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Soluble and polymer-bound palladium and platinum complexes of ferrocene derivatives Han, Nam Fong 1986

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SOLUBLE AND POLYMER-BOUND PALLADIUM AND PLATINUM COMPLEXES OF FERROCENE DERIVATIVES By NAM FONG HAN B.Sc. (Hons), University of Manitoba, 1982. A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES Department of Chemistry We accept this thesis as conforming to the required standard The University of British Columbia November 1986 (c) Nam Fong Han, 1986 In p resen t i ng this thesis in part ial fu l f i lment o f the requ i remen ts for an a d v a n c e d d e g r e e at the Un ivers i ty o f Br i t ish C o l u m b i a , I agree that the Library shal l m a k e it f reely avai lab le for re fe rence and s tudy . I fur ther agree that pe rm iss ion for ex tens i ve c o p y i n g o f th is thesis for scho la r l y p u r p o s e s may b e g ran ted by the h e a d o f m y d e p a r t m e n t o r by his o r her represen ta t i ves . It is u n d e r s t o o d that c o p y i n g o r pub l i ca t i on of this thesis for f inanc ia l ga in shal l no t b e a l l o w e d w i t h o u t m y wr i t ten p e r m i s s i o n . D e p a r t m e n t T h e Un ivers i t y o f Br i t ish C o l u m b i a 1956 M a i n M a l l V a n c o u v e r , C a n a d a V 6 T 1Y3 D a t e (A-K. VAwdk, Wfr. D E - 6 G / 8 1 ) i i ABSTRACT The preparation, characterization, and catalytic properties of some soluble and polymer-bound palladium and platinum complexes of ferrocene derivatives are described. Special emphasis has been placed on studies of the mixed "hard-soft" ligands such as PPFA and ISOPFA. X X X X H, Y = Z = PPh 2 CHMeNMe2, Y = PPh 2, Z = H CHMeNMe2, Y -= P ( i - P r ) 2 , Z CHMeNMe2, Y = Z = PPh £ = H BPPF PPFA ISOPFA BPPFA The soluble complexes (L-L)MC12 (L-L = BPPF, PPFA, ISOPFA, BPPFA; M = Pd, Pt) and [(L-L)PdS 2][C10 4] 2 (L-L = BPPF, PPFA; S = DMF, py) have been characterized by microanalyses, NMR and IR spectroscopic techniques. The cationic palladium(II) complex [(L-L)PdS 2][C10 4] 2 (L-L = PPFA, S = DMF) is an effective catalyst precursor for the hydrogenation of simple olefins at 30°C and 1 atm pressure. The rate of styrene hydro-genation depends on the substrate concentration, catalyst concentration and the solvent. The results are consistent with a homogeneous catalytic system. 111 Platlnum ( I I ) complexes ( L - L ) P t C l 2 (L-L - (S.R)-PPFA, (S.R)-ISOPFA) are e f f e c t i v e c a t a l y s t precursors f o r the h y d r o s l l y l a t l o n o f aromatic ketones with Ph 2S1H 2. The complexes with mixed " h a r d - s o f t " Ugands are b e t t e r c a t a l y s t precursors than those with d l ( t e r t i a r y phosphlne) Ugands. Under the same c o n d i t i o n s the h y d r o s l l y l a t l o n o f f e r r o c e n y l ketones r e s u l t s 1n f u r t h e r r e d u c t i o n and a f f o r d s mainly the a l k y l f e r r o c e n e products. The s t a b l e carbonlum Ion FcC^HCH^ (Fc = Fe-( C 5 H 5 ) ( C 5 H 4 ) - ) 1s reduced by Ph 2S1H 2 to FcCHgCHj 1n a thermal r e a c t i o n which 1s c a t a l y z e d by the complex ( P P F A ) P t C l 2 . The r e a c t i o n o f Ph 2S1H 2 with ( L - L ) P t C l 2 (L-L « PPFA, ISOPFA) y i e l d s a s t a b l e platlnum(IV) hydride, which e l i m i n a t e s Ph 2S1HCl 1n s o l u t i o n to a f f o r d (L-L)PtHCl. The mechanistic I m p l i c a t i o n s o f these observations are d i s c u s s e d . Polymers f u n c t i o n a l 1 z e d with ferrocene and ferrocene d e r i v a t i v e s have been prepared. Mossbauer s p e c t r o s c o p i c techniques and microanalyses are used to c h a r a c t e r i z e these polymers and t h e i r palladium and platinum complexes. In a number o f cases these r e s u l t s are confirmed by the c r o s s -13 p o l a r l z a t l o n / m a g i c - a n g l e s p i n n i n g C NMR s p e c t r o s c o p i c technique. The palladium ( I I ) and platlnum ( I I ) d e r i v a t i v e s o f the f e r r o c e n y l -amlne and -phosphlne c o n t a i n i n g polymers are e f f e c t i v e c a t a l y s t s f o r the hydrogenatlon and h y d r o s l l y l a t l o n o f o l e f i n s . A l l the c a t a l y s t s can be e a s i l y separated from the r e a c t i o n mixture and can be r e c y c l e d with no l o s s o f a c t i v i t y . The pronounced e f f e c t o f the attached Ugand 1n the palladium based polymers I n d i c a t e s t h a t f r e e metal 1s not In-volved. However, 1n the case o f platinum based c a t a l y s t s , I t 1s l i k e l y t h a t r e d u c t i o n to platinum metal takes p l a c e . i v TABLE OF CONTENTS Page TITLE 1 ABSTRACT i i TABLE OF CONTENTS i v LIST OF TABLES i x LIST OF FIGURES x i i ABBREVIATIONS x i v ACKNOWLEDGEMENTS xvi CHAPTER 1 INTRODUCTION 1 1.1 GENERAL ASPECTS OF FERROCENE DERIVATIVES 1 1.2 FERROCENYLPHOSPHIMES IN HOMOGENEOUS CATALYSIS 8 1.2.1 Hydrogenation 8 1.2.2 H y d r o s i l y l a t i o n 11 1.2.3 Grignard Cross-coupling 17 1.2.4 Other C a t a l y t i c Reactions 22 1.3 HOMOGENEOUS VERSUS HETEROGENEOUS CATALYSTS 24 1.4 GOALS OF THE PRESENT STUDY 27 CHAPTER 2 EXPERIMENTAL SECTION 28 2.1 GENERAL 28 2.1.1 Instrumentation 29 2.1.2 Hydrogenation Experiments 31 2.1.3 H y d r o s i l y l a t i o n Experiments 31 V Page 2.2 SYNTHESES OF STARTING MATERIALS 33 2.2.1 Chlorodiisopropylphosphine 33 2.2.2 Di phenyl si lane 34 2.2.3 Acetyl ferrocene 34 2.2.4 Ferrocenylethanol 34 2.2.5 Ferrocenylethyl carbonium Tetrafluoro-borate 35 2.2.6 Dilithioferrocene-TMEDA Adduct 35 2.2.7 U,H- Dimethyl ami nocyanomethyl-ferrocene 35 2.2.8 N_, N-Dimethyl ami noethyl ferrocene, FA 36 2.2.9 (S)- and (R)-N,N-Dimethyl aminoethyl-ferrocene, (S)- and (R)-FA 36 2.2.10 Polystyrene Type Polymers 37 2.3 SYNTHESES OF FERROCENYLPHOSPHINES 38 2.3.1 1,1'-Bis(diphenylphosphino)ferrocene, BPPF 38 2.3.2 2- Di phenylphosphi no-1-(N,N-dimethy1-aminoethyl)ferrocene, PPFA 39 2.3.3 2- Diisopropylphosphino-l-(t^,N-dimethyl-aminoethyl)ferrocene, ISOPFA 39 2.3.4 1' ,2-Bis(diphenylphosphino)-l-(N,N-di-methylaminoethyl)ferrocene, BPPFA . . . . . . 40 vi Page 2.4 SYNTHESES OF PALLADIUM AND PLATINUM COMPLEXES OF FERROCENYLPHOSPHINES 40 2.4.1 Palladium Complexes (L-L)PdCl2 40 2.4.2 Cationic Palladium Complexes [(L-L)PdS2][C104]2 41 2.4.3 Platinum Complexes (L-L)PtCl 2 42 2.4.4 Platinum Complex (L-L)PtHCl 43 2.5 SYNTHESES OF POLYMER-BOUND FERROCENE DERIVATIVES. 44 2.5.1 Reaction of Lithioferrocene with Bio-Beads B, Polymer-I 44 2.5.2 Reaction of Lithioferrocene with Aldehydic Resin, Polymer-II 44 2.5.3 Reaction of Dilithioferrocene-TMEDA Adduct with Bio-Beads A, Polymer-III . . . . 45 2.5.4 Reaction of Dilithioferrocene-TMEDA Adduct with Aldehydic Resin, Polymer-IV . . 46 2.5.5 Reaction of Lithium Derivative of FA with Bio-Beads B, Polymer-V 46 2.5.6 Reaction of Lithium Derivative of FA with Aldehydic Resin, Polymer-VI 46 2.5.7 Reaction of Lithium Derivative of BPPF with Aldehydic Resin, Polymer-VII 47 2.5.8 Reaction of Lithium Derivative of PPFA with Aldehydic Resin, Polymer-VIII 47 v i i Page 2.5.9 R e a c t i o n o f L i t h i u m D e r i v a t i v e o f (S,R)-PPFA w i t h A l d e h y d i c R e s i n , P o l y m e r - V I I I * .. 48 2.6 SYNTHESES OF PALLADIUM AND PLATINUM COMPLEXES OF POLYMER-BOUND FERROCENE DERIVATIVES 48 2.6.1 P a l l a d i u m Complexes 48 2.6.2 P l a t i n u m Complexes 49 CHAPTER 3 CATIONIC PALLADIUM(II) COMPLEXES OF FERROCENYL-PHOSPHINES 50 3.1 INTRODUCTION 50 3.2 RESULTS AND DISCUSSION 51 3.2.1 S y n t h e s i s and C h a r a c t e r i z a t i o n 51 3.2.2 H y d r o g e n a t i o n S t u d i e s 62 3.3 SUMMARY 72 CHAPTER 4 PLATINUM(II) COMPLEXES OF FERROCENYLPHOSPHINES 73 4.1 INTRODUCTION 73 4.2 RESULTS AND DISCUSSION 75 4.2.1 S y n t h e s i s and C h a r a c t e r i z a t i o n 75 4.2.2 H y d r o s i l y l a t i o n S t u d i e s 84 4.3 SUMMARY 103 CHAPTER 5 POLYMER-BOUND FERROCENE DERIVATIVES AND THEIR PALLADIUM AND PLATINUM COMPLEXES 105 5.1 INTRODUCTION 105 5.2 RESULTS AND DISCUSSION 107 5.2.1 S y n t h e s i s and C h a r a c t e r i z a t i o n 107 5.2.2 H y d r o g e n a t i o n S t u d i e s 130 v i i i Page 5.2.3 H y d r o s i l y l a t i o n Studies 139 5.3 SUMMARY 154 CHAPTER 6 GENERAL CONCLUSIONS AND PERSPECTIVES 155 6.1 SOLUBLE PALLADIUM(II) AND PLATINUM(II) COMPLEXES OF FERROCENYLPHOSPHINES 155 6.2 POLYMER-BOUND PALLADIUM AND PLATINUM COMPLEXES OF FERROCENE DERIVATIVES 156 REFERENCES 158 1x LIST OF TABLES Table Page 3.1 M i c r o a n a l y t i c a l r e s u l t s and melting p o i n t s f o r (L-L) and ( L - L ) P d C l 2 53 3.2 }H and ^POH } NMR data f o r (L-L) and ( L - L ) P d C l 2 .. 54 3.3 M i c r o a n a l y t i c a l r e s u l t s and melting points f o r the c a t i o n i c palladium complexes 60 3.4 ^ and 3 1 P { 1 H } NMR data f o r the c a t i o n i c palladium complexes 61 3.5 C a t a l y t i c hydrogenation o f o l e f i n s c a t a l y z e d by c a t i o n i c palladium complexes I-V 63 - 3.6 E f f e c t of EtgN i n the hydrogenation o f styrene c a t a l y z e d by complex IV 65 4.1 M i c r o a n a l y t i c a l r e s u l t s and melting p o i n t s f o r ( L - L ) P t C l 2 76 4.2 }H and ^POH } NMR data f o r ( L - L ) P t C l 2 77 4.3 H y d r o s i l y l a t i o n of acetophenone c a t a l y z e d by ( L - L ) P t C l 2 85 4.4 Asymmetric h y d r o s i l y l a t i o n o f ketones with P h 2 S i H 2 c a t a l y z e d by ((S,R)-PPFA)PtCl 2 88 4.5 Asymmetric h y d r o s i l y l a t i o n o f ketones with P h 2 S i H 2 c a t a l y z e d by ((S,R)-IS0PFA)PtCl 2 89 4.6 Asymmetric h y d r o s i l y l a t i o n o f butyrophenone with P h 2 S i H 2 c a t a l y z e d by ((S,R)-PPFA)PtCl 2 90 4.7 M i c r o a n a l y t i c a l r e s u l t s and ^H NMR data f o r FcCH,R and FcCH(0H)R 92 X Table Page 4.8 Microanalytical results for platinum hydride complexes 96 4.9 Physical and NMR data for platinum hydride complexes 99 5.1 Mossbauer parameters and microanalytical results for polymer-bound ferrocene derivatives 116 5.2 Mossbauer parameters for some ferrocene compounds . . 117 5.3 Mossbauer parameters and microanalytical results for palladium and platinum complexes of polymer-bound ferrocene derivatives 128 5.4 Hydrogenation of olefins in benzene catalyzed by polymer-VIII-Pd 132 5.5 Hydrogenation of styrene catalyzed by polymer-VHI-Pd 133 5.6 Hydrogenation of olefins catalyzed by polymer-bound palladium complexes 134 5.7 Hydrogenation of 1-hexene in MeOH 135 5.8 Hydrogenation of olefins catalyzed by polymer-bound platinum complexes 137 5.9 Hydrogenation of styrene catalyzed by polymer-bound platinum complexes 138 5.10 Hydrosilylation of styrene with HSiCl^ catalyzed by polymer-bound palladium complexes 141 xi Table Page 5.11 Microanalytical results for polymer-VIII and its palladium derivatives 143 5.12 Asymmetric hydrosilylation of styrene with HSiClg . . 145 5.13 Hydrosilylation of 1-hexene with HSiCl 3 148 5.14 Hydrosilylation of styrene with HSiClg catalyzed by polymer-bound platinum complexes 149 5.15 Hydrosilylation of olefins with HSiClg catalyzed by soluble platinum complexes (L-LjPtC^ 151 5.16 Hydrosilylation of ketones with PhgSiHg catalyzed by polymer-VIII*-Pt 152 xii LIST OF FIGURES Figure Page 1.1 Preparative routes to the chiral ferrocenyl-phosphine ligands 4 1.2 Two possible catalytic hydrogenation cycles for the dihydride catalysts: A, hydride route; B, olefin route 12 1.3 The proposed mechanism of hydrosilylation of olefins catalyzed by platinum complexes 15 1.4 The proposed mechanism of hydrosilylation of ketones catalyzed by rhodium complexes 16 1.5 Catalytic process of cross-coupling reaction catalyzed by nickel complexes 19 1.6 Proposed intermediate in Grignard cross-coupling reaction 21 3.1 32.3 MHz 3 1 P{ 1 H } NMR spectrum of (BPPF)PdCl2 56 3.2 32.3 MHz 3 1 P{ ] H } NMR spectrum of (BPPFA)PdCl2 57 3.3 32.3 MHz 3 1 P{ 1 H } NMR spectrum of (PPFA)PdCl2, A; (IS0PFA)PdCl2, B 58 3.4 Hydrogenation uptake curves for the hydrogenation of styrene catalyzed by cationic palladium complex IV at 30°C and 1 atm total pressure 67 3.5 Dependence of maximum hydrogenation rate on [styrene] 68 3.6 Dependence of maximum hydrogenation rate on [Pd] . . . 69 x i i i ure Page 3.7 Hydrogenation uptake curves for the hydrogenation of styrene; A, in the absence of Hg; B, same conditions as A with Hg added 70 4.1 121.4 MHz ^ P ^ H } NMR spectrum of (BPPF)PtCl2 . . . . 79 4.2 121.4 MHz 3 1 P { ]H } NMR spectrum of ((S,R)-BPPFA)PtCl2 80 4.3 121.4 MHz 3 1 P { ] H } NMR spectrum of ((S,R)-PPFA)PtCl2 81 4.4 121.4 MHz 3 1 P { ]H } NMR spectrum of ((S,R)-IS0PFA)PtCl2 82 4.5 The crystal structure of ((S,R)-IS0PFA)PtCl2 '83 4.6 400 MHz H^ NMR spectrum (hydride region) of (PPFA)PtCl2(H)(SiHPh2) in CD^Cl2 solution 97 4.7 400 MHz NMR spectrum (hydride region) of (IS0PFA)PtCl2(H)(SiHPh2) in CD2C12 solution 100 4.8 Proposed mechanism for the hydrosilylation of ketones with Ph 2SiH 2 catalyzed by (L-L)PtCl 2 102 5.1 Mossbauer spectrum of polymer-I I l l 5.2 Mossbauer spectrum of BPPF 112 5.3 Mossbauer spectrum of PPFA 113 5.4 Mossbauer spectrum of IS0PFA 114 5.5 Mossbauer spectrum of BPPFA 115 5.6 1 3 C CP/MAS NMR spectrum of ferrocene, A; FA, B 118 5.7 1 3 C CP/MAS NMR spectrum of polymer-I 119 x i v ABBREVIATIONS atm atmosphere bd broad doublet bm broad m u l t i p l e t BMPP benzyl methyl phenylphosphine bp b o i l i n g p o i n t BPPF 1,1'-bi s(diphenylphosphino)ferrocene BPPFA 1' ,2-bis(diphenylphosphino)-l-(f[,^-dimethylaminoethyl)-ferrocene bs broad s i n g l e t bt broad t r i p l e t Bu butyl c a t c a t a l y s t or c a t a l y s t precursor COD 1,5-cyclooctadiene CP c r o s s - p o l a r i z a t i o n DIOP 2,3-o-isopropylidene-2,3-dihydroxy-l,4-bis(diphenyl-phosphino)butane DMF N^N-dimethylformamide DMSO dimethyl s u l f o x i d e dppe bis(l,2-diphenylphosphino)ethane e.e. enantiomeric excess Et ethyl FA N_, N-d i methyl ami noethyl ferrocene Fc F e ( C 5 H 5 ) ( C 5 H 4 ) -GLC gas l i q u i d chromatography XV h hour(s) Hz hertz i - P r i s o p r o p y l IR i n f r a r e d ISOPFA 2-di i sopropylphosphi no-1-(N^N-dimethyl ami n o e t h y l ) f e r r o c e n e m m u l t i p l e t MAS magic angle s p i n n i n g MCPBA m-chloroperbenzoic a c i d Me methyl NBD norbornadiene n-Bu n-butyl NMR nuclear magnetic resonance Ph phenyl PPFA 2-diphenylphosphino-l-(N_,N-dimethylaminoethyl )ferrocene py p y r i d i n e q q u a r t e t s s i n g l e t t t r i p l e t t-Bu t e r t - b u t y l THF t e t r a h y d r o f u r a n TLC t h i n l a y e r chromatography TMEDA H»N»N.' ,N.'-tetramethylethylenediamine TMS t e t r a m e t h y l s i l a n e xvi ACKNOWLEDGEMENTS I wish to express my s i n c e r e g r a t i t u d e to P r o f e s s o r W.R. C u l l e n , my research s u p e r v i s o r , f o r h i s guidance and encouragement during the course of t h i s work. I am much indebted to Professors M.D. Fryzuk, B.R. James and J.R. Sams f o r t h e i r suggestions and comments on my work. I am very g r a t e f u l to the t e c h n i c a l s t a f f o f t h i s department, i n p a r t i c u l a r Mr. P. Borda f o r h i s expert microanalyses, Dr. 0. Chan and h i s s t a f f members f o r a s s i s t a n c e during some NMR experiments, and Mrs. A. S a l l o s f o r r e c o r d i n g a l l the Mossbauer s p e c t r a . I a l s o want to thank a l l my lab c o l l e a g u e s , i n p a r t i c u l a r Mr. C. Hampton, Mr. J . J . N i , Mr. E. Wickenheiser, Dr. I.R. B u t l e r and Mr. M.S.R. Cader f o r suggestions and a s s i s t a n c e during the preparation of t h i s thes.is. My thanks are extended to the U n i v e r s i t y of B r i t i s h Columbia and to the National Research Council of Canada f o r f i n a n c i a l support. To my parents and my w i f e , I express my g r e a t e s t thanks f o r t h e i r encouragement and unflagging f a i t h i n me and my work. 1 CHAPTER 1 INTRODUCTION 1.1 GENERAL ASPECTS OF FERROCENE DERIVATIVES The discovery of ferrocene in 1951 [1], the first of the so-called "sandwich compounds", has played a major role in the development of transition metal organometallic chemistry. There continues to be a large number of papers and reviews published which are devoted to studies of ferrocene chemistry [2-6]. For example, an annual review of ferrocene in 1984 by Marr and Rockett [2] contains 211 references; there are 233 and 199 references in the respective 1983 and 1982 reviews [3,4]. The observation that ferrocene behaves as an aromatic system [7] led to the preparation and investigation of many derivatives analogous to those of benzene [8]. In many ways, the chemistry of these two classes of compounds is similar. Thus, a number of potentially multidentate ligands for use in metal complexes were prepared utilizing metalation reactions of ferrocene. For example, the symmetrical l,l'-disubstituted ferrocenes 1_, were synthesized by way of dilithiation of ferrocene followed by treatment of the product with halophosphine, haloarsine [9-11] or dialkyl disulfide [12]. 2 l a E=P, R=Ph b E=P, R=t-Bu c E=P, R=i-Pr d E=P, R=Me e E=As, R-Me o r Ph f E=S, R=Me, i - P r , i - B u , Ph or CH £Ph Important differences between the chemistry of ferrocene derivatives and benzenoid aromatic compounds arise when the stereochemistry of these systems is considered. This is an area of great interest [13-17] due in part to the fact that ferrocene derivatives, 2, are chiral i f one ring bears two different substituents (X * Y) [13]. Thus these compounds are optically active even if X and Y do not possess an asymmetric center. Such molecules are said to have a planar element of chirality [13,18,19]. The preparation of these compounds is relatively easy, and provides access to a very wide variety of chiral ferrocene derivatives with either centers of chirality and/or planes of chirality [6,10,14,20-22]. Two descriptors for configuration are necessary if both central and planar chirality are present [13-15]. In this thesis, the f irst descriptor "S", in compound such as (S,R)-3_ refers to the configuration at the carbon atom of the -CHMeNMe2 group and the second "R", refers to the planar chirality. 3 An important event that instigated the efforts of several research groups [6,10,14,20-22] to study ferrocenylphosphines with planar chirality was a paper published by Ugi and coworkers in 1970 [15b]. These authors reported that the optical resolution of N^N-dimethylaminoethylferrocene, FA, was particularly easy; both antipodes are obtained in high yield. Furthermore, the lithiation of the amine FA was found to proceed with high stereoselectivity as shown in Figure 1.1. Thus by using the stereo-selective lithiation of FA, chiral ferrocenylphosphines 4-5_ [6,10,20-23] were prepared. A small amount of diastereomeric byproduct formed via the minor lithio derivative, 3, was removed by simple recrystallization. When a diastereomeric product such as (R,R)-4a was required, it was prepared in quantity via the silylated ferrocene derivative, equation 1.1. Ferrocenyl-phosphines such as 7_ (or 4a with -CHMeNMe2 group replaced by CH2CH3) and its diphosphine analogue 8 (or 5a with -ChMeNMe2 group replaced by CH2CH3) were prepared from 4a and 5_a, respectively [21]. These ligands have only a planar element of chirality. In addition, optically active l-(dimethyl-amino)methyl-2-(diphenylphosphino)ferrocene, £ , which is analogous to 4a 4 n - B u L i ( 1 ) n - B u L i ( i i ) n-BuLi/TMEDA ( i i i ) C1PR0 ( S , R ) - / ( R , S ) - 5 a X=H, R=Ph b X = H, R = i - P r c X=H, R=t-Bu d X=PR 2, R=t-Bu Nile, 4 : n c ^ ~ ^ ( S , R ) - / ( R , S ) - 3 ( S , S ) - / (R.R ) - 3 C l PR. Figure 1.1 P r e p a r a t i v e routes to the c h i r a l ferrocenylphosphine l i g a n d s . 5 ( R , R ) - 4 a (1.1) 6 (with CHMeNMe2 replaced by CH 2NMe 2) but lacks the carbon c e n t r a l c h i r a l i t y , was prepared by o p t i c a l r e s o l u t i o n of Its phosphlne sulf 1de/dibenzoyl-t a r t a r i c a c i d s a l t L21.24]. 7 In summary, the ferrocenylphosphines have the following unique and significant features: (i) Mono-, bis- and tris-phosphines can be prepared from the same chiral source, simply by changing the lithiation procedure, Figure 1.1. (ii) Aryl- and alkyl-phosphines can be synthesized by using different halophosphines. ( i i i ) Various kinds of functional groups such as amino, alkoxyl or hydroxyl can be introduced into the side chain, e.g. the -NMe2 group in 4_a is easily replaced by other -NR2 groups, (iv) They can contain a planar element of chirality that does not racemize or epimerize under the usual reaction condition, (v) The phosphine can have central chirality and/or planar chirality; those lacking the central chirality can be prepared, e.g. (S,R)-4_a, (R,R)-4_a and (R)-j3. (vi) They can be isolated and purified very readily because of their reasonable stability in air and orange color, making chromatographic separation easy. They are also easily recrystal1ized. (vii) Ferrocenylphosphine ligands with both P ("soft") and N ("hard") atoms present such as 4_-5_, are particularly interesting since there is a continuing interest in ligand systems containing both "soft" and "hard" donor atoms [25-28], There are now numerous reports of metal complexes containing ferrocenylphosphines as chelating bidentate ligands [5,6]. Ferrocenyl-phosphine complexes of group VIII metals have been the most widely studied and have been used as homogeneous catalysts for reactions such as hydrogenation, hydrosilylation and Grignard cross-coupling reactions. The following section will review briefly some of the interesting features of these reactions. 8 1.2 FERROCENYLPHOSPHINES IN HOMOGENEOUS CATALYSIS. 1.2.1 Hydrogenation Among all the transition metal complexes of ferrocenylphosphines, rhodium derivatives have been the most extensively studied [5,6]. The crystal structure of the cationic rhodium(I) complex [(L-L)Rh(NBD)]+, (L-L) = 4_a, shows that both N and P are bound to rhodium [29]. The same P-N binding mode is found when (L-L) = 4b [30], 4c, be and 5d [23]. Ligand 5a appears to use both P atoms to bind to rhodium [20,31]. Hence, it seems that the nature of the groups attached to phosphorus exerts a considerable influence on the choice of binding mode. Cationic rhodium(I) complexes [(L-L)Rh(NBD)]+ (L-L = ferrocenyl-phosphine ligands) are very effective catalysts in the hydrogenation of amino acid precursors such as acylaminocinnamic acid, equation 1.2 [6,20,-23). The results for the acylaminocinnamic and acylaminoacrylic acid reveal that the rates obtained with the tetraphenyl derivative, la , are higher than those obtained with alkylphosphine derivative such as lb [11]. These trends are reversed in the reduction of sterically undemanding substrates such as itaconic acid, a-methylcinnamic acid, 1-octene and cyclohexene [11]. The presence of phenyl groups can result in lower rates, for example, itaconic acid is only 21% hydrogenated in 72 h when using a catalyst derived f ran 4_a yet is 100% hydrogenated in 16 h using one derived from 4c [32]. 9 Ph. H ^ N - C 0 C H 3 H 2 H ^ N - C 0 C H 3 H PhCHo-C?r! COOH [ C a t ] * COOH (1.2) Studies of rhodium complexes of 4c, 5c and 5d [23] indicate that, in the same solvent, the planar chirality of the ligands plays an important role in determining the configuration of the hydrogenated product; e.g. the hydrogenation of itaconic acid catalyzed by the complexes of (S,R)-4c, (S,R)-5_c and (S,S)-5d resulted in (S)-, (S)- and (R)-2-methylsuccinic acid, respectively, as the reduced product [23]. Ligand 5a gives products of the opposite absolute configuration when compared to ligand 4a [29,33]. Thus, (S,R)-5a leads to (S)-acylamino acids while (S,R)-4a leads to (R)-isomers. This reversal of product configurations is also observed when using ligands 4a and 4c [32]. A higher optical yield is obtained in the hydrogenation of acylaminocinnamic acid when ligand 4a is replaced by 4c [32], whereas a lower optical yield resulted when the same substrate is hydrogenated under similar conditions using catalysts derived from 4a and 5_a by replacement of the -CH3 group on the chiral center with -Ph or i-Pr groups [22]. A modified version of 5a with the -NMe2 group replaced by OH, JO, has been used in the reduction of some prochiral carbonyl compounds [34]. The -OH group in Jp_ is believed to be crucial for the high optical yields 10 (43-955.) achieved since much lower optical yields are obtained with (R,S)-5a and (S)-8 which are both analogous to (R,S)-10_ but lack the -OH group [34]. 10 Hence, steric and electronic effects of ligands, as well as the nature of other substituents on the ligand, seem to play a very important role in these catalyzed hydrogenation reactions and one of the advantages of using ligands based on the ferrocene skeleton is the ease with which these parameters can be varied. The mechanism of homogeneous hydrogenation of olefins catalyzed by rhodium complexes has been extensively studied [35-37]. The precise mechanism may differ from system to system, but some common steps are present in most hydrogenation cycles: (i) Activation of hydrogen by formation of M-H bonds, (ii) activation of substrate by its coordination to metal, ( i i i ) hydride transfer from the central metal to the coordinated substrate, and (iv) product formation by reductive elimination. These basic steps may be combined in various ways in completing a catalytic cycle. n The majority of mononuclear and homogeneous olefin hydrogenation catalysts can be roughly classified as monohydride catalysts or dihydride catalysts [35]. The monohydride catalysts have been much less studied. The catalytic mechanism of the dihydride class is thought to involve two possible routes namely the "hydride route" and the "olefin route", Figure 1.2. Both routes may be simultaneously operative and both require vacant coordination sites on the metal for addition of H 2 and complexation of substrate. The active catalyst(s) is usually generated from the catalyst precursor. Wilkinson's earlier studies [38] and Halpern's stepwise kinetic analysis [39] for the Wilkinson catalyst RhClL3 (L = monodentate phosphine), provide evidence for the "hydride route". The mechanism of hydrogenation of some olefins catalyzed by [(L-L)Rh(Diene)]+ (L-L = chelating di(tertiary phosphine) ligands; Diene = NBD or COD) is believed to proceed via the "olefin route" [40,41]. However, it must be emphasized that these generalizations may not be always followed. For example, two research groups [42-44] independently found that catalyst precursors [(L-L)Rh(NBD)JC104 (L-L = chelating P-P or P-N di(tertiary phosphine) ligands) produce metal hydrides when hydrogen is passed through solutions of the catalyst precursors. These results indicate that some catalyst precursors with chelating di(tertiary phosphines) as ligand could function via the hydride route. 1.2.2 Hydrosilylation The addition of Si-H bonds to olefins, acetylenes, aldehydes, ana Catalyst Precursor I I H H Figure 1.2 Two possible catalytic hydrogenation cycles for the dihydride catalysts. A : hydride route; B : olefin route. 13 ketones is catalyzed by many soluble transition metal complexes L45-49]. Rhodium, palladium and nickel complexes of ferrocenylphosphines have been used in homogeneous hydrosilylation of olefins and ketones L20.47J. . The nickel complex (L-L)NiCl 2 , (L-L) = Id , catalyzes not only the addition of silicon hydrides to olefins but also the interchange of hydrogen and chlorine on silicon [50]. Thus, the catalytic hydrosilylation of trichlorosilane with 1-octene gave octyltrichlorosilane and octyldichlorosilane, both in 50% yield, equation 1.3. C 6 H 1 3 C H = C H 2 + HS1C1 3 • C 8 H 1 7 S i C l 3 + C 8 H 1 7 S 1 H C 1 2 ( 1 . 3 ) The palladium complex (L-L)PdCl2» (L-L) = 4a, is a catalyst precursor for the hydrosilylation of olefins such as styrene with trichlorosilane [51], equation 1.4. If the ligand is optically active the product is chiral and can be converted into an optically active alcohol or bromide via the potassium pentafluorosilicate derivatives, equation 1.4 L51.52]. The optical yields are only moderate (~50% e.e.). 14 0r^ + H S i c i 3 Q r 1 " (14) Rhodium complexes of chiral ligands such as 4a, 4d, 5a and 7_ are active catalyst precursors for the asymmetric hydrosilylation of ketones [47,53]. The asymmetric addition of trialkylsilanes and dialkylsilanes to prochiral ketones readily takes place at ambient temperature. It seems that the extent of asymmetric induction depends strongly upon the structure of both the chiral phosphine ligands and the hydrosilanes employed. The marked effect of the hydrosilanes on the stereoselectivity is a very characteristic feature of the asymmetric hydrosilylation of ketones [54-56]. 15 Figure 1.3 The proposed mechanism of hydrosilylation of olefins catalyzed by platinum complexes, M=Pt. 16 Figure 1.4 The proposed mechanism o f h y d r o s i l y l a t i o n o f ketones c a t a l y z e d by rhodium complexes. 17 The mechanism of hydrosilylation of olefins and ketones is not well understood [35,47]. Plausible reaction schemes can be written which rationalize the homogeneous results. However, few kinetic data are available on which to base a particular mechanism. In the case of olefins, Chalk and Harrod [57] proposed a scheme for the hydrosilylation catalyzed by platinum(II) complexes, Figure 1.3. This is analogous to that proposed for the rhodium(I)-catalyzed hydrogenation of olefins (cf. Section 1.2.1). In the case of ketones, the basic features of the proposed mechanism of rhodium-catalyzed hydrosilylation are outlined in Figure 1.4 [45J. Both paths A and B have been invoked to account for the mechanism. Path A involves the formation of an a-siloxyl alkyl-rhodium species [47] and an alkoxylrhodium complex is proposed in path B [58]. The latter path is analogous to that rhodiumd)-catalyzed hydrogenation of ketones proposed by Schrock and Osborn [59] which involves an alkoxylrhodium intermediate. 1.2.3 Grignard Cross-coupling Grignard cross-coupling is a useful carbon-carbon bond forming reaction, equation 1.5. Hayashi and coworkers [20,60-63] found that palladium and nickel complexes (L-L)MC12 (M = Ni or Pd; L-L = Ja, (S,R)-4a, (S,R)-5a, (R)-7_ or (S)-9_) catalyze a large number of cross-coupling reactions of Grignard reagents with organic halides. For example, the nickel- or palladium-catalyzed reaction of (l-phenylethyDmagnesium chloride and vinyl bromide, occurred smoothly at -20 to 0°C within several 18 hours to give optically active 3-phenyl-l-butene in very high chemical yields; in some cases optical yields up to 68% have been achieved [61]. The ferrocene planar chirality is found to be more important than the carbon central chirality and the dimethylamino group is necessary for the high stereoselectivity [61]. The stereoselectivity is not affected by introduction of substituents onto the diphenylphosphino group of the ligand but is strongly affected by changing the steric bulkiness of the secondary amino group on the ferrocenylphosphine side chain [61]. RMgX + R'X' R-R1 + MgXX' (1.5) Kumada [60] has proposed a catalytic cycle for nickel-catalyzed cross-coupling reactions as shown in Figure 1.5. Thus, a dihalo-diphosphinenickel derivative a^  reacts with a Grignard reagent to form the intermediate diorganonickel complex b which is subsequently converted to the halo(organo)nickel complex c_ by an organic halide. Reaction of c_ with the Grignard reagent then forms the new diorgano complex d^  from which the cross-coupling product f_ is released by the attack of the organic halide, possibly via the penta-coordinate intermediate The original complex _c is regenerated to complete the catalytic cycle. An alternative scheme has MgXX* Figure 1.5 C a t a l y t i c process o f c r o s s - c o u p l i n g r e a c t i o n c a t a l y z e d by n i c k e l complexes, M=N1. 20 been proposed independently by Felkin and Swierczewski [63] and Corriu and coworkers [64]. These authors have suggested a mechanism involving nickel(0) species. The catalytic cycle in Figure 1.5 seems to account for the results obtained using chiral ferrocenylphosphine ligands in the asymmetric Grignard cross-coupling reaction [20,61]. Thus, when a Grignard reagent such as (1-phenylethyl)magnesium chloride approaches the "active-catalyst" analogous to c, Figure 1.5, the dimethylamino group in the ligand is believed to dissociate from the metal and coordinate with the magnesium atom in the Grignard reagent to form the intermediate shown in Figure 1.6 [20]. This coordination is considered to occur selectively with one of the enantiomers of the racemic Grignard reagent. The group bound to the magnesium subsequently undergoes transmetallation to form the diorganometal intermediate such as e_, Figure 1.5. The optical purity and configuration of the coupling product are believed to be determined at this stage [20]. The asymmetric Grignard cross-coupling reaction can produce an optically active product even if all the Grignard reagent is racemized, equation 1.6 [20], R 1 R 2 ~ > C - R 4 R 3 optically active (1.6) 21 M=Ni or Pd R 1 =Me, R 2 = H ( S , R ) - 4 a R1=H, R 2 =Me (R ,R ) - 4 a R 1 = H , R 2 = H ( R ) - 9 Figure 1.6 Proposed intermediate i n Grignard c r o s s - c o u p l i n g r e a c t i o n . 22 Honeychuk and coworkers L65] reported that palladium derivatives of the ferrocenyl thioether, Via, and ferrocenyl selenoether, Vlb, are effective Grignard cross-coupling catalysts. These authors have proposed a mechanism similar to that shown in Figure 1.5 for the reaction. b E=Se In nickel- and palladium-catalyzed cross-coupling reactions of alkyl Grignard and alkylzinc reagents with organic halides, the complex (L-L)PdCl 2, (L-L) = l a , was found to be by far the most active and selective catalyst precursor L62J. The cross-coupled products are obtained in high yields. The large P-Pd-P angle and small Cl-Pd-Cl angle in (L-L)PdCl2 (L-L = Ja) are thought to be responsible for the high efficiency [62]. 1.2.4 Other Catalytic Reactions The palladium complex lL-L)PdCl 2 IL-L = Ja) is a catalyst precursor 23 for the hydroesterification, equation 1.7, and hydrocarboxylation, equation 1.8, of 3,3,3-trifluoropropene and pentafluorostyrene L66]. Under optimal conditions either branched products or normal products were obtained in high yields with high regioselectivities. For example, 3-(pentafluoro-phenyDpropionic acid RCH2CH2C00H (R = C 6H 5) was obtained in 93% yield with 995. regioselectivity in the hydrocarboxylation of pentafluorostyrene catalyzed by (L-L)PdCl2 (L-L = Ja)- The effect of stannous chloride on these catalytic systems was also studied and in some cases found to give better activity and regioselectivity L66j. [ C a t ] RCH=CH2 + CO + R'OH • RCH(C00R')CH 3 + RCH 2CH 2C00R' R=CF 3 o r C g F 5 ; R'=Me, E t or i - P r (1.7) [ C a t ] RCH=CH2 + CO + H 20 • RCH(C00H)CH 3 + RCH 2CH 2C00H R=CF 3 o r C 6 F 5 (1.8) The ferrocenylphosphine ligand Ja has also been used in the hydro-formylation of olefins, equation 1.9 L&7J. Thus in the ruthenium-catalyzed 24 homogeneous hydroformylation of 1-pentene, R = C 3 H 7 , equation 1.9, the ligand la induces higher normal-to-branched selectivities than PPh3 [67a]. Unmh and coworkers [67c - 67f] reported that the derivatives of la containing electron-withdrawing substituent on the Ph groups (£-Cl , m-F, _p_-CF3) give higher rates and higher normal-to-branched aldehyde ratios than the ligand la in the rhodium-catalyzed hydroformylation of olefins. [ C a t ] RCH=CH 2 + CO + H 2 RCH(CH0)CH 3 + RCH 2CH 2CH0 (1.9) 1.3 HOMOGENEOUS VERSUS HETEROGENEOUS CATALYSTS The advantages and disadvantages of using homogeneous or hetero-geneous catalysts can be briefly summarized under a number of headings [68]: (i) Separation of the catalysts. Heterogeneous catalysts are readily separated from the products at the end of the reaction. With homogeneous catalysts this is a major problem. 25 (i i) Selectivity. Homogeneous catalysts often have the advantage of giving high selectivity under relatively mild operating conditions. Heterogeneous catalysts are often less active and less selective. The activity and selectivity of a homogeneous catalyst can be tailored by varying the solvent. ( i i i ) Solvent. The range of suitable solvents for a homogeneous catalyst is often limited by the solubility characteristics of the catalyst; this clearly presents no problem for a heterogeneous catalyst. (iv) Efficiency. Every molecule in a homogeneous catalyst is available to participate in the reaction. In the case of heterogeneous catalysts only surface atoms or molecules may participate. (v) Oxygen and moisture sensitivity. Homogeneous catalysts are often organometallic compounds and are more sensitive to oxygen and moisture than most heterogeneous catalysts. (vi) Corrosion and plating out. The use of some homogeneous catalysts on a commercial scale has led to practical problems such as corrosion and plating out. An ideal catalyst would combine the advantages and simultaneously avoid the disadvantages of each catalyst. One approach to this objective is to attach soluble catalysts to insoluble supports such as organic polymers, s i l ica , alumina and clay [68,69]. The soluble catalyst attached to an insoluble support takes on the properties of a heterogeneous species at a bulk level but the interactions taking place around the metal centre are probably very similar to those found in the soluble analog. Soluble catalysts which are attached to insoluble supports have been 26 studied extensively over nany years. Such supported catalysts, heteroge-nized catalysts, have been employed for a variety of reactions such as hydrogenation, hydrosilylation and hyaroformylation L68j. As noted in previous sections, several organic reactions are known to be catalyzed by soluble transition metal complexes of ferrocenyl-phosphines and it seems that the ligands (chiral and achiral) play an important role. In view of this it would be of interest to attach ferrocene and its derivatives to inert materials and to develop the use of these materials and their metal derivatives as catalysts for heterogeneous reactions such as hydrogenation and hydrosilylation. There have been some studies concerned with supporting ferrocene derivatives on inert materials [69-72]. Ferrocenophanes such as J_2 and other ferrocene derivatives have been attached to several types of electrodes for photovoltaic purposes [71J. A number of workers L69.72J have studied polymers prepared from substituted ferrocene monomers. However, no studies on polymer-bound catalysts derived from polymer supported ferrocene derivatives have been reported and research in this field could be fruitful . R=C1, Me or Ph 12 27 1.4 GOALS OF THE PRESENT STUDY The goals of the present study can be summarized as follows: (I) The cationic palladium complexes [(L-L)PdS 2 J 2 + (L-L = chelating bidentate ligand; S = weakly coordinated solvent) are analogous to the cationic rhodium complexes L(L-L)Rh(NBD)]+. These palladium derivatives are essentially unstudied as hydrogenation catalysts [73]. Ferrocenylphosphines complexes of this type will be synthesized and their catalytic activity will be examined. (II) Platinum complexes of chiral ferrocenylphosphine (L-L)PtCl 2 are essentially unknown. These complexes will be prepared and their catalytic activity will be examined. (III) Polymer-bound catalysts derived from polymer supported ferrocene derivatives have not been explored. Methods for attaching ferrocene and its derivatives to polystyrene type polymers will be developed and the catalytic activity of the polymer-bound palladium and platinum complexes will be compared to those of their soluble counterparts. 28 CHAPTER 2 EXPERIMENTAL SECTION 2.1 GENERAL All air-sensitive reagents and products were manipulated in a nitrogen atmosphere using standard Schlenk techniques. Solvents were dried by standard methods [74]. In particular, hexane and diethyl ether were refluxed over CaH2; THF was refluxed over sodium-benzophenone; MeOH and EtOH were refluxed over magnesium and iodine; CH2C12 and MeN02 were dried over anhydrous CaS0H (5gL - 1) for 24 h and then distilled onto molecular sieves; DMF and DMSO were distilled in vacuo onto molecular sieves; py was stored over KOH (5gL - 1) for 24 h and then freshly distilled prior to use. All other solvents were either spectrophotometric grade or reagent grade and were used as received unless otherwise stated. The NajjPdCl^HjO and K 2 PtCl l t salts were generously loaned by Johnson Matthey Limited and were used as received. The liquid olefins such as styrene, o-methylstyrene, 1-hexene and cyclohexene (Aldrich Chemical Co.) were passed through a neutral alumina (Fisher Scientific Co.) column prior to use. Acetophenone, butyrophenone and isobutyrophenone (Aldrich Chemical Co.) were freshly distilled under vacuum prior to use. Al l other chemicals were either purchased or synthesized using literature methods described below, where appropriate. 29 2.1.1 Instrumentation (1) NMR spectra lH NMR spectra were recorded on Bruker WP-80, Varian XL-100, Varian XL-300 or Bruker WH-400 spectrometers operating at 80 MHz, 100 MHz, 300 MHz or 400 MHz, respectively. Proton decoupled 3 1 P NMR spectra were recorded on Bruker WP-80, Varian XL-100 or Varian XL-300 instruments operating at 32.3 MHz, 40.5 MHz or 121.4 MHz, respectively. Chemical shifts to higher frequency (lower shielding) of the standard are positive by convention; --H shifts are relative to external standard TMS (6 = 0 ppm) and 3 1 P shifts are relative to 85i H3P0n with P(0Me)3 (6 = 141 ppm) used as an external standard. The solid state 1 3 C NMR spectra were recorded on a Bruker CXP 200 MHz NMR spectrometer operating at 50.3 MHz. The chemical shifts are relative to TMS. ( i i) GLC Either a Hewlett Packard 5880A gas chromatograph equipped with an carbowax column or 20% SE-30 column, or a Varian 6000 gas chromatograph equipped with 20% tricresylphosphate column was used for GLC separation. ( i i i ) Infrared spectra Infrared spectra were recorded on a Perkin-Elmer 598 spectrophoto-meter. Solid state spectra were obtained from Nujol mulls between NaCl or Csl plates; KBr cells with path length 0.25 mm were used for solution samples. (iv) Melting points Melting points were determined using a Gallenkamp melting point 30 apparatus and are quoted without correction. (v) Elemental analyses Elemental analyses were performed by Mr. P. Borda of the University of British Columbia, Mrs. Ni of Wuhan University (China), and Canadian Microanalytical Services Ltd. (Vancouver). (vi) Mossbauer spectra 5 7 Fe Mossbauer spectra were obtained as described elsewhere [75]. Spectra were recorded at 77K and the radiation source was 5 7Co in a Cu or Rh matrix. The Doppler velocity scale was calibrated using a metallic iron foi l absorber, and isomer shifts are quoted relative to the centre of an iron foi l spectrum. (vii) Optical rotation measurements Al l optical rotations were measured at the sodium-D line (589 nm) using a Perkin-Elmer 141 spectrometer at room temperature; the cell path-length was one decimeter. The specific rotation of any chiral product was calculated using equation 2.1, [a]J = a/A.c (2.1) where [a]J = specific rotation at temperature T measured at the sodium-D line (589 nm) a = observed rotation (+) or (-). A = cell path length in decimeters c = concentration of solution in g/100 mL. 31 2.1.2 Hydrogenation Experiments All hydrogenation experiments were carried out using either method (i) for homogeneous systems or (ii) for heterogeneous systems. (i) A constant pressure gas-uptake apparatus was used as described in detail elsewhere [43]. ( i i) General procedure. The appropriate amount of heterogenized catalyst was suspended in the solvent in a Carius tube. The substrate was added, the system evacuated, and hydrogen was introduced at one atmosphere. The tube was sealed with a Teflon valve and the mixture was kept at the appropriate temperature with stirring. After the appropriate reaction time the resin was filtered off in air, washed successively (3x) with acetone and diethyl ether and dried before reuse. The hydrogenated products were identified by their known lH NM3 spectra or by GLC by comparing their retention times with those of known compounds. Other conditions for the hydrogenation experiments are given in the appropriate Tables. 2.1.3 Hydrosilylation Experiments (i) Hydrosilylation of ketones Typically, the catalyst precursor (1 mol %) was dissolved in CH2C12 (3 mL) in a Carius tube, the ketone (5 mmol) and silane (5 or 10 mmol) were then added to the tube under nitrogen. The tube was sealed using a Teflon valve and heated as shown in the appropriate Tables. After the appropriate 32 reaction time, the reaction mixture was added to 20 mL of acetone containing 4 mL of 10% aqueous HCl solution. After 2 h at 20°C, the organic phase was extracted with diethyl ether and dried over MgSO .^ The diethyl ether was evaporated and the organic residue was distilled under vacuum to afford a mixture of ketone and alcohol. These were identified by GLC and XH NMR spectra. When supported catalysts were used no solvent was needed and the resin was filtered off before the hydrolysis step. Other experimental conditions are given in the appropriate Tables. ( i i) Hydrosilylation of acetyl ferrocene and benzoyl ferrocene The catalyst precursor (1 mol %), CH2C12 (10 mL), acetylferrocene (4 mmol) and diphenylsilane (8 mmol) were mixed in a Carius tube under nitrogen. The tube was sealed as above and heated (60°C) with stirring for ~ 24 h. The reaction was monitored by TLC until there was no acetyl-ferrocene remaining. Diethyl ether (100 mL) was added to precipitate any metal complexes and the solution was filtered and evaporated to leave a red-brown oi l . Column chromatography on neutral alumina, with CHC13 as eluant, revealed the presence of first ethyl ferrocene followed by ferro-cenylethanol. Analytical and 1H NMR data for these compounds are presented in Table 4.7. In the case of benzoyl ferrocene, 2 mol% of the catalyst precursor was employed and the reaction mixture was heated for 67 h. Only benzyl-ferrocene was isolated as product after work-up using column chromato-graphy. Analytical and lH NMR data for the product are presented in Table 4.7. 33 ( i i i ) Hydrosilylation of olefins The catalyst precursor (0.01 mol%), CH2C12 (3 mL), olefin (25 mmol) and trichlorosilane (30 mmol) were mixed in a Carius tube under nitrogen, sealed and heated (70°C) with stirring for 24 h. The products were identified by comparing the retention times on GLC with those of standard compounds. When supported catalysts were used no CH2C12 was needed and the resin was filtered off in air, washed with acetone and diethyl ether and dried before reuse. The products were identified as above. Other experimental conditions are given in the appropriate Tables. When necessary the product 1-phenylethyltrichlorosilane was converted to the alcohol 1-phenylethanol using the literature procedure [51]. 2.2 SYNTHESES OF STARTING MATERIALS 2.2.1 Chlorodiisopropylphosphine [76,77] This was prepared following the procedure used for chlorodi-tert-butylphosphine [76] with slight modification. A Grignard solution of i-PrMgCl prepared from i-PrCl (78.5 g, 1 mol) and Mg turnings (24.3 g, 1 mol) in diethyl ether (800 mL) was added dropwise (2 h) through an addition funnel to a stirred diethyl ether solution (50 mL) of PCI3 (55 g, 0.4 mol). A white precipitate formed during the addition and the reaction mixture was refluxed for another two hours. The diethyl ether solution containing the product was separated 34 from the precipitate by filtration it through a medium porosity Schlenk f i l ter into a flask under nitrogen. The ether solvent was removed by distillation at atmospheric pressure to leave a yellowish o i l . This was further purified by vacuum distil lation. The product thus obtained was an air-sensitive, colorless liquid (28-35 g, 64-80%), b.p. 27°C (3 mm Hg) ( l i t . [77] b.p. 69°C (33 mm Hg)). 2.2.2 Diphenylsilane [78] This was prepared from LiAlH^ (5.6 g, 0.15 mmol) and dichloro-diphenylsilane (50 g, 0.2 mol) in 500 mL of anhydrous diethyl ether solution. After vacuum distillation the desired product was a colorless liquid (30 g, 81%), b.p. 92°C (3 mm Hg) ( l i t . b.p. 75-76°C (0.5 mm Hg)). 2.2.3 Acetyl ferrocene [17] This was prepared from ferrocene (46.5 g, 0.25 mol), acetyl chloride (22 g, 0.28 mol), and anhydrous aluminum chloride (33.5 g, 0.25 mol) in 400 mL of dry CH2C12 solution. The orange solid product obtained (51 g, 89%) was recrystallized from hot hexane, m.p. 83-85°C ( l i t . m.p. 85-86°C). 2.2.4 Ferrocenylethanol [17] This was prepared from acetyl ferrocene (25 g, 0.11 mol) and LiAlH^ (2.2 g, 0.06 mol) in 800 mL of anhydrous diethyl ether solution. The yellow-orange solid product obtained (20 g, 80%) was recrystallized from n-heptane to give yellow-orange needles, m.p. 79°C ( l i t . m.p. 78-79°C). 35 2.2.5 Ferrocenylethylcarbonium Tetrafluoroborate 179] Ferrocenylethanol (0.23 g, 1 mmol) was dissolved in 2 nt of acetic anhydride and 0.5 mL of a solution of fluoroboric acid in acetic anhydride (prepared by dissolving 1.5 mL of aqueous fluoroboric acid (42%) in 4 mL of acetic anhydride) was added and the solution was stirred for 5 minutes after which anhydrous diethyl ether (25 mL) was added to precipitate a dark solid. This was filtered off by suction and carefully washed with anhydrous diethyl ether. The dark solid product was then used irrmediately in other reactions. 2.2.6 1,1'-Dilithioferrocene-TMEDA Adduct [9,80] , This was prepared from ferrocene,(4.65 g, 25 mmol), jn-BuLi (1.6 M, 37.5 mL, 60 mmol) and TMEDA (3.5 g, 30 mmol) in 50 mL hexane solution. The product was a fine orange pyrophoric powder (7 g, 89%) which could be stored for long periods under nitrogen at room temperature. 2.2.7 N^-Dimethylaminocyanomethylferrocene [81] To a stirred solution of sodium bisulfite (52 g, 0.5 mol) in 300 mL of water was added a solution of ferrocene carboxaldehyde (108 g, 0.5 mol) in 300 mL of MeOH. The mixture was stirred for 10 minutes after which a solution of dimethylamine (30 g, 0.7 mol) in 100 mL of 50% MeOH was added followed by a solution of sodium cyanide (24.5 g, 0.5 mol) in 100 mL of water. The color changed from red to orange. Diethyl Ether (500 mL) was added and the reaction mixture was left to stir overnight after which it was extracted with ether (5 x 500 mL). The combined ether extracts were dried over anhydrous MgSO ,^ the solvent was removed under vacuum and the 36 product was obtained as golden plates (120 g, 90%). 2.2.8 N^N-Dimethylaminoethylferrocene, FA [81]. The Grignard reagent MeMgl was prepared from Mg (18 g, 0.74 mol) and Mel (105 g, 0.74 mol). To this Grignard reagent, a solution of dimethylaminocyanomethylferrocene (100 g, 0.37 mol) in freshly distilled diethyl ether (500 mL) was added dropwise, through a pressure-equalizing dropping funnel. The yellowish brown color of the aminonitrile changed to reddish orange. The reaction mixture was refluxed for 2h and stirred overnight, and then slowly treated with aqueous NH^Cl at 0°C. The ether layer was separated and the aqueous layer extracted with ether (5 x 500 mL). The combined ether solution was dried over anhydrous K 2 C0 3 , filtered, and evaporated to give an amber oil (81 g, 85%). Solid product could be obtained by recrystallizing the amber oil from MeOH [82]. 2.2.9 (S)- and (R)-N,N-Dimethylaminoethylferrocene, (S)- and (R)-FA [17] Racemic amine FA (77.1 g, 0.3 mol) and (R)-(+)-tartaric acid (45 g, 0.3 mol) were each dissolved in 150 mL of MeOH in 500 mL Erlenmeyer flasks. Both flasks were immersed in a water bath at 55°C for about 10 minutes to reach thermal equilibrium. The tartaric acid solution was.then poured into the FA solution while stirring. A few (-)-seeding crystals were added. (If no seeding crystals are available, the flask should be occasionally scratched with a glass rod to aid solid formation.) The temperature of the bath was then allowed to fall at a rate of 2 to 5° /h . Stirring was continued overnight and the precipitate of the (S)-(-)-amine tartarate was 37 collected by suction fi ltration. The mother liquor was set aside for later use. The tartarate salt was added to 20% aqueous NaOH solution in a separatory funnel and the amine extracted with CH2C12 (4 x 100 mL). The amine solution was dried over anhydrous K 2C0 3 and evaporated to give optically active amine as a dark oil (29 g, 75%). The amine thus obtained (29 g, 0.11 mol) and (R)-(+)-tartaric acid (16.5 g, 0.11 mol) each dissolved in 50 mL of MeOH were mixed and seeded as above. After slow cooling followed by the work-up procedure as described above, optically active (S)-(-)-FA was obtained (22 g, 57%), [a]jp - 12.6° (C1.5, EtOH) ( l i t . [a]jp - 14.1° (C1.5, EtOH)). The mother liquor from the first crystallization was concentrated to about one-fourth of its original volume. Diethyl ether was added slowly to the solution until precipitation was complete. The mixture was left at 0°C overnight and the (R)-(+)-amine tartarate was collected. This was recrystallized by dissolving it in a minimum amount of hot water (70-80°C) and warm acetone (the ratio of acetone to water was 10:1). The recrystallization was repeated twice and optically active (R)-(+)-FA was obtained from the tartarate as described above for the (S)-(-)-isomer (20 9, 52%), [a]p 5 + 12.5° (Cl . 5 , EtOH) ( l i t . [a]p 5 + 14.1° (C1.5, EtOH)). 2.2.10 Polystyrene Type Polymers Chioromethylated cross-linked polystyrene was obtained from Bio-Rad laboratories as Bio-Beads S-Xl 200-400 mesh, 1.34 meq/g (Bio-Beads A) and 4.2 meq/g (Bio-Beads B). The beads were washed successively (3x) with 0.5 M NaOH, 0.5 M HCl, water, MeOH, and diethyl ether, and dried to constant weight under reduced pressure. 38 The polymeric aldehyde was prepared from Bio-Beads A by DMSO oxidation [83] as described next. Bio-Beads A (30 g) were stirred in 200 mL of DMSO with 12.5 g of NaHC03 for 6 h at 155°C. The resin was then collected on a glass f i l ter , washed with DMSO, hot water, and a 2:1 mixture of dioxane and water, then rinsed with dioxane, acetone, EtOH, CH2C12, and benzene. A yield of 29 g of cream colored aldehydic resin was obtained after drying at 100°C under vacuum for 10 h. Anal. Found: C, 87.89; H, 7.24; 0, 4.73; C l , 0.0. 2.3 SYNTHESES OF FERROCENYLPHOSPHINES 2.3.1 l,l'-Bis(diphenylphosphino)ferrocene, BPPF [9] Ferrocene (20 g, 0.11 mol) was suspended in freshly distilled ji-hexane (200 mL) in a Schlenk tube. To this solution was added slowly a mixture of TMEDA (27.9 g, 0.24 mol) and ji-BuLi (148 ml, 1.6 M, 0.24 mol) in hexane. The solution was stirred for 6 h at room temperature under nitrogen and then a solution of chlorodi phenyl phosphine (53 g, 0.24 mol) in hexane (20 mL) was added dropwise over a period of 20 minutes with constant stirring. During this procedure the temperature of the solution rose. The reaction mixture was stirred overnight under nitrogen and then carefully quenched with 100 mL of distilled water at 0°C. The supernatant hexane layer was decanted from the brown solid. The brown solid was washed successively with EtOH (2 x 30 mL) and hexane (2 x 30 mL), then dissolved in hot benzene. Hot hexane was slowly added until the solution became turbid. The solution was then cooled to room temperature to give the product as orange crystals (30.5 g, 50%). 39 2.3.2 2-Di phenyl phosphi no-1-(JN[,N^ -di methyl ami noethyl )ferrocene, PPFA [21,84] Racemic FA (3 g, 11.7 mmol) was dissolved in freshly distilled anhydrous diethyl ether (30 mL) in a 250 mL Schlenk tube. To this solution was added slowly a solution of _n-BuLi (8.8 mL, 1.6 M, 14 mmol) in hexane. The mixture was stirred at room temperature for 1.5 h and chlorodiphenyl-phosphine (3 g, 14 mmol) was then added slowly. This reaction was exothermic and the color turned to yellow with the precipitation of LiCl . The mixture was stirred overnight. The reaction mixture was hydrolyzed with water at 0°C, the organic layer was separated, dried over MgSO ,^ filtered and concentrated to afford a red brown oil which crystallized from EtOH to give the product (3.2 g, 61%) as orange brown crystals. The (S,R)-PPFA was prepared in the same manner, but replacing racemic FA by (S)-FA. 2.3.3 2-Di isopropyl phosphi no- 1-(N_,_N-dimethyl ami noethyl )ferrocene, ISOPFA [10] This was prepared by the same procedure used for PPFA from racemic FA (3 g, 11.7 mmol), ji-BuLi (8.8 mL, 1.6 M, 14 mmol) and chl orodi isopropyl-phosphine (2.1 g, 14 mmol). The product (3.3 g, 75%), a red orange o i l , was analytically pure and could be recrystallized from EtOH gave 45% yield of orange brown crystals. The (S,R)-IS0PFA was prepared in the same manner, but replacing racemic FA by (S)-FA. 40 2.3.4 11,2-Bis (di phenyl phosphi no)-l-(N^-dimethyl ami noethyl )ferrocene, BPPFA [21,84] Racemic FA (3g, 11.7 mmol) was dissolved in diethyl ether (30 mL) in a Schlenk tube. To this solution was added slowly a solution of ji-BuLi (8.8 mL, 1.6 M, 14 mmol) in hexane. The mixture was stirred at room temperature for 1.5 h and then a mixture of freshly distilled TMEDA (1.6 g, 14 mmol) and _n-BuLi (8.8 mL, 1.6 M, 14 mmol) in hexane was added and stirring was continued for a further 5h at room temperature. Chloro-diphenylphosphine (5.3 g, 24 mmol) was then added to the reaction mixture and the solution was stirred overnight. The mixture was hydrolyzed with water at 0°C, and the resulting organic layer was separated, dried over MgSOj^ , filtered and concentrated to afford an oily residue which crystallized from EtOH to give pure BPPFA (3.7 g, 50%) as orange crystals. The (S.R)-BPFFA was prepared in the same manner, but replacing racemic FA by (S)-FA. Analytical, physical and NMR data for these ligands are presented in Tables 3.1 and 3.2. 2.4 SYNTHESES OF PALLADIUM AND PLATINUM COMPLEXES OF FERROCENYL-PHOSPHINES 2.4.1 Palladium Complexes (L-L)PdCl2 [61,62] (i) L-L = BPPF Dichlorobis(benzonitrile)palladium(II) (0.58 g, 1.5 mmol) (prepared from Na 2PdCl l t»4H 20 [85]) was suspended in 10 mL of benzene in a Schlenk tube. BPPF (0.94 g, 1.7 mmol) in 10 mL of benzene was added to the stirred solution. The mixture was stirred overnight at room temperature under 41 nitrogen after which the precipitate was collected by fi ltration, washed with benzene, and dried in vacuo to give a reddish orange solid (1.0 g, 91%). The solid was recrystallized either from CHC13, CH2C12 or acetone, (ii) L-L = PPFA, ISOPFA, BPPFA These complexes were prepared in the similar manner as described in (i), replacing BPPF by PPFA, ISOPFA and BPPFA, respectively. (PPFA)PdCl2 was recrystallized from CH2Cl2/hexane, yield 94%; (ISOPFA)PdCl2 and (BPPFA)PdCl2 were recrystall ized from CHC13 and were obtained in 75% and 95% yields, respectively. The analytical, physical and NMR data for (L-L)PdC1~ are given in Tables 3.1 and 3.2. 2.4.2 Cationic Palladium Complexes [(L-L)PdS 2][C10 4] 2 [86,87] These complexes were prepared essentially using the procedure of Hartley and coworkers [86,87], but with some modifications as follows: All procedures were carried out in Schlenk type apparatus in a nitrogen atmosphere. (i) L-L = BPPF, S = DMF The complex (BPPF)PdCl2 (0.37 g, 0.5 mmol) was dissolved in a mixture of CH2C12 (20 mL) and DMF (10 mL), AgClO^ (0.21 g, 1 mmol) in MeN02 (10 mL) was added with stirring. After 3 h the precipitate was filtered off and the solution taken to dryness in vacuo. The residual oily solid was extracted with CH2C12 and the combined extracts were reduced to a small volume in vacuo. Dropwise addition of anhydrous diethyl ether precipitated a solid which was isolated and purified by dissolving it in CH2C12 followed 42 by reprecipitation with anhydrous diethyl ether. After f i ltration, the dark brown solid was dried in vacuo at room temperature, yield 655.. (ii) L-L = BPPF, S = py The complex (BPPF)PdCl2 (0.37 g, 0.5 mmol) was dissolved in a mixture of CH2C12 (20 mL) and py (10 mL), AgCIO,, (0.21 g, 1 rrmol) in MeN02 (10 mL) was added with stirring. The mixture was left stirring for 3 h and worked up as above. The purple solid obtained was dried in vacuo at room temperature, yield 55%. ( i i i ) L-L = BPPF, S 2 = (DMF, Cl) This complex was prepared as in (i) except that 0.5 mmol of AgClO^ was used. The product was a dark brown solid, yield 50-60%. (iv) L-L = PFFA, S = DMF This complex was prepared as in (i) , replacing (BPPF)PdCl2 by (PPFA)PdCl2. The product was a dark brown solid, yield 52%. (v) L-L = PPFA, S = py This complex was prepared as in ( i i ) , replacing (BPPF)PdCl2 by (PPFA)PdCl2. The product was a purple solid, yield 55%. Analytical, physical and NMR data for these palladium complexes are given in Tables 3.3 and 3.4. 2.4.3 Platinum Complexes (L-L)PtCl 2 [88] These complexes were prepared according to literature methods [88] with some modifications as follows: (i) L-L = BPPF KjPtCl^ (0.42 g, 1 mmol) in 10 mL of water was treated with a 43 solution of BPPF (0.55 g, 1 mmol) in 20 mL of CH2C12. The solution mixture was stirred for about 3 h or until the aqueous phase became colorless. The organic phase was separated, dried over MgSO,^  and the solvent was reduced to a small volume. The solid product was precipitated by dropwise addition of diethyl ether. The solid was isolated and recrystallized from CH2Cl2/MeOH to give yellow crystals, yield 70%. (ii) L-L = (S.R)-PPFA, (S,R)-IS0PFA, (S,R)-BPPFA. These complexes were prepared in a similar manner to that described above, replacing BPPF by (S,R)-PPFA, (S.R)-ISOPFA and (S,R)-BPPFA, respectively. ((S,R)-PPFA)PtCl2 was recrystallized from CH2C12 by precipi-tation with diethyl ether as an orange solid, yield 63%; ((S.R)-ISOPFA)-PtCI2 was recrystallized from CH2Cl2/EtOH as orange crystals, yield 47%; and ((S,R)-BPPFA)PtCl2 was recrystallized from CHCl3/hexane as orange crystals, yield 66%. Analytical, physical and NMR data for these platinum complexes are given in Tables 4.1 and 4.2. 2.4.4 Platinum Complex (PPFA)PtHCl [26] This was prepared according to the procedures of Clark and coworkers [26] with modification. To a suspension of (PPFA)PtCl2 (0.4 g) in 15 mL of MeOH at 0°C was added a MeOH solution of sodium borohydride (0.01 g/mL) also at 0°C. The mixture was stirred under nitrogen until the color changed to brown. After stirring for about another 10 minutes the mixture was acidified with methanol ic HCl and extracted with benzene (3 x 10 mL). The benzene extract 44 was reduced in volume and ji-pentane was added to give a pale orange solid, yield 43%. Analytical, physical and NMR data for this complex are given in Tables 4.8 and 4.9. 2.5 SYNTHESES OF POLYMER-BOUND FERROCENE DERIVATIVES 2.5.1 Reaction of Lithioferrocene with Bio-Beads B, Polymer-I To a Schlenk tube was added ferrocene (2.0 g, 10.8 mmol) followed by 30 mL of anhydrous diethyl ether. The well stirred solution was treated with n-BuLi (6.8 mL, 1.6 M, 10.8 mmol) in hexane for about 3 h before the addition of 50 mL of THF followed by Bio-Beads B (1.34 g, 5.4 rrniol). The reaction mixture was left stirring for 4 days at room temperature under nitrogen and then hydrolyzed with deionized water. The resin was collected and washed successively (3x) with water, EtOH, acetone, THF, CH 2C1 2, hexane and diethyl ether, and dried under vacuum at 100°C to give polymer-I as a yellow brown resin. 2.5.2 Reaction of Lithioferrocene with Aldehydic Resin, Polymer-II Ferrocene (2 g, 10.8 rrniol) was suspended in anhydrous diethyl ether (30 mL) and ji-BuLi (6.8 mL, 1.6 M, 10.8 mmol) in hexane was added with stirring. After 2 h THF (30 mL) was added followed by aldehydic resin (1.8 g, 5.4 mmol). The mixture was left stirring for 4 days and treated as described above to give polymer-11 as orange brown resin, (a) Reaction of polymer-II with HBr, polymer-IIa Polymer-II (1 g) was suspended in 30 mL benzene. Gaseous HBr was 45 bubbled through the well stirred suspension until the color darkened becoming dark brown. The mixture was filtered, washed and dried as described in Section 2.5.1 to give polymer-IIa as a dark brown resin, (b) Reaction of polymer-IIa with HNMe2, polymer-IIb Polymer-IIa (0.5 g) was suspended in benzene (30 mL). Excess aqueous HNMe2 (42%) was then added with stirring and the color of the resin changed from dark brown to orange brown. The mixture was stirred for 10 minutes after which 30 mL of H20 was added. Following fi ltration, the resin was treated as described in Section 2.5.1 to give polymer-IIb as an orange brown resin. Alternatively, polymer-IIb could be prepared from polymer-II as described next. Polymer-II (0.5 g) was suspended in benzene (30 mL). Gaseous HBr was bubbled through the well stirred solution until the color darkened. Excess aqueous HNMe2 was then added with stirring; the dark brown color changed to orange brown. The mixture was hydrolyzed and treated as described in Section 2.5.1. 2.5.3 Reaction of Di1ithioferrocene-TMEDA Adduct with Bio-Beads A, Polymer-I 11 Solid di1ithioferrocene-TMEDA adduct (1.40 g, 4.46 mmol) was suspended in 50 mL hexane and 50 mL THF. Bio-Beads A (6.66 g, 8.92 mmol) were added with constant stirring and the mixture was treated as described in Section 2.5.1 to give polymer-III as a reddish brown resin. 46 2.5.4 Reaction of Dilithioferrocene-TMEDA Adduct with Aldehydic Resin, Polymer-IV Solid dilithioferrocene-TMEDA adduct (2.4 g, 7.5 mmol) was suspended in 50 mL hexane and 50 mL THF. Aldehydic resin (5 g, 15 mmol) was added with constant stirring and the mixture was treated as described in Section 2.5.1 to give polymer-IV as an orange resin. (a) Reaction of polymer-IV with HBr, polymer-IVa This was prepared as for polymer-IIa from polymer-IV. (b) Reaction of polymer-IVa with HNMe2, polymer-IVb This was prepared as for polymer-IIb from polymer-IVa. 2.5.5 Reaction of Lithium Derivative of FA with Bio-Beads B, Polymer-V Racemic FA (2.57 g, 10 mmol) was dissolved in anhydrous diethyl ether (30 mL) in a Schlenk tube. To this solution was added slowly a solution of _n-BuLi (6.3 mL, 1.6 M, 10 mmol) in hexane. The mixture was stirred at room temperature for 1.5 h and THF (30 mL) was added followed by Bio-Beads B (2.38 g, 10 mmol). The suspension was stirred for 4 days and the mixture was treated as described in Section 2.5.1 to give polymer-V as a yellow brown resin. 2.5.6 Reaction of Lithium Derivative of FA with Aldehydic Resin, Polymer-V I This was prepared in a manner similar to that described in Section 2.5.5 from a solution of lithio-FA (prepared from 3.3 g, 12 mmol of FA and 7.5 mL, 12 mmol of ji-BuLi) and aldehyd ic resin (4 g, 12 mmol). The same 47 work-up as described in Section 2.5.1 gave polymer-VI as a yellow brown resin. 2.5.7 Reaction of Lithium Derivative of BPPF with Aldehydic Resin, Polymer-VII BPPF (4.4 g, 8 mmol) was dissolved in 100 mL of THF/hexane (1:1). To this jn-BuLi (6 mL, 1.6 M, 9.6 mmol) was added and the mixture was stirred for 2 days before aldehydic resin (2.7 g, 8 mmol) was added. The mixture was further stirred for 4 days and treated as described-in section 2.5.1 to give polymer-VII as an orange resin. In a second experiment, BPPF was dissolved in anhydrous diethyl ether and the lithiation carried out with _n-BuLi/TMEDA as in Section 2.5.8, described next. 2.5.8 Reaction of Lithium Derivative of PPFA with Aldehydic Resin, Polymer-VIII PPFA (1.76 g, 4 mmol) was dissolved in anhydrous diethyl ether (50 mL). To this solution was added slowly a solution of jn-BuLi (2.5 mL, 1.6 M, 4 mmol) in hexane. The mixture was stirred at room temperature for 2 h and then a mixture of TMEDA (0.5 g, 4 mmol) and n-BuLi (2.5 mL, 1.6 M, 4 mmol) in hexane was added. The reaction mixture was left stirring for 2 days, after which 50 mL of THF was added followed by aldehydic resin (1.35 g, 4 mmol). The mixture was further stirred for 4 days and treated as described in Section 2.5.1 to give polymer-VIII as a brown resin. 48 2.5.9 Reaction of Lithium Derivative of (S,R)-PPFA with Aldehydic Resin, Polymer-VIII* This was prepared in a manner similar to that used for polymer-VIII, but replacing PPFA by (S.R)-PPFA. Analytical and Mossbauer data for these polymers are given in Table 5.1. 2.6 SYNTHESES OF PALLADIUM AND PLATINUM COMPLEXES OF POLYMER-BOUND FERROCENE DERIVATIVES 2.6.1 Palladium Complexes (i) Polymer-VI (1.9 g) was added to an acetone solution (30 mL) of Na 2PdClH»4H 20 (220 mg, 0.6 mmol) with stirring. The mixture was stirred and refluxed for 2 h. The orange brown palladium complex, polymer-VI-Pd was filtered off, and washed successively (3x) with water, EtOH, acetone, THF, CH 2C1 2, hexane and diethyl ether, and dried at 100°C under vacuum. ( i i) The orange brown palladium complex, polymer-VII-Pd, was prepared analogously from polymer-VII (1 g) and Na2PdCl1 +»4H20 (51 mg, 0.14 mmol). ( i i i ) The orange brown palladium complex, polymer-VIII-Pd, was prepared in the same manner from polymer-VIII (0.7 g) and Na 2PdC^»4H 20 (73 mg, 0.2 mmol). (iv) The orange brown palladium complex, polymer-VIII*-Pd, was prepared in the same manner from polymer-VIII (1 g) and Na2PdCllt-4H20 (0.11 g, 0.3 mmol). 49 2.6.2 Platinum Complexes (i) Polymer-VI (1 g) was added to a CH2Cl2/water (1:1) solution (30 mL) of KjPtCl^ (0.12 g, 0.3 mmol) with stirring. The mixture was stirred and refluxed for 5 h. The brown black platinum complex, polymer-VI-Pt was filtered off, washed, and dried as above. (ii) The dark brown platinum complex, polymer-VII-Pt, was prepared analogously from polymer-VII (1 g) and K 2PtCl 1 + (42 mg, o.i mmol). ( i i i ) The dark brown platinum complex, polymer-VIII-Pt, was prepared in the same manner from polymer-VIII (0.4 g) and K 2 PtC^ (42 mg, 0.1 mmol). * (iv) The brown platinum complex, polymer-VIII -Pt, was prepared in * the same manner from polymer-VIII (0.5 g) and K 2 PtCl l t (63 mg, 0.15 mmol). Analytical and Mossbauer data for these supported complexes are given in Table 5.3. 50 CHAPTER 3 CATIONIC PALLADIUM(II) COMPLEXES OF FERROCENYLPHOSPHINES 3.1 INTRODUCTION Homogeneous hydrogenation catalysts comprising metal complexes of phosphines and arsines are well known [36,37]. Among these, cationic rhodium(I) complexes [(L-DRhfNBDJJC^ have been the most extensively studied; (L-L) is a bidentate ligand, usually a di(tertiary phosphine) and optically active when necessary [36,37,45]. Such cationic rhodium(I) complexes of ferrocenylphosphines are effective catalyst precursors for the asymmetric hydrogenation of amino acid precursors (cf. Section 1.2.1). High optical yields are obtained. Only limited success has been achieved in attempts to use cationic derivatives of other group VIII metals as homo-geneous hydrogenation catalyst precursors. In particular, Hartley and coworkers [73,86,87,89] have reported that both the mono-cation palladium(II) derivative [(dppe)PdCl(DMF)JCIO^ in DMF and the di-cation complex [(dppe)Pd(0CMe2)2][C104]2 in CH2Cl2/0CMe2 promote the hydrogenation of styrene to ethylbenzene at 30°C and 1 atm pressure. Very high catalyst to substrate ratios (1:5) are necessary for the mono-cation to achieve reduction. The di-cation is better than the mono-cation with the same ratio being 1:10. The hydrogenation of styrene with the di-cation as catalyst is quantitative but only 10% when the mono-cation is the catalyst. 51 Since cationic palladium(II) complexes of ferrocenylphosphines were unknown at the beginning of this study, it seemed worthwhile to prepare some and study their properties. In this chapter the synthesis and charac-terization of a number of neutral and cationic palladium(II) complexes will be presented. The use of the cationic palladium(II) complexes in catalyzing the hydrogenation of olefins will also be described. 3.2 RESULTS AND DISCUSSION 3.2.1. Synthesis and Characterization The palladium(II) complexes (L-L)PdCl2 (L-L = BPPF, PPFA, ISOPFA and BPPFA) were prepared using the simple ligand exchange reaction as shown in equation 3.1; a slight excess of the appropriate ligand was used. The analytical, physical and NMR spectroscopic data of the products are summarized in Tables 3.1 and 3.2. The *H NMR spectrum of (BPPF)PdCl2 is similar to that of the free ligand except for a slight line broadening accompanied by a small chemical shift change. The 3 1P{1H} NMR spectrum of this complex, as expected, shows only one phosphorus resonance, Figure 3.1. The lH NMR data of (BPPFA)PdCl2 reveal that the -NMe2 group is not bound to palladium since only one NMe resonance is present, Table 3.2. The 31P{1H} NMR spectrum, Figure 3.2, shows two doublets, J = 22.5 Hz, with both resonances shifted down field from those of the free ligand. Thus the BPPFA ligand is bound to palladium through both phosphorus atoms as in the case of (BPPF)PdCl2. In the rhodium(I) complex, [(BPPFA)Rh(NBD)]C10^ [20,31], the BPPFA ligand is also P-P bound. 52 (PhCN) 2 PdCl 2 + L-L •+> ( L - L ) P d C l 2 + 2PhCN (3.1) L-L = P P h 2 P P h 2 BPPF M e O ^ N M e 2 PPFA ISOPFA BPPFA X=H, R=Ph X=H, R= i -Pr X=PR 2 , R=Ph A P-N binding mode is found in the rhodium(I) complex [(PPFA)Rh-(NBD)]PF6 L 2 9 ] , i .e. both the -PPh2 and -NMe2 group of PPFA are bound to the metal. The same P-N binding mode is found in the palladium complex (L-L)PdCl2 (L-L = PPFA or ISOPFA) since the 1H NMR data show two NMe resonances at room temperature, Table 3.2. The resonances of the -NMe2 group are sharp for the (PPFA)PdCl2 complex but are broad in (ISOPFA)PdCl2. This broadening is probably associated with a conformational non-rigidity as found in the complex [(L-L)Rh(NBD)]C104, where (L-L) is a ligand analogous to PPFA with -P(t-Bu) 2 replacing the -PPh2 group [23,32]. The 53 Table 3.1 M i c r o a n a l y t i c a l r e s u l t s and melting points f o r (L-L) and ( L - L ) P d C l 9 . n C a l c d . ( % ) Found{%) mp( C) Compound (decomp) C H N C H N BPPF 183 -185 73.67 5.06 - 73. 64 4.90 -PPFA 135 -136 70.76 6.39 3. 17 71. 26 6.44 2. 81 ISOPFA 57-! 59 64.39 8.58 3. 75 64. 66 8.61 3. 47 BPPFA 118 -120 72.96 5.96 2. 24 72. 57 5.98 2. 44 (BPPF)PdCl 2 262. -265 55.81 3.87 - 55. 41 3.95 -(PPFA)PdCl 2 170 -172 50.49 4.53 2. 26 50. 00 4.77 2. 04 (IS0PFA)PdCl 2 179 -181 43.65 5.82 2. 54 43. 68 5.84 2. 51 (BPPFA)PdCl 2 216 -220 50.81 4.12 1. 52 a 51. 17 4.54 1. 61 a: C a l c u l a t e d value i s based on (L-L)PdCl ?.CHCl 54 Table 3.2 ]H and 3 1 P { 1 H } NMR data f o r (L-L) and (L - L j P d C l * . Compound NMe2 Others 31 p BPPF - 4.05, 4.30(2xbt, F e ( C & H 4 ) 2 ) ; 7.31(m, Ph^) -17.61(s) PPFA 1.77(s) 1.22(d,J H H=7.2,CHMe); 3.95(s, F e ( C 5 H 5 ) ) ; 3.56-4.49(m, F e f C ^ ) & CHMe); 7.28-7.78(m, Phg) -22.02(s) ISOPFA 2.03(s) 0.81-1.51(m, CHMe & CHMeg); 2.09-2.22(m, CHMe 2); 3.99(s, F e ( C 5 H 5 ) ) ; 3.93-4.25(m, F e f C ^ ) & CHMe) -5.34(s) BPPFA 1.85(s) 1.22(d, J H H=7, CHMe); 3.45-4.45(m, ( C ^ F e t f ^ ) ) 6.87-7.76(m, f j ^ ) -23.28(s), -17.27(s) b (BPPF)PdCl 2 - 4.18, 4.40(2xbs, F e ( C & H 4 ) 2 ) ; 7.43, 8.00(2xm, 6H, 4H, Phg) 33.54(s) (PPFA)PdCl 2 2.78(s), 3.56(s) 1.42(d, J H H=7.2, CHMe); 3.40-3.70(m, CHMe); 3.80(s, F e t C ^ ) ) ; 4.29-4.50(m, F e f C ^ ) ) ; 10.61 (s) 7.20-7.70, 8.10-8.40(2xm, Ph-) Table cont'd 55 Compound NMe2 Others 3 1 p (IS0PFA)PdCl 2 (BPPFA)PdCl 2 2.30(bs), 3.33(bs) 2.33(s) 1.31-1.75(m, CHMe & CHMe_2); 2.75, 2.84(2xm, CHMe 2); 3.93-4.13(m, CHMe); 4.26(s, FejCgHg)); 4.33-4.64(m, F e t C ^ ) ) 1.31(d, J H H = 7 , CHMe); 37.26(s) 28.33 3.43-3.65, 4.13-4.68 (d, J p p=22.5) (m, ( C ^ F e f C ^ ) ) ; 36.63 5.49-5.76(m,CHMe); (d, J p p=22.5) b 6.91-8.55(m, Phu) a: A l l spectra were obtained i n CDC1-. Coupling constants are i n Hz. b: The resonance f o r P atom a d j a c e n t J t o the amine group i s at lower frequency (higher s h i e l d i n g ) . 56 1 40 n ' 1 1 1 — ' — " — i — I — i — i — i — r 35 30 -i—r Figure 3.1 32.3MHz 3 1P{ 1H } NMR spectrum of (BPPF)PdCl. 5 7 J A ' ' ' ' i i i i I i i i 35 40 "I r 30 -1 1 1 I 1 1 | 25 20 Figure 3.2 32.3MHz 3 1 P{ 1 H } NMR spectrum of (BPPFA)PdCl2. 58 PPM 1 — I — I — t r 40 I i — 1 — i — i — I — i — r 35 30 Figure 3.3 32.3MHz ^ P ^ H } NMR spectra of (PPFA)PdCl , A; (ISOPFA)PdCl2, B. 59 31P{1H} NMR spectra of (PPFA)PdCl2 and (IS0PFA)PdCl2 show the expected single phosphorus resonance, Figure 3.3. The cationic palladium(II) complexes [(L-L)PdS 2][C10j 2 (L-L = BPPF and PPFA), I-IV, were prepared as shown in equation 3.2. The analytical 2AgC10, (L-L)PdCl 9 — c CH2C12/S (L-L) = BPPF or PPFA S « DMF or py and spectroscopic data of the products, Tables 3.3 and 3.4, are in accord with their formulation. The IR spectra of al l four cationic complexes exhibit a broad band at 1090 cm - 1 and a medium sharp band at 620 cm - 1 ; these are unsplit and indicate that the perchlorate ions do not interact with the cation [91]. The complexes I and III show IR absorption bands at 1605 and 1220 cm"1 consistent with the presence of coordinated py [92a]. The complexes II and IV show a strong relatively broad absorption at 1636 cm"1 consistent with direct coordination of DMF ligands to palladium through their carbonyl oxygen atoms [92b]. The lH NMR spectra of the complexes II and IV show two broad singlet resonances for the two Me groups in the DMF ligand; these resonances are sharp in the free DMF ligand [93a]. The proton resonances for the py ligand in the complexes I and III are broader than those for the free py ligand [93b]. The 31P{1H} NMR * C(L-L)PdS2][C104]2 + 2AgCl (3.2) Table 3.3 M i c r o a n a l y t i c a l r e s u l t s and melting points f o r the c a t i o n i c palladium complexes. Complex mp(°C) (decomp) Calcd.(%) C H N Found(%) C H N [ ( B P P F ) P d ( p y ) 2 ] [ C 1 0 4 ] 2 . I [(BPPF)Pd(DMF) 2][C10 4] 2 , II [ ( P P F A ) P d ( p y ) 2 ] [ C 1 0 4 ] 2 . I l l [(PPFA)Pd(DMF) 2][C10 4] 2 . IV [(BPPF)PdCl(DMF)][C10 A] , V 194-196 51.92 3.76 155-159 47.76 4.21 158-163 47.78 4.23 144- 148 43.05 4.74 145- 148 49.13 4.31 2.75 51.24 3.98 2.66 2.71 47.27 4.23 2.55 4.64 47.35 4.34 5.00 4.71 43.20 4.86 4.23 1.55 a 49.77 4.22 1.79 Data are c a l c u l a t e d f o r the dihydrate. 61 Table 3.4 'H and 3 1 P { ' H } NMR data f o r the c a t i o n i c p a l l a d i u m 3 complexes. Complex 31 p I 4.63, 4.80(2xbm, F e C C ^ ^ ) ; 32.84(s) 6.90-7.18, 7.20-7.45, 8.58-8.88(3xbm, N C ^ ) ; 7.48-8.03(m, Phg) II 3.08, 3.33(2xbs, NMe_2); 43.23(s) 4.65(bs, F e ( C 5 H 4 ) 2 ) ; 7.38-8.15(bm, Ph^ & CHO) III 1.83(bd, CHMe); 20 . 2 0 ( s ) c 2.50, 3.43(2xbs, NMe 2); 3.90(s, FetCgHg)); 3.93-4.90(m, F e f C ^ ) & CHMe); 6.75-7.08, 7.25-7.35, 8.15-8.73(3xbm, N C ^ ) ; 7.35-8.25(m, Phg) IV 1.65(bd, CHMe); 19.20(s) d 2.53, 3.80(2xbs,NMe2); 2.95, 3.30(2xbs, CHONMe^); 3.98(s, F e f C ^ ) ) ; 4.30-4.88(m, FefCgHg) & CHMe); 7.30-8.01 (m, Ph^); 8.31-8.63(m, CHO) b a C D C l , was s o l v e n t unless otherwise s t a t e d . b C D 0 C l 0 . CCH 0C1 0. DMF. 62 spectra of complexes I-IV show the expected single phosphorus resonance, Table 3.4. The complex [(BPPF)PdCl (DMF^CIC^, V, was prepared in a similar fashion; it seems to be isolable as the dihydrate. This complex is less stable than complexes I-IV and it is difficult to obtain reproducible microanalytical results. The instability of this complex may be due to the partial formation of a chloride bridged species as found in the case of the complex [(dppe)PdCl(DMFJJCIO^ [87], equation 3.3. 2[(L-L)PdCl(DMF)]C104 Ett -L) 2 Pd 2 Cl 2 ] [C l6 4 ] 2 (L-L) •= dppe or BPPF + 2DMF (3.3) 3.2.2 Hydrogenation Studies The five cationic palladium complexes I-V were examined with regard to their ability to catalyze the hydrogenation of styrene in DMF solution at 30°C and 1 atm pressure, and all except I were effective, Table 3.5. The highest rate was achieved with complex IV, a derivative of the mixed "hard-soft" ligand PPFA. The lower reactivity of complexes I, II and V which contain the di (tertiary phosphine) BPPF, is consistent with the results of Hartley and coworkers as described in the Introduction (cf. Section 3.1) for the complex [(dppe)PdCl(DMF)]C10^. Judging by the present results, Table 3.5, the ferrocene skeleton does seem to have a positive effect on the rate of hydrogenation of styrene. 63 Table 3.5 C a t a l y t i c hydrogenation o f o l e f i n s by c a t i o n i c p a l ladium complexes I-V a. Complex O l e f i n Solvent Time(h) Product Chem. Yi e l d ( 2 ; ) b I styrene DMF 24 no product 0 II s t y r e n e DMF 24 et h y l benzene 53 II I s tyrene DMF 24 ethylbenzene 78 IV s t y r e n e DMF 2.2 et h y l benzene 100 V styrene DMF 24 et h y l benzene 20 IV styrene DMSO 2.2 et h y l benzene 56 IV styrene py 2.2 et h y l benzene 22 IV 1-hexene DMF 2.2 n-hexane 61 IV cyclohexene DMF 2.2 cyclohexane 40 IV o-acylam1noc1 -nnamic a c i d DMF 24 no product 0 IV styrene DMFC 2.2 e t h y l benzene 24 d styrene DMF 72 et h y l benzene 10 a : [ o l e f i n ] = 4.36x10 "2M; [Pd] = 8 .72xlO" 4M i n 5 mL o f s o l v e n t used; 30°C; 1 atm t o t a l pressure of hydrogen. b : GLC y i e l d based on s t a r t i n g o l e f i n . c : In presence o f excess PPFA, [PPFA]/[Pd] = 5/1. d : Complex i s [(dppe)PdCl(DMF)]C10, V CPd3 = 4xlO" 2M; [ o l e f i n ] = 0.2M. 64 Clark and coworkers L27] also reported that mixed monodentate platinum system PttDd'jC^/SnClg^HjO (L = PPh3, L' = sulphides, amines) are more effective catalyst for the hydrogenation of styrene to ethyl-benzene than PtL 2 Cl 2 or P t L ' 2 C l 2 system. The effect is attributed to the ability of the weaker ligand L' to function as a leaving group. The nature of the ligand S is also important since for (L-L) = BPPF the ease of reduction of styrene in the palladium-catalyzed system seems to be in the order of S 2 = (py)2<(Cl,DMF)<(DMF)2. The same order (py)2<(DMF)2 is found for complexes of PPFA. Similar effects are probably responsible for the lower rates of hydrogenation found for derivatives of PPFA when the solvent is changed from DMF to the more strongly coordinating DMSO or py L 9 4 ] , Thus an equilibrium such as shown in equation 3.4 might be responsible for ligand exchange on adding the catalyst precursor to the solution in solvents such as py or DMSO. [(PPFA)Pd(DMF) 2] 2 + + S 1*. [ ( P P F A ) P d S 2 ] 2 + S = DMSO or py + 2DMF (in excess) (3.4) When the reaction is carried out in DMF in the presence of excess PPFA the rate of styrene hydrogenation is lowered as well suggesting that the excess ligand is competing for sites on the metal. Indeed the color changes from brown to orange in the reaction solution during the 65 Table 3.6 E f f e c t o f Et^N i n the hydrogenation o f styrene c a t a l y z e d by complex IV a. Et 3N/Pd Observed r a t e x 10 , MS" Enhancement' 0:1 1.51 1.00 5:1 2.58 1.71 10:1 2.42 1.60 20:1 2.64 1.75 »:1 2.08 1.38 a : [ s t y r e n e ] = 4.36xlO"*M; [IV] = 8.72x10" 71 i n 5 mL of DMF; 30°C; 1 atm t o t a l pressure o f hydrogen; 1 h. b : Observed r a t e i s the maximum slope o f the gas uptake p l o t , c : Enhancement i s the r a t i o o f observed r a t e with EtgN added to that with no E t 0 N added. 66 hydrogenation in the presence of excess PPFA. This change is not observed in the absence of excess PPFA. Addition of the base triethylamine to the reaction mixture results in enhancement of the rate of catalyzed styrene hydrogenation, Table 3.6. This rate enhancement is diminished in the presence of a large excess of added base. A common interpretation of the rate enhancing effect of base on a reaction is that it encourages the heterolytic cleavage of hydrogen by metal species by mopping up protons [95]. However, it has recently been demonstrated that the role of a base may be less innocent since some amines can react with group VIII derivatives forming M-C bonds [96]. The complex IV also catalyzes the hydrogenation of 1-hexene and cyclohexene in DMF solution, Table 3.5. These reductions seem to be slower than styrene, a not so unusual observation [97a]. A disappointing aspect of the results is seen in the failure of the complex IV to catalyze the hydrogenation of a-acylaminocinnamic acid, Table 3.5, which seems to eliminate possible use of these systems for asymmetric hydrogenation. When the hydrogenation of a-acylaminocinnamic acid was carried out at 30°C and 100 psi of hydrogen for 24 h, the complex IV decomposed to palladium metal and no reduced organic product was obtained. Selected hydrogenation uptake curves for the hydrogenation of styrene catalyzed by complex IV are shown in Figure 3.4. The reaction is completed in a reasonable time when the [styrene]/[Pd] ratio is 100/1 and the solvent is DMF. The maximum rate is lower when the ratio is decreased although the reaction is essentially completed in much the same time (cf. curves A and B in Figure 3.4). Curve C in Figure 3.4 shows the more •1- 1 1 I I 2 4 6 8 10 Time x 10 , sec Figure 3.4 Hydrogen uptake curves f o r the hydrogenation o f styrene c a t a l y z e d o # by c a t i o n i c palladium complex IV a t 30 C and 1 atm t o t a l pressure. A, [styrene] = 8.72xlO" 2M, [Pd] = 8.72xlO' 4M. DMF (5 mL); B, [styrene] = 4.36xlO" 2M, [Pd] = 8.72xlO" 4M, DMF (5 mL); C, [styrene] = 4.36x10~2M, [Pd] = 8.72xlO" 4M, DMSO (5 mL). # The sc a l e does not permit the d i s p l a y o f the i n i t i a l i nduction period observed i n these experiments. Figure 3.5 Dependence of maximum hydrogenation rate on [styrene]: DMF (5 mL) at 30°C, 1 atm total pressure, [Pd] = 8.72xlO"4M. CO [Pd] x IO3, M Figure 3.6 Dependence of maximum hydrogenation r a t e on [Pd]: DMF (5 mL) at 30°C, 1 atm t o t a l pressure, [ s t y r e n e ] = 4.36xlO" 2M. 6 A O I 1 I I 0 4 8 12 Time x IO"2, sec Figure 3.7 Hydrogenation uptake curves f o r the hydrogenation o f styrene; A, same condi t i o n s as 1n Figure 3.4(A); B, same c o n d i t i o n s as A with Hg added. 71 sluggish uptake obtained in DMSO as solvent; the reaction is completed in about 27 h. The first order rate dependence of the reaction on the substrate, in DMF, is shown in Figure 3.5. The rate dependence on the palladium concentration is shown in Figure 3.6. The data for Figure 3.6 seem to indicate an init ial first order dependence which drops off with increasing concentration. These results seem to be consistent with a homogeneous system. However, a rate dependence of the reaction on solvent, substrate and catalyst concentration is also found in some heterogeneous systems [97b]. As a test for homogeneity, the hydrogenation of styrene was performed in the presence of excess mercury [98]. The data are shown in Figure 3.7. Some inhibition by mercury does occur (~ 16%) by comparison of maximum rate values. However, the effect would be expected to be much greater if the system were heterogeneous [98]. In the absence of substrate, complex IV absorbs slightly more than two moles of hydrogen per mole of palladium, a result which suggests metal hydride formation. Initial oxidative addition of hydrogen to form a palladium(IV)-hydride seems unlikely because a much higher ionization energy is needed to produce palladium(IV) than platinum(IV) species [99]. There is no 1H NMR evidence for init ial metal hydride formation in CD2C12 or CDC13 solution (It should be noted that these are not the solvents used in the hydrogenation reaction). Hence no hard evidence is yet available to indicate a possible mechanism for the hydrogenation of styrene and indeed the superiority of the "hard-soft" ligand PPFA which could conceivably be acting as a "hinge" on the metal by dissociation of 72 the -NMe2 group [20,32]. 3.3 SUMMARY The significant finding of this study is that cationic homogeneous hydrogenation catalyst precursors based on the relatively inexpensive metal, palladium, can be prepared. Although they reduce a narrower range of substrates than their cationic rhodium(I) counterparts this may be a benefit in allowing greater selectivity. The complex of the ferrocenyl-phosphine ligand, PPFA, gives higher activities than those of di(tertiary phosphine) ligands such as dppe and BPPF; this is another example of the advantages of using mixed "hard-soft" ligand. The palladium complexes of ferrocenylphosphines such as (L-L)PdCl2 have been used by others in catalyzing hydrosilylation (cf. Section 1.2.2) and Grignard cross-coupling (cf. Section 1.2.3) reactions; this is the first report of their use as hydrogenation catalyst precursors. 73 CHAPTER 4 PLATINUM(II) COMPLEXES OF FERROCENYLPHOSPHINES 4.1 INTRODUCTION Rhodium(I) complexes of c h i r a l ferrocenylphosphine ligands such as PPFA, BPPFA and t h e i r analogues are a c t i v e c a t a l y s t precursors f o r the h y d r o s i l y l a t i o n of ketones such as acetophenone, J a , equation 4.1. R-C-CH3 + R 1 R 2 S i H 2 [Cat] H +/H 2 0 H R-d-CrL I 3 OH l a R=Ph b R=Fc 3a R=Ph b R=Fc (4.1) A combination of Rh(I)/MPFA (MPFA = (R.S)-PPFA with -PMe2 r e p l a c i n g the -PPh 2 group) a f f o r d s good r e s u l t s (52% e.e.) using a-napthylphenyls1lane (2, R x = Ph, R 2 = a-naphthyl) [53]. Recently Brunner and coworkers have found that very good o p t i c a l y i e l d s f o r ketone h y d r o s i l y l a t l o n s (97%) are obtainable using rhodlum(I) d e r i v a t i v e s of "harder" (non-phosphine contai n i n g ) c h i r a l ligands such as 4 and 5_ [100-102]. 74 Derivatives of other metals such as platinum have received l i t t l e attention. Kumada and coworkers [47,103] found that platinum(II) complexes * * [L P t C l 2 ] 2 (L = chiral monodentate phosphine) catalyze the hydrosilylation of a series of alkyl phenyl ketones to give optically active alkylphenyl-carbinols in good chemical yields but low optical yields (18.6% maximum). Brunner and coworkers [102] report low optical yields from catalysts based on platinum(II) complexes of chelating amines such as 5. There are only a few reports concerning platinum(II) complexes of ferrocenylphosphines [12,104,105], but none on the synthesis and catalytic properties of platinum(II) complexes of chiral ferrocenyl phosphine ligands. The present study on the asymmetric hydrosilylation of ketones such as 1_ was initiated because of our interest in the catalytic activity of platinum(II) complexes of mixed "hard-soft" ligands such as PPFA, and 75 because of our desire to prepare chiral ferrocenylethanol, 3b. Successful use of metal complexes of ligands such as PPFA in this particular reaction would effectively enable the catalyst to breed its own chirality, an objective which has been achieved for the chiral ligand (R)-l,2-bis(diphenylphosphino)propane [106]. Such a route would be viable because 3_b is easily transformed into ,N,Ni-dimethylaminoethylferrocene, FA [107,108], an amine which is an important precursor for the synthesis of chiral ligands such as (S.R)-PPFA and (S.R)-BPPFA (cf. Section 2.3). 4.2 RESULTS AND DISCUSSION 4.2.1 Synthesis and Characterization The platinum(II) complexes (L-L)PtCl 2 (L-L = BPPF, (S.R)-PPFA, (S,R)-IS0PFA and (S,R)-BPPFA) were prepared using equimolar quantities of K 2PtCl 1 + and the appropriate ligand as shown in equation 4.2. The analytical, physical and NMR spectroscopic data for the complexes are summarized in Tables 4.1 and 4.2. K 2 P t C l 4 + (L-L) • ( L - L ) P t C l 2 + 2KC1 L-L = BPPF, (S.R)-PPFA, (S.R)-ISOPFA, (S,R)-BPPFA. (4.2) 76 Table 4.1 M i c r o a n a l y t i c a l r e s u l t s and melting p o i n t s f o r ( L - L ) P t C l 2 . mp(°C) Calcd.(%) Found[%) (L-L) (decomp) C H N C H N BPPF 158-161 (S.R)-PPFA 191-193 (S.R)-ISOPFA 195-197 (S.R)-BPPFA 187-189 49.77 3.44 0.0 43.06 4.14 1.93 8 37.59 5.01 2.19 50.20 4.29 1.54 49.25 3.49 0.0 43.16 3.83 1.90 37.49 5.23 2.05 50.78 4.32 1.55 Calculated value is based on ( L - L ) P t C l ~ . H 9 0 . 77 Table 4.2 }H and ^POH } NMR data f o r ( L - L ) P t C l * . (L-L) NMe_2 Others BPPF (S.R)-PPFA 2.97(s) 3.77(s) (S.R)-ISOPFA 2.45(bs) 3.45(bs) (S.R)-BPPFA 2.32(s) 4.20, 4.43(2xbs, F e t f ^ ) ) ; 1 2 . 5 ( J p t p = 7.49, 7.94(2xm, 6H, 4H, Ph_2) 3765.9) 1.39(d, J H H=7.2, CHMe); -11.89 3.57-3.62(m, CHMe); ( J p t p = 3.81(s, F e ( C & H 5 ) ) ; 3981.9) 4.25, 4.47(2xbs, F e t C ^ ) ) ; 7.31- 7.57, 8.19-8.25(2xm, Ph_2) 1.26-1.70(m, CHMe&CHMe 2); 9 . 5 1 ( J p t p = 2.68, 3.08(2xbm, CHMe 2); 3889.3) 3.96-4.20(m, CHMe); 4.25(s, F e f C ^ ) ; 4.32- 4.64(m, FefCgHg)) 1-31(d. J H H=7.2, CHMe); 3.42-3.58, 4.11-4.63 (m, ( C ^ j F e t C ^ ) ) ; 5.89-5.97(m, CHMe); 7.00-8.53(m, Ph_2) 15.49(d, J p t p--3860.5, J p p = 8 ) ; 8.70(d, J p t p=3720.3, J p p = 8 ) b A l l s p e c t r a were obtained i n CDC1,. Coupling constants are i n Hz. The resonance f o r P atom adjacent to the amine group i s at lower frequency (higher s h i e l d i n g ) . 78 The lH NMR spectrum of (BPPF)PtCl2 is similar to that of its palladium counterpart (cf. Section 3.2.1). The 31P{1H} NMR spectrum of (BPPF)PtCl2 is shown in Figure 4.1. This spectrum typically shows a single resonance due to 66.2% of the phosphorus nuclei coordinated to platinum nuclei other than 1 9 5 P t , and a doublet from the remaining 33.8% of the phosphorus nuclei coupled to 1 9 5 P t (I = 1/2). Hence, one observes a pseudotriplet with relative intensities of 1:4:1 with xJp tp being the separation of the two outer lines. In the case of (BPPF)PtCl2, this value is 3765.9 Hz. The lH NMR spectrum of ((S,R)-BPPFA)PtCl2 is also similar to that of its palladium counterpart (cf. Section 3.2.1) which shows only a sharp singlet for the -NMe2 group, Table 4.2. The 31P{1H} NMR spectrum, Figure 4.2, shows two doublet resonances, each with 1 9 5 P t satellites. Thus for the complex ((S,R)-BPFFA)PtCl2 both -PPh2 groups are coupled to platinum and hence the ligand is bound through both phosphorus atoms as in its palladium counterpart (cf. Section 3.2.1). For ligands such as BPPFA where there is a choice of P-N or P-P binding the only exceptions to the P-P binding mode found to date are in rhodium(I) complexes of the ligand where -PPh2 groups are replaced by -P(t-Bu) 2 groups [23]. A P-N binding mode is found in the palladium complex (L-L)PdCl2 (L-L = PPFA or ISOPFA). The same binding mode is found in the platinum complex (L-L)PtCl 2 (L-L = (S.R)-PPFA or (S.R)-ISOPFA) since the lH NMR data also show two NMe resonances at room temperature, Table 4.2. The 3765.9 Hz — i — i — i — r — i — i — i — r — i — i — i — i — | — T T T — i — i — r — i — i — i — i — | — i — i — i — i — i — i — i — i — i — | — i — i — i — r — r — i — i — i 30 25 20 1 15 10 5 0 - 5 ppm Figure 4.1 121.4 MHz ^ P ^ H } NMR spectrum of (BPPF)PtCl2. 3860.5 Hz r—n—i 1 1 1 r i 1 — i i 1 1—«—• 1 1— 3720.3 Hz 8 Hz l i r — n — i — i — i — I — i — r * — i — i — i — r * ~ i — i i — i — i — i — i — i — i — i — i — r 30 20 10 T — | — i — i — i — i — I — r -0 - 5 ppm 31n,l Figure 4.2 121.4 MHz J ,P{'H } NMR spectrum of ((S,R)-BPPFA)PtCl2. \ 3889.3 Hz 00 ro T— | — I — i — i — i — | — i — i — I — r 30 —]—i—i—i—r 20 ~~J—i—i—i—i—|—i—i—i—i—I—r 15 10 5 3 U r l Figure 4.4 121.4 MHz J , P{'H } NMR spectrum of ((S,R)-ISOPFA)PtCl2< Figure 4.5 The crystal structure of ((S,R)-ISOPFA)PtCl9 [109]. 84 resonances of the -NMe2 groups are sharp for ((S,R)-PPFA)PtCl2 complex but are broad in ((S,R)-IS0PFA)PtCl2 as in their palladium counterparts (cf. Section 3.2.1). The 3lP{lH} NMR spectra for ((S,R)-PPFA)PtCl2 and ((S,R)-ISOPFA)PtCl2 show the expected single resonance with 1 9 5 P t satellites, Figures 4.3 and 4.4. In the solid state the complex ((S,R)-IS0PFA)PtCl2, Figure 4.5, is chiral, with an S_ configuration for the amine-substituted C(ll) atom, and R configuration for the asymmetrically-substituted ferrocene moiety [109] as anticipated from the preparation procedure used [14,15a]. The platinum atom has cis-square planar coordination, to two Cl atoms and the P and N atoms of the ferrocene ligand; the coordination shows a significant distortion towards tetrahedral geometry, with Cl-Pt-P and Cl-Pt-N trans angles of 169.7(1) and 171 .8 (2 )° , respectively [109]. 4.2.2 Hydrosilylation Studies A. Reduction of aromatic ketones The platinum(II) complexes (L-L)PtCl 2 (L-L = BPPF, (S.R)-PPFA, (S.R)-ISOPFA and (S.R)-BPPFA) were examined with regard to their ability to catalyze the hydrosilylation of acetophenone in CH2C12 solution, Table 4.3. The monohydrosilanes such as HSiCl 3 , HSiEt3 and HSi(0Bu)3 give very low yields (~ 5%) of products under the conditions used in these studies. The use of the dihydrosilane Ph 2SiH 2 in the catalyzed hydrosilylation of aromatic ketones is well established [37d,45,47,56]; in the present work this dihydrosilane was used and found to be effective in terms of chemical 85 Table 4.3 H y d r o s i l y l a t i o n o f acetophenone c a t a l y z e d by ( L - L ) P t C l 2 a . (L-L) S i l a n e Chem. Y i e l d ( % ) (S.R)-PPFA HS1C1 3 5 (S.R)-PPFA H S i E t 3 0 (S.R)-PPFA H S i ( 0 B u ) 3 5 (S.R)-PPFA P h 2 S i H 2 100 (S.R)-ISOPFA P h 2 S i H 2 100 (S.R)-BPPFA P h 2 S i H 2 0 BPPF Ph 2S1H 2 0 c P h 2 S i H 2 95 aKetone/Pt = 100/1; sil a n e / k e t o n e = 2/1; CH 2C1 2 (3 mL); temp, 60°C; time, 48 h. b P r o d u c t i s phenylethanol, GLC y i e l d . cThe complex i s (PPFA)PtHCl, 7a. 86 yield of the alcohol isolated after the necessary hydrolysis step. The P-N bound complexes, ((S,R)-PPFA)PtCl2 and ((S.R-ISOPFA)PtCl2» are more active than the P-P bound complexes, ((S,R)-BPPFA)PtCl2 and (BPPF)PtCl2. This may be a further instance of the efficacious combination of "hard-soft" ligands with the appropriate metal L27,32,60], since complexes of the mixed "hard-soft" ligands are often employed in catalysis in the hope of creating a vacant site on the metal by dissociation of one end of the ligand. A number of plausible reaction mechanisms have been based on this concept, e.g. the asymmetric cross-coupling reaction studied by Kumada and coworkers L20 ,60], but there is l i t t le direct experimental evidence supporting this phenomenon. It does seem that the complex '[(L-L)Rh(NBD)]C10\ (L-L = PPFA with -AsPh2 replacing the -PPh2 group) is such an example L 3 2 ] , The hydrosilylation reaction of aromatic ketones with Ph 2SiH 2 catalyzed by ((S,R)-PPFA)PtCl2 and ((S,R)-IS0PFA)PtCl2, equation 4.3, is 0 OSIHPh 2 OH R R=CH3;(CH2)2CH3; CH(CH 3 ) 2 (4.3) 87 unsatisfactory in terms of the optical yield of the isolated alcohol, Table 4.4 to Table 4.6. In general the best optical yields (e.g. 13.2% from butyrophenone) are obtained at low temperature and low conversion. The same effect was noted by Kolb and Hetflejs [113] for the DI0P/Rh(I) catalyzed hydrosilylation of PhC0CMe3. The results in Table 4.5 show that the configuration of the product is also temperature dependent; R or S alcohols are obtained from the reaction of acetophenone catalyzed by ((S,R)-IS0PFA)PtCl2 at 20°'or 60°C, respectively. This may be due to a change in the relative populations of ligand conformations with temperature [23]. As noted above the lH NMR spectrum of ((S,R)-ISOPFA)PtCl2 indicates that the complex is conformationally non-rigid in solution. The absolute configuration of the product from acetophenone (20°C) is S for the reaction catalyzed by ((S,R)-PPFA)PtCl2, Table 4.4, but is R when the ligand is (S,R)-IS0PFA, Table 4.5. A similar reversal has been noted in the asymmetric hydrogenation of prochiral olefins when the catalyst precursors are [(L-L)Rh(NBD)]C10ltt (L-L) = (S.R)-PPFA or (S.R)-PPFA with -P(t-Bu) 2 replacing the -PPh2 group [32]. The addition of excess ligand to the reaction mixture, Table 4.6, increases the optical yield although it decreases the chemical yield. This may be because the addition discourages the dissociation of the ligand from the metal complex (vide supra) thereby ensuring that the ligand is bound in the chelate mode which would be more favored to induce asymmetry into the reaction product. The lower yield could be due to the formation of (L-L) Pt type complexes, X>1, with loss of catalytic activity. The A presence of excess PPFA resulted in the same lowering of catalytic activity Table 4.4 Asymmetric h y d r o s i l y l a t i o n o f ketones with Ph„SirL c a t a l y z e d by ((S,R)-PPFA)PtCl, a. Ketone Si lane/Ketone Product Y i e l d ( % ) b O p t i c a l Y i e l d ( % ) c C 6H 5C0CH 3 1:1 C 6H 5CH0HCH 3 85 3.8(S) C 6H 5C0CH 3 2:1 CgH5CHOHCH3 100 4.2(S) C 6H 5C0(CH 2) 2CH 3 1:1 C 6H 5CH0H(CH 2) 2CH 3 30 9.4(S) C 6H 5C0(CH 2) 2CH 3 2:1 C 6H 5CHOH(CH 2) 2CH 3 52 7-KS) CgH 5COCH(CH 3) 2 1:1 no product 0 — C 6H 5C0CH(CH 3) 2 2 : l d C 6H 5CH0HCH(CH 3) 2 27 1.2(S) aKetone/Pt = 100/1; CH 2C1 2 (3 mL); temp, 20°C; time, 48 h. bGLC y i e l d based on s t a r t i n g ketone. c 0 p t i c a l y i e l d s are c a l c u l a t e d with respect to o p t i c a l l y pure 1-phenylethanol, [ a ] D -52.5° (C2.27, CH 2C1 2)[110]; n-propylphenylcarbinol, [ a ] n -45.9°(C6.1, b e n z e n e ) [ l l l ] ; p h e n y l i s o p r o p y l -c a r b i n o l , [ a ] n -48.3°(C7, ether)[112]; and c a l i b r a t e d f o r the o p t i c a l p u r i t y o f c h i r a l l i g a n d used (90%). Configurations are quoted 1n brackets. R e a c t i o n time, 90 h. Table 4.5 Asymmetric h y d r o s i l y l a t i o n o f ketones with P h 9 S i r L c a t a l y z e d by ((S,R)-ISOPFA)PtCl, a. Ketone Silane/Ketone Temp(°C) Time(h) Product Chem. Y 1 e l d ( % ) b O p t i c a l Y i e l d ( % ) c C 6H 5C0CH 3 2:1 60 48 CgH 5CH0HCH 3 100 1.2 (S) C 6H 5C0CH 3 2:1 60 24 CgH 5CH0HCH 3 100 1.9 (S) C 6H 5C0CH 3 2:1 20 48 CgH 5CH0HCH 3 100 1.2(R) C 6H 5C0CH 3 2:1 20 24 CgH 5CH0HCH 3 29 3.9(R) C 6H 5C0CH 3 1:1 20 45 CgH 5CH0HCH 3 69 4.2 (R) C 6H 5C0(CH 2) 2CH 3 2:1 20 66 CgH 5CH0H(CH 2) 2CH 3 100 2.8 (S) C f iH 5C0(CH 2) 2CH 3 1:1 20 65 CgH 5CH0H(CH 2) 2CH 3 21 3.0 (S) C 6H 5C0(CH 2) 2CH 3 1:1 60 48 CgH 5CH0H(CH 2) 2CH 3 97 1.5 (S) CgH 5COCH(CH 3) 2 2:1 20 66 CgH 5CH0HCH(CH 3) 2 3 d C 6H 5C0CH(CH 3) 2 1:1 60 68 CgH 5CH0HCH(CH 3) 2 100 1.1 (S) aKetone/Pt = 100/1; CH 2C1 2 (3 mL); see Table 4.4 f o r footnotes b and c. d N o t recorded. Table 4.6 Asymmetric h y d r o s i l y l a t i o n o f butyrophenone with Ph 9S1rL c a t a l y z e d by ((S,R)-PPFA)PtCl~ a. Si lane/Ketone Temp(°C) T1me(h) Chem. Y1e1d(%) b O p t i c a l Y1e1d(%) c 2:1 20 48 52 7.1 (S) 2:1 20 70 86 7.2 (S) 1:1 20 48 30 9.4 (S) 1:1 20 d 48 10 12.6 (S) 1:1 4 93 10 13.2 (S) 1:1 4 e 93 29 9.1 (S) 1:1 60 48 98 1.6 (S) aKetone/Pt = 100/1; CH 2C1 2 (3 mL); see Table 4.4 f o r footnotes b and c. d(S,R)-PPFA/((S,R)-PPFA)PtC1 2 =5/1. eHC1/((S,R)-PPFA)PtCl 2 = 10/1. 91 in the hydrogenation of olefin catalyzed by [(PPFA)Pd(DMF)2]2+ (cf. Section 3.2.2). In the presence of excess HCl, Table 4.6, the chemical yield is increased but the optical yield is decreased. This may be because the addition of HCl encourages the dissociation of the dimethylamino group of the ligand from the metal complex, thus generating more vacant sites on the metal and hence a faster rate of butyrophenone hydrosilylation is achieved. The lowering of optical yield may be due to the ligand not being bound in the favorable chelate mode for the asymmetric induction to take place. B. Reduction of ferrocenyl ketones In contrast with the results described for equation 4.3, when acetylferrocene is heated with Ph 2SiH 2 in the presence of ((S.R)-PPFA)-PtCl 2 , ethylferrocene (60% yield) and ferrocenylethanol (18* yield) are produced directly, no hydrolysis step is necessary, equation 4.4, Table 4.7. Under the same conditions benzoylferrocene affords only F"c-C—R + Ph 2 S!H 2 0 R^CH,; Ph H H F c - * f c - R + F c - C - R OH ^ (4.4) Table 4.7 M i c r o a n a l y t i c a l r e s u l t s and 'H NMR data f o r FcCH 9R and FcCH(0H)R. Calcd.(%) Found(%) Compound C H C H ]H NMRa FcCH 2R -R = Me 67.38 6.54 67.68 6.30 1.22(t,J H H=7, CH 2Me); 2.35(q,J H H=7, CHgMe); 4.21(s, F e ^ g H g ) ) ; 4.70-4.75(m, F e ( C 5 H 4 ) ) R = Ph 73.97 5.80 73.58 5.91 3.75(s, CHg); 4.20(s, (CgH^FefCgH^)); 7.28(bs, Ph) FcCH(0H)R R = Me 62.67 6.09 62.77 6.04 1.45(d, J H H = 7 , Me); 1.93(bs, OH); 4.21(s, ( C ^ F e f C ^ ) ) ; 4.25-4.75(m, CH) a A l l s pectra were obtained i n CDC1,. Coupling constants are i n Hz. 93 benzylferrocene. The minor product from acetylferrocene, S-ferrocenyl-ethanol, is chiral but the optical yield is low (1.5*). This result seems to negate any hopes expressed in the Introduction (cf. Section 4.1) of producing this alcohol in useful optical yield via a catalyzed hydrosily-lation reaction. Although reduction of ketones to hydrocarbons during homogeneous catalyzed hydrosilylation is not common, polymethylhydrosiloxane will reduce nitrobenzene and benzaldehyde to aniline and toluene respectively in the presence of Pd/C [114]. Diethyl ether is obtained from the NiCl 2 catalyzed reaction of ethyl acetate with HSiEt3[115]. Stochiometric reductions of organic compounds by hydrosilanes are not unusual [116-119]. For example, Gilman and Diehl [116] showed that benzophenone can be reduced to diphenylmethane by Ph 2SiH 2 at high tempera-ture (270°C). Other diary1 ketones react similarly although acetophenone is unaffected. In the case of benzophenone this uncatalyzed reaction is believed to proceed via a siloxy intermediate Ph2CH0(SiHPh2) which can be isolated when the ketone and silane are heated at slightly lower temperature [117]. Kazakova and coworkers [118] showed that treating stoichiometric amounts of acetylferrocene with HSiEt 3/CF 3C0 2H also gave ethylferrocene. All these reductions likely involve carbonium ion intermediates as does presumably the LiAlH^/AlC^ reduction of ferrocenyl ketones to the corres-ponding alkane [8]. Since one of the well established features of the chemistry of ferrocene compounds is the stability of the a-ferrocenyl carbonium ion [8,79,120], it seems likely that it is this that accounts for 94 the different products formed by hydrosilylation of the ferrocenyl ketones. The hydrogenolysis could involve reaction of the carbonium ion FcC+HR with Ph 2SiH 2 . The carbonium ion could be formed either from FcCHRO(SiHPh2), the expected hydrosilylation product, or from an inter-mediate such as JO (vide infra) earlier in the catalytic cycle. As a test, the preformed a-ferrocenylethylcarbonium ion (cf. Section 2.2.5) was treated with Ph 2SiH 2 in CH2C12 at 60°C. The dark colour of the solution gradually fades (~ 2 days) and ethylferrocene can be isolated from the solution following the same work-up as used for the hydrosilylation of acetylferrocene (cf. Section 2.1.3). When an identical reaction is carried out in the presence of 1 mol % of ((S,R)-PPFA)PtCl2, the colour change is almost immediate (60°C, 10 minutes) and ethylferrocene is again produced. These results provide support for the suggestion that the catalyzed hydrogenolysis of the ferrocenyl ketones by Ph 2SiH 2 proceeds via the carbonium ion FcC+HR and it should be noted that the reaction, which on this basis would involve the more stable ion (R = Ph), affords only the hydrocarbon product. Some alcohol is produced when R = Me. C. Reaction of Ph 2SiH 2 with (L-L)PtCl 2 The oxidative addition of HX to platinum(II) complexes such as [PtHY(PEt3)2] (X,Y = Cl , Br, I) results in the formation of platinum(IV) hydrides in solution L121,122]. Similarly, silanes, germanes and stannanes add to (dppe)PtCl2 to give six-coordinated platinum(IV) hydrides [123]. The isolation and characterization of these and related platinum(IV) deriva-95 tives as solids is difficult and the products readily decompose to the much more stable platinum(II) species in solution [121-124]. In the present investigation it was found that reaction of excess Ph 2SiH 2 with either (PPFA)PtCl2 or (IS0PFA)PtCl2 in CD2C12 solution takes place at ambient temperature as judged by the lH NMR spectra of the mixtures. These spectra show a number of high field metal hydride resonan-ces; the absence of coupling to platinum shows that the species (uniden-tified) are exchanging hydrides. Addition of diethyl ether to the reaction solution precipitates solids which, as judged by the microanalytical data, Table 4.8, are the oxidative addition products _6, equation 4.5. The (I) Ph 2S1H 2 (II) CD-C1, or CH-C1? (L-L)PtC1 2 I 1 (L-L)PtCl 2(H)(SiHPh 2) c (111) 20 C, 2 days ' * (iv) Et20 L-L * PPFA, 6a L-L - PPFA ISOPFA. b L-L - ISOPFA product 6a is not stable in solution region), Figure 4.6, shows a doublet NMR data are essentially the same as (L-L)PtClH • Ph 2S1HCl 7a L-L « PPFA b L-L • ISOPFA (4 .5) and the lH NMR spectrum (hydride resonance with 1 9 5 P t satellites. The those of (PPFA)PtHCl, 7a, which can be Table 4.8 M i c r o a n a l y t i c a l r e s u l t s f o r platinum hydride complexes. Calcd.(%) Found(%) Complex C H N Cl C H N Cl (PPFA)PtCl 2(H)(SiHPh 2) (PPFA)PtClH (ISOPFA)PtCl 2(H)(SiHPh 2) 51.20 4.49 1.57 7.95 46.42 4.31 2.08 5.27 46.68 5.34 1.70 8.61 50.43 4.79 1.76 7.18 46.80 4.65 2.30 5.00 46.36 5.52 1.64 8.44 1 1 1 1 1 1 — -16 -17 -18 -19 -20 -21 ppm Figure 4.6 400 MHz }H NMR spectrum (hydride region) of (PPFA)PtCl 2(H)(SiHPh 2) 1n CD 2C1 2 s o l u t i o n . Impurities. 98 independently synthesized from (PPFA)PtCl2 using the procedure of Clark and coworkers [26] (cf. Section 2.4.4). The magnitude of 2 0 p H , Table 4.9, indicates that the hydride is ci_s to phosphorus [121]. The 31P{1H} NMR data, Table 4.9, indicate that 6a decomposes to 7a in solution in much the same manner as other isolated platinum(IV) hydride species [121-124]. The complex 6b also decomposes in CD 2C1 2, Figure 4.7. However, two platinum(II) hydride resonances, each with 1 9 5 P t satellites are present (6 -19.25 and -22.80, Table 4.9) of relative intensity 2.5:1. The 6 and J values indicate that either species could be complex 2b, with hydride cis to phosphorus. In this case independent synthesis of 7b was not success-ful. The complexes (BPPF)PtCl2 and (BPPFA)PtCl2 do not react with Ph 2SiH 2 under the same conditions, again showing the difference in reactivities between P-P and P-N binding. The lack of reactivity with the si lane is probably associated with the much lower catalytic activity of these species and strongly suggests that the true catalyst for these hydrosilylation and hydrogenolysis reactions is either a platinum(IV) hydride or, more likely, a platinum(II) hydride. Certainly we find that 7a is an effective catalyst for the hydrosilylation of acetophenone under the same conditions, Table 4.3. D. Mechanistic consideration The mechanism of the hydrosilylation of ketones catalyzed by metal complexes is not well established [45,47,58,113] (cf. Section 1.2.2). Hetflejs and coworkers [113] studied the kinetics of hydrosilylation of Table 4.9 Physical and NMR data for platinum hydride complexes. Complex Yleld(X) Color mp(°C) (decomp) NMR (CD2C12)@ (PPFA)PtCl2(H)(S1HPh2), 6a 30 yellow-orange 136-138 ] H : 6 -18.56, J p t H -1344. J p H -14; ^ P ^ H > : 6 9.34, (PPFA)PtClH » 7a 43 pale-orange 139-142 J p t p » 4 4 0 1 #  ] H : « -18.55, Jp t H »1341, J p H -14; 3 1P{ 1H } : 6 9.69, (ISOPFA)PtCl2(H)(S1HPh2), 6b 25 yellow 114-116 J p t p-4392 *H « -19.25, J p t H -1326. J p H -14; « -22.80, J D , U-1143. J D U -20 These complexes give very complex H NMR spectra from 0-10 ppm which are not f u l l y I n t e r p r e t e d at t h i s stage; only the hydride region 1s presented here. Coupling constants are i n Hz. The NMR data are the same as found f o r 7a, thus complex 6a 1s not present 1n s o l u t i o n . 14 Hz 1- 1326 Hz 20 Hz -19.25 ppm -22.8 ppm Figure 4.7 400 MHZ ]H NMR spectrum (hydride region) o f (IS0PFA)PtCl 2(H)(S1HPh 2) 1n CD 2C1 2 s o l u t i o n . 101 PhC0CMe3 with Ph 2SiH 2 catalyzed by DI0P/Rh(I) and concluded that the reaction must first involve the oxidative addition of the organosllicon hydride to the rhodium(l) species followed by the reaction of the ketone with the silyl-hydrido-rhodium(III) species in the rate determining step of the hydrosilylation. In order to obtain the final product, pathways involving intermediates of type 8 and 9. (M = Rh) need to be invoked \ l / Si I M - 0 — C - H I 8 H I M I C - 0 I and both have been proposed [45,47,58] (see also Figure 1.4). Kumada and coworkers [47] proposed an intermediate such as £ (M = Pt) for the r * hydrosilylation of prochiral ketones with MeCl2SiH catalyzed by [L P t C l 2 J 2 (L* = chiral phosphine such as (R)-(+)-BMPP). (L-L)PtCI 2 j Ph2SiH2 (L-L)PtCI 2(H)(SiHPh 2) -Ph2SiHCI (L-L)PtCIH r (L-L)PtCI(H)(SiHPh 2) ( O - C - H ) I 10 Ph 2SiH 2 0 = C I ( L - L ) P t C I ( O - C - H ) I o ro Figure 4.8 Proposed mechanism f o r the h y d r o s i l y l a t i o n o f ketones with P h 2 S i H 2 c a t a l y z e d by ( L - L ) P t C l 2 , (L-L) = (S.R)-PPFA or (S.R)-ISOPFA. 103 The present studies of the reaction of (L-L)PtCl 2 (L-L = PPFA, ISOPFA) with Ph 2SiH 2 provide evidence that the oxidative addition of the organosilicon hydride to platinum(II) species to afford a platinum(IV) hydride is the init ial step in the catalytic reaction. In its simplest form a likely mechanism can be written as shown in Figure 4.8 which supports a mechanism based on 8 (M = Pt). This could account for the low optical yields since the asymmetric center is developed further away from the metal atom. An intermediate such as JO could also lead to direct alcohol formation as found for the acetylferrocene reaction and direct carbonium ion formation leading to hydrogenolysis of the ferrocenyl ketones. 4.3 SUMMARY In summary, platinum(II) complexes of chiral ferrocenylphosphines are effective catalyst precursors for the hydrosilylation of aromatic ketones with Ph 2SiH 2 . Chemical yields of the alcohol obtained following hydrolysis are high (100%) but optical yields are low (13.2% e.e. max). The complexes with mixed "hard-soft" ligands are better catalyst precursors than those with di(tertiary phosphine) ligands. Under the same conditions the hydrosilylation of ferrocenyl ketones results in further reduction and affords mainly the alkylferrocene products. The stable carbonium ion FcC+HCH3 is reduced by Ph 2SiH 2 to FcCH2CH3 in a thermal reaction which is catalyzed by the complex (PPFA)PtCl2. The catalyst precursor (L-L)PtCl 2 (L-L = PPFA or ISOPFA) reacts with Ph 2SiH 2 yields the stable platinum(IV) 104 hydride. This eliminates Ph2SiHCl in solution to afford (L-L)PtHCl. 105 CHAPTER 5 POLYMER-BOUND FERROCENE DERIVATIVES AND THEIR PALLADIUM AND PLATINUM COMPLEXES 5.1 INTRODUCTION Extensive research has been devoted to attach transition metal complexes to inert supports such as organic polymers, s i l ica , alumina and clays [35,68,69]. Most of the recent work has focused on the conversion of soluble catalysts, homogeneous catalysts, into easily separated polymer-bound catalysts, heterogenized catalysts, that maintain the important properties of the soluble complexes. In the case of ferrocene derivatives there have been some studies concerned with supporting them on inert materials [69-72] (cf. Section 1.3). Heterogenized catalysts have been employed for a variety of reactions such as hydrogenation, hydrosilylation and hydroformylation [68], with hydrogenation being the most widely studied. There are some reports on the use of heterogenized catalysts in asymmetric synthesis [68,69,125]. Most of the asymmetric reactions studied to date concern olefin hydrogenation and in some cases optical yields of the reduced product up to 86% are obtained [125]. The asymmetric hydrogenation of ketones catalyzed by supported chiral complexes has also been studied, e.g. ~76% optical yield was achieved in the hydrogenation of keto-pantolactone, J , catalyzed by a supported chiral rhodium complex, equation 5.1 [126]. 106 (5.1) The asymmetric hydrosilylation of several aromatic ketones, equation 5.2, is catalyzed by rhodium derivatives of the optically active di-(tertiary phosphine) DI0P supported on polystyrene [49,56]. In the case of acetophenone (_3, R = Me), optical yields of 1-phenylethanol up to 58% are obtained using a-napthylphenylsilane (4, Rx = Ph, R2 = o-naphthyl) [56J. 107 The same reaction has been studied using chiral rhodium(I) complexes bound to inorganic supports such as si l ica and glass as the catalysts [127], but the optical yields obtained are much lower (0.4 - 19.7%). The present study is concerned with developing methods for the attachment of substituted ferrocene derivatives to polystyrene type polymers. The ultimate objective of this work is to develop the use of these polymers and their metal complexes as catalysts for heterogeneous reactions such as hydrogenation and hydrosilylation, which are catalyzed homogeneously by metal derivatives of ligands based on a ferrocene backbone (cf. Section 1.2). In this chapter, the synthesis and characterization of polymer-bound ferrocene derivatives will be presented. In addition studies of hydrogenation and hydrosilylation using palladiumUI) and platinum(II) complexes of some of these polymers will be described. 5.2 RESULTS AND DISCUSSION 5.2.1 Synthesis and Characterization A. Polymer-bound ferrocene derivatives In view of the high reactivity and ease of preparation of lithio-ferrocenes [80,128], these were the reagents of choice in experiments involving the attachment of ferrocene and its derivatives to the cross-linked chloromethylated polystyrene and to the aldehydic polymer. The reactions of lithioferrocene, dilithioferrocene and lithium derivative of FA with the two polymers are shown in equations 5.3 and 5.4. Lithioferrocene reacts with chloromethylated polystyrene to give an 108 (5.3) 109 €K^O>-CH0 Polymer-VI ( 5 . 4 ) n o iron containing product, polymer-I, equation 5 . 3 . The Massbauer spectra for polymer-I and ferrocenylphosphine ligands such as BPPF, PPFA, ISOPFA and BPPFA are shown in Figure 5.1 to Figure 5 . 5 , respectively. These spectra are clean and show the expected single doublet with the isomer shift (6) and quadrupole splitting (A) values, Table 5 . 1 , in the expected range for simple ferrocene derivatives, Table 5.2 [129-131 j . The solid state 1 3 C NMR spectrum of ferrocene is shown in Figure 5.6A [132 ] , The sharp resonance at 70.4 ppm is assigned to the ten equivalent carbon atoms of ferrocene, since a chemical shift of 67.9 ppm is quoted for the solution spectrum of ferrocene [133 ] . Figure 5.6B shows the solid state 1 3 C NMR spectrum of FA, which gives only two peaks at around 70 ppm [132] for the ferrocene ring carbon resonances. The solution spectrum of FA gives much better resolution; it shows six different resonances for the ferrocene ring carbon atoms. (The 1 3 C NMR data for FA in CDC1 3 : 6 16.1 ( C - C H 3 ) ; 40.6 (N (CH 3 ) 2 ) ; 58.4 (CHCH 3 ) ; 6 6 . 6 , 6 7 . 0 , 6 7 . 2 , 6 9 . 1 , 87.0 ( C c ^ ) ; 68.4 (CgHg)). Thus l i t t le useful structural information can be obtained from the solid state 1 3 C NMR spectrum of FA. The solid state 1 3 C NMR spectrum of polymer-I is shown in Figure 5.7 [132J. There is a broad peak at around 70 ppm which confirms the loading of a ferrocene derivative. As noted above, no useful structural informa-tion can be obtained from this spectrum. The use of THF as swelling agent was found to be essential in the reaction of lithioferrocene with chloromethylated polystyrene. Only low loadings were achieved in its absence [132] . The reaction of lithioferrocene with the aldehydic resin to produce Figure 5.1 Mossbauer spectrum of polymer-I. 112 Figure 5.2 Mossbauer spectrum of BPPF. 113 Figure 5 . 3 Mossbauer spectrum of PPFA. 114 Figure 5.4 Mossbauer spectrum of ISOPFA. 115 - 3 - 2 - 1 0 1 2 3 4 Velocity (mms"1) 1gure 5.5 Mossbauer spectrum of BPPFA. 116 Table 5.1 Mossbauer parameters and m i c r o a n a l y t i c a l r e s u l t s f o r polymer supported ferrocene d e r i v a t i v e s . Mossbauer(mms~^) A n a l y t i c a l Polymer 6 A Found(%) I 0.44 2.33 Fe(3.39); Cl(2.80) II 0.53 2.39 Fe(1.30) H a @ Br(0.93) l i b (? N(0.83) III 0.54 2.40 Fe(5.07); Cl(1.72) IV 0.54 2.39 Fe(4.40) IVa @ F e ( l . 4 7 ) ; Br(2.68) IVb <a N(0.72); Br(1.38) V 0.53 2.45 F e ( l . 2 1 ) ; C l ( 3 . 1 1 ) ; N(0.54) VI 0.53 2.42 Fe(2.83); Cl(O.O); N(0.75) VII weak weak Fe(0.30); P(0.20) # VIII 0.53 2.37 Fe(1.50); N(0.33); P(0.88) V I I I * 0.55 2.25 Fe(1.50); N(0.40); P(0.94) Not recorded. In the presence o f TMEDA, Fe(0.38); P(0.40). 117 Table 5.2 Mossbauer parameters f o r some ferrocene compounds. Compound 6(mms~^) A(mms"^) Reference Fc-H 0.48 2.40 [129] Fc-C0CH 3 0.54 2.27 [130] BPPF 0.44 2.29 [131] BPPF 0.50 2.31 @ PPFA 0.44 2.34 0 ISOPFA 0.49 2.41 BPPFA 0.52 2.35 (P This work. 118 Figure 5.6 1 3 C CP/MAS NMR spectrum of fe r r o c e n e , A; FA, B [132]. SSB denotes the sp i n n i n g s i d e bands; * denotes the s i d e bands due to the ferrocene r i n g carbon atoms. The truncated s i g n a l a t around 89 ppm i s due to the carbon atoms of the D e l r i n spinner, polyoxymethylene [132]. 119 T — i — j — i — I I l | I I—i—I—|—i—i—i—l—|—I—I—I—I—j—i—i—r 200 150 100 50 0 ppm Figure 5.7 , C T CP/MAS NMR spectrum of polymer-I [132]. SSB denotes the spinning s i d e bands; ** denotes the s i d e bands due to the broad aromatic peak at around 130 ppm. The truncated s i g n a l a t around 89 ppm i s due to the carbon atoms o f the D e l r i n spinner, polyoxymethylene [132]. 120 polymer-II, equation 5.4, was carried out under similar conditions to those used for polymer-I. Although the procedure was not optimized, the Mossbauer spectrum of polymer-II is essentially the same as that of polymer-I. The Mossbauer parameters of polymer-II, 6 0.53 rrms"1 and A 2.39 rnns"1, are in the expected range for simple ferrocene derivatives, Table 5.2, indicating that bonding a ferrocenyl moiety via a -CH(OH) group rather than a -CH 2 group as in polymer-I has l i t t le effect. Since the hydroxyl group in polymer-II is adjacent to the ferrocene moiety it was of interest to see if the polymer would behave like its soluble monomeric counterpart Fc-CH(0H)R in allowing easy displacement of -OH by other groups [107-108,134]. In particular the sequence shown in equation 5.5 has been developed for the synthesis of the very useful amine FA [107,108]. Treating a suspension of polymer-II in benzene with gaseous HBr causes darkening of color as in the homogeneous reactions [107,108] and simple filtration affords polymer-IIa. The analytical data, Table 5.1, show that 0.93% of bromine is incorporated into polymer-IIa. Although the reaction conditions have not been optimized, it is clearly facile and the derivative should be useful for further elaboration. Thus, in the present work, it has been established that polymer-IIa readily reacts with HNMe2 affording polymer-Ilb. Alternatively, polymer-II can be taken through to polymer-Ilb without isolating polymer-IIa as in its soluble monomeric counterpart, R = Me, equation 5.5 [107,108]. 121 Polymer-IVb (5.6) 122 The reaction of 1,1'-dilithioferrocene-TMEDA with chloromethylated polystyrene, under the same conditions used to prepare polymer-I, gives a very good loading of iron in the product, polymer-III, equation 5.3. The Mossbauer parameters of polymer-III, 6 0.54 rims"1 and A 2.40 rrms"1, are also in the expected range for simple ferrocene derivatives, Table 5.2. The solid state 1 3 C NMR spectrum of polymer-III is similar to that of polymer-I; it shows a broad peak at around 70 ppm confirming the loading of a ferrocene derivative [132]. The reaction of 1,1'-dilithioferrocene-TMEDA with the aldehydic resin also results in a polymeric material, polymer-IV, with a high iron content, Table 5.1. The Mossbauer parameters of polymer-IV are almost identical with those of polymer-II. Since polymer-IV is like polymer-II in having -OH groups, it reacts with HBr to give polymer-IVa, equation 5.6. Polymer-IVa has a higher bromine content than polymer-IIa reflecting the higher init ial loading. The dimethylamino derivative, polymer-IVb, can be prepared in the same manner as polymer-IIb. The solid state 1 3 C NMR spectra of polymer-IV and polymer-IVb also show a broad peak at around 70 ppm indicating the loading of a ferrocene derivative [132]. The amine FA can be resolved into its enantiomers [17] and the init ial lithiation to produce lithium derivative of FA is essentially stereospecific [15b], equation 5.7 (also see Figure 1.1), and introduces a new chiral center because of the planar chirality. This, in principal, allows reactions in equations 5.3 and 5.4 to be carried out to produce 123 FA (5.7) chiral polymers, although racemic FA was used in the present investigation. In order to encourage selective lithiation, TMEDA is not added with the jn-BuLi. The microanalytical data indicate that the reactions proceed as expected. The Mossbauer parameters, Table 5.1, of polymer-V and polymer-VI show that the attachment has taken place as anticipated. The solid state 1 3 C NMR spectra of polymer-V and polymer-VI also show a broad peak at around 70 ppm confirming the loading of a ferrocene derivative in these polymers L132J. The lithiation of BPPF with n-BuLi with or without TMEDA affords a mixture of metalated products which consist mainly of isomers of the hetero ring dilithiated species L135], equation 5.8, X = Y = 1 for L l . . , BPPF. XT-y Isomers occur because although most ferrocene substituents direct lithium mainly to the "3" position, the -PPh2 group has an enhanced tendency to 124 BPPF L1 BPPF X+Y CHO POLYMER-VII (5.8) d i r e c t metal a t i o n t o the "2" p o s i t i o n [135], making i t more l i k e a few e x c l u s i v e l y " 2 " - d i r e c t i n g s u b s t i t u e n t s [15b], e.g. equation 5.7. I t should be noted that because of the presence of planar c h i r a l i t y i n d i s u b s t i t u t e d metallocene rings some of the isomers are a c t u a l l y diastereomers. Because of these p o s s i b i l i t i e s i t seems u n l i k e l y that a well defined polymer bound BPPF l i g a n d can be prepared v i a the l i t h i u m d e r i v a t i v e of BPPF, L i BPPF, x+y and the r e s u l t s of the present study bear t h i s out. Only low loadings of li g a n d are obtained from r e a c t i o n of the l i t h i u m d e r i v a t i v e L i BPPF with the aldehydic r e s i n , equation 5.8, e i t h e r x+y i n the presence or absence of TMEDA. The Mossbauer spectrum of polymer-VII i s too weak f o r processing; t h i s i s due most probably t o the low i r o n content, Table 5.1. The "2" p o s i t i o n with respect to the amine group i s the p r i n c i p a l s i t e of l i t h i a t i o n of the l i g a n d analogous t o PPFA, with -SiMe 3 r e p l a c i n g the -PPh 2 group i n the absence of TMEDA [136]. Thus the r e a c t i o n of _n-BuLi 125 with PPFA affords the monolithiated derivative of PPFA, L1 x + yPPFA, X = 1, Y = 0, equation 5.9. However, in the present study no polymer-bound product was obtained following the reaction of this monolithiated derivative with the aldehydic resin, presumably because of the steric hindrance on the "top" ring of PPFA. The lithiation of PPFA with two moles of n-BuLi/TMEDA results mainly 1n hetero ring dilithiation although again other metalated products are present [135,136]. The dilithiated product L1 PPFA, X = Y = 1, x+y equation 5.9, is also a mixture of isomers since lithiation can occur at any of the remaining three position on the P-N substituted ring, the top ring, although the most likely position is adjacent to the amine group (vide supra). PPh 2 ( i i ) n - B u L i / TMEDA (1) n-BuLi P P h 2 PPFA L i PPFA X+Y . POLYMER-VIII (5.9) 126 The reaction of the lithium derivative Li .PPFA with the aldehydic X+y resin affords polymer-VIII. Microanalytical data, Table 5.1, show a satisfactory loading. The Mossbauer spectrum is usually a clean doublet similar to that of the unbound ferrocenylphosphine ligands as shown in Figure 5.2 to Figure 5.5. Some preparations show two doublets in the Mossbauer spectrum; the outer doublet with A 2.35 urns-1 indicates the presence of a bound ferrocene derivative while the inner doublet with its much smaller A 0.66 mms'1, indicates the presence of traces of an Fe(III) impurity. The increase in isomer shift for polymer-VIII as compared to the unbound PPFA ligand, Tables 5.1 and 5.2, is probably an indication that substitution is, as anticipated mainly on the "bottom" ring of PPFA, since the isomer shift for polymer-VIII, 6 0.53 mms-1, is almost the same as that of the BPPFA ligand, 6 0.52 mms-1. In order to prepare an optically active version of polymer-VIII, * polymer-VIII , racemic PPFA is replaced by (S.R)-PPFA. The Mossbauer * parameters of the iron doublet observed for polymer-VIII , Table 5.1, compare well with the parameters from polymer-VIII. These results give a measure of the reproducibility of the experimental procedures used. This methodology was developed to encourage polymer attachment to the bottom ring of PPFA. The microanalytical data, Table 5.1, for polymer-VIII and * polymer-VIII also agree well, indicating comparable loadings. 127 B. Palladium and platinum complexes of polymer-bound ferrocene derivatives Polymer-VI, -VII, -VIII and -VIII* all react with Na2PdCl^, equation 5.10, with incorporation of Pd and Cl as judged from the microanalytical data, Table 5.3. The Cl:Pd ratio in each is ca. 2. In polymer-VI-Pd the N a 2 P d C l 4 Polymer-Y • Polymer-Y-Pd + 2NaCl Y = VI, V I I , V I I I , V I I I * (5.10) N:Pd ratio is 2.3:1 indicating that not al l the nitrogen atoms are bound even if the complex is of the (NR 3) 2PdCl 2 type. The Mossbauer parameters of polymer-VI-Pd, Table 5.3, are essentially unchanged as compared with those of polymer-VI, Table 5.1. Polymer-VII-Pd seems to have a considerable excess of Pd for a PdCl 2 type complex since the P:Pd ratio is 1:1.7 even though the Cl:Pd ratio is much as expected. These analytical results are reproducible and it is difficult to account for them. Perhaps in this case the side chain of the polymer has become involved in binding the metal since the unbound ligand BPPF forms a chelate complex with PdCl2 of known and expected structure [62,90]. 128 Table 5.3 Mossbauer parameters and microanalytical results for palladium and platinum complexes of polymer supported ferrocene derivatives. Polymer Mbssbauer(i mms"^ ) Analytical 6 A Found(%) Vl-Pd 0.50 2.45 Pd(2.44); Cl(1.71); N(0.75) Vl-Pt 0.53 2.44 Pt(3.81); Cl(1.25); N(0.84) VH-Pd @ Pd( l . l l ) ; Cl(0.87); P(0.20) VH-Pt Pt(0.59); Cl(0.20); P(0.17) VHI-Pd 0.53 2.39 Pd(1.36); Cl(1.20); N(0.29); P(0.57) VHI-Pt 0.57 2.29 Pt(1.99); Cl(0.62); N(0.30); P(0.64) VIII*-Pd 0.57 2.23 Pd(2.23); Cl(1.95); N(0.43); P(0.94) VIII*-Pt 0.53 2.27 Pt(2.51); Cl(0.92); N(0.30); P(0.75) Not recorded. 129 In polymer-VIII-Pd, the P:Pd ratio is 1.4:1, Table 5.3. These data are reasonable for a P-N bound PdCl2 complex (cf. Section 3.2.1). This * P-N mode of binding is also found in the polymer-VIII -Pd since the P:Pd ratio is also 1.4:1. The Mossbauer parameters of polymer-VI11-Pd and polymer-VIII -Pd, Table 5.3, are l i t t le changed from those of polymer-VIII and polymer-VIII*, Table 5.1. * The four polymers, polymer-VI, -VII, -VIII and -VIII , al l react with K 2 PtCl 4 , equation 5.11, to give dark colored resins with incorporation K 2 P t C l 4 Polymer-Y • Polymer-Y-Pt + 2KC1 Y = VI, VII, V I I I , V I I I * (5.11) of Pt and Cl as judged from the microanalytical data, Table 5.3. In the case of polymer-VI-Pt, the N:Pt ratio is 3:1 indicating that not all the nitrogen atoms bind to the metal as in poymer-VI-Pd. The Cl:Pt ratio in polymer-VI-Pt is ca. 2. The same ratio is found for the other three supported platinum derivatives. The Mossbauer parameters, Tables 5.1 and 5.3, are essentially unchanged in the series polymer-VI, 130 polymer-VI-Pd and polymer-VI-Pt, showing that no oxidation of the iron takes place during the metal binding reactions [137], The loading of BPPF is low in polymer-VII, thus a low percentage of Pt is found in polymer-VII-Pt. The Mossbauer spectra of polymer-VII, polymer-VII-Pd and Polymer-VI I-Pt are all too weak for processing and therefore are not useful. The microanalytical data yield a 2:1 ratio for P:Pt in polymer-VII-Pt, indicating a chelating structure as found for many metal derivatives of the unbound BPPF ligand [90,138]. In the case of polymer-VIII-Pt, the P:Pt ratio is again 2:1. These data suggest that the ligand is not using the -NMe2 group to bind to the metal in these materials, even though the unsupported PPFA ligand is P-N bound in its platinum(II) complexes (cf. Section 4.2.2). The P-P mode of binding in polymer-V 111-Pt is also maintained to some extent in the * polymer-VIII -Pt, since the P:Pt ratio is ~1.9:1. The Mossbauer * parameters of polymer-VI I I-Pt and polymer-VIII -Pt, Table 5.3, show very * l i t t le difference from those of polymer-VIII and polymer-VIII , Table 5.1. 5.2.2 Hydrogenation Studies A. Supported palladium complexes There are many examples of studies of the catalytic properties of P-and N-bound supported catalysts [68], but l i t t le is known about the mixed P-N donor systems such as polymer-VIII-Pd. The results of a number of olefin hydrogenation reactions employing polymer-VI-Pd, polymer-VII-Pd and polymer-VIII-Pd as catalysts are summarized in Table 5.4 to Table 5.7; all three are effective. 131 Styrene and a-methylstyrene are readily hydrogenated at 1 atm pressure and 60°C in benzene in the presence of polymer-VIII-Pd, whereas cyclohexene is hydrogenated at a slower rate, Table 5.4. Under the same conditions 1-hexene is both hydrogenated and isomerized; trans-2-hexene is the major product. The catalyst can be recycled without loss of activity as is seen in runs 8-10, Table 5.4. The nature of the solvent is an important factor that can be varied in order to control the activity and selectivity of supported hydrogenation catalysts [68a]. The effect of solvent on styrene hydrogenation catalyzed by polymer-VIII-Pd is summarized in Table 5.5. The relative rate of hydrogenation increases with the solvent polarity even though benzene is a better solvent for swelling polystyrene than is MeOH or EtOH [68a,139]. Low rates are obtained in halogenated solvents such as CHC13 and CH 2C1 2, Table 5.5. Table 5.6 shows the catalytic activities of the three polymers, polymer-VI-Pd, polymer-VII-Pd and polymer-VIII-Pd, with respect to olefin hydrogenation at 30°C in MeOH. The P-N bound complex, polymer-VIII-Pd, is clearly less active than the other two. Since it seems that palladium(II) derivatives of unidentate functionalized polymers are more active hydro-genation catalysts than derivatives of bidentate [140], this provides further indirect evidence for bidentate binding in polymer-VIII-Pd as described above (cf. Section 5.2.1). It should be noted that homogeneous catalytic systems involving [(L-L)PdS 2 ] 2 + , (L-L) = PPFA a P-N bound ligand, S = DMF, show higher activity for olefin hydrogenation than the P-P bound complexes (cf. Section 3.2.2). 132 Table 5.4 Hydrogenation o f o l e f i n s i n benzene c a t a l y z e d by polymer-VIII-Pd a. Run b O l e f i n Product Y i e l d ( % ) c 1 styrene e t h y l benzene 100 2 styrene e t h y l benzene 100 3 styrene e t h y l benzene 66 4 a-methylstyrene •fsopropyl benzene 84 5 cyclohexene cyclohexane 3 6 cyclohexene cyclohexane 6 5 d 7 1-hexene iv-hexane 10 trans-2-hexene 44 cis-2-hexene 19 8 styrene e t h y l benzene 100 9 styrene ethylbenzene 100 10 styrene e t h y l benzene 100 a [ o l e f i n ] = 0.25M; o l e f i n / P d • 100/1 unless otherwise s t a t e d ; benzene (1 mL); temp, 60°C; 1 atm t o t a l pressure o f hydrogen; time, 2 h . bRun 1, o l e f i n / P d = 50/1; runs 8-10 reused c a t a l y s t from run 1 f o r the 1 s t , 2nd and 3rd times r e s p e c t i v e l y ; run 3, o l e f i n / P d = 200/1. CGLC y i e l d based on s t a r t i n g o l e f i n . dTime, 20 h . 133 Table 5.5 Hydrogenation of styrene c a t a l y z e d by polymer-VIII-Pd a. Run Solvent Y i e l d ( % ) b 1 hexane 59 2 benzene 66 3 THF 100 4 EtOH 100 5 MeOH 100 6 DMF 100 7 CHC1 3 20 8 CH 2C1 2 20 a [ o l e f i n ] = 0.25M; s o l v e n t (1 mL); o l e f i n / P d = 200/1; temp, 60°C; 1 atm t o t a l pressure o f hydrogen; time, 2 h. bGLC y i e l d based on s t a r t i n g o l e f i n . 134 Table 5.6 Hydrogenation o f o l e f i n s c a t a l y z e d by polymer-bound palladium complexes. Run Polymer O l e f i n Product Y i e l d ( % ) b 1 VHI-Pd styrene et h y l benzene 41 2 VH-Pd styrene ethyl benzene 100 3 Vl-Pd styrene ethyl benzene 99 4 VHI-Pd a-methylstyrene isopropylbenzene 17 5 VH-Pd a-methylstyrene isopropylbenzene 98 6 Vl-Pd a-methylstyrene isopropylbenzene 79 7 VHI-Pd cyclohexene cyclohexane 2 8 V l l - P d cyclohexene cyclohexane 26 9 Vl-Pd cyclohexene cyclohexane 49 a [ o l e f i n ] = 0.25M; MeOH (1 mL); o l e f i n / P d = 200/1; temp, 30°C; 1 atm t o t a l pressure o f hydrogen; time, 2 h. bGLC y i e l d based on s t a r t i n g o l e f i n . 135 Table 5.7 Hydrogenation o f 1-hexene i n MeOH . Product, Y i e l d ( % ) b Polymer hexane trans-2-hexene cis-2-hexene VHI-Pd 28 8 4 VH-Pd 46 23 11 Vl-Pd 61 31 8 See Table 5.6 f o r footnotes a and b. 136 All the catalysts are active for 1-hexene hydrogenation and isomeri-zation in MeOH, Table 5.7. Again, polymer-VIII-Pd shows the lowest rate. Under these conditions polymer-V 111-Pd affords more ji-hexane than trans-2-hexene. The reverse is true in benzene at 60°C, Table 5.4. There also appears to be less selectivity with respect to trans-2-hexene formation when polymer-VI-Pd and polymer-VII-Pd are the catalysts. After the completion of all the reactions, the supported complexes can be easily separated from the reaction mixture by filtration. There are no obvious physical changes in the catalysts especially in the color which remains unchanged. Other PdX2 complexes of supported N-donor ligands are good hydrogenation and isomerization catalysts and the oxidation state of the palladium is believed to be unchanged [141]. On the other hand PdX2 derivatives of supported unidentate phosphines seem to function as hydro-genation catalysts only after reduction to palladium(O) [142]. The cause of this reduction has been ascribed to a lower P:Pd ratio in the polymer than that required, 2:1, in the unsupported system [142]. As mentioned above the overall lower activity of polymer-VIII-Pd may be due to the bidentate nature of the supported P-N ligand in polymer-VIII. B. Supported platinum complexes The supported platinum derivatives, polymer-VI-Pt, polymer-VII-Pt, and polymer-VIII-Pt are effective catalysts for the hydrogenation of olefins, Tables 5.8 and 5.9. In the case of styrene and a-methylstyrene the relative rates of hydrogenation are comparable to those of the supported palladium(II) counterparts, Table 5.6. 137 Table 5.8 Hydrogenation of o l e f i n s c a t a l y z e d by polymer-bound platinum complexes 3. Run Polymer O l e f i n Product Y i e l d ( % ) b 1 V H I - P t 1-hexene n-hexane 100 2 V H - P t 1-hexene _n-hexane 100 3 V l - P t 1-hexene rv- hexane 100 4 V H I - P t styrene et h y l benzene 81 5 V l l - P t styrene et h y l benzene 100 6 V l - P t styrene ethyl benzene 100 7 V H I - P t o-methylstyrene isopropylbenzene 37 8 V l l - P t a-methylstyrene isopropylbenzene 85 9 V l - P t a-methylstyrene isopropylbenzene 47 10 V H I - P t cyclohexene cyclohexane 68 11 V l l - P t cyclohexene cyclohexane 100 12 V l - P t cyclohexene cyclohexane 97 a [ o l e f i n ] = 0.25M; MeOH (1 mL); o l e f i n / P t = 200/1; temp, 30°C; 1 atm t o t a l pressure of hydrogen; time, 2 h. bGLC y i e l d based on s t a r t i n g o l e f i n . 138 Table 5.9 Hydrogenation o f styrene c a t a l y z e d by polymer-bound platinum complexes. 3 Run Polymer Solvent Y i e l d ( % ) b 1 V H I - P t hexane 11 2 V H I - P t benzene 40 3 V H I - P t THF 56 4 V H I - P t MeOH 81 5 r e c y c l e - r u n 4 MeOH 78 6 r e c y c l e - r u n 5 MeOH 79 7 V l - P t hexane 15 8 V l - P t benzene 59 9 V l - P t THF 75 10 V l - P t MeOH 100 See Table 5.8 f o r footnotes a and b. 139 The results obtained in 1-hexene and cyclohexene hydrogenation, Table 5.8, are quite different from those using their palladium counterparts, Table 5.6. In the case of 1-hexene the only product isolated is _n-hexane, whereas trans-2-hexene and cis-2-hexene are also obtained using their palladium counterparts. The rate of hydrogenation of cyclo-hexene is much lower using the supported palladium(II) complexes, Table 5.6, but it is higher using supported platinum derivatives, Table 5.8. The effect of solvent on styrene hydrogenation catalyzed by polymer-Vl-Pt and polymer-VIII-Pt is summarized, in Table 5.9. The relative rate of hydrogenation increases with the solvent polarity as is found for their palladium analogues, Table 5.5. In all the reactions, polymer-VI I I-Pt is less active than the other two supported platinum complexes. The supported complexes can be easily separated from the reaction mixture by fi ltration. The color of the supported complexes changes from dark brown to greenish brown. This physical change may indicate that the oxidation state of the platinum is changed. Perhaps this is an indication of reduction to platinum metal (vide infra). 5.2.3 Hydrosilylation Studies A. Hydrosilylation of styrene catalyzed by supported palladium complexes Many group VIII metal complexes particularly those of the nickel triad homogeneously catalyze the hydrosilylation of styrene with trichlorosilane, equation 5.12. The product is either 1-phenylethyl-140 SiCI SiCI a - a d d u c t (3 -adduct (5.12) trichlorosilane (a-adduct) or 2-phenylethyltrichlorosilane (p-adduct) or a mixture of the two [46,47], Normally palladium(II) derivatives catalyze the formation of predominantly the a-adduct; the p-adduct results from reactions catalyzed by other metal derivatives such as platinum(II) and nickel(II) [46,47]. Polymer-VII-Pd and polymer-VIII-Pd are effective catalysts for the hydrosilylation of styrene with trichlorosilane, Table 5.10. As anticipated, the a-adduct is the major product at 70-90°C with some p-adduct being formed at lower temperatures. Polymer-VI-Pd is less effective as a catalyst for the same reaction, although the a:p ratio is s t i l l high. Other examples are reported [143] where palladium derivatives supported on 0-, N-, and CN-functionalized polymers show low activity as hydrosilylation catalysts. The present results seem to be in line with the report that phosphine ligands are necessary to produce homogeneous hydrosilylation catalysts from palladium(II) salts [144]. 141 Table 5.10 H y d r o s i l y l a t i o n o f styrene with H S i C l , c a t a l y z e d by polymer-bound palladium complexes . Run Polymer Adduct Temp(°C) Time(h) Y i e l d ( % ) b Adduct R a t i o c 1 VHI-Pd 40 48 51 79:21 2 VHI-Pd 70 48 99 98:2 3 VHI-Pd 90 48 100 100:0 4 VHI-Pd 70 24 90 99:1 5 VHI-Pd 90 24 100 100:0 6 VH-Pd 70 48 100 95:5 7 r e c y c l e - r u n 6 70 48 100 96:4 8 r e c y c l e - r u n 7 70 48 100 100:0 9 r e c y c l e - r u n 8 70 48 100 100:0 10 Vl-Pd 70 48 38 96:4 11 Vl-Pd 90 24 59 92:8 a 0 1 e f i n , 5nmol; s l l a n e , 6mmol; o l e f i n / P d • 1000/1. bGLC y i e l d based on s t a r t i n g o l e f i n . cThe r a t i o o f a-adduct to B-adduct. 142 Palladium metal is reported [144] to be inactive as a catalyst for olefin hydrosilylation, therefore in the present investigation, presumably reduction to the metal can be eliminated as the origin of the catalytic effect. In the case of polymer-VII-Pd, this complex can be used at least four times without loss of activity, Table 5.10, and it is interesting to note that the regioselectivity of the catalyst actually increases after the first recycling, resulting in the formation of the a-adduct exclusively. When polymer-VII-Pd and polymer-VI11-Pd are recovered after use, their color is lighter. In order to investigate this, polymer-VIII-Pd was recovered by filtration after a reaction, carefully washed with acetone and diethyl ether, and dried at 100°C under vacuum. The microanalytical data, Table 5.11, reveal no significant change in palladium content, indicating that leaching of the metal from the support is minimal. (In some cases of catalytic hydrosilylation, some loss of metal from the support has been observed [143b, 145]). The microanalytical data, Table 5.11, do show an increase in the chlorine content of the polymer and a decrease in the carbon content, indicating that there probably is a reaction between the palladium complex and trichlorosilane during the initial catalyzed reaction [144,146]. The possibility of formation of new catalytic species following air exposure during recycling should not be ignored [56], especially as optical yields are lowered progressively during recycling experiments, as will be described next. 143 Table 5.11 M i c r o a n a l y t i c a l r e s u l t s f o r polymer-VIII and i t s palladium d e r i v a t i v e s . Polymer Found (%) C H N P Pd VIII 82.58 7.00 0.33 0.0 0.88 VHI-Pd 81.74 7.00 0.29 1.20 0.57 1.36 b VHI-Pd (recovered) 77.70 6.90 0.15 2.00 0.57 1.11 a S e e a l s o Table 5.1. bSee a l s o Table 5.3. 144 B. Asymmetric hydrosilylation of styrene catalyzed by supported palladium complexes Kumada and coworkers (.51] found that the palladium(II) complex of (R,S)-PPFA is a homogeneous catalyst for the hydrosilylation of styrene with trichlorosilane (cf. Section 1.2.2). Since the same reaction is catalyzed with high regioselectivity by polymer-VI11-Pd, it was of interest to establish the effectiveness of polymer-VIII*-Pd in this regard. The o-adduct from styrene can be converted to 1-phenylethanol using the sequence shown in equation 5.13, Table 5.12. These reactions proceed (5.13) 145 Table 5.12 Asymmetric h y d r o s i l y l a t i o n o f styrene with H S i C l , a . Run Polymer Adduct Y i e l d ( % ) b Adduct R a t i o 0 O p t i c a l Y i e l d ( % ) d 1 VIII -Pd 100 100:0 15.2 (R) 2 r e c y c l e - r u n 1 100 100:0 8.5 (R) 3 r e c y c l e - r u n 2 100 100:0 8.0 (R) a 0 1 e f i n , 25mmol; s i l a n e , 30mmol; o l e f i n / P d = 1000/1; temp, 70°C; time, 48 h; see Table 5.10 f o r footnotes b and c. d 0 p t i c a l y i e l d s are c a l c u l a t e d with r e s p e c t to o p t i c a l l y pure 1-phenylethanol, [ a ] n -52.5°(C2.27, CH 2C1 2) [110]. C o n f i g u r a t i o n s are quoted i n brackets. 146 with retention and the alcohol isolated following the use of polymer-VIII -Pd as catalyst is (R)-l-phenylethanol with an optical yield of 15.2%. The optical yield is less than the 52% obtained in the homogeneous system. This result is not unusual, since lower optical yields are normally found for hydrogenation [69] and hydrosilylation [56, 68a, 127] when heterogenized versions of homogeneous catalysts are used. The absolute configuration of product, (R), is the same as would be anticipated from the results of the homogeneous reaction [51]. However, this is not always the case [127,147]. On recycling polymer-VIII*-Pd, Table 5.11, the same regioselectivity is found but the stereoselectivity decreases. This provides further evidence for catalyst modification during recycling as discussed previously. Lower optical yields were also achieved in the second hydrosilylation of ketones using a supported rhodium complex which was isolated by filtration in air, following the first hydrosilylation reaction [56]. The present results do indicate that the ligand plays an important part in the catalytic cycle and hence reduction of the complex to metal during the reaction seems unlikely. Although the asymmetric hydrosily-lation of ketones catalyzed by supported chiral complexes has been studied (cf. Section 5.1), the present study is the first example of the asymmetric hydrosilylation of olefin catalyzed by such complexes. 147 C. Hydrosilylation of 1-hexene catalyzed by supported palladium complexes Polymer-VII-Pd and polymer-VIII-Pd also catalyze the hydrosilylation of the unactivated olefin 1-hexene with trichlorosilane, equation 5.14, Table 5.13. As is usually found, 1-trichlorosilylhexane, the terminal adduct, is the only product under the same conditions as developed for the hydrosilylation of styrene, Table 5.10. Polymer-VI-Pd is inactive for the same reaction and this may due to the lack of phosphine ligand in the support as described in the hydrosilylation of styrene (vide supra). D. Hydrosilylation of olefins catalyzed by supported platinum Polymer-VI-Pt, polymer-VII-Pt and polymer-VIII-Pt are very effective catalysts for styrene hydrosilylation, Table 5.14. In this regard it is important to note that the olefin/metal ratio for the supported palladium-catalyzed reactions in Table 5.10 is 1000/1, whereas, the ratio used for the reaction in Table 5.14 is 10,000/1. The products are the p-adducts exclusively, which is a dramatic, but not unusual [47], demonstration of the effect of changing the central metal in a catalyst. + HS1CI3 (5.14) complexes and soluble (L-L)PtCl 2 complexes 148 Table 5.13 H y d r o s i l y l a t i o n o f 1-hexene with H S i C l * Run Polymer Olefin/M Product Y i e l d ( % ) b 1 VHI-Pd 1,000 15 2 VH-Pd 1,000 26 3 Vl-Pd 1,000 0 4 V H I - P t 10,000 95 5 V l l - P t 10,000 95 6 V l - P t 10,000 94 O l e f i n , 5mmol; s i l a n e , 6mmol; temp, 70°C; time, 24 h. GLC y i e l d based on s t a r t i n g o l e f i n . 149 Table 5.14 H y d r o s i l y l a t i o n o f styrene with H S i C l - c a t a l y z e d a 3 by polymer-bound platinum complexes . Run Polymer Adduct Temp(°C) Time(h) Y i e l d ( % ) b Adduct R a t i o 0 1 V H I - P t 70 24 97 0:100 2 d V H I - P t 70 24 96 0:100 3 V l l l - P t 90 24 100 0:100 4 r e c y c l e - r u n 3 90 24 95 0:100 5 V H - P t 70 24 96 0:100 6 V l - P t 70 24 99 0:100 a 0 1 e f i n , 5mmol; s i l a n e , 6mmol; o l e f i n / P t = 10,000/1; see Table 5.10 f o r footnotes b and c. ^ O l e f i n , lOmmol; s i l a n e , 5mmol. 150 The selectivity remains unchanged on recycling the catalyst, Table 5.14, and it is also unaffected by changing the olefin/si lane ratio. In some hydrosilylation reactions, the selectivity changes with changing the olefin/si lane ratio L46]. In the hydrogenation studies (cf. Section 5.2.2), the color of the three supported platinum complexes changes from dark brown to greenish brown after use. The same change is observed in the present study of olefin hydrosilylation. Perhaps this is an indication of reduction to metal in each case and could account for the similarity of their catalytic activity; Pt/C is a known hydrosilylation catalyst [148]. However, in this connection, it is claimed that supported platinum(IV) derivatives [149] afford active platinum(II) catalysts for hydrosilylation. Further reduction to platinum metal is claimed to result in lower or even zero activity [149]. All three supported platinum complexes are also very effective catalysts for the hydrosilylation of 1-hexene, Table 5.13. As is found in the supported palladium-catalyzed reactions, 1-trichlorosilylhexane is the only product obtained. Again, the supported platinum complexes are more effective than their palladium counterparts. Soluble platinum(II) complexes (L-L)PtCl 2 (L-L = BPPF, PPFA, ISOPFA and BPPFA) were also examined with regard to their ability to catalyze the hydrosilylation of olefins with trichlorosilane. The results of styrene and 1-hexene hydrosilylation are summarized in Table 5.15. As found in the hydrosilylation of ketones (cf. Section 4.2.2), the P-N bound complexes (L-L = PPFA and ISOPFA) are effective for the hydrosilylation of olefins 151 Table 5.15 H y d r o s i l y l a t i o n o f o l e f i n s with H S i C l 3 c a t a l y z e d by s o l u b l e platinum complexes ( L - L ) P t C l 9 a . Run O l e f i n (L-L) Product Y i e l d ( % ) b 1 styrene BPPF no product 0 2 styrene BPPFA no product 0 3 styrene PPFA 2-phenyl e t h y l -t r i c h l o r o s i l a n e 100 4 styrene ISOPFA 2-phenylethyl -t r i c h l o r o s i l a n e 100 5 1-hexene BPPF no product 0 6 1-hexene BPPFA no product 0 7 1-hexene PPFA 1 - t r i c h l o r o -s i l y l h e x a n e 100 8 1-hexene ISOPFA 1 - t r i c h l o r o -s i l y l h e x a n e 100 a 0 1 e f i n , 25mmol; s i l a n e , 30nmol; o l e f i n / P t = 10,000/1; CH 2C1 2 (3 mL); temp, 70°C; time, 24 h. bGLC y i e l d based on s t a r t i n g o l e f i n . 152 Table 5.16 H y d r o s i l y l a t i o n o f ketones with P h ? S i H ? c a t a l y z e d * a by polymer-VIII -Pt . Ketone Time(d) Product Chem. Y i e l d ( % ) b O p t i c a l Y i e l d ( % ) c Acetophenone 3 phenylethanol 10 1.7 (S) Acetophenone 2 d phenylethanol 95 0 Butyrophenone 6 phenylpropanol 6 e Isobutyrophenone 6 no product 0 --aKetone, lOmmol; s i l a n e , 20mmol; ketone/Pt = 1000/1; temp, 20°C. bGLC y i e l d based on s t a r t i n g ketone. c 0 p t i c a l y i e l d s are c a l c u l a t e d with respect to o p t i c a l l y pure 1-phenylethanol ( c f . Table 5.12). dTemp, 70°C. Not enough sample f o r o p t i c a l r o t a t i o n measurement. 153 while the P-P bound complexes (L-L = BPPF and BPPFA) are not. These results show that the ligands must play an important part in the catalytic cycle to achieve the activity. In contrast to the soluble system, the three supported platinum complexes, regardless of ligands, give uniform reactivity on the hydrosily-lation of olefins, Tables 5.13 and 5.14, which again suggests that platinum metal may be involved. E. Hydrosilylation of ketones catalyzed by supported platinum complexes Since soluble platinum(II) complexes (L-L = (S,R)-PPFA and (S,R)-ISOPFA) are effective catalyst precursors for the hydrosilylation of ketones (cf. Section 4.2.2), it was of interest to examine the activity of * polymer-VIII -Pt in this regard. In the present investigation, it was * found that polymer-VIII -Pt is not very effective for the hydrosilylation of ketones with diphenylsilane under the conditions used, Table 5.16. In the case of acetophenone only a 10% yield of 1-phenylethanol obtained at 20°C after 3 days; the optical yield, 1.7%, is lower than that achieved using soluble ((S,R)-PPFA)PtCl2 (cf. Section 4.2.2). The absolute configuration of the product, (S), is the same as that results from the use of soluble ((S,R)-PPFA)PtCl2 (cf. Table 4.4). When the reaction tempera-ture is raised to 70°C the chemical yield is increased but the optical yield is decreased; a similar effect is noted for the soluble case. The supported complex can also be easily separated from the reaction mixture. The color of the complex is changed as in the hydrosilylation of olefins (vide supra). 154 5.3 SUMMARY In summary, ferrocene and its derivatives can be easily supported on polystyrene polymers. The Mossbauer spectra confirm the loading of ferrocene derivatives; in some cases, solid state 1 3 C NMR spectra also show the loading but the resolution is poor. The palladium and platinum derivatives of the ferrocenyl-amine and -phosphine containing polymers are effective hydrogenation catalysts for styrene, a-methyl styrene, cyclohexene and 1-hexene. Double bond migration also occurs in the palladium-catalyzed hydrogenation of 1-hexene. The supported palladium and platinum complexes are also effective catalysts for the hydrosilylation of olefins with trichlorosilane. All catalysts can be easily separated from the reaction mixture by simple filtration and can be reused without loss of activity. In the case of platinum based polymers it is likely that reduction to platinum metal takes place. The pronounced effect of the attached ligand in the palladium based catalysts indicates that free metal is not involved in these cases. 155 CHAPTER 6 GENERAL CONCLUSIONS AND PERSPECTIVES 6.1 SOLUBLE PALLADIUM(II) AND PLATINUM(II) COMPLEXES OF FERROCENYL-PHOSPHINES The preparation, characterization, and catalytic properties of soluble palladiumUI) and platinumdl) complexes of ferrocenylphosphines have been described. Special emphasis has been placed on the studies of the mixed "hard-soft" ligands such as PPFA, ISOPFA and BPPFA. Both the P and N atoms 1n PPFA and ISOPFA ligands are bound to the metals in these complexes, whereas the P-P binding mode is found when the ligand is BPPFA. Although the nature of the binding mode in rhodium(I) complexes of these ligands has been examined [6,43], it would be desirable to investigate this in other transition metals such as iridium, ruthenium and osmium. In the present study the P-N bound palladiumdl) and platinumdl) complexes are more effective catalyst precursors than the P-P bound counterparts for the hydrogenation and hydrosilylation reactions. Soluble palladiumUI) and platinumdl) complexes of chiral phosphine ligands have been reported to be effective catalyst precursors for asymmetric hydro-esterification [150] and asymmetric hydroformylation [151] of olefins, respectively. Thus it would be worth investigating these reactions using the pal ladiumdl) and platinumdl) complexes of the chiral ferrocenyl-phosphine ligands, particularly those with mixed "hard-soft" ligand systems. 156 6.2 POLYMER-BOUND PALLADIUMUI) AND PLATINUM(II) COMPLEXES OF FERROCENE DERIVATIVES Polymers functional!zed with ferrocene and ferrocene derivatives such as FA, BPPF, PPFA and (S.R)-PPFA have been prepared. The palladium(II) and platinum(II) complexes of some of these polymers have also been prepared. These results are supported by microanalytical and Mossbauer data, and, to some extent, solid state 1 3 C NMR data. The exact nature of the binding mode in these polymer-bound complexes is not known and this remains an area to be further investigated. In this connection, the cross-polarization/magic angle spinning (CP/MAS) 3 1 P NMR spectroscopic technique could be useful. The polymer-bound palladium(II) and platinum(II) complexes are effective, reusable catalysts for the hydrogenation and hydrosilylation of olefins. In the case of the platinum based polymers, it is likely that reduction to platinum metal takes place. No free metal seems to be involved in the catalytic reactions of the palladium counterparts. However, this is an area worth investigating using electron spectroscopy for chemical analysis (ESCA) or X-ray photoelectron spectroscopic (XPS) techniques. While the synthesis and catalytic properties of palladium(II) and platinum(II) complexes of polymer-bound ferrocene derivatives have been examined, other metal complexes s t i l l remain to be studied. In particular, the rhodium(I) complexes deserve future investigation since the soluble rhodium(I) complexes of chiral ferrocenylphosphines are active catalyst 157 precursors for the asymmetric hydrogenation and hydrosilylation of olefins and ketones (cf. Sections 1.2.1 and 1.2.2). 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Trotter, "Platinum(II) Complexes of Ferrocenylphosphines as Hydrosilylation Catalysts. The Structure of (P-N)PtCl2 > (P-N) = Fe(C5H5)(C5H3(P(CHMe2)CHMeNMe2-l,2)", Inorg. Chem., in press. 3. W.R. Cullen and N.F. Han, "Polymer Supported Ferrocene Derivatives. Catalytic Hydrosilylation of Olefins by Supported Palladium and Platinum Complexes", J . Organometal. Chem., submitted. 4. W.R. Cullen and N.F. Han, "Synthesis and Catalytic Properties of Palladium and Platinum Complexes of Polymer Supported Ferrocenylphosphines", 69th. Canadian Chemical Conference, Saskatoon, Saskatchewan, IN-D3-5, 1986. 5. I.R. Butler, W.R. Cullen, N.F. Han, and J . J . Ni, "The Design, Synthesis and Use of Ferrocenylphosphines in Metal Catalyzed Reaction", 68th. Canadian Chemical Conference, Kingston, Ontario, IN-F1-03, 1985. 6. I.R. Butler, W.R. Cullen, N.F. Han, and T .J . Kim, "Metal Hydrides from Cationic Rhodium(I) Species", International Chemical Congress of Pasific Basin Societies, Honolulu, Hawaii, 07L05, 1984. 7. T.G. Appleton, I.R. Butler, W.R. Cullen, N.F. Han, and T . J . Kim, "NMR Spectra of Ferrocenylphosphines and Their Complexes with Platinum Metals", Royal Australian Chemical Institution Conference, Hobart, Tasmania, 1984. 8. W.R. Cullen, N.F. Han, and T . J . Kim, "Cationic Rhodium(I) and Palladium(II) Complexes as Catalyst Precursors for Olefins Hydrogenation", Canadian American Chemical Congress, Montreal, Quebec, INI-02, 1984. 

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