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Metal complexes of ferrocenylphosphines : catalytic properties of some rhodium complexes Kim, Tae-Jeong 1984

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METAL COMPLEXES OF FERROCENYLPHOSPHINES: CATALYTIC PROPERTIES OF SOME RHODIUM COMPLEXES by TAE-JEONG KIM M . S c , , Korea U n i v e r s i t y , 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES Depar tment o f C h e m i s t r y We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d The U n i v e r s i t y o f B r i t i s h Co lumb ia M a r c h , 1984 © Tae - J eong K im , 1984 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e h e a d o f my d e p a r t m e n t o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 7cn 111 ABSTRACT A s e r i e s o f a c h i r a l and c h i r a l f e r r o c e n y l p h o s p h i n e s have been p r epa r ed w i t h s p e c i a l emphas i s on t ho se c o n t a i n i n g b u l k y t e r t - b u t y l g roups on phos -phorus ( I and V were p r e v i o u s l y known) : R 1 R 2 R 3 R 4 I Ph Ph Ph Ph I I Ph CMe 3 Ph CMe 3 I I I Ph Ph CMe 3 CMe 3 IV CMe 3 CMe 3 CMe 3 CMe 3 R 5 R 6 R 7 V P ( C M e 3 ) 2 H H VI P ( C M e 3 ) 2 P ( C M e 3 ) 2 H VI I P ( C M e 3 ) 2 P ( C M e 3 ) 2 P ( C M e 3 ) 2 Fe / \ * .Me They form a number o f t r a n s i t i o n me ta l comp lexes such as [ R h ( L - L ) -(NBD ) ]C10 4 ( L - L = I - V I I ; NBD = n o r b o r n a d i e n e ) , M ( L - L ) X 2 (M = Pd , N i ; L - L = I - IV ; X = C I , B r ) , M ( L - L ) ( C 0 ) 4 (M = C r , Mo; L-L = I ) , and F e x ( L - L ) ( C O ) (x = 1 , y = 3 , x = 2 , y = 8 , L-L = 1 ) . A l l t h e s e l i g a n d s and t h e i r me ta l comp lexes have been f u l l y c h a r a c t e r i z e d by a n a l y t i c a l and s p e c t r o s c o p i c t e c h n i q u e s . In a number o f c a s e s t h e s e r e s u l t s a r e c o n f i r m e d by X - r a y a n a l y s e s . The c o n f i g u r a t i o n o f V I I p roved t o b e , f o r e xamp l e , ( S , S ) w i t h r e g a r d t o c e n t r a l and p l a n a r c h i r a l i t y r a t h e r t h an t he e xpe c t e d ( S ,R ) found f o r V and V I . i v The a c h i r a l Rh ( I ) comp lexes [ R h ( L - L ) ( N B D ) ] C 1 0 4 ( L - L = I - I V ) a r e e f f i c i e n t c a t a l y s t p r e c u r s o r s f o r t h e h y d r o g e n a t i o n o f a r ange o f o l e f i n s (1 atm H^, 3 0 ° C ) . The p r e s en ce o f b u l k y t e r t - b u t y l g roups enhances r e a c t i o n r a t e s e x c e p t when b u l k y o l e f i n s a r e t h e s u b s t r a t e s . The c h i r a l t r i s p h o s p h i n e Rh ( I ) complex [ R h ( L - L ) ( N B D ) ] C 1 0 4 ( L - L = V I I ) i s a v e r y e f f i c i e n t c a t a l y s t p r e c u r s o r f o r t h e a symmet r i c h y d r o g e n a t i o n o f a c y l a m i n o -c i n n a m i c , a c y l a m i n o a c r y l i c , and ( E ) - a - m e t h y l c i n n a m i c a c i d s , g i v i n g 9 1 , 9 5 , and 61% e . e . , r e s p e c t i v e l y . The c h i r a l Rh ( I ) c o m p l e x , where L -L = V I , i s a r e l a t i v e l y poor c a t a l y s t f o r a s ymme t r i c h y d r o g e n a t i o n as compared w i t h t h e o t h e r two comp lexes ( L - L = V , V I I ) . Here a g a i n t h e p r e s en ce o f t e r t -b u t y l g roups i n c r e a s e s t he r e a c t i o n r a t e s , and t h e r a t e s become g r e a t e r as t h e number o f t e r t - b u t y l g roups i n c r e a s e s . These r e s u l t s and o t h e r c ompa ra -t i v e h y d r o g e n a t i o n s t u d i e s a r e d i s c u s s e d and r a t i o n a l i z e d i n te rms o f t h e s t e r i c ( i n c l u d i n g l i g a n d c o n f o r m a t i o n ) and e l e c t r o n i c e f f e c t s o f t h e s u b s t i -t u e n t s on t h e phospho rus a t o m ( s ) . The r e a c t i o n o f ^ w i t h t h e h y d r o g e n a t i o n c a t a l y s t p r e c u r s o r [ R h ( L - L ) -(NBD ) ]C10 4 ( L - L = I I ) i n MeOH r e s u l t s i n c r y s t a l s wh i c h have t h e s t r u c t u r e [ ( L - L ) ( H ) R h ( v - H ) 3 R h ( H ) ( L - L ) ] C 1 0 4 . When L-L = I V , t h e same r e a c t i o n r e s u l t s i n a s i m i l a r rhod ium h y d r i d e a l t h o u g h t h e p o s i t i o n s o f t h e hydrogen atoms a r e no t w e l l e s t a b l i s h e d . A number o f o t h e r h y d r i d e s , some f l u x i o n a l , a r e a l s o o b t a i n e d i n v a r i o u s s o l v e n t s f rom t h e c a t a l y s t p r e c u r s o r s [ R h ( L - L ) ( N B D ) ] -C 1 0 4 ( L - L = I - V I I ) . Where p o s s i b l e t h e s e have been c h a r a c t e r i z e d on t h e b a s i s o f t h e i r NMR s p e c t r a . The i m p l i c a t i o n o f t h e s e r e s u l t s w i t h r e s p e c t t o t h e mechanisms o f c a t a l y t i c h y d r o g e n a t i o n i s d i s c u s s e d . V TABLE OF CONTENTS Page T i t l e i A b s t r a c t i i i T a b l e o f C on t en t s v L i s t o f T a b l e s x L i s t o f F i g u r e s x i i i Acknowledgement x x PART I INTRODUCTION 1 CHAPTER 1 HOMOGENEOUS CATALYTIC HYDROGENATION 2 1 .1 HISTORICAL REVIEW 2 1.2 SCOPE OF DISCUSSION 4 1.3 HYDROGENATION CATALYTIC CYCLES 6 1.3.1 Hydrogen A c t i v a t i o n 6 1.3.2 S u b s t r a t e A c t i v a t i o n 10 1.3.3 H y d r i d e T r a n s f e r n 1.3.4 P r o d u c t F o rma t i o n 12 1.3.5 Summary 14 1.4 RHODIUM-PHOSPHINE CATALYSTS 16 1.4.1 Monohyd r i de C a t a l y s t s 16 1.4.2 D i h y d r i d e C a t a l y s t s 20 v i Page CHAPTER 2 ASYMMETRIC CATALYTIC HYDROGENATION 34 2.1 GENERAL ASPECTS 34 2 .2 TERMINOLOGY 35 2 . 2 . 1 Types o f C h i r a l i t y 35 2 . 2 . 2 S t e r e o i s o m e r i C R e l a t i o n s h i p s 38 2 . 2 . 3 S t e r e o - D i f f e r e n t i a t i n g R e a c t i o n s 43 2 .3 ASYMMETRIC CATALYTIC HYDROGENATION 45 2 . 3 . 1 Gene r a l 45 2 . 3 . 2 O v e r - a l l R e a c t i o n Mechanism 47 2 . 3 . 3 Mechan isms o f E n a n t i o f a c e - D i f f e r e n t i a t i o n 50 2 .4 CHIRAL RHODIUM-PHOSPHINE CATALYSTS 60 2 . 4 . 1 L i g and s w i t h C e n t r a l C h i r a l i t y 61 2 . 4 . 2 L i g and s w i t h A x i a l C h i r a l i t y 69 2 . 4 . 3 L i g and s w i t h bo th C e n t r a l and P l a n a r C h i r a l i t y 70 CHAPTER 3 FERROCENYLPHOSPHIN.ES IN HOMOGENEOUS CATALYSIS 71 3.1 GENERAL ASPECTS 71 3 . 1 . 1 A r o m a t i c E l e c t r o p h i 1 i c S u b s t i t u t i o n 71 3 . 1 . 2 S t e r e o c h e m i s t r y o f F e r r o c ene s 72 3 .2 METAL COMPLEXES OF FERROCENYLPHOSPHINES 76 3 . 2 . 1 A symmet r i c H y d r o g e n a t i o n 76 3 . 2 . 2 O the r c a t a l y t i c R e a c t i o n s 78 3 .3 GOALS OF THE PRESENT INVESTIGATION 79 3 . 3 . 1 New R h o d i u m - F e r r o c e n y l p h o s p h i n e Complexes as 79 H y d r o g e n a t i o n C a t a l y s t s 3 . 3 . 2 O the r Me t a l Complexes o f F e r r o c e n y l p h o s p h i n e s 80 v i i Page PART I I EXPERIMENTAL 82 CHAPTER 4 GENERAL EXPERIMENTAL SECTION 83 4.1 GENERAL 83 4 . 1 . 1 M a t e r i a l s 83 4 . 1 . 2 O l e f i n S u b s t r a t e s 83 4 . 1 . 3 I n s t r u m e n t a t i o n 84 4 . 2 HYDROGENATION EXPERIMENTS 85 4 . 2 . 1 Gas -Up take A p p a r a t u s 85 4 . 2 . 2 Gas Uptake E x p e r i m e n t a l P r o c edu r e 87 4 . 2 . 3 Work up o f Hyd rogena ted P r o d u c t s 88 4 . 2 . 4 H y d r o g e n a t i o n o f t h e C a t a l y s t P r e c u r s o r s 89 4 . 3 OPTICAL ROTATION MEASUREMENTS 90 4 . 4 SYNTHESES OF STARTING MATERIALS 92 4 . 4 . 1 The Pho sph i n e s RR 'PCI 92 4 . 4 . 2 F e r r o c e n e D e r i v a t i v e s 94 4 . 4 . 3 Me ta l Complexes 97 4 . 5 SYNTHESES OF FERROCENYLPHOSPHINES 98 4 . 5 . 1 A c h i r a l L i g and s 98 4 . 5 . 2 C h i r a l L i g a n d s 101 4 . 6 SYNTHESES OF Rh(I)-FERROCENYLPHOSPHINE COMPLEXES 103 4 . 6 . 1 A c h i r a l Complexes 103 4 . 6 . 2 C h i r a l Complexes 104 v i i i Page 4 .7 SYNTHESES OF OTHER METAL-FERROCENYLPHOSPHINE 104 COMPLEXES 4 . 7 . 1 P a l l a d i u m Complexes 105 4 . 7 . 2 N i c k e l Complexes 106 4 . 7 . 3 I r o n Complexes 106 4 . 7 . 4 Group VI Me t a l Complexes 108 PART I I I RESULTS, DISCUSSION, AND CONCLUSION 109 CHAPTER 5 SYNTHESIS AND CHARACTERIZATION OF FERROCENYL- 110 PHOSPHINES AND THEIR METAL COMPLEXES 5.1 FERROCENYLPHOSPHINE LIGANDS 110 5 . 1 . 1 A c h i r a l L i g and s x 110 5 . 1 . 2 C h i r a l L i g and s 114 5 .2 CATIONIC RHODIUM(I) COMPLEXES OF FERROCENYL- 129 PHOSPHINES 5 . 2 . 1 A c h i r a l Complexes 129 5 . 2 . 2 C h i r a l Complexes 134 5 .3 OTHER METAL COMPLEXES OF FERROCENYLPHOSPHINES 157 5 . 3 . 1 P a l l a d i u m Complexes 157 5 . 3 . 2 N i c k e l Complexes 160 5 . 3 . 3 I r o n Complexes 163 5 . 3 . 4 Group VI Me ta l Complexes 166 i x Page CHAPTER 6 RHODIUM COMPLEXES OF FERROCENYLPHOSPHINES AS 171 HYDROGENATION CATALYSTS 6.1 CATALYST PRECURSORS 171 6 .2 -CATALYTIC HYDROGENATION OF OLEFINS 172 6 . 2 . 1 Nonasymmet r i c H y d r o g e n a t i o n 172 6 . 2 . 2 A symmet r i c H y d r o g e n a t i o n 176 6 . 3 HYDROGENATION OF CATALYST PRECURSORS 186 6 . 3 . 1 I n t r o d u c t i o n 186 6 . 3 . 2 H y d r o g e n a t i o n o f t h e C a t a l y s t P r e c u r s o r s 193 V I I I - X I V 6 . 3 . 3 Summary 224 CHAPTER 7 GENERAL CONCLUSION AND SUGGESTIONS FOR FUTURE STUDIES 226 7.1 FERROCENYLPHOSPHINE LIGANDS 226 7 .2 RHODIUM COMPLEXES OF FERROCENYLPHOSPHINES AS HYDRO- 226 GENATION CATALYSTS 7 .3 KINETIC AND MECHANISTIC STUDIES 227 7 .4 OTHER METAL COMPLEXES OF FERROCENYLPHOSPHINES 228 REFERENCES APPENDIX 229 242 X L IST OF TABLES T a b l e number Page Chap t e r 2 2.1 Asymmet r i c h y d r o g e n a t i o n o f ( Z ) - a - a c e t a m i d o - 63 c i n n a m i c a c i d s by Rh( I ) -D IPAMP 2 .2 Asymmet r i c h y d r o g e n a t i o n o f some o l e f i n i c a c i d s 65 w i t h RhCl[(-}-DI0P]S (S = C g H 6 ) 2 .3 Asymmet r i c h y d r o g e n a t i o n o f amino a c i d p r e c u r s o r s 67 w i t h [Rh (S , S -CH IRAPHOS) (COD) ] + Chap t e r 4 4.1 S p e c i f i c r o t a t i o n o f some c h i r a l p r o d u c t s 91 Chap t e r 5 5.1 A n a l y t i c a l and p h y s i c a l d a t a f o r t h e a c h i r a l - 115 l i g a n d s I - I V 5 .2 ] H and 3 1 P { 1 H } NMR da t a f o r t h e a c h i r a l l i g a n d s 115 I - I V 5 .3 A n a l y t i c a l and p h y s i c a l d a t a f o r t h e c h i r a l 121 l i g a n d s V - V I I 5 .4 ] H and 3 1 P { ] H } NMR da t a f o r t h e c h i r a l l i g a n d s 121 V - V I I 5 .5 A n a l y t i c a l and p h y s i c a l d a t a f o r t h e a c h i r a l 131 Rh ( I ) comp lexes [ R h ( P - P ) ( N B D ) ] C 1 0 4 x i T a b l e number Page 5 .6 ] H and 3 1 P { 1 H } NMR da t a f o r t h e a c h i r a l comp lexes 131 V I I I - X I 5 .7 Summary o f i m p o r t a n t bond pa r ame te r s f o r t h e 139 a c h i r a l R h ( I ) comp lexes V I I I - X I 5 .8 A n a l y t i c a l and p h y s i c a l d a t a f o r t h e c h i r a l R h ( I ) 141 comp lexes [Rh (P -N) ( .NBD) ]C10 4 5 .9 3 1 P { ] H } NMR da t a f o r t h e c h i r a l R h ( I ) comp lexes 141 5 .10 Some NMR da t a r e l e v a n t t o t h e c o n f o r m a t i o n a l 149 e f f e c t s o b s e r v ed i n t h e c h i r a l Rh ( I ) comp lexes X I I - X I V 5.11 A n a l y t i c a l r e s u l t s and m e l t i n g p o i n t s o f P d ( P - P ) - 158 c i 2 5.12 ] H NMR da t a f o r P d ( P - P ) C l 2 158 5 .13 M e l t i n g p o i n t s and a n a l y t i c a l d a t a f o r t h e N i ( I I ) 161 comp lexes N i ( P - P ) X 2 5.14 A n a l y t i c a l and s p e c t r o s c o p i c da t a f o r t h e i r o n 165 comp lexes X X I I I and XXIV 5 .15 A n a l y t i c a l and s p e c t r o s c o p i c d a t a f o r t h e Gp VI 167 me ta l comp lexes M ( P - P ) ( C 0 ) 4 Chap t e r 6 6.1 H y d r o g e n a t i o n o f o l e f i n s c a t a l y z e d by a c h i r a l R h ( I ) 173 comp lexes [ R h ( P - P ) N B D ) ] C 1 0 4 ( P - P = I - I V ) x i i T a b l e number Page 6 .2 Asymmet r i c h y d r o g e n a t i o n o f some o l e f i n i c a c i d s 177 w i t h [ R h ( P - N ) ( N B D ) ] C l 0 4 ( P -N = VI and V I I ) 6 . 3 A symmet r i c h y d r o g e n a t i o n o f amino a c i d p r e c u r s o r s 178 w i t h R h ( I ) comp lexes o f ( S . S ) - V I I and o t h e r r e p r e -s e n t a t i v e d i ( t e r t i a r y pho sph i ne ) l i g a n d s 6 .4 Asymmet r i c h y d r o g e n a t i o n o f some o l e f i n s w i t h 179 [ R h ( P - N ) ( N B D ) ] C 1 0 4 (P -N = V - V I I and PPFA) 6 . 5 NMR da t a ( h y d r i d e p o r t i o n ) f o r t h e hyd rogena t ed 207 s o l u t i o n (CDgOD) o f t h e c a t a l y s t p r e c u r s o r IX 6 . 6 H y d r o g e n a t i o n p r o d u c t s o f [ R h ( B B t P F ) ( N B D ) ] C 1 0 4 ( X I ) ; 213 A n a l y s e s , NMR, and O the r s x i i i F i g u r e number Chap t e r 1 1 .1 1.2 1 .3 1.4 1 .5 1.6 1 .7 1 .8 Chap t e r 2 2.1 2 .2 2 . 3 L IST OF FIGURES Page The f i r s t known example o f h y d r i d o a l k y l i n t e r - 13 med i a t e C l a s s i f i c a t i o n o f homogeneous h y d r o g e n a t i o n 15 c a t a l y t i c c y c l e s The p r o b a b l e c a t a l y t i c c y c l e s f o r h y d r o g e n a t i o n 17 ( c y c l e B) and i s o m e r i z a t i o n ( c y c l e A) o f a t e r m i n a l o l e f i n Two p o s s i b l e c a t a l y t i c h y d r o g e n a t i o n c y c l e s f o r 21 d i h y d r i d e c a t a l y s t s Ha l p e r n ' s mechanism f o r h y d r o g e n a t i o n o f c y c l o - 22 hexene by W i l k i n s o n ' s c a t a l y s t Two p o s s i b l e c a t a l y t i c h y d r o g e n a t i o n c y c l e s f o r 27 c a t i o n i c rhod ium-monophosph ine sys tems H y d r o g e n a t i o n c y c l e f o r [ R h ( D I P H 0 S ) ( S ) 2 ] + 30 C r y s t a l s t r u c t u r e o f [ R h 2 ( D I P H 0 S ) 2 ] 2 + 31 M o l e c u l e s w i t h c e n t r a l c h i r a l i t y 36 M o l e c u l e s w i t h a x i a l c h i r a l i t y 37 M o l e c u l e s w i t h p l a n a r c h i r a l i t y 38 x i v F i g u r e number Page 2 .4 O l e f i n s w i t h e q u i v a l e n t g roups a n d / o r f a c e s by 39 i n t e r n a l c ompa r i s on s 2 .5 M o l e c u l e s w i t h e n a n t i o t o p i c g roups o r f a c e s by 39 i n t e r n a l c ompa r i s on s 2 .6 M o l e c u l e s w i t h d i a s t e r e o t o p i c g roups o r f a c e s 40 by i n t e r n a l c ompa r i s on s 2 .7 E q u i v a l e n t m e t a l - o l e f i n comp lexes by e x t e r n a l 41 c ompa r i s on 2 .8 E n a n t i o m e r i c m e t a l - o l e f i n comp lexes 41 2 .9 C h i r a l d i a s t e r e o m e r i c m e t a l - o l e f i n c o m p l e x e s , no t 42 r e l a t e d by any symmetry o p e r a t i o n 2 .10 D i a s t e r e o m e r i c comp lexes formed by c o o r d i n a t i o n 43 o f a c h i r a l o l e f i n t o an a c h i r a l me t a l comp lex 2.11 An example o f e n a n t i o f a c e - d i f f e r e n t i a t i n g r e a c t i o n 46 o f a p r o c h i r a l o l e f i n by a c h i r a l r hod ium c a t a l y s t 2 .12 Some r e p r e s e n t a t i v e c h e l a t i n g d i ( t e r t i a r y a r y l - 47 pho sph i n e ) l i g a n d s 2 .13 The mechanism o f a s ymme t r i c h y d r o g e n a t i o n o f amino 49 a c i d s w i t h [ R h ( P - P ) * S 2 ] + 2.14 (A) The p r e f e r r e d c o n f o r m a t i o n o f ( S , S ) -CHIRAPHOS , 53 (R)-PROPHOS, (S ,S ) -SKEWPH0S , and (S)-CHAIRPHOS (B) The r i n g i n t e r c o n v e r s i o n p r o c e s s between two 53 d i a s t e r e o m e r i c c o n f o rme r s X V F i g u r e number Page 2 .15 Quadran t t h e o r y s u g g e s t e d by Knowles 55 2 .16 S c h e m a t i c r e a c t i o n c o o r d i n a t i o n p r o f i l e s f o r t h e 59 e n a n t i o f a c e - d i f f e r e n t i a t i n g r e a c t i o n s o f t h e d i a s t e r e o m e r i c [Rh (P -P ) ( s u b s t r a t e ) ] w i t h H 2 2.17 E a r l y examp les o f a s ymme t r i c h y d r o g e n a t i o n w i t h 62 R h L 3 C 1 3 2 .18 E a r l y examp les o f a s ymme t r i c h y d r o g e n a t i o n w i t h 62 a W i l k i n s o n t y p e c a t a l y s t 2 .19 E a r l y examp les o f c h i r a l f e r r o c e n y l p h o s p h i n e s 70 Chap t e r 3 3.1 F e r r o c ene w i t h p l a n a r c h i r a l i t y 73 3 .2 P r e p a r a t i v e r o u t e s t o f e r r o c e n y l p h o s p h i n e s w i t h 74 c e n t r a l and p l a n a r c h i r a l i t y Chap t e r 4 4.1 A p p a r a t u s f o r c o n s t a n t g a s - u p t a k e measurements 86 Chap t e r 5 5.1 P r e p a r a t i v e r o u t e s t o t h e a c h i r a l l i g a n d s I - I V 111 5 .2 3 2 . 3 MHz 3 1 P { ] H } NMR s p e c t r a o f t h e a c h i r a l l i g a n d s 116 I , I I and IV i n C g D 6 5.3 P r e p a r a t i v e r o u t e s t o t h e c h i r a l l i g a n d s V - V I I 118 x v i F i g u r e number Page 5.4 80 MHz ] H NMR s p e c t r a o f t he c h i r a l l i g a n d s V - V I I 120 i n C 6 D 5 5.5 3 2 . 3 MHz ^ P ^ H } NMR s p e c t r a o f t he c h i r a l l i g a n d s 123 V - V I I i n C g D 6 5.6 CD spec t r um o f t he c h i r a l l i g a n d ( R , S ) - V i n CHC1 3 126 5.7 The c r y s t a l s t r u c t u r e o f ( S . S ) - V I I 127 5 . 8 CD s p e c t r a o f t he c h i r a l l i g a n d s ( S , S ) - and (R , R ) - 128 V I I i n CHC1 3 5 .9 3 2 . 3 MHz 3 1 P { 1 H } NMR s p e c t r a o f t h e a c h i r a l com- 132 p l e x e s V I I , I X , and XI 5 .10 The c r y s t a l s t r u c t u r e o f the Rh ( I ) complex V I I I 135 5.11 The c r y s t a l s t r u c t u r e o f t h e Rh ( I ) complex IX 136 5 .12 The c r y s t a l s t r u c t u r e o f t h e Rh ( I ) complex X 137 5 .13 The c r y s t a l s t r u c t u r e o f t h e Rh ( I ) complex XI 138 5 .14 (A) CD s p e c t r a o f ( R . S ) - X I I and ( S . R ) - X I I I 142 (B) CD s p e c t r a o f ( R , R ) - and ( S . S ) - X I V 142 5 .15 3 2 . 3 MHz 3 1 P { 1 H } NMR s p e c t r a o f t h e c h i r a l Rh ( I ) 144 comp lexes ( S . R ) - X I I , ( S , R ) - X I I I , a n d ( S . S ) - X I V 5 .16 The c r y s t a l s t r u c t u r e o f [ R h ( S , R - P P F A ) t N B D ) ] P F g 145 5 .17 (A) The p roposed s i x -membered r i n g c o n f o r m a t i o n s 147 A and B i n v o l v e d i n t h e r i n g i n t e r c o n v e r s i o n p r o c e s s o f both ( S . R ) - X I I and - X I I I (B) The p r e f e r r e d r i n g c o n f o r m a t i o n o f ( S , S ) - X I V 147 xv i i F i g u r e number Page 5 .18 (A )&(B ) V a r i a b l e t e m p e r a t u r e 1 H NMR (400 MHz) 150 spec t r um o f ( S . R ) - X I I i n C D 2 C 1 2 5 .19 (A )& (B ) V a r i a b l e t e m p e r a t u r e ] H NMR (400 MHz) 152 spec t r um o f (S , R ) - X I 1 1 i n C D 2 C 1 2 5 .20 400 MHz ] H NMR spec t rum o f ( S . S ) - X I V i n C D 2 C 1 2 154 a t 35°C 5.21 The s t e r e o v i e w o f t h e c r y s t a l s t r u c t u r e o f 159 P d ( P - P ) C l 2 ( P - P = t he l i g a n d I ) 5 .22 The s t e r e o v i e w o f t h e c r y s t a l s t r u c t u r e o f , 162 N i ( P - P ) B r 2 ( P - P = t h e l i g a n d I) 5 .23 The s t e r e o v i e w o f t h e c r y s t a l s t r u c t u r e o f 168 M o ( P - P ) ( C 0 ) 4 ( P - P = t h e l i g a n d I ) 5 .24 Mechanism f o r [ 3 ] - f e r r o c e n o p h a n e b r i d g e r e v e r s a l 169 Chap t e r 6 6.1 (A) Four p o s s i b l e d i a s t e r e o m e r s o f [ ( P - N ) - 184 R h ( s u b s t r a t e ) ] + g e n e r a t e d from t h e c on f o rme r A , B, o r C o f [ R h ( P * - N ) ( S ) 2 ] + (B) F i v e p o s s i b l e d i a s t e r e o m e r s o f [ ( P - N ) R h ( H ) 2 ] 184 g e n e r a t e d f rom t he c on f o rme r A , B. o r C o f t ( P - N ) R h ( S ) 2 ] + 6 . 2 Some p o s s i b l e h y d r o g e n a t i o n pathways f o r [ ( L - L ) - 189 R h ( D i e n e ) ] A xv i i i F i g u r e number Page 6 .3 P o s s i b l e h y d r o g e n a t i o n pathways f o r V I I I i n CHC1 3 196 6 .4 (A )&(B) V a r i a b l e t e m p e r a t u r e 400 MHz ] H NMR spec t r um 198 ( CDgC^) o f t h e h y d r o g e n a t i o n p r o du c t (S) o f V I I I f rom CHC1 3 6 .5 The c r y s t a l s t r u c t u r e o f t h e h y d r o g e n a t i o n p r o d u c t 201 o f IX f rom MeOH, [ ( P - P ) ( H ) R h ( y - H ) 3 R h ( H ) ( P - P ) ] + ( P - P = t h e l i g a n d I I ) 6 .6 V a r i a b l e t e m p e r a t u r e 80 MHz ] H NMR spec t rum ( C D 2 C 1 2 ) 203 o f t he h y d r o g e n a t i o n p r o d u c t , [ ( P - P ) ( H ) R h ( y - H ) 3 R h ( H ) -( P - P ) ] + , o f IX f rom MeOH 6 .7 (A )& (B ) V a r i a b l e t e m p e r a t u r e ] H NMR spec t rum o f t h e 205 hyd rogena t ed s o l u t i o n (CD 3 0D) o f IX 6 . 8 The p roposed i n t r a m o l e c u l a r exchange p r o c e s s e s i n 209 t h e h yd r ogena t ed s o l u t i o n (CD 3 0D) o f t h e complex IX 6 . 9 The p a r t i a l c r y s t a l s t r u c t u r e o f t h e h y d r o g e n a t i o n 214 p r o d u c t o f t h e c a t a l y s t p r e c u r s o r XI 6 .10 (A )&(B) V a r i a b l e t e m p e r a t u r e 400 MHz ] H NMR 215 spe c t r um (CD2CI2) o f t h e h y d r o g e n a t i o n p r o d u c t o f XI f rom MeOH 6.11 The p r oposed i n t r a m o l e c u l a r exchange p r o c e s s e s i n 219 t h e CD 2C12 s o l u t i o n o f t h e h y d r o g e n a t i o n p r o d u c t ( F i g . 6 . 9 ) o f XI x i x F i g u r e number Page 6 .12 Room t e m p e r a t u r e 400 MHz ] H NMR spe c t r um ( C D 2 C 1 2 ) 221 o f t h e h y d r o g e n a t i o n p r o d u c t o f XI f rom benzene 6 . 13 Room t e m p e r a t u r e "'H NMR (400 MHz) spec t r um 223 ( C D 2 C 1 2 ) o f t h e h y d r o g e n a t i o n p r o du c t o f ( R , R ) -XIV f rom MeOH X X ACKNOWLEDGEMENTS T h i s t h e s i s c o u l d no t have been w r i t t e n w i t h o u t t h e a d v i c e and h e l p f rom a number o f p e o p l e , e s p e c i a l l y t h o s e men t i oned h e r e , who have a c t e d as bo th f r i e n d s and a d v i s o r s t o me. F i r s t o f a l l , I w i s h t o e x p r e s s my s i n c e r e g r a t i t u d e t o P r o f e s s o r W.R. C u l l e n , my r e s e a r c h a d v i s o r , f o r h i s e x p e r t g u i d an c e and a s s i s t a n c e d u r i n g t h e c o u r s e o f t h i s wo r k . My a s s o c i a t i o n w i t h him has been p l e a s a n t and r e w a r d i n g . S p e c i a l t h ank s a r e due t o D r . T . G . A p p l e t o n f o r t h e a s s i s t a n c e o f many NMR e x p e r i m e n t s and i n v a l u a b l e s u g g e s t i o n s . I am v e r y much i n d e b t e d t o P r o f e s s o r s F. Aubke , A . V . B r e e , B .R . James f o r t h e i r s u g g e s t i o n s and comments on my work and f o r p r o o f - r e a d i n g t h e m a n u s c r i p t o f t h i s t h e s i s . My t h ank s a r e e x t ended t o P r o f e s s o r F .W.B. E i n s t e i n , P r o f e s s o r J . T r o t t e r , D r . T . J o n e s , D r . S . R e t t i g and M r . S . Evans f o r t h e c r y s t a l s t r u c t u r e d e t e r m i n a t i o n s and t he h e l p t h e y have g i v e n t o me. My t hank s go a l s o t o my l a b c o l l e a g u e s D r . I . R . B u t l e r , D r . C . N u r s e , M r . N . F . Han , M r . J . J . N i f o r t h e a s s i s t a n c e o f some e x p e r i m e n t s , f o r many h e l p f u l d i s c u s s i o n s , and f o r t h e f r i e n d l y a tmosphe re c r e a t e d by them. I am v e r y g r a t e f u l t o t h e t e c h n i c a l s t a f f o f t h i s d e p a r t m e n t , i n p a r t i c u l a r D r . Chan and h i s s t a f f members f o r t h e a s s i s t a n c e o f a number o f NMR e x p e r i m e n t s , and M r . P. Bo rda f o r h i s e x p e r t m i c r o a n a l y s e s . I a l s o want t o t hank M r s . T . S c h r e i n d e r s f o r t y p i n g t h e m a n u s c r i p t . xx i To my w i f e , I e x p r e s s my g r e a t e s t t h a n k s f o r her encouragement and u n f l a g g i n g f a i t h i n me and my wo r k . x x i i To my p a r e n t s and my w i f e 1 PART I INTRODUCTION 2 CHAPTER 1 HOMOGENEOUS CATALYTIC HYDROGENATION 1.1 HISTORICAL REVIEW Homogeneous c a t a l y t i c h y d r o g e n a t i o n o f o r g a n i c s u b s t r a t e s by s o l u b l e t r a n s i t i o n - m e t a l comp lexes i s p r o b a b l y t h e most w i d e l y s t u d i e d c l a s s o f o r g a n o m e t a l l i c r e a c t i o n s . O l e f i n s have been the most t h o r o u g h l y examined s u b s t r a t e s ( e q u a t i o n 1 . 1 ) , but many o t h e r f u n c t i o n a l g roups such as a c e -t y l e n e s , a l d e h y d e s , k e t o n e s , n i t r o g r o u p s , and a r enes have a l s o been s t u d i e d . H H > c = c < + u c a t a l y s t > 2 I I The f i r s t h y d r o g e n a t i o n o f an o r g a n i c m o l e c u l e u s i n g a s o l u b l e t r a n s i -t i o n - m e t a l complex was r e p o r t e d i n 1938 by C a l v i n , who d i s c o v e r e d t h a t qu inone was r educed t o q u i n o l i n e by a cup rous a c e t a t e - g u i n o l i n e m i x t u r e a t a t m o s p h e r i c hydrogen p r e s s u r e and 100°C [ 1 ] . I g u c h i i n 1942 d i s c o v e r e d t h a t hydrogen was ab so rbed by aqueous s o l u t i o n s o f c o b a l t ( I I ) c h l o r i d e c o n t a i n i n g po t a s s i um c y a n i d e [ 2 ] ; a t room t e m p e r a t u r e t h e a b s o r p t i o n c o r r e s p o n d e d t o one hydrogen atom per c o b a l t a t om . Such s o l u t i o n s were used f o r t h e h y d r o g e n a t i o n o f v a r i o u s o r g a n i c compounds. T h i s f i n d i n g l e d t o t h e most w i d e l y s t u d i e d homogeneous h y d r o -g e n a t i o n c a t a l y s t , [ C o ( C N ) 5 ] ~. Such sys tems have been r e v i e w e d by Kw i a t e k and S e y l e r [ 3 ] . 3 In t h e e a r l y 1950 , i n v e s t i g a t o r s found t h a t h y d r o g e n a t i o n o f t h e o l e f i n was a s i d e r e a c t i o n o f t h e oxo p r o c e s s o f h y d r o f o r m y l a t i o n o f o l e f i n s by H C o ( C 0 ) 4 [ 4 - 5 ] and t h a t t h e p r o du c t a l d eh yde i t s e l f c o u l d be r educed t o a l c o h o l i n t h e same c a t a l y s t p o t . In 1954 , F l y n n and H u l b e r t d i s c o v e r e d t h a t a t l ow t e m p e r a t u r e s (= 0°C) t h e complex [ P t C C ^ ^ C ^ ^ c a t a l y z e s homogeneous ly t h e h y d r o g e n a t i o n o f e t h y l e n e [ 6 ] . R epo r t s o f t h e more a c t i v e h y d r o g e n a t i o n c a t a l y s t s i n 1960-1953 d i d i n v o l v e r u t h en i um [ 7 - 9 ] and p l a t i n u m [10 ] comp lexes and c o n s i d e r a b l e p r o g r e s s i n t h e u n d e r s t a n d i n g o f h y d r o g e n a t i o n was a l s o made d u r i n g t h i s p e r i o d by H a l p e r n ' s g roup and by o t h e r s [ 7 - 1 1 ] . Ye t v e r y s i g n i f i c a n t advances have been made by W i l k i n s o n ' s g roup i n t h e i s o l a t i o n and d e t a i l e d s t u d y o f t h e e x t r e m e l y a c t i v e h y d r o g e n a t i o n c a t a l y s t s , R h C l ( . P P h 3 ) 3 [ 12 ] and H R u C l ( P P h 3 ) 3 [ 13 ] bo th o r i g i n a l l y r e p o r t e d i n 1965 . The l a s t decade has seen a v i r t u a l l y e x p o n e n t i a l g rowth i n t h e number o f papers on t h e s u b j e c t o f homogeneous h y d r o g e n a t i o n c a t a l y z e d by t r a n s i t i o n me t a l c o m p l e x e s , w i t h a l a r g e number o f r e v i e w s and s p e c i a l i z e d t e x t s [ 1 4 - 2 7 ] . In p a r t i c u l a r , a c omprehens i v e a c coun t o f t h e who le f i e l d o f t r a n s i t i o n - m e t a l c a t a l y z e d homogeneous h y d r o g e n a t i o n has a l s o been a v a i l a b l e [ 1 6 , 2 4 ] . 4 1 . 2 SCOPE OF DISCUSSION The r e a s o n f o r t h i s u np r e c eden t ed i n t e r e s t i n homogeneous h y d r o g e n a -t i o n may l i e i n t h r e e p r i m a r y r e s e a r c h m o t i v e s . F i r s t , bo th academic and i n d u s t r i a l c h e m i s t s have been s e a r c h i n g f o r new s e l e c t i v e and s t e r e o s p e c i -f i c c a t a l y s t s y s t e m s . S e c o n d l y , i n t e r e s t i n h y d r o g e n a t i o n has been p a r t o f a g ene r a l i n v e s t i g a t i o n o f o r g a n o m e t a l l i c p a t t e r n s o f r e a c t i o n s . F i n a l l y , c h e m i s t s have hoped t h a t t he r e l a t i v e l y e a s i l y s t u d i e d homogeneous sys tems wou ld p r o v i d e i n s i g h t s i n t o t h e mode o f a c t i v a t i o n o f he t e r ogeneous c a t a -l y s t s ( b u t t h i s appea r s t o have a r a t i o n a l b a s i s o n l y i n t h e l i t t l e e x p l o r e d me t a l c l u s t e r comp lexes and i n t h e s u p p o r t e d homogeneous c a t a -l y s t s ) . Bo t h i n d u s t r i a l and academ ic r e s e a c h e r s have no t ed d i s t i n c t advan t age s o f homogeneous c a t a l y s t o v e r he t e rogeneous c o u n t e r p a r t s : (1) m i l d e r r e a c t i o n c o n d i t i o n s ; ( 2 ) ease o f c a t a l y s t r e g e n e r a t i o n ; ( 3 ) h i g h e f f i c i e n c y , s e l e c t i v i t y , and s t e r e o s p e c i f i c i t y ; ( 4 ) c o n v e n i e n c e f o r k i n e t i c s t u d y . As a r e s u l t o f t h i s i n t e r e s t t h e r e a r e now numerous t r a n s i t i o n me ta l comp lexes wh i c h can f u n c t i o n as homogeneous h y d r o g e n a t i o n c a t a l y s t s and v i r t u a l l y a l l t r a n s i t i o n m e t a l s have been s t u d i e d i n c o m b i n a t i o n w i t h v a r i o u s l i g a n d s i n an e f f o r t t o d i s c o v e r more e f f i c i e n t c a t a l y t i c sys tems [ 1 6 , 2 0 , 2 4 ] . Complexes o f t h e Group V I I I e l e m e n t s , among o t h e r s , have been found t o be t he most e f f i c i e n t c a t a l y s t s . E s p e c i a l l y e f f e c t i v e c o m b i n a t i o n s w i t h T r - a c c ep t o r l i g a n d s o r s t r o n g l i g a n d f i e l d s r e s u l t e d i n Q d l o w - s p i n c o n f i g u r a t i o n s . Such comp lexes have a number o f p r o p e r t i e s 5 wh i ch i n f l u e n c e t h e i r c a t a l y t i c a c t i v i t y and s e l e c t i v i t y . Fo r e xamp l e , bond s t a b i l i t y , l i g a n d s u b s t i t u t i o n , number o f e l e c t r o n s , and c o o r d i n a -t i o n s i t e s a v a i l a b l e a r e among t ho se p r o p e r t i e s . H e r e , i t must be r e c o g n i z e d t h a t t h e te rms " c a t a l y s t " and " c a t a l y s t p r e c u r s o r " can a p p l y t o d i s t i n c t s p e c i e s . The l a t t e r i s t h e t r a n s i t i o n -me ta l complex t h a t i s s y n t h e s i z e d and hand l ed but when s u b j e c t e d t o t h e c a t a l y t i c r e a c t i o n may undergo c o n s i d e r a b l e m o d i f i c a t i o n ( l i g a n d d i s s o -c i a t i o n and s u b s t i t u t i o n , as w e l l as me ta l v a l e n c e change) b e f o r e b e i n g c o n v e r t e d i n t o t h e a c t i v e ca~t'a'Ty.st(.s) d i r e c t l y i n v o l v e d i n t h e c a t a l y t i c c y c l e . I d e a l l y t h e s t r u c t u r e o f t h e a c t i v e s p e c i e s , as w e l l as t h a t o f a l l o t h e r i n t e r m e d i a t e s d i r e c t l y i n v o l v e d i n t h e c a t a l y t i c c y c l e s h o u l d be e s t a b l i s h e d i n o r d e r t o s t ud y t he v a r i o u s f a c t o r s i n f l u e n c i n g c a t a l y t i c b e h a v i o u r . U n f o r t u n a t e l y , s u ch i n t e r m e d i a t e s , by t h e i r v e r y n a t u r e , a r e o f t e n t o o u n s t a b l e t o i s o l a t e , and i n d i r e c t e v i d e n c e o f t h e i r c o n s t i t u t i o n must be r e l i e d o n . As a consequence few sys tems have been so t h o r o u g h l y i n v e s t i g a t e d t h a t t h e mechanism p roposed f o r them have been g e n e r a l l y a c c e p t e d . N e v e r t h e l e s s , i t i s u s e f u l t o d i s c u s s b a s i c p r o c e s s e s o c c u r r i n g i n a r e a c t i o n su ch as h y d r o g e n a t i o n , and c l a s s i f y t he c a t a l y s t s a c c o r d i n g t o t h e i r c h a r a c t e r i s t i c f e a t u r e s (mechan i sm, s e l e c t i v i t y , e t c . ) . D i s c u s s i o n i n t h i s c h a p t e r i s l i m i t e d t o h y d r o g e n a t i o n s c a t a l y z e d by t h e c l a s s o f comp lexes known as t h e "Rhod i um-Pho sph i n e " t y p e . These comp lexes have some un i que advan t age s o ve r o t h e r t r a n s i t i o n me ta l c omp l e x e s . For e x amp l e , most r e a c t i o n s r e q u i r e e a s i l y p r epa r ed and hand l ed c a t a l y s t p r e c u r s o r s . Mechanisms f o r some o f t h e s e sys tems have been s t u d i e d i n 6 c o n s i d e r a b l e d e t a i l and t h e i r c a t a l y t i c b e h a v i o u r s have a l s o been c h a r a c t e -r i z e d v e r y w e l l . Most i m p o r t a n t l y , i t has been t h i s c l a s s o f c a t a l y s t wh i ch has been emp l o yed , i n t h e m a i n , f o r a s ymme t r i c h y d r o g e n a t i o n . 1 .3 HYDROGENATION CATALYTIC CYCLES A l t h o u g h mechan isms o f homogeneous h y d r o g e n a t i o n s may d i f f e r f rom sys tem t o s y s t e m , some common f e a t u r e s a r e p r e s e n t i n a l l h y d r o g e n a t i o n c y c l e s . They a r e : (1) a c t i v a t i o n o f hydrogen by f o r m a t i o n o f M-H bonds , ( 2 ) a c t i v a t i o n o f s u b s t r a t e by i t s c o o r d i n a t i o n to m e t a l , ( 3 ) h y d r i d e t r a n s f e r f rom t h e c e n t r a l me ta l t o t h e c o o r d i n a t e d s u b s t r a t e f o l l o w e d by f o r m a t i o n o f t h e r educed p r o d u c t . These a r e now d i s c u s s e d i n t h i s s e c t i o n . 1 . 3 . 1 . Hydrogen A c t i v a t i o n The e s s e n t i a l f e a t u r e i n c a t a l y t i c h y d r o g e n a t i o n i s t h e a c t i v a t i o n o f h y d r o g e n . Y e t , the p r e c i s e manner i n w h i c h m o l e c u l a r hyd rogen r e a c t s w i t h t h e a c t i v e c a t a l y s t s p e c i e s i s no t known. One p o s s i b i l i t y ( f o r s qua r e o p l a n a r d comp l e xe s ) i s t h a t an a n t i - b o n d i n g o r b i t a l o f t h e hydrogen m o l e -c u l e a c c e p t s an e l e c t r o n f rom a f i l l e d me ta l o r b i t a l ; a n o t h e r i s t h a t t h e bond ing e l e c t r o n s o f hydrogen a t t a c k a v a c a n t me t a l o r b i t a l . In any e v e n t , a complex c o n t a i n i n g a h y d r i d e l i g a n d i s f o r m e d . The a c cumu l a t ed e v i d e n c e c o n c e r n i n g t he mechanism o f bo th homogeneous and he t e r ogeneous c a t a l y t i c h y d r o g e n a t i o n s i n d i c a t e s t h a t hydrogen atoms o f me t a l h y d r i d e s a r e t r a n s -7 f e r r e d t o t h e s u b s t r a t e i n d i s c r e t e s t e p s by " i n s e r t i o n " and " r e d u c t i v e e l i m i n a t i o n " r e a c t i o n s . Thus the f o r m a t i o n o f me t a l h y d r i d e s f rom m o l e -c u l a r hyd rogen i s an o b l i g a t o r y s t e p i n t h e c a t a l y t i c c y c l e . Two t ype s o f hyd rogen a c t i v a t i o n have been d i s t i n g u i s h e d : (A) h o m o l y t i c s p l i t t i n g by " o x i d a t i v e a d d i t i o n " o f hydrogen i n wh i c h t h r e e d i f f e r e n t p a t t e r n s can be r e c o g n i z e d , ( a ) m o n o m e t a l l i c H 2 o x i d a t i v e a d d i t i o n t o 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 comp lexes w i t h an o v e r - a l l , two e l e c t r o n change ( e q u a t i o n 1 . 2 ) , (b ) m o n o m e t a l l i c H 2 o x i d a t i v e a d d i t i o n t o c o o r d i n a t i v e l y s a t u r a t e d comp lexes accompan ied by t h e l o s s o f a l i g a n d w i t h a two - • e l e c t r o n change ( e q u a t i o n 1 . 3 ) , ( c ) b i m e t a l l i c (mononuc l ea r o r d i n u c l e a r ) H 2 o x i d a t i v e a d d i t i o n i n wh i c h t h e me ta l undergoes a o n e - e l e c t r o n change ( e q u a t i o n 1 . 4 ) . (B) h e t e r o l y t i c s p l i t t i n g wh i c h does no t r e q u i r e f o rma l o x i d a t i o n o f t h e me ta l ( e q u a t i o n 1 . 5 ) , n+2 M nC0 + H 2 ^ ^ H 2M ^ H o M n + 2 + CO 2M ( o r M n - M n ) + H c F = ^ 2 H M n + 1 M n + H, [ H M n ] ~ + H + ( 1 . 2 ) ( 1 . 3 ) ( 1 . 4 ) ( 1 . 5 ) The r e v e r s e r e a c t i o n o f e q u a t i o n ( 1 . 2 ) , ( 1 . 3 ) o r ( 1 . 4 ) i s r e f e r r e d t o as m o n o m e t a l l i c o r b i m e t a l l i c r e d u c t i v e e l i m i n a t i o n and t h e r e v e r s e r e a c t i o n o f e q u a t i o n ( 1 . 5 ) i s w e l l known as t h e p r o t o n o l y s i s o f a me t a l h y d r i d e . 8 The most t h o r o u g h l y s t u d i e d example o f c a t e g o r y ( a ) i n c l u d e s a d d i t i o n o f H 2 t o t h e f a m i l i e s o f V a s k a ' s c o m p l e x , ( R 3 P ) r ( C O ) C l ( e q u a t i o n 1.6) and Wi l k i n s o n ' s c a t a l y s t ; ( R 3 P ) 3 R h C l , wh i c h w i l l be d i s c u s s e d i n t h e nex t s e c t i o n i n more d e t a i l . OC PPh 3 O C f H \ / \ J / K + H z — - (i.6) Cl I H Me2PhP Cl Such a c o n c e r t e d hydrogen a d d i t i o n wou ld be e x p e c t e d t o a f f o r d a c i s -adduc t a n d , f o r e xamp l e , has shown t o be so f o r r e a c t i o n ( 1 . 6 ) [ 2 8 , 2 9 ] . A r e a c t i o n y i e l d i n g a t r a n s - a d d u c t has a l s o been r e p o r t e d , but t h e s e r e s u l t s seem b e s t e x p l a i n e d by i s o m e r i z a t i o n o f an i n i t i a l l y fo rmed c i s -adduc t [ 3 0 ] . S e v e r a l c o o r d i n a t i v e l y s a t u r a t e d comp lexes a dd i n g H 2 w i t h t he l o s s o f a n e u t r a l l i g a n d such as CO, R 3 P , o r N 2 ( c a t e g o r y b) a r e shown i n e q u a t i o n s ( 1 . 7 ) t o (1 . 9 ) . I r + ( C 0 ) 3 L 2 + H 2 = F = = ^ C 0 + H 2 I r + ( C 0 ) 2 L 2 ( 1 . 7 ) I r + ( C 0 ) ( P P h 2 M e ) 4 + H £ * PPh 2 Me + H 2 I r + ( CO) ( P) 3 (1 .8) H 2 R u ( N 2 ) ( P P h 3 ) 3 + H 2 > N 2 + H 4 R u ( P P h 3 ) 3 ( 1 . 9 ) I t may be c o n s i d e r e d t h a t i n t h e s e c a s e s t h e l i g a n d i s l o s t p r i o r t o H 2 a d d i t i o n t o a v o i d t h e f o r m a t i o n o f a h i g h - e n e r g y , 2 0 - e l e c t r o n i n t e r m e d i a t e 9 I t i s p r o b a b l e t h a t b i m e t a l l i c o x i d a t i v e a d d i t i o n o f H 2 ( c a t e g o r y c ) o c c u r s a t some s t a g e o f t h e c a t a l y t i c c y c l e f o r "monohyd r i d e " c a t a l y s t s ( c f . s e c t i o n 1 . 4 ) . The re i s a n o t h e r mode o f m e t a l - h y d r i d e f o r m a t i o n wh i c h does no t r e q u i r e f o rma l o x i d a t i o n o f t h e m e t a l , t h e " h e t e r o l y t i c " c l e a v a g e o f hydrogen ( e q u a t i o n 1 . 5 ) . T h i s t y p e o f r e a c t i o n i s d i f f i c u l t t o d i s t i n -g u i s h f rom o x i d a t i v e a d d i t i o n o f H 2 f o rm i ng an i n t e r m e d i a t e d i h y d r i d e a d d u c t , f o l l o w e d by d e p r o t o n a t i o n o f a h y d r i d e w i t h a base ( e q u a t i o n 1 . 1 0 ) . . M—Y + H 2 ; F = * H— M — Y : B > HM + H + BY" (1 .10) A H e t e r o l y t i c H 2 a c t i v a t i o n i s more l i k e l y w i t h me t a l comp lexes i n h i g h e r o x i d a t i o n s t a t e s where o x i d a t i v e a d d i t i o n i s l e s s f e a s i b l e . E q u a t i o n ( 1 . 1 1 ) i s an example o f t h e o v e r - a l l r e a c t i o n w i t h o u t r e g a r d t o t h e d e t a i l e d pathway o f h e t e r o l y t i c s p l i t t i n g o f hyd rogen [ 3 1 ] . E t 3 N R u X 2 ( P P h 3 ) 3 + H 2 c > H R u X ( P P h 3 ) 3 + H N E t 3 X " (1 .11) 6 6 I t can now be r e c o g n i z e d t h a t bo th h o m o l y t i c and h e t e r o l y t i c H 2 c l e a v a g e r e q u i r e t he p r e s en ce o f a v a c a n t c o o r d i n a t i o n s i t e on t h e m e t a l . Among t h e f o u r modes o f H 2 a c t i v a t i o n i t appea r s t h a t m o n o m e t a l l i c H 2 o x i d a t i v e a d d i t i o n ( e q u a t i o n 1.2) i s t h e most commonly e n c o u n t e r e d . 1 0 C o o r d i n a t e l y u n s a t u r a t e d comp lexes a r e i n v a r i a b l y more r e a c t i v e t h an ana l ogou s s a t u r a t e d comp lexes toward t h e o x i d a t i v e a d d i t i o n r e a c t i o n due t o t h e v e r y n a t u r e o f t h e r e a c t i o n . O the r f a c t o r s c o n t r o l l i n g t h e r e a c t i v i t i e s o f me t a l comp lexes can be t h e s t e r i c and e l e c t r o n i c e f f e c t s o f l i g a n d s , and t h e n a t u r e o f t h e me ta l [ 2 5 ] . The r e m a i n i n g a s p e c t o f a c t i v a t i o n i s t h a t t h i s s t e p must be r e v e r s i b l e . Not o n l y must t h e h y d r i d e complex be o f s u f f i c i e n t s t a b i l i t y t h a t i t i s r e a d i l y f o r m e d , i t must be a l s o l a b i l e enough t h a t s ub sequen t t r a n s f e r o f t h e h y d r i d e l i g a n d t o a s u b s t r a t e can o c c u r . N e v e r t h e l e s s , many h y d r i d e comp lexes wh i c h a r e c a t a l y t i c a l l y a c t i v e a r e s t a b l e enough to be c h a r a c t e r i z e d a n d / o r i s o l a t e d ( c f . s e c t i o n s 1 . 4 , 3 . 3 , and 6 . 3 ) . 1 . 3 . 2 S u b s t r a t e A c t i v a t i o n I t i s g e n e r a l l y a c c e p t e d t h a t c o o r d i n a t i o n o f a s u b s t r a t e a t a v a c a n t s i t e on t h e me ta l i s n e c e s s a r y f o r h y d r o g e n a t i o n t o p r o c e e d . The f o r m a t i o n o f a i r - o l e f i n complex s e r v e s both t o l e s s e n t h e d oub l e bond c h a r a c t e r o f t h e s u b s t r a t e ( a c t i v a t i o n ) and t o p l a c e i t i n a f a v o r a b l e p o s i t i o n ( c i s ) f o r i n t e r a c t i o n w i t h a h y d r i d e l i g a n d ( e q u a t i o n 1 . 1 2 ) . H I C HM + C = C * M — J | ( 1 . 1 2 ) C The h y d r i d e l i g a n d may be p r e s e n t i n t h e a c t i v e c a t a l y s t s p e c i e s , o r may be i n t r o d u c e d by hyd rogen a c t i v a t i o n . A l t h o u g h t h e r e has been l i t t l e d i r e c t e v i d e n c e f o r t h e f o r m a t i o n o f -rr - o l e f i n h y d r i d e comp lexes i n t h e c o u r s e o f 11 h y d r o g e n a t i o n r e a c t i o n s , a c c umu l a t e d e v i d e n c e s i n d i c a t e t h a t t r a n s f e r o f t h e h y d r i d e l i g a n d , l e a d i n g t o t h e f o r m a t i o n o f an a l k y l m e t a l i n t e r m e d i a t e , i n v o l v e s t h e o x i d a t i v e a d d i t i o n - m i g r a t o r y i n s e r t i o n sequence ( c f . s e c t i o n 1 . 4 ) . Thus i t may be assumed t h a t t h e r a t e o f t r a n s f e r o f t h e h y d r i d e i s so f a s t t h a t t h i s i n t e r m e d i a t e c anno t be d e t e c t e d . Osborn e t a l [ 32 ] s t u d i e d i n d e t a i l t h e a c t i v a t i o n o f a l k e n e s and a l k y n e s as s u b s t r a t e d u r i n g h y d r o -g e n a t i o n . 1 . 3 . 3 H y d r i d e T r a n s f e r The " i n t r a m o l e c u l a r m i g r a t o r y i n s e r t i o n " o f h y d r i d e i n t o a c o o r d i n a t e d s u b s t r a t e ( e q u a t i o n 1 .13) i s a n o t h e r o b l i g a t o r y s t e p i n t h e h y d r o g e n a t i o n c y c l e a l t h o u g h t h i s p a t h has r a r e l y been d i r e c t l y o b s e r v e d . y M—(j v * M - r C — C — H ( 1 . 1 3 ) C The m i g r a t i o n o f a h y d r i d e t o an o l e f i n i s q u i t e f a c i l e . The r e v e r s e p r o c e s s i s known as "g - h yd r i d e e l i m i n a t i o n " wh i ch i s one o f t h e most i m p o r t a n t pa ths f o r m e t a l - a l k y l d e c o m p o s i t i o n and o l e f i n i s o m e r i z a t i o n ( c f . s e c t i o n 1 . 4 ) . C o n s e q u e n t l y , comp lexes w h i c h c o n t a i n bo th o l e f i n and h y d r i d e g roups a r e r a r e a l t h o u g h t h e r e e x i s t s a known example [ 3 3 ] . I t i s b e l i e v e d t h a t t h e h y d r i d e - o l e f i n m i g r a t o r y - i n s e r t i o n s t e p i s h i g h l y s t e r e o s p e c i f i c . For t h i s r e a c t i o n t o o c c u r , t h e h y d r i d e , t h e me t a l and t h e o l e f i n i r -bond must a l l become c o p l a n a r as shown i n e q u a t i o n ( 1 . 1 4 ) . 12 MH M -H V (1 .14) T h i s s t e r e o c h e m i c a l r e q u i r e m e n t has i m p o r t a n t c o n s e q u e n c e s . For e xamp l e , c a t a l y t i c h y d r o g e n a t i o n s o f o l e f i n s must be r i g o r o u s l y c i s . 1 . 3 .4 P r o d u c t F o rma t i o n Four t y p e s o f hydrogen t r a n s f e r t o a l k y ! g roups (R) l e a d i n g t o t h e f o r m a t i o n o f h yd r ogena t ed p r o du c t (RH) and r e g e n e r a t i o n o f t he a c t i v e c a t a l y s t have been d i s t i n g u i s h e d ( e q u a t i o n s 1.15 - 1 . 1 8 ) : HM nR HM n + M nR HM n + -R HX + M nR M + RH (1 .15) 2 M n " ] + RH (1 .16) + RH (1 • 17) M n X + RH (1 .18) E q u a t i o n s ( 1 . 1 5 ) - ( 1 . 1 7 ) i n v o l v e h o m o l y t i c c l e a v a g e and a r e known as i n t r a m o l e c u l a r and i n t e r m o l e c u l a r r e d u c t i v e e l i m i n a t i o n , r e s p e c t i v e l y . In h o m o l y t i c t r a n s f e r s , t h e f o rma l o x i d a t i o n s t a t e o f t h e me ta l atom i s d e c r e a s ed but i n h e t e r o l y t i c t r a n s f e r s ( e q u a t i o n 1 .18) no change i s i n v o l v e d . R e a c t i o n s d e s c r i b e d by e q u a t i o n (1 .18) have t hu s f a r been l i m i t e d t o t h o s e sys tems wh i c h a c t i v a t e hydrogen h e t e r o l y t i c a l l y . E l e c t r o -13 p h i l i c d i s p l a c e m e n t by p r o t o n o f t h e m e t a l - b o n d e d a l k y l g roup ( w i t h r e t e n t i o n o f c o n f i g u r a t i o n ) has been sugge s t ed [ 7 , 3 4 , 3 5 ] . T r a n s f e r s shown i n e q u a t i o n s ( 1 . 1 5 ) and ( 1 . 1 7 ) have been p roposed m o s t l y f o r monohyd r i de c a t a l y s t s ( c f . s e c t i o n 1 . 4 . 1 ) . On t h e o t h e r hand , i n t r a m o l e c u l a r r e d u c t i v e e l i m i n a t i o n o f an a l k a n e f rom a c i s -h y d r i d o a l k y l m e t a l complex ( e q u a t i o n 1 .15) has f r e q u e n t l y been p o s t u l a t e d f o r d i h y d r i d e c a t a l y s t s ( c f . s e c t i o n 1 . 4 . 2 ) i n t h e b e l i e f t h a t c i s -h y d r i d o a l k y l m e t a l comp lexes a r e u s u a l l y k i n e t i c a l l y and t h e r m o d y n a m i c a l l y l e s s s t a b l e t h an t h e i r d i h y d r i d o and d i a l k y l a n a l o g u e s . Howeve r , t h e e v i d e n c e has so f a r been m a i n l y i n d i r e c t as f a i l u r e o f t h e p roposed h y d r i d o a l k y l i n t e r m e d i a t e t o a c c u m u l a t e i n d e t e c t a b l e c o n c e n t r a t i o n has g e n e r a l l y p r e c l u d e d d i r e c t o b s e r v a t i o n o f t h i s s t e p . F i g . 1 .1 : The f i r s t known examp le o f h y d r i d o a l k y l i n t e r m e d i a t e ; S = s o l v e n t [ 4 6 c ] . The i n t e r m e d i a t e shown i n F i g . 1.1 i s t h e f i r s t h y d r i d o a l k y l complex t o be d i r e c t l y o b s e r v ed i n a c a t a l y t i c h y d r o g e n a t i o n . Hal pern 14 and c owo r k e r s [ 4 6 c ] were a b l e t o i n t e r c e p t and c h a r a c t e r i z e t h i s i n t e r -m e d i a t e u s i n g l o w - t e m p e r a t u r e NMR s p e c t r o s c o p y ( H, P, C , N f o r 15 S = MeCN ) . The i n t e r m e d i a t e a c cumu l a t ed when t h e h y d r o g e n a t i o n o f m e t h y l - ( Z)-a - a c e t a m i d o c i n n a m a t e i n methano l s o l u t i o n , c a t a l y z e d by [ R h ( D I P H 0 S ) ( C H 3 0 H ) 2 ] + (DIPHOS = 1 , 2 - b i s ( d i p h e n y l p h o s p h i n o ) e t h a n e ) , was conduc t ed a t low t e m p e r a t u r e ( < - 4 0 ° C ) . A more r e c e n t r e p o r t [36 ] d e s c r i b e s t h e f o r m a t i o n o f a n a l o gou s r e l a t i v e l y s t a b l e h y d r i d o a l k y l i r i d i u r n comp lexes by i n s e r t i o n o f a c t i v a t e d o l e f i n s i n t o one o f t he I r - H bonds o f c i s -d i h y d r i d o i r i d i u m comp lexes and c o n c l u d e s t h a t such h y d r i d o a l k y l com-p l e x e s a r e i n t e r m e d i a t e s i n c a t a l y t i c h y d r o g e n a t i o n r e a c t i o n s . The s u b j e c t o f t h e f o r m a t i o n o f C-H bonds by r e d u c t i v e e l i m i n a t i o n has been r e v i e w e d r e c e n t l y by Hal pe rn [ 3 7 ] . 1 . 3 . 5 Summary So f a r f o u r b a s i c s t e p s i n v o l v e d i n homogeneous h y d r o g e n a t i o n c a t a l y -t i c c y c l e s have been d i s c u s s e d w i t h o u t r e g a r d t o t h e sequence o f each s t e p . These b a s i c s t e p s may combine i n v a r i o u s ways i n c o m p l e t i n g a c a t a -l y t i c c y c l e and t h e ma in c o m b i n a t i o n s wh i c h have been d i s t i n g u i s h e d f o r most Group V I I I me t a l complex c a t a l y s t s a r e summar ized i n F i g . 1 . 2 . The o p e r a t i o n o f s u ch h y d r o g e n a t i o n c y c l e s i n " r h o d i u m - p h o s p h i n e " s y s t ems i s d i s c u s s e d i n t h e f o l l o w i n g s e c t i o n . 15 F i g . 1.2: C l a s s i f i c a t i o n o f homogeneous h y d r o g e n a t i o n c a t a l y t i c c y c l e s . C y c l e s I - IV i n v o l v e t h e h o m o l y t i c c l e a v a g e o f H 2 ; c y c l e V i n v o l v e s h e t e r o l y t i c c l e a v a g e . M o r MH = a c t i v e c a t a l y s t ; S = s u b s t r a t e ; SH = a l k y l . 16 1 .4 RHODIUM-PHOSPHINE CATALYSTS The m o n o n u c l e a r , homogeneous r h o d i u m - p h o s p h i n e t y p e c a t a l y s t s can be r o u g h l y d i v i d e d i n t o t h e f o l l o w i n g two c l a s s e s : (1 ) monohyd r i de c a t a l y s t s h a v i n g a s i n g l e M-H g roup p r e s e n t a t some c h a r a c t e r i z e d s t a g e o f t h e c a t a l y t i c c y c l e , (2) d i h y d r i d e c a t a l y s t s h a v i ng two a d j a c e n t h y d r i d e s ( c i s -MH, , ) p r e s e n t i n one s t a g e o f t h e c a t a l y t i c c y c l e ; t h i s c l a s s o f c a t a l y s t s can be s u b d i v i d e d i n t o t h r e e g r o u p s : (A) n e u t r a l r hod ium-monophosph ine s y s t e m s , (B) c a t i o n i c rhod ium-monophosph ine s y s t e m s , (C) c a t i o n i c r h o d i u m - d i ( t e r t i a r y pho sph i ne ) s y s t e m s . Some c h a r a c t e r i s t i c f e a t u r e s o f each o f t h e s e c a t a l y s t s a r e d i s c u s s e d i n t he f o l l o w i n g s u b s e c t i o n s . 1 .4 .1 Monohyd r i de C a t a l y s t s T h i s c l a s s o f c a t a l y s t s i s w e l l e x a m p l i f i e d by t h e complex H R h ( C O ) ( P P h 3 ) 3 . A p roposed g e n e r a l i z e d c a t a l y t i c c y c l e f o r h y d r o g e n a t i o n and i s o m e r i z a t i o n by monohyd r i de c a t a l y s t s i s i l l u s t r a t e d i n F i g . 1 . 3 . The mechan isms o f monohyd r i de c a t a l y s t s have been much l e s s s t u d i e d t h an t h o s e o f t h e d i h y d r i d e c a t a l y s t s ; so c e r t a i n g r o s s f e a t u r e s o f t h e mechanism o f t h e f o rme r have no t been w e l l - e s t a b l i s h e d . A ma j o r u n c e r t a i n -t y c on ce r n s t h e h y d r o g e n o l y s i s o f t h e me t a l a l k y l i n t e r m e d i a t e t o form t he p r o d u c t s . T h i s may i n v o l v e s i m p l e o x i d a t i v e a d d i t i o n o f h y d r o g e n , f o l l o w e d by r e d u c t i v e e l i m i n a t i o n o f a l k y l - h y d r i d e ( o u t e r c i r c l e t r a n s - o r c i s - 2 - b u t e n e M e M e H M - l f H M H I R . B / C H 2 = C H C H 2 R \ 4 | r • M - M M 1 - C H 2 C H 2 C H 2 R I M e H 2 C y C H C H 2 R M e ^ C H 2 R ' ' M - C H 2 C H 2 C H 2 R C y c l e A C y c l e B F i g . 1.3: The p r o b a b l e c a t a l y t i c c y c l e s f o r h y d r o g e n a t i o n ( c y c l e B) and i s o m e r i z a t i o n ( c y c l e A) o f a t e r m i n a l o l e f i n . An a s t e r i s k i n d i c a t e s a s i t e o f u n s a t u r a t i o n on m e t a l . L i g ands on me ta l atoms a r e o m i t t e d f o r c l a r i t y . 18 o f t h e h y d r o g e n a t i o n c y c l e B i n F i g . 1 . 3 ) , o r i n t e r m o l e c u l a r r e d u c t i v e e l i m i n a t i o n o f t h e p r o d u c t a f f o r d i n g a m e t a l - m e t a l bond , f o l l o w e d by o x i d a t i v e a d d i t i o n o f hydrogen t o t h e me t a l atoms ( i n n e r c i r c l e o f t h e c y c l e B i n F i g . 1 . 3 ) . E i t h e r p a t h i s p l a u s i b l e but so f a r n e i t h e r has been w e l l - e s t a b l i s h e d i n any i n d i v i d u a l c a s e . In bo th c a s e s , howeve r , t h e f i r s t s t e p r e q u i r e s c o m p l e x a t i o n o f an o l e f i n ( s i m p l e , n on con j uga t ed ) t o 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 me ta l h y d r i d e (M - H ) . The r e v e r s i b i l i t y o f t h e f i r s t two s t e p s i n t h e c y c l e B p r o v i d e s f o r t h e i s o m e r i z a t i o n o f s i m p l e o l e f i n s and t h e i s o t o p e exchange between t h e i n i t i a l h y d r i d e * (M -H) and hyd rogens on t h e o l e f i n , r e a c t i o n s wh i c h a r e c h a r a c t e r i s t i c o f t h e monohyd r i de c a t a l y s t s . One such example o f i s o t o p e exchange i s g i v e n i n e q u a t i o n ( 1 . 1 9 ) . MD D MH C H 2 = C H R v v M—CH 2CHR v C H ^ — CDR ( 1 . 1 9 ) The m e t a l - a l k y l i n t e r m e d i a t e i n t h e i s o m e r i z a t i o n c y c l e A may u n d e r g o , i n p r i n c i p l e , two pathways t o c omp l e t e t h e c a t a l y t i c c y c l e . The f i r s t pathway i n v o l v e s t h e i s o m e r i z a t i o n o f a t e r m i n a l o l e f i n t o an i n t e r -na l o l e f i n v i a "e - h yd r i d e e l i m i n a t i o n " f o r m i n g a c i s - o r t r a n s - r r - o l e f i n c omp l e x , f o l l o w e d by d i s s o c i a t i o n o f t h e o l e f i n as a p r o du c t and r e g e n e r a -t i o n o f t h e monohyd r i de c a t a l y s t . The second pathway i n v o l v e s s i m p l e o x i d a t i v e a d d i t i o n o f H^ t o t h e m e t a l - a l k y l complex f o l l o w e d by r e d u c t i v e e l i m i n a t i o n o f H-R t o y i e l d t h e same hyd rogena t ed p r o du c t as i s o b t a i n e d from c y c l e B. 19 Bo t h s t e r i c and e l e c t r o n i c e f f e c t s p l a y i m p o r t a n t r o l e s d e t e r m i n i n g wh i c h c a t a l y t i c c y c l e w i l l o p e r a t e p r e f e r e n t i a l l y . S t e r i c b u l k a round t he me ta l i n h i b i t s bo th f o r m a t i o n o f M(.CH(Me)CH 2R) and o f M-M ( F i g . 1 . 3 ) , t h u s g i v i n g r i s e t o hyd rogena t ed products p r e d o m i n a n t l y v i a o x i d a t i v e a d d i -t i o n o f H 2 and r e d u c t i v e e l i m i n a t i o n sequences ( o u t e r c i r c l e o f c y c l e B ) . On the o t h e r hand , c a t a l y s t s w i t h s t r o n g l y a c i d i c l i g a n d ( s ) p r e f e r e n t i a l l y unde rgo t he i s o m e r i z a t i o r i c y c l e t o y i e l d i s o m e r i z e d p r o d u c t s , c i s -a n d / o r t r a n s - o l e f i n , s i n c e o x i d a t i v e a d d i t i o n o f H 2 and M-H t o M-CH 2 CH 2 CH 2 R i s r e t a r d e d . E q u a t i o n ( 1 . 2 0 ) shows h y d r o g e n a t i o n o f t e r m i n a l o l e f i n s c a t a l y z e d by a monohyd r i de c a t a l y s t HRh(C0)(PPh^)^ under m i l d c o n d i t i o n s [ 3 8 ] . H R h ( C 0 ) ( P P h J , , RCH = CH ? + H ? — > RCH ? CH. ( 1 . 2 0 ) c 25°C , <1 a t m , H 2 J The p ronounced s u b s t r a t e s e l e c t i v i t y e x h i b i t e d by t h i s c a t a l y s t i s i l l u s t r a t e d by i t s f a i l u r e t o promote t h e r e d u c t i o n o f c y c l o h e x e n e due t o t h e bu l k o f t h e pho sph i ne s [ 3 9 ] . I n t e r n a l o l e f i n s a r e i s o m e r i z e d , but a r e no t c o m p e t i t i v e l y r e d u c e d . I t i s a l s o ob s e r v ed [ 4 0 , 41] t h a t i n t h e absence o f H 2 , 1 -pen tene i s i s o m e r i z e d t o c i s - 2 - p e n t e n e , but t h i s i s ome r i s q u i c k l y c o n v e r t e d t o t h e t r a n s f o r m . I n t e r n a l o l e f i n s a r e i s o m e r i z e d more s l o w l y t h an t e r m i n a l o n e s . 20 1 .4 . 2 D i h y d r i d e C a t a l y s t s Q u i t e a number o f h y d r o g e n a t i o n c a t a l y s t s w h i c h f u n c t i o n by a d i h y -d r i d e pathway have been d i s c o v e r e d . The mechanism i s t h o u g h t t o i n v o l v e two p o s s i b l e r o u t e s , bo th o f w h i c h may be s i m u l t a n e o u s l y o p e r a t i v e ; bo th r o u t e s r e q u i r e v a c a n t c o o r d i n a t i o n s i t e s f o r a d d i t i o n o f H 2 and c o m p l e x a t i o n o f s u b s t r a t e a f t e r g e n e r a t i n g a c t i v e c a t a l y s t ( s ) f rom t h e c a t a l y s t p r e c u r s o r . As i l l u s t r a t e d i n F i g . 1 . 4 , t h e " h y d r i d e r o u t e " i n v o l v e s o x i d a t i v e a d d i t i o n o f H 2 f o l l o w e d by c o o r d i n a t i o n o f s u b s t r a t e t o form a d i h y d r i d e i n t e r m e d i a t e w i t h comp lexed s u b s t r a t e . The " u n s a t u r a t e r o u t e " c o n s i s t s o f c o o r d i n a t i o n o f s u b s t r a t e b e f o r e o x i d a t i v e - a d d i t i o n o f H 2 t o fo rm t h e same d i h y d r i d e - s u b s t r a t e i n t e r m e d i a t e . In a d d i t i o n t o t h i s i m p o r t a n t d i f f e -r e n c e between t he two r o u t e s some o t h e r f e a t u r e s a r i s e i n t h e h y d r i d e r o u t e depend ing upon t he t y p e s o f c a t a l y s t p r e c u r s o r s ( v i d e i n f r a ) . As men t i oned i n t he p r e c e e d i n g s e c t i o n t h r e e g roups o f c a t a l y s t s f a l l i n t h i s c l a s s o f d i h y d r i d e c a t a l y s t s . Each o f t h e s e w i l l be d i s c u s s e d w i t h r e f e r e n c e t o r e a c t i o n mechan isms and o t h e r g e n e r a l f e a t u r e s . (A ) N e u t r a l Rhod ium-Monophosph ine S y s t e m s . T h i s g roup o f c a t a l y s t s can be b e s t e x a m p l i f i e d by t h e complex R h C l ( P P h 3 ) 3 known as W i l k i n s o n ' s c a t a l y s t [ 1 2 , 4 2 ] . The o v e r - a l l c a t a l y t i c c y c l e and s i d e r e a c t i o n s f o r t h i s c a t a l y s t a r e o u t l i n e d i n F i g . 1.5 T h i s mechan ism i s a s y n t h e s i s o f W i l k i n s o n ' s e a r l i e r s t u d i e s [42] and H a l p e r n ' s r e c e n t s t e p w i d e k i n e t i c a n a l y s i s [ 4 3 ] , W i t h i n t h i s c a t a l y t i c s y s t e m , f i v e rhod ium i n t e r m e d i a t e s have been d i r e c t l y o b s e r v ed and c h a r a c -31 t e r i z e d , e i t h e r by s o l u t i o n P NMR s t u d i e s o r as i s o l a t e d s o l i d s : C l R h U , 21 C a t a l y s t P r e c u r s o r F i g . 1 . 4 : Two p o s s i b l e c a t a l y t i c h y d r o g e n a t i o n c y c l e s f o r d i h y d r i d e c a t a l y s t s . An a s t e r i s k on me ta l i n d i c a t e s a s i t e o f u n s a t u r a t i o n . 0£ = o l e f i n ; R = a l k y l ; RH = r educed p r o d u c t . 22 F i g . 1 . 5 : H a l p e r n ' s mechanism f o r h y d r o g e n a t i o n o f c y c l o h e x e n e by W i l k i n s o n ' s c a t a l y s t . S = s o l v e n t ; L = PPhu [ 2 5 ] . 23 C1Rh i_ 2 (C=C), R h 2 C l 2 L 4 , R h ( H ) 2 C l L 3 , and R h 2 ( H ) 2 C 1 2 L 4 . However H a l p e r n ' s s t u d i e s r e v e a l t h a t none o f t h e s e i s d i r e c t l y i n v o l v e d i n t h e k i n e t i c a l l y s i g n i f i c a n t c a t a l y t i c c y c l e wh i c h i s c o n t a i n e d i n t h e c i r c l e ( F i g . 1 . 5 ) . In f a c t , t h e a c c u m u l a t i o n o f any o f t h e s e f i v e s p e c i e s s h o u l d r e t a r d t h e o v e r - a l l r e a c t i o n r a t e . The o v e r - a l l r e a c t i o n can be d i v i d e d i n t o two p a r t s : ( a ) h y d r o g e n a t i o n o f c a t a l y s t p r e c u r s o r , C lRhL^; and (b ) r e a c t i o n o f H ^ h C l L g w i t h s u b s t r a t e , i . e . c y c l o h e x e n e . The c o m b i n a t i o n o f t h e s e two p a r t s c o r r e s p o n d s t o a " h y d r i d e r o u t e " . H a l p e r n has shown t h a t d i s s o c i a t i o n o f a l i g a n d f rom 1.5a a f f o r d s t h e 1 4 - e l e c t r o n i n t e r m e d i a t e 1.5b wh i c h t h en undergoes v e r y f a s t h y d r o -g e n a t i o n t o form t h e u n s a t u r a t e d d i h y d r i d e 1.5c wh i c h i s i n e q u i l i b r i u m w i t h f r e e PPh^, g i v i n g 1 . 5 d . T h i s r o u t e ( 1 . 5 a ? = i 1 . 5 b ^ = M . 5 c^=^ l .5d) i s much f a s t e r t h an t h e d i r e c t h y d r o g e n a t i o n o f 1 . 5 a , wh i c h was i n d e p e n -d e n t l y measured i n t h e p r e s e n c e o f e x c e s s PPh^ • W i l k i n s o n o r i g i n a l l y p roposed such a p a t h f o r h y d r o g e n a t i n g 1.5a but h i s p r o p o s a l was based on t he e r r o neou s p r e s ump t i o n t h a t t h e d i s s o c i a t i v e e q u i l i b r i u m ( 1 . 5 a^=^1 . 5b ) l i e s f a r t owa rd t h e 1 4 - e l e c t r o n c o m p l e x , 1 . 5b . More r e c e n t measurements have shown t h i s e q u i l i b r i u m t o l i e t o t h e l e f t . T h i s d i s c r e p a n c y d e r i v e s f rom t h e g r e a t a i r s e n s i t i v i t y o f 1 . 5 a , wh i ch r e a c t s w i t h 0 2 , g i v i n g d i s s o c i a t e d Ph^P = 0 and v a l u e s o f l ow a p p a r e n t m o l e c u l a r w e i g h t . A c t u a l l y t he i n t e r m e d i a t e 1.5b has a p ronounced t endency t o d i m e r i z e [44 ] and t h e d i m e r , 1 . 5 h , adds H 2 on one rhod ium atom f o rm i ng 1 . 5 i . However , i n t h e p r e sence o f H ? t h e s e s i d e r e a c t i o n s a r e i n s i g n i f i c a n t , s i n c e H ? e f f e c t i v e l y 24 i n t e r c e p t s t h e comp lex 1.5b b e f o r e i t c an d i m e r i z e . The complex 1 .5g o b s e r v e d i n t h e absence o f H 2 i s a l s o i n s i g n i f i c a n t i n t h e c a t a l y t i c h y d r o g e n a t i o n o f c y c l o h e x e n e and s i m i l a r s u b s t r a t e s . A s e p a r a t e k i n e t i c s t u d y o f t h e r e a c t i o n between t h e d i h y d r i d e 1.5d and c y c l o h e x e n e under p s e u d o - f i r s t - o r d e r c o n d i t i o n s has r e v e a l e d t h a t t h e " m i g r a t o r y i n s e r t i o n " s t e p ( 1 . 5 e -> 1 , 5 f ) i s t h e s l o w e s t s t e p i n t h e o v e r - a l l c a t a l y t i c c y c l e . The subsequen t r e d u c t i v e e l i m i n a t i o n s t e p i s a p p a r e n t l y so f a s t t h a t t h e r e v e r s e r e a c t i o n , 1 . 5 f -> 1 . 5 e , i s k i n e t i c a l l y i n s i g n i f i c a n t , t o o . I t may be no ted t h a t f o u r comp lexes ( 1 . 5 b , 1 . 5 c , 1.5e and 1 . 5 f ) a r e i n v i s i b l e i n t he sense t h a t t h e s e have not been d i r e c t l y o b s e r v e d , but t h e i r e x i s t e n c e and s t o i c h i o m e t r y were deduced f r om k i n e t i c and e q u i l i b r i u m measu remen t s . The s t e r e o c h e m i s t r y s u g g e s t e d f o r t h e p o s t u l a t e d a l k y l ; h y d r i d e i n t e r m e d i a t e 1 . 5 f i s based on t h e t r a n s e f f e c t . Tolman [45 ] used NMR t o show t h a t t h e pho sph i ne t r a n s t o h y d r i d e i n 1 ,5d i s s u b s t i t u t i o n -l a b i l e and t o a s s i g n t h e s t e r e o c h e m i s t r y o f 1 . 5 d . The g e n e r a l c h a r a c t e r i s t i c s o f t h e W i l k i n s o n c a t a l y s t can be summar ized as f o l l o w s . Uncon j uga t ed o l e f i n s and a c e t y l e n e s a r e r e a d i l y r educed under m i l d r e a c t i o n c o n d i t i o n s but such s u b s t r a t e s as a r e n e s , k e t o n e s , c a r b o x y l i c e s t e r s (and a c i d s ) , a m i d e s , and n i t r o compounds a r e no t r e d u c e d . R e l a t i v e s u b s t r a t e r e a c t i v i t i e s f o r u n c on j u ga t e d o l e f i n s t e nd t o p a r a l l e l t h e i r t e n d e n c i e s t o c o o r d i n a t e t o Rh , t hu s r e f l e c t i n g t h e s t e r i c c r o w d i n g e x e r t e d by t h e b u l k y phosph i ne l i g a n d s ( v i d e i n f r a ) . 25 However c e r t a i n good o l e f i n i c l i g a n d s appea r t o i n a c t i v a t e t h e c a t a l y s t and t o i n h i b i t t he r e d u c t i o n . These i n c l u d e e t h y l e n e and 1 . 3 - b u t a d i e n e wh i c h a r e r educed a t h i g h e r t e m p e r a t u r e o r by u s i n g R h ^ P P h ^ i n s t e a d o f R h C H P P h ^ . E x a m i n a t i o n o f t h e r e a c t i o n mechanism ( F i g . 1.5) p r o v i d e s an e x p l a n a t i o n f o r t h i s e f f e c t o f t h e more s t r o n g l y bond ing o l e f i n s i n te rms o f an a l t e r a t i o n i n mechanism (1 .5a -+ 1 .5g -> 1 ,5h ->- 1 . 5 i ) . A r e m a r k a b l e f e a t u r e o f t h i s c a t a l y s t i s t h e l a c k o f i s o m e r i z a t i o n and i s o t o p i c exchange between D 2 and p r o t o n s on t h e s o l v e n t o r o f s c r a m b l i n g between H 2 and D 2 . These r e s u l t s can be e x p l a i n e d i n t e rms o f t h e f a c t t h a t t h e r a t e - d e t e r m i n i n g s t e p i s m i g r a t o r y i n s e r t i o n o f s u b s t r a t e i n t o t h e Rh-H bond ing f o l l o w e d by t h e r a p i d p r o d u c t - f o r m i n g s t e p ( F i g . 1 . 5 ) . The a d d i t i o n o f H 2 i s s t e r e o s p e c i f i c ( c i s ) , wh i c h was p roven by W i l k i n s o n [42 ] - i n t h e d e u t e r a t i o n o f m a l e i c and f u m a r i c a c i d s t o g i v e t he meso- and d £ - d i d e u t e r o s u c c i n i c a c i d s , r e s p e c t i v e l y . Bo th r e g i o - and s t e r e o s p e c i f i c i t y o f such h y d r o g e n a t i o n s r e s u l t i n a number o f f e a t u r e s . E r g o s t e r o l a c e t a t e , f o r e x amp l e , i s r educed a t the l e a s t h i n d e r e d o l e f i n i c s i t e f rom t h e l e s s - c r o w d e d f a c e o f t h e s t e r o i d ( e q u a t i o n 1 .21) [ 2 0 ] . 26 AcO ( 1 . 2 1 ) (B) C a t i o n i c Rhod ium-Monophosph ine S y s t e m s . The complex o f t h e t y pe [ R h ( L ) 2 ( D i e n e ) ] + A ~ ( L = n e u t r a l p h o s p h i n e o r p h o s p h i t e ; D iene = 1 , 5 - c y c l o o c t a d i e n e (COD) , 2 , 5 - n o r b o r n a d i e n e (NBD) ; A" = n o n c o o r d i n a t i n g a n i o n , C lO^, BF^, P F g ) f a l l i n t o t h i s g r o u p . T h i s new sys tem has been s t u d i e d i n c o n s i d e r a b l e d e t a i l by O s b o r n ' s g roup [ 3 2 ] . T h e i r work e s t a b l i s h e s t h a t t h e c a t i o n i c d i h y d r i d e i s g ene r a t ed by t r e a t m e n t o f t h e c a t a l y s t p r e c u r s o r , [Rh(NBD) ( P P h 3 ) , , ] B F 4 , f o r e x amp l e , i n an a p p r o p r i a t e s o l v e n t S (S = a c e t o n e , THF, E tOH, e t c . ) and i n t h e absence o f s u b s t r a t e . In t h i s p r e - h y d r o g e n a t i o n s t a g e , t h e NBD l i g a n d i s r educed t o g i v e no rbo rnane and the s t r u c t u r e o f t h e d i h y d r i d e c a t a l y s t i s p roposed as a c i _ s - d i h y d r i d e w i t h t r a n s - p h o s p h i n e as shown i n e q u a t i o n ( 1 . 2 2 ) . PPh3 [ R h ( N B D ) ( P P h 3 ) 3 ] B F 4 + 3 H 2 S + no rbo rnane (1 .22) 27 .+ -[ ( D i e n e ) R h L 2 l A 1.6a 3 H 2 H 2 [ C i s - L 2 R h H 2 ] ' " H i.eb \ ^ +rT^ (01) [ L 2 R h H ] ^ + H + 1.6C R H 1 . . . [ R h L 2 ] C y c l e A [ H 2 R h L 2 ( O D ] [ H R h L 2 ( 0 D ] C y c l e B [ H 2 R h L 2 R ] i.6h i.6d i.6e ' V 6 j R H * ^ [ H R h L 2 R / L6f ' [ I ^ R h R ] ^ H 2 i.eg I s o m e r i z a t i o n f i g . 1 . 6 : Two p o s s i b l e c a t a l y t i c h y d r o g e n a t i o n c y c l e s f o r c a t i o n i c rhod ium-monophosph ine s y s t e m s . 01 = o l e f i n ; c o o r d i n a t e d s o l v e n t i s o m i t t e d . 28 As shown i n F i g . 1 . 6 , an i m p o r t a n t d i f f e r e n c e between t h e s e c a t a l y t i c sys tems and the r e l a t e d W i l k i n s o n - t y p e sys tems i s t h e p r e s en ce o f t h e Rh ( I ) monohyd r i de c a t a l y s t gove rned by e q u i l i b r i u m ; t h i s i s s e n s i t i v e t o t h e n a t u r e o f L and S and can be s h i f t e d by a d d i t i o n o f a c i d o r b a s e . T h u s , f o r e xamp l e , i n t h e p r e s en ce o f e x c e s s a c i d t h e e q u i l i b r i u m i s t i l t e d t oward t h e f o r m a t i o n o f t h e d i h y d r i d e 1 .6b wh i ch i s a m o d e r a t e l y a c t i v e h y d r o g e -n a t i o n c a t a l y s t v i a a h y d r i d e r o u t e ( c y c l e A ) . On t h e o t h e r hand , a b a s e , i . e . N E t 3 , s h i f t s t h e e q u i l i b r i u m t o t h e r i g h t t o g e n e r a t e t h e monohyd r i de 1.6c wh i c h i s a p o w e r f u l h y d r o g e n a t i o n c a t a l y s t f o r s i m p l e o l e f i n s , as w e l l as an i s o m e r i z a t i o n c a t a l y s t ( c f . s e c t i o n 1 . 4 . 1 ) . One p o s s i b l e h y d r o g e -n a t i o n mechanism v i a 1 .6c i s shown i n c y c l e B wh i c h i s one o f two h y d r o -g e n a t i o n pathways f o r monohyd r i de c a t a l y s t s i l l u s t r a t e d i n F i g . 1 . 3 . I t can be r e a d i l y seen t h a t i f t h e r a t e o f o x i d a t i v e a d d i t i o n o f H 2 t o g ene -r a t e 1 . 6 i i s r a t e d e t e r m i n i n g , t hen t h e i s o m e r i z a t i o n i n t h e f i g u r e i s r e a l i z e d . (C) C a t i o n i c R h o d i u m - D i ( t e r t i a r y pho sph i n e ) S y s t ems . The comp lexes o f the t y pe [ R h ( L - L ) ( D i e n e ) ] + A " ( L - L = c h e l a t i n g d i ( t e r t i a r y phosph ine) 1 i g a n d s ; D iene = NBD, COD; A" = C 1 0 4 , BF^, PFs> e t c . ) r e p r e s e n t t h i s g roup o f c a t a l y s t s . In g e n e r a l t h e s e comp lexes can be r e a d i l y p r e pa r ed by r e p l a c i n g two e q u i v a l e n t s o f monophosph ines w i t h one e q u i v a l e n t o f d i ( t e r t i a r y p h o s p h i n e ) . The complex hav i ng two monoden ta te pho sph i n e s ab so r b s t h r e e e q u i v a -l e n t s o f H ? , a f f o r d i n g t h e d i h y d r i d e c a t a l y s t ( e q u a t i o n 1 . 2 2 ) , whereas 29 t h o s e c o n t a i n i n g a c o n v e n t i o n a l c h e l a t i n g , b i d e n t a t e l i g a n d such as "DIPHOS" (= P h 2 P C H 2 C H 2 P P h 2 ) a b s o r b two e q u i v a l e n t s o f H 2 , y i e l d i n g t h e h i g h l y u n s a t u r a t e d complex ( e q u a t i o n 1 . 2 3 ) . [ Rh (D IPHOS ) (NBD) ] + + 2 H 2 > [ ( D I P H 0 S ) R h ( S ) 2 ] + + no rbo rnane ( 1 . 2 3 ) The d i f f e r e n c e between t h e s e two r e a c t i o n s has been r a t i o n a l i z e d on t h e b a s i s t h a t pho sph i n e s a v o i d becoming t r a n s t o h y d r i d e s whenever p o s s i b l e . H a l p e r n e t a l [ 46 ] and Brown e t a l [ 4 7 ] i n d e p e n d e n t l y e l u c i d a t e d , i n c o n s i d e r a b l e d e t a i l , t h e mechanism o f h y d r o g e n a t i o n o f some o l e f i n s i n v o l -v i n g d i ( t e r t i a r y phosph ine 1.1 i g a n d s . T h e i r work e s t a b l i s h e s t h a t t h e dom inan t mechanism f o r t h e s e sy s tems i n v o l v e s an u n s a t u r a t e r o u t e r a t h e r t h an a h y d r i d e r o u t e , as shown i n F i g . 1 . 7 . Here t h e l i g a n d ( L - L ) i s "DIPHOS" . An o l e f i n complex 1.7c i s i n e q u i l i b r i u m w i t h t h e c a t a l y s t 1 .7b wh i c h i s g e n e r a t e d f rom the r e a c t i o n o f t h e c a t a l y s t p r e c u r s o r 1.7a w i t h two e q u i v a l e n t s o f h y d r o g e n . H a l p e r n has measured e q u i l i b r i u m c o n s t a n t s Keq f o r a s e r i e s o f o l e f i n s u b s t r a t e s . A t amb ien t t e m p e r a t u r e s t h e r a t e -d e t e r m i n i n g s t e p , k-j, i n v o l v e s o x i d a t i v e a d d i t i o n o f H 2 t o t h e u n s a t u r a t e d Rh ( I ) c omp l e x , 1 . 7 c , g i v i n g a R h ( I I I ) d i h y d r i d e 1.7d wh i c h r a p i d l y fo rms 1.7e by m i g r a t o r y i n s e r t i o n and s u b s e q u e n t l y p r o d u c t by r e d u c t i v e e l i m i -n a t i o n . Th ree comp lexes i n t h e c a t a l y t i c c y c l e ( 1 . 7 b , 1.7c and 1 .7e) were 30 [(DIPHOS)Rh(NBD)]+BF4 1.7a 2H 2 [(DlPHOS)RhS2] 1.7b H N r W (DIPHOS)Rh(III) (S) (S) i.7e H KDIPHOSJRhCiJ i.7c v5J .fast (DlPHOS)Rh(III) v (S, i . 7 d 1.7: H y d r o g e n a t i o n c y c l e f o r [ R h ( D I P H O S ) ( S ) 2 ] + : S = s o l v e n t ; o l e f i n E 1 - hexene , e t c . 31 c h a r a c t e r i z e d by NMR measu remen t s , and by X - r a y d i f f r a c t i o n s ( 1 . 7 b and 1 . 7 c ) . The complex 1.7b i s a d i s o l v a t e d monomer, but i s i s o l a t e d as a b i n u c l e a r [ R h 2 ( D I P H O S ) 2 ] [ B F 4 ] 2 s a l t , i n wh i ch each Rh atom i s bonded t o two P atoms a n d , t h r ough s y m m e t r i c a l n - a r e n e c o o r d i n a t i o n , t o a pheny l r i n g o f t h e d i p h o s p h i n e l i g a n d o f t h e o t h e r Rh atom ( F i g . 1 . 8 ) . Ph-F i g . 1 . 8 : C r y s t a l s t r u c t u r e o f [ R h 2 ( D I P H 0 S ) 2 ] 2 + ; 1.7b was i s o l a t e d as t he d i m e r i c BF^" s a l t . A t low t e m p e r a t u r e s ( < - 4 0 ° C ) , k 2 , a d i s s o c i a t i v e r e a c t i o n , becomes s l o w e r t han k-j , so t h a t under t h e s e c o n d i t i o n s , 1 ,7e a c c umu l a t e and can be c h a r a c t e r i z e d by NMR ( 1 H , 3 1 P , 1 3 C , 1 5 N f o r S = M e C N 1 5 ) . As men t i oned e a r l i e r , 1.7e i s t h e f i r s t h y d r i d e a l k y l complex t o be d i r e c t l y o b s e r v e d i n a c a t a l y t i c h y d r o g e n a t i o n . F a i l u r e to i n t e r c e p t t he p roposed 1.7d r e f l e c t s 32 t he v e r y r a p i d t r a n s f o r m a t i o n o f 1 .7d t o 1 . 7e . The a f f i n i t y o f 1 .7b f o r o l e f i n s s t r o n g l y depends on t h e s t r u c t u r e o f t h e o l e f i n . The am i do -c i n n am i c a c i d forms a v e r y s t r o n g complex w i t h t h i s Rh ( I ) c e n t e r . As w i l l be seen i n Chap t e r 2 , an X - r a y s t r u c t u r e o f t h i s complex a c c o u n t s f o r i t s l a r g e a s s o c i a t i o n c o n s t a n t . The NMR s t u d i e s o f 1 .7e (where S = MeCN) r e v e a l t h e s t e r e o c h e m i s t r y shown i n F i g . 1 . 7 . In p a s s i n g f rom 1 .7d t o 1 . 7e , t h e h y d r i d e m i g r a t i n g t o t h e o l e f i n i s t r a n s t o a p h o s p h i n e . S i m i l a r r e s u l t s w i t h a range o f c h e l a t i n g pho sph i n e s have a l s o been r e p o r t e d by B a i r d e t a l [48] and Brown e t a l [ 4 7 ] , d e m o n s t r a t i n g t h a t h y d r i d e s a r e q u i t e d i s f a v o r e d i n t h e s e c a s e s and b r o a d l y s u p p o r t i n g t h e u n s a t u r a t e r o u t e f o r a r ange o f s y s t e m s . However i t must be emphas i zed t h a t t h i s g e n e r a l i z a t i o n i s not a lway s f o l l o w e d . For e x amp l e , t h e complex g e n e r a t e d f rom p r e - h y d r o g e n a t i o n o f [ Rh (AMPF ) 2 (NBD) ] + A~ (AMPP = 0 - a n i s y l -m e t h y l p h e n y l p h o s p h i n e ) has t h e two monoden ta te pho sph i ne s c i s a c c o r d i n g t o 3 1 P NMR s p e c t r a ( v i d e i n f r a ) [ 4 7 a , b] . 33 The O -methoxy g roups a r e t h ough t t o be weak l y c o o r d i n a t e d , t hus s t a b i l i z i n g t h i s u ne xpe c t e d c o o r d i n a t i o n g eome t r y . F u r t h e rmo r e t h e p r e s e n t i n v e s t i g a t i o n has f ound t h a t some comp lexes h a v i n g c h e l a t i n g phosph i ne s p roduce me ta l h y d r i d e i n t e r m e d i a t e s f rom t h e i n i t i a l h y d r o g e n a t i o n o f c a t a l y s t p r e c u r s o r s [ R h ( L - L ) ( N B D ) J C I O ^ ( L - L = c h i r a l and a c h i r a l f e r r o c e n y l p h o s p h i n e s ) , s u g g e s t i n g t h a t some c h e l a t i n g d i ( t e r t i a r y phosph ine ) c a t a l y s t s can undergo e i t h e r a h y d r i d e r o u t e o r a q u i t e d i f f e r e n t mechan ism wh i ch has no t been d i s t i n g u i s h e d so f a r . These o b s e r v a t i o n s w i l l be d i s c u s s e d i n Chap t e r 6 . 34 CHAPTER 2 ASYMMETRIC CATALYTIC HYDROGENATION 2.1 GENERAL ASPECTS Eve r s i n c e P a s t e u r , i n 1848 , succeeded i n s e p a r a t i n g two t y p e s o f J o p t i c a l l y a c t i v e c r y s t a l s f rom sodium ammonium t a r t r a t e by hand w i t h t h e a i d o f a m i c r o s c o p e , t h e r e has been a g r e a t d ea l o f i n t e r e s t i n t h e p r o -d u c t i o n o f o p t i c a l l y a c t i v e compounds . The impo r t a n c e o f t h e s e compounds f rom a p r a c t i c a l v i e w p o i n t can be r e a d i l y r e c o g n i z e d c o n s i d e r i n g t he f a c t t h a t many s u b s t a n c e s a r e needed as t he pure e n a n t i o m e r s . The pharmaceu-t i c a l i n d u s t r y , f o r i n s t a n c e , i s p a r t i c u l a r l y i n t e r e s t e d i n t h i s a r e a s i n c e an i n c r e a s i n g number o f d r u g s , f ood a d d i t i v e s , and f l a v o r i n g a gen t s a r e be i ng p r epa r ed as pu re e n a n t i o m e r s . For e x amp l e , i n t h e l a t e 1 9 6 0 ' s , i t was found t h a t L - 3 , 4 - d i o x y p h e n y l a l a n i n e (L-DOPA) c o u l d be used t o t r e a t P a r k i n s o n ' s d i s e a s e a n d , i n 1968 , Knowles e t a l [ 82 ] succeeded i n s y n t h e -s i z i n g L-DOPA w i t h a l m o s t 100% o p t i c a l y i e l d u s i n g an a s ymmet r i c W i l k i n s o n t y pe c a t a l y s t . T h e i r d i s c o v e r y p r o v i d e d t h e impe tus f o r t h e l a r g e amount o f work p u b l i s h e d s i n c e t h en i n t h e f i e l d o f a s ymmet r i c c a t a l y s i s . The f i e l d o f a s ymmet r i c s y n t h e s i s has been r e v i ewed by a number o f a u t h o r s d u r i n g t h e l a s t decade [ 4 9 - 5 3 ] . The most c omp rehen s i v e a c c oun t o f t h e who le f i e l d , c o v e r i n g a l l l i t e r a t u r e d a t a up t o 1975 , i s g i v e n i n t h e books by M o r r i s o n and Mosher [ 5 4 ] , and by Izumi and T a i [ 5 5 ] . The r e have a l s o been p u b l i s h e d o t h e r r e v i e w s [ 5 6 - 64 ] on a s ymme t r i c c a t a l y s i s w i t h 35 s p e c i a l emphas i s on a s ymmet r i c c a t a l y t i c h y d r o g e n a t i o n wh i c h i s t h e t o p i c o f t h i s c h a p t e r . 2 .2 TERMINOLOGY The re a r e s e v e r a l t e rms t h a t have been used r o u t i n e l y but somewhat c o n f u s i n g l y i n t h e f i e l d o f a s ymmet r i c s y n t h e s i s . I t i s , t h e r e f o r e , u s e -f u l t o r e v i e w t h e s e te rms b e f o r e l a u n c h i n g i n t o t h e s u b j e c t o f a s ymmet r i c c a t a -l y t i c h y d r o g e n a t i o n . The t e r m i n o l o g y here and i n t h e subsequen t d i s c u s s i o n i s based on t h e work o f many p i o n e e r s i n t h i s f i e l d [ 6 5 - 6 8 ] . 2 . 2 . 1 Types o f C h i r a l i t y I t i s w e l l known t h a t t h e o n l y r e q u i r e m e n t f o r o p t i c a l a c t i v i t y i s t h a t a m o l e c u l e s h o u l d no t be s u p e r p o s a b l e on i t s m i r r o r image . T h e r e f o r e , i n o r d e r t o a v o i d c o n f u s i o n , t he term " c h i r a l " s h o u l d be used f o r t h e n e c e s s a r y and s u f f i c i e n t c o n d i t i o n f o r t h e e x i s t e n c e o f e n a n t i o m e r s . O v e r a l l c h i r a l i t y can be f u r t h e r f a c t o r i z e d i n t o t h r e e e l e m e n t s , wh i ch a r e t r e a t e d i n t h e o r d e r o f c h i r a l c e n t e r s , c h i r a l a x e s , and c h i r a l p l a n e s whenever n e c e s s a r y . (A) C e n t r a l C h i r a l i t y The re a r e f o u r d i f f e r e n t t y p e s o f m o l e c u l e s wh i c h po s s e s s t h i s c l a s s o f c h i r a l i t y . The most f a m i l i a r and by f a r t h e most e x t e n s i v e g roup i s t h a t o f asymmetry ( p o i n t Group C- , ) , as i n C a b c c j , t h e a s ymmet r i c c a r b o n a t om . 36 2.1a 2 .1b 2 .1c F i g . 2 . 1 : M o l e c u l e s w i t h c e n t r a l c h i r a l i t y . The nex t h i g h e r symmetry p o i n t g roup c o n t a i n s one C 2 a x i s ( p o i n t Group C 2 ) ( 2 . 1 a i n F i g . 2 . 1 ) . The t h i r d o f t h e p o i n t g r o u p s , as e x a m p l i f i e d by 2 . 1 b , c o n t a i n s one a x i s as i t s o n l y symmetry ( p o i n t Group C^) . F i n a l l y , t h e f o u r t h g roup has t h r e e C 2 a x e s " ( p o i n t group D 2 ) . T h i s c a s e can be d e r i v e d f rom t e t r a h e d r a l C a a a a by c o n n e c t i n g t h e a ' s c y c l i c l y as i n 2 .1c w i t h f o u r b r i d g e s o f two k i n d s i n t r o d u c e d a l t e r n a t e l y , each b r i d g e ha v i ng a p l a n e o f symmetry . As w i l l be seen i n s e c t i o n 2 . 4 , most o f t h e c h i r a l r h o d i u m - p h o s p h i n e c a t a l y s t s adop t c h i r a l c e n t e r ( s ) as t h e s o l e s o u r c e o f c h i r a l i t y . (B) A x i a l C h i r a l i t y H e r e , t h e a x i s o f c h i r a l i t y i s d e r i v e d by d e s y m m e t r i z a t i o n f rom a a x i s : t h i s i s i t s f undamen ta l p r o p e r t y . T h i s form o f c h i r a l i t y i s e x a m p l i -f i e d b y a l l e n e s ( 2 . 2 a ) , a l k y l i d e n e - c y c l o a l k a n e s ( 2 . 2 b ) , s p i r a n e s ( 2 . 2 c ) , 37 b i a r y l s ( 2 . 2 d ) , and adman to i d s ( 2 . 2 e ) , as shown i n F i g . 2 . 2 . 2 .2a 2 .2b 2 .2c 2 .2d 2 .2e F i g . 2 . 2 : M o l e c u l e s w i t h a x i a l c h i r a l i t y . I t can be no ted t h a t , i f t h e r e i s no d i s t i n c t i o n between the f o u r g r o u p s , a , b, c , d , each compound has an a x i s . However , t h e f o u r g roups need no t a l l be d i f f e r e n t : i f a and b a r e d i f f e r e n t , and c and d a r e d i f f e r e n t , t he se m o l e c u l e s w i l l be c h i r a l . (C) P l a n a r C h i r a l i t y A p l a ne o f c h i r a l i t y i s d e r i v e d by d e s y m m e t r i z a t i o n o f a p l a ne o f symmetry i n such a way t h a t c h i r a l i t y depends on a d i s t i n c t i o n between one s i d e o f t h e p l a n e and t h e o t h e r . Thus m e t a l l o c e n e s w i t h two d i f f e r e n t s u b s t i t u e n t s i n one r i n g and o t h e r compounds shown i n F i g . 2 .3 a r e known t o p o s s e s s c h i r a l p l a n e ( s ) . 38 F i g . 2 . 3 : M o l e c u l e s w i t h p l a n a r c h i r a l i t y . 2 . 2 . 2 S t e r e o i s o m e r i c R e l a t i o n s h i p s [ 67b , 69] In d e f i n i n g t h e s p a t i a l r e l a t i o n s h i p s o f p o r t i o n s ( a toms , g r o u p s , o r f a c e s ) o f m o l e c u l e s , one must d i s t i n g u i s h between i n t e r n a l and e x t e r n a l c o m p a r i s o n s . In t h e f o r m e r , t h e c ompa r i s on t a k e s p l a c e between p o r t i o n s o f t h e same m o l e c u l e , whereas i n t h e l a t t e r i t t a k e s p l a c e between c o r r e s -pond i ng p o r t i o n s wh i c h a r e p a r t s o f d i f f e r e n t m o l e c u l e s . (A) I n t e r n a l Compar i son Groups ( o r f a c e s o f an o l e f i n ) a r e d e f i n e d as " e q u i v a l e n t " i f t h e y can be i n t e r n a l l y i n t e r c h a n g e d by a C n a x i s (<*»n>l). F i g . 2 .4 i l l u s t r a t e s some o l e f i n s w i t h e q u i v a l e n t g roups a n d / o r f a c e s . 39 Ha x ,Fo 'Ro- -Rb n_ /Rc / "- _-- no - / t = c v v c = c v / = c = = c v H i / V b Ho* > F b R b >Rd F i g . 2 . 4 : O l e f i n s w i t h e q u i v a l e n t g roups a nd / o r f a c e s by i n t e r n a l c o m p a r i s o n s . I f g roups ( o r f a c e s ) a r e i n t e r n a l l y i n t e r c h a n g e d o n l y by an imprope r a x i s o f r o t a t i o n S n ( n > l ) , t h e y a r e d e f i n e d as " e n a n t i o t o p i c " . The p a i r s o f hydrogen atoms H-j/H^ and H^/H^ i n 2.5a a r e e q u i v a l e n t , whereas t h e p a i r s o f hydrogen atoms H^/H^, H j / H ^ , H - j /H 3 , and H^/H^ a r e e n a n t i o t o p i c . A l t h o u g h two R g roups ( o r two H ' s ) i n 2 .5b a r e e q u i v a l e n t , two f a c e s o f t h e m o l e c u l e a r e e n a n t i o t o p i c . H_ / C N H. R / V c = 0 ? - < \ H 4 H 3 2.5a 2 .5b F i g . 2 . 5 : M o l e c u l e s w i t h e n a n t i o t o p i c g roups o r f a c e s by i n t e r n a l c ompa r i s on s . 40 I f g roups ( o r f a c e s ) c anno t be i n t e r n a l l y i n t e r c h a n g e d by any symmetry o p e r a t i o n , t h e y a r e d e f i n e d as " d i a s t e r e o t o p i c " ( F i g . 2 . 6 ) . 2 .6a 2 .6b F i g . 2 . 6 : M o l e c u l e s w i t h d i a s t e r e o t o p i c g roups o r f a c e s by i n t e r n a l c o m p a r i s o n s . The compound 2 .6a i s c h i r a l w h i l e 2 .6b i s a c h i r a l . The m o l e c u l e 2 .6b po s s e s s e s an e n a n t i o t o p i c p a i r o f o l e f i n i c p r o t o n s . (B) E x t e r n a l Compar i sons The i n t e r n a l symmetry c r i t e r i a a r e e q u a l l y a p p l i e d t o e x t e r n a l c o m p a r i s o n . The c o m p a r i s o n can be a c h i e v e d e i t h e r by compa r i ng two r e -s u l t i n g m o l e c u l e s , o r i n a s i m p l e way , by a p p l y i n g t h e symmetry o p e r a t i o n (Cn o r Sn) t o a m o l e c u l e then compa r i ng i t w i t h t h e r e s u l t i n g m o l e c u l e . For e x amp l e , two m e t a l - o l e f i n comp lexes shown i n F i g , 2 .7 a r e e q u i v a l e n t by e x t e r n a l c ompa r i s on s i n c e t h e two comp lexes a r e i n t e r c h a n g e a b l e by a C ? o p e r a t i o n . 41 LnM Me 'Me C 2 LnM Me^ Me ( R , S ) - 2 .7a ( S ,R ) - 2 .7a F i g . 2 . 7 : E q u i v a l e n t m e t a l - o l e f i n comp lexes by e x t e r n a l c o m p a r i s o n . I f t h e r e s u l t i n g m e t a l - o l e f i n comp lexes a r e e q u i v a l e n t by e x t e r n a l com-p a r i s o n t hen t h e f a c e s o f t h e f r e e o l e f i n a r e e q u i v a l e n t by i n t e r n a l c o m p a r i s o n , but t h e c o n v e r s e i s not a lways t r u e . The a b s o l u t e c o n f i g u -r a t i o n s o f o l e f i n i c c a r b on atoms o f 2 .7a and 2 .7b a r e d e t e r m i n e d on t h e b a s i s o f a h y p o t h e t i c a l , th ree -membered m e t a l o c y c l i c compound i n wh i ch t he c a r b on atoms adop t a p s e u d o - t e t r a h e d r a l g eome t r y . In t h e same v e i n , i f t h e comp lexes a r e e n a n t i o m e r i c ( i . e . , comp lexes a r e n o n - s u p e r p o s a b l e m i r r o r i m a g e s ) , t hen t h e f a c e s o f t h e f r e e o l e f i n a r e e n a n t i o t o p i c by i n t e r n a l c ompa r i s on ( F i g . 2 . 8 ) . LnM rP > M e ( S , S ) - 2 .8a LnM H V Me Me^ > H (R ,R ) - 2 .8b F i g . 2 . 8 : E n a n t i o n m e r i c m e t a l - o l e f i n c omp l e xe s . 42 I t can be no t ed i n F i g . 2 .8 t h a t an a c h i r a l o l e f i n w i t h e n a n t i o t o p i c f a c e s becomes c h i r a l upon c o o r d i n a t i o n t o a m e t a l . A m o l e c u l e w i t h e n a n t i o t o p i c g roups o r f a c e s i s s a i d t o be " p r o c h i r a l " . When two m e t a l o l e f i n comp lexes a r e d i a s t e r e o m e r i c by e x t e r n a l com-p a r i s o n ( i . e . , n o n - e n a n t i o m e r i c s t e r e o i s o m e r s ) , t hen t h e f r e e o l e f i n has d i a s t e r e o t o p i c f a c e s by i n t e r n a l c o m p a r i s o n . The re a r e two c a s e s where d i a s t e r e o m e r i c comp lexes can be f o rmed . They a r e : (a) a complex i n wh i ch a p r o c h i r a l o l e f i n i s c o o r d i n a t e d t o a meta l w i t h c h i r a l l i g a n d ( s ) ( F i g . 2 . 9 ) , (RH_nM Phs^ I y NHCOMe hT ^CGfeH (RRnM H \ 1 / $ » Pr7 >NHCOMe (R , 2R, 3S) (R , 2S , 3R) F i g . 2 . 9 : C h i r a l d i a s t e r e o m e r i c m e t a l - o l e f i n c o m p l e x e s , no t r e l a t e d by any symmetry o p e r a t i o n . ' ( b ) comp lexes i n wh i ch an o l e f i n w i t h d i a s t e r e o t o p i c f a c e s ( c h i r a l o r a c h i r a l ) i s c o o r d i n a t e d t o a me t a l w i t h c h i r a l o r a c h i r a l l i g a n d s ( i . e . , MLn o r (R) -MLn) ( F i g . 2 . 1 0 ) , 43 Me' Me H LnM Y ( I R , 2S , 3R) ( I R , 2R, 3S) F i g . 2 . 1 0 : D i a s t e r e o m e r i c comp lexes formed by c o o r d i n a t i o n o f a c h i r a l o l e f i n t o an a c h i r a l me t a l c o m p l e x . The MLn m o i e t y can be e i t h e r c h i r a l o r a c h i r a l . I t i s t h e i n t e r a c t i o n shown i n F i g . 2 .9 t h a t i s t h e b a s i s f o r most o f a s ymme t r i c h y d r o g e n a t i o n o f o l e f i n s c a t a l y z e d by c h i r a l Rh - pho sph i n e c o m p l e x e s . 2 . 2 . 3 S t e r e o - D i f f e r e n t i a t i n g R e a c t i o n s The term "a symmet r i c r e a c t i o n " was f i r s t used i n 1894 by F i s h e r [ 70 ] and d e f i n e d i n 1904 by Ma r ckwa ld [ 71 ] as "a r e a c t i o n wh i c h p r oduce s o p t i c a l l y a c t i v e s u b s t a n c e s f rom s y m m e t r i c a l l y c o n s t i t u t e d compounds w i t h t he i n t e r m e d i a t e use o f o p t i c a l l y a c t i v e m a t e r i a l s but w i t h t h e e x c l u s i o n o f a l l a n a l y t i c a l p r o c e s s e s " . L a t e r M o r r i s o n and Mosher [54] r e d e f i n e d an a symmet r i c r e a c t i o n as "a r e a c t i o n i n wh i c h an a c h i r a l u n i t i n an ensemb le o f s u b s t r a t e m o l e c u l e s i s c o n v e r t e d by a r e a c t a n t i n t o a c h i r a l u n i t i n such a manner t h a t t h e s t e r e o i s o m e r i c p r o d u c t s a r e p roduced i n unequa l amoun t s " . 44 I zumi and Ta i [ 5 5 ] i n t r o d u c e d t h e te rm " d i f f e r e n t i a t i o n " and c l a s s i f i e d a s ymme t r i c r e a c t i o n s i n t o two c l a s s e s o f s t e r e o - d i f f e r e n t i a t i o n r e a c t i o n s , each o f wh i c h can be f u r t h e r d i v i d e d i n t o t h r e e t y p e s as f o l l o w s : (A) When t h e c h i r a l i t y p a r t i c i p a t i n g i n t h e d i f f e r e n t i a t i o n o c c u r s i n a r e a g e n t , t h e c a t a l y s t , o r t h e r e a c t i o n med ium, t h e r e a c t i o n i s c l a s s i f i e d as an e n a n t i o - d i f f e r e n t i a t i n g r e a c t i o n . T y p i c a l l y i t y i e l d s e n a n t i o m e r s as p r o d u c t s . (B) When t h e c h i r a l i t y r e l a t e d t o t h e d i f f e r e n t i a t i o n i s p r e s e n t i n t h e s u b s t r a t e , t h e r e a c t i o n i s c l a s s i f i e d as a d i a s t e r e o - d i f f e r e n t i a t i n g r e a c t i o n . I t y i e l d s d i a s t e r e o m e r s as p r o d u c t s . (C) When t he d i f f e r e n t i a t i o n o c c u r s a t a p r o c h i r a l f a c e , p r o c h i r a l c e n t e r , o r c h i r a l c e n t e r , t h e r e a c t i o n i s c o n s i d e r e d t o be f a c e - d i f f e r e n -t i a t i n g , t o p o s - d i f f e r e n t i a t i n g , o r i s o m e r - d i f f e r e n t i a t i n g , r e s p e c t i v e l y . These new d e f i n i t i o n s and c l a s s i f i c a t i o n f o r a s ymme t r i c r e a c t i o n s i n c l u d e not o n l y t h o s e d e f i n e d by M o r r i s o n and Moshe r , but k i n e t i c r e s o l u t i o n o f enan t i ome r and d i a s t e r e o m e r s w i t h t h e e x c l u s i o n o f " a s ymmet r i c t r a n s f o r m a -t i o n " [ 5 4 ] . A l t h o u g h the t e rms a s ymme t r i c r e a c t i o n and s t e r e o - d i f f e r e n t i a -t i n g r e a c t i o n a r e used i n t e r c h a n g e a b l y , the l a t t e r , whenever n e c e s s a r y , w i l l be used t h r o u g h o u t t h i s t h e s i s . In c o n c l u s i o n , a s t e r e o - d i f f e r e n t i a t i n g r e a c t i o n i s a c h i e v e d when a m o l e c u l e c o n t a i n i n g e n a n t i o t o p i c o r d i a s t e r e o t o p i c g roups ( o r f a c e s ) i s c o n v e r t e d t o a c h i r a l m o l e c u l e i n such a way t h a t one e n a n t i o m e r ( o r d i a s t e r e o m e r ) i s formed i n e x c e s s . The e f f i c i e n c y o f e n a n t i o - d i f f e r e n t i a t i o n i s e x p r e s s e d e i t h e r as " e n a n t i o m e r i c e x c e s s ( e . e . ) " ( e q u a t i o n 2 . 1 ) o r as 45 " o p t i c a l p u r i t y " . The l a t t e r i s equa l t o t h e r o t a t i o n o f t h e p r o d u c t o f a r e a c t i o n , [ a ] r e a c t i o n , d i v i d e d by t h e r o t a t i o n o f t h e o p t i c a l l y pure compound, [ a ] pu re ( e q u a t i o n 2 . 2 ) . % e . e . = 1R1 -151 x -i 0 0 ( 2 1 ) l e i + i s i x l u u % o p t i c a l p u r i t y = [ g ] r e a c t i o n , Q 0 (2 2) [ a j p u r e The o p t i c a l y i e l d i s d e f i n e d as t h e o p t i c a l p u r i t y o r e n a n t i o m e r i c e x ce s s o f t h e r e a c t i o n p r odu c t d i v i d e d by t h e o p t i c a l p u r i t y o f t h e c h i r a l r e -agen t u s e d . When t he r e a g e n t i s o p t i c a l l y pure t h e t h r e e t e rms a r e e q u a l . 2 .3 ASYMMETRIC CATALYTIC HYDROGENATION 2 . 3 . 1 Gene r a l Of v a r i o u s t y p e s o f s t e r e o - d i f f e r e n t i a t i n g r e a c t i o n s , c a t a l y t i c e n a n t i o -d i f f e r e n t i a t i n g r e a c t i o n s a r e i n p r i n c i p l e t h e most e f f e c t i v e way o f o b -t a i n i n g o p t i c a l l y a c t i v e compounds. In t h i s r e g a r d t h e most s p e c t a c u l a r a c h i e v e m e n t s , o b t a i n i n g h i g h o p t i c a l y i e l d s a p p r o a c h i n g 100% e . e . , have been ob s e r v ed i n t h e h y d r o g e n a t i o n o f p r o c h i r a l o l e f i n i c s u b s t r a t e s . The c a t a l y s t s a r e c h i r a l r h od i um -pho sph i n e comp lexes ( F i g . 2 . 1 1 ) . 46 R H R Me [Rh]* Hz F i g . 2 . 1 1 : An example o f e n a n t i o f a c e - d i f f e r e n t i a t i n g r e a c t i o n o f a p r o c h i r a l o l e f i n by a c h i r a l r hod ium c a t a l y s t . The mechanism o f e n a n t i o f a c e - d i f f e r e n t i a t i o n (commonly c a l l e d a symmet r i c i n d u c t i o n ) i n t he r e a c t i o n s r e p r e s e n t e d i n F i g . 2.11 i s o f p a r t i c u l a r i m p o r t a n c e , and has been t h e s u b j e c t o f i n t e n s i v e s t u d i e s . T h i s i s because g e n e r a l g u i d e l i n e s can h a r d l y be g i v e n as t o how t o d e s i g n a symmet r i c r e a c t i o n s t o o b t a i n maximum o p t i c a l y i e l d s w i t h o u t a p r e c i s e knowledge o f t he mechan i sm. The l a s t decade has seen t h e bu r geon i ng o f bo th e x p e r i m e n t a l and t h e o r e t i c a l s t u d i e s i n t h i s a r e a . The f o rme r has been m a i n l y c on ce r ned w i t h t h e e m p i r i c a l m o d i f i c a t i o n o f c a t a l y s t s and s u b s t r a t e s t o i n c r e a s e o p t i c a l y i e l d s and t hu s t o g a i n an i n s i g h t i n t o t h e o r i g i n o f s t e r e o -d i f f e r e n t i a t i o n . T h i s l e a d s , i n e v i t a b l y , t o l e s s emphas i s on d e t a i l e d r e a c t i o n mechan i sm. The c l a r i f i c a t i o n o f mechanism i n te rms o f bo th k i n e t i c da t a and s t e r e o c h e m i c a l mode l s i s v i t a l t o t h e u n d e r s t a n d i n g o f the o r i g i n o f s t e r e o - d i f f e r e n t i a t i o n . The pu rpose o f t h e nex t s e c t i o n i s t o r e v i e w t h e r e s e a r c h d e vo t ed t o t h e s e s t u d i e s . 47 2 . 3 . 2 O v e r - a l l R e a c t i o n Mechanism A l t h o u g h c h i r a l r h o d i u m - p h o s p h i n e comp lexes have been employed a lmo s t u n i v e r s a l l y f o r s t u d i e s o f a s ymme t r i c c a t a l y t i c h y d r o g e n a t i o n , i t i s o n l y w i t h a r e l a t i v e l y l i m i t e d c o m b i n a t i o n o f c a t a l y s t s and s ub -s t r a t e s t h a t v e r y h i g h o p t i c a l y i e l d s (>95% e . e . ) have been o b t a i n e d . The be s t s u b s t r a t e s a r e amino a c i d p r e c u r s o r s as shown i n e q u a t i o n ( 2 . 3 ) and t h e h y d r o g e n a t i o n i s c a t a l y z e d by c a t i o n i c r h o d i u m - p h o s p h i n e sy s tems i n p o l a r s o l v e n t s such as a c e t one or a l c o h o l s : The c a t a l y t i c comp lexes t y p i c a l l y i n v o l v e c h i r a l r h o d i u m - d i ( t e r t i a r y a r y l p h o s p h i n e ) sys tems ( F i g . 2 . 1 2 ) , a l t h o u g h r e a s o n a b l y h i g h o p t i c a l y i e l d s a l s o have been ob -t a i n e d w i t h rhod ium-monophosph ine s y s t e m s . H , H N .COZR R ^ - ^ N H C O R " [ R h(L-L)] + * / C 0 2 R R C H 2 C - H N N H C O R " ( 2 , 3 ) CH; H (R .R ) -D IOP C«3 y * 3 PhP 2 (S ,S ) -CHIRAPH0S C H 3 Hm\ — CH 2 2 *• (R)-PROPHOS Ph (R ,R) -DIPAMP F i g . 2 . 1 2 : Some r e p r e s e n t a t i v e c h e l a t i n g d i ( t e r t i a r y a r y l p h o s p h i n e ) l i g a n d s . 48 The mechanism o f a s ymmet r i c h y d r o g e n a t i o n s r e p r e s e n t e d by e q u a t i o n ( 2 . 3 ) has been s t u d i e d i n c o n s i d e r a b l e d e t a i l by s e v e r a l r e s e a r c h g roups [ 4 6 , 4 7 , 64 , 7 2 - 7 4 ] . T h e i r work e s t a b l i s h e s t h a t t h e k i n e t i c and m e c h a n i s t i c f e a t u r e s o f t h e a c h i r a l [ R h ( D I P H 0 S ) ( s o l v e n t ) 2 ] + sys tem d e p i c t e d i n F i g . 1.7 [46 ] a r e v i r t u a l l y i d e n t i c a l w i t h t h o s e o f i t s c h i r a l c o u n t e r p a r t s [ R h ( l _ - L ) * ( s o l v e n t ) 2 ] + ( L - L * = DIOP, DIPAMP, CHIRAPHOS, and PROPHOS) ( F i g . 2 . 12 ) w i t h t h e e x c e p t i o n o f t h e f e a t u r e s d i s c u s s e d be low t h a t a r e s p e c i f i c a l l y r e l a t e d t o t h e f o r m a t i o n o f d i a s t e -r e o m e r i c i n t e r m e d i a t e s ( F i g . 2 . 1 3 ) . I t s h o u l d be n o t e d , however , t h a t a l m o s t a l l s t u d i e s t o da t e employ d i ( t e r t i a r y a r y l p h o s p h i n e ) l i g a n d s i n wh i c h f o u r a r y l g roups a r e bound t o p h o s p h o r u s . F i g . 2 .13 o u t l i n e s t h e mechanism o f a s ymmet r i c h y d r o g e n a t i o n d e p i c t e d by e q u a t i o n ( 2 . 3 ) . As s t a t e d p r e v i o u s l y , when t h e c h i r a l c a t a l y t i c sys tems a r e emp l o yed , t h e m e c h a n i s t i c scheme o f F i g . 1.7 must be m o d i f i e d , i n a c c o r d a n c e w i t h t h e f undamen ta l p r i n c i p l e d i s c u s s e d i n s e c t i o n 2 . 2 . 2 ( B ) , so as t o accommodate t h e f o r m a t i o n o f d i a s t e r e o m e r i c fo rms o f t h e adduc t c o r r e s p o n d i n g t o 1.7c and o f t h e f u r t h e r r e a c t i o n i n t e r m e d i a t e s . The s t r u c t u r e o f t h e [ R h ( L - L ) ( s u b s t r a t e ) ] + a ddu c t has been e s t a b l i s h e d by NMR ( 3 1 P , 1 3 C , and ] H ) and by x - r a y a n a l y s i s (when L -L = DIPHOS, R1 = P h , R 2 , R 3 = Me; when L-L = (S ,S) -CHIRAPHOS, R1 = P h , R 2 = E t , R 3 = M e ) , r e v e a l i n g c h e l a t i o n o f t h e s u b s t r a t e s t o t h e Rh atom t h r o u g h t h e c a r b o n y l p oxygen o f t h e amide group as w e l l as t h r o u g h normal n - c o o r d i n a t i o n o f t h e C = C bond [ 4 6 , 7 2 ] . The s t e r e o c h e m i s t r y o f t h e p r o d u c t can t h u s be c o r r e l a t e d w i t h t h a t o f t h e adduc t d i a s t e r e o m e r f rom wh i ch i t i s d e r i v e d 49 ROOC\ NH •WWv 111 I 2 | H 2 2 ROOC NH H 2.13a 2.13 b' H ,C09R . c = c J / \ 3 R NHCOR NH COOR • 2- ,+ 3 2.13a k 2 HN COOR . 0 \ p 2.13 b H V 1 o J S r 3 *NNH PV 0 CO2R 2.13C k 4 - [ M ( P - P ) S 2 ] + R 3 ^NH^r^COOR 2 0 V («) H H ^ > „ I o _ y k 3 | s R 3 1 SN 2 R 2OC O P M / n ^ P > « J k 4 -[M(P-*P)S2] 2.13C 2 H ROOC J>HN j Y (s) 2 . 1 3 : The mechan ism o f a s ymme t r i c h y d r o g e n a t i o n o f amino a c i d s w i t h [ M ( P - P ) S 2 ] ( P -P = CHIRAPHOS, DIPAMP; M = Rh; S = MeOH)[64 ,76d] 50 i n a c c o r d a n c e w i t h F i g . 2 . 1 3 , s i n c e i t i s known t h a t , f o r t he c a t a l y t i c sys tems e m p l o y i n g d i ( t e r t i a r y pho sph i n e ) l i g a n d s , ( i ) t h e o x i d a t i v e a d d i -t i o n o f H 2 and subsequen t s t e p s a r e i r r e v e r s i b l e , and ( i i ) t h e m i g r a t o r y i n s e r t i o n o f H 2 t o t h e c o o r d i n a t e d s u b s t r a t e i s s t e r e o s p e c i f i c g i v i n g a c i s - e n d o p r o d u c t . Thus t h e ( R ) - p r o d u c t i s p roduced f rom 2 . 1 3 a ' and t h e ( S ) - p r o d u c t f rom 2 . 1 3 a " 2 . 3 , 3 Mechan isms o f E n a n t i o f a c e - D i f f e r e n t i a t i o n Asymmet r i c h y d r o g e n a t i o n (an e n a n t i o f a c e - d i f f e r e n t i a t i n g r e a c t i o n ) as shown i n F i g . 2 . 13 i s a m u l t i s t e p p r o c e s s , and t h e r e i s more t h a n one s t a g e i n wh i c h a p a i r o f d i a s t e r e o m e r i c t r a n s i t i o n s t a t e s ( o r i n t e r m e d i a t e s ) a r e formed c o m p e t i t i v e l y , g i v i n g r i s e t o s t e r e o i s o m e r s i n d i f f e r e n t p o r t i o n s k\ k ' A — ^ > P ' ( 2 . 4 ) K d B L> i 1 . > 5, p " [ P ' ] / [ P " ] = k ^ C A l / k ' ^ C B ] = k\Kd/k\ = e A A G * / R T ( 2 . 5 ) E q u a t i o n s ( 2 . 4 ) and ( 2 . 5 ) show t h a t t h e r a t i o o f s t e r e o i s o m e r s p roduced ( e i t h e r as p r o d u c t s o r as i n t e r m e d i a t e s ) , o r t h e r a t i o o f t h e r e a c t i o n r a t e s i n c o m p e t i t i v e r e a c t i o n s , depend on t h e d i f f e r e n c e between t h e a c t i v a t i o n e n e r g i e s o f t h e t r a n s i t i o n s t a t e s AAG^ ( Cu r t i n -Hamme t t p r i n c i p l e ) [ 7 5 ] . The o r i g i n o f s t e r e o - d i f f e r e n t i a t i o n can t hu s be a s c r i b e d t o t h i s e n e r g y 51 d i f f e r e n c e w h i c h i s o f t e n r e f e r r e d t o as d i a s t e r e o t o p i c d i s c r i m i n a t i o n . E q u a t i o n ( 2 . 5 ) r e p r e s e n t s a s p e c i a l c a s e i n wh i c h o n l y a s i n g l e s t a g e p r o c e s s i s i n v o l v e d t o p roduce s t e r e o i s o m e r i c p r o d u c t s f rom two d i a s t e r e o -mers A and B, but some o t h e r c i r c u m s t a n c e s s h o u l d be t a k en i n t o c o n s i d e r a -t i o n i n a m u l t i s t e p p r o c e s s such as a s ymme t r i c h y d r o g e n a t i o n i n o r d e r t o p r e d i c t t h e deg r ee and o r i g i n o f s t e r e o - d i f f e r e n t i a t i o n . In t h i s r e g a r d two mechan isms o f e n a n t i o f a c e - d i f f e r e n t i a t i o n can be r e c o g n i z e d as f o l l o w s . (A) The use o f s t e r e o c h e m i c a l mode l s I f t h e c o r r e s p o n d i n g r a t e c o n s t a n t s i n t h e two co lumns i n F i g . 2 .13 a r e t h e same, t h a t i s , k ' 2 - k '^* ^3 = ^"3* a n c * ^'4 = ^"4* t n e n t n e e n a n t i o m e r i c e x c e s s can be d e t e rm i n ed by t h e v a l u e o f K j , i n d e p e n d e n t l y o f t he r e a c t i o n p r o c e s s . T h e r e f o r e t h e p r edom inan t enan t i ome r o f t h e p r o d u c t w i l l a r i s e f rom t he p r edom inan t d i a s t e r e o m e r o f t h e c a t a l y s t - s u b s t r a t e a d d u c t . The Cu r t i n -Hamme t t p r i n c i p l e t hen r educe s to e q u a t i o n ( 2 . 6 ) , where AAG^ i s t h e f r e e ene r g y d i f f e r e n c e between two d i a s t e r e o m e r i c t r a n s i -t i o n s t a t e s l e a d i n g t o t h e c o r r e s p o n d i n g c a t a l y s t - s u b s t r a t e a d d u c t s . [ R ] / [ S ] = K d = e A A G * / R T ( 2 . 6 ) The o t h e r way i n wh i c h can a f f e c t t h e e n a n t i o m e r i c e x c e s s i s t h a t t h e a t t a i n m e n t o f i s s l o w , name l y , t h e f i r s t s t e p ( k ' ^ / k " ^ ) i s t h e r a t e d e t e r m i n i n g s t e p . In any e v e n t , i t i s t h e p r e f e r r e d mode o f i n i t i a l b i n d i n g o f t h e p r o c h i r a l s u b s t r a t e t o t h e c a t a l y s t t h a t d i c t a t e s t h e 52 mechanism o f e n a n t i o f a c e - d i f f e r e n t i a t i o n o f t h e s e c a t a l y s t s y s t e m s . Thus i f t h e c a t a l y s t - s u b s t r a t e a ddu c t 2 .13a ( F i g . 2 .13 ) e x i s t s as a s i n g l e s t a t i c c h i r a l c o n f o r m e r 100% e . e . wou ld be e x p e c t e d i n h y d r o g e n a t i o n . T h i s t y p e o f argument has been used by B o s n i c h e t a l [ 76 ] who have sugge s t ed t h a t s t e r i c r i g i d i t y o f t h e me t a l complex c o n t a i n i n g c h i r a l d i ( t e r t i a r y a r y l p h o s p h i n e ) l i g a n d s i s a n e c e s s a r y c o n d i t i o n t o max im i z e t h e v a l u e ( F i g . 2 . 1 3 ) . Name ly , among many p o s s i b l e c h i r a l c o n f o r m a t i o n s o f f i v e membered o r h i g h e r membered c h e l a t e r i n g s formed by t h i s c l a s s o f b i d e n t a t e l i g a n d s , t h e most s t a b l e c h i r a l c o n f o r m a t i o n p r edom i na t e s due t o t h e r e s u l t o f s t e r i c r e q u i r e m e n t t h a t non -hyd rogen s u b s t i t u e n t ( s ) o f t he c h i r a l r i n g a tom(s ) be d i s p o s e d e q u a t o r . i a l l y . In F i g . 2 . 1 4 (A ) a r e shown t h e p r e f e r r e d c o n f o r m a t i o n s o f (S .S ) -CHIRAPHOS, (R)-PROPHOS, ( S , S ) -SKEWPHOS,, and (S) -CHAIRPHOS. Ex cep t f o r (S) -CHAIRPHOS, t h e y d i s p o s e t h e f o u r pheny l g roups as w e l l as t h e s u b s t i t u e n t s on t h e c a r b on back -bone i n a p r e f e r r e d c h i r a l a r r a y . As a r e s u l t a p r o c h i r a l o l e f i n a p p r o a c h i n g a me t a l atom i n c o r p o r a t i n g t h i s c h i r a l r i n g i s now i ndu ced t o adop t a p r e f e r r e d ( e n e r g e t i c a l l y more s t a b l e ) d i a s t e r e o m e r i c c o n f i g u r a t i o n by t h i s c h i r a l a r r a y o f t h e a r y l g r o u p s . I f t h e c h i r a l c o n f o r m a t i o n o f t h e s e c a t a -l y s t sys tems were non r i g i d a t l e a s t two d i a s t e r e o m e r i c c on f o rme r s wou ld r e s u l t t h r o u g h t h e r i n g i n t e r c o n v e r s i o n p r o c e s s ( F i g . 2 . 1 4 B ) . The e f f e c t wou ld be to " w a s h - o u t " any d i s c r i m i n a t i o n i n such non r i g i d s y s t e m s . The same a u t h o r s [ 76 ] have t e s t e d t h i s h y p o t h e s i s and s u c c e s s f u l l y p r e d i c t e d o p t i c a l y i e l d s and p r o d u c t c o n f i g u r a t i o n s u s i n g t h e c h i r a l l i g a n d s shown i n F i g . 2 . 1 4 . For e x amp l e , (S ,S) -CHIRAPHOS and (R)-PR0PH0S s t a b i l i z e e n an -53 F i g . 2 . 1 4 : (A) The p r e f e r r e d c o n f o r m a t i o n o f (S ,S ) -CHIRAPHOS, ( R ) -PROPHOS, (S ,S) -SKEWPHOS, and (S)-CHAIRPHOS . (B) The r i n g i n t e r c o n v e r s i o n p r o c e s s between two d i a s t e r e o -m e r i c c on f o rme r s [ 7 6 ] . The Rh atom t o wh i c h t h e two P atoms a r e bound i s o m i t t e d f o r c l a r i t y . 54 t i o m e r i c (more p r e c i s e l y d i a s t e r e o m e r i c ) r i n g c o n f o r m a t i o n s and t h e r e b y g e n e r a t e o p p o s i t e p r o d u c t c o n f i g u r a t i o n s . K n o w l e s ' g roup [77] had e a r l i e r p roduced e v i d e n c e s f o r t h e s e i d e a s on t h e b a s i s o f s t e r e o c h e m i c a l mode l s o f comp lexes o f t h e t y p e [ R h ( L - L ) -* ( D i e n e ) ] A ( L - L = c h e l a t i n g d i ( t e r t i a r y a r y l p h o s p h i n e ) ) . They s u g g e s t e d , w i t h o u t d e f i n i t i v e m e c h a n i s t i c p r o o f , t h a t t h e a b s o l u t e c o n f i g u r a t i o n s o f p r o d u c t s a r e s o l e l y d e t e r m i n e d by t h e o r i e n t a t i o n o f t h e f o u r a r y l g roups i n t h e s e c a t a l y s t p r e c u r s o r s where t h e y a r e a r r a n g e d a r ound t he me ta l i n an a l t e r n a t i n g e d g e - f a c e manner as i f t h e who le m o l e c u l e had a C 2 a x i s o f s ymme t r y : I n t h e c a s e o f (R ,R ) -D IPAMP , f o r i n s t a n c e , s u b s t i t u e n t s i n a p r o c h i r a l o l e f i n l y i n g i n t h e q u a d r a n t s 2 and 4 e x p e r i e n c e l e s s s t e r i c r e p u l s i o n t h an t h o s e l y i n g i n 1 and 3 ( F i g . 2 . 1 5 ) . T h e r e f o r e , a ( S ) - am i n o a c i d i s p roduced p r e d o m i n a n t l y f rom ( Z)-a - a c e t a m i d o c i n n a m i c a c i d b u t , i n t h e c a se o f ( E ) - o l e f i n , as i n t he t h i r d and f o u r t h b o x e s , bo th r e - and s i - f a c e s f o r c e a l a r g e g roup t o be i n a h i n d e r e d q u a d r a n t , t hu s r e s u l t i n g s l o w e r r e a c t i o n r a t e s and i n e f f i c i e n t low o p t i c a l y i e l d s [ 78 ] a l t h o u g h t h e p r e f e r r e d i s ome r i s s t i l l t h e same ( S ) - c o n f i g u r a t i o n . (B) K i n e t i c a pp r o a ch I f , howeve r , t h e r a t e c o n s t a n t s i n a g i v e n p a i r i n F i g . 2 .13 a r e d i f f e r e n t i n a l l s t e p s , t h en t h e f i n a l e n a n t i o m e r i c e x c e s s w i l l be d e t e r -mined by t h e d i f f e r e n c e i n t h e r e l a t i v e e n e r g i e s o f two d i a s t e r e o m e r i c 1 55 F i g . 2 . 1 5 : Quadrant t h e o r y s ugge s t ed by Knowles [ 7 7 ] . 56 t r a n s i t i o n s t a t e s l y i n g i n t h e r a t e - d e t e r m i n i n g s t e p ( k ' n / k " n ) . T n e Cu r t i n -Hamme t t p r i n c i p l e t h en r e q u i r e s ( c f . e q u a t i o n 2 .4 ) CR1/CS] - k ' n [ f n ] / k " n [ r ' n ] = e M G + / R T ( 2 . 7 ) Thus i n one ex t reme t h e v a l u e can be u n i t y and y e t s i g n i f i c a n t e n a n t i o - d i f f e r e n t i a t i o n w i l l be a c h i e v e d , and i n a n o t h e r e x t r eme t h e p r edom inan t e n a n t i o m e r o f t h e p r o du c t a r i s e s f rom t he m i n o r d i a s t e r e o m e r o f t h e c a t a l y s t - s u b s t r a t e adduc t due t o t h e much h i g h e r r e a c t i v i t y o f t h e m ino r d i a s t e r e o m e r . In t h i s c o n n e c t i o n H a l p e r n e t a l [ 7 3 ] , f o r t h e f i r s t t i m e , d emon s t r a t e d t h a t , f o r t h e r e a c t i o n d e p i c t e d by F i g . 2 . 1 3 , i t i s no t t h e p r e f e r r e d mode o f i n i t i a l b i n d i n g o f t h e p r o c h i r a l o l e f i n i c s u b s t r a t e t o t h e c a t a l y s t but r a t h e r d i f f e r e n c e s i n t h e r a t e s o f o x i d a t i v e -a d d i t i o n o f H 2 t h a t d i c t a t e s t h e e n a n t i o m e r i c e x c e s s . The most s t r i k i n g f e a t u r e s o f t h e i r f i n d i n g s a r e : ( i ) t h e p r edom inan t d i a s t e r e o m e r o f t h e c a t a l y s t - s u b s t r a t e adduc t [Rh( (S ,S)-CHIRAPHOS) ( s u b s t r a t e ) ] " 1 " i s t h e one i n wh i ch t h e C - r e f a c e o f t h e o l e f i n i s c o o r d i n a t e d c o n t r a r y t o t h e a Know l e ' s quad r an t t h e o r y ( c f . F i g . 2 . 1 4 ) , ( i i ) t h e c o n f i g u r a t i o n o f t h e 57 p r o du c t i s d e r i v e d f rom t he m i n o r d i a s t e r e o m e r no t t h e ma j o r o n e . E v i d e n c e f o r t h e same c o n c l u s i o n has a l s o been o b t a i n e d i n t he [ R h ( . R , R - D I P A M P ) ] + - c a t a l y z e d h y d r o g e n a t i o n o f r e l a t e d s u b s t r a t e s . Brown e t a l [ 4 7 a , c ] i n i t i a l l y r e p o r t e d t h a t , w i t h t h i s c a t a l y s t a t room t e m p e r a t u r e , t h e r a t i o o f d i a s t e r e o m e r i c c a t a l y s t - s u b s t r a t e a d d u c t s ( a l t h o u g h t h e a b s o l u t e c o n f i g u r a t i o n s c o u l d no t be a s s i g n e d ) was a p p r o x i m a t e l y equa l t o t h a t o f two e n a n t i o m e r i c p r o d u c t s . The p r e v a i l i n g c h i r a l i t y o f t h e p r o d u c t was t h a t d e r i v e d f rom t h e ma j o r d i a s t e r e o m e r . However , a t l ow t e m p e r a t u r e (^ - 4 0 ° C ) , where t h e i n t e r c o n v e r s i o n o f t he d i a s t e r e o m e r s i s f r o z e n o u t , i t was f ound t h a t o n l y t h e m i n o r d i a s t e r e o m e r r e a c t s d i r e c t l y w i t h H 2 t o y i e l d , f o r e x amp l e , t h e ( S ) - am i n o a c i d i n t h e c a s e o f ( Z ) - a - c i n n a m i c a c i d s . The ma j o r d i a s t e r e o m e r r e a c t s s l o w l y a t a r a t e i n d ependen t o f t h e H 2 c o n c e n t r a t i o n [ 6 4 , 7 4 ] . J u d g i n g f rom t h e s e o b s e r v a t i o n s , t h e m i no r d i a s t e r e o m e r s h o u l d be t h e one i n wh i c h t h e C - r e f a c e i s c o o r d i n a t e d a ( F i g . 2 .13 ) a g a i n c o n t r a r y t o t h e K n o w l e s 1 p r e d i c t i o n . Thu s , a c c o r d i n g t o t h e s e r e s u l t s , i t i s e xpe c t ed t h a t t h e e n a n t i o -m e r i c e x c e s s s h o u l d d e c r e a s e , w i t h t h e p o s s i b i l i t y o f e v e n t u a l r e v e r s a l o f p r edom inan t p r o d u c t c h i r a l i t y , w i t h i n c r e a s i n g H 2 p r e s s u r e , s i n c e t h e p r o du c t c h i r a l i t y i s a g a i n governed by t h e r e l a t i o n s h i p e x p r e s s e d i n e q u a t i o n ( 2 . 7 ) w i t h t h e i n i t i a l b i n d i n g s t e p ( k ^ ' ^ / k " - , ) becoming r a t e d e t e r -58 m i n i n g . A n o t h e r consequence i s t h a t , p r o v i d e d t h e ma j o r d i a s t e r e o m e r e x h i b i t s some r e a c t i v i t y t owa rd (as i t must i f t h e e n a n t i o m e r i c e x c e s s i s l e s s t h an 100%), t he o p t i c a l y i e l d may d e c r e a s e w i t h d e c r e a s i n g t e m p e r a t u r e due t o t h e f a c t t h a t t h e d i a s t e r e o m e r i c i n t e r c o n v e r s i o n p r o -c e s s becomes " f r o z e n o u t " a t s u f f i c i e n t l y low t e m p e r a t u r e . There a r e r e p o r t s s u p p o r t i n g t h i s argument [ 7 9 ] . The s t r i k i n g d i f f e r e n c e between r e a c t i v i t i e s o f t h e d i a s t e r e o m e r i c a d d u c t s t oward i s d i f f i c u l t t o e x p l a i n a l t h o u g h i t i s no t unexpec t ed t h a t t h e l e s s s t a b l e o f a p a i r o f d i a s t e r e o m e r s e x h i b i t s t h e h i g h e r r e a c t i v i t y due t o i t s h i g h e r i n i t i a l f r e e e n e r g y . One p o s s i b l e e x p l a n a t i o n s ugge s t ed by B o s n i c h [ 76 c ] and by H a l p e r n [64] i s t h a t , i f t h e o x i d a t i v e a d d i t i o n s t e p i s e ndo t he rm i c and r a t e d e t e r m i n i n g , t hen t h e more s t a b l e t h e c i s - d i h y d r i d e i n t e r m e d i a t e , t he l owe r w i l l be t h e c o r r e s p o n d i n g t r a n s i t i o n s t a t e e ne r g y (Hammond h y p o t h e s i s ) . The r e l a t i v e s t a b i l i t i e s o f t h e d i a s t e r e o m e r i c p r o d u c t s now become o p p o s i t e t o t h a t o f t h e p a r e n t c a t a l y s t - s u b s t r a t e a d d u c t s as shown i n F i g . 2 . 1 6 . Thus t h e r a t e o f h y d r o g e n a t i o n becomes f a s t e s t v i a t h e most s t a b l e o f f o u r d i h y d r i d o i n t e r m e d i a t e s d e r i v e d f rom t h e m i no r d i a s t e r e o m e r i c a ddu c t ( c f . F i g . 2 . 1 3 ) . The a u t h o r s r e p o r t e d t h a t t h e s p a c e - f i l l i n g mode l s were i n c o n c l u s i v e i n d e c i d i n g wh i c h o f t h e f o u r i n t e r m e d i a t e s i s t h e most s t a b l e . However , i t i s a l s o p o s s i b l e t h a t t h e H a d d i t i o n s t e p i s an e x o t h e r m i c p r o c e s s , and thus t h e r e l a t i v e r a t e s f o r t h e f o r m a t i o n o f t h e d i h y d r i d o i n t e r m e d i a t e s depends bo th on t h e r e l a t i v e r e a c t i v i t i e s o f two d i a s t e r e o m e r s ( k " 2 A ^) a n c ' o n t n e e q u i l i b r i u m c o n -c e n t r a t i o n ( k . ) o f t h e t w o . F u r t h e r m o r e , any o t h e r s t e p , f o r e x a m p l e , 59 Reaction coordinate F i g . 2 . 1 6 : S chema t i c r e a c t i o n c o o r d i n a t e p r o f i l e s f o r t h e e n a n t i o f a c e - d i f f e r e n t i a t i n g r e a c t i o n s o f t h e d i a s t e r e o m e r i c [ Rh (P - P ) ( s u b s t r a t e ) ] + w i t h H 2 [ 6 4 , 7 6 c , d ] . 60 t he m i g r a t o r y i n s e r t i o n s t e p ( k ' 3 / k " 3 ) may be r a t e d e t e r m i n i n g . In t h e e ven t t h e same a s s ump t i o n s and t h e Cu r t i n -Hamme t t p r i n c i p l e can be a p p l i e d t o d e s c r i b e t he mechanisms o f s t e r e o - d i f f e r e n t i a t i o n . I t s h o u l d be p o i n t e d ou t t h a t a t low t e m p e r a t u r e kg i s r a t e d e t e r m i n i n g f o r t he Rh-DIPHOS c a t a l y z e d h y d r o g e n a t i o n ( c f . s e c t i o n 1 . 4 . 2 ( C ) ) . F i n a l l y , i n c o n n e c t i o n w i t h t h i s mechan i sm , i t s h o u l d a l s o be p o i n t e d ou t t h a t , i f ( a l t h o u g h u n l i k e l y ) r a t e c o n s t a n t s a r e d i f f e r e n t i n a l l s t a g e s e x c e p t i n t h e r a t e d e t e r m i n i n g s t e p , then a g a i n t h e e n a n t i o m e r i c e x c e s s w i l l be d e t e r m i n e d by t h e p r e - e q u i l i b r i u m c o n s t a n t . The o v e r a l l mechan ism shown i n F i g . 2 .13 can be used t o e x p l a i n t h e r e s u l t s o f a number o f s t u d i e s . However , t h e r e a r e i n s t a n c e s where t h e e f f e c t s o f s o l v e n t , t e m p e r a t u r e , and p r e s s u r e a r e no t as e x p e c t e d ( c f . s e c t i o n 2 . 4 ) . F u r t h e r m o r e , l i t t l e has been s a i d abou t t h e p o s s i b i l i t y o f e l e c t r o n i c e f f e c t on s t e r e o - d i f f e r e n t i a t i o n and t h e e f f e c t s o f s u b s t i -t u e n t l i g a n d s o t h e r than a r y l g r o u p s . 2 .4 CHIRAL RHODIUM-PHOSPHINE CATALYSTS Most o f t h e c h i r a l c a t a l y s t s w h i c h have been s t u d i e d so f a r f o r a s ymmet r i c homogeneous h y d r o g e n a t i o n s i n v o l v e rhod ium comp lexes o f c h i r a l phosph i ne l i g a n d s . In a m a j o r i t y o f t h e s e c a s e s , i t can be assumed t h a t , as shown i n t h e p r e v i o u s s e c t i o n , k i n e t i c and m e c h a n i s t i c f e a t u r e s f o r t h e s e c h i r a l s y s tems a r e v i r t u a l l y i d e n t i c a l w i t h t h o s e o f t h e i r a c h i r a l c o u n t e r p a r t s d i s c u s s e d i n t h e p r e v i o u s c h a p t e r . W i t h t h i s i n m i n d , t h e r h o d i u m - p h o s p h i n e sys tems can be c o n v e n i e n t l y c l a s s i f i e d i n t o t h e f o l l o w i n g 61 t h r e e c l a s s e s o f c h i r a l c a t a l y s t s a c c o r d i n g t o t h e s o u r c e ( s ) o f c h i r a l i t y i n t h e l i g a n d s . They a r e : (1) L i g and s w i t h c e n t r a l c h i r a l i t y , ( 2 ) L i g and s w i t h a x i a l c h i r a l i t y , (3 ) L i g and s w i t h bo th c e n t r a l and p l a n a r c h i r a l i t y . The pu rpose o f t h i s s e c t i o n i s t o r e v i e w b r i e f l y some r e p r e s e n t a t i v e examp les o f t h e above l i g a n d s wh i c h have been s u c c e s s f u l l y employed i n a s ymme t r i c h y d r o g e n a t i o n r e a c t i o n s . 2 . 4 . 1 L i g a n d s w i t h C e n t r a l C h i r a l i t y Here t h r e e t y p e s can be r e c o g n i z e d . (A) C h i r a l i t y a t p h o s p h o r u s , R ^ f ^ P The d i s c o v e r y o f W i l k i n s o n ' s c a t a l y s t [12 ] and t h e n e a r l y s i m u l t a n e o u s deve l opmen t o f c h i r a l pho sph i ne t e c h n o l o g y by M i s l o w e t a l [ 80 ] and by Ho rne r e t a l [ 81 ] prompted i n i t i a l l y i n t e n s e r e s e a r c h on t h i s t y p e o f l i g a n d . T h i s c h o i c e was based on t h e " p r o x i m i t y r u l e " t h a t t h e c h i r a l c e n t e r s s h o u l d be as near as p o s s i b l e t o t h e c e n t r a l r hod ium atom t o o b t a i n a h i g h deg r ee o f a s ymme t r i c i n d u c t i o n . T h i s r e s t r i c t i o n i s no l o n g e r r e g a r d e d as v a l i d . The f i r s t examp les o f a s ymme t r i c h y d r o g e n a t i o n based on t h i s p r i n c i p l e were r e p o r t e d i n 1968 by Knowles e t a l [ 8 2 ] . Rhodium comp lexes o f t h e t y p e RhL^Cl^ were used i n t h e h y d r o g e n a t i o n o f a - p h e n y l a c r y l i c a c i d and i t a c o n i c a c i d under t h e c o n d i t i o n s i n d i c a t e d i n F i g . 2 . 1 7 . 62 CH P=C(Ph)COOH R h l _ 3 C l 3 / H 2 ( 2 0 atm) » C H 3 CH(Ph)COOH 15% e . e . (S) 6 0o C f C g H . 6 - E t 0 H - E t 3 N CH 2 =C(C00H)CH 2 C00H * CH 3 *CH(C00H)CH 2 C00H 3% e . e . F i g , 2 . 1 7 : E a r l y examp les o f a s ymmet r i c h y d r o g e n a t i o n w i t h R h L 3 C l 3 [ 8 2 ] . When L was ( R ) - ( - ) - m e t h y 1 p h e n y l - n - p r o p y l phosph i ne (MPPP) , 15% o p t i c a l l y pu re ( S ) - ( + ) - a - p h e n y l p r o p i o n i c a c i d and 3% o p t i c a l l y pure me thy l s u c c i n i c a c i d ( c o n f i g u r a t i o n u n r e p o r t e d ) were o b t a i n e d . The Monsanto g roup s ugge s t ed t h a t W i l k i n s o n t y p e Rh ( I ) comp lexes m i gh t be i n v o l v e d as an a c t i v e c a t a l y s t . A t t h e same t i m e , H o r n e r ' s g roup [83 ] r e p o r t e d t h e r e d u c t i o n o f a - s u b s t i t u t e d s t y r e n e s u s i n g an i n s i t u c a t a l y s t p r e pa r ed f rom (S) -MPPP ( F i g . 2 . 1 8 ) , a g a i n a s sum ing a mechanism p a r a l l e l i n g t h e one f o r W i l k i n s o n ' s c a t a l y s t . CH 2 =C(R)Ph H 2 ( l a t m ) , C 6 H 6 , 2 5 ° C -> C H 3 CH(R)Ph R = E t , 7-8% e . e . (S) ( ( S ) - M P P P ) 3 R h C l / i j i s i t u R = OMe, 3-4% e . e . (R) F i g 1 . 2 . 1 8 : E a r l y examples o f a s ymme t r i c h y d r o g e n a t i o n w i t h a W i l k i n s o n t y pe c a t a l y s t . The i n s i t u c a t a l y s t was p r epa r ed f rom [ R h ( l . 5 - h e x a d i e n e ) ] ? and (S) -MPPP [ 8 3 ] . 63 Subsequen t t o t h e s e e x p e r i m e n t s , bo th t h e Ho rne r and Monsanto g roups ex t ended t h e i r s t u d i e s t o o t h e r s u b s t r a t e s and o t h e r c h i r a l monophosph i ne s . The most s i g n i f i c a n t s u c c e s s was a c h i e v e d by Knowles e t a l [84] i n t h e h y d r o g e n a t i o n o f amino a c i d p r e c u r s o r s u s i n g c a t i o n i c rhod ium-monophosph ine c a t a l y s t s o f t h e t y pe [Rh(COD) (ACMP) 2 ]A (COD = 1 ; > 5 - c y c l o o c t a d i e n e ; A = B F 4 " , P F g " , BPh^" ; ACMP = o - a n i s y l c y c l o h e x y l m e t h y l p h o s p h i n e ) . C a t a l y s t s p r epa r ed f rom (R ) - (+) -ACMP gave ( S ) - am i no a c i d s and t h o s e c o n t a i n i n g t h e ( - ) - p h o s p h i n e gave R - e n a n t i o m e r s . In many i n s t a n c e s , t h e e n a n t i o m e r i c e x c e s s r e a ched 85-90% [ 8 4 ] . F u r t h e r s t u d i e s on ACMP by Knowles e t a l l e d t o t h e s y n t h e s i s o f a new c a t a l y s t p r e c u r s o r o f t h e t y p e [ (COD)Rh ( L - L ) ] B F 4 ( L - L = R.R-DIPAMP) wh i c h adop t s a f i v e -membe red c h e l a t e r i n g as shown i n F i g . 2 . 1 2 . E x c e l l e n t e n a n t i o m e r i c e x c e s s e s (95-96%) have been a c h i e v e d i n t h e r e d u c t i o n o f ( Z)-a - a c e t a m i d o c i n n a m i c a c i d s by t h e c a t a l y s t p r e c u r s o r ( T ab l e 2 .1 ) . T a b l e 2 . 1 : A symmet r i c h y d r o g e n a t i o n o f (Z)-a - a c e t a m i d o c i n n a m i c a c i d s by Rh ( I ) -D IPAMP [ 8 5 ] . R 1 H Me H C = C ^ C 0 2 R 1 Ph' N 2 NHCOR R Me Me Ph % e . e , 94 96 93 PhCH 2 *CH (C0 2 R ] )NHC0R 2 C o n f i g u r a t i o n S S S 64 T h i s sys tem was used s u c c e s s f u l l y no t o n l y t o r educe o t h e r a - a c e t a m i d o -a c r y l i c a c i d s w i t h h i g h o p t i c a l y i e l d s but a l s o t o p r o du c t L-DOPA on an i n d u s t r i a l s c a l e [ 8 6 ] . (B) C h i r a l i t y a t c a r b on T h i s t y p e o f l i g a n d s has s e v e r a l p r a c t i c a l a d van t age s o v e r t h e l i g a n d s d i s c u s s e d p r e v i o u s l y : i n e x p e n s i v e , n a t u r a l l y o c c u r r i n g o p t i c a l l y a c t i v e compounds can be used as s t a r t i n g m a t e r i a l s . These i n c l u d e m e n t h o l , camphor , l a c t i c a c i d , t a r t a r i c a c i d , L - h y d r o x y p r o l i n e , and v a r i o u s s a c c h a r i d e s . The p r e p a r a t i o n o f l i g a n d s w i t h c h i r a l phosphorus atoms o f n e c e s s i t y r e q u i r e s c l a s s i c a l r e s o l u t i o n s t e p s . The f i r s t rhod ium c a t a l y s t c o n t a i n i n g a c h i r a l c a r b o n a t om , d i p h e n y l n e o m e t h y l p h o s p h i n e (NMDPP) was s y n t h e s i z e d f rom mentho l [ 8 7 ] . H y d r o g e n a t i o n o f ( E)-g - m e t h y l c i n n a m i c a c i d i n t h e p r e s en c e o f RI^NMDPP^CL ( p r e p a r e d i n s i t u ) and t r i e t h y l amine ( 0 . 17 m o l / m o l . o f s u b s t r a t e ) gave ( S ) - ( + ) - 3 - p h e n y l b u t a n n i c a c i d i n 61% e . e . A t abou t t h e same t ime as t h e s u c c e s s f u l use o f NMDPP, a new, c h i r a l d i ( t e r t i a r y p h o s p h i n e ) 1 i g a n d , ( - ) - 2 , 3 - i s o p r o p y l i d e n e - 2 , 3 - d i h y d r o x y -1 , 4 - b i s ( d i p h e n y l p h o s p h i n o ) butane (DI0P) ( F i g . 2 . 1 2 ) , was p r epa r ed by Kagan e t a l [ 8 8 ] , and soon became one o f t h e be s t known c h i r a l l i g a n d s . O p t i c a l y i e l d s i n t h e range o f 70-80% have been r e p o r t e d i n t he r e d u c t i o n o f v a r i o u s o l e f i n i c a c i d s u s i n g R h C l ( R . R - D I O P ) ( S ) ( p r e p a r e d i n s i t u ) ( T ab l e 2 . 2 ) . -Fo lowing t h e d i s c o v e r y o f DIOP, a g r e a t number o f a n a l o g u e s were p r epa r ed e i t h e r t o a t t emp t t o c l a r i f y t h e r e a c t i o n mechanism o r t o 65 o b t a i n even b e t t e r o p t i c a l y i e l d s . The f undamen ta l s t r u c t u r e o f DIOP was v a r i e d by c h ang i n g e i t h e r t h e a r o m a t i c s u b s t i t u e n t s , t h e a c e t a l s u b s t i t u e n t s , o r t h e a c e t o n i d e r i n g by a c a r b o c y c l e [ 8 9 ] . T ab l e 2 . 2 : Asymmet r i c h y d r o g e n a t i o n o f some o l e f i n i c a c i d s w i t h R h C l ( - ) - D I O P ] S (S = C 6 H 6 ) [ 8 8 ] . ^ RCH 2 *CH(C0 2 H)NHC0Me % e . e . p r o d u c t : y i e l d (%) H 150 73 R ; 96 Ph 540 72 R ; 95 H 0 C g H 4 100 80 R ; 92 H .^COOH R^ NHCOMe s u b s t r a t e / R h Ach iwa i n Japan [90 ] p r epa r ed a s e r i e s o f e f f i c i e n t c h i r a l d i ( t e r t i a r y pho sph i ne ) l i g a n d s ( v i d e i n f r a ) f rom n a t u r a l L - h y d r o x y p r o l i n e . Ph2R* R=C02Bu); BPPM v ^O-BuSPPPM / \ =H ; PPM ^CH2PPh2 -COiCurks: CPPM N I R 66 The j_n s i t u Rh-BPPM c a t a l y s t w i t h added Et^N gave o p t i c a l y i e l d s up t o 91% f o r r e d u c t i o n o f s u b s t i t u t e d c i n n a m i c a c i d s t o v a r i o u s a l a n i n e s ( u s u a l l y t h e D-form) a t 50 atm hydrogen p r e s s u r e i n e t h a n o l . I t was a l s o r e p o r t e d t h a t o p t i c a l y i e l d s were s t r o n g l y dependent on bo th s o l v e n t s and t h e N - s u b s t i t u e n t s o f PPM [ 9 0 c , d] . M o r r i s o n e t a l , f rom c o m m e r c i a l l y a v a i l a b l e ( + ) - c ampho r i c a c i d , p r e pa r ed a c h i r a l d i ( t e r t i a r y - p h o s p h i n e ) l i g a n d , ( + ) - ( 1 R , 3 S ) - 1 , 2 , 2 -t r i m e t h y l - 1 , 3 - b i s ( d i p h e n y l p h o s p h i n o m e t h y l ) c y c l o p e n t a n e (CAMPHOS) . CAMPHOS R e d u c t i o n o f a,6-unsaturated c a r b o x y l i c a c i d s i n t h e p r e s en ce o f a rhod ium c a t a l y s t p r e p a r e d f rom [ R h ( C O D ) C 1 ] 2 and (+)-CAMPH0S i n a 1:1 m i x t u r e o f e t h a n o l and benzene , a t 60°C and 21 atm (H^) gave l ow o p t i c a l y i e l d s [ 5 6 ] . One o f t h e most r e m a r k a b l e s u c c e s s e s has been a c h i e v e d by F r y zuk and B o s n i c h [ 7 6 a , b] u s i n g t he complex [ R h ( S , S - C H I R A P H 0 S ) ( C 0 D ) ] + , where t he c h i r a l l i g a n d i s s y n t h e s i z e d f rom (2R, 3 R ) - b u t a n e d i o l . The ( Z ) - a - N -a c y l a m i n o a c r y l i c a c i d s u b s t r a t e s were hyd rogena ted a t amb i en t c o n d i t i o n s t o ( R ) - p r o d u c t s w i t h v e r y h i gh e n a n t i o m e r i c e x c e s s ; i n d e e d , l e u c i n e and p h e n y l a l a n i n e d e r i v a t i v e s were o b t a i n e d i n c omp l e t e p u r i t y ( T a b l e 2 . 3 ) . 67 T a b l e 2 . 3 : A symmet r i c h y d r o g e n a t i o n o f amino a c i d p r e c u r s o r s w i t h [Rh (S , S -CH IRAPHOS ) (COD) ] + [ 7 6 a ] . H COOH 1 / X . 2 H 2 ( l a t m ) , 25°C R NHCOR Rh( l ) -CHIRAPHOS > ( R ) - e n a n t i o m e r s R 1 H Ph Oh i - C 3 H 7 i - C 3 H 7 4 - H 0 C g H 3 3 -MeO-4 -AcD-C c H R 6"3 Me Ph Me Me Ph Ph Me p r o d u c t a l a n i n e pheny l a l a n i n e n l e u c i n e M t y r o s i n e DOPA % e . e . i n THF ETOH 88 99 74 100 87 80 80 91 95 89 93 72 88 83 A c r y s t a l s t r u c t u r e o f t h e c a t i o n i c m o i e t y adop t s t h e p r e f e r r e d ( S , S ) - c o n -f o r m a t i o n , t h e me thy l g roups be i ng e q u a t o r i a l l y d i s p o s e d t o g i v e t h e s i n g l e s t a t i c f i v e -membe red 6 - c h e l a t e r i n g w h i c h , as d i s c u s s e d e a r l i e r , t h e a u t h o r s b e l i e v e d t o be r e s p o n s i b l e f o r t h e h i g h o p t i c a l y i e l d s . The same a u t h o r s e x t ended t h e r a t i o n a l i z a t i o n f o r t h e d e s i g n o f (S ,S) -CHIRAPHOS t o t h e s y n t h e s i s o f (R)-PROPHOS w h i c h , when c o o r d i n a t e d t o t h e Rh a t o m , g i v e s r i s e t o t h e v i r t u a l e n a n t i o m e r i c c h i r a l c o n f o r m a t i o n ( x - c h e l a t e r i n g ) . Indeed p r o d u c t s w i t h ( S ) - c o n f i g u r a t i o n were o b t a i n e d w i t h e q u a l l y h i g h o p t i c a l y i e l d s [ 7 6 b ] , 68 D - g l u c o s e was u t i l i z e d as s t a r t i n g m a t e r i a l f o r t h e p r e p a r a t i o n o f me thy l 2 , 3 - b i s ( 0 - d i p h e n y l p h o s p h i n o ) - 4 , 6 - 0 - b e n z y l i d e n e - a - D - g l u c o p y r a n o s i d e , d e s i g n a t e d as PO-OP [ 9 1 ] . 0 P P h 2 PO-OP H y d r o g e n a t i o n o f a - a c e t a m i d o a c r y l i c a c i d s and t h e i r e s t e r s was c a r r i e d out i n t h e p r e s en ce o f [ Rh (PO -OP ) (NBD) ]PF g i n e t h a n o l a t -20°C t o 30°C and 1 atm o f H^. H igh o p t i c a l y i e l d s up to 80% was a c h i e v e d w h i l e s u b s t r a t e s w i t h o u t t h e a c e t am i do s u b s t i t u e n t s were not h yd rogena t ed . I n t e r e s t i n g l y , h i g h e r o p t i c a l y i e l d s were o b t a i n e d a t l owe r t e m p e r a t u r e s t han a t h i g h e r t e m p e r a t u r e s . (C) C h i r a l i t y a t bo th phospho rus and c a r b on The f i r s t l i g a n d s o f t h i s t y p e were t h e 1 - m e n t h y l m e t h y l p h e n y l p h o s p h i n e s (MMPP) p o s s e s s i n g o p p o s i t e c o n f i g u r a t i o n s a t phosphorus as shown be l ow . 69 i-C3H7 P h ' i Me i Ph Me MMPP S e v e r a l o l e f i n i c a c i d s were r educed by t h e c a t a l y s t p r e pa r ed f rom ( S ) -o r (R)-MMPP ( c o n f i g u r a t i o n a t P) and [ R h ( C 0 D ) C l ] 2 , i n b e n z e n e / e t h a n o l ( 1 : 1 ) i n t h e p r e s e n c e o f t r i e t h y l a m i n e . The e n a n t i o m e r i c e x c e s s r anged between 13-70% [ 9 2 ] . 2 . 4 . 2 L i g a n d s w i t h A x i a l C h i r a l i t y A new c l a s s o f pho sph i n e s c o n t a i n i n g o n l y an a x i a l e l emen t o f c h i r a l i t y has been p r epa r ed [ 9 3 ] . An i n s i t u 1 :1 [Rh ( l , 5 - h e x a d i e n e ) C l ] 2 / ( S ) - ( - ) - N A P H 0 S (NAPHOS = 2 . 2 ' - b i s ( d i p h e n y l p h o s p h i n o m e t h y l ) - 1 ,1 - b i n a p b t h y l ) sys tem ( v i d i n f r a ) hyd rogena ted a - a c e t a m i d o c i n n a m i c a c i d t o a 54% e . e . (S) u s i n g 50 atm H 2 ( t h e s o l v e n t not r e p o r t e d ) . The c o r r e s p o n d i n g d i p h e n y l -p h o s p h i t e sy s tem (X = oxygen) i n t o l u e n e - a c e t o n e was p a r t i c u l a r l y e f f e c t i v e (76% e . e . ) f o r h y d r o g e n a t i o n (95 atm) o f a - a c e t a m i d o c i n n a m i c a c i d and a - a c e t a m i d o a c r y l i c e s t e r s . X — P P h 2 X — P P h 2 70 2 . 4 . 3 L i g a n d s w i t h Bo th C e n t r a l and P l a n a r C h i r a l i t y T h i s t h i r d c l a s s o f c h i r a l l i g a n d s i s r e p r e s e n t e d by a s e r i e s o f f e r r o c e n y l p h o s p h i n e s [ 1 0 1 , 1 0 2 ] . Two l i g a n d s shown i n F i g . 2 .19 a r e , among o t h e r s , t h e f i r s t examples t h a t have been used i n a s ymme t r i c h y d r o -g e n a t i o n s t u d i e s . F i g . 2 . 1 9 : E a r l y examp les o f c h i r a l f e r r o c e n y l p h o s p h i n e s . In t h e p r e s en ce o f [Rh( l . , 5 - h e x a d i e n e ) C l ] 2 and ( S ,R ) - BPPFA i n a 1 :2 .4 r a t i o , h y d r o g e n a t i o n o f a - a c e t a m i d o a c r y l i c a c i d s was comp l e t ed i n 20 hr a t 50 atm ( H 2 ) and room t e m p e r a t u r e , g i v i n g h i g h o p t i c a l y i e l d s (85-94% e . e . ) [ 9 4 ] . A t abou t t h e same t i m e , bo th e n an t i ome r s o f PPFA were p r epa r ed by C u l l e n e t a l [ 102a ] who r e p o r t e d o p t i c a l y i e l d s i n t h e range o f 73-84% i n t h e r e d u c t i o n o f a - a c e t a m i d o c i n n a m i c a c i d s u s i n g t h e c a t a l y s t p r e c u r s o r [Rh( P P F A ) ( D i e n e ) ] + A " (D i ene = COD, NBD; A " = Cl 0 4 , B F 4 , P F g ) . I t i s t h i s c l a s s o f l i g a n d s ( a c h i r a l and c h i r a l ) w i t h w h i c h t h i s t h e s i s i s c h i e f l y c o n c e r n e d , and t he r e s u l t s w i l l be d i s c u s s e d i n more d e t a i l i n s ub sequen t c h a p t e r s . ( S , R ) - / ( R , S ) - B P P F A ( S , R ) - / ( R , S ) - P P F A \ 71 CHAPTER 3 FERROCENYLPHOSPHINES IN HOMOGENEOUS CATALYSIS 3.1 GENERAL ASPECTS S i n c e the d i s c o v e r y o f f e r r o c e n e i n 1951 [95 ] t h i s m o l e c u l e has opened a new e ra o f o r g a n o m e t a l l i c c h e m i s t r y and p l a y e d a ma jo r r o l e i n t h i s f i e l d . As a r e s u l t , t h e r e have been a v a s t number o f pape r s and r e v i e w s devo t ed t o s t u d i e s o f i t s f a s c i n a t i n g c h e m i s t r y [ 9 6 ] . Upon e x a -m i n a t i o n o f t h e l i t e r a t u r e , i t i s a p p a r e n t t h a t much i n t e r e s t has been f o c u s e d on two a s p e c t s o f t h e c h e m i s t r y o f t h i s s andw i ch compound. They a r e as f o l l o w s . 3 . 1 . 1 A r o m a t i c E l e c t r o p h i 1 i c S u b s t i t u t i o n F e r r o c ene has been shown t o undergo a r o m a t i c e l e t r o p h i l i c s u b s t i t u t i o n r e a d i l y , r e s u l t i n g i n a w ide v a r i e t y o f d e r i v a t i v e s t h r o u g h a c y l a t i o n , a l k y l a t i o n , m e t a l a t i o n , e t c . Of p a r t i c u l a r i n t e r e s t i n o r g a n o m e t a l 1 i c c h e m i s t r y i s t h e m e t a l a t i o n r e a c t i o n o f f e r r o c e n e , s i n c e a number o f p o t e n t i a l b i d e n t a t e l i g a n d s f o r me t a l comp lexes may be p r epa r ed u t i l i z i n g t h i s r e a c t i o n . For e x amp l e , s y m m e t r i c a l l y 1 , 1 ' - d i s u b s t i t u t e d f e r r o c e n e s I were p r e pa r ed by way o f d i l i t h i a t i o n o f f e r r o c e n e f o l l o w e d by t r e a t m e n t w i t h h a l o p h o s p h i n e s and h a l o a r s i n e s [ 9 7 ] . 72 ER 2 I ER2 =PPh2 (BPPF) la =PMe2(BMPF) b =AsPh2 (BPAF) c =AsMe2 (BMAF) Fe ER 2 The re a r e now numerous examp les o f me ta l comp lexes c o n t a i n i n g t h e s e compounds as c h e l a t i n g b i d e n t a t e l i g a n d s [ 9 6 c ] . 3 . 1 . 2 S t e r e o c h e m i s t r y o f F e r r o c e n e s The re has a l s o been a g r e a t dea l o f i n t e r e s t i n t h e a r ea o f s t e r e o -c h e m i s t r y o f f e r r o c e n e d e r i v a t i v e s . T h i s i n t e r e s t l i e s i n t h e f a c t t h a t , due t o t h e p a r t i c u l a r m o l e c u l a r g eome t r y , s p e c i a l p rob lems o f i s ome r i sm a r e e n c o u n t e r e d . In f a c t , s u i t a b l y s u b s t i t u t e d f e r r o c e n e s can e x h i b i t o p t i c a l i s o m e r i s m . These c h i r a l f e r r o c e n e d e r i v a t i v e s can be c l a s s i f i e d i n t o t h r e e groups : (A) F e r r o c e n e s w i t h c e n t r a l c h i r a l i t y (E) F e r r o c e n e s w i t h p l a n a r c h i r a l i t y (C) F e r r o c e n e s w i t h both c e n t r a l and p l a n a r c h i r a l i t y . Many r e p r e s e n t a t i v e s o f t h e f i r s t g roup have been p r e p a r e d , i n wh i ch t h e f e r r o c e n y l m o i e t y i s a t t a c h e d e i t h e r t o t h e c e n t e r o f c h i r a l i t y o r s e p a r a t e d f rom i t by one o r more atoms [ 9 8 ] . T h i s g roup i n c l u d e s , among o t h e r s , N , N - d i m e t h y l a m i n o - e t h y l f e r r o c e n e (FA) as shown be l ow . 73 F e F A The r e s o l u t i o n o f t h i s compound can be a c h i e v e d by a c o n v e n t i o n a l r e c r y s t a l l i z a t i o n o f d i a s t e r e o m e r i c t a r t r a t e . The second g roup o f c h i r a l . f e r r o c e n e s can be o b t a i n e d when one r i n g i s s u b s t i t u t e d w i t h a t l e a s t two d i f f e r e n t g roups as shown i n F i g . 3 . 1 . F i g . 3 . 1 : F e r r o c e n e d e r i v a t i v e s w i t h p l a n a r c h i r a l i t y . The s u b s t i t u e n t s X , Y, and Z have no c e n t e r o f c h i r a l i t y . They a r e known t o be s t a b l e t o r a c e m i z a t i o n and e p i m e r i z a t i o n . The t h i r d g roup o f c h i r a l f e r r o c e n e s ; c a n be g ene r a t e d i f e i t h e r X o r Y c a r r i e s c e n t r a l c h i r a l i t y . The l i g a n d s PPFA and BPPFA shown i n F i g . 3 . 2 a r e r e p r e s e n t a t i v e e x a m p l e s . As shown i n t h e f i g u r e , t h e s e and o t h e r r e l a t e d c h i r a l f e r r o c e n e s can be p r epa r ed by way o f t h e s t e r e o s e l e c t i v e l i t h i a t i o n o f ( R ) - o r ( S ) - F A wh i c h X=PPh2;Y=CH2CH3(PPEF) =PPh2;Y=CH2NMe2 (FcNP) X=Z=PPh2;Y=CH2CH3(BPPEF) 74 a f f o r d s t h e s t a b i l i z e d d e r i v a t i v e ( R , R ) - o r ( S , S ) - 3 . 2 a , r e s p e c t i v e l y , i n h i g h o p t i c a l y i e l d (96%) due t o t he a t t r a c t i v e i n t e r a c t i o n between L i and t h e n i t r o g e n l o ne p a i r e l e c t r o n s . r—\ Me ( 0 > C - N M e , Y H Fe —BuLi-(R)-FA alBuLi b) Buli/TMEDA c) CIER2 / — \ Me (RI-IS)-ER^PPh^BPPFA Fe (R)-(R)-3.2a (96%) I CIER2 Me C - N M e . p T Fe 2 ^ Fe (R)-(S)-3.2b NMe, (R)-(S)-ER2=PPlyPPFA; ER2=PMe2.MPFA F i g . 3 .2 : P r e p a r a t i v e r o u t e s t o f e r r o c e n y l p h o s p h i n e s w i t h c e n t r a l and p l a n a r c h i r a l i t y [ 1 0 1 , 1 02a , b ] . 75 S c h l o g e l e t a l [ 99 ] and Ugi e t a l [100] s ugge s t ed t h e f o l l o w i n g r u l e s f o r d e f i n i n g c h i r a l i t y i n t h i s t y p e o f c h i r a l f e r r o c e n e s . F i r s t , t h e p l a n a r c h i r a l i t y i s d e t e r m i n e d as f o l l o w s . The o b s e r v e r l o o k s a l o n g t h e C5 a x i s o f t h e p a r e n t r i n g s w i t h t h e more h i g h l y s u b s t i t u t e d r i n g d i r e c t e d t owa rds h i m . The p l a n a r c h i r a l i t y i s "R" i f t h e l i g a n d s X and Y ( F i g . 3 . 1 ) descend i n p r i o r i t y i n t h e s h o r t e s t c l o c k w i s e a r c ( " p r i o r i t y " he re has t h e same mean ing as used f o r t h e u sua l RS n o m e n c l a t u r e ) . L i k e w i s e , i f t h e p r i o r i t y a s c end s i n a c l o c k w i s e d i r e c t i o n , t h e p l a n a r c h i r a l i t y becomes "S".. I f more t h an t h r e e g roups a r e p r e s e n t , o n l y t h e t h r e e w i t h h i g h e s t p r i o r i t y a r e c o n s i d e r e d . S e c o n d l y , i f t h e r e a r e d i f f e r e n t t y p e s o f c h i r a l i t y i n one compound, t hen t h e ( R , S ) symbo l s w i l l r e f e r t o t h o s e v a r i o u s e l emen t s o f c h i r a l i t y i n t h e o r d e r : c e n t r a l > a x i a l > p l a n a r . F i n a l l y , i n c o n n e c t i o n w i t h t h e c e n t r a l c h i r a l i t y , i f t h e bonds p r o c e e d i n g f rom the Fe atom a r e a r b i t r a r i l y r e g a r d e d as s i n g l e bonds , t h en a s ymme t r i c s u b s t i t u t i o n o f a r i n g c au se s a l l t h e r i n g C atoms t o become c h i r a l c e n t e r s and t h e symbol (R) o r (S ) can be a s s i g n e d t o each o f t hem, i . e . ( I S ) , ( 2 R ) , e t c . T h i s t h i r d a s s i g nmen t , howeve r , w i l l no t be made i n t h i s t h e s i s f o r s i m p l i c i t y . T h e r e f o r e , i n t h e c a se o f ( R , S ) - P P F A , t h e f i r s t "R" r e f e r s t o t h e c o n f i g u r a t i o n a t t h e c a r b o n atoms o f t h e -CH(Me)NMe2 g roup and t h e second " S " t o t h e p l a n a r c h i r a l i t y ( T h i s m o l e c u l e , l i k e a l l o t h e r c h i r a l f e r r o c e n e d e r i v a t i v e s d e s c r i b e d i n t h i s t h e s i s , l a c k s a x i a l c h i r a l i t y ) . 76 3 .2 METAL COMPLEXES OF FERROCENYLPHOSPHINES R e l a t i v e l y l i t t l e a t t e n t i o n has been f o c u s ed on t h e p r e p a r a t i o n and t h e use o f f e r r o c e n y l p h o s p h i n e s ( c h i r a l and a c h i r a l ) i n homogeneous c a t a l y s i s . As a r e s u l t , t h e r e have been o n l y a few s t u d i e s i n t h i s a r e a , most o f wh i c h have been c a r r i e d ou t by Kumada e t a l I l O . l J a n d by C u l l e n e t a l [ 1 0 2 ] . T h e i r work e s t a b l i s h e s t h a t f e r r o c e n y l p h o s p h i n e s a r e v e r y u s e f u l l i g a n d s f o r me t a l comp lexes i n t h e f o l l o w i n g t h r e e t y p e s o f c a t a l y t i c r e a c t i o n s . 3 . 2 . 1 A symmet r i c H y d r o g e n a t i o n The c h i r a l l i g a n d s BPPFA and PPFA have been found t o be v e r y e f f e c -t i v e f o r R h - c a t a l y z e d a s ymme t r i c h y d r o g e n a t i o n o f a - a c e t a m i d o - c i n n a m i c and a c r y l i c a c i d s ( c f . s e c t i o n 2 .4 .3) , The c r y s t a l s t r u c t u r e o f [Rh(NBD) ( P P F A ) ] C 1 0 4 has r e c e n t l y been d e t e r m i n e d , wh i c h shows t h a t bo th N and P a r e bound t o rhod ium [ 1 0 2 b ] . On t h e o t h e r hand , i t seems t h a t BPPFA uses bo th P atoms to b i nd t o rhod ium [ 1 0 3 ] . I t i s wo r t h n o t i n g t h a t BPPFA and PPFA g i v e p r o d u c t s o f t h e o p p o s i t e a b s o l u t e c o n f i g u r a t i o n . T h u s , ( S , R ) - BPPFA l e a d s t o ( S ) - a c y l a m i n o a c i d s w h i l e ( S , R ) - P P F A l e a d s t o ( R ) - i s o m e r s . Kumada e t a l [104a] r e p o r t e d t h a t o p t i c a l y i e l d s a r e l owe r when t h e s e s u b s t r a t e s a r e h y d r o -gena ted under s i m i l a r c o n d i t i o n s u s i n g c a t a l y s t s d e r i v e d f rom m o d i f i e d BPPFA and PPFA ( i . e . by r e p l a c e m e n t o f t h e -CH^ g roup on t h e c h i r a l c e n t e r w i t h pheny l o r i s o p r o p y l g r o u p s ) . A c a t i o n i c complex [ Rh (R , S - BPP0H ) ( COD ) ] -C 1 0 4 (BPPOH i s p roduced when t h e -NMe2 g roup i s r e p l a c e d by OH) has been used f o r t h e r e d u c t i o n r o f some c h i r a l c a r b o n y l compounds a t 50 atm o f H ? 77 and 0 - 30°C . Mode ra te t o h i gh o p t i c a l y i e l d s (43 - 95%) were o b t a i n e d [ 1 0 5 ] . The OH g roup i s c r u c i a l f o r h i g h o p t i c a l y i e l d s , s i n c e much l owe r o p t i c a l y i e l d s a r e o b t a i n e d w i t h o t h e r l i g a n d s l a c k i n g t h e OH g r o u p , i . e . BPPFA, BPREF. F u r t h e r s t u d i e s on PPFA by C u l l e n e t a l l e d t o t h e s y n t h e s i s , o f a new c h i r a l l i g a n d l - N , N - d i m e t h y l a m i n o e t h y l - 2 - d i - t e r t - b u t y l p h o s p h i n o f e r r o c e n e a b b r e v i a t e d as B t PFA [102c ] ( v i d e i n f r a ) . I t was shown t h a t t h e h y d r o g e n a t i o n o f a s e r i e s o f o l e f i n s can be c omp l e t ed i n a - s h o r t e r t ime w i t h t h i s l i g a n d t han w i t h PPFA. F u r t h e r m o r e , i n some c a s e s , even h i g h e r o p t i c a l y i e l d s w i t h r e v e r s a l o f p r o d u c t c o n f i g u r a t i o n were o b t a i n e d . The re a r e few r e p o r t s o f a s ymme t r i c h y d r o g e n a t i o n by me ta l comp lexes o f a l i p h a t i c p ho sph i n e s and t h e r e s u l t s c a s t doubt on t h e c u r r e n t "dogma" r e g a r d i n g t h e mechanism o f a s ymmet r i c h y d r o g e n a t i o n ( c f . s e c t i o n 2 .3 .2) , s i n c e high] o p t i c a l y i e l d s were o b t a i n e d i n s p i t e o f t h e absence o f t h e s u p p o s e d l y n e c e s s a r y c h i r a l a r r a y o f pheny l g r o u p s . F u r t h e r m o r e , t h i s i s one o f few am inophosph i ne s wh i c h have been s u c c e s s f u l l y used i n homogeneous BVFA(V) 78 c a t a l y s i s , p a r t i c u l a r l y w i t h r hod ium [ 1 0 6 ] . T h e r e f o r e , f o r t h e s e r e a s o n s , f u r t h e r r e s e a r c h i n t o m i xed PN dono r s y s t ems i s d e s i r a b l e . The re i s a l s o a g r ow i ng i n t e r e s t i n l i g a n d sys tem c o n t a i n i n g bo th " s o f t " and " h a r d " donor atoms £ 1 0 7 ] . 3 . 2 . 2 O the r C a t a l y t i c R e a c t i o n s ; H y d r o s i l a t i o n and G r i g n a r d C r o s s C o u p l i n g The p a l l a d i u m complex P d [ ( R , S ) - P P F A ] C l 2 i s a c a t a l y s t p r e c u r s o r f o r t h e h y d r o s i l a t i o n o f o l e f i n s [ 1 0 8 ] . T h i s i s a u s e f u l p r o c edu r e s i n c e t h e p r o d u c t s can be c o n v e r t e d i n t o o p t i c a l l y a c t i v e a l c o h o l s o r b romides [ 1 0 9 ] . A no t h e r u s e f u l s y n t h e t i c a p p l i c a t i o n o f f e r r o c e n y l p h o s p h i n e s can be f ound i n t h e p a l l a d i u m and n i c k e l . c a t a l y z e d G r i g n a r d c r o s s - c o u p l i n g r e a c t i o n s ( e q u a t i o n 3 . 1 ) . RMgX + R'x' > R-R* + MgXX ' ( 3 . 1 ) Kumada e t a l [110] d i s c o v e r e d t h a t comp lexes o f t h e t y p e P d ( L - L ) X 2 and N i ( L - L ) X 2 c a t a l y z e a l a r g e number o f c r o s s - c o u p l i n g r e a c t i o n s o f s e c o n d a r y a l k y l G r i g n a r d r e a g e n t s w i t h o r g a n i c h a l i d e s . Here L -L a r e BPPF , ( S ) - F c N P , ( R ) - P P E F , ( S . R ) - P P F A , and o t h e r PPFA d e r i v a t i v e s ( F i g s . 3.1 and 3 . 2 ) . In some c a s e s , o p t i c a l y i e l d s as h i g h as 95% have been o b t a i n e d . I t i s wo r t h n o t i n g t h a t here t h e p l a n a r c h i r a l i t y seems t o p l a y a more i m p o r t a n t r o l e t h an t h e c e n t r a l c h i r a l i t y . 79 3.3 GOALS OF THE PRESENT INVESTIGATION The un i que f e a t u r e s o f f e r r o c e n y l p h o s p h i n e sys tems and o b s e r v a t i o n s l i k e t h o s e d e s c r i b e d i n t h e p r e v i o u s two s e c t i o n s i n d i c a t e t h a t more s t u d i e s on t h e s e sys tems would be d e s i r a b l e . Some o f t h e s e a t t e m p t s d u r i n g t h e p r e s e n t i n v e s t i g a t i o n can be summar ized as f o l l o w s . 3 . 3 . 1 New R h o d i u m - F e r r o c e n y l p h o s p h i n e Complexes as H y d r o g e n a t i o n C a t a l y s t s Fe Fe Fe Fe II III IV V VI VII 80 A l t h o u g h t h e c h e m i s t r y o f e a s i l y p r epa r ed s y m m e t r i c a l l y 1,1 -d i s u b s t i t u t e d f e r r o c e n e s such as I ( c f . s e c t i o n 3 . 2 . 1 ) has been e x p l o r e d q u i t e e x t e n s i v e l y , l i t t l e a t t e n t i o n has been f o c u s e d on t h e p r e p a r a t i o n and t he use o f r e l a t e d l i g a n d s I I - IV i n homogeneous c a t a l y s t s . Of p a r -t i c u l a r i n t e r e s t wou ld be t h o s e l i g a n d s c o n t a i n i n g t h e b u l k y t e r t - b u t y l g roups as w e l l as pheny l r i n g s ( I I - I V ) . In t h i s c o n n e c t i o n , t h e c h i r a l l i g a n d s V ^ V I I s h o u l d p r o v i d e f u r t h e r v a l u a b l e i n f o r m a t i o n abou t t h e e l e c t r o n i c and s t e r i c e f f e c t s o f t h o s e l i g a n d s c o n t a i n i n g t h e b u l k y t e r t -b u t y l g roups on r e a c t i o n r a t e s a n d , more i m p o r t a n t l y , t h e mechan ism o f a s ymme t r i c h y d r o g e n a t i o n . In t h i s r e g a r d , t h e s e new c h i r a l l i g a n d s d e s e r v e s p e c i a l a t t e n t i o n s i n c e t h e y not o n l y p o s s e s s t h e b u l k y a l k y l p h o s p h i n e s but a l s o be l ong t o t h e am inophosph i ne l i g a n d . I t seems a l s o d e s i r a b l e t o a t t e m p t t o i s o l a t e any r e a c t i o n i n t e r m e d i a t e s such as me ta l h y d r i d e s fo rmed i n t h e c o u r s e o f t h e c a t a l y t i c c y c l e . ' These i s s u e s w i l l be a d d r e s s e d i n Chap t e r s 5 and 6 . 3 . 3 . 2 O the r Me t a l Complexes o f F e r r o c e n y l p h o s p h i n e s I t wou ld be a l s o d e s i r a b l e t o s y n t h e s i z e a s e r i e s o f me ta l comp lexes t o e s t a b l i s h t h e s t e r i c e f f e c t s o f b u l k y phospho rus s u b s t i t u e n t s i n t h e hope t h a t t h i s wou ld h e l p e x p l a i n r a t e s and mechan ism o f c a t a l y t i c r e a c t i o n s . As p a r t o f t h e s e s t u d i e s , some o f t h e l i g a n d s d e s c r i b e d above wou ld be used t o form g roup VI and o t h e r g roup V I I I me ta l comp lexes such as (1) M ( P - P ) X 2 (M = Pd , N i ; P-P = I - IV ; X = C I , B r ) , (2 ) M ( P - P ) ( C 0 ) 4 (M = C r , Mo; P-P = I , and (3 ) some i r o n c a r b o n y l c o m p l e x e s . 81 These s y n t h e s e s , c r y s t a l s t r u c t u r e s , and o t h e r s t u d i e s w i l l be p r e s e n t e d i n Chap t e r 5. \ 82 PART I I EXPERIMENTAL 83 CHAPTER 4 GENERAL EXPERIMENTAL SECTION 4.1 GENERAL U n l e s s o t h e r w i s e s p e c i f i e d a i r - s e n s i t i v e r e a g e n t s and p r o d u c t s were m a n i p u l a t e d i n a n i t r o g e n a tmosphere u s i n g a d o u b l e - m a n i f o l d vacuum sys tem and S c h l e n k t e c h n i q u e s . 4 . 1 . 1 M a t e r i a l s A l l c ommer c i a l r e a g e n t s were o f r e a g e n t g rade and were used as r e c e i v e d u n l e s s o t h e r w i s e s t a t e d . S o l v e n t s were p u r i f i e d and d r i e d by s t a n d a r d t e c h n i q u e s . In p a r t i c u -l a r , c y c l o h e x a n e , d i e t h y l e t h e r , d i c h l o r o m e t h a n e , hexane , and THF were r e f l u x e d ove r L i A l a n d f r e s h l y d i s t i l l e d under N 2 b e f o r e u s e . Benzene and t o l u e n e were r e f l u x e d ove r sod ium w i r e and s t o r e d under N 2 o ve r mo l e -c u l a r s i e v e s , E t h a n o l and methano l were r e f l u x e d ove r magnesium and i o d i n e a n d , f r e s h l y d i s t i l l e d under N 2 b e f o r e u s e . Hydrogen was o b t a i n e d f rom t he Matheson Gas Co . and was passed t h r o u g h a "deoxo" c a t a l y t i c p u r i f i e r b e f o r e u s e . 4.1 .2 O l e f i n S u b s t r a t e s a - N - a c e t a m i d o a c r y l i c , a - N - a c e t a m i d o c i n n a m i c , and a - m e t h y l c i n n a m i c a c i d s were pu r c ha s ed f rom A l d r i c h Chemica l C o . ; i t a c o n i c a c i d , f rom Eastman Kodak C o . ; c y c l o h e x e n e , 1 - o c t e n e , and s t y r e n e f rom MCB Co . 84 A l l l i q u i d o l e f i n s were passed t h r o u g h an A l um ina ( n e u t r a l , pu r chased f rom F i s h e r S c i e n t i f i c Co . ) co lumn p r i o r t o use i n h y d r o g e -n a t i o n r e a c t i o n s . 4 . 1 . 3 I n s t r u m e n t a t i o n "'H NMR s p e c t r a were r e c o r d e d on B r u k e r WP-80 , V a r i a n X L - 1 0 0 , o r B r u k e r WH-400 s p e c t r o m e t e r s o p e r a t i n g a t 80 MHz, 100 MHz, o r 400 MHz, r e s p e c t i v e l y . 31 P r o t o n d e c oup l e d P NMR s p e c t r a were r e c o r d e d on B r u k e r WP-80 o r XL -100 s p e c t r o m e t e r s o p e r a t i n g a t 3 2 . 3 MHz o r 40 .5 MHz, r e s p e c t i v e l y . A l l c h e m i c a l s h i f t s a r e p o s i t i v e t o l owe r s h i e l d i n g . ^H s h i f t s a r e 31 r e l a t i v e t o e x t e r n a l s t a n d a r d TMS (s = 0 ppm) and P s h i f t s a r e r e l a t i v e t o 85% H 3 P 0 4 , w i t h P ( 0 M e ) 3 (6= +141.0 ppm) used as an e x t e r n a l s t a n d a r d . The peak m u l t i p l i c i t y , c o u p l i n g c o n s t a n t s , i n t e g r a t e d peak a r e a s , and p r o t o n ( o r pho spho ru s ) a s s i g n m e n t s a r e r e p o r t e d i n p a r e n t h e s e s . I n f r a r e d s p e c t r a were r e c o r d e d on a P e r k i n - E l m e r 598 s p e c t r o p h o t o -m e t e r . S o l i d s t a t e s p e c t r a were o b t a i n e d as N u j o l m u l l s between N a C l , K B r , o r C s l p l a t e s and s o l u t i o n s p e c t r a were r e c o r d e d u s i n g KBr c e l l s w i t h pa th l e n g t h 0 .25 mm. CD s p e c t r a were measured w i t h a JASC0 J - 2 0 s p e c t r o p o l a r i m e t e r . Mass s p e c t r a were o b t a i n e d u s i n g a K r a t o s MS-50 i n s t r u m e n t . A H e w l e t t P a c k a r d 5880A gas ch roma tog raph equ i pped w i t h an 0V-101 co lumn was used f o r gas l i q u i d c h r o m a t o g r a p h y . M e l t i n g p o i n t s were d e t e r m i n e d u s i n g a Ga l l enkamp M e l t i n g P o i n t a p p a r a t u s and a r e r e p o r t e d w i t h o u t c o r r e c t i o n . M i c r o a n a l y s e s were pe r f o rmed by M r . P. Bo rda o f t h i s d e p a r t m e n t . 85 4 .2 HYDROGENATION EXPERIMENTS 4 . 2 . 1 Gas -Up take Appa r a t u s A c o n s t a n t p r e s s u r e g a s - u p t a k e a p p a r a t u s shown i n F i g . 4 .1 was used f o r h y d r o g e n a t i o n . A Py rex r ound - bo t t om 25 mL f l a s k w i t h a s i d e arm was c onne c t e d v i a a g l a s s s p i r a l w i t h a t a p F t o t h e o i l manometer S t h r o u g h t h e t a p G. The o i l manometer was made o f t h i c k w a l l c a p i l l a r y t u b i n g f i l l e d w i t h n - b u t y l p h t h a l a t e , a l i q u i d w i t h n e g l i g i b l e v apo r p r e s s u r e . S was c onne c t ed t o t h e me r cu r y manometer T wh i c h c o n s i s t e d o f a c a l i b r a t e d b u r e t t e i n t h e l e f t s i d e , and a me r cu r y r e s e r v o i r i n t h e r i g h t . The r i g h t arm o f t h e me r cu r y manometer was i n t u r n connec t ed v i a a T e f l o n s t o p c o c k L t o t h e gas h a n d l i n g p a r t o f t h e a p p a r a t u s . T h i s p a r t c o n s i s t e d o f t h e me r cu r y manometer U, t h e gas i n l e t t a p 0 , t h e c o n n e c t i n g t a p M, and t a p N c o n n e c t i n g t h e sys tem t o a pump. The r e a c t i o n f l a s k was t h e r m o s t a t t e d i n a g l y c e r i n e ba th W. The ba th c o n s i s t e d o f a c y l i n d r i c a l g l a s s c o n t a i n e r s u r r ounded by p o l y s t y r e n e i n s u l a t i o n and e n c l o s e d i n a wooden box on f o u r s u p p o r t s . A m a g n e t i c s t i r r e r P was p l a c e d under t h e box . A s ha ke r Y was used t o m ix t h e r e a c t i o n s o l u t i o n . Bo th .manomete r s S and T were immersed i n ' a wa te r ba th X i n a t r a n s -p a r e n t p l e x i g l a s s c o n t a i n e r . Bo t h ba ths were i n d e p e n d e n t l y r e g u l a t e d by t h e r m o r e g u l a t o r s w i t h r e l a y c o n t r o l c i r c u i t s . The hea t was p r o v i d e d by 25 W e l o n g a t e d e l e c t r i c l i g h t b u l b s . T h e s e , w i t h t h e a i d o f m e c h a n i c a l 87 s t i r r e r s en su r ed t e m p e r a t u r e c o n t r o l w i t h i n ±0 .1°C . Time was r e c o r d e d w i t h a L ab ch ron 1405 t i m e r . 4 . 2 . 2 Gas -Up take E x p e r i m e n t a l P r o c edu r e In a t y p i c a l g a s - u p t a k e e x p e r i m e n t , t h e r e q u i r e d amount o f s u b s t r a t e and 10 mL o f s o l v e n t were p l a c e d i n f l a s k A . A c c u r a t e l y we ighed c a t a l y s t p r e c u r s o r i n bu cke t E was suspended w i t h a g l a s s hook . The f l a s k was c onne c t e d t h r o u g h t he g l a s s s p i r a l and t a p F t o t a p Q. The c o n t e n t s o f t h e f l a s k were degas sed by t h e f r e e z e and thaw me thod . D u r i n g t h i s o p e r a t i o n t h e s t o p c o c k L was c l o s e d . The gaseous r e a c t a n t was i n t r o d u c e d , w i t h t a p N c l o s e d , t h r o u g h t a p 0 a t a p r e s s u r e somewhat l owe r (^710 mmHg) t han t h a t r e q u i r e d f o r t h e e xpe r imen t (760 mm-Hg) and t hen t a p s F and M were c l o s e d . The s p i r a l and t he f l a s k were d i s c o n n e c t e d f rom Q and r e c o n n e c t e d to G w i t h t h e f l a s k b e i n g p l a c e d i n t h e t h e r m o s t a t e d ba th W. The f l a s k was shaken w i t h t h e e l e c t r i c a l s hake r Y and a l l o w e d t o r e a c h t he rma l e q u i l i -b r ium (^5 m i n ) . In t he mean t ime , t h e t a p s G, H, J , K, and N were opened t o e v a c u a t e t h e who le a p p a r a t u s e x c e p t t h e s p i r a l and t h e f l a s k . I t i s recommended t h a t H be opened b e f o r e J d u r i n g t h i s o p e r a t i o n . The t a p N was c l o s e d and t h e gaseous r e a c t a n t was a d m i t t e d t h r o u g h the t a p 0 a t r o u g h l y t h e same p r e s s u r e (^710 mmHg) as t h a t i n t h e r e a c t i o n f l a s k . Then t a p F was opened and t h e p r e s s u r e i n t h e who le a p p a r a t u s was a d j u s t e d t o t h e d e s i r e d l e v e l by o pen i n g t he t a p 0 v e r y c a r e f u l l y . Taps 0 and L were c l o s e d and a r e a d i n g o f t h e me r cu r y l e v e l i n t h e l e f t arm o f 88 t h e manometer T was t a k e n . Bu c k e t E was d ropped i n t o t h e s o l u t i o n by t u r n i n g t h e hook D. A t t h e same t ime t h e e l e c t r i c t i m e r was s t a r t e d . Any g a s - u p t a k e r e s u l t e d i n a r i s i n g o f t h e o i l l e v e l i n t h e l e f t arm o f t h e manometer S . A t a p p r o -p r i a t e t i m e s t a p L was c a r e f u l l y opened t o e q u a l i z e t h e o i l l e v e l s i n S . T h i s r e s u l t e d i n a c o r r e s p o n d i n g r i s e o f t h e me r cu r y l e v e l i n t h e l e f t arm o f t h e manometer T . The change o f h e i g h t o f t h e me r cu r y was r e c o r d e d as a f u n c t i o n o f t i m e . S i n c e t h e l e f t arm o f t h e manometer T was made o f a c a l i b r a t e d p i p e t t e t h e vo lume o f t h e gas wh i c h has r e a c t e d was known. 4 . 2 . 3 Work up o f Hyd rogena t ed P r o d u c t s The hyd rogena t ed p r o d u c t s o f t h e f o l l o w i n g o l e f i n s were i d e n t i f i e d f rom t h e i r ^H NMR s p e c t r a o r f rom gas chromatograms a f t e r t h e y were s e p a r a t e d as f o l l o w s . (A) a - N - a c e t a m i d o - a c r y l i c and c i n n a m i c a c i d s A f t e r t h e s o l v e n t was pumped o f f t h e r e s i d u e was d i s s o l v e d i n c o l d d i c h l o r o m e t h a n e (^5 mL) and t h e s o l u t i o n s t i r r e d f o r a few m i n u t e s u n t i l a y e l l o w i s h w h i t e p r e c i p i t a t e d e p o s i t e d . T h i s was s e p a r a t e d f rom t h e s o l u t i o n by f i l t r a t i o n and washed w i t h C H 2 C 1 2 s e v e r a l t i m e s t o g i v e a pu re w h i t e p r o d u c t . S i n c e t h e p r o du c t i s s l i g h t l y s o l u b l e i n C H 2 C 1 2 , t he f i l t r a t e was d r i e d and t he r e m a i n i n g s o l i d t r e a t e d as above t o r e c o v e r t h e p r odu c t q u a n t i t a t i v e l y . (B) | I t a c o n i c and a - m e t h y l c i n n a m i c a c i d s A f t e r t h e s o l v e n t was removed t h e r e s i d u e was d i s s o l v e d i n 25 mL o f 5% NaOH s o l u t i o n , s t i r r e d f o r a few m i n u t e s and f i l t e r e d t h r o u g h C e l i t e 89 t o g i v e a p a l e y e l l o w f i l t r a t e , A f t e r a c i d i f y i n g w i t h 10% HC1 , t h e s o l u t i o n was e x t r a c t e d w i t h d i e t h y l e t h e r (3 x 10 m L ) . The e t h e r a l e x t r a c t was d r i e d o v e r MgSO^, f i l t e r e d , and e v a p o r a t e d t o g i v e t h e f i n a l p r o d u c t . (C) L i q u i d O l e f i n s The hyd rogena t ed s o l u t i o n f rom s t y r e n e was vacuum d i s t i l l e d , and t h o s e f rom c y c l o h e x e n e , 1 - o c t e n e , were d i s t i l l e d a t one a tmosphe re u s i n g a m i c r o s c a l e d i s t i l l a t i o n a p p a r a t u s . 4 . 2 . 4 H y d r o g e n a t i o n o f t h e C a t a l y s t P r e c u r s o r s H y d r o g e n a t i o n o f t h e c a t a l y s t p r e c u r s o r s o f t h e t y p e [ R h ( L - L ) -(NBD ) ]C10 4 ( L - L = I - V I I ) was a l s o c a r r i e d ou t i n t h e absence o f o l e f i n s u b s t r a t e u s i n g t he f o l l o w i n g t h r e e me thods . Method A : w i t h measurement o f H 2 u p - t a k e . The a c c u r a t e l y we ighed c a t a l y s t p r e c u r s o r ( 1 . 2 x 10"^ mo l ) and an a p p r o p r i a t e s o l v e n t (3 mL) were p l a c e d i n bucke t E and f l a s k A , r e s p e c t i v e l y ( F i g . 4 . 1 ) . The t y p i c a l g a s - u p t a k e e x p e r i m e n t a l p r o c edu r e f o r t h e h y d r o g e n a t i o n o f o l e f i n s was t h en f o l l o w e d ( c f . s e c t i o n 4 . 2 . 2 ) t o r e c o r d t h e t o t a l amount o f H 2 consumed. Method B: w i t h c r y s t a l l i z a t i o n o f t h e p r o d u c t . In o r d e r t o i s o l a t e any p r o d u c t f o r m e d , t h e r e a c t i o n d e s c r i b e d i n Method A was d u p l i c a t e d as f o l l o w s . The same amount o f c a t a l y s t p r e c u r s o r and s o l v e n t were p l a c e d i n a S c h l e n k t u b e . T h i s was c onne c t e d t o a d o u b l e - m a n i f o l d vacuum sys tem w h i c h , i n t u r n , was c onne c t ed t o bo th N 2 and H 2 > The s o l u t i o n was degassed by t h e f r e e z e - a n d - t h a w me thod , and hydrogen was i n t r o d u c e d t o t h i s s o l u t i o n w i t h v i g o r o u s s t i r r i n g a t room t e m p e r a t u r e f o r 1 ^ 1 . 5 h t o en su re t h a t t he 90 r e a c t i o n was c o m p l e t e . The f i n a l s o l u t i o n was e i t h e r c o o l e d a t 0°C o r a l l o w e d t o s t a n d a t room t e m p e r a t u r e . The c r y s t a l s t hu s o b t a i n e d were i s o l a t e d i n a S c h l e n k f i l t e r , washed w i t h d i e t h y l e t h e r , d r i e d under vacuum, and r e d i s s o l v e d i n C ^ C ^ i n o r d e r t o o b t a i n a v a r i a b l e t e m p e r a t u r e NMR s p e c t r u m . In some c a s e s where c r y s t a l l i z a t i o n was u n s u c c e s s f u l , t h e s o l v e n t was removed under vacuum, and t h e r e m a i n i n g s o l i d was d i s s o l v e d i n t h e C D 2 C 1 2 . Method C: w i t h NMR m o n i t o r i n g o f t h e i n s i t u s o l u t i o n s . The c a t a l y s t p r e c u r s o r ( 5 , 0 x 10 mo l ) was d i s s o l v e d i n a d e u t e r a t e d s o l v e n t ( C D C l g , CD^OD, o r CD^CN) i n an NMR tube wh i c h was t hen c onnec t ed t o t h e vacuum sys tem d e s c r i b e d a b o v e . The s o l u t i o n was degassed as a b o v e , and then hydrogen was i n t r o d u c e d t o t h e s o l u t i o n w i t h o c c a s i o n a l s h a k i n g . As t h e gas d i f f u s e d t h r o u g h t h e s o l u t i o n and r e a c t e d w i t h t h e c o m p l e x , t h e c o l o r change p r o g r e s s e d f rom t he t o p men i s cu s t o t h e bottom o f t h e t u b e . No f u r t h e r c o l o r change was o b s e r v ed o v e r a p e r i o d o f 1 h. The v a r i a b l e t e m p e r a t u r e NMR spec t rum o f t h e i n s i t u s o l u t i o n was t hen r e c o r d e d . 4 . 3 OPTICAL ROTATION MEASUREMENTS A l l o p t i c a l r o t a t i o n v a l u e s were r e c o r d e d on a P e r k i n - E l m e r 141 s p e c t r o m e t e r a t room t e m p e r a t u r e u s i n g a one d e c i m e t e r p a t h - l e n g t h c e l l wh i ch c o u l d ho l d 1 mL o f s o l u t i o n . The r o t a t i o n s were measured a t t h e sod ium-D l i n e (589 nm), The s p e c i f i c r o t a t i o n o f any c h i r a l p r o d u c t was c a l c u l a t e d u s i n g e q u a t i o n ( 4 . 1 ) : 91 [aVD = a/l-C ( 4 . 1 ) where [ a ] p = s p e c i f i c r o t a t i o n a t t e m p e r a t u r e T measured a t t h e sod ium-D 1 i n e . a = ob s e r v ed r o t a t i o n (+) o r ( - ) l = p a t h l e n g t h o f t h e c e l l i n d e c i m e t e r s c = c o n c e n t r a t i o n o f s o l u t i o n i n g/100 mL. The e n a n t i o m e r i c e x c e s s ( e . e . ) o f t h e r educed p r o d u c t was t h en d e t e r -mined u s i n g e q u a t i o n ( 2 . 1 ) and t h e s p e c i f i c r o t a t i o n o f t h e i s o l a t e d p r o d u c t s . They a r e l i s t e d i n T a b l e 4 . 1 . T a b l e 4 . 1 : S p e c i f i c r o t a t i o n o f some c h i r a l p r o d u c t s [ 8 9 , 1 1 1 ] . S u b s t r a t e P r o du c t [ a ] a - N - a c e t a m i d o c i n n a m i c a c i d a - N - a c e t a m i d o a c r y l i c a c i d ( E ) - a -me t h y l c i n nam i c a c i d I t a c o n i c a c i d N - a c e t y l - p h e n y l a l a n i n e N - a c e t y l a n a n i n e a 3 - p h e n y l - a - m e t h y l p r o -p ano i c a c i d 2 - m e t h y l - s u c c i n i c a c i d (R) : -51 . 8 ( c l ,EtOH) (R) : + 6 6 . 5 ( c 2 , H 2 0 ) ( R ) : - 2 7 . 0 6 ( c 3 . 7 , C 5 H 6 ) (S) : + 2 7 . 0 6 ( c 3 . 7 , C 6 H 6 ) (R) : + 1 7 . 0 9 ( c l 0 . 5 , E t O H ) (S) : - 1 7 . 0 9 ( c l 0 . 5 , E t O H ) a T h e pure ( S ) - i s o m e r was assumed t o have t h e same deg ree o f o p t i c a l r o t a t i o n w i t h o p p o s i t e d i r e c t i o n . 92 4 .4 SYNTHESES OF STARTING MATERIALS A l 1 compounds d e s c r i b e d i n t h i s s e c t i o n were p r epa r ed a c c o r d i n g t o l i t e r a t u r e methods w i t h m i no r m o d i f i c a t i o n s , and were used f o r f u r t h e r r e a c t i o n s . 4 . 4 . 1 The Pho sph i n e s RR>C1 (A) C h l o r o d i - t e r t - b u t y l p h o s p h i n e ( B u t 2 P C l ) [112] The G r i g n a r d r e a g e n t t e r t - b u t y l m a g n e s i u m c h l o r i d e was p r e p a r e d as f o l 1 o w s . Magnesium t u r n i n g s ( 2 4 . 3 g , 1 mo l ) and f r e s h l y d i s t i l l e d d i e t h y l e t h e r (400 mL) were p l a c e d i n a 2 L, r o u n d - b o t t o m , t h r e e - n e c k e d f l a s k equ i pped w i t h a 500 mL, p r e s s u r e - e q u a l i z i n g d r o p p i n g f u n n e l , a r e f l u x c o n d e n s e r , a n i t r o g e n i n l e t , and a m a g n e t i c s t i r r e r . The magnesium t u r n i n g s were e t c h e d w i t h a t r a c e o f i o d i n e . The r e a c t i o n was t hen s t a r t e d by t he a d d i t i o n o f t e r t - b u t y l c h l o r i d e ( 9 2 . 5 g , 1 mo l ) d i s s o l v e d i n a t o t a l 1300 mL o f e t h e r . S u b s e q u e n t l y , t h e e t h e r a l s o l u t i o n o f Bu^Cl was added g r a d u a l l y so t h a t t h e s o l v e n t kep t a t i t s b o i l i n g p o i n t ( c a . 2h) . To c omp l e t e t he r e a c t i o n , t h e m i x t u r e was a l l o w e d t o r e f l u x f o r a n o t h e r h o u r . N . B . The immed ia te use o f t he G r i g n a r d r e a g e n t t hu s o b t a i n e d i s i m p o r t a n t . F u r t h e r m o r e , i f f o r m a t i o n o f l a r g e amounts o f a w h i t e p r e c i p i t a t e i s o b s e r v ed a t t h e end o f t he r e a c t i o n , t h e r e a c t i o n m i x t u r e s h o u l d be d i s c a r d e d . 93 To t h i s da r k g r e y s o l u t i o n o f Bu MgCl was added d r o pw i s e a t room t e m p e r a t u r e phosphorus t r i c h l o r i d e ( 3 4 . 4 g , 0 .25 mo l ) i n e t h e r (50 m L ) . A w h i t e p r e c i p i t a t e was formed i m m e d i a t e l y . The r e a c t i o n m i x t u r e was b o i l e d and was a l l o w e d t o r e f l u x f o r 2 h . Then t h e e t h e r s o l u t i o n c o n -t a i n i n g t h e p r o d u c t was s e p a r a t e d f rom t h e p r e c i p i t a t e by c a r e f u l d e c a n t i n g i n t o a 1 L, r o und - bo t t om f l a s k under N 2 t h r o u g h g l a s s w o o l . E t h e r was removed f rom t he de can t ed p r o d u c t by d i s t i l l a t i o n a t a tmosphe -r i c p r e s s u r e t o l e a v e a y e l l o w i s h o i l . T h i s was t r a n s f e r r e d i n t o a f l a s k s e t up f o r vacuum d i s t i l l a t i o n . The p r o d u c t t h u s o b t a i n e d was an a i r - s e n s i t i v e , c o l o r l e s s l i q u i d (25 g , 55%). bp 62-65°C ( 4 . 6mmHg) ( l i t . 69 - 70°C (10 mmHg)). (B) C h l o r o ( p h e n y l ) - t e r t - b u t y l p h o s p h i n e [113] D i c h l o r o p h e n y l p h o s p h i n e (179 g , 1 mo l ) i n e t h e r (500 mL) was added s l o w l y a t room t e m p e r a t u r e t o a s t i r r e d s o l u t i o n o f Bu^MgCl p r e p a r e d f rom Bu^Cl ( 1 3 8 . 8 g , 1.5 mo l ) and Mg(36 .5 g , 1.5 mo l ) i n e t h e r (1200 mL) as d e s c r i b e d a b o v e . A f t e r t h e e x o t h e r m i c r e a c t i o n d u r i n g t h e a d d i t i o n o f P h P C l 2 » t h e r e a c t i o n m i x t u r e was a l l o w e d t o r e f l u x f o r 2 h a f t e r wh i c h t h e r e s u l t i n g s u s p e n s i o n was f i l t e r e d under N 2 and t h e f i l t r a t e d i s t i l l e d a t a t m o s p h e r i c p r e s s u r e t o remove e t h e r . The r e m a i n i n g o i l y r e s i d u e was v a c u u m - d i s t i l l e d a few t i m e s u n t i l a c o l o r l e s s l i q u i d w i t h a c o n s t a n t b o i l i n g p o i n t was o b t a i n e d (120 g , 60%), bp (60 - 63°C ( 0 . 4 5 mmHg)) ( l i t . 81o ,88°C ( 0 . 8 mmHg)). 94 4 . 4 . 2 F e r r o c e n e D e r i v a t i v e s (A) 1 j ' - d i l i t h i o f e r r o c e n e - T M E D A [97] F e r r o c e n e ( 1 8 . 5 g , 0.1 mo l ) was p l a c e d i n a 250 mL S c h l e n k t u b e . A f t e r t h e t u be was e va cua t ed and r e f i l l e d w i t h N 2 , hexane (75 mL) was added . A s o l u t i o n o f n - b u t y l 1 i t h i u m i n hexane ( 1 . 6 M, 75 mL) was added t h r o u g h a p r e s s u r e e q u a l i z i n g d r o p p i n g f u n n e l . The s u s p e n s i o n was r a p i d l y s t i r r e d and f r e s h l y d i s t i l l e d N , N , N ' , N - t e t r a m e t h y l e t h y l e n e d i a m i n e (TMEDA) ( 1 6 . 3 g , 0 .14 mo l ) was added s l o w l y . The r e a c t i o n was e x o t h e r m i c and t h e f e r r o c e n e s l u r r y r e a c t e d t o g i v e a deep c h e r r y r ed s o l u t i o n . The r e a c t i o n m i x t u r e was a l l o w e d t o s t i r f o r 4 h d u r i n g wh i c h t i m e a f i n e o r ange p r e c i -p i t a t e d e p o s i t e d . T h i s was f i l t e r e d t h r o u g h a medium p o r o s i t y S c h l e n k f i l t e r and washed w i t h warm hexane (2 x 30 m L ) . D r y i n g i n vacuo y i e l d e d a f i n e o range p y r o p h o r i c powder ( 2 3 . 5 g , 75%). T h i s compound can be s t o r e d f o r l o n g p e r i o d s under N 2 a t room t e m p e r a t u r e , (B) 1,1 " - F e r r o c e n e d i y l p h e n y l p h o s p h i n e [114] 1 , 1 ' - D i l i t h i o f e r r o c e n e - T M E D A ( 5 . 0 g , 1 5 . 9 mmo l ) , i s o l a t e d as d e s -c r i b e d a b o v e , was suspended i n f r e s h l y d i s t i l l e d e t h e r (200 m L ) . To t h i s w e l l s t i r r e d s u s p e n s i o n , m a i n t a i n e d a t - 7 8 ° C , was added a s o l u t i o n o f P h P C l 2 ( 2 . 8 5 g , 15 . 9 mmol) i n d i e t h y l e t h e r (20 m L ) . The m i x t u r e was t hen a l l o w e d t o warm t o room t e m p e r a t u r e and was s t i r r e d f o r 1 h . F o l l o w i n g h y d r o l y s i s w i t h wa t e r (50 m L ) , t h e e t h e r a l l a y e r was s e p a r a t e d , d r i e d o ve r anhyd rous MgSO^, f i l t e r e d , and the s o l u t i o n vo lume reduced t o abou t 20 mL. T h i s o i l y s o l u t i o n was t hen ch romatog raphed on F l o r i s i l ( 1 0 0 - 200 m e s h ) . The r e s u l t i n g deep r ed s o l u t i o n ( n -hexane e l u a t e ) was r educed i n vo lume \ 95 a t room t e m p e r a t u r e u n t i l c r y s t a l l i z a t i o n j u s t b egan . The s o l u t i o n was then s t o r e d a t 0°C t o a f f o r d deep r e d c r y s t a l s ( 3 . 2 g , 70%). (C) N ,N - rd ime thy l am inocyanome thy l f e r r o c e n e ( F e - C H ( C N ) N M e 2 ) [ 115 ] F e r r o c e n e c a r b o x a l d e h y d e (108 g , 0 . 5 mmol) d i s s o l v e d i n methano l (300 mL) was added a t room t e m p e r a t u r e t o a s t i r r e d s o l u t i o n o f sod ium b i s u l f i t e (52 g , 0 .5 mo l ) i n wa te r (300 mL) i n a 2 L, r o und - bo t t om f l a s k . A f t e r s t i r r i n g 10 m i n . , a s o l u t i o n o f d i m e t h y l amine (30 g , 0.7 mo l ) i n 100 mL o f 50% MeOH was added t o t h e above m i x t u r e , f o l l o w e d by a s o l u t i o n o f sod ium c y a n i d e ( 2 4 . 5 g , 0 .5 mo l ) i n wa t e r (100 m L ) . The c o l o r changed f rom da r k t o o r a n g e . E t h e r (500 mL) was added and t h e r e a c t i o n m i x t u r e s t i r r e d o v e r n i g h t , t h en e x t r a c t e d w i t h e t h e r (5 x 500 m L ) . The combined e t h e r a l e x t r a c t was d r i e d ove r MgSO^, and t h e s o l v e n t removed a t a r educed p r e s s u r e . The r e s i d u a l amber o i l c r y s t a l l i z e d on add i ng p e t r o l e u m e t h e r t o g i v e t he p r o d u c t as g o l d en p l a t e s (113 g , 90%). ( D ) N , N - d i m e t h y l a m i n o e t h y l f e r r o c e n e (FA) [115] A s o l u t i o n o f F e - C H ( C N ) N M e 2 ( 8 0 . 4 g , 0 .3 mo l ) i n d r y e t h e r (500 mL) was added d r o p w i s e , t h r o u g h a p r e s s u r e e q u a l i z i n g d r o p p i n g f u n n e l , t o a s o l u t i o n o f MeMgl p r epa r ed f rom me thy l i o d i d e ( 8 5 . 2 g , 0 .6 mo l ) and Mg ( 1 4 . 6 g , 0 .6 mo l ) i n e t h e r (450 mL) i n a 2 L, r o und - bo t t om f l a s k . The y e l l o w i s h brown c o l o r o f t he a m i n o n i t r i l e changed to r e d d i s h o r a n g e . The r e a c t i o n m i x t u r e was s t i r r e d o v e r n i g h t and s l o w l y t r e a t e d w i t h a q . NH^Cl . The e t h e r a l l a y e r was s e p a r a t e d and t h e aqueous l a y e r e x t r a c t e d w i t h e t h e r (3 x 500 m L ) . The combined e t h e r a l e x t r a c t was d r i e d o v e r K ? C 0 v and e t h e r removed a t a r educed p r e s s u r e t o g i v e an amber o i l ; 96 'H NMR ( a c e t o n e - d g ) 6 1.25 ( d , 3 , M e ) , 1.98 ( s , 6 , N M e 2 ) , 3 . 48 ( q t , 1 , CH ) , 4 . 0 8 ( s , 9 , F c ) . (E) ( S ) - and ( R ) - FA: R e s o l u t i o n o f FA [100] The r a c e m i c amine ( 5 1 . 4 g , 0 .2 mo l ) and ( R ) - ( + ) - t a r t a r i c a c i d (30 g , 0 . 2 mo l ) were each d i s s o l v e d i n MeOH (70 mL) i n 250 mL E r l e nmeye r f l a s k s . Bo th f l a s k s were immersed i n a wa t e r ba th a t 55°C f o r abou t 10 min t o r e a c h t h e rma l e q u i l i b r i u m . The t a r t a r i c a c i d s o l u t i o n was t hen poured i n t o t h e FA s o l u t i o n w h i l e s t i r r i n g . The t e m p e r a t u r e o f t h e ba th was t hen a l l o w e d t o f a l l a t a r a t e o f 2 ^ 5 ° / h . When ( - ) s e e d i n g c r y s t a l s were no t a v a i l a b l e , t h e f l a s k was o c c a s i o n a l l y s c r a t c h e d w i t h a g l a s s r od t o a i d s o l i d f o r m a t i o n . S t i r r i n g was c o n t i n u e d o v e r n i g h t and t h e ( S ) ( - ) -amine t a r t a r a t e was c o l l e c t e d by s u c t i o n f i l t r a t i o n . The mothe r l i q u o r was s e t a s i d e f o r l a t e r u s e . The t a r t r a t e s a l t was added t o aqueous NaOH s o l u t i o n i n a s e p a r a t o r y f u nne l and t h e amine e x t r a c t e d w i t h e t h e r (4 x 150 m L ) . The amine s o l u t i o n was d r i e d o v e r anhyd rous K2CO3, and e v a p o r a t e d t o g i v e o p t i c a l l y a c t i v e am i ne . The amine (20 g) t hu s o b t a i n e d and ( R ) - ( + ) -t a r t a r i c a c i d ( 1 7 . 5 3 g , 0.11 m o l ) , each d i s s o l v e d i n 30 mL o f MeOH were m ixed a t 55°C and a few ( S ) ( - ) - a m i n e t a r t a r a t e c r y s t a l s were a d d e d . A f t e r s l ow c o o l i n g f o l l o w e d by t h e wo rk -up p r o c edu r e as d e s c r i b e d a b o v e , o p t i c a l l y pure ( S ) - ( - ) - F A was o b t a i n e d (15 g , 58 .4%) : [ a ] 2 5 - 1 4 . 3 ° ( c 1 . 5 , EtOH) ( l i t . 25 [ a ] p - 1 4 . 1 ° ( c 1 . 5 , E t O H ) ) . I f t h e o p t i c a l r o t a t i o n o f t h e amine was l o w e r , one a d d i t i o n a l c r y s t a l l i z a t i o n was r e q u i r e d . The mothe r l i q u o r f rom t h e f i r s t c r y s t a l l i z a t i o n was c o n c e n t r a t e d t o about o n e - f o u r t h o f i t s o r i g i n a l v o l ume . D i e t h y l e t h e r was added s l o w l y t o t h e s o l u t i o n u n t i l p r e c i p i t a t i o n 97 was c o m p l e t e . The m i x t u r e was l e f t a t 0°C o v e r n i g h t and t he ( R ) - ( + ) -amine t a r t a r a t e was c o l l e c t e d . T h i s was r e c r y s t a l 1 i z e d by d i s s o l v i n g i t i n a minimum amount o f hot wa t e r (70 - 80°C) and a d d i n g t o t h i s s o l u t i o n warm a c e t o n e i n such a way t h a t t h e r a t i o o f wa t e r t o a c e t o n e became 1 : 1 0 . O p t i c a l l y pure ( R ) - ( + ) - F A was o b t a i n e d from r e p e a t e d r e c r y s t a l l i -p c z a t i o n ( 2 ^ 3 t i m e s ) i n t h i s m o d i f i e d way: y i e l d ( 1 7 . 2 g , 58 .5%); [ a ] " + 14 . 3 ° (C 1 . 5 , EtOH) ( l i t . [ a ] 2 5 + 14 . 1 ° (C 1 . 5 , E t O H ) ) . 4 . 4 . 3 Me ta l Complexes (A) [ R h ( N B D ) C l ] 2 [116] R h C l 3 - 3 H 2 0 ( 0 . 7 g) was d i s s o l v e d i n 95% EtOH (10 mL) i n a 100 mL S c h l e n k t u b e . The s o l u t i o n was degas sed by t h e f r e e z e - a n d - t h a w me thod . To t h i s s o l u t i o n was added n o r b o r n a d i e n e (2 mL) w i t h s t i r r i n g . A y e l l o w p r e c i p i t a t e d e p o s i t e d abou t 1 h a f t e r t h e r e a c t i o n had been s t a r t e d . The r e a c t i o n m i x t u r e was f u r t h e r s t i r r e d f o r 24 h a f t e r wh i c h t ime t h e y e l l o w p r e c i p i t a t e was i s o l a t e d by f i l t r a t i o n , washed w i t h c o l d e t h a n o l (10 m L ) , and d r i e d under vacuum t o g i v e a f i n e y e l l o w powder . The p r o du c t was not p u r i f i e d f u r t h e r . (B) P d ( P h C N ) 2 C l 2 [117] A m i x t u r e o f N a 2 P d C l 4 (1 g) and b e n z o n i t r i l e (50 mL) were s t i r r e d a t 100°C f o r 30 m i n . The r e s u l t a n t r ed s o l u t i o n was f i l t e r e d and t h e f i l t r a t e poured i n t o p e t r o l e um e t h e r (200 mL) t o d e p o s i t a y e l l o w i s h o range p r e c i p i t a t e . T h i s was i s o l a t e d and c r y s t a l l i z e d f rom benzene t o a f f o r d an o r ange m i c r o c r y s t a l 1 i n e p r o d u c t ( 0 . 5 g , 50%). 98 (C) P d ( N B D ) C l 2 [117] T h i s complex was p r epa r ed by t h e d i r e c t r e a c t i o n o f P d ( P h C N ) 2 C l 2 ( 0 . 2 g , 5.21 x 1 0 " 4 mo l ) and a s l i g h t m o l a r e x c e s s o f n o r b o r n a d i e n e (3 mL) i n CHCl^ (50 m L ) . A f t e r s t i r r i n g 1 h, a y e l l o w p r e c i p i t a t e was i s o l a t e d f rom t h e s o l u t i o n , washed w i t h CHC l g , and d i s s o l v e d i n warm g l a c i a l a c e t i c a c i d . The s o l u t i o n gave a y e l l o w p r e c i p i t a t e on c o o l i n g . T h i s was washed w i t h a m i x t u r e o f methano l and a c e t o n e , and d r i e d under vacuum: y i e l d 43%. 4 . 5 SYNTHESES OF FERROCENYLPHOSPHINES A n a l y t i c a l and s p e c t r o s c o p i c da t a f o r t h e s e l i g a n d s a r e p r e s e n t e d i n Chap t e r 5 . 4 . 5 . 1 A c h i r a l L i g a n d s (A) 1 , T - B i s ( d i p h e n y l p h o s p h i n o ) f e r r o c e n e (BPPF , I ) [97] 1 , 1 ' - D i l i t h i o f e r r o c e n e TMEDA (10 g , 3 1 . 9 mmo l ) , i s o l a t e d as d e s c r i b e d p r e v i o u s l y was suspended i n f r e s h l y d i s t i l l e d n-hexane (50 mL) i n a 250 mL S c h l e n k t u b e . To t h i s s u s p e n s i o n , m a i n t a i n e d a t 0 °C , was added P h 2 P C l ( 1 4 . 5 g , 55 mmo l ) . The m i x t u r e was warmed t o room t e m p e r a t u r e and was s t i r r e d f o r 5 h . F o l l o w i n g c a r e f u l h y d r o l y s i s w i t h wa t e r (50 m L ) , t h e s u p e r n a t a n t hexane l a y e r was de can t ed f rom t h e brown s o l i d , and t h e s o l i d was washed s u c c e s s i v e l y w i t h e t h a n o l (2 x 30 mL) and hexane (3 x 30 m L ) , t hen f i n a l l y d i s s o l v e d i n hot benzene (40 mL) . Hot hexane was s l o w l y added u n t i l t h e s o l u t i o n became t u r b i d . The s o l u t i o n was t hen c o o l e d t o room t e m p e r a -99 t u r e t o g i v e f i n e o r ange c r y s t a l s ( 1 1 . 5 g , 55%). (B ) 1 , 1 ' - B i s ( p h e n y l - t e r t - b u t y l p h o s p h i n o ) f e r r o c e n e ( B P B t P F , I I ) To a w e l l s t i r r e d s u s p e n s i o n o f ( C g H ^ F e L i g - T M E D A (10 g , 3 1 . 9 mmol) i n d r y hexane (30 m L ) , m a i n t a i n e d a t - 7 8 ° C , was added s l o w l y B u t ( P h ) P C l (13 g , 65 mmol) i n d r y e t h e r (15 m L ) . The r e a c t i o n m i x t u r e was t h e n warmed t o room t e m p e r a t u r e and s t i r r e d o v e r n i g h t a f t e r wh i c h t h e m i x t u r e was h y d r o l y z e d w i t h wa t e r (20 m L ) . The o r g a n i c l a y e r was s e p a r a t e d , d r i e d o ve r MgSO^, and r educed i n vo lume t o abou t 10 mL. The o i l y s o l u t i o n was t hen ch roma tog raphed on A l um ina ( n e u t r a l , Grade I ) . Meso and r a c e m i c (d and a) i s ome r s were s e p a r a t e d by r e c h r o m a t o g r a p h i n g t h e second o range band w i t h a m i x t u r e o f p e t r o l e um e t h e r and d i e t h y l e t h e r ( 7 0 / 3 0 ) . Bo t h p r o d u c t s were i s o l a t e d as deep o r ange o i l s w h i c h s o l i d i f i e d s l o w l y on c o o l i n g (0°C) : y i e l d 55 - 60%. (C) 1 - D i p h e n y l p h o s p h i n o - 1 ' - d i - t e r t - b u t y l p h o s p h i n o f e r r o c e n e (PPb^PF, I I I ) The t i t l e compound was p r epa r ed u s i n g the r i n g c l e a v a g e r e a c t i o n o f 1,1 - f e r r o c e n e d i y l p h e n y l p h o s p h i n e . To a s t i r r e d s o l u t i o n o f 1,1 -f e r r o c e n e d i y l p h e n y l p h o s p h i n e ( 1 . 5 g , 5 .14 mmol) i n d i e t h y l e t h e r (30 mL) a t - 78°C was added d r o p w i s e p h e n y l l i t h i u m ( 1 . 9 5 M, 4 mL) i n ben zene . The m i x t u r e was a l l o w e d t o warm t o room t e m p e r a t u r e s l o w l y . The s o l u t i o n was t hen r e c o o l e d t o -78°C and e x c e s s Bu^PCl (3 mL) i n d i e t h y l e t h e r (5 mL) was added d r o p w i s e . The r e s u l t a n t m i x t u r e was s l o w l y warmed t o room t e m p e r a t u r e and was s u b s e q u e n t l y hea t ed t o a g e n t l e r e f l u x f o r 10 m i n . P r e c i p i t a t i o n o f L i C l o c c u r r e d . A f t e r s t i r r i n g a n o t h e r 30 min a t room 100 t e m p e r a t u r e t h e s o l u t i o n was h y d r o l y z e d w i t h wa t e r (20 m L ) , t h e e t h e r a l l a y e r s e p a r a t e d and d r i e d o v e r anhyd rous MgSO^. The s o l u t i o n vo lume was r e du ced t o a few mL f o l l o w i n g f i l t r a t i o n . The r e s u l t a n t o i l was ch roma tog raphed on A l um ina ( n e u t r a l , Grade I ) t o g i v e a s i n g l e o range band ( e l u t e d w i t h d i e t h y l e t h e r / p e t r o l e u m e t h e r , 1 0 / 9 0 ) . Removal o f s o l v e n t under vacuum f rom the r e s u l t i n g o range s o l u t i o n a f f o r d e d a y e l l o w c r y s t a l -l i n e s o l i d (1 .24 g , 47%). (D) 1 , 1 ' - B i s ( d i - t e r t - b u t y l p h o s p h i n o ) f e r r o c e n e ( B B t P F , IV) ( C 5 H 4 ) 2 F e L i 2 « T M E D A ( 7 . 5 g , 2 3 . 9 mmo l ) , i s o l a t e d as d e s c r i b e d p r e v i o u s l y , was suspended i n f r e s h l y d i s t i l l e d n-hexane (40 mL) i n a 250 mL S c h l e n k t u b e . To t h i s s u s p e n s i o n , m a i n t a i n e d a t - 7 8 ° C , was added B u 2 P C l ( 8 . 7 g , 4 8 . 2 mmo l ) . The m i x t u r e was a l l o w e d t o warm t o room tempe-r a t u r e and s t i r r e d o v e r n i g h t . F o l l o w i n g c a r e f u l h y d r o l y s i s w i t h wa t e r (20 m L ) , t h e hexane l a y e r was s e p a r a t e d , d r i e d o v e r anhyd rous MgSO^, f i l t e r e d , and r educed i n vo lume t o abou t 10 mL. T h i s o i l y s o l u t i o n was t hen ch roma tog raphed on A l um ina ( n e u t r a l , Grade I ) . Removal o f s o l v e n t under vacuum f rom t h e r e s u l t i n g deep o range s o l u t i o n ( t h e second band t h a t e l u t e d w i t h a m i x t u r e o f p e t r o l e um e t h e r and d i e t h y l e t h e r , 70 /30) a f f o r d e d a d a r k o i l y p r o d u c t ( 4 . 5 g , 40%). The p r o d u c t was no t p u r i f i e d f u r t h e r . N .B . C a r e f u l c h r oma tog r aphy was r e q u i r e d t o s e p a r a t e t h e p r o du c t f rom a m i x t u r e o f f e r r o c e n e and a w h i t e pho sph i ne b y - p r o d u c t t h a t e l u t e d w i t h p e t r o l e um e t h e r . 101 4 . 5 . 2 C h i r a l L i g a n d s (A) ( S , R ) - and ( R , S ) - 2 - ( d i - t e r t - b u t y l p h o s p h i n o ) - l - ( N , N - d i m e t h y l -a m i n o e t h y l ) f e r r o c e n e ( B t P F A , V ) [ 102 c ] T h i s l i g a n d was p r e p a r e d u s i n g t h e known method [102c ] and i s o l a t e d as a c r y s t a l l i n e s o l i d ; a c e t one was used f o r c r y s t a l l i z a t i o n . (B) ( S , R ) - and ( R , S ) - 1 ' , 2 - b i s ( d i - t e r t - b u t y l p h o s p h i n o ) - 1 - ( N j N -d i m e t h y l a m i n o e t h y l J f e r r o c e n e t B B ^ T F A . V I ) ( S ) - F A (3 g , 1 1 . 7 mmol) was d i s s o l v e d i n a m i x t u r e o f d i e t h y l e t h e r ( 2 . 5 mL) and n-hexane ( 3 . 5 mL) i n a S c h l e n k t u b e . To t h i s s o l u t i o n was added s l o w l y n -BuL i ( 1 . 6 M, 8 m L ) . The r e a c t i o n was s l i g h t l y e x o t h e r m i c and t h e c o l o r o f t h e s o l u t i o n changed f rom y e l l o w i s h brown t o c h e r r y r e d . The r e a c t i o n m i x t u r e was s t i r r e d f o r 2 h , and a m i x t u r e o f n -BuL i ( 1 . 6 M, 8 mL) i n hexane and TMEDA (2 mL, 11 . 7 x 1.2 mmol) was added t h r o u g h a p r e s s u r e e q u a l i z i n g d r o p p i n g f u n n e l . The r e a c t i o n was s l i g h t l y e x o t h e r m i c a g a i n , and t h e c o l o r o f t h e s o l u t i o n d e epened . The r e a c t i o n m i x t u r e was f u r t h e r s t i r r e d f o r 6 h a f t e r wh i c h BujjPCl ( 4 . 1 g , 23 mmol) was added t h r o u g h a s y r i n g e . The r e a c t i o n m i x t u r e was a l l o w e d t o s t i r a t room tempe-r a t u r e f o r 2 d a y s . F o l l o w i n g h y d r o l y s i s w i t h H^O, t h e o r g a n i c l a y e r was s e p a r a t e d , d r i e d o v e r MgSO^, f i l t e r e d , and r educed i n vo lume t o abou t 5 mL. The r e s u l t i n g r e d o i l was ch romatog raphed on n e u t r a l A l um ina (G rade I I ) t o g i v e a s i n g l e s a l m o n - r e d band ( e l u t e d w i t h d i e t h y l e t h e r / p e t r o l e u m e t h e r , 1 5 / 8 5 ) . Removal o f s o l v e n t under vacuum f rom t h e r e s u l t i n g o range s o l u t i o n a f f o r d e d a d a r k o r ange o i l ( 1 . 9 g , 30%). A t t emp ted c r y s t a l l i z a t i o n f rom a c e -t one ( o r EtOH) was u n s u c c e s s f u l . ( R , S )^BB t PFA ( V I ) was o b t a i n e d by t r e a t i n g ( R ) - FA i n t h e same manner as a b o v e . (C) ( S , S ) - and ( R , R ) - l ' . 2 . 3 ' - t r i s ( d i - t e r t - b u t y l p h o s p h i n o ) - l - ( N , N -102 d i m e t h y l a m i n o e t h y l ) f e r r o c e n e ( T B t P F A , V I I ) Ca) Method 1 ( S ) - F A (3 g , 11 . 7 mmol) was d i s s o l v e d i n d i e t h y l e t h e r (5 mL) i n a S ch l e n k t u b e . To t h i s s o l u t i o n was added n -BuL i ( 1 . 6 M, 9 mL) i n hexane . A f t e r s t i r r i n g 2 h, a m i x t u r e o f n -BuL i ( 1 . 6 M, 10 mL) i n hexane and TMEDA ( 1 . 5 g , 13 mmol) was added d r o p w i s e t h r o u g h a p r e s s u r e e q u a l i z i n g d r o p p i n g f u n n e l . The r e a c t i o n m i x t u r e was f u r t h e r s t i r r e d f o r 15 h a t room t e m p e r a -t u r e . T h i s s o l u t i o n was added d r o p w i s e t o a s o l u t i o n o f Bu^PCl ( 4 . 7 g , 26 mmol) i n d i e t h y l e t h e r (30 mL) wh i c h was p r epa r ed i n a 250 mL, r o u n d -b o t t o m , t h r e e - n e c k e d f l a s k e qu i pped w i t h a c o n d e n s e r , a N 2 i n l e t , and a p r e s s u r e e q u a l i z i n g d r o p p i n g f u n n e l . A f t e r t h e i n i t i a l e x o t h e r m i c r e a c t i o n on a d d i t i o n o f t h e F A L i 2 ' T M E D A s o l u t i o n , t h e m i x t u r e was a l l o w e d t o b o i l under r e f l u x f o r 20 h . F o l l o w i n g h y d r o l y s i s w i t h w a t e r , t h e o r g a n i c l a y e r was s e p a r a t e d , d r i e d ove r MgSO^, f i l t e r e d , and r e du ced i n vo lume t o abou t 5 mL. The r e s u l t i n g o i l y s o l u t i o n was ch romatog raphed on A l um i na ( n e u t r a l , Grade I ) . A f t e r remova l o f t h e w h i t e pho sph i ne b y - p r o d u c t by e l u t i o n w i t h p e t r o l e um e t h e r , a second s a l m o n - r e d band was e l u t e d w i t h a m i x t u r e o f d i e -t h y l e t h e r and p e t r o l e u m e t h e r ( 1 / 9 , v / v ) . Removal o f s o l v e n t s f rom t h e r e s u l t i n g o range s o l u t i o n a f f o r d e d a d a r k o i l wh i ch c r y s t a l l i z e d on a d d i n g a c e t o n e ( o r e t h a n o l ) t o g i v e t h e p r o d u c t ( S , S - T B t P F A ( 0 . 3 2 g , 4%). ( R , R ) -TB^PFA was o b t a i n e d by t r e a t i n g (R ) - FA i n the same manner as a b o v e . (b ) Method 2 To t h e i n s i t u s o l u t i o n o f FAL i 2 *TMEDA p r e p a r e d as d e s c r i b e d above was added Bu^PCl ( 7 . 4 9 , 41 mmol) a t room t e m p e r a t u r e . The r e a c t i o n m i x t u r e was s t i r r e d a t room t e m p e r a t u r e f o r 3 h d u r i n g wh i ch t ime t he d a r k r ed s o l u -t i o n t u r n e d t o b r i g h t o range w i t h p r e c i p i t a t i o n o f L i C l . The s o l u t i o n was 103 f u r t h e r s t i r r e d a t room t e m p e r a t u r e f o r 4 d a y s , and t h e p r o d u c t i s o l a t e d as r e d c r y s t a l s f o l l o w i n g t h e wo r k -up d e s c r i b e d a b o v e : y i e l d 3 ^ 4%. 4 . 6 SYNTHESES OF R h ( l ) COMPLEXES OF FERROCENYLPHOSPHINES The comp lexes o f t h e t y p e [ R h ( L - L ) ( N B D ) ] C 1 0 4 ( L - L = I * V I I ) were p r e pa r ed e s s e n t i a l l y u s i n g t he p r o c e d u r e o f S c h r o c k and Osborne [ 32e ] w i t h m i no r m o d i f i c a t i o n s , and were i s o l a t e d as deep r e d c r y s t a l s . A n a l y t i c a l , p h y s i c a l and NMR da t a f o r t h e s e compounds a r e p r e s e n t e d i n Chap t e r 5 . 4 . 6 . 1 A c h i r a l Complexes (A) [Rh( .BPPF ) (NBD) ]C10 4 ( V I I I ) [ R h ( N B D ) C l ] 2 (300 g , 0 .65 mmol) and BPPF (792 mg, 1.4 mmol) were d i s -s o l v e d i n benzene (3 mL) i n a S c h l e n k t u b e , and t h e s o l u t i o n was d e g a s s e d . To t h i s s o l u t i o n was added NaC10 4 (200 mg, 1.6 mmol) i n THF (2 m L ) . The s o l u t i o n was s t i r r e d f o r 30 m in d u r i n g wh i c h t ime a f i n e o r ange p r e c i p i t a t e d e p o s i t e d . T h i s was i s o l a t e d on a S c h l e n k f i l t e r , washed w i t h d i e t h y l e t h e r (20 m L ) , d i s s o l v e d i n CHgClg (5 m L ) , and f i l t e r e d t o remove any s o l i d i m p u r i -t y . The f i l t r a t e was r e du ced i n vo lume t o aboue 2 mL t o wh i c h was added c y c l o h e x a n e (^7 mL) w i t h o u t d i s t u r b i n g t h e d i c h l o r o m e t h a n e l a y e r . L a rge c r y s t a l s were grown by a l l o w i n g t h i s s o l u t i o n t o s t a n d a t room t e m p e r a t u r e : y i e l d 75%. (B) [ R h ( P - P ) ( N B D ) ] C 1 0 4 ( P - P = B P B ^ F , I X ; P-P = P P B t P F , X) These comp lexes were p r epa r ed i n t h e same manner as d e s c r i b e d a bo v e , r e p l a c i n g BPPF by B P B t P F and P P B t P F , r e s p e c t i v e l y : y i e l d 70 ^ 75%. (C) [ R h ( B B t P F ) ( N B D ) ] C 1 0 4 ( X I ) The benzene s o l u t i o n (2 mL) o f B B t P F (1 . 1 g , 2 .32 mmol) and [Rh(NBD) -C l ] ? (357 mg, 0 .77 mmol) was d e g a s s e d . To t h i s s o l u t i o n was added NaC10 4 104 ( 189 . 47 mg, 1.55 mmol) i n THF (2 m L ) . The m i x t u r e was a l l o w e d t o s t i r f o r 2 days a t room t e m p e r a t u r e a f t e r w h i c h t ime s o l v e n t s were removed under vacuum t o l e a v e a r e d d i s h brown s o l i d . T h i s was washed w i t h d i e t h y l e t h e r (20 m L ) , d i s s o l v e d i n C H 2 C 1 2 (2 m L ) , and f i l t e r e d t h r o u g h a S c h l e n k f i l t e r . To t h e f i l t r a t e was added a 3:2 m i x t u r e o f d i e t h y l e t h e r and e t h a n o l (.5 m L ) , and t h e s o l u t i o n was c o o l e d a t 0°C t o g i v e deep r e d c r y s t a l s . L a rge c r y s t a l s were grown as d e s c r i b e d above f o r t h e p r e p a r a t i o n o f V I I I : y i e l d 80%. 4 . 6 . 2 C h i r a l Complexes (A) [ R h ( ( S , R ) - / ( R , S ) - B t P F A ) ( . N B D ) ] C 1 0 4 ( X I I ; B t P F A = V) To a m i x t u r e o f ( S , R ) - B t P F A ( 0 . 2 4 g , 5 .9 x 1 0 " 4 mo l ) and [Rh ( .NBD)C l ] 2 ( 0 . 1 24 g , 2 .7 x 1 0 " 4 mo l ) i n MeOH (5 mL) was added NaC10 4 ( 0 . 0 7 2 g , 5 .9 x 10~ 4 mo l ) d i s s o l v e d i n MeOH (2 m L ) . The r e a c t i o n m i x t u r e was a l l o w e d t o s t i r f o r 12 h a t room t e m p e r a t u r e a f t e r wh i c h t ime t h e s o l v e n t s were removed under vacuum t o l e a v e an o r ange s o l i d . T h i s was washed w i t h d i e t h y l e t h e r s e v e r a l t i m e s , d i s s o l v e d i n CH^C^ . and f i l t e r e d t h r o u g h a S c h l e n k f i l t e r . The f i l -t r a t e was d r i e d under vacuum, and t h e r e m a i n i n g o range s o l i d was r e d i s s o l v e d i n a minimum amount o f hot e t h a n o l (^ 2 m L ) . Red c r y s t a l s were o b t a i n e d by c o o l i n g t h i s s o l u t i o n t o room t e m p e r a t u r e : y i e l d (.272, 34 mg, 55%). The ( R , S ) - c o m p l e x was p r epa r ed by t r e a t m e n t o f ( R , S ) - B t P F A i n t h e same manner . (B) [Rh(P -N) (NBD)]C10 4 ( X I I I ; P-N = (S ,R)- / ( .R , S ) - V I :XIV; P-N = ( S , S ) - / ( R , R ) - V I I ) Bo th comp lexes were p r epa r ed u s i n g t h e same p r o c edu r e as d e s c r i b e d a b o v e : y i e l d 50%. 4 .7 SYNTHESES OF OTHER METAL-FERR0CENYLPH0SPHINE COMPLEXES A n a l y t i c a l , p h y s i c a l and s p e c t r o s c o p i c d a t a f o r t h e comp lexes d e s c r i b e d 105 i n t h i s s e c t i o n a r e p r e s e n t e d i n Chap t e r 5 . 4 . 7 . 1 P a l l a d i u m Complexes P a l l a d i u m comp lexes o f t h e t y p e [ P d ( P - P ) C l 2 ] f P - P = 1 - IV ) were p r e p a r e d by t h e d i r e c t r e a c t i o n o f I^PdC l^ , P d ( N B D ) C I 2 , o r P d ( P h C N ) 2 C l 2 (10 m o l a r s c a l e ) w i t h a s l i g h t mo l a r e x c e s s o f t h e a p p r o -p r i a t e l i g a n d i n d i e t h y l e t h e r c o n t a i n i n g a few mL o f d i c h l o r o m e t h a n e . The p r o d u c t comp lexes were fo rmed as r e d / o r a n g e p r e c i p i t a t e s i n ea ch c a s e wh i ch were i s o l a t e d by f i l t r a t i o n and washed w i t h d i e t h y l e t h e r . Fo r c r y s t a l l i z a t i o n t h e p r o d u c t 300 mg) was d i s s o l v e d i n an a p p r o p r i a t e s o l v e n t o r a m i x t u r e o f s o l v e n t s . The c r y s t a l s t hu s o b t a i n e d were washed w i t h n -hexane and d r i e d i n vacuum. (A) P d ( B P P F ) C l 2 (XV). The p r o d u c t was r e c r y s t a l 1 i z e d from a c e t one t o g i v e r ed p l a t e s : y i e l d 82%. (B) P d ( B P B t P ) C l 2 (XVI ) La rge c r y s t a l s were grown by d i s s o l v i n g t h e m i c r o c r y s t a l l i n e p r o d u c t i n a m i x t u r e o f C H 2 C 1 2 and hexane , and a l l o w i n g t h e s o l v e n t s t o v a p o r i z e i n t h e a i r : y i e l d 80%. (C) P d ( P P B t P ) C l 2 - C H C l 3 ( X V I I ) For c r y s t a l l i z a t i o n t h e p r o d u c t was d i s s o l v e d i n C H 2 C 1 2 and a t op l a y e r o f c y c l o h e x a n e was a l l o w e d t o d i f f u s e s l o w l y i n t o t h e d i c h l o r o m e t h a n e l a y e r : y i e l d 80%. The CHClg c r y s t a l l i z a t i o n was c o n f i r m e d by i t s NMR. (D) P d ( B B t P F ) C l 2 ( X V I I I ) T h i s comp lex was o b t a i n e d as r e d d i s h brown n e e d l e s by c r y s t a l l i z a t i o n as d e s c r i b e d f o r X V I : y i e l d 70%. 106 4 . 7 . 2 N i c k e l Complexes N i c k e l comp lexes o f t h e t y p e N i ( P - P ) X 2 ( P - P = I , I V ; X = C l , B r ) were p r e p a r e d a c c o r d i n g t o p u b l i s h e d p r o c e d u r e s [ 1 1 8 ] : A s o l u t i o n o f t h e a p p r o p r i a t e l i g a n d ( 1 . 0 x 10 mo l ) i n e t h a n o l (20 ^ 30 mL) was p l a c e d i n a 250 mL r o u n d - b o t t o m , two -ne cked f l a s k e qu i pped w i t h a r e f l u x c o n d e n s e r , a n i t r o g e n i n l e t , and a magne t i c s t i r r e r . The s o l u t i o n was t hen b rough t t o r e f l u x and N i ( H 2 0 ) g C l 2 ( o r N i B r 2 ) ( 8 . 5 x 10~ 4 mo l ) d i s s o l v e d i n hot e t h ano l (15 mL) was a dded . A f i n e g r een p r e c i p i t a t e was formed i m m e d i a t e l y . T h i s was s e p a r a t e d by f i l t r a t i o n w h i l e t h e s o l u t i o n was s t i l l warm, washed w i t h c o l d e t h ano l s e v e r a l t i m e s , and d r i e d under vacuum. (A) N i ( B P P F ) C l 2 ( X IX ) and N i ( B P P F ) B r 2 (XX) Bo th comp lexes were i s o l a t e d as d a r k g reen p l a t e s on c r y s t a l l i z a t i o n f rom c h l o r o f o r m ; y i e l d s 65 ^ 70%. (B) N i ( B B t P F ) C l 2 ( XX I ) and N i ( B B t P F ) B r 2 ( X X I I ) These comp lexes were o b t a i n e d as g reen m i c r o c r y s t a l l i n e s o l i d s on c r y s t a l l i z a t i o n f rom a m i x t u r e o f C H 2 C 1 2 and c y c l o h e x a n e : y i e l d s 60 - 65%. 4 . 7 . 3 I r o n Complexes I r o n c a r b o n y l comp lexes F e ( B P P F ) ( C 0 ) 3 and F e 2 ( B P P F ) ( C 0 ) g were p r e -pa red u s i n g t h e g e n e r a l p r o c edu r e s d e s c r i b e d be l ow . The r e a c t i o n o f BPPF w i t h F e 3 ( C 0 ) i 2 i s a l s o d e s c r i b e d here* (A) F e ( B P P F ) ( C 0 ) 3 ( X X I I I ) A THF s o l u t i o n (30 mL) o f BPPF ( 1 . 0 x 10~ 3 mo l ) and F e 2 ( C 0 ) g ( 2 . 0 x 107 10 mo l ) ( o r F e ( C 0 ) 5 ( 1 . 0 x 10 mo l ) i n 20 mL o f benzene) was p l a c e d i n a C a r i u s t u b e . The sys tem was t hen e v a cua t e d by t h e f r e e z e - a n d - t h a w me thod , s e a l e d , and i r r a d i a t e d w i t h UV f o r 6 - 30 h . UV i r r a d i a t i o n r e a c t i o n s were c a r r i e d ou t w i t h a 200 Watt me r cu r y lamp (Hanov i a S -654 A36) under a s t r eam o f a i r . Removal o f s o l v e n t gave a s o l i d r e s i d u e wh i c h was d i s s o l v e d i n C H 2 C 1 2 (^ 4 mL) and ch romatog raphed on F l o r i s i 1 (.80 - 100 m e s h ) . The f i r s t o r ange band was e l u t e d w i t h a m i x t u r e o f d i e t h y l e t h e r and hexane ( 5 / 9 5 , v / v ) . S o l v e n t s were removed f rom t h e r e s u l t i n g o range s o l u t i o n and t h e r e m a i n i n g s o l i d c r y s t a l l i z e d f r om n-hexane t o a f f o r d t h e p r o d u c t as o r ange n e e d l e s : y i e l d 75%. The r e a c t i o n o f BPPF w i t h FetCO)^ i n benzene r e s u l t e d i n l e s s t han 5% y i e l d o f t h e above p r o d u c t . (B) F e 2 ( . B P P F ) ( C 0 ) 8 (XX IV ) T h i s compound was o b t a i n e d as t h e ma j o r p r o du c t f rom t h e r e a c t i o n o f BPPF w i t h Fe (C0 )g i n benzene as d e s c r i b e d a b o v e : y i e l d 62%. The r e a c t i o n o f BPPF ( 0 . 5 5 g , 0 .99 mmol) w i t h F e 2 ( . C 0 ) 9 ( 0 . 7 2 g , 1 .98 mmol) i n THF a l s o y i e l d e d t h i s p r o d u c t (82%) by s t i r r i n g t h e r e a c t i o n m i x t u r e a t room tempe-r a t u r e f o r 20 h, f o l l o w i n g t h e wo rk -up p r o c edu r e s f o r t h e p r e p a r a t i o n o f t h e compound XX . (C) The r e a c t i o n o f BPFF w i t h F e 3 ( . C 0 ) 1 2 A m i x t u r e o f BPPF ( 0 . 1 5 g , 0 .27 mmol) and F e 3 ( C 0 ) - | 2 ( 0 . 2 7 g , 0 .54 mmol) i n THF (25 mL) i n a S c h l e n k t ube was s t i r r e d f o r 4 h a t room t e m p e r a t u r e . Du r i n g t h i s t i m e t he i n i t i a l d a r k g r een c o l o r t u r n e d t o deep p u r p l e . Removal o f s o l v e n t under vacuum a f f o r d e d a d a r k p u r p l e r e s i d u e w h i c h was 108 ch roma tog raphed on F l o r i s i l (100 - 200 m e s h ) . The l a r g e p u r p l e b a n d , f o l l o w i n g t h e g reen band o f e x c e s s F e - ^ C O ) ^ , was e l u t e d w i t h a m i x t u r e o f d i e t h y l e t h e r and p e t r o l e um e t h e r ( 5 / 5 , v / v ) , and s o l v e n t s removed t o g i v e a da r k p u r p l e o i l . T h i s compound r e a d i l y decomposed i n s o l u t i o n but appea r s t o be r e a s o n a b l y s t a b l e i n t h e s o l i d s t a t e . I t g i v e s a t l e a s t 7 v ( C 0 ) bands i n c l u d i n g one a t 1775 cm~^. 4 . 7 . 4 Group VI Me ta l Complexes The Group VI me ta l c a r b o n y l c o m p l e x e s , M ( B P P F ) ( C 0 ) 4 (M •= C r , Mo ) , were p r e p a r e d by t h e p r o c e d u r e o f Dav i s on [118 ] w i t h m i no r m o d i f i c a t i o n . (A) C r ( B P P F ) ( C 0 ) 4 (XXV). A benzene s o l u t i o n (20 mL) c o n t a i n i n g BPPF ( 2 . 5 2 g , 4 . 5 mmol) and C r ( C 0 ) g ( 0 . 9 5 g , 4 . 5 mmol) was hea ted i n an e v a cua t e d C a r i u s t ube a t 150°C f o r 12 h . Removal o f s o l v e n t i n vacuum gave an o r ange s o l i d wh i c h was d i s s o l v e d i n a minimum amount o f CHgClg (^ 3 mL) and ch roma tog raphed on F l o r i s i l (100 ^ 200 m e s h ) . The second o range band was e l u t e d w i t h a m i x t u r e o f d i e t h y l e t h e r and p e t r o l e um e t h e r ( 4 / 6 , v / v ) , and s o l v e n t s removed t o g i v e t h e o range m i c r o c r y s t a l l i n e p r o d u c t . L a r ge c r y s t a l s were grown by d i s s o l v i n g t h e p r o d u c t i n a hot s o l u t i o n o f benzene and heptane ( 1 / 4 , v / v ) , and a l l o w i n g t h e s o l u t i o n t o c o o l s l o w l y t o room t e m p e r a t u r e : y i e l d 2 .59 g (87%). (B) M o ( B P P F ) ( C 0 ) 4 - C 6 H g (XXVI) T h i s was p r epa r ed s i m i l a r l y . The benzene o f c r y s t a l l i z a t i o n was c o n -f i r m e d by i t s c r y s t a l s t r u c t u r e : y i e l d 61%. 109 PART I I I RESULTS, DISCUSSION,AND CONCLUSION n o CHAPTER 5 SYNTHESIS AND CHARACTERIZATION OF FERROCENYLPHOSPHINES AND THEIR METAL COMPLEXES. The compounds o f most i n t e r e s t i n t h e p r e s e n t s t u d i e s a r e c h i r a l and a c h i r a l f e r r o c e n y l p h o s p h i n e l i g a n d s ; i n p a r t i c u l a r t h o s e c o n t a i n i n g b u l k y t e r t - b u t y l g roups on phosphorus f o r t h e r e a s on s g i v e n i n s e c t i o n 3 . 3 . W i t h a p p r o p r i a t e m o d i f i c a t i o n s o f known p r o c e d u r e s , a w ide r ange o f f e r r o c e n y l -pho sph i n e s and t h e i r me t a l comp lexes can be p r e p a r e d . T h i s c h a p t e r i s m a i n l y c on ce rned w i t h t h e p r e p a r a t i o n and t h e c h a r a c t e r i z a t i o n o f t h e s e l i g a n d s ( L - L ) and t h e i r r hod ium comp lexes o f t h e t y p e [ R h ( L - L ) ( N B D ) ] C 1 0 4 wh i c h a r e h y d r o g e n a t i o n c a t a l y s t p r e c u r s o r s ( c f . Chap te r 6 ) . Some o t h e r m e t a l (Group VI and V I I I ) comp lexes o f t h e s e l i g a n d s were p r e p a r e d , and a r e a l s o d e s c r i b e d . In t h e subsequen t d i s c u s s i o n t h e n o t a t i o n P-P and P-N i s a l s o used t o deno te t he a c h i r a l f e r r o c e n y l p h o s p h i n e s ( L - L = I - IV) and t h e c h i r a l ones ( L - L = V - V I I ) , r e s p e c t i v e l y . 5.1 FERROCENYLPHOSPHINE LIGANDS 5 . 1 . 1 A c h i r a l L i g and s (A) S y n t h e s e s P r e p a r a t i v e r o u t e s t o t h e a c h i r a l f e r r o c e n y l p h o s p h i n e s a r e shown i n F i g . 5 . 1 . A l l r o u t e s i n v o l v e t h e w e l l documented p r o c e d u r e f o r t h e p r e p a r a t i o n o f t h e 1 , 1 ' - d i l i t h i o f e r r o c e n e - T M E D A addu c t [ 9 7 ] . The o r ange p r e c i p i t a t e s e p a r a t e s f rom hexane s o l u t i o n as a p y r o p h o r i c powder when f e r r o c e n e i s l i t h i a t e d w i t h two m o l a r e q u i v a l e n t s o f n - BuL i i n t h e p r e s e n c e o f one e q u i -m in ( P P B W ) F i g , 5 . 1 : P r e p a r a t i v e r o u t e s t o t h e a c h i r a l l i g a n d s I - 1V . 112 v a l e n t o f TMEDA. A l t h o u g h t he c r y s t a l s t r u c t u r e o f t h i s compound has not been d e t e r m i n e d , Dav i s on [ 97 ] s ugge s t ed t h a t i t be f o r m u l a t e d as (C^H^Li) 2Fe-TMEDA on t h e b a s i s o f t h e a n a l y t i c a l r e s u l t . T h i s s t o i c h i o m e t r y has been found i n the r e l a t e d compound [ U 5 - C 5 H 4 ) 2 F e ( N 3 C g H 2 3 ) L i 2 ] 2 [ 1 1 9 ] , The re a r e d i s t i n c t a d van t age s i n u s i n g t he s o l i d d i l i t h i o f e r r o c e n e i n t h e s e p r e p a r a -t i o n s , name ly h i g h y i e l d s and no m o n o s u b s t i t u t e d pho sph i ne s a r e o b t a i n e d . The p r e v i o u s l y known compound I [97 ] was p r epa r ed by r e a c t i n g a hexane s l u r r y o f d i l i t h i o f e r r o c e n e w i t h c h l o r o d i p h e n y l p h o s p h i n e . T h i s d i ( t e r t i a r y pho sph i ne ) i s an o r a n g e , c r y s t a l l i n e s o l i d wh i c h i s a i r s t a b l e i n bo th t h e s o l i d and s o l u t i o n . A s i m p l e e x t e n s i o n r e p l a c i n g Ph^PCl by B u ^ P h J P C l and B u ^ P C l a l l o w s t h e i s o l a t i o n o f t h e new f e r r o c e n y l pho sph i ne l i g a n d s I I and I V , r e s p e c t i v e l y . B o t h l i g a n d s were o b t a i n e d as d a r k o i l s wh i c h s l o w l y s o l i d i f i e d on c o o l i n g a t 0°C. In c o n n e c t i o n w i t h t h e p r e p a r a t i o n o f I I , i t s h ou l d be p o i n t e d ou t t h a t t h i s compound can e x i s t as bo th meso • and r a c - i s o m e r s . In t h e p r e s e n t s t u d i e s t h e y were s e p a r a t e d c h r o m a t o g r a p h i c a l l y as d e s c r i b e d i n t h e e x p e r i m e n t a l s e c t i o n , but o n l y t he r a c - i s o m e r has been used f o r f u r t h e r s y n t h e s e s , s p e c t r o s c o p i c (NMR), and h y d r o g e n a t i o n s t u d i e s . The u n s y m m e t r i c a l l y 1 ,1 1 - d i s u b s t i t u t e d l i g a n d I I I was p r epa r ed v i a t h e r i n g c l e a v a g e r e a c t i o n ( e q u a t i o n 5 .1 ) o f t h e [ 1 ] - f e r r o c e n o p h a n e wh i c h was p r epa r ed f rom t he r e a c t i o n o f (CrH .L i ) ? Fe-TMEDA w i t h P h P C l ? [ 1 1 4 ] . ( 5 . 1 ) ill 113 The sub sequen t s y n t h e t i c r o u t e i n v o l v e d t he r e a c t i o n o f t h e i n t e r m e d i a t e , 1 - d i p h e n y l phosph i no -1 ' -1 i t h i o f e r r o c e n e w i t h B u ^ P C l . The compound I I I was o b t a i n e d as a y e l l o w c r y s t a l l i n e s o l i d . A l t h o u g h t h i s i s an e x t r e m e l y u s e f u l method o f a c t i v a t i n g t h e second r i n g f o r f u r t h e r s u b s t i t u t i o n , c a r e must be t a k en to m i n i m i z e t h e f o r m a t i o n o f b y p r o d u c t s . For e xamp l e , t he i n i t i a l p r o d u c t m o n o l i t h i o f e r r o c e n e d e r i v a t i v e may compete w i t h PhL i f o r t h e s u b s t r a t e [ 1 ] - f e r r o c e n o p h a n e , t hu s g i v i n g a monol i t h i o f e r r o c e n y l d e r i v a t i v e as shown i n e q u a t i o n ( 5 . 2 ) [ 1 1 4 c ] . ( 5 . 2 ) @ C^-u In o r d e r to a v o i d t h i s p o t e n t i a l c o m p l i c a t i o n , t h e p r e f e r r e d p r o cedu r e i n v o l v e d t h e s l ow a d d i t i o n o f 1.5 m o l a r e x c e s s o f PhL i to t h e [ l ] - f e r r o -cenophane i n d i e t h y l e t h e r m a i n t a i n e d a t - 7 8 ° C . An a l t e r n a t i v e r o u t e i n v o l v e s t h e s l ow a d d i t i o n o f the [ 1 ] - f e r r o c e n o p h a n e to an e q u i m o l a r q u a n t i t y o f PhL i i n hexane [ 1 1 4 c ] . 114 (B) C h a r a c t e r i z a t i o n The a n a l y t i c a l and NMR d a t a l i s t e d i n T a b l e s 5.1 and 5.2 r e s p e c t i v e l y , c o n f i r m t h e f o r m u l a t i o n o f I and t h e new l i g a n d s 11 -1V . The "*H NMR s p e c t r a o f t h e symmet r i c l i g a n d s I , I I and IV show a p a i r o f b road t r i p l e t s f o r t h e s y m m e t r i c a l l y d i s u b s t i t u t e d f e r r o c e n e r i n g s , (£5^4")2^e> i n t n e r e g i o n 6 = 4 . 0 ^ 4 . 6 ppm. The l i g a n d I I I , howeve r , shows two p a i r s o f b road t r i p l e t s f o r t h e r i n g p r o t o n s . T h i s may be due t o t he p r e s en ce o f a p a i r o f d i a s t e r e o t o p i c Cp r i n g s , each r i n g c o n t a i n i n g two p a i r s o f e n a n t i o t o p i c p r o t o n s . The c h a r a c t e r i s t i c f e a t u r e o f t h e new l i g a n d s I I - IV i s t h e p r e s en ce o f a d o u b l e t i n t h e range 1.1 to 1.3 ppm due to c o u p l i n g between phosphorus ( P, 100% abundance , s p i n = 1/2) and e q u i v a l e n t ( o r e n a n t i o t o p i c ) p r o t o n s o f t h e t e r t - b u t y l g r o u p s . 31 1 The P{ H} s p e c t r a o f t h e l i g a n d s I , I I , and IV ( F i g . 5 .2) show a sha r p s i n g l e t a t ^-17.61, 7 . 7 7 , and 26 .48 ppm, r e s p e c t i v e l y f o r t h e p a i r o f e q u i v a l e n t phospho rus a t o m s . I t c a n be no t ed t h a t t h e r e sonance peak f o r the phosphorus atoms moves to t h e l o w e r s h i e l d i n g r e g i o n as t h e s u b s t i t u t i o n 31 o f t h e pheny l g roups by t h e t e r t - b u t y l g roups p r o c e e d s . A l t h o u g h t h e P NMR o f t h e l i g a n d I I I has y e t t o be o b t a i n e d , two peaks a r e e x p e c t e d f o r the d i a s t e r e o t o p i c p a i r o f P a t oms . 5 . 1 . 2 C h i r a l L i g a n d s (A) S y n t h e s e s P r e p a r a t i v e r o u t e s t o t h e c h i r a l f e r r o c e n y l pho sph i n e s a r e shown i n F i g . 5 . 3 . 115 T a b l e 5 . 1 : A n a l y t i c a l and p h y s i c a l da t a f o r t h e a c h i r a l l i g a n d s I -1V . mp,°C Found(%) C a l c d U ) Compound (decomp. ) C H C H I 183 -185 73 . 46 4 . 96 73 . 67 5 .06 I I 56 -58 68.91 6 .95 7 0 . 0 6 7 .00 I I I - 69 .95 6 .95 7 0 . 0 6 7 .00 IV o i l - - 65 .84 9 .29 T a b l e 5 . 2 : ^ a n d ^ P i 1 HJ NMR da t a f o r t h e a c h i r a l 1 i g and s I-- I V a ' b . Compound - C 6 H 5 ( C 5 H 4 - ) F e - CMe 3 3 1 P I 7 . 30 (m ,20 ) 4 . 2 8 ( b t , 4 ) - (CDC1 3 ) 4 . 0 1 ( b t , 4 ) - 17 . 61 ( s ) r a c - I I 7 . 80 (m ,4 ) 4 . 3 2 ( b t , 4 ) 1 . 2 0 ( d , 1 8 ) <w 7 . 50 (m ,6 ) 4 . 1 0 ( b t , 4 ) (J p H = 1 2 ) 7 . 7 7 ( s ) I I I 7 . 33 (m ,10 ) 4 . 6 2 ( b t , 2 ) 1 . 1 2 ( d , 1 8 ) -4 . 4 8 ( b t , 2 ) ( J p H = 1 1 . 5 ) 4 . 3 7 ( b t , 2 ) 4 . 3 0 ( b t , 2 ) IV - 4 . 4 4 ( b t , 4 ) 1 . 2 2 ( d , 3 6 ) (CgDg) 4 . 2 8 ( b t , 4 ) (Jnu=H) 2 6 . 4 8 ( s ) H NMR s p e c t r a were o b t a i n e d i n C D C l ^ . C o u p l i n g c o n s t a n t s a r e i n H z : b t=broad t r i p l e t , d = d o u b l e t , m = m u l t i p l e t , s = s i n g l e t . 116 Fe 1 I I I I 1 I J I I 50 40 30 20 0 -10 -20 -30-40-60 Fe PBoPh II I J J I L I I I I I SO 40 30 20 10 0 -10 -20 -30 -40 -50 ' C O PBu, Fe IV _ J l A l I I I I I I I 60 40 30 20 10 0 -10 -20 -30 -40 -60 F i g . 5 . 2 : 32 . 3 MHz 3 1 p { 1 H } NMR s p e c t r a o f t h e a c h i r a l l i g a n d s I , I I and IV 117 A l l r o u t e s r e q u i r e t h e p r e p a r a t i o n and t h e r e s o l u t i o n o f FA, a key i n t e r m e d i a t e i n t h e s y n t h e s e s o f v a r i o u s c h i r a l l i g a n d s o f t h i s s o r t . FA i s r e a d i l y p r e p a r e d i n h i g h y i e l d s (> 75%) u s i n g t h e known p r o c e d u r e [115 ] as shown i n t he f i g u r e . Thus t h e n i t r i l e d e r i v a t i v e was o b t a i n e d by r e a c t i o n o f t h e b i s u l f i t e adduc t o f f e r r o c e n e c a r b o x a l d e h y d e w i t h d i m e t h y l -amine and sod ium c y a n i d e . Subsequen t r e a c t i o n o f the a m i n o n i t r i l e w i t h MeMgl r e s u l t e d i n FA. There a r e s e v e r a l o t h e r methods to p r e p a r e FA [ 100 , 1 2 0 ] . The r e s o l u t i o n o f FA w i t h ( R ) - ( + ) - t a r t a r i c a c i d was a c h i e v e d u s i n g U g i ' s p r o c edu r e [100 ] f rom wh i c h bo t h a n t i p o d e s were o b t a i n e d . The ( R ) - t a r t r a t e o f ( S ) - F A c r y s t a l l i z e d f rom m e t h a n o l , and t h e ( R , R ) -d i a s t e r e o m e r was o b t a i n e d by e v a p o r a t i n g t h e mothe r l i q u o r and c r y s t a l l i z i n g f rom aqueous a c e t o n e . The f i n a l s y n t h e t i c r o u t e s t o fo rm t h e p r e v i o u s l y known compound V and t h e new c h i r a l l i g a n d s VI and V I I a r e based on t h e known p r o c edu r e s e t o u t i n F i g . 3 . 2 . The f i g u r e shows t h a t m o n o l i t h i a t i o n o f FA f o l l o w e d by t r e a t m e n t w i t h h a l o p h o s p h i n e s a f f o r d s monophosph ino -FA l i g a n d s , and t h a t b i s p h o s p h i n o - F A l i g a n d s such as BPPFA can be p r epa r ed v i a t h e TMEDA a d d u c t o f d i l i t h i o - F A g e n e r a t e d by s t e p w i s e d i l i t h i a t i o n o f FA i n t h e p r e s en ce o f TMEDA. The f i g u r e a l s o shows t h a t t he ma j o r d i a s t e r e o m e r i c p r o d u c t s o b t a i n e d f rom ( S ) - o r ( R ) - FA have t h e c o n f i g u r a t i o n o f ( S ,R ) o r ( R , S ) . The m ino r (4%) d i a s t e r e o m e r s , ( S , S ) - o r ( R , R ) - p h o s p h i n e d e r i v a t i v e s can be e l i m i n a t e d by s i m p l e r e c r y s t a l l i z a t i o n o f t h e i n i t i a l p r o d u c t s . In t h i s way t h e p r e v i o u s l y known monophosph ino -FA V was p r epa r ed u s i n g t h e monol i t h i a t i o n o f FA f o l l o w e d by t r e a t m e n t w i t h B u ^ P C l ( a i .2 m o l a r e x c e s s ) . T h i s compound was o b t a i n e d as a r ed c r y s t a l l i n e , a i r - s t a b l e s o l i d . 118 Fe C H O O) NaHSO, -(b) HNMe2-(O NaCN ^ r C H ( C N ) Fe FA Resolution (R)-(+)-tartaric a c i d n-BuLi / \ * /Me Fe - C H , • N C H 3 ) 2 (Sh/(R)-FA (i) n-BuLi (ii) n-BuLi/TMEDA \ / \ * .Me v / NMe2 F e ^ L i \ TMEDA — L i Bu^pci V^/ NMe2 Fe PBu2 BujPCI Fe^PBu 2 Me NMe2 Fe^PBu, .Me NMe, PBu2 Bu^ P PBu2 (S,R)-/:R,S)-V (S,R)-/(R,S)- VI (S,S)-/(R,R)-VII F i g . 5.3: P r e p a r a t i v e r o u t e s t o t h e c h i r a l l i g a n d s V - V I I 119 As e x p e c t e d , t h e c o n f i g u r a t i o n o f t h e ma jo r p r odu c t (V) i s ( S , R ) and ( R , S ) , r e s p e c t i v e l y when ( S ) - and (R ) - FA i s u s e d . The CD spe c t r um o f ( R , S ) - V i s shown i n F i g . 5 . 6 . The new c h i r a l l i g a n d s VI and V I I were p r epa r ed by r e a c t i n g t h e i n s i t u s o l u t i o n o f L i ' 2 FA-TMEDA w i t h e x c e s s B u ^ P C l . In t h e p r e s e n t i n v e s t i -g a t i o n t h e f o r m a t i o n o f t h e b i s p h o s p h i n o - F A l i g a n d VI was found t o be s l ow p r o b a b l y due t o s t e r i c h i n d r a n c e . Thus t h e p r e f e r r e d p r o c e d u r e was to add a 2 .2 m o l a r e x c e s s o f B u ^ P C I to t h e i n s i t u s o l u t i o n o f L i " 2 FA-TMEDA, and a l l o w t h e m i x t u r e to s t i r f o r 1 ^2 days a t room t e m p e r a t u r e ( H e a t i n g must be a v o i d e d ) . In t h i s way t he f o r m a t i o n o f t h e monophosph ino -FA V as b y - p r o d u c t was m i n i m i z e d (< 5%), thus a l l o w i n g a c h r o m a t o g r a p h i c p u r i f i c a t i o n (The two pho sph i n e s V and VI a r e a l m o s t c h r o m a t o g r a p h i c a l l y i n s e p a r a b l e ) . The use o f t h e i s o l a t e d s o l i d L i 2 FA -TMEDA [121] i n t h i s p r e p a r a t i o n has l i t t l e advan t age o v e r t h e d i r e c t use o f t h e i n s i t u s o l u t i o n . The f i n a l p r o du c t VI was o b t a i n e d as a r ed o i l (The a t t e m p t e d c r y s t a l l i z a t i o n f rom a c e t o n e o r e t h a n o l was u n s u c c e s s f u l ) . T h i s r e a c t i o n a l s o r e s u l t e d i n t h e f o r -m a t i o n o f ( R , S ) - and ( S , R ) - V I as t h e ma jo r p r o d u c t when ( R ) - and ( S ) - F A was emp loyed , r e s p e c t i v e l y . T h i s i s c o n f i r m e d by compa r i ng t h e CD spec t r um o f t h e R h ( I ) comp lex o f VI w i t h t h a t o f t h e rhod ium comp lex o f t h e mono-pho sph i n o - FA V ( c f . F i g . 5 . 1 4 A ) . D u r i n g t h e p r e p a r a t i o n o f t h e b i s .phosph ino-FA l i g a n d V I , i t was a c c i -d e n t a l l y found t h a t f u r t h e r l i t h i a t i o n c an t a k e p l a c e . Thus i n t he p r e sence o f e x ce s s B u ^ P C l o r under f o r c i n g r e a c t i o n c o n d i t i o n s an unexpec t ed p r o d u c t , t r i s p h o s p h i n o - F A y i l , i s o b t a i n e d as d e s c r i b e d i n t h e e x p e r i m e n t a l s e c t i o n . T h i s l i g a n d ( V I I ) was p r epa r ed e i t h e r by r e a c t i n g t h e i n s i t u s o l u t i o n o f 120 L12FA-TMEDA w i t h a 3 ^ 4 m o l a r e x c e s s o f Bu 2 PC1 a t room t e m p e r a t u r e f o r 4 days o r by a d d i n g t h e i n s i t u s o l u t i o n o f Li^FA-TMEDA to a hexane s o l u t i o n o f B u ^ P C l 2 .5 m o l a r e x c e s s ) f o l l o w e d by r e f l u x i n g t h e r e a c t i o n m i x t u r e f o r abou t 20 h . The i n i t i a l o i l y p r o d u c t was r e c r y s t a l 1 i z e d f rom a c e t o n e o r e t h a n o l t o g i v e r e d a i r - s t a b l e c r y s t a l s . These f o r c i n g c o n d i t i o n s were i n i t i a l l y used i n t h e hope t h a t t h e f o r m a t i o n o f t h e b i s p h o s p h i n o - F A VI wou ld be e f f e c t e d more r e a d i l y . C o n s e q u e n t l y , any p r e p a r a t i o n o f t h e b i s p h o s p h i n o - F A s h o u l d be c a r e f u l l y m o n i t o r e d t o a v o i d t h e f o r m a t i o n o f bo th t h e monophosph ino -FA V and t h e t r i s p h o s p h i n e ^ F A V I I . A no t h e r s t r i k i n g f e a t u r e c o n c e r n i n g t he p r e p a r a t i o n o f t h e t r i s p h o s p h i n o -FA V I I i s t h a t t h e f i n a l p r o du c t ( c r y s t a l l i n e s o l i d ) has t h e c o n f i g u r a t i o n o f t h e a n t i c i p a t e d m i no r d i a s t e r e o m e r ( S , S ) o r ( R , R ) . Thus ( R ) - F A l e a d s to ( R , R ) - V I I , and ( S ) - F A to ( S . S ) - V I I . The CD s p e c t r a o f bo th ( R , R ) - and ( S , S ) - V I I a r e shown i n F i g . 5 . 8 . The c r y s t a l s t r u c t u r e i s d e s c r i b e d b e l o w . (B) C h a r a c t e r i z a t i o n The f o r m u l a t i o n o f t h e p r e v i o u s l y known V and t h e new c h i r a l l i g a n d s VI and V I I i s c o n f i r m e d by t h e a n a l y t i c a l and t h e NMR d a t a g i v e n i n Tab les 5 .3 and 5 . 4 , r e s p e c t i v e l y . In F i g s . 5.4 and 5 .5 a r e a l s o g i v e n t h e i r 1 31 1 H and P{ H} s p e c t r a . The NMR s p e c t r a o f bo th VI and V I I show complex m u l t i p l e t s f o r t h e Cp r i n g p r o t o n s i n t h e r ange 4 . 0 to 4 . 8 ppm, whereas t h e monophosph ine l i g a n d V e x h i b i t s a s h a r p s i n g l e t F 2 a t 4 . 07 ppm f o r t he u n s u b s t i t u t e d " s e c o n d " r i n g as w e l l as a m u l t i p l e t F q f o r t h e d i s u b s t i t u t e d " f i r s t " r i n g i n t h e 121 T a b l e 5 . 3 : A n a l y t i c a l and p h y s i c a l d a t a f o r t h e c h i r a l l i g a n d s V - V I I . Found(%) Ca l cd(%) Compound mp,°C ( c l . C g H g ) C H N C H N ( S , R ) - V 55-58 +178.24 41 . 02 5.57 2 .23 4 1 . 2 9 5 . 63 2 .19 ( R , S ) - V - 1 78 . 9 7 ( S . R ) - V I o i l - 2 2 . 2 0 66 .07 9 . 73 2 .57 ( R . S ) - V I +21.93 ( S . S ) - V I I 135-137 - 3 7 . 5 2 65 .68 10 . 00 2 .10 66 . 10 1 0 . 29 2 .03 ( R . R ) - V I I +36.60 T a b l e 5 . 4 : ] H and 3 1 P { ] H } N M R da t a f o r t h e c h i r a l l i g a n d s V - V I I a ' b . Compound - P ( C M e 3 ) 2 Othe r s 31 p V 1 . 4 2 ( d , 9 , J p H = 1 2 ) 0 . 8 6 ( d , 9 , J p H = 1 2 ) 1 . 3 8 ( d , - C M e , J H H = 8 ) 3 . 5 7 ( d q , - C H M e , J H H = 8 , J p H = 4 ) 2 . 1 1 ( s , - N M e 2 ) 4 . 0 7 ( s , ( C 5 H 5 - ) F e ) 4 . 1 6 - 4 . 4 6 ( m , ( C 5 H 3 - ) F e 1 3 . 3 2 ( s ) VI 1 . 6 ( d , 9 , J p H = 1 2 ) 1 . 3 ( d , 9 , J p H = 1 2 ) 1 . 2 ( d , 9 , J p H = 1 2 ) 1 . l ( d , 9 , J p H = 1 2 ) 1 . 3 5 ( d , - C M e , J H H = 8 ) 4 . 0 0 ( d q , - C H M e , J H H = 8 , J p H = 4 ) 2 . 2 0 ( s , - N M e 2 ) 4 . 1 - 4 . 5 ( m , ( C 5 H 3 - ) F e ( C 5 H 4 ) ) 1 4 . 5 3 ( s ) 2 6 . 7 4 ( s ) V I I 1 . 7 ( d , 9 , J p H = 1 2 ) 1 . 8 0 ( d , - C M e , J H H = 8 ) 1 7 . 6 7 ( s ) 1 . 5 ( d , 9 , J p H = 1 0 ) 1 . 2 ( d , 9 , J p H = 1 2 ) l . l ( d , 9 , J p H = 1 2 ) 3 . 8 0 ( d q , - C H M e , J H H = 8 , J p H = 4 ) 2 . 4 0 ( s , - N M e 2 ) 4 . 4 - 4 . 8 ( m , ( C 5 H 3 - ) 2 F e ) 2 3 . 4 9 ( s ) 2 6 . 6 3 ( s ) A l l s p e c t r a were o b t a i n e d i n C g Dg u s i n g t h e r a c em i c m i x t u r e o f each l i g a n d . C o u p l i n g c o n s t a n t s a r e i n Hz :dq=doub le t o f q u a r t , s = s i n g l e t . 122 6 5 4 3 2 1 0 6 5 4 3 2 1 0 F i g . 5 . 4 : 80 MHz H NMR s p e c t r a o f t h e c h i r a l l i g a n d s V - V I I i n C ,D 123 Fe PBu2 CWJ)^R,S)-V L 28 I I 1 I I I 24 20 16 12 I I I I I I I 28 24 20 16 12 MM©/. t * Fe ^PBuV 4 - t <S*>-AR.S>-VI i /Me Fe P B u 2 B u 2 P ^ - P B u 2 <S,S>-/(R,R)-VII 28 24 20 16 12 8 F i g . 5 . 5 : 32 . 3 MHz 3 1 P I 1 H ] NMR s p e c t r a o f t h e c h i r a l l i g a n d s V - V I I i n CgD 6 . Resonances w i t h t h e a s t e r i s k a r e due to VI as an i m p u r i t y . 124 r ange 4 . 16 to 4 . 4 6 ppm. Here t h e te rms " f i r s t " and " s e c o n d " r i n g s r e f e r t o t he Cp r i n g c o n t a i n i n g t he -CH(Me)NMe2 g roup and the o t h e r C p r i n g , r e s p e c t i v e l y , and w i l l be used i n t h e subsequen t d i s c u s s i o n . The me t h i n e p r o t o n (-CHMe) o f t h e mono- , b i s - , and t r i s p h o s p h i n e l i g a n d s a ppea r s as a d o u b l e t o f q u a r t e t s c e n t e r e d a t 3 .57 (peak C^) , 4 . 0 (peak C g ) , and 3 . 8 (peak C T ) ppm, r e s p e c t i v e l y . T h i s p a t t e r n a r i s e s due t o t h e c o u p l i n g w i t h t h e n e i g h b o r i n g phosphorus atoms (^Jp^) a s w e ^ as t h e methy l g r oup (-CHMe)' on t he a s ymme t r i c c e n t e r , as c h e c k ed by homonuc lea r (H-H) c o u p l i n g i n t h e s e l i g a n d s . The c o u p l i n g c o n s t a n t s 4 3 Jp|_| and i n t h e s e l i g a n d s a r e l i s t e d i n T a b l e 5 . 4 . The -NMe2 g roup i n t h e mono- , b i s - , and t r i s p h o s p h i n e l i g a n d s g i v e s a s h a r p s i n g l e t a t 2.11 (peak N^), 2 .20 (peak N B ) , and 2 . 40 (peak N j ) ppm, r e s p e c t i v e l y . T h i s s i n g l e t a r i s e s because o f r a p i d i n v e r s i o n a t the N a t om . The methy l g roup (-CHMe; on t he a s ymme t r i c c e n t e r i n the mono- , b i s - , and t r i s p h o s p h i n e l i g a n d s g i v e s a d o u b l e t a t 1 .38 (peak M^), 1 .35 (peak Mg ) , and 1 .8 (peak My) ppm, r e s p e c t i v e l y . The s t r i k i n g d i f f e r e n c e between V and VI o r V I I i s t h a t t he f o rmer shows two d o u b l e t s B ^ l ) and B^(2) a t 1.42 and 0 .86 ppm f o r t h e - P ( C M e 3 ) 2 g r o u p , whereas t h e l a t t e r two l i g a n d s show f o u r d o u b l e t s i n t he r ange 1.1 t o 1.7 ppm w i t h c o u p l i n g c o n s t a n t s o f 10 t o 12 Hz ( T a b l e 5 . 4 ) . Here i t i s i n t e r e s t i n g to no t e t h a t t h e t r i s p h o s p h i n e l i g a n d V I I g i v e s o n l y f o u r d o u b l e t s B j ( l ) , B T ( 2 ) , B T ( 3 ) , and B T ( 4 ) i n s t e a d o f s i x f o r t h e t h r e e -P ^ M e ^ g r o u p s . Thus t h e d o u b l e t s B j ( 2 ) and B T ( 3 ) o f h i g h e r i n t e n s i t i e s can be r e a s o n a b l y a s s i g n e d t o t h e two - P ^ M e ^ groups i n t h e second r i n g , and t h e o t h e r two B j ( l ) and By ( 2 ) t o t h e - P ( C M e 3 ) 2 g roup i n t h e f i r s t r i n g . The f o u r d o u b l e t s i n t h e b i s p h o s p h i n e l i g a n d VI can no t be e a s i l y a s s i g n e d . 125 The P{ H} NMR s p e c t r a o f t h e s e l i g a n d s ( V - V I I ) ( F i g . 5 .5 ) show, as e x p e c t e d , one , two , and t h r e e r e s onan c e p ea k s , r e s p e c t i v e l y f o r t h e P a t om(s ) w i t h t h e c h e m i c a l s h i f t s g i v e n i n T a b l e 5 . 4 . F i g . 5 .5 shows t h a t 31 t h e P peak to h i g h e r s h i e l d i n g can be a s s i g n e d t o t h e P atom i n t h e f i r s t r i n g , and t h e peak moves t o l owe r s h i e l d i n g as s u b s t i t u t i o n i n t he second r i n g p r o c e e d s . Thus t h e peak ( s ) w i t h t h e h i g h e r c h e m i c a l s h i f t s can be a s s i g n e d t o t h e P a t om( s ) i n t h e second r i n g . (C) D e t e r m i n a t i o n o f C o n f i g u r a t i o n As men t i oned p r e v i o u s l y , t h e p r e p a r a t i o n o f bo th V and VI l e d to t h e e x p e c t e d c o n f i g u r a t i o n ( R , S ) o r ( S , R ) when ( R ) - o r ( S ) - F A was used as t h e s t a r t i n g m a t e r i a l . The CD s pe c t r um o f ( R , S ) - V i s seen i n F i g . 5 .6 wh i ch shows t h e p o s i t i v e Ae(= e -e ) v a l u e s a round 545 ^ 570 and 340 ^ 385 nm, ~ Y and t h e n e g a t i v e maximum Ae v a l u e a t abou t 465 nm. T h i s p a t t e r n i s i n a c c o r d a n c e w i t h t h a t o f o t h e r known FA-based phosph i ne l i g a n d s [ 1 0 4 b ] , a l l o w i n g the i d e n t i f i c a t i o n o f t h e c o n f i g u r a t i o n o f t h i s compound. Thus , f o r e xamp l e , t h e l i g a n d s ( S . R ) - P P F A , ( S , R ) - B P P F A , and ( R ) - P P E F have the p o s i t i v e maximum and t he n e g a t i v e maximum Ae v a l u e s a round 450 % 470 'nm and 340 ^ 350 nm, r e s p e c t i v e l y , whereas (R ,S ) -MPFA g i v e s t he s pe c t r um wh i c h i s v i r t u a l l y i n t h e m i r r o r image o f t h o s e o f t h e above t h r e e l i g a n d s . Here i t can be no t ed t h a t t he l i g a n d s ( R ) - PPEF and (R ,S ) -MPFA have the o p p o s i t e p l a n a r c h i r a l i t y . A l t h o u g h t h e CD spec t r um o f t h e b i s p h o s p h i n e l i g a n d VI has y e t t o be o b t a i n e d , t h e c o n f i g u r a t i o n o f t h i s compound can be e a s i l y d e t e r m i n e d by e x am i n i n g t h e CD spe c t r um o f i t s R h ( l ) c omp l e x . T h i s w i l l be d i s c u s s e d l a t e r i n s e c t i o n 5 . 2 . 2 ( C ) . 126 127 F i g . 5 . 7 : The c r y s t a l s t r u c t u r e o f t h e c h i r a l l i g a n d ( S , S ) - V I I £ 1 2 2 ] . 128 129 Q u i t e s u r p r i s i n g l y , however , t he c o n f i g u r a t i o n o f t h e t r i s p h o s p h i n e l i g a n d V I I i s t h a t o f t h e supposed m i n o r d i a s t e r e o m e r , t h a t i s , ( R , R ) - o r ( S , S ) - V I I when ( R ) - o r ( S ) - F A i s employed as t h e s t a r t i n g m a t e r i a l . T h i s i s c o n f i r m e d by a c r y s t a l s t r u c t u r e and the CD spe c t r um o f a s a m p l e . F i g . 5.7 shows t h a t t h e compound d e r i v e d f rom ( S ) - F A has t h e ( S , S ) -c o n f i g u r a t i o n . The CD spec t r um o f t h i s c r y s t a l , as shown i n F i g . 5 . 8 , i s i n t h e m i r r o r image o f t h a t o f ( R , R ) - V I I wh i c h i s p r e p a r e d f rom ( R ) - F A . I t may be no ted by c ompa r i ng F i g . 5 .6 w i t h F i g . 5.8 t h a t t h e CD p a t t e r n o f ( R , S ) - V i s s i m i l a r t o t h a t o f ( S . S ) - V I I r a t h e r t h an ( R . R ) - V I I . I t seems t h a t p l a n a r c h i r a l i t y p l a y s an i m p o r t a n t r o l e i n d e t e r m i n i n g t he s i g n s o f A e v a l u e s . A l t h o u g h t h e r e s u l t s a r e r e p r o d u c i b l e , i t i s no t c e r t a i n a t t h i s s t a g e whe the r t h i s unexpe c t ed d i a s t e r e o m e r (R ,R ) o r ( S , S ) i s t r u e l y a the rmodynamic p r o d u c t o r t h e one p r e f e r e n t i a l l y i s o l a t e d d u r i n g t h e work up wh i c h i n v o l v e d c h r o m a t o g r a p h i c s e p a r a t i o n and r e c r y s t a l 1 i z a t i o n o f t h e d i a s t e r e o m e r i c m i x t u r e . 5.2 CATIONIC RHODIUM(I) COMPLEXES OF FERROCENYLPHOSPHINES 5 .2 .1 A c h i r a l Complexes (A) S y n t h e s e s The h y d r o g e n a t i o n c a t a l y s t p r e c u r s o r s V I I I - X I o f t h e t y p e [ R h ( P - P ) ( N B D ) ] C 1 0 4 ( P -P = I - I V ) were p r epa r ed u s i n g w e l l - e s t a b l i s h e d p r o c e -du re s [ 32e ] as d e s c r i b e d i n e q u a t i o n ( 5 . 3 ) . 130 [Rh(NBD)Cl]2 + P-P • [Rh(P-P)(NBD)]d04 ( 5 . 3 ) VIII IX X XI P-P = I III IV The t y p i c a l p r o c edu r e was t o d i s s o l v e [ R h ( N B D ) C l ] 2 and a 2 a, 2 .5 m o l a r e x c e s s o f l i g a n d i n benzene , and add to t h i s s o l u t i o n a 2 ^ 2 .5 m o l a r e x c e s s o f NaClO^ d i s s o l v e d i n THF. As a p r e c a u t i o n bo th s o l v e n t s were degassed b e f o r e t he r e a c t a n t s were m i x e d . These c o m p l e x e s , e x c e p t f o r X I , s e p a r a t e d as o r ange p r e c i p i t a t e s f rom the r e a c t i o n m i x t u r e a f t e r a s h o r t p e r i o d o f s t i r r i n g (5 min - l h ) a t room t e m p e r a t u r e . For the p r e p a -r a t i o n o f X I , t h e r e a c t i o n m i x t u r e was s t i r r e d f o r 1 - 2 days to g i v e a r e d d i s h brown s o l i d a f t e r t he s o l v e n t s had been removed . A l l t h e s e c a t a l y s t p r e c u r s o r s were o b t a i n e d i n h i g h y i e l d s (70 - 80%) as deep r ed c r y s t a l s on c r y s t a l l i z a t i o n f rom C H ^ C l 2 / c y c l o h e x a n e s o l u t i o n . A l t h o u g h t h e y a r e g e n e r a l l y s t a b l e i n bo th t h e s o l i d and s o l u t i o n , t h e complex XI was found to undergo s l i g h t d e c o m p o s i t i o n i n CHC l^ . (B) C h a r a c t e r i z a t i o n The f o r m u l a t i o n o f t h e s e p r o d u c t s i s c o n f i r m e d by t h e a n a l y t i c a l r e s u l t s ( T a b l e 5 .5 ) and t h e i r NMR s p e c t r a ( T a b l e 5.5 and F i g . 5 . 9 ) . More d i r e c t c o n f i r m a t i o n comes f rom t he c r y s t a l s t r u c t u r e s shown i n F i g s . 5 .10 -5 . 1 3 . 131 T a b l e 5 . 5 : A n a l y t i c a l and p h y s i c a l da ta f o r t h e a c h i r a l R h ( I ) comp lexes [ R h ( p - p ) ( N B D ) ] C 1 0 4 . mp°,C Found Ca lcd(%) Compound P -P (decomp,) C H C H V I I I I 192-194 57 .16 4 . 22 58 . 00 4 . 24 IX I I 182-183 54 .24 5 .28 54 .93 5.44 X I I I 179-180 53 . 70 5 .25 5 4 . 9 3 5.44 XI IV 153-155 51 .46 6 . 70 51 .55 6 .77 T a b l e 5 . 6 : ] H and 3 1 P { 1 H } NMR da t a f o r t h e a c h i r a l comp lexes V I I I - X I 3 » b . Compound - C g H 5 ( C 5 H 4 - ) F e - CMe 3 NBD 0 1 P V I I I 7 . 5 - 8 . 0 (m,20) 4 . 4 ( bm , 8 ) - 4 . 4 ( bm ,4 ) 4.1 (bm,2) 1 .5 (bm,2) (MeOH) 1 4 . 8 4 ( d ) ( J R h = 1 6 1 ) 32 . 45 IX 7 . 78 (m ,6 ) 8 . 78 (m ,4 ) 4 . 3 ( bm ,6 ) 4 . 05 (bm,2 ) 1 . l ( d , 1 8 ) ( J p H = 1 4 ) 5 . 7 (bm,2 ) 5 .2 (bm,2) 4 . 0 (bm,2 ) 1 .8 (bm,2) (MeOH) 3 2 . 5 1 ( d ) ( J R h = 1 5 5 ) 24 . 74 X 7 . 65 (m ,5 ) 7 . 85 (m ,5 ) 4 . 62 (bm ,2 ) 4 . 48 (bm,2 ) 4 . 35 (bm ,2 ) 4 . 20 (bm,2 ) 1 . 5 ( d , 1 8 ) ( J pH -12 ) 5 .7 (bm,4) 3 . 9 (bm,2 ) 1 . 7 (bm,2 ) XI 4 . 6 ( bm ,4 ) 4 . 55 (bm ,4 ) 1 . 6 ( d , 3 6 ) ( J p H = 1 2 ) 5 . 3 (bm ,4 ) 3 . 1 (bm,2 ) 2 . 8 (bm,2 ) ( C H 2 C 1 2 ) 4 5 . 8 1 ( d ) ( J R h = 1 4 8 ) 18 . 73 H NMR s p e c t r a were o b t a i n e d i n CDCl^ e x c e p t X ( a c e t o n e - d ) . C o u p l i n g c o n s t a n t s a r e i n H z , and c o o r d i n a t i o n c h em i c a l s h i f t (A ) i n ppm: d = d o u b l e t , m = m u l t i p l e t , bm=broad m u l t i p l e t . 132 -PPh„ Fe )Rh(KBD)' -PPhj VIII J I I I 1 t I 60 40 20 0 ^ r P B ^ P h Fe \ * I ( N B D ] * IX I I I I I I 1 60 40 20 0 Fe \ l h ( N B D J 4 " XI I I I I I I I 60 40 20 0 F i g . 5 . 9 : 3 2 . 3 MHz P{ H) NMR s p e c t r a o f t h e a c h i r a l comp lexes V I I I , IX and X I . 133 The H NMR spec t rum o f each o f t h e s e comp lexes c o n s i s t s o f r e s o n a n c e peaks f rom t h e c o o r d i n a t e d phosph i ne l i g a n d and f rom t h e NBD l i g a n d . The NMR p a t t e r n o f each l i g a n d i s v i r t u a l l y i d e n t i c a l w i t h t h a t o f t h e c o r r e s p o n d i n g f r e e l i g a n d e x c e p t f o r some l i n e b r o aden i n g a c compan i ed by changes i n c h em i c a l s h i f t s . T h u s , f o r e xamp l e , r e s onan c e s i n t h e pheny l r e g i o n and the f e r r o c e n y l r e g i o n a r e more s p r e a d ou t i n t h e c omp l e x , i n d i c a t i n g t h a t t h e i r r e l a t i v e o r i e n t a t i o n s and p o s i t i o n s a r e more f i x e d upon c o m p l e x a t i o n , However , l i t t l e change i n t h e c h em i c a l s h i f t and c o u p l i n g c o n s t a n t i s o b s e r v e d i n t h e - P ( C M e 3 ) r e g i o n . The NBD l i g a n d i n t h e comp lexes V I I I , X , and XI shows t h r e e b road m u l t i p l e t s , one f o r t h e b r i d g i n g c a r b on p r o t o n s ( -CHg- ) i n t h e r e g i o n 6 = 1 .5 - 2 . 8 ppm, the o t h e r f o r t h e p a i r o f p r o t o n s (-CH ) i n t h e r e g i o n <5 = 3 .1 - 4 . 1 ppm, and a n o t h e r f o r t h e f o u r o l e f i n i c p r o t o n s i n t h e r e g i o n 6 = 4 . 4 - 5.7 ppm. As e x p e c t e d , t h e complex IX e x h i b i t s two b road m u l t i p l e t s o f equa l i n t e n s i t i e s a t 5.2 and 5.7 ppm due t o t h e two d i a s t e r e o -t o p i c p a i r o f e q u i v a l e n t p r o t on s (No te t he l i g a n d i s a r a c - i s o m e r as shown i n F i g , 5 . 1 1 ) . Ye t i t i s not c l e a r why t h e complex X c o n t a i n i n g t h e unsymmetri-^ c a l l y s u b s t i t u t e d C p r i n g s shows o n l y one b road m u l t i p l e t f o r t h e o l e f i n i c p r o t on s r a t h e r t h an two . The 3 1 P { 1 H } NMR s p e c t r a o f V I I , IX and XI show the e x p e c t e d d o u b l e t s a t 1 4 . 8 4 , 32 ,51 and 45 .81 ppm, r e s p e c t i v e l y , due t o t h e c o u p l i n g o f t h e c h e l a t i n g phosph i ne s w i t h t h e Rh atom ( Rh , s p i n = 1 / 2 ) . C o u p l i n g c o n s t a n t s r ange f rom 148 to 161 H z . I t can be no t ed t h a t t h e magn i t ude o f c o o r d i n a t i o n c h em i c a l s h i f t (A) d e c r e a s e s as t he pheny l g roup i s s u b s t i t u t e d by t h e t e r t - b u t y l g roup ( T a b l e 5 . 6 ) . Thus i t i s i n t e r e s t i n g t o no t e t h a t t h e A v a l u e f o r t h e complex IX 134 i s a p p r o x i m a t e l y t h e a r i t h m e t i c mean o f t h o s e f o r t h e comp lexes V I I I and X I . The c r y s t a l s t r u c t u r e s o f t h e s e comp lexes a r e shown i n F i g s . 5 .10 -5 . 1 3 . The Rh atom i n each complex may be d e s c r i b e d , v e r y c r u d e l y , as l y i n g i n a s qua r e p l a n a r e n v i r o n m e n t , a s sum ing t h a t two d oub l e bonds o f t h e NBD l i g a n d o c cupy s i n g l e c o o r d i n a t i o n s i t e s . The comp lexes IX and XI have an a p p r o x i m a t e C 2 a x i s a l o n g t h e Rh-Fe d i r e c t i o n , whereas V I I I and X have a symmetry p l a n e . The p a r e n t f e r r o c e n e m o i e t y adop t s t h e s t a g g e r e d c o n f o r m a -t i o n i n a l l c a s e s . A number o f o t h e r i n t e r e s t i n g f e a t u r e s can a l s o be made. The most p r om inen t o f t h e s e f e a t u r e s i n c l u d e , as summar i zed i n T a b l e 5 . 7 , a v e r y w ide P-Rh-P a n g l e , e x c e p t i o n a l l y l o n g R h - P ( B u t , B u t ) d i s t a n c e s , and a l a r g e t w i s t a n g l e due to t h e s t e r i c c r owd i ng caused by t h e b u l k y t e r t - b u t y l g r o u p s . In g e n e r a l , as pheny l g roups a r e r e p l a c e d w i t h t h e more s t e r i c a l l y demanding t e r t - b u t y l g r o u p s , l o n g e r Rh-P bond , h i g h e r P-Rh-P a n g l e s , and h i g h e r t w i s t a n g l e s a r e o b t a i n e d . The b i t e a n g l e (<MP (1 ) -Rh -MP (2 ) ) i n a l l compounds a r e e s s e n t i a l l y c o n s t a n t due t o t h e r i g i d i t y o f t h e NBD l i g a n d . 5 . 2 . 2 C h i r a l Complexes (A) S y n t h e s e s The f o l l o w i n g c h i r a l r h o d i u m ( I ) comp lexes were p r e p a r e d u s i n g t h e same p r o c e d u r e d e s c r i b e d f o r t h e p r e p a r a t i o n o f t h e a c h i r a l comp lexes ( e q u a t i o n 5 . 3 ) . 135 F i g . 5 . 1 0 : The c r y s t a l s t r u c t u r e o f t h e Rh ( I ) complex V I I I [ 1 2 3 ] . 136 F i g . 5 . 1 1 : The c r y s t a l s t r u c t u r e o f t h e Rh ( I ) complex IX [ 1 2 3 ] , F i g . 5 . 1 2 : The c r y s t a l s t r u c t u r e o f t h e Rh ( I ) complex o f X [ 1 2 3 ] , 138 F i g . 5 . 1 3 : The c r y s t a l s t r u c t u r e o f t h e Rh ( I ) complex XI [ 1 0 2 d ] . 139 T a b l e 5 . 7 : Summary o f i m p o r t a n t bond pa r ame te r s f o r t h e a c h i r a l Rh ( I ) comp lexes V I I I - X I [123 ] . V I I I IX X XI R h - P ( B u t , B u t ) a - - 2.391 2 .466 2 .458 R h - P ( B u t , P h ) - 2 .416 2 .388 -Rh -P ( Ph , Ph ) 2 .335 2 .317 - 2 .356 -P-Rh-P 96 . 82 98 . 60 100 . 25 103.71 M P ( l ) - R h - M P ( 2 ) b 68 . 2 69.1 68 . 0 6 8 . 4 T w i s t a n g l e c 5.9 20 . 0 1 4 . 4 3 6 . 8 a The n o t a t i o n s P ( B u t , B u t ) o r P ( B u t , P h ) e t c . , d e f i n e t h e s u b s t i t u e n t s , o t h e r t h an c y c l o p e n t a d i e n y l , wh i c h a r e j o i n e d t o p h o s p h o r u s . b MP(1) and MP(2) a r e t h e m i d d l e p o i n t s o f t h e two o l e f i n i c C a t oms . T w i s t a n g l e i s d e f i n e d as t h e a n g l e between t h e Rh , P ( l ) , P(2) p l a n e and t h e Rh , M P ( 1 ) , MP(2) p l a n e . 140 [Rh(P*N)(NBD)]ci04 xii ; P - N = v XIII ; = VI XIV ; = VII F o l l o w i n g t he u sua l wo r k -up p r o c e d u r e s , a l l p r o d u c t s were i s o l a t e d as o r ange s o l i d s wh i c h were r e c r y s t a l l i z e d f rom e t h a n o l t o g i v e deep r e d c r y s t a l s i n mode ra te y i e l d s (50 - 55%). A l t h o u g h t h e y a r e g e n e r a l l y s t a b l e i n bo th t h e s o l i d and s o l u t i o n , s l i g h t d e c o m p o s i t i o n was o b s e r v e d i n CHC1^. (B) C h a r a c t e r i z a t i o n The a n a l y t i c a l r e s u l t s ( T a b l e 5.8) and 3 1 P { 1 H } NMR da t a ( T a b l e 5.9) c o n f i r m t h e f o r m u l a t i o n o f t h e p r e v i o u s l y known r h o d i u m ( I ) complex X I I and t h e new c h i r a l comp lexes X I I I and X IV . Here t h e c o n f i g u r a t i o n s a r e t h o s e o f the c h i r a l l i g a n d s V ~ V I I . The CD s p e c t r a o f ( R . S ) - X I I and ( S , S ) - / ( R , R ) - X I V a r e shown i n F i g s . 5 . 14 (A ) and 5 . 1 4 ( B ) , r e s p e c t i v e l y . I t i s i n t e r e s t i n g t o no t e t h a t t h e s i g n s o f s p e c i f i c r o t a t i o n and Ae o f t he f r e e l i g a n d s a r e r e v e r s e d upon c o m p l e x a t i o n ( c f . T a b l e s 5 .3 and 5.8; F i g s . 5 . 6 , 5.8 and 5 . 1 4 ) . In F i g . 5 .14 (A ) i s a l s o shown t he CD spec t rum o f t h e b i s p h o s p h i n e complex X I I I p r e pa r ed f rom ( S ) - F A . By e x a m i n i n g t h e two s p e c t r a i n F i g . 5 . 14 (A ) i t can be c o n c l u d e d t h a t t h e c o n f i g u r a t i o n o f t h e f r e e b i s p h o s p h i n e 1 i g and VI i n t h e complex X I I I i s ( S , R ) 141 T ab l e 5 . 8 : A n a l y t i c a l and p h y s i c a l d a t a f o r t h e c h i r a l comp lexes [ R h ( P - N ) ( N B D ) ] C 1 0 4 a . [ o ] D Found(X) Caldd(%) Compound mp,°C ( c 0 . 5 , C H C l 3 ) C H N C H N ( S . R ) - X I I - - 7 2 . 3 50 .17 6 .24 1 .97 5 0 . 1 2 . 6 .19 2 .02 ( R . S ) - X I I +71 .9 ( S . R ) - X I I I 121-123 - 2 9 5 , 5 2 52 .17 7 .45 1 .63 52 .90 7 .27 1 .67 ( R . S ) - X I I I +297.21 ( S . S ) - X I V 147-149 +169.39 54 .12 7 .86 1 .19 54.91 7 .93 1 .42 ( R , R ) - X I V - 1 7 0 . 8 2 T a b l e 5 . 9 : 3 1 P { 1 H } NMR da t a f o r t h e c h i r a l R h ( I ) comp lexes a ' b . Compound 31. ( S . R ) - X I I ( S . R ) - X I I I ( S . S ) - X I V (CDC1 3 ) 3 4 . 0 ( b d , J R h = 1 5 4 ) (CDCI3) 3 6 . 4 6 ( b d , J R h = 1 5 4 ) 2 5 . 8 7 ( b s ) ( C D 2 C 1 2 ) 3 8 . 0 2 ( d , J R h = 1 5 2 . 6 ) 2 7 . 8 8 ( s ) 2 5 . 3 8 ( s ) 3 The c o n f i g u r a t i o n s ( R , S ) o r ( S , R ) e t c . , a r e t h o s e o f t h e c h i r a l l i g a n d s V - V I I k C o u p l i n g c o n s t a n t s a r e i n Hz :bd=broad d o u b l e t , bs=broad s i n g l e t , s = s i n g l e t . \ 142 350 450 550 F i g . 5 . 1 4 : (A) CD s p e c t r a o f ( R . S ) - X I I and ( S . R ) - X I I I . (B) CD s p e c t r a o f ( R , R ) - and ( S , S ) - X I V . 143 as e x p e c t e d . T h i s c o n f i g u r a t i o n i s t h a t o f t h e e x p e c t e d m a j o r p r o d u c t when ( S ) - F A i s used ( t h e c o n f i g u r a t i o n o f t h e l i g a n d s V and V I I i s w e l l e s t a b l i s h e d ) . 31 1 The P{ H} NMR s p e c t r a ( F i g . 5 .15) i n d i c a t e t h a t a l l t h e s e comp lexes use N and P atoms t o form t h e rhod ium comp l e x . The c o o r d i n a t e d pho sph i n e i n t h e s e comp lexes X I I - XIV i s t he one n e i g h b o r i n g t h e -CH(Me)NMe 2 g r oups as i s known f o r [ R h ( P P F A ) ( N B D ) ] + ( F i g . 5 . 1 6 ) . T h i s can be e s t a b l i s h e d by com-31 p a r i n g t h e P s p e c t r a o f t h e s e comp lexes w i t h t h o s e o f t h e f r e e l i g a n d s V - V I I . Name ly , t h e most s h i e l d e d peak ( F i g . 5 .5) due t o t h e phospho rus i n t he f i r s t r i n g d i s a p p e a r s and i s r e p l a c e d by a d o u b l e t w i t h g r e a t e r c hem i c a l s h i f t upon c o m p l e x a t i o n ( F i g . 5 . 1 5 ) . T h e r e f o r e t h e d o u b l e t can be a s s i g n e d t o t h e pho sph i n e i n t h e f i r s t C p r i n g . O the r pho sph i ne s i g n a l s a r e o n l y s l i g h t l y a f f e c t e d by c o m p l e x a t i o n . The c o o r d i n a t e d p h o s p h i n e , i n a l l c a s e s , a ppea r s a s a d o u b l e t ( D M , D g and D j ) . The - P ( C M e 3 ) 2 g r oup i n t h e second C p r i n g appea r s as s i n g l e t w i t h l owe r c h em i c a l s h i f t : Sg and S y / S j f o r X I I I and X I V , r e s p e c t i v e l y . 31 The most s t r i k i n g d i f f e r e n c e i n t h e P NMR p a t t e r n between t h e t r i s -pho sph i ne complex XIV and t h e mono- o r b i s p h o s p h i n e complex ( X I I o r X I I I ) i s t h a t t h e r e s o n a n c e s i g n a l s f o r t h e l a t t e r two a r e q u i t e b r o a d , whereas t h e fo rmer g i v e s s h a r p s i g n a l s ( F i g . 5 . 1 5 ) . The b r o a d e n i n g i n d i c a t e s t h e e x i s t e n c e o f c o n f o rme r s i n t e r c o n v e r t i n g s l o w l y on t h e NMR t ime s c a l e . The s h a r p s i g n a l s f o r t h e f o rme r ( X IV ) i n d i c a t e t h a t t h i s complex adop t s o n l y one c o n f o r m a t i o n on t h e NMR t ime s c a l e . I t i s l i k e l y t h a t t h e s i x -membered c h e l a t e r i n g c o n f o r m a t i o n o f t h i s complex (X IV ) i s f i x e d because o f s t e r i c c r o w d i n g . B e f o r e p r e s e n t i n g f u r t h e r e v i d e n c e f o r t h e s e c o n f o r m a t i o n a l e f f e c t s , i t i s 144 F i g . 5 . 1 5 : 32 . 3 MHz 3 1 P { 1 H } NMR s p e c t r a o f t h e c h i r a l R h ( I ) comp lexes (S , R ) - X I I ( S . R ) - X I I I , and ( S . S ) - X I V . 145 u s e f u l t o d i s c u s s p o s s i b l e c o n f o r m a t i o n a l exchange p r o c e s s e s . The comp lexes X I I - X I V c o n t a i n a s i x -membered c h e l a t e r i n g whose c o n f o r m a t i o n s h o u l d be ana l o gou s t o t h a t o f c y c l o h e x e n e : t h a t i s , a h a l f -c h a i r (The Cp r i n g a c t s as t h e e q u i v a l e n t o f a C=C b o n d ) . In F i g . 5 .16 i s shown t h e c r y s t a l s t r u c t u r e o f t h e known r h o d i u m ( I ) c omp l e x , [ R h ( S , R - P P F A ) -( N B D ) ] P F g - [ 102b ] . F i g . 5 . 1 6 : The c r y s t a l s t r u c t u r e o f [ Rh ( . S 5 R -PPFA ) (NBD ) ] P F g [ 1 0 2 b ] ; PPFA = ( P h 2 P ) F A . The s i x -membered r i n g , as a n t i c i p a t e d , has a h a l f - c h a i r c o n f o r m a t i o n . I t s h o u l d be no t ed t h a t , i n t h e h a l f - c h a i r f o r m , c y c l o h e x e n e i s a c h i r a l m o l e -c u l e w i t h p l a n a r c h i r a l i t y ( o r c h i r a l c o n f o r m a t i o n ) , bu t c h a i r i n v e r s i o n r e a d i l y c o n v e r t s one e n a n t i o m e r t o t h e o t h e r ( v i d e i n f r a ) [ 1 2 4 ] . 146 ! A p p a r e n t l y t h e ana l ogous s i t u a t i o n i s found i n t h e mono- and b i s p h o s p h i n e comp lexes X I I and X I I I , a l t h o u g h t h e ene rgy b a r r i e r s t o i n v e r s i o n appea r t o be h i g h e r t han t h a t r e q u i r e d i n c y c l o h e x e n e ( c a . 6 K c a l / m o l ) [ 1 2 4 ] . The t r i s p h o s p h i n e c o m p l e x XIV seems t o have much h i g h e r ene r g y b a r r i e r t h an 31 X I I and X I I I , as s ugge s t e d by t h e P NMR r e s u l t s . On t h e b a s i s o f t h e c r y s t a l s t r u c t u r e i n F i g . 5 . 1 5 , a model can be b u i l t t o examine t h e p o s s i b l e i n v e r s i o n p r o c e s s i n comp lexes ( S , R ) - X I I and - X I I I . T h i s i s shown i n F i g . 5 . 17 (A ) t o g e t h e r w i t h the p r e f e r r e d c h e l a t e r i n g c o n f o r m a t i o n o f t h e t r i s p h o s p h i n e c o m p l e x ( S , S ) - X I V ( F i g . 5 . 1 7 B ) . Some o f t h e o b s e r v a t i o n s t h a t can be made on e x am i n i ng t h e model a r e : ( i ) t h e two c on f o rme r s A and B ( F i g . 5 .17A) a r e d i a s t e r e o t o p i c by e x t e r n a l c o m p a r i s o n , t hu s t h e s o l u t i o n c o n t a i n i n g t h e mono- o r b i s p h o s p h i n e c o m p l e x s h o u l d , i n p r i n c i p l e , g i v e two s e t s o f p r o t o n NMR s i g n a l s , each s e t r e p r e s e n t i n g a d i a s t e r e o m e r i c c on f o rme r A o r B; ( i i ) t h e r e l a t i v e s t a b i l i t i e s o f t h e two c on f o rme r s A and B s h o u l d be g r e a t l y a f f e c t e d by t h e p r e s en ce o r absence o f p h o s p h i n e ( s ) i n t h e second C p r i n g ; ( i i i ) t h e p r e f e r r e d c o n f o r m a t i o n C o f t h e t r i s p h o s p h i n e complex ( S , S ) - X I V ( F i g . 5 .17B) i s v i r t u a l l y e n a n t i o m e r i c w i t h t h e c o n f o r m a t i o n B o f t h e b i s p h o s p h i n e complex ( S , R ) - X I I I e x c e p t f o r some s l i g h t changes i n t he r e l a t i v e o r i e n t a t i o n s o f t h e s i x -membered r i n g s u b s t i t u e n t s , p a r t i c u l a r l y t h e k 147 ( S , R ) - XII : R = H ( S . R ) - XIII ; = PBu' F i g . 5 . 1 7 : (A) The p roposed s i x -membered r i n g c o n f o r m a t i o n s A and B i n v o l v e d i n t h e r i n g i n t e r c o n v e r s i o n p r o c e s s o f bo th ( S . R ) - X I I and - X I I I . (B) The p r e f e r r e d r i n g c o n f o r m a t i o n o f ( S . S ) - X I V . 148 me thy l on t h e a s ymme t r i c c e n t e r . The NMR s p e c t r a o f t h e s e t h r e e comp lexes a r e shown i n F i g s . 5 . 1 8 -5 . 2 0 . These p r o v i d e t h e da t a r e l e v a n t t o t h e r i n g i n v e r s i o n p r o c e s s ( T a b l e 5 .10 ) and p r o v i d e some s u p p o r t i n g e v i d e n c e s f o r t h e a f o r e m e n t i o n e d c o n f o r m a t i o n a l e f f e c t s . The r e s u l t s r e l a t i n g t o t h e i n d i v i d u a l comp lexes a r e as f o l l o w s . (a) Monophosph ine Complex ( S . R ) - X I I . Bo th c o n f o r m e r s A and B a r e e q u a l l y p o p u l a t e d (Ke = [ B ] / [ A ] ^ 1 ) , and t h e r a t i o does not change much o v e r t h e who le t e m p e r a t u r e r ange s t u d i e d (35° - -60°C) , In F i g s . 5 . 18 (A ) and (B) i s shown t h e v a r i a b l e t e m p e r a t u r e NMR spec t r um o f t h e monophosph ine comp lex ( S , R ) - X I I , A t 3 5 °C , a l l peaks 31 a r e q u i t e b road as s ugge s t e d by t h e P NMR r e s u l t s . The l i n e s b eg i n t o s ha r pen on c o d l i n g ( 0 ° C ) , show ing c l e a r l y two s e t s o f s i g n a l s o f equa l i n -t e n s i t i e s . Thus i f a s e t o f s i g n a l s w i t h s u b s c r i p t A i s t e m p o r a r i l y a s s i g n e d t o t h e c on f o rme r A , t h i s c on f o rme r shows , as summar i zed i n T a b l e 5 . 1 0 , a s i n g l e t F^  due t o t h e u n s u b s t i t u t e d Cp r i n g p r o t on s ( -CgH^) , a p a i r o f s i n g l e t s N^( l ) and N^C2) f o r t h e -NMe^ g r o u p , a b road q u a r t e t C/\ f o r t h e me t h i n e p r o t o n (-CHMe) c o u p l e d w i t h t h e v i c i n a l me thy l g r o u p , a d o u b l e t M^ f o r t h e me thy l (-CHMe) g roup c o u p l e d w i t h t h e me t h i n e p r o t o n , and a p a i r o f d o u b l e t s P/\( 1) and P/\(2) f o r t h e - P t C M e ^ g r o u p . The c on f o rme r B a l s o shows a s e t o f c o r r e s p o n d i n g s i g n a l s d e s i g n a t e d w i t h s u b s c r i p t B. The d o u b l e t M^ can be seen more c l e a r l y on f u r t h e r c o o l i n g ( -40°C) ( F i g . 5 . 1 8 B ) . The NMR p a t t e r n o f o t h e r p r o t o n s such as t h o s e o f t h e d i s u b s t i t u t e d Cp r i n g (-C^H^) and o f t h e NBD l i g a n d i s no t so e a s i l y d i s c u s s e d , y e t a s i m i l a r s i t u a t i o n appea r s t o e x i s t . 149 T a b l e 5 . 1 0 : Some NMR da ta r e l e v a n t t o t h e c o n f o r m a t i o n a l e f f e c t s o b s e r v e d i n t h e c h i r a l R h ( I ) comp lexes X I I - X I V a , b . Compl ex Con fo rmer •CHMe •CMe -NMe, - P ( C M e 3 ) . ( S . R ) - X I I ( S , R ) - X I I I ( S . S ) - X I V 3 . 20 ( bq ) ( J H H = 8 ) 4 . 60 ( J H H = 7 ) 4.61 ( J H H = 8 ) 1 . 63 (d ) ( J H H = 8 ) 1 . 53 (d ) ( J H H = 8 ) 1 .55 3 . 4 0 ( s ) 2 . 2 8 ( s ) 2 . 2 4 ( s ) 1 . 7 8 ( s ) 3 . 22 (bq ) 1 . 67 (d ) 3 . 4 2 ( s ) ( J H H = 7 ) 2 . 3 2 ( s ) 2 . 2 6 ( s ) 1 . 8 0 ( s ) 2 . 9 7 ( q ) 2 . 7 5 ( d ) 1 . 9 0 ( s ) ( J H H = 8 ) 2 . 4 2 ( s ) 1 . 76 (d 1 . 00 (d 1 . 52 (d 1 . 35 (d 1 , 00 (d 1 .09(d 1 .24 (d 1 . 80 (d 1 .07 (d 1 . 22 (d 1 , 37 (d 1 . 58 (d 1 ,59 (d 1 . 41 (d 1 . 40 (d 1 . 09 (d 0 .91 (d J p H = 1 2 ) J p H = 1 2 ) J p H = 1 2 ) J p H - 1 6 ) J p H = 1 6 ) J p H = 1 2 ) J P H = 1 2 > J p H = 1 6 ) J p H = 1 2 ) J p H = 1 2 ) J P H = 1 2 ) J P H = 1 2 ) J P H = 1 6 > J p H = 1 2 ) J P H = 1 2 > J p H = 1 6 ) J p H = 1 2 ) a 1 H NMR s p e c t r a were o b t a i n e d i n CD2CI 2 C o u p l i n g c o n s t a n t s a r e i n Hz : bq=broad q u a r t , d = d o u b l e t , s = s i n g l e t , q=qua r t . Chemica l s h i f t s a r e based on t h e homonuc l ea r (H-H) d e c o u p l i n g e x p e r i m e n t s 150 151 5 4 3 2 1 F i g . 5 . 18 (B ) : ' . V a r i a b l e t e m p e r a t u r e 1 H NMR (400MHz) spec t rum o f (S , R ) - X I I i n C D 0 C 1 0 . 152 35°C 5 4 3 2 1 F i g . 5 . 1 9 ( A ) : V a r i a b l e t e m p e r a t u r e ] H NMR (400MHz) spec t rum o f ( S . R ) - X I I I i n C D 0 C 1 0 . 153 5 4 3 2 1 F i g . 5 . 1 9 ( B ) : V a r i a b l e t e m p e r a t u r e 1 H NMR (400MHz) spec t rum o f (S , R ) - X I 11 154 155 A l t h o u g h t h e a s s i g nmen t o f t h e peaks F and P t o t h e c o r r e s p o n d i n g c o n -f o rme r i s p u r e l y a r b i t r a r y , , t h e o t h e r peaks C, M, and N can be s p e c i f i c a l l y a s s i g n e d w i t h o u t much d i f f i c u l t y . F i r s t l y , homonuc lea r (H-H) d e c o u p l i n g e x p e r i m e n t s r e v e a l t h a t t h e p a i r o f peaks C f t and M^ be l ong t o one s e t o f s i g n a l s , and t h e o t h e r p a i r o f peaks Cg and Mg t o t h e o t h e r s e t . S e c o n d l y , a s s i g nmen t o f t h e peak Cg t o t h e c o n f o r m e r B can be made based on t h e " r i n g c u r r e n t " e f f e c t . T h i s r e s o n a n c e appea r s i n an u n u s u a l l y l o w e r s h i e l d i n g r e g i o n t han wou ld be e x p e c t e d f rom a m e t h i n e p r o t o n i n c on f o rme r B wh i c h i s a l m o s t c o p l a n a r w i t h t h e C p r i n g ( F i g . 5 . 1 7 A ) . Thus t h i s p r o t o n can be t r e a t e d as an a r o m a t i c r i n g p r o t o n r a t h e r t han an a c e t y l e n i c p r o t o n . I t t hen f o l l o w s t h a t t h e p a i r o f peaks and M^ a r e a s s o c i a t e d wi th c on f o rme r A . The a s s i g n m e n t o f a p a i r o f s i n g l e t s N ( l ) and N(2) f o r t h e -NMe 2 g roup i s based on the i n t e n s i t y r a t i o ( I ( N A ) / I ( N g ) £ 1) and t h e ] H NMR p a t t e r n o f t h e c o r r e s p o n d i n g c on f o rme r s o f t h e b i s p h o s p h i n e complex ( S . R ) - X I I I . H e r e , as d e s c r i b e d n e x t , t h e p a i r o f peaks N ( l ) and N(2) f o r t h e -NMe 2 g roup i n t h e c on f o rme r A appea r i n a l owe r s h i e l d i n g r e g i o n t han t h o s e i n c o n f o r m e r B (See T a b l e 5.10 and F i g . 5 . 1 9 ) . (b) B i s p h o s p h i n e Complex ( S . R ) - X I I I . The c on f o rme r B seems to be p r e f e r r e d o v e r c on f o rme r A . The r a t i o o f B t o A i s a p p r o x i m a t e l y 2:1 (Ke £ 2) a t 35°C , and changes to 3:1 (Ke £ 3) on c o o l i n g (< -40°C ) as seen i n F i g s . 5 . 19 (A ) and ( B ) . The ^H NMR p a t t e r n o f each c on f o rme r o f t h i s c o m p l e x , ( S , R ) - X I I I , i s q u i t e s i m i l a r t o t h a t o f t h e c o r r e s p o n d i n g con f o rme r o f t h e monophosph ine complex ( S , R ) - X I I . A s s i gnmen t o f each s e t o f s i g n a l s ( T a b l e 5 .10) i s based 156 on s i m i l a r r e s u l t s . T h u s , a t 0 °C , t h e ma j o r c on f o rme r B shows a p a i r o f s i n g l e t s N g ( l ) and Ng(2) f o r t h e -NMe 2 g r o u p , f o u r d o u b l e t s P g O ) , P g ( 2 ) » P B ( 3 ) , and Pg (4 ) f o r t h e two -PtMeg)^, g r o u p s , a d o u b l e t Mg f o r t h e me thy l (-CHMe) on t h e a s ymme t r i c c e n t e r , and a q u a r t e t Cg f o r t h e me t h i n e p r o t o n (-CH_Me) as checked by homonuc lea r (H-H) d e c o u p l i n g a t 4 . 60 and 1.55 ppm. The m i no r c on f o rme r A a l s o e x h i b i t s a weaker s e t o f s i g n a l s l a b e l e d w i t h s u b s c r i p t A . Here a g a i n t h e NMR p a t t e r n o f t h e p r o t o n s o f t h e f e r r o c e n e m o i e t y and o f t h e NBD l i g a n d i s l e s s e a s y t o i n t e r p r e t . I n c r e a s e d s t e r i c b u l k i n t h e se cond r i n g may cause t h e c on f o rme r B t o be more s t a b l e t han t h e c on f o rme r A . One p o s s i b l e e x p l a n a t i o n wou ld be t h a t t h e c on f o rme r B can r edu ce t h e r i n g s t r a i n by d i s p o s i n g t h e two me thy l o f t h e -NMe 2 g roup away f rom t he me thy l (-CHMe) o f t h e a s ymme t r i c c e n t e r . In t h e c on f o rme r A , t h o s e two me thy l g roups a r e bo th i n an e q u a t o r i a l p o s i t i o n and one t e r t - b u t y l g roup i n an a x i a l p o s i t i o n ( F i g . 5 . 1 7 A ) . ( c ) T r i s p h o s p h i n e Complex ( S , S ) - X I V On l y one c o n f o r m a t i o n C i s seen i n t h e case o f t he t r i s p h o s p K i n e complex ( S . S ) - X I V . Thus t h e N M R p a t t e r n ( F i g . 5 .20) o f t h i s complex c o n s i s t s o f o n l y one p a i r o f s i n g l e t s N Q ( 1 ) and N^(2) f o r t he -NMe 2 g r o u p , a b road q u a r t e t C Q f o r t h e m e t h i n e p r o t o n , and f i v e d o u b l e t s 1) , P^(2 ) , P Q ( 3 ) , P Q ( 4 ) , and P Q ( 5 ) f o r t h e t h r e e - P ( C M e 3 ) 2 g roups ( a l t h o u g h s i x d o u b l e t s a r e e x p e c t e d ) . The un i q u e f e a t u r e o f t h i s c o n f o r m a t i o n i s t h a t t h e s i n g l e t M Q f o r t h e -CMe g roup has a g r e a t e r c h em i c a l s h i f t t h an i s f ound f o r t h e c on f o rme r B. T h i s s h i f t ( d e s h i e l d i n g ) can a l s o be e x p l a i n e d i n te rms o f t h e " r i n g c u r r e n t " e f f e c t s i n c e t h e me thy l g roup i n t h e c on f o rme r C ( F i g . 5 .17B) i s now c o p l a n a r w i t h t h e C p r i n g . The me t h i n e p r o t o n i s a x i a l l y 157 •d i sposed i n t h i s c o n f o r m a t i o n . The Cp r i n g p r o t o n s show a complex p a t t e r n i n t h e r ange 4 . 3 t o 4 . 6 ppm. A l t h o u g h a g a i n t h e NMR s i g n a l s f o r t h e NBD l i g a n d c a n n o t f u l l y be a s s i g n e d , two broad s i n g l e t s a r e seen a t 3 .92 and 3 .95 ppm f o r t h e -Cf^ g roup and two broad s i n g l e t s a t 4 . 9 5 and 4.81 ppm f o r two o l e f i n i c p r o t o n s . The o t h e r two o l e f i n i c p r o t o n s a r e p r o b a b l y o b s c u r ed by t he Cp r i n g r e s o n a n c e s , The r e m a i n i n g two p r o t o n s f o r t h e -CH g roups seem t o appea r i n t h e r ange 1.48 t o 1.51 ppm. A l l - i n - a l l t h e spec t r um i s much as wou ld be a n t i c i p a t e d f o r a r i g i d sys tem as d e s c r i b e d a b o v e . The r e m a i n i n g a s p e c t s o f t h e s e c o n f o r m a t i o n a l e f f e c t s w i l l be d i s c u s s e d f u r t h e r i n c o n n e c t i o n w i t h a s ymme t r i c h y d r o g e n a t i o n c a t a l y z e d by t h e s e com-p l e x e s ( c f . s e c t i o n 6 . 2 . 2 ) . 5.3 OTHER METAL COMPLEXES OF FERROCENYLPHOSPHINES 5 .3 .1 P a l l a d i u m Complexes P a l l a d i u m comp lexes o f t h e t y p e [ P d ( P - P ) C I 2 ] ( P -P = I - IV) were r e a d i l y p r e pa r ed i n h i g h y i e l d s (> 70%) by t h e d i r e c t r e a c t i o n o f I^PdCl^ o r Pd(NBD)CIg w l t n a s l i g h t m o l a r e x c e s s o f t h e a p p r o p r i a t e l i g a n d as shown i n e q u a t i o n ( 5 . 4 ) . Pd(NBD)CI2(orK2PdCI4) + P-P Pd(P-P)CI2 ( 5 . 4 ) XV ; P-P = 1 XVI ; = II XVII ; = III XVIII = IV 158 T a b l e 5 , 1 1 : A n a l y t i c a l r e s u l t s and m e l t i n g p o i n t s o f P d ( P - P ) C l 2 mp,°C Found{%) Ca lcd(%) Compound P - P (decomp,) C H C H XV I ]63 . -165 55.41 3 .92 55 ,79 3 .83 XVI I I 210. -212 51 .98 4 . 9 6 52 . 08 5.21 XVII a I I I 192. -195 45 , 80 4 . 6 0 45 . 88 4 . 59 X V I I I IV 208. -210 47.31 6 .88 47 .91 7 .00 C a l c u l a t e d v a l u e i s based on P d ( p - p ) - C H C l 3* T a b l e 5 , 1 2 : ] H NMR da ta f o r P d ( P - P ) C l 2 a ' b Compound XV XVI XVI I X V I I I " C 6 H 5 7 .43 (bm,6 ) 8 . 00 (m ,4 ) 7 , 68 (m ,6 ) 8 . 45 (m ,4 ) 7 , 3 2 - 7 . 5 2 ( m , 6 ) 7 . 8 8 - 8 . 2 3 ( m , 4 ) ( C 5 H 4 - ) 2 F e 4 . 1 8 ( b s , 4 ) 4 . 4 0 ( b s , 4 ) 4 . 0 - 4 . 4 ( m , 8 ) 3 . 8 5 ( N ,2) 4 . 32 ( bm ,2 ) 4.61 (bm,2) 4 , 90 (bm ,2 ) 4 . 6 5 ( b s , 4 ) 4 . 5 0 ( b s , 4 ) •CMe-1 . 5 3 ( d , 1 8 ) ( J p H = 1 6 ) 1 , 6 3 ( d , 1 8 ) ( J p H = 1 5 ) 1 , 6 5 ( d , 3 6 ) ( J p H = 1 4 ) A l l s p e c t r a were o b t a i n e d i n CDC13. C o u p l i n g c o n s t a n t s a r e i n Hz : bm=broad m u l t i p l e t , bs=broad s i n g l e t , d = d o u b l e t , m = m u l t i p l e t . 159 F i g . 5.21 : The s t e r e o v i e w o f t h e c r y s t a l s t r u c t u r e o f P d ( P - P ) C l 2 : P - P = the l i g a n d I [ 125 , 1 2 6 ] . 160 The t y p i c a l p r o c e d u r e was to d i s s o l v e t h e p a l l a d i u m s t a r t i n g m a t e r i a l i n a minimum amount o f C ^ C ^ o r CHC1 ^ and s l o w l y add t h e c o r r e s p o n d i n g l i g a n d d i s s o l v e d i n d i e t h y l e t h e r . A l l comp lexes s e p a r a t e d as a i r - s t a b l e , o range p r e c i p i t a t e s a f t e r s t i r r i n g 2 ^ 3h a t room t e m p e r a t u r e . The i s o l a t e d s o l i d was t h en r e c r y s t a l l i z e d f rom an a p p r o p r i a t e s o l v e n t o r s o l v e n t m i x t u r e as d e s c r i b e d i n t he e x p e r i m e n t a l s e c t i o n . The a n a l y t i c a l r e s u l t s and "'H NMR da ta a r e summar ized i n T a b l e s 5.11 and 5 . 1 2 , The "'H NMR spe c t r um o f each o f t h e s e comp lexes i s v i r t u a l l y i d e n t i c a l w i t h t h a t o f t h e c o r r e s p o n d i n g f r e e l i g a n d ( c f . T a b l e 5 .2) e x c ep t f o r s l i g h t l i n e b r o aden i ng accompan ied by a c h e m i c a l s h i f t c h a n g e . F i g . 5.21 shows t h e c r y s t a l s t r u c t u r e o f XV [126] wh i c h has a s t a g g e r e d r i n g c on f o rma -t i o n and a s qua r e p l a n a r geomet ry a round t h e Pd me ta l . 5 . 3 . 2 . N i c k e l Complexes N i c k e l comp lexes o f t h e t y p e N i ( P - P ) X 2 ( P - P = I , I V ; X = CI , B r ) were p r e p a r e d by s i m p l e r e f l u x o f an e t h a n o l i c s o l u t i o n o f t h e l i g a n d and N i C ^ - S ^ O ( o r anhyd rous N i B r ? ) as shown i n e q u a t i o n ( 5 . 5 ) . NiCI2-6H2o( or NiBr2) P-P/EtOH Ni(P-P)x2 ( 5 . 5 ) reflux XIX X X X X I X X I I P-P= I = I = IV = IV x = a = Br = CI = Br 161 T a b l e 5 . 1 3 : M e l t i n g p o i n t s and a n a l y t i c a l da ta f o r t h e N i ( I I ) comp lexes N i ( P - P ) X 2 . mp,°C Found(%) Ca1cd(%) Compound P-P X (decomp.) C H C H XIX I CI 283-285 59.81 4 . 0 5 59 . 70 4 . 0 9 XX I Br 296 -298 52 .76 3 .72 52 .82 3 .62 XXI IV CI 185-187 51 .24 6 .95 51 . 69 7 .29 XXI I IV B r 202-204 45 . 5 3 6 .53 4 5 . 0 6 6 .35 162 F i g . 5 . 2 2 : The s t e r e o v i e w o f t h e c r y s t a l s t r u c t u r e o f N i ( P - P ) B r 2 : P-P = t h e l i g a n d I [ 1 2 6 ] . 163 A l l p r o d u c t s were i s o l a t e d as da r k g r e e n , a i r - s t a b l e , p a r amagne t i c c r y s t a l s . The a n a l y t i c a l r e s u l t s and m e l t i n g p o i n t s a r e l i s t e d i n T a b l e 5 . 1 3 . The c r y s t a l s t r u c t u r e o f t he p r e v i o u s l y known compound XX was d e t e r m i n e d d u r i n g p r e s e n t s t u d i e s [ 1 2 6 ] , and shown i n F i g . 5 . 2 2 . I t shows t h a t t h i s p a r amagne t i c complex (and p r o b a b l y o t h e r s XXI and XX I I ) r e s emb l ed t h e h i g h -s p i n , p s e u d o t e t r a h e d r a l b i s ( t r i p h e n y l p h o s p h i n e ) n i c k e l ( I I ) h a l i d e s [127] r a t h e r t han t h e d i a m a g n e t i c (D I PHOS )N i X 2 compounds [ 1 2 8 ] . The g r e a t e r s t e r i c r e q u i r e m e n t and l a r g e r b i t e s i z e o f t h e l i g a n d s I and IV a r e p r o b a b l y r e s p o n s i b l e f o r t h i s p r e f e r r e d g eome t r y . 5 . 3 . 3 I r o n Complexes I r o n c o m p l e x e s , F e ( B P P F ) ( C 0 ) 3 ( X X I I I ) and F e 2 ( B P P F ) ( C 0 ) g ( X X I V ) , were p r epa r ed by t h e r e a c t i o n o f t h e l i g a n d I (BPPF) w i t h e x c e s s Fe (C0 )g o r F e ? ( C 0 ) q as shown i n e q u a t i o n ( 5 . 6 ) . Fe2(CO)^/THF, UV Fe(BPPF)(C0)3 (75%) XXIII Fe 2(BPPF)(C0) 8 (B2%) XXIV Fe ( 5 . 6 ) Fe2(BPPFXco)8 (62%) ( B P P F ) Fe(co)5 /THF.UV Fe(BPPF)(co)3 (<5^) 164 Bo th compounds were o b t a i n e d as o range c r y s t a l l i n e s o l i d s a f t e r t h e u sua l wo r k -up p r o c e d u r e s . The t r i c a r b o n y l complex X X I I I was o b t a i n e d i n a h i g h y i e l d (75%) by UV i r r a d i a t i o n o f a THF s o l u t i o n o f t h e l i g a n d and a two m o l a r e x c e s s o f Fe2( .C0)g . As shown i n e q u a t i o n ( 5 . 6 ) , t h e same r e a c t i o n m i x t u r e under d i f f e r e n t r e a c t i o n c o n d i t i o n s , i . e . s t i r r i n g a t room t e m p e r a -t u r e f o r 2 h , y i e l d s p r e d o m i n a n t l y t h e complex XXIV i n wh i c h each -PPh^ group f u n c t i o n s as a monoden ta te l i g a n d to t h e - F e ( C 0 ) 4 m o i e t y . T h i s compound was a l s o p r e p a r e d i n a h i gh y i e l d {62%) by UV i r r a d i a t i o n o f a benzene s o l u t i o n o f t h e l i g a n d and a 10 m o l a r e x c e s s o f F e ( . C 0 ) 5 . I t i s wo r t h n o t i n g t h a t t he d i s u b s t i t u t e d i r o n c a r b o n y l , ( C 0 D ) F e ( C 0 ) 3 f a i l e d t o g i v e the e x p e c t e d p r o du c t X X I I I f rom t h e r e a c t i o n w i t h t h e l i g a n d I i n benzene ( o r THF) a t room t e m p e r a t u r e . The s t a r t i n g m a t e r i a l (CODjFetCO)^ was q u a n t i t a t i v e l y r e c o v e r e d a f t e r s t i r r i n g o v e r n i g h t . The r e a c t i o n o f t h e l i g a n d I w i t h Fe^CCO)-^ y i e l d e d a ' p u r p l e o i l as a s i n g l e p r o d u c t w h i c h r e a d i l y decomposes i n s o l u t i o n . The a n a l y t i c a l r e s u l t s and s p e c t r o s c o p i c da t a f o r t h e comp lexes X X I I I and XXIV a r e l i s t e d i n T a b l e 5 . 1 4 . Mass s p e c t r a o f X X I I I and XXIV show t h e p a r e n t peaks a t m/e 694 and 8 9 0 , r e s p e c t i v e l y i n a d d i t i o n t o o t h e r peaks a s s o c i a t e d w i t h t h e l o s s o f up to t h r e e and e i g h t c a r b o n y l g r o u p s , r e s p e c t i -v e l y . The s t r u c t u r e o f t h e F e ( C 0 ) 3 d e r i v a t i v e i s e x pe c t e d t o be a t r i g o n a l b i p y r a m i d wh i c h may be f l u x i o n a l i n s o l u t i o n [ 1 2 9 ] , In t h e s o l i d s t a t e t h e l i g a n d s h o u l d be bound a t a x i a l and e q u a t o r i a l s i t e s . I n a c c o r d w i t h t h i s t h e t r i c a r b o n y l complex X X I I I shows t h r e e s t r o n g v (C0 ) bands a t 1990 , 1920 and 1892 cm~^ . The p a t t e r n o f t h e bands i s s i m i l a r t o t h a t f ound f o r o t h e r 165 T ab l e 5 . 1 4 : A n a l y t i c a l and s p e c t r o s c o p i c da t a f o r t h e i r o n comp lexes X X I I I and XXIV . Compound Found(%) C H Calcd(.%) C H v ( C 0 ) ( c m _ 1 ) Mass s p e c t r a ( m / e ) X X I I I 63 . 35 4 . 14 64.01 4 . 03 1990 ( v s ) 694 (M + ) 1920 ( s ) 666 (M + - C0 ) 1892 ( v s ) 638 (M + - 2C0 ) 610 (M + - 3C0 ) 554(BPPF) XXIV 56 .00 4 . 35 56 .66 3 . 85 2040 ( v s ) 890 (M + ) 1978 ( v s ) 862 (M + - C0 ) 1948 ( s ) 834 (M + - 2C0 ) 1 930 ( s ) 8 06 (M + - 3C0 ) 4 . 750 (M + - 5C0 ) 722 (M + - 6C0 ) 694 (M + - 7C0 ) 666 (M + - 8C0 ) 554(BPPF) 3 BPPF = t he l i g a n d I , v s=ve r y s t r o n g , s = s t r o n g . 166 ( L - L ) F e ( C 0 ) 3 d e r i v a t i v e s ( L - L = DIPHOS, D IARS ) . For e x amp l e , Fe(DIPHOS) ( C 0 ) 3 [129 ] shows t h e v (C0 ) bands a t 1 997 , 1933 and 1913 c m - 1 . I n t h e c a s e o f F e ( D I A R S ) ( C 0 ) 3 (DIARS = 1 , 2 - b i s ( d i m e t h y l a r s i n o ) b e n z e n e ) [ 1 2 9 ] , t h e v (C0 ) bands appea r a t 1 9 9 1 , 1 9 2 3 , and 1909 c m " 1 . However i t can be no t ed t h a t t h e v (C0 ) bands f o r t h e complex X X I I I appea r i n t h e l owe r f r e q u e n c y r e g i o n than t h o s e f o r t h e DIPHOS and DIARS d e r i v a t i v e s . S i m i l a r o b s e r v a t i o n r e l a t i n g t o a d rop i n CO s t r e t c h i n g f r e q u e n c y can a l s o be made f o r t h e m o n o s u b s t i t u t e d i r o n c a r b o n y l ; c o m p l e x e s . T h u s , f o r e xamp l e , t h e complex XXIV shows t h e v (C0 ) bands a t 2040 , 1978 , 1948 and 1930 c m " 1 , w h i l e F e 2 ( C 0 ) g ( D I P H 0 S ) [129] g i v e s t h e v ( C 0 ) bands a t 2058 , 1984 , 1948 and 1941 c m " 1 , and F e 2 ( C 0 ) g ( D I A R S ) a t 2 0 5 3 , 1981 and 1944 c m - 1 . These d i f f e r e n c e s may be e x p l a i n e d i n te rms o f t h e enhanced Tr - d ona t i n g a b i l i t y o f t h e l i g a n d I , as compared w i t h t h a t o f DIPHOS and DIARS. The unknown compound o b t a i n e d f rom t h e r e a c t i o n o f I w i t h F e 3 ( C 0 ) - | 2 appea r s t o have a t l e a s t 7 v (C0 ) b and s , one o f wh i c h appea r s a t 1770 c m " 1 , i n d i c a t i n g t h e p r e s en c e o f a t l e a s t one b r i d g i n g CO g roup i n t h e m o l e c u l e . However , t h e u n s t a b i l i t y and i n s o l u b i l i t y o f t h i s p r o d u c t p r e v en t ed f u r t h e r c h a r a c t e r i z a t i o n . 5 . 3 . 4 Group VI Me ta l Complexes The r e a c t i o n o f I w i t h M(C0)g (M=Cr,Mo) f o l l o w e d by c h r o m a t o g r a p h i c s e p a r a t i o n a l l o w e d t h e i s o l a t i o n o f t h e p r e v i o u s l y known compounds M ( B P F F ) ( C 0 ) 4 (XXV, M=Cr; XXV I , M=Mo) [118 ] as y e l l o w , a i r - s t a b l e c r y s t a l s . The a n a l y t i c a l r e s u l t s and s p e c t r o s c o p i c d a t a f o r XXV and XXVI a r e l i s t e d i n T ab l e 5 . 1 5 . 167 T ab l e 5 . 1 5 : A n a l y t i c a l and s p e c t r o s c o p i c da ta f o r t h e Gp VI me t a l comp lexes M ( P - P ) ( C 0 ) 4 a ' b . Compound M Found(%) Ca lcd(%) , C H C H ] H NMR (CDC1 3 ) v ( C 0 ) ( c m - 1 ) XXC Cr 63 .37 4 . 08 63 .50 3 .90 7 .52 (bm,4 ) 1 995 ( v s ) 7 .29 (bm,6 ) 1925 ( sh ) 4 . 2 3 ( b t , 4 ) 1890 ( s ) 4 . 2 1 ( b t , 4 ) 1870 ( s ) XXVI Mo 59 . 63 3 .66 59 . 86 3 .67 7 .64 (bm,4 ) 7 . 42 (bm,6 ) 4 . 3 7 ( b t , 4 ) 4 . 3 0 ( b t , 4 ) C o u p l i n g c o n s t a n t s a r e i n H z : bm=broad m u l t i p l e t , b t=broad d o u b l e t . IR i n t e n s i t y : v s=ve r y s t r o n g , s h = s h o u l d e r , s = s t r o n g . 168 F i g . 5 . 2 3 : The s t e r e o v i e w o f t h e c r y s t a l s t r u c t u r e o f M o ( P - P . ) ( C 0 ) 4 : P - P = t he l i g a n d I [ 1 2 6 ] . 169 These c o m p l e x e s , l i k e o t h e r s ( V I I I - X X I V ) , can be v i ewed as [ 3 ] -f e r r o c e n o p h a n e s . In p r i n c i p l e , t h e r e a r e two l i m i t i n g s t r u c t u r e s imposed upon t h e s e compounds by t h e s t e r i c r e q u i r e m e n t o f t h e atoms i n t h e b r i d g e . F i g . 5 . 2 4 : Mechanism f o r [ 3 ] - f e r r o c e n o p h a n e b r i d g e r e v e r s a l . They a r e 5.24a (= 5 . 2 4 a ' ) and 5 . 2 4b , i n bo th o f wh i c h an ABCD NMR p a t t e r n wou ld be e x p e c t e d f o r t h e C p r i n g p r o t o n s . However , v a r i a b l e t e m p e r a t u r e NMR s t u d i e s [130] i n d i c a t e . t h a t t h i s t y p e o f m o l e c u l e s i s f l u x i o n a l and unde rgoes r i n g i n v e r s i o n ( F i g . 5 .24) w i t h t h e e c l i p s e d c o n f o r m a t i o n ( 5 . 2 4 a ) be i ng p r e f e r r e d f o r most [ 3 ] - f e r r o c e n o p h a n e s (M = Group IV and VI atoms) . One e x c e p t i o n i s [ ( C ^ H ^ S ^ CgHg)^] where t h e C p r i n g s a r e b e l i e v e d to be s t a g g e r e d as i n 5 . 2 4 b . The b a r r i e r t o c h a i r to c h a i r r e v e r s a l can be h i g h as i n t h e S , b r i d g e (AG^ = 80 . 4 K j / m o l ) [130] i n a l i m i t i n g ABCD p a t t e r n f o r 5 . 2 4 b 170 / / t h e CgH^ g roup a t amb i en t t e m p e r a t u r e . In o t h e r c a s e s e . g . w i t h ( - C H 2 ) 2 S (AG^ = 34 . 6 k J /mo l ) [ 130 ] o r ( - S )GeMe 2 b r i d g e s t h e l i m i t i n g NMR s p e c t r a a r e o b t a i n e d o n l y on s t r o n g c o o l i n g ( c a . -100°C) [ 1 3 0 ] -The ] H NMR (400 MHz) s p e c t r a o f XXV and XXVI e x h i b i t t h e c h a r a c t e r i s t i c p a i r o f t r i p l e t s o f a f l u x i o n a l [ 3 ] - f e r r o c e n o p h a n e f o r t h e Cp r i n g p r o t on s [ 1 2 6 ] . On c o o l i n g t h e s o l u t i o n s t o -85°C o n l y a s l i g h t b r o a d e n i n g was o b s e r v e d i n t h e s p e c t r u m . S i n c e t h e Mo complex XXVI a dop t s t h e s t a g g e r e d r i n g c o n f o r m a t i o n as shown i n F i g . 5 .23 t h e b a r r i e r s t o r i n g r e v e r s a l must be l o w . 171 CHAPTER 6 RHODIUM COMPLEXES OF FERROCENYLPHOSPHINES AS HYDROGENATION CATALYSTS 6.1 CATALYST PRECURSORS In t h e p r e v i o u s c h a p t e r , t h e p r e p a r a t i o n and some p r o p e r t i e s o f t h e c a t i o n i c Rh(.I) comp lexes V I I I - XIV have been d e s c r i b e d . F o r m a l l y t h e y be l ong t o t h e g roup o f d i ( t e r t i a r y p h o s p h i n e ) R h ( I ) t y p e c a t a l y s t s ( c f . s e c t i o n 1 . 4 . 2 c ) , s i n c e i n t h e s e comp lexes e i t h e r bo th P atoms ( V I I I - X I ) o r N and P atoms ( X I I - XIV) a r e bound t o t h e rhod ium a t oms . The g e n e r a l c a t a l y t i c p r o p e r t i e s and s e v e r a l o f t h e n o t a b l e advan t age s o f t h i s g roup o f c a t a l y s t s have been d e s c r i b e d i n C h a p t e r s 1 and 2 . In p a r t i c u l a r ( i ) t h e y can be r e a d i l y p r e p a r e d , h a n d l e d , and a w ide v a r i e t y o f pho sph i ne l i g a n d s can be i n t r o d u c e d ; ( i i ) t h e y r e a c t r e a d i l y w i t h r>2 (1 a tm , 25°C) i n s o l u t i o n t o g e n e r a t e a c t i v e c a t a l y s t s , t h e d i e n e l i g a n d b e i n g q u a n t i t a t i v e l y r e d u c e d ; ( i i i ) t h e y do no t c a t a l y z e t h e i s o m e -r i z a t i o n o f t e r m i n a l o l e f i n s ; ( i v ) t h e y g i v e more c o n s i s t e n t and h i g h e r o p t i c a l y i e l d s ( L - L = c h i r a l l i g a n d s ) t h an t h e i r monoden ta te phosph i ne c o u n t e r p a r t s . As w i l l be d i s c u s s e d l a t e r , t h e p r e s e n t s y s tems V I I I - XIV e x h i b i t s e v e r a l o t h e r p o s s i b l y u n i q u e p r o p e r t i e s , one o f t h e n o t a b l e be i ng t h e f o r m a t i o n o f me t a l h y d r i d e s by r e a c t i o n w i t h H 2 i n t h e absence o f t h e s u b s t r a t e . 172 6 .2 CATALYTIC HYDROGENATION OF OLEFINS 6 . 2 . 1 Nonasymmet r i c H y d r o g e n a t i o n The r e s u l t s o f a number o f h y d r o g e n a t i o n r e a c t i o n s u s i n g t h e a c h i r a l c a t a l y s t p r e c u r s o r s V I I I - XI a r e l i s t e d i n T a b l e 6 . 1 . Under t h e s t a n d a r d c o n d i t i o n ( 30 °C , 1 atm H g ) , a l l r e a c t i o n s e x c ep t one a r e s t o i c h i o m e t r i c as checked by NMR and gas c h r oma t og r aphy . They a l l p r o ceed v e r y q u i c k l y , and most go to c o m p l e t i o n w i t h i n 15 m i n . A l l t he gas u p - t a k e p l o t s have a s h o r t i n d u c t i o n p e r i o d (T- ) f o l l o w e d by an a l m o s t l i n e a r r e g i o n c o r r e s p o n d i n g w i t h t h e maximum r a t e . Ra tes o f t h e o r d e r o f 7 x 10~ 6 m o l / s e c a r e abou t t h e maximum t h a t can be measured u s i n g t he manual g a s - u p t a k e s y s t e m . "However, t h e r e can be no doub t abou t t h e t r e n d s . T h u s , w i t h t h e e x c e p t i o n o f t h e r e d u c t i o n o f a c y l a m i n o - c i n n a m i c and - a c r y l i c a c i d s , t h e r a t e s o b t a i n e d w i t h t h e a l k y l p h o s p h i n e comp lexes ( IX - X I ) a r e g r e a t e r than t h o s e o b t a i n e d w i t h t h e t e t r a p h e n y l d e r i v a t i v e V I I I . These t r e n d s a r e r e v e r s e d i n t h e r e d u c t i o n o f somewhat s t e r i c a l l y demanding s u b s t r a t e s such as a c y l a m i n o - c i n n a m i c and - a c r y l i c a c i d s ( t h e f i r s t two s u b s t r a t e s i n T a b l e 6 . 1 ) . When t he c ompa r i s on i s made among the t h r e e a l k y l p h o s p h i n e comp lexes IX - X I , t h e r a t e s a r e g e n e r a l l y t h e s l o w e s t w i t h t h e s t e r i c a l l y most crowded complex X I . The re i s l i t t l e t o choose between IX and X so t h e e l e c t r o n i c and s t e r i c e f f e c t s seem t o be b a l a n c e d . I t i s p o s s i b l e t o a c c o u n t f o r some o f t h e g r o s s d i f f e r e n c e s d e s c r i b e d above on t he b a s i s o f t h e e l e c t r o n i c and s t e r i c e f f e c t s o f t h e l i g a n d s emp l o yed . I f c a t a l y s i s by t h e s e s y s t e m s , l i k e o t h e r d i ( t e r t i a r y p h o s p h i n e ) -173 T ab l e 6 . 1 : H y d r o g e n a t i o n o f o l e f i n s c a t a l y z e d by t h e a c h i r a l R h ( I ) comp lexes [ R h ( P - P ) ( N B D ) ] C l 0 4 ( P - P = I - I V ) a . C a t a l y s t Max. R a t e , O l e f i n p r e c u r s o r S o l v e n t T . ,S i n * T ,s CO mol / s COOH C H 9 = C / NHCOMe V I I I IX EtOH II 8 8 60 95 5 . 9 x l 0 ~ 6 3 . 6 x l 0 " 6 X 23 780 2 . 1 x l 0 " 7 XI II 27 700 3 . 2 x l 0 " 7 XI MeOH 17 375 7 . 1 x 1 0 " 7 H COOH \ / c=c P h ^ N N H C 0 M e V I I I IX EtOH II 8 15 150 150 3 . 4 x l 0 " 6 2 . 2 x l 0 ' 6 X * 20 280 1 . O x l O " 6 XI n 30 1780 1 . 4 x 1 0 " 7 XI MeOH 18 680 2 . 9 x l 0 " 7 ^COOH CH n = C \ CH 2 C0 2 H V I I I V I I I IX X EtOH MeOH II II 8 8 8 7 180 125 75 62 1 . 8 x 1 0 " 6 2 . 8 x l 0 " 6 5 . 9 x 1 0 " 6 6 . 9 x l 0 ~ 6 XI EtOH 9 90 4 .1x1 0 " 6 XI MeOH 8 200 5 . 5 x l 0 " 6 Ph \ ^ M e H x COOH V I I I IX X EtOH II 25 30 780 950 0 5 . O x l O " 7 4 . 5 x l 0 ~ 7 XI 20 600 5 . 5 x l 0 " 7 T a b l e c on t ' d . . . 174 C a t a l y s t Max. R a t e , O l e f i n p r e c u r s o r So l v en t T i n > s T ,s CO * mol / s 1 -Octene V I I I MeOH 45 32 ,000 4 . 4 x l 0 - 8 IX II 5 60 6 . 8 x l 0 ~ 6 X it 7 200 6 . 2 x l 0 " 6 XI II 15 325 3 , 5 x l 0 " 6 Cyc l ohexene V I I I MeOH 50 35 ,000 3 . 7 x l 0 " 8 IX II 10 200 2.2x1 0 " 6 X 20 520 3 , 7 x l 0 " 6 XI II 15 740 1 .1x1 0 " 6 a [ S u b s t r a t e ] = 2 . 0 0 x 1 0 " M i n 10 mL o f s o l v e n t ; [ C a t a l y s t p r e c u r s o r ] = 2 . 0 0 x l 0 " 4 M ; p(H 2) = 1 a tm; t = 30°C ; = t i m e t o c omp l e t e 100% up t ake o f H 2 ; T . n = i n d u c t i o n p e r i o d b e f o r e m e a s u r a b l e H 2 u p t a k e ; Max . 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Thus w i t h s t e r i c a l l y undemanding s u b s t r a t e s , i n c l u d i n g t h o s e w h i c h o c cupy o n l y one c o o r d i n a t i o n s i t e , r a t e s o f r e a c t i o n s h o u l d be enhanced by t h e p r e s en c e o f e l e c t r o n d o n a t i n g t e r t - b u t y l g r o u p s , as i s d r a m a t i c a l l y shown i n t h e r e d u c t i o n o f 1 - o c t ene and c y c l o h e x e n e ( T a b l e 6 . 1 ) . These two s u b s t r a t e s a r e h y d r oge -na t ed a p p r o x i m a t e l y one hundred t imes f a s t e r u s i n g t h e a l k y l p h o s p h i n e comp lexes ( I X - X I ) t h a n u s i n g t h e t e t r a p h e n y l d r i v a t i v e ( V I I I ) . As i s u sua l [ 1 3 1 ] , t h e t e r m i n a l o l e f i n 1 - o c t ene i s r educed f a s t e r t han t h e i n t e r n a l o l e f i n c y c l o h e x e n e r e g a r d l e s s o f t h e c a t a l y s t s emp l o yed . The h y d r o g e n a t i o n o f o t h e r n o n - c h e l a t i n g o l e f i n s such as s t y r e n e and 1-hexene was a l s o s t u d i e d i n o r d e r t o examine t h e g e n e r a l i t y o f t h e s e t r e n d s i n r e a c t i o n r a t e s . W i t h i n t h e e x p e r i m e n t a l e r r o r , t h e r e a c t i o n r a t e s measured w i t h t h e a l k y l p h o s p h i n e comp lexes ( I X - X I ) were i n t h e same o r d e r (10~^ m o l / s e c ) as t h a t f o r t h e r e d u c t i o n o f 1 - o c t e n e , once a g a i n t h e a l k y l p h o s p h i n e comp lexes ( I X - X I ) b e i n g more e f f i c i e n t t h an t he t e t r a p h e n y l p h o s p h i n e complex ( V I I I ) w h i c h — -8 a f f o r d s r a t e s o f t h e o r d e r o f 10 " m o l / s e c . On t h e o t h e r h a n d , when o l e f i n s have t h e a b i l i t y t o c h e l a t e t o t h e meta l c e n t e r such as a c y l a m i n o - c i n n a m i c and - a c r y l i c a c i d s , t h e e l e c t r o n i c e f f e c t s seem t o be ou twe i ghed by the s t e r i c e f f e c t s , and the o v e r a l l r a t e s a r e f a s t e r w i t h t h e t e t r a p h e n y l d e r i v a t i v e ( V I I I ) t han w i t h t h e a l k y l p h o s p h i n e comp lexes ( I X - X I ) . Howeyer , i t i s d i f f i c u l t t o e x p l a i n t h e l a c k o f r e a c t i o n o f 176 ( E ) - a - m e t h y l c i n n a m i c a c i d . In c o n n e c t i o n w i t h t h e s e r a t e d i f f e r e n c e s , i t s h o u l d be men t i oned t h a t a l l t h e r a t e s a r e v e r y much f a s t e r u s i n g t h e s e c a t a l y s t s [ R h ( P - P ) ( N B D ) ] C 1 0 4 ( V I I I - X I ) t han u s i n g t h e r e l a t e d c a t a l y s t s [Rh (P -N ) ( .NBD) ]C10 4 ( X I I - XIV) ( c f . T a b l e s 6 .2 and 6 . 4 ) . Here a g a i n t h e p r e s en ce o f pheny l g roups (P -N = PPFA) r e s u l t s i n s l o w e r r e a c t i o n s ( T a b l e 6 . 4 ) . For e x a m p l e , i t a c o n i c a c i d i s o n l y 21% r edu ced i n 72h when P-N = PPFA, y e t i s 100% r educed i n 16h when P-N = V - V I I . The r a t e s a r e even f a s t e r as t h e numbers o f t e r t - b u t y l g roups a r e i n c r e a s e d ( T a b l e 6 . 4 ) . The e f f e c t o f t h e -HVie^ g r oup i n t h e s e c h i r a l l i g a n d s (P -N) seems t o be t o l owe r t h e e l e c t r o n d e n s i t y on t h e me ta l w i t h o u t e x e r t i n g much s t e r i c i n f l u e n c e . T h i s l e a d s to s l o w e r r a t e s w i t h PPFA -based c a t a l y s t b e i n g l e s s a c t i v e t h an t h o s e c o n t a i n i n g t h e -PBUp^ g r o u p ( s ) . F i n a l l y , T a b l e 6.1 shows t h a t r e a c t i o n r a t e s i n methano l a r e g r e a t e r t han i n e t h a n o l . T h i s i s p r o b a b l y due to t h e e a s i e r s o l u b i l i t y o f t h e c a t a l y s t p r e c u r s o r s i n methano l t h an i n e t h a n o l . 6 . 2 . 2 A s ymme t r i c H y d r o g e n a t i o n The r e s u l t s o f a s ymme t r i c h y d r o g e n a t i o n r e a c t i o n s u s i n g t h e new c h i r a l c a t a l y s t p r e c u r s o r s , ( S . R ) - X I I I ( f r om VI ) and ( S . S ) - X I V ( f r om V I I ) a r e l i s t e d i n T a b l e 6 . 2 . Here t h e c o n f i g u r a t i o n i s t h a t o f t h e f r e e c h i r a l l i g a n d s VI and V I I . A number o f i n t e r e s t i n g c o n c l u s i o n s can be drawn f rom t h e t a b l e as f o l l o w s . 177 Tab l e 6 . 2 : A s ymmet r i c h y d r o g e n a t i o n o f some o l e f i n i c a c i d s w i t h [ R h ( P - N ) ( N B D ) ] C 1 0 4 (P -N = VI and V I I ) a ' b . S u b s t r a t e c " " ^ ^ C o n f i g u r a t i o n i U D S t r a x e P r e c u r s o r 0 MeOH EtOH MeOH EtOH P h \ /NHCOMe ( s . R ) - X I I I 3.1 4 . 3 . 2 4 R / C = C \ ( S . S ) - X I V 4 .2 4 . 8 86 91 S YY COOH NHCOMe 'COOH / ( S . R ) - X I I I 2 .5 3 .2 14 31 R H 2 C = C \ ( S . S ) - X I V 3 .2 3 .6 82 95 S P hx / M e d ( S . R ) - X I I I 2 . 3 2 .7 51 51 S / C = C \ ( S . S ) - X I V 3 .0 3 .5 59 61 R H COOH / C 0 0 H . ( S . R ) - X I I I - 2 . 3 - 28 S C H 2 = C \ ( S . S ) - X I V 4 . 5 4 . 7 19 38 R CH 2C00H a A l l r e a c t i o n s a r e s t o i c h i o m e t r i c . [ S u b s t r a t e ] = 4 . 0 x 1 0 " M i n 10 mL o f s o l v e n t ; [ C a t a l y s t P r e c u r s o r ] = 4 . 0 x l O ' 4 M ; p ( H 2 ) = 1 a tm ; t = 30°C ; T ime = a p p r o x i m a t e t o t a l r e a c t i o n t i m e . b O p t i c a l y i e l d s a r e based on t h e r o t a t i o n o f t h e i s o l a t e d p r o d u c t s ( c f . s e c t i o n 4 . 3 ) . c The c o n f i g u r a t i o n s ( S , R ) and ( S , S ) a r e t h o s e o f t h e c h i r a l l i g a n d s VI and V I I , r e s p e c t i v e l y . T h i s i s r educed by H 2 / ( S , S ) - X I V t o g i v e t h e ( S ) - i s o m e r ( 2 8 « e . e . ) i n b e n z e n e ( r e a c t i o n t ime >10 h ) . 178 T a b l e 6 . 3 : A s ymme t r i c h y d r o g e n a t i o n o f amino a c i d p r e c u r s o r s w i t h Rh ( I ) comp lexes o f ( S , S ) - V I I and o t h e r r e p r e s e n t a t i v e d i ( t e r t i a r y N phosph i ne ) l i g a n d s a -Xe.e. S u b s t r a t e C h i r a l L i g a n d ( C o n f i g u r a t i o n ) R e f e r e n c e Ph NHCOMe / c = c x W COOH (R .R ) -D IPAMP (S ,S) -CHIRAPHOS (R)-PROPHOS 94 (S ) 89(R) 91 (S) 85 76a 76b (S.S)-SKEWPHOS 93(R) 76c ( S . R ) - BPPFA 93 (S ) 94 BPPM 91 (R) 90a ( R . R ) -D IOP 72(R) 88b ( S . S ) - V I I 91 (S ) T a b l e 6.2 NHCOMe H 0 C = C /  2 \ COOH (R ,R) -DIPAMP 90(S) 77b (S ,S) -CHIRAPHOS 92(R) 76a (R)-PROPHOS 90(S) 76b (S,S)-SKEWPHOS 98(R) 76c (R .R ) -D IOP 73(R) 88b ( S . S ) - V I I 95 (S ) T a b l e 6 .2 The s t r u c t u r e s o f t h e above c h i r a l l i g a n d s a r e f ound i n Chap t e r 2 . 179 T a b l e 6 . 4 : A symmet r i c h y d r o g e n a t i o n o f some o l e f i n s w i t h [Rh (P -N ) (NBD) ]C10 ( P -N .= V - V I I and PPFA ) . C a t a l y s t S u b s t r a t e P r e c u r s o r 3 T ime(h) %e. e . C o n f i g u r a t i o n R e f e r e n c e Ph NHCOMe >< H COOH ( S . R ) - P P F A ( S . R ) - X I I ( S . R ) - X I I I 24 16 4 .3 76 84 4 S R R 102C 102C T ab l e 6.2 ( S . S ) - X I V 4 . 8 91 S T ab l e 6.2 NHCOMe ( S . R ) - P P F A 18 49 S 102C C H 9 = C / COOH ( S . R ) - X I I ( S . R ) - X I I I 12 3 . 2 24 31 R R 102C T a b l e 6 .2 ( S . S ) - X I V 3 .6 95 S T a b l e 6 .2 ^.COOH b CH 9=C 2 \ CH 2 C0 2 H ( S . R ) - P P F A ( S . R ) - X I I ( S . R ) - X I I I ,72 16 2 .3 33 43 28 R S S 102C 102C T a b l e 6.2 ( S . S ) - X I V 4 . 7 38 R T a b l e 6 .2 The c o n f i g u r a t i o n s ( S , R ) and ( S , S ) a r e t h o s e o f t h e c h i r a l l i g a n d s , and ( S , R ) - P P F A r e p r e s e n t s t h e c h i r a l c a t a l y s t p r e c u r s o r [ R h ( S , R - P P F A ) ( N B D ) ] -c i o 4 . T h i s i s r e du ced 21% i n 72h i n t h e p r e s en ce o f ( S . R ) - P P F A . 180 (A) O p t i c a l Y i e l d s The most s i g n i f i c a n t f i n d i n g i s t h a t t h e t r i s p h o s p h i n e compl ex XIV i s a v e r y e f f i c i e n t c a t a l y s t p r e c u r s o r f o r t h e a s ymme t r i c h y d r o g e n a t i o n o f a c y l a m i n o - c i n n a m i c and - a c r y l i c a c i d s . The o p t i c a l y i e l d s a r e 91% e . e . and 95% e . e . , r e s p e c t i v e l y when the h y d r o g e n a t i o n i s c a r r i e d o u t i n E tOH. O p t i c a l y i e l d s a r e s l i g h t l y l owe r i n MeOH. These h i g h o p t i c a l y i e l d s a r e compa rab l e w i t h t h o s e o b t a i n e d w i t h o t h e r r e p r e s e n t a t i v e c h e l a t i n g d i ( t e r t i a r y a r y l -pho sph i ne ) d e r i v a t i v e s , as shown i n T a b l e 6 . 3 . These r e s u l t s a r e r ema r k ab l e c o n s i d e r i n g t h e f a c t t h a t t h e r e i s o n l y one r e p o r t [ 102 c ] o f o l e f i n r e d u c t i o n s c a t a l y z e d by Rh comp lexes o f a l k y l p h o s p h i n e s wh i c h l a c k t he s u p p o s e d l y n e c e s s a r y - P A r 2 donors ( c f . T a b l e 6 . 4 ) . A few r e p o r t s have been p u b l i s h e d d e s c r i b i n g t h e r e d u c t i o n o f o t h e r s u b s t r a t e s . Thus Kumada e t a l [109] showed t h a t a c l o s e l y r e l a t e d P-N l i g a n d , ( PMe 2 ) FA can be used to p r e p a r e an i n s i t u Rh ( I ) c a t a l y s t p r e c u r s o r f o r t h e h y d r o s i l a t i o n o f k e t ones '. The o p t i c a l y i e l d s a r e mode ra t e K 50%). Rhod ium( I ) comp lexes o f a l k y l -phosph i ne s o f t he t y p e [ R h { ( i P r ) 2 P ( C H 2 ) n P ( i P r ) 2 } ] C 1 0 4 (n = 3 ,4) a r e r e p o r t e d t o be e f f i c i e n t f o r h y d r o g e n a t i o n o f a number o f c a r b o n y l compounds, i n c l u d i n g a l d e h y d e s [ 1 3 2 a ] . Ruthen ium comp lexes o f t h e DI0P d e r i v a t i v e s [133 ] a r e a l s o r e p o r t e d t o c a t a l y z e t h e h y d r o g e n a t i o n o f c a r b o n y l compounds and o l e f i n i c a c i d s . These r e s u l t s a r e i n t r i g u i n g because t h e d i ( t e r t i a r y a r y l p h o s p h i n e ) -based c a t a l y s t s a r e known to be i n e f f i c i e n t f o r h y d r o g e n a t i o n o f t h e c a r b o n y l g r o u p . U s i ng t h e same c o m p l e x , ( S , S ) - X I V , as c a t a l y s t , o n l y mode ra t e t o low o p t i c a l y i e l d s a r e o b t a i n e d i n t h e h y d r o g e n a t i o n o f s u b s t r a t e s l a c k i n g t h e / 181 -NCOMe g roup such as ( E)-a - m e t h y l c i n n a m i c a c i d and i t a c o n i c a c i d ( T a b l e 6 . 2 ) . t h e s e r e s u l t s seem t o endo r se t h e g e n e r a l l y a c c e p t e d f a c t t h a t c h e l a t i o n o f t h e s u b s t r a t e t h r o u g h bo t h t h e o l e f i n i c d oub l e bond and t h e c a r b o n y l o f t h e -NCOMe g r o u p , f o r i n s t a n c e , i s i m p o r t a n t i n o b t a i n i n g h i g h o p t i c a l y i e l d s . However , i t i s n o t e w o r t h y t h a t m e t h y l c i n n a m i c a c i d i s u s u a l l y o n l y s l o w l y r educed u s i n g and Rh ( I ) t y p e c a t a l y s t s [ 5 5 , 6 3 , and T a b l e 6 . 1 ] , and o p t i c a l y i e l d s g r e a t e r t han 60% have r a r e l y been o b s e r v e d ; t h e b e s t to d a t e be i ng 61.4% u s i n g t h e l i g a n d MMPP [ 9 2 ] . In g e n e r a l h i g h e r o p t i c a l y i e l d s seem to be o b t a i n e d when t h e r e d u c t i o n i s c a r r i e d ou t i n E tOH , a l t h o u g h r e a c t i o n r a t e s a r e s l i g h t l y g r e a t e r i n MeOH t han EtOH. In c o n n e c t i o n w i t h t h e s e s o l v e n t e f f e c t s i t s h o u l d be men t i oned t h a t t h e y can be v e r y s i g n i f i c a n t and even r e v e r s a l o f t h e p r o d u c t c o n f i g u -r a t i o n can be o b s e r v e d on c h ang i n g t h e s o l v e n t [62 f 7 6 c ] . The same pheno-menon was o b s e r v e d i n t h e p r e s e n t i n v e s t i g a t i o n . Thus t h e h y d r o g e n a t i o n o f ( E)-a - m e t h y l c i n n a m i c a c i d c a t a l y z e d by t h e t r i s p h o s p h i n e complex ( S , S ) - X I V r e s u l t e d i n t h e p r o d u c t o f o p p o s i t e c o n f i g u r a t i o n (S) on c h ang i n g t h e s o l v e n t EtOH ( o r MeOH) f o r benzene ( T a b l e 6 . 2 ) . T h i s was accompan ied by a much s l o w e r r e a c t i o n r a t e (>10h) and l owe r o p t i c a l y i e l d (28% e . e . ) . O the r s u b s t r a t e s have no t been i n v e s t i g a t e d to d a t e . (B) Compa r a t i v e S t u d i e s : XIV vs X I I and X I I I A f u r t h e r s t r i k i n g f e a t u r e o f t h e r e s u l t s i n T a b l e 6 .2 i s t h a t t h e t r i s p h o s p h i n e comp lex ( S , S ) - X I V i s a more e f f e c t i v e c h i r a l c a t a l y s t t han t h e b i s p h o s p h i n e comp lex ( S , R ) - X I I and o t h e r monophosph ine d e r i v a t i v e s c o n t a i n i n g 182 ( P R 2 ) F A (R = Ph , Bu ) ( c f , T a b l e 6 . 4 ) . T h u s , f o r e xamp l e , h y d r o g e n a t i o n o f a c y l a m i n o - c i n n a m i c , - a c r y l i c a c i d s , and i t a c o n i c a c i d s r e s u l t s i n a w ide sp r ead o f o p t i c a l y i e l d s u s i n g t h e c a t a l y s t p r e c u r s o r s c o n t a i n i n g t h e P-N l i g a n d s , ( P R 2 ) n FA (n = 1 , 2 ; R = Ph , B u 1 ) ( c f , T a b l e s 6 .2 and 6 . 4 ) . A n o t h e r s t r i k i n g d i f f e r e n c e between t h e t r i s p h o s p h i n e comp lex ( S . S ) - X I V and t h e o t h e r two comp lexes ( S , R ) - X I I and - X I I I i s t h a t t h e f o rme r g i v e s hyd rogena t ed p r o d u c t s o f t h e o p p o s i t e a b s o l u t e c o n f i g u r a t i o n to t h o s e o b t a i n e d by t h e l a t t e r s . For e x amp l e , t h e h y d r o g e n a t i o n o f a c y l a m i n o c i n n a m i c a c i d u s i n g t h e ( S . R ) -mono , ( S . R ) - b i s , and ( S , S ) - t r i s p h o s p h i n e comp lexes ( X I I , X I I I , and XIV) r e s u l t e d i n ( R ) - , ( R ) - , and ( S ) - p h e n y l a l a n i n e r e s p e c t i v e l y a s t h e p r o d u c t . These r e s u l t s i n d i c a t e t h a t i n t h e same s o l v e n t p l a n a r c h i r a l i t y p l a y s an i m p o r t a n t r o l e i n d e t e r m i n i n g t h e c o n f i g u r a t i o n o f t h e h yd r ogena t ed p r o d u c t s . The f o l l o w i n g c o n s i d e r a t i o n s based on c o n -f o r m a t i o n a l e f f e c t s p r o v i d e a b a s i s f o r u n d e r s t a n d i n g t h e s e d i f f e r e n c e s i n o p t i c a l y i e l d s and p r o du c t c o n f i g u r a t i o n s . (C) C o n f o r m a t i o n a l E f f e c t s I t has been shown i n s e c t i o n 5 . 2 . 2 ( B ) t h a t t h e t r i s p h o s p h i n e complex ( S . S ) - X I V a d o p t s o n l y one c o n f o r m a t i o n C, whereas t h e o t h e r two comp lexes ( S , R ) - X I I and - X I I I show two con f o rme r s A and B i n s o l u t i o n . The K e ( = [ B ] / [ A ] ) v a l u e f o r ( S . R ) - X I I and - X I I I i s a p p r o x i m a t e l y 1 and 2 , r e s p e c t i v e l y , The mechanism o f h y d r o g e n a t i o n f o r t h e s e sys tems may a l s o be d e s c r i b e d by t h a t o u t l i n e d i n F i g . 2 .13 but because t h e two ends o f t h e P-N l i g a n d s a r e d i f f e r e n t t w i c e as many 4 - c o o r d i n a t e i n t e r m e d i a t e s need t o be 183 c o n s i d e r e d . Name ly , f o u r d i a s t e r e o m e r s f o r t h e c a t a l y s t - s u b s t r a t e a ddu c t [ R h ( P - N ) ( s u b s t r a t e ) ] + a r e p roduced f rom each c on f o rme r ( A , B , o r C ) , as shown i n F i g . 6 . 1 ( A ) . I f c a t a l y s i s p r o ceeds v i a a h y d r i d e mechan ism f i v e d i a s t e r e o m e r s o f [ R h ( P - N ) ( H ) 2 ] + can be formed f rom each c on f o rme r o f t h e t y p e [ R h ( P - N ) ( S ) 2 ] + , as shown i n F i g . 6 . 1 ( B ) . T h u s , i n o r d e r t o a c h i e v e h i g h o p t i c a l y i e l d s , c a t a l y s i s by t h e s e sys tems ( X I I - X I V ) , l i k e o t h e r c a t a l y s t s , r e q u i r e s m a x i m i z a t i o n o f t h e AAG^ v a l u e among v a r i o u s p o s s i b l e d i l a s t e r eome r s i n t h e r a t e - d e t e r m i n i n g s t e p ( c f . e q u a t i o n 2 . 5 ) . Then t h e h i g h o p t i c a l y i e l d s by t h e t r i s p h o s p h i n e complex ( S , S ) - X I V may be a s s o c i a t e d w i t h t h e s t r o n g c o n f o r m a t i o n a l p r e f e -r en ce o f t h e c h i r a l c h e l a t e r i n g as a rgued by B o s n i c h e t a l ( c f . S e c t i o n 2 . 3 . 3 A ) . The f a v o r e d c o n f o r m a t i o n C ( F i g . 5 . 7B) i s t h e same as shown i n F i g . 2 .14 f o r (S .S) -CHIRAPHOS and (S ,S)-SKEWPHOS . However t h e p r o d u c t c o n f i g u r a t i o n s a r e r e v e r s e d as seen i n T a b l e 6 . 3 . T h e r e f o r e t h e c o n f o r m a t i o n a l a rguments based e n t i r e l y on c h i r a l a r r a y s o f R g roups i n - P R 2 m o i e t i e s do not h o l d i n t h i s s y s tem ( X I V ) . Undoub t ed l y t h e b u l k y f e r r o c e n y l g roup e x e r t s some i n f l u e n c e ( l e t a l o n e t he k i n e t i c f a c t o r s ) . In t h e c a s e o f c a t a l y s i s by t h e mono- o r b i s p h o s p h i n e complex ( ( S , R ) -X I I o r - X I I I ) , t h e number o f t he d i a s t e r e o m e r s f o r [Rh( P-N) ( s ub s t r a t e ) ] " 1 " ( o r [ R h ( P - N ) ( H ) 2 ] + ) ( F i g . 6 . 1 ) w i l l be doub l ed due t o t h e p r e s en ce o f t h e two d i a s t e r e o m e r i c c o n f o rme r s A and B. Under t h i s c i r c u m s t a n c e e i t h e r c on f o rme r A o r B o f t h e NBD p r e c u r s o r ( X I I o r X I I I ) c a n , i n p r i n c i p l e , l e a d to a p a i r o f the. e n a n t i o m e r i c h y d r i d o a"!kyl i n t e r m e d i a t e s , ( P - N ) R h ( H ) ( R ) , wh i ch i n t u r n y i e l d a p a i r o f e n a n t i o m e r i c p r o d u c t s v i a r e d u c t i v e e l i m i n a t i o n 184 [ ( P - N ) R h S 2 ] + R . ( p > ^ R 2 (9 H V N X I Or H V N I H V N ^ | \ H F i g . 6 , 1 : (A) Four p o s s i b l e d i a s t e r e o m e r s o f [ ( P - N ) R h ( s u b s t r a t e ] g e n e r a t e d f rom t he c on f o rme r A , B, o r C o f [ ( P - N ) R h ( S ) 2 ] . (B) F i v e p o s s i b l e d i a s t e r e o m e r s o f [ ( . P - N ) R h ( H ) ? ] + g e n e r a t e d f rom t h e c on f o rme r A , B, o r C o f [ ( P - N ) R h ( S ) 2 ] . P*N = t h e l i g a n d s V - V I I , S = s o l v e n t , M = Rh . 185 o f RH. Thus low o p t i c a l y i e l d s o b t a i n e d by ( S , R ) - X I I o r - X I I I may be a n t i c i p a t e d u n l e s s a r o u t e l e a d i n g t o any p a r t i c u l a r e n a n t i o m e r i c i n t e r -m e d i a t e ( P - N ) R h ( H ) ( R ) i s p r e f e r r e d f o r any r e a s o n . The h y d r o g e n a t i o n r e s u l t s i n T a b l e 6 .4 i n d i c a t e t h a t no such p r e f e r e n c e i s made i n t h e c a s e o f ( S . R ) - X I I and - X I I I . The c o n f o r m a t i o n a l e f f e c t s p r e s e n t e d he re may a l s o a c c oun t f o r the d i f f e r e n c e s i n t h e p r o d u c t c o n f i g u r a t i o n s caused by t h e s e c a t a l y t i c s y s t ems ( X I I - X I V ) . F i g . 5 .17 shows t h a t t h e p r e f e r r e d c o n f o r m a t i o n (C) o f ( S , S ) -XIV i s e n a n t i o m e r i c w i t h t h e ma j o r c o n f o r m a t i o n (B) o f ( S , R ) - X I I I . Thus i f t h e s e two c on f o rme r s f u n c t i o n i n t h e o p p o s i t e d i r e c t i o n i n i n d u c i n g t h e e n a n t i o f a c e - d i s c r i m i n a t i o n t h e r e s u l t s summar i zed i n T a b l e 6 .4 a r e as a n t i c i p a t e d ; ( S . S ) - X I V and ( S , R ) - X I I I g i v e t he e n a n t i o m e r i c p r o d u c t s . However , a p a r t f rom t h e c o n s i d e r a t i o n o f p l a n a r c h i r a l i t y , i t i s d i f f i c u l t to e x p l a i n why ( S , R ) - X I I and - X I I I g i v e t h e same c o n f i g u r a t i o n o f p r o d u c t s , I t i s a l s o d i f f i c u l t t o a c c oun t f o r t h e v a r i a t i o n i n o p t i c a l y i e l d s ( T a b l e 6 .4 ) caused by X I I and X I I I u n l e s s k i n e t i c f a c t o r s a r e c o n s i d e r e d . F u r t h e r m o r e , e l e c t r o n i c e f f e c t s u n d o u b t e d l y p l a y some p a r t . As seen i n T a b l e s 6 .2 and 6 . 4 , t he b i s p h o s p h i n e complex X I I I g i v e s much h i g h e r r e a c t i o n r a t e s (.4^8 t i m e s ) t han t h e monophosph ine complex X I I i n s p i t e o f i n c r e a s e d s t e r i c b u l k i n t h e se cond Cp r i n g . T h i s r a t e i n c r e a s e i s p r o b a b l y due to e l e c t r o n i c e f f e c t s wh i c h a r e s l i g h t l y ou twe i ghed by t h e s t e r i c e f f e c t s i n t h e c a s e o f t h e t r i s p h o s p h i n e complex X I V , s i n c e r e a c t i o n r a t e s a r e s l i g h t l y l o w e r w i t h XIV t h an t h o s e o b s e r v e d w i t h t h e b i s p h o s p h i n e complex X I I I ( T a b l e 6 . 2 ) . 186 6 . 3 HYDROGENATION OF CATALYST PRECURSORS 6 . 3 . 1 I n t r o d u c t i o n (A) Recen t Deve lopment As p o i n t e d ou t i n s e c t i o n 1 . 4 . 2 , an i m p o r t a n t d i s t i n c t i o n between t h e Rh-monophosph ine c a t a l y s t [ R h ( L ) 2 ( D i e n e ) ] A and t h e R h - d i ( t e r t i a r y p ho sph i n e ) c a t a l y s t [ R h ( L - L ) ( D i e n e ) ] A i s t h a t t h e f o rmer r e a c t s w i t h H 2 t o form h y d r i d e s and t h e l a t t e r does n o t . Thus a s o l v a t e [ R h ( L - L ) S ) 2 ] + (S = s o l v e n t ) wh i c h i s t h e c a t a l y s t i n t h e h y d r o g e n a t i o n r e a c t i o n i s fo rmed i n t h e i n i t i a l h y d r o g e n a t i o n o f t h e c a t a l y s t p r e c u r s o r [ R h ( L - L ) ( D i e n e ) ] A . On t h e o t h e r hand , c a t a l y t i c h y d r i d e s ( [ R h ( L ) 2 ( H ) 2 ] + ^ [ R h ( L ) 2 H ] ° + H + ) a r e fo rmed i n t h e c a s e o f [ R h ( L ) 2 ( D i e n e ) ] A (.here t h e c o o r d i n a t e d s o l v e n t s a r e o m i t t e d ) . More r e c e n t l y , howeve r , t h r e e i m p o r t a n t o b s e r v a t i o n s have been made wh i c h i n d i c a t e t h a t t h e s e g e n e r a l i t i e s may no t be c o r r e c t . Those o b s e r v a t i o n s can be summar i zed as f o l l o w s . ( a ) U n s a t u r a t e Route w i t h [ R h ( L ) 2 ( D i e n e ) ] A Hal pe rn e t a l [ 135 ] demons t r a t ed t h a t even some monophosph ine d e r i v a -t i v e s can r e a c t v i a an u n s a t u r a t e r o u t e when t he f o l l o w i n g e q u i l i b r i u m i s e s t a b l i s h e d under s u i t a b l e r e a c t i o n c o n d i t i o n s ( e q u a t i o n 6 . 1 ) . K e [ R h ( L ) 2 ( S ) 2 ( H ) 2 ] + ^ c i s , - [ R h ( L ) 2 ( S ) 2 ] + + H 2 ( 6 . 1 ) 187 The c i s - s t r u c t u r e f o r t h e s o l v a t e [ R h ( L ) 2 ( S ) 2 ] + (L = PPh^) was deduced 31 1 f rom t h e l a r g e P-Rh c o u p l i n g c o n s t a n t ( J R ^ p = 205 H z ) . For e xamp l e , t h e a n a l o g o u s c i s - s t r u c t u r e [ R h ( D I P H 0 S ) ( S ) 2 ] + has t h e v a l u e o f 203 Hz f o r ' ' jp^p [ 1 3 5 ] , A d d i t i o n a l e v i d e n c e f o r t h e r e v e r s i b i l i t y o f r e a c t i o n ( 6 . 1 ) has r e c e n t l y been r e p o r t e d [ 4 7 d ] . (b) H y d r i d e F o rma t i o n f rom [ R h ( L - L ) ( D i e n e ) ] A Brown e t a l [ 136 ] have r e c e n t l y p u b l i s h e d e v i d e n c e f o r t h e f o r m a t i o n o f h y d r i d e s f rom d i ( t e r t i a r y p h o s p h i n e ) R h ( I ) c a t a l y s t s i n t h e ab sen ce o f s u b s t r a t e ( e q u a t i o n 6 . 2 ) . 2H ^2 [ R h ( L - L ) ( N B D ) ] + — [ R h ( L - L ) ( S ) ? ] + [Rh( L -L ) ( H ) x ( S ) ? ] + ( 6 . 2 ) c Ke c The e q u i l i b r i u m c o n s t a n t Ke i s v e r y l ow when t h e l i g a n d s ( L - L ) a r e t y p i c a l c h e l a t i n g d i p h o s p h i n e s , and t h e h y d r i d e s a r e u n d e t e c t e d by u sua l t e c h n i q u e s . In t h e absence o f s u b s t r a t e , h y d r i d e f o r m a t i o n seems t o be b l o c k e d by s u b s t r a t e c o o r d i n a t i o n . N e v e r t h e l e s s , e q u a t i o n ( 6 . 2 ) s u g g e s t s t h a t t h e Ke v a l u e and t hu s t h e mechanism o f h y d r o g e n a t i o n c o u l d be g r e a t l y a f f e c t e d by t he n a t u r e o f t h e c h e l a t i n g d i ( t e r t i a r y p h o s p h i n e s ) . For i n s t a n c e a more b a s i c pho sph i n e c o u l d s t a b i l i z e t he h y d r i d e ( s ) and a l l o w h y d r o g e n a t i o n t o p roceed v i a e i t h e r t h e h y d r i d e r o u t e o r t h e u n s a t u r a t e r o u t e . In t h i s c o n n e c t i o n , O t suka e t a l [132b] have r e c e n t l y r e p o r t e d t h e i s o l a t i o n o f a s o l i d rhod ium h y d r i d e f rom t he r e a c t i o n o f e q u a t i o n ( 6 . 3 ) . 188 [ R h ( L - L ) ( N B D ) ] C 1 0 4 + H^/MeOH -> [ R h ( L - L ) ( H ) 2 ] C 1 0 4 ( 6 . 3 ) L - L = The s ugge s t e d s t r u c t u r e f o r t h e p r o du c t i s based on t h e a n a l y t i c a l and s p e c t r o s c o p i c d a t a : IR v (Rh-H) 21 0 0 , 2075 c m " 1 ; ] H NMR(CD 2 C1 0 ) 6 - 8 . 2 ( b r ) , - 1 9 . 8 ( b r ) ppm. A c r y s t a l s t r u c t u r e has not y e t been r e p o r t e d , and t h e NMR da ta do not s u p p o r t two t e r m i n a l h y d r i d e s a l t h o u g h Brown e t a l [ 136 ] r e c e n t l y p roposed t he s t r u c t u r e t o be t h a t shown be l ow . (B) P o s s i b l e H y d r o g e n a t i o n Pa thways f o r [ R h ( L - L ) ( D i e n e ) ] A The r e s u l t s d e s c r i b e d above i n d i c a t e t h a t v a r i o u s i n t e r m e d i a t e s ( o r p r o d u c t s ) c o u l d be p roduced r e v e r s i b l y i n a g i v e n r e a c t i o n , even though t h e y may not be i s o l a b l e . Some p o s s i b l e h y d r o g e n a t i o n pathways f o r t h e c a t a l y s t s o f t h e t y p e [ R h ( L - L ) ( D i e n e ) ] A a r e s e t ou t i n F i g . 6 . 2 . As w i l l be d i s c u s s e d l a t e r , t h i s g e n e r a l scheme seems to be a p p l i c a b l e t o t h e p r e s e n t c a t a l y s t sys tems V I I I - X I V . 189 [(L-L)M(NBD)]A I Hz/S i . 6.2a III [(L-L)M(S)2(H)2] 6.2b (-H+) HI 6.2C [(L-L)MH]° III . Ill. . n 2 + [(L-LXHJMI.-H^IHKL-L)] 6.2d 6 2e (-rf) [(L-L)MH]° 6.2f [(L-L)(H)M(,-H) 2M(L-L)f ("H+) 6.2g H 2 [(L-LXH)M(.-H)3M(H)(L-L)] 6.2h F i g . 6 . 2 : Some p o s s i b l e h y d r o g e n a t i o n pathways f o r I ( I - L l Rh (_D i ene ) . ]A . V a c an t s i t e s o f me ta l may be f i l l e d w i t h S . L -L = c h e l a t i n g b i d e n t a t e l i g a n d s ; M = Rh , A = CIO/,; X = A o r S ; S = s o l v e n t . 190 The f i r s t s t e p , t he f o r m a t i o n o f t h e d i s o l v a t e 6 . 2 a , i s based on t h e commonly f ound r e s u l t f o r t y p i c a l d i ( t e r t i a r y p h o s p h i n e ) R h ( I ) c a t a l y s t s . The second s t e p i n v o l v e s o x i d a t i v e a d d i t i o n o f H^ t o t h e d i s o l v a t e t o form t h e d i h y d r i d o R h ( I I I ) s p e c i e s 6 .2b o r 6 . 2 c . From t h e s e two s p e c i e s a number o f o t h e r h y d r i d e s such as 6 . 2 d - h c o u l d be formed r e v e r s i b l y by p l a u s i b l e d i m e r i z a t i o n , and d e p r o t o n a t i o n r e a c t i o n s . (C) R e l e v a n t Me ta l H y d r i d e s A l t h o u g h t h e r e a r e no p r e c e d e n t s f o r t h e monohyd r i de Rh ( I ) s p e c i e s 6 . 2 d , monophosph ine a n a l o g u e s a r e q u i t e common. In p a r t i c u l a r t h e 14 e l e c t r o n compounds R h f L ^ H can be s y n t h e s i z e d and i s o l a t e d as c r y s t a l l i n e s o l i d s when t h e l i g a n d L c a r r i e s b u l k y e l e c t r o n d o n a t i n g a 1ky l g roups such as t e r t - b u t y l o r c y c l o h e x y l ( e q u a t i o n 6 .4 ) [ 1 3 7 ] . 7 [RhH(L) 2 ] x (N 2 ) • RhH(L) 2 ( 6 . 4 ) X = 1 , L = P(CMe 3) 3 = 2, = P ( C 6 H „ ) 3 I t i s i n t e r e s t i n g t o no t e t h a t c a t i o n i c a n a l o gue s su ch as [ (D IPHOS)Rh (H) -( S ) J 2 + (S = MeCN) a r e known ( e q u a t i o n 6 .5 ) [ 4 6 a ] . [ ( D I P H 0 S ) R h ( S ) 2 ] + + HX > [( DIPHOS)Rh(H)(S) X = C 1 0 4 " , B F 4 " . P F 6 ( 6 . 5 ) 191 The h y d r i d e s o f t h e t y p e . [ ( L - L ) R h H ] 2 ° (= 6 . 2 f i n F i g . 6 . 2 ) have been r e c e n t l y d e s c r i b e d by F r y zuk [ 1 3 8 ] , as shown i n e q u a t i o n ( 6 . 6 ) . P2 [^3-(2-Me-C3H4)Rh( }] + H 2 R2 R = CHMe 2 , OCHMe2 The p r o d u c t s a r e r e p o r t e d t o be e f f i c i e n t c a t a l y s t s f o r t h e h y d r o g e n a t i o n and i s o m e r i z a t i o n o f s i m p l e o l e f i n s . The p r o d u c t , where R = 0CHMe 2 , r e a c t s w i t h t o form a d i m e r i c t e t r a h y d r i d e , [ ( L - L ) 2 R h 2 H 4 ] . The s ugge s t e d s t r u c t u r e f o r t h i s compound i s shown be low [ 1 3 8 a ] . P2 Rh \ Js ( 6 . 6 ) 52 H u £20 R2 H R2 R = OCHMe. M u e t t e r t i e s e t a l [ 139 ] have r e c e n t l y r e p o r t e d t h e c l o s e l y r e l a t e d n e u t r a l Rh (111 ) -Rh( I ) d i m e r s , [ ( P R 3 ) 4 R h 2 H 4 ] (R = OCHMe, NMe 2 ) wh i c h a r e t h e h y d r o -g e n a t i o n p r o d u c t s o f t h e c a t a l y s t p r e c u r s o r s [ R h H ( P R , ) ? ] ? . 192 [(p) 2RhHJ 2 H 2 p /HK \ ^ H t ^ H,—Rh Rh P = p ( 0 - i - C 3 H 7 ) 3 Hjj—Rh Rh Ht P ( 6 . 7 ) I t has been shown t h a t t h e p r o d u c t (R = O-c^H^ ) can be formed r e v e r s i b l y f rom t he p r e c u r s o r d i m e r , and i s f l u x i o n a l i n s o l u t i o n ( e q u a t i o n 6 . 7 ) . 1 31 Based on t h e v a r i a b l e t e m p e r a t u r e NMR ( H, P) s t u d i e s [ 1 3 9 b ] , t h e t r i p l y b r i d g e d d imer was p roposed as a g round s t a t e s t r u c t u r e f o r t h e p r o d u c t and t he doub l y b r i d g e d d ime r as an e x c i t e d s t a t e . The p r oposed s t e r e o c h e m i s t r y o f t h e t r a n s i t i o n s t a t e ( o r i n t e r m e d i a t e ) i s based on t h e c r y s t a l s t r u c t u r e o f the r e l a t e d d o u b l y b r i d g e d h y d r i d e (R = NMe 2) [ 1 3 9 c ] . Because i t i s o f i m p o r t a n c e f o r f u t u r e d i s c u s s i o n , i t i s u s e f u l t o b r i e f l y r e v i e w t he f l u x i o n a l b e h a v i o r o f p r o d u c t o f e q u a t i o n ( 6 . 7 ) . As summar i zed i n t h e A p p e n d i x , t h e low t e m p e r a t u r e ( - 80°C ) ^H NMR i s c o n s i s t e n t w i t h t h e t r i p l y b r i d g e d d imer ( e q u a t i o n 6 . 7 ) . Name ly , i t shows ( i ) a d o u b l e t o f m u l t i p l e t s f o r t h e i d e n t i c a l b r i d g i n g h y d r i d e s (6 - 7 . 8 ppm, t r a n s J p H = 180 Hz , 1 = 2 ) , ( i i ) a d o u b l e t o f m u l t i p l e t s f o r t h e 2 un i que h y d r i d e H b ( 6 - 1 1 . 1 ppm, t r a n s J p H = 89 Hz , I = 1 ) , and ( i i i ) a b road peak f o r t h e t e r m i n a l h y d r i d e H t (6 - 1 4 . 5 ppm, 1 = 1 ) . The VT ^H NMR s t ud y shows t h a t on warming from -80° t o 3°C t h e two r e s onance s 193 a s c r i b e d t o t h e t e r m i n a l h y d r i d e (H^) and t h e un i que b r i d g i n g h y d r i d e (H^ ) merge and c o a l e s c e . The r e s onan c e f o r t h e two b r i d g i n g h y d r i d e s (H^) i s u n a l t e r e d i n t h i s t e m p e r a t u r e r a n g e . On warming to 26°C , a l l peaks c o l l a p s e and on f u r t h e r warming t o 46°C a new b road s i g n a l a p p e a r s , i n d i c a t i n g t h a t a l l h y d r i d o l i g a n d s a r e engaged i n t h e exchange p r o c e s s o f t h i s t e m p e r a t u r e . The p r o d u c t s i n e q u a t i o n ( 6 . 7 ) were p r oposed as a c t i v e i n t e r m e d i a t e s i n t h e o l e f i n r e d u c t i o n s c a t a l y z e d by t h e p r e c u r s o r s [ R h H ( P R 3 ) 2 ] 2 [ 1 3 9 ] . 1 31 In t h e Append i x a r e summar ized t h e NMR ( H, P) da t a f o r some meta l h y d r i d e s and o t h e r r e l a t e d compounds . T h i s i n f o r m a t i o n i s r e l e v a n t t o t h e f u t u r e d i s c u s s i o n . 6 . 3 . 2 H y d r o g e n a t i o n o f t h e C a t a l y s t P r e c u r s o r s V I I I - X I V (A) Gene r a l O b s e r v a t i o n s The e x p e r i m e n t a l p r o c e d u r e s a r e d e s c r i b e d i n s e c t i o n 4 . 2 . 4 . ( a ) R e a c t i o n i n A l c o h o l When s o l u t i o n s o f t h e a c h i r a l c a t a l y s t p r e c u r s o r s V111 -X I i n MeOH o r EtOH a r e exposed t o H 2 (1 a t m , 30°C) t he i n i t i a l r e d d i s h o r ange c o l o r deepens t o r e d , and i n most c a s e s da r k r e d c r y s t a l s a r e o b t a i n e d a t 20°C o r on c o o l i n g (0°C) . The c h i r a l comp lexes X I I - X I V show a c o l o r change f rom r e d d i s h o r ange t o w i n e r e d . The ^H NMR s p e c t r a o f t h e s e c r y s t a l s o r t h e s o l i d r e s i d u e a f t e r s o l v e n t remova l a r e t e m p e r a t u r e dependen t and show the p r e -sence o f b r i d g i n g a n d / o r t e r m i n a l h y d r i d e s . The s o l u t i o n s o f t h e r e a c t a n t s 194 (CD 3 0D) gave v e r y complex NMR s p e c t r a ( H, P) wh i c h a r e no t f u l l y i n t e r -p r e t e d a t t h i s s t a g e . Some r e p r e s e n t a t i v e s p e c t r a a r e p r e s e n t e d i n t h e n e x t s u b s e c t i o n s . (b) R e a c t i o n s i n O the r S o l v e n t s The r e a c t i o n w i t h H 2 was c a r r i e d ou t i n v a r i o u s o t h e r s o l v e n t s such as a c e t o n e , CH^CN, C H 2 C 1 2 , and CHC l^ . The g e n e r a l o b s e r v a t i o n s a r e s i m i l a r t o t h o s e d e s c r i b e d a b o v e . T h u s , i n most c a s e s , t h e NMR s p e c t r a o f t h e s o l i d o r c r y s t a l l i n e p r o d u c t s a r e s t r o n g l y t e m p e r a t u r e dependen t , and show 1 31 t h e p r e s en ce o f b r i d g i n g a nd / o r t e r m i n a l h y d r i d e s . NMR ( H , P) m o n i t o r i n g o f t h e r e a c t i o n s i n s o l u t i o n a l s o r e v e a l s c o n s i d e r a b l e c o m p l e x i t i e s . On l y a few p a r t i c u l a r examp les w i l l be d i s c u s s e d . ( c ) C a t a l y t i c P r o p e r t i e s The h y d r o g e n a t i o n p r o d u c t s o b t a i n e d as s o l i d s f rom MeOH a r e c a t a l y t i -c a l l y a c t i v e i n o l e f i n r e d u c t i o n s . The h y d r o g e n a t i o n p r o c e d u r e g e n e r a l l y used was t h e same as t h a t d e s c r i b e d i n s e c t i o n 4 . 2 . 2 e x c e p t t h a t t h e c a t a l y s t p r e c u r s o r was r e p l a c e d by t h e i s o l a t e d s o l i d . In some ca se s t h e s u b s t r a t e was added t o t h e i n s i t u s o l u t i o n c o n t a i n i n g t h e h y d r i d e ( s ) . A l l r e d u c t i o n s a r e s t o i c h i o m e t r i c but no a t t e m p t was made t o measure k i n e t i c d a t a o r i s o l a t e any r e a c t i o n i n t e r m e d i a t e . The c a t a l y t i c p r o p e r t i e s o f t h e h y d r o g e n a t i o n p r o d u c t s o b t a i n e d f rom s o l v e n t s o t h e r t han MeOH have no t been i n v e s t i g a t e d . (B) H y d r o g e n a t i o n o f [ R h ( B P P F ) ( N B D ) J C 1 0 4 ( V I I I } The r e a c t i o n was c a r r i e d ou t i n t h r e e d i f f e r e n t s o l v e n t s , MeOH, CH^CN, 195 and C H C 1 3 . ( a ) R e a c t i o n i n MeOH T h i s r e a c t i o n r e s u l t e d i n t h e up t a k e o f 4 . 7 mo le s o f H 2 per r hod ium a tom. A d a r k brown s o l i d r ema ined a f t e r s o l v e n t r e m o v a l . The H^ NMR spec t rum ( C D 2 C 1 2 ) o f e i t h e r t h i s s o l i d o r t h e i n s i t u s o l u t i o n (CD^OD) d i d no t show any h y d r i d e r e s o n a n c e (35° - -90°C) . Brown e t a l [47d] b r i e f l y r e p o r t e d t h a t t h e same r e a c t i o n g i v e s a d i s o l v a t e [ R h ( B P P F ) ( M e 0 H ) 2 ] + i n 31 s o l u t i o n . The a s s i g n m e n t was made on t h e b a s i s o f t h e P NMR d a t a (6p 55 .3 ppm, ^^RhP = H z ) , t h e l a r g e c o u p l i n g c o n s t a n t b e i n g c o n s i s t e n t w i t h t h e pho sph i n e t r a n s t o a r e l a t i v e l y weak donor such as MeOH ( s e e a l s o Append i x f o r c ompa r i s on w i t h o t h e r r e l a t e d s p e c i e s ) . In t h e p r e s e n t i n v e s t i -31 g a t i o n , howeve r , h y d r o g e n a t i o n f o r 25 min r e s u l t e d i n a more complex P NMR s p e c t r u m . (b) R e a c t i o n i n CHC1 3 31 The P NMR spe c t r um o f t h e s o l u t i o n a f t e r h y d r o g e n a t i o n f o r a s h o r t p e r i o d (% 5 m in ) shows a new p a i r o f b road d o u b l e t s (<5p(l) 44 . 60 ppm, J R h p = 210 H z ; 6p(2) 4 4 . 4 8 ppm, J R h p = 217 Hz) i n a d d i t i o n t o t h e d o u b l e t f rom t h e NBD p r e c u r s o r ( V I I I ) . No h y d r i d e c o u p l i n g was o b s e r v e d f o r t h e s e s i g n a l s . These peaks can be i n t e r p r e t e d as a r i s i n g f rom two n o n e q u i v a l e n t pho sph i ne g r oups i n t h e n^-arene complex 6 . 3b ( F i g . 6 . 3 ) . The s t r u c t u r e o f t h e DIPHOS a n a l o g u e [ R h 2 ( D I P H 0 S ) 2 ] ( B F 4 ) 2 i s shown i n F i g . 1 . 8 . T h i s 2+ + [ R h ( D I P H 0 S ) ] 2 complex i s known t o d i s s o c i a t e i n t o monomer ic [Rh(DIPHOS)] ( o r [ R h ( D I P H 0 S ) ( M e 0 H ) 2 ] + ) i o n s when d i s s o l v e d i n MeOH [ 4 6 a ] . The m e t h a n o l i c 31 s o l u t i o n g i v e s a s i n g l e P s i g n a l ( 6 8 0 , d , J R , p = 203 H z ) . No NMR da t a have 196 [(BPPF)Rh(NBD)]d0 4 6.3a H 2 / C H C I 3 I 6.3b 6.3C F i g . 6 . 3 : P o s s i b l e h y d r o g e n a t i o n pathways f o r V I I I i n CHC1 BPPF = t h e l i g a n d I ; n = 0 o r 2 . 197 been r e c o r d e d f o r t h i s s p e c i e s i n a n o n - c o o r d i n a t i n g s o l v e n t . The ana l o gou s r e a c t i o n has been c a r r i e d o u t i n benzene where t h e s o l v e n t a g a i n p r e f e r e n -t i a l l y b i n d s t o t h e me ta l upon l o s s o f t h e NBD l i g a n d ( e q u a t i o n 6 .8 ) [ 1 4 0 ] . [Rh(L-L)(NBD)]d0 4 + H 2 / C 6 H 6 - T H F [Rh(L-L)(, 6-C 6H 6)]Cl0 4 ( 6 . 8 ) L-L = H 'PPh, 31 The P NMR da t a ( C D 2 C 1 2 ) o f t h i s p r o du c t o f known s t r u c t u r e a r e : 6p 3 1 . 4 ( d ) , J R h p = 201 .4 H z . F u r t h e r h y d r o g e n a t i o n o f V I I I r e s u l t s i n r e a c t i o n o f a l l t h e s t a r t i n g m a t e r i a l ( V I I I ) , a r e d u c t i o n o f t h e i n t e n s i t y o f t h e d o u b l e t s o f t h e p roposed n^-arene comp lex 6 . 3 b , and t h e appea r an ce o f a d o u b l e t a t 6p 54.41 ppm ( J R n p = 146 . 5 H z ) . T h i s s p e c i e s i s a h y d r i d e ( J p ^ = 19 . 5 H z ) . A d d i t i o n o f EtgN removes t h i s d o u b l e t . T h i s s p e c i e s c o u l d be a s i m p l e monohyd r i de [ ( B P P F ) R h H ] n + ( 6 . 3 c ) where t h e c ha r ge i s e i t h e r 0 o r 2 . When t h e same s o l u t i o n ( w i t h o u t amine) i s a l l o w e d t o s t a n d f o r l o n g e r p e r i o d (>2h) a f t e r i n i t i a l h y d r o g e n a t i o n , a number o f a d d i t i o n a l peaks a r i s e i n c l u d i n g a d o u b l e t o f 1:1:1 t r i p l e t s a t 53 .79 ppm ( J R n p ^ 144 H z ) . T r i p l e t s e p a r a t i o n a v e r age s 12 Hz . T h i s peak i s no t a f f e c t e d by base a d d i t i o n . The i d e n t i t y o f t h i s s p e c i e s i s u n c e r t a i n . Removal o f s o l v e n t l e a v e s a s o l i d r e s i d u e whose ^H NMR spec t r um i s shown i n F i g . 6 . 4 . j 198 I I I I I I I i I I I I I I I I I I I I I I •10 +5 0 -10 -15 -20 (d)-60°C II 1 • » ' • I ' I I I I 1 I I I I 1 I I I I 1 +10 +5 0 -10 -15 -20 I i i I i I ' i ' ' I I ' ' i I I I l I I -10 -5 0 1 -10 -15 -20 F i g . 6 . 4 ( A ) : V a r i a b l e t e m p e r a t u r e 400 MHz H NMR spec t r um ( C D 2 C 1 2 ) o f t h e h y d r o g e n a t i o n p r o du c t (S) o f V I I I f rom CHCL^. 199 (a) 0°C • • • i • i 9J J I I I •10 +5 (b)-20°C I i i i i 1 i i i i -10 -5 - 0 I i i I I I I • I -10 -15 -20 i i i I i i i i 1 -10 -15 -20 F i g . 6 . 4 ( B ) : V a r i a b l e t e m p e r a t u r e 400 mHz 'H NMR spec t r um ( C D 2 C 1 2 ) o f t h e h y d r o g e n a t i o n p r o d u c t ( s ) o f V I I I f rom CHCI3 . 200 The h y d r i d e NMR p a t t e r n a t -90°C c o n s i s t s o f a t e m p e r a t u r e i n d e p e n d e n t s i g n a l B -11 ppm) and two p a i r s o f t e m p e r a t u r e dependent m u l t i p l e t s T-| /T and ^2^2 i n t n e r a n 9 e t 0 PP m » * n e b r oadnes s o f t h e peaks p r e c l u d e s any s a t i s f a c t o r y i n t e r p r e t a t i o n . I t i s p o s s i b l e t h a t t h e s i g n a l B i s due t o a n e u t r a l monomer o r d imer s u ch as 6 .3d ( F i g . 6 . 3 ) , howeve r , t h e da t a do no t compare v e r y s a t i s f a c t o r i l y w i t h known compounds d e s c r i b e d i n e q u a t i o n s ( 6 . 6 ) and ( 6 . 7 ) ( s e e a l s o A p p e n d i x ) . N e v e r t h e l e s s t h e r e i s no doubt abou t t h e f o r m a t i o n o f h y d r i d e s p e c i e s w h i c h w i l l be e s t a b l i s h e d , ( c ) R e a c t i o n i n CH 3CN T h i s r e a c t i o n r e s u l t e d i n t h e f o r m a t i o n o f l a r g e y e l l o w c r y s t a l s on a l l o w i n g t h e h yd r ogena t ed s o l u t i o n t o s t a n d a t room t e m p e r a t u r e . The 3 1 P { 1 H } NMR spe c t r um ( C H 2 C 1 2 ) o f t h e samp le showed a d o u b l e t a t 4 5 . 0 5 ppm ( ] J R h p = 181 .9 Hz) due t o t h e d i s o l v a t e [ ( B P P F ) R h ( M e C N ) 2 ] C 1 0 4 . T h i s f o r m u l a -t i o n has been r e c e n t l y c o n f i r m e d by a c r y s t a l s t r u c t u r e d e t e r m i n a t i o n [ 1 4 1 ] , a l t h o u g h t h e a n a l y t i c a l d a t a a r e no t i n ag r eemen t : C, 5 4 . 0 1 ; H, 3 . 3 2 ; N , 3 . 3 2 . T h i s t y p e o f comp lexes where t h e l i g a n d s a r e t y p i c a l d i ( t e r t i a r y p ho sph i n e s ) have been w e l l c h a r a c t e r i z e d i n s o l u t i o n by NMR, and a r e known to be a c t i v e h y d r o g e n a t i o n c a t a l y s t s fo rmed f rom t h e d i e n e p r e c u r s o r s ( c f . s e c t i o n 1 . 4 . 2 B ) . (C) H y d r o g e n a t i o n o f [ R h ( B P B t P F ) ( N B D ) ] C 1 0 4 ( I X ) ( a ) R e a c t i o n i n MeOH A f t e r passage o f H 2 f o r 30 m i nu t e s t h e r e s u l t a n t s o l u t i o n d e p o s i t e d o r ange c r y s t a l s on s t a n d i n g a t 20 °C . The c r y s t a l s t r u c t u r e o f t h i s p r o d u c t 201 F i g . 6 . 5 : The c r y s t a l s t r u c t u r e o f t h e h y d r o g e n a t i o n p r o du c t o f IX f rom MeOH, [ ( P - P ) ( H ) R h ( y - H ) 3 R h ( H ) ( P - P ) J + ( P - P = t h e l i g a n d I I ) [ 1 4 2 ] . 202 i s shown i n F i g . 6 . 5 . The m o l e c u l e i s a u n i p o s i t i v e R h ( I I I ) d ime r w i t h t h r e e b r i d g i n g h y d r i d e s and one t e r m i n a l h y d r i d e on each Rh m e t a l . T h i s m o l e c u l e can be r o u g h l y d e s c r i b e d as p o s s e s s i n g a C 2 a x i s a l o n g t h e l i n e c o n n e c t i n g H 3 and t h e m i d d l e p o i n t o f two Rh.atoms ( v i d e i n f r a ) . Each Rh atom adop t s a p p r o x i m a t e l y an o c t a h e d r a l geomet ry ( c f . 6 . 2 h , F i g . 6 . 2 ) . T h e r e f o r e t h e i o n h a s : ( i ) a p a i r o f e q u i v a l e n t t e r m i n a l h y d r i d e s and Hg wh i ch a r e no t t r a n s t o a phosphorus a t om; ( i i ) a p a i r o f e q u i v a l e n t b r i d g i n g h y d r i d e s H-j and H 2 , each b e i n g t r a n s t o a s i n g l e phosphorus atom (H-| t r a n s t o P 2 , H 2 t r a n s to P^); ( i i i ) a u n i q u e b r i d g i n g h y d r i d e H 3 t r a n s to b o t h P-| and P^. T h u s , i f t h i s compound were n o n f l u x i o n a l i n s o l u t i o n t h r e e h y d r i d e r e s o n a n c e s i g n a l s wou ld be s e e n . However , t h i s p r o du c t shows f l u x i o n a l b e h a v i o r i n s o l u t i o n as seen i n F i g . 6 . 6 . No h y d r i d e s i g n a l was o b s e r v e d a t 35°C . C o o l i n g to 0°C r e s u l t e d i n t h e a ppea r an c e o f ( i ) a b road t e r m i n a l r e s o n a n c e a t - 2 3 . 3 ppm ( 1 = 2 ) and ( i i ) a p a i r o f b road s i g n a l s o f equa l i n t e n s i t y a t - 8 . 0 and - 9 . 4 ppm (I = 3 ) . Both s i g n a l s a r e s l i g h t l y sha rpened on f u r t h e r c o o l i n g ( - 4 0 ° ^ - 9 0 ° C ) . The f l u x i o n a l p r o c e s s e s i n t h e two r e g i o n s seem t o be i ndependen t i n t h e r ange -90° t o 0°C as seen i n F i g . 6 . 6 . Thus a p o s s i b l e exchange p r o c e s s may 203 0°c o -40 C -60°C -7 -8 -X) -22 -23 -24 -25 F i g . 6 . 6 : 1 H NMR spec t r um ( C D 2 C 1 2 ) o f t h e V a r i a b l e t e m p e r a t u r e 80 MHz h y d r o g e n a t i o n p r o d u c t , [ ( P - P ) ( H ) R h ( y - H ) 3 R h ( H ) ( P - P ) ] + , o f IX f rom MeOH. P-P = t he l i g a n d I I 204 i n v o l v e t h e s t r u c t u r e where a l l t h r e e b r i d g i n g h y d r i d e s a r e e q u i v a l e n t and t r a n s t o a s i n g l e phosphorus atom t o g i v e a b road d o u b l e t whose s e p a r a t i o n o f 112 Hz i s a s s i g n a b l e t o a t r a n s P-H c o u p l i n g ( J p H ) ( s e e a l s o Append i x f o r c o m p a r i s o n ) . S i m i l a r bu t b e t t e r r e s o l v e d and a s s i g n a b l e s p e c t r a have been r e p o r t e d f o r t h e i r i d i u m ana l o gue s [ I r n ( H ) 2 n + 1 ( D P P P ) p ] ( B F 4 ) n _ - | (n = 2 , 3 ; DPPP = P h 2 P ( C H 2 ) 3 P P h 2 ) [ 143 ] and [ I r 2 ( y - H ) 3 H 2 ( P P h 3 ) 4 ] P F g [ 1 4 4 ] . The same r e a c t i o n was c a r r i e d o u t i n CD 3 0D , and t h e s o l u t i o n m o n i t o r e d by "'H NMR 30 m i n ) . The VT NMR s p e c t r a a r e shown i n F i g . 6 . 7 , and r e l e v a n t h y d r i d e r e s o n a n c e s a r e l i s t e d i n T a b l e 6 . 5 . As summar i zed i n T a b l e 6 . 5 , t h e low t e m p e r a t u r e ( - 90°C ) h y d r i d e NMR p a t t e r n c o n s i s t s o f ( i ) a s e t o f t e m p e r a t u r e - i n d e p e n d e n t s i g n a l s T-|, T 2 and T 3 and ( i i ) a s e t o f t e m p e r a t u r e - d e p e n d e n t s i g n a l s B-|, B 2 , T 4 , T g , T g , and T y . As t h e tempe-r a t u r e i s r a i s e d t o - 6 0 ° C , b o t h p a i r s o f b r i d g i n g s i g n a l s B-|/B 2 and t e r m i n a l s i g n a l s T 4 / T g merge t o g i v e b r o a d m u l t i p l e t s B and T " , r e s p e c t i v e l y . By 0°C a l l t h e s i g n a l s e x c e p t T- j , Tg and I j have d i s a p p e a r e d . F u r t h e r warming (35°C) c au se s t h e p a i r o f m u l t i p l e t s Tg and Ty to c o a l e s c e t o a b road m u l t i p l e t T , and t h u s o n l y two s i g n a l s T^  and T a r e s een a t t h i s t e m p e r a t u r e . None o f t h e s i g n a l s a s s o c i a t e d w i t h t h e i s o l a t e d p r o d u c t a r e p r e s e n t i n t h e s e s p e c t r a ( c f . F i g s . 6 . 5 and 6 . 6 ) . The f o l l o w i n g a t t emp t ed i n t e r p r e t a t i o n o f a l l t h e s e s p e c t r a i s based on F i g s . 6 .2 and 6 . 8 . ( I ) The T empe r a t u r e - I n dependen t S i g n a l s T-| - T 3 The t e m p e r a t u r e i n v a r i a n t s i g n a l T^  a ppea r s t o be a d o u b l e t o f d o u b l e t s w i t h sma l l c o u p l i n g c o n s t a n t s (24 and 28 H z ) . The weaker s i g n a l s T 2 and T 3 a l s o g i v e t h e same p a t t e r n wh i c h i s d i f f i c u l t t o a c c o u n t f o r i n t e rms o f 205 ( c ) - 4 0 °C J ' • • • i i i i i i • • ' i • • • • i ' • ' ' i ' ' • ' •10 +5 0 (d) -60°C -10 -15 -20 -25 -30 JUUJL I ' I ' ' I ' I I ' I i ' ' i ' i i i i i i i i 1 1 i i i i i i •10 -6 -20 -25 -30 •10 +5 I ' ' • ' I ' ' ' • ' • ' • ' ' ' ' ' ' -15 -20 -25 -30 F i g . 6 . 7 ( A ) : V a r i a b l e t e m p e r a t u r e 400 MHz H NMR spect rum, o f t h e hyd rogena t ed s o l u t i o n (CDoOD) o f I X . 206 (a) +35°C jULi ' ' ' ' I ' • ' I I ' I ' 1 ' ' ' ' I ' I I ' 1 ' I ' ' •10 +5 0 •10 -15 -20 -25 -30 (b) o°c • • t • • i . , . • i •10 *5 0 I t i t i I i i i • I t i i i I i i i » 1 •K) -B -20 -25 -30 . 6 . 7 ( B ) : V a r i a b l e t e m p e r a t u r e 400 MHz H NMR spec t rum o f t h e h yd rogena t ed s o l u t i o n (CD^OD) o f I X . 207 T a b l e 6 . 5 : H NMR da t a ( h y d r i d e p o r t i o n ) f o r t h e hyd rogena t ed s o l u t i o n (CD^OD) o f t h e c a t a l y s t p r e c u r s o r IX a , b . Temp X Tempe ra t u r e - dependen t s i g n a l s T e m p e r a t u r e - i n d e p e n d e n t s i g n a l s - 90 B ^ d m , - 1 2 . 3 5 , J ( d ) = 1 7 2 , 1=2) T ^ d b d , - 1 8 . 1 3 , J ( d ) = 2 4 , B 2 ( d m , - 1 3 . 2 3 , J ( d ) = 1 8 0 , 1 = 2) J ( b d ) = 2 8 , 1=1) T 4 ( t m , - 2 1 . 8 2 , J ( t ) = 24 , 1 = 2) T 2 ( d b d , - 1 8 . 2 9 ) T 5 ( t m , - 2 2 . 4 5 , J ( t ) = 2 8 , 1=2) T 3 ( d b d , - 1 8 . 5 3 ) T 6 ( t b d ! , - 2 2 . 8 8 , J ( t ) = 2 8 , J ( b d ) = 1 2 , 1=1) T ? ( m , - 2 3 . 3 6 , 1=1) - 60 B(m, - 1 3 . 2 ) T l T ' ( m , - 2 2 . 3 ) T 2 T 6 T 3 T 7 0 T6 and J-j T l +35 T (m, - 2 3 . 3 ) T l a See a l s o F i g . 6 . 7 . b C o u p l i n g c o n s t a n t s i n H z : dm = d o u b l e t o f m u l t i p l e t s , dbd = d o u b l e t o f b road d o u b l e t s , t b d = t r i p l e t o f b road d o u b l e t s , m = m u l t i p l e t ; J ( d ) , J ( t ) , J ( b d ) , J ( d b d ) = c o u p l i n g c o n s t a n t i n each p a t t e r n ; I = r e l a t i v e i n t e n s i t y , 208 c h e l a t i n g l i g a n d s . One p o s s i b i l i t y i n v o l v i n g a d a n g l i n g pho sph i ne i s seen be! ow. H l P P S ^ . 6.8e As i n d i c a t e d i n F i g . 6 . 2 , t h i s s p e c i e s i s ana l ogous t o t h e monomer ic R h ( I ) s p e c i e s 6 .2d w h i c h i s a d i s s o c i a t i o n p r o d u c t o f t h e R h ( I I I ) d imer 6 . 2 e . In F i g . 6 .8 i s p roposed a p o s s i b l e d i s s o c i a t i v e p r o c e s s t h r o u g h wh i c h t h e above s p e c i e s can be f o r m e d . The s p e c t r a i n F i g . 6 .7 shows t h a t t h e i n t e n s i t y o f T 2 and T^ d e c r e a s e s as t h a t o f T-j i n c r e a s e s on warming ( -90° -» -60°C) , and then T-j/T^ d i s a p p e a r a t - 4 0 ° C . T h i s f l u x i o n a l b e h a v i o r i s ha rd t o e x p l a i n a l t h o u g h t h e i n t r a -m o l e c u l a r exchange p r o c e s s e s i n F i g . 6 .8 s ugge s t t h a t d i s s o c i a t i o n o f t h e d ime r s 6 . 8 a - d become i r r e v e r s i b l e a t h i g h e r t e m p e r a t u r e s (_> -40°C) t o r e s u l t i n t h e p r edom inan t f o r m a t i o n o f monomers such as shown above ( 6 . 8 e ) . The r e m a i n i n g a s p e c t o f F i g . 6 .8 i s d i s c u s s e d below'. ( I I ) O the r Tempe ra t u r e -Dependen t S i g n a l s I f t h e i s o l a t e d p r o d u c t ( F i g . 6 . 5 ) were formed r e v e r s i b l y t h r o u g h t he r o u t e 6 . 2 a ^ 6 . 2 c ^ 6 . 2 e ^ 6 . 2 g ^ 6 . 2 h ( F i g . 6 . 2 ) , t hen t h e s o l u t i o n c o u l d c o n t a i n a d oub l y b r i d g e d Rh(111) d imer ana l ogou s t o 6 . 2 e . S i n c e t h e l i g a n d 209 I . H ^ H 4 H 3 H2 1 - ^ Ps 6.8b R |lll/H l Nlll / H4 6.8a it V V 4 H 3 H2 Ps 6.8C M I! CHI;MCT H2 6.8d H3 H2 I F| 6.8b' F i g . 6 . 8 : The p roposed i n t r a m o l e c u l a r exchange p r o c e s s e s In t h e h yd r ogena t ed s o l u t i o n (CD 3 0D) o f t h e complex I X , The v a c a n t s i t e s o f me t a l may be f i l l e d w i t h S ( C D 3 0 D ) . M = Rh , P-P = t h e 1 i g a n d I I . 210 i n t h i s c a s e i s r a c - I I ( ( S , S ) - / ( R , R ) - I I ) , t h e r e a r e two p o s s i b l e c o m b i n a t i o n s t o form t h i s d i m e r : name l y , an e n a n t i o m e r i c p a i r o f d ime r s ( S , S , S , S ) - / -( R , R , R , R ) - and an e q u i v a l e n t p a i r o f d imer s ( S , S , R , R , ) - / ( R , R , S , S ) - . Here S and R r e f e r t o t h e c o n f i g u r a t i o n a t P atoms o f t h e l i g a n d I I . Each enan t i ome r such as ( S , S , S , S ) p o s s e s s e s two p a i r s o f d i a s t e r e o t o p i c h y d r i d e s H , / H ? and H^/H. by i n t e r n a l c ompa r i s on ( 6 . 8 a ) ( v i d e i n f r a ) . R lll^H^III/r^ ( S , S , S , S ) - 6 . 8 a On the o t h e r hand t h e ( S , S , R , R ) - / ( R , R , S , S ) - d i a s t e r e o m e r s po s s e s s an e q u i v a l e n t p a i r o f b r i d g i n g and o f t e r m i n a l h y d r i d e s by i n t e r n a l c o m p a r i s o n , Thus t h e s i g n a l s B-j , B 2 , T^ and Tg can be a s s i g n e d t o t h e s t r u c t u r e ( S , S , S , S ) - 6 . 8 a shown a b o v e . E i t h e r t h e d o u b l e t o f m u l t i p l e t s B-j o r B 2 i s a s s o c i a t e d w i t h H-, o r H 2 w i t h 2 J p H ( B ] ) = 172 Hz and 2 J p H ( B 2 ) = 180 H z . The t e r m i n a l h y d r i d e s H^ and H^ wou ld appea r as a t r i p l e t o f m u l t i p l e t s w i t h J p H v a l u e o f 24 and 28 Hz as seen i n T^ and T^. A d d i t i o n a l sma l l c o u p l i n g s t o Rh and /H^ a r e r e s p o n s i b l e f o r t h e m u l t i p l i c i t i e s . A l t h o u g h i t i s c o n c e i v a b l e t h a t t he s o l u t i o n c o n t a i n s t he e q u i v a l e n t p a i r o f d i a s t e r e o m e r s ( S , S , R , R ) - / ( R , R , S , S ) - , t h e low t e m p e r a t u r e ( - 90°C ) NMR p a t t e r n seems t o e x c l u d e t h i s p o s s i b i l i t y , s i n c e t h e r e s h o u l d be a d d i t i o n a l 211 s i g n a l s due t o t h e p a i r o f e q u i v a l e n t b r i d g i n g and t e r m i n a l h y d r i d e s . A n o t h e r p o s s i b l e i n t e r m e d i a t e on t h e same r e a c t i o n r o u t e ( 6 . 2 a ^ 6 . 2 c 6 . 2 e ^ 6 . 2 g ^ 6 . 2 h ) c o u l d be t h e f i v e - c o o r d i n a t e d i h y d r i d e R h ( I I I ) s p e c i e s 6 . 8 f a n a l o gou s t o 6 . 2 c . H ( >M-H VP I S 6.8f -,+ The m u l t i p l e t s Tg and Ty can be a s s i g n e d to t h i s s p e c i e s . Thus t h e a x i a l 2 1 hydrogen i s seen as a t r i p l e t o f b road d o u b l e t s Tg ( = 28 H z , = 12 H z ) . The e q u a t o r i a l hydrogen has e s s e n t i a l l y t h e same but more s p r e a d -ou t p a t t e r n ( s i g n a l Ty) p r o b a b l y because o f a g r e a t e r Jp^ . The p r i n c i p a l f e a t u r e o f t h e t e m p e r a t u r e - d e p e n d e n t s p e c t r a i s t h e c o l l a p s e o f t h e b r i d g i n g r e s onan c e s B-j and B 2 a t t h e same r a t e as t h e t e r m i -na l r e s onan ce s T^ and Tg w i t h o u t t h e appea r an ce o f any new " a v e r a g e " r e s o n a n c e . T h i s i n d i c a t e s t h a t t h e f l u x i o n a l d i m e r i c s p e c i e s 6 .8a i s s t a b l e o n l y i n t h e s o l i d s t a t e o r i n s o l u t i o n a t l ow t e m p e r a t u r e s . Any f l u x i o n a l p r o c e s s must be such as t h e exchange t e r m i n a l and b r i d g i n g hyd rogen atoms i n d e p e n d e n t l y . Such a p r o c e s s i s s e t ou t i n F i g . 6 . 8 . The most i m p o r t a n t f e a t u r e o f t h e e q u i l i b r i a shown i s t h e r e q u i r e m e n t f o r pho sph i ne d i s s o c i a t i o n (as s ugge s t ed above f o r t h e s t r u c t u r e o f 6 . 8 e ) . The exchange p r o c e s s c o u l d p roceed i n a s t e p w i s e manner (6 ,8as± 6 , 8 b ^ 6 . 8 c ( o r 6 . 8 d ) ^ 6 ,8b ^ 6 .8a ) o r i n 212 a s i m u l t a n e o u s manner ( 6 . 8 a ^ 6 . 8 c ^ 6 . 8 d ) . I f t h e exchange i s f a s t on t h e NMR t i m e s c a l e t h e d i a s t e r e o t o p i c p a i r o f b r i d g i n g h y d r i d e s H - j a n d t e r m i n a l ones H^/H^ become e q u i v a l e n t r e s u l t i n g i n t h e b road s i g n a l B and Y ( a t - 60°C) . As men t i o ned p r e v i o u s l y , a t h i g h e r t e m p e r a t u r e s (> - 6 0 ° C ) , t h e f l u x i o n a l d ime r s 6 . 8 a - d p r e sumab l y d i s s o c i a t e t o t h e monomers 6 . 8e and 6 . 8 f shown above . The r e m a i n i n g two t e m p e r a t u r e - d e p e n d e n t s i g n a l s Tg and Ty a r e n o t a l t e r e d i n t h e t e m p e r a t u r e r ange -90° t o 0 ° C , but t h e a v e r aged s i g n a l T a t 35°C s ugge s t s t h a t t h e two d i s t i n c t h y d r i d e s i n 6 . 8 f become e q u i v a l e n t . (b) R e a c t i o n i n O the r S o l v e n t s The r e a c t i o n i n CH^CN r e s u l t e d i n a y e l l o w o i l a f t e r s o l v e n t remova l ( r e a c t i o n t ime ^ 30 m i n ) . The NMR spec t rum ( C ^ C ^ ) o f t h i s p r o d u c t o r t h e i n s i t u s o l u t i o n (CD^CN) showed bo th b r i d g i n g and t e r m i n a l h y d r i d e s i n t h e r ange -11 to -27 ppm a t - 4 0 ° C . Chang ing t h e s o l v e n t t o a c e t o n e r e s u l t e d i n a d i f f e r e n t NMR p a t t e r n wh i c h a l s o showed t h e p r e s en c e o f h y d r i d e s on c o o l i n g (_> - 2 0 ° C ) . A l l t he peaks were p o o r l y r e s o l v e d . (C) H y d r o g e n a t i o n o f [ R h ( B B t P F ) ( N B D ) ] C 1 0 4 ( X I ) The r e a c t i o n was c a r r i e d ou t i n t h r e e d i f f e r e n t s o l v e n t s , MeOH, CH^CN, and CgHg. Data f o r t h e h y d r o g e n a t i o n p r o d u c t s o b t a i n e d f rom each s o l v e n t a r e l i s t e d i n T a b l e 6 . 6 . (a ) R e a c t i o n i n MeOH Deep r ed c r y s t a l s d e p o s i t e d on c o o l i n g (0°C) t h e r e a c t i o n m i x t u r e . F i g . 6 .9 shows t h e p a r t i a l c r y s t a l s t r u c t u r e o f t h i s p r o d u c t wh i c h i s a 213 T a b l e 6 . 6 : H y d r o g e n a t i o n p r o d u c t s o f [Rh(BB P F ) ( N B D ) ] C 1 0 4 ( X I ) ; A n a l y s e s , NMR, and O the r s a • R e a c t i o n P h y s i c a l ] H NMR(CD 2 C1 2 ) medium p r o p e r t y H 2 ( m o l ) A n a l y s i s MeOH deep r ed 3 . 3 C : 49 . 23 ( h y d r i d e p o r t i o n a t - 8 5 ° C ) b c r y s t a l H: 7 .36 B ^ b d , - 9 . 9 6 , j ( d ) = 1 2 0 , I = 2 ) 0 : 6 .30 B 2 ( b d , - 1 0 . 7 7 , j ( d ) = 1 2 0 , I = 3 ) CI 3 .64 T 1 ( d t d , - 2 2 . 3 8 , j ( t ) = 1 7 . 2 , J ( d ) = 2 7 , j ( d ) = 4 ) T 2 ( d t , - 2 5 . 4 6 , j ( d ) = 3 2 , J ( t ) = 3 2 ) T 3 ( d t d , - 2 7 . 6 6 , J ( t ) = 1 6 , J C d ) = 3 9 . 6 , J ( d ) = 4 ) T 4 ( b m , - 2 6 . 9 9 , I = 2 ) T 5 ( b m , - 2 7 . 0 8 , I = 1 ) C 6 H 6 deep brown 5.1 C :45 .71 5 . 0 1 ( b s ) c r y s t a l H: 6 .55 4 . 7 2 ( b s ) 0 : 1 6 . 0 0 2 . 0 8 ( d , J p H = 1 2 ) CI : 5 .94 CH 3 CN y e l l o w o i l a b H o ^ o l ) r e p r e s e n t s t h e amount o f H ? consumed per mo le o f t h e c a t a l y s t 1 p r e c u r s o r . A n a l y s i s and H NMR d a t a were o b t a i n e d f rom t h e i s o l a t e d c r y s t a l l i n e p r o d u c t . C o u p l i n g c o n s t a n t s i n H z ; bd = b road d o u b l e t , m = m u l t i p l e t , bm = b road m u l t i p l e t , bs = b road s i n g l e t , d = d o u b l e t , d t = d o u b l e t o f t r i p l e t s , d t d = d o u b l e t o f t r i p l e t s o f d o u b l e t s - J ( d ) , J ( t ) . = c o u p l i n g c o n s t a n t i n each p a t t e r n . I = r e l a t i v e i n t e n s i t y . See a l s o F i g . 6 . 1 0 . C(42) C{11) F i g . 6 . 9 : The p a r t i a l c r y s t a l s t r u c t u r e o f t h e hyd rogena t ed p r o d u c t o f t h e c a t a l y s t p r e c u r s o r XI [ 1 4 2 ] . > F i g . 6 . 1 0 ( A ) : V a r i a b l e t empe r a t u r e 400 Mhz H NMR spec t r um (CD. h y d r o g e n a t i o n p r o d u c t o f XI f rom MeOH. 217 c a t i o n i c Rh d i m e r . The +1 c h a r g e o f t h e c a t i o n was e s t a b l i s h e d by t h e l o c a t i o n o f one p e r c h l o r a t e a n i o n [ 1 4 2 ] . The b r i d g i n g h y d r i d e l i g a n d s c o u l d no t be l o c a t e d w i t h any c e r t a i n t y , and t h e t e r m i n a l ones were no t s e e n . The s t r u c t u r e mus t be o f t h e t y p e [ ( P - P ) 2 R h 2 ( H ) x ] + C l 0 ^ (x = 3 o r 5) based on t h e c h a r g e , and t h e be s t i n t e r p r e t a t i o n based on l i g a n d d i s p o s i t i o n i s a ( v -H )^ d ime r (x = 5) ana l ogous t o t h a t shown i n F i g . 6 . 5 . Once a g a i n F i g . 6 .2 can be used to p r e d i c t a p o s s i b l e r o u t e t o t h i s p r o d u c t : 6.2a^=i 6 .2b ( o r 6 . 2 c ) ^ 6 . 2 e ^ 6 . 2 g ( x = 3 ) ^ 6 . 2 h ( x = 5 ) . F u r t h e r e v i d e n c e f o r t h e p r e s en ce o f h y d r i d o l i g a n d s i s p r o v i d e d by t he ^H NMR spec t rum ( C D 2 C 1 2 ) o f t h e c r y s t a l , as shown i n F i g . 6 . 1 0 . As summar i zed i n T a b l e 6 . 6 , t h e h y d r i d e NMR p a t t e r n a t -85°C c o n s i s t s o f ( i ) a s e t o f t e m p e r a t u r e - i n d e p e n d e n t s i g n a l s T^, T 2 , and Tg and ( i i ) a s e t o f t e m p e r a t u r e - d e p e n d e n t s i g n a l s , B 2 , T 4 , and T^. On warming t he s o l u t i o n to - 6 0 ° C , bo th b r i d g i n g and t e r m i n a l r e s onan c e s B-j/B,, and T^/Tg merge t o g i v e b road m u l t i p l e t s B(> - 1 0 . 6 ppm) and T (a. - 2 7 . 5 ppm), r e s p e c t i v e l y . By 0°C both s i g n a l s B and T have c o l l a p s e d , and a new a ve r aged s i g n a l A appea r s a t - 1 7 . 2 3 ppm on f u r t h e r warming t o 3 5 °C . The a t t emp t ed i n t e r p r e -t a t i o n o f a l l t h e s e s p e c t r a i s as f o l l o w s . ( I ) The T e m p e r a t u r e - I n d e p e n d e n t S i g n a l s T-j - Tg As i n d i c a t e d i n F i g . 6 . 2 , any d i m e r i c R h ( I I I ) s p e c i e s 6 .2e c o u l d d i s s o c i a t e r e v e r s i b l y t o form [ ( L - L ) R h ( X ) ( H ) 2 ] + ( 6 . 2 c ) w h i c h i n t u r n c o u l d p roduce [ ( L - L ) R h H ] ° ( 6 . 2 d ) . Here t h e p e r c h l o r a t e (X = C 1 0 4 ) i s l i k e l y t o be c o o r d i n a t i n g because t he s o l v e n t i n t h i s c a s e i s C D 2 C 1 2 . The s t r u c t u r e s o f t h e s e two s p e c i e s , where L-L = I V , a r e shown b e l o w . 218 H ml ^Pv H - R h ' ) I V OCI0 3 6 .nd ^ / Rh —H P 6 . ne The p a i r o f s i g n a l s T-j and T^ can be a s s i g n e d t o t h e two n o n e q u i v a l e n t h y d r i d e s i n 6 . l i d . They appea r t o be a d o u b l e t o f t r i p l e t s o f d o u b l e t s 1 2 w i t h c o u p l i n g c o n s t a n t s as f o l l o w s : T-j ( J p ^ H = 27 H z , J p H = 17 . 2 H z , 2 J H H = 4 H z ) ; T 3 ( ] J R h H = 39 .6 H z , 2 J p H = 16 H z , 2 J R H = 4 H z ) . These c o u p l i n g c o n s t a n t s a r e no t u n r e a s o n a b l e as compared w i t h t h o s e l i s t e d i n A p p e n d i x . The s i g n a l T 2 w i t h f i v e l i n e s can be t r e a t e d as a d o u b l e t o f t r i p l e t s w i t h s e p a r a t i o n o f 32 Hz i n b o t h p a t t e r n s . T h i s s i g n a l can be a s s i g n e d t o t h e Rh ( I ) monohyd r i de 6 . l i e . In c o n n e c t i o n w i t h t h e s t r u c t u r e 6 . l i d , i t s h o u l d be men t i oned t h a t 31 m o n i t o r i n g t h e same r e a c t o n by P NMR i n MeOH 30 m in) r e s u l t e d i n a b road d o u b l e t (6p 8 3 . 3 ppm, ^ J R n P = 113 . 5 H z ) . Each s i g n a l i n t h e d o u b l e t was s p l i t i n t o f o u r l i n e s ( J p H = 10 Hz) when h y d r i d e c o u p l i n g was l e f t i n . These o b s e r v a t i o n s a r e c o n s i s t e n t w i t h t h e f o r m a t i o n o f 6 . l i d a l t h o u g h X c o u l d be MeOH o r CI0^ i n t h i s c a s e . The a n t i c i p a t e d d i s o l v a t e [ ( L - L ) R h -( M e O H ) 2 ] + and t h e p roposed monohyd r i de 6 . l i e were no t o b s e r v e d i n t h i s e x pe -r i m e n t . A number o f s p e c i e s were fo rmed on l e a v i n g t h e s o l u t i o n o v e r n i g h t . ( I I ) Tempe ra tu r e -Dependen t NMR P a t t e r n The t e m p e r a t u r e - d e p e n d e n t s i g n a l s (B-| , B 2 , T^, and T^) can be e x p l a i n e d i n te rms o f t h e R h ( I I I ) d ime r 6 .11a and i t s f l u x i o n a l b e h a v i o r as p roposed i n F i g . 6.11 ( c f . e q u a t i o n 6 . 7 ) . 219 r p, H 3 2+ Rh Rh H 6.11a i t R H 8 , , >»Rh ,Rh^ - p / l«' \H/ 6.11b 2+ II H 8 »V ^P H 7 2+ 6.11C F i g . 6 . 1 1 : The p roposed i n t r a m o l e c u l a r exchange p r o c e s s e s i n t h e CD^Cl s o l u t i o n o f t h e h y d r o g e n a t i o n p r o d u c t ( F i g . 6 .9) o f X I . 220 I f , a t - 8 5 ° C , o n l y one exchange p r o c e s s ( 6 . 1 1 6 . 1 1 b ) were o c c u r r i n g s l o w l y on the NMR t i m e s c a l e , t h e h y d r i d e NMR spec t r um wou ld c o n s i s t o f f i v e d i s t i n c t s i g n a l s due to H- | /H 2 , H5 / H5» H7> ^3/^4. and Hg . On t h e s e bases t h e b road d o u b l e t s B-| and B 2 can be a s s i g n e d t o t h e p a i r o f e q u i v a l e n t b r i d g i n g h y d r i d e s H^/H 2 and H^/Hg, r e s p e c t i v e l y . The r e s o n a n c e f o r t h e u n i q u e b r i d g i n g h y d r i d e Hy c o u l d be supe rpo sed on t h e h i g h e r s h i e l d i n g peak o f t h e d o u b l e t B 2 s i n c e t h e s i g n a l B 2 i s a s ymme t r i c (No t e I ( B 2 ) / I ( B - | ) = 3/2 i n T a b l e 6 . 6 ) . A l l t h e b r i d g i n g h y d r i d e s e x c ep t Hy have a s i n g l e t r a n s P a t om , a c c o u n t i n g f o r t h e l a r g e s e p a r a t i o n (120 Hz) i n bo th d o u b l e t s B-| and B 2 . T h e i r c h e m i c a l s h i f t s and c o u p l i n g c o n s t a n t s a r e c o n s i s t e n t w i t h t h o s e p r e v i o u s l y no ted f o r r e l a t e d b r i d g i n g h y d r i d e s ( c f . A p p e n d i x ) . O t he r c o u p l i n g s , H-H, Rh -H , and c i s P-H a r e t oo s m a l l t o be o b s e r v e d . The b road s i g n a l T^ and T g can t hen be a s s i g n e d t o t h e t e r m i n a l h y d r i d e s Hg/H^ and Hg , r e s p e c t i v e l y . On warming t h e s o l u t i o n ( - 85° -> - 6 0 ° C ) , t h e exchange 6.11 6 .11b s h o u l d become f a s t t o g i v e t h e ave raged s i g n a l B and T f o r t h e f i v e b r i d g i n g h y d r i d e s and t h e t h r e e t e r m i n a l o n e s , r e s p e c t i v e l y . The exchange i s s t i l l s l ow enough f o r t h e b r i d g i n g and t e r m i n a l h y d r i d e s t o be d i s t i n g u i s h e d i n t h e range -85° to -20°C ( c f . F i g . 6 . 1 0 ) . A t h i g h e r t e m p e r a t u r e s (> -20°C ) an exchange p r o c e s s such as 6 . 1 1 b ^ 6 . 1 1 c ( F i g . 6 . 11 ) seems o p e r a t i v e and a l l t h e h y d r i d o l i g a n d s become e q u i v a l e n t t o g i v e o n l y one s i g n a l : s i g n a l A . (b) R e a c t i o n i n CHgCN and CgH g H y d r o g e n a t i o n i n CHgCN r e s u l t e d i n a y e l l o w o i l a f t e r s o l v e n t r e m o v a l . A t - 9 5 ° C , t h e H^ NMR spec t r um ( C D ? C 1 ? ) o f t h i s p r o d u c t e x h i b i t e d a t l e a s t 221 Fe ,Rh(NBD)+ + H 2 CeH 6 4^ XI A-F i g . 6 . 1 2 : Room t e m p e r a t u r e 400 MHz ^ NMR spec t r um ( C D 2 C 1 2 ) o f t h e h y d r o g e n a t i o n p r o du c t o f XI f rom benzene . 222 13 s i g n a l s i n t h e r ange - 10 t o -22 ppm, some o f w h i c h a r e s t r o n g l y t e m p e r a -t u r e - d e p e n d e n t . A l l t h e peaks were p o o r l y r e s o l v e d . When a benzene s l u r r y o f t h e c a t a l y s t p r e c u r s o r XI was exposed to H 2 , t he o r ange s o l u t i o n d e p o s i t e d a d a r k brown p r e c i p i t a t e i m m e d i a t e l y . The s o l i d was s e p a r a t e d by f i l t r a t i o n and r e c r y s t a l l i z e d f rom a C ^ C l ^ / h e x a n e s o l u t i o n t o g i v e deep brown c r y s t a l s . In F i g . 6 .12 i s shown t he room tempe-r a t u r e ''H NMR spec t r um o f t h i s p r o d u c t . The spec t rum i s h i g h l y s ymme t r i c and v e r y s i m p l e . No h y d r i d e r e s onan c e was o b s e r v ed on c o o l i n g t o - 9 0 ° C . On t h e b a s i s o f t h e r e a c t i o n d e s c r i b e d i n e q u a t i o n ( 6 . 8 ) t h e p r o d u c t c o u l d be a n 6 - a r e n e c omp l e x . However t h e ^H NMR and a n a l y t i c a l r e s u l t s ( T a b l e 6 .6 ) a r e no t c o n s i s t e n t w i t h t h i s . A c r y s t a l s t r u c t u r e d e t e r m i n a t i o n i s i n p r o g r e s s [ 1 4 5 ] , (D) H y d r o g e n a t i o n o f ( R , R ) - X I V R e a c t i o n i n MeOH r e s u l t e d i n t h e u p t a k e o f 2 . 5 e q u i v a l e n t s o f H 2 and a r e d d i s h brown s o l i d a f t e r s o l v e n t r e m o v a l . In F i g . 6 .13 i s shown t h e room t e m p e r a t u r e "'H NMR spe c t r um o f t h i s p r o d u c t . The h y d r i d e NMR p a t t e r n c o n s i s t s o f a p a i r o f t r i p l e t s o f t r i p l e t s c e n t e r e d a t - 8 . 9 8 and - 8 . 5 0 ppm o f i n t e n s i t y r a t i o 6 t o 1 . C o u p l i n g s i n s i g n a l s a r e 60 . 4 and 1 7 . 6 H z . These o b s e r v a t i o n s s ugge s t t h a t t h e p r o d u c t c o u l d be o f t h e t y p e [ ( L - L ) R h H ] 2 ° . A p o s s i b l e r o u t e to t h i s p r o d u c t can be deduced f rom F i g . 6 . 2 : 6 . 2 a ^ 6 . 2 b ( o r 6 . 2 c ) ^ 6 . 2 d ^ 6 , 2 f . The NMR spec t rum f u r t h e r s u g g e s t s t h a t t h e f o l l o w i n g two g e o m e t r i c a l i s ome r s a r e s l o w l y e x c h a n g i n g , each i s ome r u n d e r g o i n g a r a p i d i n t r a m o l e c u l a r s i t e -exchange ( e q u a t i o n 6 . 9 ) . 223 F i g . 6 . 1 3 : Room t e m p e r a t u r e H NMR (400 MHz) spec t rum ( C D 2 C 1 2 ) o f t he h y d r o g e n a t i o n p r o d u c t o f ( R , R ) - X I V f rom MeOH. On l y h y d r i d e p o r t i o n i s shown. 224 ( /Rh^ Rh^ J NT P2 slow ( /Rh N: Rh' (6.9) fast fast Ni I ^ H s ^ I ^ P 2 ^Rh ^ R h C ) mi ( t r a n s ) I Rh Rri ) N ^ ^N 2 ( c i s ) _o The p a i r o f e q u i v a l e n t h y d r i d e s i n t h e t r a n s i s omer wou ld show a t r i p l e t o f t r i p l e t s f rom t he r e s u l t o f t h e f a s t i n t r a m o l e c u l a r p r o c e s s . The p a i r o f d i a s t e r e o t o p i c h y d r i d e s i n t h e c i s i s ome r become e q u i v a l e n t t h r o u g h t h i s p r o c e s s and r e s u l t i n t h e same NMR p a t t e r n . The t r a n s i s omer i s e x pe c t e d t o be more s t a b l e than t h e c i s i s omer because t h e c i s i s ome r has one b r i d g i n g h y d r i d e t r a n s to both P a t oms . Thus t h e s h a r p s e t i s r e a s o n a b l y a s s i g n e d t o t h e t r a n s i s o m e r , and t h e weaker s e t t o t h e c i s i s o m e r . The l a r g e r c o u p l i n g ( 6 0 . 4 Hz) i s p r o b a b l y due to Jp^ , and t he s m a l l e r one ( 1 7 . 6 Hz) t o J^RPH' o r v i c e v e r s a . 6 . 3 . 3 Summary I t has been shown i n t h i s s e c t i o n t h a t h y d r o g e n a t i o n o f V I I I - XIV r e s u l t s i n t h e f o r m a t i o n o f me t a l h y d r i d e s i n v a r i o u s s o l v e n t s su ch as MeOH, 225 CH^CN, and CHC l^ . In many ca se s t h e y can be i s o l a t e d as c r y s t a l l i n e s o l i d s , and t h e i r i d e n t i t y as [ ( L - L ) H R h ( H ) 3 R h ( H ) ( L - L ) ] + C 1 0 4 has been e s t a b l i s h e d i n two c a s e s . The s o l i d p r o d u c t s no t o n l y show f l u x i o n a l b e h a v i o r s bu t a l s o seem t o p roduce r e v e r s i b l y o t h e r h y d r i d e s p e c i e s i n s o l u t i o n . In o t h e r 1 on c a s e s , NMR ( H , P) m o n i t o r i n g o f r e a c t i o n s o l u t i o n a l s o r e v e a l s t h a t more t han one h y d r i d e s p e c i e s i s p roduced i n a g i v e n r e a c t i o n . 226 CHAPTER 7 GENERAL CONCLUSION AND SUGGESTIONS FOR FUTURE STUDIES 7.1 FERROCENYLPHOSPHINE LIGANDS The p r e p a r a t i o n and t h e p r o p e r t i e s o f a w i de r a n g e o f f e r r o c e n y l -phosph i ne s have been d e s c r i b e d . S p e c i a l emphas i s has been p l a c e d on t h e s y n t h e s i s o f l i g a n d s c o n t a i n i n g b u l k y t e r t - b u t y l g roups on t h e phosphorus a t oms . One o f t h e most i n t r i g u i n g f i n d i n g s r e l a t i n g t o t h e s y n t h e s i s o f t h e s e l i g a n d s i s t h a t t h e c h i r a l l i g a n d p r e c u r s o r FA can undergo t r i l i t h i a t i o n l e a d i n g t o t h e i s o l a t i o n of t h e unexpec t ed c h i r a l t r i s p h o s p h i n e l i g a n d V I I . T h i s r e a c t i o n i s u n p r e c e d e n t e d , and i t wou ld be d e s i r a b l e t o i n v e s t i g a t e i t s g e n e r a l i t y by a t t e m p t i n g t o p r e p a r e o t h e r a l k y l - and a r y l p h o s p h i n e d e r i v a t i v e s . F u r t h e r m o r e , s i n c e t h e a b s o l u t e c o n f i g u r a t i o n o f t h e p r o d u c t ( V I I ) was no t t h a t a n t i c i p a t e d , t h i s a s p e c t needs to be f u r t h e r s t u d i e d . 7 .2 RHODIUM COMPLEXES OF FERROCENYLPHOSPHINES AS HYDROGENATION CATALYSTS v C a t i o n i c R h ( I ) comp lexes o f t h e f e r r o c e n y l p h o s p h i n e s a r e v e r y e f f e c t i v e c a t a l y s t p r e c u r s o r s f o r h y d r o g e n a t i o n o f a w i d e r ange o f o l e f i n i c s u b s t r a t e s . In p a r t i c u l a r , g r e a t e r r e a c t i o n r a t e s a r e o b t a i n e d w i t h t e r t - b u t y l p h o s p h i n e comp lexes t han w i t h p h e n y l p h o s p h i n e d e r i v a t i v e s . Most s i g n i f i c a n t l y , t h e c h i r a l t r i s p h o s p h i n e complex XIV g i v e s v e r y h i g h o p t i c a l y i e l d s i n h y d r o g e n a -t i o n o f amino a c i d p r e c u r s o r s . The r e s u l t s a r e compa rab l e w i t h t h o s e o b t a i n e d w i t h t h e b e s t o f o t h e r c a t a l y s t s c o n t a i n i n g c h e l a t i n g d i ( t e r t i a r y a r y l p h o s -p h i n e s ) . I t i s a l s o a v e r y e f f e c t i v e c a t a l y s t f o r t h e r e d u c t i o n o f ( E ) - a -227 m e t h y l c i n n a m i c a c i d , g i v i n g one o f t h e h i g h e s t o p t i c a l y i e l d s eve r r e p o r t e d . These r e s u l t s d e m o n s t r a t e t h a t h i g h o p t i c a l y i e l d s can be a c h i e v e d i n t h e absence o f t h e s u p p o s e d l y n e c e s s a r y a r y l g r o u p s . In s t r i k i n g c o n t r a s t , t h e b i s p h o s p h i n e complex X I I I i s a poor c a t a l y s t p r e c u r s o r f o r a s ymmet r i c h y d r o g e n a t i o n o f t h e s u b s t r a t e s so f a r i n v e s t i g a t e d . T h e i r d i f f e r e n t b e h a v i o r s seem to be r e l a t e d t o c o n f o r m a t i o n a l e f f e c t s s i n c e t h e complex X I I I e x i s t s i n s o l u t i o n as a m i x t u r e o f two d i a s t e r e o m e r i c c o n -f o r m e r s , w h i l e t h e comp lex XIV e x i s t s as a s i n g l e c o n f o r m e r . In t h i s r e g a r d , i t wou ld be d e s i r a b l e t o c a r r y o u t c o m p a r a t i v e h y d r o g e n a t i o n s t u d i e s under v a r i o u s r e a c t i o n c o n d i t i o n s i n o r d e r t o i n v e s t i g a t e f u r t h e r t h e c o n f o r m a t i o n a l e f f e c t s . For examp le i t has been shown t h a t change o f s o l v e n t r e s u l t s i n r e v e r s a l o f t h e a b s o l u t e c o n f i g u r a t i o n o f p r o d u c t s . Tempe ra tu r e s h o u l d a l s o be an i m p o r t a n t f a c t o r s i n c e t h e c o n f o r m a t i o n a l i n t e r c o n v e r s i o n has shown t o be t e m p e r a t u r e - d e p e n d e n t . The c h i r a l comp lexes X I I - XIV c o u l d a l s o be i n v e s t i g a t e d f o r t h e h y d r o g e n a t i o n o f o t h e r f u n c t i o n a l g roups such as C = 0 , C=N, e t c . , s i n c e some Rh ( I } comp lexes d e r i y e d f rom a 1 k y l p h o s p h i n e s have been r e p o r t e d t o be more e f f e c t i v e f o r t h e r e d u c t i o n o f c a r b o n y l g roup t han t h e i r a r y l p h o s p h i n e a n a l o g u e s . 7 . 3 KINETIC AND MECHANISTIC STUDIES OF HYDROGENATION The most s i g n i f i c a n t f i n d i n g o f t h i s work i s t h a t t h e h y d r o g e n a t i o n o f t h e c a t a l y s t p r e c u r s o r s V I I I - XIV l e a d s to t h e f o r m a t i o n o f me ta l h y d r i d e s 1 31 i n v a r i o u s s o l v e n t s such as a l c o h o l , CHgCN, C H C 1 3 , e t c . NMR (. H, P) m o n i t o r i n g s u g g e s t s t h a t v a r i o u s h y d r i d e s p e c i e s a r e formed r e v e r s i b l y i n any 228 one r e a c t i o n . I n t e r e s t i n g l y , t h e a n t i c i p a t e d d i s o l v a t e [ ( L - L ) R h ( S ) 2 ] + was not o b s e r v e d when S i s MeOH o r E tOH. In many c a se s h y d r i d e s can be i s o l a t e d as c r y s t a l l i n e s o l i d s wh i c h show f l u x i o n a l b e h a v i o r s i n s o l u t i o n . T h i s un i que b e h a v i o r o f t h e p r e s e n t c a t a l y s t s y s t ems ( V I I I - XIV) may be due t o t he p r e s en ce o f t h e b u l k y t e r t - b u t y l d e r i v a t i v e s . H o w e v e r / t h i s a s p e c t needs f u r t h e r s t u d i e s . I t a l s o seems i n a p p r o p r i a t e t o make any dogma t i c s t a t e m e n t c o n c e r n i n g t h e mechan i sm( s ) o f c a t a l y t i c h y d r o g e n a t i o n o f o l e f i n s because h y d r i d e s a r e fo rmed and c o u l d be i n v o l v e d i n t h e i n i t i a l s t e p s . In t h i s r e g a r d i t i s h i g h l y recommended t h a t t h e i r c a t a l y t i c p r o p e r -t i e s be f u r t h e r i n v e s t i g a t e d by c a r r y i n g ou t c a r e f u l k i n e t i c and m e c h a n i s t i c s t u d i e s o f h y d r o g e n a t i o n . These s t u d i e s s h o u l d i n c l u d e a s ymme t r i c h y d r o g e -n a t i o n i n o r d e r t o f u r t h e r i n v e s t i g a t e t h e e l e c t r o n i c and s t e r i c e f f e c t s o f t h e c h i r a l c a t a l y s t p r e c u r s o r s on e n a n t i o f a c e - d i s c r i m i n a t i o n . 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Complex Type ^ ( h y d r i d e p o r t i o n ) 3 1 P { ] H } R e f . 6H J RhH J P H 6P J R h P J P P (A) Nonhyd r i d e s ( a ) [ R h ( L - L ) ( D i e n e ) ] + / [ R h ( L ) 2 ( D i e n e ) ] + L-L=CHIRAPHOS 58 .4 154 47d DIOP 17.1 152 47d DIPAMP 5 0 . 9 159 47d DIPHOS 5 6 . 9 156 47d PROPHOS 60 . 5 41 .8 172 139 3 4 48 L=PPh 3 27 . 6 156 47d PPh 2 Me 3 .5 140 47d (b) [ R h ( L - L ) ( M e O H ) 2 ] + / [ R h ( L ) 2 ( M e O H ) 2 ] + L-L=CHIRAPHOS 8 3 . 9 200 47d DIOP 4 3 . 0 199 47d DIPAMP 8 0 . 8 209 47d DIPHOS 81 .2 203 47d PROPHOS 86 . 7 68 . 9 204 55 202 0 0 48 L=PPh 3 57 . 2 207 47d T a b l e c o n t ' d 243 Complex Type ^ ( h y d r i d e p o r t i o n ) 3 1 P t 1 H} R e f . 6H J RhH J P H 6P J RhP Jpp (B) Monomer ic H y d r i d e s ( a ) [ Rh (D IPH0S )H ] 2 + /MeCN - 1 5 . 7 12.1 17 . 2 46a (b) [ R h ( L ) r t H ] ° L = P B u 3 ; n=2 - 1 3 . 9 ( d t ) 11 19 137a - P ^ - C 6 H 1 1 > 3 S 0 = 2 - 1 4 . 9 ( d t ) 19 23 137a P P h 3 ; n=3 - 8 . 9 (bd) 13 146 P ( 0 - i P R ) 3 ; n=3 - 7 . 2 Cm) 120 ( t r a n s ) 139b P P h 3 ; n=4 - 1 0 . 6 ( b s ) 0 16 ( c i s ) 31 .7 (m) 28 . 2 ( d i d ) 113 162 27 134 P ( . 0Me) 3 ; n=4 -11 .6 (qnd) 9 .8 35 139b ( c ) [ R h ( L - L ) ( L ) 2 H ] ° L-L= R 2 P ( C H 2 ) 2 P R 2 (R= OMe) L=PMe 3 - 9 . 8 ( t d l t ) 1 0 . 6 8 8 . 5 2 2 . 6 228 .7 ( d t ) - 2 2 . 6 ( o d t ) 185 141 7 0 . 5 138a L-L= R 2 P ( C H 2 ) 2 P R 2 (R= 0 - i P r ) - 1 0 . 4 ( t d l t ) 10 . 7 8 5 . 4 138a L= PMe 3 21 .1 (d) t r a n s - ( L . L ) -[ R h ( L ) 2 ( H ) 2 ( S ) 2 ] + L= P P h 3 ; S=MeOH 41 .8 121 47d PPh 2 Me; S= MeOH 2 3 . 8 118 47d T a b l e c o n t ' d . . . 244 V h y d r i d e p o r t i o n ) 3 T P T H } Complex Type • R e f . 6 H J RhH J PH 6 P J R h P J P P (C) D i m e r i c H y d r i d e s (a ) [ R h ( L - L ) H ] ° L-L= R 2 P ( C H 2 ) 2 P R 2 - 4 . 3 34.1 33 -35 196 .4 212 .4 138a (R= 0 - i P r ) ( b s e p ) ( : i J + 3 J ) (b) [ R h ( L ) 2 ( H ) 2 ] ° L= P ( O - i P r ) (35°C) - 7 . 1 3 4 . 2 3 6 . 6 3 .2 249 139b ( o t q n t ) (bd) P ( N M e 9 ) Q (28°C) - 9 . 2 3 3 . 3 30 . 7 132 .2 139c 2 3 ( q r t ) ( c ) [ R h 2 ( L - L ) 2 ( H ) 4 ] = R 2 P ( C H 2 ) 2 P (R= 0 - i P r ) L - L = R 2 P ( C 2 ) 2 R 2 - 7 . 2 148 138a (bm) - 1 2 . 0 ( b s ) (d ) [ R h 2 ( L ) 4 ( H ) 4 ] L= P ( 0 - i P r ) 3 ( - 85°C ) - 7 . 8 180 139b (dm) ( t r a n s ) - 11 . 1 89 (dm) ( t r a n s ) - 1 4 . 5 (b s ) (e) [ I r 2 ( H ) 2 ( p - H ) 3 ( L - L ) 2 ] + L-L= R 2 P ( C H 2 ) 3 P R 2 ( R = ph) ( - 45°C ) - 6 . 9 (d) - 7 . 9 ( t ) - 2 0 . 6 (m) 70 65 19 143 T a b l e c o n t ' d 245 V h y d r i d e p o r t i o n ) 3 1 P { ] H } Complex Type • R e f . 6 H J RhH J P H 6 P J R h P J P P ( f ) I I r 2 ( H ) 2 ( y - H ) 3 ( . L ) 4 ] + ( - 90°C ) ( - 80°C ) L= P P h , - 6 . 9 86 15 . 3 95 144a <d> 18 . 5 - 8 . 4 65 ( t ) - 2 3 . 9 ( s ) C o u p l i n g c o n s t a n t s a r e i n Hz : d t = d o u b l e t o r t r i p l e t s , bd = broad d o u b l e t , bs = broad s i n g l e t , m = m u l t i p l e t , d i d = doub l e d o u b l e t , qnd = q u i n t e t o f d o u b l e t s , od t = o v e r l a p p i n g d o u b l e t o f t r i p l e t s , t d l t = t r i p l e t o f d oub l e t r i p l e t s , bsep = broad s e p t e t , o t qn = o v e r l a p p i n g t r i p l e t o f q u i n t e t s , bm = broad m u l t i p l e t , dm = d o u b l e t o f m u l t i p l e t s , d = d o u b l e t , t = t r i p l e t , s = s i n g l e t , q r t = q u a r t e t o f t r i p l e t s . PUBLICATIONS: W . R . C u l l e n , T . J . K i m , F . W . B . E i n s t e i n , and T . J o n e s , The s t r u c t u r e o f t h e h y d r o g e n a t i o n c a t a l y s t [ ( P - P ) R h ( N B D ) ] C 1 0 . , 5 H P-P= (n - ( ( C H 3 ) 3 C ) 2 P ( C 5 H 5 ) 2 ) 2 F e and some c o m p a r a t i v e r a t e s t u d i e s . O r g a n o m e t a l l i c s , 2 , 7 1 4 - 7 1 9 ( 1 9 8 3 ) W . R . C u l l e n , T . J . K i m , I . B u t l e r , and S . R e t t i g , 1 , 1 ' - B i s p h o s p h i n o f e r r o c e n e s : S y n t h e s i s , Me ta l Complex F o rma t i o n and C r y s t a l S t r u c t u r e o f Th r ee Me ta l Comp l e xe s . O r g a n o m e t a l l i c s , i n p r e s s W . R . C u l l e n , I . B u t l e r , and T . J . K i m , S y n t h e s i s o f some i s o p r o p y l p h o s p h i n o f e r r o c e n e s . J . O r g a n o m e t a l . Chem. , i n p r e s s W . R . C u l l e n , T . J . K i m , I . B u t l e r , F . W . B . E i n s t e i n , and T . J o n e s , Me ta l h y d r i d e s f rom c a t i o n i c r h o d i u m ( I ) comp lexes o f d i ( t e r t i a r y p h o s p h i n e s ) ; i m p l i c a t i o n f o r a s ymme t r i c c a t a l y s i s . J . Chem. S o c , i n p r e s s W . R . C u l l e n , T . J . K i m , F . W . B . E i n s t e i n , and T . J o n e s , The s t r u c t u r e s o f t h r e e h y d r o g e n a t i o n c a t a l y s t s [ ( P - P ) R h ( N B D ) ] C 1 0 . 5 1 2 5 3 4 and some c o m p a r a t i v e r a t e s t u d i e s , P-P=(n -R R PC , -H . ) (n -R R P C c H j F e : 1 2 3 4 1 2 3 4 1 3 z 4 R I =R^=R J =R H =Ph; R i =R^=Ph; R =R =CMe 3 ; R =R =Ph; R =R =Ph. O r g a n o m e t a l l i c s , i n p r e s s W . R . C u l l e n , T . J . K i m , S . E v a n s , and J . T r o t t e r A s ymmet r i c h y d r o g e n a t i o n c a t a l y z e d by [ ( L - L ) R h ( N B D ) ] C l 0 4 : C o m p a r a t i v e s t u d i e s and t h e s t r u c t u r e o f a c h i r a l f e r r o c e n y l p h o s p h i n e : L-L= ( n 5 - C 5 H 5 _ n ( P R 2 ) n F e ( n 5 - C 5 H 3 ( P R 2 ) ( C H M e N M e 2 ) - l , 2 ) ; n = 0 - 2 , R = C M e 3 . J . O r g a n o m e t a l . Chem. , s u b m i t t e d f o r p u b l i c a t i o n c o n t i n u e d t o t h e nex t pag-e. In a d d i t i o n to t h e above p u b l i c a t i o n s t h e f o l l o w i n g papers have been and w i l l be p r e s e n t e d a t t h e c h em i c a l c o n f e r e n c e o f Canada and o f A u s t r a l i a . * W . R . C u l l e n , T . J . K i m , S . R e t t i g , F . B . W . E i n s t e i n , T . J o n e s , and A . J . W i l l i s , F e r r o c e n y l p h o s p h i n e R h ( I ) h y d r o g e n a t i o n c a t a l y s t s . The 66 t h C a n a d i a n Chem i ca l C o n f e r e n c e and E x h i b i t i o n , J u n e , 1983 , C a l g a r y , E d . , Canada W . R . C u l l e n , T . J . K i m , T . G . A p p l e t o n , N . F . H a n , and I . B u t l e r , NMR s p e c t r a o f f e r r o c e n y l p h o s p h i n e s and t h e i r c omp l exe s w i t h p l a t i n u m m e t a l s , The Roya l A u s t r a l i a n Chem i ca l C o n f e r e n c e , J a n u a r y , 1984 , H o b a r t , A u s t r a l i a W . R . C u l l e n , T . J . K i m , and N . F . H a n , C a t i o n i c Rhod i um( I ) and P a l l a d i u m ( I I ) Comp lexes as C a t a l y s t P r e c u r s o r s f o r O l e f i n H y d r o g e n a t i o n . The 67 t h C anad i a n Chem i c a l C o n f e r e n c e and E x h i b i t i o n , J u n e , 1984 , M o n t r e a l , Q u e , Canada , p r e s e n t e d as an i n v i t e d pape r 

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