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Electron transfer reactions of ruthenium porphyrins Barley, Mark Howard 1983

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ELECTRON TRANSFER REACTIONS OF RUTHENIUM PORPHYRINS  By  MARK HOWARD BARLEY B.A.,  Cantab., 1977  M.A., Cantab., 1981  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in  THE FACULTY OF GRADUATE STUDIES Department of Chemistry  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA June 1983 ©  Mark Howard Barley, 1983  In p r e s e n t i n g  this  thesis  i n partial  f u l f i l m e n t of the  r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y of  British  it  freely  Columbia, I agree that available  f o r reference  agree t h a t permission for  the Library  shall  and study.  I  financial  copying or p u b l i c a t i o n  gain  shall  Department o f  CU.e.MA.  The U n i v e r s i t y o f B r i t i s h 1956 Main Mall V a n c o u v e r , Canada V6T 1Y3  (3/81)  ~2X>J "7 I %3  of this  It is thesis  n o t be a l l o w e d w i t h o u t my  permission.  DE-6  thesis  s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e h e a d o f my  understood that  Date  further  f o r extensive copying of t h i s  d e p a r t m e n t o r by h i s o r h e r r e p r e s e n t a t i v e s . for  make  Columbia  written  ii  ABSTRACT  The c h e m i s t r y and e l e c t r o c h e m i s t r y o f complexes o f t h e t y p e Ru (0EP)L L I I  1  2  (L  L  ] 5  = CO, P B u , P P h , A s P h n  2  3  3  Im) were s t u d i e d and s e v e r a l examples (IMET) were o b s e r v e d . 2  1  (OEP) *L-,L ,  1 1  +  2  2  = CO o r CS,  of intramolecular e l e c t r o n t r a n s f e r  and l_ «4=CO, CS ; or R u  n i  2  C N " , CS, MeCN, py and  The e l e c t r o n i c c o n f i g u r a t i o n o f t h e o x i d i z e d  complex ( R u ( 0 E P ) L - , L , L  L-jOr L  3 >  £  2  A  or  2 u  by the n a t u r e o f t h e a x i a l  A  l u  ground s t a t e ) was shown t o be determined  ligands.  Ligand  by l i g a n d a d d i t i o n or by p h o t o l y s i s ,  exchange,  effected either  c o u l d cause e l e c t r o n t r a n s f e r  between  the metal atom and t h e p o r p h y r i n m a c r o c y c l e (IMET) r e s u l t i n g i n a new electronic configuration.  This  process  certain ligands  (P Bu ,  cation radicals  ( R u ( 0 E P ) ' ( C 0 ) L , L = v a c a n t , py and B r " )  n  3  I I  PPh , AsPh  was observed on the a d d i t i o n o f  3  3  and CN~) t o s o l u t i o n s  +  of certain and r e s u l t e d  i n r u t h e n i u m ( I I I ) p r o d u c t s , a r e a c t i o n t h a t was found t o be r e v e r s i b l e with  AsPh . 3  Electrochemical  studies  gave a r u t h e n i u m ( I I I ) p r od uct radical  of R u ( 0 E P ) (C0)P Bu H  (Ru  I I I  n  (0EP)(P Bu J ) n  +  3  3  showed t h a t o x i d a t i o n  formed v i a a c a t i o n  i n t e r m e d i a t e t h a t r a p i d l y underwent an IMET r e a c t i o n .  observations  From t h e s e  a mechanism was p o s t u l a t e d f o r t h e IMET r e a c t i o n seen on t h e  addition of ligands  to i r - c a t i o n r a d i c a l s .  l i g a n d s , a l l o f w h i c h can e x h i b i t  The c o o r d i n a t i o n o f  these  n - a c i d i c p r o p e r t i e s , t r a n s t o t h e CO  i s b e l i e v e d t o l a b i l i z e t h e c a r b o n y l whose d i s s o c i a t i o n t h e n t r i g g e r s IMET r e a c t i o n .  the  i ii  The second o x i d a t i o n o f a R u ( 0 E P ) L I I  i n one case t h e r u t h e n i u m ( I I I ) and,  i n a second c a s e ,  Ru* (0EP)(CN) . 2  species  Ru***(OEP)CP Bu ) n  o f complexes o f the type R u (Ru  i n  ruthenium(IV)  (0EP)(AsPh ) 3  Ru***(0EP)  I I I  + 2  ,  Ru  H I  (0EP)(PPh ) 3  + 2  and  partially  cytochromes  the l i m i t s  ir-cation system.  radicals  2  species  to a range  Ru  i n  ruthenium(III)  (0EP)(P Bu ) ), n  +  3  a IMET r e a c t i o n  to  species.  the f o r m a t i o n o f F e ( I I ) Within  3  Certain  +  3  A mechanism suggested f o r t h e t r a n s f e r o f e l e c t r o n s neighbouring  n  ruthenium(III)  (0EP)(P Bu )(ligand) . n  gave  "(P Bu ) ,  +  porphyrin  o f the f i v e - c o o r d i n a t e  when purged w i t h CO, were found t o undergo form c a t i o n r a d i c a l  (L f CO o r CS)  were s t u d i e d a l s o and gave access  +  3  complexes  complex  tr-cation r a d i c a l  a possible  The r e a c t i o n s  V  2  i n the m i t o c h o n d r i a l  r e s p i r a t o r y chain  porphyrin tr-cation r a d i c a l s  o f the model  between postulates  and IMET r e a c t i o n s .  system t h e observed r e a c t i o n o f the  t e n t a t i v e l y support  such a mechanism  f o r the  ruthenium  biological  iv TABLE OF CONTENTS Paae  ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES ABBREVIATIONS AND IDENTIFICATION OF COMPOUNDS ACKNOWLEDGEMENTS CHAPTER 1  INTRODUCTION  1  1.1  Porphyrins  i n Nature  "1  1.2  E l e c t r o n T r a n s p o r t and the Cytochromes  1.3  The Mechanism o f E l e c t r o n T r a n s f e r between t h e Cytochromes  19  1 .4  Other Heme Redox P r o t e i n s  24  1.5  M o d e l l i n g t h e Cytochromes  24  1.6  P o r p h y r i n C a t i o n R a d i c a l s and I n t r a m o l e c u l a r Transfer of Electrons  REFERENCES - Chapter 1 CHAPTER 2  4  ;.  29 34  APPARATUS AND EXPERIMENTAL PROCEDURE  41  2.1  General I n s t r u m e n t a t i o n and Procedures  41  2.2  E l e c t r o c h e m i c a l Apparatus and Procedures  46  2.2a  Instrumentation  46  2.2b  Apparatus and Procedures  49  2.3  P h o t o l y s i s Experiments  55  2.3a  55  Bulk P h o t o l y s i s Experiments  V  Page  2.3b  Flash Photolysis  Experiments:-  Instrument-  ation 2.3c  Flash  55 Photolysis  Experiments:-  Procedures  and D a t a C o l l e c t i o n 2.4  2.5  Materials  (1)  Gases,  Ligands  and 60  2.4a  Gases  60  2.4b  Solvents  60  2.4c  Ligands  61  2.4d  Electrolytes  62  2.4e  Miscellaneous  64  Materials  (2)  P r e p a r a t i o n o f t h e Ruthenium  Com-  . . .  65  REFERENCES - CHAPTER 3  Solvents,  Electrolytes  plexes  CHAPTER  59  2  74  SOME PRELIMINARY EXPERIMENTS 3.1  The C o o r d i n a t i o n o f L i g a n d Type R u ( 0 E P ) ( C 0 ) L H  Solvation  3.3  The S u b s t i t u t i o n o f A x i a l  o f Ru(0EP)(C0)L  3  The C o o r d i n a t i o n o f A n i o n s CH C1 2  2  as  Solvent  REFERENCES - CHAPTER  in  .  the  . ,  76  Different Solvents  Ligands  in the  3  89  Complex 102  (8)  n  3.4  L i n Complexes o f  in Solution  3.2  Ru(0EP)(C0)P Bu  76  to Ru(0EP)(C0)  (1)  in 1  1  0  1  9  3  vi  Page  CHAPTER 4  THE OXIDATION OF RUTHENIUM PORPHYRIN CARBONYL COMPLEXES Ru (OEP)(CO)L; (L = EtOH, py, Im, and MeCN.)  115  4.1  The Electrochemical Oxidation of Ru(OEP)(CO)L . .  115  4.2  The Chemical Oxidation of Ru(OEP)(CO)L  133  4.3  The Nature of the Two Cation Radicals  141  4.4  Cation Radicals of a Related Species:  n  Ru(OEP)-  (CS)py  CHAPTER 5  146  REFERENCES - CHAPTER 4  148  ADDITION OF LIGANDS TO CATION RADICALS  150  5.1  Reactions of a Five-Coordinate Cation Radical Species with Neutral and Ionic Ligands in  ^ C ^ ,  an Inert Solvent  152  5.1a  Ligands that give ruthenium(III) products  152  5.1b  Neutral ligands that give other cation r a d i c a l species of the same ground state  5.1c  Anionic ligands that give the other ground state of the cation r a d i c a l  5.Id  5.1e 5.2  164  166  Ligands that i n s t a n t l y reduce the cation radi cal  167  Discussion and Conclusions  158  Reactions of a Six-Coordinate Cation Radical Species with Ligands in CHgC^, an Inert Solvent  170  5.2a  Reactions of [Ru(0EP) '(C0)Br]  171  5.2b  Reactions of [Ru(0EP) * ( C 0 ) p y ] C l 0 "  +  +  +  4  . . .  175  vii  Page  5.2c 5.3  Reactions o f [ R u ( 0 E P ) ' ( C 0 ) I m ] C 1 0 " +  +  4  Reactions of a Cation Radical Species  . . .  in a  Coordinating Solvent 5.4  R e a c t i o n s o f Ligands Cation Radical  5.5  5.6  184 with a Related Thiocarbonyl  - Ru(0EP) '(CS)py  187  +  C o n c l u s i o n : - The R e a c t i v i t y o f C a t i o n  Radicals  towards Ligands  188  The R e d u c t i o n R e a c t i o n  192  5.6a  P o s s i b l e Mechanisms f o r the  Reduction  Reaction 5.6b  192  Experimental Studies  o f the Reduction  Reaction  198  REFERENCES - CHAPTER 5 CHAPTER 6  177  202  AN ANOMALOUS OXIDATION OF Ru(0EP)(C0)L COMPLEXES (L = P B u , P P h , and A s P h ) : THE MECHANISM OF INTRAn  3  3  3  MOLECULAR ELECTRON TRANSFER (IMET)  203  6.1  The E l e c t r o c h e m i s t r y o f R u ( 0 E P ) ( C 0 ) P B u .  6.2  The P r e p a r a t i o n o f R u  H  3  Reactions Transfer 6.3  n  Involving  1 1 J  (OEP)(P Bu ) n  3  Intramolecular  (L = P P h  203  and Some  Electron  (IMET)  219  The E l e c t r o c h e m i s t r y o f o t h e r Complexes  +  . .  3  Ru (0EP)(C0)L n  and A s P h ) t h a t g i v e r i s e t o  R u t h e n i u m ( I I I ) Products  3  226  vii i  Page  6.4  The Mechanism o f t h e I n t r a m o l e c u l a r E l e c t r o n T r a n s f e r (IMET) R e a c t i o n s between Ruthenium(II) and t h e P o r p h y r i n C a t i o n R a d i c a l  231  REFERENCES - CHAPTER 6 CHAPTER 7  MISCELLANEOUS  CHEMISTRY  239 INVOLVING RUTHENIUM(111)  PORPHYRIN SPECIES 7.1  240  The O x i d a t i o n o f R u ( O E P ) ( P B u ) 1 1  and R e l a t e d  n  3  2  Chemistry  240  7.2  The Decomposition o f [ R u  7.3  R e a c t i o n s and P r o p e r t i e s o f  I ] C I  (0EP)(P Bu ) ] Br" n  249  +  3  ftu (0EP)  2  (P Bu )] -  In  n  +  3  C10 "  252  4  7.4  R e a c t i o n s and P r o p e r t i e s o f R u ( 0 E P ) ( P B u ) B r  7.5  R e a c t i o n s and P r o p e r t i e s o f R u ^ O E P ) ( P B u ) as  I H  268  n  3  1  n  3  Prepared by the R e d u c t i o n o f [ R u ( 0 E P ) ( P B u ) ] H I  n  +  3  C10 " 4  7.6  .  273  The Formation and R e a c t i o n s o f  [Ru (0EP)(PPh ) ] I H  +  3  2  C10 ~  280  4  7.7  The Formation and R e a c t i o n s o f [ R u ( 0 E P ) ( A s P h ) ' ] i n  +  3  2  C10 ~  285  4  7.8  The O x i d a t i o n o f E t N [ R u ( 0 E P ) ( C N ) ] " +  H I  4  2  . . . .  REFERENCES - CHAPTER 7 CHAPTER 8 .  294 300  THE PHOTOLYSIS OF RUTHENIUM CARBONYL PORPHYRIN ^-CATION RADICALS  302  8.1  306  The R e s u l t s o f the P h o t o l y s i s S t u d i e s  IX  Page  8.2  CHAPTER 9  8.1a  P h o t o l y s i s of Ru(0EP) '(C0)py  306  8.1b  P h o t o l y s i s o f Ru(0EP) "(CO)  310  8.1c  Photolysis of [Ru(0EP) (CO)Br]  314  8.Id  P h o t o l y s i s o f Ru(0EP) "(CO)Im  315  8.1e  Spectra o f the Transient States  315  +  +  +-  +  D i s c u s s i o n o f the P h o t o l y s i s R e s u l t s  318  REFERENCES - CHAPTER 8  328  CONCLUSIONS  329  X  LIST OF TABLES  Ta b.l e  Page  1 .1  Properties of Mitochondrial Cytochromes  9  3.1  The V a r i a t i o n of the V i s i b l e Spectrum of Ru(OEP)(C0)L with the Nature of the Sixth Ligand L  80  3.2  Spectral Data f o r Solutions in C H C l o f Ru(0EP)(C0)L Species  3.3  The E f f e c t of Added EtOH on the Spectrum of a 10" M Solution  2  Dissolved in CH C1 2  83  2  Addition of Ethanol to a Solution of Ru(OEP)(CO)EtOH CH C1 2  3.5  in 86  2  Spectral Data for Ru(OEP)(CO)EtOH  Dissolved in Various  Solvents 3.6  90  Equilibrium Constants for the Coordination of Ligands to Ru(0EP)(C0) in Dichloromethane as Solvent  3.7  95  The Estimation of the Equilibrium Constant for the Reaction L + Ru(0EP)(C0)CH CN?=±Ru(0EPXC0)L 3  3.8  + CHgCN  97  The Wavelength of the Soret (y) Absorption Band for a Number of R u ( 0 E P ) L H  and R u ( O E P ) ( C 0 ) L Complexes U  2  . . . .  108  . . . .  112  3.9  The Coordination of Anions to Ru(0EP)(C0) in CH C1  4.10  The Reversible Reduction P o t e n t i a l s ( E i ) Observed for  2  Ru(0EP)(C0) and Ru(OEP)(C0)4Mepy  2  in Dichloromethane in the  Presence of Various E l e c t r o l y t e Anions 4.2  82  5  of Ru(OEP)(CO)EtOH 3.4  2  118  V a r i a t i o n of Reduction P o t e n t i a l s with the Nature of the S i x t h Ligand  120  xi  Page  4.3  A Comparison of Reduction P o t e n t i a l s of Ru(0EP)(C0)  in  A c e t o n i t r i l e and Dichloromethane as Solvent 4.4  Conductivity Studies of Cation Radical [ R u { 0 E P ) ' ( C 0 ) B r ] 1l  and Related Species 4.5  122 +  ,  141  Optical Spectral Data for the Ruthenium(11) Porphyrin . . Tr-Cation Radical Complexes  5.1  A Summary of the Major Products of the Reaction of Ligands with Ruthenium(II)  6.1  145  Porphyrin ir-Cation Radicals  . . . . .  A Comparison of the P o t e n t i a l s for the Electrochemical TT  Processes seen in the Oxidation of Ru  n  (0EP)(C0)P Bu  as.a  3  Function of the E l e c t r o l y t i c Co-anion Present 7.1  207  Optical Spectral Data f o r Species obtained by Oxidation of Ru (0EP)(P Bu3) n  7.2  249  n  2  The Optical Spectra of Species obtained from [Ru***(0EP)(P Bu )] C10 n  259  +  3  7.3  4  C y c l i c Voltammetry Data for Species obtained by Ligand Addition to [ R u ( 0 E P ) ( P B u ) ] C 1 0 ~ III  n  265  +  3  4  7.4  The Optical Spectral Data of R u ( 0 E P ) ( P B u )  7.5  Electrochemical Data for the Ruthenium Porphyrin Complexes  H  and Derivatives  n  3  Ru (0EP)L n  7.6  (L = P B u , P P h , AsPh , MeCN, py and CN") . . . n  2  3  3  3  279  290  The Optical Spectral Data f o r Ru { OEP) ( P P h ) , R u ( 0 E P ) 11  H  3  (AsPh ) , Et N [Ru (0EP)(CN) ]', +  3  2  4  H I  2  2  and t h e i r Oxidation  Products 8.1  153  Summary of Results of the Flash Photolysis of Species  298 Ru(0EP) "(C0)L +  319  xii  LIST OF FIGURES  Page Figure  1.1  Porphin  3  1.2  Protoporphyrin IX.  3  1.3  The s t r u c t u r e of a six-coordinate i r o n ( I I ) porphyrin complex  3  1.4  The o p t i c a l spectrum of the reduced form of cytochrome c i l l u s t r a t i n g the main features of a metalloporphyrin spectrum  1.5  6  The structures of the iron porphyrin complexes found in c y t o chromes of classes a and c  1.6  The mitochondrial electron transport chain  1.7  The d e c l i n e in free energy as electron pairs flow down the  7 11  mitochondrial transport chain to oxygen  12  1.8  Schematic diagram of the backbone chain of cytochrome bg . .  14  1.9  Schematic diagram of the backbone chain of horse heart c y t o chrome c .  1.10  Schematic representation of cytochrome c i n t e r a c t i o n s with cytochromes aa^ and c-j in the mitochondrial membrane . . . .  1.11  17  19  The proposed mechanism f o r electron t r a n s f e r between the heme groups of two cytochromes v i a cation r a d i c a l i n t e r mediates  25  1 .12  The oxidation of camphor by cytochrome P-450  25  1.13  The r e a c t i o n of i r o n ( I I ) porphyrins with oxygen to give a y-oxo-dimer as product  27  xi i i  Page  1 .14  The o p t i c a l (0EP) "] +  2 +  spectrum of the  . 2 B r ~ i n CHC1  [Co (0EP) "] m  the  +  2 + :  ;2C10 :.  A-j  u  cation radical  [Co  and t h e s p e c t r u m o f t h e  3  A  2  III species  2 u  i n " CHGI3 f o r m e d by a d d i n g AgC10  4  4  to  bromide complex  31  2.1  Designs o f q u a r t z c e l l s used  2.2  An a n a e r o b i c e . s . r .  2.3  The c o n d u c t i v i t y c e l l  in optical  spectroscopy  . . . .  cell  A schematic c i r c u i t  i n CH C1 2  diagram  conductances 45  2  f o r the c y c l i c  voltammetry  experiments 2.'5  The H - c e l l  47 and e l e c t r o d e a r r a n g e m e n t used  for  cyclic  voltammetry 2.6  50  The a p p a r a t u s  used  f o r the bulk e l e c t r o l y s i s of a  porphyrin  species 2.7  52  A flow c e l l radicals  2.8  used  to study  the o p t i c a l  spectra of  cation  during t h e i r formation  The a p p a r a t u s  used  54  f o r the bulk p h o t o l y s i s  of cation radical  solutions  56  2.9  The p i c o s e c o n d  3.lit  The o p t i c a l  spectrum of Ru(0EP)(C0)P Bu  3.2  The c h a n g e s  in optical  of PPh 3.3  3  flash  photolysis  apparatus n  3  57 i n CH C1 2  2  . . . .  78  spectrum r e s u l t i n g from t h e a d d i t i o n  t o a s o l u t i o n o f Ru(0EP)(C0)  in CH C1 2  10  to obtain the e q u i l i b r i u m constant  Ru(0EP)(;CO) + E t O H ? = i R u ( O E P ) ( C O ) E t O H  79  2  P l o t o f log ([Ru(0EP)(C0)Et0H]/[Ru(0EP)(C0)]) v s . [EtOH]  42 42  used t o o b t a i n t h e m o l a r  of porphyrin solutions 2.4  2  log  1 Q  f o r the r e a c t i o n 88  xiy  Page  3.4  Optical ligand  s p e c t r a o f CH2C12 s o l u t i o n s o f Ri)(0EP)(C0) binding experiments,  coordinate ligand; 3.5  L = EtOH,  The o p t i c a l (C0)PnBu3  3.6  4.1  i n the presence o f excess  CH3N02, AsPh3,  spectrum of the products  E t 3 N a n d Im  obtained  v/v mixture  spectrum o f Ru(OEP)(CO)CN"  an e x c e s s o f T E A + C N "  The o p t i c a l adding  CH3CN,  and t h e s p e c t r a o f t h e s i x -  i s d i s s o l v e d i n a 1:1  The o p t i c a l adding  3.7  species obtained  used i n  when  added .  .  92  Ru(OEP)-•;  of CH2Cl2/4Mepy  .  voltammogram  o f Ru(OEP)(CO)EtOH  The c y c l i c  117 voltammogram  and 0 . 0 0 5 M T E A + C 1 " 4.3  The f o r m a t i o n of  Ru(0EP)(C0)  followed 4.4  of Ru(OEP)(C0)Et0H  i n 0.05M  TBAP  i n CH2C12  of Ru(0EP)+'(C0)  124 by e l e c t r o c h e m i c a l  i n 0.05M TBAP-CH2C12  oxidation  in a flow c e l l  and  spectroscopically  The o p t i c a l  126  spectra of the e l e c t r o c h e m i c a l l y prepared  cation  radicals 4.5  4.6  127  The o p t i c a l prepared  spectrum of the c a t i o n r a d i c a l  by t h e b r o m i n e  The i n c o m p l e t e oxidation change  111  i n 0.05M  TBAP-CH2C12 4.2  110  i n C H 2 C 1 2 o b t a i n e d on  an e x c e s s o f T E A + C 1 " t o a s o l u t i o n o f R u ( 0 E P ) ( C 0 )  The c y c l i c  104  i n C H 2 C 1 2 o b t a i n e d on  t o a s o l u t i o n o f Ru( OEP) ( C O ) , .  spectrum o f Ru(OEP)(C0)C1~  .  formation  oxidation  [Ru(0EP)+'(C0)Br]  o f Ru(0EP)(C0)  o f R u ( 0 E P ) + ' ( C 0 ) M e C N by  o f R u ( O E P ) ( C 0 ) M e C N i n MeCN a s f o l l o w e d  in optical  spectrum  135 bromine by t h e 137  XV  Page  4.7  The o p t i c a l spectrum in CH C1 2  of [Ru(0EP) '(C0)Br] prepared +  2  by the oxidation of Ru(0EP)(C0), and the spectrum of Ru(0Epf'(CO) obtained by adding AgBF^ to the bromide complex . . . . 4.8  The o p t i c a l spectrum of the cation r a d i c a l Ru(0EP)  144  (CS)py  +  prepared by the electrochemical oxidation of Ru(OEP)(CS)py in 0.05M TBAP-CH C1 2  5.1  147  2  The o p t i c a l spectra of the product ( R u ( 0 E P ) ( P B u ) ) i n  n  +  3  2  obtained on adding P B u to R u ( 0 E P ) '(C0) and the n  n  +  3  ruthenium( II)  species (Ru^( OEP) ( P B u ) ) formed on reducn  3  2  t i o n of t h i s product 5.2  156  The o p t i c a l spectra of the product ( R u ( 0 E P ) ( P P h ) ) I H  +  3  2  obtained on adding PPh to Ru (0EP) '(C0) and the r u t h e I]:  +  3  nium(II) species ( R u ( 0 E P ) ( P P h ) ) formed on reduction of II  3  2  t h i s product 5.3  157  The o p t i c a l spectrum of the product ( R u ( O E P ) ( A s P h ) ) n i  +  3  obtained on adding AsPh  to R u ( 0 E P ) ' ( C O ) and purging the JI  3  2  +  s o l u t i o n with argon, and the regeneration of a cation r a d i c a l species on purging with CO 5.4  The o p t i c a l spectrum of the product mixture obtained on adding excess SbPh  5.5  159  to Ru(0EP) '( CO) in CH C1  "161  +  3  2  2  The o p t i c a l spectrum of the product obtained on adding excess TEA CN" to a s o l u t i o n of Ru(0EP) "(CO) i n CH C1 +  +  2  2  . .  163  xvi  Page  5.6  The o p t i c a l spectrum of the mixture of products (P Bu ) n  3  + 2  (Ru*^(0EP)-:  and R u ( 0 E P ) ( P B u ) B r ) obtained on adding P B u In  n  n  3  to [Ru(0EP) '(C0)Br] in CH C1  3  172  +  2  5.7  2  The o p t i c a l spectra of the mixture of products (P Bu ) n  3  P Bu n  + 2  and R u ( 0 E P ) ( P B u ) p y ) obtained on adding H I  n  +  3  to R u ( 0 E P ) '(C0)py in CH C1 , and the ruthenium(II) H  3  (Ru***(0EP)-  +  2  2  species obtained on reducing t h i s product mixture 5.8  The o p t i c a l spectra Of the products obtained on adding an excess of P B u n  5.9  176  to Ru(0EP) *(C0)Im in CH C1  179  +  3  2  2  The o p t i c a l spectrum of the ruthenium(III) product obtained on adding PPh to a s o l u t i o n of Ru(0EP) '(C0)Im in CH C1 +  3  5.10  2  2  181  The o p t i c a l spectrum of the mixture of products formed on reducing the ruthenium(III) species obtained when PPh  3  (10" M) i s added to Ru(0EP) *(CO)Im, and the changes in 3  +  the o p t i c a l spectrum on the addition of excess P P h , and 3  excess Im, r e s p e c t i v e l y 5.11  182  Optical spectra i l l u s t r a t i n g the evidence for reduction on adding excess TEA Cl" to Ru(0EP) '(C0)py +  5.12  +  The product of the reaction of pyridine with the cation r a d i c a l species ZnTPP "  195  Zinc methoxyisoporphyrin  197  +  5.13  193  xv i i  Page  5.14  The o p t i c a l  spectrum o f t h e green p r o d u c t s formed on the  r e a c t i o n o f Ru(.0EP) "(C0)py w i t h excess T E A C 1 " +  6.1  C y c l i c voltammograms o f R u C 0 E P ) ( C 0 ) P B u H  TBAP-CH C1. 2  6.2  n  tial  2  i n 0.05M  i n 0.05M  n  3  i l l u s t r a t i n g the e f f e c t of holding the poten-  a t ^+0.7V f o r 20 seconds on t h e o x i d a t i o n sweep . . .  C y c l i c voltammograms o f R u TPATFS-CH C1 2  2  1 1  (OEP)(C0)P Bu n  3  208  i n 0.05M  showing t h e e f f e c t o f a change i n t h e  maximum)sweep p o t e n t i a l 6.4  200  204 1 1  2  3  . . . .  2  C y c l i c voltammogram o f R u ( O E P ) ( C 0 ) P B u TBAP-CH C1  6.3  +  210  C y c l i c voltammograms o f R u ( 0 E P ) ( C 0 ) P B u n  n  3  showing t h e  e f f e c t o f d i f f e r e n t e l e c t r o l y t e a n i o n s on t h e n a t u r e o f the voltammogram 6.5  212  C y c l i c voltammograms o f R u ( 0 E P ) ( C 0 ) P B u J I  n  3  in the  presence o f c o o r d i n a t i n g anions (0.001M TEA C1~) and i n +  a c o o r d i n a t i n g s o l v e n t (1:1 v/v CH Cl /MeCN) 2  6.6  C y c l i c voltammogram o f Ru (0EP)CC0)P Bu n  CH C1 2  6.7  2  n  n  2  C10 " 4  i n 0.05M TBAF215  C y c l i c voltammogram o f R u ( 0 E P ) ( C 0 ) P B u  Optical  3  a f t e r s t a n d i n g f o r ^30 minutes  TPATFS-CH C1 6.8;  213  2  2  n  3  i n 0.05M  s a t u r a t e d w i t h CO  spectrum o f a sample o f  215 [Ru (0EP)(P Bu )] i n  n  +  3  221  xviii  Page  6.9  The o p t i c a l  spectrum o f a sample o f R u ( 0 E P ) ( P B u ) n i  6.11  232 i n 0.05M TBAP-  i n t h e presence o f one e q u i v a l e n t o f A s P h  2  The c y c l i c voltammogram o f R u ( 0 E P ) ( P B u ) H  2  n  . . . .  2  241 spectra of R u ( 0 E P ) ( P B u ) H  n  3  2  and  Ru (0EP)I H  242  +  3  2  The o p t i c a l spectrum o f t h e d i c a t i o n s p e c i e s R u * * * ( 0 E P ) (P Bu )  +  7.4  2  The c y c l i c voltammogram o f R u ( 0 E P ) ( P B u ) I H  n  +  3  TBAP-CH C1 2  7.5  254  Ru (0EP)(.P Bu )L ; n  +  3  s p e c t r a o f the p r o d u c t s ( i . e .  L = P P h , MeCN, CN" and B r " ) 3  o b t a i n e d on a d d i t i o n o f Ligands (P Bu ) n  i n 0.05M  2  Representative optical i n  (L) to  Ru  T I I  (0EP)256  +  3  7.6  R e p r e s e n t a t i v e c y c l i c voltammograms of the p r o d u c t s ( i . e . Ru (0EP)(P Bu )L ; H I  n  +  3  a d d i t i o n o f Ligands 7.7  246  n  3  232  2  The o p t i c a l (P Bu )  3  i n 0.05M  n  3  TBAF-CH C1  7.3  im 0.05M TBAF-  2  H  2  7.2  3  C y c l i c voltammogram o f R u ( O E P ) ( C O ) E t O H CH C1  7.1  224  n  2  in  o f excess,CO  C y c l i c voltammogram o f R u ( 0 E P ) ( C 0 ) P P h CH C1  +  3  the presence and absence 6.10  n  L = P P h , MeCN and CN") o b t a i n e d on 3  (L) to R u ( 0 E P ) ( P B u ) I H  n  263  +  3  C y c l i c voltammograms o f R u ( 0 E P ) ( P B u ) B r H I  n  3  TBAP-CH^CN and 0.05M T B A P - C H C 1 9  9  i n 0.05M 270  xix  Page  7.8  The o p t i c a l spectrum of R u ( 0 E P ) ( P B u ) formed on the II  n  3  electrochemical reduction of R u ( 0 E P ) ( P B u ) i n  n  274  +  3  7.9  The o p t i c a l spectrum of the product obtained  (Ru^OEP)II  (P Bu )py) on addition of excess pyridine to Ru  (OEP)-  3  (P Bu )  276  n  3  7.10  The o p t i c a l spectrum of the product ( R u ( 0 E P ) ( P B u ) p y ) in  n  +  3  obtained by the addition of pyridine to R u ( 0 E P ) ( P B u ) II i n  n  +  3  and the ruthenium(II)  species (Ru  (OEP)(P Bu )py) formed 3  on the reduction of t h i s species 7.11  The c y c l i c voltammogram of R u ( 0 E P ) ( P P h )  in 0.05M  H  3  TBAF-CH C1 2  7.12  277 2  281  2  The o p t i c a l spectrum of R u ( O E P ) ( P P h )  in the presence  11  3  2  of excess PPh , and the o p t i c a l spectrum of the e l e c t r o 3  chemical oxidation product ( R u ( 0 E P ) ( P P h ) ) in the H I  +  3  presence and absence of excess PPh 7.13  I H  3  + 2  in CH C1 with CO 2  2  The c y c l i c voltammogram of R u ( 0 E P ) ( A s P h ) n  3  TBAP-CH C1 2  7.15  282  3  The o p t i c a l spectrum of the mixture obtained on purging a s o l u t i o n of R u ( 0 E P ) ( P P h )  7.14  2  2  . . .  284  in 0.05M 287  2  The o p t i c a l spectrum of R u ( 0 E P ) ( A s P h ) H I  3  + 2  and the  spectrum of the mixture of the products obtained on purging a s o l u t i o n of t h i s complex with CO  288  XX  Page 7.16  T h e e . s . r . s i g n a l o b t a i n e d on p u r g i n g  Ru** (0EP)(AsPh ) J  3  + 2  w i t h CO 7.17  292  The o p t i c a l s p e c t r u m o f t h e p o s s i b l e R u ( I V )  porphyrin  s p e c i e s f o r m e d on e l e c t r o c h e m i c a l l y o x i d i z i n g R u * * * ( 0 E P ) CCN) "  295  2  7.18  The o p t i c a l s p e c t r u m o f [ R u ( 0 ) ( 0 E P ) ' ] B r ~  8.1  The g r o u n d s t a t e , o p t i c a l s p e c t r a o f t h e c a t i o n r a d i c a l  I V  +  +  ;  296  s p e c i e s used i n the f l a s h p h o t o l y s i s experiments 8.2  The o p t i c a l s p e c t r u m o f t h e r u t h e n i u m ( I I I )  ....  303  porphyrin  s p e c i e s e x t r a c t e d f r o m t h e m i x t u r e o b t a i n e d on b u l k  photo-  l y s i s o f Ru(0EP) '(C0)py  307  +  8.3  The d i f f e r e n c e s p e c t r a o b t a i n e d a t v a r i o u s t i m e u s i n g 532 nm p h o t o l y s i s f l a s h e s f o r t h e  delays  Ru(0EP) '(C0)L +  cation radical species studied 8.4  The c h a n g e i n a b s o r p t i o n a t 635 nm w i t h t i m e on  308 photolysing  R u ( 0 E P ) ' ( C 0 ) and R u ( 0 E P ) ' ( C 0 ) p y , and t h e c h a n g e i n +  +  a b s o r p t i o n a t 655 nm w i t h t i m e on p h o t o l y s i n g [ R u ( O E P )  -  (CO)Br] 8.5  311  The d i f f e r e n c e s p e c t r a o b t a i n e d on t h e f l a s h p h o t o l y s i s o f R u ( 0 E P ) " ( C O ) w i t h 355 nm p h o t o l y s i n g r a d i a t i o n  313  +  8.6  The o p t i c a l s p e c t r a o f t h e t r a n s i e n t s t a t e s o b t a i n e d  on  p h o t o l y s i n g t h e c a t i o n r a d i c a l s p e c i e s a t 532 nm as  esti-  mated from the o b s e r v e d  difference spectra  316  xx i  Page  9.1  The proposed mechanism for electron transfer between the heme groups of two cytochromes via cation radical intermediates  331  xx i i  ABBREVIATIONS AND IDENTIFICATIONS OF COMPOUNDS  ABBREVIATIONS The  following  list  o f a b b r e v i a t i o n s , many o f which are commonly  adopted i n 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  A  absorbance  A  e l e c t r o l y t e anion  A  Angstrom u n i t  2  (10"^  thesis  metres)  2  A-|  and  u  A,,  the two p o s s i b l e  u  Tr-cation  2  *  A-|  2 and  u  A£  ground s t a t e s  o f a metalloporphyrin  radical  * u  the e x c i t e d s t a t e s  o f a metal l o p o r p h y r i n T r - c a t i o n  radical A£  a h i g h e r e x c i t e d s t a t e o f the  U  metal l o p o r p h y r i n T r - c a t i o n ADP  adenosine  diphosphate  ATP  adenosine  triphosphate  As(Mesityl) AsPh  trimesitylarsine  3  triphenylarsine  3  3  acac  a c e t y l a c e t o n a t e anion  BM  Bohr magneton  n  Bu  Bu^N  normal +  ( o r TBA ) +  butyl  broiad ( i n  C  concentration  3  (C^Hg-)  tetra-n-butylammonium  b  radical  (As(CgH-j-|) ) (As(CgHg)  nmr)  A2  cation  U  ground s t a t e o f a  it  XX  °C  degree  cm  T  Celsius  centimetre  cm"*  wave number  cyst.  cysteine  D.N.  d o n o r number ( G u t m a n n )  DMF  N , N ' - d i m e t h y i f o r m a m i d e , HC0NMe  DMSO  dimethylsulphoxide  d  doublet  E  half-wave potential or r e v e r s i b l e  1  (in  (CH ) S0 3  2  nmr)  p o t e n t i a l f o r an e l e c t r o d e E-|  reduction  process  the half-wave p o t e n t i a l f o r the f i r s t process  E  2  electrode  o b s e r v e d on a v o l t a m m o g r a m  the half-wave p o t e n t i a l f o r the second  2  process Ep  electrode  o b s e r v e d on a v o l t a m m o g r a m  t h e peak p o t e n t i a l f o r t h e a n o d i c  (oxidizing)  process Ep  t h e peak p o t e n t i a l f o r t h e c a t h o d i c  (reducing)  process E'  standard  Q  reduction  p o t e n t i a l f o r IM s o l u t i o n s  o x i d i z e d and r e d u c e d s p e c i e s a t a pH o f 7 logical Et  ethyl  Et^N  pH) (C H ~) 2  5  triethylamine  Et.N , (or TEA ) +  +  tetraethylammonium  cation  of physio-  ;  •  xxi v  e  electron  e.s.r.  electron spin resonance  eq  equivalent  eV  electron volt  G  gausse  g  gram, o r e . s . r .  g-value  average g-value  (e.s.r.)  g  a v  Hb  hemoglobin  Hz  herz  h  hour  hv  l i g h t energy (Plank's constant x  I  i n t e n s i t y o f an a b s o r p t i o n ( w a v e l e n g t h a b s o r p t i o n i n nm may  I  Q  frequency)  be i n d i c a t e d by  of subscript)  i n t e n s i t y o f an a b s o r p t i o n b e f o r e t h e a d d i t i o n o f a 1 i gand  1^  i n t e n s i t y o f the a b s o r p t i o n a f t e r l i g a n d a d d i t i o n (excess l i g a n d  present)  I  n u c l e a r s p i n number  I.R.  infra-red  IMET  intramolecular electron transfer  I PA  isopropanol  Im  imidazol  Ip  t h e peak c u r r e n t f o r t h e a n o d i c  1*1  t h e peak c u r r e n t f o r t h e c a t h o d i c ( r e d u c i n g )  (oxidizing)  process process  XXV  K  degree K e l v i n , o r e q u i l i b r i u m  k  kinetic rate constant o r conductivity cell  Kcal  kilocalories  L  1 i t r e , or 1igand  L, l _ i , o r l _  constant  axial ligands to a metalloporphyrin  2  constant  complex  M  molar  M.C.D.  magnetic c i r c u l a r  M/e  r a t i o o f mass t o c h a r g e ( i n . m a s s s p e c t r o m e t r y )  Mb  myoglobin  Me  methyl  MeCN  acetonitrile  MeOH  methanol  4Mepy  4-methylpyridine  MgOEP  magnesium  MgOEP  c a t i o n r a d i c a l o f magnesium  Mol . w t .  molecular  m  m e t r e , o r m u l t i p l e t ( i n nmr)  m-H  meta-hydrogen (on a phenyl  mg  (CHg-)  octaethylporphyrin  milligram r e c i p r o c a l ohm  mins  minutes  mJ  mi H i j o u l e  mL  mill il itre  mm  millimetre ,  mole  octaethylporphyrin  weight  mho  mol  dichroism  ring)  xxvi  mV  millivolt  NADH  the reduced form o f n i c o t i n a m i d e  adenine  d i n u c l e o t i d e , the o x i d i z e d form i s NADP  NAD  +  the reduced form o f n i c o t i n a m i d e adenine d i n u c l e o ti.de d i p h o s p h a t e , the o x i d i z e d form i s  n  an  nm  nanometre (.10"^ metre)  nmr  n u c l e a r magnetic  resonance  ns  nanosecond  seconds)  OEP  octaethylporphyrin  (OEP)  NADP  +  integer  (10  cation radical  of octaethylporphyrin  2+.  (OEP)  di-cation  radical  (formed by the removal o f two  e l e c t r o n s from the p o r p h y r i n ) OMA  optical  0-H  ortho-hydrogen  P..  inorganic  P Bu  3  P(cyclohexyl ) P(0Me)  3  3  phosphate  Ph  )  4  P(C H ) 4  g  3  t r i c y c l o h e x y l phosphine PCCgH-j ^) 3 t r i m e t h y l phosphite  phenyl  (.C H -) g  5  Ph P0  triphenylphosphine  Pr  n-propyl  3  p-H  (P0  ring)  triphenylphosphine  3  Pr^N  analyser  (on a phenyl  tri-n-butylphosphine  n  PPh  multichannel  of  ( o r TPA )  oxide  (C^-)  tetra-n-propylammonium para-hydrogen  cation  (on a phenyl  ring)  octaethylporphyrin  xxv i i  pH  -1og [H ]  pKa  -log Ka  +  1 0  1 Q  -12  ps  picosecond (10  py  p y r i d i n e CCgHgN)  q  quartet (in  R  resistance  Ref.  reference  Ru(0EP)L-|l-2  general  seconds)  nmr)  formula f o r a s i x - c o o r d i n a t e  o c t a e t h y l p o r p h y r i n complex. o f the metal  is  If  ruthenium  the o x i d a t i o n  not i n d i c a t e d i t  is  state  assumed to be  Ru(II). S  solvent  SHE  standard  SbPhg  triphenylstibine  s  second, or s i n g l e t  sat.  saturated  TBA  +  o r Bu^N  +  hydrogen e l e c t r o d e  (in  tetra-n-butylammonium  nmr)  cation  TBAF  tetra-n-butylammonium t e t r a f l u o r o b o r a t e  TBAH  tetra-n-butylammonium hexafluorophosphate  TBAP  tetra-n-butylammonium  TEA  +  or Et^N  +  tetraethylammonium  perchlorate  (Bu N BF ~) +  4  (Bu N PFg~) +  4  (Bu^dO^ ) -  cation  TEAP  tetraethylammonium p e r c h l o r a t e  TEAPIC  tetraethylammonium pi c r a t e  THF  tetrahydrofuran  4  (Et N C10 ~) +  4  4  (.Et^l^C^N^Oy ) -  xxvii i  TMP  tetramesitylporphyrin  TMS  tetramethylsi lane  TPA or Pr^N +  +  tetra-n-propylammonium c a t i o n  TPAF  tetra-n-propylammonium fluoroborate  TPATFS  tetra-n-propylammonium  TPP  trifluoromethanesulphonate  meso-tetraphenylporphyrin  t  triplet (in  nmr)  u.v.  ultra-violet  V  volts  v  volume  ZnTPP  zinc tetraphenyl porphyrin  ZnTPP  cation radical of zinc tetraphenylporphyrin  a  the p r i n c i p l e v i s i b l e absorption (lower energy) o f a m e t a l l o p o r p h y r i n , o r t h e c a r b o n atoms i n a p y r r o l e or p y r i d i n e r i n g  felosest  to the n i t r o g e n  atom 6  the p r i n c i p l e v i s i b l e absorption (higher energy) o f a m e t a l l o p o r p h y r i n , o r t h e c a r b o n atoms i n a p y r r o l e o r p y r i d i n e r i n g one c a r b o n atom r e m o v e d from t h e n i t r o g e n atom  Y  the p r i n c i p l e near-u.v.  a b s o r p t i o n (Soreti) o f a  metal 1 o p o r p h y r i n , o r t h e carbon atom i n a p y r i d i n e r i n g two c a r b o n a t o m s r e m o v e d f r o m t h e n i t r o g e n atom AA  change i n  absorbance  xxix  AG  change in Gibbs free energy  AGQ  the standard change in Gibbs free energy for one molar solutions of the species concerned at a pH of 7  physiological pH)  nmr scale; TMS (tetramethyl silanei) i s defined as 0.0 parts per m i l l i o n e  molar extinction c o e f f i c i e n t  A  molar conductivity  A  m a x  wavelength of a p r i n c i p l e absorption peak  yL  microlitre  u  magnetic moment, or bonding involving the overlap of transition metal d-orbitals  y/ii  0  nuclear magnetic moment r e l a t i v e to that of a hydrogen nucleus  v  C Q  77  carbonyl stretching frequency bonding where electron density i s on either side of the i n t e m u c l e a r plane  a  bonding where electron density i s a maximum on the internuclear axis  Q  ohms  (j>  quantum y i e l d approximately  >  greater than  >>  much greater than  XXX  less  than  much 1 ess than  IDENTIFICATION OF COMPOUNDS The f o l l o w i n g numbering system w i l l r e f e r r e d to in t h i s 1  be used f o r the compounds  thesis  Ru(0EP)(C0)  la.  Ru(OEP)(CO)EtOH  3  Ru(0EP)C0)py  4  Ru(0EP)CC0)4Mepy  5  '(C0)  +  ib  [Ru(OEP) *(CO)Br]  ic  [Ru(0EP) ' ( C 0 ) C l ]  Id 2  Ru(0EP)  +  +  [Ru(0EP) *(C0)SCN] +  3a  Ru(0EP) '(C0)py  Ru(0EP)(C0)Im  5_a  Ru(0EP) '(C0)Im  6  Ru(0EP)(C0)MeCN  6a  Ru(0EP) '(C0)MeCN  7  Ru(0EP)(.P Bu )  8a  Ru(0EP) '(C0)P Bu  8b  Ru(0EP) '(C0)P Bu  8c  Ru  11a  Ru(0EP) '(C0)PPh.  8  9^ 1P_  +  +  +  n  3  2  Ru(0EP)(C0)P Bu n  3  +  n  2 +  n i  (0EP)  n  2 +  III Ru (OEP)(P Bu )Br n  3  11  Ru(0EP)(C0)PPh  12  Ru(.0EP).(PPh ) 3  2  3  +  3  '(C0)P Bu  See below i U  3  n  3  xxx i  u ii  Ru(0EP)(AsPh ) 3  [Ru  I I I  2  (0EP)(CN) l~Et N 2  11  Ru C0EP)(PPh )  16.  Ru (0EP)(AsPh )  2  17  Ru (0EP)(SbPh )  2  n i  3  + 2  i n  +  3  I n  +  3  Ru (0EP)(P Bu ) I n  +  4  n  18a  +  3  18b i i  Ru(0EP)(C0)AsPh  20  Ru (0EP)(AsPh )Br  ii  Ru (0EP)(PPh )Br  22  Ru C0EP) "(P Bu )  23  Ru(0EP)(P Bu )  19a  3  i n  3  H I  3  n i  +  n  3  2  n  3  2 4 , 26. a nd 28  see below  25  Ru(0EP)(P Bu )MeCN  27.  Ru(0EP)(.P Bu )py  29  Ru(0EP)(P Bu )PPh  n  3  n  3  n  3  30 - 32_  3  see below  33  Ru (0EP)(P Bu )CN  34  Ru (0EP)(.P Bu )Cl  H I  n  3  n i  n  3  R u ( 0 E P ) '(P Bu ) m  +  n  3  Ru (0EP) '(P Bu ) I n  2 +  n  3  Ru(0EP) *(C0)AsPh +  3  xxx i i  Some o f the f o l l o w i n g TTT Ru  r»  (0EP)(P B u ) L were prepared with a bromide c o - a n i o n as well as 3  c o - a n i o n s such as C l O ^ " . number i s  9  s i x - c o o r d i n a t e complexes o f the type  C0EP)(.P Bu n  Ru  I ]  26  Ru  I ]  28  Ru  I ]  30  Ru  I ]  l i  Ru  1 1  32  Ru  1 1  35  Ru  1 1  the complex i s a s s o c i a t e d w i t h C I ,  f o l l o w e d by " a " and i f a s s o c i a t e d with B r " a " b "  Ru  i i  If  I  3  , + '2  ( 0 E P ) ( P B u , MeCN n  +  3  I  I  (0EP)(P Bu n  3  P  y  +  (0EP)(P Bu )PPh n  3  I  I  (0EP)(P Bu n  3 j  + 3  MeOH  (0EP)(P Bu ' AsPh  3  (0EP)(P Bu ; SbPh  3  n  3  I  +  n  3  I  +  (0EP)(P Bu ] lm n  3  +  +  is  used.  inert the  xxxi i i  ACKNOWLEDGEMENTS  I wish e s p e c i a l l y to thank my supervisors, Professors David Dolphin and Brian James, f o r t h e i r , help and encouragement]in the w r i t i n g of t h i s thesis.  I/would l i k e to thank many coworkers, both past and present, f o r  helpful discussions and comments.  In p a r t i c u l a r I would l i k e to express my  gratitude to Dr. G. B i s s e t f o r useful suggestions on chromatography, Mr. P.S. P h i l l i p s f o r information on obtaining e . s . r . s p e c t r a , and Dr. T. Leung f o r many discussions on the chemistry of ruthenium porphyrin systems.  Thanks are due to Dr. T. Leung and Professor R.C. Thompson f o r  the magnetic moment determinations.  I also acknowledge the help of  Dr. G. Domazetis and Professors J.Y. Becker, and D. Hoi t e n , with whorm I collaborated on some of the work described in t h i s t h e s i s . My thanks to T i l l y Schreinders for her e x c e l l e n t typing of t h i s manuscri p t . A teaching a s s i s t a n t s h i p from the U n i v e r s i t y of B r i t i s h Columbia (1977-83) i s g r a t e f u l l y acknowledged.  1  CHAPTER 1  ^ •  1.1  INTRODUCTION  l  Porphyrins in Nature A l l porphyrins can be considered to be d e r i v a t i v e s of the parent  compound porphin (Figure 1.1).  This i s a t e t r a p y r r o T i c macrocycle with  continuous conjugation throughout the r i n g . t h i s ring involve 18 TT e l e c t r o n s .  A number of paths  through  Molecular o r b i t a l theory has shown that  c y c l i c species involving 4n+2 TT electrons (n = 1, 2, 3, 4 e t c . ) in a conjugated pathway show considerable s t a b i l i z a t i o n and a v a r i e t y of properties usually l a b e l l e d "aromatic".  Porphin d e r i v a t i v e s show the predicted  s t a b i l i z a t i o n (n = 4) and aromatic p r o p e r t i e s .  This ring i s also a strong  tetra-dentate ligand e a s i l y coordinating to metal ions to form m e t a l l o porphin (porphyrin)  derivatives.  Metalloporphyrins are widely dispersed in nature.  The best known  examples are hemoglobin, and the electron transfer proteins known as the cytochromes.  The green plant pigment chlorophyll is also c l o s e l y related  to the porphyrins. Porphyrins are c l a s s i f i e d by the substituents on the periphery of the porphin core.  A wide range of porphyrins can be synthesized in the l a b o r a -  tory but rather fewer are found in nature. natural systems i s protoporphyrin IX.  The porphyrin found in many  This, l i k e a l l porphyrins, i s a  good ligand and combines with i r o n ( I I ) ions to give a metalloporphyrin known as "heme".  This metalloporphyrin i s the prosthetic group found in some of  the cytochromes as well as hemoglobin, myoglobin and enzymes such as catalase and horseradish peroxidase (Figure  1.2).  2  The p r o t e i n s , c o n t a i n i n g i r o n p o r p h y r i n s be d i v i d e d i n t o t h r e e c a t e g o r i e s .  a t t h e i r a c t i v e s i t e , can  The f i r s t c a t e g o r y c o n t a i n s  p r o t e i n s which r e v e r s i b l y bind oxygen.  These a r e oxygen  p r o t e i n s such as hemoglobin and m y o g l o b i n .  those  transport  The second c a t e g o r y  o f p r o t e i n s t h a t a r e i n c a p a b l e o f b i n d i n g oxygen or o t h e r small but are c a p a b l e o f undergoing  consists molecules  r e v e r s i b l e o x i d a t i o n and r e d u c t i o n r e a c t i o n s .  These a r e e l e c t r o n t r a n s f e r p r o t e i n s and i n c l u d e most o f the  cytochromes.  The t h i r d c a t e g o r y i n c l u d e s those complexes c a p a b l e o f b i n d i n g oxygen and a l s o r e d u c i n g i t by t r a n s f e r o f e l e c t r o n s . incorporates  Hence t h i s t h i r d  both the p r e v i o u s l y mentioned f u n c t i o n s .  Examples  class are  cytochrome - P450, which d e t o x i f i e s f a t - s o l u b l e c h e m i c a l s by i n s e r t i n g an oxygen atom i n t o an u n a c t i v a t e d carbon-hydrogen  bond thus making the  compound more water s o l u b l e , and t h e t e r m i n a l e l e c t r o n a c c e p t o r o f the e l e c t r o n t r a n s p o r t c h a i n i n a e r o b i c r e s p i r a t i o n c a l l e d cytochrome which t r a n s f e r s  the e l e c t r o n s from the p o r p h y r i n s  e v e n t u a l l y reducing i t to water.  oxygen,  R e l a t e d complexes t o t h i s t h i r d  a r e the enzymes c a t a l a s e and h o r s e r a d i s h ions r a t h e r than  to c o o r d i n a t e d  c-oxidase,  class  p e r o x i d a s e which bind p e r o x i d e  oxygen.  These d i f f e r e n c e s i n f u n c t i o n are b e l i e v e d t o be determined by variations  i n the environment o f the heme p r o s t h e t i c group.  group i s surrounded  The heme  by the p r o t e i n apoenzyme and i n most cases i s  p l a c e by m e t a l - l i g a n d i n t e r a c t i o n s .  For t h e c e n t r a l i r o n ( I I ) i o n ,  e n e r g e t i c a l l y favoured d i s p o s i t i o n of ligands  held in the  is usually octahedral.  The p o r p h y r i n i s a p l a n a r t e t r a - d e n t a t e l i g a n d which o c c u p i e s f o u r  ligand  s i t e s l e a v i n g the two a x i a l p o s i t i o n s a v a i l a b l e f o r c o o r d i n a t i o n ( F i g u r e  1.3).  3  F i g u r e 1.1  Porphin  F i g u r e 1.2  Protoporphyrin  IX,  from Ref. 5 ) .  F i g u r e 1.3  The s t r u c t u r e o f a s i x - c o o H dinate iron(.II) porphyrin complex. The p o r p h y r i n i s r e p r e s e n t e d by t h e f o u r n i t r o g e n atoms i n a plane and the a x i a l l i g a n d s a r e denoted by ' X ' .  (modified  4  These two p o s i t i o n s  are o c c u p i e d by a m i n o - a c i d r e s i d u e s which  determine the f u n c t i o n o f the heme p r o t e i n . and m y o g l o b i n , one a x i a l  position  the o t h e r a x i a l  i s vacant a l l o w i n g  position  NO and CO) to bind to the i r o n . is  is  In  the case o f  hemoglobin  occupied by a h i s t i d i n e small  molecules  largely  ligand  and  (such as  The c o o r d i n a t i o n o f these small  O^,  molecules  u s u a l l y r e v e r s i b l e and, f o r example with 0 £ , no permanent o x i d a t i o n  the i r o n atom o c c u r s .  In  the case of e l e c t r o n t r a n s p o r t  show no r e a c t i v i t y towards are c o o r d i n a t e d s t r o n g l y oxygen m o l e c u l e .  small molecules or i o n s ,  p r o t e i n s , which  the two a x i a l  to the heme hence b l o c k i n g the access  The complexes t h a t  ligands  o f the  show oxygen b i n d i n g coupled with  subsequent e l e c t r o n t r a n s f e r to the oxygen have a s t r u c t u r e s i m i l a r t h a t o f the oxygen t r a n s p o r t  of  proteins,  but the a x i a l  to the i r o n , and the amino a c i d r e s i d u e s  surrounding  ligand  to  coordinated  the heme group,  differ  so as to s t a b i l i z e i n t e r m e d i a t e s formed in the o x i d a t i o n and r e d u c t i o n o f the complex.  1.2  E l e c t r o n T r a n s p o r t and the Cytochromes Introduction  o f glucose  to the cytochromes:  to carbon d i o x i d e and water i s  a double membrane s t r u c t u r e c a l l e d  In  Keilin  2  a mitochondrion. tissue  the  oxidation  organelle  These o r g a n e l l e s such as muscle.  s t u d i e d i n t a c t i n s e c t muscles w i t h a small  i d e n t i f i e d a number o f a b s o r p t i o n proteins.  cell  l i n k e d to a small  p a r t i c u l a r l y d e n s e l y packed i n hard working 1925  the l i v i n g  with are  In  s p e c t r o s c o p e and  peaks resembling those o f reduced hejne  These were the " H i s t o h e m a t i n s "  observed by  but i t was K e i l i n who showed t h a t the a b s o r p t i o n s  MacMunn i n 1888  were r e l a t e d to muscular  5  a c t i v i t y a n d renamed  t h e pigments "cytochromes".  t h r e e m a i n a b s o r p t i o n bands i n t h e v i s i b l e .  The cytochromes  The most i n t e n s e , and t h e  a b s o r p t i o n f u r t h e s t t o t h e b l u e end o f t h e s p e c t r u m , i s o r y band.  have  c a l l e d the Soret  T h e two w e a k e r b a n d s a r e l a b e l l e d . a a n d $. T h e w a v e l e n g t h a t  which t h e s e bands o c c u r g i v e s c o n s i d e r a b l e i n f o r m a t i o n on t h e n a t u r e o f the m e t a l l o p o r p h y r i n  ( F i g u r e 1 . 4 ) . Thus K e i l i n r e a l i z e d t h a t t h e f o u r  a b s o r p t i o n b a n d s w e r e d u e t o t h r e e d i f f e r e n t p i g m e n t s w h i c h he c l a s s i f i e d a s t y p e s a , b o r c d e p e n d i n g upon t h e w a v e l e n g t h o f t h e i r a b s o r p t i o n s . L a t e r s t u d i e s showed t h a t t h e d i f f e r e n c e i n s p e c t r a l a b s o r p t i o n was d u e t o m o d i f i c a t i o n o f t h e heme g r o u p a t t h e a c t i v e s i t e o f t h e p r o t e i n . The p r o s t h e t i c g r o u p was e i t h e r p r o t o h e m e to t h e p r o t e i n , o r a m o d i f i e d protoheme  o r protoheme c o v a l e n t l y l i n k e d known a s "Heme a " ( F i g u r e 1 . 5 ) .  T h e c y t o c h r o m e s a r e now c l a s s i f i e d a c c o r d i n g t o t h e f o l l o w i n g  scheme:- ' 4  5  ( T h e q u o t e d a b s o r p t i o n b a n d s a r e f o r t h e a band o f t h e p y r i d i n e a d d u c t o f t h e heme t y p e g r o u p i n t h e i r o n ( I I ) o x i d a t i o n s t a t e u n d e r a l k a l i n e c o n d i tions) .  1)  C y t o c h r o m e s a : ( 5 8 0 - 590 nm).  the p o r p h y r i n component  T h e p r o s t h e t i c g r o u p i s "Heme a " ,  o f which i s s i m i l a r t o protoporphyrin  IX e x c e p t f o r  the a d d i t i o n o f a l o n g carbon c h a i n and an a l d e h y d e group t o t h e p o r p h y r i n peri phery.  2)  C y t o c h r o m e s b : ( 5 5 6 - 558 nm).  T h e p r o s t h e t i c g r o u p i s heme  ( i r o n ( l l ) complex o f p r o t o p o r p h y r i n IX) and i s o n l y d i r e c t l y l i n k e d t o t h e protein v i a ligand-metal interactions.  300  1  r  400  500  600  WAVELENGTH (nm) F i g u r e 1.4  T h e o p t i c a l s p e c t r u m o f t h e r e d u c e d f o r m o f c y t o c h r o m e c ( 1 . 0 cm p a t h l e n g t h c e l l , 1 x 1 0 " M s o l u t i o n i n H2O, pH = 7.0) i l l u s t r a t i n g the main f e a t u r e s o f a m e t a l l o p o r p h y r i n spectrum ( s e e t e x t ) . From R e f . 1. 5  3)  C y t o c h r o m e s c : ( 5 4 9 - 551 nm).  The p r o s t h e t i c group i s a l s o  heme b u t t h e p o r p h y r i n i s c o v a l e n t l y l i n k e d by t h i o - e t h e r l i n k a g e s t o t h e surrounding molecule  p r o t e i n v i a t h e v i n y l groups on one edge o f t h e p r o t o p o r p h y r i n  (Figure 1.5).  A l l three types o f cytochrome a r e found i n t h e e l e c t r o n t r a n s p o r t c h a i n a s s o c i a t e d w i t h o b t a i n i n g e n e r g y f o r t h e c e l l from t h e o x i d a t i o n o f glucose.  The cytochromes a r e l i n e d a c r o s s t h e i n n e r m i t o c h o n d r i a l  membrane  IX  7  F i g u r e 1.5  The s t r u c t u r e s o f the i r o n p o r p h y r i n complexes found i n cytochromes o f c l a s s a and c . a) Heme a ; two p o s s i b l e s t r u c t u r e s of the long carbon c h a i n a r e shown on the r i g h t , b) Heme c in which heme i s c o v a l e n t l y l i n k e d to the p r o t e i n c h a i n , p a r t o f which i s a l s o shown. Both diagrams m o d i f i e d from Ref. 5.  8  in order of increasing ease of reduction, which can be measured by a reduction potential for the cytochrome.  In b i o l o g i c a l systems t h i s  quantity i s usually c a l l e d EQ which i s the standard reduction potential for IM solutions of the oxidized and reduced species at a pH of 7 ('v physiological pH) .  Hence a more negative EQ value for a cytochrome  means that the oxidized species i s more d i f f i c u l t to reduce but that once reduced the species i s a stronger reducing agent.  Hence the standard  reducing coenzymes (NADH and NADPH) found in the l i v i n g c e l l have a strongly negative E" ' value Q  -0.32 v o l t s for a two electron t r a n s f e r  with respect to the Standard Hydrogen E l e c t r o d e ) .  As the cytochromes are  to receive electrons from these reducing agents,their reduction p o t e n t i a l s aremore p o s i t i v e than those of the coenzymes.  In a l l cases a member of  the electron transport chain receives an e l e c t r o n from a member with a more negative E^  potential and then passes the electron to a species with  a more p o s i t i v e E^  p o t e n t i a l , u n t i l f i n a l l y the electron is used to  reduce oxygen, the terminal electron acceptor (Table  1.1).  Cytochromes are widely involved in the redox reactions occurring in the l i v i n g c e l l s . of the c e l l .  Some soluble cytochromes are found in the cytoplasm  The most biochemically s i g n i f i c a n t uses of cytochromes are  found in the energy-related, membrane-bound, electron transport chains of the mitochondria ( r e s p i r a t i o n ) and the chloroplasts (photosynthesis).  The  mitochondrial transport chain i s the better understood of these two and w i l l be discussed here, though the photosynthetic system has many s i m i l a rities .  9  T a b l e 1.1  Cytochrome  Mol . w t .  '(.V)  —  A b s o r p t i o n maxima i n r e d u c e d  form,  a  3  Y  25,000  +0..030  563  532  429  37,000  +0,.225  554  524  418  c  12,500  +0,.235  550  521  415  a  200,000  +0 .210  600  -  439  +0 .385  603.5  -  443  b c  a  a)  P r o p e r t i e s o f M i t o c h o n d r i a l Cytochromes  l  3  From R e f . 1.  In t h e p r o c e s s o f a e r o b i c r e s p i r a t i o n , g l u c o s e i s c o n v e r t e d t o carbon d i o x i d e i n a p r o c e s s d e s c r i b e d by t h e Krebs ( o r t h e t r i c a r b o x y l i c acid) c y c l e , which occurs i n the inner matrix o f the mitochondria.  In  t h e p r o c e s s a c e r t a i n amount o f r e d u c i n g power i n t h e form o f e l e c t r o n s i s f o r m e d a n d t h e s e a r e p i c k e d up by t h e e l e c t r o n a c c e p t o r c o - e n z y m e g r o u p s u s e d by a number o f enzymes i n r e d o x r e a c t i o n s i n t h e c e l l .  Such  c o - e n z y m e g r o u p s i n c l u d e a number o f f l a v o - p r o t e i n s as w e l l a s t h e enzyme p r o s t h e t i c group n i c o t i n a m i d e adenine d i n u c l e o t i d e (NAD).  The reduced  c o - e n z y m e g r o u p s move t o t h e i n n e r m i t o c h o n d r i a l membrane a n d t r a n s f e r the e l e c t r o n s t o a c c e p t o r s which then feed t h e e l e c t r o n s i n t o t h e t o p o f  nm.  10  the t r a n s p o r t c h a i n . sulphur  The e l e c t r o n s are used f i r s t  to reduce an i r o n -  p r o t e i n or u b i q u i n o n e , both o f which are non-heme redox p r o t e i n s ,  and are then passed on down the chain through v a r i o u s the l a s t complex (cytochrome oxidase)  cytochromes u n t i l  uses the e l e c t r o n s to reduce oxygen  to water ( F i g u r e 1.6). The purpose o f t h i s r a t h e r complicated mechanism i s t h a t i t the c e l l glucose.  to harness  allows  some o f the energy produced from the o x i d a t i o n o f  T h i s energy i n i t i a l l y r e s i d e s  i n the r e d u c i n g power o f the  e l e c t r o n s r e l e a s e d i n the Krebs c y c l e t h a t a r e used to reduce NAD to +  NADH which i s i t s e l f a strong r e d u c i n g agent + 2e*=iNADH).  Oxygen i s a strong  *-*  (E  q  =-0.32  +  f o r NAD  o x i d i z i n g agent a t pH 7, ( E  +  = +0.816V  0  f o r % 0 + 2 H + 2 e ~ * = ± H 0 ) , and hence oxygen and NADH would r e a c t +  2  +H  2  together  very r e a d i l y with r e l e a s e o f c o n s i d e r a b l e energy ( A E " = +1.136V,so f r e e 0  energy change = - 5 2 . 7 kcal mol However, the e l e c t r o n : gradually  - 1  )  which would normally be wasted.  on moving down the t r a n s p o r t chain l o s e s  f r e e energy  and where t h e r e i s a s u f f i c i e n t f r e e energy drop between two  a d j a c e n t e l e c t r o n : c a r r i e r s the e l e c t r o n t r a n s f e r i s l i n k e d to the phosphor y l a t i o n o f ADP ( A G Q ATP which i s a general cell.  = +7.3 kcal m o l "  1  f o r ADP + P = ^ A T P + H 0) to g i v e i?  2  source o f energy f o r biochemical r e a c t i o n s  The approximate p o s i t i o n s  o f ADP p h o s p h o r y l a t i o n s  F i g u r e 1.6 and the c o r r e s p o n d i n g f r e e energy changes  i n the  a r e seen i n  i n F i g u r e 1.7.  Cytochromes o f the " b " c l a s s These cytochromes,widespread i n n a t u r e , c o n t a i n a heme group i n place by 1igand-metal  held  i n t e r a c t i o n s and s e c u r e l y wrapped i n the p r o t e i n  Site I  Site II  ATP  ATP  N A D — * FP,(4Fe.S)—i»Q — » • (2Fe.S)  Figure 1.6  I  Site III ATP  *-cyt b(Fe.S)cyt ci—»-cyt c—*-cyt a<u  The m i t o c h o n d r i a l e l e c t r o n t r a n s p o r t c h a i n . E l e c t r o n s e n t e r the chain a t the p o s i t i o n s i n d i c a t e d by a r r o w s . FP i s a f l a v o p r o t e i n known as NAD Dehydrogenase, Fe S r e p r e s e n t s an i r o n - s u l p h u r p r o t e i n and Q i s u b i q u i n o n e . The o t h e r a b b r e v i a t i o n s have t h e i r usual meanings. M o d i f i e d from R e f . 1.  12  E'o kcal  O,  Figure 1.7  The decline in free energy as e l e c t r o n pairs flow down the mitochondrial transport chain to oxygen. Energy changes denoted by arrows are s u f f i c i e n t to y i e l d a mole of ATP from ADP and phosphate. Q represents ubiquinone and b, c , and a represent the corresponding cytochromes. Modified from Ref. 1.  component of the enzyme (apoenzyme ) . 6  They are found in the cytoplasm  of the c e l l as well as membrane-bound i n both of the major electron transport chains. Research on the mitochondrial cytochrome b species has been very l i m i t e d because of the great d i f f i c u l t i e s in e x t r a c t i n g i n t a c t e n z y m e ' . 8  9  Cytochrome b in the mitochondrial membrane i s believed to form a complex with cytochrome c-, , and l i e s deeply embedded in the inner membrane and 1  13  r e q u i r e s severe c o n d i t i o n s i n c l u d i n g the use o f d e t e r g e n t s t o remove i t . Because o f the m o d i f i c a t i o n s  t h a t can o c c u r when u s i n g such severe  proce-  d u r e s , a n a l y s e s o f p r e p a r a t i o n s can v a r y w i d e l y t and c o n s i d e r a b l e debate i s c o n t i n u i n g as to whether t h e r e i s o n l y one cytochrome b i n m i t o c h o n d r i a from a s i n g l e source o r whether t h e r e are a number o f d i f f e r e n t cytochromes b present in a given  membrane^ ' . 0  1 1  L i t t l e i s known g e n e r a l l y about t h e heme environment i n t h e s e membrane bound cytochromes  b.  However,a hydrophobic p r o t e i n sheath wraps  the heme group and the i n t e g r i t y o f t h i s environment seems e s s e n t i a l the o p e r a t i o n o f the c y t o c h r o m e , as seen by the e f f e c t o f 1 2  for  processes  (such as h e a t i n g ) which d i s r u p t t h i s e n v i r o n m e n t , and s h i f t t h e i n - s i t u r e d u c t i o n p o t e n t i a l by up to 300 m V  1 2 - 1 4  .  In an attempt t o r e a c h some t e n t a t i v e c o n c l u s i o n s about the s t r u c t u r e s and f u n c t i o n o f the m i t o c h o n d r i a l cytochrome b s p e c i e s a n o t h e r t y p e o f cytochrome b, found i n the endoplasmic r e t i c u l u m o f mammalian  cells,  has been c r y s t a l l i z e d and a s t r u c t u r e o b t a i n e d . T h i s i s cytochrome 1 5  and the form found i n c a l f l i v e r has been i n t e n s i v e l y s t u d i e d .  b^,  The normal  b i o c h e m i c a l f u n c t i o n o f t h i s p r o t e i n i s to a c t as an e l e c t r o n t r a n s p o r t agent i n a t h r e e membered enzyme system used t o d e s a t u r a t e f a t t y  acids  1 5  The p r o t e i n i s bound t o the membranes o f the endoplasmic r e t i c u l u m but  .  is  e a s i l y r e m o v e d ' , and c o n t a i n s a p o l y p e p t i d e o f 93 a m i n o - a c i d s and a 1 6  1 7  J. 8 n o n - c o v a l e n t l y bonded heme group. analysis  1 9 - 2 1  C r y s t a l s have been o b t a i n e d  showed the m o l e c u l e to be a p p r o x i m a t e l y c y l i n d r i c a l  h e i g h t o f 37 & and a diameter o f 31 &  (Figure 1.8).  and  X-ray  with a  The heme group i s  14  Figure 1.8  S c h e m a t i c diagram o f t h e backbone c h a i n o f cytochrome b^. The a - c a r b o n p o s i t i o n s a r e numbered i n s e q u e n c e a n d r e p r e s e n t e d by c i r c l e s whose s i z e s i n d i c a t e t h e i r r e l a t i v e d e p t h . M o d i f i e d from Ref. 19.  15  almost completely  buried i n a hydrophobic pocket a t the top o f the molecule  Two r i g i d l y p o s i t i o n e d h i s t i d i n e g r o u p s f o r m t h e a x i a l l i g a n d s t o t h e heme group. solvent  One e d g e o f t h e p o r p h y r i n 2 2  core i s s l i g h t l y exposed t o t h e e x t e r i o r  s o t h a t e l e c t r o n t r a n s f e r may o c c u r v i a t h i s heme e d g e ;  to the other partners  i n t h i s enzyme s y s t e m p o s s i b l y o p e n s up t h e heme  c r e v i c e a l 1 o w i n g m o r e o f t h e heme e d g e t o become e x p o s e d .  The b type  1 5  cytochromes found i n the mitochondrial lar  binding  membrane a r e e x p e c t e d  t o have s i m i -  structures.  Cytochromes o f the " c " c l a s s Two " c " t y p e c y t o c h r o m e s a r e f o u n d i n t h e m i t o c h o n d r i a l C y t o c h r o m e c-| i s f i r m l y a t t a c h e d  t o t h e membrane  s t r o n g l y complexed with cytochrome b.  Detergent  »  membrane.  a n d a p p e a r s t o be  treatment  i s required  to e x t r a c t cytochrome C p as i s t h e case o f cytochrome b, and t h i s serious problems i n subsequent s t u d i e s .  Cytochrome c , i n c o n t r a s t , i s found  on t h e o u t e r s u r f a c e o f t h e i n n e r m i t o c h o n d r i a l  membrane  2 5 - 2 7  , that i s in  t h e s p a c e b e t w e e n t h e two m e m b r a n e s , a n d r e q u i r e s o n l y a c i d i c for e x t r a c t i o n  2 8 - 3 0  .  presents  conditions  This water s o l u b l e cytochrome takes e l e c t r o n s  from  t h e c y t o c h r o m e b.c-j c o m p l e x ( W h i c h i s d e e p l y embedded i n t h e membrane) a n d t r a n s f e r s them t o t h e c y t o c h r o m e a a complex, w h i c h i s b e l i e v e d t o l i e 3  right across the inner membrane . 3 1  The e x t r a c t e d cytochrome c i s r e a d i l y  p u r i f i e d by e l e c t r o p h o r e s i s o r c a t i o n e x c h a n g e c h r o m a t o g r a p h y , a n d i s 3 2  the most e x t e n s i v e l y s t u d i e d o f the m i t o c h o n d r i a l  cytochromes.  c y t o c h r o m e i s s o l u b l e i n s t r o n g a q u e o u s s o l u t i o n s o f ammonium which p r e c i p i t a t e o u t most p r o t e i n i m p u r i t i e s . 3 3  The sulphate  The s t r u c t u r e and  16  f u n c t i o n o f t h i s p r o t e i n h a v e been e x t e n s i v e l y s t u d i e d a n d t h i s has h e l p e d our understanding  o f the cytochromes i n general.  Mitochondrial  c y t o c h r o m e c has a m o l e c u l a r  weight o f ^12,400  which i s s u r p r i s i n g l y independent o f t h e source o f t h e mitochondria, operates  w i t h a r e d u c t i o n p o t e n t i a l o f a b o u t +0.2'5 v o l t s  3 5  .  This  and  small  m o l e c u l e has s l i g h t l y o v e r a h u n d r e d a m i n o a c i d r e s i d u e s a n d c o n t a i n s o n e heme g r o u p t h a t i s c o v a l e n t l y l i n k e d t o t h e p r o t e i n c h a i n by two t h i o e t h e r links.  T h e two t h i o e t h e r bonds c o n n e c t two c y s t e i n e r e s i d u e s  17) t o t h e v i n y l g r o u p s o f t h e p r o t o p o r p h y r i n  IX " . 3 6  4 0  ( c y s t . 14 a n d  The t e r t i a r y  s t r u c t u r e o f t h e p r o t e i n t a k e s on a f o r m s i m i l a r t o t h a t o f a c l a m s h e l l w i t h t h e heme g r o u p d e e p l y embedded b e t w e e n t h e two j a w s w i t h o n l y o n e edge o f t h e porphyrin  r i n g exposed t o t h e external s o l v e n t (Fijgure 1 . 9 ) " 4 1  The heme p o c k e t i s v e r y h y d r o p h o b i c a n d t h i s c o n d i t i o n i s b e l i e v e d t o be r e q u i r e d t o o b t a i n a r e d u c t i o n p o t e n t i a l a s h i g h a s +0.25  volts- -The 4  i r o n c e n t r e h a s two a x i a l l i g a n d s t h a t a r e a l s o e s s e n t i a l f o r t h e r e d o x properties of the protein.  One s t r o n g l i g a n d bond i s f o r m e d by t h e  i m i d a z o l e n i t r o g e n o f h i s t i d i n e 18, w h i l e t h e s i x t h l i g a n d i s t h e sulphur a t o m o f m e t h i o n i n e 80 w h i c h f o r m s a weak bond w i t h t h e i r o n ( I I ) a t o m a n d i s b e l i e v e d t o s t a b i l i z e t h e heme i n t h e o x i d i z e d  form " . 4 5  4 8  Cytochromes o f the "a" c l a s s A p r o t e i n w i t h a c l a s s " a " t y p e v i s i b l e s p e c t r u m was known t o be i n v o l v e d i n t r a n s f e r r i n g e l e c t r o n s from cytochrome c t o oxygen, t h e terminal  electron acceptor  of the mitochondrial  transport chain.  This  17  F i g u r e 1.9  Schematic diagram o f the backbone c h a i n o f horse heart cytochrome Tine ot-carbon p o s i t i o n s are numbered i n sequence. M o d i f i e d from Ref. 41 .  c.  18  p r o t e i n was  hence c a l l e d cytochrome c o x i d a s e and was known to  bind  oxygen and use e l e c t r o n s from cytochrome c to reduce the oxygen to Detergents  were r e q u i r e d to detach the l a r g e  membrane samples  4 9 - 5 1  .  in a n a l y s i s ,  metry o f r e a c t i o n with carbon monoxide  9  >  spectral 1 + 9  .  data and the  L i k e the c l a s s  found i n the m i t o c h o n d r i a l membrane, r e l a t i v e l y l i t t l e i s s t r u c t u r e o f the p r o t e i n , although groups , 5 2  monoxide . 53  it  is  o n l y one o f which i s  One c l u s t e r o f s u b - u n i t s ,  3 7  5 1 +  '  5 5  .  l i g a n d s t o the heme a i r o n  c a l l e d cytochrome a , 3  protein  or cytochrome a a g  two copper a t o m s  5 9  '  6 0  5 7  '  5 8  .  5 5  Also  the other  c a l l e d terminal  cyto-  present in the p r o t e i n are  whose presence has been l i n k e d to the problem o f  e l e c t r o n reducing agent.  .  on the o u t s i d e o f the  r e d u c t i o n o f an oxygen m o l e c u l e by a cytochrome which i s  the  f o r m a l l y a one-  Reduction o f an oxygen molecule by one e l e c t r o n  g i v e s the e n e r g e t i c a l l y unfavoured superoxide a n i o n is  '  the heme a group  surrounds  The whole complex i s  chrome c - o x i d a s e  5 4  on the i n s i d e o f the i n n e r  known as cytochrome a and l i e s  i n n e r membrane ( F i g u r e 1.10).  sub-units  surrounds  The second c l u s t e r o f s u b - u n i t s  heme a group and i s  known about the  b e l i e v e d to be determined by  composed o f s e v e r a l  and i s c a p a b l e o f b i n d i n g oxygen, and l i e s membrane >  b cytochromes  a b l e to bind oxygen or carbon  The d i f f e r e n c e in r e a c t i v i t y i s  The whole p r o t e i n is  stoichio-  known to c o n t a i n two heme a  the nature and bonding s t r e n g t h o f the a x i a l atom.  protein  i n p r o p e r t i e s , depending upon the techniques  used, as measured by changes  prosthetic  49  p r o t e i n from the m i t o c h o n d r i a l  Due to the severe e x t r a c t i o n c o n d i t i o n s , the  showed v a r i a t i o n  water, .  6 1  .  The oxygen molecule  thought to b r i d g e a reduced copper atom and the cytochrome a  3  iron centre,  19  Figure 1,10  Schematic r e p r e s e n t a t i o n o f cytochrome c i n t e r a c t i o n s with c y t o chromes a a and c-j in the m i t o c h o n d r i a l membrane. The diagrams i l l u s t r a t e how cytochrome c may accomplish e l e c t r o n t r a n s f e r between the oxidase and cytochrome c-j by v a r i o u s p o s s i b l e mechanisms: twodimentional d i f f u s i o n on the s u r f a c e o f the membrane, a s s o c i a t i o n d i s s o c i a t i o n v i a the aqueous phase, and i n a " s o l i d - s t a t e " c o n f i g u r a t i o n t h a t i m p l i e s a t e r n a r y complex between cytochromes c-| , c , and aa . The roman numerals i n d i c a t e the s u b u n i t s o f cytochrome o x i d a s e . M o l e c u l a r weights a r e : I ^ 40,000; II ^ 20,000, III a, 15,900, IV * 11,000; VI ^ 8,000. The p o s i t i o n o f the heme groups and the net charges on the v a r i o u s components are i n d i c a t e d . M o d i f i e d from Ref. 65. 3  3  and hence can be reduced i n a t w o - e l e c t r o n process peroxide s p e c i e s .  Bound peroxide s p e c i e s  1.3  favourable  have been d e t e c t e d by r e a c t i n g  oxygen with c h e m i c a l l y reduced cytochrome a a t h i s o b s e r v a t i o n supports  to the more  3  a t low t e m p e r a t u r e s , and  the s u g g e s t i o n o f an oxygen  bridge  6 2 - 6 4  .  The Mechanism o f E l e c t r o n T r a n s f e r between the Cytochromes Most o f our knowledge o f the mechanism of e l e c t r o n t r a n s f e r  the cytochromes has come from s t u d i e s the e a s i e s t  of the m i t o c h o n d r i a l  between  i n v o l v i n g cytochrome c as t h i s  is  cytochromes to study and hence more  is  20  known a b o u t i t s s t r u c t u r e and f u n c t i o n .  Cytochrome c i s found between  6 5  25-27'  t h e two m e m b r a n e s o f t h e m i t o c h o n d r i a  and i n t e r a c t s w i t h  two  m e m b r a n e - b o u n d c o m p l e x e s , c y t o c h r o m e s bc-j , and c y t o c h r o m e s a a ^ . a r e two m a i n t h e o r i e s  6 6 - 6 9  d e s c r i b i n g the i n t e r a c t i o n s .  There  The f i r s t  postu-  l a t e s d i f f e r e n t b i n d i n g s i t e s f o r c y t o c h r o m e c-| and c y t o c h r o m e a a ^ . w o u l d a l l o w t h e c y t o c h r o m e c m o l e c u l e t o b i n d t h e o t h e r two simultaneously  complexes  and h e n c e t r a n s f e r e l e c t r o n s d i r e c t l y f r o m c y t o c h r o m e c-|  to cytochrome a.  This r e q u i r e s the formation  o f a 1:1:1  complex o f  t h r e e c o m p o n e n t s i n w h i c h t h e c y t o c h r o m e c m o l e c u l e s p a n s t h e gap t h e two m e m b r a n e - b o u n d m o l e c u l e s and i s c a l l e d t h e " s o l i d s t a t e (Figure  1.10).  This  The a l t e r n a t i v e t h e o r y s u g g e s t s s e p a r a t e l y w i t h c y t o c h r o m e c-j .  between theory"  T h i s t h e o r y has r e c e n t l y r e c e i v e d a c o n s i d e r a b l e  w i t h t h e i s o l a t i o n o f an a c t i v e s t o i c h i o m e t r i c 1:1:1  the  boost  complex . 7 0  that cytochrome c f i r s t  T h i s b i n a r y complex then  binds  dissociates  a f t e r e l e c t r o n t r a n s f e r and t h e r e d u c e d c y t o c h r o m e c e i t h e r , r o t a t e s  or  t r a n s l a t e s t h r o u g h t h e membrane s u r f a c e , o r d i s s o c i a t e s o f f t h e membrane completely  i n t o s o l u t i o n , and t h e n r e b i n d s  to cytochrome a a  s e c o n d s t a g e o f e l e c t r o n t r a n s f e r ( F i g u r e ' 1 .10).  3  f o r the  In t h i s c a s e t h e same  s i t e o f r e a c t i o n on t h e c y t o c h r o m e c m o l e c u l e c o u l d be u s e d f o r b o t h c y t o c h r o m e c-j and c y t o c h r o m e a a ^ .  T h i s seems r e a s o n a b l e  as  c y t o c h r o m e s c-j and a a ^ a r e v e r y a c i d i c w i t h c o n s i d e r a b l e n e g a t i v e on t h e o u t e r s u r f a c e o f t h e i r m o l e c u l e s , protein ' 7 1  7 2  suspected  of being a binding s i t e  both charges  whereas cytochrome c i s a b a s i c  with substantial p o s i t i v e charges,  c o l l a r which surrounds the entrance  binding  p a r t i c u l a r l y on t h e l y s i n e  t o t h e heme c l e f t a n d i s s t r o n g l y  7 3 - 7 5  .  T h i s l y s i n e c o l l a r i s formed  by  21  lysines  72, 73, 86, 87 and 88  .  A problem with t h i s mechanism i s  that  some d e t e r m i n a t i o n s o f the r a t e o f d i s s o c i a t i o n o f cytochrome c from  its  complex with cytochrome aa^ g i v e a r a t e that i s  than  the o v e r a l l r a t e o f e l e c t r o n chain  7 6  '  7 7  .  substantially  slower  t r a n s f e r through the whole e l e c t r o n t r a n s p o r t  T h i s appears to p r e c l u d e t h i s mechanism as a method o f e l e c t r o n  t r a n s f e r between cytochrome c-| and a a ^ , but other s t u d i e s o f the same d i s s o c i a t i o n have given w i d e l y ranging o f the r a t e s o b t a i n e d has  7 8  , and hence the s i g n i f i c a n c e  been g r e a t l y undermined.  so f a r to t r y and d e c i s i v e l y into similar  rates  All  experiments done  show which mechanism i s o p e r a t i n g have run  problems and given i n c o n c l u s i v e r e s u l t s .  The " s o l i d  mechanism r e q u i r e s two s e p a r a t e e l e c t r o n t r a n s f e r pathways  state"  from the  e x t e r i o r of the cytochrome c m o l e c u l e to the i r o n atom at the c e n t r e o f the heme group.  Initial  studies  i n d i c a t e d t h a t the r a t e o f e l e c t r o n t r a n s f e r 6 6  by these two pathways would be v e r y s i m i l a r and t h i s  caused Chance et a l .  r u l e out the " s o l i d s t a t e " mechanism as they f e l t t h a t  i n such an asymmetri-  cal molecule as cytochrome c the a l t e r n a t e e l e c t r o n pathways would have v e r y d i f f e r e n t a c t i v a t i o n e n e r g i e s and r a t e s o f e l e c t r o n t r a n s f e r . recent studies  have suggested the two pathways  v e r y d i f f e r e n t r a t e s and t h i s theory  6 8  '  7 9  has  More  i n cytochrome c may have  i n c r e a s e d i n t e r e s t i n the " s o l i d  state"  .  The question remains as to the p o s s i b l e  pathways  for electron  t r a n s f e r from the e x t e r i o r of the cytochrome c m o l e c u l e to the heme i r o n atom.  O x i d i z e d cytochrome c has been observed to r e a c t with a l a r g e number  of inorganic reducing a g e n t s 3 10 -10  4 - 1 - 1 M s .  6 5  , the r a t e s u s u a l l y  being w i t h i n the range  Any suggested mechanism has to e x p l a i n these f a s t  rates.  To  22  For i n s t a n c e , an i n n e r - s p h e r e mechanism r e q u i r e s the r e d u c i n g agent t o g a i n d i r e c t access t o the heme i r o n atom, so t h a t an e l e c t r o n can be transferred via a bridging ligand.  T h i s would r e q u i r e the opening o f the  heme c l e f t , and the b r e a k i n g o f the i r o n - a x i a l l i g a n d bond. r a t e f o r t h i s process  i s about 60 s  "  The e s t i m a t e d  and hence the observed  o f r e d u c t i o n e f f e c t i v e l y r u l e out an i n n e r - s p h e r e mechanism;  rates  a faster  o u t e r sphere mechanism v i a some c o n d u c t i o n path from the e x t e r i o r o f t h e p r o t e i n to the i r o n atom seems l i k e l y . suggested:  Two types o f hypotheses  the p r o t e i n mechanisms, and the " p r o t e i n - l e s s "  The p r o t e i n mechanisms  have been  mechanisms.  i n v o l v e the t r a n s p o r t o f e l e c t r o n s  through  the p r o t e i n i n some way, u s u a l l y v i a a c h a i n o f a d j a c e n t a r o m a t i c aminoacid r e s i d u e s  8 3 - 8 5  .  These mechanisms  o f a number o f a r o m a t i c r e s i d u e s d i f f e r e n t sources.  sought to e x p l a i n the c o n s e r v a t i o n  i n c cytochromes o b t a i n e d from w i d e l y  These t h e o r i e s became l e s s t e n a b l e whenever a new  cytochrome c was a n a l y s e d and one o f the s p e c i f i e d r e s i d u e s was r e p l a c e d by an a l i p h a t i c r e s i d u e .  The o t h e r major problem w i t h t h e s e mechanisms  was t h a t t y p i c a l a r o m a t i c a m i n o - a c i d r e s i d u e s  (phenylalanine, tryptophan,  t y r o s i n e and h i s t i d i n e ) a r e o n l y reduced a t e x t r e m e l y n e g a t i v e redox p o t e n t i a l s and hence the e s t i m a t e d a c t i v a t i o n energy o f e l e c t r o n t r a n s f e r through the a m i n o - a c i d r e s i d u e s was u s u a l l y v e r y h i g h ( i n some cases 50 k c a l / m o l e ) , c o m p a r e d w i t h the observed r a t e s o f e l e c t r o n t r a n s f e r which 86  u s u a l l y gave an a c t i v a t i o n energy o f about 11.3 k c a l / m o l e the p r o t e i n mechanisms  .  Hence,  have l o s t p o p u l a r i t y over the y e a r s .  The " p r o t e i n - l e s s " mechanisms f i r s t envisions  8 6 - 8 7  can be d i v i d e d i n t o two c l a s s e s .  The  the b i n d i n g o f the donor and a c c e p t o r complex, f o l l o w e d by  23  quantum m e c h a n i c a l t u n n e l l i n g o f a n e l e c t r o n b e t w e e n t h e i r o n c e n t r e s This theory  8 8  '  8 9  .  equates the i n t e r v e n i n g protein to a c l a s s i c a l b a r r i e r through  which t h e e l e c t r o n has a c e r t a i n p r o b a b i l i t y o f t u n n e l l i n g , depending  upon  the d i s t a n c e i n v o l v e d and t h e n a t u r e o f t h e i n t e r v e n i n g p r o t e i n . 9 0  Quantum m e c h a n i c a l t u n n e l l i n g i s w e l l d o c u m e n t e d ,  and t u n n e l l i n g through  t e n s o f a n g s t r o m s o f i n e r t s o l v e n t has been o b s e r v e d i n n o n - b i o c h e m i c a l systems . 9 1  The o t h e r " p r o t e i n - l e s s " m e c h a n i s m , now c o n s i d e r e d t h e m o s t r e a s o n a b l e , i n v o l v e s e l e c t r o n t r a n s f e r v i a t h e e x p o s e d heme e d g e .  Of t h e e l e c t r o n  t r a n s f e r c y t o c h r o m e s f o u n d i n m i t o c h o n d r i a , o n l y c y t o c h r o m e c h a s been c r y s t a l l i z e d and a s t r u c t u r e d e t e r m i n e d .  The non-mitochondrial c y t o -  4 1  chrome ( b ) has a l s o been c r y s t a l l i z e d a n d i s assumed 5  similar to the mitochondrial b cytochrome . 1 9  t o be s t r u c t u r a l l y  Both t h e s e c r y s t a l l i z e d  c y t o c h r o m e s h a v e been f o u n d t o c o n t a i n a heme g r o u p w i t h a p a r t i a l l y  exposed  e d g e a n d t h i s s t r o n g l y s u p p o r t s t h i s m e c h a n i s m , w h i c h r e q u i r e s t h e two heme g r o u p s o f t h e c o m b i n e d c y t o c h r o m e s t o become a d j a c e n t a n d f o r t h e i r T r - o r b i t a l s y s t e m s t o o v e r l a p . T h e p o s i t i v e c h a r g e on t h e o x i d i z e d 9 2  s p e c i e s moves f r o m t h e m e t a l c e n t r e t o t h e r e d u c e d m e t a l c e n t r e v i a p o s i t i v e l y charged i n t e r m e d i a t e s c a l l e d porphyrin Tr-cation r a d i c a l s which a r e s t a b i l i z e d by t h e d e l o c a l i z a t i o n o f t h e p o s i t i v e " h o l e " a r o u n d t h e e n t i r e conjugated system o f the p o r p h y r i n ( F i g u r e s u c h a m e c h a n i s m t o be f e a s i b l e  9 3  1.11).  Model s y s t e m s have shown  a n d o n e a i m o f t h e work d e s c r i b e d i n  thVs  t h e s i s i s t o a t t e m p t t o more f u l l y u n d e r s t a n d t h i s p r o c e s s and hence p r o v i d e more e v i d e n c e f o r t h i s mechanism.  24  1.4  O t h e r Heme Redox P r o t e i n s In a d d i t i o n t o t h e e l e c t r o n t r a n s p o r t c y t o c h r o m e s m e n t i o n e d a b o v e ,  t h e r e a r e a number o f heme enzymes w h i c h b i n d o x y g e n and o t h e r s u c h as NO,  CO, and CN",  diatomics  and, i n the case o f o x y g e n , t r a n s f e r e l e c t r o n s  from the m e t a l l o p o r p h y r i n  t o the bound m o l e c u l e .  heme p r o t e i n s ( s e e S l e c t i o n 1.1)  are expected  c y t o c h r o m e a a ^ w h i c h b i n d s and r e d u c e s  This third class of  t o h a v e some s i m i l a r i t i e s t o  oxygen to water.  C y t o c h r o m e P-450  i s an enzyme f o u n d i n m a m m a l i a n l i v e r c e l l s and i s a c t i v e i n d e t o x i f y i n g foreign chemicals  found i n the body.  The s t u d i e s r e l a t e d t o t h i s c y t o -  c h r o m e h a v e been e x t e n s i v e l y r e v i e w e d " . 9 4  9 6  A typical intensely studied  r e a c t i o n o f c y t o c h r o m e P-450 i s t h a t u s e d by a b a c t e r i u m /  to  metabolize  9 7  c a m p h o r ( F i g u r e 1.12)  .  The c a m p h o r i s h y d r o x y l a t e d  a t an u n a c t i v a t e d  bon' atom,., p r o b a b l y by a r a d i c a l m e c h a n i s m u s i n g a r e d u c e d c o o r d i n a t e d a x i a l l y a t t h e heme g r o u p . 9 8  Horseradish  oxygen  peroxidase  c a t a l a s e a r e two heme p r o t e i n t h a t b i n d and u t i l i z e h y d r o g e n r a t h e r than oxygen.  car-  molecule and  peroxide  The f o r m e r enzyme u s e s t h e o x i d i z i n g power o f h y d r o g e n  peroxide to e f f e c t a r e a c t i o n s i m i l a r to that accomplished  by c y t o c h r o m e  P-450, n a m e l y h y d r o x y l a t i o n a t an u n a c t i v a t e d c a r b o n atom o f o r g a n i c substrates  9 9 - 1 0 1  , w h i l e c a t a l a s e d e c o m p o s e s h y d r o g e n p e r o x i d e t o w a t e r and  o x y g e n i n one o f t h e f a s t e s t e n z y m i c r e a c t i o n s known. 1.5  Modelling the Cytochromes D i r e c t s t u d i e s o f many o f t h e c y t o c h r o m e s " i n v i v o " a r e v e r y l i m i t e d  due t o t h e i r membrane b o u n d n a t u r e . the mitochondria,  E x t r a c t i o n of these cytochromes,  i n many c a s e s m o d i f i e s t h e i r b e h a v i o u r  from  so t h a t r e s u l t s  25 Heme s y s t e m s become a d j a c e n t and t h e i r t r - o r b i t a l : overlap-  Fe'  •Fe  Fe E l e c t r o n t r a n s f e r i n the cytochromes t r i g g e r e d by c h a n g e i n c o n f o r m a t i o n i n t h e two p r o t e i n s on b i n d i n g .  Fe  Fe'  1  Cytochromes d i s s o c i a t e  Fe in  F i g u r e 1.11  Fe'  The p r o p o s e d m e c h a n i s m f o r e l e c t r o n t r a n s f e r b e t w e e n t h e heme g r o u p s o f two c y t o c h r o m e s v i a c a t i o n r a d i c a l i n t e r m e d i a t e s . The a x i a l l i g a n d s t o t h e m e t a l have been o m i t t e d a n d t h e p l a n a r porphyrin i s represented schematically.  F i g u r e 1.12  T h e o x i d a t i o n o f camphor  by c y t o c h r o m e P - 4 5 0 .  26  are f a r l e s s  useful ' 9  4 9  .  In attempts t o f u r t h e r understand these m e t a l l o -  p r o t e i n systems, some p r o t e i n - f r e e complexes are used t o model the n a t u r a l system.  The a c t i v e p a r t o f a cytochrome i s the m e t a l l o p o r p h y r i n p r o s t h e t i c  group whose c h e m i s t r y , however, i s undoubtedly m o d i f i e d by t h e protein.  surrounding  The m e t a l l o p o r p h y r i n can be removed i n t a c t from the c y t o c h r o m e  and the " b a r e " heme i s an obvious c a n d i d a t e as a model f o r t h e f u l l chrome.  152  cyto-  However, i t was q u i c k l y found t h a t such f o u r - c o o r d i n a t e m e t a l l o -  p o r p h y r i n s were d i f f i c u l t t o handle i n s o l u t i o n .  P e r i p h e r a l groups on  the p o r p h y r i n are very r e a c t i v e ( p a r t i c u l a r l y the v i n y l groups on p r o t o porphyrin  i x  1  0  2  -  1  0  5  )  a n d , now t h a t t h e a x i a l p o s i t i o n s are no l o n g e r  blocked by p r o t e i n , t r a c e oxygen can r e a c t r a p i d l y to g i v e  iron(III)  s p e c i e s which f i n a l l y form y - o x o - d i m e r s ; even the s i x - c o o r d i n a t e l a b i l e d e r i v a t i v e s o f the n a t u r a l l y o c c u r r i n g hemes o x i d i z e r e a d i l y o u t s i d e o f the p r o t e i n e n v i r o n m e n t . ( F i g u r e 1 . 1 3 ) chemical  1 0 7 - 1 1 1  .  Hence, d e s p i t e t h e i r c l o s e  s i m i l a r i t i e s t o the i n - v i v o c y t o c h r o m e s , t h e n a t u r a l l y o c c u r r i n g  i r o n - p o r p h y r i n systems  are not good models because o f t h e s e  difficulties.  The f i r s t problem i s e a s i e s t t o s o l v e by u s i n g s y n t h e t i c p o r p h y r i n s  such  as o c t a e t h y l p o r p h y r i n (OEP) o r meso-tetraphenyl p o r p h y r i n (TPP) t h a t have less r e a c t i v e p e r i p h e r a l groups and good s o l u b i l i t y i n non-aqueous (perhaps  solvents  themselves a model f o r the l i p i i d environment o f the membrane).  the two, OEP p r o b a b l y has the l i g a n d p r o p e r t i e s c l o s e r t o t h a t o f t h e natural  porphyrins  withdrawing)  1 1 2  ( t h e phenyl groups on TPP make i t r a t h e r e l e c t r o n  but i s f a r more d i f f i c u l t t o make than T P P  p l e x e s of both p o r p h y r i n s  have been w i d e l y s t u d i e d .  1 1 3  .  M e t a l l o com-  Of  IV  F i g u r e 1.13  The r e a c t i o n o f i r o n ( I I ) p o r p h y r i n s w i t h o x y g e n t o g i v e a y - o x o - d i m e r a s p r o d u c t . These r e a c t i o n s u s u a l l y i n v o l v e f i v e - c o o r d i n a t e i r o n p o r p h y r i n s p e c i e s . For c l a r i t y t h e f i f t h l i g a n d i n (.1) a n d s u b s e q u e n t s p e c i e s has b e e n o m i t t e d . The p o r p h y r i n i s r e p r e s e n t e d schematically. M e t a l l o p o r p h y r i n (.1) b i n d s o x y g e n t o g i v e t h e a d d u c t ( I I ) w h i c h i s t h e n a t t a c k e d by a s e c o n d i r o n p o r p h y r i n to g i v e the y-peroxo complex ( I I I ) ; t h i s then degrades to g i v e the y-oxodimer ( I V ) .  28  The s e c o n d problem o f o x i d a t i o n i s more s e r i o u s .  Low  temperature  s t u d i e s h a v e been shown t o s l o w down t h e f o r m a t i o n o f y - o x o - d i m e r s  and  h a v e a l l o w e d some s t u d i e s on t h e c h e m i s t r y o f t h e m o n o m e r i c p o r p h y r i n s  1 1 4  .  Another s o l u t i o n i s to block the approach o f the second porphyrin (steps II  I I I , F i g u r e 1.13)  centre.  by s t e r i c a l l y h i n d e r i n g a c c e s s t o t h e m e t a l  S u c h s y s t e m s h a v e been u s e d s u c c e s s f u l l y a s m o d e l s f o r h e m o g l o b i n  a n d m y o g l o b i n a s t h e bound o x y g e n d o e s n o t c a u s e p e r m a n e n t o x i d a t i o n a t t h e m e t a l c e n t r e i f d i m e r f o r m a t i o n i s s t o p p e d and h e n c e t h e s e s y s t e m s b i n d oxygen  reversibly  1 1 5  .  An a l t e r n a t i v e a p p r o a c h i s t o u s e a d i f f e r e n t m e t a l a t t h e c e n t r e o f t h e p o r p h y r i n . However, t h e c h e m i s t r y o f such a system i s v e r y dependent upon t h e m e t a l u s e d and h e n c e i t s u s e as a model  s y s t e m w i l l be d i m i n i s h e d ;  a l t h o u g h much has been l e a r n e d f r o m t h e s t u d i e s o f c o b a l t p o r p h y r i n s A compromise  i s to s u b s t i t u t e ruthenium f o r the i r o n .  Ruthenium  1 1 6  .  i s the  s e c o n d row t r a n s i t i o n e l e m e n t d i r e c t l y u n d e r i r o n i n t h e p e r i o d i c t a b l e , a n d h e n c e has c h e m i s t r y s i m i l a r t o t h a t o f i r o n , b u t t h e e n h a n c e d  ligand  f i e l d s t a b i l i z a t i o n e n e r g y o f t h e s e c o n d row e l e m e n t s ( v e r y s t r o n g i n t h e c a s e o f d ^ Ru**, l o w s p i n ) c a u s e s m o s t r e a c t i o n s t o be v e r y much s l o w e r , a n d r e a c t i v e i n t e r m e d i a t e s t o h a v e l o n g e r l i f e t i m e s a n d t o be m o r e a c c e s s i b l e for study.  In p a r t i c u l a r t h e c h a n g e o f m e t a l s h o u l d h i n d e r t h e f o r m a t i o n  o f y - o x o - d i m e r j b y t h e m e c h a n i s m shown ( F i g u r e 1 . 1 3 ) .  The c h e m i c a l s i m i l a -  r i t i e s b e t w e e n i r o n and r u t h e n i u m mean t h a t p r o c e s s e s o b s e r v e d w i t h r u t h e n i u m p o r p h y r i n s y s t e m s c a n be t e n t a t i v e l y r e l a t e d t o t h e n a t u r a l system.  I t i s hoped t h a t t h i s w i l l be p a r t i c u l a r l y t r u e o f t h e e l e c t r o n  29  transfer processes  and c a t i o n r a d i c a l r e a c t i o n s d e s c r i b e d i n t h i s t h e s i s ,  as t h e r e i s some e v i d e n c e among m e t a l l o p o r p h y r i n  1.6  Porphyrin  t h a t s i m i l a r p r o c e s s e s may  systems  1 1 7  be q u i t e w i d e s p r e a d  .  C a t i o n R a d i c a l s and I n t r a m o l e c u l a r  Transfer of Electrons  P o r p h y r i n TT c a t i o n r a d i c a l s w e r e i n i t i a l l y p o s t u l a t e d as lived intermediates  formed i n the chemical  occurring pigments.  was  oxidation of various naturally  I n t e r e s t i n t h e s e s p e c i e s was  d a t i o n o f c h l o r o p h y l l a was  short-  i n c r e a s e d when  photoxi-  f o u n d t o g i v e an e . s . r . a c t i v e s p e c i e s w h i c h  shown t o be a c h l o r i n c a t i o n r a d i c a l  1 1 8 - 1 2 0  h a v e moved m o r e t o w a r d s s y n t h e s i z i n g p o r p h y r i n  . Recently the  species.  studies  Chemical  oxida-  t i o n s w i t h b r o m i n e o r x e n o n d i f l u o r i d e h a v e y i e l d e d , i n some c a s e s , samples o f porphyrin  cation radical complexes  o x i d a t i o n can a l s o a f f e c t f o r m a t i o n  1 2 1  '  1 2 2  .  Electrochemical  of clean solutions of cation radical  s p e c i e s and has t h e a d v a n t a g e t h a t 1 i g a t i n g a n i o n i c s p e c i e s c a n be by s u i t a b l e c h o i c e o f e l e c t r o l y t e ( e . g . Bu^NvClO^ o r B u N P F g ) . +  4  o f the coordinated  a n i o n , can be v e r y s i g n i f i c a n t i n d e t e r m i n i n g  t i e s o f the c a t i o n r a d i c a l Metalloporphyrin the p o r p h y r i n r i n g . the metal although two p o s i t i v e c h a r g e s  solid  prepared  1 2 3  avoided  The the  nature proper-  .  s p e c i e s c a n be o x i d i z e d e i t h e r a t t h e m e t a l o r a t  An e a s i l y o x i d i z a b l e m e t a l c e n t r e w i l l o x i d i z e a t f u r t h e r o x i d a t i o n may on t h e m e t a l  1 2 4  '  1 2 5  .  occur a t the r i n g r a t h e r than Metal  place  ions incapable of f u r t h e r  o x i d a t i o n w i l l always cause o x i d a t i o n a t the r i n g .  The s i t e o f o x i d a t i o n  may  metal  be s t r o n g l y i n f l u e n c e d by a x i a l l i g a n d s on t h e  1 2 6  .  30  V i s i b l e spectra of the c a t i o n r a d i c a l s o f these s y n t h e t i c m e t a l l o porphyrins  f a l l i n t o two c l a s s e s  s i m i l a r t o t h a t o f Mg OEP ",  1 2 1  .  F i r s t , are those with a spectrum  w h i c h show a s t r o n g v i s i b l e a b s o r p t i o n i n  +  t h e 630 - 700 nm r e g i o n o f t h e s p e c t r u m . s i m i l a r t o t h e Zn.TPP *  strength absorption throughout independent  c l a s s are  those  s p e c t r u m w h i c h shows a n e a r l y f e a t u r e l e s s medium  +  was  The s e c o n d  the v i s i b l e .  o f the c o u n t e r - a n i o n .  The s p e c t r a l t y p e  observed  Electron spin resonance s t u d i e s  showed t h a t t h e u n p a i r e d e l e c t r o n s o c c u p i e d a d i f f e r e n t p a r t o f t h e p h y r i n m a c r o c y c l e i n t h e s e two s p e c i e s .  1 2 1  '  1  por-  T h e e . s . r . d a t a and t h e d i f f e r e n c e  i n o p t i c a l p r o p e r t i e s b e t w e e n t h e two c l a s s e s o f c a t i o n r a d i c a l w e r e e x p l a i n e d by m o l e c u l a r  orbital theory  w h i c h showed t h a t a n e u t r a l  1 2 1  p o r p h y r i n had two n e a r l y e q u i v a l e n t m o l e c u l a r two e l e c t r o n s .  o r b i t a l s that each  contained  H o w e v e r , t h e o r b i t a l s a r e o f d i f f e r e n t s y m m e t r y so t h a t  r e m o v a l o f an e l e c t r o n f r o m e i t h e r o r b i t a l g i v e s a T r - c a t i o n r a d i c a l ^whose p r o p e r t i e s depend upon the m o l e c u l a r unpaired e l e c t r o n .  o r b i t a l occupied  remaining  The c a t i o n r a d i c a l s t a t e s a r e l a b e l l e d a c c o r d i n g ?  -  +•  s p e c t r o s c o p i c n o m e n c l a t u r e , A-| :(,Mg OEP u  The importance  ?  ). o r  /\  - i  ;(Zn,.TPP.  )  to  127  of l i g a t i n g i o n i c species in cation r a d i c a l solutions ' —11  was  by t h e  seen i n the behaviour  o f Co  + •  (OEP)  12  3  .  Bromine o x i d a t i o n gave  2  a s o l u t i o n with a  A-] t y p e s p e c t r u m , w h i l e e l e c t r o c h e m i c a l o x i d a t i o n i n  p e r c h l o r a t e media  gave a  u  2  A  2 u  spectrum.  The d i f f e r e n c e was  shown t o  due t o t h e l i g a t i n g p r o p e r t i e s o f t h e b r o m i d e i o n s i n c e t h e two  be  species  c o u l d be i n t e r c o n v e r t e d by t h e a d d i t i o n o r r e m o v a l o f b r o m i d e i o n , ( F i g u r e 1.14).  T h i s was  the f i r s t r e p o r t e d case where the presence  or absence o f  WAVELENGTH  F i g u r e 1.14  The o p t i c a l s p e c t r u m o f t h e A  (nm)  cation radical [Co (0EP) '  2  r? IIl)nrS+^?i B  } a n dt h e s  P  I H  l u  o f the A  e c t r u m  2  Co"I(0EP)+-]2+.2C10 - in CHC1 ( AgClCty e b r o m i d e c o m p l e x . From R e f . 4  t 0  3  t n  2 u  +  species  )formefby 123.  adding  a l i g a n d a f f e c t e d a change i n ground s t a t e o f a c a t i o n r a d i c a l s p e c i e s . On t h e b a s i s o f t h e o b s e r v e d the intermediates  o p t i c a l s p e c t r a i t has b e e n s u g g e s t e d  (Compounds I) f o r m e d i n t h e r e a c t i o n s o f  p e r o x i d a s e and c a t a l a s e a r e i r o n ( I V ) p o r p h y r i n 2 2 with  A  2 u  evidence  and  A-|  suggests  u  ground s t a t e s r e s p e c t i v e l y that the intermediates  horseradish  cation radical species 1 2 3  .  H o w e v e r , r e c e n t M.C.D.  f o r m e d by t h e o x i d a t i o n o f  both  and c a t a l a s e a r e p o r p h y r i n T r - c a t i o n r a d i c a l s o f  horseradish peroxidase t h e same g r o u n d s t a t e  that  2 2 8  -.  32  E l e c t r o n t r a n s f e r b e t w e e n t h e c e n t r a l ' m e t a l i o n and t h e r i n g w o u l d be r e q u i r e d  f o r a c a t i o n r a d i c a l m e c h a n i s m t o be o p e r a t i v e  e l e c t r o n t r a n s f e r between the c y t o c h r o m e s . o x i d a t i o n o f Pb(OEP) which g i v e s f i r s t IV .Pb  porphyrin for  An a n a l o g y can be s e e n i n t h e  Pb (0EP) ' I ] t  and t h e n  +  t  '  2+117  (OEP) - -  .  The s e c o n d o x i d a t i o n may  but t h i s i s r a p i d l y f o l l o w e d f i n a l p r o d u c t (Scheme  occur at the metal or r i n g  by an i n t e r n a l e l e c t r o n t r a n s f e r t o g i v e  1.1) Pb (0EP) ' n i  p H 0EP) b  (  the  +  ^-4  >Pb (0EP) I I  ^  TW  *  +  9  i  Pb (0EP),^ 1 V  Pb (0EP) ' H  2 +  SCHEME 1 .1  Pd  (TPP)  shows s i m i l a r b e h a v i o u r and some c o b a l t c o m p l e x e s  1 2 9  '  1 3 0  show a  r e l a t e d i n t e r n a l e l e c t r o n t r a n s f e r mechanism. An i n t e r e s t i n g c a s e o f r e v e r s i b l e e l e c t r o n t r a n s f e r o c c u r s cation radical of N i ' ( T P P ) n  1 1 7  gave a green s o l u t i o n o f a  '  A-|  1 3 1  .  Electrochemical  cation radical species.  Warming r e g e n e r a t e d  H  Freezing  the  e.s.r.  the o r i g i n a l green  s o l u t i o n , and showed t h a t t h e i n t e r n a l e l e c t r o n t r a n s f e r b e t w e e n m e t a l the porphyrin  periphery  i s r e v e r s i b l e (Scheme  the  oxidation of N i ( T P P )  s o l u t i o n a t 77K g a v e an o r a n g e - r e d s o l i d w i t h t h e v i s i b l e and spectra of a Ni(iir)complex.  with  1.2).  and  33  F (TPP)  "  L  V  e  +e  II •• + • -iNi^dPP) -  Green  SCHEME 1.2  C  0  0  1  ' Ni :  warm  TTT (TPP)  U 1  Orange-Red  34  REFERENCES - CHAPTER 1  1.  A . L . L e h i n g e r , ' B i o c h e m i s t r y , 3 r d E d . , W o r t h , New  2.  D. K e i l i n , P r o c . R. S o c . L o n d o n , S e r . B 98, 312  3.  CA.  4a.  C o m m i s s i o n on Enzymes o f t h e I n t e r n a t i o n a l U n i o n o f B i o c h e m i s t r y , R e p o r t ( 1 9 6 1 ) . 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A c t a . 4 9 , 69 (.1981 ) .  129.  D.H. B u s c h , K. F a r m e r y , V. G o e d k e n , V. K a t o v i c , A . C . M e l n y k , C R . S p e r a t i , a n d N. T o k e l , A d v a n . Chem. S e r . 1 0 0 , 44 (.1971).  130.  N.S. Hush a n d I . S . W o o l s e y , J . Am. Chem. S o c . 9 4 , 4 1 0 7 (.1972).  131.  D. D o l p h i n , T . Niem, R.H. F e l t o n , a n d S. F u j i . t a , J . Am. Chem. S o c . 9^7, 5288 ( 1 9 7 5 ) .  P a r s o n , B i o c h i m . B i o p h y s . A c t a , 153, 248 (1968).  41  CHAPTER 2  2.1  General  APPARATUS AND  Instrumentation  and  EXPERIMENTAL PROCEDURE  Procedures  U l t r a v i o l e t and v i s i b l e a b s o r p t i o n s p e c t r a w e r e r e c o r d e d on a C a r y 17D o r 1756 pathlengths  spectrophotometer.  ( 0 . 1 , 1 and 10 cm)  The q u a r t z o p t i c a l c e l l s o f v a r i o u s  used i n t h i s work, i n c l u d i n g c e l l s  c a n be s e a l e d , a r e i l l u s t r a t e d i n F i g u r e 2.1.  The weak a b s o r p t i o n  c a t e d by an a r r o w i n a p p r o p r i a t e s p e c t r a ) a t ^880  (indi-  nm s e e n i n s p e c t r a  t o l o n g e r w a v e l e n g t h s t h a n 700 nm ( f i r s t e x a m p l e F i g u r e 5.1) CH^Cl2  that  run  i s due t o t h e  u s e d and i s a l w a y s p r e s e n t i n s p e c t r a r u n i n c e l l s o f 1 cm  path-  length or g r e a t e r . S o l i d s t a t e i n f r a - r e d s p e c t r a w e r e o b t a i n e d on a P e r k i n E l m e r grating spectrophotometer  u s i n g KBr d i s c s .  Nuclear magnetic resonance spectrometer.  457  s p e c t r a w e r e o b t a i n e d on a B r u k e r 400  S a m p l e s w e r e r u n i n C D C l g u s i n g e x t e r n a l TMS  as a r e f e r e n c e .  E . s . r . s p e c t r a w e r e r e c o r d e d on a V a r i a n E-3 s p e c t r o m e t e r .  In o r d e r  to i n t e g r a t e t h e i i s i g n a l s o f the c a t i o n r a d i c a l s p e c i e s ( S e c t i o n 4.1), t i o n s (3 x 1 0 ~ ^ M ) o f t h e r u t h e n i u m r u n i n an a n a e r o b i c e . s . r . c e l l temperatures,  immediately  ( F i g u r e 2.2), a t ambient and l i q u i d  f o l l o w e d by a s o l u t i o n o f Z n T P P  +  ZnTPP ' i s a well characterized cation r a d i c a l , +  e l e c t r o n s p i n per molecule  solu-  p o r p h y r i n i r - c a t i o n r a d i c a l s p e c i e s were nitrogen  of similar  c o n c e n t r a t i o n , u s i n g t h e same c e l l and w h e r e p o s s i b l e t h e same conditions.  MHz  1  instrument having  and t h e r e i s good e v i d e n c e t h a t d i a m a g n e t i c  one dimers  42  F i g u r e 2.1  D e s i g n s o f q u a r t z c e l l s u s e d i n o p t i c a ! s p e c t r o s c o p y : a) c y l i n d r i c a l c e l l ; b) r e c t a n g u l a r c e l l , p a t h l e n g t h = 1 cm; c ) r e c t a n g u l a r c e l l , c a n be s e a l e d by a r u b b e r s e p t u m , p a t h l e n g t h = 1 cm; d) s e a l a b l e r e c t a n g u l a r c e l l , p a t h l e n g t h = 0.1 o r 1 cm. 1  43  rrnr—  SCREW SEAL  Figure 2.2  An anaerobic e.s.r. c e l l .  DOWN  44  a r e n o t f o r m e d a t low t e m p e r a t u r e s  due t o t h e s t e r i c r e q u i r e m e n t s  of the  2  phenyl  rings .  The e . s . r . s p e c t r a o f t h e c a t i o n r a d i c a l s o l u t i o n s w e r e  i n t e g r a t e d by w e i g h i n g , t h e  c h a r t p a p e r , and c o r r e c t e d f o r t h e d i f f e r e n c e s i n  g a i n u s e d i n t h e s p e c t r a and v a r i a t i o n s i n t h e c o n c e n t r a t i o n b e t w e e n t h e s a m p l e s . Often t h i s procedure  o f comparing e . s . r . s i g n a l s gave r e s u l t s i n c o n s i s t e n t  w i t h c h a n g e s i n t h e v i s i b l e s p e c t r a ( e . g . see S e c t i o n 7 . 6 ) . i n t e g r a t e d e . s . r . s i g n a l s i s n o t an a c c u r a t e p r o c e d u r e  Comparison of  because o f the 3  i n h o m o g e n e i t y o f t h e m a g n e t i c f i e l d a c r o s s t h e c a v i t y . The m e t h o d  cannot  be u s e d t o m e a s u r e t h e c h a n g e s i n c o n c e n t r a t i o n o f c a t i o n r a d i c a l s p e c i e s in s o l u t i o n because of t h i s e f f e c t (see Section  6.2).  The m e a s u r e m e n t s o f m a g n e t i c moments were made by T. L e u n g and k  R. Thompson u s i n g t h e E v a n s m e t h o d  5  and t h e F a r a d a y m e t h o d .  C o n d u c t i v i t y m e a s u r e m e n t s w e r e made on C H ^ C ^ species  u s i n g a c e l l ( F i g u r e 2.3)  c o n j u n c t i o n w i t h a m o d e l RCM Thomas Company.  15B1  w i t h a c e l l c o n s t a n t o f 0.12  2  2  Other porphyrin s o l u t i o n s (from 5 x 1 0  H t o 5 x 10  H~  f r o m ^20  mg  mL.  M) w e r e made up  d i r e c t l y from the s o l i d u s i n g s t a n d a r d v o l u m e t r i c t e c h n i q u e s .  The r e s i s t a n -  c e s from t h e c o n d u c t i v i t y b r i d g e were d i v i d e d by t h e a p p r o p r i a t e t i o n to obtain molar c o n d u c t i v i t y c o e f f i c i e n t s  in  -  were p r e p a r e d  and t h e n made up t o 20.0 -4 -3  porphyrin  cm *  c o n d u c t i v i t y b r i d g e from A r t h u r  S o l u t i o n s o f the c a t i o n r a d i c a l  o f R u ( 0 E P ) ( C 0 ) E t 0 H (2) i n C H C 1  solutions of  concentra-  (A).  Mass s p e c t r a w e r e t a k e n on a KRAT0S-AEI MS 902 s p e c t r o m e t e r  using a  s o u r c e t e m p e r a t u r e o f 220 - 2 4 0 ° C , a d i r e c t i n s e r t i o n p r o b e , and an e l e c t r o n e n e r g y o f 70eV. Elemental  a n a l y s e s w e r e d o n e by P. B o r d a o f t h i s d e p a r t m e n t .  45  T  0  BRIDGE  HOLDER  OUTER CONTAINER  ELEC T RODE S PORPHYRIN SOLUTION  GLASS SHIELDING  F i g u r e 2,3  TUBE E L E C T R O D E S  The c o n d u c t i v i t y c e l l u s e d t o o b t a i n t h e m o l a r c o n d u c t a n c e s o f p o r p h y r i n s o l u t i o n s i n CH-Cl,,.  46  S e c t i o n 2.2  a)  E l e c t r o c h e m i c a l A p p a r a t u s and  Procedure  Instrumentation To o b t a i n c y c l i c v o l t a m m o g r a m s a s t a n d a r d t h r e e c o m p a r t m e n t H - c e l l  ( t o be d e s c r i b e d i n S e c t i o n 2.2b) priate instrumentation.  was u s e d i n c o n j u n c t i o n w i t h t h e a p p r o -  The t h e o r y  been d e s c r i b e d e l s e w h e r e ,  behind the experimental  set-up  C u r r e n t flows between the w o r k i n g e l e c t r o d e  and t h e a u x i l i a r y e l e c t r o d e , t h e r e f e r e n c e e l e c t r o d e d r a w i n g no (Figure 2.4).  has  current  T h e p o t e n t i a l o f t h e a u x i l i a r y e l e c t r o d e i s a l t e r e d so t h a t  the p o t e n t i a l of the working e l e c t r o d e with respect to the r e f e r e n c e e l e c t r o d e g o e s t h r o u g h a c o n t r o l l e d sweep o v e r t h e v e r y l i m i t e d p o t e n t i a l r a n g e t o be s t u d i e d .  H o w e v e r , due t o t h e l a r g e p o t e n t i a l d r o p b e t w e e n t h e  a u x i l i a r y and w o r k i n g e l e c t r o d e s when n o n - a q u e o u s s o l v e n t s a r e u s e d , t h i s r e q u i r e s v e r y l a r g e p o t e n t i a l d i f f e r e n c e s b e t w e e n t h e w o r k i n g and  the  a u x i l i a r y ( u s u a l l y o f t h e o r d e r o f s e v e r a l t e n s o f v o l t s ) . In t h e e x p e r i m e n t s r e p o r t e d i n t h i s t h e s i s , an EG and G PARC Model 175 U n i v e r s a l mer  ( c o n t r o l l i n g t h e r a n g e o f sweep and t h e s c a n s p e e d ) was  m o d e l 173 PAR electrode.  Program-  l i n k e d to a  P o t e n t i o s t a t which c o n t r o l l e d the p o t e n t i a l o f the a u x i l i a r y  The r e s u l t s w e r e r e l a y e d t o a T e k t r o n i c s I n c . S t o r a g e O s c i l l o s -  c o p e u t i l i z i n g t y p e 3AC  ( v e r t i c a l ) and 2A60 ( h o r i z o n t a l ) a m p l i f i e r s .  The.  t r a c e s w e r e p h o t o g r a p h e d by a T e k t r o n i c s O s c i l l o s c o p e c a m e r a ( C - 1 2 ) u s i n g P o l a r o i d f i l m (Land  type 107).  A p a i r o f w a v e s on t h e c y c l i c  voltammogram were b e l i e v e d to i n d i c a t e a r e v e r s i b l e e l e c t r o d e p r o c e s s i f the r a t i o o f the peak c u r r e n t s i / i c  a  ( i = peak c u r r e n t f o r the c  s  cathodic  47  'If  SERVO M O T O R  /VWWNAAA  V  a  / P O T E N T I A L  MONITOR  SWEEP CONTROL  ELECTRODES  F i g u r e 2.4  A schematic c i r c u i t diagram f o r the c y c l i c voltammetry experiments. The p o t e n t i a l a n d t h e c u r r e n t a r e o b t a i n e d a t t h e p o s i t i o n s j r j a r k e d "V" a n d " i " r e s p e c t i v e l y . E l e c t r o d e s a r e l a b e l l e d U follows: a) r e f e r e n c e e l e c t r o d e , b) w o r k i n g e l e c t r o d e , a n d c ) a u x i l i a r y e l e c t r o d e . See R e f . 6. a  s  48  p r o c e s s , ij? = c o r r e s p o n d i n g c u r r e n t f o r t h e a n o d i c p r o c e s s ) i s ^1;'0 and t h e s e p a r a t i o n o f t h e p e a k p o t e n t i a l s (EJ: a n d E^) t h e o r e t i c a l v a l u e o f 59 mV.  i s close to the  For non-aqueous s o l u t i o n s t h e t h e o r e t i c a l 7  v a l u e o f 59 mV i s n o t o b s e r v e d d u e t o u n c o m p e n s a t e d s o l u t i o n r e s i s t a n c e . A l l c y c l i c v o l t a m m o g r a m s w e r e o b t a i n e d u s i n g s o l u t i o n s c o n t a i n i n g ^0.05M e l e c t r o l y t e and f o r t h e experiments performed i n dichloromethane  the  t y p i c a l p e a k s e p a r a t i o n f o r a r e v e r s i b l e e l e c t r o d e p r o c e s s was 70 - 90 mV. C y c l i c voltammograms  i n C h ^ C ^ w i t h 0.1M e l e c t r o l y t e h a v e been r e p o r t e d  t o g i v e p e a k s e p a r a t i o n s o f ^ 7 0 m'V a n d t h e s l i g h t l y h i g h e r v a l u e s s e e n 7  i n t h e p r e s e n t work a r e p r o b a b l y due t o t h e lower c o n c e n t r a t i o n (and hence higher s o l u t i o n resistance) o f e l e c t r o l y t e . (E^ + E p / 2 )  T h e mean o f t h e p e a k p o t e n t i a l s  i s c a l l e d t h e half-wave p o t e n t i a l and i s quoted as t h e reduc-  t i o n p o t e n t i a l f o r the e l e c t r o d e process being considered.  A l l potentials  r e c o r d e d a r e g i v e n w i t h r e s p e c t t o t h e p o t e n t i a l o f an Ag/Sat/AifCI r e f e r e n c e e l e c t r o d e a t room t e m p e r a t u r e ( + 0 . 2 2 2 3 V vs.SHE)  and a r e u n c o r r e c t e d f o r  junction potentials. F o r c o n t r o l l e d p o t e n t i a l e l e c t r o l y s i s t h e PAR p o t e n t i o s t a t was u s e d a l o n e a n d was d i r e c t l y l i n k e d t o t h e e l e c t r o l y s i s c e l l .  An HDC-371 i n t e g r a -  t o r c o u l d be a t t a c h e d f o r t h e e x p e r i m e n t s u t i l i z i n g c o u l o m e t r y .  The required  p o t e n t i a l b e t w e e n t h e w o r k i n g a n d r e f e r e n c e e l e c t r o d e s was d i a l l e d i n t o t h e p o t e n t i o s t a t which a l t e r e d the p o t e n t i a l o f t h e a u x i l i a r y e l e c t r o d e accordingly.  49  b)  Apparatus and Procedures The H - c e l l s u s e d t o o b t a i n c y c l i c v o l t a m m o g r a m s w e r e u s u a l l y f i t t e d  w i t h f i n e o r medium f r i t s t o l i m i t t h e f l o w o f s o l v e n t between t h e t h r e e compartments  ( F i g u r e 2.5).  T h e a u x i l i a r y e l e c t r o d e was made o f p l a t i n u m  mesh s u p p o r t e d by p l a t i n u m w i r e .  T h e w o r k i n g e l e c t r o d e was a p l a t i n u m bead  s e a l e d i n t o t h e end o f a h o l l o w g l a s s t u b e .  A copper wire running into t h e  o p e n e n d o f t h i s t u b e makes c o n t a c t w i t h t h e p r o t r u d i n g bead v i a a l a y q r of mercury ( F i g u r e 2.5).  The Ag/Sat;AgCl r e f e r e n c e e l e c t r o d e c o n s i s t e d  o f a n a r r o w g l a s s t u b e s e a l e d by a p l u g o f a g a r s a t u r a t e d w i t h KC1 . A b o v e t h e a g a r p l u g was p l a c e d a s a t u r a t e d s o l u t i o n o f KC1 t o w h i c h a f e w d r o p s o f d i l u t e a q u e o u s AgNO^ s o l u t i o n w e r e a d d e d .  A s i l v e r wire, forming the  e l e c t r o d e , was t h e n i m m e r s e d i n t h e s u s p e n s i o n o f A g C l [ F i g u r e 2 . 5 ) . In a t y p i c a l e x p e r i m e n t t h e a p p a r a t u s was s e t up a s shown i n F i g u r e 2.5 a n d t h e s o l u t i o n i n t h e w o r k i n g c o m p a r t m e n t via the t e f l o n lead f o r about f i v e minutes.  purged with argon  T h e t e f l o n l e a d was t h e n r a i s e d  a b o v e t h e l e v e l o f t h e l i q u i d t o keep a l a y e r o f a r g o n a b o v e t h e s o l u t i o n . A b l a n k sweep t o c h e c k t h e p u r i t y o f t h e e l e c t r o l y t e s o l u t i o n was p e r f o r m e d before adding t h e p o r p h y r i n sample.  T h e s o l u t i o n was p e r i o d i c a l l y s t i r r e d  a n d r e c h a r g e d w i t h a r g o n by l o w e r i n g t h e t i p o f t h e a r g o n l e a d b e l o w t h e s u r f a c e o f t h e s o l v e n t , a l t h o u g h b e f o r e r u n n i n g a c y c l i c voltammogram t h e a g i t a t i o n o f t h e s o l u t i o n had t o be s t o p p e d . In c y c l i c v o l t a m m e t r y t h e c o m p o s i t i o n o f a s m a l l v o l u m e o f s o l u t i o n c l o s e t o t h e working e l e c t r o d e changes w i t h t h e p o t e n t i a l o f t h e working e l e c t r o d e t h e b u l k o f t h e s o l u t i o n o u t s i d e t h i s smal 1: j/olume r e m a i n s  • -..  \  \ 1  COPPER  W I R E  M E R C U R Y C O N T A C  S I L V E R  W I R E  A Q U E O U S +  T  KCI  O  A g C I Pt  M E S H  A G A R  Pt  B E A D  F I N E S P I N  F i g u r e 2.5  FRITS  B A R  The H c e l l and e l e c t r o d e arrangement used f o r c y c l i c voltammetry: b) w o r k i n g e l e c t r o d e , a n d c ) a u x i l i a r y e l e c t r o d e .  a)reference  electrode,  51  u n c h a n g e d due t o t h e s l o w r a t e o f d i f f u s i o n on t h e t i m e s c a l e s  concerned.  One e f f e c t o f t h i s i s t h a t t h e c y c l i c v o l t a m m o g r a m o f a r e d u c e d  and  oxidized  s p e c i e s w i l l be i d e n t i c a l p r o v i d i n g t h e o n l y d i f f e r e n c e b e t w e e n t h e species i s the presence  two  o r a b s e n c e o f an e l e c t r o n ( i . e . no c h a n g e s i n t h e  c o o r d i n a t i o n o f l i g a n d s i n the complex; f o r example R u * * ( 0 E P ) ( P B u ) 2  ij)  n  3  and  Ru (.0EP)(.P Bu ) n i  n  3  + 2  ( 9 ) , E ^ + 0 . 0 3 V - see S e c t i o n 7 . 1 ) .  This is  because c y c l i c voltammograms are u s u a l l y s t a r t e d a t p o t e n t i a l s (e.g. o r -0.2V) a t w h i c h t h e r e d u c e d  s p e c i e s w o u l d be p r e s e n t .  0.0  Hence i n the  v o l t a m m o g r a m o f t h e o x i d i z e d s p e c i e s ( i . e . 9_ i n t h e e x a m p l e a b o v e ) t h e s o l u t i o n c l o s e t o t h e e l e c t r o d e w o u l d be r e d u c e d  ( t o 7) a t t h e s t a r t o f  t h e sweep and t h u s t h e f o r m o f t h e v o l t a m m o g r a m w o u l d be i d e n t i c a l t o t h a t of the reduced  species.  I f the reduced  and o x i d i z e d s p e c i e s show i d e n t i c a l  voltammograms t h i s i s a good i n d i c a t i o n t h a t the o x i d a t i o n o r process  i n v o l v e s - no c h a n g e i n l i g a n d c o o r d i n a t i o n ( i .e.  reduction  i s r e v e r s i b l e on  a r e l a t i v e l y long time s c a l e ) although the s i t u a t i o n f o r weakly c o o r d i n a t i n g l i g a n d s s u c h as e l e c t r o l y t e a n i o n s  i s more c o n f u s i n g ( s e e  Section  4.1).  S y n t h e s i s o f o x i d i z e d s p e c i e s was a c h i e v e d u s i n g t h e c e l l shown i n F i g u r e 2.6.  The s o l u t i o n t o be e l e c t r o l y s e d (%! 5 mL) was  drical glass container.  placed in a c y l i n -  A t e f l o n cap f o r t h i s c o n t a i n e r supported  a closed  tube o f Vycor porous g l a s s (Gorning 7930), f i l l e d with e l e c t r o l y t e s o l u t i o n , and c o n t a i n i n g t h e p l a t i n u m mesh a u x i l i a r y e l e c t r o d e .  The r e f e r e n c e  electrode  was c o n s t r u c t e d as d e s c r i b e d a b o v e and h e l d by a c r a c k e d t i p e l e c t r o d e a l s o f i l l e d with e l e c t r o l y t e s o l u t i o n .  A l a r g e a r e a ( 2 0 cm ) p l a t i n u m  mesh  e l e c t r o d e was wound a r o u n d t h e V y c o r and i m m e r s e d i n t h e s o l u t i o n i n t h e  52  F i g u r e 2.6  The a p p a r a t u s  used f o r the bulk e l e c t r o l y s i s o f a p o r p h y r i n  species.  53  g l a s s c o n t a i n e r which thus formed the working  e l e c t r o d e compartment.  a t y p i c a l p r e p a r a t i o n the s o l u t i o n in the working  c o m p a r t m e n t was  In  thoroughly  p u r g e d w i t h a r g o n f o r f i v e m i n u t e s and t h e n p r e - e l e c t r o l y s e d a t a p o t e n t i a l h i g h e r t h a n t h a t t o be u s e d f o r t h e p r e p a r a t i o n , i n o r d e r t o o x i d i z e a n y trace impurities.  The p o r p h y r i n s a m p l e was t h e n a d d e d and e l e c t r o l y s e d by  s t e a d i l y i n c r e a s i n g the p o t e n t i a l , care being taken not to overload  the  potentiostat.  concen-  Solutions prepared f o r experiments -4  -3  trations 5 x 1 0  t o 1 x 10  M.  S t r o n g e r s o l u t i o n s used i n the p r e p a r a t i o n  o f new c o m p o u n d s ( p o r p h y r i n s a m p l e 100 - 200 mg) l a r g e r c o n t a i n e r (125 mL', t y p i c a l l y 5 x 10"  were t y p i c a l l y o f  3  were e l e c t r o l y z e d i n a  v o l u m e o f s o l u t i o n 40 - 50 mL) a n d w e r e  to 1 x 10" M. 2  Cation r a d i c a l samples prepared  for the f l a s h p h o t o l y s i s  and f o r s t u d i e s i n w h i c h s p e c t r a l c h a n g e s w e r e m o n i t o r e d  experiments,  during the o x i d a t i o n  p r o c e s s , r e q u i r e d the use o f a flow c e l l .  This c e l l , incorporating optical  windows w i t h  ( f o r studying the v i s i b l e  p a t h l e n g t h s o f 5 mm  Soret regions of the spectrum,  and 1 mm  r e s p e c t i v e l y ) i s shown i n F i g u r e 2.7  i t s u s e has been p r e v i o u s l y d e s c r i b e d .  and and  The s o l u t i o n ^ t o be e l e c t r o l y s e d  was p l a c e d i n t h e f l o w c e l l a n d a n y b u b b l e s c a r e f u l l y r e m o v e d t o e n s u r e continuous  column of l i q u i d throughout  the e n t i r e flow c e l l .  a s s e m b l y , s e e n i n F i g u r e 2.5, was s u p p o r t e d  by t h e t e f l o n l i d , and  i n t h e s o l u t i o n i n t h e t o p o f t h e f l o w c e l l . T h e s o l u t i o n was an o b i a t e s p i n b a r w h i c h d r o v e t h e s o l u t i o n a r o u n d trolysis.  electrode immersed  stirred  by  the flow c e l l during e l e c -  The w i n d o w s o f t h e f l o w c e l l w e r e a l i g n e d w i t h t h e s a m p l e beam  o f t h e C a r y 17D s p e c t r o m e t e r proceeded.  The  a  and s p e c t r a o b t a i n e d a s t h e e l e c t r o l y s i s  54  E L E C T R O L Y S I S CELL  C  1  1  T  - O B L A T E  3  l  SPIN  BAR  '  OPTICAL  WINDOWS  a) 5mm b) Imm  F i g u r e 2.7  WINDOW WINDOW  A f l o w c e l l used to study the o p t i c a l s p e c t r a o f c a t i o n during their formation.  radicals  55  2.3  a)  Photolysis  Experiments  Bulk P h o t o l y s i s  Experiments -5  P o r p h y r i n s o l u t i o n s t o be p h o t o l y s e d w e r e u s u a l l y 10 and w e r e p l a c e d i n a u . v . / v i s i b l e s p e c t r o s c o p y c e l l equipped  -4 t o 10  M,  ( t y p e C i n F i g u r e 2.1)  w i t h a r u b b e r s e p t u m p i e r c e d by two s y r i n g e n e e d l e s t o a l l o w  purging o f t h e s o l u t i o n d u r i n g p h o t o l y s i s ( F i g u r e 2 . 8 ) . The s o l u t i o n was t h o r o u g h l y p u r g e d w i t h a r g o n f o r f i v e m i n u t e s b e f o r e c o m m e n c i n g lysis.  photo-  T h e p h o t o l y s i n g lamp was a Model 700 lamp ( S m i t h - V i c t o r C o r p . ) w i t h  a DVY 650 w a t t q u a r t z h a l o g e n b u l b ( S y l v a n i a ) .  T h e p h o t o l y s i s c e l l was  h e l d i n s i d e a i L i e b i g ^ o n d e n s e r made o f p y r e x g l a s s a t a r a n g e o f ^ 1 0 cm from t h e lamp.  A r a p i d flow o f water through t h e condenser  o f i n f r a - r e d r a d i a t i o n from t h e p h o t o l y s i s b)  Flash P h o t o l y s i s Experiments:-  ensured  removal  light.  Instrumentation  The f o l l o w i n g e q u i p m e n t was u s e d i n c o l l a b o r a t i o n w i t h  Professor  D. H o l t e n a n d has been d e s c r i b e d e l s e w h e r e ( F i g u r e 2 . 9 ) . 1 0  A m o d e l o c k e d Nd:YAG l a s e r d e l i v e r s s i n g l e 35 p s , 1064 nm, lOmJ p u l s e s a t a r e p e t i t i o n r a t e a d j u s t a b l e up t o 1 0 H z .  R a d i a t i o n a t 1064 nm  i s s p l i t i n t o two p a r t s by a beam s p l i t t e r t o d r i v e t h e e x c i t a t i o n (pump) and m o n i t o r i n g  (probe) aspects o f t h e apparatus.  T h e pump r a d i a t i o n c a n be  c o n v e r t e d t o h a r m o n i c s a t 5 3 2 , 355 a n d 266 nm by u s i n g of potassium  dihydrogen  phosphate (KDP).  oriented, crystals  T h e h a r m o n i c a t 532 nm i s t h e m o s t  i n t e n s e w h e r e a s u s e o f t h e 355 nm h a r m o n i c e n t a i l e d an i n t e n s i t y ^ 1 % t h a t o f t h e 532 nm h a r m o n i c .  T h e e x c i t a t i o n r a d i a t i o n i s f o c u s s e d o n t o a 1 t o 2 mm  56  EXIT \ V K A /  A  R  G  O  LEAD  N  ilffw—-—SEPTU M  PORPHYRIN IN  SOLUTIO N  DICHLORO  METHANE  L I G H T  WATER  FLOWING  THROUGH  CONDENSER  F i g u r e 2.8 A p p a r a t u s u s e d f o r t h e b u l k p h o t o l y s i s o f c a t i o n r a d i c a l  solutions.  1064 nm Nd:YAG osc.  SPS  Nd:YAG amp  Quantel YG 400  KDP Parametric Generator  Vidicon  Sample  M 0.25 ra  pump  —  U - - -  -Oi.---- -'""''"''--0--- --o-D--i---0--&-0--\ hl  probe  I  i  1  1  ,'FD! x  OMA  Microcomputer  1 1 1 1 1 1 1 1 <^  ~  '  1  1  1  1  Delay Line  F i g u r e 2.9 T h e p i c o s e c o n d f l a s h p h o t o l y s i s a p p a r a t u s . BS - 5 0 % beam s p l i t t e r ; FD , FT - c r y s t a l s f o r f r e q u e n c y d o u b l i n g a n d t r i p l i n g ; F - . c o l o u r e d g l a s s f i l t e r s ; KDP - c r y s t a l s o f p o t a s s i u m d i h y d r o g e n p h o s p h a t e ; -M - m o n o c h r o m a t o r ; CL - c y l i n d r i c a l l e n s e s . M o d i f i e d f r o m a d i a g r a m k i n d l y p r o v i d e d b y D. H o l t e n .  58  d i a m e t e r s p o t i n t h e c e n t r e o f a 1 mm s a m p l e window i n a f l o w c e l l . The 1064 nm r a d i a t i o n i n t h e p r o b e l e g o f t h e a p p a r a t u s an o p t i c a l d e l a y l i n e .  traverses  T h i s c o n t r o l s t h e time d i f f e r e n c e between t h e  e x c i t a t i o n l i g h t a n d t h e m o d i f i e d probe, r a d i a t i o n r e a c h i n g t h e s a m p l e . H e n c e , a movement o f t h e r e f l e c t i n g p r i s m by 1 mm a l t e r s t h e p a t h l e n g t h t r a v e l l e d by t h e l i g h t by 2 mm w h i c h t r a n s l a t e s i n t o a c h a n g e i n d e l a y o f t h e p r o b e r a d i a t i o n by 6.6 p s . T h e d e l a y l i n e c a n t h u s a r r a n g e f o r t h e probe r a d i a t i o n t o a r r i v e a t t h e sample anywhere, from a few tens o f picoseconds  b e f o r e t h e pump r a d i a t i o n , t o g r e a t e r t h a n t e n n a n o s e c o n d s  (10 p s ) a f t e r t h e e x c i t a t i o n p u l s e .  Prior to reaching the  sample,the  d e l a y e d p r o b e r a d i a t i o n a t 1064 nm i s f o c u s s e d on a c e l l c o n t a i n i n g C C l ^ which s c a t t e r s the wavelengths a continuum  o f t h e r a d i a t i o n g i v i n g a 30ps p u l s e w i t h  o f f r e q u e n c i e s f r o m 400 nm t h r o u g h 1064 nm t o w e l l o u t i n t o  t h e i n f r a - r e d . T h e r e s i d u a l 1064 nm r a d i a t i o n n o t s c a t t e r e d i s r e m o v e d by a d i c h r o i c beam s p l i t t e r .  T h e p r o b e l i g h t i s e l o n g a t e d v e r t i c a l l y by  a p a i r o f c y l i n d r i c a l l e n s e s ( C L ) , passed through e x c i t e d and u n e x c i t e d r e g i o n s o f t h e s a m p l e , a n d f o c u s s e d o n t o t h e e n t r a n c e s l i t o f a 1/4 m monochromatbr  with the e x i t s l i t removed.  A vidicon i s oriented: across the  e x i t o f t h e monochrometer and feeds t o an o p t i c a l m u l t i c h a n n e l COMA).  T h e 0MA e l e c t r o n i c s d i s s e c t  two t r a c k s , e a c h 500 c h a n n e l s w i d e . spectrum channel  analyser  the v i d i c o n detector a c t i v e area i n t o One t r a c k r e c e i v e s t h e d i s p e r s e d  o f probe l i g h t through t h e e x c i t e d sample, w h i l e t h e second  500  t r a c k i s a l i g n e d t o r e c e i v e probe l i g h t t r a n s m i t t e d through t h e  unexcited o r r e f e r e n c e r e g i o n o f the sample.  T h e two s i g n a l s a t e a c h wave-  l e n g t h a r e compared e l e c t r o n i c a l l y and a d i f f e r e n c e spectrum  obtained  over  59  the wavelength  r a n g e ( w h i c h may  be s e v e r a l h u n d r e d nm).  Such s p e c t r a are  c o l l e c t e d by t h e c o m p u t e r f r o m s u c c e s s i v e s h o t s and s i g n a l a v e r a g e d 11  g i v e the f i n a l spectrum c)  to  12  »  Flash Photolysis Experiments:-  Procedures  and Data C o l l e c t i o n  Samples o f the p o r p h y r i n -rr-cation r a d i c a l s p e c i e s were prepared a f l o w c e l l a s d e s c r i b e d i n S e c t i o n 2.2b.  To e n s u r e a d e q u a t e  in  absorption  o f t h e p h o t o l y s i n g r a d i a t i o n , t h e p o r p h y r i n s o l u t i o n had t o be s u f f i c i e n t l y c o n c e n t r a t e d t o a b s o r b a l a r g e p r o p o r t i o n o f t h e p h o t o l y s i n g p u l s e , b u t n o t too concentratedotherwise  i n s u f f i c i e n t white l i g h t o f the monitoring  through the sample t o the d e t e c t o r .  When u s i n g t h e 1 mm  pulse got  o p t i c a l window -4  o f t h e f l o w c e l l t h e c o n c e n t r a t i o n s r e q u i r e d w e r e a b o u t 5 x 10 f  p u l s e r a d i a t i o n and 1 x 10  M f o r 532  M f o r p h o t o l y s i s u s i n g 355 nm r a d i a t i o n .  h i g h e r c o n c e n t r a t i o n r e q u i r e d f o r t h e 355 nm r a d i a t i o n i s m a i n l y due the weaker pulses produced  nm  The to  by t h e l a s e r a t t h i s f r e q u e n c y , t h o u g h t h i s i s  p a r t l y o f f s e t by t h e e n h a n c e d a b s o r p t i o n o f t h e c a t i o n r a d i c a l a t 355 ( c l o s e t o t h e S o r e t ) c o m p a r e d t o 532  nm  nm.  A f t e r completion o f the e l e c t r o c h e m i c a l p r e p a r a t i o n o f the c a t i o n r a d i c a l , t h e f l o w c e l l was  c a p p e d so t h a t t h e s o l u t i o n was s e a l e d u n d e r  a r g o n , and t h e n p o s i t i o n e d so t h a t t h e 1 mm o p t i c a l window was a t t h e p o i n t w h e r e t h e p h o t o l y s i n g and m o n i t o r i n g beams c r o s s e d ( F i g u r e 2.9)-. s o l u t i o n was s t i r r e d t h r o u g h o u t  the l a s e r experiment  nent p h o t o l y s i s o f a l i m i t e d volume. wavelength  The'-  so as t o a v o i d p e r m a -  Data w e r e c o l l e c t e d o v e r  various  r a n g e s and w i t h d i f f e r e n t d e l a y t i m e s , and a r e p r e s e n t e d as a  60  s e r i e s o f d i f f e r e n c e spectra..' From t h e s e s p e c t r a t h e d e c a y t i m e s and s p e c t r a o f t h e t r a n s i e n t i n t e r m e d i a t e s c o u l d be d e d u c e d .  As t h e d e c a y  t i m e s o f t h e i n t e r m e d i a t e s w e r e f o u n d t o be r a t h e r s h o r t c o m p a r e d t o t h e t i m e f o r t h e d e c a y o f t h e p h o t o l y s i s f l a s h (^25  ps  v e r s u s <35 ps d e c a y  t i m e f o r t h e f l a s h ) , a s i m p l e k i n e t i c p l o t was i n s u f f i c i e n t t o o b t a i n t h e d e c a y c o n s t a n t s f o r t h e i n t e r m e d i a t e s . The e f f e c t s o f t h e f l a s h be r e m o v e d by c o m p u t e r results.  had t o  a n a l y s i s to g i v e the decay c o n s t a n t quoted i n the  T h i s a n a l y s i s was  k i n d l y d o n e by P r o f e s s o r D. H o l t e n  (Washington  U n i v e r s i t y , S t . L o u i s , M i s s o u r i ) and i s n o t f u r t h e r d i s c u s s e d h e r e .  2.4  a)  M a t e r i a l s (1)  G a s e s , S o l v e n t s , L i g a n d s and  Electrolytes.  Gases C a r b o n m o n o x i d e and a r g o n w e r e o b t a i n e d f r o m L i n d e and u s e d w i t h o u t  further  b)  purification.  Solvents Nitromethane  (MC/B  Co. O m n i s o l v e ) was r e f l u x e d o v e r  phosphorus  p e n t o x i d e , and d i s t i l l e d and s t o r e d u n d e r a r g o n u n t i l r e q u i r e d .  Anhydrous  e t h a n o l was o b t a i n e d by d i s t i l l i n g 95% e t h a n o l / w a t e r f r o m m a g n e s i u m e t h o x i d e u n d e r a r g o n and u s e d  immediately.  P y r i d i n e ( B u r d i c k and J a c k s o n , D i s t i l l e d  i n G l a s s ) was r e f l u x e d and d i s t i l l e d f r o m c a l c i u m h y d r i d e u n d e r  argon,  and t h e n s t o r e d o v e r m o l e c u l a r s i e v e s (4A) u n d e r a r g o n u n t i l u s e d . T o l u e n e (MC/B  Co. O m n i s o l v e o r B u r d i c k and J a c k s o n , D i s t i l l e d i n G l a s s ) and a c e t o n i -  61  t r i l e ( B u r d i c k and J a c k s o n , D i s t i l l e d  i n G l a s s ) were r e f l u x e d o v e r  c a l c i u m h y d r i d e u n d e r a r g o n a n d t h e n d i s t i l l e d u n d e r an a r g o n  atmosphere.  T h e t o l u e n e was u s e d i m m e d i a t e l y , w h i l e t h e a c e t o n i t r i l e was s t o r e d u n d e r argon u n t i l r e q u i r e d . D i c h l o r o m e t h a n e was u s e d a s a g e n e r a l p u r p o s e s o l v e n t . B a t c h e s o f r e a g e n t g r a d e ( F i s h e r S c i e n t i f i c Co. o r C a l o g e n Co.) o f o3-4 l i t r e s p e r r  b a t c h w e r e d i s t i l l e d s l o w l y t h r o u g h a 1.3 m e t r e d i s t i l l a t i o n taining glass helices.  column con-  F o r some b a t c h e s o f s o l v e n t t h i s was i n s u f f i c i e n t t o  r e m o v e a l l t h e i m p u r i t i e s : ( a s j u d g e d by t h e u . v - . / v i s i b l e - . . s p e c t r a "of r u t h e n i u m p o r p h y r i n s a m p l e s o b t a i n e d i n t h e d i s t i l l e d s o l v e n t ) , a n d some c a l c i u m h y d r i d e had t o be a d d e d t o t h e s t i l l - p o t i n o r d e r t o r e m o v e a v o l a t i l e o x i d i z i n g agent.  Good s a m p l e s o f s o l v e n t showed a f l a t a b s o r p t i o n  s p e c t r u m i n t h e v i s i b l e a n d n e a r u . v . , g i v i n g a c u t - o f f b e l o w 231  nm.  T h i s h i g h q u a l i t y s o l v e n t was u s e d t o c h a r g e a s t i l l o v e r c a l c i u m h y d r i d e from which samples o f d i c h l o r o m e t h a n e were d i s t i l l e d under argon f o r use in e l e c t r o c h e m i c a l experiments. the  The bulk o f t h e s o l v e n t d i s t i l l e d  through,  f r a c t i o n a t i n g c o l u m n was u s e d f o r p r e p a r a t i o n s , c h r o m a t o g r a p h y ,  washing o f apparatus and s t o r a g e o f t h e Vycor g l a s s . A l l o t h e r s o l v e n t s were s p e c t r a l grade and used w i t h o u t f u r t h e r purification.  c)  Ligands T r i - n - b u t y l p h o s p h i n e (MC/B) was d i s t i l l e d a t r e d u c e d p r e s s u r e a n d  s t o r e d under argon.  T r i p h e n y l p h o s p h i n e was r e c r y s t a l 1 i z e d f r o m h o t e t h a n o l  before u s e . Tetraethylammonium  c y a n i d e ( T E A C N ~ ) ( F l u k a ) was s t o r e d o v e r +  62  p h o s p h o r u s pe.ntoxi.de. T e t r a e t h y l a m m o n i u m c h l o r i d e ( T E A C 1 ~ ) was T  on a vacuum  dried  l i n e a t ^ 8 0 ° C u n t i l c o n s t a n t mass was o b t a i n e d , a n d s t o r e d  over phosphorus pentoxide. A l l o t h e r l i g a n d s were r e a g e n t g r a d e and u s e d w i t h o u t f u r t h e r  puri-  fication.  d)  Electrolytes Tetra-n-butylammonium  p e r c h l o r a t e ( T B A P ) and t e t r a e t h y l a m m o n i u m  p e r c h l o r a t e ( T E A P ) ( b o t h f r o m G. F r e d e r i c k S m i t h C h e m i c a l Company) were r e c r y s t a l l i z e d from acetone ( s p e c t r a l grade - Eastman), the c r y s t a l s ground up a n d d r i e d f o r 24 h u n d e r v a c u u m . Tetra-n-propylammonium  t r i f l u o r o m e t h a n e s u l p h o n a t e ( T P A T F S ) was p r e -  p a r e d by f o l l o w i n g a p r o c e d u r e i n t h e l i t e r a t u r e looking crystals.  1 3  and gave e x c e l l e n t  50 g o f t e t r a - n - p r o p y l a m m o n i u m b r o m i d e ( T P A B r ~ ) was +  d i s s o l v e d i n 100 mL o f w a t e r .  To t h i s s o l u t i o n w i t h c o n s t a n t s t i r r i n g  s l o w l y a d d e d 17 mL o f t r i f l u o r o m e t h a n e s u l p h o n i c a c i d .  The r e s u l t i n g  was preci-  p i t a t e was c o l l e c t e d , washed w i t h w a t e r , d r i e d by s u c t i o n , a n d t h e n r e c r y s t a l l i z e d f r o m h o t THF.  The c r y s t a l s were c o l l e c t e d and t h e n d i s s o l v e d i n  130 mL o f d i c h l o r o m e t h a n e . T h e s o l u t i o n was b r o u g h t t o b o i l i n g a n d d i e t h y l e t h e r was s l o w l y a d d e d w i t h c o n s t a n t s t i r r i n g u n t i l a p e r m a n e n t  precipitate  was o b t a i n e d . T h e s o l u t i o n was t h e n a l l o w e d t o s l o w l y c o o l a n d t h e c r y s t a l s c o l l e c t e d , d r i e d and t h e n g r o u n d up a n d r e d r i e d u n d e r vacuum f o r 24 h, (.60% y i e l d ) . Tetra-n-butylammonium  t e t r a f l u o r o b o r a t e ( T B A F ) : T h i s was p r e p a r e d by  r e a c t i n g t e t r a - n - b u t y l a m m o n i u m b r o m i d e ( T B A B r ~ ) (.31 .8 g) w i t h ammonium +  63  fluoroborate  ( 1 0 g) i n a q u e o u s s o l u t i o n .  T h e w h i t e p r e c i p i t a t e was c o l l e c t e d ,  d r i e d by s u c t i o n , a n d t h e n r e p r e c i p i t a t e d f r o m s o l u t i o n i n m e t h a n o l ( 2 0 0 mL) by t h e s l o w a d d i t i o n o f d i s t i l l e d w a t e r ( 1 0 0 - 500 m L ) , d u r i n g r e m o v a l o f t h e m e t h a n o l on a B u c h i r o t o v a p .  The c r y s t a l s were c o l l e c t e d , washed  with  d i s t i l l e d w a t e r , d r i e d by s u c t i o n , a n d t h e n d i s s o l v e d i n a minimum v o l u m e of b o i l i n g acetone.  On s l o w c o o l i n g , t h i s s o l u t i o n d e p o s i t e d  crystals that  w e r e c o l l e c t e d , d r i e d , g r o u n d up a n d d r i e d u n d e r vacuum f o r 24 h , ( 2 5 % y i e l d ) . Like the corresponding  trifluoromethanesulphonate  to o i l out o f s o l u t i o n very e a s i l y .  salt this material  Later batches o f fluoroborate  tended  electro-  l y t e u t i l i z e d t h e t e t r a - n - p r o p y l a m m o n i u m s a l t w h i c h was p r e p a r e d by s i m i l a r methods. Tetra-n-propylammonium t e t r a f l u o r o b o r a t e  (TPAF):  20 g o f t e t r a - n -  p r o p y l a m m o n i u m b r o m i d e was d i s s o l v e d i n ^ 3 0 0 mL o f d i s t i l l e d w a t e r a n d t o t h i s s o l u t i o n was a d d e d 4 g o f ammonium f l u o r o b o r a t e  i n -v.100 mL o f w a t e r .  No p r e c i p i t a t e f o r m e d i m m e d i a t e l y b u t o n s t a n d i n g m a s s e s o f c r y s t a l s w e r e deposited.  These were c o l l e c t e d , r i n s e d w i t h d i s t i l l e d water and r e c r y s t a l -  l i z e d f r o m a minimum v o l u m e o f b o i l i n g a c e t o n e .  The c r y s t a l s obtained  from  t h e c o o l e d a c e t o n e w e r e c o l l e c t e d , d r i e d , g r o u n d up a n d d r i e d u n d e r vacuum f o r 24 h ( 3 2 % y i e l d ) . Tetra-n-butylammonium hexafluorophosphate (JBAH): Crude samples, 1 h  kindly provided  by J . T h o r n b a c k  , w e r e p u r i f i e d by r e c r y s t a l 1 i z a t i o n f r o m  hot e t h a n o l , and d r i e d under vacuum. T e t r a e t h y l ammonium  picrate (TEAPIC):  9.0 g o f p i c r i c a c i d , 3.0 g  o f p o t a s s i u m h y d r o x i d e a n d 11.5 g o f t e t r a e t h y l ammonium  perchlorate  were  64  added t o  ^150 mL o f w a t e r and v i g o r o u s l y s t i r r e d .  The a q u e o u s  solution  was d e c a n t e d f r o m u n d i s s o l v e d s o l i d ( p i c r i c a c i d ) and e x t r a c t e d w i t h ^250 mL o f d i c h l o r o m e t h a n e .  The a q u e o u s  l a y e r was r e t u r n e d t o t h e v e s s e l  containing the undissolved s o l i d , v i g o r o u s l y s t i r r e d f o r e x t r a c t i o n s t e p was r e p e a t e d . d r i e d over anhydrous  h/and t h e n t h e  The d i c h l o r o m e t h a n e f r a c t i o n s were amalgamated,  sodium s u l p h a t e , and e v a p o r a t e d to d r y n e s s .  was r e d i s s o l v e d i n C H ^ C ^  The  solid  (^40 m L ) , f i l t e r e d t o r e m o v e i n s o l u b l e i m p u r i t i e s ,  and t h e s o l v e n t s l o w l y r e m o v e d by r o t a r y e v a p o r a t i o n u n t i l c r y s t a l s o f t h e product started to p r e c i p i t a t e out.  T h e m i x t u r e was t h e n c o o l e d and t h e  c r y s t a l s o f T E A P I C w e r e c o l l e c t e d , and d r i e d f o r 24 h u n d e r vacuum ( 5 5 % yield). A l l d r i e d , p u r i f i e d samples o f e l e c t r o l y t e s were s t o r e d o v e r  phospho-  rus pentoxide.  e)  Miscellaneous Tetra-n-butylammonium  b o r o h y d r i d e ( T B A B H ~ ) was k i n d l y p r o v i d e d by +  4  1 5  B. T a r p e y , h a v i n g been p r e p a r e d by a m e t h o d p r e v i o u s l y d e s c r i b e d  .  The  s o l i d was r e c r y s t a l l i z e d f r o m e t h y l a c e t a t e , d r i e d u n d e r v a c u u m , and s t o r e d over phosphorus  pentoxide.  S i l v e r t e t r a f l u o r o b o r a t e ( A l d r i c h C h e m i c a l Co.) was s t o r e d o v e r a n h y d r o u s c a l c i u m c h l o r i d e and h a n d l e d i n a g l o v e b a g u n d e r an a r g o n a t m o s phere i n reduced l i g h t i n g c o n d i t i o n s . Ruthenium  was a v a i l a b l e as t h e t r i c h l o r i d e h y d r a t e ( 4 2 . 7 6 % Ru)  Johnson Matthey L t d .  from  The d o d e c a c a r b o n y l , R u ( C 0 ) , was p r e p a r e d f r o m t h e 3  1 2  65  chloride  by a l i t e r a t u r e p r o c e d u r e , as well  available  from Strem Chemicals.  provided by J . B . Paine III, dure  17  .  2.5  as  1 0  (2)  commercially  O c t a e t h y l p o r p h y r i n , H ( 0 E P ) , was 2  having  kindly  been prepared v i a a l i t e r a t u r e p r o c e -  Z i n c t e t r a p h e n y l p o r p h y r i n was  Materials  being  k i n d l y p r o v i d e d by C. Wei b o r n .  P r e p a r a t i o n o f the Ruthenium  Complexes  CARBONYL(ETHANOL)(OCTAETHYLPORPHINATO)RUTHENIUM(II) ( 2 ) ,  Ru(0EP)[C0)Et0H  18  In a m o d i f i e d method o f e a r l i e r workers  , 0.8 g o f H (.0EP) was 2  r e f l u x e d with 0.8 g o f R u g C C O ) ^ i n t o l u e n e (150 mL) f o r 22 h under a r g o n . When the l i . v . / v i s i b l e spectrum i n d i c a t e d complete r e a c t i o n , the s o l v e n t was removed by r o t a r y e v a p o r a t i o n . CH^C^/EtOH  and the s o l u t i o n  s o l v e n t gave s o l i d neutral  r e f l u x e d under argon  Ru(0EP)(C0)Et0H,  i n 100 mL o f 1:1  f o r 1 h.  Removal  2  CH Cl /EtOH  - 2% i s o p r o p y l  2  (50 mL o f 3:1  2  v/v).  alcohol  v/v  o f the  which was p u r i f i e d on an a c t i v i t y  alumina column ( E . Merck) made up i n d i c h l o r o m e t h a n e .  eluted with CH C1 2  The s o l i d was d i s s o l v e d  III  The product  and was r e c r y s t a l 1 i z e d from  The c r y s t a l s  were r i n s e d w i t h hexane and  d r i e d under vacuum, y i e l d 63%, V^Q = 1927 c m . - 1  Analysis:  Calculated for C  Found: C, 66.27%; H, 7.20%; N, Mass s p e c t r a l 317(15),  H  4 g  N 0 Ru: 4  2  C, 66.24%; H, 6.99%; N,  7.93%.  7.79%.  d a t a : M/e 662(..10), R u ( O E P ) ( C 0 ) ; 634(100), +  Ru(0EP) ; +  RuC0EP) .  nmr Resonances for  3 g  reasons  2+  6 T M  s^  C D C 1  3^  :  1.92(t ,24H,-CH ), 4 . 0 1 ( q , 1 6 H , - C H - ) , 9 . 9 0 (s,4H,=CH-).  due to the c o o r d i n a t e d ethanol explained in Section  2  3  3.1.  ligand  c o u l d not u s u a l l y  be d e t e c t e d  66  CARBONYL(OCTAETHYLPORPHINATO)(PYRIDINE)RUTHENIUM(II) ( 3 ) , Ru(OEP)(CO)py S a m p l e s were k i n d l y p r o v i d e d by P.D. S m i t h .  T h i s c o m p l e x was  also  19.  p r e p a r e d by t h e p r e v i o u s l y r e p o r t e d Ru(OEP)(CO)EtOH  procedure^  a s f o l l o w s : t o 150 mg o f  ( 2 ) i n 100 mL o f d i c h l o r o m e t h a n e was a d d e d 1 mL o f p y r i d i n e  and t h e m i x t u r e r e f l u x e d f o r 2 h o u r s u n d e r a r g o n .  After cooling, the s o l -  v e n t was r e m o v e d a n d t h e s o l i d c h r o m a t o g r a p h e d on an a c t i v i t y I I I n e u t r a l a l u m i n a c o l u m n made up i n d i c h l o r o m e t h a n e . T h e r e q u i r e d p r o d u c t e l u t e d out r a p i d l y w i t h d i c h l o r o m e t h a n e , w e l l ahead o f any unchanged  2_ .  The  s o l v e n t was r e m o v e d and t h e s o l i d d r i e d u n d e r v a c u u m , y i e l d 8 5 % , V^Q = 1933  cm . - 1  Analysis:  C a l c u l a t e d f o r C H N 0 R u : C, 6 8 . 0 8 % ; H, 6.67%; N, 9.45%. 4 2  4 g  5  F o u n d : C, 6 8 J 4 % ; H, 6.60%; N, 9.46%. Mass s p e c t r a l d a t a : M / e 6 6 2 ( 2 0 ) , R u ( 0 E P ) ( C 0 ) ;  634(100), Ru(0EP) ;  t  +  317(29), Ru(.0EP) . 2+  nmr 6 pyridine:  J M S  ( C D C 1 ) : 1.90(t,24H,-CH ), 3  0.89(d,2H,d-H),  3  4.89(t,2H,6-H)»  3.99(m ,16H , - C H - ) ,  9.80(s,4H,=CH-):  2  5.82(t,lH, -H). Y  CARES ON YL(.4-METHYLPYRI DINE) (OCTAETHYLPORPH INATO) RUTH EN I UM( I I ) ' ( 4 ) ;  Ru(.QEP)-  CCp)4Mepy. S a m p l e s o f t h i s c o m p l e x were k i n d l y p r o v i d e d by P.D.  CARB0NYL(IMIDAZOLE)(0CTAETHYLPQRPHINAT0)RUTHENIUM(II)  Smith.  (5) Ru(OEP)(C0)lm.  100 mg o f R u ( 0 E P ) ( C 0 ) E t 0 H ( 2 ) and 14 mg o f i m i d a z o l e w e r e d i s s o l v e d i n d i c h l o r o m e t h a n e ( 1 5 0 mL) a n d t h e n t a k e n down t o d r y n e s s on  a rotary eva-  67  porator.  The s o l i d was c h r o m a t o g r a p h e d  on an a c t i v i t y I I I a l u m i n a  the r e q u i r e d p r o d u c t e l u t i n g w i t h d i c h l o r o m e t h a n e w e l l ahead o f 2 .  T h e s o l v e n t was r e m o v e d  column,  unchanged  and t h e s o l i d d r i e d u n d e r v a c u u m , y i e l d  75%,  v^Q = 1933 cm"* . Analysis:  C a l c u l a t e d f o r C H N 0 R u : C, 6 5 . 8 2 % ; H, 6.63%; N, 4 Q  4 8  11.51%.  6  F o u n d : C, 6 5 . 8 1 % ; H, 6.42%; N, 1 1 . 4 9 % . Mass s p e c t r a l data:M/e 6 6 2 ( 1 9 ) , R u ( 0 E P ) ( C 0 ) ; . 6 3 4 ( 1 0 0 ) , +  317(18),  Ru(0EP) ; +  Ru(0EP) . 2 +  nmr 6  T M S  (CDC1 ): 3  1.86(t,24H,CH ); 3  3 . 9 3 ( m , 1 6 H , C H ) . 9.69(s,4H,=CH-). 2  By c o m p a r i s o n w i t h d a t a r e p o r t e d f o r t h e m e s o p o r p h y r i n IX d i m e t h y l e s t e r 1 8  analogue  , t h e f o l l o w i n g r e s o n a n c e ^ were a s s i g n e d f o r t h e c o o r d i n a t e d  imidazole:0.37(b,lH,5-H),  0.71(b,lH,4-H).  (OCTAETHYLPORPHINATO)BIS(TRI-N-BUTYLPHQSPHINE)RUTHENIUM(11) ( 7 ) , Ru(OEP)(P Bu ) . n  3  2  F o l l o w i n g t h e p r o c e d u r e o f G. D o m a z e t i s ' , t o 400 mg o f 2 0  (CO)EtOH  2 4  Ru (0EP)I I  (2_), d i s s o l v e d i n ^ 5 0 mL o f d i c h l o r o m e t h a n e u n d e r a r g o n , was  added  a l a r g e e x c e s s (^3 mL) o f t r i - n - b u t y l p h o s p h i n e u n t i l t h e i n i t i a l 393 nm a n d 408 nm S o r e t p e a k s had d i s a p p e a r e d .  T h e s o l v e n t was t h e n r e m o v e d  by r o t o v a p  and t h e r e s i d u a l s o l i d r i n s e d w i t h ^50 mL o f a 5% s o l u t i o n o f d i c h l o r o m e t h a n e i n a c e t o n i t r i l e i n s m a l l p o r t i o n s p r i o r t o r e c r y s t a l 1 i z a t i o n f r o m 50 mL o f a 1:1 a c e t o n i t r i l e / d i c h l o r o m e t h a n e m i x t u r e . under vacuum, y i e l d  69%.  The s o l i d o b t a i n e d was  dried  68  Analysis: N, 5 . 4 0 % .  C a l c u l a t e d f o r C g g H g g N ^ R u : C, 6 9 . 4 2 % ; H, 9.51%;  F o u n d : C, 6 9 . 2 6 % ; H, 9.60%; N, 5.60%.  Mass s p e c t r a l d a t a : M / e 1 0 3 8 ( < 0 . 1 ) , R u ( 0 E P ) ( P B u ) ; n  836(100),  +  3  2  R u ( . 0 E P j ( P B u ) ; 634(71 ) , R u ( 0 E P ) ; 4 1 8 ( 2 1 ) , R u ( 0 E P ] ( p B u ) . n  +  +  n  2 +  3  nmr 6 =CH-1:  3  T M S  ( C D C 1 ) : 1.77(t,24H,-CH ), 3  3  3.77(q,16H,-CH -), 2  T r i - n - b u t y l p h o s p h i n e : 0.28(m,l8H,-CH ),  0.23(m,12H,-CH -),  3  -1.51(b,12H,-CH -), 2  -2.24(b,12H,-CH -),  8.97(s,4H, 2  -2 . 7 8 ( t , 1 2 H , - C H - ) .  2  2  CARB0NYL(OCTAETHYLPORPHINATO)(TRI-N-BUTYLPHOSPHINE)RUTHENIUM(II), (8) Ru(.0EP)(C0)P Bu . n  3  57 mg o f R u ( O E P ) ( C 0 ) E t 0 H (2J methane  .  was d i s s o l v e d i n %20 mL o f d i c h l o r o -  I n t o t h i s s o l u t i o n was d i s s o l v e d an e q u i m o l a r q u a n t i t y o f  Ru(.OEP) ( P B u ) n  3  2  {]_) (84 mg) a n d t h e m i x t u r e was v i g o r o u s l y p u r g e d w i t h  carbon monoxide f o r twenty m i n u t e s .  The u . v l / v i s i b l e s p e c t r u m showed a  s t r o n g S o r e t a t 408 nm and t h e c o m p l e t e a b s e n c e o f p e a k s a t 393 nm (2_) and 428 nm ( 7 ) . T h e s o l v e n t was r e m o v e d a n d t h e c r u d e s o l i d was  chromatographed  on an a c t i v i t y I I I a l u m i n a c o l u m n i n d i c h l o r o m e t h a n e . T h e r e q u i r e d p r o d u c t e l u t e d o f f r a p i d l y i n dic.hil.bromethane.wel 1 a h e a d o f a n y r e s i d u a l  2_ .  The  s o l v e n t was r e m o v e d a n d t h e s o l i d d r i e d u n d e r v a c u u m , y i e d i d 6 5 % , V^Q = 1948  cm" . 1  Analysis:  C a l c u l a t e d f o r C g H N P 0 R u : C, 6 8 . 1 0 % ; H, 8.28%; N, 6.48%. 4  ? 1  4  F o u n d : C, 6 8 . 2 0 % ; H, 8 . 2 5 % ; N, 6.30%. Mass s p e c t r a l d a t a : M / e 8 3 6 ( 1 0 0 ) , R u ( O E P ) ( P B u ) ; n  +  3  (C0) ; +  634(44), Ru(0EP) ; +  418(16), R u ( 0 E P ) ( P B u ) . n  2 +  3  662(5), Ru(OEP)-  69  •-nrar 6T CCDC1 1: 1 . 8 9 ( t , 2 4 H , - C H 3 ) , 3.97(.m,l6H,-CH ~), TMS  3  tri-n-butylphosphine:  9.69(s,4H  2  0.23(t,18H,-CH ),  0.14(m,12H,-CH -),  3  -1.80(b,12H,-CH -),  2  2  -3.16(q,12H,-CH -.). 2  (OCTAETHYLPORPHINATO)BIS(TRI-N-BUTYLPHOSPHINE)RUTHENIUM(,I II )BR0MIDE  (9b),  lRu (0EP)(;pnBu ) ] Br". n i  +  3  2  A s o l u t i o n o f 420 mg o f R u ( OEP) (,P Bu ) 1 T  n  3  2  (.7) i n ^50 mL o f d i c h l o r o -  methane was t i t r a t e d w i t h a s o l u t i o n o f bromine i n d i c h l o r o m e t h a n e ized spectrophotometrically, ^  m a x  a t 410 nm, e = 210 M  - 1  cm ) - 1  (standard-  until  the  u . v . / v i s i b l e a b s o r p t i o n spectrum i n d i c a t e d c o m p l e t i o n o f r e a c t i o n ( a p p r o x i m a t e l y 0.5 e q u i v a l e n t s o f bromine per r u t h e n i u m ) .  The s o l v e n t was then  removed and the s o l i d r i n s e d w i t h hexane b e f o r e d r y i n g under vacuum. were a n a l y s e d  i m m e d i a t e l y , as the s o l i d s l o w l y decomposed t o g i v e a m i x t u r e  of Ru (;0EP)(P Bu ) n  n  3  Yield  Samples  (.7) and R u ( 0 E P ) t P B u ) B r (10) 1 n  2  (see S e c t i o n  n  3  7.2).  56%. Analysis:  Calculated for C H N P B r R u : 6 0  N, 5.02%; B r , 7.09%; P, 5.55%.  g g  4  2  C, 64.46%; H, 8.84%;  Found: C, 64.11%; H, 8.74%; N, 5.00%; B r ,  6.95%; P, 5.77%. Mass s p e c t r a l data:M/e 8 3 6 ( 1 0 0 ) , Ru(OEP) (.P Bu ) ; n  +  3  Ru(0EP) ;  418(20),  +  634 ( 7 5 ) ,  Ru(OEP)(P Bu ) . n  2 +  3  T h i s compound was shown by c o n d u c t i v i t y s t u d i e s t o be a 1 :1 2 l y t e in CH C1 2  2  ( A = 130 mho. cm ... mol  electro-  -1 ).  The magnetic moment o f t h i s complex was determined (.y= 1 .8 BM ) and c o n f i r m s the presence o f one u n p a i r e d e l e c t r o n on t h e ruthenium atom.  70 BR0M0(OCTAETHYLPORPHINATO)(TRI-N-BUTYLPHOSPHINE)RUTHENIUM(111) (10) Ru (0EP)(P Bu )Br. m  n  3  To 100 mg o f R u ( 0 E P ) ( C 0 ) P B u 1 Z  ( g ) d i s s o l v e d i n ^100 mL  n  3  dichloro-  m e t h a n e was a d d e d a s l i g h t ( > 5 % ) . ' e x c e s s o f b r o m i n e i n t h e same s o l v e n t (0.5 B r  2  p e r r u t h e n i u m ) . The r e a c t i o n was f o l l o w e d  by m o n i t o r i n g t h e l o s s o f a b s o r p t i o n a t 408 nm.  spectrophotometrically  The s o l v e n t was  removed  u n d e r vacuum a n d t h e c r u d e s o l i d c h r o m a t o g r a p h e d on an a c t i v i t y I I I a l u m i n a , column, the product e l u t i n g o f f i n 2 - 4 % methane.  isopropanol(IPA) in dichloro-  A t t h i s s t a g e t h e s p e c i e s i n s o l u t i o n Cas j u d g e d by t h e o p t i c a l  s p e c t r u m ) was n o t 1_0 b u t [ R u  I I I  COEP)(P Bu )IPA3 Br" n  +  3  formed'by the d i s -  p l a c e m e n t o f t h e b r o m i d e i o n by t h e c o o r d i n a t i n g s o l v e n t  (isopropanol).  On r e m o v a l o f s o l v e n t t h e s p e c i e s 1_0 was r e g e n e r a t e d ( s e e S e c t i o n 7.4) a n d t h e r e s u l t i n g s o l i d was d r i e d u n d e r v a c u u m . Analysis:  C a l c u l a t e d f o r C^gHy-jN^BrPRu:  N, 6.12%; B r , 8 . 7 2 % ; P, 3 . 3 8 % . B r , 8.55%; P,  C, 6 2 . 9 3 % ; H , 7.81%;  F o u n d : C, 62.93%';" til, 7 , 9 3 % ; N, 6.0.0%;  3.89%.  Mass s p e c t r a l d a t a : M / e 8 3 6 ( 1 0 0 ) , R u ( O E P ) ( P B u ) ; n  +  3  [ R u ( 0 E P ] B r ] ; 634(41 ) , R u ( 0 E P ) * ; +  +  713, 7 1 5 ( 1 ) ,  418(54), Ru(OEP)(P Bu ) . n  2 +  3  C o n d u c t i v i t y s t u d i e s i n d i c a t e d t h i s compound t o be a non e l e c t r o l y t e 2 -1 when d i s s o l v e d i n d i c h l o r o m e t h a n e (A = 2 . 0  mho.  cm .mol  ),showing t h a t the  bromide l i g a n d i s c o o r d i n a t e d . The m a g n e t i c moment o f t h i s c o m p l e x was d e t e r m i n e d (y =  2.3,  BM)  and c o n f i r m s t h e p r e s e n c e o f one u n p a i r e d e l e c t r o n on t h e r u t h e n i u m a t o m .  71  CARBONYL(OCTAETHYLPORPHINATO)(TRIPHENYLPHOSPHINE)RUTHENIUM ( I I )  (11),  Ru(0EP)(C0)PPh . 3  T h i s c o m p l e x (V^Q e l s e w h e r e , was 2 2  = 1953  c m ) , whose p r e p a r a t i o n  has b e e n  - 1  kindly provided  by G.  described  Domazetis.  (OCTAETHYLPORPHINATO)BIS(TRIPHENYLPHOSPHINE)RUTHENIUM(II) (12), Ru(OEP)(PPh ) . 3  2  T h i s c o m p l e x , t o be d e s c r i b e d T.  e l s e w h e r e , was  kindly provided  2 3  by  Leung.  (OCTAETHYLPORPHINATO) BIS (TRI PHENYLARSINE)RUTHEN I UM( II) ( 1 3 ) , R u ( O E P ) ( A s - P h j ^ . U s i n g t h e p r o c e d u r e s o u t l i n e d i n S e c t i o n 2.2,  200 mg o f R u ( O E P ) ( C O ) E t O H  d i s s o l y e d i n 50 mL o f a 0.05M s o l u t i o n o f t e t r a - n - b u t y l a m m o n i u m p e r c h l o r a t e CI^C^  was  e l e c t r o l y s e d a t 0.85  v o l t s u n d e r an a r g o n a t m o s p h e r e t o g i v e a  s o l u t i o n o f the c a t i o n r a d i c a l [Ru s o l u t i o n was  1 1  ( O E P ) "(CO)] C T 0 ~ O a ) . +  To  +  4  a d d e d 19d mg o f t r i p h e n y l a r s i n e (2.2 A s P h  3  this  p e r r u t h e n i u m ) , and  s o l u t i o n was s t i r r e d and v i g o r o u s l y p u r g e d w i t h a r g o n f o r f i v e m i n u t e s t o ensure complete r e a c t i o n .  The p r o d u c t s ( [ R u  w i t h some R u ( 0 E P ) ( C O ) (1_) o b t a i n e d J I  0.0V  to give a pink s o l u t i o n o f  evaporation  .1_3 .  I I I  (0EP)(AsPh ) ] C10 ~ +  3  2  4  The s o l v e n t was  r e m o v e d by  The d i c h l o r o m e t h a n e was  rotary dichloro-  s l o w l y r e m o v e d on a vacuum  l i n e u n t i l t h e v o l u m e o f s o l u t i o n had b e e n r e d u c e d t o ^10 mL. t h a t had d e p o s i t e d  along  from a s i d e r e a c t i o n ) were r e d u c e d a t  and t h e s o l i d d i s s o l v e d i n 50 mL o f a 2:1 m i x t u r e o f  methane/acetonitrile.  in  w e r e c o l l e c t e d and w a s h e d t h o r o u g h l y  The  (.6 x 5 mL  crystals rinses)  the  72  w i t h a c e t o n i t r i l e . T h e s o l i d was d r i e d u n d e r v a c u u m , y i e l d 6 5 % . Analysis: N, 4.50%.  C a l c u l a t e d f o r C H N A s R u : C, 6 9 . 3 8 % ; H, 5 . 9 9 % ; 7 2  7 4  4  2  F o u n d : C, 6 9 . 4 4 % ; H, 6.15%; N,  4.55%.  Mass s p e c t r a l d a t a : M / e 6 3 4 ( 1 0 0 ) , R u ( 0 E P ) ;  317(5), Ru(0EP) .  +  nmr ( S =CH-)  :  T M S  2 +  ( C D C 1 ) : 1.71 ( t , 2 4 H , - C H ) , 3 . 6 7 ( q , 1 6 H , - C H - ) , 3  triphenylarsine:  3  8.84(s,4H,  2  4.13( b , l 2 H , o - H ) ,  6.38(b,12H,m-H),  6.70(b,6H,p-H).  TETRA-ETHYLAMM0NIUM(DICYAN0)0CTAETHYLP0RPHINAT0RUTHENATE(III) ( 1 4 ) , Et N [Ru (0EP)(CN) ]". +  I H  4  2  The t e t r a - n - b u t y l a m m o n i u m a n a l o g u e o f t h i s c o m p l e x has been p r e p a r e d p r e v i o u s l y , but by a t o t a l l y d i f f e r e n t p r o c e d u r e . 2 4  U s i n g t h e p r o c e d u r e s o u t l i n e d i n S e c t i o n 2>2, 100 mg o f R u ( 0 E P ) ( C 0 ) EtOH (2_) d i s s o l v e d i n 80 mL o f a 0.01M  s o l u t i o n o f tetra-ethylammonium per-  c h l o r a t e i n CH £.1. was e l e c t r o l y z e d a t 0.85 v o l t s u n d e r a n a r g o n a t m o s p h e r e 2  2  to g i v e a s o l u t i o n o f t h e c a t i o n r a d i c a l [ R u (0EP) " ( C 0 ) ] C 1 0 " (l_a). 1 1  +  +  4  An  e x c e s s (.90 mg) o f t e t r a - e t h y l a m m o n i u m c y a n i d e ( T E A C N ~ ) was a d d e d t o t h i s +  p r o d u c t (.la) w h i c h o n s t i r r i n g i m m e d i a t e l y g a v e a d e e p o r a n g e s o l u t i o n o f 14 . The s o l v e n t was r e m o v e d by r o t a r y e v a p o r a t i o n a n d t h e s o l i d c h r o m a t o g r a p h e d on an a c t i v i t y I I I a l u m i n a c o l u m n made up i n d i c h l o r o m e t h a n e .  A  d a r k o r a n g e b a n d o f t h e r e q u i r e d p r o d u c t (1_4) was e l u t e d o f f i n d i c h l o r o methane/5%  isopropanol.  T h e s o l v e n t was r e m o v e d and t h e s o l i d d r i e d u n d e r  vacuum, y i e l d 59%. Analysis:  C a l c u l a t e d f o r C H N R u : 6 7 . 7 0 % ; H, 7 . 9 1 % ; N,  F o u n d : C, 6 7 . 6 6 % ; H, 7.99%; N,  4 6  6 4  11.78%.  7  12.01%.  73  ( T E T R A P H EN Y LPORPHI NATO) BIS (,TR I PH EN YL PH OS PH I NE) RUTH EN IUM { R u ( T P P ) (PPh ) ; 3  2  CARBON YL ( T E T R A M E S I T Y L P O R P H I N A T O ) RUTHENI U M ( ( ? 0 ) , R u ( T M P ) ( C O ) ;  and (OCTAETHYLPORPHINATO)PYRIDINE(THIOCARBONYL)RUTHENIUM w e r e k i n d l y p r o v i d e d by B. T a r p e y , G. B i s s e t , a n d P.D.  ( I I ) , Ru(OEP)(CS)py. Smith^espectively.  74  REFERENCES - CHAPTER 2  1.  J . F a j e r , D.C. B o r g , A . F o r m a n , R.H. F e l t o n , L . V e g h . a n d D. D o l p h i n , A n n . N.Y. A c a d . S c i . 2 0 6 , 349 ( 1 9 7 3 ) .  2.  L.D. S p a u l d i n g , P.G. E l l e r , J . A . B e r t r a n d , a n d R.H. F e l t o n , J . Am. Chem. S o c . 96, 9 8 2 .  3.  P.S. P h i l l i p s , P e r s o n a l c o m m u n i c a t i o n .  4.  D.F. E v a n s , J . Chem. S o c . 2003 ( 1 9 5 9 ) .  5.  B.D. C u l l i t y , ' I n t r o d u c t i o n t o M a g n e t i c M a t e r i a l s ' , A d d i s o n - W e s l e y , Reading, Mass., 1972, p. 76.  6.  C.N. R e i l l e y a n d R.W. M u r r a y , ' E l e c t r o a n a l y t i c a l P r i n c i p l e s ' , An i n t e r s c i e n c e r e p r i n t , W i l e y , New Y o r k , 1 9 6 3 , C h a p . 4 3 .  7.  G.M. B r o w n , F.R. H o p f , T . J . M e y e r , a n d D.G. W h i t t e n , J . Am. Chem. S o c . 97, 5385 0 9 7 5 ) .  8. 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D o l p h i n , u n p u b l i s h e d  24.  P.D. S m i t h , D. D o l p h i n , a n d 239. (1 981 ) .  communication.  B.R. J a m e s .  D. D o l p h i n , a n d  B.R. J a m e s ,  results.  J . O r g a n o m e t . Chem. 2 0 8 ,  76  CHAPTER 3  SOME PRELIMINARY EXPERIMENTS  The aim of the material in t h i s chapter i s to c l a r i f y the nature of some of the s t a r t i n g metal complexes and e s t a b l i s h some basic patterns of r e a c t i v i t y i n these species which w i l l then be referred to in subsequent chapters.  3 .1  The Coordination of Ligand L in Complexes of the Type Ru (OEP)(C0)L 11  in Solution The question  of the nature of Ru(0EP)(C0)L in s o l u t i o n has not been  properly addressed, and has caused considerable confusion in the l i t e r a t u r e  1 -  I t i s generally understood that strong ligands such as imidazole or pyridine w i l l remain bonded to the ruthenium atom in non-coordinating s o l v e n t s . 1  The  s i t u a t i o n i s less c l e a r for cases where the ligand L i s weaker and the confusion i s p a r t i c u l a r l y highlighted for L = EtOH which i s the s t a r t i n g complex for most studies of ruthenium porphyrins, including work described in t h i s thesis.  Results have been i n c o n s i s t e n t .  r a t i o n of a 'Ru(QEP).(C0)  Usually the f i n a l stage of prepa-  species i s c r y s t a l l i z a t i o n from an ROH/CHgCT^  1  (R = CH^, C Hg) m i x t u r e .  Chemical and X-ray analysis of the c r y s t a l l i n e  1  2  product shows the alcohol to be coordinated i n the s o l i d s t a t e ' 1  s i t u a t i o n in s o l u t i o n i s l e s s well d e f i n e d .  2  but the  Nmr studies give i n c o n s i s t e n t  r e s u l t s with Boschi et a l . not detecting any methanol in t h e i r preparation 3  of 'Ru(TPP)(.C0)  1  c r y s t a l l i z e d from Me0H/CHCl  3  [no analysis g i v e n ] , whereas  Bonnet et a l . detected coordinated EtOH by nmr in a C H C1 ^ s o l u t i o n of 2  2  Ru(TPP)(CO)EtOH.  2  77  For the purposes of the present studies i t was important to d e t e r mine i f the ethanol remained coordinated i n dichloromethane, whether t h i s was dependent on concentration and whether coordinating solvents (such as a c e t o n i t r i l e or nitromethane) would displace the ethanol. The spectra of Ru(0EP)(C0)L complexes, L = EtOH, py, 4Mepy, and Im,'in dichloromethane are t y p i c a l of metalloporphyrin systems showing a strong Soret ( y ) band at ^393 nm and two v i s i b l e p e a k s " , with the u s u a l l y 4  6  more intense a-band (see Figure 1.4 i n Chapter 1) at ^550 nm and the weaker B-band at ^515 nm.  The spectra of a l l these complexes were s i m i l a r but  with a n a l y t i c a l l y pure samples the r a t i o of the i n t e n s i t i e s of the two v i s i b l e peaks,was dependent upon the nature of the s i x t h ligand (Table  3.1),  with the ^550 nm peak both diminishing and s l i g h t l y r e d - s h i f t i n g with the systems as shown.  An extreme example of thn's trend i s seen with L = P B u , n  3  where the peaks are a c t u a l l y reversed i n i n t e n s i t y and considerably r e d s h i f t e d (Table 3.1';;  Figure 3.1).  A r e l a t i o n s h i p between these two types  of spectra..is seen in studies of the complex Ru**(OEP)(C0)PPh  3  (11) where  -5 CH2CI2solutions of an a n a l y t i c a l l y pure sample (%10  M) give a spectrum  almost i d e n t i c a l to that of Ru(0EP)(C0lEt0H (2) in the same s o l v e n t . Addition of excess of triphenylphosphine causes the 548 nm peak to r a p i d l y diminish and s l i g h t l y red s h i f t , while the 515 nm peak s h i f t s and broadens u n t i l in the presence of considerable excess phosphine (10 very s i m i l a r to that of Ru(OEP) (C0)P Bu n  3  The data s t r o n g l y suggest  v  M), a spectrum  (8) i s obtained (Figure  3.2).  that the f i v e - c o o r d i n a t e species Ru(0EPj(C0)  (]_)  gives a spectrum with the strong 548 nm absorption which i s then modified  79  F i g u r e 3,2  80  T a b l e 3.1  The V a r i a t i o n o f t h e V i s i b l e Spectrum o f Ru(OEP)(CO)L w i t h the Nature o f the Sixth Ligand L  a  L  Complex  A  (In CH C1 ) 2  2  R u ( 0 E P ) ( C 0 ) E t 0 H -, Ru(.0EP)(C0)4Mepy Ru(0EP)(C0)Im  Ru(.0EP)(C0)PPh  Ru(.0EP)(C0)P Bu n  a)  3  4Mepy  549  518  1 .54  Im  550  518  1 .38  554  524  1.11  555  525  1 .0  555  528  PPh  3  3  P Bu  -  Ratio —  Cnm).  2.3  -  3  2  515  AsPh  -  3  \  548  -  Ru(0EP)(C0)AsPh  Cnm).  EtOH  -  1  B  n  3  .68  R a t i o o f i n t e n s i t i e s o f t h e two m a j o r v i s i b l e p e a k s a a n d g ( s e e F i g u r e 1.4, S e c t i o n 1 . 2 ) .  b)  Analytically  pure sample o f t h e complex d i s s o l v e d i n C H C 1 ,  c)  A c t u a l l y Ru(OEP)(C0)H 0 as d e s c r i b e d  d)  P r e p a r e d i n s i t u by a d d i n g a l a r g e e x c e s s o f l i g a n d u n t i l no f u r t h e r  2  2  s p e c t r a l change o c c u r r e d .  2  below.  81  by t h e c o o r d i n a t i o n o f t h e s i x t h l i g a n d .  In some c a s e s t h e a d d i t i o n a l l i g a n d  seems m e r e l y t o d e c r e a s e t h e i n t e n s i t y o f t h e 548 nm a b s o r p t i o n b u t i n o t h e r s ( p a r t i c u l a r l y f o r l i g a n d s w i t h TT b o n d i n g c a p a b i l i t y u t i l i z i n g v a c a n t d - o r b i t a l s on t h e d o n o r a t o m , e . g . p h o s p h i n e s  or a r s i n e s ) a stronger p e r t u r b a t i o n  of the molecular o r b i t a l s of the metalloporphyrin y i e l d s a quite d i f f e r e n t spectrum. L = Im,  F o r t h i s p r o c e s s a p r o g r e s s i o n c a n be s e e n i n t h e s e q u e n c e AsPh^Mand P B u  (Table 3.1),  n  3  c a p a c i t y f o r Tr-bond f o r m a t i o n .  which i s a rough order of  Ligands c o n t a i n i n g phosphorus or a r s e n i c  a s t h e d o n o r atom a r e u s u a l l y c o n s i d e r e d t o be s t r o n g T r - a c c e p t o r s a t t r a n s i t i o n metal c e n t r e s ' . 7  a weak T r - a c c e p t o r » 8  8  Imidazole i s a moderate Tr-donor ' 9  1 0  pyridine  w h i l e n i t r i l e s and a l c o h o l s a r e c o n s i d e r e d t o  1 0  show v e r y weak o r n o n - e x i s t e n t T r - b o n d i n g c a p a c i t y r e s p e c t i v e l y . 7  F u l l s p e c t r a l d e t a i l s f o r a r a n g e o f Ru(.0EP)(C0)L given in Table  complexes are  3.2.  If Ru(0EP)(C0)L  d i s s o c i a t e s i n s o l u t i o n then the a d d i t i o n o f excess  l i g a n d (I), s h o u l d c h a n g e t h e s p e c t r u m ,  assuming the spectrum  i s d i f f e r e n t f r o m t h a t o f R u ( O E P ) ( C O ) (.!_).  of  Ru(0EP)(C0)L  A d d i t i o n o f ethanol (to about  2M) t o a s o l u t i o n o f R u ( O E P ) ( C O ) E t O H (>10  M) c a u s e s a s l i g h t d e c r e a s e  i n t e n s i t y of the548nmpeak (Figure 3.4a).  A d d i t i o n o f more ethanol  ^4M)  c a u s e s no f u r t h e r c h a n g e .  In c o n t r a s t , t h e a d d i t i o n o f  (to  4-methylpyridine  ( u p t o IM). t o a ^ 1 0 " M s o l u t i o n o f Ru(jDEP) ( C O ) ( 4 M e p y ) (.4) i n C H C 1 5  2  no v a r i a t i o n i n s p e c t r u m  (Table  3.3).  in  2  shows  T a b l e 3.2  82 S p e c t r a l Data f o r S o l u t i o n s i n  S p e c i e s D i s s o l v e d i n CH 01, 2  CHQCIQ  of R u ( 0 E P ) ( C 0 ) L Species n  W- > °9lO ) n m  2  ( 1  e  Ru(0EP)(C0)H 0 -  393(5.38)  548(4.58)  515(4.22)  (D  Ru(0EP)(C0) -  392(5.35)  547(4.63)  512(4.20)  (2)  Ru(OEP](CO)EtOH -  392(5.48)  548(4.53)  515(4.23)  (i)  Ru(0EP)(C0)4Mepy  396(5-43)  549(4.40)  518(4.22)  (1)  Ru(0EP)(C0)py -  396(5.41)  549(4.41 )  518(4.23)  (5)  Ru(0EP)(C0)Im  396(5.45)  550(4.36)  518(4.20)  (18)  Ru(0EP)(C0)AsPh  406(5.18)  554(4.27)  525(4.23)  407(5.28)  555(4.20)  525(4.19)  409(5.23)  555(3.97)  528(4.14)  Ru(0EP)(C0)Cf  402(5.36)  552(4.30)  521(4.20)  Ru(0EP)(C0)Br~  404(5.23)  553(4.26)  524(4.21)  Ru(0EP)(C0)CN"  407(5.57).  557(4.14)  528(4.29)  2  c 3  c  (H)  Ru(.0EP)(,C0)PPh  (8)  Ru(0EP)(C0)P Bu  3  n  3  a)  Spectrum obtained i n f r e s h l y d i s t i l l e d but undried CH^Cl^.  b)  S p e c t r u m o b t a i n e d i n Ch^CL, f r e s h l y d i s t i l l e d f r o m C a H .  c)  Spectrum obtained i n the presence o f excess l i g a n d .  d)  S p e c t r u m r e p o r t e d i n R e f . 5; X ( n m ) ( 1 o g e ) 3 9 6 ( 5 . 3 7 ) , 5 1 8 ( 4 . 2 0 ) and  2  max  549(4:.39) .  ] Q  83  The E f f e c t o f A d d e d EtOH on t h e S p e c t r u m o f a 1 0 " M S o l u t i o n  T a b l e 3.3  of Ru(0EP)(C0)Et0H Dissolved i n CH 01 o  ^ concentration  mL o f EtOH a d d e d  o f EtOH  —'—  I /I  V  g  0  0  2.26  0.1  0.4M  2.03  0.25  IM  1 .96  0.5  2M  1 .96  1 .0  4M  1 .96  a)  Volume  b)  Concentrations  c)  Undried  o f c u v e t t e u s e d ^4 mL . a r e a p p r o x i m a t e and g i v e n t o one s i g n i f i c a n t  CHXkused,  a band ^548 nm, g band ^515  The changes ( o r l a c k o f ) a r e c o n s i d e r e d  Ru(0EP)(C0)  K  o  i is  +  K L i=±  figure.  nm.  due t o E q u i l i b r i u m  3.1 ,  Ru(0EP)(C0)L  (3.1)  l a r g e f o r L = 4Mepy ( > 1 0 M ) and s m a l l e r f o r L = E t O H ;  a q u a n t i t a t i v e measurement  6  of K  - 1  f o r the ethanol  system i s d i s c u s s e d  T h e s p e c t r u m o b t a i n e d when R u ( O E P ) ( C 0 ) E t 0 H ( 2 ) i s d i s s o l v e d i n C H C 1 c o u l d be t h a t o f t h e f i v e - c o o r d i n a t e s p e c i e s R u C 0 E P ) ( _ C 0 l ?  9  QJ.  below.  84  However t h i s spectrum was very dependent upon the p u r i t y of the d i c h l o r o methane.  The experiments noted above (Table 3.3),in which f r e s h l y d i s t i l l e d  but undried CH C1 2  2  was used,gave a r a t i o of 2.3 (±;0ll) for the i n t e n s i t i e s  of the two v i s i b l e peaks CIg^g/I^i5) electrochemical experiments  With CH^Clg solvent used for  ( i . e . d i s t i l l e d d i r e c t l y from calcium hydride)  a higher peak r a t i o (2.4 or above) r e s u l t e d , with the more intense v i s i b l e peak (a) s h i f t e d to 547 nm and the weaker absorption ( B ) to 512 nm.  It  seemed possible that in the undried dichloromethane trace water coordinated to the ruthenium and the spectrum thus obtained on d i s s o l u t i o n of Ru(OEP)(CO)EtOH (2_) was possibly due to the species Ru(0EP)(C0)H 0. 2  Dissolving Ru(OEP)(CO)EtOH (5xlO M) i n a sample of CH C1 _5  2  2  freshly d i s t i l l e d  from CaH and t r a n s f e r r i n g to the c e l l under argon gave a r a t i o of peak 2  i n t e n s i t i e s of 2.66 with the absorptions now at 547 and 512 nm; leaving the c e l l opened to the atmosphere for ^ l h caused t h i s r a t i o to drop to 2.40, while saturation of the sample with water gave a r a t i o of 2.3 and a corresponding red s h i f t of the absorptions.  This strongly suggests that  water i s e f f e c t i v e at coordinating and that in the experiments described above (Tables 3.1 and 3.3) trace water i s always present as a competitive ligand.  The data are s t i l l considered v a l i d , because the r e s u l t s obtained  in dried solvent were the same except that the drop in the i n t e n s i t y r a t i o on adding L (or EtOH) was more pronounced. Even in the absence of water i t i s possible that some of the ethanol would remain  coordinated when Ru(OEP)(C0)Et0H (2) was dissolved in  dried CH C1 .  To obtain the proportions of ethanol coordinated to the  2  2  ruthenium as a function of concentration,the e q u i l i b r i u m (3.2) was studied  85  quantitatively in dried CHgCl 2  R u ( O E P ) t C O ) + EtOH F = = ^  (3.2)  Ru(OEP)(CO)EtOH  (1)  (2)  A n h y d r o u s e t h a n o l was c a r e f u l l y a d d e d i n s m a l l a l i q u o t s t o a solution of  2.  in  d r i e d CH2CI • 2  T  n e  g r a d u a l d e c l i n e o f t h e 547 - 548  a b s o r p t i o n was f o l l o w e d f r o m t h e d i g i t a l d i s p l a y o f a C a r y 1 7 .  nm  The i n t e n -  s i t i e s so o b t a i n e d were c o r r e c t e d f o r the d i l u t i o n e f f e c t o f t h e added ethanol (Table  3.4). Ru(0EP)(C0)Et0H] Ru(0EP)(C0)J[Et0HJ  Hence  log-, K = 0  Hence a p l o t o f  log \ 10  [Ru(0EP)(C0)Et0H] [Ru(.0EPH.C0)J  log  l o g 10  [Ru(0EP)(C0)Et0H] [Ru(0EP)(C0)J  vs. l o g  i n  1 0  1 Q  [EtOH] [EtOH]  s h o u l d g i v e a s t r a i g h t l i n e o f s l o p e +1 w i t h an i n t e r c e p t on t h e x - a x i s of -log^K.  The l o g - j g [ E t O H ] t e r m r e f e r s t o f r e e e t h a n o l i n s o l u t i o n b u t  in t h i s experiment  i t c a n be e q u a t e d  to the ethanol added, s i n c e t h i s i s  i n l a r g e excess compared to the c o n c e n t r a t i o n o f the complex.  The f a l l i n  absorption values i s a t t r i b u t e d to formation o f the s i x - c o o r d i n a t e species (.2) .  Thus :  86 T a b l e 3.4  A d d i t i o n o f Ethanol to a 4xlO~ M S o l u t i o n o f Ru(OEP)(CO)EtOH 5  in CH C1 0  0  ( 1 0 . 0 mL) i n a S e a l a b l e 1 cm C e l l "  Corrected I g  M l of Liquid added -  y L o f EtOH  0  0  1 2  .1 .2  3 4 5  .3 .4 .6  8  .8  10 12  1 .0 1 .2  15 20 25  1 .5 2.0 2.5  30  3.0  1 .441 1 .436  40  4.0  1 .427  1 .441 1 .433  50  5.0  1 .417  60 75  6.0 7.5  1 .411  100 105  10.0 15  110 120 140 (a)  T  547  4 7  —  log [Et0H] 1 0  , i O g  1.566-1 1 0 I - l .377  -  -  .520 .503 .491 .483  -3.786 -3 .485 -3.309 -3.184 -3.008 -2.883  -.927 -.659 -.492 -.301 -.182  1 .473 1.465  1.475  -2.786  -.106 -.032  1 .467  -2.707  .041  1 .458 1 .447  1 .460  -2.610 -2.486  .106  1 .566 1 .546 1 .532  1 .566 1.546 1 .532  1 1 1 1  1 1 1 1  .520 .502 .490 .482  1 .450 1 .445  -2.389 -2.310  .201 .250  -2.185  .291 .376  1 .425  -2.089  .468  1 .400  1 .420 1.412  -2.010 -1 .914  .531 .643  1 .382  1 .398  -1 .790  .903  .20  1 .370 1 .363  1 .386 1.380  -1 .607 -1 .482  1 .301 1 .792  30  1 .356  1 .375  -  . 1100  1.347  1 .377  -1.306 -0.786  E t h a n o l a d d e d a s a 10% s o l u t i o n i n C H C 1 2  2  -  up t o t h e f i r s t 10 y L o f  e t h a n o l , a f t e r w h i c h p u r e e t h a n o l was a d d e d . (b)  A b s o r p t i o n s a t 547 nm do n o t c o r r e s p o n d t o d a t a g i v e n i n T a b l e 3.2 f o r two m a i n r e a s o n s : - 1) D a t a i n T a b l e 3.4 r e f e r t o t h e a b s o r b a n c e a t 547 nm, n o t t h e p e a k a b s o r b a n c e ( i . e . 548 nm f o r 2_ ) . 2) D a t a f o r ]_ i n T a b l e 3.2 o b t a i n e d by r i g o r o u s l y e x c l u d i n g a t m o s p h e r i c m o i s t u r e .  87 [Ru(OEP)(CO)EtOH] [Ru(OEP)(CO)J and  l o g 10  I -I _o I-I  _  l  o ' I - I 1  co  is plotted against (I  Q  log-|Q [ E t O H ]  ( F i g u r e 3.3)  = A b s o r p t i o n o f 547 nm p e a k b e f o r e  adding  EtOH ( = 1.566) ). (.1^ = A b s o r p t i o n a t 547 nm i n t h e p r e s e n c e o f an e x c e s s o f EtOH (=  1.377)).  The p l o t i n F i g u r e 3.3 i s a s t r a i g h t l i n e w i t h a s l o p e o f ^ 0 . 8 and an i n t e r c e p t on t h e x - a x i s a t -2.74, g i v i n g an e q u i l i b r i u m c o n s t a n t o f 550 ± 70  M" . 1  Calculations using t h i s f i g u r e suggest that f o r spectroscopic s o l u t i o n s (/v5 x 1 0 " M) o f R u ( O E P ) ( C 0 ) E t 0 H ( 2 ) i n d r i e d C H C 1 5  2  t e l y 2 - 3% o f t h e c o m p l e x w i l l be i n t h e a s s o c i a t e d f o r m .  2  The  approximaspectrum  o b t a i n e d from a s o l u t i o n o f t h i s c o n c e n t r a t i o n i s c o n s i d e r e d t o be due t o Ru(OEP)(.CO).  Under t h e experimental  i n o b t a i n i n g an a c c u r a t e spectrum e l i m i n a t i o n o f t r a c e water.  c o n d i t i o n s t h e main d i f f i c u l t y  o f the five-coordinate species i s the  The s p e c t r a l data o b t a i n e d i n v e r y d r y C H C 1 , 2  with precautions taken to l i m i t the e f f e c t o f atmospheric  2  moisture, are  e n t e r e d i n T a b l e 3.2 a s b e i n g t h o s e o f t h e f i v e - c o o r d i n a t e s p e c i e s R u ( 0 E P ) ( C 0 ) (.1). "  Stronger s o l u t i o n s o f Ru(OEP)(CO)EtOH (2) i n C H C 1  d e g r e e o f a s s o c i a t i o n ; s o l u t i o n s o f ^10  2  2  show a h i g h e r  M ( t y p i c a l l y used i n e l e c t r o c h e m i c a l  p r e p a r a t i o n s ) a r e c a l c u l a t e d t o be v 5 0 % a s s o c i a t e d .  88  + 0.5  o \  \ \ \  0.4  o \  \  0.3  \ \  o \ \ o\  0.2  o \  + 0.1  Log. I 10  io-i  I - ICO  'O  0  \  - 0.1 0.2  \ \  0.3 \  0.4  \  \  - 0.5  \  o\  0.6 0.7  \ \  _J  -2.0  -2.5  •3.0  -3.5  Log [EtOH] lo  F i g u r e 3.3  Plot of log! [[Ru(0EP)(CO)EtOH]/[Ru(OEP)(CO)]] vs. l o g [EtOH] t o o b t a i n t h e e q u i l i b r i u m c o n s t a n t f o r E q u a t i o n 3 . 2 . [ R u ( O E P ) ( C O ) E t O H ] i s p r o p o r t i o n a l t o I -I and [ R u ( O E P ) ( C O ) ] i s p r o p o r t i o n a l t o I-Ico. 0  1 0  Q  89  3.2  S o l v a t i o n o f Ru(OEP)(C0)L i n D i f f e r e n t Solvents Having e s t a b l i s h e d t h a t t h e ethanol l i g a n d e s s e n t i a l l y f u l l y  d i s s o c i a t e s when R u ( O E P ) ( C O ) E t O H (2_) i s d i s s o l v e d (<10  M) i n n o n -  c o o r d i n a t i n g s o l v e n t s , t h e q u e s t i o n arose as t o whether a c o o r d i n a t i n g s o l v e n t would r e p l a c e t h e e t h a n o l ,  Ru(OEP)(CO)EtOH  +  S  (3.3).  » Ru(0EP)(.C0)S  +  EtOH  (3.3)  (il  A q u a l i t a t i v e s t u d y o f t h e s p e c t r a o b t a i n e d on d i s s o l v i n g a variety of solvents  suggested  2 in  c o o r d i n a t i o n i n many c a s e s ( T a b l e 3 . 5 ) .  The l i m i t i n g s p e c t r a r e s u l t i n g f r o m r e a c t i o n o f R u ( O E P ) ( C O ) E t O H w i t h 4-methylpyridine  and i m i d a z o l e a r e i d e n t i c a l t o t h o s e o b t a i n e d from  analy-  t i c a l l y p u r e s a m p l e s o f R u ( O E P ) C C 0 ) 4 M e p y (.4) a n d R u ( 0 E P ) ( C 0 ) I m • (5_) ( T a b l e 3.1), c o n f i r m i n g t h a t l i g a n d exchange w i t h t h e e t h a n o l has o c c u r r e d . A l l the s o l v e n t s , with t h e exception o f C ^ C ^ J probably c o o r d i n a t e  although  t h e f i g u r e n o t e d f o r c h l o r o f o r m may be d u e t o t h e p r e s e n c e o f i m p u r i t i e s (e.g. s t a b i l i z e r s ) . To o b t a i n a n i d e a o f how s t r o n g l y t h e l i g a n d s c o o r d i n a t e t o t h e Ru(0EP)(C0) approximate  molecule,  some e x p e r i m e n t s  were c a r r i e d o u t t o e s t i m a t e  equilibrium constants f o r the reaction (3.4).  Ru(0EP)(C0)  (D  +  S v  1  Ru(0EP)(.C0)S  (3.4)  90  T a b l e 3.5  S p e c t r a l Data f o r 1 0 " - 1 0 " M R u ( O E P ) ( C O ) E t O H D i s s o l v e d i n 5  Various  4  Solvents  Solvent  R a t i o o f v i s i b l e p e a k s ( / I g ) ( T a b l e 3.1) a  Ch^Cl 2 Methyl CHC1  ^2.6 2.26  Acetate  2.13  3  BuOH  2.0  EtOH  2.0  DMF  1 .82  DMSO  1 .82  CH CN  1 .8  n  3  CH N0 3  1 .76  2  Et N  1 .53  4Mepy  1 .54  Imidazole  1 .38  AsPh  1 .11  3  PPh a)  3  1 .0  3  R u ( O E P ) ( C O ) E t O H ( 2 ) d i s s o l v e d d i r e c t l y i n t h e s o l v e n t t o g i v e a 10 -4 10  b)  M solution.  Ru(OEP)(CO)EtOH (2) d i s s o l v e d i n C H C 1 2  2  with excess l i g a n d added  u n t i l no f u r t h e r s p e c t r a l c h a n g e was n o t e d .  91  A d d i t i o n o f e x c e s s l i g a n d (S) t o a s o l u t i o n o f R u ( O E P ) ( C O ) E t O H ( 2 j in dry CHgClg allowed  t h e s p e c t r u m o f t h e new s p e c i e s R u ( 0 E P ) ( C 0 ) S t o  accurately determined.  To a f r e s h s o l u t i o n o f  2_  be  i n d r i e d CHgClg i n a  s e a l a b l e 1 cm c e l l , a l i q u o t s o f t h e l i g a n d w e r e a d d e d and t h e  spectral  changes observed.  measured  The d e c r e a s e i n t h e  547 nm a b s o r p t i o n  f o r f i v e m i x t u r e s spaced e v e n l y between c o n d i t i o n s 65% c o o r d i n a t i o n  was  o f a p p r o x i m a t e l y 35 and  o f S, and f i n a l l y t h e l i m i t i n g s p e c t r u m ( a b s o r p t i o n  at  547 nm = 1^)  f o r t h i s s o l u t i o n i n the presence of excess l i g a n d S  determined.  The s p e c t r a , b e f o r e and a f t e r l i g a n d a d d i t i o n , f o r a number  o f s y s t e m s a r e s e e n i n F i g u r e 3.4; i s s e e n i n F i g u r e 3.2.  t h e a d d i t i o n o f PPh^  t o R u ( 0 E P ) ( C 0 ) (1_)  M i x t u r e s s h o w i n g b e t w e e n 35 and 65%  were used f o r a n a l y s i s because they g i v e the most a c c u r a t e F o r e a c h o f t h e f i v e s o l u t i o n s , a K v a l u e was  obtained  was  coordination estimates  (Equation  K.  of  3.5)  and  t h e s e were then a v e r a g e d . v -  K  "  [Ru(0EP)(,C0)S]  rRu(0EP)(C0)J[Sj  The c o n c e n t r a t i o n considered  t o be e q u a l  i n Ta bl e 3 .6 .  1  1  I-I  IsT  ( I and  I  (3.5)  corrected for dilution)  o f the l i g a n d f r e e i n the s o l u t i o n can u s u a l l y t o t h a t a d d e d , e x c e p t when t h e l i g a n d i s bound  s u f f i c i e n t l y s t r o n g l y (e.g., PPh^) ligand is coordinated  V  t h a t m o r e t h a n 1% o f t h e  i n any s o l u t i o n .  available  The c a l c u l a t e d K v a l u e s  are seen  be  F i g u r e 3.4  O p t i c a l s p e c t r a o f C H C 1 s o l u t i o n s o f Ru(.OEP) (.CO) u s e d i n l i g a n d Binding experiments, and t h e s p e c t r a o f the s i x - c o o r d i n a t e s p e c i e s o b t a i n e d i n the presence o f excess added l i g a n d . Ru(0EP)(C0) () ; Ru(0EP)(.C0)L ( ) 2  2  1 Ru(OEP) (CO)EtOH  a)  Ru(.0EP)(C0) + EtOH ,  b)  Ru(OEP)(CO) + CH N0 F==*Ru(0EP)(.C0)CH N0 3  2  3  2  e)  Ru(OEP)(CO) + C H C N  d)  Ru(OEP)CCO) + A s P h  3  ?  3 ?  ^Ru(OEP)(CO)CH CN 3  ^Ru(.0EP)(C0)AsPh  3  F i g u r e 3.4 c o n t i n u e d : *  500  e  600  700  500  WAVELENGTH (nm)  e) f  600  700 WAVELENGTH (nm)  R u ( 0 E P ) ( C 0 ) + Ira  i Ru(OEP)(C0)Im  ) | Ru(0EP)(C0) + Et N?= 3  =± R u ( . 0 E P ) ( C 0 ) E t N 3  95  T a b l e 3.6  E q u i l i b r i u m Constants  f o r the C o o r d i n a t i o n  R u ( O E P ) ( C O ) (1) i n D i c h l o r o m e t h a n e as  Ligating Solvent  Estimated  Added -  Solvent  Range o f K  M"'  M  1  to  D o n o r Number -  _1  8.7  8.2  -  9.3  2.7  CH CN  165  155 -  175  14.1  AsPh  2900  2750 - 3 0 5 0  31000  29000 - 32000  CH N0 3  2  3  PPh  3  3  EtOH  550  see F i g u r e  Et N  42  39 - 45  3  a)  K  of Ligands  4Mepy • -  2x1 O  Im 5.  5xl0  20.0  3,3  ^55  -  8  33.1  -  8  S o l u t i o n o f R u ( 0 E P ) ( C 0 ) (1) i n C H C 1 2  ^(3-6)xl0~ M. 5  2  Ligand  usually  a d d e d a s a 10% o r 1% s o l u t i o n i n d r i e d C H C 1 2  2  b)  From R e f .  11.  c)  M e t h o d n o t a p p l i c a b l e w i t h t h e s e l i g a n d s as a d d i t i o n o f e v e n l e s s  than  one e q u i v a l e n t o f l i g a n d showed s p e c t r a l c h a n g e s w h i c h w e r e c o n s i s t e n t w i t h 99+% K »  10  o f the a v a i l a b l e l i g a n d being coordinated. .  The numbers q u o t e d a r e f r o m c o m p e t i t i v e  w i t h CH^CN a s s o l v e n t ( s e e b e l o w ) .  This implies equilibria  that  studies  96  As e x p e c t e d  from t h e e q u i l i b r i u m d a t a , t h e d i s s o l v i n g o f a s p e c i e s  w i t h a s t r o n g l y c o o r d i n a t i n g s i x t h l i g a n d ( L = 4Mepy  o r Im) i n a m i l d l y  c o o r d i n a t i n g s o l v e n t (e.g. C H C N ) c a n 1 ead t o a m i x t u r e  o f Ru(0EP)(C0)L  3  species with t h e appropriate spectrum;  the equilibria are established  rapidly. Ru(0EP)(C0)Im  +  CH CN  » Ru(OEP)(CO)Im  3  (5)  (solvent)  R a t i o o f t h e two v i s i b l e  Observed r a t i o  (4)  (5)  I /I = a  +  CH CN  6  + Ru(OEP) (CO)CH CN ( 3 . 7 ) 3  (4)  (6)  1.54  /In  a  1 .50  »Ru(0EP)(C0)4Mepy  3  I  (6)  1 .38  =  (solvent)  '  Ru(OEP)(CO)CHgCN (3.6)  absorptions  ( a s d e f i n e d f o r T a b l e 3.1)  - Ru(.0EP)(C0)4Mepy  +  3  Observed r a t i o  1.8 1 .66  The a d d i t i o n o f an e x c e s s o f t h e s t r o n g l y bound l i g a n d d i s p l a c e s any coordinated  solvent t o give the spectrum o f the ligand-coor-  d i n a t e d s p e c i e s ( r a t i o = 1.38 f o r 5 order o f magnitude estimates to Ru(OEP)CCO)  (1).  immediately  a n d 1.54 f o r 4_ ) . From t h e s e  c a n be made o f t h e b i n d i n g o f 4Mepy  data,  a n d Im  97  Equilibrium  ( 3 . 8 ) i s a p p l i c a b l e when t h e s i x - c o o r d i n a t e  species i s dissolved i n a coordinating  solvent  Ru(OEP)(C0)L  (CH3CN).  h  L + Ru(0EP)(.C0) CH3CN ' = = s = * R u ( 0 E P ) ( C 0 ) L Using t h e method d e s c r i b e d ties (  I o t  /Ig) f o r absolute  +  CH CN  (3.8)  3  e a r l i e r , and s u b s t i t u t i n g r a t i o o f intensi  intensities, yield  t h e data summarized i n  Table 3.7. I -I h  •  I  0  *  r^r  , S.  [CH^CN] -  r  c  r  "  <  3  -  >  9  0 0  = R a t i o o f i n t e n s i t i e s o f two v i s i b l e peaks f o r Ru(.0EP)(C0)CH CN i n CH CN 3  I  3  = T h e same r a t i o f o r R u ( 0 E P ) ( C 0 ) L  ( L = 4Mepy  o r Im)  00  I  = T h e same r a t i o f o r R u ( 0 E P ) ( C 0 ) L d i s s o l v e d i n C H C N 3  [CH CN] 3  T a b l e 3".7  = Concentration The Estimation  o f n e a t C H C N , i . e . 19M. 3  o f t h e E q u i l i b r i u m C o n s t a n t f o r R e a c t i o n 3,  I 00  %L coordinated  [L] '  h  L = 4 Mepy  1.8  1.66  1 .54  54  2.3xlO" M  9.6xl0  5  L = Im  1.8  1.5  1 .38  71  1.5xlO~ M  3.2xl0  6  5  5  ;  98  Defining the equilibrium constant  3.10  a s K-| :  l  K  Ru(0EP)(C0) (1)  f o r Reaction  +• CH CN ,  !  3  > Ru(OEP)(CO)(CHgCN) (6)  (3.10)  w h e r e K-j i s known ( 1 6 5 M ~ ^ ) , l e a d s t o : v v n2  [Ru(0EP)(C0)CH CN] [Ru(0EP)(C0)][CH CN]  [Ru(0EP)(C0)L][CH^CN] [ L ] [ R u ( O E P ) (COJCHTgCN]  ?  K  X  3  Ru(0EP)(C0)L Ru(0EP)(C0)][LJ  _ "  which i s the a s s o c i a t i o n constant  K  „ assoc.  , ^-'  f o r l i g a n d L to the f i v e - c o o r d i n a t e  s p e c i e s R u ( 0 E P ) ( C 0 ) (1_). H e n c e t h e f o l l o w i n g e s t i m a t e s and a r e i n c l u d e d i n T a b l e  3  K  assoc.  (  4Mepy  2x10  8  Im  5xl0  8  was a l s o shown t o c o o r d i n a t e  w i t h R u ( 0 E P ) ( C 0 ) ('!_) i n C H C 1 . 2  )  s t r o n g l y by r e a c t i n g q u a n t i t a t i v e l y 3  n  3  (8) w e r e c o m p l i c a t e d  dissociation of the P Bu  studied above.  M _ 1  S o l v a t i o n r e a c t i o n s i n CH CN o f a n a l y t i c a l l y  2  pure samples o f Ru(OEP)(C0)P Bu c a l l y slower  o f K a r e made,  3.6.  L  P Bu  n  u  n  3  by a n a p p a r e n t k i n e t i -  compared w i t h t h e n i t r o g e n  T h e b i n d i n g s t r e n g t h of / P B u n  3  ligands  was n o t d i r e c t l y d e t e r m i n e d b u t  99  i t m u s t be v e r y s t r o n g . The b i n d i n g s t r e n g t h o f t h e l i g a n d s i s s u m m a r i z e d b e l o w :  P Bu n  3  ^ Im ^ 4Mepy >> P P h  >> A s P h  3  CH CN > E t N > C H N 0 3  3  3  > EtOH  3  2  A l s o g i v e n i n T a b l e 3.6 a r e t h e d o n o r numbers f o r t h e s e l i g a n d s as d e t e r m i n e d  by G u t m a n n .  The d o n o r numbers a r e d e r i v e d f r o m t h e e n t h a l p y  1 1  of r e a c t i o n o f the s p e c i f i e d l i g a n d with SbCl^.  Gutmann c o m p a r e d t h e  donor  numbers t o s i m i l a r m e a s u r e m e n t s u s i n g a r a n g e o f a c c e p t o r s , i n c l u d i n g t h e metal complexes S n ( C H ) C l 3  3  and V O C d c a c ^ C C H - j C N ) , and f o u n d t h a t t h e 1 1  numbers o b t a i n e d w e r e r o u g h l y i n d e p e n d e n t experiments  of the acceptor used.  In t h e  r e p o r t e d i n t h i s t h e s i s t h e a c c e p t o r was t h e f i v e - c o o r d i n a t e  c o m p l e x R u ( 0 E P ) (CO) (.]_), and i t i s s e e n f r o m T a b l e 3.6 t h a t t h e r e i s a I J  r o u g h c o r r e l a t i o n b e t w e e n t h e a s s o c i a t i o n c o n s t a n t ( E q u a t i o n 3.4) and  the  Gutmann d o n o r number ( D . N . ) . The d o n o r numbers d e r i v e d by Gutmann u t i l i z e d a m a i n g r o u p a t o m as t h e a c c e p t o r ( S b ) a n d , a l t h o u g h  metal  t h e numbers w e r e c h e c k e d by compa-  r i s o n w i t h s i m i l a r r e a c t i o n s u s i n g a t r a n s i t i o n m e t a l as a c c e p t o r ( V ) , t h e s e were a l l hard Lewis a c i d s .  The r e a c t i o n s r e p o r t e d h e r e u s e a m o d e r a -  t e l y s o f t L e w i s a c i d (.Ru**) and t h i s s u p p o r t s t h e a p p l i c a b i l i t y o f t h e d o n o r number c o n c e p t i n t r a n s i t i o n m e t a l c h e m i s t r y . from the o r d e r o f l i g a n d strength, suggested e n t r o p y o r s t e r i c e f f e c t s and t h i s may  The m a i n d i v e r g e n c e s  by Gutmann a r e o f t e n due t o  be t h e c a s e w i t h E t N 3  (see  below).  The o r d e r o f b i n d i n g s t r e n g t h o f t h e l i g a n d s s e e n a b o v e i s s i m i l a r  100  to that observed  previously for coordination to four-coordinate cobalt(II)  porphyrin species having vacant l i g a n d p o s i t i o n s . 1 2  P i p > C H - I m > Py > " B U > Im » P  3  3  PPh  3  »  E t g N > DMF  >  THF  The n e u t r a l o x y g e n d o n o r l i g a n d s b i n d w e a k l y , p o s s i b l y due t o a low enthalpy of formation f o r the ruthenium system.  o x y g e n bond as f o u n d f o r t h e c o b a l t  The same t r e n d i s s e e n i n t h e d o n o r numbers w h i c h a r e g r e a t e r f o r  n i t r o g e n (>30)  than oxygen l i g a n d s (^20).  Phosphine  complexes are  t o b i n d v e r y s t r o n g l y , p r e s u m a b l y due t o a c o m b i n a t i o n c o u p l e d w i t h -rr-backbonding ruthenium  expected  of strong a-donation  from the o v e r l a p o f the f i l l e d d - o r b i t a l s o f t h e  atom w i t h empty d - o r b i t a l s o f t h e p h o s p h o r u s i s , ( . g . P " B u ) . e  N i t r o g e n a s a d o n o r o c c u p i e s an i n t e r m e d i a t e p o s i t i o n . The s t r e n g t h s o f Im a n d 4 M e p y  3  considerable  a s l i g a n d s a r e e n h a n c e d by t h e rr-bonding  capa-  b i l i t y o f i m i d a z o l e and, f o r both l i g a n d s . a c a p a c i t y f o r backbonding the ruthenium  atom i n t o the v a c a n t t r - o r b i t a l s o f the a r o m a t i c system o f the  l i g a n d seems p l a u s i b l e . The w e a k e r b i n d i n g o f E t N  ( a much s t r o n g e r a  3  d o n o r t h a n Im o r 4 M e p y , effect.  from  a s m e a s u r e d by t h e i r p K a ' s ) may  be due t o an  R e l a t i v e l y weak b i n d i n g t o Co(.II) was r e f l e c t e d i n an  entropy  unfavourable  AS t e r m and was r a t i o n a l i z e d as due t o l o s s o f f r e e d o m o f movement o f t h e a l k y l c h a i n s , as w e l l as t h e l a c k o f any a v a i l a b l e o r b i t a l s f o r 1 2  This leaves the unexpected  weakness o f P P h  P Bu .  3  and A s P h  3  backbonding.  as l i g a n d s compared t o  A s i m i l a r c o n t r a s t i n b i n d i n g i s seen i n a c o m p a r i s o n o f b i s p h o s II n p h i n e c o m p l e x e s , o f w h i c h Ru ( 0 E P ) ( P B u ) i s u n d i s s o c i a t e d i n s o l u t i o n n  3  3  2  101  (5xl0~ M) whereas R u ^ O E P ) (PPh-^ d i s s o c i a t e s q u i t e r e a d i l y 5  1 4  under the  same c o n d i t i o n s ( E q u a t i o n 3 . 1 2 ) . K  Ru(0EP)(PPh3) F=^Ru(0EP)(PPh ) 2  3  + PPh  3  5 (K = 1.18x10 °B)  (3.12)  As t h e p h e n y l g r o u p s on t h e p h o s p h o r u s a r e e l e c t r o n w i t h d r a w i n g c o m p a r e d w i t h a l k y l g r o u p s , o n e e x p l a n a t i o n f o r t h e weak b i n d i n g o f P P h  3  w o u l d be t h a t t h e p h e n y l g r o u p s w i t h d r a w e n o u g h c h a r g e f r o m t h e p h o s p h o r u s •.:<•>.. atom t h a t t h e a-donor  capacity o f the ligand i s reduced.  argument to e x p l a i n PPh  3  However,  for this  b e i n g s u c h a weak l i g a n d c o m p a r e d w i t h 4 M e p y ,  Im  or P B u , i t would r e q u i r e a s u b s t a n t i a l drop i n e l e c t r o n i c charge donated n  3  to the m e t a l l o p o r p h y r i n group. the PPh  This i n turn would cause, the s p e c t r a o f  c o m p l e x e s t o be r a d i c a l l y d i f f e r e n t f r o m t h e c o r r e s p o n d i n g P B u n  3  3  c o m p l e x e s a n d much m o r e l i k e t h e p y r i d i n e o r a c e t o n i t r i l e complexes..' In f a c t the spectrum o f the c o r r e s p o n d i n g phosphine complexes are v e r y s i m i l a r [ T a b l e s 3.1, 3.2, a n d 3.8] a n d h e n c e t h i s e f f e c t c a n n o t be d e c i s i v e i n d e t e r m i n i n g t h e low K v a l u e f o r P P h  3  complexes.  on c o n s i d e r a t i o n o f s t e r i c e f f e c t s .  A better e x p l a n a t i o n i s found  The e x t r a s t e r i c r e q u i r e m e n t o f b u l k y  p h o s p h i n e l i g a n d s a n d t h e e f f e c t o f t h i s on t h e d i s s o c i a t i o n o f s u c h l i g a n d s f r o m t r a n s i t i o n m e t a l c o m p l e x e s has b e e n s t u d i e d . 1 5  The s t e r i c r e q u i r e m e n t  o f a p h o s p h i n e : ; l i g a n d has been d e f i n e d by a minimum c o n e a n g l e w h i c h i s t h e o p e n a n g l e o f a c o n e , c e n t r e d 2.28 & f r o m t h e p h o s p h o r u s a t o m , to e n c l o s e the Van-der-Waals l i m i t s o f the l i g a n d . 1 5  more s t e r i c a l l y demanding t h a n P B u n  3  Hence,PPh  3  required (145°) i s  (130°) but l e s s t h a n , f o r example  102  Pfcyclohexyl) (prepared  (179°),  3  In c o n t r a s t t o t h e OEP c o m p l e x . R u ( T P P ) ( C 0 ) P P h  by a d d i n g CO t o a s o l u t i o n o f R u ( T P P ) ( P P h - ^ i n C H C 1 ) shows -3 -3 2  no t e n d e n c y t o d i s s o c i a t e a t p h o s p h i n e c o n c e n t r a t i o n s o f M O solution of Ru(OEP)(C0)PPh estimated  3  2  M.  (A 10  i s ^80% a s s o c i a t e d as c a l c u l a t e d from  equilibrium constant).  p h y r i n s as l i g a n d s . a n d  The i n c r e a s e d a s s o c i a t i o n c o n s t a n t  for por-  i s i n c o n s i s t e n t with the view that the binding of  i s d o m i n a t e d by b a c k - b o n d i n g f r o m t h e r u t h e n i u m , b e c a u s e TPP  3  M  the  t h e TPP c o m p l e x r e f l e c t s t h e d i f f e r e n t e l e c t r o n i c p r o p e r t i e s o f t h e  PPh  3  more e l e c t r o n d e f i c i e n t p o r p h y r i n t h a n OEP.  The i m p o r t a n c e  is a  of steric  _3  e f f e c t s i s shown by t h e f a c t t h a t a t 10  M PPh^ d o e s n o t b i n d a t a l l t o  R u ( T M P ) ( C 0 ) ( a l t h o u g h TMP and TPP a r e v e r y s i m i l a r e l e c t r o n i c a l l y ) w h i l e P Bu  under s i m i l a r c o n d i t i o n s c o o r d i n a t e d r e a d i l y .  n  3  This e f f e c t  probably  i s due t o s t e r i c o b s t r u c t i o n o f t h e c o o r d i n a t i o n s i t e by t h e b u l k y m e s i t y l g r o u p s on 3.3  TMP..  The S u b s t i t u t i o n o f A x i a l L i g a n d s  i n t h e Complex R u ( G E P ) ( C 0 ) P B u n  3  (8)  As m e n t i o n e d i n t h e p r e v i o u s s e c t i o n , s o l v a t i o n r e a c t i o n s o f R u ( O E P ) (C0)P Bu n  3  (8J  that lead to displacement  o f the phosphine group are  c a l l y slow compared with the displacement 4Mepy)  from the c o r r e s p o n d i n g  o f o t h e r l i g a n d s ( e . g . Im  six-coordinate carbonyl complexes.  kinetiand Weakly  l i g a t i n g s o l v e n t s ( s u c h as EtOH o r C H C N ) g i v e r i s e t o s l o w s p e c t r a l c h a n g e s 3  o v e r a few d a y s a t a m b i e n t t e m p e r a t u r e , was  small  (<15%) as j u d g e d  (Im o r 4 M e p y )  and t h e f i n a l e x t e n t o f s o l v b l y s i s  by t h e s p e c t r a .  i n s m a l l a l i q u o t s (up t o 0.1M)  Addition of stronger  ligands  to a solution of Ru(0EP)(C0)-  103  P Bu  (8) i n C H C 1  n  3  2  (^5xlO" M) causes the slow l o s s o f the c h a r a c t e r i s t i c b  2  peaks o f t h e s t a r t i n g complex  and t h e g e n e r a t i o n o f s e v e r a l new a b s o r p t i o n s ,  suggesting a mixture o f products with Ru(0EP)(C0)L dominating. for  The s p e c t r u m o f p u r e R u ( O E P ) ( C 0 ) L  several days.  ( L = Im o r 4 M e p y )  pre-  i s f o r m e d on l e a v i n g t h e s o l u t i o n  The q u a l i t a t i v e d a t a s u g g e s t t h a t t h e l i g a n d d i s p l a c e m e n t  r e a c t i o n occurs v i a a process i n v o l v i n g slow d i s s o c i a t i o n o f the P B u . n  3  D i s s o c i a t i o n o f t h i s l i g a n d from R u ( 0 E P ) ( P B u ) I I  (7.) i s known t o be  n  3  2  slow . 6  In c o n t r a s t , t h e s o l u t i o n o f R u ( O E P ) ( C 0 ) P B u n  of 4Mepy/CH Cl 2  2  (4 mL)  3  i n a 50/50 v / v m i x t u r e  immediately g i v e s a spectrum dominated  by a v e r y n-::  i n t e n s e v i s i b l e p e a k a t 526 nm and a weak S o r e t a t 410 nm ( F i g u r e 3 . 5 ) . The l e s s i n t e n s e peak a t ^548 nm and t h e S o r e t a t ^393 nm a r e due t o R u ( O E P ) ( C 0 ) 4 M e p y ( 4 ) , w h i l e t h e m a j o r p r o d u c t was l a t e r shown t o be t h e mixed l i g a n d s p e c i e s R u ^ ( 0 E P ) ( P B u ) 4 M e p y n  3  by c o m p a r i s o n w i t h  Ru(OEP)-  ( P 6 u ) p y p r e p a r e d i n s o l u t i o n by a d d i n g e x c e s s p y r i d i n e t o R u ^ ( O E P ) ( P B u ) n  n  3  3  (see S e c t i o n 7.5).  T h u s , w h e r e a s g r a d u a l a d d i t i o n o f a m i n e t o 'vO.lM l e a d s  to the slow f o r m a t i o n o f Ru(0EP)(C0)4Mepy  (4J , one a d d i t i o n o f 7M a m i n e  g i v e s r a p i d d i s p l a c e m e n t o f t h e c a r b o n y l and f o r m a t i o n o f t h e m i x e d p r o d u c t [Scheme 3 . 1 ) .  ligand  T h i s r e s u l t c a n be r a t i o n a l i s e d i f t h e d i s s o c i a t i o n  o f t h e phosphine from R u ( O E P ) ( C 0 ) P B u  i s slow while the d i s s o c i a t i o n o f  n  3  t h e c a r b o n y l l i g a n d i s f a s t , and t h e m i x e d l i g a n d p r o d u c t i s o n l y s t a b l e i n t h e p r e s e n c e o f a huge e x c e s s (e.g. 7M) o f t h e a d d e d p y r i d i n e l i g a n d i n t h e p r e s e n c e o f one e q u i v a l e n t o f CO. P Bu n  3  (.8) i s much m o r e s t a b l e t h a n R u  This suggests that 1 1  Ru (0EP)(C0)I I  (OEP) ( P B u ) 4 M e p y ; w h i c h seems n  3  Figure  3.5  T h e o p t i c a l s p e c t r u m o f t h e p r o d u c t s o b t a i n e d when R u ( O E P ) ( C 0 ) P B u ( 8 ) i s d i s s o l v e d i n a 1:1 v / v m i x t u r e o f C H C 1 / 4 M e p y . n  2  2  105  reasonable of  8  considering the very large equilibrium constant  from  1  f o r the formation  ( S e c t i o n 3 . 2 ) , and t h e l a r g e e x c e s s o f P B u n  ensure complete formation  of Ru (OEP)(P Bu ) 1 1  a d d e d t o 8^ t o  (7_) ( s e e S e c t i o n 2 . 5 ) .  n  3  3  2  Due t o t h e s t a b i l i t y o f 8^ E q u i l i b r i u m 3.13 l i e s s t r o n g l y t o t h e l e f t a n d Ru (OEP)(P Bu )4Mepy 1 1  i s o n l y formed i n t h e presence o f a l a r g e excess o f  n  3  the free p y r i d i n e .  Ru(0EP)(C0)4Mepy e Ru(OEP)(C0)P Bu 1 0 M 4Mepy s 1 o W  ^ J,l  n  .  fa  ^  r l  Ru(OEP)(P Bu )4Mepy n  3  y  SCHEME- 3.1  4Mepy + RuCOEP) ( C 0 ) P B u  Ru(0EP)(.P Bu )4Mepy  n  n  3  3  + CO  (3.13)  fast A d d i t i o n o f ''4Mepy t o o t h e r R u ( O E P ) ( C 0 ) L c o m p l e x e s w i l l r e s u l t i n the displacement  o f L w i t h no p r o d u c t i o n  s i n c e r e m o v a l o f t h e CO r e q u i r e s  generally  o f mixed l i g a n d  species,  photolysis . 1 6  C o m p a r i s o n o f t h e r a t e s o f CO d i s s o c i a t i o n f r o m t h e c o m p l e x e s ;(: C0.)Me'CN;; (6) arid R u ( , 0 E P ) ( ; C 0 ) P B u !  o f a b o u t 10  n  3  ( 8 ) shows a. g r e a t e r r e a c t i v i t y b y a f a c t o r  f o r t h e l a t t e r complex, t h i s being a t t r i b u t e d t o a high  e f f e c t o f t h e p h o s p h i n e , and t h i s i s r e f l e c t e d i n t h e r e l a t i v e l y 6  s t a b i l i t y o f the five-coordinate intermediate be p r e p a r e d coordinate  Ru(OEP)-  Ru(OEP)(P Bu ) n  3  trans  high  which can  a n d s t u d i e d i n s o l u t i o n ( S e c t i o n 7.5) c o m p a r e d w i t h o t h e r  five-  s p e c i e s Ru(.0EP)L, L = MeCN, E t O H , a n d p y r i d i n e , w h i c h have n o t  106  y e t been o b t a i n e d  in solution.  The t r a n s e f f e c t o f t h e s i x t h l i g a n d L  i n c o m p l e x e s o f t h e t y p e R u ( 0 E P ) ( C 0 ) L may t h e vfy~  be i l l u s t r a t e d by t h e c h a n g e i n  i s t r e t c h i n g frequency with the l i g a n d .  F. C a l d e r a z z o  has  1 7  noted  t h a t a c a r b o n y l g r o u p a p p e a r s t o be i r r e v e r s i b l y bound i n t e r m s o f l i g a n d s u b s t i t u t i o n i f t h e V^Q . f r e q u e n c y is supported t i o n 2.4)  i s b e l o w 1935  ± 5 cm" .  Such a trend  1  by d a t a f o r Ru(.OEP) ( C O ) p y (3) ( y ^ s o l i d ) = 1 933 cm" ,-; S e c 1  and R u ( 0 E P ) ( C 0 ) M e C N (6) ( v  ( i n s o l u t i o n ) = 1935  C Q  cm" ) 1  which  5  do n o t r e a d i l y l o s e CO i n l i g a n d e x c h a n g e r e a c t i o n s and r e q u i r e p h o t o l y s i s in solvent containing the appropriate l i g a n d to obtain R u ( 0 E P ) p y  and ,  1 1  Ru (OEP)(MeCN) n  P Bug (V^Q  products .  In c o n t r a s t . t h e CO l i g a n d o f R u ( O E P ) (.CO)-  1 6  2  ( s o l i d ) = 1948  d o n o r s , and R u ( 0 E P ) ( C 0 ) spontaneously . 4  2  cm" (v  2  C Q  , - S e c t i o n 2.4)  c a n be r e p l a c e d by s t r o n g  ( i n s o l u t i o n ) = 1990  cm" ) 1  can l o s e  CO  I t i s b e l i e v e d t h a t d i s s o c i a t i o n o f CO f r o m t h e p h o s p h i n e  c o m p l e x i s a i d e d b e c a u s e P B u 2 i s a - r r - a c c e p t o r t h a t c o m p e t e s f o r t h e same n  7  b a c k - b o n d i n g - r r - e l e c t r o n d e n s i t y as t h e t r a n s c a r b o n y l . i s much m o r e i m p o r t a n t  f o r t h e s t r e n g t h o f t h e Ru-C  Pi. b a c k - b o n d i n g  t h a n t h e Ru-P  b e c a u s e t h e p h o s p h i n e i s a much s t r o n g e r o - d o n o r t h a n t h e c a r b o n T h a t p h o s p h i n e s c a n be n e t d o n o r s o f c h a r g e of H i l l l e r et a l . spectroscopy  1  8  who  studied P t ( P F ) 3  and showed t h a t t h e c h a r g e  were a p p r o x i m a t e l y  e q u a l and o p p o s i t e .  atoms make PF^ t h e l e a s t a s d o n a t i n g  4  i s supported  and N i ( P F ) 3  4  by  bond monoxide . 8  by t h e w o r k  photoelectron  s h i f t s due t o a and IT b o n d i n g As t h e e l e c t r o n - w i t h d r a w i n g  fluorine  and t h e m o s t T r - a c i d i c o f p h o s p h i n e s i t  is expected  that P Bu3  porphyrin.  T h i s a s p e c t w i l l be f r e q u e n t l y r e f e r r e d t o i n t h i s t h e s i s w h e r e  n  w i l l show a n e t c h a r g e d o n a t i o n  to the  metallo-  s t u d i e s show t h a t a r a n g e o f p h o s p h i n e l i g a n d s c a n t r i g g e r a c h a n g e i n  107  o x i d a t i o n s t a t e o f the ruthenium (II)  t o ( I I I ) (Chapter  ruthenium  atom i n a m e t a l l o p o r p h y r i n  5). Electrochemical  complex  from  studies o f a range o f  p o r p h y r i n p h o s p h i n e c o m p l e x e s g e n e r a l l y do n o t show t h a t  higher  p o t e n t i a l s a r e r e q u i r e d to o x i d i z e t h e complex, e i t h e r a t t h e metal  or at  t h e p o r p h y r i n r i n g , t h a n when t h e p h o s p h i n e i s r e p l a c e d by a l i g a n d  such  as MeCN, EtOH o r py ( S e c t i o n s 6.1, 7 . 3 ) . S u c h r e s u l t s a r e i n c o n s i s t e n t with t h e view that t h e bonding o f t h e phosphine t o t h e metal d o m i n a t e d by t h e i r - a c i d i t y o f t h e p h o s p h i n e , complexes.  This suggests  centre i s  at least i n metalloporphyrin  t h a t t h e normal chemical  behaviour  i s m o d i f i e d when t h e y a r e c i s t o a p o r p h y r i n l i g a n d .  o f phosphines  Further evidence f o r  t h i s i s seen i n t h e s p e c t r a o f t h e phosphine carbonyl complexes which a r e very s i m i l a r t o those o f t h e e l e c t r o n r i c h complexes  Ru(OEP)(CO)CI"  and  fRu(,0EP)(.C0)CN"r ( s e e T a b l e 3.2 a n d c o m p a r e F i g u r e s 3.2 a n d 3 . 6 ) , a n d , compared t o t h e s p e c t r a o f t h e p y r i d i n e complexes, t h e r e d s h i f t o f t h e Soret i s thought ( T a b l e 3.8).  to r e f l e c t increased electron density at the porphyrin  To r e c o n c i l e t h e a b o v e o b s e r v a t i o n s w i t h t h e a b i l i t y o f p h o s -  phine groups t o l a b i l i z e a trans carbonyl necessary  l i g a n d as a l s o d e s c r i b e d , i t i s  t o s u g g e s t t h a t t h e e l e c t r o n d e n s i t y d o n a t e d by t h e p h o s p h i n e i s  to o r b i t a l s o f t h e ruthenium  atom t h a t o v e r l a p w e l l w i t h t h e T T - o r b i t a l s o f  the porphyrin system but a r e u n a v a i l a b l e t o t h e carbonyl bonding.  1 9  l i g a n d f o r ir-back-  108  T a b l e 3.8  The Wavelength o f t h e Soreti'(y) of Ru (0EP)L H  Complex  and R u  1 1  A b s o r p t i o n Band f o r a Number  ( 0 E P ) ( G 0 ) L Complexes  (nm) -  (nm) i  Complex  a  a  Ru(0EP)(C0)4Mepy Ru(0EP)py  4  2  395  Ru(0EP)(C0)PPh  Ru(0EP)(C0)P Bu  Ru(0EP)(PPh )  2  -  420  Ru(0EP)CP Bu )  2  -  428  3  n  3  Ratio(I / I J -  -  3  n  3  Ru(0EP)(.C0)CN" • Ru(.0EP)(.C0)Br" -'-9 Ru(0EP)CC0)CT"  -'-3  396  1 .54  407  1 .0  408  0.68  406  0.71  404  1 .22  402  1 .23  a). W a v e l e n g t h o f t h e S o r e t a b s o r p t i o n f o r s o l u t i o n i n C H C 1 2  2  P  unless indicated  otherwise.  b) R a t i o o f t h e m a j o r v i s i b l e a b s o r p t i o n s ( a t ^ 5 5 0 nm (a) a n d a t ^ 5 2 0 nm as d e f i n e d f o r T a b l e 3 . 1 .  c ) In t h e p r e s e n c e o f e x c e s s l i g a n d ( L ) .  d) From R e f . 5, s o l u t i o n i n b e n z e n e . e.) From T a b l e 7.6, S e c t i o n 7.8. f ) From R e f . 20,. .. - ;  g) S e e S e c t i o n 3 . 4 .  (g))  109  3.4  The C o o r d i n a t i o n  o f A n i o n s t o Ru(.0EP)(C0) (]_) i n  CHQCI  2  as Solvent.  A d d i t i o n o f CN" t o a s o l u t i o n o f R u ( 0 E P ) ( C 0 ) p y h a s been shown t o y i e l d an a n i o n i c s p e c i e s  Ru(OEP)(CO)CN",  t h a t c o u l d n o t be i s o l a t e d . 2 0  The s p e c t r u m o f t h e a n i o n i c s p e c i e s i s a l s o p r o d u c e d o n a d d i t i o n o f CN" t o a s o l u t i o n o f R u ( 0 E P ) ( C 0 ) CD o b t a i n e d CH C12 2  (Figure  3.6)..  O t h e r p o s s i b l e 1 i g a t i n g a n i o n s were a l s o added t o  s p e c t r o s c o p i c s o l u t i o n s o f ]_ rjh Table 3.9.  by d i s s o l v i n g Ru(OEP)(CO)EtOH (2) i n  C H 2  "C1 . •  T n e  2  results, are recorded i n  T h e a n i o n s w e r e u s u a l l y a d d e d i n t h e f o r m o f a t e t r a a l k y l ammonium  s a l t and i n most cases  i n l a r g e excess  (up t o 5 x 10 M ) . An i m p o r t a n t  r e s u l t was t h e c o m p l e t e l a c k o f c o o r d i n a t i o n s e e n f o r t h e a n i o n s t o be used as e l e c t r o l y t e s (C10 ~, BF^", C F S 0 " and P F " ) . 4  3  3  The anion  g  t r a t i o n s were s i m i l a r t o those used i n t h e e l e c t r o c h e m i c a l  concen-  preparations  t o b e d e s c r i b e d , s o t h e r e s h o u l d be n o c o o r d i n a t i o n o f t h e s e a n i o n s ruthenium centre, a t l e a s t before oxidation. coordinating anions,the  to the  In t h e case o f these non^  s p e c t r a o f Ru(.0EP)(C0) CD  d u c i b l e ( t o w i t h i n ± 1 % ) b e f o r e and a f t e r adding  w e r e  accurately  repro-  e l e c t r o l y t e t o 0.05M c o n -  centrations . C h l o r i d e and bromide i o n s were found t o c o o r d i n a t e weakly; t h e case o f C l ~ was t y p i c a l l e a d i n g t o a l o s s o f i n t e n s i t y a t 547 nm. s p e c t r u m o f t h e Ru (OEP) (CO)CI."" s p e c i e s was o b t a i n e d ^0.05M C I " ( f i g u r e 3.7) b u t s u c h a s p e c t r u m b r o m i d e c o m p l e x b e l o w 0.25M b r o m i d e i o n . s p e c i e s , d e r i v e d f r o m R u ( O E P ) C C O ) CD i n T a b l e 3.2.  w i t h  A limiting  i n t h e presence  c o u l d n o t be o b t a i n e d  for the  The spectra o f t h e product c 1  "> " B r  a n d  C N  ">  a r e  of  recorded  anionic  2.0!  WAVELENGTH  F i g u r e 3,6  (nm)  The o p t i c a l s p e c t r u m o f R u ( O E P ) ( C O ) ( ). i n C H C 1 a n d t h e product (Ru(OEP)(CO)CN-) C ) o b t a i n e d on a d d i n g an e x c e s s ?  ( t o 'vO.OSM) o f TEA+CN".  2  .111  500  600  700 WAVELENGTH  F i g u r e 3.7  (nm)  T h e o p t i c a l s p e c t r u m o f R u ( O E P ) ( C O ) () i n C H C 1 and t h e p r o d u c t ( ,Ru(OEP)(CO)Cl-") (. .-) o b t a i n e d on a d d i n g a n e x c e s s ( t o O . 0 5 M ) o f TEA+C1-. 2  J  2  112  T a b l e 3.9  T h e C o o r d i n a t i o n o f A n i o n s t o Ru(.0EP)(.C0) ( 1 ) i n CH C1 2  A n i o n Added  (I /I.) Before Adding Anion —  In ^0.05M A n i o n S o l u t i o n  cio "  2.52  2.50  BF "  2.53  2.53  CF3SO3-  2.62  2.61  2.60  2.61  r  2.58  2.53  Br"  2.61  1 .48 -  cr  2.54  1.23 i  4  4  P F  6~  a) .  R a t i o o f v i s i b l e peaks as d e f i n e d i n T a b l e 3.1.  b).  Measured'in dried CH C1  c)  Spectrum o f .Ru(OEP)(CO)Br"  2  2  as s o l v e n t .  o b t a i n e d i n ^0.25M T P A B r " a n d r e p o r t e d +  i n T a b l e 3.2.  d)  Under t h e s e c o n d i t i o n s t h e spectrum i s t h a t o f r e p o r t e d i n T a b l e 3.2.  Ru(OEP)(CO)CI"  113  REFERENCES - CHAPTER 3  1.  a ) M. T s u t s u i , D. O s t f i e l d , a n d L.M. H o f f m a n , J . Am. Chem. S o c . 9 3 , 1820 ( 1 9 7 1 ) . b) M. T s u t s u i , D. O s t f i e l d , a n d L.M. H o f f m a n , J . C o o r d . Chem. 115 ( 1 9 7 1 ) .  1(2),  2.  J . J . B o n n e t , S . S . E a t o n , G.R. E a t o n , R.H. H o l m , a n d J . A . I b e r s , Q. Am. Chem. S o c . 9 5 , 2141 ( 1 9 7 3 ) .  3.  T. B o s c h i , G. B o n t e m p e l 1 i , a n d G.A. M a z z o c c h i n , I n o r g . C h i m . A c t a . , 3 7 , 1 55 (1 9 7 9 ) .  4.  S . S . E a t o n a n d G.R. E a t o n , J . Am. Chem. S o c . 9 7 , 235 ( 1 9 7 5 ) .  5.  A. A n t i p a s , J.W. B u c h l e r , M. G o u t e r m a n a n d P.D. S m i t h , J . Am. Chem. S o c . 1 0 0 , 3015 (.1978).  6.  S. W a l k e r , M.Sc. T h e s i s , U.B.C., V a n c o u v e r , B . C . ( 1 9 8 0 ) .  7.  F.A. C o t t o n , I n o r g . Chem..3_, 702 (.1 9 6 4 ) .  8.  W.A.G. G r a h a m , I n o r g . Chem.7_, 315 ( 1 9 6 8 ) .  9.  D.V. S t y n e s , H„C". S t y n e s , B.R. J a m e s , a n d J . A . I b e r s , J . Am. Chem. S o c . 95, 1 7 9 6 (.1973).  10.  L.M. E p s t e i n , D.K. S t r a u b , a n d C. M a r i c o n d i , I n o r g . Chem.  6_, 1720 (1 9 6 7 ) .  11.  V. G u t m a n n , 'The D o n o r - A c c e p t o r A p p r o a c h t o M o l e c u l a r I n t e r a c t i o n s ' , P l e n u m , New Y o r k , N . Y . , 1 9 7 8 .  12.  D.W. S m i t h , Ph.D. T h e s i s , U.B.C., V a n c o u v e r , B . C . ( 1 9 8 0 ) .  13.  F.A. C o t t o n a n d G. W i l k i n s o n , 'Advanced I n o r g a n i c C h e m i s t r y , 4 t h E d . , I n t e r s c i e n c e , New Y o r k , N.Y., 1 9 8 0 , p . 8 7 .  14.  T. Leung,  15.  C A . T o l m a n , J . Am. Chem. S o c . 9 2 , 2 9 5 6 (1 9 7 0 ) .  16.  F.R. H o p f , T . O ' B r i e n , W.R. S c h e i d t , a n d D.G. W h i t t e n , J . Am. Chem. S o c . 97, 277 ( 1 9 7 5 ) .  17.  F. C a l d e r a z z o , u n p u b l i s h e d d a t a q u o t e d by J . B u c h l e r , ' 'j_n ^ T h e _ P o r p h y r i n s J ; ,  1  :  Personal  communication.  L  ,(p. D o l p h i n , e d . ) , A c a d e m i c  P r e s s , i New Y o r k , 1 978, V o l .1 f p . 4 6 2 .  114  18.  I . H . H i l l i e r , V.R. S a u n d e r s , M . J . W a r e , P . J . B a s s e t , D.R. L l o y d , and N. L y n a u g h , Chem. Comm. 1 9 7 0 , 1 3 1 6 .  19.  M. G o u t e r m a n , i n T h e P o r p h y r i n s , D. D o l p h i n , ed.)., A c a d e m i c P r e s s , New Y o r k , 1 978, V o l . I l l , p." 1 6 .  20.  D. D o l p h i n , B.R. J a m e s , a n d P.D. S m i t h , J . O r g a n o m e t . Chem. 239 ( 1 9 8 1 ) .  :  208,  115  CHAPTER 4  THE OXIDATION OF RUTHENIUM PORPHYRIN CARBONYL COMPLEXES Ru** ( O E P ) ( C O ) L ; ( L = E t O H , p y , Im, arid MeCN) .  The o x i d a t i o n o f r u t h e n i u m ( I I ) give  porphyrin species RutOEP)(C0)L that  p o r p h y r i n c a t i o n r a d i c a l p r o d u c t s w i l l be c o n s i d e r e d h e r e .  o x i d a t i o n o f other complexes o f t h i s type (L = P Bu3, PPh n  give mixtures c o n t a i n i n g ruthenium(.III) Chapter  4.1  3  The  and AsPh^) t o  p r o d u c t s w i l l be c o n s i d e r e d i n  6.  The E l e c t r o c h e m i c a l O x i d a t i o n o f RuC0EP)(C0)L W h e r e a s o x i d a t i o n o f c o m p l e x e s o f t h e t y p e Ru**(OEP)(1-|) ( l ^ ) ,  L-|,L2^C0 i s o b s e r v e d t h a t i f L-| o r L  2  t o r e s u l t i n o x i d a t i o n o f the metal  i o n , i t i s known  = CO, t h e o x i d a t i o n o c c u r s a t a c o n s i d e r a b l y h i g h e r p o t e n t i a l  and a t t h e p o r p h y r i n r i n g t o g i v e a p o r p h y r i n i r - c a t i o n r a d i c a l , R u * * ( . 0 E P ) ' +  (CO)L . 1  In o u r s t u d i e s , c y c l i c v o l t a m m o g r a m s w e r e u s e d t o o b s e r v e t h e o x i d a t i o n p r o c e s s p r i o r t o t h e p r e p a r a t i o n o f s a m p l e s by b u l k e l e c t r o c h e m i s t r y .  The  m e a s u r e d p o t e n t i a l s , a n d i n some c a s e s t h e v e r y f o r m o f t h e v o l t a m m o g r a m s , w e r e f o u n d t o be d e p e n d e n t u p o n t h e e l e c t r o l y t e u s e d , t h e s o l v e n t , a n d t h e nature o f the s i x t h l i g a n d L. S a m p l e s o f R u ( O E P ) ( C O ) E t O H {2) l a r g e l y d i s s o c i a t e 10  M) s o l u t i o n i n C H C 1 2  2  in dilute (10~ 4  t o g i v e R u ( 0 E P ) ( C 0 ) (.]_) w h i c h w i l l be t h e a c t i v e  s p e c i e s p r e s e n t under these c o n d i t i o n s ( S e c t i o n 3 . 1 ) . C y c l i c voltammograms o f 1_ w i t h a n y n o n - c o o r d i n a t i n g  e l e c t r o l y t e ( s e e S e c t i o n 3.4) showed two  116  r e v e r s i b l e o x i d a t i o n s , M-0.7V and -vi-1 .2V, t h e p o t e n t i a l s s h o w i n g  some  dependence upon t h e n a t u r e o f t h e e l e c t r o l y t i c a n i o n .  cyclic  v o l t a m m o g r a m i s s e e n i n F i g u r e 4.1 e l e c t r o l y t e , are l i s t e d in Table  A typical  and t h e p o t e n t i a l s , m e a s u r e d i n 0.05M 4.1(a).  In c o n t r a s t , t h e 4 - m e t h y l p y r i d i n e l i g a n d i n t h e c o m p l e x RuCOEP)(_C0)4 Mepy ( 4 ) d i d n o t d i s s o c i a t e on d i s s o l v i n g i n d i c h l o r o m e t h a n e 3.1 a n d 3.21.  (Sections  C y c l i c voltammograms o f complex ^ were compared to s i m i l a r  v o l t a m m o g r a m s o f c o m p l e x 1_ i n o r d e r t o s t u d y t h e e f f e c t o f a s i x t h l i g a n d on t h e o x i d a t i o n p r o c e s s ( T a b l e 4 . 1 ( b ) ) . Perchlorate, hexafluorophosphate,and  trifluoromethanesul.phonate  s o l u t i o n s gave s i m i l a r p o t e n t i a l s f o r both p o r p h y r i n complexes,  while sur-  p r i s i n g l y i n t e t r a f l u o r o b o r a t e medium a l l t h e p o t e n t i a l s m e a s u r e d w e r e ^0.1  volts higher. A s i m i l a r e f f e c t i s observed 6a comparing  Ru (.0EP)(C0)P Bu I I  n  3  ( 8 ) ( s e e S e c t i o n 6.1)  c y c l i c voltammograms o f  and R u ( 0 E P ) ( P B u ) n  [7)  n  3  2  (see  S e c t i o n 7.1) o b t a i n e d i n t h e p r e s e n c e o f 0.05M TBA'F and 0.05M T B A P . the higher p o t e n t i a l s f o r these oxidations (Ru (0EP)(C0)LiCiRu (0EP) I I  and R u C 0 E P ) L < = ^ R u I I  2  I I I  I I  ( 0 E P ) L ) observed in the presence of BF ~ 2  4  Thus, +  '(C0)L  ions are  not r e s t r i c t e d to s p e c i e s where the a n i o n c o u l d c o o r d i n a t e t o the metal c e n t r e and hence p r e c l u d e s t h e p o s s i b i l i t y t h a t t h e h i g h e r p o t e n t i a l i s associated with c o o r d i n a t i o n of BF ~ 4  i o n s a l t h o u g h , as d e s c r i b e d below,  e l e c t r o l y t e a n i o n s p r o b a b l y do c o o r d i n a t e t o R u ( 0 E P ) 'CC0) +  C y c l i c v o l t a m m o g r a m s o f b o t h Ru(.0EP)(C0) CD (.4_) u s i n g t e t r a e t h y l a m m o n i u m  p i c r a t e (TEAPIC  (, 1 a ) .  and Ru(OEP)(C0)4Mepy  - 0.05M s o l u t i o n ) a s e l e c t r o l y t e  showed a much l o w e r p o t e n t i a l , f o r t h e f i r s t r e v e r s i b l e wave ( t h e s e c o n d  7TJ5  "L2  08  E(V F i g u r e 4.1  04  0  vs. Ag/AgCl)  The c y c l i c voltammogram o f Ru(OEP)(CO)EtOH (2) ( d i s s o c i a t e s t o g i v e a m i x t u r e o f J_ a n d 2 i n 1 0 " ^ t o 10~^M s o l u t i o n s ) i n 0.05M TBAP-CH Cl2. 2  2  wave c o u l d n o t Be o B s e r v e d d u e t o o x i d a t i o n o f t h e p i c r a t e a n i o n a t ^+1,4V) . This decrease i n potential suggests that large anions with a d i f f u s e d  charge  d e n s i t y may Be m o r e e f f e c t i v e a t s t a B i l i z i n g t h e c a t i o n r a d i c a l s p e c i e s . The h i g h p o t e n t i a l s m e a s u r e d f o r r e d u c t i o n p r o c e s s e s o B s e r v e d i n 3  the presence o f BF^  i o n s have Been r e p o r t e d B e f o r e  and t h e e x p l a n a t i o n  g i v e n was t h a t c a t i o n r a d i c a l s a r e s t a B i l i z e d By l a r g e d i f f u s e a n i o n s p i c r a t e ) , arid h e n c e l e s s s t a B i l i z e d by s m a l l c o m p a c t a n i o n s .  [e.g.  This effect  may e x p l a i n t h e d e c r e a s e i n p o t e n t i a l s o b s e r v e d i n t h e p r e s e n c e o f t h e p i c r a t e a n i o n a t l e a s t f o r c o m p l e x 4_ ( t h e m o r e s u b s t a n t i a l d e c r e a s e i n p o t e n t i a l s e e n f o r c o m p l e x 1_ may be d u e t o c o o r d i n a t i o n o f t h e p i c r a t e a n i o n ) compared t o t h e t h r e e a n i o n s : C l O ^ , P F " and C F S 0 ~ . -  g  this theory, explains  3  3  However,  that\  the higher potential observed i n the presence o f  118  T a b l e 4.1 T h e R e v e r s i b l e R e d u c t i o n P o t e n t i a l s ( E ^ ) o b s e r v e d f o r R u ( 0 E P ) ( C 0 ) ( 1 ) a n d Ru(.OEP) ( C 0 ) 4 M e p y Various Electrolyte 4.1  a)  (.4) i n D i c h l o r o m e t h a n e  Anions.  E ^ Values f o r Ru(0EP)(C0)  tl) E (V) ±  E -E (V)  +0.82  +1 .30  +0.48  +0.71  +1 .19  +0.48  +0.70  +1 .20  +0.50  CF3SO3-  +0.65  +1.16  +0.51  Picrate"  +0.52  Anion 4  cio " 4  P F  2  2  BF "  4.1  i n t h e Presence o f  6~  1  b) E V a l u e s f o r Ru(OEP)(C0)4Mepy ( 4 ) x  Anion  E^V)  E (.V)  Eg-E^V)  2  +0.81  +1.42  +0.61  C10 ~  +0.72  +1.31  +0.59  PF "  +0.65  +1.27  +0.62  CF3SO3"  +0.71  +1.30  +0.60  Picrate"  +0.62  BF " 4  4  g  a)  C o n c e n t r a t i o n o f p o r p h y r i n b e t w e e n 1.5 x 1 0  a n d 2.5 x 10 M, e x c e p t f o r -4 t h e p i c r a t e e x p e r i m e n t w h e r e p o r p h y r i n c o n c e n t r a t i o n was a b o u t 3.7 x 1 0 M.  b)  C o r r e s p o n d s t o t h e h a l f - w a v e p o t e n t i a l ( S e c t i o n 2.2) f o r t h e f i r s t r e v e r s i b l e e l e c t r o d e p r o c e s s , w h i c h i s shown b y b u l k e l e c t r o l y s i s ( s e e t e x t ) t o correspond t o t h e process Ru (0EP) '(.C0)L+eWRu C0EP)(;C0)L. I I  c)  I I  Corresponds t o t h e half-wave p o t e n t i a l f o r t h e second r e v e r s i b l e e l e c t r o d e process. or Ru  d)  +  I I I  T h i s c o r r e s p o n d s t o e i t h e r Ru (0EP) " (.C0)L+e*r=^Ru (0EP) ' ( C 0 ) L , II  2  H  II  (0EP) '(C0)+e- =iRu (0EP) 'CC0)L. +  I I  +  ?  C o n c e n t r a t i o n o f p o r p h y r i n b e t w e e n 2.0 x TO-4 a n d 3.0 x 1 0 ^M.  +  119  BF4~ions  has t o be d i s c o u n t e d b e c a u s e t h e B F ^ " i o n has o n l y a v e r y  smaller Van-der-Waals contact  r a d i u s t h a n C I 0 " ( 2 . 8 3 $ v s . 2.90 4  slightly  A)..  The  c o n t a c t r a d i i o f t h e a n i o n s were e s t i m a t e d f r o m t h e bond l e n g t h s f o u n d i n the a n i o n s  4  and t h e V a n - d e r - W a a l s c o n t a c t r a d i i  a t o m s (0 f o r C l O ^ " a n d F f o r B F ^ ) .  of the e l e c t r o n e g a t i v e  The two e l e c t r o l y t e a n i o n s a r e o f  -  approximately  5  t h e same s i z e and t h e s m a l l d i f f e r e n c e i s c o n s i d e r e d  insuffi-  c i e n t to e x p l a i n the s u b s t a n t i a l i n c r e a s e i n p o t e n t i a l seen f o r the t e t r a fluoroborate  anion.  C o m p a r i s o n o f t h e s e c o n d o x i d a t i o n p o t e n t i a l s f o r R u ( 0 E P ) ( C 0 ) (1_) and R u ( O E P ) C C 0 ) 4 M e p y ( 4 ) ( T a b l e 4.1) 0.1  shows t h a t t h o s e f o r .4. a r e  approximately  v o l t s h i g h e r and m u s t be due t o t h e p r e s e n c e o f t h e s i x t h l i g a n d .  The  c y c l i c v o l t a m m o g r a i m . o f R u ( O E P ) ( C 0 ) L s p e c i e s (L = v a c a n t , p y , 4Mepy and  Im)  w e r e o b t a i n e d i n 0.05M T B A C 1 0 " i n C H C 1 +  4  2  a coordinated s i x t h l i g a n d appears  2  (Table 4.2).  The p r e s e n c e  of  to d e s t a b i l i z e the d i c a t i o n species  r e l a t i v e t o t h e m o n o c a t i o n as j u d g e d  by t h e d i f f e r e n c e b e t w e e n t h e  first  and s e c o n d r e d u c t i o n p o t e n t i a l s ( E ^ - E - i ) . B o t h E-| and E^ v a l u e s a r e s e n s i t i v e t o t h e p r e s e n c e sixth ligand.  and n a t u r e o f t h e  The p y r i d i n e s a r e w e a k l y T r - a c i d i c l i g a n d s * t h a t have l i t t l e 6  e f f e c t on t h e E-| v a l u e , b u t t h e Ev> v a l u e i s i n c r e a s e d by c o o r d i n a t i o n o f p y r i d i n e t o t h e f i v e - c o o r d i n a t e s p e c i e s 1_. p y r i d i n e , imidazole i s observed  7  0.1 v o l t s on Compared t o  t o s t a b i l i z e both the m o n o c a t i o n and d i c a t i o n  and t h i s i s c o n s i d e r e d t o be due t o t h e r e l a t i v e l y h i g h ir-donor c a p a c i t y o f g  imidazole to charged complexes .  120  T a b l e 4.2  V a r i a t i o n o f Reduction  P o t e n t i a l s with the Nature o f the S i x t h  Ligand.  al b)  S p e c i e s P r e s e n t i n S o l u t i o n *-  E^V)  E (V)  Eg-E^V)  t l ) Ru(OEP)tCO) -  +0.71  +1.19  0.48  L = py  t l ) Ru(0EP)(C0)py  +0.68  +1 .27  0.59  L = 4Mepy  (4) R u t 0 E P ) t C 0 ) 4 M e p y  +0.72  +1 .31  0.59  L = Im  C5)  +0.60  +1 .21  0.60  RutOEP)tCO)Im  2  -4  , 0 x 10" C o n c e n t r a t i o n o f p o r p h y r i n b e t w e e n 1.5 x 10 a n d 3. t l ) i n C H CI . G e n e r a t e d i n s o l u t i o n by d i s s o l v i n g R u ( O E P ) ( C O ) E t O H > 2  D e s p i t e t h e v a r i a t i o n i n b o t h E-j a n d E  2  2  with the nature o f the s i x t h  l i g a n d ( T a b l e 4.2) a n d w i t h t h e e l e c t r o l y t e c o - a n i o n p r e s e n t ( T a b l e 4 . 1 ) , t h e v a l u e o f E - E ^ a p p e a r s t o be i n d e p e n d e n t 2  o f the nature o f the s i x t h 1igand  ( T a b l e 4.2) o r o f t h e e l e c t r o l y t e u s e d ( T a b l e 4 . 1 ) , a n d i s o n l y d e p e n d e n t on w h e t h e r t h e c o m p l e x i s f i v e - o r s i x - c o o r d i n a t e ( T - E - | = +0.495 ± 0.015V f o r 2  t h e f i v e c o o r d i n a t e s p e c i e s a n d +0.605 ± 0.015V f o r t h e s i x - c o o r d i n a t e s p e c i e s studied).  The apparent  s t a b i l i z a t i o n o f t h e d i c a t i o n o f s p e c i e s 1 c o m p a r e d to that  o f t h e s i x - c o o r d i n a t e s p e c i e s , c o u l d be d u e t o t h e c o o r d i n a t i o n o f t h e a n i o n t o t h e d i c a t i o n o f t h e f i v e - c o o r d i n a t e s p e c i e s Ru(.0EP) "tC0) (.1) +  b u t t h i s seems  u n l i k e l y as t h e e l e c t r o l y t e anions probably c o o r d i n a t e to t h e metal  i n j_a  (see below) and, i f t h e anions c o o r d i n a t e d o n l y t o t h e d i c a t i o n and n o t t h e  121  m o n o c a t i o n (ljO,  some v a r i a t i o n i n E - E ^ v a l u e s w i t h t h e e l e c t r o l y t e u s e d 2  w o u l d be e x p e c t e d a n d t h i s i s n o t t h e c a s e (• Another  even f o r t h e BF^" a n i o n ) .  p o s s i b l e e x p l a n a t i o n f o r t h i s e f f e c t may be d e r i v e d  from  l i g a n d f i e l d t h e o r y . T h e m a j o r d i f f e r e n c e b e t w e e n l_a_ a n d t h e s i x - c o o r d i n a t e c o m p l e x e s 3 a , 4a a n d 5a i s t h a t i n t h e l a t t e r t h e r u t h e n i u m  i s coor-  d i n a t e d t o f i v e n i t r o g e n l i g a n d s and i n t h e former case o n l y f o u r n i t r o g e n ligands are involved.  E v i d e n c e w i l l be p r e s e n t e d l a t e r t o show t h a t l_a  almost c e r t a i n l y contains a coordinated e l e c t r o l y t e anion,although a n i o n i s s o w e a k l y c o o r d i n a t e d t h a t t h e c h e m i s t r y o f l_a a p p e a r s of a f i v e - c o o r d i n a t e species (see Chapter  t o be t h a t  5),and t h i s i s u s u a l l y c o n s i d e r e d  to' be t h e s t r u c t u r e o f c o m p l e x l_a f o r t h e p u r p o s e s ligand f i e l d theory  this  of this thesis.  From  i t c a n be s e e n t h a t n i t r o g e n l i g a n d s h a v e s t r o n g l i g a n d  f i e l d s and cause c o n s i d e r a b l e s p l i t t i n g o f t h e metal d - o r b i t a l s . P e r c h l o r a t e a s a l i g a n d i s known t o h a v e a weak l i g a n d f i e l d , u s u a l l y o f a s t r e n g t h s i m i l a r t o t h a t o f t h e c h l o r i d e i o n , a l t h o u g h r e c e n t s t u d i e s on t h e 1 0  complex  Fe*^(TPP)Cl0^  suggested  t h a t i n porphyrin complexes t h e l i g a n d  f i e l d s t r e n g t h may be r e d u c e d e v e n f u r t h e r . 1 1  ruthenium  Thus,although  c a t i o n r a d i c a l s p e c i e s CRu(.0EP) 'CC0) +  RuC0EP) ' ( C 0 ) 4 M e p y ( 4 a ) a n d RuC0EP) ' ( C 0 ) l m +  f o r t h e purpose  +  a l l these  ( J _ a ) , RuC0EP) '(.C0)py ( 3 a ) , +  (jiaj) may be s i x - c o o r d i n a t e ,  o f l i g a n d f i e l d t h e o r y l a ^ w o u l d be a d i s t o r t e d s q u a r e  planar complex ( t h e carbonyl l i g a n d p r e s e n t i n g a d i f f e r e n t i n t e n s i t y o f c h a r g e d i s t r i b u t i o n f r o m t h e p o r p h y r i n m a c r o c y c l e ) , w h i l e c o m p l e x e s 3ia, 4a_ and 5a_ w o u l d show d i s t o r t e d o c t a h e d r a l g e o m e t r y . o r b i t a l s on a m e t a l  T h e o r d e r i n g o f t h e d-  i o n i s very s e n s i t i v e t o t h e geometry and charge  d i s t r i b u t i o n o f t h e s u r r o u n d i n g l i g a n d s a n d h e n c e c o u l d be v e r y d i f f e r e n t 9  122  f o r la_ c o m p a r e d t o t h e o t h e r c a t i o n r a d i c a l s p e c i e s .  The d i f f e r e n c e i n  o r d e r i n g o f t h e d - o r b i t a l s could a f f e c t t h e energies o f t h e p o r p h y r i n molec u l a r o r b i t a l s such t h a t a second e l e c t r o n i s removed ( i n f o r m a t i o n o f t h e d i c a t i o n ) f r o m a d i f f e r e n t o r b i t a l f o r l a . c o m p a r e d t o 3a_, 4a_ a n d 5a_, w h i l e t h e e n e r g i e s o f t h e p o r p h y r i n o r b i t a l s may be i n s e n s i t i v e t o t h e n a t u r e o f the a x i a l n i t r o g e n l i g a n d i n t h e l a t t e r t h r e e complexes.  T h i s would e x p l a i n  t h e l a c k o f v a r i a t i o n i n t h e v a l u e o f E -E-| w i t h t h e n a t u r e o f t h e s i x t h 2  l i g a n d d o o r d i n a t e d t o t h e c a t i o n r a d i c a l , a n d t h e d i f f e r e n t E^-E-j v a l u e o b t a i n e d f o r t h e f i v e - c o o r d i n a t e s p e c i e s l_a_. Changing  t h e s o l v e n t had a c o n s i d e r a b l e e f f e c t o n t h e r e d o x  t i a l s of the porphyrin species. n i t r i l e g a v e Ru(.OEP)(.CO)CH^CN (.6).  poten-  D i s s o l v i n g Ru (OEP) (CO) EtOH (.2) i n a c e t o a s  b  s e e n  V  t n e  u . v . / v i s i b l e spectrum (see  S e c t i o n 3 . 1 ) . C y c l i c voltammograms were o b t a i n e d i n t h e presence o f both 0.05M C 1 0 " a n d B F " . T a b l e 4 . 3 . 4  T a b l e 4.3  4  A Comparison  o f R e d u c t i o n P o t e n t i a l s o f Ru(0EP)(.C0) (.1) i n  A c e t o n i t r i l e and Dichloromethane E l e c t r o l y t e Anion  as S o l v e n t . Solvent .  CH CN -  CH C1 -  3  2  1  2  R e d u c t i o n P o t e n t i a l s (V) R e d u c t i o n P o t e n t i a l s (V) ^Z~ ^  (E -E ) 2  C10 " 4  BF ~ 4  E  1  +0.73  E  2  +1.12  E  ]  +0.75  E  2  +1.14  E  n  +0.71 (0.39)  +1.19  (0.48)  +0.82 (0.39)  +1.30  (0.48)  123  T a b l e 4.3 c o n t i n u e d a)  Porphyrin concentrations range 4 x 10"  b)  4  i n the a c e t o n i t r i l e experiments are in the  t o 8 x 10" M. 4  R e d u c t i o n p o t e n t i a l s quoted f o r d i c h l o r o m e t h a n e as s o l v e n t a r e taken f r o m T a b l e 4.1 .  W i t h CH^CN a s s o l v e n t , t h e p o t e n t i a l s o b s e r v e d a r e n e a r l y i d e n t i c a l in t h e p r e s e n c e o f both p e r c h l o r a t e and f l u o r o b o r a t e e l e c t r o l y t e s . Thus the changing o f s o l v e n t from C H C 1 2  t o CHgCN has l i t t l e e f f e c t on t h e  2  s t a b i l i t y o f t h e c a t i o n r a d i c a l i n p e r c h l o r a t e medium b u t c a u s e s a s u b s t a n t i a l increase in s t a b i l i t y of t h i s species in the presence o f fluoroborate anions.  Whatever e f f e c t i s r e s p o n s i b l e f o r the increased p o t e n t i a l s i n  the presence o f BF ~ ions i n CH C1 4  CHIgCN.  2  as s o l v e n t , i t c e a s e s t o o f u n c t i o n i n  2  T h i s i s p r o b a b l y due t o t h e g r e a t e r d i p o l e moment and s o l v a t i n g  power o f a c e t o n i t r i l e t o w a r d s c h a r g e d s p e c i e s . in the reduced v a l u e s f o r E  2  E v i d e n c e f o r t h i s i s seen  o b s e r v e d i n a c e t o n i t r i l e as s o l v e n t (a s i m i l a r  e f f e c t was o b s e r v e d f o r R u ( . 0 E P ) . C P B u ) . ( 7 ) - S e c t i o n 7.1) and a l s o II  n  3  2  r e d u c t i o n o f E ~ E ^ v a l u e s n o t e d i n T a b l e 4.3. 2  solvated than the monocation  the  T h e d i c a t i o n w i l l be m o r e  i n a p o l a r s o l v e n t s u c h a s CHgCN c o m p a r e d w i t h  the less polar dichloromethane. C y c l i c v o l t a m m o g r a m s o f Ru(OEP) ( C O ) E t O H (.2) i n an i n e r t s o l v e n t ( C H C 1 ) w i t h s t r o n g l y c o o r d i n a t i n g e l e c t r o l y t e s were d i f f e r e n t from the 2  2  usual form o f voltammogram d e s c r i b e d above.  F i g u r e 4.2 shows a c y c l i c  v o l t a m m o g r a m o f R u ( 0 E P ) ( C 0 ) ('.!_) ( f o r m e d by t h e d i s s o c i a t i o n o f an  ethanol  124  1.2  0.8  0.4  0  E(V vs. Ag/AgCl)  F i g u r e 4.2  The c y c l i c voltammogram o f Ru(OEP)(CO)EtOH (2) ( d i s s o c i a t e s t o g i v e a m i x t u r e o f 1_ a n d 2_ i n 10"4 t o 10~3M s o l u t i o n s ) i n 0.05M TBAP a n d 0.005M TEA+C1" i n C H C 1 . 2  2  l i g a n d on s o l u t i o n o f 2_ i n C H C 1 ) i n t h e p r e s e n c e 2  2  o f 0.005M T E A C 1 ~ , +  w h e r e , d u e t o o x i d a t i o n o f t h e c h l o r i d e i o n , i t was i m p o s s i b l e t o s c a n t o a p o t e n t i a l h i g h e r t h a n +1.0 v o l t s .  At such c o n c e n t r a t i o n s o f c h l o r i d e ,  o n l y a few p e r c e n t o f t h e s i x - c o o r d i n a t e s p e c i e s , (,.Ru**(.OEP)(CO)CI")  would  be p r e s e n t ( S e c t i o n 3.4) a n d h e n c e t h e o x i d a t i o n p e a k a t +0.74V i s l i k e l y due t o t h e f o r m a t i o n o f R u ( O E P ) '( CO) (l_a_). +  The c o r r e s p o n d i n g  reduction  p e a k ( a t +0.38V) i s f a r t o o d i s p l a c e d f o r t h e p r o c e s s t o be c o n s i d e r e d reversible;  c o o r d i n a t i o n o f c h l o r i d e t o t h e c a t i o n r a d i c a l c o u l d make i t  more d i f f i c u l t t o reduce  (Scheme 4 . 1 ) .  125 SCHEME 4.1 TT E =+0.74V j R u ( O E P ) ( C O ) -E . ) R u ( O E P ) '(CO) T 1 1  l x  +  -e (la)  (1)  +CT  R u ( O E P ) "(CO)' CI n  +  E =+0.38V -2 > Ru (OEP)(CO) TT H  + CT  +e  (1)  (lc)  Electrochemical oxidation o f dichloromethane  s o l u t i o n s o f Ru(0EP)(C0)  ( f r o m R u ( O E P ) ( C O ) E t O H ) o r Ru(.0EP)(.C0)L ( L = p y , 4Mepy, Im) i n t h e p r e s e n c e o f 0.05M T B A C 1 0 " o r T P A B F " a t a p o t e n t i a l a p p r o x i m a t e l y +  +  4  4  0.04 v o l t s  higher  than t h a t f o r t h e f i r s t o x i d a t i o n peak gave i n a l l cases a smooth e l e c t r o l y s i s r e s u l t i n g i n t h e f o r m a t i o n o f a deep p u r p l e s o l u t i o n ( F i g u r e 4 . 3 ) . The e l e c t r o l y s i s i n v o l v e d 1.00 ± 0.05 e q u i v a l e n t s o f e l e c t r o n s p e r m o l e o f ruthenium  porphyrin.  The spectrum o f t h e product v a r i e d with L ( F i g u r e 4 . 4 ) .  The p r i n c i p l e a b s o r p t i o n s a n d e x t i n c t i o n c o e f f i c i e n t s a r e l i s t e d i n , T a b l e 4.4 near t h e end o f t h i s Chapter  (Section 4.3).  A d d i t i o n o f a small q u a n t i t y o f t h e a p p r o p r i a t e l i g a n d t o a sample o f t h e R u ( 0 E P ) "(CO) +  Ru(0EP)  +  (,1a) s p e c i e s g a v e t h e c o r r e s p o n d i n g  (C0)L cation r a d i c a l (see Section 5.1b).  s p e c t r a a r e d u e t o the. c o n t i n u e d  spectrum f o r t h e  Hence t h e d i f f e r e n c e i n  c o o r d i n a t i o n o f t h e l i g a n d ( L = 4Mepy o r I m ) .  126  Figure 4.3  127 F i g u r e 4.4  The o p t i c a l s p e c t r a o f the e l e c t r o c h e m i c a l l y prepared c a t i o n radicals.  a  400  500  600  Wavelength (nm)  a)  Ru(OEP) '(CO) (Ja.) i n 0.05M T B A P - C H C 1 . +  2  2  The spectrum o f  Ru(.OEP) ' ( C O ) p y ( 3 a J i s a l m o s t i d e n t i c a l e x c e p t t h a t t h e +  absorptions are s l i g h t l y red-shifted (see Table 4.5).  128 F i g u r e 4.4 c o n t i n u e d :  . b -  -  i  Wavelength (nm) c)  Ru(0EP) '(C0)Im (5a) i n 0.05M TBAP-CH C1 . +  2  2  129  The a d d i t i o n of excess e l e c t r o l y t e (such as TBAP or TPAF) to a s o l u t i o n of Ru(0EP) '(C0) +  ( l a ) , prepared e l e c t r o c h e m i c a l l y in CH CI > 2  caused no detectable change in the v i s i b l e spectrum.  2  However,species l a  prepared in the absence of e l e c t r o l y t e ( e i t h e r by d i r e c t oxidation of 2 dissolved in CH C1 2  using AgBF^or by the addition of AgBiF^ to [Ru(0EP) * +  2  (CO)Br] (l_b) prepared by bromine oxidation of 1_ - see Sections 4.2 and 4.3) had a s l i g h t l y d i f f e r e n t spectrum from l_a_ prepared by electrochemistry (compare Figures 4.4a and 4.7).  In the absence of 0.05M e l e c t r o l y t e the  shoulder at%610nm i s diminished (Table 4.4).  Addition of e l e c t r o l y t e  (TBAF or TBAP) i n t e n s i f i e d t h i s shoulder giving a spectrum i d e n t i c a l to that observed for the e l e c t r o c h e m i c a l l y prepared l_a_. Addition of AgBF^ to l_a in 0.05M e l e c t r o l y t e s o l u t i o n did not change the spectrum at a l l , precluding the p o s s i b i l i t y that the s i l v e r ion i t s e l f was a f f e c t i n g the _4 _3 spectrum. Addition of small concentrations (10 to 10 M) of ethanol or methanol to an el ectrochemical l y prepared sample, of la_ caused no change, in the -2 -1 spectrum but larger concentrations (.10  to 10  M) caused loss of i n t e n s i t y  at 610 nm giving a spectrum s l i g h t l y d i f f e r e n t to that obtained in the absence of excess e l e c t r o l y t e . RuC0EP)t'(,C0)MeCN  Addition of e l e c t r o l y t e to a s o l u t i o n of  (6a) i n 1% MeCN in CH C1  v i s i b l e spectrum (see Section  2  2  caused no change in the  4.3).  The d i f f e r e n c e in o p t i c a l spectra noted here obviously depends upon the absence or presence of excess e l e c t r o l y t e and suggests that the e l e c t r o l y t e anions are coordinating to l_a_. the s o l i d state has been r e p o r t e d  12  Coordination of CI0^  to ZnTPP  in  and the same authors obtained evidence,  130  b a s e d on t h e i n f r a - r e d a b s o r p t i o n s o f t h e p e r c h l o r a t e a n i o n , t h a t a s u b s t a n t i a l p r o p o r t i o n o f t h e a n i o n r e m a i n e d c o o r d i n a t e d on d i s s o l u t i o n i n 12.  CH^C^  . H o w e v e r , t h e e l e c t r o c h e m i c a l d a t a f o r t h e o x i d a t i o n o f 1_ ( t h e  r e v e r s i b i l i t y o f the oxidation processes  and t h e i n v a r i e n c e o f E£-E^ with  e l e c t r o l y t e ) , argue against t h e coordination o f t h e e l e c t r o l y t e anion ( c o n t r a s t t h e e f f e c t on t h e e l e c t r o c h e m i c a l o x i d a t i o n o f 1_ o f a n a n i o n known t o c o o r d i n a t e , e . g . C l ~ , s e e a b o v e ) , a l t h o u g h i t s h o u l d be n o t e d t h a t ZnTPP, under t h e c o n d i t i o n s where p e r c h l o r a t e c o o r d i n a t e d t o Z n T P P " , +  13  shows c l e a r r e v e r s i b l e waves i n t h e c y c l i c v o l t a m m o g r a m From t h i s e v i d e n c e i t c a n be c o n c l u d e d t h a t t h e e l e c t r o l y t e a n i o n i s almost c e r t a i n l y c o o r d i n a t e d t o samples o f la_ prepared e l e c t r o c h e m i c a l l y , but t h a t t h e c o o r d i n a t e d a n i o n has a n e g l i g i b l e e f f e c t on t h e c h e m i s t r y or e l e c t r o c h e m i s t r y o f t h e complex la_ w h i c h i s t h e r e f o r e c o n s i d e r e d t o behave as a f i v e - c o o r d i n a t e s p e c i e s .  Coordination o f the e l e c t r o l y t e  anion c o u l d e x p l a i n t h e v i s i b l e s p e c t r a l changes o u t l i n e d above.  Addition  o f e x c e s s m e t h a n o l o r e t h a n o l t o l_a i n 0.05M e l e c t r o l y t e s o l u t i o n s h o u l d cause displacement  o f the e l e c t r o l y t e co-anion t o give the species  R u ( 0 E P ) ' ( C 0 ) R 0 H (R = Me o r E t ) . T h e l a c k o f s p e c t r a l c h a n g e o n -4 a d d i n g t h e a l c o h o l t o ^5 x 10 M c o n c e n t r a t i o n s u g g e s t s t h a t t h e a l c o h o l a t t h i s c o n c e n t r a t i o n does n o t compete e f f e c t i v e l y f o r t h e l i g a n d s i t e w i t h -2 -2 t h e e x c e s s e l e c t r o l y t e a n i o n (.5 x 10 M ) ; a h i g h e r c o n c e n t r a t i o n C>10 M) I I  +  is required to displace the anion.  In t h e samples prepared  by AgBF^ o x i -  d a t i o n , n e i t h e r t h e e t h a n o l (>1 x 1 0 ~ M ) n o r t h e B F ^ " i o n s a r e l i k e l y t o 4  be c o o r d i n a t e d t o a n y s u b s t a n t i a l d e g r e e , a n d s o t h e s p e c t r u m s e e n i n F i g u r e 4.7 i s l i k e l y t o be t h a t o f t h e g e n u i n e f i v e - c o o r d i n a t e s p e c i e s Ru(.0EP) ''[CO) +  la.  131  E l e c t r o l y s i s o f Ru(OEP)(CO)EtOH d i s s o l v e d i n a c e t o n i t r i l e ( e f f e c t i v e l y the e l e c t r o l y s i s o f Ru(OEP)(CO)MeCN i n MeCN) u s i n g 0.05M T E A C 1 0 " +  4  e l e c t r o l y t e a l s o gave a p u r p l e s o l u t i o n o f a c a t i o n r a d i c a l  as  (6a_),whose  spectrum was s i m i l a r t o t h a t o f J_a_ and 3a^  but i n d i c a t e d c o o r d i n a t e d  acetonitrile  S o l u b i l i t y problems p r e c l u d e d  ( F i g u r e 4.4b and T a b l e 4 . 4 ) .  the d e t e r m i n a t i o n o f the number o f e l e c t r o n s removed from the p o r p h y r i n complex i n t h i s r e a c t i o n , but r e p e a t i n g t h e o x i d a t i o n o f ]_ i n 1% MeCN in C ^ C ^  ( t h e p r o d u c t had an i d e n t i c a l spectrum t o t h a t o b t a i n e d i n pure  MeCN) proved t h a t t h e o x i d a t i o n process  r e q u i r e d 1.00 ± 0.05 e l e c t r o n s  as i n t h e e l e c t r o c h e m i c a l f o r m a t i o n o f l_a_, 3a_ and 5a_. All  these c a t i o n r a d i c a l samples ( l a , 3 a , 5a and 6a_) can be reduced  e l e c t r o c h e m i c a l l y , or by the a d d i t i o n o f T B A B H ~ , t o g i v e a r e d s o l u t i o n +  4  s p e c t r a l l y i d e n t i c a l t o the one c o n t a i n i n g the s t a r t i n g complex (1_, 3_, 5^ and i5 r e s p e c t i v e l y ) . E l e c t r o n s p i n resonance (e.-s.r.) s t u d i e s o f t h e s e c a t i o n showed a s t r o n g sharp (peak t o peak w i d t h = 8G)  signal  radical  a t g = 2.01  species  at  l i q u i d n i t r o g e n t e m p e r a t u r e s c o r r e s p o n d i n g t o an u n p a i r e d e l e c t r o n i n a d e l o c a l i z e d o r g a n i c system.  Integration of this signal  a s i m i l a r s o l u t i o n of ZnTPP ' +  ( s e e S e c t i o n 2.1)  by comparison w i t h  i n d i c a t e d the presence  of  one u n p a i r e d e l e c t r o n per p o r p h y r i n m o l e c u l e and was 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 o f t h e ruthenium s p e c i e s as p o r p h y r i n T r - c a t i o n r a d i c a l s .  How-  e v e r , t h e ruthenium c a t i o n r a d i c a l s o l u t i o n s , when s t u d i e d a t ambient temper a t u r e s , showed a v e r y much weaker s i g n a l as e s t i m a t e d from a TO  2  ( r e d u c e d by a f a c t o r o f 10,000 i  M s o l u t i o n o f Ru(.0EP) '(.CO)  ( l _ a ) ) . o f t h e same  +. sharpness and g v a l u e .  T h i s temperature e f f e c t was not observed f o r ZnTPP  132  ( r e d u c t i o n in i n t e n s i t y ofie.a.r. s i g n a l <30%)  on.warming  but f o r the ruthenium c a t i o n r a d i c a l  v e r s i b l e and c o u l d be repeated s e v e r a l  to room temperature was  solutions  times.  the process was r e -  No change i n c o l o u r was  observed on f r e e z i n g or thawing the ruthenium c a t i o n r a d i c a l and t h i s  solutions  p r e c l u d e s the p o s s i b i l i t y o f i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r  from the metal  to the p o r p h y r i n a c c o u n t i n g f o r the weak s i g n a l  a t room t e m p e r a t u r e . 1 4  due to a r e l a x a t i o n Solutions  The weakness  effect  1 5  o f the room temperature s i g n a l  may be  .  o f these c a t i o n r a d i c a l s  (3aJ and Ru(.0EP) * (.CO) Im (5a)) +  argon i n an a n a e r o b i c c e l l  observed  (CO)py  were r e a s o n a b l y s t a b l e i f s e a l e d under  ( S e c t i o n 2.1)  f o r s e v e r a l days without d e t e r i o r a t i o n . by evaporating, o f f the s o l v e n t  ( p a r t i c u l a r l y Ru**(.0EP)  and c o u l d be^stored i n the f r e e z e r However, s o l i d samples,  from the c a t i o n r a d i c a l  formed  and the s u p p o r t i n g  e l e c t r o l y t e , degraded in a matter o f hours to g i v e n o n - p o r p h y r i n products even i f s t o r e d in a Schlenk tube under a r g o n . s e n s i t i v e to a i r  The c a t i o n r a d i c a l s a r e v e r y  i n the s o l i d s t a t e , the products showing  to those o f a t m o s p h e r i c a l l y o x i d i z e d s o l u t i o n s appear to degrade f a s t e r than s o l u t i o n s  similar  o f 1_ i n C H g C l 2  absorptions  Solid  in the presence o f t r a c e s o f  samples air.  In an attempt to o b t a i n a s t a b l e s o l i d sample, e l e c t r o l y s i s was c a r r i e d out in the presence of p i c r a t e e l e c t r o l y t e i n the hope t h a t l a r g e a n i o n , with most o f i t s  the  n e g a t i v e charge d e l o c a l i z e d t o the p e r i p h e r y  o f the m o l e c u l e , would s t a b i l i z e the c a t i o n r a d i c a l  s p e c i e s and r e a d i l y  p r e c i p i t a t e out the p o s i t i v e l y charged complex as a p i c r a t e  salt.  133 Tetra-n-butylammonium  picrate.was  f o u n d t o be v i r t u a l l y i n s o l u b l e  i n C H C 1 g w h i l e T E A P I C was v e r y s o l u b l e and i t seemed l i k e l y t h a t l a r g e 2  c a t i o n s would p r e c i p i t a t e out i n the presence o f p i c r a t e .  However,  a d d i t i o n o f s o l i d s a m p l e s o f T E A P I C ( t o 1 0 " M) t o s o l u t i o n s o f Ru(.0EP) "(.C0) Qa) ( 1 0 " M p o r p h y r i n and 0-.05M T E A P i n C H C 1 ) g a v e no p r e +  3  2  cipitate.  2  (2) Gin e q u i . l i -  T h e e l e c t r o l y s i s o f 50 mg o f R u ( O E P ) ( C O ) ( E t O H ) 3  b r i u m w i t h Ru(.OEP)(CO) (.!_)) i n C H C 1 2  5x10  2  c o n t a i n i n g 2 x 10  M p o r p h y r i n and  M T E A P I C p r o c e e d e d s m o o t h l y b u t s l o w l y ( d u e t o low c o n c e n t r a t i o n o f f  e l e c t r o l y t e ) t o g i v e a d e e p c o l o u r e d s o l u t i o n b u t no p r e c i p i t a t e was served.  A d d i t i o n o f h e p t a n e and e v a p o r a t i o n o f t h e  CH2CI  2  gave  ob-  dark  c r y s t a l s o f a complex c o - p r e c i p i t a t i n g w i t h the excess e l e c t r o l y t e . T h e s p e c t r u m i n C H C l 2 s h o w e d t h e s o l i d t o be a c l e a n m i x t u r e o f ] R u ( 0 E P ) ' ( C 0 ) ] ;  +  2  p i c r a t e " and e x c e s s e l e c t r o l y t e .  A weak s h o u l d e r a t ^610 nm was  observed  i n the spectrum o f t h i s complex.  T h i s s h o u l d e r was u n l i k e t h a t o b s e r v e d  f o r s p e c i e s l_a_ p r e p a r e d e i t h e r i n t h e p r e s e n c e o f e x c e s s e l e c t r o l y t e o r f r o m d i r e c t o x i d a t i o n o f Ru(OEP)CCO)-(J_)  in CH C1 2  2  by A g B F . 4  This observa-  t i o n s u g g e s t s t h a t t h e p i c r a t e a n i o n was c o o r d i n a t e d t o t h e c a t i o n r a d i c a l i n s o l u t i o n , and p e r h a p s t h i s e x p l a i n s t h e u n e x p e c t e d s o l u b i l i t y o f [Ru(0EP) '(C0)] +  4.2  +  picrate".  Chemical O x i d a t i o n o f Ru(OEP)(C0)L -4 -3 A d d i t i o n o f a 10  5 x 10" M 5  ' t o 10  ( L = V a c a n t , p y , MeCN)  M s o l u t i o n o f bromine i n  s o l u t i o n o f Ru(0EP)(C0)  CH2CI2  to a  ( 1 ) ( f o r m e d by d i s s o l v i n g R u ( O E P ) (.C0) =  EtOH i n C H C 1 ) c a u s e d a c o l o u r c h a n g e f r o m r e d t h r o u g h g r e y t o g r e e n , and 9  ?  +  134  t h i s r e a c t i o n c o u l d be f o l l o w e d s p e c t r o p h o t o m e t r i c a l l y .  The g r e e n  product  s o l u t i o n s h o w e d l i t t l e c h a n g e i n o p t i c a l s p e c t r u m on t h e a d d i t i o n o f a -4 -2 s l i g h t e x c e s s o f b r o m i n e (up t o 2 x 10 M), but a l a r g e r e x c e s s ('vlO M) c a u s e d t h e s o l u t i o n t o become y e l l o w , t h e s p e c t r u m s h o w i n g t h e l o s s o f the major a b s o r p t i o n s  expected  for a porphyrin  species.  The g r e e n s o l u t i o n  showed'Ja w e l l d e f i n e d s p e c t r u m ( F i g u r e 4.5 and T a b l e 4.4) s p e c i e s p r e s e n t was (C0)  porphyrin  f o u n d t o be a s e c o n d c a t i o n r a d i c a l s p e c i e s o f Ru(.OEP)-  (.1), n a m e l y [ R u t O E P ) " ( C O ) B r ] (l_b) ( s e e b e l o w ) . +  c i e n t of the main a b s o r p t i o n 410 nm) was  and t h e  obtained  The e x t i n c t i o n c o e f f i -  peak o f bromine d i s s o l v e d i n C B C 1  from the v i s i b l e spectrum of a standard  b r o m i n e and f o u n d t o be 210 M"  1  cm .  9  9  (x ,j =  L.  c  niax  m  solution of  Using t h i s value to q u a n t i f y  -1  amount o f bromine added t o a s o l u t i o n o f  1_ , i t was  shown t h a t a p p r o x i m a t e -  l y a 40% e x c e s s o f b r o m i n e was r e q u i r e d t o c o m p l e t e t h e f o r m a t i o n ( E q u i l i b r i u m 4.1).  The r e a c t i o n t o p r e p a r e  RuC0EP)(C0). + i g B r , 2  (-D  of side  strongly  (-11)  s i m i l a r s p e c i e s from complexes o f the  2  u s u a l l y gave m i x t u r e s  type  when t h e c o m p l e x  dissolved in a  of products.  coordina-  Thus  o x i d a t i o n o f 1 i n MeCN a s s o l v e n t ( a c t u a l l y t h e o x i d a t i o n o f Ru(.OEP)(CO)-  c  -  (.4.1).  +  i s d i s s o l v e d i n C H C 1 , o r f r o m R u ( O E P ) ( C O ) E t O H {2) t i n g s o l v e n t ( e . g . MeCN).,  was  > [Ru(,0EP) '(CO)Br]  Ru(OEP)(C0)L, where L i s a l i g a n d t h a t remains c o o r d i n a t e d 2  2  +  products.  1  Attempts to prepare  o f 1 b.  the r e l a t e d complex [Ru(0EP).  (CO).CI] by o x i d a t i o n o f 1_ w i t h a s o l u t i o n o f c h l o r i n e i n C H ^ C l a f f e c t e d by t h e f o r m a t i o n  the  F i g u r e 4 .5  136  MeCN (.6)) by e x c e s s  b r o m i n e g a v e an o p t i c a l s p e c t r u m s h o w i n g  absorptions  a t 610 nm and 585 nm and e n h a n c e d a b s o r p t i o n b e t w e e n 500 and 570 Reduction  by BH^  gave incomplete  -  ( R u ( O E P ) (CO)MeCN ,-.6)  nm.  formation o f the s t a r t i n g m a t e r i a l  s u g g e s t i n g t h a t some o f t h e c o m p l e x had been i r r e -  versibly oxidized. O x i d a t i o n o f R u ( O E P ) ( C O ) M e C N (,6_) i n a c e t o n i t r i l e u s i n g s m a l l a l i q u o t s o f a b r o m i n e s o l u t i o n s h o w e d t h a t t h e f i r s t p r o d u c t was a s p e c i e s i d e n t i c a l t o t h a t f o r m e d by e l e c t r o c h e m i c a l was  oxidation of 6  ( i . e . 6a).  This  product  f o r m e d c l e a n l y w i t h good i s o s b e s t i c s f o r t h e f i r s t 50% o f t h e r e a c t i o n  ( T i g u r e 4.6).  However, attempts  m a t e r i a l caused  t o o x i d i z e t h e l a s t 20% o f t h e s t a r t i n g ,  s i d e r e a c t i o n s [ l o s s o f i s o s b e s t i c s ) and g a v e t h e s p e c t r u m  r e p o r t e d above f o l l o w i n g the a d d i t i o n o f excess cation r a d i c a l prepared  bromine.  S o l u t i o n s o f the  t h i s way w e r e v e r y u n s t a b l e and r e v e r t e d b a c k t o  t h e s t a r t i n g m a t e r i a l much f a s t e r t h a n s a m p l e s o f 6a_ p r e p a r e d c h e m i c a l l y (.see S e c t i o n 5 . 4 ) . than the expected  electro-  The f o r m a t i o n o f 6a_ i n t h i s r e a c t i o n r a t h e r  [ R u C 0 E P ) " ( C 0 ) B r ] Jb_'must be due t o r e t e n t i o n o f c o o r d i +  n a t e d MeCN a f t e r o x i d a t i o n ( E q u a t i o n  Ru (OEP) (CO) MeCN + kBr  S  z  ° ^  n  t  4.2).  )• [ R u ( 0 E P ) f ' (CO) ( M e C N ) ] B r "  (6)(  +  (6a)  Further evidence above r e a c t i o n i n C H C 1 2  (.4.2)  (Purple)  f o r t h i s s u g g e s t i o n was o b t a i n e d by r e p e a t i n g 2  - 1% MeCN as s o l v e n t .  The o p t i c a l s p e c t r u m o f t h e  s t a r t i n g c o m p l e x (2_ d i s s o l v e d i n t h e a b o v e s o l v e n t m i x t u r e ) 6_ as f o r m e d i n p u r e MeCN.  the  showed i t t o be  H o w e v e r , b r o m i n e a d d i t i o n now g a v e a g r e e n  solu-  138  t i o n o f l_b, a s shown by t h e s p e c t r u m . „ Good , i s o s b e s t i c s w e r e f o r the f i r s t 80% o f t h e r e a c t i o n , w h i 1 e caused the formation  attempts to complete the r e a c t i o n  o f some slide p r o d u c t s  r e a c t i o n , the a c e t o n i t r i l e i s present  obtained  as d e s c r i b e d a b o v e .  i n - l o w c o n c e n t r a t i o n and i s r e a d i l y  d i s p l a c e d by t h e b r o m i d e i o n g i v i n g s p e c i e s l_b ( E q u a t i o n 4 . 3 ) , t h a n 6a_ as o b s e r v e d be c o n s i d e r e d  i n p u r e MeCN.  in Section  rather  The mechanism o f t h e s e r e a c t i o n s w i l l  6.4.  R u ( 0 E P ) ( C 0 ) M e C N + J j B ^ C H ^ - 1 % MeCN  )  LRu(.0EP) ' ( C 0 ) B r ] + MeCN +  (6)  (.4.3)  ( l b ) (Green)  Reactions  in other coordinating solvents occurred  S o l u t i o n s i n pure n i t r o m e t h a n e gave the e l e c t r o c h e m i c a l ( a p p a r e n t l y ' l a _ J on o x i d a t i o n w i t h b r o m i n e . RuCOEP) ( C O l p y  In t h i s  in a s i m i l a r fashion. cation radical  A d d i t i o n o f bromine to  C3) i n p y r i d i n e i s d o m i n a t e d by s i d e r e a c t i o n s a n d f a i l s t o g i v e  a n y c a t i o n r a d i c a l s p e c i e s , w h i l e b r o m i n e o x i d a t i o n o f -3_. d i s s o l v e d i n C H C 1 2  d o e s f o r m l_b, b u t t h e p r o d u c t  i s c o n t a m i n a t e d a n d much, l e s s s t a b l e i n  s o l u t i o n than the corresponding CH C1 2  2  and b r o m i n e .  c o m p l e x f o r m e d f r o m RuC0EP)(C0)_ (.]_), i n  H e n c e , t h e o u t c o m e o f a r e a c t i o n a p p e a r s t o be  deter-  m i n e d by t h e e a s e w i t h w h i c h a n y o b s t r u c t i n g l i g a n d , t r a n s t o t h e CO, be d i s p l a c e d by t h e i n c o m i n g  l i g a n d ( i n t h i s case  Br~).  T h e s e s t u d i e s show t h a t t h e c a t i o n r a d i c a l s p e c i e s , u s u a l l y by e l e c t r o c h e m i c a l  can  prepared  o x i d a t i o n , c a n a l s o be f o r m e d by b r o m i n e o x i d a t i o n u n d e r  carefully controlled conditions.  2  139  S p e c i e s r e l a t e d t o l_b c o u l d be p r e p a r e d methods.  Thus, electrochemical  a l s o by e l e c t r o c h e m i c a l  o x i d a t i o n o f Ru(0'EP)(C0) (1_) i n C H C 1 2  2  a t -VJ-0.74V w i t h 0.05M TEAP a s s u p p o r t i n g e l e c t r o l y t e a n d 0.005M T E A C 1 " +  a s a s o u r c e o f c h l o r i d e i o n s g a v e a g r e e n c o l o u r e d s o l u t i o n w i t h an o p t i c a l s p e c t r u m s i m i l a r t o t h a t o f [ R u ( 0 E P ) " ( C O ) B r ] (1 b ) ^ a n d i s j u d g e d  t o be  +  [Ru(0EP) '(C0)Cl] +  (,1c) by c o m p a r i s o n w i t h t h e o p t i c a l s p e c t r u m o f s o l u -  t i o n s o b t a i n e d by a d d i n g T E A C 1 " t o R u ( 0 E P ) ' ( C 0 ) ( l a ) ( s e e S e c t i o n 4.3 +  +  and T a b l e 4 . 4 ) . T h i s i s c o n s i s t e n t w i t h t h e c y c l i c v o l t a m m o g r a m i n S e c t i o n 4.1 i  reported  I t i s p o s s i b l e t h a t some o f t h e c h l o r i d e e l e c t r o l y t e h a d  been e l e c t r o c h e m i c a l l y o x i d i z e d a s t h e o p t i c a l s p e c t r u m o f t h e p r o d u c t showed some f e a t u r e s ( e . g . e n h a n c e d a b s o r p t i o n a t ^ 5 7 5 nm) a l s o s e e n i n t h e o x i d a t i o n o f Ru(.OEP) (CO). ( J j by c h l o r i n e d e s c r i b e d a b o v e .  Hence, t h e  n a t u r e o f t h e c a t i o n r a d i c a l s p r o d u c e d by a n o x i d a t i o n p r o c e s s  i s deter-  m i n e d by t h e a n i o n s p r e s e n t  involution  r a t h e r than t h e method o f o x i d a -  tiidn. The c a t i o n r a d i c a l l_b was e a s i l y r e d u c e d  e l e c t r o c h e m i c a l l y o r by  T B A BH^" t o g i v e a r e d s o l u t i o n , i d e n t i c a l i n s p e c t r u m t o t h e s t a r t i n g +  material  '.QJi.. S o l u t i o n s  o f l_b s l o w l y r e v e r t e d t o 1_ i f s t o r e d u n d e r a r g o n  and t h i s p r o c e s s was a c c e l e r a t e d by l i g h t .  Removal o f s o l v e n t u n d e r  vacuum g a v e a d a r k c o l o u r e d s o l i d w h i c h d e g r a d e d i n a f e w "hours ( e v e n when s e a l e d u n d e r a r g o n ) , . l o s i n g a l l m a j o r p o r p h y r i n a b s o r p t i o n s . -E^s'.r. s t u d i e s on s o l u t i o n s o f l_b i n C H C l 2 showed b e h a v i o u r 2  similar to that o f the other  c a t i o n r a d i c a l s p e c i e s ( l a o r 3a_ - s e e S e c t i o n 4 . 1 ) . A t l i q u i d temperatures  nitrogen  a s t r o n g s h a r p ( p e a k to, p e a k w i d t h = 10G) s i g n a l a t g = 2.01  140  c o r r e s p o n d i n g t o one u n p a i r e d e l e c t r o n p e r p o r p h y r i n m o l e c u l e the c a t i o n r a d i c a l nature o f t h e complex.  As o b s e r v e d  indicated  f o rcation radicals  l a and 3 a ^ t h i s s i g n a l d i m i n i s h e d t o l e s s than 0.1% o f i t s o r i g i n a l i n t e n s i t y when t h e s o l u t i o n was warmed t o a m b i e n t To d e t e r m i n e  temperatures.  w h e t h e r t h e b r o m i d e i o n a s s o c i a t e d w i t h c o m p l e x ]b_  was c o o r d i n a t e d o r f r e e i n s o l u t i o n , some c o n d u c t i v i t y s t u d i e s w e r e i n s t i g a t e d t o c o m p a r e Vb  w i t h two d i f f e r e n t s p e c i e s : -  [Ru  1 1 1  COEP)(P^Bu.^]*-  B r " Cab), a 1:1 e l e c t r o l y t e , . a n d R u C 0 E P ) C P B u ) B r ( 1 0 ) , a p r o b a b l e n o n n i  n  3  electrolyte.  S t u d i e s w e r e made i n d i l u t e d i c h l o r o m e t h a n e  a c o n d u c t i v i t y c e l l w h o s e c e l l c o n s t a n t ( k ) was 0.12 c m  - 1  solutions using [seeSection 2.1).  The m o l a r c o n d u c t i v i t y (A) i s g i v e n b y : -  where R i s t h e measured r e s i s t a n c e and C i s t h e c o n c e n t r a t i o n i n moles p e r litre.  The data a r e r e c o r d e d i n T a b l e 4.4. The green c a t i o n r a d i c a l ( l b ) i s thus n o t an e l e c t r o l y t e i n C h ^ C ^  and [ R u ( 0 E P ) ' ( C 0 ) B r ] +  i s t h e c o r r e c t f o r m u l a t i o n f o r t h i s complex. A l l o f  t h i s e v i d e n c e s u g g e s t s t h a t t h e g r e e n s p e c i e s (.1 b) i s a s e c o n d  cation  r a d i c a l o f R u ( 0 E P ) ( C 0 ) (JJ w h i c h i s s t a b i l i z e d by t h e c o o r d i n a t i o n o f an anion (such as B r " f o r complex I B ) .  141  T a b l e 4.4  Conductivity Studies o f Cation Radical in dichloromethane  ,1b a n d R e l a t e d  as s o l v e n t .  R e s i s t a n c e (n) [Ru (;0EP)CP Bu ) ] BrI n  n  +  3  2  (%)  Species  1 .37 x 1 0  A(fi~*)  a  149  4  2.38 x 1 0  4  103  3.63 x 1 0  5  3  4.93 x 1 0  4  2  R u C 0 E P ) t P B u ) . B r (.!£) n i  n  3  [ R u ( 0 E P ) ' ( C O ) B r ] (.l_b) n  +  9.1 x 1 0  a)  1  5  M o l a r c o n d u c t i v y o f T E A C l " a t i n f i n i t e d i l u t i o n was 1 2 2 . 7 f i +  - 1  in CH C1 2  2  (from Ref. 1 6 ) . ,  4.3  T h e N a t u r e o f t h e Two  Cation  Radicals  In t h e I n t r o d u c t i o n ( s e e S e c t i o n l . e j ^ t h e f o r m a t i o n o f c a t i o n : r a d i c a l s p e c i e s o f Co I I I ( O E P ) was d i s c u s s e d '. A s i m i l a r s i t u a t i o n e x i s t s , with. 17  these ruthenium  c a r b o n y l p o r p h y r i n c a t i o n r a d i c a l s . By c o m p a r i s o n  s p e c t r a ( F i g u r e s 4.5 a n d 1.14) i t c a n be s e e n t h a t t h e g r e e n ( l b a n d l_c) a r e v e r y s i m i l a r t o t h e [ C o * * ( 0 E P ) I  +  ']^^2BLr~  of  species  complex and hence 2  c a n be a s s i g n e d t h e same g r o u n d s t a t e , n a m e l y  1 7  1 b. a n d  l_c  A^  wise,the  p u r p l e c a t i o n r a d i c a l s p e c i e s ( l _ a , 3a_ a n d 6a_) a r e s i m i l a r i n  u  . Like-  142  optical  s p e c t r a (compare F i g u r e s 4.4 a and b w i t h 1.14)  c a l l y prepared [Co state  1 6  .  (0EP) ']  2C10 and  +  4  to e l e c t r o c h e m i -  hence can be a s s i g n e d a  The spectrum o f Ru**(0EP) "(.C0)Im (5a) +  A2  ground  U  i s o f i n t e r e s t because  appears t o be a m i x t u r e o f the two ground s t a t e s .  it  In t h i s complex the  c o o r d i n a t e d i m i d a z o l e l i g a n d may be c a u s i n g a quantum-mechanical  mixing  o f the  (Figure  and  4.4c).  A  1 u  ground s t a t e s t o g i v e the spectrum observed  This subject w i l l  &e d i s c u s s e d  i n more d e t a i l  l a t e r (see  Section  8.2) . The s t u d i e s o f the c o b a l t p o r p h y r i n systems  showed t h a t the  ground  s t a t e s were determined by the c o o r d i n a t i o n ( o r n o n - c o o r d i n a t i o n ) o f the anions p r e s e n t .  A l s o t h e ground s t a t e s c o u l d be i n t e r c h a n g e d by t h e 17, .  a d d i t i o n or removal o f c o o r d i n a t e d anions^  .  The same e f f e c t s a r e  observed i n the c h e m i s t r y o f these ruthenium p o r p h y r i n i r i - c a t i o n r a d i c a l species. A d d i t i o n of Br" or CI"  ('in t h e form o f the c o r r e s p o n d i n g  tetra-  alkylammonium s a l t s ) , t o a s o l u t i o n o f the p u r p l e s p e c i e s Ru(0EP) 'CC0). +  (1 a)  l e d t o a r a p i d change i n c o l o u r from p u r p l e to g r e e n , and the product spectrum was t h a t o f a  A  l u  ground s t a t e c a t i o n r a d i c a l ;  (.CO)Br] (lb.) o r .[RuCOEpf "CCOlCl ] Q c . ) r e s p e c t i v e l y .  e i t h e r [Ru(OEP).  I f t h i s r e a c t i o n was  attempted upon a s p e c i e s w i t h a c o o r d i n a t e d s i x t h l i g a n d ( e . g . 3a_ o r 5a_) i n CH Cl2» then a l a r g e p r o p o r t i o n o f r e d u c t i o n was observed (.see 2  5.2,  b and c ) .  Section  To o b t a i n the r e v e r s e r e a c t i o n excess AgBF^ was added t o  a s o l u t i o n o f the  A  l u  ground s t a t e s p e c i e s Ob)..  The green  solution  i m m e d i a t e l y t u r n e d p u r p l e i n a v e r y c l e a n r e a c t i o n (as judged by t h e  -  143  optical  spectrum  coordinated  of'the  bromide  ion  product  solution)  (Figure 4.7).  giving  This  l_a by r e m o v a l  r e a c t i o n was  found  of  the  to  be a  2 good m e t h o d (usually plexes (1 a )  of  obtaining  prepared  A2u  by e l e c t r o c h e m i s t r y )  CRUC0EP)(C0)L,  prepared  spectra of  from  s p e c i e s 1_,  [Ru("0EP)' + ( C O ) B r ]  e l e c t r o c h e m i c a l l y , although  leads  a s l i g h t change  i n the  Ru[0EP)+'(C0)MeCN  Q6aj s e e n i n  to  [Ru(;0EP)+'CC0)Br]  (_l_b_) p r e p a r e d  The  presence or absence of  clean spectra  (as  judged  obtained  by t h i s  oxidized  snraTl q u a n t i t i e s  In  fact  not  (J)  d i r e c t l y to  be u s e d f o r  The  to  oxidizing the  chemical  cation studies  reduced  excess  4.4b  was o b t a i n e d  Ru(0EP) + ' ( C O )  electrolyte  4.1).  The  absorptions  oxidizing  by a d d i n g  due t o  power  in  on t h e  of  the  interference  this  spectrum.  AgC'I)  cation  l_a , a l t h o u g h  AgBF4  impurities)  a spectroscopic solution  due t o  spectrum  CH2C12,although  had no e f f e c t  radical  com-  i s much c l e a n e r t h a n l_a  Section  lack of the  the  (see  i n 1% MeCN i n  radicals  spectrum of  absence of  electrolyte  due  cation  traces of  p a r e n t complex mixed w i t h  A g B F 4 was c a p a b l e o f  RuC0EP)CC0) could  of  the  Figure  by t h e  p r o c e s s were  of  state  (Figure 4.7)  spectrum  of  case the  free  3, 5_ a n d 6 ) .  prepared to  ground  which radical .  of  such  from  the  solutions excess  AgBF4. The this  optical  t h e s i s are  spectral  summarized  data  of  in Table  the 4.5  cation  radical  species studied  in  144  F i g u r e 4.7  The o p t i c a l s p e c t r u m i n C H C 1 o f l b ( ) p r e p a r e d by t h e b r o m i n e o x i d a t i o n o f 1 ( f o r m e d by t h e d i s s o c i a t i o n o f 2 i n d i l u t e s o l u t i o n ) and t h e s p e c t r u m o f la. (-• ) generated on a d d i t i o n o f e x c e s s A g B F ^ . 2  2  145 T a b l e 4.5' O p t i c a l S p e c t r a l D a t a f o r t h e R u t h e n i u m ( 11) P o r p h y r i n i r - C a t i o n R a d i c a l Complexes  —  Complex  A  l_a R u ( 0 E P ) '(C0) +  m a x ^ ^ ( °9-]o ^ n m  e  1  375(5.00), 535(3.93), 587(4.00),  610(3.70)  375(5.00), 535(3.93), 587(4.00),  610(3.86)  376(4.95), 540(3.90), 590(3.99),  610(3.80)  372(4,94), 540(3.90), 588(3.99),  612(3.90)  ( F i g u r e 4.7) l a Ru(0EP) 'CC0).C10 "  -  +  4  ( F i g u r e 4.4a) 3a [ R u C 0 E P ) " ( C 0 ) p y ] C 1 0 " +  +  4  6a [ R u ( 0 E P ) ' ( ; C 0 ) M e C N ] C 1 0 " +  -  +  4  ( F i g u r e 4.4b) 5_a [ R u ( 0 E P ) * ( C 0 ) I m ] C 1 0 " +  376(4.94).," 545( 3 .89),.5,92(3 .94) , 6 1 0 ( 3 . 9 2 )  +  4  ( F i g u r e 4.4c) l b [Ru(0EP) '(C0)Br]  385(4.85),  +  • 5,80(3.86),  630(4.04)  ( F i g u r e 4.5) Ic [ R u ( 0 E P ) ' ( C 0 ) C l ]  383(4.85),  +  5 7 0 ( 3 .84) , 6 2 5 ( 3 .99)  Id [Ru(0EP) *(C0)SCN] +  5 8 7  [Ru(0EP) ' ( C S ) p y ] C l 0 " +  6 1 8  375(4.83), 535(3.88), 590(3.90),  +  4  ( F i g u r e 4.8) 8a R u ( 0 E P ) ' ( C 0 ) P B u . +  n  3  1  .  630  .850  a)  Unless o t h e r w i s e i n d i c a t e d , sol utioriinin C H C 1 .  b)  As p r e p a r e d by t h e a d d i t i o n o f A g B F 4 t o a s o l u t i o n o f l_b made by b r o m i n e oxidation o f 1 i n CF^C^.  c)  A s p r e p a r e d by e l e c t r o c h e m i c a l  d)  S p e c t r u m o b t a i n e d i n C H C 1 - 1 % MeCN by r e a c t i o n o f A g B F w i t h l_b i n t h i s sol vent.  2  2  2  2  o x i d a t i o n o f 1 i n t h e p r e s e n c e o f 0.05M TBAP. 4  146  T a b l e 4.5  (continued)  e) I m p u r e s o l u t i o n o b t a i n e d by a d d i n g a s o l u t i o n o f K S C N ~ w i t h c r o w n e t h e r i n C H p C l 2 t o l_a_ i n C H C 1 . See S e c t i o n 5.1c. Extinction coefficients not o b t a i n e d . +  2  f ) See S e c t i o n  2  4.4.  g) New a b s o r p t i o n s o b t a i n e d by p u r g i n g a s o l u t i o n o f [ R u * * * ( 0 E P ) ( P B u ) ] C I 0 4 " w i t h CO. B e l i e v e d t o be due t o t h i s c a t i o n r a d i c a l s p e c i e s . See S e c t i o n 6.2. n  +  3  4.4  Cation Radicals of a Related Species  Ru(OEP)(CS)py  E l e c t r o c h e m i c a l o x i d a t i o n o f other ruthenium the type Ru (;0EP)(C0)L H  l a t e r , ( s e e S e c t i o n s 5.1  ( L = P B u , P P h , and A s P h ) w i l l be n  3  3  3  intermediates.  r a t h e r than at the porphyrin  and S e c t i o n s 7.1,  as  c a t i o n r a d i c a l s p e c i e s a r e p r o b a b l y f o r m e d as  C o m p l e x e s t h a t do n o t c o n t a i n a c a r b o n y l  o x i d i z e at the metal  discussed  a n d 6 . 3 ) , w h e r e i t w i l l be shown t h a t t h e s e com-  plexes u s u a l l y give o x i d a t i o n at the metal the f i n a l product,though  porphyrin complexes o f '  a t a p o t e n t i a l b e l o w +0.6  7.3, and 7.6 t h r o u g h  to 7.8).  ligand generally  v o l t s (see R e f s . 1 and  18,  However, the s u b s t i t u t i o n  o f a c a r b o n y l l i g a n d by a l i g a n d o f s i m i l a r e l e c t r o n i c p r o p e r t i e s (e/g. was  f o u n d t o h a v e l i t t l e e f f e c t on t h e e l e c t r o c h e m i s t r y o f t h e c o m p l e x .  Hence,Ru(0EP)(.CS)py gave a c y c l i c voltammogram v e r y s i m i l a r to t h a t f o r R u ( 0 E P ) ( C 0 ) p y (.3). n  in dichloromethane  was  r e s u l t e d in a one-electron oxidation to give a greyish  s i m i l a r to t h a t seen f o r Ru(0EP) 'CC0)py ( T a b l e +  Careful addition of Br /CH C1 2  generated  observed  B u l k e l e c t r o l y s i s o f R u ( 0 E P ) ( . C S ) p y i n 0.05M TBAP  c o l o u r e d s o l u t i o n o f a p o r p h y r i n c a t i o n r a d i c a l , whose spectrum 4.8)  CS)  2  2  (Figure  4.4).  to a s o l u t i o n o f Ru(OEP)CCS)py  some c a t i o n r a d i c a l o f t h e o t h e r g r o u n d s t a t e (.. A ^ )  147  in a r e a c t i o n very s i m i l a r t o t h a t seen with t h e Ru(OEP)(C0)py  complex.  The r e a c t i o n r e s u l t e d i n t h e f o r m a t i o n o f some s i d e p r o d u c t s a n d t h e c a t i o n r a d i c a l p r o d u c t was r a t h e r u n s t a b l e as s e e n f o r t h e c o r r e s p o n d i n g c a r b o n y l compound. and R u ( O E P ) ( C S ) p y  The r e a c t i o n s o f c a t i o n r a d i c a l s o f b o t h R u ( O E P ) ( C O ) p y w i t h l i g a n d s w i l l be d i s c u s s e d a n d c o m p a r e d i n C h a p t e r 5.  1.0i  m  o z < a oc o in to <  0^  x10  0^-  400  500  600 WAVELENGTH  F i g u r e 4.8  Too (nm)  T h e o p t i c a l s p e c t r u m o f t h e c a t i o n r a d i c a l Ru(OEP) ( C S ) p y p r e p a r e d by t h e e l e c t r o c h e m i c a l o x i d a t i o n o f Ru(OEP)fCS)py i n 0,05M T B A P - C H C 1 . 2  2  148  REFERENCES - CHAPTER 4  1.  G.M. B r o w n , F.R. H o p f , J . A . F e r g u s o n , T . J . M e y e r , a n d D.G. Whitten., J . Am. Chem. S o c . 95_, 5939 ( 1 9 7 3 ) .  2.  W.R. T u r n e r a n d P . J . E l v i n g , A n a l . Chem. 3 7 , 4 6 7 ( 1 9 6 5 ) .  3.  V . J . B a u e r , D.L.G. C l i v e , D. D o l p h i n , J.B.. P a i n e I I I , F . L . H a r r i s , M.M. K i n g , J . L o d e r , S-W.C. Wang, a n d ( t h e l a t e ) R.B.. Woodward, J . Am. Chem. S o c . I n P r e s s .  4.  a) b)  C. F i n b a k a n d 0. H a s s e l , Z. P h y s i k . Chem. 3 2 B , 130 ( 1 9 3 6 ) . C. F i n b a k a n d 0. H a s s e l , Z. P h y s i k . Chem. J32B, 4 3 3 ( 1 9 3 6 ) .  5. 'Handbook o f C h e m i s t r y a n d P h y s i c s ' , R . C . W e a s t e d . , 52nd E d . , CRC P r e s s , C l e v e l a n d , O h i o , '1972-j p . D-146. 6.  W.A.G. G r a h a m , I n o r g . Chem. 7_, 3 1 5 ( 1 9 6 8 ) .  7.  L.M. E p s t e i n , D.K. S t r a u b , a n d C. M a r i c o n d i , I n o r g . Chem. 6, 1 7 2 0 (1967).  8.  K.M. K a d i s h , L.R. S h i n e , R.K. R h o d e s , a n d L . A . B o t t o m l e y , Chem. 2 0 , 1 2 7 4 (1981 ) .  9.  F.A. C o t t o n a n d G. W i l k i n s o n , ' A d v a n c e d W i l e y , New Y o r k , 1 9 8 0 , C h a p . 2 0 .  Inorg.  Inorganic Chemistry', 4 t h Ed.,  10.  A.B.P. L e v e r , ' I n o r g a n i c E l e c t r o n i c S p e c t r o s c o p y ' , E l s e v i e r , A m s t e r d a m , 1968, p . 3 4 8 .  11.  C A . R e e d , T. M a s h i k o , S.P. B e n t l e y , M.E. K a s t n e r , W.R. S c h e i d t , K. S p a r t a l i a n , a n d G. L a n g , J . Am. Chem. S o c . 101_, 2 9 4 8 ( 1 9 7 9 ) .  12.  L.D. S p a u l d i n g , P.G. E l l e r , J . A . B e r t r a n d , a n d R.H. F e l t o n , J . Am. Chem. S o c . 9 6 , 982 ( 1 9 7 4 ) .  13.  R.H. F e l t o n , i n 'The P o r p h y r i n s ' ( D . D o l p h i n , e d . ) , A c a d e m i c New Y o r k , 1 9 7 9 , V o l . V, C h a p . 3.  14.  D. D o l p h i n , T . N i e m , R.H. F e l t o n , a n d S . F u j i t a , J . Am. Chem. S o c . 97_, 5288 ( 1 9 7 5 ) .  15.  P.S. P h i l l i p s , P e r s o n a l  16.  G.P. A l g r a a n d S. B a i t , I n o r g . Chem. 2 0 , 1 1 0 2 ( 1 9 8 1 ) .  communication.  Press,  149  17.  D. D o l p h i n , A. F o r m a n , D.C. B o r g , J . F a j e r , and R.H. A c a d . S c i . USA 68, 614 (.1971).  Felton, Proc.  18 toc\  9 7! 5 385'(i9 7 5) ' B  W  n  H  0  f  T  ' ' J  ^  D  " ' G  W  h  i  t  t  6  n  '  J  '  ^  ^  Natl  150  CHAPTER 5  ADDITION OF LIGANDS TO CATION RADICALS  The r e a c t i o n o f r u t h e n i u m p o r p h y r i n c a t i o n r a d i c a l s ; w i t h , v a r i o u s , l i g a n d s has been f o u n d t o d e p e n d upon b o t h t h e n a t u r e o f t h e c a t i o n r a d i c a l and t h e n a t u r e o f t h e i n c o m i n g l i g a n d .  F i r s t , the reactions of a  f i v e - c o o r d i n a t e c a t i o n r a d i c a l ( s e e S e c t i o n 4.1)  supposedly  w i l l be c o n s i d e r e d .  This  s p e c i e s , ( i . e . R u ( 0 E P ) * ( C 0 ) ) on a d d i t i o n o f a l i g a n d , shows t h e m o s t +  favourable  structure for intramolecular  ruthenium(III)  product.  electron t r a n s f e r to give a  A f t e r the r e a c t i o n s o f t h i s s p e c i e s have been o u t -  l i n e d , t h e r e a c t i o n s o f t h e s i x - c o o r d i n a t e c a t i o n r a d i c a l s w i l l be  considered.  A l l r e a c t i o n s o f t h e s e r u t h e n i u m c a t i o n r a d i c a l s p e c i e s showed some r e d u c t i o n as w e l l as t h e m a j o r r e a c t i o n o b s e r v e d O c c a s i o n a l l y t h i s s i d e r e a c t i o n was in the l i g a n d added.  on l i g a n d a d d i t i o n .  due t o t h e p r e s e n c e o f r e d u c i n g  H o w e v e r , t h i s was  agents  r a r e and many r e a c t i o n s o f  c a t i o n r a d i c a l s p e c i e s i n v o l v e d a more s u b s t a n t i a l p r o p o r t i o n  these  (.20 -  50%)  o f r e d u c t i o n on a d d i t i o n o f l i g a n d s t h a t a r e c o n s i d e r e d  formally  t o be n o n - r e d u c i n g , s u c h as c h l o r i d e , t r i p h e n y l p h o s p h i n e  and a c e t o n i t r i l e .  Evidence  w i l l be p r e s e n t e d  l a t e r t o show t h a t a w i d e r a n g e o f l i g a n d s  caused t h i s reduction, probably  v i a a common m e c h a n i s m , u s u a l l y t o g i v e  t h e Ru ( J I ) . p r e c u r s o r t o t h e c a t i o n r a d i c a l i n ^ 5 0 % y i e l d . o f t h e c a t i o n r a d i c a l may  suffer degradation  The o t h e r  50%  to give various green p i g -  m e n t s , s i m i l a r i n n a t u r e t o t h o s e f o r m e d by a t m o s p h e r i c o x i d a t i o n  of  151  Ru  ( O E P ) ( C O ) (!) i n C.HgCl , o r by c h r o m a t o g r a p h y 2  s l i g h t l y a c i d i c s i l i c a columns.  o f Ru ( 0 E P ) ( C 0 ) L i  on  A l l o f these green s p e c i e s ( a p p a r e n t l y  p r e s e n t as m i x t u r e s ) a r e p o l a r ( t h e y h a v e t o be e l u t e d o f f a s i l i c a  column  w i t h e t h a n o l ) and show weak, b r o a d a b s o r p t i o n s b e t w e e n 550 and 700  nm.  T h i s r e d u c t i o n p r o c e s s a p p e a r s t o be p r e s e n t i n a l l t h e r e a c t i o n s o f t h e s e c a t i o n r a d i c a l s p e c i e s w i t h l i g a n d s . E v e n when i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r o c c u r s and a r u t h e n i u m ( I I I ) c o m p l e x i s t h e m a j o r  product,  a s m a l l p e r c e n t a g e o f r e d u c t i o n i s o b s e r v e d and i n many r e a c t i o n s t h e p r o p o r t i o n o f r e d u c t i o n i s q u i t e s u b s t a n t i a l (>5%).  F i g u r e 5.1  illustrates  the c l e a n e s t r e a c t i o n forming Ru(111) p r o d u c t s w i t h o n l y the f a i n t e s t t r a c e o f r e d u c t i o n , w h e r e a s F i g u r e 5.7 shows a r e a c t i o n l e a d i n g t o r u t h e n i u m ( I I I ) p r o d u c t s m i x e d w i t h some r e d u c e d p r o d u c t s . tion  were  S p e c t r a showing  some r e d u c -  s t i l l o b t a i n e d i n r e a c t i o n s o f t h e c l e a n e s t (as judged  u . v . / v i s i b l e s p e c t r o s c o p y ) samples o f the c a t i o n r a d i c a l s .  The r e d u c t i o n  i s u s u a l l y o b s e r v e d as a b s o r p t i o n s a t 548 and 396 nm (.408 nm i n t h e of P B u  by  presence  - F i g u r e s 5.1 and 5.7) and t h e p r e s e n c e o f t h e g r e e n p i g m e n t s  n  3  i n v a r i a b l y s e e n by t h e i r weak a b s o r p t i o n s b e t w e e n 580 and 700  is  nm.  W i t h t h e e x c e p t i o n o f c a t i o n r a d i c a l l_b ( w h i c h was p r e p a r e d  by  b r o m i n e o x i d a t i o n ) , t h e r e a c t i o n s o u t l i n e d i n t h i s c h a p t e r were g e n e r a l l y s t u d i e d u s i n g e l e c t r o c h e m i c a l l y prepared samples o f t h e a p p r o p r i a t e c a t i o n r a d i c a l i n t h e p r e s e n c e o f 0.05M TBAP a s e l e c t r o l y t e . H e n c e , e q u a t i o n s  quoted  i n t h e t e x t show p e r c h l o r a t e a s t h e a n i o n a s s o c i a t e d w i t h t h e c a t i o n r a d i c a l but t h e c h e m i s t r y i s s t i l l v a l i d i n t h e p r e s e n c e o f o t h e r e l e c t r o l y t e a n i o n s (e.g.  BF ", 4  P F ~ and g  CF S0 "). 3  3  152  The r e a c t i o n s o f r u t h e n i u m o f l i g a n d s w i l l be p r e s e n t e d chapter.  c a t i o n r a d i c a l s p e c i e s with a wide  in detail in the f i r s t fpur  range  sections of this  The major products o f these r e a c t i o n s a r e b r i e f l y summarized i n  T a b l e 5.1 a n d t h e r e s u l t s a n a l y s e d i n S e c t i o n s 5.5 a n d 5.6.  5 .1  Reactions o f a Five-Coordinate Cation Radical Species with Neutral and I o n i c L i g a n d s i n C ^ C l g , a n I n e r t S o l v e n t The r e a c t i o n o f t h e e f f e c t i v e l y - f i v e - c o o r d i n a t e c a t i o n r a d i c a l  R u ( 0 E P ) ' ( C O ) ( s e e S e c t i o n 5.5 a n d 4.1) w i t h l i g a n d s c a n be c l a s s i f i e d u n d e r +  the f o l l o w i n g  headings:  a)  Ligands that give ruthenium(III)  products.  b)  Neutral ligands that give other cation r a d i c a l species of the same g r o u n d s t a t e .  c)  A n i o n i c l i g a n d s that give t h e other ground s t a t e o f t h e c a t i o n radical (see Section 4.3).  d)  Ligands that i n s t a n t l y reduce the c a t i o n r a d i c a l .  5.1a. • _2 n A d d i t i o n o f a f e w - m U o f a 5 x 10 M s o l u t i o n o f P :  B u  s o l u t i o n o f R u ( 0 E P ) " (CO) (.la) i m m e d i a t e l y +  ( E q u a t i o n 5 . 1 ) . The spectrum  RUCOEPXP^U^  t o 4 mL o f a  g i v e s a deep orange s o l u t i o n  o f t h e p r o d u c t i s t y p i c a l o f R u ( I I I ) a n d shows  an a b s o r p t i o n a t 790 nm a n d a d o u b l e S o r e t . o b t a i n e d when  3  The s p e c t r u m  i s s i m i l a r to that  (7) i s e l e c t r o c h e m i c a l l y o r c h e m i c a l l y ( B r  2  153 T a b l e 5.1  A Summary o f t h e M a j o r P r o d u c t s o f t h e R e a c t i o n o f L i g a n d s Ruthenium(II) Porphyrin  Cation Radical — Ru(0EP) '(C0) +  la  P Bu  ft-Cation  Radicals.  Ligands  Added  PPh , AsPh and  3 >  3  3  Major  with  Products  Ru (111)  CN" py, Im, MeCN  A^  Cation Radicals  3 a , 5a a n d 6a_ 2 ^2u ^ ' R a d i c a l s 2 A Cation Radicals lu  DMSO, P h P 0 , MeOH  atl  3  B r " , C I " , SCN"  on  n  ( l b , l c _ a n d l_d) I\  BH "  Reduction  4  P(0Me) , C10 ", B F " 3  and [Ru(OEP)  (CO)Br]  lb  4  4  No r e a c t i o n  CF S0 " 3  3  P B u , CN"  Ru(III)  n  3  P P h , A s P h , p y , Im  Reduction  MeCN, T H F , MeOH ( a l l  Reduction  3  3  i n e x c e s s s e e text)': CI'  lc  Ru(OEP) '(CO)py  P Bu.  Ru(III).  3a  P P h , A s P h , CN"  n  3  CI", Br'  Im, MeCN  3  Ru(III) + Reduction p A-|  U  Cation Radical  + Reduction "Ap^ C a t i o n R a d i c a l s (5a a n d 6a)  154 T a b l e 5.1 - c o n t i n u e d  Cation Radical  Green  P Bu,  Ru(0EP) "(C0)Im  n  +  Major  Ligands Added  -  Products  Products  + Ru(.III) Ru(III)  PPh., CN", A s P h , C T  Reduction  P Bu.  Green  3  R u ( 0 E P ) "(.C0)MeCN  n  +  Products  + Reduction  6a  Ru ( 1 1 1 )  PPh.  (.In MeCN)  + CN", A s P h , C I " , B r " 3  py, Im  Reduction  Reduction ? A Cation Radicals 2u 0  (3a a n d 5a) R u ( 0 E P ) *(.C0)MeCN  P B u , PPb  6a  CN", A s P h  M  +  3  Rutin) 3  RutHI) ^Reduction 2  CI", Br" In V/o M e C N / C H C l 2  A-j C a t i o n R a d i c a l s u  2  P Bu,  :- + R e d u c t i o n Green Products  P P h , CN"  Reduction  n  Ru(OEP) "(CS)py +  3  cr  —  3  A, C a t i o n R a d i c a l lu + Reduction  Solution of cation radical i n CH C1 9  9  unless otherwise indicated  155  solution) oxidized in CH C1 2  (Section 7.1).  2  In a d d i t i o n , t h e i n s i t u  o r a n g e p r o d u c t f o r m e d c o u l d be r e d u c e d e l e c t r o c h e m i c a l l y o r by T B A B H +  to a s o l u t i o n s p e c t r a l l y i d e n t i c a l to that of genuine R u ( 0 E P ) ( P B u 3 )  4  n  (Figure 5.1).  2  (7)  F i n a l l y , t h e o r a n g e p r o d u c t was f o u n d t o be s p e c t r a l l y i d e n -  t i c a l t o a sample o f [ R u  I ] t I  ( 0 E P ) ( P B u ) ] B r " (9b_) p r e p a r e d by b r o m i n e n  +  3  2  ox n i d a t i o n o f 7^ ( s e e S e c t i o n 2 . 5 ) .  [Ru (0EP) '(C0)] C10 n  +  +  _ 4  + 2P Bu n  3  — )  [Ru  1 1 1  ( O E P ) ( P B u ) ] C l 0 " + CO n  +  3  (la)  2  4  (5.1)  (9a)  T h e r e a c t i o n o f t h e c a t i o n r a d i c a l J_a_ w i t h t r i p h e n y l p h o s p h i n e (PPh ) gives a similar result. 3  The s p e c t r u m o f t h e r e s u l t i n g o r a n g e  s o l u t i o n v a r i e s s l i g h t l y w i t h t h e amount o f e x c e s s p h o s p h i n e added ( s e e S e c t i o n 7.6) b u t t h e p r o d u c t i s e s s e n t i a l l y s p e c t r a l l y i d e n t i c a l t o t h a t o b t a i n e d by e l e c t r o c h e m i c a l l y o x i d i z i n g a u t h e n t i c s a m p l e s o f R u * * ( 0 E P ) (PPh ) 3  2  (1_2) i n C H C 1 , i n t h e p r e s e n c e o f e x c e s s P P h 2  5.2 a n d 7 . 1 2 ) .  2  3  (compare F i g u r e s  T h e o r a n g e s o l u t i o n f o r m e d on a d d i n g P P h  r e d u c e d by t e t r a b u t y l a m m o n i u m b o r o h y d r i d e ( T B A  +  BH ~) 4  3  t o J_a_ c o u l d be  to give a pink solu-  t i o n whose s p e c t r u m was s t r o n g l y d e p e n d e n t u p o n t h e q u a n t i t y o f e x c e s s phosphine added.  W i t h e x c e s s p h o s p h i n e a s t r o n g S o r e t a t 420 nm  was  o b t a i n e d b u t i n t h e p r e s e n c e o f l e s s p h o s p h i n e t h i s S o r e t was w e a k e n e d a n d a new p e a k a t 396 nm a p p e a r e d . chemistry of Ru (OEP)(PPh ) 1 1  3  ?  This behaviour i s consistent with the  (12_) d e s c r i b e d i n S e c t i o n 3.2.  As i n t h e  F i g u r e 5.1  T h e o p t i c a l s p e c t r u m o f t h e c a t i o n r a d i c a l s p e c i e s l a (. ), the spectrum o f t h e p r o d u c t (9a). f o r m e d on a d d i n g p n B u t o a s o l u t i o n o f l a ( — - - ) ; and t h e s p e c t r u m (.7) f o r m e d on r e d u c t i o n o f 9a w i t h T B A B H ~ C ).. T h e weak a b s o r p t i o n s s e e n i n 9a a n d 7 b e t w e e n 580 a n d 650 nm a n d t h e p e a k s e e n a t ^ 4 2 8 nm i n t h e s p e c t r u m o f 9a p r e s e n c e o f i m p u r i t i e s f o r m e d by s i d e r e a c t i o n s . — 3  +  4  rutheniumfUl) of the species the spectra of a r e due t o t h e  15J  1.5-  i.«H  / A  u z < to  //  //  K  o  ill  CO CD <  •  <  /  '•  \ \  \ \  f \\ i  \  x10  V. v 400  500  600  700 WAVELENGTH (nm)  Figure  5.2  The r u t h e n i u m ( . I I I ) p r o d u c t (.15) () f o r m e d by t h e a d d i t i o n o f e x c e s s ( 1 0 - M ) P P h t o t h e c a t i o n r a d i c a l l_a a n d t h e s p e c i e s f o r m e d (.12) by t h e r e d u c t i o n o f J_5 i n t h e p r e s e n c e o f e x c e s s PPho "("•"••••)• 2  3  158  r e a c t i o n w i t h P B u , a m i n o r s i d e r e a c t i o n l e a d s t o some r e d u c t i o n g i v i n g , 3  in the c o n d i t i o n s of the experiment Ru (0EP)(C0)PPh n  3  ( 4 0 6 nm S o r e t  a b o v e , a few p e r c e n t o f  band).  I t was n o t e d t h a t a d d i t i o n o f two e q u i v a l e n t s o f P P h r a d i c a l d i d not give complete was l e f t u n r e a c t e d .  contaminating  3  to the c a t i o n  c o n v e r s i o n t o R u ( J T I ) j a b o u t 10 - 1 5% o f l a  Purging such a s o l u t i o n w i t h carbon monoxide caused  a s l i g h t l o s s o f a b s o r p t i o n b e l o w 540 nm a n d a d e f i n i t e i n c r e a s e i n t h e q u a n t i t y of cation radical present.  T h i s suggests that the r e a c t i o n i s r e v e r s -  i b l e , and h e n c e an e q u i l i b r i u m . The r e a c t i o n o f t r i p h e n y l a r s i n e ( A s P h ) w i t h l_a g i v e s an e x c e l l e n t 3  example o f j u s t such a r e v e r s i b l e system. ( b e t w e e n two and t e n e q u i v a l e n t s ) o f A s P h  The a d d i t i o n o f an 3  excess  (added as s o l i d c r y s t a l s ) t o a  s p e c t r o s c o p i c s o l u t i o n o f the c a t i o n r a d i c a l w i t h s t i r r i n g gave a p u r p l e o r a n g e s o l u t i o n s h o w i n g b e t w e e n 30 - 50% c o n v e r s i o n o f l_a t o a  ruthenium(III)  c o m p l e x [ r e c o g n i z e d by t h e d i m i n i s h e d i n t e n s i t y o f a b s o r p t i o n s c h a r a c t e r i s t i c o f t h e c a t i o n r a d i c a l [500 nm t o 700 nm),  i n c r e a s e d a b s o r p t i o n between  500  a n d 550 nm a n d , a s t h e 500 - 550 nm r e g i o n c a n be c o n f u s e d by t h e f o r m a t i o n of s i d e products (e.g. Ru(OEP)(C0)L), accompanied  by a b o u t 10% r e d u c t i o n .  become b r i g h t o r a n g e , t h e s p e c t r u m t o 1§_ a n d , a f t e r ^2 m i n u t e s  t h e r i s e o f an a b s o r p t i o n a t 810  nm]  P u r g i n g w i t h a r g o n made t h e s o l u t i o n showing f u r t h e r l o s s of a b s o r p t i o n s  o f p u r g i n g , t h e c a t i o n r a d i c a l p e a k s had  due  complete-  l y d i s a p p e a r e d g i v i n g a s o l u t i o n c o n t a i n i n g m a i n l y a Ru(III) complex ( F i g u r e 5.3).  A d d i t i o n o f carbon monoxide, however r a p i d l y r e c o n v e r t e d t h e c o l o u r  F i g u r e 5.3  The o p t i c a l s p e c t r u m o f t h e c a t i o n r a d i c a l s p e c i e s l a . ( ) and t h e s p e c t r u m o f t h e R u ( I I I ) p r o d u c t ( 1 J ) f o r m e d on a d d i n g two e q u i v a l e n t s o f AsPh3 a n d p u r g i n g t h e s o l u t i o n v i g o r o u s l y w i t h argon f o r 2 min ( - • ) , and t h e r e g e n e r a t i o n o f t h e c a t i o n r a d i c a l ( l a ) by p u r g i n g t h e r u t h e n i u m ( I I I ) - c o n t a i n i n g s o l u t i o n w i t h c a r b o n monoxide f o r one m i n u t e ( ). Later experiments suggested t h a t the regenerated c a t i o n r a d i c a l c o n t a i n e d c o o r d i n a t e d ASPI13 a l t h o u g h t h e o p t i c a l s p e c t r u m was i d e n t i c a l t o ^a_ ( s e e S e c t i o n 7 . 7 ) . The i n c r e a s e d a b s o r p t i o n s a t ^515 a n d ^545 nm a r e d u e t o s i d e r e a c t i o n s g e n e r a t i n g r e d u c e d products.  160  t o p u r p l e w i t h r e g e n e r a t i o n o f t h e c a t i o n r a d i c a l i n c l o s e t o 95% y i e l d ( F i g u r e 5.3).  Purging with argon reformed the ruthenium(III) s o l u t i o n ,  and p u r g i n g a g a i n w i t h CO r e g e n e r a t e d t h e c a t i o n r a d i c a l s h o w i n g  that the  s y s t e m was r e p e a t e d l y r e v e r s i b l e ( E q u i l i b r i u m 5.2; c f . 5.1)  [Ru C0EP) '(C0)l C10 " + 2 A s P h ^ l R u . I I  +  f  4  I r i  3  (0EP)(AsPh ) ] C10 " +  3  2  4  + CO  (5.2)  (la)  P r e p a r a t i o n o f an a n a l y t i c a l l y p u r e s a m p l e o f R u * * ( O E P ) ( A s P h ) , 3  2  by  r e d u c t i o n o f the R u ( I I I ) complex o b t a i n e d i n the above r e a c t i o n , c o n c l u s i v e l y proved the i d e n t i t y o f the r u t h e n i u m ( I I I ) complex i n v o l v e d i n the above r e v e r s i b l e r e a c t i o n s t o be [ R u  1 I I  (0EP)(AsPh ) ] A" +  3  l y t e u s e d ) , ( s e e S e c t i o n s . 2 . 5 and  2  ( A " =i a n i o n o f e l e c t r o - ,  7.7).  A d d i t i o n o f t r i p h e n y l s t i b i n e ( S b P h ) t o a s o l u t i o n o f l_a a l s o g i v e s 3  an o r a n g e p r o d u c t .  However, t h e v i s i b l e spectrum  indicated that this  c o l o u r c h a n g e was m a i n l y due t o r e d u c t i o n ( F i g u r e 5 . 4 ) .  Some r u t h e n i u m ( I I I )  i s o b t a i n e d a s e v i d e n c e d by a b r o a d a b s o r p t i o n c e n t r e d a t 870 nm, d i s a p p e a r s on r e d u c t i o n w i t h T B A B H ~ . +  4  which  R e d u c t i o n a l s o g i v e s a weak S o r e t a t  423 nm, t h a t i s u n c h a n g e d on a d d i n g m o r e S b P h , t h o u g h t h i s r e g i o n i s d o m i 3  n a t e d by t h e 396 nm S o r e t o f t h e r e d u c e d s p e c i e s . In t h e sequence  P P h -> A s P h 3  3  l y more m e t a l - T i k e i n c h a r a c t e r C u e .  -> S b P h  3  t h e c e n t r a l a t o m becomes p r o g r e s s i y e - .  e a s i e r t o ' o x t d t z e : J and e v i d e n c e f o r t h i s i s . :  1000  Figure 5.4  The o p t i c a l spectrum of the cation r a d i c a l species l a (mixture obtained on adding excess SbPh, C  IT  ) and the spectrum of the product  162  provided  by t h e d o m i n a n t r e d u c t i o n n o t e d on a d d i t i o n o f S b P h ^ t o t h e  c a t i o n r a d i c a l , although a small p r o p o r t i o n of Ru(III) i s s t i l l formed  by  electron transfer. L i g a n d s c o n t a i n i n g G r o u p V e l e m e n t s as t h e d o n o r atom g e n e r a l l y g i v e e l e c t r o n t r a n s f e r and r u t h e n i u m ( I I I ) s t e r i c requirements  products.  The l i g a n d s m u s t h a v e m o d e s t  a s s e e n when s t e r i c a l l y h i n d e r e d l i g a n d s s u c h as  or A s t M e s i t y l ) ^ were u s e d .  Instead of a r e a c t i o n to give mainly  r e d u c t i o n t o 1_ and f o r m a t i o n o f some o t h e r p r o d u c t s , a b s o r b i n g wereobserved. important  The c o o r d i n a t i o n o f p h o s p h i n e t o t h e r u t h e n i u m  P^H-ji^  ruthenium(III),  a t 570 - 620  nm,  a p p e a r s t o be  f o r s u b s e q u e n t e l e c t r o n t r a n s f e r , and i f s t e r i c e f f e c t s do  not  allow c o o r d i n a t i o n , then side r e a c t i o n s appear to dominate. C y a n i d e was between the metal  a l s o found to promote i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r and t h e p o r p h y r i n l i g a n d .  e t h y l ammonium c y a n i d e  Addition of a crystal of t e t r a -  (TEA CN~) to a s p e c t r o s c o p i c s o l u t i o n of the c a t i o n +  r a d i c a l gave a spectrum c o n s i s t e n t with t h a t r e p o r t e d f o r the (CN).2 " a n i o n  1  (Figure 5.5).  ( C 0 ) ( C N ) ~ as a s e c o n d ruthenium(III)  Ru^^(OEP)-  Some r e d u c t i o n a l s o o c c u r s g i v i n g  product.  D e f i n i t i v e proof of the i d e n t i t y of the  p r o d u c t was o b t a i n e d by p r e p a r i n g an a n a l y t i c a l l y p u r e s a m p l e  o f T E A [ R u ( 0 E P ) ( C N ) 2 ] " (.1_4) by t h i s r e a c t i o n ( s e e S e c t i o n 2.5 +  Equation  I n  and  5.3),  £ R u ( 0 E P ) '(C0).] C10 ~ n  Ru^(OEP)-  +  +  4  +  2 TEA CN" +  » T E A [ R u ( . 0 E P ) ( C N ) ] ~ + CO + T E A C 1 0 " +  H I  +  2  4  163  F i g u r e 5.5  The o p t i c a l spectrum o f the c a t i o n r a d i c a l s p e c i e s J_a ( and the spectrum o f the product o b t a i n e d on adding excess TEA+CN" (-•).  )  164  5.1b In c o n t r a s t t o t h e l i g a n d s y s t e m s d e s c r i b e d a b o v e , a d d i t i o n o f pyridine or imidazole to a spectroscopic la  does not give a ruthenium(III)  solution of the cation radical  product  but instead causes the spectrum  t o change t o one c h a r a c t e r i s t i c o f a c a t i o n r a d i c a l w i t h t h e amine c o o r d i nated,  ( E q u a t i o n 5.4).  [Ru(0EP) " ( C 0 ) ] C 1 0 " + L +  +  4  ) [Ru(0EP) " ( C 0 ) L ] C 1 0 " +  (5.4)  +  4  L = p y , Im a n d MeCN  The a d d i t i o n o f 1 - 2 e q u i v a l e n t s  o f pyridine caused a s h i f t i n the  a b s o r p t i o n maximum o f t h e c a t i o n r a d i c a l f r o m 587 nm t o ^ 5 9 0 nm i n d i c a t i n g coordination of the ligand.  Further addition o f pyridine, although  causing  some r e d u c t i o n d u e t o s i d e r e a c t i o n s , had no f u r t h e r e f f e c t o n t h e 59.0 nm a b s o r p t i o n a n d no t r a c e o f r u t h e n i u m ( . I I I ) Reaction  with imidazole occurs  products  was  detected.  in a similar fashion.  The a d d i t i o n  o f o n e e q u i v a l e n t g a v e a new s p e c t r u m s i m i l a r t o t h a t r e p o r t e d f o r Ru(0EP)  +  (CO)Im ( 5 a ) ( S e c t i o n 4 . 1 ) , a l t h o u g h  R u ( O E P ) ( C O ) I m ( 5 ) was a l s o o b s e r v e d . s p e c t r u m a n d no r u t h e n i u m ( . I I I ) Triphenylphosphine  products  Excess imidazole were  detected.  Addition o f these ligands s h i f t e d the  o f l_a_ t o ^592 and 590 n m , r e s p e c t i v e l y ,  s h o u l d e r a t 610 nm.  had no e f f e c t o n t h e  o x i d e a n d DMSO b o t h showed c o o r d i n a t i o n t o l a _  a f t e r t h e a d d i t i o n o f one e q u i v a l e n t . main a b s o r p t i o n  a m i n o r r e a c t i o n t o g i v e some  and weakened t h e  165 D i l u t i o n of a s o l u t i o n of the c a t i o n r a d i c a l i n CHpCl  2  with p u r i f i e d  a c e t o n i t r i l e gave a spectrum i d e n t i c a l to t h a t o f Ru(0EP) '(C0)MeCN  (6a),  +  prepared  by e l e c t r o c h e m i c a l  o x i d a t i o n o f R u ( O E P ) ( C O ) E t O H i n MeCN ( s e e  Section  411). Reaction  o f l a ^ w i t h weak l i g a n d s s u c h a s m e t h a n o l and w a t e r showed  a number o f i n t e r e s t i n g f e a t u r e s .  I t has a l r e a d y b e e n n o t e d t h a t a d d i t i o n  o f excess methanol to a s o l u t i o n o f la_ i n C H ^ C l i n t h e 610 nm a b s o r p t i o n  2  caused a l o s s of i n t e n s i t y  o f t h e c a t i o n r a d i c a l and t h i s was  due t o c o o r d i n a t i o n o f t h e a d d e d m e t h a n o l ( s e e S e c t i o n 4 . 1 ) .  b e l i e v e d to  be  Addition  m e t h a n o l t o s o l u t i o n s o f l a _ was u s u a l l y a c c o m p a n i e d by some r e d u c t i o n  of  t h e c a t i o n r a d i c a l and  i t was  reduction observed  l a r g e l y d e t e r m i n e d by t h e q u a l i t y o f t h e e l e c t r o -  was  q u i c k l y r e a l i s e d that the proportion  of  c h e m i c a l l y p r o d u c e d c a t i o n r a d i c a l r a t h e r t h a n by t h e p r e s e n c e o f i n t h e l i g a n d ( g o o d q u a l i t y m e t h a n o l f r o m t h e same s o u r c e was reactions).  A s i m i l a r c o r r e l a t i o n was  of  impurities  used i n  n o t e d on t h e a d d i t i o n o f o t h e r  l i g a n d s ( e . g . py o r Im) t o l a _ , a l t h o u g h t h e e f f e c t was m o r e o b v i o u s  these neutral  with  m e t h a n o l as t h e a d d e d l i g a n d . The b e s t s a m p l e s s p e c t r u m , were o b t a i n e d  o f t h e c a t i o n r a d i c a l ]a_, a s j u d g e d by u . v . / v i s i b l e by s w i f t e l e c t r o l y s i s u s i n g h i g h c u r r e n t l o a d s  s t r o n g ( 1 0 ~ M) s o l u t i o n s .  S u c h s o l u t i o n s showed s l i g h t ( s 2 % ) r e d u c t i o n  t h e a d d i t i o n o f m e t h a n o l ( u p t o 20%  and on  by v o l u m e ) .  L e s s p u r e s o l u t i o n s o f l a _ ( a s j u d g e d by t h e q u a l i t y o f t h e o p t i c a l trum) were p r e p a r e d  by s l o w e r  spec-  e l e c t r o l y s i s ( d u e t o low c u r r e n t l o a d s o r ,weij.k  166  (<10~  M) s o l u t i o n s ) , t a k i n g 20 - 30 m i n u t e s f o r t h e c u r r e n t t o r e a c h <1%  o f i t s maximum v a l u e . reduction immediately  T h e s e p r e p a r a t i o n s o f l_a_ showed s u b s t a n t i a l ( 2 0 - 40%) ( p r e s u m a b l y t o R u ( 0 E P ) ( C 0 ) M e 0 H - s e e S e c t i o n 3.1) on  t h e a d d i t i o n o f m e t h a n o l t o 2 0 % by v o l u m e , a n d t h e p r o p o r t i o n o f r e d u c t i o n increased  ,on s t a n d i n g .  A d d i t i o n o f THF and, t o a l e s s e r extent -3  of reactivity.  A d d i t i o n o f 10  w a t e r showed a - s i m i l a r p a t t e r n -4  M T H F t o a 10  M s o l u t i o n o f l_a g a v e l i t t l e  r e d u c t i o n i f t h e c a t i o n r a d i c a l was o f ' h i g h p u r i t y ' , c o o r d i n a t i o n b e i n g c a t e d by t h e a l m o s t c o m p l e t e l o s s o f t h e 610 nm The r e a c t i o n  shoulder.  o f t h i s c a t i o n r a d i c a l species with methanol  t h a t i m p u r i t i e s may be g e n e r a t e d  indi-  as s i d e products  suggests  i n the electrochemical  f o r m a t i o n o f t h e c a t i o n r a d i c a l a n d t h a t t h e s e i m p u r i t i e s may c a u s e some r e d u c t i o n on a d d i t i o n o f a l i g a n d . tent presence  T h i s c o n c l u s i o n may e x p l a i n t h e p e r s i s -  o f side reactions giving reduction i n the reactions outlined  i n S e c t i o n 5.1a a n d n o t e d i n t h e I n t r o d u c t i o n t o t h i s C h a p t e r . larger proportions o f reduction observed  However,the  i n the reactions o f six-coordinate  c a t i o n r a d i c a l s p e c i e s have a d i f f e r e n t e x p l a n a t i o n ( s e e S e c t i o n 5 . 5 ) . 5.1c As m e n t i o n e d i n S e c t i o n 4 . 3 , a d d i t i o n o f T E A C 1 " t o a s o l u t i o n o f +  [ R u ( 0 E P ) ' ( C 0 ) ] C 1 0 ~ ( l a ) causes a change i n ground s t a t e with t h e formation +  +  4  o f a green s o l u t i o n and c o o r d i n a t i o n o f c h l o r i d e t o give  [Ru(0EP) '(C0)Cl] +  (.l_c). S i m i l a r l y , a d d i t i o n o f T B A B r " g a v e [ R u ( 0 E P ) '(.C0)Br] (lb_) . i i,These +  +  167  reactions are usually very clean.  TBA I " g i v e s r e d u c t i o n a s e x p e c t e d  f o r an a n i o n a s e a s i l y o x i d i z e d a s I ~ . A d d i t i o n o f c h l o r i d e and bromide  i o n s by g r i n d i n g u p t h e a p p r o p r i a t e  potassium s a l t w i t h 18-crown-6 and then d i s s o l v i n g i n C H C 1 2  to a s p e c t r o s c o p i c s o l u t i o n o f  l_a_ a l s o w o r k e d w e l l .  2  before adding  Attempts  t o add  f l u o r i d e i o n s f a i l e d , b u t SCN" c o u l d be a d d e d v i a t h e c r o w n - e t h e r t e c h n i q u e a n d g a v e an i m p u r e s p e c t r u m o f a [Ru(.0EP) ' ( C 0 ) S C N ] +  A-| g r o u n d s t a t e a t t r i b u t e d t o u  ( I d ) . (For s p e c t r a l data see Table 4.5).  5.Id The r e m a i n i n g l i g a n d s t o be c o n s i d e r e d a r e t h o s e t h a t w e r e o x i d i z e d by t h e c a t i o n r a d i c a l (.la) o r w e r e t o t a l l y i n e r t .  Tetramethyl  guanidine,  ( M e N ) C = NH, r e d u c e s t h e c a t i o n r a d i c a l i m m e d i a t e l y , on a d d i t i o n o f o n e -4 2  2  e q u i v a l e n t o f t h e b a s e t o a 10 Ru (0EP)(C0) I I  M s o l u t i o n o f la_, and c o o r d i n a t e s t o t h e  (.]_) f o r m e d , g i v i n g a s p e c t r u m t y p i c a l o f c o m p l e x e s  Ru (0EP)(C0)( nitrogen-base)(I I I  ;  5 5 0  /I  5 2 0  ^1.27, see S e c t i o n 3.1).  o f the type Triethyl-  amine (EtgN) and t - b u t y l t h i o l (Me CSH) both i n s t a n t l y reduced t h e c a t i o n 3  r a d i c a l on t h e a d d i t i o n o f o n e e q u i v a l e n t . A l l t h r e e o f t h e s e l i g a n d s a r e r e l a t i v e l y easy t o o x i d i z e , s o the r e d u c t i o n process i s probably a simple t r a n s f e r o f an e l e c t r o n t o t h e p o r p h y r i n complex.  A similar  process  p r o b a b l y o c c u r s w i t h e s t a b l i s h e d r e d u c i n g agents such as t h e b o r o h y d r i d e anion.  168  I t s h o u l d be n o t e d t h a t t h e c y a n i d e i o n , b e i n g e a s i l y o x i d i z e d , w o u l d be e x p e c t e d  t o r e d u c e t h e c a t i o n r a d i c a l . H o w e v e r , f o r c o m p l e x l_a  the c o o r d i n a t i o n o f the cyanide i o n and i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r appears f a s t e r than the r e d u c t i o n process is obtained.  in that a ruthenium(III)  product  For a s i x - c o o r d i n a t e c a t i o n r a d i c a l species (see Section  the reduction o f the c a t i o n r a d i c a l appears  f a s t e r than  5.2)  ruthenium(III)  f o r m a t i o n , s i n c e r e d u c t i o n , a n d o x i d a t i o n o f CN", a r e t h e r e a c t i o n s o b s e r v e d . A few p o t e n t i a l l i g a n d s had no e f f e c t on t h e c a t i o n r a d i c a l . Trimethylphosphite,  P ( 0 M e ) , g a v e no r e a c t i o n w h i c h i l l u s t r a t e s t h e e f f e c t 3  o f t h e e l e c t r o n e g a t i v e oxygen atoms i n r e d u c i n g t h e a v a i l a b i l i t y o f t h e l o n e p a i r on t h e p h o s p h o r u s a t o m .  The r e a c t i v i t y o f t h e e l e c t r o l y t i c anions  p e r c h l o r a t e a n d f l u o r o b o r a t e has been d i s c u s s e d e a r l i e r ( S e c t i o n 4.1)  along  with the question o f the p o s s i b l e c o o r d i n a t i o n o f these ions to the c a t i o n radical species l a .  S e c t i o n 5.1e  D i s c u s s i o n and  Conclusions  As d i s c u s s e d i n S e c t i o n 4 . 1 , e l e c t r o l y t e a n i o n s a r e b e l i e v e d t o c o o r d i n a t e t o t h e c a t i o n r a d i c a l s p e c i e s R u ( 0 E P ) '(C0) (l_a) b u t t h e +  chemistry  a nd e l e c t r o c h e m i s t r y o f t h e r e s u l t i n g c o m p l e x i s c o n s i s t e n t w i t h t h a t o f a f i v e - c o o r d i n a t e s p e c i e s and h e n c e l a . i s c o n s i d e r e d t o be " e f f e c t i v e l y " a f i v e - c o o r d i n a t e complex and i s w r i t t e n as s u c h .  An i n c o m i n g l i g a n d c a n t h u s  c o o r d i n a t e t o c o m p l e x l_a r a p i d l y and d o e s s o " i n s t a n t a n e o u s l y " by v i s i b l e i nspection.  169  Of t h e l i g a n d s t h a t p r o m o t e i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r ( i n particular P Bu  a n d C N " ) , i t s h o u l d be n o t e d t h a t t h e c o m p l e x e s R u ( O E P ) -  n  (C0)P Bu  3  a n d Ru(.OEP)(C0)CN~ show s i m i l a r s p e c t r a n o t t y p i c a l o f t h o s e  n  3  u s u a l l y observed (C0)PPh  f o r R u C 0 E P ) ( C 0 ) L complexes (see S e c t i o n 3.1).  Ru (0EP)-  n  Cll). a n d R u  3  1 1  ( O E P ) ( C O j A s P h g Cj_9) a l s o show s t r o n g l y  spectra  T I  perturbed  s p e c t r a ( s e e S e c t i o n 3 . 1 ) . The a b i l i t y o f a l i g a n d t o promote t h e e l e c t r o n t r a n s f e r r e a c t i o n does n o t c o r r e l a t e with l i g a n d s t r e n g t h ( i m i d a z o l e and p y r i d i n e b i n d much m o r e s t r o n g l y t o R u ( 0 E P ) ( C 0 ) Q)  than PPh  3  or AsPh ,  S e c t i o n 3.2) b u t i t d o e s a p p e a r t o c o r r e l a t e w i t h t h e s t r o n g l y s p e c t r a o f some R u ^ ( O E P ) ( C 0 ) L c o m p l e x e s .  The phosphines  i o n a l l form s t r o n g bonds w i t h t r a n s i t i o n metal  3  perturbed  and cyanide  ions and a r e a l s o a b l e t o  s t a b i l i z e low o x i d a t i o n s t a t e s . The l a t t e r e f f e c t i s due t o t h e -rr-acidity of t h e l i g a n d and enables  i t to l a b i l i z e a trans carbonyl  ligand, while the  f o r m e r e f f e c t ( a - d o n i c i t y ) . w h i c h may be s t r o n g l y e n h a n c e d when t h e l i g a n d in question i s c i s to a porphyrin macrocycle  (see Section 3.3), allows the  ligand to s t a b i l i z e the ruthenium(III)  product  of the ligands i s probably important.  Imidazole  donor, ' 4  formed.  The dual  i s a s t r o n g a ( a n d -ir)  a n d i s a b l e t o s t a b i l i z e r u t h e n i u m ( I I I ) ( s e e S e c t i o n 7.3) b u t  5  i t i s not a s u f f i c i e n t l y strong ir-acid to l a b i l i z e t h e carbonyl On t h e o t h e r h a n d , CO i t s e l f i s a v e r y s t r o n g l a b i l i z e a trans carbonyl group (as demonstrated of prepared  samples o f Ru ^(OEP)QC(D) )  Ru(0EP) '(C0) +  tendency  nature  1  2  -  6  group.  ir-acid and hence would by t h e i n s t a b i l i t y  but the product ( a c t u a l l y  t h e s t a r t i n g s p e c i e s f o r t h i s r e a c t i o n ) shows no  t o undergo i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r because t h e carbonyl  170  l i g a n d w o u l d be u n a b l e t o s t a b i l i z e t h e r u t h e n i u m ( I I I ) p r o d u c t . c o o r d i n a t e d c a r b o n y l l i g a n d causes complexes  of the type  to o x i d i z e a t the r i n g r a t h e r than a t the metal  The  Ru**(0EP)(C0)L  ( S e c t i o n 4.1).  I t seems  u n l i k e l y t h a t a r u t h e n i u m ( I I I ) p o r p h y r i n c a r b o n y l c o m p l e x w i l l e v e r be o b t a i n e d o t h e r t h a n as a t r a n s i e n t i n t e r m e d i a t e . complexes  of the type Ru (.0EP)(.P Bu )L , i n  n  +  3  7.3) and R u C 0 E P ) ( C N ) L , ( L = p y ) i n  1  I t s h o u l d be n o t e d t h a t  L = Im, py, CH^CN ( s e e S e c t i o n  show r e v e r s i b l e h a l f - w a v e p o t e n t i a l s  c o n s i s t e n t with o x i d a t i o n (or r e d u c t i o n ) a t the metal r a t h e r than a t the r i n g , i l l u s t r a t i n g t h e d i f f e r e n c e b e t w e e n t h e p h o s p h i n e s and c y a n i d e on t h e one h a n d , and CO a s a l i g a n d on t h e o t h e r .  This i s further evidence  f o r t h e m o d i f i e d n a t u r e o f l i g a n d s s u c h as P P h g , P B u n  t o a p o r p h y r i n m a c r o c y c l e , as m e n t i o n e d  3  i n S e c t i o n 3.3.  and A s P h g , when c i s The m e c h a n i s m o f  e l e c t r o n t r a n s f e r w i l l be d i s c u s s e d i n m o r e d e p t h i n S e c t i o n  5.2  6.4.  Reactions of a Six-Coordinated Cation Radical Species with Ligands  i n C H g C l p , an I n e r t S o l v e n t  In t h i s s e c t i o n , t h e r e a c t i o n s o f [ R u ( 0 E P ) '(.C0)Br] ( l _ b ) , I I  ,Ru(0EP) '(C0)py. +  ( 3 a ) , and  Ru(.0EP) '( C0)lm (.5a.), +  +  with ligands will  c o m p a r e d and c o n t r a s t e d w i t h t h e r e a c t i o n s d e s c r i b e d i n S e c t i o n 5.1.  be In  t h e s e t h r e e s p e c i e s t h e s i x t h l i g a n d i s j u d g e d t o be c o o r d i n a t e d t o t h e r u t h e n i u m a t o m on t h e b a s i s o f v i s i b l e s p e c t r a and o t h e r d a t a ( C h a p t e r 4 ) . However, the c o o r d i n a t e d l i g a n d i s p r e s e n t o n l y i n e q u i m o l a r q u a n t i t i e s w i t h  171  t h e p o r p h y r i n c a t i o n r a d i c a l , and h e n c e c a n be d i s p l a c e d by a s e c o n d l i g a n d r e l a t i v e l y e a s i l y . Cation radical species in the presence o f a l a r g e excess o f t h e c o o r d i n a t e d l i g a n d w i l l be c o n s i d e r e d i n t h e n e x t s e c t i o n .  5.2a  R e a c t i o n s o f [Ru(,0EP) ' ( C 0 ) B r ] ( l b ) +  -4  n  A d d i t i o n o f 1 - 2 e q u i v a l e n t s o f P Bu^ t o a 10 [Ru (0EP) '(C0)Br] I I  +  M s o l u t i o n of  (1J0 c a u s e s l o s s o f t h e c a t i o n r a d i c a l a b s o r b a n c e s ,  f o r m a t i o n o f an o r a n g e s o l u t i o n whose s p e c t r u m shows a t y p i c a l  and  ruthenium(III)  f e a t u r e i n t h e v i s i b l e ( b r o a d a b s o r p t i o n 500 - 550 nm) w i t h a d o u b l e S o r e t and o n l y v e r y weak a b s o r p t i o n s i n t h e n e a r I.R. s p e c t r a o f a u t h e n t i c samples  Comparison  with the  o f r u t h e n i u m ( I I I ) p o r p h y r i n complexes  showed  t h a t t h e m a j o r p r o d u c t was n o t t h e same as t h a t f o r m e d f r o m t h e c a t i o n r a d i c a l R u ( . 0 E P ) '(C0) ( l _ a ) , , n a m e l y II  +  Ru (0EP) (P Bu ) I H  n  3  + 2  (.9),  although  a d d i t i o n o f e x c e s s (2 - 10 e q u i v a l e n t s ) p h o s p h i n e d i d g e n e r a t e t h i s s p e c i e s ; t h e p r o d u c t i n s t e a d was Ru***(.0EP) ( _ P B u ) B r (1_0) c o n t a m i n a t e d w i t h a s m a l l n  3  p r o p o r t i o n o f ,9_ as w e l l a s some r e d u c t i o n p r o d u c t s ( F i g u r e 5 . 6 ) . r e a c t i o n s o f c a t i o n r a d i c a l s ]a_ a n d JJb w i t h P B u n  3  These  a r e s u m m a r i z e d i n Scheme  5.1. Of t h e o t h e r l i g a n d s t r i e d , o n l y c y a n i d e (when a d d e d t o VD) g a v e a p r o d u c t i d e n t i f i e d as b e i n g due t o i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r . A d d i t i o n o f a d i l u t e s o l u t i o n of TEA CN" to a 10 M +  -4  solution of  [Ru(0EP) + -  (C0)Br] (1b) r e s u l t e d i n a r e a c t i o n very s i m i l a r to t h a t r e p o r t e d f o r a d d i t i o n of t h i s l i g a n d to ^ a , although the proportion of the c a t i o n r a d i c a l s u f f e r i n g r e d u c t i o n was p r o b a b l y g r e a t e r ( 1 0 - 1 5 % ) .  2  The i d e n t i t y o f t h e m a j o r  product  I i i i i i ,  i  ij  I i|  V  i/  I |\  1/  is  !/  I;  i \  I /  i  w  i i i !  1 ! •' i  .'/  ii  I  \\ ii  II  \i \!  \\ \i  ro  \ OS  u  !  E  1  V  .x.  600  \  \  700 WAVELENGTH  F i g u r e 5.6  ^  (nm)  T h e s p e c t r u m o f t h e p r o d u c t o b t a i n e d on a d d i n g two e q u i v a l e n t s o f P Bu3 t o A ] c a t i o n r a d i c a l Ijj ( .) a n d t h e p r o d u c t on a d d i n g a f u r t h e r two e q u i v a l e n t s o f t h e p h o s p h i n e ( ' • • • • ) • T h e two e q u i v a l e n t r e a c t i o n was a c c o m p a n i e d by ^ 1 0 % r e d u c t i o n t o R u ( O E P ) ( C O ) (547 nm p e a k ) w h i c h t h e n g e n e r a t e d R u ( 0 E P ) ( C 0 ) P B u 3 (8) i n t h e p r e s e n c e o f t h e e x c e s s p h o s p h i n e ( s e e t h e s t r o n g S o r e t a t 408 nm). u  s  I]:  n  173 SCHEME  [Ru(OEP)  -(CO)]V  +  +  P Bu n  3  (>2  5.1  eq)  *  [Ru (0EP)(P Bu ) ] A I n  n  +  3  o r Br  -  2  (la) (9)  A" = C 1 0 ~ , 4  BF " 4  PF "  >10  eq  P Bu. n  [Ru(OEP) '(CO)Br] +  +  P Bu n  3  (1-2  eq)  +  Ru (OEP)(P Bu )Br I n  n  3  CO  (lb) (10)  was  confirmed  t o be  Ru  1 l i  (0EP)(CN) " 2  a t 680 nm ( s e e F i g u r e 5.5 and R e f . A d d i t i o n of excess 1b  by t h e p r e s e n c e  o f a weak p e a k c e n t r e d  1).  triphenylphosphine  ( P P h ) t o a 10~^M 3  gave i n s t a n t r e d u c t i o n r a t h e r than the expected  solution of  ruthenium(III)  Q u a n t i t a t i v e a d d i t i o n o f t h e p h o s p h i n e showed t h a t t h e p o r p h y r i n r a d i c a l was r e d u c e d  l_b  cation  i n t h e s t o i c h i o m e t r y o f one mole o f p h o s p h i n e per  moles of c a t i o n r a d i c a l . with  product.  two  The a n a l o g o u s r e a c t i o n o f t r i p h e n y l a r s i n e ( A s P h )  g a v e t h e same r e s u l t .  3  I t was  thought i n i t i a l l y that the  was a r e a c t i o n s p e c i f i c t o t h e s e two l i g a n d s , and was removal o f bromine from the s o l u t i o n ;  reduction  p r o b a b l y due t o  the  t h i s c a n r e s u l t i n t h e r e d u c t i o n o f IJJ  by p r o m o t i n g t h e b a c k r e a c t i o n o f i t s f o r m a t i o n  ( S e c t i o n 4.2,  Equation  4.1).  174  H o w e v e r , t h i s r e a s o n i n g was a b a n d o n e d on f i n d i n g t h a t t h e r e a c t i v i t y o f P P h and A s P h g t o w a r d s b r o m i n e a t low c o n c e n t r a t i o n s was  i n s u f f i c i e n t to  3  e f f e c t s u c h an e q u i l i b r i u m .  As w i l l be s e e n b e l o w t h i s r e d u c t i o n i s one  example o f a general r e a c t i o n ( S e c t i o n  5.5).  A d d i t i o n o f a l l other n e u t r a l c o o r d i n a t i n g l i g a n d s gave r e d u c t i o n as t h e d o m i n a n t r e a c t i o n . was  [Ru (.0EP) '(C0)Br] II  +  T h i s was  s e e n when t h e c a t i o n r a d i c a l  species  (1 b) o r t h e c h l o r i d e a n a l o g u e ( l c ) p r e p a r e d  T E A C 1 " t o a s o l u t i o n ofJ_RuC0EP) ' ( . C 0 ) ^ C l 0 " (_l_a). The r e d u c t i o n s +  +  4  o f t e n m o r e c o m p l e t e i n t h e l a t t e r c a s e and t h i s i s t h o u g h t the presence  o f excess c o o r d i n a t i n g anion ( C l ~ ) .  by  adding  were  t o be due  to  The e x t e n t o f r e d u c t i o n  f o r a g i v e n amount o f a d d e d n e u t r a l l i g a n d d e p e n d s u p o n i t s c o o r d i n a t i n g strength.  Thus a l a r g e excess  to give reduction  (>1000 eq) o f a c e t o n i t r i l e o r THF i s r e q u i r e d  o f ]_b, w h e r e a s s t r o n g l i g a n d s s u c h as p y r i d i n e ,  o r P P h g , e f f e c t e d r e d u c t i o n a t v e r y low c o n c e n t r a t i o n s metric).  imidazole,  (essentially stoichio-  Some r e a c t i o n s w e r e s l o w : - a d d i t i o n o f m e t h a n o l ( > 1 0 0 0 eq) t o 1 b,  f o r example, gave the spectrum o f the o t h e r ground s t a t e ( A 0 2  t o Ru**('_0EP).(jC0lMe0H. o c c u r r e d  before reduction  over a period o f several minutes.  Increasing  the p o l a r i t y o f the s o l v e n t a p p e a r s to encourage the d i s s o c i a t i o n o f the bromide from the p o r p h y r i n c a t i o n r a d i c a l MeCN ] B r ~ by t h e a c t i o n o f B r +  w h i c h then s l o w l y r e d u c e s .  2  ( s e e f o r m a t i o n o f [ R u ( . 0 E P ) '(.C0)II  on Ru(0EP)(.C0)MeCN i n MeCN - S e c t i o n  +  4.2),  I t s h o u l d be n o t e d t h a t a d d i t i o n o f e x c e s s  t o [Ru(..0EP) *(.C0)Br] (1 b) d o e s n o t c a u s e r e d u c t i o n b u t i n s t e a d p r o b a b l y +  a high proportion of the c h l o r i d e analogue p c ) .  Hence,anionic  TEA C1~ +  gives  l i g a n d s whose  175  c o o r d i n a t i o n does not change the ground to cause  s t a t e o f t h e p o r p h y r i n do n o t a p p e a r  reduction.  R e a c t i o n s o f I R U C Q E P ) * ' ( C 0 ) p y ] C l 0 ^ " (3a) n -5 A d d i t i o n o f 1 - 2 e q u i v a l e n t s o f P B u t o a 5 x 10 M s o l u t i o n o f  5.2b  +  3  Ru(0EP) '(C0)py  (3a) promotes a sequence o f r e a c t i o n s analogous  +  s e e n on a d d i n g t h i s l i g a n d t o duct spectrum  that appears  l_b.  Two  equivalents o f phosphine  i t was  n  +  3  Ru(0EP) '(C0). +  2  (]_a) ( F i g u r e 5 . 7 ) .  A d d i t i o n of excess P B u  species,  t h e same p r o d u c t ,  R u * C 0 E P ) . C P B u ) , . a s f o r m e d by a d d i t i o n o f t h e p h o s p h i n e I  gave a p r o -  t o be a m i x t u r e o f two r u t h e n i u m ( I I I )  one s h o w i n g an a b s o r p t i o n a t 790 nm w h i c h s u g g e s t e d I  to those  n  3  l i g a n d to  (up t o 4 e q u i -  v a l e n t s ) c a u s e d an i n c r e a s e i n t h e 790 nm a b s o r p t i o n t o a maximum o f t h e i n t e n s i t y o f t h e s t r o n g v i s i b l e b a n d c e n t r e d a t 520 nm ( e ^ l By c o m p a r i s o n  w i t h the s p e c t r a o b t a i n e d from the a d d i t i o n o f P B u  was  x 10^M cm ). _ 1  n  l a _ and •'Vb. , and o f g e n u i n e i d e n t i f i e d as R . u  I I I  ^30%  3  to species  samples of p o s s i b l e products, the f i n a l  (0EP)(P Bu )2 . n  +  3  product  A study of t h i s r e a c t i o n at increased  c o n c e n t r a t i o n o f 3a (2 x 10~^M) showed t h a t t h e i n t e r m e d i a t e s p e c i e s had a weak a b s o r p t i o n a t ^730 excess  phosphine  m e d i a t e was  nm;  t h i s decreased  i n i n t e n s i t y on a d d i t i o n o f  as t h e i n t e n s i t y o f t h e 790 nm p e a k i n c r e a s e d .  t e n t a t i v e l y a s s i g n e d as  seemed a r e a s o n a b l e  _ 1  Ru (0EP)(P Bu )py I n  n  3  +  The i n t e r -  since this  i n t e r m e d i a t e , and m o r e e v i d e n c e f o r t h i s d e s i g n a t i o n  w i l l be p r e s e n t e d l a t e r ( S e c t i o n 7 . 3 ) .  The m e c h a n i s m o f t h i s r e a c t i o n ,  which i s s i m i l a r to the r e a c t i o n of P B u n  Q  w i t h l_b, w i l l be d i s c u s s e d i n  1.0  cr.  1000 WAVELENGTH  F i g u r e 5.7  (nm)  T h e o p t i c a l s p e c t r u m o f t h e c a t i o n r a d i c a l s p e c i e s [ R u ( O E P ) " ( C O ) p y ] CIO4" (3a), (• ) and t h e p r o d u c t f o r m e d o n a d d i n g b e t w e e n two a n d f o u r e q u i v a l e n t s o f P Bu3 ( - , - - , - ) . T h i s p r o d u c t (mainly a mixture o f £ R u ( O E P ) ( p n B u ) J C l 0 (9a) a n d [ R u (OEP).(pnBu ).py]+Cl04" (26a).) w a s t h e n r e d u c e d w i t h TBA BH4" ( ) • T h e p r o p o r t i o n o f r e d u c t i o n t o Ru I H.0EPlCC0).P Bu 3 ~Ti[) o c c u r r i n g a s a s i d e r e a c t i o n o n a d d i n g t h e P B u was ^10% a n d gave r i s e t o a S o r e t a t 408 nm a n d a s h o u l d e r a t 555 nm. A b s o r p t i o n s b e t w e e n 570 a n d 680 nm a r e d u e t o d e g r a d e d p o r p h y r i n p r o d u c t s a l s o f o r m e d by s i d e r e a c t i o n s . n  n i  _  +  3  1 1 1  4  2  3  +  n  n  3  177  the next chapter ( S e c t i o n 6.4). r e a c t i o n i s a b o u t 15%.  The a m o u n t o f r e d u c t i o n s e e n i n a s i d e  The t r i - n - b u t y l p h o s p h i n e was t h e o n l y l i g a n d t h a t  g a v e a good y i e l d o f r u t h e n i u m ( I I I ) p r o d u c t s w i t h 3a_. T r i p h e n y l p h o s p h i n e a n d t h e a r s i n e b o t h g a v e some r u t h e n i u m ( I I I ) as w e l l as a c o n s i d e r a b l e p r o p o r t i o n o f r e d u c e d p r o d u c t ( u s u a l l y a m i x t u r e o f R u ( O E P ) ( C O ) p y (3_) and t h e c o r r e s p o n d i n g p h o s p h i n e o r a r s i n e c o m p l e x Ru(0EP)(C0)L, L = PPh  3  or A s P h ) . 3  TEA CN~ r e a c t e d i n a s i m i l a r manner. +  A d d i t i o n o f T E A C T gave a r o u g h l y 50/50 m i x t u r e o f t h e r e d u c e d p r o d u c t +  ( R u ( . 0 E P ) ( C 0 ) p y ) and t h e o t h e r g r o u n d s t a t e s p e c i e s a s s u m e d t o be II  [Ru* (.0EP) 'CC0)Cl] ( l _ c ) . I  Both p r o d u c t s were formed i n a p p r o x i m a t e l y  +  e q u a l q u a n t i t i e s r i g h t f r o m t h e s t a r t o f t h e r e a c t i o n . S p e c i e s l_c_ p r e p a r e d i n t h i s m a n n e r was n o t e d t o be r a t h e r l e s s s t a b l e t h a n p u r e • l c _ p r e p a r e d by a d d i n g T E A C 1 " t o R u ( 0 E P ) "(C0) ( l a ) . A l s o , t h e r e m a i n i n g +  H  +  [Ru(0EP) *+  ( C O ) C I ] c o m p o n e n t c o u l d be v e r y e f f e c t i v e l y r e d u c e d t o R u ( 0 E P ) ( C 0 ) p y  by  t h e a d d i t i o n o f a p p r o x i m a t e l y one e q u i v a l e n t o f p y r i d i n e ( s e e S e c t i o n 5 . 5 ) . A d d i t i o n s o f a s m a l l e x c e s s o f i m i d a z o l e t o 3a_ c a u s e s l i t t l e r e d u c t i o n but does change t h e s p e c t r u m o f t h e c a t i o n r a d i c a l t o t h a t o f  Ru(0EP) "(C0)Im +  (5a) (Table 4.5), s u g g e s t i n g t h a t the i m i d a z o l e e f f e c t i v e l y r e p l a c e s the coordinated pyridine.  5.2c  Reaction of [Ru(0EP) '(C0)Im] C10 ~ +  +  4  (5a) 2  I t had been e x p e c t e d t h a t t h e r e a c t i v i t y o f t h e  2 A-|  u  and  A  2 u  ground  s t a t e s ( e x e m p l i f i e d by t h e s i x - c o o r d i n a t e s p e c i e s TJb_ and 3a_, r e s p e c t i v e l y )  178 w o u l d be r a t h e r d i f f e r e n t , w h i l e two c a t i o n r a d i c a l s w i t h a x i a l n i t r o g e n b a s e s ( 3 a a n d 5a_)  m i g h t show s i m i l a r r e a c t i o n s . However, R u ( 0 E P ) '(C0)Im +  ( 5 a ) showed many d i f f e r e n c e s f r o m t h e c o r r e s p o n d i n g p y r i d i n e c o m p l e x ( 3 a ) , and t h i s may  be l i n k e d t o t h e p o s s i b i l i t y , as j u d g e d by s p e c t r o s c o p i c e v i -  d e n c e , t h a t 5a^ has a m i x e d g r o u n d s t a t e ( s e e S e c t i o n 4.1 and C h a p t e r 8 ) , 2 a l t h o u g h most o f the c h e m i s t r y d e s c r i b e d here i s c o n s i s t e n t w i t h the ground s t a t e .  One f a c t o r c o m p l i c a t i n g t h e c h e m i s t r y o f 5a_ i s t h a t u n l i k e  t h e r e a c t i o n s d e s c r i b e d s o f a r i n t h i s C h a p t e r , many o f t h e r e a c t i o n s o f 5a_ w e r e s l o w , t a k i n g i n some c a s e s up t o an h o u r f o r c o m p l e t i o n . In c o n t r a s t t o t h e f o r m a t i o n o f • R U ^ C O E P H P of excess P^u^  1 1  !^^  ( 9 ) by r e a c t i o n  w i t h 3a^, t h e a d d i t i o n o f two o r m o r e e q u i v a l e n t s o f t h e  phos-  p h i n e t o 5a_ g a v e a g r e e n c o l o u r e d s o l u t i o n . The i n t e n s i t y o f t h e 790 nm a b s o r p t i o n i n the spectrum i n d i c a t e d t h a t about 40% o f t h e c a t i o n r a d i c a l undergone  had  i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r to give the ruthenium(III) b i s  p h o s p h i n e c o m p l e x (9_), w h i l e r e d u c t i o n ( 4 0 7 nmyband)- a c c o u n t e d f o r ^ 1 0 % , and t h e r e m a i n i n g 50% had g i v e n g r e e n u n i d e n t i f i e d p r o d u c t s w i t h an a b s o r p t i o n p e a k a t 605 nm and a b r o a d f e a t u r e f r o m 600 - 700 nm ( F i g u r e 5 . 8 ) . these products are s p e c t r a l l y s i m i l a r t o the green pigments  Although  formed a l o n g w i t h  t h e r e d u c e d p r o d u c t s o b t a i n e d i n many o f t h e s e l i g a n d a d d i t i o n e x p e r i m e n t s ( S e c t i o n 5 . 6 b ) , t h e y a r e p r o b a b l y f o r m e d by a d i f f e r e n t m e c h a n i s m a s i n d i c a t e d by t h e l o w e r p r o p o r t i o n o f r e d u c t i o n a c c o m p a n y i n g  the r e a c t i o n (see S e c t i o n  5.5). The r e a c t i o n o f PPh^ w i t h R u ( 0 E P )  +  from t h a t w i t h t h e p y r i d i n e complex ( 3 a ) ,  (C0)lm (5a) i s a l s o v e r y d i f f e r e n t A d d i t i o n o f s o l i d PPh^ (2 - 3 mg)  F i g u r e 5.8  The o p t i c a l s p e c t r a o f t h e c a t i o n r a d i c a l s p e c i e s R u C 0 E P ) (C0)..Im 5a (o b t a i n e d on a d d i n g an e x c e s s o f P B u C + ?  n  3  ) and the p r o d u c t s  180  t o a 10  M solution of  ( 2 - 3 mins). p r o d u c t (X (X  5a_  caused the s o l u t i o n to s l o w l y turn orange  The f i n a l s p e c t r u m ( F i g u r e 5.9) i n d i c a t e s a R u ( I I I ) 745 nm) b u t n o t t h e e x p e c t e d ; R u ( 0 E P ) ( P P h , ) i n  species  + 9  810 nm) t h a t i s f o r m e d on a d d i n g P P h , t o R u ( 0 E P ) '(C0) ( l a ) . By H  a n a l o g y w i t h t h e r e a c t i o n s o f t h e p y r i d i n e complex p r o d u c t c o u l d be t h e m i x e d l i g a n d s p e c i e s  Ru  I I I  +  (3a)with P Bu ,the n  3  (0EP)(PPh )Im  and some  +  3  e v i d e n c e f o r t h i s was o b t a i n e d by r e d u c i n g t h e s o l u t i o n w i t h T B A B H ~ +  4  ( F i g u r e 5.10).  A s l o w , i n c o m p l e t e r e a c t i o n g a v e a m i x t u r e o f s p e c i e s as  j u d g e d by t h e t h r e e s e p a r a t e S o r e t bands a t 396 ( d u e t o i n c o m p l e t e l y r e d u c e d r u t n e n i u m ( I I I ) p r o d u c t ) , 408 a n d 419 nm.  A d d i t i o n of f u r t h e r PPh cau3  s e d a d e c r e a s e i n i n t e n s i t y o f t h e 4 0 8 nm a b s o r p t i o n a l o n g w i t h a s t r e n g t h e n i n g o f t h e 419 nm p e a k a t t r i b u t e d t o t h e f o r m a t i o n o f R u ( 0 E P ) ( P P h ) . n  3  instead of adding excess PPh  3  2  If,  t o t h e r e d u c e d s y s t e m , e x c e s s i m i d a z o l e was  a d d e d ( t h e r u t h e n i u m ( I I I ) s o l u t i o n was p r e p a r e d by a d d i n g a s m a l l e x c e s s (2-5  eq) o f P P h  3  t o 5a_ and was t h e n r e d u c e d ) t h e n l o s s o f t h e 419 nm p e a k  and a s h a r p i n c r e a s e i n t h e 408 nm a b s o r p t i o n was o b s e r v e d . t h a t the complex  Ru (0EP)(.PPh ) I I  3  2  Considering  (1_2) i s known t o d i s s o c i a t e i n d i l u t e  7  solution  to give a f i v e - c o o r d i n a t especies U  396 nm), a n d t h a t s u b s t i II I d  A  t u t i o n o f l i g a n d s i n r u t h e n i u m ( I I ) p o r p h y r i n complexes  is usually a fast  r e a c t i o n ( s e e S e c t i o n 3 . 2 ) , t h e f o l l o w i n g scheme t o e x p l a i n t h e r e s u l t s i s s u g g e s t e d : - Scheme 5.2 ( s e e F i g u r e s 5.10  a , b and, c ) .  1.0  F i g u r e 5.9  The o p t i c a l s p e c t r u m o f t h e ruthenium(;ill)„ p r o d u c t o b t a i n e d on a d d i n q PPho ( t o 2 x 1 0 " i a s o l u t i o n o f R u ( O E P ) + - ( C O ) I m C.5a_) i n C H C 1 . 3  2  2  0.6-^ Ul  o z < ID  OC  o </> m <  0.4H  oo ro  0.2^  350  400 WAVELENGTH (nm)  F i g u r e 5.10  450  0.0  350  400  450  WAVELENGTH (nm)  0.0  350  400  450  WAVELENGTH (nm)  a). T h e o p t i c a l s p e c t r u m o f t h e m i x t u r e o f p r o d u c t s f o r m e d on r e d u c i n g ( b y BH^"). t h e r u t h e n i u m ( I I I ) s p e c i e s o b t a i n e d when PPh3 ( 1 0 " % ) . i s a d d e d t o 5a_. mixture recorded i n a ) . b) The s p e c t r u m o b t a i n e d on a d d i n g e x c e s s ( 1 0 ~ ^ M ) P P h 3 c) The s p e c t r u m o b t a i n e d when e x c e s s ( 1 0 " M)„. i m i d a z o l e i s a d d e d t o t h e m i x t u r e r e c o r d e d i n a ) . In a l l t h r e e s p e c t r a t h e a b s o r p t i o n a t ^ 3 9 6 - 3 9 8 nm, w h i c h a p p e a r s t o be r e l a t i v e l y i n s e n s i t i v e t o t h e a d d e d l i g a n d s , i s b e l i e v e d t o be d u e t o u n r e d u c e d r u t h e n i u m ( I I I ) p r o d u c t ( s e e F i g u r e 5 . 9 ) , p r e s e n t because o f t h e slowness o f t h e b.orohydride r e d u c t i o n . t o  t n e  183  SCHEME 5.2  R u ( . O E P ) *(,CO)Itn II  + pph  +  ) Ru (0EP)(PPh )Im I n  3  +  3  +.C0  (5a) 396 nm ,  745 nm R e d u c t i o n ( e x c e s s PPh, present)  R u ( 0 E P ) ( . P P h ) = = ^ R u ( 0 E P ) ( P P h ) - = = ^* RDiu i I (I 0I E P ) ( P P h ) I m I I  i i  3  Soret  xmax •  i l  2 ?  3  419 nm  P  3  408 nm  396 nm . E x c e s s Im  E x c e s s PPh, Ru I I ( 0 E P ) ( P P h ) 3  Ru (0EP)(PPh )Im" n  2  T r a c e o f 408 nm a)  T h i s s p e c i e s n o t d e t e c t e d d u e t o p r e s e n c e o f e x c e s s PPh  b)  S e e F i g u r e 5 .1 Ob  c)  S e e F i g u r e 5.10c  3  184  Other ligands (CN , -  C I " , A s P h ) a d d e d t o R u ( O E P ) '(CO) Im H  (5a)  +  3  behaved i n a manner s i m i l a r to t h e i r r e a c t i o n s with k i n e t i c s sometimes complicated + -4 o f TEA CN  t o a 10  3a_ , a l t h o u g h s l o w -4 t h e r e s u l t s . A d d i t i o n o f a ^10 M s o l u t i o n  M solution of  5a  gave a f a s t r e a c t i o n c h a r a c t e r i z e d (5)  by r e d u c t i o n , w i t h t h e 550 and 518 nm a b s o r p t i o n s o f R u ( 0 E P ) ( C 0 ) I m being observed  and no t r a c e o f r u t h e n i u m ( I I I ) . A d d i t i o n - o f s o l i d t r i p h e n y l -  a r s i n e gave a t o t a l l y d i f f e r e n t r e a c t i o n to t h a t observed r e d u c t i o n t o 5_ ( i n c o m p l e t e  a f t e r 45 m i n u t e s ) o c c u r r e d ' ;  p r o d u c t and no c h a n g e on p u r g i n g w i t h a r g o n . 5a  caused  for PPh .  A slow  3  t h e r e was  no  Ru(III)  Addition of s o l i d TEA C1~ to +  l i t t l e r e a c t i o n i n i t i a l l y b u t a f t e r 10 m i n u t e s t h e s o l u t i o n  turned pink, the spectrum showing mainly r e d u c t i o n [Ru(0EP) '(C0)Cl] +  (l_c) b e i n g p r e s e n t .  w i t h o n l y 10 - 20%  of  A f t e r a f u r t h e r 20 m i n u t e s t h e r e  was c o m p l e t e r e d u c t i o n t o Ru(0EP)(.C0)Im (5_). 5.3  Reactions  of a Cation Radical Species in a Coordinating  In c o m p l e x e s s u c h as Ru(.0EP) ' ( C 0 ) p y +  in CH C1 2  2  ( 3 a ) and R u ( 0 E P ) " ( C 0 ) I m  the a x i a l l i g a n d trans to the carbonyl  e a s i l y d i s p l a c e d by an i n c o m i n g  ligand.  Solvent (5a)  +  i s s e e n t o be  fairly  However i n a c o o r d i n a t i n g  solvent  t h e r e w i l l be a c o m p e t i n g r e a c t i o n i n v o l v i n g t h e s u b s t i t u t i o n o f s o l v e n t molecules  at the metal  centre.  Hence,the chemistry of r e a c t i o n s  r e q u i r e c o o r d i n a t i o n o f an i n c o m i n g l i g a t i n g a b i l i t y of the solvent. (CO)MeCN i n MeCN was  prepared  l i g a n d may  that  be s t r o n g l y a f f e c t e d by t h e  To s t u d y t h e e f f e c t , a s a m p l e o f R u ( 0 E P )  and i t s r e a c t i v i t y i n t h i s s o l v e n t t o w a r d s a  +  -  185 v a r i e t y o f l i g a n d s was  investigated.  A l l t h e l i g a n d s , w h i c h on a d d i t i o n t o t h e f i v e - c o o r d i n a t e s p e c i e s (l_a) gave good samples o f r u t h e n i u m ( I I I ) , (CO)MeCN (,6a) i n MeCN. the i n t r a m o l e c u l a r  gave mixtures  when a d d e d t o R u ( 0 E P )  In g e n e r a l , t h e r e a p p e a r e d t o be c o m p e t i t i o n  between  e l e c t r o n t r a n s f e r l e a d i n g t o R u ( I I I ) and r e d u c t i o n , g e n e -  r a t i n g i n most cases the s t a r t i n g m a t e r i a l R u ^ ( 0 E P ) ( C 0 ) M e C N ( 6 ) . proportions  -  +  o f t h e two p r o d u c t s  obtained  depended upon the l i g a n d used  and w e r e s e n s i t i v e t o t h e amount o f l i g a n d a d d e d . PPhg g a v e t h e h i g h e s t p r o p o r t i o n  (80%)  Thus, the a d d i t i o n o f  o f R u ( I I I ) as p r o d u c t  t h e i n t e n s i t y o f t h e a b s o r p t i o n a t 810 nm c o r r e s p o n d i n g (22)) p r o v i d i n g a l a r g e excess of PPh  3  The  was  to  ( a s j u d g e d by Ru^^OEPHPPhg^*  a d d e d t o t h e s a m p l e o f 6a_ ( t y p i -4  c a l l y a few mg o f p h o s p h i n e a d d e d t o ^ 3 ^ mL o f a 10 MeCN).  M s o l u t i o n o f 6a_ i n  I f t h e p h o s p h i n e i s a d d e d s t o i c h i o m e t r i c a l l y as a s o l u t i o n i n C H p C l p  v i a a m i c r o l i t r e s y r i n g e , then l i t t l e ruthenium(III) t h e m a j o r r e a c t i o n b e i n g r e d u c t i o n t o g i v e 6_. e x c e s s o f PPh^  product  This suggests  i s r e q u i r e d to d i s p l a c e the coordinated  is  detected,  that a large  MeCN and t o p r o m o t e  intramolecular electron transfer. Excess P Bu2 gave a m i x t u r e o f products n  on a d d i t i o n t o 6a_.  About  o f t h e i n i t i a l c a t i o n r a d i c a l was r e d u c e d ( t o R u ^ ( O E P ) ( P ^ U g ^ (J) o f t h e e x c e s s p h o s p h i n e p r e s e n t ) , ^20%  gave a r u t h e n i u m ( l l l ) product  i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r , and t h e r e m a i n i n g (,A  max  ^600  nm).  Excess cyanide  30%  because via  50% f o r m e d g r e e n p i g m e n t s  gave i n s t a n t r e d u c t i o n to g e n e r a t e Ru(OEP)-  (C0)CN". The a b o v e r e a c t i o n s w i t h CN" and p h o s p h i n e s w e r e f a s t  (instantaneous  on m i x i n g ) , w h e r e a s a d d i t i o n o f A s P h ^ g a v e a s l o w r e a c t i o n ( t i m e >10 with the s o l u t i o n t u r n i n g g r a d u a l l y from purple to orange.  minutes)  The m a j o r r e a c t i o n  186 was  r e d u c t i o n , the p r o p o r t i o n of Ru(III) obtained  b e i n g v a r i a b l e (.0 - 3 0 % ) .  As i n t h e c a s e o f t h e o t h e r c a t i o n r a d i c a l s p e c i e s w i t h n e u t r a l l i g a n d s t r a n s t o t h e CO  (3a_  and •..5a),  l i t t l e t e n d e n c y t o be r e d u c e d  R u ( 0 E P ) ' ( C 0 ) M e C N (6a)  by m e t h a n o l (<3M)  6a_ was v e r y e f f e c t i v e l y r e d u c e d  showed  +  o r w a t e r (^6M).  However,  by T B A B r ~ o r T E A C 1 ~ w i t h o u t t h e +  formation  +  2  of a c a t i o n r a d i c a l i n the  A^  u  ground s t a t e , which c o n t r a s t s with  f o r m a t i o n o f lib and I r r e s p e c t i v e l y f r o m R u ( 0 E P ) *(CO) +  T E A I ~ a l s o q u a n t i t a t i v e l y reduced +  6a^ as e x p e c t e d .  ( l a ) . T B A B H " and +  4  Excess  i m i d a z o l e g a v e some r e d u c t i o n b u t t h e m a j o r p r o d u c t was  the  p y r i d i n e and  the p y r i d i n e  (3a)  or i m i d a z o l e (5a) form o f the c a t i o n r a d i c a l r e s p e c t i v e l y , showing t h a t t h e s e s t r o n g e r l i g a n d s e f f e c t i v e l y r e p l a c e d t h e c o o r d i n a t i n g MeCN ( s o l v e n t ) l i g a n d when p r e s e n t a t s u f f i c i e n t c o n c e n t r a t i o n . To f u r t h e r c o n f i r m t h a t t h e r e a c t i v i t y o f a c a t i o n r a d i c a l s p e c i e s is determined  by t h e e a s e o f d i s p l a c e m e n t  o f the l i g a n d t r a n s to the  CO  r a t h e r t h a n t h e e l e c t r o n i c p r o p e r t i e s o f t h i s l i g a n d , some R u ( O E P ) ( C O ) E t O H was. e l e c t r o l y s e d i n a C H C 1 2  2  s o l u t i o n c o n t a i n i n g 1% MeCN and 0.05M T B A P .  spectrum of the c a t i o n r a d i c a l obtained than  l_a  i s i d e n t i c a l to that of  s h o w i n g t h a t MeCN i s c o o r d i n a t e d .  6a_  The  rather  However, the r e a c t i o n s o f  s u c h s a m p l e s o f Ru(.0EP) '(C0)MeCN (,6a) w e r e v e r y d i f f e r e n t t o t h o s e i n p u r e +  MeCN r e p o r t e d a b o v e and w e r e a l m o s t coordinate species (Taj . ruthenium(III)  Thus P B u  bis-phosphine  i d e n t i c a l to the r e a c t i o n s of the  n  3  and P P h  3  gave the  corresponding  products with l i t t l e accompanying  reduction.  T r i p h e n y l a r s i n e gave c o n s i d e r a b l e r e d u c t i o n , but the r u t h e n i u m ( I I I ) f o r m e d c o u l d be r e v e r s i b l y r e c o n v e r t e d  five-  product  t o t h e c a t i o n r a d i c a l by t h e a d d i t i o n o f  187  CO a s i n t h e s t u d i e s on l a _ ( S e c t i o n 5 . 1 ) . C y a n i d e g a v e a m i x t u r e o f r e d u c t i o n and r u t h e n i u m ( I I I ) p r o d u c t s , w h i l e C l ~ gave a g r e e n i s h c o l o u r e d s o l u t i o n t h a t u n d e r w e n t r a p i d r e d u c t i o n (^30% i n 2 - 3 m i n u t e s ) t o R u ( O E P ) (CO)MeCN ( 6 ) .  5.4  Reactions o f Ligands with a Related Thiocarbonyl Cation Radical Ru(OEP) '(CS)py. +  The s u b s t i t u t i o n o f a CS l i g a n d f o r t h e CO o f t h e  Ru(0EP) '(C0)py +  (3a_) s p e c i e s was f o u n d t o m o d i f y o n l y s l i g h t l y t h e r e a c t i v i t y o f t h e c a t i o n radical.  T r i p h e n y l p h o s p h i n e a n d CN" b o t h e f f e c t i v e l y r e d u c e d t h e c a t i o n  r a d i c a l , w h i l e a d d i t i o n o f C l ~ gave a mixture o f Ru(0EP)(CS)py 2  and t h e  +• Ay • g r o u n d s t a t e s p e c i e s , [ R u ( O E P ) " ( C S ) C l ] , f o r m e d by d i s p l a c e m e n t o f t h e  p y r i d i n e by c h l o r i d e . T h e s e r e a c t i o n s a r e i d e n t i c a l t o t h o s e o b s e r v e d f o r the c o r r e s p o n d i n g c a r b o n y l complex ( 3 a ) . In c o n t r a s t . t h e a d d i t i o n o f P B u 2 t o R u ( 0 E P ) * ( C S ) p y n  +  gave a  d i f f e r e n t r e a c t i o n t o t h a t r e p o r t e d f o r 3a_ ( S e c t i o n 5.2b) w i t h Ru(III) and a high p r o p o r t i o n o f green products being formed.  little A similar  p r o d u c t m i x t u r e i s o b t a i n e d on a d d i n g P ^ u ^ t o R u ^ ( 0 E P ) ( C 0 ) p y (3a_) i n + -  t h e p r e s e n c e o f an e x c e s s o f p y r i d i n e (2 - 5 eq), and t h i s o b s e r v a t i o n suggests that the r e a c t i v i t y of Ru(0EP) '(CS)py +  i s similar to that of  Ru(0EP) '(C0)py, e x c e p t t h a t t h e p y r i d i n e l i g a n d i s s l i g h t l y more f i r m l y +  held i n t h e former complex.  T h i s may be r a t i o n a l i z e d b y c o n s i d e r i n g t h a t  t h e g r e a t e r T r - a c i d i t y o f CS c o m p a r e d w i t h C O  1  l e a d s t o a more e l e c t r o n  188  d e f i c i e n t m e t a l ! o p o r p h y r i n component t h a t c o o r d i n a t e s the e l e c t r o n d o n a t i n g p y r i d i n e l i g a n d more f i r m l y .  5.5  C o n c l u s i o n : - The R e a c t i v i t y o f C a t i o n R a d i c a l s t o w a r d s  Ligands  The p a t t e r n o f r e a c t i v i t y o f t h e c a t i o n r a d i c a l s w i t h l i g a n d s i s complex,  and i s n o t s u b j e c t t o a d e t a i l e d a n a l y s i s . H e n c e , t h e f o l l o w i n g  a t t e m p t t o a n a l y s e t h e c h e m i s t r y r e p o r t e d so f a r i n t h i s C h a p t e r m u s t be i n c o m p l e t e and c a n n o t e x p l a i n a l l t h e r e a c t i o n s . F o r i n s t a n c e ,  i t is  d i f f i c u l t t o r a t i o n a l i z e how t r i p h e n y l p h o s p h i n e c a n be t h e o n l y l i g a n d t o g i v e m a i n l y a, r u t h e n i u m ( I I I ) p r o d u c t on a d d i t i o n t o R u ( 0 E P ) ' ( C 0 ) I m +  and y e t t r i - n - b u t y l p h o s p h i n e g i v e s l a r g e l y r u t h e n i u m ( I I I ) when a d d e d Ru(0EP) '(C0)py +  (3aJ  w h i l e PPhg c a u s e s r e d u c t i o n .  (5a) to  A number o f t h e m e s do  emerge, however, from t h e s e r e a c t i o n s and one i s t h a t f o r a f i v e - c o o r d i n a t e c a t i o n r a d i c a l s e v e r a l r e a c t i o n s c a n o c c u r w i t h an a d d e d l i g a n d , a n d t h e p r o d u c t o f t h e r e a c t i o n i s d e t e r m i n e d by t h e n a t u r e o f t h i s i n c o m i n g P Bu3,PPh3, CN~-and"AsPh3,all n  ruthenium(III) product. with the  A-|  u  ligand.Thus,  .promote i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r t o f o r m a  The a n i o n s , C l ~ , B r ~ a n d SCN~,  yield cation radicals  g r o u n d s t a t e ( c h a r a c t e r i z e d by a s t r o n g v i s i b l e band a t 630  nm),  w h i l e MeCN, py a n d Im g i v e c o r r e s p o n d i n g s i x - c o o r d i n a t e f o r m s o f t h e c a t i o n r a d i c a l ( r e s p e c t i v e l y 6 a , 3a and  5a).  A l l t h e a b o v e r e a c t i o n s , w h i c h a r e r e a s o n a b l y c l e a n s t a r t i n g w i t h samp l e s o f .the c a t i o n r a d i c a l / [ a , , become p r o g r e s s i v e l y more m o d i f i e d as t h e s i x t h l i g a n d p o s i t i o n becomes m o r e e f f e c t i v e l y o b s t r u c t e d t o an i n c o m i n g l i g a n d . The s e n s i t i v i t y o f r e a c t i o n s t o t h e s e m o d i f i c a t i o n s ( m a i n l y r e d u c t i o n p a t h w a y s , a l t h o u g h a d i f f e r e n t m e c h a n i s m a p p e a r s t o be i n v o l v e d i n some o f t h e  189  P Bu n  3  reactions)  depends upon t h e n a t u r e o f t h e i n c o m i n g l i g a n d a n d t h e  ease o f s u b s t i t u t i o n o f t h e coordinated  ligand trans to the carbonyl.  Thus, C I " a d d i t i o n t o . a c a t i o n r a d i c a l i s extremely s e n s i t i v e t o t h e p r e s e n c e o f n e u t r a l c o o r d i n a t i n g l i g a n d s s u c h a s p y r i d i n e o r MeCN. 2 In c o n t r a s t t h e a d d i t i o n o f p y r i d i n e t o a s o l u t i o n o f a c o n t a i n i n g a n e u t r a l s i x t h l i g a n d ( e g - 6a)  cation radical  u s u a l l y has l i t t l e  ;  except possibly i n changing that s i x t h ligand.  effect  However, a d d i t i o n o f one  e q u i v a l e n t o f p y r i d i n e t o a s o l u t i o n o f l b _ o r l_c - i n w h i c h t h e s i x t h l i g a n d i s a c h a r g e d s p e c i e s a n d t h e c a t i o n r a d i c a l i s now a state, causes considerable  reduction.  These examples  ground  show t h a t t h e o r d e r  o f a d d i t i o n o f t h e l i g a n d s ( n e u t r a l l i g a n d s u c h a s p y r i d i n e o r MeCN, f o l l o w e d by an a n i o n such as C l ~ ; o r t h e a d d i t i o n o f t h e a n i o n t o g i v e a 2 A-^.-cation r a d i c a l followed  by a n e u t r a l l i g a n d s u c h a s p y r i d i n e )  does  n o t m a t t e r a l t h o u g h t h e q u a n t i t i e s o f l i g a n d a d d e d c a n be c r i t i c a l .  This  was n o t e d i n t h e a d d i t i o n o f e x c e s s c h l o r i d e t o a s o l u t i o n o f R u ( 0 E P ) ' ( C 0 ) p y +  (3a) i n CHpClp f o l l o w e d  by t h e a d d i t i o n o f m o r e p y r i d i n e ( S e c t i o n 5.2b) a n d  is also observed i n the reaction o f a s l i g h t excess o f P Bu n  3  t o 3a w h i c h  g i v e s a r u t h e n i u m ( I I I ) p r o d u c t , a l t h o u g h attempts t o mimic t h i s r e a c t i o n by adding s u f f i c i e n t p y r i d i n e t o Ru(0EP) *(CO) +  adding P Bu n  3  i n CH C1 2  2  t o form  3a  u s u a l l y resulted i n a green s o l u t i o n s i m i l a r to that  on a d d i t i o n o f P B u n  t o R u ( 0 E P ) ' ( C O ) M e C N i n MeCN. +  3  and then obtained  This i s presumably  b e c a u s e a n e x c e s s o f p y r i d i n e (more t h a n o n e e q u i v a l e n t ) was g e n e r a l l y  used  t o g e n e r a t e s p e c i e s 3a_ f r o m l_a_ a n d t h e a d d e d p h o s p h i n e c a n n o t t h e n c o m p e t e e f f e c t i v e l y f o r t h e metal s i t e and an a l t e r n a t i v e s i t e o f a t t a c k i s sought.  190  T h e r e c a n be c o n s i d e r e d metalloporphyrin  t o be t h r e e  "states" a v a i l a b l e for these  complexes d e p e n d i n g upon the p o s i t i o n o f the  " h o l e " , i . e . f r o m w h e r e an e l e c t r o n i s a b s e n t .  electron  I f the e l e c t r o n hole i s  a s s o c i a t e d with a metal o r b i t a l then the complex i s c o n s i d e r e d r u t h e n i u m ( H I ) s p e c i e s on t h e b a s i s o f i t s c h e m i s t r y . the porphyrin 2  t o be a  I f t h e h o l e i s on  l i g a n d t h e n a c a t i o n r a d i c a l r e s u l t s , w h i c h may  be o f a  2 ^lu  ^2u 9  or  molecular  r o u n c  ' s t a t e d e p e n d i n g u p o n w h i c h o f two d e g e n e r a t e  o r b i t a l s c o n t a i n the unpaired,  porphyrin  electron. Tr-cation  The e l e c t r o n t r a n s f e r t h a t o c c u r s when t h e p o r p h y r i n  r a d i c a l c h a n g e s g r o u n d s t a t e ( i . e . l_a + T B A B r ~ o r ]b_ + A g B F ^ ) c a n  also  +  be c o n s i d e r e d  an i n t r a m o l e c u l a r  e l e c t r o n t r a n s f e r , but o f a m o r e l o c a l i z e d  n a t u r e t h a n t h e m e t a l t o l i g a n d t r a n s f e r s e e n , f o r e x a m p l e , on a d d i n g P B u 2 t o \a_. n  The  state or e l e c t r o n i c c o n f i g u r a t i o n of the  c o m p l e x e s i s d e t e r m i n e d by t h e a x i a l l i g a n d s . the formation  A carbonyl  porphyrin ligand  prohibits  o f t h e R u ( I I I ) s t a t e and f o r c e s t h e c o m p l e x i n t o one o f  cation radical states.  L i g a n d s s u c h as CN",  the  P B u , PPh-^and A s P l ^ s t a b i l i z e n  3  p  the ruthenium(.III) s t a t e ;  C l ~ , Br  and SCN~  generate the  A-j  u  cation  r a d i c a l s t a t e and t h e n e u t r a l l i g a n d s s u c h as p y r i d i n e , i m i d a z o l e , MeCN and THF state.  ( o r no c o o r d i n a t e d  When a new  s p e c i e s , and  l i g a n d at a l l , e.g. l a ) give the  l i g a n d i s added to a s i x - c o o r d i n a t e  A2  u  ground  cation radical  i s expected to cause a change in the p o s i t i o n o f the  i n t h e c o m p l e x , t h e n two c o m p e t i n g r e a c t i o n s a r e s e e n t o o c c u r . is. s u c c e s s f u l  methanol,  l i g a n d e x c h a n g e with, t h e a c c o m p a n y i n g change, i n t h e  electron The  first  electronic  191  configuration or state o f t h e molecule. w i l l probably  The o v e r a l l speed o f t h i s r e a c t i o n  be d e t e r m i n e d b y t h e r a t e o f c o o r d i n a t i o n o f t h e new l i g a n d  and w i l l be i n f l u e n c e d b y t h e c o m p e t i t i v e molecules present  e f f e c t s from other l i g a t i n g  ( e . g . p y i n 3a_ o r MeCN i n 6a_).  The second r e a c t i o n  o c c u r s when t h e c a t i o n r a d i c a l m o l e c u l e f a i l s t o c h a n g e s t a t e s , d u e t o t h e l a c k o f c o o r d i n a t i o n o f t h e r e q u i s i t e l i g a n d t o s t a b i l i z e t h e new s t a t e , and t h e c o m p l e x t h e n becomes d e s t a b i l i z e d , g e n e r a l l y g i v i n g When P B u  reduction.  i s i n v o l v e d i n such a r e a c t i o n , green complexes a r e formed  n  3  r a t h e r than reduced products,  a n d t h i s r e a c t i o n may be s p e c i f i c t o t h i s  l i g a n d ( T a b l e 5 . 1 ) . T h e p o s s i b l e r e d u c t i o n m e c h a n i s m s w i l l be d i s c u s s e d i n more d e t a i l i n S e c t i o n 5.6. If t h e incoming ligand,when coordinated,  does n o t cause a change  i n s t a t e o f t h e complex (as seen i n t h e a d d i t i o n o f i m i d a z o l e o r p y r i d i n e t o R u ( 0 E P ) (.C0)MeCN i n 1% MeCN), t h e n t h e c o m p l e x shows l i t t l e t e n d e n c y + -  to reduce and, i n t h e above case, i f s u f f i c i e n t l i g a n d i s a v a i l a b l e , a new c a t i o n r a d i c a l s p e c i e s o f t h e same g r o u n d s t a t e i s o b t a i n e d o r 3a_ i s f o r m e d r e s p e c t i v e l y f r o m 6a i n t h e e x a m p l e a b o v e ) .  (e.g..5a  Hence,the  r e d u c t i o n m e c h a n i s m i s t r i g g e r e d by t h e a d d i t i o n o f a l i g a n d ( w h i c h i f i t i s successfully coordinated  t o t h e ruthenium porphyrin c a t i o n r a d i c a l complex  would cause a change i n s t a t e o f t h e m o l e c u l e v i a an i n t r a m o l e c u l a r transfer) to a six-coordinate cation radical species. PPh  3  or AsPh  j u d g e d by  electron  Thus,the addition o f  t o [ R u ( 0 E P ) ' ( C 0 ) B r ] ( 1 b ) , g i v e s t h e same p r o d u c t m i x t u r e ( a s +  3  u-.v . - ' / v i s i b l e s p e c t r a ) a s p y r i d i n e a d d e d t o l_b, o r c h l o r i d e  192  a n i o n s a d d e d t o Ru(.0EP) '(C0)MeCN (.6a) i n MeCN. +  Further evidence that  t h e s e r u t h e n i u m c a t i o n r a d i c a l s p e c i e s a r e d e s t a b i l i z e d when p r e s e n t i n s o l u t i o n w i t h two l i g a t i n g s p e c i e s ( e . g . py and C l ~ ) t h a t f a v o u r c o m p e t i n g g r o u n d s t a t e s i s s e e n by c o m p a r i n g t h e s t a b i l i t y o f [ R u ( 0 E P ) " ( C O ) C I ] +  (l_c),  p r e p a r e d i n t h e p r e s e n c e and a b s e n c e o f a c o o r d i n a t i n g n e u t r a l l i g a n d s u c h as p y r i d i n e . Complex  ,lc_ p r e p a r e d f r o m l_a i s s t a b l e ( o n l y a few  p e r c e n t o f r e d u c t i o n i n s e v e r a l h o u r s ) , b u t a t t e m p t s t o p r e p a r e l_c_ by a d d i n g T E A C 1 " t o R u ( 0 E P ) '(.C0)py ( 3 a ) g i v e s an a p p a r e n t 50/50 m i x t u r e +  +  ( a s j u d g e d f r o m t h e o p t i c a l s p e c t r a ) o f ]c_ and Ru(.OEP) ( C O ) p y ( 3 ) .  The  [ R u ( O E P ) " " ( C 0 ) C 1 ] ( l c ) p r e p a r e d by t h e l a t t e r m e t h o d i s v e r y u n s t a b l e and 1  r a p i d l y r e d u c e s (>30% i n 10 m i n u t e s ) t o R u ( 0 E P ) ( C 0 )  (.]_) ( w h i c h  coordinates the p y r i d i n e present i n s o l u t i o n to give 3 ) .  immediately  Thus,the  presence  of the p y r i d i n e i n solution e f f e c t i v e l y d e s t a b i l i z e s the c a t i o n radical s t a t e with r e s p e c t to the reduced carbonyl complex. examples  Numerous o t h e r  h a v e been n o t e d i n t h e p r e c e e d i n g s e c t i o n s ( s e e S e c t i o n s 5.2  and  5.3) and i n t h e C h a p t e r on t h e f o r m a t i o n o f t h e c a t i o n r a d i c a l s ( s e e Section  4.2).  5.6.  The R e d u c t i o n R e a c t i o n  5.6a  P o s s i b l e Mechanisms f o r the Reduction R e a c t i o n As j u d g e d by o p t i c a l s p e c t r a , t h e m a i n r e a c t i o n when t h e c a t i o n  r a d i c a l s p e c i e s i s d e s t a b i l i z e d as d e s c r i b e d a b o v e ( S e c t i o n 5.5) i s r e d u c t i o n ( F i g u r e 5.11).  The r e d u c e d p r o d u c t shows s u c h s t r o n g a b s o r p t i o n s  193  F i g u r e 5.11  O p t i c a l s p e c t r a i l l u s t r a t i n g t h e e v i d e n c e f o r r e d u c t i o n on a d d i n g e x c e s s T E A C 1 " t o R u ( 0 E P ) - ( C 0 ) p y ( 3 a ) . T h e s p e c t r u m .of t h e c a t i o n r a d i c a l 3a^ ( ), the e f f e c t o f adding excess TEA C1" ( ) d t h e f i n a l p r o d u c t s p e c t r u m on t h e a d d i t i o n o f o n e drop o f p y r i d i n e ( ) . T h e a b s o r p t i o n a t ^ 6 3 0 nm i n t h e s e c o n d s p e c t r u m i s due t o [Ru(.0EP) - ( C 0 ) C l ] ( l _ c ) . T h e p r o p o r t i o n o f l_c r e c o r d e d here i s ^25% o f t h e t o t a l p o r p h y r i n , t h e low v a l u e obs e r v e d b e i n g due t o t h e f a s t r a t e o f r e d u c t i o n o f l_c i n t h e p r e s e n c e o f p y r i d i n e , a n d some d e l a y b e f o r e r e c o r d i n g t h e s p e c t r u m . +  +  +  s  a n  +  194  in the v i s i b l e t h a t the presence o f a reduced  s p e c i e s ( i . e . 1_ o r 3)  w o u l d mask t h e a b s o r p t i o n s o f o t h e r p r o d u c t s .  Besides the possible  p r e s e n c e o f s p e c i e s a b s o r b i n g i n t h e 500 t o 550 nm r a n g e , c l o s e  examination  o f a p p r o p r i a t e s p e c t r a showed t h e f o r m a t i o n o f some m a t e r i a l s w e a k l y a b s o r b i n g i n t h e 570 - 630 nm r a n g e w h i c h w e r e s i m i l a r t o c o m p l e x e s formed i n t h e atmospheric  o x i d a t i o n o f 1_.  r a d i c a l r e q u i r e s t h a t something  Reduction o f the c a t i o n  i s being o x i d i z e d .  In most c a s e s , t h e  p o s s i b i l i t y o f r e d u c i n g i m p u r i t i e s i n t h e a d d e d l i g a n d c a n be d i s c o u n t e d , a s l i g a n d a d d e d t o l e s s t h a n one e q u i v a l e n t r e d u c e s a l l t h e o r i g i n a l c a t i o n r a d i c a l s p e c i e s w h i l e t h e same a m o u n t o f l i g a n d a d d e d t o a s o l u t i o n o f R u t 0 E P ) ' ( . C 0 ) 0 a ) c a u s e s a l m o s t no r e d u c t i o n ( < 2 % ) .  The p o s s i b i l i t y  +  t h a t t h e l i g a n d i t s e l f i s t h e r e d u c i n g a g e n t seems v e r y u n l i k e l y c o n s i d e r i n g t h e r a n g e o f l i g a n d s f o u n d t o be e f f e c t i v e : P P h , p y , C l ~ a n d MeCN, 3  none o f which a r e e a s i l y o x i d i z e d . C o n s i d e r a t i o n i l o f p o s s i b l e mechanisms r e p o r t e d f o r t h e r e a c t i o n s o f p o r p h y r i n i r - c a t i o n r a d i c a l s w i t h l i g a n d s t h r o w s some l i g h t on t h e s e reactions.  One r e p o r t d e s c r i b e s n u c l e o p h i l i c a t t a c k a t p o r p h y r i n i r - c a t i o n  r a d i c a l s by l i g a n d s s u c h a s PPhg a n d p y r i d i n e t o g i v e a 50/50 m i x t u r e o f g  a r i n g s u b s t i t u t e d p o r p h y r i n s p e c i e s and t h e reduced c a t i o n r a d i c a l ( E q u a t i o n 5 . 5 ) . A r a n g e o f s p e c i e s , s i m i l a r t o t h a t s e e n i n F i g u r e 5.12, was o b t a i n e d by u s i n g s u i t a b l e n u c l e o p h i l i c l i g a n d s ( e . g . P P h , S b P h ^ a n d 3  2 Z n T P P ' : C 1 0 ~ + py +  » ZnTPP + I Z n ( T P P - p y ) J C 1 0 " + H C 1 0 +  4  4  (5.5)  195  Ph  CIO.  Ph.  F i g u r e 5.12  4  The p r o d u c t , r e p o r t e d by Shine and c o w o r k e r s , o f t h e r e a c t i o n o f p y r i d i n e w i t h .the c a t i o n r a d i c a l s p e c i e s [ Z n T P P ] C 1 0 4 , ( m o d i f i e d from R e f . 8 ) . + -  SCN~) . O t h e r w o r k e r s  +  _  h a v e s t u d i e d s i m i l a r r e a c t i o n s w i t h MgOEP ' a n d  r e p o r t t h a t the n u c l e o p h i l i c group attacked a t t h e meso-position  rather  t h a n t h e 3 - p y r r o l i c p o s i t i o n s e e n i n TPP c o m p l e x e s . Another p o s s i b l e mechanism i n v o l v e s a d i s p r o p o r t i o n a t e o f the c a t i o n r a d i c a l t o give the reduced  reaction  p r e c u r s o r and a d i c a t i o n  g  species  , t h a t w o u l d be e x t r e m e l y  r e a c t i v e towards n u c l e o p h i l e s .  Dispro-  p o r t i o n a t i o n r e a c t i o n s o f t h e a n i o n r a d i c a l o f some s u b s t i t u t e d TPP comp l e x e s h a v e been s t u d i e d by c y c l i c v o l t a m m e t r y . 1 0  I t s h o u l d be n o t e d  that  in t h e i r s t u d i e s o f the r e a c t i o n o f n u c l e o p h i l e s with t h e ZnTPP * c a t i o n +  g  r a d i c a l , Shine e t a l  f o u n d an a n o m a l o u s r e a c t i o n o n a d d i n g m e t h a n o l a n d  196  obtained a roughly equal mixture ( F i g u r e 5.13).  No r e a c t i o n was  o f Z n T P P and z i n c  methoxyisoporphyrin  expected,as previous authors  t h a t methanol d i d not r e a c t with monocation s p e c i e s ' 1 1  had been u s e d  by s e v e r a l w o r k e r s  had  reported  and,indeed,methanol  1 2  as t h e s o l v e n t f o r c a t i o n r a d i c a l  nucleo-  9  p h i 1e s t u d i e s  .  The l a c k o f r e a c t i v i t y t o w a r d s m e t h a n o l had l e d t o  the  conclusion that the r e a c t i o n of a n u c l e o p h i l e with a c a t i o n r a d i c a l  did  n o t go v i a a d i s p r o p o r t i o n a t e m e c h a n i s m , s i n c e d i c a t i o n s w e r e known t o r e a c t r e a d i l y w i t h m e t h a n o l a n d o t h e r n u c l e o p h i l e s t o g i v e an  isoporphyrin 1 3  ( d i s t i n g u i s h e d by s t r o n g a b s o r b a n c e s a t 790 and 850 nm) p l e x , or a methoxy s u b s t i t u t e d porphyrin a proton from the isoporphyrinL,and  w i t h , an O E P  1 4  w i t h a TPP  c o m p l e x Cvla l o s s o f  n e i t h e r o f thes.e p r o d u c t s  S h i n e a n d c o w o r k e r s c o u l d o f f e r no e x p l a n a t i o n  r a t h e r than the 3-pyrrole p o s i t i o n .  were  observed.  f o r the anomalous  r e a c t i v i t y o f ZnTPP ' towards methanol, e s p e c i a l l y at the +  com-  meso-position  It is possible that this reaction  p r o c e e d s v i a d i s p r o p o r t i o n a t i o n t o a 50/50 m i x t u r e  of the parent  (ZnTPP)  and t h e d i c a t i o n , w h i c h t h e n f o r m e d t h e i s o p o r p h y r i n i n t h e u s u a l A l l r e a c t i o n s g i v i n g n u c l e o p h i l i c a t t a c k a t the porphyrin r i n g  way.  could  p o s s i b l y go v i a a s i m i l a r d i s p r o p o r t i o n a t i o n / i s o p o r p h y r i n m e c h a n i s m .  This  g  has b e e n c o n s i d e r e d above, although confuses  and d i s c a r d e d by some a u t h o r s  for the reasons  t h e a n o m a l o u s r e a c t i o n w i t h m e t h a n o l r e p o r t e d by  the i s s u e .  mentioned Shine  The d i s p r o p o r t i o n a t i o n m e c h a n i s m c o u l d be i n v o l v e d i n  the r e a c t i o n s o f the ruthenium porphyrin complexes.  A complicating  i s t h a t f o r OEP c o m p l e x e s , a d i c a t i o n r e a c t s w i t h a n o n o x i d i z a b l e  factor nucleophile  197 + Ph  >-Ph  Ph  OMe  F i g u r e 5.13  CIO. 4  Ph  Zinc m e t h o x y i s o p o r p h y r i n , ( m o d i f i e d from Ref.  to give a m e s o - s u b s t i t u t e d  porphyrin  1 5  .  be p r e d i c t e d to give the same p r o d u c t s .  8).  T h e r e f o r e , e i t h e r mechanism would However, i n most of the r e a c t i o n s  the r e d u c t i o n p o t e n t i a l of the d i c a t i o n produced would probably be higher than the o x i d a t i o n p o t e n t i a l o f the a n i o n i c s p e c i e s o f the n u c l e o p h i l i c l i g a n d . i n most cases by one of the  p r e s e n t ( o f t e n CI")  or  Hence the d i c a t i o n c o u l d be reduced d i r e c t l y ligands.  The experimental s t u d i e s  i n t o the mechanism o f the r e d u c t i o n seen  in many r e a c t i o n s with the ruthenium c a t i o n r a d i c a l s w i l l  be d e s c r i b e d  below ( S e c t i o n 5 . 6 b ) , and the data summarized and compared with the above results  from the l i t e r a t u r e .  198  Experimental  , 5.6b'|  Studies of the Reduction  Reaction  S e v e r a l r e a c t i o n s w e r e s t u d i e d : a) [ R u ( 0 E P ) ' ( C 0 ) B r ]  (lb) + PPh  +  i n C H C 1 , b) Ru(OEP)" " (C0)MeCN ( 6 a ) 1  2  2  + C I " i n MeCN, and c )  3  Ru(0EP) *(C0)+  py ( 3 a ) + C I " i n C H C 1 . 2  2  A l l these r e a c t i o n s gave t o t a l l o s s o f the usual c a t i o n r a d i c a l p e a k s and a s p e c t r u m  d o m i n a t e d by p e a k s a t ^520 and 550 nm a s s o c i a t e d w i t h  r e d u c t i o n t o t h e p a r e n t Ru(.II) c a r b o n y l compounds ( F i g u r e 5 . 1 1 ) .  The  r e a c t i o n s w e r e f a s t , e v e n when 20 o r 40 mg s a m p l e s o f p o r p h y r i n w e r e u s e d (.^10  M solutions). R e a c t i o n a) r e q u i r e s o n l y h a l f an e q u i v a l e n t o f P P h  3  to  reduce  a l l t h e c a t i o n r a d i c a l . L e s s t h a n two e q u i v a l e n t s o f t h e a d d e d l i g a n d w e r e r e q u i r e d f o r c o m p l e t e - r e d u c t i o n i n r e a c t i o n b-)..  For system c). a d d t t i o n  o f 2 e q u i v a l e n t s o f T E A C 1 " g a v e . a m i x t u r e o f [ R u ( 0 E P ) ' ( C 0 ) C l ] (l_c) +  and t h e r e d u c e d  +  s p e c i e s -Ru(;0EP)XC0).py' C3)..  An e x t r a e q u i v a l e n t o f  p y r i d i n e was: t h e n a d d e d t o e n s u r e c o m p l e t e r e d u c t i o n . C h r o m a t o g r a p h y o f t h e r e a c t i o n p r o d u c t s on an a l u m i n a  column gene-  r a l l y g a v e an i n t e n s e p i n k m o b i l e band w h i c h had an o p t i c a l s p e c t r u m of a Ru  1 1  (0EP)(.C0)L  species.  typical  Some g r e e n m a t e r i a l , u s u a l l y l e f t a t t h e t o p  o f t h e c o l u m n , c o u l d be e l u t e d o f f i n p u r e i s o p r o p a n o l ; were s p e c t r a l l y s i m i l a r t o t h o s e r e m a i n i n g  the green  compounds  on a c o l u m n u s e d t o p u r i f y  R u ( O E P ) ( C O ) E t O H d u r i n g i t s p r e p a r a t i o n (..see I n t r o d u c t i o n t o t h i s  Chapter).  No o t h e r s i g n i f i c a n t b a n d s w e r e s e e n , a l t h o u g h f o r r e a c t i o n b) a weak o r a n g e band ( c o n t a i n i n g ^ 1 0 % o f t h e p o r p h y r i n , and i n f r o n t o f t h e m a i n p i n k b a n d ) g a v e an o p t i c a l s p e c t r u m  w i t h two r o u g h l y e q u a l a b s o r p t i o n s i n t h e  199  v i s i b l e a t 525 a n d 550 nm;  an i s o l a t e d s o l i d g a v e a m a s s - s p e c t r u m  ( p e a k s a t m/e 669 a n d 7 0 6 ) c o n s i s t e n t w i t h t h e f o r m a t i o n o f a d i c h l o r o substituted porphyrin.  A s i m i l a r e x p e r i m e n t a l t r e a t m e n t f o r r e a c t i o n a)  g a v e no o t h e r m o b i l e bands e x c e p t t h e d e e p p i n k b a n d ; t h e m a s s - s p e c t r u m o f t h e i s o l a t e d s o l i d showed c o n c l u s i v e l y t h e a b s e n c e o f a p h o s p h i n e - o r bromide- s u b s t i t u t e d p o r p h y r i n . R e a c t i o n c ) was s t u d i e d i n a s i m i l a r f a s h i o n .  A f t e r chromatography  on a l u m i n a , t h e m a i n band e l u t e d o f f w i t h C ^ C ^ was r e c h r o m a t o g r a p h e d a n d a n a l y s e d by  nmr  a n d , a l t h o u g h t h e s a m p l e was i m p u r e , t h e m a j o r  p r o t o n r e s o n a n c e s were a t p o s i t i o n s i d e n t i c a l t o t h o s e o b t a i n e d f o r a sample o f Ru(OEP)(C0)py ( S e c t i o n 2 . 5 ) . S l i g h t l y over 40% o f t h e o r i g i n a l m e t a l l o p o r p h y r i n e n d e d up i n t h i s r e d u c e d f o r m , w h i c h i s r e a s o n a b l y c o n s i s t e n t with e i t h e r o f t h e mechanisms suggested i n the l a s t s e c t i o n .  The r e m a i n i n g  c a t i o n r a d i c a l p r e s u m a b l y ends u p i n t h e g r e e n p o l a r b a n d s a t t h e t o p o f t h e column (no o t h e r bands were v i s i b l e ) .  These green coloured m a t e r i a l s  show a s e r i e s o f p o o r l y d e f i n e d p e a k s b e t w e e n 500 a n d 700 nm ( F i g u r e 5 . 1 4 ) . C o n s i d e r a t i o n o f t h e c h r o m a t o g r a p h y d a t a r e p o r t e d by S h i n e e t a l s u g g e s t s - t h a t , i f an a n i o n i c n u c l e o p h i l e i s s u b s t i t u t e d i n t o t h e p o r p h y r i n r i n g ( e . g . r e a c t i o n o f ZnTPP  w i t h SCN ) , t h e s p e c i e s w i l l h a v e a p p r o x i m a t e l y  t h e same p o l a r i t y a s t h e r e d u c e d p o r p h y r i n c o m p l e x a n d may w e l l come o f f t h e c o l u m n i n t h e same f r a c t i o n .  The v i s i b l e spectrum o f such a s u b s t i t u t e d  p o r p h y r i n w o u l d a p p e a r t o be o n l y s l i g h t l y m o d i f i e d f r o m t h a t o f t h e r e d u c e d species fied).  ( n o new p e a k s , b u t t h e i n t e n s i t i e s o f t h e e x i s t i n g p e a k s a r e m o d i S u c h c o n c l u s i o n s a r e s u p p o r t e d t o some e x t e n t by t h e d a t a f o r t h e  200  1.0n  F i g u r e 5.14  T h e o p t i c a l s p e c t r u m o f t h e d i f f u s e g r e e n bands e l u t e d o f f an alumina column used t o p u r i f y t h e products o f the r e a c t i o n o f R u ( 0 E P ) -(.C0)py (3a_) w i t h e x c e s s T E A C 1 " . T h e weak p e a k a t ^548 nm i s due t o a t r a c e o f Ru ( 0 E P ) ( C 0 ) p y . +  +  n  201  small p r o p o r t i o n o f d i c h l o r o - s u b s t i t u t e d p o r p h y r i n o b t a i n e d from r e a c t i o n b).  I f t h e p o r p h y r i n i s s u b s t i t u t e d by a n e u t r a l l i g a n d , t h e r e s u l t i n g  c o m p l e x i s c h a r g e d , h e n c e m o d e r a t e l y p o l a r , and w o u l d be w e l l s e p a r a t e d f r o m t h e r e d u c e d p a r e n t on a c o l u m n ( e . g . r e a c t i o n o f ZnTPP  + py) .  The s p e c t r a o f t h e s e s p e c i e s a p p e a r  t o be m o r e e x t e n s i v e l y m o d i f i e d and  g i v e f o r e x a m p l e , w i t h ZnTPP s y s t e m s  , r e d - s h i f t e d main peaks w i t h t h e  two v e r y weak a b s o r p t i o n s o f ZnTPP  (611 and 684 nm) s h o w i n g  considerable  e n h a n c e m e n t , i n some c a s e s b e c o m i n g m o r e i n t e n s e t h a n t h e p r i n c i p a l absorption.  For Zn(OEP)  the m o d i f i c a t i o n o f the spectrum i s r a t h e r less  t h a n t h a t f o r t h e TPP c o m p l e x : ZnOEP X max  but s t i l l  - ( Z n ( 0 E P - m e s o py) \  400, 530 and 570 nm).  t y p e Ru(OEP)(|C0)L  visible  Hence,such 1  v  406, 537 and 572  nm;  a s u b s t i t u t e d complex o f the r  (assuming s i m i l a r b e h a v i o u r ) would l e a d to r e d - s h i f t e d  i n t e n s e bands.  S u c h an a r g u m e n t s u g g e s t s t h a t t h e g r e e n m a t e r i a l s  are not meso-substituted porphyrins. In c o n c l u s i o n , l i t t l e m e s o - s u b s t i t u t e d p o r p h y r i n i s f o r m e d d u r i n g t h e s e r e d u c t i o n r e a c t i o n s . Where some m e s o - s u b s t i t u t e d p r o d u c t s a r e o b t a i n e d , t h e q u a n t i t y s u g g e s t s t h a t t h e y a r e p r e s e n t as a r e s u l t o f a s i d e r e a c t i o n r a t h e r t h a n b e i n g t h e p r o d u c t o f t h e main r e a c t i o n . The mechanism o f t h e r e d u c t i o n r e a c t i o n s i s s t i l l o b s c u r e , a l t h o u g h some e v i d e n c e s u g g e s t s a d i s p r o p o r t i o n a t i o n mechanism w i t h the d i c a t i o n produced undergoing r e d u c t i o n ( b y a n i o n s , o t h e r l i g a n d s , s o l v e n t o r e v e n i m p u r i t y ) and some d e g r a d a t i o n at t h e p o r p h y r i n l i g a n d .  202  REFERENCES - CHAPTER 5  1.  P.D, S m i t h , D, Dolphin,and B.R. 239 ( 1 9 8 1 ) .  2.  A . G . S h a r p e , 'The C h e m i s t r y o f Cyano Complexes o f t h e T r a n s i t i o n M e t a l s ' , Academic P r e s s , London, 1976, p. 9.  3.  F.A. Cotton and G. W i l k i n s o n , 'Advanced I n o r g a n i c W i l e y , New York, 1980, Chap. 3.  4.  D.V. S t y n e s , H.C. S t y n e s , B.R. Soc. 95, 1796 0 9 7 3 ) .  5.  L.M. E p s t e i n , D.K. (19,67).  6.  G.R. Eaton and S.S.  E a t o n , J . Am. Chem. Soc. 97, 236  7.  T. L e u n g ,  communication.  8.  H . J . S h i n e , A.G. P a d i l l a , a n d S.-M.  9.  B. Evans and K.M. S m i t h ,  Personal  James, J , Organomet. Chem. 208,  Chemistry", 4th Ed.,  James, and J . A . I b e r s , J . Am. Chem.  S t r a u b , and C. M a r i c o n d i , I n o r g . Chem. 6, (1975).  Wu, J . Org. Chem. 44, 4069  T e t r a h e d r o n L e t t . 35, 3079  N e r i and G.S. W i l s o n , A n a l . Chem. 4 5 , 442  1720  (1979).  (1977).  10.  B.P.  (1973).  11.  D. D o l p h i n and R.H. F e l t o n , A c c . Chem. Res. _7, 26 (1 9 7 4 ) .  12.  G.H. B a r n e t t and K.M. S m i t h , J . Chem. Soc. Chem. Comm. (1976)  13.  D. D o l p h i n , R.H. F e l t o n , D.C. Borg,and 743 ( 1 9 7 0 ) .  14.  D. D o l p h i n , D.J. H a l k o , F.C. Johnson,and K. Rousseau i n ' P o r p h y r i n C h e m i s t r y Advances' (F.R. Longer e d 1 ) , Ann,. Arbor S c i e n c e , 1979, pp. 119-141.  15.  E.C. Johnson and D. D o l p h i n , Tetrahedron L e t t . 26, 2197  236.  J . F a j e r , J . Am. Chem. Soc. 92^,  (1976).  203  CHAPTER 6  AN ANOMALOUS OXIDATION OF R u ( O E P ) ( C O ) L COMPLEXES ( L = P B u ^ >. n  P P h , and A s P h ) : 3  THE MECHANISM OF INTRAMOLECULAR ELECTRON TRANSFER ( I M E T )  ?  l  As s e e n i n C h a p t e r cal  4, and f i r s t r e p o r t e d by Brown e t a l ., t h e  electrochemi-  o x i d a t i o n o f c o m p l e x e s o f t h e t y p e R u * * ( O E P ) ( C 0 ) L ( L = py, Im, E t O H , and  MeCN) o c c u r r e d a t a r e l a t i v e l y h i g h p o t e n t i a l ( c o m p a r e d t o t h a t e x p e c t e d metal  for  o x i d a t i o n R u ( I I ) ^ R u ( I I I ) ) , and was r e v e r s i b l e on t h e t i m e s c a l e o f  c y c l i c voltammetry.  The o x i d a t i o n p r o d u c t was  shown t o be a  porphyrin  Tr-cation r a d i c a l . However, c y c l i c voltammograms o f o t h e r compounds [Ru (0EP)(C0)L, n  L = P Bu , PPh 3  Elucidation of this chemistry r e a c t i o n s discussed in Chapter 6.1  and A s P h ] showed f a r m o r e c o m p l e x  n  3  3  chemistry.  suggests a mechanism f o r the e l e c t r o n t r a n s f e r 5.  The E l e c t r o c h e m i s t r y o f R u ( 0 E P ) ( C 0 ) P B u H  n  3  (8)  C y c l i c v o l t a m m e t r y o f an a n a l y t i c a l l y p u r e s a m p l e o f t h i s c o m p l e x (8_) i n 0.05M TBAP i n C H g C l » a n o n - c o o r d i n a t i n g 2  p e a k s as e x p e c t e d  a t ^+0.64V and +1.14V.  peak c o r r e s p o n d i n g  s o l v e n t , showed two  The r e d u c t i o n sweep showed a  t o t h e o x i d a t i o n peak a t +1.14V a n d o f v e r y s i m i l a r  i n t e n s i t y , suggesting that the oxidation/reduction (see S e c t i o n 2.2).  p r o c e s s was r e v e r s i b l e  However, t h e r e d u c t i o n peak c o r r e s p o n d i n g  o x i d a t i o n p e a k ( a t ^+0.64V) was much l e s s i n t e n s e and was new wave a t +0.2V ( F i g u r e 6.1a; o f R u ( 0 E P ) ( C 0 ) (X)).  oxidation  c o m p a r e F i g u r e 4.1  to the  first  f o l l o w e d by a  f o r the voltammogram  The o x i d a t i o n p o t e n t i a l o f t h e f i r s t wave i s c o n s i s -  tent with the formation of a porphyrin Tr-cation r a d i c a l , a s the p o t e n t i a l  205  r e q u i r e d (>+0.6V) i s h i g h e r t h a n t h a t e x p e c t e d metal (see S e c t i o n 7.1). c h a n g e t o a new  for oxidation at  the  This cation r a d i c a l species appears to p a r t i a l l y  s p e c i e s ( A ) , w h i c h shows a r e d u c t i o n a t +0.2V t h a t i s  t y p i c a l o f a R u ( I I I ) -»- R u ( I I ) p r o c e s s .  This suggests  that product A  has  b e e n f o r m e d by i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r f r o m t h e m e t a l t o t h e p o r p h y r i n , c o n v e r t i n g the ruthenium(II)  iT-cation radical into a  Ru(III)  porphyrin. A l t e r i n g t h e sweep r a t e o f t h e c y c l i c v o l t a m m o g r a m f r o m 50 mV/sec through  t o 5 V / s e c seemed t o h a v e l i t t l e e f f e c t on t h e r e l a t i v e i n t e n s i t i e s  o f t h e r e d u c t i o n p e a k s a t M-0.54 and +0.2V, s u g g e s t i n g o f A was  that the  formation  n o t a k i n e t i c phenomenon and t h a t an e q u i l i b r i u m m i x t u r e +  II  and t h e p o r p h y r i n i T - c a t i o n r a d i c a l s p e c i e s Ru e s t a b l i s h e d immediately tammogram).  (OEP)  of A  n  t.C0)P B u  3  (8aJ  was  ( w i t h r e s p e c t t o t h e t i m e s c a l e o f t h e c y c l i c voH.>.  R e p e a t e d s w e e p s f r o m -0.2  c o n c e n t r a t i o n o f A, and t h e p r e s e n c e  t o +1.6V  showed no b u i l d - u p i n t h e  o f an o x i d a t i o n p e a k a t ^+0.28V showed  t h a t s p e c i e s A had a r e v e r s i b l e o x i d a t i o n w i t h E M - Q 24V ( F i g u r e 6 . 1 b ) . x  H o w e v e r , i f A was  formed ' i n s t a n t a n e o u s l y '  (8a_), t h e n two o x i d a t i o n p e a k s w o u l d be e x p e c t e d t w e e n +1.0  and +1.6V  v i a the i r - c a t i o n r a d i c a l at higher potentials  , one f o r t h e s e c o n d o x i d a t i o n o f 8a_ and one f o r a  h i g h e r o x i d a t i o n o f A, i n s t e a d o f t h e s i n g l e s y m m e t r i c a l  peak seen i n  F i g u r e s 6.1a  i s t h a t A_ and  a n d b.  Two  explanations  are possible.  One  h a v e s e c o n d o x i d a t i o n waves a t t h e same p o t e n t i a l w h i l e t h e products product  be-  are non-identical.  8a_  oxidation  The a l t e r n a t i v e i s t h a t t h e s e c o n d o x i d a t i o n  f o r m e d f r o m b o t h t h e s e c o m p o u n d s i s t h e same and  hence the  second  206  o x i d a t i o n p o t e n t i a l s a r e i d e n t i c a l . Experiments r e p o r t e d below and i n S e c t i o n 7.3 show t h a t t h e f o r m e r c a s e i s m o r e l i k e l y . C y c l i c voltammograms were r e c o r d e d  i n the presence  o f d i f f e r e n t 0.05M  e l e c t r o l y t e s a l t s o l u t i o n s ( C I , B F ~ a n d CF^SO^") i n C f ^ C ^ a t p o r p h y r i n 4  concentrations  i n t h e r a n g e ( 3 . 0 t o 4.0) x 1 0 ~ M . 4  The p o t e n t i a l s  observed  f o r t h e f o r m a t i o n o f t h e d i f f e r e n t s p e c i e s ( T a b l e 6.1) v a r i e d w i t h t h e nature of the e l e c t r o l y t e co-anion 4.1 f o r t h e o x i d a t i o n o f R u almost  1 1  i n t h e same way a s r e p o r t e d i n S e c t i o n  (0EP)(C0)L.  The C 1 0 ~ and C F S 0 ~ a n i o n s 4  3  3  i d e n t i c a l potentials f o r the species studied, while the  gave  corresponding  p o t e n t i a l s u s i n g B F ~ w e r e ^0.1 v o l t s h i g h e r .  Comparison o f c y c l i c voltammo-  grams o f R u * * C 0 E P ) ( . P B u ) 2 (.7) i n t h e p r e s e n c e  o f CF^SO^  4  n  3  -  a n d B F ~ showed 4  a s i m i l a r e f f e c t ( S e c t i o n 7.1) a n d , a s t h e p o t e n t i a l s o b t a i n e d f o r t h e f i r s t r e d u c t i o n o f .7  w e r e 0.20 t o 0.22V b e l o w t h e c o r r e s p o n d i n g  (+0.08V v s + 0 . 3 0 V i n t h e p r e s e n c e  o f B F " , a n d -0.02V v s +0.18V i n t h e  t  presence  4  o f C F S 0 " ) , t h i s suggests 3  3  potential for A  t h a t A i s not R u * ( O E P ) ( P B u ) (7) 1  n  3  2  (Section 7.1). The i n t e n s i t i e s o f t h e r e d u c t i o n s c a n waves ( r e d u c t i o n o f t h e c a t i o n r a d i c a l s p e c i e s a n d t h e r e d u c t i o n o f A) a r e i n f l u e n c e d by t h e n a t u r e o f t h e e l e c t r o l y t e c o - a n i o n a n d t h e maximum o x i d i z i n g p o t e n t i a l r e a c h e d i n the c y c l i c voltammogram sweep.  F o r a n y A_ t o be o b t a i n e d a t a l l , t h e  maximum p o t e n t i a l has t o be h i g h e r t h a n t h a t o f t h e f i r s t o x i d a t i o n p e a k , c o n f i r m i n g t h a t A i s d e r i v e d from t h e f i r s t o x i d a t i o n p r o d u c t a n - c a t i o n r a d i c a l . However, t h e p r o p o r t i o n o f A observed v e r y l o w f o r a maximum sweep p o t e n t i a l o f ^+1.0V.  - presumably  was g e n e r a l l y  I f t h e sweep was h e l d  207  T a b l e 6.1  A Comparison o f t h e P o t e n t i a l s f o r t h e E l e c t r o c h e m i c a l Processes seen the  in the Oxidation of Ru Electrolytic  Co-anion  I ] [  (0EP)(C0)P Bu n  in Volts  p  1st Oxidation —  +0.64  +0.30  C10 "  +0.64  +0.54  +0.2Q  +0.62  +0.52  +0.18  CF S0 " 3  3  Corresponds  to  Ru (.0EP)(C0)P Bu n  n  Corresponds  3  n  +  n  n  <  3  Corresponds Ru  for  I I I  Ru (0EP) H  +  '(C0)P Bu  (8a)  +  e  " ) R u ( 0 E P ) CC0)P Bu. n  7 r\u  \oa_i  n  v  ui-r;  j r  1  + 2  (A)  —  >  a t t h e peak p o t e n t i a l  Ru (0EP)L L I I  1  2  of the f i r s t  p o r t i o n o f A o b t a i n e d was i n c r e a s e d ( F i g u r e 6 . 2 ) . changing  (8a) + A  n  3  (.8)  u u ^  \uj  to  (.0EP)L L  20 s e c o n d s  (8) — — >  to  R u ( 0 E P ) ' ( C 0 ) v> p Bo. u,  c)  Reduction of A —  +0.74  4  b)  Reduction —  BF " 4  a)  (8) as a F u n c t i o n o f  Present  Peak P o t e n t i a l s (_E ) Anion  3  (A")  o x i d a t i o n , then t h e p r o As m e n t i o n e d a b o v e ,  t h e s p e e d o f t h e sweep had no e f f e c t on t h e p r o p o r t i o n s o f t h e  products obtained.  208  a  1.2  0.8  0.4  0  E(V vs. Ag/AgCl)  1.2  0.8  0.4  0  E(V vs. Ag/AgCl)  Figure 6.2  C y c l i c v o l t a m m o g r a m s o f R u H ( O E P ) ( C O ) P n B u Q (8) i n 0 . 0 5 M T B A P - C H 02C^1 2 » maximum sweep p o t e n t i a l = +1?0V: a ) sweep rate TOO m V / s e c , b) sweep_ a t l O O m V / s e c b u t p o t e n t i a l h e l d a t ^ + 0 . 7 V f o r 20 s e c o n d s o n t h e o x i d a t i o n sweep 1  209  I n c r e a s i n g t h e maximum sweep p o t e n t i a l a b o v e +1.0V increase i n the proportion of A present.  caused a gradual  No s u d d e n i n c r e a s e i n A was  ob-  s e r v e d on r e a c h i n g t h e peak p o t e n t i a l f o r t h e s e c o n d o x i d a t i o n wave o f t h e complex.  However, f o r experiments  c a r r i e d o u t i n t h e p r e s e n c e o f CF^SO^"  as c o - a n i o n , the p r o p o r t i o n o f s p e c i e s A formed i n c r e a s e d d r a m a t i c a l l y when t h e maximum sweep p o t e n t i a l was r a i s e d f r o m +1.45 6.3).  T h i s e f f e c t was  t o +1.50V ( F i g u r e  not seen w i t h any o t h e r c o - a n i o n .  A possible expla-  n a t i o n i s t h a t a t h i r d o x i d a t i o n peak ( h i d d e n by t h e p r o x i m i t y o f s o l v e n t o x i d a t i o n ) o c c u r s b e t w e e n +1.45V and +1.50V.  It is possible that  remaining  c a t i o n r a d i c a l i s o x i d i z e d again at the r i n g at the p o t e n t i a l of the o x i d a t i o n wave.  second  I f s o , t h e c a r b o n y l l i g a n d w o u l d p r o b a b l y be r e t a i n e d .  I f an i m p o r t a n t s t e p i n t h e f o r m a t i o n o f A w e r e t h e d i s s o c i a t i o n o f t h e c a r b o n y l l i g a n d , t h e n t h e s e c o n d r i n g o x i d a t i o n w o u l d e x p l a i n why was  there  no s u d d e n i n c r e a s e i n t h e p r o p o r t i o n s o f A o b t a i n e d when t h e  o x i d a t i o n p r o d u c t was g e n e r a t e d  on a c y c l i c s w e e p .  second  However, a t h i r d  o x i d a t i o n a t t h e r i n g seems v e r y u n l i k e l y and has n o t been r e p o r t e d . t h i s o x i d a t i o n w o u l d h a v e t o be a t t h e m e t a l and g i v e a s p e c i e s , which would immediately decarbonylated  Hence,  ruthenium(III)  d i s s o c i a t e a c a r b o n y l l i g a n d and g i v e a  p o r p h y r i n s p e c i e s t h a t w o u l d r e d u c e b a c k t o A.  The  data  s u g g e s t t h a t d i s s o c i a t i o n o f t h e c a r b o n y l g r o u p ( w i t h an a c c o m p a n y i n g e l e c t r o n t r a n s f e r f r o m t h e m e t a l t o t h e p o r p h y r i n ) i s an i m p o r t a n t  step in the  f o r m a t i o n o f A. In g e n e r a l , f o r a g i v e n maximum sweep p o t e n t i a l , t h e p r e s e n c e C F S 0 ~ a s c o - a n i o n g a v e t h e h i g h e s t p r o p o r t i o n o f A, w h i l e B F ~ 3  3  4  of  gave the  210  E(V  VS.Ag/AgCl)  MA  + 1 6  1.2  0.8 E(V  F i g u r e 6.3  0 -  0.4  vs.Ag/AgCl)  C y c l i c v o l t a m m o g r a m s o f Ru ( O E P ) ( C O ) P B u i n 0.05M TPATFSC H C 1 : a ) maximum sweep p o t e n t i a l = + 1 . 4 5 V , b) maximum sweep p o t e n t i a l = +1.50V. n  2  2  211  lowest  ( t h e r e d u c t i o n p e a k a t +0.3V o f t e n b e i n g a l m o s t  invisible -  F i g u r e 6.4 a and b) w i t h C l O ^ " h a v i n g an i n t e r m e d i a t e e f f e c t . obvious  how t h e s e e x c e p t i o n a l l y p o o r c o o r d i n a t i n g a n i o n s e f f e c t t h e  brium t h a t generates P Bu n  3  I t i s not equili-  A from the p o r p h y r i n ir-cation r a d i c a l Ru**(0EP) *(CO)+  (8a). Known c o o r d i n a t i n g a n i o n s  s u c h as c h l o r i d e , o r c o o r d i n a t i n g  solvents  s u c h as C H C N , h a d a m a r k e d e f f e c t on t h e c y c l i c v o l t a m m o g r a m o f 8_ w i t h m o s t 3  o f t h e c a t i o n r a d i c a l p r o d u c e d on t h e o x i d a t i o n sweep b e i n g c o n v e r t e d c o m p l e x e s s i m i l a r t o A , a n d h e n c e o n l y a weak p e a k f o r t h e r e d u c t i o n 8a_ was  seen with a moderately  the presence  of  s t r o n g p e a k a t l o w p o t e n t i a l s (-0.18V i n  o f 0.001M c h l o r i d e and +0.05V i n 1:1 v / v M e C N / C H C l  see F i g u r e 6.5).  to  2  T h e s e low p o t e n t i a l s a r e t y p i c a l f o r t h e  r e d u c t i o n Ru (.111 )->Ru (.II) ( s e e S e c t i o n 7.3 and R e f . 1 ) , and a  2  as  solvent;  metal-centred ruthenium(.III)  p r o d u c t s t a b i l i z e d by c o o r d i n a t i n g a n i o n s o r s o l v e n t s w o u l d a c c o u n t  f o r the  e f f e c t o f t h e s e l i g a n d s on t h e p r o p o r t i o n o f 8a_ t h a t s u r v i v e s t h e c o m p l e t e cycle.  A l l t h i s evidence  suggests  that A is a ruthenium(III)  porphyrin  species with a s i x t h l i g a n d p o s i t i o n that i s e i t h e r vacant or contains a weakly coordinated  ligand.  C y c l i c voltammograms o f R u * * ( 0 E P ) ( C 0 ) P B u n  o f 0.05M T B A F o r T P A F showed an u n u s u a l plained.  3  (8_) t a k e n i n t h e  presence  e f f e c t t h a t as y e t r e m a i n s u n e x -  On u s i n g t h e same s o l u t i o n f o r a s e r i e s o f c y c l i c v o l t a m m o g r a m s ,  i t was n o t e d t h a t e x t r a waves g r a d u a l l y a p p e a r e d w i t h t i m e a t ^+0.96V and +0.92V ( F i g u r e 6 . 6 ) .  The p o t e n t i a l s w e r e c l o s e t o t h o s e o b s e r v e d  o x i d a t i o n o f Ru(.0EP)(C0) (1_) i n t h e same e l e c t r o l y t e , b u t i n i t i a l  f o r the contami-  a  212  E(V  VS.Ag/AgCl)  MA  + 1.6  1.2  0.8 E(V  F i g u r e 6.4  O-  0.4  VS.Ag/AgCl)  C y c l i c v o l t a m m o g r a m s o f R u ( O E P ) ( C O ) P B-J.S u. f r e s h l y prepared s o l u t i o n i n C H - C K : a) i n t h e p r e s e n c e o f 0.05M T B A F , b) i n t h e p r e s e n c e o f 0.05M T P A T F S . n  n  213  a  + 0.8 E(V  0.4  0  0.4  vs.Ag/AgCl)  b  MA  +  1.2  0.8  E(V  Figure  6.5  0.4  0 -  vs.Ag/AgCl)  a ) C y c l i c v o l t a m m o g r a m o f R u _ ( O E P ) ( C O ) P B u i n 0.05M T B A F C h ^ C l o w i t h 0.001M T E A C I " a d d e d . Maximum sweep p o t e n t i a l was +6.8V d u e t o t h e e a s e o f o x i d a t i o n o f C l ~ . b) C y c l i c v o l t a m m o g r a m o f R u ( O E P ) ( C O ) P B u i n 0.05M TBAP i n 1:1 v / v C H C l / M e C N . I  I  n  +  3  I I  n  3  2  2  214  n a t i o n f r o m t h i s s p e c i e s c o u l d be r u l e d o u t a s t h e s a m p l e s o f 8^were a n a l y t i c a l l y pure and gave e x c e l l e n t s p e c t r a . C o n t a m i n a t i o n from t h e e l e c t r o l y t e was a l s o d i s c o u n t e d s i n c e a c y c l i c v o l t a m m o g r a m o f t h e e l e c t r o l y t e s o l u t i o n b e f o r e t h e a d d i t i o n o f t h e p o r p h y r i n g a v e no waves f r o m 0 t o +1.6V.  E a r l y e x p e r i m e n t s w i t h impure samples o f Ru(OEP) ( C 0 ) P B u  had  n  3  s u g g e s t e d t h a t s p e c i e s 1_ c o u l d be g e n e r a t e d by a l i g a n d e x c h a n g e  reaction  (Equation 6.1):  2Ru(0EP)(.C0)P Bu n  (8)  ) Ru(0EP)(P Bu ) n  3  3  2  + R u ( 0 E P ) ( C 0 ) + CO  (6.1)  (I)  (7)  T h i s r e a c t i o n c o u l d e x p l a i n t h e e x t r a w a v e s a t ^+1.OV.  However, a  s o l u t i o n t h a t h a d b e e n s t o r e d f o r two h o u r s a n d g a v e v e r y p r o m i n e n t waves a t ^+1.OV showed no a b s o r p t i o n s i n t h e v i s i b l e s p e c t r u m c h a r a c t e r i s t i c o f 7_ ( 4 2 8 nm) o r 1_ ( .547 nm); t h e s p e c t r u m was i d e n t i c a l t o t h a t o f a f r e s h l y prepared s o l u t i o n o f a n a l y t i c a l l y pure Ru(OEP)(CO)P Bu n  3  (8) i n CH C1 . 2  2  H e n c e , t h e w a v e s a t ^+1 .OV a p p e a r n o t t o be c a u s e d by t h e g e n e r a t i o n o f R u ( O E P ) C C O ) (.!_)• A s t h i s e f f e c t i s s e e n o n l y i n t h e p r e s e n c e o f B F ^ i t may be l i n k e d t o t h e phenomenon o f t h e h i g h e r o x i d a t i o n p o t e n t i a l s o b s e r v e d f o r a wide range o f s p e c i e s i n t h e presence o f t h i s c o - a n i o n ( s e e S e c t i o n 4 . 1 ) . I f A_ i s f o r m e d b y a n i n i t i a l d i s s o c i a t i o n o f c a r b o n y l f r o m R u ( 0 E P ) (C0)P Bu n  3  +  -  ( 8 a ) , t h e n a c y c l i c v o l t a m m o g r a m o f 8 i n a s o l u t i o n s a t u r a t e d w i t h CO  s h o u l d show  l e s s f o r m a t i o n o f A t h a n a s i m i l a r CO f r e e s o l u t i o n .  Figure  6.7 shows a c y c l i c v o l t a m m o g r a m o f 8_ i n t h e p r e s e n c e o f 0.05M T P A T F S i n CH C1 9  9  w h i c h h a d been p u r g e d w i t h c a r b o n m o x i d e f o r f i v e m i n u t e s  immediately  + 1-6  1.2  0.8 E(V  F i g u r e 6.6  U.4  0^  vs.Ag/AgCl)  C y c l i c v o l t a m m o g r a m o f R u ( O E P ) ( C 0 ) P B u i n 0.05M a f t e r standing f o r %30 minutes, c f . Figure 6.4a. 1 1  n  3  TBAF-CH C1 ?  ?  b  nA  + 1.6  1.2  0.8 E(V  F i g u r e 6.7  0.4  0 -  vs.Ag/AgCl)  C y c l i c v o l t a m m o g r a m o f Ru ( O E P ) ( C O ) P B u i n 0.05M T P A T F S C H p C ^ . s a t u r a t e d w i t h CO i m m e d i a t e l y p r i o r t o r u n n i n g t h e c y c l i c v o l t a m m o g r a m , c f . F i g u r e 6.4b. n  3  216  p r i o r to the experiment.  The v o l t a m m o g r a m shows a c o m p l e t e l a c k o f a wave  due t o r e d u c t i o n o f A ( c f .  F i g u r e 6.4b)  o x i d a t i o n w a v e , and t h e c o r r e s p o n d i n g (8a) -»• R u ( 0 E P ) ( C 0 ) P B u H  n  3  and t h e p e a k c u r r e n t s o f t h e  r e d u c t i o n wave ( R u * * ( 0 E P ) ' ( C 0 ) P B u +  (8)) are approximately  equal.  o f the f i r s t o x i d a t i o n peak (and the c o r r e s p o n d i n g  n  o x i d a t i o n wave and t h e c o r r e s p o n d i n g  r e d u c t i o n p e a k ) has However,  r e d u c t i o n wave h a v e n o t  been d i s p l a c e d and a r e u n a f f e c t e d by t h e p r e s e n c e in s o l u t i o n suppresses  3  A l s o , the p o t e n t i a l  s h i f t e d by +0.06V (+0.64V i n F i g u r e 6.5 t o +0.70V i n F i g u r e 6>7). the second  first  o f CO.  Hence,excess  CO  t h e f o r m a t i o n o f A on e l e c t r o c h e m i c a l o x i d a t i o n o f 8.  The d a t a show t h a t A i s g e n e r a t e d x i d e f r o m t h e c a t i o n r a d i c a l 8a_.  v i a the d i s s o c i a t i o n of carbon  L o s s o f t h e CO l i g a n d f a v o u r s  mono-  intramole-  c u l a r e l e c t r o n t r a n s f e r which r a p i d l y occurs to give a ruthenium( III) p o r p h y r i n s p e c i e s (Scheme 6 . 1 ) .  These processes are a l l f a s t e q u i l i b r i a  and t h e p r o p o r t i o n o f A_ o b t a i n e d w i l l d e p e n d u p o n t h e e q u i l i b r i u m i n t h e f i r s t s t e p ( E q u a t i o n 6.2),as w e l l as the s t a b i l i z a t i o n o f the  final  ruthenium(III)  porphyrin species.  The v a r i a t i o n o f t h e p r o p o r t i o n  ruthenium(III)  products with the i d e n t i t y o f the e l e c t r o l y t e co-anions  a r i s e through c o o r d i n a t i o n of these anions anions  to A .  of may  The e l e c t r o l y t e  ( C l O ^ , BF^~ and CF^SO^") u s e d i n t h e s e e x p e r i m e n t s a r e u s u a l l y -  c o n s i d e r e d t o be n o n - c o o r d i n a t i n g  a l t h o u g h t h e p e r c h l o r a t e a n i o n i s known  2  to c o o r d i n a t e to F e ( I I I ) . A p p l y i n g s i m i l a r arguments as those used d i s c u s s i n g t h e s t r u c t u r e o f R u ( 0 E P ) '(C0) +  (l_a) i n s o l u t i o n ( s e e S e c t i o n  and n o t e t h e r e v e r s i b l e n a t u r e o f t h e r e d u c t i o n p r o c e s s e s tammogram o f A - '.l_8_i - S e c t i o n 7 . 3 ) , e f f e c t i v e l y f i v e - c o o r d i n a t e complex R u  in 4.1,  seen i n the v o l -  s p e c i e s A i s c o n s i d e r e d t o be an I I I  COEP)(_P Biul n  +  (.1_8) ( S c h e m e  6.1).  217  SCHEME 6.1  Ru(OEP)(CO)P  Bu  3  (!) -e  Ru(0EP)  Ru(.OEP) '(CO)P Bu, +  '(P Bu )  +  n  + CO  n  3  (6.2)  IMET  (8a)  Ru (OEP)(P Bu ) i n  n  +  3  ( 1 8 o r A)  CT  Ru  III  i  0 MeCN Ru (0EP)(P Bu )MeCN m  C0EP)(P"Bu )Cl  n  +  3  3  The i n d e p e n d e n c e o f t h e s e c o n d o x i d a t i o n o f '8 o n t h e p r e s e n c e o r a b s e n c e o f CO, a n d t h e e n h a n c e d d i s s o c i a t i o n o f t h e CO l i g a n d s e e n a t t h e t h i r d o x i d a t i o n p o t e n t i a l , suggest that the second oxidation generates t h e d i c a t i o n 8hj a n d t h e t h i r d o x i d a t i o n i s a t t h e m e t a l a s s e e n i n t h e p r e s e n c e of CF S0 " 3  3  i o n s ( 8 c t o 1 8 b - Scheme 6 . 2 ) .  C y c l i c voltammetry o f [ R u ( 0 E P ) ( P B u ) ] C 1 0 ~ n i  n  +  3  4  ( A , 1_8) i n t h e p r e s e n c e  o f 0.05M TBAP i n C H g C ^ ( S e c t i o n 7.3) showed a s e c o n d r e v e r s i b l e p o t e n t i a l ( a b o v e t h e Ru( I I ) f = R u ( I I I ) c o u p l e s e e n a t ^+0.2V) a t a p p r o x i m a t e l y t h e same i  p o t e n t i a l (+1 .10V) a s t h e s e c o n d o x i d a t i o n c o u p l e o f ^8 ,(8a_ t o 8b) g i v e n a s +1 .05V i n Scheme 6.2, +1 .09V i n t h e p r e s e n c e o f 0.05M p e r c h l o r a t e ) .  This  218  SCHEME 6.2 IMET  E^+0..57V Ru (.0EP)(C0)P Bu II  n  3  ,  2  R u C 0 E P ) . 'CC0);P Bu II  +  (8)  ~  n  3 t  C 0  * Ru COEP)CP Bu,l+ Iri  +C0  C8a).  n  (18)  E ^ + 1 .05 V  Ru (OEP) '(CO)P Bu. n  2 +  E ^+1 .05V x  R u ( 0 E P ) *(P Bu )  n  I H  +  n  3  (8b)  (18a)  E. .45V  Ru (0EP) m  2 + ,  (C0)P Bu n  (8c)  -^L» Ru (0EP) -(P Bu ) I n  3  2 +  n  3  (18b)  a_ P o t e n t i a l s m e a s u r e d i n t h e p r e s e n c e o f 0.05M TPATFS u s i n g ( 2 . 0 - 4.0) -4 x 10 M s o l u t i o n s o f p o r p h y r i n i n  ZW^A^.  R e a c t i o n a ) - s e e F i g u r e 6.7 . R e a c t i o n b) - s e e F i g u r e 6 . 3 . R e a c t i o n c ) - s e e F i g u r e 7.4; S e c t i o n 7 . 3 .  p r e s u m a b l y e x p l a i n s why t h e f o r m a t i o n o f 1_8 d o e s n o t c a u s e e x t r a waves i n the c y c l i c voltammogram  o f 8_.  219  The n a t u r e o f t h e p r o d u c t ( 1 8 a )  f o r m e d by t h e s e c o n d  t i a l i s u n c e r t a i n and c o u l d be a r u t h e n i u m ( I I I ) i n d i c a t e d i n Scheme 6.2 f r o m F i g u r e 6.3  or a ruthenium(IV)  oxidation  poten-  c a t i o n r a d i c a l s p e c i e s as  complex.  I t s h o u l d be  noted  t h a t t h e i n c r e a s i n g f o r m a t i o n o f 1_8 w i t h i n c r e a s i n g maximum  sweep p o t e n t i a l f r o m +1.45  t o +1.50  v o l t s (a r e a c t i o n b e l i e v e d t o go v i a t h e  f o r m a t i o n o f , and l o s s o f a c a r b o n y l  l i g a n d f r o m , 8c_) d o e s n o t i n !Tny~way~  a f f e c t t h e r e d u c t i o n wave o f t h e s e c o n d n y l a t i o n r e a c t i o n (18b)  i s reduced  couple.  The p r o d u c t o f t h e  c l e a n l y t o 18a w h o s e r e d u c t i o n i s t h e n  i n d i s t i n g u i s h a b l e f r o m t h e r e d u c t i o n o f 8b_.  As 18a i s f o r m e d ( v i a 18b)  a o n e - e l e c t r o n r e d u c t i o n from 8c, a complex f o r which t h e r e i s supporting a Ru(III) formulation, t h i s suggests  t h a t 18a i s a  i s s t i l l u n c e r t a i n , and any  e l e c t r o n t r a n s f e r between a r u t h e n i u m ( I I I )  by  evidence ruthenium(III)  T r - c a t i o n r a d i c a l and t h a t t h e r e d u c t i o n ( 1 8 b -» 18a) o c c u r s a t t h e H o w e v e r , t h e i d e n t i t y o f 18a  decarbo-  porphyrin.  intramolecular  c a t i o n r a d i c a l and a  ruthenium(IV)  porphyrin would i n v a l i d a t e the above t e n t a t i v e : c o n c l u s i o n s .  6.2  The P r e p a r a t i o n o f R u  I T I  (OEP)(P Bu ) n  +  3  and Some R e a c t i o n s  Involving  I n t r a m o l e c u l a r E l e c t r o n T r a n s f e r (IMET) Bulk e l e c t r o l y s i s o f R u ( O E P ) ( C O ) P B u 1 J  n  3  i n a 0.05M s o l u t i o n o f TBAP  i n C H C 1 2 a t a p o t e n t i a l o f ^+0.8V r e m o v e d 1>0± 0.1 2  porphyrin molecule  e l e c t r o n s per  t o g i v e an o r a n g e s o l u t i o n ( s e e S e c t i o n 2.2)  c o n c e n t r a t i o n s o f (0.5 - 1 . 0 )  x 10  M.  out the e l e c t r o l y s i s , a s o l u t i o n of R u 5% o f p o r p h y r i n - d e r i v e d  ruthenium at  With a vigorous argon purge I I I  (0EP)(P Bu )  i m p u r i t i e s (as judged  n  3  +  porphyrin through-  (18) w i t h l e s s than  by t h e u . v . / v i s i b l e s p e c t r u m )  220  was o b t a i n e d ( F i g u r e 6 . 8 ) . I f a 1 0 ~ M s o l u t i o n was u s e d f o r t h e e l e c t r o l y s i s , o r t h e p u r g i n g w i t h a r g o n was i n e f f i c i e n t , t h e n t h e p r o d u c t showed s t r o n g a d d i t i o n a l p e a k s a t ^ 7 9 0 , 610 a n d these side-products varied  590 nm.  spectrum  Proportions o f  b e t w e e n 5 t o 2 5 % , a s j u d g e d by u . v . / v i s i b l e  spectrum  a n d e„s.r.data ( s e e b e l o w ) , b e c a u s e o f t h e v a r i a b i l i t y i n r a t e o f  removing  t h e CO.  Solutions of Ru***(0EP)(P Bu ) n  {]8)  +  3  of spectroscopic strength  -4  (^10 M) showed l i t t l e i m m e d i a t e c h a n g e i n s p e c t r u m when s a t u r a t e d w i t h c a r b o n m o n o x i d e ( s e e b e l o w ) a n d w e r e s t a b l e when s t o r e d u n d e r a r g o n f o r -4 3-4  days.  S t o r i n g a CO-saturated  10  M s o l u t i o n o f 1_8 f o r o n e d a y l e d  t o l o s s o f t h e o r i g i n a l c o m p l e x , t h e v i s i b l e s p e c t r u m now b e i n g  dominated  by s t r o n g p e a k s a t 7 9 0 , ^ 5 5 0 , a n d 515 nm w i t h w e a k e r a b s o r p t i o n s a t and ^ 6 1 0 nm.  R e d u c t i o n o f t h i s s o l u t i o n w i t h t e t r a b u t y l ammonium  d r i d e caused i n t e n s i f i c a t i o n o f the a b s o r p t i o n s a t  590  borohy-^  550 a n d 515 nm, l o s s  o f t h e 790 nm band a n d t h e g e n e r a t i o n o f a v e r y s h a r p a n d d i s t i n c t i v e S o r e t a t 428 nm.  By c o m p a r i s o n  w i t h s p e c t r a l d a t a o f known p o r p h y r i n s p e c i e s  ( s e e T a b l e s 3.2, 4.4, 7 . 1 ) , i t was c o n c l u d e d t h a t t h e s l o w r e a c t i o n o f CO with R u ( 0 E P ) ( P B u ) n i  n  0 8 ) had g e n e r a t e d a m i x t u r e o f R u ( 0 E P ) ' ( C 0 ) ( l a j  +  n  3  and R u  1 1 1  (OEP) ( P B u ) n  3  (8a) and a subsequent  + 2  +  (9_), p l a u s i b l y v i a f o r m a t i o n o f t h e c a t i o n r a d i c a l l i g a n d exchange r e a c t i o n :  1.0  ro  1000 WAVELENGTH  F i g u r e 6.8  (nm)  O p t i c a l s p e c t r u m o f a s a m p l e o f [Ru ( O E P ) ( P B u ) ] C 1 0 " (J8) as p r e p a r e d by t h e e l e c t r o c h e m i c a l o x i d a t i o n o f 8. Weak a b s o r p t i o n s a t 587 a n d 610 nm a r e d u e t o some c o n t a m i n a t i n g l_a a n d t h e weak a b s o r p t i o n a t 790 nm i s due t o some 9a_. P r o p o r t i o n o f t h e s e p r o d u c t s p r e s e n t as s i d e p r o d u c t s ^ 5 % . n  3  4  222 + CO — * - CO  Ru (OEP)(P BuJ , m  n  +  3  (18)  R u ( O E P ) '(CO)P Buo n  +  (6.3)  n  (8a)  3 9 0 , 5 2 0 , 7 1 0 nm 2 R u ( 0 E P ) *(C0).P Bu n  +  ) Ru (0EP)(P Bu )  n  n i  3  n  3  (8a)  + 2  + Ru  1 1  ( 0 E P ) ' ( C O ) + CO ( 6 . 4 ) +  (9)  (la.)  790 nm  5 9 0 , 6 1 0 nm  R e a c t i o n 6.4 e x p l a i n s t h e f o r m a t i o n o f s i d e p r o d u c t s (l_a a n d 9) i n t h e p r e p a r a t i o n o f 1_8 by t h e e l e c t r o l y s i s o f 8_, a n d t h e c o n s i d e r a b l y i n c r e a s e d f o r m a t i o n o f t h e s e s i d e p r o d u c t s i f t h e c o n t i n u o u s p u r g i n g by a r g o n was o m i t t e d . The s p e c t r u m  of [Ru (0EP) (P Bu )] C10 " H I  n  +  3  4  ( 1 8 ) ( F i g u r e 6.8, T a b l e  7.2) w i t h a b r o a d a b s o r p t i o n a t ^ 5 2 0 nm a n d a weak a b s o r p t i o n a t 730 nm, is s i m i l a r t o t h a t o f other ruthenium(III) complexes, samples  of R u ( 0 E P ) (P Bu )Br i n  (1_0).  n  3  o p t i c a l spectrum  T h e S o r e t a t % 3 9 0 nm a n d t h e e n t i r e  are s t r i k i n g l y s i m i l a r to those o f R u  and R u ( . 0 E P ) ( P B u ) M e 0 H H I  i n c l u d i n g prepared  n  3  +  I I I  (0EP)(P Bu )MeCN n  +  3  ( T a b l e 7.2) t o w h i c h 18. i s r e a d i l y c o n v e r t e d by  the a d d i t i o n o f a c e t o n i t r i l e and methanol,  respectively (see Section 7.3).  A l l t h e a b o v e d a t a a r e c o n s i s t e n t w i t h 1_8 b e i n g a r u t h e n i u m ( I I I ) p o r p h y r i n complex c o n t a i n i n g one p h o s p h i n e Electron spin resonance  ligand.  s t u d i e s on p r e p a r e d samples  o f ]_8 showed t h e  p r e s e n c e o f a weak c a t i o n r a d i c a l r e s o n a n c e a t g = 2 . 0 0 , a l t h o u g h u n f o r t u n a t e l y no s i g n a l due t o t h e r u t h e n i u m ( I I I ) c e n t r e c o u l d be d e t e c t e d . s i g n a l i s a t t r i b u t e d t o l_a f o r m e d For t h e sample s t u d i e d , comparison  i n t h e side r e a c t i o n mentioned w i t h t h e s i g n a l o b t a i n e d from  This  above. standard  223  i n d i c a t e d ^2%%  s o l u t i o n s o f l_a ( s e e S e c t i o n 2.1) was  i n t h e f o r m o f ]a_ a l t h o u g h  s p e c t r a ( F i g u r e 6.9) Stronger  of the t o t a l  the p r o p o r t i o n estimated  was a b o u t  from  porphyrin optical  10%.  s o l u t i o n s (2 x 1 0 "  ( 1 8 ) w e r e s t u d i e d i n t h e n e a r I.R  3  to 5 x 10" M) o f R u 3  r e g i o n (600 - 1000  I I I  (0EP)(P Bu )  nm).  n  On s a t u r a t i o n  w i t h c a r b o n m o n o x i d e , s u c h s o l u t i o n s showed a r a p i d l o s s o f t h e 730 a b s o r p t i o n c h a r a c t e r i s t i c o f 18.. b e l o w 650 nm was o b s e r v e d  seen.  A general  nm  A considerable increase in absorption  a l s o but t h e l a c k o f a b s o r p t i o n a t 790  e l i m i n a t e d t h e p o s s i b i l i t y t h a t R e a c t i o n 6.4 was o f 1_8.  +  3  nm  i n v o l v e d i n the removal  i n c r e a s e i n a b s o r p t i o n b e t w e e n 700 and 950 nm was  also  On s t o r a g e o f t h e s o l u t i o n u n d e r c a r b o n m o n o x i d e o v e r 2 4 h ,  the  s p e c t r a l c h a n g e s showed t h a t t h e b r o a d a b s o r p t i o n b e t w e e n 700 and 950 and t h e a b s o r p t i o n b e l o w 650 nm s l o w l y d i m i n i s h e d , w h i l e a new a p p e a r e d a t 790 nm and s t r o n g a b s o r p t i o n b e l o w 610 nm was  peak  retained.  d a t a a r e c o n s i s t e n t w i t h t h e f o r m a t i o n o f some 8a_ v i a R e a c t i o n (estimated  nm  These  6.3  f r o m t h e o p t i c a l s p e c t r a t o be b e t w e e n 5 and 10% o f t h e t o t a l  porphyrin),which  then undergoes the l i g a n d exchange r e a c t i o n (6.4) a t a  slower r a t e to give the absorption c h a r a c t e r i s t i c o f R u * * * ( 0 E P ) ( P B u ) 2 n  +  3  a t 790  nm. U n f o r t u n a t e l y t h e f o r m a t i o n o f 8a_ c o u l d n o t be c o n f i r m e d -3  e.sr. s t u d i e s . S a t u r a t i n g a 1 x 10  directly  M s o l u t i o n o f 18^ w i t h CO c a u s e d  a  s l i g h t increase in the strength of a c a t i o n radical signal considered t o ]a_ b u t , a s m e n t i o n e d i n S e c t i o n 2 . 1 , t h e a c c u r a c y o f s u c h  by  due  determinations  o f t h e t o t a l number o f e l e c t r o n s p i n s i s r a t h e r low and t h e m e t h o d i s p r o -  224  1.CH  \  :I  • «  :» :/ ;/  ww  //  I  LU O  I  z <  CO  cc  o  CO 00  <  0.5H  500  700  600 WAVELENGTH (nm)  F i g u r e 6.9  O p t i c a l spectrum o f a sample o f [Ru (OEP)(P Bu )] ClO4" a f t e r purging w i t h CO f o r 3 minutes ( - ? - • — ) ; and t h e same s o l u t i o n a f t e r p u r g i n g w i t h argon t o remove t h e excess CO ( ). n  +  3  225  bably not s e n s i t i v e enough to measure small changes i n the of cation radical species.  proportion  The l a c k o f a c c u r a c y i s r e f l e c t e d i n  d i s c r e p a n c i e s , b e t w e e n t h e p r o p o r t i o n s o f l_a p r e s e n t i n s a m p l e s o f 18. as estimated  f r o m e . s . r . and o p t i c a l s p e c t r a ( s e e  above).:  S t u d i e s o f the o p t i c a l s p e c t r a o f s l i g h t l y more d i l u t e s o l u t i o n s H  x 10~ M) o f R u ( 0 E P ) ( P B u ) 3  m  n  3  monoxide generated  +  (J8)  showed t h a t p u r g i n g w i t h  carbon  a b u i l d up o f a b s o r p t i o n b e t w e e n 550 and 680 nm  with  a new peak a p p e a r i n g a t 630; nm, j-and a s l i g h t l o s s o f i n t e n s i t y b e t w e e n 500 and 550 nm.  Purging with argon caused  and a r e g e n e r a t i o n o f t h e o r i g i n a l s p e c t r u m ( F i g u r e 6.9). Ru**(0EP)  +  l o s s o f t h e 630 nm  (1_8 p l u s some c o n t a m i n a t i n g  On t h e b a s i s o f t h e s e o b s e r v a t i o n s , t h e  (C0)P Bu n  3  spectrum  la_)  of  (8a_) was j u d g e d t o c o n s i s t o f a p r o m i n e n t a b s o r p t i o n  a t 630 nm w i t h a s t r o n g t a i l t o t h e b l u e ( c f . • t h e s p e c t r u m ( C 0 ) B r ] (l_b) - T a b l e 4.4)  of]Ku (0EP) 'I I  and a weak t a i l t o t h e r e d g i v i n g a b r o a d  t i o n a t 880 nm, a b o u t one f i f t h t h e i n t e n s i t y o f t h e 630 nm 2 This spectrum  absorption  suggests a  +  absorp-  absorption.  ground s t a t e f o r 8a, although t h i s i s unusual  for a s i x - c o o r d i n a t e c a t i o n r a d i c a l species with a neutral l i g a n d trans to t h e CO ( S e c t i o n 4 . 1 ) . o f ruthenium  H o w e v e r , as s e e n t h r o u g h o u t  porphyrin carbonyl  t h i s work, the s p e c t r a  phosphine complexes are very d i f f e r e n t  from t h o s e o f complexes c o n t a i n i n g n i t r o g e n o r oxygen l i g a n d s t r a n s t o the CO ( S e c t i o n 3 . 1 ) .  Hence,cation  r a d i c a l s o f t h e same g r o u n d s t a t e may  give  d i f f e r e n t s p e c t r a f o r a phosphorus donor than f o r a n e u t r a l n i t r o g e n or oxygen donor  ( s u c h as 3a_ o r 6 a ) .  Numerous examples o f i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r a r e o b s e r v e d  in  226  the chemistry  of R u ( 0 E P ) ( P B u ) i n  n  (18).  +  3  The f o r m a t i o n  o f 18 on e i t h e r  t h e c y c l i c v o l t a m m e t r y t i m e s c a l e o r on a p r e p a r a t i v e s c a l e r e s u l t s f r o m an e l e c t r o n t r a n s f e r f r o m t h e m e t a l t o t h e p o r p h y r i n t o t h e r e a c t i o n s o u t l i n e d i n C h a p t e r 5. with the l o s s of the carbonyl obvious.  The e l e c t r o n t r a n s f e r i s a s s o c i a t e d  l i g a n d but w h i c h p r o c e s s o c c u r s  t h i s c a n be o b s e r v e d  6.3)  6.4  via displacement  The E l e c t r o c h e m i s t r y  of the carbonyl  ligand  ruthenium(III)  by p h o s p h i n e .  o f o t h e r R u ( 0 E P ) ( C 0 ) L C o m p l e x e s (L =  and A s P h g ) t h a t g i v e  PPh,  I I  r i s e to Ruthenium(III)  Products  This s e c t i o n deals with the o x i d a t i o n o f ruthenium(II) carbonyl  The  shows a s i m i l a r e l e c t r o n t r a n s f e r  as one m o l e c u l e o f t h e c a t i o n r a d i c a l (8a_) becomes a  porphyrin  formation  i s r e v e r s i b l e and  d i r e c t l y in moderately strong solutions.  exchange r e a c t i o n seen i n Equation  6.3  f i r s t i s not  As h i n t e d a t i n t h e c y c l i c v o l t a m m e t r y e x p e r i m e n t s , t h e  o f 1_8 by i n t r a m o l e c u l a r e l e c t r o n t r a n s f e r ( E q u a t i o n  process  cation radical, similar  complexes,whose chemistry  porphyrin  i s r e l a t e d to t h a t seen f o r Ru**(0EP)-  ( C 0 ) P B u , a n d c o n t r a s t s w i t h t h a t o f t h e c o m p l e x e s ( R u ( 0 E P ) ( C 0 ) L , L = py, n  H  3  MeCN and Im) d i s c u s s e d  i n C h a p t e r 4.  The l i g a n d s c o n s i d e r e d  A s P h ) a l o n g w i t h CN" g i v e r u t h e n i u m ( I I I ) 3  products  and  (Section  5.1).  a l s o to g i v e c h a r a c t e r i s t i c s p e c t r a l c h a n g e s  on a d d i t i o n t o R u ( O E P ) (CO)  (1_) ( S e c t i o n  H  3.1).  Of the four l i g a n d s ( P B u , P P h , A s P h n  3  carbonyl  3  on a d d i t i o n t o t h e c a t i o n  r a d i c a l J_a, a r e a c t i o n a l s o s e e n f o r t r i - n - b u t y l p h o s p h i n e These l i g a n d s were observed  (L = P P h  3  3  and C N " ) ,  only P Bu n  3  forms a  complex o f the t y p e R u ( 0 E P ) ( C 0 ) L t h a t does not d i s s o c i a t e L I I  227  e a s i l y i n s o l u t i o n ( S e c t i o n 3.2);  the o x i d a t i o n o f such s p e c i e s (8)  been d e s c r i b e d i n t h e l a s t two s e c t i o n s .  To m a i n t a i n  has  similar species in  s o l u t i o n , w h e r e L =- PPh and A s P h ^ , r e q u i r e d a s u b s t a n t i a l e x c e s s o f t h e :  3  free ligand.  In t h e f o l l o w i n g e x p e r i m e n t s ,  o n l y one e q u i v a l e n t o f L  a d d e d t o R u ( 0 E P ) ( C O ) E t O H (2) d i s s o l v e d i n C H C 1 H  2  Ru(.0EP)(C0) (1_), see S e c t i o n 3.1)  and, f o r PPh  o f t h e s i x - c o o r d i n a t e c o m p l e x was  estimated  g i v e n i n S e c t i o n 3.2.  T h u s , f o r a 3 x 10~^M  3  2  was  (effectively giving  and A s P h , t h e 3  proportion  from t h e a s s o c i a t i o n  constants  s o l u t i o n t y p i c a l l y used  for  c y c l i c v o l t a m m e t r y , t h e c o m p l e x w o u l d be 18% a s s o c i a t e d f o r L = A s P h  and  3  72% f o r L = P P h . 3  Electrochemical anions  ( L = CN")  e x p e r i m e n t s on s o l u t i o n s c o n t a i n i n g  f a i l e d t o g i v e a n y r e s u l t s due t o t h e f a c i l e o x i d a t i o n o f  the cyanide anion (see Section  5.Id).  A c y c l i c v o l t a m m o g r a m o f a 2 x 10" M 4  in C H C 1 2  1:1  2  s o l u t i o n o f Ru(OEP) ( C 0 ) P P h  3  i n F i g u r e 6.10. n  3  (]_]_)  3  ( u s i n g e i t h e r an a n a l y t i c a l l y p u r e s o l i d s a m p l e o r an i n s i t u  PPh / Ru(0EP)(C0)Et0H solution) i n the presence  (C0)P Bu  Ru**(0EP)(C0)CN"  o f 0.05M T P A F . i s  shown  The c y c l i c v o l t a m m o g r a m i s d i f f e r e n t f r o m t h a t o f R u ^ O E P ) -  ( 8 ) due t o t h e p a r t i a l d i s s o c i a t i o n o f t h e s i x t h l i g a n d .  Thus,,  t h e f i r s t o x i d a t i o n shows a s t r o n g wave a t +0.8V and a l s o a s u b s i d i a r y Twave' a t ^+0.7V.  When w a v e s a r e c l o s e t o g e t h e r i t i s v e r y d i f f i c u l t t o j u d g e  their individual intensities.  S i n c e s p e c i e s 8^ i n t h e p r e s e n c e  as t o s t o p t h e d i s s o c i a t i o n o f t h e c a r b o n y l o f 1_8 - s e e S e c t i o n 6.1)  o f CO  l i g a n d and i m m e d i a t e  (so  formation  g a v e a f i r s t o x i d a t i o n p e a k a t + 0 . 7 V , i t seems  l i k e l y t h a t t h e f i r s t wave i s due t o o x i d a t i o n o f t h e s i x - c o o r d i n a t e ( 1 1 ) ^ w h i l e t h e s e c o n d wave i s a s s o c i a t e d w i t h t h e f i v e - c o o r d i n a t e  species species  228  (1).  O x i d a t i o n i n both cases  w o u l d be a t t h e r i n g t o g i v e an  appropriate  Tr-cation r a d i c a l which would r e a d i l y r e a c t with f r e e phosphine Ru (0EP)(PPh ) H I  3  + 2  to give  (1_5) ( S e c t i o n 5 . 1 ) , b u t o n l y i n 50% y i e l d due t o t h e  single equivalent of PPh  3  present.  H e n c e , 50% o f t h e c a t i o n r a d i c a l s w o u l d  r e m a i n u n r e a c t e d t o g i v e a r e d u c t