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Kinetics and mechanism of hydrogenolysis of a ruthenium(II) acyl complex Joshi, Ajey Madhav 1986

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KINETICS AND MECHANISM OF HYDROGENOLYSIS OF A RUTHENIUM!II) ACYL COMPLEX  by AJEY MADHAV JOSH I B.Sc, M.Sc,  University of Poona, Poona, India, 1980  Indian I n s t i t u t e of Technology, Bombay, India, 1983  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in  THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMISTRY  We accept t h i s thesis as conforming to the required standard  The University of B r i t i s h Columbia September, 1986 © Ajey Madhav J o s h i , 1986  In  presenting  degree freely  at  this  the  available  copying  of  department publication  this or of  thesis  partial  fulfilment  University of  British  Columbia,  for  and  reference  thesis by  this  in  for  his thesis  scholarly  or for  her  Department  D a t e  DE-6(3/81)  O c f - \1  purposes  Columbia  the  requirements  I agree  I further  that  agree  may  be  It  is  representatives.  financial gain  permission.  The University of British 1956 Main Mall Vancouver, Canada V6T 1Y3  study.  of  shall  not  that  the  permission  granted  an  advanced  Library shall  by  understood be  for  allowed  for  the that  without  make  it  extensive  head  of  copying my  my or  written  ii  ABSTRACT  This thesis describes the results of k i n e t i c investigations into the hydrogenolysis of the ruthenium-acyl complex dicarbonylchloro(norbornenoyDbis(triphenylphosphine)ruthenium(II ),RuCl(C0'C H ) (C0) 7  (PPh ) » 2. 3  9  2  N,N-Dimethylacetamide (DMA) and toluene solutions of 2 react  2  with one mole equivalent of H  to give HRuCl(C0) (PPh ) , 3, and the  2  2  unsaturated aldehyde product C^HgCHO, 4. hydrogenation of 4 by a further mole of H  3  2  The subsequent, r e l a t i v e l y slow 2  to give the saturated aldehyde  CyH-jiCHO, 5, was found to be catalyzed by 3. A detailed k i n e t i c study on the hydrogenolysis of 2 in DMA solvent revealed a f i r s t - o r d e r rate dependence on LRuJjotaV  a  n  inverse dependence  on added [PPh^], and a f i r s t - to zero-order dependence on H  2  pressure.  The following mechanism is proposed to account f o r these observations:  l  k  RuCl(C0«C H )(C0) (PPh ) 7  9  2  3  2  >  <  [RuCl(C0'C H )(C0) (PPh )] 7  g  2  3  + PPh  3  -l  k  k, [RuCl(C0«C H )(C0) (PPh )] + H 7  9  2  3  •  2  [HRuCl(C0) (PPh )] 2  K' [HRuCl(C0) (PPh )] 2  3  + PPh  3  ^  •  HRuC1(C0) fPPh l :  3  :  3  + C H CH0 7  9  Values of k-j and k_-j/k have been evaluated at 65°C (k-j = 4.6±0.5xl0 2  s~\  k_-|/k = 1.7±0.2) and the a c t i v a t i o n enthalpy and entropy f o r the k-j 2  step determined (AH* = 69±7 kJmole" , As* = -126+13 JK" 1  mole' **  1  1  New, and as yet incompletely c h a r a c t e r i z e d , ruthenium complexes of stoichiometry " R u C l ( C H ) ( P P h ) " , 6, 6  9  3  H  2  RuCl(C H )(C H )(PPh ) -benzene 6  8  6  g  3  2  s o l v a t e " , 7, and RuCl^CgHg) ( P P h ) , 8, have been synthesized by the 3  reactions of 1,4-cyclohexadiene and 7 ) , and R u C l ( P P h ) 2  3  3  2  (CgH ) with HRuCl(PPh ) 'C Hg (complexes 6 Q  3  (complex 8 ) , r e s p e c t i v e l y .  3  6  Reactions of 6, 7,  and 8 in DMA with H and with CO were i n v e s t i g a t e d , and the organic and 2  inorganic products i d e n t i f i e d :  [H RuCl(PPh ) ] • C H 2  CO  3  2  2  6  1 2  [ H R u C l ( C 0 ) ( P P h ) + CgHg 2  3  2  No reaction  RuCl (CO) (PPh ) 2  2  3  2  + C H 6  8  TABLE OF CONTENTS  Paoe ABSTRACT  ii  TABLE OF CONTENTS  iv  LIST OF TABLES  viii  LIST OF FIGURES  ix  LIST OF ABBREVIATIONS  xii  ACKNOWLEDGEMENTS  xiv  Chapter I .  INTRODUCTION. .  1  1.1  General Introduction  1  1.2  Homogeneous Hydrogenation  3  1.2.1  Hydrogen A c t i v a t i o n  4  1.2.2  Hydrogenolysis  7  1.2.3  Substrate A c t i v a t i o n  8  1.3  Hydroformylation  11  1.4  Aim of Work  18  EXPERIMENTAL  19  Materials  19  2.1.1  Solvents  19  2.1.2  Gases  19  2.1.3  Other Materials  19  2.1.4  Ruthenium Compounds  Chapter I I . 2.1  . .  20  V  Page 2.1.4.1  Dichlorotris(triphenylphosphine)- . . ruthenium(II)  2.1.4.2  20  Chlorohydridotris(triphenylphosphine)mthenium(II) - benzene solvate . . .  2.1.4.3  Bromohydri d o t r i s ( t r t phenyl phosphine)ruthenium(II) - DMA solvate  2.1.4.4  23  24  24  Reaction of HRuCl(PPh )«C H with 1,43  6  6  cyclohexadiene 2.2.2  23  Carbonylchloro(propiony1)bis(triphenylphosphine)ruthenium(II)  2.2.1  .  Dicarbonylchlorohydridobis(triphenylphosphine)ruthenium(II)  2.1.4.8  22  Dicarbonylchloro(norbornenoyl)bis( t r i phenyl phosphine)ruthem'um( II)  2.1.4.7  . .  Bromohydrido(norbornadi ene)bis(triphenylphosphine)ruthenium(II).  2.1.4.6  21  Chlorohydrido(norbornadiene)bis(triphenylphosphine)ruthenium(II)  2.1.4.5  21  25  Reaction of R u C l ( P P h ) 2  cyclohexadiene  3  3  with 1,428  VI  Page 2.3  Instrumentation  28  2.4  Gas-uptake Apparatus  31  2.4.1  The Apparatus  31  2.4.2  Procedure for a Typical Experimental Run . .  34  2.4.3  Measurement of Gas S o l u b i l i t i e s  35  Chapter I I I . RESULTS AND DISCUSSION  37  3.1  The Ruthenium-acyl Complex  3.2  Hydrogenolysis of R u C l ( C 0 « C H ) ( C 0 ) ( P P h ) , 2 . . . 7  3.2.1  3.2.2 3.3  37 9  2  3  2  Stoichiometry of the Reaction, and Product Identification  40  Rate Measurements  45  Analysis of the K i n e t i c Data 3.3.1  58  Dependence of the Rate on Ruthenium Concentration, [Ru]j  3.3.2  Dependence of the Rate on Added PPh  59 3  Concentration 3.3.3  38  61  Dependence of the Rate on Hydrogen Concentration  3.4  Dependence of the Rate-constant on Temperature  3.5  Discussion  61 . .  63 67  vii  Page Chapter IV.  4.1  REACTIONS OF RUTHENIUM(II)-CYCLOHEXADIENE COMPLEXES  72  R e a c t i o n s of " R u C l ( C H ) ( P P h ) " , 6  72  6  g  3  2  4.1.1  R e a c t i o n of " R u C l ( C H ) ( P P h ) " , 6, w i t h H  4.1.2  R e a c t i o n of " R u C l ( C H ) ( P P h ) " , 6, w i t h CO  6  6  g  3  g  3  2  2  2  72 75  4.2  R e a c t i o n s of R u C l ( C H g ) ( P P h ) , 8  75  4.3  Discussion  77  Chapter V  2  6  3  2  GENERAL CONCLUSIONS AND SOME RECOMMENDATIONS FOR FUTURE WORK  82  5.1  General C o n c l u s i o n s  82  5.2  S u g g e s t i o n s f o r F u t u r e Work  83  REFERENCES  84  viii LIST OF TABLES  Table  TItie  Page  III-l  H solubility data in DMA at 65°C  II1-2  Kinetic data for hydrogenolysis of RuCl(C0*C H )7  g  (C0) (PPh ) in DMA at 65°C  51  Temperature dependence of k.u  65  2  III-3  49  2  3  2  L I S T OF FIGURES Figure  1.1a - 1.1c  Title  Page  Schematic r e p r e s e n t a t i o n of t h e types of metal hydrogen i n t e r a c t i o n s  1.2  5  Schematic r e p r e s e n t a t i o n of i n t e r a c t i o n between a metal and an a l k e n e  2.1 2.2  X  9  H n . m . r . spectrum of R u C l ( C H ) ( P P h ) 2  Anaerobic spectral  cell  6  g  3  used f o r  2  i n CDC1  3  UV-visible  spectroscopy  30  2.3  The c o n s t a n t - p r e s s u r e gas uptake apparatus  3.1  A typical  rate plot for H  2  . . . .  3 1  P{ H} 1  (b,c)  39 n . m . r . s p e c t r a i n DMA of 2, (a) b e f o r e and a f t e r h y d r o g e n o l y s i s by H , and t h a t of (d) an 2  a u t h e n t i c sample of H R u C l ( C 0 ) ( P P h ) 2  3  41  2  3.3  H i g h f i e l d H n . m . r . spectrum of £ i n CDC1  3.4  Gas chromatograms i n t o l u e n e of (a) the  l  m i x t u r e a f t e r ~ 1 mole e q u i v a l e n t H  3  . . . .  7  A typical  uptake by 2,  2  3.6  44  9  r a t e p l o t f o r t h e consumption of  second mole of H  0  the  by DMA s o l u t i o n s of 2 at 65°C  Rate p l o t f o r t h e H R u C l ( C O ) ( P P h ) 2  h y d r o g e n a t i o n of C H CH0 7  Q  3  43  reaction  (b) a s t a n d a r d s o l u t i o n of C H CH0 3.5  32  uptake by £ i n DMA at  65°C 3.2  29  2  -  46  catalyzed 47  X  LIST OF FIGURES Figure  Ti t i e  Page  3.7  H  3.8  Rate p l o t s f o r the hydrogenolysis of 2 in DMA,  2  s o l u b i l i t y i n DMA at 65°C  50  at 65°C, at various [Ruly 3.9  A rate plot analyzed f o r 1st order Ru-dependence, [Ru]  3.10  53  = 7.58xlO" M  54  3  y  Dependence of the hydrogenolysis rate on [Ru]j at 65°C  3.11  55  Dependence of the rate on added [PPh.,], at constant -3 [ R u ] (4.56x10 M), under 1 atm H pressure . . . . T  3.12  2  56  Dependence of the rate on the H pressure at [Ru]j= 2  4.56 x 10" M (a) without and (b) with added PPh 3  3  (9.66xlO" M)  57  4  3.13  Plot of l o g ( i n i t i a l  rate) against log([Ru]y)  3.14  Dependence of 1/rate on added PPh according to equation 3.10  3.15  3  . .  concentration . . . . .  62  Dependence of the rate on [H 3 according to 2  equation 3.10 3.16  60  64  Dependence of the rate-constant for hydrogenolysis of 2 on temperature  66  xi  LIST OF FIGURES • Figure 4.1  Title Rate p l o t f o r H  2  Page  uptake i n DMA by " R u C l ( C g H ) g  ( P P h ) " at 25°C 3  4.2  Rate p l o t f o r CO uptake i n DMA by " R u C l ( C g H ) g  (PPh ) \ 3  4.3  73  2  2  at 30°C  ?  6  Rate p l o t f o r CO uptake i n DMA by R u C l ( C H ) 2  (PPh ) , 3  2  at 50°C  6  g  78  xii  LIST OF ABBREVIATIONS  The f o l l o w i n g l i s t of abbreviations, most of which are commonly adopted in chemical l i t e r a t u r e , w i l l be employed in t h i s t h e s i s : 13  C( H} 1  proton broad-band decoupled carbon n.m.r.  Cp  cyclopentadienyl, C^H^  CYHD  cyclohexadiene, C H  DMA  N,N-dimethylacetamide,  dppe  l,2-bis(diphenylphosphino)ethane  Et  ethyl, C H  i.r.  infra-red  J  coupling constant, Hz  L,L'  ligands  In  natural  M  molar concentration or metal atom  Me  methyl, CH  n.m.r.  nuclear magnetic resonance  P  phosphine ligands or pressure  31  6  2  P{ H}  PPh  1  Ptol [Ru]  CH C0N(CH ) 3  3  2  (C H ) PCH CH P(C H ) 6  5  2  2  2  6  5  2  5  logarithm  3  proton broad-band decoupled phosphorus n.m.r. triphenylphosphine,  3  8  (CgH ) P 5  3  3  tri(p-tolyl)phosphine,  (p-CH C H ) P  T  t o t a l i n i t i a l concentration of R u C l ( C 0 » C H ) ( C 0 ) ( P P h )  3  g  4  3  7  UV  ultra-violet  X  halide ligands, CI, Br or I  9  2  3  xiii  6  chemical s h i f t , ppm  e  molar e x t i n c t i o n  v  frequency, cm~^  coefficient  Some of the compounds used during the course of t h i s work have been referred to by numeral symbols in t h i s thesis f o r the sake of b r e v i t y and s i m p l i c i t y .  Following is the l i s t of complexes corresponding to each  such symbol:  Symbol  Compound  1,  HRuCl(NBD)(PPh )  2  RuCl(C0'C H )(C0) (PPh )  3  HRuCl(CO) (PPh )  4  C H CH0  5  C H -,CH0  3  7  9  2  2  7  7  2  3  3  2  2  g  1  "RuCl(C H )(PPh ) " 6  9  3  2  "RuCl(C H )(C H )(PPh ) -benzene 6  g  6  8  3  RuCl (C Hg)(PPh ) 2  6  3  solvate"  2  2  0  II C0»R denotes acyl  substituent-(-C-R)  XIV  ACKNOWLEDGEMENTS  I am extremely grateful to Professor B.R. James f o r his expert guidance and encouragement throughout the course of t h i s work.  I thank  him for his time and utmost patience. I am indebted to Dr. Ian Thorburn for his assistance and helpful discussions throughout.  I also thank members of the James gang f o r t h e i r  support and f r i e n d s h i p , and f o r making useful suggestions regarding t h i s work in general. I wish to express my gratitude to Mr. David Thackray for proof-reading some early d r a f t s . The assistance and cooperation of various departmental are g r a t e f u l l y acknowledged.  services  1  CHAPTER I INTRODUCTION  1.1  General Introduction Catalysis remains one of the most active f i e l d s of chemical  research  and has been highlighted in the Pimentel report* as one of key  significance.  The last three decades have witnessed an ever-increasing  interest in the study of homogeneous c a t a l y s i s resulting i n tremendous advances and development in the area. organometallic  A large number of coordination and  compounds, p a r t i c u l a r l y those of t r a n s i t i o n metals, have  been tested for c a t a l y t i c a c t i v i t y toward a wide range of chemical reactions; these include hydrogenation of unsaturated organic o l e f i n isomerization, dehydration of t e r t i a r y alcohols,  substrates,  hydroformylation,  and water-gas s h i f t reaction, to name but a few. The r e l a t i v e merits and demerits of homogeneous and heterogeneous catalysts, especially from an industrial point of view, have been widely 3-6 discussed. "  Homogeneous c a t a l y s i s offers the following advantages over  the i n d u s t r i a l l y more prevalent i)  heterogeneous c a t a l y s i s :  Higher a c t i v i t y of homogeneous catalysts allows use of milder reaction conditions.  ii)  Higher s e l e c t i v i t y , s p e c i f i c i t y , and reproducibility of homogeneous catalysts are strongly desirable for industrial processes.  i i i ) C a t a l y t i c properties of homogeneous catalysts may be varied systematically by changing the ligands.  2  iv)  Ease of k i n e t i c and mechanistic studies of homogeneous systems by conventional spectroscopic  and k i n e t i c techniques allows f o r more  detailed mechanistic investigations. Oxygen- and moisture-sensitivity can be a problem in homogeneous c a t a l y s i s , but the principal drawback i s the d i f f i c u l t y i n separation of the reaction product(s) from the soluble catalyst.  However, i n recent  years attempts have been made to overcome this problem by anchoring homogeneous catalysts on either insoluble inorganic  supports such as  s i l i c a , alumina and z e o l i t e s , or on organic polymer supports such as polystyrene cross-linked with divinylbenzene ( D V B ) . ^  A drawback of such  cross-linked supports i s the nonequivalence of active s i t e s because of differences in a c c e s s i b i l i t y and microenvironment with resulting  8 differences in a c t i v i t y and s t a b i l i t y .  However, this problem may be  solved by using noncross-1inked polymer supports such as polyamides which also exhibit superior mechanical and thermal s t a b i l i t i e s compared to the  Q cross-linked styrene supports. A major thrust in research  on metal cluster compounds i s  9-11 supposedly aimed at mimicking c a t a l y t i c s i t e s at a surface  and, to a  lesser extent, development of "heterogenized" homogeneous c a t a l y s t s .  1 0 - 1 2  In a related vein, a better knowledge of homogeneous c a t a l y s i s p a r t i c u l a r l y at a c l u s t e r s i t e may lead to a better understanding of  9-14 heterogeneous systems. The number of industrial processes currently using homogeneous catalysts i s s t i l l  r e l a t i v e l y small.  These processes include the Wacker  process, the Oxo process, methanol carbonylation,  oligomerization of  3  d i e n e s , and some Z i e g l e r - N a t t a  systems.  Use of homogeneous c a t a l y s t s c o n t a i n i n g c h i r a l s y n t h e s e s of o p t i c a l l y r e c e n t developments. published. ^" 1  1 9  ligands  for  a c t i v e amino a c i d s i s one of t h e most e x c i t i n g , A number of comprehensive reviews have been  Currently,  t h e Monsanto Chemical Company u t i l i z e s  W i l k i n s o n - t y p e rhodium(I) c a t a l y s t w i t h c h i r a l  diphosphine ligands  a for  l a r g e s c a l e asymmetric s y n t h e s i s of t h e amino a c i d drug L-Dopa w h i c h used f o r t r e a t m e n t of P a r k i n s o n ' s d i s e a s e .  Homogeneous c h i r a l  systems a r e b e i n g deployed a l s o f o r i n d u s t r i a l of L - a s p a r t i c  a c i d and L - p h e n y l a l a n i n e ,  is  catalyst  s c a l e asymmetric  synthesis  which a r e used i n t h e s y n t h e s i s of  a p o p u l a r sugar s u b s t i t u t e food a d d i t i v e ,  aspartame - a methyl e s t e r of  the  20 dipeptide L-aspartyl-L-phenylalanine  - b e t t e r known by i t s  tradename  "Nutrasweet". 1.2  Homogeneous H y d r o g e n a t i o n Although the f i r s t  r e p o r t on homogeneous hydrogenation dates back  t o t h e y e a r 1938 when C a l v i n r e p o r t e d c a t a l y t i c r e d u c t i o n of quinone t o 21 hydroquinone u s i n g a cuprous a c e t a t e - q u i n o l i n e system, the early s i x t i e s that i n t e r e s t  i t was only  i n t h i s area r e c e i v e d a b o o s t .  Some of  t h e p i o n e e r i n g work was done by H a l p e r n ' s group i n t h i s U n i v e r s i t y 1953-61.  between  2 2  Partly potential  in  because of h i s t o r i c a l  commercial a p p l i c a t i o n s ,  reasons and p a r t l y because of  a major p o r t i o n of t h e v a s t  obvious  literature  on homogeneous c a t a l y s i s accumulated t o d a t e d e a l s w i t h homogeneous 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 o r g a n i c s u b s t r a t e s .  A number of  systems  4  have been studied i n considerable d e t a i l and t h e i r mechanisms deduced. L i t e r a t u r e on homogeneous hydrogenation, both c a t a l y t i c as well as s t o i c h i o m e t r i c , i s very well-documented. comprehensive reviews *  "  sections are also a v a i l a b l e .  A number of e x c e l l e n t ,  and s p e c i a l i z e d t e x t s , books and book 27-31  The four basic processes occurring during homogeneous hydrogenation of an unsaturated substrate by a t r a n s i t i o n metal complex are: i)  a c t i v a t i o n of molecular hydrogen  ii)  substrate a c t i v a t i o n  iii)  hydrogen t r a n s f e r to the substrate  iv)  release of the substrate and, in the case of a c a t a l y t i c r e a c t i o n , regeneration of the c a t a l y s t .  1.2.1  Hydrogen A c t i v a t i o n C a t a l y t i c properties of a metal complex are determined to a great  extent by the coordination number and electron configuration of the 32 metal. A c t i v i t y and s p e c i f i c i t y of a hydrogenation c a t a l y s t are further influenced by the e l e c t r o n i c properties, including it-effects, a-effects, 33 and also the s t e r i c properties of the surrounding l i g a n d s .  These  f a c t o r s supposedly provide the basis f o r c a t a l y s t design. For a metal complex to be able to a c t i v a t e hydrogen or the substrate, coordinative unsaturation at the metal centre i s usually  5  essential. unreactive  Coordinatively  saturated  complexes, which generally are  toward hydrogen f o r lack of a vacant active s i t e , may become  active in solution through dissociation of a l a b i l e ligand. surprisingly, complexes with d  8  Not  electron configuration which are often  coordinatively unsaturated, or the d  6  complexes which can e a s i l y become so  by loss of a ligand, constitute the largest group of hydrogenation catalysts.  However, complexes of T i , Hf, Zr and Nb which have d  electron configurations  have also been investigated f o r possible  2  or d  3  catalytic  34 a c t i v i t y with positive r e s u l t s . The nature of interaction between molecular hydrogen and a metal complex is also dictated by the electronic and s t e r i c properties of the 3 33 surrounding ligands; ' the p r i n c i p a l types of such an interaction are 24,33a (Fig. 1.1c). i) end-on (Fig. 1.1a, 1.1b) and i i ) sideways interaction  M  H, acts as an electron donor Fig.  H  M  1.1a  2  H acts as an electron acceptor 2  Fig.  1.1b  M  3-centre,2-electron t r a n s i t i o n state Fig.  1.1c  6  Kubas and co-workers  35  have reported i s o l a t i o n of molybdenum and  tungsten phosphine complexes with side-on bonded H the t r a n s i t i o n s t a t e as in F i g . 1.1c.  l i g a n d , analogous to  2  More recently, Morris et a l .  have  s u c c e s s f u l l y i s o l a t e d s i m i l a r iron and ruthenium r) -dihydrogen complexes 2  of the type t r a n s - [M( n - H ) (H) (dppe) ] B F 2  2  2  V  The c r y s t a l s t r u c t u r e of the  i r o n complex c l e a r l y shows the symmetrically coordinated -n -H l i g a n d . 2  2  The energetics of hydrogen a c t i v a t i o n have important consequences on the c a t a l y t i c a c t i v i t y of the metal complex;  while too strong a metal-  hydrogen (M-H) bond may retard or even prevent the t r a n s f e r of hydride to the coordinated substrate, too weak an i n t e r a c t i o n between the metal and hydrogen may r e s u l t in a concentration of the M-H species too small to achieve an appreciable reaction r a t e . 37 As noted by Halpern,  a c t i v a t i o n of hydrogen may involve  a) homolytic cleavage, b) di hydride formation, or c) o v e r a l l  heterolytic  s p l i t t i n g ; these can be represented by the general equations 1.1-1.3.  Homolytic  splitting  (1.1a) (1.1b)  Dihydride formation  (1.2)  Heterolytic  (1.3)  splitting  7  Further,  hydrogen a c t i v a t i o n may l e a d t o h y d r o g e n o l y s i s of a 38  m e t a l - m e t a l l o i d bond  such as M-Ge, M - S i , but most commonly a  m e t a l - c a r b o n (M-C) bond ( e q .  R-MX  n  +  1.4).  H 2  H-MX  h  +  (1.4)  R-H  These d i f f e r e n t p r o c e s s e s of hydrogen a c t i v a t i o n have been d i s c u s s e d  in  39 40 detail  In a number of review a r t i c l e s on h y d r o g e n a t i o n .  '  Of  p a r t i c u l a r r e l e v a n c e t o t h e t o p i c of t h i s t h e s i s i s t h e h y d r o g e n o l y s i s m e t a l - c a r b o n bonds, which w i l l  be c o n s i d e r e d b r i e f l y  of  in the f o l l o w i n g  section. 1.2.2  Hydrogenolysis H y d r o g e n o l y s i s , which f o r m a l l y resembles a net  heterolytic 38  splitting,  i s e x e m p l i f i e d by t h e r e a c t i o n s shown below ( e q s .  1.5-1.7).  (1.5) (1.6) (1.7)  8  The importance of s t u d i e s on h y d r o g e n o l y s i s can h a r d l y be o v e r e m p h a s i z e d , c o n s i d e r i n g t h a t a v a s t m a j o r i t y of s t o i c h i o m e t r i c as w e l l as c a t a l y t i c  h y d r o g e n a t i o n and h y d r o f o r m y l a t i o n r e a c t i o n s  h y d r o g e n o l y s i s of m e t a l - c a r b o n bond as t h e f i n a l  step.  involve  3 8 , 4 1  In a d d i t i o n ,  i n a number of i n s t a n c e s h y d r o g e n o l y s i s of metal a l k y l o r a r y l p r o v i d e s a way of g e n e r a t i n g t h e c a t a l y t i c a l l y  a c t i v e hydride  Such i s presumably t h e c a s e w i t h Z i e g l e r hydrogenation systems ( e q s . 1.8a - 1 . 8 c ) .  derivatives species.  catalyst  A l k e n e h y d r o g e n a t i o n c a t a l y z e d by  Z i e g l e r - t y p e c a t a l y s t s p r o b a b l y i n v o l v e s h y d r o g e n o l y s i s of t h e metal formed a f t e r i n i t i a l  alkyl  a l k y l a t i o n of t h e metal complex by an a l k y l a t i n g 42  agent such as A 1 R ; t h i s l e a d s to t h e c a t a l y t i c a l l y ?  MX  n  + R A1 o  RMX HMX  . n-i  R A1X + R-MX  0  n-i  0  c  + H  HMX  9  c  + ^/ C = C \  /  • >  1.2.3  HMX . .n-1  a c t i v e monohydride.  . n-1  (1.8a)  . + R-H n-1  (1.8b)  R'-MX  (1.8c)  n-1  k  Substrate A c t i v a t i o n F o r h y d r o g e n a t i o n t o p r o c e e d , c o o r d i n a t i o n of t h e u n s a t u r a t e d  s u b s t r a t e to t h e metal catalytic cycle.  i s u s u a l l y necessary at some stage d u r i n g t h e  C o o r d i n a t i o n of an u n s a t u r a t e d o r g a n i c s u b s t r a t e ,  as an a l k e n e , to metal  i s v i s u a l i z e d as o v e r l a p of t h e f i l l e d  such  n-donor  9  o r b i t a l s of t h e a l k e n e w i t h t h e o - a c c e p t o r o r b i t a l s of t h e metal (Fig.  1.2).  The s y n e r g i s t i c  i n t e r a c t i o n - back d o n a t i o n of  d e n s i t y from f i l l e d metal non-bonding o r b i t a l s t o t h e empty  electron antibonding  o r b i t a l s of t h e a l k e n e - f u r t h e r h e l p s s t a b i l i z e t h e m e t a l - a l k e n e bonding.  Fig.  1.2  R e d u c t i o n of e l e c t r o n d e n s i t y on t h e c o o r d i n a t e d a l k e n e , e v i d e n c e d by a d e c r e a s e i n t h e double bond c h a r a c t e r , alkene.  activates  as the  The s u b s t r a t e must c o o r d i n a t e t o t h e metal i n a p o s i t i o n c i s  t h e h y d r i d e f o r a subsequent hydrogen t r a n s f e r t o o c c u r .  Electron  w i t h d r a w i n g s u b s t i t u e n t s on an o l e f i n and lower o x i d a t i o n s t a t e of  the  43 metal tend to f a v o u r c o o r d i n a t i o n of t h e o l e f i n . Depending upon whether hydrogen a c t i v a t i o n precedes or substrate activation,  follows  r e a c t i o n pathways of h y d r o g e n a t i o n have been  to  10  c l a s s i f i e d as o c c u r r i n g v i a 1) a h y d r i d e or s a t u r a t e r o u t e and i i )  an  u n s a t u r a t e r o u t e , r e s p e c t i v e l y ; t h e former i s encountered more f r e q u e n t l y . A l k e n e h y d r o g e n a t l o n c a t a l y z e d by H R u C l ( P P h ) 3  example of t h e h y d r i d e r o u t e ( e q s . 1.9a,  3  p r o v i d e s an e x c e l l e n t  1.9b).^  -P HRuClP  3  + alkene  HRuCl ( a ! k e n e ) P ^ I — • RuCl ( a l k y l ) ? 2  2  (1.9a)  +P +P  +H,  RuCl(alkyl)P,  RuCl(alkyl)P  HRuClP  3  + alkane  3  (1.9b)  -P Hydrogenation of a l k e n e s c a t a l y z e d by R h C l ( P P h ) 3  3  i s thought  to  proceed by e i t h e r a s a t u r a t e or an u n s a t u r a t e r o u t e depending on t h e  45-47 s u b s t r a t e , but sometimes v i a both t h e r o u t e s s i m u l t a n e o u s l y .  A  s i m p l i f i e d u n s a t u r a t e r o u t e i s shown i n scheme 1 . 1 . Rh C l ( P P h ) 3  3  + a l k e n e j—•  RhCl ( a l k e n e ) ( P P h ) 3  3  \  -PPh.  +PPh alkane  RhCl(alkene)(PPh ) 3  HRhCl(alkyl)(PPh ) 3  +PPh 3  HRhCKalkyl ) ( P P h ) 3  -PPh. Scheme 1.1  2  2  11  1.3  Hydroformylation Discovered by Roelen in 1938,  48  hydroformylation, also known as  the "Oxo" r e a c t i o n , r e f e r s to the addition of carbon monoxide and hydrogen to an alkene to produce an aldehyde as represented by the general equation 1.10.  Hydroformylation i s i n d u s t r i a l l y one of the most  RCH=CH, + CO + H  •  9  RCH~CH,CH0 + RCHCHO  (1.10)  important and widely u t i l i z e d homogeneous c a t a l y t i c processes, with the annual worldwide production of aldehydes from unsaturated hydrocarbons 49 50 running into several m i l l i o n s of tons. l i t t l e direct application.  '  The aldehydes themselves have  However, they serve as excellent intermediates  for the production of commercially more important d e r i v a t i v e s such as alcohols (eqs. 1.11a,1.11b), acids (eq. 1.12), and amines (eq. 1.13), formed by hydrogenation, o x i d a t i o n , and reductive amination, respectively.^ H  RCH CH0  2  o  0  •  RCH CH OH 0  (1.11a)  0  r 2 n  OH RCH CHCHCH0  base  2  R (1.11b) RCH CH CHCH 0H 2  2  2  R  <  H 2  RCH CH=CCH0 2  R  )  12  RCH CH0  [0]  2  •  RCH C00H  RCH CH0 + H + NH 2  2  (1.12)  2  3  •  RCHgCHgNHg  + HgO  (1.13)  R = a l k y l , aryl  A large number of t r a n s i t i o n metal complexes catalyze the 41 50 51 hydroformylation r e a c t i o n ,  '  '  but cobalt and rhodium carbonyls as  well as phosphine - containing d e r i v a t i v e s are by far the most e f f e c t i v e and e f f i c i e n t c a t a l y s t s .  Ruthenium c a t a l y s t s , although not as e f f i c i e n t ,  are promising e s p e c i a l l y because of t h e i r r e l a t i v e l y low cost, high s t a b i l i t y , and high capacity f o r homologation r e a c t i o n s .  Of l a t e , ro  platinum complexes have also received increasing a t t e n t i o n . Hydroformylation has been the subject of numerous exhaustive 54 55 reviews,  '  and while the majority of advanced inorganic chemistry  56 texts  have sections dealing with t h i s t o p i c , a substantial amount of  patent l i t e r a t u r e on hydroformylation continues to be published every year. A number of review a r t i c l e s describe the k i n e t i c s and mechanisms of hydroformylation r e a c t i o n s .  Many cobalt and rhodium systems have been  investigated in considerable d e t a i l .  The studies on the cobalt systems  involve r e l a t i v e l y high temperatures (80-200°C) and high C0/H gas 2  pressures (20-350 atm).  The now generally accepted mechanism f o r  hydroformylation of alkenes catalyzed by Co (C0)g, the hydride HCo(C0) 2  4  being the a c t i v e species, was f i r s t proposed by Heck and Breslow i n 1961, 57 and i s o u t l i n e d in equations 1.14-1.19.  13  Co <C0)  8  HCo(C0)  4  2  HCo(CO) + RCH=CH 3  + H  •  2  •  2HCo(C0)  HCo(C0)  • HCo(CO) (RCH=CH )  2  3  + CO  3  •  2  (1.14)  4  (1.15)  RCH CH Co(C0) £  2  (1.18)  c  CO HCo(C0)  H HCo(C0)  4  o  1  ?  <  3  (1.16)  3  V  RCH CH CH0 2  \ —  2  RCH CH C0Co(C0) 2  2  3  (1.17)  CO Co (C0) 2  Co (C0)  8  2  ?  HCo(CO)  (1.19)  4  In t h e l a t e s i x t i e s , W i l k i n s o n and c o - w o r k e r s d i s s o c i a t i v e (D) as w e l l  suggested  as a s s o c i a t i v e (A) mechanisms f o r  alkene  h y d r o f o r m y l a t i o n c a t a l y z e d by r h o d i u m - t r i p h e n y l p h o s p h i n e systems under CO  mild conditions  (25°C, 1 atm C 0 / H  summarized 1n scheme 1.2.  2  pressure);  t h e mechanisms  The complex H R h ( C 0 ) ( P P h ) 2  key i n t e r m e d i a t e t h a t r e a c t e d w i t h t h e a l k e n e . mechanism was proposed by W i l k i n s o n et a l . f o r  3  2  are  was proposed as t h e  Later, a similar ruthenium-phosphine  59 systems. systems. key a c t i v e  The ruthenium(O) complex R u ( C 0 ) ( P P h ) The r u t h e n i u 2  Intermediate.  3  3  was proposed as t h e  14  15  Based on these and other mechanistic s t u d i e s , hydroformylation of alkenes catalyzed by a t r a n s i t i o n metal complex may be seen as c o n s i s t i n g of: i)  formation of a metal hydride complex, unless the precursor i t s e l f  is  a hydride, ii)  formation of a metal-alkyl intermediate presumably v i a a i t - o l e f i n i c complex,  i i i ) CO i n s e r t i o n to give the corresponding acyl intermediate, and finally, iv)  hydrogenolysis of the acyl complex by a)  to afford the product  aldehyde with regeneration of the metal hydride complex (eq. 1.18), or by b) the metal hydride to give the aldehyde and dinuclear metal precursor (eq. 1.19). The various intermediates involved have been i s o l a t e d and/or characterized s p e c t r o s c o p i c a l l y f o r a number of systems including those of c o b a l t , rhodium, i r i d i u m , and ruthenium. As described e a r l i e r (Section 1.2.1), the k i n e t i c s and mechanisms of the steps ( i ) and ( i i ) have been studied in much d e t a i l in r e l a t i o n to hydrogenation of alkenes.  S i m i l a r l y , voluminous work has been done on  e l u c i d a t i o n of the k i n e t i c and mechanistic aspects of carbonyl  insertion  reactions using manganese a l k y l carbonyls in p a r t i c u l a r . ' ^  The review  6 0  A1  a r t i c l e s by W o j c i c k i ,  A  AO  Calderazzo,  6  and Kuhlmann et a l .  among others  provide e x c e l l e n t , d e t a i l e d accounts of the progress in the understanding 64 of carbonyl i n s e r t i o n r e a c t i o n s .  Recent work from Halpern's group  on  16  nucleophilie c a t a l y s i s of the CO migratory i n s e r t i o n reaction shows evidence f o r a d i s s o c i a t i v e trapping mechanism (Scheme 1.3). L M(C0)R n  + S  L M(C0.R)(S) n  L M(C0.R)(S) + L' n  •  L L'M(C0.R) + S n  s L M(C0)R + L* -—*• n  L L*M(C0.R) n  (S = solvent) Scheme 1.3  In contrast, very l i t t l e i s known about the important product-forming step i n v o l v i n g hydrogenolysis of an acyl complex. problem concerns the general i n s t a b i l i t y of acyl complexes.  A major  Metal-acyls,  e s p e c i a l l y those of group VIII metals, are k i n e t i c a l l y unstable and may undergo very f a c i l e carbonyl d e - i n s e r t i o n as well as reductive elimination reactions, which i s why of course, complexes of cobalt, rhodium, ruthenium, and palladium usually make good hydroformylation and decarbonylation^ c a t a l y s t s . As noted above (see eqs. 1.14-1.19),  hydrogenolysis of the acyl  complex can be accomplished using either H or a metal hydride. 2  The  l a t t e r allows for s t o i c h i o m e t r i c conversion of o l e f i n s to aldehydes (eqs.  66  1.20,1.21).  R-CH=CH + 2HCo(C0) 2  4  •  RCHgCHgCHO + C o ( C 0 ) 2  ?  (1.20)  or a l t e r n a t i v e l y , R-CH=CH + 2HCo(C0) + CO 2  4  •  RCHgCHgCHO + Co (C0)g 2  (1.21)  17  Under hydroformylation conditions, prevail.  however, hydrogenolysis by H  The non-detection of HCo(C0)  consistent with t h i s , ' 6  7  by i . r .  seems to  has been considered  while some recent work of Markd and  coworkers ^~ Veveals more substantial 6  4  2  7(  evidence.  This recent work  involves one of the very few k i n e t i c investigations of hydrogenolysis of an acyl complex by H^. (n-C H *C0)Co(C0) 3  7  that H  2  4  Rate measurements on the reactions of  and ( i - C H « C 0 ) C o ( C 0 ) 3  7  4  with H  2  and with HCo(C0)  4  showed  is less reactive than the carbonyl hydride at lower temperatures  but i t s r e l a t i v e r e a c t i v i t y  increases with temperature so that under the  high temperature and pressure conditions of hydroformylation hydrogenolysis by H The complex reacts with H  2  dominates.  2  acetyldicarbonylbis(trimethylphosphite)cobalt(I)  stoichiometrically  acetaldehyde (eq. 1 . 2 2 ) .  CH «C0Co(C0) [P(0Me) ] 3  2  Thomas,  71  3  2  to form a hydridocobalt species and  7 1  + H  2  •  HCo(C0) [P(0Me) 3 2  3  2  + CH CH0 3  (1.22)  in a study of k i n e t i c s of this hydrogenolysis reaction, reported  at a Chemical Society meeting: i)  a f i r s t - o r d e r rate dependence on the acylcobalt complex concentration and,  ii)  a zero-order rate-dependence on the H  2  pressure.  that the rate c o n t r o l l i n g step involved loss of  It was suggested a coordinated  phosphite ligand, this step being followed by a r e l a t i v e l y reaction with H . 0  fast  18  1.4  AIM OF WORK As pointed out above there are very few reports of k i n e t i c  of hydrogenolysis by H of t r a n s i t i o n metal acyl complexes.  While the  2  recent work of Markd and c o w o r k e r s  6 8 - 7 0  studies  and the report i n 1971 by Thomas  71  concern mainly acyl complexes of c o b a l t , and are probably the only such studies made so f a r , no k i n e t i c studies on hydrogenolysis of ruthenium acyl complexes have been reported. The ruthenium(II) acyl complex,  dicarbonylchlorobis(triphenyl-  phosphine)norbornenoylruthenium(II), R u C l ( C 0 « C H ) ( C 0 ) ( P P h ) , was f i r s t 7  g  2  3  2  17  synthesized and characterized i n t h i s laboratory.  This a i r - s t a b l e ,  6-coordinate, 18-electron ruthenium(II) complex was found in preliminary studies during the present work to react slowly with H , and the system 2  appeared to be an excellent candidate for conducting a d e t a i l e d i n v e s t i g a t i o n into a hydrogenolysis reaction (products, stoichiometry and mechanistic aspects).  The r e s u l t s of t h i s i n v e s t i g a t i o n are described and  discussed in Chapter I I I .  Results of some experiments on related  complexes, branching out from the main body of t h i s work, are included in Chapter IV.  19  C H A P T E R  I I  E X P E R I M E N T A L  2.1  Materials  2.1.1  Solvents Spectral or a n a l y t i c a l grade solvents were obtained from MCB, BDH,  M a l l i n c k r o d t , F i s h e r , Eastman or A l d r i c h Chemical Co.  Benzene, toluene  and hexanes were refluxed w i t h , and d i s t i l l e d from, sodium metal/benzophenone under a nitrogen atmosphere.  N,N'-dimethylacetamide  (DMA) was s t i r r e d with CaH f o r at least 24 h, vacuum d i s t i l l e d at 2  35-40°C, and stored under argon in the dark.  Methanol, ethanol, and  dichloromethane were d i s t i l l e d a f t e r r e f l u x i n g with the appropriate drying agents (Mg/I f o r MeOH and EtOH, P 0 2  2  5  f o r CH C1 ). 2  2  Diethyl ether and .  n-octane were used as supplied without further p u r i f i c a t i o n .  A l l solvents  were deoxygenated p r i o r to use.  2.1.2  Gases P u r i f i e d argon ( H . P . ) , nitrogen ( U . S . P . ) , oxygen ( U . S . P . ) ,  carbon monoxide ( C P . ) , hydrogen (U.S.P.) and ethylene ( C P . ) were obtained from Union Carbide Canada L t d . ; a l l except hydrogen were used without further p u r i f i c a t i o n .  Hydrogen was passed through an Engelhard  Deoxo c a t a l y t i c hydrogen p u r i f i e r to remove traces of oxygen.  2.1.3  Other M a t e r i a l s Reagent grade triphenylphosphine (Strem Chemicals, Inc.) and  20  t r i e t h y l a m i n e (MCB) were used as s u p p l i e d , w i t h o u t f u r t h e r f o r s y n t h e t i c purposes.  Norbornadiene (Eastman) and  purification,  1,4-cyclohexadiene  ( A l d r i c h ) were p u r i f i e d by p a s s i n g through a column of a c t i v a t e d  alumina  ( F i s h e r , A-950 n e u t r a l c h r o m a t o g r a p h i c grade 80-200 mesh) p r i o r t o u s e . 5 - N o r b o r n e n e - 2 - c a r b o x a l d e h y d e was o b t a i n e d from A l d r i c h and p u r i f i e d by vacuum d i s t i l l a t i o n at 58-60°C, and s t o r e d under a r g o n .  Norbornane-2-  c a r b o x a l d e h y d e was p r e p a r e d by h y d r o g e n a t i o n of a methanol s o l u t i o n of t h e norbornene p r e c u r s o r  (5 ml) under a H  (20 ml)  atmosphere (4 atm)  2  u s i n g Pd/C as a c a t a l y s t ; methanol was pumped o f f a f t e r 5 h and t h e p r o d u c t was p u r i f i e d by d i s t i l l a t i o n .  2.1.4  Ruthenium Compounds The r u t h e n i u m , s u p p l i e d on l o a n by Johnson Matthey L t d . , was  o b t a i n e d as R u C l * x H 0 . 3  2  Depending upon t h e b a t c h , t h e ruthenium c o n t e n t  v a r i e d from 35-40%. All  s y n t h e t i c r e a c t i o n s , u n l e s s s p e c i f i e d o t h e r w i s e , were c a r r i e d  out under an atmosphere of a r g o n , employing Schlenk t e c h n i q u e s , as a l l  the  r u t h e n i u m ( I I ) complexes p r e p a r e d i n t h e c o u r s e of t h i s work were s u s c e p t i b l e t o o x i d a t i o n by a i r ,  at l e a s t  in s o l u t i o n .  2.1.4.1 Dich1orotr1s(tripheny1phosphine)ruthenium(II), Hydrated ruthenium t r i c h l o r i d e , r e f l u x e d i n methanol  r e f l u x e d f o r 3 h.  3  2  3  7 3  3  R u C l * x H 0 ( 2 . 0 g, 7 mmol) was 3  2  (400 ml) f o r 15 minutes under a N  s o l u t i o n was then c o o l e d , P P h  RuCl (PPh ) .  2  atmosphere.  (11.5 g, 43.4 mmol) added, and t h e  The  solution  The dark brown product which p r e c i p i t a t e d on c o o l i n g  21  was then f i l t e r e d , washed with methanol and vacuum dried.  Yield - 6.65 g  (99%); calcd. for C ^ H ^ C l ^ R u C:  67.61%, H:  C:  The P{ H} n.m.r. data agree with  67.60%, H:  4.70%, CI: 7.20%.  31  4.69%, CI: 7.41%;  found  !  73r those reported.  2.1.4.2 Chlorohydridotr1s(triphenylphosphine)ruthen1um(II) - benzene solvate, H R u C l ( P P h ) - C H . 3  3  g  7 4 , 7 5  6  A benzene (400 ml) suspension of RuCl (PPh ) (4.5 2  s t i r r e d with triethylamine, Et N 3  for 18 h at room temperature.  3  3  g, 4.7 mmol) was  (0.07 ml, 5.0 mmol) under a H  2  atmosphere  The v i o l e t product was f i l t e r e d , washed  f i r s t with ethanol (3 x 10 ml) to remove Et N«HCl, then with diethyl 3  ether, and vacuum dried.  The complex i s a i r - s e n s i t i v e and blackens after  a few hours exposure to a i r in the s o l i d state. extremely  a i r - s e n s i t i v e and turn green within minutes of exposure to a i r .  Yield - 4.1 g (87%); calcd. for C ^ H ^ C ^ R u C: CI: 20 °C CDC1  3.54%; found C:  71.87%, H:  :  1 7  7 5  71.86%, H:  5.21%, CI: 3.40%.  ~ * PP (RLI-H, q, 26 Hz). 3 those reported in the l i t e r a t u r e .  6  Its solutions are  m  v  R u  5.19%,  _ :  2028 cm" . 1  H  The spectroscopic data agree with  7 4  2.1.4.3 Bromohydridotris(tripheny1phosphine)ruthem'um(II) HRuBr(PPh ) »DMA. 3  DMA solvate,  76  3  A procedure similar to that used for preparation of the preceding compound (Section 2.1.4.2) was followed, but using RuBr (PPh ) as 2  3  3  22  precursor (1.0 g, 0.955 mmol) and DMA (10 ml) as the solvent.  Addition of  a base such as Et N was not necessary as the DMA solvent i s basic enough 3  to react with the HBr formed. (2x2 ml) and vacuum d r i e d .  The v i o l e t product was washed with DMA  S i m i l a r to the preceding compound, t h i s  complex i s a i r - s e n s i t i v e both in s o l i d state as well as in s o l u t i o n . Y i e l d - 0.52 g (51.6%); c a l c d . for CggH^NBrOP-jRu, C: N:  1.33%;  found C:  (literature - 2030). 1652 cm"  1  65.68%, H: 76  5.24%, N:  The i . r .  (literature - 1650),  1.41%.  65.95%, H: v  R u  _  H  :  5.25%,  2035 cm"  1  carbonyl stretch of DMA was observed at very c l o s e to the frequency for the  76  uncoordinated solvent (1660 cm" ) i n d i c a t i n g that the DMA merely occupies 1  a l a t t i c e s i t e in the c r y s t a l , s i m i l a r to the benzene molecule i n HRuCl(PPh ) -C H . 3  6 ° :-16.46 6 6 20  L  C  3  6  77  6  ppm(Ru-H, q, 26 Hz).  U  The precursor RuBr£(PPh ) 3  3  complex was kindly made a v a i l a b l e by  Dr. I. Thorburn of t h i s laboratory.  2.1.4.4 C h i o r o h y d r l d o t n o r b o r n a d i e n e ) b i s ( t r i p h e n y 1phosphine) ruthenium(II),  HRuCl(NBD)(PPh ) . 3  7 5  2  This complex was prepared by adding norbornadiene (2 ml) to a benzene (50 ml) suspension of HRuCl(PPh ) *C H 3  3  then s t i r r i n g f o r 18h at room temperature.  g  6  (1.9 g, 1.9 mmol), and  The r e s u l t i n g red-brown  s o l u t i o n was f i l t e r e d to remove any i n s o l u b l e m a t e r i a l s , and the f i l t r a t e reduced to « 25 ml and added to hexane (100 ml).  The pale brown s o l i d  which p r e c i p i t a t e d on s t i r r i n g for 6-8 h was f i l t e r e d , washed with hexane  23  (2x10 ml) and vacuum dried. C:  68.47%, H:  Yield - 1.0 g (70%); C^H-^ClPgRu requires  5.21%, CI: 4.71%; found C:  31  4.59%.  v _ : R u  H  5.20%,  ?n °r  -i CI:  68.41%, H:  .  2082 cm  1 P{ H) n.m.r. spectrum in CD C1 2  6^ ^  :-8.90 ppm(Ru-H, t , 24 Hz).  showed a single peak at 40.4 ppm.  2  The  72 spectroscopic data agree with those reported in the l i t e r a t u r e . 2.1.4.5 Synthesis of bromohydrido(norbornadiene)b1s(tr1pheny1phosphine) ruthenlum(II), HRuBr(NBD)(PPh ) . 3  2  This compound was prepared by a procedure similar to that used f o r preparing the chlorohydrido counterpart (Section 2.1.4.4), but using HRuBr(PPh ) »DMA (0.45 g, 0.43 mmol) as precursor. 3  The precipitated l i g h t  3  brown s o l i d was washed with diethyl ether (2x5 ml) i n addition to hexane (2x5 ml) on f i l t r a t i o n . C:  64.66%, H:  Br: 31  9.85%.  Yield - 0.265 g (78%); C H B r P R u  4.93%, Br:  v _ : R y  H  43  10.01%; found C:  2108 cm" .  1 P{ H} n.m.r. signal in CgD  2.1.4.6  1  g  3g  2  64.61%, H:  requires  5.04%,  o|°° :-8.43 ppm (Ru-H, t, 24.6 Hz). The C  appeared at 39.4 ppm.  Dlcarbonylchloro(norbornenoy1)bis(triphenylphosphine) ruthenium(II), R u C l ( C 0 - C H ) ( C 0 ) ( P P h ) . 7  9  2  3  72  2  A benzene (15 ml) solution of HRuCl(NBD)(PPh ) (0.3 g, 3  3.6 mmol) was s t i r r e d under CO atmosphere f o r 18 h.  2  The resulting yellow  solution was f i l t e r e d to remove any insoluble materials, and the f i l t r a t e reduced i n volume to « 5 ml.  The yellow product, which precipitated after  addition of hexanes (20 ml) to the f i l t r a t e and s t i r r i n g for 3 h, was then f i l t e r e d , washed with hexane (2x5 ml) and dried in vacuo.  Yield - 0.24 g  24  (73%).  Calcd. for C H 0 C l P R u , C: 4 6  found C:  65.75%, H:  3 9  3  4.61%, and CI: 31  1910 sh;  v  c = Q  :  1610 w.  65.91%, H:  2  The  4.11%, v  C Q  4.66%, and CI:  :  4.24%;  2024 s, 1940 vs,  1 P{ H} n.m.r. s i n g l e t was observed at  30.4 ppm in DMA. The spectroscopic data are in agreement with those 72 reported in the l i t e r a t u r e .  2.1.4.7 D i c a r b o n y l c h l o r o h y d r i d o b i s ( t r i p h e n y l p h o s p h i n e ) r u t h e n i u m ( I I ) , HRuCl(C0) (PPh ) . 2  3  7 8  2  A DMA (20 ml) suspension of HRuCl(PPh ) »CgH 3  was s t i r r e d under CO f o r 18 h. solution.  3  6  (1.0 g, 1 mmol)  The purple suspension changed to a yellow  The s o l u t i o n was concentrated to ~10 ml by removing the DMA  under reduced pressure at ~40°C.  The white s o l i d that p r e c i p i t a t e d out  was f i l t e r e d , washed f i r s t with ethanol (2x5 ml) to remove any traces of DMA, and then with acetone (5 ml), and dried under vacuum. (60%); c a l c d . f o r C g H C 1 0 P R u , C: 3  C:  63.15%, H:  31  4.35%.  2  6  2  CDC1 " • :  4  5 0  63.55%, H: p p m  3  { R u  " ' H  *»  Y i e l d - 0.43 g  4.32%, CI: 1  9  n.m.r. spectrum in DMA showed a s i n g l e t at 39.5 ppm.  A  H z )  *  4.95%; found T  h  e  3 1 p  ^ > H  The spectroscopic  78 data agree with the l i t e r a t u r e data. This complex was also prepared using benzene as solvent instead of DMA f o l l o w i n g a s i m i l a r procedure.  The white s o l i d obtained was washed  with hexane and dried under vacuum. 2.1.4.8  Carbonylchloro(propiony!)bis(tripheny1phosphine)ruthenium(II), RuCl(C0»C H )(C0){PPh ) . 2  5  3  7 9  2  A benzene (10 ml) suspension of HRuCl (CO) (PPh.,) 9  9  (0.3 g,  25  0.42 mmol) was heated at 80°C under an ethylene atmosphere (1.5 atm) f o r 5 h.  Ethanol (10 ml) was added to the cooled s o l u t i o n , a f t e r venting the  excess gas pressure.  The s o l u t i o n was reduced to approximately half the  volume, and the p r e c i p i t a t e d bright yellow s o l i d f i l t e r e d and washed with ethanol (2x5 ml), and dried under vacuum.  R e c r y s t a l l i z a t i o n from  dichloromethane/ethanol produced bright yellow c r y s t a l s of R u C l ( C 0 * C H ) ( C 0 ) ( P P h ) * C H C l , which a f t e r prolonged drying (~3 days) 2  5  3  2  2  2  under vacuum, afforded the propionyl complex RuCl(C0»C H )(C0)(PPh ) 2  Y i e l d - 0.285 g (91%); c a l c d . f o r C H C 1 0 P R u , C: 40  4.76%; found C:  Cl:  1921 s, 1892 s cm"  1  64.66%, H:  35  c  =  Q  :  v and C Q  1920,  1637 vs cm v  c  =  1640),  C  Q  2  4.73%;  : 1950 vs,  ( l i t e r a t u r e - 1957 vs, 1926 s, 1900 s ) ,  7 9  79 ( l i t e r a t u r e - 1643 v s ) .  respectively.  79  v  5.02%.  In dichloromethane s o l u t i o n  were observed at 1946, 1919 and 1640 cm"  Q  3  64.38%, H:  2  4.58%, C l :  -1 v  2  5  The  3 1  1  ( l i t e r a t u r e - 1948,  P { H } n.m.r. in CH C1 showed a s i n g l e ]  2  2  peak at 31.5 ppm. 2.2.1  Reaction of HRuCl(PPh ) »CgHg with 1,4-cyclohexadiene 3  3  In an attempt to prepare a ruthenium(II) hydridodiene complex s i m i l a r to HRuCl(NBD)(PPh ) , and p o s s i b l y the corresponding acyl complex 3  2  by subsequent reaction with CO, a benzene (20 ml) suspension of HRuCl(PPh ) »C H 3  3  6  6  1,4-cyclohexadiene  (0.7 g, 0.7 mmol) was s t i r r e d with 1.3 ml (13.8 mmol) of (CgHg) at ~ 55°C.  The i n i t i a l l y purple suspension,  which changed into a dark red s o l u t i o n over ~ 48 h, was l e f t s t i r r i n g for another 12 h and then cooled to room temperature, reduced in volume to ~ 8 ml and f i l t e r e d to remove the unreacted HRuCl(PPh ) . 3  3  was added to the f i l t r a t e and the s o l u t i o n s t i r r e d f o r 6 h.  Hexane (20 ml) The brown  26  s o l i d that p r e c i p i t a t e d was f i l t e r e d o f f , washed with hexane (2x5 ml) and vacuum d r i e d .  The yellow f i l t r a t e was retained for f u r t h e r work-up.  Y i e l d - 0.23 g (44%); c a l c d . for " R u C l ( C H ) ( P P h ) " , 6  C: Cl:  67.97%, H: 4.70%.  5.26%, C l :  The i . r .  g  4.79%; found C:  3  2  C H ClP Ru, 4 2  68.28%, H:  3 g  2  5.21%,  spectrum showed no Ru-H absorption, and also the  n.m.r. spectrum, which has yet to be f u l l y interpreted, showed no 31 h i g h - f i e l d hydride resonance(s).  The  1 P{ H} n.m.r. spectrum showed j u s t  a s i n g l e t at 40.0 ppm, which is quite close to the norbornadiene analog (40.4 ppm).  This brown complex was extremely a i r - s e n s i t i v e in s o l u t i o n ,  and s o l i d samples exposed to a i r slowly turned green within a few days. The nature of the brown s o l i d i s discussed further in Chapter IV. The yellow f i l t r a t e  (benzene:hexane) obtained along with the brown  product was concentrated to give ~ 2 ml of a dark red o i l . hexane (10 ml) p r e c i p i t a t e d a yellow s o l i d , but much of i t during washing with hexane.  Addition of redissolved  The r e l a t i v e l y high s o l u b i l i t y in a number of  organic solvents (CH C1 , MeOH, acetone, E t 0 ) posed d i f f i c u l t i e s 2  2  l a t i o n of t h i s yellow complex.  2  in i s o -  However, addition of about 5 ml n-octane  to the red o i l followed by r e f r i g e r a t i o n at 0°C f o r 2 days, p r e c i p i t a t e d the yellow complex that was q u i c k l y f i l t e r e d and dried as such under vacuum f o r 2 days.  Y i e l d - 0.16 g.  absorption in the hydride region.  The i . r .  spectrum showed no  The ^H n.m.r. spectrum in CgDg at 20°C  was again complicated, and has not yet been i n t e r p r e t e d ;  there was,  however, a complex pattern of weak high f i e l d signals in the -6 to -7 ppm 31 1 region i n d i c a t i v e of metal hydride(s) i m p u r i t i e s .  The  P{ H} spectrum  showed a broad s i n g l e t at 31.9 ppm, and also a few very low i n t e n s i t y signals which could not be assigned.  27  When the reaction between HRuCl(PPh ) *CgH and 3  3  6  1,4-cyclohexadiene  was c a r r i e d out f o r a longer period of time (~ 100 h instead of 60 h ) , only the yellow product was obtained, no brown complex could be i s o l a t e d . Of i n t e r e s t , benzene solutions of the brown s o l i d , henceforth represented as  ,,  R u C l ( C H ) ( P P h ) " , when heated with excess 1,4-CYHD at ~ 55°C for 6  9  3  2  36 h, also y i e l d e d solutions of the yellow complex.  Based on these  r e s u l t s the chemistry in benzene can be summarized as:  O  -PPh, -V 55 °C  "RuCl(C H )(PPh ) " 6  9  3  (2.1)  2  brown product 55 °C  t  O  yellow product  (2.2)  This yellow complex is t e n t a t i v e l y formulated as "RuCl(C Hg)(CgHg)(PPh ) " 6  3  2  (see Chapter IV) and is probably a benzene solvate ( c a l c d . f o r C H C l P R u , C: 72.35%, H: 5.89%; found C: 71.87%, H: 6.21%). 5 4  5 3  2  Reactions of both the brown and the yellow products with H and 2  with CO were investigated (Chapter I V ) .  These investigations are  incomplete but they do shed some l i g h t on the nature of the brown and the yellow species; f u r t h e r studies are necessary to e s t a b l i s h the exact i d e n t i t y of the two products.  28  2.2.2  Reaction of R u C l ( P P h ) with 2  3  3  1,4-cyclohexadiene  A benzene (30 ml) suspension of R u C l ( P P h ) 2  3  3  (0.5 g, 0.52 mmol)  was s t i r r e d with 1,4-CYHD (0.75 ml, 9.4 mmol) at 60°C f o r 60 h, during which time the dark brown suspension changed to a reddish yellow s o l u t i o n containing a reddish orange p r e c i p i t a t e .  The mixture was reduced in  volume to ~ 10 ml and the c r y s t a l l i n e s o l i d was f i l t e r e d o f f , washed with hexane (2x5 ml), and dried in vacuo.  Y i e l d - 0.20 g (50% based on  " R u C l ( C H ) ( P P h ) " formulation); c a l c d . f o r C H g C l P R u , C:  64.91%,  H:  The  2  6  8  3  4.87%, C l :  2  9.14%; found C:  42  64.95%, H:  3  2  2  4.64%, C l :  9.61%.  U V - v i s i b l e spectrum in DMA showed absorption maxima at 370 nm (e = 1940 M c m ) and ~ 475 nm (broad, z = 480 _1  31 The  _1  M'W ). 1  1 P{ H} n.m.r. spectrum in CD C1 showed a s i n g l e peak at 2  28.9 ppm, and a small amount of free PPh  3  2  (~ 3%) was also observed.  n.m.r. spectrum in CDC 1^ is shown in F i g . 2.1  The set of peaks in the  6 = 7-8 ppm region is assigned to the protons of the two PPh (30 H).  The  3  ligands  The remaining signal at 6 5.40 ppm integrates to 8 H, which i s  assigned to the coordinated diene moiety. Reactions of t h i s complex with H and with CO are discussed in 2  Chapter IV. 2.3  Instrumentation Infrared spectra were recorded on a Nicolet 5 DX FT-IR  spectrophotometer as Nujol mulls between Csl p l a t e s , unless s p e c i f i e d otherwise.  U V - v i s i b l e spectra were recorded on a Perkin Elmer 552A  spectrophotometer with thermostatted c e l l compartments, using anaerobic spectral c e l l s of path length 1.0 or 0.1 cm ( F i g . 2.2).  ro  0.0 ppm Fl  '9-  2  A  :  *  H  n  - - m  r  spectrum of  RuCl (C H )(PPh ) 2  g  8  0  o  '3'2  in CDC1 . 0  1  9*  2  -  2 :  Anaerobic spectral c e l l used f o r U V - v i s i b l e spectroscopy.  31  H and  P{ H}-nuclear magnetic resonance spectra were recorded on  a Bruker WP80 (80 MHz f o r H , 32.44 MHz f o r 1  (300 MHz f o r H , 121.4 MHz f o r 1  31  3 1  P { H } ) , a Varian XL300 1  P { H } or a Bruker WH400 (400 MHz f o r H) 1  l  spectrometer, a l l operating i n Fourier-transform mode, using tetramethyls i l a n e (TMS) and PPh  3  (~ -6 ppm w . r . t . 85% H P0 ) 3  4  as standards.  The  spectrometers were equipped with v a r i a b l e temperature attachments which 31 were used when necessary.  All  P n.m.r s h i f t s are reported r e l a t i v e to  85% H P 0 , with downfield s h i f t s taken as p o s i t i v e . 3  4  Gas chromatographic analyses were performed on a Carle AGC311 (constant temperature) gas chromatograph equipped with a thermal conductivity detector (TCD) as well as a flame i o n i z a t i o n detector (FID), or a temperature programmable Hewlett Packard 5830A instrument equipped with a TCD.  0V101 or 5% Carbowax c a p i l l a r y columns were used with helium  as the c a r r i e r gas. Gas uptakes f o r stoichiometric or k i n e t i c studies were measured on the constant pressure apparatus as described i n the f o l l o w i n g s e c t i o n . Elemental analyses were performed by Mr. P. Borda of t h i s department. 2.4  Gas-uptake Apparatus  2.4.1  The A p p a r a t u s  The constant pressure gas-uptake apparatus, used for  stoichio-  metric determinations and k i n e t i c studies of reactions with small gas molecules H , CO and 0 , i s represented schematically in F i g . 2.3. ?  ?  F i g . 2.3;  The constant pressure gas uptake apparatus.  33  The apparatus consisted p r i n c i p a l l y of three parts, v i z . the reaction v e s s e l , the measurement u n i t , and the gas-handling part. The reaction vessel was a small, pyrex two-neck flask (A) of approximately 25 ml capacity, with a dimpled bottom, and equipped with a dropping side-arm bucket (B).  The flask was connected to a c a p i l l a r y  oil-manometer (F) containing n-butyl phthalate - a l i q u i d of n e g l i g i b l e vapour pressure, at tap E through a f l e x i b l e glass s p i r a l tube (C).  When  clipped to a piston-and-wheel mechanical shaker (G) driven by a Welch v a r i a b l e speed e l e c t r i c motor, the flask could be held immersed i n a thermostatted o i l - b a t h (H) - a four l i t r e glass beaker f i l l e d with s i l i c o n e o i l in an insulated wooden box.  The c a p i l l a r y manometer (F) was  connected through tap I to a gas measuring burette, c o n s i s t i n g of a p r e c i s i o n bored tube (J) of known diameter, and a mercury r e s e r v o i r (K). This measuring unit was thermostatted at 25°C in a water bath (M).  The  gas burette was connected v i a a Fischer and Porter t e f l o n needle valve (0) to the gas-handling part of the apparatus, which included a gas i n l e t ( P ) , a mercury manometer (Q) and a Welch Duo-Seal rotary vacuum pump (R). S t a i n l e s s steel jacketed, e l e c t r i c a l l y i s o l a t e d heating c o i l s were used to heat the two baths.  Thermostatting was achieved by using Juno thermo-  regulators and Merc-to-Merc relay control c i r c u i t s , along with mechanical stirring.  Temperature of the two baths could be maintained w i t h i n  ± 0.05°C of the set temperatures. The gas uptake was measured with a v e r t i c a l l y mounted cathetometer, and times were recorded from a Lab-Chron 1400 timer.  34  I t was extremely i m p o r t a n t t h a t t h e apparatus be m a i n t a i n e d leak-free during a run. greasing a l l  2.4.2  High vacuum A p i e z o n N g r e a s e was used f o r  ground g l a s s j o i n t s and t a p s i n t h e a p p a r a t u s .  P r o c e d u r e f o r a T y p i c a l E x p e r i m e n t a l Run In a t y p i c a l  experiment,  10 ml of DMA ( o r the a p p r o p r i a t e  were p i p e t t e d i n t o t h e r e a c t i o n f l a s k . analytical flask  b a l a n c e i n t h e small  on t h e s i d e - a r m hook.  The complex was weighed on an  sample bucket (B) and suspended i n t h e  The f l a s k was then a t t a c h e d t o t h e  g a s - h a n d l i n g p a r t of t h e apparatus at p o i n t S through t h e g l a s s tube.  After a careful  till  spiral  d e g a s s i n g of t h e s o l u t i o n by a f r e e z e and thaw  s t a t i c vacuum p r o c e d u r e , r e p e a t e d at l e a s t t h r i c e , i n t o the f l a s k  solvent)  t h e gas p r e s s u r e was s l i g h t l y  Taps D and T were c l o s e d , t h e s p i r a l  hydrogen was i n t r o d u c e d l e s s than t h a t  arm and t h e f l a s k  desired.  removed from t h e  g a s - h a n d l i n g p a r t and a t t a c h e d t o t h e c a p i l l a r y manometer (F) at j o i n t E w i t h t h e tap D s t i l l  closed.  The f l a s k was p l a c e d i n t h e o i l  bath  preheated t o t h e d e s i r e d t e m p e r a t u r e , and c l i p p e d to t h e mechanical w h i c h was then s t a r t e d .  The r e s t of t h e apparatus upto tap D was  evacuated k e e p i n g t h e t a p s E,  I , L, N and 0 open.  About 10 minutes  (~25-30 minutes f o r gas p r e s s u r e s o f 0 . 5 atm or l e s s ) were a l l o w e d thermal  shaker  e q u i l i b r a t i o n between t h e r e a c t i o n v e s s e l  t h e shaker was then s t o p p e d .  and t h e o i l - b a t h ,  and  Meanwhile, hydrogen ( o r t h e a p p r o p r i a t e gas)  was a d m i t t e d i n t o t h e r e s t of t h e apparatus u n t i l somewhat lower than t h a t d e s i r e d . a d j u s t e d to t h e d e s i r e d v a l u e .  for  t h e gas p r e s s u r e was  Tap D was opened and t h e p r e s s u r e  35  The needle-valve (0) and taps I and L were closed, and the i n i t i a l reading of the mercury level in the gas measurement burette (J) taken. The gas pressure i n the gas-handing part was raised over that in the reaction f l a s k .  The apparatus was now ready for a run.  The bucket containing the complex was dropped into the s o l u t i o n by turning the side-arm, and the shaker and the timer were s t a r t e d .  For slow  gas uptakes tap E was kept closed most of the time, but was opened ~ 2 minutes before taking a reading to allow for e q u i l i b r a t i o n , and closed again. The gas uptake indicated by the difference in the o i l l e v e l s of the c a p i l l a r y manometer (F) was measured by c a r e f u l l y allowing the gas into the mercury r e s e r v o i r via the needle valve (0) to balance the o i l l e v e l s and noting the corresponding r i s e i n the mercury level of the burette at appropriate time i n t e r v a l s . From knowledge of the diameter of the gas burette, the volume of gas consumed could be c a l c u l a t e d from the r i s e in the height of the mercury level and expressed as moles of gas uptake per l i t r e of s o l u t i o n . _5  The apparatus was p r e c a l i b r a t e d and a value of 1.98 x 10  moles of gas  uptake per centimeter r i s e in the mercury level was c a l c u l a t e d . 2.4.3  Measurement of Gas S o l u b i l i t i e s The gas-uptake apparatus described above was used for  measure-  ment of s o l u b i l i t y of hydrogen in DMA at s p e c i f i c temperatures and pressures.  T y p i c a l l y , DMA (10 ml) was degassed using the freeze-thaw  36  procedure, the taps D and T were then closed, and the flask along with the s p i r a l arm transferred to the c a p i l l a r y manometer.  After the system upto  the tap D was evacuated, hydrogen was introduced, and i t s pressure adjusted approximately to that required.  Tap D was opened and the exact  pressure noted, the taps J , and L, and the needle valve (0) were c l o s e d , and the timer and the shaker s t a r t e d . measured.  The immediate gas-uptake was then  37  CHAPTER I I I RESULTS AND DISCUSSION  3.1  The R u t h e n i u m - a c y l The r u t h e n i u m ! I I )  Complex n o r b o r n a d i e n e (NBD) complex  HRuCl(NBD)(PPh ) ,l 3  2  75 first  r e p o r t e d by W i l k i n s o n et a l . i n 1968,  e x i s t s i n s o l u t i o n as a  s i n g l e isomer, w i t h t h e m e t a l , t h e h y d r i d e , and an a l k e n e n-bond i n a 72 c o p l a n a r c i s arrangement R e a c t i o n of t h i s  which i s f a v o u r a b l e f o r o l e f i n  insertion.  h y d r i d o d i e n e complex w i t h carbon monoxide, d e p i c t e d  in  t h e e q u a t i o n 3 . 1 , i s i r r e v e r s i b l e and l e a d s t o t h e f o r m a t i o n of t h e a c y l complex  dicarbonylchloro{norbornenoyl)bis(triphenylphosphine)-  ruthenium(II), RuCl(C0'C H )(C0) (PPh ) , 7  carbonyl i n s e r t i o n s . , 72 respectively.  9  2  3  2  2, v i a c o n s e c u t i v e o l e f i n and  i n t o t h e m e t a l - h y d r i d e and t h e m e t a l - a l k y l  bonds,  +  HRuCl(C H )(PPh ) 7  g  3  3 CO 2  •  RuCl(C0.C H )(C0) (PPh ) 7  9  2  H  1  2  3  2  (3.1)  38  Detailed  H,  J±  P { H } , and A  C r H } n.m.r. studies, including s e l e c t i v e  homonuclear decoupling experiments, by Dekleva from t h i s laboratory showed that the acyl substituent occupies the thermodynamically less favourable 72 endo p o s i t i o n of the norbornene moiety, as represented by 2. During preliminary studies in the present work, DMA and toluene solutions of 2 were found to absorb H very slowly at 1 atm H 2  and 40-60°C over a period of several hours.  2  pressure  It was decided to i n v e s t i g a t e  t h i s reaction in more d e t a i l with regard to the products, the stoichiometry, and the k i n e t i c s of the r e a c t i o n .  The r e s u l t s and  discussion of these studies are described in the following sections. The bromo- complex HRuBr(NBD)(PPh ) 3  (Section 2.1.4.5)  2  reacted  with ~ 3 mole equivalents of CO in DMA solvent at 30°C to give presumably an acyl complex analogous to 2. 3.2  Hydrogenolysis of R u C l ( C 0 « C H ) ( C 0 ) ( P P h ) , 7  g  2  3  2  2.  The DMA and the toluene solutions of 2 absorbed ~ one mole equivalent of hydrogen over about 20 hours at 65°C under 1 atm pressure of H . 2  The i n i t i a l yellow colour of the solutions became more intense during  the gas uptake.  A t y p i c a l plot of the H -uptake against time in DMA i s  shown in F i g . 3 . 1 .  2  An extremely slow absorption of H was then noted 2  beyond the f i r s t mole equivalent uptake, u n t i l f i n a l l y a t o t a l of ~ 1.9 mole equivalents of H were consumed in ~ 130 hours.  The ' e x t r a '  2  H  2  consumed a r i s e s from hydrogenation of the i n i t i a l l y formed aldehyde  product (see equation 3 . 3 ) . DMA solutions of the propionyl complex RuCl(C0*C H )(C0)(PPh ) 2  f a i l e d to react with 1 atm H„ at 65°C.  5  3  2  2.5 n  2 H  1.5 H  CO VO  0.5 H  0 + 1000  2000  3000  4000  5000  Time , m i n  6000  F i g . 3 . 1 : H uptake by 2 in DMA at 65°C under 760 t o r r H ?  7000  9  pressure.  8000  9000  40  3.2.1  S t o i c h l o m e t r y o f t h e R e a c t i o n , and P r o d u c t  Identification  As seen from t h e F i g . 3 . 1 , t h e DMA s o l u t i o n s of 2 f i n a l l y  absorb  a p p r o x i m a t e l y two moles of h* per mole of t h e ruthenium complex.  This  2  o b s e r v a t i o n i s e x p l a i n e d by ( i ) H  2  h y d r o g e n o l y s i s of 2 by t h e f i r s t mole of  l e a d i n g t o a h y d r i d o r u t h e n i u m p r o d u c t (3) and t h e c o r r e s p o n d i n g  aldehyde ( 4 ) :  RuCl(C0.C H )(C0) (PPh ) 7  9  2  3  + H -  2  2  HRuCl(C0) (PPh ) 2  H  CO  p. C l ^  and ( i i )  | CO  p  P  a relatively  I  Ru  Cl  3  2  + C H CH0 7  g  (3.2)  .CO 'CO  CHO  slow h y d r o g e n a t i o n of 4 t o t h e s a t u r a t e d aldehyde  (5) by a second mole of H : 0  a  39.5  c  30 »4 ppm  3 9 . 5 ppm  30»4 ppm  3 9 . 5 ppm  J  F i g . 3.2:  31n/l. P{ H} n.m.r. s p e c t r a i n DMA at 20°C of (a) 2 (b) 2 + H , a f t e r h e a t i n g f o r 2 h at 65°C ~ 2  ( c ) 2 + H , a f t e r h e a t i n g f o r 20 h at 65°C and (d) t h e a u t h e n t i c sample of H R u C l ( C 0 ) ( P P h ) . 2  2  3  2  42  The hydrogenolysis of 2, i n DMA, was monitored by spectroscopy.  31  1 P{ H} n.m.r.  The spectra are presented in F i g . 3.2 along with that of an  authentic sample of HRuCl(CO) (PPh ) , which was prepared by carbonylation 2  3  2  of a DMA s o l u t i o n of HRuCl(PPh ) «C H 3  3  g  6  (see Section 2 . 1 . 4 . 7 ) .  appeared at 39.5 ppm and grew in i n t e n s i t y as the H  2  A singlet  reaction proceeded;  a f t e r ~ 1 mole equivalent H -uptake the n.m.r. signal due to 2 (30*4 ppm) 2  had disappeared. Removal of DMA from the f i n a l s o l u t i o n y i e l d e d a pale yellow s o l i d which showed strong i . r .  absorption bands at 2042, 2036, 1994 and  1982 c m " , corresponding to those of the carbonyl absorption bands of 1  HRuCl(C0) (PPh ) 2  3  white s o l i d .  (2043, 2035, 1993 and 1981 c m " ) , 1  2  7 8  which however i s a  A weak absorption was also observed at ~ 1886 cm" , which i s 1  c h a r a c t e r i s t i c of an intense yellow photoisomerization product of HRuCl(C0) (PPh ) . 2  3  2  The yellow colour of the product i s o l a t e d from the  uptake solutions i s presumably due to t h i s photoisomerization product, 81 which i s of unknown geometry. F i n a l l y , a high f i e l d hydride resonance 20 °C 1 at 6 Q = -4.49 ppm ( t , 19.4 Hz) i n the H n.m.r. spectrum of 3 3 78 ( F i g . 3.3) confirms the i d e n t i t y of the inorganic product. The complex, H R u C l ( C 0 ) ( P P h ) , was f i r s t prepared in t h i s D C 1  2  3  2  78 laboratory.  Although a number of geometrical isomers are p o s s i b l e , only  one has been i s o l a t e d in pure form (the white s o l i d ) and assigned the c i s - c i s - t r a n s - s t r u c t u r e shown for 3 i n equation 3.2.  43  -2  Fig- 3.3:  High f i e l d  -3  •  i  -4  i  1  -5  1—i  -6  1—t  i  -7 ppm  H n . m . r . spectrum of 3 i n C D C U .  The u n s a t u r a t e d aldehyde p r o d u c t 4 formed d u r i n g the h y d r o g e n o l y s i s was d e t e c t e d and i d e n t i f i e d by gas chromatography by comparison w i t h a c o m m e r c i a l l y a v a i l a b l e sample o f carboxaldhyde. instrument  5-norbornene-2-  U s i n g a 3 m 0V101 column at 100°C on a C a r l e AGC311  equipped w i t h a f l a m e i o n i z a t i o n d e t e c t o r ( F I D ) , a r e t e n t i o n  t i m e of 14.8 min was measured f o r both 4 and t h e a u t h e n t i c sample of C^HgCHO i n t o l u e n e ( F i g . 3 . 4 ) .  D u r i n g h y d r o g e n o l y s i s of t h e CH^C^  s o l u t i o n s of 2, t h e d i s a p p e a r a n c e of t h e a c y l i . r . 1610 c m "  1  was accompanied by t h e appearance of a new i . r .  at 1717 c m " , which i s i d e n t i c a l 1  C,H CH0 i n C H C 1 . o  a b s o r p t i o n band at  0  0  to t h e c a r b o n y l  a b s o r p t i o n band  s t r e t c h of t h e aldehyde  44  F i g . 3.4:  Gas chromatograms of (a) the reaction mixture after ~ 1 mole equivalent H 2 i n toluene, (b) a standard solution of C7H9CHO in toluene.  2  uptake by  45  The product of the hydrogenation reaction 3.3 was s i m i l a r l y detected and i d e n t i f i e d using gas chromatographic techniques, by comparison with CyH^CHO (retention time 13.0 min under the conditions noted above), which was prepared by hydrogenation of the commercially a v a i l a b l e precursor ( 4 ) . The saturated aldehyde (5) could be detected by GC a f t e r approximately 0.9 mole equivalent of H uptake; only ~ 5-10% of 5 was 2  detected a f t e r 1 mole H uptake ( F i g . 3.4). 2  8  rate of about  1  3.5 x 10 65°C ( [ R u ]  An i n i t i a l  Ms  was c a l c u l a t e d for consumption of the second mole of H  2  at  = 4.56 x 1 0 " M, P„^ = 760 t o r r ) in the range 0.95-1.30 mole 3  T  equivalent h" -uptake ( F i g . 3 . 5 ) . 2  A very slow absorption of H was observed by DMA s o l u t i o n of 2  CyHgCHO in the presence of a s t o i c h i o m e t r i c amount of 3 at 65°C, with -8 i n i t i a l rates of the same order of magnitude (~ 10" ) as observed f o r the second mole of H^-uptake by solutions of 2.  The hydrogenation of 4 was  also found to be catalyzed by 3 at 65°C i n DMA; with [Ru] = 4.00 x 10" M 3  and [4] = 0.17 M, an i n i t i a l (Fig. 3.6).  l i n e a r rate of 1.35 x 10~ Ms" was observed 6  1  The data for t h i s s i n g l e experiment suggest the c a t a l y t i c  reaction i s c l o s e to 1st order in unsaturated aldehyde concentration. 3.2.2  Rate Measurements A constant pressure gas-uptake apparatus described e a r l i e r  (Sections 2 . 4 . 1 , 2.4.2) was used to monitor the reaction between the  46  6.5  F l  '9-  3  - 5  A t y p i c a l rate plot f o r the consumption of the second mole of H by DMA solutions of 2 at 65°C, [Ru]y = 4.56xlO" M 3  2  47  Time , s  F1  9-  3  -  6 :  R  6000  7000  a*e P^t for the HRuCl(C0 )(PPh ) -catalyzed hydrogenation of C H CH0 fn DMA at 65°C 2  7  g  3  2  48  ruthenium acyl complex and Hr,.  The H gas-uptakes were measured at t o t a l 2  -3 ruthenium complex concentrations, [Ru]y, ranging from 2.5x10 _3 8.0x10  M, at d i f f e r e n t H^-pressures  to  (190-760 t o r r ) , and at various  temperatures (50-70°C), changing only one parameter at a time.  Most  measurements were made at 65°C, the rates becoming inconveniently slower at lower temperatures.  Rates were measured for the i n i t i a l uptakes of  upto ~ 0.3-0.4 mole equivalents of h^.  DMA was chosen as the solvent over  toluene because of the convenient lower vapour pressure of the former (10-35 t o r r )  8 2  compared to that of toluene (100-300 t o r r )  temperature range employed (50-70°C).  8 3  over the  Of i n t e r e s t , l i t t l e difference was  observed in the rates of the reaction using e i t h e r DMA or toluene as solvent (see TABLE I I I - 2 ) .  The rates of H uptake by 2 remained close to 2  l i n e a r over a longer range (upto ~ 0.4 mole equivalents uptake) than expected.  This l i n e a r i t y of rates, even beyond ~ 0.2 mole equivalents  (20%) i n i t i a l uptake, is presumably due to a d d i t i o n a l contribution from the concurrent hydrogenation of the product aldehyde 4 (more discussion on p. 68) according to reaction 3.3.  Rates calculated from the analyses of  rate data f o r 1st order Ru-dependence w i t h i n i n d i v i d u a l runs in the i n i t i a l ~ 20% region were found to be almost i d e n t i c a l to the i n i t i a l rates measured d i r e c t l y from the respective H uptake plots (see f o r 2  example, F i g . 3.9 and TABLE I I I - 2 ) .  Therefore, i n i t i a l rates, which could  be measured very conveniently, have been employed throughout t h i s study. The s o l u b i l i t y of hydrogen in DMA at 65°C at various h" -pressures 2  was determined using the procedure described in Section 2.4.3, and was found to obey Henry's law at least upto one atmosphere pressure of hydrogen (TABLE I I I - l , F i g . 3 . 7 ) .  The  K value defined as the r a t i o of  49  the molar s o l u b i l i t y of hydrogen [H^] to the hydrogen pressure P(H ) in 2  t o r r , was calculated from the slope to be 2 . 8 6 x l 0  -6  Mtorr" . 1  Further  h ^ - s o l u b i l i t y data at d i f f e r e n t temperatures were taken from e a r l i e r measurements  84  from t h i s laboratory (K = 2.32 , 2 . 7 0 and 2.82x10  _  6  at 30, 50, and 60°C r e s p e c t i v e l y ) .  TABLE 111-1  S o l u b i l i t y of H  P  H  2  in DMA at 65°C.  , torr  [H ] x 10 , M 3  2  760  2.19  570  1.62  380  1.05  190  0.56  K = [H ]/P 2  H  = 2.86xl0"  6  Mtorr"  Mtorr  ,  50  3  2.5 H  H  F i g . 3.7:  H  2  solubility  i n DMA  2  pressure , t o r r  at 65°C.  900  51  TABLE II1-2 •Kinetic data f o r hydrogenolysis of RuCl (C0«C H )(C0) (PPh ) 7  g  2  3  in DMA at 65°C.  [Ru]  X  T  [H ]  I n i t i a l rate x l O , Ms"  2  xlO , M  torr  xlO M  2.50 3.13 3.88 4.56 4.81 6.03 7.58 4.56 4.56 4.56 4.56 4.56 4.56 4.56 4.56 4.56 4.56 4.56 4.56 4.80 4.80  760 760 760 760 760 760 760 660 660 570 380 190 760 570 300 760 760 760 760 760 760  2.17 2.17 2.17 2.17 2.17 2.17 2.17 1.89 1.89 1.63 1.09 0.54 2.17 1.63 0.86 2.17 2.17 2.17 2.17 2.05  3  (a) (b)  a  C  Q  (b) 0.966 M,  t 0 r r  P  (c) 2.42 M,  7  1.11 1.42 1.75 1.95 2.09 2.69 3.40 1.96 1.93 1.99 1.91 2.01. 1.22° 1.09 0.73 0.73 0.53 0.46 0.00 0.679 0.62 b  b c  d  e f  n  100 i > Total : - ( f ) At added [ P P h J x W = +  P  3  7 6 0  torr.  (d) 3.87 M,  (g)  Rate in DMA at 50°C  (h)  Rate in toluene at 50°C.  (e) 4.83 M, and (f) 45.6 M  Error in the rate values is estimated at ~5-105» from least squares analyses of the i n i t i a l - r a t e p l o t s .  1  52  The dependence of the i n i t i a l rates on the t o t a l ruthenium concentration [Rujy, hydrogen pressure, and added triphenylphosphine were studied at 65°C.  The reaction rates were also measured using h^/CO  mixtures in place of hydrogen to study any possible e f f e c t of external CO on the hydrogenolysis.  The k i n e t i c data are summarized in TABLE I I I - 2 .  F i n a l l y , the temperature dependence of the i n i t i a l rates was investigated at a s i n g l e ruthenium concentration in the absence of added PPh^ (TABLE I I I - 3 ) . The rate plots for the hydrogenolysis at 65°C under one atmosphere hydrogen pressure f o r d i f f e r e n t t o t a l ruthenium concentrations ranging _3 between 2.5-8.0 xlO  M can be seen in F i g . 3.8.  The i n d i v i d u a l rate  plots analyzed well f o r a f i r s t - o r d e r dependence on [Ru] (for example F i g . 3.9).  The p l o t of the i n i t i a l rate against the t o t a l ruthenium  concentration is shown in F i g . 3.10 and is f i r s t order in [Ruj-j-. The e f f e c t of added PPh was investigated at a t o t a l ruthenium 3  concentration of 4.56x10  M, under 1 atm H pressure. 2  The rate of  hydrogenolysis was found to decrease with added phosphine as seen in the F i g . 3.11, and at ~ 10-fold excess of PPh  3  no H  2  uptake was observed  over 24 hours. The e f f e c t of varying the H [Ru] PPh  T  3>  = 4.56xl0"  3  2  pressure was studied at  R without and with added PPh  3  ( F i g . 3.12).  Without  a zero-order dependence on H pressure was observed from 760 to 2  190 t o r r , w h i l s t at the added PPh  3  concentration of 9 . 6 6 x l 0 "  4  M, a  decrease in the rate of hydrogenolysis was observed on decreasing the H pressure from 760 to 300 t o r r . of H  9  and CO  2  For a reaction c a r r i e d out under a mixture  53  4.5-  4-  Time , s  F  *9» «83  20000  Rate plots for the hydrogenolysis of 2 fn DMA, at 65°C, at various [Ru]j. [ R u ] x l 0 , M = (a) 7.58, (b) 6.03, (c) 4.81 and (d) 3.88. 3  T  25000  54  -1.8  Rate obtained from the slope -2  3.5xl0" Ms" 7  1  (initial 20% region)  -2.2-  -2.4  o  -2.6-  -2.8-  -3-  -3.2  -r  i  10  5  Fig.  3.9:  Time t,  A r a t e plot analyzed f o r 1 [ R u ] = 7.58 x 1 0 " M 3  T  15  -order  r3  20  x 10 , s  Ru-dependence  i  25  30  i n DMA at 65°C  55  Fl  '9-  3  -  1 0 :  Dependence of the hydrogenolysis rate on [Ru] at 65°C. T  56  57  3  2.5-  0.5-  -T 100  I 200  1  300  1  I  1  400  500  600  1  700  I  1  600  900  pressure , torr  F i g . 3.12:  Dependence of the rate on the H pressure at constant (a) added [PPh ] = 0 (b) added [PPh ] = 9.66 x 10"  [Ru3  T  2  3  [Ru]  3  = 4.56xlO' M 3  T  4  M.  58  ( P „ =660 t o r r and P^Q=100 t o r r ) , the I n i t i a l rate was e s s e n t i a l l y the same as that measured under j u s t 660 t o r r H  3.3  2  (TABLE I I 1 - 2 ) .  Analysis of the K i n e t i c Data To explain the f i r s t - o r d e r dependence on [ R u ] , the inverse T  dependence on added [PPh 3, and the f i r s t - to zero-order dependence on H 3  2  pressure, the f o l l o w i n g mechanism i s proposed:  k  RuCl(C0.C H )(C0) (PPh ) 7  9  2  3  l [ R u C l ( C 0 . C H ) ( C 0 ) ( P P h ) ] + PPh  2  k  9  2  3  [HRuCl(C0) (PPh )] + PPh 2  3  where k p k_^,  and k  2  and K' represents the  (3.4)  [HRuCl(C0) (PPh )] + C H CH0  (3.5)  9  2  3  -l  k [RuCl(C0'C H )(C0) (PPh )] + H — ^ 7  3  7  2  K' — •  3  2  3  HRuCl(C0) (PPh ) 2  3  7  g  (3.6)  2  are the rate constants of the i n d i v i d u a l  steps,  equilibrium constant for reaction 3.6.  Applying the steady-state treatment to the intermediate, [RuCl(C0»C H )(C0) (PPh )], the following rate law i s obtained: 7  9  2  Rate = -  3  d[Ru] dt  T  L =  d[H ] k,k [Ru] [H ] i_ = Li Li dt k_j[PPh ] + k [ H ] ?  ?  T  3  ?  2  2  (3.7)  59  3.3.1  Dependence o f t h e R a t e on Ruthenium C o n c e n t r a t i o n , [ R u ]  T  At constant [ H ] and constant [PPh ] , the rate equation 3.7 2  3  reduces t o :  Rate = k  o b s  -[Ru]  (3.8)  T  where k  =  b 0 b S  k ,k [H ] 9  1  2  9  (3.9)  2  k_ [PPh ]+k [H ] 1  3  2  2  The Ru-dependence was measured in the absence of added PPh » 3  The  f i r s t - o r d e r Ru dependence, evident from the s t r a i g h t - l i n e plots shown i n F i g s . 3.9 and 3.10, requires that the [PPh ] term remains e f f e c t i v e l y 3  constant and/or n e g l i g i b l e .  The independence of the reaction rate on H  2  under the conditions at which the Ru dependence was measured, requires that k [ H ] » 2  2  k _ [ P P h ] , and t h i s coupled with what must be a large value 1  3  f o r K' (since the product i s HRuCl(C0) (PPh ) 2  3  2  and [PPh ] cannot increase 3  markedly during any s i n g l e run), leads to the simple f i r s t - o r d e r in metal. The slope of the plot of l o g ( i n i t i a l (Fig. 4.4xl0"  rate) v s . l o g ( [ R u ] ) also gives n=l T  3.13), where n i s the order of the reaction in Ru. 5  s"  i s obtained from the slope of the plot of i n i t i a l  1  against [ R u ]  A k  T  (Fig. 3.9).  Q b s  value of  rate  60  F i g . 3.13:  P l o t of l o g ( i n i t i a l rate) against l o g ( [ R u ] ) T  61  3.3.2  Dependence o f t h e R a t e on Added P P h  3  Concentration  The rate equation 3.7 can be rearranged to give:  k  -l  1  1  Rate  k k [Ru] [H ] 1  2  T  2  • [PPh ] + k [ R u ]  (3.10)  J 3  1  T  At constant [Ru]j and [ H ] , therefore, the plot of 1/rate vs. added [PPh ] 2  3  should be a s t r a i g h t l i n e . magnitudes of k_j and k  2  the slope, r e s p e c t i v e l y . with slope = 3 . 5 9 x l 0  9  The rate constant k p  and the r e l a t i v e  can then be c a l c u l a t e d from the i n t e r c e p t , and Such a plot ( F i g . 3.14) gives a s t r a i g h t  sM~ , and intercept = 4 . 8 6 x l 0 2  6  line  s M " , from which a kj 1  value of 4.5xl0~ s~ , and a k_^/k value of 1.6 are obtained for 5  1  2  conditions when [ R u ] = 4.56xlO" M and [H ] = 2.17xlO" M, at 65°C. 3  3  T  3.3.3  2  Dependence o f t h e R a t e on Hydrogen C o n c e n t r a t i o n  Under the conditions that k_ [PPh ] « k [ H ] i n the absence of 1  3  2  2  added PPh , the rate equation 3.7 reduces t o : 3  Rate = kjCRuDj  which i s independent of [ H ] , as found experimentally. 2  4.56x10  (3.11)  For [Ru]j =  M, i n the absence of added P P h , the rates remained reasonably 3  constant between the H pressure range 190-760 t o r r (Table II1-2, F i g . 2  3.12).  However, the rate dependence on [ H ] should eventually go from 2  zero- to f i r s t - o r d e r as the hydrogen concentration i s lowered, when  62  25  OH O  1  1  1  2  1  1  3  4  Added [PPh ] x l O , M 3  3  g. 3.14:  Dependence of 1/rate on added PPh concentration according to 3  equation 3.10 [ R u ] = 4 . 5 6 x l 0 " T  3  M, P  H  = 760 t o r r  5  63  k_-|CPPh-^J  becomes comparable to  s t r i c t l y f i r s t - o r d e r in O^] t i v e l y , the  k_i[PPh^]  »  I^Lr^].  Further, the rate should become  i f and when k_-|[PPh ] » 3  k^CH^].  Alterna-  l^tHg] condition can be achieved by addition of  PPhg, although such an addition would also r e s u l t in an o v e r a l l of the rates due to the inverse dependence on [PPh^].  lowering  The e f f e c t of [H^]  on the r a t e , at an added [PPhg] of 9.66xl0~ M, is shown in F i g . 3.12.  The  4  added [PPh^] of 9.66xl0~ M is apparently not large enough to obtain a 4  strictly first-order  dependence; nevertheless, the decrease in the rate  with the lowering of  pressure reveals the required zero- to f i r s t - o r d e r  transition. According to equation 3.10, the plot of 1/rate against  l/Lh^L  constant [Ru]j and added [PPh^], is expected to y i e l d a s t r a i g h t  at  line;  k-| and k_-|/k2 can be obtained as before from the intercept and the slope, respectively.  For [ R u ] = 4.56xl0" M, at an added [PPh ] = 9.66xl0" M, 3  T  4  3  such a p l o t ( F i g . 3.15) gives a s t r a i g h t l i n e , and values of k-j= 5.0x10"^ s and _1  k_ /k 1  2  = 1 . 9 at 65°C are c a l c u l a t e d from the intercept  sM" ) and the slope ( 7 . 9 4 x l 0 1  3.4  3  (4.43xl0  6  s) of t h i s p l o t .  Dependence of the Rate-constant on Temperature The dependence of k^  on temperature was studied between the  range 50-70°C;  the data are summarized in Table 111-3.  ln(k  1/T y i e l d s a reasonably good s t r a i g h t l i n e ( F i g . 3.16).  Q b s  / T ) vs.  Values of AH* = 69±7 kJmole"  1  The p l o t of  and AS* = -126±13 J K ^ m o l e "  from the slope and the i n t e r c e p t ,  respectively.  1  are calculated  64  F l  '9-  3  -  1 5 :  Dependence of the rate on [ H ] according to equation 3.10, 2  [Ru]  T  = 4.56xl0"  3  M, added [PPh ] = 9 . 6 6 x l 0 ' M 4  3  65  TABLE I I 1 - 3  Dependence of k  Temperature, K  Q b s  on temperature  k  obs ° ' x l  5  323  1.40  328  2.31  333  2.97  338  4.45  343  7.05  s _ 1  66  3.16:  Dependence of the rate-constant f o r hydrogenolysis of 2 on temperature  67  3.5  Discussion The approximate 2 mole equivalent H  uptake by solutions of  2  R u C l ( C 0 « C H ) ( C 0 ) ( P P h ) , 2, is explained by the hydrogenolysis of the 7  9  2  3  2  compound 2 (reaction 3 . 2 ) , and the subsequent hydrogenation of the unsaturated aldehyde product 5-norbornene-2-carboxaldehyde, 4, to the saturated norbornane-2-carboxaldehyde, 5 (reaction 3 . 3 ) .  The inorganic  product of the hydrogenolysis is i d e n t i f i e d as H R u C l ( C 0 ) ( P P h ) , 3. 2  RuCl(C0.C H MC0) (PPh ) 7  9  2  3  +H  2  2  2  3  ~  ~ ?  9  2  • HRuCl ( C 0 ) ( P P h ) + CyHgCHO  2 C H CH0 + H  3  2  — •  Independent measurements of H  2  3  2  (3.2)  4 ~ C H CH0 ?  n  ( 3 > 3 )  uptake by solutions of 4 in the  presence of 3 show that the hydrogenation to 5 is c a t a l y t i c in  The  i n i t i a l rate of hydrogenation measured in t h i s c a t a l y t i c reaction at 65°C, f o r a system with [aldehyde]: [Ru] » 42 was 1.35xlO~ Ms (Ru] = _3 4.00 x 10 M). The i n i t i a l rate of hydrogenation measured f o r a system 6  _1  containing mole equivalents of Ru and aldehyde (at a metal concentration -8  the same as in the c a t a l y t i c system) was - 3 . 8 x 10  Ms  1  .  If the  c a t a l y t i c reaction were f i r s t order in aldehyde substrate, then the -8  expected i n i t i a l c a t a l y t i c rate would be (~ 3.8x10  x42)  i.e.  1.6xlO" Ms"Vhis is close to the experimentally noted 1.35xlO~ Ms"^ value, 6  6  and strongly indicates that the c a t a l y t i c rate is Ist-order in unsaturated aldehyde.  These data are also consistent with the rate of consumption of  68  the second mole equivalent of H  £  3.5xlO~°Ms  ; [ R u ] = 4.56xlO~°M) T  measured during the H uptake by 2 ( F i g . 3 . 5 ) . 2  The hydrogenation of the unsaturated aldehyde, which i s ~ 7 times slower than the hydrogenolysis r e a c t i o n , causes l i t t l e interference in measurement of the i n i t i a l rates of the hydrogenolysis r e a c t i o n .  However,  the rate data analyses f o r a l s t - o r d e r ruthenium dependence w i t h i n a s i n g l e run ( F i g . 3.9) c l e a r l y show a deviation from the s t r a i g h t - l i n e log vs. time p l o t , towards a higher rate than expected, beyond about a 0.7 mole H -uptake.  The additional c o n t r i b u t i o n to the rate of H -uptake i s  2  2  a t t r i b u t e d to the concurrent hydrogenation of 4. The r e l a t i v e l y slow rate of hydrogenation of the unsaturated aldehyde i s consistent with previous f i n d i n g s .  In e a r l i e r studies from  7fth  t h i s laboratory,  3 was found to be q u i t e i n e f f i c i e n t as an o l e f i n  hydrogenation c a t a l y s t , under temperature and H -pressure conditions 2  QC  s i m i l a r to those used during the present work. on the R u C l ( C 0 ) ( P P h 2 ) 2  2  2  Fahey  i n 1973 reported  - catalyzed s e l e c t i v e hydrogenation of diene and  t r i e n e substrates to monoenes, and these reactions were considered to involve 3 as the c a t a l y t i c a l l a y a c t i v e species. conditions were used (130-160°C, 15-20 atm P  ), and the rates were  g  n  Much more severe  2  slowest f o r the hydrogenation of internal alkenes.  C a t a l y t i c a c t i v i t y of  Ru complexes i s commonly found to decrease with the introduction of n-acceptor carbonyl  groups.  86  As mentioned in the Introduction (Section 1.2.1), the presence of a vacant coordination s i t e on the metal i s usually essential f o r H a c t i v a t i o n to take place.  The 6-coordinate ruthenium-acyl complex  2  69  RuCl(CO-CyHg)(C0) (PPh ) 2  3  may become coordinatively unsaturated through  2  loss of a coordinated l i g a n d . The p o s s i b i l i t y of CO d i s s o c i a t i o n from 2 i s ruled out because (a) the rate of hydrogenolysis remains unaffected by the presence of external CO dicarbonyl.  and (b) the ruthenium product i s s t i l l a  Indeed, the k i n e t i c data argue unambiguously for loss of  coordinated phosphine in a slow (kj) step (eq. 3 . 4 ) . The k^ value of 4.5x10  -5  s  -1  obtained from the dependence of the  hydrogenolysis rate on added [PPh^] i s , w i t h i n experimental error, the -5 same as the k  Q b s  value of 4.4x10  -1 s  obtained from the [Ru]j-dependence,  measured i n the absence of added phosphine. c l e a r l y k_ [PPh ] « 1  H  3  k [ H ] (eq. 3.7), with the rate being independent of 2  2  from 190-760 t o r r (0.54-2.17xlO" M). 3  2  Under the l a t t e r conditions,  The steady state concentration of  PPhg must remain extremely low, and indeed the f a i l u r e to detect any free 31 PPh by  1 P{ H} n.m.r. spectroscopy in solutions of 2 means that the  3  equilibrium constant K for the d i s s o c i a t i o n of PPh  3  i s immeasurably small.  In any case, the hydrogenolysis of 2 does not r e s u l t in a build-up of f r e e PPh-j as the reaction proceeds; the equilibrium constant K  1  for reaction  OC  3.6 must presumably be very large,  and the o r i g i n a l l y d i s s o c i a t e d PPh  3  quickly coordinates to the [HRuCl(C0) (PPh )] species to form 3. 2  3  The k_^/k r a t i o of 1.6, obtained from the inverse dependence of 2  hydrogenolysis rate on added [PPh ] ( F i g . 3.14), means that the rates of 3  the phosphine association to, and hydrogenolysis of, RuCl(CO'C^Hg)( C 0 ) ( P P h ) , (eqs. 3.4, 3.5) become comparable at r e l a t i v e l y low added 2  [PPh L 3  3  Consequently, in the presence of added phosphine, the  Hp-dependence i s expected to go from zero- to f i r s t - o r d e r .  Such a s h i f t  70  in h^-dependence i s evident from the data of F i g . 3.12b (Table I I I - 2 ) , even at the r e l a t i v e l y small added [PPh ] of 9.66xlO" M ([PPh ]/[Ru] = 4  3  3  0.21) and, since the [h^] i s of the same order as the [ P P h ] , t h i s 3  immediately implies q u a l i t a t i v e l y that the k_^/k r a t i o i s c l o s e to unity. 2  -5 A l s o , the k^ value of 5.0x10  -1 s  from the H^-dependence data ( F i g .  and the k^/k,, r a t i o of 1.9 obtained 3.15) are in acceptable agreement with  those determined experimentally from the inverse PPh -dependence. 3  The measured AH* value of 69 ± 7 kJmole"  1  f o r the hydrogenolysis  reaction refers to the k^ step and i s thus the enthalpy of a c t i v a t i o n f o r phosphine d i s s o c i a t i o n from 2 i n DMA solvent.  If the activated complex  resembles c l o s e l y the f i v e - c o o r d i n a t e intermediate, then the 69 k J m o l e  -1  could approximate to the bond d i s s o c i a t i o n energy of the Ru-P bond. However, the entropy of a c t i v a t i o n (see below) strongly suggests that s o l v a t i o n of the reaction intermediate i s important, and s o l v a t i o n energies are thus l i k e l y c o n t r i b u t i n g to the o v e r a l l a c t i v a t i o n enthalpy value.  The entropy of a c t i v a t i o n has a large negative value (-126 ± 13  J K m o l e ) , which i n i t i a l l y might appear contrary to the expectation _ 1  - 1  based on a d i s s o c i a t i v e mechanism. negative AS  The only p l a u s i b l e explanation f o r a  must l i e in differences in s o l v a t i o n of the ground state  reactant and activated s t a t e ; the degree of s o l v a t i o n i n the l a t t e r must be greater.  For a t r a n s i t i o n state close to complete d i s s o c i a t i o n of the  phosphine, s o l v a t i o n of the 5-coordinate intermediate and f r e e phosphine could lead to an o v e r a l l negative entropy of a c t i v a t i o n .  A negative AS*  value f o r a rate determining ligand d i s s o c i a t i o n step i s unusual; i n solvents such as toluene the entropy of a c t i v a t i o n i s i n v a r i a b l y  positive  71  f o r such a process.  87  The nature of the solvent (in t h i s system, of  coordinating and polar character) c l e a r l y plays a key r o l e . Hydrogenolysis reactions (cf. eq. 3.2) are known to proceed often v i a o x i d a t i v e a d d i t i o n of H , followed by f a s t reductive e l i m i n a t i o n of 2  the products, TT  Ru H  2  58 59 ' and a 7-coordinate Ru(IV)-H t r a n s i t i o n state or even a 2  ^fi  ?  -(T) - H )  are both p l a u s i b l e ( k - s t e p ) .  2  2  H e t e r o l y t i c a c t i v a t i o n of  seems u n l i k e l y since the hydrogenolysis of 2 proceeds at about the same  rates in both DMA and toluene solvents (Table I I I - 2 ) .  I t would be of  considerable i n t e r e s t to measure the corresponding k i n e t i c s and a c t i v a t i o n parameters f o r the hydrogenolysis reaction in toluene. The i n a b i l i t y of the propiony! complex R u C l ( C 0 ' C H ) ( C 0 ) ( P P h ) , 2  to react with H  2  5  3  i s s u r p r i s i n g in view of the a v a i l a b i l i t y of a vacant  coordination s i t e on t h i s 5-coordinate, supposedly square-pyramidal complex.  2  79  Although blocking of the coordination s i t e by a coordinating DMA  solvent molecule i s p o s s i b l e , the complex is known to react r e v e r s i b l y 79 with CO very r a p i d l y  and t h i s was demonstrated f o r the complex in DMA  solution: RuCl(C0*C H )(C0)(PPh ) + CO 2  5  3  2  RuCl(C0-C H )(C0) (PPh ) 2  5  2  3  2  + CO  — •  RuCl(C0«C H )(C0) (PPh ) 2  c  2  3  2  [Ru(C0-C H )(CO) (PPh ) ]C1 2  5  3  3  2  (3.12)  (3.13)  72  CHAPTER IV REACTIONS OF RUTHENIUM(II)-CYCLOHEXADIENE COMPLEXES  R e a c t i o n s o f new c y c l o h e x a d i e n e d e r i v a t i v e s of r u t h e n i u m ( S e c t i o n s 2.2.1 and 2.2.2) w i t h H and w i t h CO were i n v e s t i g a t e d ; p r e l i m i n a r y 2  r e s u l t s of these s t u d i e s are d e s c r i b e d in the f o l l o w i n g s e c t i o n s .  4.1  R e a c t i o n s of " R u C l ( C H ) ( P P h ) " ,  4.1.1  R e a c t i o n of " R u C l ( C H ) ( P P h ) " ,  6  6  9  3  9  3  2  2  6 6, w i t h H  2  The brown p r o d u c t , 6, o b t a i n e d from the r e a c t i o n o f H R u C l ( P P h ) ' C H w i t h 1,4-CYHD.CgHg, ( S e c t i o n 2.2.1), r e a c t e d w i t h ~ 2.45 3  3  6  6  mole e q u i v a l e n t s o f H p e r Ru i n DMA,  a t 1 atm H p r e s s u r e .  2  2  The H  2  uptake  p l o t i s shown i n F i g . 4.1 and i n d i c a t e s a r e l a t i v e l y r a p i d r e a c t i o n w i t h an i n i t i a l 2 mole e q u i v a l e n t s o f H ,...followed by a much s l o w e r uptake o f 2  the f i n a l ~ 0.5 mole e q u i v a l e n t o f H . 2  The i n i t i a l l y r e d d i s h brown  s o l u t i o n o f 6 t u r n e d deep r e d i n c o l o u r as the uptake p r o c e e d e d . T h e r e a c t i o n was a l s o f o l l o w e d by v i s i b l e s p e c t r o p h o t o m e t r y , and a s i n g l e a b s o r p t i o n maximum was o b s e r v e d a f t e r c o m p l e t i o n o f the r e a c t i o n ( ^ 500 nm, e = 1425 M'^cm" ). 1  solvents.  =  max  The r e a c t i o n a l s o proceeded i n C H C 1 and CgHg 31 1  The room t e m p e r a t u r e  2  2  P{ H} n.m.r. spectrum o f t h e p r o d u c t ( s )  in CgDg showed peaks a t 70.5 and 45.9  ppm.  These r e s u l t s are s i m i l a r t o t h o s e o b t a i n e d by D e k l e v a i n t h i s l a b o r a t o r y d u r i n g an i n v e s t i g a t i o n of the r e a c t i o n o f H R u C l ( N B D ) ( P P h ) 3  1, w i t h H .  7 2 a  2  »  8 8  D e k l e v a f o u n d t h a t 1 r e a c t e d w i t h ~ 2.5 moles of H per 2  mole o f Ru; t h e p r o d u c t s were shown t o be a d i m e r i c r u t h e n i u m complex, [ H c R u C l ( P P h o. ) c] c (X max„ a t 500 nm, e = 1410 M ^ c r r f ; P { H } n.m.r. . 1  9  9  9  2>  3 1  1  3  2.5-  \  1.5-|  EC 1-T  0.5  i  o-To  i  i  i  10  20  30  F i g . 4.1:  Rate plot for H  i  40  2  I  50  I  60  Time x 10" , 3  I  s  70  —r90  ao  100  110  uptake in DMA by "RuCl(CgHg)(PPh ) " at 25°C  [Ru] = 2.72x10"° M.  3  2  Inset - I n i t i a l portion of the rate plot  expanded.  74  at 7 0 . 8 and 4 6 . 1 ppm i n C D ) , and f r e e norbornane {eq. 4 . 1 ) . g  HRuCl(NBD)(PPh ) 3  + 2.5 H  2  1 • -[HgRuCl(PPh ) 3  2  2  3  1  [H RuCl(PPh ) ] 2  3  2  2  + C H y  (4.1)  1 2  by gas chromatography.  s i m i l a r to r e a c t i o n 4 . 1 , t h e r e a c t i o n between 6 and H  " R u C l ( C H ) ( P P h ) " + 2.5 H 9  3  2  Interestingly,  2  1 •_[H RuCl(PPh ) D 2  3  2.2), also reacted with H  2  3  8  3  2  2  can be w r i t t e n as:  0  + C H  3  g  g  g  (4.2)  1 2  2  obtained  w i t h 1,4-CYHD ( S e c t i o n 2 . 2 . 1 , eq.  (~ 4 mole e q u i v a l e n t s of H  "RuCl(C H )(C H )(PPh ) -benzene g  2  based on t h e  solvate" formulation;  4 . 5 mole  e q u i v a l e n t s would be expected f o r a r e a c t i o n such as 4.2a) to g i v e p r o d u c t s which were found to be i d e n t i c a l  to t h o s e formed i n  reaction  4.2.  1 " R u C l ( C H ) ( C H ) ( P P h ) " + 4.5 H g  9  g  be  Therefore  t h e y e l l o w complex, 7, t h e second product  from t h e r e a c t i o n of H R u C l ( P P h ) » C H  g  must c l e a r l y  2  by comparison of t h e s p e c t r o s c o p i c d a t a , w h i l e c y c l o -  2  hexane was d e t e c t e d q u a l i t a t i v e l y  g  '  2  The i n o r g a n i c product of t h e r e a c t i o n of 6 w i t h H  6  72a 88  g  8  3  2  ?  •  -D^RuCl(PPh ) ] 3  2  2  + 2 C H g  1 2  (4.2a)  75  4.1.2  R e a c t i o n o f " R u C l ( C H ) ( P P h ) " w i t h CO 6  9  3  2  DMA solutions of 6 rapidly reacted with CO (1 atm) at 30°C.  The  brown s o l i d turned y e l l o w i s h , instantaneously, in the s o l i d s t a t e on i n t r o d u c t i o n of CO to the r e a c t i o n - f l a s k .  This was then followed by CO  uptakes of ~ 1.7 - 1.85 mole equivalents per mole of Ru ( F i g . 4.2) by the s o l u t i o n which gradually turned from reddish brown to yellow in colour during the uptake.  The inorganic product of t h i s reaction was i d e n t i f i e d  as H R u C l ( C 0 ) ( P P h ) , 3, by 2  i.r.  3  31  2  P { H } n.m.r. (39.5 ppm, s i n g l e t ) and also by 1  spectroscopy ( v : 2042, 2033, 1992 and 1982 c m " ) . 1  C Q  The <2 mole  equivalent uptakes are a t t r i b u t e d to what appears to be a s o l i d s t a t e reaction of 6 with CO. (PPh ) 3  2  Thus, u n l i k e the reaction between HRuCl(NBD)-  and CO which leads to the formation of the acyl complex (Section  3 . 1 ) , the reaction of 6 with CO presumably r e s u l t s in diene displacement with r e s u l t i n g formation of the dicarbonyl species, 3 (eq.  " R u C l ( C H ) ( P P h ) " + 2 CO 6  9  3  4.3):  • H R u C l ( C 0 ) ( P P h ) + C Hg  2  2  3  2  Reaction of the yellow "RuCl(C H )(C Hg)(PPh ) -benzene g  g  g  (4.3)  g  3  2  solvate",  7, with CO in benzene also resulted in the formation of 3.  4.2  Reactions of R u C l ( C H g ) ( P P h ) , 8 2  6  3  2  DMA solutions of 8 f a i l e d to react with 1 atm H at 65°C. Previous 2  work from t h i s laboratory has shown that a norbornadiene analogue, R u C l ( N B D ) ( P t o l ) , i s also unreactive towards H under comparable 2  3  89 conditions.  2  2  2.5 n  1.6-  3 QZ  0.5 H  °1 0  1  1000  1  2000  1  -r  3000  4000  i  5000 Time ,  F l  '9- - 4  2  1  6000  -i  7000  1  6000  1  9000  s  Rate plot for CO uptake in DMA by "RuCl ( C g H g H P P h ^ " , at 30°C [Ru] = 2.32xl0" M 3  r  10000  11000  77  However, 8 was found to react with CO, and at 50°C under 1 atm CO DMA solutions of 8 absorbed ~ 1.9 mole equivalents of CO ( F i g . 4 . 3 ) .  The  i n i t i a l l y orange s o l u t i o n changed to pale yellow during the uptake, while 31 a new peak appeared at 16.9 ppm in the  1 P{ H} n.m.r. spectrum,  accompanied by the simultaneous disappearance of the 28.9 ppm signal due to 8.  The inorganic product was i d e n t i f i e d as  cis-cis-trans RuCl (CO) (PPh ) 2  2  3  by comparison of the 90  2  with those reported in l i t e r a t u r e .  P{ H} n.m.r. data  Thus, 8 almost c e r t a i n l y undergoes a  diene displacement by CO as shown below: RuCl (C H )(PPh ) 2  4.3  6  8  3  2  + 2 CO  •  RuCl (C0) (PPh ) 2  2  3  2  + CgH  g  (4.4)  Discussion  The brown complex 6 has the stoichiometry RuCl(CgHg)(PPh ) , and 3  2  consistent with t h i s when reacted with H , 6 takes up ~ 2.5 mole equiva2  lents of H and forms [ H R u C l ( P P h ) ] 2  2  3  2  2  and free cyclohexane (eq.  4.2).  The expected formulation "HRuCl(CgH )(PPh ) " has problems in that a Ru-H Q  could not be detected f o r 6 by i . r .  3  2  or ^H n.m.r. spectroscopy;  t h i s seems  to support the existence of a cyclohexenyl (or n - a l l y l ) product rather than a 'hydridodiene' species (eq. 4 . 5 ) .  A l t e r n a t i v e l y , such non-  detection of a hydride may r e s u l t from a f a s t e q u i l i b r i u m conversion between the hydridodiene species and the species r e s u l t i n g from hydride t r a n s f e r (eq. 4 . 5 ) .  2.5  •  1000  F i g . 4.3:  •  •  2000  3000  I  4000  Time , s  I  l  5000  Rate plot for CO uptake 1n DMA by R u C l ( C H g ) ( P P h ) 2  [Ru] = 4.00 x l O ' M 3  I  6000  6  3  7000  2  at 50°C  8000  79  HRuCl(CgH )(PPh ) 8  Ru  3  RuCl(C H )(PPh ) 6  ;  H  6a  9  3  (4.5)  2  Ru  Ru  6b  6c  etc.  Some support for such an equilibrium i s provided by the r e a c t i v i t y of 6. The reaction of 6 with CO results in the formation of HRuCl(C0) (PPh ) 2  3  2  by  a net displacement of the diene, while 6 reacts with a further mole of 1,4-cyclohexadiene leading to the formation of the yellow complex, 7, which appears to contain both the C H g  C  "RuCl(CgH )PPh )J 9  6 8, H  and the diene (CgHg) moieties:  (4.6)  "RuCl(C H )(CgHg)(PPh ) " 6  3  g  9  3  2  7  6  That 7 takes up ~ 4 mole equivalents of H , and y i e l d s the same products 2  as those obtained during reaction 4.2,  is consistent with the formulation  shown. The "RuCl(CgH )(PPh ) " species i s extremely reactive. 9  3  2  For  example, the species turns yellow in the s o l i d state in the presence of CO.  These r e a c t i v i t y observations can be rationalized i f 6 existed at  least p a r t i a l l y as the coordinatively and/or e l e c t r o n i c a l l y  unsaturated  80  "hydride t r a n s f e r r e d " (6b, 6c) species, which must then react with CO 91 almost instantaneously.  Werner and Feser  have reported on a rapid  equilibrium conversion between a Rh(III) hydridoethylene complex and the corresponding ethyl-comp1 ex: [CpRhH(C H )PMe ] 2  4  — •  +  3  [CpRh(C H )PMe ] 2  5  (4.7)  +  3  The hydridoethyl ene complex was found to undergo ethylene replacement by CO and not give an acyl i n s e r t i o n product, and yet y i e l d e d an e t h y l ethyl ene- comp 1 ex on reaction with C H : 2  [CpRhH(C H )PMe ] 2  4  [CpRhH(C H )PMe ] 2  + CO  +  3  4  •  4  [CpRhH(C0)PMe ] + C H  (4.8)  +  3  2  4  + ^ ^T~^ [ C p R h ( C H ) ( C H ) P M e ]  +  3  2  2  5  2  4  (4.9)  +  3  S i m i l a r l y , the chemistry of 6 would be consistent with a rapid equilibrium 1 shown in eq. 4 . 5 .  Low temperature  H and  13 C n.m.r. studies are required  to e l u c i d a t e f u r t h e r the exact nature (geometry, configuration i n solution) of 6 (and 7 ) . The i n v e s t i g a t i o n of the reaction between 1,4-cyclohexadiene and RuCl (PPh ) 2  3  3  (Section 2.2.2) was prompted by the i n t e r e s t in the nature of  6 and 7. The orange product, 8, obtained during t h i s reaction has the stoichiometry R u C l ( C g H ) ( P P h ) , consistent with displacement of a 2  phosphine by diene. in  CDC1  3  g  3  2  I n t e r e s t i n g l y , low temperature *H n.m.r. studi<  show that a l l 8 protons of the diene are equivalent  (  6 C  DC1  81  5.40 ppm), at least down to -60°C.  The *H n.m.r. chemical s h i f t for the  diene protons i s close to that reported by Bennett and Smith coordinated arene protons of RuCl (CgHg)(PPh ) ( CDC1 6  2  3  =  3  5 , 3 8  92  f o r the  PP ^* m  One possible explanation f o r the equivalence of the 8 diene protons i s that the 1,4-cyclohexadiene may isomerise to 1,3-cyclohexadiene; rapid movement of the conjugated double-bonds in the l a t t e r , at l e a s t on the n.m.r. time-scale, could then result in the observed equivalence of the 8 protons.  Such isomerization of 1,4- to 1,3-cyclo-  hexadiene (before a subsequent dehydrogenation to an arene d e r i v a t i v e ) has 92  been suggested previously; possibility.  further studies are needed to explore t h i s  82  CHAPTER V GENERAL CONCLUSIONS AND SOME RECOMMENDATIONS FOR FUTURE WORK  5.1  General C o n c l u s i o n s The analyses of the various k i n e t i c data for the hydrogenolysis of  the acyl bond in RuCl(C0'C Hg)(C0) (PPh ) 7  mechanism has been proposed  2  3  2  are internally consistent and a  to account for the data (eqs. 3.4-3.6).  Of  interest, the f i r s t - o r d e r metal-dependence, and the zero-order H -dependence i n the absence of added phosphine, when the rate determining 2  step becomes PPh by Thomas  71  3  d i s s o c i a t i o n , are very similar to the results reported  on the cobalt(I)-phosphite system (Chapter I ) . While the  s i m i l a r i t y in the mechanism of hydrogenolysis of the Co(I) and the Ru(II) systems may  be coincidental, the prospect of a general mechanism involving  ligand dissociation as the primary slow step seems l i k e l y , at least for the hydrogenolysis of coordinatively and e l e c t r o n i c a l l y saturated metal-acyl complexes.  Obviously, more extensive k i n e t i c studies on  related systems, even for complexes of the same metal, are necessary before any conclusion regarding the generality of any mechanism can be 35 reached.  The k i n e t i c i n s t a b i l i t y of metal-acyl complexes  w i l l be a  major hurdle i n attempting systematic k i n e t i c studies on hydrogenolysis of such complexes. A new  ruthenium(II) complex of the stoichiometry  "RuCl(C H )(PPh ) ", 6  9  3  2  6, a CYHD derivative formally analogous to  HRuCl(NBD)(PPh ) , was prepared and i t s reactions with H 3  investigated. analogue,  2  While 6 reacted with H  an attempt  2  ?  and CO  in a manner identical to the  to prepare the corresponding acyl complex by  NBD  83  carbonylation was unsuccessful.  Instead, the reaction of 6 with CO  r e s u l t e d in the formation of HRuCl ( C O ^ ( P P h ^ , presumably through a diene-displacement reaction (eq. 4 . 4 ) .  The product 7 from the reaction  between 6 and 1,4-CYHD seems to have the stoichiometry "RuCKCgHgMCgHg)(PPh ) ". 3  2  Another new complex RuCl^CgHgMPPh.^, 8, was synthesized by  reaction of RuCl^tPPh^)^ and 1,4-CYHD; the diene moiety e x h i b i t s f l u x i o n a l behaviour, that makes a l l 8 protons equivalent even at -60°C.  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