Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Characterization of chlorohydridobis (tertiaryphosphine) ruthenium (II) complexes, and their use as homogeneous… Thorburn, Ian Stuart 1980

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1980_A6_7 T46.pdf [ 3.92MB ]
Metadata
JSON: 831-1.0060494.json
JSON-LD: 831-1.0060494-ld.json
RDF/XML (Pretty): 831-1.0060494-rdf.xml
RDF/JSON: 831-1.0060494-rdf.json
Turtle: 831-1.0060494-turtle.txt
N-Triples: 831-1.0060494-rdf-ntriples.txt
Original Record: 831-1.0060494-source.json
Full Text
831-1.0060494-fulltext.txt
Citation
831-1.0060494.ris

Full Text

CHARACTERIZATION OF CHLOROHYDRIDOBIS(TERTIARY-PHOSPHINE)RUTHENIUM(II) COMPLEXES, AND THEIR USE AS HOMOGENEOUS HYDROGENATION CATALYSTS By IAN STUART THORBURN B.Sc.(Hons.) U n i v e r s i t y of L e i c e s t e r , 1977 A THESIS SUBMITTED IN PARTIAL'^FULFILMENT OF • THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Chemistry We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1980 (c) Ian Stuart Thorburn 1980 In presenting th i s thes is in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary shal l make it f ree ly ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of th i s thesis for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th is thesis for f inanc ia l gain sha l l not be allowed without my writ ten permission. Department of The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date - i i -ABSTRACT The t h e s i s describes a study of the c a t a l y t i c hydrogenation of an o l e f i n i c s u b s t r a t e by the complex h y d r i d o c h l o r o b i s ( t r i p h e n y l p h o s p h i n e ) ruthenium(II) and an i n v e s t i g a t i o n of the complex i n the s o l i d s t a t e and i n s o l u t i o n . The v i s i b l e s p e c t r a of the complex, ( H R u C l ( P P h 3 ) 2 ) 2 , a t a s e r i e s of concentrations showed that Beer's law i s not obeyed, and that i n s o l u t i o n a d i s s o c i a t i v e e q u i l i b r i u m e x i s t s : ( H R u C l ( P P h 3 ) 2 ) 2 ., K - 2HRuCl(PPh 3) 2 (1) The complex i n N,N-dimethylacetamide s o l u t i o n was found to be an e f f e c t i v e c a t a l y s t f o r the homogeneous hydrogenation of hex-l-ene. A d e t a i l e d k i n e t i c study on t h i s system revealed a mechanism i n v o l v i n g i n i t i a l formation of a o - a l k y l intermediate which then r e a c t s w i t h mole-c u l a r hydrogen to produce the saturated product and regenerate the c a t a l y s t : H RuCl(PPh 3) 2 + o l e f i n •« k R u C l ( P P h 3 ) 2 ( a l k y l ) (2) k2 R u C l ( P P h 3 ) 2 ( a l k y l ) + H 2 * HRuCl(PPh 3) 2 + alkane (3) The mechanism i s q u i t e d i f f e r e n t from that reported f o r the same c a t a l y s t system but using acrylamide as s u b s t r a t e , thereby showing that the nature of the s u b s t r a t e can have a pronounced a f f e c t on the course of hydrogenation. A d d i t i o n of triphenylphosphine and l i t h i u m c h l o r i d e to the ( H R u C l ( P P h 3 ) 2 ) 2 ~ hex-l-ene system were found to decrease and increase the r a t e of hydrogenation, r e s p e c t i v e l y . The added phosphine l i k e l y competes w i t h the o l e f i n i c - i i i -s u b s t r a t e f o r a c o o r d i n a t i o n s i t e ; the r o l e of the c h l o r i d e i o n i s more u n c e r t a i n , but a more a c t i v e c a t a l y s t c o n t a i n i n g more than one c h l o r i d e l i g a n d i s the most obvious r a t i o n a l e . To enhance the s o l u b i l i t y of t h i s hydridophosphine type c a t a l y s t the t r i - p - t o l y l p h o s p h i n e analogue of the triphenylphosphine complex was 1 31 1 prepared; the v a r i a b l e temperature H and P{ H } - s o l u t i o n n.m.r. of the ( H R u C l ( P ( p - t o l y l ) ^ ) 2 ) 2 complex showed the presence of both monomer and f l u x i o n a l dimer. A d d i t i o n of dimethyl maleate to the complex i n order to o b t a i n a R u - a l k y l species (equation (2)) gave very complex spectra which could not be i n t e r p r e t e d i n terms of a s i n g l e s p e c i e s , but there was some evidence f o r a h y d r i d o ( o l e f i n ) species r a t h e r than an a l k y l . An x-ray a n a l y s i s of the p - t o l y l complex confirmed the expected chloro-bridged dimeric s t r u c t u r e of these hydridochlorobis(phosphine) species. There i s a square pyramidal c o o r d i n a t i o n geometry about each ruthenium atom, and two such centres share a b a s a l edge, but the molecule has no symmetry as a r e s u l t of the small hydride l i g a n d s a l l o w i n g d i s t o r t i o n . - i v -TABLE OF CONTENTS Page Ab s t r a c t i i Table of contents i v L i s t of t a b l e s v i i L i s t of f i g u r e s v i i i A b b r e v i a t i o n s x Acknowledgements x i Chapter I. I n t r o d u c t i o n 1 1.1 General i n t r o d u c t i o n 1 1.2 Homogeneous hydrogenation of o l e f i n i c compounds 2 1.3 Homogeneous hydrogenation us i n g ruthenium complexes 9 1.4 Aim of work 13 Chapter I I . Experimental 15 2.1 M a t e r i a l s 15 2.1.1 Solvents 15 2.1.2 Gases 15 2.1.3 O l e f i n i c substrates 15 2.1.4 Phosphine l i g a n d s 16 2.1.5 Ruthenium Compounds 16 2.1.5.1.i T r i c h l o r o b i s ( t r i p h e n y l p h o s p h i n e ) -(DMA)ruthenium(III).DMA s o l v a t e 16 2. 1 . 5 . 1 . i i T r i c h l o r o b i s ( t r i - p - t o l y l p h o s p h i n e ) -(DMA)ruthenium(III).DMA s o l v a t e 16 2.1.5.2.i H y d r i d o c h l o r o b i s ( t r i p h e n y l p h o s p h i n e ) -ruthenium(II)dimer 16 -v-2 . 1 . 5 . 2 . i i H y d r i d o c h l o r o b i s ( t r i - p - t o l y l p h o s p h i n e ) -ruthenium(II)dimer 17 2.2 Instrumentation 17 2.3 Spectrophotometry measurements 19 2.4 Fast r e a c t i o n measurements 19 2.5 Gas-uptake apparatus 19 2.5.1 Procedure f o r a t y p i c a l gas-uptake experiment 21 2.6 Gas s o l u b i l i t y measurements 24 Chapter I I I . Homogeneous hydrogenation of hex-l-ene using h y d r i d o c h l o r o b i s ( t r i p h e n y l p h o s p h i n e ) -ruthenium(II) as c a t a l y s t 25 3.1 I n t r o d u c t i o n 25 3.2 C a t a l y t i c hydrogenation of hex-l-ene 26 3.3 A n a l y s i s of k i n e t i c data 42 3.3.1 Dependence of the r a t e on c a t a l y s t c o n c e n t r a t i o n 45 3.3.2 Dependence of the r a t e on o l e f i n c o n c e n t r a t i o n 45 3.3.3 Dependence of the r a t e on hydrogen con c e n t r a t i o n 46 3.3.4.1 Dependence of the r a t e on added triphenylphosphine c o n c e n t r a t i o n 48 3.3.4.2 A spectrophotometric study of the r e a c t i o n between HRuCl(PPh,)„ and pph 3 ... 50 3.3.5.1 Dependence of the r a t e on added l i t h i u m c h l o r i d e c o n c e n t r a t i o n 58 3.3.5.2 A spectrophotometric study of the r e a c t i o n between HRuCl(PPh 3) 2 and L i C l 58 3.4 D i s c u s s i o n 61 - v i -Page Chapter IV. S t r u c t u r a l s t u d i e s on h y d r i d o c h l o r o b i s -( t r i - p - t o l y l p h o s p h i n e ) r u t h e n i u m ( I I ) 68 4.1 X-ray s t r u c t u r e determination 68 4.2 N.m.r. spectroscopy 72 4.3 Formation of a m e t a l - a l k y l species 82 Chapter V. General conclusions and some recommendations f o r f u t u r e work 89 References 92 - v i i -LIST OF TABLES Table Page I I I - l Spectrophotometric study of the e q u i l i b r i u m ( H R uCl(PPh 3) 2) n^=* nHRuCl(PPh ) i n DMA s o l u t i o n at 25° ... 30 I I I - 2 Spectrophotometric study of the e q u i l i b r i u m between HRuCl(PPh3) 2 and hex-l-ene i n DMA s o l u t i o n at 25°C 32 I I I - 3 K i n e t i c data f o r the HRuCl(PPh3) 2 c a t a l y s e d hydrogenation of hex-l-ene i n DMA at 30°C 38 I I I - 4 Stopped-flow data f o r DMA s o l u t i o n s of HRuCl(PPh 3) 2 and PPh 3 at 30°C 52 I I I - 5 Spectrophotometric study of the e q u i l i b r i u m between HRuCl(PPh ) and L i C l i n DMA s o l u t i o n at 25 °C 7 60 - v i i i -LIST OF FIGURES 2.1 Anaerobic s p e c t r a l c e l l 20 2.2 Constant pressure gas-uptake apparatus 22 3.1 A plot of molar e x t i n c t i o n c o e f f i c i e n t as a function of the concentration of HRuCl(PPh,)_ at 25°C i n DMA ... 28 3.2 A plot of l n C e Q - E/eQ - e ^ .[Ru]against ln(e-e /e„-e .[Rul T) i n accordance with 00 \J 00 J-equation 3.9 31 3.3 V i s i b l e absorption of DMA s o l u t i o n of HRuCl(PPh 3> 2 upon addition of hex-l-ene 33 3.4 Rate pl o t s for the HRuCl(PPh^)„ catalysed hydrogenation of hex-l-ene i n DMA at 30°C 35 3.5 S o l u b i l i t y of hydrogen i n DMA at various pressures at 30°C 37 3.6 Dependence of maximum rate of hydrogenation on t o t a l ruthenium concentration i n DMA at 30°C 39 3.7 Dependence of maximum rate of hydrogenation on hex-l-ene concentration i n DMA at 30°C 40 3.8 Dependence of maximum rate of hydrogenation on hydrogen concentration i n DMA at 30°C 41 3.9 Dependence of maximum rate of hydrogenation on added triphenylphosphine concentration i n DMA at 30°C 43 3.10 Dependence of maximum rate of hydrogenation on added l i t h i u m c h l o r i d e concentration i n DMA at 30°C 44 3.11 Dependence of maximum rate of hydrogenation on o l e f i n concentration as plotted according to equation (3.19) 47 3.12 Dependence of maximum rate of hydrogenation on hydrogen concentration as plotted according to equation (3.20) 49 3.13 Dependence of maximum rate of hydrogenation on [ P P h 3 ] _ 1 51 - i x -Page 3.14 P l o t of lnCA^A^) vs time of the stopped-flow data f o r the r e a c t i o n between HRuCl(PPh3) 2 and PPh 3 53 3.15 Dependence of k 0 b s on triphenylphosphine c o n c e n t r a t i o n i n DMA at 30°C 54 3.16 Dependence of k D b s o n ruthenium concentration i n DMA at 30°C 56 3.17 V i s i b l e absorption of DMA s o l u t i o n of HRuCl(PPh 3> 2 upon a d d i t i o n of l i t h i u m c h l o r i d e 59 4.1 X-ray c r y s t a l s t r u c t u r e of the ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 complex 69 4.2 C r y s t a l s t r u c t u r e of the ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 complex, and s e l e c t e d bond angles and distances 71 4.3 The v a r i a b l e temperature "'"H-n.m.r. spectra of ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 i n toluene-dg 75,76 31 1 4.4 The v a r i a b l e temperature P{ H}-n.m.r. spec t r a of ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 i n t o l u e n e - d g 77,78 4.5 The v a r i a b l e temperature "*"H-n.m.r. spectra of a 1:1 mixture of ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 and dimethyl maleate i n toluene-dg 84 31 1 4.6 The v a r i a b l e temperature P{ H}-n.m.r. spec t r a of a 1:1 mixture of ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 and dimethyl maleate i n toluene-dg 85 -x-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 of which are commonly adopted i n chemical 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 absorbance DMA N,N-dimethylacetamide,CH 3CON(CH 3) 2 J c o u p l i n g constant, Hz In n a t u r a l logarithm M molar or metal atom n.m.r. nuclear magnetic resonance PPh 3 triphenylphosphine,(C^H^) 3P P ( p - t o l y l ) 3 t r i - p - t o l y l p h o s p h i n e , ( C g H ^ C H ^ P TMS t e t r a m e t h y l s i l a n e 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 ^ T chemical s h i f t , ppm 31 1 31 P{ H} proton broad-band decoupled P n.m.r. [Ru],,, c o n c e n t r a t i o n of t o t a l ruthenium. - x i -ACKNOWLEDGEMENTS I wish to thank Professor B.R. James f o r h i s expert guidance and c o n t i n u a l encouragement throughout the course of 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 Drs. R. B a l l and J . T r o t t e r f o r the c r y s t a l s t r u c t u r e determination which solved a number of problems, and to the members of the group f o r making the past three years so enjoyable. -1-CHAPTER I  INTRODUCTION 1.1 General I n t r o d u c t i o n The f i r s t r e p o r t of c a t a l y t i c homogeneous hydrogenation of an organic substrate appeared i n 1938"'", and inv o l v e d the r e d u c t i o n of benzoquinone by c u p r i c acetate s o l u t i o n s . However, i t was not u n t i l the e a r l y s i x t i e s that i n t e r e s t i n homogeneous c a t a l y t i c systems r e a l l y began to grow, and sin c e then numerous systems have been stud i e d and t h e i r mechanisms deduced. The i n t e r e s t i n the subject has been maintained, since compared to the prevalent heterogeneous c a t a l y s i s , homogeneous 2-4 c a t a l y s i s u s u a l l y has c e r t a i n advantages : 1. Higher a c t i v i t y , so mil d e r r e a c t i o n c o n d i t i o n s may be employed. 2. Higher s e l e c t i v i t y , s t e r e o s p e c i f i c i t y , and r e p r o d u c i b i l i t y . 3. Mechanisms which may be studi e d by spectroscopic and k i n e t i c techniques. 4. C a t a l y s t s whose p r o p e r t i e s may be changed by v a r y i n g the l i g a n d s and c o n d i t i o n s . The mechanisms of heterogeneously c a t a l y s e d r e a c t i o n s are not w e l l understood, but w i t h the s t u d i e s of homogeneous systems analogies between the -2-two can be drawn, and understanding of heterogeneous systems increased. More important i s that w i t h f u r t h e r mechanistic s t u d i e s i t should e v e n t u a l l y be p o s s i b l e to design homogeneous c a t a l y s t s f o r s p e c i f i c r e a c t i o n s . The main disadvantage of homogeneous c a t a l y s i s i s the d i f f i c u l t y i n s e parating the r e a c t i o n product(s) from the s o l u b l e c a t a l y s t . To overcome t h i s problem there has been a recent development i n "supported or heterogenized homogeneous c a t a l y s i s " " * i n which the c a t a l y s t i s bonded to an i n s o l u b l e polymer support. There are two main types of support; porous i n o r g a n i c ones such as s i l i c a , z e o l i t e s or alumina, and more commonly organic polymers such as polystyrene c r o s s - l i n k e d w i t h d i v i n y l -benzene c o n t a i n i n g phosphino- or amino-substituents f o r b i n d i n g to the a c t i v e metal centre. These "supported" c a t a l y s t s ^ appear to r e t a i n most of the p r o p e r t i e s of the homogeneous c a t a l y s t s , but e l i m i n a t e the problem of separation since they can be simply f i l t e r e d out. The main commercial processes c u r r e n t l y using homogeneous c a t a l y s t s 7 8 9 are: the Wacker process , the Oxo process , some Z i e g l e r - N a t t a systems , methanol c a r b o n y l a t i o n ^ , and asymmetric syn t h e s i s of amino-acid drugs such as l - d o p a ^ . 1.2. Homogeneous Hydrogenation of O l e f i n i c Compounds For a t r a n s i t i o n metal complex to be a c t i v e f o r c a t a l y t i c hydrogenation of unsaturated substrates i t must be able t o ; 1. A c t i v a t e both hydrogen and the s u b s t r a t e . 2. Transfer hydrogen. -3-3. Release the product, and regenerate the active species. The coordination number and electron configuration of a metal complex w i l l l a r g e l y determine i t s p o t e n t i a l as a c a t a l y s t . If the complex i s c o o r d i n a t i v e l y saturated there w i l l be no vacant s i t e for a c t i v a t i o n of hydrogen or o l e f i n unless there are l a b i l e ligands present. 6 8 Complexes with a d to d configuration are frequently c o o r d i n a t i v e l y unsaturated or can become so, and the majority of c a t a l y s t s do have t h i s c o n f i g u r a t i o n . Recently however complexes of T i 5 Hf, Zr and Nb 2 3 12 which have d or d configurations were found to be c a t a l y t i c a l l y active Ligands, due to t h e i r o - e f f e c t s , i t - e f f e c t s , bond strengths, and s t e r i c 13 e f f e c t s can influence the a c t i v i t y and s p e c i f i c i t y of a hydrogenation c a t a l y s t considerably. Hydrogen a c t i v a t i o n depends on the metal complex involved, but i t 14 i s known to occur i n at l e a s t three ways namely (a) o v e r a l l h e t e r o l y t i c s p l i t t i n g , (b) homolytic s p l i t t i n g , or (c) dihydride formation. A large number of metal complexes do a c t i v a t e hydrogen but are not capable of c a t a l y t i c a l l y reducing an o l e f i n since the l a t t e r has not been activa t e d , or the M-H bond formed i s so stable that hydride transfer to the activated substrate i s i n h i b i t e d , or the hydride i s l a b i l e so the c a t a l y t i c a l l y a c t i v e species i s not present in s i g n i f i c a n t concentrations. The bonding between metal and o l e f i n i s by overlap of the n-electron density of the o l e f i n with a o-type acceptor o r b i t a l of the metal, accom-panied by back donation from f i l l e d metal d - o r b i t a l s to empty antibonding o r b i t a l s of the o l e f i n . This a c t i v a t e s the o l e f i n by reducing the double bond character, and places i t in close proximity to the hydride ligand so -4-t r a n s f e r i s not r e s t r i c t e d . The a b i l i t y of an o l e f i n t o coordinate i s enhanced i f the metal i s i n a l o v o x i d a t i o n s t a t e , and i f the o l e f i n c ontains e l e c t r o n withdrawing and small s u b s t i t u e n t s . The f o l l o w i n g examples show how o l e f i n i c s u b strates may be hydro-genated f o r each of the modes of hydrogen a c t i v a t i o n . (a) O v e r a l l H e t e r o l y t i c S p l i t t i n g 1 5 M L ^ + H 2 M L ^ H " + H + + L This type of s p l i t t i n g i s e x e m p l i f i e d by r e a c t i o n ( l . l ) 1 ^ , RhCl^" + H 2 5 = ^ HRhCl^" + H + + C l " ( l .D which i n v o l v e s s u b s t i t u t i o n of a hydride f o r another l i g a n d without change i n the o x i d a t i o n s t a t e of the metal. 17 18 There are two p l a u s i b l e mechanisms ' f o r e x p l a i n i n g h e t e r o l y t i c s p l i t t i n g . The f i r s t i n v o l v e s overlap between a f i l l e d metal o r b i t a l w i t h an empty hydrogen o r b i t a l r e s u l t i n g i n a p o l a r i z e d H^-metal i n t e r -mediate. This can l o s e the p o s i t i v e l y p o l a r i z e d end of the H 2 molecule to a se l f - g e n e r a t e d or added base to give the metal hydride: X JTYL-YI + H + base + Y~ M-Y + H 2 • M ^ <^ (1.2) \H~ *>M-H + HY V The second p o s s i b i l i t y i s that H 2 could o x i d a t i v e l y add i n t o the co-o r d i n a t i o n sphere of an an i o n - c o n t a i n i n g complex which can break down i n t o the metal hydride and the protonated anion: M-Y + H» » M^-H • M-H + HY (1.3) -5-S h i l o v and coworkers have shown"1-7 that a p l a t i n u m - t i n complex (Pt*) hydrogenates ethylene under ambient c o n d i t i o n s . Once the hydride i s formed the o l e f i n may i n s e r t i n t o the Pt*-H bond producing a o - a l k y l complex. E l e c t r o p h i l l c a t t a c k by a proton at the carbon attached to the metal ( p r o t o n o l y s i s ) r e l e a s e s the saturated product and regenerates the c a t a l y s t (1.4): P t * + C 2H A P t * ( C 2 H A ) P t * ( C 2 H 4 ) + H 2 ^ HPt*(C 2H 4) + H + (1.4) HPt*(C 2H 4) ^=*= P t * ( C 2 H 5 ) P t * ( C 2 H 5 ) + H + P t * + C 2H 6 20 21 (b) Homolytic S p l i t t i n g ' 2ML n + H 2 ^ " 2 M L n - l H + 2 L I f a metal complex h o m o l y t i c a l l y s p l i t s hydrogen,the o x i d a t i o n s t a t e and g e n e r a l l y the c o o r d i n a t i o n number of the metal are increased by one. The extent to which t h i s r e a c t i o n occurs t h e r e f o r e depends on the sus-c e p t i b i l i t y of the metal 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 . An example of such a process i s the r e v e r s i b l e 22 uptake of H_2 by aqueous s o l u t i o n s of pentacyanocobaltate(II) 2 [ C o ( C N ) 5 ] 3 " + H 2 - » 2[HCo(CN) 5] 3" (1.5) For the m a j o r i t y of o l e f i n s , r e d u c t i o n occurs by formation of an -6-23 a l k y l complex which r e a c t s w i t h another mole of the hydride complex [(CN) C o - a l k y l ] 3 ~ + [ H C o ( C N ) 5 ] 3 ~ — • 2 [ C o ( C N ) 5 ] 3 ~ + saturated (1.6) product 24 3-Recent s t u d i e s have shown t h a t , f o r Co(CN),. and Cc^(CO)g,hydro-genation of p a r t i c u l a r substrates(S) i n v o l v e s homolytic s p l i t t i n g of hydrogen followed by hydrogen atom t r a n s f e r s r a t h e r than hydride t r a n s f e r s (1.7) : HCo(CO) 4 + S •« -Co(CO) 4 + -SH HCo(CO) 4 + -SH — • -Co(CO) 4 + SH 2 (1.7) H 2-Co(CO). • Co„(C0) o — * 2HCo(C0). 4 2 o 4 (c) Dihydride f o r m a t i o n 2 5 ' 2 6 ML + H. ^=*ML H„ * n Z n z The f i n a l mode of hydrogen a c t i v a t i o n i n v o l v e s o x i d a t i v e a d d i t i o n of hydrogen to the metal, thereby i n c r e a s i n g the o x i d a t i o n s t a t e and 27 c o o r d i n a t i o n number by two. An example of t h i s i s shown i n (1.8), I r ^ K C O ) ( P P h 3 ) 2 + H 2 „ * H 2 I r i : [ C l ( C 0 ) ( P P h ^ (1.8) An o l e f i n may be reduced by two routes depending on when the d i h y d r i d e i s formed. I f the o l e f i n i s coordinated a f t e r the o x i d a t i v e a d d i t i o n of the H 2 then two consecutive t r a n s f e r s of a hydrogen atom produces the saturated product, and t h i s i s c a l l e d the "hydride" route. The a l t e r n a t i v e -7-i s c a l l e d the "unsaturated" r o u t e , and proceeds v i a c o o r d i n a t i o n of the o l e f i n followed by o x i d a t i v e a d d i t i o n of H^. Even though the same d i h y d r i d e - s u b s t r a t e intermediate i s formed by e i t h e r mechanism the "unsaturated" route i s l e s s favoured s i n c e c o o r d i n a t i o n of the substrate f i r s t would remove e l e c t r o n d e n s i t y from the metal making o x i d a t i v e 28 a d d i t i o n l e s s l i k e l y . Wilkinson's c a t a l y s t RhClCPPh^)^ has been shown to hydrogenate o l e f i n s by both r o u t e s , and pathways s i m i l a r to those 29-31 shown i n Scheme 1-1 have been proposed -8-H 2RhCl(PPh 3) 3 -PPh H 2RhCl(PPh 3) 2 •HDlef RhCl(PPh 3) 3 Olefin RhCl(PPh 3) 3(Olefin) I -PPh. RhCl(PPh 3) 2(Olefin) H 2RhCl(PPh 3) 2(01efin) HRhCl(PPh 3) 2(alkyl) •(PPh3) + (PPh3) HRhCl(PPh 3) 3(alkyl) fast jaturated product + RhCl(PPh 3) 3 Scheme 1-1 -9-1.3. Homogeneous Hydrogenation using Ruthenium Complexes 32 33 Halpern and coworkers ' showed that aqueous HC1 s o l u t i o n s c o n t a i n i n g c h l o r o r u t h e n a t e ( I I ) complexes were a c t i v e at ^80°C 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 m a l e i c , fumaric, and a c r y l i c a c i d s . This was one of the f i r s t r e p o r t s of a c t i v a t i o n of molecular hydrogen, and the p o s t u l a t e d mechanism 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 of hydrogen: (Scheme 1-2) Scheme 1-2 34 In 1965 W i l k i n s o n et a l reported that RuCl_(PPh.). and RuCl„(PPh_)_ 2 3 4 2 3 3 i n ethanol-benzene s o l u t i o n reacted w i t h hydrogen to give HRuCl(PPh^)^• In benzene s o l u t i o n the two s t a r t i n g complexes are i n e q u i l i b r i u m by l o s s or gain of a phosphine l i g a n d , but w i l l not r e a d i l y r e act w i t h hydrogen unless ethanol i s present s i n c e i t a c t s as a base,promoting hydride formation: R u C l 2 ( P P h 3 ) 3 + H 2 + base HRuCl(PPh 3) 3 + base HC1 (1.9) 35 T r i s ( t r i p h e n y l p h o s p h i n e ) h y d r i d o c h l o r o r u t h e n i u m ( I I ) has been found to be - 1 0 -o n e o f t h e m o s t a c t i v e c a t a l y s t s f o r r e d u c i n g t e r m i n a l o l e f i n s w h i l s t i n t e r n a l , c y c l i c o r s u b s t i t u t e d o l e f i n s a r e h y d r o g e n a t e d l e s s r e a d i l y . S i n c e t h e r e i s n o m e a s u r a b l e d i s s o c i a t i o n o f a p h o s p h i n e f r o m t h e s t a r t i n g , . . . , 3 6 , 3 7 , . , ,38 . h y d r i d e c o m p l e x t h e m e c h a n i s m n o w p r o p o s e d i s : H R u C l ( P P h 3 > 3 + o l e f i n „ *• H R u C l ( P P h 3 > 2 ( o l e f i n ) + P P h 3 ( l . i O ) P P h 3 H R u C l ( P P h 3 ) 2 ( o l e f i n ) R u C l ( P P h 3 ) 2 ( a l k y l ) „ *• R u C l ( P P h 3 ) 3 ( a l k y l ) ( 1 . 1 1 ) R u C l ( P P h 3 ) 3 ( a l k y l ) + H 2 • H R u C l ( P P h 3 ) 3 + a l k a n e ( 1 . 1 2 ) 3 5 T h i s c o m p a r e s t o t h e o r i g i n a l m e c h a n i s m w h e r e l o s s o f a p h o s p h i n e l i g a n d o c c u r r e d p r i o r t o b i n d i n g o f t h e o l e f i n , a n d w a s t h o u g h t t o r e m a i n d i s -s o c i a t e d t h r o u g h o u t . D u e t o i t s p o s s i b l e i n v o l v e m e n t i n t h e r e a c t i o n s o f t h e t r i s p h o s p h i n e 3 9 c o m p l e x , H R u C l ( P P h 3 ) 2 w a s p r e p a r e d s e p a r a t e l y a n d u s e d t o r e d u c e a c r y l -a m i d e . T h e k i n e t i c s s h o w e d t h a t o n c e t h e a l k y l c o m p l e x w a s f o r m e d i t r e a c t e d w i t h a m o l e o f t h e s t a r t i n g h y d r i d e t o g i v e t h e s a t u r a t e d p r o d u c t a n d a d 7 R u ( I ) s p e c i e s . T h i s s p e c i e s c o u l d e i t h e r o x i d a t i v e l y a d d h y d r o g e n t o r e g e n e r a t e t h e c a t a l y s t o r o f g r e a t e r i n t e r e s t i t c o u l d a c t i v a t e a C-H b o n d i n t h e p r o d u c t t o g i v e t h e h y d r i d e a n d a l k y l s p e c i e s ( s e e P . 2 6 ) . H R u C l ( P P h > 3 ) 3 i s a l s o c a p a b l e o f s t o i c h i o m e t r i c a l l y h y d r o g e n a t i n g o l e f i n s i n t h e a b s e n c e o f h y d r o g e n w i t h t h e s e c o n d h y d r o g e n a t o m c o m i n g 37 f r o m t h e o r t h o p o s i t i o n o f a p h e n y l r i n g o f t h e t r i p h e n y l p h o s p h i n e l i g a n d S u c h l i g a n d t o m e t a l h y d r o g e n t r a n s f e r w a s f i r s t r e p o r t e d f o r t h e H R u C l ( P P h 3 ) 3 35 s y s t e m b y W i l k i n s o n e t a l b a s e d o n i s o t o p i c s t u d i e s , a n d l a t e r s t u d i e d -11-by other w o r k e r s ^ 0 , 4 1 . Proton n.m.r. studies of the e q u i l i b r a t i o n of hydridochloro-complex i n s o l u t i o n with deuterium showed ortho-deuteration of the phosphine, and the mechanism suggested for t h i s i s shown i n Scheme 1-3. (Ph 3 P) 3 Ru CLH - P P h 3 (Ph 3P) 2 Ru Cl H H _ (Ph,P>Ru—CL - H D CL / . -f PPrv P P h . P h 2 P ^ £ > 2 j P h 2 P ^ o ) . Scheme 1-3 For the hydrogenation of o l e f i n s the r e a c t i o n begins with formation of 40 a trisphosphine a l k y l intermediate and proceeds to give the ortho-metallated complex [ ( P P h 3 > C l R u ( o - C ^ P P h ^ ] 2 and alkane. This hydrogen exchange with the phosphine ligand i s very slow compared with reaction (1.12), and so i n c a t a l y t i c hydrogenations the l a t t e r process i s k i n e t i c a l l y favoured. More recently systems i n v o l v i n g HRuCl(PPh^)^ have been used to 42 s e l e c t i v e l y hydrogenate polyenes , and to hydrogenate saturated aldehydes 43 44,45 to the alcohols , a l i p h a t i c and aromatic n i t r o compounds to the amines 46 47 and c y c l i c carboxylic acid anhydrides to Y-lactones ' , although forcing -12-c o n d i t i o n s are o f t e n r e q u i r e d . A s i m i l a r ruthenium(II) complex i s HRu(OCOR)(PPh^)^, which was 48 a l s o found by W i l k i n s o n and coworkers to e f f i c i e n t l y hydrogenate t e r m i n a l o l e f i n s . Varying the c a r b o x y l a t e group from acetate to benzoate to s a l i c y l a t e h a r d l y a l t e r e d the r a t e of hydrogenation, but they were two or three times more a c t i v e than the propionate and t r i f l u o r o a c e t a t e . The mechanism f o r hydrogenations i s thought to be the same as f o r the c h l o r o analogue. A number of ruthenium carbonyl complexes have been s t u d i e d as p o t e n t i a l c a t a l y s t s . The HRuCl(CO)(PPh^)^ complex i s capable of hydrogen-deuterium exchange and p a r t i a l l y reduces acetylene and ethylene 49 50 under ambient c o n d i t i o n s ' . The exchange process was thought to i n v o l v e an e i g h t - c o o r d i n a t e ruthenium(IV) intermediate: HRuCl (CO) ( P P h 3 ) 3 + D 2 ^ [ H R u C l ( C O ) ( P P h 3 ) 3 D 2 ] ^ D R u C l ( C O ) ( P P h 3 ) 3 + HD (1.13) but work by Schunn 5 1 has shown that more H 2 and HD i s produced than the t h e o r e t i c a l value so o r t h o m e t a l l a t i o n i s once more proposed. This complex 52 along w i t h H 2Ru(C0)(PPh 2Me) 3 appear i n a patent f o r the r e d u c t i o n of keto , f o r m y l , n i t r i l e , alkene and alkyne groups,although the c o n d i t i o n s 53 are 10-100 atm of hydrogen and 20°C to 130°C. Rempel has found RuCl 2(C0)(PPh 3> 2(DMF) to be an e f f i c i e n t c a t a l y s t f o r the hydrogenation of a l k - l - e n e s under m i l d c o n d i t i o n s once a hydride had been formed by borohydride r e d u c t i o n . A b i s - c a r b o n y l complex R u C l 2 ( C 0 ) 2 ( P P h 3 ) 2 was found~^ by Fahey to be i n d u s t r i a l l y important, s i n c e i t c a t a l y s e s hydi genation of 1,5,9-cyclododecatriene to cyclododecene w i t h a 98-99% -13-conversion. S o l u t i o n s of c h l o r o c a r b o n y l ruthenium(II) complexes have been found"*"* to c a t a l y t i c a l l y a c t i v a t e hydrogen i n the order Ru^^>Ru^ 1(CO)>Ru 1 1(CO)^, which i s c o n s i s t e n t w i t h the strong ir-acceptor CO l i g a n d s decreasing e l e c t r o n d e n s i t y on the metal,at l e a s t i n terms of a c t i v a t i n g hydrogen by o x i d a t i v e a d d i t i o n . I n t e r e s t has r e c e n t l y grown i n asymmetric hydrogenation, and there are a number of ruthenium complexes c o n t a i n i n g c h i r a l l i g a n d s which can hydrogenate p r o c h i r a l s u b s t r a t e s to give an excess of one enantiomer. One such complex i s R u 2 C l 4 [ ( - ) - d i o p ] 3 > [ ( - ) - d i o p = (-2,3-0-isopropylidene-2,-3-dihydroxy-l,4-bis(diphenylphosphino)butane] which e f f e c t s the r e d u c t i o n of a,6-unsaturated c a r b o x y l i c a c i d s w i t h up to 60% enantiomeric excess, the a c t i v e c a t a l y s t being trans-HRuCl [ ( - J - d i o p ] ^ . There are two comprehensive reviews on homogeneous hydrogenation; the f i r s t covers the l i t e r a t u r e up to 1972"^, w h i l s t the other covers 38 from 1972 to 1978 . Another review d e a l i n g w i t h c a t a l y s i s by ruthenium 58 complexes has a l s o been published. 1.4. Aim of Work The main object of the work f o r t h i s t h e s i s was to continue the i n v e s t i g a t i o n of a p a r t i c u l a r ruthenium complex as a c a t a l y s t f o r the homogeneous hydrogenation of unsaturated s u b s t r a t e s . A d e t a i l e d k i n e t i c study of the hydrogenation of acrylamide using h y d r i d o c h l o r o b i s ( t r i p h e n y l -39 phosphine)ruthenium(II) i n t h i s l a b o r a t o r y revealed the unusual mechanism o u t l i n e d i n s e c t i o n 1-3, w i t h i m p l i c a t i o n s of C-H a c t i v a t i o n by Ru* species. I t was of importance t o determine whether such C-H a c t i v a t i o n would occur i n l e s s r e a c t i v e substrates.Chapter I I I d e s c r i b e s a study of the HRuCl(PPli^)^ c a t a l y s t w i t h hex-l-ene,which was chosen s i n c e i t i s a t e r m i n a l o l e f i n w i t h - 1 4 -e s s e n t i a l l y no a c t i v a t i n g or d e a c t i v a t i n g groups. The HRuCl(PPh^)^ complex was considered to be a dimer i n the s o l i d s t a t e and i n non-polar s o l v e n t s , but i n s t r o n g l y c o o r d i n a t i n g s o l v e n t s such as DMA a solvated 39 monomer seemed l i k e l y . This i n v e s t i g a t i o n of the p h y s i c a l nature of the c a t a l y s t was continued but w i t h the t r i - p - t o l y l p h o s p h i n e analogue due to i t s increased s o l u b i l i t y ; the r e s u l t s are described i n Chapter IV. Studies w i t h the bisphosphine system must a l s o a i d i n the understanding of the mechanism of hydrogenation by the widely used RuCl 2(PPh^)^/HRuCl(PPh^) c a t a l y s t systems. -15-CIIAPTER I I  EXPERIMENTAL 2.1 M a t e r i a l s 2.1.1 Solvents - S p e c t r a l or a n a l y t i c a l grade sol v e n t s were obtained from MCB, M a l l i n c k r o d t , Eastman, or F i s h e r Chemical Co., and w i t h the exception of toluene and DMA were used without p u r i f i c a t i o n . Toluene was r e f l u x e d w i t h sodium metal w h i l s t DMA was s t i r r e d over CaH 2 f o r 24h, and vacuum d i s t i l l e d at 35-40°C. A f t e r d i s t i l l a t i o n both were kept under argon and over molecular sieves (BDH,type 5A), and the DMA was stored i n the dark. 2.1.2 Gases - Research grade hydrogen was obtained from Matheson Gas Co., and was passed through an Engelhard Deoxo c a t a l y t i c p u r i f i e r to remove traces of oxygen. P u r i f i e d argon and n i t r o g e n were su p p l i e d by Canadian L i q u i d A i r L t d . , and were used without f u r t h e r p u r i f i c a t i o n . 2.1.3 O l e f i n i c Substrates - O l e f i n s were obtained as C P . grade. Hex-l-ene was supplied by ICN Pharmaceuticals Inc., and dimethyl maleate by Eastman Organic Chemicals. Both were passed through an alumina column p r i o r to use and i n a d d i t i o n the maleate was d i s t i l l e d under vacuum. -16-2.1.4 Phosphine Ligands - Triphenylphosphine and tri-p-tolylphosphine were supplied by Eastman Kodak Co., and Strem Chemicals Inc., respectively. 31 Both were reagent grade and their purity was checked by P n.m.r. 2.1.5 Ruthenium Compounds - The ruthenium was obtained as RuCl^'311^0 which was supplied on loan from Johnson, Matthey Ltd. and contained 41.49% Ru. A l l reactions were carried out under an atmosphere of argon by employing Schlenk techniques. 2.1.5.1.i Trichlorobis(triphenylphosphine)(DMA)ruthenium(III)-DMA solvate 0.5 g of RuCl3.3H20 was dissolved in 20 ml DMA and stirred for 24h at room temperature with 1.0 g of triphenylphosphine. The green product was f i l t e r e d , carefully washed with DMA and dried under vacuum (yield-65%) Found:C(58.4), H(5.4), N(3.0); Calc. for [ R u C l ^ C ^ H ^ N ^ ] :C(58.3) , H(5.3), N(2.8); v n u j o 1 : 1630 cm"1 (uncoordinated DMA); 1590 cm"1 (coordinated max DMA) . 2.1.5.1.ii Trichlorobis(tri-p-tolylphosphine)(DMA)ruthenium(III)DMA solvate The synthesis was the same as for the triphenylphosphine complex but using a two-fold excess (1.25 g) of tri-p-tolylphosphine (Yield-57%). Found:C(60.5), H(6.0), N(2.8); Calc. for [ R u C l ^ C ^ H ^ N ^ ] :C(60.6), H(6.0), N(2.8). 2.1.5.2.i Hydridochlorobis(triphenylphosphine)ruthenium(II) dimer^9 1 g of RuCl3(PPh3)2(DMA).(DMA) and 1 g of "proton sponge" (l,8-bis(dimethylamino)-naphthalene) in 50 ml of degassed benzene were -17-s t i r r e d under an atmosphere of hydrogen at room temperature f o r 2 days. The brown suspension produced was f i l t e r e d under argon through c e l i t e to give a dark red s o l u t i o n . Slow p r e c i p i t a t i o n w i t h ethanol and c o o l i n g gave a red powder which was f i l t e r e d , washed w i t h ethanol and hexane, and d r i e d i n vacuo overnight. The f i l t r a t e l e f t a f t e r removing the red powder was concentrated by pumping o f f some benzene,and f u r t h e r p r e c i p i t -a t i o n was induced by adding ethanol and c o o l i n g . (Total y i e l d - 4 6 % ) . Found:C(65.9), H(4.83); Ca l c . f o r [ R u C l P ^ ^ H ^ ] :C(65.3) , H(4.7). 2 . 1 . 5 . 2 . i i H y d r i d o c h l o r o b i s ( t r i - p - t o l y l p h o s p h i n e ) r u t h e n i u m ( I I ) dimer This compound was prepared i n a s i m i l a r manner to the preceding complex but u s i n g RuCl^(P(p-tolyl)^) 2(DMA).(DMA) as precursor (Total y i e l d - 4 5 % ) . Found :C(68. 6) , H(5.8); Calc. f o r [ R u C l P ^ ^ H ^ ] 2 :C(68.1) , H(5.7); T^6°6. 22.8(Ru-H). 2.2 Instrumentation I n f r a r e d s p e c t r a were recorded on a P e r k i n Elmer 457 g r a t i n g spectrophotometer as N u j o l mulls on C s l p l a t e s . V i s i b l e spectra were recorded on a P e r k i n Elmer 202 spectrophotometer u s i n g an anaerobic s p e c t r a l c e l l (Figure 2.1) w i t h a quartz c e l l of 1 mm path l e n g t h . "^H nmr s p e c t r a were recorded on a Varian T-60 or XL 100 spectrometer 31 w i t h t e t r a m e t h y l s i l a n e (TMS) as standard. P nmr were recorded at 40.5 MHz u s i n g a XL 100 spectrometer equipped w i t h a v a r i a b l e temperature attachment, and operating i n the F o u r i e r transform mode. The standard 31 f o r P nmr was triphenylphosphine w i t h chemical s h i f t s being converted -18-to values r e l a t i v e to 85% H3PO^, and u p f i e l d s h i f t s are taken as p o s i t i v e . Elemental analyses were performed by Mr. P. Borda of t h i s department. -19-2.3 Spectrophotometric Measurements Since the c a t a l y t i c species are extremely a i r - s e n s i t i v e i t was necessary to c a r r y out spectrophotometric s t u d i e s under anaerobic c o n d i t i o n s by u s i n g the c e l l shown i n Figure 2.1. In a t y p i c a l experiment a weighed amount of complex was placed i n the c e l l w h i l s t 5 ml of solvent was p i p e t t e d i n t o the f l a s k . The solvent was degassed three times by employing a f r e e z e and thaw s t a t i c vacuum technique, and then saturated w i t h argon. The s o l i d and solvent were then mixed and shaken u n t i l a homogeneous s o l u t i o n was obtained. The c e l l was placed i n athermostated c e l l compartment to a l l o w the s o l u t i o n temperature to e q u i l i b r a t e , and when t h i s was achieved the spectra was run. The s u b s t r a t e could then be added and the c e l l was once more a g i t a t e d to give the p h y s i c a l e q u i l i b r i u m the s o l u t i o n . The s o l u t i o n would then be allowed to thermally e q u i l i b r i a t i and the spectra run a g a i n , and the changes i n absorbance from the i n i t i a l s p ectra recorded. 2.A Fast Reaction Measurements A l l f a s t r e a c t i o n s were studied by means of a Durrum 110 stopped-flow spectrophotometer equipped w i t h a 2 cm path length cuvette and a thermostated c e l l compartment. For a t y p i c a l experiment, a s o l u t i o n of the complex i n a solvent saturated w i t h argon was mixed with the same solvent c o n t a i n i n g s u b s t r a t e and saturated w i t h argon. 2.5 Gas-Uptake Apparatus A constant pressure gas-uptake apparatus was used i n k i n e t i c s t u d i e s and i s shown i n Figure 2.2. -20-B 7 S O C K E T . Q U A R T Z Figure 2.1 C E L L -Anaerobic S p e c t r a l C e l l -21-The pyrex two-neck r e a c t i o n f l a s k (A), equipped w i t h a dropping side-arm bucket,was attached to a f l e x i b l e g l a s s s p i r a l tube, which connected f l a s k A to a c a p i l l a r y manometer (D) at tap C. The r e a c t i o n f l a s k was c l i p p e d to a p i s t o n - r o d and wheel, which was d r i v e n by a Welch v a r i a b l e speed e l e c t r i c motor so that the f l a s k could be shaken w h i l s t h e l d i n the thermostated o i l bath (B). The o i l bath c o n s i s t e d of a f o u r - l i t r e g l a s s beaker f i l l e d w i t h s i l i c o n e o i l (Dow Corning 550), and was held i n a polystyrene-foam l i n e d wooden box w i t h a polystyrene l i d f o r i n s u l a t i o n . The c a p i l l a r y manometer contained n - b u t y l p h t h a l a t e , of n e g l i g i b l e vapour pressure; and was connected to the gas measuring burette which had a p r e c i s i o n bored tube (N) of known diameter and a mercury r e s e r v o i r (E). The c a p i l l a r y manometer and gas measuring b u r e t t e were thermostated at 25°C i n a perspex water bath. By means of an Edwards high vacuum needle v a l v e (M) the b u r e t t e was connected to the gas-handling part of the apparatus. The l a t t e r c o n s i s t e d of a mercury manometer ( F ) , the gas i n l e t (Q), and connections to a Welch Duo-Seal r o t a r y vacuum pump (G). The thermostating of the two baths was c o n t r o l l e d by Jumo thermo-regulators and Merc-to-Merc r e l a y c o n t r o l c i r c u i t s , w i t h 40 watt elongated l i g h t bulbs used f o r h e a t i n g . T h i s , w i t h mechanical s t i r r i n g meant that the temperature could be maintained w i t h i n ±0.05°C. The gas-uptake was measured w i t h a v e r t i c a l l y mounted cathetometer, and time was recorded from a Lab-Chron 1400 timer. 2.5.1 Procedure f o r a T y p i c a l Gas-Uptake Experiment In each experiment, 5 ml of DMA was p i p e t t e d i n t o the 25 ml r e a c t i o n f l a s k , and the weighed amount of o l e f i n i c s u b s t r a t e added d i r e c t l y . The Figure 2.2 Constant Pressure Gas-Uptake Apparatus -23-weighed c a t a l y s t was suspended on the hook of the side arm of the r e a c t i o n f l a s k . With the f l a s k connected to the s p i r a l arm, i t was attached to the gas handling part of the apparatus at j o i n t 0. The substrate s o l u t i o n was degassed by a freeze and thaw s t a t i c vacuum technique which was c a r r i e d out three times. The r e a c t i o n f l a s k was then f i l l e d w i t h hydrogen to a pressure s l i g h t l y l e s s than that r e q u i r e d , and taps C and P were closed. The f l a s k and s p i r a l arm could then be removed and connected to the c a p i l l a r y manometer at H. The f l a s k was placed i n the o i l bath, and attached to the motor d r i v e n shaker(I) which was then s t a r t e d . The whole system up to tap C was evacuated w i t h taps H, K, L, J and M open. A f t e r 10 minutes shaking to a t t a i n thermal e q u i l i b r a t i o n of the r e a c t i o n f l a s k and to saturate the s o l u t i o n w i t h gas, the shaking was stopped, and hydrogen was admitted to the r e s t of the apparatus at pressure s l i g h t l y l e s s than r e q u i r e d . Tap C was opened and the pressure of hydrogen increased to that d e s i r e d . The needle v a l v e , and taps K and L were c l o s e d ; and the i n i t i a l reading of the mercury l e v e l i n H taken. An experimental run was s t a r t e d by dropping the c a t a l y s t bucket, and 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 monometer (0). The manometer was balanced by a l l o w i n g gas to the b u r e t t e through the needle v a l v e and thereby m a i n t a i n i n g a constant pressure i n the r e a c t i o n f l a s k . The corresponding r i s e i n the mercury l e v e l i n N was measured at appropriate i n t e r v a l s of time. Since the diameter of the manometer (N) was known, the volume of gas consumed could be c a l c u l a t e d and expressed as moles of uptake per l i t r e of s o l u t i o n . -24-The use of a small volume of s o l u t i o n 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 , and f a s t shaking rates,ensured that d i f f u s i o n c o n t r o l of the r e a c t i o n s was e l i m i n a t e d . 2.6 Gas S o l u b i l i t y Measurements The s o l u b i l i t y of hydrogen i n DMA at s p e c i f i c temperatures and pressures was determined us i n g the gas-uptake apparatus discussed p r e v i o u s l y . The DMA was degassed, but was l e f t under vacuum when taps C and P were closed and the f l a s k w i t h s p i r a l arm t r a n s f e r r e d to the c a p i l l a r y manometer. The system was then evacuated to tap C and f i l l e d w i t h hydrogen to the approximate pressure r e q u i r e d . Tap C was opened, and the pressure immediately adjusted to that r e q u i r e d . With taps K and L, and the needle v a l v e c l o s e d , t h e timer and shaker could be s t a r t e d , and the immediate uptake of gas could be measured. -25-CHAPTER I I I HOMOGENEOUS HYDROGENATION OF HEX-1-ENE USING HYDRIDOCHLOROBIS  (TRIPHENYLPHOSPHINE) RUTHENIUM(II) AS CATALYST 3.1 I n t r o d u c t i o n A key intermediate i n the c a t a l y t i c hydrogenation of o l e f i n s by HRuCl(PPh 3) 3 (see Se c t i o n 1.3) was be l i e v e d to be a hydrido-bisphosphine 59 species. This species was l a t e r i s o l a t e d during a study of hydrogen a c t i v a t i o n by a s o l u t i o n c o n t a i n i n g RuCl,j(PPh^) 2 i n the presence of a strong base: R u C l 3 ( P P h 3 ) 2 + 1.5H2 • HRuCl(PPh 3) 2 + 2H + + 2C1~ (3.1) To t e s t the v a l i d i t y of HRuCl(PPh 3) 2 being an intermediate i t was used as c a t a l y s t i n N,N-dimethylacetamide (DMA) s o l u t i o n to hydrogenate acrylamide. There was found to be a second-order dependence on [Ru]^,, an inver s e dependence on acrylamide and on added propionamide, and a f i r s t - t o zero-order dependence on H 2. These data were explained by the f o l l o w i n g mechanism: -26-HRuCl(PPh )„ + H C=CH-C-NH 5 = ^ RuCl(PPh )(CH-C-NH) j z I II ^ 0 H 3C 0 (3.2) [ R u C l ( P P h 3 ) 2 ] 2 + CH 3CH 2CNH 2 (3. 0 (3.4) where K i s the e q u i l i b r i u m constant f o r a l k y l complex formation, and k^, k ^, and k 2 are i n d i v i d u a l r a t e constants. W h i l s t formation of an a l k y l complex by equation (3.2) i s not unusual, the next step (equation 3.3) i n v o l v i n g r e a c t i o n of the a l k y l complex w i t h another mole of hydride complex i s q u i t e novel and i n t e r e s t i n g . A r e a c t i o n such as (3.3) i s e s t a b l i s h e d ^ 1 f o r hydrogenations c a t a l y s e d by 3_ Co(CN),. , and i s thought to occur a l s o i n the h y d r o d i m e r i z a t i o n of a c r y l o -62 n i t r i l e c a t a l y s e d by R u C l 2 ( P P h 3 ) 3 . Once the saturated product i s r e l e a s e d , the d 7, l i k e l y dimeric Ru(I),species may undergo e i t h e r o x i d a t i v e a d d i t i o n of H 2 (equation 3.4) to regenerate the c a t a l y s t , or a c t i v a t e a C-H bond i n the reduced o l e f i n (the k_^ s t e p ) . A c t i v a t i o n of C-H bonds i n a l i p h a t i c com-63 8 pounds i s known f o r s i n g l e d metal cen t r e s , but not by a t w o - s i t e process, which i s i n t e r e s t i n g because of the analogy to heterogeneous a c t i v a t i o n of alkanes. To determine i f t h i s mechanism a p p l i e d to other, e s p e c i a l l y l e s s a c t i v a t e d o l e f i n s , t h e hydrogenation of hex-l-ene by DMA s o l u t i o n s of H RuCl(PPh 3) 2 was i n v e s t i g a t e d , and the k i n e t i c s and mechanism are presented here. 3.2 C a t a l y t i c Hydrogenation of Hex-l-ene The v i s i b l e spectrum of HRuCl(PPh„)„ i n DMA under argon was recorded -27-at 25°C, and shows an absorption maximum at 500 nm. Spectra were run at a s e r i e s of concentrations (Figure 3.1) and the molar e x t i n c t i o n c o e f f i c i e n t was not constant, thus Beer's law i s not obeyed as p r e v i o u s l y 39 reported. Considering that the complex i s dimeric i n the s o l i d s t a t e (Chapter IV) the obvious reason f o r the non-Beer's law behaviour i s a dimer fc monomer d i s s o c i a t i v e e q u i l i b r i u m . Assuming more g e n e r a l l y that the r e a c t i o n i s : K l ( H R u C l ( P P h 3 ) 2 ) n ^ *• nHRuCl(PPh 3) 2 (3.5) i t can be shown t h a t : [ (HRuCl(PPh,) 0) ] = - • — l R u ] T (3.6) j z n n e —e and [HRuCl (PPh,) J = — [ R u ] T (3.7) 3 2 e -e o 0 0 where [Ru]^ i s the concentration of t o t a l ruthenium present, E q i s the molar e x t i n c t i o n c o e f f i c i e n t of HRuCl(PPh 3) , and e i s the ruthenium molar e x t i n c t i o n c o e f f i c i e n t of (HRuCl(PPh„)„) , 0 0 3 2 n [ H R u C l ( P P h 3 ) 2 J n V £ " e J Therefore K± = [HRuCl (PPh„) „) J = [iuL, ( 3 * 8 ) 5 Z n 1 o T n e -e o 0 -28-0 2-0 4-0 6-0 8 - 0 [ R u ] T x 1 0 3 , M „ e n r p , i A Plot of molar extinction coefficient as a function of Figure 3 . 1 ^ p l o t ^ o f ^ ^ ^ ^ a t 2 5 o c i n D M A . -29-which y i e l d s : /e -e [ R u ] \ / E - E ^ [ R u ] \ \ o °° y \ o ° ° / A p l o t of l n ( E - E / E -e .[Ru]_) against l n ( E - e / E -e .[Ru]_) using the spectroscopic data given i n Table I I I - l should give a l i n e of slope n and i n t e r c e p t In n - l n K^. Such a p l o t i s shown i n Figure 3.2, but to o b t a i n t h i s i t was necessary to a s s i g n values of 620 M ^cm ^ and 1300 M ^cm ^ to E q and E ^ r e s p e c t i v e l y , s i n c e these l i m i t i n g e x t i n c t i o n c o e f f i c i e n t s cannot be found experimentally (see Figure 3.1). The -3 s t r a i g h t l i n e drawn has a slope of 2.0 and gives a value of 1.66 x 10 M; hence the complex i s predominantly monomeric over the c o n c e n t r a t i o n range used mainly i n the c a t a l y t i c hydrogenation s t u d i e s , and presumably e x i s t s i n a s o l v a t e d form, HRuCl(PPh^)^(DMA)^ (see Chapter I V ) . To a s o l u t i o n of the complex ([Ru]^ = 7.5 x 10 M), a measured qu a n t i t y of hex-l-ene was added d i r e c t l y , and l e f t to e q u i l i b r a t e f o r approximately 500s. The spectrum was recorded and the process repeated u n t i l a d d i t i o n of an excess (0.17 M) of o l e f i n gave the l i m i t i n g spectrum of a species considered to be R u C l ( P P h ^ ) ^ ( a l k y l ) ( s e e below). The r e a c t i n g s o l u t i o n changed colour from b r i g h t red to crimson, w i t h the i n t e n s i t y depending on the hex-l-ene c o n c e n t r a t i o n . The s p e c t r a l changes are given i n Table I I I - 2 and are shown i n Figure 3.3, and have been correct e d to a l l o w f o r d i l u t i o n . At lower o l e f i n concentrations there appears to be two i s o s b e s t i c p o i n t s ; however,these are l o s t at higher c o n c e n t r a t i o n s . These r e s u l t s may be explained q u a l i t a t i v e l y i n terms of two consecutive e q u i l i b r i a : -30-TABLE I I I - l Spectrophotometric study of the e q u i l i b r i u m ( H R u C l ( P P h 3 ) 2 ) n nHRuCl(PPh 3) 2 i n DMA s o l u t i o n at 25°C. [ R u ] T a e -E o I n A - e . [ R u l T \ e-e oo YE-E- • [ R U ] T ^ ( x l 0 3 ) M M " l " I M cm .E-e 00 X CO ' e — E o 0 0 U -e J X O oo e =620 o 0.24 695 0.11 -10.56 0.89 -8.47 0.50 700 0.12 - 9.74 0.88 -7.73 0.87 749 0.19 - 8.71 0.81 -7.26 1.50 902 0.41 -7.38 0.59 -7.04 2.17 1006 0.57 -6.70 0.43 -6.97 4.10 1110 0.72 -5.83 0.28 -6.77 7.02 1220 e =1300 CO 0.88 -5.10 0.12 -7.10 a. C a l c u l a t e d from absorbance at 500 nm. -31-80 Figure 3.2 A p l o t of l n ( E - E / E ^ E ^ - [RU] t> against l n ( E - e / e _ E -[Ru] T) i s accordance w i t h equation 3.9. -32-TABLE I I I - 2 Spectrophotometric study of the e q u i l i b r i u m between HRuCl(PPh^)^ and Hex-l-ene i n DMA s o l u t i o n at 25°C. A (500 nm) [hex-l-ene]xlO ,M A -A o A-A 0.938 0.900 0.856 0.814 0.764 0.746 0.385 0 0.319 0.737 1.106 1.630 2.102 17.000 0 0.040 0.085 0.129 0.181 0.200 0.385 0.385 0.345 0.300 0.256 0.204 0.185 0 a 1mm c e l l path -33-500 Wavelength 6 0 0 nm V i s i b l e absorption of DMA so l u t i o n of HRuCl ( P P h ^ upon a d d i t i o n of hex-l-ene. ( A W 5 x 10~3M HRuCl(PPh 3) 2 and (B), (C), (D), (E), IF;, and (G) are upon the addition of 0.319, 0.737, 1.106, 1.630, 2.102, and 17 x 10"ZM hex-l-ene. -34-(HRuCl(PPh 3) 2) 2 , 1 » 2HRuCl(PPh 3) 2 (3 . 1 0 ) K2 HRuCl(PPh 3) 2 + CH 2 - CH-(CH 2) 3-CH 3 ^ = s = t RuCl(PPh 3) 2((CH 2) 5CH 3) (3.11) -3 Taking to equal 1.66 x 10 M (equation 3.9) the concentrations of -3 dimer and monomer i n the absence of o l e f i n are calculated to be 2.70 x 1 0 M and 2.11 x 10 _ 3M respectively,and t h i s w i l l be established p r i o r to adding the substrate. Upon addi t i o n of o l e f i n the a l k y l species i s generated and there are at least three absorbing species i n s o l u t i o n , and consequently there are no i s o s b e s t i c points. I f the o l e f i n binds to both the monomer and dimer there w i l l be three separate e q u i l i b r i a among four species which w i l l again lead to a system e x h i b i t i n g no i s o s b e s t i c points. The c a t a l y t i c hydrogenation of hex-l-ene was studied by measuring the rates of hydrogen uptake by DMA solutions of HRuCl(PPh 3) 2 using the constant pressure gas-uptake apparatus described i n Section 2.3.1. The ca t a l y s t was found to be e f f i c i e n t under mild conditions, and the t y p i c a l S-shaped uptake pl o t s observed are shown i n Figure 3.4; the measured maximum hydrogenation rates were usually attained a f t e r approximately 500s. The t o t a l hydrogen uptake corresponded to v i r t u a l l y complete reduction of the hex-l-ene, and the so l u t i o n retained i t s homogeneity throughout the reaction with the f i n a l bright red so l u t i o n containing the i n i t i a l HRuCl(PPh 3> 2 complex. In the absence of substrate no uptake was observed, but i n the presence of argon instead of hydrogen the complex was found to c a t a l y t i c a l l y isomerise the o l e f i n to 85% of the 2-isomer a f t e r s t i r r i n g for one hour at 25 eC. The maximum rate of hydrogenation Figure 3.A Rate p l o t s f o r the H R u C l ( P P h 3 ) 2 ~ c a t a l y s e d hydrogenation of hex-l-ene i n DMA at 30°C. -36-of hex-2-ene was found to be approximately o n e - f i f t h of that found f o r hex-l-ene, and so judging by the uptake p l o t s (Figure 3.4) the r a t e of i s o m e r i s a t i o n i n the presence of hydrogen appears to be n e g l i g i b l e . The "standard" c o n d i t i o n s employed were a t o t a l ruthenium con-c e n t r a t i o n of 2 x 10 3M w i t h 2 x 10 S i hex-l-ene under an atmosphere of hydrogen at 30°C, although the concentrations of a l l the r e a c t a n t s were v a r i e d c o n s i d e r a b l y . The s o l u b i l i t y of hydrogen i n DMA at 30°C was deter-mined (Figure 3.5), and found to obey Henry's Law at l e a s t up to one atmosphere pressure. The dependence of the maximum r a t e on c a t a l y s t c o n c e n t r a t i o n , hydrogen pressure at two o l e f i n c o n c e n t r a t i o n s , o l e f i n c o n c e n t r a t i o n , added triphenylphosphine, and added l i t h i u m c h l o r i d e were studied (Table I I I - 3 ) . The dependence on added hexane was not i n v e s t i g a t e d due to i t s i n s o l u b i l i t y i n DMA. The p l o t of the r a t e of hydrogenation of hex-l-ene against the t o t a l ruthenium co n c e n t r a t i o n can be seen i n Figure 3.6. The r a t e approximates to f i r s t - o r d e r , but i s probably more a c c u r a t e l y described as being f i r s t order at lower concentrations and becoming l e s s than f i r s t - o r d e r at higher c o n c e n t r a t i o n s . The dependence on hex-l-ene c o n c e n t r a t i o n (Figure 3.7) i s f i r s t -order up to approximately 2 x 10 "Si, and then decreases to zero-order at >_ 1.0 M. The a f f e c t of v a r y i n g the hydrogen pressure on the maximum r a t e (Figure 3.8) shows that f i r s t - o r d e r k i n e t i c s are e x h i b i t e d at lower pressures f o r both 2 x 10 H i and 7 x 10 S i hex-l-ene, but the dependence begins to decrease at approximately 100 and 400 mm,respectively. The -37-mm [H0] x 10" M 760 570 380 190 1.76 1.32 0.88 0.43 -38-TABLE I I I - 3 K i n e t i c data f o r the H R u C l ( P P h 3 ) ^ c a t a l y s e d hydrogenation of hex-l-ene i n DMA at 30°C [ R u ] a P R [H 2] [hex-l-ene] Max. Rate 2 o 5 - 1 x l 0 3 , M mm xlO M xlO.M xlO ,M s 2.20 4.18 4.08 7.25 11.37 12.27 13.33 13.57 13.70 10.18 11.53 6.50 5.87 3.92 2.43 14.34 13.28 10.77 6.32 3.08 3.98 b 0.96 c 0.63 d 0.33 e 11.90 f 14.80S 20.60 h 24.86 1 a Fxnressed as monomer 9 . , b 1 0 5 c 3.9 M, d 6.8 M, and e 10.0 M [ P P h 3 ] x l 0 2 added r e s p e c t i v e l y l'.O M, g 2.0 M, h 5.0 M,and i 10.0 M [ L i C l ] x l 0 2 added r e s p e c t i v e l y . 0.05 760 1.76 2.00 1.00 760 1.76 2.00 2.00 760 1.76 0.09 2.00 760 1.76 2.00 2.00 760 1.76 4.65 2.00 760 1.76 5.93 2.00 760 1.76 8.24 2.00 760 1.76 10.56 2.00 760 1.76 15.17 3.00 760 1.76 2.00 4.00 760 1.76 2.00 2.00 570 1.32 2.00 2.00 380 0.88 2.00 2.00 200 0.46 2.00 2.00 100 0.23 2.00 2.00 760 1.76 7.00 2.00 570 1.32 7.00 2.00 380 0.88 7.00 2.00 200 0.46 7.00 2.00 100 0.23 7.00 2.00 760 1.76 2.00 2.00 760 1.76 2.00 2.00 760 1.76 2.00 2.00 760 1.76 2.00 2.00 760 1.76 2.00 2.00 760 1.76 2.00 2.00 760 1.76 2.00 2.00 760 1.76 2.00 f -39-12 0 [Ru] X 1 0 3 , M Figure 3.6 Dependence of maximum rate of hydrogenation on ruthenium concentration i n DMA at 30°C. - 4 0 -16 0 4-0 8-0 12-0 16-0 [Olefin] x10, M Figure 3.7 Dependence of maximum rate of hydrogenation on hex-l-ene concentration i n DMA at 3 0 ° C . Figure 3.8 Dependence of maximum r a t e of hydrogenation on hydrogen co n c e n t r a t i o n i n DMA at 30°C. -42-o v e r a l l tendency to zero-order i s more n o t i c e a b l e at the lower o l e f i n c o n c e n t r a t i o n . P l o t s of maximum r a t e versus the conc e n t r a t i o n of added t r i -phenylphosphine (Figure 3.9), and l i t h i u m c h l o r i d e (Figure 3.10) are curved and tend to show a s a t u r a t i o n e f f e c t at the higher concentrations. The r a t e i s i n h i b i t e d w i t h i n c r e a s i n g [PPh^] w h i l e the r a t e increased w i t h i n c r e a s i n g [ L i C l ] . 3.3 A n a l y s i s of K i n e t i c Data To e x p l a i n the near f i r s t - o r d e r dependence on [Ru]T» the f i r s t -to zero-order dependence on hex-l-ene, the predominantly f i r s t - o r d e r dependence on hydrogen at high s u b s t r a t e c o n c e n t r a t i o n , and the f i r s t -to zero-order dependence a t lower substrate c o n c e n t r a t i o n , the f o l l o w i n g mechanism i s proposed: k l H R u C l ( P P h 3 ) 2 + o l e f i n „ fc " R u C l ( P P h ^ ( a l k y l ) (3.12) k R u C l ( P P h 3 ) 2 ( a l k y l ) + H 2 f • HRuCl(PPh 3) 2 + alkane (3.13) where k^, k_^, and k 2 are the r a t e constants f o r the i n d i v i d u a l steps. Applying a steady-state treatment to the intermediate R u C l ( P P h 3 ) 2 ( a l k y l ) gives the r a t e equation: Rate = " d [ H 2 ] = k ^ f R u ^ t o l e f i n ] [H 2J dt [H 2]+k 1 [ o l e f i n ] (3.14) -43--44-i 1 4 0 80 12 0 [LiCD x 1 0 2 , M Figure 3.10 Dependence of maximum r a t e of hydrogenation on added l i t h i u m c h l o r i d e c o n c e n t r a t i o n i n DMA at 30°C. -45-Th e i n i t i a l induction period prior to attaining the maximum rate is probably due to the dissolution of the complex, and a build up of the steady-state concentration of the alkyl. 3.3.1 Dependence of the Rate on Catalyst Concentration (Figure 3.6) The rate equation (3.14) reduces to: Rate = k'[Ru] T (3.15) where k ^ [ o l e f i n ] [H2] k^+kj [H2]+k1 [olefin] (3.16) and therefore satisfies the essentially first-order Ru dependence shown -3 in Figure 3.6. For a total ruthenium concentration of 2 x 10 M, the -3 K value for equation 3.10 shows that there would be 1.05 x 10 M of -3 monomer and 0.48 x 10 M of dimer. However, at0.2 M hex-l-ene very l i t t l e dimer w i l l remain (Figure 3.3), and i t can be ignored then at [Ru] T = 2x10 M. The f a l l off in Ru dependence at higher concentration (Figure 3.6) is presumably due to the presence of small amounts of inactive dimer. 3.3.2 Dependence of the Rate on Olefin Concentration (Figure 3.7) At lower olefin concentrations the k^folefin] term in the denominator of the rate equation (3.14) can presumably become small compared to (k ^ + k 2[H 2]), and the rate equation reduces to one showing a f i r s t -order dependence on olefin: -46-k,k o[Ru] T[olefin][H 0] Rate 1 2 T (3.17) k_1+k2[H2] However,at higher olefin concentrations (>1 M),the k^[olefin] term must dominate and equation (3.14) becomes: Rate = k 2[Ru] T[H 2] (3.18) which is independent of olefin concentration. The rate equation (3.14) can be rearranged to give: 1 k_l + k2^ H2'' 1 1 Rate = k 1k 2[Ru] T[H 2J ' [olefin] + k^ TRul^ THp" ( 3' 1 9 ) A plot of 1/Rate versus 1/[olefin] at constant [Ru]^ and [H,,] should therefore yield a straight line; the intercept of which can be used to calculate k 2- Such a plot (Figure 3.11) gives a reasonable straight line with a k 2 value of 78 M ^ from the intercept. 3.3.3 Dependence of the Rate on Hydrogen Concentration (Figure 3.8) Considering the low olefin concentration case where equation (3.17) applies, the dependence on hydrogen should go from f i r s t - towards zero-order as the [H2] increases,as seen experimentally (Figure 3.8). When the olefin concentration i s high(>1 M) , the rate equation is (3.18), and so the rate should be s t r i c t l y first-order throughout the whole range of hydrogen concentrations. Unfortunately the olefin concentration chosen (0.7 M) was not sufficiently high, but nevertheless the data clearly show the tendency toward first-order behaviour at the higher olefin concentration. -47--48-The data can be analysed q u a n t i t a t i v e l y by rearranging equation (3.14) to g i v e : 1 k ^ + k j [ o l e f i n ] m 1 x R a t i " " k 1 k 2 [ R u ] T [ o l e f i n ] [H 2] + k 1 [ R u ] T [ o l e f i n ] ( 3 , 2 0 ) At constant [Ru]^ and [ o l e f i n ] , a p l o t of 1/Rate against 1/[H 2] at both o l e f i n concentrations y i e l d s s t r a i g h t l i n e s (Figure 3.12); the i n t e r c e p t s of which can be used t o determine k^ values of 0.28 and 0.29 M ^s \ Since the v a l u e of k 2 i s known ( S e c t i o n 3.3.2), t h i s w i t h the k^ value can be used to d e r i v e the value of k ^ from the slopes of the l i n e s from equations (3.19) and (3.20), and hence the value of k^/k_^. For an o l e f i n c o n c e n t r a t i o n of 0.2 Mthe average val u e of k ^ i s c a l c u l a t e d to be 1.4 x 1 0 ~ 2 s ~ 1 which y i e l d s a value of k /k_ x of 20 M**1, w h i l s t f o r 0.7 M -1 -2 -1 the l a t t e r i s 12 M from an average value of 2.3 x 10 s c a l c u l a t e d f o r k_^. 3.3.4.1 Dependence of the Rate on Added Triphenylphosphine Concentration (Figure 3.9) For hydrogenation r e a c t i o n s under constant [ R u ] T , [H,,], and [hex-l-ene],the r a t e decreases w i t h i n c r e a s i n g [PPh^]. A d d i t i o n of 39 triphenylphosphine to the dimer i s known to g i v e a s o l u t i o n c o n t a i n i n g the monomeric HRuCl(PPh^)^ complex. The colour of the s o l u t i o n changes w i t h i n c r e a s i n g added PPh 3 from the red of the [ H R u C l ( P P h ^ ) 2 ] 2 , HRuCl (PPh3)2 -DMA mixture to the purple colour of the t r i s ( t r i p h e n y l -phosphine) s p e c i e s : K K' J s [ H R u C l ( P P h 3 ) 2 ] 2 - 1 " H R u C l ( P P h 3 ) 2 ^ _ p p h fc H R u C l ( P P h 3 ) 3 (3.21) Figure 3.12 Dependence of maximum r a t e of hydrogenation on hydrogen concentration as p l o t t e d according to equation (3.20). -50-36 5 The value of K' i s thought to be very l a r g e (>10 ) i n benzene at 25°C and hence the phosphine competes w i t h the o l e f i n f o r a coordina-t i o n s i t e at the metal centre. The tr i s p h o s p h i n e species i s b e l i e v e d to be c a t a l y t i c a l l y i n a c t i v e f o r hydrogenation u n t i l i t d i s s o c i a t e s a phosphine l i g a n d ( S e c t i o n 1.3), hence the observed i n v e r s e dependence, (Figure 3.13). 3.3.4.2. A Spectrophotometric Study of the Reaction between HRuCl(PPh 0) 0 and PPh„ The r e a c t i o n between the bisphosphine complex and t r i p h e n y l -phosphine was found to occur w i t h a 1:1 s t o i c h i o m e t r y , but i s too f a s t to be studied using the conventional v i s i b l e spectrophotometer, and so i t was necessary to employ stopped-flow techniques. The data f o r DMA s o l u t i o n s at 30°C are presented i n Table I I I - 4 ; i n each case, except f o r the l a s t two experiments l i s t e d , the phosphine was i n excess by at l e a s t a f a c t o r of ten to maintain pseudo f i r s t - o r d e r c o n d i t i o n s i n Ru. A l l the absorbance vs time data analyzed f o r good f i r s t - o r d e r l o g p l o t s (Figure 3.14) from which ^•Q^)S were estimated. The dependence of k ^ o n [PPh^] goes from f i r s t - to zero-order w i t h i n c r e a s i n g [PPh^J (Figure 3.15). The expected independence of k , on [R u J m i s observed at the higher [PPh„], but at lower obs T J [PPh^] k Q k s does decrease w i t h i n c r e a s i n g [Ru]^, (Figure 3.16). These dependences can be r a t i o n a l i s e d q u a l i t a t i v e l y i n terms of the f o l l o w i n g mechanism: -51--52-TABLE III-4 Stopped-flow data for DMA solutions of HRuCl(PPh^)^ and PPh„ at 30°C [Ru] axl0 3,M [PPh^xlO.M 0.50 0.05 0.23 0.50 0.25 0.89 0.50 0.50 1.23 0.50 1.00 1.46 0.50 1.50 1.48 0.27 1.50 1.43 0.35 1.50 1.50 0.63 1.50 1.45 1.00 1.50 1.39 0.27 0.05 0.34 0.35 0.05 0.32 0.63 0.05 0.19 1.00 0.05 0.16 a Expressed as monomer b Determined at 440 nm -53-3-6 I I I I 1 I I 1 L_ 0 4-0 8-0 12-0 16-0 Time , s Figure 3.14 P l o t of l n ( A -A^) vs time of the stopped-flow data f o r the r e a c t i o n between HRuCl(PPh,) and PPh . -54-16 0 C\J o CO JO o to 1 0 0 H 6 0 4 0 2 0 0 5 1-0 [ppr\f] x 1° • M 15 Figure 3.15 Dependence of k on triphenylphosphine c o n c e n t r a t i o n inb5MA at 30°C. -55-k l [HRuCl(PPh 3) 2] 2 „ k X * 2HRuCl(PPh3)2 (3.22) k HRuCl(PPh 3) 2 + PPh 3 • HRuCl(PPh 3) 3 (3.23) Since equilibrium (3.22) i s established prior to the addition of PPh 3 i t is not possible to apply a steady-state treatment on the monomer, and thereby obtain a rate equation to explain the observed kinetics. At high phosphine concentration (region B of Figure 3.15) the observed rate constant (k , ) is independent of [PPh.]; and obs J any monomer present must be rapidly consumed by the PPh3 in a fast k 2 step. The spectral change observed must therefore result from the k^ step (in effect one is monitoring the conversion of any remaining dimer to the trisphosphine complex), and k ^  w i l l simply equal k^. The value of k^ is found to be 1.49 x 10 ^ s \ and _3 since k^/k_^ is known from equation 3.9 to equal 1.66 x 10 M, the value of k ^  is calculated to be 90 M \ Varying the total ruthenium concentration at high [PPh-j] (Figure 3.16) gives values with an average value for of 1.45 x 10 \ At low [PPh3] in the first-order region, k 9 must now be rate determining,this step being followed by rapid Figure 3.16 Dependence of k on ruthenium c o n c e n t r a t i o n DMA at 30°C. ° S -57-establishment of equilibrium (3.22). A rate equation can therefore be w r i t t e n : Rate = k 2[PPh 3][HRuCl(PPh 3) 2] (3.24) and since [Rul = [HRuCl (PPh,) V2[HRuC1 ( P P h 3 ) 2 ^ V k - l \ (3.25) \ V k-1 k l / k - i k 2 [ P P h 3 ] [ R u ] ' 2[HRuCl(PPh 3) 2] + k 1/k_ 1 Rate = —= -r-rr-rr-. r — , . •. 7; VJ • Z D > The dependence on [ R u ] T w i l l depend on the r e l a t i v e magnitude of 2[HRuCl(PPh 3) 2] and k^/k y With i n c r e a s i n g ruthenium c o n c e n t r a t i o n the former term w i l l i n c r e a s e i n magnitude, and the o v e r a l l dependence on ruthenium w i l l be l e s s than f i r s t - o r d e r . This i s presumably why k , decreases w i t h i n c r e a s i n g [Ru]„ at the lower [PPh~] (Figure 3.16), obs I J however, i t i s not obvious why each experiment should analyse f o r f i r s t --3 order i n ruthenium. At [Ru]^, of 0.5 x 10 M the i n i t i a l concentration of monomer i s 0.35 x 10 Mjhence the denominator of equation (3.26) -3 -3 equals (0.7 x 10 ) + (1.66 x 10 ) so the term f o r the monomer cannot be neglected. During the early stages of the re a c t i o n the monomer w i l l be replenished v i a the dimer d i s s o c i a t i n g and i f the concentration does not change too much,the f i r s t - o r d e r log plot s would be expected. At the -3 -2 -1 lowest [Ru] T (0.26 x 10 M), k o b g i s 3.4 x 10 s ; extrapolating the -3 curve of Figure 3.16 back to lower [Ru] T (0.1 x 10 M), where the rate equation (3.24) w i l l approximate to k 2[PPh 3][HRuCl(PPh^) 2J»suggests k Q b s -2 -1 w i l l be of the order of 5 x 10 s . This gives a value of k 2 of -58-approximately 10^M ^ which i s reasonably consistent with the step becoming rate determining at low [PPh^], while at high [PPh^] the k^ step i s rate l i m i t i n g . 3.3.5.1 Dependence of the Rate on Added Lithium Chloride Concentration (Figure 3.10) For hydrogenation reactions under constant [Ru]^, [H^], and [hex-l-ene], the rate was found to increase with increasing [ L i C l ] . The rate p r o f i l e suggests that at higher c h l o r i d e , a l i m i t i n g rate, some 4-5 times greater than that i n the absence of added c h l o r i d e , i s reached. Chloride ion could add to the dimer to produce more act i v e c a t a l y s t s ; 64 p o s s i b i l i t i e s include a t r i p l y - c h l o r o - b r i d g e d species,which are known , or an anion such as HRuCl^(PPh^) 2 produced from addition of CI to the monomer v i a cleavage of the dimer. Attempts to i s o l a t e the product from the chloride addition to [HRuCl (PPh^),,^ using various cations were un-su c c e s s f u l . The e f f e c t s on rate are much too large to be accounted for by changes of H 2 s o l u b i l i t y i n the DMA-LiCl solutions* indeed,the s o l u b i l i t y decreases by about 10% on adding up to 1.2M L i C l . ^ 3.3.5.2 A Spectrophotometric Study of the Reaction between HRuCl ( P P h ^ ) ^ and L i C l . _3 To a DMA s o l u t i o n of HRuCl(PPh 3) 2 (7.2 x 10 M) was added DMA solutions of L i C l , and the v i s i b l e spectrum recorded at 25°C (Figure 3.17) Changes i n the absorption maximum at 500 nm were monitored with each addition of L i C l , and the r e s u l t s are given i n Table III-5: -59-W a v e l e n g t h , nm igure 3.17 V i s i b l e absorption of DMA so l u t i o n of H R u C l ( P P h ^ upon addition of l i t h i u m c h l o r i d e . (A) 7.2 x 10_3M HRuCl(PPh 3) 2 and (B), (C), (D) and (E) are upon the addition of 0.124, 0.256, 1.136, and 1.430 x 10-2M L i C l . -60-TABLE III-5 Spectrophotometric study of the equilibrium between HRuCl(PPh,)0 and LiCl in DMA solution at 25°C A3(500 mn) [LiCl]xl0 2,M A -A o A-A OC 0.864 0 0 0.236 0.854 0.124 0.010 0.226 0.842 0.256 0.022 0.224 0.798 1.136 0.066 0.170 0.769 1.430 0.095 0.141 a 1 mm c e l l path \ -61-The sp e c t r a l changes are very s i m i l a r to those obtained for. addi t i o n of hex-l-ene to the complex, and the same problems a r i s e in i n t e r p r e t i n g them. There are no r e a l i s o s b e s t i c points which suggests that there are more than two absorbing species,so two e q u i l i b r i a analogous to those for the hex-l-ene system appear l i k e l y : K l ( H RuCl(PPh 3) 2) 2 „ fc 2HRuCl(PPh 3) 2 (3.27) K 3 + HRuCl(PPh 3) 2 + L i C l - * L i HRuCl 2(PPh 3) 2 (3.28) or a l t e r n a t i v e l y the ch l o r i d e binds to both the dimer and monomer. 3.4 Discussion The r e s u l t s show that hydridochlorobis(triphenylphosphine) ruthenium(II) i s an e f f e c t i v e and e f f i c i e n t c a t a l y s t f o r the hydro-genation of hex-l-ene. The reduction proceeds by a more "conventional" mechanism compared to the hydrogenation of acrylamide (section 3.1), thereby showing that the nature of the substrate has a pronounced a f f e c t on the course of hydrogenation. Since the complex does not obey Beer's law i t i s necessary to e s t a b l i s h which i s the reacting species i n s o l u t i o n . The v i s i b l e spectra for the binding of the o l e f i n to the complex o f f e r s l i t t l e help as the r e s u l t s can be interpreted i n terms of consecutive dimer-monomer and monomer-alkyl e q u i l i b r i a , o r even binding of the o l e f i n to both dimer and monomer,although the k i n e t i c s tend to r u l e out a c t i v a t i o n v i a the dimer. In the absence of H 2 the forward and backward re a c t i o n of equation (3.12) w i l l lead to an equilibrium concentration of the a l k y l . -62--1 -1 -2 -1 Since = 0.29 M s and k ^ averages to 1.9 x 10 s (section 3.3.3), the equilibrium constant i s 16 M and w i l l be established with an o v e r a l l rate constant of (k^folefin]+k j) at pseudo zero-order con--2 -1 d i t i o n s i n o l e f i n . This rate constant has values of 2.2 x 10 s -2 -1 -2 and 6.7 x 10 s at 10 M and 0.2 M o l e f i n r e s p e c t i v e l y . These numbers are quite consistent with the experimental time (up to 500 sec) found necessary for the establishment of equilibrium (3.12). A k^/k_^ of 16 M ^ i s also q u a l i t a t i v e l y consistent with the range of o l e f i n concentration used to bring about the s p e c t r a l changes of Figure 3.3 ( i . e . the conversion of hydride to a l k y l ) . The gas-uptakes show a predominantly f i r s t - o r d e r dependence on [Ru]^, which i s not i n agreement with the following mechanism i n which the dimer i s the major species present: (HRuCl(PPh 3) 2) 2 „ K - 2HRuCl(PPh 3) 2 (3.29) k l HRuCl(PPh 3) 2 + o l e f i n ^===^ R u C l ( P P h 3 ) 2 ( a l k y l ) (3.30) k2 RuCl ( P P h 3 ) 2 ( a l k y l ) + H 2 — • HRuCl ( P P h ^ + alkane (3.31) Such a mechanism leads to a half-order dependence on [Ru] T« There are two possible explanations f o r the f i r s t - o r d e r dependence; either the o l e f i n binds s o l e l y to the dimer and the c a t a l y s i s proceeds v i a t h i s species, or more l i k e l y , since l i t t l e of the ruthenium i s present i n the dimeric form, the monomer i s the active s i t e f o r hydrogenation. This proposal i s supported by the s l i g h t deviation from f i r s t - o r d e r dependence -63-on [Ru]^ at higher ruthenium concentrations (Figure 3.6) where more of the i n a c t i v e dimer w i l l be present, thereby reducing the monomer av a i l a b l e for c a t a l y s i s . The d i f f e r e n c e i n reaction mechanisms between t h i s system and that using acrylamide as substrate i s a t t r i b u t e d to the e f f e c t of the o l e f i n . The equilibrium constant for the reaction of acrylamide with 39 -1 the complex,which was taken to be monomer,was found to be 150 M , whilst for hex-l-ene i t was 16 M 1 (see above). For acrylamide the electron-withdrawing amide substituent w i l l enhance back donation from the f i l l e d metal d - o r b i t a l s to the empty antibonding o r b i t a l s of the o l e f i n so i t w i l l bind more strongly. Insertion of the acrylamide molecule into the Ru-H bond generates a metal-alkyl species that does not apparently undergo oxidative addition of a hydrogen molecule; one p o s s i b i l i t y i s that compared to hexyl the electron withdrawing nature of the a l k y l group removes electron density from the metal atom and reduces the a b i l i t y of the complex to undergo oxidative a d d i t i o n . 6 6 Perhaps more l i k e l y i s that the amide group coordinates to the ruthenium, and the r e s u l t i n g five-coordinate chelate intermediate would be l e s s l i k e l y to o x i d a t i v e l y add H 2. Coordination of amide i n unsaturated o l e f i n i c substrates i s well documented. 6^ Since molecular hydrogen cannot be used to complete the reduction of the acrylamide substrate another mole of hydride i s used, concomitantly producing a Ru(I) dimer which i s reverted to the active c a t a l y s t by undergoing oxidative addition of H 2 (equation 3.4). For the unactivated o l e f i n , hex-l-ene, the binding constant i s smaller, but the metal-alkyl species r e a d i l y reacts with H 2 presumably by oxidative addition, and subsequent reductive elimination -64-of hexane regenerates the c a t a l y s t . The maximum r a t e of hydrogenation f o r hex-l-ene i s f a s t e r than f o r acrylamide presumably because of the a v a i l a b i l i t y of hydrogen which i s p r e f e r r e d f o r r e a c t i v i t y w i t h the metal-a l k y l complex. 68 Hydrogenation of hex-l-ene using HRuCl(PPh^)^ as c a t a l y s t i s s i m i l a r to the bisphosphine system as i t i n v o l v e s a rate-determining r e a c t i o n of a ruthenium a l k y l w i t h molecular H^. However, the r a t e of hydrogenation of the a l k y l i s approximately eight times f a s t e r f o r the 69 38 tri s p h o s p h i n e complex. This supports the r e c e n t l y proposed mechanism f o r the hydrogenations using HRuCl(PPh^)^ (equations 1.10-12) i n which the rate-determining step i s the r e a c t i o n of B.^ w i t h RuCl(PPh^)^ ( a l k y l ) and not R u C l ( P P h ^ ^ ( a l k y l ) as o r i g i n a l l y p o s t u l a t e d . The e x t r a phosphine l i g a n d i n the t r i s p h o s p h i n e - a l k y l species i s considered to enhance the o x i d a t i v e a d d i t i o n of t o t n e metal atom and thereby increase the r a t e . Under the c o n d i t i o n s used to study the phosphine dependence (Figure 3.9) at l e a s t i n the absence of added phosphine, the r a t e i s e s s e n t i a l l y f i r s t - o r d e r i n ruthenium and o l e f i n , and almost independent of hydrogen i . e . the r a t e law approximates to k ^ [ R u ] ^ [ o l e f i n ] . In the presence of the added phosphine, l i t t l e of the dimer w i l l be present, and the system might be described by: HRuCl(PPh,), + o l e f i n *> R u C l ( P P h 3 ) 2 ( a l k y l ) +PPh3 IT H 2' f a s t (3.32) HRuCl(PPh 3) 3 HRuCl(PPh,), + alkane I n c o r p o r a t i o n of the K' e q u i l i b r i u m w i t h only the bisphosphine system -65-c o n t r i b u t i n g to the c a t a l y s i s would y i e l d the rate law: k. [Ru]_[olefin] **" ' 1 + xVph3] ( 3 - 3 3 ) The data of Figure 3.13 indi c a t e that K'[PPh 3]»l. The inverse plot 7 2 -1 y i e l d s a slope of k^[Ru]^,[ o l e f i n ] /K' of value A x 10 M sec , which corresponds to a K' value of ^ 300 M - 1. This i s c l e a r l y not consistent 36 with the much la r g e r values of K' estimated previously. The anomaly l i e s i n the f a c t that c a t a l y s i s can occur through the trisphosphine system once the o l e f i n coordinates and displaces one phosphine: HRuCl(PPh,), + o l e f i n A ~ HRuCl (PPh,) . ( o l e f i n ) 3 3 +PPh3 J I I I (3.34) H alkane + HRuCl(PPh 3) 2 R u C l ( P P h ^ ( a l k y l ) E a r l i e r studies on the trisphosphine systems had shown that the k i n e t i c dependence on was f i r s t - o r d e r , and the rate-determining step was 68 written as the reaction of the a l k y l with H^ (equation 3.34),which i s quite d i f f e r e n t from the mechanism shown i n equation (3.32). Hydro-genation through (3.34) gives the rate law: K " k 2 [ H 2 ] [ R u ] T [ o l e f i n ] R a t e = K " [ o l e f i n ] + [PPh 3] ( 3 ' 3 5 ) The rate would give a d i r e c t inverse dependence on added phosphine when [PPh3]>>K" [ o l e f i n ] , i . e . the ruthenium i s present almost e n t i r e l y as HRuCl(PPh 3) 3- The slope of the inverse plot (Figure 3.13) would then -66-be a measure of K " k 2 [ H 2 ] [ R u ] T [ o l e f i n ] . The slope y i e l d s K"k 2 to equal 0.6 M ^ so i t i s almost c e r t a i n that the experiments with added phosphine are concerned with a c t i v i t y v i a the trisphosphine species. C l e a r l y more d e t a i l e d studies on the bisphosphine system with added phosphine are required before a complete i n t e r p r e t a t i o n can be offered. C a t a l y t i c isomerisation of hex-l-ene i s not unusual, but the extent to which i t occurs i n the presence of HRuCl(PPh.j) 2 i s i n t e r e s t i n g . A number of review a r t i c l e s ^ have been presented on t h i s subject, and three mechanisms proposed: (a) Metal hydride addition-elimination RCH2CH|CH2 „ - RCH2CH-CH3 ^  RCH=CH-CH3 MH M MH (3.36) (b) T T - A l l y l hydride formation RCH2CH=CH2 M RCH CH MH CH ^ * RCH=CHCH 2 | J M (3.37) (c) Carbene formation RCH2CH=CH2 ^  " RCH 2CCH 3 M M RCH=CHCH, M (3.38) C l e a r l y i n view of the hydrido-catalyst being studied and i t s i n t e r a c t i o n with o l e f i n to give an a l k y l , mechanism (a) i s strongly favoured with the intermediate a l k y l formed i n i t i a l l y by Markovnikoff addition of the Ru-H to the coordinated hex-l-ene. A f t e r 15 h at 25°C, solutions of -67-HRuClCPPh^)^ were found"1' to isomerise hex-l-ene to 7% hex-2-ene and 1% u n i d e n t i f i e d m a t e r i a l , which i s much slower than for solutions of the bisphosphine complex i n the present work (85% conversion to hex-2-ene a f t e r 1 h ). This i s presumably due to l e s s s t e r i c crowding i n the R u C l ( P P h 3 ) 2 ( a l k y l ) intermediate and so hydride tran s f e r i s much less hindered than i n RuCl(PPh,),(alkyl). -68-CHAPTER IV STRUCTURAL STUDIES ON  HYDRIDOCHLOROBIS(TRI-p-TOLYLPHOSPHINE)RUTHENIUM(II) 4.1 X-Ray Structure Determination Preparation of ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 , as described i n Section 2.1.5.2 i i , y i e l d e d dark red c r y s t a l s ; a sin g l e c r y s t a l x-ray d i f f r a c t i o n study c a r r i e d out by R.C. B a l l i n t h i s department revealed the complex to be a chloro-bridged dimer (Figure 4-1). A square pyramidal coordi-6 37 nation geometry i s usually favoured by a f i v e coordinate d configuration , but here the structure of two such centres sharing a basal edge has no symmetry since i t Is d i s t o r t e d as a r e s u l t of the small hydride ligand. It was d i f f i c u l t to determine unequivocally the p o s i t i o n of the hydride ligands, but some electron density was found i n the positions shown, and i t i s not unreasonable that they should be located there. The p o s i t i o n of the hydride on Ru(2) may be d i f f e r e n t from that shown o as the Ru(2)-Cl(2) bond length (2.57A) i s found to be longer than the o other three Ru-Cl bond lengths (2.46-2.48A), which suggests a trans i n f l u --70-ence of the hydride l i g a n d . ^ o The distance between the ruthenium centres i s 2.80A which f a l l s o 72 within the range (2.28-2.95A) usually found for a Ru-Ru bond. However, since each metal atom has 16 electrons, and the complex i s diamagnetic (n.m.r. a c t i v e ) , there cannot formally be a metal-metal s i n g l e bond. The diamagnetism would imply a double bond but a shorter bond length than the observed value would probably be expected. Various bond lengths, and bond angles are l i s t e d with Figure 4.2. 2 73 X-ray studies on R u C l 2 ( P P h 3 ) 2 and HRuCl(PPh^)^ have shown that one ortho-hydrogen atom of a phenyl group of the coordinated phosphines o i s p a r t i c u l a r l y close to the metal atom (2.59 and 2.85A r e s p e c t i v e l y ) . 74 This i s consistent with a three-centre intermediate such as: to explain how ligand-metal hydrogen transfer (orthometallation) occurs, for example, i n deuterium exchange studies. The distance between the ortho-hydrogen atoms and ruthenium centres for the ( H R u C l ( P t p - t o l y l ) . ^ ) 9 o dimer are a l l greater than 3A, and the packing of the phenyl rings should not r e a d i l y permit orthometallation. The dimeric complex was also prepared as previously described but using deuterium as the reducing agent. The ^H n.m.r. of the product shows the hydride resonance at T22.8; and the resonance at T2.37 which i s assigned to the ortho-protons i s reduced by 50% r e l a t i v e to the resonance for the meta — protons. Since there i s no evidence for close intramolecular contact of an ortho-hydrogen atom with a metal atom i n the x-ray study of the dimer, t h i s ortho-deuteration of the phosphine i s thought to be taking place i n the monomer presumably by -71-Distance (A) Ru(l)-Ru(2) 2.80(0) Ru(l ) - P ( l ) 2.26(1) Ru(l)-P(2) 2.39(1) Ru(2)-P(3) 2.28(1) Ru(2)-P(4) 2.23(1) R u ( l ) - C l ( l ) 2.47(1) Ru(l)-Cl(2) 2.48(1) Ru(2)-Cl(l) 2.46(1) Ru(2)-Cl(2) 2.57(1) Angles (deg) P(l)-Ru(l)-P(2) 104.1(5) P ( l ) - R u ( l ) - C l ( l ) 92.1(5) P( l ) - R u ( l ) - C l ( 2 ) 167.6(5) P( 2 ) - R u ( l ) - C l ( l ) 102.9(4) P(2)-Ru(l)-Cl(2) 88.0(4) C l ( l ) - R u ( l ) - C l ( 2 ) 82.6(4) P(4)-Ru(2)-P(3) 97.6(5) P(4)-Ru(2)-Cl(l) 166.8(5) P(4)-Ru(2)-Cl(2) 94.4(5) P(3)-Ru(2)-Cl(l) 95.6(5) P(3)-Ru(2)-Cl(2) 113.8(4) Cl(l)-Ru(2)-Cl(2) 80.9(4) Figure 4.2 C r y s t a l structure of the (HRuCl(P(p-tolyl)^) 2 complex, and selected bond angles and distances. -72-the following mechanism: (Ph 3P) 2 Ru ClD CI / [(2 -DC 6 H 4 )PPh 2 ] (Ph 3 P) Ru — D — X P P h , (Ph_P) Ru—CL J i s. Ph 2P. ^. (Ph_P) Ru—CL V (Pfi„P)R u / CI Ph2P. A.2 N.m.r. Spectroscopy 31 1 The P{ H}-n.m.r. of RuCl 2(PPh 3> 3 i n CH 2C1 2 at room temperature 37 75 shows ' a s i n g l e t (6=40.9 ppm), but on cooling to -97°C the spectrum reveals a doublet (6=24.1 ppm) and a t r i p l e t (6=75.7 ppm) with a r e l a t i v e i n t e n s i t y of 2:1. This was explained i n terms of a d i s t o r t e d square pyramidal structure (I) which undergoes intramolecular rearrangement at higher temperatures. At low temperatures an AB pattern (6 =58.8, 6 = 5 3 . 0 A D (CH 2C1 2); Jp p=41.5 Hz) i s also observed, the integ r a t i o n of which i s twice that of the free PPh 3 s i g n a l , and i s at t r i b u t e d to a dimeric species ( I I ) formed by loss of a phosphine ligand: R u C l 2 ( P P h 3 ) 3 ( R u C l 2 ( P P h 3 ) 2 ) 2 + 2PPh 3 (4.1) PPh. PPh-C l . Ph 3 P' Ru' .PPh. CL Ph 3 P 'Ru .PPh-'Ru n XI PPh: -73-The tolyl-phosphine analogue, R u C l 2 ( P ( p - t o l y l ) 3 ) 3 , was reported by Armit et a l ^ , and shows a doublet (6=25.1 ppm) and a t r i p l e t (6=74.3 ppm) at -83°C, and so the structure i s the same as i n I; there i s no reported evidence f o r a species equivalent to I I . I s o l a t i o n of R u C l 2 ( P P h ^ ) ^ 31 provided a P-n.m.r. with the same AB pattern for a toluene s o l u t i o n of the complex at -70°C as previously detected for reaction (4.1), thereby confirming the dimeric structure. In DMA only a sharp s i n g l e t at 64.9 ppm i s observed which i s compatible with a s i x coordinate species such as RuCl 2(PPh 3) 2(DMA) 2. 31 37 At -74 C the proton decoupled P-n.m.r. spectrum of HRuCl(PPh^)^ shows an AX 2 pattern (6^=94.0 ppm 6^=38.4 ppm) which collapses as the temperature i s raised and coalesces to a sharp s i n g l e t at 30°C. This i s consistent with a s t a t i c structure analogous to I with the hydride r e -placing a chloride ligand. There are no resonances due to free PPh^ or any other complexes. 1 39 When [HRuCl(PPh 3) 2] 2 was prepared, the H-n.m.r. i n toluene showed a s i n g l e broad resonance i n the h i g h - f i e l d region (T=22.5-23.8 ppm). The 31 1 P{ Hln.m.r. spectrum was not well resolved at -60°C because a s u f f i c i e n t l y concentrated s o l u t i o n could not be obtained, but the two resonances observed were a t t r i b u t e d to an AB pattern of a halide-bridged structure analogous to I I . This was used as evidence that the complex was a dimer i n toluene, whilst k i n e t i c data suggested that i t was a monomer i n DMA. To help sub-s t a n t i a t e these conclusions i t was decided to study the HRuCl(P(p-tolyl)-j) 2 complex since the tolyl-phosphine would enhance the s o l u b i l i t y properties of such species. The v a r i a b l e temperature ^H-n.m.r. spectra of a degassed toluene-d Q o s o l u t i o n of [HR u C l ( P ( p - t o l y l ) 3 ) 2 3 2 (approximately 0.05 M) are shown i n -74-Figure 4.3. At 30°C the spectrum consists of resonances due to the ortho and meta protons of the phenyl rings at T2.37 and 3.10 re s p e c t i v e l y , two methyl resonances at T7.80 and 7.86, and a hydride resonance at T22.8. On lowering the temperature a l l of the resonances begin to broaden u n t i l -80°C when two hydride resonances are observed at T18.3 and 27.5, and these then sharpen somewhat with further cooling.Two methyl resonances can be seen for tolyl-phosphines trans to ligands of d i f f e r i n g trans-influence, since changes i n e l e c t r o n i c e f f e c t s w i l l be transmitted to the methyl groups by the aromatic system. The chemical s h i f t of the hydride at 30°C i s at the centre of the s h i f t s for the two resonances at -90°C so a two-site exchange process i s occurring. There are two possible 78 explanations f o r t h i s ; the resonance of bridging hydrogen i n hydrido-metal c l u s t e r s appears at higher f i e l d than that of terminally bonded hydrogen, so a bridging to terminal hydrogen exchange i s occurring. A l t e r -n a t i v e l y , when hydrogen i s trans to a ligand of high trans-influence i t s chemical s h i f t i s at the low f i e l d (below T20)while opposite a ligand of low trans-influence i t s chemical s h i f t i s at the higher part (above T20) of the h i g h - f i e l d region,so an exchange which brings the hydride trans to ligands of d i f f e r e n t trans-influence w i l l also explain the observed spectra. Unfortunately i t was not possible to cool the sample ( f r e z i n g point of toluene -95°C) s u f f i c i e n t l y low to resolve the hydride resonances and to see the phosphorus coupling. 31 1 The v a r i a b l e tennerature P-{ H}-n.m.r. spectra of the same sample as used for the ^ H-n.m.r. are shown i n Figure 4.4. At -70°C there are three resonances at 29.0, 61.3, and 78.0 ppm of r e l a t i v e i n t e n s i t y 1:2:1, a s i n g l e t at 49.5 ppm -75-7-63 Benzene Impurity 3-10 2-37 22-8 // u ^JA- ZZ I . I . I — • I I I > I • 1 . I . I 1 — I — 1 — I — ' — I — > -Figure 4.3 The v a r i a b l e temperature 1H-n.m.r. spectra of ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 in toluene-d g. Figure 4.3 continued. -77-7 0 ° C 50 30 v 10 i i I 1 L i I I 1 L J I I 1 3 1 1 Figure A.A The v a r i a b l e temperature P{ H)-n.m.r. spectra of (HRuCl(P(p-tolyl),),), i n toluene-d . (A,B,C,D,E, and ' F at 2 0 0 0 Hz sweep width and G and H at 1 0 0 0 0 Hz sweep width). -78-i i i i i i I I I I I 1 1 1 1 1 1 1 Figure A. A continued. -79-which i s assigned to the solvated monomeric species, a s i n g l e t at 26.6 ppm which i s due to O P ( p - t o l y l ) ^ , and other resonances which are probably due to small quantities of impurities from decomposition of the complex. Raising the temperature to -50°C r e s u l t s i n broadening of the resonances, and coalescence to an i n d i s t i n c t peak at approximately 70.4 ppm, and a broad hump i n the region of 40 ppm. On further warming two resonances become apparent and these sharpen up at the average of the resonances at 78.0 and 61.3 ppm and the resonances at 61.3 and 29.0 ppm. At high temperatures a s i n g l e t due to phosphine oxide i s s t i l l present but s h i f t e d downfield to 40.1 ppm. The resonance due to the monomer (58.5 ppm) i n -creases i n i n t e n s i t y with increasing temperature which i s consistent with the endothermic cleavage of the chloride bridges. As the temperature i s rais e d another resonance at 68.4 ppm i s revealed, and appears to be associated with the monomer as i t grows i n i n t e n s i t y at a s i m i l a r rate to the resonance at 58.5 ppm, but the nature of t h i s a s s o c i a t i o n i s not at a l l obvious. Addition of DMA to a sample resulted i n a downfield s h i f t of a l l the resonances and an increase i n the proportion of monomer. The l i m i t i n g f a s t and slow exchange spectra could not be obtained because of the f a c i l i t i e s a vailable,so only a tenative explanation of the species i n s o l u t i o n can be given on the basis of the broad unresolved resonances. Assuming the c r y s t a l used i n the x-ray d i f f r a c t i o n study i s re-presentative of the sample, one of the species present at low temperatures can be taken to be the halide-bridged structure with two d i s t o r t e d square pyramids sharing a basal edge. A possible process to explain the n.m.r. -80-data involves a rearrangement which brings the hydrogen nucleus a x i a l and trans to the i n i t i a l l y a x i a l phosphine with concomitant s h i f t of the equatorial phosphine: H H P = P ( p - t 0 l y l ) 3 where P eouals P ( p - t o l y l ) ^ . As drawn there i s a square pyramidal and t r i g o n a l bipyramidal geometry about the Ru i n III and IV r e s p e c t i v e l y , but the deformations due to c r y s t a l forces as shown i n the c r y s t a l structure may be reduced i n s o l u t i o n but not s u f f i c i e n t l y to produce regular geometries. 31 1 The P{ H)-n.m.r. slow exchange spectra would be expected to show an AX pattern for both species. From the studies on other ruthenium--81-phosphine complexes discussed e a r l i e r , a phosphine trans to no ligand comes at l o w f i e l d , a phosphine trans to a ligand of low trans-influence i.e.Cl ,comes s l i g h t l y u p f i e l d , and a phosphine trans to a ligand of high trans-influence i.e.P or H ,comes much further u p f i e l d . Assuming that Pg and P have s i m i l a r chemical s h i f t s , i t i s not unreasonable that III would show doublets at 78.0 and 61.3 ppm due to P and P_ r e s p e c t i v e l y , and IV A o would show doublets at 61.3 and 29.0 ppm due to P^ , and P^ r e s p e c t i v e l y . On warming the exchange process w i l l increase and the time average of two non-equivalent phosphorus s i t e s w i l l be observed. The proposed exchange mechanism also explains the hydride region of the ^H-n.m.r., since at low temperatures the hydride w i l l be trans to a phosphine or to a c h l o r i d e and therefore two resonances w i l l be observed. The mechanism most often proposed for the interconversion of t r i g o n a l 79 bipyramidal to square pyramidal i s the Berry pseudorotation, but t h i s cannot apply here since i t requires a l l the ligands to be s i m i l a r , l i t t l e d eviation from the i d e a l interbond angles, and i t has only been applied to monomers. The f l u x i o n a l process proposed here i s not unreasonable since i f i t were the phosphine (P i n III) that moved into the a x i a l a p o s i t i o n the species generated would be: -82-which would be unstable due to the i n t e r a c t i o n between the bulky phosphines P„, and hydride ligands i n the equatorial p o s i t i o n are much l e s s stable 80 than i n the a x i a l p o s i t i o n . Whilst the mechanism for rearrangement of ( H R u C l ( P ( p - t o l y l ) 3 ^ 2 i s f e a s i b l e , further studies are required using a wider range of temper-atures so that the l i m i t i n g spectra can then be obtained for v e r i f i c a t i o n . 4.3 Formation of a Metal-Alkyl Species In neither the hydridochlorobis- nor the tr i s ( t r i p h e n y l p h o s p h i n e ) -ruthenium(II) system under the conditions of hydrogenation i s there any d i r e c t evidence f o r formation of an a l k y l species v i a (4.2) i n which the o l e f i n i n s e r t s into the metal-hydride bond: HRuCl(PPh 3) n + o l e f i n ( a l k y l ) R u C l ( P P h 3 ) n (4.2) There i s however, n.m.r. e v i d e n c e ^ f o r t h i s r e v e r s i b l e r e a c t i o n i n deuterated chloroform with ethylene at high pressure (^35 atm C^H^). 1 39 A H-n.m.r. of a s u f f i c i e n t l y concentrated s o l u t i o n of (HRuCl(PPh 3)^)^ at a high acrylamide concentration showed no high f i e l d metal-hydride s i g n a l which i s at least consistent with equation (4.2). To confirm the presence of the a l k y l species i t was decided to invest i g a t e the binding of an o l e f i n to the more soluble (HRuCl(P(p-tolyl)3)2)2 complex. Maleic a c i d ^ h a d been found not to be c a t a l y t i c a l l y hydrogenated with the triphenylphosphine system due to a very large binding constant, leaving no hydride a v a i l a b l e for the subsequent hydrogenation step (see equations (3.2) and (3.3)); but t h i s substrate was unsuitable for t h i s study due to i t s i n s o l u b i l i t y i n toluene, and so the dimethyl ester was -83-chosen. Dimethyl maleate was catalytically hydrogenated by the t o l y l -phosphine analogue ([Ru]T=2xlO~3M, [olefin]=0.2M, ]H2]=1.76xlO~3M, and 30°C) but the maximum rate is slow (1.4x10 5M s ^) , so i t appears to bind well at least in terms of the mechanism outlined by equations (3.2-3). The strong binding was confirmed by observing the changes in the visible spectrum of a toluene solution of the complex upon addition of dimethyl maleate. The limiting spectrum, which is when the presumed alkyl species is f u l l y formed, was obtained upon addition of essentially an equimolar amount of the olefin per ruthenium, but a value for the binding constant could not be found due to the problems discussed in Section 3.2. A 1:1 mixture of the complex and dimethyl maleate in toluene-d D under o 1 31 argon was prepared, and the H (Figure 4.5) and P (Figure 4.6)-n.m.r. spectra were run at a series of temperatures. Compared to the ^ H-n.m.r. of the hydride complex alone at 30°C (Figure 4.3), the spectrum of the mixture shows a broadening of the phenyl resonances, and only a broad single signal at T7.8 due to the methyls of the phosphines. If the hydride region i s measured at the same amplification as the rest of the spectrum there does not appear to be a resonance, but increasing the amplification a hundred times reveals a tri p l e t at T25.3 (J=32.0 Hz)and a quartet centred at T27.0 (J=25.5Hz). The methyl resonances of the ester group are unchanged from those of the free dimethyl maleate at T6.55, whilst the olefinic protons originally at T4.01 now appear at T7.55. On cooling, a l l of the resonances broaden slowly, and the hydride signal at -70°C (not shown) is too broad to be observed but below this temperature i t begins to 31 1 sharpen up again. The P{ H)-n.m.r. spectra of the same sample shows a surprisingly large number of signals. At 30°C there are singlets at -84-6-55 Benzene Impurity 27-0 25-3 J i_ Figure 4.5 The variable temperature H-n.m.r. spectra of a 1:1 mixture of (HRuCl(P(p-tolyl)J 2* 2 a n d d i m e t h y 1 maleate in toluene-dg. -85--86-45.1 ppm and 39.2 ppm due to monomer and OPCp-tolyl)^ r e s p e c t i v e l y , two broad resonances at 67.9 and 57.0 ppm, and a number of sig n a l s of small proportion over the range 30-75 ppm. On cooling,the s i g n a l at 67.9 ppm i s resolved into an AB pattern (6A=69.8, 6fi=65.6 J=46.5 Hz), the s i g n a l at 57.0 ppm also broadens but i s not resolved, and the rest of the peaks remained unchanged. Due to a concentration problem, i t was not possible to obtain spectra below -10°C. The ^H-n.m.r. does not show a t r i p l e t or doublet which would be expected f o r a species such as VI, but i t does show a s h i f t i n the o l e f i n i c protons which could r e s u l t from binding as i n VII. I f VII i s the complex formed by binding of the o l e f i n , t h i s substrate could occupy the vacant Ru. H ^/R, u X r - ^ r - M I H C Q 2 C H 3 C C H 2 C O / ^ C H3 3ZI * * T7TT coordination s i t e of the chloro-bridged dimer(VIII) making i t les s l i k e l y to undergo rearrangement due to s t e r i c i n terference. This would explain the t r i p l e t i n the hydride region, which i s broadened s l i g h t l y due to a H - ^ R U ^ ^ / U ^ ^ P P = P ( p - T O L Y L ) : p V 4 h slow exchange process, the broad phenyl and methyl resonances of the -87-31 1 phosphines and the AB quartet observed i n the P{ H}-n.m.r. To obtain a quartet i n the hydride would require coupling to three equivalent phosphorus atoms which would be possible i f a disproportionation reaction occurs. The reac t i o n between HRuCl(PPh^)^ and C^H^NCHCHNC^H^(DAD) has 81 been shown to produce HRuCl(PPh.^(DAD) at room temperature. This complex i s i n equilibrium with a monophosphine compound and a trisphosphine one, and i s capable of disproportionating into an i o n i c compound and a mixture of other neutral species. If dimethyl maleate behaves i n a s i m i l a r manner to DAD,the trisphosphine complex would produce the quartet and the monophosphine a doublet which may be concealed beneath other resonances. Disproportionation of HR u C l ( P ( p - t o l y l ) ^ ) 2 (dimethyl maleate) into various neutral species would also explain the excessive 31 number of resonances i n the P-n.m.r., as c l e a r l y there i s not j u s t an a l k y l species i n s o l u t i o n as i s often proposed (at l e a s t not with dimethyl maleate as substrate). 69 Of i n t e r e s t , e a r l y studies i n t h i s laboratory had indicated that maleic a c i d ( i n t e r n a l o l e f i n ) behaved very d i f f e r e n t l y from a terminal o l e f i n such as hex-l-ene during c a t a l y t i c hydrogenation using HRuCl(PPh^)^. Although the rate laws were of the same form, very d i f f e r e n t actual para-meters had been a t t r i b u t e d to differences i n the substrate binding and subsequent i n s e r t i o n to give the a l k y l species: K l HRuCl(PPh 0) + o l e f i n ^ = S ± HRuCl (PPh,) ( o l e f i n ) ( 4 . 4 ) i n 3 n ft K HRuCl(PPh-) ( o l e f i n ) * RuCl (PPh 0) (alkyl) ( 4 . 5 ) J n j n 1 -88-For maleic a c i d , was found to be large and K 2 small (because of the d i f f i c u l t y of hydride tran s f e r to the i n t e r n a l o l e f i n ) , and thus the species present i n so l u t i o n at high o l e f i n concentration was A and not the a l k y l B^ , which was found to be present i n the case of the terminal o l e f i n system. The n.m.r. data i n the present maleate system support that a hydrido(olefin) species (and not an a l k y l ) i s again present. *Since t h i s t h e s i s has been completed an a r t i c l e by J.M.Towarnicky and E.P.Schram (Inorg. Chim. A c t a , 41, 55 (1980) has been p u b l i s h e d i n which the authors d e s c r i b e the formation of ( H R u C l ( P P h 3 ) 3 ) 2 - The 1H-n.m.r. spectrum of t h i s complex i n C,.D^  shows a hydride resonance a t 27.5 s p l i t 6 6 31 1 i n t o a q u a r t e t w i t h J =26 Hz. The P{ H}-n.m.r. of the same sample shows PH a s i n g l e absorption centred a t 56.9 ppm. A l l of these f e a t u r e s are s i m i l a r t o those found i n the ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 ~ dimethyl maleate system so one of the major components produced from the decomposition appears to be (HRuCl(P(p-tolyl)3 ) 3 ) 2 * 1 -89-CHAPTER V GENERAL CONCLUSIONS AND SOME RECOMMENDATIONS FOR FUTURE WORK. The k i n e t i c study on the c a t a l y t i c hydrogenation of hex-l-ene by DMA solutions of (HRuCl(PPh^^^ reveals a near f i r s t - o r d e r dependence on [Ru]^,, a f i r s t - to zero-order dependence on hex-l-ene, predominantly f i r s t - o r d e r dependence on hydrogen at high substrate concentration, and a f i r s t - to zero-order dependence at lower substrate concentration. The k i n e t i c dependences are consistent with the following mechanism: k l HRuCl(PPh 3) 2 + o l e f i n ^ fe " RuCl(PPh 3> 2(alkyl) (5.1) k R u C l ( P P h 3 ) 2 ( a l k y l ) + H 2 * H R u C l ( P P h ^ + alkane (5.2) This i s quite unlike the mechanism found previously by other workers i n th i s laboratory for the hydrogenation of acrylamide using the same complex. Here formation of the a l k y l species i s followed by a r e v e r s i b l e reaction with another mole of hydride to give the saturated product; t h i s l a s t step -90-being Important and of i n t e r e s t i n that i t involves a c t i v a t i o n of a C-H bond at a saturated carbon centre. C l e a r l y the mechanism obtained i s influenced by the substrate being used, and so a study involving a wider range of o l e f i n s including those capable of chelating i s important to e s t a b l i s h the fa c t o r s i n f l u e n c i n g the C-H bond a c t i v a t i o n . The spectrophotometric studies of the reactions between (HRuCl(PPh^) 2) 2 and hex-l-ene, triphenylphosphine, and l i t h i u m chloride were informative, but l i t t l e quantitative data could be obtained from them due to having more than one species, dimer and monomer, i n i t i a l l y present i n so l u t i o n . If the studies were c a r r i e d out at low ruthenium concentration, where the complex would e x i s t e s s e n t i a l l y as a monomer, the values of k^/k_^ (3.12), k 2(3.23),and k^(3.28) could be obtained and compared to the values obtained from the k i n e t i c a n a l y s i s . The isomerisation of hex-l-ene by (HRuCl (PPh.j) 2) 2 w a s effected very e f f i c i e n t l y , and with further studies on the isomerisation of activated and deactivated terminal or i n t e r n a l o l e f i n s the complex may be found to have p o t e n t i a l i n organic synthesis. Characterisation of ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 i n the s o l i d state was possible by a sing l e c r y s t a l x-ray d i f f r a c t i o n study. This showed the complex to be a chloro-bridged dimer with a d i s t o r t e d square pyramidal structure about each ruthenium centre as a r e s u l t of the small hydride ligands. Variable temperature n.m.r. studies of t h i s complex did not reveal the s o l i d state structure i n solu t i o n since the l i m i t i n g spectra could not be obtained. Examination of the n.m.r. spectra over a wider range of temperatures should allow the i n t e r e s t i n g f l u x i o n a l behaviour of the five-coordinate dimer to be elucidated. N.m.r. studies on a ruthenium--91-alkyl or a hydrido(olefin) species would be informative i f an olefin could be found which binds strongly, but does not cause a dispro-portionation reaction as dimethyl maleate possibly does in this study. -92-REFERENCES 1. M. Ca l v i n , Trans. Faraday Soc. , 34, 1181 (1938). 2. G. D o l c e t t i and N.W. Hoffman, Inorg. Chim. Acta, 9_, 269 (1974). 3. E. Bayer and V. Schurig, Chem. Tech., 212 (1976). 4. K.J. Skinner, C.&En. News, Feb. 7, 18 (1977). 5(a) J . Manassen, P l a t . Met. Rev., 15_, 142 (1971), and references therein. (b) Ref. 2. (c) F.R. Hartley and P.N. Vezey, Adv. Organometal. Chem., Vol. 15, Academic Press, New York, 189 (1977). 6(a) H. Heineman, Chem. Tech., JL, 286 (1971). (b) C.U. Pittman, J r . , and G.O. Evans, Chem. Tech., 3, 560 (1973). 7(a) A. Agulio, Adv. Organometal. Chem., 5^, 321 (1967). (b) G. Szonyi, Adv. Chem. Series, J70, 53 (1968). (c) P.M. Henry, "Palladium Catalyzed Oxidation of Hydrocarbons," Reidel, Holland, 1980. 8(a) I. Wender and P. Pino, eds., "Organic Synthesis v i a Metal Carbonyls," Vol. 1, Interscience-Wiley, 1968. (b) C.K. Brown and G. Wilkinson, J . Chem. Soc. (A), 2753 (1970). (c) W. R u p i l i u s , J . J . McCoy and M. Orchin, Ind. Eng. Chem. (Prod. Res. Devel.), 10, 142 (1971). (d) G.F. Pregaglia, A. Andreeta and G.F. F e r r a r i , J . Organometal. Chem., 30, 387 (1971). (e) F.J. Smith, P l a t . Met. Rev., 19, 93 (1975). (f) R. Fowler, H. Connor and R.A. Basehl, Chem. Tech., 772 (1976). 9(a) A.D. Ketley, ed., "The Stereochemistry of Macromolecules," Vols. I - I I I , Arnold (London), Dekker (N.Y.), 1967. (b) J . Boor, J r . , Ind. Eng. Chem., (Prod. Res. Devel.), 9_, 437 (1970). -93-(c) W. Cooper, Ind. Eng. Chem., 9_, 457 (1970). (d) C A . Tolman, J . Amer. Chem. S o c , 92, 6777 (1970). 10(a) J.F. Roth, J.H. Craddock, A. Hershman and F.E. Poulik, Chem. Tech., 600 (1971). (b) D. Forster, J. Amer. Chem. S o c , 98, 864 (1976). (c) D. Brodzki, C. Leclere, B. Denise and G. Pannekier, B u l l . Soc. Chim. Fr., 61 (1976). 11. W.S. Knowles, M.J. Sabacky and B.D. Vineyard, Chem. Tech., 591 (1972), N.Y. Acad. S c i . , 214, 119 (1973). 12(a) F.N. Tebbe, 2nd Joint CIC/ACS conference, 1977, Inor 087. (b) J.M. Mariguez, D.R. McAlister, R.D. Sanner, and J.E. Bercaw, J. Amer. Chem. S o c , 98, 6733 (1976). 13. G. He n r i c i - O l i v e and S. Olive, Angew. Chem. Internat. Edn., 10, 105 (1971). 14. J . Halpern, Dis. Faraday S o c , 46, 7 (1968). 15. J . Halpern and B. R. James, Can. J . Chem., 44_, 671 (1966). 16. J. Chatt and B.L. Shaw, J. Chem. S o c , 5075 (1962). 17. P.S. Hallman, B.R. McGarvey and G. Wilkinson, J . Chem. Soc. (A), 3143 (1968). 18. R. Cramer, E. Jenner, R. Lindsay and U. Stolberg, J. Amer. Chem. Soc., 85, 1691 (1963) . 19. A.P. Khrushch, N.F. Shvetsova and A.E. Shilov, Kinet. Catal. (USSR), 10, 1011 (1969). 20. J . Kwiatek, I.L. Mador and J.K. Seyler, Adv. Chem. Series, 37, 201 (1963). 21. M.G. Burnett, P.J. Connolly and C.J. Kembell, J . Chem. Soc. (A), 800 (1967). -94-22. R.G.S. Banks and J.M. P r a t t , J . Chem. Soc. (A), 854 (1968) and references therein. 23. J. Kwiatek and J.K. Seyler, Adv. Chem. Series, 70, 207 (1968). 24(a) T. Funabiki, M. Mohri, and K. Tamara, J . Chem. S o c , Dalton Trans. 1813 (1973). (b) H.M. Feder and J . Halpern, J . Amer. Chem. S o c , 97, 7186 (1975). 25. L. Vaska and J.W. D i l u z i o , J. Amer. Chem. S o c , 83, 2784 (1961). 26. P.B. Chock and J . Halpern, J. Amer. Chem. S o c , 88, 3511 (1966). 27. L. Vaska, Accounts Chem. Res., JI, 335 (1968), and references therein. 28. J.F. Young, J.A. Osborn, F.H. Jardine and G. Wilkinson, J. Chem. S o c , Chem. Comm., 131 (1965). 29. J.A. Osborn, F.H. Jardine, J.F. Young and G. Wilkinson, J . Chem. Soc. (A), 1711 (1966). 30. C A . Tolman, P.Z. Meakin, D.L. Lindner and J.P. Jesson, J . Amer. Chem. S o c , 94, 2762 (1974). 31. J . Halpern, J. Mol. Catal . , 2, 65 (1976). 32. J . Halpern, J.F. Harrod and B.R. James, J . Amer. Chem. S o c , 83, 753 (1961). 33. J . Halpern, J.F. Harrod and B.R. James, J. Amer. Chem. S o c , 88, 5150 (1966). 34. D. Evans, J.A. Osborn, F.H. Jardine and G. Wilkinson, Nature, 208, 1203 (1965). 35. P.S. Hallman, B.R. McGarvey and G. Wilkinson, J. Chem. Soc. (A), 3143 (1968). 36. B.R. James, L.D. Markham and D.K.W. Wang, J. Chem. S o c , Chem. Commun., 439 (1974). -95-37. P.R. Hoffman and K.G. Caulton, J . Amer. Chem. S o c , 97_, 4221 (1975). 38. B.R. James, Adv. Organometallic Chem., 17_, 324 (1979). 39. D.K.W. Wang, 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 B r i t i s h Columbia, Vancouver, B.C. (1978). 40. G.W. P a r s h a l l , W.H. Knoth and R.A. Schunn, J . Amer. Chem. S o c , 91, 4990 (1969). 41. J . J . Levinson and S.D. Robinson, J . Chem. S o c , (A), 639 (1970). 42. J . T s u j i and H. Suzuki, Chem. L e t t . , 1083 (1977). 43. J . T s u j i and H. Suzuki, Chem. L e t t . , 1085 (1977). 44. J.F. Knifton, J . Org. Chem. 40, 519 (1975); 41, 1200 (1976). 45. J.F. Knifton, Tetrahedron L e t t . , 2163 (1975). 46. J.E. Lyons, J . Chem. S o c , Chem. Commun., 412 (1975). 47. P. Morand and M. Kayser, J. Chem. S o c , Chem. Commun., 314 (1976). 48. D. Rose, J.D. G i l b e r t , R.P. Richardson and G. Wilkinson, J. Chem. S o c , (A) 2610 (1969). 49. L. Vaska, " P r o c 1st Intern. Conf. Organomet. Chem.", Madison, 1965, p.79. 50. L. Vaska, "Proc 8th Intern. Conf. Co-ord. Chem.", V. Gutmann, Ed., Springer-Verlag, New York, 1964 p. 99. 51. R.A. Schunn, Inorg. Chem., 9_, 2567 (1970). 52. K.C. Dewhurst, U.S. Pat. 3,454,644 from Chem. Abstr., 71, 83317 (1969). 53. Ref. 57, r e f . 1424, p.94. 54. D. Fahey i n "Cat a l y s i s i n Organic Syntheses," P.N. Rylander and H. Greenfield, Eds., Acad. Press, 1976, p. 287. -96-55(a) B.C. Hui and B.R. James, Can. J . Chem., 48, 3613 (1970). (b) R.G.Bali, B.R.James, J . T r o t t e r , D.K.W.Wang and K.R.Dixon, J.Chem.Soc, Chem. Commun. ,460 (1979) 56. B.R. James, R.S. McMillan, R.H. Morris and D.K.W. Wang, Adv. Chem. Serie s , 167, 122 (1978). 57. B.R. James, "Homogeneous Hydrogenation," Wiley, New York (1973). 58. B.R. James, Inorg. Chim. Acta Rev., 4_, 73 (1970). 59. B.R. James, A.D. Rattray and D.K.W. Wang, J. Chem. S o c , Chem. Commun., 792 (1976). 60. B.R. James and D.K.W. Wang, J. Chem. S o c , Chem. Commun., 550 (1977); in "Homogeneous C a t a l y s i s " (M. Tsutsui and Y. I s h i i , eds.), p. 35 Plenum, New York, 1978. 61. Ref. 57, p. 106. 62. J.D. McClure, R. Owyang and L.M. Slaugh, J . Organometal. Chem., 12, 8 (1968). 63(a) D.E. Webster, Adv. Organometal. Chem., 15, 147 (1977). (b) A.E. Shilov and A.A. Shteinman, Coord. Chem. Rev., 24_, 97 (1977). (c) S. Siegel and D.W. Ohrt, J. Chem. S o c , Chem. Commun., 1529 (1971). 64. P.W. Armit, W.J. Sime and T.A. Stephenson, J . Chem. S o c , Dalton Trans., 2121 (1976). 65. B.R. James and G.L. Rempel, J. Chem. S o c , Discus. Farad. Soc. 46, 48 (1968). 66. J. Chatt and S.A. Butl e r , J . Chem. S o c , Chem. Commun., 501 (1967). 67(a) A.S.C. Chan, J . J . Pluth and J. Halpern, Inorg. Chim. Acta, _3_7 L477 (1979). (b) A.S.C. Chan and J . Halpern, J . Amer. Chem. S o c , 102, 838 (1980). 68. Ref. 57, P.84. -97-69. L.D. Markham, Ph.D. D i s s e r t a t i o n , U.B.C., Vancouver, B.C., 1973. 70(a) M. Orchin, Adv. C a t a l . , 16, 1 (1966). (b) R. Cramer, Acc. Chem. Res., 1_, 186 (1968). (c) A.J. Huber and H. Reimluger, Synthesis, 1970, 405. 71. B.A. Frenz and J.A. Ibers i n " T r a n s i t i o n Metal Hydrides," E.L. Muetterties, ed., Marcel Dekker, New York, 1971, p. 41-44. 72 B.M. Mattson, J.R. Heiman and L.H. Pignolet, Inorg. Chem., 15, 564 (1976). 73. A.C. Skapski and P.G.H. Troughton, J . Chem. Soc., Chem. Commun., 1230 (1968). 74. M.A. Bennett and D.L. Milner, J . Chem. S o c , Chem. Commun., 581 (1967); J . Amer. Chem. S o c , 91, 6983 (1969). 75. P.W. Armit, A.S.F. Boyd and T.A. Stephenson, J. Chem. S o c , Dalton Trans., 1663 (1975). 76. P.W. Armit, W.J. Sime, T.A. Stephenson and L. Scott, J. Organometal. Chem., 161, 391 (1978). 77. B.R. James, L.K. Thompson and D.K. Wang, Inorg. Chim. Acta, 29, L237 (1978). 78. H.O. Kaesz and R.B. S a i l l a n t , Chem. Reviews, 72.. 231 (1972). 79. R. Holmes, R.M. Deiters and J.A. Golen, Inorg. Chem., 81, 2612 (1969). 80. P. Meakin, E.L. Muetterties and J.P. Jesson, J . Amer. Chem. S o c , 94, 5271 (1972). 81. R. Po i l b l a n c and B. Chaudret, Proc. LXth Intern. Conf. Organometal. Chem., Dijon, 1979. Abstract B21. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0060494/manifest

Comment

Related Items