The synthesis and reactivity of triangular phosphido-bridged rhodium and iridium clusters

R h o d i u m and Iridium Clusters b y

Fathi M. As s e i d

B.Sc., Brock University, 1989 M.Sc., B r ock University, 1991

A D i s s e r t a t i o n Submitted in Partial Fulfilment of the Requirement for the Degree of

D O C T O R OF PHILOSOPHY

in the Department of Chemistry

We accept this dissertation as conforming to the reauired standard

Dr. 'K.Jl^--8ixon

Stobart

Dr. G.W. Bushnell

Dr.il Ct.B. Tatum

Dr.IM. Cowie, External E x a m i n e r

® Fathi M Asseid 1995

U n i v e r s i t y of V i ctoria

All rights reserved. This dissertation m a y not be rep r o d u c e d in w hole or in part, b y p h o t o copying or o t h e r means, without

ii

A bstract

Supervisor: K.R. D ixon

R e a c t i o n of [Ir2 (cyclooctene) 4 (/x-Cl) 2] w i t h CO, H N E t 2, and H P P h2 p r ovides a synthetic route to the trinuclear, phosphido-bridged, iridium clusters; [Ir3 (/.'.-PPh2) 3 (CO) 3 (L2) ] , L = CO, or P P h 3, or L2 = DPPM, and [Ir3 (/i-PPn2) 3 (CO) 4 (BufcNC) 3] . The 4 6 - e l e c t r o n cluster, [Ir3 (/x-PPh2) 3 (CO) 3 (dppm) ] involves one formal 1 6 -electron m etal centre and two 1 8 -electron metal centres, wi t h Ir-Ir bonds average 2.805 A. In carbon m o n o x i d e atmosphere, the cluster undergoes (reversible) CO addition, to result in the 4 8-electron der i v a t i v e [Ir3 (/x- PPh2) 3 (CO) 4 (dppm)] , wi t h Ir-Ir bonds average 2.989 A. The 5 0 - e l e c t r o n cluster [Ir3 (/x-PPh2) 3 (CO) s (Bu^C) 2] involves one 1 8 - e l e c t r o n centre and two 16-electron centres, w i t h Ir-Ir bonds a v e rage 3.188 A. Comparison of the c o r r e s p o n d i n g dista n c e s , show a regular increase in Ir-Ir length 2.805, 2.989, 3.188 A, as the e l ectron count changes from 46 to 48 to 50 electrons.

Ox i d a t i v e add i t i o n to the 46 and 50 e l e c t r o n clusters [Ir3 (/i-PPh2) 3 (CO) 3 (dppm) ] , and (Ir3 (/x-PPh2) 3 (CO) 4 (Bu^C) 3] , in bo t h cases gives reaction at a single, f o r m a l l y 1 6 -electron i r i dium center. The products are [Ir3 (/x-PPh2), (CO) 3

(dppm) (X) (Y)] , X = I, Y = I or OH; X = H, Y = C l ; X = H g C l , Y = Cl, and [Ir3 (/z-PPh2) 3 (CO) 4 (Bu^C) 3 (R) ] X, R X = Mel, B z B r , I2, HC1, H g C l 2, H g B r 2, or A u P P h3Cl, respectively. The latter c o m p l e x c o n tain unusual complex cations, [Ir3 (/*-

PPh2) 3 (CO) 4 (BufcNC) 3 (R)]+, in w h ich R+ has a d d e d to a f o rmally 1 6 - e l e c t r o n iridium centre to give 1 6 - e l e c t r o n iridium

cation. T hese m a y be r e garded as arr e s t e d i n t ermediates in the a c c e p t e d m e c h a n i s m of oxidative a d d i t i o n at Ir(I), and in the p r e s e n t complex, X- remains uncoordinated.

R e a c t i o n s of the halogens Cl2, B r 2, I2, the

mercuric(II)halides, and mercu r i c ( I I ) a c e t a t e s H g R2 (R = 02CCF3, or 02C C H 3) w i t h [Rh3 (/i-PPh2) 3 (CO) 3 (La) ] , L = CO, or PPh3, o r L2 = DPPM, results in [Rh3 (/n-PPha) 3 (/n-CO) (CO)2 (/x- X )2 (L)]. A 50-electron cluster wi t h all metal - m e t a l d istances cor r e s p o n d wi t h those no r m a l l y a s s o c i a t e d w i t h formal m e tal-metal bonds.

In the last part, the synthesis and c h a r a c t e r i z a t i o n of the n ovel p h o s p h i d o - b r i d g e d trinuclear m i x e d i r i d i u m / r h o d i u m clusters is described. [IrRh2 (/.t-PPh2) 3 (CO) s] , and [Rhlr2 (^~ PPh2)3 (CO)5] react with DPPM, PPh3, B u fcNC, and P( O M e ) 3, and a fford the derivatives of these ligands. W i t h the aid of various spectroscop.i c techniques such as ID- and 2D-NMR spectroscopy, FAB-mass spectrometry, and X -ray

c r y s t a l l o g r a p h y the cluster derivatives have b e e n s t r u c t u r a l l y characterized. E x a m m i n e r s : Dr. S.R. Stobart Dr. G.W. Bushnell ^r. J.$. Tatum Dr. M. Cowie, External Ex a m i n e r

iv T A BLE OF CONTENTS Page T i t l e P a g e ... i A b s t r a c t ... ii T a b l e of C o n t e n t s ... iv List of T a b l e s ... vii L i s t of F i g u r e s ... x List of A b b r e v i a t i o n s ... xiii L i s t of C o m p l e x e s ... xiv A c k n o w l e d g e m e n t s ... xv C h a p t e r One: General I n t r o d u c t i o n ... 1

C h a p t e r Two: Synthesis of the clusters M3 (jit-PPh2) (CO)5, (M = Ir o r R h ) , and their r e a ctivity to w a r d CO, P P h 3, DPPM, B u fcNC, and P(OMe)3... 10

2.1. I n t r o d u c t i o n ... 12

2.2. R e s u l t s ... 16

2.2.1. Synthesis of M3 (/i-PPh2) 3 (CO) 5, (M = Ir or R h ) ... 16

2.2.2. C r y s t a l l o g r a p h i c A n a l y s i s ... 17

2.2.3. Spectr o s c o p i c A n a l y s i s ... 21

2.3.1. CO and B u fcNC A d d i t i o n to M3 (/i-PPh2) 3 (CO) 5, (M = Ir or Rh) . . . ... 24 2.3.2. C r y s t a l l o g r a p h i c A n a l y s i s ... 26 2.3.3. Spectr o s c o p i c A n a l y s i s ... 3 0 2.4.1. Reactions of M3 (/x-PPh2) (CO) 5, (M = Ir or Rh) w i t h DPPM, P P h 3, and P ( O M e) 3 ... 34 2.4.2. C r y s t a l l o g r a p h i c A n a l y s i s ... 3 8 2.4.3. S p e c t r o s c o p i c A n a l y s i s ... 40

2.5. D i s c u s s i o n ... 48 C h a p t e r Three: Selective oxidative a d dition at a single

centre in [Ir3 (/x-PPh2) 3 (CO) 4 (BufcNC) 3] , [Ir3 (/x-PPh2) 3 (CO) 3 (dppm) ] , and [M3(/x-PPh2) 3 (CO)3 (L)2], M = Ir or Rh, L = CO, or P P h 3. . . 53 3.1. I n t r o d u c t i o n ... 54 3.2. R e s u l t s ... 57 3.2.1. One-centre oxidative addition

reactions to

[Ir3 (/x-PPh2) 3 (CO) 4 (Bu'NC) 3] ... 57 3.2.2. Spectroscopic analysis.. ... 59 3.2.3 Crystallographic a n a l y s i s ... 62 3.3.1 Oxidative a ddition reactions to

[Ir3 (/x-PPh2) 3 (CO) 3 (dppm) ] ... 73 3.3.2. Spectroscopic a n a l y s i s ... 73 3.3.3 Crystallographic a n a l y s i s ... 75 3.4.1 Two-centre oxidative a d dition r e a c tions to

[Ir3 (/x-PPhj) 3 (CO) 4 (Bu^C) 3]

80 3.4.2. Spectroscopic a n a l y s i s ... 84 3.5.1 Reactions of [Rh3 (/x-PPh2) 3 (CO) 3 (L2) ] , (L = CO or PPh3, L2=dppm) w i t h I2, H g X2 (X=I, B r , C l , 02CCF3, and 02C C H 3) ... 8 9 3.5.2. Spectroscopic a n a l y s i s ... 94 3.5.3 Crystallographic a n a l y s i s ... 102 3.6. D i s c u s s i o n ... 108 C h a p t e r Four: Synthesis and r e a ctivity of p h o s

phido-b r i d g e d mixed iridium and r h o d i u m ... 119 4.1. I n t r o d u c t i o n ... 119 4.2.1. Synthesis of M M' 2 (/x-PPh2) 3 (CO) 5 a n d

M' M2 (/x-PPh2) 3 (CO) 5 (M=Rh, M ' = I r ) ... 122 4.3.1. Reactions of M M' 2 (/x-PPh2) 3 (CO) 5 and

vi M ' M2 (/x-PPh2) 3 (CO) 5 (M=Rh, M'=Ir) w i t h

PPh3... 123

4.3.2. Spectroscopic a n a l y s i s ... 125

4.3.3 Crys t a l l o g r a p h i c a n a l y s i s ... 133

4.4.1. Reactions of M M' 2 (/x-PPh2) 3 (CO) 5and M ' M2 (/x-PPh2) 3 (CO) 5 (M=Rh, M'=Ir) w i t h D P P M ... 13 0 4.4.2. S p e ctroscopic a n a l y s i s ... 135

4.5.1. React i o n s of MM' 2 (/x-PPh2) 3 (CO) 5and M ' M2 (/z-PPh2) 3 (CO) 5 (M=Rh, M'=Ir) w i t h B u tN C ... 144

4.5.2. Spectr o s c o p i c a n a l y s i s ... 145

4.6.1. Reactions of R h l r2 (/i-PPh2) 3 (CO) 5 and R h l r2 (/x-PPh2) 3 (CO) 5 (PPh3) 2‘ w i t h P (OMe) 3...."... 149

4.6.2. S p e ctroscopic a n a l y s i s ... 150

4.7. D i s c u s s i o n ... 152

Chap t e r Five: Conclusions and recomme n d a t i o n s for future w o r k ... 161

Chapter Six: E x p e r i m e n t a l ... 165

6.1. General p r o c e d u r e ... 166

6.2. Synthesis of c o m p o u n d s ... 167

LIST OF TABLES

Table Page

2 .1 3 1p {1H} N M R chemical shifts and c o upling constants of R h3 (/x-PPh2)3 (CO)s (2.3),

Ir, (^x-PPh,) , (CO) E (2.5a), and

Ir3 (/z-PPh2) 3 (CO) 6 (2 . 5 b )... 23

2.2 C r y s t a l l o g r a p h i c parameters for

Ir3 (/x-PPh2)3 (CO)5 (ButN C) 2 ... . 28

2.3 S e l e c t e d b o n d lengths and angles for

Ir3 (/i-PPh2) 3 (CO) 5 (BufcNC) 2 (2.7) ... 29

2.4 3 1p {1H} N M R chemical shifts and coupling constants of Ir3 (/i-PPh2)3 (CO)5 (ButN C) 2 (2.7),

Ir3 (/i-PPh2) 3 (CO) 4 (Bu,:NC) 3 (2.8), and

R h3 (M-PPh2)3 (CO)4 (ButN C) 3 (2.9)... 31

2.5 Positive ion FAB-MS of

Ir3 (/x-PPh2) 3 (CO) s (BubNC) 2 (2.7)

Ir3 (/i-PPh2) 3 (CO) 4 (BufcNC) 3 (2.8' ... 35

2.6 C r y s t a l l o g r a p h i c parameters for

R h3 (/j,-PPh2) 3 (CO) 2{P (OMe) 3 } 3 ... . 42

2 . 7 S e l e c t e d b o n d lengths and angles for

R h3 (/i-PPh2) 3 (CO) 2{P (OMe) 3 } 3 ... . , 43

3 .1 31P {1H} N M R c h emical shifts and coupling

c onst a n t s f o r (3.2-3.8 )... 61

3.2 P ositive ion FAB-MS of

[lr3 (^-PPh2) 3 (C0)4 (Bu'NC) 3 (CH3) ] +I‘ (3 .7)

[lr3 in-P P h 2) 3 (CO) 4 (BufcNC) 3 (PhCH2) ] +Br' ( 3 .8)... , 64

3.3 Infrared stretchincr frequencies for (3.2 - 3.8).... 65 3.4 C r y s t a l l o g r a p h i c parameters for

[lr3 (/x-PPh2) 3(CO) 4 (BufcNC) 3 (CH3) ] +I' (3 ._7)... . 68

3.5 S e l e c t e d b o n d lengths and angles for

rir3 (/i-PPh,) ? (CO) 4 (Bu^tfC) 3 (CH3) 1 +I" (3 . 7 )... 69

3 . 6 C r y s t a l l o g r a p h i c parameters for

[lr3 ( f i -PPh2) 3 (CO) 4 (BufcNC) 3 (PhCH2) ] +Br" (3.8)... . . 71

3 . 7 S e l e c t e d b o n d lengths and angles for

rir3 (/i-PPh,) 3 (CO) 4 (BufcNC) 3 (PhCH,) 1 +B r ‘ (3 . 8 ) ... , . 72 3 . 8 3 1p{1H} N M R c hemical shifts and c oupling constants

-viii for (3.9 - 3 . 1 3 ) ...

3 . 9 In f r a r e d stretchinq frequencies for (3.9 - 3.13). ... 19 3 .10 C r y s t a l l o g r a p h i c parameters for

[Ir, (u-PPh,), (CO), (doom) (OH) (1)1 (3.11)... 3 .11 S e l e c t e d bond lengths and angles for

d r , (u-PPh,), (CO), (dppm) (OH) (1)1 (3.11)... 3 .12 3 1P {1H} N M R chemical shifts and c o upling constants

for (3.14 - 3 . 2 0 ) ...

3 .13 I n f r a r e d stretchinq frequencies for (3.14 - 3.20) ... 90 3 .14 P o sitive ion FAB-MS of

[Ir3 (^-PPh2) 3 (CO) 4 (B^NC) 3 (CH3) (H) ] 2+ (3 .14)

rir3 (/i-PPh,), (CO) ,, (ButN C ) , (AuPPh-,) 21 2+ (3 . 1 9 ) ... ... 91 3 .15 3 1P{1H} N M R chemical shifts and coupling const a n t s

for [Rh, (u-PPh,),(CO), (u-CO) (u-I) 2 (doom) 1 (3.29) . . . . , 96 3 .16 3 1p(1H} N M R chemical shifts and coupling constants

for 3.22, 3.23a, 3.24a. 3.25, 3.26, a n d 3 . 3 4 .... 10 0 3 .17 3 1p {1H} N M R chemical shifts and c o upling constants

for [Rh, (u-PPh,), (CO), (fx-CO) (u-Br) 2 (PPh,) 21 (3.24b) . ... 104 3 .18 3 1p {1H} N M R chemical shifts and coupling c o n s tants

for 3.30, 3.31, 3.32, and 3 . 3 3 ... 107 3 .19 I n f r a r e d stretchinq frequencies for (3.22 - 3.33) .... 109 3 .20 P o sitive ion FAB-MS of

3.22, 3.24b. 3.29, and 3 . 3 3 ... , , 11 0 3 .21 C r y s t a l l o g r a p h i c parameters for

[Rh, (u-PPh,), (CO), (u-CO) (u-I) 2 (PPh3)1 ( 3 . 2 2 ) ... , , 113 3 .22 S e l e c t e d b o n d lengths and angles for

[Rh, (u-PPh,), (CO), (u-CO) (u-I) 2 (PPh3) 1 ( 3 . 2 2 ) ... 1 14 4.1 3 1P {1H} N M R chemical shifts and coupling const a n t s

[Tr Rh2 (/x-PPh2) 3 (CO) 3 (PPh3) 2] (4 .11)

[Rhlr, (jx-PPh,) 3 (CO) 3 (PPh3) ,1 (4.12)... for

. . . 127 4.2 P ositive ion FAB-MS of

[IrRh2 (/x-PPh2) 3 (CO) 3 (PPh3) 2] (4 .11)

[Rhlr, (^x-PPh,) 3 (CO) 3 (PPh3) ,1 (4.12)... 129 4.3 C r y s t a l l o g r a p h i c parameters for

4.4 S e l e c t e d bo n d lengths and angles for

[Rhlr2 (n-PPh2) 3 (CO) 3 (PPh3) 2] (4 . 1 2 ) ... 133 4.5 ^ P ^ H } N M R chemical shifts and c o upling constants for

[IrRh2 (/x-PPh2) 3 (CO) 3 (dppm) ] (4 . 1 5 )

[Rhlr2 (/i-PPh2) 3 (CO) 3 (dppm) ] (4 . 1 6 ) ... 138 4.6 P o sitive ion FAB-MS of

[IrRh2 (/i-PPh2) 3 (CO) 3 (dppm) ] (4 . 1 5 )

[Rhlr2 (/i-PPh2) 3 (CO) 3 (dppm) ] (4 . 1 6 ) ... 141 4.7 Uv / v i s and infrared da t a for

(4.13 - 4 . 1 6 ) ... 141 4.8 3 1P {1H} N M R chemical shifts and coupling constants for

[IrRh2 (M-PPh2) 3 (CO) 4 (ButNC) 3] (4 . 1 9 )

[Rhlr2 (^-PPh2) 3 (CO) 3 (BufcNC) 3) ] (4 . 2 0 )... 148 4.9 3 1P {1H} N M R chemical shifts and coupling constants for

[Rhlr2 (/x-PPh2) 3 (CO) 2{ (P (O M e ) 3) }3] (4 . 2 1 )

[Rhlr2 (/i-PPh2) 3(CO) 2 (PPh3) 2{P (OMe) 3}] (4 . 2 2 )... 155 4.10 Positive ion FAB-MS of

[Rhlr2 (/i-PPh2) 3 (CO) 2{ (P(OMe)3) }3] (4 . 2 1 )

X LI S T OF FIGURES F igur Page 2.1 3 1P {1H} N M R s p ectrum of Ir3 (/z-PPh2) 3 (CO) 5 (2 . 5 a ) . and Ir3 (/x-PPh2) 3 (CO) 6 (2 . 5 b ) ... 22 2.2 The m o l e c u l a r structutre of Ir3 (/x-PPh2) 3 (CO) s (BufcNC) 2 ... 27 2.3 3 1P { XH} N M R spectra of Ir3 (/x-PPh2) 3 (CO) 5 (B^NC) 2 (2/7) , and

Ir3 (/x-PPh2) 3 (CO) „ (BufcNC) 3 (2_a_8)... 32 2.4 3 1P {1H} N M R spectrum of

R h3 (/x-PPh2) 3 (CO) 4 (BufcNC) 3 (2^9.)... 33 2 . 5 Infrared spectra of

lr3 (/x-PPh2) 3 (CO) 5 (BusNC) 2 (2/7) , Ir3 (^-PPh2) 3 (CO) 4 (BufcNC) 3 (2^_8) , and

R h3 (/x-PPh2) 3 (CO) 4 (BufcNC) 3 (2 . 9 ) ... 36 2.6 Positive ion FAB-mass spectrum of

Ir3 (/x-PPh2) 3 (CO) 4 (Bu’ISFC) 3 (2^8)... 37 2.7 The m o l e c u l a r structutre of R h3 (/x - P P h 2) t (C O ) 2 {P (O M e ) 3 } 3 (2 . 1 3 ) ... 41 2.8 V.T. 3 1P{1H} N M R spectra of R h3 (/x - P P h 2) 3 (C O ) 2 {P ( O M e ) 3 } 3 (2 . 1 3 ) ... 46 2.9 V.T. 1H N M R spectra of R h3 (/x-PPh2) 3 (CO) 2{P (OMe) 3 } 3 (2 . 1 3 ) ... 50 2.10 3 1P{1H} N M R sp e c t r u m of Ir3 (/x-PPh2) 3 (CO) 2{P (OMe) 3 } 3..(2 . 1 4 ) ... 51 3.1 3 1P {1H} N M R s p e ctra of Ir3 (/x-PPh2) 3 (CO) 4 (BufcNC) 3 (PhCHz) ] +B r ‘ (3^8) Ir3 (/x-PPha) 3 (CO) 4 (Bu'NC) 3 (CH3) ] +I' (3/7)

Ir3 (/x-PPh2) 3 (CO) 4 (BufcN C ) , (H) ] +C1" (3^3)... 60 3.2 Positvie ion F A B-mass spectrum of

Ir3 (/x-PPh2) 3 (CO) 4 (Bu'TOC) 3 (PhCH2) ] +Br" ( 3 /9) ... 63 3.3 The m o l e c u l a r structure of

Ir3 (/x-PPh2) 3 (CO) 4(BufcNC) 3 (CH3) ] +I' ( £ / 7 )... 67 3.4 The m o l e c u l a r structure of

3.5 1P {1H} N M R spectrum of

Ir3 (,u-PPh2) 3 (CO) 3 (dppm) (H) (Cl) (3 . 1 2 ) ... 76 3.6 XH N M R s pectrum of

Ir3 (/x-PPh2) 3 (CO) 3 (dppm) (H) (Cl) (3..12) ... 77 3 .7 T h e molec u l a r structure of

Ir3 (/x-PPh2) 3 (CO), (dppm) (OH) (I) (3 . 1 1 ) ... 81 3.8 3 1P {1H} N M R spectra of

Ir3 ill-P P h 2) 3 (CO) 4 (Bu6NC) 3 (CH3) ] 2+r B F 4- (3 . 1 4 ) lr3 (^-PPha) s (CO) 4 (BufcNC) 3 (PhCH2) ] 2+br'BF4- (3 . 1 5 )

Ir3 (/x-PPh2) 3 (CO) 4 (Bu'ttC) 3 (H) (H) ] [BF4] ' 2 (3 ^ 1 6 )... 87 3.9 1P {1H} N M R spectrum of

R h3 (fi - P P h 2) 3 (C O ) 2 (/x - C O ) (/x-I)2 (dppm) (2u29_) ... 95 3.10 3 1P {1ri} N M R spectrum of

F*h,(^PPh2)3(CO)2 (/i-CO) (/i-I)2 (PPh3) ( 3 ^ 2 2 ) ... 98 3.11 3 1P {1H} N M R soectrum of

Ir3 (/x-PPh2) 3 (CO) 2 (fX-CO) (//-I) 2 (PPh3) (3^34.)... 99 3.12 3 1P {1H} N M R spe c t r u m of

R h3 (/x-PPh2) 3 (CO) 2 (/x-CO) (fi-Br) 2 (PPh3) 2 (3 .2_4bJ... 103 3.13 (a) 3iP{1H} N M R s p ectrum of

P h3 (pi-PPh2) 3 (CO) 3 (/x-CO) (/x-I) 2 (.3^30)... 105 3.13 (b) 3 1P {1H} N M R s p ectrum of

R h3 (jx-PPh2) 3 (CO) 3 (/x-CO) (/X-02C C F 3) 2 (3 . 3 33,)... 106 3.14 The molec u l a r structure of

R h3 (/x-PPh2) 3 (CO) 2 (/x-CO) (/X-l)2 (PPh3) (3 ^ 2 2 ) ... 112 4.1 3 1P{1H} COSY N M R s pectrum of [Rh3 (/x-PPh2) 3 (CO) 3 (PPh3) 2] (4.9) [Ir3 (/x-PPh2) 3 (CO) 3 (PPh3) 2] (4.1,0) [IrRh2 (/x-PPh2) 3 (CO) 3 (PPh3) 2] (4 .11) [Rhlr2 (/x-PPh2) 3 (CO) 3 (?Ph3) 2] (4 .12) ... 124 4.2 3 1P {1H} N M R spectra of [Rh3 (/i-PPh,) 3 (CO) 3 (PPh3) 2] (4^9.) [Xr3 (/x-PPh2) 3 (CO) 3 (PPh3) a] (4 . 1 0 ) [IrRh2 (/x-PPh2) 3 (CO) 3 (PPh3) 2] (4 . 1 1 ) [Rhlr2 (/x- PPh2) 3 (CO) 3 (PPh3) z] (4 . 1 2 ) ... ... 126 4.3 T h e molec u l a r structure of [Rhlr2 (/x-PPh2) 3 (CO) 3 (PPh3) 2] (4 .12) ... 131 4.4 3 1P{*-H} COSY N M R s p ectrum of [Rh3 (/X-PPh2) 3 (CO) 3 (dppm) ] (4 . 1 3 )

xii Tlr3 (/i-PPh,), (CO), (dppm) ] (4.14) TlrRh, (/i-PPh.,), (CO), (dppm) ] (4 .15) TRhlr, (/i-PPh, ) 3 (CO) (dppm) ] (4.16)... .... 13 7 4.5 3 1P {1H} N M R spectra of TRh3 (/(.-PPh,) 3 (CO), (dppm) ] (4.13) Tlr3 (/i-PPh?) 3 (CO), (dppm) ] (4.14) rRh, (/x-PPh,), (CO), (dppm) 1 (4 .15) TRhlr, (/i-PPh,) 3 (CO) 3 (dppm) 1 (4.16)... ... 139 4 . 6 Positive ion FAB-mass s p ectrum of

TRh3 (/i-PPh,), (CO), (dppm) ] (4.13) rir3 (/i-PPh,), (CO), (dppm) ] (4.14) TlrRh, (/i-PPh,), (CO), (dppm) 1 (4 .15)

TRhlr, (fi-PPh7) 3 (CO) 3 (dppm) 1 (4 . 1 6 ) .... ... ... 142 4 . 7 (a) Uv/vis spectra, and

(b) Infrared spectra of

TRh3 (/i-PPh,) 3 (CO) , (dppm) ] (4.13) rir3 (/i-PPh,) 3 (CO), (dppm) ] (4.14) TlrRh, (/i-PPh,), (CO), (dppm) 1 (4.15)

TRhlr, (/i-PPh,) 3 (CO) 3 (dppm) 1 (4.16) ... ... 143 4 . 8 3 1P { xH} C O S Y N M R s pectrum of

[Ir3 (/i-PPh2) 3 (CO) 5 (ButNC) 2] (4 .17) [Ir3 (/i-PPh2) 3 (CO) 3 (BufcNC) 3) ] (4.18) [IrRh? (/i-PPh2) 3 (CO) 4 (ButNC) 3] (4.19)

TRhlr, (/i-PPh,) 3 (CO) 3 (BufcNC) 3) 1 (4.20)... ... 146 4 . 9 3 1p{xH} N M R spectra of

[Ir3 (/i-PPh2) 3 (CO) 5 (ButNC) 2] (4 .17) [Ir3 (/i-PPh2) 3 (CO) 3 (Bu^C) 3) ] (4 .18) [IrRh2 (/i-PPh2) 3 (CO) 4 (ButNC) 3J (4.19)

TRhlr, (/i-PPh,) 3 (CO) 3 (B^NC) 3) 1 (4.20) ... ... 147 4 .10 3 1P{ XH} N M R spectrum of

[Rhlr2 (/i-PPh2) 3 (CO) 2{ (P(OMe)3) }3] (4.21)... ... 153 4 .11 3 1P{ xH} N M R s p ectrum of

B u fc L I S T OF A B B R E V I A T I O N S tertiary-butyl B u bNC tertiary-butyl isocyanide Bz benzyl COD cyclooctadiene COE cyclooctene

COSY c o rrelation s p e c troscopy

DPPM b i s ( d i p h e n y l p h o s p h i n o ) m e t h a n e DPPE bis ( d i p h e n y l p h o s p h i n o ) e t h a n e

Et ethyl

. FAB-MS _{fast at o m b o m b ardment-mass s p e c t r o m e t e r y}

I .R. infrared

L ligand

M metal

Me methyl

N M R n u c lear magnetic resonance

Ph phenyl

Pr1 isopropyl

R alkyl or aryl

THF tertahydrofuran

xiv L I S T OF COMPLEXES 2.1 _{R h 3 ix- PPh2 3 CO 3(dppm)} 2.2 Ir3 M - P P h 2 3 CO 3(dppm) 2.3 _{R h 3 /i- PPh2 3 CO 5} 2.4 _{R h 3 ix- PPh2 3 CO 3 (PPh3) 2} 2 . 5a lr3 /x-PPh2 3 CO 5 2 .5b _{Ir3 ^x-PPh2 3 CO} 6 2.6 lr3 \x-PP h 2 3 CO 3 (PPh3) 2 2.7 _{Ir3 ^ - P P h 2 3 CO 5 (BufcNC) 2} 2.8 lr3 /x-PPh2 3 CO 4 (ButNC) 3 2.9 R h 3 ix- PPh 2 3 CO 4 (ButNC) 3 2 .10 R h 3 /x-PPh2 3 CO 7 2 .11 R h 3 M - P P h 2 3 CO s (HPPh2) 2 .12 lr3 /x-PPh2 3 CO 2 (P (OMe) 3)3 2 .13 R h 3 ^ - P P h 2 3 CO 2 (P (OMe) 3) 3 3.1 = 2.8

3.2 Ir3 ix- PPh 2 3 CO 4(ButN C ) 3(1 )]+I' 3.3 lr3 /i-PPh2 3 CO 4 (ButN C ) 3(H) ]+Cl-3.4 lr3 ji-PPh2 3 CO 4 (Bi^NC) 3 (HgCl) ] +C1-3.5 lr3 M - P P h 2 3 CO 4(ButN C ) 3(HgBr)]+Br' 3.6 lr3 M-PP h 2 3 CO 4 (Bi^NC) 3 (AuPPh3) ] +C1 3.7 Ir3 /x-PPh2 3 CO 4(ButN C ) 3(Me)]+I' 3.8 lr3 M -PPh2 3 CO 4 (ButN C )3 (CH2Ph) ] +B r ’ 3.9 = 2.2

3.11 _lr3 (/x-PPh2)3 (CO) 3 dppm)(I)(OH) 3.12 lr3 (/x-PPh2)3 (CO) 3 dppm)(H)(Cl) 3 .13 lr3 (/x-PPh2)3 (CO) 3 dppm)(HgCl)(Cl) 3.14 lr3 (/x-PPh2)3 (co) 4 B u tN C )3 (CH3) ]2 +I-BF4-3 .15 lr3 (/x-PPh2)3 (co) 4 Bi^NC) 3 (PhCH2) ] 2+Br"BF4" 3.16 lr3 (/x-PPh2)3 (CO) 4 B u tN C )3 (H) (H)]2+ [BF4 ] - 2 3.17 Ir3 (/x-PPh2)3 (co) 4 B u tN C )3 (HgCl2) (HgCl,) ] 3 .18 lr3(/x-PPh2)3 (co) 4 B u ^ C ) , (HgBr2) (HgBr2) ] 3.19 l r3 (/x-PPh2)3 (co) 4 Bu fcNC) 3 (AuPPh3) 2] 2+2Cl' 3 .20 Ir3 (/x-PPh2)3 (co) 4 Bu tN C) 3 (I) 2] 2+2 I' 3.21 = 2.4 3 .22 R h3 (/x-PPh2)3 (CO)2 /x-CO) (/x-1) 2 (PPh3) 3.23a R h3 (/x-PPh2)3 (CO) (/x-CO) (/x-Cl) 2 (PPh3) 2 3 .23b R h3 (/x-PPh2)3 (C0) 2 /x-CO) (/X-Cl) 2 (PPh3) 3 .24a R h3 (/x-PPh2)3 (CO) (/x-CO) (/x-Br) 2 (PPh3) 2 3.24b R h3 (/x-PPh2)3 (CO) 2 /x-CO) (/x-Br) 2 (PPh3) 3.25 R h3 (/x-PPh2)3 (CO) 2 /x-CO) (/x-02C C F 3) 2 (PPh3) 3.26 R h3 (/x-PPh2)3 (CO) 2 /x-CO) (/x-02C C H 3) 2 (PPh3) 3.27 _{1^3 (/x-PPh2)3 (CO}) 2 /X-CO) (/x-I) 2 (PPh3) 3.28 = 2.1

3.29 = 3 .22

3.30 R h3 (/x- P P h 2)3 (CO)3 /X-CO) (/x-I) 2 3 .31 R h3 (u-PPh2)3 (CO)3 /x-CO) (/x-Br) 2 3 .32 R h3 (/x-PPh2)3 (CO) 3 /x-CO) (/x-Cl) a 3 .33 R h3 (/x- P P h 2)3(CO)3 /x-CO) (/x-0 2C C F3 ) 2 3.34 = 3 .27

4.5 IrRh2 (/x-PPh2) 3 (CO) 5 xvi 4.6 Ir2R h (jx-PPh2) 3 (CO) s 4.7 R h3 (^-PPh2)3 (CO)5 4.8 Ir3 (/x-PPh2) 3 (CO) 5 4.9 IrRh2 (/x-PPh2) 3 (CO) 3 (PPh3) 2 4.10 Ir2Rh(/x-PPh2) 3 (CO) 3 (PPh3 ) 2 4.11 R h3 (/x-PPh2) 3 (CO) 3 (PPh3) 2 4.12 Ir3 (/x-PPh2) 3 (CO) 3 (PPh3) 2 4.13 R h3 (/z-PPh2) 3 (CO) 3 (dppm) 4.14 Ir3 (/z-PPh2) 3 (CO) 3 (dppm) 4.15 IrRh2 (/x-PPh2) 3 (CO) 3 (dppm) 4.16 Ir2Rh (/x-PPh2) 3 (CO) 3 (dppm) 4.17 Ir3 {[I-PPh2) 3 (CO) 5 (BufcNC) 2 4.18 Ir3 (/x-PPhj) 3 (CO) 4 (Bi^NC) 3 4.19 R h 2Ir (/x-PPh2) 3 (CO) 4 (BufcNC) 3 4.20 R h l r2 (/x-PPh2) 3 (CO) 4 (BufcNC) 3 4.21 Ir2Rh (/i-PPh2) 3 (CO) 2 (P (OMe) 3) 3

A C K N O W L E D G E M E N T S

I w o u l d like to thank m y supervisor, Professor K.R. D i x o n for his advice and support du r i n g m y s t u d i e s .

I w o uld also like to thank m y co-workers Dr. N.J. Meanwell, Dr. D.E. B e r r y for all their invaluable help and advice throughout my y ears at U V i c .

I am v e r y grateful to Dr. J. Br o w n i n g for her wo r k on the x - r a y c r y s t a l l o g r a p h y of all of the complexes p r e s e n t e d in this work.

Finally, I w o u l d like to t hank all the members of m y family for t h eir support and encour a g e m e n t throughout m y years at U V i c .

GENERAL INTRODUCTION:

Several different d e f i n i t i o n s of metal clusters are possible, but for the p u r p o s e of this w o r k a metal

c l u s t e r is d e f i n e d as a dis c r e t e unit c o n taining at least t h ree metal atoms w h i c h are m u t u a l l y bo n d e d [1]. Interest in metal-metal b o n d e d c l usters of the t r a nsition metals has f o c used in the past two d e c a d e s o n the e l u c i d a t i o n of their structures, bonding, and spectr o s c o p i c p r o perties [2,3,4]. Of par t i c u l a r note are the efforts devoted toward their role as homogeneous and h e t e r o g e n e o u s catalysts [1,5-7]. In general metal clusters were s h own to be go o d models for surface catalysis and for u n d e r s t a n d i n g what h a p pens on m e tal surfaces dur i n g h e t e r o g e n e o u s catalysis [8,9]. The r elev a n c e of cluster c h e m i s t r y to homogeneous and

hetero g e n e o u s catalysis has b e e n e x amined and d i s c u s s e d in recent re v i e w articles [ 9 b , 9 c ] . O n l y a few examples will be c i t e d b e l o w w h i c h illustrate the g r o w i n g importance that m i x e d metal clusters sh o u l d p l a y in heterogeneous catalysis.

R e c e n t l y Puddephatt and c o - w o r k e r s [10-12] have shown that a c o o r d i n a t i v e l y u n s a t u r a t e d m etal cluster such as

[Pt3{Re (CO) 3 (P (OPh) 3) } (/i-dppm) 3] + c a n act as a model for

hetero g e n e o u s surface catalysts. This cluster was also shown t o be an intere s t i n g model for p o ssible Pt-Re b o n d i n g and metal support interactions in the important h e t e rogeneous b i m e t a l l i c Pt - R e / A l203 catalysts.

S t e a d y g r o w t h in the n u m b e r of known metal clusters has b e e n rep o r t e d in the past few years. Considerable p r ogress has been made, e s p e c i a l l y in dev e l o p i n g the systematic

a s s e m b l y of o r g a n o m e t a l l i c b u i l d i n g blocks to synthesize m e tal clusters, in p a r t i c u l a r those containing different metals, a n d in the s tudy of the relationships b e t w e e n their str u c t u r e s and p r o p e r t i e s [13-17]. Por example, synthetic s t r a tegies such as isolobal relati o n s h i p s [18,19] have p r o v e d s u c cessful in p l a n n i n g syntheses of m a n y metal clusters. S tone and c o - w o r k e r s [20] e m ployed isolobal

re l ationships to synthesize a series of d i r h o d i u m p l a t i n u m [2 0 ] a n d dirhodium and iron clusters [2 1 ] and, in a similar manner, D'Alfonso and co-workers s ynthesized m i x e d r h e n i u m p l a t i n u m clusters [22], and rhenium iridium clusters [23]. More usually, methods of preparing metal c l usters involve p y r o l y s i s of transition metal complexes u n d e r extreme

c o n ditions where there is no control over the c l u ster formed [24-28]. M a n y of the advances could not have been made

without the development of spectroscopic meth o d s and more e f f e c t i v e means of structure determination. Despite these developments, the p r e p a r a t i o n of metal clusters remains almost en t i r e l y an accidental affair.

M e tal clusters u s u ally contain single b r i d g i n g atoms or b r i d g i n g groups, w h ich g e n e rally stabilize clusters and

assist in b i n d i n g metal centres together. It is also hoped that b y mainta i n i n g metal centres in proximity, bridges can assist m o l e c u l a r rearrangements and reactions involving two or more metal centres. This thesis will co n s i d e r only

s e l e c t e d systems in which the bridging m o i ties contain p h o s p h o r u s . A m o n g the systems in w h ich pho s p h o r u s is part of a b r i d g i n g group is the phosphido ligand /i-PR2, w h i c h is found in a considerable number of dinuc l e a r and cluster

compl e x e s w h i c h may contain one, two, or three such br Ldging ligands, as i l lustrated in structures (1 . 1 -1 . 3 ). Different s ynthetic methods have been employed in w h i c h a w i d e range of m etal fragments m a y be found [31-33].

M- M M- M M . M

3 The interest in the c h e m i s t r y of t r a n sition metal

c l usters wi t h p h o s p h i d o - b r i d g e d ligands (//-PR2) is l a r gely due to their e l e c t r o n i c pro p e r t i e s as three e l e c t r o n donors, a n d their g e o m e t r i c a l flexibility. This flexi b i l i t y is e v i d e n c e d b y the e x i s t e n c e of a wide range of M- (fi-PR2) -M angles, from ca. 70° to 138° , depending on w h e t h e r metal- metal bonds are p r e s e n t o r not [34-35]. A n example of the fl e x i b i l i t y of the f o r m a l l y three electron d o n o r /x-PPh2 is p r o v i d e d b y [Fez (/i-PPh2) 2 (CO) 6] , where the Fe-P-Fe angle is 7 2 “wi t h an Fe-Fe b o n d dis t a n c e of 2.62A. U p o n o x i d a t i o n to

[Fe2(/x-PPh2)2 (CO)6]2+, the Fe-P-Fe angle increases to 105.5° w i t h an Fe-Fe b o n d d i s t a n c e of 3.63A [30]. In this case, the f l e x i b i l i t y of the p h o s p h i d o bridges allows for the forma t i o n and b r e a k i n g of metal-metal bonds without c o m p l e x fragmentation. B e l l o n et.al. [36] pr e p a r e d the novel

p h o s p h i d o - b r i d g e d d i i r i d i u m complex [{ir(CO) (PPh3) (fi-PPh2) }2] 'from the two d i f f e r e n t irid i u m hydride complexes IrH3 (PPh3 ) 3

a n d I r ( C O ) ( H ) ( P P h3 ) 3 in b o i l i n g DMF (dimethylformamide) u n d e r n i t r o g e n for three h o u r s . The two metals of

[{ir(CO) (PPh3) (fi-PPh2) }2] are connected b y a formal double b o n d 2.55lA long, an d b r i d g e d b y two PPh2 ligands. In a re l ated s tudy G e o f f r o y a n d co-workers [37] r e ported

b i n u c l e a r o x i d a t i v e a d d i t i o n to p h o s p h i d o - b r i d g e d d i r h o d i u m compl e x e s to i n v e s t i g a t e the stability of the brid g e s and changes in m e t a l - m e t a l bonds. D i p h e n y l p h o s p h i d o - b r i d g e d d i r h o d i u m compl e x e s have b e e n studied e x t e n s i v e l y b y Me e k a n d his group [38,40] . T h e y investigated the catalytic a c t i v i t y of these complexes, the stability of the p h o s p h i d o bridges b e t w e e n t r a n s i t i o n metals, and the use of 31P N M R for c h a r a c t e r i z a t i o n a n d structure elucidation.

Phosphido-b r i d g e d dim e t a l l i c complexes are of high interest Phosphido-b e c a u s e of their p o t e n t i a l to induce catalytic and stoichio m e t r i c

t r a n s f o r m a t i o n as a result of cooperative interactions b e t w e e n adjacent metals [41-47]. G eoffroy a n d co-workers

[41] e x a m i n e d the interconversion of a series of Ph2P- b r i d g e d cobalt carbonyl complexes, some of w h i c h ha v e b e e n

found to f u nction as hydroformulation catalysts or catalyst precursors. Jones and co-workers [42] also studied R2P- b r i d g e d compl e x e s focusing on the steric effects of the R g roup of R2P - . T h e y initially investigated the use of di-

t e r t - b u t ylphosphine (Bu2P) ligand, and c o n c luded that the substantial steric bu l k of the t-butyl g roup tends to limit the c o o r d i n a t i o n of other ligands to a metal centre. This m a y be the re a s o n for the difference b e t w e e n o ther

p h o s p h i d o - b r i d g e d complexes such as those of PPh2P- and those of B u ‘2P- [42b] .

A wide range of ph o s p h i d o - b r i d g e d clusters has b e e n

r e p o r t e d in recent y e a r s . Th e y v a r y in n u c l e a r i t y a n d metal combinations. Haines and co-workers have s y n t h e s i z e d and c h a r a c t e r i z e d the t e t r a nuclear clusters [Rh4 (/i-PPh2) 2 (/i- Cl) 2 (CO) 4 (PPh2H) 2] [48], and [Rh4 (/i-PPh2) 4 (/x-CO) 2 (CO) 4] [49] as part of an investigative s tudy of the potential of the d i p h e n y l p h o s p h i d o ligand, PPh2~, for stabilizing homo- and h e t e r o n u c l e a r clusters of unusual geometry and

s t e r e o c h e m i s t r y [50-52]. P h o s p h i d o - b r i d g e d t r i nuclear clusters a t t r a c t e d a nu m b e r of r e search groups in the past two decades. In 1975 Carty and co-workers r e p o r t e d the first e x a mple of the p h o s p h i d o - b r i d g e d t r i p l a t i n u m c l u ster Pt3 (/x-PPh2) 3 (PPh3) 2 (Ph) (1 . 4 ) [53], a cluster of significant importance from a synthetic and c h a r a c t e r i z a t i o n viewpoint. S y n t h e t i c a l l y the cluster is made by reflu x i n g [Pt(PPh3)4] in b e n z e n e for several days to form at first the d i m e r [Pt{/x- PPh2)2(PPh3)2] a n d later the t r i p l a t i n u m cluster. T h e c l u s t e r

c o ntains two types of bridges, one w h ere a Pt-Pt bo n d is p r e sent and one where the b o n d is absent. The cluster was later inve s t i g a t e d b y B r a u n s t e i n et a l . [35], who found it to adopt different structures in the s o lid state (1 .4 a ) or

(1 .4b) d e p e n d i n g on the solvent u s e d for crystallization. The. structural differences b e t w e e n these isomers c o n cern the m e t a l - m e t a l bonding. These 4 4 -electron clusters formally c o n tain two Pt(I) centres a n d one Pt(II) centre. 1.4 is the o n l y example of a p l a t i n u m c l u s t e r to d i s p l a y easy skeletal isomerization, a feature of great interest but rarely

e n c o u n t e r e d in clus er chemistry.

The immediate b a c k g r o u n d to this thesis begins w i t h the r e c e n t l y r eported rep r e s e n t a t i v e examples of triangular

p h o s p h i d o b r i d g e d clusters. D i x o n and R a t t r a y reported that reflux of [PdCl (PPh3) 3] [BF4] in THF (tetrahydrofuran) at

125°C led to the formation of the t r i p a l l a d i u m cluster ' [Pd3 (^-PPh2)2 (/x-Cl) (PPh3)3] [BF4] (1 . 5 ) [54]. The cluster was

fully c h a r a c t e r i z e d b y 3 1P {1H} N M R s p e c t r o s c o p y and X -ray crystallography. The p l a t i n u m t riangle is almost equatorial w i t h the C l - bridged Pd-Pd distance, 2.89

A

A.

D ixon a n d co-workers [76] r e p o r t e d that in p resence of p- toluidine (as HCl scavenger) r e a c t i o n b e t w e e n HPPh2 and

[Pd3 (/x-PPh2) 2 (/x-Cl) (PEt3) 3] [BF4] is almost instantanous at 25°C to result in the formation of the clus t e r [Pd3 (/z-PPh2) 3

(PEt3)3] [BF4] (1 . 6 ) in high yield. In 1985 D i x o n and c o ­ workers [55] re p o r t e d the synthesis and rea c t i v i t y of a n e w class of m i x e d p a l l a d i u m a n d p l a t i n u m clusters (1 . 7 ) . The study of these clusters b y 31P N M R has shown the u s e fulness of the techn i q u e in wo r k i n v o l v i n g p r e v i o u s l y difficult to char a c t e r i z e clusters. In a r e l ated s tudy Jones and c o ­ w o r k e r s [77] showed that the rea c t i o n of [Pd(CO)Cl]n w i t h L i - P B u2 at -78 °C affords the c l u s t e r [Pd3 (/x-PBu‘2) 3 (Cl) (CO) 2]

w i t h an average Pd-Pd distance of 2.980

A.

isoelectronic with the cationic clusters such as [Pd3 (/i- PPh2) 3 (PEt3) 3] [BF4] (1 . 6 ) described by Dixon and co-workers

[76] . Dh Ph Ph2P' 2 .7 5 8 A Ph, - 3.586A _)pi 2 .9 5 6 A P P h2 'P P h , _{Ph3P ^ "} Pt ■Pt-P h , ■-P-P h , 'PPh-, 1 . 4 a fro m C H2C I2/p e n ta n e 1 . 4 b fr o m t o lu e n e /p e n ta n e

The extension of these clusters to cobalt, rhodium, and iridium metals was a step taken by a few groups during the 1980's. Haines and his group reacted [ (Rh (/x-Cl) (CO) 2}2] wi t h PPh2H in the presence of a base to afford the cluster Rh3 (/x- P P h2)3(CO) 5 [56,57], ha v i n g interesting chemical properties. It involves one formal 16 e l ectron metal centre and two 18 ele c t r o n centres. There are 46 cluster .axence electrons and the Rh-Rh bonds average 2.77

A.

A.

7 differently b y H u n t s m a n and Dahl [78], who isolated it from the re a c t i o n of Co2(CO)g w i t h P2Ph4 and characterized it b y an X-ray d i f f r a c t i o n study. A few years later, Geoffroy and co-workers [58] i n v e s t i g a t e d the stability of the phosphido- bridges of the cluster Co3 (/z-PPh2) 3 (CO) 6 (1 . 9 ) . and its

fragmentation du r i n g ma s s spectrometry. A similar cluster with bri d g i n g ji-PMe2 l i g ands has been described by

Vahrenkamp and co- w o r k e r s [79]. A series of novel

d i methylphosphido b r i d g e d clusters, Fe3 (//-PMe2) 3 (NO) 3 (CO) 4 (1 . 1 0 ) , CoFe2 (/i-PMe2)3 (NO)2 (CO) 5 (1 . 1 1 ) . and Co3 (/x-PMe2)3(CO) 6 (1 .1 2 ) were rep o r t e d to have unusual structural and d y n amic properties, that were c o n f i r m e d by crystallographic a n d N M R spectroscopic studies [79]. Jones and co-workers [65]

isolated and c h a r a c t e r i z e d the cluster [Rh3 (/x-P‘Bu2) 3 (CO) 3] (1 . 1 3 ) whose structure as r e v e a l e d by X-ray cr y s t a l l a g r o p h y has two features that make it notably different from the other Ph2P - b r idged t r i m e r s .

The

coordinatively u n s a t u r a t e d since each Rh has only one terminal CO b o n d e d to it. In an independent study, Jones and co-workers T75] r e p o r t e d the iridium analogue [Ir3 (/z- PlBu2) 3 (CO)5] (1 . 1 4 ) . In Some respects, the structure of 1.14 is similar to that of [Rh3 (/z-PlBu2) 3 (CO) 3] (1 . 1 3 ) descr i b e d b y Haines and E n g l i s h [57]. Recently, Dixon and his group

[59,60] pre p a r e d i r i dium analogues of some of these Rh clusters, notably, [lr3 (/.t-PPh2) 3 (CO) 5] , a cluster of higher stability c o m p a r e d to the r h o d i u m cluster.

00 ₀₀

B u 2 _{Bu 2}

The follo w i n g chapters of this work will focus on the c h e m i s t r y of the clusters [M3 (/x-PPh2) 3 (CO) nL2] (n = 3,L --- CO or PPh3, L 2 = dppm; n = 5, L = B u ‘NC) , (M = Rh or Ir) . The

i n v e s t i g a t i o n of the reactivity of these clu s t e r s is d i v i d e d into r e a c t i o n types such as, ligand addition, ligand

substitution, and oxidative addition where applicable. The st udy is c o n c e n t r a t e d on the formation and the structural p r o p e r t i e s of the complexes produced.

Ch a p t e r two will deal w i t h different synthetic

ap p r o a c h e s to the pa r e n t clusters M3 (/i-PPh2) 3 (CO) 5, (M=Rh or Ir) w i t h more emphasis on the c h a racterization and the str u c t u r a l features of these clusters. These are

c o o r d i n a t i v e l y unsatu r a t e d clusters (46 v a l e n c e electrons) a n d are e x p e c t e d to undergo addition reactions w i t h ligands su c h as CO a n d BulWC. This addition results in structural ch a nges to the core of the cluster (i.e. b r e a k i n g of M-M bo nds a n d c h anging the degree of coordinative unsatxiration a r o u n d the m e tal c e n t r e s ) . These clusters also u n d ergo li g a n d substitution reactions. Since ligands such as dp p m

(b i s ( d i p h e n y l p h o s p h i n o ) m e t h a n e , PPh3

( t r i p h e n y l p h o s p h i n e ) ,and P ( O M e) 3 (trimethylphosphite) can ea s i l y r e p l a c e carbonyl ligands on thes^ clusters to afford h i g h l y stable clusters of significantly d i f f e r e n t chemistry.

C h a p t e r three of this thesis will be d e v o t e d entirely to the o x i d a t i v e addition chemistry of two class-s of

clusters: [M3 (/i-PPh2) 3 (CO) 4 (Bu'NC) 3] , (M=Rh or Ir) w i t h 50 v a l e n c e electrons, in w h ich there are two f o r m a l l y 16- e l e c t r o n centx~es and one 1 8 -electron centre; and [M3(-

PP h 2) 3 (CO) 3 (pt-dppm) ] , w i t h 46 valence electrons, one formally 1 6 -electron centre and two 1 8 -electron centres. Comparing the r e a c t i v i t y of these two classes of clu s t e r s towards o x i d a t i v e add i t i o n reagents such as Mel and Bz B r u n d e r mi l d

9 c o n d i t i o n s raises questions about the effect of geo m e t r y a r o u n d the metal centres involved. The c l u ster [M3(/i- P P h 2) (CO) 4 (Bu'NC) 3] (M=Rh or Ir) w i t h two f o r m a l l y 16- e l e c t r o n centres is subject to double o x i d a t i v e addition re a c t i o n s w h i c h are d e s c r i b e d in chapter three. Mild

r e a g e n t s such as Mel and BzBr react w i t h o n l y one formally 1 6 -electron centre of the cluster; however, more v i gorous r e a g e n t s such as kCl, I2, and HgX2 (X = Cl, Br, I) have the a b i l i t y to react wi t h b o t h c o o r d i n a t i v e l y u n s a t u r a t e d

c e n t r e s .

Chapter three also deals w i t h reactions of the halogens Cl 2, Br2/ and I2, the m e rcuric halides H g X2 {X=C1, Br, I) , and the m ercuric acetates HgR2 (R=02CCH3, or 02CCF3) w i t h the

c l u s t e r s [M3 (/x-PPh2) 3 (CO) nL2] (n=3,L=C0 or PPh3, L2=dppm) .

T h e p r o d u c e d clusters are stru c t u r a l l y d i f f e r e n t from those e x p e c t e d from oxidative a d dition reactions.

Finally, in chapter four, I d escribe a synthetic a p p r o a c h to ma k i n g p h o s p h i d o - b r i d g e d m i x e d i r i dium and r h o d i u m clusters w h i c h is an important step in studying p h o s p h i d o - b r i d g e d clusters in general. M i x e d metal clusters s h o w the effect of one metal centre over the other, and aid w i t h the c h a r a c t e r i z a t i o n of p h o s p h i d o - b r i d g e d cluster

systems as a whole. R e a c t i v i t y of m i x e d metal clusters d i f fers to some extent from those of the h o m o n u c l e a r clusters. W i t h the a i d of 31P N M R (ID and 2D) and FAB-MS c h a r a c t e r i z a t i o n and i d e n t i fication of two m i x e d metal cl u s t e r s is accomplished.

C H A P T E R TWO

Synthesis of the Clusters M 3 (f*-PPh2) 3 (CO) s, (M=Rh or Ir) , a n d T h eir R e a c t i v i t y T o w a r d CO, PPh3, DPPM, B:ilNC, and P ( O M e ) 3

11 2.1. I n t r o d u c t i o n

In principle, the p h osphido-bridges are able to p r e s e r v e the i n t e g r i t y of the cluster while p e r m i t t i n g the b r e a k i n g and m a k i n g of the metal-metal bonds. A wide range of clusters c o n t a i n i n g these b r i d g i n g groups have been

reported, and e x amples include, [Co3 (/^-PPh2) 2 (fi-CO) (CO) 6] [63], [Co3 (^3-PPh) (C0)9] [64], [Rh3 (/i-PBul2) 3 (CO) 3] [65,66], [Ir3(/x-PBut2)3 (CO)6] [67], [Ir3 (/x-PBul2) 3 (CO) 5] [6 8 ], [Pd3 (/x-PB u l2)3 (Cl) (C0)2] [69], [Pd3 (/x-PPh2) 3 (/i-Cl) (PPh3)3] [BF4] [54,55],

[Pt3 (/z-PPh2) 3 (Ph) (PPh3) 2] [53] , [Pt3 (/x-PPh2) 2 (/x-H) (PPh3)3] [BF4] [70], [Rh3 (/i-PPh2) 3 (CO) 5] [56], [Ir3 (/x-PPh2) 3 (CO) 5] [54], and [Co3 (/i-PPh2) 3 (CO) 5] [58] . All of the above examples of t r i n u c l e a r clusters share the similar characteristic of

ha v i n g p h o s p h i d o bridges that are flexible and contribute to the stability of the clusters u n d e r different reaction

conditions. R e a c t i v i t y of some of these clusters is ‘d e t a i l e d in the next few p a r a g r a p h s .

P h o s p h i d o - b r i d g e d trinuclear clusters are known to

u n d e r g o several types of reactions. Ligand addition, li g a n d substitution, and o x i d a t i v e add i t i o n reactions are among r e a c t i o n types that are k nown to dominate in cluster

chemistry. Ha i n e s a n d Steen [56] have s y nthesized the 46- e l e c t r o n c l u ster [Rh3 (/x-PPh2) 3 (CO) 5] wi t h average R h -Rh bonds of 2.77 A by r e a c t i n g [Rh2 (/i-Cl) 2 (CO) 4] wi t h PPh2H irj( the

/

p r e s e n c e of a base. Th e y also inv e s t i g a t e d its rea c t i v i t y w i t h CO (carbon monoxide) and PPh2H ( d i p h e n y l p h o s p h i n e ) . S a t u r a t i o n of the c l u s t e r w i t h CO converts it to [Rh3 (/x- PP h 2) 3 (CO) 9] , w h i c h de g r a d e s q u i c k l y to the unstable 50

e l e c t r o n c l u ster [Rh3 (//-PPh2) 3 (CO) 7] with average R h-Rh bonds of 3.15 A. This e x p a n s i o n from b o n d i n g to non b o n d i n g metal- metal d i s t a n c e s is a l s o present in the cluster [Rh3 (/x-

PPh2) 3 (CO) 6 (PPh2H) ] w i t h average R h - R h bonds of 3.17 A. The neutral ligand PPh3 (triphenylphosphine) substitutes CO ligands i n s t e a d of a d d i n g to [Rh3 (/x-PPh2) 3 (CO) 5] . Bi l l i g and

co- w o r k e r s [61] thermally dec o m p o s e d Rh(H) (CO) (PPh3 ) 3 to a f f o r d the clus t e r [Rh3 (^-PPh2) 3 (CO) 3 (PPh3) 2] w i t h average Rh- R h b onds of 2.78

A,

A d d i t i o n of CO ligands to the cluster [Rh3 (/z-

PtBu2)3(CO)3] was investigated b y Jones and Wright [73] . This a d d i t i o n resulted in the cluster [Rh3 (/x-P‘B u 2) 3 (/i-CO) (CO) 4]

(scheme 2.1). It was also shown to be a facile and re v e r s i b l e addition, an interesting p h e n o m e n o n that is r e levant to m a n y h o mogeneous and hetero g e n e o u s catalytic r e a c t i o n s [74]. In m a n y cases CO a d dition to transition metal clusters results in cleavage of m etal-metal bonds

[74] . In this case the Rh3 framework expands significantly, but the R h - R h bonds do not b reak completely. X-ray

c r y s t a l l o g r a p h i c studies on the product c l u s t e r revealed that the unique b r i d g i n g CO unit is well out of the Rh3

■plane, and c o o r d i n a t i o n about the unique R h centre wi t h the a d d i t i o n a l CO mo l e c u l e is tetrahedral , w h i c h is a

r e l a t i v e l y rare g e o m e t r y for f o u r - coordinate Rh(I). I n t e r e s t i n g l y the R h - R h bonds not b r i d g e d b y CO have

le n g t h e n e d c o n s i d e r a b l y (3.018

A

A).

CO) (CO) 4] is quite different from that of the PPh2-bridged ana l o g u e [Rh3 (/z-PPh2) 3 (CO) s] [56,75]. In the case of [Rh 3 (/x- PPh2 ) 3 (CO)5] , there are no bri d g i n g CO ligands; two Rh atoms e a c h b e a r two CO's and are b r i d g e d b y PPh2 that lies well out of the R h3 plane. The remai n i n g R h b e a r one CO, and the o t h e r pi-PPh2 groups lie in the Rh3 plane. U n f o r t u n a t e l y no fu r ther studies have be e n rep o r t e d on the c l u s t e r [Ir3(/x- P B u ‘2) 3 (CO) 5] , w h i c h in some respects is s t r u c t u r a l l y similar to the clusters [Rh3 (/i-PPh2) 3 (CO) 5] and [Rh3 (/i-

13

1 atm

S c h e m e 2.1

The c o o r d i natively s a t u r a t e d cluster [Co3 (/z-PPh2) 3 (CO) 6] is therm a l l y stable up to 1 1 0 °C u n d e r an N2 atmosphere.

However w h e n heated u n d e r CO p r e s s u r e it rearranges to give the d i mer [Co2 (/x-PPh2) 2 (CO) 6] in q u a n t i t a t i v e y i e l d [41a].

The cluster was also f o und to react w i t h PPhEt2

(diethylphenylphosphine) to fo r m first a m o n o s u b s t i t u t e d derivative [Co3 (/x-PPh2) 3 (PPhEt2) (CO) 5] , then a d i s ubstituted derivative [Co3 (^-PPh2) 3 (PPhEt2) 2 (CO) 4] , and finally the

trisubst i t u t e d derivative, [Co3 (/x-PPh2) 3 (PPhEt2) 3 (CO) 3] (Scheme 2.2). The severe c r o w d i n g in the t r i s u b s t i t u t e d derivative forces f r a gmentation of the c l u s t e r to p r o duce the dimer

[Co2 (fi-PPh2) 2 (PPhEt2) 2 (CO) 2] , w h i c h s u r p r i s i n g l y was found to easily reform the c l u s t e r [Co3 (//-PPh2) 3 (CO) 6] upon exposure to 1 atm of CO at 25°C.

PhJ?' OC— C o ; oc/ OC \ Z 0 .P E t2Ph PhjP PPtij .P E t2Ph --- C o -- CO -p-^” ^-CO P h , ac—C o— ■— oc/ -p” Ph, ; C o — P E tjP ti '''-CO OC^ ^PEtjPh P tv ,P ‘ P P h j ac ♦ P E t2Ph yEl2Ph PhD' PPhj O C Co-ac/ --- C o — PC t2Ph -p^ — v'-c o P h , P h2 E«2PhP^ _ ^ P" C o = oc/ ^ P " P h , = C o E l2PhP C o ---oc/ 'P* P h , - C o — P E l,P h "''-C O "PEt2Pli Scheme 2.2

Dixon a n d co-workers [54] reacted [Rh3 (/z-PPh2) 3 (CO) 5] (2 .3 ), with the chelating ligand dppm

(bis(diphenylphosphino)methane) to obtain the highly stable derivative, [Rh3 (/i-PPh2) 3 (CO) 3 (/i-dppm) ] (2_il) . They also

s u c c essfully s ynthesized the iridium analogue of [Rh3(^- PPh2) 3 (CO) 5] (2 . 3 ) . In an atmosphere of CO, the cluster

15 w h e r e a s r e action w i t h dp p m o r PPh3 results in replacement of C O to afford [Ir3 (/x-PPh2) 3 (CO) 3 (L2) ] , (L = PPh3 o r L2 = dppm) . A d d i t i o n of CO to [Ir3 (/i-PPh2) 3 (CO) 3 (/z-dppm) ] af f o r d e d the

i n t e r e s t i n g c l u s t e r [Ir3 (/z-PPh2) 3 (CO) 4 (/x-dppm) ] . The CO l i g a n d is added to the u n i q u e Ir centre l e a ding to an e x p a n s i o n of the Ir3 core, a n d r e s u l t i n g in tetrahedral g e o m e t r y around the unique Ir(I). The o b s e r v e d lengthening o f Ir-Ir bonds resembles that se e n for the c l u s t e r [Rh3 (/i- P‘B u 2) 3 (/i-CO) (CO) 4] . A l t h o u g h the Ir-Ir b o n d d i s t ances have l e n g t h e n e d s i g n i f i c a n t l y (2.99 A from 2.80

A

C O PPh O C — M M — C O1 Ph, •PPh, Ph, (2.1) M=Rh (2.2) M =Ir C O I PPh M — C O O C — M Ph, (2.3) M=Rh. L=CO (2.4) M=Rh. L= PP'n3 (2.5) M =Ir, L=CO (2.6) M =Ir, L=PPh3 D i x o n a n d co-workers [54,55] also i n v e s t i g a t e d ad d i t i o n of B u ‘N C (tert-butylisocyanide) to the c l u s t e r [M3 (/z-

P P h 2) 3 (CO) 5] , M = R h or Ir. The Bu'NC li g a n d yi e l d s a d dition p r o d u c t [M3 (/x-PPh2) 3 (CO) j (BulNC) 3] , M = Rh o r Ir, w i t h

B ulNC L B u ‘NC ph2p PPho O C — M M — C O o q/ ^ c o Ph2 (2.7) M=Ir, L=CO (2.8) M =ir. L=t-BuNC (2.9) M=Rh, L=t-BuNC 2.2. Results:

This c h a pter describes the synthesis of the cluster [Ir3 (/x-PPh2) 3 (CO) 5] (2 . 5 ) . a n d a n e w route to m a k i n g the c l u s t e r [Rh3 (/i-PPh2) 3 (CO) 5] (2 . 3 ) . In a d d i t i o n it discusses the r e a c t i v i t y of these clusters wi t h dppm, B u ‘NC, CO, and P (O M e )3

.

2.2.1- S y n t h e s e s of [M3(/x-PPh2)3(CO)s] , M=Rh(2.3) or Ir(2.5) .

T h e wo r k r e ported in this section includes a synthetic r oute to the cluster [Rh3 (/x-PPh2) 3 (CO) s] (2 . 3 ) that was

d e v i s e d b y Haines and co-workers [56]. It m a i n l y involves the r e a c t i o n of the dimer [Rh(/i-Cl) (CO) 2 ] 2 w i t h two

e q u i v a l e n t s of PPh2H in b e n zene in the p r e s e n c e of a base s u c h as HN E t2 (diethylamine) at room t e m p e r a t u r e (scheme 2.3). A so l u t i o n of [Rh3 (/i-PPh2) 3 (CO) s] (2 . 3 ) in benzene g r a d u a l l y turns b r own over a p e r i o d of 6- 8 hours r e s u lting

(pi-17 C O )2 (CO)4] [49] . The conversion, w h i c h was mo r e r a p i d in p o l a r solvents such as CH2C12 (dichlo r o m e t h a n e ) , is

i r r e v e r s i b l e and no evidence c ould be o b t a i n e d for the

f o r m a t i o n of [Rh3 (^i-PPh2)3 (CO)5] (2 . 3 ) . In the absence of the H N E t2 base, [{Rh(/x-Cl) (CO)2}2] reacts w i t h two equiva l e n t s of P P h 2H in b e n zene at room temperature to a f f o r d the 50-

e l e c t r o n cluster, [Rh3 (/x-PPh2) 3 (/i-CO) (/x-Cl) 2 (CO) 3] [62]. This c l e a r l y indicates that the cluster, [Rh3 (/x-PPh2) 3 (CO) 5] (2 . 3 ) is s u sceptible to electrophilic attack b y halogens. The s t r u c t u r a l l y similar derivative [Rh3 (/i-PPh2) 3 (CO) 3 (PPh3) 2]

(2 . 4 ) , is p r e p a r e d b y thermal d e c o m p o s i t i o n of [Rh (CO) (H) (PPh3) 3] in nonane at 120°C.

O u r alternative, route to ma k i n g the c l u s t e r [Rh3 (/x- P P h2)3 (CO)5] (2 . 3 ) involves introducing CO gas to a s o lution of the d i m e r [{Rh(/x-Cl) (COD) }2] , followed b y a d d i t i o n of H N E t2 t h e n f o llowed b y two equivalents of PPh2H to p r o duce a b r i g h t g r e e n sol u t i o n of the desired clus t e r [Rh3 (/i~

P P h2)3 (CO)5] (2 . 3 ) (scheme 2.4).

T he i r i dium analogue of [Rh3 (/x-PPh2) 3 (CO) 5] (2 . 3 ) is p r e p a r e d b y r e a c t i n g [{lr(/x-Cl) (COE)2}2] w i t h PPh2H in

b e n z e n e in pre s e n c e of the base HNEt2 (scheme 2.4) . 31P N M R d a t a in d i c a t e the pr e s e n c e of a mixture of the two clusters

[Ir3 (/i-PPh2) 3 (CO) 5] (2 . 5 a ) , and [Ir3 (/x-PPh2) 3 (CO) 6] (2 . 5 b ) . As t he s o l u t i o n is satur a t e d wi t h CO the h e x a c a r b o n y l [Ir3(^i- P P h2)3 (CO)6] (2. 5 b ) dominates. Subsequent removal of the CO s a t u r a t e d solvent in vacuo converts [Ir3 (/i-PPh2) 3 (CO) 6] (2 . 5 b ) to [Ir3 (/x-PPh2) 3 (CO) 5] (2 . 5 a ) after a p e r i o d of 2-3 hours, s h o w i n g that there is a CO reversible a d d i t i o n b e t w e e n the p e n t a - a n d the h e x a c arbonyl clusters.

2.2.2 C r y s t a l l o g r a p h i c Analysis.

T he X - r a y structure [56] has confi r m e d that [Rh3 (/x- P P h2)3 (CO)5] (2 . 3 ) is indeed the pentac a r b o n y l der i v a t i v e and

not the suspected h e x a c a r b o n y l derivative [Rh3 (/z-PPh2) 3 (CO) 6] . T h e m o l e c u l a r structure of 2.3 contains a tri a n g u l a r

s k e l e t o n of rhodium a t o m s . There is an almost p l a n a r Rh3P2 core and the third p h o s p h i d o bridge is bent so that Rh(l)- P (3)- R h (3) plane is almost p e r p e n d i c u l a r to the core. Thus P(l) a n d P (2) are o n l y s l i g h t l y out of the R h3 p lane at 0.2 9

A

A,

A,

A.

19

V

CO CO CO

\ /

\ \

21 The R h (2) centre adopts a p l a n a r g e o m e t r y w h i c h can be

a t t r i b u t e d to it b e i n g a 1 6 - e l e c t r o n centre. This c oordinative u n s a t u r a t i o n of Rh(2) m a y be due to the

p r e s e n c e of a ph e n y l g r oup o n P(3) blo c k i n g the c o o r d i n a t i o n

In our laboratory, a t t e m p t s have be e n made to obtain crystals of e i t h e r [Ir3 (/z-PPh2) 3 (CO) 5] (2 . 5 a ) . or [Ir3 (/i-PPh2)3 (CO)6] (2 . 5 b ) s u itable for X - r a y crystal l o g r a p h y studies but all of th e m p r o v e d unsuccessful.

2.2.3 S p e c t r o s c o p i c Analysis.

The 3‘p{'H} N M R s p e c t r u m of the the complex [Rh3(/x-

PPh2)3 (CO)s] (2 . 3 ) at a m b ient tempe r a t u r e consists of a b r o a d m u l t i p l e t at 274.0 p p m w h i c h is p r e s u m a b l y due to the two e q u ivalent p h o s p h i d o bridges, a n d a b r o a d singlet at 257.8 p p m a t r i b u t a b l e to the u n i q u e p h o s p h i d o b r i d g e . N o obvious change is o b s e r v e d w h e n the sample is cooled to - 4 0 °C. The s p e c t r u m also e x h i b i t s a t h i r d b r o a d multiplet at 287.9 ppm, w h i c h shifts to 1 1. 6 p p m w h e n the sample is s a t u rated w i t h CO, s u g g e s t i n g p o s s i b l e f o r m a t i o n of the saturated c l u ster

[Rh3(/i-PPh2)3(CO)9] fr o m [Rh3 (/x-PPh2) 3 (CO) 6] . The shift of signal p o s i t i o n to the h i g h f i eld region of the spectrum, c o rresponds to R2P - g r o u p b r i d g i n g n o n - b o n d e d rhodium metals of the c l u s t e r [Rh3 (/i-PPh2) 3 (CO) 9] [80]. 3 1p{'h} N M R spectra of the i r i d i u m ana l o g u e [Ir3 (/x-PPh2) 3 (CO) 5] (2 . 5 a ) and [Ir3 (/i-PPh2)3 (CO)6] (2. 5 b ) a r e s h o w n in figure (2.1). Figure 2.1a also i l l u s t r a t e s the c o e x i s t e n c e of b o t h clusters. The s p e c t r u m of 2 .5 a co n s i s t s of two sets of peaks.

s i t e . co

Figure (2.1)

3 1P{iH} NMR spectra of the clusters (a) [Ir3 (;x~PPh2) 3 (CO) 5] (2 . 5 a )

(b) [Ir3 (*i-PPh2) 3 (CO) 6] (2 . 5 b )

100

1 5 0 200

2 5 0

23 T a b l e (2.1)

3 1P { ‘h} N M R Chemical Shifts3(6 ,ppm) and Coupling C onstants (Hz) for the clusters;

[Ir3 (/x-PPh2) 3 (CO) 5] (2 . 5 a ) [Ir3 (^-PPh2)3(CO)6] (2 . 5 b ) [Rh3 (/u-PPh2) 3 (CO) 5] (2^3) ,2 P' 2.3 2 . 5a 2 .5b 6 (1,3) 264 . 0 240 . 5 174 . 8 6 (2 ) 257 . 8 100.5 174 . 8 J (1, 3 ) b 15 b J (1, 2) b J(l,4) b --J (1, 5) b -- --J ( l ,6 ) b --J (2 , 5) 1 b

-3 All coupling constants which are not listed were less than the spectrum resolution' of about 5 Hz