to fit in perfectly My life has been forever changed by her introducing me to ldquoDoctor Whordquo Many others also deserve special mention Sabine Amslinger has and will continue to provide a near endless amount of legendary stories that often border on mythological Tom Gadek was just plain awesome Vince Gandon aside from being one the best experimentalists Irsquove seen also happened to have a rather fine taste in films and music Dominik Hager excelled at getting me out of the lab for an occasional weekend of fun The elegant and refined chocolate cakes of Aude Hubaud were a rare yet very welcome occurrence Her sassy chic comments on all aspects of life however were quite copious Greg Boursalian performed an excellent job of filling the ldquocool undergradrdquo spot and I wish him the best for his own graduate school journey Steve Meier managed the Herculean task of (legally) disposing of all those old empty gas cylinders It is my great hope that Prof Sgt Meier will share many (but certainly not all) of his Berkeley experiences with the next generation of chemists that he will educate Explaining the strange and quirky aspects of American culture and the English language to Kerstin Weiszlig made for a fair number of humorous conversations Learning the stranger and quirkier aspects of German language and culture made for many more Similarly much time was spent meticulously examining the lyrics and slang expressions of assorted hip-hop songs with Sander Oldenhof Practicing kindergarten level German while sharing a fairly constant supply of Ritter Sport bars with Verena Engelhardt was another fine example of cultural exchange Despite his best efforts Kasper Moth-Poulsen has yet to convince me that Volvo is the greatest vehicle manufacturer in the known universe My cultural exposure was not limited to European interactions however and I managed to learn a little Chinese as well Apparently ldquoHao Shenrdquo

iii

means ldquoMacGyverrdquo in Mandarin I would also like to thank the rest of my co-workers past and present for all of their support They are in rough chronological order Thomas Carl Miles Carter Kaspar Schaumlrer Ingo Janser Romy Michiels Elisa Paredes Thilo Heckrodt Nicholas Cheron Alex Lee Anais Geny Samer Al-Gharabli Nicole Franssen Vladislav Kulikov Alexandra Romek Isaac Ho Zhenhua Gu Florian Montermini Nikolai Vinokurov Robert Zitterbart and Cedric Ghellamallah Bonnie Kirk skillfully handled the various arcane administrative procedures but also provided many interesting and memorable early morning conversations The finer points of NMR spectroscopy were taught to me by the indomitable Rudi Nunlist His wry humor and outlook on life were often the perfect supplement to the rigors of graduate school life Working with Chris Canlas Rudirsquos able successor has also been a pleasure I was encouraged when he was so quick to remind me that I have the same name as a bad-boy Filipino action-movie star Teaching while always quite time consuming proved to be an invaluable experience Teaching under the direction of Peter the man who wrote the book on organic chemistry was quite an adventure His passion and talent for teaching are immediately obvious and inspiring even without flipping through the Basque translation of his textbook Jon Ellmanrsquos ability to write exams that are easy to grade but difficult for students to take is similarly awe inspiring There is no doubt in my mind that Heino Nitsche has taken teaching of general chemistry to new levels of eccentricity and excitement Jean Freacutechetrsquos impressive aptitude for lecturing is perhaps surpassed only by the impressiveness of his wine collection Looking down the academic chain I have to acknowledge many of the brilliant and wonderful students that made teaching such a fantastic experience Special thanks goes to Steve Seyedin Nellie Ekmejian Jessie Zhang Yao Yue Ashley Johnson Brent Jellen Zarina Khan and Mojgan Rastegar all of whom were extraordinary students that I hope will do their part to save the world No acknowledgement could be complete without recognizing the love and support of my family in particular my mother Her love though always tough was always there My various housemates also provided me with some great times Chris Trinh my first housemate in Berkeley was a superb fellow to live with and I will always fondly remember our conversations on life love and quantum gravity Cory McLitus when he wasnrsquot slaving away in the architecture studio also became a good friend I feel no need to apologize for getting him hopelessly addicted to ldquoThe Big Bang Theoryrdquo The awesome Samra Kasim was always ready for chai good food and hearty discussions on Bollywood and all things South Asian The housemates of 1505 Oxford St are also great people Though we rarely cross paths Vicky Zhuangrsquos highly entertaining biology lab adventures are much appreciated Vannamaria Kalafonos always has something wonderful going on in the kitchen and I aspire to learn the Greek specialty of cooking for a zillion people from her The cats Pink Tuffy and especially Floyd are nice companions even though they sleep a combined 60 hours per day Many kalyānamitras helped me get through the toughest times and to them I am especially grateful A large number of my Saturday evenings were spent in the calm environs of the Berkeley Monastery where Rev Heng Surersquos Avataṃsaka Sūtra

iv

lectures gave me much to think about The monthly lectures by Ajahn Amaro Ajahn Passano and the Abhayagiri Sangha were also a wonderful learning experience Chats about long-dead ancient languages and obscure texts with Sean Kerr a fellow survivor of Dagmar Theisonrsquos German class will also be fondly remembered The NY Sangha though far away always supported me and welcomed me warmly whenever I returned home Frank Yao Hai-Dee Lee Sheila Sussman Fred Ng Martin Applebaum Josephine Verceles Tiffany Taulton Phung Tran and especially Aaron Vederman repeatedly reminded me to ldquosmile breath deep and go slowlyrdquo The many visits to Bodhi Monastery were always the high points of my summers Michael Roehm Bhikkhu Bodhi Jane Berry Henry and Lily Teoh Marcie Barth Mahendra Sagar the dearly departed Felicia Miller Ven Guo Jun Susan Chastain and the polygot Bhikkhu Analayo made every visit an unforgettable experience and never failed to remind me why I get out of bed in the morning

- 1 -

Chapter One

Properties of the [N]Phenylenes and Their Organometallic Chemistry

11 General Discussion of [N]Phenylene Properties Polycyclic aromatic hydrocarbons (PAHs) are a class of molecules that have occupied the minds of chemists for generations1 Their essential feature aromaticity is the unusual stabilization that arises from having a 4n+2 number of π-electrons in a cyclical array This seemingly simple definition obscures the fact that aromaticity continues to be one of the most scrutinized topics in modern organic chemistry2 and more rigorous definitions3 have remained elusive Much of the early work4 with PAHs was aimed at investigating theoretical issues surrounding aromaticity There has been renewed interest in these systems in recent years because they are increasingly attractive as functional materials in organic-based electronics5 Of the many different kinds of PAHs known eg 1ndash6 (Figure 11) one subclass is of particular interest the [N]phenylenes6

Anthracene Coronene Phenanthrene

Chrysene Triphenylene Pyrene

1 2 3

4 5 6

Figure 11 Some examples of polycyclic aromatic hydrocarbons The [N]phenylenes (where N = the number of benzene rings) are PAHs in which benzene and cyclobutadiene rings are fused in an alternating manner The cyclobutadiene ring imparts very unusual structural and electronic properties as seen in the simplest molecule in the series biphenylene (7) It can be described by several resonance forms (Figure 12 andashe) in which the major contributor 7c avoids formation of the highly destabilizing antiaromatic cyclobutadiene (7a 7e) and benzocyclobutadiene circuit (7b 7d) This preference is manifest in the significant bond alternation7 seen in

- 2 -

the crystal structure of biphenylene (Figure 12) which shows a clear difference in bond lengths between the formal single bonds (~143 Aring) and the shorter formal double bonds (~137 Aring)

1423

1372

Figure 12 Biphenylene bond lengths (top Aring) and resonance contributors (bottom)

An extreme example of [N]phenylene π-bond localization is triangular [4]phenylene (8) (Scheme 11) in which the three-fold peripheral fusion imparts complete cyclohexatriene character on the central ring89a This property is reflected in the reactivity of the system eg catalytic hydrogenation (9)8b epoxidation (10)8c and cyclopropanation (11)8c Scheme 11 Reactions Illustrating the Fully Bond Localized Character of the Central Benzene

Ring in Triangular [4]Phenylene 8 Bond lengths are in Aring

- 3 -

Phenylenes exhibit another interesting structural feature in contrast to other PAHs sizable deviations from planarity (Figure 13)9ab The flexibility of the phenylene framework arises from the combined effect of π- and σ-strain9ab By adopting a nonplanar geometry overlap between the π-orbitals is diminished and in turn leads to a decrease in destabilizing antiaromatic character Pyramidalization of the four-membered ring carbons also reduces σ-strain9ab a phenomenon observed in highly strained alkene systems9c

Figure 13 Crystal structures showing deviations from planarity in (a) helical [6]phenylene (12)10 (b) dimethyl triangular [4]phenylene-23-dicarboxylate (13)9a and (c) 23-bis(tri-

methylsilyl) linear [3]phenylene (14)9a

The fusion of aromatic benzene rings with antiaromatic cyclobutadiene units in the same molecule has prompted numerous experimental and theoretical discussions6 regarding the magnetic and electronic properties of the phenylenes 1H-NMR spectroscopy is one typical measure of aromaticity Protons on the exterior of aromatic rings (eg 15) show relatively low field resonances while their interior counterparts resonate at relatively high field due to the presence of a diamagnetic ring current Conversely antiaromatic rings with 4n π-electrons are paratropic and reveal the opposite disposition of the two respective types of protons (eg 16) The interplay between aromatic and antiaromatic character in the phenylenes is evident in their chemical shifts which tend to show weakly aromatic resonances (Figure 15) relative to benzene (736 ppm)

(a) (b) (c)

12 13 14

- 4 -

Figure 14 Observed 1H-NMR resonances in (a) the aromatic [18]annulene (15)11 and (b) the antiaromatic 5-bromo-19-bisdehydro-[12]annulene (16)12

Aside from NMR spectroscopy nucleus independent chemical shift (NICS)13 calculations have also proven to be useful measures of aromaticity The NICS technique works by calculating the magnetic shielding of a ldquoghost nucleusrdquo that can be positioned anywhere around a molecule For probing aromaticity the calculated point is in the center of the π-electron circuit to be examined Calculations placing the ghost nucleus 1 Aring above the plane of the molecule are often used to minimize local anisotropy and are referred to as NICS(1)14 NICS data are given in ppm and are thus comparable to experimental 1H-NMR measurements Negative NICS values indicate aromatic character while positive values suggest antiaromatic character For example the NICS(1) of benzene15 is ndash125 ppm whereas for cyclobutadiene15 it is 151 ppm NICS calculations for various phenylenes have been carried out6 and are shown in Figure 15 alongside the experimentally measured 1H-NMR chemical shifts The attenuated aromatic character of the benzene and the relatively weak antiaromatic character of the cyclobutadiene rings in phenylenes such as biphenylene (7) triangular [4]phenylene (8) and angular [4]phenylene (17) are apparent from both sets of data

Figure 15 1H-NMR (blue) and NICS(1) (green) data for selected phenylene topologies (ppm)6

The phenylenes possess multiple modes of reactivity7 as illustrated by biphenylene (7) in Scheme 12 It can undergo electrophilic aromatic substitution like other PAHs but does so selectively at the 2-position to avoid the formation of intermediates with antiaromatic character Biphenylene does not readily undergo Diels-

- 5 -

Alder reactions but was shown to react with electron-deficient benzynes to give the corresponding cycloadducts16 Opening of the highly strained four-membered ring is another prominent aspect of phenylene reactivity

Scheme 12 Illustrative Reaction Pathways of Biphenylene6

Early work17 showed that it was possible to cleave the aryl-aryl C-C bonds via thermolysis in the neat state Rupture of the four-membered ring is a key step in the rearrangement of phenylenes into other PAHs and has been observed typically under flash vacuum pyrolytic conditions18 (eg 10ndash3ndash10ndash6 torr 800ndash1000 degC) Strained ring opening on exposure to metal complexes to give metallacycles19 is discussed in further detail in Section 12 12 Overview of Phenylene Organometallic Chemistry

As mentioned above the weakly aromatic character of the phenylenes dominates their structure and reactivity In the linear phenylenes the antiaromatic contribution to structure and reactivity becomes increasingly significant A simple yet instructive explanation for this phenomenon can be seen in the various resonance structures of linear [3]phenylene (18) a selection of which is depicted in Figure 16 Even the most favorable forms a and b feature double bonds in the four-membered rings The cumulative increase in cyclobutadienoid circuits should therefore lead to an increase in antiaromatic character The relative augmentation in

- 6 -

cyclobutadienoidantiaromatic character of the linear phenylenes was confirmed6 by NMR NICS calculations and HOMO-LUMO measurements20

Figure 16

Resonance contributors to linear [3]phenylene

Cyclobutadiene is often invoked as the typical example of a highly destabilized antiaromatic system Indeed the difficulties21 in preparing and isolating it confirm theoretical predictions regarding its instability22 Attachment of a metal however is known to produce aromatic organometallic molecules of high stability23 The increased antiaromatic character of the linear phenylenes thus makes them amenable to metal complexation Cyclopentadienylcobalt cyclobutadiene complexes of linear [3]- (19)24 linear [4]- (20)25 and linear [5]phenylene (21)26 have been prepared using the well-developed cobalt-based [2+2+2] alkyne cyclotrimerization methods (Scheme 13)27

Compounds 19ndash21 constitute the only linear CpCo phenylene systems known so far

Scheme 13 Synthesis of Linear Phenylene(CpCo) Cyclobutadiene Complexes

In the metallated linear [4]- and [5]phenylene 20 and 21 respectively the CpCo unit is located on the inner cyclobutadiene ring This is curious as one would have expected the metal fragment to be bound to its outside counterpart close to the center of reactivity during the cyclotrimerization step The position of the CpCo unit was established by NMR spectroscopy2628 In addition a crystal structure of a tetrahexyl

TMS

TMS

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMSTMS

TMS

Co

CpCo(CO)2BTMSA

h

Co

Co

CpCo(CO)2BTMSA

h

CpCo(CO)2BTMSA

h

19

20

21

- 7 -

substituted linear [5]phenylene28 (Figure 17) clearly reveals the inside position of the metal fragment Difficulties in obtaining high quality crystals however precluded a detailed bond analysis of the complex The unexpected location of the CpCo unit in 20 and 21 suggested the occurrence of CpCo migration under the conditions of their preparation Detailed experiments verifying this hypothesis will be the subject of Chapter 2

Figure 17 Disordered crystal structure for the 23910-tetrakis(trimethylsilyl)-571214-

tetrahexyl linear [5]phenylene(CpCo)

In contrast to the linear phenylenes their angular relatives undergo π-metallation at the cyclohexatrienoid moieties (Figure 18) For example angular [3]phenylene (22) reacts with CpCo(C2H4)2 to form the η4-CpCo complex 2329 Similar treatment with Cr(CO)3(NH3)3 yields the η6-Cr(CO)3 analog 2430

Figure 18 η

4-CpCo (23) and η6-Cr(CO)3 (24) complexes of angular [3]phenylene (22)

In addition to 24 related chromium complexes of the triangular [4]phenylene frame eg 25 have been prepared (Scheme 14)31 Interestingly regioisomer 26 generated at relatively lower temperatures is the kinetic product of monocomplexation and rearranges thermally to 27 Double metallation is possible as illustrated in the conversion of 27 to 28 with added (naphthalene)Cr(CO)3

- 8 -

Scheme 14 Synthesis and Reactions of Triangular [4]Phenylene(Cr(CO)3) Complexes

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3(NH3)3dioxane 100 oC

14 h

(naphthalene)Cr(CO)3THF Et2O 60 oC 14 h

90 oC

(naphthalene)Cr(CO)3THF Et2O 60 oC

14 h

25

27

26

28

57 43

89

In contrast to CpCo which attaches itself exclusively to the four-membered ring in the linear phenylenes including the linear [3]phenylene frame as in 19 (Scheme 13) Fe2(CO)9 gives a plethora of complexes with the tetrasilyl derivative 29 among which the iron tricarbonyl cyclobutadiene complex 30 is only minor (Scheme 15)27 Instead other organometallic molecules such as arene complex 31 were isolated This compound contains two Fe(CO)3 units coordinated to the central benzene ring An iron-iron bond was proposed for this molecule (31a) although the spectral data are also consistent with a structure in which the Fe(CO)3 fragments are located on opposite faces (31b) Because a crystal structure could not be obtained the structural identity of 31 remains ambiguous The major products of this reaction 32 and 33 illustrate another important aspect of phenylene reactivity metal insertion into the strained ring

- 9 -

in this case involving the dinuclear Fe2(CO)6 unit Complex 33 probably originating from 32 contains an additional Fe(CO)3 moiety coordinated to the terminal benzene ring closest to the Fe2(CO)6 fragment

Scheme 15 Reaction of Linear [3]Phenylene with Fe2(CO)9

While as yet absent in the linear series a cobalt insertion product analogous to iron compounds 32 and 33 was isolated when angular phenylene 22 was exposed to excess CpCo(ethene)2 (Figure 19)32 In this case double insertion of two (CpCo)2

Figure 19 Tetranuclear CpCo-terphenylene complex 34 and its crystal structure

34

- 10 -

fragments occurred to give 34 in 71 yield Notably neither 23 nor analogs of the type 31 were detected As alluded to in Scheme 12 biphenylene (7) itself also undergoes metal insertions into the four-membered ring This type of reactivity has been observed with a range of transition metals including Co19 Mechanistically best delineated is the attack of Ni and Pt species Thus Ni(PEt3)4

33a and Ni(COD)(PMe3)233b begin with insertion of

the nickel fragment into the four-membered ring to give a metallacycle of the type 35 (Scheme 16) Subsequent dimerization assembles 36 from which Ni is extruded to furnish tetraphenylene 37 as the final product A similar reaction pathway was proposed for Pt(PEt)4

19 but proceeding via 38 to a monometallacycle 40 possibly through the intermediacy of 39 In summary the σ- and π-activation of the phenylenes endows them with rich organometallic chemical potential The synthetic and mechanistic exploration of one aspect of it namely the Ni-catalyzed cycloaddition of alkynes to the four-membered rings in angular phenylenes will be discussed in Chapter 3

Scheme 16 Reaction of Biphenylene with Nickel and Platinum Complexes

13 Direction of Work The discussions in Sections 11 and 12 have provided a brief overview of phenylene properties and their previously studied organometallic chemistry

- 11 -

respectively The aim of this thesis was to advance two aspects of prior investigations The first area examines the chemistry of the linear phenylene(CpCo) complexes In particular experiments are presented addressing the question of a possible migration of the CpCo fragment along their framework The revocable movement of a metal fragment between cyclobutadiene rings is a highly noteworthy discovery as this process has never before been reported On a practical level this mode of reactivity places linear phenylene(CpCo) complexes in the increasingly appealing class of organometallic arrays that can serve as the basis for various molecular electronic systems The reversible isomerizations described in the second chapter can potentially be employed in molecular machines and switches data storage and as will be detailed photostorage devices Experimental work in the form of detailed solid state and spectroscopic analyses is provided Computational studies are also employed to further scrutinize the novel chemistry of the abovementioned Co-based molecules The second topic of this thesis examines nickel-catalyzed insertions into the four- membered rings of angular phenylene systems Specifically the application of this reactivity to the synthesis of a class of PAHs known as [N]phenacenes is discussed Phenacenes (polyphenanthrenes) have recently shown great promise as organic transistors and conductors but advancement of this field has been hampered due to few practical syntheses The insolubility of these molecules has also been a substantial barrier to the development of phenacene-based applications The content of the third chapter explores the preparation of soluble phenacene derivatives using a tandem Ni-insertion alkyne cycloaddition reaction This new process provides an efficient widely applicable and practical synthesis of larger phenacenes using correspondingly larger angular phenylene systems Detailed mechanistic studies of this reaction are presented Experimental data are used in conjunction with computational studies to gain further insight with the optimization of the reaction by reduction of side product formation being a crucial milestone

- 12 -

Chapter Two

PhotondashThermal Haptotropism in Cyclopentadienylcobalt Complexes of Linear Phenylenes Intercyclobutadiene Metal Migration

21 Introduction As previewed in Section 12 the unexpected position of the metallic unit in the linear [4]- and [5]phenylene(CpCo) systems 20 and 21 constituted the background for the studies presented in this chapter Specifically it was hypothesized that its origin was due to the migration of the metal fragment from one cyclobutadiene ring to another a process that would constitute an unprecedented type of haptotropic shift34-36 However a prerequisite for studying such a rearrangement would be the generation of the haptoisomers of 20 and 21 (Scheme 13) bearing the CpCo appendage at the respective terminal four-membered rings a possibility obviated by their thermal method of synthesis The following describes the history that led to the discovery of photochemical conditions that circumvented this thermodynamic problem The story begins with a prior attempt to stabilize the linear phenylene frame by alkyl substitution the ultimate aim being the synthesis of members of the series with Ngt5 Such substitution was also hoped to improve solubility a facet exploited in the corresponding zigzag series37 The synthetic strategy followed that used in the preparation of the largest known linear phenylene 41 namely the CpCo-catalyzed cyclization to 21 followed by careful oxidative demetallation as shown in Scheme 21 The initial target chosen was the tetrahexyl system 43 approached via the synthesis of complex 42 (Scheme 22)28 Demetallation was thought to be facile to provide the free ligand but this anticipation proved to be erroneous

Scheme 21 Oxidative Decomplexation of Linear [5]Phenylene Complex 21

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMS

41

CoCp

21

40

CuCl2middot2H2ODME NEt3 H2O

Scheme 22 Preparation of Tetrahexyl Linear [5]Phenylene Complex 42

- 13 -

TMS

TMS

TMS

TMS

Hex

Hex

Hex

Hex

CoCp

42

CpCo(CO)2 BTMSAm-xylene ∆ hν

27

Hex Hex

HexHex

TMS

TMS

TMS

TMS

Hex Hex

HexHex

ndashCpCo

43

The demetallation of 42 under numerous conditions was unattainable However in one of these attempts an NMR sample of 42 was exposed to UV-irradiation leading to the evolution of new signals eventually assigned to originate from rearranged compound 45 (Scheme 23)28 This molecule is also a linear [5]phenylene(CpCo) complex but now has the metal fragment bound to the outer cyclobutadiene ring an arrangement that was suspected to be the initial product of the preparation of 42 (Scheme 22) That this conjecture was correct was established by heating which caused photoisomer 45 to revert to 42 An indication of the generality of this phenomenon was gleaned from 21 which underwent the same photoinduced thermally reversible haptotropic migration (Scheme 23)38 A detailed discussion of the spectral properties of these haptomers is provided in Sections 23 and 24 Scheme 23 Photoinduced Thermally Reversible Haptotropic Migration of the CpCo Fragment

in Linear [5]Phenylene(CpCo) Complexes

This discovery was deemed significant for two reasons 1 it constitutes the first observation of intercyclobutadiene metallohaptotropism and 2 there are only two previously known examples of mononuclear39 additive-free40 photothermal reversible haptotropic shifts both of which are based on Mo(PMe3)3 complexes (Scheme 24)41 Systems capable of undergoing this type of reaction are of much practical importance because of their potential employment as photostorage devices andor molecular switches42 The development and application of functional organometallic materials43 has proceeded at a relatively slow pace when compared to their non-metallated counterparts5c Thus the great prospects for discovery and advancement make this area of study particularly attractive

- 14 -

Scheme 24 Photothermal Reversible Metallohaptotropism in (a) Molybendum-Indole41a and (b) Molybendum-Isoquinoline Complexes41b

Having confirmed that an η4η4 cyclobutadiene haptotropic migration was indeed occurring mechanistic investigations2838 were begun Interestingly full conversion of the inner bound CpCo complexes to their photoisomers was never achieved The maximum ratio obtained for 2144 and 4245 was 8812 Variations of solvent (eg benzene THF CHCl3) and temperature (0ndash30degC) had no effect on this ratio Added ligands such as 15-cyclooctadiene CO and phosphines were also inconsequential Of further significance was the robustness of the photothermal cycle which could be run multiple times without decomposition Kinetic experiments were carried out to determine the activation parameters for the thermal reversal of 44 and 45 to 21 and 42 respectively These data are shown in Table 21 The isomerizations are cleanly first order a finding that was unaffected by changes in concentration22 The enthalpy of activation (∆Hne) increased only slightly with hexyl substitution (44 vs 45) The near zero entropy of activation values (∆Sne) was consistent with the occurrence of an intramolecular process

Table 21 Activation Parameters for the Conversion of Outer to Inner CpCo Complexes Under

Thermal Conditions ∆Sne Values are in Entropy Units (1 eu = calmolsdotK)

Reaction Solvent ∆H

ne (kcalmol) ∆Sne (eu)

44 to 21 C6D6 259 plusmn 04 16 plusmn 14 44 to 21 THF-d8 256 plusmn 09 01 plusmn 30 45 to 42 THF-d8 276 plusmn 08 77 plusmn 27

Consideration of the relative facility of the above haptotropic shifts made it likely that migration was occurring along the entire phenylene frame including the ldquohoppingrdquo across the central six-membered ring (Scheme 25) This degenerate equilibration should be detectable by NMR spectroscopy44 if it were sufficiently fast Unfortunately but perhaps not surprisingly considering the data in Table 21 coalescence of the spectrum of 21 could not be achieved even at temperatures as high as 120 degC Spin saturation transfer experiments (eg EXSY) also failed44 These data allowed an estimate of the lower limit for the activation energy of the internal shift of ∆Gne ge 22 kcalmol28

Scheme 25 Proposed Internal η4η4 Cyclobutadiene CpCo Migration

- 15 -

The failure of the above experiments inspired a different approach based on the following arguments The antiaromatic character of the linear phenylenes has been shown by theory and experiment to increase with size645 Consequently the effect of metalloaromatization46 makes linear [5]phenylene a better (and hence more strongly bound) ligand for CpCo than a smaller system (eg linear [3]phenylene) Indeed the enthalpy of the homodesmotic in Scheme 26 was computed by DFT methods to be Scheme 26 Calculated Homodesmotic Reaction Showing Preferential Binding of CpCo to

Linear [5]Phenylene

113 kcalmol47 If the barrier to intercyclobutadiene hopping were related to the binding energy of the metal one would expect a more loosely bound metal fragment to migrate faster The hope was therefore that the degenerate haptotropism in Scheme 27 would be observable by VT NMR methods Unfortunately these efforts failed again38 either because the anticipated acceleration was not sufficient to be observable by NMR or because the argument above (which rests solely on ground state considerations) is flawed

Scheme 27 Proposed Degenerate Haptotropic Shift in Linear [3]Phenylene Complex 19

- 16 -

The preceding discussion summarizes some of the quantitative aspects of this new type of haptotropic shift Many fundamental questions however remained to be answered Is it possible to observe the photothermal shift in other systems such as linear [3]- and [4]phenylene What is the exact mechanism of metal migration between cyclobutadiene rings In what way if any does attachment of CpCo alter the structure of the phenylene scaffold Related to these questions was the long-standing quest for an accurate crystal structure of any linear phenylene(CpCo) complex The answers are addressed in the following sections 22 Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes As recounted in Section 21 the degenerate internal haptotropic shift could not be seen by NMR in the symmetrical 19 Therefore recourse had to be taken to chemical methods involving an isomerization of the sort shown in Scheme 28

Scheme 28 Isomerization of a Desymmetrized Linear [3]Phenylene(CpCo) Complex

Initial efforts focused on attempts to desymmetrize compound 19 directly by selective electrophilic desilylation specifically protodesilylation Earlier studies48 had shown that such selectivity was possible in the reactions of bis(trimethylsilyl)benzocycloalkenes such as the benzocyclobutene depicted in Scheme 29 In this case loss of the first TMS group is approximately forty times faster than that of the second Along these lines it was thought that exposing 19 to acidic conditions would selectively remove one (or perhaps two) TMS groups before attacking the remaining silylarene positions In the event treating compound 19 with trifluoroacetic acid in carbon tetrachloride did induce protodesilylation but with no selectivity A mixture of products was obtained and its separation proved impossible (Scheme 210) In light of this setback a new synthetic scheme had to be considered that would generate a desymmetrized system directly in the CpCo-catalyzed cyclization step

- 17 -

Scheme 29 Selective Desymmetrizing Reactions of 12-Bis(trimethylsilyl)benzocyclobutene with Electrophiles

Scheme 210 Attempted Selective Protodesilylation of 19

Fortunately such a strategy had already been executed successfully in the creation of 23-bis(trimethylsilyl) linear [3]phenylene (46) and employed the iterative Scheme 211 Iterative Cyclotrimerization Route in the Synthesis of Linear [3]Phenylene 46

cyclization depicted in Scheme 21127 Its specific execution (Scheme 212) started with a Sonogashira reaction between trimethylsilylacetylene (TMSA) and 12-diiodobenzene (47) to give diyne 48 in high yield Deprotection of 48 with K2CO3 immediately followed by standard CpCo(CO)2-catalyzed alkyne cyclotrimerization649 with bis(trimethylsilyl)acetylene (BTMSA) afforded 23-bis(trimethylsilyl)biphenylene (49) Iododesilylation was then performed using pure ICl to give 23-diiodobiphenylene (50) A Sonogashira coupling between TMSA and 50 produced diyne 51 in good yield The use of a slightly modified cyclization procedure provided the new 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52) in 57 yield This protocol employed THF as a cosolvent to BTMSA thus reducing the reaction temperature in turn allowing for the CpCo to remain attached in the final product and preventing catalytic turnover252638

TMS

TMS46

+

TMS

TMS

+

TMS

TMS

+

TMS

R

TMS

dilute

[X+]

X = H D Br

TMS

TMS

[X+]

TMS

X = H D Br

X

- 18 -

Scheme 212 Synthesis of Asymmetric Linear [3]Phenylene(CpCo) 52

High dilution conditions also helped to suppress formation of cyclobutadiene(CpCo) complexes a well known side reaction in alkyne cyclization chemistry

Compound 52 like its tetrasilylated analogue 19 is a black air-sensitive solid Although it can be handled in air for brief periods of time complete decomposition occurs within 24 hours if left exposed to the ambient atmosphere Purification must always be done with neutral activity III alumina as lower activities (and silica gel) cause decomplexation to give the deep red ligand 46 as the only isolable product Critically exposing molecule 52 to UV irradiation induced the desired haptotropic shift giving its photoisomer 53 (Scheme 213) Heating 53 converted it back to 52 thus completing the photothermal cycle Interestingly close inspection of the NMR spectra of this experiment revealed that a small amount of 53 (2) always remained even on prolonged heating That this observation signaled a thermodynamic equilibrium was confirmed by dissolution of pure crystalline 52 and NMR analysis From the equilibrium constant the ∆Gdeg298 was calculated to be 23 kcalmol in favor of 52 The reasons for this energetic preference and a discussion of the NMR spectral properties of these and related complexes are presented in Section 23

Scheme 213 The Photoinduced Thermally Reversible Haptropic Shift in Linear

- 19 -

[3]Phenylene-(CpCo) 52 to Give Photoisomer Complex 53 The investigations of the equilibration depicted in Scheme 213 were all carried out in sealed Pyrex NMR tubes (J-Young or flame-sealed) using benzene-d6 andor toluene-d8 as the solvent As for the linear [5]phenylene(CpCo) system the cycle could be run multiple times without decomposition and was unaffected by changes in solvent and temperature The maximum ratio of 5352 that could be obtained on irradiation was 11 after ten hours This value is larger than that observed for its linear [5] analogs 2144 and 4245 Photoisomerization also occurs with sunlight leading to the photostationary equilibrium of 5253 = 105 Consequently care must be taken to shield 52 from direct andor indirect sunlight Indoor fluorescent lighting however did not induce CpCo migration Attempts to monitor the photoisomerization and its thermal reverse by UV-Vis spectroscopy failed because of minimal changes in the absorptions due to 52 during these processes This finding implies that the absorption spectra of 52 and 53 are not unexpectedly very similar and offers a possible explanation for the maximum photostationary ratio of 11 The activation parameters for the thermal reversal reaction (53 to 52) in Scheme 213 were obtained in the manner described in Section 21 and are shown in Table 22 The relatively high activation barriers (with respect to the NMR time scale) explain why the degenerate isomerization in 19 could not be verified by NMR experiments Qualitatively the ∆Hne values agree with the hypothesis that the more loosely bound CpCo unit in the linear [3]phenylene is relatively more mobile they are approximately 3 kcalmol lower than those of the [5]phenylene system On the other hand the ∆Sne values especially in C6D6 are positive and relatively high although still within the range acceptable for intramolecular reactions Nevertheless a crossover experiment was devised to provide a definite answer

Table 22 Activation Parameters for the Thermal Conversion of Complex 53 to 52

Solvent ∆H

ne (kcalmol) ∆Sne (eu)

C6D6 204 plusmn 14 158 plusmn 22 Toluene-d8 231 plusmn 07 60 plusmn 13

For this purpose two new linear [3]phenylene(CpCo) derivatives were required One would carry a marker on the Cp ring while the other would be labeled at the phenylene frame Execution of Scheme 213 would involve an equimolar mixture of both compounds An intramolecular mechanism would retain the integrity of the labeling while a dissociative path would lead to label scrambling The outcome of this experiment should be ascertainable by NMR spectroscopy and more rigorously by

CoTMS

TMS

CoTMS

TMS

310 365 nmsunlight

30ndash50oC52 53

- 20 -

Scheme 214 Preparation of MeCp- (54) and Deuterium Labeled (55) [3]Phenylene Complexes

mass spectrometry To this end methyl-Cp complex 54 and dideuterio compound 55 were targeted for synthesis (Scheme 214) Compound 54 was prepared by carrying out the modified cyclotrimerization reaction with MeCpCo(CO)2

50 while 55 was made using methanol-OD in the desilylation of 51 The amount of deuterium incorporation in 55 was found to be 63 as gleaned from its proton NMR spectrum Scheme 215 Crossover Experiment with Labeled Linear [3]Phenylene(CpCo) Complexes

- 21 -

Co

TMS

TMS

TMS

TMS

Co

h CoTMS

TMS

Co

D

D

TMS

TMSD

D

TMS

TMS

Co

Co

TMS

TMSD

DCo

TMS

TMS

Co

TMS

TMSD

D

+

+

+

+

mz = 510

mz = 494

56mz = 508

57mz = 496

54mz = 508

55mz = 496

58 59

53 52

Not observed

Six distinct products are possible in the crossover experiment using 54 and 55 (Scheme 215) Compounds 56 and 5 would arise as a consequence of an intramolecular shift Molecules 53 and 58 and their photoisomers 52 and 59 respectively would be the result of metal fragment dissociation Mass spectrometry would readily verify the occurrence of crossover as the masses (given in mz in Scheme 215) of the products with scrambled labels (52 53 58 59) are distinct from the masses of the starting materials (54 55) and their photoisomers (56 57) In the first part of the experiment equal amounts of 54 and 55 were mixed (shielded from light) and allowed to stand for 2 hours at room temperature The resulting 1H-NMR spectrum consisted of only the signals for 54 and 55 Similarly the mass spectrum showed molecular ion peaks matching the masses of 55 and 56 (Figure 21) The second step was irradiation Analysis of the photolyzed mixture showed new peaks due to complex 56 (the resonances of which had been obtained in a separate photothermal experiment with pure 54) with the expected integration ratio and a second set assigned to 57 identical with the spectrum of 53 but with the expected attenuated absorption for the silyl bearing arene hydrogens The relative integrations for all compounds observed were consistent with a mixture of 5455 and 5657 Mass spectral analysis of the irradiated mixture showed a pattern that was identical to that collected before irradiation (Figure 21) Finally the thermal reversal reaction was carried out by heating the photolyzed mixture at 80 degC After 30 hours the resulting

- 22 -

NMR spectrum matched that of the initial mixture of 54 and 56 in particular confirming the full protonation of 54 and the unchanged level of deuterium incorporation in the silyl

Figure 21 Molecular ion peaks for 5456 (mz = 508) and 5557 (mz = 496)

bearing arene ring of 55 The corresponding mass spectrum contained no evidence for the presence of scrambled products To conclude The haptotropic shift is non-dissociative The exact manner in which the metal traverses from one cyclobutadiene ring to the other will be examined in greater detail in Section 24

23 X-Ray Structural and Comparative NMR Analysis of Linear [3]Phenylene(CpCo) Complexes The results described in Sections 21 and 22 pose some fundamental questions beyond those concerned with the immediate details of the observed haptotropism and addressing the basic novelty of the complexes involved What actually happens to the phenylene ligand when it is ligated via a cyclobutadienoid ring This section will address this question from a structural and (NMR) magnetic point of view Only one crystal structure of a linear phenylene(CpCo) complex was known at the outset of this work namely that of [5]phenylene(CpCo) 42 (Figure 17) and its acquisition required extensive efforts at crystallization28 Unfortunately extensive disorder obviated a detailed analysis It was hoped that some of the complexes employed in the chemistry disclosed in Section 22 would be more forthcoming in this respect The challenge lay in finding the right conditions for crystal growth We began with tetrasilyl linear [3]phenylene(CpCo) 19 which had been crystallized previously by slow cooling in acetone38 These conditions and numerous others (Table 23) did not provide material suitable for X-ray diffraction Success entailed slow cooling a solution of 19 to ndash10 degC in a mixture of methanol-diethyl ether (41) The ensuing sample allowed the determination of the first high quality crystal structure of a linear phenylene (CpCo) complex obtained in collaboration with the group of Professor Tatiana Timofeeva of New Mexico Highlands University (Figure 22)

Table 23 Trial Crystallization Conditions for Linear [3]Phenylene(CpCo)19

Solvent (Ratio) Conditions Result

Acetone Slow Cooling Heterocrystalline Solid Acetone-Pentane (31) Slow Cooling Heterocrystalline Solid

Pentane-Acetone (101) Solvent Diffusion Amorphous Solid Chlorobenzene Slow Cooling Amorphous Solid

- 23 -

Acetone-Methanol (110 Slow Cooling Amorphous Solid Diethyl Ether-Methanol Slow Cooling Small Needles

Acetonitrile Slow Cooling Powder Ethyl Acetate Slow Cooling No Crystals

Ethyl Acetate-Methanol (11) Slow Cooling Amorphous Solid Methanol-Diethyl Ether (41) Slow Cooling Large Fine Needles

Figure 22 X-ray crystal structure of 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) (19) Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are

omitted for clarity Expectedly the CpCo unit is bound in an η4 fashion to the cyclobutadiene ring Also prominent is the deviation from planarity (Section 11) in the linear [3]phenylene a facet typical of the phenylenes themselves (Section 11)9a Of greater importance than these general observations however is the effect of metal complexation on the linear [3] framework The bond lengths for 19 are shown in Figure 23 and as is typical for the phenylenes6 show a certain degree of bond π-localization with measurable differences between single and double bonds However the extent of this phenomenon and its direction varies significantly when compared to the free ligand 60 A quantitative

- 24 -

comparison of the structural data for 19 with those of its ligand 60 is shown in Figure 2327

In 60 the terminal rings adopt bond alternation similar to that in biphenylene (Section 11) and the central benzene takes on a ldquobis-allylrdquo configuration both ostensibly to minimize electron density (and therefore antiaromaticity) in the four-membered rings As dictated by symmetry the two bonds spanning the central ring are of equal length (1385 Aring) Ligation by CpCo alters this picture profoundly in as much as bond alternation across the entire phenylene frame including the four-membered rings is strongly reduced (Figure 23) Generally all relatively long bonds in 60 shorten in 19 while all short bonds lengthen Some residual but attenuated biphenylene type

Co

1512(2)

1513(2)

1407(2)

1385(2)

1385(2)

1397(2)

1356(2)

1359(2)1436(2)

1397(2)

1441(2)

1411(3)(0052)

1384(3)(-0052)

1474(3)(0077)

1384(3)(-0057)

1408(3)(0052)

1448(3)(0051)

1480(3)(-0032)

1468(3)(-0045)

1437(3)(0052)

1465(3)( 0058)

1434(3)( 0049)

1352(3)(-0033)

1351(3)(-0034)

1476(3)(0069)

1495(3)(-0017)

1372(3)( 0016)

1405(3)(0008)

1376(3)(0017)

1413(3)(-0023)

1427(3)(0030)

1488(3)(-0025)

1423(3)(-0018)

(x) = (19) - (60)increasedecrease

60

19

1907(1)

1891(1)

1886(3)

1889(3)

1889(2)

1901(3)

1669

1725

Si

Si

Si

Si

Me

MeMe

Me

Me

Me

Me

MeMe

MeMe

Me

Si

Si

Me

MeMe

MeMe

Me

Si

Me

MeMe

Si

Me

MeMe

- 25 -

Figure 23 Comparison of bond lengths (in Aring) between linear [3]phenylene(CpCo)complex 19 and 2378-tetrakis(trimethylsilyl) linear [3]phenylene (60) The bond distances in 19 are shown in blue Increases in bond length in going from 60 to 19 are marked in green decreases in red

ldquobond fixationrdquo (Figure 12) remains in the vicinity of the uncomplexed cyclobutadiene Compound 19 thus provides a prime demonstration of the powerful effect of metalloaromatization46 in which the bonds of a cyclobutadiene-metal system attempt to adopt the equalized bond lengths that are a classic hallmark of aromaticity2ndash4 Encouraged by the successful development of a procedure to obtain X-ray quality crystals of 19 these techniques were applied to bis(trimethylsilyl) linear [3]phenylene(CpCo) 52 Gratifyingly with acetone as the solvent the results depicted in Figure 24 were ultimately obtained Figure 24 X-ray crystal structure of 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52)

Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are omitted for clarity

A comparison of the bond lengths of 52 with those of its corresponding linear [3]phenylene ligand 469a is given in Figure 25 Comparison with Figure 23 reveals the same type of aromatization of the ligand on attachment of the metal With these structures in hand an attempt was made to rationalize structurally the

- 26 -

thermodynamic preference for 52 in which the CpCo is located proximal to the silylated terminus in its equilibrium with 53 in which the metal is located close to the unsilylated benzene ring Focusing on the desymmetrizing ortho-bis(trimethylsilyl) unit one notes that the SiCndashCSi bond in 52 is elongated by 005 Aring on attaching the metal in 46 thus providing steric relief On the other hand the symmetry equivalent remote C7ndashC8 distance is unchanged The same effect is seen in the tetrasilyl complex 19

Figure 25 Comparison of bond lengths (in Aring) between bis(trimethylsilyl) linear [3]phenylene(CpCo) complex 52 and 23-bis(trimethylsilyl) linear [3]phenylene (46) Bond lengths for 46 are the average of four molecules in the unit cell (standard deviation = plusmn002)

Increases in bond length going from 46 to 52 are marked in green decreases in red

The observed structural changes make sense in a simple resonance picture

Co

1413(10)(007)

1406(10)(-004)

1459(10)

( 005)

1370(11)(-007)

1418(10)( 005)

1443(10)(003)

1470(10)(-005)

1465(10)(-005)

1446(10)( 008)

1485(10)( 006)

1432(10)( 004)

1347(10)(-003)

1345(10)(-002)

1492(10)( 007)

1503(11)(-002)

1379(10)(001)

1391(11)(-001)

1409(10)(004)

1418(11)(-003)

1367(11)(001)

1478(10)(-002)

1408(11)(-001)

1891(8)

1890(13)

1670

1723

SiMe

MeMe

Si

Me

Me

Me

(x) = (53) - (62)increasedecrease

SiMe

MeMe

Si

Me

Me

Me

190

145134152

139138

150

137145

136

142 137

152137 137

152

141

137 144

189

141143142140

52

46

- 27 -

(Scheme 216) Metalloaromatization alters the dominant resonance forms during intercyclobutadiene hopping such that the essentially single SiCndashCSi bond in 52 transforms into an essential double bond in 53 increasing unfavorable repulsion between the TMS groups Scheme 216 A Resonance Picture Rationale for the Preference of 52 in its Equilibrium with 53 The aromatization effect of metal complexation on the phenylene nucleus described structurally in the preceding text can also be demonstrated powerfully through the measurement of ring currents with 1H-NMR spectroscopy both by experiment and computation (NICS13 see Section 11) A relevant simple example is depicted in Figure 26(a) featuring the changes occurring when 12-bis(trimethylsilyl)benzocyclobutadiene (61) is complexed by CpCo as in 6251 The paratropic antiaromatic 8π system 61 exhibiting relatively shielded six-membered ring hydrogens turns diatropic in 62 Equally importantly and focusing on the ring current contributions of the individual cycles the paratropism of the four-membered ring in 63 shields the adjacent hydrogens more than the remote ones Conversely aromatization of this ring and the ensuing diatropism inverts this order

Figure 26 The effect CpCo complexation (a) on benzocyclobutadiene 61 and (b) linear [3]phenylene 46 Chemicals shifts are in ppm

Co SiMe3

SiMe3

Co

SiMe3

SiMe352 53

∆Gdeg298 =23 kcalmol

- 28 -

Turning to a phenylene system comparison of the NMR data for complex 52 with those for ligand 46 (Figure 26(b)) reveals the same changes not only in the vicinity of the ligated ring but also in the remote parts of the molecule Thus the hydrogens closest to the metal fragment are shifted downfield by 125 ppm in 62 and 148068 ppm in 52 when compared with 61 and 46 respectively The observed relatively large chemical shifts of the arene hydrogens proximal to the metal unit are not due to its anisotropy since its value in this area of space is (if anything) shielding5152 In addition the remote hydrogens in 52 are deshielded by 055033 ppm relative to the corresponding nuclei in 46 clearly substantiating the aromatization of the overall system upon metal complexation that was seen by structural analysis These pronounced chemical shift changes are diagnostic and greatly aided the spectral interpretations of the photochemically induced haptotropic shift experiments described in Sections 21 and 22 as illustrated for the isomerization between 52 and 53 (Scheme 217)

Scheme 217 Chemical Shift Changes in the Isomerization of 52 to 53

These NMR measurements were augmented by NICS calculations carried out in collaboration with Professor Amnon Stanger at the Technion in Haifa NICS data have the advantage that they indicate the extent of (anti)aromaticity even in rings for which the molecule has no hydrogen probe in the classical NMR experiment in this case the cyclobutadienes Computational details are given in Chapter 4 The experimentally determined proton NMR data for the series of silylated linear phenylenes from [2] to [5] and their metallated analogues in addition to the corresponding NICS(1) values of the respective parent phenylenes are shown in Figure 27 All compounds in Figure 27 are known except for the hypothetical biphenylene(CpCo) 64 which is included for comparative purposes Metalloaromatization is pronounced as all rings of the phenylene exhibit diminished or more negative NICS numbers signaling increasing aromatic and decreasing antiaromatic character respectively Again the effect is most pronounced on the rings closest to the metal bound unit tapering off (but never disappearing) with distance Most illustrative in this respect is 44 in which the penultimate and ultimate rings away from the Co still show decreases in the NICS values of 06 and 05 ppm respectively Interestingly the sum of all NICS values of 44 (ldquototal NICSrdquo13c) ndash91 is less negative than that of 21 ndash132 suggesting that 21 is more aromatic hence more stable as observed experimentally This may be fortuitous and the issue is addressed further in Section 24 Finally a caveat regarding the unusually large negative NICS values associated with the CpCo-complexed cyclobutadiene rings As pointed out by Solagrave in connection with a related study of (benzene)Cr(CO)3 which produced similar numbers53 there are local ring currents associated with the extra electrons involved in the metal to π-ligand

CoTMS

TMS796675674

678

436 CoTMS

TMS747683724

662

444

310 365 nmsunlight

30ndash50oC

52 53

- 29 -

bonding that lead to an overestimation of aromaticity Therefore to corroborate the general conclusions of metalloaromatization of this (and all other rings) in Figure 27 Stangerrsquos NICS scan method was applied54 This procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (NICSXY) and out-of-plane components (NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their

Figure 27 Experimental 1H-NMR (C6D6 blue) and computed NICS(1) (green) values for linear phenylenes and their corresponding CpCo complexes The experimental data are for the silylated

derivatives shown The NICS data are for the parent systems interpretation The data presented in Chapter 4 confirm the conclusions of this section While not reflective of ring current effects the values of the 13C chemical shifts for the linear phenylene(CpCo)complexes do provide some insight into the nature of the

- 30 -

σ-framework Comparing complex 19 with parent ligand 60 one observes two general phenomena (Figure 28) The most apparent is the upfield values for the cobalt-bound cyclobutadiene carbons (~74ndash78 ppm) in 19 arising from the local anisotropic shielding effect of the metal (vide supra) Secondly the carbon atoms in the four-membered ring not bound to the metal exhibit large deshielded values (144ndash149 ppm) This effect also seen in ligand 60 arises from the rehybridization6 of the cyclobutadiene sp2 orbitals and is observed in all phenylene topologies A comparison of the 13C-NMR data for the linear [3]- [4]- and [5]phenylene(CpCo)complexes with their respective parent ligands is given in Chapter 4

Figure 28

13C-NMR data for complex 19 and parent silylated ligand 60 Values are in ppm 24 Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift How does the CpCo moiety migrate from one cyclobutadiene unit to the next Two extreme alternatives present themselves a least-motion movement across the intervening arene unit or a more circuitous pathway along the periphery The latter is prevalent in other computed haptotropic shifts56-57 in particular those occurring in (arene)Cr(CO)3 complexes all of which choose peripheral trails56 In these the metal typically moves straight to the edge to adopt an η4 (often described as η1) trimethylenemethane-like transition state on the way to a neighboring ring as illustrated for the η6-η6 hopping in naphthaleneCr(CO)3 summarized in Scheme 218 More relevant is the computed course of the η6-η6 interconversion of (biphenylene)Cr(CO)3 (Scheme 219)57 The metal slides from the (near)center of one benzene ring to the quaternary (four-membered) ring carbon to reach a distorted trimethylenemethane maximum and then proceeds to the edge of the bridging cyclobutadiene bond This species represents a minimum on the potential energy curve and adopts an η2-like complexed cyclobutadiene topology (ldquoquasi-η4rdquo) from which it continues by the microscopic reverse on to the other benzene nucleus The relevance of these findings with respect to the intercyclobutadiene hopping of CpCo along the phenylene frame was not clear at the outset of the work described in this section The CpCo fragment has a different electronic requirement from Cr(CO)3 and interring migration in arenes (and related systems) involves aromatic electron counts of all intervening circuits

Scheme 218 Migration of Cr(CO)3 Across Naphthalene

- 31 -

Scheme 219 Migration of Cr(CO)3 Across Biphenylene

DFT calculations were carried out in collaboration with Professor Thomas Albright at the University of Houston In these studies using B3LYP 3-21G (carbonhydrogen) and LANL2DZ (cobalt) basis sets the metal fragment was placed 18 Aring above the π system with energy minimizations carried out every 02 Aring along the frame of the parent linear phenylene in question When transition states and local minima were located their structures were refined with the B3LYP 6-31G (hydrogen) 6-113G (carbon) and LANL2DZ (with inclusion of cobalt f-orbitals) basis sets More computational details are given in Chapter 4 The resulting potential energy surface for the thermal rearrangement in the parent linear [3]phenylene(CpCo)system is shown in Figure 29 Figure 210 contains enlarged images of the transition states and intermediate structures The haptotropic shift begins with the (η4-cyclobutadiene)CpCo global minimum (labeled ground state GS) assigned a relative value of 000 kcalmol An η2-cyclobutadiene transition state (TS 1) 269 kcalmol higher in energy than GS is passed before reaching a local minimum (LM) that lies 109 kcalmol above GS LM features CpCo coordinated unsymmetrically η4 to the central benzene ring thus avoiding an unstable 20 electron η6-benzene configuration (not shown) which when explicitly calculated proved to lie 36 kcalmol above LM From LM a symmetry-related second η4 structure is reached via an η3-benzene transition state (TS 2 barrier 14 kcalmol) that symmetrizes the ldquoleftrdquo with the ldquorightrdquo half of the molecule LM is 249 kcalmol higher in energy than GS The shift is completed through the reverse of the initial two movements through LM and TS 1 on the other side of the ligand to reach the second cyclobutadiene ring Thus as for Cr(CO)3 (Scheme 219) CpCo migrates along the edge of the linear phenylene but because of its differing electronic needs through distinctly different intermediates and transition states Most obvious is the internal η2-cyclobutadiene TS 1 which for Cr changes to a peripheral η2-intermediate The calculated rate determining barrier of 269 kcalmol (GS to TS 1) is slightly higher than that measured for the reversal of 53 to 52 (~23 kcalmol) Part of this discrepancy may be due to ground state activation of 53 which is ~2 kcalmol less stable than 52 The LM structure has some resemblance to the isolated η4-CpCo angular [3]phenylene 23 (Section 12) Its location in an energetic well of ~14ndash16 kcalmol (TS 1 and TS 2) suggested that it may be observable at low temperature This investigation is detailed in Section 25

- 32 -

Figure 29 Calculated potential energy profile for the thermal η4η4 haptotropic shift in linear [3]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

0

5

10

15

20

25

30

1 2 3 4Reaction Path

Co

Co

C o

C o

GS η

4

LM η

4

TS1 η

2

TS 2 η

3

00

269

109

249

Key - Global MinimumGround State (GS)- Local Minimum (LM)

- Transition State (TS)

122

3 34 4

- 33 -

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 34 -

(d) Transition state 2 η3-benzene (249 kcalmol)

Figure 210 Optimized structures and relative energies for the linear [3]phenylene(CpCo) haptotropic shift Carbon atoms are shaded grey hydrogens light grey and cobalt blue Bond

lengths are in Aring The potential energy profile for the thermal shift in the linear [5]phenylene(CpCo) system was calculated in the same manner and is shown in Figure 211 Images of the intermediates and transition states are depicted in Figure 212 Placing the metal fragment on the inner cyclobutadiene ring resulted in the lowest energy structure and was therefore set as the global minimum (GS) Two distinct haptotropic migrations inner-to-inner and inner-to-outer cyclobutadiene are now possible (Section 21) Beginning at GS the metal can proceed in the direction of TS 2 or TS 3 respectively both of which are η2 with similar barrier heights (~36 kcalmol) The former pathway is degenerate and continues from TS 2 to η4-LM 1 and then via η3 central benzene TS 1 to the symmetry related corresponding LM 1 TS 2 and finally GS involving the opposite inner four-membered ring The rate determining barrier for this process is 359 kcalmol clearly too high to be measurable by NMR techniques as found for 212838 Interior-to-exterior shifting of the cobalt continues from TS 3 on to η4-benzene LM 2 The η3-TS 3 is traversed before the second η4η2

sequence (LM3 and TS 5 respectively) ultimately leading to LM 4 which is the outer

- 35 -

cyclobutadiene coordinated structure and represents the photoisomeric species observed experimentally in Scheme 23 The computed rate-determining barrier (TS 3) of 263 kcalmol for the reverse reaction of LM 4 to GS is close to the experimentally measured values of 256ndash276 kcalmol for the derivatives in Table 21

Figure 211 Calculated potential energy profile for the η4η4 haptotropic shift in linear [5]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

40

Reaction Path

263

0

5

10

15

20

25

30

35

C o

C o

C o

C o

Co

Co Co

C o

C o Co 360 370

359 357

367

97

203 190 196

1 2 3 4 5 6 7 8 9 10

TS 1 η

3

LM 1 η

4

TS 2 η

2

GS η

4 00

TS 3 η

2 TS 4 η

3 TS 5

η2

LM 2 η

4 LM 3 η

4

LM 4 η

4

Key- Global MinimumGround State (GS)

- Local Minimum (LM)

- Transition State (TS)

- 36 -

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 37 -

(d) Transition state 4 η3-benzene (367 kcalmol)

(e) Local minimum 3 η4-benzene (190 kcalmol)

- 38 -

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 39 -

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

(i) Local minimum 1 η4-benzene (190 kcalmol)

- 40 -

(j) Transition state 1 η3-cyclobutadiene (356 kcalmol)

Figure 212 Optimized structures and relative energies for the linear [5]phenylene(CpCo) haptotropic shift Structures for the inner-to-outer cyclobutadiene migration are given by (a)ndash(g)

Species (h)ndash(j) are involved in the interior-to-interior four-membered ring pathway Carbon atoms are shaded grey hydrogen atoms light grey and cobalt blue Bond lengths are in Aring

Why does CpCo prefer complexation to the internal cyclobutadiene that is GS (as represented by 21 and 42) over LM 4 (as represented by 44 and 45) Calculations show that the energies required to distort linear [5]phenylene to the geometries found in

- 41 -

the complexed isomers are very similar (16 versus 14 kcalmol) Hence the answer must rest on electronic grounds Indeed extended Huumlckel calculations reveal that the overlap populations between the frontier orbitals on the CpCo fragment and the HOMO and the LUMO of the π system are greater for GS (00793 and 00745 respectively) than for LM 4 (00556 and 00517 respectively) A didactically more instructive valence bond view recognizes that metalloaromatization of the inside four-membered ring allows the formulation of more resonance forms that avoid antiaromatic cyclobutadiene circuits A full list of these resonance forms as well as details of the EHMO calculations are given in Chapter 4 25 Low Temperature Photochemical Studies of the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes Of the various participating species in the mechanism for intercyclobutadiene migration (Section 24) specific attention was focused on the η4-benzene intermediates that occur in both the linear [3]- and [5]phenylene haptotropic shifts These structures are energetic local minima on the reaction profiles for both systems and were of considerable intrinsic interest not only as reactive intermediates in this manifold but also because of their relationship to the isolable angular [3]phenylene(CpCo) complex 2329 (Figure 213) Figure 213 (a) Calculated structure for the η4-benzene linear [3]phenylene(CpCo)intermediate

in the haptotropic migration (b) Crystal structure of η4 angular [3]phenylene (CpCo) 23

While rare a handful of other η4-benzene-metal complexes have been isolated (Figure 214) For example two related iridium based systems benzene(CpIr) 6658 and benzene triphos(Ir) 6759 are known As expected ligation causes significant shielding of the hydrogens in the η4 portion of the ligand especially the terminal positions The η4 intermediates in the haptotropic shift are situated in wells on the potential energy surface that are ~17 kcalmol deep for the linear [5]- and ~15 kcalmol for the linear [3]phenylene complexes These values are large enough that such species might be observable by NMR spectroscopy if irradiation of the starting materials were performed at low temperature and if the excited state would relax selectively to these intermediates As a suitable candidate with which to explore this possibility the partly symmetric tetrasilyl complex 19 was chosen The generation of anticipated desymmetrized 68 would be readily detected by the appearance of 11 new singlets in the 1H- and 23 new peaks in the 13C-NMR spectra (Scheme 220)

(a) (b)

- 42 -

Figure 214 Selected relevant examples of isolated η4-benzene complexes and their proton NMR chemical shifts (ppm)

Scheme 220 Low Temperature Irradiation Experiment Designed to Generate η4-Benzene Intermediate 68

Construction of a satisfactory setup to allow for the planned low temperature irradiation was not trivial An optimal experimental configuration however was devised utilizing three pieces of equipment each of which is shown in Figure 215 The first was a custom-made Pyrex Dewar flask small enough to adequately contain an NMR tube Cooling was achieved by means of a Neslab refrigerated circulating bath Thirdly a Rayonet Photochemical Reactor was used as the light source The sample was first placed inside of the Dewar flask and cooled to the required temperature inside of the Rayonet Once cold irradiation was carried out for the desired length of time When complete the sample was transported cold to the NMR laboratory and very quickly placed inside of a pre-cooled NMR probe for analysis A solution of complex 19 was irradiated at ndash65 degC as described and its 1H-NMR spectrum recorded at ndash30 degC revealing a dramatic change The signals for 19 had almost entirely vanished and a set of new peaks appeared The new aromatic resonances were comprised of two sharp singlets at δ = 708 and 644 ppm and a broad singlet at δ = 558 ppm all of which integrated for 2 hydrogens each Another broad

649

586

316

H H

Co544

66 67 23

Ir

P(Ph2)P(Ph2) P(Ph2)

H

H

H

625

594

350

Ir

H

H

H

- 43 -

Figure 215 Cold irradiation experimental setup consisting of (a) Pyrex Dewar flask (b)

refrigerated circulating bath (c) Rayonet Photochemical Reactor with Pyrex Dewar vessel placed inside

(a) η

4 (b) η

4 (c) η

4

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

New peaks

L L

- 44 -

Figure 216 Stacked plot of the aromatic 1H-NMR spectral region recorded after the cold irradiation of 19 in toluene-d8 Peaks for 19 are indicated by blue new peaks by red arrows

Impurities are marked with and traces of free ligand 60 with L The scale is in ppm

singlet at δ = 398 ppm (5 H) was assigned to a new Cp group (Figure 217) and two new TMS singlets (9 H each not shown) were also present The new broad Cp absorption displayed peculiar behavior gradually moving to higher field (∆δ ~ 08 ppm for Cp-H) on warming from ndash30 degC to 10 degC (Figure 217) The broadened singlet at δ = 558 ppm showed similar albeit much attenuated behavior At room temperature all new peaks had disappeared leading to regeneration of the original spectrum of 19

Figure 217 Stacked plot of the Cp spectral region in the cold irradiation of 19 in toluene-d8 Peaks for molecule 19 are indicated by blue the new peaks by red arrows The scale is in ppm

In addition to these NMR observations a remarkable change in color from the redmaroon of 19 to olive green took place during the course of this experiment (Figure 218) Indeed the UV-Vis spectrum of the low temperature species is strikingly different from that of 19 showing a large broad absorbance band centered in the visible region

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

19

THF

- 45 -

Figure 218 Color change during the low temperature irradiation of 19 (a) Before irradiation (b) After irradiation

Complex 19

Low Temperature Species

0

02

04

06

08

1

12

14

16

18

2

400 430 460 490 520 550 580 610 640 670 700

Wavelength (nm)

Ab

sorb

an

ce

Figure 219 UV-Vis spectra (toluene) of 19 (at rt) shown in blue and the new compound (at ~

ndash30 degC) shown in red

at 654 nm (Figure 219) Warming the sample to room temperature restored its original red color While the observation of a new species was gratifying the NMR data posed a puzzle as they were clearly incompatible with (a static) structure 68 Instead they pointed to a molecule exhibiting mirror (or ldquotop-downrdquo) symmetry along the long molecular axis as in 19 itself The two most obvious candidates 69 and 70 (Figure

(a) η

4 (b) η

4

- 46 -

220) were ruled out as the first could not be found during the computations underlying Figure 29 and the second actually constitutes the transition state TS 1 for the thermal reverse process

Figure 220 Possible (but unlikely) structures of correct symmetry for the low temperature

photoisomer of 19 In the hope to shed further light on the nature of purported 68 low temperature 13C in conjunction with 2-D NMR (HSQC HMBC) experiments were carried out These data led to the tentative assignments shown in Figure 221 Assuming the presence of top-down symmetry as surmised by the proton spectra one would have expected to observe nine phenylene carbon signals The actual spectrum however contains only six peaks The Cp line was broadened to the point of being barely visible and no crosspeaks for the absorption at δ = 556 ppm were seen by 2-D NMR spectroscopy

Figure 221 Partial assignments of 1H-(italicized) and 13C-NMR signals of 68 The ldquotop-downrdquo plane of symmetry is indicated by the dashed purple line HMBC δ = 643 ppm correlates with δ = 1461 and 1521 ppm δ = 708 ppm correlates with δ = 1477 and 1508 ppm δ = 033 ppm

correlates with δ = 1477 ppm and δ = 036 ppm correlates with δ = 1461 ppm HSQC δ = 643 ppm correlates with δ = 1121 ppm δ = 708 ppm correlates with δ = 1227 ppm and δ = 398

ppm correlates with δ = 85 ppm The connectivity of the CpCo to the central ring is left intentionally unspecified and the choice of positioning it to the left of the center hydrogens (blue)

SiMe3

SiMe3

H

Me3Si

Me3Si

H

Co

398 (br)

HH

1461

~85 (br)

708

H

556 (br)1508

= Unobserved 13C signals

H

H

Mirrorplane

6431477 1521

033036

11211227

- 47 -

arbitrary Similarly the assignments of the groups of ldquoleftrdquo and ldquorightrdquo benzene signals are tentative and might be inverted The carbons marked could not be observed

It is thus clear that we are dealing with an unusual species and if it is 68 the molecule must be partly (but not completely) fluxional around the central ring Returning to the computed energy profile in Figure 29 one notes that central η4η4-benzene fluxionality via TS 2 with a barrier of 140 kcalmol is presaged This process which causes ldquoleftrdquo-ldquorightrdquo but not ldquotoprdquo-ldquobottomrdquo symmetrization is unlikely to be responsible for the above data as it should have given rise to two 1H-NMR singlets for the central hydrogens However considering the expected relative closeness in the respective chemical shifts of the anticipated signals (see Figure 214) accidental isochronism could not be ruled out Consequently low temperature irradiation experiments were executed with 52 in which the ldquoleftrdquo-ldquorightrdquo option of symmetrization was obviated by the substitution pattern while leaving the ldquotoprdquo-ldquobottomrdquo option intact (Scheme 221) As Scheme 221 Low Temperature Irradiation of 52 and Possible Pathways for Fluxionality of

Intermediate 71

indicated in color the latter would provide a diagnostically simple proton spectrum of only four phenylene signals The former on the other hand should show eight such peaks A potential complication of this experiment was the possibility of two regioisomeric (and non-interconverting) cobalt species located on either side of the central six-membered ring (Scheme 222) In the event the spectra shown in Figure 222 were obtained At ndash60 degC in

HH

CoTMS

TMS

CoTMS

TMS

TMS

TMS

Co

TMS

TMS

CoTMS

TMS

Co

TMS

TMS

Co

Top-bottom

cold hν ∆

Lef t-right

52 53

∆

71

or

H

HH

H

H H

H HH

HH H H

H

- 48 -

addition to unreacted 52 and photoisomer 53 a new species formed the spectral features of which implicate 71 as a ldquotop-bottomrdquo symmetrizing species Specifically the

Scheme 222 The Two Possible Regioisomers of 71 ldquoLeftrdquo and ldquoRightrdquo

71

52

53 53

53

52

TMS

TMS

Co

TMS

TMS

Co

TMS

TMS

Co

71

TMS

TMS

Co

or

Right Lef t

ndash60 degC

ndash50 degC

ndash40 degC

ndash30 degC

53

- 49 -

Figure 222 Stacked plot of the aromatic spectral region in the cold irradiation of 52 in toluene-d8 Peaks for molecule 52 are marked by blue arrows 53 in red and 71 in green Trace amounts

of free ligand bis(trimethylsilyl) linear [3]phenylene] 46 are denoted with L The scale is in ppm

unsubstituted benzene terminus hydrogens exhibit an AArsquoBBrsquo pattern at δ = 647 ppm which integrate for 4 hydrogens The central ring hydrogens appear as a broad singlet at δ = 557 ppm (2H) and the silylated terminus as a singlet at δ = 632 ppm (2H) Warming the reaction mixture to 10 degC led to the gradual disappearance of 71 with a concomitant increase of the signals assigned to 52 and 53 This experiment confirms the conclusions drawn as a result of the low temperature irradiation of 19 namely that a ldquotop-bottomrdquo symmetrizing species is generated Remarkably in view of the possibility of two regioisomers (Scheme 222) only one set of peaks is observed indicating that the excited state of 53 relaxes to settle on only one side of the central ring Which side is a matter of speculation Figure 223 compares the 1H chemical shifts of 71 with those of 68 and for calibration 52 53 and free ligands 46 and 60 For the first pair it is clear that the two species are very similar with almost identical chemical shifts of the relevant hydrogens taking into account the considerable deshielding effect of TMS substitution on the unsubstituted terminus in 73 (~07 ppm cf 52 vs 53 46 vs 60) Arguably placing the CpCo moiety to the ldquoleftrdquo as depicted in 68 and 71 aromatizes the proximal benzene by η2-complexation of the adjacent four-membered ring leaving considerable benzocyclobutadiene character on the ldquorightrdquo consistent with the associated chemical shifts

- 50 -

CoTMS

TMS796675674

678

CoTMS

TMS747683724

662

Co

TMS

TMS

52

71

53

424

642

557 632652

436 444

Co

TMS

TMS

68

398

556 643708

TMSTMS

TMS

TMS684607619

645

46

assignmenttentative

TMS

TMS

TMS

TMS623 685

60

TMS

TMS

TMS

TMS

Co

691 795745

19

441

Figure 223 1H-NMR chemical shift comparison of 68 and 71 with other relevant species A plot of the changes in concentration of 52 53 and 71 with temperature is shown in Figure 224 Within (the considerable) error and considering the unusual magnetic behavior of 71 (vide infra) it appears that the latter converts mainly to 52 in the temperature regime in which 53 is stable with respect to its thermal reverse to 52 This observation may be interpreted as indicating a lower barrier for Co migration from the center ring to the more stable cyclobutadiene haptomer

- 51 -

0

1

2

3

4

5

6

7

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Inte

gra

tio

n v

s I

nte

ra

l S

tan

da

rd

52

53

71

Figure 224 Plot of the concentration changes of 52 53 and 71 with temperature measured by the relative integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively

The ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100)

Another plot this one showing the ratios of 52 53 and 71 with respect to each other is given in Figure 225 The disappearance of 71 with rising temperature is illustrated by the increase in the ratios of 5271 and 5371 As indicated by the steep slopes the conversion of 71 into 52 and 53 is particularly fast between ndash10 and 0 degC That complex 52 is preferentially formed is again confirmed by the escalating 5253 ratio While these data do not provide a definitive answer for the location of the CpCo they are consistent with the plots shown in Figure 224 and the above discussions

- 52 -

0

1

2

3

4

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Rel

ati

ve

Inte

gra

tio

n

5271

5371

5253

Figure 225 Plot of the ratios of 52 53 and 71 against each other with temperature measured by the integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively The

ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100) Having established the topological aspects of 68 and 71 attention was turned to their peculiar NMR characteristics in the vicinity of the metal ie the broad peaks for the central hydrogens and the CpHs the broad Cp-carbon line the inability to observe 13C signals for the central benzene ring and the temperature dependent drifting of (particularly) the Cp absorption A trivial (and ultimately unsatisfying) explanation for at least peak broadening was the presence of trace paramagnetic metallic impurities60 that might have been generated during the irradiation process Spin exchange preferentially Co-based might affect the center atoms in 68 and 71 more than the remainder of the molecule although it should also cause line broadening in the isomers 19 and 52 and 53 respectively Experimentally the presence of such species was made unlikely by executing the cold irradiation experiment of 19 in the presence of the radical trap 13-cyclohexadiene which produced spectra identical to those described earlier An attractive alternative that might explain the data and in addition provide a mechanism for ldquotop-downrdquo exchange is of the intervention of triplet state cobalt species The ability of metals to change their electronic spin state and the consequences of this phenomenon on organometallic structure and reactivity are well documented61

18-Electron CpCo complexes are ground state singlets but their 16-electron counterparts accessed typically by ligand dissociation have more stable triplet configurations62 A number of CpCo and related Co species have also been reported in

- 53 -

which singlets are in thermal equilibrium with paramagnetic triplets by intersystem crossing63 Such complexes display spectral behavior very similar to that seen for 68 and 71 For example 7263b exists as a mixed spin state system in which the singlet predominates at room temperature in solution (Figure 226) On heating the triplet becomes increasingly populated shifting and broadening its NMR signals Cooling the solution back to room temperature reverses these spectral changes In addition to complexes of cobalt analogous observations have been reported for other metals such those based on hafnium64 copper65 ruthenium66 and tungsten67

Figure 226 Temperature dependent chemical shifts in CpCo derivative 72 in toluene-d8

(marked as S on the plot) The scale is in ppm

Consideration of these examples would then suggest that 6871 undergo ldquotop-downrdquo equilibration through a triplet 16-electron intermediate or that 6871 themselves are triplets or have thermally accessible triplet states from which fluxionality might occur Since the relaxation times (T1) of paramagnetic systems60a are much shorter compared to their diamagnetic counterparts measurement of this property was thought to be informative The T1 values for the proton in 68 were determined via a standard inversion recovery experiment44 and are given in Table 24 (cf Figure 220) in comparison to p-terphenyl60b

Co

CoPMe3

72

- 54 -

Table 24 1H-NMR Relaxation Times in Intermediate 68 at ndash30 degC

Resonance (ppm) T1(s) 711 2309 646 0997 556 005 398 0108

In consonance with the associated line broadening the relaxation times of the Cp

(δ = 398 ppm 0108 s) and central ring hydrogens (556 ppm 005 s) are much smaller than those of the remaining phenylene ligand (711 and 646 ppm 2309 and 0997 s respectively) the latter in turn comparing well with the values in p-terphenyl With this corroborative evidence in hand the question whether the species is itself a triplet or is in thermal equilibrium with such was addressed The answer can be obtained by using a Curie-like graph68 in which chemical shifts are plotted as a function of temperature65 A linear relationship corresponds to the presence of a triplet compound while curved behavior is indicative of a singlet-triplet equilibrium Plotting the chemical shifts of the Cp hydrogen of 68 and 71 against the inverse of temperature (Figure 227) gave distinctly curved lines supporting the notion that these species are in thermal equilibrium with their triplets The exact nature of these species however remains to be determined

156

395404

345

p-Terphenyl

- 55 -

3

32

34

36

38

4

42

44

46

00036 00038 0004 00042 00044 00046 00048

1T (K -1

)

Ch

em

ica

l S

hif

t (p

pm

)

71

68

Figure 227 Plot of the Cp chemical shift (toluene-d8) of 68 and 71 versus the inverse of temperature

DFT calculations have commenced in an attempt to find a plausible structure for such a triplet cobalt species and with it possibly arrive at a mechanism for the fluxional behavior of 68 and 71 These studies are being carried out in collaboration with Professors Tom Albright of the University of Houston and Vincent Gandon of the Universiteacute Paris-Sud 11 Preliminary results at the B3LYP6-31G(dp) and BP866-31G(dp) levels suggest the η2-cyclobutadiene structure depicted in Figure 228 It is apparent that this species corresponds topologically to singlet TS 1 in Figure 29 and 70 in Figure 220 endowed with the symmetrical requirements dictated by the experiments

- 56 -

Figure 228 Calculated structure of a triplet η2-cyclobutadiene linear [3]phenylene(CpCo)

One can therefore envision fluxionality between the two ldquotoprdquo and ldquodownrdquo η4-benzene structures via the intermediacy of a triplet η2-cyclobutadiene (Scheme 223) Further Scheme 223 Conversion of ldquoTop-Downrdquo η4-Haptomers of 68 Via a Triplet η2-Cyclobutadiene

Intermediate

computations are required to pinpoint the minimum energy crossing points between the singlet η4 and triplet η2 structures and to explain why this triplet does not collapse to the CpCo cyclobutadiene isomer This work is in progress 26 Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 All of the linear phenylene(CpCo) complexes mentioned thus far share one common feature a single CpCo unit bound to the phenylene scaffold However since there are one or more additional cyclobutadienoid rings in the series the question arises whether it might be possible to bind more than one metal fragment to the ligand If so what would be the structural consequences Would be there further metalloaromatization Would such systems be capable of light-induced haptotropism and if so how would the metals move relative to the ligand and to each other Finally would such complexes mimic structurally the variety of arrays obtained in the reaction of 29 with Fe2(CO)9 (Scheme 15) Since the linear phenylenes become increasingly more antiaromatic with size the optimal candidates for preparing such multi-metallic systems should be the higher members of the series Indeed evidence for double CpCo attachment was obtained in the form of the minor by-products 73 and 74 (Scheme 224) obtained during the

Scheme 224 Side Products in the Preparation of Linear [4]- and [5]Phenylene(CpCo)

- 57 -

Complexes by Cobalt-Catalyzed Cyclization

preparation of 20 and 21 respectively (Scheme 13) These Diels-Alder type adducts of a third BTMSA molecule to the π-frame can be envisaged to be derived from 75 and 76 respectively in which the six-membered ring flanked by the two CpCo(cyclobutadiene) units would be expected to have an unusual (biradicaloid) electronic structure Evidence for the feasibility of such arrays rests on the unique black-red syn-bis(irontricarbonyl) compound 77 whose structure was determined by X-ray analysis69 With reasonable quantities of 19 in hand the possibility of ligating a second CpCo unit to it was explored This idea was further encouraged by the observation that crude samples of bis(trimethylsilyl) linear [3] phenylene(CpCo) complex 53 contained a very small (3 ) peak at mz = 618 an exact match for the mass of a doubly metallated analog Consequently 19 was treated with one equivalent of CpCo(C2H4)2 in benzene to afford a reddish black solid (Scheme 225) The mass spectrum data exhibited a

Scheme 225 Preparation of Complex 78 from Complex 19

TMS

TMSTMS

TMS

CoCpCo(C2H4)2

22h 70 oC C6H6Linear [3]TMS4(CoCp)2

5619 78

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

74

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

73

TMS

TMS

TMS

TMSCoCpCpCo

76

TMS

TMS

TMS

TMSCoCpCpCo

75

Ph

Ph

Ph

Ph

Fe(CO)3Fe(CO)3

77

- 58 -

molecular ion peak at mz 762 corresponding to 19(CpCo)2 The 1H-NMR spectrum (acetone-d6) revealed four sharp singlets integrating in the ratio 410236 indicative of a highly symmetrical structure The chemical shift of the benzene termini (736 ppm) suggested that these rings have significant aromatic character and is similar to the value of 745 ppm seen for the hydrogen positioned farthest away from the CpCo in 19 (Figure 27) Similarly the 13C signals of the terminal rings in 78 (1505 1454 and 1258 ppm) are analogous to those from the corresponding terminal ring in 19 (1484 1433 and 1256 ppm Figure 28) Detailed analysis of 78 with two-dimensional NMR techniques (HSQC and HMBC) allowed for a complete assignment of all peaks in the 1H and 13C spectra (Figure 229) The strongly shielded (relative to the free ligand) proton (481 ppm) and carbon (537 and 571 ppm) resonances assigned to the central benzene ring clearly showed that both cobalt fragments are coordinated to the phenylene ligand at this position Interestingly these data bear a very close resemblance to those of the corresponding diiron complex 31 (Scheme 15) and are compared in Figure 229 Its central 13C resonances (688 and 582 ppm) are shifted upfield in a manner akin to 78 although not quite as much reflecting the increased electron withdrawing ability of the Fe(CO)3 group relative to CpCo70 Complex 31 like 78 exhibits aromatized terminal benzene rings as indicated by its 1H (750 ppm) and 13C (1484 1446 and 1258 ppm) chemical shifts These spectral similarities make it likely that 78 and 31 are isostructural The only structural ambiguity pertains to the orientation of the two metal fragments with respect to the π ligand a problem that had been left undecided in the assignment of structure 31 ie 31a (syn) versus b (anti Scheme 15)27 These options for 78 are

- 59 -

CpCoTMSTMS

TMS TMS

H H039 (36)

537 1258822

270

1454571

1505

481 (2) 736 (4)489 (10)

TMS TMS

TMSTMS

H

(OC)3Fe

(OC)3Fe

CpCo

78

31a

750 (4)553 (2)

036 (36)H

220

1446

1258

1484

688582

2128

Figure 229 Comparison of 1H- and 13C-NMR assignments (ppm) for molecules 78 (acetone-d6) and 31 (1H acetone-d6

13C CDCl3) Proton chemical shifts are in red and carbon in blue Integrations for the proton resonances are in green HSQC for 78 δ = 039 ppm correlates with δ = 270 ppm δ = 481 ppm correlates with δ = 537 ppm δ = 489 ppm correlates with δ = 822 δ

= 736 ppm correlates with δ = 1258 ppm HMBC for 78 δ = 036 ppm correlates with δ = 1454 ppm δ = 481 ppm correlates with δ = 571 and 1505 ppm δ = 736 ppm correlates with δ = 571 1454 and 1505 ppm The placement of the cobalt atoms in 78 is tentative (see Figure

229)

Figure 230 Possible structures for 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

- 60 -

shown in Figure 230) Both equally exotic options are precedented in the literature and corroborated by X-ray structural analyses (Figure 231)71

Figure 231 Illustrative examples of complexes with two metal fragments coordinated to the same benzene ring

Bis(CpFe) complex 7972 and its rhodium analog 8073 contain [M2(syn-micro-arene)] units in which the metals are linked58 Molecule 79 consists of two CpFe units coordinated η4 to the boat-shaped benzene ring sharing ligating carbon atoms In contrast the CpRh fragments in 80 are bound in an allyl η3 manner and the arene also adopts a boat conformation On the other hand bis[tris(tert-butyl)]toluene(CpCo) complex 8174 and the related system 8275 both exhibit [M2(anti-micro-arene)] units in which η4 coordination between the benzene ring and each of the metal fragments takes place Here the metals share carbon atoms but now involving a sandwiched ligand The arene in 81 retains a planar aromatic geometry while the benzene moiety in 82 is bent into a highly distorted chair conformation Unfortunately model structures 79ndash82 do not exhibit diagnostic NMR properties that would provide a clear distinction between synanti and planarnon-planar topologies For example the 1H-NMR peaks for the toluene ligand in anti-complex 81 range from 400ndash380 ppm74 whereas the signals for the benzene moiety in syn-bis(CpRh) 80 appear at 400ndash330 ppm73 The 13C data are similarly inconclusive as illustrated by comparison of 78 (562ndash531 ppm for the benzene ring) with 79 (648ndash525 ppm)72b An interesting property of these bis(metal) arene complexes is fluxionality of the metal fragments by haptotropic shifts along the periphery of the aromatic ring as depicted in Scheme 226 In complex 79 the hexamethylbenzene ligand (bound η4η4

in the solid state) displays a single arene resonance at 588 ppm in its room temperature carbon NMR spectrum Cooling to ndash90 degC however produces two distinct arene peaks at 525 and 648 ppm (for the shared and single-metal-bound carbons respectively as shown in 79a in Scheme 227) Fluxionality was postulated to proceed through an η3η3 intermediate (79b) that is structurally similar to Rh complex 80 which is itself a fluxional species

Scheme 226 Examples of Fluxional Processes in Dinuclear Arene Complexes 79 and 80

82 81

80 (R = CH3)

79

- 61 -

Anti-bis(β-diiminate)Rh complex 83 shows similar mobility (Scheme 226)76 A mechanism for η4η4 migration of the anti-metal fragments was proposed using the lowest energy species found by DFT calculations In these compounds the anti-metal fragments convert between η4η4 (83a 83c 83e) structures by passing through η3η3

(83b) and η4η2 (83d) transition states The energy barrier for η4η4 migration in 83 was experimentally determined to be 6 kcalmol This value is in line with other experimentally measured syn and anti dinuclear ring slippage processes which are typically le ~10 kcalmol71-75 The possibility of fluxionality in 78 might be observable if asymmetric configurations such as 78c and 78d (Figure 231) represent the lowest energy forms since they entail NMR observable desymmmetrization of the ligand Unfortunately cooling 78 in the NMR probe to temperatures as low as ndash80 degC in toluene-d8 did not reveal any signs of signal decoalescence

- 62 -

Figure 232 Possible lowest energy forms of complex 78

Hoping that further light could be shed on the disposition of the CpCo moieties in 78 by chemical transformations a brief investigation of its reactivity was undertaken For example bis(metal) arene complexes have been shown to readily undergo arene exchange reactions71 In complex 81 for example the toluene ligand is displaced by benzene at room temperature74 However heating a sample of 78 to 120 degC in toluene-d8 did not lead to any changes in the NMR spectra Turning to potential photochemical activation 78 was irradiated at various wavelengths (300ndash365 nm) These conditions as well as ambient sunlight did not cause any changes in its 1H-NMR spectrum further documenting 78 as a rather inert species X-ray crystallographic analysis would appear to be the only method of resolving the identity of complex 78 Producing suitable crystals of this molecule however has proven extremely difficult and will be the subject of future investigations 27 Summary and Outlook The work presented in this chapter published as a communication77 has detailed the first examples of η4η4 intercyclobutadiene migration and detailed mechanistic studies of this unprecedented reaction The haptotropic shift was found to be an intramolecular process with the CpCo fragment undergoing various changes in hapticity for the thermal isomerization Low temperature photolytic studies have revealed the existence of a thermally unstable intermediate species the exact structure of which is uncertain These results point to what appear to be significant differences between the photo- and thermal haptotropic pathways Further work both experimental and computational will be required to elucidate the details of the photochemical reaction In addition to the studies of linear phenylene(CpCo) haptotropism a hitherto unknown complex containing two CpCo fragments bound to linear [3]phenylene was prepared and scrutinized in preliminary form Despite extensive characterization the structure of this complex with respect to the position of the metal centers remains elusive Future work will focus on the acquisition of a crystal structure

- 63 -

Chapter 3

Nickel-Catalyzed Insertion Reactions for the Preparation of [N]Phenacene Derivatives

31 Introduction Transformations involving metal insertion into the four-membered ring of the [N]phenylenes as discussed in Section 12 represent a significant mode of reactivity with a high potential for practical synthetic utility One specific application of this chemistry is the synthesis of the phenanthrene moiety via tandem metal insertion and alkyne cycloaddition to the four-membered ring (Scheme 31) Such a methodology Scheme 31 Potential Preparation of the Phenanthrene Group from the Alkyne Cycloaddition

with Biphenylene would be valuable for the preparation of PAHs possessing phenanthrene subunits but has remained fairly unexplored Only a few examples demonstrating this transformation have been detailed previously for biphenylene (7) (Scheme 32)

Scheme 32 Metal Catalyzed Alkyne Cycloaddition Reactions with Biphenylene

The first report of this process is by Eisch in 198533a who treated biphenylene with Ni(PEt3)4 and diphenylacetylene to produce 910-diphenylphenanthrene 84 Since then a number of metals have been shown to mediate this process19 Ni systems being most relevant to this chapter Thus for example 84 can also be made using an N-heterocyclic carbene-based Ni(0) catalyst78 Bis(diisopropylphosphino)ethane Ni(alkyne) species enable similar cycloadditions of fairly hindered (trimethylsilyl)alkynes sometimes involving more complex processes of silyl group migration79 while less hindered substrates lead to 84ndash8680a A mixed phosphinoaminoethane-chelated Ni species proved more reactive enabling cycloaddition of even the encumbered tert-butyl(phenyl)acetylene to furnish the corresponding phenanthrene80b With this background in mind our attention turned to applying this reaction to larger phenylene systems Of the various topologies of phenylenes at our disposal the angular version was

R1 R2

R2R1[M]

[M]

7 R R

R = Ph (84)

R = Me (85)

R = CH2OMe (86)

RR

[Ni]

- 64 -

particularly intriguing as it offered two extreme modes of alkyne addition (Scheme 33) In the first scenario exclusive attack at the outer periphery of the four-membered rings would produce the helical shaped PAHs known as helicenes (Scheme 33a)81

Scheme 33 Alkyne Cycloaddition with Angular Phenylenes to Produce (a) Helicenes or (b) Phenacenes

Reactions occurring only at the interior or ldquobayrdquo region (Scheme 33b) however would afford a class of compounds exhibiting a linear polyphenanthrene motif that are known as [N]phenacenes82 Unselective additions would result in mixed topologies Helicenes and their various derivatives constitute a well studied83 family of molecules and continue to be a popular area of research Phenacenes in contrast have been scrutinized much less in part because only four members of the parent series are known and because for N = 5 and 6 they are extremely insoluble84 Phenacene-based applications have been slow to develop but the first reports of the utilization of these molecules as functional organic materials suggest the beginning of a rich and promising field85 Thus in 2008 [5]phenacene (picene) was demonstrated to behave as stable high performance organic field effect transistor (FET)85b Currently the most common organic polycyclic benzenoid hydrocarbon-based FETs employ acenes which have a polyanthracene structure (Figure 31) The sensitivity

Figure 31 Linearly fused benzene topology of the acenes of these systems to air however has obstructed progress in this area86 For example pentacene a commonly used acene in FETs reacts readily with oxygen to form

+ RR

Helicenes

+ RR

Phenacenesn

R

R R R R

n

R

R

R

(a)

(b)

[N]Acenes

n

- 65 -

pentacenequinone a process that severely reduces device efficiency (Scheme 34)

Scheme 34 Degradation of Pentacene to Pentacenequinone Under Aerobic Conditions

Phenacenes on the other hand are much less prone to such decomposition pathways due to their higher HOMO-LUMO gap thus rendering them less reactive85b86a Their enhanced stability relative to acenes87 makes them better candidates for molecular electronic applications In a second seminal breakthrough [5]phenacene was very recently also found to behave as a superconductor at low temperature when doped with potassium85a This work paves the way for a new class of PAH-based superconducting materials in which phenacenes may play a key role

As this chemistry advances new synthetic methods for preparing derivatives of these molecules will be required in particular those bearing solubilizing andor otherwise functionally useful substituents The most general procedure for synthesizing phenacenes as developed by Mallory88 makes use of oxidative stilbene photocyclizations (Scheme 35)8388 In this transformation irradiation of the stilbene

Scheme 35 Generic Oxidative Stilbene Photocyclization Used to Prepare Phenacenes as Illustrated for Phenanthrene

moiety leads to conrotatory electrocyclic ring closure Trapping of the resulting intermediate with oxidizing reagents such as iodine or oxygen yields the desired phenanthrene subunit The requisite stilbenes are most generally accessible via the Wittig reaction as illustrated in the synthesis of [7]phenacene derivative 87 (Scheme 36) Although the yields for the photocyclization are typically reasonable (60ndash90 )85a the major drawback of this methodology is the numerous steps associated with preparing the functional groups required for the prerequisite Wittig reaction These

- 66 -

transformations serve to decrease the overall yield of the target molecule

Scheme 36 Synthesis of [7]Phenacene 87

While laborious Malloryrsquos method addresses successfully the problem of solubility As alluded to in Section 21 large PAHs become insoluble due to the increased π-π stacking forces that are experienced between aromatic rings The best solubilizing groups for the phenacenes were found to be sterically bulky groups located in the bay regions85a These modifications distort the phenacene framework from planarity thereby disrupting π-stacking and increasing solubility as demonstrated by the tert-butyl [7]phenacene 87 (Figure 32) This approach was applied to systems as large as [11]phenacene the current record in the series85a

Br

CH3t -Bu

1 BuLi2 DMF

Br

CH2

t-Bu

CHO

CH3t-Bu

PPh3

Br

+Wittig

t-Bu t-Bu

Br CH3 1 hν2 I2

t-Bu t -Bu

Br CH3

t-Bu t-Bu

Br H2C PPh3 Br

+

t-Bu t-Bu

OHC CH3

Wittig

t-Bu t-Bu

Br Br 1 hν2 I2

t-Bu t-Bu

Br CH3

t-Bu t -Bu

t-Bu t-Bu

87

1 NBS2 PPh3

- 67 -

Figure 32 Crystal structure of tetrakis(tert-butyl) [7]phenacene 87 Hydrogens are omitted for clarity

To test the viability of angular phenylenes as substrates in Ni catalyzed alkyne cycloadditions the simplest member 22 was chosen raising a number of questions First how many and what kind of products will be formed (AndashE in Scheme 37) Will there be inherent selectivity toward helicene C or phenacene E formation respectively If not can the reaction conditions be modified so as to induce such What will be the limitations with respect to the size of substituents especially in view of the crowded fjord and bay regions of D and E respectively The work presented in this chapter carried out in collaboration with Dr Zhenhua Gu89 explores these questions

Scheme 37 Possible Cycloaddition Products of Angular [3]Phenylene 22

22

[Ni]R R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

A B

C D E

32 Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene

Before embarking on the proposed chemistry the reactivity of 22 in the presence of nickel in the form of Ni(COD)(PMe3)2 in the absence of alkynes was queried Only starting material was recovered and there was no sign of dimerization (or oligomerization) to products of the type shown in Scheme 38 a mode of reactivity

- 68 -

readily attained by biphenylene and substituted derivatives33b

Scheme 38 Attempted Dimerization of Angular [3]Phenylene 22

In contrast exposing diphenylacetylene 88 to Ni(COD)(PMe3)2 and a small excess (109 equivalents) of angular phenylene 22 generated two products in the absence of any other (Figure 39) The first molecule 89 was the result of the cycloaddition of one diphenylacetylene at the bay region and the minor component The major product constituted tetraphenyl [5]phenacene 90 derived from 22 by double bay region attack The structures of both compounds were confirmed by X-ray analysis revealing highly distorted frames89 Scheme 39 Nickel Catalyzed Cycloaddition of Angular [3]Phenylene 22 to Diphenylacetylene

Yields Based on Diphenylacetylene

The outcome of this transformation was gratifying in its seeming simplicity and selectivity Thus it appeared that metal insertion occurred exclusively to bay region bonds heralding the discovery of a new phenacene synthesis The observation of relatively large amounts of 90 could be ascribed to increased reactivity of 89 relative to 22 possibly due to steric activation by the newly introduced bay region phenyl group To test this hypothesis 89 was subjected to the cycloaddition reaction conditions (Scheme 310) Surprisingly not only was this reaction slower than that of 22 but the expected phenacene 90 was only a minor product (6 ) Instead tetraphenylbenzo[c]chrysene 91 a regioisomer of 90 as confirmed by X-ray analysis89

+

+ +

Ni(COD)(PMe3)2

22

- 69 -

was isolated in 74 yield the result of non-bay alkyne cycloaddition to 89 Therefore 89 is not the precursor of 90 Rather there must be separate reaction pathways leading to each respective product

Scheme 310 Cycloaddition Reaction of 89 with Diphenylacetylene 88

A series of semi-quantitative experiments monitored by 1H-NMR spectroscopy was carried out to shed some light on this mechanistic problem First the reaction of angular [3]phenylene 22 with diphenylacetylene 88 in Scheme 39 was addressed Because dinuclear metallic activation of the strained C-C bond in biphenylenes has been implicated in a number of studies19 it was possible that the above mechanistic duality was caused by the presence of catalytic Ni2 species in addition to the ldquoregularrdquo mononuclear alternatives Alternatively double Ni insertion before cycloaddition might be responsible for one product whereas sequential ldquonormalrdquo activation might be the origin of the other Therefore the amount of initial Ni(COD)(PMe3)2 was gradually increased and the effect of this incremental change on rate and product ratios recorded As shown in Table 31 the speed with which 89 and 90 formed was roughly proportional to the amount of metal present while the product ratio stayed unchanged

Table 31 Variation of Catalyst Loading in the Reaction of Phenylene 22 with Diphenylacetylene 88 Reactions Were Carried Out with Equimolar Amounts of 22 and 88 in

THF-d8 at 40 degC

Run Ni(COD)(PMe3)2

(mol) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

Ratio of 8990

1 50 32 times 10ndash4 031 times 10ndash4 103 2 35 20 times 10ndash4 022 times 10ndash4 91 3 7 064 times 10ndash4 0064 times 10ndash4 100

Next the amount of diphenylacetylene 88 was gradually increased from 1 to 4 equivalents (Table 32) The outcome of this series of experiments was counterintuitive as it led to a larger preference for the production of monoadduct 89 suggesting a mechanistic bifurcation in which whatever Ni species is responsible for the eventual formation of 90 is sequestered by external ligand (in this case 88)

- 70 -

Table 32 Variation of Alkyne Equivalents in the Reaction of 22 (1 equiv) with Diphenylacetylene 88 in the Presence of 50 mol of Ni(COD)(PMe3)2 Experiments Were Run

in THF-d8 at 40 degC

Run 88 (equiv) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

8990

1 10 320 times 10ndash4 031 times 10ndash4 103 2 20 220 times 10ndash4 018 times 10ndash4 122 3 40 220 times 10ndash4 011 times 10ndash4 200

Following the reaction progress by NMR spectroscopy afforded additional insights Thus mixing the ingredients at room temperature left the phenylene component untouched Instead there was a near instantaneous displacement of COD by diphenylacetylene to produce Ni(PhCequivCPh)(PMe3)2 (92) and free COD in addition to the generation of Ni(PMe3)4

90 The speed with which this complex was formed implied that it might be the active catalyst precursor Consistent with this notion higher reaction rates were observed when the reaction in Scheme 38 was carried out with pure 9291 as the catalyst (50 mol) and 05 equivalent of 88 (Table 33 Run 2) In consonance with Table 32 the lesser concentration of available free alkyne increased the relative amount of 90 formed Conversely (Run 3) using Ni(COD)(PMe3)2 with an extra equivalent of PMe3 decreased the rates of formation of 89 and 90 and increased the ratio of 8990 consistent with ligand inhibition of the activation of 92 and the external ligand effect noted in Table 32 Table 33 Variation of Catalyst in the Reaction of 22 with Diphenylacetylene 88 and its Effect

on Reaction Rate Experiments Were Run in THF-d8 at 40 degC with 1 Equivalent of 22

Run Catalyst 88

(equiv)

Rate of formation of 89 (mol

Lmiddoth)

Rate of formation

of 90 (mol Lmiddoth)

8990

1 Ni(COD)(PMe3)2 10 320 times 10ndash4 031 times 10ndash4 103 2 Ni(PhCequivCPh)(PMe3)2 (92)

(05 equivalent) 05 1270 times 10ndash4 210 times 10ndash4 60

3 Ni(COD)(PMe3)2 (05 equivalent) + PMe3 (10 equiv)

10 088 times 10ndash4 005 times 10ndash4 163

Attention was then shifted to the reaction of monoadduct 89 with 88 as in Scheme 310 (Table 34) Here increasing the amount of alkyne and catalyst favors the formation of 91 consistent with an independent pathway At low concentration of alkyne it appears that 89 reenters the manifold of its generation and proceeds on to 90 Indeed following the change in the ratio of 9190 in Run 1 (Table 34) with time reveals a decrease from 47 to the eventual 22 as 88 is depleted

- 71 -

Table 34 Variation of Catalyst Loading and Alkyne Concentration in the Reaction of 90 with Diphenylacetylene 88 Reactions Were Run in THF-d8 at 40 degC

Run 88 (equiv) Ni(COD)(PMe3)2

(mol) 9190

1 10 50 2 2 30 50 15 3 30 10 25

The information obtained from these experiments allowed a narrowing of mechanistic possibilities For example dinuclear Ni activation only one possibility of which is shown in Scheme 311 was rendered unlikely by the absence of any observable changes in product distribution of the reaction in Scheme 39

Scheme 311 Generic Example of a Dual Mechanism Based on Mono- and Dimetallic Phenylene Activation

An alternative mechanism shown in Scheme 312 was in much better agreement with the results of the various control experiments The first step would be displacement of a phosphine in the initially dominant Ni-containing species 92 by angular [3]phenylene 22 inhibited by added PMe3 From 93 oxidative addition can take place to afford metallacycle 94 Why should bay region insertion be favored Arguably the regioselectivity of this step is controlled by the lesser steric hindrance in the resulting arene fragment or relative stabilization of the polarized Ni-C(α-

PhPh

Ph Ph Ph Ph

PhPh

NiL L

Ni(COD)(PMe3)2

NiNiL L L L

PhPh

2

Ph

Ph

Ph Ph Ph Ph Ph Ph

+

+22

89

90

91 90

- 72 -

biphenylene) bond in 94 by the electron withdrawing nature of the neighboring cyclobutadienoid ring This phenomenon in biphenylene is due to the rehybridization of the four-membered ring carbons to adopt relatively larger p character in the strained linkages hence larger s character (ie electron withdrawing) in the remaining bond and manifests itself most clearly in the relative acidity of the α-hydrogens7a This step is followed by migratory insertion and reductive elimination to produce molecule 96 the mechanistic bifurcation point One branch proceeds through presumably ligand-assisted metal dissociation to generate the relatively unreactive free 89 The second entails Ni migration92 and insertion into the bay region of the remaining four-membered ring (97) before the second cycloaddition occurs generating phenacene 90

Scheme 312 Possible Mechanism for the Alkyne Cycloaddition Reaction of Angular [3]Phenylene 22

The regioselective formation of 97 may again be sterically dictated or may involve anchimeric assistance by the bay-region phenyl group as sketched in Scheme 313 specifically 99

Scheme 313 Anchimeric Assistance on Route to [5]Phenacene 90

Ph Ph

PhPhPhPh

Ph

Ph

Ph PhNi

NiMe3P Ph

Ph

Ni

Me3P Ph

Ph

NiPMe3Me3P

Ligand exchangeOxidativeaddition

Migra toryinser tion

Reductiveelimination

Ph

Ph

Me3P

Ni migra tionOxidative addition

22

92

9394

96 89

9097

Ph Ph

Ni

Me3P

Ni(PMe3

Ph

Ph

minusNi(PMe3)

95

- 73 -

This type of metal coordination to the double bond of a proximal arene ligand is common and two examples are provided based on ruthenium94 and molybdenum95 (Figure 33)

Figure 33 Examples of complexes with phenyl groups coordinating to a nearby metal center Turning to the largely selective conversion of 89 to 91 (Scheme 310) requires the postulate of preferential insertion of the metal at the non-bay region and hence a different Ni species from that in 96 possibly a Ni(PMe3)(alkyne) moiety akin to that in 93 ie 100 (Scheme 314) Bay insertion would lead to metallacycle 101 and ultimately molecule 90 The expected large degree of steric repulsion between the phenyl groups in 101 should disfavor this reaction pathway On the other hand non-bay insertion to produce 102 should be relatively less impeded and would furnish 91 Another option for the generation of 90 from 89 would be reentering the pathway described in Scheme 312 facilitated at low concentrations of alkyne consistent with the data in Table 34

Scheme 314 Proposed Mechanism for the Alkyne Cycloaddition Reaction of 89

Ni

PhMe3P

PhPh

(Me3P)Ni

PhPh(Me3P)Ni

Ph

Ph

93 98

99

Ph Ph Ph Ph

90

+

Ph Ph

Ni

Me3P

97

- 74 -

While the above mechanistic perambulations appear plausible it should be stressed that they are speculative and may be restricted to diphenylacetylene 88 as the substrate Thus both 3-hexyne 103 and 14-dimethoxy-2-butyne 106 added to 22 less selectively than 88 to provide only the bay and non-bay monoadducts 104 and 105 and 107 and 108 respectively (Scheme 315)

Scheme 315 Reaction of Angular [3]Phenylene 22 with Other Alkynes

NiMe3P PMe3

Ph Ph+

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph

Ni(PMe)3

PhPh

Ni(PMe3)

Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

92 89

101

90

102

100

91

Ni

Ph Ph

PMe3

+

R

R

THF-d8 40 oCR

R22

Ni(COD)(PMe3)2

R

R

+

R = Et 104

R = CH2OMe 107

R = Et 103

R = CH2OMe 106 R = Et 105

R = CH2OMe 108

11 45 9 68

- 75 -

In view of these uncertainties recourse was taken to DFT computations delineated in the next section 33 Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene DFT studies were carried out in collaboration with Prof Vincent Gandon of the Universiteacute Paris-Sud 11 The B3LYP 6-31G(d) basis set was used for hydrogen and carbon atoms while LANL2DZ was used for nickel Before attempting to model the more complex alkyne cycloaddition reactions in Schemes 38 and 39 the basic Ni-catalyzed addition of the parent acetylene to biphenylene in the presence of PMe3 was studied (Scheme 316) The free energies

Scheme 316 Computational Modeling of Ni-catalyzed Addition of Acetylene to Biphenylene Free Energies (∆G KcalMol) are Relative to 109 Transition State Energies are Absolute Values

for This Step

NiMe3P PMe3

NiMe3P

NiMe3P

Ni

Ni

PMe3

PMe3

+

+ PMe3+

+ PMe3

+ 2 PMe3

+ 2

(00)

(281)(37)

(140)

(12)

NiMe3P PMe3

NiMe3P

NiNiPMe3Ni

PMe3

PMe3NiMe3P

PMe3

(727) (693) (476) (374) (394) (395)

Ni

Me3P

PMe3Ni

Me3P

Ni

Ni

Me3P

PMe3NiMe3P PMe3

(590) (532)

(157) (125) (150)

Most Accessible TS

+

7

114

110

113109

111 112

Ni

Me3P

(253)

Ni

PMe3

(242)

- 76 -

(∆G) of various possible catalyst structures consisting of an assortment of combinations of nickel PMe3 and acetylene as well as those of several possible transition states and the resulting products were calculated As is evident on inspection of the values in the first part of Scheme 316 a number of species were found to be very close in energy making it difficult to pinpoint a specific structure for the initial insertion step Bis(ethyne) nickel complex 109 was established as the lowest energy nickel species and was thus assigned a relative value of 0 kcalmol The most accessible transition state 110 features the oxidative addition of the Ni(PMe3)(C2H2) fragment 114 (+ 14 kcalmol) in which the alkyne is held exo to biphenylene The corresponding endo structure 111 was found to be just slightly higher in energy by 20 kcalmol as was the bisalkyne transition state 112 It is likely that biphenylene-NiL2 complexes (two of which were calculated at relative energies 242 and 253 kcalmol) lie on the way to these maxima93 Metallacycle 113 the structure ensuing from transition state 110 constituted the lowest energy product uphill from the starting 109 by 125 kcalmol but other alternatives are nearly isoenergetic Clearly however attack by Ni(PMe3)2 or Diels-Alder type cycloadditions are not likely From 113 the species proceeds smoothly by alkyne insertion-reductive elimination to the phenanthrene product a cascade associated with a large exergonic driving force Undaunted by the relatively complicated picture that emerged with biphenylene attention was turned to the original object of scrutiny the cycloaddition reaction between angular [3]phenylene 22 and diphenylacetylene 88 to produce [5]phenacene derivative 90 Modeled in the same manner as described above the metal insertion into the four-membered ring of 22 is shown in Scheme 317 The lowest energy nickel species

- 77 -

was found to be diphenylacetylene complex 92 gratifyingly corresponding to experiment and was set to a reference value of 00 kcalmol One notes again however an array of at least 10 species all of which must be in equilibrium in the initial reaction mixture Notably the Ni-π complexes to 22 are all more than 20 kcalmol higher in energy than 92 providing a computational rationale for the failure to observe such species by NMR The first step in the optimal reaction pathway is the coordination of Ni(PMe3) to the cyclobutadiene ring of 22 which results in formation of η2-like complex 114 Again in gratifying agreement with experiment bay region insertion through transition state 115 to give 116 is favored albeit by a bare 07 kcalmol relative to its non-bay region counterpart 117 Moreover there are at least six other structures that are energetically viable in silico although insertions of Ni(PhCequivCPh)(PMe3) appear less so possibly due to steric hindrance The same observation is made for the products of insertion although 116 emerges as the thermodynamically most stable possibility

Scheme 317 Calculated Structures and Reaction Pathway for the Insertion of Nickel into the Four-Membered Ring of Angular [3]Phenylene 22 Free Energies ∆G are in KcalMol Relative

to 92

The next step was to map out the first alkyne cycloaddition (Scheme 318) Coordination of diphenylacetylene to 116 is endothermic by 139 kcalmol and after migratory insertion produces 119 Interestingly a transition state to regioisomer 95

(328) (352)

NiMe3P PMe3

(364)

NiMe3P

NiMe3P PMe3

NiPMe3

(339)

Ni

PMe3

PMe3

NiMe3PPMe3

NiMe3P

NiPMe3

(16) (04) (108) (117)

NiMe3P PMe3 Ni

Me3PNi

Me3P Ni Ni

PMe3

PMe3

+ [3]+ DPA

+ PMe3+ [3]+ DPA

+ PMe3+ [3]

+ 2 PMe3+ [3]

+ [3]+ 2 DPA

Ph Ph Ph PhPh Ph

Ph

PhPh Ph

Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

Ph

(45) (96)

(00)

(89) (134)

Most AccessibleTS

NiPMe3

+ PMe3+ [3]+ 2 DPA

(314)

Ni

+ 2 PMe3+ [3]+ DPA

Ph Ph

(294)

1i(PMe3)

Ni

PhPh

(212)

(218)

(345)

Ni

PhPh(297)

Ni

Me3P

Ni

Ph

Ph

(350)

Ni

PMe3

(303)

Ni

Ni

(43) (41)

Ph

Ph

PhPh

Ni

PMe3

NiMe3P

(-10) (-22)

(Me3P)Ni

Ni(PMe3)

Ph Ph

Ph Ph(225) (256)

+ PMe3+ 2 DPA

+ 2 PMe3+ DPA

+ PMe3+ DPA

+ PMe3+ DPA

92114

115

116118

117

- 78 -

written (arbitrarily) in Scheme 312 could not be located

Scheme 318 Calculated Reaction Pathway for the Coordination of Diphenylacetylene Migratory Insertion and Nickel Migration Free Energies ∆G are in KcalMol Transition

State Energies are Absolute Values for This Step

Subsequent reductive elimination from 119 occurs to produce nickel coordinated arene species 120 From it free 89 is presumably readily obtained by demetallation in the presence of external ligands shown only for the formation of 92 in a very favorable process (ndash487 kcalmol) This step is sufficiently exothermic to tolerate the emergence of all the calculated species in the starting line up of Scheme 317 and is presumably the source of 89 in Scheme 39 However if not removed the Ni moiety in 120 can migrate along a shallow manifold across the π frame choosing the phenyl functionalized edge of the molecule (cf Section 24) until the remaining four-membered ring is reached (121) At this point two separate reaction pathways become possible Nickel insertion on the side proximal or opposite of the phenyl groups generates 99 or 122 respectively The barriers for these transformations are similar but show a noticeable preference for the formation of 99 In addition there is a significant energy difference (175 kcalmol) between 122 and 99 in favor of the bay region metallacycle The reason is the coordination of the neighboring phenyl ring to the nickel which serves to stabilize 103 vindicating the proposal made in Scheme 313 and providing a rationale for the exclusive observation of 90 in Scheme 39 From 99 as shown in Scheme 319 coordination of diphenylacetylene (123) is followed by migratory insertion to produce 124 Insertion occurs away from the bay region so as to reduce steric repulsion due to the phenyl group in the phenanthrene part of the molecule Finally reductive elimination ensues providing phenacene-Ni

NiMe3P

NiPMe3

Ni(PMe3)

Ni Ph

PhMe3P

Ph

Ph

PhPh

(117)

126

(44)

102

( 80)

01

( 412)

Ph PhNi(PMe3)

( 389)

Ph Ph

45

Ni(PMe3)

( 408)

Ph Ph

13

PhNi

PMe3

Ph Ph

Ni(PMe)3

133

( 488)

117

( 663)

NiMe3P

( 22)

PhPh+

95

116

119

120121 122

99

NiMe3P Ph

Ph

Ph Ph

( 899)

NiMe3P PMe3

Ph Ph+

92 89

- 79 -

complex 125 At this point the stage is set for exergonic nickel dissociation to 90 and catalyst turnover

Scheme 319 Calculated Reaction Pathway for the Second Diphenylacetylene Insertion All Relative Energies (in red) are in KcalMol Transition State Energies are Absolute Values for

This Step

In conclusion of this discussion the consideration of the combined computational and experimental data affords a mechanistic picture of the cycloaddition reaction of diphenylacetylene 88 to angular [3]phenylene 22 (Scheme 39) the essential features of which are summarized in Scheme 320 The crucial point is a mechanistic bifurcation in which 89 is either released early and (nearly) irreversibly from the metal or the metal stays attached so as to effect a second cycloaddition to give 90 This mechanism implies that 91 is formed by a different mechanism involving a different Ni species

PhNi

PMe3

( 663)

+

PhNi

Ph PMe3Ph

Ph

( 403) ( 403)

PhNi

PhPMe3

PhPh

( 519)

94

93

( 696)

PhNi

PhPMe3

Ph

Ph

96

( 817)

Ph Ph Ph Ph

(MeP)3Ni

99

123

124

125

PhPh

Ph PhPh Ph

+Ni

Me3P PMe3

( 1101)

PMe3

90

- 80 -

Scheme 320 Essential Mechanistic Features of the Formation of 89 and 90 in the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene 88 and Angular [3]Phenylene 22

Consequently the reaction of 89 with diphenylacetylene to give 91 (Scheme 310) was also modeled by DFT Of the various options probed that shown in Scheme 321 proved to be most plausible The reaction pathway entails coordination of alkyne-Ni phosphine 126 to molecule 89 which generates complex 127 in a process that is found to require 228 kcalmol of energy Insertion into the non-bay region of the four-membered ring has a barrier of 16 kcalmol and provides metallacycle 128 After the second cycloaddition event benzo[c]chrysene 91 is formed Interestingly the transition state leading to insertion of nickel complex 126 into the bay region of 89 structure 129 was found to be so high in energy relative to 128 that it could not be modeled This is not unexpected as the phenyl group closest to bay region effectively blocks the approach of any catalyst species This result is consistent with the high ratio of 91 to 90 formed in Scheme 310 and the increase in this ratio at higher initial diphenylacetylene concentration Why is any 90 formed and why does its relative proportion increase at lower diphenylacetylene concentration A possible explanation is that under these conditions the concentrations of 92 and 126 are sufficiently small that 89 reenters Scheme 318 competitively

PhPhNi(PMe3)

PhPh

Ni(PMe3)

Ph Ph Ph Ph

PhPh

Ni(PMe3)

Ni

PMe3

Ph Ph

NiPhMe3P

22 116

88

120

121

99

88

90

PhPh

89

Externalligand

assistedNi migration

Regioselectiveinsertion

Regioselectiveinsertion

Mechanistic bifurcation

- 81 -

Scheme 321 Calculated Reaction Mechanism for the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene and Compound 90 Relative Energies are in KcalMol Transition

State Energies are Absolute Values for This Step

Consideration of Scheme 320 suggests that phenacene formation might be maximized by keeping the concentration of external ligand low during the course of the reaction Experiments aimed at verifying this conjecture are the subject of Section 34 in addition to presenting extensions of the methodology to higher angular phenylenes

34 Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions The experimental and computational studies described in Section 33 suggested that the decisive factor for selective formation of phenacene 90 is suppression of metal dissociation in Ni complex 120 This scenario would be achievable by maintaining a low concentration of diphenylacetylene 88 (vide supra) Previously the alkyne cycloaddition was performed with all reagents mixed together at the start of the reaction invariably resulting in a high initial concentration of 88 To obviate this occurrence an alternative procedure was devised In this new arrangement the required stoichiometric amount (in this case two equivalents) of alkyne 88 was slowly introduced to a mixture of 22 and Ni(COD)(PMe3)2 by means of a syringe pump (Scheme 322) The results of varying addition and reaction times are shown in Table 35

Scheme 322 Modified Reaction Alkyne Cycloaddition Reaction Between 22 and 89

Ph Ph

Ni(PMe3)

Ph Ph Ph Ph

Ni(PMe)3

160

Ph

Ph

PhPh

(309)(317)

Ph Ph

Ph

Ph

NiMe3P

Ph Ph

(minus573)

89

126

127 128 91

Ph Ph Ph

Ni

Ph

PMe3

129

NiMe3P PMe3

Ph Ph

(00)

92

(89)

+

- 82 -

Table 35 Variation of Alkyne Addition and Total Reaction Time in the Scheme 322

Run Addition time of 88 (h)

Total run time (h)

Yield of 89 ()

Yield of 90 ()

1 4 16 44 55 2 6 22 23 77 3 5 41 24 76 4 12 69 17 73 5 13 19 13 87

The most immediate result of the modified protocol was the quantitative conversion of 22 to cycloadduct products 89 and 90 Turning to the product ratios a four hour addition time led to a slight preference for 90 Increasing the time to six hours dramatically influenced the product distribution and 90 was isolated in 77 yield as compared to the 23 for 89 In the optimal Run 5 87 of 90 was generated vs 13 of 90 Extending the run time after the addition of diphenylacetylene had a negligible effect The successful enhancement in phenacene selectivity under these conditions makes the reaction a practical method for synthesizing compound 90 and also provides further experimental support for the proposed mechanism shown in Scheme 320 Having reached a reasonable level of understanding both the mechanistic and experimental aspects of the reaction of angular [3]phenylene 22 with diphenylacetylene attention was shifted to a larger and more challenging substrate angular [4]phenylene (17) This system could conceivably afford 17 possible adducts one of which is hexaphenyl[7]phenacene 130 (Scheme 324) Would the mechanistic features of this triple cycloaddition be sufficiently similar to those of 22 to apply the same principles and enable selectivity toward 130

+THF reflux

Ph Ph Ph PhPh

Ph

+

Ph

Ph

2 equivslow addition

22 89 90

Ni(COD)(PMe3)2(10 mol)

88

- 83 -

Scheme 324 The Possible Cycloadducts of Diphenylacetylene 88 to Angular [4]Phenylene 17

+ Ph Ph

Ph Ph

Ph Ph

PhPh

Ph

Ph

Ph Ph Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph PhPhPh

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph Ph PhPhPh

Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

PhPh

Ph Ph Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

88

17

130

- 84 -

Encouragingly a first experiment under conditions comparable to those in Scheme 39 for 22 namely reaction of angular [4]phenylene (17) with one equivalent of diphenylacetylene in the absence of high dilution indeed engendered only five products two of which monoadducts 131 and 132 were minor (Scheme 325) The major components of the mixture were molecules 133 134 and most significantly 130

Scheme 325 Nickel Catalyzed Alkyne Cycloaddition with 17 and 88

Monitoring the course of the transformation by NMR revealed that 133 is the sole initial new compound followed by gradual appearance of the others Extrapolation of the insights gained with 22 it is tempting to propose that migration of the metal in Ni-complexed 133 is the source of 134 and ultimately 130 If true [7]phenacene 130 might be made selectively by application of the slow alkyne addition procedure of Scheme 322 Scheme 326 illustrates the proposed scenario It starts with doubly regioselective Ni insertion into the central ring and from the bay region to give 135 On the basis of the electron withdrawing effect of the adjacent cyclobutadienoid rings invoked earlier in the selective formation of 94 (Scheme 312) this metallacycle would seem the most stable Again this conjecture is tentative as the appearance of the minor products 131 and 132 would indicate Metallacycle 135 would then give rise to 136 (and hence 133 by demetallation) which would connect by Ni migration and insertion to 137 Alkyne cycloaddition would result in 138 (and hence 134 by demetallation) which would connect by Ni migration and insertion to 139 Alkyne cycloaddition would result in 140 (and hence 130 by demetallation)

+

Ph Ph

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2(10 mol)THF 75 degC

5 6

33

27 28

132131

133

134 130

17

88

- 85 -

Scheme 326 Proposed Reaction Pathway to Phenacene 130 from Angular [4]Phenylene 17 via Ni Migration

The successful preparation of [5]- and [7]phenacene from angular [3]- and [4]phenylene respectively prompted an attempt to prepare [13]phenacene derivative 141 from helical [7]phenylene 14210 (Scheme 327) This transformation would make use of six alkyne cycloadditions to produce the target molecule In addition to the possibility of preparing the largest known phenacene this reaction would also serve as an interesting test of the alkyne cycloaddition methodology

Scheme 327 Proposed Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Using the slow addition procedure phenylene 142 was subjected to the alkyne cycloaddition conditions (Scheme 329) All of the starting material was consumed but the reaction ultimately resulted in an intractable mixture of products Unfortunately no conclusive structural identifications for any of the ensuing compounds could be made from the 1H-NMR data A large assortment of peaks was seen in the region of 6ndash7

Ni

PMe3

Ph

NiPMe3

Ph Ph Ph PhNi

PMe3

Ph Ph Ph

NiMe3P

135

137

Ph Ph

Ph Ph

Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2

13617

88Ni

PMe3

Ph Ph88

138 139

Ph Ph88

Ni

PMe3

140

- 86 -

ppm suggesting the presence of phenylene subunits More informative was the absence of the highly diagnostic phenacene bay region proton signals that are typically found at ~8ndash9 ppm84 signaling the absence of any phenacene product(s)

Scheme 328 Attempted Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Nevertheless mass spectral analysis clearly indicated that multiple alkyne cycloaddition had occurred (Table 36) Peaks were observed at mz = 700 1056 1234 and 1412 which correspond to the presence of single triple quadruple and quintuple alkyne adducts in the reaction mixture No signal corresponding to the mass of 141 (mz = 1590) was detected however Although the structures of the resulting products remain to be established by follow-up experiments on a larger scale the fact that five cycloadditions occurred is encouraging in the basic scientific quest for large novel polycyclic aromatic hydrocarbons

Table 36 Mass Spectral Data (FAB) of the Product Mixture of the Cycloaddition Reaction of Phenylene 142 to Diphenylacetylene 88

mz Percentage Cycloaddition count 700 13 1

1056 11 3 1234 8 4 1412 7 5

Our disappointment in the apparent failure to generate 141 in this reaction may be the result of overambitious expectations on our part Thus we assumed in analogy to the reactivity of angular systems 17 and 22 that bay region cycloaddition to one of the inner cyclobutadiene rings would be preferred ideally producing an initial structure such as 143 (Figure 38) The corresponding non-bay adduct is illustrated by 144 It is evident on comparison that such bay region reactivity would lead to constructs devoid of the helical strain present in the starting material96 as well as non-bay structures like 144 The subsequent course of the reaction however may be marred by relatively non-selective cycloadditions as already indicated for 17 (Scheme 325) Therefore it will be prudent for future investigators to return to the latter optimize its outcome and then proceed along the series in the quest for large phenacene (or other) structures

- 87 -

Figure 38 Proposed representative initial bay (143) and non-bay (144) alkyne cycloaddition products of the reaction of [7]heliphene 141 with diphenylacetylene 88

35 Summary and Outlook The first alkyne cycloaddition studies were carried with angular phenylene systems Angular [3]phenylene 22 was successfully used as a precursor to a novel phenyl substituted [5]phenacene derivative 90 Similarly hexaphenyl [7]phenacene 131 was prepared from angular [4]phenylene 17 Extensive experiment and computational mechanistic studies suggested that the optimal conditions for preparing phenacene 90 from phenylene 22 were the maintenance of a low concentration of alkyne in the reaction mixture Future work will focus on applying these conditions to the synthesis of [7]phenacene 130 from angular [4]phenylene 17 An attempt to prepare a [13]phenacene 142 from helical [7]phenylene 141 proved unsuccessful for reasons that are not well understood Nevertheless cycloaddition was found to have occurred up to five times This observation is promising with respect to the further application of the methodology described in this chapter The development of an alkyne cycloaddition-based approach to synthesizing phenacenes should greatly facilitate the study of this emerging class of molecules Future work will focus on expanding the substrate scope of the reaction by examining various functionalized alkynes the application of metal systems that may allow the isolation of crucial intermediates and the expansion of the substrate scope to the higher angular phenylenes as well as other topologies

- 88 -

Chapter Four Experimental and Computational Details

41 General Considerations

All glassware was oven-dried (180 degC) prior to use Reagents were used as received from suppliers unless otherwise noted Flash chromatography97 was performed with Merck 60 230ndash400 mesh silica gel MP EcoChrom neutral alumina was deactivated to activity III by adding 6 water by mass followed by thorough mixing98 Air sensitive compounds were handled under argon with standard Schlenk techniques andor in a nitrogen atmosphere glovebox (Vacuum Atmospheres Model Nexus) Irradiation in CpCo(CO)2 reactions was carried out with a 120V 300W slide projection lamp (ELH) positioned 5 cm away from the reaction vessel UV-irradiation experiments were conducted in a Rayonet Photochemical Reactor (RPR-100) Bis(trimethylsilyl)- and trimethylsilylacetylene (BTMSA and TMSA respectively) were distilled from molecular sieves (4 Aring) prior to use TMSA was degassed with four freeze-pump-thaw cycles while BTMSA was degassed using a 20 min Ar purge BTMSA was recycled using from all CpCo(CO)2 reactions using the following procedure The BTMSA was first removed by vacuum transfer Residual cobalt was removed by dissolving the BTMSA in pentane and washing the pentaneBMTSA layer mixture with a dilute solution of ceric ammonium nitrate in acetonitrile in a separatory funnel The denser acetonitrile layer was drained off and the pentane removed by distillation at atmospheric pressure Vacuum distillation of the BTMSA from molecular sieves afforded a product pure enough for future use All solvents were distilled under N2

immediately before use from the appropriate drying agent triethylamine (KOH pellets) benzene toluene CH2Cl2 (CaH2) THF and diethylether (Nabenzophenone) acetonitrile (CaH2) Deoxygenation of solvents andor reaction mixtures was carried out by a 20 min Ar purge or four free-pump-thaw cycles for volatile (bp lt 70 degC) mixturessolvents Ni(COD)2 (Strem) was stored and manipulated in the glovebox 1H and proton decoupled 13C spectra were measured at 500 MHz and 125 MHz respectively unless otherwise noted 1H-NMR chemical shifts are reported in ppm units relative to the signal of the solvent (CDCl3ndash726 ppm C6D6ndash715 ppm acetone-d6ndash205 ppm CD2Cl2ndash532 ppm toluene-d8ndash209 ppm (for ndashCD3) Except where noted two-dimensional NMR experiments were run under temperature control at 300 K All spectral data were processed with Bruker TopSpin 21 software Melting points were recorded in open capillary tubes using a Thomas Hoover Unimelt apparatus and are uncorrected Melting points for air-sensitive samples were carried out in flame sealed capillary tubes Mass spectral measurements (Electron Impact Fast Atom Bombardment) and elemental analyses were supplied by the Micro-Mass Facility of the College of Chemistry University of California Berkeley UV-Vis spectra were recorded on Agilent 8453 and Perkin-Elmer Lambda 35 spectrophotometers with absorbance data reported in nm (log ε) IR spectra were taken on a Perkin-Elmer Spectrum 100 Where appropriate analysis by GCMS was done with an Agilent 5973 instrument

42 Experimental Section for Chapter Two

- 89 -

2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19

A mixture of KF2 H2O (700 mg 744 mmol) [18]crown-6 (100 mg 0378 mmol) and 2378-tetrakis[(triisopropylsilyl)ethynyl] linear [3]phenylene26 (370 mg 0800 mmol) in degassed THF (25 mL) was stirred for 70 min at RT The orange solution was filtered through a plug of silica gel (1 x 3 cm) eluting with degassed THF (15 mL) providing a light-yellow solution After adding CpCo(CO)2 (260 mg 144 mmol) the solution was protected from light and added via syringe pump over a period of 6 h to a boiling mixture of degassed BTMSA (50 mL) and THF (200 mL) which was irradiated with a projector lamp under nitrogen After additional heating and irradiation for 15 h the solvents were removed by vacuum transfer and the black residue filtered through a plug of neutral alumina activity III eluting with hexaneTHF (501) The volatiles were removed and the dark brown residue crystallized from degassed acetone yielding 19 (330 mg 65 ) as black needles mp 192ndash195 degC (decomp) 1H-NMR (400 MHz C6D6) δ = 794 (s 2 H) 744 (s 2 H) 690 (s 2 H) 441 (s 5 H) 035 (s 18 H) 031 (s 18 H) ppm 13C-NMR (100 MHz C6D6) δ = 1494 1484 1433 1394 1360 1256 1155 802 781 739

269 261 ppm IR (neat) ν~ = 2951 2898 1259 1248 1073 830 799 752 cmndash1 UV-VIS (ethanol) λmax (log ε) = 288 (486) 299 (500) 352 (445) 410 (439) 438 (449) end absorption to 550 nm MS (70 eV) mz () 638 (9) [M+] 514 (100) 499 (3) 387 (2) 73 (24) HRMS (FAB) calcd for C35H47CoSi4 6382087 found 6382095 Elemental analysis calcd for C35H47CoSi4 C 6578 H 741 found 6582 721

Crystallographic information for 19 (H atoms omitted)

Table 41 Crystal Data and Structure Refinement For 19

Empirical formula C35H47CoSi4 Formula weight 63902 cryst size (mm) 025 x 020 x 005 cryst syst Triclinic refl used for unit cell determination 6958

2 θ range (deg) 245ndash2900

a (Aring) 9497(3) b (Aring) 12321(4) c (Aring) 16469(5) α (deg) 74058(5)

β (deg) 82154(5)

Me3Si

Me3Si

CoSiMe3

SiMe3

- 90 -

γ (deg) 72276(5)

V (Aring3) 17620(10) space group Pndash1 Z 2

Dcalc gcm3 1762

F000 680 micro cmndash1 645 temp ordmC ndash173

Tmax Tmin 0858 0972 no of total rflns 24355

no of unique rflns 6958

no of obsd rflns 9209

no of variables 361

Reflection to Parameter Ratio 255

R 00503

Rw 01426

Rall 00734

GOF 1006

Max Peak in Final Diff Map (endash Aring3) 0867

Min Peak in Final Diff Map (endash Aring3) ndash0755

- 91 -

Figure 41 ORTEP representation of 19

- 92 -

Table 42 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 19 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y Z U (eq)

Co1 073881(4) ndash000927(3) 060643(2) 002551(10) Si1 077416(8) ndash019090(6) 094343(4) 002594(16) Si2 113437(8) ndash016706(7) 082404(5) 003023(17) Si3 040491(7) 062139(6) 020406(4) 002291(15) Si4 005088(7) 056545(6) 030946(4) 002144(14) C1 06709(3) ndash00385(2) 079440(16) 00239(5) C2 08019(3) ndash00967(2) 083428(16) 00241(5) C3 09418(3) ndash00743(2) 079331(16) 00233(5) C4 09428(3) 00098(2) 071779(15) 00225(5) C5 08094(2) 00691(2) 067735(15) 00207(4) C6 07282(2) 01574(2) 060605(15) 00207(4) C7 07303(2) 02531(2) 053306(15) 00211(4) C8 05938(2) 03094(2) 050431(15) 00205(4) C9 05057(2) 03981(2) 043438(15) 00207(4) C10 05076(2) 04760(2) 035695(15) 00227(5) C11 03734(2) 05293(2) 031459(15) 00215(4) C12 02408(2) 05011(2) 035315(15) 00205(4) C13 02432(2) 04196(2) 043269(15) 00215(4) C14 03751(2) 03698(2) 047171(15) 00208(4) C15 04564(2) 02794(2) 054277(15) 00211(4) C16 04487(2) 01908(2) 061161(15) 00224(5) C17 05916(3) 01278(2) 064393(15) 00221(5) C18 06734(2) 00417(2) 071473(15) 00215(5) C19 05795(3) ndash02027(3) 09572(2) 00446(8) C20 08892(4) ndash03470(2) 09642(2) 00387(7) C21 07986(4) ndash01192(3) 10246(2) 00419(7) C22 11685(4) ndash03077(3) 07914(3) 00584(10) C23 11726(3) ndash01969(3) 09372(2) 00426(7) C24 12742(4) ndash00933(4) 07624(3) 00640(12) C25 05777(3) 06657(3) 020261(18) 00348(6) C26 02610(3) 07629(2) 016564(17) 00292(5) C27 04355(3) 05272(3) 012760(18) 00347(6) C28 ndash00272(3) 07195(2) 03194(2) 00360(6) C29 00487(3) 05542(3) 019882(18) 00344(6) C30 ndash00786(3) 04816(2) 037272(18) 00278(5) C31 06994(4) ndash00612(3) 05062(2) 00432(7) C32 08520(4) ndash00698(3) 05033(2) 00407(7) C33 09085(3) ndash01473(3) 05788(2) 00407(7) C34 07922(4) ndash01879(3) 06277(2) 00424(7) C35 06647(4) ndash01370(3) 05833(2) 00403(7)

- 93 -

Table 43 Bond Lengths (Aring) for Complex 19

Atom1 Atom2 Length

Co1 C5 1993(3) Co1 C6 2023(3) Co1 C17 2022(2) Co1 C18 2009(3) Co1 C31 2042(4) Co1 C32 2075(3) Co1 C33 2062(3) Co1 C34 2042(4) Co1 C35 2048(4) Si1 C2 1886(2) Si1 C19 1877(3) Si1 C20 1863(2) Si1 C21 1865(4) Si2 C3 1889(3) Si2 C22 1876(5) Si2 C23 1862(3) Si2 C24 1865(4) Si3 C11 1901(2) Si3 C25 1876(4) Si3 C26 1867(2) Si3 C27 1875(4) Si4 C12 1889(2) Si4 C28 1860(3) Si4 C29 1868(3) Si4 C30 1870(3) C1 C2 1384(4) C1 C18 1411(3) C2 C3 1474(4) C3 C4 1384(3) C4 C5 1408(3) C5 C6 1480(3) C5 C18 1448(3) C6 C7 1437(3) C6 C17 1465(4) C7 C8 1351(3) C8 C9 1495(3) C8 C15 1476(3) C9 C10 1371(3) C9 C14 1405(3) C10 C11 1423(3) C11 C12 1427(3) C12 C13 1413(3) C13 C14 1376(3)

- 94 -

C14 C15 1488(3) C15 C16 1352(3) C16 C17 1434(3) C17 C18 1468(3) C31 C32 1416(6) C31 C35 1419(4) C32 C33 1401(4) C33 C34 1411(5) C34 C35 1386(5)

Table 44 Bond Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 4325(9) C5 Co1 C17 621(1) C5 Co1 C18 4240(9) C5 Co1 C31 1629(1) C5 Co1 C32 1271(1) C5 Co1 C33 1102(1) C5 Co1 C34 1223(1) C5 Co1 C35 1556(1) C6 Co1 C17 425(1) C6 Co1 C18 6191(9) C6 Co1 C31 1253(1) C6 Co1 C32 1164(1) C6 Co1 C33 1329(1) C6 Co1 C34 1651(1) C6 Co1 C35 1550(1) C17 Co1 C18 427(1) C17 Co1 C31 1204(1) C17 Co1 C32 1451(1) C17 Co1 C33 1722(1) C17 Co1 C34 1419(1) C17 Co1 C35 1194(1) C18 Co1 C31 1517(1) C18 Co1 C32 1676(1) C18 Co1 C33 1312(1) C18 Co1 C34 1112(1) C18 Co1 C35 1198(1) C31 Co1 C32 402(1) C31 Co1 C33 673(1) C31 Co1 C34 675(1) C31 Co1 C35 406(1) C32 Co1 C33 396(1) C32 Co1 C34 672(1)

- 95 -

C32 Co1 C35 675(1) C33 Co1 C34 402(1) C33 Co1 C35 671(1) C34 Co1 C35 396(1) C2 Si1 C19 1085(1) C2 Si1 C20 1157(1) C2 Si1 C21 1096(1) C19 Si1 C20 1035(1) C19 Si1 C21 1081(2) C20 Si1 C21 1110(2) C3 Si2 C22 1071(2) C3 Si2 C23 1162(1) C3 Si2 C24 1100(2) C22 Si2 C23 1110(2) C22 Si2 C24 1067(2) C23 Si2 C24 1056(2) C11 Si3 C25 1077(1) C11 Si3 C26 1177(1) C11 Si3 C27 1083(1) C25 Si3 C26 1045(1) C25 Si3 C27 1086(1) C26 Si3 C27 1097(1) C12 Si4 C28 1099(1) C12 Si4 C29 1132(1) C12 Si4 C30 1101(1) C28 Si4 C29 1119(1) C28 Si4 C30 1066(1) C29 Si4 C30 1048(1) C2 C1 C18 1193(2) Si1 C2 C1 1130(2) Si1 C2 C3 1270(2) C1 C2 C3 1198(2) Si2 C3 C2 1260(2) Si2 C3 C4 1124(2) C2 C3 C4 1208(2) C3 C4 C5 1192(2) Co1 C5 C4 1188(2) Co1 C5 C6 695(1) Co1 C5 C18 694(1) C4 C5 C6 1498(2) C4 C5 C18 1200(2) C6 C5 C18 902(2) Co1 C6 C5 673(1) Co1 C6 C7 1267(2) Co1 C6 C17 687(1) C5 C6 C7 1474(2)

- 96 -

C5 C6 C17 893(2) C7 C6 C17 1227(2) C6 C7 C8 1121(2) C7 C8 C9 1461(2) C7 C8 C15 1251(2) C9 C8 C15 885(2) C8 C9 C10 1471(2) C8 C9 C14 912(2) C10 C9 C14 1214(2) C9 C10 C11 1186(2) Si3 C11 C10 1116(2) Si3 C11 C12 1283(2) C10 C11 C12 1197(2) Si4 C12 C11 1264(2) Si4 C12 C13 1135(2) C11 C12 C13 1201(2) C12 C13 C14 1185(2) C9 C14 C13 1216(2) C9 C14 C15 915(2) C13 C14 C15 1465(2) C8 C15 C14 888(2) C8 C15 C16 1250(2) C14 C15 C16 1458(2) C15 C16 C17 1118(2) Co1 C17 C6 688(1) Co1 C17 C16 1265(2) Co1 C17 C18 682(1) C6 C17 C16 1233(2) C6 C17 C18 900(2) C16 C17 C18 1460(2) Co1 C18 C1 1229(2) Co1 C18 C5 682(1) Co1 C18 C17 691(1) C1 C18 C5 1206(2) C1 C18 C17 1487(2) C5 C18 C17 905(2) Co1 C31 C32 712(2) Co1 C31 C35 699(2) C32 C31 C35 1077(3) Co1 C32 C31 686(2) Co1 C32 C33 697(2) C31 C32 C33 1076(3) Co1 C33 C32 707(2) Co1 C33 C34 691(2) C32 C33 C34 1081(3) Co1 C34 C33 707(2)

- 97 -

Co1 C34 C35 704(2) C33 C34 C35 1086(3) Co1 C35 C31 695(2) Co1 C35 C34 700(2) C31 C35 C34 1079(3)

Table 44 Torsion Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 ndash1479(3) C6 Co1 C5 C18 983(2) C17 Co1 C5 C4 1630(2) C17 Co1 C5 C6 ndash491(1) C17 Co1 C5 C18 492(1) C18 Co1 C5 C4 1138(2) C18 Co1 C5 C6 ndash983(2) C31 Co1 C5 C4 ndash941(4) C31 Co1 C5 C6 538(4) C31 Co1 C5 C18 1522(4) C32 Co1 C5 C4 ndash573(2) C32 Co1 C5 C6 906(2) C32 Co1 C5 C18 ndash1710(2) C33 Co1 C5 C4 ndash160(2) C33 Co1 C5 C6 1319(1) C33 Co1 C5 C18 ndash1297(2) C34 Co1 C5 C4 271(2) C34 Co1 C5 C6 1750(2) C34 Co1 C5 C18 ndash866(2) C35 Co1 C5 C4 629(4) C35 Co1 C5 C6 ndash1492(3) C35 Co1 C5 C18 ndash509(3) C5 Co1 C6 C7 1458(3) C5 Co1 C6 C17 ndash986(2) C17 Co1 C6 C5 986(2) C17 Co1 C6 C7 ndash1156(3) C18 Co1 C6 C5 491(1) C18 Co1 C6 C7 ndash1650(2) C18 Co1 C6 C17 ndash494(1) C31 Co1 C6 C5 ndash1631(2) C31 Co1 C6 C7 ndash173(3) C31 Co1 C6 C17 983(2) C32 Co1 C6 C5 ndash1170(2) C32 Co1 C6 C7 288(2) C32 Co1 C6 C17 1444(2) C33 Co1 C6 C5 ndash725(2)

- 98 -

C33 Co1 C6 C7 734(3) C33 Co1 C6 C17 ndash1710(2) C34 Co1 C6 C5 ndash166(5) C34 Co1 C6 C7 1293(5) C34 Co1 C6 C17 ndash1151(5) C35 Co1 C6 C5 1499(3) C35 Co1 C6 C7 ndash642(4) C35 Co1 C6 C17 514(3) C5 Co1 C17 C6 501(1) C5 Co1 C17 C16 1666(3) C5 Co1 C17 C18 ndash489(1) C6 Co1 C17 C16 1165(3) C6 Co1 C17 C18 ndash989(2) C18 Co1 C17 C6 989(2) C18 Co1 C17 C16 ndash1446(3) C31 Co1 C17 C6 ndash1106(2) C31 Co1 C17 C16 59(3) C31 Co1 C17 C18 1505(2) C32 Co1 C17 C6 ndash656(3) C32 Co1 C17 C16 510(3) C32 Co1 C17 C18 ndash1645(2) C33 Co1 C17 C6 571(9) C33 Co1 C17 C16 1736(8) C33 Co1 C17 C18 ndash418(9) C34 Co1 C17 C6 1578(2) C34 Co1 C17 C16 ndash857(3) C34 Co1 C17 C18 589(2) C35 Co1 C17 C6 ndash1578(2) C35 Co1 C17 C16 ndash413(3) C35 Co1 C17 C18 1033(2) C5 Co1 C18 C1 ndash1133(3) C5 Co1 C18 C17 993(2) C6 Co1 C18 C1 ndash1635(2) C6 Co1 C18 C5 ndash502(1) C6 Co1 C18 C17 491(1) C17 Co1 C18 C1 1474(3) C17 Co1 C18 C5 ndash993(2) C31 Co1 C18 C1 836(3) C31 Co1 C18 C5 ndash1632(2) C31 Co1 C18 C17 ndash638(3) C32 Co1 C18 C1 ndash779(6) C32 Co1 C18 C5 353(6) C32 Co1 C18 C17 1346(5) C33 Co1 C18 C1 ndash395(3) C33 Co1 C18 C5 737(2) C33 Co1 C18 C17 1731(2)

- 99 -

C34 Co1 C18 C1 20(2) C34 Co1 C18 C5 1152(2) C34 Co1 C18 C17 ndash1455(2) C35 Co1 C18 C1 451(3) C35 Co1 C18 C5 1583(2) C35 Co1 C18 C17 ndash1023(2) C5 Co1 C31 C32 478(5) C5 Co1 C31 C35 1656(4) C6 Co1 C31 C32 904(2) C6 Co1 C31 C35 ndash1517(2) C17 Co1 C31 C32 1412(2) C17 Co1 C31 C35 ndash1010(2) C18 Co1 C31 C32 ndash1739(2) C18 Co1 C31 C35 ndash561(3) C32 Co1 C31 C35 1179(3) C33 Co1 C31 C32 ndash370(2) C33 Co1 C31 C35 808(2) C34 Co1 C31 C32 ndash808(2) C34 Co1 C31 C35 371(2) C35 Co1 C31 C32 ndash1179(3) C5 Co1 C32 C31 ndash1642(2) C5 Co1 C32 C33 764(2) C6 Co1 C32 C31 ndash1143(2) C6 Co1 C32 C33 1263(2) C17 Co1 C32 C31 ndash710(3) C17 Co1 C32 C33 1697(2) C18 Co1 C32 C31 1666(5) C18 Co1 C32 C33 472(6) C31 Co1 C32 C33 ndash1194(3) C33 Co1 C32 C31 1194(3) C34 Co1 C32 C31 816(2) C34 Co1 C32 C33 ndash377(2) C35 Co1 C32 C31 385(2) C35 Co1 C32 C33 ndash808(2) C5 Co1 C33 C32 ndash1243(2) C5 Co1 C33 C34 1166(2) C6 Co1 C33 C32 ndash802(2) C6 Co1 C33 C34 1607(2) C17 Co1 C33 C32 ndash1309(8) C17 Co1 C33 C34 1100(9) C18 Co1 C33 C32 ndash1679(2) C18 Co1 C33 C34 730(2) C31 Co1 C33 C32 376(2) C31 Co1 C33 C34 ndash815(2) C32 Co1 C33 C34 ndash1191(3) C34 Co1 C33 C32 1191(3)

- 100 -

C35 Co1 C33 C32 818(2) C35 Co1 C33 C34 ndash373(2) C5 Co1 C34 C33 ndash833(2) C5 Co1 C34 C35 1577(2) C6 Co1 C34 C33 ndash700(5) C6 Co1 C34 C35 1711(4) C17 Co1 C34 C33 ndash1681(2) C17 Co1 C34 C35 730(3) C18 Co1 C34 C33 ndash1295(2) C18 Co1 C34 C35 1115(2) C31 Co1 C34 C33 809(2) C31 Co1 C34 C35 ndash380(2) C32 Co1 C34 C33 372(2) C32 Co1 C34 C35 ndash818(2) C33 Co1 C34 C35 ndash1189(3) C35 Co1 C34 C33 1189(3) C5 Co1 C35 C31 ndash1699(3) C5 Co1 C35 C34 ndash508(4) C6 Co1 C35 C31 663(4) C6 Co1 C35 C34 ndash1746(2) C17 Co1 C35 C31 1036(2) C17 Co1 C35 C34 ndash1373(2) C18 Co1 C35 C31 1531(2) C18 Co1 C35 C34 ndash878(2) C31 Co1 C35 C34 1191(3) C32 Co1 C35 C31 ndash382(2) C32 Co1 C35 C34 809(2) C33 Co1 C35 C31 ndash812(2) C33 Co1 C35 C34 378(2) C34 Co1 C35 C31 ndash1191(3) C19 Si1 C2 C1 118(2) C19 Si1 C2 C3 ndash1731(2) C20 Si1 C2 C1 1275(2) C20 Si1 C2 C3 ndash574(3) C21 Si1 C2 C1 ndash1061(2) C21 Si1 C2 C3 690(3) C22 Si2 C3 C2 714(3) C22 Si2 C3 C4 ndash988(2) C23 Si2 C3 C2 ndash532(3) C23 Si2 C3 C4 1365(2) C24 Si2 C3 C2 ndash1731(3) C24 Si2 C3 C4 167(3) C25 Si3 C11 C10 ndash241(2) C25 Si3 C11 C12 1624(2) C26 Si3 C11 C10 ndash1417(2) C26 Si3 C11 C12 447(3)

- 101 -

C27 Si3 C11 C10 932(2) C27 Si3 C11 C12 ndash804(2) C28 Si4 C12 C11 ndash731(2) C28 Si4 C12 C13 1055(2) C29 Si4 C12 C11 529(2) C29 Si4 C12 C13 ndash1285(2) C30 Si4 C12 C11 1698(2) C30 Si4 C12 C13 ndash116(2) C18 C1 C2 Si1 1755(2) C18 C1 C2 C3 00(4) C2 C1 C18 Co1 784(3) C2 C1 C18 C5 ndash41(4) C2 C1 C18 C17 ndash1772(4) Si1 C2 C3 Si2 198(4) Si1 C2 C3 C4 ndash1707(2) C1 C2 C3 Si2 ndash1654(2) C1 C2 C3 C4 41(4) Si2 C3 C4 C5 1668(2) C2 C3 C4 C5 ndash40(4) C3 C4 C5 Co1 ndash816(3) C3 C4 C5 C6 1799(4) C3 C4 C5 C18 ndash01(4) Co1 C5 C6 C7 ndash1233(4) Co1 C5 C6 C17 671(1) C4 C5 C6 Co1 1122(4) C4 C5 C6 C7 ndash112(7) C4 C5 C6 C17 1793(4) C18 C5 C6 Co1 ndash678(1) C18 C5 C6 C7 1688(4) C18 C5 C6 C17 ndash07(2) Co1 C5 C18 C1 1164(2) Co1 C5 C18 C17 ndash672(1) C4 C5 C18 Co1 ndash1121(2) C4 C5 C18 C1 42(3) C4 C5 C18 C17 ndash1793(2) C6 C5 C18 Co1 679(1) C6 C5 C18 C1 ndash1757(2) C6 C5 C18 C17 07(2) Co1 C6 C7 C8 858(2) C5 C6 C7 C8 ndash1683(3) C17 C6 C7 C8 ndash08(3) Co1 C6 C17 C16 ndash1205(2) Co1 C6 C17 C18 665(1) C5 C6 C17 Co1 ndash658(1) C5 C6 C17 C16 1736(2) C5 C6 C17 C18 07(2)

- 102 -

C7 C6 C17 Co1 1209(2) C7 C6 C17 C16 03(4) C7 C6 C17 C18 ndash1726(2) C6 C7 C8 C9 ndash1697(3) C6 C7 C8 C15 09(3) C7 C8 C9 C10 05(7) C7 C8 C9 C14 1728(4) C15 C8 C9 C10 ndash1718(4) C15 C8 C9 C14 05(2) C7 C8 C15 C14 ndash1752(2) C7 C8 C15 C16 ndash06(4) C9 C8 C15 C14 ndash04(2) C9 C8 C15 C16 1742(2) C8 C9 C10 C11 1714(3) C14 C9 C10 C11 05(3) C8 C9 C14 C13 ndash1756(2) C8 C9 C14 C15 ndash05(2) C10 C9 C14 C13 ndash06(4) C10 C9 C14 C15 1746(2) C9 C10 C11 Si3 ndash1741(2) C9 C10 C11 C12 01(3) Si3 C11 C12 Si4 ndash90(3) Si3 C11 C12 C13 1725(2) C10 C11 C12 Si4 1779(2) C10 C11 C12 C13 ndash07(3) Si4 C12 C13 C14 ndash1781(2) C11 C12 C13 C14 06(3) C12 C13 C14 C9 ndash00(3) C12 C13 C14 C15 ndash1713(3) C9 C14 C15 C8 05(2) C9 C14 C15 C16 ndash1717(4) C13 C14 C15 C8 1730(4) C13 C14 C15 C16 09(7) C8 C15 C16 C17 00(3) C14 C15 C16 C17 1704(3) C15 C16 C17 Co1 ndash870(3) C15 C16 C17 C6 01(3) C15 C16 C17 C18 1674(4) Co1 C17 C18 C1 ndash1195(4) Co1 C17 C18 C5 664(1) C6 C17 C18 Co1 ndash671(1) C6 C17 C18 C1 1734(4) C6 C17 C18 C5 ndash07(2) C16 C17 C18 Co1 1235(4) C16 C17 C18 C1 40(7) C16 C17 C18 C5 ndash1701(4)

- 103 -

Co1 C31 C32 C33 590(2) C35 C31 C32 Co1 ndash607(2) C35 C31 C32 C33 ndash16(4) Co1 C31 C35 C34 ndash596(3) C32 C31 C35 Co1 615(3) C32 C31 C35 C34 18(4) Co1 C32 C33 C34 592(2) C31 C32 C33 Co1 ndash583(2) C31 C32 C33 C34 09(4) Co1 C33 C34 C35 605(3) C32 C33 C34 Co1 ndash602(2) C32 C33 C34 C35 03(4) Co1 C34 C35 C31 593(3) C33 C34 C35 Co1 ndash606(2) C33 C34 C35 C31 ndash13(4)

23-Bis(trimethylsilyl) linear [3]phenylene(CpCo) 52

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (029 g 085 mmol)27 in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (014 g 101 mmol) The mixture was stirred for 15 h and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the yellow residue dissolved in ether (30 mL) Aqueous workup with sat NaCl (2 x 20 mL) followed by drying over MgSO4 and concentration in vacuo provided a yellow solid This material was redissolved in THF (15 mL) degassed (Ar) and CpCo(CO)2 (0140 g 078 mmol) added The resulting solution (protected from light with foil) was injected (syringe pump) over 8 h into a boiling mixture of THF (200 mL) and BTMSA (50 mL) while irradiating with a slide projection lamp Once addition was complete heating and irradiation were continued for another 14 h The volatiles were removed via vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (4 x 4 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed in vacuo and the residue crystallized from acetone yielding 52 (024 g 57 ) as dark red crystals mp 198ndash202 degC (decomp) 1H-NMR (500 MHz C6D6) δ = 796 (s 2 H) 678 (AArsquom 2 H) 675 (s 2 H) 674 (BBrsquom 2 H) 436 (s 5 H) 037 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1426 1393

1360 1294 1194 1149 802 779 738 268 ppm IR (neat) ν~ = 2960 2923 2853 1461 1455 1378 1260 1093 1019 800 cmndash1 UV-VIS (hexane) λmax (log ε) = 255 (393) 282 (376) 293 (sh 378) 308 (389) 348 (390) 397 (sh 335) 436 (301) 511

CoSiMe3

SiMe3

- 104 -

(262) MS (70 eV) mz () 494 (100) [M+] 370 (14) HRMS (FAB) calcd for C29H31CoSi2 4941296 found 4941292 Elemental analysis calcd for C29H31CoSi2 C 7041 H 632 found 7048 628 Crystallographic information for 52 (H atoms omitted)

Table 45 Crystal Data and Structure Refinement For 52

Empirical formula C29H31CoSi2 Formula weight 49465 cryst size (mm) 030 x 020 x 005 cryst syst Monoclinic refl used for unit cell determination 2640 2 θ range (deg) 242ndash2503 a (Aring) 4391(3) b (Aring) 7472(4) c (Aring) 16869(11) α (deg)

β (deg) 111522(11) γ (deg) V (Aring3) 5149(6) space group C2c Z 8 Dcalc gcm

3 1276

F000 2080 micro cmndash1 774

temp ordmC ndash153

Tmax Tmin 0963 0800 no of total rflns 18401 no of unique rflns 2640 no of obsd rflns 4266 no of variables 271 Reflection to Parameter Ratio 974 R 00892 Rw 02042 Rall 01248 GOF 1008 Max Peak in Final Diff Map (endash Aring3) 1051 Min Peak in Final Diff Map (endash Aring3) ndash0707

- 105 -

Figure 42 ORTEP representation of 52

- 106 -

Table 46 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 52 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y z U(eq)

Co1 006961(2) 087577(12) 038136(6) 00200(3) Si1 018827(6) 08761(5) 063753(18) 00627(9) Si2 018540(5) 05425(3) 046900(16) 00410(6) C1 012151(19) 08410(10) 05589(5) 00310(17) C2 015018(13) 07767(11) 05552(4) 00343(18) C3 015002(14) 06417(10) 04926(5) 00324(17) C4 011985(17) 05770(9) 04357(4) 00247(16) C5 009030(17) 06465(9) 04383(4) 00220(14) C6 005450(16) 06378(9) 04077(4) 00216(14) C7 002537(17) 05420(9) 03591(4) 00224(15) C8 ndash000060(18) 05847(9) 03798(4) 00246(15) C9 ndash003560(17) 05555(10) 03644(4) 00256(16) C10 ndash006399(18) 04581(10) 03174(4) 00284(17) C11 ndash009208(19) 05019(12) 03360(5) 00344(18) C12 ndash009130(19) 06274(12) 03957(5) 00340(18) C13 ndash006300(17) 07256(11) 04422(5) 00294(17) C14 ndash003558(19) 06826(10) 04247(4) 00274(16) C15 000008(18) 07212(10) 04449(4) 00251(16) C16 002653(17) 08159(10) 04925(4) 00234(15) C17 005500(17) 07741(9) 04722(4) 00231(15) C18 009090(17) 07798(10) 05007(4) 00247(15) C19 01766(3) 10793(15) 06845(9) 0098(3) C20 02181(3) 0957(2) 05901(7) 0098(3) C21 02076(3) 07068(14) 07228(7) 0098(3) C22 01946(2) 06941(13) 03925(6) 00631(17) C23 01724(2) 03224(9) 04142(7) 00631(17) C24 022363(17) 04883(16) 05614(5) 00631(17) C25 007501(19) 09264(10) 02652(4) 00281(17) C26 004279(18) 09614(10) 02593(4) 00264(16) C27 004343(18) 10945(10) 03211(4) 00271(16) C28 007584(19) 11429(10) 03645(5) 00296(17) C29 00960(2) 10392(11) 03322(5) 00321(17)

Table 47 Bond Lengths (Aring) for Complex 52

Atom1 Atom2 Length

Co1 C5 2011(7) Co1 C6 2004(7) Co1 C17 2014(8) Co1 C18 2015(6) Co1 C25 2093(8)

- 107 -

Co1 C26 2063(6) Co1 C27 2042(7) Co1 C28 2049(8) Co1 C29 206(1) Si1 C2 1890(6) Si1 C19 187(1) Si1 C20 187(2) Si1 C21 187(1) Si2 C3 1891(8) Si2 C22 187(1) Si2 C23 1870(8) Si2 C24 1869(7) C1 C2 137(1) C1 C18 1418(9) C2 C3 146(1) C3 C4 1406(8) C4 C5 141(1) C5 C6 147(1) C5 C18 144(1) C6 C7 1432(9) C6 C17 148(1) C7 C8 135(1) C8 C9 148(1) C8 C15 149(1) C9 C10 1410(9) C9 C14 139(1) C10 C11 142(1) C11 C12 137(1) C12 C13 141(1) C13 C14 138(1) C14 C15 150(1) C15 C16 1345(9) C16 C17 145(1) C17 C18 147(1) C25 C26 141(1) C25 C29 144(1) C26 C27 143(1) C27 C28 139(1) C28 C29 143(1)

Table 48 Bond Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 428(3) C5 Co1 C17 619(3)

- 108 -

C5 Co1 C18 420(3) C5 Co1 C25 1145(3) C5 Co1 C26 1372(3) C5 Co1 C27 1733(3) C5 Co1 C28 1468(3) C5 Co1 C29 1184(3) C6 Co1 C17 434(3) C6 Co1 C18 621(3) C6 Co1 C25 1219(3) C6 Co1 C26 1125(3) C6 Co1 C27 1305(3) C6 Co1 C28 1653(3) C6 Co1 C29 1539(3) C17 Co1 C18 428(3) C17 Co1 C25 1632(3) C17 Co1 C26 1307(3) C17 Co1 C27 1137(3) C17 Co1 C28 1247(3) C17 Co1 C29 1562(3) C18 Co1 C25 1460(3) C18 Co1 C26 1733(3) C18 Co1 C27 1388(3) C18 Co1 C28 1167(3) C18 Co1 C29 1194(3) C25 Co1 C26 395(3) C25 Co1 C27 680(3) C25 Co1 C28 681(3) C25 Co1 C29 406(3) C26 Co1 C27 409(3) C26 Co1 C28 674(3) C26 Co1 C29 672(3) C27 Co1 C28 397(3) C27 Co1 C29 678(3) C28 Co1 C29 407(3) C2 Si1 C19 1089(5) C2 Si1 C20 1125(5) C2 Si1 C21 1092(4) C19 Si1 C20 1053(6) C19 Si1 C21 1100(6) C20 Si1 C21 1109(6) C3 Si2 C22 1081(4) C3 Si2 C23 1089(4) C3 Si2 C24 1177(4) C22 Si2 C23 1072(4) C22 Si2 C24 1106(4) C23 Si2 C24 1039(4)

- 109 -

C2 C1 C18 1206(7) Si1 C2 C1 1141(5) Si1 C2 C3 1249(5) C1 C2 C3 1210(7) Si2 C3 C2 1296(5) Si2 C3 C4 1113(5) C2 C3 C4 1190(6) C3 C4 C5 1199(6) Co1 C5 C4 1239(5) Co1 C5 C6 684(4) Co1 C5 C18 692(4) C4 C5 C6 1484(7) C4 C5 C18 1203(6) C6 C5 C18 910(6) Co1 C6 C5 688(4) Co1 C6 C7 1280(5) Co1 C6 C17 687(4) C5 C6 C7 1473(6) C5 C6 C17 892(5) C7 C6 C17 1222(6) C6 C7 C8 1133(6) C7 C8 C9 1475(7) C7 C8 C15 1242(7) C9 C8 C15 882(6) C8 C9 C10 1454(7) C8 C9 C14 928(6) C10 C9 C14 1218(7) C9 C10 C11 1147(7) C10 C11 C12 1222(8) C11 C12 C13 1231(8) C12 C13 C14 1149(7) C9 C14 C13 1233(7) C9 C14 C15 910(6) C13 C14 C15 1457(7) C8 C15 C14 879(6) C8 C15 C16 1254(7) C14 C15 C16 1467(7) C15 C16 C17 1121(6) Co1 C17 C6 679(4) Co1 C17 C16 1300(5) Co1 C17 C18 686(4) C6 C17 C16 1227(6) C6 C17 C18 892(5) C16 C17 C18 1464(7) Co1 C18 C1 1235(5) Co1 C18 C5 688(4)

- 110 -

Co1 C18 C17 686(4) C1 C18 C5 1191(7) C1 C18 C17 1500(7) C5 C18 C17 906(6) Co1 C25 C26 691(4) Co1 C25 C29 683(4) C26 C25 C29 1065(7) Co1 C26 C25 714(4) Co1 C26 C27 688(4) C25 C26 C27 1091(6) Co1 C27 C26 704(4) Co1 C27 C28 704(5) C26 C27 C28 1079(7) Co1 C28 C27 699(5) Co1 C28 C29 699(5) C27 C28 C29 1085(7) Co1 C29 C25 711(5) Co1 C29 C28 694(5) C25 C29 C28 1080(7)

Table 49 Torsion Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 1468(8) C6 Co1 C5 C18 ndash999(5) C17 Co1 C5 C4 ndash1627(7) C17 Co1 C5 C6 504(4) C17 Co1 C5 C18 ndash494(4) C18 Co1 C5 C4 ndash1133(8) C18 Co1 C5 C6 999(5) C25 Co1 C5 C4 356(7) C25 Co1 C5 C6 ndash1113(4) C25 Co1 C5 C18 1489(4) C26 Co1 C5 C4 765(7) C26 Co1 C5 C6 ndash703(5) C26 Co1 C5 C18 ndash1702(4) C27 Co1 C5 C4 146(2) C27 Co1 C5 C6 ndash1(3) C27 Co1 C5 C18 ndash101(2) C28 Co1 C5 C4 ndash515(9) C28 Co1 C5 C6 1617(5) C28 Co1 C5 C18 619(7) C29 Co1 C5 C4 ndash98(7) C29 Co1 C5 C6 ndash1567(4) C29 Co1 C5 C18 1035(5)

- 111 -

C5 Co1 C6 C7 ndash1474(8) C5 Co1 C6 C17 977(5) C17 Co1 C6 C5 ndash977(5) C17 Co1 C6 C7 1149(8) C18 Co1 C6 C5 ndash482(4) C18 Co1 C6 C7 1644(7) C18 Co1 C6 C17 495(4) C25 Co1 C6 C5 927(5) C25 Co1 C6 C7 ndash547(7) C25 Co1 C6 C17 ndash1696(4) C26 Co1 C6 C5 1362(4) C26 Co1 C6 C7 ndash112(7) C26 Co1 C6 C17 ndash1261(4) C27 Co1 C6 C5 1799(4) C27 Co1 C6 C7 325(8) C27 Co1 C6 C17 ndash824(5) C28 Co1 C6 C5 ndash137(1) C28 Co1 C6 C7 75(1) C28 Co1 C6 C17 ndash40(1) C29 Co1 C6 C5 523(8) C29 Co1 C6 C7 ndash951(9) C29 Co1 C6 C17 1501(7) C5 Co1 C17 C6 ndash497(4) C5 Co1 C17 C16 ndash1646(8) C5 Co1 C17 C18 484(4) C6 Co1 C17 C16 ndash1149(8) C6 Co1 C17 C18 981(5) C18 Co1 C17 C6 ndash981(5) C18 Co1 C17 C16 1470(9) C25 Co1 C17 C6 32(1) C25 Co1 C17 C16 ndash83(1) C25 Co1 C17 C18 130(1) C26 Co1 C17 C6 799(5) C26 Co1 C17 C16 ndash350(8) C26 Co1 C17 C18 1780(4) C27 Co1 C17 C6 1245(4) C27 Co1 C17 C16 97(8) C27 Co1 C17 C18 ndash1373(4) C28 Co1 C17 C6 1686(4) C28 Co1 C17 C16 538(8) C28 Co1 C17 C18 ndash932(5) C29 Co1 C17 C6 ndash1471(7) C29 Co1 C17 C16 98(1) C29 Co1 C17 C18 ndash489(9) C5 Co1 C18 C1 1117(8) C5 Co1 C18 C17 ndash995(5)

- 112 -

C6 Co1 C18 C1 1609(7) C6 Co1 C18 C5 492(4) C6 Co1 C18 C17 ndash502(4) C17 Co1 C18 C1 ndash1488(8) C17 Co1 C18 C5 995(5) C25 Co1 C18 C1 544(9) C25 Co1 C18 C5 ndash573(7) C25 Co1 C18 C17 ndash1568(5) C26 Co1 C18 C1 ndash162(2) C26 Co1 C18 C5 87(3) C26 Co1 C18 C17 ndash13(3) C27 Co1 C18 C1 ndash784(8) C27 Co1 C18 C5 1699(4) C27 Co1 C18 C17 705(6) C28 Co1 C18 C1 ndash356(7) C28 Co1 C18 C5 ndash1473(4) C28 Co1 C18 C17 1133(4) C29 Co1 C18 C1 107(8) C29 Co1 C18 C5 ndash1010(5) C29 Co1 C18 C17 1595(4) C5 Co1 C25 C26 1356(4) C5 Co1 C25 C29 ndash1058(5) C6 Co1 C25 C26 873(5) C6 Co1 C25 C29 ndash1540(5) C17 Co1 C25 C26 62(1) C17 Co1 C25 C29 ndash1796(9) C18 Co1 C25 C26 1738(5) C18 Co1 C25 C29 ndash675(7) C26 Co1 C25 C29 1187(6) C27 Co1 C25 C26 ndash376(4) C27 Co1 C25 C29 810(5) C28 Co1 C25 C26 ndash806(5) C28 Co1 C25 C29 381(5) C29 Co1 C25 C26 ndash1187(6) C5 Co1 C26 C25 ndash696(6) C5 Co1 C26 C27 1703(4) C6 Co1 C26 C25 ndash1134(5) C6 Co1 C26 C27 1265(4) C17 Co1 C26 C25 ndash1604(4) C17 Co1 C26 C27 795(5) C18 Co1 C26 C25 ndash149(2) C18 Co1 C26 C27 91(3) C25 Co1 C26 C27 ndash1201(6) C27 Co1 C26 C25 1201(6) C28 Co1 C26 C25 825(5) C28 Co1 C26 C27 ndash376(4)

- 113 -

C29 Co1 C26 C25 383(5) C29 Co1 C26 C27 ndash818(5) C5 Co1 C27 C26 ndash77(3) C5 Co1 C27 C28 165(2) C6 Co1 C27 C26 ndash774(5) C6 Co1 C27 C28 1644(5) C17 Co1 C27 C26 ndash1254(4) C17 Co1 C27 C28 1163(5) C18 Co1 C27 C26 ndash1698(5) C18 Co1 C27 C28 720(6) C25 Co1 C27 C26 364(4) C25 Co1 C27 C28 ndash818(5) C26 Co1 C27 C28 ndash1182(6) C28 Co1 C27 C26 1182(6) C29 Co1 C27 C26 804(5) C29 Co1 C27 C28 ndash378(5) C5 Co1 C28 C27 ndash1768(5) C5 Co1 C28 C29 637(7) C6 Co1 C28 C27 ndash54(1) C6 Co1 C28 C29 ndash173(1) C17 Co1 C28 C27 ndash861(5) C17 Co1 C28 C29 1544(5) C18 Co1 C28 C27 ndash1355(5) C18 Co1 C28 C29 1050(5) C25 Co1 C28 C27 815(5) C25 Co1 C28 C29 ndash380(5) C26 Co1 C28 C27 387(4) C26 Co1 C28 C29 ndash809(5) C27 Co1 C28 C29 ndash1195(7) C29 Co1 C28 C27 1195(7) C5 Co1 C29 C25 953(5) C5 Co1 C29 C28 ndash1461(5) C6 Co1 C29 C25 576(9) C6 Co1 C29 C28 1762(6) C17 Co1 C29 C25 1797(7) C17 Co1 C29 C28 ndash617(9) C18 Co1 C29 C25 1437(4) C18 Co1 C29 C28 ndash977(5) C25 Co1 C29 C28 1186(7) C26 Co1 C29 C25 ndash373(4) C26 Co1 C29 C28 813(5) C27 Co1 C29 C25 ndash817(5) C27 Co1 C29 C28 369(5) C28 Co1 C29 C25 ndash1186(7) C19 Si1 C2 C1 ndash144(8) C19 Si1 C2 C3 1663(7)

- 114 -

C20 Si1 C2 C1 ndash1307(7) C20 Si1 C2 C3 500(8) C21 Si1 C2 C1 1057(7) C21 Si1 C2 C3 ndash736(7) C22 Si2 C3 C2 ndash852(7) C22 Si2 C3 C4 908(6) C23 Si2 C3 C2 1587(7) C23 Si2 C3 C4 ndash253(7) C24 Si2 C3 C2 410(8) C24 Si2 C3 C4 ndash1431(6) C18 C1 C2 Si1 1795(6) C18 C1 C2 C3 ndash1(1) C2 C1 C18 Co1 ndash817(9) C2 C1 C18 C5 1(1) C2 C1 C18 C17 173(1) Si1 C2 C3 Si2 ndash5(1) Si1 C2 C3 C4 1790(5) C1 C2 C3 Si2 1755(6) C1 C2 C3 C4 ndash0(1) Si2 C3 C4 C5 ndash1747(5) C2 C3 C4 C5 2(1) C3 C4 C5 Co1 822(8) C3 C4 C5 C6 ndash174(1) C3 C4 C5 C18 ndash2(1) Co1 C5 C6 C7 128(1) Co1 C5 C6 C17 ndash674(4) C4 C5 C6 Co1 ndash120(1) C4 C5 C6 C7 8(2) C4 C5 C6 C17 173(1) C18 C5 C6 Co1 671(4) C18 C5 C6 C7 ndash165(1) C18 C5 C6 C17 ndash03(6) Co1 C5 C18 C1 ndash1175(7) Co1 C5 C18 C17 667(4) C4 C5 C18 Co1 1179(7) C4 C5 C18 C1 0(1) C4 C5 C18 C17 ndash1754(7) C6 C5 C18 Co1 ndash663(4) C6 C5 C18 C1 1762(7) C6 C5 C18 C17 04(6) Co1 C6 C7 C8 ndash887(8) C5 C6 C7 C8 160(1) C17 C6 C7 C8 ndash2(1) Co1 C6 C17 C16 1243(7) Co1 C6 C17 C18 ndash672(4) C5 C6 C17 Co1 675(4)

- 115 -

C5 C6 C17 C16 ndash1681(7) C5 C6 C17 C18 03(5) C7 C6 C17 Co1 ndash1223(7) C7 C6 C17 C16 2(1) C7 C6 C17 C18 1705(7) C6 C7 C8 C9 ndash180(1) C6 C7 C8 C15 2(1) C7 C8 C9 C10 2(2) C7 C8 C9 C14 ndash179(1) C15 C8 C9 C10 ndash179(1) C15 C8 C9 C14 01(6) C7 C8 C15 C14 1791(7) C7 C8 C15 C16 ndash2(1) C9 C8 C15 C14 ndash01(5) C9 C8 C15 C16 1792(8) C8 C9 C10 C11 ndash180(1) C14 C9 C10 C11 1(1) C8 C9 C14 C13 1791(7) C8 C9 C14 C15 ndash01(6) C10 C9 C14 C13 ndash1(1) C10 C9 C14 C15 1796(7) C9 C10 C11 C12 ndash1(1) C10 C11 C12 C13 1(1) C11 C12 C13 C14 ndash2(1) C12 C13 C14 C9 2(1) C12 C13 C14 C15 ndash180(1) C9 C14 C15 C8 01(6) C9 C14 C15 C16 ndash179(1) C13 C14 C15 C8 ndash179(1) C13 C14 C15 C16 2(2) C8 C15 C16 C17 1(1) C14 C15 C16 C17 ndash180(1) C15 C16 C17 Co1 858(8) C15 C16 C17 C6 ndash2(1) C15 C16 C17 C18 ndash161(1) Co1 C17 C18 C1 120(1) Co1 C17 C18 C5 ndash669(4) C6 C17 C18 Co1 666(4) C6 C17 C18 C1 ndash173(1) C6 C17 C18 C5 ndash03(5) C16 C17 C18 Co1 ndash131(1) C16 C17 C18 C1 ndash11(2) C16 C17 C18 C5 162(1) Co1 C25 C26 C27 586(5) C29 C25 C26 Co1 ndash583(5) C29 C25 C26 C27 03(9)

- 116 -

Co1 C25 C29 C28 ndash598(6) C26 C25 C29 Co1 588(5) C26 C25 C29 C28 ndash10(9) Co1 C26 C27 C28 607(5) C25 C26 C27 Co1 ndash602(5) C25 C26 C27 C28 05(9) Co1 C27 C28 C29 595(6) C26 C27 C28 Co1 ndash607(5) C26 C27 C28 C29 ndash12(9) Co1 C28 C29 C25 609(6) C27 C28 C29 Co1 ndash595(6) C27 C28 C29 C25 14(9)

Photo-thermal cycle between 52 and 53

An NMR tube containing a solution of 52 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 53 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 724 (AArsquom 2 H) 683 (s 2 H) 662 (BBrsquom 2 H) 444 (s 5 H) 032 (s 18 H) ppm 13C- NMR (100 MHz C6D6) δ = 1493 1482 1430 1276 1256 1241 1155 803 796 725 222 ppm Thermal reversal could be conveniently followed by VT-NMR

Kinetic studies of the thermal CoCp migration in 53 In the glovebox 23-[bis(trimethylsilyl)] linear[3]phenylene(CpCo) 52 dissolved in the solvent of choice (C6D6 or toluene-d8) was passed through an HPLC filter and then transfered via syringe into a thick-walled NMR tube connected to a vacuum line adapter The sample was then degassed by three freeze-pump-thaw cycles and flame-sealed under vacuum Prior to the kinetic runs the mixtures were irradiated for 10 h in a Rayonet Photochemical Reactor fitted with lamps emitting at 310 and 365 nm After this treatment care was taken to exclude ambient light as it causes some isomerization The irradiated samples were then placed in the NMR spectrometer at ndash65 degC (500 MHz) which was then warmed to the required temperature In the case of the 60 degC runs the magnet was prewarmed because of the fast reaction rate at this temperature After five min the spectra were recorded The Cp signal of the photoisomer was integrated relative to the solvent peak of C6D6 or the CD3 peak of toluene-d8 and monitored as a function of time The integral from the first scan was used as [A]o Since the equilibrium constant between the isomers was 50 the kinetic analysis treated the isomerization as a first-order non-reversible process Plotting the data accordingly

CoSiMe3

SiMe3

52

CoSiMe3

SiMe3

53

hν∆

- 117 -

yielded the reaction rate constants which were used in the Eyring plots to obtain the activation parameters Kinetic studies of the thermal haptotropic shift for complex 52 Kinetic runs were executed in C6D6 as the optimum solvent A sample of 52 in degassed C6D6 or toluene-d8 was subjected to UV light for 10 h leading to maximum enrichment of 53 The sample was kept at the specified temperature and the disappearance of 53 monitored by 1H-NMR spectroscopy The reaction proved to be first-order (eq 1) consistent with an intramolecular process

[ ] [ ]Akdt

Adminus=

(1)

[ ][ ] dtkA

Ad=minus

(2)

[ ][ ]

tkA

A=minus

0

ln (3)

The rate constant (k) at 30 40 50 and 60 degC was obtained from the slope of a plot of ndashln([A][A]0) versus time (t) following eq 2 and 3 The actual error in reproducibility was estimated by the calculation of one standard deviation (σ) for a triplicate run at 60 degC The percentage error was applied for k at 30 40 and 50 degC The rate constants and their errors are given in Tables 411 and 414 The values for k and their standard deviations were used to calculate the activation enthalpy (∆HDagger) and entropy (∆SH) of the haptotropic shift The basis for these calculations is the Eyring equation (eq 4) This expression (eq 4) was transformed to eq 5 and the activation enthalpy (∆HDagger) obtained from the slope of a plot of ndashln(kT) versus 1RT The intercept (ndashC) provides the activation entropy (∆SH) following eq 6 and 7

C

TR

H

R

S

h

k

TR

H

T

k B

minus∆

=

∆+minus

∆=minus

ne

nene

lnln

( 4)

R

S

h

kC B

ne∆+= ln

(5)

minus=∆ ne

h

kCRS Bln

(6)

- 118 -

The errors in ∆HDagger and ∆SDagger were calculated based on those in the rate constants leading to two additional least square fits in the Eyring plot These fits represent the two most extreme deviations from the original plot This provides a conservative error estimate and finally the values of 204plusmn14 kcalmol for ∆HH and 158plusmn22 eu (calmolmiddotK) for ∆SH in C6D6 In order to probe for solvent effects the kinetics were also repeated in toluene-d8 The preparation of the sample followed the described procedure and the rate constants (k) were obtained at 30 40 50 and 60 degC At 60 degC three measurements were carried out to estimate the errors in reproducibility for k and the activation parameters Error propagation was done as described for the kinetic experiments in C6D6 It is assumed that those rate constants (k) show the same relative error as the ones for the rearrangement of 53 to 52 in C6D6 The activation parameters in toluene-d8 were found to be 231plusmn07 kcalmol and 60plusmn13 eu

Table 410 Kinetic Data for the Conversion of 53 to 52 in C6D6

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09657 00349 1000 09419 00599 6000 09380 00640 2000 09018 01034 9000 09038 01012 3000 08557 01558 12000 08760 01324 4000 08176 02013 15000 08418 01723 5000 07796 02490 18000 08206 01978 6000 07555 02804 21000 08010 02219 7000 07255 03210 32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 400 09541 00470 30 09888 00113 800 09197 00837 60 09820 00181 1200 08910 01154 90 09708 00296 1600 08489 01638 120 09596 00413 2000 08298 01865 150 09506 00507 2400 07954 02289 180 09416 00602 2800 07591 02756 210 09348 00674 240 09281 00746 270 09213 00819 300 09124 00917 330 09034 01016 360 08966 01091

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

- 119 -

0 10000 00000 0 10000 00000 30 09950 00050 30 09909 00092 60 09900 00101 60 09854 00147 90 09800 00202 90 09762 00241 120 09750 00253 120 09671 00335 150 09700 00305 150 09634 00372 180 09625 00382 180 09543 00468 210 09575 00434 210 09433 00583 240 09475 00539 240 09397 00622 270 09400 00619 270 09287 00740 300 09350 00672 300 09232 00799 330 09300 00726 330 09177 00858 360 09250 00780 360 09086 00959

Table 411 The Rate Constants (k) in C6D6 Calculated From the Data in Table 410 and Their

Standard Deviations (σ)

Temp (K) k (1s) σσσσ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 10809Endash05 74258Endash07 09970 171494 00688

31315 45615Endash05 31338Endash06 09948 157420 00688

32315 95118Endash05 65346Endash06 09965 150385 00688

33315 (1) 27425Endash04 09965

33315 (2) 25714Endash04 09964

33315 (3) 30051Endash04 09990

33315 (avg) 26511Endash04 18841Endash05 140101 00688

Table 412 Activation Parameters for the Kinetic Experiments in C6D6

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 90990 85414 79291 Intercept ndash1789 ndash1674 ndash1559 R

2 09869 09869 09869

∆HDagger (Jmol) 90990 85414 79291

∆HDagger (kcalmol) 217 204 190

∆SDagger (JmolmiddotK) ndash569 ndash660 ndash751

∆SDagger (eu) ndash136 ndash158 ndash180

- 120 -

(323 15 K 50 degC) y = 95118E-05x + 44505E-03

R2 = 9965

(30315 K 30 degC) y = 10809E-05x + 20474E-03

R2 = 9970

(31315 K 40 degC) y = 45615E-05x + 11689E-02

R2 = 9948

(33315 K 60 degC) y = 263387E-04x + 390297E-04

R2 = 9992

000

005

010

015

020

025

030

035

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

Figure 43 Kinetic plots for the conversion of 53 to 52 in C6D6

Table 413 Kinetic Data for the Conversion of 53 to 52 in Toluene-d8

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09556 00454 1000 09488 00526 6000 09256 00773 2000 08931 01130 9000 08956 01103 3000 08545 01572 12000 08667 01430 4000 08143 02054 15000 08343 01811 5000 07818 02461 18000 08103 02103 6000 07559 02798 21000 07863 02404 7000 07179 03314

- 121 -

32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

000 10000 00000 0 10000 00000 40000 09470 00544 30 09887 00113 80000 08934 01127 60 09775 00228 120000 08594 01515 90 09691 00314 160000 08175 02015 120 09592 00416 200000 07861 02406 150 09473 00542 240000 07502 02875 180 09381 00639 280000 06991 03579 210 09262 00767 240 09149 00889 270 09086 00959 300 08973 01083 330 08868 01202 360 08762 01321

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 30 09945 00055 30 09910 00090 60 09795 00207 60 09828 00173 90 09700 00304 90 09716 00288 120 09645 00361 120 09559 00451 150 09479 00535 150 09440 00576 180 09464 00551 180 09313 00712 210 09314 00711 210 09238 00792 240 09188 00847 240 09156 00882 270 09101 00942 270 08992 01063 300 08991 01064 300 08932 01129 330 08896 01170 330 08872 01197 360 08801 01277 360 08686 01409

- 122 -

Table 414 The Rate Constants (k) in Toluene-d8 Calculated From the Data in Table 413 and Their Standard Deviations (σ)

Temp (K) k (1s) σ σ σ σ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 11314Endash05 37152Endash07 09976 17104 05610

31315 46470Endash05 15251Endash06 09948 15723 05157

32315 12214Endash04 401074Endash06 09957 14788 04851

33315 (1) 36441Endash04 09992

33315 (2) 36124Endash04 09951

33315 (3) 38855Endash04 09956

33315 (avg) 37140Endash04 14937Endash05 13707 04496

Table 415 Activation Parameters for the Kinetic Experiments in Toluene-d8

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 96590 93523 90455 Intercept ndash2073 ndash2007 ndash1941 R

2 09962 09962 09962

∆HDagger (Jmol) 96590 93523 90455

∆HDagger (kcalmol) 2309 2235 2162

∆SDagger (JmolmiddotK) ndash2521 ndash3068 ndash3615

∆SDagger (eu) ndash602 ndash733 ndash864

- 123 -

00000

00500

01000

01500

02000

02500

03000

03500

04000

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

(31315 K 40 degC) y = 46470E-05x + 10553E-02

R2 = 9948

(32315 K 50 degC) y = 12214E-04x + 47671E-03

R2 = 9957

(33315 K 60 degC)y = 371377E-04x - 208381E-03

R2 = 9992

(30315 K 30 degC) y = 11314E-05x + 71900E-03

R2 = 9976

Figure 44 Kinetic plots for the conversion of 53 to 52 in toluene-d8

- 124 -

(C6D6) y = 85141x - 16743

R2

= 09869

(toluene-d 8) y = 93523x - 2007

R2 = 09962

13600

14600

15600

16600

17600

36100E-04

36600E-04

37100E-04

37600E-04

38100E-04

38600E-04

39100E-04

39600E-04

40100E-04

1RT (Jmol)

-ln

(kT

)

Figure 45 Eyring plots for conversion of 53 to 52 MeCpCo(CO)2

Adapted from the literature procedure50 Co2(CO)8 (809 g 2366 mmol) was added to a round bottom flask in the glovebox The flask was capped with a septum and brought out of the glovebox A reflux condenser connected to the high vacuum line was quickly exchanged with the septum under a heavy purge of argon Degassed CH2Cl2 (30 mL) was added followed by freshly cracked deoxygenated methylcyclopentadiene (135 mL 123 mmol) The mixture evolved gas upon addition of the methylcyclopentadiene indicating CO liberation The entire setup was protected from light with foil and heated to a gentle reflux using a heating mantlevariac heat source After stirring at reflux for 26 h the mixture now dark crimson in color was cooled to rt The reflux condenser was quickly exchanged for a distillation head under an Ar purge and CH2Cl2 distilled off at atmospheric pressure under Ar Vacuum distillation at 002 Torr was performed and the forerun discarded The desired complex was obtained as a red liquid (7296 g 79) bp = 31 degC (002 Torr) stored at ndash10 degC and shielded from light Note A small

CoOC CO

- 125 -

amount of methylcyclopentadiene dimer (15 ) which could not be separated was present in the isolated product This was deemed harmless however and the obtained product was used in further experiments without further purification 85 pure 1H-NMR data match those reported in the literature 1H-NMR (C6D6) δ = 145 (s 3 H) 431 (br s 2 H) 451 (br s 2 H) 23-Bis(trimethylsilyl) linear [3]phenylene(MeCpCo) 54

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (0146 g 0424 mmol) in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (0101 g 0731 mmol) The mixture was stirred for 100 min and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the remaining yellow residue was dissolved in freshly distilled THF (15 mL) The green solution was separated from the solids via canula filtration and transferred into another Schlenk flask After a 20 min Ar purge MeCpCo(CO)2 (0092 g 0403 mmol) was added and the resulting solution (protected from light with foil) injected via syringe pump over 9 h into a boiling mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 15 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (201) The volatiles were again removed under high vacuum line and the residue crystallized from acetone yielding 55 (0125 g 61 ) as black crystals mp 163ndash165 degC 1H-NMR (500 MHz C6D6) δ = 783 (s 2 H) 676 (m 4 H) 675 (s 2 H) 442 (apparent t J = 21 Hz 2 H) 427 (apparent t J = 21 Hz 2 H) 134 (s 3 H) 038 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1423 1386 1354 1293 1193 1147 899 806 798 783 739 111 279 ppm IR (neat) ν~ = 2959 2923 2853 1462 1455 1378 1260 1093 1030 802 cmndash1 UV-VIS (hexane) λmax (log ε) = 256 (368) 281 (356) 293 (359) 310 (373) 350 (368) 386 (sh 321) 437 (sh 287) 499 (sh 247) end absorption to 550 nm MS (70 eV) mz () 508 (100) [M+] 370 (28) HRMS (FAB) calcd for C30H33CoSi2 5081453 found 5081442 Photo-thermal cycle between 54 and 56

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

54

CoSiMe3

SiMe3

56

hν∆

Me Me

- 126 -

An NMR tube containing a solution of 54 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 56 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 715 (AArsquom obscured by solvent peak) 680 (s 2 H) 664 (AArsquom 2 H) 447 (apparent t J = 21 Hz 2 H) 428 (apparent t J = 21 Hz 2 H) 148 (s 3 H) 032 (s 18 H) ppm Thermal reversal could be conveniently followed by VT-NMR

14-Deuterio-23-bis(trimethylsilyl) linear [3]phenylene cyclopentadienylcobalt 55

To 23-bis(trimethylsilylethynyl)biphenylene 52 (0144 g 0418 mmol) in CH3OD (10 mL) was added freshly distilled ether (20 mL) and K2CO3 (0083 g 0600 mmol) The mixture was stirred for 100 min and monitored by TLC (hexaneCH2Cl2 51) When the starting material had disappeared the solvents were removed and the remaining yellow residue very quickly dissolved in freshly distilled THF (10 mL) The green solution was separated from the solids using a filter cannula and transferred to another Schlenk flask After a 20 min Ar purge CpCo(CO)2 (0072 g 0400 mmol) was added and the resulting solution (protected from light with foil) was injected via syringe pump over 7 h into a refluxing mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 14 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed on the high vacuum line and the residue recrystallized from acetone yielding 8 (0085 g 41 ) as dark red crystals 1H-NMR spectroscopy showed 63 incorporation of deuterium as indicated by the diminution of the peak intensity of the signal at δ = 796 (s 074 H) ppm MS (FAB) mz () 496 (100) [M+] 372 (19)

CoSiMe3

SiMe3

D

D

- 127 -

Crossover experiment with 54 and 55

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

h

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

5455

5657

A solution of complex 55 (~2 mg) and 54 (~2 mg) in C6D6 (06 mL) rigorously protected from light was analyzed by 1H-NMR spectroscopy to reveal a 1861 mixture of 5554 The peak for 55 at δ = 796 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound A mass spectrum of an aliquot gave the appropriate composite of the two respective molecular ion patterns (Figure 46) The sample was then irradiated as described for above 13 h at RT The 1H-NMR spectrum of the irradiated mixture showed the presence of the respective photoisomers of 55 and 54 There were no unidentifiable peaks the signal at δ = 7470 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound and the clearly resolved peak for 56 at δ = 7473 (s 2 H) ppm revealed unattenuated intensity An aliquot was submitted for mass spectral analysis furnishing the same pattern as that depicted above The sample was then placed in an oil bath preheated to 80 degC for 30 h a treatment that regenerated the original NMR spectrum of the mixture of 55 and 54 including the relative integration ratios Similarly mass spectral analysis resulted in the same pattern as that depicted in Figure 46

- 128 -

Figure 46 Mass spectrum from the crossover experiment between 55 and 56

Low temperature photolyses of 19 and 52 A small amount (~5 mg) of linear[3]phenylene(CpCo) 19 or 52 dissolved in toluene-d8 was added to a J-Young NMR tube in the glovebox The sealed sample was then placed inside a Pyrex Dewar flask positioned in a Rayonet Photochemical Reactor outfitted with UV-lamps emitting at 310 and 350 nm (as shown in Figure 214) Cooling was achieved with the use of a Neslab Refrigerated Circulating bath employing isopropanol as the cooling medium The cold isopropanol was pumped into and out of the Pyrex Dewar using securely fastened Tygon tubes maintaining a temperature of ndash55 to ndash50 degC Once the sample was chilled irradiation was commenced The total irradiation time varied from 25 to 4 h When analysis was required the sample was transported in another Dewar flask containing dry iceisopropanol (ndash78 degC) while the NMR spectrometer was prepared for the low temperature experiment The spectrometer was cooled (ndash80 to ndash30 degC depending on the experiment) the sample wiped with a paper towel placed inside the spinner and very quickly lowered manually with a string into the cold magnet After allowing time for the temperature to equilibrate (10 min) a spectrum was recorded For VT experiments the temperature was slowly

- 129 -

raised from ndash80 degC in 10 degree increments to 10 degC Spectra were recorded at each interval For all other experiments spectra were recorded at ndash30 degC 2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

In the glovebox 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19 (0049 g 0133 mmol) and CpCo(C2H4)2 (0025 g 0139 mmol)99 were added to a Schlenk flask The flask was sealed brought out of the box connected to a vacuum manifold and freshly distilled degassed benzene (15 mL) added The mixture was heated to 70 degC on an oil bath for 23 h before being cooled to RT The solvent was removed in vacuo giving a black residue that was rapidly filtered through a plug of neutral alumina activity III (25 x 35 cm) eluting with a mixture of hexanes and THF (1001) under nitrogen and into a Schlenk flask The solvents were again removed in vacuo and the ensuing black residue recrystallized from acetone at ndash78 degC to give pure 78 (0057 g 56 ) as black crystals 1H-NMR (400 MHz acetone-d6) δ = 039 (s 36H) 481 (s 2H) 489 (m 4H) 736 (s 4H) ppm 13C-NMR (100 MHz acetone-d6) δ = 266 5372 5710 8284 12587 14542 15054 ppm UV-VIS (hexane) λmax (log ε) 197 (334) 221 (336 sh) 244 (344) 286 (363) 386 (279 sh) 439 (258) MS (FAB) 762 (M+ 100) HRMS calcd for C40H52Si4Co2 7621810 found 7621791 43 Computational Details for Chapter Two All calculations were performed using the GAUSSIAN03100 program GaussView 30101 and ChemCraft102 were employed to input structures as well as view output results Optimized geometries were obtained at the hybrid density functional theory (DFT) using Beckersquos three-parameter exchange-correlation functional103 containing the non-local gradient correction of Lee Yang and Parr104 (B3LYP) For optimization purposes a standard basis 3-21G105 was used for hydrogen and carbon atoms For cobalt the LANL2DZ106 basis set was applied with the outermost d function released yielding a triple-zeta d basis along with the effective core potentials (ECP) to describe the core electrons For the single point energy calculations the basis sets were increased to 6-31G107 for hydrogen 6-311G108 for carbon and the modified LANL2DZ basis as described above for cobalt with an added f-orbital coefficient109 The potential energy surfaces were mapped through a scan calculation a feature also available within the GAUSSIAN03 program Transition state structures were obtained in three different steps (i) determination of initial and final products or the minimum closest to a TS (ii) a linear QST2110 search for an initial guess of a TS and

- 130 -

(iii) input of the results from (ii) into a QST3 search Transition states and minima were confirmed by carrying out frequency calculations (using the same basis as that used for the optimizations)

Calculated structures for linear [3]phenylene(CpCo) (labels from Figures 29 and 210 in Section 24)

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

C 2878616000 ndash1675635000 ndash1461246000 C 3986441000 ndash2043582000 ndash0714088000 C 3986471000 ndash2043226000 0714700000 C 2878686000 ndash1674908000 1461732000 C 1740663000 ndash1265994000 0736724000 C 1740638000 ndash1266353000 ndash0736388000 H 2884721000 ndash1731772000 ndash2551997000 H 2884845000 ndash1730511000 2552509000 C 0311237000 ndash0833174000 0748280000 C 0311204000 ndash0833522000 ndash0748106000 C ndash0893980000 ndash0698348000 ndash1520584000 C ndash0893913000 ndash0697588000 1520749000 C ndash1996288000 ndash0532216000 0744771000 C ndash1996322000 ndash0532586000 ndash0744640000 C ndash3491040000 ndash0328769000 ndash0716524000 C ndash3490989000 ndash0328300000 0716632000 C ndash4645388000 ndash0172650000 ndash1448232000 C ndash4645276000 ndash0171672000 1448326000 C ndash5836534000 ndash0014205000 ndash0697760000

- 131 -

C ndash5836481000 ndash0013731000 0697841000 H ndash0905006000 ndash0741217000 ndash2609771000 H ndash0904887000 ndash0739873000 2609960000 H ndash4666353000 ndash0168153000 ndash2539086000 H ndash6785734000 0111682000 ndash1227959000 H ndash6785641000 0112502000 1228028000 H ndash4666162000 ndash0166493000 2539178000 Co 1455829000 0662094000 ndash0000295000 C 0672548000 2613322000 0000481000 C 1502831000 2459745000 1168426000 C 2819523000 2140942000 0722371000 C 2818808000 2141294000 ndash0723848000 C 1501651000 2460224000 ndash1168394000 H ndash0391329000 2836892000 0001070000 H 1172930000 2540112000 2200200000 H 3678957000 1932268000 1353707000 H 3677612000 1932967000 ndash1356152000 H 1170676000 2541059000 ndash2199789000 H 4894703000 ndash2369906000 1230670000 H 4894651000 ndash2370516000 ndash1229936000

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

C ndash3991583000 ndash2430244000 ndash0695300000 C ndash2895249000 ndash1923385000 ndash1446977000 C ndash1838331000 ndash1436925000 ndash0718218000 C ndash0460541000 ndash0772703000 ndash0748934000

- 132 -

C 0758545000 ndash0733408000 ndash1513161000 C 1871918000 ndash0586111000 ndash0739684000 C 3374782000 ndash0432509000 ndash0717168000 C 4533131000 ndash0322603000 ndash1448209000 C 5731498000 ndash0208370000 ndash0696796000 C 5731438000 ndash0207885000 0696952000 C 4533003000 ndash0321597000 1448333000 C 3374722000 ndash0432010000 0717261000 C 1871861000 ndash0585642000 0739747000 C 0758457000 ndash0732583000 1513259000 C ndash0460578000 ndash0772439000 0748991000 C ndash1838348000 ndash1436677000 0718485000 C ndash2895298000 ndash1922892000 1447371000 C ndash3991613000 ndash2429987000 0695830000 H ndash4853881000 ndash2841402000 ndash1229010000 H ndash2909366000 ndash1943431000 ndash2538196000 H 0770744000 ndash0814782000 ndash2600896000 H 4554949000 ndash0321315000 ndash2539049000 H 6684245000 ndash0118682000 ndash1227928000 H 6684140000 ndash0117859000 1228104000 H 4554722000 ndash0319567000 2539175000 H 0770611000 ndash0813312000 2601042000 H ndash2909450000 ndash1942588000 2538596000 H ndash4853932000 ndash2840954000 1229654000 Co ndash1032604000 1030206000 ndash0000179000 C ndash2903591000 1947430000 ndash0000175000 C ndash2211742000 2430689000 ndash1177143000 C ndash1026232000 3056089000 ndash0732194000 C ndash1026229000 3056139000 0731719000 C ndash2211730000 2430773000 1176747000 H ndash3829247000 1376180000 ndash0000150000 H ndash2513347000 2264399000 ndash2207387000 H ndash0243163000 3477094000 ndash1358586000 H ndash0243137000 3477190000 1358051000 H ndash2513304000 2264572000 2207015000

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 133 -

C 4829664000 ndash1220862000 0883782000 C 3649435000 ndash0895915000 1609183000 C 2478533000 ndash0900239000 0886069000 C 0985532000 ndash0699413000 0895282000 C ndash0207413000 ndash0351140000 1567281000 C ndash1295977000 ndash0355264000 0631690000 C ndash2799524000 ndash0368596000 0647705000 C ndash3950748000 0104186000 1252743000 C ndash5173877000 ndash0370408000 0725519000 C ndash5217559000 ndash1270006000 ndash0351644000 C ndash4043168000 ndash1754445000 ndash0967619000 C ndash2843350000 ndash1293792000 ndash0444950000 C ndash1365414000 ndash1319830000 ndash0538287000 C ndash0225558000 ndash1662005000 ndash1182029000 C 0928168000 ndash1009692000 ndash0554559000 C 2436156000 ndash1209374000 ndash0509824000 C 3575395000 ndash1530032000 ndash1215144000 C 4792344000 ndash1526592000 ndash0477473000 H 5781080000 ndash1237670000 1406156000 H 3693287000 ndash0679862000 2671420000 H ndash0279175000 ndash0037747000 2601166000 H ndash3939706000 0801901000 2083798000 H ndash6106757000 ndash0031072000 1165263000 H ndash6183419000 ndash1601741000 ndash0720200000 H ndash4097586000 ndash2453276000 ndash1795561000 H ndash0137803000 ndash2306368000 ndash2049380000 H 3570207000 ndash1781979000 ndash2270507000 H 5717527000 ndash1774506000 ndash0988963000 Co 0235674000 0924694000 ndash0006080000 C 1650242000 2605908000 ndash0261710000 C 0606451000 3071372000 0583798000

C ndash0633939000 2891762000 ndash0112192000 C ndash0354070000 2388098000 ndash1431110000 C 1060641000 2182627000 ndash1507942000 H 2701380000 2562827000 ndash0018620000 H 0717262000 3431891000 1595877000 H ndash1615358000 3123686000 0274491000 H ndash1077256000 2190401000 ndash2207047000

- 134 -

H 1601331000 1788686000 ndash2355167000

(d) Transition State 2 η3-benzene (249 kcalmol)

C 5059641000 ndash0675345000 0741440000 C 3868057000 ndash0242461000 1393542000 C 2691208000 ndash0611642000 0796692000 C 1164924000 ndash0568451000 0814993000 C 0001006000 ndash0193010000 1575722000 C ndash1162903000 ndash0569406000 0815406000 C ndash2689168000 ndash0613549000 0797134000 C ndash3866228000 ndash0245076000 1394017000 C ndash5057560000 ndash0678583000 0741882000 C ndash5030442000 ndash1430649000 ndash0426732000 C ndash3802288000 ndash1812828000 ndash1038342000 C ndash2662603000 ndash1392426000 ndash0404590000 C ndash1143695000 ndash1392940000 ndash0383227000 C 0001354000 ndash1885575000 ndash1010384000 C 1146183000 ndash1392203000 ndash0383465000 C 2665098000 ndash1390792000 ndash0404876000 C 3805017000 ndash1810598000 ndash1038596000 C 5032958000 ndash1427555000 ndash0427087000 H 6017043000 ndash0408623000 1174840000 H 3916675000 0338622000 2306082000 H 0001106000 0141040000 2603832000 H ndash3915179000 0335814000 2306664000 H ndash6015116000 ndash0412488000 1175329000

- 135 -

H ndash5963925000 ndash1737868000 ndash0883265000 H ndash3794877000 ndash2406462000 ndash1944276000 H 0001449000 ndash2505619000 ndash1894591000 H 3797948000 ndash2404400000 ndash1944423000 H 5966616000 ndash1734262000 ndash0883606000 Co ndash0000294000 1006304000 0016484000 C 1144150000 2811021000 ndash0317903000 C ndash0001831000 3236912000 0413780000 C ndash1150105000 2808519000 ndash0312717000 C ndash0712506000 2257800000 ndash1588662000 C 0702130000 2259464000 ndash1591918000 H 2174046000 2940434000 ndash0021226000 H ndash0000096000 3693787000 1391408000 H ndash2178919000 2935539000 ndash0011312000 H ndash1360790000 1903514000 ndash2375388000 H 1347563000 1907002000 ndash2381795000

Calculated structures for linear [5]phenylene CpCo (labels from Figures 211 and 212 in Section 24)

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

C ndash2147283000 ndash0385762000 ndash0741520000 C ndash2146881000 ndash0382747000 0740465000 C ndash0675330000 ndash0218887000 0741228000 C ndash0675503000 ndash0222208000 ndash0743565000 C 0535474000 ndash0309864000 ndash1519364000

- 136 -

C 1654024000 ndash0363787000 ndash0743565000 C 1653968000 ndash0359108000 0742223000 C 0535464000 ndash0301263000 1517648000 C 3146303000 ndash0437352000 0715394000 C 3146555000 ndash0442081000 ndash0715839000 H 0537903000 ndash0329735000 2601810000 H 0538062000 ndash0344229000 ndash2603354000 Co ndash1585768000 1444604000 ndash0004763000 C ndash2656365000 3118646000 0813641000 C ndash1264152000 3247968000 1115884000 C ndash0546296000 3292610000 ndash0128221000 C ndash1500173000 3225060000 ndash1199322000 C ndash2801883000 3099872000 ndash0616868000 H ndash3459184000 3033020000 1530368000 H ndash0824887000 3279284000 2101474000 H 0525240000 3366953000 ndash0237713000 H ndash1272392000 3239735000 ndash2254384000 H ndash3732669000 2998753000 ndash1154572000 C ndash3315848000 ndash0698077000 1516941000 C ndash3316515000 ndash0705270000 ndash1515890000 C ndash4404590000 ndash0970491000 0742487000 C ndash4404888000 ndash0974125000 ndash0739677000 H ndash3311463000 ndash0745189000 ndash2599679000 H ndash3310191000 ndash0733014000 2600900000 C ndash5857232000 ndash1346832000 ndash0713671000 C ndash5856902000 ndash1343302000 0718959000 C ndash6992149000 ndash1638138000 ndash1445564000 C ndash6991464000 ndash1630979000 1452826000 C 4314567000 ndash0501395000 ndash1493440000 C 4313844000 ndash0491124000 1494022000

C ndash8157130000 ndash1937355000 ndash0695553000 C ndash8156796000 ndash1933908000 0704865000 H ndash7013569000 ndash1630976000 2537309000 H ndash9075842000 ndash2169721000 1232475000 H ndash9076411000 ndash2175846000 ndash1221548000 H ndash7014707000 ndash1643790000 ndash2530023000 C 5464859000 ndash0553191000 0719930000 C 5465218000 ndash0558312000 ndash0718328000 C 6977989000 ndash0635007000 ndash0714777000 C 6977565000 ndash0629511000 0717833000 H 4313279000 ndash0484164000 2577745000 H 4314609000 ndash0502067000 ndash2577185000 C 8138196000 ndash0684071000 1451266000 C 8139115000 ndash0695400000 ndash1446980000 C 9348946000 ndash0746919000 0699256000 C 9349380000 ndash0752387000 ndash0693700000

- 137 -

H 8162380000 ndash0700716000 ndash2531270000 H 8160717000 ndash0680929000 2535584000 H 10294800000 ndash0791917000 1230058000 H 10295576000 ndash0801571000 ndash1223516000

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

C ndash8026536000 ndash2149127000 ndash0697047000 C ndash6872771000 ndash1801590000 ndash1447012000 C ndash5755909000 ndash1466198000 ndash0717983000 C ndash4305789000 ndash1041476000 ndash0739357000 C ndash3218268000 ndash0750848000 ndash1510952000 C ndash2077793000 ndash0315087000 ndash0749237000 C ndash0550342000 ndash0400850000 ndash0716361000 C 0616872000 ndash0404801000 ndash1489728000 C 1770640000 ndash0412395000 ndash0716060000 C 3300443000 ndash0457807000 ndash0715861000 C 4454767000 ndash0490291000 ndash1489427000 C 5616257000 ndash0520747000 ndash0712496000 C 5616269000 ndash0520699000 0712492000 C 4454793000 ndash0490190000 1489443000 C 3300455000 ndash0457762000 0715895000 C 1770651000 ndash0412347000 0716117000 C 0616894000 ndash0404700000 1489800000 C ndash0550335000 ndash0400796000 0716454000 C ndash2077818000 ndash0315060000 0749341000 C ndash3218306000 ndash0750915000 1510996000

- 138 -

C ndash4305781000 ndash1041534000 0739359000 C ndash5755900000 ndash1466256000 0717962000 C ndash6872758000 ndash1801708000 1446971000 C ndash8026533000 ndash2149171000 0696987000 H ndash6893447000 ndash1807486000 ndash2529846000 H ndash3199702000 ndash0827686000 ndash2591829000 H 0616147000 ndash0415875000 ndash2572166000 H 4455855000 ndash0492565000 ndash2571217000 H 4455901000 ndash0492389000 2571233000 H 0616188000 ndash0415693000 2572238000 H ndash3199790000 ndash0827916000 2591862000 H ndash6893430000 ndash1807681000 2529804000 Co ndash2237895000 1566525000 ndash0000035000 C ndash0770702000 3039808000 0000091000 C ndash1582333000 3276979000 1176306000 C ndash2906316000 3484053000 0731575000 C ndash2906172000 3484095000 ndash0731735000 C ndash1582100000 3277047000 ndash1176233000 H 0281094000 2798829000 0000215000 H ndash1247438000 3209109000 2198999000 H ndash3777291000 3625124000 1353071000 H ndash3777011000 3625160000 ndash1353424000 H ndash1246943000 3209260000 ndash2198847000 H ndash8933230000 ndash2423019000 ndash1224452000 H ndash8933222000 ndash2423113000 1224377000 C 7146943000 ndash0559737000 0717588000 C 7146931000 ndash0559786000 ndash0717614000 C 8302361000 ndash0588480000 1447040000 C 8302337000 ndash0588576000 ndash1447082000 C 9516918000 ndash0618789000 ndash0692883000 C 9516929000 ndash0618742000 0692823000 H 8324450000 ndash0589130000 2529610000 H 10461320000 ndash0642422000 1224406000 H 10461300000 ndash0642481000 ndash1224480000 H 8324409000 ndash0589299000 ndash2529653000

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 139 -

C ndash7810644000 ndash2064896000 ndash0088979000 C ndash6582065000 ndash2396690000 ndash0700394000 C ndash5469369000 ndash1694626000 ndash0259356000 C ndash4011414000 ndash1478684000 ndash0398743000 C ndash2839913000 ndash1679834000 ndash1045300000 C ndash1807973000 ndash0777407000 ndash0523048000 C ndash0288034000 ndash0728447000 ndash0497727000 C 0877200000 ndash0917515000 ndash1257428000 C 2033335000 ndash0625143000 ndash0541547000 C 3550975000 ndash0572504000 ndash0566638000 C 4702932000 ndash0775398000 ndash1323945000 C 5869717000 ndash0493099000 ndash0604711000 C 5877160000 ndash0049178000 0749672000 C 4719648000 0152978000 1509600000 C 3558389000 ndash0127834000 0791889000 C 2041313000 ndash0178303000 0818968000 C 0890228000 0010834000 1576182000

C ndash0275189000 ndash0290874000 0857465000 C ndash1777915000 ndash0332627000 0896504000 C ndash3000252000 ndash0144927000 1576583000 C ndash4087655000 ndash0414543000 0681649000 C ndash5565811000 ndash0681071000 0748878000 C ndash6769777000 ndash0358061000 1349731000 C ndash7902756000 ndash1078577000 0906205000 H ndash6531350000 ndash3165530000 ndash1463988000 H ndash2656944000 ndash2379915000 ndash1852763000

- 140 -

H 0873498000 ndash1259556000 ndash2286041000 H 4697058000 ndash1113491000 ndash2353481000 H 4726794000 0489146000 2539724000 H 0892018000 0335667000 2610226000 H ndash3107471000 0242268000 2582171000 H ndash6863567000 0403771000 2116786000 Co ndash2805901000 1045228000 ndash0126008000 C ndash1966955000 3131745000 ndash0137391000 C ndash3345106000 3172285000 0219040000 C ndash4105003000 2591218000 ndash0859559000 C ndash3194452000 2177424000 ndash1877135000 C ndash1861601000 2475718000 ndash1403791000 H ndash1139494000 3467521000 0469940000 H ndash3757304000 3575577000 1132204000 H ndash5178689000 2478840000 ndash0883920000 H ndash3449207000 1717975000 ndash2819531000 H ndash0944137000 2267497000 ndash1933863000 H ndash8711780000 ndash2586977000 ndash0395882000 H ndash8871888000 ndash0864282000 1346179000 C 7394568000 0005138000 0727783000

C 7387058000 ndash0441388000 ndash0634217000 C 8557433000 0273605000 1404315000

C 8542647000 ndash0629395000 ndash1349402000 C 9760631000 ndash0352464000 ndash0653366000 C 9767843000 0080954000 0667800000 H 8586089000 0612106000 2434348000 H 10716375000 0279405000 1157078000

H 10703753000 ndash0485281000 ndash1174332000 H 8560430000 ndash0966385000 ndash2380163000

(d) Transition state 4 η3-benzene (367 kcalmol)

- 141 -

C 7669717000 ndash2174926000 ndash0105923000 C 6450462000 ndash2458728000 0544003000 C 5349535000 ndash1733337000 0120322000 C 3893688000 ndash1505268000 0269179000 C 2708972000 ndash1942858000 0838638000 C 1596115000 ndash1239419000 0370186000 C 0149218000 ndash1103313000 0368184000 C ndash1061261000 ndash1583264000 0932639000 C ndash2167377000 ndash0965378000 0405284000 C ndash3686709000 ndash0866795000 0409630000 C ndash4872520000 ndash1347856000 0960688000 C ndash5997863000 ndash0728310000 0421450000 C ndash5941471000 0288854000 ndash0586107000 C ndash4758793000 0770529000 ndash1137452000 C ndash3629556000 0150846000 ndash0598044000 C ndash2119390000 0068600000 ndash0617626000 C ndash0945265000 0548559000 ndash1173832000 C 0191709000 ndash0072876000 ndash0643629000 C 1695402000 ndash0118964000 ndash0667389000 C 2835200000 0041396000 ndash1507494000 C 3981535000 ndash0415532000 ndash0796385000 C 5449049000 ndash0747489000 ndash0920326000 C 6638556000 ndash0473422000 ndash1556289000 C 7762417000 ndash1216205000 ndash1122513000 H 6396888000 ndash3209338000 1323030000 H 2647172000 ndash2772334000 1532449000 H ndash1099468000 ndash2356302000 1688990000 H ndash4914534000 ndash2116326000 1720908000 H ndash4717626000 1537921000 ndash1898781000 H ndash0906852000 1317204000 ndash1935050000 H 2849903000 0560387000 ndash2457942000 H 6730568000 0262385000 ndash2346085000 Co 3078365000 1106450000 0223118000 C 2432920000 3235925000 0352954000 C 3805628000 3232135000 ndash0000959000 C 4525686000 2519574000 1027488000 C 3591065000 2151422000 2051886000 C 2287258000 2550618000 1620273000

- 142 -

H 1625110000 3662123000 ndash0222202000 H 4237852000 3652387000 ndash0895767000 H 5588986000 2336674000 1044912000 H 3828106000 1629983000 2966790000 H 1363656000 2417646000 2161607000 H 8562189000 ndash2715853000 0187384000 H 8723754000 ndash1039126000 ndash1591154000 C ndash7467794000 0379383000 ndash0580257000 C ndash7522920000 ndash0639213000 0428535000 C ndash8594261000 0964602000 ndash1089561000 C ndash8706397000 ndash1090617000 0945872000 C ndash9887862000 ndash0485330000 0420145000 C ndash9834353000 0499744000 ndash0555359000 H ndash8574126000 1734202000 ndash1850912000 H ndash10757407000 0931123000 ndash0925119000 H ndash10851990000 ndash0807405000 0796463000 H ndash8770071000 ndash1858056000 1706995000

(e) Local minimum 3 η4-benzene (190 kcalmol)

C ndash7704806000 ndash1625445000 ndash0076324000 C ndash6491455000 ndash1789497000 ndash0801300000 C ndash5352262000 ndash1326936000 ndash0190371000 C ndash3836374000 ndash1127906000 ndash0291559000 C ndash2669014000 ndash1876939000 ndash0775878000 C ndash1540408000 ndash1361850000 ndash0248671000 C ndash0067088000 ndash1219487000 ndash0231176000 C 1147603000 ndash1746746000 ndash0723682000

- 143 -

C 2245517000 ndash1037457000 ndash0289605000 C 3767258000 ndash0910575000 ndash0313273000 C 4961694000 ndash1439625000 ndash0795996000 C 6075343000 ndash0726547000 ndash0354068000 C 5999362000 0418026000 0498208000 C 4804020000 0947684000 0980899000 C 3691158000 0235329000 0538756000 C 2171505000 0121554000 0570963000 C 0990404000 0649716000 1051234000

C ndash0139369000 ndash0066282000 0613306000 C ndash1640889000 ndash0139469000 0665899000 C ndash2708579000 0044357000 1607074000 C ndash3890300000 ndash0515482000 1069631000 C ndash5389479000 ndash0719093000 1106627000 C ndash6553177000 ndash0561696000 1815459000 C ndash7736166000 ndash1034716000 1182797000 H ndash6489929000 ndash2263627000 ndash1775522000 H ndash2743316000 ndash2692464000 ndash1483904000 H 1201969000 ndash2617287000 ndash1364047000 H 5019196000 ndash2306567000 ndash1440440000 H 4747029000 1814065000 1626168000 H 0933710000 1519855000 1692796000 H ndash2640951000 0605584000 2529735000 H ndash6590996000 ndash0122891000 2805220000 Co ndash3231943000 0870639000 ndash0218177000 C ndash2631117000 2925280000 ndash0475333000 C ndash4019450000 2955930000 ndash0137499000 C ndash4720042000 2167067000 ndash1095287000 C ndash3768150000 1717753000 ndash2089396000 C ndash2477085000 2188405000 ndash1710046000 H ndash1832546000 3399891000 0073720000 H ndash4448788000 3419647000 0737399000 H ndash5777018000 1951944000 ndash1095854000 H ndash3999907000 1119290000 ndash2956393000 H ndash1549894000 2013889000 ndash2232360000 H ndash8630326000 ndash1978241000 ndash0517433000 H ndash8683428000 ndash0939767000 1701100000 C 7524401000 0541032000 0473497000

C 7600630000 ndash0607844000 ndash0382149000 C 8637973000 1216338000 0890053000

C 8792152000 ndash1101412000 ndash0836674000 C 9961705000 ndash0402146000 ndash0407106000 C 9887895000 0708141000 0420266000 H 8602106000 2084773000 1535736000 H 10801526000 1207625000 0721410000

H 10931894000 ndash0752974000 ndash0739605000

- 144 -

H 8871661000 ndash1966753000 ndash1482602000

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

C 7143264000 ndash2348493000 0699665000 C 6037664000 ndash1857298000 1448523000 C 4969251000 ndash1391864000 0720257000 C 3582514000 ndash0743198000 0748195000 C 2358402000 ndash0737338000 1512136000 C 1240141000 ndash0634711000 0742222000 C ndash0262684000 ndash0516912000 0716494000 C ndash1428088000 ndash0430968000 1492584000 C ndash2574224000 ndash0346717000 0719319000 C ndash4098679000 ndash0233199000 0715866000 C ndash5251323000 ndash0147278000 1490294000 C ndash6408253000 ndash0063372000 0713741000 C ndash7934932000 0047490000 0717366000 C ndash9088044000 0130556000 1446914000 C ndash10299063000 0217080000 0692638000 C ndash10298939000 0215301000 ndash0693576000 C ndash9087782000 0126841000 ndash1447398000 C ndash7934811000 0045602000 ndash0717417000 C ndash6408180000 ndash0065400000 ndash0713264000 C ndash5251144000 ndash0151514000 ndash1489420000 C ndash4098619000 ndash0235099000 ndash0714599000 C ndash2574142000 ndash0348081000 ndash0717615000 C ndash1428022000 ndash0433439000 ndash1490677000

- 145 -

C ndash0262587000 ndash0517946000 ndash0714342000 C 1239930000 ndash0636111000 ndash0739947000 C 2357013000 ndash0742891000 ndash1511730000 C 3581891000 ndash0749703000 ndash0749006000 C 4968536000 ndash1397444000 ndash0717250000 C 6036190000 ndash1868351000 ndash1443314000 C 7142499000 ndash2353756000 ndash0691900000 H 8003789000 ndash2740125000 1230531000 H 6052031000 ndash1874231000 2531931000 H 2350726000 ndash0802237000 2593967000 H ndash1427931000 ndash0429806000 2574521000 H ndash5251989000 ndash0146640000 2572026000 H ndash9110076000 0132990000 2529448000 H ndash11241535000 0285430000 1223689000 H ndash11241318000 0282253000 ndash1224971000 H ndash9109613000 0126365000 ndash2529940000 H ndash5251637000 ndash0153720000 ndash2571150000 H ndash1427824000 ndash0434279000 ndash2572612000 H 2347832000 ndash0810535000 ndash2593375000 H 6049185000 ndash1893779000 ndash2526553000 H 8002469000 ndash2749449000 ndash1220666000 Co 4148367000 1055016000 ndash0009106000 C 5996101000 2006266000 0022069000 C 5276853000 2480887000 1185002000 C 4085420000 3079352000 0718350000 C 4110596000 3077077000 ndash0745160000 C 5316353000 2474554000 ndash1168669000 H 6921324000 1451094000 0038659000 H 5556549000 2314709000 2212960000 H 3287274000 3477873000 1325692000 H 3334253000 3474398000 ndash1380859000 H 5631980000 2304731000 ndash2185537000

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 146 -

C 4893664000 ndash1209972000 0735005000 C 4893573000 ndash1213475000 ndash0730870000 C 3475382000 ndash0763132000 ndash0743915000 C 3475432000 ndash0760320000 0747049000 C 2260316000 ndash0690973000 1520580000 C 1145205000 ndash0595973000 0744946000 C 1145156000 ndash0599246000 ndash0742744000 C 2260358000 ndash0697381000 ndash1517904000 C ndash0343192000 ndash0479177000 ndash0713609000 C ndash0343168000 ndash0476032000 0715380000 H 2252105000 ndash0735285000 ndash2601934000 H 2251901000 ndash0724154000 2604763000 Co 4601208000 0736083000 ndash0002055000 C 5960130000 2243618000 ndash0721946000 C 4640007000 2540538000 ndash1172530000 C 3804522000 2681992000 ndash0008876000 C 4632302000 2544967000 1160921000 C 5955467000 2247130000 0721276000 H 6816321000 2038808000 ndash1347044000 H 4312673000 2604006000 ndash2199136000 H 2745254000 2890841000 ndash0012873000 H 4298236000 2612143000 2185222000 H 6807361000 2044890000 1353015000 C 6022290000 ndash1649780000 1464200000 C 6022277000 ndash1656609000 ndash1457900000 C 7122289000 ndash2056771000 0719324000 C 7122311000 ndash2060028000 ndash0711126000 H 6027301000 ndash1702610000 2548102000 H 8011576000 ndash2407816000 1233935000 H 8011528000 ndash2413601000 ndash1224115000 H 6027432000 ndash1714310000 ndash2541551000 C ndash1512226000 ndash0382902000 1494684000 C ndash1512274000 ndash0389473000 ndash1493257000 C ndash2658093000 ndash0297761000 0720325000 C ndash2658103000 ndash0300923000 ndash0719236000 H ndash1511446000 ndash0379165000 2578406000

- 147 -

H ndash1511531000 ndash0390614000 ndash2576954000 C ndash4169046000 ndash0190131000 ndash0714237000 C ndash4169015000 ndash0186849000 0714915000 C ndash5325016000 ndash0103295000 1491764000 C ndash5325120000 ndash0110177000 ndash1491395000 C ndash6483203000 ndash0023670000 0713863000 C ndash6483258000 ndash0027061000 ndash0713749000 H ndash5325252000 ndash0101647000 2575308000 H ndash5325471000 ndash0113799000 ndash2574933000 C ndash7997403000 0080746000 0716440000 C ndash7997524000 0076500000 ndash0716680000 C ndash9155096000 0160872000 1448927000 C ndash9155379000 0152083000 ndash1449432000 C ndash10366775000 0240123000 0695134000 C ndash10366925000 0235844000 ndash0695874000 H ndash9178696000 0150122000 ndash2533721000 H ndash11311550000 0297904000 ndash1227155000 H ndash11311298000 0305233000 1226228000 H ndash9178228000 0165001000 2533216000

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

C 8266704000 ndash2005162000 0692734000 C 7088955000 ndash1708719000 1446000000 C 5966603000 ndash1428050000 0716466000

- 148 -

C 4483884000 ndash1054830000 0713802000 C 3355736000 ndash0795879000 1487813000 C 2219848000 ndash0542568000 0715155000 C 0748349000 ndash0122254000 0743952000 C ndash0460068000 ndash0300197000 1509394000 C ndash1583463000 ndash0354552000 0739667000 C ndash3088504000 ndash0455891000 0716671000 C ndash4249167000 ndash0553278000 1491353000 C ndash5399475000 ndash0634011000 0717623000 C ndash6922525000 ndash0754459000 0717051000 C ndash8076029000 ndash0852663000 1446746000 C ndash9285359000 ndash0940991000 0693505000 C ndash9286426000 ndash0927591000 ndash0694047000 C ndash8078221000 ndash0824629000 ndash1447252000 C ndash6923651000 ndash0740632000 ndash0717519000 C ndash5400498000 ndash0620402000 ndash0717994000 C ndash4251528000 ndash0525736000 ndash1491803000 C ndash3089431000 ndash0443610000 ndash0717063000 C ndash1585243000 ndash0344579000 ndash0740307000 C ndash0463450000 ndash0290395000 ndash1513612000 C 0748496000 ndash0127629000 ndash0751652000 C 2219455000 ndash0546002000 ndash0721683000 C 3355860000 ndash0802470000 ndash1493276000 C 4483583000 ndash1057975000 ndash0718022000 C 5966360000 ndash1431783000 ndash0719354000 C 7088265000 ndash1716549000 ndash1447876000 C 8266466000 ndash2008718000 ndash0693595000 H 9183427000 ndash2233531000 1224348000 H 7110060000 ndash1714392000 2528663000 H 3353411000 ndash0803478000 2570367000 H ndash0456292000 ndash0373454000 2590614000 H ndash4248665000 ndash0564171000 2573279000 H ndash8096828000 ndash0865292000 2529266000 H ndash10227269000 ndash1021159000 1223954000 H ndash10229127000 ndash0997490000 ndash1224546000 H ndash8100648000 ndash0816347000 ndash2529785000 H ndash4252664000 ndash0517117000 ndash2573754000 H ndash0464650000 ndash0354640000 ndash2595436000 H 3353541000 ndash0815213000 ndash2575752000 H 7108905000 ndash1727728000 ndash2530504000 H 9182976000 ndash2239822000 ndash1224379000 Co 1060170000 1739352000 ndash0013647000 C 0820599000 3762931000 0679296000 C 2023158000 3250849000 1217023000 C 2833506000 2814255000 0100512000 C 2185795000 3225276000 ndash1129991000

- 149 -

C 0924349000 3753677000 ndash0780133000 H ndash0033478000 4112410000 1239126000 H 2257663000 3114053000 2260457000 H 3791311000 2322414000 0171627000 H 2565428000 3065285000 ndash2126458000 H 0160713000 4098445000 ndash1460120000

(i) Local minimum 1 η4-benzene (190 kcalmol)

C 8767525000 ndash0664628000 0869444000 C 7569070000 ndash0364489000 1586360000 C 6400497000 ndash0535559000 0896308000 C 4872998000 ndash0456407000 0896648000 C 3729258000 ndash0166123000 1633430000 C 2558863000 ndash0367557000 0899969000 C 1050529000 ndash0274920000 0917771000 C ndash0154687000 0103769000 1545183000 C ndash1231288000 ndash0039565000 0606842000 C ndash2736221000 ndash0089835000 0603708000 C ndash3901526000 0467576000 1153370000 C ndash5054648000 ndash0104455000 0647800000 C ndash6579036000 ndash0120351000 0673091000 C ndash7732820000 0402806000 1194768000 C ndash8948594000 ndash0155119000 0702959000 C ndash8958839000 ndash1167887000 ndash0247745000 C ndash7753788000 ndash1707235000 ndash0785423000 C ndash6589806000 ndash1166201000 ndash0307896000

- 150 -

C ndash5063448000 ndash1158179000 ndash0339650000 C ndash3923750000 ndash1713712000 ndash0884954000 C ndash2743411000 ndash1141750000 ndash0370168000 C ndash1264100000 ndash1152263000 ndash0442985000 C ndash0114410000 ndash1509648000 ndash1047872000 C 1001557000 ndash0717865000 ndash0509678000 C 2529242000 ndash0815059000 ndash0456630000 C 3680301000 ndash1106705000 ndash1192448000 C 4847485000 ndash0909766000 ndash0461159000 C 6375435000 ndash0989198000 ndash0464503000 C 7517684000 ndash1280530000 ndash1157992000 C 8743181000 ndash1104009000 ndash0445669000 H 9720775000 ndash0544729000 1371431000 H 7610320000 ndash0024462000 2613574000 H 3742883000 0162901000 2664422000 H ndash0241422000 0534554000 2534230000 H ndash3894210000 1260341000 1890621000 H ndash7746436000 1191936000 1936109000 H ndash9890199000 0223840000 1083439000

H ndash9908180000 ndash1561665000 ndash0592194000 H ndash7783148000 ndash2497305000 ndash1525270000 H ndash3929534000 ndash2506814000 ndash1621099000 H 0005285000 ndash2235278000 ndash1842324000 H 3664139000 ndash1453900000 ndash2217556000 H 7520111000 ndash1625509000 ndash2184413000 H 9677483000 ndash1320445000 ndash0950825000 Co 0245526000 1194775000 ndash0183529000 C ndash0498660000 3223481000 ndash0207100000 C 0902667000 3310487000 0056983000 C 1591310000 2661311000 ndash1009417000 C 0610054000 2243094000 ndash1989593000 C ndash0681576000 2592200000 ndash1494981000 H ndash1289524000 3595536000 0425619000 H 1355880000 3721411000 0946130000 H 2657726000 2519341000 ndash1088515000 H 0823168000 1743521000 ndash2921425000 H ndash1626608000 2403559000 ndash1979282000

(j) Transition state 1 η3-benzene (356 kcalmol)

- 151 -

C ndash8901354000 ndash0223681000 ndash0743434000 C ndash7695103000 0220198000 ndash1360549000 C ndash6531343000 ndash0208573000 ndash0779115000 C ndash5007706000 ndash0207407000 ndash0796109000 C ndash3863247000 0247302000 ndash1433753000 C ndash2690760000 ndash0206508000 ndash0819013000 C ndash1184933000 ndash0153490000 ndash0843116000 C ndash0016095000 0217826000 ndash1588049000 C 1142075000 ndash0155798000 ndash0877497000 C 2665172000 ndash0195830000 ndash0859864000 C 3835813000 0283152000 ndash1437197000 C 4978920000 ndash0204857000 ndash0802474000 C 6505676000 ndash0216574000 ndash0771205000 C 7678527000 0226433000 ndash1319208000 C 8875127000 ndash0251684000 ndash0703235000 C 8845790000 ndash1112691000 0383544000 C 7616005000 ndash1570592000 0948642000 C 6475812000 ndash1107284000 0353147000 C 4945633000 ndash1092812000 0320013000 C 3774824000 ndash1565295000 0903163000 C 2628495000 ndash1080676000 0265289000 C 1119158000 ndash1093642000 0244670000 C ndash0052242000 ndash1637616000 0861793000 C ndash1193959000 ndash1109215000 0331010000 C ndash2676505000 ndash1073633000 0328062000 C ndash3841325000 ndash1514463000 0979035000 C ndash4995446000 ndash1053912000 0371366000 C ndash6522185000 ndash1052982000 0381089000 C ndash7676261000 ndash1483950000 0978498000 C ndash8892512000 ndash1041633000 0378747000

- 152 -

H ndash9850267000 0087677000 ndash1164894000 H ndash7723622000 0856176000 ndash2236504000 H ndash3873085000 0886115000 ndash2307512000 H ndash0031238000 0768624000 ndash2518870000 H 3857949000 0953892000 ndash2286176000 H 7723941000 0897606000 ndash2167700000 H 9831384000 0069893000 ndash1099633000 H 9779177000 ndash1450269000 0819087000 H 7614291000 ndash2243551000 1796930000 H 3751975000 ndash2237828000 1750478000 H ndash0016047000 ndash2343040000 1681308000 H ndash3832680000 ndash2159963000 1847727000 H ndash7691389000 ndash2121828000 1853393000 H ndash9834648000 ndash1354566000 0814012000 Co ndash0004249000 1140918000 0250383000 C 0931445000 3181201000 0326993000 C ndash0487068000 3279997000 0223542000 C ndash1069741000 2607436000 1368652000 C 0008159000 2107122000 2176577000 C 1235098000 2411215000 1492603000 H 1650004000 3565479000 ndash0380430000 H ndash1033454000 3774248000 ndash0564979000 H ndash2124544000 2537255000 1584462000 H ndash0094112000 1572170000 3107766000 H 2227446000 2134637000 1815486000

LUMO

HOMO

2887

239

00862

2496

1163

1382

1418

1312

0

3155

2767

0498

2588

1531

0831

Figure 47 Orbital coefficients of linear [5]phenylene

- 153 -

Figure 48 Top view of the contour plots of (a) the HOMO and (b) the LUMO of the [5]-phenylene ligand

- 154 -

Bad

Bad

Good Good

External cyclobutadiene coordination Internal cyclobutadiene coordination

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCpCoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

Figure 49 Resonance rationale for the increased stability of internal Co coordination in linear [5]phenylene

44 NMR Data for Chapter Two

- 155 -

Figure 410 1H-NMR data for the respective parent phenylene frames experimental (C6D6) and

calculated [NICS (1) B3LYP6-31+G] Assignments by NOESY DEPT HMBC and HSQC as applicable

- 156 -

Me3Si

Me3Si

SiMe3

SiMe3

1

23

4 56

7 89

10 1112

13 1415

16

17

18

Co

222

1490

1252

1450

1433

1151

744

730

11091121

14161504

11211109

1540

1499

1224

1486

217

801

SiMe3

SiMe3

Me3Si

Me3Si

Co

802

261

1484

1256

1433

1494

1155

739

781

1360

1394

269

SiMe3

SiMe3

Co

802

1294

1149

1426

1502

1194

738

779

1363

1393

268

SiMe3

SiMe3

1241

1276

8029

725

1155

1493

1430

1256

1482

222

Co

796

678674 675 796

436

037032662

724 683 747

444

TMS

TMS

TMS

TMS

213

1474

1211

1538

1499

1112

623 685

SiMe3

SiMe3Me3Si

Me3Si SiMe3

SiMe3Me3Si

Me3Si459 Co

589 681 672 745

2201204

15131096

1535

2221252

1480

1433

1149741

801

1501 1490

1475

Figure 411 Comparison of 1H-NMR (blue) and 13C-NMR assignments (C6D6)

NICS-Scan calculations Methods The free ligands were optimized at the B3LYP6-31G and the CpCo complexes at the B3LYPLANL2DZ computational levels Analytical frequency calculations were executed to ensure real minima (Nimag = 0) GIAO-B3LYP6-31+G was used to calculate NICS values The NICS-scan procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (ipc or NICSXY) and out-of-plane components (oopc or NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their interpretation

- 157 -

Since there are no published NICS-scan studies of transition metal complexed cyclic polyenes we benchmark the method with (C6H6)Cr(CO)3

53

Figure 412 NICS-scan of benzene (left) and (benzene)Cr(CO)3 (right)

The shape of the oopc curve suggests that the diamagnetic ring current in the ligand is diminished on complexation although still prevalent Thus at r = 0 Aring (ie at the benzene plane) the oopc value [NICSZZ(0)] of the complex is less negative than that of benzene and the minimum of the curve is less negative and occurs at a larger distance (ndash29911 vs ndash31910) A larger change is observed in the ipc (which is governed by the σ electrons) which shows far more negative values in the complex relative to benzene itself (eg ndash55400 vs ndash5900 and ndash13910 vs ndash0910) Therefore isotropic NICS values are misleading with respect to the diatropism in the complex because they originate largely from the diamagnetic effect of the σ framework NICS-scans for the four-membered ring B in linear [3]phenylene and its CpCo complex are shown below

00 05 10 15 20 25 30 35 40

-34-32-30-28-26-24-22-20-18-16-14-12-10

-8-6-4-202

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

oopc ipc isotropic

pp

m

r

- 158 -

Figure 413 NICS-scan above ring B of linear [3]phenylene (left) and its CpCo complex (right) Inspection of the shape and values of the oopc curve shows that the four-membered ring in the free ligand is strongly paratropic This picture changes on CpCo complexation At or close to the ring plane the values are much less positive (12100 vs 88000) become negative at greater distance and reach a minimum of -16112 Consequently the presence of the metal clearly reduces paratropic character The ipc curve is similar to that of (benzene)Cr(CO)3 Therefore again isotropic NICS values are misleading with respect to an assessment of the size of ring current effects The two isomeric CpCo complexes of linear [5]phenylene as depicted next behave in an analogous manner and engender the same conclusions as above

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

- 159 -

Figure 414 NICS-scans of linear [5]phenylene and its CpCo complexes Top left - ring B of the free ligand Top right - ring B complexed to CpCo Bottom left - ring D of the free ligand

Bottom right - ring D complexed to CpCo The effect of CpCo complexation is also reflected in the NICS-scan properties of the remaining rings To illustrate this point the NICS-scans of the central cyclohexatrienoid ring C of linear [3]phenylene are shown below first for the free ligand then for the cyclobutadiene complex

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

- 160 -

Figure 415 NICS-scans of ring C of linear [3]phenylene Left - as a free ligand Right as a

CpCo complex of the neighboring cyclobutadiene ring B The oopc curve clearly reveals a diminution of paratropism Thus at the ring plane the oopc values of the free ligand and of the complex are 177 and 110 ppm respectively Both plots show shallow and relatively distant minima at ndash3417 and ndash7316 respectively an indication of larger diamagnetic character of the latter While the ipc values also become more negative on complexation this effect is far smaller The tables that follow provide an overview of the NICS-scan results over all component rings in linear [3]- and [5]phenylene complexed and uncomplexed The diagnostic shape of the oopc curve is designated NM for no minimum indicating paratropism and M for minimum indicating diatropism Specific values are given at r = 0 Aring r = 10 Aring and the minimum (if diamagnetic) Table 416 NICS-scan Details of the oopc for Linear [3]Phenylene and its CpCo Complex at

Ring B

Ring Shape oopc00 oopc10 Minimum A M 71 ndash107 ndash11813 AndashCpCo M ndash65 ndash228 ndash22811 B NM 880 381 BndashCpCo M 121 ndash151 ndash16112 C M 177 ndash01 ndash3418 CndashCpCo M 116 ndash17 ndash9315 D NM 880 381 DndashCpCo NM 704 237 E M 71 ndash107 ndash11813 EndashCpCo M 15 ndash148 ndash15212

00 05 10 15 20 25 30 35 40

-8-6-4-202468

101214161820

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-14-12-10

-8-6-4-202468

1012

oopc ipc isotropic

pp

m

r

- 161 -

Table 417 NICS-Scan Details of the oopc for Linear [5]Phenylene and its CpCo Complex at Ring B

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M ndash62 ndash227 ndash22811 B NM 898 396 BndashCpCo M 137 ndash148 ndash15612 C M 176 00 ndash3317 CndashCpCo M 152 ndash09 ndash8415 D NM 846 357 DndashCpCo NM 668 223 E M 164 ndash12 ndash4116 EndashCpCo M 142 ndash17 ndash5315 F NM 846 357 FndashCpCo NM 807 340 G M 176 00 ndash3317 GndashCpCo M 161 ndash04 ndash3216 H NM 898 396 HndashCpCo NM 867 378 I M 83 ndash97 ndash10813 IndashCpCo M 64 ndash109 ndash12113

Table 418 NICS-scan Details of the oopc for Lnear [5]Phenylene and its CpCo Complex at

Ring D

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M 19 ndash150 ndash15912 B NM 898 396 BndashCpCo NM 717 256 C M 176 00 ndash3317 CndashCpCo M 110 ndash122 ndash12210 D NM 846 357 DndashCpCo M 151 ndash169 ndash17311 E M 164 ndash12 ndash4116 EndashCpCo M 151 ndash169 ndash17311 F NM 846 357 FndashCpCo NM 685 231 G M 176 00 ndash3317 GndashCpCo M 148 ndash15 ndash5415 H NM 898 396 HndashCpCo NM 850 370

I M 83 ndash97 ndash10813

- 162 -

The data clearly show that on CpCo complexation the paramagnetic ring current contributions decrease (or the diamagnetic ring current contributions increase) The strongest effect is on the complexed cycle but it occurs for all rings even the most remote (eg I in the linear [5]phenylene complexed at ring B) Thus upon complexation the paratropic (and by inference antiaromatic) character of the phenylenes decrease 45 Experimental Section for Chapter Three Angular [3]phenylene 2290 angular [4]phenylene 17111 and [7]heliphene10 were prepared according to the literature Ni(COD)(PMe3)2

112 To a solution of Ni(COD)2 (0275 g 10 mmol) in dry and vigorously degassed THF (10 mL) PMe3 (020 mL 0150 g 20 mmol) was added via syringe in a single portion After stirring at RT for 24 h the mixture was transferred using a canula and filtered under Ar to remove unreacted starting material The solvent was removed on the high vacuum line and the resulting product dried for 3 h It is extremely air sensitive and must be manipulated under an inert atmosphere at all times Yellow solid (0306 g 96 ) 1H-NMR (400 MHz C6D6) δ = 412 (d J = 112 Hz 4 H) 238 (br t J = 52 Hz 4 H) 225 (t J = 52 Hz 4 H) 102 (d J = 32 Hz 18 H) ppm 31P-NMR (162 MHz C6D6) δ = ndash946 (s) ppm Adducts of diphenylacetylene 88 to angular [3]phenylene 22 ndash compounds 89 and 90

In a glove box an Ace pressure tube was charged with angular [3]phenylene 22 (0014 g 006 mmol) diphenylacetylene 88 (0098 g 0055 mmol) THF (5 mL) and Ni(COD)(PMe3)2 (70 microL 008 M in THF 0006 mmol) The reaction vessel was tightly sealed removed from the glovebox and heated to 75ndash80 oC (oil bath) for 23 h After cooling to RT the solvent was removed by rotary evaporation and the residue purified by flash chromatography on silica gel using gradient elution (101 and then 81 hexaneCH2Cl2) After a small amount of angular [3]phenylene 22 (0001 g) the monoadduct 89 (0004 g 20 ) eluted to give a yellow solid mp 195ndash196 degC 1H-NMR (500 MHz CDCl3) δ = 853 (d J = 84 Hz 1 H) 831 (d J = 80 Hz 1 H) 755 (ddd J = 16 64 80 Hz 1 H) 740ndash732 (m 2 H) 725ndash715 (m 6 H) 715ndash711 (m 2 H) 708 (d J = 65 Hz 2 H) 704 (d J = 80 Hz 1 H) 648 (t J = 72 Hz 1 H) 643 (d J = 70 Hz 1 H) 624 (t J = 75 Hz 1 H) 401 (d J = 70 Hz 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1525 15101 15096 1495 1399 13883 13879 1342 1320 1312

- 163 -

13083 13075 1282 1280 1277 1276 1275 1268 1266 1265 1264 1250 1235 1223 1179 1164 1156 ppm one peak in the region δ = 128ndash126 ppm is

presumed to be accidentally isochronous IR (KBr) ν~ = 3060 1490 1481 1442 1415 1159 1072 755 734 698 cmndash1 UV-Vis (CH3CN) λmax (log ε) 233 (442) 265 (450) 278 (sh) 294 (sh) 306 (447) 318 (449) 329 (sh) 380 (344) 399 (366) 420 (366) nm MS (70 eV) mz () 405 [M++1] (35) 404 [M+] (100) 326 (13) HRMS (EI) calcd for C32H20 4041565 found 4041571 Elemental analysis calcd for C32H20 C 9502 H 498 found 9479 460 Subsequent elution furnished 5678-tetraphenylpicene (90) (0009 g 59 ) as a white solid mp 325ndash327 degC the molecule exhibits hindered rotation of the 67-phenyl groups on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 891 (s 2 H) 885 (d J = 84 Hz 2 H) 769 (ddd J = 28 52 80 Hz 2 H) 750ndash744 (m 4 H) 744ndash732 (m 4 H) 720 (tt J = 16 72 Hz 2 H) 696 (dt J = 08 76 Hz 2 H) 689 (tt J = 09 76 Hz 2 H) 662 (br s 4 H) 617 (d J = 76 Hz 2 H) 607 (br s 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1403 1401 1377 1367 1335 1325 1324 1306 1300 1295 1292

1283 1277 1269 1264 1263 1262 1256 1254 1228 1213 ppm IR (KBr) ν~ = 3051 2922 1599 1490 1467 1442 1263 1072 1027 758 702 630 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (461) 307 (474) 352 (417) 366 (414) nm MS (70 eV) mz () 583 [M++1] (52) 582 [M+] (100) 505 (24) 504 (9) 426 (7) HRMS (EI) calcd for C46H30 5822348 found 5822336 1278-Tetraphenylbenzo[c]chrysene (91)

In a glovebox an Ace pressure tube was charged with 88 (0020 g 0050 mmol) diphenylacetylene 88 (0026 mg 0148 mmol) Ni(COD)(PMe3)2 (62 microL of a 008 M solution in THF) and THF (5 mL) The reaction vessel was sealed removed from the glovebox and heated to 85 degC for 39 h After removal of the solvent the residue was purified by flash chromatography on silica gel (eluting with 81 hexaneCH2Cl2) producing a white solid (0023 g) which was found to consist of starting material (88 18 mg) 90 (0001 g 6 ) and 91 Further purification by chromatography afforded pure 91 (0017 g 74 ) as a white solid mp 273ndash274 degC the 12-phenyl groups of 91 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 869 (d J = 95 Hz 1 H) 830ndash822 (m 1 H) 801 (d J = 75 Hz 1 H) 780ndash747 (m 2 H) 770 (ddd J = 10 70 85 Hz 1 H) 762 (dt J = 15 75 Hz 1 H) 753 (ddd J = 15 70 85 Hz 1 H) 738ndash732 (m 2 H) 730 (td J = 15 75 Hz 1 H) 729ndash722 (m 6 H) 722ndash717 (m 2 H) 717ndash710 (m 2 H) 710ndash695 (m 3 H) 680ndash640 (m 3 H) 635 (d J = 70 Hz 1 H) 623ndash595 (br s 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1418 1400 1395 1394 1378 1377 1375 1357 1323 1322 1316 1314 13113 13107 1309 1308 1307 1305 1296 1295 1288 1282 1277 1275 1274 1273 1270 12653 12647 1264 1260 1256 1253 1252 1251

- 164 -

1243 1231 1208 ppm due to extensive signal overlap four peaks are presumed to be isochronous in the regions δ = 132ndash130 and 128ndash125 ppm IR (KBr) ν~ = 3058 1601 1489 1442 1263 1073 773 762 736 699 628 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 250 (487) 313 (511) 340 (sh) nm MS(EI) mz () 583 (M++1 72) 582 (M+ 100) 505 (24) 391 (13) HRMS (EI) calcd for C46H30 5822348 found 5822341 Elemental analysis calcd for C46H30 C 8933 H 500 found 8914 493 Ni(PhCequivCPh)(PMe3)2 (92)91

In a glove box PMe3 (203 microL 0152 g 20 mmol) was mixed with a suspension of Ni(COD)2 (0275 g 10 mmol) in hexane (15 mL) Diphenylacetylene 88 (0178 g 10 mmol) was then added in one portion resulting in an immediate color change from yellow to red The mixture was stirred at room temperature for 195 h during which the color gradually turning returning to yellow Upon concentration (to ~5 mL) a yellow precipitate formed collected by filtration under nitrogen The resulting powder 92 (0370 g 95 ) was dried under vacuum providing a yellow solid 1H-NMR (500 MHz C6D6) δ = 751 (d J = 75 Hz 4 H) 717 (t J = 75 Hz 4 H) 702 (t J = 75 Hz 2 H) 101 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1406 1287 1279 196 (d JC-P = 188 Hz) ppm 31P-NMR (162 MHz C6D6) δ = ndash1282 (br s) ppm Adducts of 3-hexyne to angular [3]phenylene 22 ndash compounds 104 and 105

In a glovebox 22 (0014 mg 0060 mmol) 3-hexyne 103 (57 microL 0004 g 0050 mmol) Ni(COD)(PMe3)2 (0002 g 0005 mmol) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 14 h Flash chromatography on silica gel gave a first fraction that was recrystallized from CH2Cl2 to provide pure 104 (70 mg 45 ) as a yellow solid mp 169ndash170 degC 1H-NMR (500 MHz CDCl3) δ = 843 (d J = 70 Hz 1 H) 821 (d J = 75 Hz 1 H) 795 (d J = 70 Hz 1 H) 752 (dt J = 10 70 Hz 1 H) 748 (dt J = 10 70 Hz 1 H) 697 (d J = 75 Hz 1 H) 673ndash662 (m 3 H) 655 (d J = 55 Hz 1 H) 307 (q J = 75 Hz 2 H) 299 (q J = 75 Hz 2 H) 133 (t J = 75 Hz 3 H) 130 (t J = 75 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1530 1516 1504 1471 1360 1330 13129 13127 1307 1282 1279 1267 1263 1259 1246 1239 1228 1179 1159 1156 232 214 164 149 ppm IR (KBr) ν~ = 3045 2960 1600 1481 1414 1261 1197 1159 758 740 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (463) 299 (sh) 309 (460) 320 (462) 331 (452) 380 (356) 399 (374) 419 (371) nm MS (70 eV) mz () 309 [M++1] (26) 308 [M+] (100) 293 [M+ndash15] (8) 278 [M+ndash30] (21) HRMS (EI) calcd for C24H20 3081565 found 3081666

- 165 -

A second fraction was 105 (0002 g 11 ) isolated as a yellow solid mp 120ndash122 degC 1H-NMR (400 MHz CDCl3) δ = 830 (d J = 72 Hz 1 H) 797 (d J = 76 Hz 1 H) 761 (d J = 80 Hz 1 H) 761ndash749 (m 2 H) 700 (d J = 80 Hz 1 H) 699 (d J = 72 Hz 1 H) 674 (quint J = 76 Hz 2 H) 658 (d J = 64 Hz 1 H) 307 (q J = 76 Hz 2 H) 302 (q J = 76 Hz 2 H) 132 (t J = 76 Hz 3 H) 131 (t J = 76 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1525 1519 1489 1472 1356 1345 1324 1318 1288 1283 1279 1273 1259 1252 1251 1250 1241 1179 1165 1160 2213 2205 149 146 ppm IR (KBr) ν~ = 3063 2958 2925 1490 1442 1417 1262 1147 1099 822 762 730 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 281 (434) 291 (448) 303 (460) 313 (sh) 369 (346) 389 (373) 410 (377) nm MS (70 eV) mz () 309 [M++1] (28) 308 [M+] (100) 293 [M+ndash15] (13) 278 [M+ndash30] (21) 226 (22) 149 (29) HRMS (EI) calcd for C24H20 3081565 found 3081664 Adducts of 14-dimethoxy-2-butyne to angular [3]phenylene 22 ndash compounds 107 and 108

In a glovebox 22 (0011 g 0050 mmol) 14-dimethoxybut-2-yne 106 (0034 g 030 mmol) Ni(COD)(PMe3)2 (63 microL of a 008 M solution in THF) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 165 h The 1H-NMR spectrum of the crude indicated the formation of 107 and 108 in the ratio of 61 Flash chromatography on silica gel gave first 107 (0012 g 68 ) as a yellow solid mp 150ndash151 degC 1H-NMR (400 MHz CDCl3) δ = 841 (dd J = 32 64 Hz 1 H) 819 (d J = 80 Hz 1 H) 810 (dd J = 36 64 Hz 1 H) 754 (dd J = 36 64 Hz 2 H) 700 (d J = 80 Hz 1 H) 676 (t J = 64 Hz 1 H) 674ndash665 (m 2 H) 656 (d J = 60 Hz 1 H) 493 (s 2 H) 488 (s 2 H) 353 (s 3 H) 345 (s 3 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1527 1513 1509 1484 1336 1318 1316 1309 1296 1283 1282 1272 1270 1259 1255 1238 1225 1183 1166 1161 677 675 584 575 ppm IR (KBr) ν~ = 3072 2927 1485 1446 1417 1376 1185 1097 956 898 821 743 730 cmndash1 MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (100) 308 [M+ndash38] (26) 293 (34) 280 (15) 265 (44) HRMS (EI) calcd for C24H20O2 3401463 found 3401466 Further elution provided 108 (0002 g 9 ) as a yellow solid mp 156ndash157 degC 1H-NMR (400 MHz CDCl3) δ = 831ndash824 (m 1 H) 813ndash806 (m 1 H) 775 (d J = 80 Hz 1 H) 763ndash756 (m 2 H) 702 (d J = 80 Hz 1 H) 699 (d J = 64 Hz 1 H) 681ndash670 (m 2 H) 660 (d J = 64 Hz 1 H) 493 (s 2 H) 487 (s 2 H) 353 (s 3 H) 351 (s 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1523 1517 1505 1470 1327 1322

- 166 -

1316 1315 1297 1285 1282 1276 1268 1266 12564 12555 1252 1181 1168 1165 6804 6801 5838 5835 ppm IR (KBr) ν~ = 2925 1498 1415 1379 1262 1187 1095 1061 940 930 814 750 734 717 cmndash1 UV-Vis (CH3CN) λmax (log ε) 237 (458) 287 (462) 298 (472) 314 (sh) 371 (357) 387 (380) 407 (386) nm MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (56) 308 [M+ndashMeOH] (8) 293 (27) 279 (17) 265 (24) HRMS (EI) calcd for C24H20O2 3401463 found 3401456 Optimized cycloaddition reaction between 22 and 88 In a glovebox a round bottom flask was charged with 22 (0058 g 0257 mmol) and Ni(COD)(PMe3)2 (0008 g 0034 mmol) Both reagents were then dissolved in THF (100 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0093 g 0521 mmol) in THF (20 mL) was taken up in a gas-tight syringe and slowly added over 13 h via syringe pump to the boiling mixture of 22Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 6 h After this time mixture was cooled to RT and the solvent removed by rotary evaporation to give a yellow residue The crude product was passed through a plug of silica gel eluting with a mixture of hexanesCH2Cl2 (101) to afford a yellow solid Analysis of the product by 1H-NMR (using the solvent peak of CDCl3 as the internal standard) revealed the presence of 89 and 90 in a 1387 ratio Adducts of diphenylacetylene 88 to angular [4]phenylene 17 ndash compounds 130ndash134 In a glovebox angular [4]phenylene 17 (0036 g 012 mmol) diphenylacetylene 88 (0018 g 010 mmol) and Ni(COD)(PMe3)2 (125 microL of a 008 M solution in THF) were added to an Ace pressure tube and dissolved in THF (6 mL) The reaction vessel was sealed removed from the glovebox and stirred at 75 degC for 5 h Flash chromatography

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph Ph PhPh Ph

132131

133 134

130

- 167 -

on silica gel gave starting material (0013 g of 17) as well as a yellow residue Further purification of the latter by preparative TLC afforded (in order of elution) 132 131 133 134 and 139 Compound 130 (0008 g 28 ) was obtained as a white solid mp 360ndash363 degC (decomp) the phenyl groups located on the central benzene ring of 130 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 904 (d J = 90 Hz 2 H) 895 (d J = 90 Hz 2 H) 881 (d J = 85 Hz 2 H) 765 (ddd J = 15 65 80 Hz 2 H) 742ndash736 (m 4 H) 734 (dd J = 10 85 Hz 2 H) 721 (tt J = 15 75 Hz 2 H) 716 (d J = 75 Hz 2 H) 698 (dd J = 05 80 Hz 2 H) 693 (tt J = 10 85 Hz 2 H) 681 (tt J = 10 70 Hz 2 H) 676 (t J = 75 Hz 4 H) 656 (t J = 70 Hz 4 H) 633 (d J = 70 Hz 4 H) 614 (d J = 75 Hz 2 H) 595 (d J = 70 Hz 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 14058 14057 1403 1394 1375 1374 1345 1341 1336 1327 1324 1309 1308 1301 1294 1292 1282 1276 1268 1263 12622 12619 1259 1257 1254 1250 1227 1214 1212 ppm IR (KBr) ν~ = 3052 2923 1600 1491 1440 1261 1076 1029 809 783 759 747 700 631 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 248 (498) 306 (sh) 329 (520) 388 (463) nm MS(FAB) mz () 836 [M++2] (18) 835 [M++1] (42) 834 [M+] (54) 757 (8) HRMS (FAB) calcd for C66H42 8343287 found 8343280 Compound 131 (0003g 6) was isolated as yellow solid mp 251ndash253 degC (decomp) 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 775 (dt J = 10 80 Hz 1 H) 752 (dt J = 10 80 Hz 1 H) 746 (d J = 80 Hz 1 H) 737 (d J = 65 Hz 1 H) 726ndash721 (m 5 H) 721ndash716 (m 2 H) 716ndash711 (m 5 H) 709 (t J = 75 Hz 1 H) 705 (d J = 80 Hz 1 H) 699 (d J = 70 Hz 1 H) 619 (d J = 60 Hz 1 H) 614 (d J = 60 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1502 1492 1491 1490 1485 1444 1394 1392 1382 1371 1367 1351 13271 13268 13092 13088 1299 12898 12896 1283 12764 12760 1274 12654 12652 1261 1253 1245 1195 1184 1172 1138 1129 ppm one peak is presumed to be accidentally isochronous in the region between δ = 130ndash124 ppm IR (KBr) ν~ = 3023 2921 1602 1478 1371 1262 1026 809 795 748 725 695 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 252 (473) 285 (456) 320 (453) 335 (462) 353 (437) 370 (432) 410 (376) 431 (372) nm MS (FAB) mz () 479 [M++1] (27) 478 [M+] (70) 300 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781718 Molecule 132 (0002 g 5 ) was acquired as a yellow solid 1H-NMR (500 MHz CDCl3) δ = 726ndash721 (m 2 H) 716ndash709 (m 6 H) 695ndash690 (m 2 H) 676 (d J = 80 Hz 2 H) 673 (d J = 75 Hz 2 H) 671 (t J = 75 Hz 2 H) 665 (t J = 70 Hz 2 H) 658 (d J = 65 Hz 2 H) 648 (d J = 65 Hz 2 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1516 1510 1497 1490 1391 1372 1310 1303 1283 1281 1277 1275 1273 1264 1216 1168 1163 ppm UV-Vis (CH2Cl2) λmax (log ε) 254 (476) 294 (sh) 300 (465) 322 (sh) 338 (392) 376 (400) nm MS (FAB) mz () 479 [M++1] (50) 478 [M+] (86) 391 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781723 Adduct 133 (0017 g 33 ) was isolated as a red crystalline solid mp 290ndash291 degC 1H-NMR (500 MHz CDCl3) δ = 800 (d J = 80 Hz 2 H) 720ndash713 (m 6 H) 708ndash702 (m 4 H) 690 (d J = 80 Hz 2 H) 648 (t J = 70 Hz 2 H) 642 (d J = 70 Hz 2 H) 623 (t J = 70 Hz 2 H) 393 (d J = 70 Hz 2 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1522 1509 1506 1496 1392 1359 1315 1309 1282 1278 1277 1266 1250 1232 1181 1166 1157 ppm IR (KBr) ν~ = 3057 1489 1441 1412 1273

- 168 -

1161 810 738 709 690 623 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 271 (474) 285 (469) 345 (460) 353 (454) 414 (483) 432 (381) 460 (363) nm MS (70 eV) mz () 479 [M++1] (46) 478 [M+] (100) 400 (10) HRMS (EI) calcd for C38H22 4781722 found 4781719 Compound 134 (0009 g 27 ) was obtained as a yellow solid mp 178ndash180 degC the phenyl groups of this molecule located at the bay regions of the phenanthrene subunit are static while the others exhibit hindered rotation on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 880 (d J = 88 Hz 1 H) 879 (d J = 88 Hz 1 H) 863 (d J = 92 Hz 1 H) 834 (d J = 80 Hz 1 H) 770ndash758 (m 1 H) 748ndash732 (m 4 H) 727ndash721 (m 2 H) 721ndash710 (m 2 H) 706 (d J = 80 Hz 1 H) 702ndash691 (m 3 H) 684 (t J = 74 Hz 1 H) 673 (br s 2 H) 655 (t J = 76 Hz 2 H) 650ndash638 (m 3 H) 630ndash610 (m 4 H) 590 (d J = 76 Hz 2 H) 410 (d J = 68 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1527 1510 1509 1494 1403 1400 1399 1396 1373 1371 1339 1335 1330 1325 1324 1317 1309 1306 1305 1304 1299 1295 1291 1283 1282 1281 1277 1275 1272 1269 1268 12632 12627 1261 12562 12556 1254 1253 1239 1226 1216 1209 1180 1162 1154 ppm three peaks are presumed to be accidentally isochronous in the region δ = 128ndash125 ppm IR (KBr) ν~ = 2964 1262 1096 1022 801 701 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 267 (501) 303 (497) 335 (489) 361 (sh) 379 (464) 427 (402) 456 (377) nm MS(FAB) mz () 658 [M++2] (22) 657 [M++2] (67) 656 [M+] 1(00) 579 (12) 502 (7) HRMS (FAB) calcd for C52H32 6562504 found 6562492 Cycloaddition reaction between [7]heliphene 142 and diphenylacetylene 88 In a glovebox a round bottom flask was charged with 142 (0008 g 0152 mmol) and Ni(COD)(PMe3)2 (0001 g 0003 mmol) The mixture was then dissolved in THF (25 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0016 g 300 mmol) in THF (10 mL) was taken up in a gas-tight syringe and slowly added over 12 h via syringe pump to the boiling mixture of 142Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 12 h After this time it was cooled to RT and the solvent removed by rotary evaporation to give an orange residue The crude product was chromatographed on silica gel (25 x 165 cm) eluting first with hexaneCH2Cl2 (101 then 51) The first product collected was diphenylacetylene 88 (0005 g) followed by a yellow band Analysis of the isolated yellow solid (0002 g) revealed a large mixture of products MS(FAB) mz () 532 (70) 664 (25) 700 (13) 732 (16) 911 (21) 1056 (11) 1234 (4) 1412 (5) 46 Computational Details for Chapter Three All geometries of intermediates and transition states were optimized fully without symmetry constraints using the Gaussian 03 program100 The DFT computations were carried out using the B3LYP functional as implemented in Gaussian The nickel atom was described by a double-zeta basis set (LANL2DZ)113 and the 6-31G(d) basis set114

- 169 -

was used for the other elements Frequency calculations were performed to confirm the nature of the stationary points and to obtain zero-point energies (ZPE) The connectivity between stationary points was established by intrinsic reaction coordinate calculations (IRC) The Chemcraft program102 was used to draw the calculated structures

47 References

1) Harvey R G Polycyclic Aromatic Hydrocarbons Wiley-VCH New York 1997 2) (a) Chem Rev 2001 101 1115ndash1566 Special Issue Aromaticity (b) Chem Rev

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Chem 2002 67 1333 (b) Stanger A Chem Commun 2009 1939 4) (a) Minkin V I Glukhovtsev M N Simkin B Ya Aromaticity and Antiaromaticity

Electronic and Structural Aspects Wiley New York 1994 pp 63ndash74 (b) Garratt P J Aromaticity Wiley New York 1986 pp 30ndash34 93ndash95

5) (a) Wu J Muumlllen K In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 3 pp 90ndash139 (b) Wu J Pisula W Muumlllen K Chem Rev 2007 107 718 (c) Handbook of Organic Electronics and Photonics Nalwa H S Ed American Scientific 2008

6) Miljanić O Š Vollhardt K P C In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 4 pp 140ndash197

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Chem Rev 2005 105 3842 and the references therein (b) Steinmann S N Jana D F Wu J I-C Schleyer P v R Mo Y Corminboeuf C Angew Chem Int Ed 2009 48 9828

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Jenneskens L W Tetrahedron Lett 1994 35 4405 18) (a) Linear [3]phenylene Dosa P I Schleifenbaum A Vollhardt K P C Org Lett

2001 3 1017 (b) Angular [3]phenylene Matzger A J Vollhardt K P C Chem Commun 1997 1415 (c) Angular [4]phenylene Dosa P I Gu Z Hager D Karney W L Vollhardt K P C Chem Commun 2009 1967

19) Perthuisot C Edelbach B L Zubris D L Simhai N Iverson C N Muumlller C Satoh T Jones W D J Mol Catal A 2002 189 157

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21) (a) Deniz A A Peters K S Snyder G J Science 1999 286 1119 (b) Fattahi A Lis L Tian Z Kass P S Angew Chem Int Ed 2006 45 4984 (c) Bally T Angew Chem Int Ed 2006 45 6616

22) Anslyn E Dougherty D Modern Physical Organic Chemistry University Science Books Palo Alto 2006

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24) Mestdagh H Postdoctoral Research Report University of California Berkeley 1986

25) Hirthammer M Vollhardt K P C J Am Chem Soc 1986 108 2481 26) Blanco L Helson H E Hirthammer M Mestdagh H Spyroudis S Vollhardt K

P C Angew Chem Int Ed Engl 1987 26 1246 27) Berris B C Hovakeemian G H Lai Y-H Mestdagh H Vollhardt K P C J

Am Chem Soc 1985 107 5670 28) Dosa P I The Chemistry of Angular and Linear [N]Phenylenes PhD Thesis

University of California Berkeley 2002 29) Diercks R Eaton B E Guumlrtzgen S Jalisatgi S Matzger A J Radde R H

Vollhardt K P C J Am Chem Soc 1998 120 8247 30) (a) Nambu M Siegel J S J Am Chem Soc 1988 110 3675 (b) Nambu M

Hardcastle K Baldridge K K Siegel J S J Am Chem Soc 1992 114 369 31) Nambu M Mohler D L Hardcastle K Baldridge K K Siegel J S J Am

Chem Soc 1993 115 6138 32) Kumaraswamy S Jalisatgi S S Matzger A J Miljanić O Š Vollhardt K P C

Angew Chem Int Ed 2004 43 3711 33) (a) Eisch J J Piotrowski A M Han K I Kruumlger C Tsay Y H Organometallics

1985 4 224 (b) Schwager H Spyroudis S Vollhardt K P C J Organometallic Chem 1990 382 191

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35) Doumltz K H Jahr H C Chem Rec 2005 4 61 36) Gridnev I D Coord Chem Rev 2008 252 1798 37) Eickmeier C Holmes D Junga H Matzger A J Scherhag F Shim M

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38) Groszligmann T N Haptotropism in Linear Phenylene Complexes Diplomarbeit Thesis University of California Berkeley 2004

39) Dinculear photothermal haptotropic systems Tsuchiya K Ideta K Mogi K Sunada Y Nagashima H Dalton Trans 2008 2708 and the references therein

40) Additive assisted photothermal haptotropic systems (a) Jahr H C Nieger M Doumltz H K Chem Eur J 2005 11 5333 d) Herbert D E Tanabe M Bourke S C Lough A J Manners I J Am Chem Soc 2008 130 4166 e) Ieong N S Manners I J Organomet Chem 2008 693 802 and references therein

41) (a) Zhu G Tanski T M Churchill D G Janak K E G Parkin G J Am Chem Soc 2002 124 13658 (b) Zhu G Pang G Parkin G J Am Chem Soc 2008 130 1564

42) Selected reviews of photobased devices and molecular switches (a) Balzani V Credi A Venturi M Chem Soc Rev 2009 38 1542 (b) Kay E R Leigh D A Zerbetto F Angew Chem Int Ed 2007 46 72 (c) Photochromism Molecules and Systems Duumlrr H Bouas-Laurent H Eds Elsevier Amsterdam 2003 (d) Feringa B Molecular Switches Wiley-VCH Weinheim 2001

43) (a) a) Photofunctional Transition Metal Complexes Yam V W W Ed Springer Berlin 2007 b) Coppens P Novozhilova I Kovalevsky A Chem Rev 2002 102 861 c) Guumltlich P Garcia Y Woike T Coord Chem Rev 2001 219ndash221 839

44) (a) Lambert J B Mazozola E P Nuclear Magnetic Resonance Spectroscopy An Introduction to Princples Applications and Experimental Methods Pearson Education Upper Saddle River 2004 (b) Berger S Braun S 200 and More NMR Experiments A Practical Course Wiley-VCH Weinheim 2004 (c) Friebolin H Basic One- and Two-Dimensional NMR Spectroscopy 4th edition Wiley-VCH Weinheim 2005

45) (a) Schulman J M Disch R L J Phys Chem A 2003 107 5223 (b) Schulman J M Disch R L J Am Chem Soc 1996 118 8470 and the references cited therein

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48) Hillard III R L Vollhardt K P C J Am Chem Soc 1977 99 4058 49) Berris B C Lai Y-H Vollhardt K P C J Chem Soc Chem Commun 1982

953 50) (a) Rausch M D Genetti R A J Org Chem 1970 35 3888 (b) Hart W P

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2516 (b) Wolfart V Ramming M Gleiter R Nuber B Pritzkow H Rominger F Eur J Inorg Chem 1999 499 (c) Mitchell R H Chen Y Khalifa N Zhou P J Am Chem Soc 1998 120 1785 (d) McGlinchey M J Burns R C Hofer R Top S Jaouen G Organometallics 1986 5 104

53) Feixas F Jimeacutenez-Halla J O C Matito E Poater J Solagrave M Pol J Chem

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2007 81 783 54) (a)Stanger A J Org Chem 2006 71 883 (b) Stanger A Chem Eur J 2006 12

2745 (c) Tsipis A C Phys Chem Chem Phys 2009 11 8244 (d) Stanger A Chem Commun 2009 1939

55) For very recent literature compilations of theoretical (and experimental) treatments of haptotropism in arene metal complexes see a) Joistgen O Pfletschinger A Ciupka J Dolg M Nieger M Schnakenburg G Froumlhlich R Kataeva O Doumltz K H Organometallics 2009 28 3473 b) Pfletschinger A Dolg N J Organomet Chem 2009 694 3338 c) Jimeacutenez-Halla J O C Robles J Solagrave M Organometallics 2008 27 5230 d) Kirillov E Kahlal S Roisnel T Georgelin T Saillard J-Y Carpentier J-F Organometallics 2008 27 387 and references therein

56) Jimeacutenez-Halla J O C Robles J Solagrave M J Phys Chem A 2008 112 1202 57) Oprunenko Y Gloriozov I Lyssenko K Malyugina S Mityuk D Mstislavsky

V Guumlnther H von Firks G Ebener M J Organomet Chem 2002 656 27 58) Muumlller J Gaede P E Qiao K J Organomet Chem 1994 480 213 59) Bianchini C Caulton K G Chardon C Doublet M L Eisenstein O Jackson

S A Johnson T J Meli A Peruzzini M Streib W E Vacca A Vizzat F Organometallics 1994 13 2010

60) (a) De Boer E Van Willigen H V Prog Nuc Mag Res Spec 1967 2 111 (b) Memory J D Wilson N K NMR of Aromatic Compounds Wiley-VCH New York 1982

61) (a) Poli R Chem Rev 1996 96 2135 and the references cited therein (b) Schroumlder D Shaik S Schwartz H Acc Chem Res 2000 33 139 (c) Harvey J N Poli R Smith K M Coord Chem Rev 2003 237 347 and the references cited therein

62) For computational examples of 16 electron triplet Cp cobalt species influencing cobalt-mediated reactions see (a) Siegbahn P E M J Am Chem Soc 1996 118 1487 (b) Poli R Smith K M Eur J Inorg Chem 1999 877 (c) Carreoacuten-Macedo J-L Harvey J N J Am Chem Soc 2004 126 5789 (d) Petit A Richard P Cacelli I Poli R Chem Eur J 2006 12 813 (e) Aubert C Betschmann P Eichberg M J Gandon V Geny A Heckrodt T J Lehmann J Malacria M Masjost B Paredes E Vollhardt K P C Whitener G D Chem Eur J 2007 13 7443 (f) Gandon V Agenet N Vollhardt K P C Malacria M Aubert C J Am Chem Soc 2009 131 3007

63) Illustrative examples (a) Olson W L Stacy A M Dahl L F J Am Chem Soc 1986 108 7646 (b) Wadepohl H Galm W Pritzkow H Wolf A Chem Eur J 1996 2 1453 (c) Knijnenburg W Hetterscheid D Kooistra T M Budzelaar P H M Eur J Inorg Chem 2004 1204

64) Benito-Garagorri D Bernskoetter W H Lobkovsky E Chirik P J Organometallics 2009 28 4807

65) Fox J P Ramdhanie B Zareba A A Czernuszewicz R S Goldberg D P Inorg Chem 2004 43 6600

66) Guennic B L Floyd T Galan B R Autschbach J Keister J B Inorg Chem 2009 48 5504

67) Cremer C Burger P J Am Chem Soc 2003 125 7664

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68) Atkins P de Paula J P Physical Chemistry 8th Edition Oxford University Press Oxford 2006

69) Butters T Toda F Winters W Angew Chem Int Ed Engl 1980 19 926 70) Mann B E Taylor B F 13C Data for Organometallic Compounds Academic

London 1981 71) For a review on triple decker arene complexes and closely related syn dinuclear

systems see (a) Beck V OlsquoHare D J Organomet Chem 2004 698 3920 and the references therein For a review of trinuclear CpCo(arene) complexes see (b) Wadepohl H Angew Chem Int Ed Engl 1992 31 247 and the references therein

72) Jonas K Koepe G Schieferstein L Mynott R Kruumlger C Tsay Y-H Angew Chem Int Ed Engl 1983 22 620 Angew Chem Suppl 1983 920

73) Muumlller J Gaede P E Qiao K Angew Chem Int Ed Engl 1993 32 1697 74) Schneider J J Wolf D Janiak C Heinemann O Rust J Kruumlger C Chem

Eur J 1998 4 1982 75) Schneider J J Denninger U Heinemann O Kruumlger C Angew Chem Int Ed

Engl 1995 34 592 76) Budzelaar P H M Moonen N N P de Gelder R Smits J M M Gal A W

Chem Eur J 2000 6 2740 77) Albright T A Dosa P I Groszligmann T N Oluwakemi O Padilla R Paubelle

R Timofeeva T Vollhardt K P C Angew Chem Int Ed 2009 48 9853 78) Schaub T Radius U Chem Eur J 2005 11 5024 79) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4660 80) (a) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4040

(b) Muumlller C Lachicotte R J Jones W D Organometallics 2002 21 1975 81) Martin R H Angew Chem Int Ed Engl 1974 13 649 82) Mallory FB Butler K E Evans AC Mallory CW Tetrahedron Lett 1996 37

7176 83) Selected Reviews (a) Amemiya R Yamaguchi M Chem Rec 2008 8 116 (b)

Ruliacutešek L Exner O Cwiklik L Jungwirth P Staryacute I Pospiacutešil L Havlas Z J Phys Chem C 2007 111 14948 (c) Hopf H Classics in Hydrocarbon Chemistry Wiley-VCH Weinheim 2000 pp 321ndash330 (d) Voumlgtle F Fascinating Molecules in Organic Chemistry Wiley New York 1992 pp 156ndash180 (e) Meurer K P F Voumlgtle Top Curr Chem 1985 127 1 (f) Laarhoven W H Prinsen W J Top Curr Chem 1984 125 63

84) (a) Mallory FB Butler K E Mallory CW Beacuterubeacute A Luzik E D Brondyke E J Hiremath R Ngo P Carroll P J Tetrahedron 2001 57 3715 (b) Mallory F B Butler K E Evans A C Brondyke E J Mallory C W Yang C Ellenstein A J Am Chem Soc 1997 119 2119

85) (a) Mitsuhashi R Suzuki Y Yamanari Y Mitamura H Kambe T Ikeda N Okamoto H Fujiwara A Yamaji M Kawasaki N Maniwa Y Kubozono Y Nature 2010 464 74 (b) Okamoto H Kawasaki N Kaji Y Kubozono Y Fujiwara A Yamaji M J Am Chem Soc 2008 130 10470 (c) Tian Y H Park G Kertesz M Chem Mater 2008 20 3266

86) Recent reviews of acenes in electronic applications (a)Yamashita Y Sci Technol Adv Mater 2009 10 024313 (b) Wuumlrthner F Schmidt R ChemPhysChem

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2006 7 793 (c) Bendikov M Wudl F Chem Rev 2004 104 4891 87) NICS-based comparison of phenacene and acene properties Portella G Poater

P Bofill J M Alemany P Solagrave M J Org Chem 2005 70 2509 and the references therein

88) Mallory F B Mallory C W Org React 1984 30 1 89) Gu Z Nickel-Catalyzed Cycloaddition Reaction of [N]Phenylenes and Alkynes

Postdoctoral Report University of California Berkeley 2008 90) Preferential displacement of COD by π ligands from Ni(COD)(PMe3)2 is well

documented See eg Karsch H H Leithe A W Reisky M Witt E Organometallics 1999 18 90

91) (a) Bochmann M Hawkins I Hursthouse M B Short R L J Chem Soc Dalton Trans 1990 1213 (b) Poerschke K R Mynott R Angermund K Kruumlger C Z Naturforsch 1990 40B 199 See also (c) Bartik T Happ B Iglewsky M Bandmann H Boese R Heimbach P Hoffmann T Wenschuh E Organometallics 1992 11 1235

92) For Ni-phosphine migrations along polycyclic benzenoid ligands see eg Stanger A Vollhardt K P C Organometallics 1992 11 317

93) Edelbach B L Vicic D A Lachicotte R J Jones W D Organometallics 1998 17 4784

94) (a) Feiken N Pregosin P S Trabesinger G Scalone M Organometallics 1997 16 537 (b) Feiken N Pregosin P S Trabesinger G Albinati A Evoli G L Organometallics 1997 16 5756 (c) Geldbach T J Pregosin P S Eur J Inorg Chem 2002 1907

95) Cheng T-Y Szalda D J Hanson J C Muckerman J T Bullock R M Organometallics 2008 27 3785

96) (a) Grimme S Harren J Sobanski A Voumlgtle F Eur J Org Chem 1998 8 1491 (b) Dias J J Chem Inf Model 2005 45 562

97) Still W C Mitra A Kahn M J Org Chem 1978 43 2923 98) (a) Leonard J Lygo B Procter G Advanced Practical Organic Chemistry 2nd

ed CRC Press Boca Raton 1998 (b) Errington R J Advanced Practical Inorganic Chemistry and Metalorganic Chemistry Chapman and Hill London 1997

99) Jonas K Deffense E Habermann D Angew Chem Int Ed Engl 1983 22 716 100) Gaussian 03 Revision B03 M J Frisch G W Trucks H B Schlegel G E

Scuseria M A Robb J R Cheeseman J A Montgomery Jr T Vreven K N Kudin J C Burant J M Millam S S Iyengar J Tomasi V Barone B Mennucci M Cossi G Scalmani N Rega G A Petersson H Nakatsuji M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida T Nakajima Y Honda O Kitao H Nakai M Klene X Li J E Knox H P Hratchian J B Cross C Adamo J Jaramillo R Gomperts R E Stratmann O Yazyev A J Austin R Cammi C Pomelli J W Ochterski P Y Ayala K Morokuma G A Voth P Salvador J J Dannenberg V G Zakrzewski S Dapprich A D Daniels M C Strain O Farkas D K Malick A D Rabuck K Raghavachari J B Foresman J V Ortiz Q Cui A G Baboul S Clifford J Cioslowski B B Stefanov G Liu A Liashenko P Piskorz I Komaromi R L Martin D J Fox T Keith M A Al-Laham C Y Peng A Nanayakkara M Challacombe P M W Gill B Johnson W Chen M W Wong C Gonzalez J A Pople Gaussian Inc Pittsburgh PA

- 175 -

2003 101) wwwgaussiancom 102) wwwchemcraftprogcom 103) Becke A D J Chem Phys 1993 98 5648 104) Lee C Yang W Parr G R Phys Rev B 1988 37 785 105) Binkley J S Pople J A Hehre W J J Am Chem Soc 1980 102 939 for

hydrogen and Gordon M S Binkley J S Pople J A Pietro W J Hehre W J J Am Chem Soc 1983 104 2797

106) Hay P J Wadt W R J Chem Phys 1985 82 270 107) Hehre W J Ditchfield R Pople J A J Chem Phys B 1972 56 2257 108) Curtiss L A McGrath M P Blaudeau J-P Davis N E Binning R C Jr

Radom L J Chem Phys 1995 103 6104 109) A W Ehlers M Boumlhme S Dapprich A Gobbi A Houmlllwarth V Jonas K F

Koumlhler R Stegmann A Veldkamp G Frenking Chem Phys Lett 1993 208 111

110) QST is a synchronous transit approach to the quadratic region around the transition state structure For details see (a) J B Foresman A Frisch in Exploring Chemistry with Electronic Structure Methods A Guide to Using Gaussian Gaussian Inc Pittsburgh PA USA 1996 (b) H B Schlegel in Ab Initio Methods in Quantum Chemistry Part I Wiley Chichester 1987

111) Gu Z The Improvement of Total Synthesis of Angular [4]Phenylene and Its Flash Vacuum Pyrolysis (FVP) Study Postdoctoral Report University of California Berkeley 2008

112) Schwager H Postdoctoral Research Report University of California Berkeley 1987

113) Kuumlchle W Dolg M Stoll H Preuss H Mol Phys 1991 74 1245 114) (a) Hariharan P C Pople J A Theor Chim Acta 1973 28 213 (b) Francl M

M Petro W J Hehre W J Binkley J S Gordon M S DeFrees D J Pople J A J Chem Phys 1982 77 3654 (c) Rassolov V Pople J A Ratner M Windus T L J Chem Phys 1998 109 1223

ii

Acknowledgements

ldquoWhere would I find leather enough to cover the surface of the earth The Earth is covered over merely with the leather of my sandalsrdquo

-Shāntideva in the Bodhicaryāvatārah Ch 4 v13 Five years ago I arrived in Berkeley with a rather clear objective get (or rather survive) a PhD Though the goal never changed the all paths (scientific personal professional and spiritual) I traversed were often quite unlike anything I could have anticipated I have had the great fortune to stand on the shoulders of many giants during these past few years and it is to them that I owe my deepest gratitude First and foremost I would like to thank my advisor Peter Vollhardt for all of his support and patience The things I have learned from him are far too numerous to list but certainly the two most important are clarity and rigor two qualities that extend far beyond the chemical realm Working with so many different people was another interesting challenging and ultimately highly rewarding experience I am particularly indebted to ldquoThe Old Gangrdquo consisting in part of Phil Leonard and Ken Windler These two gentlemanly pyromaniacal firearms enthusiasts aside from showing me the ins and outs when I was a new arrival (and teaching me more than I will ever need to know about guns and explosives) soon became good and close friends No mention of The Gang would be complete without Jordan Rose Figura Despite being a chemical biologist and not actually a member of the Vollhardt Group she nonetheless (somehow) managed to fit in perfectly My life has been forever changed by her introducing me to ldquoDoctor Whordquo Many others also deserve special mention Sabine Amslinger has and will continue to provide a near endless amount of legendary stories that often border on mythological Tom Gadek was just plain awesome Vince Gandon aside from being one the best experimentalists Irsquove seen also happened to have a rather fine taste in films and music Dominik Hager excelled at getting me out of the lab for an occasional weekend of fun The elegant and refined chocolate cakes of Aude Hubaud were a rare yet very welcome occurrence Her sassy chic comments on all aspects of life however were quite copious Greg Boursalian performed an excellent job of filling the ldquocool undergradrdquo spot and I wish him the best for his own graduate school journey Steve Meier managed the Herculean task of (legally) disposing of all those old empty gas cylinders It is my great hope that Prof Sgt Meier will share many (but certainly not all) of his Berkeley experiences with the next generation of chemists that he will educate Explaining the strange and quirky aspects of American culture and the English language to Kerstin Weiszlig made for a fair number of humorous conversations Learning the stranger and quirkier aspects of German language and culture made for many more Similarly much time was spent meticulously examining the lyrics and slang expressions of assorted hip-hop songs with Sander Oldenhof Practicing kindergarten level German while sharing a fairly constant supply of Ritter Sport bars with Verena Engelhardt was another fine example of cultural exchange Despite his best efforts Kasper Moth-Poulsen has yet to convince me that Volvo is the greatest vehicle manufacturer in the known universe My cultural exposure was not limited to European interactions however and I managed to learn a little Chinese as well Apparently ldquoHao Shenrdquo

iii

means ldquoMacGyverrdquo in Mandarin I would also like to thank the rest of my co-workers past and present for all of their support They are in rough chronological order Thomas Carl Miles Carter Kaspar Schaumlrer Ingo Janser Romy Michiels Elisa Paredes Thilo Heckrodt Nicholas Cheron Alex Lee Anais Geny Samer Al-Gharabli Nicole Franssen Vladislav Kulikov Alexandra Romek Isaac Ho Zhenhua Gu Florian Montermini Nikolai Vinokurov Robert Zitterbart and Cedric Ghellamallah Bonnie Kirk skillfully handled the various arcane administrative procedures but also provided many interesting and memorable early morning conversations The finer points of NMR spectroscopy were taught to me by the indomitable Rudi Nunlist His wry humor and outlook on life were often the perfect supplement to the rigors of graduate school life Working with Chris Canlas Rudirsquos able successor has also been a pleasure I was encouraged when he was so quick to remind me that I have the same name as a bad-boy Filipino action-movie star Teaching while always quite time consuming proved to be an invaluable experience Teaching under the direction of Peter the man who wrote the book on organic chemistry was quite an adventure His passion and talent for teaching are immediately obvious and inspiring even without flipping through the Basque translation of his textbook Jon Ellmanrsquos ability to write exams that are easy to grade but difficult for students to take is similarly awe inspiring There is no doubt in my mind that Heino Nitsche has taken teaching of general chemistry to new levels of eccentricity and excitement Jean Freacutechetrsquos impressive aptitude for lecturing is perhaps surpassed only by the impressiveness of his wine collection Looking down the academic chain I have to acknowledge many of the brilliant and wonderful students that made teaching such a fantastic experience Special thanks goes to Steve Seyedin Nellie Ekmejian Jessie Zhang Yao Yue Ashley Johnson Brent Jellen Zarina Khan and Mojgan Rastegar all of whom were extraordinary students that I hope will do their part to save the world No acknowledgement could be complete without recognizing the love and support of my family in particular my mother Her love though always tough was always there My various housemates also provided me with some great times Chris Trinh my first housemate in Berkeley was a superb fellow to live with and I will always fondly remember our conversations on life love and quantum gravity Cory McLitus when he wasnrsquot slaving away in the architecture studio also became a good friend I feel no need to apologize for getting him hopelessly addicted to ldquoThe Big Bang Theoryrdquo The awesome Samra Kasim was always ready for chai good food and hearty discussions on Bollywood and all things South Asian The housemates of 1505 Oxford St are also great people Though we rarely cross paths Vicky Zhuangrsquos highly entertaining biology lab adventures are much appreciated Vannamaria Kalafonos always has something wonderful going on in the kitchen and I aspire to learn the Greek specialty of cooking for a zillion people from her The cats Pink Tuffy and especially Floyd are nice companions even though they sleep a combined 60 hours per day Many kalyānamitras helped me get through the toughest times and to them I am especially grateful A large number of my Saturday evenings were spent in the calm environs of the Berkeley Monastery where Rev Heng Surersquos Avataṃsaka Sūtra

iv

lectures gave me much to think about The monthly lectures by Ajahn Amaro Ajahn Passano and the Abhayagiri Sangha were also a wonderful learning experience Chats about long-dead ancient languages and obscure texts with Sean Kerr a fellow survivor of Dagmar Theisonrsquos German class will also be fondly remembered The NY Sangha though far away always supported me and welcomed me warmly whenever I returned home Frank Yao Hai-Dee Lee Sheila Sussman Fred Ng Martin Applebaum Josephine Verceles Tiffany Taulton Phung Tran and especially Aaron Vederman repeatedly reminded me to ldquosmile breath deep and go slowlyrdquo The many visits to Bodhi Monastery were always the high points of my summers Michael Roehm Bhikkhu Bodhi Jane Berry Henry and Lily Teoh Marcie Barth Mahendra Sagar the dearly departed Felicia Miller Ven Guo Jun Susan Chastain and the polygot Bhikkhu Analayo made every visit an unforgettable experience and never failed to remind me why I get out of bed in the morning

- 1 -

Chapter One

Properties of the [N]Phenylenes and Their Organometallic Chemistry

11 General Discussion of [N]Phenylene Properties Polycyclic aromatic hydrocarbons (PAHs) are a class of molecules that have occupied the minds of chemists for generations1 Their essential feature aromaticity is the unusual stabilization that arises from having a 4n+2 number of π-electrons in a cyclical array This seemingly simple definition obscures the fact that aromaticity continues to be one of the most scrutinized topics in modern organic chemistry2 and more rigorous definitions3 have remained elusive Much of the early work4 with PAHs was aimed at investigating theoretical issues surrounding aromaticity There has been renewed interest in these systems in recent years because they are increasingly attractive as functional materials in organic-based electronics5 Of the many different kinds of PAHs known eg 1ndash6 (Figure 11) one subclass is of particular interest the [N]phenylenes6

Anthracene Coronene Phenanthrene

Chrysene Triphenylene Pyrene

1 2 3

4 5 6

Figure 11 Some examples of polycyclic aromatic hydrocarbons The [N]phenylenes (where N = the number of benzene rings) are PAHs in which benzene and cyclobutadiene rings are fused in an alternating manner The cyclobutadiene ring imparts very unusual structural and electronic properties as seen in the simplest molecule in the series biphenylene (7) It can be described by several resonance forms (Figure 12 andashe) in which the major contributor 7c avoids formation of the highly destabilizing antiaromatic cyclobutadiene (7a 7e) and benzocyclobutadiene circuit (7b 7d) This preference is manifest in the significant bond alternation7 seen in

- 2 -

the crystal structure of biphenylene (Figure 12) which shows a clear difference in bond lengths between the formal single bonds (~143 Aring) and the shorter formal double bonds (~137 Aring)

1423

1372

Figure 12 Biphenylene bond lengths (top Aring) and resonance contributors (bottom)

An extreme example of [N]phenylene π-bond localization is triangular [4]phenylene (8) (Scheme 11) in which the three-fold peripheral fusion imparts complete cyclohexatriene character on the central ring89a This property is reflected in the reactivity of the system eg catalytic hydrogenation (9)8b epoxidation (10)8c and cyclopropanation (11)8c Scheme 11 Reactions Illustrating the Fully Bond Localized Character of the Central Benzene

Ring in Triangular [4]Phenylene 8 Bond lengths are in Aring

- 3 -

Phenylenes exhibit another interesting structural feature in contrast to other PAHs sizable deviations from planarity (Figure 13)9ab The flexibility of the phenylene framework arises from the combined effect of π- and σ-strain9ab By adopting a nonplanar geometry overlap between the π-orbitals is diminished and in turn leads to a decrease in destabilizing antiaromatic character Pyramidalization of the four-membered ring carbons also reduces σ-strain9ab a phenomenon observed in highly strained alkene systems9c

Figure 13 Crystal structures showing deviations from planarity in (a) helical [6]phenylene (12)10 (b) dimethyl triangular [4]phenylene-23-dicarboxylate (13)9a and (c) 23-bis(tri-

methylsilyl) linear [3]phenylene (14)9a

The fusion of aromatic benzene rings with antiaromatic cyclobutadiene units in the same molecule has prompted numerous experimental and theoretical discussions6 regarding the magnetic and electronic properties of the phenylenes 1H-NMR spectroscopy is one typical measure of aromaticity Protons on the exterior of aromatic rings (eg 15) show relatively low field resonances while their interior counterparts resonate at relatively high field due to the presence of a diamagnetic ring current Conversely antiaromatic rings with 4n π-electrons are paratropic and reveal the opposite disposition of the two respective types of protons (eg 16) The interplay between aromatic and antiaromatic character in the phenylenes is evident in their chemical shifts which tend to show weakly aromatic resonances (Figure 15) relative to benzene (736 ppm)

(a) (b) (c)

12 13 14

- 4 -

Figure 14 Observed 1H-NMR resonances in (a) the aromatic [18]annulene (15)11 and (b) the antiaromatic 5-bromo-19-bisdehydro-[12]annulene (16)12

Aside from NMR spectroscopy nucleus independent chemical shift (NICS)13 calculations have also proven to be useful measures of aromaticity The NICS technique works by calculating the magnetic shielding of a ldquoghost nucleusrdquo that can be positioned anywhere around a molecule For probing aromaticity the calculated point is in the center of the π-electron circuit to be examined Calculations placing the ghost nucleus 1 Aring above the plane of the molecule are often used to minimize local anisotropy and are referred to as NICS(1)14 NICS data are given in ppm and are thus comparable to experimental 1H-NMR measurements Negative NICS values indicate aromatic character while positive values suggest antiaromatic character For example the NICS(1) of benzene15 is ndash125 ppm whereas for cyclobutadiene15 it is 151 ppm NICS calculations for various phenylenes have been carried out6 and are shown in Figure 15 alongside the experimentally measured 1H-NMR chemical shifts The attenuated aromatic character of the benzene and the relatively weak antiaromatic character of the cyclobutadiene rings in phenylenes such as biphenylene (7) triangular [4]phenylene (8) and angular [4]phenylene (17) are apparent from both sets of data

Figure 15 1H-NMR (blue) and NICS(1) (green) data for selected phenylene topologies (ppm)6

The phenylenes possess multiple modes of reactivity7 as illustrated by biphenylene (7) in Scheme 12 It can undergo electrophilic aromatic substitution like other PAHs but does so selectively at the 2-position to avoid the formation of intermediates with antiaromatic character Biphenylene does not readily undergo Diels-

- 5 -

Alder reactions but was shown to react with electron-deficient benzynes to give the corresponding cycloadducts16 Opening of the highly strained four-membered ring is another prominent aspect of phenylene reactivity

Scheme 12 Illustrative Reaction Pathways of Biphenylene6

Early work17 showed that it was possible to cleave the aryl-aryl C-C bonds via thermolysis in the neat state Rupture of the four-membered ring is a key step in the rearrangement of phenylenes into other PAHs and has been observed typically under flash vacuum pyrolytic conditions18 (eg 10ndash3ndash10ndash6 torr 800ndash1000 degC) Strained ring opening on exposure to metal complexes to give metallacycles19 is discussed in further detail in Section 12 12 Overview of Phenylene Organometallic Chemistry

As mentioned above the weakly aromatic character of the phenylenes dominates their structure and reactivity In the linear phenylenes the antiaromatic contribution to structure and reactivity becomes increasingly significant A simple yet instructive explanation for this phenomenon can be seen in the various resonance structures of linear [3]phenylene (18) a selection of which is depicted in Figure 16 Even the most favorable forms a and b feature double bonds in the four-membered rings The cumulative increase in cyclobutadienoid circuits should therefore lead to an increase in antiaromatic character The relative augmentation in

- 6 -

cyclobutadienoidantiaromatic character of the linear phenylenes was confirmed6 by NMR NICS calculations and HOMO-LUMO measurements20

Figure 16

Resonance contributors to linear [3]phenylene

Cyclobutadiene is often invoked as the typical example of a highly destabilized antiaromatic system Indeed the difficulties21 in preparing and isolating it confirm theoretical predictions regarding its instability22 Attachment of a metal however is known to produce aromatic organometallic molecules of high stability23 The increased antiaromatic character of the linear phenylenes thus makes them amenable to metal complexation Cyclopentadienylcobalt cyclobutadiene complexes of linear [3]- (19)24 linear [4]- (20)25 and linear [5]phenylene (21)26 have been prepared using the well-developed cobalt-based [2+2+2] alkyne cyclotrimerization methods (Scheme 13)27

Compounds 19ndash21 constitute the only linear CpCo phenylene systems known so far

Scheme 13 Synthesis of Linear Phenylene(CpCo) Cyclobutadiene Complexes

In the metallated linear [4]- and [5]phenylene 20 and 21 respectively the CpCo unit is located on the inner cyclobutadiene ring This is curious as one would have expected the metal fragment to be bound to its outside counterpart close to the center of reactivity during the cyclotrimerization step The position of the CpCo unit was established by NMR spectroscopy2628 In addition a crystal structure of a tetrahexyl

TMS

TMS

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMSTMS

TMS

Co

CpCo(CO)2BTMSA

h

Co

Co

CpCo(CO)2BTMSA

h

CpCo(CO)2BTMSA

h

19

20

21

- 7 -

substituted linear [5]phenylene28 (Figure 17) clearly reveals the inside position of the metal fragment Difficulties in obtaining high quality crystals however precluded a detailed bond analysis of the complex The unexpected location of the CpCo unit in 20 and 21 suggested the occurrence of CpCo migration under the conditions of their preparation Detailed experiments verifying this hypothesis will be the subject of Chapter 2

Figure 17 Disordered crystal structure for the 23910-tetrakis(trimethylsilyl)-571214-

tetrahexyl linear [5]phenylene(CpCo)

In contrast to the linear phenylenes their angular relatives undergo π-metallation at the cyclohexatrienoid moieties (Figure 18) For example angular [3]phenylene (22) reacts with CpCo(C2H4)2 to form the η4-CpCo complex 2329 Similar treatment with Cr(CO)3(NH3)3 yields the η6-Cr(CO)3 analog 2430

Figure 18 η

4-CpCo (23) and η6-Cr(CO)3 (24) complexes of angular [3]phenylene (22)

In addition to 24 related chromium complexes of the triangular [4]phenylene frame eg 25 have been prepared (Scheme 14)31 Interestingly regioisomer 26 generated at relatively lower temperatures is the kinetic product of monocomplexation and rearranges thermally to 27 Double metallation is possible as illustrated in the conversion of 27 to 28 with added (naphthalene)Cr(CO)3

- 8 -

Scheme 14 Synthesis and Reactions of Triangular [4]Phenylene(Cr(CO)3) Complexes

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3(NH3)3dioxane 100 oC

14 h

(naphthalene)Cr(CO)3THF Et2O 60 oC 14 h

90 oC

(naphthalene)Cr(CO)3THF Et2O 60 oC

14 h

25

27

26

28

57 43

89

In contrast to CpCo which attaches itself exclusively to the four-membered ring in the linear phenylenes including the linear [3]phenylene frame as in 19 (Scheme 13) Fe2(CO)9 gives a plethora of complexes with the tetrasilyl derivative 29 among which the iron tricarbonyl cyclobutadiene complex 30 is only minor (Scheme 15)27 Instead other organometallic molecules such as arene complex 31 were isolated This compound contains two Fe(CO)3 units coordinated to the central benzene ring An iron-iron bond was proposed for this molecule (31a) although the spectral data are also consistent with a structure in which the Fe(CO)3 fragments are located on opposite faces (31b) Because a crystal structure could not be obtained the structural identity of 31 remains ambiguous The major products of this reaction 32 and 33 illustrate another important aspect of phenylene reactivity metal insertion into the strained ring

- 9 -

in this case involving the dinuclear Fe2(CO)6 unit Complex 33 probably originating from 32 contains an additional Fe(CO)3 moiety coordinated to the terminal benzene ring closest to the Fe2(CO)6 fragment

Scheme 15 Reaction of Linear [3]Phenylene with Fe2(CO)9

While as yet absent in the linear series a cobalt insertion product analogous to iron compounds 32 and 33 was isolated when angular phenylene 22 was exposed to excess CpCo(ethene)2 (Figure 19)32 In this case double insertion of two (CpCo)2

Figure 19 Tetranuclear CpCo-terphenylene complex 34 and its crystal structure

34

- 10 -

fragments occurred to give 34 in 71 yield Notably neither 23 nor analogs of the type 31 were detected As alluded to in Scheme 12 biphenylene (7) itself also undergoes metal insertions into the four-membered ring This type of reactivity has been observed with a range of transition metals including Co19 Mechanistically best delineated is the attack of Ni and Pt species Thus Ni(PEt3)4

33a and Ni(COD)(PMe3)233b begin with insertion of

the nickel fragment into the four-membered ring to give a metallacycle of the type 35 (Scheme 16) Subsequent dimerization assembles 36 from which Ni is extruded to furnish tetraphenylene 37 as the final product A similar reaction pathway was proposed for Pt(PEt)4

19 but proceeding via 38 to a monometallacycle 40 possibly through the intermediacy of 39 In summary the σ- and π-activation of the phenylenes endows them with rich organometallic chemical potential The synthetic and mechanistic exploration of one aspect of it namely the Ni-catalyzed cycloaddition of alkynes to the four-membered rings in angular phenylenes will be discussed in Chapter 3

Scheme 16 Reaction of Biphenylene with Nickel and Platinum Complexes

13 Direction of Work The discussions in Sections 11 and 12 have provided a brief overview of phenylene properties and their previously studied organometallic chemistry

- 11 -

respectively The aim of this thesis was to advance two aspects of prior investigations The first area examines the chemistry of the linear phenylene(CpCo) complexes In particular experiments are presented addressing the question of a possible migration of the CpCo fragment along their framework The revocable movement of a metal fragment between cyclobutadiene rings is a highly noteworthy discovery as this process has never before been reported On a practical level this mode of reactivity places linear phenylene(CpCo) complexes in the increasingly appealing class of organometallic arrays that can serve as the basis for various molecular electronic systems The reversible isomerizations described in the second chapter can potentially be employed in molecular machines and switches data storage and as will be detailed photostorage devices Experimental work in the form of detailed solid state and spectroscopic analyses is provided Computational studies are also employed to further scrutinize the novel chemistry of the abovementioned Co-based molecules The second topic of this thesis examines nickel-catalyzed insertions into the four- membered rings of angular phenylene systems Specifically the application of this reactivity to the synthesis of a class of PAHs known as [N]phenacenes is discussed Phenacenes (polyphenanthrenes) have recently shown great promise as organic transistors and conductors but advancement of this field has been hampered due to few practical syntheses The insolubility of these molecules has also been a substantial barrier to the development of phenacene-based applications The content of the third chapter explores the preparation of soluble phenacene derivatives using a tandem Ni-insertion alkyne cycloaddition reaction This new process provides an efficient widely applicable and practical synthesis of larger phenacenes using correspondingly larger angular phenylene systems Detailed mechanistic studies of this reaction are presented Experimental data are used in conjunction with computational studies to gain further insight with the optimization of the reaction by reduction of side product formation being a crucial milestone

- 12 -

Chapter Two

PhotondashThermal Haptotropism in Cyclopentadienylcobalt Complexes of Linear Phenylenes Intercyclobutadiene Metal Migration

21 Introduction As previewed in Section 12 the unexpected position of the metallic unit in the linear [4]- and [5]phenylene(CpCo) systems 20 and 21 constituted the background for the studies presented in this chapter Specifically it was hypothesized that its origin was due to the migration of the metal fragment from one cyclobutadiene ring to another a process that would constitute an unprecedented type of haptotropic shift34-36 However a prerequisite for studying such a rearrangement would be the generation of the haptoisomers of 20 and 21 (Scheme 13) bearing the CpCo appendage at the respective terminal four-membered rings a possibility obviated by their thermal method of synthesis The following describes the history that led to the discovery of photochemical conditions that circumvented this thermodynamic problem The story begins with a prior attempt to stabilize the linear phenylene frame by alkyl substitution the ultimate aim being the synthesis of members of the series with Ngt5 Such substitution was also hoped to improve solubility a facet exploited in the corresponding zigzag series37 The synthetic strategy followed that used in the preparation of the largest known linear phenylene 41 namely the CpCo-catalyzed cyclization to 21 followed by careful oxidative demetallation as shown in Scheme 21 The initial target chosen was the tetrahexyl system 43 approached via the synthesis of complex 42 (Scheme 22)28 Demetallation was thought to be facile to provide the free ligand but this anticipation proved to be erroneous

Scheme 21 Oxidative Decomplexation of Linear [5]Phenylene Complex 21

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMS

41

CoCp

21

40

CuCl2middot2H2ODME NEt3 H2O

Scheme 22 Preparation of Tetrahexyl Linear [5]Phenylene Complex 42

- 13 -

TMS

TMS

TMS

TMS

Hex

Hex

Hex

Hex

CoCp

42

CpCo(CO)2 BTMSAm-xylene ∆ hν

27

Hex Hex

HexHex

TMS

TMS

TMS

TMS

Hex Hex

HexHex

ndashCpCo

43

The demetallation of 42 under numerous conditions was unattainable However in one of these attempts an NMR sample of 42 was exposed to UV-irradiation leading to the evolution of new signals eventually assigned to originate from rearranged compound 45 (Scheme 23)28 This molecule is also a linear [5]phenylene(CpCo) complex but now has the metal fragment bound to the outer cyclobutadiene ring an arrangement that was suspected to be the initial product of the preparation of 42 (Scheme 22) That this conjecture was correct was established by heating which caused photoisomer 45 to revert to 42 An indication of the generality of this phenomenon was gleaned from 21 which underwent the same photoinduced thermally reversible haptotropic migration (Scheme 23)38 A detailed discussion of the spectral properties of these haptomers is provided in Sections 23 and 24 Scheme 23 Photoinduced Thermally Reversible Haptotropic Migration of the CpCo Fragment

in Linear [5]Phenylene(CpCo) Complexes

This discovery was deemed significant for two reasons 1 it constitutes the first observation of intercyclobutadiene metallohaptotropism and 2 there are only two previously known examples of mononuclear39 additive-free40 photothermal reversible haptotropic shifts both of which are based on Mo(PMe3)3 complexes (Scheme 24)41 Systems capable of undergoing this type of reaction are of much practical importance because of their potential employment as photostorage devices andor molecular switches42 The development and application of functional organometallic materials43 has proceeded at a relatively slow pace when compared to their non-metallated counterparts5c Thus the great prospects for discovery and advancement make this area of study particularly attractive

- 14 -

Scheme 24 Photothermal Reversible Metallohaptotropism in (a) Molybendum-Indole41a and (b) Molybendum-Isoquinoline Complexes41b

Having confirmed that an η4η4 cyclobutadiene haptotropic migration was indeed occurring mechanistic investigations2838 were begun Interestingly full conversion of the inner bound CpCo complexes to their photoisomers was never achieved The maximum ratio obtained for 2144 and 4245 was 8812 Variations of solvent (eg benzene THF CHCl3) and temperature (0ndash30degC) had no effect on this ratio Added ligands such as 15-cyclooctadiene CO and phosphines were also inconsequential Of further significance was the robustness of the photothermal cycle which could be run multiple times without decomposition Kinetic experiments were carried out to determine the activation parameters for the thermal reversal of 44 and 45 to 21 and 42 respectively These data are shown in Table 21 The isomerizations are cleanly first order a finding that was unaffected by changes in concentration22 The enthalpy of activation (∆Hne) increased only slightly with hexyl substitution (44 vs 45) The near zero entropy of activation values (∆Sne) was consistent with the occurrence of an intramolecular process

Table 21 Activation Parameters for the Conversion of Outer to Inner CpCo Complexes Under

Thermal Conditions ∆Sne Values are in Entropy Units (1 eu = calmolsdotK)

Reaction Solvent ∆H

ne (kcalmol) ∆Sne (eu)

44 to 21 C6D6 259 plusmn 04 16 plusmn 14 44 to 21 THF-d8 256 plusmn 09 01 plusmn 30 45 to 42 THF-d8 276 plusmn 08 77 plusmn 27

Consideration of the relative facility of the above haptotropic shifts made it likely that migration was occurring along the entire phenylene frame including the ldquohoppingrdquo across the central six-membered ring (Scheme 25) This degenerate equilibration should be detectable by NMR spectroscopy44 if it were sufficiently fast Unfortunately but perhaps not surprisingly considering the data in Table 21 coalescence of the spectrum of 21 could not be achieved even at temperatures as high as 120 degC Spin saturation transfer experiments (eg EXSY) also failed44 These data allowed an estimate of the lower limit for the activation energy of the internal shift of ∆Gne ge 22 kcalmol28

Scheme 25 Proposed Internal η4η4 Cyclobutadiene CpCo Migration

- 15 -

The failure of the above experiments inspired a different approach based on the following arguments The antiaromatic character of the linear phenylenes has been shown by theory and experiment to increase with size645 Consequently the effect of metalloaromatization46 makes linear [5]phenylene a better (and hence more strongly bound) ligand for CpCo than a smaller system (eg linear [3]phenylene) Indeed the enthalpy of the homodesmotic in Scheme 26 was computed by DFT methods to be Scheme 26 Calculated Homodesmotic Reaction Showing Preferential Binding of CpCo to

Linear [5]Phenylene

113 kcalmol47 If the barrier to intercyclobutadiene hopping were related to the binding energy of the metal one would expect a more loosely bound metal fragment to migrate faster The hope was therefore that the degenerate haptotropism in Scheme 27 would be observable by VT NMR methods Unfortunately these efforts failed again38 either because the anticipated acceleration was not sufficient to be observable by NMR or because the argument above (which rests solely on ground state considerations) is flawed

Scheme 27 Proposed Degenerate Haptotropic Shift in Linear [3]Phenylene Complex 19

- 16 -

The preceding discussion summarizes some of the quantitative aspects of this new type of haptotropic shift Many fundamental questions however remained to be answered Is it possible to observe the photothermal shift in other systems such as linear [3]- and [4]phenylene What is the exact mechanism of metal migration between cyclobutadiene rings In what way if any does attachment of CpCo alter the structure of the phenylene scaffold Related to these questions was the long-standing quest for an accurate crystal structure of any linear phenylene(CpCo) complex The answers are addressed in the following sections 22 Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes As recounted in Section 21 the degenerate internal haptotropic shift could not be seen by NMR in the symmetrical 19 Therefore recourse had to be taken to chemical methods involving an isomerization of the sort shown in Scheme 28

Scheme 28 Isomerization of a Desymmetrized Linear [3]Phenylene(CpCo) Complex

Initial efforts focused on attempts to desymmetrize compound 19 directly by selective electrophilic desilylation specifically protodesilylation Earlier studies48 had shown that such selectivity was possible in the reactions of bis(trimethylsilyl)benzocycloalkenes such as the benzocyclobutene depicted in Scheme 29 In this case loss of the first TMS group is approximately forty times faster than that of the second Along these lines it was thought that exposing 19 to acidic conditions would selectively remove one (or perhaps two) TMS groups before attacking the remaining silylarene positions In the event treating compound 19 with trifluoroacetic acid in carbon tetrachloride did induce protodesilylation but with no selectivity A mixture of products was obtained and its separation proved impossible (Scheme 210) In light of this setback a new synthetic scheme had to be considered that would generate a desymmetrized system directly in the CpCo-catalyzed cyclization step

- 17 -

Scheme 29 Selective Desymmetrizing Reactions of 12-Bis(trimethylsilyl)benzocyclobutene with Electrophiles

Scheme 210 Attempted Selective Protodesilylation of 19

Fortunately such a strategy had already been executed successfully in the creation of 23-bis(trimethylsilyl) linear [3]phenylene (46) and employed the iterative Scheme 211 Iterative Cyclotrimerization Route in the Synthesis of Linear [3]Phenylene 46

cyclization depicted in Scheme 21127 Its specific execution (Scheme 212) started with a Sonogashira reaction between trimethylsilylacetylene (TMSA) and 12-diiodobenzene (47) to give diyne 48 in high yield Deprotection of 48 with K2CO3 immediately followed by standard CpCo(CO)2-catalyzed alkyne cyclotrimerization649 with bis(trimethylsilyl)acetylene (BTMSA) afforded 23-bis(trimethylsilyl)biphenylene (49) Iododesilylation was then performed using pure ICl to give 23-diiodobiphenylene (50) A Sonogashira coupling between TMSA and 50 produced diyne 51 in good yield The use of a slightly modified cyclization procedure provided the new 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52) in 57 yield This protocol employed THF as a cosolvent to BTMSA thus reducing the reaction temperature in turn allowing for the CpCo to remain attached in the final product and preventing catalytic turnover252638

TMS

TMS46

+

TMS

TMS

+

TMS

TMS

+

TMS

R

TMS

dilute

[X+]

X = H D Br

TMS

TMS

[X+]

TMS

X = H D Br

X

- 18 -

Scheme 212 Synthesis of Asymmetric Linear [3]Phenylene(CpCo) 52

High dilution conditions also helped to suppress formation of cyclobutadiene(CpCo) complexes a well known side reaction in alkyne cyclization chemistry

Compound 52 like its tetrasilylated analogue 19 is a black air-sensitive solid Although it can be handled in air for brief periods of time complete decomposition occurs within 24 hours if left exposed to the ambient atmosphere Purification must always be done with neutral activity III alumina as lower activities (and silica gel) cause decomplexation to give the deep red ligand 46 as the only isolable product Critically exposing molecule 52 to UV irradiation induced the desired haptotropic shift giving its photoisomer 53 (Scheme 213) Heating 53 converted it back to 52 thus completing the photothermal cycle Interestingly close inspection of the NMR spectra of this experiment revealed that a small amount of 53 (2) always remained even on prolonged heating That this observation signaled a thermodynamic equilibrium was confirmed by dissolution of pure crystalline 52 and NMR analysis From the equilibrium constant the ∆Gdeg298 was calculated to be 23 kcalmol in favor of 52 The reasons for this energetic preference and a discussion of the NMR spectral properties of these and related complexes are presented in Section 23

Scheme 213 The Photoinduced Thermally Reversible Haptropic Shift in Linear

- 19 -

[3]Phenylene-(CpCo) 52 to Give Photoisomer Complex 53 The investigations of the equilibration depicted in Scheme 213 were all carried out in sealed Pyrex NMR tubes (J-Young or flame-sealed) using benzene-d6 andor toluene-d8 as the solvent As for the linear [5]phenylene(CpCo) system the cycle could be run multiple times without decomposition and was unaffected by changes in solvent and temperature The maximum ratio of 5352 that could be obtained on irradiation was 11 after ten hours This value is larger than that observed for its linear [5] analogs 2144 and 4245 Photoisomerization also occurs with sunlight leading to the photostationary equilibrium of 5253 = 105 Consequently care must be taken to shield 52 from direct andor indirect sunlight Indoor fluorescent lighting however did not induce CpCo migration Attempts to monitor the photoisomerization and its thermal reverse by UV-Vis spectroscopy failed because of minimal changes in the absorptions due to 52 during these processes This finding implies that the absorption spectra of 52 and 53 are not unexpectedly very similar and offers a possible explanation for the maximum photostationary ratio of 11 The activation parameters for the thermal reversal reaction (53 to 52) in Scheme 213 were obtained in the manner described in Section 21 and are shown in Table 22 The relatively high activation barriers (with respect to the NMR time scale) explain why the degenerate isomerization in 19 could not be verified by NMR experiments Qualitatively the ∆Hne values agree with the hypothesis that the more loosely bound CpCo unit in the linear [3]phenylene is relatively more mobile they are approximately 3 kcalmol lower than those of the [5]phenylene system On the other hand the ∆Sne values especially in C6D6 are positive and relatively high although still within the range acceptable for intramolecular reactions Nevertheless a crossover experiment was devised to provide a definite answer

Table 22 Activation Parameters for the Thermal Conversion of Complex 53 to 52

Solvent ∆H

ne (kcalmol) ∆Sne (eu)

C6D6 204 plusmn 14 158 plusmn 22 Toluene-d8 231 plusmn 07 60 plusmn 13

For this purpose two new linear [3]phenylene(CpCo) derivatives were required One would carry a marker on the Cp ring while the other would be labeled at the phenylene frame Execution of Scheme 213 would involve an equimolar mixture of both compounds An intramolecular mechanism would retain the integrity of the labeling while a dissociative path would lead to label scrambling The outcome of this experiment should be ascertainable by NMR spectroscopy and more rigorously by

CoTMS

TMS

CoTMS

TMS

310 365 nmsunlight

30ndash50oC52 53

- 20 -

Scheme 214 Preparation of MeCp- (54) and Deuterium Labeled (55) [3]Phenylene Complexes

mass spectrometry To this end methyl-Cp complex 54 and dideuterio compound 55 were targeted for synthesis (Scheme 214) Compound 54 was prepared by carrying out the modified cyclotrimerization reaction with MeCpCo(CO)2

50 while 55 was made using methanol-OD in the desilylation of 51 The amount of deuterium incorporation in 55 was found to be 63 as gleaned from its proton NMR spectrum Scheme 215 Crossover Experiment with Labeled Linear [3]Phenylene(CpCo) Complexes

- 21 -

Co

TMS

TMS

TMS

TMS

Co

h CoTMS

TMS

Co

D

D

TMS

TMSD

D

TMS

TMS

Co

Co

TMS

TMSD

DCo

TMS

TMS

Co

TMS

TMSD

D

+

+

+

+

mz = 510

mz = 494

56mz = 508

57mz = 496

54mz = 508

55mz = 496

58 59

53 52

Not observed

Six distinct products are possible in the crossover experiment using 54 and 55 (Scheme 215) Compounds 56 and 5 would arise as a consequence of an intramolecular shift Molecules 53 and 58 and their photoisomers 52 and 59 respectively would be the result of metal fragment dissociation Mass spectrometry would readily verify the occurrence of crossover as the masses (given in mz in Scheme 215) of the products with scrambled labels (52 53 58 59) are distinct from the masses of the starting materials (54 55) and their photoisomers (56 57) In the first part of the experiment equal amounts of 54 and 55 were mixed (shielded from light) and allowed to stand for 2 hours at room temperature The resulting 1H-NMR spectrum consisted of only the signals for 54 and 55 Similarly the mass spectrum showed molecular ion peaks matching the masses of 55 and 56 (Figure 21) The second step was irradiation Analysis of the photolyzed mixture showed new peaks due to complex 56 (the resonances of which had been obtained in a separate photothermal experiment with pure 54) with the expected integration ratio and a second set assigned to 57 identical with the spectrum of 53 but with the expected attenuated absorption for the silyl bearing arene hydrogens The relative integrations for all compounds observed were consistent with a mixture of 5455 and 5657 Mass spectral analysis of the irradiated mixture showed a pattern that was identical to that collected before irradiation (Figure 21) Finally the thermal reversal reaction was carried out by heating the photolyzed mixture at 80 degC After 30 hours the resulting

- 22 -

NMR spectrum matched that of the initial mixture of 54 and 56 in particular confirming the full protonation of 54 and the unchanged level of deuterium incorporation in the silyl

Figure 21 Molecular ion peaks for 5456 (mz = 508) and 5557 (mz = 496)

bearing arene ring of 55 The corresponding mass spectrum contained no evidence for the presence of scrambled products To conclude The haptotropic shift is non-dissociative The exact manner in which the metal traverses from one cyclobutadiene ring to the other will be examined in greater detail in Section 24

23 X-Ray Structural and Comparative NMR Analysis of Linear [3]Phenylene(CpCo) Complexes The results described in Sections 21 and 22 pose some fundamental questions beyond those concerned with the immediate details of the observed haptotropism and addressing the basic novelty of the complexes involved What actually happens to the phenylene ligand when it is ligated via a cyclobutadienoid ring This section will address this question from a structural and (NMR) magnetic point of view Only one crystal structure of a linear phenylene(CpCo) complex was known at the outset of this work namely that of [5]phenylene(CpCo) 42 (Figure 17) and its acquisition required extensive efforts at crystallization28 Unfortunately extensive disorder obviated a detailed analysis It was hoped that some of the complexes employed in the chemistry disclosed in Section 22 would be more forthcoming in this respect The challenge lay in finding the right conditions for crystal growth We began with tetrasilyl linear [3]phenylene(CpCo) 19 which had been crystallized previously by slow cooling in acetone38 These conditions and numerous others (Table 23) did not provide material suitable for X-ray diffraction Success entailed slow cooling a solution of 19 to ndash10 degC in a mixture of methanol-diethyl ether (41) The ensuing sample allowed the determination of the first high quality crystal structure of a linear phenylene (CpCo) complex obtained in collaboration with the group of Professor Tatiana Timofeeva of New Mexico Highlands University (Figure 22)

Table 23 Trial Crystallization Conditions for Linear [3]Phenylene(CpCo)19

Solvent (Ratio) Conditions Result

Acetone Slow Cooling Heterocrystalline Solid Acetone-Pentane (31) Slow Cooling Heterocrystalline Solid

Pentane-Acetone (101) Solvent Diffusion Amorphous Solid Chlorobenzene Slow Cooling Amorphous Solid

- 23 -

Acetone-Methanol (110 Slow Cooling Amorphous Solid Diethyl Ether-Methanol Slow Cooling Small Needles

Acetonitrile Slow Cooling Powder Ethyl Acetate Slow Cooling No Crystals

Ethyl Acetate-Methanol (11) Slow Cooling Amorphous Solid Methanol-Diethyl Ether (41) Slow Cooling Large Fine Needles

Figure 22 X-ray crystal structure of 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) (19) Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are

omitted for clarity Expectedly the CpCo unit is bound in an η4 fashion to the cyclobutadiene ring Also prominent is the deviation from planarity (Section 11) in the linear [3]phenylene a facet typical of the phenylenes themselves (Section 11)9a Of greater importance than these general observations however is the effect of metal complexation on the linear [3] framework The bond lengths for 19 are shown in Figure 23 and as is typical for the phenylenes6 show a certain degree of bond π-localization with measurable differences between single and double bonds However the extent of this phenomenon and its direction varies significantly when compared to the free ligand 60 A quantitative

- 24 -

comparison of the structural data for 19 with those of its ligand 60 is shown in Figure 2327

In 60 the terminal rings adopt bond alternation similar to that in biphenylene (Section 11) and the central benzene takes on a ldquobis-allylrdquo configuration both ostensibly to minimize electron density (and therefore antiaromaticity) in the four-membered rings As dictated by symmetry the two bonds spanning the central ring are of equal length (1385 Aring) Ligation by CpCo alters this picture profoundly in as much as bond alternation across the entire phenylene frame including the four-membered rings is strongly reduced (Figure 23) Generally all relatively long bonds in 60 shorten in 19 while all short bonds lengthen Some residual but attenuated biphenylene type

Co

1512(2)

1513(2)

1407(2)

1385(2)

1385(2)

1397(2)

1356(2)

1359(2)1436(2)

1397(2)

1441(2)

1411(3)(0052)

1384(3)(-0052)

1474(3)(0077)

1384(3)(-0057)

1408(3)(0052)

1448(3)(0051)

1480(3)(-0032)

1468(3)(-0045)

1437(3)(0052)

1465(3)( 0058)

1434(3)( 0049)

1352(3)(-0033)

1351(3)(-0034)

1476(3)(0069)

1495(3)(-0017)

1372(3)( 0016)

1405(3)(0008)

1376(3)(0017)

1413(3)(-0023)

1427(3)(0030)

1488(3)(-0025)

1423(3)(-0018)

(x) = (19) - (60)increasedecrease

60

19

1907(1)

1891(1)

1886(3)

1889(3)

1889(2)

1901(3)

1669

1725

Si

Si

Si

Si

Me

MeMe

Me

Me

Me

Me

MeMe

MeMe

Me

Si

Si

Me

MeMe

MeMe

Me

Si

Me

MeMe

Si

Me

MeMe

- 25 -

Figure 23 Comparison of bond lengths (in Aring) between linear [3]phenylene(CpCo)complex 19 and 2378-tetrakis(trimethylsilyl) linear [3]phenylene (60) The bond distances in 19 are shown in blue Increases in bond length in going from 60 to 19 are marked in green decreases in red

ldquobond fixationrdquo (Figure 12) remains in the vicinity of the uncomplexed cyclobutadiene Compound 19 thus provides a prime demonstration of the powerful effect of metalloaromatization46 in which the bonds of a cyclobutadiene-metal system attempt to adopt the equalized bond lengths that are a classic hallmark of aromaticity2ndash4 Encouraged by the successful development of a procedure to obtain X-ray quality crystals of 19 these techniques were applied to bis(trimethylsilyl) linear [3]phenylene(CpCo) 52 Gratifyingly with acetone as the solvent the results depicted in Figure 24 were ultimately obtained Figure 24 X-ray crystal structure of 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52)

Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are omitted for clarity

A comparison of the bond lengths of 52 with those of its corresponding linear [3]phenylene ligand 469a is given in Figure 25 Comparison with Figure 23 reveals the same type of aromatization of the ligand on attachment of the metal With these structures in hand an attempt was made to rationalize structurally the

- 26 -

thermodynamic preference for 52 in which the CpCo is located proximal to the silylated terminus in its equilibrium with 53 in which the metal is located close to the unsilylated benzene ring Focusing on the desymmetrizing ortho-bis(trimethylsilyl) unit one notes that the SiCndashCSi bond in 52 is elongated by 005 Aring on attaching the metal in 46 thus providing steric relief On the other hand the symmetry equivalent remote C7ndashC8 distance is unchanged The same effect is seen in the tetrasilyl complex 19

Figure 25 Comparison of bond lengths (in Aring) between bis(trimethylsilyl) linear [3]phenylene(CpCo) complex 52 and 23-bis(trimethylsilyl) linear [3]phenylene (46) Bond lengths for 46 are the average of four molecules in the unit cell (standard deviation = plusmn002)

Increases in bond length going from 46 to 52 are marked in green decreases in red

The observed structural changes make sense in a simple resonance picture

Co

1413(10)(007)

1406(10)(-004)

1459(10)

( 005)

1370(11)(-007)

1418(10)( 005)

1443(10)(003)

1470(10)(-005)

1465(10)(-005)

1446(10)( 008)

1485(10)( 006)

1432(10)( 004)

1347(10)(-003)

1345(10)(-002)

1492(10)( 007)

1503(11)(-002)

1379(10)(001)

1391(11)(-001)

1409(10)(004)

1418(11)(-003)

1367(11)(001)

1478(10)(-002)

1408(11)(-001)

1891(8)

1890(13)

1670

1723

SiMe

MeMe

Si

Me

Me

Me

(x) = (53) - (62)increasedecrease

SiMe

MeMe

Si

Me

Me

Me

190

145134152

139138

150

137145

136

142 137

152137 137

152

141

137 144

189

141143142140

52

46

- 27 -

(Scheme 216) Metalloaromatization alters the dominant resonance forms during intercyclobutadiene hopping such that the essentially single SiCndashCSi bond in 52 transforms into an essential double bond in 53 increasing unfavorable repulsion between the TMS groups Scheme 216 A Resonance Picture Rationale for the Preference of 52 in its Equilibrium with 53 The aromatization effect of metal complexation on the phenylene nucleus described structurally in the preceding text can also be demonstrated powerfully through the measurement of ring currents with 1H-NMR spectroscopy both by experiment and computation (NICS13 see Section 11) A relevant simple example is depicted in Figure 26(a) featuring the changes occurring when 12-bis(trimethylsilyl)benzocyclobutadiene (61) is complexed by CpCo as in 6251 The paratropic antiaromatic 8π system 61 exhibiting relatively shielded six-membered ring hydrogens turns diatropic in 62 Equally importantly and focusing on the ring current contributions of the individual cycles the paratropism of the four-membered ring in 63 shields the adjacent hydrogens more than the remote ones Conversely aromatization of this ring and the ensuing diatropism inverts this order

Figure 26 The effect CpCo complexation (a) on benzocyclobutadiene 61 and (b) linear [3]phenylene 46 Chemicals shifts are in ppm

Co SiMe3

SiMe3

Co

SiMe3

SiMe352 53

∆Gdeg298 =23 kcalmol

- 28 -

Turning to a phenylene system comparison of the NMR data for complex 52 with those for ligand 46 (Figure 26(b)) reveals the same changes not only in the vicinity of the ligated ring but also in the remote parts of the molecule Thus the hydrogens closest to the metal fragment are shifted downfield by 125 ppm in 62 and 148068 ppm in 52 when compared with 61 and 46 respectively The observed relatively large chemical shifts of the arene hydrogens proximal to the metal unit are not due to its anisotropy since its value in this area of space is (if anything) shielding5152 In addition the remote hydrogens in 52 are deshielded by 055033 ppm relative to the corresponding nuclei in 46 clearly substantiating the aromatization of the overall system upon metal complexation that was seen by structural analysis These pronounced chemical shift changes are diagnostic and greatly aided the spectral interpretations of the photochemically induced haptotropic shift experiments described in Sections 21 and 22 as illustrated for the isomerization between 52 and 53 (Scheme 217)

Scheme 217 Chemical Shift Changes in the Isomerization of 52 to 53

These NMR measurements were augmented by NICS calculations carried out in collaboration with Professor Amnon Stanger at the Technion in Haifa NICS data have the advantage that they indicate the extent of (anti)aromaticity even in rings for which the molecule has no hydrogen probe in the classical NMR experiment in this case the cyclobutadienes Computational details are given in Chapter 4 The experimentally determined proton NMR data for the series of silylated linear phenylenes from [2] to [5] and their metallated analogues in addition to the corresponding NICS(1) values of the respective parent phenylenes are shown in Figure 27 All compounds in Figure 27 are known except for the hypothetical biphenylene(CpCo) 64 which is included for comparative purposes Metalloaromatization is pronounced as all rings of the phenylene exhibit diminished or more negative NICS numbers signaling increasing aromatic and decreasing antiaromatic character respectively Again the effect is most pronounced on the rings closest to the metal bound unit tapering off (but never disappearing) with distance Most illustrative in this respect is 44 in which the penultimate and ultimate rings away from the Co still show decreases in the NICS values of 06 and 05 ppm respectively Interestingly the sum of all NICS values of 44 (ldquototal NICSrdquo13c) ndash91 is less negative than that of 21 ndash132 suggesting that 21 is more aromatic hence more stable as observed experimentally This may be fortuitous and the issue is addressed further in Section 24 Finally a caveat regarding the unusually large negative NICS values associated with the CpCo-complexed cyclobutadiene rings As pointed out by Solagrave in connection with a related study of (benzene)Cr(CO)3 which produced similar numbers53 there are local ring currents associated with the extra electrons involved in the metal to π-ligand

CoTMS

TMS796675674

678

436 CoTMS

TMS747683724

662

444

310 365 nmsunlight

30ndash50oC

52 53

- 29 -

bonding that lead to an overestimation of aromaticity Therefore to corroborate the general conclusions of metalloaromatization of this (and all other rings) in Figure 27 Stangerrsquos NICS scan method was applied54 This procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (NICSXY) and out-of-plane components (NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their

Figure 27 Experimental 1H-NMR (C6D6 blue) and computed NICS(1) (green) values for linear phenylenes and their corresponding CpCo complexes The experimental data are for the silylated

derivatives shown The NICS data are for the parent systems interpretation The data presented in Chapter 4 confirm the conclusions of this section While not reflective of ring current effects the values of the 13C chemical shifts for the linear phenylene(CpCo)complexes do provide some insight into the nature of the

- 30 -

σ-framework Comparing complex 19 with parent ligand 60 one observes two general phenomena (Figure 28) The most apparent is the upfield values for the cobalt-bound cyclobutadiene carbons (~74ndash78 ppm) in 19 arising from the local anisotropic shielding effect of the metal (vide supra) Secondly the carbon atoms in the four-membered ring not bound to the metal exhibit large deshielded values (144ndash149 ppm) This effect also seen in ligand 60 arises from the rehybridization6 of the cyclobutadiene sp2 orbitals and is observed in all phenylene topologies A comparison of the 13C-NMR data for the linear [3]- [4]- and [5]phenylene(CpCo)complexes with their respective parent ligands is given in Chapter 4

Figure 28

13C-NMR data for complex 19 and parent silylated ligand 60 Values are in ppm 24 Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift How does the CpCo moiety migrate from one cyclobutadiene unit to the next Two extreme alternatives present themselves a least-motion movement across the intervening arene unit or a more circuitous pathway along the periphery The latter is prevalent in other computed haptotropic shifts56-57 in particular those occurring in (arene)Cr(CO)3 complexes all of which choose peripheral trails56 In these the metal typically moves straight to the edge to adopt an η4 (often described as η1) trimethylenemethane-like transition state on the way to a neighboring ring as illustrated for the η6-η6 hopping in naphthaleneCr(CO)3 summarized in Scheme 218 More relevant is the computed course of the η6-η6 interconversion of (biphenylene)Cr(CO)3 (Scheme 219)57 The metal slides from the (near)center of one benzene ring to the quaternary (four-membered) ring carbon to reach a distorted trimethylenemethane maximum and then proceeds to the edge of the bridging cyclobutadiene bond This species represents a minimum on the potential energy curve and adopts an η2-like complexed cyclobutadiene topology (ldquoquasi-η4rdquo) from which it continues by the microscopic reverse on to the other benzene nucleus The relevance of these findings with respect to the intercyclobutadiene hopping of CpCo along the phenylene frame was not clear at the outset of the work described in this section The CpCo fragment has a different electronic requirement from Cr(CO)3 and interring migration in arenes (and related systems) involves aromatic electron counts of all intervening circuits

Scheme 218 Migration of Cr(CO)3 Across Naphthalene

- 31 -

Scheme 219 Migration of Cr(CO)3 Across Biphenylene

DFT calculations were carried out in collaboration with Professor Thomas Albright at the University of Houston In these studies using B3LYP 3-21G (carbonhydrogen) and LANL2DZ (cobalt) basis sets the metal fragment was placed 18 Aring above the π system with energy minimizations carried out every 02 Aring along the frame of the parent linear phenylene in question When transition states and local minima were located their structures were refined with the B3LYP 6-31G (hydrogen) 6-113G (carbon) and LANL2DZ (with inclusion of cobalt f-orbitals) basis sets More computational details are given in Chapter 4 The resulting potential energy surface for the thermal rearrangement in the parent linear [3]phenylene(CpCo)system is shown in Figure 29 Figure 210 contains enlarged images of the transition states and intermediate structures The haptotropic shift begins with the (η4-cyclobutadiene)CpCo global minimum (labeled ground state GS) assigned a relative value of 000 kcalmol An η2-cyclobutadiene transition state (TS 1) 269 kcalmol higher in energy than GS is passed before reaching a local minimum (LM) that lies 109 kcalmol above GS LM features CpCo coordinated unsymmetrically η4 to the central benzene ring thus avoiding an unstable 20 electron η6-benzene configuration (not shown) which when explicitly calculated proved to lie 36 kcalmol above LM From LM a symmetry-related second η4 structure is reached via an η3-benzene transition state (TS 2 barrier 14 kcalmol) that symmetrizes the ldquoleftrdquo with the ldquorightrdquo half of the molecule LM is 249 kcalmol higher in energy than GS The shift is completed through the reverse of the initial two movements through LM and TS 1 on the other side of the ligand to reach the second cyclobutadiene ring Thus as for Cr(CO)3 (Scheme 219) CpCo migrates along the edge of the linear phenylene but because of its differing electronic needs through distinctly different intermediates and transition states Most obvious is the internal η2-cyclobutadiene TS 1 which for Cr changes to a peripheral η2-intermediate The calculated rate determining barrier of 269 kcalmol (GS to TS 1) is slightly higher than that measured for the reversal of 53 to 52 (~23 kcalmol) Part of this discrepancy may be due to ground state activation of 53 which is ~2 kcalmol less stable than 52 The LM structure has some resemblance to the isolated η4-CpCo angular [3]phenylene 23 (Section 12) Its location in an energetic well of ~14ndash16 kcalmol (TS 1 and TS 2) suggested that it may be observable at low temperature This investigation is detailed in Section 25

- 32 -

Figure 29 Calculated potential energy profile for the thermal η4η4 haptotropic shift in linear [3]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

0

5

10

15

20

25

30

1 2 3 4Reaction Path

Co

Co

C o

C o

GS η

4

LM η

4

TS1 η

2

TS 2 η

3

00

269

109

249

Key - Global MinimumGround State (GS)- Local Minimum (LM)

- Transition State (TS)

122

3 34 4

- 33 -

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 34 -

(d) Transition state 2 η3-benzene (249 kcalmol)

Figure 210 Optimized structures and relative energies for the linear [3]phenylene(CpCo) haptotropic shift Carbon atoms are shaded grey hydrogens light grey and cobalt blue Bond

lengths are in Aring The potential energy profile for the thermal shift in the linear [5]phenylene(CpCo) system was calculated in the same manner and is shown in Figure 211 Images of the intermediates and transition states are depicted in Figure 212 Placing the metal fragment on the inner cyclobutadiene ring resulted in the lowest energy structure and was therefore set as the global minimum (GS) Two distinct haptotropic migrations inner-to-inner and inner-to-outer cyclobutadiene are now possible (Section 21) Beginning at GS the metal can proceed in the direction of TS 2 or TS 3 respectively both of which are η2 with similar barrier heights (~36 kcalmol) The former pathway is degenerate and continues from TS 2 to η4-LM 1 and then via η3 central benzene TS 1 to the symmetry related corresponding LM 1 TS 2 and finally GS involving the opposite inner four-membered ring The rate determining barrier for this process is 359 kcalmol clearly too high to be measurable by NMR techniques as found for 212838 Interior-to-exterior shifting of the cobalt continues from TS 3 on to η4-benzene LM 2 The η3-TS 3 is traversed before the second η4η2

sequence (LM3 and TS 5 respectively) ultimately leading to LM 4 which is the outer

- 35 -

cyclobutadiene coordinated structure and represents the photoisomeric species observed experimentally in Scheme 23 The computed rate-determining barrier (TS 3) of 263 kcalmol for the reverse reaction of LM 4 to GS is close to the experimentally measured values of 256ndash276 kcalmol for the derivatives in Table 21

Figure 211 Calculated potential energy profile for the η4η4 haptotropic shift in linear [5]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

40

Reaction Path

263

0

5

10

15

20

25

30

35

C o

C o

C o

C o

Co

Co Co

C o

C o Co 360 370

359 357

367

97

203 190 196

1 2 3 4 5 6 7 8 9 10

TS 1 η

3

LM 1 η

4

TS 2 η

2

GS η

4 00

TS 3 η

2 TS 4 η

3 TS 5

η2

LM 2 η

4 LM 3 η

4

LM 4 η

4

Key- Global MinimumGround State (GS)

- Local Minimum (LM)

- Transition State (TS)

- 36 -

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 37 -

(d) Transition state 4 η3-benzene (367 kcalmol)

(e) Local minimum 3 η4-benzene (190 kcalmol)

- 38 -

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 39 -

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

(i) Local minimum 1 η4-benzene (190 kcalmol)

- 40 -

(j) Transition state 1 η3-cyclobutadiene (356 kcalmol)

Figure 212 Optimized structures and relative energies for the linear [5]phenylene(CpCo) haptotropic shift Structures for the inner-to-outer cyclobutadiene migration are given by (a)ndash(g)

Species (h)ndash(j) are involved in the interior-to-interior four-membered ring pathway Carbon atoms are shaded grey hydrogen atoms light grey and cobalt blue Bond lengths are in Aring

Why does CpCo prefer complexation to the internal cyclobutadiene that is GS (as represented by 21 and 42) over LM 4 (as represented by 44 and 45) Calculations show that the energies required to distort linear [5]phenylene to the geometries found in

- 41 -

the complexed isomers are very similar (16 versus 14 kcalmol) Hence the answer must rest on electronic grounds Indeed extended Huumlckel calculations reveal that the overlap populations between the frontier orbitals on the CpCo fragment and the HOMO and the LUMO of the π system are greater for GS (00793 and 00745 respectively) than for LM 4 (00556 and 00517 respectively) A didactically more instructive valence bond view recognizes that metalloaromatization of the inside four-membered ring allows the formulation of more resonance forms that avoid antiaromatic cyclobutadiene circuits A full list of these resonance forms as well as details of the EHMO calculations are given in Chapter 4 25 Low Temperature Photochemical Studies of the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes Of the various participating species in the mechanism for intercyclobutadiene migration (Section 24) specific attention was focused on the η4-benzene intermediates that occur in both the linear [3]- and [5]phenylene haptotropic shifts These structures are energetic local minima on the reaction profiles for both systems and were of considerable intrinsic interest not only as reactive intermediates in this manifold but also because of their relationship to the isolable angular [3]phenylene(CpCo) complex 2329 (Figure 213) Figure 213 (a) Calculated structure for the η4-benzene linear [3]phenylene(CpCo)intermediate

in the haptotropic migration (b) Crystal structure of η4 angular [3]phenylene (CpCo) 23

While rare a handful of other η4-benzene-metal complexes have been isolated (Figure 214) For example two related iridium based systems benzene(CpIr) 6658 and benzene triphos(Ir) 6759 are known As expected ligation causes significant shielding of the hydrogens in the η4 portion of the ligand especially the terminal positions The η4 intermediates in the haptotropic shift are situated in wells on the potential energy surface that are ~17 kcalmol deep for the linear [5]- and ~15 kcalmol for the linear [3]phenylene complexes These values are large enough that such species might be observable by NMR spectroscopy if irradiation of the starting materials were performed at low temperature and if the excited state would relax selectively to these intermediates As a suitable candidate with which to explore this possibility the partly symmetric tetrasilyl complex 19 was chosen The generation of anticipated desymmetrized 68 would be readily detected by the appearance of 11 new singlets in the 1H- and 23 new peaks in the 13C-NMR spectra (Scheme 220)

(a) (b)

- 42 -

Figure 214 Selected relevant examples of isolated η4-benzene complexes and their proton NMR chemical shifts (ppm)

Scheme 220 Low Temperature Irradiation Experiment Designed to Generate η4-Benzene Intermediate 68

Construction of a satisfactory setup to allow for the planned low temperature irradiation was not trivial An optimal experimental configuration however was devised utilizing three pieces of equipment each of which is shown in Figure 215 The first was a custom-made Pyrex Dewar flask small enough to adequately contain an NMR tube Cooling was achieved by means of a Neslab refrigerated circulating bath Thirdly a Rayonet Photochemical Reactor was used as the light source The sample was first placed inside of the Dewar flask and cooled to the required temperature inside of the Rayonet Once cold irradiation was carried out for the desired length of time When complete the sample was transported cold to the NMR laboratory and very quickly placed inside of a pre-cooled NMR probe for analysis A solution of complex 19 was irradiated at ndash65 degC as described and its 1H-NMR spectrum recorded at ndash30 degC revealing a dramatic change The signals for 19 had almost entirely vanished and a set of new peaks appeared The new aromatic resonances were comprised of two sharp singlets at δ = 708 and 644 ppm and a broad singlet at δ = 558 ppm all of which integrated for 2 hydrogens each Another broad

649

586

316

H H

Co544

66 67 23

Ir

P(Ph2)P(Ph2) P(Ph2)

H

H

H

625

594

350

Ir

H

H

H

- 43 -

Figure 215 Cold irradiation experimental setup consisting of (a) Pyrex Dewar flask (b)

refrigerated circulating bath (c) Rayonet Photochemical Reactor with Pyrex Dewar vessel placed inside

(a) η

4 (b) η

4 (c) η

4

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

New peaks

L L

- 44 -

Figure 216 Stacked plot of the aromatic 1H-NMR spectral region recorded after the cold irradiation of 19 in toluene-d8 Peaks for 19 are indicated by blue new peaks by red arrows

Impurities are marked with and traces of free ligand 60 with L The scale is in ppm

singlet at δ = 398 ppm (5 H) was assigned to a new Cp group (Figure 217) and two new TMS singlets (9 H each not shown) were also present The new broad Cp absorption displayed peculiar behavior gradually moving to higher field (∆δ ~ 08 ppm for Cp-H) on warming from ndash30 degC to 10 degC (Figure 217) The broadened singlet at δ = 558 ppm showed similar albeit much attenuated behavior At room temperature all new peaks had disappeared leading to regeneration of the original spectrum of 19

Figure 217 Stacked plot of the Cp spectral region in the cold irradiation of 19 in toluene-d8 Peaks for molecule 19 are indicated by blue the new peaks by red arrows The scale is in ppm

In addition to these NMR observations a remarkable change in color from the redmaroon of 19 to olive green took place during the course of this experiment (Figure 218) Indeed the UV-Vis spectrum of the low temperature species is strikingly different from that of 19 showing a large broad absorbance band centered in the visible region

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

19

THF

- 45 -

Figure 218 Color change during the low temperature irradiation of 19 (a) Before irradiation (b) After irradiation

Complex 19

Low Temperature Species

0

02

04

06

08

1

12

14

16

18

2

400 430 460 490 520 550 580 610 640 670 700

Wavelength (nm)

Ab

sorb

an

ce

Figure 219 UV-Vis spectra (toluene) of 19 (at rt) shown in blue and the new compound (at ~

ndash30 degC) shown in red

at 654 nm (Figure 219) Warming the sample to room temperature restored its original red color While the observation of a new species was gratifying the NMR data posed a puzzle as they were clearly incompatible with (a static) structure 68 Instead they pointed to a molecule exhibiting mirror (or ldquotop-downrdquo) symmetry along the long molecular axis as in 19 itself The two most obvious candidates 69 and 70 (Figure

(a) η

4 (b) η

4

- 46 -

220) were ruled out as the first could not be found during the computations underlying Figure 29 and the second actually constitutes the transition state TS 1 for the thermal reverse process

Figure 220 Possible (but unlikely) structures of correct symmetry for the low temperature

photoisomer of 19 In the hope to shed further light on the nature of purported 68 low temperature 13C in conjunction with 2-D NMR (HSQC HMBC) experiments were carried out These data led to the tentative assignments shown in Figure 221 Assuming the presence of top-down symmetry as surmised by the proton spectra one would have expected to observe nine phenylene carbon signals The actual spectrum however contains only six peaks The Cp line was broadened to the point of being barely visible and no crosspeaks for the absorption at δ = 556 ppm were seen by 2-D NMR spectroscopy

Figure 221 Partial assignments of 1H-(italicized) and 13C-NMR signals of 68 The ldquotop-downrdquo plane of symmetry is indicated by the dashed purple line HMBC δ = 643 ppm correlates with δ = 1461 and 1521 ppm δ = 708 ppm correlates with δ = 1477 and 1508 ppm δ = 033 ppm

correlates with δ = 1477 ppm and δ = 036 ppm correlates with δ = 1461 ppm HSQC δ = 643 ppm correlates with δ = 1121 ppm δ = 708 ppm correlates with δ = 1227 ppm and δ = 398

ppm correlates with δ = 85 ppm The connectivity of the CpCo to the central ring is left intentionally unspecified and the choice of positioning it to the left of the center hydrogens (blue)

SiMe3

SiMe3

H

Me3Si

Me3Si

H

Co

398 (br)

HH

1461

~85 (br)

708

H

556 (br)1508

= Unobserved 13C signals

H

H

Mirrorplane

6431477 1521

033036

11211227

- 47 -

arbitrary Similarly the assignments of the groups of ldquoleftrdquo and ldquorightrdquo benzene signals are tentative and might be inverted The carbons marked could not be observed

It is thus clear that we are dealing with an unusual species and if it is 68 the molecule must be partly (but not completely) fluxional around the central ring Returning to the computed energy profile in Figure 29 one notes that central η4η4-benzene fluxionality via TS 2 with a barrier of 140 kcalmol is presaged This process which causes ldquoleftrdquo-ldquorightrdquo but not ldquotoprdquo-ldquobottomrdquo symmetrization is unlikely to be responsible for the above data as it should have given rise to two 1H-NMR singlets for the central hydrogens However considering the expected relative closeness in the respective chemical shifts of the anticipated signals (see Figure 214) accidental isochronism could not be ruled out Consequently low temperature irradiation experiments were executed with 52 in which the ldquoleftrdquo-ldquorightrdquo option of symmetrization was obviated by the substitution pattern while leaving the ldquotoprdquo-ldquobottomrdquo option intact (Scheme 221) As Scheme 221 Low Temperature Irradiation of 52 and Possible Pathways for Fluxionality of

Intermediate 71

indicated in color the latter would provide a diagnostically simple proton spectrum of only four phenylene signals The former on the other hand should show eight such peaks A potential complication of this experiment was the possibility of two regioisomeric (and non-interconverting) cobalt species located on either side of the central six-membered ring (Scheme 222) In the event the spectra shown in Figure 222 were obtained At ndash60 degC in

HH

CoTMS

TMS

CoTMS

TMS

TMS

TMS

Co

TMS

TMS

CoTMS

TMS

Co

TMS

TMS

Co

Top-bottom

cold hν ∆

Lef t-right

52 53

∆

71

or

H

HH

H

H H

H HH

HH H H

H

- 48 -

addition to unreacted 52 and photoisomer 53 a new species formed the spectral features of which implicate 71 as a ldquotop-bottomrdquo symmetrizing species Specifically the

Scheme 222 The Two Possible Regioisomers of 71 ldquoLeftrdquo and ldquoRightrdquo

71

52

53 53

53

52

TMS

TMS

Co

TMS

TMS

Co

TMS

TMS

Co

71

TMS

TMS

Co

or

Right Lef t

ndash60 degC

ndash50 degC

ndash40 degC

ndash30 degC

53

- 49 -

Figure 222 Stacked plot of the aromatic spectral region in the cold irradiation of 52 in toluene-d8 Peaks for molecule 52 are marked by blue arrows 53 in red and 71 in green Trace amounts

of free ligand bis(trimethylsilyl) linear [3]phenylene] 46 are denoted with L The scale is in ppm

unsubstituted benzene terminus hydrogens exhibit an AArsquoBBrsquo pattern at δ = 647 ppm which integrate for 4 hydrogens The central ring hydrogens appear as a broad singlet at δ = 557 ppm (2H) and the silylated terminus as a singlet at δ = 632 ppm (2H) Warming the reaction mixture to 10 degC led to the gradual disappearance of 71 with a concomitant increase of the signals assigned to 52 and 53 This experiment confirms the conclusions drawn as a result of the low temperature irradiation of 19 namely that a ldquotop-bottomrdquo symmetrizing species is generated Remarkably in view of the possibility of two regioisomers (Scheme 222) only one set of peaks is observed indicating that the excited state of 53 relaxes to settle on only one side of the central ring Which side is a matter of speculation Figure 223 compares the 1H chemical shifts of 71 with those of 68 and for calibration 52 53 and free ligands 46 and 60 For the first pair it is clear that the two species are very similar with almost identical chemical shifts of the relevant hydrogens taking into account the considerable deshielding effect of TMS substitution on the unsubstituted terminus in 73 (~07 ppm cf 52 vs 53 46 vs 60) Arguably placing the CpCo moiety to the ldquoleftrdquo as depicted in 68 and 71 aromatizes the proximal benzene by η2-complexation of the adjacent four-membered ring leaving considerable benzocyclobutadiene character on the ldquorightrdquo consistent with the associated chemical shifts

- 50 -

CoTMS

TMS796675674

678

CoTMS

TMS747683724

662

Co

TMS

TMS

52

71

53

424

642

557 632652

436 444

Co

TMS

TMS

68

398

556 643708

TMSTMS

TMS

TMS684607619

645

46

assignmenttentative

TMS

TMS

TMS

TMS623 685

60

TMS

TMS

TMS

TMS

Co

691 795745

19

441

Figure 223 1H-NMR chemical shift comparison of 68 and 71 with other relevant species A plot of the changes in concentration of 52 53 and 71 with temperature is shown in Figure 224 Within (the considerable) error and considering the unusual magnetic behavior of 71 (vide infra) it appears that the latter converts mainly to 52 in the temperature regime in which 53 is stable with respect to its thermal reverse to 52 This observation may be interpreted as indicating a lower barrier for Co migration from the center ring to the more stable cyclobutadiene haptomer

- 51 -

0

1

2

3

4

5

6

7

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Inte

gra

tio

n v

s I

nte

ra

l S

tan

da

rd

52

53

71

Figure 224 Plot of the concentration changes of 52 53 and 71 with temperature measured by the relative integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively

The ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100)

Another plot this one showing the ratios of 52 53 and 71 with respect to each other is given in Figure 225 The disappearance of 71 with rising temperature is illustrated by the increase in the ratios of 5271 and 5371 As indicated by the steep slopes the conversion of 71 into 52 and 53 is particularly fast between ndash10 and 0 degC That complex 52 is preferentially formed is again confirmed by the escalating 5253 ratio While these data do not provide a definitive answer for the location of the CpCo they are consistent with the plots shown in Figure 224 and the above discussions

- 52 -

0

1

2

3

4

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Rel

ati

ve

Inte

gra

tio

n

5271

5371

5253

Figure 225 Plot of the ratios of 52 53 and 71 against each other with temperature measured by the integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively The

ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100) Having established the topological aspects of 68 and 71 attention was turned to their peculiar NMR characteristics in the vicinity of the metal ie the broad peaks for the central hydrogens and the CpHs the broad Cp-carbon line the inability to observe 13C signals for the central benzene ring and the temperature dependent drifting of (particularly) the Cp absorption A trivial (and ultimately unsatisfying) explanation for at least peak broadening was the presence of trace paramagnetic metallic impurities60 that might have been generated during the irradiation process Spin exchange preferentially Co-based might affect the center atoms in 68 and 71 more than the remainder of the molecule although it should also cause line broadening in the isomers 19 and 52 and 53 respectively Experimentally the presence of such species was made unlikely by executing the cold irradiation experiment of 19 in the presence of the radical trap 13-cyclohexadiene which produced spectra identical to those described earlier An attractive alternative that might explain the data and in addition provide a mechanism for ldquotop-downrdquo exchange is of the intervention of triplet state cobalt species The ability of metals to change their electronic spin state and the consequences of this phenomenon on organometallic structure and reactivity are well documented61

18-Electron CpCo complexes are ground state singlets but their 16-electron counterparts accessed typically by ligand dissociation have more stable triplet configurations62 A number of CpCo and related Co species have also been reported in

- 53 -

which singlets are in thermal equilibrium with paramagnetic triplets by intersystem crossing63 Such complexes display spectral behavior very similar to that seen for 68 and 71 For example 7263b exists as a mixed spin state system in which the singlet predominates at room temperature in solution (Figure 226) On heating the triplet becomes increasingly populated shifting and broadening its NMR signals Cooling the solution back to room temperature reverses these spectral changes In addition to complexes of cobalt analogous observations have been reported for other metals such those based on hafnium64 copper65 ruthenium66 and tungsten67

Figure 226 Temperature dependent chemical shifts in CpCo derivative 72 in toluene-d8

(marked as S on the plot) The scale is in ppm

Consideration of these examples would then suggest that 6871 undergo ldquotop-downrdquo equilibration through a triplet 16-electron intermediate or that 6871 themselves are triplets or have thermally accessible triplet states from which fluxionality might occur Since the relaxation times (T1) of paramagnetic systems60a are much shorter compared to their diamagnetic counterparts measurement of this property was thought to be informative The T1 values for the proton in 68 were determined via a standard inversion recovery experiment44 and are given in Table 24 (cf Figure 220) in comparison to p-terphenyl60b

Co

CoPMe3

72

- 54 -

Table 24 1H-NMR Relaxation Times in Intermediate 68 at ndash30 degC

Resonance (ppm) T1(s) 711 2309 646 0997 556 005 398 0108

In consonance with the associated line broadening the relaxation times of the Cp

(δ = 398 ppm 0108 s) and central ring hydrogens (556 ppm 005 s) are much smaller than those of the remaining phenylene ligand (711 and 646 ppm 2309 and 0997 s respectively) the latter in turn comparing well with the values in p-terphenyl With this corroborative evidence in hand the question whether the species is itself a triplet or is in thermal equilibrium with such was addressed The answer can be obtained by using a Curie-like graph68 in which chemical shifts are plotted as a function of temperature65 A linear relationship corresponds to the presence of a triplet compound while curved behavior is indicative of a singlet-triplet equilibrium Plotting the chemical shifts of the Cp hydrogen of 68 and 71 against the inverse of temperature (Figure 227) gave distinctly curved lines supporting the notion that these species are in thermal equilibrium with their triplets The exact nature of these species however remains to be determined

156

395404

345

p-Terphenyl

- 55 -

3

32

34

36

38

4

42

44

46

00036 00038 0004 00042 00044 00046 00048

1T (K -1

)

Ch

em

ica

l S

hif

t (p

pm

)

71

68

Figure 227 Plot of the Cp chemical shift (toluene-d8) of 68 and 71 versus the inverse of temperature

DFT calculations have commenced in an attempt to find a plausible structure for such a triplet cobalt species and with it possibly arrive at a mechanism for the fluxional behavior of 68 and 71 These studies are being carried out in collaboration with Professors Tom Albright of the University of Houston and Vincent Gandon of the Universiteacute Paris-Sud 11 Preliminary results at the B3LYP6-31G(dp) and BP866-31G(dp) levels suggest the η2-cyclobutadiene structure depicted in Figure 228 It is apparent that this species corresponds topologically to singlet TS 1 in Figure 29 and 70 in Figure 220 endowed with the symmetrical requirements dictated by the experiments

- 56 -

Figure 228 Calculated structure of a triplet η2-cyclobutadiene linear [3]phenylene(CpCo)

One can therefore envision fluxionality between the two ldquotoprdquo and ldquodownrdquo η4-benzene structures via the intermediacy of a triplet η2-cyclobutadiene (Scheme 223) Further Scheme 223 Conversion of ldquoTop-Downrdquo η4-Haptomers of 68 Via a Triplet η2-Cyclobutadiene

Intermediate

computations are required to pinpoint the minimum energy crossing points between the singlet η4 and triplet η2 structures and to explain why this triplet does not collapse to the CpCo cyclobutadiene isomer This work is in progress 26 Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 All of the linear phenylene(CpCo) complexes mentioned thus far share one common feature a single CpCo unit bound to the phenylene scaffold However since there are one or more additional cyclobutadienoid rings in the series the question arises whether it might be possible to bind more than one metal fragment to the ligand If so what would be the structural consequences Would be there further metalloaromatization Would such systems be capable of light-induced haptotropism and if so how would the metals move relative to the ligand and to each other Finally would such complexes mimic structurally the variety of arrays obtained in the reaction of 29 with Fe2(CO)9 (Scheme 15) Since the linear phenylenes become increasingly more antiaromatic with size the optimal candidates for preparing such multi-metallic systems should be the higher members of the series Indeed evidence for double CpCo attachment was obtained in the form of the minor by-products 73 and 74 (Scheme 224) obtained during the

Scheme 224 Side Products in the Preparation of Linear [4]- and [5]Phenylene(CpCo)

- 57 -

Complexes by Cobalt-Catalyzed Cyclization

preparation of 20 and 21 respectively (Scheme 13) These Diels-Alder type adducts of a third BTMSA molecule to the π-frame can be envisaged to be derived from 75 and 76 respectively in which the six-membered ring flanked by the two CpCo(cyclobutadiene) units would be expected to have an unusual (biradicaloid) electronic structure Evidence for the feasibility of such arrays rests on the unique black-red syn-bis(irontricarbonyl) compound 77 whose structure was determined by X-ray analysis69 With reasonable quantities of 19 in hand the possibility of ligating a second CpCo unit to it was explored This idea was further encouraged by the observation that crude samples of bis(trimethylsilyl) linear [3] phenylene(CpCo) complex 53 contained a very small (3 ) peak at mz = 618 an exact match for the mass of a doubly metallated analog Consequently 19 was treated with one equivalent of CpCo(C2H4)2 in benzene to afford a reddish black solid (Scheme 225) The mass spectrum data exhibited a

Scheme 225 Preparation of Complex 78 from Complex 19

TMS

TMSTMS

TMS

CoCpCo(C2H4)2

22h 70 oC C6H6Linear [3]TMS4(CoCp)2

5619 78

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

74

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

73

TMS

TMS

TMS

TMSCoCpCpCo

76

TMS

TMS

TMS

TMSCoCpCpCo

75

Ph

Ph

Ph

Ph

Fe(CO)3Fe(CO)3

77

- 58 -

molecular ion peak at mz 762 corresponding to 19(CpCo)2 The 1H-NMR spectrum (acetone-d6) revealed four sharp singlets integrating in the ratio 410236 indicative of a highly symmetrical structure The chemical shift of the benzene termini (736 ppm) suggested that these rings have significant aromatic character and is similar to the value of 745 ppm seen for the hydrogen positioned farthest away from the CpCo in 19 (Figure 27) Similarly the 13C signals of the terminal rings in 78 (1505 1454 and 1258 ppm) are analogous to those from the corresponding terminal ring in 19 (1484 1433 and 1256 ppm Figure 28) Detailed analysis of 78 with two-dimensional NMR techniques (HSQC and HMBC) allowed for a complete assignment of all peaks in the 1H and 13C spectra (Figure 229) The strongly shielded (relative to the free ligand) proton (481 ppm) and carbon (537 and 571 ppm) resonances assigned to the central benzene ring clearly showed that both cobalt fragments are coordinated to the phenylene ligand at this position Interestingly these data bear a very close resemblance to those of the corresponding diiron complex 31 (Scheme 15) and are compared in Figure 229 Its central 13C resonances (688 and 582 ppm) are shifted upfield in a manner akin to 78 although not quite as much reflecting the increased electron withdrawing ability of the Fe(CO)3 group relative to CpCo70 Complex 31 like 78 exhibits aromatized terminal benzene rings as indicated by its 1H (750 ppm) and 13C (1484 1446 and 1258 ppm) chemical shifts These spectral similarities make it likely that 78 and 31 are isostructural The only structural ambiguity pertains to the orientation of the two metal fragments with respect to the π ligand a problem that had been left undecided in the assignment of structure 31 ie 31a (syn) versus b (anti Scheme 15)27 These options for 78 are

- 59 -

CpCoTMSTMS

TMS TMS

H H039 (36)

537 1258822

270

1454571

1505

481 (2) 736 (4)489 (10)

TMS TMS

TMSTMS

H

(OC)3Fe

(OC)3Fe

CpCo

78

31a

750 (4)553 (2)

036 (36)H

220

1446

1258

1484

688582

2128

Figure 229 Comparison of 1H- and 13C-NMR assignments (ppm) for molecules 78 (acetone-d6) and 31 (1H acetone-d6

13C CDCl3) Proton chemical shifts are in red and carbon in blue Integrations for the proton resonances are in green HSQC for 78 δ = 039 ppm correlates with δ = 270 ppm δ = 481 ppm correlates with δ = 537 ppm δ = 489 ppm correlates with δ = 822 δ

= 736 ppm correlates with δ = 1258 ppm HMBC for 78 δ = 036 ppm correlates with δ = 1454 ppm δ = 481 ppm correlates with δ = 571 and 1505 ppm δ = 736 ppm correlates with δ = 571 1454 and 1505 ppm The placement of the cobalt atoms in 78 is tentative (see Figure

229)

Figure 230 Possible structures for 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

- 60 -

shown in Figure 230) Both equally exotic options are precedented in the literature and corroborated by X-ray structural analyses (Figure 231)71

Figure 231 Illustrative examples of complexes with two metal fragments coordinated to the same benzene ring

Bis(CpFe) complex 7972 and its rhodium analog 8073 contain [M2(syn-micro-arene)] units in which the metals are linked58 Molecule 79 consists of two CpFe units coordinated η4 to the boat-shaped benzene ring sharing ligating carbon atoms In contrast the CpRh fragments in 80 are bound in an allyl η3 manner and the arene also adopts a boat conformation On the other hand bis[tris(tert-butyl)]toluene(CpCo) complex 8174 and the related system 8275 both exhibit [M2(anti-micro-arene)] units in which η4 coordination between the benzene ring and each of the metal fragments takes place Here the metals share carbon atoms but now involving a sandwiched ligand The arene in 81 retains a planar aromatic geometry while the benzene moiety in 82 is bent into a highly distorted chair conformation Unfortunately model structures 79ndash82 do not exhibit diagnostic NMR properties that would provide a clear distinction between synanti and planarnon-planar topologies For example the 1H-NMR peaks for the toluene ligand in anti-complex 81 range from 400ndash380 ppm74 whereas the signals for the benzene moiety in syn-bis(CpRh) 80 appear at 400ndash330 ppm73 The 13C data are similarly inconclusive as illustrated by comparison of 78 (562ndash531 ppm for the benzene ring) with 79 (648ndash525 ppm)72b An interesting property of these bis(metal) arene complexes is fluxionality of the metal fragments by haptotropic shifts along the periphery of the aromatic ring as depicted in Scheme 226 In complex 79 the hexamethylbenzene ligand (bound η4η4

in the solid state) displays a single arene resonance at 588 ppm in its room temperature carbon NMR spectrum Cooling to ndash90 degC however produces two distinct arene peaks at 525 and 648 ppm (for the shared and single-metal-bound carbons respectively as shown in 79a in Scheme 227) Fluxionality was postulated to proceed through an η3η3 intermediate (79b) that is structurally similar to Rh complex 80 which is itself a fluxional species

Scheme 226 Examples of Fluxional Processes in Dinuclear Arene Complexes 79 and 80

82 81

80 (R = CH3)

79

- 61 -

Anti-bis(β-diiminate)Rh complex 83 shows similar mobility (Scheme 226)76 A mechanism for η4η4 migration of the anti-metal fragments was proposed using the lowest energy species found by DFT calculations In these compounds the anti-metal fragments convert between η4η4 (83a 83c 83e) structures by passing through η3η3

(83b) and η4η2 (83d) transition states The energy barrier for η4η4 migration in 83 was experimentally determined to be 6 kcalmol This value is in line with other experimentally measured syn and anti dinuclear ring slippage processes which are typically le ~10 kcalmol71-75 The possibility of fluxionality in 78 might be observable if asymmetric configurations such as 78c and 78d (Figure 231) represent the lowest energy forms since they entail NMR observable desymmmetrization of the ligand Unfortunately cooling 78 in the NMR probe to temperatures as low as ndash80 degC in toluene-d8 did not reveal any signs of signal decoalescence

- 62 -

Figure 232 Possible lowest energy forms of complex 78

Hoping that further light could be shed on the disposition of the CpCo moieties in 78 by chemical transformations a brief investigation of its reactivity was undertaken For example bis(metal) arene complexes have been shown to readily undergo arene exchange reactions71 In complex 81 for example the toluene ligand is displaced by benzene at room temperature74 However heating a sample of 78 to 120 degC in toluene-d8 did not lead to any changes in the NMR spectra Turning to potential photochemical activation 78 was irradiated at various wavelengths (300ndash365 nm) These conditions as well as ambient sunlight did not cause any changes in its 1H-NMR spectrum further documenting 78 as a rather inert species X-ray crystallographic analysis would appear to be the only method of resolving the identity of complex 78 Producing suitable crystals of this molecule however has proven extremely difficult and will be the subject of future investigations 27 Summary and Outlook The work presented in this chapter published as a communication77 has detailed the first examples of η4η4 intercyclobutadiene migration and detailed mechanistic studies of this unprecedented reaction The haptotropic shift was found to be an intramolecular process with the CpCo fragment undergoing various changes in hapticity for the thermal isomerization Low temperature photolytic studies have revealed the existence of a thermally unstable intermediate species the exact structure of which is uncertain These results point to what appear to be significant differences between the photo- and thermal haptotropic pathways Further work both experimental and computational will be required to elucidate the details of the photochemical reaction In addition to the studies of linear phenylene(CpCo) haptotropism a hitherto unknown complex containing two CpCo fragments bound to linear [3]phenylene was prepared and scrutinized in preliminary form Despite extensive characterization the structure of this complex with respect to the position of the metal centers remains elusive Future work will focus on the acquisition of a crystal structure

- 63 -

Chapter 3

Nickel-Catalyzed Insertion Reactions for the Preparation of [N]Phenacene Derivatives

31 Introduction Transformations involving metal insertion into the four-membered ring of the [N]phenylenes as discussed in Section 12 represent a significant mode of reactivity with a high potential for practical synthetic utility One specific application of this chemistry is the synthesis of the phenanthrene moiety via tandem metal insertion and alkyne cycloaddition to the four-membered ring (Scheme 31) Such a methodology Scheme 31 Potential Preparation of the Phenanthrene Group from the Alkyne Cycloaddition

with Biphenylene would be valuable for the preparation of PAHs possessing phenanthrene subunits but has remained fairly unexplored Only a few examples demonstrating this transformation have been detailed previously for biphenylene (7) (Scheme 32)

Scheme 32 Metal Catalyzed Alkyne Cycloaddition Reactions with Biphenylene

The first report of this process is by Eisch in 198533a who treated biphenylene with Ni(PEt3)4 and diphenylacetylene to produce 910-diphenylphenanthrene 84 Since then a number of metals have been shown to mediate this process19 Ni systems being most relevant to this chapter Thus for example 84 can also be made using an N-heterocyclic carbene-based Ni(0) catalyst78 Bis(diisopropylphosphino)ethane Ni(alkyne) species enable similar cycloadditions of fairly hindered (trimethylsilyl)alkynes sometimes involving more complex processes of silyl group migration79 while less hindered substrates lead to 84ndash8680a A mixed phosphinoaminoethane-chelated Ni species proved more reactive enabling cycloaddition of even the encumbered tert-butyl(phenyl)acetylene to furnish the corresponding phenanthrene80b With this background in mind our attention turned to applying this reaction to larger phenylene systems Of the various topologies of phenylenes at our disposal the angular version was

R1 R2

R2R1[M]

[M]

7 R R

R = Ph (84)

R = Me (85)

R = CH2OMe (86)

RR

[Ni]

- 64 -

particularly intriguing as it offered two extreme modes of alkyne addition (Scheme 33) In the first scenario exclusive attack at the outer periphery of the four-membered rings would produce the helical shaped PAHs known as helicenes (Scheme 33a)81

Scheme 33 Alkyne Cycloaddition with Angular Phenylenes to Produce (a) Helicenes or (b) Phenacenes

Reactions occurring only at the interior or ldquobayrdquo region (Scheme 33b) however would afford a class of compounds exhibiting a linear polyphenanthrene motif that are known as [N]phenacenes82 Unselective additions would result in mixed topologies Helicenes and their various derivatives constitute a well studied83 family of molecules and continue to be a popular area of research Phenacenes in contrast have been scrutinized much less in part because only four members of the parent series are known and because for N = 5 and 6 they are extremely insoluble84 Phenacene-based applications have been slow to develop but the first reports of the utilization of these molecules as functional organic materials suggest the beginning of a rich and promising field85 Thus in 2008 [5]phenacene (picene) was demonstrated to behave as stable high performance organic field effect transistor (FET)85b Currently the most common organic polycyclic benzenoid hydrocarbon-based FETs employ acenes which have a polyanthracene structure (Figure 31) The sensitivity

Figure 31 Linearly fused benzene topology of the acenes of these systems to air however has obstructed progress in this area86 For example pentacene a commonly used acene in FETs reacts readily with oxygen to form

+ RR

Helicenes

+ RR

Phenacenesn

R

R R R R

n

R

R

R

(a)

(b)

[N]Acenes

n

- 65 -

pentacenequinone a process that severely reduces device efficiency (Scheme 34)

Scheme 34 Degradation of Pentacene to Pentacenequinone Under Aerobic Conditions

Phenacenes on the other hand are much less prone to such decomposition pathways due to their higher HOMO-LUMO gap thus rendering them less reactive85b86a Their enhanced stability relative to acenes87 makes them better candidates for molecular electronic applications In a second seminal breakthrough [5]phenacene was very recently also found to behave as a superconductor at low temperature when doped with potassium85a This work paves the way for a new class of PAH-based superconducting materials in which phenacenes may play a key role

As this chemistry advances new synthetic methods for preparing derivatives of these molecules will be required in particular those bearing solubilizing andor otherwise functionally useful substituents The most general procedure for synthesizing phenacenes as developed by Mallory88 makes use of oxidative stilbene photocyclizations (Scheme 35)8388 In this transformation irradiation of the stilbene

Scheme 35 Generic Oxidative Stilbene Photocyclization Used to Prepare Phenacenes as Illustrated for Phenanthrene

moiety leads to conrotatory electrocyclic ring closure Trapping of the resulting intermediate with oxidizing reagents such as iodine or oxygen yields the desired phenanthrene subunit The requisite stilbenes are most generally accessible via the Wittig reaction as illustrated in the synthesis of [7]phenacene derivative 87 (Scheme 36) Although the yields for the photocyclization are typically reasonable (60ndash90 )85a the major drawback of this methodology is the numerous steps associated with preparing the functional groups required for the prerequisite Wittig reaction These

- 66 -

transformations serve to decrease the overall yield of the target molecule

Scheme 36 Synthesis of [7]Phenacene 87

While laborious Malloryrsquos method addresses successfully the problem of solubility As alluded to in Section 21 large PAHs become insoluble due to the increased π-π stacking forces that are experienced between aromatic rings The best solubilizing groups for the phenacenes were found to be sterically bulky groups located in the bay regions85a These modifications distort the phenacene framework from planarity thereby disrupting π-stacking and increasing solubility as demonstrated by the tert-butyl [7]phenacene 87 (Figure 32) This approach was applied to systems as large as [11]phenacene the current record in the series85a

Br

CH3t -Bu

1 BuLi2 DMF

Br

CH2

t-Bu

CHO

CH3t-Bu

PPh3

Br

+Wittig

t-Bu t-Bu

Br CH3 1 hν2 I2

t-Bu t -Bu

Br CH3

t-Bu t-Bu

Br H2C PPh3 Br

+

t-Bu t-Bu

OHC CH3

Wittig

t-Bu t-Bu

Br Br 1 hν2 I2

t-Bu t-Bu

Br CH3

t-Bu t -Bu

t-Bu t-Bu

87

1 NBS2 PPh3

- 67 -

Figure 32 Crystal structure of tetrakis(tert-butyl) [7]phenacene 87 Hydrogens are omitted for clarity

To test the viability of angular phenylenes as substrates in Ni catalyzed alkyne cycloadditions the simplest member 22 was chosen raising a number of questions First how many and what kind of products will be formed (AndashE in Scheme 37) Will there be inherent selectivity toward helicene C or phenacene E formation respectively If not can the reaction conditions be modified so as to induce such What will be the limitations with respect to the size of substituents especially in view of the crowded fjord and bay regions of D and E respectively The work presented in this chapter carried out in collaboration with Dr Zhenhua Gu89 explores these questions

Scheme 37 Possible Cycloaddition Products of Angular [3]Phenylene 22

22

[Ni]R R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

A B

C D E

32 Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene

Before embarking on the proposed chemistry the reactivity of 22 in the presence of nickel in the form of Ni(COD)(PMe3)2 in the absence of alkynes was queried Only starting material was recovered and there was no sign of dimerization (or oligomerization) to products of the type shown in Scheme 38 a mode of reactivity

- 68 -

readily attained by biphenylene and substituted derivatives33b

Scheme 38 Attempted Dimerization of Angular [3]Phenylene 22

In contrast exposing diphenylacetylene 88 to Ni(COD)(PMe3)2 and a small excess (109 equivalents) of angular phenylene 22 generated two products in the absence of any other (Figure 39) The first molecule 89 was the result of the cycloaddition of one diphenylacetylene at the bay region and the minor component The major product constituted tetraphenyl [5]phenacene 90 derived from 22 by double bay region attack The structures of both compounds were confirmed by X-ray analysis revealing highly distorted frames89 Scheme 39 Nickel Catalyzed Cycloaddition of Angular [3]Phenylene 22 to Diphenylacetylene

Yields Based on Diphenylacetylene

The outcome of this transformation was gratifying in its seeming simplicity and selectivity Thus it appeared that metal insertion occurred exclusively to bay region bonds heralding the discovery of a new phenacene synthesis The observation of relatively large amounts of 90 could be ascribed to increased reactivity of 89 relative to 22 possibly due to steric activation by the newly introduced bay region phenyl group To test this hypothesis 89 was subjected to the cycloaddition reaction conditions (Scheme 310) Surprisingly not only was this reaction slower than that of 22 but the expected phenacene 90 was only a minor product (6 ) Instead tetraphenylbenzo[c]chrysene 91 a regioisomer of 90 as confirmed by X-ray analysis89

+

+ +

Ni(COD)(PMe3)2

22

- 69 -

was isolated in 74 yield the result of non-bay alkyne cycloaddition to 89 Therefore 89 is not the precursor of 90 Rather there must be separate reaction pathways leading to each respective product

Scheme 310 Cycloaddition Reaction of 89 with Diphenylacetylene 88

A series of semi-quantitative experiments monitored by 1H-NMR spectroscopy was carried out to shed some light on this mechanistic problem First the reaction of angular [3]phenylene 22 with diphenylacetylene 88 in Scheme 39 was addressed Because dinuclear metallic activation of the strained C-C bond in biphenylenes has been implicated in a number of studies19 it was possible that the above mechanistic duality was caused by the presence of catalytic Ni2 species in addition to the ldquoregularrdquo mononuclear alternatives Alternatively double Ni insertion before cycloaddition might be responsible for one product whereas sequential ldquonormalrdquo activation might be the origin of the other Therefore the amount of initial Ni(COD)(PMe3)2 was gradually increased and the effect of this incremental change on rate and product ratios recorded As shown in Table 31 the speed with which 89 and 90 formed was roughly proportional to the amount of metal present while the product ratio stayed unchanged

Table 31 Variation of Catalyst Loading in the Reaction of Phenylene 22 with Diphenylacetylene 88 Reactions Were Carried Out with Equimolar Amounts of 22 and 88 in

THF-d8 at 40 degC

Run Ni(COD)(PMe3)2

(mol) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

Ratio of 8990

1 50 32 times 10ndash4 031 times 10ndash4 103 2 35 20 times 10ndash4 022 times 10ndash4 91 3 7 064 times 10ndash4 0064 times 10ndash4 100

Next the amount of diphenylacetylene 88 was gradually increased from 1 to 4 equivalents (Table 32) The outcome of this series of experiments was counterintuitive as it led to a larger preference for the production of monoadduct 89 suggesting a mechanistic bifurcation in which whatever Ni species is responsible for the eventual formation of 90 is sequestered by external ligand (in this case 88)

- 70 -

Table 32 Variation of Alkyne Equivalents in the Reaction of 22 (1 equiv) with Diphenylacetylene 88 in the Presence of 50 mol of Ni(COD)(PMe3)2 Experiments Were Run

in THF-d8 at 40 degC

Run 88 (equiv) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

8990

1 10 320 times 10ndash4 031 times 10ndash4 103 2 20 220 times 10ndash4 018 times 10ndash4 122 3 40 220 times 10ndash4 011 times 10ndash4 200

Following the reaction progress by NMR spectroscopy afforded additional insights Thus mixing the ingredients at room temperature left the phenylene component untouched Instead there was a near instantaneous displacement of COD by diphenylacetylene to produce Ni(PhCequivCPh)(PMe3)2 (92) and free COD in addition to the generation of Ni(PMe3)4

90 The speed with which this complex was formed implied that it might be the active catalyst precursor Consistent with this notion higher reaction rates were observed when the reaction in Scheme 38 was carried out with pure 9291 as the catalyst (50 mol) and 05 equivalent of 88 (Table 33 Run 2) In consonance with Table 32 the lesser concentration of available free alkyne increased the relative amount of 90 formed Conversely (Run 3) using Ni(COD)(PMe3)2 with an extra equivalent of PMe3 decreased the rates of formation of 89 and 90 and increased the ratio of 8990 consistent with ligand inhibition of the activation of 92 and the external ligand effect noted in Table 32 Table 33 Variation of Catalyst in the Reaction of 22 with Diphenylacetylene 88 and its Effect

on Reaction Rate Experiments Were Run in THF-d8 at 40 degC with 1 Equivalent of 22

Run Catalyst 88

(equiv)

Rate of formation of 89 (mol

Lmiddoth)

Rate of formation

of 90 (mol Lmiddoth)

8990

1 Ni(COD)(PMe3)2 10 320 times 10ndash4 031 times 10ndash4 103 2 Ni(PhCequivCPh)(PMe3)2 (92)

(05 equivalent) 05 1270 times 10ndash4 210 times 10ndash4 60

3 Ni(COD)(PMe3)2 (05 equivalent) + PMe3 (10 equiv)

10 088 times 10ndash4 005 times 10ndash4 163

Attention was then shifted to the reaction of monoadduct 89 with 88 as in Scheme 310 (Table 34) Here increasing the amount of alkyne and catalyst favors the formation of 91 consistent with an independent pathway At low concentration of alkyne it appears that 89 reenters the manifold of its generation and proceeds on to 90 Indeed following the change in the ratio of 9190 in Run 1 (Table 34) with time reveals a decrease from 47 to the eventual 22 as 88 is depleted

- 71 -

Table 34 Variation of Catalyst Loading and Alkyne Concentration in the Reaction of 90 with Diphenylacetylene 88 Reactions Were Run in THF-d8 at 40 degC

Run 88 (equiv) Ni(COD)(PMe3)2

(mol) 9190

1 10 50 2 2 30 50 15 3 30 10 25

The information obtained from these experiments allowed a narrowing of mechanistic possibilities For example dinuclear Ni activation only one possibility of which is shown in Scheme 311 was rendered unlikely by the absence of any observable changes in product distribution of the reaction in Scheme 39

Scheme 311 Generic Example of a Dual Mechanism Based on Mono- and Dimetallic Phenylene Activation

An alternative mechanism shown in Scheme 312 was in much better agreement with the results of the various control experiments The first step would be displacement of a phosphine in the initially dominant Ni-containing species 92 by angular [3]phenylene 22 inhibited by added PMe3 From 93 oxidative addition can take place to afford metallacycle 94 Why should bay region insertion be favored Arguably the regioselectivity of this step is controlled by the lesser steric hindrance in the resulting arene fragment or relative stabilization of the polarized Ni-C(α-

PhPh

Ph Ph Ph Ph

PhPh

NiL L

Ni(COD)(PMe3)2

NiNiL L L L

PhPh

2

Ph

Ph

Ph Ph Ph Ph Ph Ph

+

+22

89

90

91 90

- 72 -

biphenylene) bond in 94 by the electron withdrawing nature of the neighboring cyclobutadienoid ring This phenomenon in biphenylene is due to the rehybridization of the four-membered ring carbons to adopt relatively larger p character in the strained linkages hence larger s character (ie electron withdrawing) in the remaining bond and manifests itself most clearly in the relative acidity of the α-hydrogens7a This step is followed by migratory insertion and reductive elimination to produce molecule 96 the mechanistic bifurcation point One branch proceeds through presumably ligand-assisted metal dissociation to generate the relatively unreactive free 89 The second entails Ni migration92 and insertion into the bay region of the remaining four-membered ring (97) before the second cycloaddition occurs generating phenacene 90

Scheme 312 Possible Mechanism for the Alkyne Cycloaddition Reaction of Angular [3]Phenylene 22

The regioselective formation of 97 may again be sterically dictated or may involve anchimeric assistance by the bay-region phenyl group as sketched in Scheme 313 specifically 99

Scheme 313 Anchimeric Assistance on Route to [5]Phenacene 90

Ph Ph

PhPhPhPh

Ph

Ph

Ph PhNi

NiMe3P Ph

Ph

Ni

Me3P Ph

Ph

NiPMe3Me3P

Ligand exchangeOxidativeaddition

Migra toryinser tion

Reductiveelimination

Ph

Ph

Me3P

Ni migra tionOxidative addition

22

92

9394

96 89

9097

Ph Ph

Ni

Me3P

Ni(PMe3

Ph

Ph

minusNi(PMe3)

95

- 73 -

This type of metal coordination to the double bond of a proximal arene ligand is common and two examples are provided based on ruthenium94 and molybdenum95 (Figure 33)

Figure 33 Examples of complexes with phenyl groups coordinating to a nearby metal center Turning to the largely selective conversion of 89 to 91 (Scheme 310) requires the postulate of preferential insertion of the metal at the non-bay region and hence a different Ni species from that in 96 possibly a Ni(PMe3)(alkyne) moiety akin to that in 93 ie 100 (Scheme 314) Bay insertion would lead to metallacycle 101 and ultimately molecule 90 The expected large degree of steric repulsion between the phenyl groups in 101 should disfavor this reaction pathway On the other hand non-bay insertion to produce 102 should be relatively less impeded and would furnish 91 Another option for the generation of 90 from 89 would be reentering the pathway described in Scheme 312 facilitated at low concentrations of alkyne consistent with the data in Table 34

Scheme 314 Proposed Mechanism for the Alkyne Cycloaddition Reaction of 89

Ni

PhMe3P

PhPh

(Me3P)Ni

PhPh(Me3P)Ni

Ph

Ph

93 98

99

Ph Ph Ph Ph

90

+

Ph Ph

Ni

Me3P

97

- 74 -

While the above mechanistic perambulations appear plausible it should be stressed that they are speculative and may be restricted to diphenylacetylene 88 as the substrate Thus both 3-hexyne 103 and 14-dimethoxy-2-butyne 106 added to 22 less selectively than 88 to provide only the bay and non-bay monoadducts 104 and 105 and 107 and 108 respectively (Scheme 315)

Scheme 315 Reaction of Angular [3]Phenylene 22 with Other Alkynes

NiMe3P PMe3

Ph Ph+

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph

Ni(PMe)3

PhPh

Ni(PMe3)

Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

92 89

101

90

102

100

91

Ni

Ph Ph

PMe3

+

R

R

THF-d8 40 oCR

R22

Ni(COD)(PMe3)2

R

R

+

R = Et 104

R = CH2OMe 107

R = Et 103

R = CH2OMe 106 R = Et 105

R = CH2OMe 108

11 45 9 68

- 75 -

In view of these uncertainties recourse was taken to DFT computations delineated in the next section 33 Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene DFT studies were carried out in collaboration with Prof Vincent Gandon of the Universiteacute Paris-Sud 11 The B3LYP 6-31G(d) basis set was used for hydrogen and carbon atoms while LANL2DZ was used for nickel Before attempting to model the more complex alkyne cycloaddition reactions in Schemes 38 and 39 the basic Ni-catalyzed addition of the parent acetylene to biphenylene in the presence of PMe3 was studied (Scheme 316) The free energies

Scheme 316 Computational Modeling of Ni-catalyzed Addition of Acetylene to Biphenylene Free Energies (∆G KcalMol) are Relative to 109 Transition State Energies are Absolute Values

for This Step

NiMe3P PMe3

NiMe3P

NiMe3P

Ni

Ni

PMe3

PMe3

+

+ PMe3+

+ PMe3

+ 2 PMe3

+ 2

(00)

(281)(37)

(140)

(12)

NiMe3P PMe3

NiMe3P

NiNiPMe3Ni

PMe3

PMe3NiMe3P

PMe3

(727) (693) (476) (374) (394) (395)

Ni

Me3P

PMe3Ni

Me3P

Ni

Ni

Me3P

PMe3NiMe3P PMe3

(590) (532)

(157) (125) (150)

Most Accessible TS

+

7

114

110

113109

111 112

Ni

Me3P

(253)

Ni

PMe3

(242)

- 76 -

(∆G) of various possible catalyst structures consisting of an assortment of combinations of nickel PMe3 and acetylene as well as those of several possible transition states and the resulting products were calculated As is evident on inspection of the values in the first part of Scheme 316 a number of species were found to be very close in energy making it difficult to pinpoint a specific structure for the initial insertion step Bis(ethyne) nickel complex 109 was established as the lowest energy nickel species and was thus assigned a relative value of 0 kcalmol The most accessible transition state 110 features the oxidative addition of the Ni(PMe3)(C2H2) fragment 114 (+ 14 kcalmol) in which the alkyne is held exo to biphenylene The corresponding endo structure 111 was found to be just slightly higher in energy by 20 kcalmol as was the bisalkyne transition state 112 It is likely that biphenylene-NiL2 complexes (two of which were calculated at relative energies 242 and 253 kcalmol) lie on the way to these maxima93 Metallacycle 113 the structure ensuing from transition state 110 constituted the lowest energy product uphill from the starting 109 by 125 kcalmol but other alternatives are nearly isoenergetic Clearly however attack by Ni(PMe3)2 or Diels-Alder type cycloadditions are not likely From 113 the species proceeds smoothly by alkyne insertion-reductive elimination to the phenanthrene product a cascade associated with a large exergonic driving force Undaunted by the relatively complicated picture that emerged with biphenylene attention was turned to the original object of scrutiny the cycloaddition reaction between angular [3]phenylene 22 and diphenylacetylene 88 to produce [5]phenacene derivative 90 Modeled in the same manner as described above the metal insertion into the four-membered ring of 22 is shown in Scheme 317 The lowest energy nickel species

- 77 -

was found to be diphenylacetylene complex 92 gratifyingly corresponding to experiment and was set to a reference value of 00 kcalmol One notes again however an array of at least 10 species all of which must be in equilibrium in the initial reaction mixture Notably the Ni-π complexes to 22 are all more than 20 kcalmol higher in energy than 92 providing a computational rationale for the failure to observe such species by NMR The first step in the optimal reaction pathway is the coordination of Ni(PMe3) to the cyclobutadiene ring of 22 which results in formation of η2-like complex 114 Again in gratifying agreement with experiment bay region insertion through transition state 115 to give 116 is favored albeit by a bare 07 kcalmol relative to its non-bay region counterpart 117 Moreover there are at least six other structures that are energetically viable in silico although insertions of Ni(PhCequivCPh)(PMe3) appear less so possibly due to steric hindrance The same observation is made for the products of insertion although 116 emerges as the thermodynamically most stable possibility

Scheme 317 Calculated Structures and Reaction Pathway for the Insertion of Nickel into the Four-Membered Ring of Angular [3]Phenylene 22 Free Energies ∆G are in KcalMol Relative

to 92

The next step was to map out the first alkyne cycloaddition (Scheme 318) Coordination of diphenylacetylene to 116 is endothermic by 139 kcalmol and after migratory insertion produces 119 Interestingly a transition state to regioisomer 95

(328) (352)

NiMe3P PMe3

(364)

NiMe3P

NiMe3P PMe3

NiPMe3

(339)

Ni

PMe3

PMe3

NiMe3PPMe3

NiMe3P

NiPMe3

(16) (04) (108) (117)

NiMe3P PMe3 Ni

Me3PNi

Me3P Ni Ni

PMe3

PMe3

+ [3]+ DPA

+ PMe3+ [3]+ DPA

+ PMe3+ [3]

+ 2 PMe3+ [3]

+ [3]+ 2 DPA

Ph Ph Ph PhPh Ph

Ph

PhPh Ph

Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

Ph

(45) (96)

(00)

(89) (134)

Most AccessibleTS

NiPMe3

+ PMe3+ [3]+ 2 DPA

(314)

Ni

+ 2 PMe3+ [3]+ DPA

Ph Ph

(294)

1i(PMe3)

Ni

PhPh

(212)

(218)

(345)

Ni

PhPh(297)

Ni

Me3P

Ni

Ph

Ph

(350)

Ni

PMe3

(303)

Ni

Ni

(43) (41)

Ph

Ph

PhPh

Ni

PMe3

NiMe3P

(-10) (-22)

(Me3P)Ni

Ni(PMe3)

Ph Ph

Ph Ph(225) (256)

+ PMe3+ 2 DPA

+ 2 PMe3+ DPA

+ PMe3+ DPA

+ PMe3+ DPA

92114

115

116118

117

- 78 -

written (arbitrarily) in Scheme 312 could not be located

Scheme 318 Calculated Reaction Pathway for the Coordination of Diphenylacetylene Migratory Insertion and Nickel Migration Free Energies ∆G are in KcalMol Transition

State Energies are Absolute Values for This Step

Subsequent reductive elimination from 119 occurs to produce nickel coordinated arene species 120 From it free 89 is presumably readily obtained by demetallation in the presence of external ligands shown only for the formation of 92 in a very favorable process (ndash487 kcalmol) This step is sufficiently exothermic to tolerate the emergence of all the calculated species in the starting line up of Scheme 317 and is presumably the source of 89 in Scheme 39 However if not removed the Ni moiety in 120 can migrate along a shallow manifold across the π frame choosing the phenyl functionalized edge of the molecule (cf Section 24) until the remaining four-membered ring is reached (121) At this point two separate reaction pathways become possible Nickel insertion on the side proximal or opposite of the phenyl groups generates 99 or 122 respectively The barriers for these transformations are similar but show a noticeable preference for the formation of 99 In addition there is a significant energy difference (175 kcalmol) between 122 and 99 in favor of the bay region metallacycle The reason is the coordination of the neighboring phenyl ring to the nickel which serves to stabilize 103 vindicating the proposal made in Scheme 313 and providing a rationale for the exclusive observation of 90 in Scheme 39 From 99 as shown in Scheme 319 coordination of diphenylacetylene (123) is followed by migratory insertion to produce 124 Insertion occurs away from the bay region so as to reduce steric repulsion due to the phenyl group in the phenanthrene part of the molecule Finally reductive elimination ensues providing phenacene-Ni

NiMe3P

NiPMe3

Ni(PMe3)

Ni Ph

PhMe3P

Ph

Ph

PhPh

(117)

126

(44)

102

( 80)

01

( 412)

Ph PhNi(PMe3)

( 389)

Ph Ph

45

Ni(PMe3)

( 408)

Ph Ph

13

PhNi

PMe3

Ph Ph

Ni(PMe)3

133

( 488)

117

( 663)

NiMe3P

( 22)

PhPh+

95

116

119

120121 122

99

NiMe3P Ph

Ph

Ph Ph

( 899)

NiMe3P PMe3

Ph Ph+

92 89

- 79 -

complex 125 At this point the stage is set for exergonic nickel dissociation to 90 and catalyst turnover

Scheme 319 Calculated Reaction Pathway for the Second Diphenylacetylene Insertion All Relative Energies (in red) are in KcalMol Transition State Energies are Absolute Values for

This Step

In conclusion of this discussion the consideration of the combined computational and experimental data affords a mechanistic picture of the cycloaddition reaction of diphenylacetylene 88 to angular [3]phenylene 22 (Scheme 39) the essential features of which are summarized in Scheme 320 The crucial point is a mechanistic bifurcation in which 89 is either released early and (nearly) irreversibly from the metal or the metal stays attached so as to effect a second cycloaddition to give 90 This mechanism implies that 91 is formed by a different mechanism involving a different Ni species

PhNi

PMe3

( 663)

+

PhNi

Ph PMe3Ph

Ph

( 403) ( 403)

PhNi

PhPMe3

PhPh

( 519)

94

93

( 696)

PhNi

PhPMe3

Ph

Ph

96

( 817)

Ph Ph Ph Ph

(MeP)3Ni

99

123

124

125

PhPh

Ph PhPh Ph

+Ni

Me3P PMe3

( 1101)

PMe3

90

- 80 -

Scheme 320 Essential Mechanistic Features of the Formation of 89 and 90 in the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene 88 and Angular [3]Phenylene 22

Consequently the reaction of 89 with diphenylacetylene to give 91 (Scheme 310) was also modeled by DFT Of the various options probed that shown in Scheme 321 proved to be most plausible The reaction pathway entails coordination of alkyne-Ni phosphine 126 to molecule 89 which generates complex 127 in a process that is found to require 228 kcalmol of energy Insertion into the non-bay region of the four-membered ring has a barrier of 16 kcalmol and provides metallacycle 128 After the second cycloaddition event benzo[c]chrysene 91 is formed Interestingly the transition state leading to insertion of nickel complex 126 into the bay region of 89 structure 129 was found to be so high in energy relative to 128 that it could not be modeled This is not unexpected as the phenyl group closest to bay region effectively blocks the approach of any catalyst species This result is consistent with the high ratio of 91 to 90 formed in Scheme 310 and the increase in this ratio at higher initial diphenylacetylene concentration Why is any 90 formed and why does its relative proportion increase at lower diphenylacetylene concentration A possible explanation is that under these conditions the concentrations of 92 and 126 are sufficiently small that 89 reenters Scheme 318 competitively

PhPhNi(PMe3)

PhPh

Ni(PMe3)

Ph Ph Ph Ph

PhPh

Ni(PMe3)

Ni

PMe3

Ph Ph

NiPhMe3P

22 116

88

120

121

99

88

90

PhPh

89

Externalligand

assistedNi migration

Regioselectiveinsertion

Regioselectiveinsertion

Mechanistic bifurcation

- 81 -

Scheme 321 Calculated Reaction Mechanism for the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene and Compound 90 Relative Energies are in KcalMol Transition

State Energies are Absolute Values for This Step

Consideration of Scheme 320 suggests that phenacene formation might be maximized by keeping the concentration of external ligand low during the course of the reaction Experiments aimed at verifying this conjecture are the subject of Section 34 in addition to presenting extensions of the methodology to higher angular phenylenes

34 Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions The experimental and computational studies described in Section 33 suggested that the decisive factor for selective formation of phenacene 90 is suppression of metal dissociation in Ni complex 120 This scenario would be achievable by maintaining a low concentration of diphenylacetylene 88 (vide supra) Previously the alkyne cycloaddition was performed with all reagents mixed together at the start of the reaction invariably resulting in a high initial concentration of 88 To obviate this occurrence an alternative procedure was devised In this new arrangement the required stoichiometric amount (in this case two equivalents) of alkyne 88 was slowly introduced to a mixture of 22 and Ni(COD)(PMe3)2 by means of a syringe pump (Scheme 322) The results of varying addition and reaction times are shown in Table 35

Scheme 322 Modified Reaction Alkyne Cycloaddition Reaction Between 22 and 89

Ph Ph

Ni(PMe3)

Ph Ph Ph Ph

Ni(PMe)3

160

Ph

Ph

PhPh

(309)(317)

Ph Ph

Ph

Ph

NiMe3P

Ph Ph

(minus573)

89

126

127 128 91

Ph Ph Ph

Ni

Ph

PMe3

129

NiMe3P PMe3

Ph Ph

(00)

92

(89)

+

- 82 -

Table 35 Variation of Alkyne Addition and Total Reaction Time in the Scheme 322

Run Addition time of 88 (h)

Total run time (h)

Yield of 89 ()

Yield of 90 ()

1 4 16 44 55 2 6 22 23 77 3 5 41 24 76 4 12 69 17 73 5 13 19 13 87

The most immediate result of the modified protocol was the quantitative conversion of 22 to cycloadduct products 89 and 90 Turning to the product ratios a four hour addition time led to a slight preference for 90 Increasing the time to six hours dramatically influenced the product distribution and 90 was isolated in 77 yield as compared to the 23 for 89 In the optimal Run 5 87 of 90 was generated vs 13 of 90 Extending the run time after the addition of diphenylacetylene had a negligible effect The successful enhancement in phenacene selectivity under these conditions makes the reaction a practical method for synthesizing compound 90 and also provides further experimental support for the proposed mechanism shown in Scheme 320 Having reached a reasonable level of understanding both the mechanistic and experimental aspects of the reaction of angular [3]phenylene 22 with diphenylacetylene attention was shifted to a larger and more challenging substrate angular [4]phenylene (17) This system could conceivably afford 17 possible adducts one of which is hexaphenyl[7]phenacene 130 (Scheme 324) Would the mechanistic features of this triple cycloaddition be sufficiently similar to those of 22 to apply the same principles and enable selectivity toward 130

+THF reflux

Ph Ph Ph PhPh

Ph

+

Ph

Ph

2 equivslow addition

22 89 90

Ni(COD)(PMe3)2(10 mol)

88

- 83 -

Scheme 324 The Possible Cycloadducts of Diphenylacetylene 88 to Angular [4]Phenylene 17

+ Ph Ph

Ph Ph

Ph Ph

PhPh

Ph

Ph

Ph Ph Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph PhPhPh

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph Ph PhPhPh

Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

PhPh

Ph Ph Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

88

17

130

- 84 -

Encouragingly a first experiment under conditions comparable to those in Scheme 39 for 22 namely reaction of angular [4]phenylene (17) with one equivalent of diphenylacetylene in the absence of high dilution indeed engendered only five products two of which monoadducts 131 and 132 were minor (Scheme 325) The major components of the mixture were molecules 133 134 and most significantly 130

Scheme 325 Nickel Catalyzed Alkyne Cycloaddition with 17 and 88

Monitoring the course of the transformation by NMR revealed that 133 is the sole initial new compound followed by gradual appearance of the others Extrapolation of the insights gained with 22 it is tempting to propose that migration of the metal in Ni-complexed 133 is the source of 134 and ultimately 130 If true [7]phenacene 130 might be made selectively by application of the slow alkyne addition procedure of Scheme 322 Scheme 326 illustrates the proposed scenario It starts with doubly regioselective Ni insertion into the central ring and from the bay region to give 135 On the basis of the electron withdrawing effect of the adjacent cyclobutadienoid rings invoked earlier in the selective formation of 94 (Scheme 312) this metallacycle would seem the most stable Again this conjecture is tentative as the appearance of the minor products 131 and 132 would indicate Metallacycle 135 would then give rise to 136 (and hence 133 by demetallation) which would connect by Ni migration and insertion to 137 Alkyne cycloaddition would result in 138 (and hence 134 by demetallation) which would connect by Ni migration and insertion to 139 Alkyne cycloaddition would result in 140 (and hence 130 by demetallation)

+

Ph Ph

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2(10 mol)THF 75 degC

5 6

33

27 28

132131

133

134 130

17

88

- 85 -

Scheme 326 Proposed Reaction Pathway to Phenacene 130 from Angular [4]Phenylene 17 via Ni Migration

The successful preparation of [5]- and [7]phenacene from angular [3]- and [4]phenylene respectively prompted an attempt to prepare [13]phenacene derivative 141 from helical [7]phenylene 14210 (Scheme 327) This transformation would make use of six alkyne cycloadditions to produce the target molecule In addition to the possibility of preparing the largest known phenacene this reaction would also serve as an interesting test of the alkyne cycloaddition methodology

Scheme 327 Proposed Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Using the slow addition procedure phenylene 142 was subjected to the alkyne cycloaddition conditions (Scheme 329) All of the starting material was consumed but the reaction ultimately resulted in an intractable mixture of products Unfortunately no conclusive structural identifications for any of the ensuing compounds could be made from the 1H-NMR data A large assortment of peaks was seen in the region of 6ndash7

Ni

PMe3

Ph

NiPMe3

Ph Ph Ph PhNi

PMe3

Ph Ph Ph

NiMe3P

135

137

Ph Ph

Ph Ph

Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2

13617

88Ni

PMe3

Ph Ph88

138 139

Ph Ph88

Ni

PMe3

140

- 86 -

ppm suggesting the presence of phenylene subunits More informative was the absence of the highly diagnostic phenacene bay region proton signals that are typically found at ~8ndash9 ppm84 signaling the absence of any phenacene product(s)

Scheme 328 Attempted Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Nevertheless mass spectral analysis clearly indicated that multiple alkyne cycloaddition had occurred (Table 36) Peaks were observed at mz = 700 1056 1234 and 1412 which correspond to the presence of single triple quadruple and quintuple alkyne adducts in the reaction mixture No signal corresponding to the mass of 141 (mz = 1590) was detected however Although the structures of the resulting products remain to be established by follow-up experiments on a larger scale the fact that five cycloadditions occurred is encouraging in the basic scientific quest for large novel polycyclic aromatic hydrocarbons

Table 36 Mass Spectral Data (FAB) of the Product Mixture of the Cycloaddition Reaction of Phenylene 142 to Diphenylacetylene 88

mz Percentage Cycloaddition count 700 13 1

1056 11 3 1234 8 4 1412 7 5

Our disappointment in the apparent failure to generate 141 in this reaction may be the result of overambitious expectations on our part Thus we assumed in analogy to the reactivity of angular systems 17 and 22 that bay region cycloaddition to one of the inner cyclobutadiene rings would be preferred ideally producing an initial structure such as 143 (Figure 38) The corresponding non-bay adduct is illustrated by 144 It is evident on comparison that such bay region reactivity would lead to constructs devoid of the helical strain present in the starting material96 as well as non-bay structures like 144 The subsequent course of the reaction however may be marred by relatively non-selective cycloadditions as already indicated for 17 (Scheme 325) Therefore it will be prudent for future investigators to return to the latter optimize its outcome and then proceed along the series in the quest for large phenacene (or other) structures

- 87 -

Figure 38 Proposed representative initial bay (143) and non-bay (144) alkyne cycloaddition products of the reaction of [7]heliphene 141 with diphenylacetylene 88

35 Summary and Outlook The first alkyne cycloaddition studies were carried with angular phenylene systems Angular [3]phenylene 22 was successfully used as a precursor to a novel phenyl substituted [5]phenacene derivative 90 Similarly hexaphenyl [7]phenacene 131 was prepared from angular [4]phenylene 17 Extensive experiment and computational mechanistic studies suggested that the optimal conditions for preparing phenacene 90 from phenylene 22 were the maintenance of a low concentration of alkyne in the reaction mixture Future work will focus on applying these conditions to the synthesis of [7]phenacene 130 from angular [4]phenylene 17 An attempt to prepare a [13]phenacene 142 from helical [7]phenylene 141 proved unsuccessful for reasons that are not well understood Nevertheless cycloaddition was found to have occurred up to five times This observation is promising with respect to the further application of the methodology described in this chapter The development of an alkyne cycloaddition-based approach to synthesizing phenacenes should greatly facilitate the study of this emerging class of molecules Future work will focus on expanding the substrate scope of the reaction by examining various functionalized alkynes the application of metal systems that may allow the isolation of crucial intermediates and the expansion of the substrate scope to the higher angular phenylenes as well as other topologies

- 88 -

Chapter Four Experimental and Computational Details

41 General Considerations

All glassware was oven-dried (180 degC) prior to use Reagents were used as received from suppliers unless otherwise noted Flash chromatography97 was performed with Merck 60 230ndash400 mesh silica gel MP EcoChrom neutral alumina was deactivated to activity III by adding 6 water by mass followed by thorough mixing98 Air sensitive compounds were handled under argon with standard Schlenk techniques andor in a nitrogen atmosphere glovebox (Vacuum Atmospheres Model Nexus) Irradiation in CpCo(CO)2 reactions was carried out with a 120V 300W slide projection lamp (ELH) positioned 5 cm away from the reaction vessel UV-irradiation experiments were conducted in a Rayonet Photochemical Reactor (RPR-100) Bis(trimethylsilyl)- and trimethylsilylacetylene (BTMSA and TMSA respectively) were distilled from molecular sieves (4 Aring) prior to use TMSA was degassed with four freeze-pump-thaw cycles while BTMSA was degassed using a 20 min Ar purge BTMSA was recycled using from all CpCo(CO)2 reactions using the following procedure The BTMSA was first removed by vacuum transfer Residual cobalt was removed by dissolving the BTMSA in pentane and washing the pentaneBMTSA layer mixture with a dilute solution of ceric ammonium nitrate in acetonitrile in a separatory funnel The denser acetonitrile layer was drained off and the pentane removed by distillation at atmospheric pressure Vacuum distillation of the BTMSA from molecular sieves afforded a product pure enough for future use All solvents were distilled under N2

immediately before use from the appropriate drying agent triethylamine (KOH pellets) benzene toluene CH2Cl2 (CaH2) THF and diethylether (Nabenzophenone) acetonitrile (CaH2) Deoxygenation of solvents andor reaction mixtures was carried out by a 20 min Ar purge or four free-pump-thaw cycles for volatile (bp lt 70 degC) mixturessolvents Ni(COD)2 (Strem) was stored and manipulated in the glovebox 1H and proton decoupled 13C spectra were measured at 500 MHz and 125 MHz respectively unless otherwise noted 1H-NMR chemical shifts are reported in ppm units relative to the signal of the solvent (CDCl3ndash726 ppm C6D6ndash715 ppm acetone-d6ndash205 ppm CD2Cl2ndash532 ppm toluene-d8ndash209 ppm (for ndashCD3) Except where noted two-dimensional NMR experiments were run under temperature control at 300 K All spectral data were processed with Bruker TopSpin 21 software Melting points were recorded in open capillary tubes using a Thomas Hoover Unimelt apparatus and are uncorrected Melting points for air-sensitive samples were carried out in flame sealed capillary tubes Mass spectral measurements (Electron Impact Fast Atom Bombardment) and elemental analyses were supplied by the Micro-Mass Facility of the College of Chemistry University of California Berkeley UV-Vis spectra were recorded on Agilent 8453 and Perkin-Elmer Lambda 35 spectrophotometers with absorbance data reported in nm (log ε) IR spectra were taken on a Perkin-Elmer Spectrum 100 Where appropriate analysis by GCMS was done with an Agilent 5973 instrument

42 Experimental Section for Chapter Two

- 89 -

2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19

A mixture of KF2 H2O (700 mg 744 mmol) [18]crown-6 (100 mg 0378 mmol) and 2378-tetrakis[(triisopropylsilyl)ethynyl] linear [3]phenylene26 (370 mg 0800 mmol) in degassed THF (25 mL) was stirred for 70 min at RT The orange solution was filtered through a plug of silica gel (1 x 3 cm) eluting with degassed THF (15 mL) providing a light-yellow solution After adding CpCo(CO)2 (260 mg 144 mmol) the solution was protected from light and added via syringe pump over a period of 6 h to a boiling mixture of degassed BTMSA (50 mL) and THF (200 mL) which was irradiated with a projector lamp under nitrogen After additional heating and irradiation for 15 h the solvents were removed by vacuum transfer and the black residue filtered through a plug of neutral alumina activity III eluting with hexaneTHF (501) The volatiles were removed and the dark brown residue crystallized from degassed acetone yielding 19 (330 mg 65 ) as black needles mp 192ndash195 degC (decomp) 1H-NMR (400 MHz C6D6) δ = 794 (s 2 H) 744 (s 2 H) 690 (s 2 H) 441 (s 5 H) 035 (s 18 H) 031 (s 18 H) ppm 13C-NMR (100 MHz C6D6) δ = 1494 1484 1433 1394 1360 1256 1155 802 781 739

269 261 ppm IR (neat) ν~ = 2951 2898 1259 1248 1073 830 799 752 cmndash1 UV-VIS (ethanol) λmax (log ε) = 288 (486) 299 (500) 352 (445) 410 (439) 438 (449) end absorption to 550 nm MS (70 eV) mz () 638 (9) [M+] 514 (100) 499 (3) 387 (2) 73 (24) HRMS (FAB) calcd for C35H47CoSi4 6382087 found 6382095 Elemental analysis calcd for C35H47CoSi4 C 6578 H 741 found 6582 721

Crystallographic information for 19 (H atoms omitted)

Table 41 Crystal Data and Structure Refinement For 19

Empirical formula C35H47CoSi4 Formula weight 63902 cryst size (mm) 025 x 020 x 005 cryst syst Triclinic refl used for unit cell determination 6958

2 θ range (deg) 245ndash2900

a (Aring) 9497(3) b (Aring) 12321(4) c (Aring) 16469(5) α (deg) 74058(5)

β (deg) 82154(5)

Me3Si

Me3Si

CoSiMe3

SiMe3

- 90 -

γ (deg) 72276(5)

V (Aring3) 17620(10) space group Pndash1 Z 2

Dcalc gcm3 1762

F000 680 micro cmndash1 645 temp ordmC ndash173

Tmax Tmin 0858 0972 no of total rflns 24355

no of unique rflns 6958

no of obsd rflns 9209

no of variables 361

Reflection to Parameter Ratio 255

R 00503

Rw 01426

Rall 00734

GOF 1006

Max Peak in Final Diff Map (endash Aring3) 0867

Min Peak in Final Diff Map (endash Aring3) ndash0755

- 91 -

Figure 41 ORTEP representation of 19

- 92 -

Table 42 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 19 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y Z U (eq)

Co1 073881(4) ndash000927(3) 060643(2) 002551(10) Si1 077416(8) ndash019090(6) 094343(4) 002594(16) Si2 113437(8) ndash016706(7) 082404(5) 003023(17) Si3 040491(7) 062139(6) 020406(4) 002291(15) Si4 005088(7) 056545(6) 030946(4) 002144(14) C1 06709(3) ndash00385(2) 079440(16) 00239(5) C2 08019(3) ndash00967(2) 083428(16) 00241(5) C3 09418(3) ndash00743(2) 079331(16) 00233(5) C4 09428(3) 00098(2) 071779(15) 00225(5) C5 08094(2) 00691(2) 067735(15) 00207(4) C6 07282(2) 01574(2) 060605(15) 00207(4) C7 07303(2) 02531(2) 053306(15) 00211(4) C8 05938(2) 03094(2) 050431(15) 00205(4) C9 05057(2) 03981(2) 043438(15) 00207(4) C10 05076(2) 04760(2) 035695(15) 00227(5) C11 03734(2) 05293(2) 031459(15) 00215(4) C12 02408(2) 05011(2) 035315(15) 00205(4) C13 02432(2) 04196(2) 043269(15) 00215(4) C14 03751(2) 03698(2) 047171(15) 00208(4) C15 04564(2) 02794(2) 054277(15) 00211(4) C16 04487(2) 01908(2) 061161(15) 00224(5) C17 05916(3) 01278(2) 064393(15) 00221(5) C18 06734(2) 00417(2) 071473(15) 00215(5) C19 05795(3) ndash02027(3) 09572(2) 00446(8) C20 08892(4) ndash03470(2) 09642(2) 00387(7) C21 07986(4) ndash01192(3) 10246(2) 00419(7) C22 11685(4) ndash03077(3) 07914(3) 00584(10) C23 11726(3) ndash01969(3) 09372(2) 00426(7) C24 12742(4) ndash00933(4) 07624(3) 00640(12) C25 05777(3) 06657(3) 020261(18) 00348(6) C26 02610(3) 07629(2) 016564(17) 00292(5) C27 04355(3) 05272(3) 012760(18) 00347(6) C28 ndash00272(3) 07195(2) 03194(2) 00360(6) C29 00487(3) 05542(3) 019882(18) 00344(6) C30 ndash00786(3) 04816(2) 037272(18) 00278(5) C31 06994(4) ndash00612(3) 05062(2) 00432(7) C32 08520(4) ndash00698(3) 05033(2) 00407(7) C33 09085(3) ndash01473(3) 05788(2) 00407(7) C34 07922(4) ndash01879(3) 06277(2) 00424(7) C35 06647(4) ndash01370(3) 05833(2) 00403(7)

- 93 -

Table 43 Bond Lengths (Aring) for Complex 19

Atom1 Atom2 Length

Co1 C5 1993(3) Co1 C6 2023(3) Co1 C17 2022(2) Co1 C18 2009(3) Co1 C31 2042(4) Co1 C32 2075(3) Co1 C33 2062(3) Co1 C34 2042(4) Co1 C35 2048(4) Si1 C2 1886(2) Si1 C19 1877(3) Si1 C20 1863(2) Si1 C21 1865(4) Si2 C3 1889(3) Si2 C22 1876(5) Si2 C23 1862(3) Si2 C24 1865(4) Si3 C11 1901(2) Si3 C25 1876(4) Si3 C26 1867(2) Si3 C27 1875(4) Si4 C12 1889(2) Si4 C28 1860(3) Si4 C29 1868(3) Si4 C30 1870(3) C1 C2 1384(4) C1 C18 1411(3) C2 C3 1474(4) C3 C4 1384(3) C4 C5 1408(3) C5 C6 1480(3) C5 C18 1448(3) C6 C7 1437(3) C6 C17 1465(4) C7 C8 1351(3) C8 C9 1495(3) C8 C15 1476(3) C9 C10 1371(3) C9 C14 1405(3) C10 C11 1423(3) C11 C12 1427(3) C12 C13 1413(3) C13 C14 1376(3)

- 94 -

C14 C15 1488(3) C15 C16 1352(3) C16 C17 1434(3) C17 C18 1468(3) C31 C32 1416(6) C31 C35 1419(4) C32 C33 1401(4) C33 C34 1411(5) C34 C35 1386(5)

Table 44 Bond Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 4325(9) C5 Co1 C17 621(1) C5 Co1 C18 4240(9) C5 Co1 C31 1629(1) C5 Co1 C32 1271(1) C5 Co1 C33 1102(1) C5 Co1 C34 1223(1) C5 Co1 C35 1556(1) C6 Co1 C17 425(1) C6 Co1 C18 6191(9) C6 Co1 C31 1253(1) C6 Co1 C32 1164(1) C6 Co1 C33 1329(1) C6 Co1 C34 1651(1) C6 Co1 C35 1550(1) C17 Co1 C18 427(1) C17 Co1 C31 1204(1) C17 Co1 C32 1451(1) C17 Co1 C33 1722(1) C17 Co1 C34 1419(1) C17 Co1 C35 1194(1) C18 Co1 C31 1517(1) C18 Co1 C32 1676(1) C18 Co1 C33 1312(1) C18 Co1 C34 1112(1) C18 Co1 C35 1198(1) C31 Co1 C32 402(1) C31 Co1 C33 673(1) C31 Co1 C34 675(1) C31 Co1 C35 406(1) C32 Co1 C33 396(1) C32 Co1 C34 672(1)

- 95 -

C32 Co1 C35 675(1) C33 Co1 C34 402(1) C33 Co1 C35 671(1) C34 Co1 C35 396(1) C2 Si1 C19 1085(1) C2 Si1 C20 1157(1) C2 Si1 C21 1096(1) C19 Si1 C20 1035(1) C19 Si1 C21 1081(2) C20 Si1 C21 1110(2) C3 Si2 C22 1071(2) C3 Si2 C23 1162(1) C3 Si2 C24 1100(2) C22 Si2 C23 1110(2) C22 Si2 C24 1067(2) C23 Si2 C24 1056(2) C11 Si3 C25 1077(1) C11 Si3 C26 1177(1) C11 Si3 C27 1083(1) C25 Si3 C26 1045(1) C25 Si3 C27 1086(1) C26 Si3 C27 1097(1) C12 Si4 C28 1099(1) C12 Si4 C29 1132(1) C12 Si4 C30 1101(1) C28 Si4 C29 1119(1) C28 Si4 C30 1066(1) C29 Si4 C30 1048(1) C2 C1 C18 1193(2) Si1 C2 C1 1130(2) Si1 C2 C3 1270(2) C1 C2 C3 1198(2) Si2 C3 C2 1260(2) Si2 C3 C4 1124(2) C2 C3 C4 1208(2) C3 C4 C5 1192(2) Co1 C5 C4 1188(2) Co1 C5 C6 695(1) Co1 C5 C18 694(1) C4 C5 C6 1498(2) C4 C5 C18 1200(2) C6 C5 C18 902(2) Co1 C6 C5 673(1) Co1 C6 C7 1267(2) Co1 C6 C17 687(1) C5 C6 C7 1474(2)

- 96 -

C5 C6 C17 893(2) C7 C6 C17 1227(2) C6 C7 C8 1121(2) C7 C8 C9 1461(2) C7 C8 C15 1251(2) C9 C8 C15 885(2) C8 C9 C10 1471(2) C8 C9 C14 912(2) C10 C9 C14 1214(2) C9 C10 C11 1186(2) Si3 C11 C10 1116(2) Si3 C11 C12 1283(2) C10 C11 C12 1197(2) Si4 C12 C11 1264(2) Si4 C12 C13 1135(2) C11 C12 C13 1201(2) C12 C13 C14 1185(2) C9 C14 C13 1216(2) C9 C14 C15 915(2) C13 C14 C15 1465(2) C8 C15 C14 888(2) C8 C15 C16 1250(2) C14 C15 C16 1458(2) C15 C16 C17 1118(2) Co1 C17 C6 688(1) Co1 C17 C16 1265(2) Co1 C17 C18 682(1) C6 C17 C16 1233(2) C6 C17 C18 900(2) C16 C17 C18 1460(2) Co1 C18 C1 1229(2) Co1 C18 C5 682(1) Co1 C18 C17 691(1) C1 C18 C5 1206(2) C1 C18 C17 1487(2) C5 C18 C17 905(2) Co1 C31 C32 712(2) Co1 C31 C35 699(2) C32 C31 C35 1077(3) Co1 C32 C31 686(2) Co1 C32 C33 697(2) C31 C32 C33 1076(3) Co1 C33 C32 707(2) Co1 C33 C34 691(2) C32 C33 C34 1081(3) Co1 C34 C33 707(2)

- 97 -

Co1 C34 C35 704(2) C33 C34 C35 1086(3) Co1 C35 C31 695(2) Co1 C35 C34 700(2) C31 C35 C34 1079(3)

Table 44 Torsion Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 ndash1479(3) C6 Co1 C5 C18 983(2) C17 Co1 C5 C4 1630(2) C17 Co1 C5 C6 ndash491(1) C17 Co1 C5 C18 492(1) C18 Co1 C5 C4 1138(2) C18 Co1 C5 C6 ndash983(2) C31 Co1 C5 C4 ndash941(4) C31 Co1 C5 C6 538(4) C31 Co1 C5 C18 1522(4) C32 Co1 C5 C4 ndash573(2) C32 Co1 C5 C6 906(2) C32 Co1 C5 C18 ndash1710(2) C33 Co1 C5 C4 ndash160(2) C33 Co1 C5 C6 1319(1) C33 Co1 C5 C18 ndash1297(2) C34 Co1 C5 C4 271(2) C34 Co1 C5 C6 1750(2) C34 Co1 C5 C18 ndash866(2) C35 Co1 C5 C4 629(4) C35 Co1 C5 C6 ndash1492(3) C35 Co1 C5 C18 ndash509(3) C5 Co1 C6 C7 1458(3) C5 Co1 C6 C17 ndash986(2) C17 Co1 C6 C5 986(2) C17 Co1 C6 C7 ndash1156(3) C18 Co1 C6 C5 491(1) C18 Co1 C6 C7 ndash1650(2) C18 Co1 C6 C17 ndash494(1) C31 Co1 C6 C5 ndash1631(2) C31 Co1 C6 C7 ndash173(3) C31 Co1 C6 C17 983(2) C32 Co1 C6 C5 ndash1170(2) C32 Co1 C6 C7 288(2) C32 Co1 C6 C17 1444(2) C33 Co1 C6 C5 ndash725(2)

- 98 -

C33 Co1 C6 C7 734(3) C33 Co1 C6 C17 ndash1710(2) C34 Co1 C6 C5 ndash166(5) C34 Co1 C6 C7 1293(5) C34 Co1 C6 C17 ndash1151(5) C35 Co1 C6 C5 1499(3) C35 Co1 C6 C7 ndash642(4) C35 Co1 C6 C17 514(3) C5 Co1 C17 C6 501(1) C5 Co1 C17 C16 1666(3) C5 Co1 C17 C18 ndash489(1) C6 Co1 C17 C16 1165(3) C6 Co1 C17 C18 ndash989(2) C18 Co1 C17 C6 989(2) C18 Co1 C17 C16 ndash1446(3) C31 Co1 C17 C6 ndash1106(2) C31 Co1 C17 C16 59(3) C31 Co1 C17 C18 1505(2) C32 Co1 C17 C6 ndash656(3) C32 Co1 C17 C16 510(3) C32 Co1 C17 C18 ndash1645(2) C33 Co1 C17 C6 571(9) C33 Co1 C17 C16 1736(8) C33 Co1 C17 C18 ndash418(9) C34 Co1 C17 C6 1578(2) C34 Co1 C17 C16 ndash857(3) C34 Co1 C17 C18 589(2) C35 Co1 C17 C6 ndash1578(2) C35 Co1 C17 C16 ndash413(3) C35 Co1 C17 C18 1033(2) C5 Co1 C18 C1 ndash1133(3) C5 Co1 C18 C17 993(2) C6 Co1 C18 C1 ndash1635(2) C6 Co1 C18 C5 ndash502(1) C6 Co1 C18 C17 491(1) C17 Co1 C18 C1 1474(3) C17 Co1 C18 C5 ndash993(2) C31 Co1 C18 C1 836(3) C31 Co1 C18 C5 ndash1632(2) C31 Co1 C18 C17 ndash638(3) C32 Co1 C18 C1 ndash779(6) C32 Co1 C18 C5 353(6) C32 Co1 C18 C17 1346(5) C33 Co1 C18 C1 ndash395(3) C33 Co1 C18 C5 737(2) C33 Co1 C18 C17 1731(2)

- 99 -

C34 Co1 C18 C1 20(2) C34 Co1 C18 C5 1152(2) C34 Co1 C18 C17 ndash1455(2) C35 Co1 C18 C1 451(3) C35 Co1 C18 C5 1583(2) C35 Co1 C18 C17 ndash1023(2) C5 Co1 C31 C32 478(5) C5 Co1 C31 C35 1656(4) C6 Co1 C31 C32 904(2) C6 Co1 C31 C35 ndash1517(2) C17 Co1 C31 C32 1412(2) C17 Co1 C31 C35 ndash1010(2) C18 Co1 C31 C32 ndash1739(2) C18 Co1 C31 C35 ndash561(3) C32 Co1 C31 C35 1179(3) C33 Co1 C31 C32 ndash370(2) C33 Co1 C31 C35 808(2) C34 Co1 C31 C32 ndash808(2) C34 Co1 C31 C35 371(2) C35 Co1 C31 C32 ndash1179(3) C5 Co1 C32 C31 ndash1642(2) C5 Co1 C32 C33 764(2) C6 Co1 C32 C31 ndash1143(2) C6 Co1 C32 C33 1263(2) C17 Co1 C32 C31 ndash710(3) C17 Co1 C32 C33 1697(2) C18 Co1 C32 C31 1666(5) C18 Co1 C32 C33 472(6) C31 Co1 C32 C33 ndash1194(3) C33 Co1 C32 C31 1194(3) C34 Co1 C32 C31 816(2) C34 Co1 C32 C33 ndash377(2) C35 Co1 C32 C31 385(2) C35 Co1 C32 C33 ndash808(2) C5 Co1 C33 C32 ndash1243(2) C5 Co1 C33 C34 1166(2) C6 Co1 C33 C32 ndash802(2) C6 Co1 C33 C34 1607(2) C17 Co1 C33 C32 ndash1309(8) C17 Co1 C33 C34 1100(9) C18 Co1 C33 C32 ndash1679(2) C18 Co1 C33 C34 730(2) C31 Co1 C33 C32 376(2) C31 Co1 C33 C34 ndash815(2) C32 Co1 C33 C34 ndash1191(3) C34 Co1 C33 C32 1191(3)

- 100 -

C35 Co1 C33 C32 818(2) C35 Co1 C33 C34 ndash373(2) C5 Co1 C34 C33 ndash833(2) C5 Co1 C34 C35 1577(2) C6 Co1 C34 C33 ndash700(5) C6 Co1 C34 C35 1711(4) C17 Co1 C34 C33 ndash1681(2) C17 Co1 C34 C35 730(3) C18 Co1 C34 C33 ndash1295(2) C18 Co1 C34 C35 1115(2) C31 Co1 C34 C33 809(2) C31 Co1 C34 C35 ndash380(2) C32 Co1 C34 C33 372(2) C32 Co1 C34 C35 ndash818(2) C33 Co1 C34 C35 ndash1189(3) C35 Co1 C34 C33 1189(3) C5 Co1 C35 C31 ndash1699(3) C5 Co1 C35 C34 ndash508(4) C6 Co1 C35 C31 663(4) C6 Co1 C35 C34 ndash1746(2) C17 Co1 C35 C31 1036(2) C17 Co1 C35 C34 ndash1373(2) C18 Co1 C35 C31 1531(2) C18 Co1 C35 C34 ndash878(2) C31 Co1 C35 C34 1191(3) C32 Co1 C35 C31 ndash382(2) C32 Co1 C35 C34 809(2) C33 Co1 C35 C31 ndash812(2) C33 Co1 C35 C34 378(2) C34 Co1 C35 C31 ndash1191(3) C19 Si1 C2 C1 118(2) C19 Si1 C2 C3 ndash1731(2) C20 Si1 C2 C1 1275(2) C20 Si1 C2 C3 ndash574(3) C21 Si1 C2 C1 ndash1061(2) C21 Si1 C2 C3 690(3) C22 Si2 C3 C2 714(3) C22 Si2 C3 C4 ndash988(2) C23 Si2 C3 C2 ndash532(3) C23 Si2 C3 C4 1365(2) C24 Si2 C3 C2 ndash1731(3) C24 Si2 C3 C4 167(3) C25 Si3 C11 C10 ndash241(2) C25 Si3 C11 C12 1624(2) C26 Si3 C11 C10 ndash1417(2) C26 Si3 C11 C12 447(3)

- 101 -

C27 Si3 C11 C10 932(2) C27 Si3 C11 C12 ndash804(2) C28 Si4 C12 C11 ndash731(2) C28 Si4 C12 C13 1055(2) C29 Si4 C12 C11 529(2) C29 Si4 C12 C13 ndash1285(2) C30 Si4 C12 C11 1698(2) C30 Si4 C12 C13 ndash116(2) C18 C1 C2 Si1 1755(2) C18 C1 C2 C3 00(4) C2 C1 C18 Co1 784(3) C2 C1 C18 C5 ndash41(4) C2 C1 C18 C17 ndash1772(4) Si1 C2 C3 Si2 198(4) Si1 C2 C3 C4 ndash1707(2) C1 C2 C3 Si2 ndash1654(2) C1 C2 C3 C4 41(4) Si2 C3 C4 C5 1668(2) C2 C3 C4 C5 ndash40(4) C3 C4 C5 Co1 ndash816(3) C3 C4 C5 C6 1799(4) C3 C4 C5 C18 ndash01(4) Co1 C5 C6 C7 ndash1233(4) Co1 C5 C6 C17 671(1) C4 C5 C6 Co1 1122(4) C4 C5 C6 C7 ndash112(7) C4 C5 C6 C17 1793(4) C18 C5 C6 Co1 ndash678(1) C18 C5 C6 C7 1688(4) C18 C5 C6 C17 ndash07(2) Co1 C5 C18 C1 1164(2) Co1 C5 C18 C17 ndash672(1) C4 C5 C18 Co1 ndash1121(2) C4 C5 C18 C1 42(3) C4 C5 C18 C17 ndash1793(2) C6 C5 C18 Co1 679(1) C6 C5 C18 C1 ndash1757(2) C6 C5 C18 C17 07(2) Co1 C6 C7 C8 858(2) C5 C6 C7 C8 ndash1683(3) C17 C6 C7 C8 ndash08(3) Co1 C6 C17 C16 ndash1205(2) Co1 C6 C17 C18 665(1) C5 C6 C17 Co1 ndash658(1) C5 C6 C17 C16 1736(2) C5 C6 C17 C18 07(2)

- 102 -

C7 C6 C17 Co1 1209(2) C7 C6 C17 C16 03(4) C7 C6 C17 C18 ndash1726(2) C6 C7 C8 C9 ndash1697(3) C6 C7 C8 C15 09(3) C7 C8 C9 C10 05(7) C7 C8 C9 C14 1728(4) C15 C8 C9 C10 ndash1718(4) C15 C8 C9 C14 05(2) C7 C8 C15 C14 ndash1752(2) C7 C8 C15 C16 ndash06(4) C9 C8 C15 C14 ndash04(2) C9 C8 C15 C16 1742(2) C8 C9 C10 C11 1714(3) C14 C9 C10 C11 05(3) C8 C9 C14 C13 ndash1756(2) C8 C9 C14 C15 ndash05(2) C10 C9 C14 C13 ndash06(4) C10 C9 C14 C15 1746(2) C9 C10 C11 Si3 ndash1741(2) C9 C10 C11 C12 01(3) Si3 C11 C12 Si4 ndash90(3) Si3 C11 C12 C13 1725(2) C10 C11 C12 Si4 1779(2) C10 C11 C12 C13 ndash07(3) Si4 C12 C13 C14 ndash1781(2) C11 C12 C13 C14 06(3) C12 C13 C14 C9 ndash00(3) C12 C13 C14 C15 ndash1713(3) C9 C14 C15 C8 05(2) C9 C14 C15 C16 ndash1717(4) C13 C14 C15 C8 1730(4) C13 C14 C15 C16 09(7) C8 C15 C16 C17 00(3) C14 C15 C16 C17 1704(3) C15 C16 C17 Co1 ndash870(3) C15 C16 C17 C6 01(3) C15 C16 C17 C18 1674(4) Co1 C17 C18 C1 ndash1195(4) Co1 C17 C18 C5 664(1) C6 C17 C18 Co1 ndash671(1) C6 C17 C18 C1 1734(4) C6 C17 C18 C5 ndash07(2) C16 C17 C18 Co1 1235(4) C16 C17 C18 C1 40(7) C16 C17 C18 C5 ndash1701(4)

- 103 -

Co1 C31 C32 C33 590(2) C35 C31 C32 Co1 ndash607(2) C35 C31 C32 C33 ndash16(4) Co1 C31 C35 C34 ndash596(3) C32 C31 C35 Co1 615(3) C32 C31 C35 C34 18(4) Co1 C32 C33 C34 592(2) C31 C32 C33 Co1 ndash583(2) C31 C32 C33 C34 09(4) Co1 C33 C34 C35 605(3) C32 C33 C34 Co1 ndash602(2) C32 C33 C34 C35 03(4) Co1 C34 C35 C31 593(3) C33 C34 C35 Co1 ndash606(2) C33 C34 C35 C31 ndash13(4)

23-Bis(trimethylsilyl) linear [3]phenylene(CpCo) 52

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (029 g 085 mmol)27 in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (014 g 101 mmol) The mixture was stirred for 15 h and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the yellow residue dissolved in ether (30 mL) Aqueous workup with sat NaCl (2 x 20 mL) followed by drying over MgSO4 and concentration in vacuo provided a yellow solid This material was redissolved in THF (15 mL) degassed (Ar) and CpCo(CO)2 (0140 g 078 mmol) added The resulting solution (protected from light with foil) was injected (syringe pump) over 8 h into a boiling mixture of THF (200 mL) and BTMSA (50 mL) while irradiating with a slide projection lamp Once addition was complete heating and irradiation were continued for another 14 h The volatiles were removed via vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (4 x 4 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed in vacuo and the residue crystallized from acetone yielding 52 (024 g 57 ) as dark red crystals mp 198ndash202 degC (decomp) 1H-NMR (500 MHz C6D6) δ = 796 (s 2 H) 678 (AArsquom 2 H) 675 (s 2 H) 674 (BBrsquom 2 H) 436 (s 5 H) 037 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1426 1393

1360 1294 1194 1149 802 779 738 268 ppm IR (neat) ν~ = 2960 2923 2853 1461 1455 1378 1260 1093 1019 800 cmndash1 UV-VIS (hexane) λmax (log ε) = 255 (393) 282 (376) 293 (sh 378) 308 (389) 348 (390) 397 (sh 335) 436 (301) 511

CoSiMe3

SiMe3

- 104 -

(262) MS (70 eV) mz () 494 (100) [M+] 370 (14) HRMS (FAB) calcd for C29H31CoSi2 4941296 found 4941292 Elemental analysis calcd for C29H31CoSi2 C 7041 H 632 found 7048 628 Crystallographic information for 52 (H atoms omitted)

Table 45 Crystal Data and Structure Refinement For 52

Empirical formula C29H31CoSi2 Formula weight 49465 cryst size (mm) 030 x 020 x 005 cryst syst Monoclinic refl used for unit cell determination 2640 2 θ range (deg) 242ndash2503 a (Aring) 4391(3) b (Aring) 7472(4) c (Aring) 16869(11) α (deg)

β (deg) 111522(11) γ (deg) V (Aring3) 5149(6) space group C2c Z 8 Dcalc gcm

3 1276

F000 2080 micro cmndash1 774

temp ordmC ndash153

Tmax Tmin 0963 0800 no of total rflns 18401 no of unique rflns 2640 no of obsd rflns 4266 no of variables 271 Reflection to Parameter Ratio 974 R 00892 Rw 02042 Rall 01248 GOF 1008 Max Peak in Final Diff Map (endash Aring3) 1051 Min Peak in Final Diff Map (endash Aring3) ndash0707

- 105 -

Figure 42 ORTEP representation of 52

- 106 -

Table 46 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 52 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y z U(eq)

Co1 006961(2) 087577(12) 038136(6) 00200(3) Si1 018827(6) 08761(5) 063753(18) 00627(9) Si2 018540(5) 05425(3) 046900(16) 00410(6) C1 012151(19) 08410(10) 05589(5) 00310(17) C2 015018(13) 07767(11) 05552(4) 00343(18) C3 015002(14) 06417(10) 04926(5) 00324(17) C4 011985(17) 05770(9) 04357(4) 00247(16) C5 009030(17) 06465(9) 04383(4) 00220(14) C6 005450(16) 06378(9) 04077(4) 00216(14) C7 002537(17) 05420(9) 03591(4) 00224(15) C8 ndash000060(18) 05847(9) 03798(4) 00246(15) C9 ndash003560(17) 05555(10) 03644(4) 00256(16) C10 ndash006399(18) 04581(10) 03174(4) 00284(17) C11 ndash009208(19) 05019(12) 03360(5) 00344(18) C12 ndash009130(19) 06274(12) 03957(5) 00340(18) C13 ndash006300(17) 07256(11) 04422(5) 00294(17) C14 ndash003558(19) 06826(10) 04247(4) 00274(16) C15 000008(18) 07212(10) 04449(4) 00251(16) C16 002653(17) 08159(10) 04925(4) 00234(15) C17 005500(17) 07741(9) 04722(4) 00231(15) C18 009090(17) 07798(10) 05007(4) 00247(15) C19 01766(3) 10793(15) 06845(9) 0098(3) C20 02181(3) 0957(2) 05901(7) 0098(3) C21 02076(3) 07068(14) 07228(7) 0098(3) C22 01946(2) 06941(13) 03925(6) 00631(17) C23 01724(2) 03224(9) 04142(7) 00631(17) C24 022363(17) 04883(16) 05614(5) 00631(17) C25 007501(19) 09264(10) 02652(4) 00281(17) C26 004279(18) 09614(10) 02593(4) 00264(16) C27 004343(18) 10945(10) 03211(4) 00271(16) C28 007584(19) 11429(10) 03645(5) 00296(17) C29 00960(2) 10392(11) 03322(5) 00321(17)

Table 47 Bond Lengths (Aring) for Complex 52

Atom1 Atom2 Length

Co1 C5 2011(7) Co1 C6 2004(7) Co1 C17 2014(8) Co1 C18 2015(6) Co1 C25 2093(8)

- 107 -

Co1 C26 2063(6) Co1 C27 2042(7) Co1 C28 2049(8) Co1 C29 206(1) Si1 C2 1890(6) Si1 C19 187(1) Si1 C20 187(2) Si1 C21 187(1) Si2 C3 1891(8) Si2 C22 187(1) Si2 C23 1870(8) Si2 C24 1869(7) C1 C2 137(1) C1 C18 1418(9) C2 C3 146(1) C3 C4 1406(8) C4 C5 141(1) C5 C6 147(1) C5 C18 144(1) C6 C7 1432(9) C6 C17 148(1) C7 C8 135(1) C8 C9 148(1) C8 C15 149(1) C9 C10 1410(9) C9 C14 139(1) C10 C11 142(1) C11 C12 137(1) C12 C13 141(1) C13 C14 138(1) C14 C15 150(1) C15 C16 1345(9) C16 C17 145(1) C17 C18 147(1) C25 C26 141(1) C25 C29 144(1) C26 C27 143(1) C27 C28 139(1) C28 C29 143(1)

Table 48 Bond Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 428(3) C5 Co1 C17 619(3)

- 108 -

C5 Co1 C18 420(3) C5 Co1 C25 1145(3) C5 Co1 C26 1372(3) C5 Co1 C27 1733(3) C5 Co1 C28 1468(3) C5 Co1 C29 1184(3) C6 Co1 C17 434(3) C6 Co1 C18 621(3) C6 Co1 C25 1219(3) C6 Co1 C26 1125(3) C6 Co1 C27 1305(3) C6 Co1 C28 1653(3) C6 Co1 C29 1539(3) C17 Co1 C18 428(3) C17 Co1 C25 1632(3) C17 Co1 C26 1307(3) C17 Co1 C27 1137(3) C17 Co1 C28 1247(3) C17 Co1 C29 1562(3) C18 Co1 C25 1460(3) C18 Co1 C26 1733(3) C18 Co1 C27 1388(3) C18 Co1 C28 1167(3) C18 Co1 C29 1194(3) C25 Co1 C26 395(3) C25 Co1 C27 680(3) C25 Co1 C28 681(3) C25 Co1 C29 406(3) C26 Co1 C27 409(3) C26 Co1 C28 674(3) C26 Co1 C29 672(3) C27 Co1 C28 397(3) C27 Co1 C29 678(3) C28 Co1 C29 407(3) C2 Si1 C19 1089(5) C2 Si1 C20 1125(5) C2 Si1 C21 1092(4) C19 Si1 C20 1053(6) C19 Si1 C21 1100(6) C20 Si1 C21 1109(6) C3 Si2 C22 1081(4) C3 Si2 C23 1089(4) C3 Si2 C24 1177(4) C22 Si2 C23 1072(4) C22 Si2 C24 1106(4) C23 Si2 C24 1039(4)

- 109 -

C2 C1 C18 1206(7) Si1 C2 C1 1141(5) Si1 C2 C3 1249(5) C1 C2 C3 1210(7) Si2 C3 C2 1296(5) Si2 C3 C4 1113(5) C2 C3 C4 1190(6) C3 C4 C5 1199(6) Co1 C5 C4 1239(5) Co1 C5 C6 684(4) Co1 C5 C18 692(4) C4 C5 C6 1484(7) C4 C5 C18 1203(6) C6 C5 C18 910(6) Co1 C6 C5 688(4) Co1 C6 C7 1280(5) Co1 C6 C17 687(4) C5 C6 C7 1473(6) C5 C6 C17 892(5) C7 C6 C17 1222(6) C6 C7 C8 1133(6) C7 C8 C9 1475(7) C7 C8 C15 1242(7) C9 C8 C15 882(6) C8 C9 C10 1454(7) C8 C9 C14 928(6) C10 C9 C14 1218(7) C9 C10 C11 1147(7) C10 C11 C12 1222(8) C11 C12 C13 1231(8) C12 C13 C14 1149(7) C9 C14 C13 1233(7) C9 C14 C15 910(6) C13 C14 C15 1457(7) C8 C15 C14 879(6) C8 C15 C16 1254(7) C14 C15 C16 1467(7) C15 C16 C17 1121(6) Co1 C17 C6 679(4) Co1 C17 C16 1300(5) Co1 C17 C18 686(4) C6 C17 C16 1227(6) C6 C17 C18 892(5) C16 C17 C18 1464(7) Co1 C18 C1 1235(5) Co1 C18 C5 688(4)

- 110 -

Co1 C18 C17 686(4) C1 C18 C5 1191(7) C1 C18 C17 1500(7) C5 C18 C17 906(6) Co1 C25 C26 691(4) Co1 C25 C29 683(4) C26 C25 C29 1065(7) Co1 C26 C25 714(4) Co1 C26 C27 688(4) C25 C26 C27 1091(6) Co1 C27 C26 704(4) Co1 C27 C28 704(5) C26 C27 C28 1079(7) Co1 C28 C27 699(5) Co1 C28 C29 699(5) C27 C28 C29 1085(7) Co1 C29 C25 711(5) Co1 C29 C28 694(5) C25 C29 C28 1080(7)

Table 49 Torsion Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 1468(8) C6 Co1 C5 C18 ndash999(5) C17 Co1 C5 C4 ndash1627(7) C17 Co1 C5 C6 504(4) C17 Co1 C5 C18 ndash494(4) C18 Co1 C5 C4 ndash1133(8) C18 Co1 C5 C6 999(5) C25 Co1 C5 C4 356(7) C25 Co1 C5 C6 ndash1113(4) C25 Co1 C5 C18 1489(4) C26 Co1 C5 C4 765(7) C26 Co1 C5 C6 ndash703(5) C26 Co1 C5 C18 ndash1702(4) C27 Co1 C5 C4 146(2) C27 Co1 C5 C6 ndash1(3) C27 Co1 C5 C18 ndash101(2) C28 Co1 C5 C4 ndash515(9) C28 Co1 C5 C6 1617(5) C28 Co1 C5 C18 619(7) C29 Co1 C5 C4 ndash98(7) C29 Co1 C5 C6 ndash1567(4) C29 Co1 C5 C18 1035(5)

- 111 -

C5 Co1 C6 C7 ndash1474(8) C5 Co1 C6 C17 977(5) C17 Co1 C6 C5 ndash977(5) C17 Co1 C6 C7 1149(8) C18 Co1 C6 C5 ndash482(4) C18 Co1 C6 C7 1644(7) C18 Co1 C6 C17 495(4) C25 Co1 C6 C5 927(5) C25 Co1 C6 C7 ndash547(7) C25 Co1 C6 C17 ndash1696(4) C26 Co1 C6 C5 1362(4) C26 Co1 C6 C7 ndash112(7) C26 Co1 C6 C17 ndash1261(4) C27 Co1 C6 C5 1799(4) C27 Co1 C6 C7 325(8) C27 Co1 C6 C17 ndash824(5) C28 Co1 C6 C5 ndash137(1) C28 Co1 C6 C7 75(1) C28 Co1 C6 C17 ndash40(1) C29 Co1 C6 C5 523(8) C29 Co1 C6 C7 ndash951(9) C29 Co1 C6 C17 1501(7) C5 Co1 C17 C6 ndash497(4) C5 Co1 C17 C16 ndash1646(8) C5 Co1 C17 C18 484(4) C6 Co1 C17 C16 ndash1149(8) C6 Co1 C17 C18 981(5) C18 Co1 C17 C6 ndash981(5) C18 Co1 C17 C16 1470(9) C25 Co1 C17 C6 32(1) C25 Co1 C17 C16 ndash83(1) C25 Co1 C17 C18 130(1) C26 Co1 C17 C6 799(5) C26 Co1 C17 C16 ndash350(8) C26 Co1 C17 C18 1780(4) C27 Co1 C17 C6 1245(4) C27 Co1 C17 C16 97(8) C27 Co1 C17 C18 ndash1373(4) C28 Co1 C17 C6 1686(4) C28 Co1 C17 C16 538(8) C28 Co1 C17 C18 ndash932(5) C29 Co1 C17 C6 ndash1471(7) C29 Co1 C17 C16 98(1) C29 Co1 C17 C18 ndash489(9) C5 Co1 C18 C1 1117(8) C5 Co1 C18 C17 ndash995(5)

- 112 -

C6 Co1 C18 C1 1609(7) C6 Co1 C18 C5 492(4) C6 Co1 C18 C17 ndash502(4) C17 Co1 C18 C1 ndash1488(8) C17 Co1 C18 C5 995(5) C25 Co1 C18 C1 544(9) C25 Co1 C18 C5 ndash573(7) C25 Co1 C18 C17 ndash1568(5) C26 Co1 C18 C1 ndash162(2) C26 Co1 C18 C5 87(3) C26 Co1 C18 C17 ndash13(3) C27 Co1 C18 C1 ndash784(8) C27 Co1 C18 C5 1699(4) C27 Co1 C18 C17 705(6) C28 Co1 C18 C1 ndash356(7) C28 Co1 C18 C5 ndash1473(4) C28 Co1 C18 C17 1133(4) C29 Co1 C18 C1 107(8) C29 Co1 C18 C5 ndash1010(5) C29 Co1 C18 C17 1595(4) C5 Co1 C25 C26 1356(4) C5 Co1 C25 C29 ndash1058(5) C6 Co1 C25 C26 873(5) C6 Co1 C25 C29 ndash1540(5) C17 Co1 C25 C26 62(1) C17 Co1 C25 C29 ndash1796(9) C18 Co1 C25 C26 1738(5) C18 Co1 C25 C29 ndash675(7) C26 Co1 C25 C29 1187(6) C27 Co1 C25 C26 ndash376(4) C27 Co1 C25 C29 810(5) C28 Co1 C25 C26 ndash806(5) C28 Co1 C25 C29 381(5) C29 Co1 C25 C26 ndash1187(6) C5 Co1 C26 C25 ndash696(6) C5 Co1 C26 C27 1703(4) C6 Co1 C26 C25 ndash1134(5) C6 Co1 C26 C27 1265(4) C17 Co1 C26 C25 ndash1604(4) C17 Co1 C26 C27 795(5) C18 Co1 C26 C25 ndash149(2) C18 Co1 C26 C27 91(3) C25 Co1 C26 C27 ndash1201(6) C27 Co1 C26 C25 1201(6) C28 Co1 C26 C25 825(5) C28 Co1 C26 C27 ndash376(4)

- 113 -

C29 Co1 C26 C25 383(5) C29 Co1 C26 C27 ndash818(5) C5 Co1 C27 C26 ndash77(3) C5 Co1 C27 C28 165(2) C6 Co1 C27 C26 ndash774(5) C6 Co1 C27 C28 1644(5) C17 Co1 C27 C26 ndash1254(4) C17 Co1 C27 C28 1163(5) C18 Co1 C27 C26 ndash1698(5) C18 Co1 C27 C28 720(6) C25 Co1 C27 C26 364(4) C25 Co1 C27 C28 ndash818(5) C26 Co1 C27 C28 ndash1182(6) C28 Co1 C27 C26 1182(6) C29 Co1 C27 C26 804(5) C29 Co1 C27 C28 ndash378(5) C5 Co1 C28 C27 ndash1768(5) C5 Co1 C28 C29 637(7) C6 Co1 C28 C27 ndash54(1) C6 Co1 C28 C29 ndash173(1) C17 Co1 C28 C27 ndash861(5) C17 Co1 C28 C29 1544(5) C18 Co1 C28 C27 ndash1355(5) C18 Co1 C28 C29 1050(5) C25 Co1 C28 C27 815(5) C25 Co1 C28 C29 ndash380(5) C26 Co1 C28 C27 387(4) C26 Co1 C28 C29 ndash809(5) C27 Co1 C28 C29 ndash1195(7) C29 Co1 C28 C27 1195(7) C5 Co1 C29 C25 953(5) C5 Co1 C29 C28 ndash1461(5) C6 Co1 C29 C25 576(9) C6 Co1 C29 C28 1762(6) C17 Co1 C29 C25 1797(7) C17 Co1 C29 C28 ndash617(9) C18 Co1 C29 C25 1437(4) C18 Co1 C29 C28 ndash977(5) C25 Co1 C29 C28 1186(7) C26 Co1 C29 C25 ndash373(4) C26 Co1 C29 C28 813(5) C27 Co1 C29 C25 ndash817(5) C27 Co1 C29 C28 369(5) C28 Co1 C29 C25 ndash1186(7) C19 Si1 C2 C1 ndash144(8) C19 Si1 C2 C3 1663(7)

- 114 -

C20 Si1 C2 C1 ndash1307(7) C20 Si1 C2 C3 500(8) C21 Si1 C2 C1 1057(7) C21 Si1 C2 C3 ndash736(7) C22 Si2 C3 C2 ndash852(7) C22 Si2 C3 C4 908(6) C23 Si2 C3 C2 1587(7) C23 Si2 C3 C4 ndash253(7) C24 Si2 C3 C2 410(8) C24 Si2 C3 C4 ndash1431(6) C18 C1 C2 Si1 1795(6) C18 C1 C2 C3 ndash1(1) C2 C1 C18 Co1 ndash817(9) C2 C1 C18 C5 1(1) C2 C1 C18 C17 173(1) Si1 C2 C3 Si2 ndash5(1) Si1 C2 C3 C4 1790(5) C1 C2 C3 Si2 1755(6) C1 C2 C3 C4 ndash0(1) Si2 C3 C4 C5 ndash1747(5) C2 C3 C4 C5 2(1) C3 C4 C5 Co1 822(8) C3 C4 C5 C6 ndash174(1) C3 C4 C5 C18 ndash2(1) Co1 C5 C6 C7 128(1) Co1 C5 C6 C17 ndash674(4) C4 C5 C6 Co1 ndash120(1) C4 C5 C6 C7 8(2) C4 C5 C6 C17 173(1) C18 C5 C6 Co1 671(4) C18 C5 C6 C7 ndash165(1) C18 C5 C6 C17 ndash03(6) Co1 C5 C18 C1 ndash1175(7) Co1 C5 C18 C17 667(4) C4 C5 C18 Co1 1179(7) C4 C5 C18 C1 0(1) C4 C5 C18 C17 ndash1754(7) C6 C5 C18 Co1 ndash663(4) C6 C5 C18 C1 1762(7) C6 C5 C18 C17 04(6) Co1 C6 C7 C8 ndash887(8) C5 C6 C7 C8 160(1) C17 C6 C7 C8 ndash2(1) Co1 C6 C17 C16 1243(7) Co1 C6 C17 C18 ndash672(4) C5 C6 C17 Co1 675(4)

- 115 -

C5 C6 C17 C16 ndash1681(7) C5 C6 C17 C18 03(5) C7 C6 C17 Co1 ndash1223(7) C7 C6 C17 C16 2(1) C7 C6 C17 C18 1705(7) C6 C7 C8 C9 ndash180(1) C6 C7 C8 C15 2(1) C7 C8 C9 C10 2(2) C7 C8 C9 C14 ndash179(1) C15 C8 C9 C10 ndash179(1) C15 C8 C9 C14 01(6) C7 C8 C15 C14 1791(7) C7 C8 C15 C16 ndash2(1) C9 C8 C15 C14 ndash01(5) C9 C8 C15 C16 1792(8) C8 C9 C10 C11 ndash180(1) C14 C9 C10 C11 1(1) C8 C9 C14 C13 1791(7) C8 C9 C14 C15 ndash01(6) C10 C9 C14 C13 ndash1(1) C10 C9 C14 C15 1796(7) C9 C10 C11 C12 ndash1(1) C10 C11 C12 C13 1(1) C11 C12 C13 C14 ndash2(1) C12 C13 C14 C9 2(1) C12 C13 C14 C15 ndash180(1) C9 C14 C15 C8 01(6) C9 C14 C15 C16 ndash179(1) C13 C14 C15 C8 ndash179(1) C13 C14 C15 C16 2(2) C8 C15 C16 C17 1(1) C14 C15 C16 C17 ndash180(1) C15 C16 C17 Co1 858(8) C15 C16 C17 C6 ndash2(1) C15 C16 C17 C18 ndash161(1) Co1 C17 C18 C1 120(1) Co1 C17 C18 C5 ndash669(4) C6 C17 C18 Co1 666(4) C6 C17 C18 C1 ndash173(1) C6 C17 C18 C5 ndash03(5) C16 C17 C18 Co1 ndash131(1) C16 C17 C18 C1 ndash11(2) C16 C17 C18 C5 162(1) Co1 C25 C26 C27 586(5) C29 C25 C26 Co1 ndash583(5) C29 C25 C26 C27 03(9)

- 116 -

Co1 C25 C29 C28 ndash598(6) C26 C25 C29 Co1 588(5) C26 C25 C29 C28 ndash10(9) Co1 C26 C27 C28 607(5) C25 C26 C27 Co1 ndash602(5) C25 C26 C27 C28 05(9) Co1 C27 C28 C29 595(6) C26 C27 C28 Co1 ndash607(5) C26 C27 C28 C29 ndash12(9) Co1 C28 C29 C25 609(6) C27 C28 C29 Co1 ndash595(6) C27 C28 C29 C25 14(9)

Photo-thermal cycle between 52 and 53

An NMR tube containing a solution of 52 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 53 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 724 (AArsquom 2 H) 683 (s 2 H) 662 (BBrsquom 2 H) 444 (s 5 H) 032 (s 18 H) ppm 13C- NMR (100 MHz C6D6) δ = 1493 1482 1430 1276 1256 1241 1155 803 796 725 222 ppm Thermal reversal could be conveniently followed by VT-NMR

Kinetic studies of the thermal CoCp migration in 53 In the glovebox 23-[bis(trimethylsilyl)] linear[3]phenylene(CpCo) 52 dissolved in the solvent of choice (C6D6 or toluene-d8) was passed through an HPLC filter and then transfered via syringe into a thick-walled NMR tube connected to a vacuum line adapter The sample was then degassed by three freeze-pump-thaw cycles and flame-sealed under vacuum Prior to the kinetic runs the mixtures were irradiated for 10 h in a Rayonet Photochemical Reactor fitted with lamps emitting at 310 and 365 nm After this treatment care was taken to exclude ambient light as it causes some isomerization The irradiated samples were then placed in the NMR spectrometer at ndash65 degC (500 MHz) which was then warmed to the required temperature In the case of the 60 degC runs the magnet was prewarmed because of the fast reaction rate at this temperature After five min the spectra were recorded The Cp signal of the photoisomer was integrated relative to the solvent peak of C6D6 or the CD3 peak of toluene-d8 and monitored as a function of time The integral from the first scan was used as [A]o Since the equilibrium constant between the isomers was 50 the kinetic analysis treated the isomerization as a first-order non-reversible process Plotting the data accordingly

CoSiMe3

SiMe3

52

CoSiMe3

SiMe3

53

hν∆

- 117 -

yielded the reaction rate constants which were used in the Eyring plots to obtain the activation parameters Kinetic studies of the thermal haptotropic shift for complex 52 Kinetic runs were executed in C6D6 as the optimum solvent A sample of 52 in degassed C6D6 or toluene-d8 was subjected to UV light for 10 h leading to maximum enrichment of 53 The sample was kept at the specified temperature and the disappearance of 53 monitored by 1H-NMR spectroscopy The reaction proved to be first-order (eq 1) consistent with an intramolecular process

[ ] [ ]Akdt

Adminus=

(1)

[ ][ ] dtkA

Ad=minus

(2)

[ ][ ]

tkA

A=minus

0

ln (3)

The rate constant (k) at 30 40 50 and 60 degC was obtained from the slope of a plot of ndashln([A][A]0) versus time (t) following eq 2 and 3 The actual error in reproducibility was estimated by the calculation of one standard deviation (σ) for a triplicate run at 60 degC The percentage error was applied for k at 30 40 and 50 degC The rate constants and their errors are given in Tables 411 and 414 The values for k and their standard deviations were used to calculate the activation enthalpy (∆HDagger) and entropy (∆SH) of the haptotropic shift The basis for these calculations is the Eyring equation (eq 4) This expression (eq 4) was transformed to eq 5 and the activation enthalpy (∆HDagger) obtained from the slope of a plot of ndashln(kT) versus 1RT The intercept (ndashC) provides the activation entropy (∆SH) following eq 6 and 7

C

TR

H

R

S

h

k

TR

H

T

k B

minus∆

=

∆+minus

∆=minus

ne

nene

lnln

( 4)

R

S

h

kC B

ne∆+= ln

(5)

minus=∆ ne

h

kCRS Bln

(6)

- 118 -

The errors in ∆HDagger and ∆SDagger were calculated based on those in the rate constants leading to two additional least square fits in the Eyring plot These fits represent the two most extreme deviations from the original plot This provides a conservative error estimate and finally the values of 204plusmn14 kcalmol for ∆HH and 158plusmn22 eu (calmolmiddotK) for ∆SH in C6D6 In order to probe for solvent effects the kinetics were also repeated in toluene-d8 The preparation of the sample followed the described procedure and the rate constants (k) were obtained at 30 40 50 and 60 degC At 60 degC three measurements were carried out to estimate the errors in reproducibility for k and the activation parameters Error propagation was done as described for the kinetic experiments in C6D6 It is assumed that those rate constants (k) show the same relative error as the ones for the rearrangement of 53 to 52 in C6D6 The activation parameters in toluene-d8 were found to be 231plusmn07 kcalmol and 60plusmn13 eu

Table 410 Kinetic Data for the Conversion of 53 to 52 in C6D6

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09657 00349 1000 09419 00599 6000 09380 00640 2000 09018 01034 9000 09038 01012 3000 08557 01558 12000 08760 01324 4000 08176 02013 15000 08418 01723 5000 07796 02490 18000 08206 01978 6000 07555 02804 21000 08010 02219 7000 07255 03210 32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 400 09541 00470 30 09888 00113 800 09197 00837 60 09820 00181 1200 08910 01154 90 09708 00296 1600 08489 01638 120 09596 00413 2000 08298 01865 150 09506 00507 2400 07954 02289 180 09416 00602 2800 07591 02756 210 09348 00674 240 09281 00746 270 09213 00819 300 09124 00917 330 09034 01016 360 08966 01091

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

- 119 -

0 10000 00000 0 10000 00000 30 09950 00050 30 09909 00092 60 09900 00101 60 09854 00147 90 09800 00202 90 09762 00241 120 09750 00253 120 09671 00335 150 09700 00305 150 09634 00372 180 09625 00382 180 09543 00468 210 09575 00434 210 09433 00583 240 09475 00539 240 09397 00622 270 09400 00619 270 09287 00740 300 09350 00672 300 09232 00799 330 09300 00726 330 09177 00858 360 09250 00780 360 09086 00959

Table 411 The Rate Constants (k) in C6D6 Calculated From the Data in Table 410 and Their

Standard Deviations (σ)

Temp (K) k (1s) σσσσ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 10809Endash05 74258Endash07 09970 171494 00688

31315 45615Endash05 31338Endash06 09948 157420 00688

32315 95118Endash05 65346Endash06 09965 150385 00688

33315 (1) 27425Endash04 09965

33315 (2) 25714Endash04 09964

33315 (3) 30051Endash04 09990

33315 (avg) 26511Endash04 18841Endash05 140101 00688

Table 412 Activation Parameters for the Kinetic Experiments in C6D6

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 90990 85414 79291 Intercept ndash1789 ndash1674 ndash1559 R

2 09869 09869 09869

∆HDagger (Jmol) 90990 85414 79291

∆HDagger (kcalmol) 217 204 190

∆SDagger (JmolmiddotK) ndash569 ndash660 ndash751

∆SDagger (eu) ndash136 ndash158 ndash180

- 120 -

(323 15 K 50 degC) y = 95118E-05x + 44505E-03

R2 = 9965

(30315 K 30 degC) y = 10809E-05x + 20474E-03

R2 = 9970

(31315 K 40 degC) y = 45615E-05x + 11689E-02

R2 = 9948

(33315 K 60 degC) y = 263387E-04x + 390297E-04

R2 = 9992

000

005

010

015

020

025

030

035

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

Figure 43 Kinetic plots for the conversion of 53 to 52 in C6D6

Table 413 Kinetic Data for the Conversion of 53 to 52 in Toluene-d8

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09556 00454 1000 09488 00526 6000 09256 00773 2000 08931 01130 9000 08956 01103 3000 08545 01572 12000 08667 01430 4000 08143 02054 15000 08343 01811 5000 07818 02461 18000 08103 02103 6000 07559 02798 21000 07863 02404 7000 07179 03314

- 121 -

32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

000 10000 00000 0 10000 00000 40000 09470 00544 30 09887 00113 80000 08934 01127 60 09775 00228 120000 08594 01515 90 09691 00314 160000 08175 02015 120 09592 00416 200000 07861 02406 150 09473 00542 240000 07502 02875 180 09381 00639 280000 06991 03579 210 09262 00767 240 09149 00889 270 09086 00959 300 08973 01083 330 08868 01202 360 08762 01321

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 30 09945 00055 30 09910 00090 60 09795 00207 60 09828 00173 90 09700 00304 90 09716 00288 120 09645 00361 120 09559 00451 150 09479 00535 150 09440 00576 180 09464 00551 180 09313 00712 210 09314 00711 210 09238 00792 240 09188 00847 240 09156 00882 270 09101 00942 270 08992 01063 300 08991 01064 300 08932 01129 330 08896 01170 330 08872 01197 360 08801 01277 360 08686 01409

- 122 -

Table 414 The Rate Constants (k) in Toluene-d8 Calculated From the Data in Table 413 and Their Standard Deviations (σ)

Temp (K) k (1s) σ σ σ σ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 11314Endash05 37152Endash07 09976 17104 05610

31315 46470Endash05 15251Endash06 09948 15723 05157

32315 12214Endash04 401074Endash06 09957 14788 04851

33315 (1) 36441Endash04 09992

33315 (2) 36124Endash04 09951

33315 (3) 38855Endash04 09956

33315 (avg) 37140Endash04 14937Endash05 13707 04496

Table 415 Activation Parameters for the Kinetic Experiments in Toluene-d8

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 96590 93523 90455 Intercept ndash2073 ndash2007 ndash1941 R

2 09962 09962 09962

∆HDagger (Jmol) 96590 93523 90455

∆HDagger (kcalmol) 2309 2235 2162

∆SDagger (JmolmiddotK) ndash2521 ndash3068 ndash3615

∆SDagger (eu) ndash602 ndash733 ndash864

- 123 -

00000

00500

01000

01500

02000

02500

03000

03500

04000

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

(31315 K 40 degC) y = 46470E-05x + 10553E-02

R2 = 9948

(32315 K 50 degC) y = 12214E-04x + 47671E-03

R2 = 9957

(33315 K 60 degC)y = 371377E-04x - 208381E-03

R2 = 9992

(30315 K 30 degC) y = 11314E-05x + 71900E-03

R2 = 9976

Figure 44 Kinetic plots for the conversion of 53 to 52 in toluene-d8

- 124 -

(C6D6) y = 85141x - 16743

R2

= 09869

(toluene-d 8) y = 93523x - 2007

R2 = 09962

13600

14600

15600

16600

17600

36100E-04

36600E-04

37100E-04

37600E-04

38100E-04

38600E-04

39100E-04

39600E-04

40100E-04

1RT (Jmol)

-ln

(kT

)

Figure 45 Eyring plots for conversion of 53 to 52 MeCpCo(CO)2

Adapted from the literature procedure50 Co2(CO)8 (809 g 2366 mmol) was added to a round bottom flask in the glovebox The flask was capped with a septum and brought out of the glovebox A reflux condenser connected to the high vacuum line was quickly exchanged with the septum under a heavy purge of argon Degassed CH2Cl2 (30 mL) was added followed by freshly cracked deoxygenated methylcyclopentadiene (135 mL 123 mmol) The mixture evolved gas upon addition of the methylcyclopentadiene indicating CO liberation The entire setup was protected from light with foil and heated to a gentle reflux using a heating mantlevariac heat source After stirring at reflux for 26 h the mixture now dark crimson in color was cooled to rt The reflux condenser was quickly exchanged for a distillation head under an Ar purge and CH2Cl2 distilled off at atmospheric pressure under Ar Vacuum distillation at 002 Torr was performed and the forerun discarded The desired complex was obtained as a red liquid (7296 g 79) bp = 31 degC (002 Torr) stored at ndash10 degC and shielded from light Note A small

CoOC CO

- 125 -

amount of methylcyclopentadiene dimer (15 ) which could not be separated was present in the isolated product This was deemed harmless however and the obtained product was used in further experiments without further purification 85 pure 1H-NMR data match those reported in the literature 1H-NMR (C6D6) δ = 145 (s 3 H) 431 (br s 2 H) 451 (br s 2 H) 23-Bis(trimethylsilyl) linear [3]phenylene(MeCpCo) 54

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (0146 g 0424 mmol) in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (0101 g 0731 mmol) The mixture was stirred for 100 min and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the remaining yellow residue was dissolved in freshly distilled THF (15 mL) The green solution was separated from the solids via canula filtration and transferred into another Schlenk flask After a 20 min Ar purge MeCpCo(CO)2 (0092 g 0403 mmol) was added and the resulting solution (protected from light with foil) injected via syringe pump over 9 h into a boiling mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 15 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (201) The volatiles were again removed under high vacuum line and the residue crystallized from acetone yielding 55 (0125 g 61 ) as black crystals mp 163ndash165 degC 1H-NMR (500 MHz C6D6) δ = 783 (s 2 H) 676 (m 4 H) 675 (s 2 H) 442 (apparent t J = 21 Hz 2 H) 427 (apparent t J = 21 Hz 2 H) 134 (s 3 H) 038 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1423 1386 1354 1293 1193 1147 899 806 798 783 739 111 279 ppm IR (neat) ν~ = 2959 2923 2853 1462 1455 1378 1260 1093 1030 802 cmndash1 UV-VIS (hexane) λmax (log ε) = 256 (368) 281 (356) 293 (359) 310 (373) 350 (368) 386 (sh 321) 437 (sh 287) 499 (sh 247) end absorption to 550 nm MS (70 eV) mz () 508 (100) [M+] 370 (28) HRMS (FAB) calcd for C30H33CoSi2 5081453 found 5081442 Photo-thermal cycle between 54 and 56

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

54

CoSiMe3

SiMe3

56

hν∆

Me Me

- 126 -

An NMR tube containing a solution of 54 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 56 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 715 (AArsquom obscured by solvent peak) 680 (s 2 H) 664 (AArsquom 2 H) 447 (apparent t J = 21 Hz 2 H) 428 (apparent t J = 21 Hz 2 H) 148 (s 3 H) 032 (s 18 H) ppm Thermal reversal could be conveniently followed by VT-NMR

14-Deuterio-23-bis(trimethylsilyl) linear [3]phenylene cyclopentadienylcobalt 55

To 23-bis(trimethylsilylethynyl)biphenylene 52 (0144 g 0418 mmol) in CH3OD (10 mL) was added freshly distilled ether (20 mL) and K2CO3 (0083 g 0600 mmol) The mixture was stirred for 100 min and monitored by TLC (hexaneCH2Cl2 51) When the starting material had disappeared the solvents were removed and the remaining yellow residue very quickly dissolved in freshly distilled THF (10 mL) The green solution was separated from the solids using a filter cannula and transferred to another Schlenk flask After a 20 min Ar purge CpCo(CO)2 (0072 g 0400 mmol) was added and the resulting solution (protected from light with foil) was injected via syringe pump over 7 h into a refluxing mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 14 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed on the high vacuum line and the residue recrystallized from acetone yielding 8 (0085 g 41 ) as dark red crystals 1H-NMR spectroscopy showed 63 incorporation of deuterium as indicated by the diminution of the peak intensity of the signal at δ = 796 (s 074 H) ppm MS (FAB) mz () 496 (100) [M+] 372 (19)

CoSiMe3

SiMe3

D

D

- 127 -

Crossover experiment with 54 and 55

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

h

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

5455

5657

A solution of complex 55 (~2 mg) and 54 (~2 mg) in C6D6 (06 mL) rigorously protected from light was analyzed by 1H-NMR spectroscopy to reveal a 1861 mixture of 5554 The peak for 55 at δ = 796 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound A mass spectrum of an aliquot gave the appropriate composite of the two respective molecular ion patterns (Figure 46) The sample was then irradiated as described for above 13 h at RT The 1H-NMR spectrum of the irradiated mixture showed the presence of the respective photoisomers of 55 and 54 There were no unidentifiable peaks the signal at δ = 7470 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound and the clearly resolved peak for 56 at δ = 7473 (s 2 H) ppm revealed unattenuated intensity An aliquot was submitted for mass spectral analysis furnishing the same pattern as that depicted above The sample was then placed in an oil bath preheated to 80 degC for 30 h a treatment that regenerated the original NMR spectrum of the mixture of 55 and 54 including the relative integration ratios Similarly mass spectral analysis resulted in the same pattern as that depicted in Figure 46

- 128 -

Figure 46 Mass spectrum from the crossover experiment between 55 and 56

Low temperature photolyses of 19 and 52 A small amount (~5 mg) of linear[3]phenylene(CpCo) 19 or 52 dissolved in toluene-d8 was added to a J-Young NMR tube in the glovebox The sealed sample was then placed inside a Pyrex Dewar flask positioned in a Rayonet Photochemical Reactor outfitted with UV-lamps emitting at 310 and 350 nm (as shown in Figure 214) Cooling was achieved with the use of a Neslab Refrigerated Circulating bath employing isopropanol as the cooling medium The cold isopropanol was pumped into and out of the Pyrex Dewar using securely fastened Tygon tubes maintaining a temperature of ndash55 to ndash50 degC Once the sample was chilled irradiation was commenced The total irradiation time varied from 25 to 4 h When analysis was required the sample was transported in another Dewar flask containing dry iceisopropanol (ndash78 degC) while the NMR spectrometer was prepared for the low temperature experiment The spectrometer was cooled (ndash80 to ndash30 degC depending on the experiment) the sample wiped with a paper towel placed inside the spinner and very quickly lowered manually with a string into the cold magnet After allowing time for the temperature to equilibrate (10 min) a spectrum was recorded For VT experiments the temperature was slowly

- 129 -

raised from ndash80 degC in 10 degree increments to 10 degC Spectra were recorded at each interval For all other experiments spectra were recorded at ndash30 degC 2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

In the glovebox 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19 (0049 g 0133 mmol) and CpCo(C2H4)2 (0025 g 0139 mmol)99 were added to a Schlenk flask The flask was sealed brought out of the box connected to a vacuum manifold and freshly distilled degassed benzene (15 mL) added The mixture was heated to 70 degC on an oil bath for 23 h before being cooled to RT The solvent was removed in vacuo giving a black residue that was rapidly filtered through a plug of neutral alumina activity III (25 x 35 cm) eluting with a mixture of hexanes and THF (1001) under nitrogen and into a Schlenk flask The solvents were again removed in vacuo and the ensuing black residue recrystallized from acetone at ndash78 degC to give pure 78 (0057 g 56 ) as black crystals 1H-NMR (400 MHz acetone-d6) δ = 039 (s 36H) 481 (s 2H) 489 (m 4H) 736 (s 4H) ppm 13C-NMR (100 MHz acetone-d6) δ = 266 5372 5710 8284 12587 14542 15054 ppm UV-VIS (hexane) λmax (log ε) 197 (334) 221 (336 sh) 244 (344) 286 (363) 386 (279 sh) 439 (258) MS (FAB) 762 (M+ 100) HRMS calcd for C40H52Si4Co2 7621810 found 7621791 43 Computational Details for Chapter Two All calculations were performed using the GAUSSIAN03100 program GaussView 30101 and ChemCraft102 were employed to input structures as well as view output results Optimized geometries were obtained at the hybrid density functional theory (DFT) using Beckersquos three-parameter exchange-correlation functional103 containing the non-local gradient correction of Lee Yang and Parr104 (B3LYP) For optimization purposes a standard basis 3-21G105 was used for hydrogen and carbon atoms For cobalt the LANL2DZ106 basis set was applied with the outermost d function released yielding a triple-zeta d basis along with the effective core potentials (ECP) to describe the core electrons For the single point energy calculations the basis sets were increased to 6-31G107 for hydrogen 6-311G108 for carbon and the modified LANL2DZ basis as described above for cobalt with an added f-orbital coefficient109 The potential energy surfaces were mapped through a scan calculation a feature also available within the GAUSSIAN03 program Transition state structures were obtained in three different steps (i) determination of initial and final products or the minimum closest to a TS (ii) a linear QST2110 search for an initial guess of a TS and

- 130 -

(iii) input of the results from (ii) into a QST3 search Transition states and minima were confirmed by carrying out frequency calculations (using the same basis as that used for the optimizations)

Calculated structures for linear [3]phenylene(CpCo) (labels from Figures 29 and 210 in Section 24)

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

C 2878616000 ndash1675635000 ndash1461246000 C 3986441000 ndash2043582000 ndash0714088000 C 3986471000 ndash2043226000 0714700000 C 2878686000 ndash1674908000 1461732000 C 1740663000 ndash1265994000 0736724000 C 1740638000 ndash1266353000 ndash0736388000 H 2884721000 ndash1731772000 ndash2551997000 H 2884845000 ndash1730511000 2552509000 C 0311237000 ndash0833174000 0748280000 C 0311204000 ndash0833522000 ndash0748106000 C ndash0893980000 ndash0698348000 ndash1520584000 C ndash0893913000 ndash0697588000 1520749000 C ndash1996288000 ndash0532216000 0744771000 C ndash1996322000 ndash0532586000 ndash0744640000 C ndash3491040000 ndash0328769000 ndash0716524000 C ndash3490989000 ndash0328300000 0716632000 C ndash4645388000 ndash0172650000 ndash1448232000 C ndash4645276000 ndash0171672000 1448326000 C ndash5836534000 ndash0014205000 ndash0697760000

- 131 -

C ndash5836481000 ndash0013731000 0697841000 H ndash0905006000 ndash0741217000 ndash2609771000 H ndash0904887000 ndash0739873000 2609960000 H ndash4666353000 ndash0168153000 ndash2539086000 H ndash6785734000 0111682000 ndash1227959000 H ndash6785641000 0112502000 1228028000 H ndash4666162000 ndash0166493000 2539178000 Co 1455829000 0662094000 ndash0000295000 C 0672548000 2613322000 0000481000 C 1502831000 2459745000 1168426000 C 2819523000 2140942000 0722371000 C 2818808000 2141294000 ndash0723848000 C 1501651000 2460224000 ndash1168394000 H ndash0391329000 2836892000 0001070000 H 1172930000 2540112000 2200200000 H 3678957000 1932268000 1353707000 H 3677612000 1932967000 ndash1356152000 H 1170676000 2541059000 ndash2199789000 H 4894703000 ndash2369906000 1230670000 H 4894651000 ndash2370516000 ndash1229936000

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

C ndash3991583000 ndash2430244000 ndash0695300000 C ndash2895249000 ndash1923385000 ndash1446977000 C ndash1838331000 ndash1436925000 ndash0718218000 C ndash0460541000 ndash0772703000 ndash0748934000

- 132 -

C 0758545000 ndash0733408000 ndash1513161000 C 1871918000 ndash0586111000 ndash0739684000 C 3374782000 ndash0432509000 ndash0717168000 C 4533131000 ndash0322603000 ndash1448209000 C 5731498000 ndash0208370000 ndash0696796000 C 5731438000 ndash0207885000 0696952000 C 4533003000 ndash0321597000 1448333000 C 3374722000 ndash0432010000 0717261000 C 1871861000 ndash0585642000 0739747000 C 0758457000 ndash0732583000 1513259000 C ndash0460578000 ndash0772439000 0748991000 C ndash1838348000 ndash1436677000 0718485000 C ndash2895298000 ndash1922892000 1447371000 C ndash3991613000 ndash2429987000 0695830000 H ndash4853881000 ndash2841402000 ndash1229010000 H ndash2909366000 ndash1943431000 ndash2538196000 H 0770744000 ndash0814782000 ndash2600896000 H 4554949000 ndash0321315000 ndash2539049000 H 6684245000 ndash0118682000 ndash1227928000 H 6684140000 ndash0117859000 1228104000 H 4554722000 ndash0319567000 2539175000 H 0770611000 ndash0813312000 2601042000 H ndash2909450000 ndash1942588000 2538596000 H ndash4853932000 ndash2840954000 1229654000 Co ndash1032604000 1030206000 ndash0000179000 C ndash2903591000 1947430000 ndash0000175000 C ndash2211742000 2430689000 ndash1177143000 C ndash1026232000 3056089000 ndash0732194000 C ndash1026229000 3056139000 0731719000 C ndash2211730000 2430773000 1176747000 H ndash3829247000 1376180000 ndash0000150000 H ndash2513347000 2264399000 ndash2207387000 H ndash0243163000 3477094000 ndash1358586000 H ndash0243137000 3477190000 1358051000 H ndash2513304000 2264572000 2207015000

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 133 -

C 4829664000 ndash1220862000 0883782000 C 3649435000 ndash0895915000 1609183000 C 2478533000 ndash0900239000 0886069000 C 0985532000 ndash0699413000 0895282000 C ndash0207413000 ndash0351140000 1567281000 C ndash1295977000 ndash0355264000 0631690000 C ndash2799524000 ndash0368596000 0647705000 C ndash3950748000 0104186000 1252743000 C ndash5173877000 ndash0370408000 0725519000 C ndash5217559000 ndash1270006000 ndash0351644000 C ndash4043168000 ndash1754445000 ndash0967619000 C ndash2843350000 ndash1293792000 ndash0444950000 C ndash1365414000 ndash1319830000 ndash0538287000 C ndash0225558000 ndash1662005000 ndash1182029000 C 0928168000 ndash1009692000 ndash0554559000 C 2436156000 ndash1209374000 ndash0509824000 C 3575395000 ndash1530032000 ndash1215144000 C 4792344000 ndash1526592000 ndash0477473000 H 5781080000 ndash1237670000 1406156000 H 3693287000 ndash0679862000 2671420000 H ndash0279175000 ndash0037747000 2601166000 H ndash3939706000 0801901000 2083798000 H ndash6106757000 ndash0031072000 1165263000 H ndash6183419000 ndash1601741000 ndash0720200000 H ndash4097586000 ndash2453276000 ndash1795561000 H ndash0137803000 ndash2306368000 ndash2049380000 H 3570207000 ndash1781979000 ndash2270507000 H 5717527000 ndash1774506000 ndash0988963000 Co 0235674000 0924694000 ndash0006080000 C 1650242000 2605908000 ndash0261710000 C 0606451000 3071372000 0583798000

C ndash0633939000 2891762000 ndash0112192000 C ndash0354070000 2388098000 ndash1431110000 C 1060641000 2182627000 ndash1507942000 H 2701380000 2562827000 ndash0018620000 H 0717262000 3431891000 1595877000 H ndash1615358000 3123686000 0274491000 H ndash1077256000 2190401000 ndash2207047000

- 134 -

H 1601331000 1788686000 ndash2355167000

(d) Transition State 2 η3-benzene (249 kcalmol)

C 5059641000 ndash0675345000 0741440000 C 3868057000 ndash0242461000 1393542000 C 2691208000 ndash0611642000 0796692000 C 1164924000 ndash0568451000 0814993000 C 0001006000 ndash0193010000 1575722000 C ndash1162903000 ndash0569406000 0815406000 C ndash2689168000 ndash0613549000 0797134000 C ndash3866228000 ndash0245076000 1394017000 C ndash5057560000 ndash0678583000 0741882000 C ndash5030442000 ndash1430649000 ndash0426732000 C ndash3802288000 ndash1812828000 ndash1038342000 C ndash2662603000 ndash1392426000 ndash0404590000 C ndash1143695000 ndash1392940000 ndash0383227000 C 0001354000 ndash1885575000 ndash1010384000 C 1146183000 ndash1392203000 ndash0383465000 C 2665098000 ndash1390792000 ndash0404876000 C 3805017000 ndash1810598000 ndash1038596000 C 5032958000 ndash1427555000 ndash0427087000 H 6017043000 ndash0408623000 1174840000 H 3916675000 0338622000 2306082000 H 0001106000 0141040000 2603832000 H ndash3915179000 0335814000 2306664000 H ndash6015116000 ndash0412488000 1175329000

- 135 -

H ndash5963925000 ndash1737868000 ndash0883265000 H ndash3794877000 ndash2406462000 ndash1944276000 H 0001449000 ndash2505619000 ndash1894591000 H 3797948000 ndash2404400000 ndash1944423000 H 5966616000 ndash1734262000 ndash0883606000 Co ndash0000294000 1006304000 0016484000 C 1144150000 2811021000 ndash0317903000 C ndash0001831000 3236912000 0413780000 C ndash1150105000 2808519000 ndash0312717000 C ndash0712506000 2257800000 ndash1588662000 C 0702130000 2259464000 ndash1591918000 H 2174046000 2940434000 ndash0021226000 H ndash0000096000 3693787000 1391408000 H ndash2178919000 2935539000 ndash0011312000 H ndash1360790000 1903514000 ndash2375388000 H 1347563000 1907002000 ndash2381795000

Calculated structures for linear [5]phenylene CpCo (labels from Figures 211 and 212 in Section 24)

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

C ndash2147283000 ndash0385762000 ndash0741520000 C ndash2146881000 ndash0382747000 0740465000 C ndash0675330000 ndash0218887000 0741228000 C ndash0675503000 ndash0222208000 ndash0743565000 C 0535474000 ndash0309864000 ndash1519364000

- 136 -

C 1654024000 ndash0363787000 ndash0743565000 C 1653968000 ndash0359108000 0742223000 C 0535464000 ndash0301263000 1517648000 C 3146303000 ndash0437352000 0715394000 C 3146555000 ndash0442081000 ndash0715839000 H 0537903000 ndash0329735000 2601810000 H 0538062000 ndash0344229000 ndash2603354000 Co ndash1585768000 1444604000 ndash0004763000 C ndash2656365000 3118646000 0813641000 C ndash1264152000 3247968000 1115884000 C ndash0546296000 3292610000 ndash0128221000 C ndash1500173000 3225060000 ndash1199322000 C ndash2801883000 3099872000 ndash0616868000 H ndash3459184000 3033020000 1530368000 H ndash0824887000 3279284000 2101474000 H 0525240000 3366953000 ndash0237713000 H ndash1272392000 3239735000 ndash2254384000 H ndash3732669000 2998753000 ndash1154572000 C ndash3315848000 ndash0698077000 1516941000 C ndash3316515000 ndash0705270000 ndash1515890000 C ndash4404590000 ndash0970491000 0742487000 C ndash4404888000 ndash0974125000 ndash0739677000 H ndash3311463000 ndash0745189000 ndash2599679000 H ndash3310191000 ndash0733014000 2600900000 C ndash5857232000 ndash1346832000 ndash0713671000 C ndash5856902000 ndash1343302000 0718959000 C ndash6992149000 ndash1638138000 ndash1445564000 C ndash6991464000 ndash1630979000 1452826000 C 4314567000 ndash0501395000 ndash1493440000 C 4313844000 ndash0491124000 1494022000

C ndash8157130000 ndash1937355000 ndash0695553000 C ndash8156796000 ndash1933908000 0704865000 H ndash7013569000 ndash1630976000 2537309000 H ndash9075842000 ndash2169721000 1232475000 H ndash9076411000 ndash2175846000 ndash1221548000 H ndash7014707000 ndash1643790000 ndash2530023000 C 5464859000 ndash0553191000 0719930000 C 5465218000 ndash0558312000 ndash0718328000 C 6977989000 ndash0635007000 ndash0714777000 C 6977565000 ndash0629511000 0717833000 H 4313279000 ndash0484164000 2577745000 H 4314609000 ndash0502067000 ndash2577185000 C 8138196000 ndash0684071000 1451266000 C 8139115000 ndash0695400000 ndash1446980000 C 9348946000 ndash0746919000 0699256000 C 9349380000 ndash0752387000 ndash0693700000

- 137 -

H 8162380000 ndash0700716000 ndash2531270000 H 8160717000 ndash0680929000 2535584000 H 10294800000 ndash0791917000 1230058000 H 10295576000 ndash0801571000 ndash1223516000

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

C ndash8026536000 ndash2149127000 ndash0697047000 C ndash6872771000 ndash1801590000 ndash1447012000 C ndash5755909000 ndash1466198000 ndash0717983000 C ndash4305789000 ndash1041476000 ndash0739357000 C ndash3218268000 ndash0750848000 ndash1510952000 C ndash2077793000 ndash0315087000 ndash0749237000 C ndash0550342000 ndash0400850000 ndash0716361000 C 0616872000 ndash0404801000 ndash1489728000 C 1770640000 ndash0412395000 ndash0716060000 C 3300443000 ndash0457807000 ndash0715861000 C 4454767000 ndash0490291000 ndash1489427000 C 5616257000 ndash0520747000 ndash0712496000 C 5616269000 ndash0520699000 0712492000 C 4454793000 ndash0490190000 1489443000 C 3300455000 ndash0457762000 0715895000 C 1770651000 ndash0412347000 0716117000 C 0616894000 ndash0404700000 1489800000 C ndash0550335000 ndash0400796000 0716454000 C ndash2077818000 ndash0315060000 0749341000 C ndash3218306000 ndash0750915000 1510996000

- 138 -

C ndash4305781000 ndash1041534000 0739359000 C ndash5755900000 ndash1466256000 0717962000 C ndash6872758000 ndash1801708000 1446971000 C ndash8026533000 ndash2149171000 0696987000 H ndash6893447000 ndash1807486000 ndash2529846000 H ndash3199702000 ndash0827686000 ndash2591829000 H 0616147000 ndash0415875000 ndash2572166000 H 4455855000 ndash0492565000 ndash2571217000 H 4455901000 ndash0492389000 2571233000 H 0616188000 ndash0415693000 2572238000 H ndash3199790000 ndash0827916000 2591862000 H ndash6893430000 ndash1807681000 2529804000 Co ndash2237895000 1566525000 ndash0000035000 C ndash0770702000 3039808000 0000091000 C ndash1582333000 3276979000 1176306000 C ndash2906316000 3484053000 0731575000 C ndash2906172000 3484095000 ndash0731735000 C ndash1582100000 3277047000 ndash1176233000 H 0281094000 2798829000 0000215000 H ndash1247438000 3209109000 2198999000 H ndash3777291000 3625124000 1353071000 H ndash3777011000 3625160000 ndash1353424000 H ndash1246943000 3209260000 ndash2198847000 H ndash8933230000 ndash2423019000 ndash1224452000 H ndash8933222000 ndash2423113000 1224377000 C 7146943000 ndash0559737000 0717588000 C 7146931000 ndash0559786000 ndash0717614000 C 8302361000 ndash0588480000 1447040000 C 8302337000 ndash0588576000 ndash1447082000 C 9516918000 ndash0618789000 ndash0692883000 C 9516929000 ndash0618742000 0692823000 H 8324450000 ndash0589130000 2529610000 H 10461320000 ndash0642422000 1224406000 H 10461300000 ndash0642481000 ndash1224480000 H 8324409000 ndash0589299000 ndash2529653000

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 139 -

C ndash7810644000 ndash2064896000 ndash0088979000 C ndash6582065000 ndash2396690000 ndash0700394000 C ndash5469369000 ndash1694626000 ndash0259356000 C ndash4011414000 ndash1478684000 ndash0398743000 C ndash2839913000 ndash1679834000 ndash1045300000 C ndash1807973000 ndash0777407000 ndash0523048000 C ndash0288034000 ndash0728447000 ndash0497727000 C 0877200000 ndash0917515000 ndash1257428000 C 2033335000 ndash0625143000 ndash0541547000 C 3550975000 ndash0572504000 ndash0566638000 C 4702932000 ndash0775398000 ndash1323945000 C 5869717000 ndash0493099000 ndash0604711000 C 5877160000 ndash0049178000 0749672000 C 4719648000 0152978000 1509600000 C 3558389000 ndash0127834000 0791889000 C 2041313000 ndash0178303000 0818968000 C 0890228000 0010834000 1576182000

C ndash0275189000 ndash0290874000 0857465000 C ndash1777915000 ndash0332627000 0896504000 C ndash3000252000 ndash0144927000 1576583000 C ndash4087655000 ndash0414543000 0681649000 C ndash5565811000 ndash0681071000 0748878000 C ndash6769777000 ndash0358061000 1349731000 C ndash7902756000 ndash1078577000 0906205000 H ndash6531350000 ndash3165530000 ndash1463988000 H ndash2656944000 ndash2379915000 ndash1852763000

- 140 -

H 0873498000 ndash1259556000 ndash2286041000 H 4697058000 ndash1113491000 ndash2353481000 H 4726794000 0489146000 2539724000 H 0892018000 0335667000 2610226000 H ndash3107471000 0242268000 2582171000 H ndash6863567000 0403771000 2116786000 Co ndash2805901000 1045228000 ndash0126008000 C ndash1966955000 3131745000 ndash0137391000 C ndash3345106000 3172285000 0219040000 C ndash4105003000 2591218000 ndash0859559000 C ndash3194452000 2177424000 ndash1877135000 C ndash1861601000 2475718000 ndash1403791000 H ndash1139494000 3467521000 0469940000 H ndash3757304000 3575577000 1132204000 H ndash5178689000 2478840000 ndash0883920000 H ndash3449207000 1717975000 ndash2819531000 H ndash0944137000 2267497000 ndash1933863000 H ndash8711780000 ndash2586977000 ndash0395882000 H ndash8871888000 ndash0864282000 1346179000 C 7394568000 0005138000 0727783000

C 7387058000 ndash0441388000 ndash0634217000 C 8557433000 0273605000 1404315000

C 8542647000 ndash0629395000 ndash1349402000 C 9760631000 ndash0352464000 ndash0653366000 C 9767843000 0080954000 0667800000 H 8586089000 0612106000 2434348000 H 10716375000 0279405000 1157078000

H 10703753000 ndash0485281000 ndash1174332000 H 8560430000 ndash0966385000 ndash2380163000

(d) Transition state 4 η3-benzene (367 kcalmol)

- 141 -

C 7669717000 ndash2174926000 ndash0105923000 C 6450462000 ndash2458728000 0544003000 C 5349535000 ndash1733337000 0120322000 C 3893688000 ndash1505268000 0269179000 C 2708972000 ndash1942858000 0838638000 C 1596115000 ndash1239419000 0370186000 C 0149218000 ndash1103313000 0368184000 C ndash1061261000 ndash1583264000 0932639000 C ndash2167377000 ndash0965378000 0405284000 C ndash3686709000 ndash0866795000 0409630000 C ndash4872520000 ndash1347856000 0960688000 C ndash5997863000 ndash0728310000 0421450000 C ndash5941471000 0288854000 ndash0586107000 C ndash4758793000 0770529000 ndash1137452000 C ndash3629556000 0150846000 ndash0598044000 C ndash2119390000 0068600000 ndash0617626000 C ndash0945265000 0548559000 ndash1173832000 C 0191709000 ndash0072876000 ndash0643629000 C 1695402000 ndash0118964000 ndash0667389000 C 2835200000 0041396000 ndash1507494000 C 3981535000 ndash0415532000 ndash0796385000 C 5449049000 ndash0747489000 ndash0920326000 C 6638556000 ndash0473422000 ndash1556289000 C 7762417000 ndash1216205000 ndash1122513000 H 6396888000 ndash3209338000 1323030000 H 2647172000 ndash2772334000 1532449000 H ndash1099468000 ndash2356302000 1688990000 H ndash4914534000 ndash2116326000 1720908000 H ndash4717626000 1537921000 ndash1898781000 H ndash0906852000 1317204000 ndash1935050000 H 2849903000 0560387000 ndash2457942000 H 6730568000 0262385000 ndash2346085000 Co 3078365000 1106450000 0223118000 C 2432920000 3235925000 0352954000 C 3805628000 3232135000 ndash0000959000 C 4525686000 2519574000 1027488000 C 3591065000 2151422000 2051886000 C 2287258000 2550618000 1620273000

- 142 -

H 1625110000 3662123000 ndash0222202000 H 4237852000 3652387000 ndash0895767000 H 5588986000 2336674000 1044912000 H 3828106000 1629983000 2966790000 H 1363656000 2417646000 2161607000 H 8562189000 ndash2715853000 0187384000 H 8723754000 ndash1039126000 ndash1591154000 C ndash7467794000 0379383000 ndash0580257000 C ndash7522920000 ndash0639213000 0428535000 C ndash8594261000 0964602000 ndash1089561000 C ndash8706397000 ndash1090617000 0945872000 C ndash9887862000 ndash0485330000 0420145000 C ndash9834353000 0499744000 ndash0555359000 H ndash8574126000 1734202000 ndash1850912000 H ndash10757407000 0931123000 ndash0925119000 H ndash10851990000 ndash0807405000 0796463000 H ndash8770071000 ndash1858056000 1706995000

(e) Local minimum 3 η4-benzene (190 kcalmol)

C ndash7704806000 ndash1625445000 ndash0076324000 C ndash6491455000 ndash1789497000 ndash0801300000 C ndash5352262000 ndash1326936000 ndash0190371000 C ndash3836374000 ndash1127906000 ndash0291559000 C ndash2669014000 ndash1876939000 ndash0775878000 C ndash1540408000 ndash1361850000 ndash0248671000 C ndash0067088000 ndash1219487000 ndash0231176000 C 1147603000 ndash1746746000 ndash0723682000

- 143 -

C 2245517000 ndash1037457000 ndash0289605000 C 3767258000 ndash0910575000 ndash0313273000 C 4961694000 ndash1439625000 ndash0795996000 C 6075343000 ndash0726547000 ndash0354068000 C 5999362000 0418026000 0498208000 C 4804020000 0947684000 0980899000 C 3691158000 0235329000 0538756000 C 2171505000 0121554000 0570963000 C 0990404000 0649716000 1051234000

C ndash0139369000 ndash0066282000 0613306000 C ndash1640889000 ndash0139469000 0665899000 C ndash2708579000 0044357000 1607074000 C ndash3890300000 ndash0515482000 1069631000 C ndash5389479000 ndash0719093000 1106627000 C ndash6553177000 ndash0561696000 1815459000 C ndash7736166000 ndash1034716000 1182797000 H ndash6489929000 ndash2263627000 ndash1775522000 H ndash2743316000 ndash2692464000 ndash1483904000 H 1201969000 ndash2617287000 ndash1364047000 H 5019196000 ndash2306567000 ndash1440440000 H 4747029000 1814065000 1626168000 H 0933710000 1519855000 1692796000 H ndash2640951000 0605584000 2529735000 H ndash6590996000 ndash0122891000 2805220000 Co ndash3231943000 0870639000 ndash0218177000 C ndash2631117000 2925280000 ndash0475333000 C ndash4019450000 2955930000 ndash0137499000 C ndash4720042000 2167067000 ndash1095287000 C ndash3768150000 1717753000 ndash2089396000 C ndash2477085000 2188405000 ndash1710046000 H ndash1832546000 3399891000 0073720000 H ndash4448788000 3419647000 0737399000 H ndash5777018000 1951944000 ndash1095854000 H ndash3999907000 1119290000 ndash2956393000 H ndash1549894000 2013889000 ndash2232360000 H ndash8630326000 ndash1978241000 ndash0517433000 H ndash8683428000 ndash0939767000 1701100000 C 7524401000 0541032000 0473497000

C 7600630000 ndash0607844000 ndash0382149000 C 8637973000 1216338000 0890053000

C 8792152000 ndash1101412000 ndash0836674000 C 9961705000 ndash0402146000 ndash0407106000 C 9887895000 0708141000 0420266000 H 8602106000 2084773000 1535736000 H 10801526000 1207625000 0721410000

H 10931894000 ndash0752974000 ndash0739605000

- 144 -

H 8871661000 ndash1966753000 ndash1482602000

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

C 7143264000 ndash2348493000 0699665000 C 6037664000 ndash1857298000 1448523000 C 4969251000 ndash1391864000 0720257000 C 3582514000 ndash0743198000 0748195000 C 2358402000 ndash0737338000 1512136000 C 1240141000 ndash0634711000 0742222000 C ndash0262684000 ndash0516912000 0716494000 C ndash1428088000 ndash0430968000 1492584000 C ndash2574224000 ndash0346717000 0719319000 C ndash4098679000 ndash0233199000 0715866000 C ndash5251323000 ndash0147278000 1490294000 C ndash6408253000 ndash0063372000 0713741000 C ndash7934932000 0047490000 0717366000 C ndash9088044000 0130556000 1446914000 C ndash10299063000 0217080000 0692638000 C ndash10298939000 0215301000 ndash0693576000 C ndash9087782000 0126841000 ndash1447398000 C ndash7934811000 0045602000 ndash0717417000 C ndash6408180000 ndash0065400000 ndash0713264000 C ndash5251144000 ndash0151514000 ndash1489420000 C ndash4098619000 ndash0235099000 ndash0714599000 C ndash2574142000 ndash0348081000 ndash0717615000 C ndash1428022000 ndash0433439000 ndash1490677000

- 145 -

C ndash0262587000 ndash0517946000 ndash0714342000 C 1239930000 ndash0636111000 ndash0739947000 C 2357013000 ndash0742891000 ndash1511730000 C 3581891000 ndash0749703000 ndash0749006000 C 4968536000 ndash1397444000 ndash0717250000 C 6036190000 ndash1868351000 ndash1443314000 C 7142499000 ndash2353756000 ndash0691900000 H 8003789000 ndash2740125000 1230531000 H 6052031000 ndash1874231000 2531931000 H 2350726000 ndash0802237000 2593967000 H ndash1427931000 ndash0429806000 2574521000 H ndash5251989000 ndash0146640000 2572026000 H ndash9110076000 0132990000 2529448000 H ndash11241535000 0285430000 1223689000 H ndash11241318000 0282253000 ndash1224971000 H ndash9109613000 0126365000 ndash2529940000 H ndash5251637000 ndash0153720000 ndash2571150000 H ndash1427824000 ndash0434279000 ndash2572612000 H 2347832000 ndash0810535000 ndash2593375000 H 6049185000 ndash1893779000 ndash2526553000 H 8002469000 ndash2749449000 ndash1220666000 Co 4148367000 1055016000 ndash0009106000 C 5996101000 2006266000 0022069000 C 5276853000 2480887000 1185002000 C 4085420000 3079352000 0718350000 C 4110596000 3077077000 ndash0745160000 C 5316353000 2474554000 ndash1168669000 H 6921324000 1451094000 0038659000 H 5556549000 2314709000 2212960000 H 3287274000 3477873000 1325692000 H 3334253000 3474398000 ndash1380859000 H 5631980000 2304731000 ndash2185537000

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 146 -

C 4893664000 ndash1209972000 0735005000 C 4893573000 ndash1213475000 ndash0730870000 C 3475382000 ndash0763132000 ndash0743915000 C 3475432000 ndash0760320000 0747049000 C 2260316000 ndash0690973000 1520580000 C 1145205000 ndash0595973000 0744946000 C 1145156000 ndash0599246000 ndash0742744000 C 2260358000 ndash0697381000 ndash1517904000 C ndash0343192000 ndash0479177000 ndash0713609000 C ndash0343168000 ndash0476032000 0715380000 H 2252105000 ndash0735285000 ndash2601934000 H 2251901000 ndash0724154000 2604763000 Co 4601208000 0736083000 ndash0002055000 C 5960130000 2243618000 ndash0721946000 C 4640007000 2540538000 ndash1172530000 C 3804522000 2681992000 ndash0008876000 C 4632302000 2544967000 1160921000 C 5955467000 2247130000 0721276000 H 6816321000 2038808000 ndash1347044000 H 4312673000 2604006000 ndash2199136000 H 2745254000 2890841000 ndash0012873000 H 4298236000 2612143000 2185222000 H 6807361000 2044890000 1353015000 C 6022290000 ndash1649780000 1464200000 C 6022277000 ndash1656609000 ndash1457900000 C 7122289000 ndash2056771000 0719324000 C 7122311000 ndash2060028000 ndash0711126000 H 6027301000 ndash1702610000 2548102000 H 8011576000 ndash2407816000 1233935000 H 8011528000 ndash2413601000 ndash1224115000 H 6027432000 ndash1714310000 ndash2541551000 C ndash1512226000 ndash0382902000 1494684000 C ndash1512274000 ndash0389473000 ndash1493257000 C ndash2658093000 ndash0297761000 0720325000 C ndash2658103000 ndash0300923000 ndash0719236000 H ndash1511446000 ndash0379165000 2578406000

- 147 -

H ndash1511531000 ndash0390614000 ndash2576954000 C ndash4169046000 ndash0190131000 ndash0714237000 C ndash4169015000 ndash0186849000 0714915000 C ndash5325016000 ndash0103295000 1491764000 C ndash5325120000 ndash0110177000 ndash1491395000 C ndash6483203000 ndash0023670000 0713863000 C ndash6483258000 ndash0027061000 ndash0713749000 H ndash5325252000 ndash0101647000 2575308000 H ndash5325471000 ndash0113799000 ndash2574933000 C ndash7997403000 0080746000 0716440000 C ndash7997524000 0076500000 ndash0716680000 C ndash9155096000 0160872000 1448927000 C ndash9155379000 0152083000 ndash1449432000 C ndash10366775000 0240123000 0695134000 C ndash10366925000 0235844000 ndash0695874000 H ndash9178696000 0150122000 ndash2533721000 H ndash11311550000 0297904000 ndash1227155000 H ndash11311298000 0305233000 1226228000 H ndash9178228000 0165001000 2533216000

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

C 8266704000 ndash2005162000 0692734000 C 7088955000 ndash1708719000 1446000000 C 5966603000 ndash1428050000 0716466000

- 148 -

C 4483884000 ndash1054830000 0713802000 C 3355736000 ndash0795879000 1487813000 C 2219848000 ndash0542568000 0715155000 C 0748349000 ndash0122254000 0743952000 C ndash0460068000 ndash0300197000 1509394000 C ndash1583463000 ndash0354552000 0739667000 C ndash3088504000 ndash0455891000 0716671000 C ndash4249167000 ndash0553278000 1491353000 C ndash5399475000 ndash0634011000 0717623000 C ndash6922525000 ndash0754459000 0717051000 C ndash8076029000 ndash0852663000 1446746000 C ndash9285359000 ndash0940991000 0693505000 C ndash9286426000 ndash0927591000 ndash0694047000 C ndash8078221000 ndash0824629000 ndash1447252000 C ndash6923651000 ndash0740632000 ndash0717519000 C ndash5400498000 ndash0620402000 ndash0717994000 C ndash4251528000 ndash0525736000 ndash1491803000 C ndash3089431000 ndash0443610000 ndash0717063000 C ndash1585243000 ndash0344579000 ndash0740307000 C ndash0463450000 ndash0290395000 ndash1513612000 C 0748496000 ndash0127629000 ndash0751652000 C 2219455000 ndash0546002000 ndash0721683000 C 3355860000 ndash0802470000 ndash1493276000 C 4483583000 ndash1057975000 ndash0718022000 C 5966360000 ndash1431783000 ndash0719354000 C 7088265000 ndash1716549000 ndash1447876000 C 8266466000 ndash2008718000 ndash0693595000 H 9183427000 ndash2233531000 1224348000 H 7110060000 ndash1714392000 2528663000 H 3353411000 ndash0803478000 2570367000 H ndash0456292000 ndash0373454000 2590614000 H ndash4248665000 ndash0564171000 2573279000 H ndash8096828000 ndash0865292000 2529266000 H ndash10227269000 ndash1021159000 1223954000 H ndash10229127000 ndash0997490000 ndash1224546000 H ndash8100648000 ndash0816347000 ndash2529785000 H ndash4252664000 ndash0517117000 ndash2573754000 H ndash0464650000 ndash0354640000 ndash2595436000 H 3353541000 ndash0815213000 ndash2575752000 H 7108905000 ndash1727728000 ndash2530504000 H 9182976000 ndash2239822000 ndash1224379000 Co 1060170000 1739352000 ndash0013647000 C 0820599000 3762931000 0679296000 C 2023158000 3250849000 1217023000 C 2833506000 2814255000 0100512000 C 2185795000 3225276000 ndash1129991000

- 149 -

C 0924349000 3753677000 ndash0780133000 H ndash0033478000 4112410000 1239126000 H 2257663000 3114053000 2260457000 H 3791311000 2322414000 0171627000 H 2565428000 3065285000 ndash2126458000 H 0160713000 4098445000 ndash1460120000

(i) Local minimum 1 η4-benzene (190 kcalmol)

C 8767525000 ndash0664628000 0869444000 C 7569070000 ndash0364489000 1586360000 C 6400497000 ndash0535559000 0896308000 C 4872998000 ndash0456407000 0896648000 C 3729258000 ndash0166123000 1633430000 C 2558863000 ndash0367557000 0899969000 C 1050529000 ndash0274920000 0917771000 C ndash0154687000 0103769000 1545183000 C ndash1231288000 ndash0039565000 0606842000 C ndash2736221000 ndash0089835000 0603708000 C ndash3901526000 0467576000 1153370000 C ndash5054648000 ndash0104455000 0647800000 C ndash6579036000 ndash0120351000 0673091000 C ndash7732820000 0402806000 1194768000 C ndash8948594000 ndash0155119000 0702959000 C ndash8958839000 ndash1167887000 ndash0247745000 C ndash7753788000 ndash1707235000 ndash0785423000 C ndash6589806000 ndash1166201000 ndash0307896000

- 150 -

C ndash5063448000 ndash1158179000 ndash0339650000 C ndash3923750000 ndash1713712000 ndash0884954000 C ndash2743411000 ndash1141750000 ndash0370168000 C ndash1264100000 ndash1152263000 ndash0442985000 C ndash0114410000 ndash1509648000 ndash1047872000 C 1001557000 ndash0717865000 ndash0509678000 C 2529242000 ndash0815059000 ndash0456630000 C 3680301000 ndash1106705000 ndash1192448000 C 4847485000 ndash0909766000 ndash0461159000 C 6375435000 ndash0989198000 ndash0464503000 C 7517684000 ndash1280530000 ndash1157992000 C 8743181000 ndash1104009000 ndash0445669000 H 9720775000 ndash0544729000 1371431000 H 7610320000 ndash0024462000 2613574000 H 3742883000 0162901000 2664422000 H ndash0241422000 0534554000 2534230000 H ndash3894210000 1260341000 1890621000 H ndash7746436000 1191936000 1936109000 H ndash9890199000 0223840000 1083439000

H ndash9908180000 ndash1561665000 ndash0592194000 H ndash7783148000 ndash2497305000 ndash1525270000 H ndash3929534000 ndash2506814000 ndash1621099000 H 0005285000 ndash2235278000 ndash1842324000 H 3664139000 ndash1453900000 ndash2217556000 H 7520111000 ndash1625509000 ndash2184413000 H 9677483000 ndash1320445000 ndash0950825000 Co 0245526000 1194775000 ndash0183529000 C ndash0498660000 3223481000 ndash0207100000 C 0902667000 3310487000 0056983000 C 1591310000 2661311000 ndash1009417000 C 0610054000 2243094000 ndash1989593000 C ndash0681576000 2592200000 ndash1494981000 H ndash1289524000 3595536000 0425619000 H 1355880000 3721411000 0946130000 H 2657726000 2519341000 ndash1088515000 H 0823168000 1743521000 ndash2921425000 H ndash1626608000 2403559000 ndash1979282000

(j) Transition state 1 η3-benzene (356 kcalmol)

- 151 -

C ndash8901354000 ndash0223681000 ndash0743434000 C ndash7695103000 0220198000 ndash1360549000 C ndash6531343000 ndash0208573000 ndash0779115000 C ndash5007706000 ndash0207407000 ndash0796109000 C ndash3863247000 0247302000 ndash1433753000 C ndash2690760000 ndash0206508000 ndash0819013000 C ndash1184933000 ndash0153490000 ndash0843116000 C ndash0016095000 0217826000 ndash1588049000 C 1142075000 ndash0155798000 ndash0877497000 C 2665172000 ndash0195830000 ndash0859864000 C 3835813000 0283152000 ndash1437197000 C 4978920000 ndash0204857000 ndash0802474000 C 6505676000 ndash0216574000 ndash0771205000 C 7678527000 0226433000 ndash1319208000 C 8875127000 ndash0251684000 ndash0703235000 C 8845790000 ndash1112691000 0383544000 C 7616005000 ndash1570592000 0948642000 C 6475812000 ndash1107284000 0353147000 C 4945633000 ndash1092812000 0320013000 C 3774824000 ndash1565295000 0903163000 C 2628495000 ndash1080676000 0265289000 C 1119158000 ndash1093642000 0244670000 C ndash0052242000 ndash1637616000 0861793000 C ndash1193959000 ndash1109215000 0331010000 C ndash2676505000 ndash1073633000 0328062000 C ndash3841325000 ndash1514463000 0979035000 C ndash4995446000 ndash1053912000 0371366000 C ndash6522185000 ndash1052982000 0381089000 C ndash7676261000 ndash1483950000 0978498000 C ndash8892512000 ndash1041633000 0378747000

- 152 -

H ndash9850267000 0087677000 ndash1164894000 H ndash7723622000 0856176000 ndash2236504000 H ndash3873085000 0886115000 ndash2307512000 H ndash0031238000 0768624000 ndash2518870000 H 3857949000 0953892000 ndash2286176000 H 7723941000 0897606000 ndash2167700000 H 9831384000 0069893000 ndash1099633000 H 9779177000 ndash1450269000 0819087000 H 7614291000 ndash2243551000 1796930000 H 3751975000 ndash2237828000 1750478000 H ndash0016047000 ndash2343040000 1681308000 H ndash3832680000 ndash2159963000 1847727000 H ndash7691389000 ndash2121828000 1853393000 H ndash9834648000 ndash1354566000 0814012000 Co ndash0004249000 1140918000 0250383000 C 0931445000 3181201000 0326993000 C ndash0487068000 3279997000 0223542000 C ndash1069741000 2607436000 1368652000 C 0008159000 2107122000 2176577000 C 1235098000 2411215000 1492603000 H 1650004000 3565479000 ndash0380430000 H ndash1033454000 3774248000 ndash0564979000 H ndash2124544000 2537255000 1584462000 H ndash0094112000 1572170000 3107766000 H 2227446000 2134637000 1815486000

LUMO

HOMO

2887

239

00862

2496

1163

1382

1418

1312

0

3155

2767

0498

2588

1531

0831

Figure 47 Orbital coefficients of linear [5]phenylene

- 153 -

Figure 48 Top view of the contour plots of (a) the HOMO and (b) the LUMO of the [5]-phenylene ligand

- 154 -

Bad

Bad

Good Good

External cyclobutadiene coordination Internal cyclobutadiene coordination

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCpCoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

Figure 49 Resonance rationale for the increased stability of internal Co coordination in linear [5]phenylene

44 NMR Data for Chapter Two

- 155 -

Figure 410 1H-NMR data for the respective parent phenylene frames experimental (C6D6) and

calculated [NICS (1) B3LYP6-31+G] Assignments by NOESY DEPT HMBC and HSQC as applicable

- 156 -

Me3Si

Me3Si

SiMe3

SiMe3

1

23

4 56

7 89

10 1112

13 1415

16

17

18

Co

222

1490

1252

1450

1433

1151

744

730

11091121

14161504

11211109

1540

1499

1224

1486

217

801

SiMe3

SiMe3

Me3Si

Me3Si

Co

802

261

1484

1256

1433

1494

1155

739

781

1360

1394

269

SiMe3

SiMe3

Co

802

1294

1149

1426

1502

1194

738

779

1363

1393

268

SiMe3

SiMe3

1241

1276

8029

725

1155

1493

1430

1256

1482

222

Co

796

678674 675 796

436

037032662

724 683 747

444

TMS

TMS

TMS

TMS

213

1474

1211

1538

1499

1112

623 685

SiMe3

SiMe3Me3Si

Me3Si SiMe3

SiMe3Me3Si

Me3Si459 Co

589 681 672 745

2201204

15131096

1535

2221252

1480

1433

1149741

801

1501 1490

1475

Figure 411 Comparison of 1H-NMR (blue) and 13C-NMR assignments (C6D6)

NICS-Scan calculations Methods The free ligands were optimized at the B3LYP6-31G and the CpCo complexes at the B3LYPLANL2DZ computational levels Analytical frequency calculations were executed to ensure real minima (Nimag = 0) GIAO-B3LYP6-31+G was used to calculate NICS values The NICS-scan procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (ipc or NICSXY) and out-of-plane components (oopc or NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their interpretation

- 157 -

Since there are no published NICS-scan studies of transition metal complexed cyclic polyenes we benchmark the method with (C6H6)Cr(CO)3

53

Figure 412 NICS-scan of benzene (left) and (benzene)Cr(CO)3 (right)

The shape of the oopc curve suggests that the diamagnetic ring current in the ligand is diminished on complexation although still prevalent Thus at r = 0 Aring (ie at the benzene plane) the oopc value [NICSZZ(0)] of the complex is less negative than that of benzene and the minimum of the curve is less negative and occurs at a larger distance (ndash29911 vs ndash31910) A larger change is observed in the ipc (which is governed by the σ electrons) which shows far more negative values in the complex relative to benzene itself (eg ndash55400 vs ndash5900 and ndash13910 vs ndash0910) Therefore isotropic NICS values are misleading with respect to the diatropism in the complex because they originate largely from the diamagnetic effect of the σ framework NICS-scans for the four-membered ring B in linear [3]phenylene and its CpCo complex are shown below

00 05 10 15 20 25 30 35 40

-34-32-30-28-26-24-22-20-18-16-14-12-10

-8-6-4-202

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

oopc ipc isotropic

pp

m

r

- 158 -

Figure 413 NICS-scan above ring B of linear [3]phenylene (left) and its CpCo complex (right) Inspection of the shape and values of the oopc curve shows that the four-membered ring in the free ligand is strongly paratropic This picture changes on CpCo complexation At or close to the ring plane the values are much less positive (12100 vs 88000) become negative at greater distance and reach a minimum of -16112 Consequently the presence of the metal clearly reduces paratropic character The ipc curve is similar to that of (benzene)Cr(CO)3 Therefore again isotropic NICS values are misleading with respect to an assessment of the size of ring current effects The two isomeric CpCo complexes of linear [5]phenylene as depicted next behave in an analogous manner and engender the same conclusions as above

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

- 159 -

Figure 414 NICS-scans of linear [5]phenylene and its CpCo complexes Top left - ring B of the free ligand Top right - ring B complexed to CpCo Bottom left - ring D of the free ligand

Bottom right - ring D complexed to CpCo The effect of CpCo complexation is also reflected in the NICS-scan properties of the remaining rings To illustrate this point the NICS-scans of the central cyclohexatrienoid ring C of linear [3]phenylene are shown below first for the free ligand then for the cyclobutadiene complex

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

- 160 -

Figure 415 NICS-scans of ring C of linear [3]phenylene Left - as a free ligand Right as a

CpCo complex of the neighboring cyclobutadiene ring B The oopc curve clearly reveals a diminution of paratropism Thus at the ring plane the oopc values of the free ligand and of the complex are 177 and 110 ppm respectively Both plots show shallow and relatively distant minima at ndash3417 and ndash7316 respectively an indication of larger diamagnetic character of the latter While the ipc values also become more negative on complexation this effect is far smaller The tables that follow provide an overview of the NICS-scan results over all component rings in linear [3]- and [5]phenylene complexed and uncomplexed The diagnostic shape of the oopc curve is designated NM for no minimum indicating paratropism and M for minimum indicating diatropism Specific values are given at r = 0 Aring r = 10 Aring and the minimum (if diamagnetic) Table 416 NICS-scan Details of the oopc for Linear [3]Phenylene and its CpCo Complex at

Ring B

Ring Shape oopc00 oopc10 Minimum A M 71 ndash107 ndash11813 AndashCpCo M ndash65 ndash228 ndash22811 B NM 880 381 BndashCpCo M 121 ndash151 ndash16112 C M 177 ndash01 ndash3418 CndashCpCo M 116 ndash17 ndash9315 D NM 880 381 DndashCpCo NM 704 237 E M 71 ndash107 ndash11813 EndashCpCo M 15 ndash148 ndash15212

00 05 10 15 20 25 30 35 40

-8-6-4-202468

101214161820

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-14-12-10

-8-6-4-202468

1012

oopc ipc isotropic

pp

m

r

- 161 -

Table 417 NICS-Scan Details of the oopc for Linear [5]Phenylene and its CpCo Complex at Ring B

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M ndash62 ndash227 ndash22811 B NM 898 396 BndashCpCo M 137 ndash148 ndash15612 C M 176 00 ndash3317 CndashCpCo M 152 ndash09 ndash8415 D NM 846 357 DndashCpCo NM 668 223 E M 164 ndash12 ndash4116 EndashCpCo M 142 ndash17 ndash5315 F NM 846 357 FndashCpCo NM 807 340 G M 176 00 ndash3317 GndashCpCo M 161 ndash04 ndash3216 H NM 898 396 HndashCpCo NM 867 378 I M 83 ndash97 ndash10813 IndashCpCo M 64 ndash109 ndash12113

Table 418 NICS-scan Details of the oopc for Lnear [5]Phenylene and its CpCo Complex at

Ring D

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M 19 ndash150 ndash15912 B NM 898 396 BndashCpCo NM 717 256 C M 176 00 ndash3317 CndashCpCo M 110 ndash122 ndash12210 D NM 846 357 DndashCpCo M 151 ndash169 ndash17311 E M 164 ndash12 ndash4116 EndashCpCo M 151 ndash169 ndash17311 F NM 846 357 FndashCpCo NM 685 231 G M 176 00 ndash3317 GndashCpCo M 148 ndash15 ndash5415 H NM 898 396 HndashCpCo NM 850 370

I M 83 ndash97 ndash10813

- 162 -

The data clearly show that on CpCo complexation the paramagnetic ring current contributions decrease (or the diamagnetic ring current contributions increase) The strongest effect is on the complexed cycle but it occurs for all rings even the most remote (eg I in the linear [5]phenylene complexed at ring B) Thus upon complexation the paratropic (and by inference antiaromatic) character of the phenylenes decrease 45 Experimental Section for Chapter Three Angular [3]phenylene 2290 angular [4]phenylene 17111 and [7]heliphene10 were prepared according to the literature Ni(COD)(PMe3)2

112 To a solution of Ni(COD)2 (0275 g 10 mmol) in dry and vigorously degassed THF (10 mL) PMe3 (020 mL 0150 g 20 mmol) was added via syringe in a single portion After stirring at RT for 24 h the mixture was transferred using a canula and filtered under Ar to remove unreacted starting material The solvent was removed on the high vacuum line and the resulting product dried for 3 h It is extremely air sensitive and must be manipulated under an inert atmosphere at all times Yellow solid (0306 g 96 ) 1H-NMR (400 MHz C6D6) δ = 412 (d J = 112 Hz 4 H) 238 (br t J = 52 Hz 4 H) 225 (t J = 52 Hz 4 H) 102 (d J = 32 Hz 18 H) ppm 31P-NMR (162 MHz C6D6) δ = ndash946 (s) ppm Adducts of diphenylacetylene 88 to angular [3]phenylene 22 ndash compounds 89 and 90

In a glove box an Ace pressure tube was charged with angular [3]phenylene 22 (0014 g 006 mmol) diphenylacetylene 88 (0098 g 0055 mmol) THF (5 mL) and Ni(COD)(PMe3)2 (70 microL 008 M in THF 0006 mmol) The reaction vessel was tightly sealed removed from the glovebox and heated to 75ndash80 oC (oil bath) for 23 h After cooling to RT the solvent was removed by rotary evaporation and the residue purified by flash chromatography on silica gel using gradient elution (101 and then 81 hexaneCH2Cl2) After a small amount of angular [3]phenylene 22 (0001 g) the monoadduct 89 (0004 g 20 ) eluted to give a yellow solid mp 195ndash196 degC 1H-NMR (500 MHz CDCl3) δ = 853 (d J = 84 Hz 1 H) 831 (d J = 80 Hz 1 H) 755 (ddd J = 16 64 80 Hz 1 H) 740ndash732 (m 2 H) 725ndash715 (m 6 H) 715ndash711 (m 2 H) 708 (d J = 65 Hz 2 H) 704 (d J = 80 Hz 1 H) 648 (t J = 72 Hz 1 H) 643 (d J = 70 Hz 1 H) 624 (t J = 75 Hz 1 H) 401 (d J = 70 Hz 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1525 15101 15096 1495 1399 13883 13879 1342 1320 1312

- 163 -

13083 13075 1282 1280 1277 1276 1275 1268 1266 1265 1264 1250 1235 1223 1179 1164 1156 ppm one peak in the region δ = 128ndash126 ppm is

presumed to be accidentally isochronous IR (KBr) ν~ = 3060 1490 1481 1442 1415 1159 1072 755 734 698 cmndash1 UV-Vis (CH3CN) λmax (log ε) 233 (442) 265 (450) 278 (sh) 294 (sh) 306 (447) 318 (449) 329 (sh) 380 (344) 399 (366) 420 (366) nm MS (70 eV) mz () 405 [M++1] (35) 404 [M+] (100) 326 (13) HRMS (EI) calcd for C32H20 4041565 found 4041571 Elemental analysis calcd for C32H20 C 9502 H 498 found 9479 460 Subsequent elution furnished 5678-tetraphenylpicene (90) (0009 g 59 ) as a white solid mp 325ndash327 degC the molecule exhibits hindered rotation of the 67-phenyl groups on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 891 (s 2 H) 885 (d J = 84 Hz 2 H) 769 (ddd J = 28 52 80 Hz 2 H) 750ndash744 (m 4 H) 744ndash732 (m 4 H) 720 (tt J = 16 72 Hz 2 H) 696 (dt J = 08 76 Hz 2 H) 689 (tt J = 09 76 Hz 2 H) 662 (br s 4 H) 617 (d J = 76 Hz 2 H) 607 (br s 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1403 1401 1377 1367 1335 1325 1324 1306 1300 1295 1292

1283 1277 1269 1264 1263 1262 1256 1254 1228 1213 ppm IR (KBr) ν~ = 3051 2922 1599 1490 1467 1442 1263 1072 1027 758 702 630 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (461) 307 (474) 352 (417) 366 (414) nm MS (70 eV) mz () 583 [M++1] (52) 582 [M+] (100) 505 (24) 504 (9) 426 (7) HRMS (EI) calcd for C46H30 5822348 found 5822336 1278-Tetraphenylbenzo[c]chrysene (91)

In a glovebox an Ace pressure tube was charged with 88 (0020 g 0050 mmol) diphenylacetylene 88 (0026 mg 0148 mmol) Ni(COD)(PMe3)2 (62 microL of a 008 M solution in THF) and THF (5 mL) The reaction vessel was sealed removed from the glovebox and heated to 85 degC for 39 h After removal of the solvent the residue was purified by flash chromatography on silica gel (eluting with 81 hexaneCH2Cl2) producing a white solid (0023 g) which was found to consist of starting material (88 18 mg) 90 (0001 g 6 ) and 91 Further purification by chromatography afforded pure 91 (0017 g 74 ) as a white solid mp 273ndash274 degC the 12-phenyl groups of 91 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 869 (d J = 95 Hz 1 H) 830ndash822 (m 1 H) 801 (d J = 75 Hz 1 H) 780ndash747 (m 2 H) 770 (ddd J = 10 70 85 Hz 1 H) 762 (dt J = 15 75 Hz 1 H) 753 (ddd J = 15 70 85 Hz 1 H) 738ndash732 (m 2 H) 730 (td J = 15 75 Hz 1 H) 729ndash722 (m 6 H) 722ndash717 (m 2 H) 717ndash710 (m 2 H) 710ndash695 (m 3 H) 680ndash640 (m 3 H) 635 (d J = 70 Hz 1 H) 623ndash595 (br s 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1418 1400 1395 1394 1378 1377 1375 1357 1323 1322 1316 1314 13113 13107 1309 1308 1307 1305 1296 1295 1288 1282 1277 1275 1274 1273 1270 12653 12647 1264 1260 1256 1253 1252 1251

- 164 -

1243 1231 1208 ppm due to extensive signal overlap four peaks are presumed to be isochronous in the regions δ = 132ndash130 and 128ndash125 ppm IR (KBr) ν~ = 3058 1601 1489 1442 1263 1073 773 762 736 699 628 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 250 (487) 313 (511) 340 (sh) nm MS(EI) mz () 583 (M++1 72) 582 (M+ 100) 505 (24) 391 (13) HRMS (EI) calcd for C46H30 5822348 found 5822341 Elemental analysis calcd for C46H30 C 8933 H 500 found 8914 493 Ni(PhCequivCPh)(PMe3)2 (92)91

In a glove box PMe3 (203 microL 0152 g 20 mmol) was mixed with a suspension of Ni(COD)2 (0275 g 10 mmol) in hexane (15 mL) Diphenylacetylene 88 (0178 g 10 mmol) was then added in one portion resulting in an immediate color change from yellow to red The mixture was stirred at room temperature for 195 h during which the color gradually turning returning to yellow Upon concentration (to ~5 mL) a yellow precipitate formed collected by filtration under nitrogen The resulting powder 92 (0370 g 95 ) was dried under vacuum providing a yellow solid 1H-NMR (500 MHz C6D6) δ = 751 (d J = 75 Hz 4 H) 717 (t J = 75 Hz 4 H) 702 (t J = 75 Hz 2 H) 101 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1406 1287 1279 196 (d JC-P = 188 Hz) ppm 31P-NMR (162 MHz C6D6) δ = ndash1282 (br s) ppm Adducts of 3-hexyne to angular [3]phenylene 22 ndash compounds 104 and 105

In a glovebox 22 (0014 mg 0060 mmol) 3-hexyne 103 (57 microL 0004 g 0050 mmol) Ni(COD)(PMe3)2 (0002 g 0005 mmol) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 14 h Flash chromatography on silica gel gave a first fraction that was recrystallized from CH2Cl2 to provide pure 104 (70 mg 45 ) as a yellow solid mp 169ndash170 degC 1H-NMR (500 MHz CDCl3) δ = 843 (d J = 70 Hz 1 H) 821 (d J = 75 Hz 1 H) 795 (d J = 70 Hz 1 H) 752 (dt J = 10 70 Hz 1 H) 748 (dt J = 10 70 Hz 1 H) 697 (d J = 75 Hz 1 H) 673ndash662 (m 3 H) 655 (d J = 55 Hz 1 H) 307 (q J = 75 Hz 2 H) 299 (q J = 75 Hz 2 H) 133 (t J = 75 Hz 3 H) 130 (t J = 75 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1530 1516 1504 1471 1360 1330 13129 13127 1307 1282 1279 1267 1263 1259 1246 1239 1228 1179 1159 1156 232 214 164 149 ppm IR (KBr) ν~ = 3045 2960 1600 1481 1414 1261 1197 1159 758 740 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (463) 299 (sh) 309 (460) 320 (462) 331 (452) 380 (356) 399 (374) 419 (371) nm MS (70 eV) mz () 309 [M++1] (26) 308 [M+] (100) 293 [M+ndash15] (8) 278 [M+ndash30] (21) HRMS (EI) calcd for C24H20 3081565 found 3081666

- 165 -

A second fraction was 105 (0002 g 11 ) isolated as a yellow solid mp 120ndash122 degC 1H-NMR (400 MHz CDCl3) δ = 830 (d J = 72 Hz 1 H) 797 (d J = 76 Hz 1 H) 761 (d J = 80 Hz 1 H) 761ndash749 (m 2 H) 700 (d J = 80 Hz 1 H) 699 (d J = 72 Hz 1 H) 674 (quint J = 76 Hz 2 H) 658 (d J = 64 Hz 1 H) 307 (q J = 76 Hz 2 H) 302 (q J = 76 Hz 2 H) 132 (t J = 76 Hz 3 H) 131 (t J = 76 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1525 1519 1489 1472 1356 1345 1324 1318 1288 1283 1279 1273 1259 1252 1251 1250 1241 1179 1165 1160 2213 2205 149 146 ppm IR (KBr) ν~ = 3063 2958 2925 1490 1442 1417 1262 1147 1099 822 762 730 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 281 (434) 291 (448) 303 (460) 313 (sh) 369 (346) 389 (373) 410 (377) nm MS (70 eV) mz () 309 [M++1] (28) 308 [M+] (100) 293 [M+ndash15] (13) 278 [M+ndash30] (21) 226 (22) 149 (29) HRMS (EI) calcd for C24H20 3081565 found 3081664 Adducts of 14-dimethoxy-2-butyne to angular [3]phenylene 22 ndash compounds 107 and 108

In a glovebox 22 (0011 g 0050 mmol) 14-dimethoxybut-2-yne 106 (0034 g 030 mmol) Ni(COD)(PMe3)2 (63 microL of a 008 M solution in THF) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 165 h The 1H-NMR spectrum of the crude indicated the formation of 107 and 108 in the ratio of 61 Flash chromatography on silica gel gave first 107 (0012 g 68 ) as a yellow solid mp 150ndash151 degC 1H-NMR (400 MHz CDCl3) δ = 841 (dd J = 32 64 Hz 1 H) 819 (d J = 80 Hz 1 H) 810 (dd J = 36 64 Hz 1 H) 754 (dd J = 36 64 Hz 2 H) 700 (d J = 80 Hz 1 H) 676 (t J = 64 Hz 1 H) 674ndash665 (m 2 H) 656 (d J = 60 Hz 1 H) 493 (s 2 H) 488 (s 2 H) 353 (s 3 H) 345 (s 3 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1527 1513 1509 1484 1336 1318 1316 1309 1296 1283 1282 1272 1270 1259 1255 1238 1225 1183 1166 1161 677 675 584 575 ppm IR (KBr) ν~ = 3072 2927 1485 1446 1417 1376 1185 1097 956 898 821 743 730 cmndash1 MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (100) 308 [M+ndash38] (26) 293 (34) 280 (15) 265 (44) HRMS (EI) calcd for C24H20O2 3401463 found 3401466 Further elution provided 108 (0002 g 9 ) as a yellow solid mp 156ndash157 degC 1H-NMR (400 MHz CDCl3) δ = 831ndash824 (m 1 H) 813ndash806 (m 1 H) 775 (d J = 80 Hz 1 H) 763ndash756 (m 2 H) 702 (d J = 80 Hz 1 H) 699 (d J = 64 Hz 1 H) 681ndash670 (m 2 H) 660 (d J = 64 Hz 1 H) 493 (s 2 H) 487 (s 2 H) 353 (s 3 H) 351 (s 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1523 1517 1505 1470 1327 1322

- 166 -

1316 1315 1297 1285 1282 1276 1268 1266 12564 12555 1252 1181 1168 1165 6804 6801 5838 5835 ppm IR (KBr) ν~ = 2925 1498 1415 1379 1262 1187 1095 1061 940 930 814 750 734 717 cmndash1 UV-Vis (CH3CN) λmax (log ε) 237 (458) 287 (462) 298 (472) 314 (sh) 371 (357) 387 (380) 407 (386) nm MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (56) 308 [M+ndashMeOH] (8) 293 (27) 279 (17) 265 (24) HRMS (EI) calcd for C24H20O2 3401463 found 3401456 Optimized cycloaddition reaction between 22 and 88 In a glovebox a round bottom flask was charged with 22 (0058 g 0257 mmol) and Ni(COD)(PMe3)2 (0008 g 0034 mmol) Both reagents were then dissolved in THF (100 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0093 g 0521 mmol) in THF (20 mL) was taken up in a gas-tight syringe and slowly added over 13 h via syringe pump to the boiling mixture of 22Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 6 h After this time mixture was cooled to RT and the solvent removed by rotary evaporation to give a yellow residue The crude product was passed through a plug of silica gel eluting with a mixture of hexanesCH2Cl2 (101) to afford a yellow solid Analysis of the product by 1H-NMR (using the solvent peak of CDCl3 as the internal standard) revealed the presence of 89 and 90 in a 1387 ratio Adducts of diphenylacetylene 88 to angular [4]phenylene 17 ndash compounds 130ndash134 In a glovebox angular [4]phenylene 17 (0036 g 012 mmol) diphenylacetylene 88 (0018 g 010 mmol) and Ni(COD)(PMe3)2 (125 microL of a 008 M solution in THF) were added to an Ace pressure tube and dissolved in THF (6 mL) The reaction vessel was sealed removed from the glovebox and stirred at 75 degC for 5 h Flash chromatography

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph Ph PhPh Ph

132131

133 134

130

- 167 -

on silica gel gave starting material (0013 g of 17) as well as a yellow residue Further purification of the latter by preparative TLC afforded (in order of elution) 132 131 133 134 and 139 Compound 130 (0008 g 28 ) was obtained as a white solid mp 360ndash363 degC (decomp) the phenyl groups located on the central benzene ring of 130 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 904 (d J = 90 Hz 2 H) 895 (d J = 90 Hz 2 H) 881 (d J = 85 Hz 2 H) 765 (ddd J = 15 65 80 Hz 2 H) 742ndash736 (m 4 H) 734 (dd J = 10 85 Hz 2 H) 721 (tt J = 15 75 Hz 2 H) 716 (d J = 75 Hz 2 H) 698 (dd J = 05 80 Hz 2 H) 693 (tt J = 10 85 Hz 2 H) 681 (tt J = 10 70 Hz 2 H) 676 (t J = 75 Hz 4 H) 656 (t J = 70 Hz 4 H) 633 (d J = 70 Hz 4 H) 614 (d J = 75 Hz 2 H) 595 (d J = 70 Hz 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 14058 14057 1403 1394 1375 1374 1345 1341 1336 1327 1324 1309 1308 1301 1294 1292 1282 1276 1268 1263 12622 12619 1259 1257 1254 1250 1227 1214 1212 ppm IR (KBr) ν~ = 3052 2923 1600 1491 1440 1261 1076 1029 809 783 759 747 700 631 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 248 (498) 306 (sh) 329 (520) 388 (463) nm MS(FAB) mz () 836 [M++2] (18) 835 [M++1] (42) 834 [M+] (54) 757 (8) HRMS (FAB) calcd for C66H42 8343287 found 8343280 Compound 131 (0003g 6) was isolated as yellow solid mp 251ndash253 degC (decomp) 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 775 (dt J = 10 80 Hz 1 H) 752 (dt J = 10 80 Hz 1 H) 746 (d J = 80 Hz 1 H) 737 (d J = 65 Hz 1 H) 726ndash721 (m 5 H) 721ndash716 (m 2 H) 716ndash711 (m 5 H) 709 (t J = 75 Hz 1 H) 705 (d J = 80 Hz 1 H) 699 (d J = 70 Hz 1 H) 619 (d J = 60 Hz 1 H) 614 (d J = 60 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1502 1492 1491 1490 1485 1444 1394 1392 1382 1371 1367 1351 13271 13268 13092 13088 1299 12898 12896 1283 12764 12760 1274 12654 12652 1261 1253 1245 1195 1184 1172 1138 1129 ppm one peak is presumed to be accidentally isochronous in the region between δ = 130ndash124 ppm IR (KBr) ν~ = 3023 2921 1602 1478 1371 1262 1026 809 795 748 725 695 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 252 (473) 285 (456) 320 (453) 335 (462) 353 (437) 370 (432) 410 (376) 431 (372) nm MS (FAB) mz () 479 [M++1] (27) 478 [M+] (70) 300 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781718 Molecule 132 (0002 g 5 ) was acquired as a yellow solid 1H-NMR (500 MHz CDCl3) δ = 726ndash721 (m 2 H) 716ndash709 (m 6 H) 695ndash690 (m 2 H) 676 (d J = 80 Hz 2 H) 673 (d J = 75 Hz 2 H) 671 (t J = 75 Hz 2 H) 665 (t J = 70 Hz 2 H) 658 (d J = 65 Hz 2 H) 648 (d J = 65 Hz 2 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1516 1510 1497 1490 1391 1372 1310 1303 1283 1281 1277 1275 1273 1264 1216 1168 1163 ppm UV-Vis (CH2Cl2) λmax (log ε) 254 (476) 294 (sh) 300 (465) 322 (sh) 338 (392) 376 (400) nm MS (FAB) mz () 479 [M++1] (50) 478 [M+] (86) 391 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781723 Adduct 133 (0017 g 33 ) was isolated as a red crystalline solid mp 290ndash291 degC 1H-NMR (500 MHz CDCl3) δ = 800 (d J = 80 Hz 2 H) 720ndash713 (m 6 H) 708ndash702 (m 4 H) 690 (d J = 80 Hz 2 H) 648 (t J = 70 Hz 2 H) 642 (d J = 70 Hz 2 H) 623 (t J = 70 Hz 2 H) 393 (d J = 70 Hz 2 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1522 1509 1506 1496 1392 1359 1315 1309 1282 1278 1277 1266 1250 1232 1181 1166 1157 ppm IR (KBr) ν~ = 3057 1489 1441 1412 1273

- 168 -

1161 810 738 709 690 623 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 271 (474) 285 (469) 345 (460) 353 (454) 414 (483) 432 (381) 460 (363) nm MS (70 eV) mz () 479 [M++1] (46) 478 [M+] (100) 400 (10) HRMS (EI) calcd for C38H22 4781722 found 4781719 Compound 134 (0009 g 27 ) was obtained as a yellow solid mp 178ndash180 degC the phenyl groups of this molecule located at the bay regions of the phenanthrene subunit are static while the others exhibit hindered rotation on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 880 (d J = 88 Hz 1 H) 879 (d J = 88 Hz 1 H) 863 (d J = 92 Hz 1 H) 834 (d J = 80 Hz 1 H) 770ndash758 (m 1 H) 748ndash732 (m 4 H) 727ndash721 (m 2 H) 721ndash710 (m 2 H) 706 (d J = 80 Hz 1 H) 702ndash691 (m 3 H) 684 (t J = 74 Hz 1 H) 673 (br s 2 H) 655 (t J = 76 Hz 2 H) 650ndash638 (m 3 H) 630ndash610 (m 4 H) 590 (d J = 76 Hz 2 H) 410 (d J = 68 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1527 1510 1509 1494 1403 1400 1399 1396 1373 1371 1339 1335 1330 1325 1324 1317 1309 1306 1305 1304 1299 1295 1291 1283 1282 1281 1277 1275 1272 1269 1268 12632 12627 1261 12562 12556 1254 1253 1239 1226 1216 1209 1180 1162 1154 ppm three peaks are presumed to be accidentally isochronous in the region δ = 128ndash125 ppm IR (KBr) ν~ = 2964 1262 1096 1022 801 701 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 267 (501) 303 (497) 335 (489) 361 (sh) 379 (464) 427 (402) 456 (377) nm MS(FAB) mz () 658 [M++2] (22) 657 [M++2] (67) 656 [M+] 1(00) 579 (12) 502 (7) HRMS (FAB) calcd for C52H32 6562504 found 6562492 Cycloaddition reaction between [7]heliphene 142 and diphenylacetylene 88 In a glovebox a round bottom flask was charged with 142 (0008 g 0152 mmol) and Ni(COD)(PMe3)2 (0001 g 0003 mmol) The mixture was then dissolved in THF (25 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0016 g 300 mmol) in THF (10 mL) was taken up in a gas-tight syringe and slowly added over 12 h via syringe pump to the boiling mixture of 142Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 12 h After this time it was cooled to RT and the solvent removed by rotary evaporation to give an orange residue The crude product was chromatographed on silica gel (25 x 165 cm) eluting first with hexaneCH2Cl2 (101 then 51) The first product collected was diphenylacetylene 88 (0005 g) followed by a yellow band Analysis of the isolated yellow solid (0002 g) revealed a large mixture of products MS(FAB) mz () 532 (70) 664 (25) 700 (13) 732 (16) 911 (21) 1056 (11) 1234 (4) 1412 (5) 46 Computational Details for Chapter Three All geometries of intermediates and transition states were optimized fully without symmetry constraints using the Gaussian 03 program100 The DFT computations were carried out using the B3LYP functional as implemented in Gaussian The nickel atom was described by a double-zeta basis set (LANL2DZ)113 and the 6-31G(d) basis set114

- 169 -

was used for the other elements Frequency calculations were performed to confirm the nature of the stationary points and to obtain zero-point energies (ZPE) The connectivity between stationary points was established by intrinsic reaction coordinate calculations (IRC) The Chemcraft program102 was used to draw the calculated structures

47 References

1) Harvey R G Polycyclic Aromatic Hydrocarbons Wiley-VCH New York 1997 2) (a) Chem Rev 2001 101 1115ndash1566 Special Issue Aromaticity (b) Chem Rev

2005 105 3343ndash3397 Special Issue Delocalization-Pi and Sigma 3) (a) Cyranski M K Krygowski T M Katritzky A R Schleyer P von R J Org

Chem 2002 67 1333 (b) Stanger A Chem Commun 2009 1939 4) (a) Minkin V I Glukhovtsev M N Simkin B Ya Aromaticity and Antiaromaticity

Electronic and Structural Aspects Wiley New York 1994 pp 63ndash74 (b) Garratt P J Aromaticity Wiley New York 1986 pp 30ndash34 93ndash95

5) (a) Wu J Muumlllen K In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 3 pp 90ndash139 (b) Wu J Pisula W Muumlllen K Chem Rev 2007 107 718 (c) Handbook of Organic Electronics and Photonics Nalwa H S Ed American Scientific 2008

6) Miljanić O Š Vollhardt K P C In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 4 pp 140ndash197

7) (a) Shepherd M K Cyclobutarenes The Chemistry of Benzocyclobutene Biphenylene and Related Compounds Elsevier Amsterdam 1991 (b) Toda F Garratt P J Chem Rev 1992 92 1685

8) (a) Diercks R Vollhardt K P C J Am Chem Soc 1986 108 3150 (b) Mohler D L Vollhardt K P C Wolff S Angew Chem Int Ed Engl 1990 29 1151 (c) Mohler D L Vollhardt K P C Wolff S Angew Chem Int Ed Engl 1995 34 563

9) (a) Holmes D Kumaraswamy S Matzger A J Vollhardt K P C Chem Eur J 1999 5 3399 (b) Dosche C Kumke M U Ariese F Bader A N Gooijer C Dosa P I Han S Miljanic O Š Vollhardt K P C Puchta R van Eikema Hommes N J R Phys Chem Chem Phys 2003 5 4563 (c) Wagner H-U Szeimies G Chandrasekhar J Schleyer P von R Pople J A Binkley J S J Am Chem Soc 1978 100 1210

10) Han S Bond A D Disch R L Holmes D Schulman J M Teat S J Vollhardt K P C Whitener G D Angew Chem Int Ed 2002 41 3223

11) Jackman L M Sondheimer F Amiel Y Ben-Efraim D A Gaoni Y Wolovsky R Bothner-By A A J Am Chem Soc 1962 84 4307

12) Untch K G Wysocki D C J Am Chem Soc 1967 89 6386 13) (a) Chen Z Wannere S C Corminboeuf C Puchta R Schleyer P von R

Chem Rev 2005 105 3842 and the references therein (b) Steinmann S N Jana D F Wu J I-C Schleyer P v R Mo Y Corminboeuf C Angew Chem Int Ed 2009 48 9828

14) Schleyer P v R Manoharan M Wang Z-X Kiran B Jiao H Puchta R van Eikema Hommes N J R Org Lett 2001 3 2465

- 170 -

15) Schulman J M Disch R L Jiao H Schleyer P v R J Phys Chem A 1998 102 8051

16) Jeany H Mason K G Sketchley J M Tetrahedron Lett 1970 11 485 17) Brown F C Choi N Coulston K J Eastwood F W Wiersum U E

Jenneskens L W Tetrahedron Lett 1994 35 4405 18) (a) Linear [3]phenylene Dosa P I Schleifenbaum A Vollhardt K P C Org Lett

2001 3 1017 (b) Angular [3]phenylene Matzger A J Vollhardt K P C Chem Commun 1997 1415 (c) Angular [4]phenylene Dosa P I Gu Z Hager D Karney W L Vollhardt K P C Chem Commun 2009 1967

19) Perthuisot C Edelbach B L Zubris D L Simhai N Iverson C N Muumlller C Satoh T Jones W D J Mol Catal A 2002 189 157

20) Dosche C Loumlhmannsroumlben H-G Bieser A Dosa P I Han S Iwamoto M Schleifenbaum A Vollhardt K P C Phys Chem Chem Phys 2002 4 2156

21) (a) Deniz A A Peters K S Snyder G J Science 1999 286 1119 (b) Fattahi A Lis L Tian Z Kass P S Angew Chem Int Ed 2006 45 4984 (c) Bally T Angew Chem Int Ed 2006 45 6616

22) Anslyn E Dougherty D Modern Physical Organic Chemistry University Science Books Palo Alto 2006

23) Crabtree R H The Organometallic Chemistry of the Transition Metals 4th Ed Wiley-VCH New York 2005

24) Mestdagh H Postdoctoral Research Report University of California Berkeley 1986

25) Hirthammer M Vollhardt K P C J Am Chem Soc 1986 108 2481 26) Blanco L Helson H E Hirthammer M Mestdagh H Spyroudis S Vollhardt K

P C Angew Chem Int Ed Engl 1987 26 1246 27) Berris B C Hovakeemian G H Lai Y-H Mestdagh H Vollhardt K P C J

Am Chem Soc 1985 107 5670 28) Dosa P I The Chemistry of Angular and Linear [N]Phenylenes PhD Thesis

University of California Berkeley 2002 29) Diercks R Eaton B E Guumlrtzgen S Jalisatgi S Matzger A J Radde R H

Vollhardt K P C J Am Chem Soc 1998 120 8247 30) (a) Nambu M Siegel J S J Am Chem Soc 1988 110 3675 (b) Nambu M

Hardcastle K Baldridge K K Siegel J S J Am Chem Soc 1992 114 369 31) Nambu M Mohler D L Hardcastle K Baldridge K K Siegel J S J Am

Chem Soc 1993 115 6138 32) Kumaraswamy S Jalisatgi S S Matzger A J Miljanić O Š Vollhardt K P C

Angew Chem Int Ed 2004 43 3711 33) (a) Eisch J J Piotrowski A M Han K I Kruumlger C Tsay Y H Organometallics

1985 4 224 (b) Schwager H Spyroudis S Vollhardt K P C J Organometallic Chem 1990 382 191

34) Albright T A Hofmann P Hoffmann R Lillya C P Dobosh P A J Am Chem Soc 1983 105 3397

35) Doumltz K H Jahr H C Chem Rec 2005 4 61 36) Gridnev I D Coord Chem Rev 2008 252 1798 37) Eickmeier C Holmes D Junga H Matzger A J Scherhag F Shim M

Vollhardt K P C Angew Chem Int Ed Engl 1999 38 800

- 171 -

38) Groszligmann T N Haptotropism in Linear Phenylene Complexes Diplomarbeit Thesis University of California Berkeley 2004

39) Dinculear photothermal haptotropic systems Tsuchiya K Ideta K Mogi K Sunada Y Nagashima H Dalton Trans 2008 2708 and the references therein

40) Additive assisted photothermal haptotropic systems (a) Jahr H C Nieger M Doumltz H K Chem Eur J 2005 11 5333 d) Herbert D E Tanabe M Bourke S C Lough A J Manners I J Am Chem Soc 2008 130 4166 e) Ieong N S Manners I J Organomet Chem 2008 693 802 and references therein

41) (a) Zhu G Tanski T M Churchill D G Janak K E G Parkin G J Am Chem Soc 2002 124 13658 (b) Zhu G Pang G Parkin G J Am Chem Soc 2008 130 1564

42) Selected reviews of photobased devices and molecular switches (a) Balzani V Credi A Venturi M Chem Soc Rev 2009 38 1542 (b) Kay E R Leigh D A Zerbetto F Angew Chem Int Ed 2007 46 72 (c) Photochromism Molecules and Systems Duumlrr H Bouas-Laurent H Eds Elsevier Amsterdam 2003 (d) Feringa B Molecular Switches Wiley-VCH Weinheim 2001

43) (a) a) Photofunctional Transition Metal Complexes Yam V W W Ed Springer Berlin 2007 b) Coppens P Novozhilova I Kovalevsky A Chem Rev 2002 102 861 c) Guumltlich P Garcia Y Woike T Coord Chem Rev 2001 219ndash221 839

44) (a) Lambert J B Mazozola E P Nuclear Magnetic Resonance Spectroscopy An Introduction to Princples Applications and Experimental Methods Pearson Education Upper Saddle River 2004 (b) Berger S Braun S 200 and More NMR Experiments A Practical Course Wiley-VCH Weinheim 2004 (c) Friebolin H Basic One- and Two-Dimensional NMR Spectroscopy 4th edition Wiley-VCH Weinheim 2005

45) (a) Schulman J M Disch R L J Phys Chem A 2003 107 5223 (b) Schulman J M Disch R L J Am Chem Soc 1996 118 8470 and the references cited therein

46) (a) Bursten B E Fenske R F Inorg Chem 1979 18 1760 (b) Chinn J W Jr Hall M B Inorg Chem 1983 22 2759 (c) Datta A Pati S K J Am Chem Soc 2005 127 3496

47) Ooloba K Haptotropic Shifts in the Linear [N]-Phenylene (N=3 4 and 5) and Angular [3]-Phenylene Cyclopentadienylcobalt Complexes PhD Thesis University of Houston 2008

48) Hillard III R L Vollhardt K P C J Am Chem Soc 1977 99 4058 49) Berris B C Lai Y-H Vollhardt K P C J Chem Soc Chem Commun 1982

953 50) (a) Rausch M D Genetti R A J Org Chem 1970 35 3888 (b) Hart W P

Rausch D M J Organometallic Chem 1988 355 455 51) Duclos R I Vollhardt K P C Yee J L S J Organomet Chem 1979 174 109 52) (a) Myers A G Sogi M Lewis M A Arvedson S P J Org Chem 2004 69

2516 (b) Wolfart V Ramming M Gleiter R Nuber B Pritzkow H Rominger F Eur J Inorg Chem 1999 499 (c) Mitchell R H Chen Y Khalifa N Zhou P J Am Chem Soc 1998 120 1785 (d) McGlinchey M J Burns R C Hofer R Top S Jaouen G Organometallics 1986 5 104

53) Feixas F Jimeacutenez-Halla J O C Matito E Poater J Solagrave M Pol J Chem

- 172 -

2007 81 783 54) (a)Stanger A J Org Chem 2006 71 883 (b) Stanger A Chem Eur J 2006 12

2745 (c) Tsipis A C Phys Chem Chem Phys 2009 11 8244 (d) Stanger A Chem Commun 2009 1939

55) For very recent literature compilations of theoretical (and experimental) treatments of haptotropism in arene metal complexes see a) Joistgen O Pfletschinger A Ciupka J Dolg M Nieger M Schnakenburg G Froumlhlich R Kataeva O Doumltz K H Organometallics 2009 28 3473 b) Pfletschinger A Dolg N J Organomet Chem 2009 694 3338 c) Jimeacutenez-Halla J O C Robles J Solagrave M Organometallics 2008 27 5230 d) Kirillov E Kahlal S Roisnel T Georgelin T Saillard J-Y Carpentier J-F Organometallics 2008 27 387 and references therein

56) Jimeacutenez-Halla J O C Robles J Solagrave M J Phys Chem A 2008 112 1202 57) Oprunenko Y Gloriozov I Lyssenko K Malyugina S Mityuk D Mstislavsky

V Guumlnther H von Firks G Ebener M J Organomet Chem 2002 656 27 58) Muumlller J Gaede P E Qiao K J Organomet Chem 1994 480 213 59) Bianchini C Caulton K G Chardon C Doublet M L Eisenstein O Jackson

S A Johnson T J Meli A Peruzzini M Streib W E Vacca A Vizzat F Organometallics 1994 13 2010

60) (a) De Boer E Van Willigen H V Prog Nuc Mag Res Spec 1967 2 111 (b) Memory J D Wilson N K NMR of Aromatic Compounds Wiley-VCH New York 1982

61) (a) Poli R Chem Rev 1996 96 2135 and the references cited therein (b) Schroumlder D Shaik S Schwartz H Acc Chem Res 2000 33 139 (c) Harvey J N Poli R Smith K M Coord Chem Rev 2003 237 347 and the references cited therein

62) For computational examples of 16 electron triplet Cp cobalt species influencing cobalt-mediated reactions see (a) Siegbahn P E M J Am Chem Soc 1996 118 1487 (b) Poli R Smith K M Eur J Inorg Chem 1999 877 (c) Carreoacuten-Macedo J-L Harvey J N J Am Chem Soc 2004 126 5789 (d) Petit A Richard P Cacelli I Poli R Chem Eur J 2006 12 813 (e) Aubert C Betschmann P Eichberg M J Gandon V Geny A Heckrodt T J Lehmann J Malacria M Masjost B Paredes E Vollhardt K P C Whitener G D Chem Eur J 2007 13 7443 (f) Gandon V Agenet N Vollhardt K P C Malacria M Aubert C J Am Chem Soc 2009 131 3007

63) Illustrative examples (a) Olson W L Stacy A M Dahl L F J Am Chem Soc 1986 108 7646 (b) Wadepohl H Galm W Pritzkow H Wolf A Chem Eur J 1996 2 1453 (c) Knijnenburg W Hetterscheid D Kooistra T M Budzelaar P H M Eur J Inorg Chem 2004 1204

64) Benito-Garagorri D Bernskoetter W H Lobkovsky E Chirik P J Organometallics 2009 28 4807

65) Fox J P Ramdhanie B Zareba A A Czernuszewicz R S Goldberg D P Inorg Chem 2004 43 6600

66) Guennic B L Floyd T Galan B R Autschbach J Keister J B Inorg Chem 2009 48 5504

67) Cremer C Burger P J Am Chem Soc 2003 125 7664

- 173 -

68) Atkins P de Paula J P Physical Chemistry 8th Edition Oxford University Press Oxford 2006

69) Butters T Toda F Winters W Angew Chem Int Ed Engl 1980 19 926 70) Mann B E Taylor B F 13C Data for Organometallic Compounds Academic

London 1981 71) For a review on triple decker arene complexes and closely related syn dinuclear

systems see (a) Beck V OlsquoHare D J Organomet Chem 2004 698 3920 and the references therein For a review of trinuclear CpCo(arene) complexes see (b) Wadepohl H Angew Chem Int Ed Engl 1992 31 247 and the references therein

72) Jonas K Koepe G Schieferstein L Mynott R Kruumlger C Tsay Y-H Angew Chem Int Ed Engl 1983 22 620 Angew Chem Suppl 1983 920

73) Muumlller J Gaede P E Qiao K Angew Chem Int Ed Engl 1993 32 1697 74) Schneider J J Wolf D Janiak C Heinemann O Rust J Kruumlger C Chem

Eur J 1998 4 1982 75) Schneider J J Denninger U Heinemann O Kruumlger C Angew Chem Int Ed

Engl 1995 34 592 76) Budzelaar P H M Moonen N N P de Gelder R Smits J M M Gal A W

Chem Eur J 2000 6 2740 77) Albright T A Dosa P I Groszligmann T N Oluwakemi O Padilla R Paubelle

R Timofeeva T Vollhardt K P C Angew Chem Int Ed 2009 48 9853 78) Schaub T Radius U Chem Eur J 2005 11 5024 79) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4660 80) (a) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4040

(b) Muumlller C Lachicotte R J Jones W D Organometallics 2002 21 1975 81) Martin R H Angew Chem Int Ed Engl 1974 13 649 82) Mallory FB Butler K E Evans AC Mallory CW Tetrahedron Lett 1996 37

7176 83) Selected Reviews (a) Amemiya R Yamaguchi M Chem Rec 2008 8 116 (b)

Ruliacutešek L Exner O Cwiklik L Jungwirth P Staryacute I Pospiacutešil L Havlas Z J Phys Chem C 2007 111 14948 (c) Hopf H Classics in Hydrocarbon Chemistry Wiley-VCH Weinheim 2000 pp 321ndash330 (d) Voumlgtle F Fascinating Molecules in Organic Chemistry Wiley New York 1992 pp 156ndash180 (e) Meurer K P F Voumlgtle Top Curr Chem 1985 127 1 (f) Laarhoven W H Prinsen W J Top Curr Chem 1984 125 63

84) (a) Mallory FB Butler K E Mallory CW Beacuterubeacute A Luzik E D Brondyke E J Hiremath R Ngo P Carroll P J Tetrahedron 2001 57 3715 (b) Mallory F B Butler K E Evans A C Brondyke E J Mallory C W Yang C Ellenstein A J Am Chem Soc 1997 119 2119

85) (a) Mitsuhashi R Suzuki Y Yamanari Y Mitamura H Kambe T Ikeda N Okamoto H Fujiwara A Yamaji M Kawasaki N Maniwa Y Kubozono Y Nature 2010 464 74 (b) Okamoto H Kawasaki N Kaji Y Kubozono Y Fujiwara A Yamaji M J Am Chem Soc 2008 130 10470 (c) Tian Y H Park G Kertesz M Chem Mater 2008 20 3266

86) Recent reviews of acenes in electronic applications (a)Yamashita Y Sci Technol Adv Mater 2009 10 024313 (b) Wuumlrthner F Schmidt R ChemPhysChem

- 174 -

2006 7 793 (c) Bendikov M Wudl F Chem Rev 2004 104 4891 87) NICS-based comparison of phenacene and acene properties Portella G Poater

P Bofill J M Alemany P Solagrave M J Org Chem 2005 70 2509 and the references therein

88) Mallory F B Mallory C W Org React 1984 30 1 89) Gu Z Nickel-Catalyzed Cycloaddition Reaction of [N]Phenylenes and Alkynes

Postdoctoral Report University of California Berkeley 2008 90) Preferential displacement of COD by π ligands from Ni(COD)(PMe3)2 is well

documented See eg Karsch H H Leithe A W Reisky M Witt E Organometallics 1999 18 90

91) (a) Bochmann M Hawkins I Hursthouse M B Short R L J Chem Soc Dalton Trans 1990 1213 (b) Poerschke K R Mynott R Angermund K Kruumlger C Z Naturforsch 1990 40B 199 See also (c) Bartik T Happ B Iglewsky M Bandmann H Boese R Heimbach P Hoffmann T Wenschuh E Organometallics 1992 11 1235

92) For Ni-phosphine migrations along polycyclic benzenoid ligands see eg Stanger A Vollhardt K P C Organometallics 1992 11 317

93) Edelbach B L Vicic D A Lachicotte R J Jones W D Organometallics 1998 17 4784

94) (a) Feiken N Pregosin P S Trabesinger G Scalone M Organometallics 1997 16 537 (b) Feiken N Pregosin P S Trabesinger G Albinati A Evoli G L Organometallics 1997 16 5756 (c) Geldbach T J Pregosin P S Eur J Inorg Chem 2002 1907

95) Cheng T-Y Szalda D J Hanson J C Muckerman J T Bullock R M Organometallics 2008 27 3785

96) (a) Grimme S Harren J Sobanski A Voumlgtle F Eur J Org Chem 1998 8 1491 (b) Dias J J Chem Inf Model 2005 45 562

97) Still W C Mitra A Kahn M J Org Chem 1978 43 2923 98) (a) Leonard J Lygo B Procter G Advanced Practical Organic Chemistry 2nd

ed CRC Press Boca Raton 1998 (b) Errington R J Advanced Practical Inorganic Chemistry and Metalorganic Chemistry Chapman and Hill London 1997

99) Jonas K Deffense E Habermann D Angew Chem Int Ed Engl 1983 22 716 100) Gaussian 03 Revision B03 M J Frisch G W Trucks H B Schlegel G E

Scuseria M A Robb J R Cheeseman J A Montgomery Jr T Vreven K N Kudin J C Burant J M Millam S S Iyengar J Tomasi V Barone B Mennucci M Cossi G Scalmani N Rega G A Petersson H Nakatsuji M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida T Nakajima Y Honda O Kitao H Nakai M Klene X Li J E Knox H P Hratchian J B Cross C Adamo J Jaramillo R Gomperts R E Stratmann O Yazyev A J Austin R Cammi C Pomelli J W Ochterski P Y Ayala K Morokuma G A Voth P Salvador J J Dannenberg V G Zakrzewski S Dapprich A D Daniels M C Strain O Farkas D K Malick A D Rabuck K Raghavachari J B Foresman J V Ortiz Q Cui A G Baboul S Clifford J Cioslowski B B Stefanov G Liu A Liashenko P Piskorz I Komaromi R L Martin D J Fox T Keith M A Al-Laham C Y Peng A Nanayakkara M Challacombe P M W Gill B Johnson W Chen M W Wong C Gonzalez J A Pople Gaussian Inc Pittsburgh PA

- 175 -

2003 101) wwwgaussiancom 102) wwwchemcraftprogcom 103) Becke A D J Chem Phys 1993 98 5648 104) Lee C Yang W Parr G R Phys Rev B 1988 37 785 105) Binkley J S Pople J A Hehre W J J Am Chem Soc 1980 102 939 for

hydrogen and Gordon M S Binkley J S Pople J A Pietro W J Hehre W J J Am Chem Soc 1983 104 2797

106) Hay P J Wadt W R J Chem Phys 1985 82 270 107) Hehre W J Ditchfield R Pople J A J Chem Phys B 1972 56 2257 108) Curtiss L A McGrath M P Blaudeau J-P Davis N E Binning R C Jr

Radom L J Chem Phys 1995 103 6104 109) A W Ehlers M Boumlhme S Dapprich A Gobbi A Houmlllwarth V Jonas K F

Koumlhler R Stegmann A Veldkamp G Frenking Chem Phys Lett 1993 208 111

110) QST is a synchronous transit approach to the quadratic region around the transition state structure For details see (a) J B Foresman A Frisch in Exploring Chemistry with Electronic Structure Methods A Guide to Using Gaussian Gaussian Inc Pittsburgh PA USA 1996 (b) H B Schlegel in Ab Initio Methods in Quantum Chemistry Part I Wiley Chichester 1987

111) Gu Z The Improvement of Total Synthesis of Angular [4]Phenylene and Its Flash Vacuum Pyrolysis (FVP) Study Postdoctoral Report University of California Berkeley 2008

112) Schwager H Postdoctoral Research Report University of California Berkeley 1987

113) Kuumlchle W Dolg M Stoll H Preuss H Mol Phys 1991 74 1245 114) (a) Hariharan P C Pople J A Theor Chim Acta 1973 28 213 (b) Francl M

M Petro W J Hehre W J Binkley J S Gordon M S DeFrees D J Pople J A J Chem Phys 1982 77 3654 (c) Rassolov V Pople J A Ratner M Windus T L J Chem Phys 1998 109 1223

iii

means ldquoMacGyverrdquo in Mandarin I would also like to thank the rest of my co-workers past and present for all of their support They are in rough chronological order Thomas Carl Miles Carter Kaspar Schaumlrer Ingo Janser Romy Michiels Elisa Paredes Thilo Heckrodt Nicholas Cheron Alex Lee Anais Geny Samer Al-Gharabli Nicole Franssen Vladislav Kulikov Alexandra Romek Isaac Ho Zhenhua Gu Florian Montermini Nikolai Vinokurov Robert Zitterbart and Cedric Ghellamallah Bonnie Kirk skillfully handled the various arcane administrative procedures but also provided many interesting and memorable early morning conversations The finer points of NMR spectroscopy were taught to me by the indomitable Rudi Nunlist His wry humor and outlook on life were often the perfect supplement to the rigors of graduate school life Working with Chris Canlas Rudirsquos able successor has also been a pleasure I was encouraged when he was so quick to remind me that I have the same name as a bad-boy Filipino action-movie star Teaching while always quite time consuming proved to be an invaluable experience Teaching under the direction of Peter the man who wrote the book on organic chemistry was quite an adventure His passion and talent for teaching are immediately obvious and inspiring even without flipping through the Basque translation of his textbook Jon Ellmanrsquos ability to write exams that are easy to grade but difficult for students to take is similarly awe inspiring There is no doubt in my mind that Heino Nitsche has taken teaching of general chemistry to new levels of eccentricity and excitement Jean Freacutechetrsquos impressive aptitude for lecturing is perhaps surpassed only by the impressiveness of his wine collection Looking down the academic chain I have to acknowledge many of the brilliant and wonderful students that made teaching such a fantastic experience Special thanks goes to Steve Seyedin Nellie Ekmejian Jessie Zhang Yao Yue Ashley Johnson Brent Jellen Zarina Khan and Mojgan Rastegar all of whom were extraordinary students that I hope will do their part to save the world No acknowledgement could be complete without recognizing the love and support of my family in particular my mother Her love though always tough was always there My various housemates also provided me with some great times Chris Trinh my first housemate in Berkeley was a superb fellow to live with and I will always fondly remember our conversations on life love and quantum gravity Cory McLitus when he wasnrsquot slaving away in the architecture studio also became a good friend I feel no need to apologize for getting him hopelessly addicted to ldquoThe Big Bang Theoryrdquo The awesome Samra Kasim was always ready for chai good food and hearty discussions on Bollywood and all things South Asian The housemates of 1505 Oxford St are also great people Though we rarely cross paths Vicky Zhuangrsquos highly entertaining biology lab adventures are much appreciated Vannamaria Kalafonos always has something wonderful going on in the kitchen and I aspire to learn the Greek specialty of cooking for a zillion people from her The cats Pink Tuffy and especially Floyd are nice companions even though they sleep a combined 60 hours per day Many kalyānamitras helped me get through the toughest times and to them I am especially grateful A large number of my Saturday evenings were spent in the calm environs of the Berkeley Monastery where Rev Heng Surersquos Avataṃsaka Sūtra

iv

lectures gave me much to think about The monthly lectures by Ajahn Amaro Ajahn Passano and the Abhayagiri Sangha were also a wonderful learning experience Chats about long-dead ancient languages and obscure texts with Sean Kerr a fellow survivor of Dagmar Theisonrsquos German class will also be fondly remembered The NY Sangha though far away always supported me and welcomed me warmly whenever I returned home Frank Yao Hai-Dee Lee Sheila Sussman Fred Ng Martin Applebaum Josephine Verceles Tiffany Taulton Phung Tran and especially Aaron Vederman repeatedly reminded me to ldquosmile breath deep and go slowlyrdquo The many visits to Bodhi Monastery were always the high points of my summers Michael Roehm Bhikkhu Bodhi Jane Berry Henry and Lily Teoh Marcie Barth Mahendra Sagar the dearly departed Felicia Miller Ven Guo Jun Susan Chastain and the polygot Bhikkhu Analayo made every visit an unforgettable experience and never failed to remind me why I get out of bed in the morning

- 1 -

Chapter One

Properties of the [N]Phenylenes and Their Organometallic Chemistry

11 General Discussion of [N]Phenylene Properties Polycyclic aromatic hydrocarbons (PAHs) are a class of molecules that have occupied the minds of chemists for generations1 Their essential feature aromaticity is the unusual stabilization that arises from having a 4n+2 number of π-electrons in a cyclical array This seemingly simple definition obscures the fact that aromaticity continues to be one of the most scrutinized topics in modern organic chemistry2 and more rigorous definitions3 have remained elusive Much of the early work4 with PAHs was aimed at investigating theoretical issues surrounding aromaticity There has been renewed interest in these systems in recent years because they are increasingly attractive as functional materials in organic-based electronics5 Of the many different kinds of PAHs known eg 1ndash6 (Figure 11) one subclass is of particular interest the [N]phenylenes6

Anthracene Coronene Phenanthrene

Chrysene Triphenylene Pyrene

1 2 3

4 5 6

Figure 11 Some examples of polycyclic aromatic hydrocarbons The [N]phenylenes (where N = the number of benzene rings) are PAHs in which benzene and cyclobutadiene rings are fused in an alternating manner The cyclobutadiene ring imparts very unusual structural and electronic properties as seen in the simplest molecule in the series biphenylene (7) It can be described by several resonance forms (Figure 12 andashe) in which the major contributor 7c avoids formation of the highly destabilizing antiaromatic cyclobutadiene (7a 7e) and benzocyclobutadiene circuit (7b 7d) This preference is manifest in the significant bond alternation7 seen in

- 2 -

the crystal structure of biphenylene (Figure 12) which shows a clear difference in bond lengths between the formal single bonds (~143 Aring) and the shorter formal double bonds (~137 Aring)

1423

1372

Figure 12 Biphenylene bond lengths (top Aring) and resonance contributors (bottom)

An extreme example of [N]phenylene π-bond localization is triangular [4]phenylene (8) (Scheme 11) in which the three-fold peripheral fusion imparts complete cyclohexatriene character on the central ring89a This property is reflected in the reactivity of the system eg catalytic hydrogenation (9)8b epoxidation (10)8c and cyclopropanation (11)8c Scheme 11 Reactions Illustrating the Fully Bond Localized Character of the Central Benzene

Ring in Triangular [4]Phenylene 8 Bond lengths are in Aring

- 3 -

Phenylenes exhibit another interesting structural feature in contrast to other PAHs sizable deviations from planarity (Figure 13)9ab The flexibility of the phenylene framework arises from the combined effect of π- and σ-strain9ab By adopting a nonplanar geometry overlap between the π-orbitals is diminished and in turn leads to a decrease in destabilizing antiaromatic character Pyramidalization of the four-membered ring carbons also reduces σ-strain9ab a phenomenon observed in highly strained alkene systems9c

Figure 13 Crystal structures showing deviations from planarity in (a) helical [6]phenylene (12)10 (b) dimethyl triangular [4]phenylene-23-dicarboxylate (13)9a and (c) 23-bis(tri-

methylsilyl) linear [3]phenylene (14)9a

The fusion of aromatic benzene rings with antiaromatic cyclobutadiene units in the same molecule has prompted numerous experimental and theoretical discussions6 regarding the magnetic and electronic properties of the phenylenes 1H-NMR spectroscopy is one typical measure of aromaticity Protons on the exterior of aromatic rings (eg 15) show relatively low field resonances while their interior counterparts resonate at relatively high field due to the presence of a diamagnetic ring current Conversely antiaromatic rings with 4n π-electrons are paratropic and reveal the opposite disposition of the two respective types of protons (eg 16) The interplay between aromatic and antiaromatic character in the phenylenes is evident in their chemical shifts which tend to show weakly aromatic resonances (Figure 15) relative to benzene (736 ppm)

(a) (b) (c)

12 13 14

- 4 -

Figure 14 Observed 1H-NMR resonances in (a) the aromatic [18]annulene (15)11 and (b) the antiaromatic 5-bromo-19-bisdehydro-[12]annulene (16)12

Aside from NMR spectroscopy nucleus independent chemical shift (NICS)13 calculations have also proven to be useful measures of aromaticity The NICS technique works by calculating the magnetic shielding of a ldquoghost nucleusrdquo that can be positioned anywhere around a molecule For probing aromaticity the calculated point is in the center of the π-electron circuit to be examined Calculations placing the ghost nucleus 1 Aring above the plane of the molecule are often used to minimize local anisotropy and are referred to as NICS(1)14 NICS data are given in ppm and are thus comparable to experimental 1H-NMR measurements Negative NICS values indicate aromatic character while positive values suggest antiaromatic character For example the NICS(1) of benzene15 is ndash125 ppm whereas for cyclobutadiene15 it is 151 ppm NICS calculations for various phenylenes have been carried out6 and are shown in Figure 15 alongside the experimentally measured 1H-NMR chemical shifts The attenuated aromatic character of the benzene and the relatively weak antiaromatic character of the cyclobutadiene rings in phenylenes such as biphenylene (7) triangular [4]phenylene (8) and angular [4]phenylene (17) are apparent from both sets of data

Figure 15 1H-NMR (blue) and NICS(1) (green) data for selected phenylene topologies (ppm)6

The phenylenes possess multiple modes of reactivity7 as illustrated by biphenylene (7) in Scheme 12 It can undergo electrophilic aromatic substitution like other PAHs but does so selectively at the 2-position to avoid the formation of intermediates with antiaromatic character Biphenylene does not readily undergo Diels-

- 5 -

Alder reactions but was shown to react with electron-deficient benzynes to give the corresponding cycloadducts16 Opening of the highly strained four-membered ring is another prominent aspect of phenylene reactivity

Scheme 12 Illustrative Reaction Pathways of Biphenylene6

Early work17 showed that it was possible to cleave the aryl-aryl C-C bonds via thermolysis in the neat state Rupture of the four-membered ring is a key step in the rearrangement of phenylenes into other PAHs and has been observed typically under flash vacuum pyrolytic conditions18 (eg 10ndash3ndash10ndash6 torr 800ndash1000 degC) Strained ring opening on exposure to metal complexes to give metallacycles19 is discussed in further detail in Section 12 12 Overview of Phenylene Organometallic Chemistry

As mentioned above the weakly aromatic character of the phenylenes dominates their structure and reactivity In the linear phenylenes the antiaromatic contribution to structure and reactivity becomes increasingly significant A simple yet instructive explanation for this phenomenon can be seen in the various resonance structures of linear [3]phenylene (18) a selection of which is depicted in Figure 16 Even the most favorable forms a and b feature double bonds in the four-membered rings The cumulative increase in cyclobutadienoid circuits should therefore lead to an increase in antiaromatic character The relative augmentation in

- 6 -

cyclobutadienoidantiaromatic character of the linear phenylenes was confirmed6 by NMR NICS calculations and HOMO-LUMO measurements20

Figure 16

Resonance contributors to linear [3]phenylene

Cyclobutadiene is often invoked as the typical example of a highly destabilized antiaromatic system Indeed the difficulties21 in preparing and isolating it confirm theoretical predictions regarding its instability22 Attachment of a metal however is known to produce aromatic organometallic molecules of high stability23 The increased antiaromatic character of the linear phenylenes thus makes them amenable to metal complexation Cyclopentadienylcobalt cyclobutadiene complexes of linear [3]- (19)24 linear [4]- (20)25 and linear [5]phenylene (21)26 have been prepared using the well-developed cobalt-based [2+2+2] alkyne cyclotrimerization methods (Scheme 13)27

Compounds 19ndash21 constitute the only linear CpCo phenylene systems known so far

Scheme 13 Synthesis of Linear Phenylene(CpCo) Cyclobutadiene Complexes

In the metallated linear [4]- and [5]phenylene 20 and 21 respectively the CpCo unit is located on the inner cyclobutadiene ring This is curious as one would have expected the metal fragment to be bound to its outside counterpart close to the center of reactivity during the cyclotrimerization step The position of the CpCo unit was established by NMR spectroscopy2628 In addition a crystal structure of a tetrahexyl

TMS

TMS

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMSTMS

TMS

Co

CpCo(CO)2BTMSA

h

Co

Co

CpCo(CO)2BTMSA

h

CpCo(CO)2BTMSA

h

19

20

21

- 7 -

substituted linear [5]phenylene28 (Figure 17) clearly reveals the inside position of the metal fragment Difficulties in obtaining high quality crystals however precluded a detailed bond analysis of the complex The unexpected location of the CpCo unit in 20 and 21 suggested the occurrence of CpCo migration under the conditions of their preparation Detailed experiments verifying this hypothesis will be the subject of Chapter 2

Figure 17 Disordered crystal structure for the 23910-tetrakis(trimethylsilyl)-571214-

tetrahexyl linear [5]phenylene(CpCo)

In contrast to the linear phenylenes their angular relatives undergo π-metallation at the cyclohexatrienoid moieties (Figure 18) For example angular [3]phenylene (22) reacts with CpCo(C2H4)2 to form the η4-CpCo complex 2329 Similar treatment with Cr(CO)3(NH3)3 yields the η6-Cr(CO)3 analog 2430

Figure 18 η

4-CpCo (23) and η6-Cr(CO)3 (24) complexes of angular [3]phenylene (22)

In addition to 24 related chromium complexes of the triangular [4]phenylene frame eg 25 have been prepared (Scheme 14)31 Interestingly regioisomer 26 generated at relatively lower temperatures is the kinetic product of monocomplexation and rearranges thermally to 27 Double metallation is possible as illustrated in the conversion of 27 to 28 with added (naphthalene)Cr(CO)3

- 8 -

Scheme 14 Synthesis and Reactions of Triangular [4]Phenylene(Cr(CO)3) Complexes

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3(NH3)3dioxane 100 oC

14 h

(naphthalene)Cr(CO)3THF Et2O 60 oC 14 h

90 oC

(naphthalene)Cr(CO)3THF Et2O 60 oC

14 h

25

27

26

28

57 43

89

In contrast to CpCo which attaches itself exclusively to the four-membered ring in the linear phenylenes including the linear [3]phenylene frame as in 19 (Scheme 13) Fe2(CO)9 gives a plethora of complexes with the tetrasilyl derivative 29 among which the iron tricarbonyl cyclobutadiene complex 30 is only minor (Scheme 15)27 Instead other organometallic molecules such as arene complex 31 were isolated This compound contains two Fe(CO)3 units coordinated to the central benzene ring An iron-iron bond was proposed for this molecule (31a) although the spectral data are also consistent with a structure in which the Fe(CO)3 fragments are located on opposite faces (31b) Because a crystal structure could not be obtained the structural identity of 31 remains ambiguous The major products of this reaction 32 and 33 illustrate another important aspect of phenylene reactivity metal insertion into the strained ring

- 9 -

in this case involving the dinuclear Fe2(CO)6 unit Complex 33 probably originating from 32 contains an additional Fe(CO)3 moiety coordinated to the terminal benzene ring closest to the Fe2(CO)6 fragment

Scheme 15 Reaction of Linear [3]Phenylene with Fe2(CO)9

While as yet absent in the linear series a cobalt insertion product analogous to iron compounds 32 and 33 was isolated when angular phenylene 22 was exposed to excess CpCo(ethene)2 (Figure 19)32 In this case double insertion of two (CpCo)2

Figure 19 Tetranuclear CpCo-terphenylene complex 34 and its crystal structure

34

- 10 -

fragments occurred to give 34 in 71 yield Notably neither 23 nor analogs of the type 31 were detected As alluded to in Scheme 12 biphenylene (7) itself also undergoes metal insertions into the four-membered ring This type of reactivity has been observed with a range of transition metals including Co19 Mechanistically best delineated is the attack of Ni and Pt species Thus Ni(PEt3)4

33a and Ni(COD)(PMe3)233b begin with insertion of

the nickel fragment into the four-membered ring to give a metallacycle of the type 35 (Scheme 16) Subsequent dimerization assembles 36 from which Ni is extruded to furnish tetraphenylene 37 as the final product A similar reaction pathway was proposed for Pt(PEt)4

19 but proceeding via 38 to a monometallacycle 40 possibly through the intermediacy of 39 In summary the σ- and π-activation of the phenylenes endows them with rich organometallic chemical potential The synthetic and mechanistic exploration of one aspect of it namely the Ni-catalyzed cycloaddition of alkynes to the four-membered rings in angular phenylenes will be discussed in Chapter 3

Scheme 16 Reaction of Biphenylene with Nickel and Platinum Complexes

13 Direction of Work The discussions in Sections 11 and 12 have provided a brief overview of phenylene properties and their previously studied organometallic chemistry

- 11 -

respectively The aim of this thesis was to advance two aspects of prior investigations The first area examines the chemistry of the linear phenylene(CpCo) complexes In particular experiments are presented addressing the question of a possible migration of the CpCo fragment along their framework The revocable movement of a metal fragment between cyclobutadiene rings is a highly noteworthy discovery as this process has never before been reported On a practical level this mode of reactivity places linear phenylene(CpCo) complexes in the increasingly appealing class of organometallic arrays that can serve as the basis for various molecular electronic systems The reversible isomerizations described in the second chapter can potentially be employed in molecular machines and switches data storage and as will be detailed photostorage devices Experimental work in the form of detailed solid state and spectroscopic analyses is provided Computational studies are also employed to further scrutinize the novel chemistry of the abovementioned Co-based molecules The second topic of this thesis examines nickel-catalyzed insertions into the four- membered rings of angular phenylene systems Specifically the application of this reactivity to the synthesis of a class of PAHs known as [N]phenacenes is discussed Phenacenes (polyphenanthrenes) have recently shown great promise as organic transistors and conductors but advancement of this field has been hampered due to few practical syntheses The insolubility of these molecules has also been a substantial barrier to the development of phenacene-based applications The content of the third chapter explores the preparation of soluble phenacene derivatives using a tandem Ni-insertion alkyne cycloaddition reaction This new process provides an efficient widely applicable and practical synthesis of larger phenacenes using correspondingly larger angular phenylene systems Detailed mechanistic studies of this reaction are presented Experimental data are used in conjunction with computational studies to gain further insight with the optimization of the reaction by reduction of side product formation being a crucial milestone

- 12 -

Chapter Two

PhotondashThermal Haptotropism in Cyclopentadienylcobalt Complexes of Linear Phenylenes Intercyclobutadiene Metal Migration

21 Introduction As previewed in Section 12 the unexpected position of the metallic unit in the linear [4]- and [5]phenylene(CpCo) systems 20 and 21 constituted the background for the studies presented in this chapter Specifically it was hypothesized that its origin was due to the migration of the metal fragment from one cyclobutadiene ring to another a process that would constitute an unprecedented type of haptotropic shift34-36 However a prerequisite for studying such a rearrangement would be the generation of the haptoisomers of 20 and 21 (Scheme 13) bearing the CpCo appendage at the respective terminal four-membered rings a possibility obviated by their thermal method of synthesis The following describes the history that led to the discovery of photochemical conditions that circumvented this thermodynamic problem The story begins with a prior attempt to stabilize the linear phenylene frame by alkyl substitution the ultimate aim being the synthesis of members of the series with Ngt5 Such substitution was also hoped to improve solubility a facet exploited in the corresponding zigzag series37 The synthetic strategy followed that used in the preparation of the largest known linear phenylene 41 namely the CpCo-catalyzed cyclization to 21 followed by careful oxidative demetallation as shown in Scheme 21 The initial target chosen was the tetrahexyl system 43 approached via the synthesis of complex 42 (Scheme 22)28 Demetallation was thought to be facile to provide the free ligand but this anticipation proved to be erroneous

Scheme 21 Oxidative Decomplexation of Linear [5]Phenylene Complex 21

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMS

41

CoCp

21

40

CuCl2middot2H2ODME NEt3 H2O

Scheme 22 Preparation of Tetrahexyl Linear [5]Phenylene Complex 42

- 13 -

TMS

TMS

TMS

TMS

Hex

Hex

Hex

Hex

CoCp

42

CpCo(CO)2 BTMSAm-xylene ∆ hν

27

Hex Hex

HexHex

TMS

TMS

TMS

TMS

Hex Hex

HexHex

ndashCpCo

43

The demetallation of 42 under numerous conditions was unattainable However in one of these attempts an NMR sample of 42 was exposed to UV-irradiation leading to the evolution of new signals eventually assigned to originate from rearranged compound 45 (Scheme 23)28 This molecule is also a linear [5]phenylene(CpCo) complex but now has the metal fragment bound to the outer cyclobutadiene ring an arrangement that was suspected to be the initial product of the preparation of 42 (Scheme 22) That this conjecture was correct was established by heating which caused photoisomer 45 to revert to 42 An indication of the generality of this phenomenon was gleaned from 21 which underwent the same photoinduced thermally reversible haptotropic migration (Scheme 23)38 A detailed discussion of the spectral properties of these haptomers is provided in Sections 23 and 24 Scheme 23 Photoinduced Thermally Reversible Haptotropic Migration of the CpCo Fragment

in Linear [5]Phenylene(CpCo) Complexes

This discovery was deemed significant for two reasons 1 it constitutes the first observation of intercyclobutadiene metallohaptotropism and 2 there are only two previously known examples of mononuclear39 additive-free40 photothermal reversible haptotropic shifts both of which are based on Mo(PMe3)3 complexes (Scheme 24)41 Systems capable of undergoing this type of reaction are of much practical importance because of their potential employment as photostorage devices andor molecular switches42 The development and application of functional organometallic materials43 has proceeded at a relatively slow pace when compared to their non-metallated counterparts5c Thus the great prospects for discovery and advancement make this area of study particularly attractive

- 14 -

Scheme 24 Photothermal Reversible Metallohaptotropism in (a) Molybendum-Indole41a and (b) Molybendum-Isoquinoline Complexes41b

Having confirmed that an η4η4 cyclobutadiene haptotropic migration was indeed occurring mechanistic investigations2838 were begun Interestingly full conversion of the inner bound CpCo complexes to their photoisomers was never achieved The maximum ratio obtained for 2144 and 4245 was 8812 Variations of solvent (eg benzene THF CHCl3) and temperature (0ndash30degC) had no effect on this ratio Added ligands such as 15-cyclooctadiene CO and phosphines were also inconsequential Of further significance was the robustness of the photothermal cycle which could be run multiple times without decomposition Kinetic experiments were carried out to determine the activation parameters for the thermal reversal of 44 and 45 to 21 and 42 respectively These data are shown in Table 21 The isomerizations are cleanly first order a finding that was unaffected by changes in concentration22 The enthalpy of activation (∆Hne) increased only slightly with hexyl substitution (44 vs 45) The near zero entropy of activation values (∆Sne) was consistent with the occurrence of an intramolecular process

Table 21 Activation Parameters for the Conversion of Outer to Inner CpCo Complexes Under

Thermal Conditions ∆Sne Values are in Entropy Units (1 eu = calmolsdotK)

Reaction Solvent ∆H

ne (kcalmol) ∆Sne (eu)

44 to 21 C6D6 259 plusmn 04 16 plusmn 14 44 to 21 THF-d8 256 plusmn 09 01 plusmn 30 45 to 42 THF-d8 276 plusmn 08 77 plusmn 27

Consideration of the relative facility of the above haptotropic shifts made it likely that migration was occurring along the entire phenylene frame including the ldquohoppingrdquo across the central six-membered ring (Scheme 25) This degenerate equilibration should be detectable by NMR spectroscopy44 if it were sufficiently fast Unfortunately but perhaps not surprisingly considering the data in Table 21 coalescence of the spectrum of 21 could not be achieved even at temperatures as high as 120 degC Spin saturation transfer experiments (eg EXSY) also failed44 These data allowed an estimate of the lower limit for the activation energy of the internal shift of ∆Gne ge 22 kcalmol28

Scheme 25 Proposed Internal η4η4 Cyclobutadiene CpCo Migration

- 15 -

The failure of the above experiments inspired a different approach based on the following arguments The antiaromatic character of the linear phenylenes has been shown by theory and experiment to increase with size645 Consequently the effect of metalloaromatization46 makes linear [5]phenylene a better (and hence more strongly bound) ligand for CpCo than a smaller system (eg linear [3]phenylene) Indeed the enthalpy of the homodesmotic in Scheme 26 was computed by DFT methods to be Scheme 26 Calculated Homodesmotic Reaction Showing Preferential Binding of CpCo to

Linear [5]Phenylene

113 kcalmol47 If the barrier to intercyclobutadiene hopping were related to the binding energy of the metal one would expect a more loosely bound metal fragment to migrate faster The hope was therefore that the degenerate haptotropism in Scheme 27 would be observable by VT NMR methods Unfortunately these efforts failed again38 either because the anticipated acceleration was not sufficient to be observable by NMR or because the argument above (which rests solely on ground state considerations) is flawed

Scheme 27 Proposed Degenerate Haptotropic Shift in Linear [3]Phenylene Complex 19

- 16 -

The preceding discussion summarizes some of the quantitative aspects of this new type of haptotropic shift Many fundamental questions however remained to be answered Is it possible to observe the photothermal shift in other systems such as linear [3]- and [4]phenylene What is the exact mechanism of metal migration between cyclobutadiene rings In what way if any does attachment of CpCo alter the structure of the phenylene scaffold Related to these questions was the long-standing quest for an accurate crystal structure of any linear phenylene(CpCo) complex The answers are addressed in the following sections 22 Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes As recounted in Section 21 the degenerate internal haptotropic shift could not be seen by NMR in the symmetrical 19 Therefore recourse had to be taken to chemical methods involving an isomerization of the sort shown in Scheme 28

Scheme 28 Isomerization of a Desymmetrized Linear [3]Phenylene(CpCo) Complex

Initial efforts focused on attempts to desymmetrize compound 19 directly by selective electrophilic desilylation specifically protodesilylation Earlier studies48 had shown that such selectivity was possible in the reactions of bis(trimethylsilyl)benzocycloalkenes such as the benzocyclobutene depicted in Scheme 29 In this case loss of the first TMS group is approximately forty times faster than that of the second Along these lines it was thought that exposing 19 to acidic conditions would selectively remove one (or perhaps two) TMS groups before attacking the remaining silylarene positions In the event treating compound 19 with trifluoroacetic acid in carbon tetrachloride did induce protodesilylation but with no selectivity A mixture of products was obtained and its separation proved impossible (Scheme 210) In light of this setback a new synthetic scheme had to be considered that would generate a desymmetrized system directly in the CpCo-catalyzed cyclization step

- 17 -

Scheme 29 Selective Desymmetrizing Reactions of 12-Bis(trimethylsilyl)benzocyclobutene with Electrophiles

Scheme 210 Attempted Selective Protodesilylation of 19

Fortunately such a strategy had already been executed successfully in the creation of 23-bis(trimethylsilyl) linear [3]phenylene (46) and employed the iterative Scheme 211 Iterative Cyclotrimerization Route in the Synthesis of Linear [3]Phenylene 46

cyclization depicted in Scheme 21127 Its specific execution (Scheme 212) started with a Sonogashira reaction between trimethylsilylacetylene (TMSA) and 12-diiodobenzene (47) to give diyne 48 in high yield Deprotection of 48 with K2CO3 immediately followed by standard CpCo(CO)2-catalyzed alkyne cyclotrimerization649 with bis(trimethylsilyl)acetylene (BTMSA) afforded 23-bis(trimethylsilyl)biphenylene (49) Iododesilylation was then performed using pure ICl to give 23-diiodobiphenylene (50) A Sonogashira coupling between TMSA and 50 produced diyne 51 in good yield The use of a slightly modified cyclization procedure provided the new 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52) in 57 yield This protocol employed THF as a cosolvent to BTMSA thus reducing the reaction temperature in turn allowing for the CpCo to remain attached in the final product and preventing catalytic turnover252638

TMS

TMS46

+

TMS

TMS

+

TMS

TMS

+

TMS

R

TMS

dilute

[X+]

X = H D Br

TMS

TMS

[X+]

TMS

X = H D Br

X

- 18 -

Scheme 212 Synthesis of Asymmetric Linear [3]Phenylene(CpCo) 52

High dilution conditions also helped to suppress formation of cyclobutadiene(CpCo) complexes a well known side reaction in alkyne cyclization chemistry

Compound 52 like its tetrasilylated analogue 19 is a black air-sensitive solid Although it can be handled in air for brief periods of time complete decomposition occurs within 24 hours if left exposed to the ambient atmosphere Purification must always be done with neutral activity III alumina as lower activities (and silica gel) cause decomplexation to give the deep red ligand 46 as the only isolable product Critically exposing molecule 52 to UV irradiation induced the desired haptotropic shift giving its photoisomer 53 (Scheme 213) Heating 53 converted it back to 52 thus completing the photothermal cycle Interestingly close inspection of the NMR spectra of this experiment revealed that a small amount of 53 (2) always remained even on prolonged heating That this observation signaled a thermodynamic equilibrium was confirmed by dissolution of pure crystalline 52 and NMR analysis From the equilibrium constant the ∆Gdeg298 was calculated to be 23 kcalmol in favor of 52 The reasons for this energetic preference and a discussion of the NMR spectral properties of these and related complexes are presented in Section 23

Scheme 213 The Photoinduced Thermally Reversible Haptropic Shift in Linear

- 19 -

[3]Phenylene-(CpCo) 52 to Give Photoisomer Complex 53 The investigations of the equilibration depicted in Scheme 213 were all carried out in sealed Pyrex NMR tubes (J-Young or flame-sealed) using benzene-d6 andor toluene-d8 as the solvent As for the linear [5]phenylene(CpCo) system the cycle could be run multiple times without decomposition and was unaffected by changes in solvent and temperature The maximum ratio of 5352 that could be obtained on irradiation was 11 after ten hours This value is larger than that observed for its linear [5] analogs 2144 and 4245 Photoisomerization also occurs with sunlight leading to the photostationary equilibrium of 5253 = 105 Consequently care must be taken to shield 52 from direct andor indirect sunlight Indoor fluorescent lighting however did not induce CpCo migration Attempts to monitor the photoisomerization and its thermal reverse by UV-Vis spectroscopy failed because of minimal changes in the absorptions due to 52 during these processes This finding implies that the absorption spectra of 52 and 53 are not unexpectedly very similar and offers a possible explanation for the maximum photostationary ratio of 11 The activation parameters for the thermal reversal reaction (53 to 52) in Scheme 213 were obtained in the manner described in Section 21 and are shown in Table 22 The relatively high activation barriers (with respect to the NMR time scale) explain why the degenerate isomerization in 19 could not be verified by NMR experiments Qualitatively the ∆Hne values agree with the hypothesis that the more loosely bound CpCo unit in the linear [3]phenylene is relatively more mobile they are approximately 3 kcalmol lower than those of the [5]phenylene system On the other hand the ∆Sne values especially in C6D6 are positive and relatively high although still within the range acceptable for intramolecular reactions Nevertheless a crossover experiment was devised to provide a definite answer

Table 22 Activation Parameters for the Thermal Conversion of Complex 53 to 52

Solvent ∆H

ne (kcalmol) ∆Sne (eu)

C6D6 204 plusmn 14 158 plusmn 22 Toluene-d8 231 plusmn 07 60 plusmn 13

For this purpose two new linear [3]phenylene(CpCo) derivatives were required One would carry a marker on the Cp ring while the other would be labeled at the phenylene frame Execution of Scheme 213 would involve an equimolar mixture of both compounds An intramolecular mechanism would retain the integrity of the labeling while a dissociative path would lead to label scrambling The outcome of this experiment should be ascertainable by NMR spectroscopy and more rigorously by

CoTMS

TMS

CoTMS

TMS

310 365 nmsunlight

30ndash50oC52 53

- 20 -

Scheme 214 Preparation of MeCp- (54) and Deuterium Labeled (55) [3]Phenylene Complexes

mass spectrometry To this end methyl-Cp complex 54 and dideuterio compound 55 were targeted for synthesis (Scheme 214) Compound 54 was prepared by carrying out the modified cyclotrimerization reaction with MeCpCo(CO)2

50 while 55 was made using methanol-OD in the desilylation of 51 The amount of deuterium incorporation in 55 was found to be 63 as gleaned from its proton NMR spectrum Scheme 215 Crossover Experiment with Labeled Linear [3]Phenylene(CpCo) Complexes

- 21 -

Co

TMS

TMS

TMS

TMS

Co

h CoTMS

TMS

Co

D

D

TMS

TMSD

D

TMS

TMS

Co

Co

TMS

TMSD

DCo

TMS

TMS

Co

TMS

TMSD

D

+

+

+

+

mz = 510

mz = 494

56mz = 508

57mz = 496

54mz = 508

55mz = 496

58 59

53 52

Not observed

Six distinct products are possible in the crossover experiment using 54 and 55 (Scheme 215) Compounds 56 and 5 would arise as a consequence of an intramolecular shift Molecules 53 and 58 and their photoisomers 52 and 59 respectively would be the result of metal fragment dissociation Mass spectrometry would readily verify the occurrence of crossover as the masses (given in mz in Scheme 215) of the products with scrambled labels (52 53 58 59) are distinct from the masses of the starting materials (54 55) and their photoisomers (56 57) In the first part of the experiment equal amounts of 54 and 55 were mixed (shielded from light) and allowed to stand for 2 hours at room temperature The resulting 1H-NMR spectrum consisted of only the signals for 54 and 55 Similarly the mass spectrum showed molecular ion peaks matching the masses of 55 and 56 (Figure 21) The second step was irradiation Analysis of the photolyzed mixture showed new peaks due to complex 56 (the resonances of which had been obtained in a separate photothermal experiment with pure 54) with the expected integration ratio and a second set assigned to 57 identical with the spectrum of 53 but with the expected attenuated absorption for the silyl bearing arene hydrogens The relative integrations for all compounds observed were consistent with a mixture of 5455 and 5657 Mass spectral analysis of the irradiated mixture showed a pattern that was identical to that collected before irradiation (Figure 21) Finally the thermal reversal reaction was carried out by heating the photolyzed mixture at 80 degC After 30 hours the resulting

- 22 -

NMR spectrum matched that of the initial mixture of 54 and 56 in particular confirming the full protonation of 54 and the unchanged level of deuterium incorporation in the silyl

Figure 21 Molecular ion peaks for 5456 (mz = 508) and 5557 (mz = 496)

bearing arene ring of 55 The corresponding mass spectrum contained no evidence for the presence of scrambled products To conclude The haptotropic shift is non-dissociative The exact manner in which the metal traverses from one cyclobutadiene ring to the other will be examined in greater detail in Section 24

23 X-Ray Structural and Comparative NMR Analysis of Linear [3]Phenylene(CpCo) Complexes The results described in Sections 21 and 22 pose some fundamental questions beyond those concerned with the immediate details of the observed haptotropism and addressing the basic novelty of the complexes involved What actually happens to the phenylene ligand when it is ligated via a cyclobutadienoid ring This section will address this question from a structural and (NMR) magnetic point of view Only one crystal structure of a linear phenylene(CpCo) complex was known at the outset of this work namely that of [5]phenylene(CpCo) 42 (Figure 17) and its acquisition required extensive efforts at crystallization28 Unfortunately extensive disorder obviated a detailed analysis It was hoped that some of the complexes employed in the chemistry disclosed in Section 22 would be more forthcoming in this respect The challenge lay in finding the right conditions for crystal growth We began with tetrasilyl linear [3]phenylene(CpCo) 19 which had been crystallized previously by slow cooling in acetone38 These conditions and numerous others (Table 23) did not provide material suitable for X-ray diffraction Success entailed slow cooling a solution of 19 to ndash10 degC in a mixture of methanol-diethyl ether (41) The ensuing sample allowed the determination of the first high quality crystal structure of a linear phenylene (CpCo) complex obtained in collaboration with the group of Professor Tatiana Timofeeva of New Mexico Highlands University (Figure 22)

Table 23 Trial Crystallization Conditions for Linear [3]Phenylene(CpCo)19

Solvent (Ratio) Conditions Result

Acetone Slow Cooling Heterocrystalline Solid Acetone-Pentane (31) Slow Cooling Heterocrystalline Solid

Pentane-Acetone (101) Solvent Diffusion Amorphous Solid Chlorobenzene Slow Cooling Amorphous Solid

- 23 -

Acetone-Methanol (110 Slow Cooling Amorphous Solid Diethyl Ether-Methanol Slow Cooling Small Needles

Acetonitrile Slow Cooling Powder Ethyl Acetate Slow Cooling No Crystals

Ethyl Acetate-Methanol (11) Slow Cooling Amorphous Solid Methanol-Diethyl Ether (41) Slow Cooling Large Fine Needles

Figure 22 X-ray crystal structure of 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) (19) Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are

omitted for clarity Expectedly the CpCo unit is bound in an η4 fashion to the cyclobutadiene ring Also prominent is the deviation from planarity (Section 11) in the linear [3]phenylene a facet typical of the phenylenes themselves (Section 11)9a Of greater importance than these general observations however is the effect of metal complexation on the linear [3] framework The bond lengths for 19 are shown in Figure 23 and as is typical for the phenylenes6 show a certain degree of bond π-localization with measurable differences between single and double bonds However the extent of this phenomenon and its direction varies significantly when compared to the free ligand 60 A quantitative

- 24 -

comparison of the structural data for 19 with those of its ligand 60 is shown in Figure 2327

In 60 the terminal rings adopt bond alternation similar to that in biphenylene (Section 11) and the central benzene takes on a ldquobis-allylrdquo configuration both ostensibly to minimize electron density (and therefore antiaromaticity) in the four-membered rings As dictated by symmetry the two bonds spanning the central ring are of equal length (1385 Aring) Ligation by CpCo alters this picture profoundly in as much as bond alternation across the entire phenylene frame including the four-membered rings is strongly reduced (Figure 23) Generally all relatively long bonds in 60 shorten in 19 while all short bonds lengthen Some residual but attenuated biphenylene type

Co

1512(2)

1513(2)

1407(2)

1385(2)

1385(2)

1397(2)

1356(2)

1359(2)1436(2)

1397(2)

1441(2)

1411(3)(0052)

1384(3)(-0052)

1474(3)(0077)

1384(3)(-0057)

1408(3)(0052)

1448(3)(0051)

1480(3)(-0032)

1468(3)(-0045)

1437(3)(0052)

1465(3)( 0058)

1434(3)( 0049)

1352(3)(-0033)

1351(3)(-0034)

1476(3)(0069)

1495(3)(-0017)

1372(3)( 0016)

1405(3)(0008)

1376(3)(0017)

1413(3)(-0023)

1427(3)(0030)

1488(3)(-0025)

1423(3)(-0018)

(x) = (19) - (60)increasedecrease

60

19

1907(1)

1891(1)

1886(3)

1889(3)

1889(2)

1901(3)

1669

1725

Si

Si

Si

Si

Me

MeMe

Me

Me

Me

Me

MeMe

MeMe

Me

Si

Si

Me

MeMe

MeMe

Me

Si

Me

MeMe

Si

Me

MeMe

- 25 -

Figure 23 Comparison of bond lengths (in Aring) between linear [3]phenylene(CpCo)complex 19 and 2378-tetrakis(trimethylsilyl) linear [3]phenylene (60) The bond distances in 19 are shown in blue Increases in bond length in going from 60 to 19 are marked in green decreases in red

ldquobond fixationrdquo (Figure 12) remains in the vicinity of the uncomplexed cyclobutadiene Compound 19 thus provides a prime demonstration of the powerful effect of metalloaromatization46 in which the bonds of a cyclobutadiene-metal system attempt to adopt the equalized bond lengths that are a classic hallmark of aromaticity2ndash4 Encouraged by the successful development of a procedure to obtain X-ray quality crystals of 19 these techniques were applied to bis(trimethylsilyl) linear [3]phenylene(CpCo) 52 Gratifyingly with acetone as the solvent the results depicted in Figure 24 were ultimately obtained Figure 24 X-ray crystal structure of 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52)

Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are omitted for clarity

A comparison of the bond lengths of 52 with those of its corresponding linear [3]phenylene ligand 469a is given in Figure 25 Comparison with Figure 23 reveals the same type of aromatization of the ligand on attachment of the metal With these structures in hand an attempt was made to rationalize structurally the

- 26 -

thermodynamic preference for 52 in which the CpCo is located proximal to the silylated terminus in its equilibrium with 53 in which the metal is located close to the unsilylated benzene ring Focusing on the desymmetrizing ortho-bis(trimethylsilyl) unit one notes that the SiCndashCSi bond in 52 is elongated by 005 Aring on attaching the metal in 46 thus providing steric relief On the other hand the symmetry equivalent remote C7ndashC8 distance is unchanged The same effect is seen in the tetrasilyl complex 19

Figure 25 Comparison of bond lengths (in Aring) between bis(trimethylsilyl) linear [3]phenylene(CpCo) complex 52 and 23-bis(trimethylsilyl) linear [3]phenylene (46) Bond lengths for 46 are the average of four molecules in the unit cell (standard deviation = plusmn002)

Increases in bond length going from 46 to 52 are marked in green decreases in red

The observed structural changes make sense in a simple resonance picture

Co

1413(10)(007)

1406(10)(-004)

1459(10)

( 005)

1370(11)(-007)

1418(10)( 005)

1443(10)(003)

1470(10)(-005)

1465(10)(-005)

1446(10)( 008)

1485(10)( 006)

1432(10)( 004)

1347(10)(-003)

1345(10)(-002)

1492(10)( 007)

1503(11)(-002)

1379(10)(001)

1391(11)(-001)

1409(10)(004)

1418(11)(-003)

1367(11)(001)

1478(10)(-002)

1408(11)(-001)

1891(8)

1890(13)

1670

1723

SiMe

MeMe

Si

Me

Me

Me

(x) = (53) - (62)increasedecrease

SiMe

MeMe

Si

Me

Me

Me

190

145134152

139138

150

137145

136

142 137

152137 137

152

141

137 144

189

141143142140

52

46

- 27 -

(Scheme 216) Metalloaromatization alters the dominant resonance forms during intercyclobutadiene hopping such that the essentially single SiCndashCSi bond in 52 transforms into an essential double bond in 53 increasing unfavorable repulsion between the TMS groups Scheme 216 A Resonance Picture Rationale for the Preference of 52 in its Equilibrium with 53 The aromatization effect of metal complexation on the phenylene nucleus described structurally in the preceding text can also be demonstrated powerfully through the measurement of ring currents with 1H-NMR spectroscopy both by experiment and computation (NICS13 see Section 11) A relevant simple example is depicted in Figure 26(a) featuring the changes occurring when 12-bis(trimethylsilyl)benzocyclobutadiene (61) is complexed by CpCo as in 6251 The paratropic antiaromatic 8π system 61 exhibiting relatively shielded six-membered ring hydrogens turns diatropic in 62 Equally importantly and focusing on the ring current contributions of the individual cycles the paratropism of the four-membered ring in 63 shields the adjacent hydrogens more than the remote ones Conversely aromatization of this ring and the ensuing diatropism inverts this order

Figure 26 The effect CpCo complexation (a) on benzocyclobutadiene 61 and (b) linear [3]phenylene 46 Chemicals shifts are in ppm

Co SiMe3

SiMe3

Co

SiMe3

SiMe352 53

∆Gdeg298 =23 kcalmol

- 28 -

Turning to a phenylene system comparison of the NMR data for complex 52 with those for ligand 46 (Figure 26(b)) reveals the same changes not only in the vicinity of the ligated ring but also in the remote parts of the molecule Thus the hydrogens closest to the metal fragment are shifted downfield by 125 ppm in 62 and 148068 ppm in 52 when compared with 61 and 46 respectively The observed relatively large chemical shifts of the arene hydrogens proximal to the metal unit are not due to its anisotropy since its value in this area of space is (if anything) shielding5152 In addition the remote hydrogens in 52 are deshielded by 055033 ppm relative to the corresponding nuclei in 46 clearly substantiating the aromatization of the overall system upon metal complexation that was seen by structural analysis These pronounced chemical shift changes are diagnostic and greatly aided the spectral interpretations of the photochemically induced haptotropic shift experiments described in Sections 21 and 22 as illustrated for the isomerization between 52 and 53 (Scheme 217)

Scheme 217 Chemical Shift Changes in the Isomerization of 52 to 53

These NMR measurements were augmented by NICS calculations carried out in collaboration with Professor Amnon Stanger at the Technion in Haifa NICS data have the advantage that they indicate the extent of (anti)aromaticity even in rings for which the molecule has no hydrogen probe in the classical NMR experiment in this case the cyclobutadienes Computational details are given in Chapter 4 The experimentally determined proton NMR data for the series of silylated linear phenylenes from [2] to [5] and their metallated analogues in addition to the corresponding NICS(1) values of the respective parent phenylenes are shown in Figure 27 All compounds in Figure 27 are known except for the hypothetical biphenylene(CpCo) 64 which is included for comparative purposes Metalloaromatization is pronounced as all rings of the phenylene exhibit diminished or more negative NICS numbers signaling increasing aromatic and decreasing antiaromatic character respectively Again the effect is most pronounced on the rings closest to the metal bound unit tapering off (but never disappearing) with distance Most illustrative in this respect is 44 in which the penultimate and ultimate rings away from the Co still show decreases in the NICS values of 06 and 05 ppm respectively Interestingly the sum of all NICS values of 44 (ldquototal NICSrdquo13c) ndash91 is less negative than that of 21 ndash132 suggesting that 21 is more aromatic hence more stable as observed experimentally This may be fortuitous and the issue is addressed further in Section 24 Finally a caveat regarding the unusually large negative NICS values associated with the CpCo-complexed cyclobutadiene rings As pointed out by Solagrave in connection with a related study of (benzene)Cr(CO)3 which produced similar numbers53 there are local ring currents associated with the extra electrons involved in the metal to π-ligand

CoTMS

TMS796675674

678

436 CoTMS

TMS747683724

662

444

310 365 nmsunlight

30ndash50oC

52 53

- 29 -

bonding that lead to an overestimation of aromaticity Therefore to corroborate the general conclusions of metalloaromatization of this (and all other rings) in Figure 27 Stangerrsquos NICS scan method was applied54 This procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (NICSXY) and out-of-plane components (NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their

Figure 27 Experimental 1H-NMR (C6D6 blue) and computed NICS(1) (green) values for linear phenylenes and their corresponding CpCo complexes The experimental data are for the silylated

derivatives shown The NICS data are for the parent systems interpretation The data presented in Chapter 4 confirm the conclusions of this section While not reflective of ring current effects the values of the 13C chemical shifts for the linear phenylene(CpCo)complexes do provide some insight into the nature of the

- 30 -

σ-framework Comparing complex 19 with parent ligand 60 one observes two general phenomena (Figure 28) The most apparent is the upfield values for the cobalt-bound cyclobutadiene carbons (~74ndash78 ppm) in 19 arising from the local anisotropic shielding effect of the metal (vide supra) Secondly the carbon atoms in the four-membered ring not bound to the metal exhibit large deshielded values (144ndash149 ppm) This effect also seen in ligand 60 arises from the rehybridization6 of the cyclobutadiene sp2 orbitals and is observed in all phenylene topologies A comparison of the 13C-NMR data for the linear [3]- [4]- and [5]phenylene(CpCo)complexes with their respective parent ligands is given in Chapter 4

Figure 28

13C-NMR data for complex 19 and parent silylated ligand 60 Values are in ppm 24 Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift How does the CpCo moiety migrate from one cyclobutadiene unit to the next Two extreme alternatives present themselves a least-motion movement across the intervening arene unit or a more circuitous pathway along the periphery The latter is prevalent in other computed haptotropic shifts56-57 in particular those occurring in (arene)Cr(CO)3 complexes all of which choose peripheral trails56 In these the metal typically moves straight to the edge to adopt an η4 (often described as η1) trimethylenemethane-like transition state on the way to a neighboring ring as illustrated for the η6-η6 hopping in naphthaleneCr(CO)3 summarized in Scheme 218 More relevant is the computed course of the η6-η6 interconversion of (biphenylene)Cr(CO)3 (Scheme 219)57 The metal slides from the (near)center of one benzene ring to the quaternary (four-membered) ring carbon to reach a distorted trimethylenemethane maximum and then proceeds to the edge of the bridging cyclobutadiene bond This species represents a minimum on the potential energy curve and adopts an η2-like complexed cyclobutadiene topology (ldquoquasi-η4rdquo) from which it continues by the microscopic reverse on to the other benzene nucleus The relevance of these findings with respect to the intercyclobutadiene hopping of CpCo along the phenylene frame was not clear at the outset of the work described in this section The CpCo fragment has a different electronic requirement from Cr(CO)3 and interring migration in arenes (and related systems) involves aromatic electron counts of all intervening circuits

Scheme 218 Migration of Cr(CO)3 Across Naphthalene

- 31 -

Scheme 219 Migration of Cr(CO)3 Across Biphenylene

DFT calculations were carried out in collaboration with Professor Thomas Albright at the University of Houston In these studies using B3LYP 3-21G (carbonhydrogen) and LANL2DZ (cobalt) basis sets the metal fragment was placed 18 Aring above the π system with energy minimizations carried out every 02 Aring along the frame of the parent linear phenylene in question When transition states and local minima were located their structures were refined with the B3LYP 6-31G (hydrogen) 6-113G (carbon) and LANL2DZ (with inclusion of cobalt f-orbitals) basis sets More computational details are given in Chapter 4 The resulting potential energy surface for the thermal rearrangement in the parent linear [3]phenylene(CpCo)system is shown in Figure 29 Figure 210 contains enlarged images of the transition states and intermediate structures The haptotropic shift begins with the (η4-cyclobutadiene)CpCo global minimum (labeled ground state GS) assigned a relative value of 000 kcalmol An η2-cyclobutadiene transition state (TS 1) 269 kcalmol higher in energy than GS is passed before reaching a local minimum (LM) that lies 109 kcalmol above GS LM features CpCo coordinated unsymmetrically η4 to the central benzene ring thus avoiding an unstable 20 electron η6-benzene configuration (not shown) which when explicitly calculated proved to lie 36 kcalmol above LM From LM a symmetry-related second η4 structure is reached via an η3-benzene transition state (TS 2 barrier 14 kcalmol) that symmetrizes the ldquoleftrdquo with the ldquorightrdquo half of the molecule LM is 249 kcalmol higher in energy than GS The shift is completed through the reverse of the initial two movements through LM and TS 1 on the other side of the ligand to reach the second cyclobutadiene ring Thus as for Cr(CO)3 (Scheme 219) CpCo migrates along the edge of the linear phenylene but because of its differing electronic needs through distinctly different intermediates and transition states Most obvious is the internal η2-cyclobutadiene TS 1 which for Cr changes to a peripheral η2-intermediate The calculated rate determining barrier of 269 kcalmol (GS to TS 1) is slightly higher than that measured for the reversal of 53 to 52 (~23 kcalmol) Part of this discrepancy may be due to ground state activation of 53 which is ~2 kcalmol less stable than 52 The LM structure has some resemblance to the isolated η4-CpCo angular [3]phenylene 23 (Section 12) Its location in an energetic well of ~14ndash16 kcalmol (TS 1 and TS 2) suggested that it may be observable at low temperature This investigation is detailed in Section 25

- 32 -

Figure 29 Calculated potential energy profile for the thermal η4η4 haptotropic shift in linear [3]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

0

5

10

15

20

25

30

1 2 3 4Reaction Path

Co

Co

C o

C o

GS η

4

LM η

4

TS1 η

2

TS 2 η

3

00

269

109

249

Key - Global MinimumGround State (GS)- Local Minimum (LM)

- Transition State (TS)

122

3 34 4

- 33 -

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 34 -

(d) Transition state 2 η3-benzene (249 kcalmol)

Figure 210 Optimized structures and relative energies for the linear [3]phenylene(CpCo) haptotropic shift Carbon atoms are shaded grey hydrogens light grey and cobalt blue Bond

lengths are in Aring The potential energy profile for the thermal shift in the linear [5]phenylene(CpCo) system was calculated in the same manner and is shown in Figure 211 Images of the intermediates and transition states are depicted in Figure 212 Placing the metal fragment on the inner cyclobutadiene ring resulted in the lowest energy structure and was therefore set as the global minimum (GS) Two distinct haptotropic migrations inner-to-inner and inner-to-outer cyclobutadiene are now possible (Section 21) Beginning at GS the metal can proceed in the direction of TS 2 or TS 3 respectively both of which are η2 with similar barrier heights (~36 kcalmol) The former pathway is degenerate and continues from TS 2 to η4-LM 1 and then via η3 central benzene TS 1 to the symmetry related corresponding LM 1 TS 2 and finally GS involving the opposite inner four-membered ring The rate determining barrier for this process is 359 kcalmol clearly too high to be measurable by NMR techniques as found for 212838 Interior-to-exterior shifting of the cobalt continues from TS 3 on to η4-benzene LM 2 The η3-TS 3 is traversed before the second η4η2

sequence (LM3 and TS 5 respectively) ultimately leading to LM 4 which is the outer

- 35 -

cyclobutadiene coordinated structure and represents the photoisomeric species observed experimentally in Scheme 23 The computed rate-determining barrier (TS 3) of 263 kcalmol for the reverse reaction of LM 4 to GS is close to the experimentally measured values of 256ndash276 kcalmol for the derivatives in Table 21

Figure 211 Calculated potential energy profile for the η4η4 haptotropic shift in linear [5]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

40

Reaction Path

263

0

5

10

15

20

25

30

35

C o

C o

C o

C o

Co

Co Co

C o

C o Co 360 370

359 357

367

97

203 190 196

1 2 3 4 5 6 7 8 9 10

TS 1 η

3

LM 1 η

4

TS 2 η

2

GS η

4 00

TS 3 η

2 TS 4 η

3 TS 5

η2

LM 2 η

4 LM 3 η

4

LM 4 η

4

Key- Global MinimumGround State (GS)

- Local Minimum (LM)

- Transition State (TS)

- 36 -

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 37 -

(d) Transition state 4 η3-benzene (367 kcalmol)

(e) Local minimum 3 η4-benzene (190 kcalmol)

- 38 -

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 39 -

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

(i) Local minimum 1 η4-benzene (190 kcalmol)

- 40 -

(j) Transition state 1 η3-cyclobutadiene (356 kcalmol)

Figure 212 Optimized structures and relative energies for the linear [5]phenylene(CpCo) haptotropic shift Structures for the inner-to-outer cyclobutadiene migration are given by (a)ndash(g)

Species (h)ndash(j) are involved in the interior-to-interior four-membered ring pathway Carbon atoms are shaded grey hydrogen atoms light grey and cobalt blue Bond lengths are in Aring

Why does CpCo prefer complexation to the internal cyclobutadiene that is GS (as represented by 21 and 42) over LM 4 (as represented by 44 and 45) Calculations show that the energies required to distort linear [5]phenylene to the geometries found in

- 41 -

the complexed isomers are very similar (16 versus 14 kcalmol) Hence the answer must rest on electronic grounds Indeed extended Huumlckel calculations reveal that the overlap populations between the frontier orbitals on the CpCo fragment and the HOMO and the LUMO of the π system are greater for GS (00793 and 00745 respectively) than for LM 4 (00556 and 00517 respectively) A didactically more instructive valence bond view recognizes that metalloaromatization of the inside four-membered ring allows the formulation of more resonance forms that avoid antiaromatic cyclobutadiene circuits A full list of these resonance forms as well as details of the EHMO calculations are given in Chapter 4 25 Low Temperature Photochemical Studies of the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes Of the various participating species in the mechanism for intercyclobutadiene migration (Section 24) specific attention was focused on the η4-benzene intermediates that occur in both the linear [3]- and [5]phenylene haptotropic shifts These structures are energetic local minima on the reaction profiles for both systems and were of considerable intrinsic interest not only as reactive intermediates in this manifold but also because of their relationship to the isolable angular [3]phenylene(CpCo) complex 2329 (Figure 213) Figure 213 (a) Calculated structure for the η4-benzene linear [3]phenylene(CpCo)intermediate

in the haptotropic migration (b) Crystal structure of η4 angular [3]phenylene (CpCo) 23

While rare a handful of other η4-benzene-metal complexes have been isolated (Figure 214) For example two related iridium based systems benzene(CpIr) 6658 and benzene triphos(Ir) 6759 are known As expected ligation causes significant shielding of the hydrogens in the η4 portion of the ligand especially the terminal positions The η4 intermediates in the haptotropic shift are situated in wells on the potential energy surface that are ~17 kcalmol deep for the linear [5]- and ~15 kcalmol for the linear [3]phenylene complexes These values are large enough that such species might be observable by NMR spectroscopy if irradiation of the starting materials were performed at low temperature and if the excited state would relax selectively to these intermediates As a suitable candidate with which to explore this possibility the partly symmetric tetrasilyl complex 19 was chosen The generation of anticipated desymmetrized 68 would be readily detected by the appearance of 11 new singlets in the 1H- and 23 new peaks in the 13C-NMR spectra (Scheme 220)

(a) (b)

- 42 -

Figure 214 Selected relevant examples of isolated η4-benzene complexes and their proton NMR chemical shifts (ppm)

Scheme 220 Low Temperature Irradiation Experiment Designed to Generate η4-Benzene Intermediate 68

Construction of a satisfactory setup to allow for the planned low temperature irradiation was not trivial An optimal experimental configuration however was devised utilizing three pieces of equipment each of which is shown in Figure 215 The first was a custom-made Pyrex Dewar flask small enough to adequately contain an NMR tube Cooling was achieved by means of a Neslab refrigerated circulating bath Thirdly a Rayonet Photochemical Reactor was used as the light source The sample was first placed inside of the Dewar flask and cooled to the required temperature inside of the Rayonet Once cold irradiation was carried out for the desired length of time When complete the sample was transported cold to the NMR laboratory and very quickly placed inside of a pre-cooled NMR probe for analysis A solution of complex 19 was irradiated at ndash65 degC as described and its 1H-NMR spectrum recorded at ndash30 degC revealing a dramatic change The signals for 19 had almost entirely vanished and a set of new peaks appeared The new aromatic resonances were comprised of two sharp singlets at δ = 708 and 644 ppm and a broad singlet at δ = 558 ppm all of which integrated for 2 hydrogens each Another broad

649

586

316

H H

Co544

66 67 23

Ir

P(Ph2)P(Ph2) P(Ph2)

H

H

H

625

594

350

Ir

H

H

H

- 43 -

Figure 215 Cold irradiation experimental setup consisting of (a) Pyrex Dewar flask (b)

refrigerated circulating bath (c) Rayonet Photochemical Reactor with Pyrex Dewar vessel placed inside

(a) η

4 (b) η

4 (c) η

4

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

New peaks

L L

- 44 -

Figure 216 Stacked plot of the aromatic 1H-NMR spectral region recorded after the cold irradiation of 19 in toluene-d8 Peaks for 19 are indicated by blue new peaks by red arrows

Impurities are marked with and traces of free ligand 60 with L The scale is in ppm

singlet at δ = 398 ppm (5 H) was assigned to a new Cp group (Figure 217) and two new TMS singlets (9 H each not shown) were also present The new broad Cp absorption displayed peculiar behavior gradually moving to higher field (∆δ ~ 08 ppm for Cp-H) on warming from ndash30 degC to 10 degC (Figure 217) The broadened singlet at δ = 558 ppm showed similar albeit much attenuated behavior At room temperature all new peaks had disappeared leading to regeneration of the original spectrum of 19

Figure 217 Stacked plot of the Cp spectral region in the cold irradiation of 19 in toluene-d8 Peaks for molecule 19 are indicated by blue the new peaks by red arrows The scale is in ppm

In addition to these NMR observations a remarkable change in color from the redmaroon of 19 to olive green took place during the course of this experiment (Figure 218) Indeed the UV-Vis spectrum of the low temperature species is strikingly different from that of 19 showing a large broad absorbance band centered in the visible region

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

19

THF

- 45 -

Figure 218 Color change during the low temperature irradiation of 19 (a) Before irradiation (b) After irradiation

Complex 19

Low Temperature Species

0

02

04

06

08

1

12

14

16

18

2

400 430 460 490 520 550 580 610 640 670 700

Wavelength (nm)

Ab

sorb

an

ce

Figure 219 UV-Vis spectra (toluene) of 19 (at rt) shown in blue and the new compound (at ~

ndash30 degC) shown in red

at 654 nm (Figure 219) Warming the sample to room temperature restored its original red color While the observation of a new species was gratifying the NMR data posed a puzzle as they were clearly incompatible with (a static) structure 68 Instead they pointed to a molecule exhibiting mirror (or ldquotop-downrdquo) symmetry along the long molecular axis as in 19 itself The two most obvious candidates 69 and 70 (Figure

(a) η

4 (b) η

4

- 46 -

220) were ruled out as the first could not be found during the computations underlying Figure 29 and the second actually constitutes the transition state TS 1 for the thermal reverse process

Figure 220 Possible (but unlikely) structures of correct symmetry for the low temperature

photoisomer of 19 In the hope to shed further light on the nature of purported 68 low temperature 13C in conjunction with 2-D NMR (HSQC HMBC) experiments were carried out These data led to the tentative assignments shown in Figure 221 Assuming the presence of top-down symmetry as surmised by the proton spectra one would have expected to observe nine phenylene carbon signals The actual spectrum however contains only six peaks The Cp line was broadened to the point of being barely visible and no crosspeaks for the absorption at δ = 556 ppm were seen by 2-D NMR spectroscopy

Figure 221 Partial assignments of 1H-(italicized) and 13C-NMR signals of 68 The ldquotop-downrdquo plane of symmetry is indicated by the dashed purple line HMBC δ = 643 ppm correlates with δ = 1461 and 1521 ppm δ = 708 ppm correlates with δ = 1477 and 1508 ppm δ = 033 ppm

correlates with δ = 1477 ppm and δ = 036 ppm correlates with δ = 1461 ppm HSQC δ = 643 ppm correlates with δ = 1121 ppm δ = 708 ppm correlates with δ = 1227 ppm and δ = 398

ppm correlates with δ = 85 ppm The connectivity of the CpCo to the central ring is left intentionally unspecified and the choice of positioning it to the left of the center hydrogens (blue)

SiMe3

SiMe3

H

Me3Si

Me3Si

H

Co

398 (br)

HH

1461

~85 (br)

708

H

556 (br)1508

= Unobserved 13C signals

H

H

Mirrorplane

6431477 1521

033036

11211227

- 47 -

arbitrary Similarly the assignments of the groups of ldquoleftrdquo and ldquorightrdquo benzene signals are tentative and might be inverted The carbons marked could not be observed

It is thus clear that we are dealing with an unusual species and if it is 68 the molecule must be partly (but not completely) fluxional around the central ring Returning to the computed energy profile in Figure 29 one notes that central η4η4-benzene fluxionality via TS 2 with a barrier of 140 kcalmol is presaged This process which causes ldquoleftrdquo-ldquorightrdquo but not ldquotoprdquo-ldquobottomrdquo symmetrization is unlikely to be responsible for the above data as it should have given rise to two 1H-NMR singlets for the central hydrogens However considering the expected relative closeness in the respective chemical shifts of the anticipated signals (see Figure 214) accidental isochronism could not be ruled out Consequently low temperature irradiation experiments were executed with 52 in which the ldquoleftrdquo-ldquorightrdquo option of symmetrization was obviated by the substitution pattern while leaving the ldquotoprdquo-ldquobottomrdquo option intact (Scheme 221) As Scheme 221 Low Temperature Irradiation of 52 and Possible Pathways for Fluxionality of

Intermediate 71

indicated in color the latter would provide a diagnostically simple proton spectrum of only four phenylene signals The former on the other hand should show eight such peaks A potential complication of this experiment was the possibility of two regioisomeric (and non-interconverting) cobalt species located on either side of the central six-membered ring (Scheme 222) In the event the spectra shown in Figure 222 were obtained At ndash60 degC in

HH

CoTMS

TMS

CoTMS

TMS

TMS

TMS

Co

TMS

TMS

CoTMS

TMS

Co

TMS

TMS

Co

Top-bottom

cold hν ∆

Lef t-right

52 53

∆

71

or

H

HH

H

H H

H HH

HH H H

H

- 48 -

addition to unreacted 52 and photoisomer 53 a new species formed the spectral features of which implicate 71 as a ldquotop-bottomrdquo symmetrizing species Specifically the

Scheme 222 The Two Possible Regioisomers of 71 ldquoLeftrdquo and ldquoRightrdquo

71

52

53 53

53

52

TMS

TMS

Co

TMS

TMS

Co

TMS

TMS

Co

71

TMS

TMS

Co

or

Right Lef t

ndash60 degC

ndash50 degC

ndash40 degC

ndash30 degC

53

- 49 -

Figure 222 Stacked plot of the aromatic spectral region in the cold irradiation of 52 in toluene-d8 Peaks for molecule 52 are marked by blue arrows 53 in red and 71 in green Trace amounts

of free ligand bis(trimethylsilyl) linear [3]phenylene] 46 are denoted with L The scale is in ppm

unsubstituted benzene terminus hydrogens exhibit an AArsquoBBrsquo pattern at δ = 647 ppm which integrate for 4 hydrogens The central ring hydrogens appear as a broad singlet at δ = 557 ppm (2H) and the silylated terminus as a singlet at δ = 632 ppm (2H) Warming the reaction mixture to 10 degC led to the gradual disappearance of 71 with a concomitant increase of the signals assigned to 52 and 53 This experiment confirms the conclusions drawn as a result of the low temperature irradiation of 19 namely that a ldquotop-bottomrdquo symmetrizing species is generated Remarkably in view of the possibility of two regioisomers (Scheme 222) only one set of peaks is observed indicating that the excited state of 53 relaxes to settle on only one side of the central ring Which side is a matter of speculation Figure 223 compares the 1H chemical shifts of 71 with those of 68 and for calibration 52 53 and free ligands 46 and 60 For the first pair it is clear that the two species are very similar with almost identical chemical shifts of the relevant hydrogens taking into account the considerable deshielding effect of TMS substitution on the unsubstituted terminus in 73 (~07 ppm cf 52 vs 53 46 vs 60) Arguably placing the CpCo moiety to the ldquoleftrdquo as depicted in 68 and 71 aromatizes the proximal benzene by η2-complexation of the adjacent four-membered ring leaving considerable benzocyclobutadiene character on the ldquorightrdquo consistent with the associated chemical shifts

- 50 -

CoTMS

TMS796675674

678

CoTMS

TMS747683724

662

Co

TMS

TMS

52

71

53

424

642

557 632652

436 444

Co

TMS

TMS

68

398

556 643708

TMSTMS

TMS

TMS684607619

645

46

assignmenttentative

TMS

TMS

TMS

TMS623 685

60

TMS

TMS

TMS

TMS

Co

691 795745

19

441

Figure 223 1H-NMR chemical shift comparison of 68 and 71 with other relevant species A plot of the changes in concentration of 52 53 and 71 with temperature is shown in Figure 224 Within (the considerable) error and considering the unusual magnetic behavior of 71 (vide infra) it appears that the latter converts mainly to 52 in the temperature regime in which 53 is stable with respect to its thermal reverse to 52 This observation may be interpreted as indicating a lower barrier for Co migration from the center ring to the more stable cyclobutadiene haptomer

- 51 -

0

1

2

3

4

5

6

7

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Inte

gra

tio

n v

s I

nte

ra

l S

tan

da

rd

52

53

71

Figure 224 Plot of the concentration changes of 52 53 and 71 with temperature measured by the relative integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively

The ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100)

Another plot this one showing the ratios of 52 53 and 71 with respect to each other is given in Figure 225 The disappearance of 71 with rising temperature is illustrated by the increase in the ratios of 5271 and 5371 As indicated by the steep slopes the conversion of 71 into 52 and 53 is particularly fast between ndash10 and 0 degC That complex 52 is preferentially formed is again confirmed by the escalating 5253 ratio While these data do not provide a definitive answer for the location of the CpCo they are consistent with the plots shown in Figure 224 and the above discussions

- 52 -

0

1

2

3

4

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Rel

ati

ve

Inte

gra

tio

n

5271

5371

5253

Figure 225 Plot of the ratios of 52 53 and 71 against each other with temperature measured by the integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively The

ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100) Having established the topological aspects of 68 and 71 attention was turned to their peculiar NMR characteristics in the vicinity of the metal ie the broad peaks for the central hydrogens and the CpHs the broad Cp-carbon line the inability to observe 13C signals for the central benzene ring and the temperature dependent drifting of (particularly) the Cp absorption A trivial (and ultimately unsatisfying) explanation for at least peak broadening was the presence of trace paramagnetic metallic impurities60 that might have been generated during the irradiation process Spin exchange preferentially Co-based might affect the center atoms in 68 and 71 more than the remainder of the molecule although it should also cause line broadening in the isomers 19 and 52 and 53 respectively Experimentally the presence of such species was made unlikely by executing the cold irradiation experiment of 19 in the presence of the radical trap 13-cyclohexadiene which produced spectra identical to those described earlier An attractive alternative that might explain the data and in addition provide a mechanism for ldquotop-downrdquo exchange is of the intervention of triplet state cobalt species The ability of metals to change their electronic spin state and the consequences of this phenomenon on organometallic structure and reactivity are well documented61

18-Electron CpCo complexes are ground state singlets but their 16-electron counterparts accessed typically by ligand dissociation have more stable triplet configurations62 A number of CpCo and related Co species have also been reported in

- 53 -

which singlets are in thermal equilibrium with paramagnetic triplets by intersystem crossing63 Such complexes display spectral behavior very similar to that seen for 68 and 71 For example 7263b exists as a mixed spin state system in which the singlet predominates at room temperature in solution (Figure 226) On heating the triplet becomes increasingly populated shifting and broadening its NMR signals Cooling the solution back to room temperature reverses these spectral changes In addition to complexes of cobalt analogous observations have been reported for other metals such those based on hafnium64 copper65 ruthenium66 and tungsten67

Figure 226 Temperature dependent chemical shifts in CpCo derivative 72 in toluene-d8

(marked as S on the plot) The scale is in ppm

Consideration of these examples would then suggest that 6871 undergo ldquotop-downrdquo equilibration through a triplet 16-electron intermediate or that 6871 themselves are triplets or have thermally accessible triplet states from which fluxionality might occur Since the relaxation times (T1) of paramagnetic systems60a are much shorter compared to their diamagnetic counterparts measurement of this property was thought to be informative The T1 values for the proton in 68 were determined via a standard inversion recovery experiment44 and are given in Table 24 (cf Figure 220) in comparison to p-terphenyl60b

Co

CoPMe3

72

- 54 -

Table 24 1H-NMR Relaxation Times in Intermediate 68 at ndash30 degC

Resonance (ppm) T1(s) 711 2309 646 0997 556 005 398 0108

In consonance with the associated line broadening the relaxation times of the Cp

(δ = 398 ppm 0108 s) and central ring hydrogens (556 ppm 005 s) are much smaller than those of the remaining phenylene ligand (711 and 646 ppm 2309 and 0997 s respectively) the latter in turn comparing well with the values in p-terphenyl With this corroborative evidence in hand the question whether the species is itself a triplet or is in thermal equilibrium with such was addressed The answer can be obtained by using a Curie-like graph68 in which chemical shifts are plotted as a function of temperature65 A linear relationship corresponds to the presence of a triplet compound while curved behavior is indicative of a singlet-triplet equilibrium Plotting the chemical shifts of the Cp hydrogen of 68 and 71 against the inverse of temperature (Figure 227) gave distinctly curved lines supporting the notion that these species are in thermal equilibrium with their triplets The exact nature of these species however remains to be determined

156

395404

345

p-Terphenyl

- 55 -

3

32

34

36

38

4

42

44

46

00036 00038 0004 00042 00044 00046 00048

1T (K -1

)

Ch

em

ica

l S

hif

t (p

pm

)

71

68

Figure 227 Plot of the Cp chemical shift (toluene-d8) of 68 and 71 versus the inverse of temperature

DFT calculations have commenced in an attempt to find a plausible structure for such a triplet cobalt species and with it possibly arrive at a mechanism for the fluxional behavior of 68 and 71 These studies are being carried out in collaboration with Professors Tom Albright of the University of Houston and Vincent Gandon of the Universiteacute Paris-Sud 11 Preliminary results at the B3LYP6-31G(dp) and BP866-31G(dp) levels suggest the η2-cyclobutadiene structure depicted in Figure 228 It is apparent that this species corresponds topologically to singlet TS 1 in Figure 29 and 70 in Figure 220 endowed with the symmetrical requirements dictated by the experiments

- 56 -

Figure 228 Calculated structure of a triplet η2-cyclobutadiene linear [3]phenylene(CpCo)

One can therefore envision fluxionality between the two ldquotoprdquo and ldquodownrdquo η4-benzene structures via the intermediacy of a triplet η2-cyclobutadiene (Scheme 223) Further Scheme 223 Conversion of ldquoTop-Downrdquo η4-Haptomers of 68 Via a Triplet η2-Cyclobutadiene

Intermediate

computations are required to pinpoint the minimum energy crossing points between the singlet η4 and triplet η2 structures and to explain why this triplet does not collapse to the CpCo cyclobutadiene isomer This work is in progress 26 Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 All of the linear phenylene(CpCo) complexes mentioned thus far share one common feature a single CpCo unit bound to the phenylene scaffold However since there are one or more additional cyclobutadienoid rings in the series the question arises whether it might be possible to bind more than one metal fragment to the ligand If so what would be the structural consequences Would be there further metalloaromatization Would such systems be capable of light-induced haptotropism and if so how would the metals move relative to the ligand and to each other Finally would such complexes mimic structurally the variety of arrays obtained in the reaction of 29 with Fe2(CO)9 (Scheme 15) Since the linear phenylenes become increasingly more antiaromatic with size the optimal candidates for preparing such multi-metallic systems should be the higher members of the series Indeed evidence for double CpCo attachment was obtained in the form of the minor by-products 73 and 74 (Scheme 224) obtained during the

Scheme 224 Side Products in the Preparation of Linear [4]- and [5]Phenylene(CpCo)

- 57 -

Complexes by Cobalt-Catalyzed Cyclization

preparation of 20 and 21 respectively (Scheme 13) These Diels-Alder type adducts of a third BTMSA molecule to the π-frame can be envisaged to be derived from 75 and 76 respectively in which the six-membered ring flanked by the two CpCo(cyclobutadiene) units would be expected to have an unusual (biradicaloid) electronic structure Evidence for the feasibility of such arrays rests on the unique black-red syn-bis(irontricarbonyl) compound 77 whose structure was determined by X-ray analysis69 With reasonable quantities of 19 in hand the possibility of ligating a second CpCo unit to it was explored This idea was further encouraged by the observation that crude samples of bis(trimethylsilyl) linear [3] phenylene(CpCo) complex 53 contained a very small (3 ) peak at mz = 618 an exact match for the mass of a doubly metallated analog Consequently 19 was treated with one equivalent of CpCo(C2H4)2 in benzene to afford a reddish black solid (Scheme 225) The mass spectrum data exhibited a

Scheme 225 Preparation of Complex 78 from Complex 19

TMS

TMSTMS

TMS

CoCpCo(C2H4)2

22h 70 oC C6H6Linear [3]TMS4(CoCp)2

5619 78

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

74

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

73

TMS

TMS

TMS

TMSCoCpCpCo

76

TMS

TMS

TMS

TMSCoCpCpCo

75

Ph

Ph

Ph

Ph

Fe(CO)3Fe(CO)3

77

- 58 -

molecular ion peak at mz 762 corresponding to 19(CpCo)2 The 1H-NMR spectrum (acetone-d6) revealed four sharp singlets integrating in the ratio 410236 indicative of a highly symmetrical structure The chemical shift of the benzene termini (736 ppm) suggested that these rings have significant aromatic character and is similar to the value of 745 ppm seen for the hydrogen positioned farthest away from the CpCo in 19 (Figure 27) Similarly the 13C signals of the terminal rings in 78 (1505 1454 and 1258 ppm) are analogous to those from the corresponding terminal ring in 19 (1484 1433 and 1256 ppm Figure 28) Detailed analysis of 78 with two-dimensional NMR techniques (HSQC and HMBC) allowed for a complete assignment of all peaks in the 1H and 13C spectra (Figure 229) The strongly shielded (relative to the free ligand) proton (481 ppm) and carbon (537 and 571 ppm) resonances assigned to the central benzene ring clearly showed that both cobalt fragments are coordinated to the phenylene ligand at this position Interestingly these data bear a very close resemblance to those of the corresponding diiron complex 31 (Scheme 15) and are compared in Figure 229 Its central 13C resonances (688 and 582 ppm) are shifted upfield in a manner akin to 78 although not quite as much reflecting the increased electron withdrawing ability of the Fe(CO)3 group relative to CpCo70 Complex 31 like 78 exhibits aromatized terminal benzene rings as indicated by its 1H (750 ppm) and 13C (1484 1446 and 1258 ppm) chemical shifts These spectral similarities make it likely that 78 and 31 are isostructural The only structural ambiguity pertains to the orientation of the two metal fragments with respect to the π ligand a problem that had been left undecided in the assignment of structure 31 ie 31a (syn) versus b (anti Scheme 15)27 These options for 78 are

- 59 -

CpCoTMSTMS

TMS TMS

H H039 (36)

537 1258822

270

1454571

1505

481 (2) 736 (4)489 (10)

TMS TMS

TMSTMS

H

(OC)3Fe

(OC)3Fe

CpCo

78

31a

750 (4)553 (2)

036 (36)H

220

1446

1258

1484

688582

2128

Figure 229 Comparison of 1H- and 13C-NMR assignments (ppm) for molecules 78 (acetone-d6) and 31 (1H acetone-d6

13C CDCl3) Proton chemical shifts are in red and carbon in blue Integrations for the proton resonances are in green HSQC for 78 δ = 039 ppm correlates with δ = 270 ppm δ = 481 ppm correlates with δ = 537 ppm δ = 489 ppm correlates with δ = 822 δ

= 736 ppm correlates with δ = 1258 ppm HMBC for 78 δ = 036 ppm correlates with δ = 1454 ppm δ = 481 ppm correlates with δ = 571 and 1505 ppm δ = 736 ppm correlates with δ = 571 1454 and 1505 ppm The placement of the cobalt atoms in 78 is tentative (see Figure

229)

Figure 230 Possible structures for 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

- 60 -

shown in Figure 230) Both equally exotic options are precedented in the literature and corroborated by X-ray structural analyses (Figure 231)71

Figure 231 Illustrative examples of complexes with two metal fragments coordinated to the same benzene ring

Bis(CpFe) complex 7972 and its rhodium analog 8073 contain [M2(syn-micro-arene)] units in which the metals are linked58 Molecule 79 consists of two CpFe units coordinated η4 to the boat-shaped benzene ring sharing ligating carbon atoms In contrast the CpRh fragments in 80 are bound in an allyl η3 manner and the arene also adopts a boat conformation On the other hand bis[tris(tert-butyl)]toluene(CpCo) complex 8174 and the related system 8275 both exhibit [M2(anti-micro-arene)] units in which η4 coordination between the benzene ring and each of the metal fragments takes place Here the metals share carbon atoms but now involving a sandwiched ligand The arene in 81 retains a planar aromatic geometry while the benzene moiety in 82 is bent into a highly distorted chair conformation Unfortunately model structures 79ndash82 do not exhibit diagnostic NMR properties that would provide a clear distinction between synanti and planarnon-planar topologies For example the 1H-NMR peaks for the toluene ligand in anti-complex 81 range from 400ndash380 ppm74 whereas the signals for the benzene moiety in syn-bis(CpRh) 80 appear at 400ndash330 ppm73 The 13C data are similarly inconclusive as illustrated by comparison of 78 (562ndash531 ppm for the benzene ring) with 79 (648ndash525 ppm)72b An interesting property of these bis(metal) arene complexes is fluxionality of the metal fragments by haptotropic shifts along the periphery of the aromatic ring as depicted in Scheme 226 In complex 79 the hexamethylbenzene ligand (bound η4η4

in the solid state) displays a single arene resonance at 588 ppm in its room temperature carbon NMR spectrum Cooling to ndash90 degC however produces two distinct arene peaks at 525 and 648 ppm (for the shared and single-metal-bound carbons respectively as shown in 79a in Scheme 227) Fluxionality was postulated to proceed through an η3η3 intermediate (79b) that is structurally similar to Rh complex 80 which is itself a fluxional species

Scheme 226 Examples of Fluxional Processes in Dinuclear Arene Complexes 79 and 80

82 81

80 (R = CH3)

79

- 61 -

Anti-bis(β-diiminate)Rh complex 83 shows similar mobility (Scheme 226)76 A mechanism for η4η4 migration of the anti-metal fragments was proposed using the lowest energy species found by DFT calculations In these compounds the anti-metal fragments convert between η4η4 (83a 83c 83e) structures by passing through η3η3

(83b) and η4η2 (83d) transition states The energy barrier for η4η4 migration in 83 was experimentally determined to be 6 kcalmol This value is in line with other experimentally measured syn and anti dinuclear ring slippage processes which are typically le ~10 kcalmol71-75 The possibility of fluxionality in 78 might be observable if asymmetric configurations such as 78c and 78d (Figure 231) represent the lowest energy forms since they entail NMR observable desymmmetrization of the ligand Unfortunately cooling 78 in the NMR probe to temperatures as low as ndash80 degC in toluene-d8 did not reveal any signs of signal decoalescence

- 62 -

Figure 232 Possible lowest energy forms of complex 78

Hoping that further light could be shed on the disposition of the CpCo moieties in 78 by chemical transformations a brief investigation of its reactivity was undertaken For example bis(metal) arene complexes have been shown to readily undergo arene exchange reactions71 In complex 81 for example the toluene ligand is displaced by benzene at room temperature74 However heating a sample of 78 to 120 degC in toluene-d8 did not lead to any changes in the NMR spectra Turning to potential photochemical activation 78 was irradiated at various wavelengths (300ndash365 nm) These conditions as well as ambient sunlight did not cause any changes in its 1H-NMR spectrum further documenting 78 as a rather inert species X-ray crystallographic analysis would appear to be the only method of resolving the identity of complex 78 Producing suitable crystals of this molecule however has proven extremely difficult and will be the subject of future investigations 27 Summary and Outlook The work presented in this chapter published as a communication77 has detailed the first examples of η4η4 intercyclobutadiene migration and detailed mechanistic studies of this unprecedented reaction The haptotropic shift was found to be an intramolecular process with the CpCo fragment undergoing various changes in hapticity for the thermal isomerization Low temperature photolytic studies have revealed the existence of a thermally unstable intermediate species the exact structure of which is uncertain These results point to what appear to be significant differences between the photo- and thermal haptotropic pathways Further work both experimental and computational will be required to elucidate the details of the photochemical reaction In addition to the studies of linear phenylene(CpCo) haptotropism a hitherto unknown complex containing two CpCo fragments bound to linear [3]phenylene was prepared and scrutinized in preliminary form Despite extensive characterization the structure of this complex with respect to the position of the metal centers remains elusive Future work will focus on the acquisition of a crystal structure

- 63 -

Chapter 3

Nickel-Catalyzed Insertion Reactions for the Preparation of [N]Phenacene Derivatives

31 Introduction Transformations involving metal insertion into the four-membered ring of the [N]phenylenes as discussed in Section 12 represent a significant mode of reactivity with a high potential for practical synthetic utility One specific application of this chemistry is the synthesis of the phenanthrene moiety via tandem metal insertion and alkyne cycloaddition to the four-membered ring (Scheme 31) Such a methodology Scheme 31 Potential Preparation of the Phenanthrene Group from the Alkyne Cycloaddition

with Biphenylene would be valuable for the preparation of PAHs possessing phenanthrene subunits but has remained fairly unexplored Only a few examples demonstrating this transformation have been detailed previously for biphenylene (7) (Scheme 32)

Scheme 32 Metal Catalyzed Alkyne Cycloaddition Reactions with Biphenylene

The first report of this process is by Eisch in 198533a who treated biphenylene with Ni(PEt3)4 and diphenylacetylene to produce 910-diphenylphenanthrene 84 Since then a number of metals have been shown to mediate this process19 Ni systems being most relevant to this chapter Thus for example 84 can also be made using an N-heterocyclic carbene-based Ni(0) catalyst78 Bis(diisopropylphosphino)ethane Ni(alkyne) species enable similar cycloadditions of fairly hindered (trimethylsilyl)alkynes sometimes involving more complex processes of silyl group migration79 while less hindered substrates lead to 84ndash8680a A mixed phosphinoaminoethane-chelated Ni species proved more reactive enabling cycloaddition of even the encumbered tert-butyl(phenyl)acetylene to furnish the corresponding phenanthrene80b With this background in mind our attention turned to applying this reaction to larger phenylene systems Of the various topologies of phenylenes at our disposal the angular version was

R1 R2

R2R1[M]

[M]

7 R R

R = Ph (84)

R = Me (85)

R = CH2OMe (86)

RR

[Ni]

- 64 -

particularly intriguing as it offered two extreme modes of alkyne addition (Scheme 33) In the first scenario exclusive attack at the outer periphery of the four-membered rings would produce the helical shaped PAHs known as helicenes (Scheme 33a)81

Scheme 33 Alkyne Cycloaddition with Angular Phenylenes to Produce (a) Helicenes or (b) Phenacenes

Reactions occurring only at the interior or ldquobayrdquo region (Scheme 33b) however would afford a class of compounds exhibiting a linear polyphenanthrene motif that are known as [N]phenacenes82 Unselective additions would result in mixed topologies Helicenes and their various derivatives constitute a well studied83 family of molecules and continue to be a popular area of research Phenacenes in contrast have been scrutinized much less in part because only four members of the parent series are known and because for N = 5 and 6 they are extremely insoluble84 Phenacene-based applications have been slow to develop but the first reports of the utilization of these molecules as functional organic materials suggest the beginning of a rich and promising field85 Thus in 2008 [5]phenacene (picene) was demonstrated to behave as stable high performance organic field effect transistor (FET)85b Currently the most common organic polycyclic benzenoid hydrocarbon-based FETs employ acenes which have a polyanthracene structure (Figure 31) The sensitivity

Figure 31 Linearly fused benzene topology of the acenes of these systems to air however has obstructed progress in this area86 For example pentacene a commonly used acene in FETs reacts readily with oxygen to form

+ RR

Helicenes

+ RR

Phenacenesn

R

R R R R

n

R

R

R

(a)

(b)

[N]Acenes

n

- 65 -

pentacenequinone a process that severely reduces device efficiency (Scheme 34)

Scheme 34 Degradation of Pentacene to Pentacenequinone Under Aerobic Conditions

Phenacenes on the other hand are much less prone to such decomposition pathways due to their higher HOMO-LUMO gap thus rendering them less reactive85b86a Their enhanced stability relative to acenes87 makes them better candidates for molecular electronic applications In a second seminal breakthrough [5]phenacene was very recently also found to behave as a superconductor at low temperature when doped with potassium85a This work paves the way for a new class of PAH-based superconducting materials in which phenacenes may play a key role

As this chemistry advances new synthetic methods for preparing derivatives of these molecules will be required in particular those bearing solubilizing andor otherwise functionally useful substituents The most general procedure for synthesizing phenacenes as developed by Mallory88 makes use of oxidative stilbene photocyclizations (Scheme 35)8388 In this transformation irradiation of the stilbene

Scheme 35 Generic Oxidative Stilbene Photocyclization Used to Prepare Phenacenes as Illustrated for Phenanthrene

moiety leads to conrotatory electrocyclic ring closure Trapping of the resulting intermediate with oxidizing reagents such as iodine or oxygen yields the desired phenanthrene subunit The requisite stilbenes are most generally accessible via the Wittig reaction as illustrated in the synthesis of [7]phenacene derivative 87 (Scheme 36) Although the yields for the photocyclization are typically reasonable (60ndash90 )85a the major drawback of this methodology is the numerous steps associated with preparing the functional groups required for the prerequisite Wittig reaction These

- 66 -

transformations serve to decrease the overall yield of the target molecule

Scheme 36 Synthesis of [7]Phenacene 87

While laborious Malloryrsquos method addresses successfully the problem of solubility As alluded to in Section 21 large PAHs become insoluble due to the increased π-π stacking forces that are experienced between aromatic rings The best solubilizing groups for the phenacenes were found to be sterically bulky groups located in the bay regions85a These modifications distort the phenacene framework from planarity thereby disrupting π-stacking and increasing solubility as demonstrated by the tert-butyl [7]phenacene 87 (Figure 32) This approach was applied to systems as large as [11]phenacene the current record in the series85a

Br

CH3t -Bu

1 BuLi2 DMF

Br

CH2

t-Bu

CHO

CH3t-Bu

PPh3

Br

+Wittig

t-Bu t-Bu

Br CH3 1 hν2 I2

t-Bu t -Bu

Br CH3

t-Bu t-Bu

Br H2C PPh3 Br

+

t-Bu t-Bu

OHC CH3

Wittig

t-Bu t-Bu

Br Br 1 hν2 I2

t-Bu t-Bu

Br CH3

t-Bu t -Bu

t-Bu t-Bu

87

1 NBS2 PPh3

- 67 -

Figure 32 Crystal structure of tetrakis(tert-butyl) [7]phenacene 87 Hydrogens are omitted for clarity

To test the viability of angular phenylenes as substrates in Ni catalyzed alkyne cycloadditions the simplest member 22 was chosen raising a number of questions First how many and what kind of products will be formed (AndashE in Scheme 37) Will there be inherent selectivity toward helicene C or phenacene E formation respectively If not can the reaction conditions be modified so as to induce such What will be the limitations with respect to the size of substituents especially in view of the crowded fjord and bay regions of D and E respectively The work presented in this chapter carried out in collaboration with Dr Zhenhua Gu89 explores these questions

Scheme 37 Possible Cycloaddition Products of Angular [3]Phenylene 22

22

[Ni]R R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

A B

C D E

32 Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene

Before embarking on the proposed chemistry the reactivity of 22 in the presence of nickel in the form of Ni(COD)(PMe3)2 in the absence of alkynes was queried Only starting material was recovered and there was no sign of dimerization (or oligomerization) to products of the type shown in Scheme 38 a mode of reactivity

- 68 -

readily attained by biphenylene and substituted derivatives33b

Scheme 38 Attempted Dimerization of Angular [3]Phenylene 22

In contrast exposing diphenylacetylene 88 to Ni(COD)(PMe3)2 and a small excess (109 equivalents) of angular phenylene 22 generated two products in the absence of any other (Figure 39) The first molecule 89 was the result of the cycloaddition of one diphenylacetylene at the bay region and the minor component The major product constituted tetraphenyl [5]phenacene 90 derived from 22 by double bay region attack The structures of both compounds were confirmed by X-ray analysis revealing highly distorted frames89 Scheme 39 Nickel Catalyzed Cycloaddition of Angular [3]Phenylene 22 to Diphenylacetylene

Yields Based on Diphenylacetylene

The outcome of this transformation was gratifying in its seeming simplicity and selectivity Thus it appeared that metal insertion occurred exclusively to bay region bonds heralding the discovery of a new phenacene synthesis The observation of relatively large amounts of 90 could be ascribed to increased reactivity of 89 relative to 22 possibly due to steric activation by the newly introduced bay region phenyl group To test this hypothesis 89 was subjected to the cycloaddition reaction conditions (Scheme 310) Surprisingly not only was this reaction slower than that of 22 but the expected phenacene 90 was only a minor product (6 ) Instead tetraphenylbenzo[c]chrysene 91 a regioisomer of 90 as confirmed by X-ray analysis89

+

+ +

Ni(COD)(PMe3)2

22

- 69 -

was isolated in 74 yield the result of non-bay alkyne cycloaddition to 89 Therefore 89 is not the precursor of 90 Rather there must be separate reaction pathways leading to each respective product

Scheme 310 Cycloaddition Reaction of 89 with Diphenylacetylene 88

A series of semi-quantitative experiments monitored by 1H-NMR spectroscopy was carried out to shed some light on this mechanistic problem First the reaction of angular [3]phenylene 22 with diphenylacetylene 88 in Scheme 39 was addressed Because dinuclear metallic activation of the strained C-C bond in biphenylenes has been implicated in a number of studies19 it was possible that the above mechanistic duality was caused by the presence of catalytic Ni2 species in addition to the ldquoregularrdquo mononuclear alternatives Alternatively double Ni insertion before cycloaddition might be responsible for one product whereas sequential ldquonormalrdquo activation might be the origin of the other Therefore the amount of initial Ni(COD)(PMe3)2 was gradually increased and the effect of this incremental change on rate and product ratios recorded As shown in Table 31 the speed with which 89 and 90 formed was roughly proportional to the amount of metal present while the product ratio stayed unchanged

Table 31 Variation of Catalyst Loading in the Reaction of Phenylene 22 with Diphenylacetylene 88 Reactions Were Carried Out with Equimolar Amounts of 22 and 88 in

THF-d8 at 40 degC

Run Ni(COD)(PMe3)2

(mol) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

Ratio of 8990

1 50 32 times 10ndash4 031 times 10ndash4 103 2 35 20 times 10ndash4 022 times 10ndash4 91 3 7 064 times 10ndash4 0064 times 10ndash4 100

Next the amount of diphenylacetylene 88 was gradually increased from 1 to 4 equivalents (Table 32) The outcome of this series of experiments was counterintuitive as it led to a larger preference for the production of monoadduct 89 suggesting a mechanistic bifurcation in which whatever Ni species is responsible for the eventual formation of 90 is sequestered by external ligand (in this case 88)

- 70 -

Table 32 Variation of Alkyne Equivalents in the Reaction of 22 (1 equiv) with Diphenylacetylene 88 in the Presence of 50 mol of Ni(COD)(PMe3)2 Experiments Were Run

in THF-d8 at 40 degC

Run 88 (equiv) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

8990

1 10 320 times 10ndash4 031 times 10ndash4 103 2 20 220 times 10ndash4 018 times 10ndash4 122 3 40 220 times 10ndash4 011 times 10ndash4 200

Following the reaction progress by NMR spectroscopy afforded additional insights Thus mixing the ingredients at room temperature left the phenylene component untouched Instead there was a near instantaneous displacement of COD by diphenylacetylene to produce Ni(PhCequivCPh)(PMe3)2 (92) and free COD in addition to the generation of Ni(PMe3)4

90 The speed with which this complex was formed implied that it might be the active catalyst precursor Consistent with this notion higher reaction rates were observed when the reaction in Scheme 38 was carried out with pure 9291 as the catalyst (50 mol) and 05 equivalent of 88 (Table 33 Run 2) In consonance with Table 32 the lesser concentration of available free alkyne increased the relative amount of 90 formed Conversely (Run 3) using Ni(COD)(PMe3)2 with an extra equivalent of PMe3 decreased the rates of formation of 89 and 90 and increased the ratio of 8990 consistent with ligand inhibition of the activation of 92 and the external ligand effect noted in Table 32 Table 33 Variation of Catalyst in the Reaction of 22 with Diphenylacetylene 88 and its Effect

on Reaction Rate Experiments Were Run in THF-d8 at 40 degC with 1 Equivalent of 22

Run Catalyst 88

(equiv)

Rate of formation of 89 (mol

Lmiddoth)

Rate of formation

of 90 (mol Lmiddoth)

8990

1 Ni(COD)(PMe3)2 10 320 times 10ndash4 031 times 10ndash4 103 2 Ni(PhCequivCPh)(PMe3)2 (92)

(05 equivalent) 05 1270 times 10ndash4 210 times 10ndash4 60

3 Ni(COD)(PMe3)2 (05 equivalent) + PMe3 (10 equiv)

10 088 times 10ndash4 005 times 10ndash4 163

Attention was then shifted to the reaction of monoadduct 89 with 88 as in Scheme 310 (Table 34) Here increasing the amount of alkyne and catalyst favors the formation of 91 consistent with an independent pathway At low concentration of alkyne it appears that 89 reenters the manifold of its generation and proceeds on to 90 Indeed following the change in the ratio of 9190 in Run 1 (Table 34) with time reveals a decrease from 47 to the eventual 22 as 88 is depleted

- 71 -

Table 34 Variation of Catalyst Loading and Alkyne Concentration in the Reaction of 90 with Diphenylacetylene 88 Reactions Were Run in THF-d8 at 40 degC

Run 88 (equiv) Ni(COD)(PMe3)2

(mol) 9190

1 10 50 2 2 30 50 15 3 30 10 25

The information obtained from these experiments allowed a narrowing of mechanistic possibilities For example dinuclear Ni activation only one possibility of which is shown in Scheme 311 was rendered unlikely by the absence of any observable changes in product distribution of the reaction in Scheme 39

Scheme 311 Generic Example of a Dual Mechanism Based on Mono- and Dimetallic Phenylene Activation

An alternative mechanism shown in Scheme 312 was in much better agreement with the results of the various control experiments The first step would be displacement of a phosphine in the initially dominant Ni-containing species 92 by angular [3]phenylene 22 inhibited by added PMe3 From 93 oxidative addition can take place to afford metallacycle 94 Why should bay region insertion be favored Arguably the regioselectivity of this step is controlled by the lesser steric hindrance in the resulting arene fragment or relative stabilization of the polarized Ni-C(α-

PhPh

Ph Ph Ph Ph

PhPh

NiL L

Ni(COD)(PMe3)2

NiNiL L L L

PhPh

2

Ph

Ph

Ph Ph Ph Ph Ph Ph

+

+22

89

90

91 90

- 72 -

biphenylene) bond in 94 by the electron withdrawing nature of the neighboring cyclobutadienoid ring This phenomenon in biphenylene is due to the rehybridization of the four-membered ring carbons to adopt relatively larger p character in the strained linkages hence larger s character (ie electron withdrawing) in the remaining bond and manifests itself most clearly in the relative acidity of the α-hydrogens7a This step is followed by migratory insertion and reductive elimination to produce molecule 96 the mechanistic bifurcation point One branch proceeds through presumably ligand-assisted metal dissociation to generate the relatively unreactive free 89 The second entails Ni migration92 and insertion into the bay region of the remaining four-membered ring (97) before the second cycloaddition occurs generating phenacene 90

Scheme 312 Possible Mechanism for the Alkyne Cycloaddition Reaction of Angular [3]Phenylene 22

The regioselective formation of 97 may again be sterically dictated or may involve anchimeric assistance by the bay-region phenyl group as sketched in Scheme 313 specifically 99

Scheme 313 Anchimeric Assistance on Route to [5]Phenacene 90

Ph Ph

PhPhPhPh

Ph

Ph

Ph PhNi

NiMe3P Ph

Ph

Ni

Me3P Ph

Ph

NiPMe3Me3P

Ligand exchangeOxidativeaddition

Migra toryinser tion

Reductiveelimination

Ph

Ph

Me3P

Ni migra tionOxidative addition

22

92

9394

96 89

9097

Ph Ph

Ni

Me3P

Ni(PMe3

Ph

Ph

minusNi(PMe3)

95

- 73 -

This type of metal coordination to the double bond of a proximal arene ligand is common and two examples are provided based on ruthenium94 and molybdenum95 (Figure 33)

Figure 33 Examples of complexes with phenyl groups coordinating to a nearby metal center Turning to the largely selective conversion of 89 to 91 (Scheme 310) requires the postulate of preferential insertion of the metal at the non-bay region and hence a different Ni species from that in 96 possibly a Ni(PMe3)(alkyne) moiety akin to that in 93 ie 100 (Scheme 314) Bay insertion would lead to metallacycle 101 and ultimately molecule 90 The expected large degree of steric repulsion between the phenyl groups in 101 should disfavor this reaction pathway On the other hand non-bay insertion to produce 102 should be relatively less impeded and would furnish 91 Another option for the generation of 90 from 89 would be reentering the pathway described in Scheme 312 facilitated at low concentrations of alkyne consistent with the data in Table 34

Scheme 314 Proposed Mechanism for the Alkyne Cycloaddition Reaction of 89

Ni

PhMe3P

PhPh

(Me3P)Ni

PhPh(Me3P)Ni

Ph

Ph

93 98

99

Ph Ph Ph Ph

90

+

Ph Ph

Ni

Me3P

97

- 74 -

While the above mechanistic perambulations appear plausible it should be stressed that they are speculative and may be restricted to diphenylacetylene 88 as the substrate Thus both 3-hexyne 103 and 14-dimethoxy-2-butyne 106 added to 22 less selectively than 88 to provide only the bay and non-bay monoadducts 104 and 105 and 107 and 108 respectively (Scheme 315)

Scheme 315 Reaction of Angular [3]Phenylene 22 with Other Alkynes

NiMe3P PMe3

Ph Ph+

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph

Ni(PMe)3

PhPh

Ni(PMe3)

Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

92 89

101

90

102

100

91

Ni

Ph Ph

PMe3

+

R

R

THF-d8 40 oCR

R22

Ni(COD)(PMe3)2

R

R

+

R = Et 104

R = CH2OMe 107

R = Et 103

R = CH2OMe 106 R = Et 105

R = CH2OMe 108

11 45 9 68

- 75 -

In view of these uncertainties recourse was taken to DFT computations delineated in the next section 33 Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene DFT studies were carried out in collaboration with Prof Vincent Gandon of the Universiteacute Paris-Sud 11 The B3LYP 6-31G(d) basis set was used for hydrogen and carbon atoms while LANL2DZ was used for nickel Before attempting to model the more complex alkyne cycloaddition reactions in Schemes 38 and 39 the basic Ni-catalyzed addition of the parent acetylene to biphenylene in the presence of PMe3 was studied (Scheme 316) The free energies

Scheme 316 Computational Modeling of Ni-catalyzed Addition of Acetylene to Biphenylene Free Energies (∆G KcalMol) are Relative to 109 Transition State Energies are Absolute Values

for This Step

NiMe3P PMe3

NiMe3P

NiMe3P

Ni

Ni

PMe3

PMe3

+

+ PMe3+

+ PMe3

+ 2 PMe3

+ 2

(00)

(281)(37)

(140)

(12)

NiMe3P PMe3

NiMe3P

NiNiPMe3Ni

PMe3

PMe3NiMe3P

PMe3

(727) (693) (476) (374) (394) (395)

Ni

Me3P

PMe3Ni

Me3P

Ni

Ni

Me3P

PMe3NiMe3P PMe3

(590) (532)

(157) (125) (150)

Most Accessible TS

+

7

114

110

113109

111 112

Ni

Me3P

(253)

Ni

PMe3

(242)

- 76 -

(∆G) of various possible catalyst structures consisting of an assortment of combinations of nickel PMe3 and acetylene as well as those of several possible transition states and the resulting products were calculated As is evident on inspection of the values in the first part of Scheme 316 a number of species were found to be very close in energy making it difficult to pinpoint a specific structure for the initial insertion step Bis(ethyne) nickel complex 109 was established as the lowest energy nickel species and was thus assigned a relative value of 0 kcalmol The most accessible transition state 110 features the oxidative addition of the Ni(PMe3)(C2H2) fragment 114 (+ 14 kcalmol) in which the alkyne is held exo to biphenylene The corresponding endo structure 111 was found to be just slightly higher in energy by 20 kcalmol as was the bisalkyne transition state 112 It is likely that biphenylene-NiL2 complexes (two of which were calculated at relative energies 242 and 253 kcalmol) lie on the way to these maxima93 Metallacycle 113 the structure ensuing from transition state 110 constituted the lowest energy product uphill from the starting 109 by 125 kcalmol but other alternatives are nearly isoenergetic Clearly however attack by Ni(PMe3)2 or Diels-Alder type cycloadditions are not likely From 113 the species proceeds smoothly by alkyne insertion-reductive elimination to the phenanthrene product a cascade associated with a large exergonic driving force Undaunted by the relatively complicated picture that emerged with biphenylene attention was turned to the original object of scrutiny the cycloaddition reaction between angular [3]phenylene 22 and diphenylacetylene 88 to produce [5]phenacene derivative 90 Modeled in the same manner as described above the metal insertion into the four-membered ring of 22 is shown in Scheme 317 The lowest energy nickel species

- 77 -

was found to be diphenylacetylene complex 92 gratifyingly corresponding to experiment and was set to a reference value of 00 kcalmol One notes again however an array of at least 10 species all of which must be in equilibrium in the initial reaction mixture Notably the Ni-π complexes to 22 are all more than 20 kcalmol higher in energy than 92 providing a computational rationale for the failure to observe such species by NMR The first step in the optimal reaction pathway is the coordination of Ni(PMe3) to the cyclobutadiene ring of 22 which results in formation of η2-like complex 114 Again in gratifying agreement with experiment bay region insertion through transition state 115 to give 116 is favored albeit by a bare 07 kcalmol relative to its non-bay region counterpart 117 Moreover there are at least six other structures that are energetically viable in silico although insertions of Ni(PhCequivCPh)(PMe3) appear less so possibly due to steric hindrance The same observation is made for the products of insertion although 116 emerges as the thermodynamically most stable possibility

Scheme 317 Calculated Structures and Reaction Pathway for the Insertion of Nickel into the Four-Membered Ring of Angular [3]Phenylene 22 Free Energies ∆G are in KcalMol Relative

to 92

The next step was to map out the first alkyne cycloaddition (Scheme 318) Coordination of diphenylacetylene to 116 is endothermic by 139 kcalmol and after migratory insertion produces 119 Interestingly a transition state to regioisomer 95

(328) (352)

NiMe3P PMe3

(364)

NiMe3P

NiMe3P PMe3

NiPMe3

(339)

Ni

PMe3

PMe3

NiMe3PPMe3

NiMe3P

NiPMe3

(16) (04) (108) (117)

NiMe3P PMe3 Ni

Me3PNi

Me3P Ni Ni

PMe3

PMe3

+ [3]+ DPA

+ PMe3+ [3]+ DPA

+ PMe3+ [3]

+ 2 PMe3+ [3]

+ [3]+ 2 DPA

Ph Ph Ph PhPh Ph

Ph

PhPh Ph

Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

Ph

(45) (96)

(00)

(89) (134)

Most AccessibleTS

NiPMe3

+ PMe3+ [3]+ 2 DPA

(314)

Ni

+ 2 PMe3+ [3]+ DPA

Ph Ph

(294)

1i(PMe3)

Ni

PhPh

(212)

(218)

(345)

Ni

PhPh(297)

Ni

Me3P

Ni

Ph

Ph

(350)

Ni

PMe3

(303)

Ni

Ni

(43) (41)

Ph

Ph

PhPh

Ni

PMe3

NiMe3P

(-10) (-22)

(Me3P)Ni

Ni(PMe3)

Ph Ph

Ph Ph(225) (256)

+ PMe3+ 2 DPA

+ 2 PMe3+ DPA

+ PMe3+ DPA

+ PMe3+ DPA

92114

115

116118

117

- 78 -

written (arbitrarily) in Scheme 312 could not be located

Scheme 318 Calculated Reaction Pathway for the Coordination of Diphenylacetylene Migratory Insertion and Nickel Migration Free Energies ∆G are in KcalMol Transition

State Energies are Absolute Values for This Step

Subsequent reductive elimination from 119 occurs to produce nickel coordinated arene species 120 From it free 89 is presumably readily obtained by demetallation in the presence of external ligands shown only for the formation of 92 in a very favorable process (ndash487 kcalmol) This step is sufficiently exothermic to tolerate the emergence of all the calculated species in the starting line up of Scheme 317 and is presumably the source of 89 in Scheme 39 However if not removed the Ni moiety in 120 can migrate along a shallow manifold across the π frame choosing the phenyl functionalized edge of the molecule (cf Section 24) until the remaining four-membered ring is reached (121) At this point two separate reaction pathways become possible Nickel insertion on the side proximal or opposite of the phenyl groups generates 99 or 122 respectively The barriers for these transformations are similar but show a noticeable preference for the formation of 99 In addition there is a significant energy difference (175 kcalmol) between 122 and 99 in favor of the bay region metallacycle The reason is the coordination of the neighboring phenyl ring to the nickel which serves to stabilize 103 vindicating the proposal made in Scheme 313 and providing a rationale for the exclusive observation of 90 in Scheme 39 From 99 as shown in Scheme 319 coordination of diphenylacetylene (123) is followed by migratory insertion to produce 124 Insertion occurs away from the bay region so as to reduce steric repulsion due to the phenyl group in the phenanthrene part of the molecule Finally reductive elimination ensues providing phenacene-Ni

NiMe3P

NiPMe3

Ni(PMe3)

Ni Ph

PhMe3P

Ph

Ph

PhPh

(117)

126

(44)

102

( 80)

01

( 412)

Ph PhNi(PMe3)

( 389)

Ph Ph

45

Ni(PMe3)

( 408)

Ph Ph

13

PhNi

PMe3

Ph Ph

Ni(PMe)3

133

( 488)

117

( 663)

NiMe3P

( 22)

PhPh+

95

116

119

120121 122

99

NiMe3P Ph

Ph

Ph Ph

( 899)

NiMe3P PMe3

Ph Ph+

92 89

- 79 -

complex 125 At this point the stage is set for exergonic nickel dissociation to 90 and catalyst turnover

Scheme 319 Calculated Reaction Pathway for the Second Diphenylacetylene Insertion All Relative Energies (in red) are in KcalMol Transition State Energies are Absolute Values for

This Step

In conclusion of this discussion the consideration of the combined computational and experimental data affords a mechanistic picture of the cycloaddition reaction of diphenylacetylene 88 to angular [3]phenylene 22 (Scheme 39) the essential features of which are summarized in Scheme 320 The crucial point is a mechanistic bifurcation in which 89 is either released early and (nearly) irreversibly from the metal or the metal stays attached so as to effect a second cycloaddition to give 90 This mechanism implies that 91 is formed by a different mechanism involving a different Ni species

PhNi

PMe3

( 663)

+

PhNi

Ph PMe3Ph

Ph

( 403) ( 403)

PhNi

PhPMe3

PhPh

( 519)

94

93

( 696)

PhNi

PhPMe3

Ph

Ph

96

( 817)

Ph Ph Ph Ph

(MeP)3Ni

99

123

124

125

PhPh

Ph PhPh Ph

+Ni

Me3P PMe3

( 1101)

PMe3

90

- 80 -

Scheme 320 Essential Mechanistic Features of the Formation of 89 and 90 in the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene 88 and Angular [3]Phenylene 22

Consequently the reaction of 89 with diphenylacetylene to give 91 (Scheme 310) was also modeled by DFT Of the various options probed that shown in Scheme 321 proved to be most plausible The reaction pathway entails coordination of alkyne-Ni phosphine 126 to molecule 89 which generates complex 127 in a process that is found to require 228 kcalmol of energy Insertion into the non-bay region of the four-membered ring has a barrier of 16 kcalmol and provides metallacycle 128 After the second cycloaddition event benzo[c]chrysene 91 is formed Interestingly the transition state leading to insertion of nickel complex 126 into the bay region of 89 structure 129 was found to be so high in energy relative to 128 that it could not be modeled This is not unexpected as the phenyl group closest to bay region effectively blocks the approach of any catalyst species This result is consistent with the high ratio of 91 to 90 formed in Scheme 310 and the increase in this ratio at higher initial diphenylacetylene concentration Why is any 90 formed and why does its relative proportion increase at lower diphenylacetylene concentration A possible explanation is that under these conditions the concentrations of 92 and 126 are sufficiently small that 89 reenters Scheme 318 competitively

PhPhNi(PMe3)

PhPh

Ni(PMe3)

Ph Ph Ph Ph

PhPh

Ni(PMe3)

Ni

PMe3

Ph Ph

NiPhMe3P

22 116

88

120

121

99

88

90

PhPh

89

Externalligand

assistedNi migration

Regioselectiveinsertion

Regioselectiveinsertion

Mechanistic bifurcation

- 81 -

Scheme 321 Calculated Reaction Mechanism for the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene and Compound 90 Relative Energies are in KcalMol Transition

State Energies are Absolute Values for This Step

Consideration of Scheme 320 suggests that phenacene formation might be maximized by keeping the concentration of external ligand low during the course of the reaction Experiments aimed at verifying this conjecture are the subject of Section 34 in addition to presenting extensions of the methodology to higher angular phenylenes

34 Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions The experimental and computational studies described in Section 33 suggested that the decisive factor for selective formation of phenacene 90 is suppression of metal dissociation in Ni complex 120 This scenario would be achievable by maintaining a low concentration of diphenylacetylene 88 (vide supra) Previously the alkyne cycloaddition was performed with all reagents mixed together at the start of the reaction invariably resulting in a high initial concentration of 88 To obviate this occurrence an alternative procedure was devised In this new arrangement the required stoichiometric amount (in this case two equivalents) of alkyne 88 was slowly introduced to a mixture of 22 and Ni(COD)(PMe3)2 by means of a syringe pump (Scheme 322) The results of varying addition and reaction times are shown in Table 35

Scheme 322 Modified Reaction Alkyne Cycloaddition Reaction Between 22 and 89

Ph Ph

Ni(PMe3)

Ph Ph Ph Ph

Ni(PMe)3

160

Ph

Ph

PhPh

(309)(317)

Ph Ph

Ph

Ph

NiMe3P

Ph Ph

(minus573)

89

126

127 128 91

Ph Ph Ph

Ni

Ph

PMe3

129

NiMe3P PMe3

Ph Ph

(00)

92

(89)

+

- 82 -

Table 35 Variation of Alkyne Addition and Total Reaction Time in the Scheme 322

Run Addition time of 88 (h)

Total run time (h)

Yield of 89 ()

Yield of 90 ()

1 4 16 44 55 2 6 22 23 77 3 5 41 24 76 4 12 69 17 73 5 13 19 13 87

The most immediate result of the modified protocol was the quantitative conversion of 22 to cycloadduct products 89 and 90 Turning to the product ratios a four hour addition time led to a slight preference for 90 Increasing the time to six hours dramatically influenced the product distribution and 90 was isolated in 77 yield as compared to the 23 for 89 In the optimal Run 5 87 of 90 was generated vs 13 of 90 Extending the run time after the addition of diphenylacetylene had a negligible effect The successful enhancement in phenacene selectivity under these conditions makes the reaction a practical method for synthesizing compound 90 and also provides further experimental support for the proposed mechanism shown in Scheme 320 Having reached a reasonable level of understanding both the mechanistic and experimental aspects of the reaction of angular [3]phenylene 22 with diphenylacetylene attention was shifted to a larger and more challenging substrate angular [4]phenylene (17) This system could conceivably afford 17 possible adducts one of which is hexaphenyl[7]phenacene 130 (Scheme 324) Would the mechanistic features of this triple cycloaddition be sufficiently similar to those of 22 to apply the same principles and enable selectivity toward 130

+THF reflux

Ph Ph Ph PhPh

Ph

+

Ph

Ph

2 equivslow addition

22 89 90

Ni(COD)(PMe3)2(10 mol)

88

- 83 -

Scheme 324 The Possible Cycloadducts of Diphenylacetylene 88 to Angular [4]Phenylene 17

+ Ph Ph

Ph Ph

Ph Ph

PhPh

Ph

Ph

Ph Ph Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph PhPhPh

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph Ph PhPhPh

Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

PhPh

Ph Ph Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

88

17

130

- 84 -

Encouragingly a first experiment under conditions comparable to those in Scheme 39 for 22 namely reaction of angular [4]phenylene (17) with one equivalent of diphenylacetylene in the absence of high dilution indeed engendered only five products two of which monoadducts 131 and 132 were minor (Scheme 325) The major components of the mixture were molecules 133 134 and most significantly 130

Scheme 325 Nickel Catalyzed Alkyne Cycloaddition with 17 and 88

Monitoring the course of the transformation by NMR revealed that 133 is the sole initial new compound followed by gradual appearance of the others Extrapolation of the insights gained with 22 it is tempting to propose that migration of the metal in Ni-complexed 133 is the source of 134 and ultimately 130 If true [7]phenacene 130 might be made selectively by application of the slow alkyne addition procedure of Scheme 322 Scheme 326 illustrates the proposed scenario It starts with doubly regioselective Ni insertion into the central ring and from the bay region to give 135 On the basis of the electron withdrawing effect of the adjacent cyclobutadienoid rings invoked earlier in the selective formation of 94 (Scheme 312) this metallacycle would seem the most stable Again this conjecture is tentative as the appearance of the minor products 131 and 132 would indicate Metallacycle 135 would then give rise to 136 (and hence 133 by demetallation) which would connect by Ni migration and insertion to 137 Alkyne cycloaddition would result in 138 (and hence 134 by demetallation) which would connect by Ni migration and insertion to 139 Alkyne cycloaddition would result in 140 (and hence 130 by demetallation)

+

Ph Ph

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2(10 mol)THF 75 degC

5 6

33

27 28

132131

133

134 130

17

88

- 85 -

Scheme 326 Proposed Reaction Pathway to Phenacene 130 from Angular [4]Phenylene 17 via Ni Migration

The successful preparation of [5]- and [7]phenacene from angular [3]- and [4]phenylene respectively prompted an attempt to prepare [13]phenacene derivative 141 from helical [7]phenylene 14210 (Scheme 327) This transformation would make use of six alkyne cycloadditions to produce the target molecule In addition to the possibility of preparing the largest known phenacene this reaction would also serve as an interesting test of the alkyne cycloaddition methodology

Scheme 327 Proposed Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Using the slow addition procedure phenylene 142 was subjected to the alkyne cycloaddition conditions (Scheme 329) All of the starting material was consumed but the reaction ultimately resulted in an intractable mixture of products Unfortunately no conclusive structural identifications for any of the ensuing compounds could be made from the 1H-NMR data A large assortment of peaks was seen in the region of 6ndash7

Ni

PMe3

Ph

NiPMe3

Ph Ph Ph PhNi

PMe3

Ph Ph Ph

NiMe3P

135

137

Ph Ph

Ph Ph

Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2

13617

88Ni

PMe3

Ph Ph88

138 139

Ph Ph88

Ni

PMe3

140

- 86 -

ppm suggesting the presence of phenylene subunits More informative was the absence of the highly diagnostic phenacene bay region proton signals that are typically found at ~8ndash9 ppm84 signaling the absence of any phenacene product(s)

Scheme 328 Attempted Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Nevertheless mass spectral analysis clearly indicated that multiple alkyne cycloaddition had occurred (Table 36) Peaks were observed at mz = 700 1056 1234 and 1412 which correspond to the presence of single triple quadruple and quintuple alkyne adducts in the reaction mixture No signal corresponding to the mass of 141 (mz = 1590) was detected however Although the structures of the resulting products remain to be established by follow-up experiments on a larger scale the fact that five cycloadditions occurred is encouraging in the basic scientific quest for large novel polycyclic aromatic hydrocarbons

Table 36 Mass Spectral Data (FAB) of the Product Mixture of the Cycloaddition Reaction of Phenylene 142 to Diphenylacetylene 88

mz Percentage Cycloaddition count 700 13 1

1056 11 3 1234 8 4 1412 7 5

Our disappointment in the apparent failure to generate 141 in this reaction may be the result of overambitious expectations on our part Thus we assumed in analogy to the reactivity of angular systems 17 and 22 that bay region cycloaddition to one of the inner cyclobutadiene rings would be preferred ideally producing an initial structure such as 143 (Figure 38) The corresponding non-bay adduct is illustrated by 144 It is evident on comparison that such bay region reactivity would lead to constructs devoid of the helical strain present in the starting material96 as well as non-bay structures like 144 The subsequent course of the reaction however may be marred by relatively non-selective cycloadditions as already indicated for 17 (Scheme 325) Therefore it will be prudent for future investigators to return to the latter optimize its outcome and then proceed along the series in the quest for large phenacene (or other) structures

- 87 -

Figure 38 Proposed representative initial bay (143) and non-bay (144) alkyne cycloaddition products of the reaction of [7]heliphene 141 with diphenylacetylene 88

35 Summary and Outlook The first alkyne cycloaddition studies were carried with angular phenylene systems Angular [3]phenylene 22 was successfully used as a precursor to a novel phenyl substituted [5]phenacene derivative 90 Similarly hexaphenyl [7]phenacene 131 was prepared from angular [4]phenylene 17 Extensive experiment and computational mechanistic studies suggested that the optimal conditions for preparing phenacene 90 from phenylene 22 were the maintenance of a low concentration of alkyne in the reaction mixture Future work will focus on applying these conditions to the synthesis of [7]phenacene 130 from angular [4]phenylene 17 An attempt to prepare a [13]phenacene 142 from helical [7]phenylene 141 proved unsuccessful for reasons that are not well understood Nevertheless cycloaddition was found to have occurred up to five times This observation is promising with respect to the further application of the methodology described in this chapter The development of an alkyne cycloaddition-based approach to synthesizing phenacenes should greatly facilitate the study of this emerging class of molecules Future work will focus on expanding the substrate scope of the reaction by examining various functionalized alkynes the application of metal systems that may allow the isolation of crucial intermediates and the expansion of the substrate scope to the higher angular phenylenes as well as other topologies

- 88 -

Chapter Four Experimental and Computational Details

41 General Considerations

All glassware was oven-dried (180 degC) prior to use Reagents were used as received from suppliers unless otherwise noted Flash chromatography97 was performed with Merck 60 230ndash400 mesh silica gel MP EcoChrom neutral alumina was deactivated to activity III by adding 6 water by mass followed by thorough mixing98 Air sensitive compounds were handled under argon with standard Schlenk techniques andor in a nitrogen atmosphere glovebox (Vacuum Atmospheres Model Nexus) Irradiation in CpCo(CO)2 reactions was carried out with a 120V 300W slide projection lamp (ELH) positioned 5 cm away from the reaction vessel UV-irradiation experiments were conducted in a Rayonet Photochemical Reactor (RPR-100) Bis(trimethylsilyl)- and trimethylsilylacetylene (BTMSA and TMSA respectively) were distilled from molecular sieves (4 Aring) prior to use TMSA was degassed with four freeze-pump-thaw cycles while BTMSA was degassed using a 20 min Ar purge BTMSA was recycled using from all CpCo(CO)2 reactions using the following procedure The BTMSA was first removed by vacuum transfer Residual cobalt was removed by dissolving the BTMSA in pentane and washing the pentaneBMTSA layer mixture with a dilute solution of ceric ammonium nitrate in acetonitrile in a separatory funnel The denser acetonitrile layer was drained off and the pentane removed by distillation at atmospheric pressure Vacuum distillation of the BTMSA from molecular sieves afforded a product pure enough for future use All solvents were distilled under N2

immediately before use from the appropriate drying agent triethylamine (KOH pellets) benzene toluene CH2Cl2 (CaH2) THF and diethylether (Nabenzophenone) acetonitrile (CaH2) Deoxygenation of solvents andor reaction mixtures was carried out by a 20 min Ar purge or four free-pump-thaw cycles for volatile (bp lt 70 degC) mixturessolvents Ni(COD)2 (Strem) was stored and manipulated in the glovebox 1H and proton decoupled 13C spectra were measured at 500 MHz and 125 MHz respectively unless otherwise noted 1H-NMR chemical shifts are reported in ppm units relative to the signal of the solvent (CDCl3ndash726 ppm C6D6ndash715 ppm acetone-d6ndash205 ppm CD2Cl2ndash532 ppm toluene-d8ndash209 ppm (for ndashCD3) Except where noted two-dimensional NMR experiments were run under temperature control at 300 K All spectral data were processed with Bruker TopSpin 21 software Melting points were recorded in open capillary tubes using a Thomas Hoover Unimelt apparatus and are uncorrected Melting points for air-sensitive samples were carried out in flame sealed capillary tubes Mass spectral measurements (Electron Impact Fast Atom Bombardment) and elemental analyses were supplied by the Micro-Mass Facility of the College of Chemistry University of California Berkeley UV-Vis spectra were recorded on Agilent 8453 and Perkin-Elmer Lambda 35 spectrophotometers with absorbance data reported in nm (log ε) IR spectra were taken on a Perkin-Elmer Spectrum 100 Where appropriate analysis by GCMS was done with an Agilent 5973 instrument

42 Experimental Section for Chapter Two

- 89 -

2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19

A mixture of KF2 H2O (700 mg 744 mmol) [18]crown-6 (100 mg 0378 mmol) and 2378-tetrakis[(triisopropylsilyl)ethynyl] linear [3]phenylene26 (370 mg 0800 mmol) in degassed THF (25 mL) was stirred for 70 min at RT The orange solution was filtered through a plug of silica gel (1 x 3 cm) eluting with degassed THF (15 mL) providing a light-yellow solution After adding CpCo(CO)2 (260 mg 144 mmol) the solution was protected from light and added via syringe pump over a period of 6 h to a boiling mixture of degassed BTMSA (50 mL) and THF (200 mL) which was irradiated with a projector lamp under nitrogen After additional heating and irradiation for 15 h the solvents were removed by vacuum transfer and the black residue filtered through a plug of neutral alumina activity III eluting with hexaneTHF (501) The volatiles were removed and the dark brown residue crystallized from degassed acetone yielding 19 (330 mg 65 ) as black needles mp 192ndash195 degC (decomp) 1H-NMR (400 MHz C6D6) δ = 794 (s 2 H) 744 (s 2 H) 690 (s 2 H) 441 (s 5 H) 035 (s 18 H) 031 (s 18 H) ppm 13C-NMR (100 MHz C6D6) δ = 1494 1484 1433 1394 1360 1256 1155 802 781 739

269 261 ppm IR (neat) ν~ = 2951 2898 1259 1248 1073 830 799 752 cmndash1 UV-VIS (ethanol) λmax (log ε) = 288 (486) 299 (500) 352 (445) 410 (439) 438 (449) end absorption to 550 nm MS (70 eV) mz () 638 (9) [M+] 514 (100) 499 (3) 387 (2) 73 (24) HRMS (FAB) calcd for C35H47CoSi4 6382087 found 6382095 Elemental analysis calcd for C35H47CoSi4 C 6578 H 741 found 6582 721

Crystallographic information for 19 (H atoms omitted)

Table 41 Crystal Data and Structure Refinement For 19

Empirical formula C35H47CoSi4 Formula weight 63902 cryst size (mm) 025 x 020 x 005 cryst syst Triclinic refl used for unit cell determination 6958

2 θ range (deg) 245ndash2900

a (Aring) 9497(3) b (Aring) 12321(4) c (Aring) 16469(5) α (deg) 74058(5)

β (deg) 82154(5)

Me3Si

Me3Si

CoSiMe3

SiMe3

- 90 -

γ (deg) 72276(5)

V (Aring3) 17620(10) space group Pndash1 Z 2

Dcalc gcm3 1762

F000 680 micro cmndash1 645 temp ordmC ndash173

Tmax Tmin 0858 0972 no of total rflns 24355

no of unique rflns 6958

no of obsd rflns 9209

no of variables 361

Reflection to Parameter Ratio 255

R 00503

Rw 01426

Rall 00734

GOF 1006

Max Peak in Final Diff Map (endash Aring3) 0867

Min Peak in Final Diff Map (endash Aring3) ndash0755

- 91 -

Figure 41 ORTEP representation of 19

- 92 -

Table 42 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 19 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y Z U (eq)

Co1 073881(4) ndash000927(3) 060643(2) 002551(10) Si1 077416(8) ndash019090(6) 094343(4) 002594(16) Si2 113437(8) ndash016706(7) 082404(5) 003023(17) Si3 040491(7) 062139(6) 020406(4) 002291(15) Si4 005088(7) 056545(6) 030946(4) 002144(14) C1 06709(3) ndash00385(2) 079440(16) 00239(5) C2 08019(3) ndash00967(2) 083428(16) 00241(5) C3 09418(3) ndash00743(2) 079331(16) 00233(5) C4 09428(3) 00098(2) 071779(15) 00225(5) C5 08094(2) 00691(2) 067735(15) 00207(4) C6 07282(2) 01574(2) 060605(15) 00207(4) C7 07303(2) 02531(2) 053306(15) 00211(4) C8 05938(2) 03094(2) 050431(15) 00205(4) C9 05057(2) 03981(2) 043438(15) 00207(4) C10 05076(2) 04760(2) 035695(15) 00227(5) C11 03734(2) 05293(2) 031459(15) 00215(4) C12 02408(2) 05011(2) 035315(15) 00205(4) C13 02432(2) 04196(2) 043269(15) 00215(4) C14 03751(2) 03698(2) 047171(15) 00208(4) C15 04564(2) 02794(2) 054277(15) 00211(4) C16 04487(2) 01908(2) 061161(15) 00224(5) C17 05916(3) 01278(2) 064393(15) 00221(5) C18 06734(2) 00417(2) 071473(15) 00215(5) C19 05795(3) ndash02027(3) 09572(2) 00446(8) C20 08892(4) ndash03470(2) 09642(2) 00387(7) C21 07986(4) ndash01192(3) 10246(2) 00419(7) C22 11685(4) ndash03077(3) 07914(3) 00584(10) C23 11726(3) ndash01969(3) 09372(2) 00426(7) C24 12742(4) ndash00933(4) 07624(3) 00640(12) C25 05777(3) 06657(3) 020261(18) 00348(6) C26 02610(3) 07629(2) 016564(17) 00292(5) C27 04355(3) 05272(3) 012760(18) 00347(6) C28 ndash00272(3) 07195(2) 03194(2) 00360(6) C29 00487(3) 05542(3) 019882(18) 00344(6) C30 ndash00786(3) 04816(2) 037272(18) 00278(5) C31 06994(4) ndash00612(3) 05062(2) 00432(7) C32 08520(4) ndash00698(3) 05033(2) 00407(7) C33 09085(3) ndash01473(3) 05788(2) 00407(7) C34 07922(4) ndash01879(3) 06277(2) 00424(7) C35 06647(4) ndash01370(3) 05833(2) 00403(7)

- 93 -

Table 43 Bond Lengths (Aring) for Complex 19

Atom1 Atom2 Length

Co1 C5 1993(3) Co1 C6 2023(3) Co1 C17 2022(2) Co1 C18 2009(3) Co1 C31 2042(4) Co1 C32 2075(3) Co1 C33 2062(3) Co1 C34 2042(4) Co1 C35 2048(4) Si1 C2 1886(2) Si1 C19 1877(3) Si1 C20 1863(2) Si1 C21 1865(4) Si2 C3 1889(3) Si2 C22 1876(5) Si2 C23 1862(3) Si2 C24 1865(4) Si3 C11 1901(2) Si3 C25 1876(4) Si3 C26 1867(2) Si3 C27 1875(4) Si4 C12 1889(2) Si4 C28 1860(3) Si4 C29 1868(3) Si4 C30 1870(3) C1 C2 1384(4) C1 C18 1411(3) C2 C3 1474(4) C3 C4 1384(3) C4 C5 1408(3) C5 C6 1480(3) C5 C18 1448(3) C6 C7 1437(3) C6 C17 1465(4) C7 C8 1351(3) C8 C9 1495(3) C8 C15 1476(3) C9 C10 1371(3) C9 C14 1405(3) C10 C11 1423(3) C11 C12 1427(3) C12 C13 1413(3) C13 C14 1376(3)

- 94 -

C14 C15 1488(3) C15 C16 1352(3) C16 C17 1434(3) C17 C18 1468(3) C31 C32 1416(6) C31 C35 1419(4) C32 C33 1401(4) C33 C34 1411(5) C34 C35 1386(5)

Table 44 Bond Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 4325(9) C5 Co1 C17 621(1) C5 Co1 C18 4240(9) C5 Co1 C31 1629(1) C5 Co1 C32 1271(1) C5 Co1 C33 1102(1) C5 Co1 C34 1223(1) C5 Co1 C35 1556(1) C6 Co1 C17 425(1) C6 Co1 C18 6191(9) C6 Co1 C31 1253(1) C6 Co1 C32 1164(1) C6 Co1 C33 1329(1) C6 Co1 C34 1651(1) C6 Co1 C35 1550(1) C17 Co1 C18 427(1) C17 Co1 C31 1204(1) C17 Co1 C32 1451(1) C17 Co1 C33 1722(1) C17 Co1 C34 1419(1) C17 Co1 C35 1194(1) C18 Co1 C31 1517(1) C18 Co1 C32 1676(1) C18 Co1 C33 1312(1) C18 Co1 C34 1112(1) C18 Co1 C35 1198(1) C31 Co1 C32 402(1) C31 Co1 C33 673(1) C31 Co1 C34 675(1) C31 Co1 C35 406(1) C32 Co1 C33 396(1) C32 Co1 C34 672(1)

- 95 -

C32 Co1 C35 675(1) C33 Co1 C34 402(1) C33 Co1 C35 671(1) C34 Co1 C35 396(1) C2 Si1 C19 1085(1) C2 Si1 C20 1157(1) C2 Si1 C21 1096(1) C19 Si1 C20 1035(1) C19 Si1 C21 1081(2) C20 Si1 C21 1110(2) C3 Si2 C22 1071(2) C3 Si2 C23 1162(1) C3 Si2 C24 1100(2) C22 Si2 C23 1110(2) C22 Si2 C24 1067(2) C23 Si2 C24 1056(2) C11 Si3 C25 1077(1) C11 Si3 C26 1177(1) C11 Si3 C27 1083(1) C25 Si3 C26 1045(1) C25 Si3 C27 1086(1) C26 Si3 C27 1097(1) C12 Si4 C28 1099(1) C12 Si4 C29 1132(1) C12 Si4 C30 1101(1) C28 Si4 C29 1119(1) C28 Si4 C30 1066(1) C29 Si4 C30 1048(1) C2 C1 C18 1193(2) Si1 C2 C1 1130(2) Si1 C2 C3 1270(2) C1 C2 C3 1198(2) Si2 C3 C2 1260(2) Si2 C3 C4 1124(2) C2 C3 C4 1208(2) C3 C4 C5 1192(2) Co1 C5 C4 1188(2) Co1 C5 C6 695(1) Co1 C5 C18 694(1) C4 C5 C6 1498(2) C4 C5 C18 1200(2) C6 C5 C18 902(2) Co1 C6 C5 673(1) Co1 C6 C7 1267(2) Co1 C6 C17 687(1) C5 C6 C7 1474(2)

- 96 -

C5 C6 C17 893(2) C7 C6 C17 1227(2) C6 C7 C8 1121(2) C7 C8 C9 1461(2) C7 C8 C15 1251(2) C9 C8 C15 885(2) C8 C9 C10 1471(2) C8 C9 C14 912(2) C10 C9 C14 1214(2) C9 C10 C11 1186(2) Si3 C11 C10 1116(2) Si3 C11 C12 1283(2) C10 C11 C12 1197(2) Si4 C12 C11 1264(2) Si4 C12 C13 1135(2) C11 C12 C13 1201(2) C12 C13 C14 1185(2) C9 C14 C13 1216(2) C9 C14 C15 915(2) C13 C14 C15 1465(2) C8 C15 C14 888(2) C8 C15 C16 1250(2) C14 C15 C16 1458(2) C15 C16 C17 1118(2) Co1 C17 C6 688(1) Co1 C17 C16 1265(2) Co1 C17 C18 682(1) C6 C17 C16 1233(2) C6 C17 C18 900(2) C16 C17 C18 1460(2) Co1 C18 C1 1229(2) Co1 C18 C5 682(1) Co1 C18 C17 691(1) C1 C18 C5 1206(2) C1 C18 C17 1487(2) C5 C18 C17 905(2) Co1 C31 C32 712(2) Co1 C31 C35 699(2) C32 C31 C35 1077(3) Co1 C32 C31 686(2) Co1 C32 C33 697(2) C31 C32 C33 1076(3) Co1 C33 C32 707(2) Co1 C33 C34 691(2) C32 C33 C34 1081(3) Co1 C34 C33 707(2)

- 97 -

Co1 C34 C35 704(2) C33 C34 C35 1086(3) Co1 C35 C31 695(2) Co1 C35 C34 700(2) C31 C35 C34 1079(3)

Table 44 Torsion Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 ndash1479(3) C6 Co1 C5 C18 983(2) C17 Co1 C5 C4 1630(2) C17 Co1 C5 C6 ndash491(1) C17 Co1 C5 C18 492(1) C18 Co1 C5 C4 1138(2) C18 Co1 C5 C6 ndash983(2) C31 Co1 C5 C4 ndash941(4) C31 Co1 C5 C6 538(4) C31 Co1 C5 C18 1522(4) C32 Co1 C5 C4 ndash573(2) C32 Co1 C5 C6 906(2) C32 Co1 C5 C18 ndash1710(2) C33 Co1 C5 C4 ndash160(2) C33 Co1 C5 C6 1319(1) C33 Co1 C5 C18 ndash1297(2) C34 Co1 C5 C4 271(2) C34 Co1 C5 C6 1750(2) C34 Co1 C5 C18 ndash866(2) C35 Co1 C5 C4 629(4) C35 Co1 C5 C6 ndash1492(3) C35 Co1 C5 C18 ndash509(3) C5 Co1 C6 C7 1458(3) C5 Co1 C6 C17 ndash986(2) C17 Co1 C6 C5 986(2) C17 Co1 C6 C7 ndash1156(3) C18 Co1 C6 C5 491(1) C18 Co1 C6 C7 ndash1650(2) C18 Co1 C6 C17 ndash494(1) C31 Co1 C6 C5 ndash1631(2) C31 Co1 C6 C7 ndash173(3) C31 Co1 C6 C17 983(2) C32 Co1 C6 C5 ndash1170(2) C32 Co1 C6 C7 288(2) C32 Co1 C6 C17 1444(2) C33 Co1 C6 C5 ndash725(2)

- 98 -

C33 Co1 C6 C7 734(3) C33 Co1 C6 C17 ndash1710(2) C34 Co1 C6 C5 ndash166(5) C34 Co1 C6 C7 1293(5) C34 Co1 C6 C17 ndash1151(5) C35 Co1 C6 C5 1499(3) C35 Co1 C6 C7 ndash642(4) C35 Co1 C6 C17 514(3) C5 Co1 C17 C6 501(1) C5 Co1 C17 C16 1666(3) C5 Co1 C17 C18 ndash489(1) C6 Co1 C17 C16 1165(3) C6 Co1 C17 C18 ndash989(2) C18 Co1 C17 C6 989(2) C18 Co1 C17 C16 ndash1446(3) C31 Co1 C17 C6 ndash1106(2) C31 Co1 C17 C16 59(3) C31 Co1 C17 C18 1505(2) C32 Co1 C17 C6 ndash656(3) C32 Co1 C17 C16 510(3) C32 Co1 C17 C18 ndash1645(2) C33 Co1 C17 C6 571(9) C33 Co1 C17 C16 1736(8) C33 Co1 C17 C18 ndash418(9) C34 Co1 C17 C6 1578(2) C34 Co1 C17 C16 ndash857(3) C34 Co1 C17 C18 589(2) C35 Co1 C17 C6 ndash1578(2) C35 Co1 C17 C16 ndash413(3) C35 Co1 C17 C18 1033(2) C5 Co1 C18 C1 ndash1133(3) C5 Co1 C18 C17 993(2) C6 Co1 C18 C1 ndash1635(2) C6 Co1 C18 C5 ndash502(1) C6 Co1 C18 C17 491(1) C17 Co1 C18 C1 1474(3) C17 Co1 C18 C5 ndash993(2) C31 Co1 C18 C1 836(3) C31 Co1 C18 C5 ndash1632(2) C31 Co1 C18 C17 ndash638(3) C32 Co1 C18 C1 ndash779(6) C32 Co1 C18 C5 353(6) C32 Co1 C18 C17 1346(5) C33 Co1 C18 C1 ndash395(3) C33 Co1 C18 C5 737(2) C33 Co1 C18 C17 1731(2)

- 99 -

C34 Co1 C18 C1 20(2) C34 Co1 C18 C5 1152(2) C34 Co1 C18 C17 ndash1455(2) C35 Co1 C18 C1 451(3) C35 Co1 C18 C5 1583(2) C35 Co1 C18 C17 ndash1023(2) C5 Co1 C31 C32 478(5) C5 Co1 C31 C35 1656(4) C6 Co1 C31 C32 904(2) C6 Co1 C31 C35 ndash1517(2) C17 Co1 C31 C32 1412(2) C17 Co1 C31 C35 ndash1010(2) C18 Co1 C31 C32 ndash1739(2) C18 Co1 C31 C35 ndash561(3) C32 Co1 C31 C35 1179(3) C33 Co1 C31 C32 ndash370(2) C33 Co1 C31 C35 808(2) C34 Co1 C31 C32 ndash808(2) C34 Co1 C31 C35 371(2) C35 Co1 C31 C32 ndash1179(3) C5 Co1 C32 C31 ndash1642(2) C5 Co1 C32 C33 764(2) C6 Co1 C32 C31 ndash1143(2) C6 Co1 C32 C33 1263(2) C17 Co1 C32 C31 ndash710(3) C17 Co1 C32 C33 1697(2) C18 Co1 C32 C31 1666(5) C18 Co1 C32 C33 472(6) C31 Co1 C32 C33 ndash1194(3) C33 Co1 C32 C31 1194(3) C34 Co1 C32 C31 816(2) C34 Co1 C32 C33 ndash377(2) C35 Co1 C32 C31 385(2) C35 Co1 C32 C33 ndash808(2) C5 Co1 C33 C32 ndash1243(2) C5 Co1 C33 C34 1166(2) C6 Co1 C33 C32 ndash802(2) C6 Co1 C33 C34 1607(2) C17 Co1 C33 C32 ndash1309(8) C17 Co1 C33 C34 1100(9) C18 Co1 C33 C32 ndash1679(2) C18 Co1 C33 C34 730(2) C31 Co1 C33 C32 376(2) C31 Co1 C33 C34 ndash815(2) C32 Co1 C33 C34 ndash1191(3) C34 Co1 C33 C32 1191(3)

- 100 -

C35 Co1 C33 C32 818(2) C35 Co1 C33 C34 ndash373(2) C5 Co1 C34 C33 ndash833(2) C5 Co1 C34 C35 1577(2) C6 Co1 C34 C33 ndash700(5) C6 Co1 C34 C35 1711(4) C17 Co1 C34 C33 ndash1681(2) C17 Co1 C34 C35 730(3) C18 Co1 C34 C33 ndash1295(2) C18 Co1 C34 C35 1115(2) C31 Co1 C34 C33 809(2) C31 Co1 C34 C35 ndash380(2) C32 Co1 C34 C33 372(2) C32 Co1 C34 C35 ndash818(2) C33 Co1 C34 C35 ndash1189(3) C35 Co1 C34 C33 1189(3) C5 Co1 C35 C31 ndash1699(3) C5 Co1 C35 C34 ndash508(4) C6 Co1 C35 C31 663(4) C6 Co1 C35 C34 ndash1746(2) C17 Co1 C35 C31 1036(2) C17 Co1 C35 C34 ndash1373(2) C18 Co1 C35 C31 1531(2) C18 Co1 C35 C34 ndash878(2) C31 Co1 C35 C34 1191(3) C32 Co1 C35 C31 ndash382(2) C32 Co1 C35 C34 809(2) C33 Co1 C35 C31 ndash812(2) C33 Co1 C35 C34 378(2) C34 Co1 C35 C31 ndash1191(3) C19 Si1 C2 C1 118(2) C19 Si1 C2 C3 ndash1731(2) C20 Si1 C2 C1 1275(2) C20 Si1 C2 C3 ndash574(3) C21 Si1 C2 C1 ndash1061(2) C21 Si1 C2 C3 690(3) C22 Si2 C3 C2 714(3) C22 Si2 C3 C4 ndash988(2) C23 Si2 C3 C2 ndash532(3) C23 Si2 C3 C4 1365(2) C24 Si2 C3 C2 ndash1731(3) C24 Si2 C3 C4 167(3) C25 Si3 C11 C10 ndash241(2) C25 Si3 C11 C12 1624(2) C26 Si3 C11 C10 ndash1417(2) C26 Si3 C11 C12 447(3)

- 101 -

C27 Si3 C11 C10 932(2) C27 Si3 C11 C12 ndash804(2) C28 Si4 C12 C11 ndash731(2) C28 Si4 C12 C13 1055(2) C29 Si4 C12 C11 529(2) C29 Si4 C12 C13 ndash1285(2) C30 Si4 C12 C11 1698(2) C30 Si4 C12 C13 ndash116(2) C18 C1 C2 Si1 1755(2) C18 C1 C2 C3 00(4) C2 C1 C18 Co1 784(3) C2 C1 C18 C5 ndash41(4) C2 C1 C18 C17 ndash1772(4) Si1 C2 C3 Si2 198(4) Si1 C2 C3 C4 ndash1707(2) C1 C2 C3 Si2 ndash1654(2) C1 C2 C3 C4 41(4) Si2 C3 C4 C5 1668(2) C2 C3 C4 C5 ndash40(4) C3 C4 C5 Co1 ndash816(3) C3 C4 C5 C6 1799(4) C3 C4 C5 C18 ndash01(4) Co1 C5 C6 C7 ndash1233(4) Co1 C5 C6 C17 671(1) C4 C5 C6 Co1 1122(4) C4 C5 C6 C7 ndash112(7) C4 C5 C6 C17 1793(4) C18 C5 C6 Co1 ndash678(1) C18 C5 C6 C7 1688(4) C18 C5 C6 C17 ndash07(2) Co1 C5 C18 C1 1164(2) Co1 C5 C18 C17 ndash672(1) C4 C5 C18 Co1 ndash1121(2) C4 C5 C18 C1 42(3) C4 C5 C18 C17 ndash1793(2) C6 C5 C18 Co1 679(1) C6 C5 C18 C1 ndash1757(2) C6 C5 C18 C17 07(2) Co1 C6 C7 C8 858(2) C5 C6 C7 C8 ndash1683(3) C17 C6 C7 C8 ndash08(3) Co1 C6 C17 C16 ndash1205(2) Co1 C6 C17 C18 665(1) C5 C6 C17 Co1 ndash658(1) C5 C6 C17 C16 1736(2) C5 C6 C17 C18 07(2)

- 102 -

C7 C6 C17 Co1 1209(2) C7 C6 C17 C16 03(4) C7 C6 C17 C18 ndash1726(2) C6 C7 C8 C9 ndash1697(3) C6 C7 C8 C15 09(3) C7 C8 C9 C10 05(7) C7 C8 C9 C14 1728(4) C15 C8 C9 C10 ndash1718(4) C15 C8 C9 C14 05(2) C7 C8 C15 C14 ndash1752(2) C7 C8 C15 C16 ndash06(4) C9 C8 C15 C14 ndash04(2) C9 C8 C15 C16 1742(2) C8 C9 C10 C11 1714(3) C14 C9 C10 C11 05(3) C8 C9 C14 C13 ndash1756(2) C8 C9 C14 C15 ndash05(2) C10 C9 C14 C13 ndash06(4) C10 C9 C14 C15 1746(2) C9 C10 C11 Si3 ndash1741(2) C9 C10 C11 C12 01(3) Si3 C11 C12 Si4 ndash90(3) Si3 C11 C12 C13 1725(2) C10 C11 C12 Si4 1779(2) C10 C11 C12 C13 ndash07(3) Si4 C12 C13 C14 ndash1781(2) C11 C12 C13 C14 06(3) C12 C13 C14 C9 ndash00(3) C12 C13 C14 C15 ndash1713(3) C9 C14 C15 C8 05(2) C9 C14 C15 C16 ndash1717(4) C13 C14 C15 C8 1730(4) C13 C14 C15 C16 09(7) C8 C15 C16 C17 00(3) C14 C15 C16 C17 1704(3) C15 C16 C17 Co1 ndash870(3) C15 C16 C17 C6 01(3) C15 C16 C17 C18 1674(4) Co1 C17 C18 C1 ndash1195(4) Co1 C17 C18 C5 664(1) C6 C17 C18 Co1 ndash671(1) C6 C17 C18 C1 1734(4) C6 C17 C18 C5 ndash07(2) C16 C17 C18 Co1 1235(4) C16 C17 C18 C1 40(7) C16 C17 C18 C5 ndash1701(4)

- 103 -

Co1 C31 C32 C33 590(2) C35 C31 C32 Co1 ndash607(2) C35 C31 C32 C33 ndash16(4) Co1 C31 C35 C34 ndash596(3) C32 C31 C35 Co1 615(3) C32 C31 C35 C34 18(4) Co1 C32 C33 C34 592(2) C31 C32 C33 Co1 ndash583(2) C31 C32 C33 C34 09(4) Co1 C33 C34 C35 605(3) C32 C33 C34 Co1 ndash602(2) C32 C33 C34 C35 03(4) Co1 C34 C35 C31 593(3) C33 C34 C35 Co1 ndash606(2) C33 C34 C35 C31 ndash13(4)

23-Bis(trimethylsilyl) linear [3]phenylene(CpCo) 52

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (029 g 085 mmol)27 in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (014 g 101 mmol) The mixture was stirred for 15 h and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the yellow residue dissolved in ether (30 mL) Aqueous workup with sat NaCl (2 x 20 mL) followed by drying over MgSO4 and concentration in vacuo provided a yellow solid This material was redissolved in THF (15 mL) degassed (Ar) and CpCo(CO)2 (0140 g 078 mmol) added The resulting solution (protected from light with foil) was injected (syringe pump) over 8 h into a boiling mixture of THF (200 mL) and BTMSA (50 mL) while irradiating with a slide projection lamp Once addition was complete heating and irradiation were continued for another 14 h The volatiles were removed via vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (4 x 4 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed in vacuo and the residue crystallized from acetone yielding 52 (024 g 57 ) as dark red crystals mp 198ndash202 degC (decomp) 1H-NMR (500 MHz C6D6) δ = 796 (s 2 H) 678 (AArsquom 2 H) 675 (s 2 H) 674 (BBrsquom 2 H) 436 (s 5 H) 037 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1426 1393

1360 1294 1194 1149 802 779 738 268 ppm IR (neat) ν~ = 2960 2923 2853 1461 1455 1378 1260 1093 1019 800 cmndash1 UV-VIS (hexane) λmax (log ε) = 255 (393) 282 (376) 293 (sh 378) 308 (389) 348 (390) 397 (sh 335) 436 (301) 511

CoSiMe3

SiMe3

- 104 -

(262) MS (70 eV) mz () 494 (100) [M+] 370 (14) HRMS (FAB) calcd for C29H31CoSi2 4941296 found 4941292 Elemental analysis calcd for C29H31CoSi2 C 7041 H 632 found 7048 628 Crystallographic information for 52 (H atoms omitted)

Table 45 Crystal Data and Structure Refinement For 52

Empirical formula C29H31CoSi2 Formula weight 49465 cryst size (mm) 030 x 020 x 005 cryst syst Monoclinic refl used for unit cell determination 2640 2 θ range (deg) 242ndash2503 a (Aring) 4391(3) b (Aring) 7472(4) c (Aring) 16869(11) α (deg)

β (deg) 111522(11) γ (deg) V (Aring3) 5149(6) space group C2c Z 8 Dcalc gcm

3 1276

F000 2080 micro cmndash1 774

temp ordmC ndash153

Tmax Tmin 0963 0800 no of total rflns 18401 no of unique rflns 2640 no of obsd rflns 4266 no of variables 271 Reflection to Parameter Ratio 974 R 00892 Rw 02042 Rall 01248 GOF 1008 Max Peak in Final Diff Map (endash Aring3) 1051 Min Peak in Final Diff Map (endash Aring3) ndash0707

- 105 -

Figure 42 ORTEP representation of 52

- 106 -

Table 46 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 52 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y z U(eq)

Co1 006961(2) 087577(12) 038136(6) 00200(3) Si1 018827(6) 08761(5) 063753(18) 00627(9) Si2 018540(5) 05425(3) 046900(16) 00410(6) C1 012151(19) 08410(10) 05589(5) 00310(17) C2 015018(13) 07767(11) 05552(4) 00343(18) C3 015002(14) 06417(10) 04926(5) 00324(17) C4 011985(17) 05770(9) 04357(4) 00247(16) C5 009030(17) 06465(9) 04383(4) 00220(14) C6 005450(16) 06378(9) 04077(4) 00216(14) C7 002537(17) 05420(9) 03591(4) 00224(15) C8 ndash000060(18) 05847(9) 03798(4) 00246(15) C9 ndash003560(17) 05555(10) 03644(4) 00256(16) C10 ndash006399(18) 04581(10) 03174(4) 00284(17) C11 ndash009208(19) 05019(12) 03360(5) 00344(18) C12 ndash009130(19) 06274(12) 03957(5) 00340(18) C13 ndash006300(17) 07256(11) 04422(5) 00294(17) C14 ndash003558(19) 06826(10) 04247(4) 00274(16) C15 000008(18) 07212(10) 04449(4) 00251(16) C16 002653(17) 08159(10) 04925(4) 00234(15) C17 005500(17) 07741(9) 04722(4) 00231(15) C18 009090(17) 07798(10) 05007(4) 00247(15) C19 01766(3) 10793(15) 06845(9) 0098(3) C20 02181(3) 0957(2) 05901(7) 0098(3) C21 02076(3) 07068(14) 07228(7) 0098(3) C22 01946(2) 06941(13) 03925(6) 00631(17) C23 01724(2) 03224(9) 04142(7) 00631(17) C24 022363(17) 04883(16) 05614(5) 00631(17) C25 007501(19) 09264(10) 02652(4) 00281(17) C26 004279(18) 09614(10) 02593(4) 00264(16) C27 004343(18) 10945(10) 03211(4) 00271(16) C28 007584(19) 11429(10) 03645(5) 00296(17) C29 00960(2) 10392(11) 03322(5) 00321(17)

Table 47 Bond Lengths (Aring) for Complex 52

Atom1 Atom2 Length

Co1 C5 2011(7) Co1 C6 2004(7) Co1 C17 2014(8) Co1 C18 2015(6) Co1 C25 2093(8)

- 107 -

Co1 C26 2063(6) Co1 C27 2042(7) Co1 C28 2049(8) Co1 C29 206(1) Si1 C2 1890(6) Si1 C19 187(1) Si1 C20 187(2) Si1 C21 187(1) Si2 C3 1891(8) Si2 C22 187(1) Si2 C23 1870(8) Si2 C24 1869(7) C1 C2 137(1) C1 C18 1418(9) C2 C3 146(1) C3 C4 1406(8) C4 C5 141(1) C5 C6 147(1) C5 C18 144(1) C6 C7 1432(9) C6 C17 148(1) C7 C8 135(1) C8 C9 148(1) C8 C15 149(1) C9 C10 1410(9) C9 C14 139(1) C10 C11 142(1) C11 C12 137(1) C12 C13 141(1) C13 C14 138(1) C14 C15 150(1) C15 C16 1345(9) C16 C17 145(1) C17 C18 147(1) C25 C26 141(1) C25 C29 144(1) C26 C27 143(1) C27 C28 139(1) C28 C29 143(1)

Table 48 Bond Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 428(3) C5 Co1 C17 619(3)

- 108 -

C5 Co1 C18 420(3) C5 Co1 C25 1145(3) C5 Co1 C26 1372(3) C5 Co1 C27 1733(3) C5 Co1 C28 1468(3) C5 Co1 C29 1184(3) C6 Co1 C17 434(3) C6 Co1 C18 621(3) C6 Co1 C25 1219(3) C6 Co1 C26 1125(3) C6 Co1 C27 1305(3) C6 Co1 C28 1653(3) C6 Co1 C29 1539(3) C17 Co1 C18 428(3) C17 Co1 C25 1632(3) C17 Co1 C26 1307(3) C17 Co1 C27 1137(3) C17 Co1 C28 1247(3) C17 Co1 C29 1562(3) C18 Co1 C25 1460(3) C18 Co1 C26 1733(3) C18 Co1 C27 1388(3) C18 Co1 C28 1167(3) C18 Co1 C29 1194(3) C25 Co1 C26 395(3) C25 Co1 C27 680(3) C25 Co1 C28 681(3) C25 Co1 C29 406(3) C26 Co1 C27 409(3) C26 Co1 C28 674(3) C26 Co1 C29 672(3) C27 Co1 C28 397(3) C27 Co1 C29 678(3) C28 Co1 C29 407(3) C2 Si1 C19 1089(5) C2 Si1 C20 1125(5) C2 Si1 C21 1092(4) C19 Si1 C20 1053(6) C19 Si1 C21 1100(6) C20 Si1 C21 1109(6) C3 Si2 C22 1081(4) C3 Si2 C23 1089(4) C3 Si2 C24 1177(4) C22 Si2 C23 1072(4) C22 Si2 C24 1106(4) C23 Si2 C24 1039(4)

- 109 -

C2 C1 C18 1206(7) Si1 C2 C1 1141(5) Si1 C2 C3 1249(5) C1 C2 C3 1210(7) Si2 C3 C2 1296(5) Si2 C3 C4 1113(5) C2 C3 C4 1190(6) C3 C4 C5 1199(6) Co1 C5 C4 1239(5) Co1 C5 C6 684(4) Co1 C5 C18 692(4) C4 C5 C6 1484(7) C4 C5 C18 1203(6) C6 C5 C18 910(6) Co1 C6 C5 688(4) Co1 C6 C7 1280(5) Co1 C6 C17 687(4) C5 C6 C7 1473(6) C5 C6 C17 892(5) C7 C6 C17 1222(6) C6 C7 C8 1133(6) C7 C8 C9 1475(7) C7 C8 C15 1242(7) C9 C8 C15 882(6) C8 C9 C10 1454(7) C8 C9 C14 928(6) C10 C9 C14 1218(7) C9 C10 C11 1147(7) C10 C11 C12 1222(8) C11 C12 C13 1231(8) C12 C13 C14 1149(7) C9 C14 C13 1233(7) C9 C14 C15 910(6) C13 C14 C15 1457(7) C8 C15 C14 879(6) C8 C15 C16 1254(7) C14 C15 C16 1467(7) C15 C16 C17 1121(6) Co1 C17 C6 679(4) Co1 C17 C16 1300(5) Co1 C17 C18 686(4) C6 C17 C16 1227(6) C6 C17 C18 892(5) C16 C17 C18 1464(7) Co1 C18 C1 1235(5) Co1 C18 C5 688(4)

- 110 -

Co1 C18 C17 686(4) C1 C18 C5 1191(7) C1 C18 C17 1500(7) C5 C18 C17 906(6) Co1 C25 C26 691(4) Co1 C25 C29 683(4) C26 C25 C29 1065(7) Co1 C26 C25 714(4) Co1 C26 C27 688(4) C25 C26 C27 1091(6) Co1 C27 C26 704(4) Co1 C27 C28 704(5) C26 C27 C28 1079(7) Co1 C28 C27 699(5) Co1 C28 C29 699(5) C27 C28 C29 1085(7) Co1 C29 C25 711(5) Co1 C29 C28 694(5) C25 C29 C28 1080(7)

Table 49 Torsion Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 1468(8) C6 Co1 C5 C18 ndash999(5) C17 Co1 C5 C4 ndash1627(7) C17 Co1 C5 C6 504(4) C17 Co1 C5 C18 ndash494(4) C18 Co1 C5 C4 ndash1133(8) C18 Co1 C5 C6 999(5) C25 Co1 C5 C4 356(7) C25 Co1 C5 C6 ndash1113(4) C25 Co1 C5 C18 1489(4) C26 Co1 C5 C4 765(7) C26 Co1 C5 C6 ndash703(5) C26 Co1 C5 C18 ndash1702(4) C27 Co1 C5 C4 146(2) C27 Co1 C5 C6 ndash1(3) C27 Co1 C5 C18 ndash101(2) C28 Co1 C5 C4 ndash515(9) C28 Co1 C5 C6 1617(5) C28 Co1 C5 C18 619(7) C29 Co1 C5 C4 ndash98(7) C29 Co1 C5 C6 ndash1567(4) C29 Co1 C5 C18 1035(5)

- 111 -

C5 Co1 C6 C7 ndash1474(8) C5 Co1 C6 C17 977(5) C17 Co1 C6 C5 ndash977(5) C17 Co1 C6 C7 1149(8) C18 Co1 C6 C5 ndash482(4) C18 Co1 C6 C7 1644(7) C18 Co1 C6 C17 495(4) C25 Co1 C6 C5 927(5) C25 Co1 C6 C7 ndash547(7) C25 Co1 C6 C17 ndash1696(4) C26 Co1 C6 C5 1362(4) C26 Co1 C6 C7 ndash112(7) C26 Co1 C6 C17 ndash1261(4) C27 Co1 C6 C5 1799(4) C27 Co1 C6 C7 325(8) C27 Co1 C6 C17 ndash824(5) C28 Co1 C6 C5 ndash137(1) C28 Co1 C6 C7 75(1) C28 Co1 C6 C17 ndash40(1) C29 Co1 C6 C5 523(8) C29 Co1 C6 C7 ndash951(9) C29 Co1 C6 C17 1501(7) C5 Co1 C17 C6 ndash497(4) C5 Co1 C17 C16 ndash1646(8) C5 Co1 C17 C18 484(4) C6 Co1 C17 C16 ndash1149(8) C6 Co1 C17 C18 981(5) C18 Co1 C17 C6 ndash981(5) C18 Co1 C17 C16 1470(9) C25 Co1 C17 C6 32(1) C25 Co1 C17 C16 ndash83(1) C25 Co1 C17 C18 130(1) C26 Co1 C17 C6 799(5) C26 Co1 C17 C16 ndash350(8) C26 Co1 C17 C18 1780(4) C27 Co1 C17 C6 1245(4) C27 Co1 C17 C16 97(8) C27 Co1 C17 C18 ndash1373(4) C28 Co1 C17 C6 1686(4) C28 Co1 C17 C16 538(8) C28 Co1 C17 C18 ndash932(5) C29 Co1 C17 C6 ndash1471(7) C29 Co1 C17 C16 98(1) C29 Co1 C17 C18 ndash489(9) C5 Co1 C18 C1 1117(8) C5 Co1 C18 C17 ndash995(5)

- 112 -

C6 Co1 C18 C1 1609(7) C6 Co1 C18 C5 492(4) C6 Co1 C18 C17 ndash502(4) C17 Co1 C18 C1 ndash1488(8) C17 Co1 C18 C5 995(5) C25 Co1 C18 C1 544(9) C25 Co1 C18 C5 ndash573(7) C25 Co1 C18 C17 ndash1568(5) C26 Co1 C18 C1 ndash162(2) C26 Co1 C18 C5 87(3) C26 Co1 C18 C17 ndash13(3) C27 Co1 C18 C1 ndash784(8) C27 Co1 C18 C5 1699(4) C27 Co1 C18 C17 705(6) C28 Co1 C18 C1 ndash356(7) C28 Co1 C18 C5 ndash1473(4) C28 Co1 C18 C17 1133(4) C29 Co1 C18 C1 107(8) C29 Co1 C18 C5 ndash1010(5) C29 Co1 C18 C17 1595(4) C5 Co1 C25 C26 1356(4) C5 Co1 C25 C29 ndash1058(5) C6 Co1 C25 C26 873(5) C6 Co1 C25 C29 ndash1540(5) C17 Co1 C25 C26 62(1) C17 Co1 C25 C29 ndash1796(9) C18 Co1 C25 C26 1738(5) C18 Co1 C25 C29 ndash675(7) C26 Co1 C25 C29 1187(6) C27 Co1 C25 C26 ndash376(4) C27 Co1 C25 C29 810(5) C28 Co1 C25 C26 ndash806(5) C28 Co1 C25 C29 381(5) C29 Co1 C25 C26 ndash1187(6) C5 Co1 C26 C25 ndash696(6) C5 Co1 C26 C27 1703(4) C6 Co1 C26 C25 ndash1134(5) C6 Co1 C26 C27 1265(4) C17 Co1 C26 C25 ndash1604(4) C17 Co1 C26 C27 795(5) C18 Co1 C26 C25 ndash149(2) C18 Co1 C26 C27 91(3) C25 Co1 C26 C27 ndash1201(6) C27 Co1 C26 C25 1201(6) C28 Co1 C26 C25 825(5) C28 Co1 C26 C27 ndash376(4)

- 113 -

C29 Co1 C26 C25 383(5) C29 Co1 C26 C27 ndash818(5) C5 Co1 C27 C26 ndash77(3) C5 Co1 C27 C28 165(2) C6 Co1 C27 C26 ndash774(5) C6 Co1 C27 C28 1644(5) C17 Co1 C27 C26 ndash1254(4) C17 Co1 C27 C28 1163(5) C18 Co1 C27 C26 ndash1698(5) C18 Co1 C27 C28 720(6) C25 Co1 C27 C26 364(4) C25 Co1 C27 C28 ndash818(5) C26 Co1 C27 C28 ndash1182(6) C28 Co1 C27 C26 1182(6) C29 Co1 C27 C26 804(5) C29 Co1 C27 C28 ndash378(5) C5 Co1 C28 C27 ndash1768(5) C5 Co1 C28 C29 637(7) C6 Co1 C28 C27 ndash54(1) C6 Co1 C28 C29 ndash173(1) C17 Co1 C28 C27 ndash861(5) C17 Co1 C28 C29 1544(5) C18 Co1 C28 C27 ndash1355(5) C18 Co1 C28 C29 1050(5) C25 Co1 C28 C27 815(5) C25 Co1 C28 C29 ndash380(5) C26 Co1 C28 C27 387(4) C26 Co1 C28 C29 ndash809(5) C27 Co1 C28 C29 ndash1195(7) C29 Co1 C28 C27 1195(7) C5 Co1 C29 C25 953(5) C5 Co1 C29 C28 ndash1461(5) C6 Co1 C29 C25 576(9) C6 Co1 C29 C28 1762(6) C17 Co1 C29 C25 1797(7) C17 Co1 C29 C28 ndash617(9) C18 Co1 C29 C25 1437(4) C18 Co1 C29 C28 ndash977(5) C25 Co1 C29 C28 1186(7) C26 Co1 C29 C25 ndash373(4) C26 Co1 C29 C28 813(5) C27 Co1 C29 C25 ndash817(5) C27 Co1 C29 C28 369(5) C28 Co1 C29 C25 ndash1186(7) C19 Si1 C2 C1 ndash144(8) C19 Si1 C2 C3 1663(7)

- 114 -

C20 Si1 C2 C1 ndash1307(7) C20 Si1 C2 C3 500(8) C21 Si1 C2 C1 1057(7) C21 Si1 C2 C3 ndash736(7) C22 Si2 C3 C2 ndash852(7) C22 Si2 C3 C4 908(6) C23 Si2 C3 C2 1587(7) C23 Si2 C3 C4 ndash253(7) C24 Si2 C3 C2 410(8) C24 Si2 C3 C4 ndash1431(6) C18 C1 C2 Si1 1795(6) C18 C1 C2 C3 ndash1(1) C2 C1 C18 Co1 ndash817(9) C2 C1 C18 C5 1(1) C2 C1 C18 C17 173(1) Si1 C2 C3 Si2 ndash5(1) Si1 C2 C3 C4 1790(5) C1 C2 C3 Si2 1755(6) C1 C2 C3 C4 ndash0(1) Si2 C3 C4 C5 ndash1747(5) C2 C3 C4 C5 2(1) C3 C4 C5 Co1 822(8) C3 C4 C5 C6 ndash174(1) C3 C4 C5 C18 ndash2(1) Co1 C5 C6 C7 128(1) Co1 C5 C6 C17 ndash674(4) C4 C5 C6 Co1 ndash120(1) C4 C5 C6 C7 8(2) C4 C5 C6 C17 173(1) C18 C5 C6 Co1 671(4) C18 C5 C6 C7 ndash165(1) C18 C5 C6 C17 ndash03(6) Co1 C5 C18 C1 ndash1175(7) Co1 C5 C18 C17 667(4) C4 C5 C18 Co1 1179(7) C4 C5 C18 C1 0(1) C4 C5 C18 C17 ndash1754(7) C6 C5 C18 Co1 ndash663(4) C6 C5 C18 C1 1762(7) C6 C5 C18 C17 04(6) Co1 C6 C7 C8 ndash887(8) C5 C6 C7 C8 160(1) C17 C6 C7 C8 ndash2(1) Co1 C6 C17 C16 1243(7) Co1 C6 C17 C18 ndash672(4) C5 C6 C17 Co1 675(4)

- 115 -

C5 C6 C17 C16 ndash1681(7) C5 C6 C17 C18 03(5) C7 C6 C17 Co1 ndash1223(7) C7 C6 C17 C16 2(1) C7 C6 C17 C18 1705(7) C6 C7 C8 C9 ndash180(1) C6 C7 C8 C15 2(1) C7 C8 C9 C10 2(2) C7 C8 C9 C14 ndash179(1) C15 C8 C9 C10 ndash179(1) C15 C8 C9 C14 01(6) C7 C8 C15 C14 1791(7) C7 C8 C15 C16 ndash2(1) C9 C8 C15 C14 ndash01(5) C9 C8 C15 C16 1792(8) C8 C9 C10 C11 ndash180(1) C14 C9 C10 C11 1(1) C8 C9 C14 C13 1791(7) C8 C9 C14 C15 ndash01(6) C10 C9 C14 C13 ndash1(1) C10 C9 C14 C15 1796(7) C9 C10 C11 C12 ndash1(1) C10 C11 C12 C13 1(1) C11 C12 C13 C14 ndash2(1) C12 C13 C14 C9 2(1) C12 C13 C14 C15 ndash180(1) C9 C14 C15 C8 01(6) C9 C14 C15 C16 ndash179(1) C13 C14 C15 C8 ndash179(1) C13 C14 C15 C16 2(2) C8 C15 C16 C17 1(1) C14 C15 C16 C17 ndash180(1) C15 C16 C17 Co1 858(8) C15 C16 C17 C6 ndash2(1) C15 C16 C17 C18 ndash161(1) Co1 C17 C18 C1 120(1) Co1 C17 C18 C5 ndash669(4) C6 C17 C18 Co1 666(4) C6 C17 C18 C1 ndash173(1) C6 C17 C18 C5 ndash03(5) C16 C17 C18 Co1 ndash131(1) C16 C17 C18 C1 ndash11(2) C16 C17 C18 C5 162(1) Co1 C25 C26 C27 586(5) C29 C25 C26 Co1 ndash583(5) C29 C25 C26 C27 03(9)

- 116 -

Co1 C25 C29 C28 ndash598(6) C26 C25 C29 Co1 588(5) C26 C25 C29 C28 ndash10(9) Co1 C26 C27 C28 607(5) C25 C26 C27 Co1 ndash602(5) C25 C26 C27 C28 05(9) Co1 C27 C28 C29 595(6) C26 C27 C28 Co1 ndash607(5) C26 C27 C28 C29 ndash12(9) Co1 C28 C29 C25 609(6) C27 C28 C29 Co1 ndash595(6) C27 C28 C29 C25 14(9)

Photo-thermal cycle between 52 and 53

An NMR tube containing a solution of 52 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 53 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 724 (AArsquom 2 H) 683 (s 2 H) 662 (BBrsquom 2 H) 444 (s 5 H) 032 (s 18 H) ppm 13C- NMR (100 MHz C6D6) δ = 1493 1482 1430 1276 1256 1241 1155 803 796 725 222 ppm Thermal reversal could be conveniently followed by VT-NMR

Kinetic studies of the thermal CoCp migration in 53 In the glovebox 23-[bis(trimethylsilyl)] linear[3]phenylene(CpCo) 52 dissolved in the solvent of choice (C6D6 or toluene-d8) was passed through an HPLC filter and then transfered via syringe into a thick-walled NMR tube connected to a vacuum line adapter The sample was then degassed by three freeze-pump-thaw cycles and flame-sealed under vacuum Prior to the kinetic runs the mixtures were irradiated for 10 h in a Rayonet Photochemical Reactor fitted with lamps emitting at 310 and 365 nm After this treatment care was taken to exclude ambient light as it causes some isomerization The irradiated samples were then placed in the NMR spectrometer at ndash65 degC (500 MHz) which was then warmed to the required temperature In the case of the 60 degC runs the magnet was prewarmed because of the fast reaction rate at this temperature After five min the spectra were recorded The Cp signal of the photoisomer was integrated relative to the solvent peak of C6D6 or the CD3 peak of toluene-d8 and monitored as a function of time The integral from the first scan was used as [A]o Since the equilibrium constant between the isomers was 50 the kinetic analysis treated the isomerization as a first-order non-reversible process Plotting the data accordingly

CoSiMe3

SiMe3

52

CoSiMe3

SiMe3

53

hν∆

- 117 -

yielded the reaction rate constants which were used in the Eyring plots to obtain the activation parameters Kinetic studies of the thermal haptotropic shift for complex 52 Kinetic runs were executed in C6D6 as the optimum solvent A sample of 52 in degassed C6D6 or toluene-d8 was subjected to UV light for 10 h leading to maximum enrichment of 53 The sample was kept at the specified temperature and the disappearance of 53 monitored by 1H-NMR spectroscopy The reaction proved to be first-order (eq 1) consistent with an intramolecular process

[ ] [ ]Akdt

Adminus=

(1)

[ ][ ] dtkA

Ad=minus

(2)

[ ][ ]

tkA

A=minus

0

ln (3)

The rate constant (k) at 30 40 50 and 60 degC was obtained from the slope of a plot of ndashln([A][A]0) versus time (t) following eq 2 and 3 The actual error in reproducibility was estimated by the calculation of one standard deviation (σ) for a triplicate run at 60 degC The percentage error was applied for k at 30 40 and 50 degC The rate constants and their errors are given in Tables 411 and 414 The values for k and their standard deviations were used to calculate the activation enthalpy (∆HDagger) and entropy (∆SH) of the haptotropic shift The basis for these calculations is the Eyring equation (eq 4) This expression (eq 4) was transformed to eq 5 and the activation enthalpy (∆HDagger) obtained from the slope of a plot of ndashln(kT) versus 1RT The intercept (ndashC) provides the activation entropy (∆SH) following eq 6 and 7

C

TR

H

R

S

h

k

TR

H

T

k B

minus∆

=

∆+minus

∆=minus

ne

nene

lnln

( 4)

R

S

h

kC B

ne∆+= ln

(5)

minus=∆ ne

h

kCRS Bln

(6)

- 118 -

The errors in ∆HDagger and ∆SDagger were calculated based on those in the rate constants leading to two additional least square fits in the Eyring plot These fits represent the two most extreme deviations from the original plot This provides a conservative error estimate and finally the values of 204plusmn14 kcalmol for ∆HH and 158plusmn22 eu (calmolmiddotK) for ∆SH in C6D6 In order to probe for solvent effects the kinetics were also repeated in toluene-d8 The preparation of the sample followed the described procedure and the rate constants (k) were obtained at 30 40 50 and 60 degC At 60 degC three measurements were carried out to estimate the errors in reproducibility for k and the activation parameters Error propagation was done as described for the kinetic experiments in C6D6 It is assumed that those rate constants (k) show the same relative error as the ones for the rearrangement of 53 to 52 in C6D6 The activation parameters in toluene-d8 were found to be 231plusmn07 kcalmol and 60plusmn13 eu

Table 410 Kinetic Data for the Conversion of 53 to 52 in C6D6

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09657 00349 1000 09419 00599 6000 09380 00640 2000 09018 01034 9000 09038 01012 3000 08557 01558 12000 08760 01324 4000 08176 02013 15000 08418 01723 5000 07796 02490 18000 08206 01978 6000 07555 02804 21000 08010 02219 7000 07255 03210 32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 400 09541 00470 30 09888 00113 800 09197 00837 60 09820 00181 1200 08910 01154 90 09708 00296 1600 08489 01638 120 09596 00413 2000 08298 01865 150 09506 00507 2400 07954 02289 180 09416 00602 2800 07591 02756 210 09348 00674 240 09281 00746 270 09213 00819 300 09124 00917 330 09034 01016 360 08966 01091

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

- 119 -

0 10000 00000 0 10000 00000 30 09950 00050 30 09909 00092 60 09900 00101 60 09854 00147 90 09800 00202 90 09762 00241 120 09750 00253 120 09671 00335 150 09700 00305 150 09634 00372 180 09625 00382 180 09543 00468 210 09575 00434 210 09433 00583 240 09475 00539 240 09397 00622 270 09400 00619 270 09287 00740 300 09350 00672 300 09232 00799 330 09300 00726 330 09177 00858 360 09250 00780 360 09086 00959

Table 411 The Rate Constants (k) in C6D6 Calculated From the Data in Table 410 and Their

Standard Deviations (σ)

Temp (K) k (1s) σσσσ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 10809Endash05 74258Endash07 09970 171494 00688

31315 45615Endash05 31338Endash06 09948 157420 00688

32315 95118Endash05 65346Endash06 09965 150385 00688

33315 (1) 27425Endash04 09965

33315 (2) 25714Endash04 09964

33315 (3) 30051Endash04 09990

33315 (avg) 26511Endash04 18841Endash05 140101 00688

Table 412 Activation Parameters for the Kinetic Experiments in C6D6

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 90990 85414 79291 Intercept ndash1789 ndash1674 ndash1559 R

2 09869 09869 09869

∆HDagger (Jmol) 90990 85414 79291

∆HDagger (kcalmol) 217 204 190

∆SDagger (JmolmiddotK) ndash569 ndash660 ndash751

∆SDagger (eu) ndash136 ndash158 ndash180

- 120 -

(323 15 K 50 degC) y = 95118E-05x + 44505E-03

R2 = 9965

(30315 K 30 degC) y = 10809E-05x + 20474E-03

R2 = 9970

(31315 K 40 degC) y = 45615E-05x + 11689E-02

R2 = 9948

(33315 K 60 degC) y = 263387E-04x + 390297E-04

R2 = 9992

000

005

010

015

020

025

030

035

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

Figure 43 Kinetic plots for the conversion of 53 to 52 in C6D6

Table 413 Kinetic Data for the Conversion of 53 to 52 in Toluene-d8

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09556 00454 1000 09488 00526 6000 09256 00773 2000 08931 01130 9000 08956 01103 3000 08545 01572 12000 08667 01430 4000 08143 02054 15000 08343 01811 5000 07818 02461 18000 08103 02103 6000 07559 02798 21000 07863 02404 7000 07179 03314

- 121 -

32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

000 10000 00000 0 10000 00000 40000 09470 00544 30 09887 00113 80000 08934 01127 60 09775 00228 120000 08594 01515 90 09691 00314 160000 08175 02015 120 09592 00416 200000 07861 02406 150 09473 00542 240000 07502 02875 180 09381 00639 280000 06991 03579 210 09262 00767 240 09149 00889 270 09086 00959 300 08973 01083 330 08868 01202 360 08762 01321

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 30 09945 00055 30 09910 00090 60 09795 00207 60 09828 00173 90 09700 00304 90 09716 00288 120 09645 00361 120 09559 00451 150 09479 00535 150 09440 00576 180 09464 00551 180 09313 00712 210 09314 00711 210 09238 00792 240 09188 00847 240 09156 00882 270 09101 00942 270 08992 01063 300 08991 01064 300 08932 01129 330 08896 01170 330 08872 01197 360 08801 01277 360 08686 01409

- 122 -

Table 414 The Rate Constants (k) in Toluene-d8 Calculated From the Data in Table 413 and Their Standard Deviations (σ)

Temp (K) k (1s) σ σ σ σ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 11314Endash05 37152Endash07 09976 17104 05610

31315 46470Endash05 15251Endash06 09948 15723 05157

32315 12214Endash04 401074Endash06 09957 14788 04851

33315 (1) 36441Endash04 09992

33315 (2) 36124Endash04 09951

33315 (3) 38855Endash04 09956

33315 (avg) 37140Endash04 14937Endash05 13707 04496

Table 415 Activation Parameters for the Kinetic Experiments in Toluene-d8

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 96590 93523 90455 Intercept ndash2073 ndash2007 ndash1941 R

2 09962 09962 09962

∆HDagger (Jmol) 96590 93523 90455

∆HDagger (kcalmol) 2309 2235 2162

∆SDagger (JmolmiddotK) ndash2521 ndash3068 ndash3615

∆SDagger (eu) ndash602 ndash733 ndash864

- 123 -

00000

00500

01000

01500

02000

02500

03000

03500

04000

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

(31315 K 40 degC) y = 46470E-05x + 10553E-02

R2 = 9948

(32315 K 50 degC) y = 12214E-04x + 47671E-03

R2 = 9957

(33315 K 60 degC)y = 371377E-04x - 208381E-03

R2 = 9992

(30315 K 30 degC) y = 11314E-05x + 71900E-03

R2 = 9976

Figure 44 Kinetic plots for the conversion of 53 to 52 in toluene-d8

- 124 -

(C6D6) y = 85141x - 16743

R2

= 09869

(toluene-d 8) y = 93523x - 2007

R2 = 09962

13600

14600

15600

16600

17600

36100E-04

36600E-04

37100E-04

37600E-04

38100E-04

38600E-04

39100E-04

39600E-04

40100E-04

1RT (Jmol)

-ln

(kT

)

Figure 45 Eyring plots for conversion of 53 to 52 MeCpCo(CO)2

Adapted from the literature procedure50 Co2(CO)8 (809 g 2366 mmol) was added to a round bottom flask in the glovebox The flask was capped with a septum and brought out of the glovebox A reflux condenser connected to the high vacuum line was quickly exchanged with the septum under a heavy purge of argon Degassed CH2Cl2 (30 mL) was added followed by freshly cracked deoxygenated methylcyclopentadiene (135 mL 123 mmol) The mixture evolved gas upon addition of the methylcyclopentadiene indicating CO liberation The entire setup was protected from light with foil and heated to a gentle reflux using a heating mantlevariac heat source After stirring at reflux for 26 h the mixture now dark crimson in color was cooled to rt The reflux condenser was quickly exchanged for a distillation head under an Ar purge and CH2Cl2 distilled off at atmospheric pressure under Ar Vacuum distillation at 002 Torr was performed and the forerun discarded The desired complex was obtained as a red liquid (7296 g 79) bp = 31 degC (002 Torr) stored at ndash10 degC and shielded from light Note A small

CoOC CO

- 125 -

amount of methylcyclopentadiene dimer (15 ) which could not be separated was present in the isolated product This was deemed harmless however and the obtained product was used in further experiments without further purification 85 pure 1H-NMR data match those reported in the literature 1H-NMR (C6D6) δ = 145 (s 3 H) 431 (br s 2 H) 451 (br s 2 H) 23-Bis(trimethylsilyl) linear [3]phenylene(MeCpCo) 54

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (0146 g 0424 mmol) in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (0101 g 0731 mmol) The mixture was stirred for 100 min and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the remaining yellow residue was dissolved in freshly distilled THF (15 mL) The green solution was separated from the solids via canula filtration and transferred into another Schlenk flask After a 20 min Ar purge MeCpCo(CO)2 (0092 g 0403 mmol) was added and the resulting solution (protected from light with foil) injected via syringe pump over 9 h into a boiling mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 15 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (201) The volatiles were again removed under high vacuum line and the residue crystallized from acetone yielding 55 (0125 g 61 ) as black crystals mp 163ndash165 degC 1H-NMR (500 MHz C6D6) δ = 783 (s 2 H) 676 (m 4 H) 675 (s 2 H) 442 (apparent t J = 21 Hz 2 H) 427 (apparent t J = 21 Hz 2 H) 134 (s 3 H) 038 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1423 1386 1354 1293 1193 1147 899 806 798 783 739 111 279 ppm IR (neat) ν~ = 2959 2923 2853 1462 1455 1378 1260 1093 1030 802 cmndash1 UV-VIS (hexane) λmax (log ε) = 256 (368) 281 (356) 293 (359) 310 (373) 350 (368) 386 (sh 321) 437 (sh 287) 499 (sh 247) end absorption to 550 nm MS (70 eV) mz () 508 (100) [M+] 370 (28) HRMS (FAB) calcd for C30H33CoSi2 5081453 found 5081442 Photo-thermal cycle between 54 and 56

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

54

CoSiMe3

SiMe3

56

hν∆

Me Me

- 126 -

An NMR tube containing a solution of 54 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 56 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 715 (AArsquom obscured by solvent peak) 680 (s 2 H) 664 (AArsquom 2 H) 447 (apparent t J = 21 Hz 2 H) 428 (apparent t J = 21 Hz 2 H) 148 (s 3 H) 032 (s 18 H) ppm Thermal reversal could be conveniently followed by VT-NMR

14-Deuterio-23-bis(trimethylsilyl) linear [3]phenylene cyclopentadienylcobalt 55

To 23-bis(trimethylsilylethynyl)biphenylene 52 (0144 g 0418 mmol) in CH3OD (10 mL) was added freshly distilled ether (20 mL) and K2CO3 (0083 g 0600 mmol) The mixture was stirred for 100 min and monitored by TLC (hexaneCH2Cl2 51) When the starting material had disappeared the solvents were removed and the remaining yellow residue very quickly dissolved in freshly distilled THF (10 mL) The green solution was separated from the solids using a filter cannula and transferred to another Schlenk flask After a 20 min Ar purge CpCo(CO)2 (0072 g 0400 mmol) was added and the resulting solution (protected from light with foil) was injected via syringe pump over 7 h into a refluxing mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 14 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed on the high vacuum line and the residue recrystallized from acetone yielding 8 (0085 g 41 ) as dark red crystals 1H-NMR spectroscopy showed 63 incorporation of deuterium as indicated by the diminution of the peak intensity of the signal at δ = 796 (s 074 H) ppm MS (FAB) mz () 496 (100) [M+] 372 (19)

CoSiMe3

SiMe3

D

D

- 127 -

Crossover experiment with 54 and 55

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

h

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

5455

5657

A solution of complex 55 (~2 mg) and 54 (~2 mg) in C6D6 (06 mL) rigorously protected from light was analyzed by 1H-NMR spectroscopy to reveal a 1861 mixture of 5554 The peak for 55 at δ = 796 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound A mass spectrum of an aliquot gave the appropriate composite of the two respective molecular ion patterns (Figure 46) The sample was then irradiated as described for above 13 h at RT The 1H-NMR spectrum of the irradiated mixture showed the presence of the respective photoisomers of 55 and 54 There were no unidentifiable peaks the signal at δ = 7470 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound and the clearly resolved peak for 56 at δ = 7473 (s 2 H) ppm revealed unattenuated intensity An aliquot was submitted for mass spectral analysis furnishing the same pattern as that depicted above The sample was then placed in an oil bath preheated to 80 degC for 30 h a treatment that regenerated the original NMR spectrum of the mixture of 55 and 54 including the relative integration ratios Similarly mass spectral analysis resulted in the same pattern as that depicted in Figure 46

- 128 -

Figure 46 Mass spectrum from the crossover experiment between 55 and 56

Low temperature photolyses of 19 and 52 A small amount (~5 mg) of linear[3]phenylene(CpCo) 19 or 52 dissolved in toluene-d8 was added to a J-Young NMR tube in the glovebox The sealed sample was then placed inside a Pyrex Dewar flask positioned in a Rayonet Photochemical Reactor outfitted with UV-lamps emitting at 310 and 350 nm (as shown in Figure 214) Cooling was achieved with the use of a Neslab Refrigerated Circulating bath employing isopropanol as the cooling medium The cold isopropanol was pumped into and out of the Pyrex Dewar using securely fastened Tygon tubes maintaining a temperature of ndash55 to ndash50 degC Once the sample was chilled irradiation was commenced The total irradiation time varied from 25 to 4 h When analysis was required the sample was transported in another Dewar flask containing dry iceisopropanol (ndash78 degC) while the NMR spectrometer was prepared for the low temperature experiment The spectrometer was cooled (ndash80 to ndash30 degC depending on the experiment) the sample wiped with a paper towel placed inside the spinner and very quickly lowered manually with a string into the cold magnet After allowing time for the temperature to equilibrate (10 min) a spectrum was recorded For VT experiments the temperature was slowly

- 129 -

raised from ndash80 degC in 10 degree increments to 10 degC Spectra were recorded at each interval For all other experiments spectra were recorded at ndash30 degC 2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

In the glovebox 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19 (0049 g 0133 mmol) and CpCo(C2H4)2 (0025 g 0139 mmol)99 were added to a Schlenk flask The flask was sealed brought out of the box connected to a vacuum manifold and freshly distilled degassed benzene (15 mL) added The mixture was heated to 70 degC on an oil bath for 23 h before being cooled to RT The solvent was removed in vacuo giving a black residue that was rapidly filtered through a plug of neutral alumina activity III (25 x 35 cm) eluting with a mixture of hexanes and THF (1001) under nitrogen and into a Schlenk flask The solvents were again removed in vacuo and the ensuing black residue recrystallized from acetone at ndash78 degC to give pure 78 (0057 g 56 ) as black crystals 1H-NMR (400 MHz acetone-d6) δ = 039 (s 36H) 481 (s 2H) 489 (m 4H) 736 (s 4H) ppm 13C-NMR (100 MHz acetone-d6) δ = 266 5372 5710 8284 12587 14542 15054 ppm UV-VIS (hexane) λmax (log ε) 197 (334) 221 (336 sh) 244 (344) 286 (363) 386 (279 sh) 439 (258) MS (FAB) 762 (M+ 100) HRMS calcd for C40H52Si4Co2 7621810 found 7621791 43 Computational Details for Chapter Two All calculations were performed using the GAUSSIAN03100 program GaussView 30101 and ChemCraft102 were employed to input structures as well as view output results Optimized geometries were obtained at the hybrid density functional theory (DFT) using Beckersquos three-parameter exchange-correlation functional103 containing the non-local gradient correction of Lee Yang and Parr104 (B3LYP) For optimization purposes a standard basis 3-21G105 was used for hydrogen and carbon atoms For cobalt the LANL2DZ106 basis set was applied with the outermost d function released yielding a triple-zeta d basis along with the effective core potentials (ECP) to describe the core electrons For the single point energy calculations the basis sets were increased to 6-31G107 for hydrogen 6-311G108 for carbon and the modified LANL2DZ basis as described above for cobalt with an added f-orbital coefficient109 The potential energy surfaces were mapped through a scan calculation a feature also available within the GAUSSIAN03 program Transition state structures were obtained in three different steps (i) determination of initial and final products or the minimum closest to a TS (ii) a linear QST2110 search for an initial guess of a TS and

- 130 -

(iii) input of the results from (ii) into a QST3 search Transition states and minima were confirmed by carrying out frequency calculations (using the same basis as that used for the optimizations)

Calculated structures for linear [3]phenylene(CpCo) (labels from Figures 29 and 210 in Section 24)

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

C 2878616000 ndash1675635000 ndash1461246000 C 3986441000 ndash2043582000 ndash0714088000 C 3986471000 ndash2043226000 0714700000 C 2878686000 ndash1674908000 1461732000 C 1740663000 ndash1265994000 0736724000 C 1740638000 ndash1266353000 ndash0736388000 H 2884721000 ndash1731772000 ndash2551997000 H 2884845000 ndash1730511000 2552509000 C 0311237000 ndash0833174000 0748280000 C 0311204000 ndash0833522000 ndash0748106000 C ndash0893980000 ndash0698348000 ndash1520584000 C ndash0893913000 ndash0697588000 1520749000 C ndash1996288000 ndash0532216000 0744771000 C ndash1996322000 ndash0532586000 ndash0744640000 C ndash3491040000 ndash0328769000 ndash0716524000 C ndash3490989000 ndash0328300000 0716632000 C ndash4645388000 ndash0172650000 ndash1448232000 C ndash4645276000 ndash0171672000 1448326000 C ndash5836534000 ndash0014205000 ndash0697760000

- 131 -

C ndash5836481000 ndash0013731000 0697841000 H ndash0905006000 ndash0741217000 ndash2609771000 H ndash0904887000 ndash0739873000 2609960000 H ndash4666353000 ndash0168153000 ndash2539086000 H ndash6785734000 0111682000 ndash1227959000 H ndash6785641000 0112502000 1228028000 H ndash4666162000 ndash0166493000 2539178000 Co 1455829000 0662094000 ndash0000295000 C 0672548000 2613322000 0000481000 C 1502831000 2459745000 1168426000 C 2819523000 2140942000 0722371000 C 2818808000 2141294000 ndash0723848000 C 1501651000 2460224000 ndash1168394000 H ndash0391329000 2836892000 0001070000 H 1172930000 2540112000 2200200000 H 3678957000 1932268000 1353707000 H 3677612000 1932967000 ndash1356152000 H 1170676000 2541059000 ndash2199789000 H 4894703000 ndash2369906000 1230670000 H 4894651000 ndash2370516000 ndash1229936000

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

C ndash3991583000 ndash2430244000 ndash0695300000 C ndash2895249000 ndash1923385000 ndash1446977000 C ndash1838331000 ndash1436925000 ndash0718218000 C ndash0460541000 ndash0772703000 ndash0748934000

- 132 -

C 0758545000 ndash0733408000 ndash1513161000 C 1871918000 ndash0586111000 ndash0739684000 C 3374782000 ndash0432509000 ndash0717168000 C 4533131000 ndash0322603000 ndash1448209000 C 5731498000 ndash0208370000 ndash0696796000 C 5731438000 ndash0207885000 0696952000 C 4533003000 ndash0321597000 1448333000 C 3374722000 ndash0432010000 0717261000 C 1871861000 ndash0585642000 0739747000 C 0758457000 ndash0732583000 1513259000 C ndash0460578000 ndash0772439000 0748991000 C ndash1838348000 ndash1436677000 0718485000 C ndash2895298000 ndash1922892000 1447371000 C ndash3991613000 ndash2429987000 0695830000 H ndash4853881000 ndash2841402000 ndash1229010000 H ndash2909366000 ndash1943431000 ndash2538196000 H 0770744000 ndash0814782000 ndash2600896000 H 4554949000 ndash0321315000 ndash2539049000 H 6684245000 ndash0118682000 ndash1227928000 H 6684140000 ndash0117859000 1228104000 H 4554722000 ndash0319567000 2539175000 H 0770611000 ndash0813312000 2601042000 H ndash2909450000 ndash1942588000 2538596000 H ndash4853932000 ndash2840954000 1229654000 Co ndash1032604000 1030206000 ndash0000179000 C ndash2903591000 1947430000 ndash0000175000 C ndash2211742000 2430689000 ndash1177143000 C ndash1026232000 3056089000 ndash0732194000 C ndash1026229000 3056139000 0731719000 C ndash2211730000 2430773000 1176747000 H ndash3829247000 1376180000 ndash0000150000 H ndash2513347000 2264399000 ndash2207387000 H ndash0243163000 3477094000 ndash1358586000 H ndash0243137000 3477190000 1358051000 H ndash2513304000 2264572000 2207015000

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 133 -

C 4829664000 ndash1220862000 0883782000 C 3649435000 ndash0895915000 1609183000 C 2478533000 ndash0900239000 0886069000 C 0985532000 ndash0699413000 0895282000 C ndash0207413000 ndash0351140000 1567281000 C ndash1295977000 ndash0355264000 0631690000 C ndash2799524000 ndash0368596000 0647705000 C ndash3950748000 0104186000 1252743000 C ndash5173877000 ndash0370408000 0725519000 C ndash5217559000 ndash1270006000 ndash0351644000 C ndash4043168000 ndash1754445000 ndash0967619000 C ndash2843350000 ndash1293792000 ndash0444950000 C ndash1365414000 ndash1319830000 ndash0538287000 C ndash0225558000 ndash1662005000 ndash1182029000 C 0928168000 ndash1009692000 ndash0554559000 C 2436156000 ndash1209374000 ndash0509824000 C 3575395000 ndash1530032000 ndash1215144000 C 4792344000 ndash1526592000 ndash0477473000 H 5781080000 ndash1237670000 1406156000 H 3693287000 ndash0679862000 2671420000 H ndash0279175000 ndash0037747000 2601166000 H ndash3939706000 0801901000 2083798000 H ndash6106757000 ndash0031072000 1165263000 H ndash6183419000 ndash1601741000 ndash0720200000 H ndash4097586000 ndash2453276000 ndash1795561000 H ndash0137803000 ndash2306368000 ndash2049380000 H 3570207000 ndash1781979000 ndash2270507000 H 5717527000 ndash1774506000 ndash0988963000 Co 0235674000 0924694000 ndash0006080000 C 1650242000 2605908000 ndash0261710000 C 0606451000 3071372000 0583798000

C ndash0633939000 2891762000 ndash0112192000 C ndash0354070000 2388098000 ndash1431110000 C 1060641000 2182627000 ndash1507942000 H 2701380000 2562827000 ndash0018620000 H 0717262000 3431891000 1595877000 H ndash1615358000 3123686000 0274491000 H ndash1077256000 2190401000 ndash2207047000

- 134 -

H 1601331000 1788686000 ndash2355167000

(d) Transition State 2 η3-benzene (249 kcalmol)

C 5059641000 ndash0675345000 0741440000 C 3868057000 ndash0242461000 1393542000 C 2691208000 ndash0611642000 0796692000 C 1164924000 ndash0568451000 0814993000 C 0001006000 ndash0193010000 1575722000 C ndash1162903000 ndash0569406000 0815406000 C ndash2689168000 ndash0613549000 0797134000 C ndash3866228000 ndash0245076000 1394017000 C ndash5057560000 ndash0678583000 0741882000 C ndash5030442000 ndash1430649000 ndash0426732000 C ndash3802288000 ndash1812828000 ndash1038342000 C ndash2662603000 ndash1392426000 ndash0404590000 C ndash1143695000 ndash1392940000 ndash0383227000 C 0001354000 ndash1885575000 ndash1010384000 C 1146183000 ndash1392203000 ndash0383465000 C 2665098000 ndash1390792000 ndash0404876000 C 3805017000 ndash1810598000 ndash1038596000 C 5032958000 ndash1427555000 ndash0427087000 H 6017043000 ndash0408623000 1174840000 H 3916675000 0338622000 2306082000 H 0001106000 0141040000 2603832000 H ndash3915179000 0335814000 2306664000 H ndash6015116000 ndash0412488000 1175329000

- 135 -

H ndash5963925000 ndash1737868000 ndash0883265000 H ndash3794877000 ndash2406462000 ndash1944276000 H 0001449000 ndash2505619000 ndash1894591000 H 3797948000 ndash2404400000 ndash1944423000 H 5966616000 ndash1734262000 ndash0883606000 Co ndash0000294000 1006304000 0016484000 C 1144150000 2811021000 ndash0317903000 C ndash0001831000 3236912000 0413780000 C ndash1150105000 2808519000 ndash0312717000 C ndash0712506000 2257800000 ndash1588662000 C 0702130000 2259464000 ndash1591918000 H 2174046000 2940434000 ndash0021226000 H ndash0000096000 3693787000 1391408000 H ndash2178919000 2935539000 ndash0011312000 H ndash1360790000 1903514000 ndash2375388000 H 1347563000 1907002000 ndash2381795000

Calculated structures for linear [5]phenylene CpCo (labels from Figures 211 and 212 in Section 24)

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

C ndash2147283000 ndash0385762000 ndash0741520000 C ndash2146881000 ndash0382747000 0740465000 C ndash0675330000 ndash0218887000 0741228000 C ndash0675503000 ndash0222208000 ndash0743565000 C 0535474000 ndash0309864000 ndash1519364000

- 136 -

C 1654024000 ndash0363787000 ndash0743565000 C 1653968000 ndash0359108000 0742223000 C 0535464000 ndash0301263000 1517648000 C 3146303000 ndash0437352000 0715394000 C 3146555000 ndash0442081000 ndash0715839000 H 0537903000 ndash0329735000 2601810000 H 0538062000 ndash0344229000 ndash2603354000 Co ndash1585768000 1444604000 ndash0004763000 C ndash2656365000 3118646000 0813641000 C ndash1264152000 3247968000 1115884000 C ndash0546296000 3292610000 ndash0128221000 C ndash1500173000 3225060000 ndash1199322000 C ndash2801883000 3099872000 ndash0616868000 H ndash3459184000 3033020000 1530368000 H ndash0824887000 3279284000 2101474000 H 0525240000 3366953000 ndash0237713000 H ndash1272392000 3239735000 ndash2254384000 H ndash3732669000 2998753000 ndash1154572000 C ndash3315848000 ndash0698077000 1516941000 C ndash3316515000 ndash0705270000 ndash1515890000 C ndash4404590000 ndash0970491000 0742487000 C ndash4404888000 ndash0974125000 ndash0739677000 H ndash3311463000 ndash0745189000 ndash2599679000 H ndash3310191000 ndash0733014000 2600900000 C ndash5857232000 ndash1346832000 ndash0713671000 C ndash5856902000 ndash1343302000 0718959000 C ndash6992149000 ndash1638138000 ndash1445564000 C ndash6991464000 ndash1630979000 1452826000 C 4314567000 ndash0501395000 ndash1493440000 C 4313844000 ndash0491124000 1494022000

C ndash8157130000 ndash1937355000 ndash0695553000 C ndash8156796000 ndash1933908000 0704865000 H ndash7013569000 ndash1630976000 2537309000 H ndash9075842000 ndash2169721000 1232475000 H ndash9076411000 ndash2175846000 ndash1221548000 H ndash7014707000 ndash1643790000 ndash2530023000 C 5464859000 ndash0553191000 0719930000 C 5465218000 ndash0558312000 ndash0718328000 C 6977989000 ndash0635007000 ndash0714777000 C 6977565000 ndash0629511000 0717833000 H 4313279000 ndash0484164000 2577745000 H 4314609000 ndash0502067000 ndash2577185000 C 8138196000 ndash0684071000 1451266000 C 8139115000 ndash0695400000 ndash1446980000 C 9348946000 ndash0746919000 0699256000 C 9349380000 ndash0752387000 ndash0693700000

- 137 -

H 8162380000 ndash0700716000 ndash2531270000 H 8160717000 ndash0680929000 2535584000 H 10294800000 ndash0791917000 1230058000 H 10295576000 ndash0801571000 ndash1223516000

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

C ndash8026536000 ndash2149127000 ndash0697047000 C ndash6872771000 ndash1801590000 ndash1447012000 C ndash5755909000 ndash1466198000 ndash0717983000 C ndash4305789000 ndash1041476000 ndash0739357000 C ndash3218268000 ndash0750848000 ndash1510952000 C ndash2077793000 ndash0315087000 ndash0749237000 C ndash0550342000 ndash0400850000 ndash0716361000 C 0616872000 ndash0404801000 ndash1489728000 C 1770640000 ndash0412395000 ndash0716060000 C 3300443000 ndash0457807000 ndash0715861000 C 4454767000 ndash0490291000 ndash1489427000 C 5616257000 ndash0520747000 ndash0712496000 C 5616269000 ndash0520699000 0712492000 C 4454793000 ndash0490190000 1489443000 C 3300455000 ndash0457762000 0715895000 C 1770651000 ndash0412347000 0716117000 C 0616894000 ndash0404700000 1489800000 C ndash0550335000 ndash0400796000 0716454000 C ndash2077818000 ndash0315060000 0749341000 C ndash3218306000 ndash0750915000 1510996000

- 138 -

C ndash4305781000 ndash1041534000 0739359000 C ndash5755900000 ndash1466256000 0717962000 C ndash6872758000 ndash1801708000 1446971000 C ndash8026533000 ndash2149171000 0696987000 H ndash6893447000 ndash1807486000 ndash2529846000 H ndash3199702000 ndash0827686000 ndash2591829000 H 0616147000 ndash0415875000 ndash2572166000 H 4455855000 ndash0492565000 ndash2571217000 H 4455901000 ndash0492389000 2571233000 H 0616188000 ndash0415693000 2572238000 H ndash3199790000 ndash0827916000 2591862000 H ndash6893430000 ndash1807681000 2529804000 Co ndash2237895000 1566525000 ndash0000035000 C ndash0770702000 3039808000 0000091000 C ndash1582333000 3276979000 1176306000 C ndash2906316000 3484053000 0731575000 C ndash2906172000 3484095000 ndash0731735000 C ndash1582100000 3277047000 ndash1176233000 H 0281094000 2798829000 0000215000 H ndash1247438000 3209109000 2198999000 H ndash3777291000 3625124000 1353071000 H ndash3777011000 3625160000 ndash1353424000 H ndash1246943000 3209260000 ndash2198847000 H ndash8933230000 ndash2423019000 ndash1224452000 H ndash8933222000 ndash2423113000 1224377000 C 7146943000 ndash0559737000 0717588000 C 7146931000 ndash0559786000 ndash0717614000 C 8302361000 ndash0588480000 1447040000 C 8302337000 ndash0588576000 ndash1447082000 C 9516918000 ndash0618789000 ndash0692883000 C 9516929000 ndash0618742000 0692823000 H 8324450000 ndash0589130000 2529610000 H 10461320000 ndash0642422000 1224406000 H 10461300000 ndash0642481000 ndash1224480000 H 8324409000 ndash0589299000 ndash2529653000

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 139 -

C ndash7810644000 ndash2064896000 ndash0088979000 C ndash6582065000 ndash2396690000 ndash0700394000 C ndash5469369000 ndash1694626000 ndash0259356000 C ndash4011414000 ndash1478684000 ndash0398743000 C ndash2839913000 ndash1679834000 ndash1045300000 C ndash1807973000 ndash0777407000 ndash0523048000 C ndash0288034000 ndash0728447000 ndash0497727000 C 0877200000 ndash0917515000 ndash1257428000 C 2033335000 ndash0625143000 ndash0541547000 C 3550975000 ndash0572504000 ndash0566638000 C 4702932000 ndash0775398000 ndash1323945000 C 5869717000 ndash0493099000 ndash0604711000 C 5877160000 ndash0049178000 0749672000 C 4719648000 0152978000 1509600000 C 3558389000 ndash0127834000 0791889000 C 2041313000 ndash0178303000 0818968000 C 0890228000 0010834000 1576182000

C ndash0275189000 ndash0290874000 0857465000 C ndash1777915000 ndash0332627000 0896504000 C ndash3000252000 ndash0144927000 1576583000 C ndash4087655000 ndash0414543000 0681649000 C ndash5565811000 ndash0681071000 0748878000 C ndash6769777000 ndash0358061000 1349731000 C ndash7902756000 ndash1078577000 0906205000 H ndash6531350000 ndash3165530000 ndash1463988000 H ndash2656944000 ndash2379915000 ndash1852763000

- 140 -

H 0873498000 ndash1259556000 ndash2286041000 H 4697058000 ndash1113491000 ndash2353481000 H 4726794000 0489146000 2539724000 H 0892018000 0335667000 2610226000 H ndash3107471000 0242268000 2582171000 H ndash6863567000 0403771000 2116786000 Co ndash2805901000 1045228000 ndash0126008000 C ndash1966955000 3131745000 ndash0137391000 C ndash3345106000 3172285000 0219040000 C ndash4105003000 2591218000 ndash0859559000 C ndash3194452000 2177424000 ndash1877135000 C ndash1861601000 2475718000 ndash1403791000 H ndash1139494000 3467521000 0469940000 H ndash3757304000 3575577000 1132204000 H ndash5178689000 2478840000 ndash0883920000 H ndash3449207000 1717975000 ndash2819531000 H ndash0944137000 2267497000 ndash1933863000 H ndash8711780000 ndash2586977000 ndash0395882000 H ndash8871888000 ndash0864282000 1346179000 C 7394568000 0005138000 0727783000

C 7387058000 ndash0441388000 ndash0634217000 C 8557433000 0273605000 1404315000

C 8542647000 ndash0629395000 ndash1349402000 C 9760631000 ndash0352464000 ndash0653366000 C 9767843000 0080954000 0667800000 H 8586089000 0612106000 2434348000 H 10716375000 0279405000 1157078000

H 10703753000 ndash0485281000 ndash1174332000 H 8560430000 ndash0966385000 ndash2380163000

(d) Transition state 4 η3-benzene (367 kcalmol)

- 141 -

C 7669717000 ndash2174926000 ndash0105923000 C 6450462000 ndash2458728000 0544003000 C 5349535000 ndash1733337000 0120322000 C 3893688000 ndash1505268000 0269179000 C 2708972000 ndash1942858000 0838638000 C 1596115000 ndash1239419000 0370186000 C 0149218000 ndash1103313000 0368184000 C ndash1061261000 ndash1583264000 0932639000 C ndash2167377000 ndash0965378000 0405284000 C ndash3686709000 ndash0866795000 0409630000 C ndash4872520000 ndash1347856000 0960688000 C ndash5997863000 ndash0728310000 0421450000 C ndash5941471000 0288854000 ndash0586107000 C ndash4758793000 0770529000 ndash1137452000 C ndash3629556000 0150846000 ndash0598044000 C ndash2119390000 0068600000 ndash0617626000 C ndash0945265000 0548559000 ndash1173832000 C 0191709000 ndash0072876000 ndash0643629000 C 1695402000 ndash0118964000 ndash0667389000 C 2835200000 0041396000 ndash1507494000 C 3981535000 ndash0415532000 ndash0796385000 C 5449049000 ndash0747489000 ndash0920326000 C 6638556000 ndash0473422000 ndash1556289000 C 7762417000 ndash1216205000 ndash1122513000 H 6396888000 ndash3209338000 1323030000 H 2647172000 ndash2772334000 1532449000 H ndash1099468000 ndash2356302000 1688990000 H ndash4914534000 ndash2116326000 1720908000 H ndash4717626000 1537921000 ndash1898781000 H ndash0906852000 1317204000 ndash1935050000 H 2849903000 0560387000 ndash2457942000 H 6730568000 0262385000 ndash2346085000 Co 3078365000 1106450000 0223118000 C 2432920000 3235925000 0352954000 C 3805628000 3232135000 ndash0000959000 C 4525686000 2519574000 1027488000 C 3591065000 2151422000 2051886000 C 2287258000 2550618000 1620273000

- 142 -

H 1625110000 3662123000 ndash0222202000 H 4237852000 3652387000 ndash0895767000 H 5588986000 2336674000 1044912000 H 3828106000 1629983000 2966790000 H 1363656000 2417646000 2161607000 H 8562189000 ndash2715853000 0187384000 H 8723754000 ndash1039126000 ndash1591154000 C ndash7467794000 0379383000 ndash0580257000 C ndash7522920000 ndash0639213000 0428535000 C ndash8594261000 0964602000 ndash1089561000 C ndash8706397000 ndash1090617000 0945872000 C ndash9887862000 ndash0485330000 0420145000 C ndash9834353000 0499744000 ndash0555359000 H ndash8574126000 1734202000 ndash1850912000 H ndash10757407000 0931123000 ndash0925119000 H ndash10851990000 ndash0807405000 0796463000 H ndash8770071000 ndash1858056000 1706995000

(e) Local minimum 3 η4-benzene (190 kcalmol)

C ndash7704806000 ndash1625445000 ndash0076324000 C ndash6491455000 ndash1789497000 ndash0801300000 C ndash5352262000 ndash1326936000 ndash0190371000 C ndash3836374000 ndash1127906000 ndash0291559000 C ndash2669014000 ndash1876939000 ndash0775878000 C ndash1540408000 ndash1361850000 ndash0248671000 C ndash0067088000 ndash1219487000 ndash0231176000 C 1147603000 ndash1746746000 ndash0723682000

- 143 -

C 2245517000 ndash1037457000 ndash0289605000 C 3767258000 ndash0910575000 ndash0313273000 C 4961694000 ndash1439625000 ndash0795996000 C 6075343000 ndash0726547000 ndash0354068000 C 5999362000 0418026000 0498208000 C 4804020000 0947684000 0980899000 C 3691158000 0235329000 0538756000 C 2171505000 0121554000 0570963000 C 0990404000 0649716000 1051234000

C ndash0139369000 ndash0066282000 0613306000 C ndash1640889000 ndash0139469000 0665899000 C ndash2708579000 0044357000 1607074000 C ndash3890300000 ndash0515482000 1069631000 C ndash5389479000 ndash0719093000 1106627000 C ndash6553177000 ndash0561696000 1815459000 C ndash7736166000 ndash1034716000 1182797000 H ndash6489929000 ndash2263627000 ndash1775522000 H ndash2743316000 ndash2692464000 ndash1483904000 H 1201969000 ndash2617287000 ndash1364047000 H 5019196000 ndash2306567000 ndash1440440000 H 4747029000 1814065000 1626168000 H 0933710000 1519855000 1692796000 H ndash2640951000 0605584000 2529735000 H ndash6590996000 ndash0122891000 2805220000 Co ndash3231943000 0870639000 ndash0218177000 C ndash2631117000 2925280000 ndash0475333000 C ndash4019450000 2955930000 ndash0137499000 C ndash4720042000 2167067000 ndash1095287000 C ndash3768150000 1717753000 ndash2089396000 C ndash2477085000 2188405000 ndash1710046000 H ndash1832546000 3399891000 0073720000 H ndash4448788000 3419647000 0737399000 H ndash5777018000 1951944000 ndash1095854000 H ndash3999907000 1119290000 ndash2956393000 H ndash1549894000 2013889000 ndash2232360000 H ndash8630326000 ndash1978241000 ndash0517433000 H ndash8683428000 ndash0939767000 1701100000 C 7524401000 0541032000 0473497000

C 7600630000 ndash0607844000 ndash0382149000 C 8637973000 1216338000 0890053000

C 8792152000 ndash1101412000 ndash0836674000 C 9961705000 ndash0402146000 ndash0407106000 C 9887895000 0708141000 0420266000 H 8602106000 2084773000 1535736000 H 10801526000 1207625000 0721410000

H 10931894000 ndash0752974000 ndash0739605000

- 144 -

H 8871661000 ndash1966753000 ndash1482602000

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

C 7143264000 ndash2348493000 0699665000 C 6037664000 ndash1857298000 1448523000 C 4969251000 ndash1391864000 0720257000 C 3582514000 ndash0743198000 0748195000 C 2358402000 ndash0737338000 1512136000 C 1240141000 ndash0634711000 0742222000 C ndash0262684000 ndash0516912000 0716494000 C ndash1428088000 ndash0430968000 1492584000 C ndash2574224000 ndash0346717000 0719319000 C ndash4098679000 ndash0233199000 0715866000 C ndash5251323000 ndash0147278000 1490294000 C ndash6408253000 ndash0063372000 0713741000 C ndash7934932000 0047490000 0717366000 C ndash9088044000 0130556000 1446914000 C ndash10299063000 0217080000 0692638000 C ndash10298939000 0215301000 ndash0693576000 C ndash9087782000 0126841000 ndash1447398000 C ndash7934811000 0045602000 ndash0717417000 C ndash6408180000 ndash0065400000 ndash0713264000 C ndash5251144000 ndash0151514000 ndash1489420000 C ndash4098619000 ndash0235099000 ndash0714599000 C ndash2574142000 ndash0348081000 ndash0717615000 C ndash1428022000 ndash0433439000 ndash1490677000

- 145 -

C ndash0262587000 ndash0517946000 ndash0714342000 C 1239930000 ndash0636111000 ndash0739947000 C 2357013000 ndash0742891000 ndash1511730000 C 3581891000 ndash0749703000 ndash0749006000 C 4968536000 ndash1397444000 ndash0717250000 C 6036190000 ndash1868351000 ndash1443314000 C 7142499000 ndash2353756000 ndash0691900000 H 8003789000 ndash2740125000 1230531000 H 6052031000 ndash1874231000 2531931000 H 2350726000 ndash0802237000 2593967000 H ndash1427931000 ndash0429806000 2574521000 H ndash5251989000 ndash0146640000 2572026000 H ndash9110076000 0132990000 2529448000 H ndash11241535000 0285430000 1223689000 H ndash11241318000 0282253000 ndash1224971000 H ndash9109613000 0126365000 ndash2529940000 H ndash5251637000 ndash0153720000 ndash2571150000 H ndash1427824000 ndash0434279000 ndash2572612000 H 2347832000 ndash0810535000 ndash2593375000 H 6049185000 ndash1893779000 ndash2526553000 H 8002469000 ndash2749449000 ndash1220666000 Co 4148367000 1055016000 ndash0009106000 C 5996101000 2006266000 0022069000 C 5276853000 2480887000 1185002000 C 4085420000 3079352000 0718350000 C 4110596000 3077077000 ndash0745160000 C 5316353000 2474554000 ndash1168669000 H 6921324000 1451094000 0038659000 H 5556549000 2314709000 2212960000 H 3287274000 3477873000 1325692000 H 3334253000 3474398000 ndash1380859000 H 5631980000 2304731000 ndash2185537000

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 146 -

C 4893664000 ndash1209972000 0735005000 C 4893573000 ndash1213475000 ndash0730870000 C 3475382000 ndash0763132000 ndash0743915000 C 3475432000 ndash0760320000 0747049000 C 2260316000 ndash0690973000 1520580000 C 1145205000 ndash0595973000 0744946000 C 1145156000 ndash0599246000 ndash0742744000 C 2260358000 ndash0697381000 ndash1517904000 C ndash0343192000 ndash0479177000 ndash0713609000 C ndash0343168000 ndash0476032000 0715380000 H 2252105000 ndash0735285000 ndash2601934000 H 2251901000 ndash0724154000 2604763000 Co 4601208000 0736083000 ndash0002055000 C 5960130000 2243618000 ndash0721946000 C 4640007000 2540538000 ndash1172530000 C 3804522000 2681992000 ndash0008876000 C 4632302000 2544967000 1160921000 C 5955467000 2247130000 0721276000 H 6816321000 2038808000 ndash1347044000 H 4312673000 2604006000 ndash2199136000 H 2745254000 2890841000 ndash0012873000 H 4298236000 2612143000 2185222000 H 6807361000 2044890000 1353015000 C 6022290000 ndash1649780000 1464200000 C 6022277000 ndash1656609000 ndash1457900000 C 7122289000 ndash2056771000 0719324000 C 7122311000 ndash2060028000 ndash0711126000 H 6027301000 ndash1702610000 2548102000 H 8011576000 ndash2407816000 1233935000 H 8011528000 ndash2413601000 ndash1224115000 H 6027432000 ndash1714310000 ndash2541551000 C ndash1512226000 ndash0382902000 1494684000 C ndash1512274000 ndash0389473000 ndash1493257000 C ndash2658093000 ndash0297761000 0720325000 C ndash2658103000 ndash0300923000 ndash0719236000 H ndash1511446000 ndash0379165000 2578406000

- 147 -

H ndash1511531000 ndash0390614000 ndash2576954000 C ndash4169046000 ndash0190131000 ndash0714237000 C ndash4169015000 ndash0186849000 0714915000 C ndash5325016000 ndash0103295000 1491764000 C ndash5325120000 ndash0110177000 ndash1491395000 C ndash6483203000 ndash0023670000 0713863000 C ndash6483258000 ndash0027061000 ndash0713749000 H ndash5325252000 ndash0101647000 2575308000 H ndash5325471000 ndash0113799000 ndash2574933000 C ndash7997403000 0080746000 0716440000 C ndash7997524000 0076500000 ndash0716680000 C ndash9155096000 0160872000 1448927000 C ndash9155379000 0152083000 ndash1449432000 C ndash10366775000 0240123000 0695134000 C ndash10366925000 0235844000 ndash0695874000 H ndash9178696000 0150122000 ndash2533721000 H ndash11311550000 0297904000 ndash1227155000 H ndash11311298000 0305233000 1226228000 H ndash9178228000 0165001000 2533216000

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

C 8266704000 ndash2005162000 0692734000 C 7088955000 ndash1708719000 1446000000 C 5966603000 ndash1428050000 0716466000

- 148 -

C 4483884000 ndash1054830000 0713802000 C 3355736000 ndash0795879000 1487813000 C 2219848000 ndash0542568000 0715155000 C 0748349000 ndash0122254000 0743952000 C ndash0460068000 ndash0300197000 1509394000 C ndash1583463000 ndash0354552000 0739667000 C ndash3088504000 ndash0455891000 0716671000 C ndash4249167000 ndash0553278000 1491353000 C ndash5399475000 ndash0634011000 0717623000 C ndash6922525000 ndash0754459000 0717051000 C ndash8076029000 ndash0852663000 1446746000 C ndash9285359000 ndash0940991000 0693505000 C ndash9286426000 ndash0927591000 ndash0694047000 C ndash8078221000 ndash0824629000 ndash1447252000 C ndash6923651000 ndash0740632000 ndash0717519000 C ndash5400498000 ndash0620402000 ndash0717994000 C ndash4251528000 ndash0525736000 ndash1491803000 C ndash3089431000 ndash0443610000 ndash0717063000 C ndash1585243000 ndash0344579000 ndash0740307000 C ndash0463450000 ndash0290395000 ndash1513612000 C 0748496000 ndash0127629000 ndash0751652000 C 2219455000 ndash0546002000 ndash0721683000 C 3355860000 ndash0802470000 ndash1493276000 C 4483583000 ndash1057975000 ndash0718022000 C 5966360000 ndash1431783000 ndash0719354000 C 7088265000 ndash1716549000 ndash1447876000 C 8266466000 ndash2008718000 ndash0693595000 H 9183427000 ndash2233531000 1224348000 H 7110060000 ndash1714392000 2528663000 H 3353411000 ndash0803478000 2570367000 H ndash0456292000 ndash0373454000 2590614000 H ndash4248665000 ndash0564171000 2573279000 H ndash8096828000 ndash0865292000 2529266000 H ndash10227269000 ndash1021159000 1223954000 H ndash10229127000 ndash0997490000 ndash1224546000 H ndash8100648000 ndash0816347000 ndash2529785000 H ndash4252664000 ndash0517117000 ndash2573754000 H ndash0464650000 ndash0354640000 ndash2595436000 H 3353541000 ndash0815213000 ndash2575752000 H 7108905000 ndash1727728000 ndash2530504000 H 9182976000 ndash2239822000 ndash1224379000 Co 1060170000 1739352000 ndash0013647000 C 0820599000 3762931000 0679296000 C 2023158000 3250849000 1217023000 C 2833506000 2814255000 0100512000 C 2185795000 3225276000 ndash1129991000

- 149 -

C 0924349000 3753677000 ndash0780133000 H ndash0033478000 4112410000 1239126000 H 2257663000 3114053000 2260457000 H 3791311000 2322414000 0171627000 H 2565428000 3065285000 ndash2126458000 H 0160713000 4098445000 ndash1460120000

(i) Local minimum 1 η4-benzene (190 kcalmol)

C 8767525000 ndash0664628000 0869444000 C 7569070000 ndash0364489000 1586360000 C 6400497000 ndash0535559000 0896308000 C 4872998000 ndash0456407000 0896648000 C 3729258000 ndash0166123000 1633430000 C 2558863000 ndash0367557000 0899969000 C 1050529000 ndash0274920000 0917771000 C ndash0154687000 0103769000 1545183000 C ndash1231288000 ndash0039565000 0606842000 C ndash2736221000 ndash0089835000 0603708000 C ndash3901526000 0467576000 1153370000 C ndash5054648000 ndash0104455000 0647800000 C ndash6579036000 ndash0120351000 0673091000 C ndash7732820000 0402806000 1194768000 C ndash8948594000 ndash0155119000 0702959000 C ndash8958839000 ndash1167887000 ndash0247745000 C ndash7753788000 ndash1707235000 ndash0785423000 C ndash6589806000 ndash1166201000 ndash0307896000

- 150 -

C ndash5063448000 ndash1158179000 ndash0339650000 C ndash3923750000 ndash1713712000 ndash0884954000 C ndash2743411000 ndash1141750000 ndash0370168000 C ndash1264100000 ndash1152263000 ndash0442985000 C ndash0114410000 ndash1509648000 ndash1047872000 C 1001557000 ndash0717865000 ndash0509678000 C 2529242000 ndash0815059000 ndash0456630000 C 3680301000 ndash1106705000 ndash1192448000 C 4847485000 ndash0909766000 ndash0461159000 C 6375435000 ndash0989198000 ndash0464503000 C 7517684000 ndash1280530000 ndash1157992000 C 8743181000 ndash1104009000 ndash0445669000 H 9720775000 ndash0544729000 1371431000 H 7610320000 ndash0024462000 2613574000 H 3742883000 0162901000 2664422000 H ndash0241422000 0534554000 2534230000 H ndash3894210000 1260341000 1890621000 H ndash7746436000 1191936000 1936109000 H ndash9890199000 0223840000 1083439000

H ndash9908180000 ndash1561665000 ndash0592194000 H ndash7783148000 ndash2497305000 ndash1525270000 H ndash3929534000 ndash2506814000 ndash1621099000 H 0005285000 ndash2235278000 ndash1842324000 H 3664139000 ndash1453900000 ndash2217556000 H 7520111000 ndash1625509000 ndash2184413000 H 9677483000 ndash1320445000 ndash0950825000 Co 0245526000 1194775000 ndash0183529000 C ndash0498660000 3223481000 ndash0207100000 C 0902667000 3310487000 0056983000 C 1591310000 2661311000 ndash1009417000 C 0610054000 2243094000 ndash1989593000 C ndash0681576000 2592200000 ndash1494981000 H ndash1289524000 3595536000 0425619000 H 1355880000 3721411000 0946130000 H 2657726000 2519341000 ndash1088515000 H 0823168000 1743521000 ndash2921425000 H ndash1626608000 2403559000 ndash1979282000

(j) Transition state 1 η3-benzene (356 kcalmol)

- 151 -

C ndash8901354000 ndash0223681000 ndash0743434000 C ndash7695103000 0220198000 ndash1360549000 C ndash6531343000 ndash0208573000 ndash0779115000 C ndash5007706000 ndash0207407000 ndash0796109000 C ndash3863247000 0247302000 ndash1433753000 C ndash2690760000 ndash0206508000 ndash0819013000 C ndash1184933000 ndash0153490000 ndash0843116000 C ndash0016095000 0217826000 ndash1588049000 C 1142075000 ndash0155798000 ndash0877497000 C 2665172000 ndash0195830000 ndash0859864000 C 3835813000 0283152000 ndash1437197000 C 4978920000 ndash0204857000 ndash0802474000 C 6505676000 ndash0216574000 ndash0771205000 C 7678527000 0226433000 ndash1319208000 C 8875127000 ndash0251684000 ndash0703235000 C 8845790000 ndash1112691000 0383544000 C 7616005000 ndash1570592000 0948642000 C 6475812000 ndash1107284000 0353147000 C 4945633000 ndash1092812000 0320013000 C 3774824000 ndash1565295000 0903163000 C 2628495000 ndash1080676000 0265289000 C 1119158000 ndash1093642000 0244670000 C ndash0052242000 ndash1637616000 0861793000 C ndash1193959000 ndash1109215000 0331010000 C ndash2676505000 ndash1073633000 0328062000 C ndash3841325000 ndash1514463000 0979035000 C ndash4995446000 ndash1053912000 0371366000 C ndash6522185000 ndash1052982000 0381089000 C ndash7676261000 ndash1483950000 0978498000 C ndash8892512000 ndash1041633000 0378747000

- 152 -

H ndash9850267000 0087677000 ndash1164894000 H ndash7723622000 0856176000 ndash2236504000 H ndash3873085000 0886115000 ndash2307512000 H ndash0031238000 0768624000 ndash2518870000 H 3857949000 0953892000 ndash2286176000 H 7723941000 0897606000 ndash2167700000 H 9831384000 0069893000 ndash1099633000 H 9779177000 ndash1450269000 0819087000 H 7614291000 ndash2243551000 1796930000 H 3751975000 ndash2237828000 1750478000 H ndash0016047000 ndash2343040000 1681308000 H ndash3832680000 ndash2159963000 1847727000 H ndash7691389000 ndash2121828000 1853393000 H ndash9834648000 ndash1354566000 0814012000 Co ndash0004249000 1140918000 0250383000 C 0931445000 3181201000 0326993000 C ndash0487068000 3279997000 0223542000 C ndash1069741000 2607436000 1368652000 C 0008159000 2107122000 2176577000 C 1235098000 2411215000 1492603000 H 1650004000 3565479000 ndash0380430000 H ndash1033454000 3774248000 ndash0564979000 H ndash2124544000 2537255000 1584462000 H ndash0094112000 1572170000 3107766000 H 2227446000 2134637000 1815486000

LUMO

HOMO

2887

239

00862

2496

1163

1382

1418

1312

0

3155

2767

0498

2588

1531

0831

Figure 47 Orbital coefficients of linear [5]phenylene

- 153 -

Figure 48 Top view of the contour plots of (a) the HOMO and (b) the LUMO of the [5]-phenylene ligand

- 154 -

Bad

Bad

Good Good

External cyclobutadiene coordination Internal cyclobutadiene coordination

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCpCoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

Figure 49 Resonance rationale for the increased stability of internal Co coordination in linear [5]phenylene

44 NMR Data for Chapter Two

- 155 -

Figure 410 1H-NMR data for the respective parent phenylene frames experimental (C6D6) and

calculated [NICS (1) B3LYP6-31+G] Assignments by NOESY DEPT HMBC and HSQC as applicable

- 156 -

Me3Si

Me3Si

SiMe3

SiMe3

1

23

4 56

7 89

10 1112

13 1415

16

17

18

Co

222

1490

1252

1450

1433

1151

744

730

11091121

14161504

11211109

1540

1499

1224

1486

217

801

SiMe3

SiMe3

Me3Si

Me3Si

Co

802

261

1484

1256

1433

1494

1155

739

781

1360

1394

269

SiMe3

SiMe3

Co

802

1294

1149

1426

1502

1194

738

779

1363

1393

268

SiMe3

SiMe3

1241

1276

8029

725

1155

1493

1430

1256

1482

222

Co

796

678674 675 796

436

037032662

724 683 747

444

TMS

TMS

TMS

TMS

213

1474

1211

1538

1499

1112

623 685

SiMe3

SiMe3Me3Si

Me3Si SiMe3

SiMe3Me3Si

Me3Si459 Co

589 681 672 745

2201204

15131096

1535

2221252

1480

1433

1149741

801

1501 1490

1475

Figure 411 Comparison of 1H-NMR (blue) and 13C-NMR assignments (C6D6)

NICS-Scan calculations Methods The free ligands were optimized at the B3LYP6-31G and the CpCo complexes at the B3LYPLANL2DZ computational levels Analytical frequency calculations were executed to ensure real minima (Nimag = 0) GIAO-B3LYP6-31+G was used to calculate NICS values The NICS-scan procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (ipc or NICSXY) and out-of-plane components (oopc or NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their interpretation

- 157 -

Since there are no published NICS-scan studies of transition metal complexed cyclic polyenes we benchmark the method with (C6H6)Cr(CO)3

53

Figure 412 NICS-scan of benzene (left) and (benzene)Cr(CO)3 (right)

The shape of the oopc curve suggests that the diamagnetic ring current in the ligand is diminished on complexation although still prevalent Thus at r = 0 Aring (ie at the benzene plane) the oopc value [NICSZZ(0)] of the complex is less negative than that of benzene and the minimum of the curve is less negative and occurs at a larger distance (ndash29911 vs ndash31910) A larger change is observed in the ipc (which is governed by the σ electrons) which shows far more negative values in the complex relative to benzene itself (eg ndash55400 vs ndash5900 and ndash13910 vs ndash0910) Therefore isotropic NICS values are misleading with respect to the diatropism in the complex because they originate largely from the diamagnetic effect of the σ framework NICS-scans for the four-membered ring B in linear [3]phenylene and its CpCo complex are shown below

00 05 10 15 20 25 30 35 40

-34-32-30-28-26-24-22-20-18-16-14-12-10

-8-6-4-202

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

oopc ipc isotropic

pp

m

r

- 158 -

Figure 413 NICS-scan above ring B of linear [3]phenylene (left) and its CpCo complex (right) Inspection of the shape and values of the oopc curve shows that the four-membered ring in the free ligand is strongly paratropic This picture changes on CpCo complexation At or close to the ring plane the values are much less positive (12100 vs 88000) become negative at greater distance and reach a minimum of -16112 Consequently the presence of the metal clearly reduces paratropic character The ipc curve is similar to that of (benzene)Cr(CO)3 Therefore again isotropic NICS values are misleading with respect to an assessment of the size of ring current effects The two isomeric CpCo complexes of linear [5]phenylene as depicted next behave in an analogous manner and engender the same conclusions as above

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

- 159 -

Figure 414 NICS-scans of linear [5]phenylene and its CpCo complexes Top left - ring B of the free ligand Top right - ring B complexed to CpCo Bottom left - ring D of the free ligand

Bottom right - ring D complexed to CpCo The effect of CpCo complexation is also reflected in the NICS-scan properties of the remaining rings To illustrate this point the NICS-scans of the central cyclohexatrienoid ring C of linear [3]phenylene are shown below first for the free ligand then for the cyclobutadiene complex

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

- 160 -

Figure 415 NICS-scans of ring C of linear [3]phenylene Left - as a free ligand Right as a

CpCo complex of the neighboring cyclobutadiene ring B The oopc curve clearly reveals a diminution of paratropism Thus at the ring plane the oopc values of the free ligand and of the complex are 177 and 110 ppm respectively Both plots show shallow and relatively distant minima at ndash3417 and ndash7316 respectively an indication of larger diamagnetic character of the latter While the ipc values also become more negative on complexation this effect is far smaller The tables that follow provide an overview of the NICS-scan results over all component rings in linear [3]- and [5]phenylene complexed and uncomplexed The diagnostic shape of the oopc curve is designated NM for no minimum indicating paratropism and M for minimum indicating diatropism Specific values are given at r = 0 Aring r = 10 Aring and the minimum (if diamagnetic) Table 416 NICS-scan Details of the oopc for Linear [3]Phenylene and its CpCo Complex at

Ring B

Ring Shape oopc00 oopc10 Minimum A M 71 ndash107 ndash11813 AndashCpCo M ndash65 ndash228 ndash22811 B NM 880 381 BndashCpCo M 121 ndash151 ndash16112 C M 177 ndash01 ndash3418 CndashCpCo M 116 ndash17 ndash9315 D NM 880 381 DndashCpCo NM 704 237 E M 71 ndash107 ndash11813 EndashCpCo M 15 ndash148 ndash15212

00 05 10 15 20 25 30 35 40

-8-6-4-202468

101214161820

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-14-12-10

-8-6-4-202468

1012

oopc ipc isotropic

pp

m

r

- 161 -

Table 417 NICS-Scan Details of the oopc for Linear [5]Phenylene and its CpCo Complex at Ring B

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M ndash62 ndash227 ndash22811 B NM 898 396 BndashCpCo M 137 ndash148 ndash15612 C M 176 00 ndash3317 CndashCpCo M 152 ndash09 ndash8415 D NM 846 357 DndashCpCo NM 668 223 E M 164 ndash12 ndash4116 EndashCpCo M 142 ndash17 ndash5315 F NM 846 357 FndashCpCo NM 807 340 G M 176 00 ndash3317 GndashCpCo M 161 ndash04 ndash3216 H NM 898 396 HndashCpCo NM 867 378 I M 83 ndash97 ndash10813 IndashCpCo M 64 ndash109 ndash12113

Table 418 NICS-scan Details of the oopc for Lnear [5]Phenylene and its CpCo Complex at

Ring D

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M 19 ndash150 ndash15912 B NM 898 396 BndashCpCo NM 717 256 C M 176 00 ndash3317 CndashCpCo M 110 ndash122 ndash12210 D NM 846 357 DndashCpCo M 151 ndash169 ndash17311 E M 164 ndash12 ndash4116 EndashCpCo M 151 ndash169 ndash17311 F NM 846 357 FndashCpCo NM 685 231 G M 176 00 ndash3317 GndashCpCo M 148 ndash15 ndash5415 H NM 898 396 HndashCpCo NM 850 370

I M 83 ndash97 ndash10813

- 162 -

The data clearly show that on CpCo complexation the paramagnetic ring current contributions decrease (or the diamagnetic ring current contributions increase) The strongest effect is on the complexed cycle but it occurs for all rings even the most remote (eg I in the linear [5]phenylene complexed at ring B) Thus upon complexation the paratropic (and by inference antiaromatic) character of the phenylenes decrease 45 Experimental Section for Chapter Three Angular [3]phenylene 2290 angular [4]phenylene 17111 and [7]heliphene10 were prepared according to the literature Ni(COD)(PMe3)2

112 To a solution of Ni(COD)2 (0275 g 10 mmol) in dry and vigorously degassed THF (10 mL) PMe3 (020 mL 0150 g 20 mmol) was added via syringe in a single portion After stirring at RT for 24 h the mixture was transferred using a canula and filtered under Ar to remove unreacted starting material The solvent was removed on the high vacuum line and the resulting product dried for 3 h It is extremely air sensitive and must be manipulated under an inert atmosphere at all times Yellow solid (0306 g 96 ) 1H-NMR (400 MHz C6D6) δ = 412 (d J = 112 Hz 4 H) 238 (br t J = 52 Hz 4 H) 225 (t J = 52 Hz 4 H) 102 (d J = 32 Hz 18 H) ppm 31P-NMR (162 MHz C6D6) δ = ndash946 (s) ppm Adducts of diphenylacetylene 88 to angular [3]phenylene 22 ndash compounds 89 and 90

In a glove box an Ace pressure tube was charged with angular [3]phenylene 22 (0014 g 006 mmol) diphenylacetylene 88 (0098 g 0055 mmol) THF (5 mL) and Ni(COD)(PMe3)2 (70 microL 008 M in THF 0006 mmol) The reaction vessel was tightly sealed removed from the glovebox and heated to 75ndash80 oC (oil bath) for 23 h After cooling to RT the solvent was removed by rotary evaporation and the residue purified by flash chromatography on silica gel using gradient elution (101 and then 81 hexaneCH2Cl2) After a small amount of angular [3]phenylene 22 (0001 g) the monoadduct 89 (0004 g 20 ) eluted to give a yellow solid mp 195ndash196 degC 1H-NMR (500 MHz CDCl3) δ = 853 (d J = 84 Hz 1 H) 831 (d J = 80 Hz 1 H) 755 (ddd J = 16 64 80 Hz 1 H) 740ndash732 (m 2 H) 725ndash715 (m 6 H) 715ndash711 (m 2 H) 708 (d J = 65 Hz 2 H) 704 (d J = 80 Hz 1 H) 648 (t J = 72 Hz 1 H) 643 (d J = 70 Hz 1 H) 624 (t J = 75 Hz 1 H) 401 (d J = 70 Hz 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1525 15101 15096 1495 1399 13883 13879 1342 1320 1312

- 163 -

13083 13075 1282 1280 1277 1276 1275 1268 1266 1265 1264 1250 1235 1223 1179 1164 1156 ppm one peak in the region δ = 128ndash126 ppm is

presumed to be accidentally isochronous IR (KBr) ν~ = 3060 1490 1481 1442 1415 1159 1072 755 734 698 cmndash1 UV-Vis (CH3CN) λmax (log ε) 233 (442) 265 (450) 278 (sh) 294 (sh) 306 (447) 318 (449) 329 (sh) 380 (344) 399 (366) 420 (366) nm MS (70 eV) mz () 405 [M++1] (35) 404 [M+] (100) 326 (13) HRMS (EI) calcd for C32H20 4041565 found 4041571 Elemental analysis calcd for C32H20 C 9502 H 498 found 9479 460 Subsequent elution furnished 5678-tetraphenylpicene (90) (0009 g 59 ) as a white solid mp 325ndash327 degC the molecule exhibits hindered rotation of the 67-phenyl groups on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 891 (s 2 H) 885 (d J = 84 Hz 2 H) 769 (ddd J = 28 52 80 Hz 2 H) 750ndash744 (m 4 H) 744ndash732 (m 4 H) 720 (tt J = 16 72 Hz 2 H) 696 (dt J = 08 76 Hz 2 H) 689 (tt J = 09 76 Hz 2 H) 662 (br s 4 H) 617 (d J = 76 Hz 2 H) 607 (br s 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1403 1401 1377 1367 1335 1325 1324 1306 1300 1295 1292

1283 1277 1269 1264 1263 1262 1256 1254 1228 1213 ppm IR (KBr) ν~ = 3051 2922 1599 1490 1467 1442 1263 1072 1027 758 702 630 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (461) 307 (474) 352 (417) 366 (414) nm MS (70 eV) mz () 583 [M++1] (52) 582 [M+] (100) 505 (24) 504 (9) 426 (7) HRMS (EI) calcd for C46H30 5822348 found 5822336 1278-Tetraphenylbenzo[c]chrysene (91)

In a glovebox an Ace pressure tube was charged with 88 (0020 g 0050 mmol) diphenylacetylene 88 (0026 mg 0148 mmol) Ni(COD)(PMe3)2 (62 microL of a 008 M solution in THF) and THF (5 mL) The reaction vessel was sealed removed from the glovebox and heated to 85 degC for 39 h After removal of the solvent the residue was purified by flash chromatography on silica gel (eluting with 81 hexaneCH2Cl2) producing a white solid (0023 g) which was found to consist of starting material (88 18 mg) 90 (0001 g 6 ) and 91 Further purification by chromatography afforded pure 91 (0017 g 74 ) as a white solid mp 273ndash274 degC the 12-phenyl groups of 91 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 869 (d J = 95 Hz 1 H) 830ndash822 (m 1 H) 801 (d J = 75 Hz 1 H) 780ndash747 (m 2 H) 770 (ddd J = 10 70 85 Hz 1 H) 762 (dt J = 15 75 Hz 1 H) 753 (ddd J = 15 70 85 Hz 1 H) 738ndash732 (m 2 H) 730 (td J = 15 75 Hz 1 H) 729ndash722 (m 6 H) 722ndash717 (m 2 H) 717ndash710 (m 2 H) 710ndash695 (m 3 H) 680ndash640 (m 3 H) 635 (d J = 70 Hz 1 H) 623ndash595 (br s 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1418 1400 1395 1394 1378 1377 1375 1357 1323 1322 1316 1314 13113 13107 1309 1308 1307 1305 1296 1295 1288 1282 1277 1275 1274 1273 1270 12653 12647 1264 1260 1256 1253 1252 1251

- 164 -

1243 1231 1208 ppm due to extensive signal overlap four peaks are presumed to be isochronous in the regions δ = 132ndash130 and 128ndash125 ppm IR (KBr) ν~ = 3058 1601 1489 1442 1263 1073 773 762 736 699 628 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 250 (487) 313 (511) 340 (sh) nm MS(EI) mz () 583 (M++1 72) 582 (M+ 100) 505 (24) 391 (13) HRMS (EI) calcd for C46H30 5822348 found 5822341 Elemental analysis calcd for C46H30 C 8933 H 500 found 8914 493 Ni(PhCequivCPh)(PMe3)2 (92)91

In a glove box PMe3 (203 microL 0152 g 20 mmol) was mixed with a suspension of Ni(COD)2 (0275 g 10 mmol) in hexane (15 mL) Diphenylacetylene 88 (0178 g 10 mmol) was then added in one portion resulting in an immediate color change from yellow to red The mixture was stirred at room temperature for 195 h during which the color gradually turning returning to yellow Upon concentration (to ~5 mL) a yellow precipitate formed collected by filtration under nitrogen The resulting powder 92 (0370 g 95 ) was dried under vacuum providing a yellow solid 1H-NMR (500 MHz C6D6) δ = 751 (d J = 75 Hz 4 H) 717 (t J = 75 Hz 4 H) 702 (t J = 75 Hz 2 H) 101 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1406 1287 1279 196 (d JC-P = 188 Hz) ppm 31P-NMR (162 MHz C6D6) δ = ndash1282 (br s) ppm Adducts of 3-hexyne to angular [3]phenylene 22 ndash compounds 104 and 105

In a glovebox 22 (0014 mg 0060 mmol) 3-hexyne 103 (57 microL 0004 g 0050 mmol) Ni(COD)(PMe3)2 (0002 g 0005 mmol) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 14 h Flash chromatography on silica gel gave a first fraction that was recrystallized from CH2Cl2 to provide pure 104 (70 mg 45 ) as a yellow solid mp 169ndash170 degC 1H-NMR (500 MHz CDCl3) δ = 843 (d J = 70 Hz 1 H) 821 (d J = 75 Hz 1 H) 795 (d J = 70 Hz 1 H) 752 (dt J = 10 70 Hz 1 H) 748 (dt J = 10 70 Hz 1 H) 697 (d J = 75 Hz 1 H) 673ndash662 (m 3 H) 655 (d J = 55 Hz 1 H) 307 (q J = 75 Hz 2 H) 299 (q J = 75 Hz 2 H) 133 (t J = 75 Hz 3 H) 130 (t J = 75 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1530 1516 1504 1471 1360 1330 13129 13127 1307 1282 1279 1267 1263 1259 1246 1239 1228 1179 1159 1156 232 214 164 149 ppm IR (KBr) ν~ = 3045 2960 1600 1481 1414 1261 1197 1159 758 740 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (463) 299 (sh) 309 (460) 320 (462) 331 (452) 380 (356) 399 (374) 419 (371) nm MS (70 eV) mz () 309 [M++1] (26) 308 [M+] (100) 293 [M+ndash15] (8) 278 [M+ndash30] (21) HRMS (EI) calcd for C24H20 3081565 found 3081666

- 165 -

A second fraction was 105 (0002 g 11 ) isolated as a yellow solid mp 120ndash122 degC 1H-NMR (400 MHz CDCl3) δ = 830 (d J = 72 Hz 1 H) 797 (d J = 76 Hz 1 H) 761 (d J = 80 Hz 1 H) 761ndash749 (m 2 H) 700 (d J = 80 Hz 1 H) 699 (d J = 72 Hz 1 H) 674 (quint J = 76 Hz 2 H) 658 (d J = 64 Hz 1 H) 307 (q J = 76 Hz 2 H) 302 (q J = 76 Hz 2 H) 132 (t J = 76 Hz 3 H) 131 (t J = 76 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1525 1519 1489 1472 1356 1345 1324 1318 1288 1283 1279 1273 1259 1252 1251 1250 1241 1179 1165 1160 2213 2205 149 146 ppm IR (KBr) ν~ = 3063 2958 2925 1490 1442 1417 1262 1147 1099 822 762 730 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 281 (434) 291 (448) 303 (460) 313 (sh) 369 (346) 389 (373) 410 (377) nm MS (70 eV) mz () 309 [M++1] (28) 308 [M+] (100) 293 [M+ndash15] (13) 278 [M+ndash30] (21) 226 (22) 149 (29) HRMS (EI) calcd for C24H20 3081565 found 3081664 Adducts of 14-dimethoxy-2-butyne to angular [3]phenylene 22 ndash compounds 107 and 108

In a glovebox 22 (0011 g 0050 mmol) 14-dimethoxybut-2-yne 106 (0034 g 030 mmol) Ni(COD)(PMe3)2 (63 microL of a 008 M solution in THF) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 165 h The 1H-NMR spectrum of the crude indicated the formation of 107 and 108 in the ratio of 61 Flash chromatography on silica gel gave first 107 (0012 g 68 ) as a yellow solid mp 150ndash151 degC 1H-NMR (400 MHz CDCl3) δ = 841 (dd J = 32 64 Hz 1 H) 819 (d J = 80 Hz 1 H) 810 (dd J = 36 64 Hz 1 H) 754 (dd J = 36 64 Hz 2 H) 700 (d J = 80 Hz 1 H) 676 (t J = 64 Hz 1 H) 674ndash665 (m 2 H) 656 (d J = 60 Hz 1 H) 493 (s 2 H) 488 (s 2 H) 353 (s 3 H) 345 (s 3 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1527 1513 1509 1484 1336 1318 1316 1309 1296 1283 1282 1272 1270 1259 1255 1238 1225 1183 1166 1161 677 675 584 575 ppm IR (KBr) ν~ = 3072 2927 1485 1446 1417 1376 1185 1097 956 898 821 743 730 cmndash1 MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (100) 308 [M+ndash38] (26) 293 (34) 280 (15) 265 (44) HRMS (EI) calcd for C24H20O2 3401463 found 3401466 Further elution provided 108 (0002 g 9 ) as a yellow solid mp 156ndash157 degC 1H-NMR (400 MHz CDCl3) δ = 831ndash824 (m 1 H) 813ndash806 (m 1 H) 775 (d J = 80 Hz 1 H) 763ndash756 (m 2 H) 702 (d J = 80 Hz 1 H) 699 (d J = 64 Hz 1 H) 681ndash670 (m 2 H) 660 (d J = 64 Hz 1 H) 493 (s 2 H) 487 (s 2 H) 353 (s 3 H) 351 (s 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1523 1517 1505 1470 1327 1322

- 166 -

1316 1315 1297 1285 1282 1276 1268 1266 12564 12555 1252 1181 1168 1165 6804 6801 5838 5835 ppm IR (KBr) ν~ = 2925 1498 1415 1379 1262 1187 1095 1061 940 930 814 750 734 717 cmndash1 UV-Vis (CH3CN) λmax (log ε) 237 (458) 287 (462) 298 (472) 314 (sh) 371 (357) 387 (380) 407 (386) nm MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (56) 308 [M+ndashMeOH] (8) 293 (27) 279 (17) 265 (24) HRMS (EI) calcd for C24H20O2 3401463 found 3401456 Optimized cycloaddition reaction between 22 and 88 In a glovebox a round bottom flask was charged with 22 (0058 g 0257 mmol) and Ni(COD)(PMe3)2 (0008 g 0034 mmol) Both reagents were then dissolved in THF (100 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0093 g 0521 mmol) in THF (20 mL) was taken up in a gas-tight syringe and slowly added over 13 h via syringe pump to the boiling mixture of 22Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 6 h After this time mixture was cooled to RT and the solvent removed by rotary evaporation to give a yellow residue The crude product was passed through a plug of silica gel eluting with a mixture of hexanesCH2Cl2 (101) to afford a yellow solid Analysis of the product by 1H-NMR (using the solvent peak of CDCl3 as the internal standard) revealed the presence of 89 and 90 in a 1387 ratio Adducts of diphenylacetylene 88 to angular [4]phenylene 17 ndash compounds 130ndash134 In a glovebox angular [4]phenylene 17 (0036 g 012 mmol) diphenylacetylene 88 (0018 g 010 mmol) and Ni(COD)(PMe3)2 (125 microL of a 008 M solution in THF) were added to an Ace pressure tube and dissolved in THF (6 mL) The reaction vessel was sealed removed from the glovebox and stirred at 75 degC for 5 h Flash chromatography

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph Ph PhPh Ph

132131

133 134

130

- 167 -

on silica gel gave starting material (0013 g of 17) as well as a yellow residue Further purification of the latter by preparative TLC afforded (in order of elution) 132 131 133 134 and 139 Compound 130 (0008 g 28 ) was obtained as a white solid mp 360ndash363 degC (decomp) the phenyl groups located on the central benzene ring of 130 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 904 (d J = 90 Hz 2 H) 895 (d J = 90 Hz 2 H) 881 (d J = 85 Hz 2 H) 765 (ddd J = 15 65 80 Hz 2 H) 742ndash736 (m 4 H) 734 (dd J = 10 85 Hz 2 H) 721 (tt J = 15 75 Hz 2 H) 716 (d J = 75 Hz 2 H) 698 (dd J = 05 80 Hz 2 H) 693 (tt J = 10 85 Hz 2 H) 681 (tt J = 10 70 Hz 2 H) 676 (t J = 75 Hz 4 H) 656 (t J = 70 Hz 4 H) 633 (d J = 70 Hz 4 H) 614 (d J = 75 Hz 2 H) 595 (d J = 70 Hz 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 14058 14057 1403 1394 1375 1374 1345 1341 1336 1327 1324 1309 1308 1301 1294 1292 1282 1276 1268 1263 12622 12619 1259 1257 1254 1250 1227 1214 1212 ppm IR (KBr) ν~ = 3052 2923 1600 1491 1440 1261 1076 1029 809 783 759 747 700 631 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 248 (498) 306 (sh) 329 (520) 388 (463) nm MS(FAB) mz () 836 [M++2] (18) 835 [M++1] (42) 834 [M+] (54) 757 (8) HRMS (FAB) calcd for C66H42 8343287 found 8343280 Compound 131 (0003g 6) was isolated as yellow solid mp 251ndash253 degC (decomp) 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 775 (dt J = 10 80 Hz 1 H) 752 (dt J = 10 80 Hz 1 H) 746 (d J = 80 Hz 1 H) 737 (d J = 65 Hz 1 H) 726ndash721 (m 5 H) 721ndash716 (m 2 H) 716ndash711 (m 5 H) 709 (t J = 75 Hz 1 H) 705 (d J = 80 Hz 1 H) 699 (d J = 70 Hz 1 H) 619 (d J = 60 Hz 1 H) 614 (d J = 60 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1502 1492 1491 1490 1485 1444 1394 1392 1382 1371 1367 1351 13271 13268 13092 13088 1299 12898 12896 1283 12764 12760 1274 12654 12652 1261 1253 1245 1195 1184 1172 1138 1129 ppm one peak is presumed to be accidentally isochronous in the region between δ = 130ndash124 ppm IR (KBr) ν~ = 3023 2921 1602 1478 1371 1262 1026 809 795 748 725 695 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 252 (473) 285 (456) 320 (453) 335 (462) 353 (437) 370 (432) 410 (376) 431 (372) nm MS (FAB) mz () 479 [M++1] (27) 478 [M+] (70) 300 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781718 Molecule 132 (0002 g 5 ) was acquired as a yellow solid 1H-NMR (500 MHz CDCl3) δ = 726ndash721 (m 2 H) 716ndash709 (m 6 H) 695ndash690 (m 2 H) 676 (d J = 80 Hz 2 H) 673 (d J = 75 Hz 2 H) 671 (t J = 75 Hz 2 H) 665 (t J = 70 Hz 2 H) 658 (d J = 65 Hz 2 H) 648 (d J = 65 Hz 2 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1516 1510 1497 1490 1391 1372 1310 1303 1283 1281 1277 1275 1273 1264 1216 1168 1163 ppm UV-Vis (CH2Cl2) λmax (log ε) 254 (476) 294 (sh) 300 (465) 322 (sh) 338 (392) 376 (400) nm MS (FAB) mz () 479 [M++1] (50) 478 [M+] (86) 391 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781723 Adduct 133 (0017 g 33 ) was isolated as a red crystalline solid mp 290ndash291 degC 1H-NMR (500 MHz CDCl3) δ = 800 (d J = 80 Hz 2 H) 720ndash713 (m 6 H) 708ndash702 (m 4 H) 690 (d J = 80 Hz 2 H) 648 (t J = 70 Hz 2 H) 642 (d J = 70 Hz 2 H) 623 (t J = 70 Hz 2 H) 393 (d J = 70 Hz 2 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1522 1509 1506 1496 1392 1359 1315 1309 1282 1278 1277 1266 1250 1232 1181 1166 1157 ppm IR (KBr) ν~ = 3057 1489 1441 1412 1273

- 168 -

1161 810 738 709 690 623 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 271 (474) 285 (469) 345 (460) 353 (454) 414 (483) 432 (381) 460 (363) nm MS (70 eV) mz () 479 [M++1] (46) 478 [M+] (100) 400 (10) HRMS (EI) calcd for C38H22 4781722 found 4781719 Compound 134 (0009 g 27 ) was obtained as a yellow solid mp 178ndash180 degC the phenyl groups of this molecule located at the bay regions of the phenanthrene subunit are static while the others exhibit hindered rotation on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 880 (d J = 88 Hz 1 H) 879 (d J = 88 Hz 1 H) 863 (d J = 92 Hz 1 H) 834 (d J = 80 Hz 1 H) 770ndash758 (m 1 H) 748ndash732 (m 4 H) 727ndash721 (m 2 H) 721ndash710 (m 2 H) 706 (d J = 80 Hz 1 H) 702ndash691 (m 3 H) 684 (t J = 74 Hz 1 H) 673 (br s 2 H) 655 (t J = 76 Hz 2 H) 650ndash638 (m 3 H) 630ndash610 (m 4 H) 590 (d J = 76 Hz 2 H) 410 (d J = 68 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1527 1510 1509 1494 1403 1400 1399 1396 1373 1371 1339 1335 1330 1325 1324 1317 1309 1306 1305 1304 1299 1295 1291 1283 1282 1281 1277 1275 1272 1269 1268 12632 12627 1261 12562 12556 1254 1253 1239 1226 1216 1209 1180 1162 1154 ppm three peaks are presumed to be accidentally isochronous in the region δ = 128ndash125 ppm IR (KBr) ν~ = 2964 1262 1096 1022 801 701 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 267 (501) 303 (497) 335 (489) 361 (sh) 379 (464) 427 (402) 456 (377) nm MS(FAB) mz () 658 [M++2] (22) 657 [M++2] (67) 656 [M+] 1(00) 579 (12) 502 (7) HRMS (FAB) calcd for C52H32 6562504 found 6562492 Cycloaddition reaction between [7]heliphene 142 and diphenylacetylene 88 In a glovebox a round bottom flask was charged with 142 (0008 g 0152 mmol) and Ni(COD)(PMe3)2 (0001 g 0003 mmol) The mixture was then dissolved in THF (25 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0016 g 300 mmol) in THF (10 mL) was taken up in a gas-tight syringe and slowly added over 12 h via syringe pump to the boiling mixture of 142Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 12 h After this time it was cooled to RT and the solvent removed by rotary evaporation to give an orange residue The crude product was chromatographed on silica gel (25 x 165 cm) eluting first with hexaneCH2Cl2 (101 then 51) The first product collected was diphenylacetylene 88 (0005 g) followed by a yellow band Analysis of the isolated yellow solid (0002 g) revealed a large mixture of products MS(FAB) mz () 532 (70) 664 (25) 700 (13) 732 (16) 911 (21) 1056 (11) 1234 (4) 1412 (5) 46 Computational Details for Chapter Three All geometries of intermediates and transition states were optimized fully without symmetry constraints using the Gaussian 03 program100 The DFT computations were carried out using the B3LYP functional as implemented in Gaussian The nickel atom was described by a double-zeta basis set (LANL2DZ)113 and the 6-31G(d) basis set114

- 169 -

was used for the other elements Frequency calculations were performed to confirm the nature of the stationary points and to obtain zero-point energies (ZPE) The connectivity between stationary points was established by intrinsic reaction coordinate calculations (IRC) The Chemcraft program102 was used to draw the calculated structures

47 References

1) Harvey R G Polycyclic Aromatic Hydrocarbons Wiley-VCH New York 1997 2) (a) Chem Rev 2001 101 1115ndash1566 Special Issue Aromaticity (b) Chem Rev

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Chem 2002 67 1333 (b) Stanger A Chem Commun 2009 1939 4) (a) Minkin V I Glukhovtsev M N Simkin B Ya Aromaticity and Antiaromaticity

Electronic and Structural Aspects Wiley New York 1994 pp 63ndash74 (b) Garratt P J Aromaticity Wiley New York 1986 pp 30ndash34 93ndash95

5) (a) Wu J Muumlllen K In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 3 pp 90ndash139 (b) Wu J Pisula W Muumlllen K Chem Rev 2007 107 718 (c) Handbook of Organic Electronics and Photonics Nalwa H S Ed American Scientific 2008

6) Miljanić O Š Vollhardt K P C In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 4 pp 140ndash197

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Chem Rev 2005 105 3842 and the references therein (b) Steinmann S N Jana D F Wu J I-C Schleyer P v R Mo Y Corminboeuf C Angew Chem Int Ed 2009 48 9828

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Jenneskens L W Tetrahedron Lett 1994 35 4405 18) (a) Linear [3]phenylene Dosa P I Schleifenbaum A Vollhardt K P C Org Lett

2001 3 1017 (b) Angular [3]phenylene Matzger A J Vollhardt K P C Chem Commun 1997 1415 (c) Angular [4]phenylene Dosa P I Gu Z Hager D Karney W L Vollhardt K P C Chem Commun 2009 1967

19) Perthuisot C Edelbach B L Zubris D L Simhai N Iverson C N Muumlller C Satoh T Jones W D J Mol Catal A 2002 189 157

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21) (a) Deniz A A Peters K S Snyder G J Science 1999 286 1119 (b) Fattahi A Lis L Tian Z Kass P S Angew Chem Int Ed 2006 45 4984 (c) Bally T Angew Chem Int Ed 2006 45 6616

22) Anslyn E Dougherty D Modern Physical Organic Chemistry University Science Books Palo Alto 2006

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24) Mestdagh H Postdoctoral Research Report University of California Berkeley 1986

25) Hirthammer M Vollhardt K P C J Am Chem Soc 1986 108 2481 26) Blanco L Helson H E Hirthammer M Mestdagh H Spyroudis S Vollhardt K

P C Angew Chem Int Ed Engl 1987 26 1246 27) Berris B C Hovakeemian G H Lai Y-H Mestdagh H Vollhardt K P C J

Am Chem Soc 1985 107 5670 28) Dosa P I The Chemistry of Angular and Linear [N]Phenylenes PhD Thesis

University of California Berkeley 2002 29) Diercks R Eaton B E Guumlrtzgen S Jalisatgi S Matzger A J Radde R H

Vollhardt K P C J Am Chem Soc 1998 120 8247 30) (a) Nambu M Siegel J S J Am Chem Soc 1988 110 3675 (b) Nambu M

Hardcastle K Baldridge K K Siegel J S J Am Chem Soc 1992 114 369 31) Nambu M Mohler D L Hardcastle K Baldridge K K Siegel J S J Am

Chem Soc 1993 115 6138 32) Kumaraswamy S Jalisatgi S S Matzger A J Miljanić O Š Vollhardt K P C

Angew Chem Int Ed 2004 43 3711 33) (a) Eisch J J Piotrowski A M Han K I Kruumlger C Tsay Y H Organometallics

1985 4 224 (b) Schwager H Spyroudis S Vollhardt K P C J Organometallic Chem 1990 382 191

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35) Doumltz K H Jahr H C Chem Rec 2005 4 61 36) Gridnev I D Coord Chem Rev 2008 252 1798 37) Eickmeier C Holmes D Junga H Matzger A J Scherhag F Shim M

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38) Groszligmann T N Haptotropism in Linear Phenylene Complexes Diplomarbeit Thesis University of California Berkeley 2004

39) Dinculear photothermal haptotropic systems Tsuchiya K Ideta K Mogi K Sunada Y Nagashima H Dalton Trans 2008 2708 and the references therein

40) Additive assisted photothermal haptotropic systems (a) Jahr H C Nieger M Doumltz H K Chem Eur J 2005 11 5333 d) Herbert D E Tanabe M Bourke S C Lough A J Manners I J Am Chem Soc 2008 130 4166 e) Ieong N S Manners I J Organomet Chem 2008 693 802 and references therein

41) (a) Zhu G Tanski T M Churchill D G Janak K E G Parkin G J Am Chem Soc 2002 124 13658 (b) Zhu G Pang G Parkin G J Am Chem Soc 2008 130 1564

42) Selected reviews of photobased devices and molecular switches (a) Balzani V Credi A Venturi M Chem Soc Rev 2009 38 1542 (b) Kay E R Leigh D A Zerbetto F Angew Chem Int Ed 2007 46 72 (c) Photochromism Molecules and Systems Duumlrr H Bouas-Laurent H Eds Elsevier Amsterdam 2003 (d) Feringa B Molecular Switches Wiley-VCH Weinheim 2001

43) (a) a) Photofunctional Transition Metal Complexes Yam V W W Ed Springer Berlin 2007 b) Coppens P Novozhilova I Kovalevsky A Chem Rev 2002 102 861 c) Guumltlich P Garcia Y Woike T Coord Chem Rev 2001 219ndash221 839

44) (a) Lambert J B Mazozola E P Nuclear Magnetic Resonance Spectroscopy An Introduction to Princples Applications and Experimental Methods Pearson Education Upper Saddle River 2004 (b) Berger S Braun S 200 and More NMR Experiments A Practical Course Wiley-VCH Weinheim 2004 (c) Friebolin H Basic One- and Two-Dimensional NMR Spectroscopy 4th edition Wiley-VCH Weinheim 2005

45) (a) Schulman J M Disch R L J Phys Chem A 2003 107 5223 (b) Schulman J M Disch R L J Am Chem Soc 1996 118 8470 and the references cited therein

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48) Hillard III R L Vollhardt K P C J Am Chem Soc 1977 99 4058 49) Berris B C Lai Y-H Vollhardt K P C J Chem Soc Chem Commun 1982

953 50) (a) Rausch M D Genetti R A J Org Chem 1970 35 3888 (b) Hart W P

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2516 (b) Wolfart V Ramming M Gleiter R Nuber B Pritzkow H Rominger F Eur J Inorg Chem 1999 499 (c) Mitchell R H Chen Y Khalifa N Zhou P J Am Chem Soc 1998 120 1785 (d) McGlinchey M J Burns R C Hofer R Top S Jaouen G Organometallics 1986 5 104

53) Feixas F Jimeacutenez-Halla J O C Matito E Poater J Solagrave M Pol J Chem

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2007 81 783 54) (a)Stanger A J Org Chem 2006 71 883 (b) Stanger A Chem Eur J 2006 12

2745 (c) Tsipis A C Phys Chem Chem Phys 2009 11 8244 (d) Stanger A Chem Commun 2009 1939

55) For very recent literature compilations of theoretical (and experimental) treatments of haptotropism in arene metal complexes see a) Joistgen O Pfletschinger A Ciupka J Dolg M Nieger M Schnakenburg G Froumlhlich R Kataeva O Doumltz K H Organometallics 2009 28 3473 b) Pfletschinger A Dolg N J Organomet Chem 2009 694 3338 c) Jimeacutenez-Halla J O C Robles J Solagrave M Organometallics 2008 27 5230 d) Kirillov E Kahlal S Roisnel T Georgelin T Saillard J-Y Carpentier J-F Organometallics 2008 27 387 and references therein

56) Jimeacutenez-Halla J O C Robles J Solagrave M J Phys Chem A 2008 112 1202 57) Oprunenko Y Gloriozov I Lyssenko K Malyugina S Mityuk D Mstislavsky

V Guumlnther H von Firks G Ebener M J Organomet Chem 2002 656 27 58) Muumlller J Gaede P E Qiao K J Organomet Chem 1994 480 213 59) Bianchini C Caulton K G Chardon C Doublet M L Eisenstein O Jackson

S A Johnson T J Meli A Peruzzini M Streib W E Vacca A Vizzat F Organometallics 1994 13 2010

60) (a) De Boer E Van Willigen H V Prog Nuc Mag Res Spec 1967 2 111 (b) Memory J D Wilson N K NMR of Aromatic Compounds Wiley-VCH New York 1982

61) (a) Poli R Chem Rev 1996 96 2135 and the references cited therein (b) Schroumlder D Shaik S Schwartz H Acc Chem Res 2000 33 139 (c) Harvey J N Poli R Smith K M Coord Chem Rev 2003 237 347 and the references cited therein

62) For computational examples of 16 electron triplet Cp cobalt species influencing cobalt-mediated reactions see (a) Siegbahn P E M J Am Chem Soc 1996 118 1487 (b) Poli R Smith K M Eur J Inorg Chem 1999 877 (c) Carreoacuten-Macedo J-L Harvey J N J Am Chem Soc 2004 126 5789 (d) Petit A Richard P Cacelli I Poli R Chem Eur J 2006 12 813 (e) Aubert C Betschmann P Eichberg M J Gandon V Geny A Heckrodt T J Lehmann J Malacria M Masjost B Paredes E Vollhardt K P C Whitener G D Chem Eur J 2007 13 7443 (f) Gandon V Agenet N Vollhardt K P C Malacria M Aubert C J Am Chem Soc 2009 131 3007

63) Illustrative examples (a) Olson W L Stacy A M Dahl L F J Am Chem Soc 1986 108 7646 (b) Wadepohl H Galm W Pritzkow H Wolf A Chem Eur J 1996 2 1453 (c) Knijnenburg W Hetterscheid D Kooistra T M Budzelaar P H M Eur J Inorg Chem 2004 1204

64) Benito-Garagorri D Bernskoetter W H Lobkovsky E Chirik P J Organometallics 2009 28 4807

65) Fox J P Ramdhanie B Zareba A A Czernuszewicz R S Goldberg D P Inorg Chem 2004 43 6600

66) Guennic B L Floyd T Galan B R Autschbach J Keister J B Inorg Chem 2009 48 5504

67) Cremer C Burger P J Am Chem Soc 2003 125 7664

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68) Atkins P de Paula J P Physical Chemistry 8th Edition Oxford University Press Oxford 2006

69) Butters T Toda F Winters W Angew Chem Int Ed Engl 1980 19 926 70) Mann B E Taylor B F 13C Data for Organometallic Compounds Academic

London 1981 71) For a review on triple decker arene complexes and closely related syn dinuclear

systems see (a) Beck V OlsquoHare D J Organomet Chem 2004 698 3920 and the references therein For a review of trinuclear CpCo(arene) complexes see (b) Wadepohl H Angew Chem Int Ed Engl 1992 31 247 and the references therein

72) Jonas K Koepe G Schieferstein L Mynott R Kruumlger C Tsay Y-H Angew Chem Int Ed Engl 1983 22 620 Angew Chem Suppl 1983 920

73) Muumlller J Gaede P E Qiao K Angew Chem Int Ed Engl 1993 32 1697 74) Schneider J J Wolf D Janiak C Heinemann O Rust J Kruumlger C Chem

Eur J 1998 4 1982 75) Schneider J J Denninger U Heinemann O Kruumlger C Angew Chem Int Ed

Engl 1995 34 592 76) Budzelaar P H M Moonen N N P de Gelder R Smits J M M Gal A W

Chem Eur J 2000 6 2740 77) Albright T A Dosa P I Groszligmann T N Oluwakemi O Padilla R Paubelle

R Timofeeva T Vollhardt K P C Angew Chem Int Ed 2009 48 9853 78) Schaub T Radius U Chem Eur J 2005 11 5024 79) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4660 80) (a) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4040

(b) Muumlller C Lachicotte R J Jones W D Organometallics 2002 21 1975 81) Martin R H Angew Chem Int Ed Engl 1974 13 649 82) Mallory FB Butler K E Evans AC Mallory CW Tetrahedron Lett 1996 37

7176 83) Selected Reviews (a) Amemiya R Yamaguchi M Chem Rec 2008 8 116 (b)

Ruliacutešek L Exner O Cwiklik L Jungwirth P Staryacute I Pospiacutešil L Havlas Z J Phys Chem C 2007 111 14948 (c) Hopf H Classics in Hydrocarbon Chemistry Wiley-VCH Weinheim 2000 pp 321ndash330 (d) Voumlgtle F Fascinating Molecules in Organic Chemistry Wiley New York 1992 pp 156ndash180 (e) Meurer K P F Voumlgtle Top Curr Chem 1985 127 1 (f) Laarhoven W H Prinsen W J Top Curr Chem 1984 125 63

84) (a) Mallory FB Butler K E Mallory CW Beacuterubeacute A Luzik E D Brondyke E J Hiremath R Ngo P Carroll P J Tetrahedron 2001 57 3715 (b) Mallory F B Butler K E Evans A C Brondyke E J Mallory C W Yang C Ellenstein A J Am Chem Soc 1997 119 2119

85) (a) Mitsuhashi R Suzuki Y Yamanari Y Mitamura H Kambe T Ikeda N Okamoto H Fujiwara A Yamaji M Kawasaki N Maniwa Y Kubozono Y Nature 2010 464 74 (b) Okamoto H Kawasaki N Kaji Y Kubozono Y Fujiwara A Yamaji M J Am Chem Soc 2008 130 10470 (c) Tian Y H Park G Kertesz M Chem Mater 2008 20 3266

86) Recent reviews of acenes in electronic applications (a)Yamashita Y Sci Technol Adv Mater 2009 10 024313 (b) Wuumlrthner F Schmidt R ChemPhysChem

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2006 7 793 (c) Bendikov M Wudl F Chem Rev 2004 104 4891 87) NICS-based comparison of phenacene and acene properties Portella G Poater

P Bofill J M Alemany P Solagrave M J Org Chem 2005 70 2509 and the references therein

88) Mallory F B Mallory C W Org React 1984 30 1 89) Gu Z Nickel-Catalyzed Cycloaddition Reaction of [N]Phenylenes and Alkynes

Postdoctoral Report University of California Berkeley 2008 90) Preferential displacement of COD by π ligands from Ni(COD)(PMe3)2 is well

documented See eg Karsch H H Leithe A W Reisky M Witt E Organometallics 1999 18 90

91) (a) Bochmann M Hawkins I Hursthouse M B Short R L J Chem Soc Dalton Trans 1990 1213 (b) Poerschke K R Mynott R Angermund K Kruumlger C Z Naturforsch 1990 40B 199 See also (c) Bartik T Happ B Iglewsky M Bandmann H Boese R Heimbach P Hoffmann T Wenschuh E Organometallics 1992 11 1235

92) For Ni-phosphine migrations along polycyclic benzenoid ligands see eg Stanger A Vollhardt K P C Organometallics 1992 11 317

93) Edelbach B L Vicic D A Lachicotte R J Jones W D Organometallics 1998 17 4784

94) (a) Feiken N Pregosin P S Trabesinger G Scalone M Organometallics 1997 16 537 (b) Feiken N Pregosin P S Trabesinger G Albinati A Evoli G L Organometallics 1997 16 5756 (c) Geldbach T J Pregosin P S Eur J Inorg Chem 2002 1907

95) Cheng T-Y Szalda D J Hanson J C Muckerman J T Bullock R M Organometallics 2008 27 3785

96) (a) Grimme S Harren J Sobanski A Voumlgtle F Eur J Org Chem 1998 8 1491 (b) Dias J J Chem Inf Model 2005 45 562

97) Still W C Mitra A Kahn M J Org Chem 1978 43 2923 98) (a) Leonard J Lygo B Procter G Advanced Practical Organic Chemistry 2nd

ed CRC Press Boca Raton 1998 (b) Errington R J Advanced Practical Inorganic Chemistry and Metalorganic Chemistry Chapman and Hill London 1997

99) Jonas K Deffense E Habermann D Angew Chem Int Ed Engl 1983 22 716 100) Gaussian 03 Revision B03 M J Frisch G W Trucks H B Schlegel G E

Scuseria M A Robb J R Cheeseman J A Montgomery Jr T Vreven K N Kudin J C Burant J M Millam S S Iyengar J Tomasi V Barone B Mennucci M Cossi G Scalmani N Rega G A Petersson H Nakatsuji M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida T Nakajima Y Honda O Kitao H Nakai M Klene X Li J E Knox H P Hratchian J B Cross C Adamo J Jaramillo R Gomperts R E Stratmann O Yazyev A J Austin R Cammi C Pomelli J W Ochterski P Y Ayala K Morokuma G A Voth P Salvador J J Dannenberg V G Zakrzewski S Dapprich A D Daniels M C Strain O Farkas D K Malick A D Rabuck K Raghavachari J B Foresman J V Ortiz Q Cui A G Baboul S Clifford J Cioslowski B B Stefanov G Liu A Liashenko P Piskorz I Komaromi R L Martin D J Fox T Keith M A Al-Laham C Y Peng A Nanayakkara M Challacombe P M W Gill B Johnson W Chen M W Wong C Gonzalez J A Pople Gaussian Inc Pittsburgh PA

- 175 -

2003 101) wwwgaussiancom 102) wwwchemcraftprogcom 103) Becke A D J Chem Phys 1993 98 5648 104) Lee C Yang W Parr G R Phys Rev B 1988 37 785 105) Binkley J S Pople J A Hehre W J J Am Chem Soc 1980 102 939 for

hydrogen and Gordon M S Binkley J S Pople J A Pietro W J Hehre W J J Am Chem Soc 1983 104 2797

106) Hay P J Wadt W R J Chem Phys 1985 82 270 107) Hehre W J Ditchfield R Pople J A J Chem Phys B 1972 56 2257 108) Curtiss L A McGrath M P Blaudeau J-P Davis N E Binning R C Jr

Radom L J Chem Phys 1995 103 6104 109) A W Ehlers M Boumlhme S Dapprich A Gobbi A Houmlllwarth V Jonas K F

Koumlhler R Stegmann A Veldkamp G Frenking Chem Phys Lett 1993 208 111

110) QST is a synchronous transit approach to the quadratic region around the transition state structure For details see (a) J B Foresman A Frisch in Exploring Chemistry with Electronic Structure Methods A Guide to Using Gaussian Gaussian Inc Pittsburgh PA USA 1996 (b) H B Schlegel in Ab Initio Methods in Quantum Chemistry Part I Wiley Chichester 1987

111) Gu Z The Improvement of Total Synthesis of Angular [4]Phenylene and Its Flash Vacuum Pyrolysis (FVP) Study Postdoctoral Report University of California Berkeley 2008

112) Schwager H Postdoctoral Research Report University of California Berkeley 1987

113) Kuumlchle W Dolg M Stoll H Preuss H Mol Phys 1991 74 1245 114) (a) Hariharan P C Pople J A Theor Chim Acta 1973 28 213 (b) Francl M

M Petro W J Hehre W J Binkley J S Gordon M S DeFrees D J Pople J A J Chem Phys 1982 77 3654 (c) Rassolov V Pople J A Ratner M Windus T L J Chem Phys 1998 109 1223

iv

lectures gave me much to think about The monthly lectures by Ajahn Amaro Ajahn Passano and the Abhayagiri Sangha were also a wonderful learning experience Chats about long-dead ancient languages and obscure texts with Sean Kerr a fellow survivor of Dagmar Theisonrsquos German class will also be fondly remembered The NY Sangha though far away always supported me and welcomed me warmly whenever I returned home Frank Yao Hai-Dee Lee Sheila Sussman Fred Ng Martin Applebaum Josephine Verceles Tiffany Taulton Phung Tran and especially Aaron Vederman repeatedly reminded me to ldquosmile breath deep and go slowlyrdquo The many visits to Bodhi Monastery were always the high points of my summers Michael Roehm Bhikkhu Bodhi Jane Berry Henry and Lily Teoh Marcie Barth Mahendra Sagar the dearly departed Felicia Miller Ven Guo Jun Susan Chastain and the polygot Bhikkhu Analayo made every visit an unforgettable experience and never failed to remind me why I get out of bed in the morning

- 1 -

Chapter One

Properties of the [N]Phenylenes and Their Organometallic Chemistry

11 General Discussion of [N]Phenylene Properties Polycyclic aromatic hydrocarbons (PAHs) are a class of molecules that have occupied the minds of chemists for generations1 Their essential feature aromaticity is the unusual stabilization that arises from having a 4n+2 number of π-electrons in a cyclical array This seemingly simple definition obscures the fact that aromaticity continues to be one of the most scrutinized topics in modern organic chemistry2 and more rigorous definitions3 have remained elusive Much of the early work4 with PAHs was aimed at investigating theoretical issues surrounding aromaticity There has been renewed interest in these systems in recent years because they are increasingly attractive as functional materials in organic-based electronics5 Of the many different kinds of PAHs known eg 1ndash6 (Figure 11) one subclass is of particular interest the [N]phenylenes6

Anthracene Coronene Phenanthrene

Chrysene Triphenylene Pyrene

1 2 3

4 5 6

Figure 11 Some examples of polycyclic aromatic hydrocarbons The [N]phenylenes (where N = the number of benzene rings) are PAHs in which benzene and cyclobutadiene rings are fused in an alternating manner The cyclobutadiene ring imparts very unusual structural and electronic properties as seen in the simplest molecule in the series biphenylene (7) It can be described by several resonance forms (Figure 12 andashe) in which the major contributor 7c avoids formation of the highly destabilizing antiaromatic cyclobutadiene (7a 7e) and benzocyclobutadiene circuit (7b 7d) This preference is manifest in the significant bond alternation7 seen in

- 2 -

the crystal structure of biphenylene (Figure 12) which shows a clear difference in bond lengths between the formal single bonds (~143 Aring) and the shorter formal double bonds (~137 Aring)

1423

1372

Figure 12 Biphenylene bond lengths (top Aring) and resonance contributors (bottom)

An extreme example of [N]phenylene π-bond localization is triangular [4]phenylene (8) (Scheme 11) in which the three-fold peripheral fusion imparts complete cyclohexatriene character on the central ring89a This property is reflected in the reactivity of the system eg catalytic hydrogenation (9)8b epoxidation (10)8c and cyclopropanation (11)8c Scheme 11 Reactions Illustrating the Fully Bond Localized Character of the Central Benzene

Ring in Triangular [4]Phenylene 8 Bond lengths are in Aring

- 3 -

Phenylenes exhibit another interesting structural feature in contrast to other PAHs sizable deviations from planarity (Figure 13)9ab The flexibility of the phenylene framework arises from the combined effect of π- and σ-strain9ab By adopting a nonplanar geometry overlap between the π-orbitals is diminished and in turn leads to a decrease in destabilizing antiaromatic character Pyramidalization of the four-membered ring carbons also reduces σ-strain9ab a phenomenon observed in highly strained alkene systems9c

Figure 13 Crystal structures showing deviations from planarity in (a) helical [6]phenylene (12)10 (b) dimethyl triangular [4]phenylene-23-dicarboxylate (13)9a and (c) 23-bis(tri-

methylsilyl) linear [3]phenylene (14)9a

The fusion of aromatic benzene rings with antiaromatic cyclobutadiene units in the same molecule has prompted numerous experimental and theoretical discussions6 regarding the magnetic and electronic properties of the phenylenes 1H-NMR spectroscopy is one typical measure of aromaticity Protons on the exterior of aromatic rings (eg 15) show relatively low field resonances while their interior counterparts resonate at relatively high field due to the presence of a diamagnetic ring current Conversely antiaromatic rings with 4n π-electrons are paratropic and reveal the opposite disposition of the two respective types of protons (eg 16) The interplay between aromatic and antiaromatic character in the phenylenes is evident in their chemical shifts which tend to show weakly aromatic resonances (Figure 15) relative to benzene (736 ppm)

(a) (b) (c)

12 13 14

- 4 -

Figure 14 Observed 1H-NMR resonances in (a) the aromatic [18]annulene (15)11 and (b) the antiaromatic 5-bromo-19-bisdehydro-[12]annulene (16)12

Aside from NMR spectroscopy nucleus independent chemical shift (NICS)13 calculations have also proven to be useful measures of aromaticity The NICS technique works by calculating the magnetic shielding of a ldquoghost nucleusrdquo that can be positioned anywhere around a molecule For probing aromaticity the calculated point is in the center of the π-electron circuit to be examined Calculations placing the ghost nucleus 1 Aring above the plane of the molecule are often used to minimize local anisotropy and are referred to as NICS(1)14 NICS data are given in ppm and are thus comparable to experimental 1H-NMR measurements Negative NICS values indicate aromatic character while positive values suggest antiaromatic character For example the NICS(1) of benzene15 is ndash125 ppm whereas for cyclobutadiene15 it is 151 ppm NICS calculations for various phenylenes have been carried out6 and are shown in Figure 15 alongside the experimentally measured 1H-NMR chemical shifts The attenuated aromatic character of the benzene and the relatively weak antiaromatic character of the cyclobutadiene rings in phenylenes such as biphenylene (7) triangular [4]phenylene (8) and angular [4]phenylene (17) are apparent from both sets of data

Figure 15 1H-NMR (blue) and NICS(1) (green) data for selected phenylene topologies (ppm)6

The phenylenes possess multiple modes of reactivity7 as illustrated by biphenylene (7) in Scheme 12 It can undergo electrophilic aromatic substitution like other PAHs but does so selectively at the 2-position to avoid the formation of intermediates with antiaromatic character Biphenylene does not readily undergo Diels-

- 5 -

Alder reactions but was shown to react with electron-deficient benzynes to give the corresponding cycloadducts16 Opening of the highly strained four-membered ring is another prominent aspect of phenylene reactivity

Scheme 12 Illustrative Reaction Pathways of Biphenylene6

Early work17 showed that it was possible to cleave the aryl-aryl C-C bonds via thermolysis in the neat state Rupture of the four-membered ring is a key step in the rearrangement of phenylenes into other PAHs and has been observed typically under flash vacuum pyrolytic conditions18 (eg 10ndash3ndash10ndash6 torr 800ndash1000 degC) Strained ring opening on exposure to metal complexes to give metallacycles19 is discussed in further detail in Section 12 12 Overview of Phenylene Organometallic Chemistry

As mentioned above the weakly aromatic character of the phenylenes dominates their structure and reactivity In the linear phenylenes the antiaromatic contribution to structure and reactivity becomes increasingly significant A simple yet instructive explanation for this phenomenon can be seen in the various resonance structures of linear [3]phenylene (18) a selection of which is depicted in Figure 16 Even the most favorable forms a and b feature double bonds in the four-membered rings The cumulative increase in cyclobutadienoid circuits should therefore lead to an increase in antiaromatic character The relative augmentation in

- 6 -

cyclobutadienoidantiaromatic character of the linear phenylenes was confirmed6 by NMR NICS calculations and HOMO-LUMO measurements20

Figure 16

Resonance contributors to linear [3]phenylene

Cyclobutadiene is often invoked as the typical example of a highly destabilized antiaromatic system Indeed the difficulties21 in preparing and isolating it confirm theoretical predictions regarding its instability22 Attachment of a metal however is known to produce aromatic organometallic molecules of high stability23 The increased antiaromatic character of the linear phenylenes thus makes them amenable to metal complexation Cyclopentadienylcobalt cyclobutadiene complexes of linear [3]- (19)24 linear [4]- (20)25 and linear [5]phenylene (21)26 have been prepared using the well-developed cobalt-based [2+2+2] alkyne cyclotrimerization methods (Scheme 13)27

Compounds 19ndash21 constitute the only linear CpCo phenylene systems known so far

Scheme 13 Synthesis of Linear Phenylene(CpCo) Cyclobutadiene Complexes

In the metallated linear [4]- and [5]phenylene 20 and 21 respectively the CpCo unit is located on the inner cyclobutadiene ring This is curious as one would have expected the metal fragment to be bound to its outside counterpart close to the center of reactivity during the cyclotrimerization step The position of the CpCo unit was established by NMR spectroscopy2628 In addition a crystal structure of a tetrahexyl

TMS

TMS

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMSTMS

TMS

Co

CpCo(CO)2BTMSA

h

Co

Co

CpCo(CO)2BTMSA

h

CpCo(CO)2BTMSA

h

19

20

21

- 7 -

substituted linear [5]phenylene28 (Figure 17) clearly reveals the inside position of the metal fragment Difficulties in obtaining high quality crystals however precluded a detailed bond analysis of the complex The unexpected location of the CpCo unit in 20 and 21 suggested the occurrence of CpCo migration under the conditions of their preparation Detailed experiments verifying this hypothesis will be the subject of Chapter 2

Figure 17 Disordered crystal structure for the 23910-tetrakis(trimethylsilyl)-571214-

tetrahexyl linear [5]phenylene(CpCo)

In contrast to the linear phenylenes their angular relatives undergo π-metallation at the cyclohexatrienoid moieties (Figure 18) For example angular [3]phenylene (22) reacts with CpCo(C2H4)2 to form the η4-CpCo complex 2329 Similar treatment with Cr(CO)3(NH3)3 yields the η6-Cr(CO)3 analog 2430

Figure 18 η

4-CpCo (23) and η6-Cr(CO)3 (24) complexes of angular [3]phenylene (22)

In addition to 24 related chromium complexes of the triangular [4]phenylene frame eg 25 have been prepared (Scheme 14)31 Interestingly regioisomer 26 generated at relatively lower temperatures is the kinetic product of monocomplexation and rearranges thermally to 27 Double metallation is possible as illustrated in the conversion of 27 to 28 with added (naphthalene)Cr(CO)3

- 8 -

Scheme 14 Synthesis and Reactions of Triangular [4]Phenylene(Cr(CO)3) Complexes

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3(NH3)3dioxane 100 oC

14 h

(naphthalene)Cr(CO)3THF Et2O 60 oC 14 h

90 oC

(naphthalene)Cr(CO)3THF Et2O 60 oC

14 h

25

27

26

28

57 43

89

In contrast to CpCo which attaches itself exclusively to the four-membered ring in the linear phenylenes including the linear [3]phenylene frame as in 19 (Scheme 13) Fe2(CO)9 gives a plethora of complexes with the tetrasilyl derivative 29 among which the iron tricarbonyl cyclobutadiene complex 30 is only minor (Scheme 15)27 Instead other organometallic molecules such as arene complex 31 were isolated This compound contains two Fe(CO)3 units coordinated to the central benzene ring An iron-iron bond was proposed for this molecule (31a) although the spectral data are also consistent with a structure in which the Fe(CO)3 fragments are located on opposite faces (31b) Because a crystal structure could not be obtained the structural identity of 31 remains ambiguous The major products of this reaction 32 and 33 illustrate another important aspect of phenylene reactivity metal insertion into the strained ring

- 9 -

in this case involving the dinuclear Fe2(CO)6 unit Complex 33 probably originating from 32 contains an additional Fe(CO)3 moiety coordinated to the terminal benzene ring closest to the Fe2(CO)6 fragment

Scheme 15 Reaction of Linear [3]Phenylene with Fe2(CO)9

While as yet absent in the linear series a cobalt insertion product analogous to iron compounds 32 and 33 was isolated when angular phenylene 22 was exposed to excess CpCo(ethene)2 (Figure 19)32 In this case double insertion of two (CpCo)2

Figure 19 Tetranuclear CpCo-terphenylene complex 34 and its crystal structure

34

- 10 -

fragments occurred to give 34 in 71 yield Notably neither 23 nor analogs of the type 31 were detected As alluded to in Scheme 12 biphenylene (7) itself also undergoes metal insertions into the four-membered ring This type of reactivity has been observed with a range of transition metals including Co19 Mechanistically best delineated is the attack of Ni and Pt species Thus Ni(PEt3)4

33a and Ni(COD)(PMe3)233b begin with insertion of

the nickel fragment into the four-membered ring to give a metallacycle of the type 35 (Scheme 16) Subsequent dimerization assembles 36 from which Ni is extruded to furnish tetraphenylene 37 as the final product A similar reaction pathway was proposed for Pt(PEt)4

19 but proceeding via 38 to a monometallacycle 40 possibly through the intermediacy of 39 In summary the σ- and π-activation of the phenylenes endows them with rich organometallic chemical potential The synthetic and mechanistic exploration of one aspect of it namely the Ni-catalyzed cycloaddition of alkynes to the four-membered rings in angular phenylenes will be discussed in Chapter 3

Scheme 16 Reaction of Biphenylene with Nickel and Platinum Complexes

13 Direction of Work The discussions in Sections 11 and 12 have provided a brief overview of phenylene properties and their previously studied organometallic chemistry

- 11 -

respectively The aim of this thesis was to advance two aspects of prior investigations The first area examines the chemistry of the linear phenylene(CpCo) complexes In particular experiments are presented addressing the question of a possible migration of the CpCo fragment along their framework The revocable movement of a metal fragment between cyclobutadiene rings is a highly noteworthy discovery as this process has never before been reported On a practical level this mode of reactivity places linear phenylene(CpCo) complexes in the increasingly appealing class of organometallic arrays that can serve as the basis for various molecular electronic systems The reversible isomerizations described in the second chapter can potentially be employed in molecular machines and switches data storage and as will be detailed photostorage devices Experimental work in the form of detailed solid state and spectroscopic analyses is provided Computational studies are also employed to further scrutinize the novel chemistry of the abovementioned Co-based molecules The second topic of this thesis examines nickel-catalyzed insertions into the four- membered rings of angular phenylene systems Specifically the application of this reactivity to the synthesis of a class of PAHs known as [N]phenacenes is discussed Phenacenes (polyphenanthrenes) have recently shown great promise as organic transistors and conductors but advancement of this field has been hampered due to few practical syntheses The insolubility of these molecules has also been a substantial barrier to the development of phenacene-based applications The content of the third chapter explores the preparation of soluble phenacene derivatives using a tandem Ni-insertion alkyne cycloaddition reaction This new process provides an efficient widely applicable and practical synthesis of larger phenacenes using correspondingly larger angular phenylene systems Detailed mechanistic studies of this reaction are presented Experimental data are used in conjunction with computational studies to gain further insight with the optimization of the reaction by reduction of side product formation being a crucial milestone

- 12 -

Chapter Two

PhotondashThermal Haptotropism in Cyclopentadienylcobalt Complexes of Linear Phenylenes Intercyclobutadiene Metal Migration

21 Introduction As previewed in Section 12 the unexpected position of the metallic unit in the linear [4]- and [5]phenylene(CpCo) systems 20 and 21 constituted the background for the studies presented in this chapter Specifically it was hypothesized that its origin was due to the migration of the metal fragment from one cyclobutadiene ring to another a process that would constitute an unprecedented type of haptotropic shift34-36 However a prerequisite for studying such a rearrangement would be the generation of the haptoisomers of 20 and 21 (Scheme 13) bearing the CpCo appendage at the respective terminal four-membered rings a possibility obviated by their thermal method of synthesis The following describes the history that led to the discovery of photochemical conditions that circumvented this thermodynamic problem The story begins with a prior attempt to stabilize the linear phenylene frame by alkyl substitution the ultimate aim being the synthesis of members of the series with Ngt5 Such substitution was also hoped to improve solubility a facet exploited in the corresponding zigzag series37 The synthetic strategy followed that used in the preparation of the largest known linear phenylene 41 namely the CpCo-catalyzed cyclization to 21 followed by careful oxidative demetallation as shown in Scheme 21 The initial target chosen was the tetrahexyl system 43 approached via the synthesis of complex 42 (Scheme 22)28 Demetallation was thought to be facile to provide the free ligand but this anticipation proved to be erroneous

Scheme 21 Oxidative Decomplexation of Linear [5]Phenylene Complex 21

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMS

41

CoCp

21

40

CuCl2middot2H2ODME NEt3 H2O

Scheme 22 Preparation of Tetrahexyl Linear [5]Phenylene Complex 42

- 13 -

TMS

TMS

TMS

TMS

Hex

Hex

Hex

Hex

CoCp

42

CpCo(CO)2 BTMSAm-xylene ∆ hν

27

Hex Hex

HexHex

TMS

TMS

TMS

TMS

Hex Hex

HexHex

ndashCpCo

43

The demetallation of 42 under numerous conditions was unattainable However in one of these attempts an NMR sample of 42 was exposed to UV-irradiation leading to the evolution of new signals eventually assigned to originate from rearranged compound 45 (Scheme 23)28 This molecule is also a linear [5]phenylene(CpCo) complex but now has the metal fragment bound to the outer cyclobutadiene ring an arrangement that was suspected to be the initial product of the preparation of 42 (Scheme 22) That this conjecture was correct was established by heating which caused photoisomer 45 to revert to 42 An indication of the generality of this phenomenon was gleaned from 21 which underwent the same photoinduced thermally reversible haptotropic migration (Scheme 23)38 A detailed discussion of the spectral properties of these haptomers is provided in Sections 23 and 24 Scheme 23 Photoinduced Thermally Reversible Haptotropic Migration of the CpCo Fragment

in Linear [5]Phenylene(CpCo) Complexes

This discovery was deemed significant for two reasons 1 it constitutes the first observation of intercyclobutadiene metallohaptotropism and 2 there are only two previously known examples of mononuclear39 additive-free40 photothermal reversible haptotropic shifts both of which are based on Mo(PMe3)3 complexes (Scheme 24)41 Systems capable of undergoing this type of reaction are of much practical importance because of their potential employment as photostorage devices andor molecular switches42 The development and application of functional organometallic materials43 has proceeded at a relatively slow pace when compared to their non-metallated counterparts5c Thus the great prospects for discovery and advancement make this area of study particularly attractive

- 14 -

Scheme 24 Photothermal Reversible Metallohaptotropism in (a) Molybendum-Indole41a and (b) Molybendum-Isoquinoline Complexes41b

Having confirmed that an η4η4 cyclobutadiene haptotropic migration was indeed occurring mechanistic investigations2838 were begun Interestingly full conversion of the inner bound CpCo complexes to their photoisomers was never achieved The maximum ratio obtained for 2144 and 4245 was 8812 Variations of solvent (eg benzene THF CHCl3) and temperature (0ndash30degC) had no effect on this ratio Added ligands such as 15-cyclooctadiene CO and phosphines were also inconsequential Of further significance was the robustness of the photothermal cycle which could be run multiple times without decomposition Kinetic experiments were carried out to determine the activation parameters for the thermal reversal of 44 and 45 to 21 and 42 respectively These data are shown in Table 21 The isomerizations are cleanly first order a finding that was unaffected by changes in concentration22 The enthalpy of activation (∆Hne) increased only slightly with hexyl substitution (44 vs 45) The near zero entropy of activation values (∆Sne) was consistent with the occurrence of an intramolecular process

Table 21 Activation Parameters for the Conversion of Outer to Inner CpCo Complexes Under

Thermal Conditions ∆Sne Values are in Entropy Units (1 eu = calmolsdotK)

Reaction Solvent ∆H

ne (kcalmol) ∆Sne (eu)

44 to 21 C6D6 259 plusmn 04 16 plusmn 14 44 to 21 THF-d8 256 plusmn 09 01 plusmn 30 45 to 42 THF-d8 276 plusmn 08 77 plusmn 27

Consideration of the relative facility of the above haptotropic shifts made it likely that migration was occurring along the entire phenylene frame including the ldquohoppingrdquo across the central six-membered ring (Scheme 25) This degenerate equilibration should be detectable by NMR spectroscopy44 if it were sufficiently fast Unfortunately but perhaps not surprisingly considering the data in Table 21 coalescence of the spectrum of 21 could not be achieved even at temperatures as high as 120 degC Spin saturation transfer experiments (eg EXSY) also failed44 These data allowed an estimate of the lower limit for the activation energy of the internal shift of ∆Gne ge 22 kcalmol28

Scheme 25 Proposed Internal η4η4 Cyclobutadiene CpCo Migration

- 15 -

The failure of the above experiments inspired a different approach based on the following arguments The antiaromatic character of the linear phenylenes has been shown by theory and experiment to increase with size645 Consequently the effect of metalloaromatization46 makes linear [5]phenylene a better (and hence more strongly bound) ligand for CpCo than a smaller system (eg linear [3]phenylene) Indeed the enthalpy of the homodesmotic in Scheme 26 was computed by DFT methods to be Scheme 26 Calculated Homodesmotic Reaction Showing Preferential Binding of CpCo to

Linear [5]Phenylene

113 kcalmol47 If the barrier to intercyclobutadiene hopping were related to the binding energy of the metal one would expect a more loosely bound metal fragment to migrate faster The hope was therefore that the degenerate haptotropism in Scheme 27 would be observable by VT NMR methods Unfortunately these efforts failed again38 either because the anticipated acceleration was not sufficient to be observable by NMR or because the argument above (which rests solely on ground state considerations) is flawed

Scheme 27 Proposed Degenerate Haptotropic Shift in Linear [3]Phenylene Complex 19

- 16 -

The preceding discussion summarizes some of the quantitative aspects of this new type of haptotropic shift Many fundamental questions however remained to be answered Is it possible to observe the photothermal shift in other systems such as linear [3]- and [4]phenylene What is the exact mechanism of metal migration between cyclobutadiene rings In what way if any does attachment of CpCo alter the structure of the phenylene scaffold Related to these questions was the long-standing quest for an accurate crystal structure of any linear phenylene(CpCo) complex The answers are addressed in the following sections 22 Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes As recounted in Section 21 the degenerate internal haptotropic shift could not be seen by NMR in the symmetrical 19 Therefore recourse had to be taken to chemical methods involving an isomerization of the sort shown in Scheme 28

Scheme 28 Isomerization of a Desymmetrized Linear [3]Phenylene(CpCo) Complex

Initial efforts focused on attempts to desymmetrize compound 19 directly by selective electrophilic desilylation specifically protodesilylation Earlier studies48 had shown that such selectivity was possible in the reactions of bis(trimethylsilyl)benzocycloalkenes such as the benzocyclobutene depicted in Scheme 29 In this case loss of the first TMS group is approximately forty times faster than that of the second Along these lines it was thought that exposing 19 to acidic conditions would selectively remove one (or perhaps two) TMS groups before attacking the remaining silylarene positions In the event treating compound 19 with trifluoroacetic acid in carbon tetrachloride did induce protodesilylation but with no selectivity A mixture of products was obtained and its separation proved impossible (Scheme 210) In light of this setback a new synthetic scheme had to be considered that would generate a desymmetrized system directly in the CpCo-catalyzed cyclization step

- 17 -

Scheme 29 Selective Desymmetrizing Reactions of 12-Bis(trimethylsilyl)benzocyclobutene with Electrophiles

Scheme 210 Attempted Selective Protodesilylation of 19

Fortunately such a strategy had already been executed successfully in the creation of 23-bis(trimethylsilyl) linear [3]phenylene (46) and employed the iterative Scheme 211 Iterative Cyclotrimerization Route in the Synthesis of Linear [3]Phenylene 46

cyclization depicted in Scheme 21127 Its specific execution (Scheme 212) started with a Sonogashira reaction between trimethylsilylacetylene (TMSA) and 12-diiodobenzene (47) to give diyne 48 in high yield Deprotection of 48 with K2CO3 immediately followed by standard CpCo(CO)2-catalyzed alkyne cyclotrimerization649 with bis(trimethylsilyl)acetylene (BTMSA) afforded 23-bis(trimethylsilyl)biphenylene (49) Iododesilylation was then performed using pure ICl to give 23-diiodobiphenylene (50) A Sonogashira coupling between TMSA and 50 produced diyne 51 in good yield The use of a slightly modified cyclization procedure provided the new 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52) in 57 yield This protocol employed THF as a cosolvent to BTMSA thus reducing the reaction temperature in turn allowing for the CpCo to remain attached in the final product and preventing catalytic turnover252638

TMS

TMS46

+

TMS

TMS

+

TMS

TMS

+

TMS

R

TMS

dilute

[X+]

X = H D Br

TMS

TMS

[X+]

TMS

X = H D Br

X

- 18 -

Scheme 212 Synthesis of Asymmetric Linear [3]Phenylene(CpCo) 52

High dilution conditions also helped to suppress formation of cyclobutadiene(CpCo) complexes a well known side reaction in alkyne cyclization chemistry

Compound 52 like its tetrasilylated analogue 19 is a black air-sensitive solid Although it can be handled in air for brief periods of time complete decomposition occurs within 24 hours if left exposed to the ambient atmosphere Purification must always be done with neutral activity III alumina as lower activities (and silica gel) cause decomplexation to give the deep red ligand 46 as the only isolable product Critically exposing molecule 52 to UV irradiation induced the desired haptotropic shift giving its photoisomer 53 (Scheme 213) Heating 53 converted it back to 52 thus completing the photothermal cycle Interestingly close inspection of the NMR spectra of this experiment revealed that a small amount of 53 (2) always remained even on prolonged heating That this observation signaled a thermodynamic equilibrium was confirmed by dissolution of pure crystalline 52 and NMR analysis From the equilibrium constant the ∆Gdeg298 was calculated to be 23 kcalmol in favor of 52 The reasons for this energetic preference and a discussion of the NMR spectral properties of these and related complexes are presented in Section 23

Scheme 213 The Photoinduced Thermally Reversible Haptropic Shift in Linear

- 19 -

[3]Phenylene-(CpCo) 52 to Give Photoisomer Complex 53 The investigations of the equilibration depicted in Scheme 213 were all carried out in sealed Pyrex NMR tubes (J-Young or flame-sealed) using benzene-d6 andor toluene-d8 as the solvent As for the linear [5]phenylene(CpCo) system the cycle could be run multiple times without decomposition and was unaffected by changes in solvent and temperature The maximum ratio of 5352 that could be obtained on irradiation was 11 after ten hours This value is larger than that observed for its linear [5] analogs 2144 and 4245 Photoisomerization also occurs with sunlight leading to the photostationary equilibrium of 5253 = 105 Consequently care must be taken to shield 52 from direct andor indirect sunlight Indoor fluorescent lighting however did not induce CpCo migration Attempts to monitor the photoisomerization and its thermal reverse by UV-Vis spectroscopy failed because of minimal changes in the absorptions due to 52 during these processes This finding implies that the absorption spectra of 52 and 53 are not unexpectedly very similar and offers a possible explanation for the maximum photostationary ratio of 11 The activation parameters for the thermal reversal reaction (53 to 52) in Scheme 213 were obtained in the manner described in Section 21 and are shown in Table 22 The relatively high activation barriers (with respect to the NMR time scale) explain why the degenerate isomerization in 19 could not be verified by NMR experiments Qualitatively the ∆Hne values agree with the hypothesis that the more loosely bound CpCo unit in the linear [3]phenylene is relatively more mobile they are approximately 3 kcalmol lower than those of the [5]phenylene system On the other hand the ∆Sne values especially in C6D6 are positive and relatively high although still within the range acceptable for intramolecular reactions Nevertheless a crossover experiment was devised to provide a definite answer

Table 22 Activation Parameters for the Thermal Conversion of Complex 53 to 52

Solvent ∆H

ne (kcalmol) ∆Sne (eu)

C6D6 204 plusmn 14 158 plusmn 22 Toluene-d8 231 plusmn 07 60 plusmn 13

For this purpose two new linear [3]phenylene(CpCo) derivatives were required One would carry a marker on the Cp ring while the other would be labeled at the phenylene frame Execution of Scheme 213 would involve an equimolar mixture of both compounds An intramolecular mechanism would retain the integrity of the labeling while a dissociative path would lead to label scrambling The outcome of this experiment should be ascertainable by NMR spectroscopy and more rigorously by

CoTMS

TMS

CoTMS

TMS

310 365 nmsunlight

30ndash50oC52 53

- 20 -

Scheme 214 Preparation of MeCp- (54) and Deuterium Labeled (55) [3]Phenylene Complexes

mass spectrometry To this end methyl-Cp complex 54 and dideuterio compound 55 were targeted for synthesis (Scheme 214) Compound 54 was prepared by carrying out the modified cyclotrimerization reaction with MeCpCo(CO)2

50 while 55 was made using methanol-OD in the desilylation of 51 The amount of deuterium incorporation in 55 was found to be 63 as gleaned from its proton NMR spectrum Scheme 215 Crossover Experiment with Labeled Linear [3]Phenylene(CpCo) Complexes

- 21 -

Co

TMS

TMS

TMS

TMS

Co

h CoTMS

TMS

Co

D

D

TMS

TMSD

D

TMS

TMS

Co

Co

TMS

TMSD

DCo

TMS

TMS

Co

TMS

TMSD

D

+

+

+

+

mz = 510

mz = 494

56mz = 508

57mz = 496

54mz = 508

55mz = 496

58 59

53 52

Not observed

Six distinct products are possible in the crossover experiment using 54 and 55 (Scheme 215) Compounds 56 and 5 would arise as a consequence of an intramolecular shift Molecules 53 and 58 and their photoisomers 52 and 59 respectively would be the result of metal fragment dissociation Mass spectrometry would readily verify the occurrence of crossover as the masses (given in mz in Scheme 215) of the products with scrambled labels (52 53 58 59) are distinct from the masses of the starting materials (54 55) and their photoisomers (56 57) In the first part of the experiment equal amounts of 54 and 55 were mixed (shielded from light) and allowed to stand for 2 hours at room temperature The resulting 1H-NMR spectrum consisted of only the signals for 54 and 55 Similarly the mass spectrum showed molecular ion peaks matching the masses of 55 and 56 (Figure 21) The second step was irradiation Analysis of the photolyzed mixture showed new peaks due to complex 56 (the resonances of which had been obtained in a separate photothermal experiment with pure 54) with the expected integration ratio and a second set assigned to 57 identical with the spectrum of 53 but with the expected attenuated absorption for the silyl bearing arene hydrogens The relative integrations for all compounds observed were consistent with a mixture of 5455 and 5657 Mass spectral analysis of the irradiated mixture showed a pattern that was identical to that collected before irradiation (Figure 21) Finally the thermal reversal reaction was carried out by heating the photolyzed mixture at 80 degC After 30 hours the resulting

- 22 -

NMR spectrum matched that of the initial mixture of 54 and 56 in particular confirming the full protonation of 54 and the unchanged level of deuterium incorporation in the silyl

Figure 21 Molecular ion peaks for 5456 (mz = 508) and 5557 (mz = 496)

bearing arene ring of 55 The corresponding mass spectrum contained no evidence for the presence of scrambled products To conclude The haptotropic shift is non-dissociative The exact manner in which the metal traverses from one cyclobutadiene ring to the other will be examined in greater detail in Section 24

23 X-Ray Structural and Comparative NMR Analysis of Linear [3]Phenylene(CpCo) Complexes The results described in Sections 21 and 22 pose some fundamental questions beyond those concerned with the immediate details of the observed haptotropism and addressing the basic novelty of the complexes involved What actually happens to the phenylene ligand when it is ligated via a cyclobutadienoid ring This section will address this question from a structural and (NMR) magnetic point of view Only one crystal structure of a linear phenylene(CpCo) complex was known at the outset of this work namely that of [5]phenylene(CpCo) 42 (Figure 17) and its acquisition required extensive efforts at crystallization28 Unfortunately extensive disorder obviated a detailed analysis It was hoped that some of the complexes employed in the chemistry disclosed in Section 22 would be more forthcoming in this respect The challenge lay in finding the right conditions for crystal growth We began with tetrasilyl linear [3]phenylene(CpCo) 19 which had been crystallized previously by slow cooling in acetone38 These conditions and numerous others (Table 23) did not provide material suitable for X-ray diffraction Success entailed slow cooling a solution of 19 to ndash10 degC in a mixture of methanol-diethyl ether (41) The ensuing sample allowed the determination of the first high quality crystal structure of a linear phenylene (CpCo) complex obtained in collaboration with the group of Professor Tatiana Timofeeva of New Mexico Highlands University (Figure 22)

Table 23 Trial Crystallization Conditions for Linear [3]Phenylene(CpCo)19

Solvent (Ratio) Conditions Result

Acetone Slow Cooling Heterocrystalline Solid Acetone-Pentane (31) Slow Cooling Heterocrystalline Solid

Pentane-Acetone (101) Solvent Diffusion Amorphous Solid Chlorobenzene Slow Cooling Amorphous Solid

- 23 -

Acetone-Methanol (110 Slow Cooling Amorphous Solid Diethyl Ether-Methanol Slow Cooling Small Needles

Acetonitrile Slow Cooling Powder Ethyl Acetate Slow Cooling No Crystals

Ethyl Acetate-Methanol (11) Slow Cooling Amorphous Solid Methanol-Diethyl Ether (41) Slow Cooling Large Fine Needles

Figure 22 X-ray crystal structure of 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) (19) Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are

omitted for clarity Expectedly the CpCo unit is bound in an η4 fashion to the cyclobutadiene ring Also prominent is the deviation from planarity (Section 11) in the linear [3]phenylene a facet typical of the phenylenes themselves (Section 11)9a Of greater importance than these general observations however is the effect of metal complexation on the linear [3] framework The bond lengths for 19 are shown in Figure 23 and as is typical for the phenylenes6 show a certain degree of bond π-localization with measurable differences between single and double bonds However the extent of this phenomenon and its direction varies significantly when compared to the free ligand 60 A quantitative

- 24 -

comparison of the structural data for 19 with those of its ligand 60 is shown in Figure 2327

In 60 the terminal rings adopt bond alternation similar to that in biphenylene (Section 11) and the central benzene takes on a ldquobis-allylrdquo configuration both ostensibly to minimize electron density (and therefore antiaromaticity) in the four-membered rings As dictated by symmetry the two bonds spanning the central ring are of equal length (1385 Aring) Ligation by CpCo alters this picture profoundly in as much as bond alternation across the entire phenylene frame including the four-membered rings is strongly reduced (Figure 23) Generally all relatively long bonds in 60 shorten in 19 while all short bonds lengthen Some residual but attenuated biphenylene type

Co

1512(2)

1513(2)

1407(2)

1385(2)

1385(2)

1397(2)

1356(2)

1359(2)1436(2)

1397(2)

1441(2)

1411(3)(0052)

1384(3)(-0052)

1474(3)(0077)

1384(3)(-0057)

1408(3)(0052)

1448(3)(0051)

1480(3)(-0032)

1468(3)(-0045)

1437(3)(0052)

1465(3)( 0058)

1434(3)( 0049)

1352(3)(-0033)

1351(3)(-0034)

1476(3)(0069)

1495(3)(-0017)

1372(3)( 0016)

1405(3)(0008)

1376(3)(0017)

1413(3)(-0023)

1427(3)(0030)

1488(3)(-0025)

1423(3)(-0018)

(x) = (19) - (60)increasedecrease

60

19

1907(1)

1891(1)

1886(3)

1889(3)

1889(2)

1901(3)

1669

1725

Si

Si

Si

Si

Me

MeMe

Me

Me

Me

Me

MeMe

MeMe

Me

Si

Si

Me

MeMe

MeMe

Me

Si

Me

MeMe

Si

Me

MeMe

- 25 -

Figure 23 Comparison of bond lengths (in Aring) between linear [3]phenylene(CpCo)complex 19 and 2378-tetrakis(trimethylsilyl) linear [3]phenylene (60) The bond distances in 19 are shown in blue Increases in bond length in going from 60 to 19 are marked in green decreases in red

ldquobond fixationrdquo (Figure 12) remains in the vicinity of the uncomplexed cyclobutadiene Compound 19 thus provides a prime demonstration of the powerful effect of metalloaromatization46 in which the bonds of a cyclobutadiene-metal system attempt to adopt the equalized bond lengths that are a classic hallmark of aromaticity2ndash4 Encouraged by the successful development of a procedure to obtain X-ray quality crystals of 19 these techniques were applied to bis(trimethylsilyl) linear [3]phenylene(CpCo) 52 Gratifyingly with acetone as the solvent the results depicted in Figure 24 were ultimately obtained Figure 24 X-ray crystal structure of 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52)

Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are omitted for clarity

A comparison of the bond lengths of 52 with those of its corresponding linear [3]phenylene ligand 469a is given in Figure 25 Comparison with Figure 23 reveals the same type of aromatization of the ligand on attachment of the metal With these structures in hand an attempt was made to rationalize structurally the

- 26 -

thermodynamic preference for 52 in which the CpCo is located proximal to the silylated terminus in its equilibrium with 53 in which the metal is located close to the unsilylated benzene ring Focusing on the desymmetrizing ortho-bis(trimethylsilyl) unit one notes that the SiCndashCSi bond in 52 is elongated by 005 Aring on attaching the metal in 46 thus providing steric relief On the other hand the symmetry equivalent remote C7ndashC8 distance is unchanged The same effect is seen in the tetrasilyl complex 19

Figure 25 Comparison of bond lengths (in Aring) between bis(trimethylsilyl) linear [3]phenylene(CpCo) complex 52 and 23-bis(trimethylsilyl) linear [3]phenylene (46) Bond lengths for 46 are the average of four molecules in the unit cell (standard deviation = plusmn002)

Increases in bond length going from 46 to 52 are marked in green decreases in red

The observed structural changes make sense in a simple resonance picture

Co

1413(10)(007)

1406(10)(-004)

1459(10)

( 005)

1370(11)(-007)

1418(10)( 005)

1443(10)(003)

1470(10)(-005)

1465(10)(-005)

1446(10)( 008)

1485(10)( 006)

1432(10)( 004)

1347(10)(-003)

1345(10)(-002)

1492(10)( 007)

1503(11)(-002)

1379(10)(001)

1391(11)(-001)

1409(10)(004)

1418(11)(-003)

1367(11)(001)

1478(10)(-002)

1408(11)(-001)

1891(8)

1890(13)

1670

1723

SiMe

MeMe

Si

Me

Me

Me

(x) = (53) - (62)increasedecrease

SiMe

MeMe

Si

Me

Me

Me

190

145134152

139138

150

137145

136

142 137

152137 137

152

141

137 144

189

141143142140

52

46

- 27 -

(Scheme 216) Metalloaromatization alters the dominant resonance forms during intercyclobutadiene hopping such that the essentially single SiCndashCSi bond in 52 transforms into an essential double bond in 53 increasing unfavorable repulsion between the TMS groups Scheme 216 A Resonance Picture Rationale for the Preference of 52 in its Equilibrium with 53 The aromatization effect of metal complexation on the phenylene nucleus described structurally in the preceding text can also be demonstrated powerfully through the measurement of ring currents with 1H-NMR spectroscopy both by experiment and computation (NICS13 see Section 11) A relevant simple example is depicted in Figure 26(a) featuring the changes occurring when 12-bis(trimethylsilyl)benzocyclobutadiene (61) is complexed by CpCo as in 6251 The paratropic antiaromatic 8π system 61 exhibiting relatively shielded six-membered ring hydrogens turns diatropic in 62 Equally importantly and focusing on the ring current contributions of the individual cycles the paratropism of the four-membered ring in 63 shields the adjacent hydrogens more than the remote ones Conversely aromatization of this ring and the ensuing diatropism inverts this order

Figure 26 The effect CpCo complexation (a) on benzocyclobutadiene 61 and (b) linear [3]phenylene 46 Chemicals shifts are in ppm

Co SiMe3

SiMe3

Co

SiMe3

SiMe352 53

∆Gdeg298 =23 kcalmol

- 28 -

Turning to a phenylene system comparison of the NMR data for complex 52 with those for ligand 46 (Figure 26(b)) reveals the same changes not only in the vicinity of the ligated ring but also in the remote parts of the molecule Thus the hydrogens closest to the metal fragment are shifted downfield by 125 ppm in 62 and 148068 ppm in 52 when compared with 61 and 46 respectively The observed relatively large chemical shifts of the arene hydrogens proximal to the metal unit are not due to its anisotropy since its value in this area of space is (if anything) shielding5152 In addition the remote hydrogens in 52 are deshielded by 055033 ppm relative to the corresponding nuclei in 46 clearly substantiating the aromatization of the overall system upon metal complexation that was seen by structural analysis These pronounced chemical shift changes are diagnostic and greatly aided the spectral interpretations of the photochemically induced haptotropic shift experiments described in Sections 21 and 22 as illustrated for the isomerization between 52 and 53 (Scheme 217)

Scheme 217 Chemical Shift Changes in the Isomerization of 52 to 53

These NMR measurements were augmented by NICS calculations carried out in collaboration with Professor Amnon Stanger at the Technion in Haifa NICS data have the advantage that they indicate the extent of (anti)aromaticity even in rings for which the molecule has no hydrogen probe in the classical NMR experiment in this case the cyclobutadienes Computational details are given in Chapter 4 The experimentally determined proton NMR data for the series of silylated linear phenylenes from [2] to [5] and their metallated analogues in addition to the corresponding NICS(1) values of the respective parent phenylenes are shown in Figure 27 All compounds in Figure 27 are known except for the hypothetical biphenylene(CpCo) 64 which is included for comparative purposes Metalloaromatization is pronounced as all rings of the phenylene exhibit diminished or more negative NICS numbers signaling increasing aromatic and decreasing antiaromatic character respectively Again the effect is most pronounced on the rings closest to the metal bound unit tapering off (but never disappearing) with distance Most illustrative in this respect is 44 in which the penultimate and ultimate rings away from the Co still show decreases in the NICS values of 06 and 05 ppm respectively Interestingly the sum of all NICS values of 44 (ldquototal NICSrdquo13c) ndash91 is less negative than that of 21 ndash132 suggesting that 21 is more aromatic hence more stable as observed experimentally This may be fortuitous and the issue is addressed further in Section 24 Finally a caveat regarding the unusually large negative NICS values associated with the CpCo-complexed cyclobutadiene rings As pointed out by Solagrave in connection with a related study of (benzene)Cr(CO)3 which produced similar numbers53 there are local ring currents associated with the extra electrons involved in the metal to π-ligand

CoTMS

TMS796675674

678

436 CoTMS

TMS747683724

662

444

310 365 nmsunlight

30ndash50oC

52 53

- 29 -

bonding that lead to an overestimation of aromaticity Therefore to corroborate the general conclusions of metalloaromatization of this (and all other rings) in Figure 27 Stangerrsquos NICS scan method was applied54 This procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (NICSXY) and out-of-plane components (NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their

Figure 27 Experimental 1H-NMR (C6D6 blue) and computed NICS(1) (green) values for linear phenylenes and their corresponding CpCo complexes The experimental data are for the silylated

derivatives shown The NICS data are for the parent systems interpretation The data presented in Chapter 4 confirm the conclusions of this section While not reflective of ring current effects the values of the 13C chemical shifts for the linear phenylene(CpCo)complexes do provide some insight into the nature of the

- 30 -

σ-framework Comparing complex 19 with parent ligand 60 one observes two general phenomena (Figure 28) The most apparent is the upfield values for the cobalt-bound cyclobutadiene carbons (~74ndash78 ppm) in 19 arising from the local anisotropic shielding effect of the metal (vide supra) Secondly the carbon atoms in the four-membered ring not bound to the metal exhibit large deshielded values (144ndash149 ppm) This effect also seen in ligand 60 arises from the rehybridization6 of the cyclobutadiene sp2 orbitals and is observed in all phenylene topologies A comparison of the 13C-NMR data for the linear [3]- [4]- and [5]phenylene(CpCo)complexes with their respective parent ligands is given in Chapter 4

Figure 28

13C-NMR data for complex 19 and parent silylated ligand 60 Values are in ppm 24 Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift How does the CpCo moiety migrate from one cyclobutadiene unit to the next Two extreme alternatives present themselves a least-motion movement across the intervening arene unit or a more circuitous pathway along the periphery The latter is prevalent in other computed haptotropic shifts56-57 in particular those occurring in (arene)Cr(CO)3 complexes all of which choose peripheral trails56 In these the metal typically moves straight to the edge to adopt an η4 (often described as η1) trimethylenemethane-like transition state on the way to a neighboring ring as illustrated for the η6-η6 hopping in naphthaleneCr(CO)3 summarized in Scheme 218 More relevant is the computed course of the η6-η6 interconversion of (biphenylene)Cr(CO)3 (Scheme 219)57 The metal slides from the (near)center of one benzene ring to the quaternary (four-membered) ring carbon to reach a distorted trimethylenemethane maximum and then proceeds to the edge of the bridging cyclobutadiene bond This species represents a minimum on the potential energy curve and adopts an η2-like complexed cyclobutadiene topology (ldquoquasi-η4rdquo) from which it continues by the microscopic reverse on to the other benzene nucleus The relevance of these findings with respect to the intercyclobutadiene hopping of CpCo along the phenylene frame was not clear at the outset of the work described in this section The CpCo fragment has a different electronic requirement from Cr(CO)3 and interring migration in arenes (and related systems) involves aromatic electron counts of all intervening circuits

Scheme 218 Migration of Cr(CO)3 Across Naphthalene

- 31 -

Scheme 219 Migration of Cr(CO)3 Across Biphenylene

DFT calculations were carried out in collaboration with Professor Thomas Albright at the University of Houston In these studies using B3LYP 3-21G (carbonhydrogen) and LANL2DZ (cobalt) basis sets the metal fragment was placed 18 Aring above the π system with energy minimizations carried out every 02 Aring along the frame of the parent linear phenylene in question When transition states and local minima were located their structures were refined with the B3LYP 6-31G (hydrogen) 6-113G (carbon) and LANL2DZ (with inclusion of cobalt f-orbitals) basis sets More computational details are given in Chapter 4 The resulting potential energy surface for the thermal rearrangement in the parent linear [3]phenylene(CpCo)system is shown in Figure 29 Figure 210 contains enlarged images of the transition states and intermediate structures The haptotropic shift begins with the (η4-cyclobutadiene)CpCo global minimum (labeled ground state GS) assigned a relative value of 000 kcalmol An η2-cyclobutadiene transition state (TS 1) 269 kcalmol higher in energy than GS is passed before reaching a local minimum (LM) that lies 109 kcalmol above GS LM features CpCo coordinated unsymmetrically η4 to the central benzene ring thus avoiding an unstable 20 electron η6-benzene configuration (not shown) which when explicitly calculated proved to lie 36 kcalmol above LM From LM a symmetry-related second η4 structure is reached via an η3-benzene transition state (TS 2 barrier 14 kcalmol) that symmetrizes the ldquoleftrdquo with the ldquorightrdquo half of the molecule LM is 249 kcalmol higher in energy than GS The shift is completed through the reverse of the initial two movements through LM and TS 1 on the other side of the ligand to reach the second cyclobutadiene ring Thus as for Cr(CO)3 (Scheme 219) CpCo migrates along the edge of the linear phenylene but because of its differing electronic needs through distinctly different intermediates and transition states Most obvious is the internal η2-cyclobutadiene TS 1 which for Cr changes to a peripheral η2-intermediate The calculated rate determining barrier of 269 kcalmol (GS to TS 1) is slightly higher than that measured for the reversal of 53 to 52 (~23 kcalmol) Part of this discrepancy may be due to ground state activation of 53 which is ~2 kcalmol less stable than 52 The LM structure has some resemblance to the isolated η4-CpCo angular [3]phenylene 23 (Section 12) Its location in an energetic well of ~14ndash16 kcalmol (TS 1 and TS 2) suggested that it may be observable at low temperature This investigation is detailed in Section 25

- 32 -

Figure 29 Calculated potential energy profile for the thermal η4η4 haptotropic shift in linear [3]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

0

5

10

15

20

25

30

1 2 3 4Reaction Path

Co

Co

C o

C o

GS η

4

LM η

4

TS1 η

2

TS 2 η

3

00

269

109

249

Key - Global MinimumGround State (GS)- Local Minimum (LM)

- Transition State (TS)

122

3 34 4

- 33 -

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 34 -

(d) Transition state 2 η3-benzene (249 kcalmol)

Figure 210 Optimized structures and relative energies for the linear [3]phenylene(CpCo) haptotropic shift Carbon atoms are shaded grey hydrogens light grey and cobalt blue Bond

lengths are in Aring The potential energy profile for the thermal shift in the linear [5]phenylene(CpCo) system was calculated in the same manner and is shown in Figure 211 Images of the intermediates and transition states are depicted in Figure 212 Placing the metal fragment on the inner cyclobutadiene ring resulted in the lowest energy structure and was therefore set as the global minimum (GS) Two distinct haptotropic migrations inner-to-inner and inner-to-outer cyclobutadiene are now possible (Section 21) Beginning at GS the metal can proceed in the direction of TS 2 or TS 3 respectively both of which are η2 with similar barrier heights (~36 kcalmol) The former pathway is degenerate and continues from TS 2 to η4-LM 1 and then via η3 central benzene TS 1 to the symmetry related corresponding LM 1 TS 2 and finally GS involving the opposite inner four-membered ring The rate determining barrier for this process is 359 kcalmol clearly too high to be measurable by NMR techniques as found for 212838 Interior-to-exterior shifting of the cobalt continues from TS 3 on to η4-benzene LM 2 The η3-TS 3 is traversed before the second η4η2

sequence (LM3 and TS 5 respectively) ultimately leading to LM 4 which is the outer

- 35 -

cyclobutadiene coordinated structure and represents the photoisomeric species observed experimentally in Scheme 23 The computed rate-determining barrier (TS 3) of 263 kcalmol for the reverse reaction of LM 4 to GS is close to the experimentally measured values of 256ndash276 kcalmol for the derivatives in Table 21

Figure 211 Calculated potential energy profile for the η4η4 haptotropic shift in linear [5]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

40

Reaction Path

263

0

5

10

15

20

25

30

35

C o

C o

C o

C o

Co

Co Co

C o

C o Co 360 370

359 357

367

97

203 190 196

1 2 3 4 5 6 7 8 9 10

TS 1 η

3

LM 1 η

4

TS 2 η

2

GS η

4 00

TS 3 η

2 TS 4 η

3 TS 5

η2

LM 2 η

4 LM 3 η

4

LM 4 η

4

Key- Global MinimumGround State (GS)

- Local Minimum (LM)

- Transition State (TS)

- 36 -

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 37 -

(d) Transition state 4 η3-benzene (367 kcalmol)

(e) Local minimum 3 η4-benzene (190 kcalmol)

- 38 -

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 39 -

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

(i) Local minimum 1 η4-benzene (190 kcalmol)

- 40 -

(j) Transition state 1 η3-cyclobutadiene (356 kcalmol)

Figure 212 Optimized structures and relative energies for the linear [5]phenylene(CpCo) haptotropic shift Structures for the inner-to-outer cyclobutadiene migration are given by (a)ndash(g)

Species (h)ndash(j) are involved in the interior-to-interior four-membered ring pathway Carbon atoms are shaded grey hydrogen atoms light grey and cobalt blue Bond lengths are in Aring

Why does CpCo prefer complexation to the internal cyclobutadiene that is GS (as represented by 21 and 42) over LM 4 (as represented by 44 and 45) Calculations show that the energies required to distort linear [5]phenylene to the geometries found in

- 41 -

the complexed isomers are very similar (16 versus 14 kcalmol) Hence the answer must rest on electronic grounds Indeed extended Huumlckel calculations reveal that the overlap populations between the frontier orbitals on the CpCo fragment and the HOMO and the LUMO of the π system are greater for GS (00793 and 00745 respectively) than for LM 4 (00556 and 00517 respectively) A didactically more instructive valence bond view recognizes that metalloaromatization of the inside four-membered ring allows the formulation of more resonance forms that avoid antiaromatic cyclobutadiene circuits A full list of these resonance forms as well as details of the EHMO calculations are given in Chapter 4 25 Low Temperature Photochemical Studies of the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes Of the various participating species in the mechanism for intercyclobutadiene migration (Section 24) specific attention was focused on the η4-benzene intermediates that occur in both the linear [3]- and [5]phenylene haptotropic shifts These structures are energetic local minima on the reaction profiles for both systems and were of considerable intrinsic interest not only as reactive intermediates in this manifold but also because of their relationship to the isolable angular [3]phenylene(CpCo) complex 2329 (Figure 213) Figure 213 (a) Calculated structure for the η4-benzene linear [3]phenylene(CpCo)intermediate

in the haptotropic migration (b) Crystal structure of η4 angular [3]phenylene (CpCo) 23

While rare a handful of other η4-benzene-metal complexes have been isolated (Figure 214) For example two related iridium based systems benzene(CpIr) 6658 and benzene triphos(Ir) 6759 are known As expected ligation causes significant shielding of the hydrogens in the η4 portion of the ligand especially the terminal positions The η4 intermediates in the haptotropic shift are situated in wells on the potential energy surface that are ~17 kcalmol deep for the linear [5]- and ~15 kcalmol for the linear [3]phenylene complexes These values are large enough that such species might be observable by NMR spectroscopy if irradiation of the starting materials were performed at low temperature and if the excited state would relax selectively to these intermediates As a suitable candidate with which to explore this possibility the partly symmetric tetrasilyl complex 19 was chosen The generation of anticipated desymmetrized 68 would be readily detected by the appearance of 11 new singlets in the 1H- and 23 new peaks in the 13C-NMR spectra (Scheme 220)

(a) (b)

- 42 -

Figure 214 Selected relevant examples of isolated η4-benzene complexes and their proton NMR chemical shifts (ppm)

Scheme 220 Low Temperature Irradiation Experiment Designed to Generate η4-Benzene Intermediate 68

Construction of a satisfactory setup to allow for the planned low temperature irradiation was not trivial An optimal experimental configuration however was devised utilizing three pieces of equipment each of which is shown in Figure 215 The first was a custom-made Pyrex Dewar flask small enough to adequately contain an NMR tube Cooling was achieved by means of a Neslab refrigerated circulating bath Thirdly a Rayonet Photochemical Reactor was used as the light source The sample was first placed inside of the Dewar flask and cooled to the required temperature inside of the Rayonet Once cold irradiation was carried out for the desired length of time When complete the sample was transported cold to the NMR laboratory and very quickly placed inside of a pre-cooled NMR probe for analysis A solution of complex 19 was irradiated at ndash65 degC as described and its 1H-NMR spectrum recorded at ndash30 degC revealing a dramatic change The signals for 19 had almost entirely vanished and a set of new peaks appeared The new aromatic resonances were comprised of two sharp singlets at δ = 708 and 644 ppm and a broad singlet at δ = 558 ppm all of which integrated for 2 hydrogens each Another broad

649

586

316

H H

Co544

66 67 23

Ir

P(Ph2)P(Ph2) P(Ph2)

H

H

H

625

594

350

Ir

H

H

H

- 43 -

Figure 215 Cold irradiation experimental setup consisting of (a) Pyrex Dewar flask (b)

refrigerated circulating bath (c) Rayonet Photochemical Reactor with Pyrex Dewar vessel placed inside

(a) η

4 (b) η

4 (c) η

4

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

New peaks

L L

- 44 -

Figure 216 Stacked plot of the aromatic 1H-NMR spectral region recorded after the cold irradiation of 19 in toluene-d8 Peaks for 19 are indicated by blue new peaks by red arrows

Impurities are marked with and traces of free ligand 60 with L The scale is in ppm

singlet at δ = 398 ppm (5 H) was assigned to a new Cp group (Figure 217) and two new TMS singlets (9 H each not shown) were also present The new broad Cp absorption displayed peculiar behavior gradually moving to higher field (∆δ ~ 08 ppm for Cp-H) on warming from ndash30 degC to 10 degC (Figure 217) The broadened singlet at δ = 558 ppm showed similar albeit much attenuated behavior At room temperature all new peaks had disappeared leading to regeneration of the original spectrum of 19

Figure 217 Stacked plot of the Cp spectral region in the cold irradiation of 19 in toluene-d8 Peaks for molecule 19 are indicated by blue the new peaks by red arrows The scale is in ppm

In addition to these NMR observations a remarkable change in color from the redmaroon of 19 to olive green took place during the course of this experiment (Figure 218) Indeed the UV-Vis spectrum of the low temperature species is strikingly different from that of 19 showing a large broad absorbance band centered in the visible region

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

19

THF

- 45 -

Figure 218 Color change during the low temperature irradiation of 19 (a) Before irradiation (b) After irradiation

Complex 19

Low Temperature Species

0

02

04

06

08

1

12

14

16

18

2

400 430 460 490 520 550 580 610 640 670 700

Wavelength (nm)

Ab

sorb

an

ce

Figure 219 UV-Vis spectra (toluene) of 19 (at rt) shown in blue and the new compound (at ~

ndash30 degC) shown in red

at 654 nm (Figure 219) Warming the sample to room temperature restored its original red color While the observation of a new species was gratifying the NMR data posed a puzzle as they were clearly incompatible with (a static) structure 68 Instead they pointed to a molecule exhibiting mirror (or ldquotop-downrdquo) symmetry along the long molecular axis as in 19 itself The two most obvious candidates 69 and 70 (Figure

(a) η

4 (b) η

4

- 46 -

220) were ruled out as the first could not be found during the computations underlying Figure 29 and the second actually constitutes the transition state TS 1 for the thermal reverse process

Figure 220 Possible (but unlikely) structures of correct symmetry for the low temperature

photoisomer of 19 In the hope to shed further light on the nature of purported 68 low temperature 13C in conjunction with 2-D NMR (HSQC HMBC) experiments were carried out These data led to the tentative assignments shown in Figure 221 Assuming the presence of top-down symmetry as surmised by the proton spectra one would have expected to observe nine phenylene carbon signals The actual spectrum however contains only six peaks The Cp line was broadened to the point of being barely visible and no crosspeaks for the absorption at δ = 556 ppm were seen by 2-D NMR spectroscopy

Figure 221 Partial assignments of 1H-(italicized) and 13C-NMR signals of 68 The ldquotop-downrdquo plane of symmetry is indicated by the dashed purple line HMBC δ = 643 ppm correlates with δ = 1461 and 1521 ppm δ = 708 ppm correlates with δ = 1477 and 1508 ppm δ = 033 ppm

correlates with δ = 1477 ppm and δ = 036 ppm correlates with δ = 1461 ppm HSQC δ = 643 ppm correlates with δ = 1121 ppm δ = 708 ppm correlates with δ = 1227 ppm and δ = 398

ppm correlates with δ = 85 ppm The connectivity of the CpCo to the central ring is left intentionally unspecified and the choice of positioning it to the left of the center hydrogens (blue)

SiMe3

SiMe3

H

Me3Si

Me3Si

H

Co

398 (br)

HH

1461

~85 (br)

708

H

556 (br)1508

= Unobserved 13C signals

H

H

Mirrorplane

6431477 1521

033036

11211227

- 47 -

arbitrary Similarly the assignments of the groups of ldquoleftrdquo and ldquorightrdquo benzene signals are tentative and might be inverted The carbons marked could not be observed

It is thus clear that we are dealing with an unusual species and if it is 68 the molecule must be partly (but not completely) fluxional around the central ring Returning to the computed energy profile in Figure 29 one notes that central η4η4-benzene fluxionality via TS 2 with a barrier of 140 kcalmol is presaged This process which causes ldquoleftrdquo-ldquorightrdquo but not ldquotoprdquo-ldquobottomrdquo symmetrization is unlikely to be responsible for the above data as it should have given rise to two 1H-NMR singlets for the central hydrogens However considering the expected relative closeness in the respective chemical shifts of the anticipated signals (see Figure 214) accidental isochronism could not be ruled out Consequently low temperature irradiation experiments were executed with 52 in which the ldquoleftrdquo-ldquorightrdquo option of symmetrization was obviated by the substitution pattern while leaving the ldquotoprdquo-ldquobottomrdquo option intact (Scheme 221) As Scheme 221 Low Temperature Irradiation of 52 and Possible Pathways for Fluxionality of

Intermediate 71

indicated in color the latter would provide a diagnostically simple proton spectrum of only four phenylene signals The former on the other hand should show eight such peaks A potential complication of this experiment was the possibility of two regioisomeric (and non-interconverting) cobalt species located on either side of the central six-membered ring (Scheme 222) In the event the spectra shown in Figure 222 were obtained At ndash60 degC in

HH

CoTMS

TMS

CoTMS

TMS

TMS

TMS

Co

TMS

TMS

CoTMS

TMS

Co

TMS

TMS

Co

Top-bottom

cold hν ∆

Lef t-right

52 53

∆

71

or

H

HH

H

H H

H HH

HH H H

H

- 48 -

addition to unreacted 52 and photoisomer 53 a new species formed the spectral features of which implicate 71 as a ldquotop-bottomrdquo symmetrizing species Specifically the

Scheme 222 The Two Possible Regioisomers of 71 ldquoLeftrdquo and ldquoRightrdquo

71

52

53 53

53

52

TMS

TMS

Co

TMS

TMS

Co

TMS

TMS

Co

71

TMS

TMS

Co

or

Right Lef t

ndash60 degC

ndash50 degC

ndash40 degC

ndash30 degC

53

- 49 -

Figure 222 Stacked plot of the aromatic spectral region in the cold irradiation of 52 in toluene-d8 Peaks for molecule 52 are marked by blue arrows 53 in red and 71 in green Trace amounts

of free ligand bis(trimethylsilyl) linear [3]phenylene] 46 are denoted with L The scale is in ppm

unsubstituted benzene terminus hydrogens exhibit an AArsquoBBrsquo pattern at δ = 647 ppm which integrate for 4 hydrogens The central ring hydrogens appear as a broad singlet at δ = 557 ppm (2H) and the silylated terminus as a singlet at δ = 632 ppm (2H) Warming the reaction mixture to 10 degC led to the gradual disappearance of 71 with a concomitant increase of the signals assigned to 52 and 53 This experiment confirms the conclusions drawn as a result of the low temperature irradiation of 19 namely that a ldquotop-bottomrdquo symmetrizing species is generated Remarkably in view of the possibility of two regioisomers (Scheme 222) only one set of peaks is observed indicating that the excited state of 53 relaxes to settle on only one side of the central ring Which side is a matter of speculation Figure 223 compares the 1H chemical shifts of 71 with those of 68 and for calibration 52 53 and free ligands 46 and 60 For the first pair it is clear that the two species are very similar with almost identical chemical shifts of the relevant hydrogens taking into account the considerable deshielding effect of TMS substitution on the unsubstituted terminus in 73 (~07 ppm cf 52 vs 53 46 vs 60) Arguably placing the CpCo moiety to the ldquoleftrdquo as depicted in 68 and 71 aromatizes the proximal benzene by η2-complexation of the adjacent four-membered ring leaving considerable benzocyclobutadiene character on the ldquorightrdquo consistent with the associated chemical shifts

- 50 -

CoTMS

TMS796675674

678

CoTMS

TMS747683724

662

Co

TMS

TMS

52

71

53

424

642

557 632652

436 444

Co

TMS

TMS

68

398

556 643708

TMSTMS

TMS

TMS684607619

645

46

assignmenttentative

TMS

TMS

TMS

TMS623 685

60

TMS

TMS

TMS

TMS

Co

691 795745

19

441

Figure 223 1H-NMR chemical shift comparison of 68 and 71 with other relevant species A plot of the changes in concentration of 52 53 and 71 with temperature is shown in Figure 224 Within (the considerable) error and considering the unusual magnetic behavior of 71 (vide infra) it appears that the latter converts mainly to 52 in the temperature regime in which 53 is stable with respect to its thermal reverse to 52 This observation may be interpreted as indicating a lower barrier for Co migration from the center ring to the more stable cyclobutadiene haptomer

- 51 -

0

1

2

3

4

5

6

7

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Inte

gra

tio

n v

s I

nte

ra

l S

tan

da

rd

52

53

71

Figure 224 Plot of the concentration changes of 52 53 and 71 with temperature measured by the relative integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively

The ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100)

Another plot this one showing the ratios of 52 53 and 71 with respect to each other is given in Figure 225 The disappearance of 71 with rising temperature is illustrated by the increase in the ratios of 5271 and 5371 As indicated by the steep slopes the conversion of 71 into 52 and 53 is particularly fast between ndash10 and 0 degC That complex 52 is preferentially formed is again confirmed by the escalating 5253 ratio While these data do not provide a definitive answer for the location of the CpCo they are consistent with the plots shown in Figure 224 and the above discussions

- 52 -

0

1

2

3

4

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Rel

ati

ve

Inte

gra

tio

n

5271

5371

5253

Figure 225 Plot of the ratios of 52 53 and 71 against each other with temperature measured by the integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively The

ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100) Having established the topological aspects of 68 and 71 attention was turned to their peculiar NMR characteristics in the vicinity of the metal ie the broad peaks for the central hydrogens and the CpHs the broad Cp-carbon line the inability to observe 13C signals for the central benzene ring and the temperature dependent drifting of (particularly) the Cp absorption A trivial (and ultimately unsatisfying) explanation for at least peak broadening was the presence of trace paramagnetic metallic impurities60 that might have been generated during the irradiation process Spin exchange preferentially Co-based might affect the center atoms in 68 and 71 more than the remainder of the molecule although it should also cause line broadening in the isomers 19 and 52 and 53 respectively Experimentally the presence of such species was made unlikely by executing the cold irradiation experiment of 19 in the presence of the radical trap 13-cyclohexadiene which produced spectra identical to those described earlier An attractive alternative that might explain the data and in addition provide a mechanism for ldquotop-downrdquo exchange is of the intervention of triplet state cobalt species The ability of metals to change their electronic spin state and the consequences of this phenomenon on organometallic structure and reactivity are well documented61

18-Electron CpCo complexes are ground state singlets but their 16-electron counterparts accessed typically by ligand dissociation have more stable triplet configurations62 A number of CpCo and related Co species have also been reported in

- 53 -

which singlets are in thermal equilibrium with paramagnetic triplets by intersystem crossing63 Such complexes display spectral behavior very similar to that seen for 68 and 71 For example 7263b exists as a mixed spin state system in which the singlet predominates at room temperature in solution (Figure 226) On heating the triplet becomes increasingly populated shifting and broadening its NMR signals Cooling the solution back to room temperature reverses these spectral changes In addition to complexes of cobalt analogous observations have been reported for other metals such those based on hafnium64 copper65 ruthenium66 and tungsten67

Figure 226 Temperature dependent chemical shifts in CpCo derivative 72 in toluene-d8

(marked as S on the plot) The scale is in ppm

Consideration of these examples would then suggest that 6871 undergo ldquotop-downrdquo equilibration through a triplet 16-electron intermediate or that 6871 themselves are triplets or have thermally accessible triplet states from which fluxionality might occur Since the relaxation times (T1) of paramagnetic systems60a are much shorter compared to their diamagnetic counterparts measurement of this property was thought to be informative The T1 values for the proton in 68 were determined via a standard inversion recovery experiment44 and are given in Table 24 (cf Figure 220) in comparison to p-terphenyl60b

Co

CoPMe3

72

- 54 -

Table 24 1H-NMR Relaxation Times in Intermediate 68 at ndash30 degC

Resonance (ppm) T1(s) 711 2309 646 0997 556 005 398 0108

In consonance with the associated line broadening the relaxation times of the Cp

(δ = 398 ppm 0108 s) and central ring hydrogens (556 ppm 005 s) are much smaller than those of the remaining phenylene ligand (711 and 646 ppm 2309 and 0997 s respectively) the latter in turn comparing well with the values in p-terphenyl With this corroborative evidence in hand the question whether the species is itself a triplet or is in thermal equilibrium with such was addressed The answer can be obtained by using a Curie-like graph68 in which chemical shifts are plotted as a function of temperature65 A linear relationship corresponds to the presence of a triplet compound while curved behavior is indicative of a singlet-triplet equilibrium Plotting the chemical shifts of the Cp hydrogen of 68 and 71 against the inverse of temperature (Figure 227) gave distinctly curved lines supporting the notion that these species are in thermal equilibrium with their triplets The exact nature of these species however remains to be determined

156

395404

345

p-Terphenyl

- 55 -

3

32

34

36

38

4

42

44

46

00036 00038 0004 00042 00044 00046 00048

1T (K -1

)

Ch

em

ica

l S

hif

t (p

pm

)

71

68

Figure 227 Plot of the Cp chemical shift (toluene-d8) of 68 and 71 versus the inverse of temperature

DFT calculations have commenced in an attempt to find a plausible structure for such a triplet cobalt species and with it possibly arrive at a mechanism for the fluxional behavior of 68 and 71 These studies are being carried out in collaboration with Professors Tom Albright of the University of Houston and Vincent Gandon of the Universiteacute Paris-Sud 11 Preliminary results at the B3LYP6-31G(dp) and BP866-31G(dp) levels suggest the η2-cyclobutadiene structure depicted in Figure 228 It is apparent that this species corresponds topologically to singlet TS 1 in Figure 29 and 70 in Figure 220 endowed with the symmetrical requirements dictated by the experiments

- 56 -

Figure 228 Calculated structure of a triplet η2-cyclobutadiene linear [3]phenylene(CpCo)

One can therefore envision fluxionality between the two ldquotoprdquo and ldquodownrdquo η4-benzene structures via the intermediacy of a triplet η2-cyclobutadiene (Scheme 223) Further Scheme 223 Conversion of ldquoTop-Downrdquo η4-Haptomers of 68 Via a Triplet η2-Cyclobutadiene

Intermediate

computations are required to pinpoint the minimum energy crossing points between the singlet η4 and triplet η2 structures and to explain why this triplet does not collapse to the CpCo cyclobutadiene isomer This work is in progress 26 Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 All of the linear phenylene(CpCo) complexes mentioned thus far share one common feature a single CpCo unit bound to the phenylene scaffold However since there are one or more additional cyclobutadienoid rings in the series the question arises whether it might be possible to bind more than one metal fragment to the ligand If so what would be the structural consequences Would be there further metalloaromatization Would such systems be capable of light-induced haptotropism and if so how would the metals move relative to the ligand and to each other Finally would such complexes mimic structurally the variety of arrays obtained in the reaction of 29 with Fe2(CO)9 (Scheme 15) Since the linear phenylenes become increasingly more antiaromatic with size the optimal candidates for preparing such multi-metallic systems should be the higher members of the series Indeed evidence for double CpCo attachment was obtained in the form of the minor by-products 73 and 74 (Scheme 224) obtained during the

Scheme 224 Side Products in the Preparation of Linear [4]- and [5]Phenylene(CpCo)

- 57 -

Complexes by Cobalt-Catalyzed Cyclization

preparation of 20 and 21 respectively (Scheme 13) These Diels-Alder type adducts of a third BTMSA molecule to the π-frame can be envisaged to be derived from 75 and 76 respectively in which the six-membered ring flanked by the two CpCo(cyclobutadiene) units would be expected to have an unusual (biradicaloid) electronic structure Evidence for the feasibility of such arrays rests on the unique black-red syn-bis(irontricarbonyl) compound 77 whose structure was determined by X-ray analysis69 With reasonable quantities of 19 in hand the possibility of ligating a second CpCo unit to it was explored This idea was further encouraged by the observation that crude samples of bis(trimethylsilyl) linear [3] phenylene(CpCo) complex 53 contained a very small (3 ) peak at mz = 618 an exact match for the mass of a doubly metallated analog Consequently 19 was treated with one equivalent of CpCo(C2H4)2 in benzene to afford a reddish black solid (Scheme 225) The mass spectrum data exhibited a

Scheme 225 Preparation of Complex 78 from Complex 19

TMS

TMSTMS

TMS

CoCpCo(C2H4)2

22h 70 oC C6H6Linear [3]TMS4(CoCp)2

5619 78

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

74

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

73

TMS

TMS

TMS

TMSCoCpCpCo

76

TMS

TMS

TMS

TMSCoCpCpCo

75

Ph

Ph

Ph

Ph

Fe(CO)3Fe(CO)3

77

- 58 -

molecular ion peak at mz 762 corresponding to 19(CpCo)2 The 1H-NMR spectrum (acetone-d6) revealed four sharp singlets integrating in the ratio 410236 indicative of a highly symmetrical structure The chemical shift of the benzene termini (736 ppm) suggested that these rings have significant aromatic character and is similar to the value of 745 ppm seen for the hydrogen positioned farthest away from the CpCo in 19 (Figure 27) Similarly the 13C signals of the terminal rings in 78 (1505 1454 and 1258 ppm) are analogous to those from the corresponding terminal ring in 19 (1484 1433 and 1256 ppm Figure 28) Detailed analysis of 78 with two-dimensional NMR techniques (HSQC and HMBC) allowed for a complete assignment of all peaks in the 1H and 13C spectra (Figure 229) The strongly shielded (relative to the free ligand) proton (481 ppm) and carbon (537 and 571 ppm) resonances assigned to the central benzene ring clearly showed that both cobalt fragments are coordinated to the phenylene ligand at this position Interestingly these data bear a very close resemblance to those of the corresponding diiron complex 31 (Scheme 15) and are compared in Figure 229 Its central 13C resonances (688 and 582 ppm) are shifted upfield in a manner akin to 78 although not quite as much reflecting the increased electron withdrawing ability of the Fe(CO)3 group relative to CpCo70 Complex 31 like 78 exhibits aromatized terminal benzene rings as indicated by its 1H (750 ppm) and 13C (1484 1446 and 1258 ppm) chemical shifts These spectral similarities make it likely that 78 and 31 are isostructural The only structural ambiguity pertains to the orientation of the two metal fragments with respect to the π ligand a problem that had been left undecided in the assignment of structure 31 ie 31a (syn) versus b (anti Scheme 15)27 These options for 78 are

- 59 -

CpCoTMSTMS

TMS TMS

H H039 (36)

537 1258822

270

1454571

1505

481 (2) 736 (4)489 (10)

TMS TMS

TMSTMS

H

(OC)3Fe

(OC)3Fe

CpCo

78

31a

750 (4)553 (2)

036 (36)H

220

1446

1258

1484

688582

2128

Figure 229 Comparison of 1H- and 13C-NMR assignments (ppm) for molecules 78 (acetone-d6) and 31 (1H acetone-d6

13C CDCl3) Proton chemical shifts are in red and carbon in blue Integrations for the proton resonances are in green HSQC for 78 δ = 039 ppm correlates with δ = 270 ppm δ = 481 ppm correlates with δ = 537 ppm δ = 489 ppm correlates with δ = 822 δ

= 736 ppm correlates with δ = 1258 ppm HMBC for 78 δ = 036 ppm correlates with δ = 1454 ppm δ = 481 ppm correlates with δ = 571 and 1505 ppm δ = 736 ppm correlates with δ = 571 1454 and 1505 ppm The placement of the cobalt atoms in 78 is tentative (see Figure

229)

Figure 230 Possible structures for 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

- 60 -

shown in Figure 230) Both equally exotic options are precedented in the literature and corroborated by X-ray structural analyses (Figure 231)71

Figure 231 Illustrative examples of complexes with two metal fragments coordinated to the same benzene ring

Bis(CpFe) complex 7972 and its rhodium analog 8073 contain [M2(syn-micro-arene)] units in which the metals are linked58 Molecule 79 consists of two CpFe units coordinated η4 to the boat-shaped benzene ring sharing ligating carbon atoms In contrast the CpRh fragments in 80 are bound in an allyl η3 manner and the arene also adopts a boat conformation On the other hand bis[tris(tert-butyl)]toluene(CpCo) complex 8174 and the related system 8275 both exhibit [M2(anti-micro-arene)] units in which η4 coordination between the benzene ring and each of the metal fragments takes place Here the metals share carbon atoms but now involving a sandwiched ligand The arene in 81 retains a planar aromatic geometry while the benzene moiety in 82 is bent into a highly distorted chair conformation Unfortunately model structures 79ndash82 do not exhibit diagnostic NMR properties that would provide a clear distinction between synanti and planarnon-planar topologies For example the 1H-NMR peaks for the toluene ligand in anti-complex 81 range from 400ndash380 ppm74 whereas the signals for the benzene moiety in syn-bis(CpRh) 80 appear at 400ndash330 ppm73 The 13C data are similarly inconclusive as illustrated by comparison of 78 (562ndash531 ppm for the benzene ring) with 79 (648ndash525 ppm)72b An interesting property of these bis(metal) arene complexes is fluxionality of the metal fragments by haptotropic shifts along the periphery of the aromatic ring as depicted in Scheme 226 In complex 79 the hexamethylbenzene ligand (bound η4η4

in the solid state) displays a single arene resonance at 588 ppm in its room temperature carbon NMR spectrum Cooling to ndash90 degC however produces two distinct arene peaks at 525 and 648 ppm (for the shared and single-metal-bound carbons respectively as shown in 79a in Scheme 227) Fluxionality was postulated to proceed through an η3η3 intermediate (79b) that is structurally similar to Rh complex 80 which is itself a fluxional species

Scheme 226 Examples of Fluxional Processes in Dinuclear Arene Complexes 79 and 80

82 81

80 (R = CH3)

79

- 61 -

Anti-bis(β-diiminate)Rh complex 83 shows similar mobility (Scheme 226)76 A mechanism for η4η4 migration of the anti-metal fragments was proposed using the lowest energy species found by DFT calculations In these compounds the anti-metal fragments convert between η4η4 (83a 83c 83e) structures by passing through η3η3

(83b) and η4η2 (83d) transition states The energy barrier for η4η4 migration in 83 was experimentally determined to be 6 kcalmol This value is in line with other experimentally measured syn and anti dinuclear ring slippage processes which are typically le ~10 kcalmol71-75 The possibility of fluxionality in 78 might be observable if asymmetric configurations such as 78c and 78d (Figure 231) represent the lowest energy forms since they entail NMR observable desymmmetrization of the ligand Unfortunately cooling 78 in the NMR probe to temperatures as low as ndash80 degC in toluene-d8 did not reveal any signs of signal decoalescence

- 62 -

Figure 232 Possible lowest energy forms of complex 78

Hoping that further light could be shed on the disposition of the CpCo moieties in 78 by chemical transformations a brief investigation of its reactivity was undertaken For example bis(metal) arene complexes have been shown to readily undergo arene exchange reactions71 In complex 81 for example the toluene ligand is displaced by benzene at room temperature74 However heating a sample of 78 to 120 degC in toluene-d8 did not lead to any changes in the NMR spectra Turning to potential photochemical activation 78 was irradiated at various wavelengths (300ndash365 nm) These conditions as well as ambient sunlight did not cause any changes in its 1H-NMR spectrum further documenting 78 as a rather inert species X-ray crystallographic analysis would appear to be the only method of resolving the identity of complex 78 Producing suitable crystals of this molecule however has proven extremely difficult and will be the subject of future investigations 27 Summary and Outlook The work presented in this chapter published as a communication77 has detailed the first examples of η4η4 intercyclobutadiene migration and detailed mechanistic studies of this unprecedented reaction The haptotropic shift was found to be an intramolecular process with the CpCo fragment undergoing various changes in hapticity for the thermal isomerization Low temperature photolytic studies have revealed the existence of a thermally unstable intermediate species the exact structure of which is uncertain These results point to what appear to be significant differences between the photo- and thermal haptotropic pathways Further work both experimental and computational will be required to elucidate the details of the photochemical reaction In addition to the studies of linear phenylene(CpCo) haptotropism a hitherto unknown complex containing two CpCo fragments bound to linear [3]phenylene was prepared and scrutinized in preliminary form Despite extensive characterization the structure of this complex with respect to the position of the metal centers remains elusive Future work will focus on the acquisition of a crystal structure

- 63 -

Chapter 3

Nickel-Catalyzed Insertion Reactions for the Preparation of [N]Phenacene Derivatives

31 Introduction Transformations involving metal insertion into the four-membered ring of the [N]phenylenes as discussed in Section 12 represent a significant mode of reactivity with a high potential for practical synthetic utility One specific application of this chemistry is the synthesis of the phenanthrene moiety via tandem metal insertion and alkyne cycloaddition to the four-membered ring (Scheme 31) Such a methodology Scheme 31 Potential Preparation of the Phenanthrene Group from the Alkyne Cycloaddition

with Biphenylene would be valuable for the preparation of PAHs possessing phenanthrene subunits but has remained fairly unexplored Only a few examples demonstrating this transformation have been detailed previously for biphenylene (7) (Scheme 32)

Scheme 32 Metal Catalyzed Alkyne Cycloaddition Reactions with Biphenylene

The first report of this process is by Eisch in 198533a who treated biphenylene with Ni(PEt3)4 and diphenylacetylene to produce 910-diphenylphenanthrene 84 Since then a number of metals have been shown to mediate this process19 Ni systems being most relevant to this chapter Thus for example 84 can also be made using an N-heterocyclic carbene-based Ni(0) catalyst78 Bis(diisopropylphosphino)ethane Ni(alkyne) species enable similar cycloadditions of fairly hindered (trimethylsilyl)alkynes sometimes involving more complex processes of silyl group migration79 while less hindered substrates lead to 84ndash8680a A mixed phosphinoaminoethane-chelated Ni species proved more reactive enabling cycloaddition of even the encumbered tert-butyl(phenyl)acetylene to furnish the corresponding phenanthrene80b With this background in mind our attention turned to applying this reaction to larger phenylene systems Of the various topologies of phenylenes at our disposal the angular version was

R1 R2

R2R1[M]

[M]

7 R R

R = Ph (84)

R = Me (85)

R = CH2OMe (86)

RR

[Ni]

- 64 -

particularly intriguing as it offered two extreme modes of alkyne addition (Scheme 33) In the first scenario exclusive attack at the outer periphery of the four-membered rings would produce the helical shaped PAHs known as helicenes (Scheme 33a)81

Scheme 33 Alkyne Cycloaddition with Angular Phenylenes to Produce (a) Helicenes or (b) Phenacenes

Reactions occurring only at the interior or ldquobayrdquo region (Scheme 33b) however would afford a class of compounds exhibiting a linear polyphenanthrene motif that are known as [N]phenacenes82 Unselective additions would result in mixed topologies Helicenes and their various derivatives constitute a well studied83 family of molecules and continue to be a popular area of research Phenacenes in contrast have been scrutinized much less in part because only four members of the parent series are known and because for N = 5 and 6 they are extremely insoluble84 Phenacene-based applications have been slow to develop but the first reports of the utilization of these molecules as functional organic materials suggest the beginning of a rich and promising field85 Thus in 2008 [5]phenacene (picene) was demonstrated to behave as stable high performance organic field effect transistor (FET)85b Currently the most common organic polycyclic benzenoid hydrocarbon-based FETs employ acenes which have a polyanthracene structure (Figure 31) The sensitivity

Figure 31 Linearly fused benzene topology of the acenes of these systems to air however has obstructed progress in this area86 For example pentacene a commonly used acene in FETs reacts readily with oxygen to form

+ RR

Helicenes

+ RR

Phenacenesn

R

R R R R

n

R

R

R

(a)

(b)

[N]Acenes

n

- 65 -

pentacenequinone a process that severely reduces device efficiency (Scheme 34)

Scheme 34 Degradation of Pentacene to Pentacenequinone Under Aerobic Conditions

Phenacenes on the other hand are much less prone to such decomposition pathways due to their higher HOMO-LUMO gap thus rendering them less reactive85b86a Their enhanced stability relative to acenes87 makes them better candidates for molecular electronic applications In a second seminal breakthrough [5]phenacene was very recently also found to behave as a superconductor at low temperature when doped with potassium85a This work paves the way for a new class of PAH-based superconducting materials in which phenacenes may play a key role

As this chemistry advances new synthetic methods for preparing derivatives of these molecules will be required in particular those bearing solubilizing andor otherwise functionally useful substituents The most general procedure for synthesizing phenacenes as developed by Mallory88 makes use of oxidative stilbene photocyclizations (Scheme 35)8388 In this transformation irradiation of the stilbene

Scheme 35 Generic Oxidative Stilbene Photocyclization Used to Prepare Phenacenes as Illustrated for Phenanthrene

moiety leads to conrotatory electrocyclic ring closure Trapping of the resulting intermediate with oxidizing reagents such as iodine or oxygen yields the desired phenanthrene subunit The requisite stilbenes are most generally accessible via the Wittig reaction as illustrated in the synthesis of [7]phenacene derivative 87 (Scheme 36) Although the yields for the photocyclization are typically reasonable (60ndash90 )85a the major drawback of this methodology is the numerous steps associated with preparing the functional groups required for the prerequisite Wittig reaction These

- 66 -

transformations serve to decrease the overall yield of the target molecule

Scheme 36 Synthesis of [7]Phenacene 87

While laborious Malloryrsquos method addresses successfully the problem of solubility As alluded to in Section 21 large PAHs become insoluble due to the increased π-π stacking forces that are experienced between aromatic rings The best solubilizing groups for the phenacenes were found to be sterically bulky groups located in the bay regions85a These modifications distort the phenacene framework from planarity thereby disrupting π-stacking and increasing solubility as demonstrated by the tert-butyl [7]phenacene 87 (Figure 32) This approach was applied to systems as large as [11]phenacene the current record in the series85a

Br

CH3t -Bu

1 BuLi2 DMF

Br

CH2

t-Bu

CHO

CH3t-Bu

PPh3

Br

+Wittig

t-Bu t-Bu

Br CH3 1 hν2 I2

t-Bu t -Bu

Br CH3

t-Bu t-Bu

Br H2C PPh3 Br

+

t-Bu t-Bu

OHC CH3

Wittig

t-Bu t-Bu

Br Br 1 hν2 I2

t-Bu t-Bu

Br CH3

t-Bu t -Bu

t-Bu t-Bu

87

1 NBS2 PPh3

- 67 -

Figure 32 Crystal structure of tetrakis(tert-butyl) [7]phenacene 87 Hydrogens are omitted for clarity

To test the viability of angular phenylenes as substrates in Ni catalyzed alkyne cycloadditions the simplest member 22 was chosen raising a number of questions First how many and what kind of products will be formed (AndashE in Scheme 37) Will there be inherent selectivity toward helicene C or phenacene E formation respectively If not can the reaction conditions be modified so as to induce such What will be the limitations with respect to the size of substituents especially in view of the crowded fjord and bay regions of D and E respectively The work presented in this chapter carried out in collaboration with Dr Zhenhua Gu89 explores these questions

Scheme 37 Possible Cycloaddition Products of Angular [3]Phenylene 22

22

[Ni]R R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

A B

C D E

32 Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene

Before embarking on the proposed chemistry the reactivity of 22 in the presence of nickel in the form of Ni(COD)(PMe3)2 in the absence of alkynes was queried Only starting material was recovered and there was no sign of dimerization (or oligomerization) to products of the type shown in Scheme 38 a mode of reactivity

- 68 -

readily attained by biphenylene and substituted derivatives33b

Scheme 38 Attempted Dimerization of Angular [3]Phenylene 22

In contrast exposing diphenylacetylene 88 to Ni(COD)(PMe3)2 and a small excess (109 equivalents) of angular phenylene 22 generated two products in the absence of any other (Figure 39) The first molecule 89 was the result of the cycloaddition of one diphenylacetylene at the bay region and the minor component The major product constituted tetraphenyl [5]phenacene 90 derived from 22 by double bay region attack The structures of both compounds were confirmed by X-ray analysis revealing highly distorted frames89 Scheme 39 Nickel Catalyzed Cycloaddition of Angular [3]Phenylene 22 to Diphenylacetylene

Yields Based on Diphenylacetylene

The outcome of this transformation was gratifying in its seeming simplicity and selectivity Thus it appeared that metal insertion occurred exclusively to bay region bonds heralding the discovery of a new phenacene synthesis The observation of relatively large amounts of 90 could be ascribed to increased reactivity of 89 relative to 22 possibly due to steric activation by the newly introduced bay region phenyl group To test this hypothesis 89 was subjected to the cycloaddition reaction conditions (Scheme 310) Surprisingly not only was this reaction slower than that of 22 but the expected phenacene 90 was only a minor product (6 ) Instead tetraphenylbenzo[c]chrysene 91 a regioisomer of 90 as confirmed by X-ray analysis89

+

+ +

Ni(COD)(PMe3)2

22

- 69 -

was isolated in 74 yield the result of non-bay alkyne cycloaddition to 89 Therefore 89 is not the precursor of 90 Rather there must be separate reaction pathways leading to each respective product

Scheme 310 Cycloaddition Reaction of 89 with Diphenylacetylene 88

A series of semi-quantitative experiments monitored by 1H-NMR spectroscopy was carried out to shed some light on this mechanistic problem First the reaction of angular [3]phenylene 22 with diphenylacetylene 88 in Scheme 39 was addressed Because dinuclear metallic activation of the strained C-C bond in biphenylenes has been implicated in a number of studies19 it was possible that the above mechanistic duality was caused by the presence of catalytic Ni2 species in addition to the ldquoregularrdquo mononuclear alternatives Alternatively double Ni insertion before cycloaddition might be responsible for one product whereas sequential ldquonormalrdquo activation might be the origin of the other Therefore the amount of initial Ni(COD)(PMe3)2 was gradually increased and the effect of this incremental change on rate and product ratios recorded As shown in Table 31 the speed with which 89 and 90 formed was roughly proportional to the amount of metal present while the product ratio stayed unchanged

Table 31 Variation of Catalyst Loading in the Reaction of Phenylene 22 with Diphenylacetylene 88 Reactions Were Carried Out with Equimolar Amounts of 22 and 88 in

THF-d8 at 40 degC

Run Ni(COD)(PMe3)2

(mol) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

Ratio of 8990

1 50 32 times 10ndash4 031 times 10ndash4 103 2 35 20 times 10ndash4 022 times 10ndash4 91 3 7 064 times 10ndash4 0064 times 10ndash4 100

Next the amount of diphenylacetylene 88 was gradually increased from 1 to 4 equivalents (Table 32) The outcome of this series of experiments was counterintuitive as it led to a larger preference for the production of monoadduct 89 suggesting a mechanistic bifurcation in which whatever Ni species is responsible for the eventual formation of 90 is sequestered by external ligand (in this case 88)

- 70 -

Table 32 Variation of Alkyne Equivalents in the Reaction of 22 (1 equiv) with Diphenylacetylene 88 in the Presence of 50 mol of Ni(COD)(PMe3)2 Experiments Were Run

in THF-d8 at 40 degC

Run 88 (equiv) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

8990

1 10 320 times 10ndash4 031 times 10ndash4 103 2 20 220 times 10ndash4 018 times 10ndash4 122 3 40 220 times 10ndash4 011 times 10ndash4 200

Following the reaction progress by NMR spectroscopy afforded additional insights Thus mixing the ingredients at room temperature left the phenylene component untouched Instead there was a near instantaneous displacement of COD by diphenylacetylene to produce Ni(PhCequivCPh)(PMe3)2 (92) and free COD in addition to the generation of Ni(PMe3)4

90 The speed with which this complex was formed implied that it might be the active catalyst precursor Consistent with this notion higher reaction rates were observed when the reaction in Scheme 38 was carried out with pure 9291 as the catalyst (50 mol) and 05 equivalent of 88 (Table 33 Run 2) In consonance with Table 32 the lesser concentration of available free alkyne increased the relative amount of 90 formed Conversely (Run 3) using Ni(COD)(PMe3)2 with an extra equivalent of PMe3 decreased the rates of formation of 89 and 90 and increased the ratio of 8990 consistent with ligand inhibition of the activation of 92 and the external ligand effect noted in Table 32 Table 33 Variation of Catalyst in the Reaction of 22 with Diphenylacetylene 88 and its Effect

on Reaction Rate Experiments Were Run in THF-d8 at 40 degC with 1 Equivalent of 22

Run Catalyst 88

(equiv)

Rate of formation of 89 (mol

Lmiddoth)

Rate of formation

of 90 (mol Lmiddoth)

8990

1 Ni(COD)(PMe3)2 10 320 times 10ndash4 031 times 10ndash4 103 2 Ni(PhCequivCPh)(PMe3)2 (92)

(05 equivalent) 05 1270 times 10ndash4 210 times 10ndash4 60

3 Ni(COD)(PMe3)2 (05 equivalent) + PMe3 (10 equiv)

10 088 times 10ndash4 005 times 10ndash4 163

Attention was then shifted to the reaction of monoadduct 89 with 88 as in Scheme 310 (Table 34) Here increasing the amount of alkyne and catalyst favors the formation of 91 consistent with an independent pathway At low concentration of alkyne it appears that 89 reenters the manifold of its generation and proceeds on to 90 Indeed following the change in the ratio of 9190 in Run 1 (Table 34) with time reveals a decrease from 47 to the eventual 22 as 88 is depleted

- 71 -

Table 34 Variation of Catalyst Loading and Alkyne Concentration in the Reaction of 90 with Diphenylacetylene 88 Reactions Were Run in THF-d8 at 40 degC

Run 88 (equiv) Ni(COD)(PMe3)2

(mol) 9190

1 10 50 2 2 30 50 15 3 30 10 25

The information obtained from these experiments allowed a narrowing of mechanistic possibilities For example dinuclear Ni activation only one possibility of which is shown in Scheme 311 was rendered unlikely by the absence of any observable changes in product distribution of the reaction in Scheme 39

Scheme 311 Generic Example of a Dual Mechanism Based on Mono- and Dimetallic Phenylene Activation

An alternative mechanism shown in Scheme 312 was in much better agreement with the results of the various control experiments The first step would be displacement of a phosphine in the initially dominant Ni-containing species 92 by angular [3]phenylene 22 inhibited by added PMe3 From 93 oxidative addition can take place to afford metallacycle 94 Why should bay region insertion be favored Arguably the regioselectivity of this step is controlled by the lesser steric hindrance in the resulting arene fragment or relative stabilization of the polarized Ni-C(α-

PhPh

Ph Ph Ph Ph

PhPh

NiL L

Ni(COD)(PMe3)2

NiNiL L L L

PhPh

2

Ph

Ph

Ph Ph Ph Ph Ph Ph

+

+22

89

90

91 90

- 72 -

biphenylene) bond in 94 by the electron withdrawing nature of the neighboring cyclobutadienoid ring This phenomenon in biphenylene is due to the rehybridization of the four-membered ring carbons to adopt relatively larger p character in the strained linkages hence larger s character (ie electron withdrawing) in the remaining bond and manifests itself most clearly in the relative acidity of the α-hydrogens7a This step is followed by migratory insertion and reductive elimination to produce molecule 96 the mechanistic bifurcation point One branch proceeds through presumably ligand-assisted metal dissociation to generate the relatively unreactive free 89 The second entails Ni migration92 and insertion into the bay region of the remaining four-membered ring (97) before the second cycloaddition occurs generating phenacene 90

Scheme 312 Possible Mechanism for the Alkyne Cycloaddition Reaction of Angular [3]Phenylene 22

The regioselective formation of 97 may again be sterically dictated or may involve anchimeric assistance by the bay-region phenyl group as sketched in Scheme 313 specifically 99

Scheme 313 Anchimeric Assistance on Route to [5]Phenacene 90

Ph Ph

PhPhPhPh

Ph

Ph

Ph PhNi

NiMe3P Ph

Ph

Ni

Me3P Ph

Ph

NiPMe3Me3P

Ligand exchangeOxidativeaddition

Migra toryinser tion

Reductiveelimination

Ph

Ph

Me3P

Ni migra tionOxidative addition

22

92

9394

96 89

9097

Ph Ph

Ni

Me3P

Ni(PMe3

Ph

Ph

minusNi(PMe3)

95

- 73 -

This type of metal coordination to the double bond of a proximal arene ligand is common and two examples are provided based on ruthenium94 and molybdenum95 (Figure 33)

Figure 33 Examples of complexes with phenyl groups coordinating to a nearby metal center Turning to the largely selective conversion of 89 to 91 (Scheme 310) requires the postulate of preferential insertion of the metal at the non-bay region and hence a different Ni species from that in 96 possibly a Ni(PMe3)(alkyne) moiety akin to that in 93 ie 100 (Scheme 314) Bay insertion would lead to metallacycle 101 and ultimately molecule 90 The expected large degree of steric repulsion between the phenyl groups in 101 should disfavor this reaction pathway On the other hand non-bay insertion to produce 102 should be relatively less impeded and would furnish 91 Another option for the generation of 90 from 89 would be reentering the pathway described in Scheme 312 facilitated at low concentrations of alkyne consistent with the data in Table 34

Scheme 314 Proposed Mechanism for the Alkyne Cycloaddition Reaction of 89

Ni

PhMe3P

PhPh

(Me3P)Ni

PhPh(Me3P)Ni

Ph

Ph

93 98

99

Ph Ph Ph Ph

90

+

Ph Ph

Ni

Me3P

97

- 74 -

While the above mechanistic perambulations appear plausible it should be stressed that they are speculative and may be restricted to diphenylacetylene 88 as the substrate Thus both 3-hexyne 103 and 14-dimethoxy-2-butyne 106 added to 22 less selectively than 88 to provide only the bay and non-bay monoadducts 104 and 105 and 107 and 108 respectively (Scheme 315)

Scheme 315 Reaction of Angular [3]Phenylene 22 with Other Alkynes

NiMe3P PMe3

Ph Ph+

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph

Ni(PMe)3

PhPh

Ni(PMe3)

Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

92 89

101

90

102

100

91

Ni

Ph Ph

PMe3

+

R

R

THF-d8 40 oCR

R22

Ni(COD)(PMe3)2

R

R

+

R = Et 104

R = CH2OMe 107

R = Et 103

R = CH2OMe 106 R = Et 105

R = CH2OMe 108

11 45 9 68

- 75 -

In view of these uncertainties recourse was taken to DFT computations delineated in the next section 33 Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene DFT studies were carried out in collaboration with Prof Vincent Gandon of the Universiteacute Paris-Sud 11 The B3LYP 6-31G(d) basis set was used for hydrogen and carbon atoms while LANL2DZ was used for nickel Before attempting to model the more complex alkyne cycloaddition reactions in Schemes 38 and 39 the basic Ni-catalyzed addition of the parent acetylene to biphenylene in the presence of PMe3 was studied (Scheme 316) The free energies

Scheme 316 Computational Modeling of Ni-catalyzed Addition of Acetylene to Biphenylene Free Energies (∆G KcalMol) are Relative to 109 Transition State Energies are Absolute Values

for This Step

NiMe3P PMe3

NiMe3P

NiMe3P

Ni

Ni

PMe3

PMe3

+

+ PMe3+

+ PMe3

+ 2 PMe3

+ 2

(00)

(281)(37)

(140)

(12)

NiMe3P PMe3

NiMe3P

NiNiPMe3Ni

PMe3

PMe3NiMe3P

PMe3

(727) (693) (476) (374) (394) (395)

Ni

Me3P

PMe3Ni

Me3P

Ni

Ni

Me3P

PMe3NiMe3P PMe3

(590) (532)

(157) (125) (150)

Most Accessible TS

+

7

114

110

113109

111 112

Ni

Me3P

(253)

Ni

PMe3

(242)

- 76 -

(∆G) of various possible catalyst structures consisting of an assortment of combinations of nickel PMe3 and acetylene as well as those of several possible transition states and the resulting products were calculated As is evident on inspection of the values in the first part of Scheme 316 a number of species were found to be very close in energy making it difficult to pinpoint a specific structure for the initial insertion step Bis(ethyne) nickel complex 109 was established as the lowest energy nickel species and was thus assigned a relative value of 0 kcalmol The most accessible transition state 110 features the oxidative addition of the Ni(PMe3)(C2H2) fragment 114 (+ 14 kcalmol) in which the alkyne is held exo to biphenylene The corresponding endo structure 111 was found to be just slightly higher in energy by 20 kcalmol as was the bisalkyne transition state 112 It is likely that biphenylene-NiL2 complexes (two of which were calculated at relative energies 242 and 253 kcalmol) lie on the way to these maxima93 Metallacycle 113 the structure ensuing from transition state 110 constituted the lowest energy product uphill from the starting 109 by 125 kcalmol but other alternatives are nearly isoenergetic Clearly however attack by Ni(PMe3)2 or Diels-Alder type cycloadditions are not likely From 113 the species proceeds smoothly by alkyne insertion-reductive elimination to the phenanthrene product a cascade associated with a large exergonic driving force Undaunted by the relatively complicated picture that emerged with biphenylene attention was turned to the original object of scrutiny the cycloaddition reaction between angular [3]phenylene 22 and diphenylacetylene 88 to produce [5]phenacene derivative 90 Modeled in the same manner as described above the metal insertion into the four-membered ring of 22 is shown in Scheme 317 The lowest energy nickel species

- 77 -

was found to be diphenylacetylene complex 92 gratifyingly corresponding to experiment and was set to a reference value of 00 kcalmol One notes again however an array of at least 10 species all of which must be in equilibrium in the initial reaction mixture Notably the Ni-π complexes to 22 are all more than 20 kcalmol higher in energy than 92 providing a computational rationale for the failure to observe such species by NMR The first step in the optimal reaction pathway is the coordination of Ni(PMe3) to the cyclobutadiene ring of 22 which results in formation of η2-like complex 114 Again in gratifying agreement with experiment bay region insertion through transition state 115 to give 116 is favored albeit by a bare 07 kcalmol relative to its non-bay region counterpart 117 Moreover there are at least six other structures that are energetically viable in silico although insertions of Ni(PhCequivCPh)(PMe3) appear less so possibly due to steric hindrance The same observation is made for the products of insertion although 116 emerges as the thermodynamically most stable possibility

Scheme 317 Calculated Structures and Reaction Pathway for the Insertion of Nickel into the Four-Membered Ring of Angular [3]Phenylene 22 Free Energies ∆G are in KcalMol Relative

to 92

The next step was to map out the first alkyne cycloaddition (Scheme 318) Coordination of diphenylacetylene to 116 is endothermic by 139 kcalmol and after migratory insertion produces 119 Interestingly a transition state to regioisomer 95

(328) (352)

NiMe3P PMe3

(364)

NiMe3P

NiMe3P PMe3

NiPMe3

(339)

Ni

PMe3

PMe3

NiMe3PPMe3

NiMe3P

NiPMe3

(16) (04) (108) (117)

NiMe3P PMe3 Ni

Me3PNi

Me3P Ni Ni

PMe3

PMe3

+ [3]+ DPA

+ PMe3+ [3]+ DPA

+ PMe3+ [3]

+ 2 PMe3+ [3]

+ [3]+ 2 DPA

Ph Ph Ph PhPh Ph

Ph

PhPh Ph

Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

Ph

(45) (96)

(00)

(89) (134)

Most AccessibleTS

NiPMe3

+ PMe3+ [3]+ 2 DPA

(314)

Ni

+ 2 PMe3+ [3]+ DPA

Ph Ph

(294)

1i(PMe3)

Ni

PhPh

(212)

(218)

(345)

Ni

PhPh(297)

Ni

Me3P

Ni

Ph

Ph

(350)

Ni

PMe3

(303)

Ni

Ni

(43) (41)

Ph

Ph

PhPh

Ni

PMe3

NiMe3P

(-10) (-22)

(Me3P)Ni

Ni(PMe3)

Ph Ph

Ph Ph(225) (256)

+ PMe3+ 2 DPA

+ 2 PMe3+ DPA

+ PMe3+ DPA

+ PMe3+ DPA

92114

115

116118

117

- 78 -

written (arbitrarily) in Scheme 312 could not be located

Scheme 318 Calculated Reaction Pathway for the Coordination of Diphenylacetylene Migratory Insertion and Nickel Migration Free Energies ∆G are in KcalMol Transition

State Energies are Absolute Values for This Step

Subsequent reductive elimination from 119 occurs to produce nickel coordinated arene species 120 From it free 89 is presumably readily obtained by demetallation in the presence of external ligands shown only for the formation of 92 in a very favorable process (ndash487 kcalmol) This step is sufficiently exothermic to tolerate the emergence of all the calculated species in the starting line up of Scheme 317 and is presumably the source of 89 in Scheme 39 However if not removed the Ni moiety in 120 can migrate along a shallow manifold across the π frame choosing the phenyl functionalized edge of the molecule (cf Section 24) until the remaining four-membered ring is reached (121) At this point two separate reaction pathways become possible Nickel insertion on the side proximal or opposite of the phenyl groups generates 99 or 122 respectively The barriers for these transformations are similar but show a noticeable preference for the formation of 99 In addition there is a significant energy difference (175 kcalmol) between 122 and 99 in favor of the bay region metallacycle The reason is the coordination of the neighboring phenyl ring to the nickel which serves to stabilize 103 vindicating the proposal made in Scheme 313 and providing a rationale for the exclusive observation of 90 in Scheme 39 From 99 as shown in Scheme 319 coordination of diphenylacetylene (123) is followed by migratory insertion to produce 124 Insertion occurs away from the bay region so as to reduce steric repulsion due to the phenyl group in the phenanthrene part of the molecule Finally reductive elimination ensues providing phenacene-Ni

NiMe3P

NiPMe3

Ni(PMe3)

Ni Ph

PhMe3P

Ph

Ph

PhPh

(117)

126

(44)

102

( 80)

01

( 412)

Ph PhNi(PMe3)

( 389)

Ph Ph

45

Ni(PMe3)

( 408)

Ph Ph

13

PhNi

PMe3

Ph Ph

Ni(PMe)3

133

( 488)

117

( 663)

NiMe3P

( 22)

PhPh+

95

116

119

120121 122

99

NiMe3P Ph

Ph

Ph Ph

( 899)

NiMe3P PMe3

Ph Ph+

92 89

- 79 -

complex 125 At this point the stage is set for exergonic nickel dissociation to 90 and catalyst turnover

Scheme 319 Calculated Reaction Pathway for the Second Diphenylacetylene Insertion All Relative Energies (in red) are in KcalMol Transition State Energies are Absolute Values for

This Step

In conclusion of this discussion the consideration of the combined computational and experimental data affords a mechanistic picture of the cycloaddition reaction of diphenylacetylene 88 to angular [3]phenylene 22 (Scheme 39) the essential features of which are summarized in Scheme 320 The crucial point is a mechanistic bifurcation in which 89 is either released early and (nearly) irreversibly from the metal or the metal stays attached so as to effect a second cycloaddition to give 90 This mechanism implies that 91 is formed by a different mechanism involving a different Ni species

PhNi

PMe3

( 663)

+

PhNi

Ph PMe3Ph

Ph

( 403) ( 403)

PhNi

PhPMe3

PhPh

( 519)

94

93

( 696)

PhNi

PhPMe3

Ph

Ph

96

( 817)

Ph Ph Ph Ph

(MeP)3Ni

99

123

124

125

PhPh

Ph PhPh Ph

+Ni

Me3P PMe3

( 1101)

PMe3

90

- 80 -

Scheme 320 Essential Mechanistic Features of the Formation of 89 and 90 in the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene 88 and Angular [3]Phenylene 22

Consequently the reaction of 89 with diphenylacetylene to give 91 (Scheme 310) was also modeled by DFT Of the various options probed that shown in Scheme 321 proved to be most plausible The reaction pathway entails coordination of alkyne-Ni phosphine 126 to molecule 89 which generates complex 127 in a process that is found to require 228 kcalmol of energy Insertion into the non-bay region of the four-membered ring has a barrier of 16 kcalmol and provides metallacycle 128 After the second cycloaddition event benzo[c]chrysene 91 is formed Interestingly the transition state leading to insertion of nickel complex 126 into the bay region of 89 structure 129 was found to be so high in energy relative to 128 that it could not be modeled This is not unexpected as the phenyl group closest to bay region effectively blocks the approach of any catalyst species This result is consistent with the high ratio of 91 to 90 formed in Scheme 310 and the increase in this ratio at higher initial diphenylacetylene concentration Why is any 90 formed and why does its relative proportion increase at lower diphenylacetylene concentration A possible explanation is that under these conditions the concentrations of 92 and 126 are sufficiently small that 89 reenters Scheme 318 competitively

PhPhNi(PMe3)

PhPh

Ni(PMe3)

Ph Ph Ph Ph

PhPh

Ni(PMe3)

Ni

PMe3

Ph Ph

NiPhMe3P

22 116

88

120

121

99

88

90

PhPh

89

Externalligand

assistedNi migration

Regioselectiveinsertion

Regioselectiveinsertion

Mechanistic bifurcation

- 81 -

Scheme 321 Calculated Reaction Mechanism for the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene and Compound 90 Relative Energies are in KcalMol Transition

State Energies are Absolute Values for This Step

Consideration of Scheme 320 suggests that phenacene formation might be maximized by keeping the concentration of external ligand low during the course of the reaction Experiments aimed at verifying this conjecture are the subject of Section 34 in addition to presenting extensions of the methodology to higher angular phenylenes

34 Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions The experimental and computational studies described in Section 33 suggested that the decisive factor for selective formation of phenacene 90 is suppression of metal dissociation in Ni complex 120 This scenario would be achievable by maintaining a low concentration of diphenylacetylene 88 (vide supra) Previously the alkyne cycloaddition was performed with all reagents mixed together at the start of the reaction invariably resulting in a high initial concentration of 88 To obviate this occurrence an alternative procedure was devised In this new arrangement the required stoichiometric amount (in this case two equivalents) of alkyne 88 was slowly introduced to a mixture of 22 and Ni(COD)(PMe3)2 by means of a syringe pump (Scheme 322) The results of varying addition and reaction times are shown in Table 35

Scheme 322 Modified Reaction Alkyne Cycloaddition Reaction Between 22 and 89

Ph Ph

Ni(PMe3)

Ph Ph Ph Ph

Ni(PMe)3

160

Ph

Ph

PhPh

(309)(317)

Ph Ph

Ph

Ph

NiMe3P

Ph Ph

(minus573)

89

126

127 128 91

Ph Ph Ph

Ni

Ph

PMe3

129

NiMe3P PMe3

Ph Ph

(00)

92

(89)

+

- 82 -

Table 35 Variation of Alkyne Addition and Total Reaction Time in the Scheme 322

Run Addition time of 88 (h)

Total run time (h)

Yield of 89 ()

Yield of 90 ()

1 4 16 44 55 2 6 22 23 77 3 5 41 24 76 4 12 69 17 73 5 13 19 13 87

The most immediate result of the modified protocol was the quantitative conversion of 22 to cycloadduct products 89 and 90 Turning to the product ratios a four hour addition time led to a slight preference for 90 Increasing the time to six hours dramatically influenced the product distribution and 90 was isolated in 77 yield as compared to the 23 for 89 In the optimal Run 5 87 of 90 was generated vs 13 of 90 Extending the run time after the addition of diphenylacetylene had a negligible effect The successful enhancement in phenacene selectivity under these conditions makes the reaction a practical method for synthesizing compound 90 and also provides further experimental support for the proposed mechanism shown in Scheme 320 Having reached a reasonable level of understanding both the mechanistic and experimental aspects of the reaction of angular [3]phenylene 22 with diphenylacetylene attention was shifted to a larger and more challenging substrate angular [4]phenylene (17) This system could conceivably afford 17 possible adducts one of which is hexaphenyl[7]phenacene 130 (Scheme 324) Would the mechanistic features of this triple cycloaddition be sufficiently similar to those of 22 to apply the same principles and enable selectivity toward 130

+THF reflux

Ph Ph Ph PhPh

Ph

+

Ph

Ph

2 equivslow addition

22 89 90

Ni(COD)(PMe3)2(10 mol)

88

- 83 -

Scheme 324 The Possible Cycloadducts of Diphenylacetylene 88 to Angular [4]Phenylene 17

+ Ph Ph

Ph Ph

Ph Ph

PhPh

Ph

Ph

Ph Ph Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph PhPhPh

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph Ph PhPhPh

Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

PhPh

Ph Ph Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

88

17

130

- 84 -

Encouragingly a first experiment under conditions comparable to those in Scheme 39 for 22 namely reaction of angular [4]phenylene (17) with one equivalent of diphenylacetylene in the absence of high dilution indeed engendered only five products two of which monoadducts 131 and 132 were minor (Scheme 325) The major components of the mixture were molecules 133 134 and most significantly 130

Scheme 325 Nickel Catalyzed Alkyne Cycloaddition with 17 and 88

Monitoring the course of the transformation by NMR revealed that 133 is the sole initial new compound followed by gradual appearance of the others Extrapolation of the insights gained with 22 it is tempting to propose that migration of the metal in Ni-complexed 133 is the source of 134 and ultimately 130 If true [7]phenacene 130 might be made selectively by application of the slow alkyne addition procedure of Scheme 322 Scheme 326 illustrates the proposed scenario It starts with doubly regioselective Ni insertion into the central ring and from the bay region to give 135 On the basis of the electron withdrawing effect of the adjacent cyclobutadienoid rings invoked earlier in the selective formation of 94 (Scheme 312) this metallacycle would seem the most stable Again this conjecture is tentative as the appearance of the minor products 131 and 132 would indicate Metallacycle 135 would then give rise to 136 (and hence 133 by demetallation) which would connect by Ni migration and insertion to 137 Alkyne cycloaddition would result in 138 (and hence 134 by demetallation) which would connect by Ni migration and insertion to 139 Alkyne cycloaddition would result in 140 (and hence 130 by demetallation)

+

Ph Ph

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2(10 mol)THF 75 degC

5 6

33

27 28

132131

133

134 130

17

88

- 85 -

Scheme 326 Proposed Reaction Pathway to Phenacene 130 from Angular [4]Phenylene 17 via Ni Migration

The successful preparation of [5]- and [7]phenacene from angular [3]- and [4]phenylene respectively prompted an attempt to prepare [13]phenacene derivative 141 from helical [7]phenylene 14210 (Scheme 327) This transformation would make use of six alkyne cycloadditions to produce the target molecule In addition to the possibility of preparing the largest known phenacene this reaction would also serve as an interesting test of the alkyne cycloaddition methodology

Scheme 327 Proposed Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Using the slow addition procedure phenylene 142 was subjected to the alkyne cycloaddition conditions (Scheme 329) All of the starting material was consumed but the reaction ultimately resulted in an intractable mixture of products Unfortunately no conclusive structural identifications for any of the ensuing compounds could be made from the 1H-NMR data A large assortment of peaks was seen in the region of 6ndash7

Ni

PMe3

Ph

NiPMe3

Ph Ph Ph PhNi

PMe3

Ph Ph Ph

NiMe3P

135

137

Ph Ph

Ph Ph

Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2

13617

88Ni

PMe3

Ph Ph88

138 139

Ph Ph88

Ni

PMe3

140

- 86 -

ppm suggesting the presence of phenylene subunits More informative was the absence of the highly diagnostic phenacene bay region proton signals that are typically found at ~8ndash9 ppm84 signaling the absence of any phenacene product(s)

Scheme 328 Attempted Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Nevertheless mass spectral analysis clearly indicated that multiple alkyne cycloaddition had occurred (Table 36) Peaks were observed at mz = 700 1056 1234 and 1412 which correspond to the presence of single triple quadruple and quintuple alkyne adducts in the reaction mixture No signal corresponding to the mass of 141 (mz = 1590) was detected however Although the structures of the resulting products remain to be established by follow-up experiments on a larger scale the fact that five cycloadditions occurred is encouraging in the basic scientific quest for large novel polycyclic aromatic hydrocarbons

Table 36 Mass Spectral Data (FAB) of the Product Mixture of the Cycloaddition Reaction of Phenylene 142 to Diphenylacetylene 88

mz Percentage Cycloaddition count 700 13 1

1056 11 3 1234 8 4 1412 7 5

Our disappointment in the apparent failure to generate 141 in this reaction may be the result of overambitious expectations on our part Thus we assumed in analogy to the reactivity of angular systems 17 and 22 that bay region cycloaddition to one of the inner cyclobutadiene rings would be preferred ideally producing an initial structure such as 143 (Figure 38) The corresponding non-bay adduct is illustrated by 144 It is evident on comparison that such bay region reactivity would lead to constructs devoid of the helical strain present in the starting material96 as well as non-bay structures like 144 The subsequent course of the reaction however may be marred by relatively non-selective cycloadditions as already indicated for 17 (Scheme 325) Therefore it will be prudent for future investigators to return to the latter optimize its outcome and then proceed along the series in the quest for large phenacene (or other) structures

- 87 -

Figure 38 Proposed representative initial bay (143) and non-bay (144) alkyne cycloaddition products of the reaction of [7]heliphene 141 with diphenylacetylene 88

35 Summary and Outlook The first alkyne cycloaddition studies were carried with angular phenylene systems Angular [3]phenylene 22 was successfully used as a precursor to a novel phenyl substituted [5]phenacene derivative 90 Similarly hexaphenyl [7]phenacene 131 was prepared from angular [4]phenylene 17 Extensive experiment and computational mechanistic studies suggested that the optimal conditions for preparing phenacene 90 from phenylene 22 were the maintenance of a low concentration of alkyne in the reaction mixture Future work will focus on applying these conditions to the synthesis of [7]phenacene 130 from angular [4]phenylene 17 An attempt to prepare a [13]phenacene 142 from helical [7]phenylene 141 proved unsuccessful for reasons that are not well understood Nevertheless cycloaddition was found to have occurred up to five times This observation is promising with respect to the further application of the methodology described in this chapter The development of an alkyne cycloaddition-based approach to synthesizing phenacenes should greatly facilitate the study of this emerging class of molecules Future work will focus on expanding the substrate scope of the reaction by examining various functionalized alkynes the application of metal systems that may allow the isolation of crucial intermediates and the expansion of the substrate scope to the higher angular phenylenes as well as other topologies

- 88 -

Chapter Four Experimental and Computational Details

41 General Considerations

All glassware was oven-dried (180 degC) prior to use Reagents were used as received from suppliers unless otherwise noted Flash chromatography97 was performed with Merck 60 230ndash400 mesh silica gel MP EcoChrom neutral alumina was deactivated to activity III by adding 6 water by mass followed by thorough mixing98 Air sensitive compounds were handled under argon with standard Schlenk techniques andor in a nitrogen atmosphere glovebox (Vacuum Atmospheres Model Nexus) Irradiation in CpCo(CO)2 reactions was carried out with a 120V 300W slide projection lamp (ELH) positioned 5 cm away from the reaction vessel UV-irradiation experiments were conducted in a Rayonet Photochemical Reactor (RPR-100) Bis(trimethylsilyl)- and trimethylsilylacetylene (BTMSA and TMSA respectively) were distilled from molecular sieves (4 Aring) prior to use TMSA was degassed with four freeze-pump-thaw cycles while BTMSA was degassed using a 20 min Ar purge BTMSA was recycled using from all CpCo(CO)2 reactions using the following procedure The BTMSA was first removed by vacuum transfer Residual cobalt was removed by dissolving the BTMSA in pentane and washing the pentaneBMTSA layer mixture with a dilute solution of ceric ammonium nitrate in acetonitrile in a separatory funnel The denser acetonitrile layer was drained off and the pentane removed by distillation at atmospheric pressure Vacuum distillation of the BTMSA from molecular sieves afforded a product pure enough for future use All solvents were distilled under N2

immediately before use from the appropriate drying agent triethylamine (KOH pellets) benzene toluene CH2Cl2 (CaH2) THF and diethylether (Nabenzophenone) acetonitrile (CaH2) Deoxygenation of solvents andor reaction mixtures was carried out by a 20 min Ar purge or four free-pump-thaw cycles for volatile (bp lt 70 degC) mixturessolvents Ni(COD)2 (Strem) was stored and manipulated in the glovebox 1H and proton decoupled 13C spectra were measured at 500 MHz and 125 MHz respectively unless otherwise noted 1H-NMR chemical shifts are reported in ppm units relative to the signal of the solvent (CDCl3ndash726 ppm C6D6ndash715 ppm acetone-d6ndash205 ppm CD2Cl2ndash532 ppm toluene-d8ndash209 ppm (for ndashCD3) Except where noted two-dimensional NMR experiments were run under temperature control at 300 K All spectral data were processed with Bruker TopSpin 21 software Melting points were recorded in open capillary tubes using a Thomas Hoover Unimelt apparatus and are uncorrected Melting points for air-sensitive samples were carried out in flame sealed capillary tubes Mass spectral measurements (Electron Impact Fast Atom Bombardment) and elemental analyses were supplied by the Micro-Mass Facility of the College of Chemistry University of California Berkeley UV-Vis spectra were recorded on Agilent 8453 and Perkin-Elmer Lambda 35 spectrophotometers with absorbance data reported in nm (log ε) IR spectra were taken on a Perkin-Elmer Spectrum 100 Where appropriate analysis by GCMS was done with an Agilent 5973 instrument

42 Experimental Section for Chapter Two

- 89 -

2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19

A mixture of KF2 H2O (700 mg 744 mmol) [18]crown-6 (100 mg 0378 mmol) and 2378-tetrakis[(triisopropylsilyl)ethynyl] linear [3]phenylene26 (370 mg 0800 mmol) in degassed THF (25 mL) was stirred for 70 min at RT The orange solution was filtered through a plug of silica gel (1 x 3 cm) eluting with degassed THF (15 mL) providing a light-yellow solution After adding CpCo(CO)2 (260 mg 144 mmol) the solution was protected from light and added via syringe pump over a period of 6 h to a boiling mixture of degassed BTMSA (50 mL) and THF (200 mL) which was irradiated with a projector lamp under nitrogen After additional heating and irradiation for 15 h the solvents were removed by vacuum transfer and the black residue filtered through a plug of neutral alumina activity III eluting with hexaneTHF (501) The volatiles were removed and the dark brown residue crystallized from degassed acetone yielding 19 (330 mg 65 ) as black needles mp 192ndash195 degC (decomp) 1H-NMR (400 MHz C6D6) δ = 794 (s 2 H) 744 (s 2 H) 690 (s 2 H) 441 (s 5 H) 035 (s 18 H) 031 (s 18 H) ppm 13C-NMR (100 MHz C6D6) δ = 1494 1484 1433 1394 1360 1256 1155 802 781 739

269 261 ppm IR (neat) ν~ = 2951 2898 1259 1248 1073 830 799 752 cmndash1 UV-VIS (ethanol) λmax (log ε) = 288 (486) 299 (500) 352 (445) 410 (439) 438 (449) end absorption to 550 nm MS (70 eV) mz () 638 (9) [M+] 514 (100) 499 (3) 387 (2) 73 (24) HRMS (FAB) calcd for C35H47CoSi4 6382087 found 6382095 Elemental analysis calcd for C35H47CoSi4 C 6578 H 741 found 6582 721

Crystallographic information for 19 (H atoms omitted)

Table 41 Crystal Data and Structure Refinement For 19

Empirical formula C35H47CoSi4 Formula weight 63902 cryst size (mm) 025 x 020 x 005 cryst syst Triclinic refl used for unit cell determination 6958

2 θ range (deg) 245ndash2900

a (Aring) 9497(3) b (Aring) 12321(4) c (Aring) 16469(5) α (deg) 74058(5)

β (deg) 82154(5)

Me3Si

Me3Si

CoSiMe3

SiMe3

- 90 -

γ (deg) 72276(5)

V (Aring3) 17620(10) space group Pndash1 Z 2

Dcalc gcm3 1762

F000 680 micro cmndash1 645 temp ordmC ndash173

Tmax Tmin 0858 0972 no of total rflns 24355

no of unique rflns 6958

no of obsd rflns 9209

no of variables 361

Reflection to Parameter Ratio 255

R 00503

Rw 01426

Rall 00734

GOF 1006

Max Peak in Final Diff Map (endash Aring3) 0867

Min Peak in Final Diff Map (endash Aring3) ndash0755

- 91 -

Figure 41 ORTEP representation of 19

- 92 -

Table 42 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 19 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y Z U (eq)

Co1 073881(4) ndash000927(3) 060643(2) 002551(10) Si1 077416(8) ndash019090(6) 094343(4) 002594(16) Si2 113437(8) ndash016706(7) 082404(5) 003023(17) Si3 040491(7) 062139(6) 020406(4) 002291(15) Si4 005088(7) 056545(6) 030946(4) 002144(14) C1 06709(3) ndash00385(2) 079440(16) 00239(5) C2 08019(3) ndash00967(2) 083428(16) 00241(5) C3 09418(3) ndash00743(2) 079331(16) 00233(5) C4 09428(3) 00098(2) 071779(15) 00225(5) C5 08094(2) 00691(2) 067735(15) 00207(4) C6 07282(2) 01574(2) 060605(15) 00207(4) C7 07303(2) 02531(2) 053306(15) 00211(4) C8 05938(2) 03094(2) 050431(15) 00205(4) C9 05057(2) 03981(2) 043438(15) 00207(4) C10 05076(2) 04760(2) 035695(15) 00227(5) C11 03734(2) 05293(2) 031459(15) 00215(4) C12 02408(2) 05011(2) 035315(15) 00205(4) C13 02432(2) 04196(2) 043269(15) 00215(4) C14 03751(2) 03698(2) 047171(15) 00208(4) C15 04564(2) 02794(2) 054277(15) 00211(4) C16 04487(2) 01908(2) 061161(15) 00224(5) C17 05916(3) 01278(2) 064393(15) 00221(5) C18 06734(2) 00417(2) 071473(15) 00215(5) C19 05795(3) ndash02027(3) 09572(2) 00446(8) C20 08892(4) ndash03470(2) 09642(2) 00387(7) C21 07986(4) ndash01192(3) 10246(2) 00419(7) C22 11685(4) ndash03077(3) 07914(3) 00584(10) C23 11726(3) ndash01969(3) 09372(2) 00426(7) C24 12742(4) ndash00933(4) 07624(3) 00640(12) C25 05777(3) 06657(3) 020261(18) 00348(6) C26 02610(3) 07629(2) 016564(17) 00292(5) C27 04355(3) 05272(3) 012760(18) 00347(6) C28 ndash00272(3) 07195(2) 03194(2) 00360(6) C29 00487(3) 05542(3) 019882(18) 00344(6) C30 ndash00786(3) 04816(2) 037272(18) 00278(5) C31 06994(4) ndash00612(3) 05062(2) 00432(7) C32 08520(4) ndash00698(3) 05033(2) 00407(7) C33 09085(3) ndash01473(3) 05788(2) 00407(7) C34 07922(4) ndash01879(3) 06277(2) 00424(7) C35 06647(4) ndash01370(3) 05833(2) 00403(7)

- 93 -

Table 43 Bond Lengths (Aring) for Complex 19

Atom1 Atom2 Length

Co1 C5 1993(3) Co1 C6 2023(3) Co1 C17 2022(2) Co1 C18 2009(3) Co1 C31 2042(4) Co1 C32 2075(3) Co1 C33 2062(3) Co1 C34 2042(4) Co1 C35 2048(4) Si1 C2 1886(2) Si1 C19 1877(3) Si1 C20 1863(2) Si1 C21 1865(4) Si2 C3 1889(3) Si2 C22 1876(5) Si2 C23 1862(3) Si2 C24 1865(4) Si3 C11 1901(2) Si3 C25 1876(4) Si3 C26 1867(2) Si3 C27 1875(4) Si4 C12 1889(2) Si4 C28 1860(3) Si4 C29 1868(3) Si4 C30 1870(3) C1 C2 1384(4) C1 C18 1411(3) C2 C3 1474(4) C3 C4 1384(3) C4 C5 1408(3) C5 C6 1480(3) C5 C18 1448(3) C6 C7 1437(3) C6 C17 1465(4) C7 C8 1351(3) C8 C9 1495(3) C8 C15 1476(3) C9 C10 1371(3) C9 C14 1405(3) C10 C11 1423(3) C11 C12 1427(3) C12 C13 1413(3) C13 C14 1376(3)

- 94 -

C14 C15 1488(3) C15 C16 1352(3) C16 C17 1434(3) C17 C18 1468(3) C31 C32 1416(6) C31 C35 1419(4) C32 C33 1401(4) C33 C34 1411(5) C34 C35 1386(5)

Table 44 Bond Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 4325(9) C5 Co1 C17 621(1) C5 Co1 C18 4240(9) C5 Co1 C31 1629(1) C5 Co1 C32 1271(1) C5 Co1 C33 1102(1) C5 Co1 C34 1223(1) C5 Co1 C35 1556(1) C6 Co1 C17 425(1) C6 Co1 C18 6191(9) C6 Co1 C31 1253(1) C6 Co1 C32 1164(1) C6 Co1 C33 1329(1) C6 Co1 C34 1651(1) C6 Co1 C35 1550(1) C17 Co1 C18 427(1) C17 Co1 C31 1204(1) C17 Co1 C32 1451(1) C17 Co1 C33 1722(1) C17 Co1 C34 1419(1) C17 Co1 C35 1194(1) C18 Co1 C31 1517(1) C18 Co1 C32 1676(1) C18 Co1 C33 1312(1) C18 Co1 C34 1112(1) C18 Co1 C35 1198(1) C31 Co1 C32 402(1) C31 Co1 C33 673(1) C31 Co1 C34 675(1) C31 Co1 C35 406(1) C32 Co1 C33 396(1) C32 Co1 C34 672(1)

- 95 -

C32 Co1 C35 675(1) C33 Co1 C34 402(1) C33 Co1 C35 671(1) C34 Co1 C35 396(1) C2 Si1 C19 1085(1) C2 Si1 C20 1157(1) C2 Si1 C21 1096(1) C19 Si1 C20 1035(1) C19 Si1 C21 1081(2) C20 Si1 C21 1110(2) C3 Si2 C22 1071(2) C3 Si2 C23 1162(1) C3 Si2 C24 1100(2) C22 Si2 C23 1110(2) C22 Si2 C24 1067(2) C23 Si2 C24 1056(2) C11 Si3 C25 1077(1) C11 Si3 C26 1177(1) C11 Si3 C27 1083(1) C25 Si3 C26 1045(1) C25 Si3 C27 1086(1) C26 Si3 C27 1097(1) C12 Si4 C28 1099(1) C12 Si4 C29 1132(1) C12 Si4 C30 1101(1) C28 Si4 C29 1119(1) C28 Si4 C30 1066(1) C29 Si4 C30 1048(1) C2 C1 C18 1193(2) Si1 C2 C1 1130(2) Si1 C2 C3 1270(2) C1 C2 C3 1198(2) Si2 C3 C2 1260(2) Si2 C3 C4 1124(2) C2 C3 C4 1208(2) C3 C4 C5 1192(2) Co1 C5 C4 1188(2) Co1 C5 C6 695(1) Co1 C5 C18 694(1) C4 C5 C6 1498(2) C4 C5 C18 1200(2) C6 C5 C18 902(2) Co1 C6 C5 673(1) Co1 C6 C7 1267(2) Co1 C6 C17 687(1) C5 C6 C7 1474(2)

- 96 -

C5 C6 C17 893(2) C7 C6 C17 1227(2) C6 C7 C8 1121(2) C7 C8 C9 1461(2) C7 C8 C15 1251(2) C9 C8 C15 885(2) C8 C9 C10 1471(2) C8 C9 C14 912(2) C10 C9 C14 1214(2) C9 C10 C11 1186(2) Si3 C11 C10 1116(2) Si3 C11 C12 1283(2) C10 C11 C12 1197(2) Si4 C12 C11 1264(2) Si4 C12 C13 1135(2) C11 C12 C13 1201(2) C12 C13 C14 1185(2) C9 C14 C13 1216(2) C9 C14 C15 915(2) C13 C14 C15 1465(2) C8 C15 C14 888(2) C8 C15 C16 1250(2) C14 C15 C16 1458(2) C15 C16 C17 1118(2) Co1 C17 C6 688(1) Co1 C17 C16 1265(2) Co1 C17 C18 682(1) C6 C17 C16 1233(2) C6 C17 C18 900(2) C16 C17 C18 1460(2) Co1 C18 C1 1229(2) Co1 C18 C5 682(1) Co1 C18 C17 691(1) C1 C18 C5 1206(2) C1 C18 C17 1487(2) C5 C18 C17 905(2) Co1 C31 C32 712(2) Co1 C31 C35 699(2) C32 C31 C35 1077(3) Co1 C32 C31 686(2) Co1 C32 C33 697(2) C31 C32 C33 1076(3) Co1 C33 C32 707(2) Co1 C33 C34 691(2) C32 C33 C34 1081(3) Co1 C34 C33 707(2)

- 97 -

Co1 C34 C35 704(2) C33 C34 C35 1086(3) Co1 C35 C31 695(2) Co1 C35 C34 700(2) C31 C35 C34 1079(3)

Table 44 Torsion Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 ndash1479(3) C6 Co1 C5 C18 983(2) C17 Co1 C5 C4 1630(2) C17 Co1 C5 C6 ndash491(1) C17 Co1 C5 C18 492(1) C18 Co1 C5 C4 1138(2) C18 Co1 C5 C6 ndash983(2) C31 Co1 C5 C4 ndash941(4) C31 Co1 C5 C6 538(4) C31 Co1 C5 C18 1522(4) C32 Co1 C5 C4 ndash573(2) C32 Co1 C5 C6 906(2) C32 Co1 C5 C18 ndash1710(2) C33 Co1 C5 C4 ndash160(2) C33 Co1 C5 C6 1319(1) C33 Co1 C5 C18 ndash1297(2) C34 Co1 C5 C4 271(2) C34 Co1 C5 C6 1750(2) C34 Co1 C5 C18 ndash866(2) C35 Co1 C5 C4 629(4) C35 Co1 C5 C6 ndash1492(3) C35 Co1 C5 C18 ndash509(3) C5 Co1 C6 C7 1458(3) C5 Co1 C6 C17 ndash986(2) C17 Co1 C6 C5 986(2) C17 Co1 C6 C7 ndash1156(3) C18 Co1 C6 C5 491(1) C18 Co1 C6 C7 ndash1650(2) C18 Co1 C6 C17 ndash494(1) C31 Co1 C6 C5 ndash1631(2) C31 Co1 C6 C7 ndash173(3) C31 Co1 C6 C17 983(2) C32 Co1 C6 C5 ndash1170(2) C32 Co1 C6 C7 288(2) C32 Co1 C6 C17 1444(2) C33 Co1 C6 C5 ndash725(2)

- 98 -

C33 Co1 C6 C7 734(3) C33 Co1 C6 C17 ndash1710(2) C34 Co1 C6 C5 ndash166(5) C34 Co1 C6 C7 1293(5) C34 Co1 C6 C17 ndash1151(5) C35 Co1 C6 C5 1499(3) C35 Co1 C6 C7 ndash642(4) C35 Co1 C6 C17 514(3) C5 Co1 C17 C6 501(1) C5 Co1 C17 C16 1666(3) C5 Co1 C17 C18 ndash489(1) C6 Co1 C17 C16 1165(3) C6 Co1 C17 C18 ndash989(2) C18 Co1 C17 C6 989(2) C18 Co1 C17 C16 ndash1446(3) C31 Co1 C17 C6 ndash1106(2) C31 Co1 C17 C16 59(3) C31 Co1 C17 C18 1505(2) C32 Co1 C17 C6 ndash656(3) C32 Co1 C17 C16 510(3) C32 Co1 C17 C18 ndash1645(2) C33 Co1 C17 C6 571(9) C33 Co1 C17 C16 1736(8) C33 Co1 C17 C18 ndash418(9) C34 Co1 C17 C6 1578(2) C34 Co1 C17 C16 ndash857(3) C34 Co1 C17 C18 589(2) C35 Co1 C17 C6 ndash1578(2) C35 Co1 C17 C16 ndash413(3) C35 Co1 C17 C18 1033(2) C5 Co1 C18 C1 ndash1133(3) C5 Co1 C18 C17 993(2) C6 Co1 C18 C1 ndash1635(2) C6 Co1 C18 C5 ndash502(1) C6 Co1 C18 C17 491(1) C17 Co1 C18 C1 1474(3) C17 Co1 C18 C5 ndash993(2) C31 Co1 C18 C1 836(3) C31 Co1 C18 C5 ndash1632(2) C31 Co1 C18 C17 ndash638(3) C32 Co1 C18 C1 ndash779(6) C32 Co1 C18 C5 353(6) C32 Co1 C18 C17 1346(5) C33 Co1 C18 C1 ndash395(3) C33 Co1 C18 C5 737(2) C33 Co1 C18 C17 1731(2)

- 99 -

C34 Co1 C18 C1 20(2) C34 Co1 C18 C5 1152(2) C34 Co1 C18 C17 ndash1455(2) C35 Co1 C18 C1 451(3) C35 Co1 C18 C5 1583(2) C35 Co1 C18 C17 ndash1023(2) C5 Co1 C31 C32 478(5) C5 Co1 C31 C35 1656(4) C6 Co1 C31 C32 904(2) C6 Co1 C31 C35 ndash1517(2) C17 Co1 C31 C32 1412(2) C17 Co1 C31 C35 ndash1010(2) C18 Co1 C31 C32 ndash1739(2) C18 Co1 C31 C35 ndash561(3) C32 Co1 C31 C35 1179(3) C33 Co1 C31 C32 ndash370(2) C33 Co1 C31 C35 808(2) C34 Co1 C31 C32 ndash808(2) C34 Co1 C31 C35 371(2) C35 Co1 C31 C32 ndash1179(3) C5 Co1 C32 C31 ndash1642(2) C5 Co1 C32 C33 764(2) C6 Co1 C32 C31 ndash1143(2) C6 Co1 C32 C33 1263(2) C17 Co1 C32 C31 ndash710(3) C17 Co1 C32 C33 1697(2) C18 Co1 C32 C31 1666(5) C18 Co1 C32 C33 472(6) C31 Co1 C32 C33 ndash1194(3) C33 Co1 C32 C31 1194(3) C34 Co1 C32 C31 816(2) C34 Co1 C32 C33 ndash377(2) C35 Co1 C32 C31 385(2) C35 Co1 C32 C33 ndash808(2) C5 Co1 C33 C32 ndash1243(2) C5 Co1 C33 C34 1166(2) C6 Co1 C33 C32 ndash802(2) C6 Co1 C33 C34 1607(2) C17 Co1 C33 C32 ndash1309(8) C17 Co1 C33 C34 1100(9) C18 Co1 C33 C32 ndash1679(2) C18 Co1 C33 C34 730(2) C31 Co1 C33 C32 376(2) C31 Co1 C33 C34 ndash815(2) C32 Co1 C33 C34 ndash1191(3) C34 Co1 C33 C32 1191(3)

- 100 -

C35 Co1 C33 C32 818(2) C35 Co1 C33 C34 ndash373(2) C5 Co1 C34 C33 ndash833(2) C5 Co1 C34 C35 1577(2) C6 Co1 C34 C33 ndash700(5) C6 Co1 C34 C35 1711(4) C17 Co1 C34 C33 ndash1681(2) C17 Co1 C34 C35 730(3) C18 Co1 C34 C33 ndash1295(2) C18 Co1 C34 C35 1115(2) C31 Co1 C34 C33 809(2) C31 Co1 C34 C35 ndash380(2) C32 Co1 C34 C33 372(2) C32 Co1 C34 C35 ndash818(2) C33 Co1 C34 C35 ndash1189(3) C35 Co1 C34 C33 1189(3) C5 Co1 C35 C31 ndash1699(3) C5 Co1 C35 C34 ndash508(4) C6 Co1 C35 C31 663(4) C6 Co1 C35 C34 ndash1746(2) C17 Co1 C35 C31 1036(2) C17 Co1 C35 C34 ndash1373(2) C18 Co1 C35 C31 1531(2) C18 Co1 C35 C34 ndash878(2) C31 Co1 C35 C34 1191(3) C32 Co1 C35 C31 ndash382(2) C32 Co1 C35 C34 809(2) C33 Co1 C35 C31 ndash812(2) C33 Co1 C35 C34 378(2) C34 Co1 C35 C31 ndash1191(3) C19 Si1 C2 C1 118(2) C19 Si1 C2 C3 ndash1731(2) C20 Si1 C2 C1 1275(2) C20 Si1 C2 C3 ndash574(3) C21 Si1 C2 C1 ndash1061(2) C21 Si1 C2 C3 690(3) C22 Si2 C3 C2 714(3) C22 Si2 C3 C4 ndash988(2) C23 Si2 C3 C2 ndash532(3) C23 Si2 C3 C4 1365(2) C24 Si2 C3 C2 ndash1731(3) C24 Si2 C3 C4 167(3) C25 Si3 C11 C10 ndash241(2) C25 Si3 C11 C12 1624(2) C26 Si3 C11 C10 ndash1417(2) C26 Si3 C11 C12 447(3)

- 101 -

C27 Si3 C11 C10 932(2) C27 Si3 C11 C12 ndash804(2) C28 Si4 C12 C11 ndash731(2) C28 Si4 C12 C13 1055(2) C29 Si4 C12 C11 529(2) C29 Si4 C12 C13 ndash1285(2) C30 Si4 C12 C11 1698(2) C30 Si4 C12 C13 ndash116(2) C18 C1 C2 Si1 1755(2) C18 C1 C2 C3 00(4) C2 C1 C18 Co1 784(3) C2 C1 C18 C5 ndash41(4) C2 C1 C18 C17 ndash1772(4) Si1 C2 C3 Si2 198(4) Si1 C2 C3 C4 ndash1707(2) C1 C2 C3 Si2 ndash1654(2) C1 C2 C3 C4 41(4) Si2 C3 C4 C5 1668(2) C2 C3 C4 C5 ndash40(4) C3 C4 C5 Co1 ndash816(3) C3 C4 C5 C6 1799(4) C3 C4 C5 C18 ndash01(4) Co1 C5 C6 C7 ndash1233(4) Co1 C5 C6 C17 671(1) C4 C5 C6 Co1 1122(4) C4 C5 C6 C7 ndash112(7) C4 C5 C6 C17 1793(4) C18 C5 C6 Co1 ndash678(1) C18 C5 C6 C7 1688(4) C18 C5 C6 C17 ndash07(2) Co1 C5 C18 C1 1164(2) Co1 C5 C18 C17 ndash672(1) C4 C5 C18 Co1 ndash1121(2) C4 C5 C18 C1 42(3) C4 C5 C18 C17 ndash1793(2) C6 C5 C18 Co1 679(1) C6 C5 C18 C1 ndash1757(2) C6 C5 C18 C17 07(2) Co1 C6 C7 C8 858(2) C5 C6 C7 C8 ndash1683(3) C17 C6 C7 C8 ndash08(3) Co1 C6 C17 C16 ndash1205(2) Co1 C6 C17 C18 665(1) C5 C6 C17 Co1 ndash658(1) C5 C6 C17 C16 1736(2) C5 C6 C17 C18 07(2)

- 102 -

C7 C6 C17 Co1 1209(2) C7 C6 C17 C16 03(4) C7 C6 C17 C18 ndash1726(2) C6 C7 C8 C9 ndash1697(3) C6 C7 C8 C15 09(3) C7 C8 C9 C10 05(7) C7 C8 C9 C14 1728(4) C15 C8 C9 C10 ndash1718(4) C15 C8 C9 C14 05(2) C7 C8 C15 C14 ndash1752(2) C7 C8 C15 C16 ndash06(4) C9 C8 C15 C14 ndash04(2) C9 C8 C15 C16 1742(2) C8 C9 C10 C11 1714(3) C14 C9 C10 C11 05(3) C8 C9 C14 C13 ndash1756(2) C8 C9 C14 C15 ndash05(2) C10 C9 C14 C13 ndash06(4) C10 C9 C14 C15 1746(2) C9 C10 C11 Si3 ndash1741(2) C9 C10 C11 C12 01(3) Si3 C11 C12 Si4 ndash90(3) Si3 C11 C12 C13 1725(2) C10 C11 C12 Si4 1779(2) C10 C11 C12 C13 ndash07(3) Si4 C12 C13 C14 ndash1781(2) C11 C12 C13 C14 06(3) C12 C13 C14 C9 ndash00(3) C12 C13 C14 C15 ndash1713(3) C9 C14 C15 C8 05(2) C9 C14 C15 C16 ndash1717(4) C13 C14 C15 C8 1730(4) C13 C14 C15 C16 09(7) C8 C15 C16 C17 00(3) C14 C15 C16 C17 1704(3) C15 C16 C17 Co1 ndash870(3) C15 C16 C17 C6 01(3) C15 C16 C17 C18 1674(4) Co1 C17 C18 C1 ndash1195(4) Co1 C17 C18 C5 664(1) C6 C17 C18 Co1 ndash671(1) C6 C17 C18 C1 1734(4) C6 C17 C18 C5 ndash07(2) C16 C17 C18 Co1 1235(4) C16 C17 C18 C1 40(7) C16 C17 C18 C5 ndash1701(4)

- 103 -

Co1 C31 C32 C33 590(2) C35 C31 C32 Co1 ndash607(2) C35 C31 C32 C33 ndash16(4) Co1 C31 C35 C34 ndash596(3) C32 C31 C35 Co1 615(3) C32 C31 C35 C34 18(4) Co1 C32 C33 C34 592(2) C31 C32 C33 Co1 ndash583(2) C31 C32 C33 C34 09(4) Co1 C33 C34 C35 605(3) C32 C33 C34 Co1 ndash602(2) C32 C33 C34 C35 03(4) Co1 C34 C35 C31 593(3) C33 C34 C35 Co1 ndash606(2) C33 C34 C35 C31 ndash13(4)

23-Bis(trimethylsilyl) linear [3]phenylene(CpCo) 52

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (029 g 085 mmol)27 in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (014 g 101 mmol) The mixture was stirred for 15 h and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the yellow residue dissolved in ether (30 mL) Aqueous workup with sat NaCl (2 x 20 mL) followed by drying over MgSO4 and concentration in vacuo provided a yellow solid This material was redissolved in THF (15 mL) degassed (Ar) and CpCo(CO)2 (0140 g 078 mmol) added The resulting solution (protected from light with foil) was injected (syringe pump) over 8 h into a boiling mixture of THF (200 mL) and BTMSA (50 mL) while irradiating with a slide projection lamp Once addition was complete heating and irradiation were continued for another 14 h The volatiles were removed via vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (4 x 4 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed in vacuo and the residue crystallized from acetone yielding 52 (024 g 57 ) as dark red crystals mp 198ndash202 degC (decomp) 1H-NMR (500 MHz C6D6) δ = 796 (s 2 H) 678 (AArsquom 2 H) 675 (s 2 H) 674 (BBrsquom 2 H) 436 (s 5 H) 037 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1426 1393

1360 1294 1194 1149 802 779 738 268 ppm IR (neat) ν~ = 2960 2923 2853 1461 1455 1378 1260 1093 1019 800 cmndash1 UV-VIS (hexane) λmax (log ε) = 255 (393) 282 (376) 293 (sh 378) 308 (389) 348 (390) 397 (sh 335) 436 (301) 511

CoSiMe3

SiMe3

- 104 -

(262) MS (70 eV) mz () 494 (100) [M+] 370 (14) HRMS (FAB) calcd for C29H31CoSi2 4941296 found 4941292 Elemental analysis calcd for C29H31CoSi2 C 7041 H 632 found 7048 628 Crystallographic information for 52 (H atoms omitted)

Table 45 Crystal Data and Structure Refinement For 52

Empirical formula C29H31CoSi2 Formula weight 49465 cryst size (mm) 030 x 020 x 005 cryst syst Monoclinic refl used for unit cell determination 2640 2 θ range (deg) 242ndash2503 a (Aring) 4391(3) b (Aring) 7472(4) c (Aring) 16869(11) α (deg)

β (deg) 111522(11) γ (deg) V (Aring3) 5149(6) space group C2c Z 8 Dcalc gcm

3 1276

F000 2080 micro cmndash1 774

temp ordmC ndash153

Tmax Tmin 0963 0800 no of total rflns 18401 no of unique rflns 2640 no of obsd rflns 4266 no of variables 271 Reflection to Parameter Ratio 974 R 00892 Rw 02042 Rall 01248 GOF 1008 Max Peak in Final Diff Map (endash Aring3) 1051 Min Peak in Final Diff Map (endash Aring3) ndash0707

- 105 -

Figure 42 ORTEP representation of 52

- 106 -

Table 46 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 52 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y z U(eq)

Co1 006961(2) 087577(12) 038136(6) 00200(3) Si1 018827(6) 08761(5) 063753(18) 00627(9) Si2 018540(5) 05425(3) 046900(16) 00410(6) C1 012151(19) 08410(10) 05589(5) 00310(17) C2 015018(13) 07767(11) 05552(4) 00343(18) C3 015002(14) 06417(10) 04926(5) 00324(17) C4 011985(17) 05770(9) 04357(4) 00247(16) C5 009030(17) 06465(9) 04383(4) 00220(14) C6 005450(16) 06378(9) 04077(4) 00216(14) C7 002537(17) 05420(9) 03591(4) 00224(15) C8 ndash000060(18) 05847(9) 03798(4) 00246(15) C9 ndash003560(17) 05555(10) 03644(4) 00256(16) C10 ndash006399(18) 04581(10) 03174(4) 00284(17) C11 ndash009208(19) 05019(12) 03360(5) 00344(18) C12 ndash009130(19) 06274(12) 03957(5) 00340(18) C13 ndash006300(17) 07256(11) 04422(5) 00294(17) C14 ndash003558(19) 06826(10) 04247(4) 00274(16) C15 000008(18) 07212(10) 04449(4) 00251(16) C16 002653(17) 08159(10) 04925(4) 00234(15) C17 005500(17) 07741(9) 04722(4) 00231(15) C18 009090(17) 07798(10) 05007(4) 00247(15) C19 01766(3) 10793(15) 06845(9) 0098(3) C20 02181(3) 0957(2) 05901(7) 0098(3) C21 02076(3) 07068(14) 07228(7) 0098(3) C22 01946(2) 06941(13) 03925(6) 00631(17) C23 01724(2) 03224(9) 04142(7) 00631(17) C24 022363(17) 04883(16) 05614(5) 00631(17) C25 007501(19) 09264(10) 02652(4) 00281(17) C26 004279(18) 09614(10) 02593(4) 00264(16) C27 004343(18) 10945(10) 03211(4) 00271(16) C28 007584(19) 11429(10) 03645(5) 00296(17) C29 00960(2) 10392(11) 03322(5) 00321(17)

Table 47 Bond Lengths (Aring) for Complex 52

Atom1 Atom2 Length

Co1 C5 2011(7) Co1 C6 2004(7) Co1 C17 2014(8) Co1 C18 2015(6) Co1 C25 2093(8)

- 107 -

Co1 C26 2063(6) Co1 C27 2042(7) Co1 C28 2049(8) Co1 C29 206(1) Si1 C2 1890(6) Si1 C19 187(1) Si1 C20 187(2) Si1 C21 187(1) Si2 C3 1891(8) Si2 C22 187(1) Si2 C23 1870(8) Si2 C24 1869(7) C1 C2 137(1) C1 C18 1418(9) C2 C3 146(1) C3 C4 1406(8) C4 C5 141(1) C5 C6 147(1) C5 C18 144(1) C6 C7 1432(9) C6 C17 148(1) C7 C8 135(1) C8 C9 148(1) C8 C15 149(1) C9 C10 1410(9) C9 C14 139(1) C10 C11 142(1) C11 C12 137(1) C12 C13 141(1) C13 C14 138(1) C14 C15 150(1) C15 C16 1345(9) C16 C17 145(1) C17 C18 147(1) C25 C26 141(1) C25 C29 144(1) C26 C27 143(1) C27 C28 139(1) C28 C29 143(1)

Table 48 Bond Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 428(3) C5 Co1 C17 619(3)

- 108 -

C5 Co1 C18 420(3) C5 Co1 C25 1145(3) C5 Co1 C26 1372(3) C5 Co1 C27 1733(3) C5 Co1 C28 1468(3) C5 Co1 C29 1184(3) C6 Co1 C17 434(3) C6 Co1 C18 621(3) C6 Co1 C25 1219(3) C6 Co1 C26 1125(3) C6 Co1 C27 1305(3) C6 Co1 C28 1653(3) C6 Co1 C29 1539(3) C17 Co1 C18 428(3) C17 Co1 C25 1632(3) C17 Co1 C26 1307(3) C17 Co1 C27 1137(3) C17 Co1 C28 1247(3) C17 Co1 C29 1562(3) C18 Co1 C25 1460(3) C18 Co1 C26 1733(3) C18 Co1 C27 1388(3) C18 Co1 C28 1167(3) C18 Co1 C29 1194(3) C25 Co1 C26 395(3) C25 Co1 C27 680(3) C25 Co1 C28 681(3) C25 Co1 C29 406(3) C26 Co1 C27 409(3) C26 Co1 C28 674(3) C26 Co1 C29 672(3) C27 Co1 C28 397(3) C27 Co1 C29 678(3) C28 Co1 C29 407(3) C2 Si1 C19 1089(5) C2 Si1 C20 1125(5) C2 Si1 C21 1092(4) C19 Si1 C20 1053(6) C19 Si1 C21 1100(6) C20 Si1 C21 1109(6) C3 Si2 C22 1081(4) C3 Si2 C23 1089(4) C3 Si2 C24 1177(4) C22 Si2 C23 1072(4) C22 Si2 C24 1106(4) C23 Si2 C24 1039(4)

- 109 -

C2 C1 C18 1206(7) Si1 C2 C1 1141(5) Si1 C2 C3 1249(5) C1 C2 C3 1210(7) Si2 C3 C2 1296(5) Si2 C3 C4 1113(5) C2 C3 C4 1190(6) C3 C4 C5 1199(6) Co1 C5 C4 1239(5) Co1 C5 C6 684(4) Co1 C5 C18 692(4) C4 C5 C6 1484(7) C4 C5 C18 1203(6) C6 C5 C18 910(6) Co1 C6 C5 688(4) Co1 C6 C7 1280(5) Co1 C6 C17 687(4) C5 C6 C7 1473(6) C5 C6 C17 892(5) C7 C6 C17 1222(6) C6 C7 C8 1133(6) C7 C8 C9 1475(7) C7 C8 C15 1242(7) C9 C8 C15 882(6) C8 C9 C10 1454(7) C8 C9 C14 928(6) C10 C9 C14 1218(7) C9 C10 C11 1147(7) C10 C11 C12 1222(8) C11 C12 C13 1231(8) C12 C13 C14 1149(7) C9 C14 C13 1233(7) C9 C14 C15 910(6) C13 C14 C15 1457(7) C8 C15 C14 879(6) C8 C15 C16 1254(7) C14 C15 C16 1467(7) C15 C16 C17 1121(6) Co1 C17 C6 679(4) Co1 C17 C16 1300(5) Co1 C17 C18 686(4) C6 C17 C16 1227(6) C6 C17 C18 892(5) C16 C17 C18 1464(7) Co1 C18 C1 1235(5) Co1 C18 C5 688(4)

- 110 -

Co1 C18 C17 686(4) C1 C18 C5 1191(7) C1 C18 C17 1500(7) C5 C18 C17 906(6) Co1 C25 C26 691(4) Co1 C25 C29 683(4) C26 C25 C29 1065(7) Co1 C26 C25 714(4) Co1 C26 C27 688(4) C25 C26 C27 1091(6) Co1 C27 C26 704(4) Co1 C27 C28 704(5) C26 C27 C28 1079(7) Co1 C28 C27 699(5) Co1 C28 C29 699(5) C27 C28 C29 1085(7) Co1 C29 C25 711(5) Co1 C29 C28 694(5) C25 C29 C28 1080(7)

Table 49 Torsion Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 1468(8) C6 Co1 C5 C18 ndash999(5) C17 Co1 C5 C4 ndash1627(7) C17 Co1 C5 C6 504(4) C17 Co1 C5 C18 ndash494(4) C18 Co1 C5 C4 ndash1133(8) C18 Co1 C5 C6 999(5) C25 Co1 C5 C4 356(7) C25 Co1 C5 C6 ndash1113(4) C25 Co1 C5 C18 1489(4) C26 Co1 C5 C4 765(7) C26 Co1 C5 C6 ndash703(5) C26 Co1 C5 C18 ndash1702(4) C27 Co1 C5 C4 146(2) C27 Co1 C5 C6 ndash1(3) C27 Co1 C5 C18 ndash101(2) C28 Co1 C5 C4 ndash515(9) C28 Co1 C5 C6 1617(5) C28 Co1 C5 C18 619(7) C29 Co1 C5 C4 ndash98(7) C29 Co1 C5 C6 ndash1567(4) C29 Co1 C5 C18 1035(5)

- 111 -

C5 Co1 C6 C7 ndash1474(8) C5 Co1 C6 C17 977(5) C17 Co1 C6 C5 ndash977(5) C17 Co1 C6 C7 1149(8) C18 Co1 C6 C5 ndash482(4) C18 Co1 C6 C7 1644(7) C18 Co1 C6 C17 495(4) C25 Co1 C6 C5 927(5) C25 Co1 C6 C7 ndash547(7) C25 Co1 C6 C17 ndash1696(4) C26 Co1 C6 C5 1362(4) C26 Co1 C6 C7 ndash112(7) C26 Co1 C6 C17 ndash1261(4) C27 Co1 C6 C5 1799(4) C27 Co1 C6 C7 325(8) C27 Co1 C6 C17 ndash824(5) C28 Co1 C6 C5 ndash137(1) C28 Co1 C6 C7 75(1) C28 Co1 C6 C17 ndash40(1) C29 Co1 C6 C5 523(8) C29 Co1 C6 C7 ndash951(9) C29 Co1 C6 C17 1501(7) C5 Co1 C17 C6 ndash497(4) C5 Co1 C17 C16 ndash1646(8) C5 Co1 C17 C18 484(4) C6 Co1 C17 C16 ndash1149(8) C6 Co1 C17 C18 981(5) C18 Co1 C17 C6 ndash981(5) C18 Co1 C17 C16 1470(9) C25 Co1 C17 C6 32(1) C25 Co1 C17 C16 ndash83(1) C25 Co1 C17 C18 130(1) C26 Co1 C17 C6 799(5) C26 Co1 C17 C16 ndash350(8) C26 Co1 C17 C18 1780(4) C27 Co1 C17 C6 1245(4) C27 Co1 C17 C16 97(8) C27 Co1 C17 C18 ndash1373(4) C28 Co1 C17 C6 1686(4) C28 Co1 C17 C16 538(8) C28 Co1 C17 C18 ndash932(5) C29 Co1 C17 C6 ndash1471(7) C29 Co1 C17 C16 98(1) C29 Co1 C17 C18 ndash489(9) C5 Co1 C18 C1 1117(8) C5 Co1 C18 C17 ndash995(5)

- 112 -

C6 Co1 C18 C1 1609(7) C6 Co1 C18 C5 492(4) C6 Co1 C18 C17 ndash502(4) C17 Co1 C18 C1 ndash1488(8) C17 Co1 C18 C5 995(5) C25 Co1 C18 C1 544(9) C25 Co1 C18 C5 ndash573(7) C25 Co1 C18 C17 ndash1568(5) C26 Co1 C18 C1 ndash162(2) C26 Co1 C18 C5 87(3) C26 Co1 C18 C17 ndash13(3) C27 Co1 C18 C1 ndash784(8) C27 Co1 C18 C5 1699(4) C27 Co1 C18 C17 705(6) C28 Co1 C18 C1 ndash356(7) C28 Co1 C18 C5 ndash1473(4) C28 Co1 C18 C17 1133(4) C29 Co1 C18 C1 107(8) C29 Co1 C18 C5 ndash1010(5) C29 Co1 C18 C17 1595(4) C5 Co1 C25 C26 1356(4) C5 Co1 C25 C29 ndash1058(5) C6 Co1 C25 C26 873(5) C6 Co1 C25 C29 ndash1540(5) C17 Co1 C25 C26 62(1) C17 Co1 C25 C29 ndash1796(9) C18 Co1 C25 C26 1738(5) C18 Co1 C25 C29 ndash675(7) C26 Co1 C25 C29 1187(6) C27 Co1 C25 C26 ndash376(4) C27 Co1 C25 C29 810(5) C28 Co1 C25 C26 ndash806(5) C28 Co1 C25 C29 381(5) C29 Co1 C25 C26 ndash1187(6) C5 Co1 C26 C25 ndash696(6) C5 Co1 C26 C27 1703(4) C6 Co1 C26 C25 ndash1134(5) C6 Co1 C26 C27 1265(4) C17 Co1 C26 C25 ndash1604(4) C17 Co1 C26 C27 795(5) C18 Co1 C26 C25 ndash149(2) C18 Co1 C26 C27 91(3) C25 Co1 C26 C27 ndash1201(6) C27 Co1 C26 C25 1201(6) C28 Co1 C26 C25 825(5) C28 Co1 C26 C27 ndash376(4)

- 113 -

C29 Co1 C26 C25 383(5) C29 Co1 C26 C27 ndash818(5) C5 Co1 C27 C26 ndash77(3) C5 Co1 C27 C28 165(2) C6 Co1 C27 C26 ndash774(5) C6 Co1 C27 C28 1644(5) C17 Co1 C27 C26 ndash1254(4) C17 Co1 C27 C28 1163(5) C18 Co1 C27 C26 ndash1698(5) C18 Co1 C27 C28 720(6) C25 Co1 C27 C26 364(4) C25 Co1 C27 C28 ndash818(5) C26 Co1 C27 C28 ndash1182(6) C28 Co1 C27 C26 1182(6) C29 Co1 C27 C26 804(5) C29 Co1 C27 C28 ndash378(5) C5 Co1 C28 C27 ndash1768(5) C5 Co1 C28 C29 637(7) C6 Co1 C28 C27 ndash54(1) C6 Co1 C28 C29 ndash173(1) C17 Co1 C28 C27 ndash861(5) C17 Co1 C28 C29 1544(5) C18 Co1 C28 C27 ndash1355(5) C18 Co1 C28 C29 1050(5) C25 Co1 C28 C27 815(5) C25 Co1 C28 C29 ndash380(5) C26 Co1 C28 C27 387(4) C26 Co1 C28 C29 ndash809(5) C27 Co1 C28 C29 ndash1195(7) C29 Co1 C28 C27 1195(7) C5 Co1 C29 C25 953(5) C5 Co1 C29 C28 ndash1461(5) C6 Co1 C29 C25 576(9) C6 Co1 C29 C28 1762(6) C17 Co1 C29 C25 1797(7) C17 Co1 C29 C28 ndash617(9) C18 Co1 C29 C25 1437(4) C18 Co1 C29 C28 ndash977(5) C25 Co1 C29 C28 1186(7) C26 Co1 C29 C25 ndash373(4) C26 Co1 C29 C28 813(5) C27 Co1 C29 C25 ndash817(5) C27 Co1 C29 C28 369(5) C28 Co1 C29 C25 ndash1186(7) C19 Si1 C2 C1 ndash144(8) C19 Si1 C2 C3 1663(7)

- 114 -

C20 Si1 C2 C1 ndash1307(7) C20 Si1 C2 C3 500(8) C21 Si1 C2 C1 1057(7) C21 Si1 C2 C3 ndash736(7) C22 Si2 C3 C2 ndash852(7) C22 Si2 C3 C4 908(6) C23 Si2 C3 C2 1587(7) C23 Si2 C3 C4 ndash253(7) C24 Si2 C3 C2 410(8) C24 Si2 C3 C4 ndash1431(6) C18 C1 C2 Si1 1795(6) C18 C1 C2 C3 ndash1(1) C2 C1 C18 Co1 ndash817(9) C2 C1 C18 C5 1(1) C2 C1 C18 C17 173(1) Si1 C2 C3 Si2 ndash5(1) Si1 C2 C3 C4 1790(5) C1 C2 C3 Si2 1755(6) C1 C2 C3 C4 ndash0(1) Si2 C3 C4 C5 ndash1747(5) C2 C3 C4 C5 2(1) C3 C4 C5 Co1 822(8) C3 C4 C5 C6 ndash174(1) C3 C4 C5 C18 ndash2(1) Co1 C5 C6 C7 128(1) Co1 C5 C6 C17 ndash674(4) C4 C5 C6 Co1 ndash120(1) C4 C5 C6 C7 8(2) C4 C5 C6 C17 173(1) C18 C5 C6 Co1 671(4) C18 C5 C6 C7 ndash165(1) C18 C5 C6 C17 ndash03(6) Co1 C5 C18 C1 ndash1175(7) Co1 C5 C18 C17 667(4) C4 C5 C18 Co1 1179(7) C4 C5 C18 C1 0(1) C4 C5 C18 C17 ndash1754(7) C6 C5 C18 Co1 ndash663(4) C6 C5 C18 C1 1762(7) C6 C5 C18 C17 04(6) Co1 C6 C7 C8 ndash887(8) C5 C6 C7 C8 160(1) C17 C6 C7 C8 ndash2(1) Co1 C6 C17 C16 1243(7) Co1 C6 C17 C18 ndash672(4) C5 C6 C17 Co1 675(4)

- 115 -

C5 C6 C17 C16 ndash1681(7) C5 C6 C17 C18 03(5) C7 C6 C17 Co1 ndash1223(7) C7 C6 C17 C16 2(1) C7 C6 C17 C18 1705(7) C6 C7 C8 C9 ndash180(1) C6 C7 C8 C15 2(1) C7 C8 C9 C10 2(2) C7 C8 C9 C14 ndash179(1) C15 C8 C9 C10 ndash179(1) C15 C8 C9 C14 01(6) C7 C8 C15 C14 1791(7) C7 C8 C15 C16 ndash2(1) C9 C8 C15 C14 ndash01(5) C9 C8 C15 C16 1792(8) C8 C9 C10 C11 ndash180(1) C14 C9 C10 C11 1(1) C8 C9 C14 C13 1791(7) C8 C9 C14 C15 ndash01(6) C10 C9 C14 C13 ndash1(1) C10 C9 C14 C15 1796(7) C9 C10 C11 C12 ndash1(1) C10 C11 C12 C13 1(1) C11 C12 C13 C14 ndash2(1) C12 C13 C14 C9 2(1) C12 C13 C14 C15 ndash180(1) C9 C14 C15 C8 01(6) C9 C14 C15 C16 ndash179(1) C13 C14 C15 C8 ndash179(1) C13 C14 C15 C16 2(2) C8 C15 C16 C17 1(1) C14 C15 C16 C17 ndash180(1) C15 C16 C17 Co1 858(8) C15 C16 C17 C6 ndash2(1) C15 C16 C17 C18 ndash161(1) Co1 C17 C18 C1 120(1) Co1 C17 C18 C5 ndash669(4) C6 C17 C18 Co1 666(4) C6 C17 C18 C1 ndash173(1) C6 C17 C18 C5 ndash03(5) C16 C17 C18 Co1 ndash131(1) C16 C17 C18 C1 ndash11(2) C16 C17 C18 C5 162(1) Co1 C25 C26 C27 586(5) C29 C25 C26 Co1 ndash583(5) C29 C25 C26 C27 03(9)

- 116 -

Co1 C25 C29 C28 ndash598(6) C26 C25 C29 Co1 588(5) C26 C25 C29 C28 ndash10(9) Co1 C26 C27 C28 607(5) C25 C26 C27 Co1 ndash602(5) C25 C26 C27 C28 05(9) Co1 C27 C28 C29 595(6) C26 C27 C28 Co1 ndash607(5) C26 C27 C28 C29 ndash12(9) Co1 C28 C29 C25 609(6) C27 C28 C29 Co1 ndash595(6) C27 C28 C29 C25 14(9)

Photo-thermal cycle between 52 and 53

An NMR tube containing a solution of 52 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 53 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 724 (AArsquom 2 H) 683 (s 2 H) 662 (BBrsquom 2 H) 444 (s 5 H) 032 (s 18 H) ppm 13C- NMR (100 MHz C6D6) δ = 1493 1482 1430 1276 1256 1241 1155 803 796 725 222 ppm Thermal reversal could be conveniently followed by VT-NMR

Kinetic studies of the thermal CoCp migration in 53 In the glovebox 23-[bis(trimethylsilyl)] linear[3]phenylene(CpCo) 52 dissolved in the solvent of choice (C6D6 or toluene-d8) was passed through an HPLC filter and then transfered via syringe into a thick-walled NMR tube connected to a vacuum line adapter The sample was then degassed by three freeze-pump-thaw cycles and flame-sealed under vacuum Prior to the kinetic runs the mixtures were irradiated for 10 h in a Rayonet Photochemical Reactor fitted with lamps emitting at 310 and 365 nm After this treatment care was taken to exclude ambient light as it causes some isomerization The irradiated samples were then placed in the NMR spectrometer at ndash65 degC (500 MHz) which was then warmed to the required temperature In the case of the 60 degC runs the magnet was prewarmed because of the fast reaction rate at this temperature After five min the spectra were recorded The Cp signal of the photoisomer was integrated relative to the solvent peak of C6D6 or the CD3 peak of toluene-d8 and monitored as a function of time The integral from the first scan was used as [A]o Since the equilibrium constant between the isomers was 50 the kinetic analysis treated the isomerization as a first-order non-reversible process Plotting the data accordingly

CoSiMe3

SiMe3

52

CoSiMe3

SiMe3

53

hν∆

- 117 -

yielded the reaction rate constants which were used in the Eyring plots to obtain the activation parameters Kinetic studies of the thermal haptotropic shift for complex 52 Kinetic runs were executed in C6D6 as the optimum solvent A sample of 52 in degassed C6D6 or toluene-d8 was subjected to UV light for 10 h leading to maximum enrichment of 53 The sample was kept at the specified temperature and the disappearance of 53 monitored by 1H-NMR spectroscopy The reaction proved to be first-order (eq 1) consistent with an intramolecular process

[ ] [ ]Akdt

Adminus=

(1)

[ ][ ] dtkA

Ad=minus

(2)

[ ][ ]

tkA

A=minus

0

ln (3)

The rate constant (k) at 30 40 50 and 60 degC was obtained from the slope of a plot of ndashln([A][A]0) versus time (t) following eq 2 and 3 The actual error in reproducibility was estimated by the calculation of one standard deviation (σ) for a triplicate run at 60 degC The percentage error was applied for k at 30 40 and 50 degC The rate constants and their errors are given in Tables 411 and 414 The values for k and their standard deviations were used to calculate the activation enthalpy (∆HDagger) and entropy (∆SH) of the haptotropic shift The basis for these calculations is the Eyring equation (eq 4) This expression (eq 4) was transformed to eq 5 and the activation enthalpy (∆HDagger) obtained from the slope of a plot of ndashln(kT) versus 1RT The intercept (ndashC) provides the activation entropy (∆SH) following eq 6 and 7

C

TR

H

R

S

h

k

TR

H

T

k B

minus∆

=

∆+minus

∆=minus

ne

nene

lnln

( 4)

R

S

h

kC B

ne∆+= ln

(5)

minus=∆ ne

h

kCRS Bln

(6)

- 118 -

The errors in ∆HDagger and ∆SDagger were calculated based on those in the rate constants leading to two additional least square fits in the Eyring plot These fits represent the two most extreme deviations from the original plot This provides a conservative error estimate and finally the values of 204plusmn14 kcalmol for ∆HH and 158plusmn22 eu (calmolmiddotK) for ∆SH in C6D6 In order to probe for solvent effects the kinetics were also repeated in toluene-d8 The preparation of the sample followed the described procedure and the rate constants (k) were obtained at 30 40 50 and 60 degC At 60 degC three measurements were carried out to estimate the errors in reproducibility for k and the activation parameters Error propagation was done as described for the kinetic experiments in C6D6 It is assumed that those rate constants (k) show the same relative error as the ones for the rearrangement of 53 to 52 in C6D6 The activation parameters in toluene-d8 were found to be 231plusmn07 kcalmol and 60plusmn13 eu

Table 410 Kinetic Data for the Conversion of 53 to 52 in C6D6

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09657 00349 1000 09419 00599 6000 09380 00640 2000 09018 01034 9000 09038 01012 3000 08557 01558 12000 08760 01324 4000 08176 02013 15000 08418 01723 5000 07796 02490 18000 08206 01978 6000 07555 02804 21000 08010 02219 7000 07255 03210 32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 400 09541 00470 30 09888 00113 800 09197 00837 60 09820 00181 1200 08910 01154 90 09708 00296 1600 08489 01638 120 09596 00413 2000 08298 01865 150 09506 00507 2400 07954 02289 180 09416 00602 2800 07591 02756 210 09348 00674 240 09281 00746 270 09213 00819 300 09124 00917 330 09034 01016 360 08966 01091

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

- 119 -

0 10000 00000 0 10000 00000 30 09950 00050 30 09909 00092 60 09900 00101 60 09854 00147 90 09800 00202 90 09762 00241 120 09750 00253 120 09671 00335 150 09700 00305 150 09634 00372 180 09625 00382 180 09543 00468 210 09575 00434 210 09433 00583 240 09475 00539 240 09397 00622 270 09400 00619 270 09287 00740 300 09350 00672 300 09232 00799 330 09300 00726 330 09177 00858 360 09250 00780 360 09086 00959

Table 411 The Rate Constants (k) in C6D6 Calculated From the Data in Table 410 and Their

Standard Deviations (σ)

Temp (K) k (1s) σσσσ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 10809Endash05 74258Endash07 09970 171494 00688

31315 45615Endash05 31338Endash06 09948 157420 00688

32315 95118Endash05 65346Endash06 09965 150385 00688

33315 (1) 27425Endash04 09965

33315 (2) 25714Endash04 09964

33315 (3) 30051Endash04 09990

33315 (avg) 26511Endash04 18841Endash05 140101 00688

Table 412 Activation Parameters for the Kinetic Experiments in C6D6

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 90990 85414 79291 Intercept ndash1789 ndash1674 ndash1559 R

2 09869 09869 09869

∆HDagger (Jmol) 90990 85414 79291

∆HDagger (kcalmol) 217 204 190

∆SDagger (JmolmiddotK) ndash569 ndash660 ndash751

∆SDagger (eu) ndash136 ndash158 ndash180

- 120 -

(323 15 K 50 degC) y = 95118E-05x + 44505E-03

R2 = 9965

(30315 K 30 degC) y = 10809E-05x + 20474E-03

R2 = 9970

(31315 K 40 degC) y = 45615E-05x + 11689E-02

R2 = 9948

(33315 K 60 degC) y = 263387E-04x + 390297E-04

R2 = 9992

000

005

010

015

020

025

030

035

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

Figure 43 Kinetic plots for the conversion of 53 to 52 in C6D6

Table 413 Kinetic Data for the Conversion of 53 to 52 in Toluene-d8

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09556 00454 1000 09488 00526 6000 09256 00773 2000 08931 01130 9000 08956 01103 3000 08545 01572 12000 08667 01430 4000 08143 02054 15000 08343 01811 5000 07818 02461 18000 08103 02103 6000 07559 02798 21000 07863 02404 7000 07179 03314

- 121 -

32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

000 10000 00000 0 10000 00000 40000 09470 00544 30 09887 00113 80000 08934 01127 60 09775 00228 120000 08594 01515 90 09691 00314 160000 08175 02015 120 09592 00416 200000 07861 02406 150 09473 00542 240000 07502 02875 180 09381 00639 280000 06991 03579 210 09262 00767 240 09149 00889 270 09086 00959 300 08973 01083 330 08868 01202 360 08762 01321

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 30 09945 00055 30 09910 00090 60 09795 00207 60 09828 00173 90 09700 00304 90 09716 00288 120 09645 00361 120 09559 00451 150 09479 00535 150 09440 00576 180 09464 00551 180 09313 00712 210 09314 00711 210 09238 00792 240 09188 00847 240 09156 00882 270 09101 00942 270 08992 01063 300 08991 01064 300 08932 01129 330 08896 01170 330 08872 01197 360 08801 01277 360 08686 01409

- 122 -

Table 414 The Rate Constants (k) in Toluene-d8 Calculated From the Data in Table 413 and Their Standard Deviations (σ)

Temp (K) k (1s) σ σ σ σ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 11314Endash05 37152Endash07 09976 17104 05610

31315 46470Endash05 15251Endash06 09948 15723 05157

32315 12214Endash04 401074Endash06 09957 14788 04851

33315 (1) 36441Endash04 09992

33315 (2) 36124Endash04 09951

33315 (3) 38855Endash04 09956

33315 (avg) 37140Endash04 14937Endash05 13707 04496

Table 415 Activation Parameters for the Kinetic Experiments in Toluene-d8

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 96590 93523 90455 Intercept ndash2073 ndash2007 ndash1941 R

2 09962 09962 09962

∆HDagger (Jmol) 96590 93523 90455

∆HDagger (kcalmol) 2309 2235 2162

∆SDagger (JmolmiddotK) ndash2521 ndash3068 ndash3615

∆SDagger (eu) ndash602 ndash733 ndash864

- 123 -

00000

00500

01000

01500

02000

02500

03000

03500

04000

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

(31315 K 40 degC) y = 46470E-05x + 10553E-02

R2 = 9948

(32315 K 50 degC) y = 12214E-04x + 47671E-03

R2 = 9957

(33315 K 60 degC)y = 371377E-04x - 208381E-03

R2 = 9992

(30315 K 30 degC) y = 11314E-05x + 71900E-03

R2 = 9976

Figure 44 Kinetic plots for the conversion of 53 to 52 in toluene-d8

- 124 -

(C6D6) y = 85141x - 16743

R2

= 09869

(toluene-d 8) y = 93523x - 2007

R2 = 09962

13600

14600

15600

16600

17600

36100E-04

36600E-04

37100E-04

37600E-04

38100E-04

38600E-04

39100E-04

39600E-04

40100E-04

1RT (Jmol)

-ln

(kT

)

Figure 45 Eyring plots for conversion of 53 to 52 MeCpCo(CO)2

Adapted from the literature procedure50 Co2(CO)8 (809 g 2366 mmol) was added to a round bottom flask in the glovebox The flask was capped with a septum and brought out of the glovebox A reflux condenser connected to the high vacuum line was quickly exchanged with the septum under a heavy purge of argon Degassed CH2Cl2 (30 mL) was added followed by freshly cracked deoxygenated methylcyclopentadiene (135 mL 123 mmol) The mixture evolved gas upon addition of the methylcyclopentadiene indicating CO liberation The entire setup was protected from light with foil and heated to a gentle reflux using a heating mantlevariac heat source After stirring at reflux for 26 h the mixture now dark crimson in color was cooled to rt The reflux condenser was quickly exchanged for a distillation head under an Ar purge and CH2Cl2 distilled off at atmospheric pressure under Ar Vacuum distillation at 002 Torr was performed and the forerun discarded The desired complex was obtained as a red liquid (7296 g 79) bp = 31 degC (002 Torr) stored at ndash10 degC and shielded from light Note A small

CoOC CO

- 125 -

amount of methylcyclopentadiene dimer (15 ) which could not be separated was present in the isolated product This was deemed harmless however and the obtained product was used in further experiments without further purification 85 pure 1H-NMR data match those reported in the literature 1H-NMR (C6D6) δ = 145 (s 3 H) 431 (br s 2 H) 451 (br s 2 H) 23-Bis(trimethylsilyl) linear [3]phenylene(MeCpCo) 54

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (0146 g 0424 mmol) in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (0101 g 0731 mmol) The mixture was stirred for 100 min and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the remaining yellow residue was dissolved in freshly distilled THF (15 mL) The green solution was separated from the solids via canula filtration and transferred into another Schlenk flask After a 20 min Ar purge MeCpCo(CO)2 (0092 g 0403 mmol) was added and the resulting solution (protected from light with foil) injected via syringe pump over 9 h into a boiling mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 15 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (201) The volatiles were again removed under high vacuum line and the residue crystallized from acetone yielding 55 (0125 g 61 ) as black crystals mp 163ndash165 degC 1H-NMR (500 MHz C6D6) δ = 783 (s 2 H) 676 (m 4 H) 675 (s 2 H) 442 (apparent t J = 21 Hz 2 H) 427 (apparent t J = 21 Hz 2 H) 134 (s 3 H) 038 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1423 1386 1354 1293 1193 1147 899 806 798 783 739 111 279 ppm IR (neat) ν~ = 2959 2923 2853 1462 1455 1378 1260 1093 1030 802 cmndash1 UV-VIS (hexane) λmax (log ε) = 256 (368) 281 (356) 293 (359) 310 (373) 350 (368) 386 (sh 321) 437 (sh 287) 499 (sh 247) end absorption to 550 nm MS (70 eV) mz () 508 (100) [M+] 370 (28) HRMS (FAB) calcd for C30H33CoSi2 5081453 found 5081442 Photo-thermal cycle between 54 and 56

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

54

CoSiMe3

SiMe3

56

hν∆

Me Me

- 126 -

An NMR tube containing a solution of 54 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 56 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 715 (AArsquom obscured by solvent peak) 680 (s 2 H) 664 (AArsquom 2 H) 447 (apparent t J = 21 Hz 2 H) 428 (apparent t J = 21 Hz 2 H) 148 (s 3 H) 032 (s 18 H) ppm Thermal reversal could be conveniently followed by VT-NMR

14-Deuterio-23-bis(trimethylsilyl) linear [3]phenylene cyclopentadienylcobalt 55

To 23-bis(trimethylsilylethynyl)biphenylene 52 (0144 g 0418 mmol) in CH3OD (10 mL) was added freshly distilled ether (20 mL) and K2CO3 (0083 g 0600 mmol) The mixture was stirred for 100 min and monitored by TLC (hexaneCH2Cl2 51) When the starting material had disappeared the solvents were removed and the remaining yellow residue very quickly dissolved in freshly distilled THF (10 mL) The green solution was separated from the solids using a filter cannula and transferred to another Schlenk flask After a 20 min Ar purge CpCo(CO)2 (0072 g 0400 mmol) was added and the resulting solution (protected from light with foil) was injected via syringe pump over 7 h into a refluxing mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 14 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed on the high vacuum line and the residue recrystallized from acetone yielding 8 (0085 g 41 ) as dark red crystals 1H-NMR spectroscopy showed 63 incorporation of deuterium as indicated by the diminution of the peak intensity of the signal at δ = 796 (s 074 H) ppm MS (FAB) mz () 496 (100) [M+] 372 (19)

CoSiMe3

SiMe3

D

D

- 127 -

Crossover experiment with 54 and 55

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

h

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

5455

5657

A solution of complex 55 (~2 mg) and 54 (~2 mg) in C6D6 (06 mL) rigorously protected from light was analyzed by 1H-NMR spectroscopy to reveal a 1861 mixture of 5554 The peak for 55 at δ = 796 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound A mass spectrum of an aliquot gave the appropriate composite of the two respective molecular ion patterns (Figure 46) The sample was then irradiated as described for above 13 h at RT The 1H-NMR spectrum of the irradiated mixture showed the presence of the respective photoisomers of 55 and 54 There were no unidentifiable peaks the signal at δ = 7470 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound and the clearly resolved peak for 56 at δ = 7473 (s 2 H) ppm revealed unattenuated intensity An aliquot was submitted for mass spectral analysis furnishing the same pattern as that depicted above The sample was then placed in an oil bath preheated to 80 degC for 30 h a treatment that regenerated the original NMR spectrum of the mixture of 55 and 54 including the relative integration ratios Similarly mass spectral analysis resulted in the same pattern as that depicted in Figure 46

- 128 -

Figure 46 Mass spectrum from the crossover experiment between 55 and 56

Low temperature photolyses of 19 and 52 A small amount (~5 mg) of linear[3]phenylene(CpCo) 19 or 52 dissolved in toluene-d8 was added to a J-Young NMR tube in the glovebox The sealed sample was then placed inside a Pyrex Dewar flask positioned in a Rayonet Photochemical Reactor outfitted with UV-lamps emitting at 310 and 350 nm (as shown in Figure 214) Cooling was achieved with the use of a Neslab Refrigerated Circulating bath employing isopropanol as the cooling medium The cold isopropanol was pumped into and out of the Pyrex Dewar using securely fastened Tygon tubes maintaining a temperature of ndash55 to ndash50 degC Once the sample was chilled irradiation was commenced The total irradiation time varied from 25 to 4 h When analysis was required the sample was transported in another Dewar flask containing dry iceisopropanol (ndash78 degC) while the NMR spectrometer was prepared for the low temperature experiment The spectrometer was cooled (ndash80 to ndash30 degC depending on the experiment) the sample wiped with a paper towel placed inside the spinner and very quickly lowered manually with a string into the cold magnet After allowing time for the temperature to equilibrate (10 min) a spectrum was recorded For VT experiments the temperature was slowly

- 129 -

raised from ndash80 degC in 10 degree increments to 10 degC Spectra were recorded at each interval For all other experiments spectra were recorded at ndash30 degC 2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

In the glovebox 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19 (0049 g 0133 mmol) and CpCo(C2H4)2 (0025 g 0139 mmol)99 were added to a Schlenk flask The flask was sealed brought out of the box connected to a vacuum manifold and freshly distilled degassed benzene (15 mL) added The mixture was heated to 70 degC on an oil bath for 23 h before being cooled to RT The solvent was removed in vacuo giving a black residue that was rapidly filtered through a plug of neutral alumina activity III (25 x 35 cm) eluting with a mixture of hexanes and THF (1001) under nitrogen and into a Schlenk flask The solvents were again removed in vacuo and the ensuing black residue recrystallized from acetone at ndash78 degC to give pure 78 (0057 g 56 ) as black crystals 1H-NMR (400 MHz acetone-d6) δ = 039 (s 36H) 481 (s 2H) 489 (m 4H) 736 (s 4H) ppm 13C-NMR (100 MHz acetone-d6) δ = 266 5372 5710 8284 12587 14542 15054 ppm UV-VIS (hexane) λmax (log ε) 197 (334) 221 (336 sh) 244 (344) 286 (363) 386 (279 sh) 439 (258) MS (FAB) 762 (M+ 100) HRMS calcd for C40H52Si4Co2 7621810 found 7621791 43 Computational Details for Chapter Two All calculations were performed using the GAUSSIAN03100 program GaussView 30101 and ChemCraft102 were employed to input structures as well as view output results Optimized geometries were obtained at the hybrid density functional theory (DFT) using Beckersquos three-parameter exchange-correlation functional103 containing the non-local gradient correction of Lee Yang and Parr104 (B3LYP) For optimization purposes a standard basis 3-21G105 was used for hydrogen and carbon atoms For cobalt the LANL2DZ106 basis set was applied with the outermost d function released yielding a triple-zeta d basis along with the effective core potentials (ECP) to describe the core electrons For the single point energy calculations the basis sets were increased to 6-31G107 for hydrogen 6-311G108 for carbon and the modified LANL2DZ basis as described above for cobalt with an added f-orbital coefficient109 The potential energy surfaces were mapped through a scan calculation a feature also available within the GAUSSIAN03 program Transition state structures were obtained in three different steps (i) determination of initial and final products or the minimum closest to a TS (ii) a linear QST2110 search for an initial guess of a TS and

- 130 -

(iii) input of the results from (ii) into a QST3 search Transition states and minima were confirmed by carrying out frequency calculations (using the same basis as that used for the optimizations)

Calculated structures for linear [3]phenylene(CpCo) (labels from Figures 29 and 210 in Section 24)

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

C 2878616000 ndash1675635000 ndash1461246000 C 3986441000 ndash2043582000 ndash0714088000 C 3986471000 ndash2043226000 0714700000 C 2878686000 ndash1674908000 1461732000 C 1740663000 ndash1265994000 0736724000 C 1740638000 ndash1266353000 ndash0736388000 H 2884721000 ndash1731772000 ndash2551997000 H 2884845000 ndash1730511000 2552509000 C 0311237000 ndash0833174000 0748280000 C 0311204000 ndash0833522000 ndash0748106000 C ndash0893980000 ndash0698348000 ndash1520584000 C ndash0893913000 ndash0697588000 1520749000 C ndash1996288000 ndash0532216000 0744771000 C ndash1996322000 ndash0532586000 ndash0744640000 C ndash3491040000 ndash0328769000 ndash0716524000 C ndash3490989000 ndash0328300000 0716632000 C ndash4645388000 ndash0172650000 ndash1448232000 C ndash4645276000 ndash0171672000 1448326000 C ndash5836534000 ndash0014205000 ndash0697760000

- 131 -

C ndash5836481000 ndash0013731000 0697841000 H ndash0905006000 ndash0741217000 ndash2609771000 H ndash0904887000 ndash0739873000 2609960000 H ndash4666353000 ndash0168153000 ndash2539086000 H ndash6785734000 0111682000 ndash1227959000 H ndash6785641000 0112502000 1228028000 H ndash4666162000 ndash0166493000 2539178000 Co 1455829000 0662094000 ndash0000295000 C 0672548000 2613322000 0000481000 C 1502831000 2459745000 1168426000 C 2819523000 2140942000 0722371000 C 2818808000 2141294000 ndash0723848000 C 1501651000 2460224000 ndash1168394000 H ndash0391329000 2836892000 0001070000 H 1172930000 2540112000 2200200000 H 3678957000 1932268000 1353707000 H 3677612000 1932967000 ndash1356152000 H 1170676000 2541059000 ndash2199789000 H 4894703000 ndash2369906000 1230670000 H 4894651000 ndash2370516000 ndash1229936000

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

C ndash3991583000 ndash2430244000 ndash0695300000 C ndash2895249000 ndash1923385000 ndash1446977000 C ndash1838331000 ndash1436925000 ndash0718218000 C ndash0460541000 ndash0772703000 ndash0748934000

- 132 -

C 0758545000 ndash0733408000 ndash1513161000 C 1871918000 ndash0586111000 ndash0739684000 C 3374782000 ndash0432509000 ndash0717168000 C 4533131000 ndash0322603000 ndash1448209000 C 5731498000 ndash0208370000 ndash0696796000 C 5731438000 ndash0207885000 0696952000 C 4533003000 ndash0321597000 1448333000 C 3374722000 ndash0432010000 0717261000 C 1871861000 ndash0585642000 0739747000 C 0758457000 ndash0732583000 1513259000 C ndash0460578000 ndash0772439000 0748991000 C ndash1838348000 ndash1436677000 0718485000 C ndash2895298000 ndash1922892000 1447371000 C ndash3991613000 ndash2429987000 0695830000 H ndash4853881000 ndash2841402000 ndash1229010000 H ndash2909366000 ndash1943431000 ndash2538196000 H 0770744000 ndash0814782000 ndash2600896000 H 4554949000 ndash0321315000 ndash2539049000 H 6684245000 ndash0118682000 ndash1227928000 H 6684140000 ndash0117859000 1228104000 H 4554722000 ndash0319567000 2539175000 H 0770611000 ndash0813312000 2601042000 H ndash2909450000 ndash1942588000 2538596000 H ndash4853932000 ndash2840954000 1229654000 Co ndash1032604000 1030206000 ndash0000179000 C ndash2903591000 1947430000 ndash0000175000 C ndash2211742000 2430689000 ndash1177143000 C ndash1026232000 3056089000 ndash0732194000 C ndash1026229000 3056139000 0731719000 C ndash2211730000 2430773000 1176747000 H ndash3829247000 1376180000 ndash0000150000 H ndash2513347000 2264399000 ndash2207387000 H ndash0243163000 3477094000 ndash1358586000 H ndash0243137000 3477190000 1358051000 H ndash2513304000 2264572000 2207015000

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 133 -

C 4829664000 ndash1220862000 0883782000 C 3649435000 ndash0895915000 1609183000 C 2478533000 ndash0900239000 0886069000 C 0985532000 ndash0699413000 0895282000 C ndash0207413000 ndash0351140000 1567281000 C ndash1295977000 ndash0355264000 0631690000 C ndash2799524000 ndash0368596000 0647705000 C ndash3950748000 0104186000 1252743000 C ndash5173877000 ndash0370408000 0725519000 C ndash5217559000 ndash1270006000 ndash0351644000 C ndash4043168000 ndash1754445000 ndash0967619000 C ndash2843350000 ndash1293792000 ndash0444950000 C ndash1365414000 ndash1319830000 ndash0538287000 C ndash0225558000 ndash1662005000 ndash1182029000 C 0928168000 ndash1009692000 ndash0554559000 C 2436156000 ndash1209374000 ndash0509824000 C 3575395000 ndash1530032000 ndash1215144000 C 4792344000 ndash1526592000 ndash0477473000 H 5781080000 ndash1237670000 1406156000 H 3693287000 ndash0679862000 2671420000 H ndash0279175000 ndash0037747000 2601166000 H ndash3939706000 0801901000 2083798000 H ndash6106757000 ndash0031072000 1165263000 H ndash6183419000 ndash1601741000 ndash0720200000 H ndash4097586000 ndash2453276000 ndash1795561000 H ndash0137803000 ndash2306368000 ndash2049380000 H 3570207000 ndash1781979000 ndash2270507000 H 5717527000 ndash1774506000 ndash0988963000 Co 0235674000 0924694000 ndash0006080000 C 1650242000 2605908000 ndash0261710000 C 0606451000 3071372000 0583798000

C ndash0633939000 2891762000 ndash0112192000 C ndash0354070000 2388098000 ndash1431110000 C 1060641000 2182627000 ndash1507942000 H 2701380000 2562827000 ndash0018620000 H 0717262000 3431891000 1595877000 H ndash1615358000 3123686000 0274491000 H ndash1077256000 2190401000 ndash2207047000

- 134 -

H 1601331000 1788686000 ndash2355167000

(d) Transition State 2 η3-benzene (249 kcalmol)

C 5059641000 ndash0675345000 0741440000 C 3868057000 ndash0242461000 1393542000 C 2691208000 ndash0611642000 0796692000 C 1164924000 ndash0568451000 0814993000 C 0001006000 ndash0193010000 1575722000 C ndash1162903000 ndash0569406000 0815406000 C ndash2689168000 ndash0613549000 0797134000 C ndash3866228000 ndash0245076000 1394017000 C ndash5057560000 ndash0678583000 0741882000 C ndash5030442000 ndash1430649000 ndash0426732000 C ndash3802288000 ndash1812828000 ndash1038342000 C ndash2662603000 ndash1392426000 ndash0404590000 C ndash1143695000 ndash1392940000 ndash0383227000 C 0001354000 ndash1885575000 ndash1010384000 C 1146183000 ndash1392203000 ndash0383465000 C 2665098000 ndash1390792000 ndash0404876000 C 3805017000 ndash1810598000 ndash1038596000 C 5032958000 ndash1427555000 ndash0427087000 H 6017043000 ndash0408623000 1174840000 H 3916675000 0338622000 2306082000 H 0001106000 0141040000 2603832000 H ndash3915179000 0335814000 2306664000 H ndash6015116000 ndash0412488000 1175329000

- 135 -

H ndash5963925000 ndash1737868000 ndash0883265000 H ndash3794877000 ndash2406462000 ndash1944276000 H 0001449000 ndash2505619000 ndash1894591000 H 3797948000 ndash2404400000 ndash1944423000 H 5966616000 ndash1734262000 ndash0883606000 Co ndash0000294000 1006304000 0016484000 C 1144150000 2811021000 ndash0317903000 C ndash0001831000 3236912000 0413780000 C ndash1150105000 2808519000 ndash0312717000 C ndash0712506000 2257800000 ndash1588662000 C 0702130000 2259464000 ndash1591918000 H 2174046000 2940434000 ndash0021226000 H ndash0000096000 3693787000 1391408000 H ndash2178919000 2935539000 ndash0011312000 H ndash1360790000 1903514000 ndash2375388000 H 1347563000 1907002000 ndash2381795000

Calculated structures for linear [5]phenylene CpCo (labels from Figures 211 and 212 in Section 24)

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

C ndash2147283000 ndash0385762000 ndash0741520000 C ndash2146881000 ndash0382747000 0740465000 C ndash0675330000 ndash0218887000 0741228000 C ndash0675503000 ndash0222208000 ndash0743565000 C 0535474000 ndash0309864000 ndash1519364000

- 136 -

C 1654024000 ndash0363787000 ndash0743565000 C 1653968000 ndash0359108000 0742223000 C 0535464000 ndash0301263000 1517648000 C 3146303000 ndash0437352000 0715394000 C 3146555000 ndash0442081000 ndash0715839000 H 0537903000 ndash0329735000 2601810000 H 0538062000 ndash0344229000 ndash2603354000 Co ndash1585768000 1444604000 ndash0004763000 C ndash2656365000 3118646000 0813641000 C ndash1264152000 3247968000 1115884000 C ndash0546296000 3292610000 ndash0128221000 C ndash1500173000 3225060000 ndash1199322000 C ndash2801883000 3099872000 ndash0616868000 H ndash3459184000 3033020000 1530368000 H ndash0824887000 3279284000 2101474000 H 0525240000 3366953000 ndash0237713000 H ndash1272392000 3239735000 ndash2254384000 H ndash3732669000 2998753000 ndash1154572000 C ndash3315848000 ndash0698077000 1516941000 C ndash3316515000 ndash0705270000 ndash1515890000 C ndash4404590000 ndash0970491000 0742487000 C ndash4404888000 ndash0974125000 ndash0739677000 H ndash3311463000 ndash0745189000 ndash2599679000 H ndash3310191000 ndash0733014000 2600900000 C ndash5857232000 ndash1346832000 ndash0713671000 C ndash5856902000 ndash1343302000 0718959000 C ndash6992149000 ndash1638138000 ndash1445564000 C ndash6991464000 ndash1630979000 1452826000 C 4314567000 ndash0501395000 ndash1493440000 C 4313844000 ndash0491124000 1494022000

C ndash8157130000 ndash1937355000 ndash0695553000 C ndash8156796000 ndash1933908000 0704865000 H ndash7013569000 ndash1630976000 2537309000 H ndash9075842000 ndash2169721000 1232475000 H ndash9076411000 ndash2175846000 ndash1221548000 H ndash7014707000 ndash1643790000 ndash2530023000 C 5464859000 ndash0553191000 0719930000 C 5465218000 ndash0558312000 ndash0718328000 C 6977989000 ndash0635007000 ndash0714777000 C 6977565000 ndash0629511000 0717833000 H 4313279000 ndash0484164000 2577745000 H 4314609000 ndash0502067000 ndash2577185000 C 8138196000 ndash0684071000 1451266000 C 8139115000 ndash0695400000 ndash1446980000 C 9348946000 ndash0746919000 0699256000 C 9349380000 ndash0752387000 ndash0693700000

- 137 -

H 8162380000 ndash0700716000 ndash2531270000 H 8160717000 ndash0680929000 2535584000 H 10294800000 ndash0791917000 1230058000 H 10295576000 ndash0801571000 ndash1223516000

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

C ndash8026536000 ndash2149127000 ndash0697047000 C ndash6872771000 ndash1801590000 ndash1447012000 C ndash5755909000 ndash1466198000 ndash0717983000 C ndash4305789000 ndash1041476000 ndash0739357000 C ndash3218268000 ndash0750848000 ndash1510952000 C ndash2077793000 ndash0315087000 ndash0749237000 C ndash0550342000 ndash0400850000 ndash0716361000 C 0616872000 ndash0404801000 ndash1489728000 C 1770640000 ndash0412395000 ndash0716060000 C 3300443000 ndash0457807000 ndash0715861000 C 4454767000 ndash0490291000 ndash1489427000 C 5616257000 ndash0520747000 ndash0712496000 C 5616269000 ndash0520699000 0712492000 C 4454793000 ndash0490190000 1489443000 C 3300455000 ndash0457762000 0715895000 C 1770651000 ndash0412347000 0716117000 C 0616894000 ndash0404700000 1489800000 C ndash0550335000 ndash0400796000 0716454000 C ndash2077818000 ndash0315060000 0749341000 C ndash3218306000 ndash0750915000 1510996000

- 138 -

C ndash4305781000 ndash1041534000 0739359000 C ndash5755900000 ndash1466256000 0717962000 C ndash6872758000 ndash1801708000 1446971000 C ndash8026533000 ndash2149171000 0696987000 H ndash6893447000 ndash1807486000 ndash2529846000 H ndash3199702000 ndash0827686000 ndash2591829000 H 0616147000 ndash0415875000 ndash2572166000 H 4455855000 ndash0492565000 ndash2571217000 H 4455901000 ndash0492389000 2571233000 H 0616188000 ndash0415693000 2572238000 H ndash3199790000 ndash0827916000 2591862000 H ndash6893430000 ndash1807681000 2529804000 Co ndash2237895000 1566525000 ndash0000035000 C ndash0770702000 3039808000 0000091000 C ndash1582333000 3276979000 1176306000 C ndash2906316000 3484053000 0731575000 C ndash2906172000 3484095000 ndash0731735000 C ndash1582100000 3277047000 ndash1176233000 H 0281094000 2798829000 0000215000 H ndash1247438000 3209109000 2198999000 H ndash3777291000 3625124000 1353071000 H ndash3777011000 3625160000 ndash1353424000 H ndash1246943000 3209260000 ndash2198847000 H ndash8933230000 ndash2423019000 ndash1224452000 H ndash8933222000 ndash2423113000 1224377000 C 7146943000 ndash0559737000 0717588000 C 7146931000 ndash0559786000 ndash0717614000 C 8302361000 ndash0588480000 1447040000 C 8302337000 ndash0588576000 ndash1447082000 C 9516918000 ndash0618789000 ndash0692883000 C 9516929000 ndash0618742000 0692823000 H 8324450000 ndash0589130000 2529610000 H 10461320000 ndash0642422000 1224406000 H 10461300000 ndash0642481000 ndash1224480000 H 8324409000 ndash0589299000 ndash2529653000

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 139 -

C ndash7810644000 ndash2064896000 ndash0088979000 C ndash6582065000 ndash2396690000 ndash0700394000 C ndash5469369000 ndash1694626000 ndash0259356000 C ndash4011414000 ndash1478684000 ndash0398743000 C ndash2839913000 ndash1679834000 ndash1045300000 C ndash1807973000 ndash0777407000 ndash0523048000 C ndash0288034000 ndash0728447000 ndash0497727000 C 0877200000 ndash0917515000 ndash1257428000 C 2033335000 ndash0625143000 ndash0541547000 C 3550975000 ndash0572504000 ndash0566638000 C 4702932000 ndash0775398000 ndash1323945000 C 5869717000 ndash0493099000 ndash0604711000 C 5877160000 ndash0049178000 0749672000 C 4719648000 0152978000 1509600000 C 3558389000 ndash0127834000 0791889000 C 2041313000 ndash0178303000 0818968000 C 0890228000 0010834000 1576182000

C ndash0275189000 ndash0290874000 0857465000 C ndash1777915000 ndash0332627000 0896504000 C ndash3000252000 ndash0144927000 1576583000 C ndash4087655000 ndash0414543000 0681649000 C ndash5565811000 ndash0681071000 0748878000 C ndash6769777000 ndash0358061000 1349731000 C ndash7902756000 ndash1078577000 0906205000 H ndash6531350000 ndash3165530000 ndash1463988000 H ndash2656944000 ndash2379915000 ndash1852763000

- 140 -

H 0873498000 ndash1259556000 ndash2286041000 H 4697058000 ndash1113491000 ndash2353481000 H 4726794000 0489146000 2539724000 H 0892018000 0335667000 2610226000 H ndash3107471000 0242268000 2582171000 H ndash6863567000 0403771000 2116786000 Co ndash2805901000 1045228000 ndash0126008000 C ndash1966955000 3131745000 ndash0137391000 C ndash3345106000 3172285000 0219040000 C ndash4105003000 2591218000 ndash0859559000 C ndash3194452000 2177424000 ndash1877135000 C ndash1861601000 2475718000 ndash1403791000 H ndash1139494000 3467521000 0469940000 H ndash3757304000 3575577000 1132204000 H ndash5178689000 2478840000 ndash0883920000 H ndash3449207000 1717975000 ndash2819531000 H ndash0944137000 2267497000 ndash1933863000 H ndash8711780000 ndash2586977000 ndash0395882000 H ndash8871888000 ndash0864282000 1346179000 C 7394568000 0005138000 0727783000

C 7387058000 ndash0441388000 ndash0634217000 C 8557433000 0273605000 1404315000

C 8542647000 ndash0629395000 ndash1349402000 C 9760631000 ndash0352464000 ndash0653366000 C 9767843000 0080954000 0667800000 H 8586089000 0612106000 2434348000 H 10716375000 0279405000 1157078000

H 10703753000 ndash0485281000 ndash1174332000 H 8560430000 ndash0966385000 ndash2380163000

(d) Transition state 4 η3-benzene (367 kcalmol)

- 141 -

C 7669717000 ndash2174926000 ndash0105923000 C 6450462000 ndash2458728000 0544003000 C 5349535000 ndash1733337000 0120322000 C 3893688000 ndash1505268000 0269179000 C 2708972000 ndash1942858000 0838638000 C 1596115000 ndash1239419000 0370186000 C 0149218000 ndash1103313000 0368184000 C ndash1061261000 ndash1583264000 0932639000 C ndash2167377000 ndash0965378000 0405284000 C ndash3686709000 ndash0866795000 0409630000 C ndash4872520000 ndash1347856000 0960688000 C ndash5997863000 ndash0728310000 0421450000 C ndash5941471000 0288854000 ndash0586107000 C ndash4758793000 0770529000 ndash1137452000 C ndash3629556000 0150846000 ndash0598044000 C ndash2119390000 0068600000 ndash0617626000 C ndash0945265000 0548559000 ndash1173832000 C 0191709000 ndash0072876000 ndash0643629000 C 1695402000 ndash0118964000 ndash0667389000 C 2835200000 0041396000 ndash1507494000 C 3981535000 ndash0415532000 ndash0796385000 C 5449049000 ndash0747489000 ndash0920326000 C 6638556000 ndash0473422000 ndash1556289000 C 7762417000 ndash1216205000 ndash1122513000 H 6396888000 ndash3209338000 1323030000 H 2647172000 ndash2772334000 1532449000 H ndash1099468000 ndash2356302000 1688990000 H ndash4914534000 ndash2116326000 1720908000 H ndash4717626000 1537921000 ndash1898781000 H ndash0906852000 1317204000 ndash1935050000 H 2849903000 0560387000 ndash2457942000 H 6730568000 0262385000 ndash2346085000 Co 3078365000 1106450000 0223118000 C 2432920000 3235925000 0352954000 C 3805628000 3232135000 ndash0000959000 C 4525686000 2519574000 1027488000 C 3591065000 2151422000 2051886000 C 2287258000 2550618000 1620273000

- 142 -

H 1625110000 3662123000 ndash0222202000 H 4237852000 3652387000 ndash0895767000 H 5588986000 2336674000 1044912000 H 3828106000 1629983000 2966790000 H 1363656000 2417646000 2161607000 H 8562189000 ndash2715853000 0187384000 H 8723754000 ndash1039126000 ndash1591154000 C ndash7467794000 0379383000 ndash0580257000 C ndash7522920000 ndash0639213000 0428535000 C ndash8594261000 0964602000 ndash1089561000 C ndash8706397000 ndash1090617000 0945872000 C ndash9887862000 ndash0485330000 0420145000 C ndash9834353000 0499744000 ndash0555359000 H ndash8574126000 1734202000 ndash1850912000 H ndash10757407000 0931123000 ndash0925119000 H ndash10851990000 ndash0807405000 0796463000 H ndash8770071000 ndash1858056000 1706995000

(e) Local minimum 3 η4-benzene (190 kcalmol)

C ndash7704806000 ndash1625445000 ndash0076324000 C ndash6491455000 ndash1789497000 ndash0801300000 C ndash5352262000 ndash1326936000 ndash0190371000 C ndash3836374000 ndash1127906000 ndash0291559000 C ndash2669014000 ndash1876939000 ndash0775878000 C ndash1540408000 ndash1361850000 ndash0248671000 C ndash0067088000 ndash1219487000 ndash0231176000 C 1147603000 ndash1746746000 ndash0723682000

- 143 -

C 2245517000 ndash1037457000 ndash0289605000 C 3767258000 ndash0910575000 ndash0313273000 C 4961694000 ndash1439625000 ndash0795996000 C 6075343000 ndash0726547000 ndash0354068000 C 5999362000 0418026000 0498208000 C 4804020000 0947684000 0980899000 C 3691158000 0235329000 0538756000 C 2171505000 0121554000 0570963000 C 0990404000 0649716000 1051234000

C ndash0139369000 ndash0066282000 0613306000 C ndash1640889000 ndash0139469000 0665899000 C ndash2708579000 0044357000 1607074000 C ndash3890300000 ndash0515482000 1069631000 C ndash5389479000 ndash0719093000 1106627000 C ndash6553177000 ndash0561696000 1815459000 C ndash7736166000 ndash1034716000 1182797000 H ndash6489929000 ndash2263627000 ndash1775522000 H ndash2743316000 ndash2692464000 ndash1483904000 H 1201969000 ndash2617287000 ndash1364047000 H 5019196000 ndash2306567000 ndash1440440000 H 4747029000 1814065000 1626168000 H 0933710000 1519855000 1692796000 H ndash2640951000 0605584000 2529735000 H ndash6590996000 ndash0122891000 2805220000 Co ndash3231943000 0870639000 ndash0218177000 C ndash2631117000 2925280000 ndash0475333000 C ndash4019450000 2955930000 ndash0137499000 C ndash4720042000 2167067000 ndash1095287000 C ndash3768150000 1717753000 ndash2089396000 C ndash2477085000 2188405000 ndash1710046000 H ndash1832546000 3399891000 0073720000 H ndash4448788000 3419647000 0737399000 H ndash5777018000 1951944000 ndash1095854000 H ndash3999907000 1119290000 ndash2956393000 H ndash1549894000 2013889000 ndash2232360000 H ndash8630326000 ndash1978241000 ndash0517433000 H ndash8683428000 ndash0939767000 1701100000 C 7524401000 0541032000 0473497000

C 7600630000 ndash0607844000 ndash0382149000 C 8637973000 1216338000 0890053000

C 8792152000 ndash1101412000 ndash0836674000 C 9961705000 ndash0402146000 ndash0407106000 C 9887895000 0708141000 0420266000 H 8602106000 2084773000 1535736000 H 10801526000 1207625000 0721410000

H 10931894000 ndash0752974000 ndash0739605000

- 144 -

H 8871661000 ndash1966753000 ndash1482602000

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

C 7143264000 ndash2348493000 0699665000 C 6037664000 ndash1857298000 1448523000 C 4969251000 ndash1391864000 0720257000 C 3582514000 ndash0743198000 0748195000 C 2358402000 ndash0737338000 1512136000 C 1240141000 ndash0634711000 0742222000 C ndash0262684000 ndash0516912000 0716494000 C ndash1428088000 ndash0430968000 1492584000 C ndash2574224000 ndash0346717000 0719319000 C ndash4098679000 ndash0233199000 0715866000 C ndash5251323000 ndash0147278000 1490294000 C ndash6408253000 ndash0063372000 0713741000 C ndash7934932000 0047490000 0717366000 C ndash9088044000 0130556000 1446914000 C ndash10299063000 0217080000 0692638000 C ndash10298939000 0215301000 ndash0693576000 C ndash9087782000 0126841000 ndash1447398000 C ndash7934811000 0045602000 ndash0717417000 C ndash6408180000 ndash0065400000 ndash0713264000 C ndash5251144000 ndash0151514000 ndash1489420000 C ndash4098619000 ndash0235099000 ndash0714599000 C ndash2574142000 ndash0348081000 ndash0717615000 C ndash1428022000 ndash0433439000 ndash1490677000

- 145 -

C ndash0262587000 ndash0517946000 ndash0714342000 C 1239930000 ndash0636111000 ndash0739947000 C 2357013000 ndash0742891000 ndash1511730000 C 3581891000 ndash0749703000 ndash0749006000 C 4968536000 ndash1397444000 ndash0717250000 C 6036190000 ndash1868351000 ndash1443314000 C 7142499000 ndash2353756000 ndash0691900000 H 8003789000 ndash2740125000 1230531000 H 6052031000 ndash1874231000 2531931000 H 2350726000 ndash0802237000 2593967000 H ndash1427931000 ndash0429806000 2574521000 H ndash5251989000 ndash0146640000 2572026000 H ndash9110076000 0132990000 2529448000 H ndash11241535000 0285430000 1223689000 H ndash11241318000 0282253000 ndash1224971000 H ndash9109613000 0126365000 ndash2529940000 H ndash5251637000 ndash0153720000 ndash2571150000 H ndash1427824000 ndash0434279000 ndash2572612000 H 2347832000 ndash0810535000 ndash2593375000 H 6049185000 ndash1893779000 ndash2526553000 H 8002469000 ndash2749449000 ndash1220666000 Co 4148367000 1055016000 ndash0009106000 C 5996101000 2006266000 0022069000 C 5276853000 2480887000 1185002000 C 4085420000 3079352000 0718350000 C 4110596000 3077077000 ndash0745160000 C 5316353000 2474554000 ndash1168669000 H 6921324000 1451094000 0038659000 H 5556549000 2314709000 2212960000 H 3287274000 3477873000 1325692000 H 3334253000 3474398000 ndash1380859000 H 5631980000 2304731000 ndash2185537000

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 146 -

C 4893664000 ndash1209972000 0735005000 C 4893573000 ndash1213475000 ndash0730870000 C 3475382000 ndash0763132000 ndash0743915000 C 3475432000 ndash0760320000 0747049000 C 2260316000 ndash0690973000 1520580000 C 1145205000 ndash0595973000 0744946000 C 1145156000 ndash0599246000 ndash0742744000 C 2260358000 ndash0697381000 ndash1517904000 C ndash0343192000 ndash0479177000 ndash0713609000 C ndash0343168000 ndash0476032000 0715380000 H 2252105000 ndash0735285000 ndash2601934000 H 2251901000 ndash0724154000 2604763000 Co 4601208000 0736083000 ndash0002055000 C 5960130000 2243618000 ndash0721946000 C 4640007000 2540538000 ndash1172530000 C 3804522000 2681992000 ndash0008876000 C 4632302000 2544967000 1160921000 C 5955467000 2247130000 0721276000 H 6816321000 2038808000 ndash1347044000 H 4312673000 2604006000 ndash2199136000 H 2745254000 2890841000 ndash0012873000 H 4298236000 2612143000 2185222000 H 6807361000 2044890000 1353015000 C 6022290000 ndash1649780000 1464200000 C 6022277000 ndash1656609000 ndash1457900000 C 7122289000 ndash2056771000 0719324000 C 7122311000 ndash2060028000 ndash0711126000 H 6027301000 ndash1702610000 2548102000 H 8011576000 ndash2407816000 1233935000 H 8011528000 ndash2413601000 ndash1224115000 H 6027432000 ndash1714310000 ndash2541551000 C ndash1512226000 ndash0382902000 1494684000 C ndash1512274000 ndash0389473000 ndash1493257000 C ndash2658093000 ndash0297761000 0720325000 C ndash2658103000 ndash0300923000 ndash0719236000 H ndash1511446000 ndash0379165000 2578406000

- 147 -

H ndash1511531000 ndash0390614000 ndash2576954000 C ndash4169046000 ndash0190131000 ndash0714237000 C ndash4169015000 ndash0186849000 0714915000 C ndash5325016000 ndash0103295000 1491764000 C ndash5325120000 ndash0110177000 ndash1491395000 C ndash6483203000 ndash0023670000 0713863000 C ndash6483258000 ndash0027061000 ndash0713749000 H ndash5325252000 ndash0101647000 2575308000 H ndash5325471000 ndash0113799000 ndash2574933000 C ndash7997403000 0080746000 0716440000 C ndash7997524000 0076500000 ndash0716680000 C ndash9155096000 0160872000 1448927000 C ndash9155379000 0152083000 ndash1449432000 C ndash10366775000 0240123000 0695134000 C ndash10366925000 0235844000 ndash0695874000 H ndash9178696000 0150122000 ndash2533721000 H ndash11311550000 0297904000 ndash1227155000 H ndash11311298000 0305233000 1226228000 H ndash9178228000 0165001000 2533216000

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

C 8266704000 ndash2005162000 0692734000 C 7088955000 ndash1708719000 1446000000 C 5966603000 ndash1428050000 0716466000

- 148 -

C 4483884000 ndash1054830000 0713802000 C 3355736000 ndash0795879000 1487813000 C 2219848000 ndash0542568000 0715155000 C 0748349000 ndash0122254000 0743952000 C ndash0460068000 ndash0300197000 1509394000 C ndash1583463000 ndash0354552000 0739667000 C ndash3088504000 ndash0455891000 0716671000 C ndash4249167000 ndash0553278000 1491353000 C ndash5399475000 ndash0634011000 0717623000 C ndash6922525000 ndash0754459000 0717051000 C ndash8076029000 ndash0852663000 1446746000 C ndash9285359000 ndash0940991000 0693505000 C ndash9286426000 ndash0927591000 ndash0694047000 C ndash8078221000 ndash0824629000 ndash1447252000 C ndash6923651000 ndash0740632000 ndash0717519000 C ndash5400498000 ndash0620402000 ndash0717994000 C ndash4251528000 ndash0525736000 ndash1491803000 C ndash3089431000 ndash0443610000 ndash0717063000 C ndash1585243000 ndash0344579000 ndash0740307000 C ndash0463450000 ndash0290395000 ndash1513612000 C 0748496000 ndash0127629000 ndash0751652000 C 2219455000 ndash0546002000 ndash0721683000 C 3355860000 ndash0802470000 ndash1493276000 C 4483583000 ndash1057975000 ndash0718022000 C 5966360000 ndash1431783000 ndash0719354000 C 7088265000 ndash1716549000 ndash1447876000 C 8266466000 ndash2008718000 ndash0693595000 H 9183427000 ndash2233531000 1224348000 H 7110060000 ndash1714392000 2528663000 H 3353411000 ndash0803478000 2570367000 H ndash0456292000 ndash0373454000 2590614000 H ndash4248665000 ndash0564171000 2573279000 H ndash8096828000 ndash0865292000 2529266000 H ndash10227269000 ndash1021159000 1223954000 H ndash10229127000 ndash0997490000 ndash1224546000 H ndash8100648000 ndash0816347000 ndash2529785000 H ndash4252664000 ndash0517117000 ndash2573754000 H ndash0464650000 ndash0354640000 ndash2595436000 H 3353541000 ndash0815213000 ndash2575752000 H 7108905000 ndash1727728000 ndash2530504000 H 9182976000 ndash2239822000 ndash1224379000 Co 1060170000 1739352000 ndash0013647000 C 0820599000 3762931000 0679296000 C 2023158000 3250849000 1217023000 C 2833506000 2814255000 0100512000 C 2185795000 3225276000 ndash1129991000

- 149 -

C 0924349000 3753677000 ndash0780133000 H ndash0033478000 4112410000 1239126000 H 2257663000 3114053000 2260457000 H 3791311000 2322414000 0171627000 H 2565428000 3065285000 ndash2126458000 H 0160713000 4098445000 ndash1460120000

(i) Local minimum 1 η4-benzene (190 kcalmol)

C 8767525000 ndash0664628000 0869444000 C 7569070000 ndash0364489000 1586360000 C 6400497000 ndash0535559000 0896308000 C 4872998000 ndash0456407000 0896648000 C 3729258000 ndash0166123000 1633430000 C 2558863000 ndash0367557000 0899969000 C 1050529000 ndash0274920000 0917771000 C ndash0154687000 0103769000 1545183000 C ndash1231288000 ndash0039565000 0606842000 C ndash2736221000 ndash0089835000 0603708000 C ndash3901526000 0467576000 1153370000 C ndash5054648000 ndash0104455000 0647800000 C ndash6579036000 ndash0120351000 0673091000 C ndash7732820000 0402806000 1194768000 C ndash8948594000 ndash0155119000 0702959000 C ndash8958839000 ndash1167887000 ndash0247745000 C ndash7753788000 ndash1707235000 ndash0785423000 C ndash6589806000 ndash1166201000 ndash0307896000

- 150 -

C ndash5063448000 ndash1158179000 ndash0339650000 C ndash3923750000 ndash1713712000 ndash0884954000 C ndash2743411000 ndash1141750000 ndash0370168000 C ndash1264100000 ndash1152263000 ndash0442985000 C ndash0114410000 ndash1509648000 ndash1047872000 C 1001557000 ndash0717865000 ndash0509678000 C 2529242000 ndash0815059000 ndash0456630000 C 3680301000 ndash1106705000 ndash1192448000 C 4847485000 ndash0909766000 ndash0461159000 C 6375435000 ndash0989198000 ndash0464503000 C 7517684000 ndash1280530000 ndash1157992000 C 8743181000 ndash1104009000 ndash0445669000 H 9720775000 ndash0544729000 1371431000 H 7610320000 ndash0024462000 2613574000 H 3742883000 0162901000 2664422000 H ndash0241422000 0534554000 2534230000 H ndash3894210000 1260341000 1890621000 H ndash7746436000 1191936000 1936109000 H ndash9890199000 0223840000 1083439000

H ndash9908180000 ndash1561665000 ndash0592194000 H ndash7783148000 ndash2497305000 ndash1525270000 H ndash3929534000 ndash2506814000 ndash1621099000 H 0005285000 ndash2235278000 ndash1842324000 H 3664139000 ndash1453900000 ndash2217556000 H 7520111000 ndash1625509000 ndash2184413000 H 9677483000 ndash1320445000 ndash0950825000 Co 0245526000 1194775000 ndash0183529000 C ndash0498660000 3223481000 ndash0207100000 C 0902667000 3310487000 0056983000 C 1591310000 2661311000 ndash1009417000 C 0610054000 2243094000 ndash1989593000 C ndash0681576000 2592200000 ndash1494981000 H ndash1289524000 3595536000 0425619000 H 1355880000 3721411000 0946130000 H 2657726000 2519341000 ndash1088515000 H 0823168000 1743521000 ndash2921425000 H ndash1626608000 2403559000 ndash1979282000

(j) Transition state 1 η3-benzene (356 kcalmol)

- 151 -

C ndash8901354000 ndash0223681000 ndash0743434000 C ndash7695103000 0220198000 ndash1360549000 C ndash6531343000 ndash0208573000 ndash0779115000 C ndash5007706000 ndash0207407000 ndash0796109000 C ndash3863247000 0247302000 ndash1433753000 C ndash2690760000 ndash0206508000 ndash0819013000 C ndash1184933000 ndash0153490000 ndash0843116000 C ndash0016095000 0217826000 ndash1588049000 C 1142075000 ndash0155798000 ndash0877497000 C 2665172000 ndash0195830000 ndash0859864000 C 3835813000 0283152000 ndash1437197000 C 4978920000 ndash0204857000 ndash0802474000 C 6505676000 ndash0216574000 ndash0771205000 C 7678527000 0226433000 ndash1319208000 C 8875127000 ndash0251684000 ndash0703235000 C 8845790000 ndash1112691000 0383544000 C 7616005000 ndash1570592000 0948642000 C 6475812000 ndash1107284000 0353147000 C 4945633000 ndash1092812000 0320013000 C 3774824000 ndash1565295000 0903163000 C 2628495000 ndash1080676000 0265289000 C 1119158000 ndash1093642000 0244670000 C ndash0052242000 ndash1637616000 0861793000 C ndash1193959000 ndash1109215000 0331010000 C ndash2676505000 ndash1073633000 0328062000 C ndash3841325000 ndash1514463000 0979035000 C ndash4995446000 ndash1053912000 0371366000 C ndash6522185000 ndash1052982000 0381089000 C ndash7676261000 ndash1483950000 0978498000 C ndash8892512000 ndash1041633000 0378747000

- 152 -

H ndash9850267000 0087677000 ndash1164894000 H ndash7723622000 0856176000 ndash2236504000 H ndash3873085000 0886115000 ndash2307512000 H ndash0031238000 0768624000 ndash2518870000 H 3857949000 0953892000 ndash2286176000 H 7723941000 0897606000 ndash2167700000 H 9831384000 0069893000 ndash1099633000 H 9779177000 ndash1450269000 0819087000 H 7614291000 ndash2243551000 1796930000 H 3751975000 ndash2237828000 1750478000 H ndash0016047000 ndash2343040000 1681308000 H ndash3832680000 ndash2159963000 1847727000 H ndash7691389000 ndash2121828000 1853393000 H ndash9834648000 ndash1354566000 0814012000 Co ndash0004249000 1140918000 0250383000 C 0931445000 3181201000 0326993000 C ndash0487068000 3279997000 0223542000 C ndash1069741000 2607436000 1368652000 C 0008159000 2107122000 2176577000 C 1235098000 2411215000 1492603000 H 1650004000 3565479000 ndash0380430000 H ndash1033454000 3774248000 ndash0564979000 H ndash2124544000 2537255000 1584462000 H ndash0094112000 1572170000 3107766000 H 2227446000 2134637000 1815486000

LUMO

HOMO

2887

239

00862

2496

1163

1382

1418

1312

0

3155

2767

0498

2588

1531

0831

Figure 47 Orbital coefficients of linear [5]phenylene

- 153 -

Figure 48 Top view of the contour plots of (a) the HOMO and (b) the LUMO of the [5]-phenylene ligand

- 154 -

Bad

Bad

Good Good

External cyclobutadiene coordination Internal cyclobutadiene coordination

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCpCoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

Figure 49 Resonance rationale for the increased stability of internal Co coordination in linear [5]phenylene

44 NMR Data for Chapter Two

- 155 -

Figure 410 1H-NMR data for the respective parent phenylene frames experimental (C6D6) and

calculated [NICS (1) B3LYP6-31+G] Assignments by NOESY DEPT HMBC and HSQC as applicable

- 156 -

Me3Si

Me3Si

SiMe3

SiMe3

1

23

4 56

7 89

10 1112

13 1415

16

17

18

Co

222

1490

1252

1450

1433

1151

744

730

11091121

14161504

11211109

1540

1499

1224

1486

217

801

SiMe3

SiMe3

Me3Si

Me3Si

Co

802

261

1484

1256

1433

1494

1155

739

781

1360

1394

269

SiMe3

SiMe3

Co

802

1294

1149

1426

1502

1194

738

779

1363

1393

268

SiMe3

SiMe3

1241

1276

8029

725

1155

1493

1430

1256

1482

222

Co

796

678674 675 796

436

037032662

724 683 747

444

TMS

TMS

TMS

TMS

213

1474

1211

1538

1499

1112

623 685

SiMe3

SiMe3Me3Si

Me3Si SiMe3

SiMe3Me3Si

Me3Si459 Co

589 681 672 745

2201204

15131096

1535

2221252

1480

1433

1149741

801

1501 1490

1475

Figure 411 Comparison of 1H-NMR (blue) and 13C-NMR assignments (C6D6)

NICS-Scan calculations Methods The free ligands were optimized at the B3LYP6-31G and the CpCo complexes at the B3LYPLANL2DZ computational levels Analytical frequency calculations were executed to ensure real minima (Nimag = 0) GIAO-B3LYP6-31+G was used to calculate NICS values The NICS-scan procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (ipc or NICSXY) and out-of-plane components (oopc or NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their interpretation

- 157 -

Since there are no published NICS-scan studies of transition metal complexed cyclic polyenes we benchmark the method with (C6H6)Cr(CO)3

53

Figure 412 NICS-scan of benzene (left) and (benzene)Cr(CO)3 (right)

The shape of the oopc curve suggests that the diamagnetic ring current in the ligand is diminished on complexation although still prevalent Thus at r = 0 Aring (ie at the benzene plane) the oopc value [NICSZZ(0)] of the complex is less negative than that of benzene and the minimum of the curve is less negative and occurs at a larger distance (ndash29911 vs ndash31910) A larger change is observed in the ipc (which is governed by the σ electrons) which shows far more negative values in the complex relative to benzene itself (eg ndash55400 vs ndash5900 and ndash13910 vs ndash0910) Therefore isotropic NICS values are misleading with respect to the diatropism in the complex because they originate largely from the diamagnetic effect of the σ framework NICS-scans for the four-membered ring B in linear [3]phenylene and its CpCo complex are shown below

00 05 10 15 20 25 30 35 40

-34-32-30-28-26-24-22-20-18-16-14-12-10

-8-6-4-202

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

oopc ipc isotropic

pp

m

r

- 158 -

Figure 413 NICS-scan above ring B of linear [3]phenylene (left) and its CpCo complex (right) Inspection of the shape and values of the oopc curve shows that the four-membered ring in the free ligand is strongly paratropic This picture changes on CpCo complexation At or close to the ring plane the values are much less positive (12100 vs 88000) become negative at greater distance and reach a minimum of -16112 Consequently the presence of the metal clearly reduces paratropic character The ipc curve is similar to that of (benzene)Cr(CO)3 Therefore again isotropic NICS values are misleading with respect to an assessment of the size of ring current effects The two isomeric CpCo complexes of linear [5]phenylene as depicted next behave in an analogous manner and engender the same conclusions as above

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

- 159 -

Figure 414 NICS-scans of linear [5]phenylene and its CpCo complexes Top left - ring B of the free ligand Top right - ring B complexed to CpCo Bottom left - ring D of the free ligand

Bottom right - ring D complexed to CpCo The effect of CpCo complexation is also reflected in the NICS-scan properties of the remaining rings To illustrate this point the NICS-scans of the central cyclohexatrienoid ring C of linear [3]phenylene are shown below first for the free ligand then for the cyclobutadiene complex

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

- 160 -

Figure 415 NICS-scans of ring C of linear [3]phenylene Left - as a free ligand Right as a

CpCo complex of the neighboring cyclobutadiene ring B The oopc curve clearly reveals a diminution of paratropism Thus at the ring plane the oopc values of the free ligand and of the complex are 177 and 110 ppm respectively Both plots show shallow and relatively distant minima at ndash3417 and ndash7316 respectively an indication of larger diamagnetic character of the latter While the ipc values also become more negative on complexation this effect is far smaller The tables that follow provide an overview of the NICS-scan results over all component rings in linear [3]- and [5]phenylene complexed and uncomplexed The diagnostic shape of the oopc curve is designated NM for no minimum indicating paratropism and M for minimum indicating diatropism Specific values are given at r = 0 Aring r = 10 Aring and the minimum (if diamagnetic) Table 416 NICS-scan Details of the oopc for Linear [3]Phenylene and its CpCo Complex at

Ring B

Ring Shape oopc00 oopc10 Minimum A M 71 ndash107 ndash11813 AndashCpCo M ndash65 ndash228 ndash22811 B NM 880 381 BndashCpCo M 121 ndash151 ndash16112 C M 177 ndash01 ndash3418 CndashCpCo M 116 ndash17 ndash9315 D NM 880 381 DndashCpCo NM 704 237 E M 71 ndash107 ndash11813 EndashCpCo M 15 ndash148 ndash15212

00 05 10 15 20 25 30 35 40

-8-6-4-202468

101214161820

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-14-12-10

-8-6-4-202468

1012

oopc ipc isotropic

pp

m

r

- 161 -

Table 417 NICS-Scan Details of the oopc for Linear [5]Phenylene and its CpCo Complex at Ring B

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M ndash62 ndash227 ndash22811 B NM 898 396 BndashCpCo M 137 ndash148 ndash15612 C M 176 00 ndash3317 CndashCpCo M 152 ndash09 ndash8415 D NM 846 357 DndashCpCo NM 668 223 E M 164 ndash12 ndash4116 EndashCpCo M 142 ndash17 ndash5315 F NM 846 357 FndashCpCo NM 807 340 G M 176 00 ndash3317 GndashCpCo M 161 ndash04 ndash3216 H NM 898 396 HndashCpCo NM 867 378 I M 83 ndash97 ndash10813 IndashCpCo M 64 ndash109 ndash12113

Table 418 NICS-scan Details of the oopc for Lnear [5]Phenylene and its CpCo Complex at

Ring D

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M 19 ndash150 ndash15912 B NM 898 396 BndashCpCo NM 717 256 C M 176 00 ndash3317 CndashCpCo M 110 ndash122 ndash12210 D NM 846 357 DndashCpCo M 151 ndash169 ndash17311 E M 164 ndash12 ndash4116 EndashCpCo M 151 ndash169 ndash17311 F NM 846 357 FndashCpCo NM 685 231 G M 176 00 ndash3317 GndashCpCo M 148 ndash15 ndash5415 H NM 898 396 HndashCpCo NM 850 370

I M 83 ndash97 ndash10813

- 162 -

The data clearly show that on CpCo complexation the paramagnetic ring current contributions decrease (or the diamagnetic ring current contributions increase) The strongest effect is on the complexed cycle but it occurs for all rings even the most remote (eg I in the linear [5]phenylene complexed at ring B) Thus upon complexation the paratropic (and by inference antiaromatic) character of the phenylenes decrease 45 Experimental Section for Chapter Three Angular [3]phenylene 2290 angular [4]phenylene 17111 and [7]heliphene10 were prepared according to the literature Ni(COD)(PMe3)2

112 To a solution of Ni(COD)2 (0275 g 10 mmol) in dry and vigorously degassed THF (10 mL) PMe3 (020 mL 0150 g 20 mmol) was added via syringe in a single portion After stirring at RT for 24 h the mixture was transferred using a canula and filtered under Ar to remove unreacted starting material The solvent was removed on the high vacuum line and the resulting product dried for 3 h It is extremely air sensitive and must be manipulated under an inert atmosphere at all times Yellow solid (0306 g 96 ) 1H-NMR (400 MHz C6D6) δ = 412 (d J = 112 Hz 4 H) 238 (br t J = 52 Hz 4 H) 225 (t J = 52 Hz 4 H) 102 (d J = 32 Hz 18 H) ppm 31P-NMR (162 MHz C6D6) δ = ndash946 (s) ppm Adducts of diphenylacetylene 88 to angular [3]phenylene 22 ndash compounds 89 and 90

In a glove box an Ace pressure tube was charged with angular [3]phenylene 22 (0014 g 006 mmol) diphenylacetylene 88 (0098 g 0055 mmol) THF (5 mL) and Ni(COD)(PMe3)2 (70 microL 008 M in THF 0006 mmol) The reaction vessel was tightly sealed removed from the glovebox and heated to 75ndash80 oC (oil bath) for 23 h After cooling to RT the solvent was removed by rotary evaporation and the residue purified by flash chromatography on silica gel using gradient elution (101 and then 81 hexaneCH2Cl2) After a small amount of angular [3]phenylene 22 (0001 g) the monoadduct 89 (0004 g 20 ) eluted to give a yellow solid mp 195ndash196 degC 1H-NMR (500 MHz CDCl3) δ = 853 (d J = 84 Hz 1 H) 831 (d J = 80 Hz 1 H) 755 (ddd J = 16 64 80 Hz 1 H) 740ndash732 (m 2 H) 725ndash715 (m 6 H) 715ndash711 (m 2 H) 708 (d J = 65 Hz 2 H) 704 (d J = 80 Hz 1 H) 648 (t J = 72 Hz 1 H) 643 (d J = 70 Hz 1 H) 624 (t J = 75 Hz 1 H) 401 (d J = 70 Hz 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1525 15101 15096 1495 1399 13883 13879 1342 1320 1312

- 163 -

13083 13075 1282 1280 1277 1276 1275 1268 1266 1265 1264 1250 1235 1223 1179 1164 1156 ppm one peak in the region δ = 128ndash126 ppm is

presumed to be accidentally isochronous IR (KBr) ν~ = 3060 1490 1481 1442 1415 1159 1072 755 734 698 cmndash1 UV-Vis (CH3CN) λmax (log ε) 233 (442) 265 (450) 278 (sh) 294 (sh) 306 (447) 318 (449) 329 (sh) 380 (344) 399 (366) 420 (366) nm MS (70 eV) mz () 405 [M++1] (35) 404 [M+] (100) 326 (13) HRMS (EI) calcd for C32H20 4041565 found 4041571 Elemental analysis calcd for C32H20 C 9502 H 498 found 9479 460 Subsequent elution furnished 5678-tetraphenylpicene (90) (0009 g 59 ) as a white solid mp 325ndash327 degC the molecule exhibits hindered rotation of the 67-phenyl groups on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 891 (s 2 H) 885 (d J = 84 Hz 2 H) 769 (ddd J = 28 52 80 Hz 2 H) 750ndash744 (m 4 H) 744ndash732 (m 4 H) 720 (tt J = 16 72 Hz 2 H) 696 (dt J = 08 76 Hz 2 H) 689 (tt J = 09 76 Hz 2 H) 662 (br s 4 H) 617 (d J = 76 Hz 2 H) 607 (br s 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1403 1401 1377 1367 1335 1325 1324 1306 1300 1295 1292

1283 1277 1269 1264 1263 1262 1256 1254 1228 1213 ppm IR (KBr) ν~ = 3051 2922 1599 1490 1467 1442 1263 1072 1027 758 702 630 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (461) 307 (474) 352 (417) 366 (414) nm MS (70 eV) mz () 583 [M++1] (52) 582 [M+] (100) 505 (24) 504 (9) 426 (7) HRMS (EI) calcd for C46H30 5822348 found 5822336 1278-Tetraphenylbenzo[c]chrysene (91)

In a glovebox an Ace pressure tube was charged with 88 (0020 g 0050 mmol) diphenylacetylene 88 (0026 mg 0148 mmol) Ni(COD)(PMe3)2 (62 microL of a 008 M solution in THF) and THF (5 mL) The reaction vessel was sealed removed from the glovebox and heated to 85 degC for 39 h After removal of the solvent the residue was purified by flash chromatography on silica gel (eluting with 81 hexaneCH2Cl2) producing a white solid (0023 g) which was found to consist of starting material (88 18 mg) 90 (0001 g 6 ) and 91 Further purification by chromatography afforded pure 91 (0017 g 74 ) as a white solid mp 273ndash274 degC the 12-phenyl groups of 91 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 869 (d J = 95 Hz 1 H) 830ndash822 (m 1 H) 801 (d J = 75 Hz 1 H) 780ndash747 (m 2 H) 770 (ddd J = 10 70 85 Hz 1 H) 762 (dt J = 15 75 Hz 1 H) 753 (ddd J = 15 70 85 Hz 1 H) 738ndash732 (m 2 H) 730 (td J = 15 75 Hz 1 H) 729ndash722 (m 6 H) 722ndash717 (m 2 H) 717ndash710 (m 2 H) 710ndash695 (m 3 H) 680ndash640 (m 3 H) 635 (d J = 70 Hz 1 H) 623ndash595 (br s 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1418 1400 1395 1394 1378 1377 1375 1357 1323 1322 1316 1314 13113 13107 1309 1308 1307 1305 1296 1295 1288 1282 1277 1275 1274 1273 1270 12653 12647 1264 1260 1256 1253 1252 1251

- 164 -

1243 1231 1208 ppm due to extensive signal overlap four peaks are presumed to be isochronous in the regions δ = 132ndash130 and 128ndash125 ppm IR (KBr) ν~ = 3058 1601 1489 1442 1263 1073 773 762 736 699 628 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 250 (487) 313 (511) 340 (sh) nm MS(EI) mz () 583 (M++1 72) 582 (M+ 100) 505 (24) 391 (13) HRMS (EI) calcd for C46H30 5822348 found 5822341 Elemental analysis calcd for C46H30 C 8933 H 500 found 8914 493 Ni(PhCequivCPh)(PMe3)2 (92)91

In a glove box PMe3 (203 microL 0152 g 20 mmol) was mixed with a suspension of Ni(COD)2 (0275 g 10 mmol) in hexane (15 mL) Diphenylacetylene 88 (0178 g 10 mmol) was then added in one portion resulting in an immediate color change from yellow to red The mixture was stirred at room temperature for 195 h during which the color gradually turning returning to yellow Upon concentration (to ~5 mL) a yellow precipitate formed collected by filtration under nitrogen The resulting powder 92 (0370 g 95 ) was dried under vacuum providing a yellow solid 1H-NMR (500 MHz C6D6) δ = 751 (d J = 75 Hz 4 H) 717 (t J = 75 Hz 4 H) 702 (t J = 75 Hz 2 H) 101 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1406 1287 1279 196 (d JC-P = 188 Hz) ppm 31P-NMR (162 MHz C6D6) δ = ndash1282 (br s) ppm Adducts of 3-hexyne to angular [3]phenylene 22 ndash compounds 104 and 105

In a glovebox 22 (0014 mg 0060 mmol) 3-hexyne 103 (57 microL 0004 g 0050 mmol) Ni(COD)(PMe3)2 (0002 g 0005 mmol) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 14 h Flash chromatography on silica gel gave a first fraction that was recrystallized from CH2Cl2 to provide pure 104 (70 mg 45 ) as a yellow solid mp 169ndash170 degC 1H-NMR (500 MHz CDCl3) δ = 843 (d J = 70 Hz 1 H) 821 (d J = 75 Hz 1 H) 795 (d J = 70 Hz 1 H) 752 (dt J = 10 70 Hz 1 H) 748 (dt J = 10 70 Hz 1 H) 697 (d J = 75 Hz 1 H) 673ndash662 (m 3 H) 655 (d J = 55 Hz 1 H) 307 (q J = 75 Hz 2 H) 299 (q J = 75 Hz 2 H) 133 (t J = 75 Hz 3 H) 130 (t J = 75 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1530 1516 1504 1471 1360 1330 13129 13127 1307 1282 1279 1267 1263 1259 1246 1239 1228 1179 1159 1156 232 214 164 149 ppm IR (KBr) ν~ = 3045 2960 1600 1481 1414 1261 1197 1159 758 740 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (463) 299 (sh) 309 (460) 320 (462) 331 (452) 380 (356) 399 (374) 419 (371) nm MS (70 eV) mz () 309 [M++1] (26) 308 [M+] (100) 293 [M+ndash15] (8) 278 [M+ndash30] (21) HRMS (EI) calcd for C24H20 3081565 found 3081666

- 165 -

A second fraction was 105 (0002 g 11 ) isolated as a yellow solid mp 120ndash122 degC 1H-NMR (400 MHz CDCl3) δ = 830 (d J = 72 Hz 1 H) 797 (d J = 76 Hz 1 H) 761 (d J = 80 Hz 1 H) 761ndash749 (m 2 H) 700 (d J = 80 Hz 1 H) 699 (d J = 72 Hz 1 H) 674 (quint J = 76 Hz 2 H) 658 (d J = 64 Hz 1 H) 307 (q J = 76 Hz 2 H) 302 (q J = 76 Hz 2 H) 132 (t J = 76 Hz 3 H) 131 (t J = 76 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1525 1519 1489 1472 1356 1345 1324 1318 1288 1283 1279 1273 1259 1252 1251 1250 1241 1179 1165 1160 2213 2205 149 146 ppm IR (KBr) ν~ = 3063 2958 2925 1490 1442 1417 1262 1147 1099 822 762 730 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 281 (434) 291 (448) 303 (460) 313 (sh) 369 (346) 389 (373) 410 (377) nm MS (70 eV) mz () 309 [M++1] (28) 308 [M+] (100) 293 [M+ndash15] (13) 278 [M+ndash30] (21) 226 (22) 149 (29) HRMS (EI) calcd for C24H20 3081565 found 3081664 Adducts of 14-dimethoxy-2-butyne to angular [3]phenylene 22 ndash compounds 107 and 108

In a glovebox 22 (0011 g 0050 mmol) 14-dimethoxybut-2-yne 106 (0034 g 030 mmol) Ni(COD)(PMe3)2 (63 microL of a 008 M solution in THF) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 165 h The 1H-NMR spectrum of the crude indicated the formation of 107 and 108 in the ratio of 61 Flash chromatography on silica gel gave first 107 (0012 g 68 ) as a yellow solid mp 150ndash151 degC 1H-NMR (400 MHz CDCl3) δ = 841 (dd J = 32 64 Hz 1 H) 819 (d J = 80 Hz 1 H) 810 (dd J = 36 64 Hz 1 H) 754 (dd J = 36 64 Hz 2 H) 700 (d J = 80 Hz 1 H) 676 (t J = 64 Hz 1 H) 674ndash665 (m 2 H) 656 (d J = 60 Hz 1 H) 493 (s 2 H) 488 (s 2 H) 353 (s 3 H) 345 (s 3 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1527 1513 1509 1484 1336 1318 1316 1309 1296 1283 1282 1272 1270 1259 1255 1238 1225 1183 1166 1161 677 675 584 575 ppm IR (KBr) ν~ = 3072 2927 1485 1446 1417 1376 1185 1097 956 898 821 743 730 cmndash1 MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (100) 308 [M+ndash38] (26) 293 (34) 280 (15) 265 (44) HRMS (EI) calcd for C24H20O2 3401463 found 3401466 Further elution provided 108 (0002 g 9 ) as a yellow solid mp 156ndash157 degC 1H-NMR (400 MHz CDCl3) δ = 831ndash824 (m 1 H) 813ndash806 (m 1 H) 775 (d J = 80 Hz 1 H) 763ndash756 (m 2 H) 702 (d J = 80 Hz 1 H) 699 (d J = 64 Hz 1 H) 681ndash670 (m 2 H) 660 (d J = 64 Hz 1 H) 493 (s 2 H) 487 (s 2 H) 353 (s 3 H) 351 (s 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1523 1517 1505 1470 1327 1322

- 166 -

1316 1315 1297 1285 1282 1276 1268 1266 12564 12555 1252 1181 1168 1165 6804 6801 5838 5835 ppm IR (KBr) ν~ = 2925 1498 1415 1379 1262 1187 1095 1061 940 930 814 750 734 717 cmndash1 UV-Vis (CH3CN) λmax (log ε) 237 (458) 287 (462) 298 (472) 314 (sh) 371 (357) 387 (380) 407 (386) nm MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (56) 308 [M+ndashMeOH] (8) 293 (27) 279 (17) 265 (24) HRMS (EI) calcd for C24H20O2 3401463 found 3401456 Optimized cycloaddition reaction between 22 and 88 In a glovebox a round bottom flask was charged with 22 (0058 g 0257 mmol) and Ni(COD)(PMe3)2 (0008 g 0034 mmol) Both reagents were then dissolved in THF (100 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0093 g 0521 mmol) in THF (20 mL) was taken up in a gas-tight syringe and slowly added over 13 h via syringe pump to the boiling mixture of 22Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 6 h After this time mixture was cooled to RT and the solvent removed by rotary evaporation to give a yellow residue The crude product was passed through a plug of silica gel eluting with a mixture of hexanesCH2Cl2 (101) to afford a yellow solid Analysis of the product by 1H-NMR (using the solvent peak of CDCl3 as the internal standard) revealed the presence of 89 and 90 in a 1387 ratio Adducts of diphenylacetylene 88 to angular [4]phenylene 17 ndash compounds 130ndash134 In a glovebox angular [4]phenylene 17 (0036 g 012 mmol) diphenylacetylene 88 (0018 g 010 mmol) and Ni(COD)(PMe3)2 (125 microL of a 008 M solution in THF) were added to an Ace pressure tube and dissolved in THF (6 mL) The reaction vessel was sealed removed from the glovebox and stirred at 75 degC for 5 h Flash chromatography

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph Ph PhPh Ph

132131

133 134

130

- 167 -

on silica gel gave starting material (0013 g of 17) as well as a yellow residue Further purification of the latter by preparative TLC afforded (in order of elution) 132 131 133 134 and 139 Compound 130 (0008 g 28 ) was obtained as a white solid mp 360ndash363 degC (decomp) the phenyl groups located on the central benzene ring of 130 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 904 (d J = 90 Hz 2 H) 895 (d J = 90 Hz 2 H) 881 (d J = 85 Hz 2 H) 765 (ddd J = 15 65 80 Hz 2 H) 742ndash736 (m 4 H) 734 (dd J = 10 85 Hz 2 H) 721 (tt J = 15 75 Hz 2 H) 716 (d J = 75 Hz 2 H) 698 (dd J = 05 80 Hz 2 H) 693 (tt J = 10 85 Hz 2 H) 681 (tt J = 10 70 Hz 2 H) 676 (t J = 75 Hz 4 H) 656 (t J = 70 Hz 4 H) 633 (d J = 70 Hz 4 H) 614 (d J = 75 Hz 2 H) 595 (d J = 70 Hz 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 14058 14057 1403 1394 1375 1374 1345 1341 1336 1327 1324 1309 1308 1301 1294 1292 1282 1276 1268 1263 12622 12619 1259 1257 1254 1250 1227 1214 1212 ppm IR (KBr) ν~ = 3052 2923 1600 1491 1440 1261 1076 1029 809 783 759 747 700 631 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 248 (498) 306 (sh) 329 (520) 388 (463) nm MS(FAB) mz () 836 [M++2] (18) 835 [M++1] (42) 834 [M+] (54) 757 (8) HRMS (FAB) calcd for C66H42 8343287 found 8343280 Compound 131 (0003g 6) was isolated as yellow solid mp 251ndash253 degC (decomp) 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 775 (dt J = 10 80 Hz 1 H) 752 (dt J = 10 80 Hz 1 H) 746 (d J = 80 Hz 1 H) 737 (d J = 65 Hz 1 H) 726ndash721 (m 5 H) 721ndash716 (m 2 H) 716ndash711 (m 5 H) 709 (t J = 75 Hz 1 H) 705 (d J = 80 Hz 1 H) 699 (d J = 70 Hz 1 H) 619 (d J = 60 Hz 1 H) 614 (d J = 60 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1502 1492 1491 1490 1485 1444 1394 1392 1382 1371 1367 1351 13271 13268 13092 13088 1299 12898 12896 1283 12764 12760 1274 12654 12652 1261 1253 1245 1195 1184 1172 1138 1129 ppm one peak is presumed to be accidentally isochronous in the region between δ = 130ndash124 ppm IR (KBr) ν~ = 3023 2921 1602 1478 1371 1262 1026 809 795 748 725 695 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 252 (473) 285 (456) 320 (453) 335 (462) 353 (437) 370 (432) 410 (376) 431 (372) nm MS (FAB) mz () 479 [M++1] (27) 478 [M+] (70) 300 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781718 Molecule 132 (0002 g 5 ) was acquired as a yellow solid 1H-NMR (500 MHz CDCl3) δ = 726ndash721 (m 2 H) 716ndash709 (m 6 H) 695ndash690 (m 2 H) 676 (d J = 80 Hz 2 H) 673 (d J = 75 Hz 2 H) 671 (t J = 75 Hz 2 H) 665 (t J = 70 Hz 2 H) 658 (d J = 65 Hz 2 H) 648 (d J = 65 Hz 2 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1516 1510 1497 1490 1391 1372 1310 1303 1283 1281 1277 1275 1273 1264 1216 1168 1163 ppm UV-Vis (CH2Cl2) λmax (log ε) 254 (476) 294 (sh) 300 (465) 322 (sh) 338 (392) 376 (400) nm MS (FAB) mz () 479 [M++1] (50) 478 [M+] (86) 391 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781723 Adduct 133 (0017 g 33 ) was isolated as a red crystalline solid mp 290ndash291 degC 1H-NMR (500 MHz CDCl3) δ = 800 (d J = 80 Hz 2 H) 720ndash713 (m 6 H) 708ndash702 (m 4 H) 690 (d J = 80 Hz 2 H) 648 (t J = 70 Hz 2 H) 642 (d J = 70 Hz 2 H) 623 (t J = 70 Hz 2 H) 393 (d J = 70 Hz 2 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1522 1509 1506 1496 1392 1359 1315 1309 1282 1278 1277 1266 1250 1232 1181 1166 1157 ppm IR (KBr) ν~ = 3057 1489 1441 1412 1273

- 168 -

1161 810 738 709 690 623 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 271 (474) 285 (469) 345 (460) 353 (454) 414 (483) 432 (381) 460 (363) nm MS (70 eV) mz () 479 [M++1] (46) 478 [M+] (100) 400 (10) HRMS (EI) calcd for C38H22 4781722 found 4781719 Compound 134 (0009 g 27 ) was obtained as a yellow solid mp 178ndash180 degC the phenyl groups of this molecule located at the bay regions of the phenanthrene subunit are static while the others exhibit hindered rotation on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 880 (d J = 88 Hz 1 H) 879 (d J = 88 Hz 1 H) 863 (d J = 92 Hz 1 H) 834 (d J = 80 Hz 1 H) 770ndash758 (m 1 H) 748ndash732 (m 4 H) 727ndash721 (m 2 H) 721ndash710 (m 2 H) 706 (d J = 80 Hz 1 H) 702ndash691 (m 3 H) 684 (t J = 74 Hz 1 H) 673 (br s 2 H) 655 (t J = 76 Hz 2 H) 650ndash638 (m 3 H) 630ndash610 (m 4 H) 590 (d J = 76 Hz 2 H) 410 (d J = 68 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1527 1510 1509 1494 1403 1400 1399 1396 1373 1371 1339 1335 1330 1325 1324 1317 1309 1306 1305 1304 1299 1295 1291 1283 1282 1281 1277 1275 1272 1269 1268 12632 12627 1261 12562 12556 1254 1253 1239 1226 1216 1209 1180 1162 1154 ppm three peaks are presumed to be accidentally isochronous in the region δ = 128ndash125 ppm IR (KBr) ν~ = 2964 1262 1096 1022 801 701 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 267 (501) 303 (497) 335 (489) 361 (sh) 379 (464) 427 (402) 456 (377) nm MS(FAB) mz () 658 [M++2] (22) 657 [M++2] (67) 656 [M+] 1(00) 579 (12) 502 (7) HRMS (FAB) calcd for C52H32 6562504 found 6562492 Cycloaddition reaction between [7]heliphene 142 and diphenylacetylene 88 In a glovebox a round bottom flask was charged with 142 (0008 g 0152 mmol) and Ni(COD)(PMe3)2 (0001 g 0003 mmol) The mixture was then dissolved in THF (25 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0016 g 300 mmol) in THF (10 mL) was taken up in a gas-tight syringe and slowly added over 12 h via syringe pump to the boiling mixture of 142Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 12 h After this time it was cooled to RT and the solvent removed by rotary evaporation to give an orange residue The crude product was chromatographed on silica gel (25 x 165 cm) eluting first with hexaneCH2Cl2 (101 then 51) The first product collected was diphenylacetylene 88 (0005 g) followed by a yellow band Analysis of the isolated yellow solid (0002 g) revealed a large mixture of products MS(FAB) mz () 532 (70) 664 (25) 700 (13) 732 (16) 911 (21) 1056 (11) 1234 (4) 1412 (5) 46 Computational Details for Chapter Three All geometries of intermediates and transition states were optimized fully without symmetry constraints using the Gaussian 03 program100 The DFT computations were carried out using the B3LYP functional as implemented in Gaussian The nickel atom was described by a double-zeta basis set (LANL2DZ)113 and the 6-31G(d) basis set114

- 169 -

was used for the other elements Frequency calculations were performed to confirm the nature of the stationary points and to obtain zero-point energies (ZPE) The connectivity between stationary points was established by intrinsic reaction coordinate calculations (IRC) The Chemcraft program102 was used to draw the calculated structures

47 References

1) Harvey R G Polycyclic Aromatic Hydrocarbons Wiley-VCH New York 1997 2) (a) Chem Rev 2001 101 1115ndash1566 Special Issue Aromaticity (b) Chem Rev

2005 105 3343ndash3397 Special Issue Delocalization-Pi and Sigma 3) (a) Cyranski M K Krygowski T M Katritzky A R Schleyer P von R J Org

Chem 2002 67 1333 (b) Stanger A Chem Commun 2009 1939 4) (a) Minkin V I Glukhovtsev M N Simkin B Ya Aromaticity and Antiaromaticity

Electronic and Structural Aspects Wiley New York 1994 pp 63ndash74 (b) Garratt P J Aromaticity Wiley New York 1986 pp 30ndash34 93ndash95

5) (a) Wu J Muumlllen K In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 3 pp 90ndash139 (b) Wu J Pisula W Muumlllen K Chem Rev 2007 107 718 (c) Handbook of Organic Electronics and Photonics Nalwa H S Ed American Scientific 2008

6) Miljanić O Š Vollhardt K P C In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 4 pp 140ndash197

7) (a) Shepherd M K Cyclobutarenes The Chemistry of Benzocyclobutene Biphenylene and Related Compounds Elsevier Amsterdam 1991 (b) Toda F Garratt P J Chem Rev 1992 92 1685

8) (a) Diercks R Vollhardt K P C J Am Chem Soc 1986 108 3150 (b) Mohler D L Vollhardt K P C Wolff S Angew Chem Int Ed Engl 1990 29 1151 (c) Mohler D L Vollhardt K P C Wolff S Angew Chem Int Ed Engl 1995 34 563

9) (a) Holmes D Kumaraswamy S Matzger A J Vollhardt K P C Chem Eur J 1999 5 3399 (b) Dosche C Kumke M U Ariese F Bader A N Gooijer C Dosa P I Han S Miljanic O Š Vollhardt K P C Puchta R van Eikema Hommes N J R Phys Chem Chem Phys 2003 5 4563 (c) Wagner H-U Szeimies G Chandrasekhar J Schleyer P von R Pople J A Binkley J S J Am Chem Soc 1978 100 1210

10) Han S Bond A D Disch R L Holmes D Schulman J M Teat S J Vollhardt K P C Whitener G D Angew Chem Int Ed 2002 41 3223

11) Jackman L M Sondheimer F Amiel Y Ben-Efraim D A Gaoni Y Wolovsky R Bothner-By A A J Am Chem Soc 1962 84 4307

12) Untch K G Wysocki D C J Am Chem Soc 1967 89 6386 13) (a) Chen Z Wannere S C Corminboeuf C Puchta R Schleyer P von R

Chem Rev 2005 105 3842 and the references therein (b) Steinmann S N Jana D F Wu J I-C Schleyer P v R Mo Y Corminboeuf C Angew Chem Int Ed 2009 48 9828

14) Schleyer P v R Manoharan M Wang Z-X Kiran B Jiao H Puchta R van Eikema Hommes N J R Org Lett 2001 3 2465

- 170 -

15) Schulman J M Disch R L Jiao H Schleyer P v R J Phys Chem A 1998 102 8051

16) Jeany H Mason K G Sketchley J M Tetrahedron Lett 1970 11 485 17) Brown F C Choi N Coulston K J Eastwood F W Wiersum U E

Jenneskens L W Tetrahedron Lett 1994 35 4405 18) (a) Linear [3]phenylene Dosa P I Schleifenbaum A Vollhardt K P C Org Lett

2001 3 1017 (b) Angular [3]phenylene Matzger A J Vollhardt K P C Chem Commun 1997 1415 (c) Angular [4]phenylene Dosa P I Gu Z Hager D Karney W L Vollhardt K P C Chem Commun 2009 1967

19) Perthuisot C Edelbach B L Zubris D L Simhai N Iverson C N Muumlller C Satoh T Jones W D J Mol Catal A 2002 189 157

20) Dosche C Loumlhmannsroumlben H-G Bieser A Dosa P I Han S Iwamoto M Schleifenbaum A Vollhardt K P C Phys Chem Chem Phys 2002 4 2156

21) (a) Deniz A A Peters K S Snyder G J Science 1999 286 1119 (b) Fattahi A Lis L Tian Z Kass P S Angew Chem Int Ed 2006 45 4984 (c) Bally T Angew Chem Int Ed 2006 45 6616

22) Anslyn E Dougherty D Modern Physical Organic Chemistry University Science Books Palo Alto 2006

23) Crabtree R H The Organometallic Chemistry of the Transition Metals 4th Ed Wiley-VCH New York 2005

24) Mestdagh H Postdoctoral Research Report University of California Berkeley 1986

25) Hirthammer M Vollhardt K P C J Am Chem Soc 1986 108 2481 26) Blanco L Helson H E Hirthammer M Mestdagh H Spyroudis S Vollhardt K

P C Angew Chem Int Ed Engl 1987 26 1246 27) Berris B C Hovakeemian G H Lai Y-H Mestdagh H Vollhardt K P C J

Am Chem Soc 1985 107 5670 28) Dosa P I The Chemistry of Angular and Linear [N]Phenylenes PhD Thesis

University of California Berkeley 2002 29) Diercks R Eaton B E Guumlrtzgen S Jalisatgi S Matzger A J Radde R H

Vollhardt K P C J Am Chem Soc 1998 120 8247 30) (a) Nambu M Siegel J S J Am Chem Soc 1988 110 3675 (b) Nambu M

Hardcastle K Baldridge K K Siegel J S J Am Chem Soc 1992 114 369 31) Nambu M Mohler D L Hardcastle K Baldridge K K Siegel J S J Am

Chem Soc 1993 115 6138 32) Kumaraswamy S Jalisatgi S S Matzger A J Miljanić O Š Vollhardt K P C

Angew Chem Int Ed 2004 43 3711 33) (a) Eisch J J Piotrowski A M Han K I Kruumlger C Tsay Y H Organometallics

1985 4 224 (b) Schwager H Spyroudis S Vollhardt K P C J Organometallic Chem 1990 382 191

34) Albright T A Hofmann P Hoffmann R Lillya C P Dobosh P A J Am Chem Soc 1983 105 3397

35) Doumltz K H Jahr H C Chem Rec 2005 4 61 36) Gridnev I D Coord Chem Rev 2008 252 1798 37) Eickmeier C Holmes D Junga H Matzger A J Scherhag F Shim M

Vollhardt K P C Angew Chem Int Ed Engl 1999 38 800

- 171 -

38) Groszligmann T N Haptotropism in Linear Phenylene Complexes Diplomarbeit Thesis University of California Berkeley 2004

39) Dinculear photothermal haptotropic systems Tsuchiya K Ideta K Mogi K Sunada Y Nagashima H Dalton Trans 2008 2708 and the references therein

40) Additive assisted photothermal haptotropic systems (a) Jahr H C Nieger M Doumltz H K Chem Eur J 2005 11 5333 d) Herbert D E Tanabe M Bourke S C Lough A J Manners I J Am Chem Soc 2008 130 4166 e) Ieong N S Manners I J Organomet Chem 2008 693 802 and references therein

41) (a) Zhu G Tanski T M Churchill D G Janak K E G Parkin G J Am Chem Soc 2002 124 13658 (b) Zhu G Pang G Parkin G J Am Chem Soc 2008 130 1564

42) Selected reviews of photobased devices and molecular switches (a) Balzani V Credi A Venturi M Chem Soc Rev 2009 38 1542 (b) Kay E R Leigh D A Zerbetto F Angew Chem Int Ed 2007 46 72 (c) Photochromism Molecules and Systems Duumlrr H Bouas-Laurent H Eds Elsevier Amsterdam 2003 (d) Feringa B Molecular Switches Wiley-VCH Weinheim 2001

43) (a) a) Photofunctional Transition Metal Complexes Yam V W W Ed Springer Berlin 2007 b) Coppens P Novozhilova I Kovalevsky A Chem Rev 2002 102 861 c) Guumltlich P Garcia Y Woike T Coord Chem Rev 2001 219ndash221 839

44) (a) Lambert J B Mazozola E P Nuclear Magnetic Resonance Spectroscopy An Introduction to Princples Applications and Experimental Methods Pearson Education Upper Saddle River 2004 (b) Berger S Braun S 200 and More NMR Experiments A Practical Course Wiley-VCH Weinheim 2004 (c) Friebolin H Basic One- and Two-Dimensional NMR Spectroscopy 4th edition Wiley-VCH Weinheim 2005

45) (a) Schulman J M Disch R L J Phys Chem A 2003 107 5223 (b) Schulman J M Disch R L J Am Chem Soc 1996 118 8470 and the references cited therein

46) (a) Bursten B E Fenske R F Inorg Chem 1979 18 1760 (b) Chinn J W Jr Hall M B Inorg Chem 1983 22 2759 (c) Datta A Pati S K J Am Chem Soc 2005 127 3496

47) Ooloba K Haptotropic Shifts in the Linear [N]-Phenylene (N=3 4 and 5) and Angular [3]-Phenylene Cyclopentadienylcobalt Complexes PhD Thesis University of Houston 2008

48) Hillard III R L Vollhardt K P C J Am Chem Soc 1977 99 4058 49) Berris B C Lai Y-H Vollhardt K P C J Chem Soc Chem Commun 1982

953 50) (a) Rausch M D Genetti R A J Org Chem 1970 35 3888 (b) Hart W P

Rausch D M J Organometallic Chem 1988 355 455 51) Duclos R I Vollhardt K P C Yee J L S J Organomet Chem 1979 174 109 52) (a) Myers A G Sogi M Lewis M A Arvedson S P J Org Chem 2004 69

2516 (b) Wolfart V Ramming M Gleiter R Nuber B Pritzkow H Rominger F Eur J Inorg Chem 1999 499 (c) Mitchell R H Chen Y Khalifa N Zhou P J Am Chem Soc 1998 120 1785 (d) McGlinchey M J Burns R C Hofer R Top S Jaouen G Organometallics 1986 5 104

53) Feixas F Jimeacutenez-Halla J O C Matito E Poater J Solagrave M Pol J Chem

- 172 -

2007 81 783 54) (a)Stanger A J Org Chem 2006 71 883 (b) Stanger A Chem Eur J 2006 12

2745 (c) Tsipis A C Phys Chem Chem Phys 2009 11 8244 (d) Stanger A Chem Commun 2009 1939

55) For very recent literature compilations of theoretical (and experimental) treatments of haptotropism in arene metal complexes see a) Joistgen O Pfletschinger A Ciupka J Dolg M Nieger M Schnakenburg G Froumlhlich R Kataeva O Doumltz K H Organometallics 2009 28 3473 b) Pfletschinger A Dolg N J Organomet Chem 2009 694 3338 c) Jimeacutenez-Halla J O C Robles J Solagrave M Organometallics 2008 27 5230 d) Kirillov E Kahlal S Roisnel T Georgelin T Saillard J-Y Carpentier J-F Organometallics 2008 27 387 and references therein

56) Jimeacutenez-Halla J O C Robles J Solagrave M J Phys Chem A 2008 112 1202 57) Oprunenko Y Gloriozov I Lyssenko K Malyugina S Mityuk D Mstislavsky

V Guumlnther H von Firks G Ebener M J Organomet Chem 2002 656 27 58) Muumlller J Gaede P E Qiao K J Organomet Chem 1994 480 213 59) Bianchini C Caulton K G Chardon C Doublet M L Eisenstein O Jackson

S A Johnson T J Meli A Peruzzini M Streib W E Vacca A Vizzat F Organometallics 1994 13 2010

60) (a) De Boer E Van Willigen H V Prog Nuc Mag Res Spec 1967 2 111 (b) Memory J D Wilson N K NMR of Aromatic Compounds Wiley-VCH New York 1982

61) (a) Poli R Chem Rev 1996 96 2135 and the references cited therein (b) Schroumlder D Shaik S Schwartz H Acc Chem Res 2000 33 139 (c) Harvey J N Poli R Smith K M Coord Chem Rev 2003 237 347 and the references cited therein

62) For computational examples of 16 electron triplet Cp cobalt species influencing cobalt-mediated reactions see (a) Siegbahn P E M J Am Chem Soc 1996 118 1487 (b) Poli R Smith K M Eur J Inorg Chem 1999 877 (c) Carreoacuten-Macedo J-L Harvey J N J Am Chem Soc 2004 126 5789 (d) Petit A Richard P Cacelli I Poli R Chem Eur J 2006 12 813 (e) Aubert C Betschmann P Eichberg M J Gandon V Geny A Heckrodt T J Lehmann J Malacria M Masjost B Paredes E Vollhardt K P C Whitener G D Chem Eur J 2007 13 7443 (f) Gandon V Agenet N Vollhardt K P C Malacria M Aubert C J Am Chem Soc 2009 131 3007

63) Illustrative examples (a) Olson W L Stacy A M Dahl L F J Am Chem Soc 1986 108 7646 (b) Wadepohl H Galm W Pritzkow H Wolf A Chem Eur J 1996 2 1453 (c) Knijnenburg W Hetterscheid D Kooistra T M Budzelaar P H M Eur J Inorg Chem 2004 1204

64) Benito-Garagorri D Bernskoetter W H Lobkovsky E Chirik P J Organometallics 2009 28 4807

65) Fox J P Ramdhanie B Zareba A A Czernuszewicz R S Goldberg D P Inorg Chem 2004 43 6600

66) Guennic B L Floyd T Galan B R Autschbach J Keister J B Inorg Chem 2009 48 5504

67) Cremer C Burger P J Am Chem Soc 2003 125 7664

- 173 -

68) Atkins P de Paula J P Physical Chemistry 8th Edition Oxford University Press Oxford 2006

69) Butters T Toda F Winters W Angew Chem Int Ed Engl 1980 19 926 70) Mann B E Taylor B F 13C Data for Organometallic Compounds Academic

London 1981 71) For a review on triple decker arene complexes and closely related syn dinuclear

systems see (a) Beck V OlsquoHare D J Organomet Chem 2004 698 3920 and the references therein For a review of trinuclear CpCo(arene) complexes see (b) Wadepohl H Angew Chem Int Ed Engl 1992 31 247 and the references therein

72) Jonas K Koepe G Schieferstein L Mynott R Kruumlger C Tsay Y-H Angew Chem Int Ed Engl 1983 22 620 Angew Chem Suppl 1983 920

73) Muumlller J Gaede P E Qiao K Angew Chem Int Ed Engl 1993 32 1697 74) Schneider J J Wolf D Janiak C Heinemann O Rust J Kruumlger C Chem

Eur J 1998 4 1982 75) Schneider J J Denninger U Heinemann O Kruumlger C Angew Chem Int Ed

Engl 1995 34 592 76) Budzelaar P H M Moonen N N P de Gelder R Smits J M M Gal A W

Chem Eur J 2000 6 2740 77) Albright T A Dosa P I Groszligmann T N Oluwakemi O Padilla R Paubelle

R Timofeeva T Vollhardt K P C Angew Chem Int Ed 2009 48 9853 78) Schaub T Radius U Chem Eur J 2005 11 5024 79) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4660 80) (a) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4040

(b) Muumlller C Lachicotte R J Jones W D Organometallics 2002 21 1975 81) Martin R H Angew Chem Int Ed Engl 1974 13 649 82) Mallory FB Butler K E Evans AC Mallory CW Tetrahedron Lett 1996 37

7176 83) Selected Reviews (a) Amemiya R Yamaguchi M Chem Rec 2008 8 116 (b)

Ruliacutešek L Exner O Cwiklik L Jungwirth P Staryacute I Pospiacutešil L Havlas Z J Phys Chem C 2007 111 14948 (c) Hopf H Classics in Hydrocarbon Chemistry Wiley-VCH Weinheim 2000 pp 321ndash330 (d) Voumlgtle F Fascinating Molecules in Organic Chemistry Wiley New York 1992 pp 156ndash180 (e) Meurer K P F Voumlgtle Top Curr Chem 1985 127 1 (f) Laarhoven W H Prinsen W J Top Curr Chem 1984 125 63

84) (a) Mallory FB Butler K E Mallory CW Beacuterubeacute A Luzik E D Brondyke E J Hiremath R Ngo P Carroll P J Tetrahedron 2001 57 3715 (b) Mallory F B Butler K E Evans A C Brondyke E J Mallory C W Yang C Ellenstein A J Am Chem Soc 1997 119 2119

85) (a) Mitsuhashi R Suzuki Y Yamanari Y Mitamura H Kambe T Ikeda N Okamoto H Fujiwara A Yamaji M Kawasaki N Maniwa Y Kubozono Y Nature 2010 464 74 (b) Okamoto H Kawasaki N Kaji Y Kubozono Y Fujiwara A Yamaji M J Am Chem Soc 2008 130 10470 (c) Tian Y H Park G Kertesz M Chem Mater 2008 20 3266

86) Recent reviews of acenes in electronic applications (a)Yamashita Y Sci Technol Adv Mater 2009 10 024313 (b) Wuumlrthner F Schmidt R ChemPhysChem

- 174 -

2006 7 793 (c) Bendikov M Wudl F Chem Rev 2004 104 4891 87) NICS-based comparison of phenacene and acene properties Portella G Poater

P Bofill J M Alemany P Solagrave M J Org Chem 2005 70 2509 and the references therein

88) Mallory F B Mallory C W Org React 1984 30 1 89) Gu Z Nickel-Catalyzed Cycloaddition Reaction of [N]Phenylenes and Alkynes

Postdoctoral Report University of California Berkeley 2008 90) Preferential displacement of COD by π ligands from Ni(COD)(PMe3)2 is well

documented See eg Karsch H H Leithe A W Reisky M Witt E Organometallics 1999 18 90

91) (a) Bochmann M Hawkins I Hursthouse M B Short R L J Chem Soc Dalton Trans 1990 1213 (b) Poerschke K R Mynott R Angermund K Kruumlger C Z Naturforsch 1990 40B 199 See also (c) Bartik T Happ B Iglewsky M Bandmann H Boese R Heimbach P Hoffmann T Wenschuh E Organometallics 1992 11 1235

92) For Ni-phosphine migrations along polycyclic benzenoid ligands see eg Stanger A Vollhardt K P C Organometallics 1992 11 317

93) Edelbach B L Vicic D A Lachicotte R J Jones W D Organometallics 1998 17 4784

94) (a) Feiken N Pregosin P S Trabesinger G Scalone M Organometallics 1997 16 537 (b) Feiken N Pregosin P S Trabesinger G Albinati A Evoli G L Organometallics 1997 16 5756 (c) Geldbach T J Pregosin P S Eur J Inorg Chem 2002 1907

95) Cheng T-Y Szalda D J Hanson J C Muckerman J T Bullock R M Organometallics 2008 27 3785

96) (a) Grimme S Harren J Sobanski A Voumlgtle F Eur J Org Chem 1998 8 1491 (b) Dias J J Chem Inf Model 2005 45 562

97) Still W C Mitra A Kahn M J Org Chem 1978 43 2923 98) (a) Leonard J Lygo B Procter G Advanced Practical Organic Chemistry 2nd

ed CRC Press Boca Raton 1998 (b) Errington R J Advanced Practical Inorganic Chemistry and Metalorganic Chemistry Chapman and Hill London 1997

99) Jonas K Deffense E Habermann D Angew Chem Int Ed Engl 1983 22 716 100) Gaussian 03 Revision B03 M J Frisch G W Trucks H B Schlegel G E

Scuseria M A Robb J R Cheeseman J A Montgomery Jr T Vreven K N Kudin J C Burant J M Millam S S Iyengar J Tomasi V Barone B Mennucci M Cossi G Scalmani N Rega G A Petersson H Nakatsuji M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida T Nakajima Y Honda O Kitao H Nakai M Klene X Li J E Knox H P Hratchian J B Cross C Adamo J Jaramillo R Gomperts R E Stratmann O Yazyev A J Austin R Cammi C Pomelli J W Ochterski P Y Ayala K Morokuma G A Voth P Salvador J J Dannenberg V G Zakrzewski S Dapprich A D Daniels M C Strain O Farkas D K Malick A D Rabuck K Raghavachari J B Foresman J V Ortiz Q Cui A G Baboul S Clifford J Cioslowski B B Stefanov G Liu A Liashenko P Piskorz I Komaromi R L Martin D J Fox T Keith M A Al-Laham C Y Peng A Nanayakkara M Challacombe P M W Gill B Johnson W Chen M W Wong C Gonzalez J A Pople Gaussian Inc Pittsburgh PA

- 175 -

2003 101) wwwgaussiancom 102) wwwchemcraftprogcom 103) Becke A D J Chem Phys 1993 98 5648 104) Lee C Yang W Parr G R Phys Rev B 1988 37 785 105) Binkley J S Pople J A Hehre W J J Am Chem Soc 1980 102 939 for

hydrogen and Gordon M S Binkley J S Pople J A Pietro W J Hehre W J J Am Chem Soc 1983 104 2797

106) Hay P J Wadt W R J Chem Phys 1985 82 270 107) Hehre W J Ditchfield R Pople J A J Chem Phys B 1972 56 2257 108) Curtiss L A McGrath M P Blaudeau J-P Davis N E Binning R C Jr

Radom L J Chem Phys 1995 103 6104 109) A W Ehlers M Boumlhme S Dapprich A Gobbi A Houmlllwarth V Jonas K F

Koumlhler R Stegmann A Veldkamp G Frenking Chem Phys Lett 1993 208 111

110) QST is a synchronous transit approach to the quadratic region around the transition state structure For details see (a) J B Foresman A Frisch in Exploring Chemistry with Electronic Structure Methods A Guide to Using Gaussian Gaussian Inc Pittsburgh PA USA 1996 (b) H B Schlegel in Ab Initio Methods in Quantum Chemistry Part I Wiley Chichester 1987

111) Gu Z The Improvement of Total Synthesis of Angular [4]Phenylene and Its Flash Vacuum Pyrolysis (FVP) Study Postdoctoral Report University of California Berkeley 2008

112) Schwager H Postdoctoral Research Report University of California Berkeley 1987

113) Kuumlchle W Dolg M Stoll H Preuss H Mol Phys 1991 74 1245 114) (a) Hariharan P C Pople J A Theor Chim Acta 1973 28 213 (b) Francl M

M Petro W J Hehre W J Binkley J S Gordon M S DeFrees D J Pople J A J Chem Phys 1982 77 3654 (c) Rassolov V Pople J A Ratner M Windus T L J Chem Phys 1998 109 1223

- 1 -

Chapter One

Properties of the [N]Phenylenes and Their Organometallic Chemistry

11 General Discussion of [N]Phenylene Properties Polycyclic aromatic hydrocarbons (PAHs) are a class of molecules that have occupied the minds of chemists for generations1 Their essential feature aromaticity is the unusual stabilization that arises from having a 4n+2 number of π-electrons in a cyclical array This seemingly simple definition obscures the fact that aromaticity continues to be one of the most scrutinized topics in modern organic chemistry2 and more rigorous definitions3 have remained elusive Much of the early work4 with PAHs was aimed at investigating theoretical issues surrounding aromaticity There has been renewed interest in these systems in recent years because they are increasingly attractive as functional materials in organic-based electronics5 Of the many different kinds of PAHs known eg 1ndash6 (Figure 11) one subclass is of particular interest the [N]phenylenes6

Anthracene Coronene Phenanthrene

Chrysene Triphenylene Pyrene

1 2 3

4 5 6

Figure 11 Some examples of polycyclic aromatic hydrocarbons The [N]phenylenes (where N = the number of benzene rings) are PAHs in which benzene and cyclobutadiene rings are fused in an alternating manner The cyclobutadiene ring imparts very unusual structural and electronic properties as seen in the simplest molecule in the series biphenylene (7) It can be described by several resonance forms (Figure 12 andashe) in which the major contributor 7c avoids formation of the highly destabilizing antiaromatic cyclobutadiene (7a 7e) and benzocyclobutadiene circuit (7b 7d) This preference is manifest in the significant bond alternation7 seen in

- 2 -

the crystal structure of biphenylene (Figure 12) which shows a clear difference in bond lengths between the formal single bonds (~143 Aring) and the shorter formal double bonds (~137 Aring)

1423

1372

Figure 12 Biphenylene bond lengths (top Aring) and resonance contributors (bottom)

An extreme example of [N]phenylene π-bond localization is triangular [4]phenylene (8) (Scheme 11) in which the three-fold peripheral fusion imparts complete cyclohexatriene character on the central ring89a This property is reflected in the reactivity of the system eg catalytic hydrogenation (9)8b epoxidation (10)8c and cyclopropanation (11)8c Scheme 11 Reactions Illustrating the Fully Bond Localized Character of the Central Benzene

Ring in Triangular [4]Phenylene 8 Bond lengths are in Aring

- 3 -

Phenylenes exhibit another interesting structural feature in contrast to other PAHs sizable deviations from planarity (Figure 13)9ab The flexibility of the phenylene framework arises from the combined effect of π- and σ-strain9ab By adopting a nonplanar geometry overlap between the π-orbitals is diminished and in turn leads to a decrease in destabilizing antiaromatic character Pyramidalization of the four-membered ring carbons also reduces σ-strain9ab a phenomenon observed in highly strained alkene systems9c

Figure 13 Crystal structures showing deviations from planarity in (a) helical [6]phenylene (12)10 (b) dimethyl triangular [4]phenylene-23-dicarboxylate (13)9a and (c) 23-bis(tri-

methylsilyl) linear [3]phenylene (14)9a

The fusion of aromatic benzene rings with antiaromatic cyclobutadiene units in the same molecule has prompted numerous experimental and theoretical discussions6 regarding the magnetic and electronic properties of the phenylenes 1H-NMR spectroscopy is one typical measure of aromaticity Protons on the exterior of aromatic rings (eg 15) show relatively low field resonances while their interior counterparts resonate at relatively high field due to the presence of a diamagnetic ring current Conversely antiaromatic rings with 4n π-electrons are paratropic and reveal the opposite disposition of the two respective types of protons (eg 16) The interplay between aromatic and antiaromatic character in the phenylenes is evident in their chemical shifts which tend to show weakly aromatic resonances (Figure 15) relative to benzene (736 ppm)

(a) (b) (c)

12 13 14

- 4 -

Figure 14 Observed 1H-NMR resonances in (a) the aromatic [18]annulene (15)11 and (b) the antiaromatic 5-bromo-19-bisdehydro-[12]annulene (16)12

Aside from NMR spectroscopy nucleus independent chemical shift (NICS)13 calculations have also proven to be useful measures of aromaticity The NICS technique works by calculating the magnetic shielding of a ldquoghost nucleusrdquo that can be positioned anywhere around a molecule For probing aromaticity the calculated point is in the center of the π-electron circuit to be examined Calculations placing the ghost nucleus 1 Aring above the plane of the molecule are often used to minimize local anisotropy and are referred to as NICS(1)14 NICS data are given in ppm and are thus comparable to experimental 1H-NMR measurements Negative NICS values indicate aromatic character while positive values suggest antiaromatic character For example the NICS(1) of benzene15 is ndash125 ppm whereas for cyclobutadiene15 it is 151 ppm NICS calculations for various phenylenes have been carried out6 and are shown in Figure 15 alongside the experimentally measured 1H-NMR chemical shifts The attenuated aromatic character of the benzene and the relatively weak antiaromatic character of the cyclobutadiene rings in phenylenes such as biphenylene (7) triangular [4]phenylene (8) and angular [4]phenylene (17) are apparent from both sets of data

Figure 15 1H-NMR (blue) and NICS(1) (green) data for selected phenylene topologies (ppm)6

The phenylenes possess multiple modes of reactivity7 as illustrated by biphenylene (7) in Scheme 12 It can undergo electrophilic aromatic substitution like other PAHs but does so selectively at the 2-position to avoid the formation of intermediates with antiaromatic character Biphenylene does not readily undergo Diels-

- 5 -

Alder reactions but was shown to react with electron-deficient benzynes to give the corresponding cycloadducts16 Opening of the highly strained four-membered ring is another prominent aspect of phenylene reactivity

Scheme 12 Illustrative Reaction Pathways of Biphenylene6

Early work17 showed that it was possible to cleave the aryl-aryl C-C bonds via thermolysis in the neat state Rupture of the four-membered ring is a key step in the rearrangement of phenylenes into other PAHs and has been observed typically under flash vacuum pyrolytic conditions18 (eg 10ndash3ndash10ndash6 torr 800ndash1000 degC) Strained ring opening on exposure to metal complexes to give metallacycles19 is discussed in further detail in Section 12 12 Overview of Phenylene Organometallic Chemistry

As mentioned above the weakly aromatic character of the phenylenes dominates their structure and reactivity In the linear phenylenes the antiaromatic contribution to structure and reactivity becomes increasingly significant A simple yet instructive explanation for this phenomenon can be seen in the various resonance structures of linear [3]phenylene (18) a selection of which is depicted in Figure 16 Even the most favorable forms a and b feature double bonds in the four-membered rings The cumulative increase in cyclobutadienoid circuits should therefore lead to an increase in antiaromatic character The relative augmentation in

- 6 -

cyclobutadienoidantiaromatic character of the linear phenylenes was confirmed6 by NMR NICS calculations and HOMO-LUMO measurements20

Figure 16

Resonance contributors to linear [3]phenylene

Cyclobutadiene is often invoked as the typical example of a highly destabilized antiaromatic system Indeed the difficulties21 in preparing and isolating it confirm theoretical predictions regarding its instability22 Attachment of a metal however is known to produce aromatic organometallic molecules of high stability23 The increased antiaromatic character of the linear phenylenes thus makes them amenable to metal complexation Cyclopentadienylcobalt cyclobutadiene complexes of linear [3]- (19)24 linear [4]- (20)25 and linear [5]phenylene (21)26 have been prepared using the well-developed cobalt-based [2+2+2] alkyne cyclotrimerization methods (Scheme 13)27

Compounds 19ndash21 constitute the only linear CpCo phenylene systems known so far

Scheme 13 Synthesis of Linear Phenylene(CpCo) Cyclobutadiene Complexes

In the metallated linear [4]- and [5]phenylene 20 and 21 respectively the CpCo unit is located on the inner cyclobutadiene ring This is curious as one would have expected the metal fragment to be bound to its outside counterpart close to the center of reactivity during the cyclotrimerization step The position of the CpCo unit was established by NMR spectroscopy2628 In addition a crystal structure of a tetrahexyl

TMS

TMS

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMSTMS

TMS

Co

CpCo(CO)2BTMSA

h

Co

Co

CpCo(CO)2BTMSA

h

CpCo(CO)2BTMSA

h

19

20

21

- 7 -

substituted linear [5]phenylene28 (Figure 17) clearly reveals the inside position of the metal fragment Difficulties in obtaining high quality crystals however precluded a detailed bond analysis of the complex The unexpected location of the CpCo unit in 20 and 21 suggested the occurrence of CpCo migration under the conditions of their preparation Detailed experiments verifying this hypothesis will be the subject of Chapter 2

Figure 17 Disordered crystal structure for the 23910-tetrakis(trimethylsilyl)-571214-

tetrahexyl linear [5]phenylene(CpCo)

In contrast to the linear phenylenes their angular relatives undergo π-metallation at the cyclohexatrienoid moieties (Figure 18) For example angular [3]phenylene (22) reacts with CpCo(C2H4)2 to form the η4-CpCo complex 2329 Similar treatment with Cr(CO)3(NH3)3 yields the η6-Cr(CO)3 analog 2430

Figure 18 η

4-CpCo (23) and η6-Cr(CO)3 (24) complexes of angular [3]phenylene (22)

In addition to 24 related chromium complexes of the triangular [4]phenylene frame eg 25 have been prepared (Scheme 14)31 Interestingly regioisomer 26 generated at relatively lower temperatures is the kinetic product of monocomplexation and rearranges thermally to 27 Double metallation is possible as illustrated in the conversion of 27 to 28 with added (naphthalene)Cr(CO)3

- 8 -

Scheme 14 Synthesis and Reactions of Triangular [4]Phenylene(Cr(CO)3) Complexes

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3

Cr(CO)3

TMS

TMS

TMS

TMS

TMS

TMS

Cr(CO)3(NH3)3dioxane 100 oC

14 h

(naphthalene)Cr(CO)3THF Et2O 60 oC 14 h

90 oC

(naphthalene)Cr(CO)3THF Et2O 60 oC

14 h

25

27

26

28

57 43

89

In contrast to CpCo which attaches itself exclusively to the four-membered ring in the linear phenylenes including the linear [3]phenylene frame as in 19 (Scheme 13) Fe2(CO)9 gives a plethora of complexes with the tetrasilyl derivative 29 among which the iron tricarbonyl cyclobutadiene complex 30 is only minor (Scheme 15)27 Instead other organometallic molecules such as arene complex 31 were isolated This compound contains two Fe(CO)3 units coordinated to the central benzene ring An iron-iron bond was proposed for this molecule (31a) although the spectral data are also consistent with a structure in which the Fe(CO)3 fragments are located on opposite faces (31b) Because a crystal structure could not be obtained the structural identity of 31 remains ambiguous The major products of this reaction 32 and 33 illustrate another important aspect of phenylene reactivity metal insertion into the strained ring

- 9 -

in this case involving the dinuclear Fe2(CO)6 unit Complex 33 probably originating from 32 contains an additional Fe(CO)3 moiety coordinated to the terminal benzene ring closest to the Fe2(CO)6 fragment

Scheme 15 Reaction of Linear [3]Phenylene with Fe2(CO)9

While as yet absent in the linear series a cobalt insertion product analogous to iron compounds 32 and 33 was isolated when angular phenylene 22 was exposed to excess CpCo(ethene)2 (Figure 19)32 In this case double insertion of two (CpCo)2

Figure 19 Tetranuclear CpCo-terphenylene complex 34 and its crystal structure

34

- 10 -

fragments occurred to give 34 in 71 yield Notably neither 23 nor analogs of the type 31 were detected As alluded to in Scheme 12 biphenylene (7) itself also undergoes metal insertions into the four-membered ring This type of reactivity has been observed with a range of transition metals including Co19 Mechanistically best delineated is the attack of Ni and Pt species Thus Ni(PEt3)4

33a and Ni(COD)(PMe3)233b begin with insertion of

the nickel fragment into the four-membered ring to give a metallacycle of the type 35 (Scheme 16) Subsequent dimerization assembles 36 from which Ni is extruded to furnish tetraphenylene 37 as the final product A similar reaction pathway was proposed for Pt(PEt)4

19 but proceeding via 38 to a monometallacycle 40 possibly through the intermediacy of 39 In summary the σ- and π-activation of the phenylenes endows them with rich organometallic chemical potential The synthetic and mechanistic exploration of one aspect of it namely the Ni-catalyzed cycloaddition of alkynes to the four-membered rings in angular phenylenes will be discussed in Chapter 3

Scheme 16 Reaction of Biphenylene with Nickel and Platinum Complexes

13 Direction of Work The discussions in Sections 11 and 12 have provided a brief overview of phenylene properties and their previously studied organometallic chemistry

- 11 -

respectively The aim of this thesis was to advance two aspects of prior investigations The first area examines the chemistry of the linear phenylene(CpCo) complexes In particular experiments are presented addressing the question of a possible migration of the CpCo fragment along their framework The revocable movement of a metal fragment between cyclobutadiene rings is a highly noteworthy discovery as this process has never before been reported On a practical level this mode of reactivity places linear phenylene(CpCo) complexes in the increasingly appealing class of organometallic arrays that can serve as the basis for various molecular electronic systems The reversible isomerizations described in the second chapter can potentially be employed in molecular machines and switches data storage and as will be detailed photostorage devices Experimental work in the form of detailed solid state and spectroscopic analyses is provided Computational studies are also employed to further scrutinize the novel chemistry of the abovementioned Co-based molecules The second topic of this thesis examines nickel-catalyzed insertions into the four- membered rings of angular phenylene systems Specifically the application of this reactivity to the synthesis of a class of PAHs known as [N]phenacenes is discussed Phenacenes (polyphenanthrenes) have recently shown great promise as organic transistors and conductors but advancement of this field has been hampered due to few practical syntheses The insolubility of these molecules has also been a substantial barrier to the development of phenacene-based applications The content of the third chapter explores the preparation of soluble phenacene derivatives using a tandem Ni-insertion alkyne cycloaddition reaction This new process provides an efficient widely applicable and practical synthesis of larger phenacenes using correspondingly larger angular phenylene systems Detailed mechanistic studies of this reaction are presented Experimental data are used in conjunction with computational studies to gain further insight with the optimization of the reaction by reduction of side product formation being a crucial milestone

- 12 -

Chapter Two

PhotondashThermal Haptotropism in Cyclopentadienylcobalt Complexes of Linear Phenylenes Intercyclobutadiene Metal Migration

21 Introduction As previewed in Section 12 the unexpected position of the metallic unit in the linear [4]- and [5]phenylene(CpCo) systems 20 and 21 constituted the background for the studies presented in this chapter Specifically it was hypothesized that its origin was due to the migration of the metal fragment from one cyclobutadiene ring to another a process that would constitute an unprecedented type of haptotropic shift34-36 However a prerequisite for studying such a rearrangement would be the generation of the haptoisomers of 20 and 21 (Scheme 13) bearing the CpCo appendage at the respective terminal four-membered rings a possibility obviated by their thermal method of synthesis The following describes the history that led to the discovery of photochemical conditions that circumvented this thermodynamic problem The story begins with a prior attempt to stabilize the linear phenylene frame by alkyl substitution the ultimate aim being the synthesis of members of the series with Ngt5 Such substitution was also hoped to improve solubility a facet exploited in the corresponding zigzag series37 The synthetic strategy followed that used in the preparation of the largest known linear phenylene 41 namely the CpCo-catalyzed cyclization to 21 followed by careful oxidative demetallation as shown in Scheme 21 The initial target chosen was the tetrahexyl system 43 approached via the synthesis of complex 42 (Scheme 22)28 Demetallation was thought to be facile to provide the free ligand but this anticipation proved to be erroneous

Scheme 21 Oxidative Decomplexation of Linear [5]Phenylene Complex 21

TMS

TMS

TMS

TMSTMS

TMS

TMS

TMS

41

CoCp

21

40

CuCl2middot2H2ODME NEt3 H2O

Scheme 22 Preparation of Tetrahexyl Linear [5]Phenylene Complex 42

- 13 -

TMS

TMS

TMS

TMS

Hex

Hex

Hex

Hex

CoCp

42

CpCo(CO)2 BTMSAm-xylene ∆ hν

27

Hex Hex

HexHex

TMS

TMS

TMS

TMS

Hex Hex

HexHex

ndashCpCo

43

The demetallation of 42 under numerous conditions was unattainable However in one of these attempts an NMR sample of 42 was exposed to UV-irradiation leading to the evolution of new signals eventually assigned to originate from rearranged compound 45 (Scheme 23)28 This molecule is also a linear [5]phenylene(CpCo) complex but now has the metal fragment bound to the outer cyclobutadiene ring an arrangement that was suspected to be the initial product of the preparation of 42 (Scheme 22) That this conjecture was correct was established by heating which caused photoisomer 45 to revert to 42 An indication of the generality of this phenomenon was gleaned from 21 which underwent the same photoinduced thermally reversible haptotropic migration (Scheme 23)38 A detailed discussion of the spectral properties of these haptomers is provided in Sections 23 and 24 Scheme 23 Photoinduced Thermally Reversible Haptotropic Migration of the CpCo Fragment

in Linear [5]Phenylene(CpCo) Complexes

This discovery was deemed significant for two reasons 1 it constitutes the first observation of intercyclobutadiene metallohaptotropism and 2 there are only two previously known examples of mononuclear39 additive-free40 photothermal reversible haptotropic shifts both of which are based on Mo(PMe3)3 complexes (Scheme 24)41 Systems capable of undergoing this type of reaction are of much practical importance because of their potential employment as photostorage devices andor molecular switches42 The development and application of functional organometallic materials43 has proceeded at a relatively slow pace when compared to their non-metallated counterparts5c Thus the great prospects for discovery and advancement make this area of study particularly attractive

- 14 -

Scheme 24 Photothermal Reversible Metallohaptotropism in (a) Molybendum-Indole41a and (b) Molybendum-Isoquinoline Complexes41b

Having confirmed that an η4η4 cyclobutadiene haptotropic migration was indeed occurring mechanistic investigations2838 were begun Interestingly full conversion of the inner bound CpCo complexes to their photoisomers was never achieved The maximum ratio obtained for 2144 and 4245 was 8812 Variations of solvent (eg benzene THF CHCl3) and temperature (0ndash30degC) had no effect on this ratio Added ligands such as 15-cyclooctadiene CO and phosphines were also inconsequential Of further significance was the robustness of the photothermal cycle which could be run multiple times without decomposition Kinetic experiments were carried out to determine the activation parameters for the thermal reversal of 44 and 45 to 21 and 42 respectively These data are shown in Table 21 The isomerizations are cleanly first order a finding that was unaffected by changes in concentration22 The enthalpy of activation (∆Hne) increased only slightly with hexyl substitution (44 vs 45) The near zero entropy of activation values (∆Sne) was consistent with the occurrence of an intramolecular process

Table 21 Activation Parameters for the Conversion of Outer to Inner CpCo Complexes Under

Thermal Conditions ∆Sne Values are in Entropy Units (1 eu = calmolsdotK)

Reaction Solvent ∆H

ne (kcalmol) ∆Sne (eu)

44 to 21 C6D6 259 plusmn 04 16 plusmn 14 44 to 21 THF-d8 256 plusmn 09 01 plusmn 30 45 to 42 THF-d8 276 plusmn 08 77 plusmn 27

Consideration of the relative facility of the above haptotropic shifts made it likely that migration was occurring along the entire phenylene frame including the ldquohoppingrdquo across the central six-membered ring (Scheme 25) This degenerate equilibration should be detectable by NMR spectroscopy44 if it were sufficiently fast Unfortunately but perhaps not surprisingly considering the data in Table 21 coalescence of the spectrum of 21 could not be achieved even at temperatures as high as 120 degC Spin saturation transfer experiments (eg EXSY) also failed44 These data allowed an estimate of the lower limit for the activation energy of the internal shift of ∆Gne ge 22 kcalmol28

Scheme 25 Proposed Internal η4η4 Cyclobutadiene CpCo Migration

- 15 -

The failure of the above experiments inspired a different approach based on the following arguments The antiaromatic character of the linear phenylenes has been shown by theory and experiment to increase with size645 Consequently the effect of metalloaromatization46 makes linear [5]phenylene a better (and hence more strongly bound) ligand for CpCo than a smaller system (eg linear [3]phenylene) Indeed the enthalpy of the homodesmotic in Scheme 26 was computed by DFT methods to be Scheme 26 Calculated Homodesmotic Reaction Showing Preferential Binding of CpCo to

Linear [5]Phenylene

113 kcalmol47 If the barrier to intercyclobutadiene hopping were related to the binding energy of the metal one would expect a more loosely bound metal fragment to migrate faster The hope was therefore that the degenerate haptotropism in Scheme 27 would be observable by VT NMR methods Unfortunately these efforts failed again38 either because the anticipated acceleration was not sufficient to be observable by NMR or because the argument above (which rests solely on ground state considerations) is flawed

Scheme 27 Proposed Degenerate Haptotropic Shift in Linear [3]Phenylene Complex 19

- 16 -

The preceding discussion summarizes some of the quantitative aspects of this new type of haptotropic shift Many fundamental questions however remained to be answered Is it possible to observe the photothermal shift in other systems such as linear [3]- and [4]phenylene What is the exact mechanism of metal migration between cyclobutadiene rings In what way if any does attachment of CpCo alter the structure of the phenylene scaffold Related to these questions was the long-standing quest for an accurate crystal structure of any linear phenylene(CpCo) complex The answers are addressed in the following sections 22 Studies of the Haptrotropic Shift in the Linear [3]Phenylene(CpCo) Complexes As recounted in Section 21 the degenerate internal haptotropic shift could not be seen by NMR in the symmetrical 19 Therefore recourse had to be taken to chemical methods involving an isomerization of the sort shown in Scheme 28

Scheme 28 Isomerization of a Desymmetrized Linear [3]Phenylene(CpCo) Complex

Initial efforts focused on attempts to desymmetrize compound 19 directly by selective electrophilic desilylation specifically protodesilylation Earlier studies48 had shown that such selectivity was possible in the reactions of bis(trimethylsilyl)benzocycloalkenes such as the benzocyclobutene depicted in Scheme 29 In this case loss of the first TMS group is approximately forty times faster than that of the second Along these lines it was thought that exposing 19 to acidic conditions would selectively remove one (or perhaps two) TMS groups before attacking the remaining silylarene positions In the event treating compound 19 with trifluoroacetic acid in carbon tetrachloride did induce protodesilylation but with no selectivity A mixture of products was obtained and its separation proved impossible (Scheme 210) In light of this setback a new synthetic scheme had to be considered that would generate a desymmetrized system directly in the CpCo-catalyzed cyclization step

- 17 -

Scheme 29 Selective Desymmetrizing Reactions of 12-Bis(trimethylsilyl)benzocyclobutene with Electrophiles

Scheme 210 Attempted Selective Protodesilylation of 19

Fortunately such a strategy had already been executed successfully in the creation of 23-bis(trimethylsilyl) linear [3]phenylene (46) and employed the iterative Scheme 211 Iterative Cyclotrimerization Route in the Synthesis of Linear [3]Phenylene 46

cyclization depicted in Scheme 21127 Its specific execution (Scheme 212) started with a Sonogashira reaction between trimethylsilylacetylene (TMSA) and 12-diiodobenzene (47) to give diyne 48 in high yield Deprotection of 48 with K2CO3 immediately followed by standard CpCo(CO)2-catalyzed alkyne cyclotrimerization649 with bis(trimethylsilyl)acetylene (BTMSA) afforded 23-bis(trimethylsilyl)biphenylene (49) Iododesilylation was then performed using pure ICl to give 23-diiodobiphenylene (50) A Sonogashira coupling between TMSA and 50 produced diyne 51 in good yield The use of a slightly modified cyclization procedure provided the new 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52) in 57 yield This protocol employed THF as a cosolvent to BTMSA thus reducing the reaction temperature in turn allowing for the CpCo to remain attached in the final product and preventing catalytic turnover252638

TMS

TMS46

+

TMS

TMS

+

TMS

TMS

+

TMS

R

TMS

dilute

[X+]

X = H D Br

TMS

TMS

[X+]

TMS

X = H D Br

X

- 18 -

Scheme 212 Synthesis of Asymmetric Linear [3]Phenylene(CpCo) 52

High dilution conditions also helped to suppress formation of cyclobutadiene(CpCo) complexes a well known side reaction in alkyne cyclization chemistry

Compound 52 like its tetrasilylated analogue 19 is a black air-sensitive solid Although it can be handled in air for brief periods of time complete decomposition occurs within 24 hours if left exposed to the ambient atmosphere Purification must always be done with neutral activity III alumina as lower activities (and silica gel) cause decomplexation to give the deep red ligand 46 as the only isolable product Critically exposing molecule 52 to UV irradiation induced the desired haptotropic shift giving its photoisomer 53 (Scheme 213) Heating 53 converted it back to 52 thus completing the photothermal cycle Interestingly close inspection of the NMR spectra of this experiment revealed that a small amount of 53 (2) always remained even on prolonged heating That this observation signaled a thermodynamic equilibrium was confirmed by dissolution of pure crystalline 52 and NMR analysis From the equilibrium constant the ∆Gdeg298 was calculated to be 23 kcalmol in favor of 52 The reasons for this energetic preference and a discussion of the NMR spectral properties of these and related complexes are presented in Section 23

Scheme 213 The Photoinduced Thermally Reversible Haptropic Shift in Linear

- 19 -

[3]Phenylene-(CpCo) 52 to Give Photoisomer Complex 53 The investigations of the equilibration depicted in Scheme 213 were all carried out in sealed Pyrex NMR tubes (J-Young or flame-sealed) using benzene-d6 andor toluene-d8 as the solvent As for the linear [5]phenylene(CpCo) system the cycle could be run multiple times without decomposition and was unaffected by changes in solvent and temperature The maximum ratio of 5352 that could be obtained on irradiation was 11 after ten hours This value is larger than that observed for its linear [5] analogs 2144 and 4245 Photoisomerization also occurs with sunlight leading to the photostationary equilibrium of 5253 = 105 Consequently care must be taken to shield 52 from direct andor indirect sunlight Indoor fluorescent lighting however did not induce CpCo migration Attempts to monitor the photoisomerization and its thermal reverse by UV-Vis spectroscopy failed because of minimal changes in the absorptions due to 52 during these processes This finding implies that the absorption spectra of 52 and 53 are not unexpectedly very similar and offers a possible explanation for the maximum photostationary ratio of 11 The activation parameters for the thermal reversal reaction (53 to 52) in Scheme 213 were obtained in the manner described in Section 21 and are shown in Table 22 The relatively high activation barriers (with respect to the NMR time scale) explain why the degenerate isomerization in 19 could not be verified by NMR experiments Qualitatively the ∆Hne values agree with the hypothesis that the more loosely bound CpCo unit in the linear [3]phenylene is relatively more mobile they are approximately 3 kcalmol lower than those of the [5]phenylene system On the other hand the ∆Sne values especially in C6D6 are positive and relatively high although still within the range acceptable for intramolecular reactions Nevertheless a crossover experiment was devised to provide a definite answer

Table 22 Activation Parameters for the Thermal Conversion of Complex 53 to 52

Solvent ∆H

ne (kcalmol) ∆Sne (eu)

C6D6 204 plusmn 14 158 plusmn 22 Toluene-d8 231 plusmn 07 60 plusmn 13

For this purpose two new linear [3]phenylene(CpCo) derivatives were required One would carry a marker on the Cp ring while the other would be labeled at the phenylene frame Execution of Scheme 213 would involve an equimolar mixture of both compounds An intramolecular mechanism would retain the integrity of the labeling while a dissociative path would lead to label scrambling The outcome of this experiment should be ascertainable by NMR spectroscopy and more rigorously by

CoTMS

TMS

CoTMS

TMS

310 365 nmsunlight

30ndash50oC52 53

- 20 -

Scheme 214 Preparation of MeCp- (54) and Deuterium Labeled (55) [3]Phenylene Complexes

mass spectrometry To this end methyl-Cp complex 54 and dideuterio compound 55 were targeted for synthesis (Scheme 214) Compound 54 was prepared by carrying out the modified cyclotrimerization reaction with MeCpCo(CO)2

50 while 55 was made using methanol-OD in the desilylation of 51 The amount of deuterium incorporation in 55 was found to be 63 as gleaned from its proton NMR spectrum Scheme 215 Crossover Experiment with Labeled Linear [3]Phenylene(CpCo) Complexes

- 21 -

Co

TMS

TMS

TMS

TMS

Co

h CoTMS

TMS

Co

D

D

TMS

TMSD

D

TMS

TMS

Co

Co

TMS

TMSD

DCo

TMS

TMS

Co

TMS

TMSD

D

+

+

+

+

mz = 510

mz = 494

56mz = 508

57mz = 496

54mz = 508

55mz = 496

58 59

53 52

Not observed

Six distinct products are possible in the crossover experiment using 54 and 55 (Scheme 215) Compounds 56 and 5 would arise as a consequence of an intramolecular shift Molecules 53 and 58 and their photoisomers 52 and 59 respectively would be the result of metal fragment dissociation Mass spectrometry would readily verify the occurrence of crossover as the masses (given in mz in Scheme 215) of the products with scrambled labels (52 53 58 59) are distinct from the masses of the starting materials (54 55) and their photoisomers (56 57) In the first part of the experiment equal amounts of 54 and 55 were mixed (shielded from light) and allowed to stand for 2 hours at room temperature The resulting 1H-NMR spectrum consisted of only the signals for 54 and 55 Similarly the mass spectrum showed molecular ion peaks matching the masses of 55 and 56 (Figure 21) The second step was irradiation Analysis of the photolyzed mixture showed new peaks due to complex 56 (the resonances of which had been obtained in a separate photothermal experiment with pure 54) with the expected integration ratio and a second set assigned to 57 identical with the spectrum of 53 but with the expected attenuated absorption for the silyl bearing arene hydrogens The relative integrations for all compounds observed were consistent with a mixture of 5455 and 5657 Mass spectral analysis of the irradiated mixture showed a pattern that was identical to that collected before irradiation (Figure 21) Finally the thermal reversal reaction was carried out by heating the photolyzed mixture at 80 degC After 30 hours the resulting

- 22 -

NMR spectrum matched that of the initial mixture of 54 and 56 in particular confirming the full protonation of 54 and the unchanged level of deuterium incorporation in the silyl

Figure 21 Molecular ion peaks for 5456 (mz = 508) and 5557 (mz = 496)

bearing arene ring of 55 The corresponding mass spectrum contained no evidence for the presence of scrambled products To conclude The haptotropic shift is non-dissociative The exact manner in which the metal traverses from one cyclobutadiene ring to the other will be examined in greater detail in Section 24

23 X-Ray Structural and Comparative NMR Analysis of Linear [3]Phenylene(CpCo) Complexes The results described in Sections 21 and 22 pose some fundamental questions beyond those concerned with the immediate details of the observed haptotropism and addressing the basic novelty of the complexes involved What actually happens to the phenylene ligand when it is ligated via a cyclobutadienoid ring This section will address this question from a structural and (NMR) magnetic point of view Only one crystal structure of a linear phenylene(CpCo) complex was known at the outset of this work namely that of [5]phenylene(CpCo) 42 (Figure 17) and its acquisition required extensive efforts at crystallization28 Unfortunately extensive disorder obviated a detailed analysis It was hoped that some of the complexes employed in the chemistry disclosed in Section 22 would be more forthcoming in this respect The challenge lay in finding the right conditions for crystal growth We began with tetrasilyl linear [3]phenylene(CpCo) 19 which had been crystallized previously by slow cooling in acetone38 These conditions and numerous others (Table 23) did not provide material suitable for X-ray diffraction Success entailed slow cooling a solution of 19 to ndash10 degC in a mixture of methanol-diethyl ether (41) The ensuing sample allowed the determination of the first high quality crystal structure of a linear phenylene (CpCo) complex obtained in collaboration with the group of Professor Tatiana Timofeeva of New Mexico Highlands University (Figure 22)

Table 23 Trial Crystallization Conditions for Linear [3]Phenylene(CpCo)19

Solvent (Ratio) Conditions Result

Acetone Slow Cooling Heterocrystalline Solid Acetone-Pentane (31) Slow Cooling Heterocrystalline Solid

Pentane-Acetone (101) Solvent Diffusion Amorphous Solid Chlorobenzene Slow Cooling Amorphous Solid

- 23 -

Acetone-Methanol (110 Slow Cooling Amorphous Solid Diethyl Ether-Methanol Slow Cooling Small Needles

Acetonitrile Slow Cooling Powder Ethyl Acetate Slow Cooling No Crystals

Ethyl Acetate-Methanol (11) Slow Cooling Amorphous Solid Methanol-Diethyl Ether (41) Slow Cooling Large Fine Needles

Figure 22 X-ray crystal structure of 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) (19) Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are

omitted for clarity Expectedly the CpCo unit is bound in an η4 fashion to the cyclobutadiene ring Also prominent is the deviation from planarity (Section 11) in the linear [3]phenylene a facet typical of the phenylenes themselves (Section 11)9a Of greater importance than these general observations however is the effect of metal complexation on the linear [3] framework The bond lengths for 19 are shown in Figure 23 and as is typical for the phenylenes6 show a certain degree of bond π-localization with measurable differences between single and double bonds However the extent of this phenomenon and its direction varies significantly when compared to the free ligand 60 A quantitative

- 24 -

comparison of the structural data for 19 with those of its ligand 60 is shown in Figure 2327

In 60 the terminal rings adopt bond alternation similar to that in biphenylene (Section 11) and the central benzene takes on a ldquobis-allylrdquo configuration both ostensibly to minimize electron density (and therefore antiaromaticity) in the four-membered rings As dictated by symmetry the two bonds spanning the central ring are of equal length (1385 Aring) Ligation by CpCo alters this picture profoundly in as much as bond alternation across the entire phenylene frame including the four-membered rings is strongly reduced (Figure 23) Generally all relatively long bonds in 60 shorten in 19 while all short bonds lengthen Some residual but attenuated biphenylene type

Co

1512(2)

1513(2)

1407(2)

1385(2)

1385(2)

1397(2)

1356(2)

1359(2)1436(2)

1397(2)

1441(2)

1411(3)(0052)

1384(3)(-0052)

1474(3)(0077)

1384(3)(-0057)

1408(3)(0052)

1448(3)(0051)

1480(3)(-0032)

1468(3)(-0045)

1437(3)(0052)

1465(3)( 0058)

1434(3)( 0049)

1352(3)(-0033)

1351(3)(-0034)

1476(3)(0069)

1495(3)(-0017)

1372(3)( 0016)

1405(3)(0008)

1376(3)(0017)

1413(3)(-0023)

1427(3)(0030)

1488(3)(-0025)

1423(3)(-0018)

(x) = (19) - (60)increasedecrease

60

19

1907(1)

1891(1)

1886(3)

1889(3)

1889(2)

1901(3)

1669

1725

Si

Si

Si

Si

Me

MeMe

Me

Me

Me

Me

MeMe

MeMe

Me

Si

Si

Me

MeMe

MeMe

Me

Si

Me

MeMe

Si

Me

MeMe

- 25 -

Figure 23 Comparison of bond lengths (in Aring) between linear [3]phenylene(CpCo)complex 19 and 2378-tetrakis(trimethylsilyl) linear [3]phenylene (60) The bond distances in 19 are shown in blue Increases in bond length in going from 60 to 19 are marked in green decreases in red

ldquobond fixationrdquo (Figure 12) remains in the vicinity of the uncomplexed cyclobutadiene Compound 19 thus provides a prime demonstration of the powerful effect of metalloaromatization46 in which the bonds of a cyclobutadiene-metal system attempt to adopt the equalized bond lengths that are a classic hallmark of aromaticity2ndash4 Encouraged by the successful development of a procedure to obtain X-ray quality crystals of 19 these techniques were applied to bis(trimethylsilyl) linear [3]phenylene(CpCo) 52 Gratifyingly with acetone as the solvent the results depicted in Figure 24 were ultimately obtained Figure 24 X-ray crystal structure of 23-bis(trimethylsilyl) linear [3]phenylene(CpCo) (52)

Carbon atoms are labeled grey silicon atoms beige and cobalt blue Hydrogen atoms are omitted for clarity

A comparison of the bond lengths of 52 with those of its corresponding linear [3]phenylene ligand 469a is given in Figure 25 Comparison with Figure 23 reveals the same type of aromatization of the ligand on attachment of the metal With these structures in hand an attempt was made to rationalize structurally the

- 26 -

thermodynamic preference for 52 in which the CpCo is located proximal to the silylated terminus in its equilibrium with 53 in which the metal is located close to the unsilylated benzene ring Focusing on the desymmetrizing ortho-bis(trimethylsilyl) unit one notes that the SiCndashCSi bond in 52 is elongated by 005 Aring on attaching the metal in 46 thus providing steric relief On the other hand the symmetry equivalent remote C7ndashC8 distance is unchanged The same effect is seen in the tetrasilyl complex 19

Figure 25 Comparison of bond lengths (in Aring) between bis(trimethylsilyl) linear [3]phenylene(CpCo) complex 52 and 23-bis(trimethylsilyl) linear [3]phenylene (46) Bond lengths for 46 are the average of four molecules in the unit cell (standard deviation = plusmn002)

Increases in bond length going from 46 to 52 are marked in green decreases in red

The observed structural changes make sense in a simple resonance picture

Co

1413(10)(007)

1406(10)(-004)

1459(10)

( 005)

1370(11)(-007)

1418(10)( 005)

1443(10)(003)

1470(10)(-005)

1465(10)(-005)

1446(10)( 008)

1485(10)( 006)

1432(10)( 004)

1347(10)(-003)

1345(10)(-002)

1492(10)( 007)

1503(11)(-002)

1379(10)(001)

1391(11)(-001)

1409(10)(004)

1418(11)(-003)

1367(11)(001)

1478(10)(-002)

1408(11)(-001)

1891(8)

1890(13)

1670

1723

SiMe

MeMe

Si

Me

Me

Me

(x) = (53) - (62)increasedecrease

SiMe

MeMe

Si

Me

Me

Me

190

145134152

139138

150

137145

136

142 137

152137 137

152

141

137 144

189

141143142140

52

46

- 27 -

(Scheme 216) Metalloaromatization alters the dominant resonance forms during intercyclobutadiene hopping such that the essentially single SiCndashCSi bond in 52 transforms into an essential double bond in 53 increasing unfavorable repulsion between the TMS groups Scheme 216 A Resonance Picture Rationale for the Preference of 52 in its Equilibrium with 53 The aromatization effect of metal complexation on the phenylene nucleus described structurally in the preceding text can also be demonstrated powerfully through the measurement of ring currents with 1H-NMR spectroscopy both by experiment and computation (NICS13 see Section 11) A relevant simple example is depicted in Figure 26(a) featuring the changes occurring when 12-bis(trimethylsilyl)benzocyclobutadiene (61) is complexed by CpCo as in 6251 The paratropic antiaromatic 8π system 61 exhibiting relatively shielded six-membered ring hydrogens turns diatropic in 62 Equally importantly and focusing on the ring current contributions of the individual cycles the paratropism of the four-membered ring in 63 shields the adjacent hydrogens more than the remote ones Conversely aromatization of this ring and the ensuing diatropism inverts this order

Figure 26 The effect CpCo complexation (a) on benzocyclobutadiene 61 and (b) linear [3]phenylene 46 Chemicals shifts are in ppm

Co SiMe3

SiMe3

Co

SiMe3

SiMe352 53

∆Gdeg298 =23 kcalmol

- 28 -

Turning to a phenylene system comparison of the NMR data for complex 52 with those for ligand 46 (Figure 26(b)) reveals the same changes not only in the vicinity of the ligated ring but also in the remote parts of the molecule Thus the hydrogens closest to the metal fragment are shifted downfield by 125 ppm in 62 and 148068 ppm in 52 when compared with 61 and 46 respectively The observed relatively large chemical shifts of the arene hydrogens proximal to the metal unit are not due to its anisotropy since its value in this area of space is (if anything) shielding5152 In addition the remote hydrogens in 52 are deshielded by 055033 ppm relative to the corresponding nuclei in 46 clearly substantiating the aromatization of the overall system upon metal complexation that was seen by structural analysis These pronounced chemical shift changes are diagnostic and greatly aided the spectral interpretations of the photochemically induced haptotropic shift experiments described in Sections 21 and 22 as illustrated for the isomerization between 52 and 53 (Scheme 217)

Scheme 217 Chemical Shift Changes in the Isomerization of 52 to 53

These NMR measurements were augmented by NICS calculations carried out in collaboration with Professor Amnon Stanger at the Technion in Haifa NICS data have the advantage that they indicate the extent of (anti)aromaticity even in rings for which the molecule has no hydrogen probe in the classical NMR experiment in this case the cyclobutadienes Computational details are given in Chapter 4 The experimentally determined proton NMR data for the series of silylated linear phenylenes from [2] to [5] and their metallated analogues in addition to the corresponding NICS(1) values of the respective parent phenylenes are shown in Figure 27 All compounds in Figure 27 are known except for the hypothetical biphenylene(CpCo) 64 which is included for comparative purposes Metalloaromatization is pronounced as all rings of the phenylene exhibit diminished or more negative NICS numbers signaling increasing aromatic and decreasing antiaromatic character respectively Again the effect is most pronounced on the rings closest to the metal bound unit tapering off (but never disappearing) with distance Most illustrative in this respect is 44 in which the penultimate and ultimate rings away from the Co still show decreases in the NICS values of 06 and 05 ppm respectively Interestingly the sum of all NICS values of 44 (ldquototal NICSrdquo13c) ndash91 is less negative than that of 21 ndash132 suggesting that 21 is more aromatic hence more stable as observed experimentally This may be fortuitous and the issue is addressed further in Section 24 Finally a caveat regarding the unusually large negative NICS values associated with the CpCo-complexed cyclobutadiene rings As pointed out by Solagrave in connection with a related study of (benzene)Cr(CO)3 which produced similar numbers53 there are local ring currents associated with the extra electrons involved in the metal to π-ligand

CoTMS

TMS796675674

678

436 CoTMS

TMS747683724

662

444

310 365 nmsunlight

30ndash50oC

52 53

- 29 -

bonding that lead to an overestimation of aromaticity Therefore to corroborate the general conclusions of metalloaromatization of this (and all other rings) in Figure 27 Stangerrsquos NICS scan method was applied54 This procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (NICSXY) and out-of-plane components (NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their

Figure 27 Experimental 1H-NMR (C6D6 blue) and computed NICS(1) (green) values for linear phenylenes and their corresponding CpCo complexes The experimental data are for the silylated

derivatives shown The NICS data are for the parent systems interpretation The data presented in Chapter 4 confirm the conclusions of this section While not reflective of ring current effects the values of the 13C chemical shifts for the linear phenylene(CpCo)complexes do provide some insight into the nature of the

- 30 -

σ-framework Comparing complex 19 with parent ligand 60 one observes two general phenomena (Figure 28) The most apparent is the upfield values for the cobalt-bound cyclobutadiene carbons (~74ndash78 ppm) in 19 arising from the local anisotropic shielding effect of the metal (vide supra) Secondly the carbon atoms in the four-membered ring not bound to the metal exhibit large deshielded values (144ndash149 ppm) This effect also seen in ligand 60 arises from the rehybridization6 of the cyclobutadiene sp2 orbitals and is observed in all phenylene topologies A comparison of the 13C-NMR data for the linear [3]- [4]- and [5]phenylene(CpCo)complexes with their respective parent ligands is given in Chapter 4

Figure 28

13C-NMR data for complex 19 and parent silylated ligand 60 Values are in ppm 24 Computational Mechanistic Studies of the η4η4 Cyclobutadiene Haptotropic Shift How does the CpCo moiety migrate from one cyclobutadiene unit to the next Two extreme alternatives present themselves a least-motion movement across the intervening arene unit or a more circuitous pathway along the periphery The latter is prevalent in other computed haptotropic shifts56-57 in particular those occurring in (arene)Cr(CO)3 complexes all of which choose peripheral trails56 In these the metal typically moves straight to the edge to adopt an η4 (often described as η1) trimethylenemethane-like transition state on the way to a neighboring ring as illustrated for the η6-η6 hopping in naphthaleneCr(CO)3 summarized in Scheme 218 More relevant is the computed course of the η6-η6 interconversion of (biphenylene)Cr(CO)3 (Scheme 219)57 The metal slides from the (near)center of one benzene ring to the quaternary (four-membered) ring carbon to reach a distorted trimethylenemethane maximum and then proceeds to the edge of the bridging cyclobutadiene bond This species represents a minimum on the potential energy curve and adopts an η2-like complexed cyclobutadiene topology (ldquoquasi-η4rdquo) from which it continues by the microscopic reverse on to the other benzene nucleus The relevance of these findings with respect to the intercyclobutadiene hopping of CpCo along the phenylene frame was not clear at the outset of the work described in this section The CpCo fragment has a different electronic requirement from Cr(CO)3 and interring migration in arenes (and related systems) involves aromatic electron counts of all intervening circuits

Scheme 218 Migration of Cr(CO)3 Across Naphthalene

- 31 -

Scheme 219 Migration of Cr(CO)3 Across Biphenylene

DFT calculations were carried out in collaboration with Professor Thomas Albright at the University of Houston In these studies using B3LYP 3-21G (carbonhydrogen) and LANL2DZ (cobalt) basis sets the metal fragment was placed 18 Aring above the π system with energy minimizations carried out every 02 Aring along the frame of the parent linear phenylene in question When transition states and local minima were located their structures were refined with the B3LYP 6-31G (hydrogen) 6-113G (carbon) and LANL2DZ (with inclusion of cobalt f-orbitals) basis sets More computational details are given in Chapter 4 The resulting potential energy surface for the thermal rearrangement in the parent linear [3]phenylene(CpCo)system is shown in Figure 29 Figure 210 contains enlarged images of the transition states and intermediate structures The haptotropic shift begins with the (η4-cyclobutadiene)CpCo global minimum (labeled ground state GS) assigned a relative value of 000 kcalmol An η2-cyclobutadiene transition state (TS 1) 269 kcalmol higher in energy than GS is passed before reaching a local minimum (LM) that lies 109 kcalmol above GS LM features CpCo coordinated unsymmetrically η4 to the central benzene ring thus avoiding an unstable 20 electron η6-benzene configuration (not shown) which when explicitly calculated proved to lie 36 kcalmol above LM From LM a symmetry-related second η4 structure is reached via an η3-benzene transition state (TS 2 barrier 14 kcalmol) that symmetrizes the ldquoleftrdquo with the ldquorightrdquo half of the molecule LM is 249 kcalmol higher in energy than GS The shift is completed through the reverse of the initial two movements through LM and TS 1 on the other side of the ligand to reach the second cyclobutadiene ring Thus as for Cr(CO)3 (Scheme 219) CpCo migrates along the edge of the linear phenylene but because of its differing electronic needs through distinctly different intermediates and transition states Most obvious is the internal η2-cyclobutadiene TS 1 which for Cr changes to a peripheral η2-intermediate The calculated rate determining barrier of 269 kcalmol (GS to TS 1) is slightly higher than that measured for the reversal of 53 to 52 (~23 kcalmol) Part of this discrepancy may be due to ground state activation of 53 which is ~2 kcalmol less stable than 52 The LM structure has some resemblance to the isolated η4-CpCo angular [3]phenylene 23 (Section 12) Its location in an energetic well of ~14ndash16 kcalmol (TS 1 and TS 2) suggested that it may be observable at low temperature This investigation is detailed in Section 25

- 32 -

Figure 29 Calculated potential energy profile for the thermal η4η4 haptotropic shift in linear [3]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

0

5

10

15

20

25

30

1 2 3 4Reaction Path

Co

Co

C o

C o

GS η

4

LM η

4

TS1 η

2

TS 2 η

3

00

269

109

249

Key - Global MinimumGround State (GS)- Local Minimum (LM)

- Transition State (TS)

122

3 34 4

- 33 -

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 34 -

(d) Transition state 2 η3-benzene (249 kcalmol)

Figure 210 Optimized structures and relative energies for the linear [3]phenylene(CpCo) haptotropic shift Carbon atoms are shaded grey hydrogens light grey and cobalt blue Bond

lengths are in Aring The potential energy profile for the thermal shift in the linear [5]phenylene(CpCo) system was calculated in the same manner and is shown in Figure 211 Images of the intermediates and transition states are depicted in Figure 212 Placing the metal fragment on the inner cyclobutadiene ring resulted in the lowest energy structure and was therefore set as the global minimum (GS) Two distinct haptotropic migrations inner-to-inner and inner-to-outer cyclobutadiene are now possible (Section 21) Beginning at GS the metal can proceed in the direction of TS 2 or TS 3 respectively both of which are η2 with similar barrier heights (~36 kcalmol) The former pathway is degenerate and continues from TS 2 to η4-LM 1 and then via η3 central benzene TS 1 to the symmetry related corresponding LM 1 TS 2 and finally GS involving the opposite inner four-membered ring The rate determining barrier for this process is 359 kcalmol clearly too high to be measurable by NMR techniques as found for 212838 Interior-to-exterior shifting of the cobalt continues from TS 3 on to η4-benzene LM 2 The η3-TS 3 is traversed before the second η4η2

sequence (LM3 and TS 5 respectively) ultimately leading to LM 4 which is the outer

- 35 -

cyclobutadiene coordinated structure and represents the photoisomeric species observed experimentally in Scheme 23 The computed rate-determining barrier (TS 3) of 263 kcalmol for the reverse reaction of LM 4 to GS is close to the experimentally measured values of 256ndash276 kcalmol for the derivatives in Table 21

Figure 211 Calculated potential energy profile for the η4η4 haptotropic shift in linear [5]phenylene(CpCo) Relative energies are shown in blue and are given in kcalmol Structure

labels and hapticity are highlighted in black and red respectively

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

40

Reaction Path

263

0

5

10

15

20

25

30

35

C o

C o

C o

C o

Co

Co Co

C o

C o Co 360 370

359 357

367

97

203 190 196

1 2 3 4 5 6 7 8 9 10

TS 1 η

3

LM 1 η

4

TS 2 η

2

GS η

4 00

TS 3 η

2 TS 4 η

3 TS 5

η2

LM 2 η

4 LM 3 η

4

LM 4 η

4

Key- Global MinimumGround State (GS)

- Local Minimum (LM)

- Transition State (TS)

- 36 -

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 37 -

(d) Transition state 4 η3-benzene (367 kcalmol)

(e) Local minimum 3 η4-benzene (190 kcalmol)

- 38 -

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 39 -

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

(i) Local minimum 1 η4-benzene (190 kcalmol)

- 40 -

(j) Transition state 1 η3-cyclobutadiene (356 kcalmol)

Figure 212 Optimized structures and relative energies for the linear [5]phenylene(CpCo) haptotropic shift Structures for the inner-to-outer cyclobutadiene migration are given by (a)ndash(g)

Species (h)ndash(j) are involved in the interior-to-interior four-membered ring pathway Carbon atoms are shaded grey hydrogen atoms light grey and cobalt blue Bond lengths are in Aring

Why does CpCo prefer complexation to the internal cyclobutadiene that is GS (as represented by 21 and 42) over LM 4 (as represented by 44 and 45) Calculations show that the energies required to distort linear [5]phenylene to the geometries found in

- 41 -

the complexed isomers are very similar (16 versus 14 kcalmol) Hence the answer must rest on electronic grounds Indeed extended Huumlckel calculations reveal that the overlap populations between the frontier orbitals on the CpCo fragment and the HOMO and the LUMO of the π system are greater for GS (00793 and 00745 respectively) than for LM 4 (00556 and 00517 respectively) A didactically more instructive valence bond view recognizes that metalloaromatization of the inside four-membered ring allows the formulation of more resonance forms that avoid antiaromatic cyclobutadiene circuits A full list of these resonance forms as well as details of the EHMO calculations are given in Chapter 4 25 Low Temperature Photochemical Studies of the Haptotropic Shift in Linear [3]Phenylene(CpCo) Complexes Of the various participating species in the mechanism for intercyclobutadiene migration (Section 24) specific attention was focused on the η4-benzene intermediates that occur in both the linear [3]- and [5]phenylene haptotropic shifts These structures are energetic local minima on the reaction profiles for both systems and were of considerable intrinsic interest not only as reactive intermediates in this manifold but also because of their relationship to the isolable angular [3]phenylene(CpCo) complex 2329 (Figure 213) Figure 213 (a) Calculated structure for the η4-benzene linear [3]phenylene(CpCo)intermediate

in the haptotropic migration (b) Crystal structure of η4 angular [3]phenylene (CpCo) 23

While rare a handful of other η4-benzene-metal complexes have been isolated (Figure 214) For example two related iridium based systems benzene(CpIr) 6658 and benzene triphos(Ir) 6759 are known As expected ligation causes significant shielding of the hydrogens in the η4 portion of the ligand especially the terminal positions The η4 intermediates in the haptotropic shift are situated in wells on the potential energy surface that are ~17 kcalmol deep for the linear [5]- and ~15 kcalmol for the linear [3]phenylene complexes These values are large enough that such species might be observable by NMR spectroscopy if irradiation of the starting materials were performed at low temperature and if the excited state would relax selectively to these intermediates As a suitable candidate with which to explore this possibility the partly symmetric tetrasilyl complex 19 was chosen The generation of anticipated desymmetrized 68 would be readily detected by the appearance of 11 new singlets in the 1H- and 23 new peaks in the 13C-NMR spectra (Scheme 220)

(a) (b)

- 42 -

Figure 214 Selected relevant examples of isolated η4-benzene complexes and their proton NMR chemical shifts (ppm)

Scheme 220 Low Temperature Irradiation Experiment Designed to Generate η4-Benzene Intermediate 68

Construction of a satisfactory setup to allow for the planned low temperature irradiation was not trivial An optimal experimental configuration however was devised utilizing three pieces of equipment each of which is shown in Figure 215 The first was a custom-made Pyrex Dewar flask small enough to adequately contain an NMR tube Cooling was achieved by means of a Neslab refrigerated circulating bath Thirdly a Rayonet Photochemical Reactor was used as the light source The sample was first placed inside of the Dewar flask and cooled to the required temperature inside of the Rayonet Once cold irradiation was carried out for the desired length of time When complete the sample was transported cold to the NMR laboratory and very quickly placed inside of a pre-cooled NMR probe for analysis A solution of complex 19 was irradiated at ndash65 degC as described and its 1H-NMR spectrum recorded at ndash30 degC revealing a dramatic change The signals for 19 had almost entirely vanished and a set of new peaks appeared The new aromatic resonances were comprised of two sharp singlets at δ = 708 and 644 ppm and a broad singlet at δ = 558 ppm all of which integrated for 2 hydrogens each Another broad

649

586

316

H H

Co544

66 67 23

Ir

P(Ph2)P(Ph2) P(Ph2)

H

H

H

625

594

350

Ir

H

H

H

- 43 -

Figure 215 Cold irradiation experimental setup consisting of (a) Pyrex Dewar flask (b)

refrigerated circulating bath (c) Rayonet Photochemical Reactor with Pyrex Dewar vessel placed inside

(a) η

4 (b) η

4 (c) η

4

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

New peaks

L L

- 44 -

Figure 216 Stacked plot of the aromatic 1H-NMR spectral region recorded after the cold irradiation of 19 in toluene-d8 Peaks for 19 are indicated by blue new peaks by red arrows

Impurities are marked with and traces of free ligand 60 with L The scale is in ppm

singlet at δ = 398 ppm (5 H) was assigned to a new Cp group (Figure 217) and two new TMS singlets (9 H each not shown) were also present The new broad Cp absorption displayed peculiar behavior gradually moving to higher field (∆δ ~ 08 ppm for Cp-H) on warming from ndash30 degC to 10 degC (Figure 217) The broadened singlet at δ = 558 ppm showed similar albeit much attenuated behavior At room temperature all new peaks had disappeared leading to regeneration of the original spectrum of 19

Figure 217 Stacked plot of the Cp spectral region in the cold irradiation of 19 in toluene-d8 Peaks for molecule 19 are indicated by blue the new peaks by red arrows The scale is in ppm

In addition to these NMR observations a remarkable change in color from the redmaroon of 19 to olive green took place during the course of this experiment (Figure 218) Indeed the UV-Vis spectrum of the low temperature species is strikingly different from that of 19 showing a large broad absorbance band centered in the visible region

ndash30 degC

ndash20 degC

ndash10 degC

0 degC

10 degC

19

THF

- 45 -

Figure 218 Color change during the low temperature irradiation of 19 (a) Before irradiation (b) After irradiation

Complex 19

Low Temperature Species

0

02

04

06

08

1

12

14

16

18

2

400 430 460 490 520 550 580 610 640 670 700

Wavelength (nm)

Ab

sorb

an

ce

Figure 219 UV-Vis spectra (toluene) of 19 (at rt) shown in blue and the new compound (at ~

ndash30 degC) shown in red

at 654 nm (Figure 219) Warming the sample to room temperature restored its original red color While the observation of a new species was gratifying the NMR data posed a puzzle as they were clearly incompatible with (a static) structure 68 Instead they pointed to a molecule exhibiting mirror (or ldquotop-downrdquo) symmetry along the long molecular axis as in 19 itself The two most obvious candidates 69 and 70 (Figure

(a) η

4 (b) η

4

- 46 -

220) were ruled out as the first could not be found during the computations underlying Figure 29 and the second actually constitutes the transition state TS 1 for the thermal reverse process

Figure 220 Possible (but unlikely) structures of correct symmetry for the low temperature

photoisomer of 19 In the hope to shed further light on the nature of purported 68 low temperature 13C in conjunction with 2-D NMR (HSQC HMBC) experiments were carried out These data led to the tentative assignments shown in Figure 221 Assuming the presence of top-down symmetry as surmised by the proton spectra one would have expected to observe nine phenylene carbon signals The actual spectrum however contains only six peaks The Cp line was broadened to the point of being barely visible and no crosspeaks for the absorption at δ = 556 ppm were seen by 2-D NMR spectroscopy

Figure 221 Partial assignments of 1H-(italicized) and 13C-NMR signals of 68 The ldquotop-downrdquo plane of symmetry is indicated by the dashed purple line HMBC δ = 643 ppm correlates with δ = 1461 and 1521 ppm δ = 708 ppm correlates with δ = 1477 and 1508 ppm δ = 033 ppm

correlates with δ = 1477 ppm and δ = 036 ppm correlates with δ = 1461 ppm HSQC δ = 643 ppm correlates with δ = 1121 ppm δ = 708 ppm correlates with δ = 1227 ppm and δ = 398

ppm correlates with δ = 85 ppm The connectivity of the CpCo to the central ring is left intentionally unspecified and the choice of positioning it to the left of the center hydrogens (blue)

SiMe3

SiMe3

H

Me3Si

Me3Si

H

Co

398 (br)

HH

1461

~85 (br)

708

H

556 (br)1508

= Unobserved 13C signals

H

H

Mirrorplane

6431477 1521

033036

11211227

- 47 -

arbitrary Similarly the assignments of the groups of ldquoleftrdquo and ldquorightrdquo benzene signals are tentative and might be inverted The carbons marked could not be observed

It is thus clear that we are dealing with an unusual species and if it is 68 the molecule must be partly (but not completely) fluxional around the central ring Returning to the computed energy profile in Figure 29 one notes that central η4η4-benzene fluxionality via TS 2 with a barrier of 140 kcalmol is presaged This process which causes ldquoleftrdquo-ldquorightrdquo but not ldquotoprdquo-ldquobottomrdquo symmetrization is unlikely to be responsible for the above data as it should have given rise to two 1H-NMR singlets for the central hydrogens However considering the expected relative closeness in the respective chemical shifts of the anticipated signals (see Figure 214) accidental isochronism could not be ruled out Consequently low temperature irradiation experiments were executed with 52 in which the ldquoleftrdquo-ldquorightrdquo option of symmetrization was obviated by the substitution pattern while leaving the ldquotoprdquo-ldquobottomrdquo option intact (Scheme 221) As Scheme 221 Low Temperature Irradiation of 52 and Possible Pathways for Fluxionality of

Intermediate 71

indicated in color the latter would provide a diagnostically simple proton spectrum of only four phenylene signals The former on the other hand should show eight such peaks A potential complication of this experiment was the possibility of two regioisomeric (and non-interconverting) cobalt species located on either side of the central six-membered ring (Scheme 222) In the event the spectra shown in Figure 222 were obtained At ndash60 degC in

HH

CoTMS

TMS

CoTMS

TMS

TMS

TMS

Co

TMS

TMS

CoTMS

TMS

Co

TMS

TMS

Co

Top-bottom

cold hν ∆

Lef t-right

52 53

∆

71

or

H

HH

H

H H

H HH

HH H H

H

- 48 -

addition to unreacted 52 and photoisomer 53 a new species formed the spectral features of which implicate 71 as a ldquotop-bottomrdquo symmetrizing species Specifically the

Scheme 222 The Two Possible Regioisomers of 71 ldquoLeftrdquo and ldquoRightrdquo

71

52

53 53

53

52

TMS

TMS

Co

TMS

TMS

Co

TMS

TMS

Co

71

TMS

TMS

Co

or

Right Lef t

ndash60 degC

ndash50 degC

ndash40 degC

ndash30 degC

53

- 49 -

Figure 222 Stacked plot of the aromatic spectral region in the cold irradiation of 52 in toluene-d8 Peaks for molecule 52 are marked by blue arrows 53 in red and 71 in green Trace amounts

of free ligand bis(trimethylsilyl) linear [3]phenylene] 46 are denoted with L The scale is in ppm

unsubstituted benzene terminus hydrogens exhibit an AArsquoBBrsquo pattern at δ = 647 ppm which integrate for 4 hydrogens The central ring hydrogens appear as a broad singlet at δ = 557 ppm (2H) and the silylated terminus as a singlet at δ = 632 ppm (2H) Warming the reaction mixture to 10 degC led to the gradual disappearance of 71 with a concomitant increase of the signals assigned to 52 and 53 This experiment confirms the conclusions drawn as a result of the low temperature irradiation of 19 namely that a ldquotop-bottomrdquo symmetrizing species is generated Remarkably in view of the possibility of two regioisomers (Scheme 222) only one set of peaks is observed indicating that the excited state of 53 relaxes to settle on only one side of the central ring Which side is a matter of speculation Figure 223 compares the 1H chemical shifts of 71 with those of 68 and for calibration 52 53 and free ligands 46 and 60 For the first pair it is clear that the two species are very similar with almost identical chemical shifts of the relevant hydrogens taking into account the considerable deshielding effect of TMS substitution on the unsubstituted terminus in 73 (~07 ppm cf 52 vs 53 46 vs 60) Arguably placing the CpCo moiety to the ldquoleftrdquo as depicted in 68 and 71 aromatizes the proximal benzene by η2-complexation of the adjacent four-membered ring leaving considerable benzocyclobutadiene character on the ldquorightrdquo consistent with the associated chemical shifts

- 50 -

CoTMS

TMS796675674

678

CoTMS

TMS747683724

662

Co

TMS

TMS

52

71

53

424

642

557 632652

436 444

Co

TMS

TMS

68

398

556 643708

TMSTMS

TMS

TMS684607619

645

46

assignmenttentative

TMS

TMS

TMS

TMS623 685

60

TMS

TMS

TMS

TMS

Co

691 795745

19

441

Figure 223 1H-NMR chemical shift comparison of 68 and 71 with other relevant species A plot of the changes in concentration of 52 53 and 71 with temperature is shown in Figure 224 Within (the considerable) error and considering the unusual magnetic behavior of 71 (vide infra) it appears that the latter converts mainly to 52 in the temperature regime in which 53 is stable with respect to its thermal reverse to 52 This observation may be interpreted as indicating a lower barrier for Co migration from the center ring to the more stable cyclobutadiene haptomer

- 51 -

0

1

2

3

4

5

6

7

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Inte

gra

tio

n v

s I

nte

ra

l S

tan

da

rd

52

53

71

Figure 224 Plot of the concentration changes of 52 53 and 71 with temperature measured by the relative integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively

The ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100)

Another plot this one showing the ratios of 52 53 and 71 with respect to each other is given in Figure 225 The disappearance of 71 with rising temperature is illustrated by the increase in the ratios of 5271 and 5371 As indicated by the steep slopes the conversion of 71 into 52 and 53 is particularly fast between ndash10 and 0 degC That complex 52 is preferentially formed is again confirmed by the escalating 5253 ratio While these data do not provide a definitive answer for the location of the CpCo they are consistent with the plots shown in Figure 224 and the above discussions

- 52 -

0

1

2

3

4

-50 -40 -30 -20 -10 0 10

Temperature (degC)

Rel

ati

ve

Inte

gra

tio

n

5271

5371

5253

Figure 225 Plot of the ratios of 52 53 and 71 against each other with temperature measured by the integrations of the peaks at δ = 796 (52) 747 (53) and 632 ppm (71) respectively The

ndashCD3 peak of toluened-d8 was used as the internal standard (set to 100) Having established the topological aspects of 68 and 71 attention was turned to their peculiar NMR characteristics in the vicinity of the metal ie the broad peaks for the central hydrogens and the CpHs the broad Cp-carbon line the inability to observe 13C signals for the central benzene ring and the temperature dependent drifting of (particularly) the Cp absorption A trivial (and ultimately unsatisfying) explanation for at least peak broadening was the presence of trace paramagnetic metallic impurities60 that might have been generated during the irradiation process Spin exchange preferentially Co-based might affect the center atoms in 68 and 71 more than the remainder of the molecule although it should also cause line broadening in the isomers 19 and 52 and 53 respectively Experimentally the presence of such species was made unlikely by executing the cold irradiation experiment of 19 in the presence of the radical trap 13-cyclohexadiene which produced spectra identical to those described earlier An attractive alternative that might explain the data and in addition provide a mechanism for ldquotop-downrdquo exchange is of the intervention of triplet state cobalt species The ability of metals to change their electronic spin state and the consequences of this phenomenon on organometallic structure and reactivity are well documented61

18-Electron CpCo complexes are ground state singlets but their 16-electron counterparts accessed typically by ligand dissociation have more stable triplet configurations62 A number of CpCo and related Co species have also been reported in

- 53 -

which singlets are in thermal equilibrium with paramagnetic triplets by intersystem crossing63 Such complexes display spectral behavior very similar to that seen for 68 and 71 For example 7263b exists as a mixed spin state system in which the singlet predominates at room temperature in solution (Figure 226) On heating the triplet becomes increasingly populated shifting and broadening its NMR signals Cooling the solution back to room temperature reverses these spectral changes In addition to complexes of cobalt analogous observations have been reported for other metals such those based on hafnium64 copper65 ruthenium66 and tungsten67

Figure 226 Temperature dependent chemical shifts in CpCo derivative 72 in toluene-d8

(marked as S on the plot) The scale is in ppm

Consideration of these examples would then suggest that 6871 undergo ldquotop-downrdquo equilibration through a triplet 16-electron intermediate or that 6871 themselves are triplets or have thermally accessible triplet states from which fluxionality might occur Since the relaxation times (T1) of paramagnetic systems60a are much shorter compared to their diamagnetic counterparts measurement of this property was thought to be informative The T1 values for the proton in 68 were determined via a standard inversion recovery experiment44 and are given in Table 24 (cf Figure 220) in comparison to p-terphenyl60b

Co

CoPMe3

72

- 54 -

Table 24 1H-NMR Relaxation Times in Intermediate 68 at ndash30 degC

Resonance (ppm) T1(s) 711 2309 646 0997 556 005 398 0108

In consonance with the associated line broadening the relaxation times of the Cp

(δ = 398 ppm 0108 s) and central ring hydrogens (556 ppm 005 s) are much smaller than those of the remaining phenylene ligand (711 and 646 ppm 2309 and 0997 s respectively) the latter in turn comparing well with the values in p-terphenyl With this corroborative evidence in hand the question whether the species is itself a triplet or is in thermal equilibrium with such was addressed The answer can be obtained by using a Curie-like graph68 in which chemical shifts are plotted as a function of temperature65 A linear relationship corresponds to the presence of a triplet compound while curved behavior is indicative of a singlet-triplet equilibrium Plotting the chemical shifts of the Cp hydrogen of 68 and 71 against the inverse of temperature (Figure 227) gave distinctly curved lines supporting the notion that these species are in thermal equilibrium with their triplets The exact nature of these species however remains to be determined

156

395404

345

p-Terphenyl

- 55 -

3

32

34

36

38

4

42

44

46

00036 00038 0004 00042 00044 00046 00048

1T (K -1

)

Ch

em

ica

l S

hif

t (p

pm

)

71

68

Figure 227 Plot of the Cp chemical shift (toluene-d8) of 68 and 71 versus the inverse of temperature

DFT calculations have commenced in an attempt to find a plausible structure for such a triplet cobalt species and with it possibly arrive at a mechanism for the fluxional behavior of 68 and 71 These studies are being carried out in collaboration with Professors Tom Albright of the University of Houston and Vincent Gandon of the Universiteacute Paris-Sud 11 Preliminary results at the B3LYP6-31G(dp) and BP866-31G(dp) levels suggest the η2-cyclobutadiene structure depicted in Figure 228 It is apparent that this species corresponds topologically to singlet TS 1 in Figure 29 and 70 in Figure 220 endowed with the symmetrical requirements dictated by the experiments

- 56 -

Figure 228 Calculated structure of a triplet η2-cyclobutadiene linear [3]phenylene(CpCo)

One can therefore envision fluxionality between the two ldquotoprdquo and ldquodownrdquo η4-benzene structures via the intermediacy of a triplet η2-cyclobutadiene (Scheme 223) Further Scheme 223 Conversion of ldquoTop-Downrdquo η4-Haptomers of 68 Via a Triplet η2-Cyclobutadiene

Intermediate

computations are required to pinpoint the minimum energy crossing points between the singlet η4 and triplet η2 structures and to explain why this triplet does not collapse to the CpCo cyclobutadiene isomer This work is in progress 26 Synthesis of Tetrakis(trimethylsilyl) Linear [3]Phenylene(CpCo)2 All of the linear phenylene(CpCo) complexes mentioned thus far share one common feature a single CpCo unit bound to the phenylene scaffold However since there are one or more additional cyclobutadienoid rings in the series the question arises whether it might be possible to bind more than one metal fragment to the ligand If so what would be the structural consequences Would be there further metalloaromatization Would such systems be capable of light-induced haptotropism and if so how would the metals move relative to the ligand and to each other Finally would such complexes mimic structurally the variety of arrays obtained in the reaction of 29 with Fe2(CO)9 (Scheme 15) Since the linear phenylenes become increasingly more antiaromatic with size the optimal candidates for preparing such multi-metallic systems should be the higher members of the series Indeed evidence for double CpCo attachment was obtained in the form of the minor by-products 73 and 74 (Scheme 224) obtained during the

Scheme 224 Side Products in the Preparation of Linear [4]- and [5]Phenylene(CpCo)

- 57 -

Complexes by Cobalt-Catalyzed Cyclization

preparation of 20 and 21 respectively (Scheme 13) These Diels-Alder type adducts of a third BTMSA molecule to the π-frame can be envisaged to be derived from 75 and 76 respectively in which the six-membered ring flanked by the two CpCo(cyclobutadiene) units would be expected to have an unusual (biradicaloid) electronic structure Evidence for the feasibility of such arrays rests on the unique black-red syn-bis(irontricarbonyl) compound 77 whose structure was determined by X-ray analysis69 With reasonable quantities of 19 in hand the possibility of ligating a second CpCo unit to it was explored This idea was further encouraged by the observation that crude samples of bis(trimethylsilyl) linear [3] phenylene(CpCo) complex 53 contained a very small (3 ) peak at mz = 618 an exact match for the mass of a doubly metallated analog Consequently 19 was treated with one equivalent of CpCo(C2H4)2 in benzene to afford a reddish black solid (Scheme 225) The mass spectrum data exhibited a

Scheme 225 Preparation of Complex 78 from Complex 19

TMS

TMSTMS

TMS

CoCpCo(C2H4)2

22h 70 oC C6H6Linear [3]TMS4(CoCp)2

5619 78

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

74

TMS

TMS

TMS

TMSCoCpCpCo

TMS

TMS

73

TMS

TMS

TMS

TMSCoCpCpCo

76

TMS

TMS

TMS

TMSCoCpCpCo

75

Ph

Ph

Ph

Ph

Fe(CO)3Fe(CO)3

77

- 58 -

molecular ion peak at mz 762 corresponding to 19(CpCo)2 The 1H-NMR spectrum (acetone-d6) revealed four sharp singlets integrating in the ratio 410236 indicative of a highly symmetrical structure The chemical shift of the benzene termini (736 ppm) suggested that these rings have significant aromatic character and is similar to the value of 745 ppm seen for the hydrogen positioned farthest away from the CpCo in 19 (Figure 27) Similarly the 13C signals of the terminal rings in 78 (1505 1454 and 1258 ppm) are analogous to those from the corresponding terminal ring in 19 (1484 1433 and 1256 ppm Figure 28) Detailed analysis of 78 with two-dimensional NMR techniques (HSQC and HMBC) allowed for a complete assignment of all peaks in the 1H and 13C spectra (Figure 229) The strongly shielded (relative to the free ligand) proton (481 ppm) and carbon (537 and 571 ppm) resonances assigned to the central benzene ring clearly showed that both cobalt fragments are coordinated to the phenylene ligand at this position Interestingly these data bear a very close resemblance to those of the corresponding diiron complex 31 (Scheme 15) and are compared in Figure 229 Its central 13C resonances (688 and 582 ppm) are shifted upfield in a manner akin to 78 although not quite as much reflecting the increased electron withdrawing ability of the Fe(CO)3 group relative to CpCo70 Complex 31 like 78 exhibits aromatized terminal benzene rings as indicated by its 1H (750 ppm) and 13C (1484 1446 and 1258 ppm) chemical shifts These spectral similarities make it likely that 78 and 31 are isostructural The only structural ambiguity pertains to the orientation of the two metal fragments with respect to the π ligand a problem that had been left undecided in the assignment of structure 31 ie 31a (syn) versus b (anti Scheme 15)27 These options for 78 are

- 59 -

CpCoTMSTMS

TMS TMS

H H039 (36)

537 1258822

270

1454571

1505

481 (2) 736 (4)489 (10)

TMS TMS

TMSTMS

H

(OC)3Fe

(OC)3Fe

CpCo

78

31a

750 (4)553 (2)

036 (36)H

220

1446

1258

1484

688582

2128

Figure 229 Comparison of 1H- and 13C-NMR assignments (ppm) for molecules 78 (acetone-d6) and 31 (1H acetone-d6

13C CDCl3) Proton chemical shifts are in red and carbon in blue Integrations for the proton resonances are in green HSQC for 78 δ = 039 ppm correlates with δ = 270 ppm δ = 481 ppm correlates with δ = 537 ppm δ = 489 ppm correlates with δ = 822 δ

= 736 ppm correlates with δ = 1258 ppm HMBC for 78 δ = 036 ppm correlates with δ = 1454 ppm δ = 481 ppm correlates with δ = 571 and 1505 ppm δ = 736 ppm correlates with δ = 571 1454 and 1505 ppm The placement of the cobalt atoms in 78 is tentative (see Figure

229)

Figure 230 Possible structures for 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

- 60 -

shown in Figure 230) Both equally exotic options are precedented in the literature and corroborated by X-ray structural analyses (Figure 231)71

Figure 231 Illustrative examples of complexes with two metal fragments coordinated to the same benzene ring

Bis(CpFe) complex 7972 and its rhodium analog 8073 contain [M2(syn-micro-arene)] units in which the metals are linked58 Molecule 79 consists of two CpFe units coordinated η4 to the boat-shaped benzene ring sharing ligating carbon atoms In contrast the CpRh fragments in 80 are bound in an allyl η3 manner and the arene also adopts a boat conformation On the other hand bis[tris(tert-butyl)]toluene(CpCo) complex 8174 and the related system 8275 both exhibit [M2(anti-micro-arene)] units in which η4 coordination between the benzene ring and each of the metal fragments takes place Here the metals share carbon atoms but now involving a sandwiched ligand The arene in 81 retains a planar aromatic geometry while the benzene moiety in 82 is bent into a highly distorted chair conformation Unfortunately model structures 79ndash82 do not exhibit diagnostic NMR properties that would provide a clear distinction between synanti and planarnon-planar topologies For example the 1H-NMR peaks for the toluene ligand in anti-complex 81 range from 400ndash380 ppm74 whereas the signals for the benzene moiety in syn-bis(CpRh) 80 appear at 400ndash330 ppm73 The 13C data are similarly inconclusive as illustrated by comparison of 78 (562ndash531 ppm for the benzene ring) with 79 (648ndash525 ppm)72b An interesting property of these bis(metal) arene complexes is fluxionality of the metal fragments by haptotropic shifts along the periphery of the aromatic ring as depicted in Scheme 226 In complex 79 the hexamethylbenzene ligand (bound η4η4

in the solid state) displays a single arene resonance at 588 ppm in its room temperature carbon NMR spectrum Cooling to ndash90 degC however produces two distinct arene peaks at 525 and 648 ppm (for the shared and single-metal-bound carbons respectively as shown in 79a in Scheme 227) Fluxionality was postulated to proceed through an η3η3 intermediate (79b) that is structurally similar to Rh complex 80 which is itself a fluxional species

Scheme 226 Examples of Fluxional Processes in Dinuclear Arene Complexes 79 and 80

82 81

80 (R = CH3)

79

- 61 -

Anti-bis(β-diiminate)Rh complex 83 shows similar mobility (Scheme 226)76 A mechanism for η4η4 migration of the anti-metal fragments was proposed using the lowest energy species found by DFT calculations In these compounds the anti-metal fragments convert between η4η4 (83a 83c 83e) structures by passing through η3η3

(83b) and η4η2 (83d) transition states The energy barrier for η4η4 migration in 83 was experimentally determined to be 6 kcalmol This value is in line with other experimentally measured syn and anti dinuclear ring slippage processes which are typically le ~10 kcalmol71-75 The possibility of fluxionality in 78 might be observable if asymmetric configurations such as 78c and 78d (Figure 231) represent the lowest energy forms since they entail NMR observable desymmmetrization of the ligand Unfortunately cooling 78 in the NMR probe to temperatures as low as ndash80 degC in toluene-d8 did not reveal any signs of signal decoalescence

- 62 -

Figure 232 Possible lowest energy forms of complex 78

Hoping that further light could be shed on the disposition of the CpCo moieties in 78 by chemical transformations a brief investigation of its reactivity was undertaken For example bis(metal) arene complexes have been shown to readily undergo arene exchange reactions71 In complex 81 for example the toluene ligand is displaced by benzene at room temperature74 However heating a sample of 78 to 120 degC in toluene-d8 did not lead to any changes in the NMR spectra Turning to potential photochemical activation 78 was irradiated at various wavelengths (300ndash365 nm) These conditions as well as ambient sunlight did not cause any changes in its 1H-NMR spectrum further documenting 78 as a rather inert species X-ray crystallographic analysis would appear to be the only method of resolving the identity of complex 78 Producing suitable crystals of this molecule however has proven extremely difficult and will be the subject of future investigations 27 Summary and Outlook The work presented in this chapter published as a communication77 has detailed the first examples of η4η4 intercyclobutadiene migration and detailed mechanistic studies of this unprecedented reaction The haptotropic shift was found to be an intramolecular process with the CpCo fragment undergoing various changes in hapticity for the thermal isomerization Low temperature photolytic studies have revealed the existence of a thermally unstable intermediate species the exact structure of which is uncertain These results point to what appear to be significant differences between the photo- and thermal haptotropic pathways Further work both experimental and computational will be required to elucidate the details of the photochemical reaction In addition to the studies of linear phenylene(CpCo) haptotropism a hitherto unknown complex containing two CpCo fragments bound to linear [3]phenylene was prepared and scrutinized in preliminary form Despite extensive characterization the structure of this complex with respect to the position of the metal centers remains elusive Future work will focus on the acquisition of a crystal structure

- 63 -

Chapter 3

Nickel-Catalyzed Insertion Reactions for the Preparation of [N]Phenacene Derivatives

31 Introduction Transformations involving metal insertion into the four-membered ring of the [N]phenylenes as discussed in Section 12 represent a significant mode of reactivity with a high potential for practical synthetic utility One specific application of this chemistry is the synthesis of the phenanthrene moiety via tandem metal insertion and alkyne cycloaddition to the four-membered ring (Scheme 31) Such a methodology Scheme 31 Potential Preparation of the Phenanthrene Group from the Alkyne Cycloaddition

with Biphenylene would be valuable for the preparation of PAHs possessing phenanthrene subunits but has remained fairly unexplored Only a few examples demonstrating this transformation have been detailed previously for biphenylene (7) (Scheme 32)

Scheme 32 Metal Catalyzed Alkyne Cycloaddition Reactions with Biphenylene

The first report of this process is by Eisch in 198533a who treated biphenylene with Ni(PEt3)4 and diphenylacetylene to produce 910-diphenylphenanthrene 84 Since then a number of metals have been shown to mediate this process19 Ni systems being most relevant to this chapter Thus for example 84 can also be made using an N-heterocyclic carbene-based Ni(0) catalyst78 Bis(diisopropylphosphino)ethane Ni(alkyne) species enable similar cycloadditions of fairly hindered (trimethylsilyl)alkynes sometimes involving more complex processes of silyl group migration79 while less hindered substrates lead to 84ndash8680a A mixed phosphinoaminoethane-chelated Ni species proved more reactive enabling cycloaddition of even the encumbered tert-butyl(phenyl)acetylene to furnish the corresponding phenanthrene80b With this background in mind our attention turned to applying this reaction to larger phenylene systems Of the various topologies of phenylenes at our disposal the angular version was

R1 R2

R2R1[M]

[M]

7 R R

R = Ph (84)

R = Me (85)

R = CH2OMe (86)

RR

[Ni]

- 64 -

particularly intriguing as it offered two extreme modes of alkyne addition (Scheme 33) In the first scenario exclusive attack at the outer periphery of the four-membered rings would produce the helical shaped PAHs known as helicenes (Scheme 33a)81

Scheme 33 Alkyne Cycloaddition with Angular Phenylenes to Produce (a) Helicenes or (b) Phenacenes

Reactions occurring only at the interior or ldquobayrdquo region (Scheme 33b) however would afford a class of compounds exhibiting a linear polyphenanthrene motif that are known as [N]phenacenes82 Unselective additions would result in mixed topologies Helicenes and their various derivatives constitute a well studied83 family of molecules and continue to be a popular area of research Phenacenes in contrast have been scrutinized much less in part because only four members of the parent series are known and because for N = 5 and 6 they are extremely insoluble84 Phenacene-based applications have been slow to develop but the first reports of the utilization of these molecules as functional organic materials suggest the beginning of a rich and promising field85 Thus in 2008 [5]phenacene (picene) was demonstrated to behave as stable high performance organic field effect transistor (FET)85b Currently the most common organic polycyclic benzenoid hydrocarbon-based FETs employ acenes which have a polyanthracene structure (Figure 31) The sensitivity

Figure 31 Linearly fused benzene topology of the acenes of these systems to air however has obstructed progress in this area86 For example pentacene a commonly used acene in FETs reacts readily with oxygen to form

+ RR

Helicenes

+ RR

Phenacenesn

R

R R R R

n

R

R

R

(a)

(b)

[N]Acenes

n

- 65 -

pentacenequinone a process that severely reduces device efficiency (Scheme 34)

Scheme 34 Degradation of Pentacene to Pentacenequinone Under Aerobic Conditions

Phenacenes on the other hand are much less prone to such decomposition pathways due to their higher HOMO-LUMO gap thus rendering them less reactive85b86a Their enhanced stability relative to acenes87 makes them better candidates for molecular electronic applications In a second seminal breakthrough [5]phenacene was very recently also found to behave as a superconductor at low temperature when doped with potassium85a This work paves the way for a new class of PAH-based superconducting materials in which phenacenes may play a key role

As this chemistry advances new synthetic methods for preparing derivatives of these molecules will be required in particular those bearing solubilizing andor otherwise functionally useful substituents The most general procedure for synthesizing phenacenes as developed by Mallory88 makes use of oxidative stilbene photocyclizations (Scheme 35)8388 In this transformation irradiation of the stilbene

Scheme 35 Generic Oxidative Stilbene Photocyclization Used to Prepare Phenacenes as Illustrated for Phenanthrene

moiety leads to conrotatory electrocyclic ring closure Trapping of the resulting intermediate with oxidizing reagents such as iodine or oxygen yields the desired phenanthrene subunit The requisite stilbenes are most generally accessible via the Wittig reaction as illustrated in the synthesis of [7]phenacene derivative 87 (Scheme 36) Although the yields for the photocyclization are typically reasonable (60ndash90 )85a the major drawback of this methodology is the numerous steps associated with preparing the functional groups required for the prerequisite Wittig reaction These

- 66 -

transformations serve to decrease the overall yield of the target molecule

Scheme 36 Synthesis of [7]Phenacene 87

While laborious Malloryrsquos method addresses successfully the problem of solubility As alluded to in Section 21 large PAHs become insoluble due to the increased π-π stacking forces that are experienced between aromatic rings The best solubilizing groups for the phenacenes were found to be sterically bulky groups located in the bay regions85a These modifications distort the phenacene framework from planarity thereby disrupting π-stacking and increasing solubility as demonstrated by the tert-butyl [7]phenacene 87 (Figure 32) This approach was applied to systems as large as [11]phenacene the current record in the series85a

Br

CH3t -Bu

1 BuLi2 DMF

Br

CH2

t-Bu

CHO

CH3t-Bu

PPh3

Br

+Wittig

t-Bu t-Bu

Br CH3 1 hν2 I2

t-Bu t -Bu

Br CH3

t-Bu t-Bu

Br H2C PPh3 Br

+

t-Bu t-Bu

OHC CH3

Wittig

t-Bu t-Bu

Br Br 1 hν2 I2

t-Bu t-Bu

Br CH3

t-Bu t -Bu

t-Bu t-Bu

87

1 NBS2 PPh3

- 67 -

Figure 32 Crystal structure of tetrakis(tert-butyl) [7]phenacene 87 Hydrogens are omitted for clarity

To test the viability of angular phenylenes as substrates in Ni catalyzed alkyne cycloadditions the simplest member 22 was chosen raising a number of questions First how many and what kind of products will be formed (AndashE in Scheme 37) Will there be inherent selectivity toward helicene C or phenacene E formation respectively If not can the reaction conditions be modified so as to induce such What will be the limitations with respect to the size of substituents especially in view of the crowded fjord and bay regions of D and E respectively The work presented in this chapter carried out in collaboration with Dr Zhenhua Gu89 explores these questions

Scheme 37 Possible Cycloaddition Products of Angular [3]Phenylene 22

22

[Ni]R R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

A B

C D E

32 Experimental Mechanistic Studies of Nickel Catalyzed Insertion-Alkyne Cycloaddition Reactions with Angular [3]Phenylene

Before embarking on the proposed chemistry the reactivity of 22 in the presence of nickel in the form of Ni(COD)(PMe3)2 in the absence of alkynes was queried Only starting material was recovered and there was no sign of dimerization (or oligomerization) to products of the type shown in Scheme 38 a mode of reactivity

- 68 -

readily attained by biphenylene and substituted derivatives33b

Scheme 38 Attempted Dimerization of Angular [3]Phenylene 22

In contrast exposing diphenylacetylene 88 to Ni(COD)(PMe3)2 and a small excess (109 equivalents) of angular phenylene 22 generated two products in the absence of any other (Figure 39) The first molecule 89 was the result of the cycloaddition of one diphenylacetylene at the bay region and the minor component The major product constituted tetraphenyl [5]phenacene 90 derived from 22 by double bay region attack The structures of both compounds were confirmed by X-ray analysis revealing highly distorted frames89 Scheme 39 Nickel Catalyzed Cycloaddition of Angular [3]Phenylene 22 to Diphenylacetylene

Yields Based on Diphenylacetylene

The outcome of this transformation was gratifying in its seeming simplicity and selectivity Thus it appeared that metal insertion occurred exclusively to bay region bonds heralding the discovery of a new phenacene synthesis The observation of relatively large amounts of 90 could be ascribed to increased reactivity of 89 relative to 22 possibly due to steric activation by the newly introduced bay region phenyl group To test this hypothesis 89 was subjected to the cycloaddition reaction conditions (Scheme 310) Surprisingly not only was this reaction slower than that of 22 but the expected phenacene 90 was only a minor product (6 ) Instead tetraphenylbenzo[c]chrysene 91 a regioisomer of 90 as confirmed by X-ray analysis89

+

+ +

Ni(COD)(PMe3)2

22

- 69 -

was isolated in 74 yield the result of non-bay alkyne cycloaddition to 89 Therefore 89 is not the precursor of 90 Rather there must be separate reaction pathways leading to each respective product

Scheme 310 Cycloaddition Reaction of 89 with Diphenylacetylene 88

A series of semi-quantitative experiments monitored by 1H-NMR spectroscopy was carried out to shed some light on this mechanistic problem First the reaction of angular [3]phenylene 22 with diphenylacetylene 88 in Scheme 39 was addressed Because dinuclear metallic activation of the strained C-C bond in biphenylenes has been implicated in a number of studies19 it was possible that the above mechanistic duality was caused by the presence of catalytic Ni2 species in addition to the ldquoregularrdquo mononuclear alternatives Alternatively double Ni insertion before cycloaddition might be responsible for one product whereas sequential ldquonormalrdquo activation might be the origin of the other Therefore the amount of initial Ni(COD)(PMe3)2 was gradually increased and the effect of this incremental change on rate and product ratios recorded As shown in Table 31 the speed with which 89 and 90 formed was roughly proportional to the amount of metal present while the product ratio stayed unchanged

Table 31 Variation of Catalyst Loading in the Reaction of Phenylene 22 with Diphenylacetylene 88 Reactions Were Carried Out with Equimolar Amounts of 22 and 88 in

THF-d8 at 40 degC

Run Ni(COD)(PMe3)2

(mol) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

Ratio of 8990

1 50 32 times 10ndash4 031 times 10ndash4 103 2 35 20 times 10ndash4 022 times 10ndash4 91 3 7 064 times 10ndash4 0064 times 10ndash4 100

Next the amount of diphenylacetylene 88 was gradually increased from 1 to 4 equivalents (Table 32) The outcome of this series of experiments was counterintuitive as it led to a larger preference for the production of monoadduct 89 suggesting a mechanistic bifurcation in which whatever Ni species is responsible for the eventual formation of 90 is sequestered by external ligand (in this case 88)

- 70 -

Table 32 Variation of Alkyne Equivalents in the Reaction of 22 (1 equiv) with Diphenylacetylene 88 in the Presence of 50 mol of Ni(COD)(PMe3)2 Experiments Were Run

in THF-d8 at 40 degC

Run 88 (equiv) Rate of formation of 89 (mol Lmiddoth)

Rate of formation of 90 (mol Lmiddoth)

8990

1 10 320 times 10ndash4 031 times 10ndash4 103 2 20 220 times 10ndash4 018 times 10ndash4 122 3 40 220 times 10ndash4 011 times 10ndash4 200

Following the reaction progress by NMR spectroscopy afforded additional insights Thus mixing the ingredients at room temperature left the phenylene component untouched Instead there was a near instantaneous displacement of COD by diphenylacetylene to produce Ni(PhCequivCPh)(PMe3)2 (92) and free COD in addition to the generation of Ni(PMe3)4

90 The speed with which this complex was formed implied that it might be the active catalyst precursor Consistent with this notion higher reaction rates were observed when the reaction in Scheme 38 was carried out with pure 9291 as the catalyst (50 mol) and 05 equivalent of 88 (Table 33 Run 2) In consonance with Table 32 the lesser concentration of available free alkyne increased the relative amount of 90 formed Conversely (Run 3) using Ni(COD)(PMe3)2 with an extra equivalent of PMe3 decreased the rates of formation of 89 and 90 and increased the ratio of 8990 consistent with ligand inhibition of the activation of 92 and the external ligand effect noted in Table 32 Table 33 Variation of Catalyst in the Reaction of 22 with Diphenylacetylene 88 and its Effect

on Reaction Rate Experiments Were Run in THF-d8 at 40 degC with 1 Equivalent of 22

Run Catalyst 88

(equiv)

Rate of formation of 89 (mol

Lmiddoth)

Rate of formation

of 90 (mol Lmiddoth)

8990

1 Ni(COD)(PMe3)2 10 320 times 10ndash4 031 times 10ndash4 103 2 Ni(PhCequivCPh)(PMe3)2 (92)

(05 equivalent) 05 1270 times 10ndash4 210 times 10ndash4 60

3 Ni(COD)(PMe3)2 (05 equivalent) + PMe3 (10 equiv)

10 088 times 10ndash4 005 times 10ndash4 163

Attention was then shifted to the reaction of monoadduct 89 with 88 as in Scheme 310 (Table 34) Here increasing the amount of alkyne and catalyst favors the formation of 91 consistent with an independent pathway At low concentration of alkyne it appears that 89 reenters the manifold of its generation and proceeds on to 90 Indeed following the change in the ratio of 9190 in Run 1 (Table 34) with time reveals a decrease from 47 to the eventual 22 as 88 is depleted

- 71 -

Table 34 Variation of Catalyst Loading and Alkyne Concentration in the Reaction of 90 with Diphenylacetylene 88 Reactions Were Run in THF-d8 at 40 degC

Run 88 (equiv) Ni(COD)(PMe3)2

(mol) 9190

1 10 50 2 2 30 50 15 3 30 10 25

The information obtained from these experiments allowed a narrowing of mechanistic possibilities For example dinuclear Ni activation only one possibility of which is shown in Scheme 311 was rendered unlikely by the absence of any observable changes in product distribution of the reaction in Scheme 39

Scheme 311 Generic Example of a Dual Mechanism Based on Mono- and Dimetallic Phenylene Activation

An alternative mechanism shown in Scheme 312 was in much better agreement with the results of the various control experiments The first step would be displacement of a phosphine in the initially dominant Ni-containing species 92 by angular [3]phenylene 22 inhibited by added PMe3 From 93 oxidative addition can take place to afford metallacycle 94 Why should bay region insertion be favored Arguably the regioselectivity of this step is controlled by the lesser steric hindrance in the resulting arene fragment or relative stabilization of the polarized Ni-C(α-

PhPh

Ph Ph Ph Ph

PhPh

NiL L

Ni(COD)(PMe3)2

NiNiL L L L

PhPh

2

Ph

Ph

Ph Ph Ph Ph Ph Ph

+

+22

89

90

91 90

- 72 -

biphenylene) bond in 94 by the electron withdrawing nature of the neighboring cyclobutadienoid ring This phenomenon in biphenylene is due to the rehybridization of the four-membered ring carbons to adopt relatively larger p character in the strained linkages hence larger s character (ie electron withdrawing) in the remaining bond and manifests itself most clearly in the relative acidity of the α-hydrogens7a This step is followed by migratory insertion and reductive elimination to produce molecule 96 the mechanistic bifurcation point One branch proceeds through presumably ligand-assisted metal dissociation to generate the relatively unreactive free 89 The second entails Ni migration92 and insertion into the bay region of the remaining four-membered ring (97) before the second cycloaddition occurs generating phenacene 90

Scheme 312 Possible Mechanism for the Alkyne Cycloaddition Reaction of Angular [3]Phenylene 22

The regioselective formation of 97 may again be sterically dictated or may involve anchimeric assistance by the bay-region phenyl group as sketched in Scheme 313 specifically 99

Scheme 313 Anchimeric Assistance on Route to [5]Phenacene 90

Ph Ph

PhPhPhPh

Ph

Ph

Ph PhNi

NiMe3P Ph

Ph

Ni

Me3P Ph

Ph

NiPMe3Me3P

Ligand exchangeOxidativeaddition

Migra toryinser tion

Reductiveelimination

Ph

Ph

Me3P

Ni migra tionOxidative addition

22

92

9394

96 89

9097

Ph Ph

Ni

Me3P

Ni(PMe3

Ph

Ph

minusNi(PMe3)

95

- 73 -

This type of metal coordination to the double bond of a proximal arene ligand is common and two examples are provided based on ruthenium94 and molybdenum95 (Figure 33)

Figure 33 Examples of complexes with phenyl groups coordinating to a nearby metal center Turning to the largely selective conversion of 89 to 91 (Scheme 310) requires the postulate of preferential insertion of the metal at the non-bay region and hence a different Ni species from that in 96 possibly a Ni(PMe3)(alkyne) moiety akin to that in 93 ie 100 (Scheme 314) Bay insertion would lead to metallacycle 101 and ultimately molecule 90 The expected large degree of steric repulsion between the phenyl groups in 101 should disfavor this reaction pathway On the other hand non-bay insertion to produce 102 should be relatively less impeded and would furnish 91 Another option for the generation of 90 from 89 would be reentering the pathway described in Scheme 312 facilitated at low concentrations of alkyne consistent with the data in Table 34

Scheme 314 Proposed Mechanism for the Alkyne Cycloaddition Reaction of 89

Ni

PhMe3P

PhPh

(Me3P)Ni

PhPh(Me3P)Ni

Ph

Ph

93 98

99

Ph Ph Ph Ph

90

+

Ph Ph

Ni

Me3P

97

- 74 -

While the above mechanistic perambulations appear plausible it should be stressed that they are speculative and may be restricted to diphenylacetylene 88 as the substrate Thus both 3-hexyne 103 and 14-dimethoxy-2-butyne 106 added to 22 less selectively than 88 to provide only the bay and non-bay monoadducts 104 and 105 and 107 and 108 respectively (Scheme 315)

Scheme 315 Reaction of Angular [3]Phenylene 22 with Other Alkynes

NiMe3P PMe3

Ph Ph+

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph

Ni(PMe)3

PhPh

Ni(PMe3)

Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

92 89

101

90

102

100

91

Ni

Ph Ph

PMe3

+

R

R

THF-d8 40 oCR

R22

Ni(COD)(PMe3)2

R

R

+

R = Et 104

R = CH2OMe 107

R = Et 103

R = CH2OMe 106 R = Et 105

R = CH2OMe 108

11 45 9 68

- 75 -

In view of these uncertainties recourse was taken to DFT computations delineated in the next section 33 Computational Mechanistic Studies of the Nickel Catalyzed Cycloadditions of Diphenylacetylene to Angular [3]Phenylene DFT studies were carried out in collaboration with Prof Vincent Gandon of the Universiteacute Paris-Sud 11 The B3LYP 6-31G(d) basis set was used for hydrogen and carbon atoms while LANL2DZ was used for nickel Before attempting to model the more complex alkyne cycloaddition reactions in Schemes 38 and 39 the basic Ni-catalyzed addition of the parent acetylene to biphenylene in the presence of PMe3 was studied (Scheme 316) The free energies

Scheme 316 Computational Modeling of Ni-catalyzed Addition of Acetylene to Biphenylene Free Energies (∆G KcalMol) are Relative to 109 Transition State Energies are Absolute Values

for This Step

NiMe3P PMe3

NiMe3P

NiMe3P

Ni

Ni

PMe3

PMe3

+

+ PMe3+

+ PMe3

+ 2 PMe3

+ 2

(00)

(281)(37)

(140)

(12)

NiMe3P PMe3

NiMe3P

NiNiPMe3Ni

PMe3

PMe3NiMe3P

PMe3

(727) (693) (476) (374) (394) (395)

Ni

Me3P

PMe3Ni

Me3P

Ni

Ni

Me3P

PMe3NiMe3P PMe3

(590) (532)

(157) (125) (150)

Most Accessible TS

+

7

114

110

113109

111 112

Ni

Me3P

(253)

Ni

PMe3

(242)

- 76 -

(∆G) of various possible catalyst structures consisting of an assortment of combinations of nickel PMe3 and acetylene as well as those of several possible transition states and the resulting products were calculated As is evident on inspection of the values in the first part of Scheme 316 a number of species were found to be very close in energy making it difficult to pinpoint a specific structure for the initial insertion step Bis(ethyne) nickel complex 109 was established as the lowest energy nickel species and was thus assigned a relative value of 0 kcalmol The most accessible transition state 110 features the oxidative addition of the Ni(PMe3)(C2H2) fragment 114 (+ 14 kcalmol) in which the alkyne is held exo to biphenylene The corresponding endo structure 111 was found to be just slightly higher in energy by 20 kcalmol as was the bisalkyne transition state 112 It is likely that biphenylene-NiL2 complexes (two of which were calculated at relative energies 242 and 253 kcalmol) lie on the way to these maxima93 Metallacycle 113 the structure ensuing from transition state 110 constituted the lowest energy product uphill from the starting 109 by 125 kcalmol but other alternatives are nearly isoenergetic Clearly however attack by Ni(PMe3)2 or Diels-Alder type cycloadditions are not likely From 113 the species proceeds smoothly by alkyne insertion-reductive elimination to the phenanthrene product a cascade associated with a large exergonic driving force Undaunted by the relatively complicated picture that emerged with biphenylene attention was turned to the original object of scrutiny the cycloaddition reaction between angular [3]phenylene 22 and diphenylacetylene 88 to produce [5]phenacene derivative 90 Modeled in the same manner as described above the metal insertion into the four-membered ring of 22 is shown in Scheme 317 The lowest energy nickel species

- 77 -

was found to be diphenylacetylene complex 92 gratifyingly corresponding to experiment and was set to a reference value of 00 kcalmol One notes again however an array of at least 10 species all of which must be in equilibrium in the initial reaction mixture Notably the Ni-π complexes to 22 are all more than 20 kcalmol higher in energy than 92 providing a computational rationale for the failure to observe such species by NMR The first step in the optimal reaction pathway is the coordination of Ni(PMe3) to the cyclobutadiene ring of 22 which results in formation of η2-like complex 114 Again in gratifying agreement with experiment bay region insertion through transition state 115 to give 116 is favored albeit by a bare 07 kcalmol relative to its non-bay region counterpart 117 Moreover there are at least six other structures that are energetically viable in silico although insertions of Ni(PhCequivCPh)(PMe3) appear less so possibly due to steric hindrance The same observation is made for the products of insertion although 116 emerges as the thermodynamically most stable possibility

Scheme 317 Calculated Structures and Reaction Pathway for the Insertion of Nickel into the Four-Membered Ring of Angular [3]Phenylene 22 Free Energies ∆G are in KcalMol Relative

to 92

The next step was to map out the first alkyne cycloaddition (Scheme 318) Coordination of diphenylacetylene to 116 is endothermic by 139 kcalmol and after migratory insertion produces 119 Interestingly a transition state to regioisomer 95

(328) (352)

NiMe3P PMe3

(364)

NiMe3P

NiMe3P PMe3

NiPMe3

(339)

Ni

PMe3

PMe3

NiMe3PPMe3

NiMe3P

NiPMe3

(16) (04) (108) (117)

NiMe3P PMe3 Ni

Me3PNi

Me3P Ni Ni

PMe3

PMe3

+ [3]+ DPA

+ PMe3+ [3]+ DPA

+ PMe3+ [3]

+ 2 PMe3+ [3]

+ [3]+ 2 DPA

Ph Ph Ph PhPh Ph

Ph

PhPh Ph

Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph

Ph

(45) (96)

(00)

(89) (134)

Most AccessibleTS

NiPMe3

+ PMe3+ [3]+ 2 DPA

(314)

Ni

+ 2 PMe3+ [3]+ DPA

Ph Ph

(294)

1i(PMe3)

Ni

PhPh

(212)

(218)

(345)

Ni

PhPh(297)

Ni

Me3P

Ni

Ph

Ph

(350)

Ni

PMe3

(303)

Ni

Ni

(43) (41)

Ph

Ph

PhPh

Ni

PMe3

NiMe3P

(-10) (-22)

(Me3P)Ni

Ni(PMe3)

Ph Ph

Ph Ph(225) (256)

+ PMe3+ 2 DPA

+ 2 PMe3+ DPA

+ PMe3+ DPA

+ PMe3+ DPA

92114

115

116118

117

- 78 -

written (arbitrarily) in Scheme 312 could not be located

Scheme 318 Calculated Reaction Pathway for the Coordination of Diphenylacetylene Migratory Insertion and Nickel Migration Free Energies ∆G are in KcalMol Transition

State Energies are Absolute Values for This Step

Subsequent reductive elimination from 119 occurs to produce nickel coordinated arene species 120 From it free 89 is presumably readily obtained by demetallation in the presence of external ligands shown only for the formation of 92 in a very favorable process (ndash487 kcalmol) This step is sufficiently exothermic to tolerate the emergence of all the calculated species in the starting line up of Scheme 317 and is presumably the source of 89 in Scheme 39 However if not removed the Ni moiety in 120 can migrate along a shallow manifold across the π frame choosing the phenyl functionalized edge of the molecule (cf Section 24) until the remaining four-membered ring is reached (121) At this point two separate reaction pathways become possible Nickel insertion on the side proximal or opposite of the phenyl groups generates 99 or 122 respectively The barriers for these transformations are similar but show a noticeable preference for the formation of 99 In addition there is a significant energy difference (175 kcalmol) between 122 and 99 in favor of the bay region metallacycle The reason is the coordination of the neighboring phenyl ring to the nickel which serves to stabilize 103 vindicating the proposal made in Scheme 313 and providing a rationale for the exclusive observation of 90 in Scheme 39 From 99 as shown in Scheme 319 coordination of diphenylacetylene (123) is followed by migratory insertion to produce 124 Insertion occurs away from the bay region so as to reduce steric repulsion due to the phenyl group in the phenanthrene part of the molecule Finally reductive elimination ensues providing phenacene-Ni

NiMe3P

NiPMe3

Ni(PMe3)

Ni Ph

PhMe3P

Ph

Ph

PhPh

(117)

126

(44)

102

( 80)

01

( 412)

Ph PhNi(PMe3)

( 389)

Ph Ph

45

Ni(PMe3)

( 408)

Ph Ph

13

PhNi

PMe3

Ph Ph

Ni(PMe)3

133

( 488)

117

( 663)

NiMe3P

( 22)

PhPh+

95

116

119

120121 122

99

NiMe3P Ph

Ph

Ph Ph

( 899)

NiMe3P PMe3

Ph Ph+

92 89

- 79 -

complex 125 At this point the stage is set for exergonic nickel dissociation to 90 and catalyst turnover

Scheme 319 Calculated Reaction Pathway for the Second Diphenylacetylene Insertion All Relative Energies (in red) are in KcalMol Transition State Energies are Absolute Values for

This Step

In conclusion of this discussion the consideration of the combined computational and experimental data affords a mechanistic picture of the cycloaddition reaction of diphenylacetylene 88 to angular [3]phenylene 22 (Scheme 39) the essential features of which are summarized in Scheme 320 The crucial point is a mechanistic bifurcation in which 89 is either released early and (nearly) irreversibly from the metal or the metal stays attached so as to effect a second cycloaddition to give 90 This mechanism implies that 91 is formed by a different mechanism involving a different Ni species

PhNi

PMe3

( 663)

+

PhNi

Ph PMe3Ph

Ph

( 403) ( 403)

PhNi

PhPMe3

PhPh

( 519)

94

93

( 696)

PhNi

PhPMe3

Ph

Ph

96

( 817)

Ph Ph Ph Ph

(MeP)3Ni

99

123

124

125

PhPh

Ph PhPh Ph

+Ni

Me3P PMe3

( 1101)

PMe3

90

- 80 -

Scheme 320 Essential Mechanistic Features of the Formation of 89 and 90 in the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene 88 and Angular [3]Phenylene 22

Consequently the reaction of 89 with diphenylacetylene to give 91 (Scheme 310) was also modeled by DFT Of the various options probed that shown in Scheme 321 proved to be most plausible The reaction pathway entails coordination of alkyne-Ni phosphine 126 to molecule 89 which generates complex 127 in a process that is found to require 228 kcalmol of energy Insertion into the non-bay region of the four-membered ring has a barrier of 16 kcalmol and provides metallacycle 128 After the second cycloaddition event benzo[c]chrysene 91 is formed Interestingly the transition state leading to insertion of nickel complex 126 into the bay region of 89 structure 129 was found to be so high in energy relative to 128 that it could not be modeled This is not unexpected as the phenyl group closest to bay region effectively blocks the approach of any catalyst species This result is consistent with the high ratio of 91 to 90 formed in Scheme 310 and the increase in this ratio at higher initial diphenylacetylene concentration Why is any 90 formed and why does its relative proportion increase at lower diphenylacetylene concentration A possible explanation is that under these conditions the concentrations of 92 and 126 are sufficiently small that 89 reenters Scheme 318 competitively

PhPhNi(PMe3)

PhPh

Ni(PMe3)

Ph Ph Ph Ph

PhPh

Ni(PMe3)

Ni

PMe3

Ph Ph

NiPhMe3P

22 116

88

120

121

99

88

90

PhPh

89

Externalligand

assistedNi migration

Regioselectiveinsertion

Regioselectiveinsertion

Mechanistic bifurcation

- 81 -

Scheme 321 Calculated Reaction Mechanism for the Nickel Catalyzed Cycloaddition Reaction Between Diphenylacetylene and Compound 90 Relative Energies are in KcalMol Transition

State Energies are Absolute Values for This Step

Consideration of Scheme 320 suggests that phenacene formation might be maximized by keeping the concentration of external ligand low during the course of the reaction Experiments aimed at verifying this conjecture are the subject of Section 34 in addition to presenting extensions of the methodology to higher angular phenylenes

34 Optimization and Application of Nickel Catalyzed Alkyne Cycloaddition Reactions The experimental and computational studies described in Section 33 suggested that the decisive factor for selective formation of phenacene 90 is suppression of metal dissociation in Ni complex 120 This scenario would be achievable by maintaining a low concentration of diphenylacetylene 88 (vide supra) Previously the alkyne cycloaddition was performed with all reagents mixed together at the start of the reaction invariably resulting in a high initial concentration of 88 To obviate this occurrence an alternative procedure was devised In this new arrangement the required stoichiometric amount (in this case two equivalents) of alkyne 88 was slowly introduced to a mixture of 22 and Ni(COD)(PMe3)2 by means of a syringe pump (Scheme 322) The results of varying addition and reaction times are shown in Table 35

Scheme 322 Modified Reaction Alkyne Cycloaddition Reaction Between 22 and 89

Ph Ph

Ni(PMe3)

Ph Ph Ph Ph

Ni(PMe)3

160

Ph

Ph

PhPh

(309)(317)

Ph Ph

Ph

Ph

NiMe3P

Ph Ph

(minus573)

89

126

127 128 91

Ph Ph Ph

Ni

Ph

PMe3

129

NiMe3P PMe3

Ph Ph

(00)

92

(89)

+

- 82 -

Table 35 Variation of Alkyne Addition and Total Reaction Time in the Scheme 322

Run Addition time of 88 (h)

Total run time (h)

Yield of 89 ()

Yield of 90 ()

1 4 16 44 55 2 6 22 23 77 3 5 41 24 76 4 12 69 17 73 5 13 19 13 87

The most immediate result of the modified protocol was the quantitative conversion of 22 to cycloadduct products 89 and 90 Turning to the product ratios a four hour addition time led to a slight preference for 90 Increasing the time to six hours dramatically influenced the product distribution and 90 was isolated in 77 yield as compared to the 23 for 89 In the optimal Run 5 87 of 90 was generated vs 13 of 90 Extending the run time after the addition of diphenylacetylene had a negligible effect The successful enhancement in phenacene selectivity under these conditions makes the reaction a practical method for synthesizing compound 90 and also provides further experimental support for the proposed mechanism shown in Scheme 320 Having reached a reasonable level of understanding both the mechanistic and experimental aspects of the reaction of angular [3]phenylene 22 with diphenylacetylene attention was shifted to a larger and more challenging substrate angular [4]phenylene (17) This system could conceivably afford 17 possible adducts one of which is hexaphenyl[7]phenacene 130 (Scheme 324) Would the mechanistic features of this triple cycloaddition be sufficiently similar to those of 22 to apply the same principles and enable selectivity toward 130

+THF reflux

Ph Ph Ph PhPh

Ph

+

Ph

Ph

2 equivslow addition

22 89 90

Ni(COD)(PMe3)2(10 mol)

88

- 83 -

Scheme 324 The Possible Cycloadducts of Diphenylacetylene 88 to Angular [4]Phenylene 17

+ Ph Ph

Ph Ph

Ph Ph

PhPh

Ph

Ph

Ph Ph Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph Ph

Ph PhPhPh

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph Ph Ph PhPhPh

Ph Ph Ph Ph

Ph

Ph

Ph Ph

Ph

Ph

Ph

Ph

PhPh

Ph

Ph

PhPh

Ph Ph Ph Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

Ph

88

17

130

- 84 -

Encouragingly a first experiment under conditions comparable to those in Scheme 39 for 22 namely reaction of angular [4]phenylene (17) with one equivalent of diphenylacetylene in the absence of high dilution indeed engendered only five products two of which monoadducts 131 and 132 were minor (Scheme 325) The major components of the mixture were molecules 133 134 and most significantly 130

Scheme 325 Nickel Catalyzed Alkyne Cycloaddition with 17 and 88

Monitoring the course of the transformation by NMR revealed that 133 is the sole initial new compound followed by gradual appearance of the others Extrapolation of the insights gained with 22 it is tempting to propose that migration of the metal in Ni-complexed 133 is the source of 134 and ultimately 130 If true [7]phenacene 130 might be made selectively by application of the slow alkyne addition procedure of Scheme 322 Scheme 326 illustrates the proposed scenario It starts with doubly regioselective Ni insertion into the central ring and from the bay region to give 135 On the basis of the electron withdrawing effect of the adjacent cyclobutadienoid rings invoked earlier in the selective formation of 94 (Scheme 312) this metallacycle would seem the most stable Again this conjecture is tentative as the appearance of the minor products 131 and 132 would indicate Metallacycle 135 would then give rise to 136 (and hence 133 by demetallation) which would connect by Ni migration and insertion to 137 Alkyne cycloaddition would result in 138 (and hence 134 by demetallation) which would connect by Ni migration and insertion to 139 Alkyne cycloaddition would result in 140 (and hence 130 by demetallation)

+

Ph Ph

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2(10 mol)THF 75 degC

5 6

33

27 28

132131

133

134 130

17

88

- 85 -

Scheme 326 Proposed Reaction Pathway to Phenacene 130 from Angular [4]Phenylene 17 via Ni Migration

The successful preparation of [5]- and [7]phenacene from angular [3]- and [4]phenylene respectively prompted an attempt to prepare [13]phenacene derivative 141 from helical [7]phenylene 14210 (Scheme 327) This transformation would make use of six alkyne cycloadditions to produce the target molecule In addition to the possibility of preparing the largest known phenacene this reaction would also serve as an interesting test of the alkyne cycloaddition methodology

Scheme 327 Proposed Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Using the slow addition procedure phenylene 142 was subjected to the alkyne cycloaddition conditions (Scheme 329) All of the starting material was consumed but the reaction ultimately resulted in an intractable mixture of products Unfortunately no conclusive structural identifications for any of the ensuing compounds could be made from the 1H-NMR data A large assortment of peaks was seen in the region of 6ndash7

Ni

PMe3

Ph

NiPMe3

Ph Ph Ph PhNi

PMe3

Ph Ph Ph

NiMe3P

135

137

Ph Ph

Ph Ph

Ph Ph Ph PhPh Ph

Ni(COD)(PMe3)2

13617

88Ni

PMe3

Ph Ph88

138 139

Ph Ph88

Ni

PMe3

140

- 86 -

ppm suggesting the presence of phenylene subunits More informative was the absence of the highly diagnostic phenacene bay region proton signals that are typically found at ~8ndash9 ppm84 signaling the absence of any phenacene product(s)

Scheme 328 Attempted Synthesis of Dodecaphenyl [13]Phenacene 141 From Helical [7]Phenylene 142

Nevertheless mass spectral analysis clearly indicated that multiple alkyne cycloaddition had occurred (Table 36) Peaks were observed at mz = 700 1056 1234 and 1412 which correspond to the presence of single triple quadruple and quintuple alkyne adducts in the reaction mixture No signal corresponding to the mass of 141 (mz = 1590) was detected however Although the structures of the resulting products remain to be established by follow-up experiments on a larger scale the fact that five cycloadditions occurred is encouraging in the basic scientific quest for large novel polycyclic aromatic hydrocarbons

Table 36 Mass Spectral Data (FAB) of the Product Mixture of the Cycloaddition Reaction of Phenylene 142 to Diphenylacetylene 88

mz Percentage Cycloaddition count 700 13 1

1056 11 3 1234 8 4 1412 7 5

Our disappointment in the apparent failure to generate 141 in this reaction may be the result of overambitious expectations on our part Thus we assumed in analogy to the reactivity of angular systems 17 and 22 that bay region cycloaddition to one of the inner cyclobutadiene rings would be preferred ideally producing an initial structure such as 143 (Figure 38) The corresponding non-bay adduct is illustrated by 144 It is evident on comparison that such bay region reactivity would lead to constructs devoid of the helical strain present in the starting material96 as well as non-bay structures like 144 The subsequent course of the reaction however may be marred by relatively non-selective cycloadditions as already indicated for 17 (Scheme 325) Therefore it will be prudent for future investigators to return to the latter optimize its outcome and then proceed along the series in the quest for large phenacene (or other) structures

- 87 -

Figure 38 Proposed representative initial bay (143) and non-bay (144) alkyne cycloaddition products of the reaction of [7]heliphene 141 with diphenylacetylene 88

35 Summary and Outlook The first alkyne cycloaddition studies were carried with angular phenylene systems Angular [3]phenylene 22 was successfully used as a precursor to a novel phenyl substituted [5]phenacene derivative 90 Similarly hexaphenyl [7]phenacene 131 was prepared from angular [4]phenylene 17 Extensive experiment and computational mechanistic studies suggested that the optimal conditions for preparing phenacene 90 from phenylene 22 were the maintenance of a low concentration of alkyne in the reaction mixture Future work will focus on applying these conditions to the synthesis of [7]phenacene 130 from angular [4]phenylene 17 An attempt to prepare a [13]phenacene 142 from helical [7]phenylene 141 proved unsuccessful for reasons that are not well understood Nevertheless cycloaddition was found to have occurred up to five times This observation is promising with respect to the further application of the methodology described in this chapter The development of an alkyne cycloaddition-based approach to synthesizing phenacenes should greatly facilitate the study of this emerging class of molecules Future work will focus on expanding the substrate scope of the reaction by examining various functionalized alkynes the application of metal systems that may allow the isolation of crucial intermediates and the expansion of the substrate scope to the higher angular phenylenes as well as other topologies

- 88 -

Chapter Four Experimental and Computational Details

41 General Considerations

All glassware was oven-dried (180 degC) prior to use Reagents were used as received from suppliers unless otherwise noted Flash chromatography97 was performed with Merck 60 230ndash400 mesh silica gel MP EcoChrom neutral alumina was deactivated to activity III by adding 6 water by mass followed by thorough mixing98 Air sensitive compounds were handled under argon with standard Schlenk techniques andor in a nitrogen atmosphere glovebox (Vacuum Atmospheres Model Nexus) Irradiation in CpCo(CO)2 reactions was carried out with a 120V 300W slide projection lamp (ELH) positioned 5 cm away from the reaction vessel UV-irradiation experiments were conducted in a Rayonet Photochemical Reactor (RPR-100) Bis(trimethylsilyl)- and trimethylsilylacetylene (BTMSA and TMSA respectively) were distilled from molecular sieves (4 Aring) prior to use TMSA was degassed with four freeze-pump-thaw cycles while BTMSA was degassed using a 20 min Ar purge BTMSA was recycled using from all CpCo(CO)2 reactions using the following procedure The BTMSA was first removed by vacuum transfer Residual cobalt was removed by dissolving the BTMSA in pentane and washing the pentaneBMTSA layer mixture with a dilute solution of ceric ammonium nitrate in acetonitrile in a separatory funnel The denser acetonitrile layer was drained off and the pentane removed by distillation at atmospheric pressure Vacuum distillation of the BTMSA from molecular sieves afforded a product pure enough for future use All solvents were distilled under N2

immediately before use from the appropriate drying agent triethylamine (KOH pellets) benzene toluene CH2Cl2 (CaH2) THF and diethylether (Nabenzophenone) acetonitrile (CaH2) Deoxygenation of solvents andor reaction mixtures was carried out by a 20 min Ar purge or four free-pump-thaw cycles for volatile (bp lt 70 degC) mixturessolvents Ni(COD)2 (Strem) was stored and manipulated in the glovebox 1H and proton decoupled 13C spectra were measured at 500 MHz and 125 MHz respectively unless otherwise noted 1H-NMR chemical shifts are reported in ppm units relative to the signal of the solvent (CDCl3ndash726 ppm C6D6ndash715 ppm acetone-d6ndash205 ppm CD2Cl2ndash532 ppm toluene-d8ndash209 ppm (for ndashCD3) Except where noted two-dimensional NMR experiments were run under temperature control at 300 K All spectral data were processed with Bruker TopSpin 21 software Melting points were recorded in open capillary tubes using a Thomas Hoover Unimelt apparatus and are uncorrected Melting points for air-sensitive samples were carried out in flame sealed capillary tubes Mass spectral measurements (Electron Impact Fast Atom Bombardment) and elemental analyses were supplied by the Micro-Mass Facility of the College of Chemistry University of California Berkeley UV-Vis spectra were recorded on Agilent 8453 and Perkin-Elmer Lambda 35 spectrophotometers with absorbance data reported in nm (log ε) IR spectra were taken on a Perkin-Elmer Spectrum 100 Where appropriate analysis by GCMS was done with an Agilent 5973 instrument

42 Experimental Section for Chapter Two

- 89 -

2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19

A mixture of KF2 H2O (700 mg 744 mmol) [18]crown-6 (100 mg 0378 mmol) and 2378-tetrakis[(triisopropylsilyl)ethynyl] linear [3]phenylene26 (370 mg 0800 mmol) in degassed THF (25 mL) was stirred for 70 min at RT The orange solution was filtered through a plug of silica gel (1 x 3 cm) eluting with degassed THF (15 mL) providing a light-yellow solution After adding CpCo(CO)2 (260 mg 144 mmol) the solution was protected from light and added via syringe pump over a period of 6 h to a boiling mixture of degassed BTMSA (50 mL) and THF (200 mL) which was irradiated with a projector lamp under nitrogen After additional heating and irradiation for 15 h the solvents were removed by vacuum transfer and the black residue filtered through a plug of neutral alumina activity III eluting with hexaneTHF (501) The volatiles were removed and the dark brown residue crystallized from degassed acetone yielding 19 (330 mg 65 ) as black needles mp 192ndash195 degC (decomp) 1H-NMR (400 MHz C6D6) δ = 794 (s 2 H) 744 (s 2 H) 690 (s 2 H) 441 (s 5 H) 035 (s 18 H) 031 (s 18 H) ppm 13C-NMR (100 MHz C6D6) δ = 1494 1484 1433 1394 1360 1256 1155 802 781 739

269 261 ppm IR (neat) ν~ = 2951 2898 1259 1248 1073 830 799 752 cmndash1 UV-VIS (ethanol) λmax (log ε) = 288 (486) 299 (500) 352 (445) 410 (439) 438 (449) end absorption to 550 nm MS (70 eV) mz () 638 (9) [M+] 514 (100) 499 (3) 387 (2) 73 (24) HRMS (FAB) calcd for C35H47CoSi4 6382087 found 6382095 Elemental analysis calcd for C35H47CoSi4 C 6578 H 741 found 6582 721

Crystallographic information for 19 (H atoms omitted)

Table 41 Crystal Data and Structure Refinement For 19

Empirical formula C35H47CoSi4 Formula weight 63902 cryst size (mm) 025 x 020 x 005 cryst syst Triclinic refl used for unit cell determination 6958

2 θ range (deg) 245ndash2900

a (Aring) 9497(3) b (Aring) 12321(4) c (Aring) 16469(5) α (deg) 74058(5)

β (deg) 82154(5)

Me3Si

Me3Si

CoSiMe3

SiMe3

- 90 -

γ (deg) 72276(5)

V (Aring3) 17620(10) space group Pndash1 Z 2

Dcalc gcm3 1762

F000 680 micro cmndash1 645 temp ordmC ndash173

Tmax Tmin 0858 0972 no of total rflns 24355

no of unique rflns 6958

no of obsd rflns 9209

no of variables 361

Reflection to Parameter Ratio 255

R 00503

Rw 01426

Rall 00734

GOF 1006

Max Peak in Final Diff Map (endash Aring3) 0867

Min Peak in Final Diff Map (endash Aring3) ndash0755

- 91 -

Figure 41 ORTEP representation of 19

- 92 -

Table 42 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 19 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y Z U (eq)

Co1 073881(4) ndash000927(3) 060643(2) 002551(10) Si1 077416(8) ndash019090(6) 094343(4) 002594(16) Si2 113437(8) ndash016706(7) 082404(5) 003023(17) Si3 040491(7) 062139(6) 020406(4) 002291(15) Si4 005088(7) 056545(6) 030946(4) 002144(14) C1 06709(3) ndash00385(2) 079440(16) 00239(5) C2 08019(3) ndash00967(2) 083428(16) 00241(5) C3 09418(3) ndash00743(2) 079331(16) 00233(5) C4 09428(3) 00098(2) 071779(15) 00225(5) C5 08094(2) 00691(2) 067735(15) 00207(4) C6 07282(2) 01574(2) 060605(15) 00207(4) C7 07303(2) 02531(2) 053306(15) 00211(4) C8 05938(2) 03094(2) 050431(15) 00205(4) C9 05057(2) 03981(2) 043438(15) 00207(4) C10 05076(2) 04760(2) 035695(15) 00227(5) C11 03734(2) 05293(2) 031459(15) 00215(4) C12 02408(2) 05011(2) 035315(15) 00205(4) C13 02432(2) 04196(2) 043269(15) 00215(4) C14 03751(2) 03698(2) 047171(15) 00208(4) C15 04564(2) 02794(2) 054277(15) 00211(4) C16 04487(2) 01908(2) 061161(15) 00224(5) C17 05916(3) 01278(2) 064393(15) 00221(5) C18 06734(2) 00417(2) 071473(15) 00215(5) C19 05795(3) ndash02027(3) 09572(2) 00446(8) C20 08892(4) ndash03470(2) 09642(2) 00387(7) C21 07986(4) ndash01192(3) 10246(2) 00419(7) C22 11685(4) ndash03077(3) 07914(3) 00584(10) C23 11726(3) ndash01969(3) 09372(2) 00426(7) C24 12742(4) ndash00933(4) 07624(3) 00640(12) C25 05777(3) 06657(3) 020261(18) 00348(6) C26 02610(3) 07629(2) 016564(17) 00292(5) C27 04355(3) 05272(3) 012760(18) 00347(6) C28 ndash00272(3) 07195(2) 03194(2) 00360(6) C29 00487(3) 05542(3) 019882(18) 00344(6) C30 ndash00786(3) 04816(2) 037272(18) 00278(5) C31 06994(4) ndash00612(3) 05062(2) 00432(7) C32 08520(4) ndash00698(3) 05033(2) 00407(7) C33 09085(3) ndash01473(3) 05788(2) 00407(7) C34 07922(4) ndash01879(3) 06277(2) 00424(7) C35 06647(4) ndash01370(3) 05833(2) 00403(7)

- 93 -

Table 43 Bond Lengths (Aring) for Complex 19

Atom1 Atom2 Length

Co1 C5 1993(3) Co1 C6 2023(3) Co1 C17 2022(2) Co1 C18 2009(3) Co1 C31 2042(4) Co1 C32 2075(3) Co1 C33 2062(3) Co1 C34 2042(4) Co1 C35 2048(4) Si1 C2 1886(2) Si1 C19 1877(3) Si1 C20 1863(2) Si1 C21 1865(4) Si2 C3 1889(3) Si2 C22 1876(5) Si2 C23 1862(3) Si2 C24 1865(4) Si3 C11 1901(2) Si3 C25 1876(4) Si3 C26 1867(2) Si3 C27 1875(4) Si4 C12 1889(2) Si4 C28 1860(3) Si4 C29 1868(3) Si4 C30 1870(3) C1 C2 1384(4) C1 C18 1411(3) C2 C3 1474(4) C3 C4 1384(3) C4 C5 1408(3) C5 C6 1480(3) C5 C18 1448(3) C6 C7 1437(3) C6 C17 1465(4) C7 C8 1351(3) C8 C9 1495(3) C8 C15 1476(3) C9 C10 1371(3) C9 C14 1405(3) C10 C11 1423(3) C11 C12 1427(3) C12 C13 1413(3) C13 C14 1376(3)

- 94 -

C14 C15 1488(3) C15 C16 1352(3) C16 C17 1434(3) C17 C18 1468(3) C31 C32 1416(6) C31 C35 1419(4) C32 C33 1401(4) C33 C34 1411(5) C34 C35 1386(5)

Table 44 Bond Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 4325(9) C5 Co1 C17 621(1) C5 Co1 C18 4240(9) C5 Co1 C31 1629(1) C5 Co1 C32 1271(1) C5 Co1 C33 1102(1) C5 Co1 C34 1223(1) C5 Co1 C35 1556(1) C6 Co1 C17 425(1) C6 Co1 C18 6191(9) C6 Co1 C31 1253(1) C6 Co1 C32 1164(1) C6 Co1 C33 1329(1) C6 Co1 C34 1651(1) C6 Co1 C35 1550(1) C17 Co1 C18 427(1) C17 Co1 C31 1204(1) C17 Co1 C32 1451(1) C17 Co1 C33 1722(1) C17 Co1 C34 1419(1) C17 Co1 C35 1194(1) C18 Co1 C31 1517(1) C18 Co1 C32 1676(1) C18 Co1 C33 1312(1) C18 Co1 C34 1112(1) C18 Co1 C35 1198(1) C31 Co1 C32 402(1) C31 Co1 C33 673(1) C31 Co1 C34 675(1) C31 Co1 C35 406(1) C32 Co1 C33 396(1) C32 Co1 C34 672(1)

- 95 -

C32 Co1 C35 675(1) C33 Co1 C34 402(1) C33 Co1 C35 671(1) C34 Co1 C35 396(1) C2 Si1 C19 1085(1) C2 Si1 C20 1157(1) C2 Si1 C21 1096(1) C19 Si1 C20 1035(1) C19 Si1 C21 1081(2) C20 Si1 C21 1110(2) C3 Si2 C22 1071(2) C3 Si2 C23 1162(1) C3 Si2 C24 1100(2) C22 Si2 C23 1110(2) C22 Si2 C24 1067(2) C23 Si2 C24 1056(2) C11 Si3 C25 1077(1) C11 Si3 C26 1177(1) C11 Si3 C27 1083(1) C25 Si3 C26 1045(1) C25 Si3 C27 1086(1) C26 Si3 C27 1097(1) C12 Si4 C28 1099(1) C12 Si4 C29 1132(1) C12 Si4 C30 1101(1) C28 Si4 C29 1119(1) C28 Si4 C30 1066(1) C29 Si4 C30 1048(1) C2 C1 C18 1193(2) Si1 C2 C1 1130(2) Si1 C2 C3 1270(2) C1 C2 C3 1198(2) Si2 C3 C2 1260(2) Si2 C3 C4 1124(2) C2 C3 C4 1208(2) C3 C4 C5 1192(2) Co1 C5 C4 1188(2) Co1 C5 C6 695(1) Co1 C5 C18 694(1) C4 C5 C6 1498(2) C4 C5 C18 1200(2) C6 C5 C18 902(2) Co1 C6 C5 673(1) Co1 C6 C7 1267(2) Co1 C6 C17 687(1) C5 C6 C7 1474(2)

- 96 -

C5 C6 C17 893(2) C7 C6 C17 1227(2) C6 C7 C8 1121(2) C7 C8 C9 1461(2) C7 C8 C15 1251(2) C9 C8 C15 885(2) C8 C9 C10 1471(2) C8 C9 C14 912(2) C10 C9 C14 1214(2) C9 C10 C11 1186(2) Si3 C11 C10 1116(2) Si3 C11 C12 1283(2) C10 C11 C12 1197(2) Si4 C12 C11 1264(2) Si4 C12 C13 1135(2) C11 C12 C13 1201(2) C12 C13 C14 1185(2) C9 C14 C13 1216(2) C9 C14 C15 915(2) C13 C14 C15 1465(2) C8 C15 C14 888(2) C8 C15 C16 1250(2) C14 C15 C16 1458(2) C15 C16 C17 1118(2) Co1 C17 C6 688(1) Co1 C17 C16 1265(2) Co1 C17 C18 682(1) C6 C17 C16 1233(2) C6 C17 C18 900(2) C16 C17 C18 1460(2) Co1 C18 C1 1229(2) Co1 C18 C5 682(1) Co1 C18 C17 691(1) C1 C18 C5 1206(2) C1 C18 C17 1487(2) C5 C18 C17 905(2) Co1 C31 C32 712(2) Co1 C31 C35 699(2) C32 C31 C35 1077(3) Co1 C32 C31 686(2) Co1 C32 C33 697(2) C31 C32 C33 1076(3) Co1 C33 C32 707(2) Co1 C33 C34 691(2) C32 C33 C34 1081(3) Co1 C34 C33 707(2)

- 97 -

Co1 C34 C35 704(2) C33 C34 C35 1086(3) Co1 C35 C31 695(2) Co1 C35 C34 700(2) C31 C35 C34 1079(3)

Table 44 Torsion Angles (deg) for Complex 19

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 ndash1479(3) C6 Co1 C5 C18 983(2) C17 Co1 C5 C4 1630(2) C17 Co1 C5 C6 ndash491(1) C17 Co1 C5 C18 492(1) C18 Co1 C5 C4 1138(2) C18 Co1 C5 C6 ndash983(2) C31 Co1 C5 C4 ndash941(4) C31 Co1 C5 C6 538(4) C31 Co1 C5 C18 1522(4) C32 Co1 C5 C4 ndash573(2) C32 Co1 C5 C6 906(2) C32 Co1 C5 C18 ndash1710(2) C33 Co1 C5 C4 ndash160(2) C33 Co1 C5 C6 1319(1) C33 Co1 C5 C18 ndash1297(2) C34 Co1 C5 C4 271(2) C34 Co1 C5 C6 1750(2) C34 Co1 C5 C18 ndash866(2) C35 Co1 C5 C4 629(4) C35 Co1 C5 C6 ndash1492(3) C35 Co1 C5 C18 ndash509(3) C5 Co1 C6 C7 1458(3) C5 Co1 C6 C17 ndash986(2) C17 Co1 C6 C5 986(2) C17 Co1 C6 C7 ndash1156(3) C18 Co1 C6 C5 491(1) C18 Co1 C6 C7 ndash1650(2) C18 Co1 C6 C17 ndash494(1) C31 Co1 C6 C5 ndash1631(2) C31 Co1 C6 C7 ndash173(3) C31 Co1 C6 C17 983(2) C32 Co1 C6 C5 ndash1170(2) C32 Co1 C6 C7 288(2) C32 Co1 C6 C17 1444(2) C33 Co1 C6 C5 ndash725(2)

- 98 -

C33 Co1 C6 C7 734(3) C33 Co1 C6 C17 ndash1710(2) C34 Co1 C6 C5 ndash166(5) C34 Co1 C6 C7 1293(5) C34 Co1 C6 C17 ndash1151(5) C35 Co1 C6 C5 1499(3) C35 Co1 C6 C7 ndash642(4) C35 Co1 C6 C17 514(3) C5 Co1 C17 C6 501(1) C5 Co1 C17 C16 1666(3) C5 Co1 C17 C18 ndash489(1) C6 Co1 C17 C16 1165(3) C6 Co1 C17 C18 ndash989(2) C18 Co1 C17 C6 989(2) C18 Co1 C17 C16 ndash1446(3) C31 Co1 C17 C6 ndash1106(2) C31 Co1 C17 C16 59(3) C31 Co1 C17 C18 1505(2) C32 Co1 C17 C6 ndash656(3) C32 Co1 C17 C16 510(3) C32 Co1 C17 C18 ndash1645(2) C33 Co1 C17 C6 571(9) C33 Co1 C17 C16 1736(8) C33 Co1 C17 C18 ndash418(9) C34 Co1 C17 C6 1578(2) C34 Co1 C17 C16 ndash857(3) C34 Co1 C17 C18 589(2) C35 Co1 C17 C6 ndash1578(2) C35 Co1 C17 C16 ndash413(3) C35 Co1 C17 C18 1033(2) C5 Co1 C18 C1 ndash1133(3) C5 Co1 C18 C17 993(2) C6 Co1 C18 C1 ndash1635(2) C6 Co1 C18 C5 ndash502(1) C6 Co1 C18 C17 491(1) C17 Co1 C18 C1 1474(3) C17 Co1 C18 C5 ndash993(2) C31 Co1 C18 C1 836(3) C31 Co1 C18 C5 ndash1632(2) C31 Co1 C18 C17 ndash638(3) C32 Co1 C18 C1 ndash779(6) C32 Co1 C18 C5 353(6) C32 Co1 C18 C17 1346(5) C33 Co1 C18 C1 ndash395(3) C33 Co1 C18 C5 737(2) C33 Co1 C18 C17 1731(2)

- 99 -

C34 Co1 C18 C1 20(2) C34 Co1 C18 C5 1152(2) C34 Co1 C18 C17 ndash1455(2) C35 Co1 C18 C1 451(3) C35 Co1 C18 C5 1583(2) C35 Co1 C18 C17 ndash1023(2) C5 Co1 C31 C32 478(5) C5 Co1 C31 C35 1656(4) C6 Co1 C31 C32 904(2) C6 Co1 C31 C35 ndash1517(2) C17 Co1 C31 C32 1412(2) C17 Co1 C31 C35 ndash1010(2) C18 Co1 C31 C32 ndash1739(2) C18 Co1 C31 C35 ndash561(3) C32 Co1 C31 C35 1179(3) C33 Co1 C31 C32 ndash370(2) C33 Co1 C31 C35 808(2) C34 Co1 C31 C32 ndash808(2) C34 Co1 C31 C35 371(2) C35 Co1 C31 C32 ndash1179(3) C5 Co1 C32 C31 ndash1642(2) C5 Co1 C32 C33 764(2) C6 Co1 C32 C31 ndash1143(2) C6 Co1 C32 C33 1263(2) C17 Co1 C32 C31 ndash710(3) C17 Co1 C32 C33 1697(2) C18 Co1 C32 C31 1666(5) C18 Co1 C32 C33 472(6) C31 Co1 C32 C33 ndash1194(3) C33 Co1 C32 C31 1194(3) C34 Co1 C32 C31 816(2) C34 Co1 C32 C33 ndash377(2) C35 Co1 C32 C31 385(2) C35 Co1 C32 C33 ndash808(2) C5 Co1 C33 C32 ndash1243(2) C5 Co1 C33 C34 1166(2) C6 Co1 C33 C32 ndash802(2) C6 Co1 C33 C34 1607(2) C17 Co1 C33 C32 ndash1309(8) C17 Co1 C33 C34 1100(9) C18 Co1 C33 C32 ndash1679(2) C18 Co1 C33 C34 730(2) C31 Co1 C33 C32 376(2) C31 Co1 C33 C34 ndash815(2) C32 Co1 C33 C34 ndash1191(3) C34 Co1 C33 C32 1191(3)

- 100 -

C35 Co1 C33 C32 818(2) C35 Co1 C33 C34 ndash373(2) C5 Co1 C34 C33 ndash833(2) C5 Co1 C34 C35 1577(2) C6 Co1 C34 C33 ndash700(5) C6 Co1 C34 C35 1711(4) C17 Co1 C34 C33 ndash1681(2) C17 Co1 C34 C35 730(3) C18 Co1 C34 C33 ndash1295(2) C18 Co1 C34 C35 1115(2) C31 Co1 C34 C33 809(2) C31 Co1 C34 C35 ndash380(2) C32 Co1 C34 C33 372(2) C32 Co1 C34 C35 ndash818(2) C33 Co1 C34 C35 ndash1189(3) C35 Co1 C34 C33 1189(3) C5 Co1 C35 C31 ndash1699(3) C5 Co1 C35 C34 ndash508(4) C6 Co1 C35 C31 663(4) C6 Co1 C35 C34 ndash1746(2) C17 Co1 C35 C31 1036(2) C17 Co1 C35 C34 ndash1373(2) C18 Co1 C35 C31 1531(2) C18 Co1 C35 C34 ndash878(2) C31 Co1 C35 C34 1191(3) C32 Co1 C35 C31 ndash382(2) C32 Co1 C35 C34 809(2) C33 Co1 C35 C31 ndash812(2) C33 Co1 C35 C34 378(2) C34 Co1 C35 C31 ndash1191(3) C19 Si1 C2 C1 118(2) C19 Si1 C2 C3 ndash1731(2) C20 Si1 C2 C1 1275(2) C20 Si1 C2 C3 ndash574(3) C21 Si1 C2 C1 ndash1061(2) C21 Si1 C2 C3 690(3) C22 Si2 C3 C2 714(3) C22 Si2 C3 C4 ndash988(2) C23 Si2 C3 C2 ndash532(3) C23 Si2 C3 C4 1365(2) C24 Si2 C3 C2 ndash1731(3) C24 Si2 C3 C4 167(3) C25 Si3 C11 C10 ndash241(2) C25 Si3 C11 C12 1624(2) C26 Si3 C11 C10 ndash1417(2) C26 Si3 C11 C12 447(3)

- 101 -

C27 Si3 C11 C10 932(2) C27 Si3 C11 C12 ndash804(2) C28 Si4 C12 C11 ndash731(2) C28 Si4 C12 C13 1055(2) C29 Si4 C12 C11 529(2) C29 Si4 C12 C13 ndash1285(2) C30 Si4 C12 C11 1698(2) C30 Si4 C12 C13 ndash116(2) C18 C1 C2 Si1 1755(2) C18 C1 C2 C3 00(4) C2 C1 C18 Co1 784(3) C2 C1 C18 C5 ndash41(4) C2 C1 C18 C17 ndash1772(4) Si1 C2 C3 Si2 198(4) Si1 C2 C3 C4 ndash1707(2) C1 C2 C3 Si2 ndash1654(2) C1 C2 C3 C4 41(4) Si2 C3 C4 C5 1668(2) C2 C3 C4 C5 ndash40(4) C3 C4 C5 Co1 ndash816(3) C3 C4 C5 C6 1799(4) C3 C4 C5 C18 ndash01(4) Co1 C5 C6 C7 ndash1233(4) Co1 C5 C6 C17 671(1) C4 C5 C6 Co1 1122(4) C4 C5 C6 C7 ndash112(7) C4 C5 C6 C17 1793(4) C18 C5 C6 Co1 ndash678(1) C18 C5 C6 C7 1688(4) C18 C5 C6 C17 ndash07(2) Co1 C5 C18 C1 1164(2) Co1 C5 C18 C17 ndash672(1) C4 C5 C18 Co1 ndash1121(2) C4 C5 C18 C1 42(3) C4 C5 C18 C17 ndash1793(2) C6 C5 C18 Co1 679(1) C6 C5 C18 C1 ndash1757(2) C6 C5 C18 C17 07(2) Co1 C6 C7 C8 858(2) C5 C6 C7 C8 ndash1683(3) C17 C6 C7 C8 ndash08(3) Co1 C6 C17 C16 ndash1205(2) Co1 C6 C17 C18 665(1) C5 C6 C17 Co1 ndash658(1) C5 C6 C17 C16 1736(2) C5 C6 C17 C18 07(2)

- 102 -

C7 C6 C17 Co1 1209(2) C7 C6 C17 C16 03(4) C7 C6 C17 C18 ndash1726(2) C6 C7 C8 C9 ndash1697(3) C6 C7 C8 C15 09(3) C7 C8 C9 C10 05(7) C7 C8 C9 C14 1728(4) C15 C8 C9 C10 ndash1718(4) C15 C8 C9 C14 05(2) C7 C8 C15 C14 ndash1752(2) C7 C8 C15 C16 ndash06(4) C9 C8 C15 C14 ndash04(2) C9 C8 C15 C16 1742(2) C8 C9 C10 C11 1714(3) C14 C9 C10 C11 05(3) C8 C9 C14 C13 ndash1756(2) C8 C9 C14 C15 ndash05(2) C10 C9 C14 C13 ndash06(4) C10 C9 C14 C15 1746(2) C9 C10 C11 Si3 ndash1741(2) C9 C10 C11 C12 01(3) Si3 C11 C12 Si4 ndash90(3) Si3 C11 C12 C13 1725(2) C10 C11 C12 Si4 1779(2) C10 C11 C12 C13 ndash07(3) Si4 C12 C13 C14 ndash1781(2) C11 C12 C13 C14 06(3) C12 C13 C14 C9 ndash00(3) C12 C13 C14 C15 ndash1713(3) C9 C14 C15 C8 05(2) C9 C14 C15 C16 ndash1717(4) C13 C14 C15 C8 1730(4) C13 C14 C15 C16 09(7) C8 C15 C16 C17 00(3) C14 C15 C16 C17 1704(3) C15 C16 C17 Co1 ndash870(3) C15 C16 C17 C6 01(3) C15 C16 C17 C18 1674(4) Co1 C17 C18 C1 ndash1195(4) Co1 C17 C18 C5 664(1) C6 C17 C18 Co1 ndash671(1) C6 C17 C18 C1 1734(4) C6 C17 C18 C5 ndash07(2) C16 C17 C18 Co1 1235(4) C16 C17 C18 C1 40(7) C16 C17 C18 C5 ndash1701(4)

- 103 -

Co1 C31 C32 C33 590(2) C35 C31 C32 Co1 ndash607(2) C35 C31 C32 C33 ndash16(4) Co1 C31 C35 C34 ndash596(3) C32 C31 C35 Co1 615(3) C32 C31 C35 C34 18(4) Co1 C32 C33 C34 592(2) C31 C32 C33 Co1 ndash583(2) C31 C32 C33 C34 09(4) Co1 C33 C34 C35 605(3) C32 C33 C34 Co1 ndash602(2) C32 C33 C34 C35 03(4) Co1 C34 C35 C31 593(3) C33 C34 C35 Co1 ndash606(2) C33 C34 C35 C31 ndash13(4)

23-Bis(trimethylsilyl) linear [3]phenylene(CpCo) 52

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (029 g 085 mmol)27 in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (014 g 101 mmol) The mixture was stirred for 15 h and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the yellow residue dissolved in ether (30 mL) Aqueous workup with sat NaCl (2 x 20 mL) followed by drying over MgSO4 and concentration in vacuo provided a yellow solid This material was redissolved in THF (15 mL) degassed (Ar) and CpCo(CO)2 (0140 g 078 mmol) added The resulting solution (protected from light with foil) was injected (syringe pump) over 8 h into a boiling mixture of THF (200 mL) and BTMSA (50 mL) while irradiating with a slide projection lamp Once addition was complete heating and irradiation were continued for another 14 h The volatiles were removed via vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (4 x 4 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed in vacuo and the residue crystallized from acetone yielding 52 (024 g 57 ) as dark red crystals mp 198ndash202 degC (decomp) 1H-NMR (500 MHz C6D6) δ = 796 (s 2 H) 678 (AArsquom 2 H) 675 (s 2 H) 674 (BBrsquom 2 H) 436 (s 5 H) 037 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1426 1393

1360 1294 1194 1149 802 779 738 268 ppm IR (neat) ν~ = 2960 2923 2853 1461 1455 1378 1260 1093 1019 800 cmndash1 UV-VIS (hexane) λmax (log ε) = 255 (393) 282 (376) 293 (sh 378) 308 (389) 348 (390) 397 (sh 335) 436 (301) 511

CoSiMe3

SiMe3

- 104 -

(262) MS (70 eV) mz () 494 (100) [M+] 370 (14) HRMS (FAB) calcd for C29H31CoSi2 4941296 found 4941292 Elemental analysis calcd for C29H31CoSi2 C 7041 H 632 found 7048 628 Crystallographic information for 52 (H atoms omitted)

Table 45 Crystal Data and Structure Refinement For 52

Empirical formula C29H31CoSi2 Formula weight 49465 cryst size (mm) 030 x 020 x 005 cryst syst Monoclinic refl used for unit cell determination 2640 2 θ range (deg) 242ndash2503 a (Aring) 4391(3) b (Aring) 7472(4) c (Aring) 16869(11) α (deg)

β (deg) 111522(11) γ (deg) V (Aring3) 5149(6) space group C2c Z 8 Dcalc gcm

3 1276

F000 2080 micro cmndash1 774

temp ordmC ndash153

Tmax Tmin 0963 0800 no of total rflns 18401 no of unique rflns 2640 no of obsd rflns 4266 no of variables 271 Reflection to Parameter Ratio 974 R 00892 Rw 02042 Rall 01248 GOF 1008 Max Peak in Final Diff Map (endash Aring3) 1051 Min Peak in Final Diff Map (endash Aring3) ndash0707

- 105 -

Figure 42 ORTEP representation of 52

- 106 -

Table 46 Atomic Coordinates and Equivalent Isotropic Displacement Parameters for 52 U(eq) is Defined as One Third of the Trace of the Orthogonalized Uij Tensor

Atom x y z U(eq)

Co1 006961(2) 087577(12) 038136(6) 00200(3) Si1 018827(6) 08761(5) 063753(18) 00627(9) Si2 018540(5) 05425(3) 046900(16) 00410(6) C1 012151(19) 08410(10) 05589(5) 00310(17) C2 015018(13) 07767(11) 05552(4) 00343(18) C3 015002(14) 06417(10) 04926(5) 00324(17) C4 011985(17) 05770(9) 04357(4) 00247(16) C5 009030(17) 06465(9) 04383(4) 00220(14) C6 005450(16) 06378(9) 04077(4) 00216(14) C7 002537(17) 05420(9) 03591(4) 00224(15) C8 ndash000060(18) 05847(9) 03798(4) 00246(15) C9 ndash003560(17) 05555(10) 03644(4) 00256(16) C10 ndash006399(18) 04581(10) 03174(4) 00284(17) C11 ndash009208(19) 05019(12) 03360(5) 00344(18) C12 ndash009130(19) 06274(12) 03957(5) 00340(18) C13 ndash006300(17) 07256(11) 04422(5) 00294(17) C14 ndash003558(19) 06826(10) 04247(4) 00274(16) C15 000008(18) 07212(10) 04449(4) 00251(16) C16 002653(17) 08159(10) 04925(4) 00234(15) C17 005500(17) 07741(9) 04722(4) 00231(15) C18 009090(17) 07798(10) 05007(4) 00247(15) C19 01766(3) 10793(15) 06845(9) 0098(3) C20 02181(3) 0957(2) 05901(7) 0098(3) C21 02076(3) 07068(14) 07228(7) 0098(3) C22 01946(2) 06941(13) 03925(6) 00631(17) C23 01724(2) 03224(9) 04142(7) 00631(17) C24 022363(17) 04883(16) 05614(5) 00631(17) C25 007501(19) 09264(10) 02652(4) 00281(17) C26 004279(18) 09614(10) 02593(4) 00264(16) C27 004343(18) 10945(10) 03211(4) 00271(16) C28 007584(19) 11429(10) 03645(5) 00296(17) C29 00960(2) 10392(11) 03322(5) 00321(17)

Table 47 Bond Lengths (Aring) for Complex 52

Atom1 Atom2 Length

Co1 C5 2011(7) Co1 C6 2004(7) Co1 C17 2014(8) Co1 C18 2015(6) Co1 C25 2093(8)

- 107 -

Co1 C26 2063(6) Co1 C27 2042(7) Co1 C28 2049(8) Co1 C29 206(1) Si1 C2 1890(6) Si1 C19 187(1) Si1 C20 187(2) Si1 C21 187(1) Si2 C3 1891(8) Si2 C22 187(1) Si2 C23 1870(8) Si2 C24 1869(7) C1 C2 137(1) C1 C18 1418(9) C2 C3 146(1) C3 C4 1406(8) C4 C5 141(1) C5 C6 147(1) C5 C18 144(1) C6 C7 1432(9) C6 C17 148(1) C7 C8 135(1) C8 C9 148(1) C8 C15 149(1) C9 C10 1410(9) C9 C14 139(1) C10 C11 142(1) C11 C12 137(1) C12 C13 141(1) C13 C14 138(1) C14 C15 150(1) C15 C16 1345(9) C16 C17 145(1) C17 C18 147(1) C25 C26 141(1) C25 C29 144(1) C26 C27 143(1) C27 C28 139(1) C28 C29 143(1)

Table 48 Bond Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Angle

C5 Co1 C6 428(3) C5 Co1 C17 619(3)

- 108 -

C5 Co1 C18 420(3) C5 Co1 C25 1145(3) C5 Co1 C26 1372(3) C5 Co1 C27 1733(3) C5 Co1 C28 1468(3) C5 Co1 C29 1184(3) C6 Co1 C17 434(3) C6 Co1 C18 621(3) C6 Co1 C25 1219(3) C6 Co1 C26 1125(3) C6 Co1 C27 1305(3) C6 Co1 C28 1653(3) C6 Co1 C29 1539(3) C17 Co1 C18 428(3) C17 Co1 C25 1632(3) C17 Co1 C26 1307(3) C17 Co1 C27 1137(3) C17 Co1 C28 1247(3) C17 Co1 C29 1562(3) C18 Co1 C25 1460(3) C18 Co1 C26 1733(3) C18 Co1 C27 1388(3) C18 Co1 C28 1167(3) C18 Co1 C29 1194(3) C25 Co1 C26 395(3) C25 Co1 C27 680(3) C25 Co1 C28 681(3) C25 Co1 C29 406(3) C26 Co1 C27 409(3) C26 Co1 C28 674(3) C26 Co1 C29 672(3) C27 Co1 C28 397(3) C27 Co1 C29 678(3) C28 Co1 C29 407(3) C2 Si1 C19 1089(5) C2 Si1 C20 1125(5) C2 Si1 C21 1092(4) C19 Si1 C20 1053(6) C19 Si1 C21 1100(6) C20 Si1 C21 1109(6) C3 Si2 C22 1081(4) C3 Si2 C23 1089(4) C3 Si2 C24 1177(4) C22 Si2 C23 1072(4) C22 Si2 C24 1106(4) C23 Si2 C24 1039(4)

- 109 -

C2 C1 C18 1206(7) Si1 C2 C1 1141(5) Si1 C2 C3 1249(5) C1 C2 C3 1210(7) Si2 C3 C2 1296(5) Si2 C3 C4 1113(5) C2 C3 C4 1190(6) C3 C4 C5 1199(6) Co1 C5 C4 1239(5) Co1 C5 C6 684(4) Co1 C5 C18 692(4) C4 C5 C6 1484(7) C4 C5 C18 1203(6) C6 C5 C18 910(6) Co1 C6 C5 688(4) Co1 C6 C7 1280(5) Co1 C6 C17 687(4) C5 C6 C7 1473(6) C5 C6 C17 892(5) C7 C6 C17 1222(6) C6 C7 C8 1133(6) C7 C8 C9 1475(7) C7 C8 C15 1242(7) C9 C8 C15 882(6) C8 C9 C10 1454(7) C8 C9 C14 928(6) C10 C9 C14 1218(7) C9 C10 C11 1147(7) C10 C11 C12 1222(8) C11 C12 C13 1231(8) C12 C13 C14 1149(7) C9 C14 C13 1233(7) C9 C14 C15 910(6) C13 C14 C15 1457(7) C8 C15 C14 879(6) C8 C15 C16 1254(7) C14 C15 C16 1467(7) C15 C16 C17 1121(6) Co1 C17 C6 679(4) Co1 C17 C16 1300(5) Co1 C17 C18 686(4) C6 C17 C16 1227(6) C6 C17 C18 892(5) C16 C17 C18 1464(7) Co1 C18 C1 1235(5) Co1 C18 C5 688(4)

- 110 -

Co1 C18 C17 686(4) C1 C18 C5 1191(7) C1 C18 C17 1500(7) C5 C18 C17 906(6) Co1 C25 C26 691(4) Co1 C25 C29 683(4) C26 C25 C29 1065(7) Co1 C26 C25 714(4) Co1 C26 C27 688(4) C25 C26 C27 1091(6) Co1 C27 C26 704(4) Co1 C27 C28 704(5) C26 C27 C28 1079(7) Co1 C28 C27 699(5) Co1 C28 C29 699(5) C27 C28 C29 1085(7) Co1 C29 C25 711(5) Co1 C29 C28 694(5) C25 C29 C28 1080(7)

Table 49 Torsion Angles (deg) for Complex 52

Atom1 Atom2 Atom3 Atom4 Torsion

C6 Co1 C5 C4 1468(8) C6 Co1 C5 C18 ndash999(5) C17 Co1 C5 C4 ndash1627(7) C17 Co1 C5 C6 504(4) C17 Co1 C5 C18 ndash494(4) C18 Co1 C5 C4 ndash1133(8) C18 Co1 C5 C6 999(5) C25 Co1 C5 C4 356(7) C25 Co1 C5 C6 ndash1113(4) C25 Co1 C5 C18 1489(4) C26 Co1 C5 C4 765(7) C26 Co1 C5 C6 ndash703(5) C26 Co1 C5 C18 ndash1702(4) C27 Co1 C5 C4 146(2) C27 Co1 C5 C6 ndash1(3) C27 Co1 C5 C18 ndash101(2) C28 Co1 C5 C4 ndash515(9) C28 Co1 C5 C6 1617(5) C28 Co1 C5 C18 619(7) C29 Co1 C5 C4 ndash98(7) C29 Co1 C5 C6 ndash1567(4) C29 Co1 C5 C18 1035(5)

- 111 -

C5 Co1 C6 C7 ndash1474(8) C5 Co1 C6 C17 977(5) C17 Co1 C6 C5 ndash977(5) C17 Co1 C6 C7 1149(8) C18 Co1 C6 C5 ndash482(4) C18 Co1 C6 C7 1644(7) C18 Co1 C6 C17 495(4) C25 Co1 C6 C5 927(5) C25 Co1 C6 C7 ndash547(7) C25 Co1 C6 C17 ndash1696(4) C26 Co1 C6 C5 1362(4) C26 Co1 C6 C7 ndash112(7) C26 Co1 C6 C17 ndash1261(4) C27 Co1 C6 C5 1799(4) C27 Co1 C6 C7 325(8) C27 Co1 C6 C17 ndash824(5) C28 Co1 C6 C5 ndash137(1) C28 Co1 C6 C7 75(1) C28 Co1 C6 C17 ndash40(1) C29 Co1 C6 C5 523(8) C29 Co1 C6 C7 ndash951(9) C29 Co1 C6 C17 1501(7) C5 Co1 C17 C6 ndash497(4) C5 Co1 C17 C16 ndash1646(8) C5 Co1 C17 C18 484(4) C6 Co1 C17 C16 ndash1149(8) C6 Co1 C17 C18 981(5) C18 Co1 C17 C6 ndash981(5) C18 Co1 C17 C16 1470(9) C25 Co1 C17 C6 32(1) C25 Co1 C17 C16 ndash83(1) C25 Co1 C17 C18 130(1) C26 Co1 C17 C6 799(5) C26 Co1 C17 C16 ndash350(8) C26 Co1 C17 C18 1780(4) C27 Co1 C17 C6 1245(4) C27 Co1 C17 C16 97(8) C27 Co1 C17 C18 ndash1373(4) C28 Co1 C17 C6 1686(4) C28 Co1 C17 C16 538(8) C28 Co1 C17 C18 ndash932(5) C29 Co1 C17 C6 ndash1471(7) C29 Co1 C17 C16 98(1) C29 Co1 C17 C18 ndash489(9) C5 Co1 C18 C1 1117(8) C5 Co1 C18 C17 ndash995(5)

- 112 -

C6 Co1 C18 C1 1609(7) C6 Co1 C18 C5 492(4) C6 Co1 C18 C17 ndash502(4) C17 Co1 C18 C1 ndash1488(8) C17 Co1 C18 C5 995(5) C25 Co1 C18 C1 544(9) C25 Co1 C18 C5 ndash573(7) C25 Co1 C18 C17 ndash1568(5) C26 Co1 C18 C1 ndash162(2) C26 Co1 C18 C5 87(3) C26 Co1 C18 C17 ndash13(3) C27 Co1 C18 C1 ndash784(8) C27 Co1 C18 C5 1699(4) C27 Co1 C18 C17 705(6) C28 Co1 C18 C1 ndash356(7) C28 Co1 C18 C5 ndash1473(4) C28 Co1 C18 C17 1133(4) C29 Co1 C18 C1 107(8) C29 Co1 C18 C5 ndash1010(5) C29 Co1 C18 C17 1595(4) C5 Co1 C25 C26 1356(4) C5 Co1 C25 C29 ndash1058(5) C6 Co1 C25 C26 873(5) C6 Co1 C25 C29 ndash1540(5) C17 Co1 C25 C26 62(1) C17 Co1 C25 C29 ndash1796(9) C18 Co1 C25 C26 1738(5) C18 Co1 C25 C29 ndash675(7) C26 Co1 C25 C29 1187(6) C27 Co1 C25 C26 ndash376(4) C27 Co1 C25 C29 810(5) C28 Co1 C25 C26 ndash806(5) C28 Co1 C25 C29 381(5) C29 Co1 C25 C26 ndash1187(6) C5 Co1 C26 C25 ndash696(6) C5 Co1 C26 C27 1703(4) C6 Co1 C26 C25 ndash1134(5) C6 Co1 C26 C27 1265(4) C17 Co1 C26 C25 ndash1604(4) C17 Co1 C26 C27 795(5) C18 Co1 C26 C25 ndash149(2) C18 Co1 C26 C27 91(3) C25 Co1 C26 C27 ndash1201(6) C27 Co1 C26 C25 1201(6) C28 Co1 C26 C25 825(5) C28 Co1 C26 C27 ndash376(4)

- 113 -

C29 Co1 C26 C25 383(5) C29 Co1 C26 C27 ndash818(5) C5 Co1 C27 C26 ndash77(3) C5 Co1 C27 C28 165(2) C6 Co1 C27 C26 ndash774(5) C6 Co1 C27 C28 1644(5) C17 Co1 C27 C26 ndash1254(4) C17 Co1 C27 C28 1163(5) C18 Co1 C27 C26 ndash1698(5) C18 Co1 C27 C28 720(6) C25 Co1 C27 C26 364(4) C25 Co1 C27 C28 ndash818(5) C26 Co1 C27 C28 ndash1182(6) C28 Co1 C27 C26 1182(6) C29 Co1 C27 C26 804(5) C29 Co1 C27 C28 ndash378(5) C5 Co1 C28 C27 ndash1768(5) C5 Co1 C28 C29 637(7) C6 Co1 C28 C27 ndash54(1) C6 Co1 C28 C29 ndash173(1) C17 Co1 C28 C27 ndash861(5) C17 Co1 C28 C29 1544(5) C18 Co1 C28 C27 ndash1355(5) C18 Co1 C28 C29 1050(5) C25 Co1 C28 C27 815(5) C25 Co1 C28 C29 ndash380(5) C26 Co1 C28 C27 387(4) C26 Co1 C28 C29 ndash809(5) C27 Co1 C28 C29 ndash1195(7) C29 Co1 C28 C27 1195(7) C5 Co1 C29 C25 953(5) C5 Co1 C29 C28 ndash1461(5) C6 Co1 C29 C25 576(9) C6 Co1 C29 C28 1762(6) C17 Co1 C29 C25 1797(7) C17 Co1 C29 C28 ndash617(9) C18 Co1 C29 C25 1437(4) C18 Co1 C29 C28 ndash977(5) C25 Co1 C29 C28 1186(7) C26 Co1 C29 C25 ndash373(4) C26 Co1 C29 C28 813(5) C27 Co1 C29 C25 ndash817(5) C27 Co1 C29 C28 369(5) C28 Co1 C29 C25 ndash1186(7) C19 Si1 C2 C1 ndash144(8) C19 Si1 C2 C3 1663(7)

- 114 -

C20 Si1 C2 C1 ndash1307(7) C20 Si1 C2 C3 500(8) C21 Si1 C2 C1 1057(7) C21 Si1 C2 C3 ndash736(7) C22 Si2 C3 C2 ndash852(7) C22 Si2 C3 C4 908(6) C23 Si2 C3 C2 1587(7) C23 Si2 C3 C4 ndash253(7) C24 Si2 C3 C2 410(8) C24 Si2 C3 C4 ndash1431(6) C18 C1 C2 Si1 1795(6) C18 C1 C2 C3 ndash1(1) C2 C1 C18 Co1 ndash817(9) C2 C1 C18 C5 1(1) C2 C1 C18 C17 173(1) Si1 C2 C3 Si2 ndash5(1) Si1 C2 C3 C4 1790(5) C1 C2 C3 Si2 1755(6) C1 C2 C3 C4 ndash0(1) Si2 C3 C4 C5 ndash1747(5) C2 C3 C4 C5 2(1) C3 C4 C5 Co1 822(8) C3 C4 C5 C6 ndash174(1) C3 C4 C5 C18 ndash2(1) Co1 C5 C6 C7 128(1) Co1 C5 C6 C17 ndash674(4) C4 C5 C6 Co1 ndash120(1) C4 C5 C6 C7 8(2) C4 C5 C6 C17 173(1) C18 C5 C6 Co1 671(4) C18 C5 C6 C7 ndash165(1) C18 C5 C6 C17 ndash03(6) Co1 C5 C18 C1 ndash1175(7) Co1 C5 C18 C17 667(4) C4 C5 C18 Co1 1179(7) C4 C5 C18 C1 0(1) C4 C5 C18 C17 ndash1754(7) C6 C5 C18 Co1 ndash663(4) C6 C5 C18 C1 1762(7) C6 C5 C18 C17 04(6) Co1 C6 C7 C8 ndash887(8) C5 C6 C7 C8 160(1) C17 C6 C7 C8 ndash2(1) Co1 C6 C17 C16 1243(7) Co1 C6 C17 C18 ndash672(4) C5 C6 C17 Co1 675(4)

- 115 -

C5 C6 C17 C16 ndash1681(7) C5 C6 C17 C18 03(5) C7 C6 C17 Co1 ndash1223(7) C7 C6 C17 C16 2(1) C7 C6 C17 C18 1705(7) C6 C7 C8 C9 ndash180(1) C6 C7 C8 C15 2(1) C7 C8 C9 C10 2(2) C7 C8 C9 C14 ndash179(1) C15 C8 C9 C10 ndash179(1) C15 C8 C9 C14 01(6) C7 C8 C15 C14 1791(7) C7 C8 C15 C16 ndash2(1) C9 C8 C15 C14 ndash01(5) C9 C8 C15 C16 1792(8) C8 C9 C10 C11 ndash180(1) C14 C9 C10 C11 1(1) C8 C9 C14 C13 1791(7) C8 C9 C14 C15 ndash01(6) C10 C9 C14 C13 ndash1(1) C10 C9 C14 C15 1796(7) C9 C10 C11 C12 ndash1(1) C10 C11 C12 C13 1(1) C11 C12 C13 C14 ndash2(1) C12 C13 C14 C9 2(1) C12 C13 C14 C15 ndash180(1) C9 C14 C15 C8 01(6) C9 C14 C15 C16 ndash179(1) C13 C14 C15 C8 ndash179(1) C13 C14 C15 C16 2(2) C8 C15 C16 C17 1(1) C14 C15 C16 C17 ndash180(1) C15 C16 C17 Co1 858(8) C15 C16 C17 C6 ndash2(1) C15 C16 C17 C18 ndash161(1) Co1 C17 C18 C1 120(1) Co1 C17 C18 C5 ndash669(4) C6 C17 C18 Co1 666(4) C6 C17 C18 C1 ndash173(1) C6 C17 C18 C5 ndash03(5) C16 C17 C18 Co1 ndash131(1) C16 C17 C18 C1 ndash11(2) C16 C17 C18 C5 162(1) Co1 C25 C26 C27 586(5) C29 C25 C26 Co1 ndash583(5) C29 C25 C26 C27 03(9)

- 116 -

Co1 C25 C29 C28 ndash598(6) C26 C25 C29 Co1 588(5) C26 C25 C29 C28 ndash10(9) Co1 C26 C27 C28 607(5) C25 C26 C27 Co1 ndash602(5) C25 C26 C27 C28 05(9) Co1 C27 C28 C29 595(6) C26 C27 C28 Co1 ndash607(5) C26 C27 C28 C29 ndash12(9) Co1 C28 C29 C25 609(6) C27 C28 C29 Co1 ndash595(6) C27 C28 C29 C25 14(9)

Photo-thermal cycle between 52 and 53

An NMR tube containing a solution of 52 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 53 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 724 (AArsquom 2 H) 683 (s 2 H) 662 (BBrsquom 2 H) 444 (s 5 H) 032 (s 18 H) ppm 13C- NMR (100 MHz C6D6) δ = 1493 1482 1430 1276 1256 1241 1155 803 796 725 222 ppm Thermal reversal could be conveniently followed by VT-NMR

Kinetic studies of the thermal CoCp migration in 53 In the glovebox 23-[bis(trimethylsilyl)] linear[3]phenylene(CpCo) 52 dissolved in the solvent of choice (C6D6 or toluene-d8) was passed through an HPLC filter and then transfered via syringe into a thick-walled NMR tube connected to a vacuum line adapter The sample was then degassed by three freeze-pump-thaw cycles and flame-sealed under vacuum Prior to the kinetic runs the mixtures were irradiated for 10 h in a Rayonet Photochemical Reactor fitted with lamps emitting at 310 and 365 nm After this treatment care was taken to exclude ambient light as it causes some isomerization The irradiated samples were then placed in the NMR spectrometer at ndash65 degC (500 MHz) which was then warmed to the required temperature In the case of the 60 degC runs the magnet was prewarmed because of the fast reaction rate at this temperature After five min the spectra were recorded The Cp signal of the photoisomer was integrated relative to the solvent peak of C6D6 or the CD3 peak of toluene-d8 and monitored as a function of time The integral from the first scan was used as [A]o Since the equilibrium constant between the isomers was 50 the kinetic analysis treated the isomerization as a first-order non-reversible process Plotting the data accordingly

CoSiMe3

SiMe3

52

CoSiMe3

SiMe3

53

hν∆

- 117 -

yielded the reaction rate constants which were used in the Eyring plots to obtain the activation parameters Kinetic studies of the thermal haptotropic shift for complex 52 Kinetic runs were executed in C6D6 as the optimum solvent A sample of 52 in degassed C6D6 or toluene-d8 was subjected to UV light for 10 h leading to maximum enrichment of 53 The sample was kept at the specified temperature and the disappearance of 53 monitored by 1H-NMR spectroscopy The reaction proved to be first-order (eq 1) consistent with an intramolecular process

[ ] [ ]Akdt

Adminus=

(1)

[ ][ ] dtkA

Ad=minus

(2)

[ ][ ]

tkA

A=minus

0

ln (3)

The rate constant (k) at 30 40 50 and 60 degC was obtained from the slope of a plot of ndashln([A][A]0) versus time (t) following eq 2 and 3 The actual error in reproducibility was estimated by the calculation of one standard deviation (σ) for a triplicate run at 60 degC The percentage error was applied for k at 30 40 and 50 degC The rate constants and their errors are given in Tables 411 and 414 The values for k and their standard deviations were used to calculate the activation enthalpy (∆HDagger) and entropy (∆SH) of the haptotropic shift The basis for these calculations is the Eyring equation (eq 4) This expression (eq 4) was transformed to eq 5 and the activation enthalpy (∆HDagger) obtained from the slope of a plot of ndashln(kT) versus 1RT The intercept (ndashC) provides the activation entropy (∆SH) following eq 6 and 7

C

TR

H

R

S

h

k

TR

H

T

k B

minus∆

=

∆+minus

∆=minus

ne

nene

lnln

( 4)

R

S

h

kC B

ne∆+= ln

(5)

minus=∆ ne

h

kCRS Bln

(6)

- 118 -

The errors in ∆HDagger and ∆SDagger were calculated based on those in the rate constants leading to two additional least square fits in the Eyring plot These fits represent the two most extreme deviations from the original plot This provides a conservative error estimate and finally the values of 204plusmn14 kcalmol for ∆HH and 158plusmn22 eu (calmolmiddotK) for ∆SH in C6D6 In order to probe for solvent effects the kinetics were also repeated in toluene-d8 The preparation of the sample followed the described procedure and the rate constants (k) were obtained at 30 40 50 and 60 degC At 60 degC three measurements were carried out to estimate the errors in reproducibility for k and the activation parameters Error propagation was done as described for the kinetic experiments in C6D6 It is assumed that those rate constants (k) show the same relative error as the ones for the rearrangement of 53 to 52 in C6D6 The activation parameters in toluene-d8 were found to be 231plusmn07 kcalmol and 60plusmn13 eu

Table 410 Kinetic Data for the Conversion of 53 to 52 in C6D6

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09657 00349 1000 09419 00599 6000 09380 00640 2000 09018 01034 9000 09038 01012 3000 08557 01558 12000 08760 01324 4000 08176 02013 15000 08418 01723 5000 07796 02490 18000 08206 01978 6000 07555 02804 21000 08010 02219 7000 07255 03210 32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 400 09541 00470 30 09888 00113 800 09197 00837 60 09820 00181 1200 08910 01154 90 09708 00296 1600 08489 01638 120 09596 00413 2000 08298 01865 150 09506 00507 2400 07954 02289 180 09416 00602 2800 07591 02756 210 09348 00674 240 09281 00746 270 09213 00819 300 09124 00917 330 09034 01016 360 08966 01091

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

- 119 -

0 10000 00000 0 10000 00000 30 09950 00050 30 09909 00092 60 09900 00101 60 09854 00147 90 09800 00202 90 09762 00241 120 09750 00253 120 09671 00335 150 09700 00305 150 09634 00372 180 09625 00382 180 09543 00468 210 09575 00434 210 09433 00583 240 09475 00539 240 09397 00622 270 09400 00619 270 09287 00740 300 09350 00672 300 09232 00799 330 09300 00726 330 09177 00858 360 09250 00780 360 09086 00959

Table 411 The Rate Constants (k) in C6D6 Calculated From the Data in Table 410 and Their

Standard Deviations (σ)

Temp (K) k (1s) σσσσ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 10809Endash05 74258Endash07 09970 171494 00688

31315 45615Endash05 31338Endash06 09948 157420 00688

32315 95118Endash05 65346Endash06 09965 150385 00688

33315 (1) 27425Endash04 09965

33315 (2) 25714Endash04 09964

33315 (3) 30051Endash04 09990

33315 (avg) 26511Endash04 18841Endash05 140101 00688

Table 412 Activation Parameters for the Kinetic Experiments in C6D6

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 90990 85414 79291 Intercept ndash1789 ndash1674 ndash1559 R

2 09869 09869 09869

∆HDagger (Jmol) 90990 85414 79291

∆HDagger (kcalmol) 217 204 190

∆SDagger (JmolmiddotK) ndash569 ndash660 ndash751

∆SDagger (eu) ndash136 ndash158 ndash180

- 120 -

(323 15 K 50 degC) y = 95118E-05x + 44505E-03

R2 = 9965

(30315 K 30 degC) y = 10809E-05x + 20474E-03

R2 = 9970

(31315 K 40 degC) y = 45615E-05x + 11689E-02

R2 = 9948

(33315 K 60 degC) y = 263387E-04x + 390297E-04

R2 = 9992

000

005

010

015

020

025

030

035

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

Figure 43 Kinetic plots for the conversion of 53 to 52 in C6D6

Table 413 Kinetic Data for the Conversion of 53 to 52 in Toluene-d8

30315 K 31315 K

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 3000 09556 00454 1000 09488 00526 6000 09256 00773 2000 08931 01130 9000 08956 01103 3000 08545 01572 12000 08667 01430 4000 08143 02054 15000 08343 01811 5000 07818 02461 18000 08103 02103 6000 07559 02798 21000 07863 02404 7000 07179 03314

- 121 -

32315 K 33315 K (1)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

000 10000 00000 0 10000 00000 40000 09470 00544 30 09887 00113 80000 08934 01127 60 09775 00228 120000 08594 01515 90 09691 00314 160000 08175 02015 120 09592 00416 200000 07861 02406 150 09473 00542 240000 07502 02875 180 09381 00639 280000 06991 03579 210 09262 00767 240 09149 00889 270 09086 00959 300 08973 01083 330 08868 01202 360 08762 01321

33315 K (2) 33315 K (3)

Time (s) Rel Conc ndashln[AAo] Time (s) Rel Conc ndashln[AAo]

0 10000 00000 0 10000 00000 30 09945 00055 30 09910 00090 60 09795 00207 60 09828 00173 90 09700 00304 90 09716 00288 120 09645 00361 120 09559 00451 150 09479 00535 150 09440 00576 180 09464 00551 180 09313 00712 210 09314 00711 210 09238 00792 240 09188 00847 240 09156 00882 270 09101 00942 270 08992 01063 300 08991 01064 300 08932 01129 330 08896 01170 330 08872 01197 360 08801 01277 360 08686 01409

- 122 -

Table 414 The Rate Constants (k) in Toluene-d8 Calculated From the Data in Table 413 and Their Standard Deviations (σ)

Temp (K) k (1s) σ σ σ σ of k (1s) R2 ndashln(kT) σ σ σ σ of ndashln(kT)

30315 11314Endash05 37152Endash07 09976 17104 05610

31315 46470Endash05 15251Endash06 09948 15723 05157

32315 12214Endash04 401074Endash06 09957 14788 04851

33315 (1) 36441Endash04 09992

33315 (2) 36124Endash04 09951

33315 (3) 38855Endash04 09956

33315 (avg) 37140Endash04 14937Endash05 13707 04496

Table 415 Activation Parameters for the Kinetic Experiments in Toluene-d8

Positive

Deviation

1egative

Deviation

Slope of Eyring Plot 96590 93523 90455 Intercept ndash2073 ndash2007 ndash1941 R

2 09962 09962 09962

∆HDagger (Jmol) 96590 93523 90455

∆HDagger (kcalmol) 2309 2235 2162

∆SDagger (JmolmiddotK) ndash2521 ndash3068 ndash3615

∆SDagger (eu) ndash602 ndash733 ndash864

- 123 -

00000

00500

01000

01500

02000

02500

03000

03500

04000

0 5000 10000 15000 20000 25000

Time (s)

ndashln

[AA

0]

30315 K 30 degC

31315 K 40 degC

32315 K 50 degC

33315 K 60 degC (avg)

(31315 K 40 degC) y = 46470E-05x + 10553E-02

R2 = 9948

(32315 K 50 degC) y = 12214E-04x + 47671E-03

R2 = 9957

(33315 K 60 degC)y = 371377E-04x - 208381E-03

R2 = 9992

(30315 K 30 degC) y = 11314E-05x + 71900E-03

R2 = 9976

Figure 44 Kinetic plots for the conversion of 53 to 52 in toluene-d8

- 124 -

(C6D6) y = 85141x - 16743

R2

= 09869

(toluene-d 8) y = 93523x - 2007

R2 = 09962

13600

14600

15600

16600

17600

36100E-04

36600E-04

37100E-04

37600E-04

38100E-04

38600E-04

39100E-04

39600E-04

40100E-04

1RT (Jmol)

-ln

(kT

)

Figure 45 Eyring plots for conversion of 53 to 52 MeCpCo(CO)2

Adapted from the literature procedure50 Co2(CO)8 (809 g 2366 mmol) was added to a round bottom flask in the glovebox The flask was capped with a septum and brought out of the glovebox A reflux condenser connected to the high vacuum line was quickly exchanged with the septum under a heavy purge of argon Degassed CH2Cl2 (30 mL) was added followed by freshly cracked deoxygenated methylcyclopentadiene (135 mL 123 mmol) The mixture evolved gas upon addition of the methylcyclopentadiene indicating CO liberation The entire setup was protected from light with foil and heated to a gentle reflux using a heating mantlevariac heat source After stirring at reflux for 26 h the mixture now dark crimson in color was cooled to rt The reflux condenser was quickly exchanged for a distillation head under an Ar purge and CH2Cl2 distilled off at atmospheric pressure under Ar Vacuum distillation at 002 Torr was performed and the forerun discarded The desired complex was obtained as a red liquid (7296 g 79) bp = 31 degC (002 Torr) stored at ndash10 degC and shielded from light Note A small

CoOC CO

- 125 -

amount of methylcyclopentadiene dimer (15 ) which could not be separated was present in the isolated product This was deemed harmless however and the obtained product was used in further experiments without further purification 85 pure 1H-NMR data match those reported in the literature 1H-NMR (C6D6) δ = 145 (s 3 H) 431 (br s 2 H) 451 (br s 2 H) 23-Bis(trimethylsilyl) linear [3]phenylene(MeCpCo) 54

To a Schlenk flask containing a solution of 23-bis(trimethylsilylethynyl)biphenylene 51 (0146 g 0424 mmol) in ether (20 mL) and CH3OH (10 mL) was added K2CO3 (0101 g 0731 mmol) The mixture was stirred for 100 min and monitored via TLC eluting with hexaneCH2Cl2 (51) After the starting material had been consumed the solvents were removed and the remaining yellow residue was dissolved in freshly distilled THF (15 mL) The green solution was separated from the solids via canula filtration and transferred into another Schlenk flask After a 20 min Ar purge MeCpCo(CO)2 (0092 g 0403 mmol) was added and the resulting solution (protected from light with foil) injected via syringe pump over 9 h into a boiling mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 15 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (201) The volatiles were again removed under high vacuum line and the residue crystallized from acetone yielding 55 (0125 g 61 ) as black crystals mp 163ndash165 degC 1H-NMR (500 MHz C6D6) δ = 783 (s 2 H) 676 (m 4 H) 675 (s 2 H) 442 (apparent t J = 21 Hz 2 H) 427 (apparent t J = 21 Hz 2 H) 134 (s 3 H) 038 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1502 1423 1386 1354 1293 1193 1147 899 806 798 783 739 111 279 ppm IR (neat) ν~ = 2959 2923 2853 1462 1455 1378 1260 1093 1030 802 cmndash1 UV-VIS (hexane) λmax (log ε) = 256 (368) 281 (356) 293 (359) 310 (373) 350 (368) 386 (sh 321) 437 (sh 287) 499 (sh 247) end absorption to 550 nm MS (70 eV) mz () 508 (100) [M+] 370 (28) HRMS (FAB) calcd for C30H33CoSi2 5081453 found 5081442 Photo-thermal cycle between 54 and 56

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

54

CoSiMe3

SiMe3

56

hν∆

Me Me

- 126 -

An NMR tube containing a solution of 54 was placed in a Rayonet photochemical reactor fitted with an equal number each of 350 and 300 nm lamps and irradiated up to 10 h to reach the photostationary state 56 1H-NMR (300 MHz C6D6) δ = 747 (s 2 H) 715 (AArsquom obscured by solvent peak) 680 (s 2 H) 664 (AArsquom 2 H) 447 (apparent t J = 21 Hz 2 H) 428 (apparent t J = 21 Hz 2 H) 148 (s 3 H) 032 (s 18 H) ppm Thermal reversal could be conveniently followed by VT-NMR

14-Deuterio-23-bis(trimethylsilyl) linear [3]phenylene cyclopentadienylcobalt 55

To 23-bis(trimethylsilylethynyl)biphenylene 52 (0144 g 0418 mmol) in CH3OD (10 mL) was added freshly distilled ether (20 mL) and K2CO3 (0083 g 0600 mmol) The mixture was stirred for 100 min and monitored by TLC (hexaneCH2Cl2 51) When the starting material had disappeared the solvents were removed and the remaining yellow residue very quickly dissolved in freshly distilled THF (10 mL) The green solution was separated from the solids using a filter cannula and transferred to another Schlenk flask After a 20 min Ar purge CpCo(CO)2 (0072 g 0400 mmol) was added and the resulting solution (protected from light with foil) was injected via syringe pump over 7 h into a refluxing mixture of THF (100 mL) and BTMSA (25 mL) which was irradiated by a slide projection lamp Heating and irradiation were continued for another 14 h The solvents were removed by vacuum transfer and the remaining black residue filtered through a plug of neutral alumina activity III (35 x 35 cm) eluting with a degassed mixture of hexaneTHF (101) The solvents were removed on the high vacuum line and the residue recrystallized from acetone yielding 8 (0085 g 41 ) as dark red crystals 1H-NMR spectroscopy showed 63 incorporation of deuterium as indicated by the diminution of the peak intensity of the signal at δ = 796 (s 074 H) ppm MS (FAB) mz () 496 (100) [M+] 372 (19)

CoSiMe3

SiMe3

D

D

- 127 -

Crossover experiment with 54 and 55

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

h

CoSiMe3

SiMe3

Me

CoSiMe3

SiMe3

D

D

+

5455

5657

A solution of complex 55 (~2 mg) and 54 (~2 mg) in C6D6 (06 mL) rigorously protected from light was analyzed by 1H-NMR spectroscopy to reveal a 1861 mixture of 5554 The peak for 55 at δ = 796 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound A mass spectrum of an aliquot gave the appropriate composite of the two respective molecular ion patterns (Figure 46) The sample was then irradiated as described for above 13 h at RT The 1H-NMR spectrum of the irradiated mixture showed the presence of the respective photoisomers of 55 and 54 There were no unidentifiable peaks the signal at δ = 7470 (s 074 H) ppm exhibited the expected integration relative to the other hydrogens in this compound and the clearly resolved peak for 56 at δ = 7473 (s 2 H) ppm revealed unattenuated intensity An aliquot was submitted for mass spectral analysis furnishing the same pattern as that depicted above The sample was then placed in an oil bath preheated to 80 degC for 30 h a treatment that regenerated the original NMR spectrum of the mixture of 55 and 54 including the relative integration ratios Similarly mass spectral analysis resulted in the same pattern as that depicted in Figure 46

- 128 -

Figure 46 Mass spectrum from the crossover experiment between 55 and 56

Low temperature photolyses of 19 and 52 A small amount (~5 mg) of linear[3]phenylene(CpCo) 19 or 52 dissolved in toluene-d8 was added to a J-Young NMR tube in the glovebox The sealed sample was then placed inside a Pyrex Dewar flask positioned in a Rayonet Photochemical Reactor outfitted with UV-lamps emitting at 310 and 350 nm (as shown in Figure 214) Cooling was achieved with the use of a Neslab Refrigerated Circulating bath employing isopropanol as the cooling medium The cold isopropanol was pumped into and out of the Pyrex Dewar using securely fastened Tygon tubes maintaining a temperature of ndash55 to ndash50 degC Once the sample was chilled irradiation was commenced The total irradiation time varied from 25 to 4 h When analysis was required the sample was transported in another Dewar flask containing dry iceisopropanol (ndash78 degC) while the NMR spectrometer was prepared for the low temperature experiment The spectrometer was cooled (ndash80 to ndash30 degC depending on the experiment) the sample wiped with a paper towel placed inside the spinner and very quickly lowered manually with a string into the cold magnet After allowing time for the temperature to equilibrate (10 min) a spectrum was recorded For VT experiments the temperature was slowly

- 129 -

raised from ndash80 degC in 10 degree increments to 10 degC Spectra were recorded at each interval For all other experiments spectra were recorded at ndash30 degC 2378-Tetrakis(trimethylsilyl) linear [3]phenylene(CpCo)2 78

In the glovebox 2378-tetrakis(trimethylsilyl) linear [3]phenylene(CpCo) 19 (0049 g 0133 mmol) and CpCo(C2H4)2 (0025 g 0139 mmol)99 were added to a Schlenk flask The flask was sealed brought out of the box connected to a vacuum manifold and freshly distilled degassed benzene (15 mL) added The mixture was heated to 70 degC on an oil bath for 23 h before being cooled to RT The solvent was removed in vacuo giving a black residue that was rapidly filtered through a plug of neutral alumina activity III (25 x 35 cm) eluting with a mixture of hexanes and THF (1001) under nitrogen and into a Schlenk flask The solvents were again removed in vacuo and the ensuing black residue recrystallized from acetone at ndash78 degC to give pure 78 (0057 g 56 ) as black crystals 1H-NMR (400 MHz acetone-d6) δ = 039 (s 36H) 481 (s 2H) 489 (m 4H) 736 (s 4H) ppm 13C-NMR (100 MHz acetone-d6) δ = 266 5372 5710 8284 12587 14542 15054 ppm UV-VIS (hexane) λmax (log ε) 197 (334) 221 (336 sh) 244 (344) 286 (363) 386 (279 sh) 439 (258) MS (FAB) 762 (M+ 100) HRMS calcd for C40H52Si4Co2 7621810 found 7621791 43 Computational Details for Chapter Two All calculations were performed using the GAUSSIAN03100 program GaussView 30101 and ChemCraft102 were employed to input structures as well as view output results Optimized geometries were obtained at the hybrid density functional theory (DFT) using Beckersquos three-parameter exchange-correlation functional103 containing the non-local gradient correction of Lee Yang and Parr104 (B3LYP) For optimization purposes a standard basis 3-21G105 was used for hydrogen and carbon atoms For cobalt the LANL2DZ106 basis set was applied with the outermost d function released yielding a triple-zeta d basis along with the effective core potentials (ECP) to describe the core electrons For the single point energy calculations the basis sets were increased to 6-31G107 for hydrogen 6-311G108 for carbon and the modified LANL2DZ basis as described above for cobalt with an added f-orbital coefficient109 The potential energy surfaces were mapped through a scan calculation a feature also available within the GAUSSIAN03 program Transition state structures were obtained in three different steps (i) determination of initial and final products or the minimum closest to a TS (ii) a linear QST2110 search for an initial guess of a TS and

- 130 -

(iii) input of the results from (ii) into a QST3 search Transition states and minima were confirmed by carrying out frequency calculations (using the same basis as that used for the optimizations)

Calculated structures for linear [3]phenylene(CpCo) (labels from Figures 29 and 210 in Section 24)

(a) Global minimum η4-cyclobutadiene (00 kcalmol)

C 2878616000 ndash1675635000 ndash1461246000 C 3986441000 ndash2043582000 ndash0714088000 C 3986471000 ndash2043226000 0714700000 C 2878686000 ndash1674908000 1461732000 C 1740663000 ndash1265994000 0736724000 C 1740638000 ndash1266353000 ndash0736388000 H 2884721000 ndash1731772000 ndash2551997000 H 2884845000 ndash1730511000 2552509000 C 0311237000 ndash0833174000 0748280000 C 0311204000 ndash0833522000 ndash0748106000 C ndash0893980000 ndash0698348000 ndash1520584000 C ndash0893913000 ndash0697588000 1520749000 C ndash1996288000 ndash0532216000 0744771000 C ndash1996322000 ndash0532586000 ndash0744640000 C ndash3491040000 ndash0328769000 ndash0716524000 C ndash3490989000 ndash0328300000 0716632000 C ndash4645388000 ndash0172650000 ndash1448232000 C ndash4645276000 ndash0171672000 1448326000 C ndash5836534000 ndash0014205000 ndash0697760000

- 131 -

C ndash5836481000 ndash0013731000 0697841000 H ndash0905006000 ndash0741217000 ndash2609771000 H ndash0904887000 ndash0739873000 2609960000 H ndash4666353000 ndash0168153000 ndash2539086000 H ndash6785734000 0111682000 ndash1227959000 H ndash6785641000 0112502000 1228028000 H ndash4666162000 ndash0166493000 2539178000 Co 1455829000 0662094000 ndash0000295000 C 0672548000 2613322000 0000481000 C 1502831000 2459745000 1168426000 C 2819523000 2140942000 0722371000 C 2818808000 2141294000 ndash0723848000 C 1501651000 2460224000 ndash1168394000 H ndash0391329000 2836892000 0001070000 H 1172930000 2540112000 2200200000 H 3678957000 1932268000 1353707000 H 3677612000 1932967000 ndash1356152000 H 1170676000 2541059000 ndash2199789000 H 4894703000 ndash2369906000 1230670000 H 4894651000 ndash2370516000 ndash1229936000

(b) Transition state 1 η2-cyclobutadiene (269 kcalmol)

C ndash3991583000 ndash2430244000 ndash0695300000 C ndash2895249000 ndash1923385000 ndash1446977000 C ndash1838331000 ndash1436925000 ndash0718218000 C ndash0460541000 ndash0772703000 ndash0748934000

- 132 -

C 0758545000 ndash0733408000 ndash1513161000 C 1871918000 ndash0586111000 ndash0739684000 C 3374782000 ndash0432509000 ndash0717168000 C 4533131000 ndash0322603000 ndash1448209000 C 5731498000 ndash0208370000 ndash0696796000 C 5731438000 ndash0207885000 0696952000 C 4533003000 ndash0321597000 1448333000 C 3374722000 ndash0432010000 0717261000 C 1871861000 ndash0585642000 0739747000 C 0758457000 ndash0732583000 1513259000 C ndash0460578000 ndash0772439000 0748991000 C ndash1838348000 ndash1436677000 0718485000 C ndash2895298000 ndash1922892000 1447371000 C ndash3991613000 ndash2429987000 0695830000 H ndash4853881000 ndash2841402000 ndash1229010000 H ndash2909366000 ndash1943431000 ndash2538196000 H 0770744000 ndash0814782000 ndash2600896000 H 4554949000 ndash0321315000 ndash2539049000 H 6684245000 ndash0118682000 ndash1227928000 H 6684140000 ndash0117859000 1228104000 H 4554722000 ndash0319567000 2539175000 H 0770611000 ndash0813312000 2601042000 H ndash2909450000 ndash1942588000 2538596000 H ndash4853932000 ndash2840954000 1229654000 Co ndash1032604000 1030206000 ndash0000179000 C ndash2903591000 1947430000 ndash0000175000 C ndash2211742000 2430689000 ndash1177143000 C ndash1026232000 3056089000 ndash0732194000 C ndash1026229000 3056139000 0731719000 C ndash2211730000 2430773000 1176747000 H ndash3829247000 1376180000 ndash0000150000 H ndash2513347000 2264399000 ndash2207387000 H ndash0243163000 3477094000 ndash1358586000 H ndash0243137000 3477190000 1358051000 H ndash2513304000 2264572000 2207015000

(c) Local minimum 1 η4-benzene (109 kcalmol)

- 133 -

C 4829664000 ndash1220862000 0883782000 C 3649435000 ndash0895915000 1609183000 C 2478533000 ndash0900239000 0886069000 C 0985532000 ndash0699413000 0895282000 C ndash0207413000 ndash0351140000 1567281000 C ndash1295977000 ndash0355264000 0631690000 C ndash2799524000 ndash0368596000 0647705000 C ndash3950748000 0104186000 1252743000 C ndash5173877000 ndash0370408000 0725519000 C ndash5217559000 ndash1270006000 ndash0351644000 C ndash4043168000 ndash1754445000 ndash0967619000 C ndash2843350000 ndash1293792000 ndash0444950000 C ndash1365414000 ndash1319830000 ndash0538287000 C ndash0225558000 ndash1662005000 ndash1182029000 C 0928168000 ndash1009692000 ndash0554559000 C 2436156000 ndash1209374000 ndash0509824000 C 3575395000 ndash1530032000 ndash1215144000 C 4792344000 ndash1526592000 ndash0477473000 H 5781080000 ndash1237670000 1406156000 H 3693287000 ndash0679862000 2671420000 H ndash0279175000 ndash0037747000 2601166000 H ndash3939706000 0801901000 2083798000 H ndash6106757000 ndash0031072000 1165263000 H ndash6183419000 ndash1601741000 ndash0720200000 H ndash4097586000 ndash2453276000 ndash1795561000 H ndash0137803000 ndash2306368000 ndash2049380000 H 3570207000 ndash1781979000 ndash2270507000 H 5717527000 ndash1774506000 ndash0988963000 Co 0235674000 0924694000 ndash0006080000 C 1650242000 2605908000 ndash0261710000 C 0606451000 3071372000 0583798000

C ndash0633939000 2891762000 ndash0112192000 C ndash0354070000 2388098000 ndash1431110000 C 1060641000 2182627000 ndash1507942000 H 2701380000 2562827000 ndash0018620000 H 0717262000 3431891000 1595877000 H ndash1615358000 3123686000 0274491000 H ndash1077256000 2190401000 ndash2207047000

- 134 -

H 1601331000 1788686000 ndash2355167000

(d) Transition State 2 η3-benzene (249 kcalmol)

C 5059641000 ndash0675345000 0741440000 C 3868057000 ndash0242461000 1393542000 C 2691208000 ndash0611642000 0796692000 C 1164924000 ndash0568451000 0814993000 C 0001006000 ndash0193010000 1575722000 C ndash1162903000 ndash0569406000 0815406000 C ndash2689168000 ndash0613549000 0797134000 C ndash3866228000 ndash0245076000 1394017000 C ndash5057560000 ndash0678583000 0741882000 C ndash5030442000 ndash1430649000 ndash0426732000 C ndash3802288000 ndash1812828000 ndash1038342000 C ndash2662603000 ndash1392426000 ndash0404590000 C ndash1143695000 ndash1392940000 ndash0383227000 C 0001354000 ndash1885575000 ndash1010384000 C 1146183000 ndash1392203000 ndash0383465000 C 2665098000 ndash1390792000 ndash0404876000 C 3805017000 ndash1810598000 ndash1038596000 C 5032958000 ndash1427555000 ndash0427087000 H 6017043000 ndash0408623000 1174840000 H 3916675000 0338622000 2306082000 H 0001106000 0141040000 2603832000 H ndash3915179000 0335814000 2306664000 H ndash6015116000 ndash0412488000 1175329000

- 135 -

H ndash5963925000 ndash1737868000 ndash0883265000 H ndash3794877000 ndash2406462000 ndash1944276000 H 0001449000 ndash2505619000 ndash1894591000 H 3797948000 ndash2404400000 ndash1944423000 H 5966616000 ndash1734262000 ndash0883606000 Co ndash0000294000 1006304000 0016484000 C 1144150000 2811021000 ndash0317903000 C ndash0001831000 3236912000 0413780000 C ndash1150105000 2808519000 ndash0312717000 C ndash0712506000 2257800000 ndash1588662000 C 0702130000 2259464000 ndash1591918000 H 2174046000 2940434000 ndash0021226000 H ndash0000096000 3693787000 1391408000 H ndash2178919000 2935539000 ndash0011312000 H ndash1360790000 1903514000 ndash2375388000 H 1347563000 1907002000 ndash2381795000

Calculated structures for linear [5]phenylene CpCo (labels from Figures 211 and 212 in Section 24)

(a) Global minimum η4-cyclobutadiene (000 kcalmol)

C ndash2147283000 ndash0385762000 ndash0741520000 C ndash2146881000 ndash0382747000 0740465000 C ndash0675330000 ndash0218887000 0741228000 C ndash0675503000 ndash0222208000 ndash0743565000 C 0535474000 ndash0309864000 ndash1519364000

- 136 -

C 1654024000 ndash0363787000 ndash0743565000 C 1653968000 ndash0359108000 0742223000 C 0535464000 ndash0301263000 1517648000 C 3146303000 ndash0437352000 0715394000 C 3146555000 ndash0442081000 ndash0715839000 H 0537903000 ndash0329735000 2601810000 H 0538062000 ndash0344229000 ndash2603354000 Co ndash1585768000 1444604000 ndash0004763000 C ndash2656365000 3118646000 0813641000 C ndash1264152000 3247968000 1115884000 C ndash0546296000 3292610000 ndash0128221000 C ndash1500173000 3225060000 ndash1199322000 C ndash2801883000 3099872000 ndash0616868000 H ndash3459184000 3033020000 1530368000 H ndash0824887000 3279284000 2101474000 H 0525240000 3366953000 ndash0237713000 H ndash1272392000 3239735000 ndash2254384000 H ndash3732669000 2998753000 ndash1154572000 C ndash3315848000 ndash0698077000 1516941000 C ndash3316515000 ndash0705270000 ndash1515890000 C ndash4404590000 ndash0970491000 0742487000 C ndash4404888000 ndash0974125000 ndash0739677000 H ndash3311463000 ndash0745189000 ndash2599679000 H ndash3310191000 ndash0733014000 2600900000 C ndash5857232000 ndash1346832000 ndash0713671000 C ndash5856902000 ndash1343302000 0718959000 C ndash6992149000 ndash1638138000 ndash1445564000 C ndash6991464000 ndash1630979000 1452826000 C 4314567000 ndash0501395000 ndash1493440000 C 4313844000 ndash0491124000 1494022000

C ndash8157130000 ndash1937355000 ndash0695553000 C ndash8156796000 ndash1933908000 0704865000 H ndash7013569000 ndash1630976000 2537309000 H ndash9075842000 ndash2169721000 1232475000 H ndash9076411000 ndash2175846000 ndash1221548000 H ndash7014707000 ndash1643790000 ndash2530023000 C 5464859000 ndash0553191000 0719930000 C 5465218000 ndash0558312000 ndash0718328000 C 6977989000 ndash0635007000 ndash0714777000 C 6977565000 ndash0629511000 0717833000 H 4313279000 ndash0484164000 2577745000 H 4314609000 ndash0502067000 ndash2577185000 C 8138196000 ndash0684071000 1451266000 C 8139115000 ndash0695400000 ndash1446980000 C 9348946000 ndash0746919000 0699256000 C 9349380000 ndash0752387000 ndash0693700000

- 137 -

H 8162380000 ndash0700716000 ndash2531270000 H 8160717000 ndash0680929000 2535584000 H 10294800000 ndash0791917000 1230058000 H 10295576000 ndash0801571000 ndash1223516000

(b) Transition state 3 η2-cyclobutadiene (370 kcalmol)

C ndash8026536000 ndash2149127000 ndash0697047000 C ndash6872771000 ndash1801590000 ndash1447012000 C ndash5755909000 ndash1466198000 ndash0717983000 C ndash4305789000 ndash1041476000 ndash0739357000 C ndash3218268000 ndash0750848000 ndash1510952000 C ndash2077793000 ndash0315087000 ndash0749237000 C ndash0550342000 ndash0400850000 ndash0716361000 C 0616872000 ndash0404801000 ndash1489728000 C 1770640000 ndash0412395000 ndash0716060000 C 3300443000 ndash0457807000 ndash0715861000 C 4454767000 ndash0490291000 ndash1489427000 C 5616257000 ndash0520747000 ndash0712496000 C 5616269000 ndash0520699000 0712492000 C 4454793000 ndash0490190000 1489443000 C 3300455000 ndash0457762000 0715895000 C 1770651000 ndash0412347000 0716117000 C 0616894000 ndash0404700000 1489800000 C ndash0550335000 ndash0400796000 0716454000 C ndash2077818000 ndash0315060000 0749341000 C ndash3218306000 ndash0750915000 1510996000

- 138 -

C ndash4305781000 ndash1041534000 0739359000 C ndash5755900000 ndash1466256000 0717962000 C ndash6872758000 ndash1801708000 1446971000 C ndash8026533000 ndash2149171000 0696987000 H ndash6893447000 ndash1807486000 ndash2529846000 H ndash3199702000 ndash0827686000 ndash2591829000 H 0616147000 ndash0415875000 ndash2572166000 H 4455855000 ndash0492565000 ndash2571217000 H 4455901000 ndash0492389000 2571233000 H 0616188000 ndash0415693000 2572238000 H ndash3199790000 ndash0827916000 2591862000 H ndash6893430000 ndash1807681000 2529804000 Co ndash2237895000 1566525000 ndash0000035000 C ndash0770702000 3039808000 0000091000 C ndash1582333000 3276979000 1176306000 C ndash2906316000 3484053000 0731575000 C ndash2906172000 3484095000 ndash0731735000 C ndash1582100000 3277047000 ndash1176233000 H 0281094000 2798829000 0000215000 H ndash1247438000 3209109000 2198999000 H ndash3777291000 3625124000 1353071000 H ndash3777011000 3625160000 ndash1353424000 H ndash1246943000 3209260000 ndash2198847000 H ndash8933230000 ndash2423019000 ndash1224452000 H ndash8933222000 ndash2423113000 1224377000 C 7146943000 ndash0559737000 0717588000 C 7146931000 ndash0559786000 ndash0717614000 C 8302361000 ndash0588480000 1447040000 C 8302337000 ndash0588576000 ndash1447082000 C 9516918000 ndash0618789000 ndash0692883000 C 9516929000 ndash0618742000 0692823000 H 8324450000 ndash0589130000 2529610000 H 10461320000 ndash0642422000 1224406000 H 10461300000 ndash0642481000 ndash1224480000 H 8324409000 ndash0589299000 ndash2529653000

(c) Local minimum 2 η4-benzene (203 kcalmol)

- 139 -

C ndash7810644000 ndash2064896000 ndash0088979000 C ndash6582065000 ndash2396690000 ndash0700394000 C ndash5469369000 ndash1694626000 ndash0259356000 C ndash4011414000 ndash1478684000 ndash0398743000 C ndash2839913000 ndash1679834000 ndash1045300000 C ndash1807973000 ndash0777407000 ndash0523048000 C ndash0288034000 ndash0728447000 ndash0497727000 C 0877200000 ndash0917515000 ndash1257428000 C 2033335000 ndash0625143000 ndash0541547000 C 3550975000 ndash0572504000 ndash0566638000 C 4702932000 ndash0775398000 ndash1323945000 C 5869717000 ndash0493099000 ndash0604711000 C 5877160000 ndash0049178000 0749672000 C 4719648000 0152978000 1509600000 C 3558389000 ndash0127834000 0791889000 C 2041313000 ndash0178303000 0818968000 C 0890228000 0010834000 1576182000

C ndash0275189000 ndash0290874000 0857465000 C ndash1777915000 ndash0332627000 0896504000 C ndash3000252000 ndash0144927000 1576583000 C ndash4087655000 ndash0414543000 0681649000 C ndash5565811000 ndash0681071000 0748878000 C ndash6769777000 ndash0358061000 1349731000 C ndash7902756000 ndash1078577000 0906205000 H ndash6531350000 ndash3165530000 ndash1463988000 H ndash2656944000 ndash2379915000 ndash1852763000

- 140 -

H 0873498000 ndash1259556000 ndash2286041000 H 4697058000 ndash1113491000 ndash2353481000 H 4726794000 0489146000 2539724000 H 0892018000 0335667000 2610226000 H ndash3107471000 0242268000 2582171000 H ndash6863567000 0403771000 2116786000 Co ndash2805901000 1045228000 ndash0126008000 C ndash1966955000 3131745000 ndash0137391000 C ndash3345106000 3172285000 0219040000 C ndash4105003000 2591218000 ndash0859559000 C ndash3194452000 2177424000 ndash1877135000 C ndash1861601000 2475718000 ndash1403791000 H ndash1139494000 3467521000 0469940000 H ndash3757304000 3575577000 1132204000 H ndash5178689000 2478840000 ndash0883920000 H ndash3449207000 1717975000 ndash2819531000 H ndash0944137000 2267497000 ndash1933863000 H ndash8711780000 ndash2586977000 ndash0395882000 H ndash8871888000 ndash0864282000 1346179000 C 7394568000 0005138000 0727783000

C 7387058000 ndash0441388000 ndash0634217000 C 8557433000 0273605000 1404315000

C 8542647000 ndash0629395000 ndash1349402000 C 9760631000 ndash0352464000 ndash0653366000 C 9767843000 0080954000 0667800000 H 8586089000 0612106000 2434348000 H 10716375000 0279405000 1157078000

H 10703753000 ndash0485281000 ndash1174332000 H 8560430000 ndash0966385000 ndash2380163000

(d) Transition state 4 η3-benzene (367 kcalmol)

- 141 -

C 7669717000 ndash2174926000 ndash0105923000 C 6450462000 ndash2458728000 0544003000 C 5349535000 ndash1733337000 0120322000 C 3893688000 ndash1505268000 0269179000 C 2708972000 ndash1942858000 0838638000 C 1596115000 ndash1239419000 0370186000 C 0149218000 ndash1103313000 0368184000 C ndash1061261000 ndash1583264000 0932639000 C ndash2167377000 ndash0965378000 0405284000 C ndash3686709000 ndash0866795000 0409630000 C ndash4872520000 ndash1347856000 0960688000 C ndash5997863000 ndash0728310000 0421450000 C ndash5941471000 0288854000 ndash0586107000 C ndash4758793000 0770529000 ndash1137452000 C ndash3629556000 0150846000 ndash0598044000 C ndash2119390000 0068600000 ndash0617626000 C ndash0945265000 0548559000 ndash1173832000 C 0191709000 ndash0072876000 ndash0643629000 C 1695402000 ndash0118964000 ndash0667389000 C 2835200000 0041396000 ndash1507494000 C 3981535000 ndash0415532000 ndash0796385000 C 5449049000 ndash0747489000 ndash0920326000 C 6638556000 ndash0473422000 ndash1556289000 C 7762417000 ndash1216205000 ndash1122513000 H 6396888000 ndash3209338000 1323030000 H 2647172000 ndash2772334000 1532449000 H ndash1099468000 ndash2356302000 1688990000 H ndash4914534000 ndash2116326000 1720908000 H ndash4717626000 1537921000 ndash1898781000 H ndash0906852000 1317204000 ndash1935050000 H 2849903000 0560387000 ndash2457942000 H 6730568000 0262385000 ndash2346085000 Co 3078365000 1106450000 0223118000 C 2432920000 3235925000 0352954000 C 3805628000 3232135000 ndash0000959000 C 4525686000 2519574000 1027488000 C 3591065000 2151422000 2051886000 C 2287258000 2550618000 1620273000

- 142 -

H 1625110000 3662123000 ndash0222202000 H 4237852000 3652387000 ndash0895767000 H 5588986000 2336674000 1044912000 H 3828106000 1629983000 2966790000 H 1363656000 2417646000 2161607000 H 8562189000 ndash2715853000 0187384000 H 8723754000 ndash1039126000 ndash1591154000 C ndash7467794000 0379383000 ndash0580257000 C ndash7522920000 ndash0639213000 0428535000 C ndash8594261000 0964602000 ndash1089561000 C ndash8706397000 ndash1090617000 0945872000 C ndash9887862000 ndash0485330000 0420145000 C ndash9834353000 0499744000 ndash0555359000 H ndash8574126000 1734202000 ndash1850912000 H ndash10757407000 0931123000 ndash0925119000 H ndash10851990000 ndash0807405000 0796463000 H ndash8770071000 ndash1858056000 1706995000

(e) Local minimum 3 η4-benzene (190 kcalmol)

C ndash7704806000 ndash1625445000 ndash0076324000 C ndash6491455000 ndash1789497000 ndash0801300000 C ndash5352262000 ndash1326936000 ndash0190371000 C ndash3836374000 ndash1127906000 ndash0291559000 C ndash2669014000 ndash1876939000 ndash0775878000 C ndash1540408000 ndash1361850000 ndash0248671000 C ndash0067088000 ndash1219487000 ndash0231176000 C 1147603000 ndash1746746000 ndash0723682000

- 143 -

C 2245517000 ndash1037457000 ndash0289605000 C 3767258000 ndash0910575000 ndash0313273000 C 4961694000 ndash1439625000 ndash0795996000 C 6075343000 ndash0726547000 ndash0354068000 C 5999362000 0418026000 0498208000 C 4804020000 0947684000 0980899000 C 3691158000 0235329000 0538756000 C 2171505000 0121554000 0570963000 C 0990404000 0649716000 1051234000

C ndash0139369000 ndash0066282000 0613306000 C ndash1640889000 ndash0139469000 0665899000 C ndash2708579000 0044357000 1607074000 C ndash3890300000 ndash0515482000 1069631000 C ndash5389479000 ndash0719093000 1106627000 C ndash6553177000 ndash0561696000 1815459000 C ndash7736166000 ndash1034716000 1182797000 H ndash6489929000 ndash2263627000 ndash1775522000 H ndash2743316000 ndash2692464000 ndash1483904000 H 1201969000 ndash2617287000 ndash1364047000 H 5019196000 ndash2306567000 ndash1440440000 H 4747029000 1814065000 1626168000 H 0933710000 1519855000 1692796000 H ndash2640951000 0605584000 2529735000 H ndash6590996000 ndash0122891000 2805220000 Co ndash3231943000 0870639000 ndash0218177000 C ndash2631117000 2925280000 ndash0475333000 C ndash4019450000 2955930000 ndash0137499000 C ndash4720042000 2167067000 ndash1095287000 C ndash3768150000 1717753000 ndash2089396000 C ndash2477085000 2188405000 ndash1710046000 H ndash1832546000 3399891000 0073720000 H ndash4448788000 3419647000 0737399000 H ndash5777018000 1951944000 ndash1095854000 H ndash3999907000 1119290000 ndash2956393000 H ndash1549894000 2013889000 ndash2232360000 H ndash8630326000 ndash1978241000 ndash0517433000 H ndash8683428000 ndash0939767000 1701100000 C 7524401000 0541032000 0473497000

C 7600630000 ndash0607844000 ndash0382149000 C 8637973000 1216338000 0890053000

C 8792152000 ndash1101412000 ndash0836674000 C 9961705000 ndash0402146000 ndash0407106000 C 9887895000 0708141000 0420266000 H 8602106000 2084773000 1535736000 H 10801526000 1207625000 0721410000

H 10931894000 ndash0752974000 ndash0739605000

- 144 -

H 8871661000 ndash1966753000 ndash1482602000

(f) Transition state 5 η2-cyclobutadiene (360 kcalmol)

C 7143264000 ndash2348493000 0699665000 C 6037664000 ndash1857298000 1448523000 C 4969251000 ndash1391864000 0720257000 C 3582514000 ndash0743198000 0748195000 C 2358402000 ndash0737338000 1512136000 C 1240141000 ndash0634711000 0742222000 C ndash0262684000 ndash0516912000 0716494000 C ndash1428088000 ndash0430968000 1492584000 C ndash2574224000 ndash0346717000 0719319000 C ndash4098679000 ndash0233199000 0715866000 C ndash5251323000 ndash0147278000 1490294000 C ndash6408253000 ndash0063372000 0713741000 C ndash7934932000 0047490000 0717366000 C ndash9088044000 0130556000 1446914000 C ndash10299063000 0217080000 0692638000 C ndash10298939000 0215301000 ndash0693576000 C ndash9087782000 0126841000 ndash1447398000 C ndash7934811000 0045602000 ndash0717417000 C ndash6408180000 ndash0065400000 ndash0713264000 C ndash5251144000 ndash0151514000 ndash1489420000 C ndash4098619000 ndash0235099000 ndash0714599000 C ndash2574142000 ndash0348081000 ndash0717615000 C ndash1428022000 ndash0433439000 ndash1490677000

- 145 -

C ndash0262587000 ndash0517946000 ndash0714342000 C 1239930000 ndash0636111000 ndash0739947000 C 2357013000 ndash0742891000 ndash1511730000 C 3581891000 ndash0749703000 ndash0749006000 C 4968536000 ndash1397444000 ndash0717250000 C 6036190000 ndash1868351000 ndash1443314000 C 7142499000 ndash2353756000 ndash0691900000 H 8003789000 ndash2740125000 1230531000 H 6052031000 ndash1874231000 2531931000 H 2350726000 ndash0802237000 2593967000 H ndash1427931000 ndash0429806000 2574521000 H ndash5251989000 ndash0146640000 2572026000 H ndash9110076000 0132990000 2529448000 H ndash11241535000 0285430000 1223689000 H ndash11241318000 0282253000 ndash1224971000 H ndash9109613000 0126365000 ndash2529940000 H ndash5251637000 ndash0153720000 ndash2571150000 H ndash1427824000 ndash0434279000 ndash2572612000 H 2347832000 ndash0810535000 ndash2593375000 H 6049185000 ndash1893779000 ndash2526553000 H 8002469000 ndash2749449000 ndash1220666000 Co 4148367000 1055016000 ndash0009106000 C 5996101000 2006266000 0022069000 C 5276853000 2480887000 1185002000 C 4085420000 3079352000 0718350000 C 4110596000 3077077000 ndash0745160000 C 5316353000 2474554000 ndash1168669000 H 6921324000 1451094000 0038659000 H 5556549000 2314709000 2212960000 H 3287274000 3477873000 1325692000 H 3334253000 3474398000 ndash1380859000 H 5631980000 2304731000 ndash2185537000

(g) Local minimum 4 η4-cyclobutadiene (97 kcalmol)

- 146 -

C 4893664000 ndash1209972000 0735005000 C 4893573000 ndash1213475000 ndash0730870000 C 3475382000 ndash0763132000 ndash0743915000 C 3475432000 ndash0760320000 0747049000 C 2260316000 ndash0690973000 1520580000 C 1145205000 ndash0595973000 0744946000 C 1145156000 ndash0599246000 ndash0742744000 C 2260358000 ndash0697381000 ndash1517904000 C ndash0343192000 ndash0479177000 ndash0713609000 C ndash0343168000 ndash0476032000 0715380000 H 2252105000 ndash0735285000 ndash2601934000 H 2251901000 ndash0724154000 2604763000 Co 4601208000 0736083000 ndash0002055000 C 5960130000 2243618000 ndash0721946000 C 4640007000 2540538000 ndash1172530000 C 3804522000 2681992000 ndash0008876000 C 4632302000 2544967000 1160921000 C 5955467000 2247130000 0721276000 H 6816321000 2038808000 ndash1347044000 H 4312673000 2604006000 ndash2199136000 H 2745254000 2890841000 ndash0012873000 H 4298236000 2612143000 2185222000 H 6807361000 2044890000 1353015000 C 6022290000 ndash1649780000 1464200000 C 6022277000 ndash1656609000 ndash1457900000 C 7122289000 ndash2056771000 0719324000 C 7122311000 ndash2060028000 ndash0711126000 H 6027301000 ndash1702610000 2548102000 H 8011576000 ndash2407816000 1233935000 H 8011528000 ndash2413601000 ndash1224115000 H 6027432000 ndash1714310000 ndash2541551000 C ndash1512226000 ndash0382902000 1494684000 C ndash1512274000 ndash0389473000 ndash1493257000 C ndash2658093000 ndash0297761000 0720325000 C ndash2658103000 ndash0300923000 ndash0719236000 H ndash1511446000 ndash0379165000 2578406000

- 147 -

H ndash1511531000 ndash0390614000 ndash2576954000 C ndash4169046000 ndash0190131000 ndash0714237000 C ndash4169015000 ndash0186849000 0714915000 C ndash5325016000 ndash0103295000 1491764000 C ndash5325120000 ndash0110177000 ndash1491395000 C ndash6483203000 ndash0023670000 0713863000 C ndash6483258000 ndash0027061000 ndash0713749000 H ndash5325252000 ndash0101647000 2575308000 H ndash5325471000 ndash0113799000 ndash2574933000 C ndash7997403000 0080746000 0716440000 C ndash7997524000 0076500000 ndash0716680000 C ndash9155096000 0160872000 1448927000 C ndash9155379000 0152083000 ndash1449432000 C ndash10366775000 0240123000 0695134000 C ndash10366925000 0235844000 ndash0695874000 H ndash9178696000 0150122000 ndash2533721000 H ndash11311550000 0297904000 ndash1227155000 H ndash11311298000 0305233000 1226228000 H ndash9178228000 0165001000 2533216000

(h) Transition state 2 η2-cyclobutadiene (357 kcalmol)

C 8266704000 ndash2005162000 0692734000 C 7088955000 ndash1708719000 1446000000 C 5966603000 ndash1428050000 0716466000

- 148 -

C 4483884000 ndash1054830000 0713802000 C 3355736000 ndash0795879000 1487813000 C 2219848000 ndash0542568000 0715155000 C 0748349000 ndash0122254000 0743952000 C ndash0460068000 ndash0300197000 1509394000 C ndash1583463000 ndash0354552000 0739667000 C ndash3088504000 ndash0455891000 0716671000 C ndash4249167000 ndash0553278000 1491353000 C ndash5399475000 ndash0634011000 0717623000 C ndash6922525000 ndash0754459000 0717051000 C ndash8076029000 ndash0852663000 1446746000 C ndash9285359000 ndash0940991000 0693505000 C ndash9286426000 ndash0927591000 ndash0694047000 C ndash8078221000 ndash0824629000 ndash1447252000 C ndash6923651000 ndash0740632000 ndash0717519000 C ndash5400498000 ndash0620402000 ndash0717994000 C ndash4251528000 ndash0525736000 ndash1491803000 C ndash3089431000 ndash0443610000 ndash0717063000 C ndash1585243000 ndash0344579000 ndash0740307000 C ndash0463450000 ndash0290395000 ndash1513612000 C 0748496000 ndash0127629000 ndash0751652000 C 2219455000 ndash0546002000 ndash0721683000 C 3355860000 ndash0802470000 ndash1493276000 C 4483583000 ndash1057975000 ndash0718022000 C 5966360000 ndash1431783000 ndash0719354000 C 7088265000 ndash1716549000 ndash1447876000 C 8266466000 ndash2008718000 ndash0693595000 H 9183427000 ndash2233531000 1224348000 H 7110060000 ndash1714392000 2528663000 H 3353411000 ndash0803478000 2570367000 H ndash0456292000 ndash0373454000 2590614000 H ndash4248665000 ndash0564171000 2573279000 H ndash8096828000 ndash0865292000 2529266000 H ndash10227269000 ndash1021159000 1223954000 H ndash10229127000 ndash0997490000 ndash1224546000 H ndash8100648000 ndash0816347000 ndash2529785000 H ndash4252664000 ndash0517117000 ndash2573754000 H ndash0464650000 ndash0354640000 ndash2595436000 H 3353541000 ndash0815213000 ndash2575752000 H 7108905000 ndash1727728000 ndash2530504000 H 9182976000 ndash2239822000 ndash1224379000 Co 1060170000 1739352000 ndash0013647000 C 0820599000 3762931000 0679296000 C 2023158000 3250849000 1217023000 C 2833506000 2814255000 0100512000 C 2185795000 3225276000 ndash1129991000

- 149 -

C 0924349000 3753677000 ndash0780133000 H ndash0033478000 4112410000 1239126000 H 2257663000 3114053000 2260457000 H 3791311000 2322414000 0171627000 H 2565428000 3065285000 ndash2126458000 H 0160713000 4098445000 ndash1460120000

(i) Local minimum 1 η4-benzene (190 kcalmol)

C 8767525000 ndash0664628000 0869444000 C 7569070000 ndash0364489000 1586360000 C 6400497000 ndash0535559000 0896308000 C 4872998000 ndash0456407000 0896648000 C 3729258000 ndash0166123000 1633430000 C 2558863000 ndash0367557000 0899969000 C 1050529000 ndash0274920000 0917771000 C ndash0154687000 0103769000 1545183000 C ndash1231288000 ndash0039565000 0606842000 C ndash2736221000 ndash0089835000 0603708000 C ndash3901526000 0467576000 1153370000 C ndash5054648000 ndash0104455000 0647800000 C ndash6579036000 ndash0120351000 0673091000 C ndash7732820000 0402806000 1194768000 C ndash8948594000 ndash0155119000 0702959000 C ndash8958839000 ndash1167887000 ndash0247745000 C ndash7753788000 ndash1707235000 ndash0785423000 C ndash6589806000 ndash1166201000 ndash0307896000

- 150 -

C ndash5063448000 ndash1158179000 ndash0339650000 C ndash3923750000 ndash1713712000 ndash0884954000 C ndash2743411000 ndash1141750000 ndash0370168000 C ndash1264100000 ndash1152263000 ndash0442985000 C ndash0114410000 ndash1509648000 ndash1047872000 C 1001557000 ndash0717865000 ndash0509678000 C 2529242000 ndash0815059000 ndash0456630000 C 3680301000 ndash1106705000 ndash1192448000 C 4847485000 ndash0909766000 ndash0461159000 C 6375435000 ndash0989198000 ndash0464503000 C 7517684000 ndash1280530000 ndash1157992000 C 8743181000 ndash1104009000 ndash0445669000 H 9720775000 ndash0544729000 1371431000 H 7610320000 ndash0024462000 2613574000 H 3742883000 0162901000 2664422000 H ndash0241422000 0534554000 2534230000 H ndash3894210000 1260341000 1890621000 H ndash7746436000 1191936000 1936109000 H ndash9890199000 0223840000 1083439000

H ndash9908180000 ndash1561665000 ndash0592194000 H ndash7783148000 ndash2497305000 ndash1525270000 H ndash3929534000 ndash2506814000 ndash1621099000 H 0005285000 ndash2235278000 ndash1842324000 H 3664139000 ndash1453900000 ndash2217556000 H 7520111000 ndash1625509000 ndash2184413000 H 9677483000 ndash1320445000 ndash0950825000 Co 0245526000 1194775000 ndash0183529000 C ndash0498660000 3223481000 ndash0207100000 C 0902667000 3310487000 0056983000 C 1591310000 2661311000 ndash1009417000 C 0610054000 2243094000 ndash1989593000 C ndash0681576000 2592200000 ndash1494981000 H ndash1289524000 3595536000 0425619000 H 1355880000 3721411000 0946130000 H 2657726000 2519341000 ndash1088515000 H 0823168000 1743521000 ndash2921425000 H ndash1626608000 2403559000 ndash1979282000

(j) Transition state 1 η3-benzene (356 kcalmol)

- 151 -

C ndash8901354000 ndash0223681000 ndash0743434000 C ndash7695103000 0220198000 ndash1360549000 C ndash6531343000 ndash0208573000 ndash0779115000 C ndash5007706000 ndash0207407000 ndash0796109000 C ndash3863247000 0247302000 ndash1433753000 C ndash2690760000 ndash0206508000 ndash0819013000 C ndash1184933000 ndash0153490000 ndash0843116000 C ndash0016095000 0217826000 ndash1588049000 C 1142075000 ndash0155798000 ndash0877497000 C 2665172000 ndash0195830000 ndash0859864000 C 3835813000 0283152000 ndash1437197000 C 4978920000 ndash0204857000 ndash0802474000 C 6505676000 ndash0216574000 ndash0771205000 C 7678527000 0226433000 ndash1319208000 C 8875127000 ndash0251684000 ndash0703235000 C 8845790000 ndash1112691000 0383544000 C 7616005000 ndash1570592000 0948642000 C 6475812000 ndash1107284000 0353147000 C 4945633000 ndash1092812000 0320013000 C 3774824000 ndash1565295000 0903163000 C 2628495000 ndash1080676000 0265289000 C 1119158000 ndash1093642000 0244670000 C ndash0052242000 ndash1637616000 0861793000 C ndash1193959000 ndash1109215000 0331010000 C ndash2676505000 ndash1073633000 0328062000 C ndash3841325000 ndash1514463000 0979035000 C ndash4995446000 ndash1053912000 0371366000 C ndash6522185000 ndash1052982000 0381089000 C ndash7676261000 ndash1483950000 0978498000 C ndash8892512000 ndash1041633000 0378747000

- 152 -

H ndash9850267000 0087677000 ndash1164894000 H ndash7723622000 0856176000 ndash2236504000 H ndash3873085000 0886115000 ndash2307512000 H ndash0031238000 0768624000 ndash2518870000 H 3857949000 0953892000 ndash2286176000 H 7723941000 0897606000 ndash2167700000 H 9831384000 0069893000 ndash1099633000 H 9779177000 ndash1450269000 0819087000 H 7614291000 ndash2243551000 1796930000 H 3751975000 ndash2237828000 1750478000 H ndash0016047000 ndash2343040000 1681308000 H ndash3832680000 ndash2159963000 1847727000 H ndash7691389000 ndash2121828000 1853393000 H ndash9834648000 ndash1354566000 0814012000 Co ndash0004249000 1140918000 0250383000 C 0931445000 3181201000 0326993000 C ndash0487068000 3279997000 0223542000 C ndash1069741000 2607436000 1368652000 C 0008159000 2107122000 2176577000 C 1235098000 2411215000 1492603000 H 1650004000 3565479000 ndash0380430000 H ndash1033454000 3774248000 ndash0564979000 H ndash2124544000 2537255000 1584462000 H ndash0094112000 1572170000 3107766000 H 2227446000 2134637000 1815486000

LUMO

HOMO

2887

239

00862

2496

1163

1382

1418

1312

0

3155

2767

0498

2588

1531

0831

Figure 47 Orbital coefficients of linear [5]phenylene

- 153 -

Figure 48 Top view of the contour plots of (a) the HOMO and (b) the LUMO of the [5]-phenylene ligand

- 154 -

Bad

Bad

Good Good

External cyclobutadiene coordination Internal cyclobutadiene coordination

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCpCoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

CoCp

Figure 49 Resonance rationale for the increased stability of internal Co coordination in linear [5]phenylene

44 NMR Data for Chapter Two

- 155 -

Figure 410 1H-NMR data for the respective parent phenylene frames experimental (C6D6) and

calculated [NICS (1) B3LYP6-31+G] Assignments by NOESY DEPT HMBC and HSQC as applicable

- 156 -

Me3Si

Me3Si

SiMe3

SiMe3

1

23

4 56

7 89

10 1112

13 1415

16

17

18

Co

222

1490

1252

1450

1433

1151

744

730

11091121

14161504

11211109

1540

1499

1224

1486

217

801

SiMe3

SiMe3

Me3Si

Me3Si

Co

802

261

1484

1256

1433

1494

1155

739

781

1360

1394

269

SiMe3

SiMe3

Co

802

1294

1149

1426

1502

1194

738

779

1363

1393

268

SiMe3

SiMe3

1241

1276

8029

725

1155

1493

1430

1256

1482

222

Co

796

678674 675 796

436

037032662

724 683 747

444

TMS

TMS

TMS

TMS

213

1474

1211

1538

1499

1112

623 685

SiMe3

SiMe3Me3Si

Me3Si SiMe3

SiMe3Me3Si

Me3Si459 Co

589 681 672 745

2201204

15131096

1535

2221252

1480

1433

1149741

801

1501 1490

1475

Figure 411 Comparison of 1H-NMR (blue) and 13C-NMR assignments (C6D6)

NICS-Scan calculations Methods The free ligands were optimized at the B3LYP6-31G and the CpCo complexes at the B3LYPLANL2DZ computational levels Analytical frequency calculations were executed to ensure real minima (Nimag = 0) GIAO-B3LYP6-31+G was used to calculate NICS values The NICS-scan procedure is indicative of para- and diamagnetic ring currents in carbocycles and consists of (a) dissection of NICS values into in-plane (ipc or NICSXY) and out-of-plane components (oopc or NICSZZ) in which the latter is the π ring current diagnostic and (b) composition of graphical plots of the values of the NICS components versus distance r (from the ring centroid under scrutiny) and their interpretation

- 157 -

Since there are no published NICS-scan studies of transition metal complexed cyclic polyenes we benchmark the method with (C6H6)Cr(CO)3

53

Figure 412 NICS-scan of benzene (left) and (benzene)Cr(CO)3 (right)

The shape of the oopc curve suggests that the diamagnetic ring current in the ligand is diminished on complexation although still prevalent Thus at r = 0 Aring (ie at the benzene plane) the oopc value [NICSZZ(0)] of the complex is less negative than that of benzene and the minimum of the curve is less negative and occurs at a larger distance (ndash29911 vs ndash31910) A larger change is observed in the ipc (which is governed by the σ electrons) which shows far more negative values in the complex relative to benzene itself (eg ndash55400 vs ndash5900 and ndash13910 vs ndash0910) Therefore isotropic NICS values are misleading with respect to the diatropism in the complex because they originate largely from the diamagnetic effect of the σ framework NICS-scans for the four-membered ring B in linear [3]phenylene and its CpCo complex are shown below

00 05 10 15 20 25 30 35 40

-34-32-30-28-26-24-22-20-18-16-14-12-10

-8-6-4-202

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

oopc ipc isotropic

pp

m

r

- 158 -

Figure 413 NICS-scan above ring B of linear [3]phenylene (left) and its CpCo complex (right) Inspection of the shape and values of the oopc curve shows that the four-membered ring in the free ligand is strongly paratropic This picture changes on CpCo complexation At or close to the ring plane the values are much less positive (12100 vs 88000) become negative at greater distance and reach a minimum of -16112 Consequently the presence of the metal clearly reduces paratropic character The ipc curve is similar to that of (benzene)Cr(CO)3 Therefore again isotropic NICS values are misleading with respect to an assessment of the size of ring current effects The two isomeric CpCo complexes of linear [5]phenylene as depicted next behave in an analogous manner and engender the same conclusions as above

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

ppm

r

- 159 -

Figure 414 NICS-scans of linear [5]phenylene and its CpCo complexes Top left - ring B of the free ligand Top right - ring B complexed to CpCo Bottom left - ring D of the free ligand

Bottom right - ring D complexed to CpCo The effect of CpCo complexation is also reflected in the NICS-scan properties of the remaining rings To illustrate this point the NICS-scans of the central cyclohexatrienoid ring C of linear [3]phenylene are shown below first for the free ligand then for the cyclobutadiene complex

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-20

0

20

40

60

80

100

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-60

-50

-40

-30

-20

-10

0

10

20

oopc ipc isotropic

pp

m

r

- 160 -

Figure 415 NICS-scans of ring C of linear [3]phenylene Left - as a free ligand Right as a

CpCo complex of the neighboring cyclobutadiene ring B The oopc curve clearly reveals a diminution of paratropism Thus at the ring plane the oopc values of the free ligand and of the complex are 177 and 110 ppm respectively Both plots show shallow and relatively distant minima at ndash3417 and ndash7316 respectively an indication of larger diamagnetic character of the latter While the ipc values also become more negative on complexation this effect is far smaller The tables that follow provide an overview of the NICS-scan results over all component rings in linear [3]- and [5]phenylene complexed and uncomplexed The diagnostic shape of the oopc curve is designated NM for no minimum indicating paratropism and M for minimum indicating diatropism Specific values are given at r = 0 Aring r = 10 Aring and the minimum (if diamagnetic) Table 416 NICS-scan Details of the oopc for Linear [3]Phenylene and its CpCo Complex at

Ring B

Ring Shape oopc00 oopc10 Minimum A M 71 ndash107 ndash11813 AndashCpCo M ndash65 ndash228 ndash22811 B NM 880 381 BndashCpCo M 121 ndash151 ndash16112 C M 177 ndash01 ndash3418 CndashCpCo M 116 ndash17 ndash9315 D NM 880 381 DndashCpCo NM 704 237 E M 71 ndash107 ndash11813 EndashCpCo M 15 ndash148 ndash15212

00 05 10 15 20 25 30 35 40

-8-6-4-202468

101214161820

oopc ipc isotropic

pp

m

r

00 05 10 15 20 25 30 35 40

-14-12-10

-8-6-4-202468

1012

oopc ipc isotropic

pp

m

r

- 161 -

Table 417 NICS-Scan Details of the oopc for Linear [5]Phenylene and its CpCo Complex at Ring B

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M ndash62 ndash227 ndash22811 B NM 898 396 BndashCpCo M 137 ndash148 ndash15612 C M 176 00 ndash3317 CndashCpCo M 152 ndash09 ndash8415 D NM 846 357 DndashCpCo NM 668 223 E M 164 ndash12 ndash4116 EndashCpCo M 142 ndash17 ndash5315 F NM 846 357 FndashCpCo NM 807 340 G M 176 00 ndash3317 GndashCpCo M 161 ndash04 ndash3216 H NM 898 396 HndashCpCo NM 867 378 I M 83 ndash97 ndash10813 IndashCpCo M 64 ndash109 ndash12113

Table 418 NICS-scan Details of the oopc for Lnear [5]Phenylene and its CpCo Complex at

Ring D

Ring Shape oopc00 oopc10 Minimum A M 83 ndash97 ndash10813 AndashCpCo M 19 ndash150 ndash15912 B NM 898 396 BndashCpCo NM 717 256 C M 176 00 ndash3317 CndashCpCo M 110 ndash122 ndash12210 D NM 846 357 DndashCpCo M 151 ndash169 ndash17311 E M 164 ndash12 ndash4116 EndashCpCo M 151 ndash169 ndash17311 F NM 846 357 FndashCpCo NM 685 231 G M 176 00 ndash3317 GndashCpCo M 148 ndash15 ndash5415 H NM 898 396 HndashCpCo NM 850 370

I M 83 ndash97 ndash10813

- 162 -

The data clearly show that on CpCo complexation the paramagnetic ring current contributions decrease (or the diamagnetic ring current contributions increase) The strongest effect is on the complexed cycle but it occurs for all rings even the most remote (eg I in the linear [5]phenylene complexed at ring B) Thus upon complexation the paratropic (and by inference antiaromatic) character of the phenylenes decrease 45 Experimental Section for Chapter Three Angular [3]phenylene 2290 angular [4]phenylene 17111 and [7]heliphene10 were prepared according to the literature Ni(COD)(PMe3)2

112 To a solution of Ni(COD)2 (0275 g 10 mmol) in dry and vigorously degassed THF (10 mL) PMe3 (020 mL 0150 g 20 mmol) was added via syringe in a single portion After stirring at RT for 24 h the mixture was transferred using a canula and filtered under Ar to remove unreacted starting material The solvent was removed on the high vacuum line and the resulting product dried for 3 h It is extremely air sensitive and must be manipulated under an inert atmosphere at all times Yellow solid (0306 g 96 ) 1H-NMR (400 MHz C6D6) δ = 412 (d J = 112 Hz 4 H) 238 (br t J = 52 Hz 4 H) 225 (t J = 52 Hz 4 H) 102 (d J = 32 Hz 18 H) ppm 31P-NMR (162 MHz C6D6) δ = ndash946 (s) ppm Adducts of diphenylacetylene 88 to angular [3]phenylene 22 ndash compounds 89 and 90

In a glove box an Ace pressure tube was charged with angular [3]phenylene 22 (0014 g 006 mmol) diphenylacetylene 88 (0098 g 0055 mmol) THF (5 mL) and Ni(COD)(PMe3)2 (70 microL 008 M in THF 0006 mmol) The reaction vessel was tightly sealed removed from the glovebox and heated to 75ndash80 oC (oil bath) for 23 h After cooling to RT the solvent was removed by rotary evaporation and the residue purified by flash chromatography on silica gel using gradient elution (101 and then 81 hexaneCH2Cl2) After a small amount of angular [3]phenylene 22 (0001 g) the monoadduct 89 (0004 g 20 ) eluted to give a yellow solid mp 195ndash196 degC 1H-NMR (500 MHz CDCl3) δ = 853 (d J = 84 Hz 1 H) 831 (d J = 80 Hz 1 H) 755 (ddd J = 16 64 80 Hz 1 H) 740ndash732 (m 2 H) 725ndash715 (m 6 H) 715ndash711 (m 2 H) 708 (d J = 65 Hz 2 H) 704 (d J = 80 Hz 1 H) 648 (t J = 72 Hz 1 H) 643 (d J = 70 Hz 1 H) 624 (t J = 75 Hz 1 H) 401 (d J = 70 Hz 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1525 15101 15096 1495 1399 13883 13879 1342 1320 1312

- 163 -

13083 13075 1282 1280 1277 1276 1275 1268 1266 1265 1264 1250 1235 1223 1179 1164 1156 ppm one peak in the region δ = 128ndash126 ppm is

presumed to be accidentally isochronous IR (KBr) ν~ = 3060 1490 1481 1442 1415 1159 1072 755 734 698 cmndash1 UV-Vis (CH3CN) λmax (log ε) 233 (442) 265 (450) 278 (sh) 294 (sh) 306 (447) 318 (449) 329 (sh) 380 (344) 399 (366) 420 (366) nm MS (70 eV) mz () 405 [M++1] (35) 404 [M+] (100) 326 (13) HRMS (EI) calcd for C32H20 4041565 found 4041571 Elemental analysis calcd for C32H20 C 9502 H 498 found 9479 460 Subsequent elution furnished 5678-tetraphenylpicene (90) (0009 g 59 ) as a white solid mp 325ndash327 degC the molecule exhibits hindered rotation of the 67-phenyl groups on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 891 (s 2 H) 885 (d J = 84 Hz 2 H) 769 (ddd J = 28 52 80 Hz 2 H) 750ndash744 (m 4 H) 744ndash732 (m 4 H) 720 (tt J = 16 72 Hz 2 H) 696 (dt J = 08 76 Hz 2 H) 689 (tt J = 09 76 Hz 2 H) 662 (br s 4 H) 617 (d J = 76 Hz 2 H) 607 (br s 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1403 1401 1377 1367 1335 1325 1324 1306 1300 1295 1292

1283 1277 1269 1264 1263 1262 1256 1254 1228 1213 ppm IR (KBr) ν~ = 3051 2922 1599 1490 1467 1442 1263 1072 1027 758 702 630 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (461) 307 (474) 352 (417) 366 (414) nm MS (70 eV) mz () 583 [M++1] (52) 582 [M+] (100) 505 (24) 504 (9) 426 (7) HRMS (EI) calcd for C46H30 5822348 found 5822336 1278-Tetraphenylbenzo[c]chrysene (91)

In a glovebox an Ace pressure tube was charged with 88 (0020 g 0050 mmol) diphenylacetylene 88 (0026 mg 0148 mmol) Ni(COD)(PMe3)2 (62 microL of a 008 M solution in THF) and THF (5 mL) The reaction vessel was sealed removed from the glovebox and heated to 85 degC for 39 h After removal of the solvent the residue was purified by flash chromatography on silica gel (eluting with 81 hexaneCH2Cl2) producing a white solid (0023 g) which was found to consist of starting material (88 18 mg) 90 (0001 g 6 ) and 91 Further purification by chromatography afforded pure 91 (0017 g 74 ) as a white solid mp 273ndash274 degC the 12-phenyl groups of 91 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 869 (d J = 95 Hz 1 H) 830ndash822 (m 1 H) 801 (d J = 75 Hz 1 H) 780ndash747 (m 2 H) 770 (ddd J = 10 70 85 Hz 1 H) 762 (dt J = 15 75 Hz 1 H) 753 (ddd J = 15 70 85 Hz 1 H) 738ndash732 (m 2 H) 730 (td J = 15 75 Hz 1 H) 729ndash722 (m 6 H) 722ndash717 (m 2 H) 717ndash710 (m 2 H) 710ndash695 (m 3 H) 680ndash640 (m 3 H) 635 (d J = 70 Hz 1 H) 623ndash595 (br s 1 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1418 1400 1395 1394 1378 1377 1375 1357 1323 1322 1316 1314 13113 13107 1309 1308 1307 1305 1296 1295 1288 1282 1277 1275 1274 1273 1270 12653 12647 1264 1260 1256 1253 1252 1251

- 164 -

1243 1231 1208 ppm due to extensive signal overlap four peaks are presumed to be isochronous in the regions δ = 132ndash130 and 128ndash125 ppm IR (KBr) ν~ = 3058 1601 1489 1442 1263 1073 773 762 736 699 628 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 250 (487) 313 (511) 340 (sh) nm MS(EI) mz () 583 (M++1 72) 582 (M+ 100) 505 (24) 391 (13) HRMS (EI) calcd for C46H30 5822348 found 5822341 Elemental analysis calcd for C46H30 C 8933 H 500 found 8914 493 Ni(PhCequivCPh)(PMe3)2 (92)91

In a glove box PMe3 (203 microL 0152 g 20 mmol) was mixed with a suspension of Ni(COD)2 (0275 g 10 mmol) in hexane (15 mL) Diphenylacetylene 88 (0178 g 10 mmol) was then added in one portion resulting in an immediate color change from yellow to red The mixture was stirred at room temperature for 195 h during which the color gradually turning returning to yellow Upon concentration (to ~5 mL) a yellow precipitate formed collected by filtration under nitrogen The resulting powder 92 (0370 g 95 ) was dried under vacuum providing a yellow solid 1H-NMR (500 MHz C6D6) δ = 751 (d J = 75 Hz 4 H) 717 (t J = 75 Hz 4 H) 702 (t J = 75 Hz 2 H) 101 (s 18 H) ppm 13C-NMR (125 MHz C6D6) δ = 1406 1287 1279 196 (d JC-P = 188 Hz) ppm 31P-NMR (162 MHz C6D6) δ = ndash1282 (br s) ppm Adducts of 3-hexyne to angular [3]phenylene 22 ndash compounds 104 and 105

In a glovebox 22 (0014 mg 0060 mmol) 3-hexyne 103 (57 microL 0004 g 0050 mmol) Ni(COD)(PMe3)2 (0002 g 0005 mmol) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 14 h Flash chromatography on silica gel gave a first fraction that was recrystallized from CH2Cl2 to provide pure 104 (70 mg 45 ) as a yellow solid mp 169ndash170 degC 1H-NMR (500 MHz CDCl3) δ = 843 (d J = 70 Hz 1 H) 821 (d J = 75 Hz 1 H) 795 (d J = 70 Hz 1 H) 752 (dt J = 10 70 Hz 1 H) 748 (dt J = 10 70 Hz 1 H) 697 (d J = 75 Hz 1 H) 673ndash662 (m 3 H) 655 (d J = 55 Hz 1 H) 307 (q J = 75 Hz 2 H) 299 (q J = 75 Hz 2 H) 133 (t J = 75 Hz 3 H) 130 (t J = 75 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1530 1516 1504 1471 1360 1330 13129 13127 1307 1282 1279 1267 1263 1259 1246 1239 1228 1179 1159 1156 232 214 164 149 ppm IR (KBr) ν~ = 3045 2960 1600 1481 1414 1261 1197 1159 758 740 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 266 (463) 299 (sh) 309 (460) 320 (462) 331 (452) 380 (356) 399 (374) 419 (371) nm MS (70 eV) mz () 309 [M++1] (26) 308 [M+] (100) 293 [M+ndash15] (8) 278 [M+ndash30] (21) HRMS (EI) calcd for C24H20 3081565 found 3081666

- 165 -

A second fraction was 105 (0002 g 11 ) isolated as a yellow solid mp 120ndash122 degC 1H-NMR (400 MHz CDCl3) δ = 830 (d J = 72 Hz 1 H) 797 (d J = 76 Hz 1 H) 761 (d J = 80 Hz 1 H) 761ndash749 (m 2 H) 700 (d J = 80 Hz 1 H) 699 (d J = 72 Hz 1 H) 674 (quint J = 76 Hz 2 H) 658 (d J = 64 Hz 1 H) 307 (q J = 76 Hz 2 H) 302 (q J = 76 Hz 2 H) 132 (t J = 76 Hz 3 H) 131 (t J = 76 Hz 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1525 1519 1489 1472 1356 1345 1324 1318 1288 1283 1279 1273 1259 1252 1251 1250 1241 1179 1165 1160 2213 2205 149 146 ppm IR (KBr) ν~ = 3063 2958 2925 1490 1442 1417 1262 1147 1099 822 762 730 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 281 (434) 291 (448) 303 (460) 313 (sh) 369 (346) 389 (373) 410 (377) nm MS (70 eV) mz () 309 [M++1] (28) 308 [M+] (100) 293 [M+ndash15] (13) 278 [M+ndash30] (21) 226 (22) 149 (29) HRMS (EI) calcd for C24H20 3081565 found 3081664 Adducts of 14-dimethoxy-2-butyne to angular [3]phenylene 22 ndash compounds 107 and 108

In a glovebox 22 (0011 g 0050 mmol) 14-dimethoxybut-2-yne 106 (0034 g 030 mmol) Ni(COD)(PMe3)2 (63 microL of a 008 M solution in THF) and THF (5 mL) were added to an Ace pressure tube The reaction vessel was sealed and the mixture stirred at 75 degC for 165 h The 1H-NMR spectrum of the crude indicated the formation of 107 and 108 in the ratio of 61 Flash chromatography on silica gel gave first 107 (0012 g 68 ) as a yellow solid mp 150ndash151 degC 1H-NMR (400 MHz CDCl3) δ = 841 (dd J = 32 64 Hz 1 H) 819 (d J = 80 Hz 1 H) 810 (dd J = 36 64 Hz 1 H) 754 (dd J = 36 64 Hz 2 H) 700 (d J = 80 Hz 1 H) 676 (t J = 64 Hz 1 H) 674ndash665 (m 2 H) 656 (d J = 60 Hz 1 H) 493 (s 2 H) 488 (s 2 H) 353 (s 3 H) 345 (s 3 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1527 1513 1509 1484 1336 1318 1316 1309 1296 1283 1282 1272 1270 1259 1255 1238 1225 1183 1166 1161 677 675 584 575 ppm IR (KBr) ν~ = 3072 2927 1485 1446 1417 1376 1185 1097 956 898 821 743 730 cmndash1 MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (100) 308 [M+ndash38] (26) 293 (34) 280 (15) 265 (44) HRMS (EI) calcd for C24H20O2 3401463 found 3401466 Further elution provided 108 (0002 g 9 ) as a yellow solid mp 156ndash157 degC 1H-NMR (400 MHz CDCl3) δ = 831ndash824 (m 1 H) 813ndash806 (m 1 H) 775 (d J = 80 Hz 1 H) 763ndash756 (m 2 H) 702 (d J = 80 Hz 1 H) 699 (d J = 64 Hz 1 H) 681ndash670 (m 2 H) 660 (d J = 64 Hz 1 H) 493 (s 2 H) 487 (s 2 H) 353 (s 3 H) 351 (s 3 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1523 1517 1505 1470 1327 1322

- 166 -

1316 1315 1297 1285 1282 1276 1268 1266 12564 12555 1252 1181 1168 1165 6804 6801 5838 5835 ppm IR (KBr) ν~ = 2925 1498 1415 1379 1262 1187 1095 1061 940 930 814 750 734 717 cmndash1 UV-Vis (CH3CN) λmax (log ε) 237 (458) 287 (462) 298 (472) 314 (sh) 371 (357) 387 (380) 407 (386) nm MS (70 eV) mz () 341 [M++1] (16) 340 [M+] (56) 308 [M+ndashMeOH] (8) 293 (27) 279 (17) 265 (24) HRMS (EI) calcd for C24H20O2 3401463 found 3401456 Optimized cycloaddition reaction between 22 and 88 In a glovebox a round bottom flask was charged with 22 (0058 g 0257 mmol) and Ni(COD)(PMe3)2 (0008 g 0034 mmol) Both reagents were then dissolved in THF (100 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0093 g 0521 mmol) in THF (20 mL) was taken up in a gas-tight syringe and slowly added over 13 h via syringe pump to the boiling mixture of 22Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 6 h After this time mixture was cooled to RT and the solvent removed by rotary evaporation to give a yellow residue The crude product was passed through a plug of silica gel eluting with a mixture of hexanesCH2Cl2 (101) to afford a yellow solid Analysis of the product by 1H-NMR (using the solvent peak of CDCl3 as the internal standard) revealed the presence of 89 and 90 in a 1387 ratio Adducts of diphenylacetylene 88 to angular [4]phenylene 17 ndash compounds 130ndash134 In a glovebox angular [4]phenylene 17 (0036 g 012 mmol) diphenylacetylene 88 (0018 g 010 mmol) and Ni(COD)(PMe3)2 (125 microL of a 008 M solution in THF) were added to an Ace pressure tube and dissolved in THF (6 mL) The reaction vessel was sealed removed from the glovebox and stirred at 75 degC for 5 h Flash chromatography

Ph Ph

Ph Ph

PhPh

Ph Ph Ph Ph

Ph Ph Ph PhPh Ph

132131

133 134

130

- 167 -

on silica gel gave starting material (0013 g of 17) as well as a yellow residue Further purification of the latter by preparative TLC afforded (in order of elution) 132 131 133 134 and 139 Compound 130 (0008 g 28 ) was obtained as a white solid mp 360ndash363 degC (decomp) the phenyl groups located on the central benzene ring of 130 exhibit hindered rotation on the NMR timescale 1H-NMR (500 MHz CDCl3) δ = 904 (d J = 90 Hz 2 H) 895 (d J = 90 Hz 2 H) 881 (d J = 85 Hz 2 H) 765 (ddd J = 15 65 80 Hz 2 H) 742ndash736 (m 4 H) 734 (dd J = 10 85 Hz 2 H) 721 (tt J = 15 75 Hz 2 H) 716 (d J = 75 Hz 2 H) 698 (dd J = 05 80 Hz 2 H) 693 (tt J = 10 85 Hz 2 H) 681 (tt J = 10 70 Hz 2 H) 676 (t J = 75 Hz 4 H) 656 (t J = 70 Hz 4 H) 633 (d J = 70 Hz 4 H) 614 (d J = 75 Hz 2 H) 595 (d J = 70 Hz 4 H) ppm 13C-NMR (125 MHz CDCl3) δ = 14058 14057 1403 1394 1375 1374 1345 1341 1336 1327 1324 1309 1308 1301 1294 1292 1282 1276 1268 1263 12622 12619 1259 1257 1254 1250 1227 1214 1212 ppm IR (KBr) ν~ = 3052 2923 1600 1491 1440 1261 1076 1029 809 783 759 747 700 631 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 248 (498) 306 (sh) 329 (520) 388 (463) nm MS(FAB) mz () 836 [M++2] (18) 835 [M++1] (42) 834 [M+] (54) 757 (8) HRMS (FAB) calcd for C66H42 8343287 found 8343280 Compound 131 (0003g 6) was isolated as yellow solid mp 251ndash253 degC (decomp) 1H-NMR (500 MHz CDCl3) δ = 880 (d J = 80 Hz 1 H) 775 (dt J = 10 80 Hz 1 H) 752 (dt J = 10 80 Hz 1 H) 746 (d J = 80 Hz 1 H) 737 (d J = 65 Hz 1 H) 726ndash721 (m 5 H) 721ndash716 (m 2 H) 716ndash711 (m 5 H) 709 (t J = 75 Hz 1 H) 705 (d J = 80 Hz 1 H) 699 (d J = 70 Hz 1 H) 619 (d J = 60 Hz 1 H) 614 (d J = 60 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1502 1492 1491 1490 1485 1444 1394 1392 1382 1371 1367 1351 13271 13268 13092 13088 1299 12898 12896 1283 12764 12760 1274 12654 12652 1261 1253 1245 1195 1184 1172 1138 1129 ppm one peak is presumed to be accidentally isochronous in the region between δ = 130ndash124 ppm IR (KBr) ν~ = 3023 2921 1602 1478 1371 1262 1026 809 795 748 725 695 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 252 (473) 285 (456) 320 (453) 335 (462) 353 (437) 370 (432) 410 (376) 431 (372) nm MS (FAB) mz () 479 [M++1] (27) 478 [M+] (70) 300 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781718 Molecule 132 (0002 g 5 ) was acquired as a yellow solid 1H-NMR (500 MHz CDCl3) δ = 726ndash721 (m 2 H) 716ndash709 (m 6 H) 695ndash690 (m 2 H) 676 (d J = 80 Hz 2 H) 673 (d J = 75 Hz 2 H) 671 (t J = 75 Hz 2 H) 665 (t J = 70 Hz 2 H) 658 (d J = 65 Hz 2 H) 648 (d J = 65 Hz 2 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1516 1510 1497 1490 1391 1372 1310 1303 1283 1281 1277 1275 1273 1264 1216 1168 1163 ppm UV-Vis (CH2Cl2) λmax (log ε) 254 (476) 294 (sh) 300 (465) 322 (sh) 338 (392) 376 (400) nm MS (FAB) mz () 479 [M++1] (50) 478 [M+] (86) 391 (100) HRMS (FAB) calcd for C38H22 4781722 found 4781723 Adduct 133 (0017 g 33 ) was isolated as a red crystalline solid mp 290ndash291 degC 1H-NMR (500 MHz CDCl3) δ = 800 (d J = 80 Hz 2 H) 720ndash713 (m 6 H) 708ndash702 (m 4 H) 690 (d J = 80 Hz 2 H) 648 (t J = 70 Hz 2 H) 642 (d J = 70 Hz 2 H) 623 (t J = 70 Hz 2 H) 393 (d J = 70 Hz 2 H) ppm 13C-NMR (100 MHz CDCl3) δ = 1522 1509 1506 1496 1392 1359 1315 1309 1282 1278 1277 1266 1250 1232 1181 1166 1157 ppm IR (KBr) ν~ = 3057 1489 1441 1412 1273

- 168 -

1161 810 738 709 690 623 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 271 (474) 285 (469) 345 (460) 353 (454) 414 (483) 432 (381) 460 (363) nm MS (70 eV) mz () 479 [M++1] (46) 478 [M+] (100) 400 (10) HRMS (EI) calcd for C38H22 4781722 found 4781719 Compound 134 (0009 g 27 ) was obtained as a yellow solid mp 178ndash180 degC the phenyl groups of this molecule located at the bay regions of the phenanthrene subunit are static while the others exhibit hindered rotation on the NMR time scale 1H-NMR (400 MHz CDCl3) δ = 880 (d J = 88 Hz 1 H) 879 (d J = 88 Hz 1 H) 863 (d J = 92 Hz 1 H) 834 (d J = 80 Hz 1 H) 770ndash758 (m 1 H) 748ndash732 (m 4 H) 727ndash721 (m 2 H) 721ndash710 (m 2 H) 706 (d J = 80 Hz 1 H) 702ndash691 (m 3 H) 684 (t J = 74 Hz 1 H) 673 (br s 2 H) 655 (t J = 76 Hz 2 H) 650ndash638 (m 3 H) 630ndash610 (m 4 H) 590 (d J = 76 Hz 2 H) 410 (d J = 68 Hz 1 H) ppm 13C-NMR (125 MHz CDCl3) δ = 1527 1510 1509 1494 1403 1400 1399 1396 1373 1371 1339 1335 1330 1325 1324 1317 1309 1306 1305 1304 1299 1295 1291 1283 1282 1281 1277 1275 1272 1269 1268 12632 12627 1261 12562 12556 1254 1253 1239 1226 1216 1209 1180 1162 1154 ppm three peaks are presumed to be accidentally isochronous in the region δ = 128ndash125 ppm IR (KBr) ν~ = 2964 1262 1096 1022 801 701 cmndash1 UV-Vis (CH2Cl2) λmax (log ε) 267 (501) 303 (497) 335 (489) 361 (sh) 379 (464) 427 (402) 456 (377) nm MS(FAB) mz () 658 [M++2] (22) 657 [M++2] (67) 656 [M+] 1(00) 579 (12) 502 (7) HRMS (FAB) calcd for C52H32 6562504 found 6562492 Cycloaddition reaction between [7]heliphene 142 and diphenylacetylene 88 In a glovebox a round bottom flask was charged with 142 (0008 g 0152 mmol) and Ni(COD)(PMe3)2 (0001 g 0003 mmol) The mixture was then dissolved in THF (25 mL) A reflux condenser fitted with a vacuum line adapter was attached to the flask The assembly was sealed removed from the glovebox connected to the vacuum line flushed with Ar and the glass stopper quickly replaced with a septum under a purge of Ar A solution of diphenylacetylene 88 (0016 g 300 mmol) in THF (10 mL) was taken up in a gas-tight syringe and slowly added over 12 h via syringe pump to the boiling mixture of 142Ni(COD)(PMe3)2 Upon complete addition of the diphenylacetylene solution the reaction mixture was stirred at reflux for an extra 12 h After this time it was cooled to RT and the solvent removed by rotary evaporation to give an orange residue The crude product was chromatographed on silica gel (25 x 165 cm) eluting first with hexaneCH2Cl2 (101 then 51) The first product collected was diphenylacetylene 88 (0005 g) followed by a yellow band Analysis of the isolated yellow solid (0002 g) revealed a large mixture of products MS(FAB) mz () 532 (70) 664 (25) 700 (13) 732 (16) 911 (21) 1056 (11) 1234 (4) 1412 (5) 46 Computational Details for Chapter Three All geometries of intermediates and transition states were optimized fully without symmetry constraints using the Gaussian 03 program100 The DFT computations were carried out using the B3LYP functional as implemented in Gaussian The nickel atom was described by a double-zeta basis set (LANL2DZ)113 and the 6-31G(d) basis set114

- 169 -

was used for the other elements Frequency calculations were performed to confirm the nature of the stationary points and to obtain zero-point energies (ZPE) The connectivity between stationary points was established by intrinsic reaction coordinate calculations (IRC) The Chemcraft program102 was used to draw the calculated structures

47 References

1) Harvey R G Polycyclic Aromatic Hydrocarbons Wiley-VCH New York 1997 2) (a) Chem Rev 2001 101 1115ndash1566 Special Issue Aromaticity (b) Chem Rev

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Chem 2002 67 1333 (b) Stanger A Chem Commun 2009 1939 4) (a) Minkin V I Glukhovtsev M N Simkin B Ya Aromaticity and Antiaromaticity

Electronic and Structural Aspects Wiley New York 1994 pp 63ndash74 (b) Garratt P J Aromaticity Wiley New York 1986 pp 30ndash34 93ndash95

5) (a) Wu J Muumlllen K In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 3 pp 90ndash139 (b) Wu J Pisula W Muumlllen K Chem Rev 2007 107 718 (c) Handbook of Organic Electronics and Photonics Nalwa H S Ed American Scientific 2008

6) Miljanić O Š Vollhardt K P C In Carbon Rich Compounds Molecules to Materials Haley M M Tykwinski R R Eds Wiley-VCH Weinheim 2006 Chapter 4 pp 140ndash197

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Chem Rev 2005 105 3842 and the references therein (b) Steinmann S N Jana D F Wu J I-C Schleyer P v R Mo Y Corminboeuf C Angew Chem Int Ed 2009 48 9828

14) Schleyer P v R Manoharan M Wang Z-X Kiran B Jiao H Puchta R van Eikema Hommes N J R Org Lett 2001 3 2465

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Jenneskens L W Tetrahedron Lett 1994 35 4405 18) (a) Linear [3]phenylene Dosa P I Schleifenbaum A Vollhardt K P C Org Lett

2001 3 1017 (b) Angular [3]phenylene Matzger A J Vollhardt K P C Chem Commun 1997 1415 (c) Angular [4]phenylene Dosa P I Gu Z Hager D Karney W L Vollhardt K P C Chem Commun 2009 1967

19) Perthuisot C Edelbach B L Zubris D L Simhai N Iverson C N Muumlller C Satoh T Jones W D J Mol Catal A 2002 189 157

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21) (a) Deniz A A Peters K S Snyder G J Science 1999 286 1119 (b) Fattahi A Lis L Tian Z Kass P S Angew Chem Int Ed 2006 45 4984 (c) Bally T Angew Chem Int Ed 2006 45 6616

22) Anslyn E Dougherty D Modern Physical Organic Chemistry University Science Books Palo Alto 2006

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24) Mestdagh H Postdoctoral Research Report University of California Berkeley 1986

25) Hirthammer M Vollhardt K P C J Am Chem Soc 1986 108 2481 26) Blanco L Helson H E Hirthammer M Mestdagh H Spyroudis S Vollhardt K

P C Angew Chem Int Ed Engl 1987 26 1246 27) Berris B C Hovakeemian G H Lai Y-H Mestdagh H Vollhardt K P C J

Am Chem Soc 1985 107 5670 28) Dosa P I The Chemistry of Angular and Linear [N]Phenylenes PhD Thesis

University of California Berkeley 2002 29) Diercks R Eaton B E Guumlrtzgen S Jalisatgi S Matzger A J Radde R H

Vollhardt K P C J Am Chem Soc 1998 120 8247 30) (a) Nambu M Siegel J S J Am Chem Soc 1988 110 3675 (b) Nambu M

Hardcastle K Baldridge K K Siegel J S J Am Chem Soc 1992 114 369 31) Nambu M Mohler D L Hardcastle K Baldridge K K Siegel J S J Am

Chem Soc 1993 115 6138 32) Kumaraswamy S Jalisatgi S S Matzger A J Miljanić O Š Vollhardt K P C

Angew Chem Int Ed 2004 43 3711 33) (a) Eisch J J Piotrowski A M Han K I Kruumlger C Tsay Y H Organometallics

1985 4 224 (b) Schwager H Spyroudis S Vollhardt K P C J Organometallic Chem 1990 382 191

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35) Doumltz K H Jahr H C Chem Rec 2005 4 61 36) Gridnev I D Coord Chem Rev 2008 252 1798 37) Eickmeier C Holmes D Junga H Matzger A J Scherhag F Shim M

Vollhardt K P C Angew Chem Int Ed Engl 1999 38 800

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38) Groszligmann T N Haptotropism in Linear Phenylene Complexes Diplomarbeit Thesis University of California Berkeley 2004

39) Dinculear photothermal haptotropic systems Tsuchiya K Ideta K Mogi K Sunada Y Nagashima H Dalton Trans 2008 2708 and the references therein

40) Additive assisted photothermal haptotropic systems (a) Jahr H C Nieger M Doumltz H K Chem Eur J 2005 11 5333 d) Herbert D E Tanabe M Bourke S C Lough A J Manners I J Am Chem Soc 2008 130 4166 e) Ieong N S Manners I J Organomet Chem 2008 693 802 and references therein

41) (a) Zhu G Tanski T M Churchill D G Janak K E G Parkin G J Am Chem Soc 2002 124 13658 (b) Zhu G Pang G Parkin G J Am Chem Soc 2008 130 1564

42) Selected reviews of photobased devices and molecular switches (a) Balzani V Credi A Venturi M Chem Soc Rev 2009 38 1542 (b) Kay E R Leigh D A Zerbetto F Angew Chem Int Ed 2007 46 72 (c) Photochromism Molecules and Systems Duumlrr H Bouas-Laurent H Eds Elsevier Amsterdam 2003 (d) Feringa B Molecular Switches Wiley-VCH Weinheim 2001

43) (a) a) Photofunctional Transition Metal Complexes Yam V W W Ed Springer Berlin 2007 b) Coppens P Novozhilova I Kovalevsky A Chem Rev 2002 102 861 c) Guumltlich P Garcia Y Woike T Coord Chem Rev 2001 219ndash221 839

44) (a) Lambert J B Mazozola E P Nuclear Magnetic Resonance Spectroscopy An Introduction to Princples Applications and Experimental Methods Pearson Education Upper Saddle River 2004 (b) Berger S Braun S 200 and More NMR Experiments A Practical Course Wiley-VCH Weinheim 2004 (c) Friebolin H Basic One- and Two-Dimensional NMR Spectroscopy 4th edition Wiley-VCH Weinheim 2005

45) (a) Schulman J M Disch R L J Phys Chem A 2003 107 5223 (b) Schulman J M Disch R L J Am Chem Soc 1996 118 8470 and the references cited therein

46) (a) Bursten B E Fenske R F Inorg Chem 1979 18 1760 (b) Chinn J W Jr Hall M B Inorg Chem 1983 22 2759 (c) Datta A Pati S K J Am Chem Soc 2005 127 3496

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48) Hillard III R L Vollhardt K P C J Am Chem Soc 1977 99 4058 49) Berris B C Lai Y-H Vollhardt K P C J Chem Soc Chem Commun 1982

953 50) (a) Rausch M D Genetti R A J Org Chem 1970 35 3888 (b) Hart W P

Rausch D M J Organometallic Chem 1988 355 455 51) Duclos R I Vollhardt K P C Yee J L S J Organomet Chem 1979 174 109 52) (a) Myers A G Sogi M Lewis M A Arvedson S P J Org Chem 2004 69

2516 (b) Wolfart V Ramming M Gleiter R Nuber B Pritzkow H Rominger F Eur J Inorg Chem 1999 499 (c) Mitchell R H Chen Y Khalifa N Zhou P J Am Chem Soc 1998 120 1785 (d) McGlinchey M J Burns R C Hofer R Top S Jaouen G Organometallics 1986 5 104

53) Feixas F Jimeacutenez-Halla J O C Matito E Poater J Solagrave M Pol J Chem

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2007 81 783 54) (a)Stanger A J Org Chem 2006 71 883 (b) Stanger A Chem Eur J 2006 12

2745 (c) Tsipis A C Phys Chem Chem Phys 2009 11 8244 (d) Stanger A Chem Commun 2009 1939

55) For very recent literature compilations of theoretical (and experimental) treatments of haptotropism in arene metal complexes see a) Joistgen O Pfletschinger A Ciupka J Dolg M Nieger M Schnakenburg G Froumlhlich R Kataeva O Doumltz K H Organometallics 2009 28 3473 b) Pfletschinger A Dolg N J Organomet Chem 2009 694 3338 c) Jimeacutenez-Halla J O C Robles J Solagrave M Organometallics 2008 27 5230 d) Kirillov E Kahlal S Roisnel T Georgelin T Saillard J-Y Carpentier J-F Organometallics 2008 27 387 and references therein

56) Jimeacutenez-Halla J O C Robles J Solagrave M J Phys Chem A 2008 112 1202 57) Oprunenko Y Gloriozov I Lyssenko K Malyugina S Mityuk D Mstislavsky

V Guumlnther H von Firks G Ebener M J Organomet Chem 2002 656 27 58) Muumlller J Gaede P E Qiao K J Organomet Chem 1994 480 213 59) Bianchini C Caulton K G Chardon C Doublet M L Eisenstein O Jackson

S A Johnson T J Meli A Peruzzini M Streib W E Vacca A Vizzat F Organometallics 1994 13 2010

60) (a) De Boer E Van Willigen H V Prog Nuc Mag Res Spec 1967 2 111 (b) Memory J D Wilson N K NMR of Aromatic Compounds Wiley-VCH New York 1982

61) (a) Poli R Chem Rev 1996 96 2135 and the references cited therein (b) Schroumlder D Shaik S Schwartz H Acc Chem Res 2000 33 139 (c) Harvey J N Poli R Smith K M Coord Chem Rev 2003 237 347 and the references cited therein

62) For computational examples of 16 electron triplet Cp cobalt species influencing cobalt-mediated reactions see (a) Siegbahn P E M J Am Chem Soc 1996 118 1487 (b) Poli R Smith K M Eur J Inorg Chem 1999 877 (c) Carreoacuten-Macedo J-L Harvey J N J Am Chem Soc 2004 126 5789 (d) Petit A Richard P Cacelli I Poli R Chem Eur J 2006 12 813 (e) Aubert C Betschmann P Eichberg M J Gandon V Geny A Heckrodt T J Lehmann J Malacria M Masjost B Paredes E Vollhardt K P C Whitener G D Chem Eur J 2007 13 7443 (f) Gandon V Agenet N Vollhardt K P C Malacria M Aubert C J Am Chem Soc 2009 131 3007

63) Illustrative examples (a) Olson W L Stacy A M Dahl L F J Am Chem Soc 1986 108 7646 (b) Wadepohl H Galm W Pritzkow H Wolf A Chem Eur J 1996 2 1453 (c) Knijnenburg W Hetterscheid D Kooistra T M Budzelaar P H M Eur J Inorg Chem 2004 1204

64) Benito-Garagorri D Bernskoetter W H Lobkovsky E Chirik P J Organometallics 2009 28 4807

65) Fox J P Ramdhanie B Zareba A A Czernuszewicz R S Goldberg D P Inorg Chem 2004 43 6600

66) Guennic B L Floyd T Galan B R Autschbach J Keister J B Inorg Chem 2009 48 5504

67) Cremer C Burger P J Am Chem Soc 2003 125 7664

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68) Atkins P de Paula J P Physical Chemistry 8th Edition Oxford University Press Oxford 2006

69) Butters T Toda F Winters W Angew Chem Int Ed Engl 1980 19 926 70) Mann B E Taylor B F 13C Data for Organometallic Compounds Academic

London 1981 71) For a review on triple decker arene complexes and closely related syn dinuclear

systems see (a) Beck V OlsquoHare D J Organomet Chem 2004 698 3920 and the references therein For a review of trinuclear CpCo(arene) complexes see (b) Wadepohl H Angew Chem Int Ed Engl 1992 31 247 and the references therein

72) Jonas K Koepe G Schieferstein L Mynott R Kruumlger C Tsay Y-H Angew Chem Int Ed Engl 1983 22 620 Angew Chem Suppl 1983 920

73) Muumlller J Gaede P E Qiao K Angew Chem Int Ed Engl 1993 32 1697 74) Schneider J J Wolf D Janiak C Heinemann O Rust J Kruumlger C Chem

Eur J 1998 4 1982 75) Schneider J J Denninger U Heinemann O Kruumlger C Angew Chem Int Ed

Engl 1995 34 592 76) Budzelaar P H M Moonen N N P de Gelder R Smits J M M Gal A W

Chem Eur J 2000 6 2740 77) Albright T A Dosa P I Groszligmann T N Oluwakemi O Padilla R Paubelle

R Timofeeva T Vollhardt K P C Angew Chem Int Ed 2009 48 9853 78) Schaub T Radius U Chem Eur J 2005 11 5024 79) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4660 80) (a) Edelbach B L Lachicotte R J Jones W D Organometallics 1999 18 4040

(b) Muumlller C Lachicotte R J Jones W D Organometallics 2002 21 1975 81) Martin R H Angew Chem Int Ed Engl 1974 13 649 82) Mallory FB Butler K E Evans AC Mallory CW Tetrahedron Lett 1996 37

7176 83) Selected Reviews (a) Amemiya R Yamaguchi M Chem Rec 2008 8 116 (b)

Ruliacutešek L Exner O Cwiklik L Jungwirth P Staryacute I Pospiacutešil L Havlas Z J Phys Chem C 2007 111 14948 (c) Hopf H Classics in Hydrocarbon Chemistry Wiley-VCH Weinheim 2000 pp 321ndash330 (d) Voumlgtle F Fascinating Molecules in Organic Chemistry Wiley New York 1992 pp 156ndash180 (e) Meurer K P F Voumlgtle Top Curr Chem 1985 127 1 (f) Laarhoven W H Prinsen W J Top Curr Chem 1984 125 63

84) (a) Mallory FB Butler K E Mallory CW Beacuterubeacute A Luzik E D Brondyke E J Hiremath R Ngo P Carroll P J Tetrahedron 2001 57 3715 (b) Mallory F B Butler K E Evans A C Brondyke E J Mallory C W Yang C Ellenstein A J Am Chem Soc 1997 119 2119

85) (a) Mitsuhashi R Suzuki Y Yamanari Y Mitamura H Kambe T Ikeda N Okamoto H Fujiwara A Yamaji M Kawasaki N Maniwa Y Kubozono Y Nature 2010 464 74 (b) Okamoto H Kawasaki N Kaji Y Kubozono Y Fujiwara A Yamaji M J Am Chem Soc 2008 130 10470 (c) Tian Y H Park G Kertesz M Chem Mater 2008 20 3266

86) Recent reviews of acenes in electronic applications (a)Yamashita Y Sci Technol Adv Mater 2009 10 024313 (b) Wuumlrthner F Schmidt R ChemPhysChem

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2006 7 793 (c) Bendikov M Wudl F Chem Rev 2004 104 4891 87) NICS-based comparison of phenacene and acene properties Portella G Poater

P Bofill J M Alemany P Solagrave M J Org Chem 2005 70 2509 and the references therein

88) Mallory F B Mallory C W Org React 1984 30 1 89) Gu Z Nickel-Catalyzed Cycloaddition Reaction of [N]Phenylenes and Alkynes

Postdoctoral Report University of California Berkeley 2008 90) Preferential displacement of COD by π ligands from Ni(COD)(PMe3)2 is well

documented See eg Karsch H H Leithe A W Reisky M Witt E Organometallics 1999 18 90

91) (a) Bochmann M Hawkins I Hursthouse M B Short R L J Chem Soc Dalton Trans 1990 1213 (b) Poerschke K R Mynott R Angermund K Kruumlger C Z Naturforsch 1990 40B 199 See also (c) Bartik T Happ B Iglewsky M Bandmann H Boese R Heimbach P Hoffmann T Wenschuh E Organometallics 1992 11 1235

92) For Ni-phosphine migrations along polycyclic benzenoid ligands see eg Stanger A Vollhardt K P C Organometallics 1992 11 317

93) Edelbach B L Vicic D A Lachicotte R J Jones W D Organometallics 1998 17 4784

94) (a) Feiken N Pregosin P S Trabesinger G Scalone M Organometallics 1997 16 537 (b) Feiken N Pregosin P S Trabesinger G Albinati A Evoli G L Organometallics 1997 16 5756 (c) Geldbach T J Pregosin P S Eur J Inorg Chem 2002 1907

95) Cheng T-Y Szalda D J Hanson J C Muckerman J T Bullock R M Organometallics 2008 27 3785

96) (a) Grimme S Harren J Sobanski A Voumlgtle F Eur J Org Chem 1998 8 1491 (b) Dias J J Chem Inf Model 2005 45 562

97) Still W C Mitra A Kahn M J Org Chem 1978 43 2923 98) (a) Leonard J Lygo B Procter G Advanced Practical Organic Chemistry 2nd

ed CRC Press Boca Raton 1998 (b) Errington R J Advanced Practical Inorganic Chemistry and Metalorganic Chemistry Chapman and Hill London 1997

99) Jonas K Deffense E Habermann D Angew Chem Int Ed Engl 1983 22 716 100) Gaussian 03 Revision B03 M J Frisch G W Trucks H B Schlegel G E

Scuseria M A Robb J R Cheeseman J A Montgomery Jr T Vreven K N Kudin J C Burant J M Millam S S Iyengar J Tomasi V Barone B Mennucci M Cossi G Scalmani N Rega G A Petersson H Nakatsuji M Hada M Ehara K Toyota R Fukuda J Hasegawa M Ishida T Nakajima Y Honda O Kitao H Nakai M Klene X Li J E Knox H P Hratchian J B Cross C Adamo J Jaramillo R Gomperts R E Stratmann O Yazyev A J Austin R Cammi C Pomelli J W Ochterski P Y Ayala K Morokuma G A Voth P Salvador J J Dannenberg V G Zakrzewski S Dapprich A D Daniels M C Strain O Farkas D K Malick A D Rabuck K Raghavachari J B Foresman J V Ortiz Q Cui A G Baboul S Clifford J Cioslowski B B Stefanov G Liu A Liashenko P Piskorz I Komaromi R L Martin D J Fox T Keith M A Al-Laham C Y Peng A Nanayakkara M Challacombe P M W Gill B Johnson W Chen M W Wong C Gonzalez J A Pople Gaussian Inc Pittsburgh PA

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2003 101) wwwgaussiancom 102) wwwchemcraftprogcom 103) Becke A D J Chem Phys 1993 98 5648 104) Lee C Yang W Parr G R Phys Rev B 1988 37 785 105) Binkley J S Pople J A Hehre W J J Am Chem Soc 1980 102 939 for

hydrogen and Gordon M S Binkley J S Pople J A Pietro W J Hehre W J J Am Chem Soc 1983 104 2797

106) Hay P J Wadt W R J Chem Phys 1985 82 270 107) Hehre W J Ditchfield R Pople J A J Chem Phys B 1972 56 2257 108) Curtiss L A McGrath M P Blaudeau J-P Davis N E Binning R C Jr

Radom L J Chem Phys 1995 103 6104 109) A W Ehlers M Boumlhme S Dapprich A Gobbi A Houmlllwarth V Jonas K F

Koumlhler R Stegmann A Veldkamp G Frenking Chem Phys Lett 1993 208 111

110) QST is a synchronous transit approach to the quadratic region around the transition state structure For details see (a) J B Foresman A Frisch in Exploring Chemistry with Electronic Structure Methods A Guide to Using Gaussian Gaussian Inc Pittsburgh PA USA 1996 (b) H B Schlegel in Ab Initio Methods in Quantum Chemistry Part I Wiley Chichester 1987

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