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A study of ruthenium complexes containing chelating ditertiary phosphines Thorburn, Ian Stuart 1985

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A STUDY OF RUTHENIUM COMPLEXES CONTAINING CHELATING DITERTIARY PHOSPHINES BY IAN STUART THORBURN M.Sc, U n i v e r s i t y of B r i t i s h Columbia, 1980 B . S c , U n i v e r s i t y of L e i c e s t e r , 1977 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES Department of Chemistry We accept t h i s t h e s i s as conforming to the required standard The U n i v e r s i t y of B r i t i s h Columbia January, 1985 © Ian Stuart Thorburn, 1985 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of QA.£(A\STR-^  The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6 (3/81) - i i -ABSTRACT Mixed-valence complexes of ruthenium of general formula Ru2Cl^(P-P)2> P-P = chiraphos, norphos, dppp, dppb or diop, have been prepared by reaction of RuCl^P2(DMA).DMA, P = PPh^ or P(p- t o l y l ) ^ , w i t h one equivalent of the appropriate d i t e r t i a r y phosphine. The s o l i d state structure of the chiraphos de r i v a t i v e i s shown to be a symmetrical t r i p l y chloro-bridged dimer by X-ray analysis. The extent of electron d e l o c a l i s a t i o n i n these mixed-valence complexes has been studied by means of t h e i r intervalence tran s f e r bands i n the near-infrared region. A low energy absorption i s assigned to the dinuclear complex? however, a d d i t i o n a l absorptions at higher energy indicate more than one species i s present i n s o l u t i o n . Investigations of the reaction of Ru^Cl^(chiraphos^ with i n DMA show t h i s to be an a u t o c a t a l y t i c reaction, but attempts to elucidate mechanistic d e t a i l s have been unsuccessful. The product generated i n s i t u by reaction with i s the i o n i c species, [ R u ^ C l ^ c h i r a p h o s ^ ] DMAH+. The neutral complexes [ H U C I 2 ( P - P ) ] 2 , P-P = chiraphos, dppp, dppb, or diop, are i s o l a t e d v i a such an i o n i c complex, or a l t e r n a t i v e l y by reaction i n toluene i n the presence of added base. N.m.r. studies show the neutral complexes to have structure I, but the complexes r e a d i l y adopt a t r i p l y chloro-bridged structure (II) i n the presence of coordinating solvents (S). p Cl I II The complexes [RuClgCP-P) » P-P = chiraphos or diop, catalyse the asymmetric hydrogenation of p r o c h i r a l alkenes. The nature of the phosphine and substrate are found to be s i g n i f i c a n t i n terms of the hydrogenation rate, % e.e., and product configuration. Hydrogenation of (Z)-a-acetamidocinnamic acid with 97$ e.e. has been achieved using the chiraphos d e r i v a t i v e . An unusual increase i n % e.e. of the hydrogenated substrate with decreasing temperature i s observed. The reaction of Ru2Cl^(dppb)2(acetone).acetone, 1, with has been investigated. In DMA, i n the presence of added base, a hydrido-complex i s generated, but has not been i s o l a t e d pure. The reaction of _1 with H 2 i n CH^^/CH^OH produces the dinuclear complex, Ru ?Hp(CO)Cl 5(dppb)„ ( i l l ) . This product i s also III - i v -formed i n the absence of H 2, and i s thought to a r i s e v i a base promoted decarbonylation of methanol. Addition of norbornadiene (nbd) to 1_ produces RuCl 2(nbd) (dppb), 1 31 which has been characterised by H- and P-n.m.r., and elemental and X-ray an a l y s i s . The reaction of t h i s complex with H 2 i s complicated by i n i t i a l d i s s o c i a t i o n of the norbornadiene li g a n d . However, one of the minor products i s thought to be RuHCl(nbd)(dppb), a stable hydrido-alkene complex, even i n the presence of H^. Cationic complexes of ruthenium(ll) have been prepared from _1 and Ru^Cl^. (dppb) 2 by halide abstraction using AgPFg . These are the dinuclear complexes [ R u 2 C l j ( d p p b ) 2 ( S ) n ] + P F g , n = 2, S = a c e t o n i t r i l e and n = 1, S = acetone; and the mononuclear complexes [RuCl(dppb)(ClL^N) ] +PFg~ and [RuCl(dppb) (ri 6-toluene) ] +PF 6~ . The reaction of [RuCl(dppb)(CH 5CN) 5] +PF 6~ with H 2 , r e s u l t s i n reduction of the a c e t o n i t r i l e ligands to triethylamine. The c a t a l y t i c properties of t h i s complex have also been investigated f o r the hydrogenation of n i t r i l e and imine substrates. - V -TABLE OP CONTENTS Page Abstract i i Table of contents v L i s t of tables x L i s t of figures x i Abbreviations and symbols xv Acknowledgements x v i i i Chapter I Introduction 1 1.1 General introduction 1 1.2 Asymmetric hydrogenation of p r o c h i r a l alkenes. . . 2 1.3 General overview of hydrogen a c t i v a t i o n and the homogeneous hydrogenation of alkenes 10 1.4 Scope of th i s thesis 17 Chapter II Experimental 19 2.1 Materials 19 2.1.1 Solvents 19 2.1.2 Gases 19 2.1.3 Phosphines 20 2.1.4 Alkene substrates 20 2.1.5 Other materials 21 2.1.6 DMA S a l t s . 21 2.1.6.1 N,N-Dimethylacetamidehydrochloride 21 2.1.6.2 N ,N-Dimethylacetamidehydrobromide 22 2.1.7 Ruthenium Compounds 22 2.1.7.1 Trichlorobis(triphenylphosphine)(DMA)ruthenium (III).DMA solvate 23 2.1.7.2 Trichlorobis(tri-p-tolylphosphine)(DMA)ruthenium (III).DMA solvate 23 - v i -2.1.7.3 T r i - y - c h l o r o - d i c h l o r o b i s ( b i d e n t a t e p h o s p h i n e ) d i r u t h e n i u m ( l l , I I I ) , P-P = dppb o r d i o p 23 2.1.7.4 T r i - u - c h l o r o - d i c h l o r o b i s ( b i d e n t a t e p h o s p h i n e ) d i r u t h e n i u m ( l l , 1 1 1 ) , P-P = c h i r a p h o s , n o r p h o s , dppp 24 2.1.7.5 D i c h l o r o b i s ( b i d e n t a t e p h o s p h i n e ) r u t h e n i u m ( I I ) d i m e r s , P-P = dppb, dppp 25 2.1.7.6 D i c h l o r o b i s ( b i d e n t a t e p h o s p h i n e ) r u t h e n i u m ( I I ) d i m e r s , P-P = d i o p , c h i r a p h o s 26 2.1.7.7 T r i - u - c h l o r o b i s [ c h l o r o ( 1 , 4 - d i p h e n y l p h o s p h i n o -b u t a n e ) r u t h e n i u m ( l l ) ] PSH + 27 2.1.7.8 M - y - c h l o r o - y - h y d r i d o - h y d r i d o ( c a r b o n y l ) b i s -( l , 4 - d i p h e n y l p h o s p h i n o b u t a n e ) d i r u t h e n i u m ( l l ) . . . 27 2.1.7.9 D i c h l o r o ( n o r b o r n a d i e n e ) ( 1 , 4 - d i p h e n y l p h o s p h i n o -b utane) r u t h e n i u m ( l l ) 28 2.1.7.10 T r i c h l o r o ( 1 , 4 - d i p h e n y l p h o s p h i n o b u t a n e ) r u t h e n i u m ( I I ) d i m e r 29 2.1.7.11 T r i - u - c h l o r o b i s [ a c e t o n i t r i l e ( 1 , 4 - d i p h e n y l -p h o s p h i n o b u t a n e ) r u t h e n i u m ( l l ) ] h e x a f l u o r o -phosphate 29 2.1.7.12 T r i s ( a c e t o n i t r i l e ) c h l o r o ( l , 4 - d i p h e n y l p h o s p h i n o -butane ) ruthe n i u m ( 11 ) h e x a f l u o r o p h o s p h a t e 30 2.1.7.13 ( A c e t o n e ) t r i - y - c h l o r o b i s [ ( l , 4 - d i p h e n y l -p h o s p h i n o b u t a n e ) r u t h e n i u m ( l l ) ] h e x a f l u o r o p h o s p h a t e 30 2.1.7.14 C h l o r o ( r / * - t o l u e n e ) ( 1 , 4 - d i p h e n y l p h o s p h i n o -b u t a n e ) r u t h e n i u m ( l l ) h e x a f l u o r o p h o s p h a t e 31 2.1.7.15 R e a c t i o n between [ R u C l ( d p p b ) ( C H 3 C N ) 5 ] + PFg" and H 2 32 2.2 I n s t r u m e n t a t i o n 33 2.3 I s o l a t i o n o f h y d r o g e n a t e d a l k e n e p r o d u c t s 34 2.4 O p t i c a l r o t a t i o n measurements 35 - v i i -Chapter III A study of chloro-bridged diruthenium(II,IIl) complexes containing chelating c h i r a l and nonchiral d i t e r t i a r y phosphine ligands 37 3.1 General introduction 37 3.2 Preparation of t r i - y - c h l o r o - d i c h l o r o b i s -(bidentate phosphine)diruthenium(H,IIl) complexes 38 3.3 X-Ray structure determination R u 2 C l ^ ( c h i r a p h o s ) 2 . 42 3.4 Magnetic s u s c e p t i b i l i t y measurements 46 3.5 El e c t r o n i c s p e c t r a l data 46 3.5.1 Near-infrared spectra 46 3.5.2 V i s i b l e spectra 51 3.5.3 Discussion of e l e c t r o n i c s p e c t r a l data 55 3.6 Disproportionation of Ru 2Cl,-(P-P) 2 63 3.7 A c t i v a t i o n of molecular hydrogen by the R u 2 C l 5 ( P - P ) 2 complexes 68 3.7.1 Stoichiometry of the reaction i n DMA 68 3.7.2 Spectral studies 70 3.7.3 Conductivity measurements 75 3.7.3.1 Conductivity measurements on DMA.HC1 and DMA.HBr . 76 3.7.3.2 Analysis of conductivity measurements on H 2~ reduced solutions of Ru 2 C l ^ ( c h i r a p h o s ) 2 i n DMA 79 3.7.4 Reaction of Ru 2Cl^(P-P) 2 complexes with H 2 i n toluene 82 Chapter IV Synthesis and ch a r a c t e r i s a t i o n of dimeric ruthenium(ll) complexes and t h e i r a p p l i c a t i o n as asymmetric hydrogenation c a t a l y s t s 85 4.1 Introduction 85 4.2 Synthesis of [ R u C l 2 ( P - P ) ] 2 complexes 87 4.3 3 1P{ 1H}-N.m.r. studies 91 4.3.1 Studies i n non-coordinating solvents 91 4.3.2 Studies i n coordinating solvents 98 4.4 Asymmetric hydrogenation of p r o c h i r a l alkenes. . . I l l - v i i i -4.4.1 D i s c u s s i o n 117 C h a p t e r V G e n e r a t i o n o f r u t h e n i u m h y d r i d e complexes 122 5.1 I n t r o d u c t i o n 122 5.2 R e a c t i o n o f RugCl^Cdppb^Cacetone) .acetone w i t h H 2 i n DMA 123 5 . 3 F o r m a t i o n o f d i - y - c h l o r o - y - h y d r i d o - h y d r i d o -( c a r b o n y l ) b i s ( d p p b ) d i r u t h e n i u m ( l l ) 126 5.3.1 P r e p a r a t i o n 126 5.3.2 C h a r a c t e r i s a t i o n 128 5.3.3 D i s c u s s i o n 129 5.4 P r e p a r a t i o n o f d i c h l o r o n o r b o r n a d i e n e ( d p p b ) -r u t h e n i u m ( l l ) . 0 . 5 C ^ H g , and i t s r e a c t i v i t y w i t h E^. 140 5.4.1 P r e p a r a t i o n and c h a r a c t e r i s a t i o n 140 5.4.2 R e a c t i o n w i t h H 2 145 C h a p t e r V I C a t i o n i c complexes o f r u t h e n i u m ( I I ) 150 6.1 I n t r o d u c t i o n 150 6.2 R e s u l t s 151 6.2.1 F o r m a t i o n o f d i n u c l e a r c a t i o n i c complexes 151 6.2.1.1 T r i - u - c h l o r o b i s [ a c e t o n i t r i l e ( 1 , 4 - d i p h e n y l p h o s p h i n o -b utane) r u t h e n i u m ( I I ) ] h e x a f l u o r o p h o s p h a t e 151 6.2.1.2 ( A c e t o n e ) t r i - y - c h l o r o b i s [ l , 4 - d i p h e n y l p h o s p h i n o -b u t a n e ) r u t h e n i u m ( l l ) ] h e x a f l u o r o p h o s p h a t e 155 6.2.2 F o r m a t i o n o f mononuclear c a t i o n i c complexes. . . . 157 6.2.2.1 T r i s a c e t o n i t r i l e c h l o r o ( 1 , 4 - d i p h e n y l p h o s p h i n o -b u t a n e ) r u t h e n i u m ( I I ) h e x a f l u o r o p h o s p h a t e 157 6.2.2.2 C h l o r o ( n . 6 - t o l u e n e ) ( 1 , 4 - d i p h e n y l p h o s p h i n o b u t a n e ) -r u t h e n i u m ( l l ) h e x a f l u o r o p h o s p h a t e 160 6.3 D i s c u s s i o n 162 6.4 R e a c t i o n o f c a t i o n i c complexes w i t h hydrogen . . . 170 6.4.1 D i s c u s s i o n 176 - ix -Chapter VII General conclusions and recommendations f o r future work 180 References 188 - X -L i s t of Tables Page 3.1 Selected bond lengths and bond angles f o r Ru^Cl^Cchiraphos)^ 44 3.2 Near-infrared s p e c t r a l data f o r R u ^ C l ^ c h i r a p h o s ) 2 49 3.3 Near-infrared spectral data f o r the Ri^Clp.(P-P) 2 complexes P-P = dppb, diop, dppp or norphos 52 3.4 Equivalent conductivity of Ru 2Cl(-( chiraphos ) 2 i n DMA 77 3.5 D i l u t i o n c o n d u c t i v i t i e s of DMA.HC1 and DMA.HBr i n DMA 78 3.6 Equivalent conductivity of [RuCl 2(dppb) 2]~PSH + i n DMA 83 4.1 3 1P{ 1H}-N.m.r. data f o r [RuCl 2(P-P) J 2 complexes 92 4.2 •51P{1H}-N.m.r. data f o r [RuCl 2(chiraphos) ] 2 i n CD„Cl 0-acetone and toluene-d Q-DMA 104 4.3 5 1P{ 1H}-N.m.r. data f o r L R u C l 2 ( d p p b ) J 2 i n CD 2Cl 2-acetone. . . 106 4.4 Asymmetric hydrogenation of unsaturated substrates using [RuCl 2((R,R)-diop ) J 2 114 4.5 Asymmetric hydrogenation of unsaturated substrates using [R u C l 2 ( ( S , S ) - c h i r a p h o s ) ] 2 115 4.6 Hydrogenation of p r o c h i r a l alkenes by ruthenium-diop complexes 118 5.1 Selected bond lengths and bond angles f o r RuCl 2(nbd)(dppb) . . 144 31 1 6.1 P{ H}-N.m.r. data f o r c a t i o n i c ruthenium complexes 164 6.2 Conductivity data f o r c a t i o n i c ruthenium complexes 164 6.3 Base parameters f o r acetone and a c e t o n i t r i l e 165 6.4 Hydrogenation of alkenes by neutral and c a t i o n i c complexes . . 171 - x i -L i s t of Figures Page 1.1 Selected c h i r a l phosphines f o r asymmetric c a t a l y s i s 5 1.2 Proposed scheme f o r the c a t a l y t i c asymmetric hydrogenation of p r o c h i r a l alkenes by rhodium c a t a l y s t s 8 2.1 Schematic representation of an anaerobic s p e c t r a l c e l l . . . . 34 3.1 An ORTEP diagram of the Ru 2 C l ^ ( c h i r a p h o s ) 2 molecule 43 3.2 Near-infrared spectra of Ru 2Cl,_(chiraphos) 2 i n CDCl^ and CC1 4 47 3.3 Near-infrared spectra of Ru 2Cl^(P-P) 2, P-P=norphos, dppp and dppb, i n CDCl^ 50 3.4 V i s i b l e spectra of Ru 2Cl^(P-P) 2, P-P=norphos, dppp and dppb, i n CDCl^ 53 3.5 V i s i b l e spectra of R u 2 C l 5 ( c h i r a p h o s ) 2 i n CDCl^ and CCl^. . . . 54 3.6 V i s i b l e spectra of Ru 2Cl,-(chiraphos) 2 i n CD^NC^ and CD^CN a f t e r complete loss of absorption i n the near-infrared region. 54 2 3.7 Plot of v vs. (1/n - l/D ) f o r the high energy niflx s near-infrared band of Ru 2 C l ^ ( c h i r a p h o s ) 2 60 3.8 Changes i n v i s i b l e spectrum with time f o r a DMSO sol u t i o n of Ru 2 C l ^ ( c h i r a p h o s ) 2 64 3.9 V i s i b l e spectra of [RuCl 3(dppb)] 2, [ R u 2 C l 3 ( d p p b ) 2 ( C H 5 C N ) 2 ] + PF g and R u 2 C l 5 ( d p p b ) 2 i n CH^CN 66 3.10 V i s i b l e spectra of [RuCl^dppb) ] 2 > [RuCl 2(dppb) ] 2 and R u 2 C l 5 ( d p p b ) 2 i n DMSO 67 - x i i -3.11 Uptake plots for the reaction between Ru 2Cl^(chiraphos)^ and H 2 i n DMA at 25°C 69 3.12 Changes i n absorbance f o r the reaction of Ru 2 C l ^ ( c h i r a p h o s ) 2 and H 2 i n DMA at 25°C 71 3.13 Spectral changes at 530 nm with time f o r the reaction of R u 2 C l 5 ( c h i r a p h o s ) 2 and i n DMA at 25°C 73 3.14 Plot of rate of change of absorbance with time against concentration of Ru„Cl c (chiraphos) 0 73 <L 5 ^ 3.15 Onsager plot f o r H 2~reduced Ru 2 C l ^ ( c h i r a p h o s ) 2 i n DMA 77 3.16 Onsager plots for DMA.HC1 and DMA.HBr i n DMA 78 2 2 2 3.17 Plot of SA against Cf S A i n accordance with equation 3.12. . 80 3.18 Onsager plot f o r [Ru 2Cl 5(dppb) 2]~PSH + i n DMA at 25°C . . . . . 83 4.1 V i s i b l e spectra of [ R u C l 2 ( c h i r a p h o s ) ] 2 i n toluene,acetone and DMA 90 4.2 V i s i b l e spectrum obtained upon addition of one equivalent of dppb to [RuCl 2(dppb)] 2 i n DMA 90 4.3 P{ H;-N.m.r. spectra of [ R u C l 2 ( c h i r a p h o s ) J 2 i n CD 2C1 2 at 30°C and -50°C 93 4.4 P{ H}-N.m.r. spectra of [ R u C l 2 ( c h i r a p h o s ) ] 2 as a function of temperature i n toluene-dg 94 31 1 4.5 P{ H}-N.m.r. spectra of [ R u C l 2 ( c h i r a p h o s ) ] 2 as a function of temperature i n CD 2Cl 2~acetone 99 31 1 4.6 P{ H}-N.m.r. spectra of [ R u C l 2 ( c h i r a p h o s ) ] 2 as a function of temperature i n toluene-dg-DMA 102 31 1 4.7 P{ H}-N.m.r. spectra of Ru 2Cl^(dppb) 2(acetone).acetone as a function of temperature i n CD„Cl ?-acetone 105 - x i i i -4.8 P r o c h i r a l alkenes used i n hydrogenation studies and t h e i r reduced form 112 5.1 5 1Pt 1H}-N.m.r. spectrum (CD 2C1 2, -95°C) of the f i n a l product obtained from the reaction of Ru 2Cl 4(dppb) 2(acetone) acetone with H 2 125 5.2 H i g h - f i e l d region of the ^ "H-n.m.r. spectrum of Ru 2H 2(C0)Cl 2(dppb) 2 i n CD 2C1 2 129 31 1 5.3 P{ H}-N.m.r. spectrum of Ru 2H 2(C0)Cl 2(dppb) 2 i n CD 2C1 2 . . . 130 5.4 Simulated 5 1P{ 1H}-n.m.r. spectrum of R u ^ ( C 0 ) C 1 2 ( d p p b ) 2 . . . 130 5.5 '51P{1H}-N.m.r. spectrum of [ R u 2 H 2 C l ( P ( p - t o l y l ) 2 ] 2 i n CD 2C1 2 at -95°C 134 31 1 5.6 Simulated P{ H}-n.m.r. spectrum of the tetranuclear species R u 4 H 4 ( P P h 3 ) 6 ( P P h 2 ) 2 ( 0 H ) 2 ( C 0 ) 2 ( a c e t o n e ) 2 136 5.7 An ORTEP diagram of the RuCl 2(nbd)(dppb) molecule 143 6.1 V i s i b l e spectra of [ R u ^ l ^ d p p b ^ C H ^ C N ^ ^ P F g -i n CH 0C1„ and CH^CN 153 ^ d 3 6.2 Onsager plots f o r [Ru 2Cl 5(dppb) 2(CH 5CN) 2] +PF 6~ i n CH 2C1 2 and CH^CN 154 6.3 ^P^HJ-N.m.r. spectrum of [ R u ^ l ^ d p p b ^ a c e t o n e ) ] + P F 6 ~ i n CD 2Cl 2-acetone at -70"C 157 6.4 Onsager plot f o r [RuCl(dppb) (CH 3CN) 3] +PF 6~ i n CH CN 159 6.5 Low-field region of the ^ "H-n.m.r. spectrum of ft + — [RuCl(dppb)(n -toluene)] PF g i n CD 2C1 2 161 6.6 Uptake plot f o r the reaction of [RuCl(dppb)(CH ; 5CN) 5] PF g with H 2 i n DMA at 50°C 173 - x i v -6.7 P{ H}-N.m.r. spectrum of f i n a l yellow compound obtained from r e a c t i o n of [RuCl(dppb)(CH 5CN) 3] +PF 6~ with H 2 175 6.8 H 2-Uptake p l o t f o r [RuCl(dppb)(CH 5CN) 3] +PF 6~ with a d d i t i o n of CHjCN 176 6.9 Uptake p l o t f o r imine r e d u c t i o n 177 - X V -ABBREVIATIONS AND SYMBOLS The f o l l o w i n g l i s t o f a b b r e v i a t i o n s and symbols w i l l be employed i n t h i s t h e s i s . A b b r e v i a t i o n s f o r phosphine l i g a n d s not f r e q u e n t l y used a r e p r e s e n t e d a t the end o f t h i s s e c t i o n . A a n g s t r o m ( s ) A absorbance atm atmosphere; 1 atm. = 760 mm Hg C e q u i v a l e n t c o n c e n t r a t i o n eq u c h i r a p h o s ( 2 S , 3 S ) - b i s ( d i p h e n y l p h o s p h i n o ) b u t a n e cod 1 , 5 - c y c l o o c t a d i e n e d d a y ( s ) ; d o u b l e t d i o p (2R.3R) o r (2S , 3 S ) - 0 - i s o p r o p y l i d e n e - 2 , 3 -d i h y d r o x y - l , 4 - b i s ( d i p h e n y l p h o s p h i n o ) b u t a n e DMA N , N - d i m e t h y l a c e t a m i d e , CH^CO.N(CH 5) 2 DMA.HC1 N , N - d i m e t h y l a c e t a m i d e h y d r o c h l o r i d e DMA.HBr N , N - d i m e t h y l a c e t a m i d e h y d r o b r o m i d e DMSO d i m e t h y l s u l p h o x i d e dppb 1 , 4 - b i s ( d i p h e n y l p h o s p h i n o ) b u t a n e dppe 1 , 2 - b i s ( d i p h e n y l p h o s p h i n o ) e t h a n e dppp 1 , 3 - b i s ( d i p h e n y l p h o s p h i n o ) p r o p a n e D s t a t i c d i e l e c t r i c c o n s t a n t s e.e. e n a n t i o m e r i c e x c e s s g gram(s) h h o u r ( s ) Hz h e r t z , c y c l e s p e r second i . r . i n f r a r e d - x v i -J coupling constant, i n Hz k rate constant K equilibrium constant log logarithm m medium M molar, moles per l i t e r mL m i l l i l i t e r m.p. melting point n o p t i c a l d i e l e c t r i c constant nbd norbornadiene nm nanometers n.m.r. nuclear magnetic resonance norphos (R,R)-(-)-2-exo-3-endobis(diphenylphosphino)-bicyclo [2.2.ljheptene Ph phenyl P-P chelating d i t e r t i a r y phosphine PPh^ triphenylphosphine ppm parts per m i l l i o n PS Proton Sponge, l,8-bis(dimethylamino)-naphthalene PS.HC1 Proton Sponge hydrochloride P ( p - t o l y l ) ^ t r i ( p - t o l y l ) p h o s p h i n e s second(s); s i n g l e t ; strong 5 solvent t time; t r i p l e t TMS tetramethylsilane v:v volume by volume w weak X anionic ligand 6 chemical s h i f t i n ppm downfield from standard A difference Av-, /p bandwidth at h a l f i n t e n s i t y -1 -1 e molar e x t i n c t i o n c o e f f i c i e n t , M cm X wavelength, nm - x v i i -max Xo A e Ao V V V max [ ] {XH} Phosphines Bppfa CAMP DiCAMP DiPAMP diphos MPPP NMDPP PAMP PCy 5 Prophos wavelength of maximum absorbance, nm l i m i t i n g i o n i c conductance - 1 2 equivalent molar conductivity, ohm cm mole equivalent conductance at i n f i n i t e d i l u t i o n , ohm cm mole magnetic s u s c e p t i b i l i t y , BM frequency, cm frequency of maximum absorbance, cm ^  concentration broadband proton decoupled bisphenylphosphineferrocenylamine £-anisylmethylphenylphosphine 1 , 2 - b i s (_o-anisylcyclohexylphosphino) ethane 1 ,2-bis(_o-anisylphenylphosphino) ethane 1 , 2-bis(diphenylphosphino)ethane (dppe) methylphenylpropylphosphine neomenthyldiphenylphosphine _o-anisylmethylphenylphosphine tricylcohexylphosphine 1 , 2-bis(diphenylphosphino)propane - X V l l l ACKNOWLEDGEMENTS I wish to express my sincerest appreciation and thanks to Professor B. R. James f o r his guidance and support throughout the course of t h i s work. Many thanks must also go the members of the group (past and present) who shared i n both exasperation and i n s p i r a t i o n , not merely colleagues but as f r i e n d s . I wish to thank Drs. S. J. Ret t i g and M. Ponnuswamy and Mr. S. Evans f o r c r y s t a l structure determinations, both successful and unsuccessful. The s k i l l f u l t e c h n i cal assistance of the microanalyse glass-blowing, n.m.r., e l e c t r i c a l and mechanical services are g r a t e f u l l y acknowledged. I am indebted to John Haynes f o r h i s dili g e n c e i n proof-reading th i s manuscript. F i n a l l y , I would l i k e to dedicate t h i s thesis to Kate and Paul, f o r t h e i r support, and f o r t o l e r a t i n g neglect and i r a s c i b i l i t y . - 1 -CHAPTER I  INTRODUCTION 1.1 General Introduction The a b i l i t y of t r a n s i t i o n metal complexes to catalyse processes such as hydrogenation, hydroformylation, h y d r o s i l y l a t i o n , hydrocyanation, epoxidation, and C-C bond formation i s well established"'". The use of homogeneous ca t a l y s t s f o r such reactions i s of i n t e r e s t since compared to the i n d u s t r i a l l y prevalent heterogeneous systems they generally provide higher a c t i v i t y and s p e c i f i c i t y , and mechanistic d e t a i l s are 2 generally attainable . Perhaps the most important feature of homogeneous systems i s that the properties of the c a t a l y s t may be changed by simply varying the ligands and reaction conditions to obtain optimum r e s u l t s . Such c a t a l y s t s also allow, by incorporation of a u x i l i a r y c h i r a l i t y , the p o s s i b i l i t y of asymmetric synthesis i n which enantiomeric products are produced i n unequal amounts. The use of o p t i c a l l y active compounds f o r e i t h e r b i o l o g i c a l or chemical synthetic purposes i s often such that one p a r t i c u l a r enantiomer i s required since s p e c i f i c a c t i v i t y i s usually related to only one form. I s o l a t i o n of a single form i s usually brought about by using 3 biochemical processes or by the c o s t l y process of r e s o l u t i o n of a - 2 -racemic mixture. The use of homogeneous cata l y s t s containing c h i r a l ligands provides a viable a l t e r n a t i v e f o r producing s p e c i f i c compounds, and has been suc c e s s f u l l y applied f o r a v a r i e t y of asymmetric 4 transformations . For these c a t a l y s t s to be successful i t i s necessary f o r the c h i r a l complex to i n t e r a c t with a substrate by the so-c a l l e d diastereotopic i n t e r a c t i o n , to generate diastereomeric t r a n s i t i o n states at the configuration determining step. The free energy difference between these t r a n s i t i o n states determines the product composition of a k i n e t i c a l l y c o n t r o l l e d asymmetric synthesis. A measure of the e f f i c i e n c y of a p a r t i c u l a r synthesis i s the enantiomeric excess, which i s defined as: % enantiomeric excess {% e.e.) = |%R - %S| ( l . l ) 1.2 Asymmetric Hydrogenation of P r o c h i r a l Alkenes Of p a r t i c u l a r relevance to the studies i n t h i s thesis i s the asymmetric hydrogenation of p r o c h i r a l alkenes i n accordance with equation 1.2. H2 R l R 2C=CHR 3 • H 1 H 2 C « H C H 2 H 3 ^ Transformations of t h i s type have been studied extensively using c h i r a l rhodium c a t a l y s t s and, whilst a b r i e f overview w i l l be presented here, 4-9 numerous comprehensive reviews have been published One of the f i r s t examples of asymmetric hydrogenation, but i n the heterogeneous phase, was by Akabori et al}® who hydrogenated various oxime and oxazolone derivatives using m e t a l l i c palladium absorbed on s i l k . Due to the inherent d i f f i c u l t i e s with heterogeneous ca t a l y s t s few - 3 -11 12 e f f e c t i v e systems ' have been f o u n d . The use o f s o l u b l e t r a n s i t i o n m e t a l c a t a l y s t s o f f e r s a more c o n t r o l l e d system, and r e s e a r c h i n t h i s f i e l d was i n i t i a t e d i n 1968 w i t h t h e p r e p a r a t i o n o f c h i r a l p h o s p h i n e s o f the t y p e , P*PhR^R 2, wh i c h c o n t a i n a c h i r a l phosphorus atom. 13 Replacement o f t r i p h e n y l p h o s p h i n e i n W i l k i n s o n ' s c a t a l y s t , R h C l ( P P h ^ ) ^ , w h i c h i s a c a t a l y s t p r e c u r s o r f o r t h e e f f e c t i v e h y d r o g e n a t i o n o f a l k e n e s , by c h i r a l p h o s p h i n e s l e d t o the h y d r o g e n a t i o n . 14 o f s u b s t i t u t e d s t y r e n e s w i t h a low but s i g n i f i c a n t % e.e. . T h i s p r o v i d e d the i m p e t u s p r i m a r i l y f o r t h e development o f o t h e r c h i r a l 15 p h o s p h i n e s ; the f i r s t s i g n i f i c a n t ones were NMDPP , a monodentate l i g a n d c o n t a i n i n g a c h i r a l c a r b o n atom i n the neomenthyl s u b s t i t u e n t , and DIOP"''^, a b i d e n t a t e l i g a n d w i t h c h i r a l c a r b o n s i n t h e b r i d g i n g p o r t i o n o f the m o l e c u l e . From t h e s e t h r e e b a s i c t y p e s o f c h i r a l p h o s p h i n e , t h e development has been p r o l i f i c w i t h v a r i a t i o n s i n the groups on t h e phosphorus atoms, and i n t h e n a t u r e o f t h e s k e l e t o n w h i c h h o l d s t h e two phosphorus atoms i n t h e c a s e o f b i d e n t a t e l i g a n d s , o r b o t h . I n t h e space o f 10 y e a r s o v e r 130 d i f f e r e n t p h o s p h i n e s have been 17 s y n t h e s i s e d and, when i n c o r p o r a t e d i n t o a rhodium c a t a l y s t , a wide s p e c t r u m o f d a t a ( i n terms o f % e.e.) has r e s u l t e d . W i t h t h e s y n t h e s i s o f new p h o s p h i n e s has come the need o f new ways t o g e n e r a t e t h e c a t a l y s t p r e c u r s o r compared t o t h e o r i g i n a l s t u d i e s . Two b a s i c r o u t e s have been employed: (a) g e n e r a t i o n i n s i t u by d i s p l a c e m e n t o f a c o o r d i n a t e d d i e n e i n [ R h C l ( d i e n e ) ] ^ w i t h the a p p r o p r i a t e amount o f p h o s p h i n e ( L ) , and ( b ) , more r e c e n t l y , i s o l a t i o n as [ R h ( d i e n e ) L 2 ] + X by d i s p l a c e m e n t o f c h l o r i d e by a n o t h e r a n i o n - 4 -such as P F , - , CIO ~ o r BF ~. 6 4 4 H i g h s t e r e o s e l e c t i v i t y , w i t h e n a n t i o m e r i c e x c e s s e s i n some ca s e s o f e s s e n t i a l l y 100$, has been o b t a i n e d f o r t h e r e d u c t i o n o f c e r t a i n a l k e n e s . A s e l e c t i o n o f the ph o s p h i n e l i g a n d s used w i t h Rh t h a t show h i g h asymmetric i n d u c t i o n s and a c t i v i t i e s i s g i v e n i n F i g u r e 1.1. W h i l s t c o r r e l a t i o n s have been p r o p o s e d ' ' t o e x p l a i n how a b s o l u t e c o n f i g u r a t i o n s o f a d i p h o s p h i n e and t h e reduced a l k e n e a r e r e l a t e d , t h e r e i s no s i m p l e e x p l a n a t i o n as t o why one p a r t i c u l a r p h o s p h i n e i s more e f f e c t i v e t h a n a n o t h e r . T h i s i s perh a p s b e s t i l l u s t r a t e d by t h e s e r i e s : C 3 H 7 ^ M e 2 - A n ^ M e a - A n ^ M e Ph Ph 2-An 4-Ph C H 2 -2 L C-An^pCH 2-P h o s p h i n e MPPP PAMP CAMP $ e.e. 25$ 50-60% 80-88$ DiPAMP 95$ DiCAMP 64$ f o r t he r e d u c t i o n o f ( Z ) - a - a c e t a m i d o c i n n a m i c a c i d ' . S u c c e s s i v e s u b s t i t u t i o n o f an o-methoxyphenyl and a c y c l o h e x y l group f o r t h e i s o p r o p y l and p h e n y l groups o f m e t h y l p r o p y l p h e n y l p h o s p h i n e (MPPP) t o produce PAMP and CAMP, r e s p e c t i v e l y , r e s u l t s i n a marked i n c r e a s e i n e n a n t i o m e r i c e x c e s s . " D i m e r i s a t i o n " o f PAMP t o produce t h e more r i g i d DiPAMP r e s u l t s i n an optimum s t r u c t u r e y e t DiCAMP, wh i c h might be e x p e c t e d t o g i v e e q u a l l y good r e s u l t s , i s i n f a c t i n f e r i o r . B i d e n t a t e p h o s p h i n e s a r e g e n e r a l l y more e f f i c i e n t t h a n t h e monodentate, s i n c e t he l a t t e r have a c e r t a i n amount o f r o t a t i o n a l freedom w h i c h p e r m i t s a - 5 -" J l p P h 2 US) J>l^PPh H X^OMe H R = R' = Me : Chiraphos 1 8 [OJ Diop R = Me, R' = H : Prophos 1 9 DiPAMP R R H, R' = OMe OMe, R' = H 3-Poop' Me^  H NMe, Bppf a 2 2 Me H^Ph N -pPh, c N- P P h2 H^Ph Me Pnnp^^ Phellanphos 2 5 Norphos PPh, 2 4 Me CAMP26 R = £-methoxyphenyl R' = cyclohexyl Figure 1 . 1 Selected c h i r a l phosphines f o r asymmetric c a t a l y s i s . - 6 -v a r i e t y o f d i a s t e r e o t o p i c i n t e r a c t i o n s upon a l k e n e c o o r d i n a t i o n . U l t i m a t e l y i t i s the s t e r i c o r p o l a r c o n s t r a i n t s imposed by the m o l e c u l a r framework o f t h e ph o s p h i n e t h a t d e t e r m i n e s the e x t e n t t o w h i c h asymmetric i n d u c t i o n t a k e s p l a c e d u r i n g c a t a l y s i s . I n t h e p r o c e s s o f p r o d u c i n g a l a r g e number o f c h i r a l rhodium 17 complexes a wide v a r i e t y o f p r o c h i r a l a l k e n e s have been r e d u c e d The c h o i c e o f a l k e n e i s an i m p o r t a n t f a c t o r , s i n c e u n f o r t u n a t e l y t he s u b s t r a t e a l s o c o n t r i b u t e s t o the asymmetric i n d u c t i o n . P r o c h i r a l a l k e n e s can be d i v i d e d i n t o two br o a d c l a s s e s . The f i r s t i s c o m p r i s e d o f t h e s i m p l e a l k e n e s such as a - e t h y l s t y r e n e , f o r w h i c h e n a n t i o m e r i c e x c e s s e s a r e i n v a r i a b l y l ow. The second c o n s i s t s o f s u b s t r a t e s w h i c h have p o l a r groups c l o s e t o t h e d o u b l e bond, such as the d e r i v a t i v e s o f a - a c y l a m i n o a c r y l i c a c i d s : C00R 2 1 / R -CH=C \ 3 NH-CO-R^ 30 X - r a y a n a l y s i s has shown t h a t s u c h groups p r o v i d e a s e c o n d a r y i n t e r a c t i o n w i t h t h e m e t a l , and t h e s e t y p e s o f a l k e n e s a r e i n g e n e r a l a s y m m e t r i c a l l y r e d u c e d more e f f i c i e n t l y . O t h e r a l k e n e s i n t h i s c l a s s s u c h as d e r i v a t i v e s o f i t a c o n i c a c i d , CH 2=C(C0 2H)CH 2C0 2H, however, 31 t e n d t o g i v e l o w e r e n a n t i o m e r i c e x c e s s e s , w h i c h i s b e l i e v e d t o be a consequence o f i n t e r m o l e c u l a r H-bonding i n t e r a c t i o n s t h a t p r e v e n t c h e l a t i o n . 32 Of c o m m e r c i a l i m p o r t a n c e i s t h e r e d u c t i o n : - 7 -R x /NHCOCHj H 2 ^NHCOCHj x m 2 /C=C • RCH2CH. — m * . — • RCH 2CH^ H C0 2H "Rh-DiPAMP" ^ C 0 2 H ^ C 0 2 H R=3,4-dihydroxyphenyl 35% e.e. L-DOPA since the i n i t i a l l y reduced product i s r e a d i l y transformed into the amino acid L-DOPA, a drug f o r t r e a t i n g Parkinson's disease. Other commercial processes u t i l i s i n g c h i r a l rhodium complexes have been 4 considered , but only that f o r L-DOPA i s i n large scale production. Whilst extensive q u a l i t a t i v e synthetic studies have shown the p o t e n t i a l and complexity of asymmetric hydrogenation, i t i s quantitative k i n e t i c studies which have provided an understanding of the c a t a l y t i c mechanism, and allowed for the design of better systems. The major contributions i n t h i s respect came from studies of the extremely e f f e c t i v e chiraphos and DiPAMP (and nonchiral analogue diphos) 33 complexes by Halpern's group . Addition of a-amino acid precursors to [Rh(P-P)(MeOH) n] + species, generated by the reduction of the diene precursor, r e s u l t s i n the formation of two diastereomeric complexes which d i f f e r i n the o l e f i n i c face coordinated, and which can 31 34 be distinguished by P-n.m.r. It was o r i g i n a l l y thought that the s t e r e o s e l e c t i v i t y of the reduction was determined by the i n i t i a l diasteromeric r a t i o . However, the chiraphos system with ethyl-(Z)-a-acetamidocinnamate showed only one diastereomer to be present i n s o l u t i o n and the X-ray analysis of the i s o l a t e d product showed that the face of the alkene which i s coordinated to the metal i s not the one 35 that i s predominantly reduced . Combined n.m.r. and k i n e t i c studies 36 led to the c a t a l y t i c scheme i n Figure 1.2 being proposed Figure 1 . 2 Proposed scheme for the c a t a l y t i c asymmetric hydrogenation of p r o c h i r a l alkenes by rhodium c a t a l y s t s . - 9 -The i n i t i a l binding of the alkene to the c a t a l y s t to form the diastereomeric complexes A' and A" i s not the key step, but rather t h e i r subsequent r e a c t i v i t y with that determines the 31 e n a n t i o s e l e c t i v i t y . The X-ray analysis and P-n.m.r. data show that A' i s the major i n i t i a l adduct, but the greater r e a c t i v i t y of the minor one leads to the R isomer as the p r i n c i p l e product (e.e. = 95$). For the [Rh(R,R-DiPAMP)] +- catalysed hydrogenation of methyl-(Z)-a-acetamidocinnamate at 25°C the k i n e t i c parameters K^, = 3.7 x 10^ " M ^, K r = 3.3 x 10 3 M"1, k 2, = 1.1 M-W1 and ^ „ - 6.4 x 10 2 M ^ s e c " 1 were obtained. The c_a. 580 f o l d higher r e a c t i v i t y of A" i n t h i s case compensates f o r i t s lower concentration, and r e s u l t s i n formation of the S enantiomer i n greater than 96$ enantiomeric excess. This mechanism also explains the observed dependence of o p t i c a l y i e l d with hydrogen pressure. Increasing the hydrogen concentration increases the rate-determining oxidative addition step (k^, and k^ ,,) u n t i l eventually the stereochemistry of the reaction becomes s o l e l y determined by the i n i t i a l binding of substrate to c a t a l y s t . In the [Rh(R,R-DiPAMP)] -system t h i s leads to increased proportions of the R enantiomer. By f a r the most extensive research i n the f i e l d of asymmetric hydrogenation has been directed towards rhodium systems containing c h i r a l phosphines. Hydrogenation by other c h i r a l metal complexes to date have shown low r e a c t i v i t y and/or s p e c i f i c i t y , and r e l a t i v e l y few examples are known. These include Ziegler-type c a t a l y s t s involving titanium-cyclopentadiene complexes , complex cobalt systems which - 10 -catalyse the reduction of conjugated double bonds, and ruthenium complexes which are discussed in Section 4.1. 1.3 General Overview of Hydrogen Activation and the Homogeneous  Hydrogenation of Alkenes A key step i n the hydrogenation of alkenes or other unsaturated substrates i s the activation of hydrogen, although this i s not the only prerequisite for the metal complex to be active. The uncatalysed addition of hydrogen to an alkene, whilst being thermodynamically favourable 3 9 in the ground state i s a symmetry forbidden process . A transition metal complex can catalyse hydrogenation reactions by overcoming the net symmetry restrictions through a series of symmetry allowed reaction steps involving a metal hydride intermediate. Hydrogenation is accomplished by activation of both hydrogen and substrate, but the system must also be capable of transferring the hydrogen and releasing the reduced product. Effective hydrogenation catalysts are generally of the group VIII metals 6 8 in low i n i t i a l oxidation states (d-d ). These are frequently coordinatively unsaturated thereby allowing sites for activation, and accommodating an increase in the formal oxidation state. Catalytic activity has been found for other transition metal complexes, notably 40 41 42 2 3 those of Ti , Zr , and Nb which have d or d configurations. Activation of hydrogen can occur in two basic ways depending largely on the metal complex used: (a) oxidative addition via a three-centre transition state that results in homolytic cleavage of the - 11 -H-H bond, and (b) h e t e r o l y t i c c l e a v a g e o f the bond t o form a h y d r i d e and p r o t o n . (a) O x i d a t i v e a d d i t i o n 4 3 ML + H . . j = ^ ML H v ' n 2 n 2 C o n s i d e r i n g a h y d r i d e l i g a n d as a f o r m a l l y -1 u n i t , t h i s mode o f a c t i v a t i o n r e s u l t s i n the f o r m a t i o n o f a d i h y d r i d e ( o r p o l y h y d r i d e i f h y d r i d e l i g a n d s a r e a l r e a d y p r e s e n t ) w i t h an i n c r e a s e i n t h e o x i d a t i o n s t a t e o f t h e m e t a l by two. The d i h y d r i d e p r o d u c t s formed have a c i s geometry f o r the two h y d r o g e n s , a l t h o u g h i n p r i n c i p l e a t r a n s c o n c e r t e d 44 a d d i t i o n i s a l l o w e d . The r e a c t i o n i s o f t e n r e v e r s i b l e , t h e f o r w a r d 45 r e a c t i o n b e i n g promoted by low i n i t i a l o x i d a t i o n s t a t e , h i g h m e t a l b a s i c i t y and c o o r d i n a t i v e u n s a t u r a t i o n . F o r t h e s e r e a s o n s t h e r e a c t i o n Q i s commonly o b s e r v e d f o r s q u a r e p l a n a r d complexes w h i c h upon a d d i t i o n form the f a v o u r e d o c t a h e d r a l d^ c o n f i g u r a t i o n . Examples o f 46-48 t h i s t y p e o f a c t i v a t i o n a r e : R h C l ( P C y 3 ) 2 + H 2 , R h H 2 C l ( P C y 5 ) 2 (1.3) R u ( C 0 ) 2 ( P P h 5 ) 5 + H 2 ^ = ± R u H 2 ( C 0 ) 2 ( P P h 3 ) 2 + P P h 3 (1.4) I r C l ( P P h ) + H 2 h I r H 2 C l ( P P h 5 ) 3 (1.5) The f i r s t two examples g e n e r a t e c a t a l y t i c a l l y a c t i v e d i h y d r i d e s , the second p r o c e e d i n g w i t h l o s s o f a p h o s p h i n e l i g a n d , w h i l s t t h e p r o d u c t o f r e a c t i o n 1.5 i s i n a c t i v e . The f o r m a t i o n o f i n a c t i v e d i h y d r i d e complexes i s n o t u n u s u a l s i n c e , i f the m e t a l - h y d r i d e bonds a r e t h e r m o d y n a m i c a l l y o r k i n e t i c a l l y too s t a b l e , hydrogen t r a n s f e r t o t h e a l k e n e w i l l not o c c u r . - 1 2 -The general mechanism f o r alkene hydrogenation i n v o l v i n g dihydride c a t a l y s t s involves two possible routes depending on when the dihydride i s formed (Scheme l - l ) . Coordination of the alkene a f t e r oxidative addition of the Hg, followed by two consecutive hydrogen atom transfers, produces the saturated product, v i a the so-called "hydride" route. The a l t e r n a t i v e "unsaturate" route proceeds with 2 / N H, M +• V 1 r* / C = c s II HM\ /H \ / MH A H 2 C M A alkene * M Scheme 1 - 1 coordination of the alkene followed by oxidative addition of H^. Both routes generate the same dihydride-substrate intermediate, but generally the unsaturate route i s less favoured since p r i o r coordination of the substrate i s expected to remove electron density from the metal making subsequent oxidative addition of l e s s probable. In cases where the unsaturate route does occur, the substrate acts as a ligand i n s t a b i l i s i n g the subsequently formed metal hydride, as i s generally thought to be the case i n the asymmetric hydrogenation discussed previously (Section 1 . 2 ) . Wilkinson's c a t a l y s t 4 9 , RhCl(PPh_), f - 1 3 -which coordinates both alkene and hydrogen separately, has been shown to 50 51 e f f i c i e n t l y hydrogenate alkenes by both routes ' Whilst monomeric complexes generally give r i s e to dihydride species, differences are found f o r dimeric complexes. Equation 1.6 shows an oxidative addition of IL, that r e s u l t s i n a dimeric product Bu t P H 3 P \ / S \ / C 0 / I r I r + H 2 • [ l r H ( y - S B u t ) ( C 0 ) ( P P h 3 ) ] 2 (1.6) OC S x x P P h 5 Bu* 52 with one hydrogen atom bound to each metal . The addition i s thought to occur at one metal centre, followed by hydride migration from I r ( l l l ) to I r ( l ) ; the r e s u l t i n g formally I r ( l l ) atoms a t t a i n an 18-electron configuration through metal-metal bond formation. The related complexes [lr(y-S)(C0)(dppm)] 2 5 5 and [ R h C l ( P P h 5 ) 2 ] 2 5 4 also add H 2 > but i n these cases migration does not occur and mixed-valence products with a dihydride on one metal centre are formed. Oxidative" addition of hydrogen to pentacyanocobaltate(ll) (equation 1.7) i s 55 unusual i n that a monohydride i s generated : 2Co(CH) 5 3~ or C o 2 ( C N ) 1 0 6 ~ + H 2 • 2CoH(CN) 5 5 - (1.7) I t i s uncertain whether t h i s reaction involves a d i r e c t termolecular step, H 2 addition to undetectable amounts of dimer, or by hydride a b s t r a c t i o n from transient dihydrides. The hydrogenation of alkenes employing t h i s c a t a l y s t i s also unusual i n that the saturated product i s formed generally v i a binuclear reductive elimination from the reaction 56 of a metal a l k y l with a metal hydride complex . Hydrogen atom transfers - 14 -without coordination of the substrate have also been demonstrated f o r the pentacyanocobaltate(ll) c a t a l y s t " ^ , as well as f o r CoHCCO)^"^. Whilst the hydride ligand has been considered as a -1 unit, the shortcomings i n t h i s d e s c r i p t i o n are apparent. Homolytic cleavage of n2 o n l y becomes an oxidative addition when electrons are transferred from the metal to the hydrogen atoms. However, such cleavage may be 58 formulated.in three ways depending on the metals involved (equations 1.8 a-c). The products d i f f e r only i n the p o s i t i o n of the 2M n + or (M Q +) 2+ H:H 2Mn(.H) * 2M n _ 1(H) 2M n + 1(:H) (1.8a) (1.8b) (1.8c) electrons o r i g i n a l l y associated with the hydrogen atom. The detection of hydrogen atom transfers by HCo(CN)^ i n hydrogenation studies implies that the hydrogen i s better pictured as a s t a b i l i s e d atom (equation 1.8a) rather than a hydride (equation 1.8c), at least i n the t r a n s i t i o n state. A l t e r n a t i v e l y , addition of H 2 to [ l r ( c o d ) L 2 ] and Llr(cod) 2] has been considered'''* to be reductive rather than oxidative i n character (equation 1.8b). (b) H e t e r o l y t i c Cleavage ML + H_ ML _H~ + H++ L v n eL n—± This type of hydrogen a c t i v a t i o n involves a net s u b s t i t u t i o n of a hydride f o r another ligand without changing the oxidation state of the metal. Usually the ligand substituted i s a halide, such as shown^ i n equation 1.9, although the hydrogenolysis of metal-alkyl, a r y l or a l l y l - 15 -bonds also generates monohydrides i n formally analogous reactions. The r e v e r s i b l e nature of these reactions i s generally not RuCl 2(PPh 5) 3+ H 2 <. k RuHClCPPh^)^ + H++ C l " (1.9) observed i f the released proton i s s t a b i l i s e d by base, which can be e i t h e r an i n i t i a l l y coordinated ligand, the solvent, or an e x t e r n a l l y added base. There are two p l a u s i b l e mechanisms f o r explaining the net 58 h e t e r o l y t i c cleavage of hydrogen . The f i r s t involves oxidative addition of H 2 to form a dihydride, which subsequently breaks down v i a reductive elimination i n t o the metal hydride and protonated anion: M - X + H 2 • M——H • M - H + HX (1.10) Such a process seems reasonable f o r metals i n low oxidation states such as R u ( l l ) (Equation 1.9), which could proceed v i a a seven coordinate Ru(lV) intermediate. For metals i n higher oxidation states, e.g. R u ( l l l ) and R h ( l l l ) , a d i f f e r e n t mechanism i s invoked where overlap between a f i l l e d metal o r b i t a l with an empty hydrogen o r b i t a l r e s u l t s i n a polarized Hg-metal intermediate: M X M - X + H 2 + j ! • M - H + HX ( l . l l ) " H — H + Loss of the p o s i t i v e l y polarized end of the H 2 molecule to the - 16 -s e l f - g e n e r a t e d , o r added base X, g i v e s r i s e t o the m e t a l h y d r i d e . As f o r t h e d i h y d r i d e c a t a l y s t s g e n e r a t e d by o x i d a t i v e a d d i t i o n , t h e complexes t h a t h e t e r o l y t i c a l l y s p l i t hydrogen can h y d r o g e n a t e a l k e n e s by two r o u t e s as shown i n Scheme 1-2. F o r m a t i o n o f t h e monohydride p r i o r t o a l k e n e a c t i v a t i o n i s known as t h e h y d r i d e r o u t e , w h i c h i s e x h i b i t e d f o r e x a m p l e ^ by t r i c h l o r o s t a n n a t e ( l l ) complexes o f P t ( l l ) . H e t e r o l y t i c c l e a v a g e o f H^ by a m e t a l - a l k e n e complex c o n s t i t u t e s t h e u n s a t u r a t e r o u t e , and has been s u b s t a n t i a t e d f o r 62 c h l o r o r u t h e n a t e ( l l ) s p e c i e s MH H f **** ^ ' / , H, MH -^ H > = C N M\ _ /H \ / C M - l l + H, C / \ Scheme 1-2 The i n t e r a c t i o n between hydrogen and t r a n s i t i o n m e t a l complexes i s c l e a r l y o f i m p o r t a n c e f o r b o t h s t o i c h i o m e t r i c and c a t a l y t i c r e a c t i o n s . The l i t e r a t u r e d e a l i n g w i t h t h i s t o p i c i s e x t e n s i v e , but comprehensive 58 63—66 r e v i e w s c o v e r i n g the l i t e r a t u r e t o 1982 have been p u b l i s h e d ' - 17 -1.4 Scope o f t h i s T h e s i s 13 S i n c e t h e m o d i f i c a t i o n o f W i l k i n s o n ' s c a t a l y s t , R h C l C P P h ^ ) ^ , to i n c l u d e c h i r a l p h o s p h i n e s , the employment o f rhodium c a t a l y s t s f o r the asymmetric h y d r o g e n a t i o n o f p r o c h i r a l a l k e n e s has been e x t e n s i v e ( S e c t i o n 1.2). M o d i f i c a t i o n o f o t h e r t r a n s i t i o n m e t a l complexes which a r e known t o be c a t a l y t i c a l l y a c t i v e , however, has been v e r y l i m i t e d . The main o b j e c t i v e o f t h e work f o r t h i s t h e s i s was t o p r e p a r e a r u t h e n i u m - h y d r i d e complex c o n t a i n i n g a c h i r a l b i d e n t a t e p h o s p h i n e , f o r t h e purpose o f a d e t a i l e d asymmetric h y d r o g e n a t i o n s t u d y . Due t o t h e h i g h c o s t o f c h i r a l p h o s p h i n e s t h e work i n c l u d e d t h e use o f n o n c h i r a l d i t e r t i a r y p h o s p h i n e s , and much o f t h e g e n e r a l c h e m i s t r y was performed on complexes c o n t a i n i n g t h e s e p h o s p h i n e s . The v e r y n a t u r e o f known r u t h e n i u m h y d r i d e complexes p r e c l u d e d d i r e c t m o d i f i c a t i o n so i t was n e c e s s a r y t o g e n e r a t e them by a l t e r n a t i v e methods. The i s o l a t i o n o f t h e m i x e d - v a l e n c e complexes o f g e n e r a l f o r m u l a R u 2 C l ^ ( P - P ) 2 (P-P = b i d e n t a t e p h o s p h i n e ) was t h e f i r s t s t e p ( C h a p t e r I I I ) . An X - r a y s t u d y o f the c h i r a p h o s d e r i v a t i v e c o n f i r m e d t h e s t r u c t u r e i n the s o l i d s t a t e but the n a t u r e o f t h e s e complexes i n s o l u t i o n was s t r o n g l y dependent on the s o l v e n t . T h i s was m o n i t o r e d by changes i n t h e i r n e a r - i n f r a r e d s p e c t r a . The r e a c t i o n s of t h e s e complexes w i t h hydrogen g e n e r a t e d i o n i c s p e c i e s i n s i t u , and t h e s e r e a c t i o n s were i n v e s t i g a t e d i n an a t t e m p t t o a s c e r t a i n m e c h a n i s t i c d e t a i l s . C h a p t e r IV d e s c r i b e s the n e u t r a l complexes, [ R u C l 2 ( P - P ) ] 2 i s o l a t e d from t h e r e d u c t i o n o f the m i x e d - v a l e n c e complexes. V a r i a b l e - 18 -temperature n.m.r. was p r i m a r i l y used to e s t a b l i s h the nature of these complexes i n s o l u t i o n . Complexes of t h i s type had been previously detected spectroscopically, but these were the f i r s t examples of i s o l a t e d complexes. In the case of the c h i r a l phosphines (where P-P = chiraphos and diop), the complexes were tested as c a t a l y s t s f o r asymmetric hydrogenation of p r o c h i r a l alkenes. Various routes were attempted i n order to prepare a hydrido-complex (Chapter V). The generation of hydride species from [RuCl 2(dppb)] 2 and RuCl 2(nbd)(dppb) using H 2 was observed. However, the only compound to be i s o l a t e d and well characterised was Ru 2H 2Cl 2(C0)(dppb) 2 f o r which molecular hydrogen was not necessary f o r synthesis. Chapter VI deals with c a t i o n i c complexes prepared by halide abstraction from Ru 2Cl^(dppb) 2 and [RuCl 2(dppb)]^ using AgPFg. These were prepared as p o t e n t i a l hydride precursors and consequently t h e i r reactions with hydrogen were studied. Whilst the goal of i s o l a t i n g a hydrido-complex f o r a study of the asymmetric hydrogenation of p r o c h i r a l alkenes was not achieved, the p o t e n t i a l of ruthenium phosphine complexes f o r t h i s purpose i s demonstrated, and routes f o r generating hydrido-species are provided. - 19 -CHAPTER I I EXPERIMENTAL 2.1 M a t e r i a l s 2.1.1 S o l v e n t s S p e c t r o q u a l i t y grade s o l v e n t s were o b t a i n e d f r o m A l d r i c h , Eastman, F i s h e r , M a l l i n c k r o d t , B.D.H. o r M.C.B. C h e m i c a l Co. Benzene, hexanes and t o l u e n e were d i s t i l l e d from sodium/benzophenone/2,5,8,11,14 -67 pentaoxapentadecane ( A l d r i c h ) under one atmosphere o f n i t r o g e n D i s t i l l a t i o n under n i t r o g e n o f a c e t o n e was from anhydrous I^CO^, o f d i c h l o r o m e t h a n e from ^2^5' a n < ^ a l c o n ° l s from t h e c o r r e s p o n d i n g magnesium a l k o x i d e . A c e t o n i t r i l e and DMA were s t i r r e d o v e r CaH2 f o r 24 h p r i o r t o f r a c t i o n a l d i s t i l l a t i o n , w h i c h f o r DMA was under vacuum. A f t e r d i s t i l l a t i o n b o t h a c e t o n i t r i l e and DMA were s t o r e d under a r g o n i n the d a r k . F o r s p e c t r o p h o t o m e t r y s t u d i e s t h o s e s o l v e n t s n ot d i s t i l l e d were d r i e d by s t o r i n g o v e r m o l e c u l a r s i e v e s (BDH ty p e 5 A ) . Anhydrous d i e t h y l e t h e r was used w i t h o u t f u r t h e r p u r i f i c a t i o n . 2.1.2 Gases R e s e a r c h grade hydrogen was o b t a i n e d from U n i o n C a r b i d e Canada L t d . , and Matheson Gas Co., and was pas s e d t h r o u g h an E n g e l h a r d Deoxo - 20 -c a t a l y t i c p u r i f i e r to remove trac e oxygen. P u r i f i e d argon and n i t r o g e n were supplied by Union Carbide Canada L t d . , and Matheson Gas Co. or Canada L i q u i d A i r L t d . Lecture b o t t l e s of anhydrous hydrogen c h l o r i d e and hydrogen bromide were obtained from Matheson Gas Co. A l l gases, with the exception of hydrogen, were used without f u r t h e r p u r i f i c a t i o n . 2.1.3 Phosphines Triphenylphosphine ( A l d r i c h or Eastman Kodak Co.), t r i ( p - t o l y l ) p h o s p h i n e , 1,2-diphenylphosphinoethane (dppe), 1,3-diphenylphosphinopropane (dppp), 1,4-diphenylphosphinobutane (dppb), (2S , 3 S)-bis(diphenylphosphino)butane ( c h i r a p h o s ) , and (2R,3R)-(-)-2,3,-0-isopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino)butane ( ( - ) - d i o p ) (Strem) were used as supplied f o r s y n t h e s i s . A l i t e r a t u r e method was used to prepare (R,R)-(-)-2-exo-3-endobis(diphenylphosphino)-68 b i c y c l o [ 2 . 2 . l ] h e p t e n e (norphos) 2.1.4 Alkene Substrates I t a c o n i c a c i d (methylenesuccinic acid) was supplied by Eastman Kodak Co., (Z)-a-acetamidocinnamic and a-acetamidoacrylic a c i d s , and c i t r a c o n i c a c i d (methylmaleic a c i d ) by Fluka Chemical Co., and acrylamide (propenamide) by K & K Labor a t o r i e s Inc. These substrates were r e c r y s t a l l i s e d from hot ethanol to y i e l d c o l o u r l e s s c r y s t a l s , and t h e i r '''H-n.m.r. spectra recorded to confirm p u r i t y . Hex-l-ene and styrene were obtained from A l d r i c h , and were passed through an alumina - 21 -column p r i o r to use. Atropic acid (2-phenylpropenoic acid) was prepared as follows: 36 g (0.2 mol) of ethyl atropate (prepared according to Ames and Davy^ 9) was saponified by r e f l u x i n g f o r 4 h with 30 g (0.74 mol) of NaOH i n 250 mL water. The basic mixture was a c i d i f i e d and the atropic acid extracted with three 100 mL portions of d i e t h y l ether. Evaporation of the solvent produced a white powder which was r e c r y s t a l l i s e d from hot ethanol to y i e l d 24 g (79% y i e l d ) of atropic a c i d : 6 D M S 0 : 5.97 (doublet, IH, -C=CH), 6.27 (doublet, IH, -C=CH), 7.43 (5H, aromatic). 2.1.5 Other Materials Norbornadiene (Eastman) was p u r i f i e d by passing through a column of alumina p r i o r to use. S i l v e r hexafluorophosphate (Alpha Inorganics) was stored i n the dark i n a desiccator under vacuum. Po l y v i n y l p y r i d i n e was kindly supplied by R e i l l y International Chemicals Inc. Proton Sponge, l,8-bis(dimethylamino)naphthalene ( A l d r i c h ) , was p u r i f i e d by passing a petroleum ether (30 oC-60°C) s o l u t i o n through an alumina column. Concentration of the s o l u t i o n y i e l d s proton sponge as a white s o l i d . 2.1.6 DMA Sa l t s 2.1.6.1 N,N-Dimethylacetamidehydrochloride, DMA.HC1 Anhydrous HC1 was bubbled into DMA (30 mL) to produce a copious white p r e c i p i t a t e . The mixture was f i l t e r e d under argon, washed well with d i e t h y l ether and vacuum dri e d . R e c r y s t a l l i s a t i o n from - 22 -a c e t o n e / d i e t h y l e t h e r a f f o r d e d c o l o u r l e s s , e x t r e m e l y h y g r o s c o p i c c r y s t a l s o f DMA.HC1. Y i e l d : 13.5 g ( 3 4 $ ) ; C ^ Q C I N O r e q u i r e s C : 38.87, H :. 8.10, N : 11.34$; found C : 38.8, H : 8.2, N : 11.3$, 6CDC1 : 2 , 6 0 ( s ' 5 H CV-)' 3 ' 2 2 6 H » ( C H 3 ) 2 N - ) f 15.60 ( s , IH, p r o t o n ) . 2.1.6.2 N , N - D i m e t h y l a c e t a m i d e h y d r o b r o m i d e , DMA.HBr T h i s was p r e p a r e d i n an a n a l o g o u s way t o t h e p r e c e d i n g compound, but u s i n g anhydrous hydrogen bromide. Y i e l d : 15.1 g ( 2 8 $ ) ; C 4 H 1 Q B r N 0 r e q u i r e s C : 28.57, H : 5.95, N : 8.33$; found C : 28.6, H : 5.8, N : 8.5$; 6QJ)C1 : 2.76 ( s , 3H, C H ^ - ) , 3.27 ( S , 6H, ( C H 5 ) 2 N - ) , 14.8 ( s , IH, p r o t o n ) . 2.1.7 Ruthenium Compounds The r u t h e n i u m was o b t a i n e d as R u C l ^ ^ R ^ O w h i c h was s u p p l i e d on l o a n from Johnson M a t t h e y L t d . The p r o p o r t i o n o f Ru v a r i e d from 39 t o 42$ d e p e n d i n g on b a t c h . A l l r e a c t i o n s were c a r r i e d out i n deoxygenated s o l v e n t s under an atmosphere o f a r g o n by e m p l o y i n g S c h l e n k t e c h n i q u e s u n l e s s s p e c i f i e d o t h e r w i s e . A d d i t i o n a l c h a r a c t e r i s a t i o n d a t a a r e p r e s e n t e d i n t h e d e s i g n a t e d s e c t i o n s o f the t h e s i s . - 23 -2.1.7.1 T r i c h l o r o b i s ( t r i p h e n y l p h o s p h i n e ) ( D M A ) r u t h e n i u m ( I I I ) . D M A s o l v a t e , R u C l 5 ( P P h 5 ) 2 ( D M A ) . D M A R u C l .3H 20 (2.0 g, 7.6 mmol) i n 60 mL DMA was s t i r r e d f o r 24 h a t room t e m p e r a t u r e w i t h PPh^ (4.0 g, 15.3 mmol). The g r e e n a i r - s t a b l e p r o d u c t was f i l t e r e d , c a r e f u l l y washed w i t h DMA, r i n s e d w i t h hexanes and d r i e d under vacuum. Y i e l d : 4.6 g ( 6 6 $ ) ; C . .H, oN„0^Cl_P-Ru 44 4o 2 2 3 2 r e q u i r e s C : 58.31, H : 5.30, N : 3.09, C l : 11.76$; found C : 58.1, H : 5.3, N : 3.1, C l : 11.8$; v : 1630 cm" 1 ( u n c o o r d i n a t e d max DMA), 1590 cm" 1 ( c o o r d i n a t e d DMA). 2.1.7.2 T r i c h l o r o b i s ( t r i - p - t o l y l p h o s p h i n e ) ( D M A ) r u t h e n i u m ( I I I ) . D M A  s o l v a t e , R u C l 5 ( P ( p - t o l y l ) 5 ) 2 ( D M A ) . D M A The s y n t h e s i s was t h e same as d e s c r i b e d f o r the t r i p h e n y l p h o s p h i n e complex, but u s i n g a two f o l d e x c e s s o f P ( p - t o l y l ) 3 (4.7 g, 15.3 mmol). Y i e l d 4.0 g ( 7 6 $ ) ; C 2 ° 2 C 1 J P r e ( l u i r e s C : 60.64, H : 6.06, N : 2.83, C l : 10.76$; found C : 60.5, H : 6.1, N : 2.9, C l ' : 10.6$; V m a x : 1638 cm" 1 ( u n c o o r d i n a t e d DMA), 1595 cm "'"(coordinated DMA). 2.1.7.3 T r i - u - c h l o r o - d i c h l o r o b i s ( b i d e n t a t e p h o s p h i n e ) d i r u t h e n i u m ( I I , I I I ) , R u 2 C l 5 ( P - P ) 2 , P-P = dppb o r d i o p ( S e c t i o n s 3.2-3.5) A s u s p e n s i o n o f R u C l ^ P P h ^ ^ D M A ) .DMA ( l g, 1.1 mmol) and one e q u i v a l e n t o f t h e a p p r o p r i a t e b i d e n t a t e p h o s p h i n e was r e f l u x e d i n 150 mL o f hexanes under n i t r o g e n f o r 24 h. The red-brown p r o d u c t was f i l t e r e d , washed w e l l w i t h hexanes and vacuum d r i e d . R e c r y s t a l l i s a t i o n - 24 -from CH^Cl^-diethyl ether gave a i r - s t a b l e red powders. P-P = dppb : 0.47 g ( l . l mmol) of dppb used. Y i e l d : 0.49 g (72$); C ^ H ^ C l ^ R ^ requires C : 54.57, H : 4.59, C l : 14.38$; found C : 54.7, H : 4.6, C l : 14.2$; v : max 338 cm - 1 (Ru-Cl); m.p.: 198°C ( d e c ) . P-P = diop : 0.55 g ( l . l mmol) of diop used. Y i e l d : 0.50 g (66$); C~H,,0.'Cl cP,Ru o requires b i : b4 4 5 4 c. C : 54.09, H : 4.65, Cl : 12.90$; found C : 53.9, H : 4.8, Cl : 12.8$; v : 340 cm - 1 (Ru-Cl); m.p.: 207°C ( d e c ) . 2.1.7.4 Tri- u - c h l o r o - d i c h l o r o b i s ( b i d e n t a t e phosphine)diruthenium(II,III) R u ^ C l ^ P-P^, P-P = chiraphos, norphos, dppp (Sections 3.2-3.5) The preparative procedure f o r these complexes i s the same as f o r the dppb and diop analogues described i n the preceding section, but using RuCl 3(P(p-tolyl) 3) 2(DMA).DMA (l.O g, 1.0 mmol) and the appropriate bidentate phosphine. P-P = chiraphos: 0.43 g (l.O mmol) of chiraphos used. Y i e l d : 0.51 g (82$); C gH g C l ^ R U g requires C : 54.57, H : 4.59, C l : 14.38$; found C : 54.7, H : 4.6, Cl : 14.2$; v : 340 cm"1 (Ru-Cl); m.p. : 242°C ( d e c ) . P-P = norphos: 0.46 g (l.O mmol) of norphos used. Y i e l d : 0.32 g (49$); C ^ H ^ C l ^ R ^ requires C : 57.08, H : 4.30, Cl : 13.62$; found C : 56.7, H : 4.5, Cl : 13.8$ v : 331 cm - 1 (Ru-Cl); m.p.: 262°C ( d e c ) . - 25 -P-P = dppp: 0.41 g (l.O mmol) of dppp used. Y i e l d : 0.26 g ( 4 3 $ ) ; C ^ H ^ C l ^ P a ^ re q u i r e s C : 53.84, H : 4.32; C l : 14.75$; found C : 53.7, H : 4.5, C l : 14.6$; v : 340 cm - 1 (Ru-Cl); m.p.: 214°C ( d e c ) , max r 2.1.7.5 D i c h l o r o b i s ( b i d e n t a t e phosphine)ruthenium(II) dimers, |_RuCl 2(P-P)] 2, P-P = dppb, dppp (Sections 4.2 and 4.3) R u 2 C l 5 ( P - P ) 2 , P - P = dppb or dppp (1.0 g, 0.81 mmol) i n DMA (30 mL) was s t i r r e d under IL, ( l atm.) f o r 16 h. The volume of the r e s u l t i n g brown s o l u t i o n was reduced to 5 mL, a f t e r which methanol (40 mL) was added, and the suspension s t i r r e d f o r 3 h. The r e s u l t i n g orange s o l i d was f i l t e r e d , washed with methanol and vacuum d r i e d to give a brown s o l i d . The s o l i d obtained by t h i s method o c c a s i o n a l l y contained n i t r o g e n present as DMA i m p u r i t y (by elemental a n a l y s i s ) which could be removed by r e c r y s t a l l i s a t i o n from C H 2 C l 2 - d i e t h y l ether. P-P - dppb: Y i e l d : 0.83 g (85$); C 5 6 H 5 6 C l 4 P 4 R u 2 . H 2 0 req u i r e s C : 55.35, H : 4.78, C l : 11.70$; found C : 55.4, H : 5.0, C l : 11.5$ P-P = dppp: Y i e l d : 0.39 g (40$); C H ^ C l P RUg.HgO r e q u i r e s C : 54.64, H : 4.55, C l : 11.97$; found C : 54.7, H : 4.8, C l : 11.9$ The dppb complex was p a r t i c u l a r l y hygroscopic and a i r - s e n s i t i v e , r e a d i l y t u r n i n g green. A more s t a b l e form of t h i s complex was obtained by d i s s o l u t i o n i n CH 2C1 2 (20 mL) to which an equal volume of acetone was added. S t i r r i n g the s o l u t i o n causes p r e c i p i t a t i o n of an orange - 26 -s o l i d which was f i l t e r e d , washed with d i e t h y l ether, and vacuum d r i e d . The complex was i d e n t i f i e d as R u 2 C l 4 ( d p p b ) 2 ( a c e t o n e ) .acetone. Y i e l d : 0.72 g (68$); C ^ H ^ C l ^ R ^ req u i r e s C : 56.71, H : 5.18, 0 : 2.44, C l : 10.82$; found C : 56.5, H : 5.1, 0 : 2.6, C l : 10.6$; v m a x : 1705 cm-"'" (uncoordinated acetone), 1645 cm-"'" (coordinated acetone). 2.1.7.6 D i c h l o r o b i s ( b i d e n t a t e phosphine)ruthenium(ll) dimers, [ R u C l 2 ( P - P ) ] 2 , P-P = diop, chiraphos (Sections 4.2 and 4.3) P o l y v i n y l p y r i d i n e (3 g) was deoxygenated by pumping on the s o l i d . p r i o r to a d d i t i o n of 60 mL of toluene, and then s t i r r i n g the suspension under Ar and o c c a s i o n a l l y a p a r t i a l vacuum at ca. 60°C f o r 0.5 h. This suspension was added to R u 2 C l j - ( P - P ) 2 , P-P = diop or chiraphos, and s t i r r e d under H 2 ( l atm.) f o r 24 h. Separation of the i n s o l u b l e polymer by f i l t r a t i o n l e f t a brown s o l u t i o n which was reduced i n volume to 10 mL. Hexanes were added, and the s o l u t i o n set aside to allow formation of an orange c r y s t a l l i n e s o l i d i n the case of P-P = chiraphos, and a brown s o l i d f o r the diop complex. The product was f i l t e r e d , washed with hexanes and vacuum d r i e d . The volume of f i l t r a t e was reduced and f u r t h e r p r e c i p i t a t i o n induced by adding more hexanes. P-P - diop: Y i e l d : 0.79 g (81$); CggHg 0 C l ^ R i i g r e q u i r e s C : 55.52, H : 4.78, C l : 10.60$; found C : 55.7, H : 5.0, C l : 10.8$ P-P = chiraphos: Y i e l d : 0.76 g (78$); C 5 6 H 5 g C l 4 P 4 R u 2 r e q u i r e s C : 56.19, H : 4.68, C l : 11.87$; found C : 56.3, H : 4.8, C l : 11.7$ - 27 -The chiraphos complex was also obtained as an acetone adduct by concentration of the brown sol u t i o n to 10 mL to which an equal volume of acetone was added. P r e c i p i t a t i o n with hexanes produced an orange s o l i d i d e n t i f i e d as Ru 2 C l 4 ( c h i r a p h o s ) 2 ( a c e t o n e ) . Y i e l d : 0.75 g (74$); ° 5 9 H 6 2 0 C 1 4 P 4 R u 2 requires C : 56.46, H : 4.94, 0 : 1.28, Cl : 11.32$; found C : 56 . 3 , H : 4 . 9 , 0 : 1.4, Cl : 11 .3$ ; v : max 1624 cm ^ (coordinated acetone). 2.1.7.7 Tri-u-chlorobis[chloro(1,4-diphenylphosphinobutane)- ruthenium(ll)] PSH +, [Ru 2C± 5(dppb) 2]~PSH + (Section 3.7.4) Ru 2Cl^(dppb) 2 (0.5 g, 0.4 mmol) and Proton Sponge (0.3 g, 1.4 mmol) were dissolved i n toluene (60 mL), and s t i r r e d under H 2 ( l atm.) f o r 16 h. The brown so l u t i o n was concentrated to 20 mL; th i s caused p r e c i p i t a t i o n of an orange s o l i d which was f i l t e r e d , washed well with hexanes and vacuum dri e d . Y i e l d : 0.43 g (73$); C_„H r 7 [ rN 0Cl i rP .Ru0 ( U (o d 5 4 d requires C : 58.07, H : 5.18, N : 1.94, Cl : 12.27$; found C : 58.1, H : 5.4, N : 1.9, Cl : 12.1$ 3 1P{ 1H}-n.m.r. (CD 2C1 2 > 30°C), s, 53.6 ppm. 2.1.7.8 Di-u-chloro-y-hydrido-hydrido(carbonyl)bis(1,4-diphenyl- phosphinobutane )diruthenium( I I ) , Ru 2H 2(C0)Cl 2(dppb) 2 (Section 5.3) Ru 4Cl 4(dppb) 2(acetone).acetone (0.5 g, 0.38 mmol) and Proton Sponge (0.4 g, 1.9 mmol) were s t i r r e d under Ar i n CH 2C1 2 (30 mL) and MeOH (20 mL) f o r 24 h. The red solu t i o n was concentrated to 10 mL causing p r e c i p i t a t i o n of an orange s o l i d . The mixture was f i l t e r e d and - 28 -the s o l i d washed with hexanes (10 mL), and vacuum d r i e d . The s o l i d was extracted w i t h d i e t h y l ether (60 mL), and the f i l t r a t e concentrated to 20 mL. P r e c i p i t a t i o n with hexanes afforded red c r y s t a l l i n e m a t e r i a l or an orange powder; the s o l i d s were f i l t e r e d , washed with hexanes and vacuum d r i e d . The f i l t r a t e was concentrated and f u r t h e r p r e c i p i t a t i o n induced by adding more hexanes. Y i e l d : 0.19 g (A3%);; C 5 7 H 5 8 0 C l 2 P 4 R u 2 r e q u i r e s C : 59.12, H : 5.01, 0 : 1.38$; found C : 59.2, H : 5.1, 0 : 1.6$; v : 2030 cm - 1 (w, Ru-H) and 1953 infix cm - 1 ( s , Ru-CO). 2.1.7.9 Dichloro(norbornadiene)(1,4-diphenylphosphinobutane)-ruthenium(II) RuCl 2(dppb)(nbd) ( S e c t i o n 5.4) Norbornadiene (4 mL, 39 mmol) was added to a suspension of Ru 2Cl 4(dppb)(acetone).acetone (l.O g, 0.76 mmol) i n benzene (50 mL). A f t e r 24 h, the volume of the r e s u l t i n g orange s o l u t i o n was reduced under vacuum to 20 mL and d i e t h y l ether added. Slow p r e c i p i t a t i o n afforded a brown c r y s t a l l i n e m a t e r i a l w h i l s t t r i t u r a t i o n produced an orange powder; the s o l i d s were f i l t e r e d , washed with d i e t h y l ether, and vacuum d r i e d . The product contained a molecule of benzene per two molecules of complex (evident i n the X-ray c r y s t a l s t r u c t u r e ) which could not be completely removed even a f t e r d r y i n g at 100°C f o r 6 h under vacuum. Y i e l d : 0.71 g (64$); C_ CH_ CC1J?-Ru.0.5 C,H. 00 3D d. d o o r e q u i r e s C : 62.55, H : 5.35, C l : 9.74$; found C : 62.5, H : 5.4, Cl : 9.5$. - 29 -2.1.7.10 T r i c h l o r o ( l > 4 - d i p h e n y l p h o s p h i n o b u t a n e ) r u t h e n i u i i i ( l I I ) d i m e r , [ R u C l 5 ( d p p b ) ] 2 ( S e c t i o n 3.6) To R u 2 C l 5 ( d p p b ) 2 (1.0 g, 0.81 mmol) i n CH^CN (60 mL) was added AgPF g (0.103 g, 0.41 mmol) i n CH^CN (10 mL), and t h e s o l u t i o n s t i r r e d f o r 0.5 h. The p a l e r e d s o l u t i o n was f i l t e r e d t h r o u g h C e l i t e , and the f i l t r a t e e v a p o r a t e d t o a r e d o i l . A d d i t i o n o f C^H^ (50 mL) and r a p i d s t i r r i n g f o r 16 h cause p r e c i p i t a t i o n o f a p a l e r e d s o l i d . The m i x t u r e was f i l t e r e d , and t h e s o l i d washed w i t h CgHg t o y i e l d a y e l l o w s o l i d ( i d e n t i f i e d as L R u 2 C l 3 ( d p p b ) 2 ( C H 5 C H ) 2 ] + P F 6 ~ , see n e x t s e c t i o n ) . The f i l t r a t e and washings were combined, c o n c e n t r a t e d t o 10 mL, and hexanes (40 mL) added t o cause p r e c i p i t a t i o n o f a red-brown s o l i d . T h i s was f i l t e r e d , washed w e l l w i t h hexanes and vacuum d r i e d . The p r o d u c t was r e c r y s t a l l i s e d from C H 2 C l 2 / h e x a n e s t o g i v e a maroon compound. Y i e l d : 0.18 g ( 3 5 $ ) ; C^gH^gClgP^R^ r e q u i r e s C : 53.00, H : 4.42, C l : 16.8$; found C : 52.9, H : 4.51 C l : 16.6$; v : 352 c m - 1 ( R u - C l ) ; m.p. : 238°C ( d e c ) , max 2.1.7.11 T r i - y - c h l o r o b i s [ a c e t o n i t r i l e ( l , 4 - d i p h e n y I p h o s p h i n o b u t a n e ) - r u t h e n i u m ( I I ) ] H e x a f l u o r o p h o s p h a t e , [ R u 2 C l 5 ( d p p b ) 2 ( C H 5 C N ) 2 ] + FF~ ( S e c t i o n 6.2.1.1) The complex i s i s o l a t e d from t h e r e a c t i o n o f R u 2 C l ^ ( d p p b ) 2 and AgPFg i n CH^CN, as d e s c r i b e d i n t h e p r e v i o u s s e c t i o n . The b e n z e n e - i n s o l u b l e y e l l o w s o l i d was r e c r y s t a l l i s e d from C H 2 C l 2 / h e x a n e s t o y i e l d a b r i g h t y e l l o w compound i d e n t i f i e d as [ R u 2 C l 5 ( d p p b ) 2 ( C H 3 C N ) 2 ] + P F 6 ~ . Y i e l d : 0.39 g ( 7 0 $ ) ; - 30 -C 6 0 H 6 2 N 2 C 1 3 F 6 P 5 R U 2 r e 1 u i r e s c : 51.89, H : 4.47, N : 2.02, C l : 7.68$; found C : 52.1, H : 4.5, N : 2.0, C l : 7.7$; v Q : 2315 ID. 9.X and 2280 c m - 1 ( c o o r d i n a t e d CH^CN), 840 and 568 c m - 1 ( n o n - c o o r d i n a t e d P F ^ - ) . 2.1.7.12 T r i s ( a c e t o n i t r i l e ) c h l o r o ( 1 , 4 - d i p h e n y l p h o s p h i n o b u t a n e ) r u t h e n i u m ( I I )  H e x a f l u o r o p h o s p h a t e , [RuCl(dppb)(CH^ClO^]" 1 " PFg" ( S e c t i o n 6.2.2.1) To R ^ C l ^ d p p b ^ a c e t o n e ) .acetone ( l . O g, 0.76 mmol) d i s s o l v e d i n CH^CN (50 mL) was added AgPFg (0.385 g, 1.52 mmol) i n CEjCN (10 mL). The s o l u t i o n was s t i r r e d f o r 0.5 h, f i l t e r e d t h r o u g h C e l i t e , and t h e f i l t r a t e c o n c e n t r a t e d t o 10 mL. A d d i t i o n o f d i e t h y l e t h e r (40 mL) w i t h r a p i d s t i r r i n g p r e c i p i t a t e s a p a l e y e l l o w p r o d u c t w h i c h was f i l t e r e d , washed w i t h d i e t h y l e t h e r and vacuum d r i e d . R e c r y s t a l l i s a t i o n from C H ^ C ^ / d i e t h y l e t h e r gave a y e l l o w c r y s t a l l i n e p r o d u c t . Y i e l d : 0.93 g ( 7 2 $ ) ; C_ .H_„N.,ClF,;P.,Ru.Ho0 r e q u i r e s C : 48.08, H : 4.60, N : 4.95, 34 3 I 3 6 3 d C l : 4.18$; found C : 48.4, H : 4.5, N : 4.9$, C l : 4.0$; V : 2268 c m - 1 ( c o o r d i n a t e d CH,CN), 840 and 572 c m - 1 max 3 ( n o n - c o o r d i n a t e d P F g ) and 285 cm ( R u - C l ) 2.1.7.13 ( A c e t o n e ) t r i - y - c h l o r o b i s [ ( 1 , 4 - d i p h e n y l p h o s p h i n o b u t a n e )  r u t h e n i u m ( I I ) ] H e x a f l u o r o p h o s p h a t e , [ R u 2 C l 3 ( d p p b ) 2 ( a c e t o n e ) ] P F g ( S e c t i o n 6.2.1.2) To R u 2 C l 4 ( d p p b ) 2 ( a c e t o n e ) . a c e t o n e ( l . O g, 0.76 mmol) d i s s o l v e d i n C H g C ^ (25 mL) and a c e t o n e (25 mL) was added AgPF^ - 31 -(0.194 g, 0.76 mmol) i n a c e t o n e (10 mL). The s o l u t i o n was s t i r r e d a t c a . 40°C f o r 2 h and t h e n f i l t e r e d t h r o u g h C e l i t e . The f i l t r a t e was c o n c e n t r a t e d t o 10 mL and d i e t h y l e t h e r (40 mL) added t o b r i n g about p r e c i p i t a t i o n o f an orange s o l i d . The m i x t u r e was f i l t e r e d and the s o l i d washed w i t h benzene (40 mL) and d i e t h y l e t h e r (30 mL). The s o l i d was r e c r y s t a l l i s e d from C H 2 C l 2 / a c e t o n e ( 1 : 1 , V:V) by s l o w p r e c i p i t a t i o n w i t h d i e t h y l e t h e r . Y i e l d : 0.69 g ( 6 6 $ ) ; C 5 9 H 6 2 0 C 1 3 F 6 P 5 R u 2 r e ( l u i r e s c : 51.93, H : 4.55, C l : 7.81$; found C : 51»7, H : 4.5, C l : 7.8$; v : 1670 c m - 1 ( c o o r d i n a t e d max a c e t o n e ) , 848 and 570 cm""1" ( n o n - c o o r d i n a t e d P F ^ - ) . 2.1.7.14 C h l o r o ( - t o l u e n e ) ( 1 , 4 - d i p h e n y l p h o s p h i n o b u t a n e ) r u t h e n i u m  ( I I ) H e x a f l u o r o p h o s p h a t e , [ R u C l ( d p p b ) ( r ^ - t o l u e n e ) ] + PFg ( S e c t i o n 6.2.2.2) To R u 2 C l 4 ( d p p b ) 2 ( a c e t o n e ) . a c e t o n e ( l . O g, 0.76 mmol) p a r t i a l l y d i s s o l v e d i n t o l u e n e (40 mL) and a c e t o n e (30 mL) was added AgPFg (0.385 g, 1.52 mmol) i n a c e t o n e (10 mL). The s o l u t i o n was s t i r r e d a t c a . 40°C f o r 2 h and t h e n f i l t e r e d t h r o u g h C e l i t e . The f i l t r a t e was c o n c e n t r a t e d t o 10 mL and d i e t h y l e t h e r (40 mL) added t o b r i n g about p r e c i p i t a t i o n o f a p a l e orange s o l i d . The m i x t u r e was f i l t e r e d and t h e s o l i d washed w i t h benzene (40 mL) and d i e t h y l e t h e r (30 mL). Slow r e c r y s t a l l i s a t i o n from C H 2 C l 2 / a c e t o n e (1:1, v:v) by p r e c i p i t a t i o n w i t h d i e t h y l e t h e r i n i t i a l l y a f f o r d s a y e l l o w s o l i d . F u r t h e r work-up o f t h e f i l t r a t e a f t e r s e p a r a t i o n o f t h e y e l l o w s o l i d y i e l d s an orange p r o d u c t i d e n t i f i e d as [ R u C l (dppb) ( a c e t o n e ) J - 32 -PFg~. The yellow compound was r e c r y s t a l l i s e d from acetone/diethyl ether to produce a dark yellow c r y s t a l l i n e material. Y i e l d : 0.47 g (40$); C 3 5H 5 6CLF 6P 3Ru requires C : 52.53, H : 4.50, C l : 4.55$; found C : 52.5, H : 4.7, Cl : 4.7$; v : 840 and 568 cm - 1 max (non-coordinated PFg") and 302 cm - 1 (Ru-Cl). 2.1.7.15 R e a c t i o n between [ R u C l ( d p p b ) ( C H ^ C N ) ^ ] 4 PF^" and H^, ( S e c t i o n 6.4) A DMA s o l u t i o n (25 mL) o f [ R u C l ( d p p b ) ( C H ^ C N ^ ] * PFg" (0.5 g, 0.60 mmol) and P r o t o n Sponge (0.3 g, 1.40 mmol) was s t i r r e d u nder 1 atm. tL, f o r 2 d. The orange s o l u t i o n was f i l t e r e d t o remove an o f f - w h i t e m a t e r i a l . The f i l t r a t e was e v a p o r a t e d under vacuum t o an o i l w h i c h was d i s s o l v e d i n a c e t o n e (20 mL) t o produce an orange s o l u t i o n w h i c h s l o w l y t u r n e d y e l l o w . A d d i t i o n o f d i e t h y l e t h e r (40 mL) p r e c i p i t a t e d a y e l l o w s o l i d w h i c h was f i l t e r e d , washed w i t h d i e t h y l e t h e r and vacuum d r i e d . E x t r a c t i o n o f t h e y e l l o w s o l i d w i t h C I ^ C ^ (50 mL) y i e l d s a w h i t e i n s o l u b l e m a t e r i a l and a y e l l o w s o l u t i o n . The m i x t u r e was f i l t e r e d , the f i l t r a t e c o n c e n t r a t e d t o 10 mL and d i e t h y l e t h e r added t o i n d u c e p r e c i p i t a t i o n o f a y e l l o w s o l i d . C h a r a c t e r i s a t i o n o f t h e i n i t i a l o f f - w h i t e s o l i d and f i n a l y e l l o w s o l i d i s p r e s e n t e d i n S e c t i o n 6.4. The w h i t e C l ^ C ^ - i n s o l u b l e m a t e r i a l was i d e n t i f i e d as P S H +PF, : C, .H., 0N„F P r e q u i r e s o 14 i y 2 o C : 46.67, H : 5.28, N : 7.77$; found C : 46.4, H :" 5.2, N : 7.7$; 6(CD 3CN): 3.15 ( s , 12H, -M-CH^), 7.8 (m, 6H, a r o m a t i c ) , 18.70 (s I H , p r o t o n ) . - 3 3 -2.2 I n s t r u m e n t a t i o n I n f r a r e d s p e c t r a were r e c o r d e d on a P e r k i n E l m e r 598 g r a t i n g s p e c t r o p h o t o m e t e r o r a N i c o l e t 5DX FT-IE i n s t r u m e n t . S p e c t r a were o b t a i n e d as N u j o l m u l l s between C s l p l a t e s , and c a l i b r a t e d w i t h the 1601 cm ^ peak o f p o l y s t y r e n e . N e a r - i n f r a r e d s p e c t r a were r e c o r d e d on a Cary 17D s p e c t r o p h o t o m e t e r , and v i s i b l e s p e c t r a were r e c o r d e d on P e r k i n E l m e r 553A o r Cary 17D s p e c t r o p h o t o m e t e r s . A n a e r o b i c s p e c t r a l c e l l s , as shown s c h e m a t i c a l l y i n F i g u r e 2.1, w i t h q u a r t z c e l l s o f 1.0 and 0.1 cm p a t h l e n g t h were used, and were t h e r m o s t a t e d when n e c e s s a r y . I n most c a s e s the weighed sample was p l a c e d i n t h e q u a r t z c e l l w h i l s t t h e s o l v e n t was deoxygenated by a f r e e z e and thaw s t a t i c vacuum t e c h n i q u e i n t h e s i d e a r m f l a s k p r i o r t o m i x i n g . Gas u p t a k e s f o r s t o i c h i o m e t r i c , k i n e t i c o r h y d r o g e n a t i o n p u r p o s e s were measured on t h e c o n s t a n t p r e s s u r e g a s - u p t a k e a p p a r a t u s d e s c r i b e d e l s e w h e r e ^ . ^"H-n.m.r. s p e c t r a were r e c o r d e d on B r u k e r WP80, V a r i a n XL100 o r B r u k e r WH400 s p e c t r o m e t e r s w i t h t e t r a m e t h y l s i l a n e (TMS) a t 60.0 as 31 1 s t a n d a r d . P{ H}-n.m.r. s p e c t r a were r e c o r d e d on V a r i a n XL100 (40.5 MHz f o r 5 1 P ) o r B r u k e r WP80 (32.4 MHz f o r 3 1 P ) 31 1 s p e c t r o m e t e r s . The s t a n d a r d f o r P{ H}-n.m.r. s p e c t r a was t h e s i g n a l f o r t r i p h e n y l p h o s p h i n e a t -6 ppm, t h i s b e i n g r e l a t i v e t o 85$ 71 H^PO^ . D o w n f i e l d s h i f t s a r e t a k e n as p o s i t i v e and a r e r e p o r t e d r e l a t i v e t o 85$ H^PO^. A l l s p e c t r o m e t e r s were o p e r a t e d i n t h e F o u r i e r t r a n s f o r m mode and were eq u i p p e d w i t h v a r i a b l e t e m p e r a t u r e a t t a c h m e n t s . - 34 -Quartz Cell F i g u r e 2.1 Sc h e m a t i c r e p r e s e n t a t i o n o f an a n a e r o b i c s p e c t r a l c e l l . C o n d u c t i v i t y measurements were made a t 25°C under a n a e r o b i c c o n d i t i o n s u s i n g a Thomas S e r f a s s c o n d u c t i v i t y b r i d g e and c e l l . M e l t i n g p o i n t s were r e c o r d e d u s i n g a F i s h e r Johns M e l t i n g P o i n t a p p a r a t u s and a r e u n c o r r e c t e d . E l e m e n t a l a n a l y s e s were p e r f o r m e d by Mr. P. Borda o f t h i s d epartment. ^ 2.3 I s o l a t i o n o f Hydrogenated A l k e n e P r o d u c t s F o r s o l i d p r o d u c t s r e s u l t i n g from t h e h y d r o g e n a t i o n e x p e r i m e n t s , the s o l u t i o n m i x t u r e was e v a p o r a t e d t o a v i s c o u s o i l from w h i c h t h e - 3 5 -products were separated as follows (alkene substrates are l i s t e d ) : (a) Itaconic, c i t r a c o n i c and atropic acids: The residue was dissolved i n 2 5 mL of 5 $ NaOH solut i o n , s t i r r e d b r i e f l y and f i l t e r e d through C e l i t e to give a colourless f i l t r a t e . The f i l t r a t e was a c i d i f i e d with 1 0 $ H C 1 and extracted twice with d i e t h y l ether ( 2 5 mL). The ethereal extracts were dried with anhydrous MgSO^, f i l t e r e d and concentrated to afford the saturated acid. (b) N-a-acetamido-acrylic and -cinnamic acids: The residue was dissolved i n 2 0 mL of C H 2 C I 2 and s t i r r e d u n t i l an off-white compound separated. This was f i l t e r e d and washed well with CHgClg to give a pure white product. Further p u r i f i c a t i o n , i f necessary, was by d i s s o l u t i o n i n water ( 5 mL) and extraction with 2 0 mL CHCl^. The aqueous layer was then freeze-dried to recover the product. (c) Acrylamide: The residue was heated to 1 0 0 ° C under vacuum when white c r y s t a l s of propionamide sublimed. The l i q u i d products obtained from the hydrogenation of styrene and hex-l-ene were separated from the so l u t i o n mixture by d i s t i l l a t i o n . The products so obtained were i d e n t i f i e d by t h e i r ^"H-n.m.r. spectra, and t h e i r % p u r i t y determined. For the hydrogenated p r o c h i r a l alkenes, the products were used also f o r the determination of t h e i r o p t i c a l r o t a t i o n i n the appropriate solvents (Section 4 . 4 ) . 2 . 4 Optical Rotation Measurements A l l o p t i c a l r o t a t i o n values were measured on a Perkin Elmer 1 4 1 polarimeter at room temperature using a one decimeter path length c e l l . - 36 -The r o t a t i o n s were measured at the sodium-D l i n e ( 5 8 9 nm), and the s p e c i f i c r o t a t i o n c a l c u l a t e d using the equation: [a]J = lOO.a ~ T 7 ^ ~ ( 2 . 1 ) Where [a]p = s p e c i f i c r o t a t i o n at temperature T measured at the sodium-D l i n e . a = observed o p t i c a l r o t a t i o n 1 = path length of c e l l i n decimeters C = concentration of s o l u t i o n i n g / 1 0 0 mL s o l v e n t . The percentage enantiomeric excess (% e.e.) of the hydrogenated product was determined according to the equation: e.e, [ a l ^ of sample , N = D x 1 0 0 ( 2 . 2 ) [ a ] ^ of pure enantiomer - 3 7 CHAPTER III A STUDY OF CHLORO-BRIDGED DIRUTHENIUM(II, III) COMPLEXES  CONTAINING CHELATING CHIRAL AND NONCHIRAL DITERTIARY PHOSHINE LIGANDS 3 . 1 General Introduction Studies on ruthenium complexes containing chelating diphoshine 7 2 ligands were i n i t i a t e d by Chatt and Hayter with the synthesis of an extensive series of complexes of general formula RuX2(P-P)2 and RuXYCP-P^, where X and Y are anionic ligands such as halides, pseudohalides, hydrides, or a-bonded a l k y l and a r y l groups, and P-P represents a chelating diphosphine. Other workers u t i l i s i n g a v a r i e t y of diphosphines have since prepared coordinatively unsaturated 7 3 7 4 7 5 7 7 7 7 complexes, ' as well as carbonyl and n i t r o s y l derivatives Considering the extensive l i t e r a t u r e on the chemistry, properties and c a t a l y t i c a p p lications of t e r t i a r y phosphine complexes of ruthenium, i t i s s u r p r i s i n g that the chemistry of analogous diphosphine complexes i s r e l a t i v e l y undeveloped. A possible explanation i s the inherent s t a b i l i t y associated with having two diphosphines per ruthenium, while coordinatively unsaturated complexes containing only one diphosphine have not been reported. - 38 -T h i s c h a p t e r p r e s e n t s a s t u d y o f m i x e d - v a l e n c e complexes o f g e n e r a l f o r m u l a R u 2 C l ^ ( P - P ) 2 > where P-P r e p r e s e n t s the c h i r a l d i p h o s p h i n e s , c h i r a p h o s ( I ) , norphos ( I I ) , and d i o p ( I I I ) , and d i p h o s p h i n e s o f the t y p e P h 2 P ( C H 2 ) n P P h 2 where n=4 (dppb) and n=3 ( d p p p ) . A d e s c r i p t i o n o f t h e i r p r e p a r a t i o n , c h a r a c t e r i s a t i o n , and i n I E r e a c t i o n s w i t h hydrogen i s p r e s e n t e d . To p r e v e n t r e p e t i t i o n i n t h e e n s u i n g t e x t P-P w i l l r e p r e s e n t a l l o f the p h o s p h i n e s above u n l e s s s p e c i f i c a l l y d e s i g n a t e d . 3.2 P r e p a r a t i o n o f T r i - u - c h l o r o - d i c h l o r o b i s ( b i d e n t a t e p h o s p h i n e ) -d i r u t h e n i u m ( l l , I I I ) , R u 0 C l c ( P - P ) _ S e v e r a l methods were t r i e d i n an a t t e m p t t o produce a r u t h e n i u m complex c o n t a i n i n g o n l y one c h e l a t i n g d i p h o s p h i n e . These i n c l u d e d the r e a c t i o n s o u t l i n e d i n e q u a t i o n s 3.1 - 3.5 ( r e f e r e n c e s r e f e r r i n g t o R u C l 5 x H 2 0 + P-P • R u C l ^ P - P ) (3.1) 7°, -RuCl ( P - P ) P P h , + HBF. — ^ 3 4 • R u C l 2 ( P - P ) + HPPh + B F 4 _ (3.2) [ R u C l 2 ( c o d ) ] 8 0 + P-P • R u C l 2 ( c o d ) ( P - P ) (3.3) 81 R u C l 2 ( n b d ) ( p - t o l u i d i n e ) 2 + P-P R u C l 2 ( n b d ) ( P - P ) (3.4) R u C l 3 ( P P h 5 ) 2 ( D M A ) . D M A + P-P • RuCl,(P-P)(DMA) 3 (3.5) - 3 9 -l i t e r a t u r e methods used f o r the preparation of s t a r t i n g m a terials). The products given i n these reaction schemes are those that were expected to be produced, but none of these complexes were suc c e s s f u l l y i s o l a t e d . The reaction involving phosphine ligand exchange at R u ( l l l ) (equation 3 . 5 ) did, however, produce binuclear complexes of general formula R u 2 C l 5 ( P - P ) 2 . Refluxing RuCl.j(PPh 3) 2(DMA) .DMA with one equivalent of ei t h e r dppb or diop i n hexanes under anaerobic conditions led to the exchange of the triphenylphosphine ligands by the bidentate phosphine. This exchange was accompanied by concomitant dimerisation and reduction to produce i n high y i e l d the insoluble complexes Ru0Cl,-(P-P)„, d o d where P-P = dppb or diop. The exchange was confirmed by i s o l a t i n g the free PPh., from the f i l t r a t e a f t e r removal of the insoluble red o product. In both cases only PPh^ was detected by H-n.m.r. This preparative procedure was unsuccessful i n the case of a l l other P-P ligands as evidenced by the "'"H-n.m.r. of the free phosphine. However, using the tolylphosphine d e r i v a t i v e , RuCl 3(P(p-tolyl).j) 2(DMA).DMA as precursor, afforded the analogous Ru 2Cl^(P-P) 2 complexes f o r the remaining diphosphines with the exception of dppe. P u l l preparative d e t a i l s are given i n sections 2 . 1 . 7 . 3 and 2 . 1 . 7 . 4 The method of ligand exchange has been used previously to prepare the s e r i e s of complexes trans-RuHCl(P-P) 2 > where P-P = dppm, dppe, dppp, dppb, and diop, from RuHCl(PPh 3) 3.DMA; and the complexes R u 2 C l 4 ( d i o p ) 5 and RuCl 2(PPh ) (diop) from RuCl 2(PPh ) . These exchanges - 40 -r e s u l t i n incorporation of more than one diphosphine or one diphosphine with retention of a monodentate phosphine. To prepare mono(diphosphine) complexes therefore necessitated the choice of a more appropriate ruthenium precursor. The choice of RuCl^P^DMA) .DMA, where P = PPh^ or P ( p - t o l y l ) 3 > seemed appropriate i n that due to the li m i t e d number of coordination s i t e s a v a i l a b l e the exchange would simply produce RuCl 5(P-P)(DMA). The mixed-valence complexes Ru 2Cl,-(P-P) 2 were i n fact the i s o l a b l e products, and the nature of the exchange was determined by the monodentate phosphine. Both dppb and diop form seven-membered rings upon coordination and the siz e of t h i s r i n g r e l a t i v e to those formed with the other diphosphines appears to enhance the displacement of PPh^. In the case of dppp which forms a six-membered ri n g , chiraphos and norphos which form five-membered rings, the successful exchange with the tolylphosphine i s presumably due to 82 t h i s monodentate phosphine being s l i g h t l y more l a b i l e than PPh^ Int e r e s t i n g l y , the exchange i s accompanied by reduction at the metal, presumably by the monodentate phosphine p r i o r to dimer formation, although formation of a R u 2 ^ ' ^ * complex and subsequent one ele c t r o n reduction cannot be ruled out. Reduction by phosphines i s not uncommon} however, a co-reducing agent such as water i s required i n the formation of RuCl^(FTh^)^. In the present synthesis, however, reduction ensues even under anaerobic conditions and i n d i s t i l l e d solvent with the p a r t i c i p a t i o n of the l i b e r a t e d phosphine. The 31 1 P{ H}-n.m.r. of the free phosphine does show the presence of - 4 1 -phosphine oxide i n the r a t i o 1 POCp-tolyl)^ : 6 P ( p - t o l y l ) 3 which i s close to that calculated ( 1 : 7 ) f o r the reduction of 5 0 $ of the Ru A p l a u s i b l e mechanism to explain the formation of the complexes Ru0Cl,- (P-P)„ i s shown i n Scheme 3 - 1 . ^ 5 2 I I I RuCI3P2 P= monodentate phosphine p—P = bidentate + P-P c0> Cl<" | ^P -2P Reduction i  RuCI2(P-P) RuCI3(P-P) Ru2CI5(P-P)2 C , ' - l ^ P ) Dimerisation Ru2CI6(P-P)2 Reduction Ru2CI5(P-P)2 Scheme 3 - 1 Support f o r the route i n v o l v i n g reduction p r i o r to "dimerisation" comes from the i s o l a t i o n of small amounts ( < 1 0 $ of the t o t a l y i e l d ) of Ru 1 1 species. Work-up of the f i l t r a t e from the r e c r y s t a l l i s a t i o n r e s u l t s i n more of the o r i g i n a l product contaminated with, i n the case of P-P=chiraphos, yellow c r y s t a l s of trans-RuCl 0(chiraphos)„ and, - 42 -f o r P-P=dppb, g r e e n c r y s t a l s o f [ R u C l ^ d p p b ) . ^ These p r o d u c t s were c h a r a c t e r i s e d by: X - r a y a n a l y s i s f o r t h e c h i r a p h o s complex, and by e l e m e n t a l a n a l y s i s (Cg^Hg^Cl^PgRUp^ r e q u i r e s C:62.15, H:5.18, C l : 8 . 7 3 $ ; found C:61.9, H:5.0, C l : 8 . 5 $ ) and v i s i b l e s p e c t r u m f o r t he 73 known dppb complex The exchange o f dppe w i t h e i t h e r o f the RuCl^P^DMA) .DMA (P=PPh 3 > P ( p - t o l y l ) 3 ) p r e c u r s o r s was u n s u c c e s s f u l , and the o n l y p r o d u c t i s o l a t e d i n s i g n i f i c a n t y i e l d was t r a n s - R u C l ^ ( d p p e ) ^ . The re a s o n f o r t h i s i s not o b v i o u s s i n c e dppe i s a n a l o g o u s t o c h i r a p h o s and norphos i n t h a t a five-membered r i n g i s formed upon c o o r d i n a t i o n . 3.3 X-Ray S t r u c t u r e D e t e r m i n a t i o n o f T r i - u - c h l o r o - d i c h l o r o - b i s ( c h i r a p h o s ) d i r u t h e n i u m ( I I , I I I ) , R u 2 C l ^ ( c h i r a p h o s ) 2 The complexes, Ru 2Cl^(P-P) 2»after r e c r y s t a l l i s a t i o n were u s u a l l y o b t a i n e d as r e d powders; t h e e x c e p t i o n was the c h i r a p h o s d e r i v a t i v e w h i c h i n v a r i a b l y formed d a r k r e d c r y s t a l s . A s i n g l e c r y s t a l X - r a y d i f f r a c t i o n s t u d y c a r r i e d out by S. J . R e t t i g o f t h i s department r e v e a l e d t h e complex t o be the h i g h l y s y m m e t r i c a l y ^ - c h l o r o - b r i d g e d complex shown i n F i g u r e 3.1. The c o o r d i n a t i o n sphere about each r u t h e n i u m i s o c t a h e d r a l , and the m e t a l t o l i g a n d bond d i s t a n c e s and a n g l e s a t b o t h c e n t r e s a r e e s s e n t i a l l y i d e n t i c a l • ( T a b l e 3.1). Two o f the b r i d g i n g c h l o r o - l i g a n d s ( C l ( 2 ) and Cl(3)) a r e t r a n s - t o phosphorus atoms and have l o n g e r R u - Cl d i s t a n c e s ( a v e r a g e 2.49A) compared t o t h o s e f o r the t h i r d b r i d g i n g c h l o r o - l i g a n d ( a v e r a g e 2.36A) w h i c h i s t r a n s - t o the two t e r m i n a l c h l o r o - l i g a n d s , due t o the s t r o n g e r t r a n s - 44 -T a b l e 3.1 S e l e c t e d Bond Lengths and Bond A n g l e s f o r Ru„Cl c; ( c h i r a p h o s ) 0 * Bond L e n g t h (A) A n g l e Degrees E u ( l ) - C l ( l ) 2.365(1) - ci(i; R u ( l ) - C l ( 2 ) 80.24 (5) R u ( l ) - C l ( 2 ) 2.476(1) ci(i ; - R u ( l ) - C l ( 3 ) 78.90 (5) R u ( l ) - C l ( 3 ) 2.527(1) ci(i; - R u ( l ) - C l ( 4 ) 169.76 (5) R u ( l ) - C l ( 4 ) 2.370(1) ci(i ; - R u ( l ) - P(D 102.93 (5) R u ( l ) - P(D 2.266(1) ci(i; - R u ( l ) - P ( 2 ) 94.80 (5) R u ( l ) - P ( 2 ) 2.267(1) 01(2; ) - R u ( l ) - C l ( 3 ) 81.53 (5) Ru(2) - C l ( l ) 2.351(1) 01(2; ) - R u ( l ) - C l ( 4 ) 92.81 (5) Ru(2) - C l ( 2 ) 2.477(1) 01(2; ) - R u ( l ) - P(D 176.48 (5) Ru(2) - C l ( 3 ) 2.483(1) C l ( 2 , ) - R u ( l ) - P ( 2 ) 96.64 (5) Ru(2) - C l ( 5 ) 2.358(1) ci(3: ) - R u ( l ) - C l ( 4 ) 92.71 (6) Ru(2) - P ( 3 ) 2.287(1) C l ( 3 , ) - R u ( l ) - P(D 97.49 (5) Ru(2) - P ( 4 ) 2.278(1) C l ( 3 , ) - R u ( l ) - P ( 2 ) 173.64 (5) R u ( l ) - Ru(2) 3.251(1) C l ( 4 ) - R u ( l ) - P(D 83.84 (5) C l ( 4 , ) - R u ( l ) - P ( 2 ) 93.46 (6) P(D - R u ( l ) - P ( 2 ) 84.69 (5) A c c o r d i n g t o numbering scheme i n F i g u r e 3.1. E s t i m a t e d s t a n d a r d d e v i a t i o n s g i v e n i n p a r e n t h e s e s . - 45 -influence of the phosphine ligands. This shortening of the Ru-Cl(l) bond length r e s u l t s i n a wider Ru-Cl(l)-Ru bond angle compared to the other two Ru-Cl-Ru angles. Two regular octahedra sharing one face have 1/2 a bridging angle , where <J) i s given by cos(<()/2) = (2/3) hence <j> = 70.5°. In t h i s complex the average bridging angle i s 83.4°, and hence the ruthenium atoms are further apart than they would be i n a regular c o f a c i a l bioctahedron. The distance between the ruthenium centres (3.25A) i s well outside the range (2.28 - 2.95A) usually found f o r a Ru-Ru b o n d 8 3 " 8 9 . The Ru-P lengths (average 2.28A) are comparable to those found i n ruthenium complexes containing t e r t i a r y phosphmes An analogous mixed-valence complex of ruthenium(ll,111) containing 91 monodentate phosphines has been reported previously. Nicholson i s o l a t e d the complex Ru^Cl^(P(n-butyl)^)^, from a concentrated ethanolic s o l u t i o n of RuCl^ and tri-n-butylphosphine. The 92 structure was elucidated as; 3 \ X ""'/,„ ^ 3 R^P MIHIIMIIH R u ^ — C l Wmmm^L R U ,, I 11 Cl Cl r C l ^  ^ PR 5 Unlike the chiraphos complex, i t i s unsymmetrical i n that one of the octahedra has been rotated by ±120° about the Ru-Ru vector. Even so, the two octahedra are very s i m i l a r to one another, and as f o r the chiraphos complex i t i s not possible to assign formal valence states to the ruthenium atoms on a purely c r y s t a l l o g r a p h i c basis. - 46 -3.4 M a g n e t i c S u s c e p t i b i l i t y Measurements The m a g n e tic s u s c e p t i b i l i t i e s were d e t e r m i n e d by Evans' 93 method . M e t h y l e n e c h l o r i d e s o l u t i o n s c o n t a i n i n g a p p r o x i m a t e l y 2% t - b u t a n o l were used a t ambient t e m p e r a t u r e s . V a l u e s o f V e f f a r e g i v e n below and a r e c o n s i s t e n t w i t h one u n p a i r e d e l e c t r o n p e r m o l e c u l e . Due t o l i m i t e d s o l u b i l i t y o f the dppb and dppp complexes, the p a r a m a g n e t i c s h i f t s f o r t h e s e systems c o u l d n o t be measured a c c u r a t e l y . S o l u t i o n y e f f , B.M. R u 2 C l 5 ( c h i r a p h o s ) 2 1.95 R u 2 C l 5 ( n o r p h o s ) 2 2.01 R u 2 C l 5 ( d i o p ) 2 1.78 3.5 E l e c t r o n i c S p e c t r a l .Data 3.5.1 N e a r - I n f r a r e d S p e c t r a I n t e r v a l e n c e charge t r a n s f e r t r a n s i t i o n s a r e a c h a r a c t e r i s t i c f e a t u r e o f m i x e d - v a l e n c e complexes, t h e s e t r a n s i t i o n s o f t e n o c c u r r i n g i n the low e nergy n e a r - i n f r a r e d r e g i o n o f t h e s p e c t r u m . The s p e c t r a i n t h i s r e g i o n f o r R u 2 C l ( - ( c h i r a p h o s ) , , i n CDCl^ and C C l ^ under a n a e r o b i c c o n d i t i o n s a r e p r e s e n t e d i n F i g u r e 3.2, and the i n s e t shows the h i g h energy a b s o r p t i o n i n CDCl^ and DMA on an expanded s c a l e . U n f o r t u n a t e l y the complete a b s o r p t i o n s p e c t r u m a t l o n g e r w a v e l e n g t h s (>2600 nm) c o u l d n o t be s t u d i e d because o f t h e l i m i t a t i o n s o f the s p e c t r o p h o t o m e t e r . V a l u e s o f X , v , e, and Av, /„ r max' max ' 1/2 were o b t a i n e d i n a v a r i e t y o f s o l v e n t s and t h e r e s u l t s a r e summarised i n - 47 -Figure 3.2 Near-infrared spectra of Ik^Cl^Cchiraphos^ in CDC1, and CC1.. 3 4 Inset shows high energy absorption obtained in CHC1, and DMA. - 48 -T a b l e 3.2. S p e c t r a were m a i n l y r e c o r d e d u s i n g 0.1 cm matched c e l l s , and d e u t e r a t e d s o l v e n t s were used whenever p o s s i b l e t o m i n i m i s e the i n t e r f e r e n c e o f s o l v e n t i n f r a r e d o v e r t o n e a b s o r p t i o n s . The weaker a b s o r p t i o n a t ca_. 1100 nm was s t u d i e d i n d e p e n d e n t l y so t h a t more a c c u r a t e d a t a c o u l d be o b t a i n e d ; t h e s h o r t e r w a v e l e n g t h a l l o w e d f o r the use o f n o n - d e u t e r a t e d s o l v e n t s i n matched 1.0 cm c e l l s . The n e a r - i . r . a b s o r p t i o n s o f R u ^ C l ^ C c h i r a p h o s ) ^ i n CDCl^ obeyed B e e r ' s law -3 -2 o v e r the c o n c e n t r a t i o n range 1.5 x 10 t o 1.5 x 10 M. The s p e c t r a i n DMS0-d, and CD_N0„ were s i m i l a r , but were found t o d e c r e a s e i n o 3 2 i n t e n s i t y w i t h time u n t i l t h e r e was no a b s o r p t i o n i n t h i s r e g i o n . The t i m e s t a k e n f o r complete d i s a p p e a r a n c e o f the a b s o r p t i o n s were a p p r o x i m a t e l y l h and 5h f o r DMSO-d^ and CD^NO^ s o l u t i o n s , r e s p e c t i v e l y . I n DMA t h e r e was a 10$ d e c r e a s e i n t h e a b s o r p t i o n a t 2340 nm o v e r 24h, w h i l s t i n CD^CN t h e r e was no a b s o r p t i o n o b s e r v e d , i m p l y i n g an i n s t a n t a n e o u s l o s s o f a b s o r p t i o n upon d i s s o l u t i o n . The s o l i d s t a t e s p e c t r u m measured a f t e r e v a p o r a t i o n o f t h e CD^NO^ s o l v e n t f o l l o w i n g complete l o s s o f the n e a r - i . r . a b s o r p t i o n bands d i d not show r e g e n e r a t i o n o f t h e s e a b s o r p t i o n s . E v a p o r a t i o n o f a C C l ^ s o l u t i o n produced s o l i d whose s p e c t r u m was i d e n t i c a l t o t h a t o b s e r v e d i n s o l u t i o n , and r e d i s s o l v i n g the sample i n CDCl^ y i e l d e d t h e s p e c t r u m o r i g i n a l l y found i n t h i s s o l v e n t . The CDC1, s o l u t i o n s p e c t r a f o r Ru 0Cl c(P-P)„, (P-P = n o r p h o s , 3 d 5 d dppp and dppb) a r e shown i n F i g u r e 3.3. The s p e c t r u m f o r the d i o p a n a l o g u e i s e s s e n t i a l l y i d e n t i c a l t o t h a t found f o r t h e dppb complex. W h i l s t t h e s e complexes were not s t u d i e d as e x t e n s i v e l y as the - 49 -T a b l e 3.2 N e a r - I n f r a r e d . S p e c t r a l Data f o r R u ^ C l , - ( c h i r a p h o s ) ^ S o l v e n t ( l / n 2 - l / D ) a X (v ) e b Av n , 0 .cm" 1 s max max^ ^ ^ 1/2 nm±10 (cm~ ) M~ cm" Found C a l c , CD 5N0 2 C 4 H 6 0 3 d DMA DMS0-d 6 CDCl^ ( C H 5 ) 2 C 0 C 6 H 5 C H 3 e cc i 4 e 0.498 2340 (4270) 5530 1660 3140 1150 (8700) 490 5030 4480 0.481 2340 (4270) 5510 1650 3140 1150 (8700) 530 3600 4480 0.457 2340 (4270) 5460 1650 3140 1120 (8930) 510 5380 4540 0.438 2350 (4260) 1190 (8400) 0.266 2350 (4260) 5540 1630 3140 1090 (9170) 660 4410 4600 0.493 1150 (8700) 550 5180 4480 0.381 980 (10200) 660 4410 4854 0.027 2050 (4880) 1100 880 (11360) 2060 3580 5120 0.018 2050 (4880) 1030 880 (11360) 2170 3320 5120 ( a ) V a l u e s c a l c u l a t e d u s i n g i n d i c e s o f r e f r a c t i o n (n) and b u l k d i e l e c t r i c c o n s t a n t s ( D s ) g i v e n i n R e f . 94. (b) M o l a r e x t i n c t i o n c o e f f i c i e n t s i n CD 3N0 2 and DMA c a l c u l a t e d f o r i n i t i a l a b sorbance o b s e r v e d . No v a l u e i s g i v e n f o r DMSO-dg due t o a p p r e c i a b l e l o s s o f a b s o r p t i o n even f o r i n i t i a l s p e c t r a . ( c ) Av ] _ / 2 i s t h e band w i d t h a t h a l f - h e i g h t . D e t e r mined by-assuming a G u a s s i a n band shape f o r t h e h i g h energy s l o p e , and c a l c u l a t e d u s i n g e q u a t i o n 3.6 ( s e e t e x t ) . (d) P r o p y l e n e c a r b o n a t e . (e) S i n c e t h e low energy a b s o r p t i o n i s so br o a d t h e v a l u e s g i v e n f o r X m a x a r e f o r a s e l e c t e d w a v e l e n g t h ; v a l u e f o r A v x / 2 c o u l d n o t be c a l c u l a t e d a c c u r a t e l y . - 50 -i—,—,—|—|—|—|—|—|—j—,—|—|—|—|—|—|—|—|—j—| ' 1000 2000 Wavelength , nm Figure 3 . 3 Near-infrared spectra of R u 2 C l 5 ( P - P ) 2 , P-P=norphos, dppp and dppb i n CDCl^. - 51 -c h i r a p h o s a n a l o g u e , the s p e c t r a were r e c o r d e d i n o t h e r s o l v e n t s and the d a t a a r e g i v e n i n T a b l e 3.3 The s o l i d s t a t e s p e c t r a (KBr p e l l e t s ) o f t h e c h i r a p h o s and dppb complexes showed t h e same a b s o r p t i o n s a t low energy as were found i n s o l u t i o n . The r e d u c t i o n o f DMA s o l u t i o n s o f a l l t h e complexes w i t h t o produce the R u ^ ' " ^ congeners (see S e c t i o n 3.7) r e s u l t e d i n a l o s s o f a b s o r p t i o n i n the n e a r - i . r . r e g i o n . 3.5.2 V i s i b l e S p e c t r a The v i s i b l e s p e c t r a o f the R u 2 C i ^ ( P - P ) 2 complexes a r e a l l s i m i l a r i n DMA o r ' C D C l ^ , a l t h o u g h some v a r i a t i o n s i n i n t e n s i t i e s and a b s o r p t i o n p o s i t i o n s a r e o b s e r v e d w i t h c h a n g i n g p h o s p h i n e , as shown i n F i g u r e 3.4 f o r P-P = n o r p h o s , dppp and dppb. The spec t r u m f o r P-P = d i o p i s the same as t h a t f o r the dppb complex. The d r a s t i c d i f f e r e n c e s i n t he n e a r - i . r . o b s e r v e d f o r R u 2 C l ^ ( c h i r a p h o s ) 2 i n t o l u e n e ( o r C C l ^ ) compared t o CDCl^ a r e accompanied by o n l y s l i g h t changes i n the v i s i b l e r e g i o n . The spec t r u m i n t o l u e n e o r C C l ^ r e s e m b l e s t h a t o f the dppb a n a l o g u e i n CDC l ^ w i t h a s h o u l d e r a t 450 nm i n s t e a d o f a maximum a t 420 nm. The f i n a l s p e c t r a o b t a i n e d i n b o t h DMSO-dg and CD 3N0 2 a r e the same, but a r e s u b s t a n t i a l l y d i f f e r e n t from t h a t measured i n CDCl^ as i s t h e s p e c t r u m i n CH^CN. The s p e c t r a o f R u 2 C l j - ( c h i r a p h o s ) 2 i n CDCl^ and C C l ^ a r e p r e s e n t e d i n F i g u r e 3.5, and t h o s e o b t a i n e d i n CD_N0„ and CH-.CN a r e p r e s e n t e d i n 3 2 3 F i g u r e 3.6. F r e s h l y p r e p a r e d DMA s o l u t i o n s o f Ru 2Cl,-(chiraphos),-. - 52 -T a b l e 3.3 N e a r - I n f r a r e d S p e c t r a l Data f o r the Complexes Ru^Clr- ( P - P ) , Complexes , P-P = dppb, d i o p , dppp o r norphos P-P S o l v e n t X max nm+lC ( v ) max' 1 ( c m - 1 ) b e M cm A v l / 2 Obser. -1 ,cm C a l c . dppb CDC1 3 2050 (4880) 1180 970 (10310) 890 3040 4880 DMA 2050 (4880) 850 970 (10310) 540 3040 4880 cci 4 2050 (4880) 1290 970 (10310) 1080 3100 4880 d i o p C D C I 3 2050 (4880) 1410 950 (10530) 1030 2940 4932 DMA 2050 (4880) 1140 950 (10530) 784 2940 4932 dppp C D C I 3 2060 (4850) 2070 3500 3350 960 (10420) 1590 3650 4910 norphos C D C I 3 2350 (4260) 3240 2220 3135 950 (10530) 2820 4390 4932 (a) [ R u 1 1 ' 1 1 1 ] = 2.0 (± 0.2) x 1 0 _ 5 M i n each case e x c e p t f o r P-P = dppb i n C C l ^ : [ R u ^ 1 ' 1 1 1 ] = 4.15 x 1 0 - 4 M , and P-P = dppp: [ R u 1 1 ' 1 1 1 ] = 5.85 x 10" 4M. (b) E x t i n c t i o n c o e f f i c i e n t p e r [ R u * 1 , 1 1 1 ] ; due t o broad n e s s o f low energy band, t h e g i v e n v a l u e s a r e c a l c u l a t e d f o r a p a r t i c u l a r w a v e l e n g t h . ( c ) C a l c u l a t e d i n a c c o r d a n c e w i t h e q u a t i o n 3.6, and assuming a G u a s s i a n band shape f o r the h i g h energy s l o p e ( s e e t e x t ) . - 5 3 -300 400 500 600 700 Wavelength , nm Figure 3 . 4 V i s i b l e spectra of R u 2 C l 5 ( P - P ) 2 , P-P=norphos, dppp and dppb i n CDCl^ ([Ru 2] = 2 . 0 ( ± 0 . 2 ) x 1 0 ~ 3 M). - 5 4 -400 700 500 600 Wavelength , nm Figure 3 . 5 V i s i b l e spectra of Ru 2Cl^(chiraphos),, i n CDCl^ and C C 1 , 50 E o 4-0 30 C O O x CO 2'0-\ 400 700 500 600 Wavelength , nm Figure 3 . 6 V i s i b l e spectra of Ru 2Cl,-(chiraphos) 2 i n CD^NOg and CH^CN a f t e r complete loss of absorption i n the near-infrared region. - 55 -obey Beer's law, but on standing s l i g h t changes i n the spectra are observed. The dppb analogue does not obey Beer's law; the ext i n c t i o n c o e f f i c i e n t f o r the absorption at 370 nm increases and those at 520 and 450 nm decrease with d i l u t i o n . 3.5.3 Discussion of E l e c t r o n i c Spectral Data Intervalence transfer ( i . T . ) bands of mixed-valence complexes r e s u l t from the electron transfer process: + + M/V^/\M < >M y ^ y \ y \ M + where M i s a metal centre, M i t s one-electron oxidation product, and / v \ denotes bridging ligands. The extent of electron d e l o c a l i s a t i o n between the metal centres contributes s i g n i f i c a n t l y to the ease of transfer, and therefore, has a strong influence on the 95 physical properties of such complexes. Robin and Day have used the degree of d e l o c a l i s a t i o n as a c r i t e r i o n f o r d i s t i n g u i s h i n g three broad classes of mixed-valence binuclear complexes: Class I: The i n t e r a c t i o n between M and M+ centres i s weak as a r e s u l t of large i n t e r m e t a l l i c distances or very d i f f e r e n t metal coordination spheres. These factors produce a strongly l o c a l i s e d system i n which the complex exhibits properties observed f o r i s o l a t e d + mononuclear M and M species. The I.T. bands are of high energy (u.v. region). Class I I : The metal ions have i d e n t i c a l or near i d e n t i c a l coordination environments, but have distinguishable valences due to only s l i g h t d e l o c a l i s a t i o n . This r e s u l t s i n properties which may not be - 56 -associated with the i s o l a t e d u n i t s . Class III-A: The i n t e r a c t i o n between the' two centres i s large and electron d e l o c a l i s a t i o n i s complete. The metal ions are i n d i s t i n g u i s h a b l e and the complex shows only properties discernable for a ( M / V \ M ) u n i t . The I.T. band of such complexes i s most often observed at low energy ( n e a r - i . r . ) . The most extensive research i n t h i s f i e l d has been on i o n i c complexes of the type [Ru(NH 3)^] 2L-L^ + where L-L i s a bridging 5 6 group, and these systems have been reviewed along with other d - d 96 97 species by Creutz . Theoretical models describing the intervalence charge transfer process have also been developed. The 98 treatment of Hush describes the c h a r a c t e r i s t i c s of the Class II system where the absorption band represents the t r a n s i t i o n : [ M , M + ] ^ M T ' • [ M + , M ] * op This electron transfer t r a n s i t i o n occurs instantaneously on the v i b r a t i o n a l time scale and r e s u l t s i n the metal ions being i n the equilibrium coordination spheres of the other oxidation state. Therefore, the energy between the ground and excited mixed-valence states, EQp> i s determined by the excess v i b r a t i o n a l energy of the excited state over the ground state. For such a system Hush predicts that the bandwidth at h a l f i n t e n s i t y , Av^y2> ^ s a f u n c " t i o n of the energy of the I.T. band, v , where max' V = (Av, / 0 ) 2 cm 1 (3.6) max 1/2 2310 - 5 7 -The energy of the I.T. band i s also solvent dependent since both inner sphere and outer sphere (solvent) v i b r a t i o n a l modes contribute to the excess v i b r a t i o n a l energy of the I.T. excited state. This manifests i t s e l f as a l i n e a r r e l a t i o n s h i p between E and ( l / n - l/D ) op s where n and D are the o p t i c a l and s t a t i c d i e l e c t r i c constants of the s r solvent, r e s p e c t i v e l y . For a Class III-A system, i n which the I.T. band represents an e l e c t r o n i c t r a n s i t i o n between the ground and excited state molecular o r b i t a l s of the completely delocalised (M-M)+ complex, Hush's theories are not a p p l i c a b l e . The nature of the valence state i n Ru2Cl^(chiraphos)^ i s of fundamental importance as i t i s the representative member of a new class 5 6 of d -d mixed-valence dinuclear metal complexes. The high s o l u b i l i t y of the complex also permits in v e s t i g a t i o n s i n a wide v a r i e t y of solvents. The structure of Ru2Cl^(chiraphos)2 (Figure 3 . 1 ) shows that the ruthenium centres have very s i m i l a r c r y s t a l l o g r a p h i c environments which c l e a r l y rules out a Class I formulation. The s l i g h t inequivalence of the metal centres and lack of c r y s t a l l o g r a p h i c a l l y imposed metal ion equivalence argues for the formulation of Ru2Cl^(chiraphos)2 as a Class II compound, although the inequivalence could r e s u l t from s o l i d state packing within the c r y s t a l . The properties of the complex i n s o l u t i o n , however, are c l e a r l y dependent on the solvent and d i r e c t c l a s s i f i c a t i o n i s not immediately obvious. Even so,the fa c t that the absorptions detected i n the n e a r - i . r . are not observed i n e i t h e r the Ru^'"^ or R u 1 ^ congeners (Section 3 . 6 ) shows that these - 58 -absorption bands r e s u l t from intervalence t r a n s i t i o n s . Prom Figure 3.4 i t i s apparent that RugCl^Cchiraphos) 2 can exis t i n two basic forms, that found i n toluene or CC1. and that found ' 4 i n the other solvents used. The l a t t e r case w i l l be considered f i r s t , i n which the complex exhibits the main absorption at ca. 2340 nm and a less intense one at ca_. 1100 nm. The properties of the band at ca. 2340 nm deviate considerably from those predicted by Hush f o r a Class II system. From equation 3.6 the calculated band width at half-height i s 3140 cm which i s very much larger than the observed value, assuming the curves to be Gaussian, of _ca. 1650 cm "S also there i s n e g l i g i b l e v a r i a t i o n i n the energy of t h i s band with changing solvent. These data suggest the a l t e r n a t i v e Class III-A formulation, i n contradiction to the Class II based on the c r y s t a l structure. Assuming the c r y s t a l i s representative of the complex i t would appear that the s l i g h t differences observed between the ruthenium centres are a res u l t of packing forces. A Class III-A formulation seems reasonable i n view of the short metal-metal distance together with the p a r t i c i p a t i o n of the bridging chloride 3p o r b i t a l s which could f a c i l i t a t e strong o r b i t a l i n t e r a c t i o n to produce a delocalised system. The existence of a second I.T. band i s unexpected although 99 II III t h e o r e t i c a l l y not impossible . For a Ru 2 ' species, where both metals are i n s i t e s of octahedral symmetry, intervalence t r a n s f e r occurs when a R u ( l l ) t _ electron i s transferred to a R u ( l l l ) t 0 2g dg acceptor o r b i t a l . Transfer to a R u ( l l l ) e acceptor o r b i t a l would r e s u l t i n a second I.T. absorption, but of much higher energy. In the - 59 -present case, the second n e a r - i . r . band probably a r i s e s from other species. The I.T. band at c_a. 1100 nm appears s i m i l a r to that observed f o r a Class II system i n that the exact p o s i t i o n varies with solvent, but 2 the required l i n e a r dependence of v with ( l / n - l/D ) i s infix s c l e a r l y not observed (Figure 3.7). Closer examination of the band shape shows i t i s not symmetrical, and since the band i s s e n s i t i v e to the change i n solvent i t appears to be composite i n character. This conclusion i s strengthened by the observed value of which i n most cases i s greater than that calculated by equation 3.6. A tentative explanation f o r t h i s I.T. band i s the presence of polynuclear mixed-valence species. This suggestion i s supported by the observed i r r e v e r s i b l e disproportionation i n CH^CN, DMSO-dg, C D ^ ] ^ and to a c e r t a i n extent DMA (Section 3.6) i n accordance with the equation: 2 R u 2 C l 5 ( P - P ) 2 • [ R u C l 2 ( P - P ) ] 2 + [H u C l 3 ( P - P ) ] 2 (3.7) which r e s u l t s i n complete loss of absorption i n the n e a r - i . r . Formation of the dimeric products requires invoking a tetranuclear intermediate species (Section 3.6) through which chloride ion and electron transfer occurs. I f such a species was s u f f i c i e n t l y l ong-lived, i t would be expected to show only s l i g h t d e l o c a l i s a t i o n due to the unsymmetrical nature of the terminal and bridging metal centres, thereby tending to a Class II system. D i s s o c i a t i o n of any binuclear species to solvated monomers could generate t r i n u c l e a r species such as Ru 3Clg(P-P) 3 by complexation of a monomer with the o r i g i n a l dimers. Such a d d i t i o n a l - 60 -10-E o CO " I o K X 9 -8 ©CDCI3 —I— 0-3 ©CH 2 CI 2 DMA-O DMSO-dg© CD3NO2 C 4 H 6 0 3-^)p (CH3)2CO (n2" D S ) — i — 0-4 0-5 F i g u r e 3.7 P l o t o f v v s . ( l / n max 1/D ) f o r the h i g h energy n e a r - i n f r a r e d band o f R u 2 C l ^ ( c h i r a p h o s ) . s p e c i e s c o u l d e x p l a i n the c o m p o s i t e n a t u r e o f t h e band a t _ca. 1100 nm. I n t o l u e n e o r C C l ^ t h e n e a r - i . r . s p e c t r u m o f Ru o 0 1 . - ( c h i r a p h o s ) 0 changes d r a m a t i c a l l y , and shows o n l y a broad a b s o r p t i o n a t low energy and a s i n g l e s y m m e t r i c a l band a t 880 nm ( F i g u r e 3 . 2 ) . That the p r i n c i p a l low energy a b s o r p t i o n o b s e r v e d p r e v i o u s l y i s not p r e s e n t i n t o l u e n e o r C C l ^ , w h i c h a r e n o n - p o l a r and e s s e n t i a l l y n o n - s o l v a t i n g , r e f l e c t s t he need o f a s o l v e n t sphere about t h i s complex - 61 -t o m a i n t a i n a t r i p l y c h l o r o - b r i d g e d b i n u c l e a r s t r u c t u r e . T h i s was shown by e v a p o r a t i o n o f a C C l ^ s o l u t i o n t o y i e l d a s o l i d - s t a t e s p e c t r u m the same as ob s e r v e d i n s o l u t i o n , w h i l e a d d i t i o n o f CDCl^ t o the s o l i d p r oduced the spec t r u m o r i g i n a l l y o b s e r v e d i n t h i s s o l v e n t . S i n c e no such s o l v e n t s phere i s a v a i l a b l e i n t o l u e n e o r C C l ^ , t h e complex c o u l d undergo d i m e r i s a t i o n t o the t e t r a n u c l e a r s p e c i e s d i s c u s s e d p r e v i o u s l y , a l t h o u g h some o f the b i n u c l e a r s p e c i e s must s t i l l r e main i n o r d e r t o e x p l a i n t h e broad u n r e s o l v e d band found a t low energy. S i n c e t h e a b s o r p t i o n a t 880 nm i s s y m m e t r i c a l , t h e p r e s e n c e o f o n l y one p o l y n u c l e a r s p e c i e s i s s u g g e s t e d . The s i m i l a r i t y between the n e a r - i . r . and v i s i b l e s p e c t r a o f F a ^ C l j - ( c h i r a p h o s ^ i n t o l u e n e o r C C l ^ and Ru^Cl^Cdppb)^ i n a l l s o l v e n t s used s u g g e s t s t h a t t h e same m i x t u r e o f t e t r a n u c l e a r and b i n u c l e a r s p e c i e s i s p r e s e n t . The s p e c t r u m o f t h e dppb d e r i v a t i v e i s i n v a r i a n t t o s o l v e n t ( C D C l ^ , C C l ^ o r DMA), w h i c h i m p l i e s t h a t f o r m a t i o n o f t h e t e t r a n u c l e a r s p e c i e s i s d e t e r m i n e d by t h e l a r g e r r i n g s i z e r e l a t i v e t o c h i r a p h o s r a t h e r t h a n by a s o l v e n t e f f e c t . B e e r ' s law i s n o t obeyed f o r R u ^ C l r - ( d p p b ) ^ i n DMA, and so d i s p r o p o r t i o n a t i o n i n a c c o r d a n c e w i t h e q u a t i o n 3.2 i s assumed. The b e h a v i o u r o f t h e R u 2 C l ^ ( d p p p ) 2 system ( F i g u r e 3.3) appears t o be i n t e r m e d i a t e between t h a t o f dppb and t h a t o f c h i r a p h o s , the system showing s i n g l e , r e l a t i v e l y i n t e n s e a b s o r p t i o n s a t 2060 and 960 nm. The e x t r e m e l y low s o l u b i l i t y o f t h i s complex p r e v e n t s measurement o f the n e a r - i . r . s p e c t r a i n o t h e r s o l v e n t s . - 62 -W h i l s t t he assignment o f I.T. bands t o p o l y n u c l e a r s p e c i e s i s n e c e s s a r i l y t e n t a t i v e u n t i l such s p e c i e s a r e i s o l a t e d and c h a r a c t e r i s e d 100 t h e r e i s a p r e c e d e n t f o r t h i s i n the l i t e r a t u r e . A l i m i t e d s t u d y o f a C u ^ C u ^ - m a c r o c y c l i c - l i g a n d complex r e v e a l e d two I.T. a b s o r p t i o n s a t 1725 and 1175 nm, the l a t t e r b e i n g s o l v e n t dependent. E v i d e n c e f o r p o s s i b l e f o r m a t i o n o f t e t r a n u c l e a r s p e c i e s from the dimer was o b t a i n e d from t h e EPE spect r u m o f a f r o z e n a c e t o n i t r i l e s o l u t i o n w h i c h showed a d d i t i o n a l a b s o r p t i o n s a s s i g n a b l e t o such a s p e c i e s . The n e a r - i . r . s p e c t r a o f th e p o l y n u c l e a r s p e c i e s [ ( N H 5 ) 5 R u ( p z - E u ( N H 5 ) 4 ) n - p z - R u ( N H 3 ) 5 ] ( 2 n + 1 ) + ) w h e r e pz = p y r a z i n e and n = 3-6, r e p o r t e d by Taube's g r o u p " ^ 1 show s h i f t s t o h i g h e r energy w i t h i n c r e a s i n g n. F o r th e case o f n = 3, the a b s o r p t i o n i s c o m p o s i t e and s e n s i t i v e t o s o l v e n t , but no d e f i n i t e c o n c l u s i o n s were drawn. M i x e d - v a l e n c e complexes o f c h l o r o - b r i d g e d r u t h e n i u m complexes hav been examined p r e v i o u s l y , but t h e s e were g e n e r a t e d e l e c t r o c h e m i c a l l y i n 102 s i t u w h i c h r e s t r i c t s a n a l y s i s . Johnson e t a l . g e n e r a t e d [ ( 2 , 2 ' - b i p y r i d i n e ^ E u C l ^ 3 * , but t h i s decomposed r e a d i l y and s p e c t r a l d a t a were n o t o b t a i n e d . The most c l o s e l y r e l a t e d systems' 1"^ 3 t o t h o s e s t u d i e d h e r e a r e the t r i p l y c h l o r o - b r i d g e d d i r u t h e n i u m complexes o f g e n e r a l t y p e C l R u C l - E u C l J where, L i s a 2~3c x j y j— y s o f t n e u t r a l l i g a n d and Z = -1 t o +2. Of t h e s e , t h e s y m m e t r i c a l s p e c i e [ P ^ E u C ^ E u P ^ ] 2 * , P = P E t 2 P h , and [ A S 2 C 1 B U C 1 3 R U C 1 A S 2 ] , As = A s ( t o l y l ) 5 , were found t o be d e l o c a l i s e d s y s t e m s . T h e i r n e a r - i . r . s p e c t r a i n 0.5 M n - B u 4 N B F 4 / C H 2 C l 2 a t 233 K r e v e a l a b s o r p t i o n maxima a t 2230 (e= 3750 M~ 1cm~ 1) and 1695 nm ( e= 1700 M~ 1cm~ 1) f o r t h e p h o s p h i n e and - 63 -arsine species, respectively. These data are s i m i l a r to those found here, at le a s t f o r Ru 2Clj- (chiraphos) 2 i n polar solvents. The authors also note the existence of an ad d i t i o n a l band whose p o s i t i o n appears to p a r a l l e l the degree of i n t e r a c t i o n between the metal centres. No d e t a i l s were given, but th i s band could correspond to the absorption observed at higher energy i n the present work. 3 . 6 Disproportionation of Ru^Cl,-(P-P) The loss of the absorption bands i n the n e a r - i . r . spectra of R u 2 C l 5 ( P - P ) 2 P-P = chiraphos or dppb, i n CH^CN, DMSO-dg and CD.jN02, and to a c e r t a i n extent DMA (Section 3 . 5 ) implies that the mixed valence complexes undergo disproportionation i n these solvents. The f i n a l v i s i b l e spectrum obtained for R u 2 C l ^ ( c h i r a p h o s ) 2 was s i m i l a r i n both DMSO-dg and CD^ NO,,, but was markedly d i f f e r e n t to that obtained i n CH^CN (Figure 3 . 6 ) . Similar s o l u t i o n behaviour was observed f o r the dppb analogue. The disproportionation of Ru 2 C l ^ ( c h i r a p h o s ) 2 i n DMSO solvent (Figure 3 . 8 ) proceeds with i s o s b e s t i c points at 403 and 345 nm. In addition to ex h i b i t i n g d i f f e r e n t v i s i b l e spectra, a c e t o n i t r i l e solutions of the dppb and chiraphos complexes gave molar c o n d u c t i v i t i e s -1 2 -1 -3 of 112 ohm cm mole (2 x 10 M solutions) whereas no conductance was observed i n the other solvents. This value i s t y p i c a l of a uni-valent e l e c t r o l y t e ; however, simple d i s s o c i a t i o n of a chloride ion can be ruled out since t h i s would s t i l l r e s u l t i n a mixed-valence species which should exhibit an intervalence charge-transfer band. - 64 -—I 1 1 1 1 400 600 800 Wavelength , nm Figure 3.8 Changes i n v i s i b l e spectrum with time f o r a DMSO sol u t i o n ' of RuCl,-(chiraphos) ?. In order to determine the species present i n solu t i o n the metathesis reaction of R u ^ ^ l ^ d p p b ^ and AgPF^ (2:1 mole r a t i o ) i n CH^CN was performed as described i n Section 2.1.7.10. Two complexes were i s o l a t e d : [R U C1^(dppb)] 2, a maroon s o l i d which i s assumed to be a R u 1 1 1 dimer by analogy to r i 91 |_Ru 2Cl 3(P(n-butyl) 3)2J2 a n d i n contrast to the green monomeric R u C l ^ ^ M A ) .DMA, P = PPh^ or P ( p - t o l y l ) 3 complexes from which the mixed-valence complexes are i n i t i a l l y prepared. The lack of coordinated solvent suggests a coordinatively saturated species - 65 -(Structure 3-1). The second product i s the dimeric [Eu 2Cl 3(dppb) 2(CH 5CN) 2] PF,- species f o r which ch a r a c t e r i s a t i o n and discussion i s given i n Section 6.2.1.1 and 6.3,respectively. The v i s i b l e spectra of i s o l a t e d [RuCl 3(dppb)]^ and [Ru 2Cl 3(dppb) 2(CH 3CN) 2] PFg i n a c e t o n i t r i l e are shown i n Figure 3.9. Superposition of these spectra r e s u l t i n e s s e n t i a l l y an i d e n t i c a l spectrum to that observed f o r Ru 2Cl^(dppb) 2 i n t h i s solvent thereby suggesting that disproportionation of the l a t t e r to these complexes does occur. Neither of the i s o l a t e d complexes exhibit absorptions i n the n e a r - i . r . as i s to be expected f o r single valence complexes. Since Ru 2Cl^(chiraphos) 2 i n CH^CN gives the same v i s i b l e spectrum and conductivity i t i s assumed that t h i s complex undergoes the same disproportionation although the products have not been i s o l a t e d . In DMSO-dg and CD^NO^ the loss of the n e a r - i . r . absorptions f o r Ru 2Cl^(P-P) 2 P-P = chiraphos and dppb are slower but s t i l l suggest that disproportionation also occurs i n these solvents. However, the lack of conductivity and the difference i n f i n a l spectra compared to - 66 -[ R u 2 C l 3 ( d p p b ) 2 ( C H 3 C N ) 2 ] P F 6 [ R u C l 3 ( d p p b ) ] 2 - R u 2 C l 5 ( d p p b ) 2 \ \ \ \ \ s \ \ A V \ \ \ \ \ \ \ . N. •— | n ' 1 400 • 1 | 1 | 500 600 Wavelength, nm F i g u r e 3.9 V i s i b l e s p e c t r a o f L R u C l 3 ( d p p b ) ] 2 , [ R u 2 C l ( d p p b ) 2 ( C H C N ) 2 ] + P F 6 ~ and R u 2 C l 5 ( d p p b ) 2 i n CH CH. [ R u * 1 1 , 1 1 1 ] = [ R u * 1 ' 1 1 ] = 2.80 x 10" 4M, [ R u " ' 1 1 1 ] = 5.60 x 1 0 _ 4 M . t h a t observed' i n CHjCN i n d i c a t e t h a t d i s p r o p o r t i o n a t i o n i s o n l y t o t h e n e u t r a l d i m e r i c complexes. T h i s i s s u p p o r t e d by the v i s i b l e s p e c t r a o f DMSO s o l u t i o n s o f [ R u C l ^ d p p b ) J 2 and [ R u C l 2 ( d p p b ) J 2; the l a t t e r i s i s o l a t e d as d e s c r i b e d i n S e c t i o n 4.2. S u p e r p o s i t i o n o f t h e s e s p e c t r a g i v e s t h e same spec t r u m as o b t a i n e d f o r R u 2 C l ^ ( d p p b ) 2 ( F i g u r e 3.10). The f o r m a t i o n o f d i m e r i c p r o d u c t s from the d i s p r o p o r t i o n a t i o n o f R u 2 C l ^ ( P - P ) 2 , P-P = c h i r a p h o s o r dppb, can be e x p l a i n e d by two mechanisms. The f i r s t i n v o l v e s d i s s o c i a t i o n o f Ru P C l r - ( P - P ) ? t o - 67 -1-5-0> u c (0 A o (A < 1 0 -0-5 [RuCl 2(dppb)] 2 [RuC±5(dppb)] 2 Ru 2Cl 5(dppb) 2 / v\ Sy / \ / \ V-v. V. V V. V w • i 400 I ' l l 5 0 0 600 Wavelength, nm Figure 3.10 Visible spectra of [RuCl 3(dppb)] 2, LRuCl 2(dppb)] 2, and Ru 2Cl 5(dppb) 2 in DMSO. [Ru* 1 1' 1 1 1] = [Ru"' 1 1] = 1.90 x 10-4M, [ R u " ' 1 1 1 ] = 3.80 x IO"4*. monomeric Ru and Ru complexes which then undergo dimerisation. The second involves i n i t i a l dimerisation to generate a tetranuclear species which by unsymmetrical bridge-cleavage generates the dimeric products (Scheme 3-H). Whilst monomeric Ru^^ species are observed in acetonitrile (section 6.2.1.1), the presence of dimeric Ru"^ "^  in this solvent and only dimers in the other solvents tend to support the second proposal. In CH^ CN the disproportionation of R^Cl,. (P-P) 2 must be rapid as loss of absorption in the near-i.r. is instantaneous - 68 -2 R u 2 C l 5 ( P - P ) 2 — [ R u C l 2 ( P - P ) ] 2 + [ R u C l 3 ( P - P ) ] 2 SCHEME 3-1I upon d i s s o l u t i o n . I n DMSO-dg and CD^NO^ t h e p r o c e s s i s much s l o w e r ( l h and 5 h r e s p e c t i v e l y ) and, i f the t e t r a n u c l e a r s p e c i e s i s s u f f i c i e n t l y l o n g - l i v e d , t h i s c o u l d a c c o u n t f o r a d d i t i o n a l a b s o r p t i o n ( s ) o b s e r v e d i n t h e n e a r - i . r . r e g i o n ( S e c t i o n 3 .5). 3.7 A c t i v a t i o n o f M o l e c u l a r Hydrogen by t h e R u ^ C l ^ P - P ) . , Complexes 3.7.1 S t o i c h i o m e t r y o f the R e a c t i o n i n DMA The R u 2 C l t - ( P - P ) 2 complexes i n DMA r e a d i l y a b s o r b hydrogen a t 20-30°C w i t h an accompanying c o l o u r change from r e d t o orange-brown. The f i n a l gas up t a k e c o r r e s p o n d e d t o h a l f a mole o f H 2 p e r mole o f complex i n each case e x c e p t f o r P-P norphos w h i c h a t 50°C showed an a d d i t i o n a l s l ow u p t a k e o f two moles o f H 2. F o r P-P = c h i r a p h o s t he gas u p t a k e s were s u f f i c i e n t l y s l o w so t h a t d e t a i l e d k i n e t i c p l o t s c o u l d be o b t a i n e d ( F i g u r e 3 . 1 l ) . These show an i n d u c t i o n p e r i o d f o l l o w e d by a marked a c c e l e r a t i o n i n r a t e ; t h e i n d u c t i o n was n o t due t o s l o w d i s s o l u t i o n o f the complex because a homogeneous s o l u t i o n was o b t a i n e d i m m e d i a t e l y . The r e a c t i o n s show f e a t u r e s c h a r a c t e r i s t i c o f an - 69 -2 4 6 8 10 Time x10"3, s Figure 3.11 Uptake plots f o r the reaction between Ru„Clr-(chiraphos) 9 and H II III 3 i n DMA at 2 5 ° C [Ru 2 ' j x 10 = 10.00 ( • ) , 7.57 ( • ) , 4.88 (•) and 3.00 M (•) [H 2] = 0.88 x 10~3M. Inset shows log plot f o r data where [ R u " ' 1 1 1 ] = 10.00 x 10 5M - 70 -a u t o c a t a l y t i c r e a c t i o n . For P-P = dppb or diop under s i m i l a r c o n d i t i o n s , the uptake was much more r a p i d and was complete w i t h i n 500 seconds. The f i n a l s t o i c h i o m e t r y i s c o n s i s t e n t with r e d u c t i o n of the mixed-valence complexes to a Ru,,11 '"^ species (see a l s o S e c t i o n 3.7.3.2) as o u t l i n e d i n equation 3.8. R u 2 C l 5 ( P - P ) 2 + 0.5H2 • R u 2 C l 4 ( P - P ) 2 + H + + C l " (3.8) The a d d i t i o n a l uptake of two moles of H 2 f o r P=P = norphos i s presumably a r e s u l t of the reduction of the carbon-carbon double bond i n 24 the phosphine l i g a n d which has been observed p r e v i o u s l y The use of DMA, a p o l a r a p r o t i c s o l v e n t , promotes the reduction since i n toluene n e g l i g i b l e r e a c t i o n occurs unless base i s added (Sec t i o n 3.7.4). The f i n a l orange-brown s o l u t i o n s were a i r - s e n s i t i v e r e t u r n i n g to t h e i r o r i g i n a l red c o l o u r and then s l o w l y t u r n i n g green. 3.7.2 S p e c t r a l Studies The gas uptakes f o r the r e d u c t i o n of R u 2 C l ^ ( c h i r a p h o s ) 2 i n DMA were s u f f i c i e n t l y slow to be measured a c c u r a t e l y , but due to the small uptake involved, a more convenient method f o r studying the r e a c t i o n k i n e t i c s employing smaller amounts of complex was v i s i b l e spectroscopy. Upon red u c t i o n of R u 2 C l ^ ( c h i r a p h o s ) 2 , new absorption maxima are observed at 456, 365(sh), and 300 nm, and the r e a c t i o n proceeds with i s o s b e s t i c p o i n t s at 356 and 292 nm, as shown i n Figure 3.12. Monitoring the changes i n absorbance at a s i n g l e wavelength r e s u l t s i n 300 400 500 600 700 Wavelength, nm Figure 3 . 1 2 Changes i n absorbance f o r the reaction of Ru ?Clr-(chiraphos)p and H p i n DMA at 2 5°C. - 72 -p l o t s ( F i g u r e 3-13) w h i c h have a maximum s l o p e a t c a . h a l f t he t o t a l a b s o r b a n c e change. D i f f e r e n t i a t i n g t h e p l o t s g r a p h i c a l l y g i v e s r i s e t o the c u r v e s shown i n F i g u r e 3.14 w h i c h a r e n e a r l y s y m m e t r i c a l about the 50$ r e a c t i o n p o i n t , and a r e t y p i c a l o f an a u t o c a t a l y t i c p r o c e s s 1 ^ 4 . An e x t e n s i v e s t u d y was c a r r i e d out i n w h i c h s o l u t i o n s were f r e s h l y p r e p a r e d f o r each measurement. Dependences o f the i n i t i a l and maximum r a t e s on [ R u ^ 1 ' 1 1 1 ] , [ H 2 ] , [DMA.HCl] and te m p e r a t u r e were d e t e r m i n e d . A mechanism t o r a t i o n a l i s e t h e k i n e t i c s has n o t been f o r m u l a t e d , s i n c e i t was l a t e r o b s e r v e d t h a t an i n i t i a l l y p r e p a r e d s t o c k s o l u t i o n o f R u 2 C l ^ ( c h i r a p h o s ) 2 was not under e q u i l i b r i u m c o n d i t i o n s . The i n i t i a l and maximum r a t e s measured under the same c o n d i t i o n s i n c r e a s e d m a r k e d l y on s t o r a g e o f t h e s o l u t i o n , even i n t h e d a r k . W h i l s t changes i n r a t e were o b s e r v e d , t h e v i s i b l e s p e c t r u m o f t h e s o l u t i o n remained e s s e n t i a l l y unchanged w i t h t i m e ( t h e m o n i t o r i n g o f the n e a r - i . r . r e g i o n ( S e c t i o n 3.5.1) was c a r r i e d out o n l y i n l a t e r w o r k ) . A l t h o u g h the " n o n - e q u i l i b r a t i o n " d a t a c o u l d n o t be r e a d i l y a n a l y s e d , p o i n t s m e r i t d i s c u s s i o n . Our i n t e r e s t i n the r e d u c t i o n o f R u 2 C l j - ( P - P ) 2 was i n t h e a u t o c a t a l y t i c n a t u r e o f t h e r e a c t i o n w h i c h , , • • - .. 104-106 . . . i s r e l a t i v e l y uncommon i n i n o r g a n i c r e a c t i o n s i n v o l v i n g gas m o l e c u l e s . An u n d e r s t a n d i n g o f such a u t o c a t a l y t i c b e h a v i o u r c o u l d o f f e r some i n s i g h t i n t o H 2 a c t i v a t i o n by hydrogenase systems w h i c h appear t o o p e r a t e v i a i r o n c l u s t e r s p e c i e s , and an a n a l o g y t o an a u t o c a t a l y t i c RU*VRU**VH2 system has been s u g g e s t e d 1 ^ . The c a t a l y t i c a l l y a c t i v e s p e c i e s i n t h e a u t o c a t a l y t i c R u 2 C l ^ ( c h i r a p h o s ) system i s presumably a R u ( l l ) s p e c i e s whose c o n c e n t r a t i o n c o n t i n u a l l y i n c r e a s e s - 73 -• , 1 1 1 • 1 1 • 1 2 3 4 Time x10~ 3, s Figure 3.13 Spectral changes at 530nm with time for the reaction of R u 0 C l K ( c h i r a p h o s ) 0 and H ? i n DMA at 25°C. Reaction I I I I I -4 monitored at 530nm [Ru 2 ' ] : ( l ) = 7.56 x 10 M, (2) = 4.24 x 10"4M. [H 2] = 1.76 x 10"5M. 1 0 0 -[RU2B,bi] K104 . M Figure 3.14 Plot of rate of change of absorbance with time against concentration of RUpClj- (chiraphos) „. - 74 -w i t h r e a c t i o n t i m e . T h i s i s s u p p o r t e d f u r t h e r by t h e o b s e r v e d i n c r e a s e i n i n i t i a l and maximum r a t e s w i t h s t o r a g e time o f DMA s o l u t i o n ; t h i s i s a r e s u l t o f s l o w d i s p r o p o r t i o n a t i o n ( S e c t i o n 3.5.6) w h i c h i n c r e a s e s the i n i t i a l c o n c e n t r a t i o n o f [ R u C l 2 ( P - P ) ] 2» G r e a t e r i n i t i a l d i s p r o p o r t i o n a t i o n c o u l d be a f a c t o r i n t h e much f a s t e r r e d u c t i o n s f ound f o r R u ^ l ^ . ( d p p b ) 2 and the d i o p a n a l o g u e . The H 0 - u p t a k e s by R u 0 C l [ r ( c h i r a p h o s ) _ a t the h i g h e r d. ^ 5 d. r u t h e n i u m c o n c e n t r a t i o n ( F i g u r e 3.11) a r e s i m i l a r , q u a l i t a t i v e l y , t o t h o s e found f o r t h e r e d u c t i o n o f R u ( l V ) by R u ( l l l ) i n HC1 s o l u t i o n s , f o r w h i c h t h e mechanism o u t l i n e d i n e q u a t i o n s 3.9 and 3.10 was p r o p o s e d " ^ 6 . k Ru + H 2 1 R u I i : [ H " + H + (3.9) k -1 R u i n H - + 2 R u I V * £ t _ _ * 3 R u m + H + (3.10) I n t h e c h i r a p h o s system t h e r e q u i r e d l i n e a r dependence o f l o g [ R u " ] v s . t i m e i n a n a l o g y t o t h i s mechanism was not o b t a i n e d ( F i g u r e 3 . 1 l ) . T h i s i s p o s s i b l y due t o i n h i b i t i o n o f t h e r a t e , p a r t i c u l a r l y a t t h e l a t e r s t a g e s , because o f f o r m a t i o n o f the l e s s a c t i v e [ R u 2 C l j . ( c h i r a p h o s ) 2 ] H , a s p e c i e s t h a t i s known t o be formed from R u 2 C l ^ ( c h i r a p h o s ) 2 i n t h e p r e s e n c e o f c h l o r i d e ( S e c t i o n 3.7.3). T h i s was d e m o n s t r a t e d by m o n i t o r i n g the r e d u c t i o n o f F e C l ^ by H 2 u s i n g a H 2 ~ r e d u c e d s o l u t i o n o f R u 2 C l ^ ( c h i r a p h o s ) 2 . The r e a c t i o n b e i n g c a t a l y s e d i s g i v e n i n e q u a t i o n 3.11, and p r o c e e d s a t 1 atm. and 25°C f o r c a . 4.5 t u r n o v e r s b e f o r e s t o p p i n g . W h i l s t t h e - 75 -2 F e m c i 3 + H 2 • 2?eUCl2 + 2 H + + 2 C l " (3.11) c o n c e n t r a t i o n o f HC1 i s i n c r e a s i n g c o n t i n u a l l y , t h e r u t h e n i u m ( l l ) c o n c e n t r a t i o n remains c o n s t a n t , and so the r e a c t i o n p r o c e e d s u n t i l f o r m a t i o n o f t h e i n a c t i v e i o n i c s p e c i e s i s c o m p l e t e . I n t h e p r e s e n c e o f p r o t o n sponge (PS) t h e i r o n ( l l l ) r e d u c t i o n p r o c e e d s a t a comparable r a t e f o r 7 t u r n o v e r s when the f o r m a t i o n o f [ R U 2 C 1 J - ( c h i r a p h o s ) ^ ] PSH i s c o n s i d e r e d t o p r e v e n t f u r t h e r r e d u c t i o n . I n the p r e s e n c e o f a 4 0 - f o l d e x c e s s o f DMA.HC1 no r e d u c t i o n o f F e C l ^ o c c u r s . At l o w e r c o n c e n t r a t i o n s o f t h e complex, the u p t a k e p l o t s f o r t h e H 2 ~ r e d u c t i o n o f R u 2 C l , - ( c h i r a p h o s ) 2 show a d e f i n i t e s t e p - w i s e b e h a v i o u r ( F i g u r e 3.11), w h i c h i n d i c a t e s t h a t two c o n s e c u t i v e r e a c t i o n s a r e o c c u r r i n g . These c o u l d c o r r e s p o n d t o t h e r e d u c t i o n , by a R u 1 1 s p e c i e s , o f Ru 2Cl<-( c h i r a p h o s ) 2 > and a l s o o f R u 2 C l g ( c h i r a p h o s ) 2 formed from the d i s p r o p o r t i o n a t i o n r e a c t i o n ( S e c t i o n 3 . 6 ) . I n v i e w o f t h e complex n a t u r e o f Ru 2Cl,-(chiraphos),_, i n s o l u t i o n i t i s not s u r p r i s i n g t h a t t h e " n o n - e q u i l i b r i a t e d " k i n e t i c d a t a c o u l d n o t be a n a l y s e d r e a d i l y . However, the s t u d y does s e r v e t o p o i n t out t h a t a r e a c t i o n p r o c e e d i n g w i t h i s o s b e s t i c p o i n t s i n t h e v i s i b l e s p e c t r a l r e g i o n i s n o t n e c e s s a r i l y a s i m p l e one. 3.7.3 C o n d u c t i v i t y Measurements The p r o d u c t i s o l a t e d from t h e H 2 ~ r e d u c t i o n o f R u 2 C l ^ ( c h i r a p h o s ) 2 i n DMA i s t h e R u 2 C l 4 ( c h i r a p h o s ) 2 dimer g i v e n i n e q u a t i o n 3.8 ( S e c t i o n 4 . 2 ) ; however, t h i s was not the p r o d u c t g e n e r a t e d i n s i t u . DMA - 76 -s o l u t i o n s o f t h e m i x e d - v a l e n c e c h i r a p h o s complex a r e n o n - c o n d u c t i n g , but on r e d u c t i o n c onductance i s o b s e r v e d , and t h e r e s u l t s o f measurements o b t a i n e d by s u c c e s s i v e d i l u t i o n under an atmosphere o f a t 25°C a r e g i v e n i n T a b l e 3.4. The e q u i v a l e n t c onductance A g , v a r i e s l i n e a r l y w i t h t he s q u a r e - r o o t o f the e q u i v a l e n t c o n c e n t r a t i o n , assuming a 1:1 e l e c t r o l y t e ( F i g u r e 3 . 1 5 ) , i n a c c o r d a n c e w i t h t he Onsager l i m i t i n g 108 law . The i n t e r c e p t w h i c h r e p r e s e n t s the e q u i v a l e n t c o n d u c t a n c e a t -1 2 -1 i n f i n i t e d i l u t i o n , A Q i s 35.3 ohm cm mole . I n o r d e r t o d e t e r m i n e t h e n a t u r e o f the s p e c i e s g e n e r a t e d by t h e H ^ - r e d u c t i o n , the c o n d u c t i v i t y o f HC1 and HBr was s t u d i e d , s i n c e t he l i m i t i n g i o n i c e q u i v a l e n t c o n d u c t i v i t i e s o f t h e p r o t o n and c h l o r i d e i o n i n DMA had not been measured p r e v i o u s l y . 3.7.3.1 C o n d u c t i v i t y Measurements on DMA.HC1 and DMA.HBr A c o n v e n i e n t s o u r c e o f HC1 and HBr f o r c o n d u c t i v i t y measurements were the DMA s a l t s o f t h e s e a c i d s w h i c h were p r e p a r e d as d e s c r i b e d i n S e c t i o n 2.1.6. D i l u t i o n c o n d u c t i v i t i e s were d e t e r m i n e d f o r b o t h s a l t s i n DMA a t 25°C under a r g o n , and t h e r e s u l t s a r e g i v e n i n T a b l e 3.5. A 1 / 2 p l o t o f A v s . C ' i s l i n e a r f o r DMA.HBr, but shows marked r e eq ' c u r v a t u r e f o r DMA.HC1 ( F i g u r e 3 . 1 6 ) . The l i m i t i n g c o n d u c t a n c e , A Q , -1 2 -1 f o r DMA.HBr i s 65.4 ohm cm mole . The Onsager l i m i t i n g law a p p l i e s o n l y t o s t r o n g e l e c t r o l y t e s , and i s c l e a r l y u n s u i t a b l e f o r 109 DMA.HC1 so r e c o u r s e was made t o t h e F o u s s - S h e d l o v s k y t r e a t m e n t f o r weak e l e c t r o l y t e s . The fu n d a m e n t a l e q u a t i o n i n v o l v e d may be w r i t t e n a s : - 77 -Table 3.4 Equivalent Conductivity of RupCl^(chiraphos)? i n DMA at 25° C [Ru 2] x 104,M A e, ohm'-'-cm^ mole--'-P r i o r to reaction with hydrogen 11.42 1.7 After complete reaction with hydrogen 3 11.42 29.1 6.95 31.1 4.63 31.2 3.19 31.9 2.16 32.6 1.69 33.5 a) Measured under an atmosphere of hydrogen [Ru2]^ x102, Figure 3.15 Onsager plot f o r H 9-reduced Ru 2Cl^(chiraphos)^, i n DMA at 25°C. - 78 -Table 3.5 D i l u t i o n Conductivities of DMA.HC1 and DMA.HBr i n DMA at 25"C DMA.HC1 DMA.HBr [DMA.HCl] A e [DMA.HBr] A e x 105,M ohm "'"cm^ mole 1 x 105,M v. - 1 2 i -1 ohm cm mole 13.76 6.1 11.92 41.1 6.88 8.5 9.54 42.5 3.44 11.5 7.63 45.4 1.72 15.6 6.11 47.1 1.86 21.2 3.H 52.2 1.43 27.1 1.55 56.1 1.22 35.1 1.78 58.9 7 C H - 79 -SA = A - C f 2 S 2 A 2 (3.12) o K A o where S = (Z/2 + / 1 + ( Z / 2 ) 2 ) 2 Z = a /CA / A Q 3 / 2 a = Onsager c o e f f i c i e n t f = a c t i v i t y c o e f f i c i e n t from ( - l o g f ) = 8 JTT± and K = d i s s o c i a t i o n c o n s t a n t . S u b s t i t u t i o n o f the e x p e r i m e n t a l v a l u e s and known c o n s t a n t s i n t o 2 2 2 e q u a t i o n 3.12, and p l o t t i n g SA v s . Cf S A g i v e s a l i n e a r p l o t ( F i g u r e 3.17), where the v a l u e o f t h e o r d i n a t e i n t e r c e p t c o r r e s p o n d s t o A Q and the s l o p e i s e q u i v a l e n t t o - l / K A . The l i m i t i n g -1 2 -1 conductance f o r DMA.HC1 i s found t o be 69.8 ohm cm mole , and -4 the d i s s o c i a t i o n c o n s t a n t i s 1.1 x 10 M. The l i m i t i n g i o n i c c o nductance (A ~) r e p o r t e d f o r t he bromide i o n 1 1 0 i n DMA a t 25°C i s 43.2 ohm~ 1cm 2mole~ 1. A p p l y i n g K o h l r a u s c h ' s law o f i n d e p e n d e n t i o n i c m o b i l i t i e s , A = X + X (= 65.4 o o o -1 2 -1 ohm cm mole f o r DMA.HBr), t h e v a l u e o f the l i m i t i n g c o n ductance -1 2 -1 f o r the s o l v a t e d p r o t o n i s t h e r e f o r e 22.2 ohm cm mole and -1 2 -1 X C l " = 69.8 - 22.2 = 47.6 ohm cm mole . o 3.7.3.2 A n a l y s i s o f C o n d u c t i v i t y Measurements on H 2 Reduced S o l u t i o n s 1/2 o f R u 2 C l r - ( c h i r a p h o s ) 2 i n DMA The marked d i f f e r e n c e s between t h e p l o t s o f AQ v s . C eq f o r t h e reduced s o l u t i o n s o f R u 2 C l ^ ( c h i r a p h o s ) 2 ( F i g u r e 3.15) and DMA.HC1 ( F i g u r e 3.16) show t h a t f r e e HC1 i s n o t l i b e r a t e d as g i v e n i n - 80 -F i g u r e 3.17 P l o t of SA a g a i n s t Cf S A i n a c c o r d a n c e w i t h e q u a t i o n 3.12. e q u a t i o n 3.8. A f e a s i b l e r e a c t i o n s t i l l c o n s i s t e n t w i t h t h e s t o i c h i o m e t r y i s 3.13. where the c h l o r i d e i o n p r o d u c t shown i n R u 2 C l 5 ( c h i r a p h o s ) 2 + 0.5H 2 [ R u 2 C l 5 ( c h i r a p h o s ) 2 ] ~ H + (3.13) e q u a t i o n 3.8 has added t o t h e R u 1 1 dimer p r o d u c t t o g i v e presumably a t r i p l y c h l o r o - b r i d g e d a n i o n w i t h t h e s o l v a t e d p r o t o n as t h e c o u n t e r - i o n (see b e l o w ) . F u r t h e r s u p p o r t f o r t h i s i o n i c p r o d u c t comes - 81 -from the calculated l i m i t i n g conductance, which f o r |_Ru„ClR (chiraphos)-] can be estimated from Stokes law: r s ( 3 . 1 4 ) o i n which F i s the Faraday, N i s Avogardro's number, T) i s the v i s c o s i t y _ 3 of the solvent (9.19 x 10 poise for DMA), and r i s the Stokes s radius of the anion. Assuming the anion to have the same cry s t a l l o g r a p h i c radius as that found for R ^ C l ^ chiraphos)^ -1 2 -1 ( 7 . 1 4 A ) , the calculated X Q i s 12 . 4 ohm cm mole . Since + - 1 2 - 1 A H i s 22.2 ohm cm mole , the calculated value of A o o -1 2 -1 for the product of equation 3 . 1 5 i s 3 4 . 6 ohm cm mole which i s i n excellent agreement with the experimental value of 3 5 . 3 v. -1 2 - . " I ohm cm mole More d i r e c t evidence f o r the nature of the anion comes from the 31 1 P{ H}- n.m.r. spectrum of the i n s i t u product generated i n DMA/toluene-d R (v:v = 1:1). The spectrum consists of an AB quartet temperature to - 5 0 ° C . This i s consistent with structure 3 - H where the inequivalence of the phosphines i s a r e s u l t of the ligand being c h i r a l U A = 8 8 . 2 6 , 6 B = 8 0 . 3 5 ppm 3 6 . 8 Hz) from ambient Cl DMAH + 3 - H - 82 -(see S e c t i o n 4.3.2). The spectrum of the analogous dppb complex under the same c o n d i t i o n s e x h i b i t s only a s i n g l e t at 50.9 ppm. The product was i s o l a t e d as the protonated amide c h l o r i d e s a l t by evaporation of the DMA under reduced pressure and a d d i t i o n of deoxygenated hexanes to the r e s u l t i n g o i l ; t h i s produced an orange p r e c i p i t a t e which was f i l t e r e d , washed w e l l with degassed hexanes and d r i e d i n vacuo. A n a l y s i s : (C, AH,,Cl rN0P.Ru 0) requires ou oo 5 4 2 C:54.61, H:5.01, N:1.06$; found C : 5 5 . 1 9 , H:4.98, N:0.96#. A d d i t i o n of deoxygenated methanol to the o i l , however, d i s p l a c e s the DMA.HC1 and the n e u t r a l R u 2 C l 4 ( c h i r a p h o s ) 2 complex can be i s o l a t e d ( S e c t i o n 4.2). 3.7.4 Reaction of Ru^Cl^P-P),, Complexes with Hp i n Toluene The t i t l e complexes are unreactive towards hydrogen i n toluene unless a base i s present. This r e a c t i o n was stu d i e d f o r R u 2 C l ^ ( d p p b ) 2 using Proton Sponge, PS, as base. The gas uptake shows the r e a c t i o n proceeds with absorption of 0.5 H 2:Ru 2 1-'-» 1 1 1, and i s accompanied by a colour change from red to orange-brown as found f o r the study i n DMA i n the absence of added base. The r e a c t i o n i s much TT I T slower, but i s again c o n s i s t e n t with reduction to a Ru 2 > species which i s found to contain PS.HC1, and which can be i s o l a t e d as described i n S e c t i o n 2.1.7.7. The product analyses f o r [ R u 2 C l 5 ( d p p b ) 2 ] ~ P S H + ; the HC1 produced i n the re d u c t i o n reacts with the base to produce PS.HC1 which subsequently adds to the n e u t r a l dimer. The v a r i a t i o n of c o n d u c t i v i t y i n DMA with c o n c e n t r a t i o n was determined at 25°C under argon (Table 3.6); t h i s gives a l i n e a r Onsager - 83 -T a b l e 3.6 D i l u t i o n C o n d u c t i v i t i e s o f [ R u ? C l 5 ( d p p b ) 2 ] " P S H + i n DMA a t 25"C [ H u 2 ] A e [ R u 2 J A e 3 - 1 2 - 1 ^ l ? x 10 ,M ohm cm mole x 10 ,M ohm cm mole 1.79 26.6 0.57 32.0 1-35 28.5 0.43 33.1 1.01 30.3 0.32 33.8 0.76 31.1 0.16 35.4 - 84 -plot (Figure 3.18) from which the l i m i t i n g conductance i s 38.7 -1 2 - 1 - 1 2 -1 ohm cm mole as compared to 35.3 ohm cm mole found for-[ R u 2 C l 5 ( c h i r a p h o s ) 2 ] ~ DMAH+. Assuming [Ru 2Clj- (dppb) 2]~ to have the same l i m i t i n g i o n i c conductance as the chiraphos d e r i v a t i v e (12.4 ohm "'"cm^ mole 1 ) , the l i m i t i n g conductance f o r PSH + i s 26.3 -1 2 -1 ohm cm mole : This value i s somewhat greater than that found -1 2 -1 fo r the solvated proton i n DMA (22.2 ohm cm mole ), implying f o r the l a t t e r , perhaps, that the proton i s bonded to more than one molecule of DMA which would re s u l t i n a lower i o n i c mobility. The 5 1P{ 1H}-n.m.r. spectrum of [Ru 2Cl 5(dppb ) 2 J~PSH + i n CD 2C1 2 i s a s i n g l e t (53.6 ppm) from ambient temperature to -70°C. This i s consistent with the complex having the same structure (3-H) as found f o r the i n s i t u generated [Ru 2Cl 5(dppb) 2]~DMAH + (previous s e c t i o n ) . - 85 -CHAPTER IV SYNTHESIS AND CHARACTERISATION OF DIMERIC RUTHENIUM(II) COMPLEXES AND  THEIR APPLICATION AS ASYMMETRIC HYDROGENATION CATALYSTS 4 . 1 Introduction The use of rhodium phosphine complexes as asymmetric hydrogenation cat a l y s t s has been studied extensively, and with a number of phosphines i t i s possible to hydrogenate derivatives of a-acylaminoacrylic acids with >y0$ e.e (Section l . l ) . I d e a l l y , a c a t a l y s t f o r general chemical synthetic use should be able to asymmetrically hydrogenate any p r o c h i r a l alkene, or s e l e c t i v e l y hydrogenate one diastereomer of a c h i r a l alkene with high enantiomeric excess. Towards t h i s goal, the development of highly enantioselective c a t a l y s t s i s preferred, rather than production of more c h i r a l phosphines. This can be achieved e i t h e r by using c h i r a l ligands other than phosphines or by using c a t a l y s t s which hydrogenate by d i f f e r e n t mechanisms, and which hopefully are more discriminatory. Research i n these two areas has been l i m i t e d , and to date, not too 4 successful . In t h i s laboratory, ruthenium complexes containing c h i r a l phosphine and sulfoxides have been prepared and used as asymmetric hydrogenation catalysts"""''. An exchange reaction using RuCl„(PPh,)., - 8 6 -and the c h i r a l phosphine diop produced R u ^ l ^ d i o p ) ^ , a complex co n t a i n i n g a b r i d g i n g diop l i g a n d . This complex i n DMA was found to absorb 1 or 2 moles of H 2 per dimer i n the absence and presence of diop, r e s p e c t i v e l y , i n accordance w i t h equations 4.1 and 4.2. The hydride product, 1, could be prepared independently by a Ru C l (diop) + H • RuH C l ( d i o p ) 2 + R u C l 2 ( d i o p ) + HC1 (4.1) 1 R u 2 C l ( d i o p ) ^ + 2H 2 d l o p » 2RuHCl(diop) 2 + 2HC1 (4.2) phosphine exchange method from RuHCl(PPh 3) 3 and diop. Although 1^  was o r i g i n a l l y thought to have the hydride c i s to c h l o r i d e , the 112 c r y s t a l s t r u c t u r e l a t e r showed i t to be a trans c o n f i g u r a t i o n Analogues of _1 with the diphosphines dppm, dppe and dppp were 79 c a t a l y t i c a l l y i n a c t i v e f o r hydrogenation , c l e a r l y i m p l y i n g that s t e r i c f a c t o r s a s s o c i a t e d w i t h the seven-membered r i n g of diop upon c o o r d i n a t i o n were important. The diop complexes hydrogenated under mil d c o n d i t i o n s a v a r i e t y of p r o c h i r a l alkenes w i t h modest enantiomeric excesses (up to 59$ e . e . ) ^ 1 . Hydrogenations using R u ^ j C l ^ d i o p ) ^ were complicated by the presence of two ruthenium species (equation 4.1) which r e s u l t e d i n reduced products d i f f e r i n g i n e.e. from those found using R u H C l ( d i o p ) 2 alone. This suggested that R u C l 2 ( d i o p ) , a species that was not i s o l a t e d , d i d c o n t r i b u t e to the hydrogenation. K i n e t i c data f o r the hydrogenation of acrylamide and a t r o p i c a c i d c a t a l y s e d by Ru H C l ( d i o p ) 2 were c o n s i s t e n t with the mechanism shown i n equations 4.3 - 4.5. - 87 -R u H C l ( d i o p ) 2 + alkene -R u C l ( a l k y l ) ( d i o p ) + H 2 *• f a s t RuHCl(diop) + diop • R u C l ( a l k y l ) ( d i o p ) + diop (4.3) RuHCl(diop) + s a t . product (4.4) RuHCl(diop) 2 (4.5) The d i s s o c i a t i o n of a diop l i g a n d i n the f i r s t step i s necessary f o r c a t a l y t i c a c t i v i t y , but how t h i s i n f l u e n c e s the extent of asymmetric i n d u c t i o n i s not obvious. In the present study the use of complexes c o n t a i n i n g one bidentate phosphine per ruthenium e l i m i n a t e s the need f o r l i g a n d d i s s o c i a t i o n , and d e t a i l s of these asymmetric hydrogenation c a t a l y s t s are given i n t h i s Chapter. Ruthenium complexes c o n t a i n i n g c h i r a l phosphines have a l s o been used f o r a number of other asymmetric transformations. The c l u s t e r R u 4 H 4 ( C 0 ) g ( d i o p ) 2 has been used f o r the hydrogenation of p r o c h i r a l substrates c o n t a i n i n g C=C, C=0 or C=N- groups, using e i t h e r 113 H 2 or i n some cases by hydrogen t r a n s f e r from a l c o h o l s . These 114 types of reductions have a l s o been s t u d i e d by Ohkubo et a l . using R u 2 C l 4 ( d i o p ) 3 . However i n both these reports more vigorous c o n d i t i o n s were r e q u i r e d . 4.2 Synthesis of [ R u C l 2 ( P - P ) J 2 Complexes The r e a c t i o n of the mixed-valence complexes R u 2 C l ^ ( P - P ) 2 , P - P = chiraphos, dppp, dppb and diop, w i t h H 2 i n DMA generates the i o n i c species [ R U 2 C 1 5 ( P - P ) 2 J " DMAH+ ( S e c t i o n 3.7) i n accordance with equation 4.6. From t h i s r e a c t i o n the n e u t r a l species - 8 8 -R u 2 C l 5 ( P - P ) 2 + 0.5H2 D M A » [ R u 2 C l 5 ( P - P ) 2 ] " DMAH+ (4.6) [RuCl 2(P-P)J 2 can be obtained by addition of methanol which causes displacement of DMA.HC1 and p r e c i p i t a t i o n of the product. In the case of P-P = diop or dppb, the [ R u C l 2 ( P - P ) ] 2 complexes have been observed s p e c t r o s c o p i c a l l y (Section 4.3.1) by disproportionation of other complexes i n s i t u , but have not been i s o l a t e d previously. The preparation of the chiraphos and diop complexes were complicated by t h e i r high s o l u b i l i t y i n methanol, and necessitated the use of small quantities of solvent and cooling to bring about p r e c i p i t a t i o n . The products so obtained are generally i n r e l a t i v e l y low y i e l d (ca. 40$) and DMA impurity i s present, as indicated by elemental a n a l y s i s . For t h i s reason an a l t e r n a t i v e procedure was devised. Since the use of Proton Sponge as added base i n toluene generated an i o n i c species analogous to that formed i n DMA (Section 3.7.4), the use of pol y v i n y l p y r i d i n e seemed appropriate. This base i s polymeric and remains so as the hydrochloride s a l t , thereby making addition to the [R u C l 2 ( P - P ) ] 2 complexes improbable, and separation by f i l t r a t i o n i s e a s i l y accomplished. This method gave good y i e l d s of the desired diop and chiraphos complexes. F u l l preparative d e t a i l s are given i n Sections 31 1 2.1.7.5 and 2.1.7.6, and t h e i r c h a r a c t e r i s a t i o n by P{ H}-n.m.r. i s presented i n the following section. A l l of the complexes are hygroscopic and, with the exception of [Ru C l ? ( c h i r a p h o s ) ] ? , are very a i r s e n s i t i v e , turning green on - 89 -exposure to a i r . The molecular weight of the chiraphos complex was 115 determined by the Signer method to be 1100 which i s i n reasonable agreement w i t h that expected f o r a dimeric species ( c a l c . 1196). The chiraphos complex obeys Beer's law i n DMA; however, the v i s i b l e spectrum i s solvent dependent (Figure 4.1). A d d i t i o n of one equivalent of dppb to a DMA s o l u t i o n of the dppb analogue produces a change i n colour from brown to green. The v i s i b l e spectrum of the r e s u l t i n g s o l u t i o n (Figure 4.2) i s the same as that p r e v i o u s l y reported 73 f o r [RuCl 2(dppb)^ ^ ] 2 . In the present study the formation of t h i s phosphine-bridged b i n u c l e a r complex i s i n accordance w i t h : [ R u C l 2 ( d p p b ) ] 2 + dppb P P .Cl k - * * V (4.7) More a i r s t a b l e forms of the [ R u C l 2 ( P - P ) ] 2 complexes could be obtained by r e c r y s t a l l i s a t i o n i n the presence of a c o o r d i n a t i n g solvent such as acetone. With P-P = dppb, the product so obtained has the formula Ru 2Cl 4(dppb) 2(acetone).acetone and shows i . r . s t r e t c h e s at 1645 and 1705cm which are assigned to coordinated and uncoordinated acetone, r e s p e c t i v e l y . For the P-P = chiraphos complex only coordinated acetone was present as c h a r a c t e r i s e d by a s i n g l e v„„ (1645 S C 6X OH© cm ^) and by elemental a n a l y s i s . Wavelength , nm Figure 4 . 2 V i s i b l e spectrum obtained upon addition of one equivalent of dppb to [RuCl ?(dppb)] 9 i n DMA. - 91 -4.3 • ? 1 F { 1 H ) - N.m.r. S t u d i e s 4.3.1 S t u d i e s i n N o n - C o o r d i n a t i n g S o l v e n t s 31 1 The P{ H}-n.m.r. s p e c t r a o f t h e complexes [ R u C l 2 ( P - P ) ] 2 , P-P = d i o p , dppb and dppp, i n C D 2 C 1 2 a l l c o n s i s t o f an AB p a t t e r n , c e n t r e d a t 48.6, 57.9 and 54.3 ppm r e s p e c t i v e l y . The c h e m i c a l s h i f t s o f t h e s e p a t t e r n s v a r y s l i g h t l y w i t h t e m p e r a t u r e w h i l s t t h e c o u p l i n g remains c o n s t a n t ( T a b l e 4 . 1 ) . The s p e c t r a o f [ R u C l 2 ( c h i r a p h o s ) ] 2 i n C D 2 C 1 2 o r t o l u e n e - d g , h o w e v e r , show two i n d e p e n d e n t AB systems a t h i g h e r f r e q u e n c y o f e q u a l i n t e g r a t e d i n t e n s i t y . These two systems have been d e s i g n a t e d AB and CD on t h e b a s i s o f c h e m i c a l s h i f t (<5^g - 83, 6Q D - 82 ppm), a l t h o u g h a d e f i n i t e a s s i gnment i s n o t p o s s i b l e s i n c e t h e c o u p l i n g c o n s t a n t i s t h e 2 same f o r each res o n a n c e ( J = 39.1 H z ) . I n a d d i t i o n , on s t a n d i n g t h e c h i r a p h o s complex i n C D 2 C 1 2 d e v e l o p s a s i n g l e t a t 82 ppm, t h e 31 1 i n t e n s i t y o f w h i c h i n c r e a s e s w i t h t i m e . The P{ H}-n.m.r. d a t a f o r a l l o f the complexes a r e p r e s e n t e d i n T a b l e 4.1, and F i g u r e s 4.3 and 4.4 show t h e s p e c t r a f o r [ R u C l 2 ( c h i r a p h o s ) ] 2 i n C D 2 C 1 2 and t o l u e n e - d g , r e s p e c t i v e l y . W h i l s t t h e s p e c t r a o f t h e c h i r a p h o s complex and t h o s e o f t h e d i o p , dppb, and dppp complexes show marked d i f f e r e n c e , a l l a r e c o n s i s t e n t w i t h a d i m e r i c s t r u c t u r e , s i n c e a monomeric R u C l 2 ( P - P ) s p e c i e s would 31 1 p r o d u c e a s i n g l e t i n t h e P{ H}-n.m.r. s p e c t r u m f o r e i t h e r a t e t r a h e d r a l o r s q u a r e - p l a n a r c o n f i g u r a t i o n . The o b s e r v e d r e s o n a n c e p a t t e r n s a r e a t t r i b u t e d t o t h e complexes h a v i n g a b r i d g e d s t r u c t u r e w i t h two s q u a r e p y r a m i d s s h a r i n g a b a s a l edge ( s t r u c t u r e 4 - 1 ) , w h i c h i s - 92 -Table 4.1 . 3 1F{ 1H}-N.m.r*. Data For [ R u C l 2 ( P - P ) ] 2 Complexes 3 ( i ) [ R u C l 2 ( d p p b ) ] 2 > CD 2C1 2, 2 J A B = 46.8 Hz Temperature, "C P A P B 0 62.0 53.7 -70 62.2 5 4 . 3 ( i i ) [ R u C l 2 ( d i o p ) ] 2 , CD 2C1 2, 2 J A B = 46.4 Hz Temperature, "C P A Pg 30 50.0 47.1 ( i i i ) [ R u C l 2 ( d p p p ) ] 2 , CD 2C1 2, 2 J A B = 57.4 Hz Temperature, °C P A Pg -70 58.0 50.5 ( i v ) [ R u C l 2 ( c h i r a p h o s ) ] 2 , CD 2C1 2, 2 J A B = 2JQJ) = 39.1 Hz Temperature, °C P A P £ P Q P D S i n g l e t ^ 30 87.8 7 7 . 9 87.1 77.9 81.2 -70 88.4 76.7 8 6 . 3 75.7 81.0 (v) [RuCl„(chiraphos)] 0 , t o l u e n e - d o f d. o 2 2 JAB' JCD' =39.1 Hz Temperature, °C P A P B p c PD 30 88.5 77.7 87.7 75.9 -10 88.1 76.1 87.0 75.8 -50 87.5 75.7 86.1 75.1 a Chemical s h i f t s i n ppm, r e l a t i v e to 85$ ^PO^ b This s i n g l e t develops on standing and i s absent i n f r e s h l y prepared samples. - 93 -, : . 1 1 1 90 80 70 ppm Figure 4.3 3 1P{ 1H}-N.m.r. spectra of [R u C l 2 ( c h i r a p h o s ) ] 2 i n CD 2C1 2 at 30°C and -50°C at 32.4 MHz. - 94 -1 1 1 1 i 1 90 80 70 ppm F i g u r e 4 .4 P{ H } - N . m . r . s p e c t r a of [ R u C l 2 ( c h i r a p h o s ) ] 2 as a f u n c t i o n of temperature i n t o l u e n e - d g at 32.4 MHz. - 9 5 -analogous to that proposed f o r [ R u C l 2 ( P P h j ) 2 ] 2 In such a 1 2 structure f o r P-P = dppb or dppp, P^(^ u ) i s equivalent to P^(^ u ), GT PA 4-1 s i m i l a r l y f o r Pg, but P^ i s not equivalent to Pg and a s i n g l e AB pattern r e s u l t s . The two AB patterns observed f o r [ R u C l 2 ( c h i r a p h o s ) ] 2 are also consistent with a structure such as 4-1. Incorporation of c h i r a l i t y i nto the phosphine back-bone r e s u l t s i n P^CRu1) no longer being 2 1 equivalent to P^( Rn ), and Pg(Ru ) i s inequivalent to 2 Pg(Ru ). In such a case a diastereotopic p a i r of inequivalent phosphines may generate two AB patterns i n a 1:1 r a t i o , as observed. This explanation, however, requires the diastereomer of structure 4-1 to have a c c i d e n t a l l y degenerate resonances or there to be rapid interconversion between the two. An a l t e r n a t i v e explanation i s that the diastereotopic p a i r of phosphines on the two ruthenium centres are degenerate and the two AB patterns then a r i s e from an inequivalence of the two diastereomers. In t h i s case the diastereomers would have to be formed i n equal proportions to explain the observed 1:1 integrated i n t e n s i t y r a t i o of the two patterns. Dimeric chloro-bridged ruthenium complexes have a propensity to form t r i p l y - b r i d g e d species (Section - 96 -4.3.2), and interconversion of diastereomers, v i a such an intermediate, i s not unreasonable as shown i n Scheme 4-1. A sing l e species rather than two diastereomers i s therefore considered to give r i s e to the observed two AB patterns. Scheme 4-1 31 1 Surprisingly, the P{ H}-n.m.r. of [ R u C l 2 ( d i o p ) ] 2 i s a singl e AB pattern although diop i s c h i r a l and the complex would be 31 expected to exhibit a P spectrum s i m i l a r to that of the chiraphos d e r i v a t i v e . Diop gives r i s e to a la r g e r r i n g s i z e upon coordination, and i s somewhat more f l e x i b l e than the r i g i d chiraphos ligand; so possibly s l i g h t f l u c t u a t i o n of the phosphine removes any inequivalence or a l t e r n a t i v e l y they are simply c o i n c i d e n t a l l y degenerate. The generation of a s i n g l e t at 81 ppm i n the spectrum of [ R u C l 2 ( c h i r a p h o s ) ] 2 i n CD 2C1 2 on standing i s not r e a d i l y explained. A s i n g l e t has been observed previously f o r [ R u C l 2 ( P P h j ) 2 ] 2 but only i n polar, coordinating solvents such as DMA, and has been assigned to a solvated monomer11^. Since t h i s s i n g l e t constitutes a p r i n c i p a l resonance i n the spectra of the - 97 -chiraphos complex i n CDp^^-acetone as a r e s u l t of the presence of the coordinating solvent (see next Section), i t i s possible that trace water generates a corresponding s i n g l e t i n the CD 2C1 2 solvent. The absence of the s i n g l e t i n f r e s h l y prepared samples, which are prepared using dry glassware and solvents under anaerobic conditions suggests a possible slow leaching of water from the n.m.r. tube. 31 1 The ^ P T H } -n.m.r. of [RuCl 2(diop) ] 2 has been observed 79 previously i n the spectrum of RuCl^diopJPPh^ as a r e s u l t of p a r t i a l d i s s o c i a t i o n of triphenylphosphine i n toluene (equation 4.8). In addition to the ABX pattern expected f o r the s t a r t i n g complex, an AB RuCl 2(diop)PPh 3 ^ l/2[RuCl 2(diop)] 2 + PPh 5 (4.8) pattern (6^ = 51.5. <5g = 49.2 ppm, J A £ = 50Hz) of integrated i n t e n s i t y twice that of the free ligand s i g n a l was observed. During an 117 analogous study on the RuCl 2(dppb)PPh 3 complex Jung et a l . have reported recently the n.m.r. parameters f o r the dppb complex ( 6 A = 62.6, 6.g E 54.4 ppm, J A g = 47Hz) which, as f o r the diop complex, are i n good agreement with those obtained i n the present study with the i s o l a t e d complexes. F i n a l l y , the v a r i a t i o n i n chemical s h i f t s f o r coordinated 118 199 diphosphines of varying r i n g s i z e i s not unusual ' , and i n v a r i a b l y the f i v e membered chelates of diphos-type ligands, as i n , 31 chiraphos, exhibit the largest P-n.m.r. coordination chemical 119 s h i f t s . This phenomenon i s usually considered to be due to a large - 98 -d e s h i e l d i n g c o n t r i b u t i o n a r i s i n g f r o m s t r a i n i n t h e five-membered r i n g 120 a l t h o u g h t h e s i t u a t i o n a p p e ars more complex i n t h a t t h e c o o r d i n a t i o n s h i f t f o r four-membered c h e l a t e s i s n o t as l a r g e . 4.3.2 S t u d i e s i n C o o r d i n a t i n g S o l v e n t s The v i s i b l e s p e c t r u m o f [RuCl^Cchiraphos) ] ^ i n s o l u t i o n • ( F i g u r e 4.1) shows marked d i f f e r e n c e s when e i t h e r t o l u e n e , DMA o r a c e t o n e a r e used as s o l v e n t s . I n a l l s o l v e n t s t h e complex i s b e l i e v e d t o be d i m e r i c , but i n t h e c a s e o f DMA o r a c e t o n e , s o l v e n t i n t e r a c t i o n i s i n v o k e d t o e x p l a i n t h e s p e c t r a l d i f f e r e n c e s and t h e i s o l a t i o n o f complexes c o n t a i n i n g c o o r d i n a t e d s o l v e n t ( S e c t i o n 4 . 2 ) . I n o r d e r t o 31 1 a s c e r t a i n t h e n a t u r e o f t h i s i n t e r a c t i o n t h e P{ H}-n.m.r. s p e c t r a o f DMA and a c e t o n e s o l u t i o n s were o b t a i n e d . The a d d i t i o n o f a c e t o n e t o a f r e s h l y p r e p a r e d CDp^lp^ s o l u t i o n o f [ R U C I 2 ( c h i r a p h o s ) ] 2 ( w h i c h e x h i b i t s no s i n g l e t a t 81 ppm) p r o d u c e s a t i m e - i n v a r i a n t s p e c t r u m c o n s i s t i n g o f a s i n g l e AB p a t t e r n , 2 - 83.4 ppm, J = 37.8 Hz and a s i n g l e t a t 80.9 ppm o f e q u a l i n t e g r a t e d i n t e n s i t y r a t i o . C o o l i n g t h e s o l u t i o n d i m i n i s h e s t h e p r o p o r t i o n o f the s i n g l e t and a second AB p a t t e r n ( d e s i g n a t e d CD, (5 O T. - 82.8 ppm, J = 34.2 Hz) becomes a p p a r e n t o f i n t e n s i t y 01/ PP l e s s t h a n t h e o r i g i n a l AB p a t t e r n w h i c h remains e s s e n t i a l l y unchanged ( F i g u r e 4 . 5 ) . A t -90°C th e two AB p a t t e r n s a r e c l e a r l y r e s o l v e d i n e s s e n t i a l l y a 1:1 r a t i o , w i t h t h e s i n g l e t s t i l l p r e s e n t a t _ca. 5% i n t e g r a t e d i n t e n s i t y . The same s p e c t r a a r e o b t a i n e d u s i n g i s o l a t e d R u C l ( c h i r a p h o s ) ( a c e t o n e ) i n C D ^ C l ^ - a c e t o n e , but i n - 99 -1 1 ' 1 100 90 80 70 ppm 31" 1 Figure 4i5 P{ H}-N.m.r. spectra of [ R u C l ? ( c h i r a p h o s ) ] 2 as a function of temperature i n CD 2Cl 2-acetone at 32.4 MHz. Continued on next page - 101 -CD^Cl^ alone the spectrum shows only two broad unresolved resonances centred at 83.3 and 72.4 ppm even to -60°C. 31 1 The P{ H}-n.m.r. spectrum of [RuCl 2(chiraphos) ] 2 i n toluene-dg-DMA at various temperatures i s shown i n Figure 4.6. In t h i s solvent mixture the major species i s one containing two independent AB systems, assigned as AB and CD. At 30"C the high f i e l d resonances are c o i n c i d e n t a l , but on lowering the temperature the two patterns separate, due to d i f f e r e n t v a r i a t i o n s i n chemical s h i f t s with temperature u n t i l at -60°C, 6^ = 82.9 ppm, J^g = 36.6 Hz and 6Q-Q = 80.7 ppm, JQ-Q - 34.1 Hz. C l e a r l y evident are resonances due to other species, the parameters f o r which cannot be r e a d i l y elucidated. The n.m.r. parameters f o r the p r i n c i p l e resonances of [HuCl.( chiraphos)] i n toluene-d 0-DMA and CD 0Cl„-acetone are d d O d d given i n Table 4.2. In order to determine i f any of the resonances f o r the chiraphos complex i n eit h e r DMA or acetone are as a r e s u l t of the ligand being 31 1 c h i r a l , the P{ H}-n.m.r. spectrum of Ru 2Cl 4(dppb) 2(acetone). acetone i n CD 2Cl 2-acetone was recorded (Figure 4.7). At ambient temperature the spectrum i s unresolved, but at -40°C three AB patterns 2 are observed, a lower f i e l d pattern centred at 57.9 ppm ( J = 46.8 2 Hz) and two higher f i e l d patterns ($^g = 50.9, J^g = 44.8 Hz 2 and 6pp = 49.0 ppm, = 39.2 Hz) which are complicated i n appearance because of t h e i r s i m i l a r chemical s h i f t s . On further cooling of the s o l u t i o n , the integrated i n t e n s i t y of the higher f i e l d resonances increase at the expense of those at lower f i e l d . The spectra f o r t h i s - 102 -1 I 1 90 80 70 ppm 31 1 F i g u r e 4.6 P{ H}-N.m.r. s p e c t r a o f [ R u C l g ( c h i r a p h o s ) ] 2 as a f u n c t i o n o f t e m p e r a t u r e i n toluene-dg-DMA a t 40.5 MHz. C o n t i n u e d on n e x t page - 104 -T a b l e 4.3 31 1 -P{ H}-N.m.r. Data F o r [ R u C l 2 ( c h i r a p h o s ) ] 2 i n , a C D 2 C l 2 - A c e t o n e and Toluene-d^-DMA C D 2 C l 2 - a c e t o n e ( v / v = 3:1) 2 J A B = 3 7 . 8 Hz, 2 J C D = 3 4 . Temperature, "C 30 88.9 0 88.4 -30 88.0 -50 87.6 -70 87.2 -80 87.0 -90 86.8 Hz P £ P c P D S i n g l e t 78.7 80.9 78.0 80.8 77.6 81.4 79.0 80.6 77.3 81.7 78.2 80.6 77.2 82.0 77.3 80.6 77.1 82.3 76.8 80.6 77.1 82.6 76.4 80.6 Toluene-dg-DMA ( v/v = 3:1) 2 ' A B = 36.6 Hz, % D = Temperature, °C P A P B P C P D 30 88.8 79.8 84.3 79.8 0 88.5 78.3 83.3 78.5 -20 88.3 77.9 83.4 78.2 -40 88.3 77.9 83.4 78.2 -60 88.1 77.7 83.3 78.1 = 34.1 Hz C h e m i c a l s h i f t s i n ppm, r e l a t i v e l y t o 85$ H^PO 105 -70 I 60 ~1 50 -80' 40 ppm 31 1 F i g u r e 4.7 P{ H}-N.m.r. s p e c t r a o f R i ^ C l ^ ( d p p b ) 2 ( a c e t o n e ) .acetone as a f u n c t i o n o f t e m p e r a t u r e i n C D 2 C l 2 - a c e t o n e a t 40.5 MHz. - 106 -system are shown i n Figure 4 . 7 , and parameters are given i n Table 4 . 3 . The addition of coordinating solvents to solutions of the [RuCl^CP-P)] 2 complexes, P-P = chiraphos and dppb, produces marked changes i n the n.m.r. spectra and, f o r the chiraphos complex, d i f f e r e n t behaviour i s observed i n DMA to that i n acetone s o l u t i o n . For a l l of the systems studied, the p r i n c i p l e species produces two AB patterns suggesting that the complexes remain dimeric i n the presence of these coordinating solvents. The spectra are most e a s i l y interpreted i n terms of a t r i p l y chloro-bridged dimer i n which the two ends of the unit are d i f f e r e n t because of coordination of the solvent (structure 4 - H ) . Table 4 .3 5 1P{ 1H}-N.m.r. Data For [RuCl 2(dppb)] 2 i n CD 2Cl 2-Acetone* CD 2Cl 2-acetone (v:v = 3 :1) 2 j A B = 4 4 * 8 H z > 2 j C D = 5 9 .2 Hz, 2 j = EF 46 .8 Hz Temperature, °C P A P B p c P D P E P F -40 52.0 49.9 49.6 48.3 62.0 53.7 -60 52.1 49.9 49 .8 48.5 62 .0 53.9 -80 52.1 52.0 49 .8 48.7 62 .0 53.9 * Chemical s h i f t s i n ppm, r e l a t i v e to 85$ H^PO^. - 107 -c l l l v R u ^ ^^ R uJ* » * « i P S= Solvent Cl c 4-II The d i f f e r e n c e s i n s p e c t r a f o r t h e t h r e e systems a r i s e s f r o m d i f f e r e n t s o l u t e - s o l v e n t i n t e r a c t i o n s . F o r [RuC± 2(chiraphos)] 2 i n C D 2 C l 2 - a c e t o n e t h e s p e c t r u m a t 30°C i s a. s i m p l e AB p a t t e r n ( = 37.8 Hz) and a s i n g l e t . The AB p a t t e r n i s a s s i g n e d t o t h e r e s o n a n c e s o f t h e ( P - P ) ( C l ) R u C l j p o r t i o n o f t h e m o l e c u l e , w h i c h i s i n a l o c k e d c o n f o r m a t i o n (assuming t h e t r i p l e c h l o r o - b r i d g e does n o t undergo r e a r r a n g e m e n t ) and rema i n s so t h r o u g h o u t t h e t e m p e r a t u r e range s t u d i e d . S u p p o r t f o r t h i s l o c k e d c o n f o r m a t i o n comes from the same c o u p l i n g ( J = 37.8 Hz) found f o r [ R u ^ C l , - ( c h i r a p h o s ) 0 l ( S e c t i o n pp 2 5 2 3.7.3), i n w h i c h b o t h ends o f t h e di m e r have t h i s c o n f o r m a t i o n . The s i n g l e t may be r a t i o n a l i s e d by i n v o k i n g an e q u i l i b r i u m between f r e e and 2 c o o r d i n a t e d s o l v e n t a t Ru , t h e exchange b e i n g r a p i d on t h e n.m.r. ti m e s c a l e . Assuming t h a t t h e s o l v e n t can c o o r d i n a t e a t any o f t h e t h r e e n o n - b r i d g i n g s i t e s , t h e n t h i s w i l l r e s u l t i n a s c r a m b l i n g o f t h e Pp and Pp phosphorus atoms and g e n e r a t i o n o f a s i n g l e r e s o n a n c e . Such a s c r a m b l i n g , however, w i l l n o t e f f e c t t h e r e s o n a n c e s o f P^ and PT, s i n c e t h e s e a r e al w a y s d i a s t e r e o t o p i c as a r e s u l t o f t h e c h i r a l i t y D i n t h e back-bone. On c o o l i n g t h e s o l u t i o n , t h e i n t e n s i t y o f t h e s i n g l e t - 108 -d e c r e a s e s , presumably because t h e e q u i l i b r i u m f a v o u r s s o l v e n t c o o r d i n a t i o n , and t h e t h e r m o d y n a m i c a l l y more s t a b l e p r o d u c t i s formed w i t h t h e s o l v e n t o c c u p y i n g one p a r t i c u l a r s i t e . F u r t h e r c o o l i n g i n c r e a s e s t h e p r o p o r t i o n o f t h e second AB p a t t e r n a t t h e expense o f the s i n g l e t due t o t h e g e n e r a t i o n o f t h e more r i g i d Cl^RuCs)(P-P) m o i e t y . S i n c e o n l y one s e t o f two AB p a t t e r n s i s o b s e r v e d , e i t h e r one d i a s t e r e o m e r i s p r e s e n t o r i n t e r c o n v e r s i o n by exchange o f t e r m i n a l and b r i d g i n g c h l o r i d e s makes t h e d i a s t e r e o m e r s d e g e n e r a t e . T h i s proposed e x p l a n a t i o n c o u l d be t e s t e d e x p e r i m e n t a l l y i f t h e n o n - c h i r a l a n alogue [ R u C l 2 ( d p p e ) ] 2 was p r e p a r e d . I n C D 2 C l 2 - a c e t o n e t h i s would be 31 1 e x p e c t e d t o e x h i b i t two s i n g l e t s i n t h e P{ H}-n.m.r. s p e c t r u m a t ambient t e m p e r a t u r e , and on c o o l i n g produce t h e e x p e c t e d two AB p a t t e r n s . However, t h e r e q u i r e d p r e c u r s o r complex R u 2 C l ^ ( d p p e ) 2 c o u l d n ot be p r e p a r e d ( S e c t i o n 3 - 2 ) . Such a thermodynamic e q u i l i b r i u m a l s o e x p l a i n s t h e o b s e r v e d two broad u n r e s o l v e d r e s o n a n c e s f o r R u 2 C l 4 ( c h i r a p h o s ) 2 ( a c e t o n e ) i n C D 2 C 1 2 . I n t h e absence o f s i g n i f i c a n t amounts o f ac e t o n e t h e complex w i l l r e v e r t p r i n c i p a l l y t o s t r u c t u r e 4-1, and o n l y a s m a l l p r o p o r t i o n w i l l be p r e s e n t as t h e t r i p l y c h l o r o - b r i d g e d s p e c i e s . T h i s i s e x p e c t e d t o produce an a v e r a g i n g o f t h e r e s o n a n c e s between t h e s e s p e c i e s , and presumably t h e s i g n a l s c o u l d be r e s o l v e d o n l y a t l o w e r t e m p e r a t u r e s beyond t h e l i m i t a t i o n s imposed by t h e s o l v e n t . Of p a r t i c u l a r i n t e r e s t was t h e i n t e r a c t i o n o f [ R u C l 2 ( c h i r a p h o s ) ] 2 w i t h DMA. T h i s s h o u l d g i v e i n f o r m a t i o n on s p e c i e s o r i g i n a l l y p r e s e n t i n t h e h y d r o g e n a t i o n s t u d i e s i n t h i s s o l v e n t - 109 -which are described i n subsequent s e c t i o n s . A d d i t i o n of DMA to a toluene-dg s o l u t i o n of the chiraphos complex generates the spec t r a shown i n Figure 4.6. In t h i s case the two AB patter n s assigned to s t r u c t u r e 4-II are evident at 30°C, suggesting that the c o o r d i n a t i o n of DMA at l e a s t i n toluene, i s much stronger than c o o r d i n a t i o n of acetone i n CD2CI2. On c o o l i n g the system, the almost c o i n c i d e n t a l higher f i e l d resonances s h i f t to v a r y i n g degrees and make the two AB patterns become c l e a r l y apparent. The resonances centred at 6 - 81 ppm, Jpp = 34.1 Hz, are assigned to the Cl^RuCS)(P-P) moiety s i n c e the coupling constant i s e s s e n t i a l l y the same as that found when S = acetone (34.2 Hz). A l s o apparent i n the spectra are s e v e r a l l e s s intense resonances which cannot be r e a d i l y assigned. Since DMA i s a stronger donor than acetone the products may be now k i n e t i c a l l y c o n t r o l l e d , and w h i l s t c o o r d i n a t i o n of solvent at one s i t e may be favoured, c o o r d i n a t i o n at the two other s i t e s w i l l generate diastereomers which could give r i s e to the a d d i t i o n a l resonances. A l t e r n a t i v e l y , c o o r d i n a t i o n at the two vacant s i t e s of a doubly chloro-bridged complex i s p o s s i b l e , and assignment of the resonances must await w e l l - r e s o l v e d s p e c t r a or i s o l a t i o n of the p a r t i c u l a r s p e c i e s . The s p e c t r a of RugCl^CdppbJ^acetone) .acetone i n CD2Cl2-acetone (Figure 4.7) i s a l s o assigned to s t r u c t u r e 4 - I I . However, another type of e q u i l i b r i u m must e x i s t : at ambient temperatures the spectra are unresolved, but on c o o l i n g to -40°C three AB patte r n s are observed, the higher f i e l d p a i r being of equal i n t e g r a t e d i n t e n s i t y . The lower f i e l d p a t t e r n ($ = 57.9 ppm, - 110 -2 Jjjvp = 46.8 Hz) i s assigned to the doubly chloro-bridged s t r u c t u r e observed i n the absence of c o o r d i n a t i n g solvent (6= 57.8 ppm, J = 46.8 Hz, S e c t i o n 4.3.1). The higher f i e l d patterns assignable to the t r i p l y chloro-bridged species are not immediately obvious, since i n both cases A<5/J i s s m a l l , causing the outer resonances to be of low i n t e n s i t y . The spectra are a l s o complicated by the p r o x i m i t y of the two overlapping patterns ( 6 ^ = 50.9, &CJ) = 49.0 ppm). On f u r t h e r c o o l i n g the system,the p r o p o r t i o n of the solvent-coordinated species increases w i t h l o s s of the s o l v e n t - f r e e complex. As w i t h [ R u C l 2 ( c h i r a p h o s ) ] 2 i n C l ^ C ^ - a c e t o n e , the b i n d i n g of acetone to the dppb analogue cannot be s t r o n g . The system does d i f f e r though, i n that the solvent exchange must be slow on the n.m.r. time s c a l e because resonances of the i n d i v i d u a l species are observed. The formation of t r i p l y c h l o r o - b r i d g e d species has been observed p r e v i o u s l y i n a number of triphenylphosphine complexes. The complexes 121 122 of general formula, R u 2 C l 5 ( L ) ( P P h ^ where L = CO , CS , PF^ 1 2 3 , N 2 1 2 4 , DMA67, and a c e t o n e 6 7 have been i s o l a t e d or generated i n s i t u . In each case two AB patterns are observed, one 31 1 having r e l a t i v e l y constant P{ H}-n.m.r. parameters U^g 2 - 48 ppm, J = 36-38 Hz) which i s assigned to the C l 3 R u C l ( P P h . j ) 2 p o r t i o n of the molecule. In none of these examples i s a c l e a r l y defined dynamic e q u i l i b r i u m observed as found i n the present study. For the complexes c o n t a i n i n g the u-acids (L = CO, CS, PF^) t h i s seems reasonable, i n that these l i g a n d s w i l l not r e a d i l y d i s s o c i a t e . For L = DMA or acetone, the spectra are s t r o n g l y - I l l -t e m p e r a t u r e dependent, and a t ambient t e m p e r a t u r e t h e g r e a t e r f l u c t i o n a l i t y o f t h e monodentate r e l a t i v e t o b i d e n t a t e p h o s p h i n e s p r e s u m a b l y i n h i b i t s o b s e r v a t i o n o f any e q u i l i b r i a . W h i l s t complexes o f t h e t y p e P 2 ( L ) C l R u C l 2 R u C l ( L ) P 2 a r e known 121 122 (L = CO , CS ) , t h e r e a p p e a r s t o be a g r e a t e r p r o p e n s i t y f o r d i m e r i c r u t h e n i u m c h l o r o - c o m p l e x e s t o form t r i p l y c h l o r o - b r i d g e d s p e c i e s c o n t a i n i n g one L. T h i s i s e v i d e n t , i n t h e p r e s e n t s t u d y f r o m t h e 31 1 P{ H}-n.m.r. s p e c t r a o b t a i n e d i n t h e p r e s e n c e o f c o o r d i n a t i n g s o l v e n t s and DMA.HC1, ( g e n e r a t e d i n s i t u , S e c t i o n 3 . 6 ) , and i s s u p p o r t e d by i s o l a t i o n o f complexes c o n t a i n i n g a s i n g l e c o o r d i n a t e d s o l v e n t m o l e c u l e , as c h a r a c t e r i s e d by e l e m e n t a l a n a l y s i s and i n f r a r e d s p e c t r o s c o p y . 4.4 Asymmetric H y d r o g e n a t i o n o f P r o c h i r a l A l k e n e s A s t u d y o f t h e h y d r o g e n a t i o n o f v a r i o u s p r o c h i r a l a l k e n e s u s i n g t h e complexes [ R u C l 2 ( d i o p ) ] 2 and [ R u C l 2 ( c h i r a p h o s ) ] 2 was u n d e r t a k e n t o d e t e r m i n e t h e i r p o t e n t i a l as c a t a l y s t s o r c a t a l y s t p r e c u r s o r s . A l l e x p e r i m e n t s were p e r f o r m e d on a c o n s t a n t p r e s s u r e g a s - u p t a k e a p p a r a t u s . I n a t y p i c a l e x p e r i m e n t c j u 0.2 g o f s u b s t r a t e was d i s s o l v e d i n DMA (5 mL) and t h e s o l u t i o n deoxygenated p r i o r t o a d d i t i o n o f H 2 and complex. The s t u d y was l i m i t e d t o t h o s e s u b s t r a t e s w h i c h were r e a d i l y a v a i l a b l e , and whose reduced form had a known s p e c i f i c r o t a t i o n ( F i g u r e 4.8) from w h i c h t h e e n a n t i o m e r i c e x c e s s e s were c a l c u l a t e d . F o r each e x p e r i m e n t t h e r e was a 2 0 0 - f o l d e x c e s s o f s u b s t r a t e p e r r u t h e n i u m - 112 -CH 2C0 2H H 2 C = C N • H, C0 2H I t a c o n i c A c i d R(+)- and S ( - ) - 2 - m e t h y l s u c c i n i c a c i d [ a ] 2 5 = ±17.09° ( c l 0 . 5 , C 2H 50H) 125 H C H -^ Q = C ' / + H 2 R ( + ) - and S ( - ) - 2 - m e t h y l s u c c i n i c a c i d H 0 o C X N C 0 . H 25 , sl25 2 2 [ a ] * 3 = ±17.09° ( c l 0 . 5 , C ^ O H ) C i t r a c o n i c A c i d C H H C=C + H 2 *• R ( - ) - and S( + )- 2 - p h e n y l p r o p a n o i c a c i d ° ° 2 H [ a ] 2 5 = ±76.1° ( c 8 . 0 6 , C H C l ^ ) 1 2 6 A t r o p i c A c i d NHCOCH, H 2 C = C ^ + H 2 »~ N - A c e t y l -[R(+) o r S ( - ) ] - a l a n i n e C ° 2 H [ a ] 2 5 = ±66.5° ( c 2 , H 2 0 ) 1 2 7 a - A c e t a m i d o a c r y l i c A c i d C,HK NHCOCH, ° 5 X C = C + H N - A c e t y l - [ R ( - ) o r S( + ) J - p h e n y l a l a n i n e ^ ^ 2 [ c ] f - ,46.5- (cl, C 2H 50H) 1 2 8 ( Z ) - a - A c e t a m i d o c i n n a m i c A c i d F i g u r e 4.8 P r o c h i r a l a l k e n e s used i n h y d r o g e n a t i o n s t u d i e s and t h e i r r e d uced form. The s p e c i f i c r o t a t i o n s g i v e n a r e t h o s e r e p o r t e d f o r the pure e n a n t i o m e r . - 1 1 3 -dimer. The uptakes showed an induction period of up to 5 0 0 s before l i n e a r rates were attained and reduction was generally monitored u n t i l the reaction was complete. I s o l a t i o n and c h a r a c t e r i s a t i o n of the reduced product were as described i n Section 2 . 3 . The r e s u l t s of hydrogenation studies at various temperatures using [ R u C l 2 ( d i o p ) ] 2 are given i n Table 4 . 4 , whilst those f o r the chiraphos analogue are i n Table 4 . 5 . The time taken f o r complete hydrogenation varied considerably, but i n general the chiraphos complex was more e f f i c i e n t . For both complexes the reduction of the t r i - s u b s t i t u t e d alkenes, c i t r a c o n i c and (Z)-a-acetamidocinnamic acids, was much slower compared to the other alkenes which are a l l terminal, presumably because of s t e r i c e f f e c t s . Examination of the product configuration r e s u l t s y i e l d s no obvious o v e r a l l c o r r e l a t i o n between product and ligand configurations. The (R,R)-diop complex, except i n the case of N-acetamidoacrylic acid gives reduced products of the opposite (S)- configuration, whilst f o r the chiraphos complex there i s no such trend. The v a r i a t i o n i n % e.e with the substrate also o f f e r s l i t t l e information as to the nature of the catalyst-substrate i n t e r a c t i o n f o r e i t h e r complex or f o r a comparison of the two. The diop complex i s more e f f e c t i v e f o r those alkenes containing only acid groups, but i s e s s e n t i a l l y non-discriminatory towards the acetamido-acrylic and -cinnamic acids. Hydrogenation, u t i l i s i n g the chiraphos complex, shows s i m i l a r trends except f o r the marked asymmetric reduction of (Z)-a-acetamidocinnamic acid which at 3 0 ° y i e l d s e s s e n t i a l l y one enantiomer. Another feature of t h i s l a t t e r case i s the dramatic - 114 -T a b l e 4.4 Asymmetric H y d r o g e n a t i o n o f U n s a t u r a t e d S u b s t r a t e s U s i n g [ R u C l 0 ( ( R , R ) - d i o p ) ] 2-S u b s t r a t e Temp., °C e.e, P r o d . C o n f i g . A pprox. t o t a l r e a c t i o n time I t a c o n i c A c i d 30 50 70 56 53 51 S S S 3d 12h 5h I t a c o n i c A c i d C i t r a c o n i c A c i d 50 70 38 43 7d 2d A t r o p i c A c i d 50 70 32 25 S S 15h 6h a - A c e t a m i d o a c r y l i c 50 A c i d 70 3 2 R R 8d 3d ( Z ) - a - A c e t a m i d o c i n n a m i c 50 A c i d 70 2 0 16d 5d a) [ R u J = 1.00 (±0.05) x 10 M, [ a l k e n e ] = 2.00 (±0.15) x 10~'LM, 760 mm H . b) R u 2 C l ^ ( ( R , R ) - d i o p ) 2 as c a t a l y s t . c ) 70$ c o m p l e t i o n . - 115 -T a b l e 4.5 Asymmetric H y d r o g e n a t i o n o f U n s a t u r a t e d S u b s t r a t e s U s i n g [ R u C l ( ( S , S ) - c h i r a p h o s ) 2-S u b s t r a t e Temp., % e.e, P r o d . °C C o n f i g . Approx. t o t a l r e a c t i o n time I t a c o n i c A c i d 50 50* 70 39 40 35 R R R 3.5h 3.5h 45 min. C i t r a c o n i c A c i d 70 15 18h A t r o p i c A c i d 50 70 12 10 S S 21h 5h a - A c e t a m i d o a c r y l i c 50 A c i d 70 4 5 S S 24h 6h ( Z ) - a - A c e t a m i d o c i n n a m i c 30 A c i d 50 70 97 63 19 S S s 24h 5h 1.5h a) [ R u 2 ] = 1.00 (± 0.03) x 1 0 _ 3 M , [ a l k e n e ] = 2.00 (± 0.15) x 1 0 _ 1 M , 760mm H 2» b) T e s t f o r r e p r o d u c i b i l i t y . - 116 -increase i n % e.e. with a lowering of the temperature, a feature that i s common to reductions of a l l alkenes catalysed by both complexes, but unfortunately not to the same extent. Reduction of i t a c o n i c acid with the diop mixed-valence complex, Ru„Cl [ r(diop)„, proceeds at a much slower rate and with a lower d o ^ asymmetric induction than with the dimeric ruthenium (II) complex under the same conditions. The main purpose of t h i s hydrogenation study was to determine i f the complexes [ R u C l 2 ( P - P ) ] 2 , P-P = chiraphos or diop, were sui t a b l e f o r asymmetric hydrogenation. Of importance though i s the nature of the c a t a l y t i c a l l y active species (dimeric, monomeric, hydride or alkene complex ?) . In order to investigate t h i s , the r e a c t i v i t y of the chiraphos complex was studied with: substrate alone, and with H 2 alone. Addition of up to a 200-fold excess of (Z)-a-acetamidocinnamic acid to DMA solutions of the complex i n the absence of H 2 produced no changes i n the v i s i b l e spectra suggesting no binding of substrate. In the absence of substrate a 3.0 x 10 M DMA s o l u t i o n of [ R u C l 2 ( c h i r a p h o s ) ] 2 at 50°C, gave a H 2 uptake corresponding to 1.0Ru2:0.20H2 a f t e r 150s. In the presence of Proton Sponge at the same conditions the uptake increased to 1.0Ru2:1.57H2. That the reaction with H 2 i s base-promoted, suggests the formation of a ruthenium-hydride species v i a reductive elimination of HC1, rather than formation of a neutral or i o n i c dihydride. The time taken f o r Reuptake i n the absence of substrate i s comparable to the induction period observed i n the c a t a l y t i c hydrogenation studies, hence i n i t i a l - 117 -f o r m a t i o n o f an a c t i v e h y d r i d o - s p e c i e s a p p ears p r o b a b l e (see a l s o S e c t i o n 5 . 2 ) . 4.4.1 D i s c u s s i o n The h y d r o g e n a t i o n o f p r o c h i r a l a l k e n e s u t i l i s i n g [ R u C l 2 ( c h i r a p h o s ) ] 2 o r t h e d i o p a n a l o g u e as c a t a l y s t p r e c u r s o r s p r o c e e d s i n r e l a t i v e l y m i l d c o n d i t i o n s . The wide v a r i a t i o n i n r a t e s , p r o d u c t c o n f i g u r a t i o n , and % e.e. i n d i c a t e t h a t b o t h t h e n a t u r e o f t h e c h i r a l p h o s p h i n e l i g a n d and s u b s t r a t e a r e s i g n i f i c a n t f a c t o r s i n t h e o v e r a l l p r o c e s s . S p e c u l a t i o n as t o t h e n a t u r e o f t h e s u b t r a t e - c a t a l y s t i n t e r a c t i o n i n o r d e r t o e x p l a i n t h e s e l a r g e v a r i a t i o n s , f o r example by 8 a p p l y i n g Knowles e m p e r i c a l q u a d r a n t r u l e , i s t e m p t i n g . However, w i t h o u t a b e t t e r u n d e r s t a n d i n g o f t h e c a t a l y t i c a l l y a c t i v e s p e c i e s and m e c h a n i s t i c d e t a i l s , s u c h s p e c u l a t i o n i s n o t a p p r o p r i a t e . I n s t e a d , a c o m p a r i s o n w i t h the d a t a o b t a i n e d by o t h e r w o r k e r s u s i n g o t h e r c a t a l y s t s w i l l be p r e s e n t e d . Of p a r t i c u l a r r e l e v a n c e a r e t h e d a t a o b t a i n e d p r e v i o u s l y u s i n g t h e complexes R u H C l ( d i o p ) 2 and R u ^ l ^ d i o p ) ^ ( S e c t i o n 4 . 1 ) . T a b l e 4.6 g i v e s t h e d a t a f o r t h e s e complexes a t 60°C"''" and t h o s e o b t a i n e d i n t h i s s t u d y a t 50°C. The o b s e r v e d d i f f e r e n c e s i n p r o d u c t c o n f i g u r a t i o n must s i m p l y be as a r e s u l t o f u s i n g p h o s p h i n e l i g a n d s o f o p p o s i t e c o n f i g u r a t i o n . S i n c e R ^ C l ^ d i o p ) ^ r e a c t s w i t h H 2 t o g e n e r a t e R u H C l ( d i o p ) 2 and [ R u C l 2 ( d i o p ) ] 2 ( e q u a t i o n 4 . 1 ) , any d i f f e r e n c e s between t h e b r i d g e d - d i o p complex and t h a t o f t h e i s o l a t e d h y d r i d e must be a t t r i b u t e d t o [ R u C l _ ( d i o p ) ] _ . The h i g h e r % e.e. found f o r t h e - 118 -Table 4.6 Hydrogenation of P r o c h i r a l Alkenes by Ruthenium-Diop Complexes Substrate Catalyst RuHCl((+)diop) 2 Ru 2Cl4((+)diop) 3 Prod. %e.e. Config. Prod. %e.e. Config. [ R u C l 2 ( ( - ) d i o p ) ] 2 Prod. %e.e. Config. Atropic Acid R(-) Itaconic Acid R( +) a-Acetamidoacrylic Acid Ci t r a c o n i c Acid 27 23 R(-) H( + ) S(-) 40 38 59 0 S( + ) S(-) H( + ) S(-) 32 53 3 43 hydrogenation of atropic and i t a c o n i c acids, using R u ^ l ^ d i o p ) ^ r e l a t i v e to the hydride complex, i s consistent with the higher e n a n t i o s e l e c t i v i t y obtained using the [ R u C l 2 ( d i o p ) ] 2 complex. The reason f o r the large difference (and apparent inconsistency) i n the data f o r the other two p r o c h i r a l alkenes i s not obvious. For RuHCl(diop) 2 to become c a t a l y t i c a l l y active the complex must undergo i n i t i a l d i s s o c i a t i o n of a diop ligand"''"'""'" (equation 4.3). Since the use of the " d i o p - d e f i c i e n t " species should eliminate the need f o r such a d i s s o c i a t i o n step i t was hoped that t h i s would increase the e n a n t i o s e l e c t i v i t y . For the reduction of i t a c o n i c acid the asymmetric induction i s s i g n i f i c a n t l y better (Table 4.6), but f o r atropic acid only - 1 1 9 -a m a r g i n a l i n c r e a s e i n % e.e. i s found between t h e s e two complexes. The i n i t i a l d i s s o c i a t i o n o f a p h o s p h i n e l i g a n d f r o m R u H C l ( d i o p ) 2 as a p r e r e q u i s i t e s t e p f o r c a t a l y t i c a c t i v i t y r e s t r i c t s t h e t y p e o f d i s p h o s p h i n e t h a t can be u s e d . F o r P-P = dppm, dppe, and dppp, w h i c h a r e l e s s b u l k y t h a n d i o p , l i g a n d d i s s o c i a t i o n p r e s umably does n o t o c c u r , as t h e c o r r e s p o n d i n g Ru h y d r i d e s a r e c a t a l y t i c a l l y i n a c t i v e f o r 79 h y d r o g e n a t i o n . The use o f t h e [ R u C l 2 ( P - P ) ] 2 complexes as c a t a l y s t p r e c u r s o r s p r o v i d e s a v i a b l e a l t e r n a t i v e f o r t h e i n c o r p o r a t i o n o f any d i p h o s p h i n e w i t h p r esumably a good chance o f some a c t i v i t y . T h i s i s e x e m p l i f i e d by t h e c h i r a p h o s system: t h e R u H C l ( c h i r a p h o s ) 2 complex would be e x p e c t e d t o be c a t a l y t i c a l l y i n a c t i v e by a n a l o g y t o t h e c o r r e s p o n d i n g dppe complex, w h i l s t [RuC± 2(chiraphos)] 2 has been shown t o be a c t i v e . W i t h t h e n o t a b l e e x c e p t i o n o f t h e a - a c e t a m i d o - a c r y l i c and - c i n n a m i c a c i d s , t h e h y d r o g e n a t i o n o f t h e o t h e r p r o c h i r a l a l k e n e s u s i n g [ R u C l 2 ( c h i r a p h o s ) J 2 p r o d u c e s o n l y modest e n a n t i o m e r i c e x c e s s e s ( T a b l e 4.5). The h y d r o g e n a t i o n o f ( Z ) - a - a c e t a m i d o c i n n a m i c a c i d a t 30°C w i t h 97$ e.e. i s i n s h a r p c o n t r a s t t o t h e h y d r o g e n a t i o n o f a - a c e t a m i d o a c r y l i c a c i d w h i c h p r o c e e d s e s s e n t i a l l y w i t h no e n a n t i o s e l e c t i v i t y . The most o b v i o u s e x p l a n a t i o n l i e s i n t h e p r e s e n c e o f t h e b u l k y p h e n y l group. T h i s may p l a y a r o l e i n t h e s t e p a t w h i c h a s ymmetric i n d u c t i o n t a k e s p l a c e ; an i n t e r a c t i o n o f t h e p h e n y l group w i t h the r i g i d a r r a y o f p h e n y l groups o f t h e p h o s p h i n e would r e s u l t i n t h e f a v o u r e d f o r m a t i o n o f one d i a s t e r e o m e r . The absence o f suc h a b u l k y s u b s t i t u e n t on t h e a l k e n e , as i n a - a c e t a m i d o a c r y l i c a c i d , c l e a r l y - 120 -generates "equivalent" diastereomers at the asymmetric induction step. The hydrogenation of (Z)-a-acetamidocinnamic acid compares favourably with that found using [Rh((S,S)-chiraphos)] (89$ e.e. (R) i n ethanol) but a product of opposite configuration i s generated; t h i s implies a s u b s t a n t i a l l y d i f f e r e n t mechanism f o r c h i r a l recognition. For the hydrogenation of a-acetamidoacrylic acid,however the substrate-catalyst i n t e r a c t i o n i s non-discriminatory which i s i n sharp 18 contrast to the rhodium system f o r t h i s substrate (91$ e.e. i n ethanol). Of p a r t i c u l a r i n t e r e s t i s the observed increase i n $ e.e with decreasing temperature f o r e s s e n t i a l l y a l l substrates and both [RUCI 2(P-P)] 2 complexes. For the rhodium-catalysed hydrogenation (Section 1.2) the e n a n t i o s e l e c t i v i t y a r i s e s from the greater r e a c t i v i t y of the minor diastereomeric catalyst-substrate adduct towards H 2 rather than the i n i t i a l proportions of the diastereomers. The proposed 33 mechanism pr e d i c t s that lowering the temperature w i l l reduce the rate of interconversion of the diastereomeric adducts as t h i s has a higher a c t i v a t i o n enthalpy than the subsequent reaction with H 2 > Since i t i s the interconversion of adducts which determines the e n a n t i o s e l e c t i v i t y of the reaction, a reduction of the interconversion rate leads to a reduction i n $ e.e. This has been observed i n some 129 130 rhodium-catalysed systems ' , and i n one case the o p t i c a l y i e l d increased from 0 to 60$ e.e. i n going from 0° to 100 OC 1 3°. For the ruthenium-catalysed hydrogenations i n the present study the opposite phenomenon i s observed; t h i s i s p a r t i c u l a r l y dramatic for the - 121 -hydrogenation of (Z)-a-acetamidocinnamic acid by the chiraphos complex which shows a decrease from 97 to 19% e.e. i n going from 30° to 70°C. This suggests that e i t h e r the major diastereomer at the asymmetric induction step has the greater r e a c t i v i t y or, a r e s t r i c t i o n of motion of the coordinated substrate occurs with lowering the temperature. The hydrogenation of i t a c o n i c acid using E u ^ l ^ d i o p ) , , as c a t a l y s t precursor proceeds at a slower rate and gives a lower e.e. r e l a t i v e to [ E u C l 2 ( d i o p ) ] 2 (Table 4.4). The reduction i n rate i s presumably due to the formation of i n a c t i v e [ i h ^ C l ^ d i o p ) , ^ ] DMAH+ (Section 3.7) formed by add i t i o n of the HC1 generated i n the reduction of the mixed-valence complex to the active c a t a l y s t precursor. How formation of the anion a f f e c t s the e n a n t i o s e l e c t i v i t y i s not c l e a r j however, the hydrogenation i n v o l v i n g [ B u C l 2 ( P - P ) ] 2 requires i n i t i a l generation of the hydrido-species and therefore simultaneous generation of HC1. Addition of generated HC1 to the s t a r t i n g complex also generates some [ E u 2 C l ^ ( P - P ) 2 J (Section 5.2) and t h i s should also a f f e c t the rate and o p t i c a l y i e l d . Consequently the f u l l p o t e n t i a l of the 1:1 Eu:(P-P) c a t a l y t i c systems has not been r e a l i s e d . The use of an i s o l a t e d hydrido-species i s . expected to give improved r e s u l t s , and would be invaluable i n attempts to elucidate mechanistic d e t a i l s . - 122 -CHAPTER V GENERATION OF RUTHENIUM HYDRIDE COMPLEXES 5.1 I n t r o d u c t i o n The p r e p a r a t i o n o f t r a n s i t i o n m e t a l h y d r i d e complexes has been 58 a c c o m p l i s h e d by a number o f methods : u s i n g m o l e c u l a r H,,, o x i d a t i v e a d d i t i o n o f HX, p r o t o n a t i o n , hydrogen t r a n s f e r from a l c o h o l s , BH^ - o r AlH^j" (and t h e i r d e r i v a t i v e s ) , r e d u c i n g a g e n t s ( i . e . h y d r a z i n e , f o r m i c a c i d , a l k a l i m e t a l s ) , and i n t r a m o l e c u l a r hydrogen t r a n s f e r from o r g a n i c l i g a n d s . The method used o b v i o u s l y depends on t h e n a t u r e o f t h e s t a r t i n g compound and t h e s t a b i l i t y o f t h e p r o d u c t s . I n t h i s l a b o r a t o r y H 2 i s most f r e q u e n t l y u s e d , as t h i s r e a g e n t i s most l i k e l y t o g e n e r a t e t h e h y d r i d e s p e c i e s p r e s e n t i n c a t a l y t i c h y d r o g e n a t i o n s t h a t u t i l i s e H^ gas as t h e s o u r c e o f h y d r o g e n . The g e n e r a t i o n o f h y d r i d o - p h o s p h i n e complexes o f r u t h e n i u m u s i n g H 2 i s u s u a l l y from a h a l i d e p r e c u r s o r and, s i n c e s u c h a r e a c t i o n g e n e r a t e s HX ( S e c t i o n 1.3), a base i s commonly r e q u i r e d , as e x e m p l i f i e d 131 6*7 by e q u a t i o n s (5.1) and (5.2) , where P i s a monodentate p h o s p h i n e : R u C l 0 P , + H. N E t 3 (5.D 2 R u C l 5 P 2 + 4 H 2 PS ^ [ R u H 2 C l P 2 J 2 + 4PSH +C1 (5 .2) - 123 -The choice of base i s important: f o r example, i f reaction 5.2 i s c a r r i e d out i n the absence of Proton Sponge (PS), and a weakly basic solvent (DMA) i s used, the reduction proceeds only to 132 [ R u C l , ^ ^ ' Triethylamine (pKfi = 10.6) r e a d i l y promotes hydride formation; however, complications can a r i s e through coordination 133 and/or dehydrogenation of t h i s strong base . The use of Proton Sponge i s favoured, since i t i s a s u f f i c i e n t l y strong base (pK„ = 11.3)f and i s generally thought to be unable to coordinate because of s t e r i c hindrance about the nitrogen atom. • In the present study, the i s o l a t i o n of a hydride complex was p r i m a r i l y of i n t e r e s t i n order to determine the active species present i n , and mechanistic d e t a i l s of, the alkene hydrogenations (Section 4 . 4 ) . Attempts to generate hydrido-species d i r e c t l y from the mixed-valence complexes R u 2 C l 3 ( P - P ) 2 were unsuccessful i n DMA or i n toluene with added Proton Sponge (Section 3 . 7 ) . In both cases reduction occurs, but the apparent high a f f i n i t y of the product f o r C l " leads to generation of [Ru 2Cl 5(P-P) 2]~BH + (B = DMA or PS). A l t e r n a t i v e routes were therefore necessary, and t h i s chapter describes the generation of three hydride complexes. 5.2 Reaction of Ru 2Cl 4(dppb) 2(acetone).acetone ( l ) with H 2  i n DMA The H 2-uptake (at 1 atm.) of a DMA s o l u t i o n of 1 at 30°C i n the presence of Proton Sponge corresponded to 1.0 Ru 2: 1.6 H 2 over 1 h. This f r a c t i o n a l uptake i s inconsistent with the complete formation - 124 -o f any s i m p l e h y d r i d o - c o m p l e x . The r e a c t i o n was t h e r e f o r e p e r f o r m e d on a p r e p a r a t i v e s c a l e i n an a t t e m p t t o i s o l a t e and c h a r a c t e r i s e t h e h y d r i d e p r o d u c t . A DMA s o l u t i o n (40 ml) o f _1 ( l . O g, 0.76 mmol) and P r o t o n Sponge (0.6 g, 2.8 mmol) was s t i r r e d under 1 atm. H 2 a t ambient t e m p e r a t u r e f o r 16 h. The r e s u l t i n g r e d s o l u t i o n was c o n c e n t r a t e d t o a v i s c o u s o i l t o w h i c h C^Hg (40 mL) was added w i t h s t i r r i n g t o cause d i s s o l u t i o n . The s o l u t i o n was f i l t e r e d t h r o u g h C e l i t e , and c o n c e n t r a t e d t o _ca_. 20 mL. Three s u c c e s s i v e s l o w p r e c i p i t a t i o n s by a d d i t i o n o f hexanes and f u r t h e r c o n c e n t r a t i o n a f f o r d c j u 0.6 g o f an orange complex i d e n t i f i e d as [ E u 2 C l 5 ( d p p b ) 2 ] " P S H + [ ^ P ^ H l - n . m . r . , (CD 2C1 2) s, 54.6 ppm, and e l e m e n t a l a n a l y s i s , ( S e c t i o n 2.1.7.7)]. The f i l t r a t e l e f t a f t e r r e moval o f t h i s p r o d u c t was e v a p o r a t e d t o d r y n e s s and t a k e n up i n CgHg (5 mL). To t h e r e d s o l u t i o n was added d i e t h y l e t h e r t o b r i n g about p r e c i p i t a t i o n o f an orange-brown p r o d u c t (50 mg). 31 1 The P{ H}-n.m.r. s p e c t r u m ( C D C l g , -95°C) o f t h i s f i n a l p r o d u c t ( F i g u r e 5 . l ) c l e a r l y shows the p r e s e n c e o f more t h a n one p h o s p h o r u s - c o n t a i n i n g s p e c i e s o f w h i c h o n l y [ R u 2 C l ^ ( d p p b ) 2 ] PSH i s o b v i o u s l y a s s i g n a b l e . However, t h e "''H-n.m.r (CD 2C1 2, ambient t e m p e r a t u r e ) does show broad h y d r i d e r e s o n a n c e s a t -17.65 6 ( t , J = 32 Hz) and -21.90 6 ( t , J = 32 Hz) i n an a p p r o x i m a t e 1:1 r a t i o . The r e a c t i o n o f 1^  w i t h H 2 does, t h e r e f o r e , g e n e r a t e h y d r i d e s p e c i e s but t h e s e have n o t y e t been i s o l a t e d o r c h a r a c t e r i s e d . Some p o i n t s c o n c e r n i n g t h e i s o l a t i o n o f [ R u 9 C l c - ( d p p b ) ] _ P S H + m e r i t - 125 -"51 1 Figure 5.1 P{ H}-N.m.r. spectrum (CD 2C1 2, -95°C) of the f i n a l product obtained from the r e a c t i o n of Eu 9Cl.(dppb)p(acetone).acetone w i t h H ?. c o n s i d e r a t i o n . The r e a c t i o n of the triphenylphosphine analogue of 67 [ R u C l 2 ( d p p b ) ] 2 , i n the presence of added base has been shown to give a Reuptake s t o i c h i o m e t r y c o n s i s t e n t w i t h : [ R u C l 2 ( P P h 3 ) 2 ] 2 + 3H 2 D a s e ^ [ R u H 2 C l ( P P h 3 ) 2 ] 2 + 2HC1 (5.3) The hydride product, although not i s o l a t e d by t h i s route, was 31 1 c h a r a c t e r i s e d ( P{ H}-n.m.r. and v i s i b l e spectra) by comparison - 126 -w i t h an a u t h e n t i c sample. A t t h e o n s e t o f the p r e s e n t s t u d y i t was hoped t h a t t h e b i d e n t a t e p h o s p h i n e a n a l o g u e s would undergo a c o r r e s p o n d i n g r e a c t i o n . The low H 2 s t o i c h i o m e t r y and i s o l a t i o n o f [ R u 2 C l j _ ( d p p b ) 2 ] PSH c l e a r l y show, however, t h a t t h i s i s n o t the c a s e . The g e n e r a t i o n o f a h y d r i d o - s p e c i e s from _1 r e s u l t s p resumably i n s i m u l t a n e o u s g e n e r a t i o n o f HC1, but u n l i k e t h e PPh^ an a l o g u e , t h e h i g h c h l o r i d e a f f i n i t y o f t h e s t a r t i n g m a t e r i a l r e s u l t s i n the f o r m a t i o n o f t h e i o n i c complex w h i c h i s u n r e a c t i v e towards H 2 > A d d i t i o n o f c h l o r i d e t o [ R u C l 2 ( P P h 3 ) 2 ] 2 i n t h e absence o f H 2 67 a l s o r e s u l t s i n f o r m a t i o n o f a p e n t a c h l o r o d i r u t h e n i u m a n i o n ; however, t h i s must be more r e a c t i v e t h a n t h e dppb a n a l o g u e . The h i g h s o l u b i l i t y o f [ R u 2 C l ^ ( d p p b ) 2 ] P SH + i n benzene s u g g e s t s a n o n - d i s s o c i a t e d s t r u c t u r e w h i c h i s u n f o r t u n a t e , s i n c e e a s i e r s e p a r a t i o n o f t h i s s p e c i e s would p r o b a b l y m i t i g a t e i s o l a t i o n o f t h e h y d r i d e complex. 5.3 F o r m a t i o n o f D i - y - c h l o r o - y - h y d r i d o - h y d r i d o - ( c a r b o n y l ) -b i s ( d p p b ) d i r u t h e n d u m ( l l ) , R u 2 H 2 ( C 0 ) C l 2 ( d p p b ) 2 , 2 I 5.3.1 P r e p a r a t i o n The H i j - r e d u c t i o n o f R u 2 C l ^ ( d p p b ) 2 i n DMA g e n e r a t e s i n  s i t u t h e i o n i c complex, [ R u 2 C l 5 ( d p p b ) 2 ] ~ DMAH + ( S e c t i o n 3.7.3.2). A d d i t i o n o f methanol c a u s e s d i s p l a c e m e n t o f DMA.HC1 and t h e n e u t r a l complex, [ R u C l 2 ( d p p b ) ] 2 can be i s o l a t e d ( S e c t i o n 4 . 2 ) . S i n c e a t t e m p t s t o g e n e r a t e a h y d r i d o - c o m p l e x from R u 2 C l 4 ( d p p b ) 2 ( a c e t o n e ) . a c e t o n e , _1, l e d t o t h e f o r m a t i o n o f l a r g e - 127 -proportions of [Ru 2Clj-(dppb ) 2 J PSH (previous Section), the use of methanol as solvent to displace the PS.HC1, and promote the reaction with H 2 seemed f e a s i b l e . The i n s o l u b i l i t y of the s t a r t i n g complex i n methanol necessitated the use of a second solvent. The solvent chosen was CH 2C1 2 since _1 i s very soluble i n t h i s , and also i t was hoped that a f t e r reaction with IL,, concentration of the s o l u t i o n would f i r s t remove the CH 2C1 2 and cause p r e c i p i t a t i o n of the product, whilst the PS.HC1 "generated and excess Proton Sponge would be soluble i n the methanol. From the reaction of 1_ with H 2 i n the presence of Proton Sponge i n CH^Cl^/MeOH (1:1 by volume) the complex R u 2 ^ 2 ^ ^ ^ 1 2 ^ d P P ^ ^ 2 ' —' w a s i s°l ated and characterised (next Section). The i s o l a t i o n was somewhat f o r t u i t o u s i n that addition of d i e t h y l ether to wash the product i n i t i a l l y obtained, caused d i s s o l u t i o n of the hydrido-carbonyl complex and f a c i l i t a t e d easy separation from the d i e t h y l ether-insoluble material which remains uncharacterised. To confirm the assignment of a weak absorption i n the i n f r a r e d spectrum of 2 to ^ the reaction was repeated using D 2. Of i n t e r e s t , the product obtained, gave the same in f r a r e d spectrum, and more importantly, the ''"H-n.m.r. spectrum showed the same hydride resonances i n the correct integrated r a t i o as found f o r the ^-generated product. This strongly suggested that H 2 was not involved i n the formation of 2, and t h i s was then confirmed by i s o l a t i o n when the reaction was performed under argon. D e t a i l s of the preparation of 2 are given i n Section 2.1.7.8. - 128 -5.3.2 C h a r a c t e r i s a t i o n . The R u 2 H 2 ( C 0 ) C l 2 ( d p p b ) 2 complex (2) i n C D 2 C 1 2 a t ambient t e m p e r a t u r e e x h i b i t s two h i g h - f i e l d r e s o n a n c e s i n t h e '''H-n.m.r. sp e c t r u m ( F i g u r e 5.2). These h y d r i d e r e s o n a n c e s a r e a t r i p l e t (-19.816, J = 3 0 H z ) , and a d o u b l e t o f t r i p l e t s o f d o u b l e t s (-9.49 6, J = 83, 15, 8 H z ) . The h y d r i d e r e s o n a n c e s have an i n t e g r a t i o n r a t i o o f 1:1, and t h e i r combined i n t e g r a t i o n i s l / 2 0 t h o f t h a t f o r t h e p h e n y l r e s o n a n c e s o f t h e dppb l i g a n d . Phosphorus d e c o u p l i n g r e s u l t e d i n c o l l a p s e o f t h e h y d r i d e r e s o n a n c e s t o two s i n g l e t s . The 5 1 P { 1 H } - n . m . r . s p e c t r u m o f 2 ( C D 2 C 1 2 , 30°C) i s shown i n F i g u r e 5.3. The complex e x h i b i t s f o u r d i s c r e t e r e s o n a n c e s ( a s s i g n e d on t h e b a s i s o f c h e m i c a l s h i f t ) a t 68.2 ( P ( l ) ) , 58.0 ( P ( 2 ) ) , 46.4 ( P ( 3 ) ) and 17.0 ( P ( 4 ) ) ppm i n t h e i n t e n s i t y r a t i o 1:1:1:1. Of t h e s e , t h e d e c e p t i v e l y s i m p l e t r i p l e t ( P ( 2 ) ) a p p e a r s t o a r i s e from c o u p l i n g t o a l l o t h e r phosphorus atoms, t h e c o u p l i n g s b e i n g u n r e s o l v e d as t h e y a r e comparable t o t h e l i n e - w i d t h s o f t h e s i g n a l s . P ( l ) i s o n l y c o u p l e d t o P ( 2 ) , whereas P ( 3 ) and P ( 4 ) c o u p l e t o one a n o t h e r as w e l l as t o P ( 2 ) . The s i m u l a t e d s p e c t r u m i s shown i n F i g u r e 5.4. The 31 1 P{ H}-n.m.r. s p e c t r u m o f 2 was i d e n t i c a l i n DMA, CgDg, and i n C D 2 C 1 2 a t -30°C. A t t e m p t s t o s e l e c t i v e l y d e c o u p l e the p r o t o n r e s o n a n c e s o f t h e dppb l i g a n d were u n s u c c e s s f u l . The i n f r a r e d s p e c t r u m o f 2_ shows a b s o r p t i o n s a t 2030 (w, t e r m i n a l Ru-H) and 1953 cm ^ ( s , t e r m i n a l CO), and no a b s o r p t i o n s a t t r i b u t a b l e t o a t e r m i n a l R u - C l s t r e t c h . - 129 -T •9rf -10 Figure 5.2 H i g h - f i e l d region of the H-n.m.r. spectrum of Ru 2H 2(C0)Cl 2(dppb) 2 i n CD 2C1 2 at 400 MHz. 5.3.3 Discussion The i s o l a t i o n of Ru 2H 2(C0)Cl 2(dppb) 2, 2, from just s t i r r i n g Ru 2Cl 4(dppb) 2(acetone).acetone i n CH2Cl2/MeOH at room temperature was unexpected. The formation of 2 under argon, as well as i n the presence of H 2 or D 2,strongly suggests that methanol i s acting as a reducing agent and a source of CO. The stoichiometry shown i n equation 5.4 shows perhaps the simplest p o s s i b i l i t y ; the decarbonylation reaction w i l l be discussed i n further d e t a i l at the end of t h i s section. PS R u 2 C ± 4 ( d p p b ) 2 + CH OH Ru 2H 2(C0)Cl 2(dppb) 2 + 2HC1 (5.4) To r a t i o n a l i s e the a v a i l a b l e spectroscopic data, structure 5-1 i s proposed f o r 2, i n which the geometry about each ruthenium atom i s pseudo-octahedral. The l a b e l l i n g scheme f o r the phosphorus atoms i s - 130 -P(D 68.2 ppm P ( 2 ) 58.0 ppm P ( 3 ) 46.4 ppm P ( 4 ) 17.0 ppm 31 1 F i g u r e 5.3 P{ H}-N.m.r. s p e c t r u m o f R u 2 H 2 ( C 0 ) C l 2 ( d p p b ) 2 i n C D 2 C 1 2 a t ambient t e m p e r a t u r e a t 32.4 MHz. J v. F i g u r e 5.4 S i m u l a t e d P{ H}-n.m.r. s p e c t r u m o f R u 2 H 2 ( C 0 ) C l 2 ( d p p b ) , - 131 -0C\R ^ R /T (2)P^7R \ / R U ^ « P ( 3 ) (V (2) > H < 1 > 5 - 1 based on t h e c h e m i c a l s h i f t d a t a p r e s e n t e d i n S e c t i o n 5.3.2. The t r i p l e t o b s e r v e d a t h i g h f i e l d i n t h e 1H-n.m.r. sp e c t r u m o f 2 can be a s s i g n e d t o t h e t e r m i n a l h y d r i d e ( H ( l ) ) , w h i c h i s c o u p l e d 2 e q u a l l y t o t h e two c i s - p h o s p h o r u s n u c l e i ( J p ^ = 30 H z ) . The b r i d g i n g h y d r i d e , however, i s c o u p l e d t o a l l f o u r phosphorus atoms. The 2 l a r g e s t c o u p l i n g ( J p ^ = 83 Hz) i s w i t h i n t h e range n o r m a l l y found f o r t r a n s c o u p l i n g c o n s t a n t s i n mononuclear complexes o f r u t h e n i u m ( l l ) (60 - 90 H z ) 1 3 4 , and t h e r e f o r e a r i s e s f r o m c o u p l i n g t o P ( 4 ) . The a d d i t i o n a l s m a l l e r c o u p l i n g s a r e c o n s i s t e n t w i t h t h e r e m a i n i n g phosphorus atoms b e i n g c i s , and i t i s n o t u n r e a s o n a b l e t h a t 2 j P ( l ) - H ( 2 ) = 2 j P ( 2 ) - H ( 2 ) = 1 5 H Z a n d 2 j P ( 3 ) - H ( 2 ) = 8 H z ' T h e u n o b s e r v e d c o u p l i n g i n d i c a t e s t h a t i t i s q u i t e s m a l l w h i c h i s n o t 134 u n u s u a l f o r p o l y h y d r i d e complexes o b s e r v e d f o r 2 i s one o f 67, 135 31 1 The P{ H}-n.m.r. s p e c t r u m o b s e r v e d f o r 2 i s one o f an i n c r e a s i n g number found f o r p o l y n u c l e a r - r u t h e n i u m complexes The c h e m i c a l s h i f t o f P ( 4 ) , 17.0 ppm, i s o f much l o w e r f r e q u e n c y t h a n t h e o t h e r s , w h i c h i s c o n s i s t e n t w i t h t h e phosphorus b e i n g t r a n s t o a h y d r i d e . However, t h e P ( 4 ) r e s o n a n c e i s n o t t o such low f i e l d as i s 136 o b s e r v e d f o r phosphorus t r a n s t o a t e r m i n a l h y d r i d e , and s u g g e s t s - 132 -t h a t a t r a n s b r i d g i n g h y d r i d e does n o t have such a marked e f f e c t on t h e c h e m i c a l s h i f t . To e x p l a i n t h e o b s e r v e d c o u p l i n g phenomena i t i s assumed t h a t a l l phosphorus atoms on the same r u t h e n i u m atom a r e c o u p l e d . S i n c e no c o u p l i n g i s o b s e r v e d between P ( l ) and P(4), t h e s e must be on d i f f e r e n t 2 r u t h e n i u m atoms. The o b s e r v e d J p ( i ) _ p ( 2 ) = 44.1 Hz n e c e s s i t a t e s P ( l ) and P ( 2 ) t o be on t h e same r u t h e n i u m ( R u 1 ) , w h i c h i s n o t u n r e a s o n a b l e c o n s i d e r i n g t h e i r s i m i l a r c h e m i c a l s h i f t s , and c o n s e q u e n t l y 2 P ( 3 ) and P(4) a r e a s s i g n e d t o atoms on Ru . Whether t h e p o s i t i o n s o f P ( l ) and P ( 2 ) a r e as shown i n 5-1 o r a r e i n t h e r e v e r s e d f o r m , cannot be d e t e r m i n e d , but i s o f s i g n i f i c a n c e i n terms o f t h e c h e m i c a l s h i f t s (68.2 v s . 58.0 ppm) and t h e t r a n s f e r o f c o u p l i n g between t h e r u t h e n i u m c e n t r e s t o P ( 2 ) ( 4 J p ( 4 ) _ p ( 2 ) = 39.7 Hz and 4 J p ( 3 ) _ p ( 2 ) = 2 - 9 H z ) . The d i f f e r e n c e i n c h e m i c a l e n v i r o n m e n t s o f P ( l ) and P ( 2 ) i s e x p e c t e d t o produce d i f f e r e n c e s i n c h e m i c a l s h i f t , but w h i c h arrangement p r o d u c e s t h e o b s e r v e d c o u p l i n g i s n o t o b v i o u s . The t r a n s f e r o f c o u p l i n g between r u t h e n i u m - r u t h e n i u m c e n t r e s has been o b s e r v e d i n compounds o f t h e g e n e r a l t y p e s 5 - H , w h i c h c o n t a i n a 3 Ru-Ru bond. The o b s e r v e d c o u p l i n g c o n s t a n t s ( J p p = 82-189 Hz) CO, X CO cd R U € x^ CO 5-II - 133 -3 appear t o be a f u n c t i o n o f t h e Ru-X-Ru b r i d g e a n g l e , w i t h Jpp 137 i n c r e a s i n g from X = h a l o t o c a r b o x y l a t o t o methoxo . These v a l u e s 2 a r e comparable t o t h e Jpp c o u p l i n g c o n s t a n t s found f o r mononuclear t r a n s phosphorus atoms, w h i c h r e f l e c t s t he h i g h degree o f o v e r l a p o f t h e 137 Ru-Ru o r b i t a l s i n P-Ru-Ru-P m o i e t i e s . I n t h e p r e s e n t s t u d y , t h e l a c k o f a Ru-Ru bond ( a s e v i d e n c e d by t h e complexes d i a m a g n e t i c c h a r a c t e r ) i m p l i e s t h a t a m e t a l - m e t a l bond i s n o t a p r e r e q u i s i t e f o r t r a n s f e r o f c o u p l i n g , a l t h o u g h some degree o f o v e r l a p o f t h e Ru o r b i t a l s i s perhaps e s s e n t i a l v i a t h e b r i d g i n g h y d r i d e . 31 1 A P{ H}-n.m.r. s p e c t r u m w i t h t h e p h o s p h i n e p r o t o n s s e l e c t i v e l y d e c o u p l e d was n o t o b t a i n e d d e s p i t e a t t e m p t s a t measurement; but t h i s would c o n f i r m t h e a s s i g n m e n t s o f P(3) and P(4). To u n e q u i v o c a l l y a s s i g n t h e p o s i t i o n s o f P ( l ) and P ( 2 ) r e q u i r e s t h e o r e t i c a l 4 c o n s i d e r a t i o n s o f Jpp c o u p l i n g . 31 1 As m e n t i o n e d , t h e P{ H}-n.m.r. s p e c t r u m o b s e r v e d f o r 2 has c h a r a c t e r i s t i c s e s s e n t i a l l y t h e same as f o r two p r e v i o u s l y r e p o r t e d s p e c t r a o f h y d r i d o - p h o s p h i n e complexes. Of t h e s e , t h e t e t r a - h y d r i d o 67 complex [ R u H 2 C l ( P ( p - t o l y l ) 3 ) 2 ] 2 , 3, most c l o s e l y r e s e m b l e s 31 1 2_ i n terms o f proposed s t r u c t u r e s ( 5 - H l ) . The P{ H}-n.m.r. s p e c t r u m o f 3. i n C D 2 C 1 2 i s o n l y r e s o l v e d a t -95°C ( F i g u r e 5 .5) i n d i c a t i n g a low a c t i v a t i o n b a r r i e r f o r rearrangement by a proposed 67 h y d r i d e s c r a m b l i n g . Each m e t a l i s f o r m a l l y R u ( l l l ) and a Ru-Ru bond was pro p o s e d t o e x p l a i n t h e o b s e r v e d d i a m a g n e t i s m and t r a n s f e r o f c o u p l i n g between r u t h e n i u m c e n t r e s . The d i f f e r e n c e i n s t r u c t u r e p r o p o s e d f o r 2 compared t o t h a t shown i n 5 - I H , b e s i d e s t h e change i n - 134 -•2-1 -i Figure 5.5 P{ H}-N.m.r. spectrum of [ E u 2 H 2 C l ( P ( p - t o l y l ) 2 ] 2 i n CD 2C1 2 at -95°C (from reference 67, reproduced with permission). a,P»7 ^ \H(2) (3)H ( 1 ) P(2) 5 - I H - 135 -p h o s p h i n e l i g a n d , i s r e p l a c e m e n t o f t h e two t e r m i n a l H(2) l i g a n d s by a 31 1 c a r b o n y l l i g a n d . That the P{ H}-n.m.r. s p e c t r u m o f 2 i s r e s o l v e d a t ambient t e m p e r a t u r e i n d i c a t e s t h e absence o f any f a c i l e r e a rrangement p r o c e s s , and a s t a b l e o c t a h e d r a l geometry about each r u t h e n i u m . 31 1 The o t h e r complex t o e x h i b i t s i m i l a r P{ H}-n.m.r. 135 c h a r a c t e r i s t i c s i s t h e t e t r a n u c l e a r s p e c i e s , Hu H ( 0 H ) 2 ( P P h 2 ) 2 ( C 0 ) 2 ( P P h 5 ) 6 ( M e 2 C ' 0 ) 2 , f o r w h i c h t h e s p e c t r u m has been s i m u l a t e d ( F i g u r e 5.6) u s i n g t h e p a r a m e t e r s g i v e n i n r e f e r e n c e 135. The complex was p r e p a r e d by r e f l u x i n g R u H C l t P P h . ^ i n a c e t o n e (< 1% H 20 added) w i t h KOH. Based on a c r y s t a l l o g r a p h i c a l l y d e t e r m i n e d m o l e c u l a r w e i g h t , e l e m e n t a l a n a l y s i s , i n f r a r e d , and "^H and 31 P-n.m.r. s p e c t r o s c o p y , t h e s t r u c t u r e s 5-V and 5-VI were proposed t o a c c o u n t f o r c a . 90% o f t h e d a t a . The complex was shown t o form by r e a c t i o n o f RuH 2(C0) ( P P h ^ and RuH(OH) ( P P h 5 ) 2 ( a c e t o n e ) w i t h l o s s o f benzene ( g . l . c . d e t e c t e d ) and PPh^ l i g a n d s . These i n t e r m e d i a t e s a r o s e , r e s p e c t i v e l y , from t h e b a s e - c a t a l y s e d d e c a r b o n y l a t i o n o f a c e t o n e and from t h e r e a c t i o n o f KOH w i t h R u H C l ( P P h j ) 3 . A b r i d g i n g d i p h e n y l p h o s p h i d o group was i n v o k e d t o r a t i o n a l i s e t h e o b s e r v e d t r a n s f e r o f c o u p l i n g i n t h e t e t r a n u c l e a r s p e c i e s . S i n c e t h e r e p o r t o f t h i s complex, i t has been o b s e r v e d t h a t b r i d g i n g o rganophosphido l i g a n d s i n complexes c o n t a i n i n g m e t a l - m e t a l bonds e x h i b i t l a r g e d o w n f i e l d s h i f t s (100-250 ppm), w h i l s t i n complexes c o n t a i n i n g no m e t a l - m e t a l bond, t h e p h o s p h i d o r e s o n a n c e i s s h i f t e d 138 u p f i e l d ( c a . -100 ppm) . T h i s s u g g e s t s t h a t i n r e f e r e n c e 135, - 136 -P(D 75.3 ppm P(2) 71.5' ppm P(3) 55.4 ppm P(4) 26.6 ppm J V. 31 1 Figure 5.6 Simulated P{ H}-n.m.r. spectrum of the t e t r a n u c l e a r species R u 4 H 4 ( P P h 5 ) 6 ( P P h 2 ) 2 ( 0 H ) 2 ( C 0 ) 2 ( a c e t o n e ) 2 using the parameters given i n reference 135. - 137 -p erhaps t h e a s s ignment o f a phosphorus l a b e l l e d , P ( 2 ) (71.5 ppm), t o a b r i d g i n g d i p h e n y l p h o s p h i d o l i g a n d i s i n e r r o r , and t h a t a s t r u c t u r e a k i n t o t h a t proposed f o r 2_ and 3 w i t h b r i d g i n g h y d r o x y - l i g a n d s i s more r e a s o n a b l e . W h i l s t t h e s p e c t r o s c o p i c d a t a f o r 2 appear c o n s i s t e n t w i t h s t r u c t u r e 5-1» an i m p o r t a n t q u e s t i o n i s how t h i s complex i s g e n e r a t e d from R u 2 C l 4 ( d p p b ) 2 ( a c e t o n e ) . a c e t o n e . The f o r m a t i o n o f 2 i n t h e absence o f H 2 i m p l i e s t h a t m e t h a n o l i s a c t i n g as r e d u c i n g agent and as a s o u r c e o f CO. However, i n v o l v e m e n t o f a c e t o n e ( p r e s e n t i n t h e s t a r t i n g m a t e r i a l l ) cannot be r u l e d out by a n a l o g y t o t h e f o r m a t i o n o f t h e t e t r a n u c l e a r s p e c i e s i n a c e t o n e . The d e c a r b o n y l a t i o n o f m e t hanol on m e t a l s u r f a c e s i s w e l l 139 documented , but few examples e x i s t o f b a s e - u n a s s i s t e d 140 d e c a r b o n y l a t i o n o f t h i s a l c o h o l by d i s c r e t e m e t a l complexes . F o r example, t h e R h C l ( P P h j ) 3 complex w h i c h r e a d i l y d e c a r b o n y l a t e s 141 o r g a n i c s u b s t r a t e s , shows no t e n d e n c y t o d e c a r b o n y l a t e m e t hanol even a t 80°C. C o n s i d e r a b l e i n t e r e s t i n t h i s f i e l d stems from p o s s i b l e 142 m e c h a n i s t i c r e l a t i o n s h i p s t o F i s c h e r - T r o p s c h s y n t h e s i s and t h e use o f m e t h a n o l as a hydrogen s o u r c e i n homogeneously c a t a l y s e d 143 h y d r o g e n a t i o n s The g e n e r a t i o n o f r u t h e n i u m c a r b o n y l and h y d r i d o c a r b o n y l complexes by t h e r e a c t i o n o f a l c o h o l s , e s p e c i a l l y e t h a n o l and i s o p r o p a n o l , i s common. The r e a c t i o n s u s u a l l y r e q u i r e t h e use o f a l k o x i d e s a l t s o r t h e i r i n s i t u g e n e r a t i o n by added base, as e x e m p l i f i e d by: - 138 -[ R u 2 C l 5 ( P E t 2 P h ) 6 ] c i + a l l y l a l c o h o l [ R U C l 2 ( C 0 ) 2 ( P E t 2 P h ) 2 ] 1 4 4 (5.5) [ R u 2 C l 5 ( P E t 2 P h ) 6 ] c l + C 2H 50H [ R u H C l ( C 0 ) ( P E t 2 P h ) 2 ] 1 4 4 (5.6) R u H C l ( P P h 3 ) 3 + NaOMe R u H 2 ( C 0 ) ( P P l ^ ) 1 5 5 (5.7) I n a d d i t i o n t o the g e n e r a t i o n o f c a r b o n y l o r h y d r i d o c a r b o n y l c o m p l e x e s , r e a c t i o n s o f t h i s t y p e produce f r a g m e n t s a r i s i n g from d e g r a d a t i o n o f t h e a l c o h o l ( i . e . methane from e t h a n o l ' ' " 4 4 , e q u a t i o n 5.6). An a p p e a l i n g p o s s i b i l i t y f o r t h e f o r m a t i o n o f 2 i s t h e s t o i c h i o m e t r y shown i n r e a c t i o n 5.4. A p l a u s i b l e mechanism i s shown i n 135 144 145 Scheme 5-1, based on t h o s e p r e v i o u s l y p o s t u l a t e d ' f o r a l c o h o l d e c a r b o n y l a t i o n , w i t h t h e e x t r a r e q u i r e m e n t s t h a t t h e d i n u c l e a r i t y o f the complex i s r e t a i n e d t h r o u g h o u t , and no degraded f r a g m e n t s o f methanol a r e p r o d u c e d . The proposed mechanism i s a d m i t t e d l y s p e c u l a t i v e , but does s e r v e t o show t h e g e n e r a l i n t e r m e d i a t e s t y p i c a l l y i n v o l v e d i n t h e d e c a r b o n y l a t i o n o f a l c o h o l s . The 135 144 p r o p o s e d ' i n i t i a l s t e p f o r d e c a r b o n y l a t i o n i n Ru systems i s b e l i e v e d t o be f o r m a t i o n o f a R u - a l k o x i d e s p e c i e s . I n t h e p r e v i o u s l y c i t e d examples ( e q u a t i o n s 5.5-5.7), t h i s was v i a t h e a l k o x i d e s a l t , b u t i n t h e p r e s e n t s t u d y t h i s c o u l d be promoted by a b s t r a c t i o n o f HC1 by added P r o t o n Sponge. The subsequent f o r m a t i o n o f a me t h a n a l adduct and f o r m y l complex has been c o n f i r m e d f o r t h e r e a c t i o n o f R u H C l ( P P h 3 ) 3 w i t h NaOMe by t h e i r i n d e p e n d e n t g e n e r a t i o n o r s p e c t r o s c o p i c 135 c h a r a c t e r i s a t i o n A second p o s s i b l e mechanism f o r t h e f o r m a t i o n o f 2 i n v o l v e s t he g e n e r a t i o n o f mononuclear complexes and t h e i r subsequent r e c o m b i n a t i o n : - 139 -""no *Ru4f Z>Ru + MeOH -HCI Cl • x C l ^ « o . . « ^ 0 M e ^ » C I ^ hydride transfer P #C,*> >-OCH2 / \ <£ci«5*' ^ . hydride P^Ru\cl/Ru>y^ 'mi9ration H hydride transfer -HCI P v C L ,OCH, Ru-Cl 7 \ H / \ 7 'Ru Cl ">Ru^ *C-H hydride transfer CO H Scheme 5 - 1 - 140 -R u 2 C l 4 ( d p p b ) 2 + 2Me0H 2RuHCl(dppb) + 2CH 20 ( 5.8) R u 2 C l 4 ( d p p b ) 2 + 2MeOH ^ 2RuHCl(C0)(dppb) + H 2 ( 5.9) RuHCl(dppb) + RuHCl(C0)(dppb) — R u 2 H 2 C l 2 ( C 0 ) ( d p p b ) 2 (5.10) Such a mechanism r e s u l t s i n the generation of degraded alcohol fragments (CH 20 and H 2), and consequently could be supported by t h e i r detection. 5.4 Preparation of Dichloronorbornadiene(dppb)ruthenium(ll).0.5CgHg >  RuCl 2(nbd)(dppb).0 . 5 CgHg,_4, and i t s r e a c t i v i t y with H 2 In order to overcome the problem of addition of HC1, generated by reduction of Ru 2Cl 4(dppb) 2(acetone).acetone, to the complex i t s e l f (Section 5 . 2 ) , the attempted use of a monomeric percursor seemed worthwhile. For t h i s purpose RuCl 2(nbd)(dppb) was prepared because the dialkene was expected to s t a b i l i s e the mononuclear fragment and yet could be e a s i l y removed by hydrogenation as norbornane, and then allow f o r subsequent formation of a hydrido-complex. 5.4.1 Preparation and Characterisation S t i r r i n g a suspension of Ru 2Cl 4(dppb) 2(acetone).acetone with an excess of norbonadiene i n benzene produces a brown s o l u t i o n . Concentration of t h i s s o l u t i o n and p r e c i p i t a t i o n with hexanes y i e l d s 4 as a yellow powder or brown c r y s t a l l i n e material (Section 2.1.7.9). The use of benzene i s important since i f the reaction i s performed i n toluene a product of i n f e r i o r a n a l y t i c a l q u a l i t y i s obtained. This i s - 141 -p r e s u m a b l y because a t t h e c o n c e n t r a t i o n s t a g e t h e n o r b o r n a d i e n e w i l l be more r e a d i l y removed t h a n t h e t o l u e n e , and t h e e x c e s s o f d i a l k e n e w i l l no l o n g e r be m a i n t a i n e d . R e c r y s t a l l i s a t i o n o f t h e sample i s a l s o u n s a t i s f a c t o r y , s i n c e f r o m C H 2 C l 2 / h e x a n e s an orange p r o d u c t was o b t a i n e d and i d e n t i f i e d as R ^ C l ^ ( d p p b ) 2 ( e l e m e n t a l a n a l y s i s ) . 31 1 The P{ H}-n.m.r. s p e c t r u m o f 4 i n C D 2 C 1 2 a t ambient t e m p e r a t u r e e x h i b i t s a s i n g l e t a t 17.0 ppm. The i n t e n s i t y o f t h i s s i g n a l t h e n d e c r e a s e s w i t h t i m e and an AB q u a r t e t ( P ^ = 62.8, P £ = 53.5 ppm, J = 46.8 H z ) , a s s i g n a b l e t o [ R u C l 2 ( d p p b ) ] ( S e c t i o n 4 . 2 ) , becomes a p p a r e n t . A f t e r 24 b t h e s i n g l e t c o n s t i t u t e s _ca. 40$ o f the i n t e g r a t e d i n t e n s i t y . The ^"H-n.m.r. sp e c t r u m o f an "aged" CD C l s o l u t i o n shows t h e p r e s e n c e o f b o t h c o o r d i n a t e d (3.6 6 , ( b r o a d m u l t i p l e t o l e f i n i c p r o t o n s ) , and f r e e (6.8 6 ( t ) o l e f i n i c p r o t o n s ) n o r b o r n a d i e n e . These f i n d i n g s a r e c o n s i s t e n t w i t h 4^  u n d e r g o i n g d i s s o c i a t i o n o f the d i a l k e n e l i g a n d i n s o l u t i o n , e q u a t i o n 5.11. The monodentate R u C l 2 ( n b d ) ( d p p b ) l / 2 [ R u C l 2 ( d p p b ) ] 2 + nbd (5.11) p h o s p h i n e a n a l o g u e o f 4, R u C l 2 ( n b d ) ( P ( p - t o l y l ) . j ) 2 , has been p r e v i o u s l y p r e p a r e d ( P{ H}-n.m.r. (CgDg):20.6 ppm ( s ) ) , but i s n o t r e p o r t e d t o undergo d i s s o c i a t i o n . I n o r d e r t o c o n f i r m t h a t 4^  was a monomeric complex and n o t s i m p l y an a l k e n e adduct o f t h e d i m e r i c s t a r t i n g compound, a s i n g l e c r y s t a l X - r a y d i f f r a c t i o n s t u d y was c a r r i e d out by S. Evans and M. - 142 -Ponnuswamy of t h i s department. The c r y s t a l l o g r a p h i c a n a l y s i s showed A_ to be a mononuclear-dialkene complex that c r y s t a l l i s e s w i t h one molecule of benzene per two molecules of ruthenium complex. The complex has pseudo-octahedral geometry about the r u t h e n i u m ( l l ) as shown i n Figure 5.7. The c h l o r o - l i g a n d s are s l i g h t l y d i s t o r t e d from a trans c o n f i g u r a t i o n ( C l ( l ) - R u - C l ( 2 ) = 168.4°) which i s p o s s i b l y due to s t e r i c e f f e c t s imposed by the d i a l k e n e . The norbornadiene moiety i s bound through both double bonds, which are consequently lengthened (l . 3 7 ( l ) A ) compared to those i n the f r e e l i g a n d (l.35k)^^ as a r e s u l t of the p a r t i c i p a t i o n of n-electrons i n the bonding to the metal. The distances from ruthenium to the centre (CT) of the coordinated double bonds, [c(2)-C(3)] ( C T ( l ) ) and [c(5)-C(6)] (CT(2)), are 2.21 and 2.15A, r e s p e c t i v e l y . The angle CT(l)-Ru-CT(2) i s 66.5°. Table 5.1 l i s t s s e l e c t e d bond lengths and angles. A s e r i e s of complexes analogous to 4_ have been prepared using 146 amines r a t h e r than phosphines. The c r y s t a l s t r u c t u r e of RuC^Cnbd) ( p i p e r i d i n e ^ s i m i l a r l y has a d i s t o r t e d octahedral geometry with trans c h l o r o - l i g a n d s . The distance from the metal to the centre of the double bonds i n the p i p e r i d i n e complex i s 2.07A, and the angle subtended by the coordinated norbornadine i s 69.7°. For the average d i s t a n c e i s 2.18A and the angle i s 66.5°; t h i s shows that the coordinated norbornadiene i s l e s s s t r o n g l y bound, presumably because of the stronger trans e f f e c t of the phosphine compared to the p i p e r i d i n e l i g a n d . This i s r e f l e c t e d a l s o to some extent i n the length of the double bonds which are 0.02A longer i n the p i p e r i d i n e complex - 143 -CM CM O Figure 5.7 An ORTEP diagram of the RuCl ?(nbd)(dppb) molecule. - 144 -T a b l e 5.1 S e l e c t e d Bond L e n g t h s and Bond A n g l e s f o r R u C l 2 ( n b d ) (dppb) .0.5C/-Hg* Bond Length(A) A n g l e Degrees R u - C l ( l ) 2.437 (1) C l ( l ) - R u - C l ( 2 ) 168.37 (4) R u - C l ( 2 ) 2.437 (1) C l ( l ) - R u - P ( l ) 87.32 (4) R u - P ( l ) 2.399 (1) C l ( l ) - R u - P ( 2 ) 95.80 (4) Ru-P(2) 2.384 (1) C l ( 2 ) - R u - P ( l ) 81.86 (3) Ru-C(2) 2.322 (4) C l ( 2 ) - R u - P - ( 2 ) 81.61 (3) Ru-C(3) 2.308 (4) P ( l ) - R u - P ( 2 ) 98.16 (3) Ru-C(5) 2.254 (4) Ru-C(6) 2.252 (4) [ C T ( l ) ] - R u - [ C T ( 2 ) ] 66.50 R u - [ C T ( l ) ] 2.212 R u - [ C T ( 2 ) ] 2.146 A c c o r d i n g t o numbering scheme i n F i g u r e 5.7. E s t i m a t e d s t a n d a r d d e v i a t i o n g i v e n i n p a r e n t h e s e s . C T ( l ) and CT(2) r e f e r t o t h e c e n t r e o f t h e c o o r d i n a t e d d o u b l e bonds [ c ( 2 ) - C ( 3 ) ] a n d [ c ( 5 ) - C ( 6 ) ] r e s p e c t i v e l y . - 1 4 5 -r e l a t i v e to that found i n 4 ( 1 . 3 9 A vs. 1 . 3 7 A ) . 5 . 4 . 2 Reaction with The use of EuCl 2(nbd)(dppb ) . 0 . 5 C 6Hg'4 as a hydride precursor seemed appropriate, since the complex i s mononuclear and i t appeared f e a s i b l e to remove the dialkene by reduction. However, the d i s s o c i a t i o n of 4_ (equation 5 . 5 ) could c l e a r l y lead to complications i n i n v e s t i g a t i o n s of the r e a c t i v i t y with H 2, as [RuCl 2(dppb)] 2 i s known to react with H 2 (Section 5 . 2 ) . In order to asce r t a i n the extent to which the d i s s o c i a t i o n of A_ a f f e c t s the reaction, the hydrogen uptake of a DMA so l u t i o n of A_ at 50°C i n the presence of Proton Sponge was monitored. The uptake corresponded to 1 . 7 H 2 : 1 . 0 Ru a f t e r 1 . 5 h, at which point the reaction was complete. This low stoichiometry implies that not a l l , i f any, of the norbornadiene i s being hydrogenated. Support f o r t h i s comes from the attempted c a t a l y t i c hydrogenation of norbornadiene using Ru 2Cl 4(dppb) 2(acetone).acetone. This complex r e a d i l y hydrogenates acrylamide, hex-l-ene, and styrene (Table 6 . 4 , Section 6 . 4 ) . Under the same conditions the hydrogenation of norbornadiene i s much slower (max. rate = 1 . 4 x 1 0 ^ M s 1 ) and stops a f t e r _ca. 3 h with an uptake corresponding to the reduction of only 2 . 5 $ of the ava i l a b l e substrate. The i n a b i l i t y to reduce norbornadiene suggests a c a t a l y t i c a l l y i n a c t i v e complex i s being formed during reaction with H 2. The H 2-reduction of 4_ was attempted on a preparative scale i n order to i s o l a t e any such complex. The preparative method was the same as used - 146 -f o r t h e r e d u c t i o n o f R u 2 C l 4 ( d p p b ) 2 ( a c e t o n e ) . a c e t o n e ( S e c t i o n 5.2) and, w h i l s t a d i f f e r e n t h y d r i d e p r o d u c t was o b t a i n e d ( v i d e i n f r a ) t h e p r i n c i p l e p r o d u c t (0.7 g) was [ R u 2 C l 2 ( d p p b ) 2 ] ~ P S H + . The brown p r o d u c t (60 mg) o b t a i n e d a f t e r s e p a r a t i o n o f t h e i o n i c complex, was a n a l y t i c a l l y impure but a l l o w e d f o r i d e n t i f i c a t i o n o f a component. The 31 1 p r i n c i p l e r e s o n a n c e i n t h e P{ H}-n.m.r. s p e c t r u m (CgDg, 30°C) o f t h e m i n o r impure p r o d u c t i s a s i n g l e t (42.9 ppm), but t h e r e a r e a l s o o t h e r u n a s s i g n a b l e r e s o n a n c e s t o l o w e r f i e l d . However, t h e ''"H-n.m.r. sp e c t r u m shows broad r e s o n a n c e s a s s i g n e d t o t h e o l e f i n i c p r o t o n s o f c o o r d i n a t e d n o r b o r n a d i e n e (3.96) and a h y d r i d e r e s o n a n c e ( t , -9.686, J = 21 H z ) . To e x p l a i n t h e a v a i l a b l e u p t a k e and l i m i t e d n.m.r. d a t a i t i s p r o p o s e d t h a t one o f t h e p r o d u c t s o f t h e r e d u c t i o n o f 4 i s R u H C l ( n b d ) ( d p p b ) ( 5 - V I I ) . W h i l s t s u c h a c o n c l u s i o n must be t e n t a t i v e u n t i l P—P = dppb 11-11 - nbd 5-VII t h e complex has been i s o l a t e d p u r e , s t r o n g s u p p o r t comes from t h e n.m.r. d a t a f o r t h e PPh, a n a l o g u e . 3 131 W i l k i n s o n and c o w o r k e r s r e p o r t e d t h e p r e p a r a t i o n o f R u H C l ( n b d ) ( P P h 3 ) 2 by t h e i n t e r a c t i o n o f R u H C l ( P P h 5 ) 5 and n o r b o r n a d i e n e . The complex was o r i g i n a l l y c o n s i d e r e d t o be a m i x t u r e o f - 147 -isomers because of the large number of resonances due to the d i a l k e n e . Other w o r k e r s 1 4 7 have si n c e shown that only one isomer e x i s t s which has the s t r u c t u r e on which the dppb analogue i s based ( 5 - V I l ) . The 31 1 P{ H}-n.m.r. spectrum of RuHCl(nbd)(PPh 3) 2 c o n s i s t e d of a s i n g l e t (40.6 ppm), w h i l s t the "''H-n.m.r. spectrum e x h i b i t e d a t r i p l e t 2 (-8.886, Jpjj = 24 Hz) assigned to the hydride, and resonances at 3.45 and 3.636 due to the o l e f i n i c protons. The c l o s e s i m i l a r i t y between the data f o r the dppb and PPh^ hydrido-complexes suggests 67 analogous s t r u c t u r e s . I t i s noted that i n the p r e p a r a t i o n of RuHCl(nbd)(PPh^^ attempts to improve the y i e l d by reducing the volume of the s o l u t i o n p r i o r to p r e c i p i t a t i o n of the product, or by scaling-up the r e a c t i o n compared to the o r i g i n a l reported p r e p a r a t i o n , gave impure products. Considering the procedure found necessary f o r i s o l a t i n g "RuHCl(nbd)(dppb)" i t i s perhaps not s u r p r i s i n g that the 31 1 P{ H}-n.m.r. spectrum shows a d d i t i o n a l resonances of u n i d e n t i f i e d s p e c i e s . Of i n t e r e s t i s how the hydrido-alkene complex i s generated from 4. The monodentate phosphine analogue of A, R u C l 2 ( n b d ) ( P ( p - t o l y l ) 3 ) 2 , 67 i s reported as being unreactive towards H 2. I f t h i s i s true f o r the dppb complex, hydride formation must a r i s e from the [ R u C l 2 ( d p p b ) ] 2 generated by d i s s o c i a t i o n (equation 5.5). The H 2 ~ r e d u c t i o n of t h i s dimer generates HCI which i s trapped by the added Proton Sponge but adds to the s t a r t i n g complex to generate [ R u 2 C l 5 ( d p p b ) 2 ] _ P S H + ( S e c t i o n 5.2). The norbornadiene l i b e r a t e d from the d i s s o c i a t i o n apparently s t a b i l i s e s the hydride - 148 -intermediate to y i e l d RuHCl(nbd)(dppb): RuCl ?(nbd)(dppb) • [ R u C l ? ( d p p b ) ] ? + nbd 1 H 2 "RuHCl(dppb)" + HC1 nbd [ R u C l 2 ( d p p b ) ] 2 RuHCl(nbd)(dppb) [ R u 2 C l 5 ( d p p b ) 2 ] ~ P S H + The reported p r e p a r a t i o n of R u H C l ( n b d ) ( P P h ^ by phosphine-displacement from the hydrido-percursor complex RuHCl(PPhj) 3 r e q u i r e s no hydrogen; however, the hydrido-dialkene 67 complex does react w i t h H 2 . In DMA the hydrogen-uptake corresponded to 2.5 H2:1.0 Ru, which i s e n t i r e l y c o n s i s t e n t w i t h the transfo r m a t i o n : RuHCl(nbd)(PPh 3) 2 + 2.5H 2—^0.5 [ H 2 R u C l ( P P h 3 ) 2 J 2 + norbornane (5.12) 6*7 1 31 1 The r e a c t i o n was a l s o monitored by H- and P{ H}-n.m.r. and revealed i n i t i a l formation of RuHClCPPhj)^ and subsequent slow generation of [ H 2 R u C l ( P P h 3 ) 2 J 2 and norbornane. A f t e r 2 d only the products of equation 5.12 were observed. The i n i t i a l generation of the t r i s p h o s p h i n e complex n e c e s s i t a t e s the concurrent formation of a phosphine-deficient complex, although no such species was detected. No mechanistic d e t a i l s were proposed f o r the re d u c t i o n of the norbornadiene l i g a n d ; however, the involvement of the tris p h o s p h i n e or phosphine - 149 -d e f i c i e n t complex cannot be r u l e d out. In the present study, the generation of RuHCl(nbd)(dppb) i n the presence of H 2 suggests that i t i s a more s t a b l e hydrido-dialkene complex, at l e a s t with respect to r e a c t i o n w i t h H 2, than the PPh^ analogue. The bidentate phosphine i s u n l i k e l y to undergo d i s s o c i a t i o n and consequently no phosphine-deficient or t r i s p h o s p h i n e complexes w i l l be generated. This suggests that r e d u c t i o n of the norbornadiene i n the PPhj system perhaps a r i s e s from the i n i t i a l l y formed in t e r m e d i a t e s , r a t h e r than from m i g r a t i o n - i n s e r t i o n of alkene i n t o the metal-hydride bond w i t h i n the s t a r t i n g m a t e r i a l RuHCl(nbd)(PPhj) 2, followed by r e a c t i o n w i t h H,,. W h i l s t the r e s u l t s i n the present study suggest q u i t e d i f f e r e n t r e a c t i v i t y w i t h H 2 of the norbornadiene complexes c o n t a i n i n g bidentate compared to monodentate phosphines, a p r e p a r a t i v e route to produce a n a l y t i c a l l y pure RuHCl(nbd)(dppb) i s necessary to q u a n t i f y such d i f f e r e n c e s . - 150 -CHAPTER VI CATIONIC COMPLEXES OF RUTHENIUM(Il) 6.1 I n t r o d u c t i o n The a p p l i c a t i o n of n e u t r a l ruthenium-phosphine complexes as 63 65 homogeneous hydrogenation c a t a l y s t s i s w e l l documented ' , but only l i m i t e d a t t e n t i o n has been paid to i o n i c ruthenium complexes. A species that has been i n v e s t i g a t e d i s the a n i o n i c hydride complex [ ( P h 5 P ) 2 P h 2 P ( C 6 H 4 ) R u H 2 ] ~ K + . C 1 ( ) H 8 . ( E t 2 0 ) which was prepared as a p o s s i b l e c a t a l y t i c analogue of L i A l H ^ f o r the red u c t i o n of p o l a r organic s u b s t r a t e s . Indeed, t h i s complex was found to hydrogenate 148 149 ketones, e s t e r s , n i t r i l e s and pol y n u c l e a r aromatics . Recent 150 hydrogenation s t u d i e s of t h i s orthometalated complex have shown the presence of three a n i o n i c polyhydride complexes, although which one i s rele v a n t to the hydrogenation of p o l a r substrates has not been determined. C a t i o n i c complexes generated i n s i t u from the a c t i o n of f l u o r o b o r i c a c i d on r u t h e n i u m ( l l ) carboxylato-triphenylphosphine 151 complexes have a l s o been found to hydrogenate alkenes . The a c t i v e species i n t h i s case was i n i t i a l l y thought to be [RuCPPh^),,] , 152 although l a t e r work suggested the presence of the c a t i o n i c hydride complex A p o s s i b l e explanation f o r the l i m i t e d a t t e n t i o n i s that few - 151 -general methods have been reported f o r the p r e p a r a t i o n of such ruthenium phosphine complexes. The a n i o n i c complex mentioned p r e v i o u s l y was prepared by the r e d u c t i o n of RuHC^PPh^)^ with potassium-naphthalene at low temperatures, w h i l s t the c a t i o n i c complexes are most f r e q u e n t l y prepared by hydride a b s t r a c t i o n from e i t h e r hydride- or a l l y l -complexes. The use of s a l t s of non-coordinating anions f o r h a l i d e 153 a b s t r a c t i o n has been used to prepare complexes such as [Ru(cod)Cl(CH.jCN) 3] + , the coordinated dialkene of which can be s u b s t i t u t e d by various l i g a n d s i n c l u d i n g phosphine. In the present study, the i s o l a t i o n of i o n i c complexes as p o t e n t i a l hydride precursors was of i n t e r e s t because of the d i f f i c u l t i e s encountered i n the p r e p a r a t i o n of hydride complexes from the n e u t r a l ruthenium complexes (Chapter V). The study was l i m i t e d to the generation of c a t i o n i c complexes by h a l i d e a b s t r a c t i o n from ruthenium complexes c o n t a i n i n g the dppb l i g a n d . The p r e p a r a t i o n , c h a r a c t e r i s a t i o n of mono- and d i n u c l e a r complexes and t h e i r r e a c t i v i t y w i t h hydrogen i s discussed. 6.2 R e s u l t s 6.2.1 Formation of Dinuclear C a t i o n i c Complexes 6.2.1.1 T r i - u - c h l o r o b i s [ a c e t o n i t r i l e ( l , 4 - d i p h e n y l p h o s p h i n o b u t a n e ) ruthenium(II)] Hexafluorophosphate, [ R u 2 C l 5 ( d p p b ) 2 ( C H 5 C N ) 2 ] + P F 6 ~ , 5 A c e t o n i t r i l e s o l u t i o n s of Ru„Cl,.(dppb)0 were found to d o d undergo d i s p r o p o r t i o n a t i o n as monitored by l o s s of absorption i n the n e a r - i n f r a r e d ( S e c t i o n 3.6). These s o l u t i o n s a l s o gave molar - 152 -c o n d u c t i v i t i e s of 112 ohm cm mole 1 ([Rug ] = 2 x 10~\) (see S e c t i o n 6.3). A d d i t i o n of AgPFg to a c e t o n i t r i l e s o l u t i o n s of Ru^Cl (dppb) (1:2 mole r a t i o ) l e d to p r e c i p i t a t i o n of AgCl and a 2 5 2 change i n c o l o u r of the s o l u t i o n from red to pink. From the s o l u t i o n the complexes [ R u C l ^ d p p b ) ] ^ and 5_ were i s o l a t e d (Sections 2.1.7.10 and 2.1.7.11). The i s o l a t e d complexes suggested a d i s p r o p o r t i o n a t i o n c o n s i s t e n t w i t h : 2 R u 2 C l 5 ( d p p b ) 2 CHjCN *• [ R u C l 2 ( d p p b ) ] 2 + [ R u C l 5 ( d p p b ) ] 2 J A g P F g [Ru2Cl3(dppb) 2(CH 3CN) 2] +PF6~ + AgCl (6.1) The elemental a n a l y s i s of the yellow hexafluorophosphate s a l t i s c o n s i s t e n t w i t h two a c e t o n i t r i l e molecules per complex. These are a l s o evident i n the s o l i d s t a t e i n f r a r e d spectrum as weak absorptions a t 2315 and 2280 cm ^ . The i n f r a r e d spectrum a l s o shows absorptions c h a r a c t e r i s t i c of non-coordinated PFg~ at 840 and 568 cm - 1, and the absence of t e r m i n a l Ru-Cl s t r e t c h i n g i n the 250-350 cm ^  r e g i o n . The 31 1 P{ H}-n.m.r. spectrum of 3_ i n CD^Cl^ c o n s i s t s of an AB quartet 2 (6^ = 49.6, 6g = 46.6 ppm; J^g = 36.6 Hz) and a septet due to the PFg" anion (6 = -145.3 ppm, J = 710.4 Hz). These data are c o n s i s t e n t w i t h 5^  being a t r i p l y c hloro-bridged species ( S t r u c t u r e 31 1 6-1). The P{ H)-n.m.r. spectrum i n CD^CN, however, c o n s i s t s of a r .Cl. Ru 6-1 PF " P -P = dppb S = CH 3CN - 153 -s i n g l e t ( 6 = 40.6 ppm) and a septet due to the PF^ - anion (fi = -146.1 ppm, J = 708.0 Hz). This d i f f e r e n c e between dichloromethane and a c e t o n i t r i l e s o l u t i o n s of jj i s a l s o apparent i n the v i s i b l e spectra and c o n d u c t i v i t y measurements. The v i s i b l e spectrum i n CH 2C1 2 shows an absorption maximum at 374 nm which s h i f t s to 317 nm i n CH^CN wi t h no l o s s of i n t e n s i t y (e = 2950 M "'"cm 1 ) as shown i n Figure 6.1. D i l u t i o n c o n d u c t i v i t y measurements i n both s o l v e n t s under argon at 25°C y i e l d l i n e a r Onsager p l o t s (Figure 6.2). The l i m i t i n g conductance i n 3-0 -T E o i I \ I \ ' \ / \ S 2 0 -i o \ \ \ \ \ \ \ \ \ \ CH 2 CI 2 X CH 3 CN CO 1 0 -\ \ \ \ \ \ \ \ \ \ \ \ — i 1 1 400 500 600 Wavelength , nm Figure 6.1 V i s i b l e spectra of [ R u 2 C l 3 ( d p p b ) 2 ( C H 5 C N ) 2 ] + P F 6 i n CH 2C1 2 and CH_CN. - 155 -CH-CN i s 240.0 ohm cm mole which i s outside the range g e n e r a l l y accept 3 -1 2 -1 f o r 1:1 e l e c t r o l y t e s i n t h i s s olvent (120-160 ohm cm mole ), 154 although examples of p a r t i c u l a r l y high c o n d u c t i v i t i e s are known The value found f o r 5_ i n CH^CN i s a l s o i n marked con t r a s t to that -1 2 -1 found i n CB^C^ (59.3 ohm cm mole ). In a c e t o n i t r i l e the high c o n d u c t i v i t y and the presence of only a s i n g l e t i n the 3 1P{^H}-n.m.r. suggest d i s s o c i a t i o n (equation 6.2); such a proposal i s supported by i s o l a t i o n of the mononuclear P i V - species ( S e c t i o n 6.2.2.1). acetone, e x i s t s as a t r i p l y chloro-bridged species w i t h one coordinated solvent molecule, 6 - I I , ( S e c t i o n 4.3.2). Due to the apparent s t a b i l i t y (6.2) 6.2.1.2 (Acetone)tri-y-chlorobis[l,4-diphenylphosphinobutane)ruthenium  ( I I ) ] Hexaf luorophosphate, [ R U g C l ^ d p p b ^ a c e t o n e ) ] + PFg~ , 6 The complex [RuClp(dppb)] ? i n donor s o l v e n t s , such as 6-II of the t r i p l e c h l o r o - b r i d g e , a b s t r a c t i o n of the t e r m i n a l c h l o r i d e appeared to be a p o t e n t i a l route f o r the generation of d i n u c l e a r - 156 -c a t i o n i c complexes. Reaction of t h i s complex i n e i t h e r toluene- or CH^Cl^-acetone mixtures w i t h one equivalent of AgPFg s l o w l y produces a brown s o l u t i o n w i t h p r e c i p i t a t i o n of AgCl. The pale orange product i s o l a t e d from the s o l u t i o n gave an elemental a n a l y s i s c o n s i s t e n t w i t h f o r m u l a t i o n [ R U g C L ^ d p p b ^ a c e t o n e ) ] + P F g » §_ (S e c t i o n 2.1.7.13). The i . r . spectrum of 6^  shows an absorption f o r coordinated acetone (1663 cm "*"), strong absorptions f o r non-coordinated PFg~ (840 and 568 cm "*") and no absorption i s assignable to a t e r m i n a l c h l o r i d e . The p r i n c i p l e resonances expected f o r the d i n u c l e a r c a t i o n i n 31 1 the P{ H}-n.m.r. spectrum of 6_ are unresolved i n CDgClg or CDgClg-acetone mixtures even at -70°C. The spectrum i n CD^Cl^-acetone a t -70°C (Figure 6.3) shows resonances centred at ca. 47.5 ppm with no d i s c e r n a b l e coupling constants, a s i n g l e t (15$ of the i n t e g r a t e d i n t e n s i t y of the low f i e l d resonances) at 32.8 ppm, and a septet (6 = -146.0 ppm, J = 710.5 Hz) due to the PFg" anion. The s i n g l e t i s assigned to a mononuclear species by analogy to the f i n d i n g s i n CH^CN as solvent (previous Section) and, w h i l s t the unresolved resonances are assigned to the d i n u c l e a r c a t i o n , the complexity suggests the presence of more than one spe c i e s . A p o s s i b l e explanation i s a ra p i d e q u i l i b r i u m between mono- and b i s - solvated s p e c i e s : R u ^ C l ^ R u / + • J*"** ^ R u « » » « M H , p S=acetone - 157 -A 60 40 20 // -80 -100 -120 -140 -160 -180ppm Figure 6.3 P{ H}-N.m.r. spectrum of [ R u 2 C l 3 ( d p p b ) 2 ( a c e t o n e ) ] P F g i n CD 2Cl 2-acetone at -70°C at 32.4 MHz. A CH 2C1 2 s o l u t i o n of 6 ([Ru 2] = 2 x 10"°M) gave a -1 2 -1 conductance of 39.6 ohm cm mole , c o n s i s t e n t w i t h the presence of a 1:1 e l e c t r o l y t e . 6.2.2 Formation of Mononuclear C a t i o n i c Complexes 6.2.2.1 T r i s ( a c e t o n i t r i l e ) c h l o r o ( l > 4 - d i p h e n y l p h o s p h i n o b u t a n e ) r u t h e n i u m ( I I )  Hexafluorophosphate, [RuCl(dppb)(CH 3CN) 5] + , 7 The s o l u t i o n p r o p e r t i e s of [ R u ^ l ^ d p p b ^ C H ^ C N ^ ] * P F g , 5, i n a c e t o n i t r i l e suggest d i s s o c i a t i o n of the complex i n t o mononuclear species (S e c t i o n 6.2.1.1). This was supported by f u r t h e r - 158 -r e a c t i o n of jj with AgPFg (1:1 mole r a t i o ) i n CH^CN, from which the pale yellow complex [RuCl(dppb)(CH C N ) j ] + PFg~, 7, was i s o l a t e d . This complex could be prepared more e a s i l y from Ru2Cl^(dppb) 2(acetone). acetone, by metathesis, w i t h two equivalents of AgPFg i n CH^CN (Sect i o n 2.1.7.12). The s o l i d s t a t e i . r . spectrum shows absorptions f o r coordinated CH^CN (2268 c m - 1 ) , non-coordinated PFg"(840 and 572 cm"1) and a ter m i n a l Ru-Cl s t r e t c h (285 cm 1 ) . 31 1 The p r i n c i p l e resonances i n the P{ H}-n.m.r. spectrum of 1_ at ambient temperature are a s i n g l e t (6 = 40.6 ppm i n CD^CN; 6 = 41.2 ppm i n C I ^ C ^ ) and a high f i e l d septet a t t r i b u t e d to the PFg~ anion. The s i n g l e t i s c o n s i s t e n t w i t h the a c e t o n i t r i l e l i g a n d s being i n a fac-arrangement ( 6 - I I I ) : R u s PF-P-P = dppb S = CH 3CN 6 - I I I In a d d i t i o n , the P{ H}-n.m.r. spectrum i n CD^Cl^ shows an a d d i t i o n a l s i n g l e t at 38.7 ppm ( 5$ i n t e g r a t e d i n t e n s i t y ) , which i s assigned to a f i v e - c o o r d i n a t e species a r i s i n g from d i s s o c i a t i o n of an a c e t o n i t r i l e l i g a n d . Support f o r t h i s proposal comes from the a d d i t i o n of CD_CN (ca. 10$) to the s o l u t i o n which causes t h i s a d d i t i o n a l - 159 -s i n g l e t to disappear, and from the r e a c t i v i t y of 1_ w i t h ( S e c t i o n 6.4). The spectrum of J i n CD CN a l s o shows an AB quartet ( 6 . = 2 42.5, = 35.7 ppm; J = 34.2 Hz) corresponding to ca. 15$ of a AH — the i n t e g r a t e d i n t e n s i t y of the low f i e l d resonances. The quartet i s a t t r i b u t e d to an isomer of the complex w i t h a mer-arrangement of the a c e t o n i t r i l e l i g a n d s i n CH_CN s o l u t i o n . y i e l d a l i n e a r Onsager p l o t w i t h a l i m i t i n g conductance of 126.5 —1 2 —1 ohm cm mole (Figure 6.4). The molar c o n d u c t i v i t y i n CH^Cl^ ([Ru] = 2 x 10~3M) was 19.8 ohm" 1cm 2mole~ 1. D i l u t i o n c o n d u c t i v i t y measurements on 7 i n CH,CN under argon 130-O 0> <^  100-2 3 * 5 6 7 [Ru] y 2 x102, Figure 6.4 Onsager p l o t f o r [RuCl(dppb)(CH,CN),] +PF f i~ i n CH CN at 25°C - 160 -6.2.2.2 Chloro(n -toluene)(1,4-diphenylphosphinobutane)ruthenium(II)  Hexafluorophosphate, [RuCl(dppb)(r/'-toluene)] +PF g , 8 The ^ 1P{ 1H}-n.m.r. spectrum of [ R u 2 C l 3 ( d p p b ) 2 ( a c e t o n e i n CD^Clg-acetone (S e c t i o n 6.2.1.2) shows a s i n g l e t which i s assigned to a mononuclear species that i s presumably analogous to the a c e t o n i t r i l e complex J_ discussed p r e v i o u s l y . In an attempt to i s o l a t e the mononuclear acetone species the r e a c t i o n of R u ^ C l ^ d p p b ^ ^ c e t o n e ) .acetone with two e q u i v a l e n t s of AgPFg i n toluene-acetone mixture was c a r r i e d out. The pale orange product e v e n t u a l l y obtained appeared to be the same as when one equivalent of AgPF g was used. However, slow r e c r y s t a l l i s a t i o n of t h i s product from CHgClg-acetone by p r e c i p i t a t i o n w i t h d i e t h y l ether i n i t i a l l y afforded a b r i g h t y e l l o w c r y s t a l l i n e product. A d d i t i o n of more d i e t h y l ether to the f i l t r a t e r e s u l t e d i n p r e c i p i t a t i o n of a pale orange product that was i d e n t i f i e d as [ R u 2 C l 5 ( d p p b ) 2 ( a c e t o n e ) ] + P F 6 ~ ( i . r . , 5 1P{ 1H}-n.m.r., and elemental a n a l y s i s ) . The y e l l o w product i n i t i a l l y formed was c h a r a c t e r i s e d as [RuCl(dppb)(r^-toluene)] +PFg , 8 ( S e c t i o n 2.1.7.14). The presence of a ir-bonded phenyl r i n g i s evident i n the ^H-n.m.r. spectrum (Figure 6.5). The resonances due to the ortho-, meta-, and para-protons of the coordinated toluene are s h i f t e d to a higher f i e l d compared to f r e e toluene, and are a f f e c t e d to v a r y i n g degrees by the metal to give r i s e to separate s i g n a l s . The s p e c t r a may be i n t e r p r e t e d on a f i r s t - o r d e r b a s i s w i t h assignment of the resonances at 65.74(t), 4.95(d) and 4.34(t) ppm to the meta-, ortho- and - 161 -CHDC12/ CH 2C1 2 Meta Ortho Para —i— 6 4 6 Figure 6.5 L o w - f i e l d region of the "Si-n. [RuCl(dppb ) ( n 6-toluene)] +PF m.r..spectrum of 6 i n CD 2C1 2 at 400 MHz. para-protons, r e s p e c t i v e l y ( J o m = " l p m = 6 Hz, ^ 0^~ 0 Hz). The r e l a t i v e i n t e n s i t y of the coordinated toluene i s one quarter of that f o r the phenyl resonances of the phosphine which are at 67.3-7.7 ppm. The 31 1 P{ H}-n.m.r. spectrum of 8 i n CI>2C12 c o n s i s t s of a s i n g l e t at 31.9 ppm which i s i n v a r i a n t to temperature to -60°C. These f i n d i n g s are c o n s i s t e n t w i t h 8 having a pseudotetrahedral geometry as shown i n s t r u c t u r e 6-IV. The s o l i d s t a t e i . r . spectrum of 8 shows a t e r m i n a l Ru-Cl s t r e t c h (302 cm * ) , and non-coordinated PFg~ (840 and 568 cm 1 ) . - 162 -A dichloromethane s o l u t i o n ([Ru] = 2 X 10 M) of 8 has a -1 2 -1 conductance of 28.9 ohm cm mole which i s c o n s i s t e n t w i t h the complex being a 1:1 e l e c t r o l y t e . 6.3 D i s c u s s i o n The method of h a l i d e a b s t r a c t i o n using sodium or s i l v e r s a l t s of non-coordinating anions i s f r e q u e n t l y used to generate c a t i o n i c 155 t r a n s i t i o n metal complexes. In t h i s l a b o r a t o r y , attempts to generate c a t i o n i c complexes by t h i s method from ruthenium phosphine complexes such as RuCl^CPPh^)^, produced s i l v e r - p h o s p h i n e adducts as the only c h a r a c t e r i s a b l e products. Since i n the present study the s t a r t i n g compounds conta i n bidentate phosphines, which are l e s s l i k e l y to undergo d i s s o c i a t i o n , the use of s i l v e r s a l t s seemed f e a s i b l e . Indeed, t h i s method l e d to the i s o l a t i o n of complexes which may a l l be thought of as c o n t a i n i n g the 12-ele c t r o n RuCl(dppb) u n i t . In the d i n u c l e a r complexes [Ru„Cl_(dppb) (S) ] + , n = 2, S = 2 3 2 n a c e t o n i t r i l e ( 5 ) ; and n = 1, S = acetone ( 6 ) , the 12-electron - 163 -moiety i s s t a b i l i s e d by the " c h e l a t i n g - l i g a n d " RuClgCdppb) and s o l v e n t , w h i l s t i n the mononuclear examples [RuCl(dppb)(CHjCN)^] (j), and [ R u C l ( d p p b ) ( r ^ - t o l u e n e ) ] + (8), the 12-electron u n i t 31 1 i s s t a b i l i s e d by solvent alone. P{ H}-n.m.r. and c o n d u c t i v i t y data f o r these complexes are l i s t e d i n Tables 6.1 and 6.2, r e s p e c t i v e l y . The preparation of the d i n u c l e a r c a t i o n s i s by independent routes: 5_ i s prepared by anion exchange, w h i l s t 6^  i s prepared by a b s t r a c t i o n of a non-dissociated c h l o r i d e l i g a n d . Complexes of t h i s type c o n t a i n i n g monodentate phosphines have been reported 121 p r e v i o u s l y , but r a t h e r than solvent occupying the vacant c o o r d i n a t i o n s i t e s the strong n-acids CO and CS are present. The d i n u c l e a r c a t i o n s jj and 6^  e x h i b i t q u i t e d i f f e r e n t s o l u t i o n behaviour, although i n CH^Cl^ both give molar c o n d u c t i v i t i e s which are c o n s i s t e n t with the d i n u c l e a r i t y of the 31 1 i s o l a t e d complex. The P{ H}-n.m.r. spectrum of 5_ i n CD^Clg shows that the a c e t o n i t r i l e remains coordinated to both metal centres thereby generating a s i n g l e AB p a t t e r n . The spectra of 6^  e x h i b i t unresolved resonances i n CD^Clg even i n the presence of acetone and at low temperatures. The data are c o n s i s t e n t w i t h the i n a b i l i t y of the [(dppb)RuCljRu(dppb)] + moiety to coordinate two acetone molecules i n the s o l i d s t a t e or i n s o l u t i o n . The weaker i n t e r a c t i o n of acetone compared to a c e t o n i t r i l e w i t h the c a t i o n i c complex i s , perhaps, unexpected c o n s i d e r i n g the base parameters f o r these s o l v e n t s (Table 6.3). The values f o r both s o l v e n t s are s i m i l a r yet c l e a r l y the - 164 -Table 6.1 31TW1 P{ H}-N.m.r. Data f o r C a t i o n i c Complexes Cation Solvent Resonances [ R u 2 C l 3 ( d p p b ) 2 ( C H 3 C N ) 2 ] + [ R u C l (dppb) ( a c e t o n e ) ] + 2 3 2 fac-[RuCl(dppb)(CH^CN) ] + mer-[RuCl(dppb)(CH^CN)^] + [RuCl(dppb)(CH 3CN) 2] + [ R u C l ( d p p b ) ( n 6 - t o l u e n e ) ] + CD 2C1 2 <5A=49.6, 6£=46.6 ppm, J A £=36.6 Hz CD 2C1 2 m u l t i p l e t s centred at 47.5 ppm -acetone CD,CN 3 sing l e t : 4 0 . 6 ppm CD 2C1 2 s i n g l e t : 4 1 . 2 ppm CD^CN 6A=42.5, «B=35.7 ppm, 2J A B=34.2 Hz CD 2C1 2 s i n g l e t : 3 8 . 7 ppm CD 2C1 2 s i n g l e t : 3 1 . 9 ppm Table 6.2 Complex C o n d u c t i v i t y Data f o r C a t i o n i c Complexes Solvent A A e o [ R u 2 C l 5 ( d p p b ) 2 ( C H 5 C N ) 2 ] + P F 6 " [ R u 2 C l 5 ( d p p b ) 2 ( a c e t o n e ) ] + P F 6 " [RuCl(dppb)(CH 3CN) 3] +PF 6" [RuCl(dppb)(n 6-toluene)] +PJV CH3CN CH 2C1 2 CH 2C1 2 CH,CN 3 CH 2C1 2 CH 2C1 2 39.6 19.8 28.9 240.0 59.3 126.5 -1 2 -1 (a) Values given are i n ohm cm mole (b) [ R u J = [Ru] = 2 x 10" 5 M - 165 -Table 6.3 Base Parameters f o r Acetone and A c e t o n i t r i l e Parameter Values f o r : Acetone A c e t o n i t r i l e Donor number 17.0 14.1 Acceptor number 12.5 19.3 C B b 2.33 1.34 E £ b 0.99 0.89 Cg/E^ 2.36 1.51 a. Values taken from J.E. Huheey, "Inorganic Chemistry", 2nd e d i t i o n , Harper and Row, New York, 1978; Tables 7.4B and 8.4. b. See a l s o R.S. Drago and B.C. Vayland, J . Am. Chem. S o c , 87, 3571 (1965). c o o r d i n a t i n g a b i l i t y towards R u ( l l ) i n the present study i s q u i t e d i f f e r e n t . W h i l s t Gutmann's donor-acceptor model i s perhaps ambiguous sin c e the corresponding a c i d parameters of r u t h e n i u m ( l l ) are not known, Drago's C^/E^ model s t i l l p r e d i c t s that acetone should coordinate more s t r o n g l y than CH^CN. I t i s p o s s i b l e that the Eg and C B values do not r e f l e c t the p r e f e r r e d c o o r d i n a t i o n of n i t r o g e n donor l i g a n d s to ruthenium or that the weaker b i n d i n g of acetone simply a r i s e s from g r e a t e r s t e r i c hindrance compared to CH^CN. This d i f f e r e n c e between acetone and a c e t o n i t r i l e a l s o manifests - 166 -i t s e l f i n t h e i r a b i l i t y to s t a b i l i s e mononuclear s p e c i e s . In CH^CN, 3_ r e a d i l y undergoes d i s s o c i a t i o n to generate [RuCl(dppb)(CH^CN)^] X , X = C l or PFg. This i s evident by the high c o n d u c t i v i t y ( A q = 240 -1 2 -1 ohm cm mole ) and the presence of only a s i n g l e t i n the 3 1 1 3 1 X P{ H}-n.m.r. spectrum. The P{ H}-n.m.r. spectrum of 6 i n CD2Cl2/acetone does show a s i n g l e t assigned to a mononuclear species; however, the complex s t i l l e x i s t s predominantly as a d i n u c l e a r s p e c i e s . The f a c t that 5_ i s generated from R ^ C l ^ d p p b ^ i n CH^CN (equation 6.1), i n which j> has been shown to e x i s t as a mononuclear s p e c i e s , shows that c o o r d i n a t i o n to the RuCl(dppb) moiety of the " c h e l a t i n g " R uC^^ppb) l i g a n d i s thermodynamically more s t a b l e than c o o r d i n a t i o n of three a c e t o n i t r i l e l i g a n d s . The d i s s o c i a t i o n of 5. was confirmed by i s o l a t i o n of [RuCl(dppb)(CH 5CN) 5] + PP g , 7, by r e a c t i o n of 5 w i t h one equivalent 31 1 of AgPFg. The main resonance observed i n the P{ H}-n.m.r. spectrum of 5_ i n CD^C^ or CD^CN i s a s i n g l e t which suggests that the complex adopts a f a c - c o n f i g u r a t i o n . The a c e t o n i t r i l e l i g a n d s are l a b i l e , as evidenced by an a d d i t i o n a l s i n g l e t observed i n CD^Cl^, which i s assigned to a f i v e coordinate [RuCl(dppb)(CHjCN) 2] + species; and by the a b i l i t y to undergo rearrangement to the mer-configuration that probably i s r e s p o n s i b l e f o r the AB quartet observed i n CD^CN. Monodentate phosphine analogues (P = PPh^, PMePl^ and 153 PMe2?h) have been prepared p r e v i o u s l y , equation 6.3; however, no spectroscopic data were provided f o r comparison w i t h the data obtained i n the present study. - 167 -NH 4PF 6 [ ( c o d ) R u C l 2 J X : •» [(cod)RuCl(CH 5CN) 3] +PF 6" 2P (6.3) [RUCIP 2(CH 3CK) 3] +PF 6 The c o n d u c t i v i t y data obtained f o r 7 i n CH^CN are a l s o q u a n t i t a t i v e l y c o n s i s t e n t w i t h those found f o r 5_. The l i m i t i n g conductance of 1_ i s 126.5 ohm ''"cm^ mole 1 and, s i n c e 1 ' ' 6 _ - 1 2 - 1 X QPFg = 102.8 ohm cm mole , the l i m i t i n g conductance f o r -1 2 -1 the c a t i o n i c mononuclear species i s 23.7 ohm cm mole . Using — —1 2 —1 157 the l i m i t i n g conductance of C l (91.6 ohm cm mole" ) , the value expected f o r d i s s o c i a t i o n of jj i n accordance with equation 6.2 -1 2 -1 i s t h e r e f o r e ((2 x 23.7) + 102.8 + 91.6) = 241.8 ohm cm mole " —1 2 —1 which i s i n e x c e l l e n t agreement with that found (240.0 ohm cm mole ). The molar c o n d u c t i v i t y f o r the mixed-valence complex, R u 2 C l ^ ( d p p b ) 2 , ( S e c t i o n 6.2.1.1) i s a l s o c o n s i s t e n t w i t h that found f o r 7_. In a c e t o n i t r i l e , the i n i t i a l d i s p o r p o r t i o n a t i o n of R u 2 C l ^ ( d p p b ) 2 (equation 6.4) generates the dimeric R u ( l l ) complex which i s expected to undergo subsequent c h l o r i d e d i s s o c i a t i o n s (equation 6.5) i n an manner analogous to that found f o r the PF^~ s a l t s i n a c e t o n i t r i l e . 2 R u 2 C l 5 ( d p p b ) 2 • [ R u C l 2 ( d p p b ) ] 2 + [ R u C l 3 ( d p p b ) ] 2 (6.4) S = CH5CN [ R u C l 2 ( d p p b ) ] 2 • [ R u 2 C l 3 ( d p p b ) 2 S 2 ] + C l " • 2 [ R u C l ( d p p b ) S 3 J + C l ~ (6.5) - 168 -Since the conc e n t r a t i o n of the f i n a l mononuclear product i s the same as the i n i t i a l [ R u " ' ^ " ] complex, the measured conductance f o r [RuCl ( d p p b ) ( C H 3 C N ) 3 ] + C l " ([Ru] = 2 X 10~ 5M, A g = 112 ohm" 1cm 2mole~ 1) compares favourably w i t h that found f o r the analogous PFg~ s a l t , 1_. -1 2 -1 The molar c o n d u c t i v i t y of "]_ i n CH^Clg (19.8 ohm cm mole ) i s s u r p r i s i n g l y lower than that expected f o r the d i n u c l e a r a c e t o n i t r i l e complex (3) at the same conc e n t r a t i o n (from Figure 6.2; A g = 45.5 -1 2 -1 ohm cm mole ). This i s a l s o apparent from the c o n d u c t i v i t y of the d i n u c l e a r acetone complex (6_) which has a higher value (39.6 -1 2 -1 ohm cm mole ) compared to the mononuclear toluene complex (8) —1 2 —1 (28.9 ohm cm mole ). The solvent chosen f o r c o n d u c t i v i t y measurements should have a high d i e l e c t r i c constant and good s o l v a t i n g p r o p e r t i e s . Dichloromethane does not f i t e i t h e r of these c r i t e r i a , but was used si n c e i t was the only solvent i n which the complexes 5_ - 8 r e a d i l y d i s s o l v e d . W h i l s t the values obtained are i n the same range 121 122 found f o r other 1:1 e l e c t r o l y t e s ' , the unusually low c o n d u c t i v i t y f o r mononuclear complexes presumably a r i s e s from the low d i e l e c t r i c constant of the s o l v e n t . The d i s s o c i a t i o n of [ R U g C l ^ d p p b ^ a c e t o n e ) ] + PFg" (§) i n a manner analogous to the a c e t o n i t r i l e complex (5_) i s evidenced by 31 1 the s i n g l e t (32.8 ppm) i n the P{ H}-n.m.r. The attempted i s o l a t i o n of the mononuclear acetone complex v i a r e a c t i o n of R u ^ C l ^ d p p b ^ ^ c e t o n e ) .acetone w i t h 2 equiv a l e n t s of AgPFg i n a toluene-acetone solvent mixture was unsu c c e s s f u l , and l e d to the •6 ^ 6 + -i s o l a t i o n of the mononuclear complex [RuCl(dppb)(n -toluene)] PF,- (8). - 169 -Toluene was used simply to a i d d i s s o l u t i o n of the s t a r t i n g m a t e r i a l , but c l e a r l y was more e f f e c t i v e at s t a b i l i s i n g the RuCl(dppb) u n i t r a t h e r than three acetone molecules. In r e t r o s p e c t , t h i s perhaps i s not s u r p r i s i n g s i n c e the 12-electron u n i t i s i s o e l e c t r o n i c w i t h Cr(C0).j which r e a d i l y coordinates s i x - e l e c t r o n donors to form s t a b l e 1 8 - e l e c t r o n systems 1"^. The presence of coordinated toluene i s u n e q u i v o c a l l y confirmed by the proton resonsances between 64.34 - 5.74 ppm (Figure 6.5). The s h i f t to higher f i e l d of these resonances r e l a t i v e to f r e e toluene i s 159 thought to a r i s e from the f o l l o w i n g e f f e c t s : withdrawal of TT-electron d e n s i t y from the aromatic r i n g by the metal, quenching of r i n g c u r rents by i n t e r a c t i o n w i t h the metal, and by magnetic anisotropy of the r e s t of the metal complex. Hydrido-monodentate phosphine 160 analogues of 8 have been prepared f o r a s e r i e s of arenes , i n c l u d i n g PPh^ i t s e l f 1 6 1 . The complex [RuH(r, 6-toluene) ( P P h ^ J * BF^~ was prepared by hydride a b s t r a c t i o n from RuH^PPh^)^ i n the presence of toluene. This complex shows resonances f o r the coordinated phenyl at 64.6, 5.3 and 6.4 ppm f o r the ortho-, meta-, and para-protons, r e s p e c t i v e l y . Complex 8 e x h i b i t s s i m i l a r chemical s h i f t s f o r the ortho- (64.95 ppm) and meta- (65.74 ppm) protons, but the para-proton i s s h i f t e d to even higher f i e l d (64.34 ppm). The para-proton must e c l i p s e e i t h e r the b r i d g i n g p o r t i o n of bidentate phosphine or the c h l o r i d e l i g a n d depending on the o r i e n t a t i o n of the phenyl r i n g ( S t r u c t u r e 6-IV), and t h i s could cause s h i e l d i n g of the proton r e s u l t i n g i n a subsequent u p f i e l d s h i f t . - 170 -The i s o l a t i o n of 8 was unexpected but i s of i n t e r e s t as i t shows the a b i l i t y of the RuCl(dppb) moiety to form iT-arene complexes, and to separate the resonances of the ortho-, meta-, and para-protons. The development of such u-arene complexes i s t h e r e f o r e p o t e n t i a l l y u s e f u l as n.m.r. s h i f t reagents f o r aromatic r i n g s ; as at present, only c y c l o d e x t r i n s 1 ^ 2 and the ruthenium c o m p l e x e s 1 ^ mentioned p r e v i o u s l y are e f f e c t i v e . Although unproven, the complex [RuCl(dppb)(CH 5CN) 5] +PF 6" should be an i d e a l i n - s i t u s h i f t reagent as the l a b i l i t y of the a c e t o n i t r i l e l i g a n d s w i l l a l l o w easy c o o r d i n a t i o n of an aromatic r i n g . 6.4 Reaction of C a t i o n i c Complexes with Hydrogen The primary reason f o r the generation of the c a t i o n i c complexes discussed above was as hydride p r e c u r s o r s , and as p o t e n t i a l hydrogenation c a t a l y s t s . In order to determine i f the c a t i o n i c complexes were c a t a l y t i c a l l y a c t i v e a b r i e f study of alkene hydrogenation u s i n g [Ru0Cl_.(dppb)„(acetone)]+PF, (6) and <L j d. o — [RuCl(dppb)(CH_CN)„]+PF/(7) was undertaken. The n e u t r a l 5 5 b — complex RUgCl^Cdppb)£(acetone).acetone (_l) was a l s o used as a c a t a l y s t f o r comparison. Table 6.4 l i s t s the maximum r a t e s observed, and the time taken f o r red u c t i o n of 50$ of the substrate (T-jyg)* The data--in Table 6.4 show that the c a t i o n i c complexes are capable of hydrogenating alkenes, but e x h i b i t q u i t e d i f f e r e n t r e a c t i v i t y . The a c e t o n i t r i l e complex i s g e n e r a l l y l e s s r e a c t i v e , and shows d i s c r i m i n a t i o n towards the s u b s t r a t e s . The d i f f e r e n c e s i n r a t e - 171 -Table 6.4 Hydrogenation of Alkenes by N e u t r a l and C a t i o n i c Complexes C a t a l y s t (6) (7) (1) Substrate Max. Rate T l / 2 Max. Rate T l / 2 Max. Rate T l / 2 ( x l 0 4 , M s - 1 ) (s) ( x l O ^ M s " 1 ) (s) ( x l 0 4 , M s _ 1 ) (s) Hex-l-ene 7.4 310 0.8 2300 4.9 480 Styrene 2.7 730 2.4 750 3.0 600 Acrylamide 2.6 790 0.1 13000 1.3 820 (a) [6] = [7] = [1] = 2 x 10~ 5M, [alkene] = 0.4 M, 1 atm.H 2, DMA, 50°C f o r hydrogenation ca t a l y s e d by 1_ are presumably because of the d i f f e r e n t e l e c t r o n i c and s t e r i c c o n t r i b u t i o n s of the s u b s t r a t e . The rates observed f o r j> are p a r t i c u l a r l y h igh, and are comparable to those found f o r the n e u t r a l complex 1_; the s i m i l a r r e a c t i v i t y p a t t e r n perhaps suggests an a c t i v e species common to both. In the absence of s u b s t r a t e , 6^  and 1_ were found to react w i t h H 2. The H 2~uptake at 50°C f o r a DMA s o l u t i o n of 6 i n the presence of added base (Proton Sponge) corresponded to 1.0 Ru 2:1.35 H 2 the value being i n c o n s i s t e n t w i t h generation of any simple hydrido-complex. Since 6_ undergoes d i s s o c i a t i o n i n the presence of 31 1 acetone to mononuclear species ( P( H}-n.m.r. evidence, S e c t i o n 6.2.1.2), analogous behaviour seems l i k e l y i n DMA (equation 6.6). The - 172 -observed s t o i c h i o m e t r y with H 2 could r e s u l t from r e a c t i o n of the mono-[ R u 2 C l 5 ( d p p b ) 2 ( a c e t o n e ) ] + •> 2[RuCl(dppb)S n] + + C l " (6.6) or d i n u c l e a r species or both. The i s o l a t i o n of the a c t i v e species was not attempted due to a n t i c i p a t e d d i f f i c u l t i e s i n separating the mixture of products. The Hg-uptake f o r 7_ i n the absence of s u b s t r a t e , using the same c o n d i t i o n s as f o r 6^, corresponded to 6.85 moles H 2 per mole of complex. The uptake-plot (Figure 6.6) shows an i n f l e x i o n corresponding to ca.. 1 equivalent of hydrogen. This i s followed by uptake of 5.85 moles H 2 per Ru which i s q u a n t i t a t i v e l y c o n s i s t e n t w i t h r e d u c t i o n of the n i t r i l e group of the a c e t o n i t r i l e l i g a n d s : [RuCl(dppb)(CH 3CH) 3] +PF 6~ + 7H 2-*[RuH(dppb) ( C ^ N H ^ J " ^ " + HCl (6.7) The c o o r d i n a t i o n of ethylamine i s necessary to account f o r the observed s t o i c h i o m e t r y : since ethylamine i s a gas, i f i t were l i b e r a t e d from the r e d u c t i o n the net uptake would only correspond to 4 moles of gas per mole of 1_. In an attempt to confirm the r e a c t i o n proposed i n equation 6.7, the hydrogenation was conducted on a p r e p a r a t i v e s c a l e ( S e c t i o n 2.1.7.15). A f t e r r e a c t i o n w i t h H 2 f o r 2 d the DMA s o l u t i o n p r e c i p i t a t e d an o f f - w h i t e s o l i d . This was i n s o l u b l e i n most organic s o l v e n t s which precluded r e c r y s t a l l i s a t i o n and n.m.r. s t u d i e s . The - 173 -- 174 -i n f r a r e d spectrum of the s o l i d shows medium absorptions at 3300, 3221, 3191 and 3144 cm 1 (coordinated amine), and a strong a b s o r p t i o n at 1997 cm - 1 ( h y d r i d e ) . The elemental a n a l y s i s found (C : 58.4, H : 6.6, N : 4.3$) i s very c l o s e to that expected f o r RuHCl(dppb) (C 2H,-NH 2) 2 (C : 58.76, H : 6.58, N : 4.28$). The unexpected l o s s of PF &~ ( i . r . evidence) suggested that anion exchange between the product and the HCI generated by r e d u c t i o n had occurred. This was confirmed by the eventual i s o l a t i o n of a white s o l i d coproduct i d e n t i f i e d by elemental a n a l y s i s , 1 + - / \ i . r . and H-n.m.r. as PSH PF^ (PS = Proton Sponge). The product + l e f t a f t e r s e p a r a t i o n of the PSH PFg was a y e l l o w compound, which e x h i b i t e d a weak absorption at 3300 cm 1 ( v ^ ) , and absorptions due to non-coordinated PFg~ i n the i n f r a r e d spectrum. The "*"H-n.m.r. 31 1 spectrum e x h i b i t e d no hydride resonance, w h i l s t the P{ H}-n.m.r. spectrum (Figure 6.7) shows that more than one species i s present. Attempts to separate these species have been un s u c c e s s f u l , but the l a c k of hydride and amine absorptions suggests these are decomposition products r e s u l t i n g from the anion-exchange or work-up procedure. The H 2~uptake f o r 1_ i s c o n s i s t e n t w i t h the s t o i c h i o m e t r i c r e d u c t i o n of three a c e t o n i t r i l e l i g a n d s . To f u r t h e r confirm that r e d u c t i o n of -C=N was o c c u r r i n g , the r e a c t i o n of 1_ w i t h H 2 i n the presence of CH^CN was i n v e s t i g a t e d . D i r e c t a d d i t i o n of 1_ to DMA/CH^CN s o l u t i o n (9:1, v:v) gave no H 2~uptake; however, i n j e c t i o n of 10 uL .(0.2 M) of CH^CN to a DMA s o l u t i o n (10 mL) of 7 which had already undergone some r e a c t i o n w i t h H 5 gave the uptake p l o t shown i n - 175 -40 ppm 31 1 Figure 6.7 P{ H}-N.m.r. spectrum of f i n a l y e llow compound obtained from r e a c t i o n of [RuCl(dppb)(CH CN) ] +PF ~ with H . Figure 6.8. The uptake p r i o r to a d d i t i o n of CH^CN i s the same as observed f o r the st o i c h i o m e t r y determination. A f t e r i n j e c t i o n , the r a t e of hydrogenation f a l l s - o f f markedly, but a f t e r 4 d the t o t a l uptake corresponds to 9.6 H2:1.0 Ru at which p o i n t the monitoring was stopped. The hydrogenation of n i t r i l e s presumably proceeds v i a imine inter m e d i a t e s ; t h i s was tested f o r , by the r e a c t i o n of 7_ w i t h H 2 i n the presence of N-(2-phenylpropylidene)-2-propyl-amine, C 6H 5CH(CH 5)C=N-CH(CH 5) 2, (prepared according to James and 163 Young ). In t h i s r e a c t i o n the imine was i n i t i a l l y present i n a 170-fold excess, and the temperature increased to 65°C i n order to - 176 -10-Time , h Figure 6.8 H 2~Uptake p l o t f o r [RuCl(dppb)(CH 3CN) 5] +PF 6~ with a d d i t i o n of CH,CN. increase the r a t e . A f t e r 50 h, the H^-uptake corresponded to 50 turnovers at which point the monitoring was stopped (Figure 6.9). 6.4.1 D i s c u s s i o n The a d d i t i o n a l H^-uptake obtained upon i n j e c t i o n of CH^CN compared to the uptake i n i t s absence i s very small but s i g n i f i c a n t . The f a c t that there i s a d d i t i o n a l uptake supports the proposal that r e d u c t i o n of CH-CN i s o c c u r r i n g . - 177 -10 20 30 40 50 Time , h Figure 6.9 Uptake p l o t f o r imine r e d u c t i o n . The l a c k of Hg-uptake when J_ i s added d i r e c t l y to a DMA/CH,CN s o l u t i o n i n d i c a t e s that i n i t i a l l o s s of a coordinated 3 a c e t o n i t r i l e l i g a n d i s necessary f o r c a t a l y t i c a c t i v i t y . The 31 1 P{ H}-n.m.r. spectrum of J_ i n CDgClg shows a s i n g l e t (38.7 ppm) which was assigned to a 5-coordinate species s i n c e a d d i t i o n of CH^CN caused t h i s resonance to disappear. This i s c o n s i s t e n t with the uptake data, since generation of a vacant s i t e f o r Hg-coordination would be necessary f o r i n i t i a l hydride generation (equations 6.8 and - 178 -6.9) ; i n the presence of CH^CN the d i s s o c i a t i o n would not be favoured, [RuCl(dppb)(CH,CN),] +PF,~—•[RuCl(dppb) ( C H , C N ) J + P F / + CH,CN (6.8) J 0 o 3 2 b 3 [RuCl(dppb)(CH 3CN) 2] +PF 6~—2-H>[RuH(dppb)(CH 3CN) 2] +PF 6" + HCI (6.9) The i n f l e x i o n step observed i n the H 2~uptake of 7, corresponding to ca. 1 equivalent of H 2, i s c o n s i s t e n t w i t h formation of a h y d r i d o - a c e t o n i t r i l e complex. This i s probably the i n i t i a l l y a c t i v e s p e c i e s , but subsequent r e d u c t i o n of the a c e t o n i t r i l e generates presumably mono-, b i s - , and t r i s - e t h y l a m i n e complexes which must a l s o be a c t i v e . The a d d i t i o n of CH,CN a f t e r 2-5 h i s the r e f o r e to a s o l u t i o n 3 c o n t a i n i n g an a c t i v e s p e c i e s , and subsequent r e d u c t i o n occurs. For the t r i s - e t h y l a m i n e complex to be a c t i v e , i t has to undergo d i s s o c i a t i o n to allo w f o r c o o r d i n a t i o n of the n i t r i l e . The a d d i t i o n a l uptake obtained when CHjCN i s added i s very slow, and suggests that d i s s o c i a t i o n of an ethylamine l i g a n d i s not favoured. The r e d u c t i o n of n i t r i l e s to amines has been accomplished by a 63 number of t r a n s i t i o n metal complexes . Ruthenium complexes that c a t a l y s e t h i s process i n c l u d e 1 6 4 R u C l 2 ( P P h 3 ) 2 , RuHCl(CO) ( P P h ^ , RuH_(PMePH_)„ and RuHCl(CO)(PPh_)„, but f o r c i n g c o n d i t i o n are 2 2 4 3 3 165 required (10-120 atm. H 2, 20-130°C). Ceni n i et a l . J have stud i e d some c a t a l y t i c p r o p e r t i e s of amine complexes derived from R u C l 2 ( P P h 3 ) 3 . U n l i k e the present study, however, t h e i r i n v e s t i g a t i o n s have been d i r e c t e d towards the reverse r e a c t i o n , - 179 -o x i d a t i o n of amines to n i t r i l e s , and under mi l d c o n d i t i o n s ( l atm. Og, 80°C) have s u c c e s s f u l l y converted benzylamine to b e n z o n i t r i l e . Complex J. i s a l s o capable of reducing other unsaturated s u b s t r a t e s . The reduction of simple alkenes and the imine, N-(2-phenylpropylidene)-2-propyl-amine, proceed at s i g n i f i c a n t l y f a s t e r r a t e s compared to the r e d u c t i o n of a c e t o n i t r i l e . The increased rates suggest that these substrates are capable of d i s p l a c i n g the coordinated CH^CN, and thereby prevent formation of l e s s - a c t i v e ethylamine species. The r e d u c t i o n of the imine to N-(2-phenylpropyl)-N-(2-propyl)amine i s a l s o expected to lead to the formation of Ru-amine complexes, but s i n c e the amine i s bulky, i t i s l i k e l y to bind considerably weaker than ethylamine. This i s c o n s i s t e n t w i t h the high turnover and measured r a t e , although the observed f a l l - o f f i n r a t e w i t h time i n d i c a t e formation of l e s s a c t i v e s p e c i e s . In order to determine i f the l e s s a c t i v e species a r i s e from the reduced imine or from ethylamine, i t w i l l be necessary to prepare a complex analogous to 1_ but w i t h non-reducible solvent l i g a n d s . The r e d u c t i o n of imines i s a r e l a t i v e l y undeveloped f i e l d compared to the r e d u c t i o n of other unsaturated s u b s t r a t e s . C a t a l y s t s capable of imine-reduction i n c l u d e phosphine complexes of Rh^"^ 0s 1 6 9 and R u 1 6 9 , R h ( p y r i d i n e ) 5 C l 5 1 7 2 , and F e ( C 0 ) 5 1 7 3 . Of p a r t i c u l a r i n t e r e s t would be the use of a c h i r a l phosphine i n the present study as to date only modest enantiomeric excesses have been 170 171 obtained f o r the asymmetric r e d u c t i o n of p r o c h i r a l imines ' - 180 -CHAPTER VII GENERAL CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK The aim of the work described i n t h i s t h e s i s was to develop s y n t h e t i c routes f o r the prep a r a t i o n of ruthenium complexes c o n t a i n i n g one d i t e r t i a r y phosphine l i g a n d per metal centre. I n c o r p o r a t i o n of a c h i r a l d i t e r t i a r y phosphine l i g a n d , would then a l l o w these complexes to be tes t e d as p o t e n t i a l asymmetric hydrogenation c a t a l y s t s . Due to the high cost of c h i r a l phosphines most of the i n v e s t i g a t i o n s i n the present study were l i m i t e d to n o n c h i r a l phosphines, i n p a r t i c u l a r dppb. Sev e r a l important f i n d i n g s are summarised below, together w i t h some suggestions f o r f u t u r e work. The mixed-valence complexes, R u 2 C l ^ ( P - P ) 2 , P-P = chiraphos, norphos, dppp, diop, or dppb were synthesised by phosphine exchange from a mononuclear R u ( l l l ) s t a r t i n g compound i n hexanes: R u C l 3 ( P ) 2 + P-P *> 0.5 R u 2 C l 5 ( P - P ) 2 ' (7.1) P=PPh 5 or P ( p - t o l y l ) The phosphine exchange was dependent on the monodentate phosphine precursor, and appears to have l i m i t e d a p p l i c a t i o n as attempts to prepare the mixed-valence dppe analogue were unsuccessful using e i t h e r - 181 -the PPh^ or P ( p - t o l y l ) 3 complex. Hexanes were chosen as solvent as the ruthenium complexes are i n s o l u b l e throughout the r e a c t i o n w h i l s t the phosphines ( e i t h e r added or l i b e r a t e d ) are s o l u b l e , thereby f a c i l i t a t i n g e a s i e r s e p a r a t i o n . The use of a higher b o i l i n g p o i n t solvent ( i . e . octane), or a solvent i n which the ruthenium complexes are s l i g h t l y s o l u b l e ( i . e . benzene), might improve the phosphine exchange to in c l u d e a l l bidentate phosphines, and e l i m i n a t e the need f o r d i f f e r e n t monodentate phosphine precursor complexes. A s i n g l e c r y s t a l X-ray determination of RugCl^(chiraphos),, showed the complex to be t r i p l y c h l o r o - b r i d g e d , w i t h the de s i r e d one d i t e r t i a r y phosphine per ruthenium ( s t r u c t u r e 7.1). The s t r u c t u r e f o r the P-P = norphos, dppb, diop or dppb analogues are bel i e v e d to be the same, but t h i s has not been proven unambiguously. The s o l u t i o n p r o p e r t i e s of the R^Cl^- ( P - P ) 2 complexes were most conveniently studied by examination of the i n t e r v a l e n c e charge t r a n s f e r t r a n s i t i o n s i n the n e a r - i n f r a r e d s p e c t r a . The chiraphos d e r i v a t i v e e x h i b i t s strong solvent dependencies with absorptions due to at l e a s t two species. For example, i n CDCl^ the p r i n c i p l e absorption i s at low energy (ca. 2350 nm), and i s assigned to the complex having 7.1 - 182 -the same s t r u c t u r e i n s o l u t i o n as i n the s o l i d s t a t e . In C C l ^ the low energy absorption i s broad and unresolved, but there i s a more intense a b s o r p t i o n at 880 nm. The t e n t a t i v e assignment of the high energy absorption to a t e t r a n u c l e a r species needs s u b s t a n t i a t i n g i f the s o l u t i o n p r o p e r t i e s of R u 2 C l ^ ( c h i r a p h o s ) 2 are to be f u l l y understood. The i n t e r v a l e n c e charge t r a n s f e r t r a n s i t i o n s f o r the other phosphine analogues were not so e x t e n s i v e l y s t u d i e d . P r e l i m i n a r y investigations,however, show these to e x h i b i t unique n e a r - i n f r a r e d spectra compared to the chiraphos complex i n the same s o l v e n t . The r e a c t i o n of the R u 2 C l ^ ( P - P ) 2 complexes w i t h H 2 i n DMA generated i n s i t u i o n i c d i r u t h e n i u m ( l l ) complexes: R u 2 C l 5 ( P - P ) 2 + 0.5 H 2 • [ R u 2 C l 5 ( P - P ) 2 ] " DMAH+ (7.2) The r e d u c t i o n was found to be a u t o c a t a l y t i c , but attempts to a s c e r t a i n mechanistic d e t a i l s by k i n e t i c measurements of the H 2~uptake, or changes i n v i s i b l e spectrum were un s u c c e s s f u l . This i s presumably due to the presence of more than one species ( n e a r - i . r . evidence), which was not determined u n t i l l a t e r . From the i o n i c product generated i n s i t u (equation 7.2) the n e u t r a l complexes, [RuCl 2(P-P)] 2,were i s o l a t e d by a d d i t i o n of methanol to d i s p l a c e the HCl generated by re d u c t i o n . For P-P = chiraphos or diop, the complexes were more c o n v i e n t l y prepared by redu c t i o n i n toluene i n the presence of added based, p o l y v i n y l p y r i d i n e . - 183 -The [ R u C l 2 ( P - P ) ] 2 complexes i n non-coordinating s o l v e n t s , a l l e x h i b i t 22 i P{ H}-n.m.r. spec t r a c o n s i s t e n t w i t h the dimeric f o r m u l a t i o n : P C l Ru 7.II In the presence of c o o r d i n a t i n g s o l v e n t s (acetone or DMA), [ R u C l ^ ( c h i r a p h o s ) ] 2 and the dppb analogue were shown by 31 1 P{ H}-n.m.r. to adopt a t r i p l y c hloro-bridged s t r u c t u r e w i t h c o o r d i n a t i o n of one solvent molecule: C l C l / P N \ #^ '*''% / \ P - P = c h i r a P n o s o r d P P D P mini Ru-^Cl ^ ^ R u i u up S = Solvent \ S \ C 1 / N s DMA s o l u t i o n s of [ R u C l 2 ( P - P ) ] 2 , P-P = chiraphos or diop c a t a l y s e d the asymmetric hydrogenation of p r o c h i r a l alkenes. The r a t e of hydrogenation,'product c o n f i g u r a t i o n , and % e.e. v a r i e d c o n s i d e r a b l y , with the nature of the c h i r a l phosphine, and of the substrate,being s i g n i f i c a n t f a c t o r s i n the o v e r a l l process. The most notable r e s u l t was an observed hydrogenation of (Z)-a-acetamidocinnamic a c i d w i t h 97$ e.e. using the chiraphos complex. S t e r i c f a c t o r s a r i s i n g from the bulky phenyl group on t h i s substrate appear important, and could be e a s i l y - 184 -sub s t a n t i a t e d by hydrogenating other s u b s t i t u t e d a-aminoacrylic a c i d s . The hydrogenation study a l s o showed the % e.e. to increase with lowering the temperature f o r e s s e n t i a l l y a l l the substrates used, and f o r both complexes. In order to e x p l a i n the unusual temperature dependence, and the e f f i c i e n t hydrogenation of (Z)-a-acetamidocinnamic a c i d i t w i l l be necessary to obt a i n mechanistic d e t a i l s . This might be achieved by using the [ B u C l 2 ( P - P ) ] 2 complexes, but i d e a l l y the a c t i v e hydrido-species should be i s o l a t e d , and used f o r n.m.r. and k i n e t i c s t u d i e s of the hydrogenation process. Attempts to i s o l a t e such a hydrido-species from [ E U C I ^ C P - P ) ] 2 were u n s u c c e s s f u l . The r e a c t i o n of DMA s o l u t i o n s of the dppb complex with H 2 i n the presence of Proton Sponge d i d generate a hydride complex ("Si-n.m.r. evidence), although the p r i n c i p l e product i s o l a t e d was [Ru 2Clj-(dppb) 2]~PSH +. This i o n i c product i s formed by a d d i t i o n of the HCl (as PSH C l ), generated by r e d u c t i o n , to the s t a r t i n g complex. An improved p r e p a r a t i v e procedure i s c l e a r l y required i f the hydride complex i s to be i s o l a t e d pure. This might be achieved using a d i f f e r e n t base, such as NEt,. Pro t o n a t i o n of NEt_ generates 3 3 a smaller c a t i o n which might not s t a b i l i s e [Bu 2Cl,-(dppb),,] to + the same extent as PSH , thereby i n h i b i t i n g anion formation. A l t e r n a t i v e l y the use of L i A l H ^ or i t s d e r i v a t i v e s would e l i m i n a t e the need f o r HCl removal. Further attempts to generate a hydrido-complex l e d to the pre p a r a t i o n and c h a r a c t e r i s a t i o n of EuCl 2(nbd)(dppb), and a b r i e f i n v e s t i g a t i o n of the r e a c t i o n with H ?. A s i n g l e c r y s t a l X-ray - 185 -determination showed the complex to be mononuclear with coordinated d i a l k e n e , but i n s o l u t i o n the complex was found to undergo d i s s o c i a t i o n : RuCl 2(nbd)(dppb) • 0.5 [ R u C l 2 ( P - P ) ] 2 + nbd (7.3) The r e a c t i o n w i t h H 2 i n the presence of Proton Sponge generated a hydride complex (n.m.r. evidence) which i s thought to be RuHCl(nbd)(dppb), but again the major product of the r e a c t i o n was [Ru 2Cl^(dppb) 2]~PSH +. The formation of a hydrido-alkene complex i n the presence H 2 i s unexpected, and merits f u r t h e r i n v e s t i g a t i o n . The i s o l a t i o n of RuHCl(nbd)(dppb) i n high y i e l d could p o s s i b l y be achieved by reducing RuCl 2(nbd)(dppb) i n the presence of excess norbornadiene, or by using a d i f f e r e n t base. An a l t e r n a t i v e route v i a a d d i t i o n of norbornadiene to an i s o l a t e d hydrido-complex i s the most a t t r a c t i v e ; however, t h i s r e q u i r e s a s u i t a b l e method f o r generation of a precursor hydride complex (vide supra). The i s o l a t i o n of R u H 2 ( C 0 ) C l 2 ( d p p b ) 2 by s t i r r i n g a CH 2Cl 2/Me0H s o l t u i o n of Ru 2Cl^(dppb) 2(acetone).acetone with Proton Sponge, was unexpected. The product i s thought to form by successive hydrogen atom t r a n s f e r s from a Ru-methoxide intermediate, although mechanistic d e t a i l s are needed. W h i l s t not r e l a t e d to the hydrogenation s t u d i e s p r e v i o u s l y discussed, the c a t a l y t i c p r o p e r t i e s of R u 2 H 2 ( C 0 ) C l 2 ( d p p b ) 2 should be examined. Assuming the complex to b e : k i n e t i c a l l y a c t i v e , a p p l i c a t i o n as a t r a n s f e r hydrogenation c a t a l y s t using methanol or higher a l c o h o l s appears f e a s i b l e . - 186 -The r e a c t i o n of RUgCl^(dppb) 2 and R u 2 C l 4 ( d p p b ) 2 ( a c e t o n e ) .acetone with the appropriate amount of AgPFg produces mono- and d i n u c l e a r c a t i o n i c complexes. Of these the complex [RuCl(n. 6-toluene) (dppb) ] PFg i s p a r t i c u l a r l y i n t e r e s t i n g due to the presence of coordinated toluene. The "4i-n.m.r. of t h i s complex e x h i b i t s a separation and u p f i e l d s h i f t of the ortho-, meta-, and para-protons of the coordinated toluene r e l a t i v e to f r e e toluene. The development of such 71-arene complexes i s ther e f o r e p o t e n t i a l l y u s e f u l as n.m.r. s h i f t reagents f o r aromatic r i n g s . The procedure f o r i s o l a t i o n of t h i s n-arene complex negates general a p p l i c a t i o n , but using [RuCl(dppb)(CHjCN) 3] +PFg as an i n s i t u reagent seems f e a s i b l e . The a c e t o n i t r i l e l i g a n d s of t h i s complex are l a b i l e 31 1 ( P{ H}-n.m.r. evidence), and should be e a s i l y d i s p l a c e d by an arene l i g a n d . The [RuCl(dppb)(CH 5CN) 3] PF 6~complex i s a l s o of i n t e r e s t f o r i t s apparent a b i l i t y to hydrogenate h i t r i l e and imine s u b s t r a t e s . In the absence of substrate the complex re a c t s w i t h hydrogen with a stoic h i o m e t r y of 1.0 Ru:6.85 H 2. This i s c o n s i s t e n t w i t h r e d u c t i o n of the a c e t o n i t r i l e l i g a n d s to ethylamine: + 7H 2 _ [RuCl(dppb)(CH 3CN) 5] PF 6 •[RuCl(dppb) (CgH NHgJj] PF g (7. The proposed product was not i s o l a t e d due to complications a r i s i n g from anion exchange, and an a l t e r n a t i v e procedure i s necessary. - 187 -The c a t a l y t i c r e duction of the a c e t o n i t r i l e and imine were shown to occur by Hg-uptake beyond that found f o r the complex i n the absence of s u b s t r a t e . The r e d u c t i o n of a c e t o n i t r i l e i s extremely slow. This i s thought to be due to the t r i s e t h y l a m i n e complex (equation 7.4) having to undergo l i g a n d d i s s o c i a t i o n i n order to f u r t h e r reduce a c e t o n i t r i l e . As the hydrogenation proceeds the c o n c e n t r a t i o n of ethylamine i n c r e a s e s , and t h e r e f o r e the d i s s o c i a t i o n of ethylamine l i g a n d w i l l be l e s s favoured. A p h y s i c a l means of removing the ethylamine i s r e q u i r e d , p o s s i b l y by conducting the r e d u c t i o n i n a c i d i c media, although t h i s might i n h i b i t i n i t i a l hydride formation. The r e d u c t i o n of the imine using [ R u C l ( d p p b ) ( C E ^ C I S ) ^ ? ? ^ was considerably f a s t e r than that found f o r the reduction of a c e t o n i t r i l e . The presence of r e d u c i b l e a c e t o n i t r i l e l i g a n d c l e a r l y complicates the study. In order to i n v e s t i g a t e the imine hydrogenation s u c c e s s f u l l y , i t w i l l be necessary to have a non-reducible l a b i l e l i g a n d f o r the RuCl(dppb) moiety. I f such a c a t a l y t i c system can be developed, the i n c o r p o r a t i o n of a c h i r a l phosphine w i l l a l low f o r the asymmetric hydrogenation of p r o c h i r a l imines. - 188 -REFERENCES 1. (a) G.W. 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