SYNTHESIS OF AMIDINTES AND AMlDLNATES WITH rn-TERPHENYL SUBSTITUENTS

SUMUDU DEEPA ABEYSEKERA

Thesis submitted in partial fulfillment of the requirements for

the Degree of Master of Science (Chemistry)

Acadia University Spring Convocation 200 1

O by SUMUDU DEEPA ABEYSEKERA, 2001

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My parents who continue to be my guiding light

TABLE OF CONTENTS

List of Tables

List of Figures

List of Schemes

Abstract

List of Abbreviations

Acknowledgements

Chapter 1 Introduction

1.1 General

1.2 StructureofAmidines

1.3 Synthesis of Arnidines

1.4 Nomenclature of Amidines

1.5 Overview of Amidinate Ligands

1.6 Bonding Modes of Amidinate ligands

1.7 Steric Effects on the Amidinate Ligand

1.8 m-Terphenyls

1.9 Thesis Report

Chapter 2 Results and Discussion

2.1 Preparation of m-terpheny 1 precursors

2 4 1 ) Trihalobenzene via diazotization

2.2 Preparation of m-terphenyls

xiv

2.2(1) Synthesis via two-aryne sequence (Route 1)

2.2(2) Identifcat ion of [CH3***I] interactions in the

crystai structures of 2.4 (b,c)

2.2(3) Synthesis of 2,4,6-triphenylbromobenzene v ia

electrophiic aromatic substitution (Route 2)

2.3 Preparation of amidines

2.3(1) Mono-amidines

2.3(2) Solid state structures 0f2.6 (a,b)

2.3(3) Bis;amidines

2.4 Preparation of amidinate complexes

2.4(1) Dialkylaluminum amidinate complexes

2.4(2) Solid state structures of 2.8 (a&)

2.4(3) Stability of the diakyialurninurn amidinate complexes

2.5 Attempted preparation of arnidines with steric bulk on both

C and N centers

Chapter 3 Conclusions

Chapter 4 Future work

Chapter 5 Experirnental Methods

References

APPENDICES

A Crystallograp hic Data

1. Crystailographic data for 2.4 b

2. Crystallograhic data for 2 . 4 ~

3. Crystallographic data for 2.6a

4. Crystallographic data for 2.6b

5. Crystallographic data for 2.7a

6. CrystaEographic data for 2.8a

7. Crystallographic data for 2.8 b

8. Cry stallograp hic data for N, N'dimesit y lcarbodümide

LIST OF TABLES

Table 2.1 Chernical data relevant to the m-terphenyls synthesized via route I

Table 2.2 van der Waals radii of selected atoms

Table 2.3 Selected bond lengths and bond angles of 2.4 (b,~)

Table 2.4 Characterization data for 2.6 (a,b)

Table 2.5 Selected bond lengths and bond angles of amidines

Table 2.6 Characterization data for 2.7 (a, 6)

Table 2.7 Characterization data for 2.8 (a,b)

Table 2.8 Selected bond lengths and bond angles of amidines and amidinates

LIST OF FIGURES

Figu re 1.1 Generalized structures of amidines and amidinates

Figure 1.2 General structure of an amidine

Figure 1.3 Oxygen based analogues of amidines

Figure 1.4 General structure of amidines relevant to this research project

Figure 1.5 Isomers of amidines

Figure 1.6 Resonance structures and resonance hybrid form of amidinate ligand

Figure 1.7 Bonding modes of amidinate ligand

Figure 1.8 Bridging dinuclear bonding mode

Figure 1.9 Geometry o f amidinate complexes according to the

number of Ligands attached

Figure 1.10 Steric effects of ligand substituents

Figure 1.11 Bowl shaped environment of m-terphenyl substituted

amidinate ligand

Figure 1.12 General structure of an m-terphenyl ligand and other buky ligands

Figure 1.13 Energy rninimized 3D structure of the rn-terphenyl,

2,6-dimesityiodo benzene

Figure 2.1 ORTEP view of 2.4b

Figure 2.2 ORTEP view of 2 . 4 ~

Figure 2.3 [CH3-I] interactions in 2.4b

Figu re 2.4 [CH3*4] interactions in 2.4~

Figure 2.5 Packing diagram of 2.4b

Figure 2.6 ORTEP view of 2.6a

Figure 2.7 ORTEP view of 2.6b

Figure 2.8 bis and tris(benzarnidine)derivatives

Figure 2.9 ORTEP view of t.7a

Figu te 2.10 ORTEP view of 2.8a

Figure 2.11 ORTEP diagram of 2.8b

Figure 2.12 Packing diagram of 2.8a

Figure 2.13 A graphical view of the seven atoms along the Ai-C vector

of aluminurn amidinate complexes

Figure 2.14 View of 2.8b along Al-C vector

Figure 2.15 ORTEP view of N,N'-dimesitylcarbodiimide

Figure 4.1 An amidine with steric bulk on both C and N centers

LIST OF SCHEMES

Scheme 1-1 Synthetic pathway for the preparation of arnidines 3

Scheme 2-1 Preparationoftrihalobenzene compounds via diazotization reaction 16

Scheme 2.2 Synthesis o f rn-terphenyls via a two-aryne sequence 17

Scheme 2 J Electrophilic aromatic substitution of 1,3,5-triphenylbenzene 25

Scheme 2.4 Preparation of buky amidines via lithiated terphenyls 26

Scheme 2-4 Preparation of dialky Ialuminum amidinate complexes 36

Scheme 2-6 Hydrolysis of aluminum amidinate complexes 46

xii

Sterically demanding amidines, N, N'-düsopropyl-2,4,6-triphenylbenzamidine

2.6a, and N.V-dicyclohexyl-2,4,6-triphenylbenzamidine 2.6b, have k e n prepared via

reaction of the correspondhg carbodiimide with 2,4,6-tnphenylphenyUithium (generated

in siîu via lithiation of 2,4,6-triphenylbromobenzene). Ln addition, the bis-amidine

derivatives 2.7 (a,b) were also prepared. The terphenyl group on the central carbon of

the N-C=N systern provides steric protection in the plane of the amidinate ligand and

perhaps more importantly, above and below the amidine plane. Hence, the

diaikylaIuminum amidinate complexes 2.8a and 2.8b (prepared by reacting the rnono-

amidines with AI(CH3)3) are resistant to hydrolysis for a considerable arnount of time in

their crystailine state. The mono-amidines, bis-amidines, and the aluminum amidinate

complexes have been comprehensively characterized by spectroscopic methods and in

most cases by X-ray cry stailographic analysis.

m-Terphenyls were prepared by two methods. The first method was the reaction

of tnhalobenzene derivatives with Grignard reagents that proceeds via an aryne

intermediate. This was used to prepare the terphenyls 2.4 (a,b,c)- The second method

used to prepare the terphenyl 2.5 proceeds via an electrophilic aromatic substitution

reaction of a triphenylbenzene. Two terphenyl derivatives, 2.4 (b,c), were characterized

by X-ray crystdography and these exhibit unique [CH3-.II interactions.

. . . xlll

LIST OF ABBREVIATIONS

b

BuLi

CSD

Et20

h

IR

Mes

es*

ml

mo 1

mm0 1

*P.

MS

NMR

ORTEP

T H .

broad signal

butyllithium

Canadian Structural Database

diethy i ether

hour

h h e d

2,4,6-ttunethylphenyl

2.4,6-tri-tert-butyIpheny1

miililitre

rno le

rnillimo le

melting point

Mass Spectroscopy

Nuclear Magnetic Resonance

Oak Ridge Thermal Ellipsoid Plot

Tetrahydro fiiran

xiv

ACKNOWLEDGEMENTS

1 thank rny parents for instilling in me the value and joy of knowledge. They have

given me the strength and courage to face disappointment and success with grace and

dignity. I hope 1 will be able to bestow upon rny daughters the same.

Words c m hardly express the gratitude I feel for Dr. Jason Clyburne, my thesis

s u p e ~ s o r , for his guidance, encouragement and enthusiasm that have been delightful

inspirations. He has helped m e immensely in developing the ability to approach

problems in every possible direction. 1 am amazed at the capacity for patience and

tolerance in such a young professor; for I can only imagine the challenges he faced in

undertaking to supervise a student at the threshold of half a century ! I feel privileged to

be his student and have worked under his supervision with great pleasure. 1 wish him and

Jeanne Clyburne, who has been a very supportive fiend, the very best at Simon Fraser

University.

A special thank you is extended to Manju, my husband. Without his financial

support 1 would not have k e n able to attend Acadia University. 1 would like to Iet rny

daughters know how much 1 appreciate them for taking responsibility for their education

at an early age. I am very proud of their ability to complete their schooIwork without

constant supervision that has given me the opportunity to pursue my studies.

1 would like to thank the past and present staff at the chemistry department for

keeping me interested in chemistry with excellent instructions. In the same note, 1 must

thank Chris Scott who sparked my interest in Chemistry.

Tarnara Hamilton is profùsely thanked for editing my thesis and for helping me

understand the cornputer programs crucial for completing the thesis. Carla Dumeresque

is thanked for lifting up my sprits with her youthful exuberance.

A warm appreciation is extended to Avril Bird and Kristha Palczynski for their

countless arnicable gestures. They have helped me work with the least amount of

hstration.

Percy Blair is acknowledged for the pride he shows in maintainhg the sparkling

floors in the chemistry building that are most welcorning.

1 would like to acknowledge Dr. Don Hooper and Dr Michael Lurnsden at the -

Atlantic Region Magnet ic Resonance Center for providing NMR spectra, Dr. Stanley

Cameron and Katherine Robertson at Dalhousie University and Dr. Hilary Jenkins at St-

Mary's University for X-ray crystal structures, Dr. Ken MacFarlane at Simon Fraser

University for providing mass spectra, and Dr. Me1 Schriver at Atlantic Baptist

University for providing equipment.

Acadia University and the Natural Sciences and Engineering Research Council of

Canada are ackno wledged for their haticial support.

CHAPTER 1

INTRODUCTION

1.1 General

There has k e n an exponential growth in the application of organometallic

chemistry in catalysis during the latter half of the 2 0 ~ century.' The desire to expmd this

knowledge base has resulted in the investigation of heteroatom-containhg ligand systems

related to dlenes, alkynes and akenes. The effects on the reactivity of the metal center

by m o d i m g its electron density and coordination sites have k e n closely studied in

these stems.^ In general al1 nitrogen containhg compounds with a lone pair of

electrons can act as potential nitrogen donor ligands to an electron deficient metal centerS3

Thus, neutral amidines and their corresponding amidino (amidinate) anions

(Figure 1.1) have emerged as prominent players in the quest for comprehension of

coordination chemistry and reactivity of metal complexes.2

am idine am idino (amidinate)

Figure 1.1 - Generalized structures of amidines and amidinates

The ability of arnidines to act as stable and robust ligands for transition metal and

fielement complexes has made a significant impact OR catalytic systems. Moreover, they

fünction as cyclopentadienyl replacement ligands and have the potential to be

incorporated into the design of new homogeneous catalysts.' Amidine metal complexes

have been s h o w to catalyze a wide variety of reactions such as olefin polymerization,

ketone and aldehyde reductions, and the water gas shift reaction.'

1.2 Stmcture of Amidines

\ N-H

Figure 1.2 - General structure of an amidine

Amidines are compounds with an N-C-N backbone. Their amide-Iike nitrogen

center has a formal single bond and the irnino nitrogen has a forma1 double bond to the

centrai carbon atom (Figure 1.2). They are considered as nitrogen analogues of

carboxylic acids, esters, and amides that are illustrated in Figure 1 .3.6

d' R ' C 'i

O-H

carboxylic acid ester amide

Figure 1.3 - Oxygen based analogues of amidines

1.3 Synthesis of Amidines

Gerhardt synthesized the first amidine in 1858, by the reaction of aniline with

N-phenylbenzimidyl ~hloride.~ The credit for the revival of arnidine chemistry is given to

Sanger for the synthesis of N, N, N f tris(trhethysi1ys) benzarnidine,

PhC(=NSiMe3)p(SiMe,)zl, in 1973, by the following reaction4

Scheme 1.1 - Synthetic pathway for the preparation of amidines

The above synthetic pathway was optirnized by Oakley and CO-workers by refluxing

the reaction in toluene for 5-6 ha7 Using this procedure, they have prepared a wide range

of persilylated amidines with both electron donating and electron withdrawing

substituents. Synthetic routes to amidines have been reviewed!

1.4 Nomenclature of Amidines

The nomenclature of amidines is rather complicated due to the occurrence of E, 2,

syn and anti isomers. In addition, the possibility of tautomerism due to proton transfer

£kom one nitrogen atom to the other must be taken into consideration, although, in most

cases only one of the tautorneric forms is detected by spectroscopie methodsa8 An

extensive coverage of the nomenclature of acyclic and cyciic amidines with varying

substituents is given in The Chemistry of Amidines and Imidates by S . ~ a t a i . ~ The system

described here, with respect to Figure 1.4, is airned at gaining an understanding of the

nomenclature of amidines relevant to the research work presented in this thesis.

R' = 2,4,6-ûiphenlylbenzene R~ = [sopropyl or Cyclohexyl

Figure 1.4 - General structure of amidines relevant to this research project

Amidines are narned according to the acid or the amide obtained after its

hydrolysis. Thus, when R' = H, CHs, or Cs&, the compound is a formamidine, an

acetamidine, or a benzamidine r e ~ ~ e c t i v e l ~ . ~ The E, Z isomers are assigned with respect

to pnority groups around the C=N double bond. The syn and anti assignrnents are

accorded with respect to priority groups around the C-N single bonds6 Figure 1.5

illustrates the nomenclature of amidines according to E, Z syn. and anri isomerism.

TR2 RI-c

\ N-H

Figure 1.5 - Isorners of amidiues

1.5 Overview of Amidinate Ligands

The anionic derivative of an amidine is the armidinate or the amidino group,

F~NCR'NR~]- (Figure 1 4, which is rerniniscent of the carboxylate ion, FCOO]-.~ The

monoanionic, 2 or 4-electron donor amidinate Ligand binds readily to a wide range of

main group elements, as weU as transition, lanthanide, and actinide metals. 5,9,10

R~ R~

Figure 1.6 - Resonance structures and resonance hybrid forrn of amidinate ligand

The effect of ligand geometry on the coordination environment of the central

metal has attracted much attention in the field of organometallic chemistry. The

bidentate three-atom bridging amidinate ligand, with its capacity for different binding

modes, presents an ideal system to study these effects. An added advantage is the ability

to change the stenc b u k and electronic properties of the ligand with different substituents

to modZy the ligand geometry. ' ' . 1 2

1.6 Bonding Modes of Amidinate Ligand

The versatility of the amidinate ligand depends, to a great extent, on its various

bonding modes that arïse fkom the lone pair o f electrons on each of the nitrogen atoms.

Of the binding patterns conceived, the rnost cornrnon are the monodentate, bidentate, and

bridging modes (Figure 1 -7). 2,13.14

R7-

monodentate bidentate bndging

Figure 1.7 - Bonding modes of amidinate ligands

Ano ther prominent bonding arrangement features M-M bonding in dinuclear

cornpounds. The high basicity of the ligand and its ability to hold the metal atoms in

close proximity to each other plays a major roie in the formation of multiple bonds

between metal atorns, as illustrated in Figure 1 .8.'.15

Fig 1.8 - Bridging dinuclear bonding mode

The geometry around the metal center depends on the number of ligands

coordinated to the metal, Mono-amidinate, bis-amidinate and ris-amidinate complexes

adopt tetrahedral, trigonal bipyramidal, and octahedral structures respectively, with the

ligands coordinated in an almo st symmetrical manner (Figure 1 -9). l6

bis-amidinate tris-amidinate

Figure 1.9 - Geometry of amidinate complexes according to the number of ligands attached

1.7 Steric Effects on the Amidinate Ligand

The coordination environment at the metal center can be modified with different

substituents at the nitrogen and carbon atorns- 11-16 Sterically demanding substituents on

the carbon and nitrogen atorns tend to push the lone pair of electrons on the nitrogen

atoms towards the metal center. It causes a reduction in the RNM angle and an increase

in the CNR angle as shown in Figure 1.10

Monodentate or bridging Chelating

Figure 1.10 - Steric effect of ligand substituents

The lone pair of electrons pointing towards the metal center favors the chelating

bonding mode over the bridging bonding mode. On the other hand, non-bulky hydrogen

and methyl groups on the carbon center favor the bridging or rnonodentate bonding

modes. For the bridging mode to occur, at least one of the substituents, either on the

carbon or the nitrogen, must be sterically undemanding. l 6

Buky substituents, such as adamantyl, on the nitrogen center confier steric

hindrance primarily in the amidine plane. " Attempts to change the steric bulk on the

nitrogen atoms have resulted in an amidine with the "super buky" 2,6-diisopropylphenyl

substituent on the nitrogen atoms. It has been synthesized by modiQing the standard

organic synthetic route described by ~anger . '* S terïcally demanding substituents, such as the m-terpheny l group, on the central

carbon atom provide steric protection in the plane of the ligand as well as above and

below the plane of the ligand. This creates a bowl shaped environment in the amidinate

ligand, as illustrated in Figure 1.1 I , that c m stabilize unusual coordination patterns. l7

Fig 1-11 - Bowi shaped enviroment of m-terphenyl substituted amidinate ligand

An exarnple is the yttrium mono-amidinate cornplex, isolated with the incorporation of an

m-terphenyl on the central carbon of N, Nf-diisopropyl amidine. The amidine without the

m-terphenyl group tends to give yttrium bis-amidinate complexes.'7

1.8 m-Terphenyls

The unprecedented progress in the chemistry of Iow-coordinate heavier main

group elements (Le. n 2 3) can be attributed, to a large extent, to the use of stencally

dernanding ligands, and recently, to the rn-terphenyl substituent. Figures 1.12 and 1.13

show the well-protected pocket formed by the buUcy mesityl groups meta to each other on

a benzene ring. The presence of these arornatic substituents renders steric hindrance at a

rather long distance fiom the atom bonded to position 1 of the central 2,6-disubstituted

phenyl ring. This is an ideal environment to prepare atomic centers exhibiting

unconventional bonding patterns. 19.20

2A.6-mmethylphenyl (mesityi or Mes}

Figure 1.12 - General structure of an m-terpbenyl ligand and other b u l b ligands

Figure 1.12 - Energy miaimized CEEM 3D MOPAC structure of the m-terphenyl,

2,6-dimesityiiodobeazene

The synthesis of bis(2,4,6-tri-tert-butylphenyl)diphosphene, Mes*P=PMes*, in

1981, has becorne the corner-stone in the elucidation of unusual bonding patterns.2'

Recently, the rn-terphenyl, 2,6-dimesitylphenyl has been utilized to stabilize P=P bonds2'

The double bond between the two P atorns is stabilized by the steric hindrance of the

superMesity i (Mes*) and rn-terpheny l groups respectively. They prevent the

oligomernrization of the phosphhidene units (RP) by hindering close proximity of

molecules." For example, molecules exhibithg multiple bonds between heavy main

group elements show kinetic stability provided by an increase in activation energy for

~li~ornerization?~ However, studies show that the thermodynamic stability irnparted by

steric strain of bulky groups also plays a significant role in preventing dirneri~ation?~

Organometallic derivatives of the terphenyls are employed as transfer reagents.

They are usually Grignard or lithium derivat ives generated in situ, via metathesis

reactions. In a recent report on the structures of m-terphenyllithium complexes, it was

shown that the number of THF adducts in the complexes was determuied by the nature of

the stencally demanding terphenyl ligands. Increased steric crowding resuhed in iower

aggregation numbers fonning monomeric aryllithium species suc h as DnpLi(THF)z,

where Dnp = 2,6-di(l-naphthyl)phenyl.25 Lithium complexes with less stencally

demanding groups aggregate to form dimeric and tetrameric complexes. 26

The stable stannaneselone (Sn=Se) compound is given as an example to illustrate

the synthetic utility of m-terphenyls. The stability of a th-chalcogen double bond has

k e n attributed to the efficient steric protection of an rn-terphenyl, 2,2-düsopropyl-m-

terphenyl-2'-yl. Known stannaneselones (Sn=Se) without the terphenyl group are

restricted to those stabilized by intramolecular base coordination. In these molecules, the

electron deficient tin center is highly perturbed by electron donation &om a nitrogen atom

(intramo lecular base stabi~ization).~~ Without intramolecular stabilization, at ambient

temperatues, Sn=Se double bonds with less buky groups such as, CH(Si-)2 and

CHMe2, readily dimerize, giving Sn2Se2 four membered rings.

Rak and CO-workers have investigated rn-terphenyl derivatives of strongly

electropositive lanthanide elements for their structural characterization2' A h a 1 no te of

interest is the potential use of terphenyls as a-bonded ligand systems for the rehtively

large Ianthanide cations that rnay perhaps be used as an alternative to rnetallocene-based

catdyst stems.^^

1.9 Thesis Report

rn-Terpheny 1s are indispensable ligands in the stabilizat ion of unusual

coordination envùonrnents. To this extent, the rn-terphenyls constitute an integral feature

in the research work reported herein. Their synthesis starting fiom trihalo benzene

derivatives and Grignard reagents via an aryne interrnediate can be fomd in sections

2.1(1) and 2.2(1). Although midine chernistry with the terphenyl substituent 2.5, is the

centra1 theme of the report, the [CH3*-*Il interactions exhibited by compounds 2.4b and

2 . 4 ~ merit discussion. They are discussed in section 2.2(2).

The terphenyl used in the preparation of arnidines reported in this thesis is the

phenyl ligand prepared from 2,4,6-trïphenylbromobenzene, 2.5. Synthesis of 2.5 via an

electrophilic aromatic substitution reaction that gives excellent results is discussed in

section 2.2(3).

The synthesis of bulky mono-amidines through an in situ generation of the

lithiated terpehenyl is discussed in section 2.3 (1 ). Their so lid-state structural

characterization is discussed in section 2.3(2). The preparation and characteristics of bis-

amidines are discussed in section 2.3(3).

The prirnary purpose of the preparation of the bulky amidines is to have an easy

access to the bidentate, monoanionic amidinate ligand. An amidinate ligand with steric

buk on the carbon center was envisioned to be suitable to stabilize hitherto unstable

bonds in main group element complexes. To illustrate the robustness of complexes

possessing large amidinate ligands, dimethylaluminum amidinate complexes were

prepared. Their preparation, structurai characterization, and stability are discussed in

section 2-4,

Section 2.5 discusses amidines with steric bu& on C and N centers- The

preparation and structural characterization of N,W-dhnesitylcarbodiimide are included in

the discussion.

CHAPTER 2

RESULTS AND DISCUSSION

The sterically demanding rn-terphenyls that confer s t e k protection to element

centers with unusual coordination environments is a key feature of the work described in

this thesis. Amidines with m-terphenyl substituents on their central carbon are prepared

by lithiation of the terphenyl ligand and subsequent reaction with a carbodiimide. Two

synthetic routes have been explored in the preparation of the requisite m-terphenyls. The

first route involves reaction of trihalobenzene derivatives with Grignard reagentsI9 and

the second route uses an electrophilic aromat ic substitution reaction. The preparation of

trihaiobenzene derivatives is discussed at the beginning of the section followed by a

discussion of their conversion to the corresponding rn-terphenyls.

2.1 Preparation of m-terphenyl precursors

2.1(1) - Trihatobenzene via diazotization The trihalobenzene derivatives are prepared by a classic diazotization reaction. In

a typical experiment, a dibromoaniline derivative is suspended in HC1 and treated with an

aqueous solution of NaNOz to give a diazonium salt. The nitrosonium ion (NO3 formed

by the reaction of NaNOz with HC1 is unstable at room temperature; therefore, the

rextion is performed at temperatures below 5°C. After an hour of stirring, the reaction is

quenched with an aqueous solution of KI. The diazonium ion readily evo lves nitrogen in

the presence of a more nucleophilic species such as the iodide ion, providing a facile

route to the desired 1,2,3-trihalo benzene compounds (Scheme 2. I).~'

diazonium salt

2-2

Scheme 2.1 - Preparation of trihalobenzene compounds via diazotization reaction

Preparation of 2,6-dibromoiodobenzene, 2.3a followed a modified procedure

given by art." The iso lated product was recrystallized in toluene and 2.3a was obtained

with a 78% yield. Compound 2.3b was recrystallized in hexane with a 73% yield. They

were identified by their melting points and were characterized by IR, NMR ('H and "c)

and mass spectral analysis.

2.2 Preparation of m-terphenyls

2.241) - Synthesis via a two-aryne sequence (Route 1)

The rn-terphenyls, 2,6-dimesityliodobenzene 2.4a, 2,6-dimesityl-4-

methyliodobenzene 2.4b, and 2,6-diphenyl-4-methyliodobenzene 2.4c, were prepared by

reacting 2.3a and 2.3b with three equivalents of the corresponding Grignard reagents

followed by an G quench. Scheme 2.2 illustrates the postulated reaction mechanism.

Initially, the trihalobenzene undergoes a halogen-metal exchange at the iodine center,

fo llowed by elimination that produces an aqme intermediate. A I ,2 addition o f a

Grignard reagent occurs and repetition of the process produces a bis-aryl Grignard

compound. An I2 quench results in the desired iodo rn-terpheny 1 compound 2.4.

2.4a, R = H, Ar = Mes 2.4b, R= CH3. Ar = Mes 2 . 4 ~ R = CH;. Ar = Ph

Scheme 2 3 - Synthesis of m-terphenyls via a two-aryne sequence

M e r an aqueous workup and recrystallization, the compounds 2.4(a9b9c) were

isolated in reasonable yields and characterized by IR, NMR ('H and "c), and mass

spectral analysis. Relevant data for purification, yield, and melting points of these

compounds are given in Table 2.1.

Table 2.1 - Chernical data relevant to the m-terphenyls synthesized via route 1

Data 1 Compound

Name

Structure

1 1 methvliodobenzene 1 rnethviiociobenzene

2.4a 2.4b 2 .4~ 2,6-dimesityl iodobenzene 2,6-dimesityl-4- 2,6-diphenyt-4-

methyliodobenzene rnethyl iodo benzene

MoIecular formula MoIecular Weight

solvent I l I

c24H25 1 440.36 dm01

Phenylmagnesiurn brom ide methanol

2.2(2) - Identification of [CH3**.I] interactions in the crystal structures of

2.4b and 2 . 4 ~

X-ray crystal structure analysis of 2.4b and 2 . 4 ~ reveal their predicted molecular

structure as shown by their ORTEP views in Figures 2.1 and 2.2. Crystal data for these

compounds are given in Appendix A, pages A2 and A9 respectively. The planar

structure of the benzene rings with methyl and hydrogen attachrnents is clearly indicated

in the ORTEP views. The C-C and C-1 bond lengths and bond angles are unrernarkable.

An interesting feature is revealed upon examination of the packing diagram of

2.4b and 2 . 4 ~ . Both of these compounds show [CH3-Il interactions of 3.168(5)A

iilustrated in Figures 2.3 and 2.4. Figure 2.5 illustrates another view of the packing

design of 2 Ab.

CZSH27I 454.39 dm01

Mesitylrnagnesium brom ide toluene

Grignard ragent

RecrystalIization

Yield Meltine oint

C I ~ H I S ~ 370.23 h o 1

Mesityhagnesium brornide hexane

47% 22 1-222°C

39% 2 18-2 I9OC

34% 100- 102°C

Figure 2.1 -The ORTEP view of the 2,Mimesityl4methytidobell~eue, 2.4b Selected bond Iengths [A]: I(1)-C(1) 2.135(5), C(1)-C(2) 1.382(7), C(2)-C(11) 1.503(6), C(l2)-C(15) 1 .S4O(S). Selected bond angles [ O ] : C(l2)-C(I1)-C(2) I I9.7(2), C(2)-C(1)-I(1) 1 17.8(3), C(I 1)-C(12)-C(15) 12 1.6(3)

F i r e 2 2 - The ORTEP view of &Miphenyl4methyiiodobe11zene, L4c Selected bond lengths [A]: I(l)-C(l) 2,105(2), C(1)-C(2) 1.395, C(2)€(11) 1.496 Selected bond angles ["j: C(1)-C(2)-C(I1) I23.3(2), C(2)-C( 1 )-[( l) 1 l9.48(17)

Figure 2.3 - [a-Q interactions in crystalline 2,6-dimesityE4-methyLiOdok~1~ene, 2.4b C--01, 3.529(1)A; H--01, 3.168(5)A; 1--OH-C, 173"

Figure 2 4 - [CH3-11 interactions in 56-diphenyl4methyliodobenzene, 2.442 C-1, 4.02(2)A; H.4, 3.16(2)A; 1--OH-C, 1 50°

Figure 2.5 - Packhg diagram of 2,~imesityl4methyliodobenzene, Z4b

Thus fa, intermolecular contacts to halogen atoms have been thought of as very

weak, insignificant interactions. Increasingly, data is king gathered to demonstrate that

these forces have a significant effect on the overall structure. Halogen atoms covalently

bonded to carbon, fonn short, directional contacts to H, N, 0, and S. 3233 Geometrical

trends observed for these contacts are rationalized by assurning that the contacts are

electrostatic in nature. It has k e n suggested that [C-H*-Cl] interactions are shi lar to

hydrogen bonds. However, the corresponding CC-H*-Br] and [C-Hm*-I] contacts, due to

the reduced electronegativity of Br and 1, are questionable.33 Nevertheless, [CHP-[]

interactions are observed in the crystal structures of 2.4b and 2 .4~ . The van der Waals

radii of relevant a t o r n ~ , ~ ~ selected bond lengths, and bond angles of 2.4 (b,c) are compiled

in Tables 2.2 and 2-3.

Table 2.2 Table 2.3

1 Van-der Waals ( radii -i-i ( Selected bond lengths and [ I angles I

The [CH3*4] interactions of both 2.4b and 2 . 4 ~ are less than the sum of the van

der Waals radii of H and 1, and CH3 and 1, that are calculated to be 3.35A and 4.15A

respectively. A complete search of the CSD reveals that these are the shortest [CH3-41

interactions yet identified. It is possible that though they are weak, in situations where

rnarginally weak interactions are possible (Le in IT stacking of arornatics) the overall

structure may accommodate formation of [CH3*-Il bonds.

2,2(3) - Synthesis of 2,4,6-triphenylbromobenzene via electrophilic aromatic

substitution (Route 2)

The compound 2,4,6-triphenylbromobenzene 2.5, is the precursor of the

m-terphenyl used in the preparation of bulky amidines reported in this thesis. It is

prepared v i a brornination of 1,3,S-triphenylbenzene dissolved in CS2. The reaction is

stirred for 12 hours after the addition of Br2. The solvent is evaporated and the resulting

solid is washed with hot methanoL3' Recrystallization of 2.5 can be achieved in

isopropylalco hol.

The synthetic route shown in Scheme 2.3 is an electrophilic aromatic substitution

reaction in which one o f the hydrogen atoms in the central arornatic ring is substituted by

bromine. The solvent CS2 acts as the weak Lewis acid catalyst often required in these

reactions. An added advantage is that CS2, with its low boiling point of46"C, is easy to

remove afier completion o f the reaction.

+ HBr

Scheme 2.3 - Electrophilic aromatic substitution of I,3,5-triphenylbenzeae

The white solid isolated with a 94% yield was identified by the melting point

(1 28- 1 2g°C), which was in agreement with the literature value (1 29- 1 30°C)-

Spectroscopic studies, IR, NMR ('H and I3c), and mass spectral analysis confumed the

identity of 2.5.

2.3 Preparation of amidines

2.3(1) Mono-am idines

Amidines with bulky substituents on the central carbon atom have steric

protection in the amidine plane. The use o f the rn-terphenyl extends this steric protection

to above and below the arnidine plane. Most amidine preparations mentioned in the

literature produce amidines with substituents such as H, CH3, C6H5 on the central carbon-

Recently, Arnold has described a synthetic route to the preparation of amidinate

complexes with buky rn-terphenyl substituents on the central carbon of the amidinate

ligand. l7 His preparation invo lves the generation of an rn-terpheny 1 substituted amidine,

which is lithiated and reacted with metal halides to obtain the amidinate c ~ r n ~ t e x e s . ' ~ In

this research project, amidines with m-terpheny 1s were prepared by reacting lithiated

terphenyls, generated insitu, with carbodiirnides (R-N=C=N-R), according to Scheme 2.4

s h o w below.

Th

BuLi - EtzO hexane

2.6a, R = isopropyl 2.6b, R = cyclohexyl,

Scheme 2.4 - Preparation of bulky amidines via Iithiated terphenyls

The terphenyl2.5 is easily metallated by combining it with 1.6 M BuLi in hexane

and stirring for four hours. Triphenylphenylli'thium reacts readily with a carbodiimide to

produce a lithiated amidinate. Quenching the amidinate with water followed by

extraction with CHzClz and recrystallization fiom toluene produces the neutral amidine.

The identity of N, N'-diisopropyl-2,4,6-triphenylbenzamidie 2.6a, and

N. N'-dicyclo hexyl-2,4,6-triphenylbenzaxnidine 2.6 b, has been confirmed by the

characterization data given in Table 2.4 and by X-ray crystallographic analysis.

Table 2.4 - Characterization data for 2.6a and 2*6b

Data Name

Structure

Molecular formula Elemental Anaiysis Calculated Found Molecular weipht Mass spectrum (M3 Yield Melting point IR (cm-') N-H C=N C-N ['HI-NMR N-H C-N-CH C=N-CH [ 'Jc~-N-~~ Amidine carbon

1 tri~henvlbenzam idine 1 tri~henvlbenzamidine

- -

70 eV, m/z , 432 48%

-

70 eV, m/z, 5 13 50%

The N-H, C=N, and C-N stretching fiequencies are in agreement with IR spectral

kequencies reported for other ami di ne^.^ NMR solution studies ('H and I3c) in CDCI,

confirm the- presence of isopropyl and cyclohexyl groups in two diRerent chemical

environments; namely, as an imine nitrogen substituent and as an amine nitrogen

substituent. However, the signais for these resonances are broadened due to

interconversion between 2-syn and E-syn isomers that occur on an NMR tirnescale. This

phenomenon has been observed in amidines with rn-terphenyl substituents on the central

carbon atom," as well as in amidines with buky substituents such as

2,6-diisopropylphenyl on the nitrogen atorn. I8

2.3(2) Solid state structures of 2.6a and 2.6b

An X-ray crystallographic study was performed on the compounds 2.6a and 2.6b

to appreciate the steric demands of the m-terphenyl group with respect to the amidine

itagrnent. ORTEP views of the molecuIar structures of the arnidines are given in Figures

2.6 and 2.7 with selected bond Iengths and bond angles. Crystal data for these

compounds are given in Appendix A, pages A1 6 and A37 respectively.

The molecular structures of the amidine compounds show that they exist in the E-

syn configuration. In general, the E conformation is energetically more favored than its Z

co~nterpart .~

Figure 2.6 - ORTEP view of the molecular structure of 2.6a showïog the labeling scheme. Thermal ellipsoids are shown at 50% probability level; seleded bond lengths [A]: N(1)-C(1) 1368(4), N(1)-C(2) i.462(4), N(1)-H(1 ) 0-8900, N(2)-C(I) 1.282(4), N(2)-C(5) 1.460(4), C(l )-C(8) 1.5 13(4)j selected bond angles CO]: C(1)-N(I)-C(2) 122-5(3), C(1)-N(I)-H(1) 121 -8, C(2)-N(1)-H(I) 1 12-2, C(1)-N(2)-C(5) 120-7(3), N(2)€(1)-N(1) 120.2(3), N(2)-C(1)-C(8) 126.4(3), N(i )-C(I)-C(8) 1 13.4(3), N(I)-C(1 )-C(8)- C(9) 70.7(4).

Figure 2.7 - OR'lXP view of the molecular structure of 2.6b showing the labeling scheme. Thermal ellipsoids are shown at 50% probability level; selected bond Iengths [A]: N(1)-C(1) 1.379(4), N( 1 )-C(2) 1.450(4), N( 1)-H( I ) 0.8600, N(2)-C( 1) 1.283(3), N(2)-C(8) 1.462(4), C( 1)-C( 14) 1.498(4); selected bond angles [O]: C(I)-N(1)-C(2) 122.9(2), C(1)-N(1)-H(1) 1 18.6, C(2)-N( 1)-H(1) 1 18.6, C(i)- N(2)-C(8) 120-5(2), N(2>C( 1)-N(1) 1 l9.8(3), N(2)-C(l )-C(14) 126.2(3), N( 1 )-C(I )-C( I 4) 1 14.0(2), N(1 )-C(1 )-C(I4)-C( 1 5) -70.29(0.34).

Table 2.5 compares selected bond

N,N-bis(2,6-diisopropylphenyl)-4-t01uarnid

3 1

2.6b and

~henyl and

R' is 4-CH3C6& For ciarity, the data in the table refer to the general amidine structure

given below.

lengths and bond angles of 2-6a,

inel' in which R is 2,6-diisopropylp

Table 2.5 - Selected bond lengths and bond angles of amidines

The bond lengths of the arnidines included in Table 2.5 do not show a significant

deviation from each other. Nor do the C-N and C=N bond lengths differ fio m 1.344(1 )A

and 1.298(1)A respectively, given for the simple a~etamidine.~

Bond length [A] N( 1 )-a 1 N(l )-R N(1)-H W ) - C ( 1) N(2)-R C( 1 )-RI

(DipWCWCHK6&) , 1.344(3) 1.422(3)

- 1 -3 17(3) 1.429(3) 1.483(3 1

2-6a 1.368(4) 1.462(4)

0.89OO(calculated) 1.282(4) 1.460(4) 1.5 13(4)

2.6b 1.379(4) 1.450(4)

O .8600(calcu~ated) 1.283(3) 1.462(4) 1.498(4)

The bond angles around the central carbon atorn of the amidines conform to a

trigonal planar geometry with a total of ca. 360". The N(1)-C(1)-N(2) angle is the ideal

120° which is geornetrically expected for an sp2 hybridized carbon. This angle is

consistent with the presence of the double bond between N(2) and C(1). The geometry

around the N(1) atom is trigonal planar. Although the individual bond angles are not

strictly 120°, the total of the bond angels is ca. 360". The deviation of the geometry

around the N(1) fiom the tetrahedral geometry rnay perhaps be due to the steric effects of

the m-terpheny 1 substituent. Unfortunately, reported bond angles are unavailable for

cornparison. Changes in the bond angles upon complex formation are discussed with

metal amidinate complexes,

2.3(3) Bk-am idines

Bis-amidines are compounds with two amidine functionalities on a central organic

substituent. Bis-arnidines with isopropyl and cyclohexyl amidine groups were

serendipitously prepared by using two equivalents of butyllithium to generate bis-

lithiated 2,4,6-triphenylbenzene and reacting it with the corresponding carbodiimide.

After an aqueous work up and recrystallization h m toluene, bis-N. N1-diisopropyl-2.4.6-

triphenylbenzarnidine 2.7a, and bis-N, NI-dicyclohexyl-2,4,6-triphenylbenzamkbe 2.7b

were isolated in good yield. They were characterized and their identity was confmed by

the parameters given in Table 2.6. X-ray crystallographic analysis of 2.7a further

confkmed its bis-amidine funct ionaiity.

Table 2.6 - Characterization data for 2.7a and 2.7b

I l

Molecular formula 1 C38b6N4

2.7b Bis-N. N'-dicyc lohexyl-2,4,6-

triphenylbenzam idine

Parameter Name

2.7a Bis-MN'-diisopropyl-2,4,6-

triphenylbenzarnidine

Elemental Anabsis Calculated Found Molecular weight Mass çpectnmi (rvr3 Yield Melting point JR (cm-') N-H C=N

Structure

C-N ['HJ-NMR

N-H C-N-CH

It is interesting to note here the lack o f information with regards to molecules

posessing multiarnidine fiinctionalities (Le., more than one amidine fiinct ional group in

the same rnolecule). Two derivatives have k e n reported and they have both k e n

prepared using the same synthetic r n e t h o d ~ l o ~ ~ . ~ Treatment of 1,Cdicyanobenzene and/

or 1,3,5-tricyanobenzene with 2 or 3 equivalents of LïN(SiMe3)z respectively, followed

by silylation yielded para-disubstituted bis-benzamidine and trisubstituted

N-Cy

Ph Ph ' \ * / /

C, 8 1 -68; H, 8.30; N, 10.03% C, 8 1.48; H, 8.43; N, 9.82Y0

558-8 g/mol 70 eV, m/z, 558

54% 197-198"

3400 1590

C=N-CH [ ' 3 c l - ~ ~ ~ Amidine carbon

C, 83-52; H, 8.69; N, 7.79% C, 83.69; H, 8.80; N, 6.52%

7 19.05 g/rnol -

40% 202-2OS0C

3400 1590

13 10

3-5 1 2.35, 1.85

1320

3.5 1 2.8 1-2-36

3.74, 3.28

not observed

3.06,2.61

not observed

tris-benzamidine shown in Figure 2.8. Further information with regards to their behavior

as ligands in coordination chemistry is not available.

Me3SrX Y S iMe3 :cec, Me3SïN=C (MG i)2N N(S iMe3)z

a CH /N!3ihk3 /

(S iMe3)zN \

N(SiMe3h

bis-benzamidine

tris-benzamidine

Figure 2.8 -bis and tris(ùenzamidine) derivatives

The ORTEP view of the bis-amidine, 2.7a is given in Figure 2.9 with selected

bond lengths and bond angles that are sirnilar to those found in the mono-amidines. The

crystal data is given in Appendix A, page A58.

Figure 2.9 - ORTEP view of the isopropyl bis-amidine, 2.7a showing the atom-labelling scheme- Thermal ellipsoids are shown at 50% probability level; setected bond lengths [A]: N(I )-C(1 ) 1.295(2), N(1)-C(2) l.466(2), N(2)-C(1) 1.35 1 (2), N(2)€(5) 1.459(2), C(1)-C(2 1) 1.507(2), N(3)-C(8) 1.388(2), N(3)-C(9) 1 -464(3), N(4)-C(8) 1.363(2), N(4)-C(12) 1.458(2), C(8)-C(36) 1.507(3); selected bond angles ["] : C(1)-N( 1 >.C(2) 120.15( 17), C(1)-N(3)-C(S) 128. I 1 ( 1 7), C(8)-N(3)-C(9) l2O.88( 1 8). C(8)-N(4)-C( 12) 123.04(18), N(1)-C(1)-C(2 1) 1 14.63(16), N(2)-C(1)-C(2 1) 1 19.1 1(16), N(3)-C(8)-C(36) 127.44(16), N(4)- C(8)-C(36) 1 1 1.17( 17).

2.4 Preparation of amidinate complexes

2.4(1) - Diaikylaiuminumamidînate complexes

The discovery of the heterogeneous Zigler-Natta catalytic system, Al(CzH&

Tic&, has revolutionized chernical industry and propelled it towards the search of

homogeneous catalytic ~ ~ s t e r n s . ~ ~ Novel ~trogen- based compounds, with potential

catalytic act ivity, continue to expand this field of study3'. OrganoalumLium compounds

with amidinate ligands have been investigated with respect to homogeneous ~a t a l~s i s '~ .

The ability of the amidinate ligand to change the structure and reactivity of the metal

center by varying substituents on the ligand has been a key factor in the advances made

with alurninum amidiante complexes.39

In order to prepare robust aluminum amidinate complexes, the amidines 2.6a and

2.6b were dissolved in toluene and reacted with an excess of AI(CH3), in hexane and

stirred oveniig ht (Sc heme 2.5).

2.8a, R = isopropyl 2.8b, R = cycIohexyl

Scheme 2.5 - Preparation of alumioum amidinate complexes

After solvent removal in vacuo the solid material was recrystallized fiom Etfi

and toluene respect ively. The result hg well-de fmed block crystals were identified as

2.8a and 2.8b by the characterization data given in Table 2.7 and by X-ray

crystal tograp hic mlysis.

Tabte 2.7 - Characterization data for aluminum ami(

Data Narne Structure

Molecular formula Elemental Anaiysis

Molecular weight Yield Meltinn voint IR (cm-') C-N

i z 7 ~ 1 - NMR ['Hl-- AI-CH3 N-CH

C, 81.1 1; H, 7.63; Al, 5.52; N, 5.73% C, 76.32; H, 7.55; N, 5.02%

170 (verv broad)

not O bserved

liante complexes, 2.8a and 2.8b

C, 82.36; H, 7.87; AL, 4.74; N, 4.93% C, 77.89; H, 7-78, N, 4.50%

184 (very broad)

- -

not observed

In the IR spectra of the reaction products 2.8a and 2.8b, the N-H stretching

Eequency of the amidines at 3420-3400 cm-' is absent. This is consistent with the

reaction Scheme 2.5. Likewise, NMR studies show the disappearance of the signal

attributed to the N-H resonance. In addition, the isopropyl and cyclohexyl groups

become equivalent. The Ai-CH3 resonances occur at ca. 0.1 ppm- These observations

are consistent with 'H NMR studies of similar compounds with Cz,-syrnrnetric

dialkylalurninum s t ruc t~res .~~ The i 3 ~ N M R signal for AI-C however, is broad due to the

27 Al quadrupole. Similar to previously chacterized aluminum amidinate derivatives,

the 2 7 ~ NMR signal that occurs between 184-1 70 ppm is also broad.I6

2,4(2) Solid state structures of 2.8a and 2-86

The molecular structure and atom-labeling scheme of alurninum amidinate

complexes, 2.8a and 2.8b are illustrated in figures 2.10 and 2.1 1. The packing design for

2.8a is given in Figure 2.12. Crystal data for these compounds are given in Appendix A,

pages A70 and A87 respectively. The crystals of the complexes consist of discrete

molecules that do not display unusual intermolecular interactions.

Figure 2.10 - ORTEP view of the di=ilkylaluiiiinum amidinate cornplex, 2.8a showing the atom labeling scheme. Thermal eltipsoids are s h o w at 50% probability level; selected bond lengths [A]:AI(I)- N(1) 1.9 17(3), Al(1)-C(19) 1.947(3), AI(1)-C(l) 2.351 (4), N(1)-C(I) 1.325(3), N(1)-C(2) 1.465(4), C(1)- C(5) 1.506(5). Selected bond angles r]: N(1)-AI(1 )-N(1 ) 68.6(2), C(19)-Al(1)-C(19) 1 17.4(2), C(1 )-N( 1 )- C(2) 127.8(3), C(1)-N(l )-Al 9 1.1 (2), C(2)-N(1)-AI(1) 14 12(2) N( 1 )-C( I)-C(S) I25.4(2), N(1)-C( 1 )-C(5)- C(6) 64.24(O 20).

Figure 2.11 - ORTEP view of the dialkylaluminum amidinate compiex 2.8b, showing the atom labeling scheme. Thermal ellipsoids are shown at 5û% probability Ievel; selected bond lengths [A]:AI(I)- N(1) 1-936(5), Al(l)-N(2) I.942(5), AL(1)-C(39) 1.944(7), AI(I)-C(1) 1.325(7), N(1)-C(l) 1,325(7), N(I)- C(2) 1.447, N(2>C(1) 1.328(7), C(t )-C(14) 1.508(7). Selected bond angles ["]: N(1)-AI(1)-N(2) 68.5(2), N(1)-Al(1)€(39) 145.8(3), C( 1 )-N( 1)-Al(1) 90.5(4), N(l )-C(I)-N(2) 1 1 O.8(6), C( 1 )-N( 1)-C(2) l26.6(6), N(1)-C(1 )-C(14) l24.S(6), N(l )-C( 1)-C(I4)-C(l5) -69.95(0-75)

Figure 2.12 - Packing diagram of diaikj4aluminum amidinate, 2.8a.

Table 2.8 sumrnarizes selected bond lengths and bond angles of the amidines,

2.6a, 2.6b and their corresponding aluminum amidinate complexes, 2.8a and 2.8b. Also

ïncluded are the alurninum arnidinate complexes reported by ~0rdon . l~ For clarity, the

data in the table refers to the amidine and arnidinate structures given below.

Table 2.8 Selected bond lengtbs and bond angles of amidines and corresponding amidinates

The formation of the four memebered AI-N-C-N ring system delocaIizes the

N-C-N bonding in the amidines. In the arnidines the bonds f?om the nitrogen atoms îo

the carbon center, N(1)-C(l), (C-N) and N(2)-C(1) (C=N) are localized- As revealed

both by crystallographic studies and H NMR studies in solution, these bonds are

equivalent in the arnidinate complexes. Their bond length, 1.325(3)& is between the

single and double bond lengths, 1.368(4)A and 1.282(4)A respectively, of the arnidines.

This is consistent with a bond order of 1.5 in delocalized N-C-N bonding systems.

Furthemore, the bonds fiom the aluminum center to the two nitrogen atorns are

experimentally the same, which confirms the syrnmetrical bonding pattern of the

amidinate complexes, 2.8 (a,b). There is very little change in the bond distances, C-R',

N(1)-R, and N(2)-R, of the arnidinates f?om those of the amidines,

The surn of the bond angles around C(1) is ca- 360°, which confirrns a trigona1

planar geometry, consistent with anticipated spL geometry. However, the 120" N(1)-

C(1)-N(2) angle in the amidines is reduced to a tight 109" due to the presence of the four

membered ring. It is compensated for by an increase in the RI-~(1)-N(I) angle. As

expected, the C(1)-N(1)-R, R-N(1)-AI, C(1)-N(2)-R, and EL-N(2)-AI angles are increased

while the C(1)-N(1)-A1 and C(1)-N(2)-AI angles are ca. an acute 90". They can be

explained by the steric interactions between the rn-terphenyl groups on C(1) and the R

groups on nitrogen atoms that force the lone pair of electrons on the nitrogen atoms

towards the center of the arnidinate ligand. In addition the m-terphenyl group on the

central carbon provides steric protection above and below the plane of the arnidinate

ligand which is clearly illustrated in the projection along the Al-C vector that passes

through seven atoms as shown in Figure 2.1 3. The crystal structure view along the AI-C

vector of 2.8b is given in Figure 2.14.

The Al-CH3 bond length closely resembles the terminal AI-CH3 bond distance

observed by Vranka and Amma in the dirneric trimethylalumhum crystal structurePo

However, the bond angles around the Al center do not represent the bond angles of a

tetrahedron. The acute 68.6", N( 1 )-ALN(2) angle indicates considerable strain around

the Al center. The changes in the bond angles c o n f ï i that the coordination environment

at the Al center has k e n affecteci by the steric interactions of the substituents on the

amidinate ligand.

Figure 2.13 -The seven atoms along the Al-C vector of the diaikylalunainurn amidinate complexes

Figure 214 - View of28b along the AI-C vector

2.4(3) Stability of the dialkylaluminum amidinate complexes

Hydrolysis of the aluminum amidinate complexes, after k i n g exposed to air,

results in the regeneration of the amidine compounds as shown in Scheme 2 .6 .

further hydrolysis

Scherne 2.6 - Hydrolysis of aluminum amidinate complexes

A timed assay of the IR s p e c t m s show that the N-H stretch at CU. 3420 cm-'

reappears only d e r the amidinate complexes have k e n exposed to air for at least fifieen

minutes. This is in s h q contrast to other aluminum alkyl compounds with Al-C bonds

that are highly sensitive to air, moisture and are spontaneously flamrnable in air.'' In

fact, a strong OH band at 3500 cm-' is observed for A1(CHJ3 in hexane, aeer it has k e n

exposed to air for only one minute. The stability of the aluminum amidinate complexes

reported in this thesis may be attributed to the steric protection imparted by the m-

terphenyl group substituted on the central carbon atom of the amidinate ligand.

2.5 Attempted synthesis of amidines with steric bulk o n both C and N centers

The preparation of amidines with steric bulk o n C and N centers was attempted by

frst synthesizùig the compound, N. Nr-dimesitylcarbodiimide, Mes-N=C=N-Mes, via a

two step procedure. The carbodiimide was characterized by sepectrosco pic met hods and

X-ray crystailographic analysis. Its X-ray crystal structure is shown in Figure 2. t 5.

Crystal data are given in Appendix A, page A1 13. A single attempt was made to prepare

the amidine, which was unsuccessful and should to be repeated.

Figure 2.15 -The ORTEP view of the molecular structure of N,Nl-dimesitylcarMiimide showing the labeling scheme

Selected bond lengths [A]: N(1 )-C(1) 1.2 17(2), N(1)-C(I1) 1.409(2), N(2)-C(1) 1.2 12(2), N(2)-C(2 1) 1.407(2); Selected bond angles [ O ] : C(I )-N(1)-C(11) 135.85, C(1)-N(2)-C(2 1) 137.74(17), N(2)-C(I )-N(I ) 167.8(2)

CHAPTER 3

CONCLUSIONS

The rn-terphenyls 2.4(a,b,c) were prepared by the reaction of their trihalobenzene

derivatives with Grignard reagents that proceed via an aryne intermediate. Unusual

[CH3-.I] interactions were observed in cornpounds, 2.4(b,c). The surn of the van der

Walls radii of CH3 and 1 is greater than the distance between the [CH3***I] interactions.

The substituted terphenyl, 2.5 was prepared in good yield through a simple

electrophilic arornat ic substitution reaction. After k ing lithiated, it was reacted with

N,N1-diisopropyl and N,M-dicyclohexyl carbodiimide that resulted in the formation of

sterically demanding amidines 2.6a and 2.6b. The use of two equivalents of BuLi in the

lit hiation process gave the bis-amidines, 2.7a and 2.7 b. Spectroscopic and X-ray

crystallographic data show that the amidine nitrogens are in different chemical

enviro m e n t S.

The ro bust dilaky lalurninum amidinate complexes, 2.8a and 2.8 b were prepared

by reacting their corresponding arnidines with Al(CH3);. Spectroscopic and X-ray

crystallographic data confirm that the Al center of the complexes is attached to both

nitrogen atoms in a symrnetrical bidentate bonding mode.

CHAPTER 4

FUTURE WORK

The intriguing [CH3-a11 interactions observed in the rn-terphenyl compounds

2.3b and 2.3~ should be further investigated to obtain a comprehensive understanding of

their structural chemistry. Solid state crystallographic studies should be performed on

2,6-dimesityl-4-methylbro mo bemene to see if [CH3-.Br] interactions are O bserved.

Synthesis of amidines with steric bulk at both the C and N centers should also be

pursued. MN'-dimesitylcarbodiimide should be prepared on a multigrarn scale and

reacted with 2,6-dimesitylphenyllithium which would result in the bulky arnidine shown

in Figure 4.1. This ligand should stabilize low coordination environrnents in heavy main

group elements. Hence, the coordination patterns and reactivity of the main group

element amidinate complexes with this bullcy ligand should be investigated.

Figure 4.1 - An amidine with steric bulk on C and N centers

Multiple lithiations of 2,4,6-triphenylbromobenzene should be attempted to

ascertain the positions o f lithiation as well as to establish the maximum number of

amidine fünct ional ities that can be incorporated ont0 the trïphenylp heny l fiarne work.

The chernistry ofpoly-amidines should also be examineci.

CHAPTER 5

EXPERTMENTAL METHODS

5.1 General

An M-Braun UL-99-245 dry box and standard Schlenk techniques on a double

manifold vzcuurn line were used in the manipulation of air and moisture sensitive

compounds. Anhydrous solvents were used as received ftom Aldrich Chemicai

Company. NMR spectra were recorded on a Bruker AC 250 spectrometer in five

millimeter quartz tubes at the Atlantic Region Magnetic Resonance Center. 'H and

I3C{'EI) chernical shifts are reported in parts per million (pprn) downfeld fkom

tetramethylsilane (TMS) and are calibrated to the residual signal of the solvent. The ''AI

NMR were obtained on a Bruker AMX 400 spectrometer in a 10 mm tube with

[AI(H~O)~]'+ as external reference. Infiared spectra were obtained using a Perkin-Eimer

Mode1 683 spectrometer with the % transmittance values reported in cm-'. Melting

points were measured using a Mel-Temp apparatus and are uncorrected. Elemental

analyses were performed by At lant ic Micro lab (Norcross, Ga). Electron impact mass

spectral data were obtained at Simon Fraser University (Burnaby, B.C.) using an WP

5985 GC mass spectrometer-

Details of referenced procedures are given due to extensive changes made in the

preparation of the compounds mentioned.

5.2 Synthesis of m-Terphenyl precu mors

5.2(1) - 2,6-Dibmrnoiodobenzene (2.3a) 3' To a stirred suspension of 2,6-dibromoaniline (20.0 g, 79.7 mrnol) and

concentrated HCI (80 ml), N&O2 (6.6 g, 95.6 mmol), disso lved in ca, 30 ml water was

added drop-wise, while keeping the reaction mixture on ice. The resulting yelIow

solution was stirred for I h and poured through a g las wool filter into a stirred solution of

KI (133 g, 801 mm01 in 200 ml water)- After 2 h of stirring, 50 ml of 1 N NazS03 was

added to the reaction flask and the resulting mixture was extracted with CH2C12- The

combined organic iayers were washed with 10% NaOH, water, and then dried over

anhydrous MgSO4. After solvent removal, the solid was recrystallized from warm

toluene. The pale yellow crystals were characterized as 2,6-Dibromoiodobenzene (22.4

g, 61.9 rnrnol, 78%), mp. 93-94OC, (lit. 98-99°C).

IR (Nu.04 cm-'): 15401-11, 1 4 2 0 1 ~ 1 2 4 0 ~ 1200m, 1 l8Om, 1 1 4 0 ~ 1 1 1 Om, 7 7 0 ~ 720m.

'H NMR (CDCI,): 6 = 7.55 (d, 2H, JH-H 7.9 Hz), 7.06 (t, lH, JH-H 7.9 Hz).

13 C{'H)NMR (CDCS): 6 = 13 1.1, 130.3, quaternary carbon signals not observed.

MS (70 eV, rnfz %): 364 (M+2) (49), 362 (h/lf) (100), 337 (19), 235 (40), 233 (20) 156

(22), 154 (24), 127 (28), 75(37), 74 (36).

5.2(2) - 2,6-Dibromo-4-rnethyliodobenzene (2.3 b) '' To a stirred suspension of 2,6-dibromo-4-methylaniline (25.0 g, 94.3 rnmol) and a

1:l h u r e of concentrated HC1 and glacial acetic acid (160 ml), an aqueous solution of

NaN02 (7.80 g, 113 mmol in 40 ml water) was added drop-wise while maintaining the

temperature below 5OC, and stirred for I h The resulting yellow solution was decanted

and filtered through g las wool into a stirred solution of EU (156 g, 940 mm01 in 250 ml

water) and stirred for lh. To the resulting brick red suspension, 330 ml CH2C12 and 100

ml 1 N Na2S03 were added respectively. The aqueous layer was extracted twice with

CH2C12. The combined organic layers were washed with 10% NaOH and water and dried

over anhydrous MgS04. M e r solvent removal, the solid was dissolved in wann hexane

and filtered to remove insoluble irnpurities. The filtrate formed a crearn colored solid

that was characterized as 2,6-Dibrorno-4-methyliodobenzene (26.0 g, 69.2 rnmo l, 73 %),

mp. 59-61°C, (lit. 5 1-540~)".

IR (Nujol, cm-'): 1525111, 1405s, 850111, 740s.

'H NMR (CDCl3): 6 = 7.4 (s, 2H), 2.55 (s, 3H).

')c ('H) NMEt (CDC13): 6 = 141.1, 132.0, 130.9, 130.8,20.4.

MS (70 eV, m/z %): 378 (M+2) (47), 376 (m (LOO), 374 (49), 297(33), 295 (32), 170 (43), 168 (43), 127 (33), 89 (71), 63 (30).

5.3 Synthesis of m-Terphenyls

5.3(1) - 2,6-Dimesityliodobenzene (2.4a)31 To a solution of 2,6-Dibromoiodobenzene (12.0 g, 33.2 mmol) in 100 ml of THF,

100 ml (1 00 mmol) of L M 2-mesitylmagnesium bromide was added drop wise, and

stirred for 3 h at room temperature. To the resulting reaction mixture, 12.7 g (50.0 mmol)

of iodine was added and stirred overnight. This was dissolved in CU iOO ml of 1 N

Na2S03 and extracted with ether. The organic layer was washed with water, then with

saturated NaCl and dried over anhydrous MgS04. After filtration and solvent removal,

the residue was recrystallized fiom hexane. The white solid was characterized as

2,6-dimesityliodobenzene (6.78 g, 15.4 mmo l,47%) m.p. 22 1-222°C.

IR (Nujol cm-'): 850w, 800w, 740m.

'H NMR (CDC13): 6 = 7.46 (t, IH, JH-H 7-3 HZ), 7.07 (d, 2H, JH-H 7.3 HZ), 6-96 (S 4H),

2.35 (s, 6H), 1.98 (s, 12H).

' 3 ~ ( ' ~ ) ~ ~ ~ (CDCl3): 6 = 135.4, 128.1, 127.8, 21 -2, 20.2, quaternary carbon signals

not observed.

MS (70 eV, m/z %): 440 (100), 298 @O), 283 (20), 133 (17).

5.3(2) - 2,6-Dimesityl-4-methyliodobenzene (2.4b) The synthesis of 2,6-dimesityl-4methyliodobenzene followed the procedure

given for the synthesis of 2,6-dimesityliodobenzene. To a suspension of 2,6-dibromo-4-

methyliodobenzene (25.0 g, 66.5 mmol), in 200 ml of THF, 200 ml (200 mmol) of 1 M 2-

mesitylmagnesiumbromide was added &op-wise and stirred for 3 h at room temperature.

To the resuiting precipitate, 25.3 g (99.8 rnmol) of iodine was added and stirred

overnight. The reaction mixture was then dissolved in ca. 200 ml of 1 N Na2S03 and

extracted with ether. The organic layer was washed with water and saturated NaCl and

dried over anhydrous MgS04. After solvent removal, the white solid was recrystallized

from warm toluene resulting in large, coloriess crystals. These were characterized as 2,6-

dimesityl-4-methyliodobenzene. (1 1.9 g, 26.2 m o l , 39%), m.p. 2 18-2 19OC.

IR (Nujol, cm-'): 2710w, 161 O m , 1560m,101 O m , 870% 860x11, 850m 750w.

'H NMR (CDCI,): 6 = 6.96 (s, 4H), 6.91 (s, 2H), 2.35 (s, 9H), 2.00 (s, 12HJ

"C{'H}NMR (CDC13): 6 = 146.8, 142.1, 138.7, 137.1, 135.4, 128.6, 128.0,21.3,20.3.

MS (70 eV, m/z %): 455 ( M t l ) (60), 454 (m (100), 327 (27), 3 12 (22). X-Ray: Orthorhombic, space group Pnma, a = 24.0626(12) & b = 9.192495) A, c =

9.8726(5) a = 90°, P = 90°, y = 90°, V = 2183.8(2)A3, Z = 4, D = 1.382 mg.rrï3, p =

1 -472 mm-', R p>2sigma(I)], R1 = 0.0410, wR2 = 0.1243. (H. Jenkins)

5.3(3) - 2,6-Diphenyl-4-methyliodobenzene (2.4~)

The synthesis of 2,6-diphenyl-4-methyliodobenzene followed the procedure given

for the synthesis of 2,6-dimesityliodobenzene. To a suspension of 2,6-Dibromo-4-

methyliodobenzene (12.5 g, 33.3 mmol) in 100 ml of Tm, 100 ml (100 mmol) of 1 M

phenylmagnesiumbrornide was added drop-wise and stirred for 3 h at room temperature.

Iodine (12.7 g, 50.0 rnrnol) was added to the reaction mixture and stirred overnignt. A

solution of ca. 100 ml of 1 N Na2S03 was added to the reaction mixture and the slurry

was extracted with ether. The organic layer was sequentially washed with water,

saturated NaCl, and dried over anhydrous MgS04. After solvent removal, the residue

was dissolved in hot rnethanol and filtered. Upon cooling, the filtrate formed well-

defined crystals that were characterized as 2,4-dipheny l-4-methy liodo benzene. (4.20 g

1 1 -4 rnmol, 34% ) m.p. 100- 102OC.

IR (Nujol, cm-'): 3 0 6 0 ~ 3 0 4 0 ~ ~ 3020s, 14901-11, 1440s, 1370s, 1060m 1030s. 8651-11,

760s, 700s.

'H NMR (CDCl3): 6 = 7.48-7.35 (m lOH), 7.09 (s, 2H), 2.37 (s, 3H).

' 3 ~ { 1 ~ ~ ~ ~ ~ ( C D C 1 3 ) : 6 = 147.9, 145.6, 137.5, 129.7, 129.4, 127.9, 127.3,20.7.

X-Ray: Monoclinic, space group = P2(I)/n, a = 10.78 18(15)& b = 9.0474(13)& c =

16.971(2)% a = 90° ,O = 103.963(3)O y = 90° V = 1606.6(4)A3, Z = 4, D = 1.53 1 rng.m3

p = 1 -98 1 mm-', R [I>Zsigma(I)] R 1 = 0.0246, wR2 = 0.0623 (H. Jenkins)

5.3(4) - 2,4,6-Triphenylbrornobenzene (2.5) 35

To a solution of 1,3,5-trïphenyIbenzene (15.0 g, 48.9 mmol), in 110 ml of CS2, 5

ml, (1 00 mmoi) of bromine was added drop-wise and left stimng overnight. After

solvent removal the residue was washed with hot methanol to give a white, powdery solid

that was characterized as 2,4,6-triphenylbromobenzene (1 7.7 g, 46 .O rnmo 1, 94%), m- p.

128-12g°C, (lit- 129-130°C).

IR: 3 0 4 0 ~ 1360s, 755xn,690m,

'H NMR (CDCI,): 6 = 7.65-7.26 (m, 15H), 7.1 1 (s, 2H).

' 3 ~ { 1 ~ ) ~ ~ ~ (CDCb): 6 = 144.2, 129.5, 128.9, 128.7, 128.0, 127.8, 127.6, 127.0.

MS (70 eV, rn/z): 386 (Mtl) (99), 384 (1 OO), 302 (28) 289 (27).

5.4 Synthesis of amidines

5.4(1) - N,N'-diisopropyC2,4,6-trip henylbenzamidine (2.6a) "" To a suspension of 15.0 g (38.9 mmol) of 2,4,6-triphenylbromobenzene in 60 ml

anhydrous diethylether and 10 ml anhydrous hexane, 25.0 ml (40.0 m o l ) of 1.6 M

butyllithium was added drop-wise, and stirred for 4 h at room temperature. To the

resulting bright yellow solution, 5.0 g (39.6 rnmo 1) of IV, NI-diisopropylcarbodiirnide

dissolved in ca 15 ml of THF was added drop-wise, and stirred overnight. After

quenching with water, the reaction mixture was transferred to a separatory fume1 and

extracted with CH2Ch. The organic layer was washed with water and saturated NaCl and

dried over anhydrous magnesium sulfate. AAer rernoval of so lvent, the yellow solid was

dissolved in warm toluene and filtered to remove insoluble white LiBr. Upon cooling,

the filtrate formed well-defmed crystals that were characterized as MN'-diisopropyl-

2,4,6-triphenylbeflzafnidine (8.14 g, 18.8 mrnol, 48%), m-p. 159- 1 60°C.

Elemental Anal: Calcd: C, 86.07; H, 7.46; N, 6.48 %

Found: C, 86.09; H+ 7-51; N, 6.45 %

IR (Nujol., cm-'): 3 4 2 0 ~ ~ 3080w, 3 0 4 0 ~ ~ 3 0 2 0 ~ 1620s7 1590s, 1490s, 1480s, 1445s,

13 tom, 2601-11, 1 1 8 0 ~ 890m,770s, 725m, 700s.

I H NMR (CD2CI2): S = 7.66-7.27 (III, 17H), 3.77 (b, IH), 3.43 (b, IH), 3.14 (b, lH), 1.03

(b, OH), 0.55 (b, 6H).

' 3 ~ { ' ~ } ~ ~ (CD2C12): 6 = 152.0, 142.9, 142.2, 141.8, 141.7, 140.8, 133.3, 129.7,

128.6, 128.5, 128.3, 128.2, 128.0, 127.9, 127.7,25.0, 22.6.

MS (70 eV, d z ) : 432 (M+) (13), 374(21), 355(100) 332(92), 58 (26), 43 (47).

X-Ray: Orthorhombic, space group P21212~, a = 10.979(2)& b = 28.248(2)& c =

8.229(2)& a = 90°, P = 90°, y = 90°, V = 25552.2(7)& Z = 4, D = 1.126 rng.nY3, ,u =

0.495 mm-', R p.2sigma (I)] RI = 0.0326, wR2 = 0.0841. (S. Carneron)

5.4(2) - N,N'-Dicyclohexyl-2,4,64riphenylbenzarnidine (2.6b)

The synthesis of 2.6b followed the procedure given for the synthesis of N,N'-

diisopropyl-2,4,6-triphenylbenzamidine, 2.6a. A suspension of 7.70 g (20.0 mrnol) of

2,4,6-triphenylbromobenzene in 30 ml anhydrous diethylether and 5 mi hexane was

stirred at room temperature. To this. 15.0 ml (24.0 m o l ) of 1.6 M butyllithiurn was

added dropwise and stirred for 4h. To the resulting yellow solution 4.50 g (2 1.8 mrnol)

N,Nldicyclohexylcarbodiimide dissolved in CU. 10 ml T l 3 was added drop-wise and

stïrred oveniight. After quenching with water, the reaction mixture was extracted with

CH2Cl2, washed with water and saturated NaCl and dried over anhydrous MgS04. M e r

solvent removal the yellow soIid was dissolved in warrn toluene and filtered to rernove

insoluble LiBr. Upon cooling, the filtrate formed well-defmed crystals that were

characterized as 2.6b. Yield, 5.85 g (1 1.4 mm01 50%). m.p. 189-1 90°C.

Elemental Anal: CaIcd: C, 86.67; H, 7.86; N, 5.46 %

Found: C, 85.33; H, 8.02; N, 5.34 %

IR (Nujol, cm-'): 3400s, 3080111, 3 0 6 0 1 ~ 1620s, 1590s, 13001q 1280w, 12501x1, 890m

775w, 760m,700s.

'H NMR (CD2C12): 6 = 7.80-7.26 (m, 17H), 3.12 (b, lm, 2.85 (b, IH), 2.37 (s, lH),

1.85-0.13 (III, 19H).

"c{'H)NMR (CDzC12): 6 = 142.5, 140.9, 140.6, 138.5, 136.9, 133.8, 129.5, 129.4,

129.3, 128.7, 128.2, 128.0, 127.8, 127.5, 127.0, 125.8, 125.6, 36.9, 36.6, 35.1, 34.3, 33.8,

32-4,31.9. 26.9,26.7,26.1,26.0, 25-9,25.8, 25.6,21.7.

MS (70 eV, rn/z %): 513 (M+l) (5), 512 (M?) (7), 429 (74), 347(88), 332(99), 330 (48),

3 17 (32), 98 (50), 83 (21), 67 (18), 56 (28), 55 (lOO), 42 (1 5).

X-Ray: Monoclinic, space group P Zlh, a = 12.089(4)& b = 16.87195)A, c =

14.998(3)A, a = 90°, f l = 103.5 1(2)O, y = 90°, V= 2975(2)A3, Z = 4, D = 1.145 mgam", p

= 0.66 mm-', R p>2sigma(I)] R1 = 0.0526, wR2 = 0.1416. (S. Cameron)

5.5 Synthesis of Bk-amidines

5.5(1) - Bk-Nfl"-Diisopropyl-2,4,6-triphenylbenzamidine (2.7a) To a suspension of 15.0 g (38.9 rnmol) 2,4,6-triphenylbromobenzene in 60 ml

anhydrous diethylether and IO ml anhydrous hexane, 50.0 ml (80.0 mrnol) of 1.6 M

butyllithium was added &op-wise and the reaction mixture was stirred for 4h at room

temperature, To the resulting solution, 5.0 g (39.6 mrnol) of N,N'-

diisopropylcarbodiimide dissolved in ca 15 ml of THF was added &op-wise and stirred

overnight. After quenching with water, the reaction mixture was extracted with CH2CI2.

The organic layer was then washed with water and saturated NaCl and dried over

anhydrous MgS04. After removal of solvent, the reminkg solid was dissolved in warm

toluene and filtered to remove insoluble LBr. Upon cooling, the filtrate forrned well-

defined crystals that were characterized as 2.7a. (6.0 g, 10.7 m o l , 54%), mp. 197-

198°C.

Elemental Anal: Calcd: C, 8 1-68; H, 8.30; N, 10.03 %

Found: C, 8 1-48; H, 8.43 ; N, 9.82 %

IR (Nujol, cm1): 3 4 0 0 ~ 3 l8Os, 3 12011-1, 3060x11, 3 0 2 0 ~ ~ 3010s, 1620s, 1610s, 1590s,

1540s, 1490~x1, 1445s, 1435s, 1350s. 1 3 2 0 ~ 23101~ 1290111, 1 1 7 0 ~ 1150m, 1120m,

8 8 0 ~ 765s, 750s, 700s.

'H NMR (CDClr): 6 = 8.02-7.16 (m, 16H), 3.74 @, lH), 3.51 (b, 2H), 3.28 (b, l m , 2.35

(b, lH), 1-85 (b, l m , 1.43-0.18 (Q 24H - CH3's )-

' 3 ~ { ' ~ } ~ ~ ~ (CDCls): 6 = 152.6, 140.3, 129.3, 128.7, 128.3, 127.5, 127.3, 127.1, 26.0,

25-6,24.1,22.9.

MS (70 eV, m/z): 558 (m (6), 458 (77), 357(80), 58 (52),43(100).

X-Ray: Triclhic, space group P-1, a = 9.0339(16)& b = 10.1074(18)& c = 18.51 1(3)A,

a = 98.273(3)O, ,û = 90.256(4)", y = 99322(4)", V = 1649.8(5)A3, Z = 2, D = 1.125

mg/m3, p = 0.066 me', R p>2sigma(I)] R1 = 0.0513, wR2 = 0.0972. (S. Cameron)

5.5(2) - Bis-N,NTyclohexyl-2,4,6-triphenylbenzamidine (2.7b)

To a suspension of 15.0 g (38.9 mmol) 2,4,6-triphenylbromobenzene in 60 ml

anhydrous diethylether and 10 ml hexane, 50.0 ml (80.0 mmol) of 1.6 M butyllithium

was added drop-wise and stirred for 4h at room temperature. To the resulting solution,

8 .O g (3 8.7 mmol) of N. NI-düsopropylcarbodiimide dissolved in ca 20 ml THF was added

dropwise and stirred ovemight. After quenching with water, the reaction mixture was

extracted with CH2C12. The organic layer was then washed with water and saturated

NaCl and dried over anhydrous MgS04. After solvent removal, the remaining solid was

dissolved in warm toluene and filtered to remove insoluble LiBr. Upon cooling, the

filtrate formed well-defuied crystals that were characterized as 2.7b. (5.74 g, 7.98 mrnol,

54%), mp. 202-205°C.

Elemental Anal: Calcd: C, 83 S Z ; H, 8.69; N, 7.79 %

Found: C, 83.69; H, 8.80; N, 6.52 %

IR (Nujol, cm-'): 3620w, 3400- 3 2 0 0 ~ 3060m, 1620s, 1590s, 1540s, 1490s, 1 3 2 0 ~

1 3 0 0 1 ~ 1 2 5 0 ~ 1 1 Som, 1 lOOw, 890s, 760s, 730s, 700s.

'H NMR (CDCl3): 6 = 7.71-7.13 (m, 16H), 3.51 @, ZH), 3.06 (b, l m , 2.82 (b, lH), 2.61

(b, IH), 2.36 (b, lH), 1.69-1.00 (a 40H).

"C{~H)NMR (CDCb): 6 = 129.2, 129.1, 128.9, 128.72, 128.2, 128.1, 127.4, 127.4,

127.2, 126.9, 125.3,25.4, 25.1, 21.5.

5.6 Synthesis of amidinate complexes

5.6(1) - [(C6H2Ph3)C( Ni-Pr)2Al(CH3)21, (2.8a)

MN'-Düsopropyltriphenylbenzamidine (1 .O0 g, 2.3 1 rnmol) was dissolved in ca.

20 ml of toluene. 2 ml (4.0 rnmoI) of 2M AMe3 in hexane was added drop-wise and

stked over night. The solvents were rernoved in vucuo, and the resulting solid was

dissolved in diethylether and filtered to remove a small arnount of insoluble material.

Upon standing for one day, large cubic crystals were isolated and characterized as

[(C3H17N)2C((Ph)3Ph)Al(CH3)d- Yield, 0.55 g, 1.12 rnrnol, 50%. mp. >250°C.

Elemental Anal: Calcd: C, 8 1.1 1; H, 7.63; N, 5-73; Al, 5.52 %

Found: C, 76.32; H, 7-55; N, 5-02 %

LR (Nujol, cm-'): 3080w, 3040w, 3020w, 1490m 1370% 13401-11, 1270w, 1 l8Ow,

1 120w, 890w, 7 7 0 ~ 760q 7 2 S q 700s, 6 8 0 ~ 6 6 5 m

1 H NMR (CD2Cl2): 6 = 7.81-7.33 (m, 17K), 3.00 (s, 2H), 0-48 (s, 12m, -0.82 (s, 6H).

1 3 c { ' ~ ) ~ ~ F t (CD2Ch): 6 = 142.0, 140.6, 129.7, 129.4, 128.8, 128.2, 127.6, 25.0, -10.2

(very broad) .

"AI NMR (C6Ds) : 6 = 170 (very broad).

X-Ray: Orhorhombic, space group Pbcn, a = 14.1 15(3)A, b = 15.5 15(3)A, c =

1 3.377(3)A7 a = 90°, P = 90°, y = 90°, V = 2929.5(9)A3, Z = 8, p = 0.759 mm-', R

D>2sigma (I)] R1 = 0.0372, wR2 = 0.0953. (S. Cameron)

5.6 (2) - [(C~HZP~~)C(NC~)ZA~(CH~)~~, (2-8b)

The synthesis of this compound is sirnilar to that of 2.8a. 2.6b (1.00 g, 1.95

rnmol) was dissolved in ca. 20 ml of toluene, 4 ml (8-0 rnmol) of 2M Able3 in hexane

was added drop-wise and stirred overnight. The solvents were rernoved in vacuo, and the

resulting solid was dissolved in toluene and filtered to remove a small amount of

insoluble material. Upon standing for one day, colorless crystals were isolated and

characterized as [(C3Hi7N)2C((Ph)3Ph)Al(CH3)Z]3 Y ield, 0.70 g, 1 -23 rnmo 1, 64%. m.p.

222-225°C.

Elementai Anal: Caicd: C, 82.36; H, 7.97; N, 4.93; Al, 4.74 %

Found: C, 77.89; H, 7.84; N, 4.50 %

IR (Nujol, cm-'): 1630111, 1590w, 1 2 5 5 ~ 1 0 7 5 ~ 1030m, 890m, 800m 760m, 750111,

700s, 680111

'H NMR (CD2Ch): 6 = 7.76-7.33 (m, 17H), 1.38 (s, 2H), 0.72 (s, 20H), -0.77 (s, 6H).

' 3 ~ { ' ~ ) ~ ~ (CDzCh): 6 = 170.3, 142.7, 142.0, 140.9, 129.6, 129.4, 128.8, 128.8,

128.4, 128.2, 127.5, 125.6, 35.7, 25-9, 25.8, -8.0 (very broad).

"AI $&fR (C6D6) : ô = 184 (very broad).

X-Ray: Monocluùc, space group PZi/c, a = 13.619(2)& b = 12.291(2)& c =

20.958(2)% a = 90°, P = 102.002(8)0, y = 90°, V = 343 1.3(7)A3, 2 = 4, p = 0.712 mm-', R

D>2sigma (I)] R1 = 0.0453, wR2 = 0.0968. (S. Cameron)

5.6(3) - Attempted synthesis of other Amidinate complexes

In an attempt to prepare amidinate complexes of other main group elements,

stoichiometric quantities of 2.6a and 2.6b were combined with 1.6 M BuLi, 1 M PhMgBr,

1 M BCG, Ph2PCl, and 1,3- 1 -dimesity-imidazo 1-2-ylidene. Products were iso Iated, but

due to difficulty in transfer to Halifax for analysis, these were not comprehensively

characterized.

5.7 Synthesis of Amidine Precursors

5.7(1) - ~,~~(2,4,6-trirneth~l~hen~l)th i ~ u r e a ' ~ (Carbodiimide precursor) To a mixture of 100 ml (712 mmol) of 2,4,6-trùnethylaniline and 100 ml (1.7

mol) of carbon disulfide, 100 ml of 40% sodium hydroxide was added very slowly with

stimng. Next, 100 ml of ethanol was added to the reaction vesse1 and stirred for 2-3 h.

To the resulting dark orange solution, a few ice cubes were added and left ovemight. The

resulting precipitate was washed several tirnes with water and then with hexane. The

white solid isolated was characterized as N,Nr-(2,4,6-trimethylpheny1)thiourea (37.0g,

119 mrnoI, 33%), m.p. 195497°C.

IR (Nujol, cm-'): 3340q 3 2 6 0 ~ 3 180x11, 2140% 1525s, 1490s, l34Om, 1240rns, 1 2 2 0 ~

1200m,870m, 855m

' H NMR (CDCI,) : 6 = 6.86 (s, 2H), 6.49 (s, 2H), 2.3 8 (s, 6H), 2.25 (s, 12H). ' 3 ~ { ' ~ ) ~ ~ ~ (CDC4): 6 = 136.1, 129.8, 129.1, 21.1, 18.5, 18.1. quatemary carbun not

O bserved.

MS (70 eV, d z ) : 312 (m (58), 297 (100), 278 (29), 135 (81), 134 (49), 120 (31), 91 (29)-

5.7(2) - ~,~~-(2,4,6-trirneth~1~hen~l)carbodiimide~

N,Nt-dimesitylthiourea (35.0 g 1 12 rnrnol) was stirred with 500 ml of

di~hiorornethane~ 500 ml of 5% sodium hypochlorite (NaOC 1, commercial bleach-Javex),

15 g of sodium carbonate and 0.8 g of copper(I) chloride were added to the reaction

vesse1 and stirred for ca. 48 h. The reaction d u r e was extracted with water and dried

over anhydrous MgS04. After solvent removal, methanoühexane, 75/25, was added and

the resulting precipitate was filtered. The filtrate, which was covered and lefi at room

temperature, formed large, orange cryst als that were c haracterized as

NN'-(2,4,6-trimethylpheny1)carbodiimide (6.97 g, 25 mmol, 22%), mp. 3 5-3 8°C.

R (Nujol, cm-'): 2160s, 2080s, 1210w, 905w, 850w.

'H NMR (CDC13): 6 = 2.389 (s, 18H), 6.848 (s, 4H).

1 3 ~ ( ' ~ ~ ~ ~ ~ (cDc~~): 6 = 129.8, 129.1, 128.9, 128.8,21 .O, 20.7, 18.5.

MS (70 eV, d z ) : 278 (M+) (100), 145 (17), 91 (15).

X-Ray: Trïclinic, space group-1, a = 8.4412(6)% b = 8.6584(6)% c = 1 1.7739(9)A, a =

76.7430(10)O, 8 = 75.5140(10)0, y = 82.6940(10)O, V = 808.74(10)A3, 2 = 2, 0 = 1.143

mg/m3, p = 0.067 mm-', R [I>2sigma(I)] R1 = 0.0520, wR2 = 0.1667. (H. Jenkins)

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Crystaiiographic data for compounds

2.4 (b,c), 2.6 (a,b), 2.7a, 2.8 (a,b), N,N'-dimesityicarbodiim ide

Crystallographic data for the compound 2,6,-dirnesityl-4-methyliodobenzene

2.4 b

Table 1. Crystal data and structure refinement for jcl4m.

Identification code jcl4m

Empirical formuta C25 H27 1

Formula weigh t 454.37

Temperature 223(2) K

Wavelength 0-7 1 073 A

Cxystal systern Orthorhornbic

Space group Pnma

Unit cet1 dimensions a = 24.0626(12) A b = 9.1924(5) A c = 9.8726(5) A

Volume 2183.8(2) A3

z 4 Density (calculateci) 1.382 Mg/m3

Absorption coefficient 1.472 mm-'

F(000) 920

Crystal size -2 x .3 x -3 mm3

Theta range for data collection 1-69 to 25-00".

index ranges -2g

Table 2- Atornic coordinates ( x IO4) and equivalent isotropie displacement parameters (A2x IO3)

'J tensor- for jcl4m. U(eq) is defined as one third o f the trace of the orthogonalized U.'

Table 3. Bond lengths [A] and angles [O] for jcl4rn.

Syrnmetry transformations used to generate equivalent atoms:

# 1 &-y+ l12,z

Table 4. Anisotropic displacemen t parameters (AZx 1 03) for jc I4m - The an isotropie displacement factor exponent takes the form: -29[ h2 a*2U1' + ... + 2 h k a* b* UI2 ]

A8

Table 5. Hydrogen coordinates ( x f 04) and isotropie displacemen t parameters (A2x 10 3,

for jcl4m.

Crystallograp hic data for the compound 2,6-dipheny i-4-met hy liodo benzene

4 . 3 ~

Volume

z Density (calculated)

Absorption coefficient

F(000)

Crystal size

Theta range for data collection

index ranges

Reflections colkcted

independent reflections

Completenes to theta = 26-00"

Absorption correction

Refinement method

Data / restraints / parameters

Goodness-of-fit on F2

Final R indices [1>2sigma(l)]

R indices (al1 data)

Extinction coefficient

Largest diK peak and hole

Table 1. CrystaI data and structure refinement for jason23m.

Identification code jason23m

Empirical formula Cl9 Hl5 I

Formula weigh t 3 70.2 1

T m perature 293(2) K

Wavelength 0.71073 A Crystal system Monoclinic

Space group P2( 1 )/n

Unit ce11 dimensions a = 10.78 18(15) A b = 9.0474(13) A

c = 16.971(2) A 1606.q4) A3

4

1.53 1 Mg/m3

1.98 1 mm-'

728

-2 x .2 x -3 mm3

2.04 to 26.00°.

- 1 ()

Al 1

Table 2. Atomic coordinates ( x IO4) and equivalent isotropie displacement parameters (A2x [ O 3 )

for jason23m. U(eq) is defined as one thud of the trace of the orthogonalized UG tensor.

Table 3. Bond lengths [A] and angles [O] for jason23m.

Symmetry tram fmations used to generate equivalent atorns:

A14

Table 4- Anisotropic displacement parameters (&x IO3) for jason23m. The anisotropic

displacernent fâctor exponent takes the form: -2$[ h2 a*ZU[ [ + ... + 2 h k a* b* V 2 ]

A15

Table S. Hydrogen coordinates ( x 1 04) and isotropie disp tacemen t parameters (AZx 10 3,

for jason23rn-

H(3A)

W A )

W7A)

H(7B)

W7C)

H(12A)

H(13A)

H(14A)

H( 1 SA)

H(16A)

H(22A)

H(23 A)

H(24A)

H(25A)

H(26A)

Crsytallographic data for N, N '-diisopropyl-2,4,6-trip henylbenzarnidine

2.6a

T a b l e 1. Crystal data and structure refinement.

Identification code

Empirical formula

Formula weight

Temperature

Wavelength

Crystal systern

Space group

Unit ce11 dimensions

Volume

z

Density (calculatedl

Absorption coefficient

F ( 0 0 0 )

Crystal size

Theta range for data collection

Index ranges

Reflections collected

Lndependent reflections

Absorption correction

Max- and min, transmission

Refinement method

Data / restraints / parameters

Goodness-of -f it on F~

Final R indices [ I > 2 s i g m a ( I ) ]

R indices ( a l 1 data)

jason42

C31 832 N2

432 . 6 1

293 ( 2 ) K

1 - 5 4 1 8 i

Orthorhombic

P212121

a = 1 0 . 9 7 9 ( 2 ) A alpha = 90° b = 2 8 . 2 4 8 ( 2 ) a beta = 90° c = 8 . 2 2 9 ( 2 ) A gamma = 90°

2552.2 (7)A3

4

1 .126 ~ ~ / m ~

0 ,495 mm-'

928

0 - 5 0 x 0 .50 x 0 .30 mm

3.13" to 63.56O

0