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

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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 o f 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 t h e Department of Chemistry We a c c e p t t h i s t h e s i s as conforming t o t h e required  standard  THE UNIVERSITY OF BRITISH COLUMBIA September, 1980 (c) I a n S t u a r t Thorburn 1980  In p r e s e n t i n g t h i s  thesis  in p a r t i a l  f u l f i l m e n t o f the requirements f o r  an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, the I  Library shall  f u r t h e r agree  for  freely available  that permission  for  r e f e r e n c e and  f o r e x t e n s i v e copying o f t h i s  that  study. thesis  s c h o l a r l y purposes may be granted by the Head of my Department or  by h i s of  make i t  I agree  this  representatives. thesis  It  is understood that copying or p u b l i c a t i o n  f o r f i n a n c i a l gain s h a l l  written permission.  Department of The U n i v e r s i t y o f B r i t i s h  2075 Wesbrook Place Vancouver, Canada V6T 1W5  Date  Columbia  not be allowed without my  -ii-  ABSTRACT The  t h e s i s d e s c r i b e s a study o f the c a t a l y t i c h y d r o g e n a t i o n  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) in  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  solution. 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  a t  a  2  c o n c e n t r a t i o n s showed t h a t Beer's law i s not obeyed, and  s e r i e s of  that i n s o l u t i o n  a dissociative equilibrium exists: (HRuCl(PPh ) ) 3  The  2  2  .,  - 2HRuCl(PPh )  K  3  (1)  2  complex i n N,N-dimethylacetamide s o l u t i o n was  e f f e c t i v e c a t a l y s t f o r the homogeneous h y d r o g e n a t i o n  found t o be  an  of h e x - l - e n e .  A  d e t a i l e d k i n e t i c study on t h i s system r e v e a l e d a mechanism i n v o l v i n g i n i t i a l f o r m a t i o n o f a o - a l k y l i n t e r m e d i a t e w h i c h then r e a c t s w i t h molec u l a r hydrogen t o produce the s a t u r a t e d product  HRuCl(PPh ) 3  2  + olefin  •«  k  RuCl(PPh ) (alkyl) + H 3  2  2  the  catalyst:  RuCl(PPh ) (alkyl)  (2)  *  (3)  3  k  and r e g e n e r a t e  2  2 HRuCl(PPh ) 3  2  + alkane  The mechanism i s q u i t e d i f f e r e n t from t h a t r e p o r t e d f o r the same c a t a l y s t system but u s i n g a c r y l a m i d e  as s u b s t r a t e , thereby  showing t h a t the  o f the s u b s t r a t e can have a pronounced a f f e c t on the course o f A d d i t i o n of t r i p h e n y l p h o s p h i n e  and l i t h i u m c h l o r i d e t o the  h e x - l - e n e system were found t o d e c r e a s e and respectively.  The  hydrogenation.  (HRuCl(PPh ) ) ~ 3  i n c r e a s e the r a t e of  added phosphine l i k e l y competes w i t h the  nature  2  2  hydrogenation,  olefinic  -iii-  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 ; t h e r o l e o f t h e c h l o r i d e i o n i s more u n c e r t a i n , b u t 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 t h e most o b v i o u s r a t i o n a l e . To enhance t h e s o l u b i l i t y o f t h i s h y d r i d o p h o s p h i n e 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 t h e t r i p h e n y l p h o s p h i n e 1 p r e p a r e d ; t h e v a r i a b l e temperature  31  H and  complex was  1  P{ H } - s o l u t i o n n.m.r. of t h e  ( H R u C l ( P ( p - t o l y l ) ^ ) ) 2 complex showed the presence o f b o t h monomer and 2  f l u x i o n a l dimer.  A d d i t i o n of d i m e t h y l maleate t o t h e complex i n o r d e r  to obtain a Ru-alkyl species  (equation  (2))  gave v e r y complex s p e c t r a  w h i c h c o u l d n o t be i n t e r p r e t e d i n terms o f a s i n g l e s p e c i e s , b u t t h e r e was some e v i d e n c e f o r a h y d r i d o ( o l e f i n ) s p e c i e s r a t h e r than an a l k y l . An x - r a y a n a l y s i s o f the p - t o l y l complex c o n f i r m e d the expected chloro-bridged species.  d i m e r i c s t r u c t u r e o f these  hydridochlorobis(phosphine)  There i s a square p y r a m i d a l c o o r d i n a t i o n geometry about each  ruthenium atom, and two such c e n t r e s  share a b a s a l edge, b u t the m o l e c u l e  has no symmetry as a r e s u l t o f t h e s m a l l h y d r i d e distortion.  ligands  allowing  -ivTABLE OF CONTENTS  Page Abstract  i i  Table o f c o n t e n t s  iv  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  viii  Abbreviations  x  Acknowledgements Chapter I .  x i  Introduction  1  1.1  General i n t r o d u c t i o n  1  1.2  Homogeneous h y d r o g e n a t i o n o f o l e f i n i c compounds  2  1.3  Homogeneous h y d r o g e n a t i o n u s i n g r u t h e n i u m complexes  1.4  Aim o f work  Chapter I I . 2.1  9 13  Experimental  15  Materials  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  Trichlorobis(triphenylphosphine)(DMA)ruthenium(III).DMA s o l v a t e 2.1.5.1.ii Trichlorobis(tri-p-tolylphosphine)(DMA)ruthenium(III).DMA s o l v a t e 2.1.5.2.i  Hydridochlorobis(triphenylphosphine)ruthenium(II)dimer  16 16 16  -v-  2.1.5.2.ii  Hydridochlorobis(tri-p-tolylphosphine)ruthenium(II)dimer  17  2.2  Instrumentation  17  2.3  S p e c t r o p h o t o m e t r y measurements  19  2.4  F a s t r e a c t i o n measurements  19  2.5  Gas-uptake a p p a r a t u s  19  2.5.1 2.6  P r o c e d u r e f o r a t y p i c a l gas-uptake experiment  Gas s o l u b i l i t y measurements  21 24  Chapter I I I . Homogeneous h y d r o g e n a t i o n o f h e x - l - e n e u s i n g hydridochlorobis(triphenylphosphine)r u t h e n i u m ( I I ) as c a t a l y s t  25  3.1  Introduction  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 3.3.2 3.3.3  Dependence of t h e r a t e on c a t a l y s t concentration  45  Dependence o f the r a t e on o l e f i n concentration  45  Dependence of t h e r a t e on hydrogen concentration  46  3.3.4.1 3.3.4.2  Dependence o f t h e r a t e on added triphenylphosphine concentration  48  A s p e c t r o p h o t o m e t r i c study o f t h e r e a c t i o n between HRuCl(PPh,)„ and pph ...  50  Dependence of the r a t e on added l i t h i u m chloride concentration  58  A s p e c t r o p h o t o m e t r i c study o f t h e r e a c t i o n between H R u C l ( P P h ) and L i C l  58  3  3.3.5.1 3.3.5.2  3  3.4  Discussion  2  61  -viPage Chapter IV.  S t r u c t u r a l s t u d i e s on  hydridochlorobis-  (tri-p-tolylphosphine)ruthenium(II)  68  4.1  X-ray s t r u c t u r e d e t e r m i n a t i o n  68  4.2 4.3  N.m.r. s p e c t r o s c o p y F o r m a t i o n of a m e t a l - a l k y l s p e c i e s  72 82  Chapter V. References  General conclusions f o r f u t u r e work  and  some recommendations 89 92  -viiLIST OF TABLES Table III-l  Page Spectrophotometric study of the e q u i l i b r i u m ( H R u C l ( P P h ) ) ^ = * nHRuCl(PPh ) i n DMA s o l u t i o n a t 25° ...  30  Spectrophotometric study of the e q u i l i b r i u m between H R u C l ( P P h 3 ) and h e x - l - e n e i n DMA s o l u t i o n a t 25°C  32  K i n e t i c data f o r the HRuCl(PPh3) catalysed h y d r o g e n a t i o n o f h e x - l - e n e i n DMA a t 30°C  38  Stopped-flow d a t a f o r DMA s o l u t i o n s o f HRuCl(PPh ) and P P h a t 30°C  52  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 a t 25 °C 7  60  3  III-2  2  n  2  III-3  III-4  2  3  III-5  2  3  -viii-  LIST OF FIGURES  2.1  Anaerobic  2.2  Constant p r e s s u r e  3.1  A p l o t 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 f u n c t i o n o f the c o n c e n t r a t i o n o f HRuCl(PPh,)_ a t 25°C i n DMA ...  3.2  spectral c e l l  20  gas-uptake apparatus  22  28  A p l o t of l n C e Q - E / e Q - e ^ . [ R u ] a g a i n s t ln(e-e /e„-e . [ R u l ) i n accordance w i t h T  00  equation 3.3  3.9  3.5  3.6  3.7  3.8  3.9  3.10  3.11  3.12  3.13  J-  31  V i s i b l e a b s o r p t i o n of DMA s o l u t i o n o f H R u C l ( P P h > upon a d d i t i o n o f hex-l-ene  33  Rate p l o t s f o r t h e HRuCl(PPh^)„ c a t a l y s e d hydrogenation o f hex-l-ene i n DMA a t 30°C  35  S o l u b i l i t y o f hydrogen i n DMA a t v a r i o u s p r e s s u r e s a t 30°C  37  Dependence of maximum r a t e o f hydrogenation on t o t a l ruthenium c o n c e n t r a t i o n i n DMA a t 30°C  39  Dependence o f maximum r a t e o f hydrogenation hex-l-ene c o n c e n t r a t i o n i n DMA a t 30°C  on 40  Dependence o f maximum r a t e o f hydrogenation hydrogen c o n c e n t r a t i o n i n DMA a t 30°C  on  3  3.4  00  \J  2  41  Dependence o f maximum r a t e of hydrogenation on added t r i p h e n y l p h o s p h i n e c o n c e n t r a t i o n i n DMA at 30°C  43  Dependence o f maximum r a t e o f 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 a t 30°C  44  Dependence o f maximum r a t e o f hydrogenation on o l e f i n c o n c e n t r a t i o n as p l o t t e d a c c o r d i n g t o e q u a t i o n (3.19)  47  Dependence o f maximum r a t e o f hydrogenation on hydrogen c o n c e n t r a t i o n as p l o t t e d a c c o r d i n g to e q u a t i o n (3.20)  49  Dependence [PPh ]  51  _ 1  3  o f maximum r a t e o f hydrogenation  on  -ixPage 3.14  P l o t o f lnCA^A^) v s time o f the s t o p p e d - f l o w d a t a f o r t h e r e a c t i o n between H R u C l ( P P h 3 ) and P P h  53  Dependence o f k b on t r i p h e n y l p h o s p h i n e c o n c e n t r a t i o n i n DMA a t 30°C  54  Dependence o f k b DMA a t 30°C  56  2  3.15 3.16 3.17 4.1  4.2 4.3  0  D  s  o  V i s i b l e a b s o r p t i o n o f DMA s o l u t i o n o f H R u C l ( P P h > upon a d d i t i o n o f l i t h i u m c h l o r i d e 3  59 3  2  2  69  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 complex, and s e l e c t e d bond a n g l e s and d i s t a n c e s  71  The v a r i a b l e temperature "'"H-n.m.r. s p e c t r a o f ( H R u C l ( P ( p - t o l y l ) ) ) i n toluene-dg  75,76  31 1 The v a r i a b l e temperature P{ H}-n.m.r. s p e c t r a o f (HRuCl(P(p-tolyl) ) ) i n toluene-d  77,78  The v a r i a b l e temperature "*"H-n.m.r. s p e c t r a o f a 1:1 m i x t u r e o f ( H R u C l ( P ( p - t o l y l ) ) ) and d i m e t h y l maleate i n t o l u e n e - d g  84  31 1 The v a r i a b l e temperature P{ H}-n.m.r. s p e c t r a o f a 1:1 m i x t u r e o f ( H R u C l ( P ( p - t o l y l ) ) ) and dimethyl maleate i n toluene-dg  85  2  2  2  2  2  g  3  4.6  2  X-ray c r y s t a l s t r u c t u r e o f t h e ( H R u C l ( P ( p - t o l y l ) ) ) complex  3  4.5  ruthenium concentration i n  n  s  3  4.4  3  2  2  3  2  2  -x-  ABBREVIATIONS The f o l l o w i n g l i s t o f a b b r e v i a t i o n s , most o f w h i c h a r e commonly adopted  i n c h e m i c a l l i t e r a t u r e , w i l l be employed i n t h i s  thesis.  A  absorbance  DMA  N,N-dimethylacetamide,CH CON(CH )  J  c o u p l i n g c o n s t a n t , Hz  In  natural logarithm  M  m o l a r o r m e t a l atom  n.m.r.  n u c l e a r magnetic  PPh  3  TMS  resonance 3  3  tri-p-tolylphosphine,(CgH^CH^P tetramethylsilane  e  molar e x t i n c t i o n  v  f r e q u e n c y , cm ^  T  c h e m i c a l s h i f t , ppm  31  1 P{ H}  [Ru],,,  2  triphenylphosphine,(C^H^) P  3  P(p-tolyl)  3  coefficient  p r o t o n broad-band decoupled concentration of t o t a l  31 P n.m.r.  ruthenium.  -xi-  ACKNOWLEDGEMENTS I w i s h t o thank P r o f e s s o r B.R. James f o r h i s e x p e r t guidance and c o n t i n u a l encouragement throughout t h e c o u r s e o f t h i s work. I would a l s o l i k e t o e x p r e s s my g r a t i t u d e t o D r s . 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 d e t e r m i n a t i o n which solved a number o f problems, and t o the members o f t h e group f o r making t h e past t h r e e y e a r s so e n j o y a b l e .  -1-  CHAPTER I INTRODUCTION  1.1  General Introduction The  f i r s t r e p o r t o f c a t a l y t i c homogeneous h y d r o g e n a t i o n o f an  o r g a n i c s u b s t r a t e appeared i n 1938"'", and i n v o l v e d t h e r e d u c t i o n o f benzoquinone by c u p r i c a c e t a t e s o l u t i o n s .  However, i t was n o t u n t i l t h e  e a r l y s i x t i e s t h a t 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 t o grow, and s i n c e then numerous systems have been s t u d i e d and t h e i r mechanisms deduced.  The i n t e r e s t i n t h e s u b j e c t has been  maintained,  s i n c e compared t o the p r e v a l e n t 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.  H i g h e r a c t i v i t y , so m i l 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.  H i g h e r 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 w h i c h may be s t u d i e d by s p e c t r o s c o p i c and k i n e t i c  techniques. 4. and  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 t h e l i g a n d s  conditions. The mechanisms o f h e t e r o g e n e o u s l y c a t a l y s e d r e a c t i o n s a r e n o t w e l l  u n d e r s t o o d , but w i t h t h e s t u d i e s o f homogeneous systems a n a l o g i e s between t h e  -2-  two can  be drawn, and u n d e r s t a n d i n g  of heterogeneous systems i n c r e a s e d .  More i m p o r t a n t i s t h a t w i t h f u r t h e r m e c h a n i s t i c s t u d i e s i t s h o u l d e v e n t u a l l y be p o s s i b l e to d e s i g n homogeneous c a t a l y s t s f o r s p e c i f i c reactions. The main d i s a d v a n t a g e  of homogeneous c a t a l y s i s i s the  difficulty  i n s e p a r a t i n g the r e a c t i o n p r o d u c t ( 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 t h e r e has been a r e c e n t development i n "supported or h e t e r o g e n i z e d homogeneous c a t a l y s i s " " * i n w h i c h the c a t a l y s t i s bonded t o an i n s o l u b l e polymer s u p p o r t .  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 a l u m i n a , and more commonly o r g a n i c polymers such as p o l y s t y r e n e 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- o r a m i n o - s u b s t i t u e n t s f o r b i n d i n g t o the a c t i v e metal centre.  These " s u p p o r t e d " c a t a l y s t s ^ appear t o 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 s e p a r a t i o n s i n c e they can be s i m p l y f i l t e r e d  out.  The main commercial p r o c e s s e s c u r r e n t l y u s i n g homogeneous c a t a l y s t s a r e : the Wacker p r o c e s s  7  , the Oxo  process  8  methanol c a r b o n y l a t i o n ^ , and asymmetric s y n t h e s i s of a m i n o - a c i d such as  1.2.  9  , some Z i e g l e r - N a t t a systems , drugs  l-dopa^.  Homogeneous H y d r o g e n a t i o n  of O l e f i n i c Compounds  For a t r a n s i t i o n m e t a l complex t o be a c t i v e f o r c a t a l y t i c o f u n s a t u r a t e d s u b s t r a t e s i t must be a b l e t o ; 1.  A c t i v a t e b o t h hydrogen and the s u b s t r a t e .  2.  T r a n s f e r hydrogen.  hydrogenation  -3-  3.  R e l e a s e the p r o d u c t , and  The  c o o r d i n a t i o n number and  r e g e n e r a t e the a c t i v e  species.  e l e c t r o n c o n f i g u r a t i o n of a m e t a l  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 . complex i s c o o r d i n a t i v e l y s a t u r a t e d  Complexes w i t h a d  the  t h e r e w i l l be no v a c a n t s i t e f o r  a c t i v a t i o n of hydrogen or o l e f i n u n l e s s 6  If  t h e r e are l a b i l e l i g a n d s  present.  8  to d  c o n f i g u r a t i o n are  u n s a t u r a t e d or can become so, and  frequently  the m a j o r i t y  coordinatively  of c a t a l y s t s do  have  this configuration. R e c e n t l y however complexes of T i Hf, Zr and 2 3 which have d or d c o n f i g u r a t i o n s were found to be c a t a l y t i c a l l y  Nb  5  L i g a n d s , 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 s t r e n g t h s ,  and  active  12  steric  13 effects  can  i n f l u e n c e the a c t i v i t y  catalyst  considerably.  Hydrogen a c t i v a t i o n depends on  and  specificity  of a h y d r o g e n a t i o n  the metal complex  i n v o l v e d , but i t  14 i s known to o c c u r i n at l e a s t t h r e e ways splitting,  (b) h o m o l y t i c s p l i t t i n g , or  namely  (a) o v e r a l l h e t e r o l y t i c  (c) d i h y d r i d e  number of metal complexes do a c t i v a t e hydrogen but catalytically or the M-H substrate  reducing  i s i n h i b i t e d , or the h y d r i d e  density  i s not  present  are not  s i n c e the l a t t e r has  bond formed i s so s t a b l e that h y d r i d e  a c t i v e species The  an o l e f i n  not  olefin  large  c a p a b l e of been a c t i v a t e d , activated  catalytically  concentrations.  i s by  of the o l e f i n w i t h a o-type a c c e p t o r  A  t r a n s f e r to the  i s l a b i l e so the  in significant  bonding between m e t a l and  formation.  overlap  orbital  of the  n-electron  of the m e t a l , accom-  panied by back d o n a t i o n from f i l l e d m e t a l d - o r b i t a l s t o empty  antibonding  o r b i t a l s of the o l e f i n .  the  bond c h a r a c t e r ,  and  T h i s a c t i v a t e s the o l e f i n by  places  i t i n close proximity  reducing  t o the h y d r i d e  double  ligand  so  -4-  t r a n s f e r i s n o t r e s t r i c t e d . The a b i l i t y o f an o l e f i n t o c o o r d i n a t e i s enhanced i f t h e m e t a l 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 t h e o l e f i n contains  e l e c t r o n w i t h d r a w i n g and s m a l l  The  substituents.  f o l l o w i n g examples show how o l e f i n i c s u b s t r a t e s may be h y d r o -  genated f o r each o f t h e modes o f hydrogen a c t i v a t i o n . (a)  Overall Heterolytic S p l i t t i n g  1 5  ML^ + H  This type o f s p l i t t i n g i s exemplified  RhCl^" + H  2  5 = ^ HRhCl^" + H  +  2  ML^H"+ H  by r e a c t i o n  +  + L  (l.l) ^, 1  (l.D  + Cl"  which i n v o l v e s s u b s t i t u t i o n o f a hydride f o r another l i g a n d without change i n t h e o x i d a t i o n s t a t e o f t h e m e t a l . 17 18 There a r e two p l a u s i b l e mechanisms splitting.  '  f o rexplaining heterolytic  The f i r s t i n v o l v e s o v e r l a p between a f i l l e d m e t a l 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.  T h i s can l o s e t h e p o s i t i v e l y p o l a r i z e d end o f t h e H  to a self-generated  o r added base t o g i v e t h e m e t a l X  M-Y + H  2  JTYL-YI  • M^ \H~  second p o s s i b i l i t y i s t h a t H  hydride:  base + Y~ (1.2)  2  c o u l d o x i d a t i v e l y add i n t o t h e c o -  i n t o t h e m e t a l h y d r i d e and t h e p r o t o n a t e d » M^-H  molecule  *>M-H + HY  o r d i n a t i o n s p h e r e o f an a n i o n - c o n t a i n i n g  M-Y + H»  +  <^  V  The  + H  2  complex w h i c h c a n b r e a k down anion:  • M-H + HY  (1.3)  -5-  S h i l o v and coworkers have shown"  t h a t a p l a t i n u m - t i n complex  1-7  ( P t * ) hydrogenates e t h y l e n e under ambient c o n d i t i o n s .  Once t h e h y d r i d e  i s formed t h e o l e f i n may i n s e r t i n t o t h e Pt*-H bond p r o d u c i n g 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 p r o t o n a t t h e carbon a t t a c h e d  to the  m e t a l ( p r o t o n o l y s i s ) r e l e a s e s t h e s a t u r a t e d p r o d u c t and r e g e n e r a t e s the c a t a l y s t ( 1 . 4 ) :  Pt* + C H 2  Pt*(C H )  A  2  Pt*(C H ) + H 2  4  2  ^  A  HPt*(C H ) + H 2  +  4  (1.4) HPt*(C H ) 2  ^=*=  4  Pt*(C H ) + H 2  (b)  Pt*(C H ) 2  5  Pt* + C H  +  5  2  Homolytic S p l i t t i n g  6  20 21 ' 2ML + H n  ^  2  "  2  M  L  n-l  H  +  2  L  I f a m e t a l 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 t h e c o o r d i n a t i o n number o f t h e m e t a l a r e i n c r e a s e d by one.  The  extent  t o which t h i s r e a c t i o n o c c u r s t h e r e f o r e depends on t h e s u s -  c e p t i b i l i t y o f t h e m e t a l t o o x i d a t i o n , and t h e a b i l i t y t o expand i t s coordination s h e l l .  An example o f such a p r o c e s s i s t h e r e v e r s i b l e 22  u p t a k e o f H_ by aqueous s o l u t i o n s o f 2  2[Co(CN) ] " + H 3  5  2  -  pentacyanocobaltate(II)  » 2[HCo(CN) ] " 3  5  (1.5)  For t h e m a j o r i t y o f o l e f i n s , r e d u c t i o n o c c u r s by f o r m a t i o n  o f an  -6-  a l k y l complex w h i c h r e a c t s w i t h a n o t h e r mole o f t h e h y d r i d e  complex  23  [(CN) C o - a l k y l ] ~ + [ H C o ( C N ) ] ~ — • 2 [ C o ( C N ) ] ~ + s a t u r a t e d product 3  3  3  5  5  24 Recent s t u d i e s genation  (1.6)  3have shown t h a t , f o r Co(CN),.  of p a r t i c u l a r s u b s t r a t e s ( S )  and Cc^(CO)g,hydro-  involves homolytic  s p l i t t i n g of  hydrogen f o l l o w e d by hydrogen atom t r a n s f e r s r a t h e r t h a n h y d r i d e t r a n s f e r s (1.7) :  HCo(CO) + S 4  •«  -Co(CO)  HCo(CO) + -SH — • 4  -Co(CO)  +  4  -SH  + SH  4  (1.7)  2  H 2-Co(CO).  • Co„(C0) 2 o  (c)  Dihydride *  — *  o  4  formation ' 2 5  2 6  2HCo(C0). 4  ML  n  + H. ^=*ML H„ Z n z  The f i n a l mode o f 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 t o t h e m e t a l , t h e r e b y 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.  Ir^KCO) (PPh ) 3  2  + H  2  An example  „  * H Ir  i : [  2  of t h i s i s shown i n ( 1 . 8 ) ,  Cl(C0) ( P P h ^  (1.8)  An o l e f i n may be reduced by two r o u t e s depending on when t h e d i h y d r i d e i s formed. I f t h e o l e f i n i s c o o r d i n a t e d the H  2  t h e n two c o n s e c u t i v e  a f t e r t h e o x i d a t i v e a d d i t i o n of  t r a n s f e r s of a hydrogen atom produces t h e  s a t u r a t e d p r o d u c t , and t h i s i s c a l l e d t h e " h y d r i d e "  r o u t e . The a l t e r n a t i v e  -7-  i s c a l l e d the " u n s a t u r a t e d "  r o u t e , and  proceeds v i a c o o r d i n a t i o n of  t h e o l e f i n f o l l o w e d by o x i d a t i v e a d d i t i o n o f H^. dihydride-substrate intermediate "unsaturated"  Even though the same  i s formed by e i t h e r mechanism the  r o u t e 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 m e t a l making o x i d a t i v e addition less l i k e l y .  Wilkinson's  28 c a t a l y s t RhClCPPh^)^ has been shown  t o hydrogenate o l e f i n s by b o t h r o u t e s , and pathways s i m i l a r t o t h o s e 29-31 shown i n Scheme 1-1  have been proposed  -8-  RhCl(PPh ) 3  3  Olefin  H RhCl(PPh ) 2  3  RhCl(PPh ) (Olefin) 3  3  I  -PPh H RhCl(PPh ) 2  3  3  -PPh.  RhCl(PPh ) (Olefin) 3  2  2  •HDlef H RhCl(PPh ) (01efin) 2  3  2  HRhCl(PPh ) (alkyl) 3  •(PPh ) 3  2  + (PPh ) 3  HRhCl(PPh ) (alkyl) 3  3  fast jaturated product + R h C l ( P P h ) 3  Scheme 1-1  3  -9-  1.3.  Homogeneous H y d r o g e n a t i o n u s i n g Ruthenium  Complexes  32 33 Halpern  and coworkers  '  showed t h a t 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 a t ^80°C f o r the hydrogenation  o f c e r t a i n s u b s t i t u t e d e t h y l e n e s c o n t a i n i n g an a c t i v a t e d  d o u b l e bond,such as m a l e i c , f u m a r i c , and a c r y l i c a c i d s . the f i r s t r e p o r t s o f a c t i v a t i o n o f m o l e c u l a r  T h i s was one of  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 I n 1965 W i l k i n s o n et a l r e p o r t e d  t h a t R u C l _ ( P P h . ) . and RuCl„(PPh_)_ 2 3 4 2 3 3  i n e t h a n o l - b e n z e n e s o l u t i o n r e a c t e d w i t h hydrogen t o g i v e HRuCl(PPh^)^•  In  benzene s o l u t i o n the two s t a r t i n g complexes a r e i n e q u i l i b r i u m by l o s s or g a i n of a phosphine l i g a n d , but w i l l not r e a d i l y r e a c t w i t h hydrogen ethanol i s present RuCl (PPh ) 2  3  3  s i n c e i t a c t s as a b a s e , p r o m o t i n g h y d r i d e + H  2  + base  HRuCl(PPh ) 3  3  + base  unless  formation: (1.9)  HC1  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  35  t o be  -10-  one  of  the  internal, Since  most cyclic  there  , . . . hydride  active  is  or  catalysts  substituted  for  reducing  olefins  are  no m e a s u r a b l e d i s s o c i a t i o n  , 36,37 complex  HRuCl(PPh > 3  the  +  3  terminal  „  *•  less  readily.  a phosphine  from  the  of  HRuCl(PPh > (olefin) + 3  3  (olefin)  2  RuCl (PPh ) 3  2  starting  . is:  PPh  2  PPh HRuCl ( P P h )  whilst  hydrogenated  , . ,,38 m e c h a n i s m now p r o p o s e d  olefin  olefins  (alkyl)  „  (l.iO)  3  3  *•  RuCl (PPh ) 3  3  (alkyl)  (1.11)  RuCl ( P P h ) 3  (alkyl)  3  + H  •  2  HRuCl(PPh ) 3  +  3  alkane  (1.12)  35 This  compares  occurred  to  prior  sociated  the  to  binding  complex,  to  its  possible  HRuCl(PPh ) 3  amide.  The  kinetics  reacted  with  a mole  to  a d  Ru(I)  7  regenerate  bond  in  the  the  where  olefin,  in  the  the o r t h o ligand to  system by  prepared  showed of  the  3  to is  that  loss  and was  This or  give also  absence of  in  the  of  a phosphine  thought  the  alkyl  hydride  species could of  the  greater hydride  capable hydrogen  reactions 39  separately  once  starting  catalyst  product  3  from Such  the  involvement  was  2  species.  HRuCl (PPh> ) olefins  of  mechanism  to  remain  ligand dis-  throughout.  Due  and  original  of  to  and used  the  trisphosphine  reduce  c o m p l e x was  formed  give  either  alkyl  the  saturated  oxidatively it  could  acrylit product  add  activate  s p e c i e s (see  stoichiometrically  with  the  to  interest and  of  hydrogen a  C-H  P.26).  hydrogenating  second hydrogen  atom  coming  37  p o s i t i o n of a phenyl r i n g of the t r i p h e n y l p h o s p h i n e ligand m e t a l h y d r o g e n t r a n s f e r was 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 ) 35 W i l k i n s o n et a l b a s e d on i s o t o p i c s t u d i e s , and l a t e r studied 3  3  -11-  by o t h e r w o r k e r s ^  0 , 4 1  .  P r o t o n n.m.r. s t u d i e s 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 w i t h deuterium  of  the mechanism suggested  the phosphine,  Scheme  and  showed o r t h o - d e u t e r a t i o n  f o r t h i s i s shown i n  1-3. H  -PPh (Ph P) Ru 3  3  _  (Ph P) Ru Cl H  3  CLH  3  2  (Ph,P>Ru—CL  - H  D  /  CL  . -f PPrv  2  j  PPh.  Ph P^£>  Ph P^o). 2  2  Scheme  1-3  For the h y d r o g e n a t i o n of o l e f i n s the r e a c t i o n b e g i n s w i t h f o r m a t i o n of 40 a trisphosphine alkyl metallated  complex  intermediate  [(PPh >ClRu(o-C^PPh^ ]  exchange w i t h the phosphine (1.12), and  and proceeds  3  2  ligand  t o g i v e the o r t h o -  and a l k a n e .  T h i s hydrogen  i s v e r y slow compared w i t h r e a c t i o n  so i n c a t a l y t i c h y d r o g e n a t i o n s  the l a t t e r p r o c e s s i s k i n e t i c a l l y  favoured. More r e c e n t l y systems i n v o l v i n g HRuCl(PPh^)^ have been used t o 42 s e l e c t i v e l y hydrogenate p o l y e n e s , and t o hydrogenate s a t u r a t e d aldehydes 43 44,45 to the a l c o h o l s , a l i p h a t i c and aromatic n i t r o compounds t o the amines 46 47 and c y c l i c c a r b o x y l i c a c i d a n h y d r i d e s t o Y - l a c t o n e s ' , although f o r c i n g  -12-  c o n d i t i o n s are often required. A s i m i l a r ruthenium(II)  complex i s HRu(OCOR)(PPh^)^, w h i c h  was  48 a l s o found by W i l k i n s o n and terminal o l e f i n s .  coworkers  t o e f f i c i e n t l y hydrogenate  V a r y i n g the c a r b o x y l a t e group from a c e t a t e t o benzoate  to s a l i c y l a t e hardly a l t e r e d  the r a t e of h y d r o g e n a t i o n ,  two o r t h r e e t i m e s more a c t i v e  than the p r o p i o n a t e  and  but they were trifluoroacetate.  The mechanism f o r h y d r o g e n a t i o n s i s thought t o be the same as f o r the c h l o r o analogue. A number of r u t h e n i u m c a r b o n y l complexes have been s t u d i e d potential catalysts.  The HRuCl(CO)(PPh^)^ complex i s c a p a b l e of  hydrogen-deuterium exchange and p a r t i a l l y r e d u c e s a c e t y l e n e and 49 50 under ambient c o n d i t i o n s  '  .  The  an e i g h t - c o o r d i n a t e r u t h e n i u m ( I V ) HRuCl (CO) ( P P h ) 3  as  3  exchange p r o c e s s was  ethylene  thought t o i n v o l v e  intermediate:  + D ^[HRuCl(CO)(PPh ) D ]^DRuCl(CO)(PPh ) 2  3  3  2  3  3  +  (1.13) but work by S c h u n n  5 1  has shown t h a t more H  2  and HD  i s produced than the  t h e o r e t i c a l v a l u e so o r t h o m e t a l l a t i o n i s once more proposed. T h i s complex 52 along with H Ru(C0)(PPh Me) 2  keto  2  3  appear i n a p a t e n t  f o r the r e d u c t i o n of  , f o r m y l , n i t r i l e , a l k e n e and a l k y n e g r o u p s , a l t h o u g h the  conditions 53  a r e 10-100 atm  o f hydrogen and  20°C t o 130°C. Rempel has  R u C l ( C 0 ) ( P P h > ( D M F ) t o be an e f f i c i e n t c a t a l y s t 2  3  2  found  f o r the h y d r o g e n a t i o n  o f 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 h y d r i d e had been formed by b o r o h y d r i d e 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 ( C 0 ) ( P P h ) was 2  2  3  2  f o u n d ~ ^ by Fahey t o be i n d u s t r i a l l y i m p o r t a n t , s i n c e i t c a t a l y s e s hydi genation  of 1 , 5 , 9 - c y c l o d o d e c a t r i e n e  t o c y c l o d o d e c e n e w i t h a 98-99%  HD  -13-  c o n v e r s i o n . S o l u t i o n s o f c h l o r o c a r b o n y l r u t h e n i u m ( I I ) complexes have been found"*"* t o c a t a l y t i c a l l y a c t i v a t e hydrogen i n t h e o r d e r Ru^^>Ru^ (CO)>Ru (CO)^, 1  11  w h i c h i s c o n s i s t e n t w i t h t h e s t r o n g i r - a c c e p t o r CO l i g a n d s d e c r e a s i n g e l e c t r o n d e n s i t y on the m e t a l , a t l e a s t i n terms o f a c t i v a t i n g hydrogen by  oxidative  addit ion. I n t e r e s t has r e c e n t l y grown i n asymmetric h y d r o g e n a t i o n , and a r e a number of ruthenium hydrogenate  there  complexes c o n t a i n i n g c h i r a l l i g a n d s w h i c h  can  p r o c h i r a l s u b s t r a t e s t o g i v e an excess of one enantiomer.  such complex i s R u C l [ ( - ) - d i o p ] 2  4  3 >  [(-)-diop =  One  (-2,3-0-isopropylidene-  2 , - 3 - d i h y d r o x y - l , 4 - b i s ( d i p h e n y l p h o s p h i n o ) b u t a n e ] w h i c h e f f e c t s the r e d u c t i o n of a , 6 - u n s a t u r a t e d  c a r b o x y l i c a c i d s w i t h up to 60% e n a n t i o m e r i c e x c e s s , the  a c t i v e c a t a l y s t being trans-HRuCl [ ( - J - d i o p ] ^ . There a r e two comprehensive r e v i e w s on homogeneous h y d r o g e n a t i o n ; the f i r s t c o v e r s t h e l i t e r a t u r e up t o 1972"^, w h i l s t t h e o t h e r c o v e r s 38 from 1972  t o 1978  .  Another  r e v i e w d e a l i n g w i t h c a t a l y s i s by  ruthenium  58 complexes 1.4.  has a l s o been p u b l i s h e d .  Aim of Work The main o b j e c t of the work f o r t h i s t h e s i s was  to c o n t i n u e  the  i n v e s t i g a t i o n o f 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 h y d r o g e n a t i o n study of the h y d r o g e n a t i o n  of u n s a t u r a t e d s u b s t r a t e s .  A detailed  kinetic  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 this laboratory  r e v e a l e d 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 I t was  of importance  t o determine whether such C-H  a c t i v a t i o n by Ru* s p e c i e s . a c t i v a t i o n would  i n l e s s r e a c t i v e s u b s t r a t e s . C h a p t e r I I I d e s c r i b e s a s t u d y of the c a t a l y s t w i t h hex-l-ene,which  was  occur  HRuCl(PPli^)^  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  -14-  e s s e n t i a l l y no a c t i v a t i n g o r d e a c t i v a t i n g groups. complex was c o n s i d e r e d  The HRuCl(PPh^)^  t o be a dimer i n t h e s o l i d s t a t e and i n n o n - p o l a r  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 s o l v a t e d  39 monomer seemed l i k e l y .  T h i s i n v e s t i g a t i o n o f t h e p h y s i c a l n a t u r e of  the c a t a l y s t was c o n t i n u e d but w i t h t h e 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.  S t u d i e s w i t h t h e b i s p h o s p h i n e system must a l s o a i d i n t h e u n d e r s t a n d i n g of t h e mechanism of h y d r o g e n a t i o n by t h e w i d e l y c a t a l y s t systems.  used R u C l ( P P h ^ ) ^ / H R u C l ( P P h ^ ) 2  -15-  CIIAPTER I I EXPERIMENTAL  2.1  Materials  2.1.1  S o l v e n t s - S p e c t r a l o r a n a l y t i c a l grade s o l v e n t s were o b t a i n e d  from MCB,  M a l l i n c k r o d t , Eastman, o r F i s h e r Chemical Co., and w i t h the  e x c e p t i o n of t o l u e n e and DMA  were used w i t h o u t 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 m e t a l w h i l s t DMA CaH  f o r 24h, and vacuum d i s t i l l e d a t 35-40°C.  2  was  s t i r r e d over  After d i s t i l l a t i o n  both  were kept under argon and over m o l e c u l a r s i e v e s (BDH,type 5 A ) , and the DMA  was  2.1.2  s t o r e d i n the d a r k .  Gases - Research grade hydrogen was o b t a i n e d from Matheson Gas  Co.,  and was passed through an E n g e l h a r d Deoxo c a t a l y t i c p u r i f i e r t o remove t r a c e s of oxygen. P u r i f i e d argon and n i t r o g e n were s u p p l i e d by L i q u i d A i r L t d . , and were used w i t h o u t f u r t h e r  2.1.3  Olefinic  purification.  S u b s t r a t e s - O l e f i n s were o b t a i n e d as C P .  Hex-l-ene was  Canadian  grade.  s u p p l i e d by ICN P h a r m a c e u t i c a l s I n c . , and d i m e t h y l  m a l e a t e by Eastman O r g a n i c C h e m i c a l s .  Both were passed t h r o u g h an alumina  column p r i o r t o use and i n a d d i t i o n the m a l e a t e 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 0.5 g of RuCl .3H 0 was dissolved i n 20 ml DMA 3  and s t i r r e d for 24h at  2  room temperature with 1.0 g of triphenylphosphine. f i l t e r e d , c a r e f u l l y washed with DMA  solvate  The green product  was  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);  n u j o 1 v  max  :  1630 cm"  1  (uncoordinated DMA);  1590 cm"  1  (coordinated  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 RuCl (PPh ) (DMA).(DMA) and 1 g of "proton 3  3  2  (l,8-bis(dimethylamino)-naphthalene)  sponge"  i n 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 s u s p e n s i o n  produced was  t o g i v e a d a r k red s o l u t i o n . gave a r e d powder w h i c h was  a t i o n was  concentrated induced  Slow p r e c i p i t a t i o n w i t h e t h a n o l and  f i l t e r e d , washed w i t h e t h a n o l and  and d r i e d i n vacuo o v e r n i g h t . powder was  f i l t e r e d under argon through c e l i t e  The  hexane,  f i l t r a t e l e f t a f t e r removing the red  by pumping o f f some benzene,and f u r t h e r p r e c i p i t -  by a d d i n g e t h a n o l and  cooling.  (Total yield-46%).  Found:C(65.9), H ( 4 . 8 3 ) ; C a l c . f o r [ R u C l P ^ ^ H ^ ]  2.1.5.2.ii  :C(65.3) , H ( 4 . 7 ) .  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  T h i s compound was  prepared i n a s i m i l a r manner to the  preceding  complex but u s i n g R u C l ^ ( P ( p - t o l y l ) ^ ) ( D M A ) . ( D M A ) as p r e c u r s o r 2  yield-45%).  cooling  (Total  Found :C(68. 6) , H ( 5 . 8 ) ; C a l c . f o r [ R u C l P ^ ^ H ^ ] :C(68.1) , 2  H ( 5 . 7 ) ; T^6°6. 2 . 8 ( R u - H ) . 2  2.2  Instrumentation I n f r a r e d s p e c t r a were r e c o r d e d  on a P e r k i n Elmer 457  grating  s p e c t r o p h o t o m e t e r as N u j o l m u l l s on C s l p l a t e s . V i s i b l e s p e c t r a were r e c o r d e d u s i n g an a n a e r o b i c  spectral c e l l  on a P e r k i n Elmer 202  ( F i g u r e 2.1)  spectrophotometer  w i t h a q u a r t z c e l l of 1  mm  path l e n g t h . ^"H nmr  s p e c t r a were r e c o r d e d  on a V a r i a n 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) MHz  u s i n g a XL 100  a t t a c h m e n t , and  as s t a n d a r d .  P nmr  were r e c o r d e d  at  40.5  s p e c t r o m e t e r equipped w i t h a v a r i a b l e temperature  operating  i n the F o u r i e r t r a n s f o r m mode.  The  standard  31 for  P nmr  was  triphenylphosphine  with chemical  s h i f t s being  converted  -18-  to v a l u e s r e l a t i v e t o 85% H PO^, and u p f i e l d 3  s h i f t s a r e taken as  E l e m e n t a l a n a l y s e s were performed by Mr. P. Borda o f t h i s  positive. department.  -19-  2.3  Spectrophotometric  Measurements  S i n c e the c a t a l y t i c s p e c i e s a r e e x t r e m e l y necessary  t o c a r r y out s p e c t r o p h o t o m e t r i c  a i r - s e n s i t i v e i t was  s t u d i e s under  c o n d i t i o n s by u s i n g the c e l l shown i n F i g u r e 2.1.  p i p e t t e d i n t o the f l a s k . The  employing a f r e e z e and w i t h argon.  The  In a t y p i c a l experiment  p l a c e d i n the c e l l w h i l s t 5 ml of s o l v e n t  a weighed amount o f complex was was  anaerobic  s o l v e n t was  degassed t h r e e times  thaw s t a t i c vacuum t e c h n i q u e , and  s o l i d and  homogeneous s o l u t i o n was  s o l v e n t were then mixed and  obtained.  The  c e l l was  by  then s a t u r a t e d  shaken u n t i l a  placed i n  athermostated  c e l l compartment t o a l l o w the s o l u t i o n temperature t o e q u i l i b r a t e , when t h i s was added and  the c e l l was  the s o l u t i o n . and  The  the s p e c t r a was  r u n . The  s u b s t r a t e c o u l d then be  once more a g i t a t e d t o g i v e the p h y s i c a l e q u i l i b r i u m  s o l u t i o n would then be a l l o w e d  the s p e c t r a run a g a i n , and  spectra  2.A  achieved  to thermally  equilibriati  the changes i n absorbance from the  F a s t R e a c t i o n Measurements stopped-  f l o w s p e c t r o p h o t o m e t e r equipped w i t h a 2 cm path l e n g t h c u v e t t e and thermostated  c e l l compartment.  s o l v e n t c o n t a i n i n g s u b s t r a t e and  a  For a t y p i c a l e x p e r i m e n t , a s o l u t i o n of  the complex i n a s o l v e n t s a t u r a t e d w i t h argon was  mixed w i t h the same  s a t u r a t e d w i t h argon.  Gas-Uptake Apparatus A constant  and  initial  recorded.  A l l f a s t r e a c t i o n s were s t u d i e d by means of a Durrum 110  2.5  and  pressure  i s shown i n F i g u r e  gas-uptake a p p a r a t u s was  2.2.  used i n k i n e t i c  studies  -20-  B7  QUARTZ  F i g u r e 2.1  CELL-  Anaerobic S p e c t r a l C e l l  SOCKET.  -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 d r o p p i n g s i d e - a r m bucket,was  attached to a f l e x i b l e glass s p i r a l tube, which  connected f l a s k A t o a c a p i l l a r y manometer (D) a t t a p C.  The  reaction  f l a s k was c l i p p e d t o a p i s t o n - r o d and w h e e l , w h i c h 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 t h a t the f l a s k c o u l d be w h i l s t h e l d i n the t h e r m o s t a t e d o i l b a t h ( B ) .  shaken  The o i l b a t h 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 C o r n i n g 5 5 0 ) ,  and was h e l d i n a p o l y s t y r e n e - f o a m l i n e d wooden box w i t h a p o l y s t y r e n e lid for insulation.  The c a p i l l a r y manometer c o n t a i n e d 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 p r e s s u r e ; and was  connected t o the gas  measuring  b u r e t t e w h i c h had a p r e c i s i o n bored tube (N) of known d i a m e t e r 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 t h e r m o s t a t e d a t 25°C i n a perspex w a t e r b a t h .  By means of  an Edwards h i g h vacuum n e e d l e v a l v e (M) the b u r e t t e was connected t o the g a s - h a n d l i n g p a r t of the a p p a r a t u s . manometer ( F ) , t h e gas i n l e t r o t a r y vacuum pump (G).  The l a t t e r c o n s i s t e d of a mercury  (Q), and c o n n e c t i o n s t o a Welch  Duo-Seal  The t h e r m o s t a t i n g of t h e two b a t h s was  by Jumo t h e r m o - r e g u l a t o r s and Merc-to-Merc  controlled  relay control c i r c u i t s , with  40 w a t t e l o n g a t e d l i g h t b u l b s used f o r h e a t i n g . T h i s , w i t h m e c h a n i c a l s t i r r i n g meant t h a t the temperature c o u l d be m a i n t a i n e d 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 c a t h e t o m e t e r , and time was r e c o r d e d from a Lab-Chron 2.5.1  1400  timer.  P r o c e d u r e f o r a T y p i c a l Gas-Uptake Experiment I n each e x p e r i m e n t , 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 t h e 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  F i g u r e 2.2  Constant P r e s s u r e Gas-Uptake Apparatus  -23-  weighed c a t a l y s t was reaction flask.  suspended on the hook of the s i d e arm of the  With the f l a s k connected  t o the s p i r a l arm,  i t was  a t t a c h e d t o the gas h a n d l i n g p a r t of the apparatus at j o i n t 0.  The  s u b s t r a t e s o l u t i o n was degassed by a f r e e z e and thaw s t a t i c vacuum t e c h n i q u e which was  c a r r i e d out t h r e e t i m e s .  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 t o a p r e s s u r e s l i g h t l y l e s s than t h a t r e q u i r e d , and t a p s C and P were c l o s e d . removed and connected  The  f l a s k and s p i r a l arm c o u l d then be  t o the c a p i l l a r y manometer a t H.  The  flask  was  p l a c e d i n the o i l b a t h , and a t t a c h e d t o the motor d r i v e n s h a k e r ( I ) which was  then s t a r t e d .  The whole system up t o tap C was  H, K, L, J and M open.  evacuated w i t h taps  A f t e r 10 m i n u t e s s h a k i n g t o a t t a i n  thermal  e q u i l i b r a t i o n o f the r e a c t i o n f l a s k and to s a t u r a t e the s o l u t i o n w i t h gas, the s h a k i n g was  s t o p p e d , and hydrogen was  a d m i t t e d t o the r e s t of  the a p p a r a t u s at p r e s s u r e s l i g h t l y l e s s than r e q u i r e d . and the p r e s s u r e of hydrogen i n c r e a s e d t o t h a t d e s i r e d .  Tap C was  opened  The n e e d l e v a l v e ,  and t a p s K and L were c l o s e d ; and the i n i t i a l r e a d i n g of the mercury l e v e l i n H taken. An e x p e r i m e n t a l run was  s t a r t e d by d r o p p i n g the c a t a l y s t  and s t a r t i n g the shaker and t i m e r .  The gas-uptake  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).  was  bucket,  i n d i c a t e d by  The manometer  the  was  b a l a n c e d by a l l o w i n g gas t o the b u r e t t e through the n e e d l e v a l v e and thereby m a i n t a i n i n g a c o n s t a n t p r e s s u r e i n the r e a c t i o n f l a s k .  The  c o r r e s p o n d i n g r i s e i n the mercury l e v e l i n N was measured at a p p r o p r i a t e i n t e r v a l s of t i m e .  S i n c e the diameter of the manometer (N) was  known,  the volume of gas consumed c o u l d be c a l c u l a t e d and expressed as moles of uptake per l i t r e o f s o l u t i o n .  -24-  The use of a s m a l l 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  of the r e a c t i o n s was 2.6  eliminated.  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  p r e s s u r e s was previously.  at s p e c i f i c t e m p e r a t u r e s  The DMA  c a p i l l a r y manometer.  was  degassed, but was  the p r e s s u r e  l e f t under vacuum when t a p s  the f l a s k w i t h s p i r a l arm  The  system was  immediately adjusted  the n e e d l e v a l v e c l o s e d , t h e  t r a n s f e r r e d to  then evacuated t o tap C and  w i t h hydrogen t o the a p p r o x i m a t e p r e s s u r e  L, and  and  d e t e r m i n e d u s i n g the gas-uptake a p p a r a t u s d i s c u s s e d  C and P were c l o s e d and  and  that d i f f u s i o n c o n t r o l  required.  Tap  to that r e q u i r e d .  t i m e r and  C was  the filled  opened,  With t a p s K  and  shaker c o u l d be s t a r t e d , and  the immediate uptake of gas c o u l d be measured.  -25-  CHAPTER I I I  HOMOGENEOUS HYDROGENATION OF HEX-1-ENE USING HYDRIDOCHLOROBIS (TRIPHENYLPHOSPHINE) RUTHENIUM(II) AS CATALYST  3.1  Introduction A key i n t e r m e d i a t e i n t h e c a t a l y t i c h y d r o g e n a t i o n  HRuCl(PPh ) 3  3  (see S e c t i o n 1.3) was b e l i e v e d t o be a  o f o l e f i n s by  hydrido-bisphosphine 59  species.  T h i s s p e c i e s was l a t e r i s o l a t e d d u r i n g a study  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 R u C l , j ( P P h ^ )  2  o f hydrogen  i n the presence of a  strong base: RuCl (PPh ) 3  3  2  + 1.5H  2  • HRuCl(PPh ) 3  To t e s t t h e v a l i d i t y o f H R u C l ( P P h ) 3  2  + 2 H + 2C1~ +  2  (3.1)  b e i n g an i n t e r m e d i a t e 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 t o hydrogenate acrylamide. There was found t o be a second-order dependence on [Ru]^,, an i n v e r s e dependence on a c r y l a m i d e and on added p r o p i o n a m i d e , and a f i r s t - t o z e r o - o r d e r dependence on H . 2  t h e f o l l o w i n g mechanism:  These d a t a were e x p l a i n e d by  -26HRuCl(PPh )„ + H C=CH-C-NH 5 = ^ j z I II ^ 0  (3.2)  RuCl(PPh ) ( C H - C - N H ) HC 3  0  [RuCl(PPh ) ] 3  2  2  + CH CH CNH 3  2  2  (3.  0 (3.4) where K i s the e q u i l i b r i u m c o n s t a n t f o r a l k y l complex f o r m a t i o n , k ^, and  k  are i n d i v i d u a l r a t e  2  Whilst  formation  k^,  constants.  of an a l k y l complex by e q u a t i o n (3.2)  u n u s u a l , the n e x t s t e p  and  (equation  3.3)  i s not  i n v o l v i n g r e a c t i o n of t h e  alkyl  complex w i t h a n o t h e r mole of h y d r i d e complex i s q u i t e n o v e l and i n t e r e s t i n g . A r e a c t i o n such as 3_ Co(CN),. , and  (3.3)  is established^  2  the d , l i k e l y d i m e r i c 7  2  (equation  f o r hydrogenations catalysed  i s thought t o o c c u r a l s o i n the h y d r o d i m e r i z a t i o n 62  n i t r i l e c a t a l y s e d by R u C l ( P P h ) .  H  1  3.4)  3  Ru(I),species  Once the s a t u r a t e d may  step).  63  of a c r y l o -  product i s r e l e a s e d ,  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  t o r e g e n e r a t e the c a t a l y s t , or a c t i v a t e a C-H  reduced o l e f i n (the k_^  pounds i s known  3  by  A c t i v a t i o n of C-H  bond i n the  bonds i n a l i p h a t i c  com-  8 for single d  m e t a l c e n t r e s , but not by a  two-site  p r o c e s s , w h i c h i s i n t e r e s t i n g because of the analogy t o heterogeneous a c t i v a t i o n of  alkanes.  To d e t e r m i n e i f t h i s mechanism a p p l i e d t o o t h e r , 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 h y d r o g e n a t i o n of h e x - l - e n e by DMA HRuCl(PPh ) 3  2  was  i n v e s t i g a t e d , and  s o l u t i o n s of  the k i n e t i c s and mechanism a r e p r e s e n t e d  here. 3.2 C a t a l y t i c H y d r o g e n a t i o n of Hex-l-ene The v i s i b l e spectrum of HRuCl(PPh„)„ i n DMA  under argon was  recorded  -27-  a t 25°C, and shows an a b s o r p t i o n maximum a t 500 nm.  S p e c t r a were run  a t a s e r i e s of c o n c e n t r a t i o n s ( F i g u r e 3.1) and the molar  extinction  c o e f f i c i e n t was not c o n s t a n t , thus Beer's law i s not obeyed as p r e v i o u s l y 39 reported.  C o n s i d e r i n g t h a t t h e complex i s d i m e r i c i n the s o l i d  state  (Chapter IV) t h e o b v i o u s r e a s o n f o r the non-Beer's law b e h a v i o u r 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  t h a t the r e a c t i o n i s : K  (HRuCl(PPh ) ) 3  2  n  l  ^  *•  nHRuCl(PPh ) 3  (3.5)  2  i t can be shown t h a t :  [ (HRuCl(PPh,) ) ] j z n  =  [HRuCl (PPh,) J 3 2  =  0  and  - • — n e —e  e  —  o  [ R u ]  -e0 0  l R u ]  T  (3.6)  T  (3.7)  where [ R u ] ^ i s the c o n c e n t r a t i o n of t o t a l r u t h e n i u m p r e s e n t , E and e  00  q  i s t h e molar e x t i n c t i o n c o e f f i c i e n t of H R u C l ( P P h ) , 3  i s the r u t h e n i u m 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 2 n  [HRuCl(PPh ) J 3  Therefore  K  ±  V  n  2  = [HRuCl (PPh„) „) J 5 Z n  £  "  J  e  [iuL,  =  1 n  e  o -e o  0  ( 3  T  *  8 )  -28-  0  [Ru] „ , i Figure 3 . 1 e  n  r  p  6-0  4-0  2-0  8-0  x10 , M 3  T  A Plot of molar extinction c o e f f i c i e n t as a function of ^ p l o t ^ o f ^ ^ ^ ^ o DMA. a  t  2  5  c  i  n  -29-  which y i e l d s : /e -e \ o  / E - E ^ [Ru]\  [Ru]\  y  °°  \o°°  A p l o t of l n ( E - E / E -e  /  .[Ru]_) a g a i n s t l n ( E - e  / E -e  .[Ru]_) u s i n g  the s p e c t r o s c o p i c d a t a g i v e n i n T a b l e I I I - l s h o u l d g i v e a l i n e o f n and  i n t e r c e p t I n n - l n K^.  to o b t a i n t h i s i t was 1300 M ^cm  ^ to E  q  Such a p l o t i s shown i n F i g u r e 3.2,  necessary  t o a s s i g n v a l u e s of 620 M ^cm  slope but  ^ and  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 e x p e r i m e n t a l l y  (see F i g u r e 3.1).  The -3  s t r a i g h t l i n e drawn has a s l o p e of 2.0 hence the complex i s p r e d o m i n a n t l y used m a i n l y  and g i v e s a  v a l u e of 1.66  x 10  monomeric over the c o n c e n t r a t i o n range  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 o f the complex ( [ R u ] ^ = 7.5 x 10 q u a n t i t y o f h e x - l - e n e was approximately  500s.  The  added d i r e c t l y , and l e f t t o e q u i l i b r a t e f o r spectrum was  u n t i l a d d i t i o n of an e x c e s s (0.17 M) of a species considered  M), a measured  recorded  and  the p r o c e s s  of o l e f i n gave the l i m i t i n g  t o be R u C l ( P P h ^ ) ^ ( a l k y l ) ( s e e b e l o w ) .  s o l u t i o n changed c o l o u r from b r i g h t r e d to c r i m s o n , w i t h the depending on the h e x - l - e n e c o n c e n t r a t i o n .  The  i n T a b l e I I I - 2 and a r e shown i n F i g u r e 3.3, allow for d i l u t i o n .  equilibria:  spectrum  The r e a c t i n g intensity  s p e c t r a l changes a r e  given  and have been c o r r e c t e d t o  At lower o l e f i n c o n c e n t r a t i o n s t h e r e appears t o be  two i s o s b e s t i c p o i n t s ; however,these a r e l o s t a t h i g h e r These r e s u l t s may  repeated  be e x p l a i n e d  qualitatively  concentrations.  i n terms of two  consecutive  M;  -30-  TABLE I I I - l S p e c t r o p h o t o m e t r i c study o f t h e e q u i l i b r i u m (HRuCl(PPh ) ) 3  [Ru]  a " l "I M cm  (xl0 )M  nHRuCl(PPh ) 3  n  e  T  M  3  2  o  -E  .E-e 00  InA-e X  2  i n DMA s o l u t i o n a t 25°C.  . [Rul \  CO  T  '  e-e  Y-E  oo  e— E o  00  •  E  U X  [ R U ]  -e O  J 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  0.88  -5.10  0.12  -7.10  e =1300 CO  a.  Calculated  from absorbance a t 500 nm.  T^  -31-  80  F i g u r e 3.2  A p l o t of l n ( E - E / E ^ E ^ - [RU] > against t  ln(E-e /  e  _  E  - [ R u ] ) i s accordance w i t h e q u a t i o n 3.9. T  -32-  TABLE I I I - 2 S p e c t r o p h o t o m e t r i c study of t h e 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 a t 25°C.  A (500 nm)  [ h e x - l - e n e ] x l O ,M  A -A o  A-A  0.938  0  0  0.385  0.900  0.319  0.040  0.345  0.856  0.737  0.085  0.300  0.814  1.106  0.129  0.256  0.764  1.630  0.181  0.204  0.746  2.102  0.200  0.185  0.385  17.000  0.385  0  a  1mm c e l l  path  -33-  500 Wavelength V i s i b l e a b s o r p t i o n of DMA  6  0  0  nm s o l u t i o n of HRuCl ( P P h ^  upon  a d d i t i o n of hex-l-ene. (AW 5 x 10~ M H R u C l ( P P h ) and ( B ) , ( C ) , (D), ( E ) , IF;, and (G) a r e upon t h e a d d i t i o n of 0.319, 0.737, 1.106, 1.630, 2.102, and 17 x 10" M h e x - l - e n e . 3  3  2  Z  -34-  (HRuCl(PPh ) ) 3  2  ,  2  »  1  2HRuCl(PPh ) 3  (3.10)  2  2 - CH-(CH ) -CH ^ = s = t K  HRuCl(PPh ) 3  + CH  2  2  2  3  3  RuCl(PPh ) ((CH ) CH ) 3  2  2  5  (3.11)  3  -3 t o e q u a l 1.66 x 10 M ( e q u a t i o n 3.9) t h e c o n c e n t r a t i o n s of  Taking  -3 dimer and  and monomer i n the absence  2.11 x 10 M r e s p e c t i v e l y , a n d _3  substrate.  I f t h e o l e f i n b i n d s t o b o t h the monomer and  t h e r e w i l l be t h r e e s e p a r a t e e q u i l i b r i a among f o u r s p e c i e s which again lead  t o 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 h y d r o g e n a t i o n o f hex-l-ene was s t u d i e d by measuring t h e r a t e s o f hydrogen  uptake by DMA s o l u t i o n s o f H R u C l ( P P h ) 3  c o n s t a n t p r e s s u r e gas-uptake  2  u s i n g the  apparatus d e s c r i b e d i n S e c t i o n 2.3.1.  c a t a l y s t was found t o be e f f i c i e n t  The  under m i l d c o n d i t i o n s , and t h e t y p i c a l  S-shaped uptake p l o t s observed a r e shown i n F i g u r e 3.4; t h e measured maximum h y d r o g e n a t i o n r a t e s were u s u a l l y a t t a i n e d a f t e r a p p r o x i m a t e l y 500s.  The t o t a l hydrogen  uptake corresponded  to v i r t u a l l y  r e d u c t i o n o f the h e x - l - e n e , and t h e s o l u t i o n r e t a i n e d throughout  3  2  complex.  I n the absence  complete  i t s homogeneity  the r e a c t i o n with the f i n a l bright red s o l u t i o n  the i n i t i a l H R u C l ( P P h >  containing  of s u b s t r a t e no uptake  was o b s e r v e d , but i n t h e presence of argon i n s t e a d of hydrogen was found t o c a t a l y t i c a l l y after stirring  M  s p e c i e s i s generated and t h e r e  t h r e e a b s o r b i n g s p e c i e s i n s o l u t i o n , and c o n s e q u e n t l y t h e r e  a r e no i s o s b e s t i c p o i n t s .  will  t o be 2.70 x 1 0  t h i s w i l l be e s t a b l i s h e d p r i o r t o adding t h e  Upon a d d i t i o n o f o l e f i n t h e a l k y l  are a t l e a s t  dimer  of o l e f i n are c a l c u l a t e d  the complex  i s o m e r i s e the o l e f i n t o 85% o f t h e 2-isomer  f o r one hour at 25 C. e  The maximum r a t e of h y d r o g e n a t i o n  F i g u r e 3.A  Rate p l o t s f o r the H R u C l ( P P h ) ~ c a t a l y s e d o f h e x - l - e n e i n DMA at 30°C. 3  2  hydrogenation  -36-  of hex-2-ene was  found t o be a p p r o x i m a t e l y  o n e - f i f t h of t h a t found f o r  h e x - l - e n e , and so j u d g i n g by t h e u p t a k e p l o t s ( F i g u r e 3.4)  the r a t e of  i s o m e r i s a t i o n i n the p r e s e n c e of hydrogen appears t o be n e g l i g i b l e . The  " s t a n d a r d " c o n d i t i o n s employed were a t o t a l r u t h e n i u m con-  c e n t r a t i o n of 2 x 10 M w i t h 2 x 10 S i h e x - l - e n e 3  under an atmosphere of  hydrogen a t 30°C, a l t h o u g h the c o n c e n t r a t i o n s of a l l the r e a c t a n t s were varied considerably.  The  mined ( F i g u r e 3.5), and atmosphere p r e s s u r e .  s o l u b i l i t y of hydrogen i n DMA  found t o obey Henry's Law  a t 30°C was  a t l e a s t up to  The dependence of the maximum r a t e on  deter-  one  catalyst  c o n c e n t r a t i o n , hydrogen p r e s s u r e a t 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 t r i p h e n y l p h o s p h i n e , 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  due t o i t s i n s o l u b i l i t y i n  DMA.  The p l o t o f the r a t e of h y d r o g e n a t i o n  of hex-l-ene  r u t h e n i u m c o n c e n t r a t i o n can be seen i n F i g u r e 3.6. to  not i n v e s t i g a t e d  a g a i n s t the  total  The r a t e a p p r o x i m a t e s  f i r s t - o r d e r , but i s p r o b a b l y more a c c u r a t e l y d e s c r i b e d as b e i n g  first  o r d e r a t lower c o n c e n t r a t i o n s and becoming l e s s than f i r s t - o r d e r a t h i g h e r concentrations. The dependence on h e x - l - e n e o r d e r up to a p p r o x i m a t e l y >_ 1.0  c o n c e n t r a t i o n ( F i g u r e 3.7)  2 x 10 " S i , and  then d e c r e a s e s  is first-  to zero-order  at  M. The a f f e c t of v a r y i n g the hydrogen p r e s s u r e on the maximum r a t e  ( F i g u r e 3.8)  shows t h a t f i r s t - o r d e r k i n e t i c s a r e e x h i b i t e d a t  lower  p r e s s u r e s f o r b o t h 2 x 10 H i and 7 x 10 S i h e x - l - e n e , but t h e dependence begins  to decrease at approximately  100 and 400 m m , r e s p e c t i v e l y .  The  -37-  mm  760 570 380 190  [H ] x 10" 0  1.76 1.32 0.88 0.43  M  -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 ) ^ c a t a l y s e d 3  h y d r o g e n a t i o n o f h e x - l - e n e i n DMA a t 30°C [  R u  ]  P  a  [H ]  R  2  2  o  xl0 ,M  mm  xlO M  0.05 1.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 3.00 4.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00  760 760 760 760 760 760 760 760 760 760 760 570 380 200 100 760 570 380 200 100 760 760 760 760 760 760 760 760  1.76 1.76 1.76 1.76 1.76 1.76 1.76 1.76 1.76 1.76 1.76 1.32 0.88 0.46 0.23 1.76 1.32 0.88 0.46 0.23 1.76 1.76 1.76 1.76 1.76 1.76 1.76 1.76  3  a b  [hex-l-ene] xlO.M  Max. Rate 5 - 1 x l O ,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 0.96 0.63 0.33 11.90 14.80S 20.60 24.86  2.00 2.00 0.09 2.00 4.65 5.93 8.24 10.56 15.17 2.00 2.00 2.00 2.00 2.00 2.00 7.00 7.00 7.00 7.00 7.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00  b  c  d  e  f  h  1  F x n r e s s e d as monomer 9 . , 1 0 5 c 3.9 M, d 6.8 M, and e 10.0 M [ P P h ] x l 0 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 added r e s p e c t i v e l y . 2  3  2  f  -39-  12 0  [Ru] F i g u r e 3.6  X10 , M 3  Dependence of maximum r a t e of h y d r o g e n a t i o n ruthenium c o n c e n t r a t i o n i n DMA at 30°C.  on  -40-  16 0  4-0  8-0  12-0  16-0  [Olefin] x10, M F i g u r e 3.7  Dependence of maximum r a t e of h y d r o g e n a t i o n on hex-l-ene c o n c e n t r a t i o n i n DMA at 3 0 ° C .  F i g u r e 3.8  Dependence of maximum r a t e o f h y d r o g e n a t i o n on hydrogen c o 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 t o z e r o - o r d e r  i s more n o t i c e a b l e a t t h e lower  olefin  concentration. P l o t s o f maximum r a t e v e r s u s  t h e c o n c e n t r a t i o n o f added  tri-  p h e n y l p h o s p h i n e ( F i g u r e 3.9), and l i t h i u m c h l o r i d e ( F i g u r e 3.10) a r e c u r v e d and t e n d t o show a s a t u r a t i o n e f f e c t a t t h e h i g h e r  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 t h e r a t e i n c r e a s e d with increasing [LiCl]. 3.3  A n a l y s i s o f K i n e t i c Data To e x p l a i n t h e n e a r f i r s t - o r d e r dependence on [Ru] » t h e f i r s t T  to  z e r o - o r d e r dependence on h e x - l - e n e ,  the predominantly  first-order  dependence on hydrogen a t h i g h s u b s t r a t e c o n c e n t r a t i o n , and t h e f i r s t to z e r o - o r d e r dependence a t lower s u b s t r a t e c o n c e n t r a t i o n , t h e f o l l o w i n g mechanism i s proposed:  k  HRuCl(PPh ) 3  2  + olefin  „  l "  fc  RuCl(PPh^(alkyl)  (3.12)  k RuCl(PPh ) (alkyl) + H 3  2  where k^, k_^, and k  2  • HRuCl(PPh )  f 2  3  Rate  =  "  d [ H  dt  2  + alkane  (3.13)  are the r a t e constants f o r the i n d i v i d u a l  A p p l y i n g a s t e a d y - s t a t e treatment gives the r a t e  2  to the intermediate  steps.  RuCl(PPh ) (alkyl) 3  2  equation:  ]  =  k ^ f R u ^ t o l e f in] [H J 2  [H ]+k [ o l e f i n ] 2  1  (3.14)  -43-  -44-  i  1  4  0  80  12 0  [LiCD x 1 0 2 , M F i g u r e 3.10  Dependence o f maximum r a t e o f h y d r o g e n a t i o n 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 a t 30°C.  -45-  Th e i n i t i a l  induction period prior to attaining the maximum rate  i s probably due to the d i s s o l u t i o n of the complex, and a b u i l d up of the steady-state concentration of the a l k y l . 3.3.1  Dependence of the Rate on Catalyst Concentration (Figure  3.6)  The rate equation (3.14) reduces to: Rate = k'[Ru]  (3.15)  T  where k ^ [ o l e f i n ] [H ] 2  (3.16)  k ^ + k j [H ]+k [olefin] 2  1  and therefore s a t i s f i e s the e s s e n t i a l l y f i r s t - o r d e r Ru dependence shown -3 i n Figure 3.6. For a t o t a l 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  (Figure 3.6)  M.  The f a l l o f f i n Ru dependence at higher concentration  i s presumably due to the presence of small amounts of  inactive dimer. 3.3.2  Dependence of the Rate on O l e f i n Concentration  (Figure  3.7)  At lower o l e f i n concentrations the k ^ f o l e f i n ] term i n the denominator of  the rate equation (3.14) can presumably become small compared to  (k ^ + k [ H ] ) , and the rate equation reduces to one showing a 2  2  order dependence on o l e f i n :  first-  -46-  k,k [Ru] [olefin][H ] o  1  Rate  T  2  0  (3.17)  T  k_ +k [H ] 1  2  2  However,at higher o l e f i n concentrations (>1 M),the k ^ [ o l e f i n ] term must dominate and equation (3.14) becomes: Rate = k [Ru] [H ] 2  T  (3.18)  2  which i s independent of o l e f i n concentration.  The rate equation (3.14)  can be rearranged to give:  1 Rate  k =  _l 2^ 2'' + k  H  k k [Ru] [H J 1  2  T  2  1 ' [olefin]  1  +  k^TRul^THp"  A plot of 1/Rate versus 1/[olefin] at constant  ( 3  [Ru]^ and  [H,,]  '  1 9 )  should  therefore y i e l d a straight l i n e ; the intercept of which can be used to calculate k -  Such a plot (Figure 3.11)  2  l i n e with a k 3.3.3  2  value of 78 M  gives a reasonable straight  ^ from the intercept.  Dependence of the Rate on Hydrogen Concentration  (Figure  3.8)  Considering the low o l e f i n concentration case where equation  (3.17)  applies, the dependence on hydrogen should go from f i r s t - towards zeroorder as the [H ] 2  increases,as seen experimentally (Figure 3.8).  When the o l e f i n concentration i s high(>1 M) , the rate equation i s (3.18), and so the rate should be s t r i c t l y f i r s t - o r d e r the whole range of hydrogen concentrations.  throughout  Unfortunately the o l e f i n  concentration chosen (0.7 M) was not s u f f i c i e n t l y high, but nevertheless the data c l e a r l y show the tendency toward f i r s t - o r d e r behaviour higher o l e f i n concentration.  at the  -47-  -48-  The d a t a can be a n a l y s e d q u a n t i t a t i v e l y by r e a r r a n g i n g e q u a t i o n (3.14) t o g i v e : k^+kj [olefin]  1  Rati""  m  k k [Ru] [olefin] 1  2  At constant  T  1  x  [H ]  k [Ru] [olefin]  +  2  1  ( 3 , 2 0 )  T  [ R u ] ^ and [ o l e f i n ] , a p l o t o f 1/Rate a g a i n s t 1 / [ H ] a t b o t h 2  o l e f i n c o n c e n t r a t i o n s y i e l d s s t r a i g h t l i n e s ( F i g u r e 3.12); t h e i n t e r c e p t s o f w h i c h can be used t o d e t e r m i n e k^ v a l u e s o f 0.28 and 0.29 M ^s \ the v a l u e of k  i s known ( S e c t i o n 3.3.2), t h i s w i t h t h e k^ v a l u e can be  2  used t o d e r i v e t h e v a l u e o f k ^ from equations  Since  t h e s l o p e s of t h e l i n e s from  (3.19) and ( 3 . 2 0 ) , and hence the v a l u e of k^/k_^.  F o r an  o l e f i n c o n c e n t r a t i o n o f 0.2 M t h e average v a l u e of k ^ i s c a l c u l a t e d t o be 1.4 x 1 0 ~ s ~ 2  which y i e l d s a value of k /k_  1  the l a t t e r i s 12 M for  -1  o f 20 M**, w h i l s t f o r 0.7 1  x  from an average v a l u e of 2.3 x 10  -2 -1 s calculated  k_^.  3.3.4.1 Dependence o f t h e Rate on Added T r i p h e n y l p h o s p h i n e (Figure  Concentration  3.9)  For hydrogenation  r e a c t i o n s under c o n s t a n t  [ R u ] , [H,,], and T  [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 t r i p h e n y l p h o s p h i n e t o t h e dimer i s known t h e monomeric H R u C l ( P P h ^ ) ^ complex. w i t h i n c r e a s i n g added P P h  3  to give a s o l u t i o n containing  The c o l o u r o f the s o l u t i o n  from t h e r e d of t h e  changes  [HRuCl(PPh^) ] , 2  2  HRuCl (PPh3)22-DMA m i x t u r e t o t h e p u r p l e c o l o u r o f t h e t r i s ( t r i p h e n y l phosphine) s p e c i e s : K Js[HRuCl(PPh ) ] -  1  3  2  2  K' " HRuCl(PPh ) 3  2  ^_  fc p p h  HRuCl(PPh ) 3  3  (3.21)  M  Figure  3.12  Dependence of maximum r a t e of h y d r o g e n a t i o n hydrogen c o n c e n t r a t i o n as p l o t t e d a c c o r d i n g e q u a t i o n (3.20).  on to  -50The v a l u e o f K' i s thought  36  25°C and hence t h e phosphine  5 t o be v e r y l a r g e (>10 ) i n benzene a t competes w i t h t h e o l e f i n f o r a c o o r d i n a -  t i o n s i t e a t t h e m e t a l c e n t r e . The t r i s p h o s p h i n e s p e c i e s i s b e l i e v e d t o be c a t a l y t i c a l l y i n a c t i v e f o r h y d r o g e n a t i o n u n t i l i t d i s s o c i a t e s a phosphine dependence,  3.3.4.2.  l i g a n d ( S e c t i o n 1.3), hence t h e observed i n v e r s e ( F i g u r e 3.13).  A S p e c t r o p h o t o m e t r i c Study o f t h e R e a c t i o n between HRuCl(PPh ) 0  0  and PPh„  The r e a c t i o n between t h e b i s p h o s p h i n e complex and t r i p h e n y l phosphine was found t o occur w i t h a 1:1 s t o i c h i o m e t r y , b u t i s t o o f a s t t o be s t u d i e d u s i n g t h e c o n v e n t i o n a l v i s i b l e  spectrophotometer,  and so i t was n e c e s s a r y t o employ s t o p p e d - f l o w t e c h n i q u e s .  The d a t a  f o r DMA s o l u t i o n s a t 30°C a r e p r e s e n t e d i n T a b l e I I I - 4 ; i n each c a s e , except f o r t h e l a s t two experiments l i s t e d , the phosphine was i n excess by a t l e a s t a f a c t o r o f t e n t o m a i n t a i n 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 t h e absorbance v s time d a t a a n a l y z e d f o r good f i r s t - o r d e r l o g p l o t s ( F i g u r e 3.14) from which ^• ^ were e s t i m a t e d . Q  The dependence o f k ^ w i t h i n c r e a s i n g [PPh^J  o n  )S  [PPh^] goes from f i r s t - t o z e r o - o r d e r  ( F i g u r e 3.15).  The expected  independence  o f k , on [ R u J i s observed a t t h e h i g h e r [PPh„], b u t a t lower obs T J m  [PPh^] k k Q  s  does d e c r e a s e w i t h i n c r e a s i n g [ R u ] ^ , ( F i g u r e 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 t h e f o l l o w i n g mechanism:  -51-  -52-  TABLE III-4 Stopped-flow data f o r DMA solutions of HRuCl(PPh^)^ and PPh„ at 30°C  [Ru] xl0 ,M a  3  [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  0  I  I  4-0  I  1  8-0  I  I  12-0  1  L_  16-0  Time , s F i g u r e 3.14  P l o t of l n ( A -A^) v s time of t h e s t o p p e d - f l o w d a t a f o r the r e a c t i o n between HRuCl(PPh,) and PPh .  -54-  16  0  100H  to  C\J  o CO  JO  o  6  0  4  0  2  0  1-0  05  [ \f] ° • ppr  Figure  3.15  x1  M  Dependence of k on t r i p h e n y l p h o s p h i n e c o n c e n t r a t i o n in 5MA a t 30°C. b  15  -55-  k  [HRuCl(PPh ) ] 3  2  2  „  X k  l  * 2HRuCl(PPh ) 3  (3.22)  2  k HRuCl(PPh ) + PPh 3  2  3  • HRuCl(PPh ) 3  (3.23)  3  Since equilibrium (3.22) i s established prior to the addition of PPh  3  i t i s 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 , ) i s independent of [PPh.]; and obs  J  any monomer present must be rapidly consumed by the PPh k  2  step.  3  i n a fast  The spectral change observed must therefore r e s u l t from  the k^ step (in effect one i s monitoring the conversion of any remaining dimer to the trisphosphine complex), and k ^ simply equal k^.  will  The value of k^ i s found to be 1.49 x 10 ^s \ and _3  since k^/k_^ i s known from equation 3.9 to equal 1.66 x 10 value of k ^ i s calculated to be 90 M  \  Varying the t o t a l ruthenium  concentration at high [PPh-j] (Figure 3.16) gives average value f o r region, k  9  of 1.45 x 10  \  M, the  values with an  At low [PPh ] i n the f i r s t - o r d e r 3  must now be rate determining,this step being followed by rapid  F i g u r e 3.16  Dependence of k DMA at 30°C. °  on ruthenium c o n c e n t r a t i o n S  -57-  establishment  o f e q u i l i b r i u m (3.22).  A r a t e e q u a t i o n can t h e r e f o r e  be w r i t t e n :  Rate = k [ P P h ] [ H R u C l ( P P h ) ] 2  3  3  (3.24)  2  V  2[HRuC1  and  s i n c e [Rul = [HRuCl (PPh,)  (  \  k  Rate  =  l  / k  -i 2 k  [ P P h  3  3  The  ] [ R u ]  —= -r-rr-rr-. r — 2[HRuCl(PPh ) ] 2  dependence on [ R u ]  2[HRuCl(PPh ) ] 3  2  and k^/k y  t h e former term w i l l  T  ,  .  P  P  h  )  (3.25)  k  '  7;  •.  + k /k_ 1  will  V  •  Z  D  >  depend on t h e r e l a t i v e magnitude o f  i n c r e a s e i n m a g n i t u d e , and t h e o v e r a l l dependence T h i s i s presumably  [Ru]„ a t t h e l o w e r I  why  [PPh~] ( F i g u r e J  3.16),  should analyse f o r f i r s t -  -3 A t [Ru]^, o f 0.5 x 10 M the i n i t i a l  concentration  monomer i s 0.35 x 10 Mjhence the denominator o f e q u a t i o n  equals  J  1  however, i t i s n o t o b v i o u s why each experiment  of  k  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  decreases w i t h i n c r e a s i n g  o r d e r i n ruthenium.  V -l\  V -1  on r u t h e n i u m w i l l be l e s s t h a n f i r s t - o r d e r . k , obs  3 2^  (3.26)  -3 -3 (0.7 x 10 ) + (1.66 x 10 ) so t h e term f o r the monomer cannot  be n e g l e c t e d .  D u r i n g t h e e a r l y s t a g e s o f the r e a c t i o n the monomer w i l l  be r e p l e n i s h e d v i a the dimer d i s s o c i a t i n g and i f t h e c o n c e n t r a t i o n does not change too much,the f i r s t - o r d e r l o g p l o t s would be expected. lowest  -3 [ R u ] (0.26 x 10 M), k T  o b g  curve o f F i g u r e 3.16 back t o lower equation  At the  -2 -1 i s 3.4 x 10 s ; e x t r a p o l a t i n g the -3 [ R u ] (0.1 x 10 M), where t h e r a t e T  (3.24) w i l l approximate t o k [ P P h ] [ H R u C l ( P P h ^ ) J » s u g g e s t s  -2 -1 w i l l be o f t h e o r d e r o f 5 x 10 s .  2  3  2  T h i s gives a value of k  2  of  k  Q b s  -58-  approximately  10^M  ^ which i s r e a s o n a b l y c o n s i s t e n t w i t h  s t e p becoming r a t e d e t e r m i n i n g a t low k^  step i s rate  3.3.5.1  [PPh^], w h i l e a t h i g h  [PPh^] the  limiting.  Dependence of the Rate 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 (Figure  3.10)  For h y d r o g e n a t i o n  r e a c t i o n s under c o n s t a n t  [ h e x - l - e n e ] , the r a t e was rate p r o f i l e 4-5  the  found  [Ru]^,  [H^], and  to i n c r e a s e with i n c r e a s i n g  [LiCl].  The  suggests t h a t at h i g h e r c h l o r i d e , a l i m i t i n g r a t e , some  times g r e a t e r than t h a t  C h l o r i d e i o n c o u l d add  i n the absence o f added c h l o r i d e , i s reached.  t o the dimer t o produce more a c t i v e  catalysts; 64  possibilities or  include a triply-chloro-bridged  an a n i o n such as H R u C l ^ ( P P h ^ )  2  monomer v i a c l e a v a g e o f the dimer.  produced  s p e c i e s , w h i c h a r e known  from a d d i t i o n o f CI  ,  to the  Attempts to i s o l a t e the product  from  the c h l o r i d e a d d i t i o n t o [HRuCl (PPh^),,^ u s i n g v a r i o u s c a t i o n s were  un-  successful.  for  The  by changes of H solubility 3.3.5.2  2  e f f e c t s on r a t e a r e much too l a r g e t o be accounted solubility  i n the DMA-LiCl s o l u t i o n s *  d e c r e a s e s by about  A Spectrophotometric and  10% on adding up t o 1.2M Study  indeed,the LiCl.^ HRuCl(PPh^)^  of the R e a c t i o n between  LiCl. _3  To a DMA  s o l u t i o n of H R u C l ( P P h )  s o l u t i o n s of L i C l ,  3  and  the v i s i b l e  2  spectrum  Changes i n the a b s o r p t i o n maximum a t 500 a d d i t i o n of L i C l ,  and  (7.2 x 10  M) was  added  DMA  r e c o r d e d a t 25°C ( F i g u r e  nm were monitored  the r e s u l t s are g i v e n i n T a b l e  with  III-5:  each  3.17)  -59-  Wavelength , nm i g u r e 3.17  V i s i b l e a b s o r p t i o n of DMA s o l u t i o n of H R u C l ( P P h ^ 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 . (A) 7.2 x 10 M HRuCl(PPh ) 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 . _3  3  2  -60-  TABLE III-5 Spectrophotometric study of the equilibrium between HRuCl(PPh,) and L i C l i n DMA solution at 25°C 0  [LiCl]xl0 ,M  A -A o  A-A  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 (500 mn) 3  a  1 mm c e l l path  2  OC  \  -61-  The s p e c t r a l changes a r e v e r y s i m i l a r to those o b t a i n e d f o r . a d d i t i o n o f hex-l-ene t o the complex, and the same problems a r i s e i n i n t e r p r e t i n g them. There a r e no r e a l i s o s b e s t i c p o i n t s which s u g g e s t s t h a t t h e r e a r e more than two a b s o r b i n g s p e c i e s , s o two analogous t o t h o s e f o r t h e h e x - l - e n e system appear  K  (HRuCl(PPh ) ) 3  2  „  2  l  2HRuCl(PPh )  fc  3  K  HRuCl(PPh ) 3  + LiCl  2  -  3  equilibria  likely:  (3.27)  2  + * L i HRuCl (PPh ) 2  3  (3.28)  2  or a l t e r n a t i v e l y the c h l o r i d e b i n d s t o b o t h the dimer and monomer.  3.4  Discussion The r e s u l t s show t h a t  hydridochlorobis(triphenylphosphine)  r u t h e n i u m ( I I ) i s an e f f e c t i v e and e f f i c i e n t g e n a t i o n of h e x - l - e n e . mechanism compared  c a t a l y s t f o r the h y d r o -  The r e d u c t i o n proceeds by a more " c o n v e n t i o n a l "  to the h y d r o g e n a t i o n of a c r y l a m i d e ( s e c t i o n 3.1),  thereby showing t h a t the n a t u r e of the s u b s t r a t e has a pronounced  affect  on the c o u r s e of h y d r o g e n a t i o n . S i n c e the complex does not obey Beer's law i t i s n e c e s s a r y t o e s t a b l i s h which i s t h e r e a c t i n g s p e c i e s i n s o l u t i o n .  The  visible  s p e c t r a f o r the b i n d i n g of the o l e f i n to the complex o f f e r s l i t t l e as the r e s u l t s can be i n t e r p r e t e d  help  i n terms of c o n s e c u t i v e dimer-monomer  and monomer-alkyl e q u i l i b r i a , o r even b i n d i n g of the o l e f i n t o b o t h dimer and monomer,although dimer. equation  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  In the absence of H  2  the forward and backward  r e a c t i o n of  (3.12) w i l l l e a d t o an e q u i l i b r i u m c o n c e n t r a t i o n of t h e a l k y l .  -62-  Since  = 0.29  M  -1 -1 s and  k ^ averages  the e q u i l i b r i u m c o n s t a n t i s 16 M  to 1.9  x 10  -2  s  -1  ( s e c t i o n 3.3.3),  and w i l l be e s t a b l i s h e d w i t h  o v e r a l l r a t e c o n s t a n t of ( k ^ f o l e f i n ] + k j)  an  a t pseudo z e r o - o r d e r  con-  -2 ditions  in olefin.  T h i s r a t e c o n s t a n t has v a l u e s of 2.2  -2 -1 and  6.7  x 10  s  -2  s  a t 10  M and  0.2  M olefin respectively.  are q u i t e c o n s i s t e n t w i t h the e x p e r i m e n t a l time necessary  x 10  -1  f o r the e s t a b l i s h m e n t of e q u i l i b r i u m  16 M ^ i s a l s o q u a l i t a t i v e l y c o n c e n t r a t i o n used  (up to 500 (3.12).  These numbers sec)  found  A k^/k_^ of  c o n s i s t e n t w i t h the range of o l e f i n  t o b r i n g about the s p e c t r a l changes of F i g u r e  3.3  ( i . e . the c o n v e r s i o n of h y d r i d e to a l k y l ) . The  gas-uptakes show a predominantly  first-order  dependence on  [Ru]^, which i s not i n agreement w i t h the f o l l o w i n g mechanism i n which the dimer i s the major s p e c i e s p r e s e n t : (HRuCl(PPh ) ) „ - 2HRuCl(PPh )  (3.29)  K  3  2  2  3  l + olefin ^===^  2  k  HRuCl(PPh ) 3  2  k  RuCl ( P P h ) ( a l k y l ) + H 3  2  2  2  RuCl(PPh ) (alkyl) 3  — •  (3.30)  2  HRuCl ( P P h ^  + alkane  Such a mechanism l e a d s t o a h a l f - o r d e r dependence on a r e two  (3.31)  [Ru] « T  There  p o s s i b l e e x p l a n a t i o n s f o r the f i r s t - o r d e r dependence; e i t h e r  o l e f i n binds s o l e l y  t o the dimer and the c a t a l y s i s  s p e c i e s , o r more l i k e l y ,  since l i t t l e  proceeds  of the ruthenium  v i a this  i s present i n  the d i m e r i c form, the monomer i s the a c t i v e s i t e f o r h y d r o g e n a t i o n . p r o p o s a l i s supported  the  by the s l i g h t d e v i a t i o n from f i r s t - o r d e r  This  dependence  -63-  on  [Ru]^ at h i g h e r  ruthenium c o n c e n t r a t i o n s  the i n a c t i v e dimer w i l l be p r e s e n t , available for The  thereby r e d u c i n g  where more of  the monomer  catalysis.  d i f f e r e n c e i n r e a c t i o n mechanisms between t h i s system  t h a t u s i n g a c r y l a m i d e as s u b s t r a t e olefin.  ( F i g u r e 3.6)  The  e q u i l i b r i u m constant  and  i s a t t r i b u t e d to the e f f e c t of  the  f o r the r e a c t i o n of a c r y l a m i d e w i t h 39  the complex,which was  -1  taken to be monomer,was found  w h i l s t f o r hex-l-ene i t was  16 M  1  to be  150  (see above). For a c r y l a m i d e  M  ,  the  e l e c t r o n - w i t h d r a w i n g amide s u b s t i t u e n t w i l l enhance back d o n a t i o n from the f i l l e d m e t a l d - o r b i t a l s to the empty a n t i b o n d i n g o l e f i n so i t w i l l b i n d more s t r o n g l y . m o l e c u l e i n t o the Ru-H not  apparently  possibility  o r b i t a l s of  I n s e r t i o n of the  bond generates a m e t a l - a l k y l  the  acrylamide  species  t h a t does  undergo o x i d a t i v e a d d i t i o n o f a hydrogen m o l e c u l e ;  i s t h a t compared to h e x y l  one  the e l e c t r o n withdrawing n a t u r e  of the a l k y l group removes e l e c t r o n d e n s i t y  from the metal atom  and  reduces the a b i l i t y of the complex to undergo o x i d a t i v e  addition.  Perhaps more l i k e l y  to the  and  i s that the amide group c o o r d i n a t e s  the r e s u l t i n g f i v e - c o o r d i n a t e c h e l a t e i n t e r m e d i a t e  likely  to o x i d a t i v e l y add  olefinic  substrates  H. 2  Coordination  i s w e l l documented. ^  would be  of H  2  (equation  constant  i s used, c o n c o m i t a n t l y  substrate  p r o d u c i n g a Ru(I)  dimer  to the a c t i v e c a t a l y s t by undergoing o x i d a t i v e a d d i t i o n  3.4).  For  i s s m a l l e r , but  presumably by  less  of amide i n u n s a t u r a t e d  cannot be used to complete the r e d u c t i o n of the a c r y l a m i d e  which i s r e v e r t e d  ruthenium,  Since m o l e c u l a r hydrogen  6  another mole of h y d r i d e  6 6  the u n a c t i v a t e d  the m e t a l - a l k y l  o x i d a t i v e a d d i t i o n , and  o l e f i n , h e x - l - e n e , the  binding  species r e a d i l y reacts with  subsequent r e d u c t i v e  H  elimination  2  -64-  of hexane r e g e n e r a t e s the c a t a l y s t .  The maximum r a t e of h y d r o g e n a t i o n  f o r h e x - l - e n e i s f a s t e r than f o r a c r y l a m i d e presumably because of the a v a i l a b i l i t y of hydrogen w h i c h 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 m e t a l a l k y l complex. 68 H y d r o g e n a t i o n of h e x - l - e n e u s i n g HRuCl(PPh^)^ as c a t a l y s t  is  s i m i l a r t o the b i s p h o s p h i n e system as i t i n v o l v e s a r a t e - d e t e r m i n i n g r e a c t i o n of a ruthenium a l k y l w i t h m o l e c u l a r H^.  However, the r a t e of  h y d r o g e n a t i o n of the a l k y l i s a p p r o x i m a t e l y e i g h t times f a s t e r f o r the 69 38 t r i s p h o s p h i n e complex. T h i s s u p p o r t s the r e c e n t l y proposed mechanism f o r the h y d r o g e n a t i o n s u s i n g HRuCl(PPh^)^ ( e q u a t i o n s 1.10-12) i n w h i c h the r a t e - d e t e r m i n i n g s t e p i s the r e a c t i o n of B.^ w i t h R u C l ( P P h ^ ) ^ ( 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 s p e c i e s i s c o n s i d e r e d t o 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  m e t a l atom and t h e r e b y i n c r e a s e the r a t e .  Under the c o n d i t i o n s used t o s t u d y the phosphine dependence ( F i g u r e 3.9) a t 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 t o k ^ [ R u ] ^ [ o l e f i n ] .  I n the presence of  the added phosphine, l i t t l e of the dimer w i l l be p r e s e n t , and the system might be d e s c r i b e d by:  HRuCl(PPh,), + o l e f i n +PPh3 IT  *>  RuCl(PPh ) (alkyl) 3  H  HRuCl(PPh ) 3  3  2  2'  fast  (3.32)  HRuCl(PPh,), + alkane  I n c o r p o r a t i o n o f the K' e q u i l i b r i u m w i t h o n l y the b i s p h o s p h i n e system  -65-  c o n t r i b u t i n g t o the c a t a l y s i s would y i e l d  the r a t e law:  k. [ R u ] _ [ o l e f i n ]  **" ' 1 + xVph ]  (3  3  The d a t a o f F i g u r e 3.13 i n d i c a t e t h a t K ' [ P P h ] » l . 3  y i e l d s a s l o p e o f k^[Ru]^,[ o l e f i n ] /K' of v a l u e c o r r e s p o n d s t o a K' v a l u e with  o f ^300 M . -1  t h e much l a r g e r v a l u e s  -  33)  The i n v e r s e p l o t  7 2 -1 A x 10 M sec , which  T h i s i s c l e a r l y not c o n s i s t e n t  o f K' estimated  previously.  36  The anomaly l i e s i n t h e f a c t t h a t c a t a l y s i s can occur through the t r i s p h o s p h i n e system once the o l e f i n c o o r d i n a t e s  and d i s p l a c e s one  phosphine:  HRuCl(PPh,), + o l e f i n A  3 3  ~  +PPh  HRuCl (PPh,) . ( o l e f i n )  JI  3  II  (3.34)  H alkane + HRuCl(PPh ) 3  Earlier  RuCl(PPh^(alkyl)  2  s t u d i e s on the t r i s p h o s p h i n e  dependence on  systems had shown t h a t the k i n e t i c  was f i r s t - o r d e r , and the r a t e - d e t e r m i n i n g  step was  68 w r i t t e n as the r e a c t i o n of the a l k y l w i t h H^  (equation  i s q u i t e d i f f e r e n t from t h e mechanism shown i n equation genation  3.34),which (3.32).  Hydro-  through (3.34) g i v e s the r a t e law: K"k [H ][Ru] [olefin] 2  R  a  t  e  =  2  T  K " [ o l e f i n ] + [PPh ] 3  The r a t e would g i v e a d i r e c t [PPh ]>>K" [ o l e f i n ] , i . e . 3  HRuCl(PPh ) 3  3  ( 3  '  3 5 )  i n v e r s e dependence on added phosphine when  the ruthenium i s present  almost e n t i r e l y a s  The s l o p e of t h e i n v e r s e p l o t ( F i g u r e 3.13) would then  -66-  be a measure o f 0.6 M  K"k [H ][Ru] [olefin]. 2  2  T  ^ so i t i s almost  phosphine a r e concerned C l e a r l y more d e t a i l e d  The s l o p e y i e l d s  c e r t a i n t h a t t h e experiments  K"k  2  t o equal  w i t h added  with a c t i v i t y v i a the trisphosphine species.  s t u d i e s on t h e b i s p h o s p h i n e  system w i t h added  phosphine a r e r e q u i r e d b e f o r e a complete i n t e r p r e t a t i o n can be o f f e r e d . Catalytic to  i s o m e r i s a t i o n of hex-l-ene  which i t o c c u r s i n t h e presence  i s not u n u s u a l , but the extent  o f HRuCl(PPh.j)  number o f review a r t i c l e s ^ have been p r e s e n t e d t h r e e mechanisms  2  i s interesting.  A  on t h i s s u b j e c t , and  proposed:  (a) M e t a l h y d r i d e a d d i t i o n - e l i m i n a t i o n  RCH CH|CH „ 2  2  - RCH CH-CH ^ 2  MH  3  3  M  (b) T T - A l l y l h y d r i d e  (3.36)  RCH=CH-CH MH  formation CH  RCH CH=CH 2  2  Carbene  ^  (3.37)  * RCH=CHCH | M  J  formation  RCH CH=CH ^ 2  2  MH  M  (c)  CH  RCH  2  " RCH CCH 2  M  M  M  (3.38)  RCH=CHCH,  3  C l e a r l y i n view o f t h e h y d r i d o - c a t a l y s t b e i n g s t u d i e d and i t s i n t e r a c t i o n with o l e f i n  t o g i v e an a l k y l , mechanism  intermediate a l k y l to  formed i n i t i a l l y  the coordinated hex-l-ene.  (a) i s s t r o n g l y f a v o u r e d w i t h the  by M a r k o v n i k o f f  A f t e r 15 h  a d d i t i o n of t h e Ru-H  a t 25°C, s o l u t i o n s of  -67-  HRuClCPPh^)^ were found" ' t o i s o m e r i s e hex-l-ene 1  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 of the b i s p h o s p h i n e  t o 7% hex-2-ene and  than f o r s o l u t i o n s  complex i n t h e p r e s e n t work (85% c o n v e r s i o n to  hex-2-ene a f t e r 1 h ) .  T h i s i s presumably due t o l e s s s t e r i c  crowding  i n the R u C l ( P P h ) ( a l k y l ) i n t e r m e d i a t e and so h y d r i d e t r a n s f e r i s much 3  l e s s hindered  2  than i n R u C l ( P P h , ) , ( a l k y l ) .  -68-  CHAPTER IV  STRUCTURAL  STUDIES ON  HYDRIDOCHLOROBIS(TRI-p-TOLYLPHOSPHINE)RUTHENIUM(II)  4.1  X-Ray S t r u c t u r e  Determination  P r e p a r a t i o n o f ( H R u C l ( P ( p - t o l y l ) ) ) , as d e s c r i b e d 3  2  2  i n Section  2.1.5.2 i i , y i e l d e d dark r e d c r y s t a l s ; a s i n g l e c r y s t a l x-ray study to  c a r r i e d out by R.C. B a l l i n t h i s department r e v e a l e d  be a c h l o r o - b r i d g e d dimer  ( F i g u r e 4-1).  diffraction  the complex  A square p y r a m i d a l  coordi-  6 n a t i o n geometry i s u s u a l l y favoured  by a f i v e c o o r d i n a t e d  37 configuration  but here the s t r u c t u r e o f two such c e n t r e s s h a r i n g a b a s a l edge has no symmetry s i n c e i t I s d i s t o r t e d as a r e s u l t o f the s m a l l h y d r i d e l i g a n d . I t was d i f f i c u l t  t o determine u n e q u i v o c a l l y  the p o s i t i o n o f the  h y d r i d e l i g a n d s , but some e l e c t r o n d e n s i t y was found i n the p o s i t i o n s shown, and i t i s not unreasonable t h a t they should be l o c a t e d The  p o s i t i o n of the h y d r i d e  on Ru(2) may be d i f f e r e n t  there.  from t h a t shown  o  as the R u ( 2 ) - C l ( 2 ) bond l e n g t h  (2.57A) i s found t o be l o n g e r than the  o t h e r t h r e e Ru-Cl bond l e n g t h s  (2.46-2.48A), which s u g g e s t s a t r a n s  o  influ-  ,  -70ence of the h y d r i d e l i g a n d . ^ o  The d i s t a n c e between the ruthenium c e n t r e s i s 2.80A which 72  o  w i t h i n the range  falls  (2.28-2.95A) u s u a l l y found  s i n c e each metal atom has 16  f o r a Ru-Ru bond.  However,  e l e c t r o n s , and the complex i s diamagnetic  (n.m.r. a c t i v e ) , t h e r e cannot f o r m a l l y be a metal-metal s i n g l e bond. The diamagnetism  would imply a double bond but a s h o r t e r bond l e n g t h than the  observed v a l u e would p r o b a b l y be expected. V a r i o u s bond l e n g t h s , and bond a n g l e s are l i s t e d w i t h F i g u r e 4.2. X-ray s t u d i e s on R u C l ( P P h ) 2  3  2 2  and HRuCl(PPh^)^  73  have shown that  one ortho-hydrogen atom of a phenyl group of the c o o r d i n a t e d phosphines o  i s p a r t i c u l a r l y c l o s e 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 a s :  to e x p l a i n how  l i g a n d - m e t a l hydrogen  transfer  f o r example, i n deuterium exchange s t u d i e s .  (orthometallation) o c c u r s , The d i s t a n c e between the  ortho-hydrogen atoms and ruthenium c e n t r e s f o r the ( H R u C l ( P t p - t o l y l ) . ^ )  9  o  dimer are a l l g r e a t e r than 3A, and the p a c k i n g o f the phenyl r i n g s should not r e a d i l y permit o r t h o m e t a l l a t i o n . The d i m e r i c complex was  a l s o prepared  as p r e v i o u s l y d e s c r i b e d but u s i n g deuterium as the r e d u c i n g agent. ^H n.m.r. of the product shows the h y d r i d e resonance at T22.8; and resonance at T2.37 which  The the  i s a s s i g n e d t o the o r t h o - p r o t o n s i s reduced by  50% r e l a t i v e to the resonance f o r the meta — p r o t o n s . S i n c e t h e r e i s no evidence f o r c l o s e i n t r a m o l e c u l a r c o n t a c t of an ortho-hydrogen atom w i t h a metal atom i n the x - r a y study of the dimer, t h i s o r t h o - d e u t e r a t i o n of the phosphine  i s thought t o be t a k i n g p l a c e i n the monomer presumably  by  -71-  Distance Ru(l)-Ru(2) Ru(l)-P(l) Ru(l)-P(2) Ru(2)-P(3) Ru(2)-P(4) Ru(l)-Cl(l) Ru(l)-Cl(2) Ru(2)-Cl(l) Ru(2)-Cl(2)  Figure  4.2  (A) 2.80(0) 2.26(1) 2.39(1) 2.28(1) 2.23(1) 2.47(1) 2.48(1) 2.46(1) 2.57(1)  Angles  (deg)  P(l)-Ru(l)-P(2) P(l)-Ru(l)-Cl(l) P(l)-Ru(l)-Cl(2) P(2)-Ru(l)-Cl(l) P(2)-Ru(l)-Cl(2) Cl(l)-Ru(l)-Cl(2) P(4)-Ru(2)-P(3) P(4)-Ru(2)-Cl(l) P(4)-Ru(2)-Cl(2) P(3)-Ru(2)-Cl(l) P(3)-Ru(2)-Cl(2) Cl(l)-Ru(2)-Cl(2)  104.1(5) 92.1(5) 167.6(5) 102.9(4) 88.0(4) 82.6(4) 97.6(5) 166.8(5) 94.4(5) 95.6(5) 113.8(4) 80.9(4)  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 ) ^ ) and s e l e c t e d bond a n g l e s and d i s t a n c e s .  2  complex,  -72-  the f o l l o w i n g mechanism:  ( P h P ) Ru C l D 3  (Ph_P) R u — C L  2  J  i s. Ph P. 2  [(2-DC H )PPh ](Ph P) 6  4  2  3  /  CI  CI  Ru — D — X  ^. (Ph_P) R u — C L  PPh,  V  (Pfi„P)R  / u  Ph P. 2  A.2  N.m.r. S p e c t r o s c o p y 31 The  1 P{ H}-n.m.r. o f R u C l ( P P h > 2  3  i n CH C1  3  2  2  a t room temperature  37 75 shows  '  (6=40.9 ppm), but on c o o l i n g t o -97°C  a singlet  r e v e a l s a d o u b l e t (6=24.1 ppm) and a t r i p l e t i n t e n s i t y o f 2:1.  T h i s was e x p l a i n e d  pyramidal s t r u c t u r e  (6=75.7 ppm) w i t h a r e l a t i v e  i n terms o f a d i s t o r t e d  (I) which undergoes  higher temperatures.  t h e spectrum  square  i n t r a m o l e c u l a r rearrangement a t  At low temperatures an AB p a t t e r n  ( 6 =58.8, 6 = 5 3 . 0 D  A  (CH C1 ); 2  2  Jp p=41.5 Hz) i s a l s o o b s e r v e d , t h e i n t e g r a t i o n o f which  that o f t h e f r e e P P h  3  s i g n a l , and i s a t t r i b u t e d  formed by l o s s o f a phosphine l i g a n d : (RuCl (PPh ) ) RuCl (PPh ) 2  3  2  3  3  2  .PPh.  3  .PPh-  CL 'Ru  'Ru  Ru' Ph P'  (4.1)  3  PPh-  PPh. Cl.  to a dimeric species ( I I )  + 2PPh  2  Ph P 3  i s twice  n  XI PPh:  -73-  The  t o l y l - p h o s p h i n e analogue, R u C l 2 ( P ( p - t o l y l ) ) , was r e p o r t e d by Armit 3  et a l ^ , and shows a d o u b l e t  3  (6=25.1 ppm) and a t r i p l e t  (6=74.3 ppm) a t  -83°C, and so the s t r u c t u r e i s t h e same as i n I ; t h e r e i s no r e p o r t e d evidence  f o r a species equivalent  to I I .  I s o l a t i o n of R u C l ( P P h ^ ) ^ 2  31 provided  a  P-n.m.r. w i t h  t h e same AB p a t t e r n f o r a t o l u e n e s o l u t i o n  of the complex a t -70°C as p r e v i o u s l y d e t e c t e d confirming  the d i m e r i c  structure.  i s observed which i s compatible  f o r r e a c t i o n (4.1),  thereby  In DMA only a sharp s i n g l e t a t 64.9 ppm  with a s i x coordinate  s p e c i e s such as  RuCl (PPh ) (DMA) . 2  3  2  2  At -74 C the proton shows an A X  2  pattern  decoupled  consistent with a s t a t i c  to a sharp s i n g l e t at 30°C.  s t r u c t u r e analogous t o I w i t h  placing a chloride ligand. other  37 P-n.m.r. spectrum o f HRuCl(PPh^)^  (6^=94.0 ppm 6^=38.4 ppm) which c o l l a p s e s as t h e  temperature i s r a i s e d and c o a l e s c e s  any  31  the h y d r i d e r e -  There a r e no resonances due t o f r e e PPh^ or  complexes.  When [ H R u C l ( P P h ) ] 3  2  2  was prepared,  the  1  H-n.m.r. i n t o l u e n e  a s i n g l e broad resonance i n the h i g h - f i e l d r e g i o n 31  This i s  showed  (T=22.5-23.8 ppm).  39  The  1 P{ Hln.m.r. spectrum was not w e l l r e s o l v e d a t -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 c o u l d not be o b t a i n e d ,  but the two resonances observed  were a t t r i b u t e d t o an AB p a t t e r n of a h a l i d e - b r i d g e d s t r u c t u r e analogous to I I .  T h i s was used as evidence  t h a t t h e complex was a dimer i n t o l u e n e ,  w h i l s t k i n e t i c d a t a suggested t h a t i t was a monomer i n DMA. s t a n t i a t e these c o n c l u s i o n s  i t was decided  to study  To h e l p  sub-  the H R u C l ( P ( p - t o l y l ) - j )  complex s i n c e the t o l y l - p h o s p h i n e would enhance the s o l u b i l i t y  properties  of such s p e c i e s . The v a r i a b l e temperature ^H-n.m.r. s p e c t r a of a degassed  toluene-d  Q  o  solution of [HRuCl(P(p-tolyl) ) 3 3  2  2  (approximately  0.05 M) are shown i n  2  -74-  F i g u r e 4.3. and  A t 30°C the spectrum c o n s i s t s o f resonances due t o the ortho  meta p r o t o n s o f t h e phenyl r i n g s a t T2.37 and 3.10 r e s p e c t i v e l y , two  methyl resonances a t T7.80 and 7.86, and a h y d r i d e On l o w e r i n g  resonance a t T22.8.  the temperature a l l o f the resonances b e g i n to broaden u n t i l  -80°C when two h y d r i d e  resonances a r e observed a t T18.3 and 27.5, and  these then sharpen somewhat w i t h f u r t h e r cooling.Two methyl resonances can be seen f o r t o l y l - p h o s p h i n e s t r a n s  to l i g a n d s o f d i f f e r i n g  trans-  i n f l u e n c e , s i n c e 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 t r a n s m i t t e d methyl groups by the aromatic system. at 30°C i s a t the c e n t r e so a t w o - s i t e  to the  The c h e m i c a l s h i f t o f the h y d r i d e  o f the s h i f t s f o r the two resonances a t -90°C  exchange p r o c e s s i s o c c u r r i n g .  There a r e two p o s s i b l e  78 explanations  for this;  the resonance o f b r i d g i n g hydrogen i n h y d r i d o -  metal c l u s t e r s appears a t h i g h e r  field  than t h a t o f t e r m i n a l l y bonded  hydrogen, so a b r i d g i n g t o t e r m i n a l hydrogen exchange i s o c c u r r i n g . A l t e r n a t i v e l y , when hydrogen i s t r a n s chemical s h i f t low  t o a l i g a n d of h i g h  trans-influence i t s  i s a t t h e low f i e l d ( b e l o w T20)while o p p o s i t e  t r a n s - i n f l u e n c e i t s chemical s h i f t  of the h i g h - f i e l d r e g i o n , s o  i s a t the h i g h e r  an exchange which b r i n g s  part  a ligand of (above T20)  the h y d r i d e  t r a n s to  l i g a n d s o f d i f f e r e n t t r a n s - i n f l u e n c e w i l l a l s o e x p l a i n the observed Unfortunately toluene see  i t was n o t p o s s i b l e to c o o l the sample ( f r e z i n g p o i n t of  -95°C) s u f f i c i e n t l y low t o r e s o l v e the h y d r i d e  the phosphorus  resonances and to  coupling.  31 The  spectra.  v a r i a b l e tennerature  1 P-{ H}-n.m.r. s p e c t r a o f the same sample as used  f o r the ^H-n.m.r. a r e shown i n F i g u r e 4.4.  A t -70°C t h e r e a r e three  resonances  a t 29.0, 61.3, and 78.0 ppm o f 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 a t 49.5 ppm  -757-63  22-8 Benzene Impurity 3-10 2-37  //  ^JA-  ZZ  u I  .  I  .  I  Figure  —  •  4.3  I  I  I  >  I  •  .  1  I  .  I  1—I—1—I—'—I—>-  The v a r i a b l e temperature H-n.m.r. s p e c t r a o f (HRuCl(P(p-tolyl) ) ) in toluene-d . 1  3  2  2  g  F i g u r e 4.3  continued.  -77-  70°C  50  30 v  10  i  Figure  A.A  i  I  1  L  i  I  I  J  L  1 31  1  I  I  1  The v a r i a b l e temperature P{ H)-n.m.r. s p e c t r a of ( H R u C l ( P ( p - t o l y l ) , ) , ) , i n t o l u e n e - d . (A,B,C,D,E, and ' F a t 2 0 0 0 Hz sweep w i d t h and G and H a t 1 0 0 0 0 Hz sweep width).  -78-  i  i  i  i  i  i  Figure A. A  I  I  I  I  continued.  I  1  1  1  1  1  1  1  -79-  which i s a s s i g n e d t o the s o l v a t e d monomeric s p e c i e s , a s i n g l e t a t 26.6 ppm which i s due t o O P ( p - t o l y l ) ^ , and o t h e r resonances which a r e probably due  t o s m a l l q u a n t i t i e s o f i m p u r i t i e s from d e c o m p o s i t i o n o f t h e complex.  R a i s i n g the temperature  t o -50°C r e s u l t s i n broadening o f t h e resonances,  and c o a l e s c e n c e t o an i n d i s t i n c t peak a t a p p r o x i m a t e l y 70.4 ppm, and a broad hump i n the r e g i o n o f 40 ppm.  On f u r t h e r warming two resonances  become apparent and these sharpen up a t the average o f the resonances a t 78.0  and 61.3 ppm and t h e resonances a t 61.3 and 29.0 ppm.  temperatures a s i n g l e t due t o phosphine downfield  t o 40.1 ppm.  oxide i s s t i l l  At high  p r e s e n t but s h i f t e d  The resonance due t o the monomer (58.5 ppm)  in-  c r e a s e s i n i n t e n s i t y w i t h i n c r e a s i n g temperature which i s c o n s i s t e n t w i t h t h e endothermic  c l e a v a g e o f the c h l o r i d e b r i d g e s .  As the temperature i s  r a i s e d another resonance a t 68.4 ppm i s r e v e a l e d , and appears t o be a s s o c i a t e d w i t h the monomer as i t grows i n i n t e n s i t y a t a s i m i l a r  rate  to the resonance a t 58.5 ppm, but the n a t u r e o f t h i s a s s o c i a t i o n i s not at a l l obvious.  A d d i t i o n o f DMA  t o a sample r e s u l t e d i n a d o w n f i e l d  s h i f t o f a l l the resonances and an i n c r e a s e i n the p r o p o r t i o n o f monomer. The l i m i t i n g f a s t and slow exchange s p e c t r a c o u l d n o t be o b t a i n e d because of the f a c i l i t i e s a v a i l a b l e , s o o n l y a t e n a t i v e e x p l a n a t i o n o f the s p e c i e s i n s o l u t i o n can be g i v e n on the b a s i s of the broad u n r e s o l v e d resonances. Assuming t h e c r y s t a l used  i n t h e x-ray d i f f r a c t i o n  study i s r e -  p r e s e n t a t i v e o f the sample, one of the s p e c i e s p r e s e n t a t low temperatures can be taken t o be the h a l i d e - b r i d g e d s t r u c t u r e w i t h two d i s t o r t e d pyramids  s h a r i n g a b a s a l edge.  square  A p o s s i b l e p r o c e s s t o e x p l a i n the n.m.r.  -80-  data i n v o l v e s a rearrangement and t r a n s to the i n i t i a l l y equatorial  which b r i n g s the hydrogen  a x i a l phosphine w i t h concomitant  axial  shift  of the  phosphine:  H P =  where P e o u a l s P ( p - t o l y l ) ^ . trigonal  nucleus  H P(p-t0lyl)  As drawn t h e r e i s a square p y r a m i d a l and  b i p y r a m i d a l geometry about  but the d e f o r m a t i o n s due t o c r y s t a l s t r u c t u r e may be reduced  3  the Ru i n I I I and IV r e s p e c t i v e l y , f o r c e s as shown i n the c r y s t a l  i n s o l u t i o n but not s u f f i c i e n t l y t o produce  r e g u l a r geometries. 31 The  1 P{ H)-n.m.r. slow exchange s p e c t r a would be expected t o show  an AX p a t t e r n f o r both s p e c i e s .  From the s t u d i e s on o t h e r  ruthenium-  -81-  phosphine complexes d i s c u s s e d  e a r l i e r , a phosphine t r a n s to no  comes at l o w f i e l d , a phosphine t r a n s t o a l i g a n d o f low i.e.Cl ,comes s l i g h t l y u p f i e l d , and  trans-influence  a phosphine t r a n s to a l i g a n d of  t r a n s - i n f l u e n c e i.e.P or H ,comes much f u r t h e r u p f i e l d . and  P  have s i m i l a r c h e m i c a l s h i f t s , i t i s not  show d o u b l e t s at 78.0  and  61.3  ppm  due  to P  and  29.0  On warming the exchange p r o c e s s w i l l two  ppm  and  exchange mechanism a l s o e x p l a i n s s i n c e at low  a c h l o r i d e and The  t h e r e f o r e two  P_  r e s p e c t i v e l y , and  to P^, and  i n c r e a s e and  P^  cannot a p p l y  The  proposed  r e g i o n of the ^H-n.m.r.,  w i l l be  t r a n s to a phosphine or  resonances w i l l be  to square p y r a m i d a l i s the Berry  to monomers.  The  i d e a l interbond  angles,  and  pseudorotation,  i t has  p o s i t i o n the s p e c i e s  generated would  be:  but  this  similar, l i t t l e  unreasonable  i n I I I ) t h a t moved i n t o the a  of t r i g o n a l  o n l y been a p p l i e d  f l u x i o n a l p r o c e s s proposed here i s not  s i n c e i f i t were the phosphine (P  to  observed.  here s i n c e i t r e q u i r e s a l l the l i g a n d s t o be  d e v i a t i o n from the  IV  respectively.  mechanism most o f t e n proposed f o r the i n t e r c o n v e r s i o n 79  bipyramidal  Pg  the time average of  observed.  the h y d r i d e  temperatures the h y d r i d e  Assuming that  o  due  n o n - e q u i v a l e n t phosphorus s i t e s w i l l be  high  unreasonable t h a t I I I would  A would show d o u b l e t s at 61.3  ligand  axial  -82-  which would be u n s t a b l e due t o t h e i n t e r a c t i o n between the b u l k y  phosphines  P „ , and h y d r i d e l i g a n d s i n the e q u a t o r i a l p o s i t i o n a r e much l e s s s t a b l e than i n t h e a x i a l  position.  80 (HRuCl(P(p-tolyl)3^2  W h i l s t t h e mechanism f o r rearrangement of  i s f e a s i b l e , f u r t h e r s t u d i e s a r e r e q u i r e d u s i n g a w i d e r range o f tempera t u r e s so t h a t the l i m i t i n g s p e c t r a can then be o b t a i n e d f o r v e r i f i c a t i o n .  4.3  Formation  of a M e t a l - A l k y l S p e c i e s  I n n e i t h e r t h e h y d r i d o c h l o r o b i s - n o r the t r 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 c o n d i t i o n s o f h y d r o g e n a t i o n direct  evidence  olefin  i n s e r t s i n t o the m e t a l - h y d r i d e  f o r f o r m a t i o n o f an a l k y l s p e c i e s v i a (4.2) i n which the  HRuCl(PPh ) 3  n  + olefin  bond:  (alkyl)RuCl(PPh ) 3  There i s however, n.m.r. e v i d e n c e ^ f o r deuterated  A  (4.2)  n  this reversible reaction in  chloroform with ethylene at high pressure  1  i s t h e r e any  (^35 atm  C^H^).  39 H-n.m.r.  of a s u f f i c i e n t l y concentrated  at a h i g h a c r y l a m i d e  s o l u t i o n of  c o n c e n t r a t i o n showed no h i g h f i e l d  s i g n a l which i s a t l e a s t c o n s i s t e n t w i t h e q u a t i o n To c o n f i r m the presence  (HRuCl(PPh )^)^ 3  metal-hydride  (4.2).  o f the a l k y l s p e c i e s i t was d e c i d e d t o  i n v e s t i g a t e t h e b i n d i n g o f an o l e f i n t o t h e more s o l u b l e ( H R u C l ( P ( p - t o l y l ) 3 ) 2 ) 2 complex.  Maleic a c i d ^ h a d  been found n o t t o be c a t a l y t i c a l l y  hydrogenated  w i t h t h e t r i p h e n y l p h o s p h i n e system due t o a v e r y l a r g e b i n d i n g constant, l e a v i n g no h y d r i d e a v a i l a b l e f o r the subsequent h y d r o g e n a t i o n equations  s t e p (see  (3.2) and ( 3 . 3 ) ) ; but t h i s s u b s t r a t e was u n s u i t a b l e f o r t h i s  study due t o i t s i n s o l u b i l i t y  i n t o l u e n e , and so t h e d i m e t h y l e s t e r was  -83chosen.  Dimethyl maleate was c a t a l y t i c a l l y hydrogenated by the t o l y l -  phosphine analogue ([Ru] =2xlO~ M, [olefin]=0.2M, ]H ]=1.76xlO~ M, and 3  3  T  2  30°C) but the maximum rate i s slow (1.4x10 M 5  s ^) , so i t appears to bind  well at least i n terms of the mechanism outlined by equations (3.2-3). The strong binding was confirmed by observing the changes i n the v i s i b l e spectrum of a toluene solution of the complex upon addition of dimethyl maleate.  The l i m i t i n g spectrum, which i s when the presumed a l k y l species  i s f u l l y formed, was obtained upon addition of e s s e n t i a l l y an equimolar amount of the o l e f i n per ruthenium, but a value for the binding constant could not be found due to the problems discussed i n Section  3.2.  A 1:1 mixture of the complex and dimethyl maleate i n toluene-d  D  under  o  argon was prepared, and the  1 31 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 t r i 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 o l e f i n i c protons o r i g i n a l l y 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) i s too broad to be observed but below t h i s temperature i t begins to 31 sharpen up again.  The  1 P{ H)-n.m.r. spectra of the same sample shows  a s u r p r i s i n g l y large number of signals.  At 30°C there are s i n g l e t s at  -846-55  Benzene Impurity  27-0 25-3  i_  J  Figure 4.5  The variable temperature H-n.m.r. spectra of a 1:1 mixture of (HRuCl(P(p-tolyl)J 2* 2 y maleate in toluene-dg. a  n  d  d i m e t h  1  -85-  -86-  45.1 ppm and 39.2 ppm due t o monomer and O P C p - t o l y l ) ^ r e s p e c t i v e l y , two broad reson a n c e s a t 67.9 and 57.0 ppm, and a number o f s i g n a l s o f s m a l l On c o o l i n g , t h e s i g n a l a t 67.9 ppm  p r o p o r t i o n over t h e range 30-75 ppm.  i s r e s o l v e d i n t o an AB p a t t e r n (6 =69.8, 6 =65.6 J=46.5 H z ) , t h e s i g n a l A  at  57.0 ppm a l s o broadens but i s not r e s o l v e d , and t h e r e s t  remained unchanged. to  fi  of the peaks  Due t o a c o n c e n t r a t i o n problem, i t was not p o s s i b l e  o b t a i n s p e c t r a 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 s p e c i e s such as V I , but i t does show a s h i f t i n the o l e f i n i c p r o t o n s which c o u l d r e s u l t  from b i n d i n g as i n V I I .  formed by b i n d i n g o f the o l e f i n ,  Ru.  3ZI  t h i s s u b s t r a t e c o u l d occupy the vacant  ^/ , R  H C C H  2 rC-O^/ r^ C- MH3 *  t o undergo rearrangement due t o s t e r i c the t r i p l e t i n the h y d r i d e  p  ^  H  C Q  2  C H  3  T7TT  *  -  X  u  I  coordination s i t e of the chloro-bridged  H  I f V I I i s the complex  d i m e r ( V I I I ) making i t l e s s interference.  T h i s would e x p l a i n  r e g i o n , which i s broadened s l i g h t l y  R  U  ^  ^ /  V 4  U  ^ ^  P  likely  P=  due t o a  P(p-TOLYL)  h  slow exchange p r o c e s s , t h e broad phenyl and methyl resonances of the  :  -87-  phosphines and t h e AB q u a r t e t observed i n t h e  31  1 P{ H}-n.m.r.  a q u a r t e t i n t h e h y d r i d e would r e q u i r e c o u p l i n g t o t h r e e  To o b t a i n  equivalent  phosphorus atoms which would be p o s s i b l e i f a d i s p r o p o r t i o n a t i o n r e a c t i o n occurs.  The r e a c t i o n between HRuCl(PPh^)^ and C^H^NCHCHNC^H^(DAD) has 81  been shown  t o produce HRuCl(PPh.^(DAD) a t room temperature.  This  complex i s i n e q u i l i b r i u m w i t h a monophosphine compound and a t r i s p h o s p h i n e one,  and i s capable  o f d i s p r o p o r t i o n a t i n g i n t o an i o n i c compound and a  mixture of other n e u t r a l s p e c i e s .  I f d i m e t h y l maleate behaves i n a  s i m i l a r manner t o DAD,the t r i s p h o s p h i n e complex would produce t h e q u a r t e t and t h e monophosphine a doublet which may be concealed beneath o t h e r resonances. D i s p r o p o r t i o n a t i o n of H R u C l ( P ( p - t o l y l ) ^ ) (dimethyl 2  maleate) i n t o v a r i o u s n e u t r a l s p e c i e s would a l s o e x p l a i n t h e e x c e s s i v e  31 number o f resonances i n t h e  P-n.m.r., as c l e a r l y t h e r e i s not j u s t an  a l k y l s p e c i e s i n s o l u t i o n as i s o f t e n proposed  (at l e a s t not w i t h  dimethyl  maleate as s u b s t r a t e ) .  69 Of i n t e r e s t , e a r l y s t u d i e s i n t h i s l a b o r a t o r y maleic  acid  had i n d i c a t e d t h a t  ( i n t e r n a l o l e f i n ) behaved v e r y d i f f e r e n t l y from a t e r m i n a l  o l e f i n such a s hex-l-ene d u r i n g c a t a l y t i c hydrogenation  u s i n g HRuCl(PPh^)^.  Although t h e r a t e laws were o f the same form, v e r y d i f f e r e n t a c t u a l p a r a meters had been a t t r i b u t e d t o d i f f e r e n c e s i n t h e s u b s t r a t e b i n d i n g and subsequent i n s e r t i o n t o g i v e t h e a l k y l s p e c i e s : l HRuCl(PPh ) + o l e f i n ^ = S ± HRuCl (PPh,) ( o l e f i n ) i n 3 n K  0  HRuCl(PPh-) ( o l e f i n ) J n  K  (4.4)  ft * RuCl (PPh ) ( a l k y l ) j n 0  1  (4.5)  -88-  For m a l e i c a c i d ,  was  found  to be l a r g e and K  2  s m a l l (because  d i f f i c u l t y o f h y d r i d e t r a n s f e r to the i n t e r n a l o l e f i n ) , and s p e c i e s present  o l e f i n system.  thus  i n s o l u t i o n at h i g h o l e f i n c o n c e n t r a t i o n was  the a l k y l B^, which was  found  to be present  of  the  the  A and  not  i n the case of the t e r m i n a l  The n.m.r. data i n the present maleate system  t h a t a h y d r i d o ( o l e f i n ) s p e c i e s (and not an a l k y l ) i s a g a i n  support  present.  * S i n c e 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  ( I n o r g . Chim. A c t a , 41, 55 (1980) has been p u b l i s h e d i n  w h i c h t h e a u t h o r s d e s c r i b e t h e f o r m a t i o n o f ( H R u C l ( P P h ) ) - The H-n.m.r. 1  3  3  2  spectrum o f t h i s complex i n C,.D^ shows a h y d r i d e 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. o f t h e same sample shows PH  a s i n g l e a b s o r p t i o n c e n t r e d a t 56.9 ppm. A l l o f t h e s e f e a t u r e s a r e s i m i l a r t o t h o s e found i n t h e ( H R u C l ( P ( p - t o l y l ) ) ) ~ d i m e t h y l m a l e a t e system so 3  2  2  one o f t h e major components produced from t h e d e c o m p o s i t i o n appears t o 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 t h e c a t a l y t i c h y d r o g e n a t i o n o f hex-l-ene by  DMA s o l u t i o n s o f ( H R u C l ( P P h ^ ^ ^ on  [Ru]^,, a f i r s t -  r e v e a l s a near f i r s t - o r d e r  t o z e r o - o r d e r dependence on hex-l-ene,  f i r s t - o r d e r dependence on hydrogen a first-  dependence  predominantly  a t h i g h s u b s t r a t e c o n c e n t r a t i o n , and  to z e r o - o r d e r dependence a t lower s u b s t r a t e c o n c e n t r a t i o n . The  k i n e t i c dependences a r e c o n s i s t e n t w i t h t h e f o l l o w i n g mechanism:  k  HRuCl(PPh ) 3  2  + olefin ^  l fe  " RuCl(PPh > (alkyl) 3  2  (5.1)  k RuCl(PPh ) (alkyl) + H 3  2  2  * H R u C l ( P P h ^ + alkane  (5.2)  T h i s i s q u i t e u n l i k e t h e mechanism found p r e v i o u s l y by o t h e r workers i n t h i s l a b o r a t o r y f o r the h y d r o g e n a t i o n of a c r y l a m i d e u s i n g the same complex. Here f o r m a t i o n o f t h e a l k y l s p e c i e s i s f o l l o w e d by a r e v e r s i b l e  reaction  w i t h another mole o f h y d r i d e to g i v e the s a t u r a t e d p r o d u c t ; t h i s l a s t  step  -90b e i n g Important and o f i n t e r e s t i n t h a t i t i n v o l v e s a c t i v a t i o n o f a C-H bond a t a s a t u r a t e d influenced  carbon c e n t r e .  by the s u b s t r a t e  C l e a r l y t h e mechanism o b t a i n e d i s  b e i n g used, and so a study i n v o l v i n g a  wider range o f o l e f i n s i n c l u d i n g those c a p a b l e o f c h e l a t i n g i s important to e s t a b l i s h the f a 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  s p e c t r o p h o t o m e t r i c s t u d i e s of the r e a c t i o n s between  (HRuCl(PPh^) ) 2  and  hex-l-ene, triphenylphosphine,  and l i t h i u m c h l o r i d e were  but  little  be o b t a i n e d from them due to h a v i n g  q u a n t i t a t i v e data could  more than one s p e c i e s , dimer and monomer, i n i t i a l l y  informative,  present i n s o l u t i o n .  I f the s t u d i e s were c a r r i e d out a t low ruthenium c o n c e n t r a t i o n , the complex would e x i s t  2  where  e s s e n t i a l l y as a monomer, the v a l u e s o f k^/k_^  (3.12), k ( 3 . 2 3 ) , a n d k^(3.28) c o u l d  be o b t a i n e d and compared t o the v a l u e s  2  o b t a i n e d from the k i n e t i c a n a l y s i s . The  isomerisation  o f hex-l-ene by (HRuCl (PPh.j) ) 2  w  2  a  s  e f f e c t e d very  e f f i c i e n t l y , and w i t h f u r t h e r s t u d i e s on the i s o m e r i s a t i o n 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 o r g a n i c Characterisation  synthesis.  of ( H R u C l ( P ( p - t o l y l ) ) ) 3  2  2  i n the s o l i d  p o s s i b l e by a s i n g l e c r y s t a l x - r a y d i f f r a c t i o n study. complex t o be a c h l o r o - b r i d g e d  Variable  r e v e a l the s o l i d  showed the  as a r e s u l t of the s m a l l  hydride  temperature n.m.r. s t u d i e s o f t h i s complex d i d not  state structure  c o u l d not be o b t a i n e d .  i n s o l u t i o n s i n c e the l i m i t i n g  Examination of the n.m.r. s p e c t r a  range o f temperatures should a l l o w the  This  s t a t e was  dimer w i t h a d i s t o r t e d square p y r a m i d a l  s t r u c t u r e about each ruthenium c e n t r e ligands.  of a c t i v a t e d  spectra  over a wider  the i n t e r e s t i n g f l u x i o n a l behaviour of  f i v e - c o o r d i n a t e dimer t o be e l u c i d a t e d .  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