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Activation of hydrogen, olefins, oxygen and carbon monoxide by rhodium complexes in non-aqueous solvents Ng, Flora Tak Tak 1970

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ACTIVATION OF HYDROGEN, OLEFINS, OXYGEN AND CARBON MONOXIDE BY RHODIUM COMPLEXES IN NON-AQUEOUS SOLVENTS  By  FLORA TAK TAK NG B.Sc. M.Sc,  ( G e n e r a l ) , The U n i v e r s i t y o f Hong Kong, 1966 The U n i v e r s i t y of B r i t i s h Columbia, 1968  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE  REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  i n the Department of CHEMISTRY  We accept t h i s required  THE  t h e s i s as conforming t o the  standard  UNIVERSITY OF BRITISH COLUMBIA J u l y , 1970  In  presenting  this  an a d v a n c e d d e g r e e the I  Library  further,agree  for  scholarly  by h i s of  shall  this  thesis  in p a r t i a l  fulfilment  of  at  University  of  Columbia,  the  make  tha  it  freely  permission  available  thesis  for  It  is  financial  gain  of  a The U n i v e r s i t y  V a n c o u v e r 8,  Date  fo^  of  British  Canada  Columbia  J*<Ai. t9/?o  by  shall  requirements  reference copying of  I  agree  and  not  copying or  be a l l o w e d  for  that  study.  this  thesis  t h e Head o f my D e p a r t m e n t  understood that  written permission.  Department  for  for extensive  p u r p o s e s may be g r a n t e d  representatives.  British  the  or  publication  without  my  ABSTRACT  Kinetic  s t u d i e s o f a number o f i n t e r e s t i n g and s i g n i f i c a n t  r e a c t i o n s i n v o l v i n g a c t i v a t i o n o f hydrogen, o l e f i n s , oxygen and carbon monoxide by s o l u t i o n s o f rhodium complexes c o n t a i n i n g s u l p h u r and/or chloride ligands are described. The  c i s 1,2,3-trichlorotris(diethylsulphide)rhodium  ( I I I ) complex,  RhCl.j(Et2S) g and the c o r r e s p o n d i n g d i b e n z y l s u l p h i d e complex, RhCl2(Bz2S).j  i n N,N  -dimethylacetamide  (DMA) s o l u t i o n were found to  be e f f e c t i v e c a t a l y s t s f o r the homogeneous h y d r o g e n a t i o n fumaric and t r a n s - c i n n a m i c a c i d s .  of maleic,  The k i n e t i c data a r e c o n s i s t e n t w i t h  a d i s s o c i a t i o n of a s u l p h u r l i g a n d p r i o r to the hydrogen r e d u c t i o n o f rhodium  ( I I I ) to rhodium  by r a p i d complexing  The rhodium  (I) i s s t a b l i z e d i n s o l u t i o n  w i t h the o l e f i n to produce a R h ' " ( o l e f i n ) ^  complex (L = a u x i l i a r y determining  (I).  l i g a n d s ) which then r e a c t s w i t h  in.a r a t e  step to produce the s a t u r a t e d p a r a f f i n and rhodium ( I ) .  In some i n s t a n c e s , more complex k i n e t i c s r e s u l t e d when one of the auxiliary  l i g a n d s i n the Rh'*" ( o l e f i n ) ! ^ complex d i s s o c i a t e s p r i o r to  r e a c t i o n w i t h B^; a unique t i o n has been observed. catalyzed hydrogenation rhodium  apparent  zero order i n c a t a l y s t  I s o m e r i z a t i o n was observed  i n the RhCl^(Et2S)2  of fumaric a c i d and a mechanism  involving  ( I I I ) a l k y l i n t e r m e d i a t e seems l i k e l y .  The  c y c l o o c t e n e complex, [Rh(C H .) C1]„, i n DMA was found, to be 0  O  a convenient adding  concentra-  i-H  Z  source f o r p r e p a r i n g rhodium  Z  (I) complexes"'in  s i t u " by  the d e s i r e d l i g a n d s , f o r example^ c h l o r i d e or d i e t h y l s u l p h i d e .  K i n e t i c data o b t a i n e d u s i n g such s o l u t i o n s a r e i n good agreement w i t h the h y d r o g e n a t i o n  data o b t a i n e d by s t a r t i n g  from  the c o r r e s p o n d i n g  - iii  rhodium  ( I I I ) complexes.  intermediates from rhodium  -  T h i s r e s u l t c o n f i r m s t h a t rhodium  are i n v o l v e d  i n the c a t a l y t i c h y d r o g e n a t i o n s t a r t i n g  ( I I I ) complexes.  D u r i n g s t u d i e s to i n v e s t i g a t e the e f f e c t of s o l v e n t h y d r o g e n a t i o n of o l e f i n s by rhodium sulphoxide  (DMSO) was  to d i m e t h y l s u l p h i d e BhCl^'3E^0.  The  and  by Rh  2  II][  (DMSO) to produce Rh  (DMSO)H~  RhCl^-SH^O a  hydrogen. [Rh(C H .) C l ] i n DMA o 14 2. L  c o n t a i n i n g L i C l was  Q  o l e f i n s , oxygen and of a rhodium  found  the a c t i v a t i o n of hydrogen  carbon monoxide c o u l d a l s o be  activated.  (I) m o l e c u l a r oxygen complex, Rh^(02) and  subsequent c a t a l y z e d o x i d a t i o n of the DMA in detail.  appears to be  111  the o x i d a t i o n of DMSO to dimethyl, sulphone u s i n g  a v e r s a t i l e c a t a l y s t , f o r besides  were s t u d i e d  and  k i n e t i c s were c o n s i s t e n t w i t h a r a t e d e t e r m i n i n g  s o l u t i o n of  formation  hydrogen  and water i n the presence of R h C l 2 ( E t 2 S ) ^  m i x t u r e of oxygen and  to be  catalytic  ( I I I ) complexes, d i m e t h y l  which then decomposes to the p r o d u c t s i n a f a s t s t e p . also catalyzed  on  found to be c a t a l y t i c a l l y reduced by  h e t e r o l y t i c s p l i t t i n g of H  The  (I)  The  irreversible.  formation An  s o l v e n t and  The a  cyclooctene  of the Rh^(02) complex  E.S.R. s i g n a l , p o s s i b l y due  to  species  II'such as Rh  0^  was  a l s o observed.  suggest the e q u i l i b r i u m f o r m a t i o n r a t e d e t e r m i n i n g step seems l i k e l y . S o l u t i o n s of  k i n e t i c s of the  oxidation  of the Rh^(02) complex f o l l o w e d  to g i v e the p r o d u c t s .  0  1/  converted more s l o w l y  2  species.  by  A f r e e r a d i c a l mechanism  [ R h ( C H ) . C l ] „ i n LiCl/DMA r e a d i l y r e a c t e d o 14- 2. 2,  carbon monoxide to form a R h ^ ( C 0 ) complex was  The  with  A s o l u t i o n of the oxygen  to the R h ^ C O ^ s p e c i e s  in a •  a  -  IV -  r e a c t i o n whose observed r a t e was determined by the d i s s o c i a t i o n of the c o o r d i n a t e d oxygen.  Preliminary  studies  CO and 0^ i s c o n v e r t e d c a t a l y t i c a l l y i n LiCl/DMA.  indicated  t h a t a m i x t u r e of  to CO2 by a s o l u t i o n o f  [RMCgH^^Cl^  TABLE OF CONTENTS Page  ABSTRACT  1  LIST OF TABLES  .  1  xi  LIST OF FIGURES  xiv  ABBREVIATIONS  xix  ACKNOWLEDGEMENTS  xxiv  CHAPTER I .  INTRODUCTION  1  1.1  General  Introduction  1  1.2  Aim and O u t l i n e o f the Work  1.3  C a t a l y t i c A c t i v a t i o n of Molecular  1  Hydrogen  4  1.4  Homogeneous C a t a l y t i c Hydrogenation  1.41  Inorganic Substrates  6  1.42  Organic  8  1.5  M o l e c u l a r Oxygen Complexes and T h e i r Role i n Homogeneous C a t a l y s i s L i t e r a t u r e Reports on C a t a l y t i c P r o p e r t i e s o f Rhodium Complexes  1.6  1.61  ....  Substrates  Rhodium Complexes as  6  12 18  Hydrogenation  Catalysts  18  1.62  C a t a l y t i c Isomerization of O l e f i n s  21  1.63  P o l y m e r i z a t i o n of O l e f i n s and A c e t y l e n e s  23  1.64  C a r b o n y l a t i o n and D e c a r b o n y l a t i o n Reactions  27  1.7  Carbonyl  Complexes o f Rhodium  1.8  M o l e c u l a r oxygen complexes of Rhodium ..  32 34  - vi-  Page CHAPTER I I .  CHAPTER I I I .  APPARATUS AND EXPERIMENTAL PROCEDURE  36  2.1  Materials  36  2.11  Rhodium Complexes  36  2.12  Organic Ligands and S u b s t r a t e s  37  2.13  Gases  38  2.14  Solvents  38  2.15  Other M a t e r i a l s  39  2.2  Apparatus  39  2.3  Procedure f o r a T y p i c a l Gas Uptake Experiment  41  2.4  Gas S o l u b i l i t y Measurements  43  2.5  R e a c t i o n Product A n a l y s e s  43  2.51  Solid  43  2.52  L i q u i d products  44  2.53  Gaseous P r o d u c t s  44  2.54  Solid  45  2.6  Instrumentation  f o r Gas Uptake Measurements...  Organic Products  Inorganic Products  45  CATALYTIC HYDROGENATION OF OLEFINIC ACIDS BY RHODIUM ( I I I ) COMPLEXES CONTAINING SULPHUR LIGANDS  47  3.1  General I n t r o d u c t i o n  47  3.2  Summary of the P r e v i o u s l y S t u d i e d RhCl (Et S) /MA/H /DMA System .' 3  3  2  3  3.21  The I n i t i a l Rate  3.22  The L i n e a r Rate  2  :  4  48 50 5  2  - v i iPage 3.3  RhCl (Et S) 3  of  CHAPTER IV.  2  3  Catalyzed  Hydrogenation  CA i n DMA  '  54  3.31  The I n i t i a l Rate  54  3.32  The L i n e a r Rate  62  3.4  C a t a l y t i c A c t i v i t y of R h C l ( B z S )  3.5  K i n e t i c s of t h e R h C l ( B z S ) Hydrogenation of MA i n DMA  3  3  2  2  2  i n DMA  71  Catalyzed  3  72  3.51  The I n i t i a l Rate  72  3.52  The L i n e a r Rate  77  3.6  The C a t a l y t i c A c t i v i t y o f [ R h C l ( D T H ) ] C l  86  3.7  Conclusion  86  2  2  CATALYTIC HYDROGENATION AND ISOMERISATION OF FUMARIC ACID CATALYZED BY R h C l ( E t S ) i n DMA..  87  4.1  Introduction  87  4.2  S t o i c h i o m e t r y o f the R h C l ( E t S ) / F A / H / D M A System  3  4.3  2  3  3  2  3  2  87  K i n e t i c s o f the R h C l ( E t S ) / F A / H / D M A 3  2  3  2  System  89  4.31  The I n i t i a l Rate  94  4.32  The "Hydrogenation"  4.4  D e u t e r a t i o n and S t e r e o c h e m i s t r y of the H  2  or D  2  Region  addition  98  102  4.5  Hydrogenation  of a M i x t u r e o f FA and MA  4.6  D i s c u s s i o n of the K i n e t i c R e s u l t s f o r the  104  FA System  106  4.61  The I n i t i a l Rate  106  4.62  The "Hydrogenation"  Region  108  - viii Page CHAPTER V.  DISCUSSION OF THE RHODIUM ( I I I ) SULPHUR CATALYSED HYDROGENATION  OF OLEFINS  118  5.1  General D i s c u s s i o n  118  5.11  I n i t i a l R e d u c t i o n , Formation o f a Rh ( o l e f i n ) Complex  119  C a t a l y t i c Hydrogenation  124  1  5.12  CHAPTER V I .  CATALYTIC HYDROGENATION OF MALEIC ACID BY RHODIUM ( I ) CHLORO AND SULPHUR COMPLEXES IN DMA.  I  6.1  General Introduction  130  6.2  Attempted P r e p a r a t i o n s o f the Rh''" Complexes C o n t a i n i n g Sulphur Ligands ...  130  6.3  The R h ( E t S ) I  2  '.  1  3  2  K i n e t i c s o f the R h ( E t S ) C a t a l y z e d I  2  Hydrogenation o f MA  134  6.4  The R h C l C a t a l y z e d Hydrogenation o f MA.  136  6.41  K i n e t i c s o f the Rh^Cl C a t a l y z e d Hydrogen-  I  a t i o n o f MA  147  6.5  D i s c u s s i o n o f the Rh"'" Systems...........  147  6.6  Comparison o f the S u b s t r a t e Hydrogenation Rate i n the R h ! and R h Systems  155  HYDROGEN REDUCTION OF DIMETHYL.SULPHOXIDE CATALYZED BY RHODIUM ( I I I ) COMPLEXES CONTAINING CHLORIDE AND.SULPHIDE LIGANDS  160  7.1  General Introduction  160  7.2  RhCl .3H 0 Catalyzed H  7.3  RhCl (Et S)  1  CHAPTER V I I .  0  C a t a l y z e d Hydrogenation o f  MA i n DMA 6.31  3  3  3  DMSO  2  2  3  1  1  2  R e d u c t i o n o f DMSO  Catalyzed H  2  161  Reduction of 164  - ix -  Page 7.4  Kinetics  7.5  Discussion  172  7.6  C a t a l y z e d O x i d a t i o n and R e d u c t i o n of DMSO by RhCU.3H 0 U s i n g a M i x t u r e of H and 0  178  2  CHAPTER V I I I .  of the C a t a l y z e d Reductions  ...  2  ACTIVATION OF MOLECULAR OXYGEN BY  BIS(CYCLO-  OCTENE)CHLORO RHODIUM (I) IN DMA  182  8.1  Introduction  182  8.2  F o r m a t i o n of the M o l e c u l a r Oxygen Complex  182  8.3  C a t a l y t i c A c t i v i t y of Rh^O DMA  187  8.31  Kinetics  ) in LiCl/  of the C a t a l y t i c O x i d a t i o n  by  the R h ( 0 ) Complex i n LiCl/DMA  191  Other C a t a l y t i c Systems I n v o l v i n g the Oxygenation A c t i v i t y of [ R h C C g H ^ ^ C l ] ^  200  8.5  Discussion  206  8.51  F o r m a t i o n of the M o l e c u l a r Oxygen Complex  206  8.52  F o r m a t i o n of M o l e c u l a r i n Other S o l v e n t s  211  I  2  8.4  8.53  8.54  CHAPTER IX.  165  Oxygen Complexes  C a t a l y t i c O x i d a t i o n C a t a l y z e d by R h ( 0 i n LiCl/DMA I  P o s t u l a t e d Mechanism f o r the Oxidation  FORMATION AND COMPLEXES  PROPERTIES OF  9.1  General  Introduction  9.2  R e a c t i o n of LiCl/DMA  ) 212  Catalytic 214  SOME RHODIUM CARBONYL 222 222  [Rh(CgH ) Cl] l 4  2  2  w i t h CO  in 222  - x -  Page  9.3  C a t a l y t i c R e a c t i o n Between the Coordinated  CHAPTER X.  CO and 0  9.4  Reaction of R h C l ( E t S )  9.5  Discussion  9.51  The [ R h ( C H  9.52  The R h C l ( E t S )  3  g  3  228  2  2  3  w i t h Co i n DMA.  232 l 4  2  ) Cl] 2  3  2  System  System  GENERAL CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK  REFERENCES  APPENDIX I .  230  232 236  238  244  SOLUBILITY DATA FOR OXYGEN IN N,N -DIMETHYLACETAMIDE  258  LIST OF TABLES Page RhCl (Et S) 3  2  I.  3  C a t a l y z e d Hydrogenation of CA i n DMA  The e f f e c t of [Rh], [ H ] , [CA], [ L i C l ] and 2  on the i n i t i a l  [Et S] 2  rate  57  II.  Temperature dependence of k,  60  III.  The e f f e c t of [Rh], [ H ] , [CA], [ L i C l ] and 2  [Et S] 2  on the l i n e a r r a t e IV.  Temperature dependence of h y d r o g e n a t i o n r a t e  RhCl (Bz S) 3  63  2  V.  3  C a t a l y z e d Hydrogenation of MA  Dependence  of i n i t i a l  ....  68  i n DMA  r a t e on [Rh], [H^], [MA],  [ L i C l ] and [Bz S]  74  VI.  Temperature dependence of  78  VII.  Dependence  of l i n e a r r a t e on [Rh], [H,,],  [ L i C l ] and  [Bz S]  2  [MA], 80  2  V I I I . Temperature dependence of the h y d r o g e n a t i o n r a t e .  RhCl (Et S) 3  2  IX.  3  C a t a l y z e d Hydrogenation of FA i n DMA  k' v a l u e s f o r the R h C l ( E t S ) 3  2  3  c a t a l y z e d hydrogen-  a t i o n of FA i n DMA X.  84  90  The e f f e c t of [Rh], [ H J , [FA] and a d d i t i v e s on 2  the  initial  rate  95  XI.  Temperature dependence o f k^  99  XII.  V a r i a t i o n of l i n e a r r a t e w i t h  [FA]  101  - xii Page XIII.  Temperature dependence  Comparison of the Rate and A c t i v a t i o n Different  Rh  XIV.  1 1 1  and O l e f i n  o f k'  103  Parameters f o r the  Systems.  Rate c o n s t a n t s and a c t i v a t i o n parameters f o r the Rh''" ( o l e f i n ) f o r m a t i o n from Rh^"*" i n DMA  XV.  122  Rate c o n s t a n t s and a c t i v a t i o n parameters f o r the h y d r o g e n a t i o n o f Rh''"(olefin) complex i n DMA....  C a t a l y z e d Hydrogenation o f MA by a S o l u t i o n in  o f [Rh(CgH^) C 1 ] 2  127  2  Et S/DMA 2  XVI.  , K i n e t i c data under " a i r f r e e " c o n d i t i o n s  XVII.  Kinetic  XVIII.  Temperature dependence  135  d a t a a t 80°  137 of k^  C a t a l y z e d Hydrogenation o f MA by a S o l u t i o n  139  of [RMCgH^) C l ] 2  2  i n 0.45 M LiCl/DMA  XIX.  K i n e t i c data a t 80°  XX.  Temperature dependence  XXI. Comparison o f k III Rh  2  148 of k  2  151  v a l u e s and a c t i v a t i o n parameters f o r the  I and Rh c a t a l y z e d  h y d r o g e n a t i o n of MA i n DMA  15 6  - xiii Page Rh  1 1 1  Catalyzed XXII.  H  2  Reduction o f DMSO  K i n e t i c d a t a f o r the R h C l . 3 H 0 c a t a l y z e d 3  reduction  2  H  2  o f DMSO  1&  X X I I I . K i n e t i c d a t a f o r the R h C l ( E t S ) 3  2  catalyzed  3  H  2  r e d u c t i o n of DMSO XXIV.  1  6  7  1  7  0  Temperature dependence o f k i n the R h C l . 3 H 0 3  catalyzed XXV.  2  r e d u c t i o n o f DMSO  Temperature dependence o f k i n the caralyzed H  XXVI.  6  2  RhCl .(Et S) 3  2  3  r e d u c t i o n o f DMSO  l  7  ^  Comparison o f the a c t i v a t i o n parameters f o r the  heterplytic  splitting  i n R h C l . 3 H 0 and R h C l ( E t S ) 3  2  3  2  3  complexes  i n DMA and DMSO  Catalyzed  176  O x i d a t i o n by a S o l u t i o n o f [ R M C g H ^ ^ C l ) ^ i n 0.5M  LiCl/DMA  XXVII. V a r i a t i o n o f r a t e w i t h  [Rh]  192  XXVIII V a r i a t i o n o f r a t e w i t h  [0 ]  194  XXIX.  E f f e c t o f a d d i t i v e s on r a t e  196  XXX.  Temperature dependence o f k and K  202  2  A c t i v a t i o n o f CO by a S o l u t i o n o f [RhCCgH^) C l ]  i n 0.5M LiCl/DMA  2  XXXI.  K i n e t i c data f o r the f o r m a t i o n species  i n DMA  o f Rh " c a r b o n y l 1  227  LIST OF FIGURES Page 1.  Apparatus f o r constant  pressure  gas uptake measure-  ments 2.  40  Rate p l o t s f o r the R h C l ( E t S ) 3  h y d r o g e n a t i o n of MA  RhCl (Et S) 3  RhCl  2  i n DMA  2  catalyzed  3  a t 80°  .49  c a t a l y z e d h y d r o g e n a t i o n of CA i n DMA  3  3.  Rate p l o t s a t 55° f o r v a r i o u s  4.  Dependence of i n i t i a l r a t e on [Rh]  58  5.  Dependence of i n i t i a l r a t e on [H ]  59  6.  Arrhenius  61  7.  Dependence of l i n e a r r a t e on [Rh]  8.  Dependence of l i n e a r r a t e on [ H ]  9.  Arrhenius  3 <  [Rh] and [ H ]  55  2  2  p l o t f o r the i n i t i a l r e d u c t i o n  64 ,. . . .  2  (Bz S) 2  3  p l o t f o r the h y d r o g e n a t i o n  c a t a l y z e d h y d r o g e n a t i o n of MA  65 69  i n DMA  10.  A t y p i c a l r a t e p l o t a t 80°  73  11.  Dependence of i n i t i a l r a t e on [Rh]  75  12.  Dependence of i n i t i a l r a t e on [ H ]  76  13.  Arrhenius  79  14.  Dependence of l i n e a r r a t e on [Rh]  81  15.  Dependence of l i n e a r r a t e on [ H ]  83  16.  Arrhenius  85  2  p l o t f o r the i n i t i a l  reduction  2  p l o t f o r the h y d r o g e n a t i o n  - xv Page RhCl (Et S) 3  2  3  catalyzed  hydrogenation  o f FA i n DMA  17.  Rate p l o t s a t 80° f o r d i f f e r e n t [FA]  8  18.  Rate p l o t and the c o r r e s p o n d i n g l n p l o t a t 80° ....  91  19.  V a r i a t i o n o f k' w i t h  [Rh]  9  2  20.  V a r i a t i o n o f k' w i t h  [H ]  9  3  21.  Dependence of i n i t i a l  r a t e on [Rh]  9  o  22.  Dependence of i n i t i a l  r a t e on [ H ]  23.  A r r h e n i u s p l o t f o r the i n i t i a l r e d u c t i o n  24.  Rate p l o t f o r the c a t a l y z e d  2  Absorption spectra  hydrogenation  100 of a  3  in  0  5  1  0  9  2  A r r h e n i u s p l o t f o r the h y d r o g e n a t i o n  Catalyzed hydrogenation  1  o f R h C l . 3 H 0 and MA i n 0.5M  LiCl/DMA 26.  ?  9  2  mixture of MA and FA a t 80° 25.  8  H4  o f MA by a s o l u t i o n o f [ R h ( C H g  l 4  ) Cl] 2  2  Et S/DMA 2  27.  Rate p l o t s a t 80° f o r a s o l u t i o n made up i n a i r ; and for  a s o l u t i o n made up i n the absence of a i r w i t h i t s  corresponding l o g p l o t  133  28.  V a r i a t i o n of l i n e a r r a t e w i t h  [Rh]  138  29.  V a r i a t i o n of l i n e a r r a t e w i t h  [H,,]  138  30.  A r r h e n i u s p l o t f o r the h y d r o g e n a t i o n  140  - xvi -  Page Catalyzed hydrogenation  o f MA by a s o l u t i o n o f [ R h ( C g H ^ ) ^Cl] ^  i n 0.45M LiCl/DMA  31.  Rate p l o t s a t 80° f o r v a r i o u s [Rh]  32.  Absorption s p e c t r a of [ R h ( C H ) C 1 ] g  1 4  141  2  DMA i n vacuum and under d i f f e r e n t 0  2  i n 0.5M L i C l / pressure at  2  room temperature 33.  144  Absorption spectra of [Rh(CgH^) Cl] 2  and MA i n  2  0.45M LiCl/DMA i n vacuum a t room temperature 34.  Absorption spectra of [ R h ( C g H ^ ) C l ] 2  0.45M LiCl/DMA under H  H  2  2  145  and MA i n  2  a t room temperature  146  35.  V a r i a t i o n of r a t e with  [Rh]  149  36.  V a r i a t i o n of r a t e with  [H ]  ^50  37.  A r r h e n i u s p l o t f o r the h y d r o g e n a t i o n  2  152  r e d u c t i o n o f DMSO c a t a l y z e d by R h C l . 3 H 0 and R h C l ( E t S ) 3  2  3  2  3  complexes  38.  Rate p l o t s a t 80°  162  39.  V a r i a t i o n of r a t e with  40.  V a r i a t i o n of r a t e with p'H  41.  Arrhenius plots f o r reduction  42.  A r a t e p l o t f o r the r e a c t i o n o f R h C l . 3 H 0 and  [Rh]  168 169  2  171 3  2  DMSO u s i n g a mixture o f E , and 0„ a t 80°  179  - xvii -  Page E.S.R. s p e c t r a  of a s o l u t i o n of [ R h C C g H ^ ) C 1 ] 2  i n 0.5M  2  LiCl/  DMA under a i r  43.  E.S.R. spectrum of Rh^CO^) complex a t room temperature  44.  184  E.S.R. spectrum o f R h ( 0 ) complex a t 77°K  185  I  2  Catalyzed oxidation  by a s o l u t i o n of [ R h ( C g l L ^ ) C 1 ] 2  2  i n 0.45M  LiCl/DMA  45.  Rate p l o t s  46.  Dependence of r a t e on [Rh]  193  47.  Dependence o f r a t e  195  48.  Variation  49.  P l o t of 1 / r a t e - k " a g a i n s t l / [  ]  201  50.  A r r h e n i u s p l o t f o r the o x i d a t i o n  203  51.  Rate p l o t and the c o r r e s p o n d i n g l o g p l o t f o r the reaction  Activation  f o r the c a t a l y z e d  i n p'0  of r a t e w i t h  of  [Rh(C H 8  l 4  oxidation  a t 80°  2  [CgH^]  ) Cl] 2  2  188  197  n 2  i n e t h a n o l a t 50°  of CO by a s o l u t i o n of [ R h ( C g H ) C l ] l 4  2  2  205  i n 0.5M  LiCl/DMA  52.  Rate p l o t and the c o r r e s p o n d i n g l o g p l o t f o r the f o r m a t i o n of Rh^CO),, a t 80°  223  - xviii  Page  53.  Rate  p l o t and the c o r r e s p o n d i n g l o g p l o t f o r the  f o r m a t i o n of Rh"*"(C0) a t 80° i n a s o l u t i o n c o n t a i n i n g 2  the f u l l y formed  Rh^CC^) complex  225  54.  Rate p l o t f o r the r e a c t i o n  55.  Rate p l o t and the c o r r e s p o n d i n g l o g p l o t f o r m a t i o n of R h ( C 0 ) I  at  Appendix  56.  2  of R h ( C 0 )  i n a DMA  I  2  solution  with  a t 80°  229  f o r the of R h C l ( E t S > 3  2  3  231  80°  1  S o l u b i l i t y of 0  2  i n DMA  a t 87°, 80°, 75°, 70° and 25°  259  ABBREVIATIONS  The  following l i s t  adopted i n chemical  of a b b r e v i a t i o n s , most of them are  commonly  r e s e a r c h l i t e r a t u r e , w i l l be employed i n t h i s  thesis. All  temperatures are i n °C u n l e s s s p e c i f i c a l l y denoted by  acac  a c e t y l a c e t o n a t e anion,  acacen  N,N'-ethylenebis(acetylacetoniminato) H  2  H  N=  0  o -  atmosphere  bipy  2,2'-bipyridyl  3  ^ -W  b.p.  boiling  Bz  b e n z y l , CgH^CH^  CA  cinnamic  N-^  point  H  H  acid, C,H 6 5 C  Calc  calculated  3  2  :N  atm  CH C0CHC0CH  X  C0„H 2  °K.  -  cobaloxime  XX -  bis(dimethylglyoximato)cobalt  0  H3C  0  .  ^  /-  c  C H  Co CH  H3C  DMA  N,N -dimethylacetamide,  .CH CON(CH >  DMF, dmf  dimethylformamide, HCON(CH )  DMSO  d i m e t h y l sulphoxide  DPPH  2,2-diphenyl-l-picrylhydrazol,  DTH  2,5-dithiahexane,  en  ethylendiamine,  E.S.R.  electron spin  Et  ethyl,  FA  fumaric a c i d  3  3  C H 2  2  (CH ) S 0 2  (NO )  CH SCH CH SCH 3  2  2  H NCH CH NH 2  2  2  2  resonance  5  H  COOH  x  C=C HOOC^  ^H  CN fmn  2  H ^C=C(^  fumaronitrile,  H  N  CN  3  (C H ) 6  5  2  xxi  -  I.R.  -  infrared  ligand  natural  ln  logarithm  m e t a l atom  maleic  MA  acid,  C=C HOOC"  Me  methyl, CH,  Me-O-Salen  methyoxysalen  N.M.R.  n u c l e a r magnetic  o-phen  o-phenathrolin  X  COOH  resonance  =-N  Ph  partial  pressure  phenyl,  CH g  5  Ph P  triphenylphosphine  Pr  isopropyl  3  N  - XXII -  pyridine \ = N  alkyl,  aryl  N , N ' - e t h y l e n e b i s (salicyl:..deneiminato)  H C=rN  N = C H -C 'H  HJr  N  2  ,N'-imino-di-n-propybis(salicylideneiminato)  W  //  \  HC=N I (H C b  succinic acid,  //  °A\  0  N=CH I N—(CH ) H  H0 CCH CH COOH 2  2  2  symmetrically  NC tetracyanoethylene,  ^CN ^0=0 NC C N X  X  triethylenetetramine, H N C H C H N H C H C H N H C H C H N H 2  halogen u n l e s s s t a t e d  molar e x t i n c t i o n  2  2  otherwise.  2  2  2  2  2  -  xxiii  frequency,  ultraviolet  cm  ACKNOWLEDGEMENTS  I wish to express my g r a t i t u d e t o Dr. B.R. James f o r h i s h e l p , guidance and encouragement throughout t h e c o u r s e o f r e s e a r c h and preparation of t h i s  thesis.  I wish to thank Dr. G.L. Rempel f o r v a l u a b l e s u g g e s t i o n s and discussions. I wish to thank Dr. E. O c h i a i f o r h i s h e l p i n the E.S.R. measurements and d i s c u s s i o n s . I a l s o wish t o thank Dr. R. Stewart f o r h i s h e l p i n p r e p a r i n g this  thesis.  CHAPTER I INTRODUCTION  1.1  General In the past  the f i e l d  Introduction f i v e years  important advancements have been made i n  of homogeneous c a t a l y s i s . Among the most  significant  developments are the d i s c o v e r y and e l u c i d a t i o n of v a r i o u s new, often novel, c a t a l y t i c New  r e a c t i o n s of t r a n s i t i o n metal i o n s and compounds.  c a t a l y s t s f o r r e a c t i o n s such as h y d r o g e n a t i o n of o l e f i n s , h y d r o -  f o r m y l a t i o n of o l e f i n s polymerization  (oxo p r o c e s s ) , d i m e r i z a t i o n of e t h y l e n e  of d i e n e s ,  double bond m i g r a t i o n  of o l e f i n s to aldehydes and v i n y l e s t e r s and  and  decarbonylation  been r e p o r t e d .  in olefins,  (Wacker p r o c e s s ) ,  r e a c t i o n s , the h y d r a t i o n of a c e t y l e n e s ,  The group V I I I p l a t i n u m  and  oxidation carbonylation e t c . have  m e t a l complexes have been  found to be p a r t i c u l a r l y a c t i v e f o r such r e a c t i o n s .  Homogeneous, c a t a l y s  has a t t r a c t e d much i n t e r e s t i n r e c e n t years because of the n o v e l t y of the chemistry  1.2  i t r e v e a l s and i t s p o t e n t i a l a p p l i c a t i o n s .  Aim and O u t l i n e of the Work The main o b j e c t of the p r e s e n t  work was  initially  f u r t h e r the use of rhodium complexes p a r t i c u l a r l y sulphide  those  to i n v e s t i g a t e containing  l i g a n d s i n non-aqueous s o l v e n t s f o r the a c t i v a t i o n of  molecular  - 2 hydrogen f o r c a t a l y t i c h y d r o g e n a t i o n r e a c t i o n s . a c t i v a t i o n of m o l e c u l a r hydrogen was  In i n s t a n c e s where  observed, the d e t a i l e d  kinetics  of the r e a c t i o n s were i n v e s t i g a t e d and r e a c t i o n mechanisms have been postulated. Some r e s u l t s o b t a i n e d i n t h i s l a b o r a t o r y showed t h a t rhodium trichloride trihydrate,  12 '  RhCl.j3H 0, and c i s 1 , 2 , 3 - t r i c h l o r o t r i s 2  3 4 ( d i e t h y l s u l p h i d e ) rhodium ( I I I ) , (DMA)  '  R h C l ^ ( E t S ) ^ , i n dimethylacetamide 2  s o l u t i o n were e f f e c t i v e c a t a l y s t s f o r the h y d r o g e n a t i o n of o l e f i n s .  D e t a i l e d k i n e t i c s t u d i e s suggested t h a t the rhodium were a c t i v a t e d by r e d u c t i o n to rhodium  ( I I I ) complexes  (I) complexes v i a h e t e r o l y t i c  s p l i t t i n g of the hydrogen m o l e c u l e ( s e c t i o n 1.3).  The rhodium (I)  complexes were s t a b l i z e d i n s o l u t i o n through r a p i d complexing w i t h the o l e f i n i c substrate.  F u r t h e r r e a c t i o n of the rhodium (I) o l e f i n  complex  w i t h hydrogen produced the p a r a f f i n and r e g e n e r a t e d the rhodium (I) catalyst.  The mechanism p o s t u l a t e d i s r e p r e s e n t e d  Rh  Rh  ITT  1  +  +  H  2  —  olefin  1 R  fa  s  I  h  >  t  +  +  (1.1)  Rh (olefin)  (1.2)  I  T  Rh ( o l e f i n )  2H  below:  T  +  ( l i g a n d s such as C l , H^O,  H  — ^ >  2  Rh  E t S , DMA 2  +  paraffin  (1.3)  have been o m i t t e d ) . 3 4  Other than our r e p o r t on the c a t a l y t i c a c t i v i t y o f R h C l ( E t S ) , 3  2  3  '  no o t h e r c a t a l y t i c systems u s i n g rhodium complexes w i t h s u l p h u r l i g a n d s haye been r e p o r t e d , a l t h o u g h B a i l a r and Tayim^ have r e p o r t e d complexes of the type M X ( Q P h ) 2  n  2  that  (M = P t o r Pd; X = h a l i d e ; Q = P or As  - 3 -  when n = 3; and S o r Se when n = 2; Ph = phenyl) c a t a l y z e the hydrogenat i o n of nonaromatic co-catalyst.  p o l y o l e f i n s but o n l y i n the presence of S n C ^ as  In the present work, the h y d r o g e n a t i o n o f v a r i o u s o l e f i n i c  s u b s t r a t e s c a t a l y z e d by RhCl^CEt^S)^ were s t u d i e d i n more d e t a i l and these s t u d i e s were extended  to o t h e r s u l p h u r l i g a n d systems  (Chapters I I I - V ) .  Solvent e f f e c t s have been shown to be of prime importance i n determining the a c t i v i t y o f rhodium  c h l o r i d e h y d r o g e n a t i o n catalysts."'"  Dimethyl s u l p h o x i d e (DMSO) was used to some e x t e n t i n the p r e s e n t work as a s o l v e n t medium i n an attempt t i o n was observed i n tiie absence  to study such e f f e c t s and of any s u b s t r a t e .  hydrogena-  T h i s has been  shown^ t o be a c a t a l y t i c r e d u c t i o n of the s o l v e n t and these s t u d i e s w i l l a l s o be d e s c r i b e d (Chapter V I I ) . 1-4 Our e a r l i e r s t u d i e s  suggested t h a t rhodium  responsible f o r c a t a l y t i c a c t i v i t y . phenylphosphine)rhodium  (I),''  Furthermore,  RhCl^h^P)^,  (I) complexes were chlorotris(tri-  had been found to be an  extremely a c t i v e c a t a l y s t f o r h y d r o g e n a t i o n r e a c t i o n s . these r e p o r t s , p r e p a r a t i o n s of rhodium  Encouraged  by  (I) complexes w i t h s u l p h u r  c o n t a i n i n g l i g a n d s were attempted, w i t h a view to i n v e s t i g a t e  their  catalytic properties. However, no such rhodium (I) complexes were i s o l a t e d , although the b i s ( c y c l o - o c t e n e ) c h l o r o - r h o d i u m (I) complex [Rh (C H.. . )„C1] , was found to be a convenient source f o r p r e p a r i n g " i n o 14 2 2 0  n  s i t u " t h i s type of s p e c i e s , whose c a t a l y t i c a c t i v i t y was s t u d i e d (Chapter V I ) . In the course o f s t u d y i n g the c a t a l y t i c a c t i v i t y of some rhodium (I) complexes f o r homogeneous h y d r o g e n a t i o n , i t was found that the s o l u t i o n was s e n s i t i v e to t r a c e s of oxygen and t h a t no o x i d a t i o n to the rhodium(III) s t a t e was o c c u r r i n g .  F u r t h e r i n v e s t i g a t i o n showed t h a t  - 4 -  [ R h C C g H ^ ^ C l ] 2 i n DMA  forms a 1:1  complex w i t h m o l e c u l a r oxygen.  The  c u r r e n t i n t e r e s t i n the f o r m a t i o n and p r o p e r t i e s of m o l e c u l a r oxygen complexes f o r c a t a l y t i c oxygenation  reaction's ( s e c t i o n 1.5)  us to extend our aim and study i n d e t a i l  the f o r m a t i o n and  a c t i v i t y of t h i s m o l e c u l a r oxygen complex The a c t i v i t y of some rhodium towards h y d r o g e n a t i o n  (Chapter  (I) c a r b o n y l complexes  and o x i d a t i o n were a l s o b r i e f l y  y e a r s on the a c t i v a t i o n of hydrogen and of rhodium complexes i n s o l u t i o n .  catalytic  VIII).  ( I I I ) and rhodium  A c o n s i d e r a b l e amount of l i t e r a t u r e has  decided  appeared  s t u d i e d (Chapter I X ) . i n the l a s t  few  the c a t a l y t i c aspects g e n e r a l l y  There a r e , however, r e l a t i v e l y  r e p o r t s on'the a c t i v a t i o n of m o l e c u l a r oxygen.  few  Some of the more  p e r t i n e n t data r e p o r t e d on g e n e r a l c a t a l y s i s by rhodium complexes and 0^  w i l l be presented a f t e r s e c t i o n s on  1.3  activation.  ;  C a t a l y t i c A c t i v a t i o n of M o l e c u l a r Hydrogen The  ability  to a c t i v a t e m o l e c u l a r hydrogen homogeneously i n  :  s o l u t i o n has been found f o r a l a r g e number of t r a n s i t i o n metal i o n s 11-17 and  complexes.  In each case, i t appears  that R  i s s p l i t by  c a t a l y s t , w i t h the f o r m a t i o n o f a h y d r i d o - t r a n s i t i o n metal which acts, as the r e a c t i v e i n t e r m e d i a t e f o r c a t a l y t i c  the  complex  hydrogenation.  Three d i s t i n c t mechanisms f o r the a c t i v a t i o n of H^ have been r e c o g n i z e d and are e x e m p l i f i e d by e q u a t i o n s ( 1 . 4 ) - ( 1 . 6 ) . Heterolytic  Ru  I I i :  splitting:  Cl, b  3  +  H  0  i  18  »  Ru b  I I I  Cl H c  3  +  H  +  +  Cl  (1.4)  11-15  - 5 -  19-21 Homolytic s p l i t t i n g  2Co "(CN) I3  :  +  3 5  H  22 Dihydride formation  Ir CKCO)(Ph P) I  3  Heterolytic  2  >  2  2Co (CN) H m  (1.5)  3  5  23 '  :  +  H  2  >  Ir  I I ] 1  H Cl(CO)(Ph P) 2  3  (1.6)  2  s p l i t t i n g as e x e m p l i f i e d by e q u a t i o n (1.4) i s  p r o b a b l y the most w i d e s p r e a d mechanism f o r the a c t i v a t i o n of H solution.  2  in  I t i s e s s e n t i a l l y a s u b s t i t u t i o n a l p r o c e s s i n which one of  the o r i g i n a l l i g a n d s of the c a t a l y s t i s r e p l a c e d by H , w i t h o u t any change i n the f o r m a l o x i d a t i o n number of the m e t a l atom. towards H  Reactivity  i n such cases i s t h e r e f o r e governed by the s t a b i l i t y of  2  the h y d r i d e complex, the ease  of the d i s p l a c e m e n t of the o r i g i n a l  l i g a n d and the a v a i l a b i l i t y of a s u i t a b l e base (which may  be the s o l v e n t  m o l e c u l e o r the d i s p l a c e d l i g a n d i t s e l f ) t o s t a b i l i z e the r e l e a s e d proton.  12  15  '  For example, the r e a c t i v i t y of copper  2 A  (II)  and  25  silver  (I)  complexes show an i n v e r s e dependence on the s t a b i l i t y of  the m e t a l - l i g a n d bond and a d i r e c t dependence on the b a s i c i t y of the ligand. The o t h e r two mechanisms of  s p l i t t i n g , namely h o m o l y t i c s p l i t t i n g  and d i h y d r i d e f o r m a t i o n , i n v o l v e f o r m a l o x i d a t i o n of the m e t a l i o n and the h y d r i d e f o r m a t i o n i s c l o s e l y l i n k e d to the s u s c e p t i b i l i t y of the m e t a l to o x i d a t i o n and the a b i l i t y of the m e t a l i o n t o expand i t s coordination s h e l l . ^  For a g i v e n m e t a l i o n , r e a c t i v i t y i s expected to  - 6 -  be  enhanced by  l i g a n d s which are most e f f e c t i v e i n s t a b i l i z i n g  3higher  oxidation states.  towards R  Thus the high  , as compared w i t h the c o r r e s p o n d i n g r e a c t i v i t i e s of  i s o n i t r i l e or d i m e t h y l g l y o x i m e c o b a l t reflect  r e a c t i v i t y of Co(CN)^  the g r e a t e r  the  ( I I ) complexes, i s thought  e f f e c t i v e n e s s of the CN  to  ligands i n s t a b l i z i n g  cobalt  ( I I I ) r e l a t i v e to c o b a l t ( I I ) . Regarding d i h y d r i d e formag t i o n , square p l a n a r d complexes have been found to r e a d i l y undergo o x i d a t i v e a d d i t i o n of to g i v e the c o r r e s p o n d i n g d complexes,and IA 15 the ease of o x i d a t i v e a d d i t i o n by  '  27 '  ( s u b j e c t to some m o d i f i c a t i o n  l i g a n d v a r i a t i o n ) i s expected to f o l l o w the approximate sequence 0s°  > Ru°  „ II Pt >>  1.4  > Fe°,  Pd  >>  Ir  Nl  1  > Rh  ,  1  >  Co , 1  . II Au  Homogeneous C a t a l y t i c Hydrogenation The  formed by  r e a c t i v e n a t u r e of the h y d r i d o - t r a n s i t i o n metal complexes the p r e v i o u s l y d e s c r i b e d mechanisms p e r m i t s them to  as i n t e r m e d i a t e s i n o r g a n i c and  1.41  '  26  function  i n homogeneous h y d r o g e n a t i o n r e a c t i o n s f o r both  organic  Inorganic  substrates.  substrates  L i t e r a t u r e reports  show t h a t h o m o l y t i c and  heterolytic splitting  of hydrogen are observed i n the a c t i v a t i o n step f o r the r e d u c t i o n inorganic substrates. C a l v i n and  An  Wilmarth  28  example of each w i l l be showed t h a t  Cu  I  of  given.  acetate,  i n quinoline  - 7 -  s o l u t i o n , c a t a l y z e d homogeneously the r e d u c t i o n o f Cu"'"''". determining  s t e p i s thought to be the h o m o l y t i c  The r a t e  s p l i t t i n g o f H^,  f o l l o w e d by a f a s t step i n v o l v i n g r e d u c t i o n o f the s u b s t r a t e . r a t e of  uptake i s p r o p o r t i o n a l t o the  square of the cX  2Cu  I  l — ^  II 2Cu H  k  H  k  Harrod  c o n c e n t r a t i o n and the  concentration.  +  Cu^B.  The  +  Cu  - l 2CU  1 1  29  and Halpern  (1.7)  +  1  H  (1.8)  +  III showed t h a t i n the r e d u c t i o n o f Fe ,  c a t a l y z e d by RhCl^H^O i n aqueous 3 M HC1, the r a t e determining i n v o l v e d h e t e r o l y t i c s p l i t t i n g o f U^. Rh'"''"H , then reduces F e I I  The h y d r i d e  intermediate,  i n a f a s t step r e g e n e r a t i n g  1 1 1  step  the i n i t i a l  Ill Rh  species.  Rh  The r e a c t i o n scheme can be r e p r e s e n t e d  k  TTT  +  1" — ^  H  Rh  TTT H  +  H  as f o l l o w s :  +  (1.9)  2  -1 Rh *  +  111  D i r e c t evidence  2Fe  Rh  Z I 1  i n the c o r r e s p o n d i n g  1  18 30 '  to  to rhodium  sometimes t r a n s f o r m  J  III  H  -  >  Rh  1  2Fe  T I  +  H  +  (1.10)  step has been  1  ^u  s t u d i e s w i t h deuterium.  Rh  +  f o r the e q u i l i b r i a i n the i n i t i a l r>  obtained  1 1 1  system by i s o t o p i c exchange  Rhodium ( I I I ) h y d r i d e s a r e w e l l known  T  +  31 32 '  (I) p l u s a p r o t o n ,  H  +  (1.11)  - 8and the reduction of f e r r i c could involve a rhodium (I) species.  31  Complexes of copper ( I I ) , s i l v e r (I), mercury ( I I ) , palladium ( I I ) , ruthenium (III), cobalt (II) have also been found to be active catalysts f o r the hydrogen reduction of inorganic substates"^ v i a such homolytic or h e t e r o l y t i c processes.  1.42  Organic substrates Homogeneous c a t a l y t i c hydrogenation of organic substrates may be  effected through transfer of hydrogen from hydrido-transition metal complexes.  The following examples i l l u s t r a t e how this can be r e a l i s e d  for each of the three mechanisms of s p l i t t i n g of hydrogen (heterolytic, homolytic and dihydride formation) described i n section 1.3. Heterolytic s p l i t t i n g of molecular hydrogen i s exemplified by the chlororuthenate  (II) catalyzed hydrogenation of o l e f i n i c carboxylic  33 acids such as fumaric and maleic acids i n aqueous solutions.  The  mechanism can be pictured as follows:  1/  — Ru—+  N / H — C — C— H  Scheme I  <  H  +  / — R u — C — C — II  The r a t e d e t e r m i n i n g step i s the h e t e r o l y t i c s p l i t t i n g o f 1:1 Ru"*""*" ( o l e f i n )  n-complex.  by a  The h y d r i d o Ru ( o l e f i n ) ir-complex  then  r e a r r a n g e s to a R u - a l k y l a-complex, through the " i n s e r t i o n " o f the o l e f i n i n t o the Ru-H bond; n u c l e o p h i l i c a t t a c k by a p r o t o n g i v e s the hydrogenated  product and r e g e n e r a t e s the c a t a l y s t .  Two f e a t u r e s of t h i s mechanism, namely c o o r d i n a t i o n o f the o l e f i n to the metal as a n-bonded l i g a n d and " i n s e r t i o n " of the o l e f i n i n t o a metal-hydrogen  bond,are encountered  c a t a l y z e d hydrogenation Pentacyanocobalt  reactions.  ( I I ) i s found to c a t a l y z e homogeneously the  h y d r o g e n a t i o n of conjugated o l e f i n s  t h a t the r e a c t i o n proceeds by the f o l l o w i n g  2[Co(CN)J  [HCo(CN) ]  +  3  5  3  +  H  n  CH =CHCH=CH 2  2  [CH CH=CHCH Co(CN) ] 2  5  mechanism:  ^  2[HCo(CN),]  >  [CH CH=CHCH Co(CN) ]  [HCo(CN) ] 3  19-21  such as b u t a d i e n e , i n 19 20-21 D e t a i l e d s t u d i e s by de V r i e s , Kwiatek and S e y l e r  aqueous s o l u t i o n . suggested  i n a number o f o t h e r homogeneously  3  3  ~ >  (1.12)  3  3  2  ~  . (1.13)  3  CH CH CH=CH 3  2  2  + 2[Co(CN> ] 5  _ ; (1.14)  -CN "  /™2 CH',  > \ \  CH  3  +CN~  7  [Co(CN).] A-  [HCo(CN) ]  3  > CH„CH=CHCH„ + j  o  2[Co(CN)J J  - 10 -  The cobalt  initial  step i n v o l v e s h o m o l y t i c  s p l i t t i n g of  ( I I ) , f o l l o w e d by complexing o f the butadiene  by pentacyanoto g i v e the  3intermediate the h y d r i d o  [CH^CHhCHCH^Co (CN),-]  .  T h i s then undergoes r e a c t i o n w i t h  s p e c i e s i n two d i f f e r e n t ways, depending on cyanide  3c o n c e n t r a t i o n , to g i v e 1 or 2-butene. However, the [Co(CN),.] c a t a l y z e d hydrogenation o f cinnamate [C^H^-C^CHCO^] has been suggested  34 to i n v o l v e a r a d i c a l a n i o n  2[Co(CN)J  +  3  5  [HCo(CN) ] ~ 3  5  +  intermediate.  H  ^  0  2  5  2  (1.15)  3  i>  x  [C H CH=CHC0 ]~ 6  2[HCo(CN)J  —>  [Co(CN) ] ~ 3  5  +  [C^CH^HCO^]" (1.16)  [ H C o ( C N ) J ~ + [C,H CH.CHCOj~ 3  c  j  b  D  2  >  [Co(CN) ] ~+  2  3  c  [C,H CH-CH C0J~ c  o  0 _>  D  2  2  2  (1.17) W i l k i n s o n and coworkers r e p o r t e d that RhCltPh^P).^ i s an a c t i v e c a t a l y s t f o r homogeneous h y d r o g e n a t i o n i s o l a t e d double bonds, but not e t h y l e n e i t s e l f .  i n benzene  of o l e f i n s c o n t a i n i n g  The mechanism o f the  r e a c t i o n i n v o l v e s the f o r m a t i o n o f the c i s d i h y d r i d e R h C l ( P h ^ P ) ^ H , 2  t h i s then r e a c t s w i t h the o l e f i n i n the r a t e determining produce the p a r a f f i n . on i t s a b i l i t y  The a c t i v i t y of the RhCl(Ph,jP)  3  step to .  complex depends  to d i s s o c i a t e i n s o l u t i o n to form the a c t i v e s p e c i e s .  R h C l ( P h P ) S where S i s the s o l v e n t molecule which can be e a s i l y 3  2  d i s p l a c e d by the o l e f i n or hydrogen. k i n e t i c data i s as f o l l o w s :  A mechanism c o n s i s t e n t w i t h the  - 11 -  RhCl(J?h,P)  solvent  0  N  R h  Cl(ph P)  +  0  PPh,  (1.18)  Ph P 3  l — ^ K  RhCl(Ph P) 3  +  2  H  2  H RhCl(Ph P) 2  3  k  2 olefin K  2  1  olefin  k"  RhCl(Ph-P) . ( o l e f i n ) 5  tt  1  RhCl(Ph„p) J  2  +  0  z  paraffin  Scheme I I  g W i l k i n s o n and coworkers  showed that under t h e i r e x p e r i m e n t a l  c o n d i t i o n s the k" path i s of n e g l i g i b l e s i g n i f i c a n c e and the p a r a f f i n i s produced  s o l e l y by the a t t a c k of the o l e f i n on the d i h y d r i d e s p e c i e s . 35  A v e r y s i m i l a r r e a c t i o n scheme has been proposed  by James and Memon  f o r the h y d r o g e n a t i o n of o l e f i n s u s i n g I r C l ( C O ) ( P h P ) 3  workers concluded t h a t the k".path i s the more l i k e l y  although these  2  hydrogenation  36 p r o c e s s . ^Work by C a n d l i n and Oldham c a t a l y z e d by R h C l ( P h P ) 3  3  has i n d i c a t e d  that  hydrogenation  can occur by both r o u t e s .  The mechanism of h y d r o g e n a t i o n of u n s a t u r a t e d s u b s t r a t e s can be regarded as one i n v o l v i n g t h r e e steps:"''"'"  (1)  hydrogen  activation,  (2) s u b s t r a t e a c t i v a t i o n , (3) hydrogen t r a n s f e r . The q u e s t i o n as to whether both o l e f i n and hydrogen a c t i v a t i o n are r e q u i r e d a t the same time or whether o n l y one needs to be a c t i v a t e d has been the s u b j e c t of 11 i n t e r e s t f o r some time. Some r e c e n t s t u d i e s have i n d i c a t e d t h a t  9 37 a c t i v a t i o n of both are r e q u i r e d .  '  The  t r a n s f e r of hydrogen  to o l e f i n s  - 12 -  i n the monohydride systems (or the h y d r o m e t a l l a t i o n step) i s an example of a much wider c l a s s of " i n s e r t i o n t y p e " r e a c t i o n s which a r e commonly observed  i n many c a t a l y t i c reactions."''''" ^-- ' ^ >  3  The p r o c e s s o f  hydrogen t r a n s f e r i n the c i s - d i h y d r i d e systems (e.g. from  RhCl^h^P)^^)  remains somewhat u n c e r t a i n ; t h i s was o r i g i n a l l y thought to involve g simultaneous t r a n s f e r of both hydrogens, each by a t h r e e c e n t r e t r a n s i tion state.  More r e c e n t d a t a ,  39-41  are t r a n s f e r r e d c o n s e c u t i v e l y ,  however, suggest  involving a  a-alkyl  t h a t the hydrogens intermediate.  42 At the r e c e n t Faraday S o c i e t y Meeting,  a subsidiaryquestion of  g e n e r a l i n t e r e s t was the e x t e n t o f f o r m a t i o n and l i f e t i m e o f these i n t e r m e d i a t e s , s i n c e r e p r o d u c t i o n o f the h y d r i d o - o l e f i n complexes b e f o r e the s a t u r a t e d hydrocarbon i s formed can g i v e r i s e to c a t a l y t i c isomerization: CH_~CH-CH~~ 2| I •« H-M  CH -CH-CH ~~ j | 2 M 0  CH -CH=CH~~ 3 j M-H  0  (1.19)  40 Bond and H i l l y a r d  r e p o r t e d the f o r m a t i o n o f c o n s i d e r a b l e q u a n t i t i e s  of i s o m e r i z e d o l e f i n d u r i n g h y d r o g e n a t i o n  o f 1-pentene, c a t a l y z e d by  RhClCPh^P) ^. Abley  S i m i l a r but l e s s d e t a i l e d o b s e r v a t i o n s were r e p o r t e d by 43 and M c Q u i l l i n s u g g e s t i n g t h a t a l k y l complexes a r e indeed formed. 1 2 41  The mechanism proposed by J a m e s and Rempel ' ' g e n a t i o n a l s o i n v o l v e d an a l k y l 1.5  Molecular  for maleic  a c i d hydro-  intermediate.  Oxygen Complexes and T h e i r Role  Catalysis Synthetic r e v e r s i b l e oxygen-carrying  i n Homogeneous ,  complexes have been o f i n t e r e s t  - 13  -  as model compounds i n the study of r e v e r s i b l e o x y g e n a t i o n mechanisms i n v o l v e d i n the v e r y  complex n a t u r a l oxygen c a r r i e r s , e.g.  and haemocyanins  as a means of s e p a r a t i n g m o l e c u l a r oxygen from  air.  The  first  compound was  and  bis-salicylaldehyde-ethylenediimine-cobalt  some 30 y e a r s ago. those of C o ^ , few  (II)  studied  45 '  Since  then a number of c h e l a t e s , e s p e c i a l l y  have been found to be r e v e r s i b l e oxygen c a r r i e r s , ^ s t u d i e s of a d e f i n i t i v e n a t u r e have been c a r r i e d out or p o o r l y  on  characterised.  R e c e n t l y , t h e r e have been r e p o r t s of the E.S.R. spectrum of these . , 55-57 (oxygen) complexes. 58 Vaska's  discovery  of the r e v e r s i b l e m o l e c u l a r oxygen  I r C l ( C O ) ( P h ^ P ) 2 i s of g r e a t Lr(O^Cl (C0)(Ph P)2 may 3  well-characterised.  be  importance s i n c e the 1:1  r e c r y s t a l l i z e d and  the two  oxygen atoms are found to be  from the I r atom,with the 0-0  d i s t a n c e ' ( 1 . 3 0 A)  longer  A)  and  s i g n i f i c a n t l y shorter  and corresponding c l o s e l y to 0  _  2  o  (1.28  A).  The  equidistant  than t h a t  than t h a t of 0^  equivalence  atoms i s c o n s i s t e n t w i t h G r i f f i t h ' s ^ model of the  °  (1.49A),  oxygen c a r r i e r ) .  t h a t the 0-0  bond  C a l v i n " ^ that r e v e r s i b i l i t y  length  consistent  probably  depends upon some e l e c t r o n t r a n s f e r from m e t a l to oxygen, but sufficient  of  of the oxygen  i s s i g n i f i c a n t l y s h o r t e r than t h a t i n a t y p i c a l p e r o x i d e are w i t h the views of M a r t e l l and  2  T r - b o n d i n g of  m o l e c u l a r oxygen to i r o n i n oxyhaemoglobin ( a l s o a 1:1 f a c t t h a t oxygen uptake i s r e v e r s i b l e and  and  on  o  (1.21  1 1  oxygen adduct ,  been performed  o  Co  carrier  i s extremely s t a b l e  X-ray s t u d i e s " ^ h a v e  Ir (O2) Cl (COXPh^P^, and  The  ^  4  these s p e c i e s because they are g e n e r a l l y u n s t a b l e  m o l e c u l a r O2  the  example of a s y n t h e t i c r e v e r s i b l e o x y g e n - c a r r y i n g  44  but very  the haemoglobins  not  t r a n s f e r to b r i n g about i r r e v e r s i b l e o x i d a t i o n of the m e t a l .  - 14 -  In t h i s case, t h i s t r a n s f e r seems to approximate the 0-0  to one e l e c t r o n ,  d i s t a n c e corresponds c l o s e l y to t h a t i n 0^  p r e d i c t s an o x i d a t i o n s t a t e of a d^ diamagnetic.  Ir " " 1  1  .  since  However, t h i s  and y e t the compound i s  The s i t u a t i o n i s c l e a r l y more complex than simple  e l e c t r o n t r a n s f e r from the m e t a l to the oxygen,and more r e c e n t 62 interpretations  63 '  of the bonding i n v o l v e a d o p t i o n of a t h r e e - c e n t r e  m o l e c u l a r o r b i t a l scheme f o r the metal and two oxygen atoms; the l e n g t h of the 0-0  bond and the s t r e n g t h of the bonding  to the m e t a l atom  are p a r t i c u l a r l y s e n s i t i v e to the e l e c t r o n e g a t i v i t y of the o t h e r 62 coordinated ligands. I r i d i u m complexes are b e s t thought o f as f i v e 62 63 c o o r d i n a t e w i t h a ir-bonding 0^ m o l e c u l e . metal-oxygen  '  The s t r e n g t h of the  bond i s r e l a t e d to the e l e c t r o n d e n s i t y a v a i l a b l e i n the  metal atom f o r back-bonding  to the a n t i b o n d i n g m o l e c u l a r o r b i t a l s on the  0^ m o l e c u l e . S i n c e the d i s c o v e r y of the I r ^ ^ l C C O ^ h ^ P ) ^  complex, m o l e c u l a r 8 10 oxygen has been found to add to s e v e r a l r e a c t i v e d and d metal 26,65-67 . . . , . : complexes to form diamagnetic compounds w i t h r e t e n t i o n o f the 0-0 bond. These i n c l u d e complexes o f I r 58-60,62-64,68-70^1 64,71-73^ £  1  p  Ru  0 74  _,0  75-77  , Pd  _ 0 75,76,78 , Pt  , • 0 75-77,79 , and N i  '  .  >  The most s i g n i f i c a n t p r o p e r t y of some of these m o l e c u l a r oxygen complexes i s t h e i r a b i l i t y mild conditions.  to oxygenate  s u b s t r a t e s under u n u s u a l l y  Both s t o i c h i o m e t r i c and c a t a l y t i c o x i d a t i o n s have  been d e s c r i b e d .  For example, a u t o x i d a t i o n s of t r i p h e n y l p h o s p h i n e ^ 77 79 and t - b u t y l i s o c y a n i d e ' are c a t a l y z e d by oxygen complexes of p a l l a d i u m and n i c k e l . S t o i c h i o m e t r i c o x i d a t i o n s of gaseous non-metal oxides such as CO,  26  NO,  80  SO2,  81  N0 , 2  81  and CO^  82  have been observed  and o r g a n i c compounds such as cyclohexene a n d e t h y l b e n z e n e ;  have been  - 15 -  found  to undergo a u t o x i d a t i o n s c a t a l y z e d by these m o l e c u l a r  oxygen  80,83-85 complexes. The mechanism  of these c a t a l y t i c o x i d a t i o n s i s a s u b j e c t of  current i n t e r e s t . " ^  Two mechanisms,  one i n v o l v i n g a d i s s o c i a t i v e  "oxygen i n s e r t i o n " step and the o t h e r i n v o l v i n g f r e e r a d i c a l s have been proposed to date. The k i n e t i c s o f the c a t a l y t i c o x i d a t i o n o f t r i p h e n y l p h o s p h i n e to t r i p h e n y l p h o s p h i n e oxide by t e t r a k i s t r i p h e n y l p h o s p h i n e p l a t i n u m benzene have been s t u d i e d by H a l p e r n and c o w o r k e r s . ^  The mechanism of  8  the r e a c t i o n i n v o l v e s the i n i t i a l  f o r m a t i o n of a p l a t i n u m  oxygen complex which then f u r t h e r r e a c t s w i t h excess  (0) m o l e c u l a r  triphenylphosphine  to produce the t r i p h e n y l p h o s p h i n e oxide through a d i s s o c i a t i v e i n s e r t i o n " step.  The mechanism  Pt(Ph„P) 3 ' k  benzene  3  3  "oxygen  of the r e a c t i o n i s r e p r e s e n t e d below: Pt(Ph P) 3  +  3  Ph P  (1.20)  3  K  k  Pt(Ph P)  (0) i n  +  0  l  2  Pt(Ph P) 0 3  2  +  2  Ph P  (1.21)  3  Ph P 3  Pt(Ph P) 0 3  2  2  / ' - "9  + Ph P  Ph.P— Pt'' ;  3  3  \ ^6 ~Ph P 3  (1.22)  Pt(Ph_P)_ + 3 3  2Ph„P0 3  2Ph P 4-—— fast  0Ph P 3  Ph P—Pt 3  ' 0Ph P 3  Kurkov,  Pasky  and L a v i g n e  phosphine)rhodium(I)  84  proposed t h a t the c h l o r o t r i s ( t r i p h e n y l -  catalyzed autoxidatlons  o f cyclohexene and e t h y l -  benzene i n v o l v e a f r e e - r a d i c a l c h a i n mechanism. r e a c t i o n was demonstrated by hydroquinone.  by t h e complete  i n h i b i t i o n of the o x i d a t i o n  They proposed t h a t rhodium,  c a t a l y z e s c h a i n i n i t i a t i o n by a  ROOH  +  Rh  ROOH  +  Rh  1  1 1  The c h a i n n a t u r e o f the  by analogy w i t h c o b a l t ,  Haber-Weiss type mechanism.  >  R0-  +  >  WO- +  OH  +  Rh  H  +  Rh  +  87  i (1.23)  1 1  (1.24)  1  An a l t e r n a t i v e mechanism which i n v o l v e s a two e l e c t r o n t r a n s f e r was  also  suggested:  2R00H  +  Rh  2R00H  +  Rh  >  1  1 1 1  2R0-  > 2R00-  T h i s mechanism r e q u i r e s t e r m o l e c u l a r likely.  +  F o r the case o f c o b a l t ,  20H  +  2H  +  +  Rh  +  (1.25)  1 1 1  Rh  (1.26)  1  r e a c t i o n s and i s c o n s i d e r e d  88 89 ' i t has been shown t h a t  less  electron  t r a n s f e r i n v o l v e s a p r i o r complex f o r m a t i o n between t h e h y d r o p e r o x i d e and the c a t a l y s t .  Autoxidation  of diphenylmethane  c a t a l y z e d by  90 RhCl(CO)(Ph^P)^  i s a l s o thought to go through a Haber-Weiss type  mechanism i n v o l v i n g one e l e c t r o n t r a n s f e r . 48 Fallab  has suggested t h a t t h e p o l a r i s a t i o n of t h e 0^ molecule  as a r e s u l t o f the more o r l e s s l a b i l e l i n k a g e w i t h the a c t i v a t o r  - 17 -  m o l e c u l e M ( t r a n s i t i o n m e t a l complex) may be s u f f i c i e n t  to f a c i l i t a t e  r e a c t i o n w i t h an a u t o x i d i z a b l e s u b s t r a t e RH:  M  M  +  6 +  0  0  6 2  ^  2  +  M  6 +  0  >  RH  (1.27)  6 2  M  +  R-  +  HCy  (1.28)  In p r i n c i p l e , a s t r o n g l y e l e c t r o p o s i t i v e a c t i v a t o r M c o u l d cause h e t e r o l y s i s o f the 0^ molecule i n t o  h i g h l y r e a c t i v e atomic p a r t i c l e s ;  48 however, such a r e a c t i o n has never been observed i n p r a c t i s e .  K  &  +  0  &  >  M  +  0  +  +  0  • (1.29)  The mechanisms of these a u t o x i d a t i o n s promoted by m o l e c u l a r complexes remain to be c l a r i f i e d .  I t seems l i k e l y  oxygen  t h a t i n many  i n s t a n c e s both t h e s u b s t r a t e and t h e oxygen m o l e c u l e must be i n t h e same 26 c o o r d i n a t i o n sphere f o r o x y g e n a t i o n to take p l a c e .  The f a c i l e  o x i d a t i o n o f l i g a n d s such as CO, i s o c y a n i d e s and phosphines lends to  t h e above s u p p o s i t i o n .  support  These r e a c t i o n s c o u l d then be c o n s i d e r e d as  examples o f m e t a l i o n promoted, atom t r a n s f e r redox r e a c t i o n s . The ... •J • * • u _ _ 80,83,84,90 • , studied autoxidations of organic substrates ' ' seem to show a 26 f r e e r a d i c a l mechanism.  Collman  i n d i c a t e d that n o n - r a d i c a l  autoxida-  t i o n s may be found f o r o r g a n i c s u b s t r a t e s which can be i n c o r p o r a t e d i n the c o o r d i n a t e d  sphere a d j a c e n t  t o the c o o r d i n a t e d oxygen. 91  e x i s t e n c e of numerous oxygenases, metalloenzymes, d i r e c t o x y g e n a t i o n of o r g a n i c s u b s t r a t e s  The  which c a t a l y z e the  (at. l e a s t i n some i n s t a n c e s by  - 18  -  n o n - r a d i c a l pathways), s u s t a i n s the e x p e c t a t i o n fer oxidations  of o r g a n i c  substrates  t h a t n o n - r a d i c a l , atom trans-  by metal-oxygen complexes would  be  realized. 1.6  L i t e r a t u r e Reports on the C a t a l y t i c P r o p e r t i e s of Rhodium Complexes  < 92  A very  comprehensive review, by James  on the r e a c t i o n s  and  c a t a l y t i c p r o p e r t i e s of rhodium complexes i n s o l u t i o n surveyed l i t e r a t u r e up  to the middle of 1966.  Since  t h i s time a  the  considerable  number of p u b l i c a t i o n s have appeared on t h i s t o p i c .  Rhodium(I)  and  rhodium(III) complexes, p a r t i c u l a r l y w i t h c o o r d i n a t e d  phosphines  and.  halides,have  u s u a l l y been i n v o l v e d .  A l i t e r a t u r e survey of  c a t a l y t i c r e a c t i o n s which are p e r t i n e n t b r i e f l y described 1.61  i n the f o l l o w i n g  to the p r e s e n t  these  work w i l l  be  sections.  Rhodium Complexes as Hydrogenation C a t a l y s t s 93 In 1939,  Iguti  i R h C N H ^ ^ C ^ J C l and  first RhCl  3  reported  that  [Rh(NH ) (H 0)]C1 ,  i n aqueous a c e t a t e  hydrogen f o r r e d u c t i o n of quinone,  3  5  2  3  s o l u t i o n a c t i v a t e d molecular  f u m a r i c a c i d and  sodium  nitrite.  However, t r a c e s of m e t a l l i c rhodium, a p o w e r f u l heterogeneous c a t a l y s t , 31 were found d u r i n g some r e c e n t l y s t u d i e d s i m i l a r r e a c t i o n s , and the above 29 systems may i n 1959  have been h e t e r o g e n e o u s l y c a t a l y z e d .  found t h a t c h l o r o r h o d a t e ( I I I )  species  H a l p e r n and  i n aqueous s o l u t i o n s  c a t a l y z e d homogeneously the hydrogen r e d u c t i o n of the f e r r i c 31 Extension  of t h i s work by James and  l a b i l e chlororhodate(III) a c t i v i t y of the s p e c i e s  Rempel  Harrod  ion.  showed t h a t o n l y the  s p e c i e s were e f f e c t i v e c a t a l y s t s .  i n c r e a s i n g w i t h i n c r e a s i n g numbers of  anionic,  The coordinated  - 19 -  chloride ligands.  These c h l o r o r h o d a t e ( I I I ) s p e c i e s i n aqueous a c i d s o l u -  t i o n s were not e f f e c t i v e f o r homogeneous h y d r o g e n a t i o n substances.  However RhCl^OH^O i n DMA  s o l u t i o n was  of  found to c a t a l y z e  the hydrogen r e d u c t i o n of v a r i o u s s u b s t i t u t e d e t h y l e n e s e t h y l1e n e  i t s e l14 f=.  31  >  rhodium(m)  a n <  ^  of o l e f i n s and  acetylenes  3  95  rhodium(I) complexes as homogeneous c a t a l y s t s i n  1,2,6-Rh(py) C l ,  3  3  triphenylphosphine [RhCN(Ph P ) ]  ,  2  The  group, have r e p o r t e d  u s i n g a number of  e t h a n o l , benzene or ethanol-benzene m i x t u r e s . RhCl -3H 0,  1 2 ' as w e l l as  94  A number of workers, p a r t i c u l a r l y W i l k i n s o n ' s the h y d r o g e n a t i o n  olefinic  98  These complexes i n c l u d e  95 96 96 » Rh Cl [SnCl -EtOH] and 2  2  2  derivatives l , 2 , 3 - R h C l ( P h P ) , 3  RhH(C0)(Ph P )  d e t a i l e d k i n e t i c s of these  99-102 y  3  and  3  the  4  9 6  3  '  RhCl(Ph P) . J "  9 7  1  0  3  RhCl(CO) ( P h g P ^ .  103  J ,  -  104 U W  systems have not g e n e r a l l y been g i v e n  because the m a j o r i t y of these systems are q u i t e complex:  f o r example,  h e x - l - e n e , a f r e q u e n t l y used o l e f i n s u b s t r a t e i s c a t a l y t i c a l l y isomerized formation  by ethanolic R h C l y 3H 0. 2  H i l l y a r d ^ reported 4  of c o n s i d e r a b l e q u a n t i t i e s of i s o m e r i z e d  hydrogenation  of 1-pentene c a t a l y z e d by  RhCl(Ph P) ^ ^ 3  hydrogenation linkages.  Bond and  The  3  olefin  the  during  RhCl(Ph P) . 3  3  i n benzene i s an extremely a c t i v e c a t a l y s t f o r the  of compounds c o n t a i n i n g i s o l a t e d o l e f i n i c and a c e t y l e n i c c a t a l y t i c a c t i v i t y of R h X ( P h P ) 3  3  8 9 ' i n c r e a s e d i n the 36  o r d e r X = C l < Br < I.  Recently  homogeneous hydrogenation and  C a n d l i n and  Oldham  of mixed u n s a t u r a t e d  p a r t i c i p a t i o n of two  They r e p o r t e d  the  substrates using  found t h a t the degree of s e l e c t i v i t y a c h i e v e d  the a d d i t i o n of p o l a r s o l v e n t s .  studied  RhCl(Ph P)  can be enhanced by  t h a t the degree of  k i n e t i c a l l y i n d i s t i n g u i s h a b l e forward  routes, i . e .  3  3  - 20 -  v i a s u b s t r a t e a t t a c k on a h y d r i d o i n t e r m e d i a t e , or hydrogen a t t a c k on a substrate intermediate, determining  (see Scheme I I ) may  the degree of s e l e c t i v i t y .  u s i n g RhCltPh^P)^ RhClCPh^P)^ was  a l s o be of importance i n  Hydrogenation  of c y c l o a l k e n e s  were a l s o r e p o r t e d by o t h e r groups."""^ "*"^  used i n the s e l e c t i v e r e d u c t i o n of s t e r o i d  carbonyl  109 groups  and  i n a v a r i e t y of o r g a n i c syntheses  involving  selective  1 10-1 1 T  hydrogenation,. found  R h C l ( C ^ ) (Ph P)  2  and R h C l H ( P h P ) 2  3  were a l s o  to be a c t i v e c a t a l y s t s f o r the r e d u c t i o n of a l k y n e s and  the l a t t e r complex becoming a c t i v e as a Rh was  3  found  to c a t a l y z e the h y d r o g e n a t i o n  I  * 36 species.  of t e r m i n a l and  alkenes,  Rh(NO)(Ph P) 3  cyclic  olefins.  114  99-102 The  rhodium c a r b o n y l complexes RhH(CO)(Ph P)  and  3  RhCl (CO) (Ph P) "*"^ '  a l s o c a t a l y z e the h y d r o g e n a t i o n  3  3  2  r e a c t i o n s but  these  complexes, u n l i k e R h C l ( P h P ) show no d e t e c t a b l e r e a c t i o n w i t h hydrogen or . . 7,99,M0,102JI)3 . . 100,102,115. . olefin. RhH(CO)(Ph P) ' ' i s a c t i v e f o r a v a r i e t y of 3  r  3  T  3  3  other c a t a l y t i c r e a c t i o n s , such as hydrogen-deuterium exchange, i s o m e r i z a t i o n and h y d r o f o r m y l a t i o n of a l k e n e s . of R h C l ( C O ) ( P h P )  The  catalytic  i s much l e s s than t h a t of the RhCl(Ph P )  3  3  activity species.  S u b s t i t u t i o n of CO i n t o c h l o r o r u t h e n a t e ( I I ) complexes s i m i l a r l y • A  A  i n decreased  «.•  • ,  1  1  7  results  6  activity.  Wilkinson's"'""'"  7  group r e c e n t l y r e p o r t e d t h a t the p r o t o n a t i o n of  Rh (C0Me)^ by aqueous HBF^ 2  produced the green,  a i r stable,  diamagnetic  4+ ion, Rh  2  .  On a d d i t i o n of l i g a n d s , n o t a b l y P ^ ^ '  c a t i o n i c s p e c i e s p r o v i d e new  RhH(CO)(Ph P) 3  3  resulting  systems f o r c a t a l y t i c r e a c t i o n s , i n  p a r t i c u l a r , f o r the h y d r o g e n a t i o n system has an advantage over  the  of alkynes and a l k e n e s .  This  the o t h e r complexes such as R h C l ( P h P )  because i t w i l l o p e r a t e  3  3  and  i n p o l a r media such as methanol.  - 21 Osborn and (S =  coworkers**^ r e p o r t e d  (CH ) CO, C ^ O H ) 3  the Rh''"'""*  i n tetrahydrofuran  2  cations  [RhH (Ph P) S ] 2  e f f e c t i v e l y catalyze  3  2  2  the 119  h y d r o g e n a t i o n of o l e f i n i c and reported  that  a c e t y l e n i c bonds. J a r d i n e and  [py (4nf)RhCl (BH^) ] [py = p y r i d i n e , dmf 2  2  McQuillin  = dimethylformamide]  i s an extremely a c t i v e c a t a l y s t f o r h y d r o g e n a t i o n of o c t - l - e n e cycloalkenes,and  shows h i g h  and  s e l e c t i v i t y i n the homogeneous h y d r o g e n a t i o n  4 5 of 3-oxo-A ' - s t e r o i d s .  C a t a l y t i c asymmetric h y d r o g e n a t i o n u s i n g * i o p t i c a l l y a c t i v e rhodium complexes RhCl^L^, where L = P PhMePr or * 120 PhP(CH *CHMeEt) has been r e p o r t e d . Trichlorotris(4-biphenyl-l2  2  napthylphenyl phosphine)rhodium(III) were a l s o r e p o r t e d  121  and  the rhodium aminophosphine  as h y d r o g e n a t i o n c a t a l y s t s .  RhClCPh^As)^ and  RhClCPh^Sb)^ are l e s s e f f i c i e n t  f o r homogeneous  hydrogenation ''" compared to RhClCPh^P)^.  No  complexes appear  However, R h C l ( E t S )  7  has  to have been s t u d i e d .  been shown to be  ethylene  and  corresponding 3  s u l phide hide 2  3  3,4 ,  an a c t i v e c a t a l y s t f o r the h y d r o g e n a t i o n of  s u b s t i t u t e d ethylenes  s p e c i e s are thought to be  1.62  122  i n DMA,  and  intermediate  rhodium(I)  involved.  C a t a l y t i c Isomerization  of O l e f i n s  Of r e l a t e d i n t e r e s t to c a t a l y t i c h y d r o g e n a t i o n r e a c t i o n s , i s the c a t a l y z e d i s o m e r i z a t i o n of o l e f i n s ; i n some systems, i s o m e r i z a t i o n  may  accompany h y d r o g e n a t i o n . Complexes of rhodium have been i n t e n s i v e l y s t u d i e d as  isomerization  123"~"126 catalysts.  The  major c o n t r i b u t i o n s are  c a t a l y s t i n e t h a n o l i c HCl containing  Rh**  1  and  Rh*  i s obtained  those by Cramer; as an e q u i l i b r i u m m i x t u r e  an a c t i v e ;  by a f a s t a n a e r o b i c r e a c t i o n of i n a c t i v e  +  - 22 -  [(C H ) RhCl] 2  4  2  reported and  other  or ( a c a c H M C ^ )  2  2  w i t h HC1. Harrod and C h a l k  the i s o m e r i z a t i o n of o l e f i n s c a t a l y z e d by rhodium p l a t i n u m m e t a l complexes.  s p e c i e s were thought to be h y d r i d e via  alkyl  In these systems,the  1 0 5  trichloride catalytic  complexes,and i s o m e r i z a t i o n  occurred  intermediates. 127  Reinhart  and Lasky  studied  the i s o m e r i z a t i o n o f  1,3-cycloocta-  d i e n e to 1 , 5 - c y c l o o c t a d i e n e , i n the presence of R h C l ^ and p o s t u l a t e d a somewhat d i f f e r e n t mechanism i n v o l v i n g rearrangement through a i T - a l l y l hydride  intermediate:  -CH -CH=CH„ Z i Z  »  I ~-CH„ * Z  -CH-'  • M  -CH=CH-CH„ i 3  MH  (1.30)  M  A s i m i l a r study i n v o l v i n g i s o m e r i z a t i o n of c i s , t r a n s  1,5-cyclodecadiene 128  has  been e x p l a i n e d  i n terms o f a h y d r i d o - a l k y l  129 More r e c e n t data showed t h a t i r - a l l y l i c i n the i s o m e r i z a t i o n o f c y c l o o c t a d i e n e s .  intermediate.  complexes a r e  intermediates  43 Abley and M c Q u i l l i n isomerize  oct-l-ene  found that R h C l ( P h P ) 3  i n the absence of hydrogen.  3  and R h C l ( C O ) ( P t ^ P )  2  S i m i l a r s t u d i e s by  39 B i e l l m a n n and Jung using  showed that hydrogen i s n e c e s s a r y f o r i s o m e r i z a t i o n  R h C l ( P h P ) , i m p l y i n g RhH^Cl ( P h P ) 3  3  3  they proposed the f o r m a t i o n  i s the a c t i v e  o f an a l k y l rhodium h y d r i d e  104 139 RhCl(CO)(Ph P) ' 'was r e p o r t e d 3  2  2  heptene i n the presence of H^.  to c a t a l y z e 41 Ugo  catalyst,and as an  intermediate.  the i s o m e r i z a t i o n of 1-  suggested that a t low temperatures  the  co-catalytic activity  of hydrogen to form h y d r i d e s  i s necessary,  but  by i n c r e a s i n g the temperature, the source of hydrogen can be the  - 23 olefin itself,  v i a a b s t r a c t i o n of hydrogen i n the a l l y l i c  position.  130 W e l l s and coworkers they b e l i e v e t h a t containing  studied  isomerization  the c a t a l y t i c  a "vacant s i t e "  species  for olefin  using  RhCl^CPh^P)^ and  i n s o l u t i o n are hydrides  coordination.  For the mechanism o f o l e f i n i s o m e r i z a t i o n , most workers 17,42,104,126,130,131 , , , agree that a m e t a l - a l k y l must be formed. By l o s s o f a hydrogen atom from the carbon atom o t h e r hydrogen atemwas aided, an i s o m e r i z e d a p r o d u c t a f t e r dlscoordination At p r e s e n t  than  t h a t t o which the f i r s t  o l e f i n i s formed and may appear as  (see S e c t i o n 1.42, e q u a t i o n 1.19).  i t cannot be f i r m l y s t a t e d t h a t i s o m e r i z a t i o n i s  a s s o c i a t e d w i t h h y d r o g e n a t i o n , but s e v e r a l o b s e r v a t i o n s  suggest  that 17  it  requires  1.63  ( o r a t l e a s t i s f a c i l i t a t e d by) m o l e c u l a r hydrogen.  Polymerization  o f O l e f i n s and A c e t y l e n e s  Rhodium c h l o r i d e o r n i t r a t e c a t a l y z e s polymerization  s t e r e o s p e c i f i c a l l y the  of b u t a d i e n e i n water o r a l c o h o l t o c r y s t a l l i n e  trans-  132 133 1,4-butadiene. on  '  Butadiene p o l y m e r i z a t i o n  the a d d i t i o n o f r e d u c i n g  agents.  i s greatly  accelerated  T h i s suggests the p a r t i c i p a t i o n of  a lower o x i d a t i o n s t a t e , p o s s i b l y Rh * or a l t e r n a t i v e l y a hydride 13A 135 complex. N a t t a and coworkers r e p o r t e d the R h C l ^ c a t a l y z e d polymerization  o f c y c l o b u t e n e s i n aqueous emulsion t o a c r y s t a l l i n e  p o l y c y c l o b u t y l e n a m e r - 2 o c c u r r i n g v i a a mechanism i n v o l v i n g  coordinated  136 anions.  Bawn and coworkers  solution polymerization  c a r r i e d out a m e c h a n i s t i c  study o f the  o f b u t a d i e n e to l o n g c h a i n polymers i n the  presence of rhodium s a l t s , and concluded t h a t the a c t i v e s p e c i e s a rhodium(I) T T - a l l y l i c hydride.  complex but i n s t e a d a T p - a l l y l i c  The p o l y m e r i z a t i o n  i s not  rhodium(III)  o f b u t a d i e n e c a t a l y z e d by rhodium n i t r a t e 137  in  ethanol  has a l s o been s t u d i e d by E.S.R. s p e c t r o s c o p y .  A radical  - 24 was formed d u r i n g p o l y m e r i z a t i o n . ..and  the steady  state concentration  of the r a d i c a l was i n p r o p o r t i o n to the c o n c e n t r a t i o n of n i t r a t e added. However, a r a d i c a l i n h i b i t o r such as hydroquinone d i d not i n h i b i t polymerization,and  a l s o no random polymer p r o d u c t s were o b t a i n e d .  i n c o n s i s t e n c y was r a t i o n a l i z e d by p o s t u l a t i o n of a mechanism involving a coordinated r a d i c a l Rh  2 +  ( i . e . an a l l y l  The  ,  r a d i c a l c o o r d i n a t e d to  ). 138 Anderson and coworkers  r e p o r t e d the rhodium c h l o r i d e c a t a l y z e d  a d d i t i o n of e t h y l e n e and p r o p y l e n e and  1,3-pentadiene.  to such dimers as b u t a d i e n e ,  Rhodium d e r i v a t i v e s were found  d i m e r i z a t i o n of e t h y l e n e to butenes, butadiene and methyl a c r y l a t e to d i m e t h y l 2-hexenedioate.  isoprene  to c a t a l y z e the'  to 2 , 4 , 6 - o c t a t r i e n e The e x c l u s i v e l y  s t r a i g h t c h a i n s t r u c t u r e s of the l a t t e r two dimers a r e i n marked c o n t r a s t to the c y c l i c and branched c h a i n d i m e r i c p r o d u c t s formed by 139 the o t h e r methods. Rhodium c h l o r i d e was a l s o r e p o r t e d to c a t a l y z e the d i m e r i z a t i o n s of alkenes to a m i x t u r e o f branched and s t r a i g h t 140 c h a i n isomers.  Cramer  has i n v e s t i g a t e d i n d e t a i l the mechanism of  the rhodium c h l o r i d e c a t a l y z e d e t h y l e n e d i m e r i z a t i o n i n e t h a n o l i c HC1 s o l u t i o n ; the a c t i v e c a t a l y s t appears to be the a n i o n  [(C^H^)^Rh^Cl^] .  The a n i o n i s o b t a i n e d d i r e c t l y by d i s s o l u t i o n of [ ( C ^ H ^ ) ^ R h ^ C l ] ^ " e t h a n o l i c HC1.  Cramer has p o s t u l a t e d the f o l l o w i n g mechanism:  in  -  25  -  CH,  CH,  Cl  CH CH  Cl  Cl  2  3  iS2 H  Cl  Cl'  C1  L  H„ Cl  Cl - CH CH CH=CH 3  2CH =CH 2  2  2  - L  2  CHCH CH 2  3  CH CH CH CH 2  Clr Rh  I  /CH  2  2  2  -(H + C l )  Cl  Scheme I I I  (L = s o l v e n t )  This involves Ca)  p r o t o n a t i o n o f the b i s C e t h y l e n e ) r h o d i u m ( I )  rhodium Cb)  complex to an e t h y l  ( I I I ) e t h y l e n e complex.  t h e r a t e determining  rearrangement of the e t h y l - r h o d i u m ( I I I )  e t h y l e n e complex to the b u t y l - r h o d i u m  ( I I I ) complex.  (c)  ( I I I ) complex to rhodium (I) and  t h e c o l l a p s e o f the b u t y l r h o d i u m  butene. (d)  c o o r d i n a t i o n o f t h i s r e s u l t i n g rhodium ( I ) i n step  (c) w i t h two  moles o f e t h y l e n e t o p r o v i d e the i n i t i a l b i s ( e t h y l e n e ) r h o d i u m (I) complex  - 26  -  141 T e y s s i e and  coworkers  reported  m e r i z a t i o n of p h e n y l a c e t y l e n e is  thought not  t h a t RhCl^'SR^O c a t a l y z e s the  i n benzene-ethanol s o l u t i o n .  to be of the r a d i c a l type but may 142  the emulsion p o l y m e r i z a t i o n of b u t a d i e n e rhodium diene  The  poly-  mechanism  be s i m i l a r to t h a t of  which i n v o l v e s f o r m a t i o n  of a  complex.  Rhodium (I) square p l a n a r complexes have a l s o been found  efficient 143-145  f o r the a l l e n e p o l y m e r i z a t i o n i n both p o l a r and n o n - p o l a r media. 146 M a i t l i s and McVey  have s t u d i e d the o l i g o m e r i z a t i o n of  by d i c a r b o n y l complexes such as ir-CgH,_Rh(C0)2 and  diphenylacetylene  [ClRhCCO^J^-  Collman  147 and Rang have prepared a s e r i e s of mononuclear a c e t y l e n e complexes which are p o s s i b l e i n t e r m e d i a t e s i n metal c a t a l y z e d c y c l o o l i g o m e r i z a t i o n s 148 and p o l y m e r i z a t i o n s of a c e t y l e n e s . Katz r e p o r t e d the d i m e r i z a t i o n of 149 norbornadiene c a t a l y z e d by RhClCPh^P)^.  Wilkinson  et a l  that h e x a f l u o r o - 2 - b u t y n e can be o l i g o m e r i z e d by rhodium and  (I) complexes,  they r e c e n t l y r e p o r t e d the d i m e r i z a t i o n of monosubstituted a-hydroxy-  a c e t y l e n e u s i n g RhCl(Ph^P) -"*" °  The mechanism proposed f o r t h i s  5  3  l a t t e r system i s r e p r e s e n t e d  Ph„P H C  T  Rh  p  C  h  R  C  -  C  H  I  p  e  2  C  X  0  /  C II; C  R C III ,C Rh I '. Cl  T T T  i  3  M  e  2  „  — »  ; C  x / °  H  (C)  OH Me_C 2  -  v  Cl  /  /  C=C  H H  X  H  0 (D)  " Ph„P  „  >  (B)  ,H J, H I Rh  S>€' / \ H Me C  H  i  (A)  \  ,  T T T  -  M  RC^ C  • 3  I 2 -0  below: R ' C Ph P HI 3 C C Rh^ Cl 0  ,C1  I M e  have shown  H +  \  I, Rh"Cl(Ph„P) (S) 3 2 0  C CR  •..  Scheme IV  (S = s o l v e n t , i n (C) and (D) the Ph^P groups a r e "omitted f o r c l a r i t y )  - 27 -  (a)  the a c e t y l e n e r e a c t s w i t h  the s o l v a t e d R h C l ^ h ^ P ^ S to g i v e a  square p l a n a r complex of rhodium  (I) w i t h  t r a n s phosphine groups. g  (b)  an o x i d a t i v e c i s - a d d i t i o n of a second a c e t y l e n e molecule to the d  rhodium (I) complex (A). (c)  an a c e t y l i d e group t r a n s f e r from the metal to a carbon atom of  the c o o r d i n a t e d a c e t y l e n e v i a a f o u r - c e n t r e t r a n s i t i o n s t a t e (c) to the p e n t a c o o r d i n a t e d  rhodium  (III) species  leads  (D) i n which the dimer  i s bound to the rhodium by a a bond. (d)  f i n a l l y , a hydride  t r a n s f e r v i a a 3-centre  transition state  produces the dimer.  92 James, of p o i n t s  i n h i s review first  on rhodium complexes, emphasized a number 140  documented by Cramer,  which are v e r y  important,  i n g e n e r a l , f o r r e a c t i o n s of c o o r d i n a t e d o l e f i n s i n c l u d i n g  hydrogenation,  i s o m e r i z a t i o n and p o l y m e r i z a t i o n .  ( i ) the  r e v e r s i b l e o x i d a t i o n of Rh* hydride, and  These main p o i n t s a r e :  by a p r o t o n i c a c i d  to g i v e a Rh***  ( i i ) the i n s e r t i o n of c o o r d i n a t e d o l e f i n between an a l k y l  the m e t a l i o n to which i t i s a t t a c h e d ,  hydrogen i n rhodium ( I I I ) a l k y l and  (iii)  the l a b i l i t y  o l e f i n complexes,  group  of  ( i v ) the ,  importance of a p p r o p r i a t e a u x i l i a r y l i g a n d s to the c a t a l y t i c ness of rhodium.  effective:  The r e a c t i v i t y and r e a c t i o n models f o r h y d r o g e n a t i o n , i s o m e r i z a t i o n J I . .. -i -i • 67,126,151-153 and p o l y m e r i z a t i o n have been the s u b j e c t of some r e c e n t reviews. '  1.64  C a r b o n y l a t i o n and D e c a r b o n y l a t i o n  Reactions  A number of p l a t i n u m m e t a l h a l i d e s have been shown to decarbonyl a t e a v a r i e t y of o r g a n i c compounds, i n c l u d i n g a l c o h o l s ,  aldehydes,  - 28 -  e t h e r s , ketones and a c y l h a l i d e s w i t h the r e s u l t i n g carbonyls.  f o r m a t i o n of metal  Rhodium (I) complexes have been found to be a c t i v e f o r  such r e a c t i o n s . T s u j i and O h n o * ~ ^ ' h a v e r e p o r t e d t h a t RhClCPh^P)^ aldehydes smoothly  at room temperature  p a r a f f i n and RhCl(CO)(Ph^P)^.  decarbonylates  to g i v e the c o r r e s p o n d i n g  Primary aldehydes and most  secondary  aldehydes, except aldehydes w i t h l a r g e r s t e r i c h i n d r a n c e , are decarbonylated e a s i l y .  F u r t h e r s t u d i e s by the same workers*"'"''  showed t h a t a c y l h a l i d e s are a l s o d e c a r b o n y l a t e d to g i v e the o l e f i n s and hydrogen  h a l i d e s . The homogeneous d e c a r b o n y l a t i o n r e a c t i o n s  can  a l s o be c a r r i e d out i n the presence of c a t a l y t i c amounts o f RhCl(CO)(Ph^P)^  at h i g h e r temperatures around  200°*^^'*^  7  i n contrast  to R h C l ^ h ^ P ) ^ which must be used i n s t o i c h i o m e t r i c q u a n t i t i e s at a lower temperature.  RhCl(CO)(Ph^P)^ was  a l s o found to d e c a r b o n y l a t e  aromatic a c i d h a l i d e s * " ^ to g i v e aromatic h a l i d e s .  The mechanism  p o s t u l a t e d f o r d e c a r b o n y l a t i o n of a c y l h a l i d e s i s f o r m u l a t e d below:  -  29  -  RhCl(Ph P) S 3  2  CO  c  Ph_P-Rh-Ph_P + RC1 + o l e f i n + HC1 3  I  "  ^~  3  o  Rh  cr" | ^ C l Ph P 3  (G)  ( B )  Scheme V  The  first  step  involves  reaction of RhCl(Ph P) 3  3  (A) w i t h a c y l  h a l i d e i n an o x i d a t i v e - a d d i t i o n to g i v e the f i v e - c o o r d i n a t e d complex  (E) which was i s o l a t e d .  converted i n t o a six-coordinated a c y l - a l k y l arrangement. RhCl(CO)(Ph P )  0  acyl  When heated i n absence o f CO, E i s alkylcarbonyl  complex  (G) by the  F i n a l l y G i s converted i n t o the o l e f i n and  (B) by a b s t r a c t i n g hydrogen a t the 3 - p o s i t i o n j w h e r e  - 30 there  i s no such hydrogen, a l k y l o r a r y l h a l i d e s a r e formed.  The  o x i d a t i v e a d d i t i o n to form complex E from A i s not r e v e r s i b l e and decarbo n y l a t i o n by t h i s complex i s s t o i c h i o m e t r i c . t i o n using  The c a t a l y t i c  decarbonyla-  RhCl(CO)(Ph^P)2 proceeds through the f o r m a t i o n o f a c y l  complex (F) by o x i d a t i v e - a d d i t i o n . carbon monoxide, CO i s l o s t  When F was heated i n absence o f  and the f i v e - c o o r d i n a t e  ed. Then G i s formed from E as b e f o r e . was e x p l a i n e d  i n a s i m i l a r way.  a c y l complex E was form-  The d e c a r b o n y l a t i o n  o f aldehydes  A l t h o u g h the o x i d a t i v e a d d i t i o n o f  aldehydes i s not known and c o u l d not be s u b s t a n t i a t e d * " ^  T s u j i and  155 Ohno  concluded that  under m i l d (a)  conditions  complexes which a r e a c t i v e f o r d e c a r b o n y l a t i o n s h o u l d s a t i s f y the f o l l o w i n g  requirements:  the complex should be o f a f u l l y reduced low v a l e n c e s t a t e ;  (b) the  complex should be c o o r d i n a t i v e l y u n s a t u r a t e d so t h a t i t can undergo o x i d a t i v e - a d d i t i o n by a c y l h a l i d e s o r aldehydes;  (c) the complex  should c o o r d i n a t e  complex.  CO s t r o n g l y  to form a c a r b o n y l  W i l k i n s o n and coworkers*"^ * ^ a l s o r e p o r t e d e f f i c i e n t f o r decarbonylation  that R h C l ( P h P ) i s 3  o f aldehydes and a c y l h a l i d e s .  A d e t a i l e d k i n e t i c s t u d y * ^ f o r the d e c a r b o n y l a t i o n been g i v e n .  Oxidative-addition  r a t e d e t e r m i n i n g step  i n the d e c a r b o n y l a t i o n  species  was . d e t e c t e d  o f aldehydes has  o f the aldehyde i s thought to be the and the scheme p o s t u l a t e d  was v e r y s i m i l a r to t h a t o f T s u j i and Ohno.*"^ intermediate  3  No h y d r i d o o r a c y l  i n t h i s r e a c t i o n although c l o s e l y r e l a t e d  o f these types have been c h a r a c t e r i z e d  i n the r e a c t i o n s o f ICQ  -ICC  o l e f i n s with RhC^HtPl^P)  and o f a c y l h a l i d e s w i t h R h C l ( P h P ) , 3  3  159 The  scheme  followed  postulated  f o r the d e c a r b o n y l a t i o n  t h a t o f T s u j i and Ohno.*"'"'  of a c y l h a l i d e s  '  - 31  -  The mechanisms p o s t u l a t e d f o r d e c a r b o n y l a t i o n of aldehydes  and  a c y l h a l i d e s by rhodium complexes are s i m i l a r to those p o s t u l a t e d f o r palladium  metal. 162-164  Blum and  coworkers  reported  the RhClCPh^P)^ c a t a l y z e d  d e c a r b o n y l a t i o n of a r o y l h a l i d e s to the c o r r e s p o n d i n g  aryl  compounds.  They p o s t u l a t e d a scheme s i m i l a r  Ohno  although  to t h a t o f T s u j i and  they were unable to d e t e c t the i n t e r m e d i a t e 16 3 RhCl^(COR)(Ph^P)2•  Blum and  coworkers  t h a t the e s s e n t i a l i n t e r m e d i a t e  corresponding  questioned  to E,  the  i n the d e c a r b o n y l a t i o n  assumption  reaction i s  RhCl(CO)(Ph P) 3  2  RhCl(Ph P) 3  3  has  a l s o been r e p o r t e d to d e c a r b o n y l a t e  complexes, C^H^Fe(CO)^(COR), where R = CH ,  CgH^,  3  R h C l ( C O ) ( P h ? ) 2 and 3  labelling product  the c o r r e s p o n d i n g  '  3  hexanoic a c i d g i v e s pent-2-ene.  i s a b s t r a c t e d and  The  final  o l e f i n are formed per atom of rhodium.  The  the  final  h a l i d e s and  155  '''"  RhCl(CO)(Et2PhP)^  step i s thought Carbonylation  b e n z y l h a l i d e s i n the presence of pressure  3  successfully carried out,  and  to t h r e e m o l e c u l e s of  first  c a t a l y t i c amounts of R h C l ( C O ) ( P h P ) ^ under CO  thought to be  Isotopic  5  saturated carboxylic  complex i s  the f o r m a t i o n of the c a r b o x y l a t e complex.  r e a c t i o n s of a l l y l  5  propionic acid gives ethylene,  the s t o i c h i o m e t r y appears complex s i n c e up  be  6  1  i s heated w i t h  a c i d s , o l e f i n s are produced; e.g.  to  3  through m e t h y l group m i g r a t i o n . 166 167  When R h C l ( E t 2 P h P ) 2  but  acyl  C H ( C H ) C H , to g i v e  i r o n a l k y l complex. *^  i n d i c a t e s t h a t a t e r m i n a l CO  i s obtained  the i r o n  57  and  have been  the mechanism of the r e a c t i o n i s  the r e v e r s e of the d e c a r b o x y l a t i o n r e a c t i o n .  These c a r b o n y l a t i o n and  decarbonylation  be v e r y u s e f u l i n o r g a n i c syntheses  r e a c t i o n s are p r o v i n g  s i n c e they  can be c a r r i e d  out  to  - 32 -  smoothly  under m i l d c o n d i t i o n s .  1.7  168  C a r b o n y l Complexes o f Rhodium  169 Hieber and L a g a l l y  found  a stream of CO produced s a t u r a t i n g the CO  that h y d r a t e d RhCl^ when heated i n  [Rh(CO) C1] ; 2  the r e a c t i o n was  2  stream w i t h methanol.  promoted by  When h y d r a t e d RhCl^  was  heated w i t h CO f o r 24 hours a t 200 atmospheres and 200°, HRh(CO)^ obtained.  Stone and c o w o r k e r s * ^  prepared Rh  7  was  (CO).., by t r e a t i n g a  lb  o  d i l u t e methanol s o l u t i o n of RhCl^'SH^O w i t h CO a t 40 atmospheres a t 171 60°, w h i l e C h i n i and Martinengo r e p o r t e d the s y n t h e s i s of R h ^ ( C 0 ) ^ and Rh^(CO)^^ by a d d i t i o n of water to a s o l u t i o n of [ R h ( C O ) C 1 ] , i n o r g a n i c 172 2  2  s o l v e n t s a t u r a t e d w i t h CO a t atmospheric  pressure.  2  A b e l and  Stone  had w r i t t e n a v e r y comprehensive review on the c h e m i s t r y o f  transition  metal c a r b o n y l s e s p e c i a l l y i n terms of s t r u c t u r a l c o n s i d e r a t i o n s .  A  l a r g e number of both mono and d i c a r b o n y l d e r i v a t i v e s of rhodium (I) 92 have been prepared from the [ R h C l ( C O ) ] 2  2  dimer.  These i n c l u d e the  s e r i e s of complexes R h L ( C 0 ) X where X = Ar^P, Ar^As, Ar^Sb,  (PhO)^  2  X = C l , I, S C N ; lRh (C0) X J " 2  2  2  4  the anions  1 7 3  (X = Br, I ) ;  i s the c a r b o x y l a t e , n i t r a t e , [Rh(CO)^PR^J (CO)  1 7 5 2  [Rh(CO) 1  7  '  4  1  7  5  X Z  2  ^~'  C 1  '  B r  '  ^  a  n  2  d  2  where X  t h i o c y a n a t e , s u l p h a t e or c y a n i d e ; * " * ' * ^ 7  where R = C^H^.;"'" the amine  and the complexes  =  the compounds [ R h ( C 0 ) X ]  77  n  ( X  and  complexes  (0-ketone) R h ( C 0 ) . 2  1 7 8  7  RhCl(amine)-  iK^H R h ( C 0 )  1 7 9 2  and  i t s mono and d i s u b s t i t u t e d d e r i v a t i v e s c o n t a i n i n g phosphines, p h o s p h i t e s 180 181 and i s o n i t r i l e s have been p r e p a r e d . P o w e l l and Shaw r e p o r t e d the p r e p a r a t i o n s of R h C l ( C 0 ) ( C H ) , 2  2  [ R h ( C O ) ( P h P ) ( t c n e ) C l ] and 2  3  2  2  4  2  [ R h C l ^ t ( C O ) ] ^ and  [ R h C ^ E t (CO) (PMe Ph) . 2  trans[Rh(CO) LXC1] where L = p y r i d i n e or 2  p - t o l u i d i n e ; x = t e t r a c y a n o e t h y l e n e (tcne) and f u m a r o n i t r i l e  (fmn) have  - 33 -  been r e c e n t l y r e p o r t e d .  182  Kemmitt and N i c o l s  183  v a r i e t y of f l u o r o - o l e f i n s r e a c t w i t h RhClCPh^P)^ the c a r b o n y l complexes (CgF^Pt^P  2  (L = P h P , 3  and R h ^ C ^ L ^ to g i v e  (C^F^P,  ( C g F ^ P h P or  ) and they suggested t h a t CO i s formed by the a c t i o n of t r a c e s  of water p r e s e n t . and  RhCl(CO)L  reported that a  R e c e n t l y two i o n i c c a r b o n y l complexes  [Rh(CO)^O-phenlClO^ The complex  have been  reported.  [Rh(CO) bipy]C10 2  184  RhCl (CO) ( P h ^ P ^ has been s y n t h e s i z e d by the  A u i 4= i i, i 166,167 , . , 8,154,155,157-160 d e c a r b o n y l a t i o n of a l c o h o l s , aldehydes, n  ... 155-160,167 i u i-A 162-164 , 185 acylhalides, aroyl halides, dimethylformamide, f  dioxan and c e r t a i n ketones by u s i n g R h C l ( P h P ) 3  3  185  itself  n  m  a  m  1  A  o  u s i n g RhCl^ i n the presence of Ph^P  (see S e c t i o n  or  1.64).  186 Chatt and Shaw complexes  r e p o r t e d the f o r m a t i o n of rhodium  carbonyl  by p r o l o n g e d treatment of rhodium c h l o r i d e s o l u t i o n s w i t h  CO i n b o i l i n g e t h a n o l f o l l o w e d by a d d i t i o n of the phosphine or a r s i n e to p r o v i d e R h C l ( C 0 ) L 1 187 James and Rempel '  r e p o r t e d the k i n e t i c s t u d i e s o f the  f o r m a t i o n of { R h ( C 0 ) C l ] 2  where L = phosphine or a r s i n e .  2  2  s p e c i e s through CO r e d u c t i o n of the aqueous  s o l u t i o n s of R h C l * 3 H 0 under m i l d c o n d i t i o n s . There was another l a t e r 188 r e p o r t on s i m i l a r f i n d i n g s . However, i n DMA, d i f f e r e n t k i n e t i c s 189 3  2  f o r the f o r m a t i o n of [ R b ( C O ) C l ] 2  2  were observed  show the n e c e s s i t y o f a c o o r d i n a t e d water  and these s t u d i e s  (or h y d r o x i d e ) on rhodium ( I I I )  f o r r e d u c t i o n by CO to o c c u r . g  Complexes such as R h C l ( C O ) ( P h P ) 3  2  of d  configuration  undergo  o x i d a t i v e - a d d i t i o n r e a c t i o n s by adding a wide v a r i e t y of c o v a l e n t molecules to form h e x a c o o r d i n a t e d complexes of d configur 26,27,100,190,191 , ,. , , . ation. The rhodium complexes have l e s s tendency to -  4  -  34  27  undergo o x i d a t i v e - a d d i t i o n s than the i r i d i u m analogues, 191  192  d e r i v a t i v e s w i t h SC^,  195  tetracyanoethylene  HCl,  organic halides,  and a c e t y l e n e s  147  193  but 193  halogens,  have been p r e p a r e d .  '  194  Recently  196  Deeming and Shaw  r e p o r t e d the o x i d a t i v e - a d d i t i o n r e a c t i o n s o f RX,  where R = m e t h y l , a c y l , a l l y l o r s u l p h o n y l h a l i d e s , w i t h t r a n s complexes o f the type to  give  [RhX(CO)L ] 2  (X = h a l i d e , L = P M e ^ h o r A s M e ^ h )  [RhX R(CO)L ]. 2  2  E q u i l i b r i a such a s :  Rh Cl(CO)(Ph P)  + H  I  3  2  2  ^  Rh  I l : i  Cl(CO)(Ph P) H 3  and t h e c o r r e s p o n d i n g r e a c t i o n s w i t h m o l e c u l a r the  e q u i l i b r i a l i e f a r t o the l e f t .  197  n 2  2  (1.31)  2  and CO do e x i s t , b u t  A l t h o u g h rhodium ( I ) c a r b o n y l s  may be q u i t e s t a b l e thermodynamically they a r e h i g h l y l a b i l e ; e.g. the  l i g a n d s o f RhCl(CO)(Ph P) 3  undergo r a p i d exchange,  198  199  '  a  consequence o f t h e f a c i l e S^2 exchange p r o c e s s which i s p o s s i b l e w i t h 8  four-coordinate d  complexes.  S u b s t i t u t i o n o f CO i n rhodium c a r b o n y l  complexes has been s t u d i e d by v a r i o u s workers and b o t h a s s o c i a t i v e i, • u .J andA A d i-s s o c i• a t i v e mechanisms have u been r e p o r « te d. 198-203 1 0 ?  Of the rhodium c a r b o n y l d e r i v a t i v e s o n l y RhCl(CO)(Ph P )  2  1 0 3  '  •  99-102  and R h H ( C O ) ( P h P ) 3  3  have so f a r been r e p o r t e d as a c t i v e  for  homogeneous h y d r o g e n a t i o n (see S e c t i o n  1.8  M o l e c u l a r Oxygen Complexes  catalysts  1.61).  o f Rhodium  M o l e c u l a r oxygen complexes o f rhodium have n o t been w e l l c h a r a c t e r i z e d . . The d e t a i l s o f the p r e p a r a t i o n s o f these complexes be p r e s e n t e d below.  will  - 35 -  RhClCPh^P)^  1 1 1  dichloromethane takes up 1 mole of oxygen y i e l d i n g  l i g h t brown R h ( 0 ) C l ( P h p > 2  3  be d i s p l a c e d by donor  2  (0.5 C H C 1 ) c r y s t a l s . 2  2  72  The oxygen can  72 ligands,such as CO to g i v e R h C l ( C O ) ( P h ^ P ) . 71 2  dichloromethane, R h C l ( P h A s ) 3  3  r e a d i l y absorbs 1 mole of 0  mole of Rh to g i v e a s p e c i e s w i t h p o s s i b l e formula R h C l ( 0 )  2  In  per  (Ph^As^nCH^Cl,^.  2  The 0 ~ c o n t a i n i n g adduct r e a c t s w i t h CO i n c h l o r o f o r m to produce 2  RhCl(CO)(Ph^As) directly  2  i n d i c a t i n g t h a t the oxygen i s most l i k e l y c o o r d i n a t e d  to the m e t a l atom and that no t r i p h e n y l a r s i n e o x i d e i s p r e s e n t .  An u n s o l v a t e d sample of the oxygen adduct h a v i n g the f o r m u l a R h C l ( 0 ) 2  ( P h ^ A s ) ^ * was attempted  i s o l a t e d when the p r e p a r a t i o n of R h C l ( P h A s )  3  was  inair.  The r e a c t i o n of rhodium  3  (l,5-cyclo-octadiene)phenyl(triphenylphosphine)  (I) w i t h gaseous  oxygen i n the presence of excess  triphenyl-  phosphine  i s r e p o r t e d to y i e l d a diamagnetic p r o d u c t of e m p i r i c a l 73 formula R h ( 0 ) ( P h ^ P ) ^ . S i n c e t h i s i s diamagnetic i t must be d i m e r i c or have an e x t r a l i g a n d e.g. h y d r i d e , which was u n d e t e c t e d . 2  By a s i m i l a r procedure, Rh(Ph,jP) ( P h ^ A s ) ^ ^ w a s a l s o p r e p a r e d . 204 James and P a v l i s  in—this  73  l a b o r a t o r y have shown t h a t the d i m e r i c  4anion f R h C l ( S n C l ^ ) ^ ] 2  2  i n acetone s o l u t i o n r e a d i l y absorbs m o l e c u l a r  oxygen which i s thereby a c t i v a t e d f o r o x i d a t i o n of t r i p h e n y l p h o s p h i n e .  CHAPTER I I APPARATUS AND  2.1  Materials  2.11  Rhodium Complexes  EXPERIMENTAL PROCEDURE  The c i s - 1 , 2 , 3 - t r i c h l o r o t r i s ( d i e t h y l s u l p h i d e ) r h o d i u m  (III),  205 RhCl^Et^S).^  was prepared  a c c o r d i n g t o the l i t e r a t u r e  d i e t h y l s u l p h i d e , E t ^ S , w i t h RhCl^-SH^O c r y s t a l l i n e compound analysis  The orange  had the c o r r e c t m e l t i n g p o i n t o f 127° and  micro-  (C = 28.87, H = 6.44, S = 19.33, C l = 23.3%) was fairly consistent w i t h  that c a l c u l a t e d f o r R h C l ( E t S ) 3  22.3%).  i n ethanol.  by r e f l u x i n g  2  3  V i s i b l e and u l t r a v i o l e t  (C = 30.2, H = 6.30, S = 19.42, C l = s p e c t r a i n e t h a n o l gave peaks a t 205  421 my 424 my  (e = 300) and 292 my (e = 370) and 292 my  The  (e = 20100) d i f f e r e n t (e = 25800).  bis(cyclo-octene)chloro-rhodium  from those  (I) complex,  reported,  [RMCgH^^Cl^j  206 was prepared ethanol.  by s t i r r i n g RhCl^SH^O w i t h c y c l o o c t e n e , C g H ^ , i n  The m i c r o c r y s t a l l i n e y e l l o w compound was i d e n t i f i e d  i t s m e l t i n g p o i n t , i n f r a r e d spectrum and a n a l y s i s (found: H = 9.71%, C a l c : C = 53.56, H = 7.81%). y - d i c h l o r o t e t r a e t h y l e n e d i r h o d i u m ( I ) , (C^^^Kh^l^,  from  C =53.56:  was  prepared  123 according  to the method o f Cramer  from e t h y l e n e  and RhCl^SH^O i n  aqueous methanol s o l u t i o n and s t o r e d under r e f r i g e r a t i o n .  - 37 -  The p r e p a r a t i o n of d i c h l o r o b i s ( 2 , 5 - d i t h i a h e x a n e ) r h o d i u m ( I I I ) c h l o r i d e was  207  c a r r i e d out a c c o r d i n g to l i t e r a t u r e  the compound even a f t e r r e p e a t e d r e c r y s t a l l i z a t i o n H = 4.607.,Calc: some  C = 21.20  formed  A new  first  3  C =  2  C = 14.5,  a s o l u t i o n of RhCl^-SH^O i n 100% molar r a t i o of 3:1  of Bz2S:Rh.  o b t a i n e d immediately  e t h a n o l a t room temperature  on s l i g h t warming and t h i s was  3  2  (Calc:  3  The  showed two  sharp bands at 317  region for  (Rh-Cl) mode.  RhCl (Et S) 3  2  3  207  cm '  f a r I.R. 1  208  S = 11.3,  spectrum  and 340 cm  1  The f a r I.R.  complex showed bands a t 316  cm  complexes o f t h i s type are expected to have two 207 (Rh-Cl) modes.  '  Comparison of the two 3  R h C l ' 3 H 0 was 2  was  of  calculated Cl =  11.80%).  RhCl (Bz S) 3  2  3  which are i n the spectrum of the known 1  and 344 infrared  cm  Cis  active  208  suggested t h a t R h C l ( B z S ) 3  i n the  A n a l y s i s of the complex (C = 59.24,  C = 59.30, H = 4.93,  The compound melts at 186°.  to  washed w i t h  S = 11.58, C l = 11.47%) agreed w e l l w i t h t h a t  RhCl (Bz S)  2  3  f a r I.R.  spectra  has the c i s - c o n f i g u r a t i o n .  o b t a i n e d from Platinum Chemicals and s t o r e d  over  s i l i c a gel i n a desiccator. 2.12  3.0%),  (III),  A yellow c r y s t a l l i n e p r e c i p i t a t e  e t h a n o l and d r i e d under vacuum. H = 5.05,  H =  i n the p r e p a r a t i o n .  prepared by adding d i b e n z y l s u l p h i d e , Bz^S,  3  18.30  H = 4.40%) suggested the presence of  complex t r i c h l o r o t r i s ( d i b e n z y l s u l p h i d e ) r h o d i u m  R h C l ( B z S ) , was  cis  (found:  trichloro(2,5-dithiahexane)rhodium(III)(calc:  which was  for  but a n a l y s i s o f  Organic Ligands and S u b s t r a t e s D i e t h y l s u l p h i d e was  o b t a i n e d from Eastman Organic  Chemicals.  - 38  -  Dibenzyl sulphide, cyclooctene, diphenyl sulphide, 2,5-dithiahexane were o b t a i n e d from K and K L a b o r a t o r i e s . further  A l l these were used w i t h o u t  purification.  Maleic acid  (Eastman Kodak, C P .  grade) was  recrystallized  water or w a t e r / e t h a n o l b e f o r e use.  The p u r i t y  point determination.  (Eastman O r g a n i c ) and f u m a r i c  acid  Cinnamic a c i d  was  from  checked by m e l t i n g  ( F i s c h e r S c i e n t i f i c ) were of a reagent grade and were used as such.  2.13  Gases Purified  hydrogen was  hydrogen was  o b t a i n e d from Matheson Company.  passed through a Deoxo c a t a l y t i c p u r i f i e r to remove t r a c e s  of oxygen b e f o r e use. o b t a i n e d as C P .  Carbon monoxide, deuterium and e t h y l e n e were  grade from Matheson Company.  oxygen were from Canadian L i q u i d  2.14  The  Purified  n i t r o g e n and  A i r Company.  Solvents N,N-dimethylacetamide  Organic Chemicals (Kodak).  (b.p. 165-166°) was Purification  c a l c i u m h y d r i d e under n i t r o g e n atmosphere d i s t i l l a t i o n under a n i t r o g e n atmosphere. f r a c t i o n was  collected  purified  involved s t i r r i n g  over  f o r 40 hours, f o l l o w e d by The c o n s t a n t b o i l i n g  d i r e c t l y onto L i n d e 4A M o l e c u l a r s i e v e and  s t o r e d under n i t r o g e n atmosphere. grade) was  o b t a i n e d from Eastman  by s t o r i n g  Dimethyl s u l p h o x i d e (Baker a n a l y s e d  over CaH^  under  f o l l o w e d by d i s t i l l a t i o n under reduced p r e s s u r e . L i n d e 4A m o l e c u l a r s i e v e and s t o r e d under S p e c t r a grade benzene  f o r long I t was  periods,  collected  N^.  and dichloromethane were o b t a i n e d from  onto  39  -  Fisher  Scientific.  S c i e n t i f i c and was  2.15  -  Dimethylformamide used w i t h o u t f u r t h e r  was  o b t a i n e d from F i s c h e r  purification.  Other M a t e r i a l s p-Toluenesulphonic  a c i d and t r i p h e n y l p h o s p h i n e were A.R.  o b t a i n e d from Eastman Kodak, the l a t t e r was benzene-ethanol b e f o r e use. from A l l i e d  Chemical Co.  recrystallized  L i t h i u m c h l o r i d e was  A.R.  grade  from  grade o b t a i n e d  2 : 4 - D i n i t r o p h e n y l h y d r a z i n e was A.R.  grade  o b t a i n e d from B.D.H. L a b o r a t o r y . A l l o t h e r c h e m i c a l s used were of reagent grade. was  Distilled  water  always used when water d i l u t i o n s or aqueous s o l u t i o n p r e p a r a t i o n s  were n e c e s s a r y .  2.2  Apparatus f o r Gas Uptake Measurements A c o n s t a n t p r e s s u r e gas uptake apparatus as shown i n F i g u r e I  was  used f o r k i n e t i c  studies.  The pyrex r e a c t i o n v e s s e l  (A), which c o u l d be c l i p p e d to a m e t a l  rod shaken by motor (I) d u r i n g the r e a c t i o n , was s p i r a l g l a s s arrangement tap  (H).  w i t h tap (C) to the o i l manometer (D) through  The o i l manometer which c o n s i s t e d of a c a p i l l a r y U tube  f i l l e d with butyl phthalate was  connected by a  (a l i q u i d of n e g l i g i b l e vapour p r e s s u r e )  connected to the gas measuring b u r e t t e c o n s i s t i n g o f a mercury  reservoir  (E) and a p r e c i s i o n bored tube (N) of known diameter.  gas measuring b u r e t t e was vacuum n e e d l e v a l v e  The  i n t u r n connected through a Edward's h i g h  (M) to the gas h a n d l i n g p a r t of the a p p a r a t u s ,  which c o n s i s t e d of a mercury manometer ( F ) , the gas i n l e t  (Y) and  Figure 1.  Apparatus f o r c o n s t a n t gas-uptake measurements.  - 41 -  c o n n e c t i o n s to the Welch Duo S e a l r o t a r y vacuum pump (G). The r e a c t i o n f l a s k  (A) was thermostated i n a s i l i c o n e o i l (Dow  Corning 550 f l u i d ) bath (B).  I t consisted of a four l i t r e  glass  beaker i n s u l a t e d by p o l y s t y r e n e foam on a l l s i d e s and e n c l o s e d by a wooden box w i t h a c i r c u l a r h o l e f o r o b s e r v i n g the c o l o u r changes r e a c t i o n mixture. s t y r e n e foam.  o f the  The top o f the o i l - b a t h was w e l l covered by p o l y -  The gas b u r e t t e was immersed i n a thermostated water  bath made from a perspex r e c t a n g u l a r tank.  Both thermostat  baths  were o p e r a t e d u s i n g "Jumo" thermo r e g u l a t o r s w i t h "mere to mere" r e l a y c o n t r o l c i r c u i t s and h e a t i n g p r o v i d e d by 25 watt e l o n g a t e d l i g h t bulbs.  These t o g e t h e r w i t h m e c h a n i c a l s t i r r i n g  t u r e c o n t r o l to w i t h i n ± 0 . 1 ° . was  tempera-  A v e r t i c a l l y mounted t r a v e l l i n g  used to f o l l o w the gas uptake.  telescope  A l a b - c h r o n 1400 timer was used  to r e c o r d the time d u r i n g the k i n e t i c  2.3  ensured  experiments.  Procedure f o r a T y p i c a l Gas Uptake  Experiment  For each experiment, the r e q u i r e d amount o f rhodium complex was weighed  out o r , i f i n s o l u t i o n , p i p e t t e d i n t o r e a c t i o n f l a s k  the s o l u t i o n was made up w i t h the r e q u i r e d amount o f s o l v e n t . was  added  to the above s o l u t i o n i f r e q u i r e d .  (A) and Substrate  I n experiments where the  rhodium complex i n s o l u t i o n was a i r s e n s i t i v e , a r e a c t i o n f l a s k w i t h a side-arm f i t t e d w i t h a hook a t the end was used. was weighed  i n t o a s m a l l g l a s s bucket suspended  The rhodium  complex  from t h e s i d e arm which,  a f t e r removal of a i r from the system, was r o t a t e d t o drop the bucket the s o l u t i o n .  The r e a c t i o n f l a s k  into  (A) was then connected by the s p i r a l  and tap (C) to the g a s - h a n d l i n g p a r t o f the apparatus a t ( 0 ) .  The  :  - 42 r e a c t a n t s o l u t i o n was warming.  The  degassed  r e a c t a n t gas was  by a l t e r n a t e c o o l i n g w i t h pumping admitted  than that r e q u i r e d f o r the experiment closed.  The whole system up to tap  a t a p r e s s u r e somewhat l e s s  and  then taps  (H) was  f l a s k and  (J) and  (M) open.  from  (0) and  t r a n s f e r r e d i n t o the thermostated  closed. up  Gas was  to tap  then admitted  ( C ) , which was  whole system was  (H) and  tap  were s t a r t e d  The  Tap  (J) and  apparatus  was  r e a d i n g of the mercury l e v e l i n  (L) were c l o s e d and  the timer and  (N)  shaker  the o i l l e v e l on the left hand s i d e  to m a i n t a i n zero d i f f e r e n c e i n l e v e l s , g a s , was  i n t o the gas measuring b u r e t t e through  i n h e i g h t of the. mercury was of  was  the needle v a l v e  tap  (J)  and  (M) to g i v e a c o r r e s p o n d i n g r i s e of mercury i n (N).  diameter  (Q)  simultaneously.  of the manometer rose and  valve  opened  pumped out, tap  reaction pressure required  As a r e s u l t of any gas uptake,  admitted  (H) was  spiral  then opened so t h a t the p r e s s u r e i n the  equalised.  Taps (K) and  Tap  to the r e s t of the gas uptake  (M) were c l o s e d w h i l e the i n i t i a l taken.  o i l b a t h w i t h the  (H).  (C) was  a d j u s t e d by u s i n g the mercury manometer.  was  (P) were  s p i r a l arrangement were d i s c o n n e c t e d  to the o i l manometer through  and a f t e r the a i r between tap  (C) and  pumped down w i t h taps (K),  (L),  connected  The  and  (N) was  noted as a f u n c t i o n of time.  needle The  change  S i n c e the  known, the c o r r e s p o n d i n g volume of gas used  was  found and an uptake p l o t of gas consumption i n m o l e s / l i t r e a g a i n s t time c o u l d be drawn.  ;  The use of a s m a l l volume of s o l u t i o n indented v e s s e l  30 ml)  5 ml), a r e l a t i v e l y large  and a h i g h shaking r a t e ensured  of d i f f u s i o n c o n t r o l i n the r a t e of gas  consumption.  the absence  - 43 -  2.4  Gas  S o l u b i l i t y Measurements  Some experiments were c a r r i e d out to determine approximate s o l u b i l i t i e s i n the s o l v e n t s employed a t the c o n d i t i o n s o f and p r e s s u r e used i n k i n e t i c experiments. determined by f i t t i n g  gas  temperature  These s o l u b i l i t i e s were  the p r e v i o u s l y d e s c r i b e d gas-uptake  apparatus  ( F i g u r e I) w i t h a r e a c t i o n f l a s k c o n t a i n i n g a stopcock i n i t s neck. The e n t i r e system of s o l v e n t was DMA  i n c l u d i n g the r e a c t i o n f l a s k w i t h a measured amount  pumped down a t room temperature;  the s o l v e n t s s t u d i e d ,  and DMSO, have low vapour p r e s s u r e s a t room temperature.  tap on the f l a s k was  now  c l o s e d and  B at the d e s i r e d temperature.  The  the f l a s k p l a c e d i n the o i l b a t h system was  now  evacuated  f l a s k tap and  then f i l l e d w i t h the gas to the approximate  desired.  f l a s k tap was  The  immediately  now  to t h a t r e q u i r e d .  shaker s t a r t e d .  The uptake was  temperature  to the  p r e s s u r e •;  opened and  the p r e s s u r e adjusted,  Taps (K) and  (L) were c l o s e d and  the  measured as d e s c r i b e d i n s e c t i o n : 2.3  and the s o l u b i l i t y of the gas i n the p a r t i c u l a r particular  The  s o l v e n t a t the  and p r e s s u r e c o u l d be e v a l u a t e d .  The  determined  s o l u b i l i t y data are r e c o r d e d i n Appendix I .  2.5  R e a c t i o n Product A n a l y s e s  2.51  S o l i d Organic Products For i s o l a t i o n of o r g a n i c h y d r o g e n a t i o n p r o d u c t s i n dimethylacetamide,  the s o l v e n t was  removed by pumping through a l i q u i d n i t r o g e n c o l d  The r e s i d u e i n the m a l e i c and fumaric a c i d systems was w h i l e pumping was  maintained.  of the f l a s k and was  The product was  trap  heated g e n t l y  sublimed onto the neck  c o l l e c t e d and r e c r y s t a l l i z e d .  The product  was  - 44 identified  from i t s m e l t i n g p o i n t and I.R. spectrum  (KBr d i s c o r N u j o l  M u l l method). The o x i d a t i o n product o b t a i n e d from the c a t a l y z e d o x i d a t i o n o f DMSO u s i n g a m i x t u r e o f  was i s o l a t e d by the above d e s c r i b e d method  and a f t e r r e c r y s t a l l i z a t i o n was i d e n t i f i e d by I.R. and m e l t i n g p o i n t .  2.52  Liquid  Products  L i q u i d o r g a n i c p r o d u c t s , H^O and s o l v e n t were s e p a r a t e d from the i n o r g a n i c compounds of the f i n a l r e a c t i o n m i x t u r e by vacuum pumping and  c o l l e c t e d through a  cold trap.  A n a l y s i s was performed  i na  gas chromatograph w i t h a s u i t a b l e column, the r e t e n t i o n time and peak area o f each product b e i n g compared w i t h s t a n d a r d s o l u t i o n s , and f o r the [Rh(CgH ^) C l ^ c a t a l y z e d o x i d a t i o n system, collect  the product as i t came through  attempts were made to  the column.  were used f o r i d e n t i f i c a t i o n of t h e p r o d u c t .  N.M.R. and I.R.  Formation o f d e r i v a t i v e s  c h a r a c t e r i s t i c o f a p a r t i c u l a r f u n c t i o n a l group i n o r g a n i c compounds were a l s o used  f o r s e p a r a t i o n and i d e n t i f i c a t i o n of the product i n the  [Rh(CgH ^) C l ^ c a t a l y z e d o x i d a t i o n system.  2.53  Gaseous Products When gaseous p r o d u c t s were i n d i c a t e d o r q u e s t i o n a b l e i n a g i v e n  r e a c t i o n , a gas. sample was c o l l e c t e d a t the end o f the r e a c t i o n and was  a n a l y z e d . •' The technique i n v o l v e d use o f a double-necked  f l a s k , one neck, b e i n g connected stopcock. was  t o an evacuated  reaction  sample b u l b w i t h a  A t the completion o f the r e a c t i o n the stopcock on the b u l b  opened and a gas sample c o l l e c t e d .  The sample was then a n a l y z e d  - 45 -  by mass spectrometry. gaseous  Chemical t e s t s were a l s o used to i d e n t i f y the  product.  2.54  S o l i d Inorganic  Products  I n o r g a n i c p r o d u c t s were i s o l a t e d by r e d u c i n g  the f i n a l r e a c t i o n  s o l u t i o n to low volumes by pumping through a l i q u i d N^ c o l d t r a p . T h i s was sometimes f o l l o w e d by the a d d i t i o n of a complexing l i g a n d i n a s m a l l volume of an a p p r o p r i a t e s o l v e n t . immediately  The s o l i d s , which formed  o r on slow e v a p o r a t i o n , were c o l l e c t e d and r e c r y s t a l l i s e d  from an a p p r o p r i a t e s o l v e n t o r s o l v e n t m i x t u r e .  The s o l i d s were  c h a r a c t e r i s e d by means of some or a l l of the f o l l o w i n g : point determination, microanalysis.  melting,  I.R. spectrum, conductance measurement and  Microanalyses  were performed by Mr. Borda of t h i s  Department.  2.6  Instrumentation V i s i b l e and u l t r a v i o l e t a b s o r p t i o n s p e c t r a were r e c o r d e d  a P e r k i n Elmer 202 spectrometer; w i t h a thermostated  t h i s c o u l d be f i t t e d when  c e l l compartment.  or 1 cm path l e n g t h s were used. carrying a quickfit j o i n t  Matched s i l i c a  necessary  c e l l s of 1 mm  A c e l l f i t t e d w i t h a micro  for fitting  using  stopcock,  i n t o a s i d e arm o f f l a s k s  c o n t a i n i n g the s o l u t i o n kept under vacuum o r a p a r t i c u l a r  gaseous  atmosphere, was:used to take s p e c t r a of such s o l u t i o n s . I n f r a r e d s p e c t r a were recorded  on P e r k i n Elmer(P.E.) 21, P.E.  I n f r a c o r d 137 and P.E. I n f r a c o r d g r a t i n g spectrophotometer 457 u s i n g KBr d i s c s or n u j o l mulls. of 0.1 mm  or l.mm  NaCl, KBr, C s l p l a t e s and l i q u i d  cells  (NaCl, AgCl)  path l e n g t h s were used. F a r I.R. s p e c t r a were k i n d l y  - 46 -  r e c o r d e d by Mr. A.H. H a r d i n of t h i s department on a double beam P e r k i n Elmer 301  spectrophotometer.  N.M.R. s p e c t r a were o b t a i n e d on V a r i a n H.R.-100 and A-60 n u c l e a r magnetic resonance s p e c t r o m e t e r s .  E.S.R. s p e c t r a were r e c o r d e d on a  V a r i a n A s s o c i a t e s E 3 e l e c t r o n s p i n resonance An aerograph  spectrometer.  model A 90 P gas chromatograph and Beckman GC-2A chromat  graphy u n i t w i t h d i n o n y l p h t h a l a t e column xi?ere used f o r a n a l y s e s of the liquid  samples.  C o n d u c t i v i t y measurements were c a r r i e d out u s i n g a Thomas S e r f a s s c o n d u c t i v i t y b r i d g e model RCM 15 BI w i t h d i p type c o n d u c t i v i t y c e l l s of c e l l c o n s t a n t s of about 0.1 cm *. M e l t i n g p o i n t s were determined p o i n t apparatus  on a S u p e r i o r E l e c t r i c m e l t i n g  and were u n c o r r e c t e d .  Mass s p e c t r a were r e c o r d e d on an  A s s o c i a t e d E l e c t r i c a l I n d u s t r i e s MS 9 mass  spectrometer.  CHAPTER I I I CATALYTIC HYDROGENATION  OF OLEFINIC ACIDS BY RHODIUM ( I I I ) COMPLEXES  CONTAINING SULPHUR LIGANDS  3.1  General  Introduction  In s e a r c h  f o r e f f e c t s of coordinated  l i g a n d s , p a r t i c u l a r l y ir-acceptors, 3 4  on the c a t a l y t i c a c t i v i t y of rhodium complexes, R h C l ^ E t ^ S ^ been found i n t h i s l a b o r a t o r y t o be an e f f i c i e n t homogeneous h y d r o g e n a t i o n o f m a l e i c  '  had  c a t a l y s t f o r the  a c i d (MA), e t h y l e n e  and  trans-cinnamic  acid  (CA). F u r t h e r  d e t a i l e d k i n e t i c s t u d i e s u s i n g CA and fumaric  (FA)  as s u b s t r a t e s were c a r r i e d out t o l e a r n more about the f a c t o r s  governing the s t a b i l i t y o f the p o s t u l a t e d complexes formed genation.  intermediate  (see s e c t i o n 1.2) and i t s l a b i l i t y  acid  Rh (olefin) 1  f o r subsequent hydro-  The h y d r o g e n a t i o n o f FA proved to be somewhat complex because  of accompanying i s o m e r i z a t i o n and i s thus t r e a t e d s e p a r a t e l y i n Chapter IV.  A new R h C l ^ B z , ^ ) . ^ complex was prepared to study the e f f e c t o f  o t h e r monodentate c o o r d i n a t i n g s u l p h u r The  l i g a n d s on c a t a l y t i c  a c t i v i t y of a rhodium complex c o n t a i n i n g c h e l a t e d  dichlorobis(2,5-dithiahexane)rhodium  (III) c h l o r i d e ,  activity.  sulphur  ligands,  [RhCl (DTH) ]Cl 2  2  was a l s o i n v e s t i g a t e d . The  data o b t a i n e d  f o r the p r e v i o u s l y s t u d i e d RhCl.j ( E ^ S ) ^  catalyzed  3 4 h y d r o g e n a t i o n of MA described  '  are of p a r t i c u l a r relevance  i n t h i s chapter  and w i l l  to the s t u d i e s t o be  f i r s t be summarized i n s e c t i o n 3.2.  - 48 -  3.2  Summary o f the P r e v i o u s l y S t u d i e d c <- ' System 3  RhCl (E^S) /MA/H /DMA 3  3  2  4  The k i n e t i c s o f the h y d r o g e n a t i o n were s t u d i e d by f o l l o w i n g uptake i n the c o n s t a n t p r e s s u r e gas uptake apparatus. p l o t s a r e shown i n F i g u r e 2. s t e a d i l y decreased approaching observed  The i n i t i a l more r a p i d uptake o f  to a constant v a l u e which p e r s i s t e d up to r e g i o n s  the end p o i n t .  A t l a t e r stages m e t a l l i c rhodium was  and t h i s c o i n c i d e d w i t h t h e o b s e r v a t i o n o f an i n c r e a s e i n  hydrogenation of  T y p i c a l uptake  rate.  The  s t o i c h i o m e t r y corresponded  Rh*** to Rh* and the complete h y d r o g e n a t i o n  to the r e d u c t i o n  of MA to s u c c i n i c  acid  III (SA).  In the absence o f MA, the i n i t i a l  reduced by  to t h e m e t a l .  Rh  complex was r a p i d l y  No h y d r i d e i n t e r m e d i a t e s were d e t e c t e d  d u r i n g these r e a c t i o n s . The v i s i b l e spectrum  i n DMA a t room  temperature  showed an a b s o r p t i o n maxima a t 426 my w i t h an e x t i n c t i o n  coefficient  308, which decreased to  80°.  of R h C l ( E t S ) 3  2  3  to a c o n s t a n t v a l u e 270 on h e a t i n g t h e s o l u t i o n  When excess Et^S was added to the s o l u t i o n e s s e n t i a l l y the same  a b s o r p t i o n peak appeared  a t 426 my (e = 317) but the O.D. d i d not  change even on h e a t i n g to 8 0 ° .  These data suggested  an e q u i l i b r i u m  i n v o l v i n g d i s s o c i a t i o n o f a Et^S l i g a n d . No i n i t i a l in  complexing  between the Rh*** complex and MA was observed  DMA. When L i C l was added i n a 6:1 r a t i o  ( L i C l : R h ) to a s o l u t i o n o f  R h C l ( E t S ) i n DMA a steady spectrum w i t h a b s o r p t i o n maxima a t h i g h e r wavelength (X . 453 my, e = 163, s h o u l d e r 530 my, e = 46.7) was ° max 3  2  3  o b t a i n e d on s t a n d i n g o r h e a t i n g to 80°.  T h i s i n d i c a t e d the presence  of a  - 49  -  4.0  Time, sec  Figure  2.  Rate p l o t s f o r the R h C l ( E t S ) 3  of MA  i n DMA,  (0) 8.19  (80°,  725  2  mm  x 10~ M, (A) 5.15 3  YL^  x  3  catalyzed 3.0  x 10- M  10 M). _3  2  hydrogenation MA,  [Rh]  :  - 50 -  new h i g h e r The  chloro species.  spectrum o f a s o l u t i o n d u r i n g the h y d r o g e n a t i o n  a shoulder a t 430 my at  (e 218), i n d i c a t i n g a R h  d i f f e r e n t stages  s p e c i e s a t the l i n e a r  and  Rh  1  uptake p l o t s were a n a l y z e d  The I n i t i a l The  initial  and  uptake r e g i o n e x h i b i t e d the presence o f the same  by measuring the i n i t i a l  Rate  r a t e was thought t o i n v o l v e the r e d u c t i o n o f R h ^ The i n i t i a l  The i n i t i a l  r a t e law was  = k,[Rh ] [ H ]  (3.1)  0  J  1  L  "  2  J  w i t h a mean k^ v a l u e of 1.92 M '''sec H  1  at 80°. A s l i g h t  kinetic  D  i s o t o p e e f f e c t k^ 2/k^ 2 = 1.10 was observed,  k^ was e s s e n t i a l l y  independent o f added s t r o n g a c i d ( p - t o l u e n e s u l p h o n i c •. a c i d ) .  and w i t h of  to  ]  dt  the i n i t i a l  1  o r d e r i n [Rh ] ( t o t a l rhodium c o n c e n t r a t i o n ) , and [H^]  independent o f [MA].  d[H  slope  region.  which-was s t a b i l i z e d by r a p i d complexing w i t h MA.  r a t e was f i r s t  Samples taken  region.  the s l o p e o f the l i n e a r  3.21  species.  throughout the l i n e a r  e s s e n t i a l l y the same spectrum s u g g e s t i n g  The  1  r e g i o n showed  r a t e showed an i n v e r s e dependence on added  the l a t t e r a l i m i t i n g r a t e was o b t a i n e d  Tit^S  However, and L i C l  a t about a 1:1 r a t i o  [ C l ] '. [Rh]. These i n h i b i t i o n s on r a t e t o g e t h e r w i t h the s p e c t r o -  s c o p i c changes suggested t h e r e was a t l e a s t d i s s o c i a t i o n o f Et^S from 209 the s t a r t i n g R h C l ( E t 2 S ) 2 complex. 3  The f i n d i n g s o f Dwyer and Nyholm  suggested t h a t the d i s s o c i a t i o n o f Et^S from the complex i n aqueous a c i d  - 51 -  a l c o h o l i c s o l u t i o n s occurs more readily than the d i s s o c i a t i o n of the Cl  ligand.  The k i n e t i c r e s u l t s f o r the i n i t i a l  f o r a p r e - d i s s o c i a t i o n of  K  RhCl_(Et S),  3  Rh  II3:  2  l  RhCl,(Et.S) 3 z z  2  + H  Rh  2  Rh  MA  +  0  H  +  1  2  1 5  RhCl (Et S)  Rh  t S:  E  0  5  r a t e analyzed w e l l  f a S t  +  1  >  H  I I I  Et_S z  Cl (Et S) H" 3  2  2  (3.2)  + H  (3.3)  +  (3.4)  +  Rh*(MA)  (3.5)  These r e a c t i o n s y i e l d e d the r a t e law,  R  a  t  e  Equation  -  - d[H ] 2  _____  (3.6)  The v a l u e of K  __________  +  +  K ^ t R h , ] [H ] 2  k c a l mole  1  -1  *i r  ,  TT  2  (1.97 M ~ s e c ~ 1  t  1  a t 80°) were  a g a i n s t [ E t S ] ; the a c t i v a t i o n p a r a 2  and AS^  t  = -21.4  e.u. were  determined  for k . The data was  6 )  (3.7)  ,  k.[Rh. ] [H ]  (0.047 M a t 80°) and k  = 12.9  (3.  S]  o b t a i n e d from the p l o t of Rate meters AH^  2  i s r e a r r a n g e d to g i v e  [Et Rate  K^ERh ][H ]  -  r a t e i n h i b i t i o n by added C l , t o g e t h e r w i t h the a s c r i b e d to the presence  of a new  spectral  h i g h e r c h l o r o s p e c i e s of  - 52 -  lower r e a c t i v i t y , p o s s i b l y efficient because  3.22  [ R h C l ^ ( E t ^ S ) ^ ] , which was expected to be l e s s  towards h e t e r o l y t i c s p l i t t i n g o f H.^ than RhCl^(Et^S)^DMA  of the e a s i e r displacement o f the DMA m o l e c u l e i n the l a t t e r .  The L i n e a r Rate The extended  l i n e a r r e g i o n of the uptake p l o t s was a s s o c i a t e d w i t h  the h y d r o g e n a t i o n of MA. [H^] and independent  The l i n e a r r a t e was f i r s t  of [MA].  sulphonic a c i d d i d not a f f e c t  o r d e r i n [Rh ] and  A d d i t i o n of Et^S, L i C l or p-toluene the l i n e a r  rate.  F o l l o w i n g the production of Rh"" (MA) r e p r e s e n t e d by e q u a t i o n s 1  (3.. 2) to  (3.5), a m e c h a n i s t i c scheme f o r h y d r o g e n a t i o n c o n s i s t e n t w i t h the k i n e t i c data i s as f o l l o w s :  I Rh (MA)  Rh  1  +  2 • I -=-* Rh  k  +  MA  The data were f i t t e d  H  2  f a S t  >  +  SA  (3.8)  Rh (MA)  (3.5)  I  to a r a t e law o f the form  -d[H„] dt  .  =  k j R h , ][H„] 2 ' 2L  J  (3.9)  1  to g i v e a mean k^ v a l u e o f 0.34 M "'"sec . 1  AH  t 2  The a c t i v a t i o n  t -1 and tsS^ > were 21.4 K c a l mole and -1.0 e.u.  small isotope e f f e c t In the absence  (xJ^2l\^2  parameters,  respectively.  = 1.05) was observed.  of MA o r when the amount o f MA p r e s e n t was  A  - 53 insufficient  to f u l l y  form t h e Rh*(MA) complex, m e t a l was produced  by e i t h e r one o f the r e a c t i o n s ,  R h  or  *  Rh  R h  +  1  The i n i t i a l l y  "J  2  +  R h  fast.  H 2  formed  form R h C l ( E t S ) y ( D M A ) x  °  z  H  (3.10)  Rh°  l a b i l e Rh  +  H  +  (3.11)  s p e c i e s was thought to be o f the  where x+y+z = 4.  The h y d r o g e n a t i o n was compared  to the homogeneous h y d r o g e n a t i o n of o l e f i n s c a t a l y z e d by I r ( C 0 ) C 1 ( P h ^ P ) ^ which d i s s o l v e s i n s o l u t i o n to g i v e Ir(C0)C1(Ph^P) and Ph^P, and was d i s c u s s e d i n terms o f the mechanism g i v e n below:  C- C—H  Scheme VI  (L = l i g a n d , i n c l u d i n g  solvent)  35  - 54  3.3  RhCl (Et S) 3  2  -  C a t a l y z e d H y d r o g e n a t i o n of CA i n  3  DMA  -2 A y e l l o w s o l u t i o n of about 10 found ^1  M in RhCl (Et S) 3  to homogeneously hydrogenate CA at 55°  atm.  2  absence of  reaction with H  3  2  added to a s o l u t i o n of R h C l ( E t S ) 3  2  uptake corresponded  2  the complete hydrogenation x 10~  M Rh,  3  3.0  observed  of CA.  x 10~  when [Rh] or  A d d i t i o n of CA has of  RhCl (Et S) 3  initial  2  RhCl (Et S) at  2  442  my  The and  3  i n DMA  3  i n DMA  suggesting  CA.  1  Initial  initial  Rate  The  system  spectrum  t h e r e i s no  A s o l u t i o n of CA  and  r e g i o n showed a  shoulder  species.  Initial  ; the l i n e a r MA  obtained  the r e g i o n of l i n e a r rate  k i n e t i c s of t h i s system were examined i n the i n i t i a l  The  found  and  (E = 3 0 0 ) , i n d i c a t i v e of a Rh  to Rh  and  1  proved to be  e f f e c t on the v i s i b l e  (see s e c t i o n 3.2)  CA as i n the c o r r e s p o n d i n g  The  to R h  v a r i e d (Figure 3).  e s s e n t i a l l y no  the l i n e a r r e g i o n s e p a r a t e l y . III I  3.31  was  was  1 1 1  1  2  i n the l i n e a r h y d r o g e n a t i o n  the r e d u c t i o n of Rh of  stoichiometry  x•-10~ M H  c u r v a t u r e f o l l o w e d by  2  hydrogena-  An e s s e n t i a l l y l i n e a r p l o t  M CA and '2.40  2  [H ]  complexing between R h  3  i n the  apparatus.  to the r e d u c t i o n of R h ^  f o r t u i t o u s s i n c e more i n i t i a l was  The  and  3  f o l l o w e d i n the c o n s t a n t p r e s s u r e gas uptake  the H  5.0  i n DMA  2  3  T y p i c a l gas uptake p l o t s a r e shown i n f i g u r e 3.  at  deposited  RhCl (Et S) .  Excess CA was t i o n was  CA showed no  was  and hydrogen p r e s s u r e  At h i g h e r temperatures^around 80°, m e t a l was  d u r i n g the r e a c t i o n .  of  i n DMA  3  region  rate i s associated with  rate, w i t h the  ( s e c t i o n s 3.2,  hydrogenation  3.21,  3.22).  •  r a t e c o u l d be measured w i t h c o n s i d e r a b l e accuracy  to be f i r s t  o r d e r i n [Rh] and  [H ] and  independent of  and  [CA]  - 55 -  0  1000  2000 Time,sec  F i g u r e 3.  Rate p l o t s f o r the R h C l ( E t S ) 3  CA i n DMA [Rh]: 5.0  2  3  a t 55° {(2.40 x 10~ M  H  3  (0) 5.0 x 10~ M, (A) 1.0 3  x 10~ M 3  Rh,  1.92  x 10~ M 3  c a t a l y z e d h y d r o g e n a t i o n of  „ , 2  2 ?  x 10 3.0  3.0 _ 2  x 10~ M 2  CA,  ) ; (a):  x 10~ M 2  CA)}.  - 56 when the l a t t e r was 4,5).  The  average  -  v a r i e d between 0.03 v a l u e of  M-0.06 M  at 55° i s 0.50 H  s l i g h t deuterium  isotope effect  2-  r a t e i s i n h i b i t e d by the a d d i t i o n of L i C l  rate  M *sec *.  There i s a  D  (k^ 2/k^  r e a c h i n g a l i m i t i n g v a l u e at ^ 0.01  (Table I , F i g u r e s  M;  1.15).  The  initial  (0.0025 M to 0.05  Et S  also inhibited  2  M) the  initial  (Table I ) . A good A r r h e n i u s r a t e p l o t was  o b t a i n e d f o r the temperature  50-60° w i t h a c t i v a t i o n parameters AH^' K c a l mole * and  0.6  _ 2.0  I n h i b i t i o n by E t S  e.u.,  AS^  respectively  suggests  2  and  equal to 20.0  Z  range 0.6  (Table I I , F i g u r e 6 ) .  the s o l v a t e d s p e c i e s R h C l ^ ( E t S ) D M A 2  2  i s formed by d i s s o c i a t i o n of E t S as i n the c o r r e s p o n d i n g MA system. Th e v a l u e e s t i m a t e d from e q u a t i o n (3.7), u s i n g the s i n g l e datum 2  at  0.05  0.01  M  M Et S 2  at 55°  -1  and k  t  ^ % k  (c f . K  ±  = 0.50 = 0.047 M  M _1  -1  sec  -1  , was  of the o r d e r of  at 8 0 ° ) which appears 4  somewhat low f o r the o b s e r v a t i o n of the good f i r s t on  to be  o r d e r dependence  [Rh ]. The k^ v a l u e and  reaction  a c t i v a t i o n parameters r e f e r to the r e d u c t i o n  ( e q u a t i o n 3.3).  The k^ v a l u e , 0.50  comparable to the k^ v a l u e of 0.47 ponding  MA  M *sec * a t 55°, i s  M *sec * e s t i m a t e d f o r the c o r r e s -  system from the temperature  dependence.  Surprisingly,  however, the a c t i v a t i o n parameters are q u i t e d i f f e r e n t . d i s c u s s e d l a t e r i n Chapter  V,  s e c t i o n 5.12.  f o r m a t i o n of the Rh*(CA) complex i s thought same as i n the c o r r e s p o n d i n g MA  This w i l l  The mechanism f o r the to be e s s e n t i a l l y  system (equations 3.2  to  3.5).  the  be  TABLE I RhCl (Et S) 3  2  C a t a l y z e d Hydrogenation of CA  3  K i n e t i c Data a t 55° i n DMA The e f f e c t o f [Rh], [H ] , [CA], [ L i C l ] and [Et„S] on the i n i t i a l  [Rh] x 10  3  [CA] M  x 10  2  [H ]  M  x 10  3  k  I n i t i a l Rate  2  M  x 10  M sec"  6  ±  M sec  1  _ 1  -  1.0  3.0  2.40  3.21  2.5  3.0  2.40  3.40  0.57  5.0  3.0  2.40  5.80  0.49  6.5  3.0  2.40  7.72  0.50  8.0  3.0  . 2.40  9.62  0.50  10.0  3.0  2.40  12.00  0.50  15.0  3.0  2.40  16.84  0.47  5.0  6.0  2.40  6.00  0.50  5.0  3.0  1.92  4.80  0.50  5.0  3.0  1.28  3.20  0.50  5.0  3.0  0.90  2.30  0.51  5.0  3.0  2.40  3.40  0.28  a  5.0  3.0  2.40  2.20  0.18  b  5.0  3.0  2.40  1.20  0.10°  5.0  3.0  2.40  1.00  0.08  d  5.0  3.0  2.40  5.20  0.43  e  5.0  3.0  2.40  0.80  0.07  f  1  0.0025 M L i C l  1  0.05 M L i C l  added;  added;  e  •  0.005 M L i C l added;  b  D  2  i n place of H ; 2  f  c  0,.01 M L i C l  0.05  added;  M E t S added. 2  rate.  - 58  F i g u r e 4.  RhCl (Et^S)^ 3  -  c a t a l y z e d h y d r o g e n a t i o n of CA  Dependence of i n i t i a l r a t e on 3.0  x 10~ M 2  CA).  [Rh],  (2.40  i n DMA x 10 M 3  at H^,  55°.  - 59 -  - 60  -  TABLE I I RhCl (Et S) 3  2  3  C a t a l y z e d Hydrogenation of CA  in  DMA  Temperature dependence of [Rh] = 5.0  T  x 10~  [H ]  3  M,  [CAJ = 3.0  x 10~  Initial  2  M  Slope  x 10^ M sec  k  1  ^  x 10  52  2.40  4.02  55  2.40  5.80  58  2.39  8.01  0.67  61  2.38  10.03  0.84  3  M  2  M "'"sec  1  0.34 ,  0.49  - 61 -  - 62 -  3.32  The  L i n e a r Rate  The k i n e t i c data were q u i t e d i f f e r e n t system.  The  r a t e of h y d r o g e n a t i o n  to those found  increases with  f o r the  [Rh] at  lower  c o n c e n t r a t i o n s but approaches a c o n s t a n t v a l u e a t about 0.015 (Table I I I , F i g u r e 7). of  [MA]  The  rate i s f i r s t  (Table I I I , F i g u r e 8).-  o r d e r i n [H^] and  A d d i t i o n of L i C l i n h i b i t e d  a t i o n r a t e r e a c h i n g a l i m i t i n g v a l u e at 0.01 also i n h i b i t e d The LiCl,  M  [Rh]  independent the hydrogen-  a d d i t i o n of  Et^S  the r a t e (Table_ I I I ) .  dependence on  suggests  M LiCl;  MA  [Rh], t o g e t h e r w i t h the i n h i b i t i o n by Et^S  t h a t t h e r e i s d i s s o c i a t i o n of e i t h e r C l  the Rh*(CA) complex. t a k i n g i n t o account  or Et^S  or from  A g e n e r a l m e c h a n i s t i c scheme f o r hydrogenation, possible Cl  or Et^S  dissociation,is  represented  below  Rh  I  K  (CA)X  n  2  Rh  >5  I  (CA)X  (I)  Rh  I  2 -=-*  k n  T  or C l , DMA  . n-1  X  (3.12)  l i g a n d i s o m i t t e d , the  number i s l i k e l y  (CA)X _  Rh X  +  (ID  (X stands f o r Et^S coordination  . n-1  1  +  +  CA  H  2  fact-  >  to, be  I Rh X  Rh  T  (CA)X  total  4)  +  product  (3.13)  . n-1  (3.14)  F o l l o w i n g the d i s s o c i a t i o n of X, Rh*(CA)X _^ r e a c t s w i t h B. i n a n  r a t e d e t e r m i n i n g s t e p . t o g i v e the hydrogenated r a t e of h y d r o g e n a t i o n  i s g i v e n by  product and  Rh*X  .. n-1  The  - 63 -  TABLE I I I RhCl (Et S) 3  2  3  Catalyzed  H y d r o g e n a t i o n of CA  K i n e t i c Data a t 55° i n DMA The  e f f e c t of  [Rh],  [Rh] x 10  3  [ H ] ,[CA], 2  [LiCl]  and [Et S] on the  [CA] M  x 10  2  [H ]  Linear  2  M  x 10  linear  rate  x 10^ M sec  M  3  rate  1.0  3.0  2.40  2.48  2.5  3.0  2.40  3.40  5.0  3.0  2.40  4.60  6.5  3.0  2.40  5.08  8.0  3.0  2.40  5.52  10.0  3.0  2.40  6.16  15.0  3.0  2.40  6.32  5.0  6.0  2.40  4.40  5.0  3.0  1.92  3.69  5.0  3.0  1.28  2.60  5.0  3.0  0.90  2.21  5.0  3.0  2.40  3.10  a  5.0  3.0  2.40  2.32  b  5.0  3.0  2.40  1.60  C  5.0  3.0  2.40  1.60  d  5.0  3.0  2.40  4.00  e  5.0  3.0  2.40  0.40  f  a  0.0025 M L i C l added;  d  0.05 M L i C l  added;  6  0.005 M L i C l D  added;  instead of H ;  f  C  0.01 M L i C l  added;  0.05 M (Et S) added.  1  oO  '  0  1  1  1  4-0  [Rh] x 1 0 , 3  Figure  7. "'RhCl '(Et S) - catalyzed" hydrogenation 3  on [Rh]  2  3  (2.40  10~ M 3  x  H  2>  3.0  1  8.0  x 10^ M 2  1  1  16.0  M  of CA i n DMA CA)  1  12.0  a t 55°.  Dependence of l i n e a r  rate  - 65 -  - 66 -d[H ] d  Expressing  =  t  k [Rh (CA)X _ ][H ]  (3.15)  1  2  n  1  2  [Rh"'" (CA)X^_^] i n terms of [Rh ] g i v e s -d[H ]  k K [ R h ,][H ]  2  ~ d t ~  2  2  K  =  2  2  +  [X]  ( 3  -  1 6 )  The c o n c e n t r a t i o n of X expressed i n terms of [Rh ] , t a k i n g i n t o account the d i s s o c i a t i o n o f e i t h e r E t S or C l  d u r i n g the p r o d u c t i o n of  2  the Rh^(CA)X  complex  (see s e c t i o n 3.31) i s of the form  [X] = [ I I ] + a[Rh ]  K  to be 1 or 2)  (3.17)  _ [II][X] • [Rh. ] - [ I I ]  2  ([X] - a[Rh =  ])[X] (3.18)  (a + l ) [ R h ]-[X] (a[Rh  Thus  (a i s l i k e l y  ]-K )± / ( a [ R h . . ] - K ) + 4 K ( a + l ) [ R h ] - j -2  0  [X] =  0  Only the p o s i t i v e r o o t i s m e a n i n g f u l . i n t o equation  S u b s t i t u t i o n of e q u a t i o n  k K [Rh ][H ] —  ;  -r  (3.19)  2  At v e r y low [Rh ] , e q u a t i o n  -d[-H ] '  (3.20)  ::  K +a[Rh, ]  dt  (3.19)  (3.16) g i v e s  -d[H ] dt  0  J K  2 2  + 2(a+2)K [Rh 2  ] + a [Rh ] 2  2  3.20 can be approximated to  k K [Rh, ][H J K  .K„  2~  +  -T  =  k [Rh ] [ H J 2 2" 0  l  J L  (3.21)  - 67 At v e r y h i g h  [Rh, ] or when [Rh, ] ^> K  -d[H ]  k K [ R h .][H ]  2  2  dt  2  2  a[Rh  ]  a[Rh  2 k K  The mechanism based the  +  —  T  ] T  [H ] — - —  (3.22)  on E t S  or C l  2  [Rh] dependence ( F i g u r e 7) and  d i s s o c i a t i o n i s favoured  —  d i s s o c i a t i o n i s consistent with  the H  (see p. 7 0 ) .  dependence ( F i g u r e 8 ) .  2  The  Et S 2  f i n a l r e a c t i v e Rh*(CA)X n-1 3 4  complex has  at l e a s t 1 c o o r d i n a t e d E t S 2  catalyzed hydrogenation RhCl^" 3H 0*' in  are q u i t e d i f f e r e n t  From the i n i t i a l  to  t 0.3  2  from  those of the  system and hence 'a' i n e q u a t i o n 3.17  3  to be 1.  v a l u e of k K  2  systems which i s a t t r i b u t e d to the Et,,S c o o r d i n a t i o n to  2  the R h C l ^ E t , ^ )  be 1.5  s i n c e the r a t e s o f R h C l ^ ( E t S ) ^ '  2  M  _ 1  sec  as 2.8  i s very  s l o p e of F i g u r e 7, the v a l u e of k  _ 1  a t 55°. -3 -1  x 10  sec  The  r a t e a t 0.015  , hence K  2  was  M  likely  was  2  Rh*  found  [Rh ] gave the  e s t i m a t e d to be 1.9  _  -3 K0.4) , x u s10i n g M. the The singK l e vdatum added e E t S ] (K^ equals 0.05 alue a et s t i0.05 m a t e dM from q ut aSt i o(n[ E3.7 repla ced M by 2  2  2  p l u s the d i s s o c i a t e d E t S  a r i s i n g from the p r o d u c t i o n of Rh*(CA)X _^)and  2  k  ^ k  = 1.5  ± 0.3  M  -1  n  sec  -1  , was  These two methods of c a l c u l a t i n g K  of the o r d e r of 1.4 2  i s shown i n T a b l e  assuming v a r i a t i o n i n r a t e w i t h temperature  AH  ... 2  e.u.  2 >  ± 0.9  K c a l mole  x 10  -3  M.  _]_  IV;  i s due p r i n c i p a l l y to the  the r e a s o n a b l e A r r h e n i u s p l o t  v a l u e of 21.3  ± 0.3  agree q u i t e w e l l .  The dependence of r a t e on temperature  changes i n k  2  and a A S  ( F i g u r e 9) i n d i c a t e s a  J. 2  v a l u e of 5.6 ±  1.8  - 68 -  TABLE IV RhCl (Et S) 3  2  3  C a t a l y z e d Hydrogenation of CA i n DMA  Temperature Dependence of the Hydrogenation Rate [Rh] = 5.0 x 1 0 ~  T °r ^  [H ] 3  M,  [CA] = 3.0 x 1 0 ~  Linear  2  x 10  3  M  x 10  6  Rate M sec  52  2.32  3.32  55  2.32  4.60  58  2.32  6.48  61  2.32  8.40  2  M  - 69 -  \  - 70 The  -  mechanism of the CA h y d r o g e n a t i o n i s presumably s i m i l a r to  that of the MA  system but n o t a b l e  dependences on both added Et^S  d i f f e r e n c e s are the  and  Cl  as w e l l as the unusual  dependence i n the CA  system; a d d i t i o n of Et^S  the r e a c t i o n of MA.  I t i s p o s s i b l e that species  e q u i l i b r i u m of the i s very  would be observed. effects since  sterically  The  the two  this respect.  system, no  systems are not  However, c o o r d i n a t e d  s i t e and  system,  10*36,106 d i s s o c i a t i o n  7  occurs b e f o r e  H  a d d i t i o n and  i n h i b i t i o n by  The  reaching  concentration" solubility,  or C l  to any e l e c t r o n i c different in  perhaps b l o c k i n g a  prospective  (Scheme VI)  requires  2  i t seems l i k e l y here t h a t d i s s o c i a t i o n  could block  2  oxidative  the s i t e r e q u i r e d by  addition  the  hydride.  of a l i m i t i n g r a t e w i t h i n c r e a s i n g " c a t a l y s t  of an a c t i v e c a t a l y s t formed by  =»  M + L active  first  l i m i t i n g h a l f order i n rate  due  If  RhclCPh^P) (solvent)  t o  such an o b s e r v a t i o n  the r a t e w i l l be  i n an  In the w e l l known RhClCPh^P)^  i s most u n u s u a l , and  ML  inhibit  trans-CA would g i v e a more  2  A d d i t i o n of C l  Et^S  expected to be v e r y  of E t S w i l l r e l i e v e overcrowding to promote the H reaction.  n  f o r both systems.  the o x i d a t i v e a d d i t i o n step  c o o r d i n a t i o n of 2 c i s h y d r i d e s .  d i d not  [& ]  (I) i s i n v o l v e d  i n h i b i t i o n i s p r o b a b l y not  crowded complex than the MA,  coordination  or C l  type shown i n e q u a t i o n 3.12  l a r g e f o r the MA  inverse  order  at h i g h e r  ( F i g u r e 7) i n the CA  has  except f o r a l i m i t a t i o n not been observed.  by  In the  case  d i s s o c i a t i o n , s u c h as :  (K s m a l l )  at low Rh  Rh  (3.23)  concentration  concentrations.  The  and  reach a  levelling off  system r e s u l t s from the Et S l i b e r a t e d i n  the r e d u c t i o n o f Rh  to Rh  , inhibiting  the d i s s o c i a t i o n of the  R h * ( o l e f i n ) complex to produce the a c t i v e form  3.4  C a t a l y t i c A c t i v i t y of R h C l ( B z S ) 3  The new  RhCl (Bz S) 3  2  2  complex was  3  f o r the h y d r o g e n a t i o n o f MA,  ( e q u a t i o n 3.12).  in  2  DMA  found to-be an a c t i v e  FA and CA i n DMA.  catalyst  These s t u d i e s were  c a r r i e d out f o r purpose of comparison w i t h the c o r r e s p o n d i n g E t S 2  systems  to i n v e s t i g a t e p o s s i b l e s t e r i c or e l e c t r o n i c e f f e c t s on  replac-  i n g the e t h y l groups by b e n z y l groups, p a r t i c u l a r l y w i t h r e g a r d to s t a b i l i z a t i o n of the Rh*  intermediates.  —2 A 10  M RhCl (Bz S) 3  2  3  i n DMA  homogeneously hydrogenated MA  and 1 atm of E^; w i t h FA and CA, m e t a l was at 80°. was  V,  produced d u r i n g the r e a c t i o n  At 55° homogeneous h y d r o g e n a t i o n of FA o c c u r r e d , but metal  s t i l l produced d u r i n g the CA h y d r o g e n a t i o n .  be due  a t 80°  T h i s was  to the lower s t a b i l i t y of the R h * ( o l e f i n ) formed  s e c t i o n s 5.1  and 5.11).  The R h C l ( B z S ) 3  2  3  the m e t a l a t 80° i n the absence o f s u b s t r a t e .  thought to  (see Chapter  complex i s reduced to The k i n e t i c s of the  h y d r o g e n a t i o n of MA were s t u d i e d i n d e t a i l and w i l l be r e p o r t e d i n section  3.5.  At room temperature, the v i s i b l e spectrum of the orange of the complex i n DMA which changed  showed a b s o r p t i o n maxima at 430 my  to a steady spectrum  to 80° f o r 10 minutes. the presence of MA,  (X  440 my,  e = 388)  (e =  solution 438)  on h e a t i n g  The same s p e c t r a l changes were observed i n  FA or CA i n d i c a t i n g  r e a c t w i t h the Rh*** complex.  t h a t these s u b s t r a t e s do not  - 72  -  K i n e t i c s of the R h C l ^ C B z ^ S ) ^ C a t a l y z e d  3.5 The  k i n e t i c s of t h i s system were s t u d i e d  Hydrogenation of MA  i n the same way  as  in  the  3 4 c o r r e s p o n d i n g R h C l ^ C E t ^ S ) ^ c a t a l y z e d h y d r o g e n a t i o n of MA s e c t i o n 3.2).  A t y p i c a l gas  more r a p i d i n i t i a l  p e r s i s t e d u n t i l near the end  showed a s h o u l d e r at 430  3.51  The The  rate i s f i r s t  (Table V,  Figures  e q u a t i o n 3.1 complex.  Initial  The  and  11,  of R h  to R h  1 1 1  1  and  The the  e = 284  which suggests  a Rh  1  stoichio-  complete  spectrum taken i n the h y d r o g e n a t i o n my,  The  a l i n e a r r e g i o n which  p o i n t when m e t a l d e p o s i t e d .  metry corresponded to the r e d u c t i o n The  (see  uptake p l o t i s shown i n f i g u r e 10.  uptake i s f o l l o w e d by  h y d r o g e n a t i o n of MA.  '  region  species.  Rate order 12).  i n [Rh The  J and  r a t e law  of k^  and  independent of  [MA]  i s of the form shown i n  r e f e r s to the r e d u c t i o n  average v a l u e  [H^]  of R h  i s 3.55  to form a Rh^(MA)  1 1 1  M ^sec  p r e c i p i t a t i o n i n the uptake experiments  The  ( F i g u r e 10)  p o i n t of metal  i n d i c a t e s that  the  complex i s s t a b l i z e d by h a v i n g a minimum of 1 mole of MA  per mole of  Rh  Addition  0.05  and  the Rh^(MA) complex i s a c t i v e f o r h y d r o g e n a t i o n .  M p-toluenesulphonic  a c i d had  no  significant  H slight  deuterium i s o t o p e e f f e c t , k^  A d d i t i o n of 0.005 M L i C l  of  e f f e c t on r a t e .  D 2/k^  (at the  1:1  2 = 1.1,  was  observed.  r a t i o of Cl~:Rh) decreased  markedly to a v a l u e which changed l i t t l e on  f u r t h e r a d d i t i o n of C l ;  a d d i t i o n of Bz^S  rate  a l s o i n h i b i t e d the i n i t i a l  data suggest t h a t Bz^S for  the  d i s s o c i a t e s to p r o v i d e  a c t i v a t i o n of H^  A  (Table V).  a vacant s i t e  k  These required  as i n the s i m i l a r R h C l ^ E t ^ S ) . ^ c a t a l y z e d h y d r o 3 4 g e n a t i o n of o l e f i n i c a c i d s ' (see s e c t i o n s 3.21, 3.31). The r e a c t i o n s  DMA  2000  4000  6000  8000  10,000  Time, sec F i g u r e 10.  Rate p l o t f o r the R h C l ( B z S ) 3  (2.5 x 1 0 M _3  2  3  c a t a l y z e d h y d r o g e n a t i o n of MA i n DMA  Rh, 2.32 x 10" M H , 3  2  3.0 x 10~ M 2  MA).  at 80°,  - 74 TABLE V RhCl^CBz^S)^ C a t a l y z e d  Hydrogenation o f MA  K i n e t i c Data a t 80° i n DMA Dependence o f i n i t i a l  r a t e On [Rh], [ H ] , 2  [MA],  [ L i C l ] and  [Bz S] 2  [MA]  [H ]  x 10 M  x 10 M  x 10 M  0.5  3.0  2.32  4.52  3.89  1.0  3.0  2.32  7.60  3.28  2.5  3.0  2.32  20.00  3.45  5.0  3.0  2.32  40.00  3.45  7.5  3.0  2.32  56.80  3.27  10.0  3.0  2.32  78.00  3.45  15.0  6.0  2.32  90.00  2.59  5.0  6.0  2.32  42.00  3.62  5.0  3.0  0.49  10.30  4.10  5.0  3.0  0.99  18.00  3.63  5.0  3.0  1.70  29.20  3.43  5.0  3.0  2.49  44.70  3.59  5.0  3.0  2.32  . 1.12  o.oi  5.0  3.0  2.32  1.40  0.12  b  5.0  3.0  2.32  12.20  1.05  C  5.0  3.0  2.32  4.48  0.39  d  5.0  3.0  2.32  36.00  3.10  6  5.0  3.0  2.32  36.00  3.10  f  [Rh] 3  a  2  b  Initial  2  3  C  2  2  k  d  0.10 M acid.  l  M sec  x 10^ M sec *  M LiCl; 0.05 M B z S ; 0.045 f 0.05 M p - t o l u e n e s u l p h o n i c D^ i n s t e a d of H ; 0.005 M L i C l ;  rate  Bz S; 2  a  -  75  -  - 76 -  F i g u r e 12.  RhCl (Bz^S) 3  3  c a t a l y z e d h y d r o g e n a t i o n of MA  • Dependence of i n i t i a l 3.0  x 10~ M 2  MA).  i n DMA  r a t e i n [H^], (5.0 x 10 M 3  a t 80°. Rh,  for  the i n i t i a l  r e d u c t i o n of the RhCl^CBz^S)^ complex are of the  shown i n e q u a t i o n s initial 1.6  3.2-3.5.  A n a l y s i s of the d a t a on the i n h i b i t i o n of  r a t e by ~&z^S a c c o r d i n g to e q u a t i o n 3.7  ± 0.3  x 10  form  g i v e s a v a l u e of  K^,  M at 80° which i n d i c a t e s t h a t the complex i s ~ 80%  d i s s o c i a t e d a t 0.005 M[Rh], and  a" k  v a l u e of 4.3  M *sec *.  approaches the k^_ v a l u e s i n c e the d i s s o c i a t i o n i s . a b o u t 80% (see equations  3.1  and  k^  complete  3.6).  K i n e t i c measurements over  the temperature  range  yielded  a reasonable A r r h e n i u s r a t e p l o t  (Table VI, F i g u r e 13).  parameters were found  _ 2.4  to be 27.8  r e s p e c t i v e l y , which are thought  K c a l mole * and  to r e f e r to the  The 23.0  activation - 8.0  e.u.  reaction  k Rh  The to  I ] : i  Cl (Bz S) 3  lower  2  +  2  H  Rh  2  3  and CA systems.  2  2  3  3  2  +  2  y  of lower r e a c t i v i t y  of MA.  (3.24)  +  similar of  MA  towards h e t e r o l y t i c  3.24.  Rate the  However, the k i n e t i c s of t h i s system are more  c o m p l i c a t e d than f o r the c o r r e s p o n d i n g R h C l ( E t S ) 3  dependence o f . h y d r o g e n a t i o n r a t e w i t h F i g u r e 14;  H  to the p r o d u c t i o n of a h i g h e r  l i n e a r r e g i o n i n the uptake p l o t i s a s s o c i a t e d w i t h  hydrogenation  higher  2  catalyzed hydrogenation  as r e p r e s e n t e d i n e q u a t i o n  The.Linear The  2  T h i s i s p r o b a b l y due  chloro species^ [ R h C l ^ ( B z S ) ]  3.52  C l ( B z S ) H~  l i m i t i n g rate with increasing c h l o r i d e i s very  t h a t obs erved f o r the R h C l ( E t S )  splitting'of H  i : t I  the r a t e appears  2  3  system.  The  [Rh] i s shown i n T a b l e VII  to be approaching  a constant value at  [Rh] which i s v e r y s i m i l a r to the R h C l ( E t S ) 3  2  3  catalyzed  and  - 78 -  TABLE VI RhCl (Bz S) 3  2  C a t a l y z e d Hydrogenation  3  of MA i n DMA  Temperature Dependence of [Rh] = 5.0 x 1 0 ~ T C°  [H J 2  x 10  3  M  3  M,  [MA] = 3.0 x 1 0 ~  2  M  I n i t i a l Slope x  loS.sec"  1  k .  M sec - 1  70  2.36  18.0  1.53  75  2.34  25.6  2.19  80  2.32  40.0  3.45  85  2.30  68.0  5.92  90  2.25  120.0  10.70  - 79 -  0.8  oo o 0.4  0 2.75  2.85  2.95  (~ x 1 0 ) , K" 3  F i g u r e 13.  RhCl (Bz2S) 3  Arrhenius  3  c a t a l y z e d h y d r o g e n a t i o n of MA  p l o t f o r the i n i t i a l  (5.0 x 1 0 M _3  1  Rh,  3.0  x 10~ M 2  reduction, MA).  in  DMA,  - 80 -  TABLE V I I RhCl (Bz S) 3  2  C a t a l y z e d Hydrogenation o f MA  3  K i n e t i c Data a t 80° i n DMA Dependence of l i n e a r r a t e on [Rh], [ H ] ,  [MA], [ L i C l ] and  2  [Rh] x 10  a  3  [MA] M  x 10  2  2  x 10  3  2  Linear rate  IH ]  M  [Bz S]  M  x 10^ M sec  0.5  3.0  2.32  1.40  1.0  3.0  2.32  2.20  2.5  3.0  2.32  3.42  5.0  3.0  2.32  5.60  7.5  3.0  2.32  7.00  10.0  3.0  2.32  8.00  15.0  6.0  2.32  5.0  6.0  2.32  5.62  5.0  3.0  0.49  1.23  5.0  3.0  0.99  2.20  5.0  3.0  1.70  3.66  5.0  3.0  2.49  5.54  5.0  3.0  2.32  4.17  3  5.0  3.0  2.32  2.20  b  5.0  3.0  . 2.32  4.00  c  5.0  3.0  2.32  1.76  d  5.0  3.0  2.32  5.00  e  5.0  3.0  2.32  5.00  f  0.005 M L i C l ;  b  0.045 M L i C l ;  D„ i n p l a c e o f H •  C  10.00-11.50  0.05 M B z S ; 2  0.05 M p - t o l u e n e s u l p h o n i c  d  0.10 M B z S ; 2  acid.  1  gure 14.  RhCl  (Bz„S)  catalyzed, h y d r o g e n a t i o n of MA i n DMA -3 -? r a t e on [Rh], (2.32 x 10 M ' , 3.0 x 10 M MA).  a t 80°.. Dependence of l i n e a r  - 82  hydrogenation [H ]  of CA  (see s e c t i o n 3.32).  (Table V I I , F i g u r e 15)  2  B z S or L i C l i n h i b i t e d 2  contrasted with of MA.  The  or L i C l .  -  and  The  rate i s f i r s t  independent of  [MA].  the r a t e of h y d r o g e n a t i o n  the c o r r e s p o n d i n g  RhCl (Et S) 3  2  in  A d d i t i o n of  (Table V I I ) , which catalyzed  3  order  hydrogenation  observed r a t e i n h i b i t i o n suggested d i s s o c i a t i o n of B z S 2  D i s s o c i a t i o n of B z S i s thought to be more l i k e l y because 2  t h i s would r e l i e v e the s t e r i c crowding i n the Rh^MA) complex d u r i n g the o x i d a t i v e a d d i t i o n of the 2 c i s h y d r i d e s  (Scheme V I ) .  Other s t u d i e s  210 have i n d i c a t e d t h a t i n AuCl,j(Bz S)  , B z S i s more l a b i l e than the C l ,  2  and  t h i s was  F i g u r e 14,  2  a t t r i b u t e d to s t e r i c f a c t o r s . (equation  3.21)  k  From the i n i t i a l  s l o p e of  was  found to be 1.2 ± 0.2 M ''"sec The 6 —1 l i m i t i n g r a t e c o u l d be around (11-20) x 10 M sec , g i v i n g K of the -3 -1 -1 magnitude (5.7) x 10 M. A v a l u e of k , 1.08 M sec , and K , of the 2 -2 2  2  0  2  o r d e r of 10  M,  were o b t a i n e d  from the i n v e r s e dependence on  [ B z S ] (Table VII) u s i n g e q u a t i o n 2  3.7  A d d i t i o n of p - t o l u e n e s u l p h o n i c . the r a t e .  principally A H  2  +  and  2  2  to changes i n k  respectively.  AS^"  fc  by  k ). 2  2  on  is  (Table V I I ) .  Assuming v a r i a t i o n i n r a t e w i t h  and  k  p r a c t i c a l l y no e f f e c t  temperature dependence of r a t e of h y d r o g e n a t i o n  Table V I I I .  gave  a c i d had  by K  There i s a s l i g h t deuterium i s o t o p e e f f e c t when D  used i n p l a c e of H The  (replacing  2 >  as 21.0  temperature i s  the good A r r h e n i u s ± 0.9  i s shown i n  Kcal mole"  1  rate plot  and  0.5  due (Figure  + 2.5  e.u.,  16)  - 84 -  TABLE V I I I RhCl (Bz S) 3  2  3  C a t a l y z e d Hydrogenation o f MA  i n DMA  Temperature Dependence of the Hydrogenation Rate [Rh] = 5.0 x 1 0 ~  T °C  [H^] x 10  o  M  3  M,  MA = 3.0 x 1 0  _ 2  M  Rate of Hydrogenation x 10  A  M sec  70  2.36  1.92  75  2.34  3.04  80  2.32  5.60  85  2.30  7.36  90  2.25  12.20  —1  - 85 -  F i g u r e 16.  A r r h e n i u s p l o t f o r the R h C l ^ l B ^ S ^ of MA  i n DMA,  (5.0 x 10~ M 3  Rh,  3.0  catalyzed x 10~ M 2  hydrogenation  MA).  - 86 3.6  The No  -  C a t a l y t i c A c t i v i t y of  [RhCl (DTH)  pure sample of the complex was  s e c t i o n 2.11).  Preliminary  obtained  studies using  ]C1 (see Chapter I I ,  the somewhat impure  s t a r t i n g m a t e r i a l i n d i c a t e d that the complex i n DMA homogeneous h y d r o g e n a t i o n of MA made to p u r i f y the  3.7  at 80°.  Hence no  i s not  active for  f u r t h e r attempt  was  complex.  Conclusion Rli"*"  complexes c o n t a i n i n g monodentate s u l p h u r  11  l i g a n d s i n DMA  a c t i v e c a t a l y s t s f o r homogeneous h y d r o g e n a t i o n of o l e f i n s . b a s i c mechanism i n v o l v e s r e d u c t i o n i n s o l u t i o n by Rh (olefin) 1  complexes.  complexes and described  The  1  The  s t a b i l i t y and  sections  complexes b e i n g  i n a c t i v i t y of  1  The  which i s s t a b i l i z e d  f o r h y d r o g e n a t i o n are  l a b i l i t y of these hydrogenation  5.11-5.12  Further  the  Rh (olefin) 1  will  be  support f o r  the  the a c t i v e c a t a l y s t s i s shown i n Chapter  [RhCl (DTH) ] C l i n DMA  to the c h e l a t i n g s u l p h u r  d i s s o c i a t i o n i s p o s s i b l e to p r o v i d e  the  VI.  f o r homogeneous hydro-  2  g e n a t i o n i s almost c e r t a i n l y due  activity.  to R h  1 1 1  active species  the d e t a i l e d mechanism of  i n Chapter V,  Rh (olefin) The  the o l e f i n .  of R h  are  ligands;  no  "vacant" s i t e n e c e s s a r y f o r  In general,complexes w i t h c h e l a t i n g l i g a n d s are not  active  207 catalysts. hydride  Walton  species  i n ethanol, I t was  reported  and  that  [ R h C l ( D T H ) ^ ] C l i s unable to form 2  the Rh^^-S bond i s v e r y  i . e . R h C l ( D T H ) ( P h P ) was 3  3  s t a b l e to r e d u c t i o n by  i s o l a t e d i n s t e a d of  suggested t h a t the mechanism f o r the p r o d u c t i o n  goes v i a a s p e c i e s  such as  [RhCl (DTH) (Ph P)] 2  molecules i s monodentate, f o l l o w e d formation  of the new  Rh-Cl bond.  2  by  3  Ph^P  RhCl(Ph P) . 3  3  of R h C l ( D T H ) ( P h P ) 3  i n which one  the l o s s of t h a t DTH  3  of the  DTH  molecule  and  CHAPTER IV CATALYTIC HYDROGENATION AND ISOMERIZATION OF FUMARIC ACID CATALYZED BY R h C l ( E t S ) 3  4.1  2  IN DMA  3  Introduction As d e s c r i b e d i n s e c t i o n 3.1, FA was used as one o f the s u b s t r a t e s  i n the study  o f hydrogenations c a t a l y z e d by R h C l ( E t S ) 3  k i n e t i c s of the h y d r o g e n a t i o n accompanying i s o m e r i z a t i o n . accompany hydrogenation and  1.62).  4.2  2  i n DMA.  The  o f FA proved t o be q u i t e complex due to an I s o m e r i z a t i o n has been found p r e v i o u s l y to  c a t a l y z e d by rhodium complexes  The f o l l o w i n g d e s c r i b e s such a study  Stoichiometry  3  ( s e c t i o n s 1.42  in detail.  o f the R h C l ( E t S ) / F A / H / D M A System 3  2  3  2  _2 A y e l l o w s o l u t i o n of about 10  M RhCl (Et S) 3  2  3  i n DMA,containing  excess FA,was found to absorb hydrogen a t convenient and hydrogen p r e s s u r e  o f about 1 atmosphere.  The r a t e of H  was measured i n the same way as the R h C l ( E t S ) 3  of MA  ( s e c t i o n 3.2).  Typical H  2  r a t e s from 40-80°  2  3  catalyzed  2  uptake hydrogenation  uptake p l o t s are shown i n F i g u r e 17;  the s t o i c h i o m e t r y a t the p o i n t o f metal p r e c i p i t a t i o n corresponded to I I I T  the r e d u c t i o n o f Rh  to Rh  and the complete h y d r o g e n a t i o n  At 0.03 M FA ( F i g u r e 17) the f a s t i n i t i a l uptake of H  2  o f FA.  was f o l l o w e d by  a c o n t i n u a l l y d e c r e a s i n g r a t e w i t h no l i n e a r r e g i o n as observed i n • 3 4 the c o r r e s p o n d i n g MA ' system ( F i g u r e 2 ) ; a l i n e a r r e g i o n was observed  -  88  -  -  however, a t h i g h e r  [FA]  89  ( F i g u r e 17).  the i n i t i a l p a r t of a hydrogenation a b s o r p t i o n at 1960 There was was  cm  3  at  which had  430 mu  ?  a very  2  3  stretch.  of complexing between FA and R h  i n DMA.  reacted with H  (e = 338);  3  f o r ^1 min  2  a t 80° showed a  a s o l u t i o n sample i n which about 2/3  had been hydrogenated showed a s l i g h t s h o u l d e r a t 440 my These s o l u t i o n s were s e n s i t i v e to a i r . such  FA to a and  3  FA  shoulder of the  (e =  FA  236).  i s probably present i n  1  K i n e t i c s of the R h C l ( E t S ) / F A / H / D M A 3  In  to  there  solutions.  4.3  for  Rh  as  1 1 1  A s o l u t i o n of R h C l ( E t S ) 2  during  broad  change i n the v i s i b l e spectrum on adding  s o l u t i o n of R h C l ( E t S ) i n DMA  reaction showed  which c o u l d i n d i c a t e a Rh-H  1  no evidence  p r a c t i c a l l y no  A s o l u t i o n sample taken  experiments w i t h 0.03  first Rh  1  2  M  3  implies a f i r s t  of FA to SA  o r d e r decrease  System  [FA], the uptake p l o t s analyzed w e l l  o r d e r dependence on t o t a l H  and hydrogenation  2  uptake, i . e . r e d u c t i o n of  2  (Table IX, F i g u r e 18).  Rh  1 1 1  This  i n [FA] s i n c e the r e d u c t i o n of  Rh  1 1 1  3 4 has been shown to be f i r s t s m a l l amount of H  '  In any  r e q u i r e d to reduce R h ^  2  significantly affect o r d e r dependence on k',  order.  the In p l o t ,  X v i i i c h  [FA] at < 0.03  1  case, the to Rh^  i s u n l i k e l y to  must demonstrate a  [FA].  The  pseudo f i r s t  o b t a i n e d from the In p l o t s , are shown i n T a b l e IX,  approximate f i r s t mate f i r s t effect k  order.dependence on /k'  1  H  measured.  order dependence on  2  =1.1  and  [H ] 2  relatively  [Rh]  ( F i g u r e 19)  ( F i g u r e 20).  first order  constants  they showed an and  an a p p r o x i -  A small isotope  an enhancement of r a t e by added a c i d were  D 2  A d d i t i o n of 0.005 M L i C l markedly i n h i b i t e d  the r a t e and  a  - 90 -  TABLE IX k' Values  f o r the R h C l ( E t S ) 3  2  3  C a t a l y z e d Hydrogenation  at 8 0 ° , [FA] = 3.0 x 1 0 ~  [Rh] x 10  3  2  x 10  in x 10  3  _  sec  1.25  2.32  0.40  2.50  2.32  1.00  5.00  2.32  1.80  7.50  2.32  2.30  5.00  1.64  0.98  5.00  0.96  0.60  5.00  2.32  1.60  5.00  2.32  3.22  5.00  2.32  0.30°  5.00  2.32  1.46  D„ i n p l a c e of H.; C  M  3  M  k»  [H ] M  2  0.005 M [ L i C l ] ;  d  o f FA i n DMA  1  a  b  d  0.10 M p - t o l u e n e s u l p h o n i c ' a c i d ; 0.005 M  [Et S]. 2  H-0.04  o  H M  H-0.84  u  I  CO  VO  O ca  -1.64 400  800  1200  Time, sec F i g u r e 18.  Rate p l o t and of FA i n DMA absorbed  the c o r r e s p o n d i n g l n p l o t f o r the R h C l ( E t S ) 3  at 80°.  (2.5 x 10~ M ITT (A) l n [Rh + FA]. 3  Rh,  2.32  x 10 M -3  H  2  3.0  3  c a t a l y z e d hydrogenation x 10~ M 2  FA).  (0)  H 2  0  - 93 -  - 94 -  s l i g h t decrease higher  i n r a t e was observed  [ F A ] , the r a t e p l o t s  on a d d i t i o n o f 0.005 M Et^S.  At  ( F i g u r e 17) d i d not a n a l y z e f o r f i r s t  order. An o v e r a l l f i r s t  o r d e r l n p l o t appeared  to be i n c o m p a t i b l e w i t h  the two r a t e d e t e r m i n i n g s t e p s , namely the i n i t i a l f o l l o w e d by h y d r o g e n a t i o n  r e d u c t i o n o f Rh***  as p o s t u l a t e d f o r the o t h e r Rh  III  catalyzed  1 4 hydrogenations  i n DMA  ' (see Chapter  III).  a n a l y s i s o f the Rh*** systems i n Chapter were a n a l y z e d by measuring the i n i t i a l  Hence by analogy w i t h the  I I I , a l l the uptake p l o t s  s l o p e , thought  to i n v o l v e  r e d u c t i o n o f Rh*** to Rh*, and when p o s s i b l e , the r a t e s o f the extended l i n e a r r e g i o n a s s o c i a t e d w i t h the h y d r o g e n a t i o n 4.31  The I n i t i a l The  initial  process.  Rate  r a t e i s seen t o be f i r s t  o r d e r i n [Rh. ] and t ^ ] ,  (Table X, F i g u r e s 21,22) and e s s e n t i a l l y independent  o f [FA] w h i l e  the l a t t e r was v a r i e d from 0.03-0.12 M. Thus the r a t e law i n i t i a l l y i s  -d[H ] =  dt  k. [Rh ] [ H J 1 "2 JL  (4.1)  J  Values o f k^ a t 80° a r e g i v e n i n T a b l e X, the mean v a l u e b e i n g 7.40 M H There i s a s l i g h t k i n e t i c i s o t o p e e f f e c t of  p-toluenesulphonic... a c i d had l i t t l e  of  Et S 2  D  (k^ 2/k^ 2 = 1.1).  Addition  e f f e c t on the r a t e ; w h i l e  addition  and L i C l r e t a r d e d the r a t e s (Table X) as i n the R h C l ( E t S ) 3  catalyzed hydrogenation combination  of k  fc  and  of MA.  -1 -1 sec  2  3  As b e f o r e k^ can be c o n s i d e r e d as a  as r e p r e s e n t e d i n equations  3.1-3.3 and 3.6.  - 95 -  TABLE X RhCl (Et S) 3  2  C a t a l y z e d Hydrogenation  3  o f FA i n DMA  K i n e t i c Data a t 80° The iRh] x 10  2  {FA] M  3  E f f e c t o f [Rh], [ H ] and [FA] and a d d i t i v e s on the i n i t i a l r a t e  x 10  M  2  [H ]  I n i t i a l Rate  2  x 10  3  M  x 10  5  k  M sec"  ±  M sec  1  _ 1  5.0  3.0  2.32  8.4  7.25  5.0  6.0  2.32  9.0  7.75  5.0  9.0  2.32  9.2  7.95  5.0  12.0  2.32  9.0  7.80  5.0  50.0  2.32  4.8  4.14  1.25  3.0  2.32  2.0  7.20  2.5  3.0  2.32  4.0  7.20  7.5  3.0  2.32  12.4  7.15  5.0  3.0  1.64  5.9  7.20  5.0  3.0  0.96  3.5  7.20  5.0  3.0  2.32  1.2  1.16  5.0  3.0  2.32  7.2  6.20  5.0  3.0  2.32  1.3  1.10°  5.0  3.0  2.32  8.0  6.90  d  5.0  3.0  2.32  8.0  6.90  6  a  '  0. 005 M L i C l ;  b  0.005 M E t S ;  0.1 M p - t o l u e n e s u l p h o n i c  2  acid.  C  0.05 M E t S ; 2  d  D  2  a  b  i n s t e a d of  -  96  -  [Rh]  Figure  21.  RhCl (Et S) 3  2  2  3.0  3  M  c a t a l y z e d h y d r o g e n a t i o n of FA  3  Dependence of i n i t i a l H,  x 10 ,  x 10~ M 2  FA).  r a t e on  [Rh],  (2.32  in x 10  DMA. 3  M  - 97 -  - 98 A YL v a l u e of 0.07  M at 80°  RhCl (Et S) and Et.S 3 I _ I 0  0.05  0  f o r the d i s s o c i a t i o n of R h C l ( E t S ) 3  (equation 3.2)  0  M added Et^S u s i n g e q u a t i o n  was  3.7  obtained  and k  2  to  3  from the r a t e at  = k^ = 7.4  M *sec *.  The  3 4 value i s comparable to t h a t determined f o r the MA  system, '  0.047 M at 80°. K i n e t i c measurements of k^ over  the temperature range 70-84°  (Table XI) gave a good A r r h e n i u s r a t e p l o t ( F i g u r e 23). The a c t i v a t i o n T ~f —1 parameters AH^ and AS^ , 14.3 - 0-5 K c a l mole and -14.4 ± 3.8 e.u., r e f e r to the r e a c t i o n  RhCl (Et S) 3  4.32  The  2  +  2  H  2  >  Rh  I l : L  Cl (Et S) H 3  2  2  +  H  (3.3)  +  "Hydrogenation" Region  A f t e r the i n i t i a l  r a p i d uptake of H  2  f o r the f i r s t  500  l a t t e r p a r t of the uptake must be a s s o c i a t e d mainly w i t h a  sec.  the  hydrogenation  process. The k i n e t i c data at FA > 0.06 the l i n e a r s l o p e increasing  M were a n a l y z e d by measurement of  (Table X I I ) ; the r a t e perhaps decreased  [FA], a p p a r e n t l y approaching  somewhat w i t h  a l i m i t i n g v a l u e at 0.5  M  [FA]. For data at 0.03  M  [FA], the k' v a l u e s a s s o c i a t e d w i t h the hydrogen-  a t i o n are shown i n Table IX, and shown i n F i g u r e s 19 and A d d i t i o n of 0.05 w i t h s l o p e 1.8 initial  x.10  20  the dependences on  [Rh]  and  [H ] 2  are  (see s e c t i o n 4.3).  M E t S to 0.03 2  FA r e s u l t e d i n a l i n e a r  ^ M sec * (Table XII) which was  r a t e (1.3 x 10 ^ M sec * ) .  region  g r e a t e r than  the  - 99 -  TABLE XI RhCl (Et S) 3  2  3  C a t a l y z e d Hydrogenation of FA i n DMA Temperature Dependence of  [Rh T °C  1 1 1  ]  = 5.0 x 1 0 ~ [H ] x 10  3  M  3  M,  [FA] = 3.0 x 1 0 ~  2  M  I n i t i a l Rate x 10  5 M sec  k^ 1  -  M  1 sec  70  2.36  4.40  3.70  74.5  2.34  5.60  4.80  80  2.32  8.40  7.25  84  2.30  12.50  10.00  - 100  -  1.1  2.78  2.82  2.86 (1/T x 1 0 ) 3  Figure  23.  RhCl (Et S) 3  2  3  , K.  1  c a t a l y z e d h y d r o g e n a t i o n of FA i n  A r r h e n i u s p l o t f o r the i n i t i a l r e d u c t i o n 3.0 x 1 0 ~  2  2.90  M FA).  DMA.  -3 (5.0 x 10 ~" M  Rh,  - 101 -  TABLE XII RhCl  (Et S)  Catalyzed  Hydrogenation o f FA i n DMA  K i n e t i c Data a t 80° V a r i a t i o n of L i n e a r Rate w i t h [Rh]  [FA] M  x 10  L i n e a r Rate  2  *y  O  x 10  [H ] o  M  x 10  [FA]  R  M  x 10  M sec  k  1  M  1  2  sec  5.0  6.0  2.32  - 1.80*  1.55  5.0  9.0  2.32  1.34  1,15  5.0  12.0  2.32  1.56  1.34  5.0  50.0  2.32  1.12  0.97  5.0  3.0  2.32  3  0.05  M  a  [Et S]. 2  C e r t a i n l y not a f i r s t linear  1.84  region.  order p l o t , but there i s no  well-defined  - 102  V a r i a t i o n of k' w i t h  4.4  Deuteration Following  ( s e c t i o n 4.31,  temperature i s shown i n T a b l e  and  Stereochemistry  the p r o d u c t i o n equations  -  of Rh*  of the  XIII.  or  from the i n i t i a l  Addition reduction  3.2-3.4) the Rh*(FA) complex i s thought to  the a c t i v e c a t a l y s t f o r h y d r o g e n a t i o n  as i n the c o r r e s p o n d i n g  be  MA  3 4 system. '  Hcwever, the dependence on  dependence at < 0.03  M  [FA] and  [FA], i . e . f i r s t  independence of  order  [FA] at h i g h e r  suggested t h a t some e q u i l i b r i u m i s i n v o l v e d i n the f o r m a t i o n Rh*(FA) complex and  [FA],  of  the  t h i s c o u l d r e a d i l y g i v e r i s e to the observed  kinetics I  Rh  F ——*  K  +  FA  v  Rh  I  (FA)  • (4.2)  T h i s e q u i l i b r i u m would, however, l e a v e some " f r e e " Rh* which under E metal was  i s known to r e a d i l y decompose to metal.  observed i n the FA system except at the end  Hence some s t a b i l i z i n g system. to MA was  MA  i n solution,  l i g a n d other  conditions.  undertaken to i n v e s t i g a t e such a  of the r e a c t i o n .  than FA must be p r e s e n t  seemed an a t t r a c t i v e p o s s i b i l i t y  under the hydrogenation  However, no  s i n c e FA might be  symmetrically  8.23  p and  8.39  isomerized  Hence a d e u t e r a t i o n  study  possibility.  In the FA system, the d e u t e r o s u c c i n i c a c i d o b t a i n e d bands at 8.12  i n the  showed sharp  u i n d i c a t i n g a m i x t u r e of meso-  d i d e u t e r a t e d , DL-symmetrically  dideuterated  and  211 unsymmetrically symmetrically  dideuterated  SA.  The  e x i s t e n c e of the meso-  d i d e u t e r i a t e d SA i s c o n s i s t e n t w i t h  d u r i n g hydrogenation  assuming c i s a d d i t i o n of the  i s o m e r i z a t i o n of (see Chapter  FA V,  - 103 -  TABLE X I I I RhCl (Et S) 3  2  C a t a l y z e d Hydrogenation of FA i n DMA  3  Temperature Dependence of k' [Rh] = 5.0 x 1 0 ~  T °C  3  M,  [FA] = 3.0 x 1 0 ~  [H ] 2  x 10  3  M  2  k'  x 10  3  70  2.36  0.70  74.5  2.34  1.00  80  2.32  1.80  84  2.30  2.15  sec  M  - 104 -  section  5.12).  The d e u t e r o s u c c i n i c a c i d o b t a i n e d  of MA c a t a l y z e d by R h C l ( E t S ) 3  2  3  showed sharp bands a t 8.10 y and 8.39 y  c o n s i s t e n t w i t h a m i x t u r e of meso s y m m e t r i c a l l y unsymmetrically  dideuterated  from the d e u t e r a t e d  product  SA.  assuming c i s a d d i t i o n o f  The  initial The  3  uptake f o l l o w e d by two c o n s e c u t i v e slope 2  be 1.89 M ''"sec  2  which i s almost i d e n t i c a l to the k^ v a l u e  1  4  The f i r s t  2  sec . 1  uptake a t the break off r e g i o n i n the f i r s t  e i t h e r complete hydrogenation to R h . 1  5  -  6 - 1 M sec  The s t o i c h i o m e t r y  l i n e a r r a t e corresponded  o f MA o r FA and complete r e d u c t i o n o f  When the r a t i o o f [FA] t o [MA] was changed to 0.045M:0.03M,  and h y d r o g e n a t i o n of 2.2 x 10  (1.92 M "'"sec "*")  l i n e a r r a t e was 3.0 x 10  of H  first  M sec '''([Rh] = 5.0 x  2  the second l i n e a r r a t e was 4.5 x 10 %  1 1 1  5  (Figure 24).  Assuming the r a t e i s f i r s t  and  Rh  consisted of a rapid  [ H ] and independent of [MA] and [FA], k^ was found to  found i n the MA system.  to  3  o f a m i x t u r e o f FA (0.03  l i n e a r regions  measured was 2.2 x 10  -3 M, [ H ] = 2.32 x 10 M, T = 8 0 ° ) .  o r d e r i n [Rh],  o f the k i n e t i c s  o f a m i x t u r e o f MA and FA.  (0.03 M) c a t a l y z e d by R h C l ( E t S )  initial  -3  o f FA and MA  H^ uptake p l o t f o r the hydrogenation  M) and MA  ; the s i m p l e r  conclusion.  observed FA i s o m e r i z a t i o n prompted the study  of the h y d r o g e n a t i o n  10  this  Hydrogenation o f a M i x t u r e The  d i d e u t e r a t e d and  No i s o m e r i z a t i o n o f MA i s e v i d e n t  k i n e t i c s i n the MA system supports  4.5  from the d e u t e r a t i o n  c a r r i e d out under the same c o n d i t i o n s , an i n i t i a l  M sec  1  was observed f o l l o w e d by a l i n e a r r e g i o n  —6 —1 l i n e a r r a t e o f 3.2 x 10 M sec  and a s l i g h t l y h i g h e r  rate  with linear  - 105 -  4000  8000  12,000  Time, sec F i g u r e 24.  Rate p l o t f o r the R h C l ( E t S > 3  2  mixture o f MA and FA i n DMA 2.32 x 10" M H , 3  2  3  catalyzed hydrogenation of a  a t 8 0 ° , (5.0 x 10~ M 3  [MA] = [FA] = 3.0 x 10~ M). 2  Rh,  - 106  r a t e , 4.4  x 10  —6  M sec  —1  .  The  break o f f r e g i o n of the f i r s t  -  s t o i c h i o m e t r y of  uptake at  l i n e a r r a t e corresponded to the III  hydrogenation  of MA  the r a t e i s f i r s t  to SA and  [H^]  and  to Rh  0.38  .  independent of  l i n e a r r a t e s gave a k  Assuming [MA]  or  v a l u e of 0.27 2  and  complete  I  r e d u c t i o n of Rh  o r d e r i n [Rh],  the average of the f i r s t  the  [FA],  M ''"sec  1  the average of the second l i n e a r r a t e s gave a k  value  of  M~ sec~ . 1  1  Deuterated  product  sharp bands at 8.10 meso- and  obtained  y , 8.23  DL-symmetrically  dideuterated  from the m i x t u r e of FA and MA  y and  8.40  y c o n s i s t e n t w i t h a m i x t u r e of  dideuterated  SA and  D i s c u s s i o n of the K i n e t i c R e s u l t s  4.61  The  f o r the FA  System.  I n i t i a l Kate  initial  ponding MA  unsymmetrically  SA.  4.6  The  showed  r e d u c t i o n i s thought to be  the same as i n the c o r r e s -  system which i n v o l v e s a s o l v e n t a s s i s t e d d i s s o c i a t i o n of  R h C l ^ C E t ^ S ) ^ f o l l o w e d by  the r a t e d e t e r m i n i n g  heterolytic splitting  of  H. 2  RhCl (Et S)  3  RhCl (Et S)  2  3  3  2  2  K ^  +  systems  (k^  FA  .= 7.40  3  H  I t i s not c l e a r why MA  RhCl (Et S)  1 2  2  Rh  the i n i t i a l M  -1  sec  -1  , k^  III  +  2  Et S  Cl (Et S) H 3  2  = 1.92  measurement f o r the r e d u c t i o n of R h C l ( E t S ) 3  2  3  M  -  2  r a t e s should MA  (3.2)  2  -1  +  differ sec  by H  2  -1  H  +  (3.3)  f o r the FA  ).  at 80°  An  and  independent  to g i v e metal  - 107  gave a f i r s t The  -  o r d e r dependence on  v a l u e of  [H,,], w i t h a  o b t a i n e d by i n i t i a l  v a l u e of 3.00  s l o p e method was  2.40  M *sec  M *sec *.  *. Some  FA e r r o r i s expected from the i n i t i a l of 7.40  M *sec  s l o p e measurement but  * seems too l a r g e to be accounted f o r by  of a " b u i l d up"  i n the i n i t i a l  r a t e due  to ensuing  the k^ the  i s p o s s i b l e t h a t once s m a l l amounts of Rh*  catalytic  s u b s t i t u t i o n process  occurs  assumption  hydrogenation.  There i s a p o s s i b l e r a t i o n a l i z a t i o n f o r the apparent It  value  discrepancy.  s p e c i e s are produced, a  at the Rh*** c e n t r e to g i v e a  R h * * * ( o l e f i n ) complex. Such r e a c t i o n s are w e l l s u b s t a n t i a t e d f o r III I 187 212-216 Rh -Rh systems ' and may r e q u i r e the p r e s e n c e of as l i t t l e -6 I 215 as 10 M Rh . The o v e r a l l r e a c t i o n i s d e p i c t e d below  Rh  it-  III  Rh*  +  +  H  1  Rh  2  olefin  *  I  +  2H  +  (4.3)  Rh* ( o l e f i n )  (4.4)  2e ,1- T . N ^ T ^ Rh (.olefin) + Rh  (olefin)Rh*-Cl-Rh***  1 1 1  C  > Rh  I I I . . .. . , _ , I ( o l e f i n ) + Rh (4.5)  i  Rh  The  III  k  (olefin)  +  B.  l  "intermediate"  (4.6)  " i n t e r m e d i a t e " would be expected to f i n a l l y produce the  complex.  The  initial  Rh*(olefin)  r a t e b e i n g measured c o u l d thus i n c l u d e some  123 126 c o n t r i b u t i o n from e q u a t i o n  4.6.  Cramer  has  postulated  the  III e x i s t e n c e of Rh  ( o l e f i n ) complexes i n the c a t a l y z e d  hydrogenation  of o l e f i n s . An attempt was  made to o b t a i n some evidence  f o r the p r o d u c t i o n  of  /  - 108 -  such a Rh "''(olefin) complex.  The changes i n s p e c t r a o f a s o l u t i o n of  11  RhCl '3H.0 and MA i n DMA a f t e r s u b j e c t i o n to H a t 80° f o r ^ 200 s e c 3 2 2 0  and  then e v a c u a t i o n uptake d u r i n g  were s t u d i e d  ( F i g u r e 25).  There was no measurable  the 200 sec but the i n i t i a l spectrum  changed somewhat (curve II) ; on s t a n d i n g  (Curve 1)  i n vacuum, the spectrum changed  to t h a t shown i n curve I I I . An i s o s b e s t i c p o i n t a t 458 my was observed i n d i c a t i n g a m i x t u r e o f 2 s p e c i e s , p o s s i b l y Rh H^O, DMA l i g a n d s a r e o m i t t e d ) . being  a m i x t u r e o f Rh  III  III  III (MA) ( C l ,  The p o s s i b i l i t y o f s p e c t r a If and III  and the measured uptake corresponded to 40%  I to Rh , the recorded  spectrum i s t h a t shown i n  curve I V w h i c h a l s o passed through the i s o s b e s t i c 4.62  and Rh  I and Rh (MA) cannot be excluded, however, s i n c e  on f u r t h e r s u b j e c t i o n to  r e d u c t i o n o f Rh  III  point.  The Hydrogenation Region A mechanism (mechanism I) which can e x p l a i n a t l e a s t  the f i r s t [FA]  order  qualitatively  dependence on [FA] a t 0.03 M [FA] and independence o f  at higher  [FA], i s o m e r i z a t i o n o f the FA to MA, and f i r s t  order  dependence on [Rh ] and [U^i i s as f o l l o w s  Rh  III  Rh  Rh  Ii:i  H  Ii:t  k  +  H  +  H  ->  FA  l  III Rh H  2  *  Rh  >  +  1  Rh  1 1 1  H  1 1 1  (4.7)  (4.8)  (alkyl) ^  +  .  +  +H Rh  + H  +  +  SA  ^  = >  Rh  I1[I  H  +  MA  (4.9)  - 110 I  Rh  K  I  Rh  I  +  FA  +  MA  F  I Rh (FA)  Si  Rh  I  (4.2)  (MA)  (4.10)  2 -=->  I Rh  +  SA  (4.11)  3 —^»  I Rh  +  SA  (4.12)  = k [H ] [Rh (FA) ] + k [H ] [Rh (MA) ]  (4.13)  Rh  I  Rh  k  (FA)  +  H  2  (MA)  +  H  2  k  The r a t e of h y d r o g e n a t i o n  i s g i v e n by  -d[H ]  k %[Rh ][H ][MA] I  = k K [Rh ][FA][H ] + I  2  [Rh, ]  F  3  2  = [Rh ] +  [Rh (FA)] +  1  2  [Rh (MA)]  1  (4.14)  1  [Rh ] + K [ R h ] [ F A ] + K ^ R h ^ f M A ] 1  1  p  <[Rh ]{l + Kp [FA] + K^MA]} I  Hence equation  -d[H ]  (k K [H ][FA] + k K [H ][MA])[Rh  2  dt  4.13 becomes  2  =  p  2  1  3  + Kp [FA] +  Whether r e a c t i o n 4.11 or 4.12  M  2  ]  k^MA]  predominates w i l l  v a l u e of k K p [ F A ] and k ^ ^ M A ] and t h i s w i l l 2  (4.15)  depend on the r e l a t i v e i n t u r n depend on the  / - Ill i s o m e r i z a t i o n r a t e which determines [MA].  the r e l a t i v e amounts o f [FA] and  The f a s t e r r a t e s i n the FA system t o g e t h e r w i t h the r e s u l t o f the  FA/MA mixture  s t r o n g l y suggest  later discussion).  that  > k^ and t h a t k_ <  (see a l s o  The i s o m e r i z a t i o n r a t e w i l l be determined  by the  e q u i l i b r i a d e f i n e d i n e q u a t i o n 4.9 but i t must be o f the same o r d e r as the h y d r o g e n a t i o n deuterated The  r a t e because o f the observed  complex k i n e t i c s and  products.  l i n e a r r a t e s observed  the h y d r o g e n a t i o n  at higher  [FA] a r e thought  t o be due t o  o f FA s i n c e the measured r a t e s a r e some three  g r e a t e r than the MA system under c o r r e s p o n d i n g c o n d i t i o n s . i n t h i s l i n e a r r e g i o n the complex i s p r e s e n t almost i.e.  K_[FA] > K^[MA] and e q u a t i o n 4.15 reduces  -d[H d  The k  2  times  Presumably  e n t i r e l y as Rh*(FA) .  to simply  ]  t  =  k [H ][Rh] 2  (4.16)  2  v a l u e so c a l c u l a t e d a r e g i v e n i n T a b l e X I I ; the v a l u e g i v e n a t  h i g h e s t [ F A ] , 0.97 M *sec * i s l i k e l y  to be the b e s t v a l u e f o r r e a c t i o n  4.11. At the lower  [FA], the k i n e t i c s w i l l be more c o m p l i c a t e d s i n c e as  the MA i s produced, i t w i l l  compete f o r the c o o r d i n a t i o n w i t h Rh* and  s i n c e the Rh*(MA) complex hydrogenates d e c r e a s i n g r a t e w i l l be observed order p l o t s ) .  (the d a t a i n f a c t a n a l y z e f o r f i r s t  As the r e a c t i o n proceeds  numerator and the K^MA]  more s l o w l y a c o n t i n u a l l y  the k^K^jH^][MA] term i n the  term i n the denominator o f e q u a t i o n 4.15 w i l l  i n c r e a s e i n v a l u e w h i l e the K [FA] term w i l l d e c r e a s e . it  i s p o s s i b l e t h a t the k K [H ] [FA] term s t i l l 0  S i n c e k„ > k.  predominates i n the  - 112  numerator.  The  r a t e law e s s e n t i a l l y reduces  -d[H ]  2  ~dt  first  to  k K [H ][FA][Rh..]  2  The  -  F  2  1 + K^MA]  =  + K tFA]  (4.17)  F  o r d e r p l o t s which demonstrate e s s e n t i a l l y f i r s t  s u b s t r a t e c o u l d be c o n s i s t e n t w i t h e q u a t i o n 4.17; to  i t depends on what happens  the v a l u e of K^fMA] + Kp[FA] as the r e a c t i o n proceeds.  remains e s s e n t i a l l y c o n s t a n t the r a t e w i l l be f i r s t [FA] term w i l l be decreased by i s o m e r i z a t i o n to MA the  [MA]  i s expected  to i n c r e a s e due  on the r e l a t i v e magnitude of  o r d e r i n [FA]. and  f o r the  l  n  2  '  =  p  2  dependence on  concentration.  reason-  values  ]  i n Table  (  [Rh ] ( f i g u r e 19) a l t h o u g h a p p r o x i m a t e l y  This could r e s u l t  4  l  l  8  )  IX.  o r d e r does show a d e f i n i t e tendency  first  to lower o r d e r w i t h i n c r e a s i n g  from a g r e a t e r c o n t r i b u t i o n from  i s o m e r i z a t i o n r e a c t i o n r e f l e c t e d i n a h i g h e r [MA] or  Depending  1 + Kp [FA] + l y M A ]  The k' v a l u e s are l i s t e d The  The k'  SA;  p l o t s then become e q u a l to  k K [H ][Rh k  The  r e d u c t i o n to  the denominator c o u l d be  a b l y c o n s i s t e n t over a f a i r p o r t i o n of the r e a c t i o n . obtained  If this  to the i s o m e r i z a t i o n .  and K^,,  order i n  term i n e q u a t i o n  a c o n t r i b u t i o n from the k^K^^MA] [H,,] term i n e q u a t i o n The k i n e t i c s are c l e a r l y d i f f i c u l t to a n a l y z e  Rh the 4.18  4.15.  quantitatively  without knowledge of the r a t e of the accompanying i s o m e r i z a t i o n but the d a t a observed r e a c t i o n scheme.  are i n s e m i q u a n t i t a t i v e  agreement w i t h the  proposed  - 113  -  Assuming t h a t the v a r i a t i o n i n k' w i t h p r i n c i p a l l y to v a r i a t i o n i n k^,  the r e a s o n a b l e  (Table. X I I I , F i g u r e 26) y i e l d e d A H ^ K c a l mole * and The  -0.8  i 4.2  temperature i s  and  AS  Arrhenius values  + 2  of 20.7  be of s i g n i f i c a n c e s i n c e a d d i t i o n of H  +  acid,  hydrogenation 4.9).  Pt**alkyls. * 2  A 7  (mechanism I I ) which would a l s o account  f o r the c o n t i n u a l decrease i n hydrogenation  r a t e and  the i s o m e r i z a t i o n  i s as f o l l o w s :  Rh***  +  (equation  r e p o r t e d such a r e a c t i o n u s i n g  A more obvious mechanism  f  1.5  system, c o u l d  c o u l d enhance the  by p r o t o n a t i o n of the Rh**''" a l k y l i n t e r m e d i a t e  Rh  ±  M p-toluenesulphonic  which i s a unique o b s e r v a t i o n f o r the FA h y d r o g e n a t i o n  of FA to MA  rate plot  e.u. r e s p e c t i v e l y .  i n c r e a s e i n r a t e on adding 0.1  r e c e n t paper has  due  FA  +  ^"P  H  >  2  Rh  T  Rh*  +  2H  k  (FA) +  H  2  (4.3)  +  ? -=->•  Rh  T  +  SA  (I) (4.19)  k.  Rh  T  +  MA  Rh  T  (MA)  +  H  0  — R h  T  +  SA  (ID I s o m e r i z a t i o n c o u l d occur  d i r e c t l y v i a conversion  of Rh*(FA) to  Rh*(MA) by r o t a t i o n about the double bond which i s weakened by c o o r d i n a t i o n to the m e t a l c e n t r e . given  by  Then, the hydrogenation  rate i s  - 114  2.78  -  2.82  2.86  (1/T x 1 0 ) , K 3  i g u r e 26.  2.90  1  R h C l ^ ( E t S ) ^ c a t a l y z e d h y d r o g e n a t i o n of FA i n 2  A r r h e n i u s p l o t f o r the h y d r o g e n a t i o n M Rh,  3.0  x 10  M  FA)  DMA  (5.0 x  10  -3  - 115 -  -d[H ] _____  _J£_!  =  k [I][H ]  =  2  +  2  k [II][H ] 3  (4.20)  2  Assuming t h a t the c o n t r i b u t i o n from the r e a c t i o n between Rh*(MA) and H_ i s r e l a t i v e l y s m a l l , and p u t t i n g 2  I  equation  -  I e 4 o k  =  f c  [Rh ]e 4 k  (4.21)  t  (4.20) becomes  =  k [ H ] [ R h ]e V 2  k [SA]  =  (4.22)  2  [H ] [ R h ] p [1 - e V ] 4  (4.23)  k  However, e q u a t i o n 4.23 does not account f o r the k i n e t i c d a t a , i . e . a first  order decrease o f [FA] ( F i g u r e 18); hence mechanism  thought to be l e s s In  mechanism  likely. I , i s o m e r i z a t i o n goes through a Rh***H  whereas i n mechanism  intermediate  I I , i s o m e r i z a t i o n goes through Rh*.  t h a t a c h o i c e c o u l d be made between the two mechanisms out  II i s  I t seemed  by c a r r y i n g  experiments s t a r t i n g w i t h a Rh* s o l u t i o n . A s t o c k s o l u t i o n o f [Rh(C H..)_C1]„ i n E t S/DMA, E t S : R h = 2 : 1 , 0  0  A, was found to be a convenient source f o r R h * ( E t S ) s p e c i e s (see 2  Chapter VI f o r d e t a i l s ) .  When FA was added to A and h y d r o g e n a t i o n  attempted a t 80°, an i n i t i a l region  i n d u c t i o n p e r i o d f o l l o w e d by a l i n e a r  ( r a t e = 3.5 x 1 0 ~ M. s e c " * , 5  [Rh] = 5.0 x 1 0 ~ M, [FA] = 3.0 x 3  _2 10  M, H  2  = 1 atm) was observed t i l l  about h a l f o f the FA was  - 116 hydrogenated; m e t a l was then produced.  I f MA i s used i n s t e a d o f FA,  a l i n e a r r a t e p e r s i s t e n t up to almost complete h y d r o g e n a t i o n o f MA without metal p r o d u c t i o n  was observed  (Chapter V I ) .  When 0.01 M  L i C l was added to A (to g i v e a c h l o r i d e c o n c e n t r a t i o n present  i n the c o r r e s p o n d i n g R h  under the same c o n d i t i o n s , = 1 atm,  T  linear region up  1 1 1  e q u a l to t h a t  system) and h y d r o g e n a t i o n attempted  -3 -2 ([Rh] = 5.0 x 10 M, [FA] = 3.0 x 10 M,  = 8 0 ° ) , an i n i t i a l  ( r a t e = 1.16 x 10  5  induction period  followed  by a  M s e c "*") was observed which p e r s i s t e d  t o about 80% h y d r o g e n a t i o n o f FA.  The l i n e a r r a t e was almost  i d e n t i c a l to the h y d r o g e n a t i o n o f FA a t h i g h  [FA] (Table X I I ,  5.0 x 1 0 ~ M,[FA] = 0.5 M, H  = 8 0 ° , r a t e = 1.12 x  3  10  - 5 - 1 M sec  ).  I Rh .  = 1 atm,  These r e s u l t s show t h a t  than Rh^(MA) i . e . via  2  <  Wilkinson  T  [Rh] =  I (a) Rh (FA) i s a weaker complex  and (b) t h a t i s o m e r i z a t i o n i s not o c c u r r i n g  8 et a l reported  that R h C l ( P h P ) 3  3  d i d not catalyze  the c i s - t r a n s i s o m e r i z a t i o n of a 1:1 m i x t u r e o f c i s and t r a n s hex-2enes or i s o m e r i z a t i o n of h e x - l - e n e . Thus mechanism I i s concluded to be the one r e s p o n s i b l e  f o r the  h y d r o g e n a t i o n and i s o m e r i z a t i o n o f FA c a t a l y z e d by R h C l ( E t S ) 3  DMA.  Mechanism I a l s o accounts f o r the h y d r o g e n a t i o n o f MA  by R h C l ( E t S ) 3  constant  2  3 4 ' (see s e c t i o n 3.2, 3.21 and 3.23).  3  f o r the f o r m a t i o n  2  in  3  catalyzed  The e q u i l i b r i u m  of the Rh (MA) complex i s thought to be 1  X greater  than t h a t f o r the Rh (FA) complex f o r s t e r i c reasons.  some A g ( o l e f i n ) 1  than the t r a n s .  In  complexes, the c i s form i s known to be more s t a b l e  218  219 '•  I The s t a b i l i t y of the Rh (MA) complex i s  thought to d r i v e e q u a t i o n 4.8 completely to the r i g h t and hence no Rh^^^H  would be p r e s e n t  to g i v e r i s e to the i s o m e r i z a t i o n  path.  - 117  The r e s u l t s on the h y d r o g e n a t i o n of the m i x t u r e o f FA and MA a r e particularly interesting.  I n i t i a l l y the c o n c e n t r a t i o n  o f FA and MA  are such t h a t the Rh* w i l l be p r e s e n t m a i n l y as Rh*(MA) s i n c e K^. > K_.  Thus the Rh*(MA) complex w i l l be hydrogenated  though  i s greater  than k^ and the f i r s t  linear rate  first  even  ( F i g u r e 24) o f  3.0 x 10 ^ M s e c * i s c l o s e to t h a t f o r the h y d r o g e n a t i o n o f MA, (4.25 x 10 ^ M s e c *) f o r the same c o n d i t i o n s . curve o f F i g u r e substrate  24 i n d i c a t e s a r e a s o n a b l y s e l e c t i v e h y d r o g e n a t i o n o f the  (presumably  dideuterated  SA.  The i n f l e x i o n i n the  MA) and t h i s c o u l d g i v e r i s e t o the meso-symmetrically  The second l i n e a r r e g i o n i s presumably  w i t h the i s o m e r i z a t i o n and h y d r o g e n a t i o n o f FA. t h i s r e g i o n i s so l i n e a r and why the r a t e  I t i s n o t c l e a r why  (4.4 x 10 ^ M s e c *) i s  c l o s e to t h a t o f the h y d r o g e n a t i o n o f MA. isomerized  connected  T h i s suggests t h a t FA i s  to MA i n t h i s system b e f o r e the h y d r o g e n a t i o n s t a r t s and >  y e t the i s o l a t e d DL-sym-dideuterated  SA s h o u l d r e s u l t from c i s T)^ 36  a d d i t i o n to FA.  C a n d l i n and Oldham  have a l s o i n d i c a t e d that i n d i v i d u a l  r a t e s of h y d r o g e n a t i o n a r e the wrong c r i t e r i a w i l l hydrogenate a l s o observed  most r a p i d l y i n a m i x t u r e .  to p r e d i c t which  substrate  The same workers have  that the i n d i v i d u a l h y d r o g e n a t i o n r a t e o f a s u b s t r a t e  i n a m i x t u r e may be d i f f e r e n t from t h a t when the s i n g l e s u b s t r a t e i s being hydrogenated. ^ 3  i  CHAPTER V DISCUSSION OF THE R h  SULPHUR CATALYZED HYDROGENATION  1 1 1  OF OLEFINS 5.1  General D i s c u s s i o n RhCl^CEt^S)^ and RhCl^CBz^S)^ a r e a c t i v e c a t a l y s t s f o r the  3 4 homogeneous hydrogenation acid.  of maleic,  '  fumaric and t r a n s - c i n n a m i c  The more r a p i d metal p r o d u c t i o n i n systems u s i n g fumaric and  t r a n s - c i n n a m i c a c i d suggests  t h a t t r a n s - o l e f i n s form l e s s s t a b l e complexes  with Rh .  T h i s can be r a t i o n a l i z e d i n terms o f s t e r i c and e l e c t r o n i c 219 e f f e c t s , although the s t e r i c f a c t o r i s p r o b a b l y more important. The I 12 Rh produced i n the RhCl^-3H 0/olefin/H^/DMA systems ' formed s t a b l e 1  2  complexes w i t h m a l e i c a c i d , w h i l e w i t h fumaric and t r a n s - c i n n a m i c  acid,  1 2 m e t a l was produced  more r e a d i l y .  '  The l a b i l i t y and s t a b i l i t y o f these  R h ( o l e f i n ) complexes a r e major f a c t o r s i n d e t e r m i n i n g 1  genation.  the r a t e o f hydro-  I f the R h ( o l e f i n ) complex i s too s t a b l e , h y d r o g e n a t i o n 1  become very slow. hydrogenation.of  T h i s has been observed f o r the RhCl^-SH^O c a t a l y z e d 1 2 s u b s t i t u t e d e t h y l e n e s ' and i n the R h C l ( P h P ) 8 3  c a t a l y z e d hydrogenation  of t e t r a f l u o r o e t h y l e n e .  1  s i g n i f i c a n t amounts of " f r e e " R h 3  7 3  1  0  1  3  I n the p r e s e n t  s y s t e m s , i f the R h ( o l e f i n ) complex i s not s u f f i c i e n t l y  In the R h C l ( P h P )  might  stable,  a r e p r e s e n t and metal i s produced.  systems, the R h  1  i s s t a b i l i z e d against  r e d u c t i o n or d i s p r o p o r t i o n a t i o n t o metal even i n the absence of o l e f i n s  - 119 by t h e Ph^P which i s a b e t t e r Tr-acceptor, than Et^S o r B Z 2 S . e l e c t r o n i c and s t e r i c  f a c t o r s of a u x i l i a r y  The  l i g a n d s , namely C l , DMA,  R^S (R = Et o r Bz) i n t h e systems r e p o r t e d i n t h i s work, seem t o be o f importance  i n promoting  or i n h i b i t i n g c a t a l y t i c  I s o m e r i z a t i o n has been observed i s o m e r i z a t i o n of FA . i n v o l v e s of  activity.  to accompany h y d r o g e n a t i o n .  The  an a l k y l i n t e r m e d i a t e v i a i n s e r t i o n  t h e o l e f i n i n t o t h e Rh***-H  bond  ( e q u a t i o n 4.9).  Such i s o m e r i z a t i o n 17 39 43  is  commonly thought  to go through a l k y l i n t e r m e d i a t e s ,  ( s e c t i o n s 1.42 and 1.62).  A Rh  1 1 1  '  '  a l k y l , ( R h * * * C l Et(CO) , where  x > 2181) has been i s o l a t e d by P o w e l l and Shaw, a l t h o u g h the a n a l y s i s 220 i s not too good. W i l k i n s o n ' s group  [ R h E t ( N H ) ] X (X = Br", i " , C 1 0  have i s o l a t e d pure c r y s t a l l i n e  2 +  3  5  y  _ 4  salts,  and S O ^ . y = 1 o r 2) , i n which  the E t group i s a-bonded t o Rh. The d e t a i l e d mechanism f o r the i n i t i a l subsequent next  r e d u c t i o n o f Rh*** and  h y d r o g e n a t i o n of the s u b s t r a t e w i l l be d i s c u s s e d i n the  two s e c t i o n s .  5.11  I n i t i a l R e d u c t i o n , Formation o f a R h * ( o l e f i n ) Complex The k i n e t i c s o f the i n i t i a l  (Chapters I I I o r IV) a r e f i r s t independent  o f the o l e f i n .  r e d u c t i o n f o r a l l t h e systems s t u d i e d  o r d e r i n [Rh ] and [H^] and  S o l v e n t a s s i s t e d d i s s o c i a t i o n of the  3 4 Et^S to is  '  o r Bz^S l i g a n d p r o v i d e s an a c t i v e s i t e f o r the a c t i v a t i o n o f  form a Rh* ( o l e f i n ) complex.  thought  to be important.  The donor s t r e n g t h o f the s o l v e n t  The i n a c t i v i t y o f R h C l ( E t 2 S ) i n 3  benzene i s due i n p a r t to t h e l a c k of the s o l v e n t a s s i s t e d of  the Et2S.  3 4 '  DMSO was a l s o used f o r the h y d r o g e n a t i o n  3  dissociation i n an  - 120 attempt to study  the e f f e c t of s o l v e n t i n these systems and w i l l  d i s c u s s e d s e p a r a t e l y i n Chapter s o l v e n t was The  -  V I I , s i n c e a n o v e l r e d u c t i o n of  be the  observed.  r a t e determining  steps f o r f o r m a t i o n of the R h ( o l e f i n ) 1  complex i n the R h C l ^ E t ^ S ^ i n equations  5.1  RhCl (Et S) 2  RhCl (Bz S) 3  systems a r e  represented  5.2.  and  3  and RhCl^Bz^S).^  2  2  2  1  +  H  2  +  H  2  Rh  -i>  Rh  III  Cl (Et S) H 3  I i : i  2  -  2  Cl (Bz S) H" 3  2  2  +  H  +  H  +  (5.1)  (5.2)  +  1-4 Previous studies  suggested  that h e t e r o l y t i c s p l i t t i n g  most probable path f o r a c t i v a t i o n of i s a moderately The  b r e a k i n g of the H-H  the  bond occur i n a  f o r the a c t i v a t i o n of H  by the o t h e r groups.  species R h ( p y ) C l 3  3  by R h  2  1 1 1  has  3  2  [ R h ( C N ) ( H 0 ) H ] ~ and  7 1  '  A c t i v a t i o n of H  2  by  the o c t a h e d r a l  Other R h  1 1 1  h y d r i d e s such as  [ R h ( t r i e n ) C l H ] have been r e p o r t e d .  2  +  2  been  31  i n e t h a n o l r e s u l t s i n the e l i m i n a t i o n of HC1  f o r m a t i o n of R h ( p y ) C l H .  The  that  process.  29  4  DMA  i s favoured.  i s o t o p e e f f e c t suggests  2  bond and making of the Rh-H  Heterolytic splitting  observed  reduction.  p o l a r s o l v e n t and h e t e r o l y t i c s p l i t t i n g  absence of any measurable D  concerted  i n the i n i t i a l  i s the  and  [Rh(NH )  H]  9 2  g e n e r a l mechanism f o r the f o r m a t i o n of the R h ( o l e f i n ) 1  complex i s r e p r e s e n t e d below. k III 1 III Rh + H -±> Rh H 2  +  H  +  (5.3)  2 +  ,  - 121 -  K Rh  Rh  I i : [  III  H  H  Rh  -  -  1  2  + olefin  +  H  Rh  (5.4)  +  3  III  (alkyl)  ^  Rh  III -  H  ^  (5.5) olefin  isomerized  Rh  I  K  +  olefin  4  I Rh ( o l e f i n )  ( c o o r d i n a t e d l i g a n d s such as C l , E t ^ S , ^z^S, DMA  The magnitude of  +  (5.6) are omitted).  i s thought t o determine t h e p r o b a b i l i t y o f  i s o m e r i z a t i o n and the complexity Comparison.of the k^ v a l u e s  o f the k i n e t i c s o f the system. and a c t i v a t i o n parameters f o r the  formation  o f the v a r i o u s R h ( o l e f i n ) complexes and the e q u i l i b r i u m  constants  f o r the i n i t i a l  1  k^ v a l u e , 7.4 M ''"sec \ to  the MA system.  d i s s o c i a t i o n a r e shown i n T a b l e XIV.  The  f o r the FA system seems somewhat h i g h compared  S i m i l a r d i s c r e p a n c i e s i n the k^ v a l u e s f o r  d i f f e r e n t o l e f i n s have been observed f o r the RhCl^'St^O c a t a l y z e d 1 2 hydrogenation formation through  of o l e f i n s i n DMA.  '  These may be r a t i o n a l i z e d by the  of the Rh "'" ( o l e f i n ) complexes i n the i n i t i a l catalytic  s u b s t i t u t i o n i n v o l v i n g Rh^jand i n such cases  values, i . e . r a t e of h e t e r o l y t i c s p l i t t i n g of H w i l l be dependent on the o l e f i n .  step,  The a c t i v a t i o n parameters f o r the  Although the k^ v a l u e o b t a i n e d  hydrogenation  k^  i n the i n i t i a l  R h C l ^ E t ^ S ^ systems i n v o l v i n g FA and MA a r e not v e r y however.  reduction  11  different  f o r the R h C l ( E t 2 S ) 3  3  catalyzed  o f MA, m i x t u r e o f MA and FA, and CA a r e comparable and  c l o s e to the k^ v a l u e  f o r the hydrogen r e d u c t i o n of R h C l ( E t 2 S ) 3  absence o f o l e f i n , t h i s seems f o r t u i t o u s s i n c e the a c t i v a t i o n  3  i n the  - 122 -  TABLE XIV Rate Constants  and A c t i v a t i o n  Parameters f o r R h * ( o l e f i n )  Complex Formation from Rh* * i n DMA 1  Initial  Olefin  Complex  T °C  RhCl (Et S) 3  2  K  M  t  I  K  sec  80  1.92  55  0.47  MA + FA  80  1.89  MA  3  K c a l mole  e.u.  l  M  12.9  -21.4  0.047  a  RhCl (Et S)  3  FA  80  7.4  14.3  -14.4  0.073  RhCl (Et S)  3  CA  55  0.50  20.0  0.6  0.010  RhCl -3H 0  MA  80  1.67  17.3  - 9.2  -  RhCl -3H o"  MA  80  0.74  17.3  -10.8  -  RhCl (Bz S)  MA  80  3.55  27.8  23.0  0.016  Nil  80  2.4  b  -  -  -  3.0  C  -  -  -  3  2  3  3  2  2  3  3  2  3  RhCl (Et S) 3  2  3  1.2 M LiCl/DMA media. Value  o b t a i n e d by d i r e c t c a l c u l a t i o n  assuming the A r r h e n i u s  from the k^ v a l u e a t 80°,  r a t e e q u a t i o n h o l d s f o r the temperature  range 55-80°. I n i t i a l s l o p e method. From f i r s t order l o g p l o t .  - 123  parameters f o r the CA and u n f a v o u r a b l e AH p o s i t i v e AS^  f  value  value.  MA  -  systems are q u i t e d i f f e r e n t .  i n the CA  The  system i s compensated by  a c t i v a t i o n parameters f o r the  c a t a l y z e d h y d r o g e n a t i o n s of MA  The  and  more  the more  RhCl^CEt^S)^  FA are s i m i l a r to those of  the  1 2 PvhCl^'SI^O  '  c a t a l y z e d h y d r o g e n a t i o n of MA  to i n v o l v e h e t e r o l y t i c s p l i t t i n g by R h The  l a r g e and  p o s i t i v e AS^'  value  which i s a g a i n  thought  as the r a t e d e t e r m i n i n g  1 1 1  f o r the f o r m a t i o n  step.  of the Rh*(MA)  complex i n the R h C l ^ C B ^ S ) ^ system accounts f o r the f a s t e r r a t e compared to the Et^S  and  the c h l o r i d e systems.  The  reason f o r q u i t e  d i f f e r e n t a c t i v a t i o n parameters i n t h i s system i s not does suggest t h a t a d i f f e r e n t mechanism i s o p e r a t i n g . 221 222 suggestions r e c e n t l y of H  2  '  by Ru** complexes may  obvious, i t There have been  that the s o - c a l l e d h e t e r o l y t i c s p l i t t i n g proceed i n some cases v i a  dihydride  if.oer. m a t i o n .  Rh**Cl P 2  3  + H  2  *  [ R u * C l H P ] —> V  2  2  3  Ru**ClHP  3  +  HCl  (5.7) where P = Ph P 3  A s i m i l a r r e a c t i o n here would i n v o l v e a Rh^  s t a t e , a reasonably w e l l  223 substantiated  valence state  and would be  expected to have a  h i g h a c t i v a t i o n energy because of the c o n t r i b u t i o n of the energy of the v a l e n c e e l e c t r o n s . v i a h e t e r o l y t i c . s p l i t t i n g of H t h i s may  not be  promotion  Although r e a c t i o n s s a i d to proceed u s u a l l y have a s m a l l i s o t o p e  2  effect**  a u s e f u l c r i t e r i a s i n c e the k i n e t i c i s o t o p e e f f e c t I 23 to I r complexes i s a l s o s m a l l .  f o r the o x i d a t i v e a d d i t i o n of H  2  - 124 -  5.12  Catalytic The  Hydrogenation  t h r e e b a s i c steps o f h y d r o g e n a t i o n ,  ( i i ) hydrogen a c t i v a t i o n to  1 1  ( i ) substrate a c t i v a t i o n  ( i i i ) hydrogen t r a n s f e r (see s e c t i o n s 1.4  1.42) a r e thought to be i n v o l v e d i n the R h C l ( E t S ) 3  c a t a l y z e d hydrogenations The  o f MA,  2  and  RhCl (Bz S) 3  2  3  FA and CA.  s u b s t r a t e ( o l e f i n ) i s a c t i v a t e d through c o o r d i n a t i o n to R h . 1  R h ( o l e f i n ) then r e a c t s w i t h H^ i n a r a t e d e t e r m i n i n g 1  the p a r a f f i n  ( a f t e r H^ t r a n s f e r ) and R h  complexing w i t h f u r t h e r o l e f i n .  Rh  I  K  +  olefin  I Rh ( o l e f i n ) +  4  2  I Rh  2  +  2  the  which i s s t a b i l i z e d by  1  below  I Rh ( o l e f i n )  k  H  step t o produce  The mechanism i s r e p r e s e n t e d  ( c o o r d i n a t e d l i g a n d s such as C l , E t S ,  If  3  v a l u e i n equation  (5.6)  paraffin  B z S , DMA 2  (5.8)  are omitted).  5.6 i s s u f f i c i e n t l y  order dependence on [Rh, ] and [ H ] would be observed 2  large, a f i r s t as i n the  3 4 RhCl (Et S)  2  auxiliary  l i g a n d s i n the R h ( o l e f i n ) complex d i s s o c i a t e s p r i o r t o  3  2  c a t a l y z e d hydrogenation  '  If  one o f the  1  r e a c t i o n with H , 2  e.g. i n the R h C l ( E t S ) 3  CA and the R h C l ( B z S ) 3  2  2  v a l u e shown i n e q u a t i o n  2  3  c a t a l y z e d hydrogenation  catalyzed hydrogenation  dependence on [Rh .] r e s u l t s  equation  o f MA.  of  of MA, a complex  (see s e c t i o n s 3.32 and 3.52).  I f the  5.6 i s s m a l l e r than the e q u i l i b r i u m shown i n  5.5, i s o m e r i z a t i o n o f o l e f i n may occur  i n t e r m e d i a t e as i n the R h C l ( E t S ) 3  2  3  through t h e R h  catalyzed hydrogenation  there w i l l be a between zero and f i r s t  1 1 1  (alkyl)  o f FA and  order dependence on the o l e f i n .  - 125 Following  the r e a s o n i n g  through d i h y d r i d e f o r m a t i o n Hydride f o r m a t i o n the second step  1 2 Rempel, ' a c t i v a t i o n  of James and i s preferred  i s accompanied by  ( s e c t i o n 3.22,  3  12 '  DMA,  2  and  benzene. prior  and  RhCl (Et S) 3  the R h C l ( P h P ) 3  2  7  1  3  0  3  IrCl(CO)(Ph^P) ,  3 4 ' c a t a l y z e d h y d r o g e n a t i o n of MA  the  olefin.  of t r a n s f e r i s u n c e r t a i n .  that the t r a n s f e r of b o t h h y d r i d e s  Rh-H  in  c a t a l y z e d h y d r o g e n a t i o n of o l e f i n s i n  Hydrogenation i s completed by hydrogen t r a n s f e r .  centre  35  2  In the l a t t e r , however, the d i h y d r i d e i s thought to form  to r e a c t i o n w i t h  process  metal,  of the o l e f i n i c bond.  S i m i l a r mechanisms have been proposed f o r the RhCl -3H 0  Scheme V I ) .  f o r m a l o x i d a t i o n of the  involves hydrometallation  of  t r a n s i t i o n s t a t e i f the  Wilkinson^  The  actual  et a l have suggested  i s simultaneous,  o l e f i n occupies  each by  a  three  a p o s i t i o n c i s to both  bonds.  (5.9)  . A , 17,39,42,106,107 , , . , More r e c e n t data suggest that the h y d r i d e s transferred  consecutively, v i a a l k y l  intermediates.  C i s a d d i t i o n i s g e n e r a l l y thought to be hydrogenations. been r e p o r t e d  8 9 224 ' '  One  are  operative i n catalyzed  d e f i n i t e i n s t a n c e of t r a n s a d d i t i o n has  i n the r e d u c t i o n of d i p h e n y l a c e t y l e n e u s i n g  a  225 py RhCl -Me NCHO-NaBH 3  3  2  dideuterated  4  catalyst  SA o b t a i n e d  system.  The  unsymmetrically  from the d e u t e r a t i o n s t u d i e s p r o b a b l y  from the e q u i l i b r i a i n v o l v i n g c i s a d d i t i o n of the D  2  through  arises  alkyl  - 126 intermediates  D H  R  H H  R  CHR-CHDR  CHR-CD R CH^R-CD P, +  /  Rh  Rh  Scheme V I I  H  H  (R = COOH, t h i s scheme a l s o h o l d s f o r  C=C R  The present  ) R  s m a l l deuterium i s o t o p e e f f e c t observed w i t h k^ i n the studied  a d d i t i o n of H But  X  systems i s s i m i l a r to t h a t observed f o r the o x i d a t i v e ( D ) to the square p l a n a r  2  2  IrCl(CO)(Ph^P)  the s m a l l i s o t o p e e f f e c t has a l s o been a t t r i b u t e d  23 2  complex.  to the hydrogen  8 transfer  step.  Comparison of the k^ v a l u e s  and a c t i v a t i o n parameters f o r the  d i f f e r e n t Rh*** sulphur and c h l o r i d e c a t a l y z e d h y d r o g e n a t i o n s a r e shown i n T a b l e XV. Good a donor l i g a n d s a r e thought to promote o x i d a t i v e  226 additions  and t h i s i s p o s s i b l y r e f l e c t e d i n the h i g h e r  k^ v a l u e  f o r the RhCl *3H 0 c a t a l y z e d h y d r o g e n a t i o n of MA compared to the 3  - 127 TABLE XV Rate Constants and A c t i v a t i o n Parameter f o r Hydrogenation of R h * ( o l e f i n ) Complex i n DMA Initial Complex  Olefin  T  k  °C RhCl (Et S)  3  RhCl (Et S)  3  3  3  2  2  RhCl (Et S )  3  RhCl "3H 0 3  2  RhCl '3H 0 3  a  2  RhCl (Bz S) 3  3  2  3  M  2  AH  T  z  AS„ z  +  sec  K c a l mole *  e.u.  K  2 z  M  MA  80  0.33  21.4-  -1.0  -  FA  80  0.97  20.7  -0.8  -  CA  55  1.20  21.3  +5.6  MA  80  -  -  -  -  ' MA  80  1.54  18.4  -6.1  -  MA  80  1.20  21.0  +0.5  .010  1.2 M LiCl/DMA media.  K  .019  2 = d i s s o c i a t i o n constant of R h * ( o l e f i n ) . "  - 128  RhCl^CEt^S)^  -  and R h C l ^ C l ^ S ) ^ systems  donor than Bz^S  or Et^S.  similar i n their  Bz^S  since chloride i s a better  and Et^S are thought  a donor p r o p e r t i e s .  The  to be v e r y  v a l u e (1.20 M *sec  *)  f o r the d i b e n z y l system i s some 4 times h i g h e r than the d i e t h y l (k^ = 0.33  M *sec *) but the Bz^S  system  i n v o l v e s a Rh*  one l e s s c o o r d i n a t e d sulphur l i g a n d than the Et^S  0  system  species with  system.  The r a t e of h y d r o g e n a t i o n of d i f f e r e n t o l e f i n s c a t a l y z e d by RhCl (Et2S) 3  maleic acid  3  i s i n the o r d e r , t r a n s - c i n n a m i c a c i d  > fumaric a c i d >  (Table XV) which i s . p r o b a b l y i n the r e v e r s e o r d e r of the  s t a b i l i t y of the R h * ( o l e f i n ) complex.  The  t r e n d i s the o p p o s i t e to  t h a t observed i n the RhCl(Ph P) » » 3 6 c a t a l y z e d h y d r o g e n a t i o n where 8  9  3  the s t e r i c a l l y h i n d e r e d and t r a n s s u b s t i t u t e d o l e f i n s are l e s s  prone  to h y d r o g e n a t i o n than the l e s s s t e r i c a l l y h i n d e r e d and c i s s u b s t i t u t e d a l k e n e s , e.g. cyclohexene i s hydrogenated 1-methylcyclohexene,  9  fifty  times f a s t e r than a  and cis-4-methylpent-2-ene  i s hydrogenated  9  times f a s t e r than the t r a n s - i s o m e r . ( t r a n s ) i s hydrogenated  In the p r e s e n t systems,  t h r e e times f a s t e r , than the MA  should be noted, however, t h a t these w o r k e r s ' ' ^ 8  the complexing step.  between the o l e f i n and the Rh*  9  3  four  FA  (cis). It  p o s t u l a t e that  i s the r a t e d e t e r m i n i n g  I t seems l i k e l y t h a t the ease of complex f o r m a t i o n decreases  w i t h the presence of bulky s u b s t i t u e n t s on the o l e f i n and  the t r a n s  o l e f i n i s more h i n d e r e d than the c i s o l e f i n s i n c e o n l y c e r t a i n d i r e c t i o n s of approach complexing  of the o l e f i n to the metal w i l l  to take p l a c e .  In the p r e s e n t systems, however, the r a t e  d e t e r m i n i n g step of h y d r o g e n a t i o n i s thought  X  permit  to i n v o l v e d i h y d r i d e  f o r m a t i o n and the Rh ( o l e f i n ) complex i s thought to be formed i n a f a s t step p r i o r to d i h y d r i d e f o r m a t i o n . The s t a b i l i t y o f the R h * ( o l e f i n )  - 129  -  complexes are c l e a r l y c r u c i a l f a c t o r s i n d e t e r m i n i n g activity.  catalytic  The Rh^(FA) complex i s l e s s s t a b l e than the Rh*(MA) complex  and hence the r a t e of h y d r o g e n a t i o n of R h ^ F A ) i s enhanced. c o n t a i n i n g e l e c t r o n withdrawing alkoxy are hydrogenated  s u b s t i t u e n t s , e.g. n i t r i t e ,  Substrates carbo-  extremely r a p i d l y u s i n g the RhClCPh^P)^ c a t a l y s t .  The a c t i v a t i o n parameters  f o r the h y d r o g e n a t i o n  (Table XV)  are i n  the normal range f o r a b i m o l e c u l a r r e a c t i o n i n s o l u t i o n between an i o n and a n e u t r a l m o l e c u l e .  Such r e a c t i o n s are expected to be  favoured i n a medium of lower d i e l e c t r i c  constant due  to g r e a t e r 227  a t t r a c t i o n between the i o n and  the induced d i p o l e of the m o l e c u l e .  An i n t e r m e d i a t e i n which both the o l e f i n and  are c o o r d i n a t e d to  the atom seems n e c e s s a r y f o r h y d r o g e n a t i o n to b e g i n . can a c t i v a t e m o l e c u l a r hydrogen o tr  IrCl(CO)(Ph P )  2  q u i t e r a p i d l y and r e v e r s i b l y ,  o o Q  '  •  2  e.g.  o  i n benzene and RhCl<Ph P)  are unable to c a t a l y t i c a l l y hydrogenate of H  S p e c i e s which  or do so o n l y v e r y s l o w l y .  i n p y r i d i n e or t o l u e n e  o l e f i n s a t 25° or 1 atmosphere  A d i h y d r i d e s p e c i e s which forms  i s c o o r d i n a t i v e l y s a t u r a t e d and t h e r e i s no vacant s i t e f o r o l e f i n coordination.  I f a s o l v e n t a s s i s t e d d i s s o c i a t i o n of one of the Ph^P 8 35  l i g a n d o c c u r s , the complex becomes a c t i v e f o r h y d r o g e n a t i o n . ' A d d i t i o n of excess Ph^P  i n the above systems r e v e r s e s the d i s s o c i a t i o n  and h y d r o g e n a t i o n i s i n h i b i t e d .  CHAPTER VI  CATALYTIC HYDROGENATION OF MALEIC ACID BY -  6.1  General Rh*  COMPLEXES IN  complexes are known to be  complexes w i t h c h l o r o v i a reduction  thought to be  12 '  and  DMA  a c t i v e c a t a l y s t s f o r hydrogenation l i g a n d s . ^ 10J36,106  sulphur  ligands  of the Rh*** complexes  the a c t i v e s p e c i e s  Thus, p r e p a r a t i o n s  of Rh*  6.2  catalytic  D  e  (see C h a p t e r ; I I I , I V )  are  f o r c a t a l y t i c h y d r o g e n a t i o n of  c h l o r o and  sulphur  olefins.  complexes were attempted investigated.  s t u d i e s would g i v e f u r t h e r i n s i g h t i n t o the mechanism of of o l e f i n s c a t a l y z e d by  _^I( i fj-)  3 4 ' formed " i n s i t u " i n  and,where s u c c e s s f u l , the c a t a l y t i c a c t i v i t y was  l i g a n d s on  SULPHUR  Introduction  e s p e c i a l l y when s t a b i l i z e d by Ph^P  DMA  RHODIUM (I) CHLORO AND  Rh*** complexes i n DMA  and  These  hydrogenation  the e f f e c t  of  activity.  Attempted P r e p a r a t i o n s  o f Rh*  Complexes C o n t a i n i n g  Sulphur  Ligands No  Rh*  complexes w i t h R^S  type l i g a n d s  appear to have been r e p o r t e d .  Since  l i k e Ph^P,  ph^Sb  as PV^S,  *^ Ph^As  7  B z S and 2  7  -*-0,71 ^ a  Rh*  (R = a l k y l , p h e n y l or  forms complexes w i t h  7  Et2S, were thought l i k e l y  ligands  TT-acceptor l i g a n d s to form s t a b l e Rh*  aryl)  such  complexes.  - 131 -  However, we c o u l d n o t i s o l a t e any such  complexes.  The attempted methods o f p r e p a r a t i o n were as f o l l o w s .  Stoichio-  m e t r i c amounts o f l i g a n d s were added to e t h a n o l i c s o l u t i o n s o f RhCl^'SH^O i n the 1:2 or 1:3 r a t i o o f R h : l i g a n d .  No v i s i b l e change i n  c o l o u r was observed i n c o l d e t h a n o l i c s o l u t i o n s .  On g e n t l e warming,  the s o l u t i o n w i t h Bz^S y i e l d e d a y e l l o w p r e c i p i t a t e o f B h C l ^ B z ^ ) . ^ (Chapter I I , s e c t i o n 2.11)  f  w h i l e no changes were observed i n s o l u t i o n s  con-  t a i n i n g Ph S and E t S . When the s o l u t i o n s were r e f l u x e d metal was d e p o s i t e d 2  2  i n s o l u t i o n s c o n t a i n i n g Ph S and E t S . 2  2  When H  2  was passed through the  c o l d e t h a n o l i c s o l u t i o n s , no v i s i b l e change was observed;but was  d e p o s i t e d i n a l l the s o l u t i o n s .  attempted was  a t 60° m e t a l  The above p r e p a r a t i o n s were a l s o  i n DMA but t h e r e was e i t h e r no v i s i b l e change o r e l s e m e t a l  found. Since no simple and convenient method was found f o r the p r e p a r a t i o n  of R h  1  complexes c o n t a i n i n g R S l i g a n d s , p r e p a r a t i o n s o f such complexes 2  " i n s i t u " were attempted.  as s t a r t i n g m a t e r i a l s . f o r use because state.  123  '"'" '' 2  [Rh(C„H.).Cl]. and [Rh(C_H .)_C1]_ were used z 4 z z o 14 z z 1  [Rh(C H ) Cl] 2  4  2  2  was found to be l e s s amenable  of the slow decomposition o f the complex i n s o l i d [Rh(C„H . )„C1] was found t o be v e r y u s e f u l f o r p r e p a r i n g o 14 z z 1  0  " i n s i t u " R h ( E t S ) , R h ^ B z S) or R h C l I  I  2  black p r e c i p i t a t e ,  complexes i n DMA; w i t h Ph S, a  p r o b a b l y m e t a l , was o b t a i n e d and t h i s was not  studied further. A gas chromatogram of the s o l v e n t pumped o f f from t h e DMA s o l u t i o n of [Rh(C H .)C1] w i t h added Et„S o r C l showed the presence o f o 14 z z Q  2 moles of c y c l o o c t e n e per mole o f Rh (Beckman G.C. 2A i n s t r u m e n t , d i n o n y l p h t h a l a t e column, r e t e n t i o n time = 12 min, 160 ma, 160°, p r e s s u r e gauge s e t t i n g = 10).  - 132  6.3  The R h ( E t S ) I  2  -  C a t a l y z e d Hydrogenation of MA  [ R h C C g H ^ ^ C l ^ i s s p a r i n g l y s o l u b l e i n DMA, Et^S, Rh:Et2S = 1:2, showed a continuum 450 my  i s 460.  The orange-red s o l u t i o n was  s p e c i e s . Such Rh*(Et2S)  at 80° and 1 atm of H^.  was  s t a b l e to a i r a t room  e a t 450 my  decreased to 400 suggest-  The s p e c t r a i n d i c a t e the presence  s o l u t i o n s were found to hydrogenate  i n d u c t i o n p e r i o d f o l l o w e d by a l i n e a r  The spectrum of the s o l u t i o n d u r i n g the h y d r o g e n a t i o n r e g i o n  a continuum and e s s e n t i a l l y the same as the s o l u t i o n b e f o r e hydro-  genation  (e  = 390 at 450 my).  Hydrogenation c a r r i e d out i n the s p e c i a l  a i r - f r e e " d e v i c e (see s e c t i o n 2.3) was  e at  A t y p i c a l gas uptake p l o t i s shown i n  F i g u r e 27, t h e r e i s an i n i t i a l region.  o b t a i n e d which  i n the v i s i b l e r e g i o n at l e a s t down to 350 my;  i n g complexing between Rh* and MA.  MA  DMA  but on a d d i t i o n of  i n a i r , an orange red s o l u t i o n was  temperature and on adding excess MA,  of Rh*  in  i n which a s o l u t i o n o f MA  c a r e f u l l y degassed b e f o r e i n t r o d u c i n g  and  Et^S  [Rh (C H., . ) „C1] „ showed a D  O  i-H  _  _  c o n t i n u a l decrease i n r a t e .  The d i s c r e p a n c y i n two r a t e p l o t s of t h i s  k i n d l e d to the f i n d i n g t h a t  [RhtCgH^^Cl^  the Rh*(Et2S) Under R^ O2  l  n  i n LiCl/DMA  complex form m o l e c u l a r oxygen complexes  the absence o f MA,  and r e v e r t s back to a Rh  and  possibly  (Chapter V I I I ) .  the Rh^(O^) complex r e a d i l y l o s e s the hydride species  (Chapter V I I I ) .  The  s t o i c h i o m e t r y o f R^ uptake f o r both uptake p l o t s i n F i g u r e 27 a t the p o i n t of metal p r e c i p i t a t i o n corresponded to complete h y d r o g e n a t i o n o f MA  to SA. An unexpected amount of R  appeared.  In the absence o f MA,  reduced by R  uptake was  observed a f t e r the m e t a l had  the Rh*(Et2S)  s o l u t i o n was  rapidly  to the m e t a l and an uptake more than the r e d u c t i o n of  - 134 Rh  to Rh° was  1  for  a g a i n observed.  The Rh^CEt^S) s o l u t i o n was  homogeneous h y d r o g e n a t i o n  produced  -  of c y c l o o c t e n e ; metal was  together w i t h a v e r y f a s t  absorption.  a f t e r metal p r o d u c t i o n i s p r o b a b l y due of  CgH^.  The  inactive  rapidly Uptake  to the heterogeneous r e d u c t i o n  More q u a n t i t a t i v e data on t h i s e x t r a  uptake i n the  Rh^Cl system i s i n agreement w i t h t h i s c o n c l u s i o n ( s e c t i o n When the R h ^ E ^ S ) s o l u t i o n was no gas uptake was  observed  disproportionation 5.0 cm  x 10  -  for  and  a 1:1  6.31  1.3  through  The molar conductances  M s t o c k s o l u t i o n of Rh  e l e c t r o l y t e i n DMA  at 80° f o r 5000 sec,  2  produced^possibly  - 1 2 - 1 cm mole , respectively.  ohm  6.4).  I  (E^S)  —1  i s expressed  -1  2 —1 229 cm mole  1  [Rh]  ohm  The molar conductance  i s around 46-60 ohm  a l l these s t u d i e s , the  for a  were 0.7  K i n e t i c s of the R h ( E t 2 S ) C a t a l y z e d Hydrogenation In  of  and metal was  3 2 M and 2.0 x 10  2 - 1 mole  kept under N  (equation 3.10).  observed  of  MA  i n terms of m o l a r i t y  monomeric rhodium s p e c i e s ( i . e . twice the dimer c o n c e n t r a t i o n ) . A few r e a c t i o n s were c a r r i e d out i n the s p e c i a l a i r - f r e e d e v i c e . -  At 2.5  x 10  order on H [MA],  second  3  and  and  -  3  5.0  x 10  consumption  2  M  [Rh], the r a t e p l o t s a n a l y z e d f o r f i r s t  ( F i g u r e 27) i . e . f i r s t  the pseudo f i r s t  order dependence on  order r a t e constants  [Rh]  (Table XVI).  the r a t e p l o t d i d not a n a l y z e f o r f i r s t k' v a l u e showed between f i r s t XVI).  At 0.06  that at 0.03  M  M  [MA],  [MA],  x 10  kept the same (Table XVI). system was  and  sec  ( k ) show an approximate _2 T  At 1.0  x 10  4  sec"  1  which was  [Rh],  [MA]. 2  The  (Table  d i f f e r e n t ; from  , when a l l the o t h e r v a r i a b l e s  Because of the c o m p l i c a t e d  not s t u d i e d f u r t h e r .  M  o r d e r dependence on  zero o r d e r dependence on H  k' = 1.4 x 10~ -4 -1  3.7  o r d e r dependence on .  are  kineticsthis  - 135 -  TABLE XVI K i n e t i c Data f o r the [Rh (C H.. . ) C1] o IH- 2 2 0  of MA  i n Et^S/DMA Media Under " A i r F r e e " (Rh:Et S = 2  [Rh] x 10  3  [MA] M  C a t a l y z e d Hydrogenation  0  M  pH  2  mm  Conditions  1:2) [H J  k»  2  x 10  3  M  x IQ  T sec"  4  1  °C  5.0  0.03  725  2.32  10.40  80  2.5  0.03  725  2.40  1.04  55  5.0  0.03  725  2.40  3.68  55  10.0  0.03  725  2.40  —  55  5.0  0.06  725  2.40  1.38  55  5.0  0.03  377  1.22  2.53  55  5.0  0.03  226  0.73  1.50  55  - 136 -  A more d e t a i l e d study was made on the s t o c k s o l u t i o n s o f Rh^CEt^S) made up i n a i r s i n c e simple k i n e t i c s r e s u l t e d . measured; f i r s t were observed  The l i n e a r r a t e s were  o r d e r dependence on [Rh],  [H^] and independence o f [MA]  (Table XVII, F i g u r e s 28,29).  The k i n e t i c d a t a gave the  r a t e law  -d[H ]  dt and  the average  =  k [l R h J]L [ H j 0  2  value of k  2  as 2.85 M *sec *. H  deuterium  (6.1)  - "" "2-  isotope e f f e c t ,  D 2/k^ 2 = 1.2.  There was a s l i g h t  p-Toluenesulphonic  acid  had p r a c t i c a l l y no e f f e c t on the r a t e . LiCl inhibited -1 of  0.56 M  the r a t e of h y d r o g e n a t i o n  and a c o n s t a n t k^ v a l u e  -1 sec , was o b t a i n e d on a d d i t i o n of 0.015-0.125 M L i C l .  A d d i t i o n of 0.05 M C R,, d i d not i n h i b i t 8 14 a d d i t i o n of 0.005 M E t S (Table X V I I ) .  the r a t e , n e i t h e r d i d the  D  2  A good A r r h e n i u s p l o t was o b t a i n e d f o r the temperature  t 70-84° and the a c t i v a t i o n parameters A H 14.1+ 6.4  0.5 K c a l m o l e "  1  range  t and A S  2  2  were found  to be  and -17.4 I 0.4 e.u. (Table X V I I I , F i g u r e 3 0 ) .  The Rh C l C a t a l y z e d Hydrogenation  o f MA  Stock s o l u t i o n s o f [Rh (C H.. . ) „C1] _ i n 0.45 M LiCl/DMA were made o ±4 I Z 0  up i n a i r ; a m o l e c u l a r oxygen complex i s i n i t i a l l y r e v e r t s t o a h y d r i d e w i t h the l o s s o f 0 s t o c k s o l u t i o n s were e f f i c i e n t MA a t 80° and 1 atm R^.  2  under H  2  formed but t h i s (Chapter V I I I ) .  Such  f o r the homogeneous h y d r o g e n a t i o n o f  Typical linear H  2  uptake p l o t s a r e shown i n  F i g u r e 31; the r a t e s t a r t e d t o f a l l o f f i n the r e g i o n where the r a t i o  - 137 TABLE XVII R h ( E t S ) C a t a l y z e d Hydrogenation of MA I  2  K i n e t i c Data at 80°  1:2)  (Rh:Et S = 2  [Rh] x  10  3  [MA] M  M  1.0  0.03  2.5  i n DMA  PH,  [H ]  mm  10  x  3  2.32  0.03  725 725  4.0  0.03  5.0 5.0  0.03 0.06  5.0  0.03 0.03 0.03 0.03 0.03 0.03 0.03  5,0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 0.45 0.05 g 0.05  0.03 0.03 0.03 0.03 M LiCl;  b  0.125  b  x  10"* M  sec  2.32  2.68 3.04  725  2.32  2.64  2.84  725 725 148  2.32 2.32  3.34 3.00  2.88 2.58  0.47  194 378 793  0.62 1.22  0.64 0.87 1.90 3.49 0.82 0.68 0.64 0.66 4.80 4.32 3.24 3.21  2.72 2.81 3.16 2.74 0.71 0.58  2.54 2.32 2.32 2.32 2.32 2.32 2.32 2.32 2.32 2.32  M LiCl;  M p- t o l u e n e s u l p h o n i c M cyclooctene;  M  -1 2 -1 M sec k  1  0.62 1.76  725 725 725 725 725 725 725 725 725  0.03 0.03  L i n e a r Rate  2  C  0.03 f  acid;  0.01  0.005 M Et s ; 2  a  b  0.55° 0.57 d  4.05  3.79 0.79 2.76  f  8  h  2.70 M  LiCl;  d  0.015  2.33 M LiCl;  M p-toluenesulphonic  ^  6  i n p l a c e of B.^.  acid;  1  - 138  -  a cu CO  X (U  u cd M  y< cfl  CU  C  6.0 Figure  28.  Rh  (Et^S) c a t a l y z e d h y d r o g e n a t i o n  V a r i a t i o n of l i n e a r r a t e w i t h 3.0  x 10~ M 2  of MA  [Rh],  i n DMA  (2.32  a t 80°.  x 10  M  H  MA).  o  cu  CO  o CU ca  r-l  ca cu  n  [H ] 2  Figure  29.  Rh  x  ( E t S ) catalyzed hydrogenation 2  V a r i a t i o n of l i n e a r r a t e w i t h 3.0  10"  x 10~ M 2  MA). ;  of MA  [H ], 2  i n DMA  (5.0 x 10  at M  80 Rh,  c  2>  - 139 -  TABLE XVIII R h ( E t S ) Catalyzed I  2  Hydrogenation o f MA  i n DMA  Temperature Dependence o f [Rh] = 5.0 x I f f T  [H,,]  °C  x 10  3  M  3  M,  [MA] = 3.0 x 1 0 ~  2  M  L i n e a r Rate  k  M sec"  M sec~'  1  2  _1  70  2.36  1.80  1.53  74.5  2.34  2.40  2.05  8  0  2.32  3.34  2.88  84  2.30  4.32  3.76  - 140  F i g u r e 30.  -  A r r h e n i u s p l o t f o r the Rh of MA  i n DMA,  (5.0 x 10~ M 3  ( E t S ) c a t a l y z e d hydrogenation 2  Rh,  3.0  x 10~ M 2  MA).  - 141 -  0  500  1000  1500  2000  2500  Time, sec F i g u r e 31.  T y p i c a l r a t e p l o t s f o r the Rh C l c a t a l y z e d h y d r o g e n a t i o n o f MA i n 0.45 M LiCl/DMA a t 8 0 ° . [Rh.]:  (0) 5.0 x 10~ M, 3  (2.32 x 10~ M R 3  ( A ) 1.8 x 10~ M) 3  3.0 x 1 0 M MA; _2  - 142 of Rh:MA i s 1:1  and the s t o i c h i o m e t r y of the  uptake a t the p o i n t of  metal p r e c i p i t a t i o n corresponded to the complete h y d r o g e n a t i o n of MA * a f a s t e r uptake f o l l o w e d m e t a l p r o d u c t i o n c l o s e l y to the r e d u c t i o n o f c y c l o o c t e n e ) . was  (the s t o i c h i o m e t r y c o r r e s p o n d i n g An i n i t i a l  induction period  a l s o observed s i m i l a r to t h a t i n the R h ^ E t ^ S ) system  (Section  A r e a c t i o n c a r r i e d out i n the s p e c i a l " a i r f r e e " d e v i c e , l i k e Rh (Et2S)  system, shox^ed a f i r s t  1  t h i s was  not s t u d i e d f u r t h e r .  produced.  o r d e r dependence on  6.4).  the  consumption  In the absence of MA,  m e t a l was  rapidly  Rh^Cl d i d not homogeneously hydrogenate C H., . . o 14 0  The v i s i b l e spectrum of a s t o c k s o l u t i o n of [ R h ( C g H ^ ) ^ C l ] ^ i 0.45  M LiCl/DMA made up i n a i r showed a s l i g h t  e = 230.  A d d i t i o n of MA had l i t t l e  at 450 my,  e = 250, was  observed.  showed a s h o u l d e r at 450 my, was  and  shoulder  The spectrum o f a hydrogenated  solution  e = 290; t h i s changed when the s o l u t i o n  steady spectrum w i t h an a b s o r p t i o n maxima at 440 my (e = 124) i n d i c a t i v e o f . R h  was  my,  e f f e c t on the spectrum, a s h o u l d e r  exposed to a i r a t room temperature and f i n a l l y  broad peak at 543  a t 400  n  1 1 1  after  3 days, a  (e = 420) and a  chloride ' 1  2  species  observed ( c f . RhCl -3H 0 i n 1.2 M LiCl/DMA, A 444 my, e = 343, 3 2 max A 548, e = 115). The same changes i n spectrum (A 400 my, e 332, max max A 540, e = 120) were observed a f t e r the hydrogenated s o l u t i o n had max . o  r e a c t e d w i t h 0^ f o r 100 sec at 80° and the t o t a l 0^ uptake corresponded c l o s e l y to o x i d a t i o n of R h 10~  5  1  to R h  1 1 1  (1.2 x 10  5  moles of 0^ per 2.5  x  moles of Rh). S p e c t r a l s t u d i e s of [Rh(C H..)„C1]„ 0  o  14 2  i n LiCl/DMA media w i t h o r  2  without MA were a l s o c a r r i e d out i n vacuum and under 0^ and IL, atmospheres  u s i n g the s p e c i a l c e l l attachment d e s c r i b e d i n s e c t i o n  2.6  - 143 to  -  study the p o s s i b l e complexing between Rh* In  and  MA.  vacuum, [Rh(C-H,.).Cl]_ i n 0.5 M LiCl/DMA o 14 2. _  down to 350 my,  e at 450 my  = 228.  gave a  On exposing t h i s s o l u t i o n to  d i f f e r e n t 0^ p r e s s u r e s , a s h o u l d e r developed a t 450 my; e a t 450 my  = 182,  at 760 mm  (  [Rh(C H .).C1] i n 0.45 o 14 / _ 0  1  f o r 15 min,  = 168  w i t h 0.03  down to 350 my,  s t a n d i n g a t room temperature 182 a t 450 my;  at 450 my  M LiCl/DMA  0  showed a continuum i n i t i a l l y  e  continuum  0^,  ( F i g u r e 32). M MA,  E a t 450 my  A, i n vacuum ~ = 250.  On  the spectrum changed, e =  on f u r t h e r s t a n d i n g a t room temperature  hours a s h o u l d e r developed a t 450 my,  a t 73 mm  E = 246.  f o r a few  Such changes were  thought to be due to the slow f o r m a t i o n of a Rh*(MA) complex at room temperature.  I f the s o l u t i o n of A i s l e f t  a b s o r p t i o n maxima at 448,  E = 266, and 544,  i n a i r f o r 3 hours, JB, e = 110, were observed;  and e v e n t u a l l y a f t e r 2 days, a steady spectrum was 444,  E = 404,  A max  550,  E = 126)  ( F i g u r e 33). < = >  w i t h B. at 80° f o r 500 s e c , a s l i g h t E  a t 450 my,  i s 290  When A was 468 my was  observed  When B was ' — •  s h o u l d e r a t 430 my  (^_  ax  treated  i s observed,  my.  made up under H  observed, £ = 188.  2  a t room temperature, a s h o u l d e r a t  T h i s spectrum changed s l o w l y w i t h time  ( F i g u r e 34),an i s o s b e s t i c p o i n t was  observed.  A f t e r 3 hours at room  temperature, a s l i g h t s h o u l d e r developed a t 450 my,  e = 220.  changes were a c c e l e r a t e d by h e a t i n g to 60° f o r a few minutes. s o l u t i o n on s t a n d i n g i n a i r a t room temperature gave A max E = 400 and X at 550 my. e = 124. max  These Such a  a t 444  my,  I •II  200  •III \ 4-1  C  \  d) •H  N \  O  N  •H  m  4-1  cu o o e o  o  100  •H \  X  w  400  F i g u r e 32.  500 Wavelength, m\i  600  A b s o r p t i o n s p e c t r a of [ R h C C g H ^ ^ C l ] ^ i n 0.5M LiCl/DMA at room temperature. (I) i n vacuum  ( I I ) under 73 mm 0^ ( I I I ) under 760 mm  of  0^  -  145  -  390  490 Wavelength,  F i g u r e 33.  590 my  A b s o r p t i o n s p e c t r a of [Rh(C H.. . )~C1] and MA i n 0.45M LiCl/DMA o ±4 z 0  i n vacuum a t room temperature.  (I) i n i t i a l  spectrum,  15 min., ( I I I ) a f t e r 3 hours, (IV) the s o l u t i o n 2 days, B, (V) B t r e a t e d w i t h H  0  left  a t 80° f o r 500 s e c .  (II) after i n a i r for  - 146 -  390  490 Wavelength,  F i g u r e 34.  590 my  A b s o r p t i o n s p e c t r a of [Rh(C H.. .) .Gl] . i n 0.45M LiCl/DMA O ±H Z. Z 0  at room temperature. hour,  (III) after  (I) i n i t i a l  spectrum,  3 hours, (IV) the s o l u t i o n  under  (II) after  left  1/2  i n a i r 2 days.  - 147 6.41  K i n e t i c s o f the Rh*Cl C a t a l y z e d Hydrogenations  o f MA  Stock s o l u t i o n s o f Rh*Cl made up i n a i r were used and k i n e t i c d a t a were o b t a i n e d by measuring  the l i n e a r  uptake p l o t s .  0.015-0.060 M [MA], the r a t e o f h y d r o g e n a t i o n was f i r s t [H ] and independent  From  o r d e r i n [Rh],  o f [MA] ([Rh]=[monomer]) (Table XIX, F i g u r e s 35,36),  The r a t e law i s of the form shown i n e q u a t i o n 6.1, the average k v a l u e was found to be 2.1 M  sec  A good A r r h e n i u s r a t e p l o t was observed f o r the temperature 70-85° (Table XX, F i g u r e 37) w i t h a c t i v a t i o n parameters  range  AR^ * = 18.0 ± 1  —1 0.5 K c a l mole  6.5  and AS ' = -6.8 ± 1.4 e.u. 2  D i s c u s s i o n o f the Rh* Systems The u.v. and v i s i b l e s p e c t r o p h o t o m e r i c and k i n e t i c d a t a i . e .  pseudo zero o r d e r k i n e t i c s  ( c f . Chapter  I I I ) suggest t h a t the  hydrogenations o f MA d e s c r i b e d i n s e c t i o n 5.3 and 5.4 were c a t a l y z e d by R h * ( E t S ) and Rh*Cl s p e c i e s , r e s p e c t i v e l y . 2  of g i 4 from C  H  [Rh(CgH^^)^Cl]  206 2  The easy  has p r o v i d e d a g e n e r a l method f o r  p r e p a r i n g o t h e r Rh* complexes, e.g. R h C l ^ h ^ P ) . ^ ' * ^  The observed  8  first  displacement  o r d e r dependences on [Rh], u s i n g s t o c k s o l u t i o n s o f R h * ( E t S ) and  Rh*Cljgive  2  no evidence f o r a dimer  —=•  monomer e q u i l i b r i u m and  i n d i c a t e s e i t h e r the d i m e r i c s p e c i e s i s a c t i v e or e l s e t h a t the dimer d i s s o c i a t e s c o m p l e t e l y to a c t i v e monomer under these e x p e r i m e n t a l conditions.  The l a t t e r seems much more l i k e l y ;  t h e r e a r e no c l e a r  cases o f h y d r o g e n a t i o n through d i m e r i c c a t a l y t i c s p e c i e s . are l i k e l y  E t S or C l 2  to c l e a v e the c h l o r i d e b r i d g e s i n [Rh(C H .)_C1]„ i n DMA to o 14 z z g i v e monomeric Rh* s p e c i e s . Complexes such as [ R h ( C 0 ) C l ] a r e r e a d i l y 0  n  2  2  - 148  -  TABLE XIX Rh*Cl C a t a l y z e d Hydrogenation of MA K i n e t i c Data a t 80° i n 0.45 M  [MA]  [Rh] 10  3  M  M  PH  2  mm  Linear  [H ] 2  x 10  3  LiCl/DMA  M  Rate  x 10^ M sec  2 l M sec'-1 k  1  M  1.0  0.03  725  2.32  0.48  2.06  1.8  0.03  725  2.32  0.76  1.84  2.5  0.03  725  2.32  1.16  2.07  4.0  0.03  725  2.32  1.90  2.04  5.0  0.03  725  2.32  2.48  2.14  2.5  0.03  214  0.70  0.33  1.86  2.5  0.03  371  1.18  0.58  1.96  2.5  0.03  459  1.48  0.73  1.96  2.5  0.03  636  2.04  1.06  2.5  0.03  783  2.51  1.31  2.08  2.5  0.06  725  2.32  1.00  1.72  2.5  0.015  725  2.32  1.20  2.07  •  2.08  - 149 -  3.0  TRhJ x 1 0 , M 3  F i g u r e 35.  Rh C l c a t a l y z e d h y d r o g e n a t i o n of MA  i n 0.45M LiCl/DMA a t 8 0 ° .  V a r i a t i o n of r a t e w i t h [Rh], (2.32 x 1 0 M _3  H„, 3.0 x 10~ M 2  MA).  - 150 -  - 151 -  TABLE XX Rh Cl Catalyzed I  Hydrogenation of MA i n 0.45 M LiCl/DMA  Temperature Dependence of k [Rh] = 2.5 x 1 0 ~ T °C  [H^] x 10  3  M  3  M,  2  [MA] = 0.03 L i n e a r Rate x 10  5  M sec"  1  M sec _ 1  70  2.36  0.56  0.95  75.2  2.34  0.88  1.50  80  2.32  1.16  2.07  85  2.30  1.80  3.13  - 152 -  - 153 174,175,230 c l e a v e d by donor l i g a n d s , i n c l u d i n g the C l dimeric  ion.  The f a c t  that  [Rh(C H.. . ) „C1]. i s o n l y s l i g h t l y s o l u b l e i n DMA but d i s s o l v e s O 14 Z _ r e a d i l y on a d d i t i o n o f Et„S o r C l agrees w i t h t h i s . C H.. . has been L o 14 0  0  shown t o d i s s o c i a t e c o m p l e t e l y from t h e i n i t i a l hence C l , DMA o r Et^S w i l l occupy  complex i n s o l u t i o n  the vacant c o o r d i n a t i o n  sites.  Added C g H ^ d i d not i n t e r f e r e w i t h the c a t a l y t i c h y d r o g e n a t i o n of  such  activity  solutions.  W i l k i n s o n e t a l * ^ found t h a t a s o l u t i o n c o n t a i n i n g Pb^P and [ R h ( C ^ ^ C l ^ (Ph^PrRh = 3:1) i n benzene gave the same k i n e t i c r e s u l t s f o r hydrogenat i o n of o l e f i n s as u s i n g RhClCPh^P)^ c r y s t a l s i n benzene. The  s p e c t r a l changes o f the s o l u t i o n o f [Rh(C H..)„C1]  in LiCl/  0  DMA w i t h MA i n vacuum s t r o n g l y suggest the slow complexing MA and Rh* a t room temperature.  between  T h i s f i n a l s o l u t i o n showed a spectrum  v e r y s i m i l a r to t h e s t o c k s o l u t i o n o f Rh*Cl w i t h MA s u g g e s t i n g t h a t i n the hydrogenations d e s c r i b e d , the i n i t i a l formed  by d i s p l a c i n g the 0^ i n Rh*0  2  s p e c i e s p r e s e n t was Rh*(MA)  which was p r e s e n t i n i t i a l l y  i n the  stock s o l u t i o n s . I n some m o l e c u l a r oxygen complexes, displacement o f ^ i -i r • i i 77,80,90 0^ by o l e f i n has been r e p o r t e d .  Rh*(0 ) 2  A different in  +  MA  >  Rh* (MA)  +  °  (6.2)  2  spectrum was observed i n i t i a l l y  when [Rh(C H .)„C1] o 14 _ 0  0.45 LiCl/DMA w i t h MA was kept under H_ as compared to that kept  under vacuum.  2  T h i s suggested the presence o f a Rh h y d r i d e s p e c i e s .  On s t a n d i n g a t room temperature 60° f o r a few minutes  f o r a few hours or when heated up to  the spectrum  approached  t h a t o f a Rh*(MA) s p e c i e s .  - 154 The i s o s b e s t i c p o i n t i s h i g h l y s u g g e s t i v e o f a m i x t u r e o f 2 s p e c i e s p r o b a b l y Rh^^H  and Rh^CMA) i n s o l u t i o n .  Hence the R h (MA)  i s probably  1  p r e s e n t under the h y d r o g e n a t i o n c o n d i t i o n s , i . e . a t 8 0 ° . All  the s p e c t r a l evidence s t r o n g l y suggests the e x i s t e n c e of a Rh^MA)  complex i n the Rh^Cl system d u r i n g the h y d r o g e n a t i o n c o n d i t i o n s ; a s i m i l a r R h (MA)  complex i s a g a i n v e r y l i k e l y formed  1  i n the R h ^ E t ^ S )  system p r i o r t o h y d r o g e n a t i o n . The k i n e t i c s of h y d r o g e n a t i o n f o r both systems u s i n g s t o c k s o l u t i o n s made i n a i r a r e simple w i t h a f i r s t [H^] and independence  o f [MA].  o r d e r dependence on [Rh],  The Rh^(MA) complex formed  i n the two  I systems r e a c t s w i t h H^ i n a r a t e d e t e r m i n i n g step to g i v e Rh the R h  1  and SA;  then f u r t h e r r e a c t s w i t h MA i n a f a s t s t e p .  R h (MA) 1  Rh  1  +  +  MA  H  - -» 2  2  f a S t  >  Rh  1  +  SA  '  , (6.3)  Rh^(MA)  (6.4)  These c o n c l u s i o n s a r e i n agreement w i t h the r e s u l t s from the RhCl (Et S) 3  2  3  3 4 12 ' and R h C l ^ 3 H 0 ' c a t a l y z e d h y d r o g e n a t i o n o f MA.  The k i n e t i c d a t a from the few experiments " a i r - f r e e " c o n d i t i o n s f o r the Rh ( E t S ) system 2  arid dimer e q u i l i b r i u m might be i n v o l v e d . be important i n promoting stock s o l u t i o n s .  performed  i n the  suggest t h a t some monomer  Oxygen and a time f a c t o r c o u l d  the f o r m a t i o n o f monomeric s p e c i e s i n the  Q u i t e s i m i l a r c o m p l i c a t e d k i n e t i c s have been observed 12  i n the R h C l * 3 H 0 ' c a t a l y z e d 3  2  h y d r o g e n a t i o n o f MA i n the absence  pf .  added L i C l and these were i n t e r p r e t e d i n terms o f d i m e r i c Rh^(MA) species.  - 155  6.6  -  Comparison of the S u b s t r a t e Hydrogenation and  Rh^  Rates i n the  Rh  1 1 1  Systems III  The k i n e t i c data o b t a i n e d f o r the v a r i o u s Rh  I and Rh  systems  ( e x c l u d i n g the data f o r the R h ^ E ^ S ) system i n " a i r f r e e " c o n d i t i o n s ) are summarized i n Table XXI.  Hydrogenation  to i n v o l v e the a c t i v a t i o n of H^ through I o x i d a t i v e a d d i t i o n f o r both Rh 5.12)> almost  The  is  (Et^S) and Rh C l systems  (see s e c t i o n  a c t i v a t i o n parameters o b t a i n e d f o r the Rh^Cl system are  i d e n t i c a l w i t h those r e p o r t e d f o r the h y d r o g e n a t i o n 3  determining  1  w i t h the R h C l ( E t S ) 3  D i f f e r e n t Rh  2  3  2  This  the same r a t e  system i s r e f l e c t e d i n the lower  The  faster  kR.^  value.  s p e c i e s are i n v o l v e d i n the R l ^ E ^ S c a t a l y z e d hydrogena-  When 0.015-0.125 M C l ~ was has a maximum of 1 C l (Table X V I I ) .  i s different  f o r the two  systems.  added to the R h ( E t S ) system, which 1  2  per mole of Rh, T h i s lower  comparable to the k^ v a l u e 0.33 3  step i n  i n the R h ^ E t ^ S ) c a t a l y z e d system as compared  t i o n s s i n c e the r a t i o of Rh:Cl  RhCl (Et S)  i n t e r m e d i a t e s and  1  s t e p s are l i k e l y i n v o l v e d i n both systems.  r a t e of h y d r o g e n a t i o n  2  M LiCl/DI4A m e d i a . '  2  shows t h a t the same r e a c t i v e Rh  obtained  thought  dihydride formation v i a I  the R h C l - 3 H 0 c a t a l y z e d system i n 1.2  3  ( e q u a t i o n 6.3)  a lower value  M "'"sec  1  system which c o n t a i n s 3 C l  on a d d i t i o n of 0.005 M Et^S  l i m i t i n g rate  (0.56  f o r the per Rh.  initially  was  M "'"sec "*") i s more corresponding N o n - i n h i b i t i o n of r a t e  to the R h ^ E ^ S ) system i s s i g n i f i c a n t  because t h i s shows a maximum of 2 moles of Et^S are c o o r d i n a t e d per I 3 4 mole of Rh . P r e v i o u s s t u d i e s ' i n d i c a t e d t h a t 1 mole of E t S d i s s o c i a t e s per mole of R h C l ( E t S ) p r i o r to r e d u c t i o n of the complex to 2  3  Rh  1  (Chapter  I I I , equations  2  3  3.2-3.5).  - 156 -  TABLE XXI Comparison of k Rh  Initial  V a l u e s and A c t i v a t i o n Parameters f o r the R h  A k  M  2  3  2  Rh (Et S) I  2  Rh (Et S) I  3  Rhhl  a  b  2  0  sec  K c a l mole  -1  -  2.85  14.1  -17.4  —  1.0  —  18.4  -  6.1  2.1  18.0  -  6.8  media.  2/k  1.05 1.2  —  1.5  LiCl.  H 2  e'.u.  21.4  R e s u l t f o r a d d i t i o n of 0.015-0.125 M  i n 0.45 M LiCl/DMA  k  2  0.33  i n 1.2 M LiCl/DMA media. C  + H  2  0.56  a  2  RhCl '3H O  and  C a t a l y z e d H y d r o g e n a t i o n of MA i n DMA  Complex  RhCl (Et S)  1 1 1  1.08  —  D 2  2  - 157 -  It  i s interesting  t o s p e c u l a t e on t h e a c t i v e Rh* s p e c i e s  to be p r e s e n t f o r r e a c t i o n 4,2 i n the v a r i o u s systems XXI. the  listed  The Rh^CEt^S) system can i n v o l v e a maximum o f 1 C l n e u t r a l RhCl(Et2S) (MA)  complex  2  produce a l e s s r e a c t i v e  seems l i k e l y ;  [RhCl (Et S)MA] 2  2  2  2  i n Table  p e r Rh and  a d d i t i o n of C l  species.  system c o u l d produce t h e [ R h C l ( E t S ) M A ]  likely  The R h C l ( E t S ) 3  complex  2  could 3  " i n s i t u " , with the 4  addition of C l  having l i t t l e  effect  on r e a c t i v i t y as observed.  R h C l o r R h C l - 3 H 0 systems i n 1.2 M L i C l DMA media I  3  2  2[RhCl (MA)]  involve  G  r [RhCl (DMA)(MA)] 2  (no E t S )  The  could  2  s p e c i e s ; i f t h e former, the  d a t a i n T a b l e XXI i n d i c a t e s d e c r e a s i n g r e a c t i v i t y  i n the t r e n d  2RhCl(Et S) MA 2  if  2  > [RhCl MA]  the l a t t e r ,  > [ R h C l ( E t S)(MA)]  3  which appears  2  r e a c t i v i t y would  [RhCl (DMA)(MA)]~ > [ R h C l ( E t 2  decrease i n t h e t r e n d R h C l ( E t S ) ( M A ) > 2  2  S)(MA)]~. 118 231  Two groups have r e c e n t l y diene l i g a n d i n complexes  unlikely;  '  shown t h a t the h a l i d e and n o t t h e  such as [ R h ( C g H ^ ) C l ] 2  can be r e p l a c e d by  2  phosphine  (L) to g i v e c a t i o n i c s p e c i e s such as [ R h ( C H „ ) L „ ] i f the o 1_ 2 r e a c t i o n i s c a r r i e d out i n p o l a r s o l v e n t s . The c a t i o n i c s p e c i e s a r e +  Q  1  a l s o c a t a l y s t s f o r homogeneous h y d r o g e n a t i o n through d i h y d r i d e 118 formation. of  -  The conductance measurement however shows no e v i d e n c e  c h l o r i d e d i s s o c i a t i o n i n the R h * E t S system.  The d i e n e l i g a n d i s  2  presumably more s t r o n g l y attached than the monoene. The i n d u c t i o n p e r i o d observed i n the Rh ( E t S ) system and i n t h e 2  Rh*Cl system c o u l d be due t o e v o l u t i o n of 0 complex  2  from the m o l e c u l a r oxygen  p r e s e n t i n t h e s t o c k s o l u t i o n s which a r e made up i n a i r  ( e q u a t i o n 6.2).  [Rh(C H .)„C1]„ D  O  m o l e c u l a r oxygen  1  ±H  Z  i n 0.5 M LiCl/DMA was found t o form  Z  complexes which under 11^ atmospheres  l o s e the 0^,.  - 158  (Chapter V I I I ) . The  -  f o r m a t i o n of m o l e c u l a r 0„ complex by 2  in  Et^S/DMA was  presumably  [Rh(C H..)„C1]~ o 14 2 2 0  not s t u d i e d but the system does c a t a l y z e o x i d a t i o n  forms an oxygen complex  (Chapter VIII).  The  i n d u c t i o n p e r i o d f o r s o l u t i o n s made up i n absence r e a s o n i n g , i . e . 0^ has sn  initial  absence  and  of the  of a i r support  this  d e a c t i v a t i n g e f f e c t presumably, by  occupying a c o o r d i n a t i o n p o s i t i o n r e q u i r e d  f o r hydride or o l e f i n *  h y d r o g e n a t i o n s c a t a l y z e d by IrCKCOXPh^P)^,traces  In  of 0^ i n c r e a s e d : the  35 r a t e of h y d r o g e n a t i o n by a f a c t o r of 100. of  0^ or ^2^2  S i m i l a r l y small traces 232  ^-  n c r e a s e  t  n  a c t i v i t y of R h C l ^ h ^ P ) ^ .  e  These r a t e  232 enhancements are thought c o o r d i n a t e d Ph^PO and  to be due  to the o x i d a t i o n o f Ph^P  the r e s u l t i n g p r o d u c t i o n of a vacant  to  non-  coordination  s i t e f o r the s u b s t r a t e . RhCl-^Et^S^  i n benzene i s not a c t i v e f o r homogeneous  hydrogena-  3 4 tion  '  and t h i s was  initial  r e d u c t i o n process  media. ' 3  in  thought  a 2:1  from the i n h i b i t i o n of the  (equations 3.2  Wilkinson et a l  4  to r e s u l t  r a t i o of E t ^ S ^ h  1  0  and  3.3)  found t h a t a d d i t i o n of Et_S to 2  result of  y e l l o w s o l u t i o n darkened  the R h ( o l e f i n ) are important 1  d u r i n g the exposure  for activity  Maleic acid i s a better Tr-acceptor ligand 1  time.  to s t a b i l i z e  the R h  s i m i l a r to cyclohexene  1  i n DMA.  This and  of the system  than cyclohexene  The p r e s e n t work ( s e c t i o n s 6.3.and 6.4)  a c i d i s homogeneously hydrogenated fails  0  hydrogenations, the  supports f u r t h e r the s u g g e s t i o n t h a t the s t a b i l i t y  w i t h Rh .  [Rh(C H..)„C1]„ o 14 2 2  i n benzene gave i n a c t i v e s o l u t i o n s for,  h y d r o g e n a t i o n o f cyclohexene and d u r i n g attempted initial  i n the n o n - p o l a r  lability  ( s e c t i o n 5.1 and  complexes  shows t h a t m a l e i c  i n p r e f e r e n c e to c y c l o o c t e n e which C y c l o o c t e n e i s thought  to be  i n i t s e l e c t r o n i c p r o p e r t i e s and p r o b a b l y does  ).  - 159 not  s t a b l i z e Rh.  1  probably  r e s p o n s i b l e f o r the darkening  i n Wilkinson's An  a g a i n s t r e d u c t i o n to the m e t a l .  from a MA  my,  of the r e a c t i o n s o l u t i o n noted  report.  intermediate  peak at 675  green s o l u t i o n (shoulder  e = 140)  hydrogenation  to R h  1  1 1  experiment was  (1/40^ per Rh).  o x i d a t i o n r e a c t i o n of  absence of c o o r d i n a t e d  The  r e a c t e d w i t h 0^ was  [Rh(C H .) C l ] i n DMA o 14 2. z 0  0  olefins  7  of MA,  equivalent  to a  to o x i d a t i o n  1 1 1  .  0  to o  the  i n the  z These green s o l u t i o n s  Such green s o l u t i o n s showed suggesting  the presence of  The  green s o l u t i o n s are a l s o a c t i v e  however, no d e t a i l e d s t u d i e s were c a r r i e d  P r e l i m i n a r y s t u d i e s i n d i c a t e d that the green c o l o u r was  converted  broad  t r a n s i t i o n m e t a l complexes have been 233  to have g values around 4.  f o r the hydrogenation out.  Some d  at 80°  with molecular  (Chapter VIII).  a sharp E.S.R. s i g n a l w i t h a g v a l u e of 4.63  shown  e = 172,  system i s q u i t e d i f f e r e n t  o x i d i z e o n l y v e r y s l o w l y i n a i r to R h  paramagnetic s p e c i e s .  at 475 my,  c o u l d be o b t a i n e d when the Rh^Cl s o l u t i o n  stage where the s t o i c h i o m e t r y of 0^ uptake of Rh  Such r e d u c t i o n i s  readily  to the orange red c o l o u r c h a r a c t e r i s t i c of the Rh^Cl XI 234235 complex p r i o r to hydrogenation of the o l e f i n . Rh acetates ' . 'aire known  to  by  be  green i n a c e t i c a c i d s o l u t i o n s .  green s o l u t i o n s o b t a i n e d or R h ( S A ) s p e c i e s . 11  The  i n the p r e s e n t  Thus the  s t u d i e s may  c a t a l y t i c hydrogenation  intermediate  w e l l contain  property  Rh (MA) 11  of Rh^"*" 4  1  s p e c i e s has r e c e n t l y been r e p o r t e d . The p r e s e n t s t u d i e s suggest t h a t II I Rh i s reduced to Rh b e f o r e hydrogenation starts.  1  7  CHAPTER V I I III HYDROGEN REDUCTION OF DIMETHYL SULPHOXIDE CATALYZED BY Rh  COMPLEXES  CONTAINING CHLORIDE AND SULPHIDE LIGANDS 7.1  General The  Introduction  c a t a l y t i c a c t i v i t y o f platinum  m e t a l complexes as homogeneous  2 3 8 9 35 h y d r o g e n a t i o n c a t a l y s t s i s v e r y dependent on the s o l v e n t media ' ' » ' and  f o r example, the a c t i v i t y o f R h C l ^ ^ ^ O and R h C l ( E t S ) 3  2  3  i s very  1-4 much enhanced i n the c o o r d i n a t i n g a p r o t i c s o l v e n t DMA.  Investigation  of such s o l v e n t e f f e c t s l e d t o the study o f the c a t a l y t i c a c t i v i t y o f R h C l - 3 H 0 and R h C l ( E t S ) 3  2  3  2  the absence o f any o r g a n i c  i n DMSO.  3  A hydrogenation occurred i n  s u b s t r a t e ; t h i s was found t o be a c a t a l y t i c  r e d u c t i o n o f the s o l v e n t and these s t u d i e s w i l l be d e s c r i b e d  i n this  chapter. DMSO has been w i d e l y  used as an advantageous medium f o r i n o r g a n i c  r e a c t i o n s because o f i t s a b i l i t y t o d i s s o l v e f a i r l y h i g h c o n c e n t r a t i o n s c • n _ 236,237 ,, , J ^ • i of many i n o r g a n i c s o l u t e s and has been used e x t e n s i v e l y as an o x i d i z i n g agent i n o r g a n i c  synthesis.  A few group I I I - V main group  h a l i d e s have been .shown t o reduce DMSO; most t r a n s i t i o n metal h a l i d e s 238 form c o o r d i n a t i o n compounds  a l t h o u g h niobium and tantalum penta-  h a l i d e s do a b s t r a c t the oxygen atom o f t h e s u l p h o x i d e  t o form t h e  .  - 161 c o r r e s p o n d i n g o x y h a l i d e and halogen s u b s t i t u t e d s u l p h i d e s .  239  The  p r e s e n t i n v e s t i g a t i o n shows that molecular hydrogen can be a c t i v a t e d III by Rh  complexes  f o r r e d u c t i o n o f DMSO t o d i m e t h y l s u l p h i d e  (DMS) and  i s c o n s i d e r e d important i n view o f the p r e s e n t e x t e n s i v e use o f t h i s solvent. 7.2  RhCl -3H 0 Catalyzed H 3  2  2  R e d u c t i o n o f DMSO  The v i s i b l e spectrum o f a s o l u t i o n o f RhCl^-SH^O i n DMSO changed s l o w l y w i t h time a t room temperature,presumably due t o t h e e q u i l i b r a t i o n between complexes. to 80°,and  T h i s change c o u l d be accomplished r a p i d l y by h e a t i n g  t h e steady spectrum o f the orange s o l u t i o n showed a b s o r p t i o n  maxima a t 360 my (e = 380) and 435 my (e = 270). found t o absorb H  2  a t measurable r a t e s from 70-90° w i t h o u t p r o d u c i n g  metal, u n l i k e r e a c t i o n s o f Rh*** complexes w i t h „ and r e f e r e n c e s  Such s o l u t i o n s a r e  2  i n DMA (Chapter I I I  1-4).  The k i n e t i c s o f the r e d u c t i o n were f o l l o w e d by measuring the r a t e of H  2  consumption a t constant p r e s s u r e .  The i n i t i a l  concentration of  Rh*** i n these experiments was i n the range o f 0.01-0.03 M. pressure of „  2  The p a r t i a l  was v a r i e d from 130-800 mm. ' The s o l u b i l i t y o f H i n 2  DMSO i s q u i t e s m a l l , but was determined t o be about 6.0 x 10 ^ M, atm * at 80°.  A typical H  2  uptake p l o t i s shown i n F i g u r e 38; a l i n e a r  uptake p l o t i s observed f o r 3 hours and then the r a t e f a l l s o f f v e r y slowly.  There i s no obvious s t o i c h i o m e t r i c r e l a t i o n s h i p between the B.^  uptake and the amount o f Rh used; an uptake was f o l l o w e d up to 1.0 M f o r a s o l u t i o n o f 0.03 M i n [Rh] and the uptake was s t i l l  continuing.  In the absence o f the rhodium complex, t h e r e was no measurable over 3 hours.  uptake  No r e a c t i o n s o t h e r than e q u i l i b r a t i o n were observed .  - 163 between RhCl^-311^0  and DMSO i n the absence o f  under the c o n d i t i o n s  of k i n e t i c experiments. The v i s i b l e a b s o r p t i o n s p e c t r a o f s o l u t i o n samples taken d u r i n g the l i n e a r uptake r e g i o n were unchanged  from t h a t o f the s t a r t i n g  s o l u t i o n , showing t h a t the r e a c t i o n i s c a t a l y t i c w i t h r e s p e c t to Rh ''"; 11  no R h  1 1 1  h y d r i d e s were d e t e c t e d .  The r e d u c t i o n p r o d u c t s o f DMSO were s e p a r a t e d from the i n o r g a n i c complex by d i s t i l l a t i o n and i d e n t i f i e d by gas chromatography u s i n g a d i n o n y l p h t h a l a t e column and a p r o t o n N.M.R. spectrum. r e a c t i o n p r o d u c t s i n s o l u t i o n i n which 1.0 moles o f gave lle^S  A n a l y s i s o f the had been consumed  and H^O^both about 1 mole f o r each mole o f  consumed.  (G.C. 2A i n s t r u m e n t , 160°, 160 ma, p r e s s u r e gauge setting=10,retention timeiM^S (3 m i n ) , H^O (5 min), t f o r H^O around 5.0 t o 5.5). a b l e by N.M.R. i n the s t a r t i n g p u r i f i e d DMSO.  No water was d e t e c t -  The c a t a l y z e d r e a c t i o n i s  thus  (CH ) SO 3  2  +  H  2  >  (CH ) S 3  2  +  H 0  (7.1)  2  The g r a d u a l f a l l o f f i n the h y d r o g e n a t i o n r a t e i s p a r a l l e l e d by a decrease i n the i n t e n s i t y o f the orange s o l u t i o n and a f t e r a 15 hour experiment the f i n a l s o l u t i o n i s yellow,showing a s i n g l e maxima a t 390 my (e = 42.5) i n d i c a t i n g l i k e l y  absorption  f o r m a t i o n o f the R h  1  state.  T h i s s o l u t i o n i s s t a b l e i n a i r f o r many hours a t room temperature b u t on h e a t i n g t o 80° under oxygen o v e r n i g h t , a n orange s o l u t i o n a g a i n w i t h the c h a r a c t e r i s t i c spectrum o f R h • A 430 my, e = 300). max  1 1 1  species  resulted  (A 380 my, e = 410, max  - 164 -  Attempts were made t o i s o l a t e a pure i n o r g a n i c complex a f t e r a long hydrogenation off  reaction.  An orange s o l i d was o b t a i n e d by pumping  the s o l v e n t under reduced p r e s s u r e .  Attempts t o r e c r y s t a l l i z e t h e  s o l i d were n o t s u c c e s s f u l ; water was used t o wash o f f the excess s o l v e n t from the i n i t i a l  gummy p r o d u c t .  The s o l i d r e s i d u e so o b t a i n e d  showed  s t r o n g I.R. bands a t 1120, 1020 and 980 cm *; a m i c r o a n a l y s i s y i e l d e d the d a t a :  C = 16.5; H = 4.2; C l = 25.0%.  an approximately  The molar conductance f o r  -12 -1 0.001 M s o l u t i o n i n DMSO was about 50 ohm cm mole -1  The molar conductance o f KC1 was measured t o be about 60 ohm On r e d i s s o l v i n g the i s o l a t e d r e s i d u e i n DMSO, a spectrum of a Rh* s p e c i e s was e v i d e n t 0.004 M s o l u t i o n ) .  7.3  2  approximately  Catalyzed H  When R h C l ( E t S )  3  was used i n p l a c e o f R h C l ' 3 H 0 r e s u l t s  those  2  2  2  Reduction  characteristic  3  3  o f DMSO 3  d e s c r i b e d i n the p r e v i o u s  l i n e a r r a t e s were somewhat H  388, e-400 f o r an  2  s e c t i o n were o b t a i n e d  g r e a t e r f o r the s u l p h u r  similar  although t h e  system.  A typical  uptake p l o t i s shown i n F i g u r e 38; a g a i n a f a l l o f f i n l i n e a r  a f t e r 3 hours was observed. The  initial  -1  cm mole  RhCl (Et S) 3  to  (A max  2  rate !  e q u i l i b r a t e d s o l u t i o n of R h C l ( E t S ) 3  2  3  i n DMSO showed  a b s o r p t i o n maxima a t 370 my (e = 500) and 430 my (e = 300); t h i s  f  spectrum  remained unchanged d u r i n g t h e l i n e a r uptake r e g i o n . The 7.1)  products  o f DMSO r e d u c t i o n were a g a i n Me S .and R^O 2  (equation  - 165 7.4  K i n e t i c s o f the C a t a l y z e d Reductions The  uptake p l o t s were a n a l y z e d by measuring rates i n the l o n g  l i n e a r region.  T a b l e s XXII and XXIII summarize the k i n e t i c d a t a f o r  the RhCl^-SH^O system and the RhCl^CEt^S)^ system r e s p e c t i v e l y . S i m i l a r k i n e t i c s were observed f o r the two systems. The r a t e i s f i r s t  o r d e r i n [Rh ] and [H^] f o r b o t h systems  (Tables XXII, X X I I I , F i g u r e s 39,40).  The r a t e law i s thus  -d[H ] d  t  =  k[Rh, ] [ H ]  (7.2)  2  The v a l u e s of k were c a l c u l a t e d from the s l o p e s of the f i g u r e s 39 and 40 and by d i r e c t c a l c u l a t i o n  (Tables XXII, X X I I I ) .  The average v a l u e o f k  at 80° f o r the RhCl^'SH^O system i s 1.94 M ''"see \ v a l u e of k f o r R h C l ( E t S ) 3  2  3  system i s 3.35 M  _ 1  sec  and the average _ 1  a t 80°.  Good A r r h e n i u s r a t e p l o t s were observed f o r both systems (Tables XXIV and XXV, F i g u r e 41). R h C l - 3 H 0 and R h C l ( E t S ) 3  2  3  2  The a c t i v a t i o n parameters f o r the  systems are AH = +  3  mole ,AS = 18.0 ± 3.0 e.u.« and AH = _1  T  +  27.0 ± 1.0 K c a l  16.8 ± 0.5 K c a l m o l e "  1  ,  AS. = +  -9.0 i 1.0 e.u., r e s p e c t i v e l y . H No measurable deuterium i s o t o p e e f f e c t , k  D 2f\r^2 = 0.96, was  2  observed f o r the R h C l » 3 H 0 system; a d d i t i o n of p - t o l u e n e s u l p h o n i c 3  2  a c i d had no s i g n i f i c a n t e f f e c t on  the r a t e .  The v a l u e of k was  independent of added 0.1 M Me S (Table X X I I ) , a l t h o u g h the l i n e a r 2  r a t e f e l l o f f much more r a p i d l y f o r t h i s A d d i t i o n of up to 2.2 M H 0 2  experiment.  had no e f f e c t on k f o r the d i e t h y l  s u l p h i d e system; h i g h e r c o n c e n t r a t i o n s of water  (up to 40% by volume)  - 166  r-  TABLE XXII RhCl -3H 0 Catalyzed H 3  2  2  R e d u c t i o n o f DMSO  ' K i n e t i c Data a t 80° [Rh]  H  2  5 * -x 10 M  mm  x 10 M 2  3  [H ]  2  k  Rate  x 10^ M sec *  M sec  0.5  746  6.0  0.54  1.80  1.0  746  6.0  1.02  1.70  2.0  746  6.0  2.28  1.89  3.0  746  6.0  3.50  1.94  3.0  804  6.5  3.83  1.96  3.0  486  3.9  2.72  2.30  3.0  236  1.9  1.36  2.37  3.0  746  6.0  3.63  2.01  a  3.0  746  6.0  4.30  2.39  b  2.0  746  6.0  2.30  1.91°  D  2  i n s t e a d of H  2  k p-Toluenesulphonic C  Linear  a c i d 0.1 M.  0.1 M Me S 2  S o l u b i l i t y was e s t i m a t e d from t h e s o l u b i l i t y o f H i n DMSO a t 746 mm 2  assuming  Henry's law a p p l i e d .  - 167 -  TABLE XXIII RhCl (Et S) 3  2  3  C a t a l y z e d R e d u c t i o n o f DMSO K i n e t i c Data a t 80°  [Rh]  P'H  x 10 M  a  2  mm  2  x 10  k  L i n e a r Rate  [H ]  2  x 10^ M sec *  M~  M sec  0.5  746  6.0  1.04  3.56  1.0  746  6.0  2.10  3.50  1.5  746  6.0  2.92  3.24  2.0  746  6.0  3.68  3.07  1.0  . 814  6.5  2.20  3.37  1.0  628  5.0  1.69  3.35  1.0  383  3.1  1.07  3.47  1.0  135  1.1  0.35  3.22  1.0  746  6.0  2.00  3.33  1.0  746  -  4.20  1.0  746  -  4.60°  2.2 M H 0; 2  b  20%  (volume) H 0 ; 2  C  b  -  40% (volume) H 0 .  S o l u b i l i t y was e s t i m a t e d from the s o l u b i l i t y 746 mm, assuming Henry's law a p p l i e s .  2  of H  2  i n DMSO a t  a  - 168 -  - 170 -  TABLE XXIV RhCl '3H 0 C a t a l y z e d R e d u c t i o n o f DMSO Temperature Dependence o f k [Rh] = 3.0 x 1 0 ~ T C  p'H c  2  x 10 M  mm  M  L i n e a r Rate  [H ]  2  2  5  6 "I x 10 M sec  M sec  70  751  ^6.0  0.91  0.50  75  749  ^6.0  1.86  1.03  80  746  6.0  3.50  1.94  85  742  %6.0  5.25  2.93  TABLE XXV RhCl (Et S) 3  2  3  C a t a l y z e d R e d u c t i o n o f DMSO  Temperature Dependence o f k -2 [Rh] = 1.0 x 10 M T  2  C°  mm  70  [H ] 2  L i n e a r Rate  x 10 M  x 10^ M sec  751  ^6.0  1.00  1.67  75  749  ^6.0  1.40  2.34  80  746  6.0  2.10  3.50  85  742  ^6.0  3.10  5.16  90  737  ^6.0  4.30  7.16  5  1  M sec  -  171  -  - 172 -  i n c r e a s e d the r a t e by a f a c t o r o f 2.5.  7.5  Discussion The  r a t e law f o r the c a t a l y z e d r e d u c t i o n o f DMSO ( e q u a t i o n 7.2)  t o g e t h e r w i t h the s p e c t r o s c o p i c data showed t h a t  reacts with R h *  1 1  s p e c i e s t o g i v e an i n t e r m e d i a t e which i s then decomposed t o Me S, R^O 2  and  the i n i t i a l  Rh*** complex.  In p o l a r s o l v e n t s such as water, e t h a n o l and DMA, r e a c t i o n o f molecular  w i t h Rh*** complexes can g i v e r i s e t o i n t e r m e d i a t e h y d r i d e s  formed through  h e t e r o l y t i c s p l i t t i n g o f the „  molecule*' ' ' * 2  2  4  In the  7  240 h i g h l y p o l a r DMSO ( d i e l e c t r i c c o n s t a n t 49 a t 20°) to be the r a t e d e t e r m i n i n g  Rh***(DMS0)  (Cl  +  t h i s i s again  likely  step.  H  2  -k—^  Rh***(DMS0)H  and Et^S l i g a n d s are  +  H  (7.3)  +  omitted)  1 2 4 29 Such r e a c t i o n s show l i t t l e measurable i s o t o p e e f f e c t .  ' ' '  There  are no r a t e data on the dependence on [DMSO] but s i n c e the h y d r i d e intermediate w i l l  c o n t a i n c o o r d i n a t e d DMSO, the subsequent step must  be the r a p i d decomposition  t o p r o d u c t s w i t h r e g e n e r a t i o n o f the  c a t a l y s t which r a p i d l y c o o r d i n a t e s w i t h f u r t h e r DMSO. T T T  Rh  The  i j +  (DMSO)H  ———>  T  Rh  TT  +  Me„S +  H 0 o  e s s e n t i a l independence o f k on a c i d i s c o n s i s t e n t w i t h  :  (7.4)  the back  - 173 r e a c t i o n of equation  7.3 n o t competing w i t h r e a c t i o n shown i n e q u a t i o n  7.4. 241 Johnson and Walton  have i s o l a t e d the RhCl^CDMSO)^ complex from  s o l u t i o n s o f RhCl^'SH^O i n DMSO and t h i s s p e c i e s i s l i k e l y  t o be p r e s e n t  i n the e q u i l i b r a t e d s o l u t i o n s o f RhCl^'SH^O used i n the present 240 According  t o Gutmann,  the donor s t r e n g t h o f DMSO i s g r e a t e r  studies.  than  f o r water, the c o n c e n t r a t i o n o f which w i l l be a maximum o f 0.3 M (3 times the [Rh]). intermediates  is  favoured  RhCl H(DMS0) 2  3  o r [RhCl H(DMSO) ]~ a r e the most 3  2  produced i n the r e a c t i o n (see e q u a t i o n 242  s i n c e some r e c e n t work  ligands i n RhCl (DMSO) 3  3  7.3).  likely  The l a t t e r  i n d i c a t e d t h a t one o f the DMSO  i s extremely l a b i l e and can r e a d i l y be d i s p l a c e d  by C l " . The  d e t a i l e d path o f r e a c t i o n ( e q u a t i o n 7.4) i s u n c e r t a i n . ;DMSO  complexes o f t r a n s i t i o n metals are w e l l known t o c o o r d i n a t e g e n e r a l l y 243 I I 244 245 I I 244 through the oxygen atom. Although P t , ' Pd , and Ir have been shown t o c o n t a i n DMSO bonded through the s u l p h u r atom; these c o n c l u s i o n s were o r i g i n a l l y drawn from I.R. s p e c t r a 1  1  1  p a r t i c u l a r l y i n the S-0 s t r e t c h i n g r e g i o n , b u t some have been v e r i f i e d 241 by X-ray work.  Johnson and Walton  draw no d e f i n i t e c o n c l u s i o n s  the f a r I.R. data about the bonding i n the R h C l ( D M S O ) 3  the e x i s t e n c e o f t h e s t r o n g S-0 band a t 1120 cm d u r i n g the p r e s e n t through the s u l p h u r 4  through the s u l p h u r and  930 cm  1  complex, b u t  i n a sample we made  s t u d i e s s t r o n g l y suggests bonding o f the DMSO atom.  Other r e c e n t data r e p o r t s t h a t i n .7  1 /  Na[RhCl (DMS0) ] ,  1  3  from  .  .  1  ^ SO  1 i e s a t about 1113 cm , i n d i c a t i n g bonding 242 -1 atom; i n R h C l ( D M S O ) , two bands a t 1140 cm 3  3  were i n t e r p r e t e d i n terms o f 2 s u l p h u r bonded and 1 oxygen  - 174  bonded DMSO l i g a n d s . believed  The oxygen bonded DMSO i n R h C l ( D M S 0 ) i s 3  t o be l a b i l e .  2 A- 2  The c a t i o n Pd(DMSO)^  2I  3  has been shown t o  248 c o n t a i n both s u l p h u r and oxygen bonded DMSO. A p l a u s i b l e mechanism f o r the r e a c t i o n written  7.4) can be  f o r S bonding  1/  //  — Rh / \ /  (equation  H  S-CH. \ CH  — — >  3  1  3  f / /  +  — Rh*-S-CH / | •\ CH  >  0  3  —Rh/ I  +  2  H 0  +  o  Me„S (7.5)  2  1  3  (I)  Protonation  i /  H  (ID  o f the b a s i c oxygen atom  a t t a c k by the c o o r d i n a t e d  hydride  249  would g i v e I I .  Nucleophilic  (a t y p i c a l i n s e r t i o n r e a c t i o n o f an 38  u n s a t u r a t e d moiety i n t o a metal h y d r i d e bond  ) would l e a d t o e l i m i n a -  t i o n o f W^p and Me^S, e i t h e r f r e e o r c o o r d i n a t e d s t a b i l i t y o f rhodium d i m e t h y l s u l p h i d e initial not  complexes.  The constancy o f t h e  r e a c t i o n r a t e and v i s i b l e spectrum i n d i c a t e t h a t the Me^S i s  coordinated  rapid f a l l  i n this region.  In the system w i t h added Me2S,the more  o f f i n r a t e suggests t h a t Me^S may w e l l c o o r d i n a t e  concentration by  depending on the  b u i l d s up (see l a t e r d i s c u s s i o n ) .  a d d i t i o n o f up t o 2.2 M H 0 t o the R h C l ( E t S ) 2  3  2  as i t s  No e f f e c t i s observed 3  system; thus water  does n o t cause the r e t a r d a t i o n i n r a t e and i s a l s o u n l i k e l y t o be coordinated  t o the rhodium a t t h i s c o n c e n t r a t i o n .  about the i n c r e a s e  i n rate at higher  [^0]  involved  and a l s o the s o l u b i l i t y o f H 250 than i n DMSO.  2  Little  can be s a i d  5 aquo complexes may be  i s some 10 times g r e a t e r  I n H„0  - 175  -  An i n t e r e s t i n g p o s s i b i l i t y f o r the o v e r a l l r e d u c t i o n r e a c t i o n i s that i n t e r m e d i a t e I I i s formed i n a simple c o n c e r t e d step by approach of the  molecule  s p l i t t i n g of the  the  to the rhodium-DMSO complex; the h e t e r o l y t i c  molecule would be " b u i l t  i n t o " such a mechanism  which would be i n d i s t i n g u i s h a b l e from the k i n e t i c p o i n t of view. The d i e t h y l s u l p h i d e system i s about twice as a c t i v e at 80° as t r i c h l o r i d e system; the v i s i b l e a b s o r p t i o n spectrum Rh  1 1 1  shows a d i f f e r e n t  complex i s i n i t i a l l y p r e s e n t i n s o l u t i o n and i t must have  c o o r d i n a t e d Et^S. Hence the f a l l  Et^S i s a somewhat s t r o n g e r donor l i g a n d than  o f f i n r a t e ( F i g u r e 38)  c o o r d i n a t i o n of Me^S The for  to R h  1 1 1  i s not thought  Me^S.  to be due  to the  .  s i g n i f i c a n c e of the d i f f e r e n c e i n the a c t i v a t i o n parameters  the two systems s t u d i e d i p not c l e a r but i t may  be r e l a t e d to the  d i f f e r e n c e i n the charges of the r e a c t i n g complex. for  the  example, c a t i o n i c s p e c i e s of the type  (x + y = 4) c o u l d be p r e s e n t . which R h C l ' 3 H 0 ' 3  2  complexes through R h  In the Et^S  [RhCl.(Et S) 9  3  2  3  '  have been reduced  h y d r i d e i n t e r m e d i a t e s , the E t S  1 1 1  (DMSO) ]  In some r e l a t e d systems i n DMA,  and R h C l ( E t S )  2  system, +  in  to Rh  system a g a i n  showed a lower e n t h a l p y of a c t i v a t i o n and a more u n f a v o u r a b l e  entropy  (Table XXVI). The  fall  l o s s of Rh  I* -j- -j*  Rh  111  o f f i n c a t a l y t i c a c t i v i t y i s thought  to be due  h y d r i d e s which can e a s i l y d i s s o c i a t e i n t o Rh  !!  >  Rh  1  +  H  to the  ^-  species.  (7.6)  +  The e x p e r i m e n t a l data s t r o n g l y i n d i c a t e t h a t i n the r e g i o n of r a t e some Rh  I  complexes are. p r e s e n t .  ^ ^ ^2  The decomposition  of Rh  lower III H to  '  - 176 -  TABLE XXVI Comparison o f the A c t i v a t i o n Parameters  f o r the H e t e r o l y t i c  Splitting  i n R h C l ' 3 H 0 and R h C l ( E t S ) Complexes i n DMA and DMSO 3  2  3  2  1-4  6  DMA AH  Kcal/mole  DMSO AS e.u.  A H Kcal/mole 1  AS e.u.  RhCl '3H 0  17.3  - 9.2  27.0  18  RhCl (Et S)  12.9  -19.2  16.8  - 9  3  3  2  2  - 177 Rh*  i s a f a s t r e a c t i o n and the p r o d u c t i o n o f Rh* w i l l depend on t h e  comparative r a t e s o f the decomposition equation  o f the h y d r i d e  according to  7.6 and i t s r e a c t i o n w i t h DMSO a c c o r d i n g t o e q u a t i o n 7.5.  P r o d u c t i o n o f Rh* would be more f a v o u r a b l e a t h i g h e r l i g a n d i s expected  [Me^S] s i n c e t h i s  t o s t a b i l i z e t h e lower v a l e n t s t a t e (more c l a s s b  character). A n a l y s i s o f the i n o r g a n i c r e s i d u e i s o l a t e d from the RhCl^'BH^O catalyzed reduction  (C = 16.5;  H = 4.2; C l = 25.0%) suggested  t h e r e a r e 3 moles o f C l per mole o f Rh. complexes a r e [(DMSO)H] [ R h C l ( M e S ) ] 3  2  that  P l a u s i b l e formulae f o r Rh*  ( c a l c . C = 16.8;  24.8%) and [(DMSO)H] [RhCl (DMSO)] (C = 16.1; 3  H = 4.7; C l =  H = 4.5; C l = 23.9%).  A  251 [(DMF) H] [Pd Clg] 2  2  2  has been r e p o r t e d .  can e a s i l y be p r o t o n a t e d ,  although  as c a t i o n s have been r e p o r t e d .  DMSO i s a b a s i c s o l v e n t and  no complexes w i t h p r o t o n a t e d  The c o n d u c t i v i t y data suggest  r e s i d u e i n DMSO behaves as an e l e c t r o l y t e although too low f o r a 2:1 e l e c t r o l y t i c .  DMSO  that t h e  the c o n d u c t i v i t y i s  T h i s r e s i d u e c o u l d presumably c o n t a i n  some n e u t r a l Rh*** s p e c i e s which c o u l d account f o r the low c o n d u c t i v i t y . However, the v i s i b l e spectrum suggested  the presence o f Rh* s p e c i e s o n l y . -1 -1  The  impure orange s o l i d gave s t r o n g I.R. bands a t 1120 cm  and  980 cm *.  The f i r s t  i s a t t r i b u t e d t o the SO s t r e t c h o f a s u l p h u r  bonded DMSO; and the l a t t e r  two may be a s s i g n e d  c o o r d i n a t e d DMSO and Me S although 2  oxygen bonded DMSO. although  , 1020 cm  to r o c k i n g modes o f  the band a t 980 cm * may be due t o  There are no r e p o r t s on Rh* a l k y l s u l p h i d e complexes  a Rh*Cl(CO) ( D M S O ) c o m p l e x  i s known.  c l a s s b c h a r a c t e r than Rh*** i s thought l i k e l y the sulphur atom o f DMSO.  Rh* w i t h i t s more  to coordinate  through  - 178 The  k i n e t i c data could  hydrogen r e d u c t i o n 7.6,  followed  a l s o be c o n s i s t e n t w i t h a r a t e  t o Rh* through r e a c t i o n s  determining  shown i n e q u a t i o n s 7.4 t o  by a r a p i d o x i d a t i o n o f Rh* by DMSO.  However, DMSO  i i «.i i, T . 11 241 _ IX 252 complexes o*f low v a li e n t- t r a n s i• «t-i•o n metals such as Mn , Ru ,  I 35 Ir  ,  I 175 Rh  are known and the f i n a l r e a c t i o n s o l u t i o n appears t o ;  c o n t a i n Rh*,  so such a mechanism appears t o be . u n l i k e l y and a r e a c t i o n  through Rh***H~ i s h i g h l y complex c o n t a i n i n g w i t h DMSO a t 80°.  7.6  favoured.  A s o l u t i o n o f t h e [Rh(C H.. .,) „C1] _ o 14- Z Z the l a b i l e C H.. . l i g a n d showed no redox r e a c t i o n o 14 0  0  Catalyzed  Oxidation  and R e d u c t i o n ' o f DMSO by RhCl ' 3 ^ 0 ,  Using a M i x t u r e o f H^ and 0^ The  observation  that  the f i n a l y e l l o w s o l u t i o n was o x i d i z e d  slowly  by 0^ back t o Rh*** (see s e c t i o n 7.2) suggested the use o f a H^/O^ mixture might prevent the slow f a l l o f f i n r e a c t i o n r a t e . experiment u s i n g RhCl^OH^O in  a m i x t u r e o f 500 mm R  i n DMSO, the i n i t i a l  and 250 mm 0^ w i t h 0.03 M  r a t e was that expected f o r the  reaction  the absence o f oxygen; however, the r a t e now showed a u t o c a t a l y t i c  behaviour b e f o r e r e a c h i n g  a steady r a t e o f 1.3 x 10 ^ M sec *, some  3 times f a s t e r than the i n i t i a l off  I n an  over a 3 hour p e r i o d  r a t e , and showed no s i g n o f f a l l i n g  ( F i g u r e 42).  No r e a c t i o n was observed  between RhCl^'SH^O d i s s o l v e d i n DMSO and oxygen. The  r e a c t i o n p r o d u c t s were i s o l a t e d by pumping o f f the s o l v e n t a t  reduced p r e s s u r e .  With warming and more pumping, a w h i t e s o l i d was  i s o l a t e d from the r e s i d u a l m e t a l complex and was r e c r y s t a l l i z e d chloroform.  from  The pure white s o l i d so o b t a i n e d was i d e n t i f i e d by I.R. and  10.56 L_  7.92  id cj  x u  5.28 h"  o  CO  x  2.64  r  4000  8000 Time, sec  F i g u r e 42.  Rate p l o t f o r the r e a c t i o n o f R h C l - 3 H 0 and DMSO u s i n g a m i x t u r e 3  at 80°, (p'H = 500 mm, 2  p'0  2  = 300 mm,  2  3.0 x 1 0 "  2  M Rh).  - 18.0 melting  point  t o be d i m e t h y l sulphone  H^O and Me^S were a l s o i d e n t i f i e d These r e a c t i o n s  (Me^SO^)•  i n the f i n a l  S m a l l e r amounts o f reaction solution.  i n v o l v i n g H^/O^ m i x t u r e s are p a r t i c u l a r l y i n t e r e s t -  253 ing.  Trocha-Grimshaw and Henbest  have r e p o r t e d  that s o l u t i o n s of  R h C l ^ o r HtRhCl^CDMSO)^] i n h o t p r o p a n - 2 - o l / w a t e r m i x t u r e s c a t a l y z e t h e o x i d a t i o n o f DMSO t o M e 2 S 0 2  air  a l t h o u g h no mechanism was suggested.  RhCl^-SH^O i n DMSO showed no r e a c t i v i t y that  towards O2 and i t seems  the a l c o h o l i c medium i s n e c e s s a r y t o f u r n i s h i n t e r m e d i a t e  species.  254  catalysts.  These workers Rh  1  2  increase  s t a t e that hydrides  to r e a c t i o n  27,  ^and  a r e the most e f f e c t i v e  (7.6).  these c o u l d w e l l be produced from R h  i n r a t e o f gas uptake u s i n g  I produced Rh s p e c i e s .  s o l u t i o n o r the R h  1  111  !!  Hence from these c o n s i d e r a t i o n s the the B. /0  m i x t u r e i s c e r t a i n l y due  to an induced c a t a l y t i c o x i d a t i o n through Rh^^^H slowly  hydride  complexes are known t o a c t i v a t e m o l e c u l a r 0^ through an o x i -  dative addition r e a c t i o n ^ ' according  253  likely  intermediate  o r the  III The i n a c t i v i t y o f e i t h e r t h e i n i t i a l Rh  s o l u t i o n s from the h y d r o g e n a t i o n experiments towards  ©2 i n d i c a t e s t h a t R h ^ ^ H  may be d i r e c t l y i n v o l v e d  as oxygen  Some r e c e n t work on the RuC^CPh^P)^ c a t a l y z e d a u t o x i d a t i o n  carriers. of e t h y l -  83 benzenes has a l s o i n d i c a t e d t h a t i n t e r m e d i a t e No  c a t a l y t i c o x i d a t i o n was observed u s i n g  hydrides  are involved.  s o l u t i o n s o f [Rh(C H .) Cl]„ o 14 2 2 D  i n DMSO, a l t h o u g h t h i s complex was found t o a c t i v a t e m o l e c u l a r oxygen i n DMA (see Chapter V I I I ) . DMSO i n these systems p l a y s b o t h the p a r t o f the s u b s t r a t e solvent.  Preliminary  s t u d i e s o f the R h C l ( E t 2 S )  of MA i n DMSO i n d i c a t e d t h a t initial  3  3  catalyzed  the r a t e p l o t c o n s i s t e d  r e g i o n o f more r a p i d uptake f o l l o w e d  and the  hydrogenation  o f two p a r t s ; an  by a second l i n e a r  region  - 181 -  ([Rh]  = 0.01 M, [MA] = 0.03 M, p'R^ = 746 mm, T = 80°; —6  2.82  x 10  —1 M sec  son o f the i n i t i a l  initial  —6 , second l i n e a r r a t e = 1.68 x 10  —1 M sec  r a t e w i t h t h e r a t e o f the R h C l ( E t 2 S ) 3  (equation  The second l i n e a r r a t e i s p o s s i b l y due t o the h y d r o g e n a t i o n o f A r a t e constant  f o r the R h C l ( E t 2 S ) 3  3  catalyzed hydrogenation of  MA i n DMSO, assuming that t h e second l i n e a r r a t e i s f i r s t and  Compari-  rate i s  p o s s i b l y a s s o c i a t e d w i t h the r e d u c t i o n o f Rh*** t o Rh***H  MA.  ).  catalyzed  3  r e d u c t i o n o f DMSO (Table XXIII) suggested t h a t the i n i t i a l  7.3).  rate =  order  [H^], was c a l c u l a t e d t o be 2.7 M *sec * which was some e i g h t  i n [Rh] times  3 4 f a s t e r than the c o r r e s p o n d i n g system i n DMA. ' are complicated use  Since  the measurements  by the c a t a l y t i c r e d u c t i o n o f the DMSO s o l v e n t , t h e  o f DMSO as a s o l v e n t media f o r the R h C l ( E t S ) 3  2  c a t a l y z e d h y d r o g e n a t i o n o f o l e f i n s was n o t f u r t h e r  3  and R h C l ^ H ^ O studied.  CHAPTER V I I I ACTIVATION OF MOLECULAR OXYGEN BY BIS(CYCLO-OCTENE)CHLORO RHODIUM ( I ) IN DMA  8.1  Introduction The d i f f e r e n c e i n observed k i n e t i c s f o r the h y d r o g e n a t i o n o f  o l e f i n i c s u b s t r a t e s by [ R h ( C g H ^ ) 2 ^ 1 ] 2 ^ 2 ^ * Et  n D  M  A  »  u  s  i  n  g  completely  a i r f r e e c o n d i t i o n s i n s t e a d o f s t o c k solutions,made up i n a i r . l e d to the i n v e s t i g a t i o n o f the r e a c t i o n o f t h i s complex w i t h oxygen. R e a c t i o n s o f t r a n s i t i o n metal complexes w i t h m o l e c u l a r oxygen a r e of much c u r r e n t i n t e r e s t  (see s e c t i o n 1.5).  Very few k i n e t i c  studies  of the f o r m a t i o n and c a t a l y t i c a c t i v i t y o f m o l e c u l a r oxygen complexes have been r e p o r t e d and the f o l l o w i n g d e s c r i b e s such a study.  8.2  Formation o f the M o l e c u l a r Oxygen Complex At room temperature  o r 80°, a s o l u t i o n o f [Rh(C H .) Cl]„ i n o 14 / L 0  0.5 M LiCl/DMA, 1, r a p i d l y absorbed oxygen i n a 1:1 r a t i o o f O^iRh ([Rh] = [monomer]).  T h i s was accompanied  change from r e d to dark brown. oxygenated  by a r a p i d  colour  The I.R. s p e c t r a o f the r e s u l t i n g  s o l u t i o n showed a f a i r l y  s t r o n g a b s o r p t i o n a t 893 cm: *, i n 58 71 255  the r e g i o n o f the 0-0 s t r e t c h o f a c o o r d i n a t e d 0^ molecule^ which was absent i n the i n i t i a l r e d s o l u t i o n .  '  '  On p r o l o n g e d pumping o f  - 183 the  dark brown "oxygenated" s o l u t i o n s a t room temperature or 8 0 ° ,  the  i n i t i a l r e d c o l o u r o f the "unoxygenated"  r e s t o r e d , and such r e s u l t i n g  "deoxygenated"  1/10 °f the amount o f 0^ r e q u i r e d to f u l l y  s o l u t i o n c o u l d not be s o l u t i o n s absorbed  about  form the Rh^CO^) complex.  The o x i d a t i o n s t a t e o f the complex i s w r i t t e n f o r m a l l y as Rh^, but the  exact e l e c t r o n i c c o n f i g u r a t i o n may i n c l u d e Rh^O^  o r Rh^^O^ •  An e q u i l i b r i u m such a s :  Rh  +  1  >  0„  Rh^O.)  I  ( l i g a n d s such as C g H ^ , C l , DMA  p r o b a b l y e x i s t s but l i e s Oxygenated  (8.1)  2  are omitted).  f a r to the r i g h t a t room temperature and 80°.  and s t o c k s o l u t i o n s  ( i n a i r ) o f 1 showed a symmetrical  E.S.R. s i g n a l at room temperature w i t h a v a l u e , g > av  ( F i g u r e 43). 3 lines  At l i q u i d  o f 2.0485  1$ temperature, the s i g n a l i s s p l i t  into  ( F i g u r e 44) w i t h g^, g^ and g^ v a l u e s o f 2.1157, 2.0367,  1.9728 r e s p e c t i v e l y .  The average v a l u e o f g^, g^ and g^ i s 2.0417,  v e r y c l o s e to the g  value.  solution, to  No E.S.R. s i g n a l was observed f o r a  o f 1, kept under vacuum and when such a s o l u t i o n i s exposed  a i r or 0.,the E.S.R. s i g n a l b u i l d s up. A  When [Rh(C_H..).Cl]_ (0.02 M) o ±4 / /  was d i s s o l v e d i n an evacuated s o l u t i o n of 2 , 2 - d i p h e n y l - l - p i c r y l h y d r a z o l , DPPH (0.06 M), i n LiCl/DMA, ?  did  not take u p ' 0  DPPH was observed If  2  e v o l u t i o n was observed and such a s o l u t i o n  f o r 5000 sec a t 80° and o n l y the E.S.R. s i g n a l o f (g = 2.0036).  i s passed throughthe dark brown "oxygenated" s o l u t i o n a t  80° f o r ~ 100 sec ( i f l e f t under 11^ f o r a l o n g e r time a t 80° or a t  - 184  F i g u r e 43.  E.S.R. spectrum of Rh at room temperature.  -  ( 0 ^ complex i n 0.5M  LiCl/DMA  0  - 185 -  186 -  room temperature f o r a few hours, metal was formed), a r e d s o l u t i o n was o b t a i n e d .  The I.R. o f t h i s r e d s o l u t i o n showed a s t r o n g -1  -1  a b s o r p t i o n a t 1980 cm No apparent  uptake was observed and t h i s  the f o l l o w i n g  absorption.  c o u l d be c o n s i s t e n t w i t h  reaction.  Rh (0 ) I  2  The Rh***H  and the d i s a p p e a r a n c e o f the 893 cm  +  H  >  2  R h  m  H  2  +  0  (8.2)  2  was s t a b l e a t room temperature i n a i r f o r s e v e r a l hours.as  2  evidenced from the I.R. s p e c t r a .  However, no Rh-H bond s i g n a l  from  0-40 T u n i t s was observed i n the p r o t o n N.M.R. s p e c t r a f o r a s a t u r a t e d s o l u t i o n a t room temperature.  T h i s c o u l d be due to p r o t o n exchange  o c c u r r i n g between the h y d r i d e and the DMA  solvent.  The v i s i b l e spectrum o f a s o l u t i o n of JL i n 0.5 M LiCl/DMA vacuum o r N atmosphere  2  under  (E = 450 my, E = 228) changed when s u b j e c t e d to an  of 0  ( s h o u l d e r 460 my, e = 162) ( F i g u r e 32).  2  An attempt  was made to determine the e q u i l i b r i u m c o n s t a n t o f the f o r m a t i o n of the R h * ( 0 ) complex  ( e q u a t i o n 8.1) from the s p e c t r o p h o t o m e t r i c data,  2  assuming  that i n vacuum the spectrum o b t a i n e d was t h a t o f the i n i t i a l I  s t a r t i n g Rh 0  2  species  ( 0 f r e e ) ; the s p e c t r a of s o l u t i o n s formed 2  over the p r e s s u r e range of about 200-800 mm were almost  under  identical;  i n d i c a t i n g t h a t the oxygen complex was f u l l y formed over t h i s p r e s s u r e range.  Only a t lower p r e s s u r e was complex f o r m a t i o n incomplete and  d i f f e r e n c e s i n s p e c t r a observed E. and E _ f o r Rh A D  I  ( F i g u r e 32).  The e x t i n c t i o n  coefficients  I and Rh(0„) r e s p e c t i v e l y were determined a t 450.my. /  The o p t i c a l d e n s i t y a t 450 my o f a s o l u t i o n t r e a t e d w i t h 71 mm 0^ was measured.  ;  From the e q u a t i o n  - 187 -  {e  + e (K) [0 ]}[Rh]  =  1  +  K[0 ]  ( 8  2  and t a k i n g the e s t i m a t e d v a l u e of [ 0 ] to be 0.7 x 10  _3  2  M  '  3 )  (Appendix I ) , 3  the  v a l u e o f K a t room temperature was  determined to be = 5.0 x 10  However, the procedure cannot be e n t i r e l y v a l i d not  show the expected isosbestic  monomer  — d i m e r  But the complex  point.  A c o m p l i c a t i o n might be a  I  2  C a t a l y t i c A c t i v i t y of Rh^O F o l l o w i n g the i n i t i a l  ( s e c t i o n 8.2)  Some v a l u e s of K, f o r  ( s e c t i o n 8.31,  T a b l e XXX).  ) i n LiCl/DMA  r a p i d oxygen uptake of s o l u t i o n s o f 1 i n  a f u r t h e r slower uptake was  observed which c o u l d be  measured c o n v e n i e n t l y over the temperature range 70-90°. s o l u t i o n s o f 1 (shoulder a t 450 mu, studies.  Stock  e = 230) were used i n the k i n e t i c  A t y p i c a l gas uptake p l o t i s shown i n F i g u r e 45 which,  an i n i t i a l  mm  been o b t a i n e d from the k i n e t i c d a t a  the r e a c t i o n of R h ( 0 > w i t h DMA  8.3  solution.  f o r m a t i o n does o c c u r at oxygen p r e s s u r e up to 200  and so K must be of that o r d e r of magnitude.  of  M  s i n c e the s p e c t r a do  e q u i l i b r i u m i n v o l v e d i n the a i r f r e e  temperatures between 70-90°,have  -1  " i n s t a n t a n e o u s " uptake, c o n s i s t e d of a l i n e a r  f o l l o w e d by a r e g i o n of g r a d u a l d e c r e a s i n g r a t e .  after  region  The i n i t i a l  rapid  uptake i s a s s o c i a t e d w i t h the c o m p l e t i o n of the f o r m a t i o n of the Rh*(0 ) 2  complex.  There was 0  2  For  no obvious s t o i c h i o m e t r i c r e l a t i o n s h i p between the t o t a l  absorbed a t the end of a r e a c t i o n and the amount of Rh used. [RhJ = .0.001 M, 0  2  uptake i n excess of 10:1 mole r a t i o of 0 :Rh  has been f o l l o w e d ; at 0.14  2  M [Rh], a 5:1 mole r a t i o of 0 :Rh uptake 2  - 188 -  0  2000  4000  6000  Time, sec ure 45.  Typical 0  uptake p l o t f o r the R h ( 0 ) c a t a l y z e d I  2  i n 0.5M L i C l / D M A  2  a t 8 0 ° , (3.75 x 10"3M 0  Rh, ( A ) i n the absence of Rh)  oxidation  (0) 1.0 x 1 0 M _ 2  - 189 was of  observed; w h i l e a t 0.05 0 :Rh was  observed.  2  0^ and LiCl/DMA was  M  -  [Rh], o n l y a 3:1 mole r a t i o n  In the absence  observed,  of Rh,  "the b l a n k  a v e r y slow r e a c t i o n between  reaction"  ( F i g u r e 45).  The  r a t e of the b l a n k r e a c t i o n i s p r a c t i c a l l y independent  o f 0^ p r e s s u r e  from 40 to 800 mm.  essentially  In the absence  r e a c t i o n between DMA  and  of L i C l ,  t h e r e was  no  02  The v i s i b l e a b s o r p t i o n s p e c t r a of s o l u t i o n samples taken i n the l i n e a r r e g i o n were the same as t h a t of the solution indicating the i n i t i a l  initial  oxygenated  that the r e a c t i o n i s c a t a l y t i c w i t h r e s p e c t to  s t a r t i n g rhodium  s p e c i e s , i . e . Rh^O,,).  The g r a d u a l f a l l o f f i n the r a t e of r e a c t i o n i s p a r a l l e l e d the appearance initial  by  of a g r e e n i s h t i n g e to the dark brown c o l o u r o f the  solution.  A broad a b s o r p t i o n maxima a t 690 my,  e = 86,  was  measured f o r a f i n a l r e l a t i v e l y u n r e a c t i v e s o l u t i o n . When  a  f i n a l g r e e n i s h brown s o l u t i o n was  treated with H  the c o l o u r of the s o l u t i o n changed to red and such found to undergo r e a c t i o n w i t h 0 the f a l l o f f i n r a t e . species with H oxidation. with H  2  The  2  2  a solution  a t 80°,  2  was  a t a r a t e comparable to t h a t b e f o r e  Thus treatment of the l e s s " a c t i v e "  Rh  r e g e n e r a t e s the a c t i v e i n i t i a l Rh s p e c i e s f o r c a t a l y t i c  Prolonged treatment of the dark brownish  at 80° produced  green  solution  metal.  i d e n t i f i c a t i o n of p r o d u c t s proved  to be v e r y  difficult;  attempts were made to i d e n t i f y the p r o d u c t s i n the gaseous phase, l i q u i d phase and the r e s i d u a l s o l i d  phase.  Gaseous samples a f t e r a l o n g r e a c t i o n were c o l l e c t e d i n an evacuated g l a s s bulb and mass spectrometry on such samples showed the presence of 28, 32, 44, 45 and 46 peaks i n the s p e c t r a a f t e r a l l o w i n g for  the background.  CO  and Me„NH were thought  to be p r e s e n t i n the  - 190  -  i<  sample.  One  I.R.  of the major peaks f o r DMA  s p e c t r a of the d i s t i l l a t e  (43) was  pumped o f f from the o x i d i z e d  s o l u t i o n showed e s s e n t i a l l y the same peaks as DMA, band a t 1725  cm  and  1  and p o s s i b l y a  another  ^C=C^  or  band a t 820  — C-C^  absent.  cm  group.  1  except  for a  showing a ^C=0  group  Four peaks were o b t a i n e d  from the gas chromatogram u s i n g a d i n o n y l p h t h a l a t e column; r e t e n t i o n times were 5 min,  12 min,  23 min  instrument,  160 ma,  p r e s s u r e gauge s e t t i n g = 10).  of  160°,  and  40 min  respectively.  (G.C.  Comparison  the r e t e n t i o n time w i t h t h a t of a u t h e n t i c samples showed t h a t  these were due  to r e s p e c t i v e l y water, c y c l o o c t e n e , DMA  and  an unknown.  Attempts were made to t r a p the sample t h a t came out a t 40 min Aerograph model A90P gas however, not enough was  chromatograph and  1725  cm \  oxidized solution. a t 170°  c o l l e c t e d f o r complete i d e n t i f i c a t i o n purposes.  prepared  The  from the d i s t i l l a t e  recrystallized  and a n a l y s i s (found:  gave a m o l e c u l a r  54.8;  an  of a  ^C=0  group  A 2 , 4 - d i n i t r o p h e n y l h y d r a z i n e d e r i v a t i v e of the unknown  c a r b o n y l compound was  melted  using  a d i n o n y l p h t h a l a t e column;  s p e c t r a of the " c o l l e c t e d " sample showed the presence at  2A  H = 5.88;  formula  the  2,4-dinitrophenylhydrazone  C=54,66; H = 5.92;  corresponding  N = 18.3%).  pumped o f f from  to C  .H N.0.. 14 l o 4 4 o  N = 18.13%) (Calc:  C =  N.M.R. s p e c t r a of the 2 , 4 - d i n i t r o p h e n y l  h y d r a z i n e . d e r i v a t i v e of the unknown c a r b o n y l i n CDCl^ gave the same s p e c t r a as the 2 , 4 - d i n i t r o p h e n y l h y d r a z i n e d e r i v a t i v e of which melted product of  a t 173°.  These r e s u l t s i n d i c a t e t h a t c y c l o o c t a n o n e  is a  of the o x i d a t i o n a l t h o u g h r e t e n t i o n time of an a u t h e n t i c sample  cyclooctanone The  cyclooctanone,  i n DMA  i n o r g a n i c and  was  70  min.  s o l i d o r g a n i c r e s i d u e o b t a i n e d a f t e r removal of  I.R.  - 191  -  the d i s t i l l a t e from pumping o f f the s o l v e n t was I.R.  s o l u b l e i n water.  The  s p e c t r a of the s o l i d r e s i d u e showed the presence of a Rh-CO  s t r e t c h at 1980  cm  coul_bedue to a NO  * and  s t r e t c h , but  unequivocally s i n c e DMA i n the I.R.  cm  t h i s c o u l d not be  showed a band a t 960  of the s o l i d  elsewhere, however. picric  another s t r e t c h at 970  residue.  cm  Bands due  Attempts to i s o l a t e  *.  T h i s l a t t e r band  determined  which was to DMA  now  absent  were observed  the p o s s i b l e Me^NO by  adding  a c i d d i s s o l v e d i n e t h a n o l were u n s u c c e s s f u l .  8.31  K i n e t i c s of the C a t a l y t i c O x i d a t i o n by  the R h ^ C O ^ )  Complex  i n LiCl/DMA The  oxygen uptake p l o t s were a n a l y z e d  the l i n e a r r e g i o n .  V a r i a t i o n of r a t e w i t h  by measuring the r a t e s i n [Rh]  gave a s t r a i g h t  w i t h a p o s i t i v e i n t e r c e p t (Table XXVII, F i g u r e 46). different had  a slight  oxygen was but  stock s o l u t i o n ( i . e . d i f f e r e n t effect  on r a t e  approximately  the order  decreased  a l i m i t i n g value  ( F i g u r e 46).  first with  "age"  order  The  at v e r y  Use  of the  line  of a  solution)  dependence of r a t e low 0^ p r e s s u r e  i n c r e a s i n g pressure  at about > h a l f an atmosphere  and  on  (< 50  mm)  the r a t e reached  (Table XXVIII,  Figure  47). A d d i t i o n of water up ^ 2.  to 1.1  M i n c r e a s e d the r a t e by  F u r t h e r a d d i t i o n of water up  (Table XXIX).  to 5.6  A d d i t i o n of c y c l o o c t e n e  M had  little  a f a c t o r of  effect  i n c r e a s e d the r a t e and  the  dependence of r a t e on added c y c l o o c t e n e  i s perhaps approaching a  l i m i t i n g value  at h i g h e r  (Table XXIX, F i g u r e 48).  r a t e decreased  with  concentrations  i n c r e a s i n g [ C l J , but  a l i m i t i n g v a l u e was  The  observed  - 192 -  TABLE XXVII R h ( 0 ) C a t a l y z e d O x i d a t i o n i n 0.5M I  2  LiCl/DMA  K i n e t i c Data a t 80° V a r i a t i o n of Rate w i t h [Rh]  P'O  [Rh] x  [o ] 2  2  10 M  mm  3  x 10 M* 3  Rate x 10^M  sec *  1.0  725  3.75  1.20  2.0  725  3.75  1.48  4.0  725  3.75  1.88  5.0  725  3.75  2.28  5.0  725  3.75  2.56  7.5  725  3.75  2.88  10.0  725  3.75  3.68  see  appendix  1  from another s t o c k  solution  a  - 193 -  F i g u r e 46.  Rh  (0 ) c a t a l y z e d o x i d a t i o n i n 0.5M  Dependence of r a t e on a different  stock  [Rh],  solution)  (3.75  LiCl/DMA at x 10~ M 3  0^,  80°.  (A)  - 194 -  TABLE XXVIII R h ( 0 ) Catalyzed Oxidation i n 0.5 M LiCl/DMA X  2  K i n e t i c Data from 70-87° V a r i a t i o n of Rate with [O,^] , [Rh] = 5.0 x 10  P'O  2  mm  1 [o ]  [o ] 2  T  Rate  k"  3  M Rate-k"  1 Rate-k"  x 10  x 10"  2  3 * -3 -1 x 10 M x 10 M  °C  x 10  6  x 10  6  6  M sec  M sec  M sec  M sec  23  0.13  7.68  80  1.16  0.60  0.56  17.8  44  0.23  4.35  80  1.50  0.60  0.90  11.1  70  0.38  2.66  80  1.82  0.60  1.22  8.2  96  0.50  2.00  80  1.90  0.60  1.30  7.7  129  0.68 -  1.48  80  2.07  0.60  1.47  6.8  241  1.25  0.80  80  2.18  0.60  1.58  6.4  372  1.93  0.52  80  2.36  0.60  1.76  5.7  725  3.75  0.27  80  2.56  0.60  1.96  5.1  51  0.36  0.28  70  0.60  0.23  0.37  27.0  147  1.00  0.98  70  0.89  0.23  0.66  15.1  257  1.73  0.53  70  1.08  0.23  0.85  11.7  738  4.95  0.19  70  1.20  0.23  0.97  10.3  53  0.30  3.33  75  1.23  0.45  0.78  12.8  140  . 0.80  1.25  75  1.51  0.45  1.06  9.5  253  1.42  0.71  75  1.63  0.45  1.18  8.5  731  4.15  0.24  75  1.76  0.45  1.31  7.6  29  0.20  5.00  87  2.66  0.87  1.79  5.6  114  0.60  1.67  87 .  3.54  0.87  2.67  3.8  210  1.00  i.oo  87  4.25  0.87  3.38  3.0  710  3.03  0.32  87  5.20  0.87  4.33  2.3  k" = Rate of r e a c t i o n of LiCl/DMA and 0 " see Appendix I.  5  i n absence of Rh.  - 196 -  TABLE XXIX C a t a l y z e d O x i d a t i o n i n LiCl/DMA K i n e t i c Data a t 80° E f f e c t o f A d d i t i v e s on Rate [Rh] x 10  P  '0  M  3  [o ]  2  Rate  2  mm  5.0  725  5.0  725  5.0  725'  x 10  3  M  LiCl  x 10^ M sec 2.28  3.75  -  1  Additive  M Nil  a  0.50  b  0.50  1.1 M H 0  4.80°  0.50  5.6 M H 0  0.50  Nil  0.50  0.05 M C H  0.47  4.64  2  2  10.0  725  3.75  4.60  10.0  725  3.75  9.20  6  10.0  725  3.75  19.20  f  10.0  725  3.75  27.20  g  5.0  725  3.75  2.60  h  0.50  0.50 M C H 8 14 1.0 M C H... 8 14 Nil  5.0  725  3.75  1.92  1  0.50  0.0025 M DPPH  10.0  725  3.75  3.66  j  0.50  Nil  10.0  725  3.75  1.68  k  0.50  0.01 M DPPH  10.0  725  3.75  0.80  1  0.50  0.02 M DPPH  5.0  725  3.75  5.20  m  0.10  Nil  5.0  725  3.75  4.00  n  0.25  Nil  5.0  725  3.75  3.60°  0.50  Nil  5.0  725  3.75  3.60  P  1.00  Nil  5.0  725  3.75  0.92  q  0.50  Nil .  5.0  345  1.74  15.50  r  0.50  Nil  5.0  545  2.75  7.40  S  0.50  Nil  a,b ,c h,i m  0.44  g  0  t  n  a  r  e  f  r e s  i  1 4  1 7  a  I  .. . d, e, f , g are the same s t o c k is o l u t i o n ; a r e the same s t o c k  are the same s t o c k s o l u t i o n ;  > »°>P  d  solution  k 1 ' a r e the same s t o c k s o l u t i o n ;  h l y made up s o l u t i o n s ;  ^ 2 month o l d s t o c k  solution,  r s greenish i n colour; see appendix  1  '  m i x t u r e o f Hp/Oj, where t o t a l p r e s s u r e = 1 atm.  - 197  V a r i a t i o n of r a t e w i t h 1.0  x 10 M _ 2  [Rh])  -  [CgH^],  (3.75  3 X  1 0  M 0  ,  - 198 -  from 0.5-1.0 M  [ C l ] (Table XXIX).  The o x i d a t i o n r e a c t i o n was n o t i n h i b i t e d i n the dark. DPPH, a f r e e r a d i c a l i n h i b i t o r , i n DPPH:Pvh (F.h = 0.005 M) slowed  the r a t i o o f 0.5:1 mole r a t i o o f  the o x i d a t i o n by an amount e q u a l t o the  b l a n k r e a c t i o n ; w h i l e a d d i t i o n o f DPPH to Rh 2:1 mole r a t i o s slowed respectively. the  (0.01 M) i n the 1:1 and  the o x i d a t i o n by a f a c t o r of 1/2 and 1/4  A d d i t i o n o f 10:1 mole r a t i o o f DPPH:Rh  0^ uptake  A d d i t i o n of  completely.  (0.01 M)  inhibited  The b l a n k r e a c t i o n was c o m p l e t e l y i n h i b i t e d  by the a d d i t i o n of 0.03 M DPPH. When the f i n a l mixture  (345 mm  g r e e n i s h brown s o l u t i o n was t r e a t e d w i t h an O^/B.^  0^, 380 mm  B.^) an i n c r e a s e i n r a t e was observed without  metal product a t t h e end of 4 hours a t 80° (Table XXIX). c o l o u r o f the s o l u t i o n was y e l l o w i s h .  The  final  The l i n e a r r e g i o n o f the gas  uptake p l o t was c o n s i d e r a b l y l o n g e r than when 0^ alone was used. a m i x t u r e r i c h e r i n 0^ was observed of  (545 mm  (Table XXIX).  0^ (165 mm  O2,  O2,  180 mm  When  H^) was used a slower r a t e  When the p r o p o r t i o n of H^ was i n excess  570 mm ,H ) metal was  produced.  The k i n e t i c data over the l i n e a r r e g i o n c o u l d be c o n s i s t e n t w i t h the  f o l l o w i n g mechanism  L Rh  L Rh  +  1  0  L  Rh ^.)  Co ) — p r o d u c t s  Rh  I  +  L  (8.4)  1  +  L  x  L  Rh  I  . Rh  (8.5)  (8.6)  - 199  LiCl/DMA.  +  0  f  a  S  >  t  2  LiCl/DMA/O  -  LiCl/DMA/O  products  (L^ = l i g a n d s such as DMA  or C g H ^ ,  (8.8)  Cl  omitted)  F o l l o w i n g the f o r m a t i o n of the L R h ( 0  ) complex (see  1  s e c t i o n 8.51)  (8.7)  later,  the r a t e d e t e r m i n i n g step i s the decomposition  of  L R h ( 0 „ ) to g i v e the products w i t h the r e g e n e r a t i o n of L Rh . 1  The  1  X  X  b l a n k r e a c t i o n i s r e p r e s e n t e d by equations 8.7  and  8.8.  The  rate  law f o r the above r e a c t i o n mechanism ( e q u a t i o n 8.4-8.8) i s of the  Rate  =  -d[0 ] — — = k[L Rh  (0 )'J + k  x  1  2  form  [LiCl/DMA/C^]  k [ L R h ( 0 )] + k"  (8.9)  X  X  *u  E x p r e s s i n g the r a t e i n terms of the t o t a l monomeric [Rh] c o n c e n t r a t i o n (see s e c t i o n 8.51)  -d[0  If K[0 ] 2  ]  -^r-  R a t e =  »  e q u a t i o n 8.9  kK[0  =  becomes  ][Rh]  i* [o ] K  +  k  2  1, e q u a t i o n 8.10  "  reduces  ( 8  -  1 0 )  to  -d[0 J Rate =  The  d  = k[Rh]  t  k"  (8.11)  dependence of r a t e on iRh] a t 725 mm  a c c o r d i n g to e q u a t i o n 8.11 2.96  +  x 10~  4  sec"  1  and  at 80° was  the v a l u e of k was  and k"=0.8 x 1 0 ~  6  M sec"  1  found  ( F i g u r e 46).  analyzed to be The  value  - 200 of k" e s t i m a t e d 10  -6  M sec  -  f o r the blank r e a c t i o n at 80°  Rate-k"  t a k i n g k" as 0.6  2  x 10 % -3  The  2.96  x 10  gives  [O^J was sec \  (8-12)  analyzed a c c o r d i n g to e q u a t i o n  the v a l u e s of k, 4.25  x 10  dependence and  M  , at 80°, were o b t a i n e d  [0^] dependence,is due  solutions  f o r the two  different  temperatures  \  (Table XXVIII, F i g u r e  s e r i e s of experiments.  The  XXX).  ;  to be  XXVIII);  were  practically  The K v a l u e a t 70°  seems  An A r r h e n i u s r a t e p l o t f o r the r a t e constant k i s  t  +  AH  to be 21.9  (Table  temperatures  o b t a i n e d from independent measurements and were found  anomalously l o w ( T a b l e  stock  r a t e data a t  were a n a l y s e d as f o r those at 80°  independent of 0^ p r e s s u r e from 40 to 800 mm.  and  AS  + 1.2  f o r the r e a c t i o n ( e q u a t i o n 8.5) -1  K c a l mole  and -7.8  + 2.6  e.u.  were  respectively  (k = 2.96  x 10~  8.4  Other C a t a l y t i c Systems I n v o l v i n g the Oxygenation A c t i v i t y of No  observed  3  sec" ). 1  [Rh(CgH ) Cl] l 4  2  2  o x i d a t i o n of e t h a n o l  (0.06 M)  (no o x i d a t i o n product  or Ph P 3  The  —fi of added Ph P was  2.08  (0.03 M)  was  d e t e c t e d ) when these were used as  o x i d i z a b l e s u b s t r a t e s i n LiCl/DMA media. presence  49).  [Rh]  to the use of d i f f e r e n t  f o r these c a l c u l a t i o n s , v a l u e s of k" a t d i f f e r e n t  shown i n F i g u r e 50;  sec  4  8.12;  -1  d i s c r e p a n c y between the k v a l u e , as o b t a i n e d from the  determined  x  + Tn4rr k[Rh]  kK[0 ][Rh]  dependence of r a t e on  and K,  0.6  "I  Rearrangement of e q u a t i o n 8.10  The  ( F i g u r e 45) was  x 10  r a t e of o x i d a t i o n i n the  —1  M sec  —3  ([Rh] = 5.0  x 10  M,  - 201 -  o CO  C  •H Ct) 00 cd  I  o •u r4 UH  o •u o  rH CM  O 00 Ct)  Q  g  rH CJ> •H  cn 1  o rH  s  X , ' — 1  rH|0  CNl  •  o  c  •H  t—I  C  O •H 4J  cd  T3 •H O  T3 CD N > N rH  £  Pi  cd S •u cn cd i o  ^  o  o  rH N  CM X  N-'  1—1  O  Pi ' ' C3N  ass  H  ^_oi  (U M 3 50 •H  - 202 TABLE XXX R h ( 0 ) C a t a l y z e d O x i d a t i o n i n 0.5 M LiCl/DMA I  2  Temperature Dependence of k and K [Rh] = 5.0 x 1 0 ~  T  M  3  [0 ]  k  2  3  *  -1  4 x 10  sec  -3  °C  x 10  25  -  70  4.95  2.15  1.38  75  4.15  2.77  4.25  80  3.75  4.25  2.92  87  3.61  9.10  1.90  See appendix 1.  M  K  -  x 10  5.00  M  - 20.3 -  - 204 -  p'0 = 725 mm,  80°) which was s l i g h t l y lower than when no Ph.jP was  2  present  ( c f . T a b l e XXVII).  The r a t e of o x i d a t i o n i n the presence of M sec"  added e t h a n o l was 0.60 x 10 750 mm,  T  ([Rh] = 5.0 x 10  M, p ' 0 = 2  = 50°).  A s o l u t i o n of [Rh(C H .)„C1]„ 0  o  i n DMF showed no c a t a l y t i c  1  LH  Z  oxidation  Z  p r o p e r t i e s over a p e r i o d of 3 hours a t 80°. The i n i t i a l orange r e d c o l o u r was unchanged  at the end of the r e a c t i o n .  When the same  r e a c t i o n was c a r r i e d out i n 0.5 M LiCl/DMF media, a v e r y slow r e a c t i o n was observed.  No i n i t i a l  r a p i d uptake o f 0^ was apparent.  no 0^ uptake was apparent i n DMSO as s o l v e n t At  5 0 ° , a s o l u t i o n of [Rh(CgH^) C 1 ] 2  2  51).  media.  i n ethanol,made  absorbed 4.1 x 10 ^ moles o f 0^ f o r 2.5 x 10  T h i s c o u l d r e f e r to a f i r s t was b e i n g  up i n a i r ,  moles o f Rh  The uptake a n a l y z e d f a i r l y w e l l f o r a f i r s t  consumption w i t h the pseudo f i r s t  Similarly,  o r d e r on 0^ -4  o r d e r constant 4.18 x 10  order dependence  (Figure  -1  sec  on c y c l o o c t e n e which  oxidized. (8.1)  Rh  8 14  +  o x i d a t i o n products  (8.13)  T h e r e f o r e the r a t e law would be g i v e n by e q u a t i o n 8.14  -d[0 ] 9  dt  kK[Rh][0 ][C H ] 2  g  1 4  (8.14)  1 + K[0 ] 2  F u r t h e r s t u d i e s a r e r e q u i r e d on t h i s  system.  0  2000  4000  6000  8000  Time, sec F i g u r e 51.  Rate p l o t and the c o r r e s p o n d i n g l o g p l o t f o r the r e a c t i o n 0  i n e t h a n o l a t 50°, (5.0 x 10 M Rh, 3.75 x 10 J  2  (A) l o g  [CgH  1 4  ].  M 0 ) 2  o f [Rh(C H.. . )„C1] _ w i t h 0  (0) 0  2  absorbed,  - 206  The  -  complex [RhCCgH^^)2CI] ,dissolves ;  2  benzene, dichloromethane  and  e a s i l y i n s o l v e n t s such  chloroform,to give yellow  which on s t a n d i n g i n a i r g i v e brown p r e c i p i t a t e s .  as  solutions  I t seemed  that  m o l e c u l a r oxygen complexes were p o s s i b l y b e i n g p r e c i p i t a t e d i n such solutions. [Rh(C H.. . ) „C1] _ was d i s s o l v e d i n benzene i n the absence of a i r at room o XH- 2 2 Q  temperature.  The  under 0^,  x 10 ^ moles of O2 uptake b e i n g observed  8.0  10 ^ moles of Rh,  initial  orange y e l l o w s o l u t i o n darkened i n two  and a brown p r e c i p i t a t e was  a v e r y broad  a b s o r p t i o n around 1100  cm  1  .  If ^  O2 under the same c o n d i t i o n s , no uptake and no observed  8.5  Discussion  8.51  Formation  of  initial  again  1600  used  of cm  1  the and  i n s t e a d of  c o l o u r changes were overnight,  of the M o l e c u l a r Oxygen Complex  r a p i d O2 uptake at room temperature  _1 i s a s s o c i a t e d w i t h the f o r m a t i o n of a m o l e c u l a r  catalyzed hydrogenation the O2 uptake,  x  observed.  p r o b a b l y monomeric as suggested  of  was  \  I.R.  i n t h r e e hours; on l e a v i n g such a s o l u t i o n under ^  a brown p r e c i p i t a t e was  The  f o r 10.0  obtained.  brown p r e c i p i t a t e showed a b s o r p t i o n peaks at 3460 cm  hours  by the k i n e t i c  (see s e c t i o n 6.4).  i . e . 1:1  The  or 80°  in a  solution  complex which i s  data of the  Rh  1  exact s t o i c h i o m e t r y  mole r a t i o of 02:Rh and  the appearance of 255  0-0  s t r e t c h t y p i c a l of a mono-nuclear m o l e c u l a r oxygen complex  are v e r y good evidence  f o r the f o r m a t i o n of a 1:1  monomeric m o l e c u l a r  rhodium oxygen complex. Hie f o r m a t i o n of t h i s R h ( 0 „ ) 1  complex was  to a v e r y l a r g e e x t e n t  the  - 207 irreversible. complex  The e q u i l i b r i u m c o n s t a n t f o r the f o r m a t i o n o f the R h ^ i ^ )  ( e q u a t i o n 8.1) determined  from s p e c t r o s c o p i c and k i n e t i c  was of the o r d e r o f (2.0-5.0) x 1 0  3  M  (Table XXX) which i n d i c a t e s t h a t  - 1  the Rh (02) complex i s formed t o the e x t e n t o f  90% a t 760 mm 0^ f o r a  I  -3 5.0 x 10 M Rh s o l u t i o n .  Crumbliss  that f o r a r e v e r s i b l e oxygenation  data  and Basolo  o f Co (acacen)  53  have r e p o r t e d  i n DMA a t - 1 0 ° , the K  value f o r  Co (acacen) + DMF + 0  was 1.3 x 10  2  M  -1  .  o  2  r  Co(acacen)DMF(0„) Z  (8.15)  No r e v e r s i b l e Rh(02) complex has been r e p o r t e d  72 a l t h o u g h CO has been found  to d i s p l a c e 0  A s o l u t i o n o f Rh (02) was found I  ( s e c t i o n 9.3).  2  i n R h ( 0 ) ( P h P ) C 1 (0.SCR^C^) .  to absorb  2  3  2  CO t o produce R h ^ C O ^  K i n e t i c data f o r the f o r m a t i o n o f the R h ^ C O ^  complex  y i e l d e d the r a t e constant f o r the backward r e a c t i o n o f e q u a t i o n 8.1 as -3 0.64 x 10  -1 sec  a t 80° ( s e c t i o n s 9.2 and 9.51, e q u a t i o n s  9.1 and 9.2,  T a b l e XXXI) which combined w i t h the K v a l u e gave the r a t e constant f o r the forward r e a c t i o n o f e q u a t i o n 8.1 as 1.87 M "'"sec "*" a t 8 0 ° . On comparison other d  w i t h the f o r m u l a t i o n of the oxygen complexes o f  systems, f o r example, I r ( C 0 ) C 1 ( P h ^ P ) ^ ( 0 ^ ) , ^ p o s s i b l e  8  formulae  f o r the m o l e c u l a r oxygen complex a r e Rh(0 )C1 (DMA) where z x y  x + y = 4.  C g H ^ has been shown to be p r e s e n t as " f r e e " l i g a n d s i n  s o l u t i o n s of 1_ (see s e c t i o n 6.2). The l a b i l i t y o f the O 2 l i g a n d i n Rh(0 )C1 (DMA) i s shown by the r a p i d displacement o f 0„ by H„ ( s e c t i o n z x y z z 8.2 and e q u a t i o n 8.2). Rh(02)Cl (DMA)  M a l e i c a c i d has been shown to d i s p l a c e O 2 i n  ( s e c t i o n 6.5).  x  The appearance o f one Rh-H s t r e t c h f o r a  p o s s i b l e d i h y d r i d e f o r m a t i o n i s c o n s i s t e n t w i t h the f o r m u l a t i o n RhCl(DMA).^ but w i t h t r a n s h y d r i d e s ; a c i s h y d r i d e would, however, have been a n t i c i p a t e d , as i n R h C l ( P h P ) H . 3  2  2  8  The problem o f s t e r e o s p e c i f i c i t y o f the a d d i t i o n o f  - 208 g  d i a t o m i c m o l e c u l e s to square p l a n a r d  systems  i s presently a controversial  one' w i t h t h e r o l e o f the s o l v e n t b e i n g p a r t i c u l a r l y i m p o r t a n t ; subsequent  i s o m e r i z a t i o n o f the i n i t i a l  possible complication.  oxidative addition i s a further  A very probable formula f o r R h ^ ) i n L i C l / 1  DMA media i s Rh(0 )Cl(DMA) . 2  The  i r r e v e r s i b i l i t y o f 0^ uptake i s l a r g e l y determined by t h e  e l e c t r o n e g a t i v i t y o f the l i g a n d s around IR(0 )C1(CO)(Ph^P) 2  2  the m e t a l .  The well-known  complex i s a r e v e r s i b l e oxygen c a r r i e r w h i l e the 58—60  iodo analogue, I r ( 0 ^ ) I ( C O ) ( P h ^ P ) , i s an i r r e v e r s i b l e one.  The  lower e l e c t r o n e g a t i v i t y o f the i o d i n e atom r e s u l t s i n t h e oxygen molecule b e i n g bonded more s t r o n g l y w i t h r e s u l t i n g of  the m o l e c u l a r oxygen c o m p l e x . ^  i r r e v e r s i b l e formation  G r i f f i t h ^ * has proposed t h a t t h e  0^ molecule i n oxygenated heme i s i n the e x c i t e d s i n g l e t  s t a t e and  bonding proceeds by d o n a t i o n o f e l e c t r o n s from the i r - o r b i t a l  to a  vacant o r b i t a l on the c e n t r a l m e t a l i o n ; t h i s s e t s up a d i p o l e reduces the e x t e n t o f d o n a t i o n .  which  T h i s d i p o l e i s s i m u l t a n e o u s l y reduced  by back, d o n a t i o n from the c e n t r a l metal i o n , u s i n g i t s f i l l e d d orbitals  to the T r - o r b i t a l s o f the 0^ group.  attachment of  Thus the s t r e n g t h o f  o f oxygen to t h e c a r r i e r i s dependent  e l e c t r o n s a t the c e n t r a l metal i o n .  upon the a v a i l a b i l i t y  I t i s therefore conceivable  t h a t , i n Rh(0^)01(DMA)^, t h e 0^ m o l e c u l e w i l l be bound because both DMA and C l  irreversibly  a r e a donors and weak T r - a c c e p t o r s .  A c c o r d i n g to i t s p o s i t i o n i n the e l e c t r o c h e m i c a l s e r i e s , m o l e c u l a r 1  A v e r y r e c e n t paper by D.M. B l a k e and M. Kubota 989 (1970)) summarizes the r e l e v e n t d a t a .  ( I n o r g . Chem., 9_,  I  -  209  -  oxygen i s a p o w e r f u l o x i d i z i n g agent and  Rh'" complexes are known to  be  1  III r e a d i l y o x i d i z e d to Rh  i n b o t h aqueous arid non-aqueous  solvent  12 media. ' The f a c t o r s t h a t govern the f o r m a t i o n of a m o l e c u l a r oxygen complex i n p r e f e r e n c e to o x i d a t i o n i s thought to be r e l a t e d to the 46  reduction  p o t e n t i a l s of the m e t a l i o n s .  of the m e t a l i o n s can be  adjusted  by  The  reduction  potentials  c o o r d i n a t i o n w i t h the p r o p e r  I t i s t h e r e f o r e p o s s i b l e to p r e d i c t which complex would a c t as oxygen c a r r i e r  i f the r e d u c t i o n  such r e d u c t i o n p o t e n t i a l s of rhodium and  reported  i n non-aqueous s o l v e n t  a  i n the  s t e r i c f a c t o r s xv-ere c o n s i d e r e d .  s o l v e n t media were known and no  p o t e n t i a l s of the l i g a n d s  ligands.  given  Unfortunately  i t s complexes have been  systems.  A s t r i k i n g f e a t u r e of the i r i d i u m oxygen complexes,  e.g.  I r C l ( C O ) ( P h P ) ( 0 ) and I r l ( C O ) ( P h P ) ( 0 > , i s t h a t the l i g a n d s , w i t h the e x c e p t i o n of C l , belong to the c l a s s of r e a d i l y p o l a r i z a b l e soft" 3  Lewis bases. ii  2  CO  2  and  2  Ph^P  are  ri  i s a l s o s o f t , o w i n g to i t s containing  only  2  t y p i c a l ir-acceptors,  Tr-acceptor  " s o f t " l i g a n d s w i l l be  (soft).  2 5 7  properties.  0  2  Thus a complex  s t a b l i z e d by a  "symbiotic"  258 effect.  Macrocyclic  u n s a t u r a t e d l i g a n d s such as p o r p h y r i n s  or  p h t h a l o c y a n i n s change the c o o r d i n a t i v e p r o p e r t i e s of the metal i o n , e.g. 0  Co** and  Fe** to such an e x t e n t ,  apparently  can' be bound i n measurable q u a n t i t i e s ^ . 8  2  metal i o n can be  caused to b i n d 0  unsaturated ligands  such as  monodentate l i g a n d s  such as CN  2  not  making i t so s o f t  In the case of Co**,  o n l y by  the  polydentate  ( s a l i c y l a l d e h y d e imine) but 259 or NH^.  also  A l a r g e number of  r e c e n t l y r e p o r t e d mononuclear m o l e c u l a r oxygen complexes IT - a c c e p t o r  ligands  such as Ph^P  by  or Ph^As ( s e c t i o n 1.5  the  contain  and  1.8)  that the  - 210 -  which may be of g r e a t importance i n s t a b l i z i n g the low o x i d a t i o n s t a t e of the metal i o n and i n a d j u s t i n g the metal i o n t o the r i g h t p o t e n t i a l f o r formation  o f a molecular  oxygen complex.  DMA i s g e n e r a l l y thought to c o o r d i n a t e the oxygen  2 6Q  to metal i o n s  b u t complexes c o n t a i n i n g DMA as a c h e l a t e d  through ligand  260  and b r i d g i n g l i g a n d  have been proposed i n which c o o r d i n a t i o n  n i t r o g e n must be i n v o l v e d .  A number o f C o  1 1  chelates ^'^ 4  through  with  c o o r d i n a t i o n through n i t r o g e n and oxygen of one l i g a n d a r e known to form r e v e r s i b l e molecular  oxygen complexes.  Coordination  o f DMA i n a  complex such as ^ ( 0 ^ ) 0 1 (DMA)^ c o u l d i n v o l v e bonding through n i t r o g e n atoms o r c h e l a t i o n through oxygen and n i t r o g e n . The and  absence of an E.S.R. s i g n a l i n s o l u t i o n s of JL kept i n vacuum,  the " b u i l d - u p "  of the E.S.R. s i g n a l on exposing such a s o l u t i o n to  a i r or oxygen show t h a t the s i g n a l i s due to some paramagnetic s p e c i e s formed i n the presence o f a i r i n 0^. been i d e n t i f i e d e x a c t l y b u t i t i s probably of O2 to Rh. F u r t h e r work i s i n progress  The s i g n a l has not  caused by t h e c o o r d i n a t i o n  i n t h i s l a b o r a t o r y on the  E.S.R. aspects  o f the system. There a r e a number o f r e p o r t s on the II 54-57 E.S.R. s i g n a l o f Co oxygen complexes. An e i g h t l i n e spectrum  a r i s i n g from the i n t e r a c t i o n of an unpaired 59  Co nucleus  e l e c t r o n with a single'  • (I = 7/2) was observed f o r the systems  "cobaloximes(II)",  54  Co^O-MeO S a l e n ) , ^ ^ Co ' " ( v i t a m i n B- ) ~ ^ and C o (acacen) and lZr II thus support the monomeric n a t u r e o f these Co oxygen complexes. A II f i f t e e n l i n e spectrum has been observed f o r a b i n u c l e a r Co oxygen 1  species.  54  1  These workers  1 1  54-57  concluded from the E.S.R. s p e c t r a  that  - 211 -  i n mononuclear s p e c i e s w i t h 0^ Co^^O^  t h e unpaired  and the mononuclear C o .  1 1  electron i s l a r g e l y associated  oxygen complexes a r e formulated  There a r e no r e p o r t s on the E.S.R. s p e c t r a o f RhCC^)  complexes.  The E.S.R. spectrum of t h e present  s t u d i e d Rh^CO^) complex  seems t o suggest t h a t t h e s i g n a l i s l a r g e l y due to 0^ value  as  since i t s g  and l i n e shape a r e c l o s e l y s i m i l a r to some r e p o r t e d 0^ 261  species.  No s p l i t t i n g by the Rh n u c l e u s  (I = 1/2) i s observed;  w i t h i t s s m a l l e r n u c l e a r magnetic moment, t h e Rh n u c l e u s i s expected to cause a s m a l l e r h y p e r - f i n e s p l i t t i n g than the Co n u c l e u s . Hence on II 54-57 II-analogy w i t h the Co systems, Rh 0^ i s the most p r o b a b l e e l e c t r o n i c s t r u c t u r e of the Rh^CO^) complex.  I t i s of i n t e r e s t that  the m o l e c u l a r oxygen complexes o f a l l the other  8 10 d 'and d systems,  I r , Pd^, P t ^ , N i ^ have been w e l l c h a r a c t e r i z e d and a r e diamagnetic (p.14). 1  The  reported  i Rh  complexes  6  71~ 73 ' are i l l - c h a r a c t e r i z e d ;  although  73 Rh(Ph^P)^(0^)  was r e p o r t e d  to be diamagnetic. The former group  apparently  c a t a l y z e oxygenation by atom t r a n s f e r mechanism and the l a t t e r by a f r e e r a d i c a l mechanism.  The o x i d a t i o n i n the present  discussed  i n s e c t i o n 8.53.  8.52  Formation of M o l e c u l a r  Oxygen Complexes i n Other  I t i s s u r p r i s i n g that no i n i t i a l s o l u t i o n s of [ R h ( C H g  to be very  1 4  ) Cl] 2  2  work w i l l be  Solvents  r a p i d 0^ uptake was apparent i n  i n DMSO and DMF, s i n c e these a r e thought  s i m i l a r to DMA i n s o l v e n t p r o p e r t i e s .  I t i s significant  that a d d i t i o n , of C l d i d promote t h e 0^ uptake i n the DMF s o l u t i o n . 52 Calderazzo and coworkers  reported  that the oxygenation o f Co(Salen)  was promoted i n some a p r o t i c s o l v e n t s by t h e a d d i t i o n of a n i o n i c l i g a n d s , e.g.: SCN~, N ~ and CH C0 ~. 3  3  2  They a l s o found  that Co(Salen)  - 212 -  r e a d i l y forms a b i n u c l e a r m o l e c u l a r oxygen complex i n DMF however, i n DMA,  oxygenation was hindered  and t h i s was a t t r i b u t e d  52 f a c t o r s . The oxygenation of [Rh(C H .) C l ] i n DMA o 14 _ I  to s t e r i c  with  Q  no added C l  was not s t u d i e d because the complex was o n l y  s o l u b l e i n DMA. The brown p r e c i p i t a t e : o b t a i n e d i n chloroform, air  and DMSO,  benzene or  or oxygen are  species.  slightly  when s o l u t i o n s of [Rh(C H..).Cl]„ o 14 _ I D  dichloromethane,were allowed to stand i n  l i k e l y to be some s o r t of oxygenated Rh  In benzene s o l u t i o n , an oxygen uptake i n the 0.8:1  mole  r a t i o of 0 :Rh was observed but the I.R. d a t a d i d not i n d i c a t e the 2  existence  of an 0-0 s t r e t c h t y p i c a l of the mononuclear m o l e c u l a r 255 52 oxygen s p e c i e s . C a l d e r a z z o and coworkers has t e n t a t i v e l y -1 assigned  a weak band at 1140 cm  Co 3-methyloxysalen, p y 0 r  2  f o r the brown p r e c i p i t a t e .  to the 0-0  species  s t r e t c h i n a monomeric  and a band was observed at 1100 cm *  However, the bands at 3400 cm * and  1600 cm * are more l i k e l y a t t r i b u t e d to the OH s p e c i e s .  The appearance  of a brown p r e c i p i t a t e i n a s o l u t i o n of [Rh(C H .) Cl]„ i n benzene o 14 _ 2. 0  kept under  overnight  i s not too c o n c l u s i v e ;  t h i s may be due to  t r a c e s of a i r l e a k i n g i n t o the s o l u t i o n or t r a c e s of 0^ i m p u r i t y i n the N .  •  2  . T 8.53  C a t a l y t i c Oxidation The observed 0  complex f o r m a t i o n and  CgH^^.  DMA  that r e q u i r e d  2  Catalyzed  by Rh  (0 ) i n LiCl/DMA  uptake a f t e r the i n i t i a l m o l e c u l a r oxygen  i s due to the R h * ( 0 ) c a t a l y z e d o x i d a t i o n of 2  must be o x i d i z e d s i n c e the 0  f o r j u s t the C g H ^  oxidation.  2  DMA  uptake i s i n excess o f The i n h i b i t i o n of the  - 213 formation  o f the R h * ( 0 ) complex i n the presence o f DPPH and the 2  e v o l u t i o n o f gases observed on adding  [Rh(C H_ .).Cl]„ to an evacuated 0  s o l u t i o n o f LiCl/DMA w i t h DPPH suggests t h a t a r e a c t i o n occurs between DPPH and the [Rh(CgH ^) C l ] .  N  2  i s probably evolved.  2  o x i d a t i o n i s not p h o t o s e n s i t i z e d involved  The c a t a l y t i c  b u t a f r e e r a d i c a l mechanism might be  s i n c e a d d i t i o n o f DPPH i n a 10:1 mole r a t i o o f DPPH:Rh, i n h i b i t e d  the c a t a l y t i c o x i d a t i o n c o m p l e t e l y , w h i l e a d d i t i o n of 0.5:1, 1:1 and 2:1 mole r a t i o s o f DPPH:Rh decreased the r a t e  (Table XXIX).  The b l a n k  r e a c t i o n i s amost c e r t a i n l y a f r e e r a d i c a l r e a c t i o n s i n c e a d d i t i o n o f 0.03  M DPPH stopped the b l a n k r e a c t i o n c o m p l e t e l y . The  observed k i n e t i c s i n the l i n e a r r e g i o n a r e simple but the  o v e r a l l o x i d a t i o n r e a c t i o n c l e a r l y becomes v e r y  complicated  s i n c e CO  a b s t r a c t i o n was observed i n the course o f o x i d a t i o n and Me NH was 2  detected  by mass spectrometry.  c a t a l y t i c a l l y o x i d i z e d to C 0 was d e t e c t e d  i n the system.  i n l i n e a r region that r e g i o n .  2  The CO a b s t r a c t e d (Chapter I X ) .  i s thought to be  The f o r m a t i o n  of C 0  The k i n e t i c s and the observed 0  2  2  uptake  suggested that CO a b s t r a c t i o n i s n o t o c c u r r i n g i n  The p r o d u c t i o n  o f Me^NO from the o x i d a t i o n o f Me^N  r e s u l t i n g from the CO a b s t r a c t i o n of DMA appeared l i k e l y but attempts to i s o l a t e Me^NO as the p i c r a t e The  fall  failed.  o f f i n l i n e a r r a t e i n the course o f the c a t a l y t i c  o x i d a t i o n i s p r o b a b l y due to the slow o x i d a t i o n of Rh* to Rh** which i s incapable  o f forming the m o l e c u l a r oxygen complex.  the a c t i v e s p e c i e s by H supports t h i s argument. a longer  2  Regeneration of  treatment o f the l e s s " a c t i v e " s o l u t i o n s ^2^2 i m  x  l i n e a r and the r a t e o f 0  t  u  r  e  s  appeared to be a b l e to m a i n t a i n  uptake i s comparable to t h a t when  - 214 -  0^ was used a l o n e .  D i f f e r e n t s t o c k s o l u t i o n s ( F i g u r e 46) showed  s l i g h t l y d i f f e r e n t a c t i v i t i e s p o s s i b l y due to slow o x i d a t i o n of Rh"*" to R h  1 1  .  I n s o l u t i o n , the r a p i d d e t e r i o r a t i o n o f a l l the C o  1 1  oxygen c a r r y i n g c h e l a t e s i s due to the i r r e v e r s i b l e o x i d a t i o n o f C o _ I I I 46 Co  ;  . ...  ,  .  .  ^ II  s i m i l a r d e t e r i o r a t i o n of a Fe  .  ,  . „  1 1  46 ,  oxygen c a r r y i n g c h e l a t e  has  been observed. The  dependence of r a t e on added CgH-j^ i s not too c l e a r .  rate determining  step i n the absence o f added C H.. probably 0  involves  the o x i d a t i o n of DMA  (equation  the r a t e determining  step may i n v o l v e the o x i d a t i o n o f C g H ^ which  c o u l d now be i n c o r p o r a t e d The  8.5).  The  I n the presence of added C g H ^ ,  i n the c o o r d i n a t i o n  i n c r e a s e i n r a t e when H^O  sphere.  (one of the o x i d a t i o n p r o d u c t s )  was added may be due to the change i n d i e l e c t r i c media or the i n c r e a s e d  s o l u b i l i t y o f 0^.  constant  I n any case,  i n the o x i d a t i o n r a t e i s u n l i k e l y to be due to H^O 8.54  o f the  the f a l l o f f  production.  P o s t u l a t e d Mechanism f o r the C a t a l y t i c O x i d a t i o n Two g e n e r a l paths f o r oxygenation o f s u b s t r a t e s  molecular  c a t a l y z e d by  oxygen complexes have been proposed, namely; one i n v o l v i n g  " d i s s o c i a t i v e oxygen i n s e r t i o n "  (oxygen atom t r a n s f e r ) and the other  i n v o l v i n g f r e e r a d i c a l s (see s e c t i o n 1.5). evidence i n the present  There i s no s t r o n g  work that the o x i d a t i o n proceeds v i a a f r e e  r a d i c a l mechanism; DPPH c l e a r l y r e a c t s w i t h  the Rh  I ' s p e c i e s i n the  absence o f 0^ and i n h i b i t e s the r e a c t i o n i n t h i s way.  However, the  II* existence  o f a s p e c i e s such as Rh  0^  which might r e a d i l y i n i t i a t e  a f r e e r a d i c a l r e a c t i o n and the f a c t t h a t a l l other  oxidations  - 215 - i A u vu c a t a l y z e d by Rh  i 80,83,84,90 , , . complexes have been shown t o be f r e e  1  fc  r a d i c a l r e a c t i o n s suggest t h a t the p r e s e n t  system may i n v o l v e a s i m i l a r  process. A Haber-Weiss type mechanism i n v o l v i n g one o r two e l e c t r o n t r a n s f e r 84 90 has been proposed  '  oxidation of organic the R h C l ( C O ) ( P h P ) 3  2  i n the R h C l ( P h P ) 3  substrates  and RhCl (CO) ( P l ^ P ^  3  catalyzed  ( s e c t i o n 1.5, e q u a t i o n s 1.23-1.26).  In  c a t a l y z e d o x i d a t i o n o f diphenylmethane,the a c t i v e  c a t a l y s t i s thought t o be R h C l ( C O ) ( P t ^ P ) ( 0 ) o r some s o r t o f 2  2  hydroperoxide. The  a u t o x i d a t i o n of amides which may be regarded as model  substances f o r n y l o n has not y e t been as e x t e n s i v e l y s t u d i e d as t h a t 262 263 of the hydrocarbons. Sharkey and Mochel p o s t u l a t e d a scheme 2 f o r t h e a u t o x i d a t i o n o f amides, of t h e g e n e r a l formula R'CONHCHR , H which i s analogous to t h a t f o r the a u t o x i d a t i o n o f hydrocarbons. the assumption  t h a t the C-H bond d o t t e d  weaker than the others^  On  i n the above formula i s  these workers p o s t u l a t e d the 2  h y d r o p e r o x i d e R'C0NHCH(00H )R autoxidation products, studied  as t h e i n t e r m e d i a t e  f o r the u l t i m a t e  p a r t i c u l a r l y R'CONH^,R CH0 and R C00H. 2  the sodium anthraquinone-2-sulphonate  2  Riches  2 6 4  photosensitized  a u t o x i d a t i o n of amides and concluded t h a t a r e a c t i o n mechanism i n v o l v i n g f r e e r a d i c a l s i s p o s t u l a t e d but a c h a i n r e a c t i o n i s excluded, i . e . the r e a c t i o n R0 2  +  RH  »-  R00H  +  R-  (8.15)  i s n e g l i g i b l e and the a u t o x i d a t i o n p r o d u c t s a r e formed mainly by a  - 216 -  RC^* +  i° -  r e a c t  A c c o r d i n g t o Sharkey  n  CH^CONHCH^, HCHO and HCOOH might DMA.  and Mochel's scheme  be expected as o x i d a t i o n p r o d u c t s o f  C a r b o n y l a b s t r a c t i o n from CH^CONHCH^ would produce  amine p r o d u c t , Me^NH. a l s o occur It account  263  the observed  C a r b o n y l a b s t r a c t i o n from HCHO and HCOOH c o u l d  (see s e c t i o n 1.64).  i sdifficult  to p r e s e n t a v e r y r e a l i s t i c  r e a c t i o n scheme to  f o r the observed p r o d u c t s p a r t i c u l a r l y s i n c e t h e n a t u r e o f the  o x i d a t i o n product o f DMA was not s u b s t a n t i a t e d . which i s thought  However, a scheme  to c o n t a i n some o f the p r o b a b l e r e a c t i o n s  involved  i s as f o l l o w s : 0  CH  V C-N. /  \  /  CH,  C-N  /  3  CH  3  Rh  0  CH„  0 +  0. 2  K  CH,  \ ' C-N' / CH  3  3  (8.16)  \ 3  I  CH  3  -  H A  Rh  0  2  CH_  CH_  3  CH  r a t e determining H* or H a b s t r a c t i o n  >  + OOH +  Rh  CH C0  +  3  \ 3  II. _ Rh 0  N-CH  2  (8.17a)  2  CH, or  0^ i n s e r t i o n  Rh  1  +  -CH (OOH) CH C0 3  (8.17b)  - 217 -  0  (8.18b)  CH,  CH, ^N-CH  +  2  C  H  _  N  2  N  CH CO 3  CH,  fast chain COCH, t e r m i n a t i o n  H  +  CH.-N 2  CH  3  < \  CH 'C0  \  3  CH CO  "COCH 3 (8.19)  3  CH. fast  / CH -N  >  3  COCH  >N-CH (OOH)  C H  N-CH -CH -N'  ,CH /  . 3  \ x  f act  >  3  (8.20) COCH  molecular  products  (8.21)  3  H  +  OOH  fast *  H  2°2  (8.22)  - 218  As mentioned  -  i n s e c t i o n 8.3,  i t i s s u r p r i s i n g t h a t CgH^O  was  i d e n t i f i e d as a product from the prepared 2 , 4 - d i n i t r o p h e n y l h y d r a z i n e derivative.  The r e t e n t i o n time i n the gas chromatogram i n d i c a t e d a  keto product d i f f e r e n t from CgH^O  was  obtained.  3-Cyclohexene  80 hydroperoxide was  postulated  as the l i k e l y  i n t e r m e d i a t e i n the  RhClCPh^P)^ c a t a l y z e d o x i d a t i o n o f cyclohexene hence p r o d u c t i o n of cyclooctene-3-one considered very l i k e l y  to  ( e q u a t i o n 8.18b) was  i n the p r e s e n t system.  Cyclooctanone c o u l d be  produced v i a a q u e s t i o n a b l e r e a c t i o n such as 8.18a. cyclooctanone  cyclohexene-3-one;  d e r i v a t i v e c o u l d be produced  Alternatively  the  from the r e d u c t i o n of  cyclooctene-3-one by the 2 , 4 - d i n i t r o p h e n y l h y d r a z i n e / H C l reagent. The p o s s i b l e DMA o x i d a t i o n p r o d u c t , (CH CONCH - C H ) , N , N ' - d i a c e t y l N,N-dimethylethylenediamine, was not i d e n t i f i e d but i t c o u l d be i n the s o l i d r e s i d u e .  R a d i c a l d i m e r i z a t i o n o f DMA  by t - b u t y l p e r o x i d e  to y i e l d - N , N ' - d i a c e t y l - N , N ' - d i m e t h y l e t h y l e n e d i a m i n e ( m . p . 265 been r e p o r t e d .  90-92°) has  However, n o r e p o r t s on the p r o p e r t i e s of  compound were found.  this  Many f r u i t l e s s attempts were made to i s o l a t e  t h i s p o s s i b l e compound from the s o l i d r e s i d u e of the o x i d a t i o n mixture.  The p o s s i b l e CH^CONHCH^ product would be d i f f i c u l t  and c h a r a c t e r i z e from the f i n a l r e a c t i o n m i x t u r e . to be one product i n these r e a c t i o n s  Water was  reaction  to i s o l a t e shown  ( e q u a t i o n 8.18b).  An analogy w i t h the o t h e r Rh c a t a l y z e d o x i d a t i o n of o r g a n i c substrates,  8 4  ' ^ a Haber-Weiss type mechanism i n v o l v i n g R h  can be w r i t t e n as  and  Rh^  1  follows:  + 3  1  H  0  2  (8.23a)  - 219 -  OOH  (8.23b)  ROOH  +  Rh  RO  +  RO  ROOH  +  Rh  R0  A similar  2  +  R0  1  1 1  >  RO  >  molecular products  (8.25)  ROO  (8.26)  —>  *  2  +  OH  +  H  +  +  +  Rh  Rh  (8.24)  1 1  1  molecular products  (8.27)  scheme f o r t r a n s f e r o f two e l e c t r o n s , i n v o l v i n g Rh* and R h  1 1 1  ,  i s p o s s i b l e . I n t h e p r e s e n t system, t h e f o r m a t i o n o f the R h ( 0 )complex 1  e s t a b l i s h e d and the e l e c t r o n i c s t r u c t u r e of the m o l e c u l a r oxygen II* complex i s thought  to be Rh  0  2  hence i t appears  i n v o l v i n g H a b s t r a c t i o n or hydroperoxide c o o r d i n a t e d oxygen  that a r e a c t i o n  f o r m a t i o n v i a i n s e r t i o n of  :  the  ( e q u a t i o n 8.17) i s the l i k e l y r a t e d e t e r m i n i n g  step. The blank r e a c t i o n i s d e f i n i t e l y f r e e r a d i c a l i n n a t u r e .  Trace  266 metal has been proposed  f o r the a p p a r e n t l y u n c a t a l y z e d a u t o x i d a t i o n  and has been invoked f o r r e a c t i o n s of the metal w i t h m o l e c u l a r v i a a complex which i n v o l v e s m e t a l , 0  2  oxygen  and s u b s t a t e o r s o l v e n t , e.g.  - 220 -  M (0 )(XH)  >  n +  2  ( i n the present  The  system, M  M  ( n + 1 ) +  X  +  0 H  (8.28)  2  = L i , XH = CH C0NCH CH H)  n +  +  3  3  2  Rh* systems i n v o l v i n g MA (Chapter VI) d i d not c a t a l y z e  the a u t o x i d a t i o n of DMA and C H .. o 14 90 D  f i n d i n g o f F i n e ' s group,  T h i s i s i n good agreement w i t h t h e  where the c a t a l y t i c  e f f e c t of RhCl(CO)(Ph P) 3  2  i n the a u t o x i d a t i o n of diphenylmethane becomes more and more i n h i b i t e d with  the i n c r e a s e d  degree of complexing to a more s t r o n g l y  electrophilic  olefin. I t has been suggested e a r l i e r  (p. 213 ) t h a t the f a l l o f f i n c a t a l y t i c I II a c t i v i t y of t h e o x i d a t i o n i s due to o x i d a t i o n of Rh to Rh . However the r e t a r d a t i o n o f r a t e may be due to a s e l f i n h i b i t i n g or auto. 267 retardation reaction. " i n s i t u " formation  Such r e t a r d a t i o n s have been shown to be due to  of oxidation side products.  i n t o any a u t o x i d a t i o n the c o m p l i c a t i n g  g e n e r a l l y occur u n t i l a c o n s i d e r a b l e The  introduces  f a c t o r t h a t t h e observed r a t e  may be determined by t h e r a t e o f f o r m a t i o n than the s t a b i l i t y of the s u b s t r a t e .  T h i s phenomenon  o f the i n h i b i t i o n i t s e l f  rather  However, such r e t a r d a t i o n s do not amount o f o x i d a t i o n has taken p l a c e .  c a t a l y t i c o x i d a t i o n a c t i v i t y of the R h * ( 0 ) complex i n t h e 2  present  system i s due l a r g e l y to the r e a c t i v e n a t u r e o f the 0 m o l e c u l e 1 II * s i n c e the e l e c t r o n i c s t r u c t u r e o f Rh ) thought to be Rh ( 0 ) . 2  2  Hence the 0 oxidation. and  0  2  2  molecule on bonding to rhodium becomes a c t i v a t e d and i n i t i a t e s I t appears t h e r e f o r e , i n t h i s sytem, both the s u b s t r a t e  are incorporated  oxidation The  i n t o t h e c o o r d i n a t i o n sphere o f Rh b e f o r e  occurs. a c t i v a t i o n enthalpy  o f the p r e s e n t  system i s 21.9 j 1-2 K c a l  - 221 mole  1  which i s very c l o s e to the energy d i f f e r e n c e between the  3 ground s t a t e to the f i r s t mole \  although  e x c i t e d s t a t e of 0^,  t h i s i s probably  1  Z —>  A  =22.1  Kcal  f o r t u i t o u s s i n c e the a c t i v a t i o n  energy of that o r d e r i s v e r y common. The  observed  p r e s s u r e i s v e r y s i m i l a r to that f o r r e a c t i o n s  dependence of r a t e  involving  on  free  268 radicals,  although  i n t h i s p r e s e n t system, the dependence of r a t e  p r e s s u r e i s governed by the K v a l u e f o r the f o r m a t i o n of the complex.  Rh^CC^)  on  CHAPTER IX  FORMATION AND  9.1  PROPERTIES OF  General  SOME RHODIUM CARBONYL COMPLEXES  Introduction  T h i s chapter  d e s c r i b e s v e r y p r e l i m i n a r y s t u d i e s of the  of rhodium c a r b o n y l  complexes v i a d i r e c t c a r b o n y l a t i o n w i t h  s o l u t i o n and v i a CO a b s t r a c t i o n from the s o l v e n t . initiated and  decarbonylation  of s o l v e n t i n  The  abstracted  to CO2 under the  CO  conditions.  is likely The  to be  these rhodium c a r b o n y l  Reaction  The  of  [Rh(C H ^ ) C 1 ] g  LiCl/DMA r e a d i l y absorbed CO  2053 cm (•(CO  -1  The  and  gaseous 0^  2  also b r i e f l y  2  i n a i r ) of  w i t h CO  which are v e r y 2058 cm" ). 1  of  i n LiCl/DMA  [Rh(CgH^) Cl]  i n about a 2:1  seems  studied.  2  2  in  0.5M  mole r a t i o of CO:Rh.  i n i t i a l brownish red s o l u t i o n turned  of the c a r b o n y l a t e d  = 1974,  CO  oxidation  c a t a l y t i c hydrogenation a c t i v i t y  complexes was  A s t o c k s o l u t i o n (kept  ( F i g u r e 52)  converted  s t u d i e s show t h a t such  r e a c t i o n between c o o r d i n a t e d  worthy of f u r t h e r study.  I.R.  in  These s t u d i e s were  the o x i d a t i o n s t u d i e s . (Chapter V I I I )  The  CO  to i n v e s t i g a t e the a c t i v a t i o n of CO by rhodium complexes  a l s o to l e a r n more of the suspected  9.2  formation  pale  s o l u t i o n showed bands at 1974  s i m i l a r to t h a t r e p o r t e d  for  yellow. cm  and  [Rh(C0) Cl ] 2  2  -  1 7  - 224  No  c o l o u r change was  -  observed when the p a l e y e l l o w s o l u t i o n  pumped on f o r a few hours a t 40° and ing No  s o l u t i o n showed the same two f u r t h e r CO uptake was  the I.R.  I.R.  observed  spectrum  bands a t 1974  f o r such a  of the  cm  and  1  2  by the a d d i t i o n of t e t r a p h e n y l a r s o n i u m c h l o r i d e  when Ph^P  was  powder was at  1960  y e l l o w s o l i d was  cm  174  not i s o l a t e d . Gas  but  I.R.  spectrum  2053 cm  species  2  surprisingly  e v o l u t i o n was  added to the c a r b o n y l a t e d s o l u t i o n and  obtained.  result-  solution.  Attempts were made to i s o l a t e the p o s s i b l e [ R h ( C O ) C l ]  the expected  was  observed  a pale yellow  of t h i s y e l l o w powder showed  which i s v e r y s i m i l a r to t h a t r e p o r t e d f o r  1  173 RhCl(CO)(Ph P) 3  2  A t y p i c a l gas uptake p l o t [Rh(C  ( F i g u r e 52) f o r a s t o c k s o l u t i o n of  H ) C l ] i n LiCl/DMA c o n s i s t e d of an i n i t i a l o 14 Z Z  rapid  f o l l o w e d by a r e g i o n of d e c r e a s i n g r a t e ; the i n i t i a l was  not observed  complex was  ( F i g u r e 53)  The  [Monomer].(Chapter V I I I ) s o l u t i o n s were used 1  and  Rh (0 ). I  2  The  i s thought  initial  section  to be due  9.5)  1  1  2  to the r e a c t i o n of CO to r e a c t i o n of CO  ing  the f u l l y  which r e f e r r e d  1  2  to a f i r s t  - moles of  A good f i r s t  o b t a i n e d f o r the experiment  formed R h ( 0 ) and  with  with  The gas uptake p l o t s were a n a l y z e d  a t time t ) a g a i n s t time, t .  ( F i g u r e 53) was  Rh^O^  + R h ( 0 ) where [Rh ] =  by p l o t t i n g the l o g ( t o t a l moles of gas absorbed absorbed  formed  r a p i d uptake when s t o c k  the l a t t e r p a r t of the uptake due (See  uptake  s t o c k s o l u t i o n i s b e l i e v e d to  c o n t a i n some oxygen complex, i . e . [Rh ] = R h  Rh  rapid  when a s o l u t i o n c o n t a i n i n g the f u l l y  used.  uptake  plot  using a solution contain-  the pseudo f i r s t  order decrease  order  gas  order constant,  in [Rh (0 )] I  2  i s shown i n  k,  -  225  -  Time, sec  F i g u r e 53.  Rate p l o t and the c o r r e s p o n d i n g l o g p l o t of R h ( C O ) I  3.75  2  x 10~ M 3  i n 0.5M 0 ) . 2  LiCl/DMA a t 80°  f o r the f o r m a t i o n  (1.3 x 10~ M 2  Rh ^), 1  (0) gas absorbed, (A) l o g [ R h ^ ) ] . 1  - 226  -  T a b l e XXXI; a 1:1 mole r a t i o of gas:Rh was the  absorbed.  I.R.  s p e c t r a of  r e s u l t i n g p a l e y e l l o w s o l u t i o n showed bands a t 2060 cm * and  cm *.  1980  For experiments u s i n g the s t o c k s o l u t i o n s , the l o g p l o t  c o r r e s p o n d i n g to the l a t t e r s t a g e s of the gas uptake gave a good straight  line  ( F i g u r e 52) from which the l i s t e d k v a l u e s (Table XXXI)  were determined.  The f i r s t  [CO] and a f i r s t  o r d e r c o n s t a n t s showed independence  o r d e r dependence on  [Rh^O^].  Uptake of CO i n a 1:1 mole o f C0:Rh was of  [Rh(C H g  1 4  observed f o r a s o l u t i o n  ) C l ] i n 0.5 M LiCl/DMA made up i n the absence of 2  on  0  2  2 >  -2 The CO uptake was  completed i n 80 s e c . at 80°  ([Rh] = 1.0 x 10  M,  _3 [CO] = 5.0 x 10  M)  and no f u r t h e r CO uptake was  4 hours at 80°.  I.R.  p r o b a b l y missed.  CO absorbed was  e q u i v a l e n t to 1.5:1  the same r e a c t i o n was  absorbed was of  CO was  cm *; some of the i n i t i a l  I f the same r e a c t i o n was  uptake p l o t a n a l y z e d f o r f i r s t If  after  spectrum o f the r e s u l t i n g p a l e y e l l o w s o l u t i o n  showed bands at 2060 cm * and 1980 was  observed even  equivalent  CO  uptake  c a r r i e d out a t 6 0 ° , the  mole r a t i o of C0:Rh.  o r d e r decrease i n [Rh"'"]  This  CO  (Table XXXI).  c a r r i e d out at room temperature, the CO to a 2:1 mole r a t i o o f C0:Rh; the f i r s t  absorbed r a p i d l y and the second mole of CO was  mole  absorbed  over a p e r i o d of s e v e r a l hours. A d d i t i o n o f MA  to the c a r b o n y l a t e d s o l u t i o n r e s u l t e d i n an  i n t e n s e y e l l o w s o l u t i o n and gas e v o l u t i o n was to  1 atm of K„ at 80°, no gas uptake was  observed.  On  subjection  observed f o r two hours.  - 227 -  TABLE XXXI Formation  of R h  1  Carbonyl S p e c i e s i n DMA  Summary of  T  [Rh ]  °C  K i n e t i c Data"  CO mm  [CO]  .  xl0 M 3  k x 10 -1 sec  80  0.5  725  5.0  0.63  80  1.0  725  5.0  0.63  80  2.0  725  5.0  0.65  80  1.0  406  2.6  0.65  60  1.0  745  5.2  0.28  60  1.0  745  5.2'  0.51  80  2.0  725  5.0  0.65  Data r e f e r r e d  to s t o c k s o l u t i o n s  of [ R h ( C g H ^ ) ^ C l ] ^ i -  n  LiCl/DMA a s o l u t i o n make up i n the " a i r f r e e " d e v i c e . a s o l u t i o n c o n t a i n i n g the f u l l y formed  Rh^CO^)  complex.  a b  0.5M  3  - 228 -  9.3  C a t a l y t i c R e a c t i o n Between the C o o r d i n a t e d CO and 0^ The rhodium c a r b o n y l complexes  complex  i n 0.5M  w i t h O2.  prepared from the [ R h ( C g R \ ^ ) C l ] 2  LiCl/DMA e r e found to-undergo i n t e r e s t i n g  reactions  W  When the c a r b o n y l a t e d s o l u t i o n was  2  l e f t a t room  temperature under a i r f o r a few days, a brownish r e d s o l u t i o n w i t h an I.R; was  band a t 2100  observed.  cm  1  and a v e r y s l i g h t  I f the s o l u t i o n was  reacted with 0  excess of that r e q u i r e d f o r o x i d a t i o n - o f Rh An 0  2  uptake p l o t f o r a 0.01  s h o u l d e r a t 2130  I  2  to Rh  at 8 0 ° , 0 III  was  cm uptake i n  2  observed.  M Rh s o l u t i o n is•shown i n F i g u r e 54; a v e r y slow  i n i t i a l uptake f o l l o w e d by a more l i n e a r r e g i o n w i t h a r a t e (3.2 x 10 "'M sec ^) which was  seven times f a s t e r than the R h ( 0 )  catalyzed oxidation  x 10 ^M sec \  observed. of  (c f . 4.6  1  2  The s t o i c h i o m e t r y of 0  the f i r s t  consumed  2  T a b l e XXVII) was  uptake a t the break o f f r e g i o n  l i n e a r r a t e corresponded c l o s e l y to 1 mole of  per mole of c o o r d i n a t e d CO.  A f t e r the i n i t i a l  0  more r a p i d  —6 l i n e a r r a t e , a second r e g i o n of l i n e a r r a t e which was  —  1  M sec  I  2  The r e s u l t i n g g r e e n i s h brown s o l u t i o n 1  2  spectrum of the r e s u l t i n g brown s o l u t i o n showed bands a t 1290, and 830 cm  1  I.R. 1140  .  A s t o c k s o l u t i o n of [Rh(C H..)_C1]_ 0  o 14 4  was  (shoulder a t  e = 260) suggested the presence of R h ( 0 ) s p e c i e s .  (1.0 x 10  )  c l o s e to the r a t e of the R h ( 0 ) c a t a l y z e d o x i d a t i o n  observed. 450 m U,  (6.6 x 10  2  2  i n 0.5M  LiCl/DMA  2  moles of Rh) r e a c t e d w i t h a m i x t u r e of 0  2  (370 mm)  and  -4 and a f t e r 3 hours, 1.0 x 10 moles of gas were apparently consumed; -4 and a f t e r 3 days a t o t a l of 2.2 x 10 moles of gas were a p p a r e n t l y consumed CO  (380 mm)  - 230 and p o s s i b l y a v e r y slow r e a c t i o n was s t i l l  occurring.  metry i n d i c a t e d CO^ i s produced i n the gaseous phase. of  Mass s p e c t r o I.R. spectrum  the p a l e y e l l o w s o l u t i o n showed peaks a t 2060 cm * and 1960 cm *.  The v i s i b l e spectrum gave a A a t 400 my max When a s o l u t i o n of [ R h ( C g H ^ ) C 1 ] 2  under N  2  f o r two days a t 80°, no N  (e = 130).  i n 0.5M LiCl/DMA was kept  uptake was observed  2  and the I.R.  spectrum showed a band a t 1940 cm * which i s a t t r i b u t e d t o Rh-CO s t r e t c h ; the Rh-CO s p e c i e s was formed v i a CO a b s t r a c t i o n from the s o l v e n t DMA.  is  thought  presence  CO a b s t r a c t i o n under 0_ atmosphere by [Rh(C H..)„C1]» L o 14 A L 0  to be p r e s e n t  of 0  I n the  a t 80°, the CO a b s t r a c t e d i s a l s o b e l i e v e d to be  2  o x i d i z e d to C0 2  9.4  i n the c a t a l y t i c o x i d a t i o n system.  (Chapter  VIII)  R e a c t i o n of R h C l ( E t S ) 3  2  3  w i t h CO i n DMA  An orange r e d s o l u t i o n o f RhCl (Et„S)„ i n DMA 3 2 3 0  e = 308) r e a d i l y absorbed pale yellow s o l u t i o n  (A 426 my, max  two moles o f CO per mole o f Rh t o g i v e a  (A 340 my, e = 2730). max  I.R. o f the r e s u l t i n g  -1 -1 p a l e y e l l o w s o l u t i o n showed two bands a t 2062 cm and 1976 cm T h i s p a l e y e l l o w s o l u t i o n turned orange on s t a n d i n g f o r a day i n a i r at  room temperature  (shoulder a t 450 my, e = 420).  The r e s u l t i n g  orange r e d s o l u t i o n showed a Rh-CO band a t 2060 cm *. Preliminary studies indicated analyzed f o r a f i r s t  t h a t the CO uptake p l o t  ( F i g u r e 55)  order l o s s i n [Rh**''"] and the pseudo f i r s t  -3 -1 constant was 7.85 x 10 sec a t 80°. order constant was found  A t 60°, the pseudo  -3 -1 t o be 1.45 x 10 sec  first  order  Time, sec Figure  55.  - 232 Prolonged pumping remove the CO  (a few  -  hours at room temperature) d i d  i n the rhodium c a r b o n y l  s p e c i e s s i n c e no  not  CO uptake  was  measured on such s o l u t i o n s . When MA carbonyl  was  added to the s o l u t i o n c o n t a i n i n g the rhodium  s p e c i e s , e v o l u t i o n was  observed and  the r e s u l t i n g s o l u t i o n  d i d not a c t as a homogeneous h y d r o g e n a t i o n c a t a l y s t f o r  9.5  Discussion  9.51  The  [Rh(C H ) Cl] g  1 4  2  System  2  S p e c t r a l evidence i n d i c a t e s t h a t a R h ( C O )  species,  1  [Rh(CO) Cl ]~ 2  o r  MA.  2  p o s s i b l y RhCl(CO) (DMA)(which would account f o r 2  l a c k of p r e c i p i t a t i o n of P h A s [ R h ( C O ) +  4  i s formed i n the r e a c t i o n s of  C 1 2  2  ^~  [Rh(C H ) C1] g  l 4  2  o  2  a d d i t i o n of  n  with  CO  the  Ph As Cl~) +  4  i n DMA.  The o no  p r e p a r a t i o n of  [Rh(CO) Cl] 2  2  from  [Rh(C H ) Cl] g  1 4  2  2  has  been  P r e l i m i n a r y k i n e t i c data on the r e a c t i o n s of s t o c k of  [Rh(CgH ) Cl] 1 4  2  2  i n g step i s f i r s t The  i n LiCl/DMA w i t h CO order  solutions  suggest t h a t the r a t e d e t e r m i n -  i n [ R h ( 0 ) ] and I  2  d i f f e r e n c e i n the k i n e t i c data  reported.  independent of CO  f o r reactions using stock s o l u t i o n s ,  a s o l u t i o n c o n t a i n i n g the f u l l y formed R h ( 0 ) complex and 1  2  f r e e " s o l u t i o n s suggests t h a t the r a t e determining production of CO  of the " a c t i v e " R h  s o l u t i o n s of  moles 4  The  1  2  H  two  [Rh(CgH^ ) Cl]  been shown to form the R h ( 0 ) complex.  [Rh(C  k i n e t i c data  species.  2  the " a i r  step i s the  s p e c i e s which then p i c k s up  i n a f a s t step to produce the R h * ( C 0 )  i n LiCl/DMA has  The  1  (Table XXXI),  2  2  stock  .)„C1]„ i n LiCl/DMA c o n t a i n some R h ( 0 „ ) s p e c i e s . o 14 Z Z Z  c o u l d be  i n v o l v i n g stock s o l u t i o n s .  1  consistent with  the f o l l o w i n g r e a c t i o n s  - 233  -  R h ( 0 ) — —v  Rh  Rh  Rh (CO)  k  Z  2  + 2C0  1  f a S t  >  + 0  1  (9.1)  2  (9.2)  I  2  k i s known to be r e l a t i v e l y s m a l l s i n c e the e q u i l i b r i u m i n e q u a t i o n 9.1  i s not d i s p l a c e d  f r e e " Rh  to the r i g h t on removal of gases; the " a i r  s o l u t i o n s do have a h i g h a f f i n i t y  1  v e r y r a p i d CO uptake f o r such s o l u t i o n s . s o l u t i o n s , Rh at  f o r CO as seen by the  S t a r t i n g w i t h the s t o c k  w i l l absorb CO v e r y r a p i d l y ; R h ( 0 ) w i l l  1  absorb  1  2  a r a t e governed by  k.  The r e a c t i o n between R h  1  and CO has  also  been shown to be a f a s t step i n the f o r m a t i o n of [ R h ( C O ) C l ] 2  CO  species  2  1 187 from R h C l . 3 H 0 and CO i n both aqueous and non-aqueous media. ' 3  '  2  The e v o l u t i o n of 0 stoichiometry  2  ( e q u a t i o n 9.1)  c o u l d account f o r the somewhat low  (-1.6:1) of the observed gas uptake  i n v o l v i n g stock solutions  189  (see F i g u r e 52) and  i n reactions  the 1:1 s t o i c h i o m e t r y  for  a s o l u t i o n c o n t a i n i n g the f u l l y formed Rti^CC^) complex. The 72 71 oxygen molecule i n R h C l ( 0 ) ( P h g P ) and R h C l ( 0 ) ( P h ^ A s ) has been 2  2  found to be r e a d i l y d i s p l a c e d by CO i n dichloromethane. The r e a c t i o n between R h ( C 0 ) 1  2  and 0  2  i s of s p e c i a l i n t e r e s t i n  269 view of the r e c e n t r e p o r t s on complexes c o n t a i n i n g C 0 , 2- 270 82 and 0 C 0 as l i g a n d s . Pt ( C O ^ ( P l ^ P ) has been formed  C0^  2  3  passing  2  and C 0  (I.R. f o r C 0 " , 1680, 2  3  2  1180,  3  815 and 760 c m " ) . 1  3  3  7^82 '  m i x t u r e i n t o a s o l u t i o n of P t ( P h P ) .  peroxy carbonate complex P t ( 0 C 0 ) ( P h P ) 20C0 >1678, 1250,  ,  by  2  an 0  2  815, and 778 cm  3  -1  formed by the a c t i o n of m o l e c u l a r 0  .  2  270 2  was  3  An i n t e r m e d i a t e a l s o i s o l a t e d , (I.R. f o r  A carbonate complex has a l s o been on a c o o r d i n a t e d CO  74  ,  - 234 -  «2  Os-CO  '  y Os  ;  C= 0  (9.3)  ^ O ^ (I.R. f o r C 0 ~ , 1710, 1030, 760 and 662  cm" )  2  1  3  26 and  the a c t i o n o f CO on a m o l e c u l a r  0^ complex  .0 Pt'  The_complex  0 + CO  ^ P t ^ ^ C —0  [Co(NH^(C0) ]  +  3  1365, 1052, 738 and 690 cm  has C 0  -1 271 .  (9.4)  a b s o r p t i o n bands a t 1482,  2 3  R e a c t i o n o f a rhodium c a r b o n y l  complex w i t h 0^ i s a l s o r e p o r t e d to produce a complex c o n t a i n i n g a coordinated  C0  Rh (CO) (Ph P) 2  4  3  2  4  ligand.  + 0  269  2  • Rh (C0) (C0 )(Ph P)  2  2  F i n a l l y the r e a c t i o n o f 0 has been r e p r e s e n t e d  [Rh(CO) C l ]  +0  —1 (I.R. f o r C 0 , 1498, 1368 and 813 cm )  2  2  with  II]  3  [Rh(C0) Cl ] 2  3  + CO + P h P 0  (9.5)  3  i n aqueous a c i d s o l u t i o n  2  9.6.^  by e q u a t i o n  H [Rh  2  -(C0 )(C0)C1 ]  [Rh  2  I ] C I  (C0)Cl  ]  2  +  Cl C0  2  +  H0 2  (9.6) The I.R. r e p o r t e d f o r c o o r d i n a t e d a l l measured  cm the s o l i d  carbonate  (or peroxycarbonate) a r e  samples i n n u j o l o r KBr d i s c s and a r e c l e a r l y  not as unambiguously a s s i g n e d a s , f o r example, a c a r b o n y l band. might be d i f f i c u l t  to d e t e c t a C 0  23  l i g a n d i n DMA  solution.  It  - 235 The bands a t 2130-2100 cm  i n the c a r b o n y l a t e d  1  i n a i r at room temperature c o u l d be due  solution  left  to Rh*"'"''" c a r b o n y l s p e c i e s ^ * 2  2although  no bands a s s i g n a b l e to CO^  were e v i d e n t .  study a t 80°  ( F i g u r e 54)  of the f i r s t  l i n e a r r e g i o n ( i . e . 1:1  i s probably  CO and  kinetic  the s t o i c h i o m e t r y of 0^ uptake a t the  end  mole r a t i o of c o o r d i n a t e d  s i g n i f i c a n t , the c o o r d i n a t e d CO  removed as CO^  In the  i s almost  00:0^)  certainly  (see f o l l o w i n g d i s c u s s i o n on the r e a c t i o n i n v o l v i n g  0^ m i x t u r e ) but  i t i s not c l e a r how  nature of the uptake p l o t a r i s e s . s o l u t i o n suggest  the s t o i c h i o m e t r y or  The v i s i b l e s p e c t r a of the  the presence of Rh^O^) s p e c i e s .  the  final  T h i s , together  with  the r a t e of 0^ uptake i n the l a t e r stages of the 0^ uptake,suggests catalytic o x i d a t i o n of DMA  and  CgH-^  c o u l d be  The  t a k i n g p l a c e . (See Chapter  VIII)  r e a c t i o n between [Rh (C H., . ) „C1] „ and a mixture of CO and 0 o 14 z z z suggest t h a t the CO i s c a t a l y t i c a l l y o x i d i z e d to C0^. In the presence of both CO and O^, Rh*(C0)2 w i l l be p r e f e r a b l y formed. The by  x  n  0  o  s t o i c h i o m e t r i c o x i d a t i o n of c o o r d i n a t e d CO aqueous HCl  188 i s shown i n e q u a t i o n 9.6.  thought to i n v o l v e o x i d a t i v e a d d i t i o n of 0^ intermediate  [Rh  III  (CO^)(C0)C1 ]  2-  3  by C l  to produce the  [Rh  III  (CO^)(C0)C1 ]  III  C1 (C0)]  2-  5  s t u d i e d system, f o r m a t i o n of 2-  3  was  octahedral  c o n t a i n i n g the c o o r d i n a t e d  to form the s t a b l e [Rh  In the p r e s e n t  [RMCO^C^]"  The mechanism  i o n which i n a c i d media would decompose to g i v e C0^ anated  in  CO^  2-  and be f u r t h e r  complex. the  i s p o s s i b l e , however t h e r e i s no a c i d  present  2to decompose the c o o r d i n a t e d possibility and 0  2  CO^  to g i v e C O 2 .  There i s a l s o  the  t h a t the CO2 i s produced d i r e c t l y from the c o o r d i n a t e d  ( e q u a t i o n 9.7).  The u s u a l DMA  o x i d a t i o n i s suppressed  CO  because  - 236 the Rh^CC^) s p e c i e s i s not present.  Rh (CO)  + | 0  I  2  — R h  2  Rh (CO) + CO  ( C O )  I  • Rh (CO)  I  + C0  (9.7)  2  (9.8)  I  2  F u r t h e r s t u d i e s a r e r e q u i r e d to u n r a v e l t h i s system.  9.52  The R h C l ( E t S ) 3  2  3  System  Preliminary studies i n d i c a t e that R h C l ( E t S ) 3  two moles of CO to produce a R h ( C O )  species  1  Cl  a r e omitted) i n a process  2  involving f i r s t  2  3  i n DMA r e a c t s w i t h  ( l i g a n d s such as E t S and 2  order decrease  in [Rh  1 1 1  ].  189 In the r e a c t i o n of R h C l . 3 H 0 3  produced v i a two steps c a r b o n y l rhodate  w i t h CO i n DMA,  2  [Rh(CO) Cl ] 2  2  was  ( i ) s u b s t i t u t i o n o f CO to produce a c h l o r o  ( I I I ) s p e c i e s f o l l o w e d by ( i i ) a slow i n s e r t i o n  r e a c t i o n i n v o l v i n g c o o r d i n a t e d OH  to produce R h  CO i n a f a s t step t o produce [ R h ( C O ) C l ] . 2  which then p i c k s up  1  The r e a c t i o n mechanism i s  2  d e p i c t e d below (H 0)Rh  TTT X  X  2  TTT  k + CO  (H 0)Rh CO III , , Rh (COOH) 2  Rh  I  + 2C0  —  k  1  ^  (H 0)Rh  ?  TTT  (9.9) -T-  (9.10) (9.11)  2  fast  T . • Rti(C0)  3  reaction.  (CO)  —=-*• Rh (COOH) + H fast T + • Rh + C 0 + H  However i n the r e a c t i o n o f R h C l ( E t S ) water present  TTT  2  3  (9.12)  o  w i t h CO, t h e r e i s no c o o r d i n a t e d  and the k i n e t i c s do not suggest  two d i s t i n c t  stages  The E t S may be r e s p o n s i b l e f o r the r e d u c t i o n o f R h 2  1 1 1  i n the  ( C O ) to  - 237 -  give R h * ( C 0 ) 2  species.  The Rh^CCO^ s p e c i e s produced from t h e c a r b o x y l a t i o n o f DMA  272 solutionsof RhClg(Et2S>  3  and RhCl^.SK^O  reacts with  Rh***CO; no c o n t i n u o u s gas uptake was o b s e r v e d . both CO and O2 need occur.  to be a c t i v a t e d  I t appears  f o r the c a t a l y t i c  that  o x i d a t i o n to  [ R h C C g H ^ ^ C l ] ^ has been shown to a c t i v a t e b o t h 0^ and CO,  whereas R h C l . 3 H 0 and R h C l ( E t S ) 3  2  3  2  CO has an i n h i b i t i n g e f f e c t p r o p e r t y o f Rh* s p e c i e s . of  to produce  3  do not a c t i v a t e 0 2  on the c a t a l y t i c h y d r o g e n a t i o n  Decrease i n a c t i v i t y w i t h the i n t r o d u c t i o n  c a r b o n y l groups i n t o the m e t a l complexes  o t h e r rhodium systems.* metal i o n and w i l l  CO w i l l withdraw  has been observed i n  e l e c t r o n d e n s i t y from the  i n c r e a s e t h e energy r e q u i r e d 8  molecular  i n the o x i d a t i v e a d d i t i o n  step.  to a c t i v a t e  CHAPTER X GENERAL CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK  The  work d e s c r i b e d  i n t h i s t h e s i s has i n v o l v e d k i n e t i c s t u d i e s  of the c a t a l y t i c a c t i v a t i o n o f H ^ , o l e f i n s , 0^ and CO by rhodium complexes containing  sulphur  RhCl (Et S) 3  2  3  and/or  chloride ligands.  and R h C l ( B z S ) 3  2  3  i n DMA were found to a c t i v a t e H  for  homogeneous h y d r o g e n a t i o n of o l e f i n s ,  and  trans-cinnamic  acid.  such as m a l e i c ,  fumaric  The k i n e t i c data a r e b a s i c a l l y c o n s i s t e n t  w i t h a p r e v i o u s l y p o s t u l a t e d mechanism i n v o l v i n g an i n i t i a l reduction  a u x i l i a r y ligand)  saturated  subsequently r e a c t w i t h H  2  complexes  to produce the  p a r a f f i n and Rh* a g a i n .  the Rh*** complexes occurs b e f o r e step.  reaction with H  T h i s step was o r i g i n a l l y  2  the R h C l ( E t S ) 2  3  l i g a n d from  i n the i n i t i a l  thought to be independent  of o l e f i n , but some v a r i a t i o n i n the r a t e c o n s t a n t s 3  2  the r e s u l t i n g R h * ( o l e f i n ) L  A p r e d i s s b c i a t i o n step i n v o l v i n g l o s s of a sulphur  reduction  H  of Rh**'"' to Rh* which i s then s t a b l i z e d i n s o l u t i o n by  r a p i d complexing w i t h the o l e f i n ; (L =  2  f o r t h i s step i n  c a t a l y z e d h y d r o g e n a t i o n of FA and MA suggest t h a t  may not be so, and some s p e c t r o s c o p i c  evidence suggests t h a t  Rh***(olefin)  complexes may be produced v i a a c a t a l y t i c s u b s t i t u t i o n p r o c e s s involving Rh*(olefin)L  .  The s p e c t r o s c o p i c  this  evidence i s not s t r o n g .  - 239 However, t h i s p o s s i b l e p r o d u c t i o n of R h  1 1 1  ( o l e f i n ) complexes, u s i n g a  r e d u c t a n t o t h e r than H^ for the p r o d u c t i o n of the R h  1  c a t a l y s t , seems  worth f u r t h e r s t u d y i n g . The k i n e t i c s o f the o l e f i n h y d r o g e n a t i o n r e a c t i o n depend  markedly  on the n a t u r e of the R h ( o l e f i n ) c o m p l e x , i . e . the s t r u c t u r e o f the 1  o l e f i n and  the l i g a n d s L on the Rh .  In some i n s t a n c e s , one of the  1  X s u l p h u r l i g a n d s i n the Rh  ( o l e f i n ) ! ^ complex has to d i s s o c i a t e to  p r o v i d e a vacant s i t e , p r e s u m a b l y n e c e s s a r y f o r o x i d a t i v e a d d i t i o n of H^.  These c o n c l u s i o n s r e s u l t e d from a unique o b s e r v a t i o n i n the  RhCl (Et2S) 3  3  RhCl (Bz2S)2 3  tion i s f i r s t  c a t a l y z e d h y d r o g e n a t i o n of CA and p o s s i b l y i n the c a t a l y z e d h y d r o g e n a t i o n of MA o r d e r at v e r y low  (zero o r d e r ) a t h i g h [Rh]. produced  i n the i n i t i a l R h  t h a t the r a t e of  hydrogena-  [Rh] and reaches a l i m i t i n g v a l u e  T h i s r e s u l t s from the f r e e s u l p h u r l i g a n d 1 1 1  to R h  1  r e d u c t i o n step i n h i b i t i n g  d i s s o c i a t i o n of the R h ( o l e f i n ) ^ complex to produce 1  I s o m e r i z a t i o n of FA to MA was c a t a l y z e d h y d r o g e n a t i o n of FA. more s t a b l e thermodynamically,  the a c t i v e  observed i n the R h C l ( E t 2 S ) 3  Although the t r a n s a c i d 1  requirements i n the R h ( o l e f i n ) L 1  n  complex.  because  form.  3  (FA) i s  the Rh (FA) complex appears  l e s s s t a b l e than the Rh^O-IA) complex presumably  the  of  to be steric  I s o m e r i z a t i o n was" thought  III to  occur through a Rh  H  intermediate.  The k i n e t i c s of the  RhCl.j(Et2S)^ c a t a l y z e d h y d r o g e n a t i o n of FA are c o m p l i c a t e d of  the accompanying  because  isomerization.  U n s u c c e s s f u l attempts were made to p r e p a r e R h  1  s u l p h u r complexes  f o r use as h y d r o g e n a t i o n c a t a l y s t s . However, the c y c l o o c t e n e complex, [Rh(C H .)„C1]„,in DMA proved to be a v e r y u s e f u l source f o r o 14 L L~ 0  1  - 240 -  p r e p a r i n g Rh* complexes " i n s i t u " by adding the d e s i r e d e.g. C l  and Et S, s i n c e C H Q  . l i g a n d was  very e a s i l y  ligand,  displaced.  Simple k i n e t i c s were observed f o r h y d r o g e n a t i o n r e a c t i o n s u s i n g such stock s o l u t i o n s  (which are thought  to c o n t a i n monomeric s p e c i e s )  and the k i n e t i c data are i n good agreement w i t h the h y d r o g e n a t i o n data o b t a i n e d by s t a r t i n g from the c o r r e s p o n d i n g Rh*** systems. r e s u l t c o n f i r m s t h a t Rh*  i n t e r m e d i a t e s are i n v o l v e d i n the  h y d r o g e n a t i o n s t a r t i n g from Rh*** complexes.  The C„H O  systems was  not homogeneously hydrogenated  i t s weaker bonding  and  This  catalytic  . i n these  Rh*  A.H  t h i s was  a t t r i b u t e d to  (V-acceptor p r o p e r t y ) compared w i t h MA.  Hence  t h i s c a t a l y s t system c o u l d be developed u s e f u l l y f o r s e l e c t i v e  hydrogena-  t i o n s i n c e one of the major f a c t o r s must be the s t a b i l i t y of the m e t a l s u b s t r a t e complex. A green s o l u t i o n o b t a i n e d when the hydrogenated olefin solution I II (from the Rh C l system) i s l e f t i n a i r p r o b a b l y c o n t a i n s a Rh species.  An E.S.R. s i g n a l suggest t h a t the s p e c i e s i s l i k e l y  monomeric and i t would be worthwhile "green" complex.  a t t e m p t i n g to i s o l a t e  The most w e l l - e s t a b l i s h e d Rh  II  to be  this  s p e c i e s i s the Rh  II  a c e t a t e dimer, a l t h o u g h r e c e n t l y some Rh** phosphine monomers were also reported.  I r r e p r o d u c i b i l i t y of the k i n e t i c data i n some  R h C l ^ h ^ P ^ systems i s thought  to be due  to t r a c e s of Rh** s p e c i e s .  The study of the c a t a l y t i c a c t i v i t y of the "green" s o l u t i o n would g i v e f u r t h e r i n s i g h t i n t o the a c t i v i t y of rhodium oxidation  species i n d i f f e r e n t  states.  DMSO was  used p r i m a r i l y to study the e f f e c t of s o l v e n t  c a t a l y t i c h y d r o g e n a t i o n of o l e f i n s by Rh  III  on  complexes; however,  -  241  -  R h C l ^ C E t ^ S ) ^ and RhCl^-SH^O were found to c a t a l y z e the r e d u c t i o n o f DMSO to DMS and water. heterolytic splitting  The k i n e t i c s i n d i c a t e d a r a t e of H  by Rh  2  l:EI  (DMSO) to produce R h  which then decomposes t o Me S and H^O i n a f a s t 2  fall  off i ncatalytic activity  III I the Rh (DMSO)H t o Rh .  and H  by R h C l ' 3 H 0 u s i n g  2  3  2  i s w e l l worth i n v e s t i g a t i n g s i n c e a R h  2  An e v e n t u a l  The d e t a i l e d mechanism o f an observed 2  2  step.  (DMSO)H~  1 1 1  i s thought to be due to d e c o m p o s i t i o n o f  c a t a l y t i c o x i d a t i o n o f DMSO t o M e S 0 of 0  determining  111  !!  a mixture species  :  appears t o be the a c t i v e oxygen c a r r i e r and t h i s o f f e r s the a t t r a c t i v e speculation The  that H 0 2  2  might be i n v o l v e d  i n the c a t a l y z e d  oxidation.  s o l u t i o n o f [ R h ( C H . . ) _ C 1 ] - i n LiCl/DMA has been found t o be o ±H 2 2 0  a very v e r s a t i l e c a t a l y s t , f o r b e s i d e s olefins, 0  2  2  and CO can a l s o be a c t i v a t e d .  complex and a subsequent c a t a l y z e d cyclooctene  the a c t i v a t i o n o f H and  were s t u d i e d  The f o r m a t i o n  of a Rh^CO^  o x i d a t i o n o f the DMA s o l v e n t and  i ndetail.  The f o r m a t i o n  o f the Rh"*"(0 ) 2  complex appears t o be i r r e v e r s i b l e ; an E.S.R. s i g n a l p o s s i b l y due t o II " a s p e c i e s such as Rh - 0 was a l s o observed. Previously reported 2  , ,8  1  oxygen complexes o f d  , ,10  and d  .  _ I  species,  „.0  ,„ 0  _,0  I r , N i , Pd  and P t  magnetic ;Rb} m o l e c u l a r oxygen complexes a r e i l l - c h a r a c t e r i z e d Rh(0  )(Ph P)  o x i d a t i o n are  was r e p o r t e d  simple and the mechanism i n v o l v e s Z  2  and  are a l l d i a although  to be diamagnetic.The k i n e t i c s o f the c a t a l y z e d  t i o n o f the R h ( 0 ) complex f o l l o w e d give  -,, ,.  the e q u i l i b r i u m forma-  by the r a t e d e t e r m i n i n g step t o  the p r o d u c t s . The d e t a i l e d n a t u r e o f the r a t e d e t e r m i n i n g  steps  the i d e n t i f i c a t i o n o f a l l t h e o x i d a t i o n p r o d u c t s proved t o be v e r y  difficult.  A f r e e r a d i c a l mechanism seems t o be l i k e l y  t h i s i s not proved unequivocally  s i n c e the f r e e r a d i c a l  involved  although  i n h i b i t o r DPPH  V 242  r e a c t s i t s e l f w i t h Rh*.  There i s a g r e a t d e a l o f c u r r e n t  interest i n  the mechanism o f o x i d a t i o n through m o l e c u l a r oxygen complexes. oxygen atom t r a n s f e r and f r e e r a d i c a l p r o c e s s e s have been  Both  postulated.  Oxygenation r e a c t i o n s w i t h N i ^ , Pd^ and P t ^ complexes have been considered  to be atom t r a n s f e r r e a c t i o n s , w h i l e Rh* systems appears  to c a t a l y z e oxygenation v i a f r e e r a d i c a l p r o c e s s e s . the E.S.R. s i g n a l i n the present  The f i n d i n g o f  system seems most s i g n i f i c a n t and  i n d i c a t e s that the o x i d a t i o n mechanism may depend on the magnetic II*~ p r o p e r t i e s of the c a t a l y s t , s i n c e s p e c i e s  such as Rh  0^ may w e l l  i n i t i a t e f r e e r a d i c a l hydroperoxide p r o c e s s e s by p r o t o n o r hydrogen atom t r a n s f e r .  More d e t a i l e d E.S.R. s t u d i e s a r e r e q u i r e d  the e l e c t r o n i c s t r u c t u r e of the R h * ( 0 ) complex.  The p r e s e n t  2  could be extended by u s i n g other oxidizable substrates. i n ethanol  i s very  Preliminary  to e l u c i d a t e system  s o l v e n t systems and a v a r i e t y o f other  The p r e l i m i n a r y  r e s u l t on a c a t a l y z e d  oxidation  promising.  s t u d i e s i n d i c a t e that an oxygen-free s o l u t i o n o f  [ R h ( C H ) C l ] i n 0.5 M LiCl/DMA r e a c t s r a p i d l y w i t h CO to produce I I a Rh ( C 0 ) s p e c i e s . A s o l u t i o n o f Rh ( 0 ) absorbs CO more s l o w l y and g  1 4  2  2  2  2  the k i n e t i c s i n d i c a t e the r a t e d e t e r m i n i n g step i s t h e d i s s o c i a t i o n of Rh*(P ) to Rh* and 0 2  f o l l o w e d by a f a s t step i n v o l v i n g the r e a c t i o n  2  I I of Rh and CO to produce Rh (C0> .  I Such Rh ( C 0 )  2  0  2  to produce C 0 . 2  A mixture of 0  2  and C 0  2  1  solutions react with  i s converted  by a s o l u t i o n of [ R h ( C H . ) . C l ] . i n LiCl/DMA. Q  2  catalytically  The n a t u r e o f t h i s  c a t a l y t i c r e a c t i o n , which could i n v o l v e carbonate, peroxycarbonate o r carbon d i o x i d e complexes i s worth f u r t h e r i n v e s t i g a t i o n , p a r t i c u l a r l y i n view of the p r e s e n t  CO p o l l u t i o n problem.  In agreement w i t h t h e r e s u l t s o f other workers, t h e i n t r o d u c t i o n  -  of  c o o r d i n a t e d CO was  found  243  -  to have an i n h i b i t i n g  c a t a l y t i c h y d r o g e n a t i o n p r o p e r t y of rhodium  e f f e c t on  the  (I) complexes.  F i n a l l y , p o s s i b l e a c t i v a t i o n of o t h e r s m a l l c o v a l e n t gaseous m o l e c u l e s such as C 0 , S 0 2  i n DMA  2  ,N0 , 2  and o t h e r s o l v e n t s i s worthy of  CH 2  e t c . , by  investigation.  [RhCCgH^) C1] 2  REFERENCES  1.  G.L. Rempel, Ph.D. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, 1968.  2.  B.R. James and G.L. 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Chemie, 95,  APPENDIX I  SOLUBILITY DATA FOR OXYGEN IN N,N  Al  The S o l u b i l i t y  -DIMETHYLACETAMIDE  of Oxygen i n DMA  The s o l u b i l i t y o f oxygen i n DMA a t s p e c i f i c p r e s s u r e s were e s t i m a t e d by the method d e s c r i b e d s e c t i o n 2.4. 87°,  temperatures and i n Chapter I I ,  F i g u r e 56 shows the s o l u b i l i t y of 0^ from 0-800 mm a t  8 0 ° , 75°, 7 0 ° , and 25°.  - 259 -  

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