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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 June 1983 © Mark Howard Barley, COLUMBIA 1983 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head of my department or by h i s or her r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department of CU.e.MA. The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date ~2X>J "7 I %3 DE-6 (3/81) i i ABSTRACT The chemis t ry and e l e c t r o c h e m i s t r y o f complexes o f the type R u I I ( 0 E P ) L 1 L 2 ( L ] 5 L 2 = CO, P n B u 3 , P P h 3 , A s P h 3 > CN", CS, MeCN, py and Im) were s tud ied and seve ra l examples of 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) were observed. 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 the o x i d i z e d complex ( R u n i ( 0 E P ) L - , L 2 , L 1 and l_2«4=CO, CS ; or R u 1 1 (OEP) + *L - ,L £ , 2 2 L-jOr L 2 = CO or CS, A 2 u or A l u ground s t a t e ) was shown to be determined by the nature o f the a x i a l l i g a n d s . Ligand exchange, e f f e c t e d e i t h e r by l i g and a d d i t i o n or by p h o t o l y s i s , could cause e l e c t r o n t r a n s f e r between the metal atom and the porphyr in macrocyc le (IMET) r e s u l t i n g i n a new e l e c t r o n i c c o n f i g u r a t i o n . Th is process was observed on the a d d i t i o n o f c e r t a i n l i gands ( P n B u 3 , P P h 3 , A sPh 3 and CN~) to s o l u t i o n s o f c e r t a i n c a t i o n r a d i c a l s ( R u I I ( 0 E P ) + ' ( C 0 ) L , L = vacant , py and B r " ) and r e s u l t e d in ruthen ium( I I I ) p roduc t s , a r e a c t i o n tha t was found to be r e v e r s i b l e w i t h A sPh 3 . E l e c t r ochem ica l s t ud i e s of R u H ( 0 E P ) ( C0 )P n Bu 3 showed t ha t o x i d a t i o n gave a ruthen ium( I I I ) product ( R u I I I ( 0 E P ) ( P n B u 3 J + ) formed v i a a c a t i o n r a d i c a l i n te rmed ia te tha t r a p i d l y underwent an IMET r e a c t i o n . From these observat ions a mechanism was po s tu l a ted f o r the IMET r e a c t i o n seen on the a d d i t i o n o f l i gands to i r - c a t i o n r a d i c a l s . The coo rd i na t i on o f these l i g a n d s , a l l o f which can e x h i b i t n - a c i d i c p r o p e r t i e s , t rans to the CO i s be l i e ved to l a b i l i z e the carbonyl whose d i s s o c i a t i o n then t r i g g e r s the IMET r e a c t i o n . i i i The second oxidat ion o f a R u I I ( 0 E P ) L 2 complex (L f CO or CS) gave in one case the ruthenium(II I) t r -cat ion r ad i ca l Ru*** (0EP) + " ( P n B u 3 ) 2 , and, in a second case, a poss ib le ruthenium(IV) porphyrin species R u * V ( 0 E P ) ( C N ) 2 . The react ions o f the f i ve -coord ina te ruthenium(II I) species Ru*** (OEP)CP n Bu 3 ) + were studied a l so and gave access to a range of complexes of the type R u I I I ( 0 E P ) ( P n B u 3 ) ( l i g a n d ) + . Certa in ruthenium(III) complexes ( R u i n ( 0 E P ) ( A s P h 3 ) 2 + , R u H I ( 0 E P ) ( P P h 3 ) 2 + and R u i n ( 0 E P ) ( P n B u 3 ) + ) , when purged with CO, were found to undergo p a r t i a l l y a IMET react ion to form cat ion rad i ca l spec ie s . A mechanism suggested for the t r a n s f e r o f e lectrons between neighbouring cytochromes in the mitochondrial re sp i ra to ry chain postulates the formation o f Fe(II) porphyrin t r - ca t i on r ad i ca l s and IMET reac t i on s . Within the l i m i t s o f the model system the observed react ion of the ruthenium i r - c a t i o n r ad i ca l s t e n t a t i v e l y support such a mechanism for the b i o l o g i ca l system. i v 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 Porphyr ins i n Nature "1 1.2 E l e c t r on Transport and the Cytochromes 4 1.3 The Mechanism o f E l e c t r on Trans fe r between the Cytochromes 19 1 .4 Other Heme Redox P ro te in s 24 1.5 Mode l l i ng the Cytochromes 24 1.6 Porphyr in Cat ion Rad ica l s and I n t ramo lecu la r T rans fe r o f E l ec t ron s 29 REFERENCES - Chapter 1 ;. 34 CHAPTER 2 APPARATUS AND EXPERIMENTAL PROCEDURE 41 2.1 General Inst rumentat ion and Procedures 41 2.2 E lec t rochemica l Apparatus and Procedures 46 2.2a Instrumentat ion 46 2.2b Apparatus and Procedures 49 2.3 Pho to l y s i s Experiments 55 2.3a Bulk Pho t o l y s i s Experiments 55 V Page 2.3b F l a s h P h o t o l y s i s E x p e r i m e n t s : - I n s t r u m e n t -a t i o n 55 2 .3c F l a s h P h o t o l y s i s E x p e r i m e n t s : - P r o c e d u r e s and Data C o l l e c t i o n 59 2.4 M a t e r i a l s (1) Ga se s , S o l v e n t s , L i g a n d s and E l e c t r o l y t e s 60 2.4a Gases 60 2.4b S o l v e n t s 60 2.4c L i g a n d s 61 2.4d E l e c t r o l y t e s 62 2.4e M i s c e l l a n e o u s 64 2.5 M a t e r i a l s (2) P r e p a r a t i o n o f t h e Ruthen ium Com-p l e x e s . . . 65 REFERENCES - CHAPTER 2 74 CHAPTER 3 SOME PRELIMINARY EXPERIMENTS 76 3.1 The C o o r d i n a t i o n o f L i g a n d L i n Complexes o f t h e Type R u H ( 0 E P ) ( C 0 ) L i n S o l u t i o n . . , 76 3.2 S o l v a t i o n o f Ru (0EP ) (C0 ) L i n D i f f e r e n t S o l v e n t s 89 3.3 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 ( 0 E P ) ( C 0 ) P n B u 3 (8) 102 3.4 The C o o r d i n a t i o n o f An i on s t o Ru (0EP ) (C0 ) (1 ) i n C H 2 C 1 2 as S o l v e n t 1 0 9 REFERENCES - CHAPTER 3 1 1 3 vi Page CHAPTER 4 THE OXIDATION OF RUTHENIUM PORPHYRIN CARBONYL COMPLEXES Ru n(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: Ru(OEP)-(CS)py 146 REFERENCES - CHAPTER 4 148 CHAPTER 5 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 radical species of the same ground state 164 5.1c Anionic ligands that give the other ground state of the cation radical 166 5.Id Ligands that in s tant ly reduce the cation radi cal 167 5.1e Discussion and Conclusions 158 5.2 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) + * (C0)py] + Cl0 4 " . . . 175 v i i Page 5.2c Reactions o f [ Ru (0EP ) + ' ( C0 ) Im] + C10 4 " . . . 177 5.3 React ions of a Cat ion Radica l Species in a Coord ina t ing So lvent 184 5.4 React ions of Ligands with a Related Thiocarbonyl Cat ion Radica l - Ru(0EP) + ' (CS )py 187 5.5 Conc l u s i on : - The R e a c t i v i t y of Cat ion Rad ica l s towards Ligands 188 5.6 The Reduction React ion 192 5.6a Po s s i b l e Mechanisms fo r the Reduction React ion 192 5.6b Experimental Studies o f the Reduction React ion 198 REFERENCES - CHAPTER 5 202 CHAPTER 6 AN ANOMALOUS OXIDATION OF Ru(0EP)(C0)L COMPLEXES (L = P n B u 3 , P P h 3 , and AsPh 3 ) : THE MECHANISM OF INTRA-MOLECULAR ELECTRON TRANSFER (IMET) 203 6.1 The E l e c t r o chem i s t r y o f R u H ( 0 E P ) ( C 0 ) P n B u 3 . . . 203 6.2 The P reparat ion o f R u 1 1 J ( O E P ) ( P n B u 3 ) + and Some Reactions I nvo l v ing I n t ramo lecu la r E l e c t r on T rans fe r (IMET) 219 6.3 The E l e c t r o chem i s t r y o f o ther R u n ( 0 E P ) ( C 0 ) L Complexes (L = PPh 3 and AsPh 3 ) t ha t g ive r i s e to Ruthenium(I I I ) Products 226 v i i i Page 6.4 The Mechanism of the In t ramolecu la r E l e c t r on T rans fe r (IMET) React ions between Ruthenium(II) and the Porphyr in Cat ion Radica l 231 REFERENCES - CHAPTER 6 239 CHAPTER 7 MISCELLANEOUS CHEMISTRY INVOLVING RUTHENIUM(111) PORPHYRIN SPECIES 240 7.1 The Ox ida t i on of R u 1 1 ( O E P ) ( P n B u 3 ) 2 and Related Chemistry 240 7.2 The Decomposition o f [ R u I ] C I ( 0 E P ) ( P n B u 3 ) 2 ] + B r " 249 7.3 React ions and P r ope r t i e s o f ftuIn(0EP) ( P n B u 3 ) ] + -C10 4 " 252 7.4 React ions and P r ope r t i e s o f R u I H ( 0 E P ) ( P n Bu 3 ) B r 268 7.5 React ions and P r ope r t i e s o f Ru 1 ^OEP) ( P n B u 3 ) as Prepared by the Reduction o f [ R u H I ( 0 E P ) ( P n B u 3 ) ] + -C10 4 " . 273 7.6 The Formation and React ions o f [ R u I H ( 0 E P ) ( P P h 3 ) 2 ] + -C10 4 ~ 280 7.7 The Formation and Reactions of [ R u i n ( 0 E P ) ( A sPh 3 ) ' 2 ] + -C10 4 ~ 285 7.8 The Ox idat ion o f E t 4 N + [ R u H I ( 0 E P ) ( C N ) 2 ] " . . . . 294 REFERENCES - CHAPTER 7 300 CHAPTER 8 THE PHOTOLYSIS OF RUTHENIUM CARBONYL PORPHYRIN ^-CATION . RADICALS 302 8.1 The Resu l t s of the Pho to l y s i s S tud ies 306 IX Page 8.1a Pho to l y s i s of Ru(0EP) + ' ( C0 )py 306 8.1b Pho to l y s i s o f Ru(0EP) + "(CO) 310 8.1c Pho to l y s i s o f [Ru(0EP) + - (CO)Br ] 314 8.Id Pho to l y s i s of Ru(0EP) +"(CO)Im 315 8.1e Spectra o f the T rans ien t States 315 8.2 D i scuss ion o f the Pho to l y s i s Resu l t s 318 REFERENCES - CHAPTER 8 328 CHAPTER 9 CONCLUSIONS 329 X LIST OF TABLES Ta b.l e Page 1 .1 Properties of Mitochondrial Cytochromes 9 3.1 The Variat ion 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 for Solutions in CH 2 Cl 2 of Ru(0EP)(C0)L Species 82 3.3 The Effect of Added EtOH on the Spectrum of a 10"5M Solution of Ru(OEP)(CO)EtOH Dissolved in CH 2C1 2 83 3.4 Addition of Ethanol to a Solution of Ru(OEP)(CO)EtOH in CH 2C1 2 86 3.5 Spectral Data for Ru(OEP)(CO)EtOH Dissolved in Various Solvents 90 3.6 Equil ibrium Constants for the Coordination of Ligands to Ru(0EP)(C0) in Dichloromethane as Solvent 95 3.7 The Estimation of the Equil ibrium Constant for the Reaction L + Ru(0EP)(C0)CH3CN?=±Ru(0EPXC0)L + CHgCN 97 3.8 The Wavelength of the Soret (y) Absorption Band for a Number of Ru H (0EP)L 2 and R u U ( O E P ) ( C 0 ) L Complexes . . . . 108 3.9 The Coordination of Anions to Ru(0EP)(C0) in CH 2C1 2 . . . . 112 4.10 The Reversible Reduction Potentials (E i ) Observed for Ru(0EP)(C0) and Ru(OEP)(C0)4Mepy in Dichloromethane in the Presence of Various E lect ro ly te Anions 118 4.2 Var iat ion of Reduction Potentials with the Nature of the S ixth Ligand 120 xi Page 4.3 A Comparison of Reduction Potentials of Ru(0EP)(C0) in Ace ton i t r i l e and Dichloromethane as Solvent 122 4.4 Conductivity Studies of Cation Radical [Ru 1 l {0EP) + ' (C0)Br] and Related Species , 141 4.5 Optical Spectral Data for the Ruthenium(11) Porphyrin . . Tr-Cation Radical Complexes 145 5.1 A Summary of the Major Products of the Reaction of Ligands with Ruthenium(II) Porphyrin ir -Cat ion Radicals . . . . . 153 6.1 A Comparison of the Potentials for the Electrochemical T T n Processes seen in the Oxidation of Ru (0EP)(C0)P Bu 3 as.a Function of the E l e c t r o l y t i c Co-anion Present 207 7.1 Optical Spectral Data for Species obtained by Oxidation of Ru n (0EP) (P n Bu3) 2 249 7.2 The Optical Spectra of Species obtained from [Ru***(0EP)-(P n Bu 3 ) ] + C10 4 - 259 7.3 Cycl ic Voltammetry Data for Species obtained by Ligand Addition to [Ru I I I ( 0EP ) (P n Bu 3 ) ] + C10 4 ~ 265 7.4 The Optical Spectral Data of Ru H (0EP)(P n Bu 3 ) and Derivatives 279 7.5 Electrochemical Data for the Ruthenium Porphyrin Complexes Ru n ( 0EP )L 2 (L = P n Bu 3 , PPh 3 , AsPh 3, MeCN, py and CN") . . . 290 7.6 The Optical Spectral Data for Ru 1 1{ OEP) ( PPh 3 ) 2 , Ru H ( 0EP ) -(AsPh 3 ) 2 , E t 4 N + [ R u H I ( 0 E P ) ( C N ) 2 ] ' , and the i r Oxidation Products 298 8.1 Summary of Results of the Flash Photolysis of Ru(0EP) +"(C0)L Species 319 x i i LIST OF FIGURES Page Figure 1.1 Porphin 3 1.2 Protoporphyrin IX. 3 1.3 The structure of a six-coordinate iron(I I ) porphyrin complex 3 1.4 The opt ica 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 6 1.5 The structures of the iron porphyrin complexes found in cyto-chromes of classes a and c 7 1.6 The mitochondrial electron transport chain 11 1.7 The decline in free energy as electron pairs flow down the 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 cyto-chrome c. 17 1.10 Schematic representation of cytochrome c interactions with cytochromes aa^ and c-j in the mitochondrial membrane . . . . 19 1.11 The proposed mechanism for electron transfer between the heme groups of two cytochromes v ia cation radical i n t e r -mediates 25 1 .12 The oxidation of camphor by cytochrome P-450 25 1.13 The reaction of i ron( I I ) porphyrins with oxygen to give a y-oxo-dimer as product 27 x i i i Page 2 I I I 1 .14 The o p t i c a l s p e c t r u m o f t h e A - j u c a t i o n r a d i c a l [Co ( 0 E P ) + " ] 2 + . 2 B r ~ i n CHC13 and t h e spec t rum o f t h e 2 A 2 u s p e c i e s [ C o m ( 0 E P ) + " ] 2 + : ; 2 C 1 0 4 : . in " CHGI3 formed by a d d i n g AgC10 4 t o t h e bromide complex 31 2.1 De s i gn s o f q u a r t z c e l l s u sed i n o p t i c a l s p e c t r o s c o p y . . . . 42 2.2 An a n a e r o b i c e . s . r . c e l l 42 2.3 The c o n d u c t i v i t y c e l l used 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 2 C1 2 45 2.4 A s c h e m a t i c c i r c u i t d i a g r am f o r 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 47 2.'5 The H - c e l l and e l e c t r o d e a r r angement used f o r c y c l i c v o l t a m m e t r y 50 2.6 The a p p a r a t u s used f o r t h e b u l k e l e c t r o l y s i s o f a p o r p h y r i n s p e c i e s 52 2.7 A f l o w c e l l u sed t o s t u d y t h e o p t i c a l s p e c t r a o f c a t i o n r a d i c a l s d u r i n g t h e i r f o r m a t i o n 54 2.8 The a p p a r a t u s used 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 s o l u t i o n s 56 2.9 The 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 57 3 . l i t The o p t i c a l s pec t r um o f Ru (0EP) (C0 )P n Bu 3 i n CH 2 C1 2 . . . . 78 3.2 The changes i n o p t i c a l s pec t rum r e s u l t i n g f rom t h e a d d i t i o n o f P P h 3 t o a s o l u t i o n o f Ru(0EP)(C0) i n CH 2 C1 2 79 3.3 P l o t o f log 1 0 ( [Ru (0EP)(C0)Et0H ]/[Ru (0EP)(C0)] ) v s . l o g 1 Q [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 the r e a c t i o n Ru(0EP)(;CO) + E t O H ? = i R u ( O E P ) ( C O ) E t O H 88 x i y Page 3 . 4 O p t i c a l s p e c t r a o f C H 2 C 1 2 s o l u t i o n s o f R i ) ( 0 E P ) ( C 0 ) u s e d i n l i g a n d b i n d i n g e x p e r i m e n t s , a n d t h e s p e c t r a 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 o b t a i n e d i n t h e p r e s e n c e o f e x c e s s a d d e d l i g a n d ; L = E t O H , C H 3 C N , C H 3 N 0 2 , A s P h 3 , E t 3 N a n d Im . . . 92 3 . 5 The 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 n B u 3 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 2 C l 2 / 4 M e p y 104 3 . 6 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 ) C N " i n C H 2 C 1 2 o b t a i n e d on a d d i n g an e x c e s s o f T E A + C N " t o a s o l u t i o n o f Ru( OEP) ( C O ) , . . 110 3 . 7 The o p t i c a l s p e c t r u m o f R u ( O E P ) ( C 0 ) C 1 ~ i n C H 2 C 1 2 o b t a i n e d on a d d i n g 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 ) 111 4 . 1 The 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 ) E t O H i n 0 . 0 5 M T B A P - C H 2 C 1 2 117 4 . 2 The 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 ) E t 0 H i n 0 . 0 5 M TBAP and 0 . 0 0 5 M T E A + C 1 " i n C H 2 C 1 2 124 4 . 3 The f o r m a t i o n o f R u ( 0 E P ) + ' ( C 0 ) 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 ( 0 E P ) ( C 0 ) i n 0 . 0 5 M T B A P - C H 2 C 1 2 i n a f l o w c e l l a n d f o l l o w e d s p e c t r o s c o p i c a l l y 126 4 . 4 The o p t i c a l s p e c t r a o f t h e e l e c t r o c h e m i c a l l y p r e p a r e d c a t i o n r a d i c a l s 127 4 . 5 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 [ R u ( 0 E P ) + ' ( C 0 ) B r ] 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 R u ( 0 E P ) ( C 0 ) 135 4 . 6 The i n c o m p l e t e f o r m a t i o n o f R u ( 0 E P ) + ' ( C 0 ) M e C N by b r o m i n e o x i d a t i o n 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 by t h e c h a n g e i n o p t i c a l s p e c t r u m 137 XV Page 4.7 The opt ica l spectrum in CH 2C1 2 of [Ru(0EP) + ' (C0)Br] prepared by the oxidation of Ru(0EP)(C0), and the spectrum of Ru(0Epf'-(CO) obtained by adding AgBF^ to the bromide complex . . . . 144 4.8 The opt ica l spectrum of the cation radical Ru(0EP) + (CS)py prepared by the electrochemical oxidation of Ru(OEP)(CS)py in 0.05M TBAP-CH2C12 147 5.1 The opt ica l spectra of the product ( R u i n ( 0 E P ) ( P n B u 3 ) 2 + ) obtained on adding P n Bu 3 to Ru n (0EP) + '(C0) and the ruthenium( II) species (Ru^( OEP) (P n Bu 3 ) 2 ) formed on reduc-t ion of th i s product 156 5.2 The opt ica l spectra of the product ( R u I H ( 0 E P ) ( P P h 3 ) 2 + ) obtained on adding PPh 3 to Ru I ] :(0EP) + '(C0) and the ruthe-nium(II) species (Ru I I (0EP)(PPh 3 ) 2 ) formed on reduction of th i s product 157 5.3 The opt ical spectrum of the product (Ru n i (OEP ) (A sPh 3 ) 2 + ) obtained on adding AsPh 3 to Ru J I (0EP) + ' (CO) and purging the solut ion with argon, and the regeneration of a cation radical species on purging with CO 159 5.4 The opt ica l spectrum of the product mixture obtained on adding excess SbPh 3 to Ru(0EP) + '( CO) in CH 2C1 2 "161 5.5 The opt ica l spectrum of the product obtained on adding excess TEA+CN" to a solut ion of Ru(0EP)+"(CO) in CH 2C1 2 . . 163 xvi Page 5.6 The opt ica l spectrum of the mixture of products (Ru*^(0EP)-: ( P n B u 3 ) 2 + and Ru I n ( 0EP ) (P n Bu 3 )B r ) obtained on adding P n Bu 3 to [Ru(0EP) + '(C0)Br] in CH 2C1 2 172 5.7 The opt ica l spectra of the mixture of products (Ru***(0EP)-( P n B u 3 ) 2 + and Ru H I ( 0EP ) (P n Bu 3 )py + ) obtained on adding P n Bu 3 to Ru H (0EP) + '(C0)py in CH 2C1 2, and the ruthenium(II) species obtained on reducing th i s product mixture 176 5.8 The opt ica l spectra Of the products obtained on adding an excess of P n Bu 3 to Ru(0EP)+*(C0)Im in CH 2C1 2 179 5.9 The opt ica l spectrum of the ruthenium(III) product obtained on adding PPh 3 to a solut ion of Ru(0EP) + '(C0)Im in CH 2C1 2 181 5.10 The opt ica l spectrum of the mixture of products formed on reducing the ruthenium(III) species obtained when PPh 3 (10" 3M) i s added to Ru(0EP) + *(CO)Im, and the changes in the opt ica l spectrum on the addition of excess PPh 3 , and excess Im, respectively 182 5.11 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 193 5.12 The product of the reaction of pyridine with the cation radical species ZnTPP+" 195 5.13 Zinc methoxyisoporphyrin 197 xv i i Page 5.14 The o p t i c a l spectrum o f the green products formed on the r e a c t i o n o f Ru(.0EP) + "(C0)py w i th excess TEA + C1" . . . . 200 6.1 C y c l i c voltammograms of Ru H C0EP) (C0 )P n Bu 3 i n 0.05M TBAP-CH 2C1. 2 204 6.2 C y c l i c voltammogram o f Ru 1 1 (OEP ) (C0 )P n Bu 3 i n 0.05M TBAP-CH 2 C1 2 i l l u s t r a t i n g the e f f e c t of ho ld ing the poten-t i a l at ^+0.7V f o r 20 seconds on the o x i d a t i o n sweep . . . 208 6.3 C y c l i c voltammograms o f R u 1 1 (OEP)(C0)P n Bu 3 i n 0.05M TPATFS-CH 2C1 2 showing the e f f e c t o f a change i n the maximum)sweep p o t e n t i a l 210 6.4 C y c l i c voltammograms of R u n ( 0 E P ) (C0 )P n Bu 3 showing the e f f e c t of d i f f e r e n t e l e c t r o l y t e anions on the nature o f the voltammogram 212 6.5 C y c l i c voltammograms o f R u J I ( 0 E P ) ( C 0 ) P n B u 3 i n the presence o f coo rd i na t i n g anions (0.001M TEA +C1~) and i n a coo rd i na t i n g so l ven t (1:1 v/v CH 2Cl 2/MeCN) 213 6.6 C y c l i c voltammogram of Ru n(0EP)CC0)P nBu 3 i n 0.05M TBAF-CH 2 C1 2 a f t e r s tand ing f o r ^30 minutes 215 6.7 C y c l i c voltammogram of R u n ( 0 E P ) ( C 0 ) P n B u 3 i n 0.05M TPATFS-CH 2C1 2 s a tu ra ted with CO 215 6.8; Op t i ca l spectrum of a sample o f [ R u i n ( 0 E P ) ( P n B u 3 ) ] + -C10 4 " 221 x v i i i Page 6.9 The o p t i c a l spectrum o f a sample o f R u n i ( 0 E P ) ( P n B u 3 ) + i n the presence and absence of excess,CO 224 6.10 C y c l i c voltammogram o f R u n ( 0 E P ) ( C 0 ) P P h 3 im 0.05M TBAF-CH 2 C1 2 232 6.11 C y c l i c voltammogram of Ru H (OEP)(CO)EtOH i n 0.05M TBAP-CH 2 C1 2 i n the presence o f one equ i va len t o f AsPh 3 . . . . 232 7.1 The c y c l i c voltammogram of R u H ( 0 E P ) ( P n B u 3 ) 2 i n 0.05M TBAF-CH 2 C1 2 241 7.2 The o p t i c a l spec t ra of R u H ( 0 E P ) ( P n B u 3 ) 2 and R u I H ( 0 E P ) -( P n B u 3 ) 2 + 242 7.3 The o p t i c a l spectrum o f the d i c a t i o n spec ies Ru * * * ( 0 EP ) + -( P n B u 3 ) 2 246 7.4 The c y c l i c voltammogram of R u I H ( 0 E P ) ( P n B u 3 ) + i n 0.05M TBAP-CH 2 C1 2 254 7.5 Representat ive o p t i c a l spect ra o f the products ( i . e . R u i n ( 0 E P ) ( . P n B u 3 ) L + ; L = P P h 3 , MeCN, CN" and B r " ) obta ined on a d d i t i o n o f Ligands (L) to R u T I I ( 0 E P ) -( P n B u 3 ) + 256 7.6 Representat ive c y c l i c voltammograms of the products ( i . e . R u H I ( 0 E P ) ( P n B u 3 ) L + ; L = P P h 3 , MeCN and CN") obta ined on a d d i t i o n o f Ligands (L) to R u I H ( 0 E P ) ( P n B u 3 ) + 263 7.7 C y c l i c voltammograms o f R u H I ( 0 E P ) ( P n B u 3 ) B r i n 0.05M TBAP-CH^CN and 0.05M TBAP-CH 9 C1 9 270 xix Page 7.8 The opt ica l spectrum of Ru I I (0EP)(P n Bu 3 ) formed on the electrochemical reduction of Ru i n ( 0EP ) (P n Bu 3 ) + 274 7.9 The optical spectrum of the product obtained (Ru^OEP) -II (P Bu 3)py) on addition of excess pyridine to Ru (OEP)-(P nBu 3) 276 7.10 The opt ica l spectrum of the product (Ru i n (0EP) (P n Bu 3 )py + ) obtained by the addition of pyridine to Ru i n ( 0EP ) (P nBu 3) + II and the ruthenium(II) species (Ru (OEP)(P Bu 3)py) formed on the reduction of th i s species 277 7.11 The c y c l i c voltammogram of Ru H (0EP) (PPh 3 ) 2 in 0.05M TBAF-CH2C12 281 7.12 The opt ica l spectrum of Ru 1 1 (OEP)(PPh 3 ) 2 in the presence of excess PPh 3 , and the opt ica l spectrum of the e lec t ro -chemical oxidation product ( R u H I ( 0 E P ) ( P P h 3 ) 2 + ) in the presence and absence of excess PPh 3 282 7.13 The opt ica l spectrum of the mixture obtained on purging a solut ion of R u I H ( 0 E P ) ( P P h 3 ) 2 + in CH 2C1 2 with CO . . . 284 7.14 The c y c l i c voltammogram of Ru n (0EP) (AsPh 3 ) 2 in 0.05M TBAP-CH2C12 287 7.15 The opt ical spectrum of R u H I ( 0 E P ) ( A s P h 3 ) 2 + and the spectrum of the mixture of the products obtained on purging a solut ion of th 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 R u * * J ( 0 E P ) ( A s P h 3 ) 2 + w i t h CO 292 7.17 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 ) p o r p h y r i n 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 ) -C C N ) 2 " 295 7.18 T h e o p t i c a l s p e c t r u m o f [ R u I V ( 0 ) ( 0 E P ) + ' ] + B r ~ ; 296 8.1 T h e 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 s p e c i e s u s e d i n t h e f l a s h p h o t o l y s i s e x p e r i m e n t s . . . . 303 8.2 T h e 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 ) p o r p h y r i n 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 p h o t o -l y s i s o f R u(0EP) + ' ( C 0 ) p y 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 d e l a y s 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 R u ( 0 E P ) + ' ( C 0 ) L c a t i o n r a d i c a l s p e c i e s s t u d i e d 308 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 p h o t o l y s i n g 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 [Ru(OEP) -( C O ) B r ] 311 8.5 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 T h e 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 e s t i -m a t e d f r o m t h e o b s e r v e d d i f f e r e n c e s p e c t r a 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 fo l lowing l i s t of abbrev iat ions , many of which are commonly adopted in research l i t e r a t u r e , w i l l be employed in th i s thes i s A absorbance A e l e c t r o l y t e anion A Angstrom uni t ( 1 0 " ^ metres) 2 2 A-|u and A,,u the two poss ib le ground states o f a metal loporphyrin Tr -cat ion rad ica l 2 * 2 * A-|u and A £ u the exc i ted states o f a metal loporphyr in Tr - ca t ion rad ica l A £ U a higher exc i ted state of the A2U ground state of a metal loporphyr in Tr -cat ion rad ica l ADP adenosine diphosphate ATP adenosine tr iphosphate A s ( M e s i t y l ) 3 t r i m e s i t y l a r s i n e (As(CgH-j-|)3) AsPh 3 t r i pheny la r s ine (As(CgHg) 3 acac acetylacetonate anion BM Bohr magneton n Bu normal butyl (C^Hg-) Bu^N + (or TBA +) tetra-n-butylammonium cat ion b broiad ( in nmr) C concentrat ion XX i t T °C d e g r e e C e l s i u s cm c e n t i m e t r e cm"* wave number c y s t . c y s t e i n e D.N. d o n o r number (Gutmann) DMF N , N ' - d i m e t h y i f o r m a m i d e , HC0NMe 2 DMSO d i m e t h y l s u l p h o x i d e ( C H 3 ) 2 S 0 d d o u b l e t ( i n nmr) E1 h a l f - w a v e p o t e n t i a l o r 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 f o r an e l e c t r o d e p r o c e s s E-| t h e h a l f - w a v e p o t e n t i a l f o r t h e f i r s t e l e c t r o d e p r o c e s s o b s e r v e d on a v oltammogram E 2 t h e h a l f - w a v e p o t e n t i a l f o r t h e s e c o n d e l e c t r o d e p r o c e s s o b s e r v e d on a v oltammogram Ep 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 ( o x i d i z i n g ) p r o c e s s 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 ( r e d u c i n g ) p r o c e s s E Q ' s t a n d a r d r e d u c t i o n p o t e n t i a l f o r IM s o l u t i o n s o f 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 p h y s i o - ; • l o g i c a l pH) E t e t h y l ( C 2 H 5 ~ ) E t ^ N t r i e t h y l a m i n e E t . N + , ( o r T E A + ) t e t r a e t h y l a m m o n i u m c a t i o n x x i v e e l e c t r o n e . s . r . e l e c t r o n s p i n r e s o n a n c e eq e q u i v a l e n t eV e l e c t r o n v o l t G g a u s s e g gram, o r e . s . r . g - v a l u e g a v a v e r a g e g - v a l u e ( e . s . r . ) Hb h e m o g l o b i n Hz h e r z h h o u r hv l i g h t e n e r g y ( P l a n k ' s c o n s t a n t x f r e q u e n c y ) 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 o f a b s o r p t i o n i n nm may be i n d i c a t e d by s u b s c r i p t ) I Q 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 t h e 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 ( e x c e s s l i g a n d p r e s e n t ) I n u c l e a r s p i n number I.R. i n f r a - r e d IMET 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 PA i s o p r o p a n o l Im i m i d a z o l Ip t h e peak c u r r e n t f o r t h e a n o d i c ( o x i d i z i n g ) p r o c e s s 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 ) p r o c e s s XXV K d e g r e e K e l v i n , o r e q u i l i b r i u m c o n s t a n t k k i n e t i c r a t e c o n s t a n t o r c o n d u c t i v i t y c e l l c o n s t a n t K c a l k i l o c a l o r i e s L 1 i t r e , o r 1 i g a n d L, l _ i , o r l _ 2 a x i a l l i g a n d s t o a m e t a l l o p o r p h y r i n c o m p l e x M m o l a r M.C.D. m a g n e t i c c i r c u l a r d i c h r o i s m 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 m y o g l o b i n Me m e t h y l (CHg-) MeCN a c e t o n i t r i l e MeOH m e t h a n o l 4Mepy 4 - m e t h y l p y r i d i n e MgOEP magnesium o c t a e t h y l p o r p h y r i n MgOEP c a t i o n r a d i c a l o f magnesium o c t a e t h y l p o r p h y r i n Mol . wt. m o l e c u l a r w e i g h t m m e t r e , o r m u l t i p l e t ( i n nmr) m-H m e t a - h y d r o g e n ( o n a p h e n y l r i n g ) mg m i l l i g r a m mho r e c i p r o c a l ohm mi n s m i n u t e s mJ mi H i j o u l e mL m i l l i l i t r e mm m i l l i m e t r e mol , m o l e xxvi mV m i l l i v o l t NADH the reduced form of nicotinamide adenine d inuc l eo t i de , the oxid ized form is NAD+ NADP the reduced form of nicotinamide adenine d inuc leo-ti.de diphosphate, the ox id ized form is NADP+ n an integer nm nanometre (.10"^ metre) nmr nuclear magnetic resonance ns nanosecond (10 seconds) OEP octaethylporphyr in (OEP) cat ion rad ica l o f octaethylporphyr in 2+. (OEP) d i - c a t i o n rad ica l (formed by the removal o f two e lectrons from the porphyrin) of octaethylporphyr in OMA opt i ca l multichannel analyser 0-H ortho-hydrogen (on a phenyl r ing) P.. inorganic phosphate (P0 4 ) P n Bu 3 t r i -n -buty lphosph ine P ( C 4 H g ) 3 P(cyclohexyl ) 3 t r i c yc l ohexy l phosphine PCCgH-j ^ ) 3 P(0Me) 3 tr imethyl phosphite PPh 3 tr iphenylphosphine Ph phenyl (.C gH5-) Ph 3P0 tr iphenylphosphine oxide Pr n-propyl ( C ^ - ) Pr^N (or TPA ) tetra-n-propylammonium cat ion p-H para-hydrogen (on a phenyl r ing) xxv i i pH -1og 1 0 [H + ] pKa - l o g 1 Q K a -12 ps picosecond (10 seconds) py pyr id ine CCgHgN) q quartet ( in nmr) R res i s tance Ref. reference Ru(0EP)L-|l-2 general formula for a s ix -coord inate ruthenium octaethylporphyr in complex. I f the oxidat ion s tate of the metal i s not ind icated i t i s assumed to be Ru(I I). S solvent SHE standard hydrogen e lectrode SbPhg t r i p h e n y l s t i b i n e s second, or s i ng le t ( in nmr) sa t . saturated TBA + or Bu^N + tetra-n-butylammonium cat ion TBAF tetra-n-butylammonium tet ra f luoroborate (Bu 4 N + BF 4 ~) TBAH tetra-n-butylammonium hexafluorophosphate (Bu 4N +PFg~) TBAP tetra-n-butylammonium perchlorate ( B u ^ d O ^ - ) TEA + or E t^N + tetraethylammonium cat ion TEAP tetraethylammonium perchlorate (Et 4 N + C10 4 ~) TEAPIC tetraethylammonium pi crate ( .Et^l^C^N^Oy - ) THF tetrahydrofuran x x v i i i TMP t e t r a m e s i t y l p o r p h y r i n TMS t e t r a m e t h y l s i l a n e T P A + o r P r ^ N + t e t r a - n - p r o p y l a m m o n i u m c a t i o n TPAF t e t r a - n - p r o p y l a m m o n i u m f l u o r o b o r a t e TPATFS t e t r a - n - p r o p y l a m m o n i u m 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 TPP m e s o - t e t r a p h e n y l p o r p h y r i n t t r i p l e t ( i n nmr) u.v. u l t r a - v i o l e t V v o l t s v v olume ZnTPP z i n c t e t r a p h e n y l p o r p h y r i n ZnTPP c a t i o n r a d i c a l o f z i n c t e t r a p h e n y l p o r p h y r i n a t h e p r i n c i p l e v i s i b l e a b s o r p t i o n ( l o w e r e n e r g y ) 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 felosest t o t h e n i t r o g e n atom 6 t h e p r i n c i p l e v i s i b l e a b s o r p t i o n ( h i g h e r e n e r g y ) 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 re m o v e d f r o m t h e n i t r o g e n atom Y t h e p r i n c i p l e n e a r - u . v . a b s o r p t i o n ( S o r e t i ) o f a m e t a l 1 o p o r p h y r i n , o r t h e c a r b o n atom i n a p y r i d i n e r i n g two c a r b o n atoms removed f r o m t h e n i t r o g e n atom AA c h a n g e i n a b s o r b a n c e 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) is defined as 0.0 parts per million e molar extinction coefficient A molar conductivity A m a x wavelength of a principle absorption peak yL microlitre u magnetic moment, or bonding involving the overlap of transition metal d-orbitals y / i i 0 nuclear magnetic moment relative to that of a hydrogen nucleus v C Q carbonyl stretching frequency 77 bonding where electron density is on either side of the intemuclear plane a bonding where electron density is a maximum on the internuclear axis Q ohms (j> quantum yield approximately > greater than >> much greater than XXX less than much 1 ess than IDENTIFICATION OF COMPOUNDS The fo l lowing numbering system w i l l be used fo r the compounds re ferred to in th i s thes i s 1 Ru(0EP)(C0) Ru(OEP)(CO)EtOH Ru(0EP)C0)py Ru(0EP)CC0)4Mepy Ru(0EP)(C0)Im Ru(0EP)(C0)MeCN Ru(0EP)(.P nBu 3) 2 8 Ru(0EP)(C0)P nBu 3 2 3 4 5 6 7 9^  See below III 1P_ R u i U ( O E P ) ( P n B u 3 ) B r 1 1 Ru(0EP)(C0)PPh 3 1 2 Ru(.0EP).(PPh3)2 la. Ru(0EP) + '(C0) i b [Ru(OEP) +*(CO)Br] i c [Ru(0EP) + ' (C0)Cl ] I d [Ru(0EP) +*(C0)SCN] 3a Ru(0EP) + ' (C0)py 5_a 6a 8a 8b 8c Ru(0EP) + ' (C0)Im Ru(0EP) + '(C0)MeCN Ru(0EP) + ' (C0)P n Bu 3 Ru(0EP ) 2 + ' ( C0 )P n Bu 3 R u n i ( 0 E P ) 2 + ' ( C 0 ) P n B u 3 11a Ru(0EP) + ' (C0)PPh. xxx i u R u ( 0 E P ) ( A s P h 3 ) 2 i i [ R u I I I ( 0 E P ) ( C N ) 2 l ~ E t 4 N + 11 R u n i C 0 E P ) ( P P h 3 ) 2 + 16. R u i n ( 0 E P ) ( A s P h 3 ) 2 + 17 R u I n ( 0 E P ) ( S b P h 3 ) 2 + R u I n ( 0 E P ) ( P n B u 3 ) + i i R u ( 0 E P ) ( C 0 ) A s P h 3 20 R u i n ( 0 E P ) ( A s P h 3 ) B r i i R u H I ( 0 E P ) ( P P h 3 ) B r 22 R u n i C 0 E P ) + " ( P n B u 3 ) 2 23 R u ( 0 E P ) ( P n B u 3 ) 24, 26. and 28 s e e b e l o w 25 R u ( 0 E P ) ( P n B u 3 ) M e C N 27. R u ( 0 E P ) ( . P n B u 3 ) p y 29 R u ( 0 E P ) ( P n B u 3 ) P P h 3 30 - 32_ s e e b e l o w 33 R u H I ( 0 E P ) ( P n B u 3 ) C N 34 R u n i ( 0 E P ) ( . P n B u 3 ) C l 18a R u m ( 0 E P ) + ' ( P n B u 3 ) 18b R u I n ( 0 E P ) 2 + ' ( P n B u 3 ) 19a R u ( 0 E P ) + * ( C 0 ) A s P h 3 xxx i i Some of the fol lowing s ix -coord inate complexes of the type T T T r» Ru (0EP)(P Bu 3)L were prepared with a bromide co-anion as well as i ne r t co-anions such as ClO^". I f the complex i s associated with C I , the number i s followed by "a " and i f associated with Br" a "b" i s used. 9 Ru C0EP)(.P nBu 3 , + '2 i i R uI ] I ( 0EP ) (P n Bu 3 , MeCN+ 26 R u I ] I ( 0 E P ) ( P n B u 3 P y + 28 R u I ] I ( 0 E P ) ( P n B u 3 )PPh 3 + 30 R u I ] I ( 0 E P ) ( P n B u 3 j MeOH+ l i Ru 1 1 I ( 0 E P ) ( P n B u 3 ' A s P h 3 + 32 Ru 1 1 I ( 0 E P ) ( P n B u 3 ; SbPh 3 + 35 Ru 1 1 I (0EP ) (P n Bu 3 ] lm + xxxi i i ACKNOWLEDGEMENTS I wish espec ia l ly to thank my supervisors, Professors David Dolphin and Brian James, for their, help and encouragement]in the wr i t ing of th i s thes i s . I/would l i k e to thank many coworkers, both past and present, for helpful discussions and comments. In par t i cu la r I would l i k e to express my gratitude to Dr. G. Bisset for useful suggestions on chromatography, Mr. P.S. P h i l l i p s for information on obtaining e.s . r . spectra, and Dr. T. Leung for many discussions on the chemistry of ruthenium porphyrin systems. Thanks are due to Dr. T. Leung and Professor R.C. Thompson for the magnetic moment determinations. I also acknowledge the help of Dr. G. Domazetis and Professors J.Y. Becker, and D. Hoi ten, with whorm I collaborated on some of the work described in th i s thes i s . My thanks to T i l l y Schreinders for her excel lent typing of th i s manuscri pt. A teaching assistantship from the Univers ity of B r i t i s h Columbia (1977-83) i s g ra te fu l l y acknowledged. 1 CHAPTER 1 INTRODUCTION ^ • l 1.1 Porphyrins in Nature A l l porphyrins can be considered to be der ivat ives of the parent compound porphin (Figure 1.1). This i s atetrapyrroTic macrocycle with continuous conjugation throughout the r i ng . A number of paths through th i s r ing involve 18 TT e lectrons. Molecular o rb i ta l theory has shown that c y c l i c species involving 4n+2 TT electrons (n = 1, 2, 3, 4 etc.) in a con-jugated pathway show considerable s t ab i l i z a t i o n and a var iety of properties usually label led "aromatic". Porphin der ivat ives show the predicted s t a b i l i z a t i o n (n = 4) and aromatic properties. This r ing i s also a strong tetra-dentate ligand eas i l y coordinating to metal ions to form metal lo-porphin (porphyrin) der ivat ives . 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 losely 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 labora-tory but rather fewer are found in nature. The porphyrin found in many natural systems i s protoporphyrin IX. This, l i k e a l l porphyrins, i s a good ligand and combines with i ron( 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 on ta i n i n g i r on porphyr ins a t t h e i r a c t i v e s i t e , can be d i v i ded i n t o three c a t e g o r i e s . The f i r s t category conta ins those p ro te in s which r e v e r s i b l y bind oxygen. These are oxygen t r an spo r t p ro te in s such as hemoglobin and myoglobin. The second category con s i s t s of p ro te in s t ha t are incapab le o f b ind ing oxygen or other small molecules but are capable o f undergoing r e v e r s i b l e o x i d a t i o n and reduc t i on r e a c t i o n s . These are e l e c t r o n t r a n s f e r p ro te i n s and i nc l ude most o f the cytochromes. The t h i r d category inc ludes those complexes capable o f b ind ing oxygen and a l so reduc ing i t by t r a n s f e r o f e l e c t r o n s . Hence t h i s t h i r d c l a s s i nco rpo ra te s both the p rev i ou s l y mentioned f u n c t i o n s . Examples are cytochrome - P450, which d e t o x i f i e s f a t - s o l u b l e chemicals by i n s e r t i n g an oxygen atom i n t o an unac t i va ted carbon-hydrogen bond thus making the compound more water s o l u b l e , and the te rmina l e l e c t r o n acceptor o f the e l e c t r o n t r an spo r t chain in ae rob ic r e s p i r a t i o n c a l l e d cytochrome c - ox i da se , which t r a n s f e r s the e l ec t r on s from the porphyr ins to coord inated oxygen, e v e n t u a l l y reduc ing i t to water. Related complexes to t h i s t h i r d c l a s s are the enzymes c a t a l a s e and hor serad i sh peroxidase which bind perox ide ions r a the r than oxygen. These d i f f e r e n c e s i n f u n c t i o n are be l ieved to be determined by v a r i a t i o n s in the environment of the heme p r o s t h e t i c group. The heme group i s surrounded by the p ro te i n apoenzyme and i n most cases i s held in p lace 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 the c e n t r a l i r o n ( I I ) i o n , the 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 o f l i gands i s u s u a l l y o c t a h e d r a l . The porphyr in i s a p lanar t e t r a - d e n t a t e l i g and which occupies four l i g and s i t e s l e av i ng 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 coo rd i na t i on (F igure 1.3). 3 Figure 1.1 Porphin Figure 1.2 P rotoporphyr in IX , (modi f ied from Ref. 5 ) . Figure 1.3 The s t r u c t u r e of a s i x - c o o H d inate i ron( . I I ) porphyr in complex. The porphyr in i s represented by the four n i t rogen atoms i n a plane and the a x i a l l i gands are denoted by ' X ' . 4 These two pos i t ions are occupied by amino-acid residues which l a r ge l y determine the funct ion of the heme p ro te in . In the case of hemoglobin and myoglobin, one ax ia l pos i t ion i s occupied by a h i s t i d i ne l igand and the other ax ia l pos i t ion i s vacant al lowing small molecules (such as O^, NO and CO) to bind to the i r on . The coordinat ion of these small molecules i s usua l ly rever s ib le and, for example with 0£, no permanent ox idat ion of the iron atom occurs. In the case of e lect ron transport p ro te ins , which show no r e a c t i v i t y towards small molecules or ions , the two ax ia l l igands are coordinated s trong ly to the heme hence blocking the access of the oxygen molecule. The complexes that show oxygen binding coupled with subsequent e lectron t rans fer to the oxygen have a s tructure s im i l a r to that of the oxygen transport prote ins , but the ax ia l l igand coordinated to the i r o n , and the amino ac id residues surrounding the heme group, d i f f e r so as to s t a b i l i z e intermediates formed in the ox idat ion and reduct ion of the complex. 1.2 E lectron Transport and the Cytochromes Introduction to the cytochromes: In the l i v i n g c e l l the ox idat ion of glucose to carbon d ioxide and water is l inked to a small organel le with a double membrane s t ructure ca l l ed a mitochondrion. These organel les are p a r t i c u l a r l y densely packed in hard working t i s sue such as muscle. In 1925 K e i l i n 2 studied i n tac t insect muscles with a small spectroscope and i d e n t i f i e d a number of absorption peaks resembling those of reduced hejne prote ins . These were the "Histohematins" observed by MacMunn in 1888 but i t was K e i l i n who showed that the absorptions were re l a ted to muscular 5 a c t i v i t y a n d renamed t h e p i g m e n t s " c y t o c h r o m e s " . T h e c y t o c h r o m e s have 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 . T he most i n t e n s e , a n d 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 c a l l e d t h e S o r e t o r y b a n d . The two w e a k e r b a n d s a r e l a b e l l e d . a and $. The w a v e l e n g t h a t w h i c h 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 t h e 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 bands were due 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 due 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 o r p r o t o h e m e 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 , o r a m o d i f i e d p r o t o h e m e known as "Heme a " ( F i g u r e 1 . 5 ) . The 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 s c h e m e : - 4 ' 5 ( T h e q u o t e d a b s o r p t i o n bands 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 -t i o n s ) . 1) C y t o c h r o m e s a : ( 5 8 0 - 590 nm). The p r o s t h e t i c g r o u p i s "Heme a " , t h e p o r p h y r i n c o m p o n e n t o f w h i c h i s s i m i l a r t o p r o t o p o r p h y r i n IX e x c e p t f o r t h e a d d i t i o n o f a l o n g c a r b o n c h a i n a n d an a l d e h y d e g r o u p t o t h e p o r p h y r i n p e r i p h e r y . 2) C y t o c h r o m e s b: ( 5 5 6 - 558 nm). The p r o s t h e t i c g r o u p i s heme ( i r o n ( l l ) c o m p l e x 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 p r o t e i n v i a l i g a n d - m e t a l i n t e r a c t i o n s . 1 r 3 0 0 4 0 0 5 0 0 6 0 0 WAVELENGTH (nm) F i g u r e 1.4 The 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 10" 5M 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 t h e m a i n 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 s p e c t r u m ( s e e t e x t ) . From R e f . 1. 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 g r o u p 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 s u r r o u n d i n g p r o t e i n v i a t h e v i n y l g r o u p s on o n e edge o f t h e p r o t o p o r p h y r i n IX m o l e c u l e ( F i g u r e 1 . 5 ) . A l l t h r e e t y p e s o f c y t o c h r o m e a r e f o u n d 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 f r o m t h e o x i d a t i o n o f g l u c o s e . The c y t o c h r o m e s 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 7 Figure 1.5 The structures of the iron porphyrin complexes found in cytochromes of c lass a and c . a) Heme a; two poss ib le s tructures of the long carbon chain are shown on the r i g h t , b) Heme c in which heme is cova lent ly l inked to the protein cha in , part of which is a l so shown. Both diagrams modif ied from Ref. 5. 8 in order of increasing ease of reduction, which can be measured by a reduction potential for the cytochrome. In b io logical systems th i s quantity i s usually cal led 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 is more d i f f i c u l t to reduce but that once reduced the species is 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"Q' value -0.32 volts for a two electron transfer with respect to the Standard Hydrogen Electrode). As the cytochromes are to receive electrons from these reducing agents,their reduction potentials aremore pos it ive than those of the coenzymes. In a l l cases a member of the electron transport chain receives an electron from a member with a more negative E^ potential and then passes the electron to a species with a more pos it ive E^ potent i a l , un 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 . Some soluble cytochromes are found in the cytoplasm of the c e l l . The most biochemically s i gn i f i cant uses of cytochromes are found in the energy-related, membrane-bound, electron transport chains of the mitochondria (respirat ion) 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 -r i t i e s . 9 T a b l e 1.1 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 C y t o c h r o m e s — C y t o c h r o m e Mol . wt. '(.V) A b s o r p t i o n maxima i n r e d u c e d f o r m , nm. a 3 Y b 25,000 +0. .030 563 532 429 c l 3 7,000 +0, .225 554 524 418 c 12,500 +0, .235 550 521 415 a 200,000 +0 .210 600 - 439 a 3 +0 .385 603.5 - 443 a) 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 c a r b o n 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 K r e b s ( o r t h e t r i c a r b o x y l i c a c i d ) c y c l e , w h i c h o c c u r s i n t h e i n n e r m a t r i x o f t h e m i t o c h o n d r i a . 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 f o r m o f e l e c t r o n s i s f o r m e d and 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 co-enzyme 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 . S u c h co-enzyme 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 as t h e enzyme p r o s t h e t i c g r o u p n i c o t i n a m i d e a d e n i n e d i n u c l e o t i d e ( N A D ) . The r e d u c e d 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 t h e e l e c t r o n s t o a c c e p t o r s w h i c h t h e n f e e d t h e e l e c t r o n s i n t o t h e t o p o f 10 the transport cha in. The e lectrons are used f i r s t to reduce an i r o n -sulphur protein or ubiquinone, both of which are non-heme redox pro te in s , and are then passed on down the chain through various cytochromes u n t i l the l a s t complex (cytochrome oxidase) uses the e lectrons to reduce oxygen to water (Figure 1.6). The purpose o f th i s rather complicated mechanism is that i t allows the c e l l to harness some of the energy produced from the ox idat ion of glucose. This energy i n i t i a l l y res ides in the reducing power of the electrons released in the Krebs cyc le that are used to reduce NAD+ to *-* + + NADH which is i t s e l f a strong reducing agent ( E q =-0.32 for NAD + H + 2e *= iNADH). Oxygen is a strong ox id i z ing agent at pH 7, ( E 0 = +0.816V for %0 2 + 2H + + 2 e ~ * = ± H 2 0 ) , and hence oxygen and NADH would react together very r e a d i l y with re lease of considerable energy (AE 0 " = +1.136V,so free energy change = -52.7 kcal mol - 1 ) which would normally be wasted. However, the electron: on moving down the transport chain loses f ree energy gradual ly and where there i s a s u f f i c i e n t f ree energy drop between two adjacent e l e c t r o n : c a r r i e r s the e lec t ron t rans fer i s l inked to the phospho-r y l a t i o n of ADP (AGQ = +7.3 kcal mo l " 1 for ADP + P i ?=^ATP + H 20) to give ATP which i s a general source of energy for biochemical react ions in the c e l l . The approximate pos i t ions of ADP phosphorylations are seen in Figure 1.6 and the corresponding f ree energy changes in Figure 1.7. Cytochromes of the "b" c lass These cytochromes,widespread in nature, contain a heme group held in place by 1igand-metal in teract ions and securely wrapped in the prote in Site I ATP Site II ATP I Site III ATP NAD—* FP,(4Fe.S)—i»Q —»• (2Fe.S) *-cyt b(Fe.S)cyt ci—»-cyt c—*-cyt a<u Figure 1.6 The mitochondria l e lectron transport cha in . E lectrons enter the chain at the pos i t ions ind icated by arrows. FP i s a f l avoprote in known as NAD Dehydrogenase, Fe S represents an i ron-su lphur protein and Q is ubiquinone. The other abbreviat ions have t h e i r usual meanings. Modif ied from Ref. 1. 12 E'o kcal O, Figure 1.7 The decline in free energy as electron pairs flow down the mitochondrial transport chain to oxygen. Energy changes denoted by arrows are s u f f i c i en 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 in both of the major electron transport chains. Research on the mitochondrial cytochrome b species has been very l imited because of the great d i f f i c u l t i e s in extracting intact enzyme 8 ' 9 . Cytochrome b in the mitochondrial membrane is believed to form a complex with cytochrome c-,1, and l i e s deeply embedded in the inner membrane and 13 r equ i r e s severe c ond i t i o n s i n c l ud i n g the use o f detergents to remove i t . Because of the m o d i f i c a t i o n s that can occur when us ing such severe proce-dures , analyses o f p reparat ions can va ry w ide l y t and con s i de rab le debate i s cont inu ing as to whether there i s on ly one cytochrome b i n mi tochondr ia from a s i n g l e source or whether there are a number of d i f f e r e n t cytochromes b present i n a given m e m b r a n e ^ 0 ' 1 1 . L i t t l e i s known g e n e r a l l y about the heme environment i n these membrane bound cytochromes b. However,a hydrophobic p ro te 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 fo r the operat ion o f the c y t o c h r o m e 1 2 , as seen by the e f f e c t of processes (such as heat ing) which d i s r u p t t h i s environment, and s h i f t the i n - s i t u r educ t i on p o t e n t i a l by up to 300 m V 1 2 - 1 4 . In an attempt to reach some t e n t a t i v e conc lu s ions about the s t r u c -tu res and f u n c t i o n o f the m i tochondr i a l cytochrome b spec ies another type o f cytochrome b, found in the endoplasmic r e t i c u l um of mammalian c e l l s , 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 1 5 . Th is i s cytochrome b^, 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 ud i ed . The normal b iochemical f unc t i on o f t h i s p r o t e i n i s to ac t as an e l e c t r o n t r an spo r t agent i n a three membered enzyme system used to desaturate f a t t y a c i d s 1 5 . The p ro te i n i s bound to the membranes o f the endoplasmic r e t i c u l um but i s e a s i l y r e m o v e d 1 6 ' 1 7 , and conta ins a po lypept ide o f 93 amino-acids and a J. 8 non - cova l en t l y bonded heme group. C r y s t a l s have been obta ined and X- ray a n a l y s i s 1 9 - 2 1 showed the molecule to be approx imately c y l i n d r i c a l w i t h a he ight o f 37 & and a diameter o f 31 & (F igure 1.8). The heme group i s 14 F i g u r e 1 . 8 S c h e m a t i c d i a g r a m o f t h e b a c k b o n e c h a i n o f c y t o c h r o m e b ^ . The a - c a r b o n p o s i t i o n s a r e n u m b e r e d 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 w h o s e 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 f r o m R e f . 1 9 . 15 a l m o s t c o m p l e t e l y b u r i e d i n a h y d r o p h o b i c p o c k e t a t t h e t o p o f t h e m o l e c u l e 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 g r o u p . One edge o f t h e p o r p h y r i n c o r e i s s l i g h t l y e x p o s e d t o t h e e x t e r i o r s o l v e n t 2 2 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 ; b i n d i n g t o t h e o t h e r p a r t n e r s 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 more o f t h e heme edge t o become e x p o s e d 1 5 . The b t y p e c y t o c h r o m e s f o u n d i n t h e m i t o c h o n d r i a l membrane a r e e x p e c t e d t o have s i m i -l a r s t r u c t u r e s . C y t o c h r o m e s o f t h e " 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 membrane. 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 » a n d a p p e a r s t o be s t r o n g l y c o m p l e x e d w i t h c y t o c h r o m e b. D e t e r g e n t t r e a t m e n t i s r e q u i r e d t o e x t r a c t c y t o c h r o m e C p as i s t h e c a s e o f c y t o c h r o m e b , a n d t h i s p r e s e n t s s e r i o u s p r o b l e m s i n s u b s e q u e n t s t u d i e s . C y t o c h r o m e c , i n c o n t r a s t , i s f o u n d 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 m e m b r a n e 2 5 - 2 7 , t h a t i s i n t h e s p a c e b e t w e e n t h e two membranes, and r e q u i r e s o n l y a c i d i c c o n d i t i o n s f o r e x t r a c t i o n 2 8 - 3 0 . T h i s w a t e r s o l u b l e c y t o c h r o m e t a k e s e l e c t r o n s f r o m 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) and 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 3 c o m p l e x , w h i c h i s b e l i e v e d t o l i e r i g h t a c r o s s t h e i n n e r m e m b r a n e 3 1 . The e x t r a c t e d c y t o c h r o m e 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 3 2 , a nd i s t h e m o s t e x t e n s i v e l y s t u d i e d o f 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 s . T h e 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 s u l p h a t e w h i c h p r e c i p i t a t e o u t m o s t p r o t e i n i m p u r i t i e s 3 3 . T h e s t r u c t u r e a n d 16 f u n c t i o n o f t h i s p r o t e i n have been e x t e n s i v e l y s t u d i e d and t h i s has h e l p e d o u r u n d e r s t a n d i n g o f t h e c y t o c h r o m e s i n g e n e r a l . M i t o c h o n d r i a l c y t o c h r o m e c has a m o l e c u l a r w e i g h t o f ^12,400 w h i c h i s s u r p r i s i n g l y i n d e p e n d e n t o f t h e s o u r c e o f t h e m i t o c h o n d r i a , a n d o p e r a t e s 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 . T h i s s m a l l 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 one 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 l i n k s . T he 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 ( c y s t . 14 a n d 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 I X 3 6 " 4 0 . T h e 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 between t h e two j a w s w i t h o n l y one e d g e o f t h e p o r p h y r i n r i n g e x p o s e d t o t h e e x t e r n a l s o l v e n t ( F i j g u r e 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 nd 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 as h i g h as +0.25 v o l t s - 4 - T h e i r o n c e n t r e has 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 p r o p e r t i e s o f t h e p r o t e i n . 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 s u l p h u r atom 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 ) atom and 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 f o r m 4 5 " 4 8 . C y t o c h r o m e s o f t h e " 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 f r o m c y t o c h r o m e c t o o x y g e n , 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 t h e m i t o c h o n d r i a l t r a n s p o r t c h a i n . T h i s 17 Figure 1.9 Schematic diagram of the backbone chain of horse heart cytochrome c. Tine ot-carbon pos i t ions are numbered in sequence. Modif ied from Ref. 41 . 18 protein was hence c a l l e d cytochrome c oxidase and was known to bind oxygen and use e lectrons from cytochrome c to reduce the oxygen to water, 4 9 . Detergents were required to detach the large protein from the mitochondrial m e m b r a n e 4 9 - 5 1 . Due to the severe extract ion cond i t ions , the protein samples showed va r i a t i on in p roper t ie s , depending upon the techniques used, as measured by changes in ana l y s i s , spectra l data and the s t o i c h i o -metry of react ion with carbon monoxide 9 > 1 + 9 . Like the c la s s b cytochromes found in the mitochondrial membrane, r e l a t i v e l y l i t t l e i s known about the s t ructure of the p ro te i n , although i t is known to contain two heme a prosthet ic g r o u p s 5 2 , only one of which is able to bind oxygen or carbon monoxide 5 3 . The d i f f e rence in r e a c t i v i t y i s bel ieved to be determined by the nature and bonding strength of the ax ia l l igands to the heme a iron atom. The whole protein is composed of several prote in s u b - u n i t s 5 4 ' 5 5 . One c l u s te r of sub-un i t s , c a l l e d cytochrome a 3 , surrounds the heme a group and is capable of binding oxygen, and l i e s on the ins ide of the inner membrane 3 7 > 5 1 + ' 5 5 . The second c l u s te r o f sub-units surrounds the other heme a group and is known as cytochrome a and l i e s on the outside of the inner membrane (Figure 1.10). The whole complex is c a l l ed terminal cy to -chrome c-oxidase or cytochrome a a g 5 7 ' 5 8 . Also present in the prote in are two copper a t o m s 5 9 ' 6 0 whose presence has been l inked to the problem of the reduction of an oxygen molecule by a cytochrome which i s formal ly a one-e lect ron reducing agent. Reduction of an oxygen molecule by one e lect ron gives the e n e r g e t i c a l l y unfavoured superoxide a n i o n 6 1 . The oxygen molecule is thought to bridge a reduced copper atom and the cytochrome a 3 i ron cent re , 19 Figure 1,10 Schematic representat ion of cytochrome c in terac t ions with cy to -chromes a a 3 and c-j in the mitochondrial membrane. The diagrams i l l u s t r a t e how cytochrome c may accomplish e lect ron t rans fe r between the oxidase and cytochrome c-j by various poss ib le mechanisms: two-dimentional d i f f u s i on on the surface of the membrane, a s s o c i a t i o n -d i s soc i a t i on v ia the aqueous phase, and in a " s o l i d - s t a t e " con f i gu -ra t ion that impl ies a ternary complex between cytochromes c-| , c , and a a 3 . The roman numerals ind icate the subunits of cytochrome oxidase. Molecular weights are: I ^ 40,000; II ^  20,000, III a, 15,900, IV * 11,000; VI ^  8,000. The pos i t ion of the heme groups and the net charges on the various components are i nd i ca ted . Modif ied from Ref. 65. and hence can be reduced in a two-electron process to the more favourable peroxide spec ies . Bound peroxide species have been detected by reac t ing oxygen with chemical ly reduced cytochrome a a 3 at low temperatures, and th i s observation supports the suggestion of an oxygen b r i d g e 6 2 - 6 4 . 1.3 The Mechanism of E lectron Transfer between the Cytochromes Most of our knowledge o f the mechanism of e lectron t rans fer between the cytochromes has come from studies invo lv ing cytochrome c as t h i s is the eas iest of the mitochondrial 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 6 5 . C y t o c h r o m e c i s f o u n d b e t w e e n 2 5 - 2 7 ' t h e two membranes o f t h e m i t o c h o n d r i a a n d i n t e r a c t s w i t h two membrane-bound 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 ^ . T h e r e 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 t h e i n t e r a c t i o n s . T h e f i r s t p o s t u -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 ^ . T h i s 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 c o m p l e x e s s i m u l t a n e o u s l y 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-| t o c y t o c h r o m e a . T h i s r e q u i r e s t h e f o r m a t i o n o f a 1:1:1 c o m p l e x o f t h e t h r e e c o m p onents 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 between t h e two membrane-bound 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 t h e o r y " ( F i g u r e 1.10). 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 b o o s t 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 c o m p l e x 7 0 . T h e 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 t h a t c y t o c h r o m e c f i r s t b i n d 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 . T h i s b i n a r y c o m p l e x t h e n d i s s o c i a t e s 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 o r 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 c o m p l e t e l y i n t o s o l u t i o n , and t h e n r e b i n d s t o c y t o c h r o m e a a 3 f o r t h e 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). 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 i n d i n g 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 b o t h 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 c h a r g e s 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 , w h e r e a s c y t o c h r o m e c i s a b a s i c p r o t e i n 7 1 ' 7 2 w i t h s u b s t a n t i a l p o s i t i v e c h a r g e s , p a r t i c u l a r l y on t h e l y s i n e c o l l a r w h i c h s u r r o u n d s t h e e n t r a n c 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 s u s p e c t e d o f b e i n g a b i n d i n g s i t e 7 3 - 7 5 . T h i s l y s i n e c o l l a r i s f o r m e d by 21 lys ines 72, 73, 86, 87 and 88 . A problem with th i s mechanism i s that some determinations of the rate of d i s soc i a t i on o f cytochrome c from i t s complex with cytochrome aa^ give a rate that i s sub s t an t i a l l y slower than the overa l l rate of e lectron t rans fer through the whole e lect ron transport c h a i n 7 6 ' 7 7 . This appears to preclude th i s mechanism as a method of e lectron t rans fer between cytochrome c-| and aa^, but other studies o f the same d i s -soc ia t ion have given widely ranging r a t e s 7 8 , and hence the s i gn i f i c ance of the rates obtained has been g reat ly undermined. A l l experiments done so far to t ry and d e c i s i v e l y show which mechanism is operat ing have run into s i m i l a r problems and given inconc lus ive r e s u l t s . The " s o l i d s t a te " mechanism requires two separate e lect ron t rans fer pathways from the ex te r i o r of the cytochrome c molecule to the i ron atom at the centre of the heme group. I n i t i a l studies ind icated that the rate of e lec t ron t rans fer 6 6 by these two pathways would be very s im i l a r and th i s caused Chance et a l . To ru le out the " s o l i d s ta te " mechanism as they f e l t that in such an asymmetri-cal molecule as cytochrome c the a l ternate e lec t ron pathways would have very d i f f e r e n t a c t i va t i on energies and rates of e lectron t r ans fe r . More recent studies have suggested the two pathways in cytochrome c may have very d i f f e r e n t rates and th i s has increased i n te re s t in the " s o l i d s t a te " t h e o r y 6 8 ' 7 9 . The question remains as to the poss ib le pathways for e lec t ron t rans fer from the ex te r i o r of the cytochrome c molecule to the heme i ron atom. Oxidized cytochrome c has been observed to react with a large number of inorganic reducing a g e n t s 6 5 , the rates usua l ly being within the range 3 4 - 1 - 1 10 -10 M s . Any suggested mechanism has to explain these fas t r a te s . 22 For i n s t ance , an inner - sphere mechanism requ i re s the reduc ing agent to gain d i r e c t access to the heme i r on atom, so that an e l e c t r o n can be t r a n s f e r r e d v i a a b r i dg i ng l i g a n d . This would r equ i r e the opening of the heme c l e f t , and the breaking o f the i r o n - a x i a l l i g and bond. The est imated r a te f o r t h i s process i s about 60 s " and hence the observed ra tes of r educ t i on e f f e c t i v e l y r u l e out an inner - sphere mechanism; a f a s t e r outer sphere mechanism v i a some conduction path from the e x t e r i o r o f the p r o t e i n to the i r on atom seems l i k e l y . Two types o f hypotheses have been suggested: the p ro te i n mechanisms, and the " p r o t e i n - l e s s " mechanisms. The p ro te i n mechanisms i n vo l ve the t r an spo 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 cha in o f adjacent aromatic amino-a c i d r e s i d u e s 8 3 - 8 5 . These mechanisms sought to exp l a i n the conservat ion o f a number of aromat ic res idues i n c cytochromes obta ined from w ide l y d i f f e r e n t sources. These t heo r i e s became l e s s tenable whenever a new cytochrome c was analysed and one o f the s p e c i f i e d res idues was rep laced by an a l i p h a t i c r e s i d u e . The other major problem w i th these mechanisms was that t y p i c a l aromatic amino-acid res idues ( pheny l a l an i ne , t ryptophan, t y r o s i ne and h i s t i d i n e ) are on ly reduced at extremely negat ive redox p o t e n t i a l s and hence the est imated 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 amino-ac id res idues was u s u a l l y very high ( i n some cases 50 kca l/mole 8 6 ) , compared w i t h the observed ra tes o f e l e c t r o n t r a n s f e r which u s u a l l y gave an a c t i v a t i o n energy of about 11.3 k c a l / m o l e 8 6 - 8 7 . Hence, the p ro te i n mechanisms have l o s t p o p u l a r i t y over the yea r s . The " p r o t e i n - l e s s " mechanisms can be d i v i ded i n t o two c l a s s e s . The f i r s t env i s i on s the b ind ing o f the donor and acceptor complex, f o l l owed 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 an e l e c t r o n between t h e i r o n c e n t r e s 8 8 ' 8 9 . T h i s t h e o r y e q u a t e s t h e i n t e r v e n i n g p r o t e i n t o a c l a s s i c a l b a r r i e r t h r o u g h w h i c h 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 , d e p e n d i n g upon t h e 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 , a nd t u n n e l l i n g t h r o u g h 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 s y s t e m s 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 . O f 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 has been c r y s t a l l i z e d a n d a s t r u c t u r e d e t e r m i n e d 4 1 . T h e n o n - m i t o c h o n d r i a l c y t o -c hrome ( b 5 ) has a l s o b e e n c r y s t a l l i z e d a n d i s assumed t o be s t r u c t u r a l l y s i m i l a r t o t h e m i t o c h o n d r i a l b c y t o c h r o m e 1 9 . B o t h 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 e x p o s e d e d g e a nd 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 and 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 9 2 . The 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 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 c h a r g e d i n t e r m e d i a t e s c a l l e d 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 w h i c h 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 c o n j u g a t e d s y s t e m o f t h e p o r p h y r i n ( F i g u r e 1.11). Model s y s t e m s have shown 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 and 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 a nd h e n c e p r o v i d e more e v i d e n c e f o r t h i s m e c h a n i s m . 24 1.4 O t h e r Heme Redox P r o t e i n s I n 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 d i a t o m i c s s u c h as NO, CO, and CN", a n d , i n t h e c a s e 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 f r o m t h e m e t a l l o p o r p h y r i n t o t h e bound m o l e c u l e . T h i s t h i r d c l a s s o f heme p r o t e i n s ( s e e S l e c t i o n 1.1) a r e e x p e c t e d t o h a v e some s i m i l a r i t i e s t o 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 o x y g e n t o w a t e r . C y t o c h r o m e P-450 i s an enzyme f o u n d i n mammalian 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 f o r e i g n c h e m i c a l s f o u n d i n t h e b o d y . 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 hrome have 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 t y p i c a l i n t e n s e l y s t u d i e d 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 t o m e t a b o l i z e / 9 7 camphor ( F i g u r e 1.12) . The camphor 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 c a r -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 o x y g e n m o l e c u l e 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 . H o r s e r a d i s h p e r o x i d a s e a n d 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 p e r o x i d e r a t h e r t h a n o x y g e n . 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 p e r o x i d e t o e f f e c t a r e a c t i o n s i m i l a r t o t h a t a c c o m p l i s h e d 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 s u b s t r a t e s 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 M o d e l l i n g t h e C y t o c h r o m e s 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 bound n a t u r e . E x t r a c t i o n o f t h e s e c y t o c h r o m e s , f r o m t h e m i t o c h o n d r i a , 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 s o t h a t r e s u l t s 25 Fe' Heme s y s t e m s become a d j a c e n t a nd t h e i r t r - o r b i t a l : o v e r l a p -•Fe Fe E l e c t r o n t r a n s f e r i n t h e c y t o c h r o m e s 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 . Fe1 Fe' C y t o c h r o m e s d i s s o c i a t e Fe in Fe' F i g u r e 1.11 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 between 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 nd t h e p l a n a r p o r p h y r i n i s r e p r e s e n t e d s c h e m a t i c a l l y . F i g u r e 1.12 The o x i d a t i o n o f camphor by c y t o c h r o m e P-450. 26 are f a r l e s s u s e f u l 9 ' 4 9 . In attempts to f u r t h e r understand these m e t a l l o -p ro te i n systems, some p r o t e i n - f r e e complexes are used to model the natura l system. The a c t i v e par t o f a cytochrome i s the meta l l opo rphy r i n p r o s t h e t i c group whose chemistry, however, i s undoubtedly mod i f ied by the surrounding p r o t e i n . The meta l l opo rphy r i n can be removed i n t a c t from the cytochrome 1 5 2 and the "ba re " heme i s an obvious candidate as a model f o r the f u l l c y t o -chrome. However, i t was q u i c k l y found tha t such f ou r - coo rd i na te m e t a l l o -porphyr ins were d i f f i c u l t to handle i n s o l u t i o n . Pe r i phe ra l groups on the porphyr in 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 ro to -porphyr in i x 1 0 2 - 1 0 5 ) and, now tha t the a x i a l p o s i t i o n s are no longer blocked by p r o t e i n , t r a ce oxygen can r eac t r a p i d l y to g ive i r o n ( I I I ) spec ies which f i n a l l y form y-oxo-d imers ; 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 cu r r i n g hemes o x i d i z e r e a d i l y ou t s i de o f the p ro te i n env i ronment. (F igure 1 . 1 3 ) 1 0 7 - 1 1 1 . Hence, de sp i te t h e i r c l o se chemical s i m i l a r i t i e s to the i n - v i v o cytochromes, the n a t u r a l l y o c cu r r i n g i r on -po rphy r i n systems are not good models because o f these d i f f i c u l t i e s . The f i r s t problem i s ea s i e s t to so lve by us ing s yn the t i c porphyr ins such as oc tae thy l porphyr in (OEP) or meso-tetraphenyl porphyr in (TPP) that have less r e a c t i v e pe r i phe ra l groups and good s o l u b i l i t y i n non-aqueous so lvents (perhaps themselves a model f o r the l i p i i d environment o f the membrane). Of the two, OEP probably has the l i g and p rope r t i e s c l o s e r to tha t o f the natura l p o r p h y r i n s 1 1 2 ( the phenyl groups on TPP make i t r a ther e l e c t r o n withdrawing) but i s f a r more d i f f i c u l t to make than T P P 1 1 3 . Me ta l l o com-plexes of both porphyr ins have been w ide l y s t u d i e d . 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 . T h e s e 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 . F o r 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 been 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 s c h e m a t i c a l l y . 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 t o g i v e t h e y - p e r o x o c o m p l e x ( I I I ) ; t h i s t h e n d e g r a d e s t o g i v e t h e y - o x o -d i m e r ( I V ) . 28 The s e c o n d p r o b l e m o f o x i d a t i o n i s more s e r i o u s . Low t e m p e r a t u r e 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 have 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 . A n o t h e r s o l u t i o n i s t o b l o c k t h e a p p r o a c h o f t h e s e c o n d p o r p h y r i n ( s t e p s I I I I I , F i g u r e 1.13) 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 c e n t r e . S u c h s y s t e m s have 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 and 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 o x y g e n r e v e r s i b l y 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 s u c h a s y s t e m i s v e r y d e p e n d e n t upon t h e m e t a l u s e d and hence 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 1 1 6 . A c o m p r o m i s e i s t o s u b s t i t u t e r u t h e n i u m f o r t h e i r o n . R u t h e n i u m i s t h e 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 l i g a n d 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**, low 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 more a c c e s s i b l e f o r s t u d y . 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 etween 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 s y s t e m . 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 t r a n s f e r p r o c e s s e s 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 t h a t s i m i l a r p r o c e s s e s may be q u i t e w i d e s p r e a d among m e t a l l o p o r p h y r i n s y s t e m s 1 1 7 . 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 T r a n s f e r o f E l e c t r o n s P o r p h y r i n TT c a t i o n r a d i c a l s were i n i t i a l l y p o s t u l a t e d as s h o r t -l i v e d i n t e r m e d i a t e s f o r m e d i n t h e c h e m i c a l o x i d a t i o n o f v a r i o u s n a t u r a l l y o c c u r r i n g p i g m e n t s . I n t e r e s t i n t h e s e s p e c i e s was i n c r e a s e d when p h o t o x i -d a t i o n o f c h l o r o p h y l l a was 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 was 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 . R e c e n t l y t h e s t u d i e s have moved more 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 s p e c i e s . C h e m i c a l o x i d a -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 , s o l i d s a m p l e s o f p o r p h y r i n c a t i o n r a d i c a l c o m p l e x e s 1 2 1 ' 1 2 2 . E l e c t r o c h e m i c a l o x i d a t i o n c a n a l s o a f f e c t f o r m a t i o n o f c l e a n s o l u 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 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 a v o i d e d 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 4 N + P F g ) . The n a t u r e o f t h e c o o r d i n a t e d a n i o n , c a n 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 h e p r o p e r -t i e s o f t h e c a t i o n r a d i c a l p r e p a r e d 1 2 3 . M e t a l l o p o r p h y r i n 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 t h e p o r p h y r i n r i n g . 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 t h e m e t a l a l t h o u g h f u r t h e r o x i d a t i o n may o c c u r a t t h e r i n g r a t h e r t h a n p l a c e two p o s i t i v e c h a r g e s on t h e m e t a l 1 2 4 ' 1 2 5 . M e t a l i o n s i n c a p a b l e o f f u r t h e r o x i d a t i o n w i l l a l w a y s c a u s e o x i d a t i o n a t t h e r i n g . T h e s i t e o f o x i d a t i o n may 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 m e t a l 1 2 6 . 30 V i s i b l e 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 f t h e s e s y n t h e t i c m e t a l l o -p o r p h y r i n s f a l l i n t o two c l a s s e s 1 2 1 . F i r s t , a r e t h o s e w i t h a s p e c t r u m s i m i l a r t o t h a t o f Mg OEP +", 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 . The s e c o n d c l a s s a r e t h o s e s i m i l a r t o t h e Zn.TPP +* 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 s t r e n g t h a b s o r p t i o n t h r o u g h o u t t h e v i s i b l e . T h e s p e c t r a l t y p e o b s e r v e d was i n d e p e n d e n t o f t h e c o u n t e r - a n i o n . E l e c t r o n s p i n r e s o n a n c e s t u d i e s 1 2 1 ' 1 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 o r -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 . 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 were e x p l a i n e d by m o l e c u l a r o r b i t a l t h e o r y 1 2 1 w h i c h showed t h a t a n e u t r a l 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 o r b i t a l s t h a t e a c h c o n t a i n e d two e l e c t r o n s . However, 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 symmetry s o 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 d e p e n d upon t h e m o l e c u l a r o r b i t a l o c c u p i e d by t h e r e m a i n i n g u n p a i r e d e l e c t r o n . 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 t o ? - +• ? - i 1 2 7 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-|u :(,Mg OEP ). o r /\ ;(Zn,.TPP. ) T h e i m p o r t a n c e o f l i g a t i n g i o n i c s p e c i e s i n c a t i o n r a d i c a l s o l u t i o n s ' — 1 1 + • 12 3 was s e e n i n t h e b e h a v i o u r o f Co (OEP) . B r o m i n e o x i d a t i o n g a v e 2 a s o l u t i o n w i t h a A-] u 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 2 p e r c h l o r a t e m e d i a g a v e a A 2 u s p e c t r u m . T h e d i f f e r e n c e was shown t o be 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 s p e c i e s 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 . 1 4 ) . T h i s was t h e f i r s t r e p o r t e d c a s e where t h e p r e s e n c e o r a b s e n c e o f WAVELENGTH (nm) 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 2 A l u c a t i o n r a d i c a l [ C o I H ( 0 E P ) + ' r?BIIl)nrS+^?i } a n d t h e s P e c t r u m o f t h e 2 A 2 u s p e c i e s C o " I ( 0 E P ) + - ] 2 + . 2 C 1 0 4 - i n C H C 1 3 ( ) f o r m e f b y a d d i n g AgClCty t 0 t n e b r o m i d e c o m p l e x . From R e f . 123. a l i g a n d a f f e c t e d a ch a n g e i n g r o u n d 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 o p t i c a l s p e c t r a i t has been s u g g e s t e d t h a t t h e i n t e r m e d i a t e s (Compounds I) f o r m e d i n t h e r e a c t i o n s o f h o r s e r a d i s h 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 c a t i o n r a d i c a l s p e c i e s 2 2 w i t h A 2 u and A-|u g r o u n d s t a t e s r e s p e c t i v e l y 1 2 3 . H o wever, r e c e n t M.C.D. e v i d e n c e s u g g e s t s t h a t t h e i n t e r m e d i a t e s f o r m e d by t h e o x i d a t i o n o f b o t h h o r s e r a d i s h p e r o x i d a s e 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 t h e same g r o u n d s t a t e 2 2 8 - . 32 E l e c t r o n t r a n s f e r between t h e c e n t r a l ' m e t a l i o n and t h e p o r p h y r i n 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 f o r e l e c t r o n t r a n s f e r b etween t h e c y t o c h r o m e s . An a n a l o g y c a n be s e e n i n t h e o x i d a t i o n o f Pb(OEP) w h i c h g i v e s f i r s t P b I ] t ( 0 E P ) + ' and t h e n ' t IV 2 + 1 1 7 .Pb (OEP) - - . The s e c o n d o x i d a t i o n may o c c u r a t t h e m e t a l o r r i n g b u t t h i s i s r a p i d l y f o l l o w e d 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 t h e f i n a l p r o d u c t (Scheme 1.1) P b n i ( 0 E P ) + ' ^ - 4 TW 9 i p b H ( 0 E P ) > P b I I ( 0 E P ) + - * P b 1 V ( 0 E P ) , ^ ^ P b H ( 0 E P ) 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 m e c h a n i s m . 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 w i t h t h e c a t i o n r a d i c a l o f N i ' n ( T P P ) 1 1 7 ' 1 3 1 . 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 N i H ( T P P ) g a v e a g r e e n s o l u t i o n o f a A-| c a t i o n r a d i c a l s p e c i e s . F r e e z i n g t h e 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 e . s . r . s p e c t r a o f a N i ( i i r ) c o m p l e x . Warming r e g e n e r a t e d t h e o r i g i n a l g r e e n s o l u t i o n , a n d 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 etween m e t a l a n d t h e p o r p h y r i n p e r i p h e r y i s r e v e r s i b l e (Scheme 1 . 2 ) . 33 F " e II •  + • C 0 0 1 TTT L ( T P P ) V - i N i ^ d P P ) - ' : N i U 1 ( T P P ) +e warm G r e e n O r a n g e - R e d SCHEME 1.2 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 1 , 3 r d E d . , W o r t h , New Y o r k 1 9 7 5 . 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 ( 1 9 2 5 ) . 3. C A . MacMunn, H o p p e - S e y l e r ' s Z. P h y s i o l Chem. 13_, 497-499 ( 1 8 8 9 ) . 4 a . 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S o c . 9^7, 5288 ( 1 9 7 5 ) . 41 CHAPTER 2 APPARATUS AND EXPERIMENTAL PROCEDURE 2.1 G e n e r a l I n s t r u m e n t a t i o n and P r o c e d u r e s 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 were r e c o r d e d on a C a r y 17D o r 1756 s p e c t r o p h o t o m e t e r . 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 p a t h l e n g t h s ( 0 . 1 , 1 and 10 cm) u s e d i n t h i s w o r k , i n c l u d i n g c e l l s t h a t 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. T h e weak a b s o r p t i o n ( i n d i -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 nm s e e n i n s p e c t r a r u n 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) i s due t o t h e C H ^ C l 2 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 p a t h -l e n g t h o r 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 were o b t a i n e d on a P e r k i n E l m e r 457 g r a t i n g s p e c t r o p h o t o m e t e r u s i n g KBr d i s c s . N u c l e a r m a g n e t i c r e s o n a n c e s p e c t r a were o b t a i n e d o n a B r u k e r 400 MHz s p e c t r o m e t e r . S a m p l e s were 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 were 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 t o i n t e g r a t e t h e i i s i g n a l s 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 ( S e c t i o n 4 . 1 ) , s o l u -t i o n s (3 x 1 0 ~ ^ M ) o f t h e r u t h e n i u m 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 r u n i n an a n a e r o b i c e . s . r . c e l l ( F i g u r e 2 . 2 ) , a t a m b i e n t a n d 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 , i m m e d i a t e l y 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 + o f s i m i l a r 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 where p o s s i b l e t h e same i n s t r u m e n t c o n d i t i o n s . Z n T P P + ' i s a w e l l c h a r a c t e r i z e d c a t i o n r a d i c a l , 1 h a v i n g one e l e c t r o n s p i n p e r m o l e c u l e a n d 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 d i m e r s 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 1 ! 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. 43 rrnr— S C R E W D O W N S E A L Figure 2.2 An anaerobic e.s.r. c e l l . 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 o f t h e 2 p h e n y l r i n g s . 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 were 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 . O f t e n t h i s p r o c e d u r e o f c o m p a r i n g e . s . r . s i g n a l s g a v e 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 . s e e S e c t i o n 7 . 6 ) . C o m p a r i s o n o f 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 b e c a u s e o f t h e 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 . T h e method c a n n o t 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 i n s o l u t i o n b e c a u s e o f t h i s e f f e c t ( s e e S e c t i o n 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 eung and k 5 R. Thompson u s i n g t h e E v a n s m e t h o d 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 were made on C H ^ C ^ s o l u t i o n s o f p o r p h y r i n s p e c i e s u s i n g a c e l l ( F i g u r e 2.3) w i t h a c e l l c o n s t a n t o f 0.12 cm -* i n c o n j u n c t i o n w i t h a model RCM 15B1 c o n d u c t i v i t y b r i d g e f r o m A r t h u r H~ Thomas Company. S o l u t i o n s o f t h e c a t i o n r a d i c a l were p r e p a r e d f r o m ^20 mg o f R u ( 0 E P ) ( C 0 ) E t 0 H ( 2 ) i n C H 2 C 1 2 and t h e n made up t o 20.0 mL. -4 -3 O t h e r p o r p h y r i n s o l u t i o n s ( f r o m 5 x 1 0 H t o 5 x 10 M) were made up d i r e c t l y f r o m t h e 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 f r o m 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 c o n c e n t r a -t i o n t o o b t a i n m o l a r c o n d u c t i v i t y c o e f f i c i e n t s ( A ) . Mass s p e c t r a were t a k e n on a KRAT0S-AEI MS 902 s p e c t r o m e t e r u s i n g 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. E l e m e n t a l a n a l y s e s were done 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 B R I D G E P O R P H Y R I N S O L U T I O N H O L D E R O U T E R C O N T A I N E R E L E C T R O D E S G L A S S T U B E S H I E L D I N G E L E C T R O D E S F i g u r e 2,3 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 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 P r o c e d u r e a) I n s t r u m e n t a t i o n To o b t a i n c y c l i c v o l tammograms 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) 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 -p r i a t e i n s t r u m e n t a t i o n . The t h e o r y b e h i n d t h e e x p e r i m e n t a l s e t - u p has been d e s c r i b e d e l s e w h e r e , C u r r e n t f l o w s between t h e 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 c u r r e n t ( F i g u r e 2 . 4 ) . 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 s o t h a t t h e p o t e n t i a l o f t h e w o r k i n g e l e c t r o d e w i t h r e s p e c t t o t h e 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 . However, 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 between t h e w o r k i n g and t h e 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 ) . I n t h e e x p e r i -m ents 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 P r o g r a m -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 l i n k e d t o a model 173 PAR P o t e n t i o s t a t w h i c h c o n t r o l l e d 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 . The r e s u l t s were 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 ) a n d 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 were 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 ( L a n d t y p e 1 0 7 ) . A p a i r o f waves on t h e c y c l i c v o ltammogram were b e l i e v e d t o 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 t h e r a t i o o f t h e p eak c u r r e n t s i c / i a s ( i c = p eak c u r r e n t f o r t h e c a t h o d i c 47 ' I f SERVO M O T O R /VWWNAAA a V / P O T E N T I A L MONITOR SWEEP CONTROL ELECTRODES F i g u r e 2.4 A s c h e m a t i c c i r c u i t d i a g r a m f o r 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 . The p o t e n t i a l and 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" and " 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 a s f o l l o w s : 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 , and c ) a u x i l i a r y e l e c t r o d e . See R e f . 6. 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 peak p o t e n t i a l s (EJ: and E^) i s c l o s e t o t h e t h e o r e t i c a l v a l u e o f 59 mV. F o r n o n - a q u e o u s 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 due 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 oltammograms were 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 e x p e r i m e n t s p e r f o r m e d i n d i c h l o r o m e t h a n e t h e t y p i c a l p e ak 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 have been r e p o r t e d t o g i v e peak s e p a r a t i o n s o f ^70 m'V7 and 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 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 l o w e r c o n c e n t r a t i o n ( a n d h e n c e h i g h e r s o l u t i o n r e s i s t a n c e ) o f e l e c t r o l y t e . T h e mean o f t h e peak p o t e n t i a l s (E^ + E p / 2 ) i s c a l l e d t h e h a l f - w a v e p o t e n t i a l and i s q u o t e d a s t h e r e d u c -t i o n p o t e n t i a l f o r t h e e l e c t r o d e p r o c e s s b e i n g c o n s i d e r e d . A l l p o t e n t i a l s 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 A g / S a t / A i f C I 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 (+0.2223V vs.SHE) and a r e u n c o r r e c t e d f o r j u n c t i o n p o t e n t i a l s . 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 and 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 . T h e r e q u i r e d p o t e n t i a l b etween 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 w h i c h a l t e r e d 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 a c c o r d i n g -l y . 49 b) A p p a r a t u s a nd P r o c e d u r e s 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 oltammograms were 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 c o m p a r t m e n t s ( F i g u r e 2 . 5 ) . The 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 c o p p e r w i r e r u n n i n g i n t o t h e open end 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 o f m e r c u r y ( F i g u r e 2 . 5 ) . The A g / S a t ; A g C l 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 . Abo 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 few 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 were a d d e d . A s i l v e r w i r e , f o r m i n g t h e e l e c t r o d e , was t h e n immersed 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 and 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 p u r g e d w i t h a r g o n v i a t h e t e f l o n l e a d f o r a b o u t f i v e m i n u t e s . The 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 b e f o r e a d d i n g t h e p o r p h y r i n s a m p l e . The 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 v o l t a m m o g r a m 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 w o r k i n g e l e c t r o d e c h a n g e s w i t h t h e p o t e n t i a l o f t h e w o r k i n g 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 M E R C U R Y C O N T A C T W I R E S I L V E R W I R E A Q U E O U S K C I + A g C I A G A R P t B E A D P t M E S H F I N E FRITS O S P I N B A R F i g u r e 2.5 T h e H c e l l a n d e l e c t r o d e a r r a n g e m e n t u s e d f o r c y c l i c v o l t a m m e t r y : 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 . 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 c o n c e r n e d . 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 oltammogram o f a r e d u c e d a n d o x i d i z e d 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 between t h e two s p e c i e s i s t h e p r e s e n c e 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 t h e c o m p l e x ; f o r e xample R u * * ( 0 E P ) ( P n B u 3 ) 2 ij) and R u n i ( . 0 E P ) ( . P n B u 3 ) 2 + ( 9 ) , E ^ + 0 . 0 3 V - s e e S e c t i o n 7 . 1 ) . T h i s i s b e c a u s e c y c l i c v o l tammograms a r e 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 . 0.0 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 . H e nce i n t h e v o l tammogram 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 voltammogram w o u l d be i d e n t i c a l t o t h a t o f t h e r e d u c e d s p e c i e s . I f t h e r e d u c e d 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 v o l t ammograms t h i s i s a good i n d i c a t i o n t h a t t h e o x i d a t i o n o r r e d u c t i o n p r o c e s s 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. i s r e v e r s i b l e on a r e l a t i v e l y l o n g t i m e s c a l e ) a l t h o u g h t h e s i t u a t i o n f o r w e a k l y 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 S e c t i o n 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 p l a c e d i n a c y l i n -d r i c a l g l a s s c o n t a i n e r . A t e f l o n c a p f o r t h i s c o n t a i n e r s u p p o r t e d a c l o s e d t u b e o f V y c o r p o r o u s g l a s s ( G o r n i n g 7 9 3 0 ) , f i l l e d w i t h 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 . T h e r e f e r e n c e e l e c t r o d e 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 w i t h 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 immersed 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 u s e d f o r t h e b u l k e l e c t r o l y s i s o f a p o r p h y r i n s p e c i e s . 53 g l a s s c o n t a i n e r w h i c h t h u s f o r m e d t h e w o r k i n g e l e c t r o d e c o m p a r t m e n t . In a t y p i c a l p r e p a r a t i o n 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 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 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 t r a c e i m p u r i t i e s . T h e 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 t h e p o t e n t i a l , c a r e b e i n g t a k e n n o t t o o v e r l o a d t h e p o t e n t i o s t a t . S o l u t i o n s p r e p a r e d f o r e x p e r i m e n t s were t y p i c a l l y o f c o n c e n --4 -3 t r a t i o n s 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 u s e d i n t h e p r e p a r a t i o n o f new compounds ( p o r p h y r i n s a m p l e 100 - 200 mg) were e l e c t r o l y z e d i n a l a r g e r c o n t a i n e r (125 mL', v o l u m e o f s o l u t i o n 40 - 50 mL) a n d were t y p i c a l l y 5 x 1 0 " 3 t o 1 x 10" 2M. C a t i o n r a d i c a l s a m p l e s p r e p a r e d f o r t h e f l a s h p h o t o l y s i s e x p e r i m e n t 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 were m o n i t o r e d d u r i n g t h e o x i d a t i o n p r o c e s s , r e q u i r e d t h e u s e o f a f l o w c e l l . T h i s c e l l , i n c o r p o r a t i n g o p t i c a l windows w i t h p a t h l e n g t h s o f 5 mm and 1 mm ( f o r s t u d y i n g t h e v i s i b l e a nd S o r e t r e g i o n s o f t h e s p e c t r u m , 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 and 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 . T h e 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 removed t o e n s u r e a c o n t i n u o u s c o l u m n o f l i q u i d t h r o u g h o u t t h e e n t i r e f l o w c e l l . The e l e c t r o d e 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 immersed 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 s t i r r e d by 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 t h e f l o w c e l l d u r i n g e l e c -t r o l y s i s . The windows o f t h e f l o w c e l l were 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 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 p r o c e e d e d . 54 E L E C T R O L Y S I S C E L L - O B L A T E SPIN BAR 1 C 1 3 ' l T OPTICAL WINDOWS a) 5mm WINDOW b) Imm WINDOW F i g u r e 2.7 A f l o w c e l l u s e d t o s t u d y t h e o p t i c a l s p e c t r a o f c a t i o n r a d i c a l s d u r i n g t h e i r f o r m a t i o n . 55 2.3 P h o t o l y s i s E x p e r i m e n t s a) B u l k P h o t o l y s i s E x p e r i m e n t s -5 -4 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 were u s u a l l y 10 t o 10 M, and were 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 ( t y p e C i n F i g u r e 2.1) e q u i p p e d w i t h a r u b b e r septum 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 p u r g i n g 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 ) . T h e 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 commencing p h o t o -l y s i s . T he 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 ) . The 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 ^10 cm f r o m t h e lamp. A r a p i d f l o w o f w a t e r t h r o u g h t h e c o n d e n s e r e n s u r e d r e m o v a l o f i n f r a - r e d r a d i a t i o n f r o m t h e p h o t o l y s i s l i g h t . b) F l a s h P h o t o l y s i s E x p e r i m e n t s : - I n s t r u m e n t a t i o n 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 P r o f e s s o r 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 1 0 ( F i g u r e 2 . 9 ) . 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 10Hz. 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 ( p r o b e ) a s p e c t s o f t h e a p p a r a t u s . The 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 532, 355 and 266 nm by u s i n g o r i e n t e d , 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 ( K D P ) . The 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 . The 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 E X I T \ V K A / A R G O N L E A D ilffw—-—SEPTU M L I G H T P O R P H Y R I N S O L U T I O N IN D I C H L O R O M E T H A N E W A T E R F L O W I N G T H R O U G H C O N D E N S E R 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 s o l u t i o n s . 1064 nm Nd:YAG osc. SPS Nd:YAG amp Quantel YG 400 KDP Parametric Generator M 0.25 ra Vidicon -Oi.----Sample pump — U - - --'""''"''--0---hl--o-D--i---0--&-0--\ probe 1 I i 1 ,'FD! OMA Microcomputer 1 1 x ~ ' 1 1 1 1 1 1 1 1 1 1 <^ Delay Line F i g u r e 2.9 The 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 by 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 . T he 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 t r a v e r s e s an o p t i c a l d e l a y l i n e . T h i s c o n t r o l s t h e t i m e d i f f e r e n c e b e t w e e n t h e e x c i t a t i o n l i g h t and 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 . The 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 p r o b e r a d i a t i o n t o a r r i v e a t t h e s a m p l e a n y w h e r e , f r o m a few t e n s o f p i c o s e c o n d s 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 (1 0 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 . P r i o r t o r e a c h i n g t h e s a m p l e , t h e 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 ^ w h i c h s c a t t e r s t h e w a v e l e n g t h s 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 a c o n t i n u u m 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 . The 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 ) , p a s s e d t h r o u g h 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 , and 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 mono-c h r o m a t b r w i t h t h e e x i t s l i t r e m o v e d . A v i d i c o n i s o r i e n t e d : a c r o s s t h e e x i t o f t h e m o n o c h r o m e t e r and f e e d s t o an o p t i c a l m u l t i c h a n n e l a n a l y s e r COMA). The 0MA e l e c t r o n i c s d i s s e c t t h e v i d i c o n d e t e c t o r a c t i v e a r e a i n t o two t r a c k s , e a c h 500 c h a n n e l s w i d e . 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 s p e c t r u m o f p r o b e l i g h t t h r o u g h t h e e x c i t e d s a m p l e , w h i l e t h e s e c o n d 500 c h a n n e l t r a c k i s a l i g n e d t o r e c e i v e p r o b e l i g h t t r a n s m i t t e d t h r o u g h t h e u n e x c i t e d o r r e f e r e n c e r e g i o n o f t h e s a m p l e . 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 c o m p a r e d e l e c t r o n i c a l l y a n d a d i f f e r e n c e s p e c t r u m o b t a i n e d o v e r 59 t h e w a v e l e n g t h 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). S u c h s p e c t r a a r e 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 t o 11 12 g i v e t h e f i n a l s p e c t r u m » c ) F l a s h P h o t o l y s i s E x p e r i m e n t s : - P r o c e d u r e s and Data C o l l e c t i o n S a m p l es o f t h e p o r p h y r i n - r r - c a t i o n r a d i c a l s p e c i e s w e r e p r e p a r e d i n 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 a b s o r p t i o n 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 c o n c e n t r a t e d o t h e r w i s e i n s u f f i c i e n t w h i t e l i g h t o f t h e m o n i t o r i n g p u l s e g o t t h r o u g h t h e s a m p l e t o t h e d e t e c t o r . When u s i n g t h e 1 mm o p t i c a l window -4 o f t h e f l o w c e l l f 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 were a b o u t 5 x 10 M f o r 532 nm p u l s e r a d i a t i o n and 1 x 10 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 . The 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 d u e t o t h e w e a k e r p u l s e s p r o d u c e d 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 nm ( 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. A f t e r c o m p l e t i o n o f t h e 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 t h e 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 ere 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)-. T h e ' -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 t h e l a s e r e x p e r i m e n t s o as t o a v o i d p erma-n e n t p h o t o l y s i s o f a l i m i t e d v o l u m e . Data were c o l l e c t e d o v e r v a r i o u s w a v e l e n g t h 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 were 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 had t o be r e m o v e d by c o m p u t e r a n a l y s i s t o g i v e t h e d e c a y c o n s t a n t q u o t e d i n t h e r e s u l t s . T h i s a n a l y s i s was k i n d l y done by P r o f e s s o r D. H o l t e n ( W a s h i n g t o n 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 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 E l e c t r o l y t e s . a) G a s e s C a r b o n m o n o x i d e and a r g o n were 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 f u r t h e r p u r i f i c a t i o n . b) S o l v e n t s N i t r o m e t h a n e (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 p h o s p h o r u s p e n t o x i d e , and d i s t i l l e d a n d 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 . A n h y d r o u s 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 magnesium e t h o x i d e u n d e r a r g o n and u s e d i m m e d i a t e l y . 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 a r g o n , 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 a t m o s p h e r e . 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 a r g o n 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 as 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 ro3-4 l i t r e s p e r b a t c h were 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 c o l u m n c o n -t a i n i n g g l a s s h e l i c e s . 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 remove 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 remove a v o l a t i l e o x i d i z i n g a g e n t . 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 f r o m w h i c h s a m p l e s o f d i c h l o r o m e t h a n e w e r e d i s t i l l e d u n d e r a r g o n f o r u s e i n e l e c t r o c h e m i c a l e x p e r i m e n t s . T h e b u l k o f t h e s o l v e n t d i s t i l l e d t h r o u g h , t h e 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 , w a s h i n g o f a p p a r a t u s a nd s t o r a g e o f t h e V y c o r 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 g r a d e a n d u s e d w i t h o u t f u r t h e r p u r i f i c a t i o n . c) L i g a n d s 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 and s t o r e d u n d e r a r g o n . 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 b e f o r e u s e . 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 ~ ) ( 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 T C 1 ~ ) was d r i e d on a vacuum 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 o v e r p h o s p h o r u s p e n t o x i d e . 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 p u r i -f i c a t i o n . d) E l e c t r o l y t e s 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 (TBAP) 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 (TEAP) ( 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 f r o m a c e t o n e ( s p e c t r a l g r a d e - E a s t m a n ) , t h e c r y s t a l s g r o u n d up and d r i e d f o r 24 h u n d e r v acuum. T e t r a - n - p r o p y l a m m o n i u m 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 1 3 and g a v e e x c e l l e n t l o o k i n g c r y s t a l s . 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 was 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 . T h e r e s u l t i n g p r e c i -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 . The 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 p r e c i p i t a t e 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 nd 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 and r e d r i e d u n d e r vacuum f o r 24 h, (.60% y i e l d ) . T e t r a - n - b u t y l a m m o n i u m 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 f l u o r o b o r a t e ( 1 0 g) i n a q u e o u s s o l u t i o n . The 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 mL), 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 w e r e c o l l e c t e d , washed w i t h 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 , and t h e n d i s s o l v e d i n a minimum v o l u m e o f b o i l i n g a c e t o n e . 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 c r y s t a l s t h a t w e re c o l l e c t e d , d r i e d , g r o u n d up and d r i e d u n d e r vacuum f o r 24 h, ( 2 5 % y i e l d ) . L i k e t h e c o r r e s p o n d i n g 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 s a l t t h i s m a t e r i a l t e n d e d t o o i l o u t o f s o l u t i o n v e r y e a s i l y . L a t e r b a t c h e s o f f l u o r o b o r a t e e l e c t r o -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 m e t h o d s . T e t r a - n - p r o p y l a m m o n i u m t e t r a f l u o r o b o r a t e ( T P A F ) : 20 g o f t e t r a - n -p r opylammonium b r o m i d e was d i s s o l v e d i n ^300 mL o f d i s t i l l e d w a t e r a nd 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 on s t a n d i n g m a s s e s o f c r y s t a l s were d e p o s i t e d . T h e s e 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 w a t e r a n d 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 . T h e c r y s t a l s o b t a i n e d f r o m t h e c o o l e d a c e t o n e were c o l l e c t e d , d r i e d , g r o u n d up and d r i e d u n d e r vacuum f o r 24 h ( 3 2 % y i e l d ) . T e t r a - n - b u t y l a m m o n i u m h e x a f l u o r o p h o s p h a t e ( J B A H ) : C r u d e s a m p l e s , 1 h k i n d l y p r o v i d e d by J . T h o r n b a c k , were 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 h o t e t h a n o l , a n d d r i e d u n d e r v acuum. T e t r a e t h y l ammonium p i c r a t e ( T E A P I C ) : 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 p e r c h l o r a t e 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 s o l u t i o n 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 c o n t a i n i n g t h e u n d i s s o l v e d 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 h/and t h e n t h e e x t r a c t i o n s t e p was r e p e a t e d . T h e 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 a m a l g a m a t e d , d r i e d o v e r a n h y d r o u s s o d i u m s u l p h a t e , a n d e v a p o r a t e d t o d r y n e s s . The s o l i d was r e d i s s o l v e d i n C H ^ C ^ (^40 m L ) , f i l t e r e d t o remove 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 removed 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 p r o d u c t s t a r t e d t o p r e c i p i t a t e o u t . 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 were c o l l e c t e d , a nd d r i e d f o r 24 h u n d e r vacuum ( 5 5 % y i e l d ) . A l l d r i e d , p u r i f i e d s a m p l e s 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 p h o s p h o -r u s p e n t o x i d e . e) M i s c e l l a n e o u s T e t r a - n - 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 + B H 4 ~ ) was k i n d l y p r o v i d e d by 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 acuum, and s t o r e d o v e r p h o s p h o r u s p e n t o x i d e . 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 -p h e r e i n r e d u c e d l i g h t i n g c o n d i t i o n s . R u t h e n i u m 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) f r o m J o h n s o n M a t t h e y L t d . The d o d e c a c a r b o n y l , R u 3 ( C 0 ) 1 2 , was p r e p a r e d f r o m t h e 65 ch lor ide by a l i t e r a t u r e p r o c e d u r e 1 0 , as well as being commercially ava i l ab le from Strem Chemicals. Octaethy lporphyr in, H 2 (0EP), was k indly provided by J .B . Paine III, having been prepared v ia a l i t e r a t u r e proce-1 7 dure . Zinc tetraphenylporphyrin was k indly provided by C. Wei born. 2.5 Mater ia l s (2) Preparation of the Ruthenium Complexes CARBONYL(ETHANOL)(OCTAETHYLPORPHINATO)RUTHENIUM(II) (2 ) , Ru(0EP)[C0)Et0H 18 In a modif ied method of e a r l i e r workers , 0.8 g of H2(.0EP) was re f luxed with 0.8 g o f RugCCO)^ in toluene (150 mL) fo r 22 h under argon. When the l i . v . / v i s i b l e spectrum ind icated complete r e a c t i o n , the so lvent was removed by rotary evaporation. The s o l i d was d isso lved in 100 mL of 1:1 v/v CH^C^/EtOH and the so lut ion ref luxed under argon fo r 1 h. Removal o f the solvent gave s o l i d Ru(0EP)(C0)Et0H, which was p u r i f i e d on an a c t i v i t y III neutral alumina column (E. Merck) made up in dichloromethane. The product eluted with CH 2 C1 2 - 2% isopropyl a lcohol and was recrys ta l 1 ized from CH 2 Cl 2 /EtOH (50 mL of 3:1 v / v ) . The c ry s ta l s were r insed with hexane and dr ied under vacuum, y i e l d 63%, V^Q = 1927 c m - 1 . Ana ly s i s : Calculated for C 3 g H 4 g N 4 0 2 R u : C, 66.24%; H, 6.99%; N, 7.93%. Found: C, 66.27%; H, 7.20%; N, 7.79%. Mass spect ra l data: M/e 662(..10), Ru(OEP)(C0) +; 634(100), Ru(0EP) + ; 317(15), RuC0EP) 2 + . nmr 6 T M s ^ C D C 1 3 ^ : 1.92(t ,24H,-CH3), 4.01(q,16H,-CH 2 -),9.90 (s,4H,=CH-). Resonances due to the coordinated ethanol l igand could not usua l ly be detected for reasons explained in Section 3.1. 66 CARBONYL(OCTAETHYLPORPHINATO)(PYRIDINE)RUTHENIUM(II) ( 3 ) , R u ( O E P ) ( C O ) p y 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 a l s o 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 p r o c e d u r e ^ as f o l l o w s : t o 150 mg o f R u ( O E P ) ( C O ) E t O H ( 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 . A f t e r c o o l i n g , 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 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 o u t 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 a h e a d o f a n y u n c h a n g e d 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 acuum, y i e l d 8 5 % , V^Q = 1933 c m - 1 . A n a l y s i s : C a l c u l a t e d f o r C 4 2 H 4 g N 5 0 R u : C, 68.08%; H, 6.67%; N, 9.45%. 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 ) t ; 6 3 4 ( 1 0 0 ) , R u ( 0 E P ) + ; 3 1 7 ( 2 9 ) , R u ( . 0 E P ) 2 + . nmr 6 J M S ( C D C 1 3 ) : 1 . 9 0 ( t , 2 4 H , - C H 3 ) , 3.99(m ,16H , - C H 2 - ) , 9.80(s,4H,=CH-): p y r i d i n e : 0 . 8 9 ( d , 2 H , d - H ) , 4.89(t,2H,6-H)» 5 . 8 2 ( t , l H , Y - H ) . 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. S m i t h . CARB0NYL(IMIDAZOLE)(0CTAETHYLPQRPHINAT0)RUTHENIUM(II) ( 5 ) R u ( O E P ) ( C 0 ) l m . 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) and t h e n t a k e n down t o d r y n e s s on a r o t a r y e v a -67 p o r a t o r . 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 c o l u m n , t h e 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 a h e a d o f u n c h a n g e d 2 . The s o l v e n t was removed 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 7 5 % , v^Q = 1933 cm"* . A n a l y s i s : C a l c u l a t e d f o r C 4 Q H 4 8 N 6 0 R u : C, 65.82%; H, 6.63%; N, 1 1 . 5 1 % . 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 d a t a : M / e 6 6 2 ( 1 9 ) , R u ( 0 E P ) ( C 0 ) + ; . 6 3 4 ( 1 0 0 ) , R u ( 0 E P ) + ; 3 1 7 ( 1 8 ) , R u ( 0 E P ) 2 + . nmr 6 T M S ( C D C 1 3 ) : 1 . 8 6 ( t , 2 4 H , C H 3 ) ; 3.93(m,16H,CH 2) . 9.69(s,4H,=CH-). 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 a n a l o g u e , 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 i m i d a z o l e : -0 . 3 7 ( b , l H , 5 - H ) , 0 . 7 1 ( b , l H , 4 - H ) . (OCTAETHYLPORPHINATO)BIS(TRI-N-BUTYLPHQSPHINE)RUTHENIUM(11) ( 7 ) , R u ( O E P ) -( P n B u 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 2 0 ' 2 4 , t o 400 mg o f R u I I ( 0 E P ) -( C O ) E t O H (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 a d d e d 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 . The s o l v e n t was t h e n removed 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 . The s o l i d o b t a i n e d was d r i e d u n d e r vacuum, y i e l d 6 9 % . 68 A n a l y s i s : 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%; N, 5.40%. F o u n d : C, 69.26%; 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 n B u 3 ) 2 + ; 8 3 6 ( 1 0 0 ) , R u ( . 0 E P j ( P n B u 3 ) + ; 634(71 ) , R u ( 0 E P ) + ; 4 1 8 ( 2 1 ) , R u ( 0 E P ] ( p n B u 3 ) 2 + . nmr 6 T M S ( C D C 1 3 ) : 1 . 7 7 ( t , 2 4 H , - C H 3 ) , 3 . 7 7 ( q , 1 6 H , - C H 2 - ) , 8 . 9 7 ( s , 4 H , =CH-1: T r i - n - b u t y l p h o s p h i n e : 0 . 2 8 ( m , l 8 H , - C H 3 ) , 0.23(m,12H,-CH 2-), - 1 . 5 1 ( b , 1 2 H , - C H 2 - ) , - 2 . 2 4 ( b , 1 2 H , - C H 2 - ) , -2 . 7 8 ( t , 1 2 H , - C H 2 - ) . CARB0NYL(OCTAETHYLPORPHINATO)(TRI-N-BUTYLPHOSPHINE)RUTHENIUM(II), ( 8 ) R u ( . 0 E P ) ( C 0 ) P n B u 3 . 57 mg o f R u ( O E P ) ( C 0 ) E t 0 H (2J was d i s s o l v e d i n %20 mL o f d i c h l o r o -m e t h a n e . 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 n B u 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 c a r b o n m o n o x i d e f o r t w e n t y 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 ) . The s o l v e n t was removed and t h e c r u d e 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 c o l u m n i n d i c h l o r o m e t h a n e . The 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 and t h e s o l i d d r i e d u n d e r vacuum, y i e d i d 65%, V^Q = 1948 cm" 1. A n a l y s i s : C a l c u l a t e d f o r C 4 g H ? 1 N 4 P 0 R u : C, 68.10%; H, 8.28%; N, 6.48%. F o u n d : C, 6 8 . 2 0 % ; H, 8.25%; 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 n B u 3 ) + ; 6 6 2 ( 5 ) , R u ( O E P ) -( C 0 ) + ; 6 3 4 ( 4 4 ) , R u ( 0 E P ) + ; 4 1 8 ( 1 6 ) , R u ( 0 E P ) ( P n B u 3 ) 2 + . 69 •-nrar 6TT M SCCDC1 31: 1.89(t,24H,-CH3), 3.97(.m,l6H,-CH 2~), 9.69(s,4H t r i - n - b u t y l p h o s p h i n e : 0 .23 ( t ,18H, -CH 3 ) , 0.14(m,12H,-CH 2 -), -1 .80 (b ,12H, -CH 2 - ) , -3.16(q,12H,-CH 2 -.). (OCTAETHYLPORPHINATO)BIS(TRI-N-BUTYLPHOSPHINE)RUTHENIUM(,I II )BR0MIDE (9b) , l R u n i ( 0 E P ) ( ; p n B u 3 ) 2 ] + B r " . A s o l u t i o n o f 420 mg o f Ru 1 T ( OEP) (,PnBu3)2 (.7) i n ^50 mL of d i c h l o r o -methane was t i t r a t e d w i th a s o l u t i o n o f bromine in dichloromethane ( s tandard-ized s p e c t r o p h o t o m e t r i c a l l y , ^ m a x a t 410 nm, e = 210 M - 1 c m - 1 ) u n t i l the u.v./v i s ib le abso rp t ion spectrum i n d i c a t e d complet ion o f r e a c t i o n ( app rox i -mately 0.5 equ i va l en t s o f bromine per ruthenium). The so l vent was then removed and the s o l i d r i n sed w i th hexane before d ry ing under vacuum. Samples were analysed immediate ly, as the s o l i d s l ow l y decomposed to g i ve a mix ture o f R u n ( ; 0 E P ) ( P n B u 3 ) 2 (.7) and Ru 1 n ( 0 E P ) tP n Bu 3 )B r (10) (see Sec t i on 7.2) . Y i e l d 56%. A n a l y s i s : Ca l cu l a ted f o r C 6 0 H g g N 4 P 2 B r R u : C, 64.46%; H, 8.84%; N, 5.02%; B r , 7.09%; P, 5.55%. Found: C, 64.11%; H, 8.74%; N, 5.00%; B r , 6.95%; P, 5.77%. Mass s pec t r a l data:M/e 836(100), Ru(OEP) (.P nBu 3) + ; 634 (75 ) , Ru(0EP) + ; 418(20), R u ( O E P )(P n B u 3 ) 2 + . Th is compound was shown by c o n d u c t i v i t y s t ud i e s to be a 1 :1 e l e c t r o -2 -1 l y t e i n CH 2 C1 2 ( A = 130 mho. cm ... mol ). The magnetic moment of t h i s complex was determined (.y= 1 .8 BM ) and conf i rms the presence o f one unpaired e l e c t r o n on the ruthenium atom. 70 BR0M0(OCTAETHYLPORPHINATO)(TRI-N-BUTYLPHOSPHINE)RUTHENIUM(111) ( 1 0 ) R u m ( 0 E P ) ( P n B u 3 ) B r . To 100 mg o f R u 1 Z ( 0 E P ) ( C 0 ) P n B u 3 ( g ) d i s s o l v e d i n ^100 mL d i c h l o r o -m e t h a n e was a d d e d a s l i g h t ( >5%).'excess 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 s p e c t r o p h o t o m e t r i c a l l y 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. The s o l v e n t was r e m o v e d 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 , c o l u m n , t h e p r o d u c t e l u t i n g o f f i n 2 - 4 % i s o p r o p a n o l ( I P A ) i n d i c h l o r o -m e t h a n e . 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 C O E P ) ( P n B u 3 ) I P A 3 + B r " f o r m e d ' b y t h e 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 ( i s o p r o p a n o l ) . 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 vacuum. A n a l y s i s : C a l c u l a t e d f o r C^gHy-jN^BrPRu: C, 62.93%; H , 7.81%; N, 6.12%; B r , 8.72%; P, 3.38%. F o u n d : C, 62.93%';" til, 7,93%; N, 6.0.0%; B r , 8.55%; P, 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 n B u 3 ) + ; 7 1 3 , 7 1 5 ( 1 ) , [ R u ( 0 E P ] B r ] + ; 634(41 ) , R u ( 0 E P ) + * ; 4 1 8 ( 5 4 ) , R u ( O E P ) ( P n B u 3 ) 2 + . 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 ) , s h o w i n g t h a t t h e b r o m i d e 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 ) ( 1 1 ) , R u ( 0 E P ) ( C 0 ) P P h 3 . T h i s c o m p l e x (V^Q = 1953 c m - 1 ) , whose p r e p a r a t i o n has b e e n d e s c r i b e d e l s e w h e r e 2 2 , was k i n d l y p r o v i d e d by G. D o m a z e t i s . (OCTAETHYLPORPHINATO)BIS(TRIPHENYLPHOSPHINE)RUTHENIUM(II) ( 1 2 ) , R u ( O E P ) -( P P h 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 e l s e w h e r e 2 3 , was k i n d l y p r o v i d e d by T. L e u n g . (OCTAETHYLPORPHINATO) BIS (TRI PHENYLARSINE)RUTHEN I UM( I I ) ( 1 3 ) , Ru(OEP) ( 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 i n C I ^ 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 t h e c a t i o n r a d i c a l [ R u 1 1 ( O E P ) + "(CO)] + C T 0 4 ~ O a ) . To t h i s s o l u t i o n was 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 p e r r u t h e n i u m ) , and t h e 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 e n s u r e c o m p l e t e r e a c t i o n . The p r o d u c t s ( [ R u I I I ( 0 E P ) ( A s P h 3 ) 2 ] + C 1 0 4 ~ a l o n g w i t h some R u J I ( 0 E P ) ( C O ) (1_) o b t a i n e d f r o m a s i d e r e a c t i o n ) were r e d u c e d a t 0.0V t o g i v e a p i n k s o l u t i o n o f .1_3 . 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 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 d i c h l o r o -m e t h a n e / a c e t o n i t r i l e . The d i c h l o r o m e t h a n e was 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 been r e d u c e d t o ^10 mL. The c r y s t a l s t h a t had d e p o s i t e d w ere c o l l e c t e d and washed t h o r o u g h l y (.6 x 5 mL r i n s e s ) 72 w i t h a c e t o n i t r i l e . The s o l i d was d r i e d u n d e r vacuum, y i e l d 6 5 % . A n a l y s i s : C a l c u l a t e d f o r C 7 2 H 7 4 N 4 A s 2 R u : C, 6 9 . 3 8 % ; H, 5.99%; N, 4.50%. 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 ) + ; 3 1 7 ( 5 ) , R u ( 0 E P ) 2 + . nmr ( S T M S ( C D C 1 3 ) : 1.71 ( t , 2 4 H , - C H 3 ) , 3 . 6 7 ( q , 1 6 H , - C H 2 - ) , 8 . 8 4 ( s , 4 H , = C H-) : t r i p h e n y l a r s i n e : 4.13( b , l 2H,o-H), 6.38(b,12H,m-H), 6 . 7 0 ( b , 6 H , p - H ) . TETRA-ETHYLAMM0NIUM(DICYAN0)0CTAETHYLP0RPHINAT0RUTHENATE(III) ( 1 4 ) , E t 4 N + [ R u I H ( 0 E P ) ( C N ) 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 2 4 , b u t 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 . 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 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 i n CH 2£.1. 2 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 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 t h e c a t i o n r a d i c a l [ R u 1 1 ( 0 E P ) + " ( C 0 ) ] + C 1 0 4 " ( l _ a ) . 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 -m e t h a n e / 5 % i s o p r o p a n o l . The s o l v e n t was removed 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%. A n a l y s i s : C a l c u l a t e d f o r C 4 6 H 6 4 N 7 R u : 6 7 . 7 0 % ; H, 7.91%; N, 1 2 . 0 1 % . F o u n d : C, 6 7 . 6 6 % ; H, 7.99%; N, 11.78%. 73 (TETRAP H EN Y LPORPHI NATO) BIS (,TR I PH EN YL PH OS PH I NE) RUTH EN IUM { R u ( T P P ) -( P P h 3 ) 2 ; CARBON YL (TETRAMESITYLPORPHINATO) RUTHENI UM( ( ? 0 ) , R u ( T M P ) ( C O ) ; a n d (OCTAETHYLPORPHINATO)PYRIDINE(THIOCARBONYL)RUTHENIUM ( I I ) , R u ( O E P ) ( C S ) p y . were 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. S m i t h ^ e s p e c t i v e l y . 74 REFERENCES - CHAPTER 2 1. J . F a j e r , D.C. B o r g , A. Fo 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 nd R.H. F e l t o n , J . Am. Chem. S o c . 96, 982. 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 , R e a d i n g , M a s s . , 1 9 7 2 , p . 7 6 . 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. Brown, 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. 'Handbook o f C h e m i s t r y a nd P h y s i c s ' , - R.C. Weast ed.. , 5 4 t h E d . , CRC P r e s s , C I e v e l a n d , Ohio,- 1 974, p. D - l T l . 9. R.K. D i N e l l o , K. R o u s s e a u , a n d D. D o l p h i n , A n n . N.Y. A c a d . S c i . 2 44, 9.4 (.1975). 10. D. Madge a n d M.W. W i n d s o r , Chem. P h y s . L e t t . 2 7 , 31 0 9 7 4 ) . 11. D. H o l t e n a nd M.W. W i n d s o r , Photob.iochem. P h o t o b i o p h y s . 1_, 243 ( 1 9 8 0 ) . 1 2 . B . I . G r e e n e , R.M. H o c h s t r a s s e r , R.B. Weisman,and W.A. E a t o n , P r o c . N a t l . A c a d . S c i . USA 75_, 5255 ( 1 9 7 8 ) . 1 3 . K. R o u s s e a u , G.C. F a r r i n g t o n , , a n d D. D o l p h i n , J . O r g a n i c . Chem. 37^ 3968 ( 1 9 7 2 ) . 14. D. D o l p h i n , B.R. James, A . J . M u r r a y , a n d J.R. T h o r n b a c k , C a n . J . Chem. ' 5 8 , T l 2 5 ( V 9 8 0 _ ) 1 5 . A. B r o n d s t r d m , V. J u n g g r e n , a n d B. Lamm, T e t r a h e d r o n L e t t . 31_, 3173 (.1972). 16. A. M a n t o v a n i and S. C e n i n i , i n ' I n o r g a n i c S y n t h e s i s ' , ( F . B a s o l o e d . ) , M c G r a w - H i l l , New Y o r k , 1 9 7 6 , V o l . X V I , p . 47. 75 1 7 . J . B . P a i n e I I I , W.B. K i r s h n e r , D.W. M o s k o w i t z , a n d D. D o l p h i n , J . O r g . Chem. 41_, 3857 (1976) . 18. M. T s u t s u i , D. Ostfield»,and L.M. H o f f m a n , J . Am. Chem. S o c . 93_, 1820 (1971 ) . 19. 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 . 100, 3015 ( 1 9 7 8 ) . 2 0 . G. D o m a z e t i s , P e r s o n a l c o m m u n i c a t i o n . 2 1 . G. D o m a z e t i s , B.R. James, a n d D. D o l p h i n , I n o r g . C h i m . A c t a . 54_, L47 ( 1 9 8 1 ) . 2 2 . M.H. B a r l e y , J . Y . B e c k e r , G. D o m a z e t i s , D. D o l p h i n , a n d B.R. J a m e s , C a n . J . Chem., S u b m i t t e d . 2 3 . T. L e u n g , B.R. James, and D. D o l p h i n , u n p u b l i s h e d r e s u l t s . 2 4 . P.D. S m i t h , D. D o l p h i n , a n d B.R. J a m e s . J . O r g a n o m e t . Chem. 208, 239. (1 981 ) . 76 CHAPTER 3 SOME PRELIMINARY EXPERIMENTS The aim of the material in th i s chapter i s to c l a r i f y the nature of some of the start ing metal complexes and establ i sh some basic patterns of r e a c t i v i t y in 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 1 1(OEP)(C0)L  in Solution The question of the nature of Ru(0EP)(C0)L in solut ion 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 so lvent s 1 . The s i tuat ion i s less c lear for cases where the ligand L i s weaker and the con-fusion i s pa r t i cu l a r l y highlighted for L = EtOH which i s the s ta r t ing complex for most studies of ruthenium porphyrins, including work described in th i s thes i s . Results have been inconsistent. Usually the f i n a l stage of prepa-rat ion of a 'Ru(QEP).(C0)1 species i s c r y s t a l l i z a t i o n from an ROH/CHgCT^ (R = CH^, C2Hg) mixture 1 . Chemical and X-ray analysis of the c r y s t a l l i n e product shows the alcohol to be coordinated in the so l id s t a t e 1 ' 2 but the s i tuat ion in so lut ion i s less well defined. Nmr studies give inconsistent resu lts with Boschi et a l . 3 not detecting any methanol in the i r preparation of 'Ru(TPP)(.C0)1 c r y s t a l l i z ed from Me0H/CHCl3 [no analysis g iven], whereas Bonnet et a l . 2 detected coordinated EtOH by nmr in a C2H2C1 ^ solution of Ru(TPP)(CO)EtOH. 77 For the purposes of the present studies i t was important to deter-mine i f the ethanol remained coordinated in dichloromethane, whether th i s was dependent on concentration and whether coordinating solvents (such as a ce ton 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 typ ica l of metalloporphyrin systems showing a strong Soret ( y ) band at ^393 nm and two v i s i b l e peaks 4 " 6 , with the usually more intense a-band (see Figure 1.4 in Chapter 1) at ^550 nm and the weaker B-band at ^515 nm. The spectra of a l l these complexes were s imi lar but with ana l y t i c a l l y pure samples the ra t i o of the i n tens i t i e s of the two v i s i b l e peaks,was dependent upon the nature of the s ix th l igand (Table 3.1), with the ^550 nm peak both diminishing and s l i g h t l y red- sh i f t ing with the systems as shown. An extreme example of thn's trend is seen with L = P n Bu 3 , where the peaks are actua l l y reversed in intens i ty and considerably red-shifted (Table 3.1';; Figure 3.1). A re lat ionsh ip between these two types of spectra..is seen in studies of the complex Ru**(OEP)(C0)PPh 3 (11) where -5 CH2CI2solutions of an ana l y t i c a l l y pure sample (%10 M) give a spectrum almost ident ica l to that of Ru(0EP)(C0lEt0H (2) in the same solvent. Addition of excess of triphenylphosphine causes the 548 nm peak to rap id ly diminish and s l i g h t l y red s h i f t , while the 515 nm peak sh i f t s and broadens un t i l in the presence of considerable excess phosphine (10 M), a spectrum very s imi lar to that of Ru(OEP) (C0)P nBu 3- v (8) i s obtained (Figure 3.2). The data strongly suggest that the f ive-coordinate species Ru(0EPj(C0) (]_) gives a spectrum with the strong 548 nm absorption which is then modified 79 Figure 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 S p e c t r u m o f R u ( O E P ) ( C O ) L w i t h t h e N a t u r e o f t h e S i x t h L i g a n d L Complex L a B ( I n C H 2 C 1 2 ) A 1 Cnm). \ 2 Cnm). R a t i o — R u ( 0 E P ) ( C 0 ) E t 0 H -, - EtOH 548 515 2.3 Ru(.0EP)(C0)4Mepy - 4Mepy 549 518 1 .54 R u ( 0 E P ) ( C 0 ) I m - Im 550 518 1 .38 R u ( 0 E P ) ( C 0 ) A s P h 3 - A s P h 3 554 524 1.11 R u ( . 0 E P ) ( C 0 ) P P h 3 - P P h 3 555 525 1 .0 R u ( . 0 E P ) ( C 0 ) P n B u 3 - P n B u 3 555 528 .68 a) 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 and g ( s e e F i g u r e 1.4, S e c t i o n 1 . 2 ) . b) 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 e c o m p l e x d i s s o l v e d i n C H 2 C 1 2 , c ) A c t u a l l y R u ( O E P ) ( C 0 ) H 2 0 as d e s c r i b e d b e l o w . 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 s p e c t r a l c h a n g e o c c u r r e d . 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 om, e . g . p h o s p h i n e s o r a r s i n e s ) a s t r o n g e r p e r t u r b a t i o n o f t h e m o l e c u l a r o r b i t a l s o f t h e m e t a l l o p o r p h y r i n y i e l d s a q u i t e d i f f e r e n t s p e c t r u m . 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 L = Im, A s P h ^ M a n d P n B u 3 ( T a b l e 3 . 1 ) , w h i c h i s a r o u g h o r d e r o f c a p a c i t y f o r Tr-bond f o r m a t i o n . L i g a n d s c o n t a i n i n g p h o s p h o r u s o r 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 m e t a l c e n t r e s 7 ' 8 . I m i d a z o l e i s a m o d e r a t e T r - d o n o r 9 ' 1 0 p y r i d i n e a weak T r - a c c e p t o r 8 » 1 0 w h i l e n i t r i l e s a n d a l c o h o l s a r e c o n s i d e r e d t o 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 c o m p l e x e s a r e g i v e n i n T a b l e 3.2. I f R u ( 0 E P ) ( C 0 ) L d i s s o c i a t e s i n s o l u t i o n t h e n t h e a d d i t i o n o f e x c e s s 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 , a s s u m i n g t h e s p e c t r u m o f R u ( 0 E P ) ( C 0 ) L 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 ) (.!_). A d d i t i o n o f e t h a n o l ( t o a b o u t 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 i n t e n s i t y o f t h e 5 4 8 n m p e a k ( F i g u r e 3 . 4 a ) . A d d i t i o n o f more e t h a n o l ( t o ^4M) c a u s e s no f u r t h e r c h a n g e . I n c o n t r a s t , t h e a d d i t i o n o f 4 - m e t h y l p y r i d i n e ( u p t o IM). t o a ^10" 5M s o l u t i o n o f Ru(jDEP) ( C O ) ( 4 M e p y ) (.4) i n C H 2 C 1 2 shows no v a r i a t i o n i n s p e c t r u m ( T a b l e 3 . 3 ) . 82 T a b l e 3.2 S p e c t r a l D ata f o r S o l u t i o n s i n CHQCIQ o f R u n ( 0 E P ) ( C 0 ) L S p e c i e s S p e c i e s D i s s o l v e d i n CH 201, 2 W - n m > ( 1 ° 9 l O e ) R u ( 0 E P ) ( C 0 ) H 2 0 - 3 9 3 ( 5 . 3 8 ) 5 4 8 ( 4 . 5 8 ) 5 1 5 ( 4 . 2 2 ) (D R u ( 0 E P ) ( C 0 ) - 3 9 2 ( 5 . 3 5 ) 5 4 7 ( 4 . 6 3 ) 5 1 2 ( 4 . 2 0 ) (2) R u ( O E P ] ( C O ) E t O H - 3 9 2 ( 5 . 4 8 ) 5 4 8 ( 4 . 5 3 ) 5 1 5 ( 4 . 2 3 ) (i) R u ( 0 E P ) ( C 0 ) 4 M e p y 3 9 6 ( 5 - 4 3 ) 5 4 9 ( 4 . 4 0 ) 5 1 8 ( 4 . 2 2 ) (1) R u ( 0 E P ) ( C 0 ) p y - 3 9 6 ( 5 . 4 1 ) 549(4.41 ) 5 1 8 ( 4 . 2 3 ) (5 ) R u ( 0 E P ) ( C 0 ) I m 3 9 6 ( 5 . 4 5 ) 5 5 0 ( 4 . 3 6 ) 5 1 8 ( 4 . 2 0 ) (1 8 ) c R u ( 0 E P ) ( C 0 ) A s P h 3 4 0 6 ( 5 . 1 8 ) 5 5 4 ( 4 . 2 7 ) 5 2 5 ( 4 . 2 3 ) (H) c Ru(.0EP)(,C0)PPh 3 4 0 7 ( 5 . 2 8 ) 5 5 5 ( 4 . 2 0 ) 5 2 5 ( 4 . 1 9 ) (8) R u ( 0 E P ) ( C 0 ) P n B u 3 4 0 9 ( 5 . 2 3 ) 5 5 5 ( 3 . 9 7 ) 5 2 8 ( 4 . 1 4 ) R u ( 0 E P ) ( C 0 ) C f 4 0 2 ( 5 . 3 6 ) 5 5 2 ( 4 . 3 0 ) 5 2 1 ( 4 . 2 0 ) R u ( 0 E P ) ( C 0 ) B r ~ 4 0 4 ( 5 . 2 3 ) 5 5 3 ( 4 . 2 6 ) 5 2 4 ( 4 . 2 1 ) R u ( 0 E P ) ( C 0 ) C N " 4 0 7 ( 5 . 5 7 ) . 5 5 7 ( 4 . 1 4 ) 5 2 8 ( 4 . 2 9 ) a) S p e c t r u m o b t a i n e d i n f r e s h l y d i s t i l l e d b u t u n d r i e d C H ^ C l ^ . 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 2 . c ) S p e c t r u m o b t a i n e d i n 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 . d) S p e c t r u m r e p o r t e d i n R e f . 5; X m a x ( n m ) ( 1 o g ] Q e ) 3 9 6 ( 5 . 3 7 ) , 5 1 8 ( 4 . 2 0 ) and 549(4:.39) . 83 T a b l e 3.3 The E f f e c t o f Added 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  o f R u ( 0 E P ) ( C 0 ) E t 0 H D i s s o l v e d i n C H o 0 1 o mL o f EtOH a d d e d ^ c o n c e n t r a t i o n 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 o f c u v e t t e u s e d ^4 mL . b) C o n c e n t r a t i o n s 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 f i g u r e . c ) U n d r i e d C H X k u s e d , a band ^548 nm, g band ^515 nm. The c h a n g e s ( o r l a c k o f ) a r e c o n s i d e r e d due t o E q u i l i b r i u m 3.1 , K R u ( 0 E P ) ( C 0 ) + L i = ± R u ( 0 E P ) ( C 0 ) L ( 3 . 1 ) K i i s l a r g e f o r L = 4Mepy ( > 1 0 6 M - 1 ) 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 m e a s u r e m e n t o f K f o r t h e e t h a n o l s y s t e m i s d i s c u s s e d b e l o w . T h e s p e c t r u m o b t a i n e d when Ru(OEP) ( C 0 ) E t 0 H (2) i s d i s s o l v e d i n C H ? C 1 9 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 QJ. 84 However th i s spectrum was very dependent upon the pur ity of the d i ch lo ro -methane. The experiments noted above (Table 3.3),in which freshly d i s t i l l e d but undried CH 2C1 2 was used,gave a ra t i o of 2.3 (±;0ll) for the i n tens i t i e s of the two v i s i b l e peaks CIg^g/I^i5) - With CH^Clg solvent used for electrochemical experiments ( 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) resu l ted, with the more intense v i s i b l e peak (a) sh i fted 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 so lut ion of Ru(OEP)(CO)EtOH (2_) was possibly due to the species Ru(0EP)(C0)H20. Dissolving Ru(OEP)(CO)EtOH (5xlO _ 5M) in a sample of CH 2C1 2 f reshly d i s t i l l e d from CaH2 and t ransferr ing to the c e l l under argon gave a r a t i o of peak in tens 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 ^ lh caused th i s r a t i o to drop to 2.40, while saturation of the sample with water gave a ra 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 fect i ve at coordinating and that in the experiments described above (Tables 3.1 and 3.3) trace water i s always present as a competitive l i gand. The data are s t i l l considered v a l i d , because the results obtained in dried solvent were the same except that the drop in the in tens i ty ra t io 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 2C1 2. To obtain the proportions of ethanol coordinated to the ruthenium as a function of concentration,the equil ibrium (3.2) was studied 85 q u a n t i t a t i v e l y i n d r i e d C H g C l 2 -R u ( O E P ) t C O ) + EtOH F = = ^ R u ( O E P ) ( C O ) E t O H ( 1 ) (2) ( 3 . 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 s o l u t i o n o f 2. i n 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 nm 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 . The i n t e n -s i t i e s s o o b t a i n e d w e r e c o r r e c t e d f o r t h e d i l u t i o n e f f e c t o f t h e a d d e d e t h a n o l ( T a b l e 3 . 4 ) . R u ( 0 E P ) ( C 0 ) E t 0 H ] R u ( 0 E P ) ( C 0 ) J [ E t 0 H J Hence l o g - , 0 K = l o g i n \ 10 Hence a p l o t o f l o g 10 [ R u ( 0 E P ) ( C 0 ) E t 0 H ] [Ru(.0EPH.C0)J [ R u ( 0 E P ) ( C 0 ) E t 0 H ] [ R u ( 0 E P ) ( C 0 ) J l o g 1 0 [ E t O H ] vs. l o g 1 Q [ E t O H ] 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 o f - l o g ^ 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 i n t h i s e x p e r i m e n t i t c a n be e q u a t e d t o t h e e t h a n o l a d d e d , s i n c e t h i s i s i n l a r g e e x c e s s c o m p a r e d t o t h e c o n c e n t r a t i o n o f t h e c o m p l e x . T h e f a l l i n a b s o r p t i o n v a l u e s i s a t t r i b u t e d t o f o r m a t i o n 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 (.2) . T h u s : 86 T a b l e 3.4 A d d i t i o n o f E t h a n o l t o a 4 x l O ~ 5 M S o l u t i o n o f R u ( O E P ) ( C O ) E t O H  i n C H 0 C 1 0 ( 1 0 . 0 mL) i n a S e a l a b l e 1 cm C e l l " M l o f L i q u i d a d d e d -y L o f EtOH T 5 4 7 C o r r e c t e d I g 4 7 — l o g 1 0 [ E t 0 H ] , 1.566-1 i O g 1 0 I - l .377 0 0 1 .566 1 .566 - -1 .1 1 .546 1.546 -3.786 -.927 2 .2 1 .532 1 .532 -3 .485 -.659 3 .3 1 .520 1 .520 -3.309 -.492 4 .4 1 .502 1 .503 -3.184 -.301 5 .6 1 .490 1 .491 -3.008 -.182 8 .8 1 .482 1 .483 -2.883 -.106 10 1 .0 1 .473 1.475 -2.786 -.032 12 1 .2 1.465 1 .467 -2.707 .041 15 1 .5 1 .458 1 .460 -2.610 .106 20 2.0 1 .447 1 .450 -2.486 .201 25 2.5 1 .441 1 .445 -2.389 .250 30 3.0 1 .436 1 .441 -2.310 .291 40 4.0 1 .427 1 .433 -2.185 .376 50 5.0 1 .417 1 .425 -2.089 .468 60 6.0 1 .411 1 .420 -2.010 .531 75 7.5 1 .400 1.412 -1 .914 .643 100 10.0 1 .382 1 .398 -1 .790 .903 105 15 1 .370 1 .386 -1 .607 1 .301 110 .20 1 .363 1.380 -1 .482 1 .792 120 30 1 .356 1 .375 -1.306 -140 . 1100 1.347 1 .377 -0.786 -( a ) E t h a n o l a d d e d as a 10% s o l u t i o n i n C H 2 C 1 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 peak 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 [ R u ( O E P ) ( C O ) E t O H ] _ lo ' 1 [ R u ( O E P ) ( C O ) J I - I c o i s p l o t t e d a g a i n s t log-|Q [ E t O H ] ( F i g u r e 3.3) ( I Q = A b s o r p t i o n o f 547 nm peak b e f o r e a d d i n g 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 . 3 7 7 ) ) . 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 an d 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 a n 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. C a l c u l a t i o n s u s i n g t h i s f i g u r e s u g g e s t t h a t f o r s p e c t r o s c o p i c s o l u t i o n s (/v5 x 1 0 " 5 M) o f R u ( O E P ) ( C 0 ) E t 0 H ( 2 ) i n d r i e d C H 2 C 1 2 a p p r o x i m a -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 . The s p e c t r u m o b t a i n e d f r o m 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 d u e t o Ru(OEP)(.CO). U n d e r t h e e x p e r i m e n t a l c o n d i t i o n s t h e m a i n d i f f i c u l t y i n o b t a i n i n g an a c c u r a t e s p e c t r u m 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 i s t h e e l i m i n a t i o n o f t r a c e w a t e r . The s p e c t r a l d a t a o b t a i n e d i n v e r y d r y C H 2 C 1 2 , w i t h p r e c a u t i o n s t a k e n t o l i m i t t h e e f f e c t o f a t m o s p h e r i c m o i s t u r e , a r e e n t e r e d i n T a b l e 3.2 as 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). " S t r o n g e r s o l u t i o n s o f R u ( O E P ) ( C O ) E t O H ( 2 ) i n C H 2 C 1 2 show a h i g h e r 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 M ( t y p i c a l l y u s e d 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 . and l o g 10 I - I _ o I - I 88 Log. i o - i  1 0 I I - I CO + 0.5 0.4 0.3 0.2 + 0.1 0 - 0.1 0.2 0.3 0.4 - 0.5 0.6 0.7 o \ \ \ \ o \ \ \ \ o \ \ o\ o \ 'O \ \ \ \ \ \ \ o\ \ \ _J -2.0 -2.5 •3.0 -3.5 Log l o [EtOH] F i g u r e 3.3 P l o t o f l o g ! 0 [ [ R u ( 0 E P ) ( C O ) E t O H ] / [ R u ( O E P ) ( C O ) ] ] v s . l o g 1 0 [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 . [Ru(OEP) (CO)EtOH] i s p r o p o r t i o n a l t o IQ-I and [Ru (OEP) (CO) ] i s p r o p o r t i o n a l t o I-Ico. 89 3.2 S o l v a t i o n o f R u ( O E P ) ( C 0 ) L i n D i f f e r e n t S o l v e n t s H a v i n g e s t a b l i s h e d t h a t t h e e t h a n o l 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 a r o s e as t o w h e t h e r a c o o r d i n a t i n g s o l v e n t w o u l d r e p l a c e t h e e t h a n o l , ( 3 . 3 ) . R u ( O E P ) ( C O ) E t O H + S » Ru(0EP)(.C0)S + EtOH ( 3 . 3 ) ( i l 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 2 i n a v a r i e t y o f s o l v e n t s s u g g e s t e d 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 - m e t h y l p y r i d i n e 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 f r o m a n a l y -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) and 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 e x c h a n g e 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 t h e s o l v e n t s , w i t h t h e e x c e p t i o n o f C ^ C ^ J p r o b a b l y c o o r d i n a t e a l t h o u g h 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 due 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 R u ( 0 E P ) ( C 0 ) m o l e c u l e , 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 a p p r o x i m a t e e q u i l i b r i u m c o n s t a n t s f o r t h e r e a c t i o n ( 3 . 4 ) . R u ( 0 E P ) ( C 0 ) + S v 1 Ru(0EP)(.C0)S (D ( 3 . 4 ) 90 T a b l e 3.5 S p e c t r a l Data f o r 1 0 " 5 - 10" 4M R u ( O E P ) ( C O ) E t O H D i s s o l v e d i n V a r i o u s S o l v e n t s S o l v e n t R a t i o o f v i s i b l e p e a k s ( a / I g ) ( T a b l e 3.1) C h ^ C l 2 ^2.6 M e t h y l A c e t a t e 2.26 C H C 1 3 2.13 nBuOH 2.0 EtOH 2.0 DMF 1 .82 DMSO 1 .82 CH 3CN 1 .8 C H 3 N 0 2 1 .76 E t 3 N 1 .53 4Mepy 1 .54 I m i d a z o l e 1 .38 A s P h 3 1 .11 P P h 3 1 .0 a) 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 M s o l u t i o n . b) R u ( O E P ) ( C O ) E t O H ( 2 ) d i s s o l v e d i n C H 2 C 1 2 w i t h e x c e s s l i g a n d a d d e d 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 i n d r y C H g C l g a l l o w e d 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 be a c c u r a t e l y d e t e r m i n e d . To a f r e s h s o l u t i o n o f 2_ i n d r i e d C H g C l g 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 were a d d e d and t h e s p e c t r a l c h a n g e s o b s e r v e d . T h e 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 was m e a s u r e d f o r f i v e m i x t u r e s s p a c e d e v e n l y b etween c o n d i t i o n s o f a p p r o x i m a t e l y 35 and 65% c o o r d i n a t i o n 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 a t 547 nm = 1^) f o r t h i s s o l u t i o n i n 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 S was d e t e r m i n e d . T h e s p e c t r a , b e f o r e a n d 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; t h e a d d i t i o n o f PPh^ t o R u ( 0 E P ) ( C 0 ) (1_) i s s e e n i n F i g u r e 3.2. M i x t u r e s s h o w i n g between 35 a n d 65% c o o r d i n a t i o n w e r e u s e d f o r a n a l y s i s b e c a u s e t h e y g i v e t h e m o s t a c c u r a t e e s t i m a t e s o f K. 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 o b t a i n e d ( E q u a t i o n 3.5) and t h e s e were t h e n a v e r a g e d . v - [ R u ( 0 E P ) ( , C 0 ) S ]  K " r R u ( 0 E P ) ( C 0 ) J [ S j V 1 I - I 1 IsT ( 3 . 5 ) ( I and I c o r r e c t e d f o r d i l u t i o n ) The c o n c e n t r a t i o n o f t h e l i g a n d f r e e i n t h e s o l u t i o n c a n u s u a l l y be c o n s i d e r e d t o be e q u a l 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^) t h a t more t h a n 1% o f t h e a v a i l a b l e l i g a n d i s c o o r d i n a t e d i n a n y s o l u t i o n . The c a l c u l a t e d K v a l u e s a r e s e e n i n Ta b l e 3 .6 . F i g u r e 3.4 O p t i c a l s p e c t r a o f CH 2 C 1 2 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 B i n d i n g e x p e r i m e n t s , a n d t h e s p e c t r a 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 o b t a i n e d i n t h e p r e s e n c e o f e x c e s s a d d e d l i g a n d . R u ( 0 E P ) ( C 0 ) (- ) ; Ru(0EP)(.C0)L ( ) a) Ru(.0EP)(C0) + EtOH , 1 Ru(OEP) (CO) E t O H b) R u ( O E P ) ( C O ) + C H 3 N 0 2 F = = * R u ( 0 E P ) ( . C 0 ) C H 3 N 0 2 e) d) R u ( O E P ) ( C O ) + C H 3 C N ? Ru(OEP)CCO) + A s P h 3 ? ^ R u ( O E P ) ( C O ) C H 3 C N ^ R u ( . 0 E P ) ( C 0 ) A s P h 3 F i g u r e 3.4 c o n t i n u e d : * e 500 600 700 500 WAVELENGTH (nm) 600 700 WAVELENGTH (nm) e) R u ( 0 E P ) ( C 0 ) + Ira f ) | R u ( 0 E P ) ( C 0 ) + E t 3 N ? = i R u ( O E P ) ( C 0 ) I m =± R u ( . 0 E P ) ( C 0 ) E t 3 N 95 T a b l e 3.6 E q u i l i b r i u m C o n s t a n t s f o r t h e C o o r d i n a t i o n o f L i g a n d s t o  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 a s S o l v e n t L i g a t i n g S o l v e n t E s t i m a t e d K Range o f K Donor Number -A d d e d - M"'1 M _ 1 C H 3 N 0 2 8.7 8.2 - 9.3 2.7 CH 3CN 165 155 - 175 14.1 A s P h 3 2900 2750 - 3050 P P h 3 31000 29000 - 32000 EtOH 550 s e e F i g u r e 3,3 20.0 E t 3 N 42 39 - 45 ^55 4Mepy • - 2x1 O 8 - 33.1 Im 5. 5 x l 0 8 -a) S o l u t i o n o f R u ( 0 E P ) ( C 0 ) ( 1 ) i n C H 2 C 1 2 ^ ( 3 - 6 ) x l 0 ~ 5 M . L i g a n d u s u a l l y 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 2 C 1 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 t h a n 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 were c o n s i s t e n t w i t h 99+% o f t h e a v a i l a b l e l i g a n d b e i n g c o o r d i n a t e d . T h i s i m p l i e s t h a t K » 10 . 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 e q u i l i b r i a s t u d i e s w i t h CH^CN a s s o l v e n t ( s e e b e l o w ) . 96 As e x p e c t e d f r o m 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. CH 3CN) c a n 1 ead t o a m i x t u r e o f R u ( 0 E P ) ( C 0 ) L s p e c i e s w i t h t h e a p p r o p r i a t e s p e c t r u m ; t h e e q u i l i b r i a a r e e s t a b l i s h e d r a p i d l y . R u ( 0 E P ) ( C 0 ) I m + CH 3CN » R u ( O E P ) ( C O ) I m + Ru ( O E P ) ( C O ) C H g C N ( 3 . 6 ) (5) ( s o l v e n t ) (5) (6) R a t i o o f t h e two v i s i b l e a b s o r p t i o n s ( a s d e f i n e d f o r T a b l e 3.1) I / I = a 6 O b s e r v e d r a t i o = - Ru(.0EP)(C0)4Mepy + CH 3CN » R u ( 0 E P ) ( C 0 ) 4 M e p y + Ru(OEP) ( C O ) C H 3 C N ( 3 . 7 ) ( 4 ) ( s o l v e n t ) (4) (6) 1.54 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 i m m e d i a t e l y d i s p l a c e s a n y c o o r d i n a t e d s o l v e n t t o g i v e t h e s p e c t r u m o f t h e l i g a n d - c o o r -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 and 1.54 f o r 4_ ) . From t h e s e d a t a , o r d e r o f m a g n i t u d e e s t i m a t e s c a n be made o f t h e b i n d i n g o f 4Mepy and Im t o Ru(OEP)CCO) (1) . 1 .38 1 .50 ' I /In a 3 O b s e r v e d r a t i o 97 E q u i l i b r i u m ( 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 R u ( O E P ) ( C 0 ) L s p e c i e s i s d i s s o l v e d i n a c o o r d i n a t i n g s o l v e n t (CH3CN). h L + Ru(0EP)(.C0) CH3CN ' = = s = * Ru (0EP) (C0)L + CH 3CN ( 3 . 8 ) U s i n g t h e method d e s c r i b e d 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 i n t e n s i ; t i e s ( I o t / I g ) f o r a b s o l u t e i n t e n s i t i e s , y i e l d t h e d a t a s u m m a r i z e d i n T a b l e 3.7. I - I [CH^CN] h • r^r * - r c r " < 3 - 9 > , S. 0 0 I = 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 p e a k s f o r 0 Ru(.0EP)(C0)CH 3CN i n CH 3CN I = The same r a t i o f o r R u ( 0 E P ) ( C 0 ) L ( L = 4M e p y o r Im) 0 0 I = The 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 CH 3CN [ C H 3 C N ] = C o n c e n t r a t i o n o f n e a t CH 3CN, i . e . 19M. T a b l e 3".7 The E s t i m a t i o n 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 0 0 % L c o o r d i n a t e d [ L ] ' h L = 4 Mepy 1.8 1.66 1 .54 54 2 . 3 x l O " 5 M 9 . 6 x l 0 5 L = Im 1.8 1.5 1 .38 71 1 . 5 x l O ~ 5 M 3 . 2 x l 0 6 98 D e f i n i n g 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 3.10 a s K-| : K l R u ( 0 E P ) ( C 0 ) +• CH 3CN , ! > R u ( O E P ) ( C O ) ( C H g C N ) ( 3 . 1 0 ) ( 1 ) (6) where K-j i s known ( 1 6 5 M ~ ^ ) , l e a d s t o : v v [ R u ( 0 E P ) ( C 0 ) C H ? C N ] - [ R u ( 0 E P ) ( C 0 ) L ] [ C H ^ C N ] nK2 [ R u ( 0 E P ) ( C 0 ) ] [ C H 3 C N ] X [ L ] [ R u ( O E P ) (COJCHTgCN] R u ( 0 E P ) ( C 0 ) L _ „ , n R u ( 0 E P ) ( C 0 ) ] [ L J " K a s s o c . ^-' u w h i c h i s t h e a s s o c i a t i o n c o n s t a n t f o r l i g a n d L 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 R u ( 0 E P ) ( C 0 ) (1_). Hence t h e f o l l o w i n g e s t i m a t e s o f K a r e made, and a r e i n c l u d e d i n T a b l e 3.6. L K a s s o c . ( M _ 1 ) 4Mepy 2 x 1 0 8 Im 5 x l 0 8 P B u 3 was a l s o shown t o c o o r d i n a t e 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 w i t h R u ( 0 E P ) ( C 0 ) ('!_) i n C H 2 C 1 2 . S o l v a t i o n r e a c t i o n s i n CH 3CN o f a n a l y 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 0 ) P n B u 3 (8) were c o m p l i c a t e d by an a p p a r e n t k i n e t i -c a l l y s l o w e r d i s s o c i a t i o n o f t h e P n B u 3 c o m p a r e d w i t h t h e n i t r o g e n l i g a n d s s t u d i e d a b o v e . The b i n d i n g s t r e n g t h of / P n B u 3 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 n B u 3 ^ Im ^ 4Mepy >> P P h 3 >> A s P h 3 > EtOH CH 3CN > E t 3 N > C H 3 N 0 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 1 1 . 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 o f r e a c t i o n o f t h e s p e c i f i e d l i g a n d w i t h S b C l ^ . Gutmann c o m p a r e d t h e d o n o r 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 m e t a l c o m p l e x e s S n ( C H 3 ) 3 C l and V O C d c a c ^ C C H - j C N ) 1 1 , and f o u n d t h a t t h e 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 o f t h e a c c e p t o r u s e d . 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 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 I J ( 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 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 t h e 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 m e t a l atom 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 t h e numbers were 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 h a r d L e w i s 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 . The m a i n d i v e r g e n c e s f r o m t h e o r d e r o f l i g a n d s t r e n g t h , s u g g e s t e d by Gutmann a r e o f t e n due t o 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 be t h e c a s e w i t h E t 3 N ( s e e b e l o w ) . 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 t o t h a t o b s e r v e d p r e v i o u s l y f o r c o o r d i n a t i o n t o f o u r - c o o r d i n a t e c o b a l t ( I I ) p o r p h y r i n s p e c i e s h a v i n g v a c a n t l i g a n d p o s i t i o n s 1 2 . P i p > CH 3-Im > Py > P " B U 3 > Im » P P h 3 » EtgN > 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 e n t h a l p y o f f o r m a t i o n f o r t h e r u t h e n i u m 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 s y s t e m . 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) t h a n o x y g e n l i g a n d s ( ^ 2 0 ) . P h o s p h i n e c o m p l e x e s a r e e x p e c t e d 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 o f s t r o n g a - d o n a t i o n c o u p l e d w i t h -rr-backbonding f r o m t h e o v e r l a p o f t h e f i l l e d d - o r b i t a l s o f t h e r u t h e n i u m 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 , ( e . g . P " B u 3 ) . 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 c o n s i d e r a b l e s t r e n g t h s o f Im a n d 4Mepy 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 c a p a -b i l i t y o f i m i d a z o l e a n d , f o r b o t h l i g a n d s . a c a p a c i t y f o r 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 atom i n t o t h e v a c a n t t r - o r b i t a l s o f t h e a r o m a t i c s y s t e m o f t h e l i g a n d seems p l a u s i b l e . The w e a ker b i n d i n g o f E t 3 N ( a much s t r o n g e r a d o n o r t h a n Im o r 4 M e p y , 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 e n t r o p y e f f e c t . 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 u n f a v o u r a b l e 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 1 2 , a s w e l l a s t h e l a c k o f a n y a v a i l a b l e o r b i t a l s f o r b a c k b o n d i n g . T h i s l e a v e s t h e u n e x p e c t e d w e a k n e s s o f P P h 3 a n d A s P h 3 a s l i g a n d s c o m p a r e d t o P n B u 3 . 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 s e e n i n a c o m p a r i s o n o f b i s p h o s -I I 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 3 ) 2 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 101 ( 5 x l 0 ~ 5 M ) w h e r e a s R u ^ O E P ) ( P P h - ^ d i s s o c i a t e s q u i t e r e a d i l y 1 4 u n d e r t h e same c o n d i t i o n s ( E q u a t i o n 3 . 1 2 ) . K 5 R u ( 0 E P ) ( P P h 3 ) 2 F = ^ R u ( 0 E P ) ( P P h 3 ) + P P h 3 (K = 1.18x10 °B) ( 3 . 1 2 ) 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 enough 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 c a p a c i t y o f t h e l i g a n d i s r e d u c e d . However, f o r t h i s a r g u m e n t t o e x p l a i n P P h 3 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 o r P n B u 3 , i t w o u l d r e q u i r e a s u b s t a n t i a l d r o p i n e l e c t r o n i c c h a r g e d o n a t e d t o t h e m e t a l l o p o r p h y r i n g r o u p . T h i s i n t u r n w o u l d c a u s e , t h e s p e c t r a o f t h e P P h 3 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 n B u 3 c o m p l e x e s and much more 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 t h e s p e c t r u m o f 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 c o m p l e x e s a r e v e r y s i m i l a r [ T a b l e s 3.1, 3.2, and 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 c o m p l e x e s . A b e t t e r e x p l a n a t i o n i s f o u n d 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 . 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 and 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 atom, r e q u i r e d t o e n c l o s e t h e V a n - d e r - W a a l s l i m i t s o f t h e l i g a n d 1 5 . H e n c e , P P h 3 ( 1 4 5 ° ) i s more s t e r i c a l l y d e m a n d i n g t h a n P n B u 3 ( 1 3 0 ° ) b u t l e s s t h a n , f o r e x a m p l e 102 P f c y c l o h e x y l ) 3 ( 1 7 9 ° ) , 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 3 ( p r e p a r e d 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 2 C 1 2 ) shows -3 -3 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 M. (A 10 M s o l u t i o n o f R u ( O E P ) ( C 0 ) P P h 3 i s ^ 8 0 % a s s o c i a t e d a s c a l c u l a t e d f r o m t h e e s t i m a t e d e q u i l i b r i u m c o n s t a n t ) . T h e 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 f o r 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 p o r -p h y r i n s a s l i g a n d s . a n d i s i n c o n s i s t e n t w i t h t h e v i e w t h a t t h e b i n d i n g o f P P h 3 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 i s a 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. T h e i m p o r t a n c e o f s t e r i c _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 a n d 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 n B u 3 u n d e r 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 . T h i s e f f e c t p r o b a b l y 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 TMP.. 3.3 T h e 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 n B u 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 ) -( C 0 ) P n B u 3 (8J t h a t l e a d t o d i s p l a c e m e n t o f t h e p h o s p h i n e g r o u p a r e k i n e t i -c a l l y s l o w c o m p a r e d w i t h t h e d i s p l a c e m e n t o f o t h e r l i g a n d s ( e . g . Im and 4Mepy) f r o m t h 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 c a r b o n y l c o m p l e x e s . W e a k l y l i g a t i n g s o l v e n t s ( s u c h as EtOH o r CH 3CN) 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 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 , a n d 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 was s m a l l (<15%) as j u d g e d by t h e s p e c t r a . A d d i t i o n o f s t r o n g e r l i g a n d s (Im o r 4Mepy) i n s m a l l a l i q u o t s (up t o 0.1M) t o a s o l u t i o n o f R u ( 0 E P ) ( C 0 ) -103 P n B u 3 ( 8 ) i n C H 2 C 1 2 (^5xlO" bM) c a u s e s t h e s l o w l o s s o f t h e c h a r a c t e r i s t i c p e a k s o f t h e s t a r t i n g c o m p l e x 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 , s u g g e s t i n g a m i x t u r e o f p r o d u c t s w i t h R u ( 0 E P ) ( C 0 ) L ( L = Im o r 4Mepy) p r e -d o m i n a t i n g . The s p e c t r u m o f p u r e R u ( O E P ) ( C 0 ) L 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 f o r s e v e r a l d a y s . T h e 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 o c c u r s v i a a p r o c e s s i n v o l v i n g s l o w d i s s o c i a t i o n o f t h e P n B u 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 f r o m R u I I ( 0 E P ) ( P n B u 3 ) 2 (7.) i s known t o be s l o w 6 . I n 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 n B u 3 i n a 50/50 v / v m i x t u r e o f 4 M e p y / C H 2 C l 2 (4 mL) i m m e d i a t e l y g i v e s a s p e c t r u m d o m i n a t e d by a v e r y i n t e n s e v i s i b l e p e ak a t 526 nm and a weak S o r e t a t 410 nm ( F i g u r e 3 . 5 ) . n-:: 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 m i x e d l i g a n d s p e c i e s R u ^ ( 0 E P ) ( P n B u 3 ) 4 M e p y by c o m p a r i s o n w i t h R u ( O E P ) -( P n 6 u 3 ) 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 n B u 3 ) ( s e e 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 t o t h e s l o w f o r m a t i o n o f R u ( 0 E P ) ( C 0 ) 4 M e p y (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 l i g a n d p r o d u c t [Scheme 3 . 1 ) . 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 p h o s p h i n e f r o m R u ( O E P ) ( C 0 ) P n B u 3 i s s l o w w h i l 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 i s f a s t , a nd 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. T h i s s u g g e s t s t h a t R u I I ( 0 E P ) ( C 0 ) -P n B u 3 (.8) i s much more s t a b l e t h a n R u 1 1 (OEP) ( P n B u 3 ) 4 M e p y ; w h i c h seems F i g u r e 3.5 The 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 n 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 2 C 1 2 / 4 M e p y . 105 r e a s o n a b l e c o n s i d e r i n g t h e v e r y l a r g e e q u i l i b r i u m c o n s t a n t f o r t h e f o r m a t i o n o f 8 f r o m 1 ( 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 n B u 3 a d d e d t o 8^  t o e n s u r e c o m p l e t e f o r m a t i o n o f R u 1 1 ( O E P ) ( P n B u 3 ) 2 (7_) ( s e e S e c t i o n 2 . 5 ) . 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 and R u 1 1 ( O E P ) ( P n B u 3 ) 4 M e p y i s o n l y f o r m e d i n t h e p r e s e n c e o f a l a r g e e x c e s s o f t h e f r e e p y r i d i n e . R u ( 0 E P ) ( C 0 ) 4 M e p y e s 1 o W R u ( O E P ) ( C 0 ) P n B u ^faJ,l . R u ( O E P ) ( P n B u 3 ) 4 M e p y 1 0 r l M 4Mepy ^ y SCHEME- 3.1 4Mepy + RuCOEP) ( C 0 ) P n B u 3 R u ( 0 E P ) ( . P n B u 3 ) 4 M e p y + CO ( 3 . 1 3 ) f a s t 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 g e n e r a l l y r e s u l t i n t h e d i s p l a c e m e n t o f L w i t h no p r o d u c t i o n o f m i x e d l i g a n d s p e c i e s , 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 p h o t o l y s i s 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 R u ( O E P ) -;(:!C0.)Me'CN;; (6) arid R u(,0EP)(;C0)P nBu 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 o f a b o u t 10 f o r t h e l a t t e r c o m p l e x , t h i s b e i n g a t t r i b u t e d t o a h i g h t r a n s e f f e c t o f t h e p h o s p h i n e 6 , a nd 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 h i g h s t a b i l i t y o f t h e f i v e - c o o r d i n a t e i n t e r m e d i a t e R u ( O E P ) ( P n B u 3 ) w h i c h c a n be p r e p a r e d 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 f i v e -c o o r d i n a t e s p e c i e s Ru(.0EP)L, L = MeCN, E t O H , and 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 i n s o l u t i o n . 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 be i l l u s t r a t e d by t h e c h a n g e i n t h e vfy~ i s t r e t c h i n g f r e q u e n c y w i t h t h e l i g a n d . F. C a l d e r a z z o 1 7 has n o t e d 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 i s b e l o w 1935 ± 5 cm" 1. S u c h a t r e n d i s s u p p o r t e d by d a t a f o r Ru(.OEP) ( C O ) p y ( 3 ) ( y ^ s o l i d ) = 1 933 cm" 1,-; S e c -t i o n 2.4) and R u ( 0 E P ) ( C 0 ) M e C N ( 6 ) ( v C Q ( i n s o l u t i o n ) = 1935 c m " 1 ) 5 w h i c h 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 i n s o l v e n t c o n t a i n i n g t h e a p p r o p r i a t e l i g a n d t o o b t a i n R u 1 1 ( 0 E P ) p y 2 a n d , R u n ( O E P ) ( M e C N ) 2 p r o d u c t s 1 6 . I n c o n t r a s t . t h e CO l i g a n d o f Ru(OEP) (.CO)-P Bug (V^Q ( s o l i d ) = 1948 cm" , - 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 d o n o r s , and R u ( 0 E P ) ( C 0 ) 2 ( v C Q ( i n s o l u t i o n ) = 1990 cm" 1) c a n l o s e CO s p o n t a n e o u s l y 4 . 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 n B u 2 i s a - r r - a c c e p t o r 7 t h a t c o m p e t e s f o r t h e same 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 . Pi. b a c k - b o n d i n g i s much more 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 t h a n t h e Ru-P bond 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 m o n o x i d e 8 . 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 i s s u p p o r t e d by t h e work o f H i l l l e r e t a l . 1 8 who s t u d i e d P t ( P F 3 ) 4 a n d N i ( P F 3 ) 4 by p h o t o e l e c t r o n s p e c t r o s c o p y a n d showed t h a t t h e c h a r g e s h i f t s due t o a and IT b o n d i n g w e r e 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 . As t h e e l e c t r o n - w i t h d r a w i n g f l u o r i n e atoms make PF^ t h e l e a s t a s d o n a t i n g 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 i s e x p e c t e d t h a t P n B u 3 w i l l show a n e t c h a r g e d o n a t i o n t o t h e m e t a l l o -p o r p h y r i n . 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 where 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 t h e r u t h e n i u m atom i n a m e t a l l o p o r p h y r i n c o m p l e x f r o m ( I I ) t o ( I I I ) ( C h a p t e r 5 ) . E l e c t r o c h e m i c a l s t u d i e s o f a r a n g e o f r u t h e n i u m 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 h i g h e r p o t e n t i a l s a r e r e q u i r e d t o o x i d i z e t h e c o m p l e x , e i t h e r a t t h e m e t a l o r a t 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 s u c h a s 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 w i t h t h e v i e w t h a t t h e b o n d i n g o f t h e p h o s p h i n e t o t h e m e t a l c e n t r e i s 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 , a t l e a s t i n m e t a l l o p o r p h y r i n c o m p l e x e s . T h i s s u g g e s t s t h a t t h e n o r m a l c h e m i c a l b e h a v i o u r o f p h o s p h i n e s 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 . F u r t h e r e v i d e n c e f o r t h i s i s s e e n i n t h e s p e c t r a o f t h e p h o s p h i n e c a r b o n y l c o m p l e x e s w h i c h a r e v e r y s i m i l a r t o t h o s e o f t h e e l e c t r o n r i c h c o m p l e x e s R u ( O E P ) ( C O ) C I " and fRu(,0EP)(.C0)CN"r ( s e e T a b l e 3.2 and c o m p a r e F i g u r e s 3.2 a n d 3 . 6 ) , a n d , c o m p a r e d 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 c o m p l e x e s , t h e r e d s h i f t o f t h e S o r e t i s t h o u g h t t o r e f l e c t i n c r e a s e d e l e c t r o n d e n s i t y a t t h e p o r p h y r i n 1 9 ( T a b l e 3.8). 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 -p h i n e g r o u p s t o l a b i l i z e a t r a n s c a r b o n y l l i g a n d a s a l s o d e s c r i b e d , i t i s n e c e s s a r y 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 t o o r b i t a l s o f t h e r u t h e n i u m 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 t h e p o r p h y r i n s y s t e m b u t a r e u n a v a i l a b l e t o t h e c a r b o n y l l i g a n d f o r i r - b a c k -b o n d i n g . 108 T a b l e 3.8 The W a v e l e n g t h o f t h e S o r e t i ' ( y ) A b s o r p t i o n Band f o r a Number  o f R u H ( 0 E P ) L and R u 1 1 ( 0 E P ) ( G 0 ) L C o m p l e x e s Complex (nm) a- Complex (nm) i R a t i o ( I / I J -a P R u ( 0 E P ) ( C 0 ) 4 M e p y 396 1 .54 R u ( 0 E P ) p y 2 4 395 R u ( 0 E P ) ( C 0 ) P P h 3 - 407 1 .0 R u ( 0 E P ) ( P P h 3 ) 2 - 420 R u ( 0 E P ) ( C 0 ) P n B u 3 408 0.68 R u ( 0 E P ) C P n B u 3 ) 2 - 428 R u ( 0 E P ) ( . C 0 ) C N " 406 0.71 • Ru(.0EP)(.C0)Br" -'-9 404 1 .22 Ru(0EP ) C C 0)CT" -'-3 402 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 2 C 1 2 u n l e s s i n d i c a t e d o t h e r w i s e . 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 50 nm (a) and a t ^520 nm (g)) 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) See S e c t i o n 3.4. 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 C H Q C I 2 a s S o l v e n t . 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 has been shown t o y i e l d an a n i o n i c s p e c i e s R u ( O E P ) ( C O ) C N " , 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 on 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 by d i s s o l v i n g R u ( O E P ) ( C O ) E t O H ( 2 ) i n C H 2C12 ( F i g u r e 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 a d d e d 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 C H 2 " C 1 2 . • T n e r e s u l t s , a r e r e c o r d e d i n T a b l e 3 . 9 . The a n i o n s were 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 a n d i n most c a s e s i n l a r g e e x c e s s ( 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 u s e d a s e l e c t r o l y t e s ( C 1 0 4 ~ , B F ^ " , C F 3 S 0 3 " a n d P F g " ) . The a n i o n c o n c e n -t r a t i o n s were s i m i l a r t o t h o s e u s e d i n t h e 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 t o be d e s c r i b e d , so t h e r e s h o u l d be no 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 t o t h e r u t h e n i u m c e n t r e , a t l e a s t b e f o r e o x i d a t i o n . In t h e c a s e o f t h e s e n o n ^ c o o r d i n a t i n g a n i o n s , t h e s p e c t r a o f Ru(.0EP)(C0) CD w e r e a c c u r a t e l y r e p r o -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 a d d i n g e l e c t r o l y t e t o 0.05M c o n -c e n t r a t i o n s . C h l o r i d e a n d b r o m i d e i o n s were f o u n d t o c o o r d i n a t e w e a k l y ; t h e c a s e 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. A l i m i t i n g 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 i n t h e p r e s e n c e o f ^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 c o u l d n o t be o b t a i n e d f o r t h e 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 . T h e s p e c t r a o f t h e p r o d u c t a n i o n i c s p e c i e s , d e r i v e d f r o m Ru(OEP)CCO) CD w i t h c 1 " > B r" a n d C N " > a r e r e c o r d e d i n T a b l e 3.2. 2.0! WAVELENGTH (nm) F i g u r e 3,6 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 2 and t h e p r o d u c t ( R u ( O E P ) ( C O ) C N - ) 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". .111 5 0 0 6 0 0 700 WAVELENGTH (nm) F i g u r e 3.7 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 2 C 1 2 and t h e p r o d u c t ( J,Ru(OEP)(CO)Cl-") (. .-) o b t a i n e d on a d d i n g an e x c e s s ( t o O . 0 5 M ) o f TEA+C1-. 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 2C1 A n i o n Added ( I / I . ) -B e f o r e A d d i n g A n i o n — In ^0.05M A n i o n S o l u t i o n cio 4" 2.52 2.50 B F 4 " 2.53 2.53 C F 3 S O 3 - 2.62 2.61 P F 6 ~ 2.60 2.61 r 2.58 2.53 B r " 2.61 1 .48 -c r 2.54 1.23 i a) . R a t i o o f v i s i b l e p e a k s a s d e f i n e d i n T a b l e 3.1. b) . M e a s u r e d ' i n d r i e d C H 2 C 1 2 as s o l v e n t . c ) S p e c t r u m o f . R u ( O E P ) ( C O ) B r " 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) U n d e r t h e s e c o n d i t i o n s t h e s p e c t r u m i s t h a t o f R u ( O E P ) ( C O ) C I " r e p o r t e d i n T a b l e 3.2. 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. 1 ( 2 ) , 115 ( 1 9 7 1 ) . 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. Holm, and J.A. I b e r s , Q. Am. Chem. S o c . 95, 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 , and G.A. M a z z o c c h i n , I n o r g . Chim. A c t a . , 3 7 , 1 55 (1 9 7 9 ) . 4. S.S. E a t o n a nd G.R. E a t o n , J . Am. Chem. S o c . 97, 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 nd 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. Graham, 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, 1796 (.1973). 10. L.M. E p s t e i n , D.K. S t r a u b , a nd C. M a r i c o n d i , I n o r g . Chem. 6_, 1720 (1 9 6 7 ) . 1 1 . V. Gutmann, '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.,1978. 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 ) . 1 3 . F.A. C o t t o n a nd 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 1 , 4 t h E d . , I n t e r s c i e n c e , New Y o r k , N.Y., 1980, p . 8 7 . 14. T. L e u n g , : P e r s o n a l c o m m u n i c a t i o n . 15. C A . T o l m a n , J . Am. Chem. S o c . 9 2 , 2956 (1 9 7 0 ) . 1 6 . F.R. H o p f , T. O ' B r i e n , W.R. S c h e i d t , and 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 , L ' 'j_n ^ T h e _ P o r p h y r i n s J ; , ,(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 1 8 . I.H. H i l l i e r , V.R. S a u n d e r s , M.J. Ware, 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. 1970, 1 3 1 6 . 19. M. G o u t e r m a n , i n The 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." 16. 20 . D. D o l p h i n , B.R. James, and P.D. S m i t h , J . O r g a n o m e t . Chem. 2 0 8 , 239 ( 1 9 8 1 ) . 115 CHAPTER 4 THE OXIDATION OF RUTHENIUM PORPHYRIN CARBONYL COMPLEXES  Ru** ( O E P ) ( C O ) L ; ( L = EtOH, 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 ) p o r p h y r i n s p e c i e s R u t O E P ) ( C 0 ) L t h a t g i v e 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 . T h e o x i d a t i o n o f o t h e r c o m p l e x e s o f t h i s t y p e ( L = P n B u 3 , P P h 3 and A s P h ^ ) t o g i v e m i x t u r e s c o n t a i n i n g r u t h e n i u m ( . I I I ) 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 C h a p t e r 6. 4.1 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 R u C 0 E P ) ( C 0 ) L Whereas 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 o r e s u l t i n o x i d a t i o n o f t h e m e t a l i o n , i t i s known t h a t i f L-| o r L 2 = 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 ) + ' -( C O ) L 1 . In o u r s t u d i e s , c y c l i c v o l tammograms were 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 , were f o u n d t o be d e p e n d e n t upon 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 n a t u r e o f t h e 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 i n d i l u t e ( 1 0 ~ 4 -10 M) s o l u t i o n i n C H 2 C 1 2 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 u n d e r t h e s e 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 v o l t a m m o g r a m s 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 d e p e n d e n c e 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 . A t y p i c a l c y c l i c v oltammogram i s s e e n i n F i g u r e 4.1 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 e l e c t r o l y t e , a r e l i s t e d i n T a b l e 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 ( S e c t i o n s 3.1 a n d 3.21. C y c l i c v o l tammograms o f c o m p l e x ^ were c o m p a r e d t o s i m i l a r v o ltammograms 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 ) ) . P e r c h l o r a t e , h e x a f l u o r o p h o s p h a t e , a n d 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 s o l u t i o n s g a v e s i m i l a r p o t e n t i a l s f o r b o t h p o r p h y r i n c o m p l e x e s , w h i l e s u r -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 were ^0.1 v o l t s h i g h e r . A s i m i l a r e f f e c t i s o b s e r v e d 6 a c o m p a r i n g c y c l i c v o l t a m m o g r a m s o f R u I I ( . 0 E P ) ( C 0 ) P n B u 3 ( 8 ) ( s e e S e c t i o n 6.1) and R u n ( 0 E P ) ( P n B u 3 ) 2 [7) ( s e e 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 TBAP. T h u s , t h e h i g h e r p o t e n t i a l s f o r t h e s e o x i d a t i o n s ( R u I I ( 0 E P ) ( C 0 ) L i C i R u I I ( 0 E P ) + ' ( C 0 ) L a n d R u I I C 0 E P ) L 2 < = ^ R u I I I ( 0 E P ) L 2 ) o b s e r v e d i n t h e p r e s e n c e o f B F 4 ~ i o n s a r e n o t r e s t r i c t e d t o s p e c i e s where t h e a n i o n c o u l d c o o r d i n a t e t o t h e m e t a l c e n t r e a n d 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 a s s o c i a t e d w i t h c o o r d i n a t i o n o f B F 4 ~ i o n s a l t h o u g h , a s d e s c r i b e d b e l o w , 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) (, 1 a ) . C y c l i c v o l tammograms o f b o t h Ru(.0EP)(C0) CD a n d R u ( O E P ) ( C 0 ) 4 M e p y (.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 ( T E A P I C - 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 04 0 E(V vs. Ag/AgCl) F i g u r e 4.1 The c y c l i c voltammogram o f R u ( O E P ) ( C O ) E t O H ( 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_ and 2 i n 10"^ t o 10~^M s o l u t i o n s ) i n 0.05M T B A P - C H 2 C l 2 . 2 wave c o u l d n o t Be o B s e r v e d due 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) . T h i s d e c r e a s e i n p o t e n t i a l s u g g e s t s t h a t l a r g e a n i o n s w i t h a d i f f u s e d c h a r g e d e n s i t y may Be more 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 t h e p r e s e n c e 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 [ e . g . 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 . T h i s e f f e c t 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 more 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 due 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 g " a n d C F 3 S 0 3 ~ . However, t h a t \ t h i s t h e o r y , e x p l a i n s t h e h i g h e r p o t e n t i a l o b s e r v e d i n t h e p r e s e n c e o f 118 T a b l e 4.1 The 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 ) and Ru(.OEP) ( C 0 ) 4 M e p y (.4) i n D i c h l o r o m e t h a n e i n t h e P r e s e n c e o f  V a r i o u s E l e c t r o l y t e A n i o n s . 4.1 a) E ^ V a l u e s f o r R u ( 0 E P ) ( C 0 ) t l ) -A n i o n E 2 ( V ) ± E 2 - E 1 ( V ) B F 4 " +0.82 +1 .30 +0.48 c i o 4 " +0.71 +1 .19 +0.48 P F 6 ~ +0.70 +1 .20 +0.50 CF3SO3- +0.65 +1.16 +0.51 P i c r a t e " +0.52 4.1 b) E x V a l u e s f o r Ru(OEP) ( C 0)4Mepy ( 4 ) -A n i o n E ^ V ) E 2(.V) E g - E ^ V ) B F 4 " +0.81 +1.42 +0.61 C10 4 ~ +0.72 +1.31 +0.59 P F g " +0.65 +1.27 +0.62 CF3SO3" +0.71 +1.30 +0.60 P i c r a t e " +0.62 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 between 1.5 x 10 and 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 where 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 10 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 by 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 c o r r e s p o n d t o t h e p r o c e s s R u I I ( 0 E P ) + ' ( . C 0 ) L + e W R u I I C 0 E P ) ( ; C 0 ) L . c) 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 f o r t h e s e c o n d 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 . T h i s c o r r e s p o n d s t o e i t h e r Ru I I(0EP) 2" H(.C0)L+e*r=^Ru I I(0EP) + ' ( C 0 ) L , o r R u I I I ( 0 E P ) + ' ( C 0 ) + e - ? = i R u I I ( 0 E P ) + ' C C 0 ) L . d) 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 10 ^M. 119 B F 4 ~ i o n s 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 s l i g h t l y s m a l l e r V a n - d e r - W a a l s c o n t a c t r a d i u s t h a n C I 0 4 " ( 2 . 8 3 $ v s . 2.90 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 t h e 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 5 o f t h e e l e c t r o n e g a t i v e atoms ( 0 f o r C l O ^ " a n d F f o r B F ^ - ) . T h e two e l e c t r o l y t e a n i o n s a r e o f a p p r o x i m a t e l y 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 i n s u f f i -c i e n t t o e x p l a i n t h e 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 s e e n f o r t h e t e t r a -f l u o r o b o r a t e a n i o n . 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 Ru(OEP)CC0)4Mepy ( 4 ) ( T a b l e 4.1) shows t h a t t h o s e f o r .4. a r e a p p r o x i m a t e l y 0.1 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 . T h e c y c l i c v o ltammograim.of 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 4 " i n C H 2 C 1 2 ( T a b l e 4 . 2 ) . The p r e s e n c e o f a c o o r d i n a t e d s i x t h l i g a n d a p p e a r s t o d e s t a b i l i z e t h e d i c a t i o n s p e c i e s 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 f i r s t a n d 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 and n a t u r e o f t h e s i x t h l i g a n d . T h e 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 6 * 7 t h a t h a v e l i t t l e 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 0.1 v o l t s on 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_. Compared t o p y r i d i n e , i m i d a z o l e i s o b s e r v e d t o s t a b i l i z e b o t h t h e m o n o c a t i o n a n d 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 i m i d a z o l e t o c h a r g e d c o m p l e x e s . 120 T a b l e 4.2 V a r i a t i o n o f R e d u c t i o n P o t e n t i a l s w i t h t h e N a t u r e o f t h e S i x t h  L i g a n d . 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 2 ( V ) E g - E ^ V ) t l ) R u ( O E P ) t C O ) - +0.71 +1.19 0.48 L = py t l ) R u ( 0 E P ) ( C 0 ) p y +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) R u t O E P ) t C O ) I m +0.60 +1 .21 0.60 a l b) -4 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. 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(OEP)(CO)EtOH> , 0 x 10" t l ) i n C H 2 CI 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 and E 2 w i t h t h e n a t u r e o f t h e 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 2 - E ^ a p p e a r s t o be i n d e p e n d e n t o f t h e n a t u r e o f t h e s i x t h 1 i g a n d ( 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 2 - E - | = +0.495 ± 0.015V 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 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 s t u d i e d ) . The a p p a r e n t 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 t h a 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 , c o u l d be due 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) + " t C 0 ) (.1) b u t t h i s seems u n l i k e l y a s t h e 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 c o o r d i n a t e t o t h e m e t a l i n j_a ( s e e b e l o w ) a n d , i f t h e a n i o n s 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 a n d 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 2 - 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 w o u l d be e x p e c t e d and t h i s i s n o t t h e c a s e (• e v e n f o r t h e BF^" a n i o n ) . A n o t h e r 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 f r o m l i g a n d f i e l d t h e o r y . The m a j o r d i f f e r e n c e between l_a_ and 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 c o o r -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 a n d i n t h e f o r m e r c a s e o n l y f o u r n i t r o g e n l i g a n d s a r e i n v o l v e d . 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 a l m o s t c e r t a i n l y c o n t a i n s a c o o r d i n a t e d e l e c t r o l y t e a n i o n , a l t h o u g h t h i s a n i o n i s so 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 t o be 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 ( s e e C h a p t e r 5 ) , a n d 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 o f t h i s t h e s i s . From l i g a n d f i e l d t h e o r y 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 have s t r o n g l i g a n d f i e l d s a n d c a u s e 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 m e t a l 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 have 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 1 0 , 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 c o m p l e x F e * ^ ( T P P ) C l 0 ^ s u g g e s t e d t h a t i n p o r p h y r i n c o m p l e x e s 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 . T h u s , a l t h o u g h a l l 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 CRu(.0EP) + 'CC0) ( J _ a ) , RuC0EP) + '(.C0)py ( 3 a ) , RuC0EP) + '(C0)4Mepy ( 4 a ) and RuC0EP) + ' ( C 0 ) l m ( j i a j ) may be s i x - c o o r d i n a t e , f o r t h e p u r p o s 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 p l a n a r c o m p l e x ( t h e c a r b o n y l 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 . T h e o r d e r i n g o f t h e d-o r b i t a l s on a m e t a l i o n i s v e r y s e n s i t i v e t o t h e g e o m e t r y a n d c h a r g e 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 9 and h e n c e c o u l d be v e r y d i f f e r e n t 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 . T h e 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 c o u l d a f f e c t 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 m o l e -c u l a r o r b i t a l s s u c h t h a t a s e c o n d e l e c t r o n i s r e m o v e d ( 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 t h e 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 c o m p l e x e s . T h i s w o u l d 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 2-E-| w i t h t h e n a t u r e o f t h e s i x t h 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_. C h a n g i n g 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 on t h e r e d o x p o t e n -t i a l s o f t h e p o r p h y r i n s p e c i e s . D i s s o l v i n g Ru (OEP) (CO) EtOH (.2) i n a c e t o -n i t r i l e g a v e Ru(.OEP)(.CO)CH^CN (.6). a s s e e n bV t n e u . v . / v i s i b l e s p e c t r u m ( s e e S e c t i o n 3 . 1 ) . C y c l i c v oltammograms were o b t a i n e d i n t h e p r e s e n c e o f b o t h 0.05M C 1 0 4 " and B F 4 " . T a b l e 4.3. T a b l e 4.3 A C o m p a r i s o n 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 a n d D i c h l o r o m e t h a n e a s S o l v e n t . E l e c t r o l y t e A n i o n S o l v e n t . CH 3CN - C H 2 C 1 2 - 1 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) ( E 2 - E n ) ^Z~E^ C 1 0 4 " E 1 +0.73 +0.71 E 2 +1.12 ( 0 . 3 9 ) +1.19 ( 0 . 4 8 ) B F 4 ~ E ] +0.75 +0.82 E 2 +1.14 ( 0 . 3 9 ) +1.30 ( 0 . 4 8 ) T a b l e 4.3 c o n t i n u e d 123 a) P o r p h y r i n c o n c e n t r a t i o n s i n t h e a c e t o n i t r i l e e x p e r i m e n t s a r e i n t h e r a n g e 4 x 1 0 " 4 t o 8 x 10" 4M. b) R e d u c t i o n p o t e n t i a l s q u o t e d f o r d i c h l o r o m e t h a n e a s s o l v e n t a r e t a k e n 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 i n t h e p r e s e n c e o f b o t h 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 e l e c t r o l y t e s . Thus t h e c h a n g i n g o f s o l v e n t f r o m C H 2 C 1 2 t o CHgCN has l i t t l e e f f e c t on t h e 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 i n c r e a s e i n s t a b i l i t y o f t h i s s p e c i e s i n t h e p r e s e n c e o f f l u o r o b o r a t e a n i o n s . W h a t e v e r e f f e c t i s r e s p o n s i b l e f o r t h e i n c r e a s e d p o t e n t i a l s i n t h e p r e s e n c e o f B F 4 ~ i o n s i n C H 2 C 1 2 a s 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 CHIgCN. 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 . E v i d e n c e f o r t h i s i s s e e n i n t h e r e d u c e d v a l u e s f o r E 2 o b s e r v e d i n a c e t o n i t r i l e a s 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 I I ( . 0 E P ) . C P n B u 3 ) . 2 ( 7 ) - S e c t i o n 7.1) and a l s o t h e r e d u c t i o n o f E 2 ~ E ^ v a l u e s n o t e d i n T a b l e 4.3. T h e d i c a t i o n w i l l be m o r e s o l v a t e d t h a n t h e m o n o c a t i o n 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 t h e l e s s p o l a r d i c h l o r o m e t h a n e . C y c l i c v oltammograms 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 2 C 1 2 ) 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 f r o m t h e u s u a l f o r m o f voltammogram d e s c r i b e d a b o v e . F i g u r e 4.2 shows a c y c l i c v o ltammogram 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 e t h a n o l 124 1.2 0.8 0.4 0 E(V vs. Ag/AgCl) F i g u r e 4.2 T h e c y c l i c voltammogram o f R u ( O E P ) ( C O ) E t O H ( 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_ and 2_ i n 10"4 t o 10~3M s o l u t i o n s ) i n 0.05M TBAP and 0.005M TEA+C1" i n C H 2 C 1 2 . l i g a n d on s o l u t i o n o f 2_ i n C H 2 C 1 2 ) i n t h e p r e s e n c e 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 . A t s u c h 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") w o u l d be p r e s e n t ( S e c t i o n 3.4) and h e n c e t h e o x i d a t i o n peak 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 Ru(OEP) + '( CO) (l_a_). The c o r r e s p o n d i n g r e d u c t i o n peak ( 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 r e v e r s i b l e ; 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 r e d u c e (Scheme 4 . 1 ) . 125 SCHEME 4.1 TT E =+0.74V j T R u l x ( O E P ) ( C O ) -E . ) R u 1 1 ( O E P ) + '(CO) ( 1 ) -e ( l a ) + CT R u n ( O E P ) + "(CO)' CI ( l c ) E =+0.38V T T -2 > R u H ( O E P ) ( C O ) +e + C T ( 1 ) 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 d i c h l o r o m e t h a n e s o l u t i o n s o f R u ( 0 E P ) ( C 0 ) ( 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 4 " o r T P A + B F 4 " 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 0.04 v o l t s h i g h e r t h a n t h a t f o r t h e f i r s t o x i d a t i o n p eak g a v e i n a l l c a s e s a s m o o t h 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 ) . T h e 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 r u t h e n i u m p o r p h y r i n . The s p e c t r u m o f t h e p r o d u c t v a r i e d w i t h 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 n e a r t h e end o f t h i s C h a p t e r ( S e c t i o n 4 . 3 ) . A d d i t i o n o f a s m a l l 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 s a m p l e o f t h e Ru(0EP) + "(CO) (,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 s p e c t r u m f o r t h e R u ( 0 E P ) + ( C 0 ) L c a t i o n r a d i c a l ( s e e S e c t i o n 5 . 1 b ) . Hence t h e d i f f e r e n c e i n s p e c t r a a r e due t o the. c o n t i n u e d 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 Im). 126 Figure 4.3 127 F i g u r e 4.4 T h e o p t i c a l s p e c t r a o f t h e e l e c t r o c h e m i c a l l y p r e p a r e d c a t i o n r a d i c a l s . a 4 0 0 5 0 0 6 0 0 Wavelength (nm) a) Ru(OEP) + '(CO) (Ja.) i n 0.05M T B A P - C H 2 C 1 2 . The s p e c t r u m 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 a b s o r p t i o n s a r e s l i g h t l y r e d - s h i f t e d ( s e e T a b l e 4 . 5 ) . 128 Figure 4.4 con t inued: . b - - i Wavelength (nm) c) Ru(0EP) + '(C0)Im (5a) i n 0.05M TBAP-CH 2C1 2. 129 The addit ion of excess e lec t ro l y te (such as TBAP or TPAF) to a solut ion of Ru(0EP) + '(C0) ( l a ) , prepared electrochemically in CH2CI2> caused no detectable change in the v i s i b l e spectrum. However,species la prepared in the absence of e lec t ro l y te (either by d i rect oxidation of 2 dissolved in CH 2C1 2 using AgBF^or by the addition of AgBiF^ to [Ru(0EP) +* -(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 ferent spectrum from l_a_ prepared by electrochemistry (compare Figures 4.4a and 4.7). In the absence of 0.05M e lec t ro l y te the shoulder at%610nm i s diminished (Table 4.4). Addition of e lec t ro l y te (TBAF or TBAP) i n tens i f i ed th i s shoulder giving a spectrum ident ica l to that observed for the electrochemical ly prepared l_a_. Addition of AgBF^ to l_a in 0.05M e lec t ro l y te solution 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 af fect ing 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 in tens i ty at 610 nm giving a spectrum s l i g h t l y d i f ferent to that obtained in the absence of excess e l ec t ro l y te . Addition of e lec t ro l y te to a solut ion of RuC0EP)t'(,C0)MeCN (6a) in 1% MeCN in CH 2C1 2 caused no change in the v i s i b l e spectrum (see Section 4.3). The difference in opt ica l spectra noted here obviously depends upon the absence or presence of excess e lect ro ly te and suggests that the e l ec t ro -l y te anions are coordinating to l_a_. Coordination of CI0^ to ZnTPP in the so l id state has been repor ted 1 2 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. C H ^ C ^ . However, 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 t h e o x i d a t i o n p r o c e s s e s and t h e i n v a r i e n c e o f E £ - E ^ w i t h e l e c t r o l y t e ) , a r g u e a g a i n s t t h e c o o r d i n a t i o n o f t h e e l e c t r o l y t e a n i o n ( 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 an 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, u n d e r t h e c o n d i t i o n s w here 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 + " , 1 3 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 voltammogram 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 a l m o s t c e r t a i n l y c o o r d i n a t e d t o s a m p l e s o f l a _ p r e p a r e d e l e c t r o c h e m i c a l l y , b u t 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 o r e l e c t r o c h e m i s t r y o f t h e co m p l e x l a _ 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 b e h a v e as a f i v e - c o o r d i n a t e s p e c i e s . C o o r d i n a t i o n o f t h e e l e c t r o l y t e a n i o n 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 c h a n g e s o u t l i n e d a b o v e . A d d i t i o n 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 c a u s e d i s p l a c e m e n t o f t h e e l e c t r o l y t e c o - a n i o n t o g i v e t h e s p e c i e s R u I I ( 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 on -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 d o e s 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 s r e q u i r e d t o d i s p l a c e t h e a n i o n . In t h e s a m p l e s p r e p a r e d by A g B F ^ 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 10~ 4M) n o r t h e B F ^ " i o n s a r e l i k e l y t o 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 so 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) l a . 131 E l e c t r o l y s i s of Ru(OEP)(CO)EtOH d i s s o l v ed 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 in MeCN) us ing 0.05M TEA + C10 4 " as e l e c t r o l y t e a l s o gave a purple s o l u t i o n o f a c a t i on r a d i c a l (6a_),whose spectrum was s i m i l a r to tha t o f J_a_ and 3a^ but i n d i c a t e d coord inated a c e t o n i t r i l e (F igure 4.4b and Table 4 . 4 ) . S o l u b i l i t y problems prec luded the determinat ion o f the number of e l e c t r on s removed from the porphyr in complex i n t h i s r e a c t i o n , but r epea t i ng the o x i d a t i o n o f ]_ i n 1% MeCN in C ^ C ^ (the product had an i d e n t i c a l spectrum to tha t obta ined i n pure MeCN) proved that the o x i d a t i o n process r equ i red 1.00 ± 0.05 e l e c t r o n s as i n the e l ec t r ochemica l format ion o f l_a_, 3a_ and 5a_. A l l these c a t i o n r a d i c a l samples ( l a , 3a, 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 TBA + BH 4 ~, to g ive a red 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 the one con ta 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 on sp in resonance (e.-s.r.) s tud ie s o f these c a t i o n r a d i c a l spec ies showed a st rong sharp (peak to peak width = 8G) s i gna l a t g = 2.01 a t l i q u i d n i t r ogen temperatures corresponding to an unpaired e l e c t r o n i n a d e l o c a l i z e d o rgan ic system. I n teg ra t i on o f t h i s s i gna l by comparison w i th a s i m i l a r s o l u t i o n o f ZnTPP + ' (see Sect ion 2.1) i n d i c a t e d the presence o f one unpaired e l e c t r on per porphyr in molecule and was c on s i s t en t w i th the fo rmu la t i on o f the ruthenium spec ies as porphyr in Tr -cat ion r a d i c a l s . How-ever , the 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 tud ied at ambient tempe-r a t u r e s , showed a very much weaker s i gna l (reduced by a f a c t o r o f 10,000 2 i as est imated from a TO M s o l u t i o n o f Ru(.0EP) '(.CO) ( l_a)).of the same +. sharpness and g va l ue . This temperature e f f e c t was not observed f o r ZnTPP 132 (reduction in i n t e n s i t y ofie.a.r. s ignal on.warming to room temperature was <30%) but for the ruthenium cat ion rad ica l so lut ions the process was r e -ve r s i b l e and could be repeated several t imes. No change in colour was observed on f reez ing or thawing the ruthenium cat ion rad ica l so lut ions and th i s precludes the p o s s i b i l i t y o f intramolecular e lect ron t rans fer from the metal to the porphyrin accounting for the weak s ignal observed at room tempera ture 1 4 . The weakness of the room temperature s igna l may be due to a re laxat ion e f f e c t 1 5 . Solut ions of these cat ion rad i ca l s ( p a r t i c u l a r l y Ru**(.0EP) (CO)py (3aJ and Ru(.0EP) + * (.CO) Im (5a)) were reasonably s table i f sealed under argon in an anaerobic c e l l (Section 2.1) and could be^stored in the f reezer fo r several days without d e t e r i o r a t i o n . However, s o l i d samples, formed by evaporating, o f f the solvent from the cat ion rad ica l and the supporting e l e c t r o l y t e , degraded in a matter o f hours to give non-porphyrin products even i f stored in a Schlenk tube under argon. The cat ion r ad i ca l s are very sens i t i ve to a i r in the s o l i d s t a t e , the products showing s im i l a r absorptions to those of atmospherical ly ox id ized so lut ions of 1_ in CHgCl 2 - So l id samples appear to degrade fa s ter than so lut ions in the presence of traces of a i r . In an attempt to obtain a s tab le s o l i d sample, e l e c t r o l y s i s was ca r r ied out in the presence of p i c ra te e l e c t r o l y t e in the hope that the large an ion, with most of i t s negative charge de loca l i zed to the periphery of the molecule, would s t a b i l i z e the cat ion rad ica l species and r e a d i l y p rec i p i t a te out the p o s i t i v e l y charged complex as a p i c ra te s a l t . 133 T e t r a - n - b u t y l a m m o n i u m p i c r a t e . w a s 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 2 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 c a t i o n s w o u l d p r e c i p i t a t e o u t i n t h e p r e s e n c e 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 " 3 M p o r p h y r i n and 0-.05M TEAP i n C H 2 C 1 2 ) g a v e no p r e -c i p i t a t e . 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 ) (2) Gin e q u i . l i -3 b r i u m w i t h Ru(.OEP)(CO) (.!_)) i n C H 2 C 1 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 5 x 1 0 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 deep 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 o b -s e r v e d . 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 CH2CI2 gave d a r k c r y s t a l s o f a c o m p l e x c o - p r e c i p i t a t i n g w i t h t h e e x c e s s 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 2 C l 2 showed 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 ]Ru(0EP) + ' ( C 0 ) ] + p i c r a t e " a n d 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 o b s e r v e d i n t h e s p e c t r u m o f t h i s c o m p l e x . 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 fr o m d i r e c t o x i d a t i o n o f Ru(OEP)CCO)-(J_) i n C H 2 C 1 2 by A g B F 4 . T h i s o b s e r v a -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 , a nd 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 [ R u ( 0 E P ) + ' ( C 0 ) ] + p i c r a t e " . 4.2 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 0 ) L ( L = V a c a n t , p y , MeCN) -4 -3 A d d i t i o n o f a 10 ' t o 10 M s o l u t i o n o f b r o m i n e i n CH2CI2 t o a 5 x 10" 5M s o l u t i o n o f R u ( 0 E P ) ( C 0 ) ( 1 ) ( f o r m e d by d i s s o l v i n g Ru(OEP) (.C0) = EtOH i n C H 9 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 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 p r o d u c t s o l u t i o n showed 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 ( u p t o 2 x 10 M), b u t 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 t h e m a j o r a b s o r p t i o n s e x p e c t e d f o r a p o r p h y r i n s p e c i e s . T h e 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) and t h e p o r p h y r i n s p e c i e s p r e s e n t was 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)-(C0) (.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 ) . The e x t i n c t i o n c o e f f i -c i e n t o f t h e m a i n a b s o r p t i o n peak o f b r o m i n e d i s s o l v e d i n C B 9 C 1 9 ( x m , j = L. c niax 410 nm) was o b t a i n e d f r o m t h e v i s i b l e s p e c t r u m o f a s t a n d a r d s o l u t i o n o f b r o m i n e and f o u n d t o be 210 M" 1 c m - 1 . U s i n g t h i s v a l u e t o q u a n t i f y t h e amount o f b r o m i n e a d d e d 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 4 0 % 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 o f 1 b. ( E q u i l i b r i u m 4 . 1 ) . T h e r e a c t i o n t o p r e p a r e t h e r e l a t e d c o m p l e x [ R u ( 0 E P ) . + -(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 2 was s t r o n g l y a f f e c t e d by 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 . RuC0EP)(C0). + i g B r 2 , > [ R u ( , 0 E P ) + ' ( C O ) B r ] (.4.1). (-D 1 (-11) A t t e m p t s t o p r e p a r e s i m i l a r s p e c i e s f r o m 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 , where L i s a l i g a n d t h a t r e m a i n s c o o r d i n a t e d when t h e c o m p l e x i s d i s s o l v e d i n C H 2 C 1 2 , o r f r o m R u ( O E P ) ( C O ) E t O H {2) d i s s o l v e d i n a c o o r d i n a -t i n g s o l v e n t ( e . g . MeCN)., u s u a l l y g ave m i x t u r e s o f p r o d u c t s . T h u s 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 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 a b s o r p t i o n s 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 between 500 and 570 nm. R e d u c t i o n by B H ^ - g a v e i n c o m p l e t e f o r m a t i o n o f t h e s t a r t i n g m a t e r i a l ( R u ( O E P ) (CO)MeCN ,-.6) 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 -v e r s i b l y o x i d i z e d . O x i d a t i o n o f Ru(OEP)(CO)MeCN (,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 o x i d a t i o n o f 6 ( i . e . 6 a ) . T h i s p r o d u c t was 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 5 0 % o f t h e r e a c t i o n ( T i g u r e 4 . 6 ) . However, a t t e m p t s t o o x i d i z e t h e l a s t 2 0 % o f t h e s t a r t i n g , m a t e r i a l c a u s e d 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 a b o v e f o l l o w i n g t h e a d d i t i o n o f e x c e s s b r o m i n e . S o l u t i o n s o f t h e c a t i o n r a d i c a l p r e p a r e d t h i s way were v e r y u n s t a b l e and r e v e r t e d back 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 e l e c t r o -c h e m i c a l l y (.see S e c t i o n 5 . 4 ) . T h e 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 t h a n t h e e x p e c t e d [ 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 4 . 2 ) . Ru (OEP) (CO) MeCN + kBrz S ° ^ n t )• [ R u ( 0 E P ) f ' (CO) ( M e C N ) ] + B r " (.4.2) ( 6 ) ( ( 6 a ) ( P u r p l e ) F u r t h e r e v i d e n c e 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 t h e a b o v e r e a c t i o n i n C H 2 C 1 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 ) showed i t t o be 6_ as f o r m e d i n p u r e MeCN. However, 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 s o l u -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 were o b t a i n e d f o r t h e f i r s t 8 0 % o f t h e r e a c t i o n , w h i 1 e a t t e m p t s t o c o m p l e t e t h e r e a c t i o n c a u s e d t h e f o r m a t i o n o f some s l i d e p r o d u c t s as d e s c r i b e d a b o v e . In t h i s r e a c t i o n , t h e a c e t o n i t r i l e i s p r e s e n t 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 ) , r a t h e r t h a n 6a_ as o b s e r v e d i n p u r e MeCN. T h e m e c h a n i s m o f t h e s e r e a c t i o n s w i l l be c o n s i d e r e d i n S e c t i o n 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 (.4.3) ( 6 ) ( l b ) ( G r e e n ) R e a c t i o n s i n o t h e r c o o r d i n a t i n g s o l v e n t s o c c u r r e d i n a s i m i l a r f a s h i o n . S o l u t i o n s i n p u r e n i t r o m e t h a n e g a v e t h e e l e c t r o c h e m i c a l c a t i o n r a d 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 . A d d i t i o n o f b r o m i n e t o RuCOEP) ( C O l p y 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 2 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 t h a n t h e c o r r e s p o n d i n g c o m p l e x f o r m e d f r o m RuC0EP)(C0)_ (.]_), i n C H 2 C 1 2 and b r o m i n e . 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 d e t e r -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, c a n 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 c a s e B r ~ ) . 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 p r e p a r e d 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 , 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 c a r e f u l l y c o n t r o l l e d c o n d i t i o n s . 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 a l s o by e l e c t r o c h e m i c a l m e t h o d s . T h u s , 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 2 C 1 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 [ R u ( 0 E P ) + ' ( C 0 ) C l ] (,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 oltammogram r e p o r t e d i n S e c t i o n 4.1 i 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 had 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 as 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 ^575 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 . H e n c e , 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 an o x i d a t i o n p r o c e s s i s d e t e r -m i n e d by t h e a n i o n s p r e s e n t i n v o l u t i o n r a t h e r t h a n t h e m e t h o d o f o x i d a -t i i d n . T he 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 m a t e r i a l '.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 few "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 2 C l 2 showed b e h a v i o u r s i m i l a r t o t h a t 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 ( 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 n i t r o g e n t e m p e r a t u r e s a s t r o n g s h a r p ( p e a k to, peak 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 i n d i c a t e d t h e c a t i o n r a d i c a l n a t u r e o f t h e c o m p l e x . As o b s e r v e d f o r c a t i o n r a d i c a l s l a a n d 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 t h a n 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 t e m p e r a t u r e s . To d e t e r m i n e 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 were i n s t i -g a t e d t o compare Vb w i t h two d i f f e r e n t s p e c i e s : - [ R u 1 1 1 C O E P ) ( P ^ B u . ^ ] * -B r " Cab), a 1:1 e l e c t r o l y t e , . and R u n i C 0 E P ) C P n B u 3 ) B r ( 1 0 ) , a p r o b a b l e n o n -e l e c t r o l y t e . S t u d i e s were made i n d i l u t e d i c h l o r o m e t h a n e s o l u t i o n s u s i n g a c o n d u c t i v i t y c e l l whose c e l l c o n s t a n t ( k ) was 0.12 c m - 1 [ s e e S e c t i o n 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 m e a s u r e d r e s i s t a n c e a n d C i s t h e c o n c e n t r a t i o n i n m o l e s p e r l i t r e . T he d a t a a r e r e c o r d e d i n T a b l e 4.4. T h e g r e e n c a t i o n r a d i c a l ( l b ) i s t h u s 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 c o m p l e x . 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 c a t i o n r a d i c a l o f R u ( 0 E P ) ( C 0 ) ( J J 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 a n i o n ( s u c h as B r " f o r c o m p l e x I B ) . 141 T a b l e 4.4 C o n d u c t i v i t y S t u d i e s o f C a t i o n R a d i c a l ,1b and R e l a t e d S p e c i e s i n d i c h l o r o m e t h a n e as s o l v e n t . R e s i s t a n c e (n) A ( f i ~ * ) a [ R u I n ( ; 0 E P ) C P n B u 3 ) 2 ] + B r - ( % ) 1 .37 x 1 0 4 R u n i C 0 E P ) t P n B u 3 ) . B r (.!£) 149 2.38 x 1 0 4 103 3.63 x 1 0 5 3 4.93 x 1 0 4 2 [ R u n ( 0 E P ) + ' ( C O ) B r ] (.l_b) 9.1 x 1 0 5 1 a) 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 i n C H 2 C 1 2 ( f r o m R e f . 1 6 ) . , 4.3 The N a t u r e o f t h e Two C a t i o n R a d i c a l s 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 I I I 1 7' s p e c i e s o f Co (OEP) 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 , w i t h . t h e s e r u t h e n i u m 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 o f 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 s p e c i e s ( l b and l_c) a r e v e r y s i m i l a r t o t h e [ C o * I * ( 0 E P ) + ' ] ^ ^ 2 B L r ~ c o m p l e x a n d h e n c e 2 1 7 1 b. a n d l_c 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 A ^ u . L i k e -w i s e , t h e 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 142 o p t i c a l spectra (compare F igures 4.4 a and b w i th 1.14) to e l e c t r o chem i -c a l l y prepared [Co (0EP) + ' ] 2C10 4 and hence can be ass igned a A2 U ground s t a t e 1 6 . The spectrum of Ru**(0EP) + "(.C0)Im (5a) i s o f i n t e r e s t because i t appears to be a mixture o f the two ground s t a t e s . In t h i s complex the coord inated imidazo le l i g and may be caus ing a quantum-mechanical mix ing of the and A 1 u ground s ta te s to give the spectrum observed (F igure 4 . 4 c ) . Th is subject w i l l &e d i scussed i n more d e t a i l l a t e r (see Sect ion 8.2) . The s tud ie s o f the coba l t porphyr in systems showed that the ground s ta te s were determined by the coo rd i na t i on (or non-coord inat ion ) o f the anions p resent . A l so the ground s ta te s could be interchanged by the 17, . a d d i t i o n or removal of coord inated anions^ . The same e f f e c t s are observed i n the chemistry o f these ruthenium porphyr in i r i - ca t ion r a d i c a l s pec i e s . Add i t i on o f B r " or C I " ('in the form of the corresponding t e t r a -alkylammonium sa l t s ) , to a s o l u t i o n o f the purple species Ru(0EP) + 'CC0). (1 a) led to a r ap id change i n co lou r from purp le to green, and the product spectrum was that 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 ; e i t h e r [Ru(OEP). -(.CO)Br] (lb.) or .[RuCOEpf "CCOlCl ] Q c . ) r e s p e c t i v e l y . I f t h i s r e a c t i o n was attempted upon a spec ies w i th a coord inated s i x t h l i g and ( e . g . 3a_ or 5a_) in CH 2Cl2» then a l a rge p ropor t i on o f r educ t i on was observed (.see Sec t i on 5.2, b and c ) . To ob ta in the reverse r e a c t i o n excess AgBF^ was added to a s o l u t i o n of the A l u ground s t a t e species Ob).. The green s o l u t i o n immediately turned purple i n a very c l ean r e a c t i o n (as judged by the 143 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 l u t i o n ) g i v i n g l_a by r e m o v a l o f t h e c o o r d i n a t e d b r o m i d e i o n ( F i g u r e 4 . 7 ) . T h i s r e a c t i o n was f o u n d t o be a 2 good m e t h o d o f o b t a i n i n g s p e c t r a o f A 2 u g r o u n d s t a t e c a t i o n r a d i c a l s ( u s u a l l y p r e p a r e d by e l e c t r o c h e m i s t r y ) f r e e o f t r a c e s o f t h e r e d u c e d c o m -p l e x e s CRUC0EP)(C0 )L , s p e c i e s 1_, 3, 5_ a n d 6 ) . The s p e c t r u m o f R u ( 0 E P ) + ' ( C O ) (1 a ) p r e p a r e d f r o m [Ru("0EP)' + ( C O ) B r ] ( F i g u r e 4 . 7 ) i s much c l e a n e r t h a n l_a p r e p a r e d e l e c t r o c h e m i c a l l y , a l t h o u g h t h e a b s e n c e o f e x c e s s e l e c t r o l y t e l e a d s t o a s l i g h t c h a n g e i n t h e s p e c t r u m ( s e e S e c t i o n 4 . 1 ) . The s p e c t r u m o f R u [ 0 E P ) + ' ( C 0 ) M e C N Q6aj s e e n i n F i g u r e 4 . 4 b was o b t a i n e d by a d d i n g A g B F 4 t o [ R u ( ; 0 E P ) + ' C C 0 ) B r ] (_l_b_) p r e p a r e d i n 1% MeCN i n C H 2 C 1 2 , a l t h o u g h i n t h i s c a s e t h e p r e s e n c e o r a b s e n c e o f e l e c t r o l y t e had no e f f e c t on t h e s p e c t r u m . The c l e a n s p e c t r a ( a s j u d g e d by t h e l a c k o f a b s o r p t i o n s due t o i m p u r i t i e s ) o b t a i n e d by t h i s p r o c e s s w e r e due t o t h e o x i d i z i n g power o f AgC ' I ) w h i c h o x i d i z e d snraTl q u a n t i t i e s o f p a r e n t c o m p l e x m i x e d w i t h t h e c a t i o n r a d i c a l . I n f a c t A g B F 4 was c a p a b l e o f o x i d i z i n g a s p e c t r o s c o p i c s o l u t i o n o f R u C 0 E P ) C C 0 ) ( J ) d i r e c t l y t o t h e c a t i o n r a d i c a l l_a , a l t h o u g h s u c h s o l u t i o n s c o u l d n o t be u s e d f o r c h e m i c a l s t u d i e s due t o i n t e r f e r e n c e f r o m t h e e x c e s s A g B F 4 . The o p t i c a l s p e c t r a l d a t 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 s t u d i e d i n t h i s t h e s i s a r e s u m m a r i z e d i n T a b l e 4 . 5 144 F i g u r e 4.7 T h e o p t i c a l s p e c t r u m i n C H 2 C 1 2 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. (-• ) g e n e r a t e d on a d d i t i o n o f e x c e s s AgBF^. 145 T a b l e 4.5' O p t i c a l S p e c t r a l D ata 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 C o m p l e x e s — Complex A m a x ^ n m ^ ( 1 °9-]o e ^ l_a R u (0EP) + '(C0) - 3 7 5 ( 5 . 0 0 ) , 5 3 5 ( 3 . 9 3 ) , 5 8 7 ( 4 . 0 0 ) , 6 1 0 ( 3 . 7 0 ) ( F i g u r e 4.7) l a R u ( 0 E P ) + ' C C 0 ) . C 1 0 4 " - 3 7 5 ( 5 . 0 0 ) , 5 3 5 ( 3 . 9 3 ) , 5 8 7 ( 4 . 0 0 ) , 6 1 0 ( 3 . 8 6 ) ( F i g u r e 4.4a) 3a [ R u C 0 E P ) + " ( C 0 ) p y ] + C 1 0 4 " 3 7 6 ( 4 . 9 5 ) , 5 4 0 ( 3 . 9 0 ) , 5 9 0 ( 3 . 9 9 ) , 6 1 0 ( 3 . 8 0 ) 6a [ R u ( 0 E P ) + ' ( ; C 0 ) M e C N ] + C 1 0 4 " - 3 7 2 ( 4 , 9 4 ) , 5 4 0 ( 3 . 9 0 ) , 5 8 8 ( 3 . 9 9 ) , 6 1 2 ( 3 . 9 0 ) ( F i g u r e 4.4b) 5_a [ R u ( 0 E P ) + * ( C 0 ) I m ] + C 1 0 4 " 376(4.94).," 545( 3 .89),.5,92(3 .94) , 6 1 0 ( 3 . 9 2 ) ( F i g u r e 4.4c) l b [ R u ( 0 E P ) + ' ( C 0 ) B r ] 3 8 5 ( 4 . 8 5 ) , • 5,80(3.86), 6 3 0 ( 4 . 0 4 ) ( F i g u r e 4.5) Ic [ R u ( 0 E P ) + ' ( C 0 ) C l ] 3 8 3 ( 4 . 8 5 ) , 5 7 0 ( 3 .84) , 6 2 5 ( 3 .99) I d [ R u ( 0 E P ) + * ( C 0 ) S C N ] - 5 8 7 6 1 8 [Ru(0EP) + ' ( C S ) p y ] + C l 0 4 " - 3 7 5 ( 4 . 8 3 ) , 5 3 5 ( 3 . 8 8 ) , 5 9 0 ( 3 . 9 0 ) , ( F i g u r e 4.8) 8a Ru(0EP) + ' ( C 0 ) P n B u 3 . 1 . 630 . 8 5 0 a) U n l e s s o t h e r w i s e i n d i c a t e d , s o l u t i o r i i n i n C H 2 C 1 2 . b) As p r e p a r e d by t h e a d d i t i o n o f AgBF4 t o a s o l u t i o n o f l_b made by b r o m i n e o x i d a t i o n o f 1 i n C F ^ C ^ . c) As p r e p a r e d 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 1 i n t h e p r e s e n c e o f 0.05M TBAP. d) S p e c t r u m o b t a i n e d i n C H 2 C 1 2 - 1 % MeCN by r e a c t i o n o f A g B F 4 w i t h l_b i n t h i s s o l v e n t . 146 T a b l e 4.5 ( c o n t i n u e d ) e) Impure 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 +SCN~ w i t h c r o w n -e t h e r i n CHpCl2 t o l_a_ i n C H 2 C 1 2 . See S e c t i o n 5.1c. E x t i n c t i o n c o e f f i c i e n t s n o t o b t a i n e d . f ) See S e c t i o n 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 n B u 3 ) ] + CI0 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 . S e e S e c t i o n 6.2. 4.4 C a t i o n R a d i c a l s o f a R e l a t e d S p e c i e s R u ( O E P ) ( C S ) p y 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 o t h e r r u t h e n i u m p o r p h y r i n c o m p l e x e s o f ' t h e t y p e R u H ( ; 0 E P ) ( C 0 ) L ( L = P n B u 3 , P P h 3 , and A s P h 3 ) w i l l be d i s c u s s e d l a t e r , ( s e e S e c t i o n s 5.1 a n d 6 . 3 ) , where i t w i l l be shown t h a t t h e s e com-p l e x e s u s u a l l y g i v e o x i d a t i o n a t t h e m e t a l r a t h e r t h a n a t t h e p o r p h y r i n as t h e f i n a l p r o d u c t , t h o u g h 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 i n t e r m e d i a t e s . 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 l i g a n d g e n e r a l l y o x i d i z e a t t h e m e t a l a t a p o t e n t i a l b e l o w +0.6 v o l t s ( s e e R e f s . 1 a n d 18, and S e c t i o n s 7.1, 7.3, and 7.6 t h r o u g h t o 7 . 8 ) . H o wever, t h e 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. CS) 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 . H e n c e , R u ( 0 E P ) ( . C S ) p y g a v e a c y c l i c v oltammogram v e r y s i m i l a r t o t h a t o b s e r v e d f o r R u n ( 0 E P ) ( C 0 ) p y (.3). 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 i n d i c h l o r o m e t h a n e r e s u l t e d i n a o n e - e l e c t r o n o x i d a t i o n t o g i v e a g r e y i s h 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 s p e c t r u m ( F i g u r e 4 . 8 ) was s i m i l a r t o t h a t s e e n f o r R u ( 0 E P ) + ' C C 0 ) p y ( T a b l e 4 . 4 ) . C a r e f u l a d d i t i o n o f B r 2 / C H 2 C 1 2 t o a s o l u t i o n o f R u ( O E P ) C C S ) p y g e n e r a t e d 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 i n a r e a c t i o n v e r y s i m i l a r t o t h a t s e e n w i t h t h e R u ( O E P ) ( C 0 ) p y c o m p l e x . 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 nd 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. 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 and R u ( O E P ) ( C S ) 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 com 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 Too WAVELENGTH (nm) F i g u r e 4.8 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 2 C 1 2 . 148 REFERENCES - CHAPTER 4 1. G.M. Brown, 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 , 467 ( 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, and ( t h e l a t e ) R.B.. Woodward, J . Am. Chem. S o c . In P r e s s . 4. a) 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. 32B, 130 ( 1 9 3 6 ) . 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. J32B, 433 ( 1 9 3 6 ) . 5. 'Handbook o f C h e m i s t r y and 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. Graham, I n o r g . Chem. 7_, 315 ( 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, 1720 ( 1 9 6 7 ) . 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 , I n o r g . Chem. 2 0 , 1274 (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 I n o r g a n i c C h e m i s t r y ' , 4 t h E d . , W i l e y , New Y o r k , 1980, Chap. 20. 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 msterdam, 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_, 2948 ( 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 . 96, 982 ( 1 9 7 4 ) . 1 3 . 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 P r e s s , New Y o r k , 1979, V o l . V, Ch a p . 3. 14. D. D o l p h i n , T. Niem, R.H. F e l t o n , and 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 c o m m u n i c a t i o n . 16. G.P. A l g r a and S. B a i t , I n o r g . Chem. 20, 1 1 0 2 ( 1 9 8 1 ) . 149 17. D. D o l p h i n , A. F o rman, D.C. B o r g , J . F a j e r , and R.H. F e l t o n , P r o c . N a t l A c a d . S c i . USA 68, 614 (.1971). 18 toc\ 9 B 7! W 5 n 385'( i9 H 7 0 5) f ' T ' J ' ^ D " G ' W h i t t 6 n ' J ' ^ ^ 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 , t h e r e a c t i o n s o f a s u p p o s e d 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 ( s e e S e c t i o n 4.1) w i l l be c o n s i d e r e d . T h i s 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 f a v o u r a b l e s t r u c t u r e f o r 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 g i v e a r u t h e n i u m ( I I I ) p r o d u c t . A f t e r t h e 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 c o n s i d e r e d . 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 a s 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 on l i g a n d a d d i t i o n . 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 due t o t h e p r e s e n c e o f r e d u c i n g a g e n t s i n t h e l i g a n d a d d e d . However, t h i s was r a r e a n d many 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 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 (.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 f o r m a l l y t o be n o n - r e d u c i n g , s u c h a s 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 . 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 a w i d e r a n g e o f l i g a n d s c a u s e d t h i s r e d u c t i o n , p r o b a b l y 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 . T h e o t h e r 5 0 % o f t h e c a t i o n r a d i c a l may s u f f e r d e g r a d a t i o n t o g i v e v a r i o u s g r e e n 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 o f 151 Ru ( O E P ) ( C O ) (!) i n C.HgCl 2, o r by c h r o m a t o g r a p h y o f Ru i ( 0 E P ) ( C 0 ) L on s l i g h t l y a c i d i c s i l i c a c o l u m n s . A l l o f t h e s e g r e e n 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 have t o be e l u t e d o f f a s i l i c a c o l u m n 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 between 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 p r o d u c t , 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 i l l u s t r a t e s t h e c l e a n e s t r e a c t i o n f o r m i n g Ru(111) p r o d u c t s w i t h o n l y t h e 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 . S p e c t r a s h o w i n g some r e d u c -t i o n w ere 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 ( a s j u d g e d by u . v . / v i s i b l e s p e c t r o s c o p y ) s a m p l e s o f t h e c a t i o n r a d i c a l s . T h e 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 p r e s e n c e o f P n B u 3 - 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 i s 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 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 p r e p a r e d s a m p l e s 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 q u o t e d 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 b u t 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 . B F 4 " , P F g ~ a n d C F 3 S 0 3 " ) . 152 The r e a c t i o n s o f 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 w i t h a w i d e r a n g e o f l i g a n d s w i l l be p r e s e n t e d i n d e t a i l i n t h e f i r s t f p u r s e c t i o n s o f t h i s c h a p t e r . T h e m a j o r p r o d u c t s o f t h e s e r e a c t i o n s a r e b r i e f l y s u m m a r i z e d i n T a b l e 5.1 and 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 and 5.6. 5 .1 R e a c t i o n s o f 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 p e c i e s w i t h N e u t r a l  and I o n i c L i g a n d s i n C ^ C l g , an 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 and 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 t h e f o l l o w i n g h e a d i n g s : a) L i g a n d s t h a t g i v e r u t h e n i u m ( I I I ) p r o d u c t s . b) N e u t r a l l i g a n d s t h a t g i v 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 o f t h e 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 t h a t g i v e t h e o t h e r g r o u n d s t a t e o f t h 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 . 3 ) . d) L i g a n d s t h a t i n s t a n t l y r e d u c e t h e 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 3 t o 4 mL o f a 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 g i v e s a de e p o r a n g e s o l u t i o n ( E q u a t i o n 5 . 1 ) . The s p e c t r u m 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 and a d o u b l e S o r e t . The s p e c t r u m i s s i m i l a r t o t h a t o b t a i n e d when R U C O E P X P ^ U ^ ( 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 w i t h  R u t h e n i u m ( I I ) P o r p h y r i n ft-Cation R a d i c a l s . C a t i o n R a d i c a l — L i g a n d s Added M a j o r P r o d u c t s R u ( 0 E P ) + ' ( C 0 ) l a [ R u(OEP) ( C O ) B r ] l b P B u 3 > P P h 3 , A s P h 3 a n d CN" p y , Im, MeCN DMSO, P h 3 P 0 , MeOH B r " , C I " , SCN" I \ B H 4 " P ( 0 M e ) 3 , C 1 0 4 " , B F 4 " and C F 3 S 0 3 " P n B u 3 , CN" P P h 3 , A s P h 3 , p y , Im MeCN, THF, MeOH ( a l l i n e x c e s s s e e text)': C I ' Ru ( 1 1 1 ) A ^ C a t i o n R a d i c a l s 3 a , 5a and 6a_ 2 ^2u ^ a t l' o n R a d i c a l s 2 A n C a t i o n R a d i c a l s l u ( l b , l c _ a n d l_d) R e d u c t i o n No r e a c t i o n R u ( I I I ) R e d u c t i o n R e d u c t i o n l c Ru(OEP) ' ( C O ) p y 3a P nBu. P P h 3 , A s P h 3 , CN" C I " , B r ' Im, MeCN R u ( I I I ) . R u ( I I I ) + R e d u c t i o n p A-|U C a t i o n R a d i c a l + R e d u c t i o n "Ap^ C a t i o n R a d i c a l s ( 5 a a n d 6a) 154 T a b l e 5.1 - c o n t i n u e d C a t i o n R a d i c a l - L i g a n d s A d d e d M a j o r P r o d u c t s R u ( 0 E P ) + " ( C 0 ) I m R u ( 0 E P ) + "(.C0)MeCN 6a (.In MeCN) Ru( 0 E P ) + *(.C0)MeCN 6a In V/o M e C N / C H 2 C l 2 R u ( O E P ) + " ( C S ) p y P nBu, PPh., CN", A s P h 3 , C T P n B u . PPh. CN", A s P h 3 , C I " , Br" py, Im P M B u 3 , P P b 3 CN", A s P h 3 C I " , B r " P n B u , P P h 3 , CN" c r G r e e n P r o d u c t s + Ru(.III) R u ( I I I ) R e d u c t i o n G r e e n P r o d u c t s + R e d u c t i o n Ru ( 1 1 1 ) + R e d u c t i o n R e d u c t i o n ? A 0 C a t i o n R a d i c a l s 2u (3a a n d 5a) R u t i n ) R u t H I ) ^ R e d u c t i o n 2 A - j u C a t i o n R a d i c a l s :- + R e d u c t i o n G r e e n P r o d u c t s R e d u c t i o n A, C a t i o n R a d i c a l l u + R e d u c t i o n — S o l u t i o n o f c a t i o n r a d i c a l i n C H 9 C 1 9 u n l e s s o t h e r w i s e i n d i c a t e d 155 s o l u t i o n ) o x i d i z e d i n C H 2 C 1 2 ( S e c t i o n 7 . 1 ) . 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 4 t o 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 t o t h a t o f g e n u i n e R u ( 0 E P ) ( P n B u 3 ) 2 ( 7 ) ( F i g u r e 5 . 1 ) . 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 s a m p l e o f [ R u I ] t I ( 0 E P ) ( P n B u 3 ) 2 ] + B r " (9b_) p r e p a r e d by b r o m i n e ox n i d a t i o n o f 7^  ( s e e S e c t i o n 2 . 5 ) . [ R u n ( 0 E P ) + ' ( C 0 ) ] + C 1 0 4 _ + 2 P n B u 3 — ) [ R u 1 1 1 ( O E P ) ( P n B u 3 ) 2 ] + C l 0 4 " + CO ( 5 . 1 ) ( l a ) ( 9 a ) The 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 ( P P h 3 ) g i v e s a s i m i l a r r e s u l t . 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 a d d e d ( 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 ) -( P P h 3 ) 2 (1_2) i n C H 2 C 1 2 , i n t h e p r e s e n c e o f e x c e s s P P h 3 ( c o m p a r e F i g u r e s 5.2 and 7 . 1 2 ) . The 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 3 t o J_a_ c o u l d be 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~) t o g i v e a p i n k s o l u -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 upon t h e q u a n t i t y o f e x c e s s p h o s p h i n e a d d e d . 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 weakened a n d a new peak a t 396 nm a p p e a r e d . T h i s b e h a v i o u r i s c o n s i s t e n t w i t h t h e c h e m i s t r y o f R u 1 1 ( O E P ) ( P P h 3 ) ? (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 (. ) , t h e s p e c t r u m o f t h e r u t h e n i u m f U l ) 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 3 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 o f t h e s p e c i e s (.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 4 ~ C ).. T h e weak a b s o r p t i o n s s e e n i n t h e s p e c t r a o f 9a a n d 7 between 580 and 650 nm a n d t h e peak s e e n a t ^428 nm i n t h e s p e c t r u m o f 9a a r e due 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 f o r m e d by s i d e r e a c t i o n s . — 15J 1.5-i.«H u z < to K o CO CD < ill • < i \ / x10 / A '• // \ \ // \ \ f \\ V. v 400 500 600 700 WAVELENGTH (nm) F i g u r e 5.2 The r u t hen i um( . I I I ) p r o d u c t (.15) (- ) fo rmed by t he a d d i t i o n o f e x c e s s ( 1 0 - 2 M) P P h 3 t o t h e c a t i o n r a d i c a l l_a and t h e s p e c i e s fo rmed (.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 "("•"••••)• 158 r e a c t i o n w i t h P B u 3 , 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 , i n t h e c o n d i t i o n s o f t h e e x p e r i m e n t a b o v e , a few p e r c e n t o f c o n t a m i n a t i n g R u n ( 0 E P ) ( C 0 ) P P h 3 ( 4 0 6 nm S o r e t b a n d ) . 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 3 t o t h e c a t i o n r a d i c a l d i d n o t g i v e c o m p l e t e 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 was l e f t u n r e a c t e d . P u r g i n g s u c h a s o l u t i o n w i t h c a r b o n m o n o x i d e c a u s e d 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 o f c a t i o n r a d i c a l p r e s e n t . T h i s s u g g e s t s t h a t t h e r e a c t i o n i s r e v e r s -i b l e , a nd 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 3 ) w i t h l_a g i v e s an e x c e l l e n t e x a m p l e o f j u s t s u c h a r e v e r s i b l e s y s t e m . The a d d i t i o n o f an e x c e s s ( 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 3 ( a d d e d a s 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 t h e 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 g a v e 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 between 30 - 50% c o n v e r s i o n o f l_a t o a r u t h e n i u m ( I I I ) 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 [ 5 0 0 nm t o 700 nm), i n c r e a s e d a b s o r p t i o n b e t w e e n 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 o f s i d e p r o d u c t s ( e . g . R u ( O E P ) ( C 0 ) L ) , t h e r i s e o f an a b s o r p t i o n a t 810 nm] a c c o m p a n i e d by a b o u t 10% r e d u c t i o n . 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 become b r i g h t o r a n g e , t h e s p e c t r u m s h o w i n g f u r t h e r l o s s o f a b s o r p t i o n s d u e t o 1§_ a n d , a f t e r ^2 m i n u t e 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 c o m p l e t e -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 R u ( I I I ) c o m p l e x ( F i g u r e 5 . 3 ) . A d d i t i o n o f c a r b o n m o n o x i d e , 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 pec t r um 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 (1J) formed on a d d i n g two e q u i v a l e n t s o f AsPh3 and 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 a r g o n f o r 2 m in ( - • ) , 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 rbon monox ide f o r one m i n u t e ( ) . L a t e r e x p e r i m e n t s s ugge s ted t h a t t h e r e g e n e r a t e d 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 pec t rum was i d e n t i c a l t o ^a_ ( s ee 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 and ^545 nm a r e due 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 educed p r o d u c t s . 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 ) . P u r g i n g w i t h a r g o n r e f o r m 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 , 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 t h a t t h e 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) [ R u I I C 0 E P ) + ' ( C 0 ) l f C 1 0 4 " + 2 A s P h 3 ^ l R u . I r i ( 0 E P ) ( A s P h 3 ) 2 ] + C 1 0 4 " + CO ( 5 . 2 ) ( l a ) 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 t h e R u ( I I I ) c o m p l e x o b t a i n e d i n t h e a b o v e r e a c t i o n , c o n c l u s i v e l y p r o v e d t h e i d e n t i t y o f t h e r u t h e n i u m ( I I I ) c o m p l e x i n v o l v e d i n t h e a b o v e 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 ( 0 E P ) ( A s P h 3 ) 2 ] + A " ( A " =i a n i o n o f e l e c t r o - , l y t e u s e d ) , ( s e e S e c t i o n s . 2 . 5 a n d 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 3 ) t o a s o l u t i o n o f l_a a l s o g i v e s 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 s p e c t r u m i n d i c a t e d t h a t t h i s 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, w h i c h 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 ~ . 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 more S b P h 3 , t h o u g h t h i s r e g i o n i s d o m i -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 . I n t h e s e q u e n c e P P h 3 -> A s P h 3 -> S b P h 3 t h e c e n t r a l atom becomes p r o g r e s s i y e - . 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 . 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 opt ica l spectrum of the cation radical species la (- ) and the spectrum of the product mixture obtained on adding excess SbPh, C IT 162 p r o v i d e d 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 , a l t h o u g h a s m a l l p r o p o r t i o n o f R u ( I I I ) i s s t i l l f o r m e d by e l e c t r o n t r a n s f e r . L i g a n d s c o n t a i n i n g Group 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 ) p r o d u c t s . T h e l i g a n d s must have m o d e s t s t e r i c r e q u i r e m e n t s 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 P ^ H - j i ^ o r A s t M e s i t y l ) ^ were u s e d . I n s t e a d o f a r e a c t i o n t o g i v e m a i n l y r u t h e n i u m ( I I I ) , 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 a t 570 - 620 nm, w e r e o b s e r v e d . T h e 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 a p p e a r s t o be i m p o r t a n t 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 , a n d i f s t e r i c e f f e c t s do n o t a l l o w c o o r d i n a t i o n , t h e n s i d e r e a c t i o n s a p p e a r t o d o m i n a t e . C y a n i d e was a l s o f o u n d t o 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 b etween t h e m e t a l and t h e p o r p h y r i n l i g a n d . A d d i t i o n o f a c r y s t a l o f t e t r a -e t h y l ammonium c y a n i d e ( T E A + C N ~ ) 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 t h e c a t i o n r a d i c a l g a v e a s p e c t r u m c o n s i s t e n t w i t h t h a t r e p o r t e d f o r t h e R u ^ ^ ( O E P ) -(CN).2 " a n i o n 1 ( F i g u r e 5 . 5 ) . 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 R u ^ ( O E P ) -( C 0 ) ( C N ) ~ a s a s e c o n d p r o d u c t . D e f i n i t i v e p r o o f o f t h e i d e n t i t y o f t h e r u t h e n i u m ( I I I ) 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 I n ( 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 a n d E q u a t i o n 5 . 3 ) , £ R u n ( 0 E P ) + ' ( C 0 ) . ] + C 1 0 4 ~ + 2 T E A + C N " » T E A + [ R u H I ( . 0 E P ) ( C N ) 2 ] ~ + CO + T E A + C 1 0 4 " 163 Figure 5.5 The o p t i c a l spectrum of the c a t i on r a d i c a l spec ies J_a ( ) and the spectrum of the product obta ined 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 p y r i d i n e o r i m i d a z o l e 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 t h e c a t i o n r a d i c a l l a d o e s n o t g i v e a r u t h e n i u m ( I I I ) p r o d u c t b u t i n s t e a d c a u s e s t h e s p e c t r u m t o c h a n g e 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 a m i n e c o o r d i -n a t e d , ( E q u a t i o n 5.4). [ R u ( 0 E P ) + " ( C 0 ) ] + C 1 0 4 " + L ) [ R u ( 0 E P ) + " ( C 0 ) L ] + C 1 0 4 " ( 5 . 4 ) L = p y , Im and 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 p y r i d i n e c a u s e d a s h i f t i n t h e 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 c o o r d i n a t i o n o f t h e l i g a n d . F u r t h e r a d d i t i o n o f p y r i d i n e , a l t h o u g h c a u s i n g some r e d u c t i o n due 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 on 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 ) p r o d u c t s was d e t e c t e d . R e a c t i o n w i t h i m i d a z o l e o c c u r s i n a s i m i l a r f a s h i o n . 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 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 R u ( 0 E P ) + (CO)Im ( 5 a ) ( S e c t i o n 4 . 1 ) , a l t h o u g h a m i n o r r e a c t i o n t o g i v e some R u ( O E P ) ( C O ) I m ( 5 ) was a l s o o b s e r v e d . E x c e s s i m i d a z o l e had no e f f e c t on t h e s p e c t r u m and no r u t h e n i u m ( . I I I ) p r o d u c t s were d e t e c t e d . T r i p h e n y l p h o s p h i n 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 . A d d i t i o n o f t h e s e l i g a n d s s h i f t e d t h e m a i n a b s o r p t i o n o f l_a_ t o ^592 and 590 n m , r e s p e c t i v e l y , and weakened t h e s h o u l d e r a t 610 nm. 165 D i l u t i o n o f 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 i n C H p C l 2 w i t h p u r i f i e d a c e t o n i t r i l e g a v e a s p e c t r u m i d e n t i c a l t o t h a t o f R u ( 0 E P ) + ' ( C 0 ) M e C N ( 6 a ) , p r e p a r e d 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 S e c t i o n 4 1 1 ) . R e a c t i o n 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 been 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 m e t h a n o l t o a s o l u t i o n o f l a _ i n C H ^ C l 2 c a u s e d a l o s s o f i n t e n s i t y i n t h e 610 nm 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 n d t h i s was b e l i e v e d t o be 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 ) . A d d i t i o n o f 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 o f t h e c a t i o n r a d i c a l and i t was q u i c k l y r e a l i s e d t h a t t h e p r o p o r t i o n o f r e d u c t i o n o b s e r v e d was 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 -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 m p u r i t i e s 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 u s e d i n t h e s e r e a c t i o n s ) . A s i m i l a r c o r r e l a t i o n was n o t e d on t h e a d d i t i o n o f o t h e r n e u t r a l 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 more o b v i o u s w i t h 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 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 s p e c t r u m , were o b t a i n e d 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 a n d 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 on 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% 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 s p e c -t r u m ) were p r e p a r e d by s l o w e r 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 . 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%) r e d u c t i o n i m m e d i a t e l y ( 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 20% by v o l u m e , a nd 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 n c r e a s e d ,on s t a n d i n g . A d d i t i o n o f THF a n d , t o a l e s s e r e x t e n t w a t e r showed a - s i m i l a r p a t t e r n -3 -4 o f r e a c t i v i t y . A d d i t i o n o f 10 M THF 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 i n d i -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 s h o u l d e r . The r e a c t i o n o f t h i s c a t i o n r a d i c a l s p e c i e s w i t h m e t h a n o l s u g g e s t s 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 as s i d e p r o d u c t s 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 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 . 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 -t e n t p r e s e n c e o f s i d e r e a c t i o n s g i v i n g r e d u c t i o n i n t h e r e a c t i o n s o u t l i n e d 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 . H o w e v e r , t h e l a r g e r p r o p o r t i o n s o f r e d u c t i o n o b s e r v e d i n t h e r e a c t i o n s o f 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 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 4 ~ ( l a ) c a u s e s a c h a n g e i n g r o u n d s t a t e w i t h t h e f o r m a t i o n o f a g r e e n s o l u t i o n a n d c o o r d i n a t i o n o f c h l o r i d e t o g i v e [ R u ( 0 E P ) + ' ( C 0 ) C l ] (.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 r e a c t i o n s a r e u s u a l l y v e r y c l e a n . TBA I " g i v e s r e d u c t i o n as e x p e c t e d f o r an a n i o n as e a s i l y o x i d i z e d as I ~ . A d d i t i o n o f c h l o r i d e a n d b r o m i d e i o n s by g r i n d i n g up t h e a p p r o p r i a t e p o t a s s i u m s a l t w i t h 1 8 - c r o w n - 6 and t h e n d i s s o l v i n g i n C H 2 C 1 2 b e f o r e a d d i n g 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 l_a_ a l s o w o r k e d w e l l . A t t e m p t s 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 nd g a v e an i m p u r e s p e c t r u m o f a A-|u g r o u n d s t a t e a t t r i b u t e d t o [Ru(.0EP) + ' ( C 0 ) S C N ] ( I d ) . ( F o r s p e c t r a l d a t a s e e T a b l e 4 . 5 ) . 5 . I d 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 were t o t a l l y i n e r t . T e t r a m e t h y l g u a n i d i n e , ( M e 2 N ) 2 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 one -4 e q u i v a l e n t o f t h e b a s e t o a 10 M s o l u t i o n o f l a _ , a nd c o o r d i n a t e s t o t h e R u I I ( 0 E P ) ( C 0 ) (.]_) 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 o f t h e t y p e R u I I ( 0 E P ) ( C 0 ) ( ; n i t r o g e n - b a s e ) ( I 5 5 0 / I 5 2 0 ^ 1 . 2 7 , s e e S e c t i o n 3 . 1 ) . T r i e t h y l -a mine ( E t g N ) a n d t - b u t y l t h i o l ( Me 3CSH) b o t h i n s t a n t 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 on t h e a d d i t i o n o f one 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 e a s y t o o x i d i z e , s o t h e r e d u c t i o n p r o c e s s i s p r o b a b l y a s i m p l e 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 c o m p l e x . A s i m i l a r p r o c e s s 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 a g e n t s s u c h as t h e b o r o h y d r i d e a n i o n . 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 wever, f o r c o m p l e x l_a t h e c o o r d i n a t i o n o f t h e c y a n i d e i o n a n d 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 p p e a r s f a s t e r t h a n t h e r e d u c t i o n p r o c e s s i n t h a t a r u t h e n i u m ( I I I ) p r o d u c t i s o b t a i n e d . F o r 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 s p e c i e s ( s e e S e c t i o n 5.2) t h e 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 a p p e a r s f a s t e r t h a n r u t h e n i u m ( I I I ) 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 . T r i m e t h y l p h o s p h i t e , P ( 0 M e ) 3 , 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 o f t h e e l e c t r o n e g a t i v e o x y g e n 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 . T h e 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 a n i o n s 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) a l o n g w i t h t h e q u e s t i o n o f t h e p o s s i b l e c o o r d i n a t i o n o f t h e s e i o n s 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 l a . S e c t i o n 5.1e D i s c u s s i o n and C o n c l u s i o n s 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 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 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 c o m p l e x and i s w r i t t e n a s 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 so " i n s t a n t a n e o u s l y " by v i s i b l e i n s p e c t i o n . 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 p a r t i c u l a r P n B u 3 and 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 ) -( C 0 ) P n B u 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 s p e c t r a u s u a l l y o b s e r v e d f o r R u n C 0 E P ) ( C 0 ) L c o m p l e x e s ( s e e S e c t i o n 3 . 1 ) . R u T I ( 0 E P ) -( C 0 ) P P h 3 Cll). and R u 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 p e r t u r b e d 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 p r o m o t e 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 d o e s n o t c o r r e l a t e w i t h l i g a n d s t r e n g t h ( i m i d a z o l e a n d p y r i d i n e b i n d much more s t r o n g l y t o R u ( 0 E P ) ( C 0 ) Q) t h a n P P h 3 o r A s P h 3 , 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 p e r t u r b e d 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 p h o s p h i n e s a n d c y a n i d e i o n a l l f o r m s t r o n g bonds w i t h t r a n s i t i o n m e t a l i o n s a n d a r e a l s o a b l e t o s t a b i l i z e l o w o x i d a t i o n s t a t e s . T h e l a t t e r e f f e c t i s due t o t h e - r r - a c i d i t y o f t h e l i g a n d a n d e n a b l e s i t t o l a b i l i z e a t r a n s c a r b o n y l l i g a n d , w h i l e t h e 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 i n q u e s t i o n i s c i s t o a p o r p h y r i n m a c r o c y c l e ( s e e S e c t i o n 3 . 3 ) , a l l o w s t h e l i g a n d 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 f o r m e d . T h e d u a l n a t u r e o f t h e l i g a n d s i s p r o b a b l y i m p o r t a n t . I m i d a z o l e i s a s t r o n g a ( a n d -ir) d o n o r , 4 ' 5 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 i t i s n o t a s u f f i c i e n t l y s t r o n g i r - a c i d t o l a b i l i z e t h e c a r b o n y l g r o u p . On t h e o t h e r hand , CO i t s e l f i s a v e r y s t r o n g i r - a c i d a n d h e n c e w o u l d l a b i l i z e a t r a n s c a r b o n y l g r o u p ( a s d e m o n s t r a t e d by t h e i n s t a b i l i t y o f p r e p a r e d s a m p l e s o f R u 1 ^ ( O E P ) Q C ( D ) 2 ) 6 b u t t h e p r o d u c t ( a c t u a l l y R u ( 0 E P ) + ' ( C 0 ) - 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 e n d e n c y t o u n d e r g 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 b e c a u s e t h e c a r b o n y l 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 . T h e 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 c a u s e s 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 t o o x i d i z e a t t h e r i n g r a t h e r t h a n a t t h e m e t a 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 a s a t r a n s i e n t i n t e r m e d i a t e . I t s h o u l d be n o t e d t h a t c o m p l e x e s o f t h e t y p e R u i n ( . 0 E P ) ( . P n B u 3 ) L + , L = Im, p y , CH^CN ( s e e S e c t i o n 7.3) and R u i n C 0 E P ) ( C N ) L , ( L = p y ) 1 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 w i t h o x i d a t i o n ( o r r e d u c t i o n ) a t t h e m e t a l r a t h e r t h a n a t t h e 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 between 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 . T h i s i s f u r t h e r e v i d e n c e 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 PPhg, P n B u 3 and A s P h g , when c i s 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 i n S e c t i o n 3.3. 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 more d e p t h i n S e c t i o n 6.4. 5.2 R e a c t i o n s o f a S i x - C o o r d i n a t e d 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  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 I I ( 0 E P ) + '(.C0)Br] ( l _ b ) , , R u ( 0 E P ) + ' ( C 0 ) p y . ( 3 a ) , and Ru(.0EP) + '( C0)lm (.5a.), w i t h l i g a n d s w i l l be 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. 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 atom 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 ) . H owever, t h e 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 , a nd 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 . C a t i o n r a d i c a l s p e c i e s i n t h e p r e s e n c e o f a l a r g e e x c e s s 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 ) n -4 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 M s o l u t i o n o f [ R u I I ( 0 E P ) + ' ( C 0 ) B r ] (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 , and 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 r u t h e n i u m ( I I I ) 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. C o m p a r i s o n w i t h t h e s p e c t r a o f a u t h e n t i c s a m p l e s o f r u t h e n i u m ( I I I ) p o r p h y r i n c o m p l e x e s 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 I I ( . 0 E P ) + '(C0) ( l _ a ) , , n a m e l y R u I H ( 0 E P ) ( P n B u 3 ) 2 + (.9), a l t h o u g h 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 nBu 3)Br (1_0) c o n t a m i n a t e d w i t h a s m a l l 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 ) . T h e s e 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 n B u 3 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 o f T E A + C N " t o a 1 0 - 4 M s o l u t i o n o f [ R u ( 0 E P ) + - -( C 0 ) B r ] ( 1 b ) r e s u l t e d i n a r e a c t i o n v e r y s i m i l a r t o t h a t r e p o r t e d f o r a d d i t i o n o f t h i s l i g a n d t o ^ a , a l t h o u g h t h e p r o p o r t i o n o f t h e 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 % ) . T h e i d e n t i t y o f t h e m a j o r p r o d u c t 2 OS \ i I i| I |\ I; is i ii w I i i i i i , i j i / 1/ I / ! / .'/ II V I i i i i \ ! 1 ! '• i \ i \ i \ i \ ! \\ \ i u ! E 1 V r o .x. ^ \ \ 600 700 WAVELENGTH (nm) F i g u r e 5.6 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 ] u c a t i o n r a d i c a l I j j ( .) s 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 I ] : ( 0 E P ) ( C 0 ) P n 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). 173 SCHEME 5.1 [Ru(OEP) + -(CO)]V + P n B u 3 (>2 e q ) ( l a ) * [ R u I n ( 0 E P ) ( P n B u 3 ) 2 ] + A - o r B r (9) A" = C 1 0 4 ~ , B F 4 " PF " [ R u ( O E P ) + ' ( C O ) B r ] + P n B u 3 ( 1 - 2 e q ) ( l b ) >10 eq P n B u . R u I n ( O E P ) ( P n B u 3 ) B r (1 0 ) + CO was c o n f i r m e d t o be R u 1 l i ( 0 E P ) ( C N ) 2 " by t h e p r e s e n c e o f a weak peak c e n t r e d a t 680 nm ( s e e F i g u r e 5.5 a n d R e f . 1 ) . A d d i t i o n o f e x c e s s t r i p h e n y l p h o s p h i n e ( P P h 3 ) t o a 10~^M s o l u t i o n o f 1b g a v e i n s t a n t r e d u c t i o n r a t h e r t h a n t h e e x p e c t e d r u t h e n i u m ( I I I ) p r o d u c t . 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 c a t i o n r a d i c a l was r e d u c e d i n t h e s t o i c h i o m e t r y o f o n e m o l e o f p h o s p h i n e p e r two m o l e s o f c a t i o n r a d i c a l . 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 3 ) w i t h l_b g a v e t h e same r e s u l t . I t was t h o u g h t i n i t i a l l y t h a t t h e r e d u c t i o n 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 , a n d was p r o b a b l y due t o t h e r e m o v a l o f b r o m i n e f r o m t h e s o l u t i o n ; 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, E q u a t i o n 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 3 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 t o 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 e x a m p l e o f a g e n e r a l 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 o t h e r 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 g a v e r e d u c t i o n a s t h e d o m i n a n t r e a c t i o n . 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 s p e c i e s was [ R u I I ( . 0 E P ) + ' ( C 0 ) B r ] (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 by a d d i n g T E A + C 1 " t o a s o l u t i o n ofJ_RuC0EP) + ' ( . C 0 ) ^ C l 0 4 " (_l_a). T h e r e d u c t i o n s were o f t e n more 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 t o be due t o t h e p r e s e n c e o f e x c e s s c o o r d i n a t i n g a n i o n ( C l ~ ) . 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 upon i t s c o o r d i n a t i n g s t r e n g t h . Thus a l a r g e e x c e s s (>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 t o g i v e r e d u c t i o n 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 , i m i d a z o l e , o r PPhg, 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 ( e s s e n t i a l l y s t o i c h i o -m e t r i c ) . 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 (>1000 eq) t o 1 b, f o r e x a m p l e , g a v e t h e s p e c t r u m o f t h e o t h e r g r o u n d s t a t e ( A 2 0 b e f o r e r e d u c t i o n t o Ru**('_0EP).(jC0lMe0H. o c c u r r e d o v e r a p e r i o d o f s e v e r a l m i n u t e s . I n c r e a s i n g t h e p o l a r i t y o f t h e s o l v e n t a p p e a r s t o e n c o u r a g e t h e d i s s o c i a t i o n o f t h e b r o m i d e f r o m 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 ( s e e f o r m a t i o n o f [ R u I I ( . 0 E P ) + '(.C0)-MeCN ] + B r ~ by t h e a c t i o n o f B r 2 on Ru(0EP)(.C0)MeCN i n MeCN - S e c t i o n 4 . 2 ) , w h i c h then s l o w l y r e d u c e s . 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 E A + C 1 ~ 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 g i v e s a h i g h p r o p o r t i o n o f t h e c h l o r i d e a n a l o g u e p c ) . H e n c e , a n i o n i c l i g a n d s whose 175 c o o r d i n a t i o n d o e s n o t c h a n g e t h e g r o u n d 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 t o c a u s e r e d u c t i o n . 5.2b 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 ^ " ( 3 a ) 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 3 t o a 5 x 10 M s o l u t i o n o f R u ( 0 E P ) + ' ( C 0 ) p y ( 3 a ) p r o m o t e s a s e q u e n c e o f r e a c t i o n s a n a l o g o u s t o t h o s e s e e n on a d d i n g t h i s l i g a n d t o l_b. Two e q u i v a l e n t s o f p h o s p h i n e g a v e a p r o -d u c t s p e c t r u m t h a t a p p e a r s 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 ) s p e c i e s , 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 t was t h e same p r o d u c t , R u I * I C 0 E P ) . C P n B u 3 ) 2 + , . 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 l i g a n d t o R u ( 0 E P ) + ' ( C 0 ) . (]_a) ( F i g u r e 5 . 7 ) . A d d i t i o n o f e x c e s s P n B u 3 ( u p 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 ^ 3 0 % 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 x 1 0 ^ M _ 1 c m _ 1 ) . By c o m p a r i s o n w i t h t h e s p e c t r a o b t a i n e d f r o m t h e a d d i t i o n o f P n B u 3 t o s p e c i e s l a _ and •'Vb. , and o f g e n u i n e s a m p l e s o f p o s s i b l e p r o d u c t s , t h e f i n a l p r o d u c t was i d e n t i f i e d a s R . u I I I ( 0 E P ) ( P n B u 3 ) 2 + . A s t u d y o f t h i s r e a c t i o n a t i n c r e a s e d 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 nm; t h i s d e c r e a s e d i n i n t e n s i t y on a d d i t i o n o f e x c e s s p h o s p h i n e as t h e i n t e n s i t y o f t h e 790 nm peak i n c r e a s e d . T h e i n t e r -m e d i a t e was t e n t a t i v e l y a s s i g n e d a s R u I n ( 0 E P ) ( P n B u 3 ) p y + s i n c e t h i s seemed a r e a s o n a b l e i n t e r m e d i a t e , and more 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 ) . T h e m e c h a n i s m o f t h i s r e a c t i o n , w h i c h i s s i m i l a r t o t h e r e a c t i o n o f P n B u 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 (nm) F i g u r e 5.7 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 [Ru (OEP) "( C O ) p y ] CIO4" (3a), (• ) a n d t h e p r o d u c t f o r m e d on 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 PnBu3 ( - , - - , - ) . T h i s p r o d u c t ( m a i n l y a m i x t u r e o f £ R u n i ( O E P ) ( p n B u 3 ) 2 J + C l 0 4 _ (9a) a n d [ R u 1 1 1 (OEP).(pnBu 3).py]+Cl0 4 " (26a).) was 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 IH.0EPlCC0).P nBu3~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 on a d d i n g t h e P n B u 3 was ^10% and gave r i s e t o a S o r e t a t 408 nm and 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 due 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 . 177 t h e n e x t c h a p t e r ( S e c t i o n 6 . 4 ) . The amount o f r e d u c t i o n s e e n i n a s i d e r e a c t i o n i s a b o u t 1 5 % . 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 a s 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 R u ( 0 E P ) ( C 0 ) L , L = P P h 3 o r A s P h 3 ) . T E A + C N ~ r e a c t e d i n a s i m i l a r m a n n e r . A d d i t i o n o f T E A + C T g a v e 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 I I ( . 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 [Ru* I(.0EP) + ' C C 0 ) C l ] ( l _ c ) . B o t h p r o d u c t s w e r e f o r m e d 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 manner 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 H ( 0 E P ) + "(C0) ( l a ) . A l s o , t h e r e m a i n i n g [ R u ( 0 E P ) + * -( 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 b u t d o e s c h a n g e 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 R u ( 0 E P ) + " ( C 0 ) I m ( 5 a ) ( T a b l e 4 . 5 ) , s u g g e s t i n g t h a t t h e 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 t h e c o o r d i n a t e d p y r i d i n e . 5.2c R e a c t i o n o f [ R u ( 0 E P ) + ' ( C 0 ) I m ] + C 1 0 4 ~ ( 5 a ) 2 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 A-|u and A 2 u g r o u n d 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 ) + ' ( C 0 ) I m ( 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 m o s t o f t h e c h e m i s t r y d e s c r i b e d h e r e i s c o n s i s t e n t w i t h t h e g r o u n d 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 ere 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 1 1 ! ^ ^ ( 9 ) by r e a c t i o n o f e x c e s s P ^ u ^ 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 p h o s -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 t h e s p e c t r u m i n d i c a t e d t h a t a b o u t 4 0 % o f t h e c a t i o n r a d i c a l had u n d e r g o n 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 t o g i v e t h e r u t h e n i u m ( I I I ) 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 ak 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 ) . A l t h o u g h t h e s e p r o d u c t s a r e s p e c t r a l l y s i m i l a r t o t h e g r e e n p i g m e n t s f o r m e d 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 t h e r e a c t i o n ( s e e 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 ) + ( C 0 ) l m ( 5 a ) i s a l s o v e r y d i f f e r e n t f r o m t h a t w i t h t h e p y r i d i n e c o m p l e x ( 3 a ) , 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 RuC0EP) + ?(C0)..Im 5a (- ) a n d t h e p r o d u c t s 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 n B u 3 C 180 t o a 10 M s o l u t i o n o f 5a_ c a u s e d t h e s o l u t i o n t o s l o w l y t u r n o r a n g e ( 2 - 3 m i n s ) . 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 ) p r o d u c t (X 745 nm) b u t n o t t h e e x p e c t e d ; R u i n ( 0 E P ) ( P P h , ) 9 + s p e c i e s (X 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 H ( 0 E P ) + '(C0) ( l a ) . By 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 c o m p l e x ( 3 a ) w i t h P n B u 3 , t h e 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 R u I I I ( 0 E P ) ( P P h 3 ) I m + and some 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 . 1 0 ) . 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 o f f u r t h e r P P h 3 c a u -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 peak 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 n ( 0 E P ) ( P P h 3 ) 2 . I f , i n s t e a d o f a d d i n g e x c e s s P P h 3 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 e q ) 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 peak 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 . C o n s i d e r i n g t h a t t h e c o m p l e x R u I I ( 0 E P ) ( . P P h 3 ) 2 (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 s o l u t i o n t o g i v e a f i v e - c o o r d i n a t e s p e c i e s 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 c o m p l e x e s i s u s u a l l y a f a s t 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 T h e 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 " 3 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 2 C 1 2 . U l o z < ID OC o </> m < 0.6-^ 0.4H 0.2^ 350 400 WAVELENGTH (nm) 450 0.0 350 400 WAVELENGTH (nm) 450 oo r o 0.0 350 400 WAVELENGTH (nm) 450 F i g u r e 5.10 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_. 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)PPh3 t o t n e m i x t u r e r e c o r d e d i n a ) . b) c) T h e 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 ^396-398 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 due 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 b e c a u s e o f t h e s l o w n e s s o f t h e b . o r o h y d r i d e r e d u c t i o n . 183 SCHEME 5.2 Ru I I(.OEP) + *(,CO)Itn ( 5 a ) + p p h 3 ) R u I n ( 0 E P ) ( P P h 3 ) I m + +.C0 396 nm , 745 nm R e d u c t i o n ( e x c e s s PPh, p r e s e n t ) R u I I ( 0 E P ) ( . P P h 3 ) 2 ? = = ^ R u i i ( 0 E P ) ( P P h 3 ) P = = ^ R u i l ( 0 E P ) ( P P h 3 ) I m - I I * Di i I S o r e t x • max 419 nm 396 nm 408 nm E x c e s s PPh, . E x c e s s Im I I Ru ( 0 E P ) ( P P h 3 ) 2 R u n ( 0 E P ) ( P P h 3 ) I m " T r a c e o f 408 nm a ) b) c ) T h i s s p e c i e s n o t d e t e c t e d due t o p r e s e n c e o f e x c e s s PPh See F i g u r e 5 .1 Ob See F i g u r e 5.10c 184 O t h e r l i g a n d s ( C N - , C I " , A s P h 3 ) a d d e d t o R u H ( O E P ) + '(CO) Im ( 5 a ) b e h a v e d i n a manner s i m i l a r t o t h e i r r e a c t i o n s w i t h 3a_ , a l t h o u g h s l o w -4 k i n e t i c s s o m e t i m e s c o m p l i c a t e d 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 + - -4 o f TEA CN t o a 10 M s o l u t i o n o f 5a g a v e 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 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 (5) b e i n g o b s e r v e d 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 g a v e 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 t o t h a t o b s e r v e d f o r P P h 3 . A s l o w 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 ' ; t h e r e was no R u ( I I I ) 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 . A d d i t i o n o f s o l i d T E A + C 1 ~ t o 5a c a u s e d 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 t u r n e d p i n k , t h e s p e c t r u m s h o w i n g m a i n l y r e d u c t i o n w i t h o n l y 10 - 2 0 % o f [ R u ( 0 E P ) + ' ( C 0 ) C l ] ( l _ c ) b e i n g p r e s e n t . 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 R e a c t i o n s o f a C a t i o n R a d i c a l S p e c i e s i n a C o o r d i n a t i n g S o l v e n t In c o m p l e x e s s u c h as Ru(.0EP) + ' ( C 0 ) p y ( 3 a ) and R u ( 0 E P ) + " ( C 0 ) I m ( 5 a ) i n C H 2 C 1 2 t h e a x i a l l i g a n d t r a n s t o t h e c a r b o n y l i s s e e n t o be f a i r l y 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 l i g a n d . However i n a c o o r d i n a t i n g s o l v e n t 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 m o l e c u l e s a t t h e m e t a l c e n t r e . H e n c e , t h e c h e m i s t r y o f r e a c t i o n s t h a t 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 n d may be s t r o n g l y a f f e c t e d by t h e l i g a t i n g a b i l i t y o f t h e s o l v e n t . 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 ) + -(CO)MeCN i n MeCN was p r e p a r e d 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 i n v e s t i g a t e d . 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) g a v e good s a m p l e s o f r u t h e n i u m ( I I I ) , g a v e m i x t u r e s when a d d e d t o R u ( 0 E P ) + -(CO)MeCN (,6a) i n MeCN. 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 b e t w e e n 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 l e a d i n g t o R u ( I I I ) a n d r e d u c t i o n , g e n e -r a t i n g i n m o s t c a s e s t h e 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 ) . The p r o p o r t i o n s o f t h e two p r o d u c t s o b t a i n e d d e p e n d e d upon t h e l i g a n d u s e d a n d 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 . T h u s , t h e a d d i t i o n o f 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 ( 8 0 % ) o f R u ( I I I ) as p r o d u c t ( a s j u d g e d by 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 t o R u ^ ^ O E P H P P h g ^ * ( 2 2 ) ) p r o v i d i n g a l a r g e e x c e s s o f P P h 3 was 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 M s o l u t i o n o f 6a_ i n MeCN). 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 , t h e n l i t t l e r u t h e n i u m ( I I I ) p r o d u c t i s d e t e c t e d , 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_. T h i s s u g g e s t s t h a t a l a r g e e x c e s s o f PPh^ i s r e q u i r e d t o d i s p l a c e t h e c o o r d i n a t e d MeCN and t o 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 . E x c e s s P n B u 2 g a v e a m i x t u r e o f p r o d u c t s on a d d i t i o n t o 6a_. A b o u t 30% 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) b e c a u s e 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 ) , ^ 2 0 % g a v e a r u t h e n i u m ( l l l ) p r o d u c t v i a 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 50% f o r m e d g r e e n p i g m e n t s (,A m a x ^600 nm). E x c e s s c y a n i d e g a v e i n s t a n t r e d u c t i o n t o g e n e r a t e R u ( O E P ) -( C 0 ) C N " . The a b o v e r e a c t i o n s w i t h CN" a n d p h o s p h i n e s were f a s t ( i n s t a n t a n e o u s 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 m i n u t e s ) w i t h t h e s o l u t i o n t u r n i n g g r a d u a l l y f r o m p u r p l e t o o r a n g e . 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 , t h e p r o p o r t i o n o f R u ( I I I ) o b t a i n e d 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), R u ( 0 E P ) + ' ( C 0 ) M e C N (6a) showed l i t t l e t e n d e n c y t o be r e d u c e d by m e t h a n o l (<3M) o r w a t e r (^6M). H o w e v e r , 6a_ was v e r y e f f e c t i v e l y r e d u c e d by T B A + B r ~ o r T E A + C 1 ~ w i t h o u t t h e f o r m a t i o n 2 o f a c a t i o n r a d i c a l i n t h e A^ u g r o u n d s t a t e , w h i c h c o n t r a s t s w i t h t h e 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 Ru(0EP) + *(CO) ( l a ) . T B A + B H 4 " and T E A + I ~ a l s o q u a n t i t a t i v e l y r e d u c e d 6a^ as e x p e c t e d . E x c e s s p y r i d i n e and 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 t h e p y r i d i n e ( 3 a ) o r i m i d a z o l e ( 5 a ) f o r m 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 , s h o w i n g 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 i s d e t e r m i n e d by t h e e a s e o f d i s p l a c e m e n t o f t h e l i g a n d t r a n s t o t h e 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 2 C 1 2 s o l u t i o n c o n t a i n i n g 1% MeCN and 0.05M TBAP. The 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 o b t a i n e d i s i d e n t i c a l t o t h a t o f 6a_ r a t h e r t h a n l_a 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 . H o wever, t h e 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) were 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 were a l m o s t i d e n t i c a l t o t h e r e a c t i o n s 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 ( T a j . T h u s P n B u 3 and P P h 3 g a v e t h e c o r r e s p o n d i n g r u t h e n i u m ( I I I ) b i s - p h o s p h i n e p r o d u c t s w i t h l i t t l e a c c o m p a n y i n g r e d u c t i o n . T r i p h e n y l a r s i n e g a v e c o n s i d e r a b l e r e d u c t i o n , b u t t h e r u t h e n i u m ( I I I ) p r o d u c t 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 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 as 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 a n d 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 ~ g a v e 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 R e a c t i o n s o f L i g a n d s w i t h a R e l a t e d T h i o c a r b o n y l C a t i o n R a d i c a l -R u ( O E P ) + ' ( C S ) p y . 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 R u ( 0 E P ) + ' ( C 0 ) p y (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 r a d i c a l . T r i p h e n y l p h o s p h i n e and 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 ~ g a v e a m i x t u r e o f R u ( 0 E P ) ( C S ) p y and t h e 2 + • 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 t h e c o r r e s p o n d i n g c a r b o n y l c o m p l e x ( 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 n B u 2 t o R u ( 0 E P ) + * ( C S ) p y g a v e 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 l i t t l e R u ( I I I ) a nd a h i g h p r o p o r t i o n o f g r e e n p r o d u c t s b e i n g f o r m e d . A s i m i l a r 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 e q ) , a n d t h i s o b s e r v a t i o n s u g g e s t s t h a t t h e r e a c t i v i t y o f R u ( 0 E P ) + ' ( C S ) p y i s s i m i l a r t o t h a t o f R u ( 0 E P ) + ' ( C 0 ) p y , 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 h e l d i n t h e f o r m e r c o m p l e x . T h i s may be r a t i o n a l i z e d by 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 com p a r e d w i t h CO 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 c o m p o n e n t t h a t c o o r d i n a t e s t h e 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 L i g a n d s 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 c o m p l e x , 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 i s 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 ( 5 a ) 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 t o R u ( 0 E P ) + ' ( C 0 ) p y (3aJ w h i l e PPhg c a u s e s r e d u c t i o n . A number o f themes do e m e r g e , however, f r o m t h e s e r e a c t i o n s a n d o n e 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 l i g a n d . T h u s , P n B u 3 , P P h 3 , C N ~ - a n d " A s P h 3 , a l l .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 r u t h e n i u m ( I I I ) p r o d u c t . The a n i o n s , C l ~ , B r ~ a n d SCN~, y i e l d c a t i o n r a d i c a l s w i t h t h e A-|u 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 5 a ) . 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 sam-p 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 more 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 n B u 3 r e a c t i o n s ) d e p e n d s 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 e a s e o f s u b s t i t u t i o n o f t h e c o o r d i n a t e d l i g a n d t r a n s t o t h e c a r b o n y l . T h u s , 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 e x t r e m e l y 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 as 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 a t i o n r a d i c a l 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) u s u a l l y has l i t t l e e f f e c t e x c e p t p o s s i b l y i n c h a n g i n g t h a t s i x t h l i g a n d . H o w e v e r , 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 lb_ 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 g r o u n d s t a t e , c a u s e s c o n s i d e r a b l e r e d u c t i o n . T h e s e e x a m p l e s 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 as 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 s u c h 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 - ^ . - c a t i o n r a d i c a l f o l l o w e d by a 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 ) d o e s 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 . T h i s 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 ( 3 a ) i n C H p C l p f o l l o w e d by t h e a d d i t i o n o f more p y r i d i n e ( S e c t i o n 5.2b) and i s a l s o o b s e r v e d i n t h e r e a c t i o n o f a s l i g h t e x c e s s o f P n B u 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 a t t e m p t s t o m i m i c t h i s r e a c t i o n by a d d i n g s u f f i c i e n t p y r i d i n e t o R u ( 0 E P ) + * ( C O ) i n C H 2 C 1 2 t o f o r m 3a and t h e n a d d i n g P n B u 3 u s u a l l y r e s u l t e d i n a g r e e n s o l u t i o n s i m i l a r t o t h a t o b t a i n e d on a d d i t i o n o f P n B u 3 t o R u ( 0 E P ) + ' ( C O ) M e C N i n MeCN. T h i s i s p r e s u m a b l y 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 u s e d t o g e n e r a t e s p e c i e s 3a_ f r o m l_a_ and 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 m e t a l s i t e a n d 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 s o u g h t . 190 T h e r e c a n be c o n s i d e r e d t o be t h r e e " s t a t e s " a v a i l a b l e f o r t h e s e m e t a l l o p o r p h y r i n c o m p l e x e s d e p e n d i n g upon t h e p o s i t i o n o f t h e e l e c t r o n " h o l e " , i . e . f r o m where a n e l e c t r o n i s a b s e n t . I f t h e e l e c t r o n h o l e i s a s s o c i a t e d w i t h a m e t a l o r b i t a l t h e n t h e c o m p l e x i s c o n s i d e r e d t o be a 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 . I f t h e h o l e i s on t h e p o r p h y r i n 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 2 ^ l u o r ^2u 9 r o u n c ' s t a t e d e p e n d i n g upon w h i c h o f two d e g e n e r a t e p o r p h y r i n m o l e c u l a r o r b i t a l s c o n t a i n t h e u n p a i r e d , e l e c t r o n . 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 T r - c a t i o 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_ + AgBF^) c a n a l s o 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 , b u t o f a more 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 n B u 2 t o \a_. T h e s t a t e o r 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 p o r p h y r i n 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 . A c a r b o n y l l i g a n d p r o h i b i t s t h e f o r m a t i o n 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 t h e c a t i o n r a d i c a l s t a t e s . L i g a n d s s u c h as CN", P n B u 3 , PPh-^and A s P l ^ s t a b i l i z e p t h e r u t h e n i u m ( . I I I ) s t a t e ; C l ~ , B r and SCN~ g e n e r a t e t h e A - j u c a t i o n r a d i c a l s t a t e a n d t h e n e u t r a l l i g a n d s s u c h a s p y r i d i n e , i m i d a z o l e , m e t h a n o l , MeCN and THF ( o r no c o o r d i n a t e d l i g a n d a t a l l , e . g . l a ) g i v e t h e A 2 u g r o u n d s t a t e . When a new l i g a n d i s a d d e d t o 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 s p e c i e s , a n d i s e x p e c t e d t o c a u s e a c h a n g e i n t h e p o s i t i o n o f t h e e l e c t r o n 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 . The f i r s t i s . s u c c e s s f u l l i g a n d e x c h a n g e w i t h , t h e a c c o m p a n y i n g change, i n t h e e l e c t r o n i c 191 c o n f i g u r a t i o n o r s t a t e o f t h e m o l e c u l e . T h e o v e r a l l s p e e d o f t h i s r e a c t i o n w i l l p r o b a b l y be d e t e r m i n e d by 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 by t h e c o m p e t i t i v e e f f e c t s f r o m o t h e r l i g a t i n g m o l e c u l e s p r e s e n t ( e . g . py i n 3a_ o r MeCN i n 6a_). The s e c o n d 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 , due 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 r e d u c t i o n . When P n B u 3 i s i n v o l v e d i n s u c h a r e a c t i o n , g r e e n c o m p l e x e s a r e f o r m e d r a t h e r t h a n r e d u c e d p r o d u c t s , 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 ) . The 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. I f t h e i n c o m i n g l i g a n d , w h e n c o o r d i n a t e d , d o e s n o t c a u s e a c h a n g e i n s t a t e o f t h e c o m p l e x ( a s s e e n 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 t o r e d u c e a n d , i n t h e a b o v e c a s e , 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 ( e . g . . 5 a 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 ) . H e n c e , t h e 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 s u c c e s s f u l l y 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 p o r p h y r i n c a t i o n r a d i c a l c o m p l e x w o u l d c a u s e a c h a n g e 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 e l e c t r o n t r a n s f e r ) t o 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 s p e c i e s . T h u s , t h e a d d i t i o n o f P P h 3 o r A s P h 3 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 j u d g e d by u-.v . - ' / v i s i b l e s p e c t r a ) as 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. F u r t h e r e v i d e n c e t h a t 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 ) " 1 " ( 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 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 i m m e d i a t e l y c o o r d i n a t e s t h e p y r i d i n e p r e s e n t i n s o l u t i o n t o g i v e 3 ) . T h u s , t h e p r e s e n c e o f t h e p y r i d i n e i n s o l u t i o n e f f e c t i v e l y d e s t a b i l i z e s t h e c a t i o n r a d i c a l s t a t e w i t h r e s p e c t t o t h e r e d u c e d c a r b o n y l c o m p l e x . Numerous o t h e r e x a m p l e s 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 S e c t i o n 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 M e c h a n i s m s f o r t h e R e d u c t i o n 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 . 1 1 ) . 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 ) . The 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^ ( ) , t h e e f f e c t o f a d d i n g e x c e s s T E A + C 1 " ( ) s a n 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 d r o p o f p y r i d i n e ( ) . The a b s o r p t i o n a t ^630 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 he p r o p o r t i o n o f l_c r e c o r d e d h e r e i s ^ 2 5 % o f t h e t o t a l p o r p h y r i n , t h e l o w v a l u e o b -s 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 . 194 i n t h e v i s i b l e t h a t t h e p r e s e n c e o f a r e d u c e d 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 . B e s i d e s t h e p o s s i b l e 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 e x a m i n a t i o n 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 were s i m i l a r t o c o m p l e x e s f o r m e d i n t h e a t m o s p h e r i c o x i d a t i o n o f 1_. 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 r e q u i r e s t h a t s o m e t h i n g i s b e i n g o x i d i z e d . In m o s t 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 amount 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 3 , p y , C l ~ and MeCN, none o f w h i c h 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 m e c h a n i s m s 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 r e a c t i o n s . 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 and 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 a nd t h e r e d u c e d 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 3 , S b P h ^ a n d 2 ZnTPP +':C10 ~ + py » ZnTPP + I Z n(TPP-py)J + C 1 0 4 " + H C 1 0 4 ( 5 . 5 ) 195 P h Ph. C I O . 4 F i g u r e 5.12 The p r o d u c t , r e p o r t e d by S h i n e a n d 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 f r o m R e f . 8 ) . SCN~) . O t h e r w o r k e r s have 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 t h e n u c l e o p h i l i c g r o u p a t t a c k e d a t t h e m e s o - p o s i t i o n r a t h e r 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 . A n o t h e r p o s s i b l e m e c h a n i s m 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 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 t o g i v e t h e r e d u c e d p r e c u r s o r and a d i c a t i o n g s p e c i e s , 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 t o w a r d s n u c l e o p h i l e s . D i s p r o -p o r t i o n a t i o n r e a c t i o n 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 com-p l e x e s have 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 t h a t i n t h e i r s t u d i e s o f t h e r e a c t i o n o f n u c l e o p h i l e s w i t h t h e Z n T P P + * c a t i o n g r a d i c a l , S h i n e 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 on a d d i n g m e t h a n o l a nd 196 o b t a i n e d a r o u g h l y e q u a l m i x t u r e o f ZnTPP and z i n c m e t h o x y i s o p o r p h y r i n ( F i g u r e 5 . 1 3 ) . No r e a c t i o n was e x p e c t e d , a s p r e v i o u s a u t h o r s had r e p o r t e d t h a t m e t h a n o l d i d n o t r e a c t w i t h m o n o c a t i o n s p e c i e s 1 1 ' 1 2 a n d , i n d e e d , m e t h a n o l had been u s e d by s e v e r a l w o r k e r s a s 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 n u c l e o -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 t h e c o n c l u s i o n t h a t t h e r e a c t i o n o f a n u c l e o p h i l e w i t h a c a t i o n r a d i c a l d i d 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 were 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 i s o p o r p h y r i n 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) w i t h a TPP com-p l e x , o r a m e t h o x y s u b s t i t u t e d p o r p h y r i n w i t h , an O E P 1 4 c o m p l e x Cvla l o s s o f a p r o t o n f r o m t h e i s o p o r p h y r i n L , a n d n e i t h e r o f thes.e p r o d u c t s were o b s e r v e d . 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 f o r t h e a n o m a l o u s r e a c t i v i t y o f Z n T P P + ' t o w a r d s m e t h a n o l , e s p e c i a l l y a t t h e m e s o - p o s i t i o n r a t h e r t h a n t h e 3 - p y r r o l e p o s i t i o n . I t i s p o s s i b l e t h a t t h i s r e a c t i o n 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 o f t h e p a r e n t ( Z n T P P ) 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 way. 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 t h e p o r p h y r i n r i n g c o u l d 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 . T h i s g has been c o n s i d e r e d and d i s c a r d e d by some a u t h o r s f o r t h e r e a s o n s m e n t i o n e d a b o v e , a l t h o u g h 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 S h i n e c o n f u s e s t h e i s s u e . 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 t h e r e a c t i o n s o f t h e r u t h e n i u m p o r p h y r i n c o m p l e x e s . A c o m p l i c a t i n g f a c t o r 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 n u c l e o p h i l e 197 + Ph Ph >-Ph CIO. 4 OMe Ph Figure 5.13 Zinc methoxyisoporphyrin, (modified from Ref. 8 ) . to give a meso-substituted p o r p h y r i n 1 5 . There fore ,e i ther mechanism would be predicted to give the same products. However, in most of the react ions the reduct ion potent ia l of the d i ca t ion produced would probably be higher than the oxidat ion potent ia l of the an ion ic species present (often CI") or of the nuc leoph i l i c l i gand . Hence the d i ca t i on could be reduced d i r e c t l y in most cases by one of the l i gands. The experimental studies into the mechanism of the reduction seen in many react ions with the ruthenium cat ion r ad i ca l s w i l l be described below (Section 5.6b), and the data summarized and compared with the above resu l t s from the l i t e r a t u r e . 198 , 5 .6b ' | E x p e r i m e n t a l S t u d i e s o f t h e R e d u c t i o n R e a c t i o n S e v e r a l r e a c t i o n s were s t u d i e d : a) [ R u ( 0 E P ) + ' ( C 0 ) B r ] ( l b ) + P P h 3 i n C H 2 C 1 2 , b) Ru(OEP)" 1" (C0)MeCN ( 6 a ) + C I " i n MeCN, and c ) R u ( 0 E P ) + * ( C 0 ) -py ( 3 a ) + C I " i n C H 2 C 1 2 . A l l t h e s e r e a c t i o n s g a v e t o t a l l o s s o f t h e u s u a l 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 a n d 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 were u s e d (.^10 M s o l u t i o n s ) . 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 t o r e d u c e 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 were 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-).. F o r s y s t e m 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 c o l u m n g e n e -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 t y p i c a l o f a R u 1 1 ( 0 E P ) ( . C 0 ) L s p e c i e s . 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 ; t h e g r e e n compounds 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 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 C h a p t e r ) . No o t h e r s i g n i f i c a n t bands 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 band) 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 and 706) 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 -s u b s t i t u t e d p o r p h y r i n . 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 b r o m i d e - 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 c h r o m a t o g r a p h y 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 and 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 s a m p l e o f R u ( O E P ) ( C 0 ) p y ( S e c t i o n 2 . 5 ) . S l i g h t l y o v e r 4 0 % 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 w i t h e i t h e r o f t h e m e c h a n i s m s s u g g e s t e d i n t h e 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 up i n t h e g r e e n p o l a r bands a t t h e t o p o f t h e c o l u m n (no o t h e r bands were v i s i b l e ) . T h e s e g r e e n c o l o u r e d 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 between 500 and 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 ave 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 and 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 . T h e v i s i b l e s p e c t r u m o f s u c h 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 s p e c i e s (no 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 -f i e d ) . 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 The 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 a l u m i n a c o l u m n u s e d t o p u r i f y t h e p r o d u c t s o f t h e r e a c t i o n o f Ru(0EP) + -(.C0)py (3a_) w i t h e x c e s s T E A + C 1 " . The weak peak a t ^548 nm i s due t o a t r a c e o f Ru n ( 0 E P ) ( C 0 ) p y . 201 s m a l l 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 f r o m 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 more 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 m a i n p e a k s 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 c o n s i d e r a b l e 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 more i n t e n s e t h a n t h e p r i n c i p a l v i s i b l e a b s o r p t i o n . F o r Z n ( O E P ) t h e m o d i f i c a t i o n o f t h e s p e c t r u m i s r a t h e r l e s s t h a n t h a t f o r t h e TPP c o m p l e x : - ( Z n ( 0 E P - m e s o py) \ v 406, 537 and 572 nm; ZnOEP X 400, 530 and 570 nm). H e n c e , s u c h a s u b s t i t u t e d c o m p l e x o f t h e max 1 r t y p e Ru(OEP)(|C0)L ( a s s u m i n g s i m i l a r b e h a v i o u r ) w o u l d l e a d t o r e d - s h i f t e d b u t s t i l l i n t e n s e b a n d s . 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 a r e n o t m e s o - s u b s t i t u t e d p o r p h y r i n s . 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 a s 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 m a i n r e a c t i o n . T h e m e c h a n i s m 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 m e c h a n i s m w i t h t h e d i c a t i o n p r o d u c e d u n d e r g o i n g 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 a t 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, Smith, D, Dolphin,and B.R. James, J , Organomet. Chem. 208, 239 (1981). 2. A.G. Sharpe, 'The Chemistry o f Cyano Complexes o f the T r a n s i t i o n M e t a l s ' , Academic Pres s , London, 1976, p. 9. 3. F.A. Cotton and G. W i l k i n s o n , 'Advanced Inorganic Chemi s t r y " , 4th Ed. , W i l ey , New York, 1980, Chap. 3. 4. D.V. S tynes, H.C. Stynes, B.R. James, and J .A . I be r s , J . Am. Chem. Soc. 95, 1796 0 9 7 3 ) . 5. L.M. E p s t e i n , D.K. St raub, and C. Ma r i cond i , Inorg. Chem. 6, 1720 (19,67). 6. G.R. Eaton and S.S. Eaton, J . Am. Chem. Soc. 97, 236 (1975). 7. T. L e u n g , Personal communication. 8. H.J . Sh ine, A.G. P a d i l l a , a n d S.-M. Wu, J . Org. Chem. 44, 4069 (1979). 9. B. Evans and K.M. Smi th , Tetrahedron L e t t . 35, 3079 (1977). 10. B.P. Neri and G.S. W i l s on , Ana l . Chem. 45, 442 (1973). 11. D. Dolphin and R.H. F e l t o n , Acc . Chem. Res. _7, 26 (1 974). 12. G.H. Barnett and K.M. Smith, J . Chem. Soc. Chem. Comm. (1976) 236. 13. D. Do lph in , R.H. F e l t o n , D.C. Borg,and J . F a j e r , J . Am. Chem. Soc. 92 ,^ 743 (1970). 14. D. Do lph in , D.J. Ha lko, F.C. Johnson,and K. Rousseau i n ' Po rphy r i n Chemistry Advances ' (F.R. Longer ed1), Ann,. Arbor Sc ience , 1979, pp. 119-141. 15. E.C. Johnson and D. Do lph in , Tetrahedron L e t t . 26, 2197 (1976). 203 CHAPTER 6 AN ANOMALOUS OXIDATION OF Ru(OEP) ( C O ) L COMPLEXES ( L = P n B u ^ >. P P h 3 , and A s P h ? ) : THE MECHANISM OF INTRAMOLECULAR ELECTRON TRANSFER (IMET) l As s e e n i n C h a p t e r 4, and f i r s t r e p o r t e d by Brown e t a l ., 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 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 = p y , Im, EtOH, 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 f o r m e t a l 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 v o l t a m m e t r y . T h e o x i d a t i o n p r o d u c t was shown t o be a p o r p h y r i n T r - c a t i o n r a d i c a l . However, c y c l i c v o l tammograms o f o t h e r compounds [ R u n ( 0 E P ) ( C 0 ) L , L = P n B u 3 , P P h 3 and A s P h 3 ] showed f a r more c o m p l e x c h e m i s t r y . E l u c i d a t i o n o f t h i s c h e m i s t r y s u g g e s t s a m e c h a n i s m f o r 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 s d i s c u s s e d i n C h a p t e r 5. 6.1 T h e E l e c t r o c h e m i s t r y o f R u H ( 0 E P ) ( C 0 ) P n B u 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 2 » a n o n - c o o r d i n a t i n g s o l v e n t , showed two o x i d a t i o n p eaks a s e x p e c t e d a t ^+0.64V and +1.14V. Th e r e d u c t i o n sweep showed a p e a k c o r r e s p o n d i n g 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 , s u g g e s t i n g t h a t t h e o x i d a t i o n / r e d u c t i o n p r o c e s s was r e v e r s i b l e ( s e e S e c t i o n 2 . 2 ) . 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 t o t h e f i r s t o x i d a t i o n p eak ( a t ^+0.64V) was much l e s s i n t e n s e a n d was f o l l o w e d by a new wave a t +0.2V ( F i g u r e 6.1a; c o m p a r e F i g u r e 4.1 f o r t h e v o l t a m m o g r a m o f R u ( 0 E P ) ( C 0 ) (X)). 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 -t e n t w i t h t h e f o r m a t i o n o f a p o r p h y r i n T r - c a t i o n r a d i c a l , a s t h e 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 f o r o x i d a t i o n a t t h e m e t a l ( s e e S e c t i o n 7 . 1 ) . T h i s c a t i o n r a d i c a l s p e c i e s a p p e a r s t o p a r t i a l l y c h a n g e t o a new 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 . T h i s s u g g e s t s t h a t p r o d u c t A has b een 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 t h e r u t h e n i u m ( I I ) i T - c a t i o n r a d i c a l i n t o a R u ( I I I ) p o r p h y r i n . 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 voltammogram f r o m 50 mV/sec t h r o u g h 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 t h a t t h e f o r m a t i o n o f A was 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 o f A II + n and t h e p o r p h y r i n i T-cation r a d i c a l s p e c i e s Ru (OEP) t.C0)P B u 3 ( 8 a J was e s t a b l i s h e d i m m e d i a t e l y ( 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.>. tammogram). R e p e a t e d sweeps f r o m -0.2 t o +1.6V showed no b u i l d - u p i n t h e 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 o f an o x i d a t i o n p eak 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 x M - Q 24V ( F i g u r e 6 . 1 b ) . H o wever, i f A was f o r m e d ' i n s t a n t a n e o u s l y ' v i a t h e i r - c a t i o n r a d i c a l (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 a t h i g h e r p o t e n t i a l s be-t ween +1.0 and +1.6V , 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 p eak s e e n i n F i g u r e s 6.1a a n d b. Two e x p l a n a t i o n s a r e p o s s i b l e . One i s t h a t A_ and 8a_ have 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 o x i d a t i o n p r o d u c t s a r e n o n - i d e n t i c a l . T h e 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 p r o d u c t f o r m e d f r o m b o t h t h e s e compounds i s t h e same and h e n c e t h e s e c o n d 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 . E x p e r i m e n t s r e p o r t e d b e l o w 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 more l i k e l y . C y c l i c v o l tammograms were r e c o r d e d i n t h e p r e s e n c e 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 4 ~ a n d CF^SO^") i n C f ^ C ^ a t p o r p h y r i n c o n c e n t r a t i o n s i n t h e r a n g e ( 3 . 0 t o 4.0) x 10~ 4M. The p o t e n t i a l s o b s e r v e d 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 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 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 4.1 f o r t h e o x i d a t i o n o f R u 1 1 ( 0 E P ) ( C 0 ) L . The C 1 0 4 ~ and C F 3 S 0 3 ~ a n i o n s g a v e a l m o s t i d e n t i c a l p o t e n t i a l s f o r t h e s p e c i e s s t u d i e d , w h i l e t h e c o r r e s p o n d i n g p o t e n t i a l s u s i n g B F 4 ~ were ^0.1 v o l t s h i g h e r . C o m p a r i s o n o f c y c l i c v o l t a m m o -grams o f R u * * C 0 E P ) ( . P n B u 3 ) 2 (.7) i n t h e p r e s e n c e o f C F ^ S O ^ - and B F 4 ~ showed 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 were 0.20 t o 0.22V below t h e c o r r e s p o n d i n g p o t e n t i a l f o r A (+0.08V v s t + 0 . 3 0 V i n t h e p r e s e n c e o f B F 4 " , a n d -0.02V v s +0.18V i n t h e p r e s e n c e o f C F 3 S 0 3 " ) , t h i s s u g g e s t s t h a t A i s n o t R u 1 * ( O E P ) ( P n B u 3 ) 2 (7) ( S e c t i o n 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 nd 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 nd 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 t h e c y c l i c v o l tammogram 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 f r o m t h e f i r s t o x i d a t i o n p r o d u c t - p r e s u m a