,

, .

STUDIES OF GROUP VI I I TRANSITlOt: .flETAt, PPrJSPHItlF COMPLEXES

•

..

,I

STUDIES .OF OROuJ,

•

IAAflSITION METJ\L',- PHOSPHPIE COMPLEXES

by

~HLLIAll JANES LOUCH. B. Sc.

I

A Thesis

./ Submitted to the Faculty of Gradua te Studi es

in Partial Fulfilment of the p,equirements

f0'O the Degree

~Doctor of Philosophy

•

McMaster University

. January 197il.

~ William James Louch , 1974D (

..~

,DOCTOR OF PHILOSOPHY

. (.Chemi stry}

"

MeI-'ASTER UNIVERS lTYHamilton. Ontario.

d

TITLE: Studies of Group VIII Transition Metal Phosphine Complexes

the Group VIII transition metal series. The

the results of a study of phosphine complexes

of some selected mem

.AUTHOR: . Hilliam James Louc.h. B.Sc. (McMaster)

SUPERVISOIi: Dr. D. R. Eaton

NUMBER OF PAGES: IX. 170

SCQPE AND cormNTS: ~

This work descr'~es

aim of this work was to investigate possible correlations between the

·electronic properties of these metal :9mplexes "and their stabilities, ..

<HId .lil~ilities. It was felt that such a study miaht prove sionificant

since many of the complexes studied are catalytically active in a number

of homoaeneous systems. Elucidation of the factors influencina the

efficiency of such homogeneo~s catalytic systems is important from both

practical and theoretical points of view.

Some electronic properties of the complexes were investigated•using a 19F Nuclear Magnetic Resonance technique. This method is

based upon th~measurement of the 19F chemical shifts of complexes of

(pFC6H4)3P and (m-FC6f14)3P" The results of this aspect of the work are

discussed in Chapter V; i.e .• the data is discussed in terms of the

"electron affjity" of the _central metal. LIn order to study the correlation of the "electron affinity" of

./the central metal with the rates and equilibrium constants for reactlons

_ of these complex~s. a 'number of li?and exchange reactions were studied.

Chapter III presents the results for such reactions .of some palladium(II)

phosphine complexes. In the course of this Mork the fo~tion of four

coordinate palladium phosphine cations was demonstrated. Tre forma~ion

1i ~

~separticuL

-'

was shown to be,highlY,sensitive to the nature of the

phosphine used. Chapter IV \presents the resu'lt's for SOrle

.phosphi e ligand exchan~e ~eactions of the complexes trans[(C6HS)3PI2MCOX

(r~ ~ ftlf a d Ir., X ~ C1, ·flrani I) JS I'le11 as some exchange reactions of.the complexes [(C6HS)lJ 3RhX (X = Cl, flr and I). It I'las shown that

the course of these reactions was hiahly dependent upon the nature of

the particular phosphine used in the exchange reaction and on the halide

present.

The results described in ~hapters III, IV and V are discussed

at SOlne len{)th in Chapter -'Ii. In -this final chapter"; it is arcued..that the resul ts of the preceeding three ch~ters can be rational ized.

in terr'1s of the donor and acceptor properties of

acceptor and donor properties of the metal .. The

toe ligands and the19results of the r nmr

study are used to provide a mea~ure of the acceptor properties of the

metal complexe~ and data from the lit~rature, based primarily on infra-

red studies are used as a basis for discussion of ligand donor properties.

The results presented are consistent with the hypothesis that maximum

stability is achieved by optimum matchina of liaand donor/acceptor prop­

erties Ivith the ~ccePtor/donor propefties of. the metal.

Chapters I and II are largely introductory. IChapter I includes

a brief review of .t~e chemistry of the complexes and ligands discussed 'i

in this work. Chapter II 'lives the basic theories to nuclear magnetic,

resonance, and conduct i vi ty, the two, phys i ca1 techn iques used throughout

the experimental \'Iork reported in this thesis.

,.

iii

/

/

\

ACKNOliLEDGEI:Ern,

The outhor ,)'iOuld 1ike to groteflllly ocknowl edge the guidance

ond encourogement extended to him duri ng the course of thi s ~:ork by

the members of ~he magnetic resononce group ond in porticulor to Dr.

D. R. Eoton. In oddition'ihonks ore ex(ended to the N1m staff both at

Hdloster University and the Conodion 220 r·IHz rmR Center. Finally,,

the potience and understonding of my l'life, Fay, mode the completion

of this \-Iork possib,le.

I,j

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iv

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CHAPTER

TABLE OF corlTEIITS

PAGE

Introduction to the Chemistry of Group VIII Phosphine

Complexes.

2-5 Conductivity

II Theory of Nuclear r'agnetic Resonance and Theory of

Conductivity -'\

'2-1 Introduction to Nuclear r'a~netJc Resonance

t1f~R and Ra te Processes,~

Exchange Lifetimes from

I

1-1

1-2

2-2

2-3

2-4

}n'troduction

Chemistry of Phosphine and Substituted Phosphines, '

Transition Metal Phosphine Co~rlexes

\Chemistry of Group VIII Phosphine Complexes

\

NNR Spectra of Coordinated r~ethyl Phosphines \

1

1

5

6

9

24~

2<1

3-( \,13

35

39

2-6 Experimental Considerations Re0ardin~ Conductivity

Measurements 40

,2-7 Conductivity in Non-Aqueou~Solutions 40

III Studi.cs on Pa 11 adi um{ I I) Phosphine COPlplexes

3-1 Introduction

3-2 Experlmenta 1 Results '\ "A. III I1MR Resu1 ts

B. Conducti vity Results

3-3 SUlT1T1ary

3-4 Exper'lmenta 1 ~-

"~/ v

<12

43

43

59

71•72

J

CIiJ\Pl'ER

,1(

PAGr

IV S;udies on Rhodium!I) and Iridium!I) Phosphine Complexes

4-1 Introduction

4-Z Expe,-itllental Results

7~

74

77

4-3 . Exc/Jan<le f(eaction of' Rhodiul'l!I) and Iridium!I) Carbonyl

Phosphine Complexes wit~ !CH3)(C6

H5)l find

(CH3)2(CGH5 )P 77

4-4 .ExchalHlC Reactions of'Rhodiuni(I) "alide Conllllexes wittl

(CH3)(CG

H5)l and (C"3)Z(C6H5 )P .07

4-5 Summary ]113••

V. 19

NNR Study of Complexes of (rC6':4 )l lOR .F •5-1 Introduction lOR

f\'5-2 Substituent Parameters ". .100\.

19r m·m Chemi ca 1 Shi its "5-3 as an [1 ectron Density Prone ]] G.•

5-4 Discussion 123

5-5 ExperiT:1Cntal 133

VI Discussion of. RlYsul ts .13G

6-1 . Relative Stability.

137

6-2 Relative lability 138

6-3 Donor/Acceptor Properties 139

6-4 Palladium(II) Phosphine C?mplexes.- 140

6-5 Rhodium(I) and Iridium(I) Pllosphine Complexes 152

APPEflDIX Determination of Relative Equil ibrium Constants

IllIOGRAPHY

, .

vi

.. ~1(;4

~ ,"

(

LI ST OF, TAI1USJ'

TML r "\ PAGE

1-1 Hydroqcn L1ptake 'of Solutions Con-tainino [RhCl (C8

H4

}212

and Val'ious Phosphines. 15

l-?..... ' '-

2-1

Kinetic Pal'a~letel's for Ligand Exchange in L2~'X2 Systems.'

Oissocia~ion Constants fOrKI in Various Solvents. 41~

3-1

3-2

3-3

NMR Results for tIle Complexes L/tX2 and Lltx+ /.

, (L = (CII3

)2(C 6H5

)P) . 47

mlR Rcsul ts for the Complexes LZ

PdX2

. +and LldX 49

Equilibrium'Constants for the Reaction LldX2 + (C6H5)l· 58

3-4 Relati~e Equilibrium tonstants fo~

+ -LldX2 +" L -. LldX + X

3-5 Rates for Exchange Rea~tions of Pa'lladium Complexes.

3-6 Properties of the Complexes L2PdX;~

4-1 mlR Data fOI" Complexes Oerived from trans[(C6

115)ll/COX

4-2 NMR Data for the Complexes L3

RhX

4-3 Rate Data 'for L2

f-lCOX + L

5-1 PKa's in the l1~nzoAc Acid Series.

Tolrwn's Substituent Parameters x.- ,

lIammett P Values for Some Equilibrium

'"

Sizes,of Val>ious Phosphorus Liqands.

vii

131

144

150

67 ~70

n10<1

lOS'

106-

112

113

115

124-125

'131

141-142

Reactions;

/

for the Reaction

(FC6H

4)l Complexes.

(FC6

H4

)(C611r.)l Complexes./- :>

of 01 and v co tor Some Phosphine Carbonyl

Fquilibrium Constants,+ -

L -. LldX + X .

Relative

L/dX2 +

Comparison

Complexes.

Substituent Constants~

"J9 F Chemical Shifts of

19F Chpl1lical Shifts 'of•

6-1

6-2

5-6

5-2

5-3 ;"

5-4

5-5

6-3

!

It,I

I

LIST OF' FIGURES

FIGUr:t---~<

PAGr

2-1 Energy Level Dia'lram for a .proton in a f!annetic Field II. 26

2-2 TelnperatureTffect on tam Line Shape in Fxchannino

sYs terlS. 3/\

2-3

3-1

3-Z

Calculated Spectra for the X3

AA'X3' Case.

Cis and Trans I~o~ers of L2

PdX2

.

220 ~Hz Spectra of Solutions Containinn

clS[(CH3

)2{C6

HS

)PJ ldC1 2 ~lith added (CII3

)2(C6"S)'

37

d2

3-S

4-1

4-2

4-4

P.Z

1\8

80

90

SZ

54 \~60-61

fiZ-C3

64-65

Conductivity vs ~ for L2

PdC1Z

+ LO.., L

Conductivity vs IT for LZ

Pdr.r2

+ LO.

Conductivity vs hfor L2

Pdl2

+ LO.

Chemical Shift of (CH3)2(C6I1S)P vs ft for

trans[(C6I1S)}'12RhCOCl + (CH3 )Z(C6

I1S)P,

Chemical Shift of (CII3

)(C6I!S)/ vs hfor

trans [ (C6

HS

) llZRhCOCl + ((1'3) (C6I1S)l·. L . .

Conductivity versus IT for trans[(C6IJS

)/1z/lhCOCl +

.' (CII3 )(C6HS)/' \

Chemical Shift of (CII3

)(CG

IIS)l vs hfor

trans [( C6I1S

)lJ zI rCOCl + (CH3 )( C6I!S; l·Cond'lctivity versus hfor trans[(C6I1S)llZlrCnCl +

(Clt3 )(C6 I1S)l·4-6 Conductivity versus ft for trans[(C

6f's)llZlrCnCl +

4-3

3-3 220 r1Hz Spectra of Solutions Containino

[(CII3 )(CGIIS)lJ ldrlr

2with added (CI!3)(C

6H

S)l.

3-4 -.'--320 1·1Hz Spectra of [( Cl 13HCEHS

)/lldC1 2 Sh,owi no a

. Mixture of Isomers.

3-6

4-5

3-7

Q'>- ,.

v,i i i

!I-,

FI GUrE

~. -.

PAGE

Acids vs ~ - for theo

4-7

4-8

4-10

5-1

5-2

Chemical S~ift of (CH3

)(CGI'S)l vs hfor

trans[(C6HS)/J 2 IrCORr + (C1I3 ) (CGlIs)l·

. '" . LConductiVIty vs ~ for trans[(C6HS)3PJ2IrCORr +

(CH3 )(C6HS)/'

Co'nductivity vs ~1 for trans [(C6f's)lJ

ZI1-COllr +

(CIl3)2(C6HS)P,

220 ~ll!z Spectrur:l of (CII3

)2(C6

I1S

)P added to

[(C 6HS

) lJ 3Rh C;1.

Plot of PKa in the Benzoic Acid Series vs PKa in the

Phenylacetic Acid Series.

Plot of lo~ ~o for Phenylacetic

Benzoic Acid Series.

93

95

98

100

110

III

6-1

6-2

T

6-3

Plot of Relative Equilibriu~ Constant vs [x for.' +-

L2

PdX2

+ L : L3

PdX + X . I~S,G,7

Plot of Kequilib vs LX for the r.eaction 1~9

. L2

Ni (CN)Z + L, L3

Ni (cr~ and L2

CO(SCN)Z + L. L3CO(scn)2'

Variation of Charqe in the tl'ans[(C6HS)3PJ 2IrCOX

Series.!

156

A-I

-16-4 Variation of Charne in the trans[(C61'S)lJ

ZRhCOCl

Series.

L1 1Plot of L versus L- for the reactionZ 2 _L

2PdC1

2+ L + L

3PdCl+ + Cl .

158

167

A-2

A-3

L1 1Plot of L vs L for the reaction

22+L2P~Rr2 + L ., L

3PdBr + Br

L1. 1 .Plot of L vs G for the r action

2 (. + _L

2Pd I 2 + L ., L Pd I +

ix

)

168-9

170

•

QiflPTER_I

~J!O_~J:UrJE,cor''rLE>~ES I~I GROUP VIII TRMISITIOri r'HAL CIHHSTRY

1.1 .!J~T.R00c::U-=.CT'-..:Ic::0:..c1~

,r'1etals of the ClrOUp VIII series h'1ve lon~ heen knOl'ln as active

cdtalysts, heino lise'.! extensively as h."teropeneous catalyots. in both

indllstrial and laboratory scale reilctions. 1·10re recently,coPlplexes of

these ",et,lls !lilve been found to t'e active as homoqeneous catalysts.

Such systenJs have been extensively studied beciluse of their inherent

interest ilnd tlleir potential industrial applications. Several recent

stlldies have led to a rather detailed understanding of the catalytic

process. It has been found that tile detailed reaction mechanisms of

"spveral such processes hilve a nur~ber of features in common. These can

he illustrated by considerin~ two of the better known cases.

The "oxo" process is a particularly well understoocf hOl'lO~eneously

catalyzed reaction in which an aldehyde is produced from il ter~inal ole­

fin. The PI'oposed mechanism for this reaction is shown below}

f1Co(CO}4 t IICo(CO}., + CO•

R H H" I~ .::__...~ ~o (CO) 3 .

CHZ

}

2

, .slIcll thl' orillin,11 IlII'cll,ln1srii 111,1.1' not.h!' l'ntirely COITt'Ct.. I/OI.I'Vl'r. for

llll' pllrposl' of illll~;tl·,llioll. Hi1kil1~,OI1'S oriqinalllll'ch,ll1isllI is slloI.n

be 101.,

[.I

rI;,

r-'[(C(ltl~)lJJHIlCl : [(Cr,IIS)/J 2HIlCl(solv('I1I) + P(r.(iIl~;lJ

I(C(il/~I)/J2HIlCl(solvl'nt.) ~ 11 2 : [(Cr,II~i)lJ(~HIll//l

[(C(il/~)/1;,Hhl'2Cl ~ ell2 C1I 2 ': [(C 6I1 S)/Jllhl/?C1(CI/2 \.112)

""[(C(il/~,l/JHhll/l(CIl2'Cl/;,)+ solvl'l1t: [(C(iIlS)3PJ2IlhCl(sI11vl'nl.)tCI/1":l

"

lllt'sl' 1lIt'c1hlnisllIs ~.how ft'atlll'l's 1.llich ,11'1' C0l1111011 to 111-111.1"

1. llll' COlllp1l'X IIsl'd in slIcll a 1'l',lction is OftC'11 only till' prt'clIl'sor

til the C<1Ll1ytical1y activl' species and ,1I1r·~l1itiil1 dh:;oei,lt.iol1 of

,1 1iq,11111 is OftI'll l'eqllired.;:... -.....

2, llll' 1I1l'Cllilnhlll cOl1sists of ,1 series of steps e,lell of wllieh llIay b('(": ..

vil'l'/lid ,IS il 1i<l,lIHl C'xch,ln<le rl'Jctioll. In sOllie CilSI'S. tlll'l'l' is-il

dirl'ct I'XClhlnqe betl.l'(,11 ~ol1\p1(,xl'd ,1I1d fl'C'e 1i<j,1Ilds. In other CilSPS

(\'.'

the 1'l'p1,lcC'IlIL'llt of solvC'l1t llIily be involved. In 'yet othl'l' CilS('S ~,.l'"

"insl'rtioil 1'l',lc!.ions") there is il re,ll'r<ln<]l'l1lellt of 1i<]illlds il1reildv

llrl'srnt to <livl"IH'I. li1l<1nds. 1I0wever. in e,ld Cilse the centril1

,,,met,11 h,lS il di fferC'nt 1ill,lnd .el1VirOnllll'nt <1t the comp1rtion of a

step thiln it poss(,ssl'd ,1t the beqinnirHl of that step. Fnquiry

into the oriqin of the drivinq fOl'cesl.hich filvour changes in,

1iqill1d cnvironlllcilt is obviolls1y l1C'l'til1Cnt to iln underst,lndino

3

of homofJeneous ciltalvsis .."

It is usual. to distinguish steric ilnd electronic factors in

discussing the reactivity of metal complexes. Steric' filctors,althoLJ~h

not Ivell understood in detilil, aloe intuitively straightforward, at leilst

in principle. There is obviously a limit to the. number of bulky li~ands

which can be ilccomodated around a metal atom Of~~~iven size. Electronic

factors ilre, however, less straightforward. ligands are usually

regarded primarily as electron donors but it.has long been reco~niled

that in these covalent complexes the electron accepting abilities of

a ligand can have 'a marked infl~nce on the bonding. It is also re­

cognized that the electronic requirements of different metal atoms in

different oxidation states are not the same. Thus, the range of stable, ,

complexes formed I'lith Ni(O) is quite different to that formed by Co(lll).

Initially it is expected that the stability ilnd lability of a metal

complex will depend upon a combination of the donor/acceptor properties

of the various ligands and the atceptor/donor prooerties of the metill

centre. The primary objective of the present study is therefore to

seek ~ome measures of these donor and acceptor properties and to

investigate possible correlations of these properties Ivith the stabil ities

anG labilities of metal complexes.

It is appar.ent that the factors involved are in part thermo­

dynamic and in part kinetic. Some combination~ of certain ligands wi~h

a given metal are mOl'e stable than others while two complexes of

comparable stability milY differ markedly in their rates of 1 igand

exchange. 80th aspects

efficiency of catalytic

are important inJ!

reaction s,chemes

determinin~ the overall .

such as those shown above.

IlfI,

4

It has been often observed that relatively minor changes in the nature

of the ligands can very markedly affect catalytic efficiency. Organic

chemists have achieved a large measure of understanding of aliphatic

and aromatic substitution processes in terms of electronic charge"distributions. The above catalytic processes are much more complicated

and ready solutions are not to be expected., Nevertheless, the basic

driving forces are unli~ely to be different from lhose encountered in

other-areas of chemistry. This thesis represents an attempt to elucidate

some of the factors determining the efficiency of ligand exchange.

The complexes chosen for study were substituted phosphine

complexes of group VIII metals. These complexes were chosen for

several reasons. A num6er of them are well-known homogeneous cataly6ts

whereas others are inert, at least in the reactions thus far investigated.

In most cases a series of complexes with a variety of phosphines can, '

be obtained and their relative stabilities investigated. Furthermore,

many of the complexes have been 'kno~m for a considerable leng.0 of

time and their properties and reactivities hav'e been extensively studied.'

Finally, the complexes are readily available commercially, or can be

easily prepared, and are all reasonably stable.

Since all the complexes chosen contain substituted phosphine,

the exchange of comp} exed and free phosphine was. chosen as the exchange(

reaction for study. This exchange of free and complexed phosphine was

observpd by nuclear magnetic resonance (NMR). The reason for this is!

two-fold. Since the observed "chemical shift" (see Chapter II) for. ,

free and complexed phosphine are usually soml?what different, high-

resolution instruments can often distinguish between free and complexed

5

ligands. This technique also has the advantage that the time scale

of observation of the M1R experiment (~ 10-?" sec) is of the same order..as the rate of many chemical reactions. This, in favourable cases,

makes possible the study of reaction rates which are too fast for

classical methods.

In several cases, the exchange reactions studied led' to the

Compounds of phosphorus(III) have been known for over one

hundred years; The simplest c~mpound which. gives this name to the

entire range of phosphorus(III) compounds is phosphine PH3. This

compound was first characterized by Rose3 in 1826. 'This compound

is very reactive,being rapidly attackeq by oxygen or water. The

halophosphines PX3 (X = F, Cl, Br, I) have als~ been characterized.

Since both types of compounds are very reactive, their use in transi­

tion metal chemistry has been somewhat limited.

Alkyl and aryl phosphines R3P where R is an alkyl or aryl

group are also well-known.' Triphenylphosphine, (C6HS)3P, is particularly

stable and readily soluble in a wide range of organ~c solvents and1-

has been widely used as a ligand in transition metal chemistry. The

preparation and properties of substituted phosphines has been thoroughly

rev)ewed. 4,S In general, the organophosphorus(III) compounds can be

in solution, this method is particularly suited to the study of

forma~ion of charged species. The study of such reactions was carried

•

PHOSPH Ir~ES

out by means of conduttivity measurements. Since conductivity is a

measur~ 9f the concentration of c~rrent carriers (charged species)

reactions producing ionic products.

1.2-·CHFtIISTRY o( PflOSP~:INE M:D SUBSTITUTED

,,!!i,~

f

,I