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Activation of molecular hydrogen in solution by complexes of univalent, divalent, and trivalent ruthenium Hui, Benjamin Ching-Yue 1969

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ACTIVATION OF MOLECULAR HYDROGEN IN SOLUTION BY COMPLEXES OF UNIVALENT, DIVALENT AND TRIVALENT RUTHENIUM BY • BENJAMIN CHING-YUE HUI B.Sc. (Hons.) The U n i v e r s i t y of Hong Kong, 1965 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of CHEMISTRY We accept t h i s t h e s i s as conforming to the re q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1969 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the r e q u i r e m e n t s f o r an advanced degr.ee a t the U n i v e r s i t y o f B r i t i s h C olumbia, I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and Study. I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u rposes may be g r a n t e d by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date ABSTRACT K i n e t i c s tudies of a number of i n t e r e s t i n g and s i g n i f i c a n t react ions i n v o l v i n g r e a c t i o n of molecular hydrogen, o l e f i n s and carbon monoxide with so lut ions o f ruthenium c h l o r i d e complexes are descr ibed . Ruthenium t r i c h l o r i d e t r i h y d r a t e , "RuCl - . 3H-0" , which i s a mixture o f ruthenium(III) and ruthenium(IV), was found to react with molecular hydrogen i n dimethylacetamide (DMA) s o l u t i o n under mi ld c o n d i t i o n s , to produce ruthenium(II) and ruthenium(I) i n successive steps i n v o l v i n g a c t i v a t i o n of the hydrogen by ruthenium(ITI) and ruthenium(II): R UN + + H _ R u H ( n - 1 ) + + H + (1) R u H f n - 1 ) + + Ru 1 1* — , 2 R u C n " 1 ) + + H + (2) In aqueous a c i d s o l u t i o n , the reverse of r e a c t i o n (1) prevents reduct ion of ruthenium(III) ; i n DMA, a more b a s i c so lvent , the re leased proton i s s t a b i l i z e d and reduct ion i s observed a l l the way to the univa lent s ta te . Convincing evidence was found for the existence of ruthenium(I) i n DMA, although no w e l l - c h a r a c t e r i z e d ruthenium(I) s o l i d complexes were i s o l a t e d . The present studies are the f i r s t reported on the s o l u t i o n chemistry of ruthenium(I) c h l o r i d e s . Ruthenium(I) c h l o r i d e complexes i n DMA ( 8 0 ° ) were found to a c t i v a t e molecular hydrogen through d ihydr ide formation for the • cata lyzed reduct ion of o l e f i n s . The fo l lowing mechanism i s i n d i c a t e d : K Ru* -r^*- 2 R U 1 ( K D 4 l O " 5 M ) (3) k R u I + H2 -~=_ R u I H h 2 ( k 1 »  kl ) ( 4 )  k " l v III 2 I Ru H- + o l e f i n >- Ru + alkane (5) Accompanying o l e f i n isomerization and some deuterium isotope studies suggest that reaction ( 5 ) goes through an a-a l k y l hydride intermediate,-the hydrogen t r a n s f e r process involving two consecutive single hydrogen atom transfers to a coordinated o l e f i n . Addition of triphenylphosphine (PPh_) to the ruthenium(I) c a t a l y s t s o l u t i o n decreases the hydrogenation rate. However, reaction of hydrogen with a ruthenium (T) s o l u t i o n con-taini n g PPh- and no substrate gave evidence for the formation of a hydride species. In the presence of PPh-, reaction of H- with ruthenium(II) chloride i n DMA does not produce ruthenium(I). The ruthenium(II) hydride intermediate i s s t a b i l i z e d by the phosphine ligand y i e l d i n g the w e l l -known complex RuHCl(PPh_)_ which has been found to be extremely active i n c a talyzing the hydrogenation of o l e f i n s . An extremely simple method fo r the preparation of the c a t a l y s t " i n s i t u " i s demonstrated, again u t i l i s i n g the basic properties of DMA. A mechanism involving a predissocia-t i o n of the c a t a l y s t , and formation of an a - a l k y l intermediate i s thought to be operative i n the catalyzed hydrogenation of o l e f i n s : K RuHCl(PPh_)_ — R u H C l ( P P h _ ) 2 + PPh_ (6) K 2 RuHCl(PPh_) 2 + o l e f i n — R u C l ( P P h _ ) 2 (alkyl) (7) - i v -RuCl(PPh_) 2 (a lky l ) + H . RuHCl(PPh_) 2 + alkane (8) Both ruthenium(I) and ruthenium(II) chlorides i n DMA were found to absorb carbon monoxide r e a d i l y at ambient temperatures, producing Ru I(CO) and R u I ( C O ) 2 , and Ru I ] [ (CO) and R u I I ( C O ) 2 r e s p e c t i v e l y . The i n t r o d u c t i o n of carbonyl groups in to these ruthenium complexes was found to i n h i b i t c a t a l y t i c a c t i v i t y for the hydrogenation of o l e f i n s . 2-The anion [RuCl^(bipyridine) ] , i n 3 M HC1, was found to be a hydrogenation ca ta ly s t for o l e f i n reduc t ion , though not a very e f f i c i e n t one. A mechanism s i m i l a r to the RuHCl(PPh_)_ cata lyzed system seems to be i n v o l v e d , and i s qu i te d i f f e r e n t to that reported for a corresponding system i n v o l v i n g the te trach lororuthenate ( I I ) complex, [ R u C l 4 ] 2 " . - V -TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS v LIST OF TABLES x LIST OF FIGURES x i i i ABBREVIATIONS x v i i i ACKNOWLEDGMENTS x x CHAPTER I. INTRODUCTION 1 1.1. Aim of Work 1 1.2. A c t i v a t i o n of Molecular Hydrogen and Homo-geneous C a t a l y t i c Hydrogenation 4 1.2.1. Mechanisms of Hydrogen A c t i v a t i o n 4 1.2.2. Homogeneous C a t a l y t i c Hydrogenation 6 1.3. L i t e r a t u r e Reports on the C a t a l y t i c P r o p e r t i e s of Ruthenium Complexes 11 1.3.1. Homogeneous Hydrogenation 11 1.3.2. P o l y m e r i z a t i o n of O l e f i n s and Acetylenes .... 13 1.3.3. A r y l a t i o n and A l k y l a t i o n of O l e f i n s 15 1.3.4. O x i d a t i o n of O l e f i n s 16 1.3.5. Hydration of Acetylenes 17 1.3.6. Hydroformylation Reactions 18 1.3.7. Carbonylation and Decarbonylation Reactions . 18 1.3.8. Hydrogen M i g r a t i o n and Isomerization Reactions 20 1.3.9. Ruthenium Complexes Containing Molecular Nitrogen and Oxygen 22 - v i -CHAPTER I I . APPARATUS AND EXPERIMENTAL PROCEDURE 25 2.1. M a t e r i a l s 25 2.1.1. Ruthenium S a l t s 25 2.1.2. Gases 26 2.1.3. Other M a t e r i a l s 26 2.2. Apparatus f o r Constant Pressure Gas-Uptake Measurements 27 2.3. Procedure f o r a T y p i c a l Gas-Uptake Experiment. 29 2.4. Reaction Product A n a l y s i s 31 2.4.1. S o l i d Organic Products 31 2.4.2. Inorganic Products 31 2.5. Instrumentation 32 CHAPTER I I I . REACTIONS USING SOLUTIONS OF RUTHENIUM 2,2'-BIPYRIDYL COMPLEXES ... 33 3.1. The Reactions I n v o l v i n g Hydrogen i n Aqueous Hy d r o c h l o r i c A c i d S o l u t i o n 33 3.1.1. Results and D i s c u s s i o n of the C a t a l y t i c Hydrogenation 39 3.2. Reactions I n v o l v i n g Other Gaseous Molecules... 48 CHAPTER IV. CATALYTIC ACTIVATION OF MOLECULAR HYDROGEN BY RUTHENIUM CHLORIDE COMPLEXES IN DMA 50 4.1. I n t r o d u c t i o n 50 4.2. A c t i v a t i o n of Molecular Hydrogen by Ruthenium ( I I I ) C h l o r i d e Complexes 51 - v i i -4.2.1. A u t o c a t a l y t i c Reduction of Ruthenium(IV) (Production of R u 1 1 1 ) 51 4.2.2. C a t a l y t i c Reduction o f Molecular Oxygen 61 4.2.3. C a t a l y t i c Reduction of Ru*** at Higher Temperatures (Production of Ru**) 68 4.2.4. D i s c u s s i o n o f K i n e t i c R e sults f o r A c t i v a t i o n of H 2 by Ru(III) 70 4.3. A c t i v a t i o n of Molecular Hydrogen by Ruthenium (I I ) C h l o r i d e Complexes (Production o f Ru*)... 78 4.3.1. Stoichiometry 78 4.3.2. K i n e t i c s o f the Hydrogen Reduction o f Ruthenium (II ) i n DMA 8 1 4.3.3. D i s c u s s i o n 8 2 CHAPTER V. RUTHENIUM(I) CHLORIDE CATALYZED HYDROGENATION OF OLEFINIC COMPOUNDS IN DMA 9 1 5.1. I n t r o d u c t i o n 91. 5.2. The Ruthenium(I) C h l o r i d e - M a l e i c and Fumaric A c i d Systems i n DMA 9 ^ 5.3. K i n e t i c Measurements 9 6 5.3.1. The Ma l e i c A c i d System 9 7 5.3.2. The Fumaric A c i d System 1 0 2 5.4. Di s c u s s i o n of K i n e t i c Results 108 5.4.1. Dependence of the Rate on Substrate Concentra-t i o n 114 5.4.2. Dependence on Temperature 115 - v i i i -5.4.3. Dependence on Added C h l o r i d e 119 5.4.4. I s o m e r i z a t i o n o f M a l e i c A c i d 120 5.4.5. Deuteration and Stereochemistry of A d d i t i o n to O l e f i n s 121 5.5. General D i s c u s s i o n on C a t a l y t i c Hydrogenation Using Ruthenium (I) 122 CHAPTER VI. FORMATION OF A RUTHENIUM(III) HYDRIDE SPECIES FROM RUTHENIUM(I) SOLUTIONS 125 6.1. I n t r o d u c t i o n 125 6.2. Formation of A Ruthenium(III) Hydride 125 6.3. C a t a l y t i c A c t i v i t y of the Hydride Species .... 131 CHAPTER V I I . HOMOGENEOUS HYDROGENATION OF MALEIC ACID USING HYDRIDOCHLOROTRIS(TRIPHENYLPHOSPHINE)RUTHENIUM (II) AS CATALYST 134 7.1. I n t r o d u c t i o n 134 7.2. Production of H y d r i d o c h l o r o t r i s ( t r i p h e n y l -phosphine)ruthenium(II) i n DMA S o l u t i o n 136 7.3. C a t a l y t i c Hydrogenation of M a l e i c A c i d 140 7.3.1. Dependence on Triphenylphosphine Concentration 146 7.3.2. Dependence on M a l e i c A c i d Concentration 146 7.3.3. Dependence on C a t a l y s t Concentration 152 7.3.4. Dependence on Hydrogen Pressure 152 7.4. Di s c u s s i o n o f K i n e t i c Results 156 7.4.1. Dependence on Substrate Concentration 160 7.4.2. Dependence on Triphenylphosphine Concentration 161 - i x -7.4.3. Dependence on C a t a l y s t Concentration 163 7.4.4. Dependence on Temperature 165 7.5. D i s c u s s i o n 167 CHAPTER V I I I . DIRECT CARBONYLATION OF SOME RUTHENIUM CHLORIDE COMPLEXES IN DMA 171 8.1. D i r e c t Carbonylation of Ruthenium(II) C h l o r i d e Complexes i n DMA 171 8.1.1. I n t r o d u c t i o n 171 8.1.2. Stoichiometry 172 8.1.3. K i n e t i c s of the F i r s t Stage 174 8.1.4. K i n e t i c s of the Second Stage 177 8.1.5. D i s c u s s i o n 182 8.1.6. C a t a l y t i c Hydrogenation Using Ru 1* Species i n DMA 193 8.2. D i r e c t Carbonylation of Ruthenium(I) C h l o r i d e Complexes i n DMA 194 8.2.1. Stoichiometry 194 8.2.2. K i n e t i c s o f the F i r s t Stage 198 8.2.3. K i n e t i c s of the Second Stage 201 8.2.4. D i s c u s s i o n 201 8.2.5. C a t a l y t i c Hydrogenation Using Ru 1 Species i n DMA 206 CHAPTER IX GENERAL CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK 208 REFERENCES 216 - X -LIST OF TABLES Number Page 2-[RuCl^(bipy)] cata lyzed hydrogenation of maleic a c i d i n aqueous s o l u t i o n s . 40 I K i n e t i c data Ruthenium(III) c h l o r i d e cata lyzed hydrogen reduct ion o f Ru(IV) i n DMA s o l u t i o n s . II K i n e t i c data 56 III Temperature dependence o f 59 Ruthenium(III) c h l o r i d e cata lyzed hydrogen reduct ion of 0- i n DMA s o l u t i o n s . IV K i n e t i c data 64 V Temperature dependence of kj 66 Ruthenium(III) c h l o r i d e cata lyzed hydrogen reduct ion of Ru(III) i n DMA s o l u t i o n s . VI K i n e t i c data at 8 0 ° 71 VII Temperature dependence o f k^ 72 C a t a l y t i c reduct ion of Ru(II) by hydrogen i n DMA s o l u t i o n s . VIII K i n e t i c data at 8 0 ° 83 IX Temperature dependence o f k^ 84 X E f f e c t of c h l o r i d e on r e a c t i o n rates at 8 0 ° 86 Ruthenium(I) c h l o r i d e cata lyzed hydrogenation of maleic a c i d i n DMA s o l u t i o n s . XI K i n e t i c data of i n i t i a l ra t e at 80 0 98 XII Temperature dependence of i n i t i a l ra te 99 - x i -Number Page Ruthenium(I) c h l o r i d e cata lyzed hydrogenation of fumaric a c i d i n DMA s o l u t i o n s . XIII K i n e t i c data at 8 0 ° 105 XIV K i n e t i c data of the l a t e r reg ion of maleic a c i d uptake p lo t s at 8 0 ° 106 XV Temperature dependence of some k i n e t i c data 117 Formation of Ru(III) tr iphenylphosphine hydride i n DMA s o l u t i o n s . XVI K i n e t i c data at 8 0 ° 129 Ruthenium(III) tr iphenylphosphine hydride cata lyzed hydrogenation o f maleic a c i d in DMA s o l u t i o n s . XVII K i n e t i c data at 8 0 ° 133 RuHCl(PPh_)_ cata lyzed hydrogenation o f maleic a c i d i n DMA s o l u t i o n s . XVIII Dependence of i n i t i a l rate on [PPh_] and [M.A.] at 3 5 ° 147 XIX Dependence of i n i t i a l ra te on [ R u 1 1 ] and [H ] at 3 5 ° . . 148 XX Temperature dependence o f k, 149 Formation of ruthenium(II) carbonyls i n DMA s o l u t i o n s . XXI Summary of k i n e t i c data for the formation of Ru*"*"(C0) at 8 0 ° 1 ? 6 XXII Temperature dependence of k^ for the formation of R u H ( C 0 ) 178 XXIII Summary of k i n e t i c data for the formation of R u ^ C C O ) -at 8 0 ° 181 XXIV Temperature dependence o f k^ for the formation of R u H ( C 0 ) 2 185 - x i i -Number Page XXV E f f e c t o f temperature on ra te constants for the formation o f R u n ( C O ) 2 191 Formation of ruthenium(I) carbonyls i n DMA s o l u t i o n s . XXVI K i n e t i c data for the formation of R u 1 (CO) 200 XXVII K i n e t i c data for the formation of R u I ( C 0 ) o 203 - x i i i -LIST OF FIGURES Figure Page 1 Apparatus for constant pressure gas-uptake measurement. 28 2-2 Absorpt ion spectra of (A) K R u C l 4 ( b i p y ) , (B) [RuCl 4 (b ipy) ] , (C) [ R u C l 4 ( b i p y ) ] 2 " - M.A. complex . . . 34 3 E f f e c t o f maleic a c i d on the absorbance at 517 my o f 2-a [RuCl 4 (b ipy) ] - M.A. complex 36 4 Determination o f formation constant (K^) of the [ R u C l 4 ( b i p y ) ] 2 _ - M.A. complex 37 2-[RuCl 4 (b ipy) ] cata lyzed hydrogenation of maleic a c i d i n aqueous HC1 s o l u t i o n s . 5 Rate p l o t at 8 0 ° 38 6 Dependence of l i n e a r ra te on [ R u 1 1 ] at 8 0 ° 41 7 Dependence o f l i n e a r ra te on [H_] at 8 0 ° 41 8 Dependence of l i n e a r ra te on [M.A.] at 8 0 ° 42 9 P lo t o f ( r a t e ) - 1 v s . ( M . A . ) - 1 46 10 Arrhenius p l o t 47 A u t o c a t a l y t i c reduct ion of Ru(IV) by H_ i n DMA s o l u t i o n s . 11 Rate p l o t s at 35° 52 12 Absorpt ion spectra of ' R u * ^ ' , Ru^"'", Ru"*"*, and Ru* i n DMA 54 13 Log p l o t s for the a u t o c a t a l y t i c reduct ion of R u ( I V ) . . . . 55 14 Absorpt ion spectra of "RuCl_ .3H 2 0" i n DMA 5 8 15 Arrhenius p l o t 60 - x i v -Figure Page Ruthenium(III) c a t a l y z e d hydrogen r e d u c t i o n of 0^ i n DMA s o l u t i o n s . 16 Rate p l o t s at 50° 6 2 17 Dependence of r a t e on [RuCl .3H-0] 65 18 Dependence of r a t e on [H-] 65 19 Arrhenius p l o t 67 Ruthenium(III) c h l o r i d e c a t a l y z e d hydrogen r e d u c t i o n of Ru(III) i n DMA s o l u t i o n s . 20 Rate p l o t s at 80° 6 9 21 Arrhenius p l o t 7 ^ C a t a l y t i c r e d u c t i o n of Ru(II) by i n DMA s o l u t i o n s . 22 Rate p l o t at 80° 7 9 23 Arrhenius p l o t 8 5 24 E f f e c t of c h l o r i d e on the r a t e at 80° 8 7 Ruthenium(I) c h l o r i d e c a t a l y z e d hydrogenation of o l e f i n i c compounds i n DMA s o l u t i o n s . 25 Rate p l o t s f o r hydrogenation o f M.A. at 80° f o r I Q2 various [Ru ] V J 26 Rate p l o t s f o r hydrogenation o f M.A. at 80° f o r various [H-] 9 ^ 27 Rate p l o t f o r hydrogenation of F.A. at 80° 9 5 28 Dependence of i n i t i a l r a t e of hydrogenation of M.A. on [Ru 1] at 80° 1 0 0 - XV -Figure Page 29 Dependence of i n i t i a l r a t e of hydrogenation of M.A. On [ R u 1 ] 1 7 2 at 80° 100 30 Dependence o f i n i t i a l r a t e o f hydrogenation o f M.A. on [H_] at 80° 101 31 Depdendence of i n i t i a l r a t e of hydrogenation of M.A. on [M.A.] at 80° 103 32 Inverse dependence of i n i t i a l r a t e of hydrogenation of M.A. on [Cl~] at 80° 104 33 Dependence of r a t e of hydrogenation of F.A. on [Ru*] at 80° 107 I 1/2 34 Dependence of r a t e of hydrogenation of F.A. on [Ru ] at 80° 107 35 Dependence of r a t e of hydrogenation of F.A. on [H-] at 80° 109 36 Dependence of r a t e of hydrogenation of F.A. on [F.A.] at 80° 110 37 Inverse dependence of r a t e o f hydrogenation o f F.A. on [ C I - ] at 80° I l l 38 Dependence of i n i t i a l r a t e on [M.A.] and [F.A.] ....... 116 39 P l o t of log k-K^ vs. ( T ) " 1 118 Formation of Ru(III) triphenylphosphine hydride i n DMA s o l u t i o n s . 40 Rate p l o t at 80° 126 - x v i -Figure Page Ruthenium(III) tr iphenylphosphine hydride cata lyzed hydrogenation of maleic a c i d i n DMA s o l u t i o n s . 41 Rate p l o t at 8 0 ° 132 RuHCl(PPh_),j cata lyzed hydrogenation of maleic a c i d i n DMA s o l u t i o n s . 42 Rate p l o t for the product ion of RuHCl(PPh_) 3 i n DMA at 8 0 ° 1 3 7 43 Rate p lo t s for hydrogenation o f M.A. for various [PPh_] at 35° 142 44 Rate p l o t s f o r hydrogenation o f M.A. f or various [Ru**] at 35° 143 45 Rate p l o t s for hydrogenati on of M.A. for various [Ru ] at 35° 144 46 Rate p l o t s for hydrogenation of M.A. f or various [M.A.] at 35° 145 47 Dependence of i n i t i a l ra t e on [PPh^] at 3 5 ° 150 48 Inverse dependence of i n i t i a l ra te on [PPh^] at 3 5 ° . . . 151 49 Dependence of i n i t i a l ra te on [M.A.] at 3 5 ° 153 50 Dependence o f i n i t i a l rate on [M.A.] at 3 5 ° 153 51 Dependence of i n i t i a l rate on [Ru**] at 35° 154 52 Dependence of i n i t i a l ra te on [ R u * * ] a t 35° 154 53 Dependence o f i n i t i a l rate on [Ru**] at 3 5 ° 155 54 Dependence of i n i t i a l ra t e on [H_] at 3 5 ° 157 55 Dependence of i n i t i a l ra te on [M.A.] at 3 5 ° 162 - x v i i -Figure Page 56 Dependence of i n i t i a l ra te oh [Ru**] at 3 5 ° 164 57 Arrhenius p l o t 166 Formation of ruthenium(II) carbonyls i n DMA s o l u t i o n s . 58 Uptake of CO by Ru(II) c h l o r i d e s o l u t i o n at 8 0 ° 173 59 K i n e t i c p l o t for the formation of Ru**(C0) at 8 0 ° 175 60 Arrhenius p l o t for the formation o f Ru**(C0) 179 61 F i r s t - o r d e r p l o t for the formation o f Ru**(C0)- at 8 0 ° . 180 62 Dependence o f k^ for the formation of Ru**(C0) 2 on [CO] at 8 0 ° 183 63 Inverse dependence of k 2 on [Cl~] at 8 0 ° 184 64 Dependence of rate of formation of Ru**(C0) 2 on [CO] at various temperatures 190 65 Arrhenius p l o t for the formation of Ru**(C0) 2 192 Formation o f ruthenium(I) carbonyls i n DMA s o l u t i o n . 66 Uptake of CO by Ru(I) c h l o r i d e s o l u t i o n at 3 0 ° . . . . 195 67 Uptake of CO by Ru(I) c h l o r i d e s o l u t i o n at 8 0 ° 196 68 K i n e t i c p l o t for the formation o f Ru*C0 at 8 0 ° 199 69 F i r s t - o r d e r p lo t for the formation of Ru*(C0)- at 3 0 ° and 8 0 ° 202 70 Arrhenius p l o t for the formation o f Ru (CO) 204 - x v i i i -ABBREVIATIONS The f o l l o w i n g l i s t of a b b r e v i a t i o n s , most o f which are commonly adopted i n chemical research l i t e r a t u r e , w i l l be employed i n t h i s t h e s i s . A l l temperatures are i n °C unless s p e c i f i c a l l y denoted °K. acac acetylacetonate an a c r y l o n i t r i l e aq aquated, water bipy 2 , 2 ' - b i p y r i d y l DMA dimethylacetamide, CH C0N(CH ) DMF dimethylformamide, HC0N(CH 3) 2 DMSO dimethylsulphoxide, (CH_) 2S0 en ethylenediamine, NH CH CH NH E.S.R. e l e c t r o n s p i n resonance Et e t h y l F.A. fumaric a c i d I.R. i n f r a r e d •L l i g a n d M metal atom M.A. maleic a c i d Me methyl N.M.R. nuclear magnetic resonance Ph phenyl PPh 3 triphenylphosphine R a l k y l 2 - x i x -S.A. s u c c i n i c a c i d U.V. u l t r a v i o l e t e molar e x t i n c t i o n c o e f f i c i e n t v frequency, cm * X' c o r r e c t e d molar s u s c e p t i b i l i t y - XX -ACKNOWLEDGMENTS I wish to thank Dr. B.R. James f o r h i s expert guidance and co n t i n u a l encouragement throughout the course o f t h i s work. I would a l s o l i k e to express my g r a t i t u d e to Dr. G.B. P o r t e r f o r h i s help i n preparing t h i s t h e s i s . F i n a n c i a l support from the N a t i o n a l Research Council of Canada i s g r a t e f u l l y acknowledged. CHAPTER I INTRODUCTION 1.1. Aim of Work Since the f i r s t o bservation of homogeneous r e d u c t i o n of q u i n o l i n e s o l u t i o n s of benzoquinone by hydrogen i n the presence of c u p r i c acetate i n 1938*, a v a r i e t y o f other c a t a l y t i c homogeneous hydrogenation systems have been found; a large number of these have been discovered w i t h i n the l a s t seven t o eight years. Several recent reviews have appeared, 2—5 6 p a r t i c u l a r l y those of Halpern and an a r t i c l e by Frankel and Dutton was a l s o a v a i l a b l e to us. Homogeneous hydrogenation was a l s o the 7 subject of a recent Faraday S o c i e t y meeting. The main object of t h i s work was to i n v e s t i g a t e the use of ruthenium complexes i n s o l u t i o n f o r the a c t i v a t i o n of molecular hydrogen. When c a t a l y t i c a c t i v i t y was observed, d e t a i l e d k i n e t i c s of the r e a c t i o n s were i n v e s t i g a t e d and r e a c t i o n mechanisms p o s t u l a t e d . When these studies were commenced i n 1965, r e l a t i v e l y l i t t l e work had been reported on systems i n v o l v i n g ruthenium complexes. Halpern g and h i s group had shown that a c i d s o l u t i o n s c o n t a i n i n g ruthenium(II) c h l o r i d e complexes were a c t i v e c a t a l y s t s f o r the hydrogenation of c e r t a i n s u b s t i t u t e d ethylenes c o n t a i n i n g an a c t i v a t e d double bond, such as maleic, fumaric and a c r y l i c a c i d s . The mechanism p o s t u l a t e d i s shown i n Scheme I. The ruthenium(II) complexes r a p i d l y w i t h the o l e f i n ; - 2 -the rate-determining step i s thought to be r e a c t i o n of hydrogen with t h i s TT-complex to give an intermediate hydride species w i t h the l i b e r a -t i o n of a proton. I C +H — R u I A t i l TT-Comp lex -Ru'-|| / l C + H + , C = = C v ( f a s t ) (2) -Ru<-| -Ru-H - R ' U ^ C ' c^ a-Complex + H H V C - c ' Scheme I N u c l e o p h i l i c a t t a c k by the hydride l i g a n d at a carbon atom leads to hydrometalation o f the o l e f i n i c bond. E l e c t r o p h i l i c a t t a c k by a proton at the carbon attached to the metal l i b e r a t e s the reduced o l e f i n and regenerates the ruthenium c a t a l y s t . Evidence f o r the existence of the unstable hydride intermediate was obtained from some exchange experiments. In these systems the ruthenium i s thought to be 2- 9 present as the an i o n i c [RuCl^] species. Chatt and Hayter had i s o l a t e d s t a b l e hydrides of the type trans-RuHX (diphosphine)^ (X=C1, Br or I) by r e a c t i o n of cis-RuX 2(diphosphine) w i t h l i t h i u m aluminum hydride, although these c i s compounds were too unr e a c t i v e to react d i r e c t l y w i t h hydrogen. I t seemed that complexes o f the type RuC^-2-( b i p y r i d y l ) 2 or [ R u C l ^ ( b i p y r i d y l ) ] which had been prepared by Dwyer 10 2-et a l . might have p r o p e r t i e s intermediate between those o f [RuCl.] - 3 -and RuX.(diphosphine)- as regards to r e a c t i v i t y toward hydrogen. Chapter I I I describes some studies using b i p y r i d y l complexes although t h i s area was not very f r u i t f u l . Using scheme I , Halpern and coworkers suggested that hydro-genation proceeds when step (2) s u c c e s s f u l l y competes w i t h the r e v e r s a l of step ( 1 ) , and t h i s i s expected when an electron-withdrawing s u b s t i t u e n t increases the r a t e of hydrogenation by favouring nucleo-p h i l i c a t t a c k of the hydride l i g a n d on the double bond. This suggested that l e s s r e a c t i v e o l e f i n s (such as ethylene) could be hydrogenated i f the r a t e of competing back r e a c t i o n of (2) could be lowered, e.g., by reducing the a c i d i t y of the medium. This i s not p o s s i b l e i n aqueous s o l u t i o n because of the i n s t a b i l i t y of ruthenium(II) i n t h i s medium at low a c i d i t i e s , * ' ' " but, encouraged by some r e s u l t s i n t h i s l a b o r a t o r y t h a t 12 13 showed c a t a l y t i c a c t i v i t y of some rhodium and i r i d i u m complexes was very much enhanced i n c o o r d i n a t i n g solvents such as dimethylacetamide (DMA), we examined the a c t i v i t y of ruthenium c h l o r i d e complexes i n t h i s medium (ChaptersIV-VIII), and the s t u d i e s and r e s u l t s obtained i n t h i s solvent system c o n s t i t u t e the bulk of t h i s t h e s i s . Carbonyl complexes, p a r t i c u l a r l y of the platinum group metals, are of considerable i n t e r e s t as p o t e n t i a l c a t a l y s t s f o r a whole range 14 15 of organic s y n t h e t i c r e a c t i o n s , ' i n c l u d i n g hydrogenation and c a r b o n y l a t i o n , and a s e c t i o n of t h i s t h e s i s (Chapter V I I I ) i s concerned with the formation and p r o p e r t i e s of some ruthenium carbonyl complexes. During the l a s t few years a remarkable amount has been published g e n e r a l l y on ruthenium chemistry and i n p a r t i c u l a r on the - 4 -c a t a l y t i c aspects of ruthenium complexes i n s o l u t i o n . A f t e r a b r i e f review on the mechanisms of hydrogen a c t i v a t i o n , some of the more p e r t i n e n t data w i t h regards to t h i s t h e s i s w i l l be presented. 1.2. A c t i v a t i o n of Molecular Hydrogen and Homogeneous C a t a l y t i c Hydrogenation 1.2.1. Mechanisms of Hydrogen A c t i v a t i o n The a b i l i t y to c a t a l y z e c e r t a i n r e a c t i o n s o f molecular hydrogen homogeneously has been demonstrated f o r many t r a n s i t i o n metal ions and 2 5 16 17 complexes ' ' . In each case i t appears that H^ i s s p l i t by the c a t a l y s t w i t h the formation of a r e a c t i v e t r a n s i t i o n metal hydride complex as an intermediate (which may or may not be detected). The mechanism of formation of the hydride i n t e r m e d i a t e s , as w e l l as t h e i r s t a b i l i t y and l a b i l i t y , enters i n t o a c o n s i d e r a t i o n o f the r e a c t i v i t y of metal complexes toward hydrogen. Three d i s t i n c t mechanisms by which 2-5 t h i s can occur have been recognized. (A) H e t e r o l y t i c S p l i t t i n g of Hydrogen r 12 18-20 This i s i l l u s t r a t e d by the f o l l o w i n g examples, ' R h H I + H- R h n i H - + H + (1,1) C u 1 1 + H ;_—_ C u H H " + H + (1,2) ( l i g a n d species such as CI , H_0 have been omitted) These may be regarded as s u b s t i t u t i o n a l processes, (e.g., replacement of a c h l o r i d e l i g a n d by a hydride i o n ) , i n which there i s no change i n the o x i d a t i o n s t a t e of the metal i o n . R e a c t i v i t y i s thus governed by the s u b s t i t u t i o n l a b i l i t y of the complex, by the s t a b i l i t y of the hydride formed, and by the presence of a s u i t a b l e base to s t a b i l i z e the r e l e a s e d proton. (B) Homolytic S p l i t t i n g of Hydrogen An example of t h i s i s the r e v e r s i b l e uptake of H 2 by aqueous s o l u t i o n s of [ C o i : E ( C N ) 5 ] 3 ~ , 2 1 2 [ C o H ( C N ) 5 ] 3 " + H 2 --—_• 2 [ H C o I n ( C N ) _ ] 3 " (1,3) The hydride formation i s accompanied by formal o x i d a t i o n of the metal, and r e a c t i v i t y i s c l o s e l y l i n k e d to the s u s c e p t i b i l i t y of the l a t t e r to o x i d a t i o n , and the a b i l i t y to expand i t s c o o r d i n a t i o n s h e l l . (C) A d d i t i o n of Hydrogen to form a Dihydride 8 C o o r d i n a t i v e l y unsaturated d complexes, such as t r a n s -22 c h l o r o c a r b o n y l b i s ( t r i p h e n y l p h o s p h i n e ) i r i d i u m ( I ) , add the hydrogen molecule r e v e r s i b l y i n an o x i d a t i v e - a d d i t i o n r e a c t i o n , i n which both the c o o r d i n a t i o n number and o x i d a t i o n number increase by two. I r ^ l f C O ) ( P P h 3 ) 2 + H 2 —*• I r I H C l ( C 0 ) ( P P h 3 ) 2 H 2 (1,4) g For square planar d complexes the expected order of the tendency towards o x i d a t i o n , and hence of r e a c t i v i t y towards H 2, i s , 5 23 (subject to m o d i f i c a t i o n by l i g a n d v a r i a t i o n ) , ' 0s° >Ru° >Fe°, I r 1 > Rh 1 > C o I , P t H > P d ^ N i 1 1 , A u 1 1 1 - 6 -1.2.2. Homogeneous C a t a l y t i c Hydrogenation The r e a c t i v e nature of the hydride complexes formed by the above mechanisms permits them to f u n c t i o n as intermediates i n homogeneous c a t a l y t i c hydrogenation r e a c t i o n s . (A) Inorganic Substrates 18 One example i s provided by the work of Harrod and Halpern who showed that rhodium(III) i n 3M h y d r o c h l o r i c a c i d c a t a l y z e s homo-geneously the r e d u c t i o n of i r o n ( I I I ) . The rate-determining h e t e r o l y t i c s p l i t t i n g of H^ i s followed by a f a s t step i n v o l v i n g r e d u c t i o n of the s u b s t r a t e by the hydride. R h 1 1 1 + H n R h m H " + H + (1,5) k - l R h n V " ' + 2 F e I H J g ^ R h I H + 2 F e n + H + (1,6) Evidence f o r the hydrogen a c t i v a t i o n step has been obtained f o r the 24 25 corresponding ruthenium(III) system ' by i s o t o p i c exchange e x p e r i -ments using deuterium gas. The d e t a i l e d nature of the f a s t step i s , 12 26 of course, not known. Rhodium(III) hydride species are w e l l known ' to sometimes transform to rhodium(I) plus a proton, R h m H ~ —*• Rh 1 + H + (1,7) and the r e d u c t i o n of the f e r r i c species could i n v o l v e rhodium(I) species. In the copper(I) acetate c a t a l y z e d r e d u c t i o n of c o p p e r ( I I ) , 27 i n q u i n o l i n e s o l u t i o n , i s thought to be s p l i t h o m o l y t i c a l l y i n the rate-determining step, s i n c e the r a t e of uptake i s p r o p o r t i o n a l to the H- c o n c e n t r a t i o n and the square of the cuprous c o n c e n t r a t i o n : I k l I I -2Cu + H- — i - * - 2Cu H (1,8) 2 -f k - l C u 1 1 ^ + C u 1 1 * > 2CU 1 + H + (1,9) Complexes of c o p p e r ( I I ) , s i l v e r ( I ) , m e r c u r y ( I I ) , p a l l a d i u m ( I I ) , r u t h e n i u m ( I I I ) , c o b a l t ( I I ) have a l s o been found to be a c t i v e c a t a l y s t s f o r the hydrogen r e d u c t i o n of i n o r g a n i c oxidants e.g., i r o n ( I I I ) or 2 chromium(VI) v i a such h e t e r o l y t i c or homolytic processes. (B) Organic Substrates The homogeneous c a t a l y t i c hydrogenation of organic substrates such as o l e f i n s has a t t r a c t e d enormous a t t e n t i o n i n recent years. I t i s w e l l e s t a b l i s h e d that there are three mechanisms whereby a metal atom i n a complex can a c t i v a t e molecular hydrogen (Section 1.2.1.), and a l l three have been p o s t u l a t e d f o r c a t a l y t i c hydrogenation of o l e f i n i c 2 5 16 17 substances ' ' . I t i s convenient t o consider an example of each of these i n t u r n . g The system p r e v i o u s l y discussed i n S e c t i o n 1.1. (Scheme I) i s the best documented example of one i n v o l v i n g h e t e r o l y t i c s p l i t t i n g of the hydrogen molecule by a metal complex, i n t h i s case an o l e f i n iT-complex of c h l o r o r u t h e n a t e ( I I ) . Hydrogenation of an o l e f i n by a mechanism i n v o l v i n g the homolytic s p l i t t i n g o f hydrogen i s i l l u s t r a t e d by the pentacyanocobalt-- 8 -a t e ( I I ) c a t a l y z e d hydrogenation o£ butadiene i n aqueous s o l u t i o n . 28 D e t a i l e d s t u d i e s suggest that t h i s r e a c t i o n proceeds by the f o l l o w i n g mechanism (Scheme I I ) : 2 [ C o H ( C N ) 5 ] 3 " + H 2 2 [ H C o m ( C N ) 5 ] 3 " [ H C o I ] : i ( C N ) 5 ] 3 ~ + CH2=CH-CH=CH2 >- [(NC) 5Co-CH 2-CH=CH-CH_] 3" [HCo(CN) ] 3 " [(NC)_Co-CH -CH=CH-CH_] f. _ *- CH_CH0CH=CH-L 5 - 2 3 J (1,2-addition) 3 2 2 a-complex -CN + 3-+CN 2[Co(CN)_] Ch [HCo(CN) ] 3 " (NC) .Co < ;CH r-r——-^r. ^ CH_CH=CHCH_ J4 •/ (1,4 a d d i t i o n ) 3 3 CH N C H 3 r r - a l l y l C O m P l e X 2[Co(CN) 5] 3-Scheme I I The cyanide dependence e q u i l i b r i u m between the a and ir intermediates accounts f o r the observation that hydrogenation at high [CN ] y i e l d s mainly 1-butene and at low [CN ] , mainly trans 2-butene. I t should be noted t h a t f r e e r a d i c a l mechanisms have been p o s t u l a t e d f o r c e r t a i n pentacyanocobalt(II) c a t a l y z e d hydrogenations f o l l o w i n g the i n i t i a l homo l y t i c s p l i t t i n g of U^. On the ba s i s of k i n e t i c observations 29 Simandi and Nagy proposed the f o l l o w i n g mechanisms f o r the hydrogena-t i o n of cinnamic a c i d : (S=C6H5CH, =CHCO- ; HS=C6H_CH2CHCO- ; H_S=_6H CH^K^CC^ ) J6 5 2 2 ' 2 6 5 2 2[Co(CN)_] 3 + H 2 — ^ 2[HCo(CN)_] 3" (1,10) [HCo(CN)_] 5" + S [Co(CN)_] 3" + HS (1,11) [HCo(CN)_] 3~ + HS y- [Co(CN)_] 3" + H_S (1,12) The hydrogenation of ethylene and other o l e f i n s c a t a l y z e d homogeneously by t r i s ( t r i p h e n y l p h o s p h i n e ) c h l o r o r h o d i u m ( I ) i n benzene 30 31" s o l u t i o n was discovered by Wilkinson and coworkers ' , and i n v o l v e s the formation of an intermediate c i s - d i h y d r i d e f o r the hydrogen a c t i v a t i o n (Scheme I I I ) . RhCl(PPh-)- S O l v e n t > RhCl(PPh_) 2(S) + PPh_ PPh. K , RhCl(PPh_) 2(S) + H 2 - -_ H 2RhCl(PPh-) 2(S) K2 o l e f i n o l e f i n RhCl(PPh_) 2 ( o l e f i n ) —-f *• RhCl (PPh_) 2 (S) + p a r a f f i n Scheme I I I The system i n v o l v e s the d i s s o c i a t i o n of the complex i n s o l u t i o n to give a s o l v a t e d s p e c i e s , RhCl(PPh_) 2(S) (where S = s o l v e n t ) , which has a s i t e f o r c o o r d i n a t i o n of the o l e f i n by displacement of so l v e n t . The benzene s o l u t i o n of RhCl(PPh_)_ i t s e l f takes up molecular hydrogen - 10 -and the hydride r a p i d l y reduces any o l e f i n present. These workers concluded that p a r a f f i n production occurs s o l e l y by the k^ path, the uncomplexed o l e f i n a t t a c k i n g the d i h y d r i d e at the vacant s i t e to g i v e a t r a n s i t i o n s t a t e i n which both hydrogen and o l e f i n are bound to metal. 13 A very s i m i l a r r e a c t i o n scheme has been proposed by James and Memon f o r the hydrogenation o f o l e f i n s using IrCOCl(PPh_)^ although these workers concluded that the path was the more l i k e l y hydrogenation 32 process. Some recent work by Candlin and Oldham i n d i c a t e s that hydrogenation by the RhdfPPh^)- c a t a l y s t can occur by both routes. The mechanism o f c a t a l y t i c hydrogenation of unsaturated sub-s t r a t e s g e n e r a l l y can conveniently be regarded as one i n v o l v i n g three steps: (1) hydrogen a c t i v a t i o n , (2) substrate a c t i v a t i o n , (3) hydrogen t r a n s f e r . Whether (1) and (2) occur at the same time, or only one of them needs to be a c t i v a t e d has been a subject of i n t e r e s t f o r some 2 time although the more recent d e t a i l e d s t u d i e s i n d i c a t e that a c t i v a t i o n o f both are r e q u i r e d . The t r a n s f e r of hydrogen i n the monohydride systems e.g., Scheme I and I I , (or the hydrometalation step) i s an example of a much wider c l a s s of i n s e r t i o n type r e a c t i o n s whose general widespread r o l e i n c a t a l y t i c r e a c t i o n s has been discussed i n d e t a i l 2-5 33 elsewhere. ' The process of hydrogen t r a n s f e r i n the c i s d i h y d r i d e 30 systems remains somewhat u n c e r t a i n ; t h i s was o r i g i n a l l y suggested to i n v o l v e simultaneous t r a n s f e r of both hydrogens,each by a three center t r a n s i t i o n s t a t e : - 11 -+ HC - CH More recent data however suggests that the hydrogens are t r a n s f e r r e d c o n s e c u t i v e l y , a a - a l k y l hydride intermediate being i n v o l v e d . 1.3. L i t e r a t u r e Reports on the C a t a l y t i c P r o p e r t i e s of Ruthenium Complexes Compared with rhodium, palladium and platinum, the chemistry of ruthenium complexes has been r e l a t i v e l y l i t t l e s t u d i e d . A number of ruthenium complexes have been reported t o be a c t i v e f o r a v a r i e t y of c a t a l y t i c r e a c t i o n s but the k i n e t i c s have not i n general been st u d i e d i n any d e t a i l . P o s s i b l e mechanisms i n v o l v i n g i n s e r t i o n r e a c t i o n s , 2-5 common i n c a t a l y t i c systems, have u s u a l l y been presented. 1.3.1. Homogeneous Hydrogenation Ruthenium(III) c h l o r i d e complexes were known to a c t i v a t e 24 25 molecular hydrogen v i a a h e t e r o l y t i c s p l i t t i n g ' of the hydrogen molecule, and c a t a l y z e the r e d u c t i o n of i r o n ( I I I ) and ruthenium(IV) under homogeneous c o n d i t i o n s i n aqueous h y d r o c h l o r i c a c i d s o l u t i o n s . Other st u d i e s i n v o l v i n g aqueous s o l u t i o n i n c l u d e that already considered - 12 (Scheme I ) , on the hydrogenation of o l e f i n s i n a c i d s o l u t i o n cata lyzed 8 by ruthenium(II) ch lor ide complexes , and the a c t i v a t i o n of by [ R u ( C O ) ( H 2 0 ) C 1 4 ] 2 _ for the reduct ion of [ R u ( C O ) C l _ ] 2 ~ . 3 7 1-Octene i n n-heptane s o l u t i o n i s homogeneously hydrogenated using a ca ta ly s t mixture of ruthenium(III) acetylacetonate and t r i i s o -38 b u t y l aluminum; t h i s i s an example of a so luble Z e i g l e r - t y p e c a t a l y s t , the reac t ion presumably i n v o l v i n g i n i t i a l formation of a ruthenium a l k y l intermediate . There i s a report that so lut ions of ruthenium t r i c h l o r i d e 39 i n dimethylformamide homogeneously hydrogenate d icyc lopentadiene . More we l l defined systems i n non-aqueous media are those i n v o l v i n g the d ich lorot ' r i s (triphenylphosphine) ruthenium (I I) complex, as reported 40-43 r e c e n t l y by Wilkinson and h i s group; t h i s i s an e f f e c t i v e c a t a l y s t for the homogeneous hydrogenation of a v a r i e t y o f unsaturated substances. The ruthenium(II) complex forms an intermediate hydride i n benzene-ethanol s o l u t i o n , RuCl 2 (PPh_)_ +.H + base *• RuHCT(PPh_)_ + base HC1 (1,13) the re leased proton being s t a b i l i z e d by the base, e thanol . The hydrido-ch lorotr i s ( tr iphenylphosphine)ruthenium(II ) has been i s o l a t e d and c h a r a c t e r i z e d , ^ 2 a n d i s the most ac t ive c a t a l y s t yet discovered for the homogeneous hydrogenation of a l k - l - e n e s i n benzene or toluene s o l u t i o n . Deta i l ed k i n e t i c studies were not reported due to s o l u b i l i t y problems and the extreme s e n s i t i v i t y of the ca ta ly s t to oxygen. However, d i s s o c i a t i o n of the c a t a l y s t to give RuHCl(PPh_) 2 fol lowed by - 13 -attack of o l e f i n to give an a l k y l intermediate was suggested. The 42 l a t e s t paper very r e c e n t l y reported on t h i s system was of extreme i n t e r e s t to us s i n c e our s t u d i e s had l e d us to the "same" c a t a l y t i c system i n DMA s o l u t i o n , where we had experienced no d i f f i c u l t i e s i n studying the k i n e t i c s (Chapter V I I ) . 1.3.2. P o l y m e r i z a t i o n of O l e f i n s and Acetylenes Ruthenium t r i c h l o r i d e has been found to c a t a l y z e the polymer-45 i z a t i o n of a c e t y l e n i c compounds, e.g., heptyne-1, phenylacetylene, i n a c e t o n i t r i l e , ethanol or water, i n the presence of a h y d r i d i c reducing agent (such as l i t h i u m borohydrides, l i t h i u m aluminum hydride or diborane). Nonhydridic reducing agents (sodium t h i o s u l p h a t e , hydra-zine) were i n e f f e c t i v e as a c o c a t a l y s t . I t was suggested that the c a t a l y t i c a c t i v e species i s a lower v a l e n t ruthenium hydride species which forms complexes with acetylene. In these complexes, the metal atom may act as a hydride t r a n s f e r agent, p e r m i t t i n g t r a n s f e r of hydrogen from one a c e t y l e n i c substrate molecule to another, two or more of which being complexed with the metal atom. Ruthenium(III) c h l o r i d e i n ethanol under high pressure of _2 hydrogen (200-600 l b . i n . ) c a t a l y z e s the end-to-end d i m e r i z a t i o n of 46 a c r y l o n i t r i l e . The r e a c t i o n d i d not proceed 'in the absence of hydrogen. An intermediate complex i n which a hydride i o n and two moles of a c r y l o n i t r i l e are coordinated to ruthenium was proposed. 47 B i l l i g et a l . reported the e f f e c t on the same r e a c t i o n of adding SnCl- (or Et^NSnCl-) together w i t h b i f u n c t i o n a l amines such as N-methylmorpholine and/or b i f u n c t i o n a l a l c o h o l s such as M e t h y l c e l l o s o l v e . - 14 -The net r e s u l t of i n c l u s i o n of these ligands i s a lowering of minimum hydrogen pressure requirement. The mechanism proposed f o r the low-pressure r e a c t i o n i n v o l v e s a ruthenium(IV) hydride species: CN CN „ _.. TT „, . H CN H H Ru*J H (I) ( I I ) " ( H I ) ( I I I ) + CH_ = CH-CN y NC.CH-.CH2-RuIV-CH=CH.CN (1,15) (IV) (IV) + CH2=CHCN *• (I) + NC.CH=CH-CH-.CH2.CN • (1,16) Other ruthenium complexes, such as R u ^ C l (C H ), R u n i ( a c a c ) _ , R u H C l 2 ( P P h 3 ) 4 , R u n c i 2 ( P P h 3 ) 2 a n 2 , R u 1 1 (acac) (PPh 3) , were a l s o reported to be a c t i v e c a t a l y s t s f o r the d i m e r i z a t i o n of 48 a c r y l o n i t r i l e i n ethanol. Triphenylphosphine complexes of R u d j i n p o l a r s o l v e n t s , 49 p a r t i c u l a r l y i n water, c a t a l y z e the p o l y m e r i z a t i o n of butadiene. C i s -and trans-1,4-polybutadiene and cis- 1 , 2 polybutadiene have been obtained by using a 6:1 r a t i o o f PPh 3 to RuCl- at 25°C. Ruthenium c h l o r i d e a l s o c a t a l y z e s the d i m e r i z a t i o n of ethylene to butene, butadiene to 2,4,6-octatriene, CH3CH=CH-CH=CH-CH=CHCH3, and methyl a c r y l a t e , CH-=CHC00CH__ to dimethyl 2-hexenedioate, CH OOCCH=CHCH CH.COOCH , i n ethanol or methanol and at temperatures 50-210°C.3^ An i n t e r e s t i n g feature o f these r e a c t i o n s i s that e x c l u s i v e l y s t r a i g h t - c h a i n dimers were obtained. Ruthenium complexes, such as RuCl 3.nH 20, RuCl 3/PPh 3 or R u C l 2 ( P P h 3 ) 3 systems i n ethanol have a l s o been reported to c a t a l y z e - 15 -p o l y m e r i z a t i o n of a l i e n e d * The mechanism of the r e a c t i o n was not discussed. S o l u t i o n s o f c h l o r o r u t h e n a t e ( I I ) i n h y d r o c h l o r i c a c i d have been shown to form a 1:1 ir-complex with ethylene according to the 52 f o l l o w i n g scheme, although there was no subsequent rearrangement or c a t a l y t i c p o l y m e r i z a t i o n i n the system: k R u n c i —-L R u n C l . + C l " (1.17) n n-1 k - l k R u I I C l n _ 1 + C 2H 4 — R u I I ( C 2 H 4 ) C l n _ 1 (1,18) Ruthenium complexes g e n e r a l l y appear to be much l e s s e f f i c i e n t than the more f a m i l i a r n i c k e l compounds i n such p o l y m e r i z a t i o n r e a c t i o n s . 1.3.3. A r y l a t i o n and A l k y l a t i o n of O l e f i n s Group V I I I metals (Pd, Rh and Ru) a l k y l s and a r y l s have been 53 prepared by r e a c t i o n s of the metal h a l i d e s w i t h Grignard reagents. The a l k y l or a r y l group V I I I metal s a l t s i n p o l a r s o l v e n t s such as methanol, a c e t o n i t r i l e or a c e t i c a c i d are unstable and, i n the presence of an o l e f i n , add to the o l e f i n forming a l k y l e t h y l or a r y l e t h y l - m e t a l s a l t s which then r a p i d l y decompose i n t o metal hydride and a l k y l a t e d or a r y l a t e d o l e f i n . For example, R u i n c i 3 + PhHgCl -—>- P h R u m C l 2 + H g C l 2 (1,19) - 16 -H H H H I I I \ / 1 1 PhRu C l . + C=C — * . Ph-C-C-RuCl- (1,20) 2 / \ I I 2 H COCH H COCH 0 0 6 (I) Ph H \ / (I) v C=C + [HRuCl 2] (1,21) H COCH 0 5 The r e a c t i o n thus provides an extremely convenient method f o r the synthesis o f a wide v a r i e t y of o l e f i n i c compounds. The r e a c t i o n may be made c a t a l y t i c w i t h respect to the metal s a l t s by using c u p r i c c h l o r i d e , a i r and hydrogen c h l o r i d e as reo x i d a n t s . 1.3.4. Oxi d a t i o n of O l e f i n s I I I 2-[Ru Clj-fH^O)] i n the presence of c i t r i c a c i d and c u p r i c c h l o r i d e c a t a l y t i c a l l y o x i d i z e s an ethylene/oxygen mixture to aceta l d e -54 hyde i n a c i d aqueous s o l u t i o n s . On comparison with the mechanism po s t u l a t e d f o r the Pd(II) o x i d a t i o n of C,,H4,^ the mechanism i s thought to i n v o l v e a r a p i d r e v e r s i b l e C,JH4 uptake followed by a slow o x i d a t i v e h y d r o l y s i s step: R u H I C l n + C 2H 4 ^ [ R u I I I ( C 2 H 4 ) C l n _ 1 ] + + C l " (1.22) [ R u n i ( C H ) C l ] + + HO y R u ^ l „ + CH CHO + HC1 + H + L V 2 4 J n - l J 2 n-2 3 (1.23) The r e a c t i o n becomes c a t a l y t i c i n the presence of c u p r i c s a l t s and oxygen due to the r e a c t i o n s - 17 -R u I C l n _ - + 2CuCl_ • R u n i C l n + 2 C u C l 2 " (1,24) 2CuCl 2 " + l / 2 0 2 + 2HC1 • 2CuCl_~ + H 2 0 (1.25) The c u p r i c ox id izes Ru* back to Ru*** and the r e s u l t i n g cuprous s tate i s r e o x i d i z e d by the oxygen present . Ruthenium(III) c h l o r i d e complexes themselves appear i n a c t i v e and a c i t r a t e complex must be invo lved . Although the above equations give a s a t i s f a c t o r y account o f the c a t a l y t i c o x i d a t i o n , the k i n e t i c dependence on C u + + suggests that a ternary complex i n v o l v i n g Ru*** , Cu** and c i t r a t e might be invo lved . 1 .3 .5 . Hydrat ion of Acetylenes 37 56 Halpern , James and Kemp ' found that ruthenium(III) c h l o r i d e , i n aqueous a c i d s o l u t i o n , i s an e f f e c t i v e c a t a l y s t for the hydrat ion of ace ty l en i c compounds. An intermediate ir-complex, which rearranges to add the metal ion and hydroxide across the unsaturated bond ( i n s e r t i o n r e a c t i o n ) , i s thought to be formed i n the rate-determining step, Ru OH I , k i I \ / — Ru —OH- + HC=CH ——y — R u - O H _ • C=C (1.26) ' \ 2 T H C 5 C H H H (I) + H + ' H + 1/ (I) -^-> - R u - + CH CHO (1.27) An important conc lus ion of t h i s study was that the hydrat ion r e a c t i o n involved a l i gand water molecule. 2-[RuCl_(H_0)] was the most ac t ive chlorocomplex for the 2- : hydrat ion o f acetylenes; [Ru(CO) (I^OJCl^] was less ac t ive and [Ru(CO) 2 C1 4 ] ' II was completely i n a c t i v e . Ru c h l o r i d e complexes were very i n e f f i c i e n t 57 due to the r a p i d formation of carbonyl complexes under these condit ions (see Sect ion 1 . 3 . 7 . ) . Work i n t h i s laboratory has r e c e n t l y shown that f luoroethylenes are c a t a l y t i c a l l y hydrated by chlororuthenate(II ) complexes i n a c i d 58 aqueous so lut ions to aldehydes and a c i d s . 1.3.6. Hydroformylation Reactions Information on the use o f ruthenium ca ta ly s t s for the hydro-formylat ion r e a c t i o n H N y c a t a l v s t v 1 1 C=C + CO + H.O y > CH-C-C=0 (1,28) ' ^ 2 • | i s very l i m i t e d and suggests that they are not very e f f i c i e n t . The complex R u C l 2 ( P P h _ ) 4 , however has been found to give low y i e l d s o f 40 59 aldehyde from hept - l - ene . * The most e f f e c t i v e ruthenium complex i s Ru(C0) 3(PPh.j) 2 ^ which gives more than 80% y i e l d s of hexaldehyde from pent - l - ene at 100°C and 100 atmosphere t o t a l p r e s s u r e ^ * ^ (C0:H 2 = 1:1). 1 .3.7. Carbonylat ion and Decarbonylat ion Reactions A number of plat inum metal ha l ides have'been shown to decarbonylate a v a r i e t y of organic compounds i n c l u d i n g a l c o h o l s , aldehydes, et h e r s , ketones and a c y l h a l i d e s w i t h the r e s u l t i n g formation I 31 61 63 of metal carbonyl complexes. Carbonyl complexes of Rh , ' - I I 63-70 I I I 67 - I I 63,67,68 _ 111,67 , T I 65 . Ru , Ru Os , Os , and I r have been so prepared. These r e a c t i o n s o f f e r p o t e n t i a l c a t a l y t i c processes and i n some cases these have been s u b s t a n t i a t e d ; f o r example, RhCl(PPh_)_ c a t a l y t i c a l l y converts a r o y l c h l o r i d e s , bromides and cyanides to the 71 72 corresponding a r y l h a l i d e s and n i t r i l e s . ' 69 Halpern and Kemp reported a d e t a i l e d k i n e t i c study of the decarbonylation of formic a c i d by c h l o r o r u t h e n a t e ( I I ) complexes i n aqueous a c i d s o l u t i o n s . The proposed mechanism inv o l v e d an i n i t i a l d i s s o c i a t i o n of a c h l o r o r u t h e n a t e ( I I ) complex: R u H C l »- R u H C l . + CI (1,29) n -f n-1 R u H C l . + HCOOH 1- R u H C l . (CO) + H„0 (1,30) n-1 n-1^ J 2 K ' ' 73 Related to t h i s i s the work o f Coffey who reported t h a t s e v e r a l platinum metal complexes, i n c l u d i n g RuHBr (CO) (PR_) and 9 RuHCl(diphos)-, c a t a l y z e the decomposition of formic a c i d to H- and CO-. D i r e c t c a r b o n y l a t i o n of s o l u t i o n s c o n t a i n i n g platinum metal complexes using carbon monoxide under m i l d c o n d i t i o n s a f f o r d s convenient s y n t h e t i c routes f o r the p r e p a r a t i o n of a wide range of carbonyl 1 37,41,66,74-77 T , . U 1 . ., _ . . T T T . complexes. In aqueous h y d r o c h l o r i c a c i d , ruthenium(III) c h l o r i d e absorbs one mole of CO per mole o f ruthenium at 65-80°C and 37 2-1 atmosphere pressure, and the complex [Ru(C0)Cl_] was i s o l a t e d as the ammonium s a l t . Ruthenium(II) c h l o r i d e takes up two moles o f CO i n - 20 -two steps to give Ru^fCO) and Ru I*(CO)- r e s p e c t i v e l y , and the complexes [Ru(CO)(H 20)C1 4] 2~, [ R u ( C 0 ) 2 C l 4 ] 2 " and R u ( C 0 ) 2 C l 2 were i s o l a t e d . In a l c o h o l i c s o l u t i o n , ruthenium(III) c h l o r i d e absorbs carbon monoxide to give a blood-red c a r b o n y l - c o n t a i n i n g s o l u t i o n ^ from which a number of phosphine ( a r s i n e ) - c a r b o n y l and diene-carbonyl r u t h e n i u m ^ complexes have been prepared. The c a t a l y t i c a c t i v i t y of ruthenium carbonyl complexes has 2- 2-i n general been l i t t l e s t u d i e d . [Ru(CO)(H 20)C1 4] and [ R u ( C O ) 2 _ l 4 ] have been s t u d i e d f o r c a t a l y t i c hydrogenation and h y d r a t i o n i n aqueous 37 s o l u t i o n s and i t was concluded that i n t r o d u c t i o n of carbonyl ligands i n t o the c h l o r o r u t h e n a t e ( I I ) complexes markedly decreased c a t a l y t i c a c t i v i t y . C a t a l y t i c c a r b o n y l a t i o n r e a c t i o n s , which have been e x t e n s i v e l y 78 s t u d i e d f o r some palladium systems, seem r a r e i n ruthenium chemistry although such^a process must be i n v o l v e d i n the hydroformylation r e a c t i o n s 76 79 mentioned p r e v i o u s l y (Section 1.3.6.), and r e c e n t l y [Ru(C0) 4__ ' has been shown to c a t a l y z e the c a r b o n y l a t i o n of acetylene to hydroquinone 80 i n anhydrous c o n d i t i o n s or i n t e t r a h y d r o f u r a n , or dioxan media. 1.3.8. Hydrogen M i g r a t i o n and Isomerization Reactions Complexes of many t r a n s i t i o n metals, p a r t i c u l a r l y group V I I I metals, have been found to c a t a l y z e the m i g r a t i o n of a hydrogen atom 81 or hydride i o n . A common featu r e of a l l these c a t a l y s t s i s the need f o r a c o c a t a l y s t . This i s u s u a l l y e t h a n o l , but secondary and t e r t i a r y a l c o h o l s , e t h e r s , ketones and c a r b o x y l i c a c i d s can be used. Hydrogen can a l s o f u n c t i o n as a c o c a t a l y s t . Both i n t e r m o l e c u l a r and i n t r a m o l e c u l a r hydrogen m i g r a t i o n r e a c t i o n s c a t a l y z e d by c h l o r o r u t h e n a t e ( I I ) complexes 8 2 have been observed with a l l y l a l c o h o l s , 2CH =CHCH OH y CH =CHCH_ + CH2=CHCHO + H 20 (1,31) CH =CHCH OH > CH CH CHO (1,32) The r e a c t i o n l i k e l y proceeds through an intermediate Tr-complex. A good example o f a system i n v o l v i n g hydride t r a n s f e r was that 83 reported by Chatt and Davidson on the tautomeric e q u i l i b r i u m i n v o l v i n g the complex trans-RufMe-PC^CH-PN^^, Me (1,33) In some decarbonylation r e a c t i o n s (Section 1.3.7.) a hydride 64 group i s sometimes coordinated i n the product metal complex, e.g., RuCl- •+ PPh 3 + a l c o h o l s >• RuHCl (CO) (PPh_) (1,34) In these a l c o h o l systems, the hydride group i s b e l i e v e d to come from 66 an a l k o x i d e group. 84 Wells and coworkers have r e c e n t l y reported that RuHCl(PPh_)_ i n benzene s o l u t i o n c a t a l y z e s the i s o m e r i z a t i o n of pent-l-ene; the . mechanism i s thought to i n v o l v e a l k y l i ntermediates, and such a scheme 85 has been f r e q u e n t l y p o s t u l a t e d f o r such i s o m e r i z a t i o n : CH =CH-CH. * CH_-CH-CH 0— *- CH„CH=CH— f. 2| 2 -« 3 j 2 -< 3 j (1,35) H-M M M-H 1.3.9. Ruthenium Complexes Containing Molecular Nitrogen and Oxygen Recently, complexes of molecular n i t r o g e n w i t h compounds of 23 8 6 8 7 I I the group V I I I metals have been obtained. ' ' [Ru (NH_)_N-]X-was f i r s t prepared by the r e a c t i o n of RuCl_ w i t h hydrazine hydrate i n 88 I I 2+ water. Reaction of gaseous n i t r o g e n w i t h [Ru (NH_)j.OH-] r e s u l t s i n the production of [Ru 1 1(NH_)N ] 2 + and the dimeric [(NH_)_RuN-Ru(NHj^f+ 90 Very r e c e n t l y , ruthenium(II) d i n i t r o g e n complexes [Ru(NH_)^(N-) ]Br_ T 91 and [Ru(en)2(N-)2J(Ph 4B)^ have been reported. I t i s assumed, by analogy w i t h the metal carbonyls, t h a t there i s extensive double bonding between the metal and the l i g a n d . This can be considered as a a-bond, formed by donation of the lone p a i r of e l e c t r o n s on one of the n i t r o g e n atoms to a vacant metal o r b i t a l , together w i t h a IT-bond formed by donation o f e l e c t r o n s i n the p r e v i o u s l y nonbonding d (or hydrid) o r b i t a l s on the metal to an antibonding i T - o r b i t a l on the n i t r o g e n molecule. The quest f o r a substance which w i l l c a t a l y z e the r e d u c t i o n of molecular n i t r o g e n under moderate c o n d i t i o n s has long challenged chemists. The discovery of the t r a n s i t i o n metal n i t r o g e n complexes has - 23 -put them one step forward i n understanding b i o l o g i c a l n i t r o g e n - f i x a t i o n . The development of n i t r o g e n - f i x a t i o n c a t a l y s t s i s s t i l l i n an embryonic stage, although Van Tamelen's group have r e c e n t l y reported that a mixture of t i t a n i u m t e t r a i s o p r o p o x i d e and a reducing agent such as sodium naphthalide i n t e t r a h y d r o f u r a n / i s o p r o p y l a l c o h o l s o l u t i o n c a t a l y t i c a l l y 92 converts N_ or a i r to NH_ at room temperature and atmospheric pressure. 8 Molecular oxygen adds to s e v e r a l o f the more r e a c t i v e d and j l O _ i -< 23,93 . T I n, I ...o . o , _. o d metal complexes, i n c l u d i n g I r , Rh , N i , Os and Ru complexes, to form diamagnetic compounds which r e t a i n an 0-0 bond. Ru(0 )C1(NO)(PPh,) 3J2 has been prepared by the r e a c t i o n of RuCl(CO)(NO)(PPh_) with oxygen, 94 PPh. OC C l R u—NO PPh. PPh. Ru NO (1,36) 0 I ^ C l PPh_ The geometry of the adduct i s depicted as octahedral by analogy w i t h 95 the e l e c t r o n i c a l l y s i m i l a r complex Ir(0_)C1(CO)(PPh_)_. Ru(0^)Cl(NO)(PPh_)^ was found under c e r t a i n c o n d i t i o n s to o x i d i z e the coordinated n i t r o s y l 96 group to a c o v a l e n t l y bound n i t r a t e , C l NO PPh. Ru PPh. CO C l NO. PPh. Ru PPh. CO CO (1,37) - 24 -The most s i g n i f i c a n t property o f these diamagnetic oxygen complexes i s t h e i r a b i l i t y to oxygenate substrates under u s u a l l y m i l d c o n d i t i o n s . Both s t o i c h i o m e t r i c and c a t a l y t i c o x i d a t i o n s have been 23 97 described f o r oxygen complexes of pal l a d i u m , n i c k e l , and rhodium, and i t seems l i k e l y that ruthenium oxygen complexes are a l s o p o s s i b l e o x i d a t i o n c a t a l y s t s . CHAPTER I I APPARATUS AND EXPERIMENTAL PROCEDURE 2.1. M a t e r i a l s 2.1.1. Ruthenium S a l t s The source of ruthenium was RuCl_.3H-0 from Platinum Chemicals, or (NH^) 2Ru(H 20)Cl,- from Johnson Matthey. Although designated as ruthenium(III) compounds, they are most l i k e l y the hydroxy s a l t s (NH 4) 2Ru I V(OH)Cl_ and R u I V C l _ ( O H ) 2 H 2 0 . 2 4 , 5 8 The v i s i b l e a bsorption s p e c t r a of a 3 M HC1 s o l u t i o n of the "RuCl_.3H 20" and a measured H 2 24 uptake f o r the r e d u c t i o n of t h i s s o l u t i o n to Ru(III) i n d i c a t e d that the m a t e r i a l contained about 70% Ru(IV). A stock s o l u t i o n of RuCl^-^^O i n DMA was made by d i s s o l v i n g RuCl_.3H 20 i n d i s t i l l e d DMA; the s o l u t i o n was kept under N 2 a l l the time. Potassium pentachloroaquoruthenate(III), K 2RuCl-(H 20), was 98 prepared according to the method of Mercer and Buckley from RuCl_.3H 20. Potassium (or ammonium) t e t r a c h l o r o b i p y r i d i n e r u t h e n a t e ( I I I ) , K[RuCl^(CjgHgNp] was prepared according to the l i t e r a t u r e * ^ v i a b i p y r i d i n i u m t e t r a c h l o r o b i p y r i d i n e r u t h e n a t e ( I I I ) 1-hydrate and t e t r a c h l o r o -bipyridineruthenium(IV) 1-hydrate (Scheme I V ) . (Found: C, 27.24%; H, 1.99%; N, 6.46%. Calcd. f o r KRuCl .C. flH_N„: C, 27.40%; H, 1.84%; N, 6.40%). - 26 -K 2RuCl_H 20 + 2bipy HC1 [ H b i p y ] [ R u ( b i p y ) C l 4 ] + H 2 0 + C l " Cl„ N H 4 R u ( b i p y ) C l 4 < H ^ H / C I ° H R u ( b i p y ) C l 4 . H ^ Scheme IV The corresponding 1,10-phenanthroline d e r i v a t i v e was prepared by a s i m i l a r method. However a pure compound could not be obtained due to the d i f f i c u l t i e s i n the o x i d a t i o n step. 2.1.2. Gases P u r i f i e d hydrogen was obtained from Matheson Co. The hydrogen was passed through a Deoxo c a t a l y t i c p u r i f i e r to remove tra c e s of oxygen before use. Carbon monoxide, ethylene, acetylene, deuterium, and v i n y l f l u o r i d e were obtained as C P . grade from Matheson Co. Nitrogen and oxygen were from Canadian L i q u i d A i r Co. 2.1.3. Other M a t e r i a l s N,N-dimethylacetamide (DMA) was an Eastman Organic Chemical. I t was p u r i f i e d by s t i r r i n g over calcium hydride and d i s t i l l i n g under reduced pressure. The p u r i f i e d DMA was kept on Linde 4A molecular sieve under n i t r o g e n atmosphere. F i s h e r S c i e n t i f i c concentrated HC1 was d i l u t e d to give stock HC1 s o l u t i o n s . M a l e i c , fumaric a c i d and maleic anhydride were obtained as C P . grade from Eastman Organic Chemical, and were r e c r y s t a l l i z e d from - 27 -appropriate solvents before use. p_-Toluenesulphonic a c i d and tr iphenylphosphine were A . R . grade obtained from Eastman Kodak; the l a t t e r was r e c r y s t a l l i z e d from benzene/ethanol . 2 , 2 ' - B i p y r i d i n e and o-phenanthrol ine were from K § K Laborator i e s . Anhydrous FeCl_ was from K § K Laboratories and l i t h i u m c h l o r i d e was A . R . grade obtained from A l l i e d Chemical Co. Ti tanium(III ) c h l o r i d e so lut ions were obtained by d i s s o l v i n g 98.6% s o l i d t i tan ium t r i c h l o r i d e , from Alpha Inorganic I n c . , i n 3 M HC1 or p u r i f i e d DMA, under N_ atmosphere. A l l other chemicals used were o f reagent grade and d i s t i l l e d water was used i n a l l experiments. 2.2. Apparatus for Constant Pressure Gas-Uptake Measurements A constant pressure gas-uptake apparatus was used for the k i n e t i c s tud ies . A diagram of the apparatus i s shown i n Figure 1. A glass s p i r a l arrangement connected a c a p i l l a r y manometer D at tap C to the pyrex-glass r e a c t i o n f l a s k A; two-necked r e a c t i o n f lasks with one neck f i t t e d with a serum cap or a sampling tube could a l so be used. The f l a s k , which could be c l i p p e d to a metal p i s t o n - r o d and wheel dr iven by a Welch v a r i a b l e speed e l e c t r i c motor for shaking purposes, was immersed i n a thermostated bath B conta in ing Dow Corning (55G F lu id ) s i l i c o n e o i l at a des ired temperature. The c a p i l l a r y manometer D containing buty l phthalate (a l i q u i d of n e g l i g i b l e vapour pressure) was connected to the gas measuring buret te c o n s i s t i n g of a mercury r e s e r v o i r E and a p r e c i s i o n bored tube N o f known diameter. Both the c a p i l l a r y Figure 1. Apparatus for constant pressure gas-uptake measurements. - 29 -manometer and the gas b u r e t t e were housed i n a thermostated water bath made from a perspex r e c t a n g u l a r tank at 25°C. The gas b u r e t t e was i n t u r n connected, by means of an Edward's high vacuum needle v a l v e M, to the gas handling p a r t o f the apparatus, which c o n s i s t e d o f a mercury manometer F, the gas i n l e t Y and connections to the Welch Duo Seal r o t a r y vacuum pump G. The s i l i c o n e o i l bath c o n s i s t e d o f a four l i t r e g l a s s beaker i n s u l a t e d by p o l y s t y r e ne foam on a l l s i d e s and enclosed by a wooden box w i t h a c i r c u l a r h o l e s u i t a b l e f o r viewing the r e a c t i o n v e s s e l . The top of the o i l bath was w e l l covered by s t e r o foam. A Jumo thermo r e g u l a t o r with a Merc to Merc r e l a y c o n t r o l c i r c u i t , and heating provided by a 25 watt elongated l i g h t bulb were used f o r the operation of both thermostat u n i t s . With mechanical s t i r r i n g and good i n s u l a t i o n , the temperature could be maintained to w i t h i n ± 0.05°C. A v e r t i c a l l y mounted t r a v e l l i n g telescope was used to f o l l o w the gas uptake. A Lab-Chron 1400 timer was used to record the time during the k i n e t i c experiments. 2.3. Procedure f o r a T y p i c a l Gas-Uptake Experiment For each experiment, known amounts of the reactants e.g., ruthenium complex, s u b s t r a t e , e t c . , were p i p e t t e d or added from a glass capsule i n t o the r e a c t i o n f l a s k A which was then connected by the s p i r a l and tap C to the gas handling p a r t of the apparatus at 0. In c a t a l y t i c hydrogenation experiments when the ruthenium complex s o l u t i o n was a i r -s e n s i t i v e , the r e a c t i o n f l a s k with the ruthenium s o l u t i o n prepared ' i n s i t u ' was f r o z e n i n l i q u i d N„. Substrate was then added from a glass - 30 -capsule and the f l a s k q u i c k l y evacuated before any subsequent treatment. The reactant s o l u t i o n i n the r e a c t i o n f l a s k was degassed by repeated c o o l i n g and warming under vacuum. The r e a c t i o n v e s s e l was then f i l l e d w ith the reactant gas at a pressure somewhat l e s s than t h a t r e q u i r e d f o r the experiment. The taps C and P were c l o s e d and the r e a c t i o n f l a s k complete w i t h the s p i r a l was disconnected from 0 and attached to the c a p i l l a r y manometer at H, the f l a s k being placed i n the o i l bath and attached to the motor d r i v e n shaker I. The whole system up to tap C was then pumped down with taps H, K, L, J , and M open. Reactant gas : was admitted to the r e s t of the apparatus beyond C to a pressure •  s l i g h t l y l e s s than that d e s i r e d f o r r e a c t i o n . Tap C was then opened and pressure adjusted to the d e s i r e d r e a c t i o n pressure by i n t r o d u c t i o n of gas through Y. A run was s t a r t e d by c l o s i n g tapsK and L and simultaneously s t a r t i n g the shaker and timer. The gas uptake was i n d i c a t e d by the d i f f e r e n c e i n the o i l l e v e l s of the manometer. The manometer was; balanced by l e t t i n g gas i n t o the b u r e t t e through the needle valve i n order t o maintain a constant pressure i n the r e a c t i o n f l a s k . This would r e s u l t i n a r i s e of the l e v e l i n N. The change i n height of the mercury l e v e l w i t h respect to time was recorded. Since the diameter of the tube N was known, the volume of the gas consumed could be c a l c u l a t e d and expressed as moles per l i t r e of s o l u t i o n . A r a p i d shaking r a t e together w i t h the use of small volumes of s o l u t i o n (4-6 m l . ) , i n a r e l a t i v e l y l a r g e indented r e a c t i o n f l a s k (30 ml.) ensured absence of d i f f u s i o n c o n t r o l ( i . e . , due to slow d i s s o l u t i o n of the reactant gas). - 31 -2.4. Reaction Product A n a l y s i s 2.4.1. S o l i d Organic Products For i s o l a t i o n of organic hydrogenated products ( s u c c i n i c a c i d f o r the maleic a c i d systems) i n dimethylacetamide s o l u t i o n , a procedure i n v o l v i n g evaporation and su b l i m a t i o n was employed. The solvent was removed by pumping through a l i q u i d n i t r o g e n c o l d t r a p . The res i d u e was then heated g e n t l y w h i l e pumping was maintained. The organic product sublimed onto the neck of the r e a c t i o n f l a s k . The sublimate was c o l l e c t e d and r e c r y s t a l l i z e d before i d e n t i f i c a t i o n by i n f r a r e d (KBr d i s c method) and m e l t i n g p o i n t . 2.4.2. Inorganic Products The f i n a l r e a c t i o n s o l u t i o n was s i m i l a r l y reduced to a small volume. Samples o f the concentrated s o l u t i o n were removed by means of a micro-syringe i n j e c t e d through a serum cap. The samples were then t r a n s f e r r e d , under a n i t r o g e n atmosphere i f necessary, to v i s i b l e / U . V . or I.R. c e l l s or N.M.R. tubes again f i t t e d w i t h serum caps, f o r subsequent measurements. For i s o l a t i o n of s o l i d products, a complexing l i g a n d ( p a r t i c u -l a r l y PPh_) was sometimes added to the concentrated r e a c t i o n s o l u t i o n s . Benzene and ether were used to separate the s o l i d s . Attempts to c h a r a c t e r i z e s o l i d s were made by u t i l i z i n g i n f r a r e d s p e c t r a , micro-a n a l y s i s , mass s p e c t r a , E.S.R. s p e c t r a , magnetic s u s c e p t i b i l i t y measure-ments, molecular weight determination and melting-point determination. - 32 -2.5. Instrumentation V i s i b l e and u l t r a v i o l e t a b s o r p t i o n s p e c t r a were recorded on e i t h e r a Cary 14 recording spectrophotometer or a P e r k i n Elmer 202 spectrophotometer. Matched s i l i c a c e l l s of 1 mm. or 1 cm. path length were used. I n f r a r e d s p e c t r a o f s o l u t i o n s were recorded on a P e r k i n Elmer I n f r a c o r d 137 using d i s p o s a b l e AgCl c e l l s or NaCl c e l l s . S o l i d samples were recorded on a P e r k i n Elmer model 21 using KBr d i s c s . N.M.R. spect r a were obtained on Varian HR-100 and A-60 nuclear magnetic resonance spectrometers. Mass s p e c t r a were obtained on an Associated E l e c t r i c a l I n d u s t r i e s MS 9 mass spectrometer. E.S.R. spec t r a and s u s c e p t i b i l i t y measurements were k i n d l y recorded f o r us by Dr. F.G. Herring and Dr. R.C. Thompson r e s p e c t i v e l y , of t h i s department. M e l t i n g p o i n t s were measured on a Superior E l e c t r i c m e l t i n g p o i n t apparatus and are uncorrected. CHAPTER III REACTIONS USING SOLUTIONS OF RUTHENIUM 2,2 *-BIPYRIDYL COMPLEXES 3 .1 . The Reactions Involv ing Hydrogen i n Aqueous Hydroch lor ic A c i d S o l u t i o n K[RuCl^ (bipy)] was found to be unreact ive towards hydrogen _3 at 80°C i n 3 M HC1 s o l u t i o n (^ 10 M i n Ru; v i s i b l e spectrum shown i n Figure 2, A ) , and d i d not cata lyze the reduct ion of maleic ac id or f e r r i c c h l o r i d e . A d d i t i o n of T i C l _ i n 3 M HC1 to the (NH 4 ) [RuCl 4 (b ipy) ] i n the absence of a i r y i e l d e d a red s o l u t i o n (Figure 2, B) which reacted very slowly at 80°C with H - , with the product ion of the ruthenium metal . The product ion of the red solutions presumably containing the anion 2- 10 [RuCl^(bipy)] , was b r i e f l y noted by Dwyer and coworkers although no fur ther studies on the species were reported . This R u ( I I ) - b i p y r i d y l complex i n 3 M HC1 r a p i d l y formed a yellow s o l u t i o n at 80°C i n the presence of excess maleic ac id (Figure 2, C ) , and on comparison with 8 52 the prev ious ly s tudied chlororuthenate(II ) systems, ' th i s i s l i k e l y to invo lve formation of a ir-complex. The extent of complex formation was determined by measuring the decrease i n absorbance at 517 my.,, where the r u t h e n i u m ( I I ) - b i p y r i d y l complex absorbs s trongly and the o l e f i n complex absorbs n e g l i g i b l y (Figure 2) . The dependence of the extent of complex formation on the concentrat ion of maleic a c i d i s shown i n - 35 -Figure 3. I t was found that t h i s dependence could be f i t t e d by an e q u i l i b r i u m r e l a t i o n d erived f o r the formation of a 1:1 ruthenium(II)• o l e f i n complex, i . e . , [ R u H C l 4 ( b i p y ) ] 2 _ + M.A. " - ^ [ R u H C l _ (bipy) (M. A.) ] 2 (3,1) 3 -1 w i t h a formation constant of % 2x10 M at 25°C. The data of Figure 3 may be analyzed by p l o t t i n g T + D / E against 1 / D according to the equation :*^a T £ M A 1 1 T L + °/ £A= — © ' C3.2) where T^ i s the t o t a l maleic a c i d c o n c e n t r a t i o n , D i s the absorbance at 2-517 my, and i s the e x t i n c t i o n c o e f f i c i e n t of [RuCl^(bipy)] , and the value of estimated from the slope and i n t e r c e p t of the reasonably l i n e a r p l o t (Figure 4). A c i d s o l u t i o n s of the r u t h e n i u m ( I I ) - b i p y r i d y l complex c o n t a i n -ing a l a r g e excess of maleic a c i d at 80°C were found to absorb very s l o w l y f o r about 1 hour i n an a u t o c a t a l y t i c manner before reaching a r e g i o n of l i n e a r uptake (Figure 5). uptake measurements showed that complete r e d u c t i o n of maleic a c i d occurred. The c o l o u r of the i n i t i a l s o l u t i o n was the yellow-orange of the o l e f i n complex. Towards the end-point of the H_ uptake, the colour of the s o l u t i o n became the 2-red c o l o u r of the [ R u C l 4 ( b i p y ) ] species and metal s t a r t e d to p r e c i p i -t a t e . The r a t e of hydrogenation of maleic a c i d was measured i n the l i n e a r r e g i o n of the uptake p l o t . Unfortunately with these sytems traces \ - 36 -0.0 I | | | | 0.0 1.0 2.0 3.0 4.0 [M.A.] x 10 3 M Figure 3. E f f e c t of maleic a c i d on the absorbance at 517 my of a 3 M HC1 s o l u t i o n c o n t a i n i n g 5.0 x 10" 4 M ruthenium(II) bipy complex. Complex formed at 80°; O.D. measurements made at room temperature. - 37 -- 39 -of metal were sometimes observed while the s o l u t i o n was s t i l l yellow-orange, and t h i s caused us to abandon our i n i t i a l thoughts of a d e t a i l e d study and extension to other systems using substituted b i p y r i d y l and phenanthrolines i n the hope of c o r r e l a t i n g homogeneous c a t a l y t i c a c t i v i t y with e l e c t r o n i c and s t e r i c e f f e c t s . 2_ Nevertheless the k i n e t i c data for t h i s [RuCl^(bipy)] catalyzed hydrogenation of maleic a c i d i n HC1 appeared quite good and reproducible, and are presented i n the following section. However, the r e s u l t s and discussion perhaps should be regarded with some caution since m e t a l l i c ruthenium i s a heterogeneous c a t a l y s t f o r such o l e f i n hydro-8 genation. 3.1.1. Results and Discussion of the C a t a l y t i c Hydrogenation K i n e t i c measurements were made with Ru(II) solutions containing a large excess of T i C l _ which ensured complete reduction of the s t a r t i n g Ru(III) s a l t to Ru(II). The r e s u l t s of the k i n e t i c measurements are summarized i n Table I. The l i n e a r rate of r e a c t i o n was f i r s t - o r d e r i n 2_ [RuCl^(bipy)] and i n H-, between zero and f i r s t - o r d e r i n maleic acid (Figure 6-8), and was e s s e n t i a l l y independent of T i C l _ . The rate apparently decreases with increasing [H +] and [CI ] although the e f f e c t s 18 are small and could be due to diff e r e n c e i n H. s o l u b i l i t y . At the high [M.A.] the rate-law at constant [H +] and [CI ] becomes " d [ H 2 ] : - I I - , -.. .2-dt k[RuXiCl4(bipyr ][H_] (3,3) - 40 -Table I 2-[RuCT^(bipy)] c a t a l y z e d hydrogenation of maleic a c i d i n aqueous 3 M h y d r o c h l o r i c a c i d at 80°C K i n e t i c Data [ R u C l 4 ( b i p y ) ] 2 _ [M.A.] [ T i C l 3 ] H 2 * [H 2] Linear Rate x l 0 3 , M x l 0 2 , M M mm xl 0 4 , M x l 0 6 , M S - 1 3.3 1.80 0.10 450 3, .60 1.40 2.5 1.80 0.10 450 3, .60 1.10 2.0 1.70 0.10 450 3, .60 0.78 3.4 1.80 0.10 360 2. .89 1.10 3.3 1.80 0.10 285 2. .28 0.77 3.4 1.80 0.10 252 2. .02 0.73 3.3 1.80 0.10 204 1. .63 0.60 3.3 1.80 0.10 133 1. .07 0.45 3.3 1.80 0.10 102 0, .82 0.34 3.4 2.70 0.10 450 3. .60 1.53 3.3 1.10 0.10 450 3. .60 1.20 3.3 1.10 0.84 450 3. .60 1.03 3.3 0.65 0.10 450 3. .60 0.98 3.3 1.80 0.10 450 3. ,60 1.29 a 3.4 1.80 0.10 450 3. .60 1.27 b 3.3 1.80 0.10 450 3, .60 1.60° 3.3 1.80 0.10 510 3. .91 0.82 d 3.3 1.80 0.10 560 4. .32 0.35 6 * Estimated from the known p a r t i a l pressure of 3 M HC1 using the s o l u b i l i t y data of S e i d e l l . " a 2 M L i C l b 6 M HC1 ° 1 M HC1 + 2 M L i C l d 75°C 6 70°C S O rH X CD •P cd rH r-l cd c 1.5 L 1.0 0.5 0.0 [H 9] x 10 4, M Figure 7. Dependence of l i n e a r r a t e of hydrogenation of maleic a c i d on [H 2] i n 3 M HC1 at 80°. (0.34 x 10~ 2 M R u C l 4 b i p y 2 - , 0.018 M M.A., 0.1 M T i C l 3 ) . - 42 -Figure 8. Dependence of l i n e a r r a t e of hydrogenation of maleic a c i d on [M.A.] i n 3 M HC1 at 80°. (0.34 x 10~ 2 M R u n C l 4 b i p y z " , 450 mm. H 2, 0.1 M T i C l j ) . - 43 -which i s of the same form as that i n v o l v e d i n the c h l o r o r u t h e n a t e ( I I ) g system (and S e c t i o n 1 . 1 . ) where a l i n e a r r a t e was observed throughout, and the f o l l o w i n g mechanism, II f a s t I I Ru + o l e f i n *• Ru ( o l e f i n ) (3,4) R u 1 1 ( o l e f i n ) + H- R u 1 1 + p a r a f f i n (3,5) was p o s t u l a t e d . However the present b i p y r i d y l system d i f f e r s i n the presence of an i n i t i a l a u t o c a t a l y t i c r e g i o n and i n the dependence on M.A. at lower M.A. concentrations. The formation constant o f the [RuCl-(bipy)(M.A.)] complex shows that t h i s species i s f u l l y formed at the s t a r t o f the hydrogenation experiments, when the hydrogenation r a t e i s p r a c t i c a l l y zero; t h i s suggests that r e a c t i o n (3,5) i s not in v o l v e d i n t h i s system. The i n i t i a l slow uptake of H_ i n d i c a t e s p o s s i b l e formation of .an a c t i v e hydride intermediate p a r t i c u l a r l y s i n c e the a u t o c a t a l y t i c region ceases at an uptake stage corresponding to roughly 1 mole H~ • I I 2-per mole Ru . A l s o the red [RuCl^(bipy)] species i t s e l f i s reduced by H. to metal presumably through a hydride intermediate and, 1 2 on comparison w i t h a s i m i l a r two e l e c t r o n r e d u c t i o n i n v o l v i n g R h ( I I I ) , may w e l l proceed as f o l l o w s : [ R u C l 4 ( b i p y ) ] 2 _ + H- > [ R u H C l - ( b i p y ) ] 2 " + H + + C l " (3,6) I [ R u H C l - ( b i p y ) ] 2 - > Ru° + H + + bi p y + 3 C l " (3,7) - 44 -There w i l l be small amounts of I present i n the system and a mechanism such as the f o l l o w i n g (Scheme V) i s c o n s i s t e n t w i t h the k i n e t i c data. - I I - H 2 C l + [Ru Cl (bipy) (M.A.)] >- no r e a c t i o n M.A. [ R u n C l A ( b i p y ) ] 2 _ + H 2 •-—U [ R u n H C l / ( b i p y ) ] 2 + H + + C l ' 4' I M.A. [ R u n H C l 3 ( b i p y ) ] 2 " + S.A. +~-- [ R u H H C l 2 ( b i p y ) (M.A. ) ] " + C l ' I I I I I Scheme V The intermediate hydride I I must complex r a p i d l y w i t h M.A. to form I I I which l i k e l y rearranges to a a - a l k y l complex. Reaction of platinum metal hydrides i n c l u d i n g those of Ru 1* w i t h o l e f i n s to g i v e metal a l k y l s i s w e l l substantiated. 4 2>62,100 ^ o r e d e t a i l e d d i s c u s s i o n of c a t a l y t i c hydrogenation processes w i l l be l e f t to Chapters V and VII when more d e t a i l e d s t u d i e s on r e l a t e d systems i n DMA w i l l be considered. The a u t o c a t a l y t i c r e g i o n i s then due to the slow b u i l d up of I I (and hence I I I ) . Once the steady s t a t e c o n c e n t r a t i o n of I I I has b u i l t up a l i n e a r r a t e w i l l r e s u l t from a rate-determining s p l i t t i n g by the a - a l k y l complex; such r e a c t i o n s of a l k y l with hydrogen to y i e l d -, i j - j , ^ . : , 42,101-103 „ metal hydrides have al s o been p o s t u l a t e d p r e v i o u s l y . For Scheme V, the rate-law i n the l i n e a r r e gion becomes - 45 -•d[H_] k 2 K 2 [ H 2 ] [ M . A . ] [ R u I I ] t o t a l dt 1 + K [M.A.] At the highest [M.A.]. I l l i s f u l l y formed and the r a t e approaches the l i n e a r value k [H ] [Ru 1 1] ... The data at the highest [M.A.] g i v e k2== 1.3 M~*Sec~* at 80°C; at lower [M.A.], I I I i s not f u l l y formed and the r a t e w i l l decrease. Traces of metal sometimes found could w e l l be due to decomposition of I I (Equation 3,7). The data on the maleic a c i d dependence (Figure 8) i n d i c a t e that i s ^  170 M which i s obtained from a p l o t of 1/Rate against 1/M.A. (Figure 9) according to the equation: (3,9) 1 1 1 1 k 2 i s estimated to be 1.57 M *Sec 1 from the i n t e r c e p t and i s i n good agreement w i t h the value obtained p r e v i o u s l y . Measurements over the temperature range 70-80°C (Table I) gave a good Arrhenius p l o t (Figure 10) and the a c t i v a t i o n parameters AH 2 — 38 t 2 kcal/mole and AS 2 t=44 _ 5 eu. The value o f k 2 i s about one h a l f the value of the correspond-g ing r a t e constant f o r the c h l o r o r u t h e n a t e ( I I ) system; the l a t t e r r a t e -determining step i s thought to i n v o l v e h e t e r o l y t i c s p l i t t i n g o f by a Ru 1* o l e f i n -rr-complex; k 2 most l i k e l y i n v o l v e s h e t e r o l y t i c s p l i t t i n g o f H 2 by a Ru** a - a l k y l complex. The ruthenium(III) complex [RuCl^(bipy)] , u n l i k e 2- 24 [RuCl_(H 20)] , does not c a t a l y z e the r e d u c t i o n o f f e r r i c o r Q maleic a c i d i n HC1 s o l u t i o n s presumably s i n c e the intermediate hydride - 47 -- 4 8 -i s not so r e a d i l y formed by s u b s t i t u t i o n of H f o r C l (compare equation 3,6) and i s r e a d i l y explained by the expected lower r e l a t i v e l a b i l i t y of c h l o r i d e i n the [RuCl^(bipy)] complex. The c h l o r i d e i n [ R u ^ C l ^ f b i p y ) ] i s again more l a b i l e because o f the higher negative charge of the complex. By using a more b a s i c r e a c t i o n medium i t was hoped to promote a r e a c t i o n such as (3,6) f o r the ruthenium(III) complex, [RuCl^fbipy)] . However DMA s o l u t i o n s of t h i s complex were s t i l l u n r e a c t i v e towards at 80°C and s t i l l d i d not c a t a l y z e the H^ r e d u c t i o n of f e r r i c or maleic a c i d . 3.2. Reactions I n v o l v i n g Other Gaseous Molecules (NH^)[RuCl^(bipy)] i s only s p a r i n g l y s o l u b l e i n 3 M HC1 ('v 10" 3 M i n Ru) . At 80°C HC1 s o l u t i o n s of (NHj) [ R u C l 4 ( b i p y ) ] were unr e a c t i v e towards CO, C^H^ and C^ri^. ^ [ R u C l ^ - f ^ O ) ] has been found to 37 56 be an a c t i v e c a t a l y s t f o r the hy d r a t i o n of ac e t y l e n e s , ' and t h i s i s thought to be due to the presence of the l i g a n d water molecule which i s not present, however, i n the r u t h e n i u m ( I I I ) - b i p y r i d y l complex. (NH 4 ) [ R u C l 4 ( b i p y ) ] i n DMA at 80°C absorbs one mole of CO per mole Ru to give a red s o l u t i o n (the r e a c t i o n i s f i r s t - o r d e r i n ruthenium). The r e s u l t i n g carbonyl complex i s l i k e l y to be RuCl,j(C0)bipy ( v ^ = 2050 cm *) which was found to be unr e a c t i v e i n c a t a l y z i n g the hydrogenation of maleic a c i d . The red [ R u I 1 [ C l 4 ( b i p y ) ] 2 ~ s o l u t i o n i n 3 M HC1 reacted w i t h CO at 80°C to give a yellow-brown s o l u t i o n and a dark p r e c i p i t a t e . Under 2-s i m i l a r c o n d i t i o n s , 3 M HC1 s o l u t i o n of [ R u C l 4 ( b i p y ) ] reacted w i t h C„H to give a reddish-brown s o l u t i o n and a white p r e c i p i t a t e . The CHAPTER IV CATALYTIC ACTIVATION OF MOLECULAR HYDROGEN BY RUTHENIUM CHLORIDE COMPLEXES IN DMA 4.1. I n t r o d u c t i o n As reviewed i n Chapter I many t r a n s i t i o n metal ions and complexes have been found to a c t i v a t e molecular hydrogen i n both aqueous 2-5 and non-aqueous s o l v e n t s . Among these, ruthenium(III) c h l o r i d e was found to a c t i v a t e i n aqueous HC1 s o l u t i o n , and to c a t a l y z e the 24 re d u c t i o n by H- of Ru(IV) and F e ( I I I ) . As discussed i n Se c t i o n 1.1., i t was d e s i r a b l e t o extend these s t u d i e s to l e s s a c i d i c media, and t h i s Chapter describes the k i n e t i c s of the a c t i v a t i o n o f H. by ruthenium c h l o r i d e complexes i n DMA. The observed r e a c t i o n s were much more complex than had been a n t i c i p a t e d , and some considerable time was spent before a r r i v i n g at the best c o n d i t i o n s to study the various steps i n v o l v e d ; a f u r t h e r problem was that only the s a l t RuCl_.3H-0, which i s a mixture of Ru(III) and Ru(IV) (Section 2.1.), was s u f f i c i e n t l y s o l u b l e f o r the s t u d i e s . K-RuCl-(H.0) and (NH .)[RuCl_(OH)1, a v a i l a b l e as pure ruthenium(111) and 2 5 2 4 b > • ruthenium(IV) compounds, were e s s e n t i a l l y i n s o l u b l e . - 51 -4.2. A c t i v a t i o n of Molecular Hydrogen by Ruthenium(III) C h l o r i d e Complexes I I I 4.2.1. A u t o c a t a l y t i c Reduction o f Ruthenium(IV) (Production of Ru ) (A) Stoichiometry S o l u t i o n s of "RuCl_.3H 20" (^  70% Ru I V) i n DMA were found to absorb W^, i n i t i a l l y i n an a u t o c a t a l y t i c manner (Figure 11), at measurable rat e s i n the temperature range 30-55°. The s t o i c h i o m e t r y of the t o t a l H 2uptake at the l e v e l l i n g o f f r e g i o n corresponds to about 0.5 mole H. per mole of Ru*^, and presumably i n v o l v e s r e d u c t i o n of Ru*^ to Ru*** ; • *v; - j . 24 as i n the aqueous a c i d system: 2Ru* V + H 2 y 2Ru*** + 2H + (4,1) A subsequent slow r e a c t i o n (% 15 hr.) of the Ru*** with H 2 then occurred, the r a t e o f which became conveniently measurable at the higher tempera-tures 60-80° (see Figure 20). Again the uptake of H 2 overnight at corresponded to about 0.5 mole of H 2 per mole of Ru***, and t h i s 30° together with the production of a blue c o l o u r , i s thought to i n v o l v e the production of Ru**: 2Ru*** + H y 2Ru** + 2H + (4,2) The o r i g i n a l red-brown RuCl^.SH^ s o l u t i o n , which showed a broad absorption band i n the region 400-550 my, g r a d u a l l y became y e l l o w i s h -green (450 my, e = 1750) a f t e r the absorption of the f i r s t h a l f mole of 0 1000 2000 3000 Time Sec Figure 11. Rate p l o t s f o r the a u t o c a t a l y t i c r e d u c t i o n o f Ru*^ by H i n DMA at 35°. 379 mm. H 2; [RuCl 3.3H 20]: (0) 2 x 10~ 2 M; (A) 1 x 1 0 - 2 M. 53 H 2, and f i n a l l y became blue (652 my, e = 1200) at the end pf the slower r e a c t i o n (Figure 12). C h l o r o r u t h e n a t e ( I I ) complexes i n aqueous s o l u t i o n s 8 are known to be blue and the recorded s p e c t r a must be approximately those of Ru 1*, Ru*** and Ru*^ i n DMA. The greenish t i n g e i n the Ru*** s o l u t i o n i s undoubtedly due to small amounts of Ru**. The broad band of "Ru*^" i s due p a r t l y to the presence of ^30% of Ru***; a l l o w i n g f o r t h i s would give a peak absorption at ^ 510 my (e -\J400) f o r Ru*^ at the recorded c o n c e n t r a t i o n . (B) K i n e t i c s of the Reaction at the Lower Temperature i n DMA. The nature of the uptake p l o t s (Figure 11) suggested that the r e a c t i o n e x h i b i t e d a u t o c a t a l y s i s . The a u t o c a t a l y t i c behaviour may be explained i n terms of c a t a l y s i s of the r e a c t i o n by Ru***, and f i t t e d by a r a t e law of the form shown i n Equation (4,3) f o r the s t o i c h i o m e t r y of r e a c t i o n (4,1). dt 2 dt 1 L 2 J With [H 2] constant during the course of each experiment, t h i s y i e l d s on i n t e g r a t i o n , log[Ru***] = l o g [ R u i n ] . n i t i a l + 2k 1[H 2]t/2.303 (4,4) According to Equation (4,4), p l o t s of log[Ru***] vs. time (Figure 13) were found to be l i n e a r over the major p o r t i o n of each experiment and the slopes y i e l d e d c o n s i s t e n t values of k^ (Table I I ) . The non-zero 20 I 1 1 1 I I | I 350 400 450 500 550 600 650 700 750 Wavelength, my Figure 12. Absorption spectra o f "Ru ", Ru **, Ru 1* and Ru* i n DMA at c o n c e n t r a t i o n of 2.0 x 10~ 2 M. - 55 --1.7i 0 500 1000 1500 2000 2500 Time Sec gure 13. A u t o c a t a l y t i c r e d u c t i o n of R u I V by H 2 i n DMA at 3 5 ° . (379 mm. H 2) [RuCl 3 . 3 H 2 0 ] : (0) 2.0 x 10~2 M, (A)1.0 x 10~2 M. - 56 -Table I I IV Ruthenium(III) c h l o r i d e c a t a l y z e d hydrogen r e d u c t i o n of Ru i n DMA K i n e t i c data [RuCl_.3H 20] H 2 [H_] + [ L i C l ] Temperature k l x 10 2, M mm. x 10 3, M M °C M - V 1 2.00 756 1. 80 35 0.77 2.00 584 1. 39 35 0.79 2.00 379 0. ,91 35 0.72 2.00 193 0. .46 35 0.67 1.50 379 0. .91 35 0.72 1.00 379 0. ,91 35 0.67 0.50 379 0. .91 35 0.78 2.00 725 2. ,32 80 too f a s t 2.00 725 2. ,32 0.1 80 0.85 2.00 725 2. ,32 0.5 80 1.30 * DMA used without p u r i f i c a t i o n . Reference 104. k^ obtained from log p l o t (Equation 4,4) assuming 30% Ru present i n i t i a l l y as Ru***. 57 -i n i t i a l r a t e s observed i n these systems are due to the presence of about 30% of the ruthenium being present as r u t h e n i u m ( I I I ) . The mean value of at 35° i s 0.73 M *S * and was e s s e n t i a l l y independent of [Ru***] and [H^]. k^ seems to be dependent on c h l o r i d e c o n c e n t r a t i o n i n a complex way; however a constant i o n i c s t r e n g t h was not maintained, and i n any case v a r i a t i o n i n c h l o r i d e c o n c e n t r a t i o n may w e l l a f f e c t the d i s t r i b u t i o n of c h l o r o complexes present i n i t i a l l y . I t was n o t i c e d t h a t the v i s i b l e absorption spectrum of the i n i t i a l RuCl^.SP^O s o l u t i o n v a r i e d w i t h c o n c e n t r a t i o n (Figure 14); a l i m i t i n g spectrum (V) was reached on successive d i l u t i o n . The s p e c t r a could r e s u l t from e q u i l i b r i a such as monomer -—>- dimer -—>- polymer only the monomer being present at the lowest c o n c e n t r a t i o n . Such e q u i l i b r i a are w e l l e s t a b l i s h e d f o r the s o l u t i o n s of ruthenium(IV) c h l o r i d e s i n aqueous HC1 s o l u t i o n s . * ^ ^ The observed f i r s t order dependence on ruthenium(III) suggests a s i n g l e species of t h i s valency s t a t e e x i s t s over the c o n c e n t r a t i o n range used, (or l e s s l i k e l y a number of species w i t h equal r e a c t i v i t y ) ; i t a l s o suggests that steps i n the process i n v o l v i n g ruthenium(IV) must be r e l a t i v e l y f a s t (Section 4.2.4.). K i n e t i c measurements over the temperature range of 30-55° y i e l d a good Arrhenius p l o t (Table I I I , Figure 15) which i s f i t t e d by the equation k = 8.7 x 10* 3 exp[-20,500/RT]M _ 1S"* (4,5) - 58 -Figure 14. Absorption s p e c t r a of R u C l v 3 H 2 0 i n DMA [RuCl 3.3H 20]: I , 2.05 x 10-2 M ; I I , 1.36 x 10" 2 M; I I I , 0.68 x 10" 2 M; IV 0.34 x l O - 2 M; V, 0.17 x 10' 2 M. - 59 -Table I I I IV * Ruthenium(III) c h l o r i d e c a t a l y z e d hydrogen r e d u c t i o n of Ru i n DMA Temperature dependence of [RuCl-.3H 20] = 2.05 x 10~ 2 M Temperature [H_] k +  k l °C x 10 3, M M S 30 0.87 0.16 35 0.90 0.23 40 0.94 0.42 45 0.96 0.65 50 0.98 1.20 55 1.01 1.64 * DMA p u r i f i e d . f k n obtained from log p l o t assuming 30% Ru present i n i t i a l l y as Ru*** Figure 15. Arrhenius plot for the ruthenium(III) chloride catalyzed reduction of Ru I V in DMA. - 61 -The corresponding values of AH and AS are 19.9 t 1.0 kcal/mole and + 3.2 t 2.0 eu r e s p e c t i v e l y . Some e a r l y experiments were c a r r i e d out using the DMA as purchased as Eastman Grade (highest p u r i t y ) . Later s t u d i e s using the p u r i f i e d solvent gave r a t e s about 3 times lower although the general k i n e t i c s and observations were i d e n t i c a l . Water i s the most l i k e l y i mpurity to cause t h i s discrepancy. 4.2.2. C a t a l y t i c Reduction of Molecular Oxygen The previous system i s seen to be a ruthenium(III) c a t a l y z e d hydrogen r e d u c t i o n of Ru*^ i n which the r e d u c t i o n product i s a l s o the c a t a l y s t (see the d i s c u s s i o n 4.2.4.). More evidence to support the mechanism could c l e a r l y be sought from systems using other r e d u c i b l e s u b s t r a t e s . A number were t r i e d ; some very simple k i n e t i c s were observed using molecular oxygen as the s u b s t r a t e , and these r e s u l t s w i l l now be described. S o l u t i o n s of "RuCl_.3H 20" i n DMA reacted w i t h a 0.1-0.5' r a t i o of H^ to 0^. The uptake p l o t s were l i n e a r (Figure 16). The spectrum and colour of the RuCl_ s o l u t i o n remained unchanged before and a f t e r the r e a c t i o n , suggesting no r e d u c t i o n of Ru*^ took p l a c e , the concentra-t i o n of Ru*** thus remains constant. During a r e a c t i o n the p a r t i a l pressures of and 0^ (and hence t h e i r concentrations i n s o l u t i o n s ) were a l s o kept constant. Thus the r e a c t i o n i s one of pseudo-zero-order. The k i n e t i c r e s u l t s show a good f i r s t - o r d e r dependence on RuCl_.3H 20 _3 up to 0.02 M and a f i r s t - o r d e r dependence on H at l e a s t up to 0.8 x 10 M, - 62 -0 1000 2000 Time Sec Figure 16. Rate p l o t s f o r the R u 1 1 * c a t a l y z e d hydrogen r e d u c t i o n of 0 2 i n DMA at 50°. 0.02 M RuClg. (0) 158 mm. H2, 594 mm. 0 2; (A) 93 mm. H 2, 659 mm. 0 2 63 the r e a c t i o n being independent of 0^ pressure from 450-700 mm. (Table IV, Figures 17 and 18). No k i n e t i c isotope e f f e c t was observed. Again I I I Ru was found t o be the a c t i v e s p e c i e s , s i n c e the r a t e increased w i t h more Ru*** i n i t i a l l y present i n the s o l u t i o n . The r a t e law can thus be formulated, — k ^ R u 1 1 1 ] ^ ] = k ^ F L j (4,6) The o v e r a l l r e a c t i o n o c c u r r i n g (on comparison w i t h Equation 4,1) i s presumably 2 H 2 + °2 ' " 2 H 2 ° ("4'7'' i n the presence of c a t a l y t i c Ru***. To determine k^ the r a t e of uptake i s r e q u i r e d ; t h i s i s the r a t e l i s t e d i n Table IV and V and i s 2/3 the t o t a l measured r a t e which w i l l i n c l u d e 0^ consumption. The average b i m o l e c u l a r r a t e constant k^, obtained i s 2.76 M *S * at 50°. K i n e t i c measurements over the temperature range of 30-70° y i e l d a good Arrhenius p l o t (Table V, Figure 19) and the a c t i v a t i o n parameters AH + = 19.3 t 1.0 kcal/mole and AS f = +2.3 t 2.0 eu. Somewhat lower rates were again observed w i t h p u r i f i e d DMA. Within experimental e r r o r the a c t i v a t i o n parameters are the same as those f o r the a u t o c a t a l y t i c r e d u c t i o n of Ru*^ (Section 4.2.1.) and t h i s suggests a common r a t e -determining step f o r both systems. . .. - 64 -Table IV Ruthenium(III) c h l o r i d e c a t a l y z e d hydrogen r e d u c t i o n of 0- i n DMA K i n e t i c data [RuCl_.3H 20] H 2 [H 2] °2 Temp. Rate k +  k l x 10 2, M mm. x 10 3, M mm. °C x 10 6, MS"1 M-1C-1 M S 2.00 295 0.77 457 50 11.68 2.53 2.00 232 0.61 520 50 7.55 2.06 2.00 192 0.50 560 50 8.20 2.74 2.00 158 0.41 594 50 6.07 2.46 2.00 118 0.31 637 50 4.63 2.49 2.00 93 0.24 659 50 3.60 2.50 2.00 54 0.14 698 50 2.27 2.70 1.50 295 0.77 457 50 8.87 2.56 1.50 192 0.50 560 50 6.23 2.77 1.00 295 0.77 457 50 6.00 2.60 1.00 192 0.50 560 50 4.24 2.83 0.50 295 0.77 457 50 3.14 2.72 0.50 192 0.50 560 50 2.30 3.02 1.30 # 380 0.94 375 40 2.10 1.32 1.30** 380 0.94 375 40 3.13 0.93 1.12* 366 0.97 386 50 1.93 1.37 1.12* 382 1.01 370 50 2.09 1.43 b . t # a DMA used without p u r i f i c a t i o n . Assuming 30% Ru present i n i t i a l l y as D i f f e r e n t batch of RUC1-.3H 2<J (found [ R u 1 " ] = [ R a n i ] i n i t i a l + 0.19 x 10" of Ru . Ru I I I to c o n t a i n about 13% Ru 2 I I I ) M by a u t o c a t a l y t i c r e d u c t i o n D 2 i n place o f U^. - 65 -0.0 0.5 1.0 1.5 2.0 [RuCl 3] x 10 2, M Figure 17. Dependence of the r a t e of r e d u c t i o n of 0 2 i n DMA on [ R U C I 3 ] at 50°. [H 2] : (0) 295 mm; (A ) 192 mm. - 66 -Table V Ruthenium(III) c h l o r i d e c a t a l y z e d hydrogen r e d u c t i o n of i n DMA 't Temperature dependence of [RuCl .3H 0] = 2.05 x 1 0 _ 2 M 0 = 457 mm. Temperature °C [H 2] x 10 3, M Rate x 10 6, MS - 1 i k l 3 -1 x 10 , S k #  k l M - V 1 30 0.69 0.77 1.12 0.18 35 0.71 1.64 2.31 0.39 40 0.74 2.49 3.37 0,56 45 0.76 4.23 5.57 0.93 50 0.77 8.00 10.40 1.73 55 0.80 11.01 13.75 2.29 60 0.81 23.20 28.63 4.77 70 0.83 51.20 61.75 10.30 * DMA p u r i f i e d . t 1 I I I k^ = k^[Ru ] as defined i n Equation (4,6). # I I I Assuming 30% Ru present i n i t i a l l y as Ru - 67 --1.0 2.90 3.00 3.10 3.20 3.30 -1 3 -1 (T) x 10 , K Figure 19. Arrhenius p l o t f o r the r e d u c t i o n of Q 2 i n DMA s o l u t i o n by H_. - 68 -4.2-3- C a t a l y t i c Reduction of Ru*** at Higher Temperatures (Produc- t i o n of Ru**) Ruthenium(III) c h l o r i d e complexes were found t o be reduced to blue Ru** by H- very s l o w l y at 35° i n DMA s o l u t i o n a f t e r the r e l a t i v e l y r a p i d a u t o c a t a l y t i c r e d u c t i o n of Ru*^ to Ru***. However at higher temperatures (<\, 80°), Ru*** was produced very r a p i d l y from RuCl_.3H 20 s o l u t i o n , and the r a t e of the Ru*** to Ru** r e a c t i o n became measurable. S u r p r i s i n g l y at these higher temperatures yet a f u r t h e r r e a c t i o n was then observed, t h i s i n v o l v i n g another 0.5 mole of H_ uptake per mole of Ru and t h i s i s b e l i e v e d to i n v o l v e r e d u c t i o n of Ru** to Ru* (see Se c t i o n 4.3.). An uptake p l o t at 80°, as shown i n Figure 20, can be d i v i d e d i n t o three stages as represented by the broken l i n e s and has been analyzed approximately as f o l l o w s . The H^ r e q u i r e d f o r the reduc-t i o n to Ru*** was sometimes observed as an 'instantaneous' uptake i n under 100 sec. This was followed by the r e d u c t i o n of Ru*** to Ru** i n an uptake i n i t i a l l y i n d i c a t i n g p s e u d o - f i r s t - o r d e r type uptake. Excluding the Ru*^ to Ru*** r e d u c t i o n , about a f u r t h e r 1.0 mole of H-was consumed, c o n s i s t e n t w i t h the r e a c t i o n s : 2RU**1 + H 2 » 2Ru** + 2H + (4,8) 2Ru** + H 2 » 2Ru* + 2H + (4,9) The second r e a c t i o n (Equation 4,9) was found, to be f i r s t - o r d e r i n both Ru and H 2 w i t h a second-order r a t e constant of about 0.1 M *S * at 80°. Such a r a t e constant could be evaluated from a standard f i r s t - o r d e r 2 . 0 0 . 0 A _ | I 1 | T ) 4 0 0 0 8 0 0 0 1 2 , 0 0 0 1 6 7 0 0 0 Time, Sec. gure 2 0 . Rate p l o t f o r the c a t a l y t i c r e d u c t i o n of R u C l 3 i n DMA at 80° ( 0 . 0 2 M R u C l 3 , 0 . 5 9 x 1 0 " 3 M H-). - 70 -p l o t found f o r the l a t t e r part of the uptake p l o t (Figure 20) when e s s e n t i a l l y no Ru*** remains. This system has been s t u d i e d s e p a r a t e l y using prepared s o l u t i o n s of Ru**, and w i l l be discussed i n more d e t a i l i n S e c t i o n 4.3. Although the uptake data f o r the r e d u c t i o n o f Ru*** to Ru** stage are complicated by a precursory i n i t i a l r a p i d r e a c t i o n and a subsequent slower one, a considerable p o r t i o n of the p l o t d i d f i t a p s e u d o - f i r s t - o r d e r log p l o t (Figure 20), and the data were c o n s i s t e n t with a rate-law of the form -d[H_] in T T T _ | _ 2 i _ - I d [ R u _ i _ k [ R u I H ] [ H j ( 4 } 1 0 ) dt 2 dt 1 L 2 The log p l o t s were obtained by assuming the decrease i n ruthenium i s p r o p o r t i o n a l to the uptake. From the slopes the p s e u d o - f i r s t - o r d e r constants can be evaluated, from which the bimolec u l a r r a t e constant k^ was c a l c u l a t e d . The r e s u l t s are summarised i n Table VI. Measurements of k^ over the temperature range 65-80° (Table VII) y i e l d a good Arrhenius p l o t (Figure 21) from which the f o l l o w i n g a c t i v a t i o n parameters were determined + = 15.5 t 1.5 kcal/mole AH AS + = -16.4 t 3.0 eu 4.2.4. D i s c u s s i o n of K i n e t i c Results f o r A c t i v a t i o n of H,, by Ru(I I I ) The k i n e t i c data f o r the r e a c t i o n s described i n Sections 4.2.1., 2 ,2.2. and 4.2.3. f o r the r e d u c t i o n of Ru*\ 0 and Ru*** r e s p e c t i v e l y - 71 -Table VI I I I Ruthenium(III) c h l o r i d e c a t a l y z e d hydrogen r e d u c t i o n of Ru i n DMA K i n e t i c data at 80° H2 [H_] k l x 10 2, M mm. x 10 3, M M - V 1 2.00 725 2.32 0.24 2.00 546 1.75 0.20 2.00 366 1.17 0.23 2.00 187 0.59 0.23 1.00 725 2.32 0.24 1.00 546 1.75 0.22 2.00 366 1.17 0.06 a 1.30 b 366 1.17 0.33 1.30 b 366 1.17 0.28° 1.30 b 366 1.17 0.21 d DMA used without p u r i f i c a t i o n . a 1.0 M L i C l D i f f e r e n t batch of RuCl_.3H 20 C O.085 M p-toluene sulphonic a c i d ^ 0.93 M p-toluene sulphonic a c i d . - 72 -Table VII I I I Ruthenium(III) c h l o r i d e c a t a l y z e d hydrogen r e d u c t i o n of Ru i n DMA Temperature dependence of k^ [ R u 1 1 1 ] = 0.02 M Temperature [H 2i k l °C x 10 3, M M - V 1 80 2.32 0.23 75 2.22 0.16 70 2.17 0.12 65 2.13 0.08 * DMA used without p u r i f i c a t i o n . 74 a l l gave the r a t e law -d[H 2] d t - k j R u 1 1 1 ] ^ ] (4,11) The r e a c t i o n s must proceed through some intermediate which i n v o l v e s a c t i v a t i o n of molecular hydrogen by Ru***. As mentioned before, t h i s process can be r e a l i z e d by e i t h e r a h e t e r o l y t i c or homplytic s p l i t t i n g mechanism. The energies r e q u i r e d f o r the h e t e r o l y t i c and homolytic s p l i t t i n g o f i n water can be estimated by means of the Born-Haber c y c l e 106 2(aq) T i e t e r o l y t i c -> H , , + H , . (aq) (aq) + V + SH" (4,12) o r i — 2 H ' f •» + E " 1 H+1 •» + H~ r i 2(g) (g) < (g) (g) where S r e f e r s to h y d r a t i o n enthalpy; the other symbols are s e l f explanatory. E h e t e r o l y t i c = ^ + ^ _ E + I + D + (S^ } = -260 - 108 - 17 + 313 + 1 0 4 + 2 k c a l = +34 k c a l - 75 -2(aq) 2(g) "homolytic -> 2H-2H-(aq) + S. (g) (4,13) "homolytic " SH- + ° + V - 2 + 1 0 4 + 2 +104 k c a l Consequently, unless two hydrogen atoms can be accepted simultaneously by some species i n s o l u t i o n , the i o n i c s p l i t t i n g should be favoured i n s o l v e n t s of high p o l a r i t y . DMA can be regarded as a moderately high 107 p o l a r solvent ( d i e l e c t r i c constant 38 at 2 0 ° ) , and i t seems l i k e l y that the i n i t i a l step i n these c a t a l y t i c reductions w i l l i n v o l v e a h e t e r o l y t i c s p l i t t i n g of hydrogen w i t h the formation of a Ru***H 24 25 intermediate as i n aqueous s o l u t i o n . ' The f i r s t - o r d e r dependence on ruthenium i s c o n s i s t e n t w i t h t h i s . A di h y d r i d e intermediate seems r a t h e r u n l i k e l y . Dihydride formation has been reported f o r square i A 8 i i , D , I 22,30 n o 60,83 . planar d complexes o n l y , such as Rh , Ru , i n an o x i d a t i v e - a d d i t i o n r e a c t i o n . Thus a mechanism i n v o l v i n g a rate-determining h e t e r o l y t i c s p l i t t i n g of by Ru*** with the formation of a metal-hydride complex, which could then reduce the sub s t r a t e i n a subsequent step, i s suggested: Ru*** + H, '1 _ III - + y Ru H + H (4,14) - 76 -R u n V + 2 R u I V —?-»- 3 R u H I + H + (4,15) I I I " 3 I I I 2Ru H + 0 2 — 2 R u + 20H (4,16) Ru***H~ + R u H I — 2 R u H + H + (4,17) The f o l l o w i n g summarizes some of the data obtained: k 5 5 M" 1S" 1 + AH kcal/mole f AS eu R u I V 1.64 19.9 + 3. .2 °2 2.29 19.3 + 2. .3 R u 1 1 1 0.04 (extrapolated value) 15.5 -16. .4 The complete rate-law f o r a mechanism of t h i s type i s r e a d i l y shown, by assuming a steady s t a t e concentration of the hydride, t o be: -d[H ] k [H +] = k ^ H R u 1 1 1 ] (1 - ^ } k_ 1[H +] + k„ , .[substrate] (4,18) The second term i n the bracket represents the competition of the hydride to react w i t h the r e d u c i b l e s u b s t r a t e or reproduce H,, from the back r e a c t i o n of (4,14). The Ru*^ and 0^ systems give e s s e n t i a l l y the same r a t e constants and a c t i v a t i o n parameters, suggesting that they o x i d i z e the Ru***H r a p i d l y ; that i s k^ and k^ are l a r g e , r e a c t i o n (4,14) i s i r r e v e r s i b l e , and the rate-law reduces to i t s simple form of (4,11); the k i n e t i c data r e f e r to k^ of r e a c t i o n (4,14). However the data f o r the Ru*** r e d u c t i o n show a r a t e constant "k^" about 50 times lower, and t h i s - 77 could r e s u l t from the r e v e r s a l of step (4,14) competing e f f e c t i v e l y w i t h step (4,17); compared with Ru*^ and 0_, Ru*** c h l o r i d e complexes are not as e f f i c i e n t an o x i d i z i n g system and i n f a c t c h l o r o r u t h e n a t e ( I I ) i s a 108 strong reducing agent. The data suggest that the term k _ 1 [ H + ] / { k _ - [ H + ] + k 4[Ru***]} i s c l o s e to u n i t y , i n f a c t about 49/50 at 55°; the k^[Ru***] term w i l l be small compared to the k ^[H +] term and the r a t e w i l l s t i l l t h e r e f o r e show a f i r s t order dependence on Ru*** as observed (Table V I ) . I f t h i s reasoning i s c o r r e c t then t h i s sytem should show an i n v e r s e a c i d dependence according to Equation (4,18) and the f a c t that the above term must be c l o s e to u n i t y gives a dependence i n v e r s e l y p r o p o r t i o n a l to [ H + ] . There i s of course some a c i d present i n i t i a l l y - from the process producing the Ru*** from Ru*^ and p o s s i b l y from the water of h y d r a t i o n of the s t a r t i n g m a t e r i a l although the f a t e of t h i s water i s u n c e r t a i n . However, the i n v e r s e a c i d dependence noted i s much l e s s than a n t i c i p a t e d from the above d i s c u s s i o n . A p o s s i b l e c o m p l i c a t i o n i s that a d d i t i o n of a c i d would a f f e c t the d i s t r i -b u t i o n of the s t a r t i n g ruthenium(III) complexes ( p a r t i c u l a r l y hydroxy species) w i t h r e s u l t i n g d i f f e r e n t a c t i v i t y . A f u r t h e r c o m p l i c a t i o n i s that i n the experiments i n v o l v i n g a d d i t i o n of a c i d , a constant i o n i c s trength i s not maintained because of the d i f f i c u l t y of f i n d i n g a s u i t a b l e i n e r t anion f o r Ru** systems; the commonly used p e r c h l o r a t e io n i s reduced by Ru**.*^ Some support f o r the c o n t r i b u t i o n of the back r e a c t i o n of r e a c t i o n (4,14) i n the Ru*** system here i s the f a c t that i n aqueous 3 M HC1 s o l u t i o n at 80°, no r e d u c t i o n of Ru*** to Ru** 24 25 i s observed at a l l over s e v e r a l hours; ' t h i s r e d u c t i o n i s promoted under the l e s s a c i d c o n d i t i o n s i n DMA. - 78 -For the a u t o c a t a l y t i c r e d u c t i o n of Ru*^ by H_ i n 3 M HC1, the t f 65° corresponding values of AH and AS are 23.1 k c a l and +6 eu (k = -1 -1 24 0.22 M S ). The r a t e of a r e a c t i o n such as (4,14) producing ions i n s o l u t i o n g e n e r a l l y increases w i t h the p o l a r i t y of the s o l v e n t ; ***"* however the d i e l e c t r i c constants f o r DMA and 3 M HC1 (estimated to be ~30**^) are probably s i m i l a r and a more important f a c t o r i s l i k e l y to be the grea t e r b a s i c s t r e n g t h ( c o o r d i n a t i n g a b i l i t y ) of the DMA molecule compared to water. DMA could a s s i s t the forward step of r e a c t i o n (4,14) by s t a b i l i s a t i o n of the rel e a s e d proton, and a l s o by a s s i s t i n g the d i s s o c i a t i o n o f the i n i t i a l octahedral ruthenium (111) complex."'"'''* 4.3. A c t i v a t i o n o f Molecular Hydrogen by Ruthenium(II) C h l o r i d e Complexes (Production of Ru*) 4.3.1. Stoichiometry DMA s o l u t i o n s of RuCl-.3H_0 were found to react at 80° w i t h a I I I f u r t h e r mole of H. per mole of Ru a f t e r the production of the Ru stage (Section 4.2.3., Figure 20). No metal was produced at the end of the r e a c t i o n . A c o n s i s t e n t r e s u l t was observed when a blue Ru** DMA s o l u t i o n (prepared by p u t t i n g RuCl_ s o l u t i o n under 1 atm H^ at room temperature f o r 15-20 hr.) was t r e a t e d w i t h H- at 80° (Figure 22); 0.5 mole per mole of Ru** was absorbed i n a p s e u d o - f i r s t - o r d e r manner, and the f i n a l s o l u t i o n was dark brown (Figure 12). The brown s o l u t i o n s could a l s o be produced by T i C l _ r e d u c t i o n of 'RuCl_' s o l u t i o n i n DMA. Proton magnetic resonance and I.R. spe c t r a of the brown s o l u t i o n s showed no metal-hydrogen bond. Thus we conclude that these s o l u t i o n s c o n t a i n u n i v a l e n t ruthenium. Time,Sec Figure 22. Rate p l o t f o r the c a t a l y t i c r e d u c t i o n of R u 1 1 by H 2 i n DMA at 80° (725 mm. H 2, 0.02 M R u 1 1 ) . Inset: p l o t of l o g f R u 1 1 ] vs. time - 80 -2Ru** + H 2 — v 2RU 1 + H + (4,19) The brown s o l u t i o n s were s e n s i t i v e to a i r and a s t o i c h i o m e t r i c o x i d a t i o n w i t h oxygen at room temperature y i e l d e d Ru***. Numerous attempts were made to i s o l a t e some ruthenium(I) complexes from the brown s o l u t i o n s but with l i t t l e success. The only previous r e p o r t s of the i s o l a t i o n of ruthenium(I) compounds concern 112 113 some r a t h e r p o o r l y c h a r a c t e r i z e d carbonyls, [Ru(C0)Br] , [Ru(CO) I] ; 114 the dimer [Ru(CO) (PMe^)] 2 a n d a dimeric species RuNOI 2L 2 (L = p y r i d i n e , b i p y r i d y l and methyldiphenylarsine) which contains a Ru-Ru bond and i o d i d e b r i d g e s . * * ^ TT-acceptor ligands such as triphenylphosphine and CO are known to s t a b i l i z e low valency s t a t e of t r a n s i t i o n metals. The '2 brown s o l u t i o n s d i d react w i t h CO to give Ru*(CO) (Chapter V I I I ) but no Ru* s o l i d complexes could be i s o l a t e d . A d d i t i o n of benzene to a concentrated ruthenium(I) s o l u t i o n i n the presence of about 4 f o l d excess PPh,, y i e l d e d a dark s o l i d (Elemental a n a l y s i s Ru, 51.38%; C l , 27.25%; C, 15.19%; H, 2.98%) which has a r a t i o of Cl/Ru = 3/2. The I.R. spectrum of t h i s s o l i d showed the absence of any PPh., or metal-hydride. The s o l i d could be r e d i s s o l v e d i n DMA to produce the o r i g i n a l brown s o l u t i o n . An E.S.R. spectrum of the s o l i d d i d not g i v e any appreciable s i g n a l and a s u s c e p t i b i l i t y measure-M ment gave a small but s i g n i f i c a n t v a l u e , ( x ' M = 253 x 10 ^ c.g.s.) 7 which could be c o n s i s t e n t w i t h a s p i n - p a i r e d d system w i t h metal-metal v 115 bonding. A d d i t i o n of ether to the benzene f i l t r a t e remaining, a f t e r 51 -removal of the dark product, slowly y i e l d e d a grey s o l i d . The I.R". spectrum of t h i s grey s o l i d (KBr d i s c ) showed the presence of PPh- and a l s o a CO band ( v = 1956 cm - 1) (melting p o i n t % 175°). Elemental a n a l y s i s gave Ru, 23.10%; C l , 16.44%; C, 50.04% and H, 3.86%, showing two c h l o r i d e s per Ru and i n d i c a t i n g the p o s s i b i l i t y o f a ruthenium(II) complex, formed by a i r o x i d a t i o n . The source of the carbonyl group i s of i n t e r e s t . Carbonyl a b s t r a c t i o n r e a c t i o n s are w e l l known (Chapter I S e c t i o n 1.3.7.), and have been observed f o r simple c h l o r o r u t h e n a t e ( I I ) complexes*^ and triphenylphosphine complexes of r u t h e n i u m ( I I ) T h e o r i g i n a l brown Ru* s o l u t i o n s show no carbonyl band i n the I.R. and so the source of the carbonyl i s most l i k e l y the ether added during the s e p a r a t i o n procedure. Such a b s t r a c t i o n s from ethers have been reported , 116 p r e v i o u s l y . In view of the recent reports concerning the production of molecular complexes of t r a n s i t i o n metals - i n p a r t i c u l a r the produc-t i o n of a complex formed by bubbling N- through s o l u t i o n s of some ruthenium triphenylphosphine complexes (thought to be Ru**),**' ? the brown s o l u t i o n s w i t h and without added PPh- were subjected to N_ and N2/H- mixtures at temperatures up to 80°. No r e a c t i o n was observed however, and no metal-nitrogen s t r e t c h was observed i n the I.R. of the r e s u l t i n g s o l u t i o n s . 4.3.2. K i n e t i c s of the Hydrogen Reduction of Ruthenium(II) i n ; DMA The uptake of hydrogen was found to obey the second-order rate-law: " d ^ H 2 ^ 1 d [ R u H ] . r n II l r„ 1 r A O A V - _• 1 _ t J = k.[Ru ][H_] (4,20) dt - 82 -where i s a second-order r a t e constant. Values o f k^ were determined using Equation (4,20) from the slopes of f i r s t - o r d e r l og p l o t s such as that depicted i n Figure 22. The k i n e t i c r e s u l t s are summarized i n Table V I I I . The average value o f k j was found to be 0.17 M - 1S~ 1 at 80° (compared to % 0.1 M  lS * obtained i n Se c t i o n 4.2.3. where the solvent was not p u r i f i e d ) . A k i n e t i c isotope e f f e c t was observed, k^/k^ = 3. There was no s i g n i f i c a n t a c i d dependence. A good Arrhenius p l o t was obtained from k i n e t i c measurements over the temperature range of 60 -80° (Table IX, Figure 23), and y i e l d e d * i * ti-the a c t i v a t i o n parameters AH = 16.6 t 1.0 kcal/mole and AS = -13.2 t 2.0 eu. The e f f e c t of added c h l o r i d e on the r e a c t i o n r a t e i s shown i n Table X and Figure 24. The r a t e constant shows a sharp decrease i n added C l up to about 0.05 M and then increase and passes through a maximum at about 1.0 M added C l . Unfortunately the i o n i c s t r e n g t h of the s o l u t i o n could not be maintained constant i n these experiments i n I I 109 i n v o l v i n g Ru 4.3.3. D i s c u s s i o n The k i n e t i c s of the r e a c t i o n are s i m i l a r to those observed i n r e a c t i o n s i n v o l v i n g a c t i v a t i o n of by Ru(III ) and again suggest the formation of a hydride intermediate i n a rate-determining step, R u 1 1 + H —U. R u n H ~ + H + (4,21) R u H H + R u H ^ 2RU 1 + H + (4,22) - 83 -Table V I I I C a t a l y t i c r e d u c t i o n of Ru** by H. i n DMA K i n e t i c data at 80° I I * [Ru ] H 2 [H 2] k l x 10 2, M mm. x l u \ M + M-*S-* 2.05 200 0.64 0.23 2.05 309 0.99 0.17 2.05 408 1.30 0.17 2.05 551 1.76 0.15 2.05 651 2.08 0.17 2.05 725 2.32 0.18 2.10 725 2.32 0.17 a 2.10 725 2.32 0.06 b 1.54 408 1.30 0.18 1.03 408 1.30 0.16 1.03 408 1.30 0.19 0.51 408 1.30 0.17 * I I Ru prepared by the r e a c t i o n of on RuCl_ DMA s o l u t i o n s at room temperature f o r 15-20 hrs. a 0.068 M p-toluene sulphonic a c i d . D„ i n pl a c e of H - 84 -Table IX C a t a l y t i c r e d u c t i o n of Ru** by i n DMA Temperature dependence of k^ [Ru**] = 2.05 x 10" 2 M Temperature [H^] k^ °C x 10 3, M M"*S" 80 1.30 0.17 75 1.29 0.12 70 1.25 0.09 65 1.25 0.06 60 1.20 0.04 - 86 -Table X C a t a l y t i c r e d u c t i o n of Ru* 1 by i n DMA E f f e c t o f c h l o r i d e on r e a c t i o n r a t e s at 80° [Ru 1 1] = 2.05 x 10" 2 M [H ] = 1.30 x 10" 3 M [ L i C l ] kl [ L i C l ] k_ M M" 1S" 1 M M _ 1 S _ 1 0.02 0.10 0.50 0.10 0.04 0.07 1.00 0.13 0.05 0.04 1.50 0.12 0.10 0.05 2.00 0.10 0.30 0.09 2.50 0.09 - 87 -0.20 0.15 h 0.10 0-05 0.0 Figure 24. Effect of added chloride on the rate of reduction of Ru in DMA at 80° (2.05 x 10~2 M Ru 1 1 408 mm. H ). - 88 -Further data given i n Chapter VII (Section 7.2.) confirm t h i s h e t e r o l y t i c s p l i t t i n g mechanism. The absence of an a c i d dependence suggests t h a t k 2 > > k 1' * n o t n e : r s i - m i l a r systems i n v o l v i n g h e t e r o l y t i c s p l i t t i n g o f 25 the H-, i n c l u d i n g the aqueous c h l o r o r u t h e n a t e ( I I I ) system, very small isotope e f f e c t s have been observed, and t h i s has been i n t e r p r e t e d as metal hydride formation and hydrogen breaking o c c u r r i n g i n a concerted step. The k i n e t i c isotope e f f e c t of about 3 here suggests that greater d i s s o c i a t i o n of the H-H bond i s important, p r i o r to formation of the a c t i v a t e d complex; t h i s may r e f l e c t a somewhat weaker metal hydrogen bond i n a ruthenium(II) system compared to the ruthenium(III) system. The e f f e c t of c h l o r i d e v a r i a t i o n i s probably due to two f a c t o r s . H e n r y , 5 5 measuring the r a t e of o x i d a t i o n of ethylene by aqueous p a l l a d i u m ( I I ) c h l o r i d e s o l u t i o n s , a l s o found a remarkably s i m i l a r depend-ence of the r a t e on the c h l o r i d e i o n concentrations and a t t r i b u t e d the i n i t i a l decrease i n r a t e to the presence of d i f f e r e n t chloro complexes, and the remaining v a r i a t i o n to s a l t e f f e c t s . Such e f f e c t s could w e l l e x p l a i n the data of the present system. The present work i s the f i r s t to give d i r e c t evidence f o r the e x i s t e n c e of thermodynamically s t a b l e Ru* complexes i n s o l u t i o n . However, i t s presence has sometimes been p o s t u l a t e d i n aqueous systems. Ru** i n d i l u t e HC1 s o l u t i o n was found to r e a c t w i t h H- s l o w l y at 80° to g i v e 118 metal. Grube and Nann found that r e d u c t i o n of ruthenium t r i c h l o r i d e i n h y d r o c h l o r i c a c i d with z i n c proceeded to the d i v a l e n t s t a t e i n concentrated a c i d , but i n d i l u t e a c i d metal r e s u l t e d and t h i s was thought to be due to d i s p r o p o r t i o n a t i o n of Ru*: 2Ru* * Ru** + Ru° (4,23) - 89 -The standard r e d u c t i o n p o t e n t i a l of the r e a c t i o n R u 1 1 + e Ru 1 (4,24) was estimated to be i n the range ^ -0.04 v o l t s . However, l a t e r s t u d i e s 119 by Dwyer et a l . suggested that ruthenium(I) d i d not e x i s t i n aqueous s o l u t i o n . 120 Adamson has r e c e n t l y suggested that h i g h l y l a b i l e ruthenium(I) may be extremely a c t i v e i n c a t a l y z i n g the i s o t o p i c exchange r e a c t i o n : R u C l 6 3 " + 3 6 C 1 --—>- R u C l 5 3 6 C l 3 " + C l (4,25) i n HC1 s o l u t i o n , although no evidence f o r i t s existence was found. I t seems that the solvent plays an important r o l e i n producing and hence s t a b i l i z i n g the u n i v a l e n t ruthenium complexes. In aqueous a c i d s o l u t i o n s the reverse of r e a c t i o n (4,21) prevents the e f f e c t i v e r e d u c t i o n of Ru**. In the more b a s i c DMA the r e l e a s e d proton i s s t a b i l i z e d and the forward r e a c t i o n i s a s s i s t e d , j u s t as the production of Ru** from Ru*** i s promoted (Section 4.2.4.). DMA must be coordinated to the Ru* species i n s o l u t i o n . A number of t r a n s i t i o n metal complexes have been prepared 121-127 which c o n t a i n coordinated DMA although none have been reported f o r ruthenium. Coordination i s u s u a l l y through the oxygen atom although 127 121 DMA can act as a b i d e n t a t e l i g a n d . Lantzke and Watts suggested that the s t r e n g t h of some solvents as ligands to be H 20 = DMA << DMF < DMSO - 90 -122 However according to Gutmann, the donor str e n g t h of DMA i s gre a t e r than f o r water. The i n f l u e n c e of the organic solvent may be thermo-dynamic i n character - due to change i n the c a t a l y t i c a c t i v i t y of Ru**,' e.g., to changes of the e f f e c t i v e charge on Ru**, or k i n e t i c i n character due to changes of the r a t e o f the s u b s t i t u t i o n process (4,21). No q u a n t i t a t i v e redox p o t e n t i a l data are a v a i l a b l e for the e s t i m a t i o n o f an e q u i l i b r i u m such as (4,23). In aqueous systems such a d i s p r o p o r t i o n a t i o n could occur through a H atom t r a n s f e r mechanism as has been suggested 128 f o r a number of e l e c t r o n t r a n s f e r r e a c t i o n s between metal aquo i o n s ; such a mechanism would be r u l e d out i n a solvent such as DMA. CHAPTER V RUTHENIUM(I) CHLORIDE CATALYZED HYDROGENATION OF OLEFINIC COMPOUNDS IN DMA 5.1. I n t r o d u c t i o n During the i n v e s t i g a t i o n o f the a c t i v a t i o n of molecular hydrogen by ruthenium c h l o r i d e complexes, the formation of the brown ruthenium(I) s o l u t i o n s was observed. These s o l u t i o n s were then s t u d i e d to see i f they were a c t i v e c a t a l y t i c a l l y f o r the hydrogenation of o l e f i n i c compounds. The brown s o l u t i o n s could be prepared from hydrogen red u c t i o n of R u * \ Ru*** or Ru**, and were thus themselves v i s i b l y I I I u n r e a c t i v e towards hydrogen; however, s o l u t i o n s of Ru i n aqueous HC1 are u n r e a c t i v e towards H^ but do show a c t i v i t y i n the presence of 24 su b s t r a t e s . This Chapter describes these s t u d i e s ; c a t a l y z e d hydro-, genation of o l e f i n i c compounds was observed and the k i n e t i c s and mechanism of the r e a c t i o n were i n v e s t i g a t e d i n DMA s o l u t i o n and are presented here. 5.2. The Ruthenium(I) C h l o r i d e - M a l e i c and Fumaric A c i d Systems i n DMA In dimethylacetamide, ruthenium(I) c h l o r i d e complexes, prepared by r e d u c t i o n of RuCl^ w i t h H^, were found to be e f f i c i e n t c a t a l y s t s f o r the homogeneous hydrogenation of maleic and fumaric acids at ambient - 92 -temperatures and hydrogen pressures of 1 atm or l e s s . Figures 25 and 26 show t y p i c a l gas uptake p l o t s at 80° f o r a v a r i e t y of ruthenium concentrations and pressures f o r the maleic a c i d system. The r e a c t i o n r a t e showed a c o n t i n u a l f a l l o f f but around 1500 sec decreased r a t h e r more sharply than might have been expected. The curves beyond about 1500 sec gave a good p s e u d o - f i r s t - o r d e r l o g p l o t at constant H- pressure (Figure 25) f o r the su b s t r a t e c o n c e n t r a t i o n ( i n i t i a l maleic a c i d c o n c e n t r a t i o n 0.022-0.11 M). When fumaric a c i d was used as a s u b s t r a t e , no sharp d i s c o n t i n u i t y i n the uptake p l o t , which showed a good f i r s t -order dependence on F.A. at low [F.A.], was observed (Figure 27). Ge n e r a l l y there was a short i n d u c t i o n p e r i o d of about 100-200 seconds no matter which su b s t r a t e a c i d was used. The t o t a l hydrogen uptake agreed w e l l with the s t o i c h i o m e t r y f o r complete r e d u c t i o n of the o l e f i n present. No metal was produced and the s u c c i n i c a c i d was i s o l a t e d and i d e n t i f i e d . No uptake was observed, of course, i n the absence of maleic (or fumaric) a c i d . The v i s i b l e absorption spectrum of a f r e s h l y prepared ruthenium(I) c h l o r i d e s o l u t i o n i s shown i n Figure 3. The sp e c t r a a t - a s e r i e s of concentrations do not f o l l o w Beer's law. For a 2.1 x 10 M I -2 Ru s o l u t i o n , E = 435 at 500 my; but f o r a 0.01 x 10 M s o l u t i o n e = 700. These data together with the data on the s o l i d i s o l a t e d from these s o l u t i o n s (Section 4.3.) i n d i c a t e that ruthenium(I) c h l o r i d e i s present i n DMA s o l u t i o n as a dimer —>* monomer e q u i l i b r i u m , the dimer having c h l o r i d e bridges and p o s s i b l y a Ru-Ru bond. There was no evidence f o r the formation of a Ru*-maleic a c i d complex as the absorption spectrum remained unchanged when excess of maleic a c i d was added to a Ru* s o l u t i o n . Time,Sec Figure 25. Rate p l o t s f o r the ruthenium(I) c h l o r i d e c a t a l y z e d hydrogenation of maleic a c i d i n DMA at 80° (725 mm. H 2 0.051 M maleic a c i d ) . Ru: (0) 2.1 x 10"2M; ( A ) 0.26xl0~ 2M; (D)ptot< log[M.A.]. vs.' time (Ru 1 = 2.1 x 10" 2 M). [F.A.] estimated to be ^ 3.2 x 1 0 - 2 M. 0 2000 4000 6000 8000 10,000 Time,Sec Figure 26. Rate p l o t s f o r the ruthenium(I) c h l o r i d e c a t a l y z e d hydrogenation of maleic a c i d i n DMA at 80°. (0.53 x 10~2 M Ru 1, 0.051 M maleic a c i d ) . H 2: (0) 725 mm.; ( A ) 2 0 0 mm. - 96 -An N.M.R. proton spectrum and I.R. spectrum of a s u f f i c i e n t l y concentrated s o l u t i o n from a maleic a c i d hydrogenation r e a c t i o n gave no metal-hydrogen bond s i g n a l , i n d i c a t i n g no dete c t a b l e ruthenium hydride species. However t h i s observation does not r u l e out e q u i l i b r i a such as Ru 1 + H 2 - j - * R u I I I h 2 t 5 ' 1 ) Ru 1 + H --—+• RulH~ + H + (5,2) 2Ru J + H ^ 2 R u H H (5,3) which could l i e e s s e n t i a l l y completely to the l e f t . Thus the v i s i b l e s p e c t r a o f the brown s o l u t i o n s remained e s s e n t i a l l y constant throughout the c a t a l y t i c hydrogenation experiments. Ru* d i d not react with C^H^ at 80° and 1 atm t o t a l pressure, although uptake was observed with a mixture of ll and C^H^ at 80° -i n d i c a t i n g hydrogenation to ethane. The r a t e p l o t was e s s e n t i a l l y l i n e a r (rate = 0.54 x 10" 6MS - 1 with 2.10 x 1 0 _ 2 M Ru*, 430 mm. and 294 mm. H^). Again no change i n colour and v i s i b l e a bsorption spectrum of the s o l u t i o n were observed, and the pseudo-zero-order l i n e a r p l o t i s con-s i s t e n t with a constant [Ru*], while maintaining the H 2 and C^H^ pressures and concentrations constant i n the uptake apparatus. 5.3. K i n e t i c Measurements The gas uptake p l o t s f o r the hydrogenation of maleic a c i d c l e a r l y d i d not f i t e i t h e r f i r s t - o r d e r or second-order k i n e t i c s . The l i n e a r p l o t s of l o g [ o l e f i n ] vs. time were obtained from the l a t e r - 97 -regions of the uptake p l o t and the p s e u d o - f i r s t - o r d e r r a t e constants k' evaluated - these values are thought (Section 5.3.2.) to r e f e r to the hydrogenation of fumaric a c i d (Table XIV). The i n i t i a l r a t e s of the uptake p l o t s could be measured with reasonable accuracy and these r e f e r to the hydrogenation o f maleic a c i d (Tables XI and X I I ) . For the hydrogenation of fumaric a c i d , the uptake p l o t s analyzed f o r simple p s e u d o - f i r s t - o r d e r r e a c t i o n s only at lower fumaric _2 a c i d concentrations (< 5.2 x 10 M), and the k' values are given i n Table X I I I . At higher fumaric a c i d c o n c e n t r a t i o n s , good l o g p l o t s were not obtained and consequently the i n i t i a l r a t e s were taken (Table X I I I ) . 5.3.1. The M a l e i c A c i d System The i n i t i a l r ates of hydrogenation of maleic a c i d have been measured and the dependence on c a t a l y s t c o n c e n t r a t i o n , pressure, substrate c o n c e n t r a t i o n , c h l o r i d e , a c i d (Table XI) and temperature (Table XII) were i n v e s t i g a t e d . The p l o t showing the i n i t i a l r a t e of hydrogenation of maleic a c i d against the ruthenium(I) c h l o r i d e c o n c e n t r a t i o n i s shown i n Figure 28. The r a t e does not increase l i n e a r l y with i n c r e a s i n g c a t a l y s t c o ncentration. The p l o t of t h i s i n i t i a l r a t e against the square root of the c a t a l y s t c o n c e n t r a t i o n (Figure 29) i s l i n e a r and passes through the o r i g i n , showing a h a l f - o r d e r dependence on ruthenium. The dependence of the i n i t i a l r a t e on hydrogen pressure can be seen from Figure 30. I t shows a good f i r s t - o r d e r dependence at l e a s t - 98 -Table XI Ruthenium(I) c h l o r i d e cata lyzed hydrogenation of maleic a c i d i n DMA K i n e t i c data o f i n i t i a l rate at 8 0 ° [Ru 1] H 2 [H 2] [M.A.] I n i t i a l rate x 1 0 2 , M mm. x 1 0 3 , M x 1 0 2 , M x 1 0 5 , MS" 1 2.10 725 2.32 5.10 4.75 1.05 725 2.32 5.05 3.13 0.53 725 2.32 5.05 2.49 0.26 725 2.32 5.05 1.75 0.11 725 2.32 5.05 0.99 0.53 651 2.08 5.00 2.18 0.53 400 1.28 5.05 • 1.52 0.53 200 0.64 5.10 0.87 0.53 725 2.32 2.13 1.16 0.53 . 725 2.32 3.25 1.73 0.53 725 2.32 6.50 2.70 0.53 725 2.32 10.90 3.68 0.53 725 2.32 5.30 1 .72 a 0.53 725 2.32 5.05 1.73 b 0.53 725 2.32 5.00 1.42 C 0.53 725 2.32 5.00 1.20 d 0.53 725 2.32 5.00 0.82 G 0.53 725 2.32 4.90 2 .28 £ 0.53 725 2.32 5.10 2 .37 g a D 2 i n p lace o f H b 0.013 M L i C l ° 0.026 M L i C l d 0.05 M L i C l 0.10 M L i C l 0.05 M p-toluene sulphonic ac id & 0.10 M p-toluene sulphonic ac id - 99 -Table XII Ruthenium(I) chl o r i d e catalyzed hydrogenation of maleic acid i n DMA Temperature dependence of i n i t i a l rate [Ru 1] = 0.53 x 10" 2 M Temperature [H^] [M.A.] I n i t i a l rate °C x 10 3, M x 10 2, M x 10 5, MS - 1 80 2. .32 . 10. .90 3, .68 6. .50 2 .70 5. .05 2, .49 3. .25 1, .73 2. .13 1, .16 70 2. .22 10. .50 2, .85 - 6. .57 2, .35 2. .18 1. .02 60 2. .18 10. .20 2. .57 5. ,10 1. ,71 2. ,85 1. ,18 5.0 - 100 -_ •r-l c 4.0 3 . 0 U 2 . 0 L 1.0L 0.0_)_ l I | I 0.0 0.5 1.0 1.5 2.0 [ R u 1 ] * !02> M Figure 28. Dependence of i n i t i a l r a t e of hydrogenation of M.A. i n DMA on [Ru 1] at 80°. (725 mm. H2-, 0.051 M maleic a c i d ) . Figure 29. Dependence of i n i t i a l r a t e of hydrogenation o f M.A. i n DMA on [ R u 1 ] 1 / 2 at 80°. (725 mm. H 2, 0.051 M maleic a c i d ) . - 101 -- 102 -at l e a s t up to 725 mm. H . A k i n e t i c isotope e f f e c t (R^/R-) of 1.35 Z n L) was observed. The dependence of the i n i t i a l r a t e s on maleic a c i d concentra-, t i o n i s shown i n Figure 31. The r a t e s do not increase l i n e a r l y w i t h i n c r e a s i n g o l e f i n concentration but approach asymptotic v a l u e s , i n d i c a t i n g between a zero and f i r s t - o r d e r dependence on the o l e f i n . A marked inverse dependence on added c h l o r i d e c o n c e n t r a t i o n was noted over the range 0-0.1 M and a reasonably l i n e a r p l o t was obtained on p l o t t i n g ( i n i t i a l r a t e ) 1 against [ C l - ] " A ( F i g u r e 32). Unf o r t u n a t e l y , the t o t a l s a l t s t r e n g t h could not be kept constant i n these experiments. A d d i t i o n of p-toluene sulphonic a c i d (a strong acid) up to 0.1 M had e s s e n t i a l l y no e f f e c t on the i n i t i a l r a t e . 5.3.2. The Fumaric A c i d System The r a t e of H. uptake i n the l a t e r r e g i o n of the maleic. a c i d system corresponded to the se p a r a t e l y s t u d i e d r a t e of hydrogenation o f * fumaric a c i d (compare s t a r r e d data i n Tables X I I I and XIV). I t was thus concluded that maleic a c i d isomerized to the more s t a b l e fumaric a c i d during the e a r l i e r stages of the hydrogenation r e a c t i o n s , and hence the r a t e measured i n the l a t e r r e gion r e f e r s to the hydrogenation of fumaric a c i d (Table XIV). A p l o t of k' f o r the hydrogenation of fumaric a c i d against the ruthenium(I) c h l o r i d e concentration i s shown i n Figure 33 (Table XIV). Again i t shows a h a l f - o r d e r dependence on the c a t a l y s t concentra-t i o n (Figure 34). - 103 -4.0 i :  Figure 31. Dependence of i n i t i a l r a t e of hydrogenation of M.A. i n DMA on [M.A.]. (0.53 x 10~ 2 M Ru 1). (0) 80°, 725 mm. H2; (A) 70°, 737 mm. H 2; ( • ) 60°, 725 mm. H2. - 104 -Figure 32. Inverse dependence of i n i t i a l r a t e of hydrogenation of M.A. i n DMA on [ L i C l ] at 80°. (725 mm. H 2, 0.53 x 1 0 - 2 M Ru 1, 0.05 M M.A.). - 105 -Table X I I I Ruthenium(I) c h l o r i d e c a t a l y z e d hydrogenation of fumaric a c i d i n DMA K i n e t i c data at 80° [Ru 1] H- [H ] [F.A.] k* I n i t i a l r a t e x 10 2, M mm. x 10 i 3 , M x 10 i 2 , M 4 -1 x 10 , S x 10 -6, MS"1 0.53 725 2. 32 15. 60 - 11. 10 0.53 725 2. 32 10. 70 - 6. 45 # 0.53 725 2. 32 7. 25 - 7. 97 0.53 725 2. 32 5. 17 * 1.20 6. 21 0.53 725 2. 32 3. 00 1.36* 4. 10 0.53 725 2. 32 1. 80 * 1.23 2. 21 D- i n p l a c e of H-. * * To be compared with the s t a r r e d values i n Table XIV. - 106 -Table XIV Ruthenium(I) c h l o r i d e c a t a l y z e d hydrogenation o f fumaric a c i d i n DMA K i n e t i c data of the l a t e r r e g ion of maleic a c i d uptake p l o t s at 80° [Ru 1] H 2 [H 2] [ F . A . ]+ k' 1 I n i t i a l r a t e x 10 2, M mm. x 10 3, M x 10 2, M 4 -1 x 10 , S x 10 6,MS _ 1 2.10 725 2. .32 3.20 2. ,05 6 .56 1.05 725 1 2. 32 2.80 1. ,52 4. .25 0.53 725 2. 32 2.75 1. ,02 2, .80 0.26 725 2. ,32 2.30 0. .92 2, .12 0.11 725 2. ,32 2.40 0. ,59 1 .41 0.53 651 2. 08 2.90 1. .12 3, .25 0.53 400 1. ,28 2.70 0. ,73 1, .97 0.53 200 0. 64 2.90 0. .39 1. .15 0.53 725 2. ,32 1.50 1. .21 1, .82 0.53 725 2. ,32 2.10 1. ,26 2, .65 0.53 725 2. 32 3.95 1. * ,30 5, .15 0.53 725 2. ,32 5.40 1. * ,28 6. .90 0.53 725 2. ,32 3.25 1. .23 3, .98 a 0.53 725 2. ,32 2.80 0. ,63 1, ,76 b 0.53 725 2. 32 2.80 0. ,41 1. ,18 C 0.53 725 2. 32 2.50 0. ,30 0. ,75 d 0.53 725 2. 32 2.55 0. ,18 0. ,45 6 0.53 725 2. ,32 2.65 1. ,15 3, ,05 f 0.53 725 2. .32 2.55 1, ,31 3. ,35 g [F.A.] estimated from the p l o t of log[M.A.] vs. time, e.g., Figure 25. C a l c u l a t e d from the k' value and substrate c o n c e n t r a t i o n . * * To be compared with the s t a r r e d values i n Table X I I I . a D 2 i n place of H 2 b 0.013 M L i C l ° 0.026 M L i C l d 0.05 M L i C l e 0.10 M L i C l f 0.05 M p-toluene sulphonic a c i d g 0.10 M p-toluene sulphonic a c i d . - 107 -2.0 1.0 Figure 34. Dependence of r a t e of hydrogenation of F.A. on [Ru 1] at 80° i n DMA. (725 mm. H_, 0.025 M F.A.). - 108 -The p l o t of k' vs. hydrogen concentration (Figure 35) shows a good f i r s t - o r d e r dependence on hydrogen. The r a t i o of the r a t e of r e d u c t i o n using hydrogen to that of deuterium i s approximately u n i t y at lower F.A. concentrations (Table XIV) but at higher concentrations appears to be about 1.50 (Table X I I I ) . The dependence of the i n i t i a l r a t e ( c a l c u l a t e d from k' values or measured) on the fumaric a c i d c o n c e n t r a t i o n i s shown i n Figure 36. I t i s s i m i l a r to that f o r the maleic a c i d system being f i r s t - o r d e r at lower fumaric a c i d c o n c e n t r a t i o n and becoming zero-order at higher concentrations. This dependence c l e a r l y shows why good f i r s t - o r d e r log p l o t s are not obtained at the higher o l e f i n c o n c e n t r a t i o n s . As i n the maleic a c i d system, an inverse dependence on c h l o r i d e c o n c e n t r a t i o n was observed (Figure 37); the r a t e was not s i g n i f i c a n t l y a f f e c t e d on adding a strong a c i d . 5.4. D i s c u s s i o n of K i n e t i c Results A c t i v a t i o n of hydrogen must occur by processes such as (5,1), (5,2), or (5,3) (Section 5.2.). The l a s t of these can be r u l e d because of the observed dependence on ruthenium. Reaction (5,2) i s c e r t a i n l y p o s s i b l e i n a p o l a r solvent such as DMA and i n f a c t the r e a c t i o n s discussed i n the previous chapter are thought to occur through such a h e t e r o l y t i c s p l i t t i n g . However the observed dependence on o l e f i n taken together w i t h the independence on a c i d are c o n s i s t e n t only wit h r e a c t i o n (5,1) f o r a c t i v a t i o n of hydrogen (see l a t e r ) . The t r a n s f e r of the hydrogen molecule to the o l e f i n i n s o l u t i o n v i a a c a t a l y s t complex species i s thought to occur by e i t h e r one or both - 109 -- I l l -Figure 37. Inverse dependence of r a t e of hydrogenation of F.A. on [ L i C l ] at 80° i n DMA. (725 mm. H 2, 0.53 x 10" 2 M Ru 1, 0.027 M F.A.). - 112 -13 30 32 of two p o s s i b l e paths: ' ' (1) att a c k o f uncomplexed o l e f i n on the dihydrido-complex at a vacant s i t e to give a t r a n s i t i o n s t a t e i n which both hydrogen and o l e f i n are bound to the metal atom; (2) attack of molecular hydrogen on an o l e f i n complex to give the same t r a n s i t i o n s t a t e . The ruthenium(I) c h l o r i d e s o l u t i o n s almost c e r t a i n l y c o n t a i n some dimeric species and the k i n e t i c dependence on ruthenium supports t h i s . The k i n e t i c data alone are c o n s i s t e n t w i t h a dimer monomer p r e - e q u i l i b r i u m followed by r e a c t i o n of the monomeric Ru species w i t h H- or o l e f i n according to the f o l l o w i n g scheme: R 1 K ° R u 2 ^ 2Ru k I Ru + H 1 2 Ru HV K2 o l e f i n Ru ( o l e f i n ) 2. o l e f i n -*- Ru + p a r a f f i n H, (Ligands being omitted) Scheme VI The i n i t i a l short i n d u c t i o n p e r i o d observed could be r e l a t e d to the establishment of the p r e - e q u i l i b r i u m . The k_ and k_ paths are i n d i s t i n g u i s h a b l e k i n e t i c a l l y i f the e q u i l i b r i a and are set up q u i c k l y s i n c e the r a t e of hydrogen uptake i s given by: - 113 -•d[H 2] ( k ^ • ^ [ H ^ t M . A . l f R u 1 ] (5,4) DT 1 + V m- a- ] + v H 2 ] + ^"^{o^ys This i s the expression f o r r e a c t i o n by both paths; the k^K^ and k^K^ terms r e f e r r e s p e c t i v e l y to the k 2 and k^ paths; k^K^ becomes zero i f the k 2 path predominates and v i c e v e r s a . The terms i n the denominator, taken from l e f t to r i g h t , represent the amounts present as monomer, o l e f i n complex, hydride complex and dimer r e s p e c t i v e l y . The observed f i r s t -order dependence on i m p l i e s that the K^[H 2] term i s small which means that Ru***H2 w i l l not be d e t e c t a b l e ; however between zero and f i r s t -order dependence on o l e f i n i m p l i e s that the K2[M.A.] i s s i g n i f i c a n t and t h a t there i s an appreciable c o n c e n t r a t i o n of the o l e f i n complex i n I s o l u t i o n . However the Ru s o l u t i o n s do not re a c t with maleic a c i d or ethylene and the spectrum of the r e a c t i n g s o l u t i o n remained unchanged throughout a k i n e t i c run. A l l the observations can be accounted f o r i f the r e a c t i o n occurs s o l e l y by the k 2 path with the hydride formation not being a r a p i d e q u i l i b r i u m , i . e . I KD I R u 2 2 R u ( 5 ' 5 ) R u I + H2 ~ — R u I H H 2 + (Cl") (5,6) R u n i H + o l e f i n — ^ Ru 1 + product (5,7) Such a mechanism assuming a steady s t a t e concentration of Ru***^ y i e l d s the r a t e law: - 114 -Rate -d t H 2 ] dt . I T 1/2 - d [ o l e f i n ] dt k l k 2 K D ^ R u I t o t a l t 0 1 ^ 1 " 1 ^ k j^CCl"] + k . [ o l e f i n ] (5,8) 1/2 I where K' = (K /2) ' and [Ru ] i s the t o t a l ruthenium(I) c h l o r i d e L) 1J "co"ca.x co n c e n t r a t i o n expressed i n terms of m o l e s / l i t r e of Ru monomer. The d e r i v a t i o n of t h i s rate-law g i v i n g the h a l f order i n ruthenium i n v o l v e s the assumption that K_ i s s m a l l , that i s , p r a c t i c a l l y a l l the ruthenium i s present as dimer at the concentrations used i n the k i n e t i c runs. Since no uptake i s observed i n the absence of o l e f i n k_^ must be greater than k^. Reaction (5,7) i s w r i t t e n i n v o l v i n g a molecular d i h y d r i d e s i n c e a h e t e r o l y t i c s p l i t t i n g of would give proton production and such a mechanism would give an i n v e r s e dependence of the r a t e on added a c i d at lower o l e f i n c o n c e n t r a t i o n s ; t h i s was not observed. Evidence f o r the production of a ruthenium(LTI) hydride species i n the presence of triphenylphosphine i s given i n the next chapter. Reaction (5,6) w i l l i n v o l v e displacement of Cl or solvent l i g a n d ; the rate-law (5,8) has been w r i t t e n assuming the former (Section 5.4.3.). I f a solvent molecule i s i n v o l v e d k _ , [ C l ] w i l l be replaced by k_^[solvent] or k^. 5.4.1. Dependence of the Rate on Substrate Concentration Equation (5,8) can be w r i t t e n i n the form Rate k . j t C l ] 1 [ o l e f i n ] k ^ ' f H - H R u 1 ] 1 7 2 t o t a l (5,9) - 115 -Thus a p l o t o f 1/rate against 1 / [ o l e f i n ] at constant [U^] and t R u I ] t o t a i should y i e l d a s t r a i g h t l i n e from which k^K^ and k_^[CT ] A 2 can be c a l c u l a t e d from the i n t e r c e p t and the slope r e s p e c t i v e l y . Figure 38 shows such p l o t s which give good s t r a i g h t l i n e s . Values of these constants are summarised i n Table XV f o r three d i f f e r e n t temperatures. At very high o l e f i n c oncentration the rate-law becomes Rate = k ^ t R u 1 ] ^ r p y (5,10) The data f o r the fumaric a c i d system (Figure 36) do approach t h i s l i m i t i n g r a t e % 12 x 10 ^ MS * and gives k^K^ % 0.7 S * which agrees reasonably w e l l w i t h the value from the l i n e a r p l o t i n Figure 38. The k^K^ values determined from the l i n e s drawn are e s s e n t i a l l y independent of the two o l e f i n s used and t h i s gives strong support f o r the suggested mechanism, although these values are very s e n s i t i v e to the i n t e r c e p t value. k 2 f o r the maleic a c i d i s about four times that f o r the fumaric a c i d system. 5.4.2. Dependence on Temperature An Arrhenius p l o t of log k^K^ vs. T * gives a reasonably good s t r a i g h t l i n e (Figure 39). The observed temperature dependence of t h i s composite constant (k^K^) i s most l i k e l y due p r i m a r i l y to the k^ term, since e q u i l i b r i u m constants are g e n e r a l l y very much l e s s temperature dependent. From the h a l f - o r d e r dependence on Ru, even at the lowest 1 - 3 -5 [Ru ] used ('v 10 M), the upper l i m i t of K Q must be ^ 10 M; hence the lowest value of k.. i s ^ 100 M *S * at 80°. The a c t i v a t i o n parameters - 116 -0.0 0.2 0.4 0.6 [ o l e f i n ] - 1 x 10~ 2, M~ Figure 38. Dependence of i n i t i a l r a t e on the o l e f i n c o n c e n t r a t i o n p l o t t e d i n accord w i t h Equation (5,9). M a l e i c a c i d : (0) 80°; (A) 70°;. ( O ) 60°, 0.53 x 10" 2 M Ru 1, 725 mm. H,. Fumaric a c i d ( • ) 80°, 0.53 x 10" 2 M Ru 1, 725 mm. H2. - 117 -Table XV Ruthenium(I) c h l o r i d e c a t a l y z e d hydrogenation of o l e f i n i c compounds i n DMA Temperature dependence of some k i n e t i c data [Ru 1] , = 0.53 x 10" 2 M [ H J = 725 mm. 1 J t o t a l 2 Temperature Substrate k ^ [ C l ]/k 2 k l K D >C M S" 1 80 maleic a c i d 0.16 0.59 70 maleic a c i d 0.10 0.34 60 maleic a c i d 0.06 0.22 80 fumaric a c i d 0.55 0.45 - 118 -- 119 obtained, assuming such a value of k^, are AH = 10.9 - 1.0 kcal/mole r 23,93,129 4 . and AS = -18 t 6 eu. Although no great accuracy can be claimed f o  these'values, they are of the same order as those commonly observed 8 I f o r the r e a c t i o n s of d ( I r ) complexes with 0-, H_ and CH_I e t c . , and are a l s o i n the normal range f o r a b i m o l e c u l a r r e a c t i o n i n s o l u t i o n 130 between an i o n and a n e u t r a l molecule. The small enthalpy of a c t i v a t i o n and large negative entropy of a c t i v a t i o n are c o n s i s t e n t with a t r a n s i t i o n s t a t e or intermediate which i s an o x i d a t i v e adduct. 5.4.3 Dependence on Added C h l o r i d e The i n v e r s e dependence on c h l o r i d e c o n c e n t r a t i o n c o u l d r e s u l t from the reverse of r e a c t i o n (5,6) according to the rate-law shown i n Equation (5,8). According to Equation (5,9) a p l o t o f ( i n i t a l r a t e) * against [Cl ] at constant [ o l e f i n ] should y i e l d a s t r a i g h t l i n e . Figures 32 and 37 show such p l o t s f o r the M.A. and F.A. system r e s p e c t i v e l y which give good s t r a i g h t l i n e s . The a b s c i s s a represent the added ; 1 c h l o r i d e and do not i n c l u d e any c o n t r i b u t i o n from the s t a r t i n g compound, RuCl-.3H-0; i n c l u d i n g t h i s unknown amount would d i s p l a c e each a b s c i s s a value by a constant increment. The slopes would be unaffected by t h i s 1/2 • 1/2 c o r r e c t i o n and they y i e l d values of 7.0 M S (M.A.) and 89.5 M S (.F.A.) f o r k j/k'^k.Kp a t 8 ^ ° * These values are not too c o n s i s t e n t with the data i n Table XV s i n c e the k- value f o r F.A. must be about 4 times l e s s than the value f o r the M.A. system. The discrepancy i s thought to a r i s e from e i t h e r a) f a i l u r e to maintain a constant i o n i c s t r e n g t h i n the c h l o r i d e v a r i a t i o n experiments or b) added c h l o r i d e a f f e c t i n g the inverse d i s t r i b u t i o n of c h l o r i d e complex present. The l i n e a r p l o t s obtained f o r the c h l o r i d e v a r i a t i o n could be f o r t u i t o u s . - 120 -5.4.4. Is o m e r i z a t i o n of Maleic A c i d The f a c t that maleic a c i d isomerized to the more s t a b l e fumaric a c i d i s of i n t e r e s t s i n c e t h i s does not occur j u s t i n DMA s o l u t i o n 7 I at 80°. No evidence was found f o r complexing between M.A. and Ru and t h i s i n d i c a t e s that i s o m e r i z a t i o n i s under the hydrogenation c o n d i t i o n s , and not simply a metal c a t a l y z e d process e i t h e r , although t h i s p o i n t was not checked experimentally. However i t seems l i k e l y that the H^ i s necessary f o r i s o m e r i z a t i o n and a s i m i l a r r e s u l t has been observed I 35 f o r a Rh system. A w e l l e s t a b l i s h e d mechanism f o r o l e f i n i someriza-t i o n i n v o l v e s the r e v e r s i b l e formation of metal a l k y l s through metal 85 o l e f i n hydride complexes; R >R R " .R R H c = c — c — c —>- c = c i X H — H ' 1 X H — „ / i N M M M\ ' (5,11) In the present system such a mechanism e x i s t s i f the hydrogen molecule t r a n s f e r occurs i n two consecutive s i n g l e hydrogen t r a n s f e r steps: R u H I H 2 + o l e f i n ; S l ° W > R u H I H 2 ( o l e f i n ) (5,12) I I I I I I I Ru H 2 ( o l e f i n ) —*• Ru H ( a l k y l ) ——*• Ru + saturated product (5,13) T r - o l e f i n complex a - a l k y l complex Recent evidence i n some rhodium systems supports such a t r a n s f e r - 121 -mechanism; 3 4 3 ^ the next s e c t i o n gives some evidence f o r such a process i n the present system. 5.4.5. Deuteration and Stereochemistry o f A d d i t i o n to O l e f i n s Deuterium r e d u c t i o n can be used to determine the stereochemistry 8 30 of the a d d i t i o n r e a c t i o n using maleic and fumaric a c i d ' s i n c e the 131 corresponding d i d e u t e r o s u c c i n i c acids have been c h a r a c t e r i z e d . From fumaric a c i d , the s u c c i n i c a c i d product had bands at 7.5-7.7 y (broad), 8.09 y ( s t r o n g ) , 8.35 y ( s t r o n g ) , 8.47 y (sharp s h o u l d e r ) , 8.65 y (sho u l d e r ) , 9.45 y (weak), 11.65 y (medium), which i s c o n s i s t e n t w i t h a mixture of DL- sym-1,2-dideuterosuccinic a c i d and unsymmetrical d i d e u t e r o s u c c i n i c a c i d (H0 2C.CH 2~CD 2.C0 2H). A c i s - a d d i t i o n of deuterium to fumaric a c i d would give the DL- sym- 1,2-dideuterosuccinic a c i d as a main product. The unsymmetrical d i d e u t e r o s u c c i n i c a c i d can r e s u l t from the e q u i l i b r i u m (5,13), e.g., (Scheme V I I ) . - 122 -5.5. General D i s c u s s i o n on C a t a l y t i c Hydrogenation Using Ruthenium(I) General thoughts on the mechanisms of c a t a l y t i c hydrogena-2-5 30 31 132 t i o n s ' ' ' have been considered i n Chapter I. The mechanisms i n v o l v e the f o l l o w i n g three steps: (1) hydrogen a c t i v a t i o n , (2) substrate a c t i v a t i o n , (3) hydrogen t r a n s f e r . The Ru 1 i n s o l u t i o n e x i s t s as a dimer probably w i t h a metal-metal bond together w i t h c h l o r i d e b r i d g e s . A monomeric species a c t i v a t e s the molecular hydrogen. The k i n e t i c data are c o n s i s t e n t only w i t h a c t i v a t i o n of hydrogen through d i h y d r i d e formation followed by a r a t e -determining process i n v o l v i n g o l e f i n (Scheme V I I I ) : L (L = C l , H^O, s o l v e n t , S = solvent) Scheme V I I I - 123 -The r e l a t i v e l y small deuterium isotope e f f e c t o f 1.5 observed i n the fumaric a c i d system at high fumaric a c i d c o n c e n t r a t i o n r e f e r s to the k^ value f o r the d i h y d r i d e formation, and suggests a synchronous breaking of the H-H bond and making of Ru-H bonds. S i m i l a r small isotope e f f e c t s have been observed f o r the o x i d a t i v e a d d i t i o n of to I r C l ( C O ) ( P P h 3 ) 2 , 1 2 9 R h ( a l k y l ) H ( C O ) P P h 3 1 3 2 and a Rh 1 o l e f i n c o m p l e x . 1 3 3 The attack of the o l e f i n on to the hydrogenated c a t a l y s t must 31 correspond to a t r u e c o o r d i n a t i o n . Indeed i t has been shown by v a r y i n g the o l e f i n s that the c a t a l y t i c - p r o c e s s i s made e a s i e r by the same f a c t o r s which u s u a l l y s t a b i l i z e o l e f i n i c complexes of Ag 1 and P t 1 1 . This suggests that the o l e f i n complexation on the hydrogenated metal species i s the rate-determining step r a t h e r than the subsequent ' t r a n s f e r ' steps. The low r a t e of hydrogenation of fumaric a c i d compared to maleic a c i d can be a t t r i b u t e d to a s t e r i c e f f e c t , the trans isomer being more hindered i n forming the -rr-hydrido o l e f i n complex. Following o l e f i n a c t i v a t i o n the next step i s the " i n s e r t i o n " of the o l e f i n across the metal-hydrogen bond, a w e l l s u b s t a n t i a t e d r e a c t i o n . 4 2 ' ^ 2 ' 1 ( ^ Such a r e a c t i o n step would r e q u i r e the promotion of the e l e c t r o n ( s ) of the Ru-H bond to the anti-bonding o r b i t a l of the o l e f i n , w i t h the t r a n s f e r of the hydrogen atom and formation of an a l k y l d e r i v a t i v e . Such a step should be favoured when the antibonding o r b i t a l o f the coordinated o l e f i n i s r e l a t i v e l y empty. Complete unoccupation never happens when the metal has an e l e c t r o n i c c o n f i g u r a t i o n 3 higher than d . Because the usual homogeneous c a t a l y s t s f o r hydrogena-3 t i o n have an e l e c t r o n i c d c o n f i g u r a t i o n corresponding to more than d the mechanism o f o l e f i n i n s e r t i o n across the metal-hydrogen bond must be - 124 -more complex. The a l k y l hydride could then decompose d i r e c t l y to s a t u r a t e d product and regenerate the c a t a l y s t . Wilkinson and h i s group^ 1 have shown that o l e f i n a d d i t i o n to the hydrido compound RhCl^H (PPh^) to give a Rh^** a l k y l i s much e a s i e r w i t h ethylene than w i t h t e t r a f l u o r o e t h y l e n e . This i s c o n s i s t e n t with a four centre i n s e r t i o n mechanism, because the t e t r a f l u o r o e t h y l e n e i s a much b e t t e r TT acceptor than ethylene, but the back-donation to the o l e f i n must be i n any case very weak. The a i n t e r a c t i o n of the o l e f i n with the metal seems to be the most important f a c t o r . The a c t u a l process of hydrogen t r a n s f e r remains then somewhat u n c e r t a i n , but the observed i s o m e r i z a t i o n process, and the unsymmetrical d i d e u t e r o s u c c i n i c a c i d i s o l a t e d , i n d i c a t e two successive H atom t r a n s f e r . The r e s u l t i n g o v e r a l l c i s a d d i t i o n of hydrogen r e q u i r e s that the f i n a l decomposition of the a l k y l hydride i n v o l v e s r e t e n t i o n of c o n f i g u r a t i o n at the carbon atom attached to the metal. S u b s t i t u t i o n of the carbon atom of t r a n s i t i o n metal a l k y l s has been l i t t l e s t u d i e d , but i n the 134 case of Hg a l k y l s such r e t e n t i o n of c o n f i g u r a t i o n i s u s u a l l y observed. The mechanism shown i n Scheme V I I I i s s i m i l a r to that proposed 30 f o r the RhCl(PPh 3)2 c a t a l y z e d hydrogenation of o l e f i n s i n benzene, 13 I 133 and the I r C l ( C O ) ( P P h ^ ) 2 ar>d R h c h l o r i d e c a t a l y z e d hydrogenation of maleic a c i d i n DMA. However i n the f i r s t system a synchronous i n s e r t i o n of the o l e f i n to the two H atoms was p o s t u l a t e d , and i n the l a s t two cases, pre-coordinated of the o l e f i n p r i o r to the a c t i v a t i o n of hydrogen was proposed. CHAPTER VI FORMATION OF A RUTHENIUM(III) HYDRIDE SPECIES FROM RUTHENIUM(I) SOLUTIONS 6.1. I n t r o d u c t i o n The previous chapter i n v o l v e s the a c t i v a t i o n of molecular hydrogen by ruthenium(I) complexes f o r the r e d u c t i o n of o l e f i n i c sub-s t r a t e s ; the intermediate hydride species p o s t u l a t e d i s a ruthenium(III) d i h y d r i d e species Ru^^^H^ (Equation 5,1). The most a c t i v e homogeneous 42 3 hydrogenation c a t a l y s t s yet disc o v e r e d , RuHCl(PPh^)^ and RhClfPPh^)^ both contain coordinated triphenylphosphine. To i n v e s t i g a t e the p o s s i b l e a c t i v i t y of ruthenium(I) triphenylphosphine complexes, t h i s l i g a n d was added to the ruthenium(I) s o l u t i o n s and t h e i r r e a c t i v i t y to hydrogen and hydrogen/olefin mixtures s t u d i e d . The system i n f a c t was very i n e f f i c i e n t f o r o l e f i n r e d u c t i o n but the st u d i e s d i d give evidence f o r formation of a ruthenium(III) d i h y d r i d e species. 6.2. Formation of a Ruthenium(III) Hydride In the absence of substrate the brown DMA s o l u t i o n s o f ruthenium(I) c h l o r i d e i n the presence of triphenylphosphine (1:4) were found to absorb slowly one mole of hydrogen per mole of ruthenium. An uptake p l o t f o r t h i s r e a c t i o n i s shown i n Figure 40. No hydrogen Time, hr. Figure 40. Rate p l o t f o r the formation of ruthenium(III) hydride by the r e a c t i o n of ruthenium(I) w i t h H 2 i n PPh 3 at 80° i n DMA (0.021 M Ru 1, 0.074 M PPh 3, 725 mm. H 2 ) . - 127 -uptake had been observed i n the absence of triphenylphosphine. The Ru* c h l o r i d e s o l u t i o n s darkened somewhat on the a d d i t i o n of t r i p h e n y l -phosphine but showed no f u r t h e r v i s i b l e change with H 2 uptake. The f i n a l dark drown s o l u t i o n showed a s i n g l e Ru-H s t r e t c h i n g frequency (1900 cm *) , i n the normal r e g i o n f o r a t r a n s i t i o n - m e t a l hydride bond. The o v e r a l l s t o i c h i o m e t r y then corresponds to a r e a c t i o n such as: ( P P h 3 ) n R u I + H 2 —*- ( P P h 3 ) n R u H I H 2 (6,1) A molecular d i h y d r i d e i s i n i t i a l l y assumed on the evidence f o r such a species present i n the c a t a l y t i c hydrogenation s t u d i e s described i n the l a s t chapter. The uptake p l o t , however, does not analyze f o r a p s e u d o - f i r s t - o r d e r r e a c t i o n i n t o t a l Ru*. Instead, a good f i r s t - o r d e r log p l o t i s obtained f o r the f i r s t 0.5 mole of H 2 absorbed per Ru* atom (Figure 40); the log p l o t s are l i n e a r f o r about 80% of the r e a c t i o n to the h a l f end-point stage. Such an a n a l y s i s i s c o n s i s t e n t w i t h an i n i t i a l r e a c t i o n of with a dimeric s p e c i e s , e.g., (PPh 3) nRu* + H 2 — (PPh 3) nRu**H 2 (6,2) The second 0.5 mole of H^, which was absorbed very s l o w l y indeed, must i n v o l v e a r e a c t i o n g i v i n g a product c o n t a i n i n g 1 mole of per mole of Ru* monomer, (PPh 3) nRu**H 2 + H 2 ( P P h 3 ) n R u * * * ( H 2 ) 2 (6,3) - 128 -or ( P P h 3 ) n R u 2 T H 2 + H 2 — * • 2 ( P P h ^ R u 1 1 1 ^ (6,4) For the f i r s t 0.5 mole of H 2 absorbed, the k i n e t i c data (Table XVI) i n d i c a t e d a second-order rate-law of the form -d[H I k . [ R u J ( P P h J J [ H J (6,5) dt *V1L""2 ^ 3'n J L 2 J The nature of the reactant and product species i n s o l u t i o n f o r t h i s system are not c l e a r l y s u b s t a n t i a t e d , except f o r the f a c t s that the f i n a l product contains coordinated hydride and t r i p h e n y l -phosphine, and that t h i s i s formed i n i t i a l l y from a dimeric species i n two k i n e t i c a l l y d i s t i n c t stages. The data i n Table XVI show that there i s no s u b s t a n t i a l dependence on PPh^ even when t h i s i s present i n only a 2:1 excess over the ruthenium(I) c o n c e n t r a t i o n . The r e a c t i o n i s c l e a r l y not j u s t s t a b i l i z a t i o n of the Ru*"'""'"H2 produced according to the f o l l o w i n g : i . e . Ru* —^>- 2Ru X (6,6) I 1 I I I Ru + H 2 — ± - f Ru H (6,7) TTT Fa<;t Ru H + PPh 3 • •» hydride (6,8) The f i n a l hydride s o l u t i o n i s s e n s i t i v e to a i r as i n d i c a t e d by the gradual disappearance of the I.R. band at 1900 cm } The k i n e t i c s and observations could be c o n s i s t e n t w i t h the r e a c t i o n o f w i t h a dimeric ruthenium(I) triphenylphosphine complex - 129 -Table XVI Formation of a ruthenium triphenylphosphine hydride i n DMA K i n e t i c data at 80° [Ru 1] [Ru*] [PPh 3] H 2 [H 2] k 1 x l p 2 , M x 10 2, M x 10 2, M mm. x 10 3, M x 10 2, M _ 1S 2.10 1.05 7.40 725 2.32 4.28 1.30 0.65 5.20 725 2.32 4.34 1.30 0.65 2.70 725 2.32 3.86 1.30 0.65 5.20 525 1.68 4.12 1.30 0.65 5.20 322 1.03 4.24 0.65 0.33 2.60 725 2.32 4.60 - 130 -i n i t i a l l y forming a species such as H H Ru Ru ( i ) where S = solvent or triphenylphosphine. (I) could then react more slo w l y w i t h a f u r t h e r mole of H per mole of dimer to give the complex Ru C l . 'Cl' Ru H ( I I ) Some i n d i r e c t evidence f o r such r e a c t i o n s i s provided by the f a c t that the dimeric rhodium(I) complex [RhCl(PPh^)^\ ^ absorbs 2 moles of H 9 per mole of complex to give the s p e c i e s , 30 H. C l Rh Rh S C l H H although the k i n e t i c s of the r e a c t i o n were not reported. - 131 -6.3. C a t a l y t i c A c t i v i t y of the Hydride Species The c a t a l y t i c a c t i v i t y of the ruthenium(III) triphenylphosphine hydride species f o r hydrogenation of maleic a c i d was s t u d i e d by adding the s u b s t r a t e to the s o l u t i o n formed from a 2 day r e a c t i o n of H^ w i t h the ruthenium(I) triphenylphosphine mixture (1:4) at 80°, and then f o l l o w i n g any f u r t h e r H uptake. The system d i d show a c t i v i t y but i t was q u i t e slow (Figure 41); an i n i t i a l a u t o c a t a l y t i c r e g i o n was observed and the t o t a l gas uptake was s t o i c h i o m e t r i c f o r r e d u c t i o n of the maleic a c i d . The system d i d not seem worthwhile i n v e s t i g a t i n g i n any d e t a i l but the l i n e a r r a t e s from the three experiments s t u d i e d are given i n Table XVII. The a u t o c a t a l y t i c r e gion could w e l l r e s u l t from d i s s o c i a t i o n of a dimer and the r e a c t i o n could be i n h i b i t e d by excess f r e e t r i -phenylphosphine. Under comparable c o n d i t i o n s the system i s about 5 times l e s s a c t i v e f o r maleic a c i d hydrogenation than the Ru* system described i n the l a s t chapter (no triphenylphosphine added). The important c o n c l u s i o n of t h i s chapter i s that a ruthenium hydride species can be formed from r e a c t i o n of molecular hydrogen with ruthenium(I). - 133 -Table XVII Ruthenium(III)-triphenylphosphine hydride Catalyzed hydrogenation of maleic a c i d i n DMA K i n e t i c data at 80° [M.A.] [H 2] Linear r a t e x 10 2, M x 10 3, M x 10 6, MS"1 1.30 5.20 6.10 2.32 6.00 1.30 5.20 3.10 2.32 3.77 0.65 2.60 6.00 2.32 5.63 [ R u i n H 2 ( P P h ) n ] [ P P h 3 ] i n i t i a l x 10 2, M x 10 2, M CHAPTER VII HOMOGENEOUS HYDROGENATION OF MALEIC ACID USING HYDRIDOCHLOROTRIS(TRIPHENYLPHOSPHINE)RUTHENIUM(II) AS CATALYST 7.1. I n t r o d u c t i o n 30 C h l o r o t r i s ( t r i p h e n y l p h o s p h i n e ) r h o d i u m ( I ) has been found to be an extremely e f f e c t i v e c a t a l y s t f o r the homogeneous hydrogenation of some unsaturated organic substances. Wilkinson et a l . l a t e r prepared 41 the analogous ruthenium (I I) complex, R u C l 2 ( P P h 3 ) 3 , and als o found i t a c t i v e as a homogeneous c a t a l y s t i n hydrogenation of o l e f i n s and a c e t y l e n e s . 4 ^ The analogy between the Rh* and Ru** complexes i s that both d i s s o c i a t e i n benzene s o l u t i o n to give c o o r d i n a t i v e l y unsaturated s p e c i e s , RhCl (PPh ) S ° l v e n t > RhCl(PPh ) S + PPh (7,1) ' PPh 3 R u C l 2 ( P P h 3 ) 3 s o l v e n t ) R u C l 2 ( P P h 3 ) 2 S + PPh 3 (7,2) ' P P h 3 I.R. (v„ ,~2000 cm * ) , N.M.R. spectroscopy (T„ = 28.6) and elemental Ru-H H a n a l y s i s showed that a hydrido s p e c i e s , RuHCl(PPh 3) 3, i s the a c t i v e 40 c a t a l y s t i n the ruthenium system. The intermediate h y d r i d o - s p e c i e s , h y d r i d o c h l o r o t r i s ( t r i p h e n y l -42 phosphine)ruthenium(II) had been prepared by the r e a c t i o n of H 2 w i t h - 135 -a benzene-ethanol (1:1) s o l u t i o n of R u C l 2 ( P P h 3 ) 3 , by a s i m i l a r r e a c t i o n i n pure benzene i n the presence of a base, or by r e f l u x i n g a mixture of RuC^CPPh^)., and sodium borohydride i n benzene c o n t a i n i n g a l i t t l e water o r te t r a h y d r o f u r a n . The complex i s a v i o l e t - b l a c k shiny c r y s t a l l i n e s o l i d and i s red v o i l e t i n s o l u t i o n (benzene, toluene or 44 chloroform). An X-ray d i f f r a c t i o n study of t h i s complex has shown that the s t r u c t u r e of RuHCl(PPh_)„,C,.H, i s a h i g h l y d i s t o r t e d t r i g o n a l 5 5 6 o bipyramid w i t h the PPh^ groups approximately e q u a t o r i a l and the hydride and c h l o r i d e i n approximately a x i a l p o s i t i o n s . RuHCT ( P P h ^ ) i s an extremely e f f e c t i v e c a t a l y s t f o r the 42 hydrogenation of alkenes i n benzene or toluene. However a d e t a i l e d k i n e t i c study could not be made due to s o l u b i l i t y problems, s e n s i t i v i t y of the system towards oxygen, some d i f f u s i o n c o n t r o l i n the r a p i d H^ uptake, and e f f e c t s of c a t a l y s t poisoning. On comparison w i t h a c a t a l y s t 132 system i n v o l v i n g RhH(CO)(PPh^)^ Wilkinson's group suggested t h a t the r e a c t i o n goes by a d i s s o c i a t i o n step of the c a t a l y s t to give the square monomer, RuHCl(PPh^) 2, then r e a c t i o n w i t h the alkene to form an a l k y l , f o l l o w e d by cleavage w i t h H : RuHCl ( P P h 3 ) 3 RuHCl ( P P h 3 ) 2 + PPh 3 (7,3) RuHCl ( P P h 3 ) 2 + o l e f i n »* RuCl (PPh 3) ( a l k y l ) (7,4) R u C l ( P P h 3 ) 2 ( a l k y l ) + H £ — R u H C l ( P P h 3 ) 2 + alkane (7,5) C l e a r l y our work i n v o l v i n g the c a t a l y t i c hydrogenation s t u d i e s us i n g the ruthenium(I) s o l u t i o n s i n the absence and presence of t r i p h e n y l -- 136 -phosphine (Chapter V and VI) was c l o s e l y r e l a t e d to the simultaneous studies of Wilkinson's group on the Ru**HCl (PPh^)^ system i n benzene. We found t h a t we could r e a d i l y produce t h i s c a t a l y s t " i n s i t u " i n DMA s o l u t i o n s without the a d d i t i o n of f r e e base r e p o r t e d l y r e q u i r e d i n benzene s o l u t i o n s . Bearing i n mind that u n l i k e benzene, DMA i s a strong coordinat-in g and r a t h e r b a s i c s o l v e n t , k i n e t i c s t u d i e s were made i n DMA s o l u t i o n and are presented i n t h i s chapter. Good r e p r o d u c i b l e data were obtained and r e a c t i o n mechanisms c o n s i s t e n t w i t h these are proposed and discussed here. -7.2. Production of H y d r i d o c h l o r o t r i s ( t r i p h e n y l p h o s p h i n e ) r u t h e n i u m ( I I ) i n DMA S o l u t i o n H y d r i d o c h l o r o t r i s ( t r i p h e n y l p h o s p h i n e ) r u t h e n i u m ( I I ) , RuHCl(PPh^)^ was prepared by heating a "RuCl^.SH^O'VDMA s o l u t i o n w i t h a four f o l d excess of triphenylphosphine under 1 atmosphere H at 80° f o r about 30 minutes. The i n i t i a l reddish-brown s o l u t i o n ( R u * \ Ru***) changed to a v i o l e t red s o l u t i o n (A = 515 my e= 850 f o r a 1.30 x 10 ^ M Ru ^ max s o l u t i o n ) . Hydrogen uptake measurements at 35° during t h i s r e a c t i o n showed that one mole of H^ was consumed per mole of ruthenium (Figure 42). The i n f r a - r e d spectrum of t h i s v i o l e t red s o l u t i o n had a band at 1920 cm * w i t h a shoulder at 1950 cm *, i n d i c a t i n g the presence of Ru-H bonds. However, a high f i e l d N.M.R. spectrum d i d not show any Ru-H s i g n a l probably due to the d i f f i c u l t y i n g e t t i n g a s u f f i c i e n t l y concentrated s o l u t i o n and the s e n s i t i v i t y of the s o l u t i o n to oxygen; proton exchange with the solvent i s a l s o probable. Treatment of a Time, sec. Figure 42. Rate p l o t f o r the production of RuHCl(PPh 3) 3 from " R u C l 3 " and H 2 i n DMA at 35° (756 mm. H 2. 1.3 x 10" 2 M RuCl 3.3H 20, 5.2 x 10" 2 M PPh 3). 138 "RuClg" s o l u t i o n at room temperature i n the absence of a i r w i t h about a 10 f o l d excess of PPh., y i e l d e d a brown s o l u t i o n which presumably contains the known species RuCl^CPPh^)^ since t h i s complex i s prepared 41 by such a r e a c t i o n . The brown s o l u t i o n turned purple-red r a t h e r q u i c k l y when H 2 was bubbled through i t . Presumably the H 2 uptake measured at 35° corresponds to the production of the Ru** hydride from the R u C l 2 ( P P h g ) s p e c i e s . Of i n t e r e s t i s that no colour change was observed when a four f o l d excess of triphenylphosphine was added to I I a blue Ru c h l o r i d e s o l u t i o n , although at 60° and under 1 atm pressure the s o l u t i o n changed to purple red very slowly w i t h the uptake of 1 mole of H 2 per mole of Ru**. These p o i n t s give i n s i g h t i n t o how the hydride i s formed from the RuCl^/PPh^/H^ r e a c t i o n i n DMA: P P h 3 II R u C l 3 + H 2 Ru HCl(PPh ) (7,6) Rud 2(PPh,,) 3 i s not produced from Ru** with PPh,, although the hydride can be formed from Ru** presumably through the mechanism: Ru** + H_ — R u * * H " + H + (7,7) 2 slow I I - P P h 3 II Ru H . =-»• Ru H(PPh ) (7,8) v o i l e t red Instead of the intermediate hydride reducing f u r t h e r Ru** to the u n i v a l e n t s t a t e (Equation 4,21 and 4,22, S e c t i o n 4.3.3.) i t i s s t a b l i z e d as a triphenylphosphine complex (k^ ^ 0.057 M *S * at 60° compared to 0.04 M *S * obtained from the Ru**/Ru* system under s i m i l a r - 139 -c o n d i t i o n s ) . However no blue Ru** intermediate i s observed i n r e a c t i o n (7,6) and the hydride must be formed from the d i r e c t r e a c t i o n of H^ with RuC^tPPh,,)^; t h i s complex l i k e l y r e s u l t s from triphenylphosphine reduction of a R u * * * C l 3 ( P P h 3 ) 3 s p e c i e s : Ru* V + 4PPh 3 — — » Ru***(PPh 3) 3 + Ph 3PO (7,9) Ru***(PPh 3) 3 + PPh 3 • Ru**(PPh 3) 3 + Ph 3PO (7,10) R u * * C r o ( P P h J 7 + H„ f a S t ) Ru**HCl(PPh„)„ + H + + C l " Z O . J Z o o (7,11) Triphenylphosphine oxide i s presumably the o x i d a t i o n product of r e a c t i o n (7,9) and (7,10), the oxygen coming from water present i n the system. 42 Reaction (7,11) normally r e q u i r e s the presence of a base which s t a b i l i z e s the r e l e a s e d proton; i n t h i s system the b a s i c DMA i s thought to p l a y such a r o l e . However a hydride formation i n v o l v i n g a hydride t r a n s f e r from the ortho p o s i t i o n of a phenyl group to Ru cannot be excluded , ^ . 135,136 completely. The red v i o l e t RuHCl(PPh 3) 3 s o l u t i o n was extremely s e n s i t i v e to a i r t u r n i n g green r a t h e r q u i c k l y , w i t h green c r y s t a l s separating on 42 standing. Wilkinson et a l . reported a s i m i l a r o b s ervation although the green s o l i d has not yet been c h a r a c t e r i z e d . Reaction of the v i o l e t red s o l u t i o n w i t h CO r e s u l t e d i n a greenish-yellow s o l u t i o n , 2 moles of CO being absorbed. I.R. spectrum of t h i s carbonyl s o l u t i o n has bands at 2050 and 1980 cm * besides a hydride band, suggesting the two CO groups are c i s to each other i n a complex such as Ru**HCl(CO)^(PPh 3)^. This h y d r i d o b i s c a r b o n y l s o l u t i o n was found to be i n a c t i v e as a hydrogenation - 140 -c a t a l y s t and as a hydroformylation c a t a l y s t . A d d i t i o n of 2 , 2 1 - b i p y r i d i n e to the v i o l e t red s o l u t i o n gave a brown s o l u t i o n which was probably 42 RuHCl(bipy)(PPh 3)^ a s reported by W i l k i n s o n . Reaction of a f r e s h l y prepared v i o l e t red s o l u t i o n w i t h ethylene or v i n y l f l u o r i d e r a p i d l y produced at room temperature brown s o l u t i o n s which showed no band i n the r e g i o n 1900-2000 cm *, which i s i n the normal r e g i o n f o r t r a n s i t i o n metal-hydride s t r e t c h . The brown s o l u t i o n obtained from the ethylene r e a c t i o n reacted w i t h H^ at 80° r a p i d l y and the colour changed t o the i n i t i a l v i o l e t r e d , suggesting r e d u c t i o n to ethane. These data are c o n s i s t e n t w i t h r e a c t i o n s such as R u n H C l ( P P h 3 ) 2 + o l e f i n ^ Ru I ] CCl ( a l k y l ) (PPh 3) (7,12) Wilkinson's group reported such a r e a c t i o n f o r C^H^ but only at 35 atm C 2H^ pressure. Unfortunately N.M.R. evidence could not be obtained to show the presence of an a l k y l or f l u o r o a l k y l product i n our r e a c t i o n s . A l l our observations and the method of p r e p a r a t i o n i n d i c a t e d that the v i o l e t red hydrido complex i n our DMA s o l u t i o n i s the species RuHCl(PPh 3) 3 prepared by Wilkinson et a l . The two Ru-H I.R. bands observed i n s o l u t i o n are thought t o be due to an e q u i l i b r i u m mixture of the u n d i s s o c i a t e d and s o l v a t e d species i n s o l u t i o n (Equation 7,3). 7.3. C a t a l y t i c Hydrogenation of M a l e i c A c i d DMA s o l u t i o n s of RuHCl(PPh 3) 3 prepared as described i n S e c t i o n 7.2. were found to be exceedingly e f f e c t i v e i n c a t a l y z i n g the hydrogenation of maleic a c i d . The s u b s t r a t e was weighed i n a glass capsule and added - 141 -to the frozen c a t a l y s t s o l u t i o n . The f r o z e n s o l u t i o n and gas b u r r e t t e were then degassed to preclude any t r a c e of a i r p r i o r to admitting H^, and r e p r o d u c i b l e r e s u l t s were obtained i n t h i s way. The gas uptake p l o t s at 35° f o r a v a r i e t y of triphenylphosphine, ruthenium, maleic a c i d concentrations are shown i n Figure 43-46. The c o n c e n t r a t i o n of t r i -phenylphosphine noted on these Figures and subsequent Tables XVIII-XX i s the amount i n i t i a l l y used l e s s the amount used f o r r e d u c t i o n of the Ru*^ to Ru**. The t o t a l uptake of hydrogen i n d i c a t e d complete r e d u c t i o n of the maleic a c i d . No metal was v i s i b l e at the end of the r e a c t i o n s . The colour of the i n i t i a l r e a c t i n g s o l u t i o n s v a r i e d w i t h the r a t i o of maleic a c i d c o n c e n t r a t i o n to that of ruthenium and a l s o depended on the PPhg c o n c e n t r a t i o n . With i n c r e a s i n g [M.A.] the colour changed from r e d - v i o l e t , red-yellow to completely yellow at higher maleic a c i d c o n c e n t r a t i o n . The f i n a l s o l u t i o n a f t e r complete hydrogenation of the s u b s t r a t e r e t a i n e d the i n i t i a l r e d - v i o l e t colour of the ruthenium(II) hydridochlorotriphenylphosphine complex. No poisoning of the c a t a l y s t occurred under the hydrogenation c o n d i t i o n s s i n c e a d d i t i o n of more maleic a c i d to the same i n i t i a l c oncentration and r e - i n i t i a t i n g hydro-genation y i e l d e d the same i n i t i a l uptake r a t e . A d d i t i o n of 2,2-diphenyl-_2 1 - p i c r y l hydrazyl (1.7 x 10 M), i t s e l f a f r e e r a d i c a l and a commonly used i n h i b i t o r f o r f r e e r a d i c a l r e a c t i o n s , had no e f f e c t on the r e a c t i o n . Fumaric a c i d was s i m i l a r l y hydrogenated under the same co n d i t i o n s but at a r a t e about h a l f that observed f o r maleic a c i d . The gas uptake p l o t s f o r the hydrogenation of maleic a c i d g e n e r a l l y d i d not analyze f o r any simple o v e r a l l f i r s t - o r d e r or second-4.0 Time, sec Figure 44. Rate p l o t s f o r the RuHCl(PPh 3) 3 c a t a l y z e d hydrogenation of maleic a c i d i n DMA at 35°. CO.04 M M.A. 756 mm. H-). (0) 1.30 x 10-2 M R u 1 1 , 3:90 x 10" 2 M PPh 3; (A) 0.40 x l O " 2 M R u 1 1 , 1.20 x 10~ 2 M PPh 3; ( O ) 0.20 x 10" 2 M R u 1 1 , 0.6 x 10" 2 M PPh . Oq C H fD H 2 absorbed x 10 , M S p a P p a C r t P r - l r t 13 r-HOJ CD PT 1 - . U l OJ o13 /—> r-" i-j ^ O C D O O r t ( / ) • w T-J ' O CD 4*. rt) O O . O r t • S H H - M _ < C \ 3 r t CD ' ^ h^X > CD . ! - •< . PO o C U l i - J X O INOUI n O O S r-> § "0 70 a * n C • p r HH OJ » M W * ; • o p ON r t 00 ^ P, O l -X N 1—1 O CD O • CL. 1 U l hOK> PT s x a. o T) H O O 1 3 O W o PT I CD OJ N ) 3 v p 2 r t 4=» • H -• p a o H oo C 3 H* l— 1 n g H O CD X »• rt, r - ^ 3 O O P I ' M K ) CD O H -2 • o OJ T3 tD P 13 O PT X H-OJ P-. >» I—' O H -4^  I P3 ISJ to a •P- S 2 > x t/1 CD n o i fO - 145 -W ' 01 x- psqaosqe c\\ < o s "* a o c o • H /—> TJ O • H >—' o rt o • • H < : CD . •-" s rt 6 ^ to MH £ O Cu c O S • H +-> CM rt i C o CD i—l M O X f-l ' T3 00 X \D ,C • CD -N CM 1—1 rt • + J E rt g o tOLO to rC •> C L , r-H • C L , H S rH OS o 1—1 •5 s o • OS CM' o 0 o f—\ rC rH •P o X rH V > O CM MH LO ' *\ to o 4-> V LO O CM i—1 o PHO. • LO o CD to +-> r—^ rt 4-> < OS rt — ' CD U • H - 146 -order r e a c t i o n . The r a t e f a l l s o f f r a p i d l y when the maleic a c i d concentra-t i o n drops below the r a t i o [M.A.]/[Ru 1 1] = 1/1 (Figures 43-46). The i n i t i a l r a t e of hydrogen uptake was obtained from the tangent to the p l o t o f hydrogen uptake against time. The uptake p l o t s g e n e r a l l y showed q u i t e a s u b s t a n t i a l r e g i o n of l i n e a r i t y up to about 500 sec and the i n i t i a l r a t e s could be measured r e a d i l y . The dependence of these r a t e s on triphenylphosphine and substrate concentrations (Table X V I I I ) , c a t a l y s t and hydrogen concentrations (Table XIX) were s t u d i e d . The temperature dependence data are summarized i n Table XX. 7.3.1. Dependence on Triphenylphosphine Concentration A p l o t showing the i n i t i a l r a t e of hydrogenation of maleic a c i d against the triphenylphosphine c o n c e n t r a t i o n (that coordinated t o Ru** + ' f r e e ' triphenylphosphine) i s shown i n Figure 47. The r a t e s approach a lower l i m i t i n g value at high concentrations of PPh^- A p l o t of the -r e c i p r o c a l of the r a t e against t h i s PPh-, c o n c e n t r a t i o n (Figure 48) i s l i n e a r at l e a s t f o r [PPh^]/[Ru**] ^.3, and gives a p o s i t i v e i n t e r c e p t on the o r d i n a t e a x i s f o r zero triphenylphosphine. 7.3.2. Dependence on M a l e i c A c i d Concentration For r e a c t i o n s c a r r i e d out using a r a t i o of [PPhg]/[Ru**] = 3/1, the r a t e s do not increase l i n e a r l y w i t h i n c r e a s i n g o l e f i n c o n c e n t r a t i o n but appear to be approaching an asymptotic value (Figure 49). This i n d i c a t e s that the dependence of the i n i t i a l r a t e on the o l e f i n i s between zero and f i r s t - o r d e r , the order decreasing with i n c r e a s i n g o l e f i n c o n c e n t r a t i o n . - 147 -Table XVIII RuHCl (PPh^)., c a t a l y z e d hydrogenation of maleic a c i d i n DMA Dependence of i n i t i a l r a t e on PPh^ and M.A. concentrations at 35° [*."] [PPh 3] [M.A.] H 2 [H 2] I n i t i a l r a t e x 10 2, M x 10 2, M x 10 2, M mm. x 10 3, M x 10 5, MS - 1 0.65 1.45 4.00 756 1, .79 3.33 0.65 1.95 4.00 756 1, .79 3.03 0.65 4.55 4.00 756 1, .79 2.33 0.65 7.05 4.00 756 1. .79 1.95 0.65 8.70 4.00 756 1, .79 1.69 0.65 11.25 4.00 756 1. .79 1.49 0.65 12.85 4.00 756 1, .79 1.40 0.65 14.55 4.00 756 1. .79 1.31 1.30 3.90 4.00 756 1. .79 4.19 1.30 3.90 2.03 756 1. .79 3.05 1.30 3.90 1.21 756 1. .79 2.50 1.30 . 3.90 0.98 756 1. .79 2.17 0.52 4.68 6.00 756 1. .79 2.40 0.52 4.68 4.00 ' 756 .79 2.27 0.52 4.68 2.50 756 1. ,79 1.82 0.52 4.68 1.81 756 1. ,79 1.51 0.52 4.68 1.00 756 1. ,79 1.02 - 148 -Table XIX RuHCl ( P P h ^ ) c a t a l y z e d hydrogenation of maleic a c i d i n DMA Dependence of i n i t i a l r a t e on Ru** and H„ concentrations at 35° [ R u 1 1 ] [PPh 3] [M.A.] H 2 [H 2] I n i t i a l r a t e x 10 2, M x 10 2, M x 10 2, M mm. x 10 3, M x 10 5, MS"* 1.30 3.90 4.00 756 1.79 4.19 0.91 2.73 4.00 756 1.79 3.71 0.65 1.95 4.00 756 1.79 3.03 0.40 1.20 4.00 756 1.79 2.42 0.20 0.60 4.00 756 1.79 1.50 0.20 0.60 6.00 756 1.79 1.66 0. 20 0.60 6.00 756 1.79 0.86 a 0.20 0.60 6.00 756 1.79 1.43 b 0.20 0.60 6.00 756 1.79 1.49° 0. 20 0.60 6.00 756 1.79 1.49 d 0.20 0.60 6.00 756 1.79 2.40 6 • 0.13 5.07 4.00 756 1.79 0.43 0.26 4.94 4.00 756 1.79 1.04 0.39 4.81 4.00 756 1.79 1.61 0.52 4.68 4.00 756 1.79 2.11 0.65 4.55 4.00 756 1.79 2.33 1.30 3.90 4.00 683 1.62 3.84 1.30 3.90 4.00 583 1.38 3.10 1.30 3.90 4.00 440 1.04 2.45 1.30 3.90 4.00 231 0.55 1.36 Fumaric a c i d i n place of maleic a c i d . RuDCl(PPh 3) 3 and D^  i n place of RuHCl(PPh I and H . ° RuDCl(PPh 3) 3 i n place of RuHCl(PPhj) 3. D ? i n place of H ?. 0.031 M p-toluene sulphonic a c i d added. - 149 -Table XX RuHCl (PPh,,) 3 c a t a l y z e d hydrogenation of maleic a c i d i n DMA * Temperature dependence of k [Ru 1 1] = 0.2 x 10 2 , M [PPh 3]= 0.6 x 10 2 , M [M.A.] = 6.0 x 10" 2, M Temperature [H 2] I n i t i a l r a t e k °C x 10 3, M x 10 5, MS - 1 M S 30 1.73 1.01 2.9 35 1.79 1.66 4.6 40 1.86 2.45 6.6 45 1.92 4.05 10.5 * Defined by Equation (7,17) i n S e c t i o n 7.4. - 152 -A curve of s i m i l a r type was observed f o r r e a c t i o n s " f l o o d e d " w i t h triphenylphosphine ([PPh,,] / [Ru**] = 10) (Figure 50), showing a s i m i l a r dependence of the i n i t i a l r a t e on the o l e f i n . 7.3.3. Dependence on C a t a l y s t Concentration Figure 51 shows the dependence of the i n i t i a l r a t e of hydro-genation of maleic a c i d on the Ru** c o n c e n t r a t i o n , the triphenylphosphine c o n c e n t r a t i o n being kept at a constant r a t i o of [PPh^]/[Ru**] = 3. Again the r a t e s do not increase l i n e a r l y w i t h i n c r e a s i n g [Ru**]. A p l o t of the i n i t i a l r a t e against the square-root of Ru** c o n c e n t r a t i o n , however, gives a reasonably good s t r a i g h t l i n e at high c a t a l y s t c o n c e n t r a t i o n s , which passes through the o r i g i n (Figure 52). Hence with a 3:1 r a t i o of [PPhg] to [Ru**], the r e a c t i o n seems to show a h a l f - o r d e r dependence on ruthenium co n c e n t r a t i o n at higher c a t a l y s t c o ncentrations. In r e a c t i o n s " f l o o d e d " w i t h large excess of PPh^ ([Ru**] = 0.13 x 10~ 2 M to 0.52 x 10" 2 M, [PPh 3J/[Ru**] = 8-9), the dependence of i n i t i a l r a t e on the c a t a l y s t c o n c e n t r a t i o n i s l i n e a r up to about 0.5 x -2 10 M (Figure 53). At higher c a t a l y s t concentrations but at about _2 the same PPh^ c o n c e n t r a t i o n ( ^ 4 x 1 0 M), i t becomes l e s s than f i r s t -order. 7.3.4. Dependence on Hydrogen Pressure _ 2 From r e s u l t s under a set of c o n d i t i o n s using 1.30 x 10 M I I -2 Ru , 3.90 x 10 M PPh^, 0.04 M maleic a c i d and various hydrogen pressures, the p l o t of i n i t i a l r a t e against hydrogen concentration i s O.Oi 0.0 2.0 4.0 [M.A.] x 10 2, M Figure 49. Dependence of i n i t i a l r a t e of hydrogenation o f M.A. i n DMA at 3.90 x 10 on [M.A.] (725 mm. H 2,l< 3-35 •2 M PPh,) (Table XVIII) 30 x l O - 2 M Ru , Figure 50. Dependence of i n i t i a l r a t e of hydrogenation o f M.A. i n DMA at 35° on [M.A.] (725 mm. H 2, 0.52 x 10~ 2 M Ru 1 1, 4.68 x 1 0 - 2 M PPh 3) (Table X V I I I ) . - 154 -/ " n o t experimental 0-°g_. J I _ _ J 0 0.4 0.8 1.2 [Ru ] x 10 , M Figure 51. Dependence of i n i t i a l r a t e o f hydrogenation o f M.A. i n DMA at 35° on [ R u 1 1 ] (725 mm. H 2, 0.04 M M.A. [ P P h 3 ] / [ R u 1 1 ] = 3/1) (Table XIX). Figure 52. Dependence of i n i t i a l r a t e o f hydrogenation o f M.A. i n DMA at 35° on [ R u 1 ! ] 1 / 2 (725 mm. H 2, 0.04 M M.A. [ P P h 3 ] / [ R u 1 1 ] = 3/1). - 155 -o CD o CD cd OS cd • H 4-J 4.0 3.0 2.0 £ i . o 0.0. 0.0 0.4 0.8 1.2 [Ru 1 1] x 10 2, M Figure 53. Dependence of i n i t i a l r a t e of hydrogenation of M.A. i n DMA at 35° on [Ru 1 1] (725 mm [ R u 1 1 ] , M) (Table XIX). 2, 0.04 M M.A. [PPh 3] 5.2 x 10 - 156 -s t r i c t l y l i n e a r w i t h zero i n t e r c e p t (Figure 54). No k i n e t i c isotope e f f e c t was observed (R^/R^ = 1 to 1.05) when and/or RuDCl(PPhg) 3 were used i n p l a c e of H 2 and/or RuHCl(PPh^)^. 7.4. D i s c u s s i o n of K i n e t i c Results As mentioned before (Chapter V, S e c t i o n 5.4.), the t r a n s f e r of hydrogen molecules to the o l e f i n i n s o l u t i o n v i a a c a t a l y s t complex species can occur by e i t h e r one or both of two p o s s i b l e paths: A K . „ slow , ,_ , _ . A + S -—y AS — > products ; (7,13a) k k A + H — A H . — p r o d u c t s (7,13b) Z Z o k - l where A i s the c a t a l y s t and S the s u b s t r a t e . As we have seen (Chapter V) both mechamisms w i l l y i e l d s i m i l a r rate-laws and the k i n e t i c data i n t h i s Ru** system are c o n s i s t e n t w i t h e i t h e r path. However, a) there i s a r a p i d change i n the colour of the r e a c t i n g s o l u t i o n when an o l e f i n i s added, i . e . , evidence f o r AS; b) there i s no evidence f o r AH^ and 132 c) on comparison w i t h o l e f i n hydrogenation c a t a l y z e d by RhH(CO)(PPh^)^, the mechanism shown i n Equation (7,13a) i s s t r o n g l y favoured and i s assumed to be o p e r a t i v e . The k i n e t i c data and observations are a l l s a t i s f a c t o r i l y explained by such a mechanism. A l s o , a n a l y s i s of the k i n e t i c data y i e l d s a value f o r the e q u i l i b r i u m constant (K) which agrees w e l l w i t h a s p e c t r o s c o p i c a l l y determined value (see l a t e r ) . A 3_ mechanism v i a f r e e r a d i c a l s , which has been p o s t u l a t e d f o r a [Co(CN)j.H] 29 c a t a l y z e d hydrogenation (Section 1.2.2.) i s r u l e d out s i n c e c a t a l y t i c i - 157 -- 158 -hydrogenation of the o l e f i n s t i l l takes place i n the presence of 2,2-d i p h e n y l - l - p i c r y l h y d r a z y l . The i n v e r s e dependence of the i n i t i a l r a t e on the t r i p h e n y l -phosphine c o n c e n t r a t i o n i s c o n s i s t e n t with a d i s s o c i a t i o n of the c a t a l y s t to give k i n e t i c a l l y s i g n i f i c a n t amounts of a square monomer, RuHCl(PPh 3) 2 42 (which probably has trans PPh 3 groups ); t h i s then r e a c t s w i t h and reduces the o l e f i n according to the f o l l o w i n g scheme: K l RuHCl (PPh,) , *• RuHCl(PPh,)„ + PPh, (7,14) v i o l e t - r e d (I) — ( I I ) K RuHCl(PPh,)_ + o l e f i n 2 > RuCl(PPh,) ( a l k y l ) (7,15) ( I I I ) k RuCl ( P P h 3 ) 2 ( a l k y l ) + H 2 RuHCl ( P P h 3 ) 2 + p a r a f f i n yellow (7,16) where i s the d i s s o c i a t i o n constant of the complex RuHCl(PPh 3) 3, K 2 i s the formation constant of the o l e f i n complex (or a - a l k y l intermediate) and k the r a t e constant f o r the rate-determining step. Such a mechanism would lead to the f o l l o w i n g r a t e expression (Subscript T r e f e r s to t o t a l c o n c e n t r a t i o n ) : -d[H ] Rate (R) = —-jjr=- = k [H 2] [ a l k y l complex] (7,17) In terms of the t o t a l [Ru I ]'] r r, t h i s becomes k K 2 [ H 2 ] [ R u H ] T [ o l e f i n ] R = 1 + K [ o l e f i n ] + [PPh 3]/K 1 ( 7 ' 1 8 ) - 159 -where [PPh^] and [ o l e f i n ] r e f e r to the f r e e concentrations o f these species and the terms i n the denominator, taken from l e f t to r i g h t , i n d i c a t e the concentrations of I I , I I I , and I r e s p e c t i v e l y (Equation 7,14 to 7,16). Equation (7,18) may be used when the o l e f i n and PPh^ are both present i n large excess and the [PPh,,] and [ o l e f i n ] then r e f e r to the t o t a l added concentrations of these reagents. At lower o l e f i n c o n c e n t r a t i o n s , the f r e e o l e f i n c o ncentration terms i n Equation ( 7 , 1 8 ) w i l l be equal to that added, l e s s the concentra-t i o n o f the complex I I I . This modifies Equation (7,18) and gi v e s : k K.[H ] [ R u 1 1 ] [ o l e f i n ] ^ _ z z t - (y 1 + K 2 [ o l e f i n ] T + K 2 [ R u H ] T + [ P P h ^ / I ^ A l s o , s i n c e the [PPh,] = [PPh,] + 2 [ I I ] + 2 [ I I I ] + 3[I] 5 T o t a l J = [PPh 3] + 2 {[II] + [ I I I ] + [I]} + [I] = [PPh 3] + 2 [ R u H ] T + [I] , [PPh 3] = [ P P h 3 ] T - 2 [ R u H ] T - [I] (7,20) In the experiments s t u d i e d the i n i t i a l s o l u t i o n was red d i s h when a high [ P P h 3 ] T was used, and [I] « [ P P h 3 ] T ; at low [ P P h 3 ] T ( [ P P h j ] / [ R u 1 1 ] = 2) and ruthenium i s present mainly as I I and I I I , and hence [I] << [PPhg]^. Thus under the experimental c o n d i t i o n s , the r e l a t i o n s h i p [PPh 3] - [ P P h 3 ] T - 2 [ R u T I ] T (7,21) always holds. S u b s t i t u t i n g Equation (7,21) i n t o (7,19) g i v e s , - 160 -k K 2[H 2] [ R u H ] T [ o l e f i n ] (7,22) R = 1 + K 2 [ o l e f i n ] T + [ P P h 3 ] T / K 1 + (K 2 - 2/1^)[Ru 1 1] T Although t h i s expression i s complex, some l i m i t i n g forms which c l e a r l y e x i s t i n some of the experimental c o n d i t i o n s used are r e l a t i v e l y simple, and the data analyzed a c c o r d i n g l y . For example, at low c a t a l y s t concen-t r a t i o n with [PPhg]/[Ru**] = 3 and r e l a t i v e l y high c o n c e n t r a t i o n of o l e f i n ( [ o l e f i n ] / [ R u * * ] - 30), Equation (7,22) reduces to the simple form: r a t e i s independent of the o l e f i n c o n c e n t r a t i o n . This can be seen more r e a d i l y as a l i m i t i n g form of Equation (7,18) and the simple r a t e law (7,23) r e s u l t s s i n c e a l l the ruthenium i s present as the a l k y l complex I I I . The c a t a l y t i c hydrogenation r e s u l t s from the two steps (7,15) and (7,16), and, as long as excess o l e f i n i s present, gives r i s e to a pseudo-zero-order k i n e t i c s and a l i n e a r uptake p l o t (see f o r example the slowest uptake p l o t i n Figure 44 and the f a s t e s t uptake p l o t i n Figure R = k [ H 2 ] [ R u * * ] T (7,23) s i n c e K 2 [ o l e f i n ] T » {I + [ P P h ^ / I ^ + (K - 2/Kj)[Ru ] } and the 43). 7.4.1. Dependence on Substrate Concentration Equation (7,22) can be w r i t t e n i n the form: 1_ R 1 + [ P P h 3 ] T / K 1 + (K 2 - 2/ K 1 ) [ R u * * ] T { 1 } + 1 k K 2 [ H 2 ] [ R u H ] T k [ H 2 ] [ R u * * ] T (7,24) - 161 -At high triphenylphosphine c o n c e n t r a t i o n s , the term [PPh^]^, i s e s s e n t i a l l y constant and so at constant [Ru**]^ and [H ] a p l o t of 1/Rate against 1/[M.A.]^, i s found to give a s t r a i g h t l i n e (Figure 55) from which k can be c a l c u l a t e d from the i n t e r c e p t . The value of k obtained at 35° i s 4.2 M~ 1S - 1. The slope of the same p l o t gives the r e l a t i o n s h i p : 6.75 x 10" 3 k K1K2 = K + 0.52 x 1 0 _ 2 K K 2 + 3.64'x 10" 2 (7,25) 7.4.2. Dependence on Triphenylphosphine Concentration Rearranging Equation (7,24) g i v e s , 1 1 - , 1 1 2 1 . R k [ H 2 ] [ R u H ] T [M.A.] T KjK^M.A.l.j, K 2 [ R u H ] T [ M . A . ] ? [ P P h 3 ] T + TT (7,26) k K 1 K 2 [ H 2 ] [ R u ] T [ M . A . ] T Thus using data at constant [ H 2 ] , [ R u * 1 ] ^ and [M.A.] T an inverse depend-ence of the r a t e on [PPh^]^ i s a n t i c i p a t e d , and i s evident i n Figure 48. From the i n t e r c e p t and slop of the s t r a i g h t l i n e obtained, the f o l l o w i n g r e l a t i o n s h i p s can be d e r i v e d : 1.79 x 10 2 K 2K 2 + 0.385 x 10 4 Kj = 500 (7,27) k K 1K 2 = 6.91 (7,28) - 162 -Figure 55. Dependence of i n i t i a l r a t e on [M.A.] at 35° as p l o t t e d i n accord w i t h Equation (7,24) (Table X V I I I , Figure 50). - 1 6 3 -From Equations ( 7 , 2 5 ) , ( 7 , 2 7 ) and ( 7 , 2 8 ) , values of k and K 2 can be obtained. For the d i s s o c i a t i o n step, = 0 . 0 2 8 M ; and f o r the formation of the a l k y l complex, = 7 8 M 1 at 3 5 ° . The r a t e constant f o r the rate-determining step, k i s thus 3 . 2 M *S *, i n good agreement - 1 - 1 w i t h the value obtained i n S e c t i o n 7 . 4 . 1 . ( 4 . 2 M S ) c o n s i d e r i n g the u n c e r t a i n t y i n f i n d i n g the i n t e r c e p t . The value of K^ K,, measured s p e c t r o s c o p i c a l l y by f o l l o w i n g the decrease i n absorbance at 5 1 7 my of a v i o l e t - r e d s o l u t i o n i n M . A . , i s ^ 1 . 5 2 at room temperature f o r a s o l u t i o n with high [PPh 3] ( 1 . 1 2 x 1 0 " 2 M R u 1 1 , 1 5 . 8 x 1 0 ~ 2 M PPh 3, 7 . 9 1 x 1 0 M M . A . ) , and i s c o n s i s t e n t w i t h the value obtained from k i n e t i c r e s u l t s = 2 . 1 8 ) . 7 . 4 . 3 . Dependence on C a t a l y s t Concentration For r e a c t i o n s flooded w i t h PP1>3 at a constant [M.A.]^,, a p l o t o f 1/Rate against 1 / t R u 1 1 ] ^ should y i e l d a s t r a i g h t l i n e i n accord with the equation: j .1 + [ P P h 3 ] T / K 1 + K 2[M.A.] T 1 K 2 - 2 /Kj { 7 - r — > + R k K 2 [ H 2 ] [ M . A . ] T [ R U I I ] T K K 2 [ H 2 ] [ M . A . ] T ( 7 , 2 9 ) and such a p l o t i s shown i n Figure 5 6 . The l i n e e s s e n t i a l l y goes through the o r i g i n which i n d i c a t e s that the f i n a l term of Equation ( 7 , 2 9 ) approximates to zero. This means i n e f f e c t that f o r these condi-t i o n s the rate-law ( 7 , 1 8 ) holds as might be expected s i n c e the t r i p h e n y l -phosphine and o l e f i n are i n large excess. C l e a r l y the r a t e should give I I I I a f i r s t - o r d e r dependence on [Ru ] at low [Ru ] ^ and constant [ M . A . ] ^ - 164 -0.0 1.0 2.0 3.0 4.0 I I -1 -2 [Ru ] x 10 , M Figure 56. Dependence of i n i t i a l r a t e on [ R u 1 1 ] at 35° as p l o t t e d i n accord w i t h Equation (7,29) (Figure 53). - 165 -and [PPh^]^ as observed (Figure 53). The measured slopes of the l i n e s i n Figure 53 (slope = 4.0 x 10~ 3 S - 1 ) and Figure 56 (0.25 x 10 3 S) are simply the inv e r s e o f each other. At [ P P h 3 ] T / [ R u I ] : ] T = 3 and low [M.A.] , and p a r t i c u l a r l y at I I I I higher [Ru J ^ , a h a l f - o r d e r dependence on [Ru ] ^ i s apparently observed (Figure 52). According to the rate-law (7,22) at low [ P P h 3 ] T and [ o l e f i n ] ^ the terms i n v o l v i n g [ R u * * ^ i n the denominator become more s i g n i f i c a n t , p a r t i c u l a r l y so at higher [Ru**]^,; thus the order i n Ru w i l l become < 1 which i s c o n s i s t e n t w i t h the data i n Figure 51. The dependence seem t o approximate to 1/2 order at the higher [Ru**]^,, although t h i s may be f o r t u i t o u s . 7.4.4. Dependence on Temperature As mentioned p r e v i o u s l y at high maleic a c i d c o n c e n t r a t i o n and low [ R u * * ] T , the r a t e expression approximates to R = k [ H 2 ] [ R u I I ] T (7,30) The value of k obtained i n such experiments i s 4.6 M~*S~* at 35° (Table XX) (compare with 4.2 and 3.2 M *S * obtained from the more rigorous treatment). The r e a c t i o n was st u d i e d under these c o n d i t i o n s over a temperature range 30-45° (Table XX). A good Arrhenius p l o t t was obtained (Figure 57) y i e l d i n g the a c t i v a t i o n parameters: AH = 4* 15.8 _ 1.0 kcal/mole and AS = -4.5 t 2 eu. - 166 -- 167 -7.5. D i s c u s s i o n The mechanisms of c a t a l y t i c hydrogenation of o l e f i n s have been discussed i n Chapters I and V. This d i s c u s s i o n here i s i n t i m a t e l y r e l a t e d to that i n the recent paper on t h i s system i n benzene s o l u t i o n 42 by Wilkinson and h i s group; however some d i f f e r e n c e s i n experimental r e s u l t s are noted. The p r i n c i p a l c a t a l y s t species i s presumably the. planar species RuHCl(PPh^)^ produced by d i s s o c i a t i o n , and which probably 42 4? has trans phosphine l i g a n d s . Wilkinson and h i s group " observed a n o n - l i n e a r dependence on c a t a l y s t c o n c e n t r a t i o n i n benzene s o l u t i o n but could not a s c e r t a i n whether t h i s was due to d i s s o c i a t i o n of the complex or i t s incomplete d i s s o l u t i o n . The present work shows that such a dependence r e s u l t s from the e q u i l i b r i a shown i n r e a c t i o n s (7,14) and (7,15). From the values of K.^  and and the t o t a l [PPh^] and [ o l e f i n ] the concentrations of the u n d i s s o c i a t e d c a t a l y s t RuHCl(PPh^)^> the s o l v a t e d s p e c i e s , RuHCl(PPh^)^, and the a l k y l complex are r e a d i l y estimated. The value of 0.028 M shows that the c a t a l y s t i s about 80% d i s s o c i a t e d i n the absence of o l e f i n and excess PPh^ up to the _2 c a t a l y s t concentrations of 10 M used i n t h i s work. O l e f i n a c t i v a t i o n i s thought to take p l a c e before the hydrogen t r a n s f e r step as i n Scheme IX. The hydride t r a n s f e r to coordinated o l e f i n i s considered to proceed through a f o u r - c e n t r e t r a n s i t i o n s t a t e . In order to have hydrogenation proceed, the mechanism re q u i r e s a f i n i t e standing c o n c e n t r a t i o n of the a l k y l intermediate. The rate-determining step could be e i t h e r o x i d a t i v e a d d i t i o n of molecular hydrogen to the a l k y l to form an octahedral ruthenium(IV) s p e c i e s , or the r e d u c t i v e e l i m i n a t i o n of alkane by hydrogen t r a n s f e r i n t h i s species (Scheme X). A d i r e c t hydrogenolysis of the Ru-C bond seem i n t r i n s i c a l l y - 168 -much less l i k e l y . H P P * 3 PPh Ru 1 1 . PPh, PPh, H PPh PPh, y ^ Cl PPh, ; II Ru y C l PPh, H H„ y x C l PPh, P P * 3 C-H PPh 3 C 'Ru Cl PPh, y C l Ru IL HC-CH Scheme IX P P ? 3 V 1' C l C-CH PPh, P P * 3 H Ru II Cl PPh, PPh i3 PPh, PPh, PPh, H H Ru IV C-C-H Cl l I H Ru . Cl .H •C < 1 VH HC-CH Scheme X - 169 -f t The a c t i v a t i o n parameters (AH = 15.8 kcal/mole, AS = -4.5 eu) are s i m i l a r to those observed for o l e f i n hydrogenation catalyzed by 113 f RhH(CO)(PPh^) 3 where a s i m i l a r mechanism was postulated (AH = 10.6 + kcal/mole, AS = -8 eu); a rate-determining oxidative-addition of H^ to a Rh 1 a l k y l was preferred. In t h i s rhodium system, i t was proposed that the a c t i v e species i s the d i s s o c i a t e d complex RhH(CO)(PPh^) 2. The fa c t that i n RhH(C0)(PPh 3) 2 the hydride i s trans to carbon monoxide, whereas i n the square ruthenium(II) species i t would be trans to c h l o r i d e , suggested that hydrogen t r a n s f e r should be easier for the rhodium 42 complex. However since the ruthenium system i s f a r more a c t i v e , i t could be that oxidative-addition of H^ to the a l k y l or the reductive elimination of alkane by hydrogen t r a n s f e r i n t h i s species i s easier 42 than i n the rhodium case. A subsidiary question of general i n t e r e s t i s the extent to which a l k y l intermediates are formed from the hydrido-o l e f i n complexes before the saturated hydrocarbon i s formed. Considering f i r s t the complexity constant for the formation of the five-coordinate hydrido intermediate, RuHCl(alkene)(PPh^) 2, the s t e r i c hindrance exper-ienced i n the five-coordinate intermediate i s l i k e l y to be less than that i n the square a l k y l so i t appears that the formation of the l a t t e r i s c r i t i c a l . Only i f the l i f e t i m e of t h i s a l k y l i s s u f f i c i e n t l y long can oxidative-addition of hydrogen occur. Unfortunately our data gives no d i r e c t evidence for the a l k y l complex, although r e a c t i o n between the hydride and o l e f i n did occur and the Ru-hydride i n f r a r e d band did disappear. Comparison of our experimental data with those of Wilkinson's group'*2 shows two apparent d i f f e r e n c e s . F i r s t l y , i n r e l a t i o n to the 170 -l a s t p o i n t , Wilkinson's group found no evidence of i n t e r a c t i o n between the RuHClCPPh^)^ complex and t h e i r o l e f i n i c substrates at t h e i r hydrogena-t i o n c o n d i t i o n s and secondly, the present system i n DMA seems to be about 100 times l e s s a c t i v e f o r hydrogenation than those f o r which comparable data are reported i n Wilkinson' paper. This l a t t e r point i s i n some ways fo r t u n a t e s i n c e the r a t e s i n DMA were conveniently measurable; the very high r a t e s i n benzene s o l u t i o n were subject to d i f f u s i o n c o n t r o l making k i n e t i c data d i f f i c u l t to o b t a i n . In comparison of r a t e s , i t should be noted t h a t besides the use of q u i t e d i f f e r e n t solvents the r a t e data a v a i l a b l e are p e r t i n e n t to q u i t e d i f f e r e n t organic s u b s t r a t e s . The very f a s t r e a c t i o n s i n Wilkinson's work r e f e r s to terminal o l e f i n s such as o c t - l - e n e . I n t e r n a l , c y c l i c and s u b s t i t u t e d a l k - l - e n e s were hydrogenated up to 2000 times more s l o w l y , so the maleic a c i d data may f a l l i n t o l i n e w i t h t h i s . A s i n g l e r e a c t i o n was c a r r i e d out using o c t - l - e n e as s u b s t r a t e i n DMA at 35° and the r a t e was found however, to be only about 3 times f a s t e r than the hydrogenation of maleic a c i d -2 I I -2 under the same c o n d i t i o n s (0.78 x 10 M Ru , 2.34 x 10 M PPh 3, 2.55 M o c t - l - e n e , 756 mm. H^, r a t e = 10.35 x 10 5 M). However, d i f f u s i o n c o n t r o l i n the r a p i d uptake, and the d i f f e r e n t solvent system might be important. We d i d f i n d that ethylene could be hydrogenated and that i t d i d react w i t h the c a t a l y s t at hydrogenation c o n d i t i o n s (1 atm and ~ 30°). The paper by Wilkinson's group does not s t a t e whether ethylene i s hydrogenated or not, but r e p o r t s that the r e a c t i o n w i t h the c a t a l y s t to give a brown s o l u t i o n occurs only at high ethylene pressures (35 atm) at room temperature. The s o l u b i l i t y of C^H^ i n the 2 media used seems 104 137 to be of the same order of magnitude, ' so i t i s p o s s i b l e that the hydride complex d i s s o c i a t e s according to Equation (7,3), to a much greater extent i n DMA than i n benzene. CHAPTER V I I I DIRECT CARBONYLATION OF SOME RUTHENIUM CHLORIDE COMPLEXES IN DMA SOLUTION Carbonyl complexes of the group V I I I metals, i n c l u d i n g those of the platinum metals, have been shown i n many cases to be a c t i v e 14 15 c a t a l y s t s f o r a whole range of s y n t h e t i c organic r e a c t i o n s '. (see Section 1.1 and 1.3.7.), as w e l l as a c t i v a t i n g carbon monoxide f o r 74 138 re d u c t i o n processes i n s o l u t i o n . ' The study of the formation of carbonyl complexes by d i r e c t c a r b o n y l a t i o n i n s o l u t i o n using carbon monoxide i s considered important i n e l u c i d a t i n g the nature of the species present i n r e l a t i o n to the p o t e n t i a l c a t a l y t i c p r o p e r t i e s of such complexes. Of p a r t i c u l a r i n t e r e s t was the p o s s i b i l i t y of r e a c t i o n with the ruthenium(I) s o l u t i o n s and such r e a c t i o n was observed (Section 8.2.). Reaction w i t h ruthenium(II) s o l u t i o n was a n t i c i p a t e d 37 because of a corresponding r e a c t i o n reported i n aqueous systems; again r e a c t i o n was observed but s i g n i f i c a n t d i f f e r e n c e s were apparent between the two solvent systems. 8.1. D i r e c t Carbonylation of Ruthenium(II) Chloride Complexes i n DMA 8.1.1. I n t r o d u c t i o n Carbon monoxide had p r e v i o u s l y been found to re a c t with c h l o r o r u t h e n a t e ( I I I ) and ch l o r o r u t h e n a t e ( I I ) complexes i n aqueous hydro-- 172 -c h l o r i c a c i d s o l u t i o n s at 80° and 1 atm pressure, to form the carbonyl i 2ci 4] d e r i v a t i v e s [Ru(C0)Cl ] 2 " , [Ru(CO)(H 0 ) C 1 . ] 2 , and [Ru(CO) C l . ] 2 , 3 7 The r e a c t i o n s i n v o l v i n g Ru** chloro complexes i n DMA were found to proceed q u i t e d i f f e r e n t l y k i n e t i c a l l y and u s u a l l y w i t h f a s t e r r a t e s due p a r t l y to the higher s o l u b i l i t y of carbon monoxide i n DMA. The r e a c t i o n of CO w i t h DMA s o l u t i o n s of R u * * C l n > prepared as described i n S e c t i o n 4.3.1., i s reported i n t h i s s e c t i o n . 8.1.2. Stoichiometry S o l u t i o n s of R u * * C l n i n DMA absorbed CO very r e a d i l y at pressures up to 1 atm i n the temperature range 65-80°, the t o t a l uptake of CO corresponding c l o s e l y to 2 moles of CO per mole of ruthenium as shown i n Figure 58. This absorption occurred i n two d i s t i n c t stages, the f i r s t mole of CO being taken up r e l a t i v e l y r a p i d l y O 1 hr at 80°) and the second mole more slowly O 10 h r ) . The absorption of the f i r s t mole of CO was accompanied by a colour change from deep blue to green (X = 385 mp, e ^1000, X = 450 my, e ^1000), and of the second mole max max by a c o l o u r change from green to yellow (X = 465 mp, e = 430). These max observations suggest a two-step c a r b o n y l a t i o n r e a c t i o n : Ru** + CO » Ru**(C0) (8,1) Ru**(C0) + CO y Ru**(C0) 2 (8,2) Consistent w i t h t h i s , the I.R. spectrum of a green Ru**(C0) s o l u t i o n showed a broad band at 1910-1960 cm"*, while the yellow Ru**(C0) 2 1^ 1000 2000 3000 4000 Time, Sec. 36,000 I I , Figure 58. Uptake of CO by a 0.021 M solution of Ru C l n in DMA (550 mm. CO, 80 ). The broken lines correspond to the uptake of 1 mole of CO and 2 moles of CO respectively, per mole of Ru I I - 174 s o l u t i o n showed two bands at 2040 and 1960 cm * i n d i c a t i v e of c i s carbonyls. The r e a c t i o n i s very s i m i l a r to the one i n aqueous HC1 as regards the 37 o v e r a l l s t o i c h i o m e t r y , the form of uptake curve and colour changes. 8.1.3. K i n e t i c s of the F i r s t Stage The s t o i c h i o m e t r y of the r e a c t i o n f o r the f i r s t stage can be represented by: R u 1 1 + CO Ru**(C0) (8,1) The formation of Ru**(C0) was found to obey the f i r s t - o r d e r r a t e law: -djRui 1! = d[Ru**(C0)] h [ R u l l } ( 8 ) 3 ) where k^ i s a t r u e f i r s t - o r d e r r a t e constant being independent of CO c o n c e n t r a t i o n . Values of k^ were determined using Equation (8,3) from the slopes of f i r s t - o r d e r log p l o t s such as that depicted i n Figure 59; the s t o i c h i o m e t r i c r e l a t i o n : [Ru 1 1] + [ R u H ( C 0 ) ] = [ R u I I ] i n i t i a i ( 8> 4) was used to compute [Ru**] from the observed CO uptake. The values of k^ thus obtained are summarized i n Table XXI. The r a t e was l i t t l e a f f e c t e d on a d d i t i o n of L i C l up to 0.5 M; at higher c h l o r i d e concentrations k^ increased somewhat but the s i g n i f i c a n t v a r i a t i o n s i n i o n i c s t r e n g t h probably prevent any q u a n t i t a t i v e t e s t i n g of the C l dependence. A d d i t i o n of 0.5 M H o0 a l s o increased k, somewhat. - 175 --1.6 Time, Sec Figure 59. K i n e t i c p l o t f o r the formation o f Ru(CO) i n DMA (0.021 M RuII, 550 mm. CO, 80°). (0) CO absorbed; ( • ) l o g f R u 1 ! ] . the broken l i n e corresponds to the uptake of 1 mole of CO per mole of Ru**. - 176 -Table XXI Formation of Ru H(CO) i n DMA Summary of k i n e t i c data at 80° [ R u 1 1 ] CO * [CO] k l x 1 0 2, M mm. x 10 3, M 3 -1 x 10 , S 2.10 725 4.70 1.49 2.10 550 3.56 1.57 2.10 408 2.65 1.45 2.10 267 1.73 1,45 2.10 149 0.97 1.26 1.58 550 3.56 1.45 1.05 550 3.56 1.46 0.53 550 3.56 1.28 2.10 725 4.70 1.93 E 2.10 725 4.70 1.54 b 2.10 725 4.70 1.32° 2.10 725 4.70 1.36 d 2.10 725 4.70 2.03 6 2.10 725 4.70 £ 2.18 * For s o l u b i l i t y of CO i n DMA see reference 104. a 0.5 M H 20 b 0.1 M L i C l C 0.2 M L i C l d 0.5 M L i C l 6 1.5 M L i C l f 2.0 M L i C l - 177 Measurement of the temperature dependence of (Table XXII) y i e l d e d a good Arrhenius p l o t (Figure 60) from which the f o l l o w i n g a c t i v a t i o n parameters were determined: AHj*1* = 16.9 + 2 kcal/mole, A S ^ = -24 ! 8 eu 8.1.4. K i n e t i c s o f the Second Stage The measured uptake of CO f o r the second stage corresponded c l o s e l y to one mole of CO per mole of Ru**(C0). At constant [CO] and [Cl ] the uptake of carbon monoxide was found to f o l l o w p s e u d o - f i r s t -order k i n e t i c s , the r a t e being p r o p o r t i o n a l to the r e s i d u a l concentra-t i o n o f Ru**(CO), i . e . , Again the r e l a t i o n [Ru**(C0)] + [Ru**(C0) 2] = [ R u * * ( C 0 ) ] . n i t i a l (8,6) was used t o compute [Ru**(C0)] from the observed uptake of CO. k^ was evaluated from the slopes of f i r s t - o r d e r l o g p l o t s such as shown i n Figure 61, and was found t o be independent of the i n i t i a l Ru** concentra--2 -2 t i o n when the l a t t e r was v a r i e d from 2.10 x 10 M to 0.53 x 10 M. Table XXIII summarizes the k i n e t i c r e s u l t s of experiments at 80°. The k i n e t i c dependence on the carbon monoxide conc e n t r a t i o n i s complex, corresponding t o an apparent order i n CO of < 1; t h i s apparent order - 178 -Table XXII Formation of Ru n(CO) i n DMA Temperature dependence of k^ [ R u 1 1 ] = 2.10 x 10" 2 M Temperature [CO] k^ °C x 10 3, M x 10 3, S 80 4.70 1.49 80 2.65 1.45 75 4.71 1.04 75 2.71 1.07 70 4.87 0.86 70 2.78 0.76 65 4.95 0.48 65 2.84 0.56 - 179 -Time, Sec. Figure 61. F i r s t - o r d e r r a t e p l o t s f o r the uptake o f CO by Ru**(C0) s o l u t i o n s i n DMA at 80°. (0) 0.021 M RuII,. 550 mm. CO; ( • ) 0.021 M R u 1 1 , 725 mm. CO; (A) 0.011 M R u 1 1 , 550 mm. CO. - 181 -Table XXIII II Formation of Ru (CO) i n DMA Summary of k i n e t i c data at 80° [ R u H ( C 0 ) ] CO [CO] x 10 2, M mm. x 10 3, M x 10 4, S" 1 2.10 725 4.70 1.68 2.10 550 3.56 1.48 2.10 408 2.65 1.26 2.10 267 1.73 1.00 2.10 149 0.97 0.59 1.58 550 3.56 1.23 1.05 550 3.56 1.43 0.53 550 3.56 1.38 2.10 725 4.70 1.34 a 2.10 725 4.70 1.68 b - 2.10 725 4.70 1.09 C 2.10 725 4.80 0.72 d 2.10 725 4.70 0.29 6 2.10 725 4.70 f 0.23 a 0.5 M H 20 b 0.1 M L i C l ° 0.2 M L i C l d 0. .5 M L i C l 6 1.5 M L i C l 2.0 M L i C l - 182 -decreases with i n c r e a s i n g CO c o n c e n t r a t i o n , the r a t e tending to approach a l i m i t i n g value (Figure 62). There i s an apparent in v e r s e dependence of the r a t e on L i C l c o n c e n t r a t i o n (Figure 63), but again, u n f o r t u n a t e l y , no s u i t a b l e i n e r t anion could be found which could be s u b s t i t u t e d f o r C l i n order t o keep the i o n i c strength constant i n these experiments. The temperature dependence of k^ i s summarized i n Table XXIV. 8.1.5. D i s c u s s i o n The k i n e t i c r e s u l t s f o r the i n i t i a l stage, showing a zero dependence on CO, i n d i c a t e that the formation of Ru**(CO) could proceed through a mechanism i n v o l v i n g some p r e d i s s o c i a t i o n of the type, !<• I I 1 I I LRu C l —±—y Ru C l + L (8,7) n +-j n k - l TT fact TT Ru C l + CO f > Ru C l (CO) (8,8) n k n J v J where L may be c h l o r i d e , DMA o r , more u n l i k e l y , li^O (OH ) . Such a mechanism would y i e l d the r a t e - l a w , -d[Ru I 1 :ci ] n J , r n I I dt: = k ^ R u ^ C l J (8,9) which i s a l i m i t i n g form of the general rate-law -d[Ru I ICl ] k k [ R u H C l ] [CO] n n (8,10) dt k _ 1 L L ] + k [CO] - 1 8 3 -- 184 -- 185 -Table XXIV Formation of R u T I ( C 0 ) 2 i n DMA Temperature dependence of [Ru n(CO}] = 2.10.x 10" 2, M Temperature [CO] k 2 °C x 10 3, M x 10 4, S" 1 80 4.70 1.68 3.56 1.48 2.65 1.26 1.73 1.00 0.97 0.59 75 4.71 1.07 2.71 0.84 70 4.87 0.71 2.78 0.57 65 4,95 0.38 2.84 0.33 - 186 -when k >> k ^. Since the r a t e i s e s s e n t i a l l y independent of CO even at the lowest pressures used, i t i s impossible to t e s t the system f o r an inverse dependence on L s i n c e the k [CO] term i n the deonominator always predominates. I f L i s c h l o r i d e , r e a c t i o n (8,7) could be a solvent a s s i s t e d d i s s o c i a t i o n and (together with r e a c t i o n 8,8) such an o v e r a l l mechanism has been p o s t u l a t e d p r e v i o u s l y f o r s u b s t i t u t i o n r e a c t i o n s i n v o l v i n g carbonyls. 139,140 The rate-law f o r the corresponding r e a c t i o n i n aqueous HC1 2- 37 i n v o l v i n g the RuCl^ species i s I I . - - ^ ^ - k'[Ru n][C0] (8,11) No d i s c u s s i o n of the mechanism was presented but the rate-law could s t i l l be c o n s i s t e n t with r e a c t i o n s (8,7) and (8,8). I f k ^ [L ] i s large compared with k [CO], i . e . , the back.reaction of (8,7) competes favourably with r e a c t i o n (8,8), then the rate-laws are equivalent w i t h k'= k^k /k ^ [L ] And indeed a marked inv e r s e dependence on added c h l o r i d e (of the r i g h t order of magnitude) was observed. The s o l u b i l i t y of CO i s some ten times l e s s i n H^ O than i n DMA and t h i s could be one f a c t o r g i v i n g r i s e to the observed d i f f e r e n t rate-laws. A rate-law such as (8,10) gives a CO dependence of the form shown below DMA r a t e - 187 -In aqueous media the system could l i e i n the f i r s t - o r d e r dependence r e g i o n , and i n D M A i n the zero-order r e g i o n . Some evidence f o r a pre-d i s s o c i a t i o n step i n the aqueous sytem i s that the reported a c t i v a t i o n t t parameters of AH = 19 kcal/mole, AS = -5 eu are very s i m i l a r to 2- t those reported f o r the r e a c t i o n of RuCl^ with ethylene (AH = 22,8 t 52 t kcal/mole, AS = -4 eu) and with formic a c i d ( A H =23.5 kcal/mole, t 69 AS = -5 eu) where the p r e d i s s o c i a t i o n step R u C 142 " 7 — R u C l 3 " + C l " (8,12) seems w e l l s u b s t a n t i a t e d f o r both systems. In the D M A system, the maximum p o s s i b l e number of c h l o r i d e s i n i t i a l l y coordinated i s 3 and a process such as R u C 1 3 ~ * R " C 1 2 + C l (solvent omitted) (8,13) f seems more compatible w i t h the AS values (^  -24 eu) than e q u i l i b r i a i n v o l v i n g lower c h l o r o species s i n c e such i o n i z a t i o n processes t 141 142 g e n e r a l l y have much l a r g e r negative AS values. ' ' The somewhat t lower AH value (16.9 kcal/mole) might be expected i f these e q u i l i b r i a are s o l v e n t a s s i s t e d processes because of the somewhat greater donor 122 power of D M A compared to H^O. Very s i m i l a r conclusions have been drawn regarding a c t i v a t i o n parameters f o r r e a c t i o n of CO with RhCl^ 104 i n HC1 and D M A media. I t i s i n t e r e s t i n g to note that very s i m i l a r a c t i v a t i o n parameters r e s u l t f o r the r e a c t i o n s of both CO and H„ . - 188 -(AK + = 16.6 kcal/mole, AS + = -13.3 eu) with R u * * C l n i n DMA, and the p o s s i b i l i t y of the H 2 r e a c t i o n i n v o l v i n g an intermediate from a . d i s s o c i a t i o n step cannot be completely r u l e d out. The i n v e r s e k i n e t i c dependence of the r e a c t i o n f o r the formation of Ru**(CO) 2 on the C l c o n c e n t r a t i o n along w i t h the observa-t i o n that the r a t e tends to approach a l i m i t i n g value w i t h i n c r e a s i n g carbon monoxide con c e n t r a t i o n i n d i c a t e more d e f i n i t e l y a mechanism i n v o l v i n g a p r e d i s s o c i a t i o n f o r the second stage of the r e a c t i o n : Ru**Cl n(CO) 2> Ru**Cl n_ 1(CO) + C l " (8,14) k-2 k Ru**Cl n (CO) + CO — ^ Ru**Cl , (C0)_ (8,15) n-1 n-1 2 Assuming the steady s t a t e approximation f o r the intermediate Ru**Cl .(CO) t h i s mechanism y i e l d s the rate-law: n-1 -d[Ru**Cl n_ 1(CO)] k 2k 3[Ru**Cl n_ 1(CO)][CO] (8,16) d t k _ 2 [ C l ~ ] + k 3[CO] At constant [ C l ] and [CO], we may w r i t e , k' = k 2 k 3 [ C O ] / ( k _ 2 [ C l " ] + k 3[CO]) (8,17) hence 189 The l i n e a r p l o t o f l / k ^ versus 1/[C0] at 80° at constant [ C l ] , shown i n Figure 64, i s i n accord w i t h t h i s r e l a t i o n and y i e l d s the value of and (k 2 [ C l ~ ] / k 3 ) l i s t e d i n Table XXV. Results from more l i m i t e d data at other temperatures are a l s o i n c l u d e d . The value of k^ obtained from - 4 - 1 the p l o t of 1/k^ against [Cl ] (Figure 63) i s about 2.5 x 10 S i n -4 -1 good agreement w i t h the value l i s t e d i n Table XXV (3.12 x 10 S ) at 80°. A p l o t o f l o g k 2 versus T 1 (Figure 65) y i e l d s a good s t r a i g h t t l i n e together w i t h the a c t i v a t i o n parameters AH^ = 28.1 t 1.5 kcal/mole and A S 2 + = +4.7 ! 2 eu. The r e a c t i o n i s s i m i l a r to that between ruthenium(II) and formic a c i d i n aqueous HC1 s o l u t i o n , which y i e l d s a ruthenium(II)-carbonyl 69 complex. . A mechanism s i m i l a r to that proposed here i s i n v o l v e d : I I 2- i I I -Ru C l -r-^-» Ru C l 3 + C l (8,19) R u n C l 3 _ + HCOOH 2> R u n c i 3 ( C 0 ) " + H^ O (8,20) although the mechanism of the second step was not e l u c i d a t e d . The ease of d i s s o c i a t i o n of a c h l o r i d e l i g a n d w i l l be greater f o r the more l a b i l e systems i n the R u ^ C l complexes, i . e . , w i t h i n c r e a s i n g number of c h l o r i d e (and the k^ value f o r r e a c t i o n i n v o l v i n g R u ^ C l ^ f C O ) , n probably 2 or 3, i n the DMA system i s much l e s s than the aqueous system i n v o l v i n g 2-RuCl^ ) , and the general trends i n r e a c t i v i t i e s of these systems i n DMA and aqueous media are i n l i n e w i t h t h i s . No d e t a i l e d k i n e t i c s were reported f o r the formation of R u 1 1 ( C 0 ) 2 from Ru^(CO) i n aqueous HC1 s o l u t i o n , due to the slowness of the r e a c t i o n . - 190 -- 191 -Table XXV Formation of Ru i : [(CO) 2 i n DMA E f f e c t s of temperature on r a t e constants Temperature k _ 2 [ C l 1/k^  °C x 10 4, S"1 x 10 3, M 80 3.12 4.02 75 1.73 2.91 70 0.98 1.80 65 0.49 1.63 - 192 -- 193 -8.1.6. C a t a l y t i c Hydrogenation Using Ru** Species i n DMA A s o l u t i o n of Ru**(CO) was found to c a t a l y z e the hydrogenation of maleic a c i d at 80° ( I n i t i a l r a t e = 2.6 x 10" 5 MS - 1 f o r a 1.3 x 10" 2 M II -2 Ru CO s o l u t i o n , 3.6 x 10 M maleic a c i d and 725 mm. H^; r a t e f a l l s o f f ) , and no r e d u c t i o n to Ru* occurred. Ru**(C0) 2 was found to be completely u n r e a c t i v e . S o l u t i o n s of Ru** c h l o r i d e d i d c a t a l y z e the hydrogenation of maleic a c i d ( I n i t i a l r a t e = 6.3 x 10~ 5 MS"* f o r a 2.1 x 1 0 - 2 M Ru** s o l u t i o n , 5.0 x 10 M maleic a c i d and 725 mm. H^ at 80°) although the system i s complex because of the accompanying r e d u c t i o n to Ru*; Ru** i s reduced at a much slower r a t e to Ru* (Section 4.3.) ( I n i t i a l r a t e = 0.83 x 10~ 5 MS"* f o r a 2.1 x 10~ 2 M s o l u t i o n and 725 mm. H 2 at 80°), and so the 6.3 x 10 3 MS * r a t e l i k e l y r e f e r s to the Ru** c h l o r i d e c a t a l y z e d r e d u c t i o n . The decrease i n a c t i v i t y o f a complex towards hydrogen when a l i g a n d o f strong i r - a c i d i t y i s coordinated to the metal has been explained as due to the withdrawal o f e l e c t r o n d e n s i t y from the metal 30 r e s u l t i n g i n an increase i n promotional energy. Carbon monoxide, being a strong i r-acid, would thus decrease the r e a c t i v i t y of ruthenium(II) i n a c t i v a t i n g molecular hydrogen. CO c l e a r l y s t a b i l i z e s the d i v a l e n t s t a t e towards r e a c t i v i t y w i t h H^, and the r e l a t i v e e f f i c i e n c y o f the ruthenium(II) systems f o r hydrogenation i s seen to be: Ru** > Ru**(C0) > Ru**(C0) 2 37 as found i n the corresponding aqueous systems. - 194 -8.2. D i r e c t Carbonylation of Ruthenium(I) C h l o r i d e Complexes i n DMA 8.2.1. Stoichiometry Ruthenium(I) c h l o r i d e complexes i n DMA, prepared by the r e a c t i o n of H w i t h RuCl 3.3H 20 at 80° (Chapter IV, Se c t i o n 4.3.), absorbed carbon monoxide i n the temperature range 30-80°. The t o t a l measured gas uptake corresponded c l o s e l y to a 2:1 mole r a t i o of carbon monoxide to ruthenium (Figures 66 and 67). Roughly h a l f of the f i r s t mole o f CO was taken up extremely r a p i d l y even at room temperature and was i n d i c a t i v e of an i n i t i a l r a p i d e q u i l i b r i u m i n v o l v i n g CO ab s o r p t i o n ; the second h a l f of the f i r s t mole of CO was taken up more slo w l y w i t h decreasing r a t e (Figures 66 and 67). The second mole of CO was absorbed at a much slower r a t e . Depending on the c o n d i t i o n s , the uptake p l o t s sometimes showed a much more pronounced i n f l e x i o n at the 1:1 stage (Figure 67). These data again suggested a 2 step c a r b o n y l a t i o n r e a c t i o n i n v o l v i n g the a d d i t i o n of one and two CO groups: Ru 1 + CO ——*• Ru J(CO) (8,21) Ru :(C0) + CO »- R u X ( C 0 ) 2 (8,22) although i t should be remembered that ruthenium(I) c h l o r i d e complexes e x i s t as a dimer —> monomer e q u i l i b r i u m i n DMA s o l u t i o n (Chapter IV and V). The o r i g i n a l brown colour o f ruthenium(I) c h l o r i d e i n DMA remained v i s i b l y unchanged a f t e r the CO absorption. An I.R. spectrum of a s o l u t i o n c o n t a i n i n g Ru*(CO) a f t e r the f i r s t mole of CO uptake, showed 4.0 o.oCh 0 Figure 66. 4000 i 8000 I 12,000 1 16,000 Time, Sec. 20,000 Uptake o f CO by a 0.021 M Ru(I) c h l o r i d e DMA s o l u t i o n (757 mm. CO, 30°) broken l i n e s correspond to the uptake of 1 mole of CO and 2 moles of CO r e s p e c t i v e l y , per mole of Ru*. The o u 4000 6000 8000 Time, Sec, Figure 67. Uptake of CO by a 0.021 M R u ( I ) c h l o r i d e DMA s o l u t i o n (660 mm. CO, 80°). The broken l i n e s correspond to the uptake of 1 mole of CO and 2 moles of CO r e s p e c t i v e l y , per mole of Ru 1. - 197 -a broad band at a, 2000 cm *. The f i n a l Ru*(C0) 2 s o l u t i o n had bands at 2030 cm * and 1900 cm * i n d i c a t i n g the presence of two CO groups. These bands are at lower wavenumbers than observed f o r DMA s o l u t i o n s c o n t a i n i n g Ru**(C0) 2 (2040 and 1960 cm *) and t h i s i s c o n s i s t e n t w i t h involvement of a lower valency s t a t e of the metal. Oxygen o x i d i z e d the brown Ru*(CO) 2 s o l u t i o n at 80° very r a p i d l y to a yellow s o l u t i o n which was i d e n t i f i e d s p e c t r o s c o p i c a l l y to be Ru**(CO) 2 ^max = m l - 0 ; a t l ° w e r temperatures t h i s r e a c t i o n was followed by gas uptake and was shown to be a s t o i c h i o m e t r i c o x i d a t i o n of Ru* to Ru**, g i v i n g i n c i d e n t a l l y f u r t h e r evidence of the existence of u n i v a l e n t Ru i n the brown s o l u t i o n s : Ru*(C0) 2 + l / 4 0 2 y Ru**(C0) 2 (8,23) In the presence of L i C l (0.1 M) the brown Ru*(C0) 2 s o l u t i o n turned deep I I I 2-red i n a i r s l o w l y ; t h i s could be due to the formation of a[Ru Cl^(CO)] 37 complex which gives a deep red s o l u t i o n i n aqueous systems. The r e a c t i o n of CO w i t h DMA s o l u t i o n s of Ru*** was not i n v e s t i g a t e d . Many attempts were made to i s o l a t e a ruthenium(I) carbonyl complex, p a r t i c u l a r l y by the a d d i t i o n of triphenylphosphine. From Ru*(C0) 2 s o l u t i o n s c o n t a i n i n g PPh^ a yellow c r y s t a l l i n e s o l i d s l o w l y separated i n a i r . However the pale yellow s o l i d (I.R. KBr d i s c V^Q = 2050, 1990 cm"1; decomposed ^ 272°; elemental a n a l y s i s C = 60.88%, H = 3.96%) i s undoubtedly Ru**Cl 2(CO) 2(PPh 3) 2, 3 7' 4* , 6° probably formed v i a Ru**(C0) 2 species. - 198 -8.2.2. K i n e t i c s of the F i r s t Stage Part of the CO uptake i n the f i r s t stage was too r a p i d f o r accurate measurements to be made. However the remaining r a t e up to c l o s e to the 1:1 stage analyzed w e l l f o r a f i r s t - o r d e r dependence on t o t a l Ru* assuming the s t o i c h i o m e t r y r e l a t i o n s h i p [ R u I ] T o t a l = [RuVo)] + [Ru1] (8,24) That i s the f i r s t - o r d e r rate-law 4 f W l : . d [ R J ( C O ) l . k [ R u I j ( 8 ) 2 5 ) i s obeyed, k^ was determined from the slope of the log p l o t s such as that shown i n Figure 68 and the values of k^ thus obtained are summarized i n Table XXVI. k^ was found to be independent of CO over the range i n v e s t i g a t e d . An important e f f e c t was observed i n experiments i n which c h l o r i d e was added; w i t h i n c r e a s i n g c h l o r i d e the amount of CO absorbed " i n s t a n t a n e o u s l y " a l s o increased. At an added c h l o r i d e c o n c e n t r a t i o n of 0.1 M, with a 0.02 M Ru* s o l u t i o n , about 1 mole of CO per mole pf Ru* was r a p i d l y absorbed; some s c a t t e r was observed i n these experiments because of the r a p i d uptake and d i f f i c u l t y i n measurement, but the trend seemed d e f i n i t e , k^ was found to be remarkably i n s e n s i t i v e to change i n f temperature, and an Arrhenius p l o t gives a AH value o f only about 2 kcal/mole. - 199 -The broken l i n e s correspond to the uptake of 1 mole of CO per mole of Ru* . .. ^ t o t a l - 200 -Table XXVI Formation of Ru 1(CO) i n DMA K i n e t i c data ^ t o t a l CO [CO] Temperature k l x 10 2, M mm. x 10 3, M °C x 10 3, S" 1 2.10 725 4.70 80 2.78 2.10 660 4.28 80 2.05 2.10 550 3.56 80 2.56 2.10 347 2.25 80 2.27 1.58 550 3.56 80 2.37 1.05 550 3.56 80 2.07 2.10 720 4.71 75 2.81 2.10 737 4.87 70 2.63 2.10 742 4.95 65 2.49 2.10 745 5.03 60 2.30 2.10 757 5.40 30 2.05 - 201 -8.2.3. K i n e t i c s o f the Second Stage The r e a c t i o n f o r t h i s second stage can be represented by: Ru (CO) + CO (8,26) I The formation of Ru (CO) was found to obey the second-order rate-law At constant CO c o n c e n t r a t i o n the r e a c t i o n thus e x h i b i t e d p s e u d o - f i r s t -order k i n e t i c behaviour. Values of k^ were determined using Equation (8,27) from the slopes of f i r s t - o r d e r log p l o t s such as that shown i n Figure 69. The values of k 2 obtained are summarized i n Table XXVII. A d d i t i o n of c h l o r i d e up to 1.0 M only had a small e f f e c t on k^. Measurements of k^ over the temperature range 30-80° (Table XXVII) y i e l d e d a good Arrhenius p l o t (Figure 70) from which the f o l l o w i n g a c t i v a t i o n parameters were determined: -dtRu^CO)] _ d r V ( co ) 2 ] = k 2[Ru I(C0)][C0] (8,27) dt ; dt AH 2 + = 13.6 t 1.0 kcal/mole, AS 2 = -23.1 1 S eu 8.2.4. D i s c u s s i o n The k i n e t i c r e s u l t s suggested that the formation of Ru*(CO) may go through mechanism such as - 203 -Table XXVII Formation of R u I ( C 0 ) 2 i n K i n e t i c data DMA [Ru r(C0)] CO [CO] Temperature k 2 x 10 2, M mm. x 10 3, M °C M-V1 2.10 725 4.70 80 0.25 2.10 660 4.28 80 0.21 2.10 550 3.56 80 0.22 2.10 347 2.25 80 0.26 1.58 550 3.56 80 0.24 1.05 550 3.56 80 0.20 2.10 720 4.71 75 0.21 2.10 737 4.87 70 0.15 2.10 742 4.95 65 0.11 2.10 745 5.03 60 0.09 2.10 755 5.31 40 0.02 2.10 757 5.40 30 0.01 2.10 634 4.52 30 0.01 2.05 725 4.70 80 0.22 2.05 725. 4.70 80 0.16 a 2.05 725 4.70 80 0.12 b 2.05 725 4.70 80 0.16° a 0.05 M L i C l b 0.1 M L i C l C 1.0 M L i C l - 205 -Ru I + CO f a s t Ru (CO) (8,29) This would y i e l d the rate-law = k[Ru*] (8,30) dt which i s c o n s i s t e n t w i t h the experimental rate-law (8,25) with k = k^. The i n i t i a l f a s t CO uptake would have to r e s u l t from some monomeric Ru 1 i n i t i a l l y present (^  50% of the t o t a l Ru 1). However the k i n e t i c data f o r the Ru* c a t a l y z e d hydrogenation of maleic a c i d (Chapter V) i n d i c a t e d that the metal i s present almost e n t i r e l y as a dimeric form (presumably w i t h c h l o r i d e bridges) p a r t i c u l a r l y at the higher ruthenium concentrations (Kp ^ 10 3 M). Hence a more r a t i o n a l explanation would i n v o l v e an i n i t i a l r a p i d r e a c t i o n of the dimer with CO: CO f a s t (8,31) + The subsequent steps (Cl ?) k -y Ru (CO) + Ru I (8,32) k* CO with k < k*, could account f o r the rate-law (8,25) f o r the formation of - 206 -Ru* (CO) w i t h k = k^. The rate-determining step i s thus cleavage of the dimer. C h l o r i d e amongst other donors i s w e l l known to cleave c h l o r i d e -143 144 ; bridged dimers of platinum metals, ' and the r a p i d uptake of 1 mole of CO per mole of Ru* at higher c h l o r i d e concentrations can be r e a d i l y accounted f o r . There appears to be no published data on r e a c t i o n s of CO w i t h dimeric complexes of platinum metals i n s o l u t i o n but recent work i n t h i s 145 146 4-l a b o r a t o r y has shown that the dimeric anion [RhCl(SnCl^)^\ r e a c t s r a p i d l y w i t h CO i n acetone s o l u t i o n to form a carbonyl although the s t o i c h i o m e t r y of the r e a c t i o n has not yet been e l u c i d a t e d . The k i n e t i c s of cleavage r e a c t i o n s such as (8,32) a l s o do not appear t o have been s t u d i e d ; the a c t i v a t i o n enthalpy of ~2 kcal/mole does seem remarkably low but i t may be c o n s i s t e n t w i t h a process i n v o l v i n g cleavage by c h l o r i d e w i t h formation of new metal c h l o r i d e bonds. The formation of Ru*(CO) could go through e i t h e r a d i r e c t S^2 mechanism, or through a p r e d i s s o c i a t i o n step as shown f o r the formation of Ru**(C0) 2 s p e c i e s ; the k i n e t i c data of Table XXVII are not s u f f i c i e n t to d i s t i n g u i s h between these two. 8.2.5. C a t a l y t i c Hydrogenation Using Ru* Species i n DMA Ru*(C0) 2 was found to be u n r e a c t i v e i n a c t i v a t i n g molecular hydrogen, while Ru*(CO) c a t a l y z e d , very s l o w l y , the r e d u c t i o n of maleic a c i d at 80°. The r e a c t i o n r a t e decreased w i t h time but had an i n i t i a l r a t e of 2.60 x 10" 5 MS-* f o r 0.013 M Ru*(CO), 0.036 M M.A. and 725 mm. H2_ This r a t e i s about 1/3 that measured f o r Ru* c h l o r i d e i n corresponding - 207 -c o n d i t i o n s . Again c a t a l y t i c a c t i v i t y towards of these ruthenium(I) •complexes f a l l s i n the trend Ru 1 > Ru^CO) > R u I ( C 0 ) 2 CHAPTER IX GENERAL CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK The most important f i n d i n g i n the present s t u d i e s i s the production and existence of u n i v a l e n t ruthenium i n s o l u t i o n . Such species have been p o s t u l a t e d p r e v i o u s l y to occur as intermediates i n a number of systems i n aqueous s o l u t i o n , p a r t i c u l a r l y i n v o l v i n g redox r e a c t i o n s , but evidence f o r these was exceedingly scant. A few re p o r t s have appeared on the existence of ruthenium(I) compounds i n the s o l i d s t a t e but the m a j o r i t y of these are not too convincing and the s o l i d s are p o o r l y c h a r a c t e r i z e d . The ruthenium(I) species have been produced i n the non-aqueous s o l v e n t , dimethylacetamide (DMA), by the hydrogen r e d u c t i o n o f ruthenium c h l o r i d e s ( R u 1 1 , R u 1 1 1 or Ru 1^). Other solvent systems have not yet been s t u d i e d , although ruthenium(I) i s not produced in.aqueous systems by the same procedure. Ruthenium(II) i n aqueous a c i d s o l u t i o n (3 M HC1) i s thermodynamically s t a b l e and i s reduced by H^ to the metal; i n l e s s a c i d i c media (0.5 M HC1), ruthenium(II) reduces water. The present s t u d i e s are the f i r s t reported on the s o l u t i o n chemistry of ruthenium c h l o r i d e s i n a non-aqueous s o l v e n t , and are thought to be s i g n i f i c a n t and of importance i n view of very recent l i t e r a t u r e concerning the use of ruthenium complexes ( p a r t i c u l a r l y the 'simple' c h l o r i d e s ) i n non-aqueous solv e n t s as c a t a l y s t s f o r a whole - 209 -range of c a t a l y t i c r e a c t i o n s , such as hydrogenation, p o l y m e r i z a t i o n , hydroformylation, i s o m e r i z a t i o n , and o x i d a t i o n of unsaturated o r g a n i c s ; some of these processes obviously use hydrogen as a n e c e s s i t y , others such as i s o m e r i z a t i o n and p o l y m e r i z a t i o n are f r e q u e n t l y enhanced under a hydrogen atmosphere. The hydrogen r e d u c t i o n of ruthenium c h l o r i d e s i s thought to in v o l v e h e t e r o l y t i c s p l i t t i n g of the molecule: R u n + + H 2 -A* R u H ( n - 1 ) + + H + (9,1) R u H ( n - 1 ) + + R u n + 2 R u C n - ^ + + H + (9,2) (ligands omitted) In aqueous a c i d s o l u t i o n the reverse o f (9,1) prevents r e d u c t i o n of Ru***; i n DMA, a b a s i c s o l v e n t , the re l e a s e d proton i s s t a b i l i z e d and re d u c t i o n i s observed a l l the way to the u n i v a l e n t s t a t e . Unfortunately no w e l l - c h a r a c t e r i z e d ruthenium(I) species have been i s o l a t e d from the c h l o r i d e s o l u t i o n s or from s o l u t i o n s c o n t a i n i n g ruthenium(I) carbonyl s p e c i e s , d e s p i t e considerable e f f o r t . However the existence f o r the u n i v a l e n t s t a t e i n the brown s o l u t i o n s i s convincing and may be summarized below: (A) The brown s o l u t i o n s may be prepared by r e d u c t i o n of Ru** w i t h 0.5 mole H 2 per mole Ru**, and no metal-hydrogen bond i s detected. Ru** + 1/2H2 Ru* + H + (9,3) - 210 -(B) The brown s o l u t i o n s are o x i d i z e d to R u 1 1 1 by oxygen with the expected s t o i c h i o m e t r y Ru 1 + 1/20 »- R u 1 1 1 (9,4) (C) The brown s o l u t i o n s react with 2 moles carbon monoxide per mole Ru to produce a s o l u t i o n which can be o x i d i z e d with oxygen (with the expected stoichiometry) to a yellow s o l u t i o n c o n t a i n i n g R u 1 1 ( C 0 ) 2 • R u T ( C 0 ) 2 + l / 4 0 2 »- R u H ( C 0 ) 2 (9,5) Further s t u d i e s i n the area of ruthenium(I) s o l u t i o n chemistry and f u r t h e r e f f o r t to i s o l a t e w e l l - c h a r a c t e r i z e d Ru(I) compounds seem e s s e n t i a l . S o l u t i o n s of ruthenium(I) have been found t o be q u i t e e f f i c i e n t f o r the c a t a l y z e d hydrogenation of maleic and fumaric acids under m i l d c o n d i t i o n s ; c i s a d d i t i o n of H 2 across the o l e f i n i c bond i s observed. An observed h a l f - o r d e r dependence on ruthenium concentration i s c o n s i s t e n t w i t h the ruthenium(I) being present i n s o l u t i o n p r a c t i c a l l y e n t i r e l y as dimers at concentrations >. 10 M. Some spectrophotometric data, and f u r t h e r k i n e t i c evidence from a) the r e a c t i o n of H 2 w i t h the ruthenium(I) s o l u t i o n c o n t a i n i n g PPh^, and b) the r e a c t i o n of CO w i t h the ruthenium(I) s o l u t i o n , a l s o i n d i c a t e s the presence of dimeric species. The r e a c t i o n scheme f o r the c a t a l y z e d hydrogenation i s p o s t u l a t e d as f o l l o w s , I KD I R u 2 > 2Ru (9,6) - 211 -V I 1 I I I Ru + H > Ru II + C l ~% -1 ( k _ l » kP v-I I I 2 I Ru + o l e f i n *- Ru + product The brown s o l u t i o n s themselves show no r e a c t i o n w i t h e i t h e r W or the substrate alone under the hydrogenation c o n d i t i o n s ; t h i s i s l i k e l y due to the predominance of the dimeric s t a t e of the c a t a l y s t . An extremely a c t i v e c a t a l y s t system could r e s u l t from a p u r e l y monomeric ruthenium(I) s p e c i e s . The system was i n c i d e n t a l l y found to be e f f i c i e n t f o r c a t a l y z i n g the i s o m e r i z a t i o n of maleic a c i d to fumaric a c i d , and t h i s s t r o n g l y suggests that the t r a n s f e r process i n r e a c t i o n (9,8) i n v o l v e s two consecutive s i n g l e H atom t r a n s f e r s to a coordinated o l e f i n i . e . , v i a a a - a l k y l hydride complex. Since the most a c t i v e hydrogenation c a t a l y s t s yet discovered c o n t a i n coordinated PPh^, the Ru* c a t a l y s t system was r e i n v e s t i g a t e d i n the presence of t h i s l i g a n d ; the PPh^ system was found i n f a c t to be much l e s s a c t i v e , but the s t u d i e s gave evidence that a ruthenium hydride species can be formed from r e a c t i o n of molecular hydrogen with ruthenium(I) ( c f . Equation 9,7). The ruthenium(I) s o l u t i o n s were found to have a strong a f f i n i t y f o r gaseous carbon monoxide and there was some evidence that i t p o s s i b l y decarbonylates ether. Such d e c a r b o n y l a t i o n - c a r b o n y l a t i o n r e a c t i o n s are f i n d i n g i n c r e a s i n g use i n organic syntheses and i n some cases, w i t h rhodium(I) complexes, have been made c a t a l y t i c . This aspect of the work seems w e l l worth f u r t h e r study. (9,7) (9,8) - 212 -In the presence of PPh 3, r e a c t i o n of w i t h R u ( I I I , IV) s a l t s i n DMA does not produce Ru 1 systems; the Ru* 1 hydride intermediate i n a r e a c t i o n such as (9,1) i s s t a b i l i z e d by the phosphine l i g a n d . Such a r e a c t i o n y i e l d s then the ruthenium(II) hydride complex RuHCl(PPh^)^, which has been reported to be the most a c t i v e homogeneous hydrogenation c a t a l y s t yet discovered; i t i s much more e f f i c i e n t than the f a m i l i a r heterogeneous Adams c a t a l y s t , and i s h i g h l y s p e c i f i c f o r t e r m i n a l o l e f i n s . The present s t u d i e s give i n s i g h t i n t o the mechanism of formation of the hydrido complex and of considerable i n t e r e s t i s that i n a b a s i c solvent such as DMA the f i n a l step R u H C l 2 ( P P h 3 ) 3 + H 2 »- R u n H C l ( P P h 3 ) + H + + C l " (9,9) i s promoted to such an extent that the usual a d d i t i o n of a base, such as EtgN, r e p o r t e d l y necessary, i s no longer r e q u i r e d ; the r e a c t i o n presents an extremely simple method at low temperatures (35-80°) f o r the p r e p a r a t i o n of the c a t a l y s t ' i n s i t u ' . This c a t a l y s t was r e c e n t l y discovered by Wilkinson's group and t h e i r s t u d i e s were c a r r i e d out i n benzene s o l u t i o n s ; f o r a number of p r a c t i c a l reasons they were unable to o b t a i n r e l i a b l e k i n e t i c data f o r c a t a l y z e d hydrogenation r e a c t i o n s , although they d i d p o s t u l a t e the f o l l o w i n g mechanism: k l RuHCl ( P P h 3 ) 3 —=-»• RuHCl ( P P h 3 ) 2 + PPh 3 (9,10) K RuHCl(PPh 3) 2 + o l e f i n RuCl(PPh 3) ( a l k y l ) (9,11) R u C l ( P P h 3 ) 2 ( a l k y l ) + H 2 — ^ RuHCl(PPh 3) 2 + alkane (9,12) - 213 -The present s t u d i e s i n DMA using maleic a c i d as substrate y i e l d e d e x c e l l e n t and r e p r o d u c i b l e k i n e t i c data which are e n t i r e l y c o n s i s t e n t w i t h the above mechanism, and have given a quantitative e s t i m a t i o n of the important constants K^, and k. Some stu d i e s i n aqueous a c i d s o l u t i o n s i n v o l v i n g the use of I I 2-the a n i o n i c complex, [Ru C l ^ ( b i p y ) ] , as a hydrogenation c a t a l y s t seemed promising but were not pursued because t r a c e s of metal (a heterogeneous c a t a l y s t ) were sometimes observed at low sub s t r a t e concentra-t i o n s . However some meaningful k i n e t i c data were obtained and a mechanism s i m i l a r to that o u t l i n e d above i n Equations (9,9), (9,11) and (9,12) seemed p l a u s i b l e . The mechanism i s q u i t e d i f f e r e n t to th a t p o s t u l a t e d by Halpern's group f o r ca t a l y z e d hydrogenation using the a n i o n i c species I I 2-Ru C l ^ , and the d i f f e r e n c e can r e a d i l y be accounted f o r i n terms o f the degree of c o o r d i n a t i o n and c h l o r i d e l a b i l i t y of the complexes i n v o l v e d . The c o m p l i c a t i o n of metal production might w e l l be avoided using a d i f f e r e n t solvent system, and data g i v i n g c o r r e l a t i o n between c a t a l y t i c a c t i v i t y and the b i p y r i d y l ( i . e . , using a range of s u b s t i t u t e d b i p y r i d y l s ) could be v a l u a b l e . The present s t u d i e s are of p a r t i c u l a r i n t e r e s t i n that they i n v o l v e the formation, i n one way or another, of metal hydride complexes by three valency s t a t e s o f the same metal, namely ruthenium(I), ( I I ) and ( I I I ) . The f a c t that hydrogen a c t i v a t o r s are i n general e l e c t r o n - r i c h 30 147 systems has l e d some workers ' to suggest that the primary i n t e r -a c t i o n of molecular H^ i n s o l u t i o n w i t h a metal species i n v o l v e s the f e e d i n g - i n of e l e c t r o n d e n s i t y i n f i l l e d metal o r b i t a l s to an acceptor 147 o r b i t a l of one atom of the hydrogen molecule. Nyholm has t e n t a t i v e l y suggested that an anti-bonding o r b i t a l could be used as an acceptor. - 214 -93 148 Other workers, ' however, have suggested that the bonding e l e c t r o n s of hydrogen could attack a vacant metal o r b i t a l . I f a complex a c t i v a t e d H 2 through d i h y d r i d e formation, the process i n v o l v e s o x i d a t i o n of the metal 30 and of prime importance i s the s o - c a l l e d promotional energy of the metal. For a comparable s e r i e s of complexes with d i f f e r e n t valency states of the same metal, such an energy would be lower w i t h lower valency. In our ruthenium systems the data f o r the ruthenium(I) c h l o r i d e c a t a l y z e d hydrogenation of o l e f i n s are c o n s i s t e n t only with a c t i v a t i o n through a d i h y d r i d e , Ru 1 + H 2 ^ R u I H H 2 (9,13) The data on the a c t i v a t i o n of by ruthenium(II) and ruthenium(III) c h l o r i d e complexes show no such evidence and on comparison with s i m i l a r systems i n aqueous media these systems almost c e r t a i n l y i n v o l v e a h e t e r o l y t i c s p l i t t i n g of H 2 molecule, e.g., R u 1 1 1 + H *• R u H I H + H + (9,14) Considering hydride as j u s t another a n i o n i c l i g a n d such as c h l o r i d e or hydroxide, one might expect the metal-hydride bond to be stronger with i n c r e a s i n g valency of the metal, and hydride formation through h e t e r o l y t i c f i s s i o n thus favoured w i t h the higher valency s t a t e . Perhaps s u r p r i s i n g l y no ruthenium(III) monohydride complex has yet been prepared. Ruthenium(II) 42 83 hydrides i s o l a t e d ' a l s o c o n t a i n u-acceptor ligands such as CO and t e r t i a r y phosphines; they e f f e c t i v e l y decrease the e l e c t r o n d e n s i t y on the metal by back donation and could favour the hydride formation. The - 215 -production of a ruthenium(III) monohydride complex seems f e a s i b l e and i n 14 t h i s context i t i s of i n t e r e s t that an a i r - s t a b l e rhodium(III) hydride, [RhHfNH^) j_]SO^, c o n t a i n i n g no Tr-acceptor l i g a n d has been i s o l a t e d . I t i s very d i f f i c u l t to attempt any general c o r r e l a t i o n between c a t a l y t i c a c t i v i t y f o r o l e f i n hydrogenation and the e l e c t r o n i c s t r u c t u r e of the c a t a l y s t i n v e s t i g a t e d . However c e r t a i n p o i n t s are worthy of note: (A) The s t u d i e s f u r t h e r s u b s t a n t i a t e that i n t r o d u c t i o n of CO i n t o a metal complex i n h i b i t s i t s a c t i v i t y , presumably due to the Tr-acceptor l i g a n d i n c r e a s i n g the promotion energy f o r d i h y d r i d e formation by a species such as Ru*. (B) The l i m i t e d data on the ruthenium(II) chloride/DMA system i n d i c a t e i t s a c t i v i t y i s probably s i m i l a r to that of ruthenium(I) to which i t i s reduced under the hydrogenation c o n d i t i o n s . (C) A d d i t i o n of PPh^ to ruthenium(I) c h l o r i d e s o l u t i o n s decreases the a c t i v i t y by a f a c t o r of about 5, while a d d i t i o n of PPh^ to ruthenium(II) c h l o r i d e s o l u t i o n s g r e a t l y increases the hydrogenation r a t e . Using the ideas formulated above t h i s could be due to the Tr-acceptor l i g a n d i n h i b i t i n g formation of a Ru* d i h y d r i d e and favouring formation of the Ru -H species. 2-(D) The a c t i v i t y of the [RuCl^(bipy)] system ( a c t i v e c a t a l y s t i s 2- 2-probably [RuHCl^(bipy)] i s about h a l f that of the RuCl^ system although q u i t e d i f f e r e n t mechanisms operate, due to the f a c t that [ R u C l ^ ( o l e f i n ) ] does a c t i v a t e hydrogen, while [ R u C l ^ ( b i p y ) ( o l e f i n ) ] does not, presumably because i t i s c o o r d i n a t i v e l y saturated. - 216 -REFERENCES 1. M. C a l v i n , Trans Faraday S o c , 34, 1181 (1938). 2. J . Halpern, Ann. Rev. Phys. Chem., j_6, 103 (1965). 3. J . Halpern, Proc. 3rd. I n t e r n . Congr. C a t a l y s i s , Amsterdam, 1964, North H o l l a n d , Amsterdam, 1_, 146 (1965). 4. J . Halpern, Chem. Eng. News, 44, 68 (1966). 5. J . Halpern, Adv. i n Chem. S e r i e s , V o l . 70, Am. Chem. S o c , Washington, D.C, 1968, p. 1. 6. E.N. Frankel and H.J. Dutton, Hydrogenation w i t h homogeneous and heterogeneous c a t a l y s i s , Topics i n L i p i d chemistry, Ed. Gunstone, to be p u b l i s h e d , Logos Press. 7. D i s s . Faraday S o c , Homogeneous c a t a l y s i s with s p e c i a l reference t o hydrogenation and o x i d a t i o n , U n i v e r s i t y of L i v e r p o o l , Sept. 1968. 8. J . Halpern, J . Harrod and B.R. James, J . Am. Chem. S o c , 8_3, 753 (1961); i b i d . , 88_, 5150 (1966). 9. J . Chatt and R.G. Hayter, J . Chem. Soc. A, 2605 (1961). 10. F.P. Dwyer, H.A. Goodwin and E.C. Gyarfas, Aust. J . Chem., _16, 42 (1963). 11. G.A. Rechnitz and H.A. Catherino, Inorg. Chem., £, 112 (1965). 12. B.R. James and G.L. Rempel, Can. J . Chem., 44, 233 (1966). 13. B.R. James and N.A. Memon, Can. J . Chem., 46, 217 (1968). 14. CW. B i r d , T r a n s i t i o n metal intermediates i n organic syntheses, Logos Press, London, 1967. 15. Organic s y n t h e s i s v i a metal carbonyls, V o l . 1, ed. I. Wender and P. Pino, I n t e r s c i e n c e , New York, 1968. - 217 -16. G.C. Bond, Platinum Metals Rev., 8_, 92 (1964); i b i d . , 13, 23 (1969). 17. G.C. Bond, Ann. Reports, Chem. S o c , 63, 27 (1966). 18. J.F. Harrod and J . Halpern, Can. J . Chem., 37, 1933 (1959). 19. E. Peters and J . Halpern, Can. J . Chem., 35_, 356 (1955); J . Phys. Chem. , 59, 793 (1955). 20. J . Halpern, E.R. Macgregor and E. Pe t e r s , J . Phys. Chem., 60, 1455 (1956). 21. R.G.S. Banks and J.M. P r a t t , J . Chem. Soc. A, 854 (1968) and references t h e r e i n . 22. L. Vaska, Accounts Chem. Res. 1_, 335 (1968) and references t h e r e i n . 23. J . Collman, Accounts Chem. Res., 1^ , 136 (1968). 24. J.F. Harrod, S. Ciccone and J . Halpern, Can. J . Chem., 39, 1372 (1961). 25. J . Halpern and B.R. James, Can. J . Chem., 4£, 671 (1966). 26. A. Sacco, R. Ugo and A. Moles, J . Chem. Soc. A, 1670 (1966). 27. M. C a l v i n and W.K. Wilmarth, J . Am. Chem. S o c , 78_, 1301 (1956). 28. J . Kwiatek and J.K. S e y l e r , Adv. Chem. S e r i e s , V o l . 70, Am. Chem. S o c , Washington, D.C, 1968, p. 207 and references t h e r e i n . 29. L. Simandi and F. Nagy, P r o c Symp. Coord. Chem., Tihany, Hungary, 1964, p. 83, Akademiai Kiado, Budapest, 1965. 30. J.A. Osborn, F.H. J a r d i n e , J.F. Young and G. W i l k i n s o n , J . Chem. Soc. A, 1711 (1966). 31. F.H. J a r d i n e , J.A. Osborn and G. W i l k i n s o n , J . Chem. Soc. A, 1574 (1967). 32. J.P. Candlin and A.P. Oldham, Discuss. Faraday S o c , 46, 60 (1968). - 2 1 8 -33. R.F. Heck, Adv. Chem. S e r i e s , V o l . 4£, Am. Chem. S o c , Washington, D.C, 1965, p. 181. 34. J.F. Biellmann and M.J. Jung, J . Am. Chem. S o c , 90, 1673 (1968). 35. G.C. Bond and R.A. H i i l y a r d , Discuss. Faraday S o c , 4j6, 20 (1968). 36. Discuss. Faraday Soc., D i s c u s s i o n remarks, 46, 86 (1968). 37. J . Halpern, B.R. James and A.L.W. Kemp, J . Am. Chem. S o c , 88^, 5142 (1966). 38. M.F. Sloan, A.S. Matlock and D.S. Breslow,J. Am. Chem. S o c , 85_, 4014 (1963). 39. P.N. Rylander, N. H i m e l s t e i n , D.R. Ste e l e and J . K r e i d l , Englehard Ind. Tech. B u l l . , 3, 61 (1962). 40. D. Evans, J . Osborn, F. J a r d i n e and G. W i l k i n s o n , Nature, 208, 1203 (1965). 41. T.A. Stephenson and G. W i l k i n s o n , J . Inorg. Nucl. Chem., 28, 945 (1966). 42. P.S. Hallman, B.R. McGarvey and G. W i l k i n s o n , J . Chem. Soc. A, 3143 (1968). 43. P.S. Hallman, D. Evans, J.A. Osborn and G. W i l k i n s o n , Chem. Commun., 305 (1967). 44. A.C. Skapski and P.G.H. Troughton, Chem. Commun., 1230 (1968). 45. L.B. L u t t i n g e r and E.C. Colthrup, J . Org. Chem., 27% 3752 (1962). 46. A. Misono, Y. Uchida, M. H i d a i , H. Shinohara and Y. Watanabe, B u l l . Chem. Soc. Japan, 41_, 396 (1968). 47. E. B i l l i g , C.B. Strow and R.L. P r u e t t , Chem. Commun., 1307 (1968). 48. A. Misono, Y. Uchida, M. H i d a i and I. Inomata, Chem. Commun., 705 (1968). - 219 -49. A.J. Canale, W.A. Hewett, T.M. Shryne and E.A. Youngman, Chem. and Ind., 1054 (1962). 50. T. Alderson, E.L. Jenner and R.V. Lindsey, J r . , J . Am. Chem. S o c , 87, 5638 (1965). 51. S. Otsuka and A. Nakamura, J . Polymer Science, Part B, Polymer L e t t e r s , 5_, 973 (1967) . 52. J . Halpern and B.R. James, Can. J . Chem., 44, 495 (1966). 5.3. R.F. Heck, J . Am. Chem. S o c , 9£, 5578 (1968). 54. A. Osipov, K.I. Matveev and N.N. S h u l ' t s , Russ. J . Inorg. Chem., 1_2, 993 (1967) . 55. P. Henry, J . Am. Chem. S o c , 8j5, 3246 (1964). 56. J . Halpern, B.R. James and A.L.W. Kemp, J . Am. Chem. S o c , 83, 4097 (1961). 57. eA.L.W. Kemp, Ph.D. D i s s e r t a t i o n , U n i v e r s i t y o f Chicago, 1964. 58. B.R. James and J . Louie, Inorg. Chim. A c t a , ( i n p r e s s ) . (a) J . Louie, M.Sc Th e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1968. 59. D. Evans, J.A. Osborn and G. W i l k i n s o n , J . Chem. Soc. A, 3133 (1968). 60. J.P. Collman and W.R. Roper, J . Am. Chem. S o c , 87_, 4008 (1965). 61. M.C. B a i r d , J.T. Mague, J.A. Osborn and G. Wi l k i n s o n , J . Chem. Soc. A, 1347 (1967); M.C. B a i r d , C.J. Nyman and G. Wi l k i n s o n , J . Chem. Soc. A, 348 (1968). 62. M.C. B a i r d , D.N. Lawson, J.T. Mague, J.A. Osborn and G. W i l k i n s o n , Chem. Commun., 129 (1966). 63. J . Chatt and B.L. Shaw, Chem. and Ind., 931 (1960); 290 (1961). 64. L. Vaska and J.W. D i L u z i o , J . Am. Chem. S o c , 83, 1262 (1961). - 220 -65. L. Vaska and J.W. D i L u z i o , J . Am. Chem. S o c , 83_, 1262 (1961). 65. L. Vaska and J.W. D i L u z i o , J . Am. Chem. S o c , 83_, 2784 (1961). 66. J . Chatt, B.L. Shaw and-A.E. F i e l d s , J . Chem. S o c A, 3466 (1964). 67. L. Vaska, Chem. and Ind., 1402 (1961). 68. L. Vaska, J . Am. Chem. S o c , 86, 1943 (1964). 69. J . Halpern and A.W.L. Kemp, J . Am. Chem. S o c , 88^, 5147 (1966). 70. R.H. P r i n c e and K.A. Raspin, J . Chem. S o c A, 612 (1969) and references t h e r e i n . 71. J . Blum, Tetrahedron L e t t e r s , 1605 (1966). 72. J . Blum, E. Oppenheimer and E.D. Bergmann, J . Am. Chem. S o c , 89, '2338 (1967). 73. R.S. Coffey, Chem. Commun., 923 (1967). 74. B.R. James and G.L. Rempel, J . Chem. Soc. A, 79 (1969). 75. S.D. Robinson and G. W i l k i n s o n , J . Chem. S o c A,. 300 (1966). 76. M.I. Bruce and F.G.A. Stone, J . Chem. S o c A, 1238 (1967). 77. J.. Kingston and G. W i l k i n s o n , J . Inorg. Nucl. Chem., 28, 2709 (1966) 78. See f o r examples papers i n P r e p r i n t s , D i v i s i o n of Petroleum Chemistry, Inc., Am. Chem. S o c , 14-, No. 2, 1969, p. B149, B159, B170 and references t h e r e i n . 79. J . Ca n d l i n , K. J o s h i and D. Thompson, Chem. and Ind., 1960 (1966). 80. P. Pino, G. Braca, G. Sbrana and A. Cuccuru, Chem. and Ind., 1732 (1968). 81. Ref. 14, p. 69. 8 2 . J.K. Nicholson and B.L. Shaw, Proc. Chem.Soc, 282 (1963). 83. J . Chatt and J.M. Davidson, J . Chem. Soc. A, 843 (1965). 84. B. Hudson, P.C. T a y l o r , D.E. Webster, and P.B. We l l s , D i s s . Faraday S o c , 46, 37 (1968). - 221 -85. M. Orchin, Adv. C a t a l y s i s , _16, 1 (1966). 86. A.D. A l l e n and F. Bottomley, Accounts Chem. Res., 1_, 360 (1968) and references t h e r e i n . 87. R. Murray and D.C. Smith, Coord. Chem. Rev., 3_, 429 (1968). 88. A.D. A l l e n , F. Bottomley, R.O. H a r r i s , V.P. Re i n s a l u and C.V. Senoff, J . Am. Chem. S o c , 89, 5595 (1967). 89. D.E. H a r r i s o n and H. Taube, J . Am. Chem. S o c , 89, 5706 (1967). 90. J.E. Fergusson and J.L. Love, Chem. Commun., 399 (1969). 91. L.A.P. Kane-Mcguire, P.S. Sheridan, F. Basolo and R.G. Pearson, J . Am. Chem. S o c , 90, 5295 (1968). 92. E.E. van Tamelen, R.B. Fechter, S.W. S c h n e l l e r , G. Boche, R.H. Greeley, B. Akermark, J . Am. Chem. S o c , 91_, 1551 (1969). 93. S. Carra and R. Ugo, Inorg. Chim. Acta Reviews, 1_, 49 (1967). 94. K.R. Laing and W.R. Roper, Chem. Commun., 1556 (1968). 95. J.A. Ibers and S.J. Laplaca, Science, 145, 920 (1964). 96.. K.R. Laing and W.R. Roper, Chem. Commun., 1568 (1968). 97. J . Blum, H. Rosenmen and E. Bergman, Tetrahedron L e t t e r s , _38_, 3665 (1967). 98. E.E. Mercer and R.R. Buckley, Inorg. Chem., 4, 1692 (1965). 99. A. S e i d e l l , S o l u b i l i t i e s o f i n o r g a n i c and metal organic compounds, 4th ed., V o l . 1, D. Van Nostrand Co., Inc., New York, N.Y. 100. H.C. Clark and W.S. Tsang, Chem. Commun., 123 (1966). 101. L. Vaska, Inorg. Nucl. Chem. L e t t e r s 1_, 89 (1965.). 102. N. Hagihara, M. Yamagaki and M. Takesada, A b s t r a c t s of 3rd Int e r n . Symp. Organometallic Chem. (Munich 1967), p. 330. - 222 -103. C. O'Connor, G. Yagupsky, D. Evans and G. Wi l k i n s o n , Chem. Commun., 420 (1968) . 104. G.L. Rempel, Ph.D. t h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1968. 105. J.L. Woodhead and J.M. F l e t c h e r , United Kingdom Atomic Energy A u t h o r i t y , Report AERE R4123, 1962. 106. F. Basolo and R.G. Pearson, Mechanisms of Inorganic Reactions, 2nd ed., John W i l e y a n d Sons, Inc., New York, N.Y., 1967, p. 611. 107. Du Pont product i n f o r m a t i o n b u l l e t i n s ; DMA general i n f o r m a t i o n b u l l e t i n , a review o f c a t a l y t i c and s y n t h e t i c a p p l i c a t i o n s f o r DMF and DMA, I n d u s t r i a l and Biochemicals Department, E.I. Du Pont de Nemours § Co., Wilmington, Delaware. 108. G. C h a r i o t , Selected Constants, O x i d a t i o n Reduction P o t e n t i a l s , Pergamon, P a r i s , 1958. 109. H.H. Cady, Aqueous chemistry o f ruthenium i n +2, +3 and +4 o x i d a t i o n s t a t e s , Ph.D. d i s s e r t a t i o n , U n i v e r s i t y of C a l i f o r n i a , Berkeley, 1957. 110. A.A. Frost and R.G. Pearson, K i n e t i c s and mechanism, A study of homogeneous chemical r e a c t i o n s , 2nd ed., John Wiley § Sons, Inc., New York, 1961, p. 136. 111. Ref. 106, p. 134, 239 and 585. 112. W. Manchot and E. Enk, Ber., 63, 1635 (1930). 113. W. Manchot and W.J. Manchot, Z. Anorg. Allgem. Chem., 226, 388, 410 (1936). 114. J.P. C a n d l i n , K.K. J o s h i and D.T. Thompson, Chem. and Ind., 1960 (1966). 115. R.J. I r v i n g and P.G. Laye, J . Chem. Soc. A, 161 (1966). - 223 -116. A. Rusina and A.A. Vlcek, Nature, 206, 295 (1965). 117. A. Yamamoto, S. Kitazume and S. Ikeda, J . Am. Chem. S o c , 90, 1089 (1968). 118. G. Grube and H. Nann, Z e i t . f u r Electrochem. , 46_, 661 (1939). 119. J.R. Backhouse and F.P. Dwyer, J . Proc. Roy. S o c , N.S. Wales, 83, 146 (1949). 120. M.G. Adamson, J . Chem. Soc. A, 1370 (1968). 121. I.R. Lantzke and D.W. Watts, J . Am. Chem. S o c , 8£, 815 (1967). 122. V. Gutmann, papers presented at conference on non-aqueous solvent chemistry, Hamilton, O n t a r i o , Canada, June 1967; Coord. Chem. Rev. 2, 239 (1967). 123. CD. Schmulbach and R. Drago, J . Am. Chem. S o c , 8_2, 4484 (1960). 124. W. B u l l . S. Madan and J . W i l l i s , Inorg. Chem., 2, 303 (1963). 125. R. Drago, R. Carlson and K. P u r c e l l , Inorg. Chem., 4_, 15 (1965). 126. S.K. Madan and A.M. Donohue, J . Inorg. Nucl. Chem., 28_, 1617 (1966) 127. A.J. Carty, Can. J . Chem., 44, 1881 (1966). 128. R.W. Dodson and N. Davidson, J . Phys. Chem., 5_6, 866 (1952). 129. P.B. Chock and J . Halpern, J . Am. Chem. S o c , 8_8, 3511 (1966). 130. Ref. 110, p. 147. 131. C.R. Ch i l d s and K. Bloch, J . Org. Chem., 26, 1630 (1961). 132. C. O'Connor and G. Wi l k i n s o n , J . Chem. Soc. A, 2665 (1968). 133. B.R. James and G.L. Rempel, Discuss. Faraday S o c , 46, 48 (1968). 134. R.E. Dessy and F. P a u l i k , B u l l . Soc. Chim., 1373 (1963). 135. M.A. Bennet and D.L. M i l n e r , Chem. Commun., 581 (1967). 136. S. Bresadola, P. Rigo and A. Turco, Chem. Commun., 1205 (1968). - 224 -137. I n t e r n a t i o n a l C r i t i c a l Tables, V o l . I l l , Ed. E.W. Washburn, McGraw-Hill, New York, 1926, p. 269. 138. V.D. Markov and A.B. Fasman, Zh. F i z . Khim., 40, 1564 (1966). 139. Ref. 106, p. 580. 140. R.J. A n g e l i c i , Organomet. Chem. Rev., 3_, 173 (1968). 141. Ref. 110, p. 138. 142. B.R. James and G.L. Rempel, Can. J . Chem., 46_, 571 (1968). 143. D.N. Lawson and G. Wi l k i n s o n , J . Chem. Soc. A, 1900 (1965). 144. L.M. V a l l a r i n o , I n o r g . Chem., 4, 161 (1965). 145. D. P a v l i s , Unpublished r e s u l t s . 146. J.F. Young, R.D. G i l l a r d and G. W i l k i n s o n , J . Chem. Soc. A, 5776 (1964). 147. R.S. Nyholm, Proc. 3rd In t e r n . Congr. C a t a l y s i s , Amsterdam, 1964, North H o l l a n d , Amsterdam, 1_, 25 (1965). 148. J . Halpern, Adv. i n C a t a l y s i s , 11_, 301 (1959). 149. J.A. Osborn, A.R. Powell and G. W i l k i n s o n , Chem. Commun., 461 (1966). 

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