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Electron-deficient porphyrins Terazono, Yuichi 2001

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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 S by Y U I C H I T E R A Z O N O B.Eng . , K u m a m o t o University, Japan, 1987 M . E n g . , K u m a m o t o University, Japan, 1989 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F D O C T O R O F P H I L O S O P H Y in T H E F A C U L T Y O F G R A D U A T E S T U D I E S Department o f Chemistry W e accept this thesis as conforming to the requited standard T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A July 2001 (C) Y u i c h i Terazono, 2001 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver, Canada DE-6 (2/88) 11 ABSTRACT The search for effective porphyrin catalysts for oxygenations that mimic the functions o f cytochrome P-450 has led to the synthesis o f electron-deficient porphyrins. N o v e l P-ttifluoromerhyl-OT^-tetJ:aphenylporphyrins were prepared by the copper assisted trifluoromethylation using P-bromo-w^o-tetraphenylporphyrins and in-situ generated C F 3 C u via the pyrolysis o f C F 3 C 0 2 N a / C u I or the metathesis o f trifluoromethylcadmium ( (CF 3 ) 2 Cd + C F j C d B r / C u B r ) . A l though multiple trifluoromethylation was difficult due to the steric bulk o f the —CF 3 group, the existence o f various ^wo-tetraphenylporphyrins with perfluoroalkyl moieties was affirmed. Partially trifluoromethylated porphyrins H 2 T P P ( C F 3 ) 2 (46a), H 2 T P P ( C F 3 ) 3 (47a), H 2 T P P ( C F 3 ) 4 (48a), and H 2 T P P ( C F 3 ) 3 ( C F 2 C F 3 ) (52a) were obtained by trifluoromethylation o f Z n ( T P P B r 4 ) (45b) foUowed by demetallation. Z n ( T P P ( C F 3 ) 4 ) (48b), C o ( T P P ( C F 3 ) 4 ) (48e) F e ( T P P ( C F 3 ) 4 ) C l (48f), and F e ( T P P ( C F 3 ) 3 ( C F 2 C F 3 ) ) C l (52c) were also synthesized from the corresponding free-base porphyrins. These metalloporphyrins, as wel l as free-base porphyrins, were used for the analysis o f the electronic and the steric effects o f the —CF 3 groups o n the Ph C F , 46a Ph C F 3 F 3 C Ph 48a : M = 2 H + 48b : M = Zn(II) 48e : M = Co(II) 48f : M = Fe(III)Cl F 3 C Ph 52a:M = 2 H + 52c : M = Fe(III)Cl Ill porphyrin macrocycle by UV-visible and lH N M R spectroscopy, cyclic voltammetry, and X-ray crystallography. These analyses not only suggested that novel p-trifluoromethylporphyrins were electron-deficient but also showed that those porphyrins take bacteriochlorin-like distorted electronic structures; a fixed 187t-electronic pathway. A n X-ray crystal structure of 48b revealed severe macrocycle distortion into a saddle shape due to the steric interaction between the —CF 3 and the meso-phenyl groups. Catalytic oxidations of cyclohexane and cyclohexene using 48f and 52c as catalysts, iodosylbenzene (PhIO) as an oxidant and the above-mentioned substrates showed that they were not superior to one of the best porphyrin catalysts, Fe(TDCPPCl 8 )Cl (10d) and porphyrin 48f and 52c were not very stable in the oxidation runs. Although the prepared novel porphyrins were not satisfactory as P-450 model compounds, interesting electronic and structural properties of the zwj-0-tettaphenylporphyrins partially trifluoromethylated at the pyrrolic P-positions of antipodal pyrroles were revealed. The steric and electronic effects of the —CF 3 groups on the pyrrolic P-positions of zmo-teteaphenylporphyrin were also compared to those of P-methyl analogues (57a, 58a, 59a, and 59b) in order to compare these effects distincdy. Ph CH, Ph 58a A r = 2,6-dichlorophenyl Ph C H 3 / - I N s ,N=/ Ph—(\ M / / - P h H 3 C Ph 59a : M = 2 H + 59b : M = Zn(II) IV TABLE OF CONTENTS ABSTRACT n TABLE OF CONTENTS iv LIST OF TABLES vii LIST OF FIGURES viii LIST OF SCHEMES xi LIST OF ABBREVIA TIONS xii NOMENCLATURE xvii ACKNOWLEDGEMENT xix CHAPTER I 1 A. Introduction 1 B. Metaloporphyrins as cytochrome P-450 model compounds 5 1. Cytochromes P-450 5 a. Distribution, nomenclature, and structure 5 b. Function and mode of action 6 c. Mechanisms of hydrocarbon oxidation 8 (1) Mechanism of alkane hydroxylation 8 (2) Mechanism of alkene epoxidation 9 2. Synthetic metalloporphyrins as P-450 rnirnics 11 a. Structures of porphyrins that appear in this section 11 b. Synthetic methods for the major players in the early development of P-450 mimics 12 (1) Condensation of pyrrole with arylaldehydes 12 (2) p-Perchlorinated and perbrominated meso-arylporphyrins 13 c. Early development of P-450 mimics 14 d. Electron-withdrawing effects on catalytic activities 16 e. Newer generation of electron-deficient porphyrins 22 (1) P-Perfluoro-meso-tetraatylporphyrins 22 (2) P-Nitro-meso-tetrakis(2,6-dichlorophenyl)porphyrins 25 (3) meso-Tetrakis(perfluoroalkyl)porphyrins 28 3. Design concept for a new P-450 mimic 30 a. Basic concept 30 b. Potential advantages of trifluoromethyl substituents 31 C. Synthetic strategy for P-trifluoromethylation of meso-tetraphenylporphyrin 32 1. Brief overview of trifluoromethylation 32 a. Fluorination of an existing aryl substituent (Scheme 1-3) 33 b. Introduction of trifluoromethyl groups 33 (1) Transfer of CF 3 " (Scheme l-4(a)) 33 (2) Transfer of C F 3 + (Scheme l-4(b)) , 34 2. Copper assisted trifluoromethylation 35 a. C F 3 C u from pyrolysis o f sodium trifluoromethyl acetate i n the presence o f Cu(I) halide 35 b. C F 3 C u from metathesis o f trifluorometiiylcadmium wi th Cu(I) halide 37 (1) Trifluoromethylation 37 (2) Synthesis of trifluoromethylcadmium 37 D . Analysis of porphyrins 38 1. UV-v i s ib le absorption spectroscopy 38 a. Characteristics o f UV-v i s ib le absorption spectra o f porphyrins and metalloporphyrins 38 b. Electron-withdrawing effects on UV-vis ib le absorption spectra 41 2. Redox potentials o f porphyrins 43 a. General redox properties o f porphyrins in non-aqueous media 43 (1) Technique, solvent, and supporting electrolytes 43 (2) Porphyrin ring redox properties in free-base and metalloporphyrins 44 (3) Iron porphyrins 44 b. Effects o f substituents on the redox potentials o f derivatives o f T P P 47 (1) Aryl-ring-substituted TPPs 47 (2) fJ-Substituted TPPs 49 (3) Conclusion 54 3. lH N M R spectroscopy 55 a. Porphyrin ring current effect 55 b. Concentration effect 55 c. N - H tautomerism 57 4. Spectrophotometric titration 59 a. Evaluation o f p K , o f N H 59 b. Determination o f central metal — ligand binding constant 61 E . Goals of this thesis 63 CHAPTER II 64 A. Synthesis of P-trifluotomethyl- and P-methyl-weso-tetraphenylporphyrins 64 1. Trifluoromethylation 65 a. Synthesis o f precursors 66 b. Trifluoromethylation by pyrolysis o f C F 3 C 0 2 N a / C u l 67 (1) Reaction using Cu(TPPBr 8) (7c) 67 (2) Reactions using M T P P B r 4 (M = Zn(II), Cu(II), and Ni(II)) (45b,45c,and 45d) 69 c. Trifluoromethylation by C F 3 C u generated by the metathesis o f tiifluorometiiylcadmium and C u B r 72 (1) Preliminary experiments 72 (2) Optimization of the yield for P-tetrakis(trifluoromethyl)-meso-tetraphenylporphyrin....76 2. Methylation 88 3. Metallation 90 a. Synthesis o f Zn(II) and Co(II) complex o f 48 91 b. Synthesis o f Fe(III) complexes o f 48 and 52 92 4. Summary 95 B. Analysis of P-trifluoromethyl-weso-tetraphenylporphyrins..../ 95 VI 1. UV-visible spectra of synthesized novel porphyrins 97 a. Free-base porphyrins 98 (1) UV-visible spectra in C H 2 C 1 2 98 (2) Absorbance vs. concentration of 48a • 109 b. UV-visible spectra of metalloporphyrins 110 2. N M R spectroscopy 116 a. Determination of electronic pathway of P-tdfluoromethylporphyrins 117 b. Unusual ' H N M R chemical shift for pyrrolic p-protons of H 2 TPP(CF 3 ) 4 (48a) 126 3. Redox potentials 134 a. Free-base P-trifluoromethyl-^m-tetraphenylporphyrins 136 b. Zn(II) porphyrins 144 c. Fe(III) porphyrins 151 4. Crystal structures 153 a. Preparation of the crystals and crystallographic data 153 b. Structure details 155 (1) Core size, Z n displacement, and axial coordination 155 (2) Effects of antipodal P-substitation 161 (3) Macrocycle distortion 164 (4) Orientation of the axial ligand 169 5. Specttophotometric titration 172 a. Titration of 48a with strong organic bases in CH 2Ci2 173 (1) Titration with D B U 173 (2) Titration with E t 3 N 176 b. Titration of Co(rPP(CF3)4) (48e) with pyridine and imidazole 176 6. Summary 182 C. Catalytic oxidation of cyclohexane and cyclohexene 184 CHAPTER III 188 A. Conclusions 188 B. Future work 189 CHAPTER IV 195 A. Chemicals 195 B. Instrumentation 195 C. Procedures 197 D. Preparation of materials 202 REFERENCES 220 APPENDICES 233 A. UV-visible spectra of diacids of 48a and 59a 233 B. Crystallographic Data 234 v i i LIST O F T A B L E S Table 1-1. Yields o f typical (3-perhalogenation reactions p.14 Table 1-2. Relationship between catalyst i ron redox potentials and activities 19 Table 1-3. O" values for different substituents 31 Table 1-4. The first reduction and oxidation potentials for 36 - 39 54 Table 1-5. Formation constants for pyridine binding in C H 2 C 1 2 at 25 °C 62 Table 2-1. Results o f trifluoromethylation by the pyrolysis method 71 Table 2-2. Trifluoromethylation by metathesis using M T P P B r 4 (45) 75 Table 2-3. Products obtained by the reaction at 70 °C for 88 h 78 Table 2-4. R f values for metal-free perfluoroalkylated porphyrins 79 Table 2-5. Isolated P-perfluoroalkyl-^fo-tetraphenylporphyrins 82 Table 2-6. Comparison o f UV-v i s ib le absorption maxima 99 Table 2-7. UV-vis ib le absorption maxima o f metalloporphyrins 114 Table 2-8. Chemical shift values o f Zn(II) P-tetrasubstituted wt?.ra-tettaphenylporphyrins 133 Table 2-9. Redox potentials o f P-substituted wwo-tetraphenylporphyrins i n C H 2 C 1 2 . 140 Table 2-10. Redox potentials o f P-substituted ^.r^teteaphenylporphyrin Zn(II) complexes i n C H 2 C 1 2 147 Table 2-11. Redox potentials o f Fe(III) porphyrin chloride complexes 152 Table 2-12. Crystallographic data for 45b-(MeOH)-(DMF), 48b-(EtOH) 3, and 59b - (THF) 1 6 - (CHCl 3 ) 0 4 154 Table 2-13. Core size, selected bond lengths and bond angles 159 Table 2-14. Cp-Cp bond lengths i n antipodally P-tetrasubstituted ^^o-tetraphenylporphyrins 164 Table 2-15. Binding constants o f Co(II) porphyrins for base binding i n i n C H 2 C 1 2 . . . 182 Table 2-16. Oxidat ion o f cyclohexane and cyclohexene using Fe(III) porphyrins and iodosylbenzene i n C H 2 C 1 2 185 Table B-l-a A t o m i c coordinates and B e q for Z n ( T P P ( C F 3 ) 4 ) - ( E t O H ) 3 234 Table B-l-b Anisotropic displacement parameters for Z n ( T P P ( C F 3 ) 4 ) - ( E t O H ) 3 236 Table B-2-a A t o m i c coordinates and B c q for Z n ( T P P B r 4 ) - ( M e O H ) - ( D M F ) 238 Table B-2-b Anisotropic displacement parameters for Z n ( T P P B r 4 ) - ( M e O H ) - ( D M F ) . 2 4 0 Table B-3-a A t o m i c coordinates and B e q for Z n f T T ^ C H ^ - C I H F ) , 6 - ( C H C l 3 ) 0 4 242 Table B-3-b Anisotropic displacement parameters for ZnCrPP(CH 3 ) 4 )-CiHF) 1 6 -(CHCl 3 ) 0 . 4 244 Vlll LIST O F FIGURES Figure 1-1. Protoporphyrin F X Fe complex p . l Figure 1-2. Examples o f electron-deficient porphyrins 2 Figure 1-3. Example o f salen Mn(IH) complex 3 Figure 1-4. Act ive site and hydrophobic pocket o f cytochrome P-450 c a m 5 Figure 1-5. Catalytic cycle o f cytochrome P-450 7 Figure 1-6. Mechanism o f alkane hydroxylation by cytochrome P-450 9 Figure 1-7. Mechanism o f the oxidation o f olefins by cytochrome P-450 10 Figure 1-8. Porphyrins used in P-450 model studies 11 Figure 1-9. Reaction o f oxo Fe(FV) porphyrin Tt-cation radical with alkene and / - B u O O H 18 Figure 1-10. Catalytic cycle for isobutane hydroxylation by 0 2 and 8d proposed by El l is and Lyons 20 Figure 1-11. Synthesis o f p-polynitto-OT^-tefi:alds(2,6-dicUorophenyl)porphyrins 26 Figure 1-12. Synthesis o f wm>-tetJ:aMs(perfluoroalkyi)porphyrins 29 Figure 1-13. Removal o f water by use o f a toluene-azeotrope i n the pentafluoroethylation o f a-iodonaphthalene 36 Figure 1-14. UV-vis ib le spectra o f «?^ - t e t r apheny lpo rphyr ins C H 2 C 1 2 39 Figure 1-15. Symmetries o f Z n ( T P P ) (2b), H 2 T P P (2a) and [ H 4 T P P ] 2 + 40 Figure 1-16. Example o f the UV-v i s ib le spectral change by electron-withdrawing effects 42 Figure 1-17. Cyclic voltammogram o f H 2 T P P (2a) in C H 2 C 1 2 45 Figure 1-18. Cyclic voltammogram o f F e ( T P P ) C l (2d) i n C P ^ C h . 46 Figure 1-19. P lot o f E 1 / 2 vs. 4a for the electrode reactions o f H 2 TP(/>-X)P (31a) 48 Figure 1-20. First reduction and oxidation potentials vs, # o f C N groups for (a) H 2 T P P ( C N ) S (34a) and (b) C u T P P ( C N ) x (34c) 51 Figure 1-21. P lo t o f the first oxidation and the first reduction potential for F e f T P P B r J C l (35a) using P h C N as solvent 52 Figure 1-22. Side view o f the crystal structures o f H 2 T M P (3a), H 2 T M P C 1 4 (36), H 2 T M P B r 4 (37), and H 2 T M P C 1 8 (38) 53 Figure 1-23. 200 M H z } H N M R spectrum o f H 2 T P P (2a) in C D C 1 3 at 298 K 56 Figure 1-24. Plot o f ' H chemical shift o f meso-Hvs. porphyrin concentration for 40a. 58 Figure 1-25. Tautomerism in H 2 T P P (2a) 59 Figure 1-26. Relative populations o f 42a and 42b at 200 K in C D 2 C 1 2 60 Figure 2-1. UV-vis ib le spectra during trifluoromethylation o f 45b at 70 °C 77 Figure 2-2. UV-vis ib le spectra during trifluoromethylation o f 45b at 110 °C 81 Figure 2-3. 3,4-Dibromopyrrole and 3,4-bis(trifluoromethyl)pyrrole modeled by HyperChem 84 Figure 2-4. UV-vis ib le spectra o f the orange compound and H 2 T P P ( C F 3 ) 4 (48a) 87 Figure 2-5. UV-vis ib le spectra o f P-tafluorometiiyl-wwo-tettaphenylporphyrins, (a)46a, (b)47a, and (c)48a i n C H 2 C 1 2 101 Figure 2-6. UV-vis ib le spectra o f P-tetrabromo-OTc?j(9-tetraphenylporphyrins (45a) i n C H 2 C 1 2 102 IX Figure 2-7. UV-visible spectra of P-memyl-w^o-tettaphenylporphyrins, (a)57a, (b)58a, and (c)59a in CH 2 C1 2 103 Figure 2-8. UV-visible spectra of 52a in CH 2 C1 2 106 Figure 2-9. UV-visible spectra of bacteriochlorin (64) 108 Figure 2-10. UV-visible spectral change of H 2 TPP(CF 3 ) 4 (48a) I l l Figure 2-11. UV-visible spectral change of H 2 TPP(CF,) 3 (CF 2 CF 3 ) (52a) 112 Figure 2-12. UV-visible spectra of Zn(TPP(CF 3) 4) (48b) and Co(TPP(CF 3) 4) (48e) in CH 2 C1 2 : 113 Figure 2-13. UV-visible spectra of [Fe(TPP(CF3)4)]Cl (48f), [FeTPP(CF 3) 3(CF 2CF 3)]Cl (52c), and [Fe(TPPBr4)]Cl (45e) 115 Figure 2-14. 400 M H z *H N M R spectra of H 2 T P P B r 4 (45a) in CDC1 3 at room temperature 118 Figure 2-15. 400 M H z ' H N M R spectra of H 2 TPP(CF 3 ) 3 (47a) in CDC1 3 at room temperature 120 Figure 2-16. 400 M H z C O S Y spectra of H 2 TPP(CF 3 ) 3 (47a) 121 Figure 2-17. 18^-electron pathway of H 2 TPP(CF 3 ) 3 (47a) 122 Figure 2-18. 200 M H z ' H N M R spectra of H 2 TPP(CF 3 ) 3 (47a) in the presence of and in the absence of residual water in CDC1 3 123 Figure 2-19. 400 M H z ' H N M R spectra of H 2 TPP(CH 3 ) 3 (58a) in CDC1 3 at room temperature 125 Figure 2-20. 200 M H z ' H N M R spectra of (a) H 2 T P P (2a), (b) H 2 T P P B r 4 (45a), (c) H 2 TPP(CF 3 ) 4 (48a) and (d) H 2 TPP(CH 3 ) 4 (59a) in C 6 D 6 at room temperature 127 Figure 2-21. 400 M H z ' H N M R spectra of diacid of (a) H 2 TPP(CF 3 ) 4 (48a), (b) H 2 T P P B r 4 (45a) and (c) H 2 TPP(CH 3 ) 4 (59a) in T F A - d at room temperature 130 Figure 2-22. Structures of (a) [H 4 TPP] 2 + and (b) [H 4 TPP(CH 3 ) 4 ] 2 + 132 Figure 2-23. Cyclic voltammograms of (a) H 2 TPP(CF 3 ) 2 (46a) and (b) H 2 TPP(CF 3 ) 3 (47a) 137 Figure 2-24. Cyclic voltammograms of H 2 TPP(CF 3 ) 4 (48a) at different scan rates 138 Figure 2-25. Cyclic voltammograms of (a) H 2 TPP(CH 3 ) 2 (57a), (b) H 2 TPP(CH 3 ) 3 (58a), and (c) H 2 TPP(CH 3 ) 4 (59a) 139 Figure 2-26. Redox potentials of (a) H 2 TPP(CF 3 ) X (x = 0 (2a), 2 (46a), 3 (47a), and 4 (48a)  and (b) H 2 TPP(CH 3 ) X (x = 0 (2a), 2 (57a), 3 (58a), and 4 (59a).  143 Figure 2-27. Energy level diagram for H O M O s and L U M O s of the four generic metalloporphyrin classes 145 Figure 2-28. (a) Cyclic voltammogram of Zn(TPP(CF 3 ) 4 ) (48b). (b) 4a vs. 1st oxidation and 1st reduction potentials of P-tetrasubstituted meso-tetraphenylporphyrinato Zn(II) (Zn(TPP) (2b), Zn(TPP(CN) 4 (34b, x=4), Zn(TPPBr 4) (45b), Zn(TPP(CF 3) 4) (48b)  146 Figure 2-29. The H O M O - L U M O gap of P-substituted wao-arylporphyrin Zn(II) complexes 149 Figure 2-30-45b. X-ray crystal structures of 45b-(MeOH)'(DMF) 156 Figure 2-30-48b. X-ray crystal structures of 48b- (EtOH) 3 157 Figure 2-30-59b. X-ray crystal structures of 59b-(THF)16-(CHCl3)04 158 X Figure 2-31. Schematic illustration of the steric effects of antipodal (3-substituents and meso-phenyl groups on the macrocycle of (3-tetrasubstituted meso-tetraphenylporphyrin 163 Figure 2-32. Perpendicular atomic displacements of the Z n porphyrins, relative to the N 4 mean plane 166 Figure 2-33. Orientations of phenyl and C F , groups in 48b 168 Figure 2-34. Orientations of phenyl and C H 3 groups in 59b 170 Figure 2-35. UV-visible spectral change in titration of H 2 TPP(CF 3 ) 4 (48a) with D B U in CH 2 C1 2 174 Figure 2-36 Logarithmic analysis of the spectral data for the addition of D B U to H 2 TPP(CF 3 ) 4 (48a) in CH 2 C1 2 175 Figure 2-37. UV-visible spectral change in titration of H 2TPP(CF 3) 4(48a) with E t 3 N in CH 2 C1 2 177 Figure 2-38. Titration of Co(TPP(CF 3) 4) (48e) in CH 2 C1 2 with pyridine at 25.0 °C 178 Figure 2-39. Spectral changes in the pyridine addition to Co(TPP(CF3)4)-(Py)(48e-(Py)) i n C H 2 C l 2 a t 2 5 . 0 ° C 179 Figure 2-40. Logarithmic analysis of the spectral data for the addition of pyridine to Co(TPP(CF3)4)(48e) in CH 2 C1 2 181 Figure 4-1. Electrochemical cell and electrodes 196 Figure 4-2. Possible isomers for (3-tris(tjifluoromemyl)-OTWt9-tetraphenylporphyrin..210 Figure A - l . UV-visible spectra of freebase porphyrins, H 2 TPP(CF 3 ) 4 (48a) and H 2 TPP(CH 3 ) 4 (59a) in CH 2 C1 2 and their diacids in CH 2 C1 2 containing 0.5%(v)TFA 233 XI LIST OF SCHEMES Scheme 1-1. Synthesis of w^o-tetraarylporphyrins p.12 Scheme 1-2. P-Halogenation of /W^ro-tetraarylporphyrin 14 Scheme 1-3. Fluorination of an existing aryl substituent 33 Scheme 1-4. Introduction of a triiluoromethyl group 34 Scheme 1-5. Trifluoromethylation of aromatic halide by pyrolysis of C F 3 C 0 2 N a 36 Scheme 2-1. Trifluoromethylation strategies 66 Scheme 2-2. Trifluoromethylation of P-octabromo-wwo-tetraphenylporphyrinato Cu(II) (7c) by pyrolysis of C F 3 C 0 2 N a / C u I 68 Scheme 2-3. Trifluoromethylation of P-tetrabromo-^j'o-porphyrins (45) by pyrolysis of C F 3 C 0 2 N a / C u I 70 Scheme 2-4. Trifluoromethylation of P-tetrabromo-wi?j"o-porphyrins (45) by metathesis of C F 3 - C d / C u B r / H M P A 74 Scheme 2-5. Product distribution in trifluoromethylation of 45b by metathesis at 70, 90, and 110 °C 85 Scheme 2-6. Methylation of 45b 89 Scheme 2-7. Insertion of Zn(II) and Co(II) into H 2 TPP(CF 3 ) 4 (48a) 91 Scheme 2-8. Synthesis of Fe(TPP(CF 3) 4)Cl (48f) and Fe(TPPBr 4)Cl (45e) 93 Scheme 2-9. (a)187t-electron pathway of bacteriochlorin (64) and (b) the possible electronic pathway of p-trifluoromethylporphyrins 108 Scheme 2-10. Atom designations used in Table 2-13 155 Scheme 2-11. Schematic representation of macrocyclic distortion and axial coordination in 45b-(MeOH), 59b-(THF), and 48b(EtOH) 171 Scheme 3-1. wwo-Tettaltis(2,6-bis(trifluoromethyl)phenyl)porphyrin (66) 192 Scheme 3-2. Formation of oxo Fe(rV) porphyrin u-cation radical from Fe(III) porphyrin and hydrogen peroxide 194 xii LIST OF ABBREVIATIONS Abs. Absorbance A r C F 3 Trifluoromethyl aryl compound A r l Iodo aryl compound B Lewis base br, bs Broad, broad singlet B u C N Butyronitrile t-Bu /-Butyl Calcd. Calculated C F 3 - C d C F 3 C d X + (CF 3) 2Cd, X = CI or Br Cone. Concentrated Co(TP(z>-OCH3)P) 5,10,15,20-Tetralds(4-memoxyphenyl)porphyrinatocobalt(Ii) Co(TPFPPF 8) 2,3,7,8,12,13,17,18-Octafluoro-5,l 0,15,20-tetralris(perfluorophenyl)porphyrrnatocobalt(Ii) Co(TPP(CN) 4) 2,3,12,13-Tetracyano-5,l 0,15,20-tetraphenylporphyrinatocobalt(II) CofTPPFg) 2,3,7,8,12,13,17,18-Octafluoro-5,l 0,15,20-tettaphenylporphyrmatocobalt(II) Cu(TPP(CN)0 P-Polycyano-5,10,15,20-tetraphenylporphyrinatocopper(Ii) Cu(TPP) 5,10,15,20-Tetraphenylporphyrinatocopper(H) Cu(TPPBr 4) 2,3,12,13,-Tetrabromo-5,l 0,15,20-tetraphenylporphyrinatocopper(II) Cu(TPPBr 8) 2,3,7,8,12,13,17,18-Octabromo-5,10,15,20-tetraphenylporphyrinatocopper(II) Cys Cysteine d Doublet D B U l,8-Diazabicyclo[5.4.0]undec-7-ene D D Q 2,3-Dichloro-5,6-dicyanoquinone D M F N,N-Dimethylformamide D M S O Dimethylsulfoxide E v 2 (1) First half-wave oxidation potential E £ (1) First half-wave reduction potential E°; 2 (2 ) Second half-wave oxidation potential (2) Second half-wave reduction potential EI Electron impact eq. Equimolar E t £ > Diethylether E t 3 N Trietiiylamine E t O H Ethanol F.W. Formula weight F A B Fast atom bombardment F c / F c + Ferrocene/ferrocenium Fe((C 3F 7) 4P)Cl Chloro[5,10,15,20-tetiakis(heptafluoropropyl)porphyrinato]rron(IIi) F e ( T D C P P ) C l F e ( T O C P P B r g ) C l F e ( T D C P P C l 8 ) C l F e ( T D C P P F 8 ) C l Fe(TMP)Cl Fe(TP(w-X)P)Cl Fe(TP(/)-X)P)Cl F e ( T P C P P ) C l F e ( T P C P P C l 8 ) C l F e ( T P F P P ) C l F e C T P F P P B r ^ C l FefTPFPPF^Cl FeCrPP(CF 3)3(CF 2CF 3))Cl Fe(rPP(CF 3) 4)Cl [FeCrPP(CF3)4]20 F e ( T P P ( C N ) 4 ) C l F e ( T P P ) C l Fe(TPPBi4)Cl F e f T P P B r J C l F e t T P P F ^ C l G C h H 2 ( C F 3 ) 4 P H 2 D P P H 2 T D C P P H 2 T D C P P ( N 0 2 ) X H 2 T M P H 2 T M P B r 4 H 2 T M P B r 8 H 2 T M P C 1 4 H 2 TP(/>-X)P H 2 T P C P P CUoro[5,10,15,20-tetrakis(2,6-chcHorophenyl)porphyrmato]iron(III) CWoro[2,3J3,12,13 )17,18-octabromo-5 )10,15 )20-terj:akis(2,6-cUcMorophenyl)porphyrmato]iron(III) ChJoro[2,3,7 )8,12,13,17,18-octachloro-5,10,15,20-tetrakis(2,6-dicmorophenyl)porphyrinato]iron(III) CMom[2,3JA12,13,17,18-octafluoro-5,10,15,20-tetrakis(2,6-cUchlorophenyl)porphyrinato]iron(III) Chloro(5, l 0,15,20-tetomesitylporphyrinato)iron(III) Chloro [5,10,15,20-tetrakis (3-substituted phenyl)porphyrinato]iron(III) Chloro[5,10,15,20-tetrakis(4-substituted phenyl)porphyrinato]iron(III) CUoro[5,10,15,20-tetralds(percUorophenyl)porphyrinato] Chloro[2,3,7,8,12,13,17,18-octachloro-5,10,15,20-tettakis(percUorophenyl)porphyrmato]iron(III) CUoro[5,10,15,20-teUakis(perfluorophenyl)porphyrinato]iron( Chloro [2,3,7,8,12,13,17,18-octachloro-5,l 0,15,20-tettakis(perfluorophenylphenyl)porphyrinato]iron(III) Chloro[2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tettakis(perfluorophenyl)porphyrinato]iron(IIi) Chloro [7,8,17 -tris (trifluoromethyl) -18-pentafluoroethyl-5,10,15,20-tetraphenylporphyrinato]iron(III) Chloro[7,8,l 7,18-tetxakis(trifluoromethyl)-5,l 0,15,20-tetraphenylporphyrinato]iron(III) (u-Oxo)bis [2,3,12,13-tetealds(trifluoromemyl)-5,l 0,15,20-tetraphenylporphyrinatoiron(Iir)] Chloro(2,3,12,l 3-tetracyano-5,10,l 5,20-tetraphenylporphyrinato)iron(III) Chloro(5 , l 0,15,20-tetraphenylporphyrinato)iron(Iir) Chloro(7,8, l 7,18-tetrabromo-5,l 0,15,20-teteaphenylporp>hyrinato)iron(III) Chloro(P-polybromo-5,l 0,15,20-tettaphenyporphyrinato)kon( Chloro(2,3,7,8,12,l 3,17,18-octafluoro-5,l 0,15,20-teteaphenylporphyrinato)iron(III) Gas chromatography hour(s) 5,10,15,20-tettalds(ttifluoromemyl)po]^hyrin 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin 5,10,15,20-Tetrakis(2,6-dichlorophenyl)porphyrin p-Polynitro-5,10,15,20-tetealds(2,6-dicUorophenyl)porphyrin 5,10,15,20-Tetramesitylporphyrin 7,8,17,18-Tetrabromo-5,10,15,20-tetramesitylporphyrin 7,8,17,18-Octabromo-5,l 0,15,20-tetramesitylporphyrin 7,8,17,18-Tetrachloro-5,l 0,15,20-tetramesitylporphyrin 5,10,15,20-Tetrakis(4-substituted phenyl)porphyrin 5,10,15,20-Tettakis(perchlorophenyl)porphyrin XIV H 2 T P F P P 5,10,15,20-Tetrakis(perfluorophenyl)porphyrin H 2 T P P 5,10,15,20-Teteaphenylporphyrin H 2 TPP(CF 3 ) 2 p-Bis(tofluoromethyl)-5,l 0,15,20-teteaphenyporphyrin H 2 TPP(CF 3 ) 3 7,8,17-Tris(ttifluorornethyl)-5,l 0,15,20-tetraphenyporphyrin H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) 7,8,17-Tris(tofluoromethyl)-l 8-pentafluoroethyl-5,l 0,15,20-teteaphenylporphyrin H 2 TPP(CF,) 4 7,8,17,18-Tettakis(trifluoromethyl)-5,l 0,15,20-tetraphenyporphyrin H 2 TPP(CH 3 ) 2 P-Dimethyl-5,10,15,20-tettaphenyporphyrin H 2 TPP(CH 3 ) 3 7,8,17-Trimethyl-5,l 0,15,20-tetraphenyporphyrin H 2 T P P ( C H 3 ) 4 7,8,17,18-Tetramethyl-5,l 0,15,20-tetraphenyporphyrin [H 4 TPP(CH 3 ) 4 ] 2 + 7,8,17,18-Tetramethyl-5,l 0,15,20-tetraphenyporphyrin diprotonated dication H 2 TPP(CN) X P-Polycyano-5,10,15,20-tetraphenylporphyrin H 2 TPP(X) 2 (or 7)-X substituted 5,10,15,20-tetraphenylporphyrin H 2 T P P P h 4 R 4 2,7,12,17-Tetraphenyl-3,8,l3,18-R substituted porphyrin [H 4 TPP] 2 + 5,10,15,20-Tetraphenylporphyrin diprotonated dication H M P A Hexamethylphosphoramide H O A c Acetic acid H O M O Highest unoccupied molecular orbital HR-MS High resolution mass spectrometry Im Imidazole z'-Pr z'-Propyl LR-MS Low resolution mass spectrometry LSIMS Liquid secondary ion mass spectrometry L U M O Lowest unoccupied molecular orbital m Meta m Multiplet M e C N Acetonitrile l -Melm 1 (or N)-Methylimidazole M e O H Methanol (Me 3Si) 2NLi lithium bis(trimethylsilyl)amide rnin minute(s) MnCTDCPP^O, ) , ) P-Polynitro-5,10,15,20-tetalris(2,6-dicMorophenyl)porphyrinato manganese(II) M n f T D C P P C N O ^ C l Chloro[P-polynitro-5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato]manganese(IH) Mn(TE>CPP)Cl Chloro[5,l 0,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato]manganese(III) MnCTDCPPBr^Cl Chloro[2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tettakis(2,6-dichlorophenyl)porphyrinato]manganese(III) Mn(TDCPPF 8 ) 2,3,7,8,12,13,17,18-Octafluoro-5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinatomanganese(Ii) Mn(TDCPPF 8 )Cl Chloro[2,3,7,8,12,13,17,18-Octafluoro-5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato]manganese(IH) X V MnCTPFPPFg) 2,3,7,8,12,13,17,18-Octafluoro-5,l 0,15,20-tettalds(perfluorophenyl)porphyrmatomanganese(ir) Mn(TPPF 8) 2,3,7,8,12,13,17,18-Octafluoro-5,l 0,15,20-tetraphenylporphyrinatomanganese (II) Mn(TPPF 8 )Cl Chloto(2,3,7,8,12,13,17,18-octafluoto-5,10,15^0-tettaphenylporphyrinato)manganese(III) MS Mass spectrometry N A D H Nicotinamide adenine dinucleotide N A D P H Nicotinamide adenine dinucleotide phosphate N-alumina Neutral alumina Ni(TPPBr 4) 2,3,12,13,-Tetrabromo-5,10,15,20-tetraphenylporphyrinatonickel(ir) NBS N-Bromosuccinamide N C S N-Chlorosuccinamide N M P N-Methylpyrrolidone N M R Nuclear Magnetic Resonance 0 Ortho O A c Acetate O E P 2,3,7,8,12,13,17,18-Octaethylporphyrin ligand O E T P P 2,3,7,8,12,13,17,18-Octaethyl-5,l 0,15,20-tetraphenylporphyrinato ligand O R T E P Oak Ridge thermal ellipsoid plot O T f Triflate or trifluoromethanesulfonate P Para PFIB Perfluoroiodosylbenzene P h C N Benzonitrile PhIO Iodosylbenzene Py Pyridine pyrr-P-H pyrrolic P-protons q Quartet Rf (Distance moved by solute) / (distance moved by solvent front) in T L C r.t. Room temperature s Singlet S C E Saturated calomel electrode T Temperature T B A B F 4 Tetrabutylammonium tetrafluoroborate T B A P Tetrabutylammonium perchlorate T B A P F 6 Tetrabutylammonium hexafluorophosphate T C Q 2,3,5,6-Tetrachloroquinone T E A P Tettaethylammonium perchlorate Temp. Temperature T F A Trifluoroacetic acid T H F Tetrahydrofuran T L C . Thin layer chromatography TPP 5,10,15,20-Tetraphenylporphyrinato ligand U V Ultraviolet XVI vdW van der Waals ZnjTDCPPlNCg, ) (3-Polynitro-5,10,15,20-tetrakis(2,6-<dicUorophenyl)porphyrinatozinc(II) Zn(TDCPP) 5,10,15,20-Tetrakis (2,6-dicUorophenyl)porphyrinatozinc(Ii) Zn(TDCPPBr 8 ) 2,3,7,8,12,13,17,18-Octabromo-5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinatozinc(II) Zn(TPFPP) 5,10,15,20-Tettakis(perfluorophenyl)porphyrinatozinc(II) Zn(TPFPPBr 8) 2,3,7,8,12,13,17,18-Octabromo-5,l 0,15,20-tettakis(perfluorophenyl)porphyrinatozinc(II) ZnCTPPCCFj)^ P-Bis(ttifluoromemyl)-5,10,15,20-tetraphenylporphyrinatozinc(II) ZnCrPP(CF3)3(CF2CF3)) 7,8,17-Tris(trifluorornethyl)-l 8-pentafluoroediyl-5,l 0,15,20-tettaphenylporphyrinatozinc(Ii) Zn(rPP(CF3)3) 7,8,17-Tris(trifluoromethyl)-5,l 0,15,20-tettaphenylporphyrrnatozinc(Ii) Zn(TPP(CF 3) 4) 2,3,12,13-Tetrakis(trifluoromethyl)-5,10,15,20-tettaphenylporphyrinatozinc (II) Zn(TPP) 5,10,15,20-Tettaphenylporphyrinatozinc(II) Zn(TPPBr 4) 2,3,12,13-Tettabromo-5,10,15,20-tetophenyporphyrinatozinc(II) Zn(OMPTPP) 2,3,7,8,12,13,17,18-Octamethyl-5,l 0,15,20-Tetraphenylporphyrinatozinc(II) Zn(TPBC) 2,3,12,13-Tetrahydro-5,l 0,15,20-teteaphenylporphyrinatozinc(II) or ^wo-tetraphenylbacteriochlorinzinc^i) XVII N O M E N C L A T U R E The porphyrin core is a cyclic tetrapyrrolic system consisting of 20 carbons, four nitrogens, and two hydrogens. Porphyrins are formally derived from porphin (I) by substitution of some or all of the peripheral positions. The peripheral positions are numbered as shown in la and lb. Ia follows IUPAC (International Union of Pure and Applied Chemistry) and IUB (International IUPAC numbering system Fischer numbering system Union of Biochemistry) nomenclature. 1 There is also an alternate system of nomenclature based on the numbering system shown in lb which was developed by Hans Fischer.^ In modern porphyrin chemistry, the former system of nomenclature (Ia) is adopted to name the large number of synthetic and newly isolated porphyrins systematically. In IUPAC-IUB nomenclature (Ia), positions 1,4,6,9,11,14,16,19 are termed the pyrrolic a-positions, 2,3,7,8,12,13,17,18 are the pyrrolic P-positions and interpyrrolic methine positions 5,10,15,20 are /w.ro-posirions. For example, compound II is named 5,10,15,20-tetraphenylporphyrin or wwo-teteaphenylporphyrin. For the ligand name, porphyrin is changed to porphyrinato or porphinato as 5,10,15,20-tetealds(2,6-dicMorophenyl)porphyrinatozinc(ir) (or meso-tettakis(2,6-dichlorophenyl)porphyrinatozinc(ir;) (III). If the pyrrolic p-positions are partially substituted xvii i and no metal is coordinated to the porphyrin, the pyrrolic oc-carbon o f the pyrrole to which a hydrogen attached is numbered first. Fo r example, compound IV is 7,8,17,18-tetrabromo-5,10,15,20-tetraphenylporphyrin (or 7,8,17,18-tefjrabromo-^j-o-tettaphenylporphyrin). W h e n a metal is coordinated, the pyrrolic a-carbon o f the pyrrole with substituents on the pyrrolic P-position is numbered first as 2,3,12,13-tetramemyl-5,10,15,20-tettaphenylporphyrinatozinc(II) (or 2,3,12,13-tetomemyl-^jo-tetraphenylporphyrinatozinc(l])) (V). XIX A C K N O W L E D G E M E N T I would like to express my sincere gratitude to Professor David Dolphin for his guidance, patience and encouragement throughout my entire research work. I also wish to take this opportunity to thank members of Dolphin's lab for an enjoyable working environment. Special thanks to Dr. Alison Thompson, Dr. Ethan Sternberg, and Dr. Elizabeth Cheu for proofreading sections of this thesis. Especially, without Dr. Thompson's encouragement, I could not have ' continued my writing. I would like to thank Professor Brian James for allowing me to use the cyclic voltammetry apparatus in his lab. Thanks also to Dr. Ian Baird for showing me how to use the apparatus. I also would like to thank Dr. Nick Burlinson for taking the time for his advice and helpful discussions about N M R spectroscopy. Thanks also to Ms. Marietta Austria and Ms. Liane Darge for taking nice N M R spectra and for teaching me how to use the N M R machines, to Mr. Peter Borda in the microanalysis lab, Drs. Steve Rettig and Brian Patrick in the X-ray crystallography lab, staff in the Mass Spectrometry lab for their technical support, and to Mr. Brian Ditchburn in the glass shop for making the electrochemical cell. Thanks also to those people, over the years, who made it an enjoyable experience for me to work in the department of Chemistry at UBC. Special thanks to Dr. Yoshikata Koga for his encouragement and to Drs. Alavi Saman and Mari Kono for their friendship and memorable time in Vancouver. I am also very grateful to Professor Akinori Jyo at Kumamoto University, Japan, who introduced to me a fascinating realm of chemistry. Last, I would like to thank my wife Miyuki whose smile and patience were essential to completion of this thesis. 1 CHAPTER I I n t r o d u c t i o n A. Introduction Hemoproteins perform vital functions in nature. These include molecular oxygen transport and storage-^, electron transfer^, molecular oxygen activation^, a n c j the metabolism of organic intermediates. 10-12 "T^Q prosthetic group for most hemoproteins is the protoporphyrin IX Fe complex (Figure 1-1), despite the varying functions of this family of proteins. 13,14 'pj i e presence of the protoporporphyrin IX skeleton within various hemoproteins of different function is intriguing and many model studies using synthetic porphyrins have been performed in attempts to identify the mechanism of action of hemoproteins. 1 Figure 1-1. Protoporphyrin IX Fe complex. Synthetic porphyrins used in model studies of hemoproteins have been prepared using design strategies involving both structural and electronic modifications. Early examples of structurally modified porphyrins used in the model studies of hemoglobins and myoglobins include sterically hindered derivatives!5-17 w n i i e recent examples have explored non-planar derivatives.!8-20 s m d y of nonplanar porphyrins is motivated by the hypothesis that fine-tuning of the porphyrin macrocycle conformation by the protein scaffold of hemoproteins is one way that nature might use to control the functions of prosthetic groups in tetrapyrrole-protein complexes. 18,19,21 -24 Electronically modified porphyrins incorporating strong electron-withdrawing substituents form a class called "electron-deficient porphyrins" (Figure 1-2). Strictly speaking, the term "electron-deficient" refers to compounds for which full octets are not achieved in the Lewis R 2 R 1 R 2 R 1 = Aryl, C n F 2 n + 1 R 2 = F, CI, Br, N 0 2 M = 2 H + , Zn(II), Fe(III)Cl, Mn(IU)Cl R 2 R1 R 2 Figure 1-2. Examples of electron-deficient porphyrins. structure25 (e.g. B 2 H 6 ) . However, the term is arbitrarily used in the literature to refer to porphyrins in which the electron density of the macrocycle has been lowered by the presence of strong electton-withdrawing substituents. Many electron-deficient porphyrins have been reported, largely as a result of studies directed towards the determination of the ability of their metal complexes (such as Cr(III), Mn(III), or Fe(III)) to mimic cytochrome P-450.26-28 Cytochrome P-450 enzymes include the protoporphyrin LX Fe(III) complex and are responsible for O z activation and oxygen atom transfer (oxygenation) in substrates witiiin biological systems.^ Biological oxygenation has attracted much attention because the biological systems perform selective oxidation under mild reaction conditions using the abundant oxidant 0 2 and release water only as a by-product.13,14 Besides P-450, enzymes methane monooxygenase and copper oxygenases such as phenylalanine hydroxylases or tyrosinase are also known as enzymes that catalyze oxygen transfer in substrates utilizing O z and model studies have been continued in order to understand the mechanisms of the enzymes. 13,14 Elucidation of the mechanisms may potentially aid in the development of useful transition metal catalysts for both fundamental and industrial chemistry. In fundamental developments some potentially useful metal complexes that are not derived from biological systems have also been introduced and studied as oxidation catalysts.29 The most successful examples are Mn(III) complexes of derivatives of salen (Figure 1-3).^,31 The catalytic system with the complexes formed the basis for the development in asymmetric catalytic epoxidation using iodosylbenzene or NaOCl. In industry, some important organic intermediates have been synthesized by catalytic oxidation. For example, oxidation of ethylene to ethylene oxide using A g O or propene to acrolein using B i 2 M o O e as the catalysts is the worldwide known oxidation processes.32 Figure 1-3. Example of salen Mn(III) complex 4 Oxidation by biological systems is much more sophisticated than such industrial processes in terms of the range of the substrates and the reaction conditions. 13,14 In spite of these advantages, porphyrins have not been used in industry, although potential commercial applications of some of the metalloporphyrin systems have been shown.^3 The major reasons for this are probably cosdy preparation and instability of the metalloporphyrins in catalytic oxidations. However, successful development of a system potentially derived from biological systems such as P-450 is still in strong demand for fine, economical, and environmentally friendly chernistry.26,29 Thus, porphyrins have been the major subject in catalytic oxidations for years. In particular, electron-deficiency has been thought to be essential for mimics for P-450 enzymes in order to acquire efficiency and robustness of catalysts34-48 a n c j fae s e arch for a "perfect" P-450 mimic continues, as described in chapter I of this thesis. This thesis documents the synthesis and investigation of the properties of some novel electron-deficient porphyrins. In particular, the design, synthesis and electronic properties of p-trifluoromethyl-«?^o-tetraphenylporphyrins will be discussed, in relation to their potential application as cytochrome P-450 rnirnics. The first part of Chapter I is a review of the development of electron-deficient porphyrins as P-450 mimics, followed by the discussion of design strategies employed for the preparation of novel P-tafluoromediy-^j-o-tetraphenylporphyrins. The remaining part of this chapter is a review of the various analytical methods applicable for the characterization of porphyrins and the evaluation of electron deficiency within the porphyrinogenic macrocycle. 5 B . Metalloporphyrins as cytochrome P-450 model compounds /. Cytochromes P-450 a. Distribution, nomenclature, and structure Cytochromes P-450 (P-450s) are intercellular proteins with molecular weights between 50 prosthetic group. ' P-450s are widely distributed in nature from bacteria to mammals. ' It was found that reduction o f the Fe(III) form o f a P-450 enzyme to its Fe(II) state, followed by coordination o f carbon monoxide results i n the formation o f an intense absorption band with a maximum at about 450 n m in the optical spectrum.49 This phenomenon led Omura and Sato to name this type o f substance P-450 (a pigment that absorbs light at and 60 k D . ' >^ They contain protoporphyrin I X Fe(III) complex (often called "heme") as the 450 n m ) - 4 9 Tyrosine Phenylalanine Cysteine Figure 1-4. Ac t ive site and hydrophobic pocket o f cytochrome P -450 c a m . D a r k atoms show hydrogen bonding (a), hydrophobic interaction (b), and coordination sphere o f the heme (c). Adapted from reference 13. To date, several P-450 structures are known and it has been shown that all stmcture-determined P-450s share a common protein fold.50 Thus, the heme is buried in the hydrophobic pocket of the protein structure and is coordinated to the thiolate ligand of a terminal cysteine moiety.^, 14,50 The heme-thiolate ligand environment is highly conserved in all P-450s, whatever the exact function of particular enzymes.^ Figure 1-4 shows the X-ray crystal structure of the active site of camphor bound cytochrome P-450cam.51 The protoporphyrin IX Fe(III) complex, the axial thiolate ligand, and the bound camphor as a substrate can been seen within this protein structure. b. Function and mode of action P-450s play an essential role in the metabolism of endogenous substances (e.g. steroids) and in the detoxification and degradation of substances in animals, plants, and bacteria. 13,14 P-450s catalyze the oxidation of organic substrates by molecular oxygen in cooperation with reducing agents ( N A D H , flavoprotein and iron-sulfur proteins). 14 As shown in equation (1.1a), alkanes are oxidized to alcohols^ and alkenes are oxidized to epoxides (1.1b), by action of P-450 catalysis. Similar catalysis is effected by synthetic Fe(III) and Mn(III) porphyrins. ^ 3 R C H 2 - H + 0 2 + 2 H + + 2e" • R C H 2 - O H + H 2 0 ( l . la) X> (!' lb) Figure 1-5 shows the currendy accepted mode of action of P-450s.l3>14 c a talyti c cycle is initiated by incorporation of a substrate molecule (RH) into the hydrophobic pocket of the protein where the heme-thiolate complex is located. This is accompanied by concomitant loss of a water molecule from the hexa-coordinate Fe(III) complex (T). This step results in a = [protoporphyrin IX]2' S"-Cys Figure 1-5. Catalytic cycle of cytochrome P-450. 8 penta-coordinate complex (2) wi th high-spin Fe(III). A n electron donated by N A D P H is transferred to the complex via electron-transfer systems such as flavoprotein or iron-sulfur proteins and reduces (2) to the high-spin penta-coordinate Fe(II) complex (3). This complex subsequendy binds 0 2 to form the low-spin oxy Fe(II) complex (4). The F e ( I I ) / 0 2 moiety is possibly modified to F e ( I I I ) / 0 2 i n (5). The one-electron reduction o f (5) forms the low-spin peroxo Fe(III) complex (6). T w o protons add to this species and one molecule o f water is released. Thus cleavage o f the O - O bond results i n the oxo Fe(rV) porphyrin cation radical (7), which reacts with the hydrocarbon substrate to yield an alcohol (or an epoxide when an olefin is incorporated). The heme returns to the resting form (1) after the coordination o f water. A s indicated i n Figure 1-5, the cycle can be bypassed (via a "shunt path") by adding oxygen donors ( X - O ) such as iodosylbenzene. Since P-450s can catalyze the cleavage o f strong C - H bonds i n hydrocarbons (e.g. 400 k j / m o l for cyclohexane)54 under ambient conditions, chemists have been intrigued to mimic the remarkable function o f these enzymes using synthetic metalloporphyrins. It should be noted that no simple (i.e., non-enzyme) complex o f Fe(III) has been described which really can use /-alkyl hydroperoxides to mimic a monooxygenase (i.e., P-450 like) catalyzed oxidation o f alkanes.55 c. Mechanisms of hydrocarbon oxidation (1) Mechanism of alkane hydroxylation Figure 1-6 shows a general scheme for the cytochrome P-450 catalyzed hydroxylation o f alkanes. A s discussed in the previous section, the oxo Fe(IV) porphyrin cation radical is the active species. The mechanism is considered to occur first by hydrogen atom abstraction from the substrate followed by rapid transformation o f the metal-bound hydroxy radical to an intermediate alkyl radical. T h e n combination o f the hydroxy radical wi th alkyl radical forms the alcohol and the porphyrin returns to the resting s t a t e d Format ion o f the side product is also shown i n Figure 1-6; escape o f the alkyl radical from the cage o f the transition state, initiates a radical chain autoxidation that produces ketone.56 O / - T l < * R " H * R ,H Fe(lll)J) + ROH alcohol escape •R O , = porphyrin 71 cation radical R-H = alkane - • R O O * t ketone Figure 1-6. Mechanism o f alkane hydroxylation by cytochrome P-450. (2) Mechanism of alkene epoxidation Mechanisms for epoxidation by P-450s are more complicated than that for hydroxylation.53,57 Figure 1-7 (p. 10) shows a unified mechanism for the epoxidation o f olefins by cytochrome P-450 summarized from the literature.58~61 Firstly, the charge transfer complex (1) is formed. This complex then collapses to the carbocation complex (2) by electrophilic addition o f the oxo Fe(rV) porphyrin 71-cation radical to the olefin. R ing closure o f (2) forms the epoxide (3) and Fe(III) porphyrin. Several side products are also formed. Hydride and group migration results i n the aldehyde (4) and the ketone (5) respectively. In each side-reaction Fe(III) porphyrin is generated. N-Alky la t i on to give (6) and iron-carbon bond formation to give (7) can also occur. Al though the major product is always the epoxide (3), the 10 extent of each of the alternative pathways depends on the individual porphyrins and substrates.53 ^ R o R R 6 R R + o epoxidation R R O R R H migration • o Fe(l l l ) R R O R - + R R migration O R Fe-C bond formation R R Figure 1-7. Mechanism of the oxidation of olefins by cytochrome P-450 or metalloporphyrins. 11 2. Synthetic metalloporphyrins as P-450 mimics a. Structures of porphyrins that appear in this section In order to proceed, the major porphyrins that appear i n section B.2.b are shown i n Figure 1-8. Section B.2.b. documents the investigation o f synthetic porphyrins and metalloporphyrins as P-450 mimics. Porphyrin R i r ) R 2 M ( T P P ) (2) phenyl H M ( T M P ) (3) mesityl H M ( T P F P P ) (4) perfluorophenyl H M ( T D C P P ) (5) 2,6-dichlorophenyl H M ( T P C P P ) (6) perchlorophenyl H M f r P P B r g ) (7) phenyl B r M(TPFPPBrg ) (8) perfluorophenyl B r M f T D C P P B r g ) (9) 2,6-dichlorophenyl B r M f T D C P P C L ) (10) 2,6-dichlorophenyl CI M ( T P C P P C 1 8 ) (11) perchlorophenyl CI M ( T P P F 8 ) (12) phenyl F M ( T D C P P F 8 ) (13) 2,6-dichlorophenyl F MCTPFPPFs) (14) perfluorophenyl F M C T D C P P C N O ^ f l S ) 2,6-dichlorophenyl N 0 2 or H M ( C n F 7 n + 1 ) 4 P (16) C F ^ n 1 2n+l H (a) M = 2 H ; (b) M = Zn(II); (c) M = Cu(H); (d) M = Fe(III)Cl; (e) M = Fe(II); (f) M = Mn(I I I )Cl ; (g) M = Mn(II) Pmeso PmeSO'. meso-rposixion o f porphyrin ** Catalogue for R 1 aryl groups R 1 R 3 R 4 R 5 phenyl H H H mesityl C H 3 H C H 3 perfluorophenyl F F F 2,6-dichlorophenyl CI H H perchlorophenyl CI CI CI Figure 1-8. Porphyrins used i n P-450 mode l studies. 12 b. Synthetic methods for the major players in the early development of PA 50 mimics (1) Condensation of pyrrole with arylaldehydes Porphyrins used in early P-450 model studies were symmetric and easy to prepare,-^ via the condensation of equimolar quantities of pyrrole (or a 3,4-disubstituted pyrrole) and an arylaldehyde, followed by oxidation. 62-67 This strategy was originally used by Rothmund, who reacted pyrrole and benzaldehyde in pyridine in a sealed flask at 150 °C for 24 h to yield «?MO-tetraphenylporphyrin (H 2TPP) (2a) in about 3% yield.°2 The yield was improved up to 40 % by Adler, Longo and coworkers who carried out the reaction in propionic acid or acetic acid open to the air (Scheme 1-1 Path y4).63,64 Reasoning that porphyrin is formed via the formation of porphyrinogen (17)65, o N C II O P a t h / * Propionic or acet ic acid/air Path B H + Scheme 1-1. Synthesis of wwo-tetraarylporphyrins. Lindsey et al. revised the method devised by Rothmund, and Adler-Longo.66 The Iindsey method (Scheme 1-1 Path 13)66 j s a two-step one-pot procedure whereby the pyrrole and the 13 aldehyde are condensed with a catalytic amount of acid under anaerobic conditions to form porphyrinogen, which is subsequently oxidized to porphyrin by an oxidant such as 2,3,5,6-tetrachloro-quinone (TCQ) or 2,3-clicMoro-5,6-dicyano-quinone (DDQ). The initial reaction is carried out in a chlorinated solvent such as CH 2 C1 2 or CHC1 3 at room temperature for about 1 h before the oxidant is added. One drawback relating to this method is the rather low reaction concentrations (as low as 10"2 M ) . 6 6 However, the mild reaction conditions of this method have allowed the synthesis of WOT-tetramesitylporphyrin (H 2 TMP) (3a), «?&ro-tetrakis-(perfluorophenyl)porphyrin (H 2TPFPP) (4a), ^j-o-tetralds(2,6-dicruorophenyl)porphyrin (H 2 TDCPP) (5a), and OTWo-tettaltis(perchlorophenyl)porphyrin (H 2TPCPP) (6a) (see Figure 1-8, p. 11)67 w n 0 s e syntheses and isolation had not been possible by the Rothmund or Adler-Longo methods. 6 3 - 6 4 Metallation of porphyrins to give metalloporphyrins is generally achieved by the reaction of porphyrin with a metal salt under various conditions.6^>6^ Thus, access to Fe(III) or Mn(III) complexes of porphyrins 2-6 that were important for P-450 model studies became possible. (2) /3-Perchlorinated andperbrominated meso-arylporphyrins (3-Octachloro and P-octabromo-tettaarylporphyrins cannot be synthesized by condensation of 3,4-dichloro- or 3,4-dibromopyrrole and aryl aldehydes due to the difficulty incurred in preparation of the requisite 3,4-dihalopyrroles.^^ Direct chlorination and bromination of the P-pyrrolic positions of porphyrins have been reported to be extremely efficient to effect structural and electronic modifications of tetta-arylporphyrins (Scheme 1-2).^ 0 p-Chlorination^l -^4 and bromination34,44,71,75-77 D f metallated porphyrins can be achieved using various cMorinating (Cl2, N-chlorosuccinamide (NCS)) and brominating (Br2, 14 N-bromosuccinamide (NBS)) reagents in numerous solvents (CHC13, CC14, C 2 H 2 C1 4 and MeOH). Metallation of porphyrins prior to this reaction is necessary in order to complete P-halogenation.^O As shown in Table 1-1, yields for P-halogenation are generally high. Due to the ease of synthesis, and their unique characteristics, halogenated porphyrins have been extensively studied as P-450 mimics. X = Br and CI Scheme 1-2. P-Halogenation of OTWo-tetraarylporphyrin. Ar = phenyl, mesityl, perfluorophenyl, 2,6-dichlorophenyl, perchlorophenyl, M = Ni(II), Cu(II), Zn(II), Mn(III)Cl and Fe(III)Cl. Table 1-1. Yields of typical P-perhalogenation reactions. Starting porphyrin P-halogenated Yield (%) Reference Cu(TPP) (2c) Cu(TPPBr 8) (7c) 75 75 Zn(TPFPP) (4b) Zn(TPFPPBr 8) (8b) 60-80 78 Zn(TDCPP) (5b) Zn(TDCPPBr 8 ) (9b) 71 34 Fe(TPCPP)Cl (6d) Fe(TPCPPCl 8)Cl (lid) 85 73 c. Early development of P-450 mimics In 1979 Groves et al. investigated the oxidation of several hydrocarbons using a synthetic porphyrin, Fe(TPP)Cl (2d) (Figure 1-8, p.11), as catalyst and iodosylbenzene (PhIO) as oxidant 15 and demonstrated the P-450-like catalytic activity of the metalloporphyrin via a "shunt path" mechanism.79 For example, cyclohexene and cyclohexane were converted into cyclohexene oxide (55 %) and cyclohexanol (8 %) respectively.^ This original work pioneered model studies towards the investigation of other metal complexes of TPP (such as 1 (^111)80,81^ Cr(III)825 Q r Ru(VI)83)) the effect of basic axial ligands84-87; the effect of oxygen donors88-915 a n c j u s e Q f 0 2 as oxidant in the presence of a coreductant (such as N a B H 4 or Zn(Hg) for Fe(III/II) reduction to mimic the natural P-450 oxidation process.92-95 Although the TPP-based catalysts (first-generation catalysts) were relatively effective mimics of P-450 reactions, there was a problem in that their catalytic activity was rapidly decreased by oxidative degradation of the metalloporphyrins.26-28 Since the oxidative degradation of metalloporphyrins is known to occur readily at the meso ring position^^^ protection of this position became an important goal for the improvement of catalytic activity. Two approaches were developed for the protection of the ^jo-positions; protection of the meso-X50%\Xuor\s> from the oxidant by bulky adjacent groups-^ and the introduction of strong electton-withdrawing groups, which is also important to obtain an active metal center.99 Groves et al. showed that Fe(TMP)Cl (3d) (Figure 1-8, p.11) can resist, to some extent, oxidative degradation due to the steric effect of bulky mesityl groups at the wwo-positions.98 Also, Chang and Ebina carried out the epoxidation of cyclohexene with an electron-deficient, Fe(TPFPP)Cl (4d) (Figure 1-8) and PhIO as oxidant and obtained cyclohexene oxide in 95 % yield.99 When both steric bulk at the Wcvo-positions and electton-withdrawing groups are combined witiiin a wwo-arylporphyrin, catalytic behavior is improved tremendously. In 1984, Traylor et al. reported a turnover (mole of product/mole of catalyst) of 10,000 and 85 % yield in 16 the epoxidation of norbornene using Fe(TDCPP)Cl (5d) (Figure 1-8) and pentafluoroiodosylbenzene (PFIB) as oxidant. These improved metalloporphyrins, 3d, 4d, and 5d, are called second-generation catalysts.26,28 Although the second-generation catalysts effectively catalyze the epoxidation of alkenes, the oxidative degradation of these Fe(III) porphyrins is still noticeably severe during alkane hydroxylation.28 J N a n attempt to synthesize more robust catalysts, perhalogenation at the p-pyrrolic positions was performed to give third-generation catalysts. The first third-generation catalyst, Fe(TDCPPBr 8 )Cl (9d) (Figure 1-8) was reported by Traylor and Tsuchiya in 1987. 3 4 In 1990, three more third-generation catalysts, FeCTPFPPBr^Cl (8d)44(Figure 1-8), Fe(TDCPPCl 8)Cl(10d) 7 3(Figurel-8) and FeCTPCPPCkJCl (lid)7 3(Figure 1-8) were reported. These metalloporphyrins are much more electron-deficient compared to the first and the second generations, as a result of P-Br and CI substituents. This can be appreciated by consideration of the Fe(III/II) redox potentials of the iron porphyrins. For example, the Fe(III/II) redox potential of l id is positively shifted by 0.64 V from that of Fe(TPP)Cl (2d) (Figure 1-8).73 The effects of electron-withdrawing substituents were further investigated due to the ready synthesis of these highly electron-deficient porphyrins (section B.2.a.(2). in this chapter) and resulting increase in catalytic activity.26-28 d. Electron-withdrawing effects on catalytic activities Before we move into this subject, we should keep in mind that investigations of catalytic oxidation are normally conducted in the presence of excess substrate. Therefore, for example, oxidation of alkane is forced to cease at the formation of alcohol, and alcohol to ketone by catalysis is not a competing reaction. We should also keep in mind that the detailed reaction 17 conditions such as reaction media, mole ratio of reactants, or oxidants are different from one report to another, which makes direct comparison of product yields between different experiments very difficult. Thus, the comparison of the catalysts should be done within experiments performed under the same conditions. Traylor et al. studied the hydroxylation of cyclohexane and norbornane using Fe(TDCPPBr 8 )Cl (9d) (Figure 1-8) and PFIB as oxidant. 101 The yield of cyclohexanol was 93% based on the consumed PFIB with a high ratio of alcohol to ketone (37/1). The hydroxylation of cyclohexane using Fe(TPP)Cl (2d) (Figure 1-8) and PhIO gave an alcohol to ketone ratio of 12/1.52 As explained in section B.l.c.(l)., formation of the ketone side product results from the escape of the alkyl radical from the cage of the transition state.-^ In other words, the oxo Fe(TV) porphyrin 7t-cation radical obtained from electron-deficient 9d is more reactive than that formed from 2d and thus gives the alkyl radical less opportunity to escape from the cage. 101 The hydroxylation of norbornane with 9d and PFIB gave the corresponding alcohol in 82 % yield with much higher selectivity for alcohol (alcohol to ketone > 99/1).101 Traylor et al. also investigated the reactivity of the oxo Fe(rV) porphyrin 7t-cation radical towards the bond cleavage of / -BuOO-H and alkene epoxidation (Figure 1-9). 102,103 jt l s necessary to prevent the side reaction (Path B) in order to obtain a high yield of epoxide (Path A) using A B u O O H as an oxygen donor (Figure 1-9). The value o£kA/kB, where kA = rate of epoxidation and kB = rate of /-BuOO' formation, indicates selectivity for the epoxidation (Path A). When Fe(TMP)Cl (3d) (Figure 1-8) was used as a catalyst, kA/kB = 0.01 for cyclic alkenes andABuOOH, while kA/kB > 1 with Fe(TPFPP)Cl (4d) (Figure 1-8) and FefTDCPPBr^Cl (9d) 18 (Figure 1-8) as the strength o f the electron-withclrawing substituents was increased. 103 Moreover, the rate o f metalloporphyrin destruction was also decreased. 102 (Path A) alkene CI O \ P P I R Q F e ( l l l ) J ) >• ( Fe(IV) 7^) = porphyrin dianion i-a = porphyrin 71-cation radical epoxide (Path S) f-BuOOH f-BuOO • Figure 1-9. Reaction o f oxo Fe(IV) porphyrin 7t-cation radical wi th alkene and ^ - B u O O H . Bartol i et al. compared the effectiveness o f Fe(III) porphyrin catalysts (5d and lOd) (Figure 1-8) i n the hydroxylation o f heptane using PhIO.40 The total yields (heptanols + heptanones) by 5d, and lOd were 36 and 80 % , respectively. The regioselectivities for the position o f hydroxylation (2, 3, and 4 positions o f heptane) were 58:30:12 (positions 2:3:4) for 5d and 43:40:16 for lOd. Higher reactivity o f the oxo Fe(TV) porphyrin 7T.-cation radical o f the more electron-deficient metalloporphyrin 10b leads to lower regioselectivity o f hydroxylation. Carrier et al. showed that hydroxylation o f anisole wi th M n ( T D C P P ) C l (5f) (Figure 1-8) and H 2 O z as an oxygen donor gives ^wra-hydroxyanisole with 95 % regioselectivity and i n 50 % yield, while wi th M n ( T D C P P B r 8 ) C l (91) (Figure 1-8) 75 % regioselectivity occurs and 70 % yield o f hydroxyanisole obtained.^ 0 These results can similarly be explained by the higher reactivity o f the third-generation catalyst 9f compared to the more electron rich 5f. Ell is and Lyons reported the oxidation o f isobutane using Fe(III) porphyrins and molecular oxygen without the requirement for a coreductant.44,45 F e ( T P F P P B r 8 ) C l (8d) (Figure 1-8) catalyzed the oxidation o f isobutane to /-butanol more efficiently than the second-19 generation catalyst F e ( T P F P P ) C l (4d) (Figure 1-8) in terms o f the product yield and turnover.44,45 -ph e u s e Q f resulted in the formation o f Abutanol wi th greater than 90 % selectivity and a total turnover o f 12,000. The catalytic activity o f 8d was maintained for 74 h. Table 1-2 shows the Fe(III)/(H) redox potentials and catalytic activities (turnovers) observed for the oxidation o f isobutane with Fe(III) porphyrins o f different generations, and electronic properties, under identical condition.45 Electron-deficiency is reflected by the positively shifted Fe(Iir)/(II) redox potentials o f the second and the third-generation catalysts, (4d and 8d) respectively. It was believed that catalytic activity could be mapped by an increase o f the Fe(III)/ (II) redox potentials, highlighting the inherent relationship between electron-deficiency and catalytic activity o f the metaUoporphyrin.45 Table 1-2. Relationship between catalyst i ron redox potentials and activities/ Catalyst F e ( I I I ) / ( I I ) , E 1 / 2 ( V ) b Tota l turnovers 0 Fe(rPP)Cl (2d) -0.221 0 F e ( T P F P P ) C l (4d) +0.07 1160 F e C T P F P P B r ^ C l (8d) +0.19 1800 aRef.45. b Cyc l i c voltammetry i n C H 2 C 1 2 vs. S C E . Supporting electrolyte; tetrabutylammonium perchlorate ( T B A P ) . c M o l e o f product /mole o f catalyst for the oxidation o f isobutane i n benzene at 60°C. El l is and Lyons proposed a mechanism to rationalize the oxidation o f isobutane by the catalyst and 0 2 alone (Figure 1-10).44,45 ' p i u s mechanism includes three key assumptions; (i) due to the positively shifted i ron redox potential, Fe(II) is produced by homolytic cleavage o f Fe(f f l ) -Cl (1), (ii) after the successful binding o f 0 2 to give (2), formation o f the u—peroxodimer (3) and then the catalytically active oxo Fe(TV) porphyrin (4) occurs which then oxidizes the substrate, via H abstraction and a ' O H rebound mechanism (6), (iii) due to the bulky 20 Figure 1-10. Catalytic cycle for isobutane hydroxylation by 0 2 and 8d proposed by Ellis and Lyons. Reference 44 and 45. 21 and severely distorted porphyrin structure, formation of the ^-oxodimer (5), which is catalytically inactive^ 04,105^ i s suppressed. The experimental data obtained, and the mechanism described by Ellis and Lyons, was extremely interesting since it involves the least expensive oxygen atom source, 0 2 , as the oxidant. 106 In fact, subsequent studies revealed that Fe^TPFPPBrg) (8e) (Figure 1-8) is extremely stable and binding of oxygen to this species is unlikely. 104,107 Grinstaff etal.^^ showed that an alternative radical-chain autoxidation mechanism is operative in the experiments carried out by Ellis and Lyons.44 Additionally, Bottcher et al. showed that molecular modeling based on a radical-chain autoxidation mechanism fit well with the catalytic activities of 8d (Figure 1-8) in alkane hydroxylation using O2.104 The role of 8d in a radical-autoxidation mechanism was thought to involve the decomposition of alkyl hydroperoxide. 104,107 j n o m e r words, electron-deficient porphyrin 8d is a very efficient catalyst for hydroperoxide decomposition and, therefore, oxidation. In summary, metalloporphyrins substituted with bulky and/or electron-withdrawing substituents are much more efficient and robust catalyst than unsubstituted metalloporphyrins. Investigations regarding the relationship between electron-deficiency and catalytic activity or robustness is still an active area in P-450 mimic research.42,43,47,48 The next section of this thesis will further discuss the effects of the introduction of electron-witlidrawing substituents onto the periphery of metalloporphyrin macrocycles. 22 e. Newer generation of electron-deficient porphyrins (1) (5-Verfluoro-meso-tetraarylporphyrins (a) Synthesis Direct fluorination of Zn(TPFPP) (4b) (Figure 1-8) using C o F 3 or AgF in CH 2 C1 2 was reported in 1989^8 D U t this method has not been utilized by others because it is itreproducible.28 Recent successful synthesis of 3,4-difluoropyrrolel09 has enabled the synthesis of (3-octafluoro-tetraarylporphyrins (12-14) (Figure 1-8) by condensation of the 3,4-difluoropyrrole and aryl aldehydes. 3 6- 4 1 > 4 3 Metallation using Mn(II) gave MnfTPPF^Cl (12i), Mn(TPPF 8) (12g), MnCTDCPPF^Cl (13f), and MnfTDCPPFg) (13g). MnfTPFPPFg) (14g) (Figure 1-8) was the only manganese species obtainable for 14 due to the strong electron-withdrawing effect of the substituents. Normally Mn(III) is the most stable oxidation state in M n porphyrin chemistry but Mn(II) porphyrin can be isolated as a stable compound due to the high electron-deficiency of porphyrin ligands 13 and 14 . 4 3 Fe(III) porphyrins of 12-14 were also synthesized.4^ (b) Robustness test Porhiel et al. evaluated the robustness of iron and manganese complexes towards oxidative degradation of 12-14 by observing the decrease in Soret absorption (see section D.l.a. for a description of the use of UV-vis absorption spectroscopy for the study of porphyrins and metalloporphyrins) in the presence of oxidants PhIO and H 2 0 2 in the absence of substrate . 42,4-3 Oxidative degradation of the metalloporphyrins would inevitably result in a decrease in the intensities of the UV-visible absorption band. Thus, UV-visible spectroscopy provides an ideal method for determination of the robustness to oxidation of the potential catalysts. 23 FeCTPPFgJCl (12d), FefTDCPPF^Cl (13d) and FefTPFPPF^Cl (14d) (Figure 1-8) were less stable to oxidation than the second-generation catalysts Fe(TPFPP)Cl (4d) and Fe(TDCPP)Cl (5d) (Figure l-8).42 Interestingly, 14d, which is the most electron-deficient species based on the porphyrin ring redox potential of zinc derivatives (the first ring oxidation potential for ZnfTPFPPFg) (14b) (Figure 1-8), 1.70 V vs. SCE; for Zn(TPP) (2b) (Figure 1-8), 0.80 V vs. S C E in CH 2 C1 2 ) 3 6 ; w a s the least robust towards oxidative degradation when comparing 12d-14d, 4d, and 5d.42 The manganese complexes Mn(TPPF 8 )Cl (121), Mn(TPPF 8) (12g), MntTDCPPF^Cl (13f), Mn(TDCPPF 8 ) (13g) and Mn(TPFPPF g) (14g) (Figure 1-8) with PhIO as oxidant showed similar stability towards oxdative degradation to that of Mn(TPFPP)Cl (4f) and Mn(TDCPP)Cl (5f) (Figure 1-8). With H 2 0 2 as oxidant, 12f, g and 13f, g were less stable than 2f, 4f and 5f. Metalloporphyrin 14g remained as the Mn(II) species even in the presence of H 2 0 2 , suffering no oxidation.42 It is reasonable to expect that a higher ring oxidation potential of a porphyrin ligand would be advantageous to increase the stability of the porphyrin catalyst to oxidation but these results suggest that the presence of strong electron-withdrawing groups is not always accompanied by robustness and high activity of the corresponding catalyst. (c) Oxidat ion studies Hydroxylation of cyclohexane and epoxidation of cyclooctene with iron complexes 12d - 14d and PhIO in CH 2 C1 2 gave similar results to those found using 4d and 5d as catalysts ie 10-30 turnovers/1.5 h for both substrates. However, the oxidation of cyclooctene with 12d — 14d and H 2 0 2 was found to be less successful (3-4 turnovers) than with 4d and 5d (10-60 turnovers).42 These results concur with the results of the robustness test. Interestingly, 14d was 24 the only compound that catalyzed the hydroxylation o f benzene to phenol, which is more difficult than hydroxylation o f an alkane i n terms o f the C - H bond cleavage ( C - H bond energy is 400 k j / m o i for cyclohexane and 464 k j / m o l for b e n z e n e ) ^ wi th 2 turnovers in the presence o f H 2 0 2 . 4 2 This may imply that the oxo Fe(TV) porphyrin 7t-cation radical formed from 14d is reactive towards the strong C - H bond o f benzene, but oxidative destruction o f itself is extremely competitive due to its high reactivity. Cyclohexane oxidation with manganese complexes 13f, g and 14g, wh ich feature both electton-withdrawing groups at the /#£fo-positions and electron-withdrawing fluorine substituents at all o f the P-positions, and P h I O i n C H 2 C 1 2 resulted in 10 - 30 % yield (cyclohexanol + cyclohexanone). There was little improvement from the oxidation o f cyclohexane with 4f and 5f, which do not have P-substituents. The oxidation o f cyclooctene with 13f, g and 14g and H 2 0 2 i n C H 2 C 1 2 / C H 3 C N ( 1 / 1 ) d id not give epoxide, while 4f and 5f yielded epoxide i n 69 % and >98 % , respectively. (d) C o n c l u s i o n F r o m the results shown above, Porhiel et al. concluded that instability towards oxidative degradation and low catalytic activities o f p-octafluoro-wwo-tettarylporphyrins might arise from the combination o f catalyst susceptibility to nucleophilic attack, potential oxidative decomposition o f the metal oxo species, and extremely stable low oxidation metal state (e.g. Mn(ir)).42,43 Evidently, the introduction o f strong and plentiful electton-withdrawing groups per se does not result i n effective P-450 mimic catalysts. 25 (2) B-Nitro-meso4etrakis(2,6-dichlorophenyl)porphyrins (a) Synthesis Ozette et al. have reported the syntheses of fj-polynitroporphyrins and the positively shifted reduction potential of Zn(II), Ni(II)37,110 a n ( j Mn(II)lll complexes of $-mSio-meso-tetrakis(2,6-dichlorophenyl)porphyrins (15). The reaction scheme for the synthesis of 15 is shown in Figure 1-11. Titration of Zn(TDCPP) (5b) with red fuming H N O J - C F J S O J H - ^ S O ^ O (1:0.12:0.06) selectively produces Z n ^ D C P P ^ O ^ J (15b) according to the amount of nitrating agent used. The yields are 78, 90, 86, 93, 80, 95, 90, and 50 % for 15b with x = 1,2,3,4,5,6,7, and 8 respectively.37 The Zn(II) complexes, 15b (x = 1 - 8) can be demetallated with acid to obtain free-base 15a, which is subsequendy reacted with manganese(Ii) acetate to obtain M n complexes. M n complexes bearing one to four P-nitro groups can be converted to M n f T D C P P f N O ^ C l (15£ x = 1 - 3) by treatment with gaseous HC1 in aerobic CH 2 C1 2 . For x = 5, the treatment with HC1 leads to a mixture of M n f T O C P P f N O ^ C l (15f: x = 5) and Mn(TDCPP(N0 2 ) x ) (15g: x = 5). For x = 6, 7, and 8, it is only possible to isolate the M n t T D C P P t N C g j (15g: x = 6 - 8) . 4 7 (b) Oxidat ion studies The electron-withdrawing effects observed as a result of nitration are remarkable. Compound 15b (x=8, +0.155 V vs. S C E ) gives the highest reported first reduction potential of 1.44 V , positively shifted from 5b (-1.28 V vs. S C E ) . H 0 Manganese complexes of compounds 15f and g exhibit a remarkably wide span of Mn(IIi)/Mn(II) redox potentials that range from — 0.29 to +1.15 V (vs. S C E in CFLCkJ .47,111 26 Ar= N N v ( N 0 2 ) x Zn(TDCPP) 5b H + Ar Zn(TDCPP(N02)x) X = 1 -8 15b ( N 0 2 ) x i) Mn(OAc)2 ii) HCI gas in CH 2CI 2 Ar H 2TDCPP(N0 2) x X = 1 -8 15a For x = 1 - 4: Mn(TDCPP(N02)x)CI 15f(x = 1 -4) For x = 5 : Mn(TDCPP(N02)x)CI and Mn(TDCPP(N02)x) 15forl5g (x = 5) For x = 6 - 8: Mn(TDCPP(N02)x) 15g (x = 6 - 8) Figure 1-11. Synthesis of P-polynitto-/»wo-tetakis(2,6-dichlorophenyl)porphyrins. 27 Bartoli et al. studied the hydroxylation of anisole and naphthalene using manganese complexes of 15 and H 2 0 2 as an oxygen transfer reagent and found interesting relationships between the catalytic activity and the electron-deficiency of the metalloporphyrins.^7 Comparison of M n f T D C P P t N O ^ C l (15f: x = 1 - 4), M n f T D C P P ^ O , ) ^ (15g: x = 5 - 8) and Mn(TDCPP)Cl (5f) (Figure 1-11) as catalysts showed that 15f (x = 1), 15f (x = 2), 15f (x = 3), and 15f (x = 4) gave 97, 96, 98, and 79 % yield respectively for the hydroxylation of anisole and 79, 83, 69, and 49 % yield respectively for the hydroxylation of naphthalene.^"7 Regioselectivity decreased as the number of nitro groups increased; for the hydroxylation of anisole, the product ratio of (/wra-hydroxylated anisole/o^o-hydroxylated anisole) was 13, 11, and 9 and for the naphthalene, (a-hydroxylated naphthalene/(5-hydroxylated naphthalene) was 10, 9, and 8 with the catalysts 15f (x = 1), 15f (x = 2), and 15f (x = 3) respectively. Both the yield and the regioselectivity for the hydroxylation of anisole by 15f (x = 1) were improved compared to the results obtained with 5f. Interestingly, the total yield of product obtained from the hydroxylation of anisole was observed to be low when catalysts containing more than five nitro groups on the p-pyrrolic positions were used, despite the increased electron-deficiency of the macrocycle. As an extreme example, 15g (x=8) gave the oxidation products in less than 2 % yield for both anisole and naphthalene hydroxylation.^7 (c) Conc lus ion P-Nitrated Mn(IIi)-porphyrins show increased catalytic activity compared to the second generation catalyst, Mn(TDCPP)Cl (5f) (Figure 1-8). However, the number of P-nitro substituents must be carefully controlled since over-nitration (more than five nitro substituents) 28 results in a severe loss of catalytic activity. This may be due to the stability and catalytic inactivity of the Mn(II) oxidation state under the influence of highly electron-deficient porphyrins. (3) meso-Tetrakis(perfluoroalkjl)porphyrins (a) Synthesis and oxidation studies There are three methods to synthesize »wo-tettaltis(perfluoroalkyl)porphyrins (Figure 1-12). Two methods involve the synthesis of perfluoro-l-(2-pyrroryl)-l-alcohol (18), which can be synthesized from the reaction of pyrrole and perfluoroalkyl aldehyde hydrate (Path A) or the reaction of pyrrole and perfluoroacyl chloride (Path B). Pyrrole 18 undergoes addition and cyclization in dry benzene to form porphyrinogen 19 that is oxidized to the porphyrin 16a with D D Q . The yield obtained by DiMagno et al. for 16a (n = 3) (OTWo-tetrakis(heptafluoropropyl)porphyrin) was 37 % based on 18 . 3 8 The yields obtained by Golltf/'tf/. by this method for 16a (n = 1) (^j-o-tettalds(tjifluorometFiyl)porphyrin), 16a (n = 3), and 16a (n = 7) (wwo-tetj:alds(pentedecafluoroheptyl)porphyrin) were 16, 38, and 34 % based on 18 respectively.3^ Alternately Wijesekera reported the synthesis of 16 via dipyrromethane 20 in which the yields for 16a (n = 1) and 16a (n = 3) were 6 and 9 % respectively based on 20.112 The strong electron-withdrawing effect due to the perfluoroalkyl groups is reflected in the first oxidation and reduction potentials of the Z n porphyrin. For example Z n porphyrin 16b (n = 3) has +1.46 V (the first oxidation) and -0.72 V (the first reduction) vs. S C E , which are greatly changed from +0.79 V and -1.39 V vs. S C E for Zn(TPP) (2b) (Figure 1-8) in P h C N . 3 8 There are only a few studies regarding Fe(II) and Fe(III) complexes of I 6 H 3 and catalytic oxidation using these Fe complexes.48 According to Moore et al., the catalytic activity of Fe(II) complex of 16 (16e) is the same as the second and the third generation catalysts 29 H 0 > H + 2 O N H Cn^2n+1 Path A C6H6/molecular sieves, 4A Path B -4H 2Q ° Y C I . O C nF2n+1 N H 1 THF/triethylamine 2.NaBH 4 K . C n F n r2n+1 F 2n+ lC n ff C n F 2 n + 1 F 2 n + 1 C n " H > DDQ H H THF/HCI 20 Path C / C n F 2 n + i Metallation 16b: M = Zn(l) 16e: M = Fe(l) O N H H O ^ O H C nF2n+1 o r H 0 ^ J 0 C H 3 Cn^n + I Figure 1-12. Synthesis of wwo-tetrakis(perfluoroalkyl)porphyrins. 30 Fe(TPFPP) (4e) and Fe(TPFPPBr 8) (8e) (Figure 1-8) in hydroxylation of isobutane and there was a slight improvement of robustness of 16e from that of 4e and 8e.48 In order to conclude whether Fe(II or III) (or other metal such as Cr or Mn) complexes of wwo-tetraltis(perfluoroalkyl)porphyrins are effective as P-450 model compounds, more detailed studies will be required. 3. Design concept for a new P-450 mimic a. Basic concept The basic concept for a new P-450 mimic was constructed based on the previous studies of P-450 rnimics using electron-deficient porphyrins. It has been shown that electron-withdrawing substituents are mandatory to protect the porphyrin macrocycle from oxidative degradation and to enhance the reactivity of the oxo iron intermediate. However, as seen in the oxidation studies using p-perfluoro-wwo-tetraarylporphyrins (12-14) (Figure 1-8) and P-polynitro-^j-o-tetralds(2,6-dicUorophenyl)porphyrins (15) (Figure 1-11), extremely strong or plentiful electron-withdrawing groups may deactivate the catalysts and/or facilitate decomposition of the macrocycle by nucleophilic attack. Therefore, a moderate electronic effect would be ideal. Steric effects should also be considered as an important factor, in order to increase the robustness of the catalysts. Introduction of bulky substituents onto the porphyrin macrocycle prevents unnecessary contact of the porphyrin core with oxidants (oxo metal intermediate, PhIO, R O O H , etc) and prevents the formation ofthe p-oxodimer which is catalytically inactive. 104,105 As a bulky and electron-withdrawing substituent, the trifluoromethyl group (-CF3) is a good choice. Perfluoroalkyl groups have already been introduced on the OTW0-position38,39 a n c j indeed on the P-pyrrolic positionsll4-U8 Q f porphyrins. However, there have been no literature 31 reports o f the introduction o f trifluoromethyl (or perfluoroalkyl) groups o n the (3-pyrrolic positions o f wwo-tetraarylporphyrins as far as the author is aware. A s ^wo-tetraarylporphyrins have been well studied as P-450 mimics, the synthesis and characterization o f P~trifluoromethyl (or perfluoroalkyl)-/W£f0-tettaarylporphyrins may provide potentially new and improved catalysts. b. Potential advantages of trifluoromethyl substituents Accord ing to the Hammett equation,! 19 electton-withdrawing or electron-releasing ability o f substituents can be expressed as a quantitative measure called substituent constant value (a). Some substituent constant values are summarized in Table 1-3. H i g h and positive o~ values correlate to strong electron-withdrawing ability o f substituents. Table 1-3. a values for different substituents. a Substituent -CF3 0.54 0.43 - C H 3 -0.17 -0.07 - H 0.00 0.00 -F 0.06 0.34 -CI 0.23 0.37 - B r 0.23 0.39 - C N 0.66 0.56 - N Q 2 0.78 0.71 a Values are from ref. 120,121. A s a typical reaction to determine this quantity, ionization constants o f the carboxylic group in substituted benzoic acids i n water at 25 °C has been selected^; rj = log ( K / i Q , where K is the ionization constant o f benzoic acid and is that o f substituted benzoic acid, m and p denote that the O" value was determined at meta and para substitution respectively. A s shown in Table 1-3, the - C F 3 group does not have the highest a values and thus it is not the strongest electton-wididrawing group. However , due to the high electronegativity o f fluorine (3.98 o n Pauling's scale)122 a n d relatively similar sizes o f the fluorine and hydrogen 32 atoms (the van der Waal's radii of F and H are 1.35 and 1.20 A, respectively) 123 fluorinated molecules have some unique properties. 124 The above-mentioned characteristics of fluorine substituents increase the oxidative, hydrolytic, and thermal stability of fluorinated molecules compared to the parent hydrocarbon (the C-F bond energy is about 116 kcal/mol.124 cf. the C - H bond energy of 104 kcal/mol.125). I n addition, the estimated van der Waals radius of the trifluoromethyl group is at least 2.2 A126. Despite the similar sizes of - F and - H , the trifluoromethyl group is slightly larger than the methyl group (2.0 A123). Thus, the thermal stability and steric bulkiness of the trifluoromethyl group should be advantageous of the protection of the macrocycle. In summary, the unique electronic, steric, and physical properties of the —CF 3 group may be able to make P-trifluoromethyl-^j-o-tettaphenylporphyrin metal complexes ideal candidates as potential P-450 mimics. C. Synthetic strategy for P-trifluoromethylation of weso-tetraphenylporphyrin Although 3,4-bis(trifluoromethyl)pyrrole is available in excellent yieldsl27,128; n o condensation of this pyrrole with aldehydes to give a P-octalds(tofluorometliyl)-porphyrin has yet been reported. Presumably, cyclization with aldehydes is unlikely due to the low electron density at the a positions of the pyrrole. 129 Therefore, direct P-trifluoromeurylation of a porphyrin is the preferred route to p-ttifluorometiiylporphyrins. /. Brief overview of trifluoromethylation The synthesis of perfluoroalkyl-substituted aromatics falls into three classes. 33 a. Fluorination of an existing aryl substituent (Scheme 1-3) As examples of this category, (a) substitution of chloride substituents of a trichloromethyl group with antimony trifluoride or hydrogen fluoride^O and (b) fluorination of a carboxylic acid by sulfur tetrafluoride with hydrogen fluoride as a catalyst^3! have been reported. Obviously, the drawbacks of the use of these methods include challenges in the preparation of appropriately substituted ^j-o-tetraphenylporphyrins and technical difficulties associated with the handling of SbF 3, H F and SF4.132 Therefore, the application of these methods is limited. 00 r rC h 3 °'2 » fY°a* S b F 3 o r H F > > ^ r - C F 3 C 0 0 H S F 4 H F (cat.) (b) Scheme 1-3. Fluorination of an existing aryl substituent. (a) Substitution of chloride substituents with fluoride, and (b) fluorination of a carboxylic acid. b. Introduction of trifluoromethyl groups (1) Transfer of CF f (Scheme l-4(a)) Perfluoroalkyl organometallic reagents have been studied extensively and it is known that a number of them, especially those of copper, mercury, cadmium, and zinc, are useful reagents for trifluoromethyl anion transfer to organic compounds. 1 3 3 Some organosilicon perfluoroalkyl compounds are also good trifluoromethyl anion transfer reagents, although only a few applications to aromatic compounds have been reported. ^ 3 ^ 34 (a) X X=Ior Br (b) e.g. C F 3 M or (CF 3) 2M M=Cu, Hg, Cd, or Zn C F , 0 2 NO^CiN 0 2 ^ F 3 C 22 , dryTHF "4 Scheme 1-4. Introduction o f a trifluoromethyl group.(a) Transfer o f CF 3 ~, and (b) transfer o f C F 3 + . (2) Transfer of CF}+ (Scheme 1-4(b)) Electrophilic perfluoroalkylating reagents are also known. Indeed, Tamiaki^ /a / . synthesized (3- and ^j -o-tafluoromethyl-5,15-bis(3,5-di-Abutylphenyl)porphyrins (21) using S-(tofluoromethyl)-3,7-dinitrobenzothiophene trifluoromethanesulfonate (22) i n dry T H F . ^ 8 However , the yields were poor with a mixture o f regioisomers obtained (16% o f 23, 4 % o f 24, and 1 % o f 25 for M=Zn(II ) ) and 55 - 62 % o f starting materials were tecovered. Unl ike p-halogenation34,44,70-77 o r n i t r a t i on 3 7 , this method seems to be inefficient for the modification o f p-pyrrolic positions. 35 O f the above-mentioned methods and reagents, perfluoroalkylcopper reagents have received more attention than any other perfluoroalkyl organometallic compounds due to their ease of preparation and ready availability. 133 A number of examples of perfluoroalkylation of aromatic compounds have been reported. 133 However, there are no literature reports of the application of perfluoroalkylcopper reagents to porphyrins. 2. Copper assisted trifluoromethylation The pioneering work of McLoughlin and Throwerl32 a n c J Kobayashi ^i?/ . 136,137 identified trifluoromethyl copper reagents as ideal coupling reagents for trifluoromethylation of aromatic halides. Perfluoroalkylcopper reagents have been prepared by the following three methods: (i) reaction of CF 3 I or C F 2 B r 2 with metallic copper in a coordinating solvent at elevated temperatures 132; (ii) pyrolysis of tafluoroacetate in the presence of Cu(T) halides!36,137. (iii) metathesis reactions of mfluoromethylorganometallic reagents with metallic copper or Cu(T) halides. In method (i), there is a technical difficulty in handling the precursors (in spite of the high temperature (100-140°C) of the reactions, the b.p. of perfluoromethyl halide is low, e.g. CF 3 I: —22.5°C) and another major drawback is the high cost of the perfluoroalkylhalide.133 Methods (ii) and (iii) do not require special equipment and the cost of the materials are reasonable. 133 Methods (ii) and (iii) are detailed below. a. CF3Cu from pyrolysis of sodium trifluoromethyl acetate in the presence of Cu(I) halide Trifluoromethylation via pyrolysis of sodium or potassium trifluoromethylacetate in the presence of Cu(I) halide is the least costly and least hazardous methodology for introduction of the trifluoromethyl group into aromatic compounds.133 As shown in scheme 1-5 (Path A), in the presence of Cu(I) halide, pyrolysis, or decomposition (decarboxylation) of sodium 36 N M P Ar l + C F 3 C 0 2 N a / C u l • A r C F 3 (Path A) 1 4 ° - 1 6 0 ° C 4 0 - 7 8 o / 0 -^U- C F 3 H + A r H (Path B) (side products) Scheme 1-5. Trifluoromethylation of aromatic halide by pyrolysis of C F 3 C 0 2 N a . trifluoroacetate in aprotic polar solvents such as N-methylpyrrolidone (NMP) or D M F at around 150 °C generates the active trifluoromethylating agent C F 3 C u and copper assisted substitution gives the trifluoromethyl aromatic compound. Residual water, which largely arises from the hygroscopic trifluoroacetate salt, causes serious problems including loss of active C F 3 C u and dehalogenation of the substrate to form fluoroform and hydrogenated aromatic compounds as shown in Path B. In order to minimize the side reaction, Freskos^8 employed a toluene-azeotrope to distill off any trace water before the reaction temperature was brought up to 155 °C (Figure 1-13). With this method, only two equivalents of perfluorocarboxylate are required and the yields of the products were moderate to excellent. toluene + water distillation at 1 2 0 ° C toluene DMF C F 3 C F 2 C 0 2 K Cu? trace water 155 °C 2 h C F 2 C F 3 90 % Figure 1-13. Removal of water by use of a toluene-azeotrope in the pentafluoroethylation of a-iodonaphthalene. 37 b. CF}Cu from metathesis of trifluoromethylcadmium with Cu(I) halide (1) Trifluoromethylation Bur ton et al. showed that difluoromemylcadmiurn, C F 3 - C d (a mixture o f C F 3 C d X and ( C F 3 ) 2 C d , X = C 1 or Br) is an excellent precursor for generation o f the active C F 3 " transfer agent, C F 3 C u , and can be used for high-yield multiple trifluoromethylation o f aromatic halides. 133,139,140 -phg tnfluoromemylcadmium reagent undergoes metathesis, or an exchange reaction with Cu(I) halide to give C F 3 C u at - 40°C in 90 - 100 % yield ( 1 . 2 ) . 1 4 0 In-situ generated (CF3)2Cd CuX ^ C F 3 C u Uh3UdBr -40°C C F 3 C u then attacks the brominated or iodinated site o f aromatic compounds. 133,139 s ^ e reaction is perfluoroalkyl chain oligomerization which occurs at higher temperature (equations (1.3) and (1.4)).133 However, addition o f the same volume o f hexamethylphosphoramide ( H M P A ) to the volume o f trifluoromethylcadmium reagent, which is given at 1 M i n D M F solution,139 inhibits the oligomerization.133 CF3Cu y »» CF3CF2Cu (1.3) DMF CF3Cu • CF3(CF2)nCu (1.4) 90-100°C (2) Synthesis of trifluoromethylcadmium Trifluorometiiylcadmium is synthesized from dibromodifluoromethane and cadmium powder i n D M F . The proposed reaction mechanisms!39 a r e shown i n equation (1.5) - (1.11). The reaction is initiated by electron transfer from cadmium to the electronegative carbon in C F 2 B r 2 (1.5). This is followed by a second electron transfer to facilitate the loss o f bromide ions (1.6) and to give a reactive difluorocarbene (26) (1.7). This species reacts wi th D M F (1.8) 38 and the resultant dimemyl(iifluoromemylamine (27) releases fluoride ion (1.9) which reacts with another molecule of difluorocarbene to form a trifluoromethyl anion (1.10). Finally the CF 3 ~ ion combines with CdJ3r+ or C d 2 + to form CF 3 CdBr and(CF 3) 2Cd, respectively (1.11). C F 2 B r 2 + C d C d + [ C F 2 B r 2 ] * (1.5) C d + [ C F 2 B r 2 f - C d 2 + + [CF 2 Br ] " + Br" (1.6) [CF 2 Br ] " • : C F 2 + Br" (1.7) : C F 2 + ( C H 3 ) 2 N C H = 0 *~ ( C H 3 ) 2 N C F 2 H + C O (1.8) 26 27 ( C H 3 ) 2 N C F 2 H ^ [ ( C H 3 ) 2 N + = C F H ] + F" (1.9) 27 : C F 2 + F" - C F 3 " (1.10) 26 C F 3 " Br and C d 2 ^ ( C p 3 ) 2 C d + C F 3 C d B r (l.il) Thus, Cu(I) assisted trifluoromethylation is an efficient method for the preparation of trifluoromethylated aromatic compounds. D . Analysis of porphyrins /. UV-visible absorption spectroscopy a. Characteristics of UV-visible absorption spectra of porphyrins and metalloporphyrins Porphyrins exhibit characteristic absorption properties in the UV-visible region. 141,142 j n Figure 1-14, UV-visible absorption spectra of free-base, diprotonated, and metallated (with Figure 1-14. U V - v i s i b l e spectra o f /^.ro-tettaphenylporphyrins i n C H 2 C 1 2 . (a) H 2 T P P (2a) (solid line) and H 4 T P P 2 + (narrow line), (b) Z n T P P (2b). " Q bands are mult ipl ied by five. 40 Zn(II)) forms o f ^.ro-teteaphenylporphyrin (TPP) are shown. Porphyrins show an intense absorption near 400 n m (s ~ 4 x 10 5 M ' c m 1 ) , which is referred to as the Soret band (also called the B band). Porphyrins also exhibit less intense bands, usually found between 500 and 700 nm, which are referred to as the Q bands.141,142 -ph e origins o f the Soret and the Q bands are 71-71* excitation from the ground state to the second and the first excited singlet state, respectively. 142 The Q bands split into two bands!42 for porphyrins such as Z n ( T P P ) (2b) (Figure 1-8) as shown in Figure l-14(b). The lower-energy band o f the two Q bands, which is referred to as Q (0,0), corresponds to the excitation o f an electron from the ground to the lowest-energy excited singlet state and the higher-energy band, Q (1,0), including one mode o f vibrational excitation. 142 For the free-base, each Q band is further split into two bands due to the breaking o f the D4i symmetry o f the porphyrin ring by the central proton axis as D2/l symmetry is achieved (Figure 1-15).142 Thus, Q (0,0) and Q (1,0) split into 0,(0,0), Q y(0,0) and QX(1,0), Q (1,0).142 The addition o f acid to the free-base results i n protonation o f each inner nitrogen and the spectrum o f porphyrin dication (Figure 1-15) returns to the D 4 h - type (Figure 1-14(a) (gray line). 142 H 2 T P P 2+ [ H 4 T P P ] 2+ D 4h Figure 1-15. Symmetries o f Z n ( T P P ) (2b), H 2 T P P (2a) and [ H 4 T P P ] 2 41 b. Electron-withdrawing effects on UV-visible absorption spectra Electron-withclrawing substituents stabilize the highest occupied molecular orbital (HOMO) (ft) and the lowest unoccupied molecular orbital (LUMO)(7t*) orbitals of porphyrins.143 Since UV-visible spectra of porphyrins reflect the 7t-7t* electronic transition, changes in the UV-visible absorption spectra are observed if the H O M O and the L U M O are affected (differently by the electronic effects of substituents.39,144 j n o n e c a s e ; such as in the example shown in Figure 1-16, (only Q bands are shown - the Soret band also shifts to a longer wavelength)!41; it is known that replacement of an ethyl group of etioporphyrin I (28) with a electton-withdrawing carboxylic group results in a red-shift of the UV-visible bands in rhodoporphyrin X V (29). The red-shifts of the absorption bands imply contraction of the H O M O - L U M O gap. Alternatively, replacement of ^jo-phenyl groups of H 2 T P P (2a) (Figure 1-8) with pentafluorophenyl groups to give H 2 T P F P P (4a) (Figure 1-8) causes the bands to shift from 418 (Soret), 514, 549, 590, and 646 nm (Q bands) for 2a in CH 2 C1 2 to 410, 505, 535, 582, and 645 nm for 4a, i.e. a minor blue-shift. This phenomenon implies that the H O M O -L U M O gap is expanded by the electton-withdrawing effect of the wwo-perfluorophenyl groups. The blue-shifts of the absorption bands are also observed in P-perfluoro-wwo-arylporphyrins, 12a, 13a, and 14a (Figure 1-8) from H 2 T P P . Accordingly, either H O M O - L U M O gap contraction (red-shift) or expansion (blue-shift) may occur due to the introduction of electton-withdrawing substituents. Unfortunately, it is rare to observe a pure electronic effect of substituents on the UV-visible spectra, for it is well known that macrocycle distortion causes red-shifts in UV-visible absorption bands of the porphyrin.144-147 p o r example, the UV-visible spectrum of severely distorted Zn(II) complex of P-octamethyl-«?wo-tettaphenylporphyrin (Zn(OMTPP)) (30) (p.43)(442, 574, and 630 nm in C H . C L ) 1 4 7 shows 500 550 600 650 500 550 600 650 Wavelength (nm) Wavelength (nm) Porphyr in 2 3 7 8 12 13 17 18 Et ioporphyr in-I (28) M e E t M e E t M e E t M e E t R h o d o p o r p h y r i n - X V (29) M e E t M e E t M e C 0 2 H P H M e 5, 10, 15 and 20 = H , Me=methyl , Et=ethyl , P H = C H 2 C H 2 C 0 2 H Figure 1-16. Example o f the U V - v i s i b l e spectral change by electton-withdrawing effects. U V - v i s i b l e spectra were adapted from reference 141. 43 enormous red-shifts compared to Z n ( T P P ) (419, 548, and 582 n m i n C H j C L ) . Macrocycle distortion causes destabilization o f the H O M O which also leads to contraction o f the H O M O -L U M O gap, and thus the red-shifts o f the absorption b a n d s . 1 4 4 " 1 4 6 Z n ( O M T P P ) (30) 2. Redox potentials ofporphyrins a. General redox properties of porphyrins in non-aqueous media (1) Technique, solvent, and supporting electrolytes Although redox properties o f porphyrins have been studied by various techniques 1 4 8 , cyclic voltammetry has been the method o f choice for the investigation o f the electrochemisty o f p o r p h y r i n s , 1 4 8 ' 1 4 9 and several solvents such as D M F , D M S O , M e C N , B u C N , P h C N , or C H 2 C 1 2 have been used. 1 4 9 , i 5 0 Q n e Q f fae most c o m m o n solvents is C H 2 C 1 2 due to its weak binding properties, ability to solubilize porphyrins and its large cathodic and anodic range close to ± 1.9 V vs. S C E . 1 5 0 Therefore, a wide range o f redox potentials can be studied i n C H 2 C 1 2 . 1 5 0 The most c o m m o n supporting electrolytes, which are used to increase the conductivity o f the solution, are tetrabutylammonium perchlorate ( T B A P ) , tettaethylammonium perchlorate ( T E A P ) , tetrabutylammonium tetrafluoroborate ( T B A B F 4 ) , and tetrabutylammonium hexafluorophosphate ( T B A P F J in which C 1 0 4 , BF 4 " , and PF 6 " can be considered as non-binding anions. A l l o f the salts are highly soluble in non-aqueous solvents. 44 (2) Porphyrin ring redox properties in free-base and metalloporphyrins Ftee-base and many metalloporphyrins undergo two one-electron oxidations and two one-electron reductions, all of which occur at the conjugated 7t-ring system of the porphyrin macrocycle. 1^ 0 Figure 1-17 shows the cyclic voltammogram of H 2 T P P (2a) in CH 2 C1 2 , which reveals a typical example of two one-electron oxidations and two one-electron reductions. The former reactions correspond to the movement of two electrons from the H O M O and to the L U M O . Therefore, the difference in the half-wave potentials for the first oxidation and the first reduction, E ° / 2 ( l ) - E,r/2(1), is considered to correspond to the size of the H O M O - L U M O g a p . 1 4 9 - 1 5 0 A systematic study showed that E™2(1) - E $ ( l ) = 2.25 ± 0.15 V and constant differences between E,%(1) and E° / 2 (2)) (=AE 1° / X 2) and between E $ ( l ) and E$(2) (=AE1re/2) were observed for 25 metal complexes of octaethylporphyrin (OEP).151 The H O M O - L U M O gap, E ° / 2 ( l ) - E{/2(1) = 2.25 V approximately agrees with the theoretically calculated value of 2.18 eV for most metalloporphyrins.152 A similar experimental observation was also obtained for the different metal complexes of TPP.153 Thus, ring redox potentials of a porphyrin are pretty much constant throughout the free-base and the series of metal complexes. (3) Iron porphyrins As this thesis describes some electrochemistry of iron porphyrins, redox properties of iron porphyrins are briefly described here. Most synthetic iron porphyrins show three to four electron transfer reactions in a variety of nonaqueous solvents. 150 Figure 1-18 shows a cyclic voltammogram of Fe(TPP)Cl (2d) (Figure 1-8) measured by the author. A reduction Fe(III) to Fe(ir) generally occurs between +0.2 and —0.5 V vs. SCE.150 The most negative reduction potential shown could be Fe(II)/Fe(T) or Ph 2a E ] / 2 ( 2 ) : p 2 + + e <— —> p-+ E l 7 2 ( l ) : p-+ + e" <- P P + e" <— -> P'-Ev 2 ( l ) : P'- + e" <- -> p2-l i i i i E°;2(2) M rf 1 - r - i r e ^ /r\\ r i 1 E 1 / 2 ( 2 ) 1 H O M O - L U M O gap j , j 1 E ^ O ) Er; 2(i) i i i i • •1.50 M.00 »0.50 0.00 -0.50 -1.00 -1.50 V vs. S C E Figure 1-17. Cycl ic vol tammogram o f H 2 T P P (2a) i n C H 2 C 1 2 , 0.1 M T B A P ; scan rate, 50 m V / s . Adapted from reference 149. Figure 1-18. Cycl ic vol tammogram o f F e ( T P P ) C l (2d) i n C H 2 C 1 2 , 0.1 M T B A P F 6 scan rate, 100 m V / s ; F c / F c + = ferrocene/ferrocenium coupling, 0.46 V vs. S C E . 47 Fe(II)/(Fe(II) porphyrin 7t-anion) couple.150 -ph e assignment of this potential has long been a subject of controversy. 154,155 Some studies show the likeliness of the assignment of Fe(I) depending on the solution conditions and porphyrins.150 Each anodic reaction around ~1.1 V and ~1.6 V corresponds to removal of an electron from the TPP macrocycle. 150 b. Effects of substituents on the redox potentials of derivatives of TPP (1) Aryl-ring-substituted TPPs Kadish and Morrison measured half-wave potentials of seven H2TP(/)-X)P (31a) ((/>-X) represents the para positions of meso-phenyl groups are substituted by substituent X) in various solvents. 156 In order to analyze the results quantitatively as a function ofthe substituent, Kadish and Morrison employed the Hammett linear free energy equation and expressed a relationship as shown in equation (1.12), where E * 2 and E , " 2 are the half-wave potentials for TPP substituted A E 1 / 2 = E * 2 - E ^ = erp (1.12) with X and H at the phenyl para-position, respectively, and CT is a Hammett constant for X , and p is a constant value under the same experimental conditions. As shown in Figure 1-19, plots of E 1 / 2 values vs. 4CT for each electrode reaction were linear, indicating that macrocycle oxidations become more difficult and reductions become easier as the substituents become more electron-withdrawing. 156 Similarly, five electrode reactions (P-Fe(T)/P~"-Fe(I), where P is porphyrin, in addition to the four electrode reactions in Figure 1-18) were examined for nineteen different FefTPf>X)P)Cl (31b) and Fe(TP(w-X)P)Cl (32b) systems. Linearity of the E 1 / 2 vs. 4CT for these reactions in CH 2 C1 2 was observed. 157 Linearity of the plots was also observed for other 49 metaUoporphyrin species such as those containing C o ^ I ) 1 ^ Mn(III)159,160> Cu(II) 1 60, and Zn(II). 1 60 (2) B-Substituted TPPs The electrochemistry of P-substituted TPPs has been analyzed in two ways. The first method of analysis involves a series of p-mono-substituted TPPs with different substituents. The second analysis involves the series of TPPs P-substituted with zero to eight substituents of the same kind. (a) P-Mono-substituted T P P s with different substituents Giraudeau et al. examined the ring redox potentials of TPP substituted at a p-pyrrolic posistion by substituent X (H2TPP(X)) (33) in C H 2 C 1 2 . 1 6 1 As observed in the phenyl substituted TPPs, (Figure 1-19), E 1 / 2 vs. 4a plots showed that the oxidation and the reduction potentials increase almost linearly with the increase of a value of the substituents.161 33 X = H , OEt , Br, CI, C N , N Q 2 50 (b) P -Subs t i tu ted T P P s w i t h m o r e t h a n o n e s u b s t i t u e n t o f the same k i n d Giraudeau et al. studied a series o f P-cyano-wtf.ro-tettaphenylporphyrins (34). Figure 1-20 shows plots o f the first oxidation and reduction vs. the number o f substituents for the free-base (34a) and the C u complex (34c).161 Analysis o f the plots i n Figure 1-20 (p.51) reveals that the reduction potentials change linearly with the number o f cyano groups but that plots o f the oxidation potentials are non-linear for both free-base and C u complexes. Extreme cases o f the non-linearity o f the E 1 / 2 for the oxidation vs. number o f substituents are shown by Kad i sh eta/., who measured the redox potentials o f a series o f P-brominated T P P derivatives (35). 162-164 Figure 1-21 (p.52) shows the plots o f E 1 / 2 for the first oxidation and reduction vs. extent o f brornination for 35a. 162 For the first reduction, (Fe(in)/Fe(II)) linearity is maintained, but this is not the case for the oxidation; the first oxidation potential is maximized at x = 2 for 35a as shown in Figure 1-21.162 Similar results were obtained for Zn(II) complexes, 35b.l64 Ochsenbein et al. demonstrated, by using cyclic voltammetry and X-ray crystal structure studies, that conformational changes within molecules affect the redox potentials o f P-halogenated tetraarylporphyrins (36 - 39).165 Crystal structures o f 3a and 36 - 38 (/mo-mesityl groups omitted i n the diagrams o f the X-ray crystal structures) show that the macrocycle is progressively distorted as the size and number o f the substituents increases. This is presumably due to increased steric interactions between the substituents (Figure 1-22 (p.53)). Table 1-4 (p.54) shows the first reduction and oxidation E 1 / 2 for 3a and 36 - 38. Regardless o f the nature o f the substituents, the increase o f the E f c 2 ( A E ^ 2 ) wi th increasing number o f the substituents is -1.5" 0 1 2 3 # of C N group Figure 1-20. First reduction(O) and oxidation potentials (•) vs. # of C N groups for (a) H 2 T P P ( C N ) X (34a) and (b) CuTPP(CN) x (34c). The plots were produced from the values reported in reference 161. Figure 1-22. Side view of the crystal structures of H 2 T M P (3a), H 2 T M P C 1 4 (36) H 2 T M P B r 4 (37), and H 2 T M P C 1 8 (38) (the meso-mesityl groups are omitted for clarity). Adapted from reference 165. 54 almost constant (— +0.3 V), while A E 1 / 2 is obviously lower in the severely distorted porphyrins than in the planar macrocycles. This infers that the H O M O is destabilized by macrocycle distortion. The results shown in this section correlate to the red-shifts ( H O M O - L U M O gap contraction) observed in the UV-visible spectra which also correspond with macrocycle distortion (see section D.l.b.). Table 1-4. The first reduction and oxidation potentials for 36 - 39.a Porphyrin Halogen substituents pRed ^1/2 T7Rcd ^1/2 AE*1 3a — -1.41 +0.91 +0.29 +0.24 36 4C1 -1.12 +1.15 +0.27 -0.10 38 8C1 -0.85 +1.05 3a -1.41 +0.91 +0.32 +0.21 37 4Br -1.09 +1.12 +0.25 -0.13 39 8Br -0.84 +0.99 a E 1 / 2 in V vs. SCE: solvent CH 2 C1 2 , electrolyte T B A P F 6 . T=25 °C, ref.165 (3) Conclusion In summary, for porphyrin macrocycles without conformational change, the presence of election-withdrawing effects linearly increases both the first reduction and the first oxidation potentials. This is the case for phenyl-substituted and P-mono-substituted TPPs. However, when the macrocycle is distorted, an expected increase in the first oxidation potential by an electron-withdrawing effect is offset by destabilization of the H O M O due to macrocycle distortion, while linearity for the first reduction potential (ring reduction or Fe(III)/Fe(II)) vs. an expected electron-withdrawing effect is maintained. Therefore, one can deduce the electron-withdrawing 55 effects imposed upon a porphyrin macrocycle by comparing the first reduction potential of one porphyrin with the value of another. 3. 1H NMR spectroscopy a. Porphyrin ring current effect ' H N M R spectroscopy of porphyrins is a valuable technique to enable analysis and characterization. Chemical shifts observed in ' H N M R spectra of diamagnetic porphyrins can be assigned and rationalized by considering the porphyrin ring current effect which is characteristic of aromatic compounds . ! 6 6 ' ! 6 7 p o r a n aromatic system such as a porphyrin, the magnetic deshielding resulting from the ring current is positive for nuclei on the outside of the ring current (for meso and P-substituents), and negative for nuclei positioned within the ring current (for N - H proton). i 6 6 j l 6 7 This shielding and deshielding results in massive chemical shifts of signals compared to those of signals due to non-aromatic systems. Figure 1-23 (p.56) shows the ' H N M R spectrum of H 2 T P P (2a) in CDC1 3 at 298 K recorded by the author. A remarkable deshielding effect due to the induced paramagnetic field that is caused by the ring current is observed as a downfield shift of the signal due to the p-pyrrolic proton (8.86 ppm) of the porphyrin compared to that of pyrrole (~6 p p m ) . 1 6 7 > 1 6 8 O n the contrary, the N - H proton is strongly shielded by the induced diamagnetic field and the effect is observed as an enormous upfield chemical shift (-2.76 ppm) of the porphyrin N - H compared to that of N - H signal (7-12 ppm) in pyrrole i t se l f . 1 6 7 ' 1 6 8 b. Concentration effect It is well known that porphyrins aggregate in s o l u t i o n 1 6 6 ' 1 6 9 and this phenomenon has been extensively studied in solution using N M R spectroscopy. 1 70-172 j± typical experiment to a 2a a: P-pyrrole H (8.86 ppm) b: ortbo-phenyl H (8.22 ppm) c: meta,para-phenyl H (7.76 ppm) d: N - H (-2.76 ppm) I ' 1 1 1 I ' ' 1 ' I 1 ' ' 1 I 1 ' ' ' I ' ' 1 1 I 1 1 I 1 1 1 1 I ' ' ' - r - p - " - i - p - ' - ' - H ' ' ' ' I ' ' ' 1 I 1 ' ' ' - T ' - i - r - r 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 Chemical shift (ppm) Figure 1-23. 200 M H z XH N M R spectrum of H 2 T P P (2a) in CDC1 3 at 298 K . 57 detect aggregation of porphyrins is to measure the chemical shift at various concentrations.171,172 Figure 1-24 (p.58) shows the change of the chemical shift due to meso-ptoton of 40a with the concentration change, according to Ono etal.^72 rjue t o 71-71 aggregation, the chemical shift of the shielded meso-ptoton is shifted by the induced diamagnetic field of the porphyrins. Furthermore, the same experiment with 40b showed that less aggregation occurs compared to the electron-deficient 40a (the result for 40b is not shown). The reason why the electron-deficient porphyrin tends to aggregate more is not well understood. c. N-H tautomerism Figure 1-25 (p.59) shows the N - H tautomerism for ^jo-tetraphenylporphyrin. Several other tautomers are also possible by locating two inner protons on adjacent nitrogens! 6 6 (the structures are not shown) but they are less stable due to penetration of each hydrogen into the van der Waals sphere of the other.! 4! Although two tautomers (41a and 41b) exist as the most probable structures!4! for H 2 T P P , H A and H B cannot be distinguished using N M R spectroscopy due to the fast exchange between 41a and 41b on the N M R time scale at room temperature.!6 6 In other words, H 2 T P P of symmetry D 2 h is observed as an average of 41a and 41b of D 4 h symmetry at room temperature by N M R spectroscopy. However, this exchange is slowed below 220 K and two signals for H A and H B can be observed.!7 3,174 As shown in Figure 1-25, H A is located on the conjugated 187t-electron pathway (presented by the dotted line) and H B is located on the isolated double bonds. Crossley et al. studied tautomerism of sixteen different (3-mono-substimted-TPPs (42) by *H N M R spectroscopy at 200 K in CD 2 C1 2 and found that the position of the N H tautomeric Figure 1-24. Plot of chemical shift of meso-H vs. porphyrin concentration for 40a. Adapted from reference 172. 59 Figure 1-25. Tautomerism in H 2 T P P (2a). Ellipses indicate isolated double bonds. equilibrium is affected by the nature of the s u b s t i t u e n t s . A s shown in Figure 1-26 (p.60), for R = C N , N 0 2 , O C O P h , Cl, Br, C H O , OMe, SPh, N H C O M e , and O H G a rg e lY electron-withdrawing groups) the dominant tautomer has the substituent positioned on an isolated double bond. For R = C H = C H 2 , N H 2 , (CH^Me, Me, and C H M e 2 , the major tautomer has the substituent positioned on the aromatic derealization pathway. Thus, the effects of electron-withdrawing substituents may be appreciated by analysis of the ' H N M R spectra of porphyrins at low temperature, and assessment of N H tautomerism observed therein. 4. Spectrophotometric titration In this section, two techniques for the evaluation of electron-deficiency of a porphyrin by spectrophotometry are described. a. Evaluation ofpKa o/NH 2+ P K 4 + PK3 PK2 PKI o P H 4 2 • P H , • P H ? • P H " — - P 2 " (1.13) The free-base parent porphyrin (PEQ can be protonated twice on its imine type nitrogen atoms to form mono- (PH 3 +) or di-cation (PH 4 2 +) species, or can lose two pyrrole type protons Ph 42a Ph 42b 42a R 42b >99 C N -97 N 0 2 3 94 O C O P h 6 94 CI 6 91 Br 9 84 C H O 16 82 OMe 18 81 SPh 19 73 N H C O M e 27 61 O H 39 38 C H 2 O H 62 33 C H = C H 2 67 22 N H 2 78 21 ( C H ^ M e 79 19 Me 81 9 C H M e 2 91 Figure 1-26. Relative populations of 42a and 42b at 200 K in CD 2 C1 2 . Adapted from reference 175. 61 to produce mono- (PH') or di-anion (P2~), equation (1.13). 1 6 9 The values pX 3 and pi<C4 have been well documented to be between 3 and 9.141,169 Q n m e c o n trary , piC, and pK2 are estimated to be in the order of 16^ 7 6 and have not been studied well. Recently, Woller and DiMagno have determined the piC, values of P-octafluoro-w&ro-tetraarylporphyrins H 2 T P P F 8 (12a) and H 2 T P F P P F 8 (14a) (Figure 1-8, p. 11) by spectrophotometric titration with D B U in CH2C12.36 The titration showed a difference of +3.9 and + 0.2 xpKa units from D B U for 12a and 14a, respectively. Since this method of analysis is performed in a common solvent for porphyrins (CH^Cy, it should be applicable to other electron-deficient porphyrins in order to assess the extent of electron density withdrawal from the macrocycle by the substituents. b. Determination of central metal — ligand binding constant PCo( l l ) + B - PCo( l l )B (1.14) K2 PCo( l l )B + B • P C o ( l l ) B 2 (1.15) P = porphyrin, B = Lewis base It is known that Lewis bases such as pyridine bind to four-coordinate porphyrin cobalt complexes as shown in equations (1.14) and (1.15). 177-180 Walker studied the axial coordination of Co(TP(p-OCH 3)P) (43) (p.62) with amines to investigate the electronic and steric influence on the 0 2 binding behavior of the Co(II) porphyrin complex.178 Lrn et alX^^ and Smirnov (^2/180 evaluated the electron-deficiency of the Co(II) complex of P-cyanoporphyrin (34c) and Co(II) complexes of P-octafluoroporphyrins (12h and 14h), 62 Ar' 43 respectively. As summarized in Table 1-5, electron-deficient porphyrins show higher log lvalues than that of 43, that is, 34c, 12h, and 14h bind pyridine more tighdy than 43. Thus, central metal-axial ligand binding constants may also be determined by spectrophotometric titration and the electron-deficiency of porphyrins can be evaluated by comparing the binding constants. Table 1-5. Formation constants for pyridine binding in CH 2 C1 2 at 25°C Porphyrin log*; logK 2 Reference 43 2.7 178 34c 4.2 -0.35 179 12h 4.3 -0.08 180 14h 5.9 1.03 180 63 Electron-deficiency alone may not guarantee high efficiency and robustness of porphyrin catalysts but now we are sure that electron-deficiency is a necessity for the desired oxidation catalyst. Thus, evaluation of the electron-deficiency of porphyrins is important in the development of P-450 mimics. As shown above, UV-visible, 1 H N M R spectroscopy, electrochemistry, X-ray crystallography, and spectrophotometic titration can all be used, alone and in combination, to assess the effects of electron-withdrawing substituents on the properties of porphyrins and metalloporphyrins. E. Goals of this thesis The overall goal of this thesis is to contribute to the research field of cyctochrome P-450 rnirnics. The initial approach in search of an active and robust metalloporphyrin as a P-450 mimic was to prepare novel electron-deficient (3-trifluoromethyl-^j'o-tetraphenylporphyrins including Zn(II), Co(II), and Fe(III) complexes of the species. The major part of this thesis concentrates on analysis of the electron-deficiency of the porphyrins by the UV-visible and N M R spectroscopies, cyclic voltammetry, and X-ray crystallography. In order to make the properties of the novel porphyrins clearer, the results of analysis are compared with known electron-deficient porphyrins. Electron-releasing P-methyl-wtfJo-tetraphenylporphyrins were also prepared to show an interesting comparison with P-trifluoromethylporphyrin in electronic and structural effects of the substituents. Finally results of oxidation of cyclohexane and cyclohexene using Fe(III) porphyrins as catalysts are shown, and the usefulness of P-trifluoromethyl-OTwo-tetraphenylporphyrins as P-450 mimics is discussed. 64 CHAPTER II Results and Discussion A. Synthesis of P-trifluoromethyl- and p-methyl-meso-tetraphenylporphyrins The trifluoromethyl group may be an advantageous substituent when directly introduced onto the porphyrin macrocycle in order to improve the efficacy of metalloporphyrins as catalysts for oxidations due to its strong electron-withdrawing effect, bulkiness and stability (Chapter I, section B.3). Direct attachment of trifluoromethyl or perfluoroalkyl groups onto the porphyrin macrocycle at the /w.ro-positions of porphin (I) (nomenclature, p.viii)38,39,112 a n ( j m e P-positions of ^jo-diarylporphyrinl 1 8 has been reported, but there are no reports of P-trifluoromethyl-w^o-tetraarylporphyrin in the literature. As described in chapter I, major players in the development of P-450 mimics using synthetic porphyrins are meso tettaarylporphyrins with electron-withdrawing substituents on the p-pyrrolic positions (see chapter I, section B.2.). Accordingly, the main purpose of this research is to initiate and investigate the chemistry of p-trifluoromethyl-^j"o-tetraphenylporphyrins. The first part of this section describes the synthesis of P-tjifluoromethyl-^j'o-porphyrins. The second part describes the synthesis of p-methyl-^jo-tetraphenylporphyrins. P-Methyl-wwo-tetraphenylporphyrins were compared with the corresponding P-trifluoromethyl- analogues in order to investigate the contrasting electronic characteristics of —CH 3 and - C F 3 groups; electron-releasing vs. electron-withdrawing(Table 1-3, p.31). Analysis by comparison may allow the effects of the electron-withdrawing C F 3 group on the porphyrin macrocycle to be fully assessed. Finally, the synthesis of Zn(II), Co(II), and Fe(III) complexes of P-tetealds(ttifluorometliyl)-OTW<?-tetJ:aphenylporphyrin is described. These metalloporphyrins were required to investigate the nature of the novel 65 porphyrins by cyclic voltammetry, spectrophotometric titration, and X-ray crystallography. The catalytic oxidation of cyclohexane and cyclohexene was subsequently conducted using novel Fe(III) porphyrins as catalysts. /. Trifluoromethylation It has been mentioned that direct introduction of —CF 3 groups onto the P-pyrrolic postions of porphyrins is most easily achieved using Cu(I) assisted trifluoromethylation (chapter I, section C), which can be classified into two methods; (i) pyrolysis of trifluoromethyl acetate and (ii) metathesis of tofluoromethylcadniium in the presence of Cu(I) halide. The active trifluoromethylating reagent is C F 3 C u and iodinated or brominated aromatic compounds are required for both methods (Chapter I, section C.2.). Several proposed mechanisms for copper assisted nucleophilic substitution of halogenated aromatic compounds have been reviewed in the literature. 1 8 1 The strategy adopted for P-trifluoromethylation is shown in Scheme 2-1. Metalloporphyrins as starting materials were required in order to prevent formation of the Cu(I) and Cu(II) complexes by the reaction of the free-base porphyrins with C F 3 C u (even though a free-base porphyrin was tested in a trifluoromethylation by the metathesis method). It has been reported that the use of iodinated aromatic compounds generally gives higher yields of trifluoromethyl aromatic compounds than the use of brominated ones for Cu(I) assisted trifluoromethylation.133 Accordingly, P-iodo-«?wo-tetraphenylporphyrins would be ideal substrates for Cu(I) assisted trifluoromethylation but the iodination of porphyrins has proved to be difficult, presumably due to the large steric bulk of the iodinium cation. 1 8^ Although iodination at the wwo-position of 5,15-diarylporphyrins is known, 1 8 3 >! 8 4 effective multiple 66 P-iodination has not been reported. 1 8 2 Consequendy, the precursors chosen were P-brominated-OTtfj'o-tetraphenylporphyrins, which are much easier to prepare. Br Ph M = 2H + , Zn(ll), Cu(ll), Ni(ll) CF 3 Cu by pyrolysis CF 3 Cu by pyrolysis Products CF 3 Cu by metathesis Products Products Scheme 2-1. Trifluoromethylation strategies. The trifluoromethylation strategies outlined in Scheme 2-1 are described in detail in the following sections. a. Synthesis ofprecursors The precursors chosen for Cu(I) assisted p-trifluoromethylation according to Scheme 2-1 were the readily obtainable CufTPPBr^ fJc) (Scheme 2-2), H 2 T P P B r 4 (45a), Zn(TPPBr 4) (45b), Cu(TPPBr 4) (45c), and Ni(TPPBr 4) (45d) (Scheme 2-3). Bromination of 2c (Figure 1-8) and 2a using NBS gave 7c7^ and 45a185,186 ^ yields of 75 - 80 %. The structures of the porphyrin 7c and 45a were confirmed by mass spectrometry and N M R spectroscopy. Zn(II), Cu(II), and Ni(II) complexes of 45a were synthesized by the general porphyrin metallation method. 6 8 This 67 metal insertion method is conducted in hot D M F in the presence of metal salts and produced the corresponding metalloporphyrins (45b, 45c, and 45d) with > 90 % yield. b. Trifluoromethylation by pyrolysis of CFjCO^Na/ Cul (1) Reaction using CufTPPBrg) (7c) Scheme 2-2 shows the attempted trifluoromethylation of Cu^TPPBrg) (7c) by pyrolysis of C F 3 C 0 2 N a / C u l in D M F . Firstly, trace amount of water in the mixture was removed by the use of a. toluene-azeotrope under an atmosphere of N 2 . After toluene was distilled out, the temperature was then raised to 150- 155 °C, and held for 2 h under N 2 . Pyrolysis of C F 3 C 0 2 N a was observed indirectly by gas evolution (presumed to be C O ^ for the first 10-15 min from the point the temperature had reached 150 °C. The reaction was monitored by UV-visible spectroscopy. The Soret band of the reaction mixture (466 nm for 7c) was observed at 434 nm at 30 min and no other changes were subsequently observed. Thin-layer chromatography (TLC) of the product mixture (44c) using various combinations of organic solvents and silica-gel plates did not show a satisfactory separation of the trifluoromethylated Cu(II) complexes (44c). Low resolution EI mass spectrometry of 44c showed tettalds(trifluoromethyl)-^j-o-tetraphenylporphyrinato Cu(II) (44c (x = 4)) as the major product in 100% intensity. Compounds 44c (x = 2), 44c (x = 3), 44c (x = 5), and 44c (x = 6) were also detected in 30, 74, 57, and 2 % intensities respectively. No sign of bromine groups on porphyrins in the reaction mixture was observed by mass spectrometry. Presumably reductive elimination of halogen had occurred. 187 A free-base mixture (44b) was obtained when Cu(II) complex 44c was treated with concentrated H 2 S 0 4 and neutralized with 10 % aqueous N a H C 0 3 . T L C analysis of free-base mixture 44a showed a better resolution than that observed for the Cu(II) complex mixture 44c and at least six compounds were observed by T L C analysis. Since the spots on the T L C plate 68 Ph 44a TLC T More than 6 compounds Scheme 2-2. Trifluoromethylation of P-octabromo-OT^o-tetraphenylporphyrinato Cu(II) (7c) by pyrolysis of C F 3 C 0 2 N a / C u I . i)toluene-azeotrope, 120 °C, N 2 ii)150 - 155 °C, 2 h, N 2 , iii)conc. H 2 S 0 4 , iv)10 % aq. N a H C 0 3 . 69 smeared and were so close together, isolation of the compounds was not attempted. Evidently, regioisomers and partially substituted P-tnfluoromethyl-TPPs existed in the mixture. This preliminary trifluoromethylation using p-octabromo-TPP (7c) led the author to use P-tetrabromo-TPPs (45b, 45c, and 45d) as precursors in an attempt to effect a cleaner reaction. (2) Reactions using MTPPBr4 (M = Zn(II), Cu(II), andNi(II)) (45b,45c,and 45d) The previous experiment showed that a significant number of partially trifluoromethylated porphyrins are produced due to reductive dehalogenation of brominated positions, since no bromine substituents are left after the reaction. As a result of this incomplete trifluoromethylation, various porphyrins, presumably including some regioisomers, are produced. In order to simplify the reaction, the P-tetrabrominated porphyrins, Zn(TPPBr 4) (45b), Cu(TPPBr 4) (45c), and Ni(TPPBr 4) (45d) (Scheme 2-3) were used. The central metal was varied in order to investigate the effect of metals upon reactivity in trifluoromethylation. The reaction procedure for trifluoromethylation by the pyrolysis method is as described in Scheme 2-2. After trifluoromethylation using any of the three metal complexes (45b, 45c, and 45d), the EI mass spectrum of the product mixture showed three mass peaks corresponding to P-bis-, P-tris- and P-tetralds(ttifluoromethyl)-^j-o-tettaphenylporphyrins (M(TPP(CF3)2)(46), M(rPP(CF3)3)(47), M(rPP(CF3)4)(48) (M = Zn(Ii), Cu(II), or Ni(H)) but T L C analysis (silica gel plate, CHCl 3 /pet . ether) of the product mixture (for any of Zn(II), Cu(II), and Ni(II)) showed smearing of the spots and did not show separation of 46, 47, and 48. Fortunately, it was found that free-bases (H 2 TPP(CF 3 ) 2 (46a), H 2 TPP(CF 3 ) 3 (47a), and H 2 TPP(CF 3 ) 4 (48a)  can be well separated on a preparative silica gel plate. The free-base porphyrins (46a, 47a, and 48a) were thus isolated, after demetalation of the product mixture, by silica gel chromatography (this statement 70 CF 3 C0 2 Na/Cul toluene/DMF i, a MTPPBr 4 (45) a: M = 2H+ b: M = Zn(ll), c: M = Cu(ll), d: M = Ni(ll) Scheme 2-3. Trifluoromethylation of P-tetrabromo-«?tfJO-porphyrins (45) by pyrolysis of C F 3 C 0 2 N a / C u I . ^toluene-azeottope, 120 °C, N 2 , ii) 150 - 155 °C, N 2 , 1 h iii)conc. H 2 S 0 4 , iv)10%aq. N a H C 0 3 71 applies to product mixtures in any complex form of Zn(II), Cu(II), and Ni(II)). Isolated free-base porphyrins H 2 TPP(CF 3 ) 2 (46a), H 2 TPP(CF 3 ) 3 (47a). and H 2 TPP(CF 3 ) 4 (48a) were identified by low resolution EI mass spectrometry, 1 H and 1 9 F N M R spectroscopy, and elemental analysis. Assignment of the N M R spectrum of 46a was difficult because peaks could not be assigned to a specific structure of H 2 TPP(CF 3 ) 2 . It is believed that 46a is a mixture of symmetric regioisomers, 46a' and 46a", which were not separated by chromatography. The results of trifluoromethylation of |3-tetrabromo-OTtfjo-tetraphenylporophyrins by pyrolysis of C F 3 C 0 2 N a / C u I are summarized in Table 2-1. The yield of P-tettalds(trifluoromethyl)porphyrin (48a) by this method was always low, while (3-bis- and P-tris(tjifluorometiiyl)porphyrins (46a and 47a) were produced as major products in about 20 - 40 % yield. Variation of the central metal did not significantly affect the yields. It seems that reductive debrornination is dominant in the reaction and this governs the product distribution. 46a' 46a" Table 2-1. Results of trifluoromethylation by pyrolysis methoda. Starting Material M Solvent Time/h Product (%)b 45b Zn(II) D M F 1 46a(16),47a(29), 48a(2.5) D M F 24 46a(21), 47a(19), 48a(3) 45c Cu(II) D M F 1 46a(37), 47a(29), 48a(5) 45d Ni(H) D M F 1 46a(28),47a(18),48a(3) a Porphyrin/CuI/CF 3 CO 2 Na=l/16/40. Temp. = 150 °C. b Yields are calculated based on M(TPPBr 4) (45). 72 In summary, the yields of the separated P-tettalds^fluoromethyl)-^^-teteaphenylporphyrin were low by use of the pyrolysis method but isolation of three novel P-trifluoromemylporphyrins (46a, 47a, and 48a) which are important for analysis of electron-deficiency of porphyrin macrocycles was allowed by this experiment. Trifluoromethylation by the pyrolysis method is easy to perform. Specifically, handling of the reagents is facile and the reagents are not expensive. However, this method requires high temperatures (150 °C) in order to generate the active C F 3 C u species and thus Cu(I) assisted substitution is hampered by reductive debromination of the starting material. Consequendy, one drawback of this method is that significant amounts of partially trifluoromethylated porphyrins are produced. Thus, trifluoromethylation under milder conditions was needed, especially for multiple trifluoromethylation, in order to avoid unnecessary debromination. c. Trifluoromethylation by CFfZu generated by the metathesis of trifluoromethylcadmium and CuBr The active trifluoromethyl agent in Cu(I) assisted trifluoromethylation is C F 3 C u , which is common to both the pyrolysis and metathesis methods. A n important difference between the two methods concerns the in-situ generation of C F 3 C u . In the pyrolysis method, C F 3 C u is generated from C F 3 C O z N a and Cu(I) halide at about 150 °C. O n the other hand, in the metathesis method, C F 3 C u is generated from trifluoromediylcadmium (mixture of (CF 3) 2Cd and CF 3CdBr) and Cu(I) halide at — 40 °C (see chapter I, section C.2.). The low reaction temperature required for the metathesis method enables the trifluoromethylation to be performed under milder conditions. The reduced temperature prevents reductive dehalogenation. (1) Preliminary experiments Trifluoromethylation using H 2 T P P B r 4 (45a), Zn(TPPBr 4) (45b), Cu(TPPBr 4) (45c), and Ni(TPPBr 4) (45d) with C F 3 C u generated by the metathesis of trifluoromeflrylcadmium and CuBr 73 was examined to assess the effect of the central metal upon reactivity. The reaction is shown in Scheme 2-4. According to literature precedence,^39 m e reaction was conducted at 70 °C for several hours in D M F using compounds H 2 T P P B r 4 (45a), Zn(TPPBr 4) (45b), Cu(TPPBr 4) (45c), and Ni(TPPBr 4) (45d). Since the work-up procedure is similar for all of the reactions, the procedure is only described for the reaction with 45b as the starting material. After the reaction, D M F and some of the H M P A were distilled off under reduced pressure. The green viscous residue was diluted with acetone and filtered. EI mass spectrometry of the mixture showed that it contained not only Za(TPV(CF^ (46b), Z n C T P P ^ ^ ) (47b), and Zn(TPP(CF 3) 4) (48b), but also partially brominated and partially trifluoromethylated products (49b, see Scheme 2-4). The crude yield of compound mixture 49b was significant (~ 40 % based on 45b). After the mixture containing compounds 46b —49b was treated with cone. H 2 S 0 4 and neutralized with 10% aqueous N a H C 0 3 , free-bases 46a - 48a were isolated by silica gel chromatography. Free-bases of 49 could not be isolated because the spots were co-eluted, thus appearing as a broad band. The results are summarized in Table 2-2. The Cu(II) and Ni(II) complexes (45c and 45d) were not very soluble in D M F at 70 °C and thus trifluoromethylation reactions were unsuccessful; no tetralds-trifluoromethyl product was obtained and more than 70% of the starting materials was recovered. Trifluoromethylation using free-base porphyrin (45a) was also unsuccessful. Free-base porphyrin 45a was metallated with CuBr under the metathesis conditions and Cu(TPPBr 4) (45c) precipitated out of solution and also small amount of Cu deposition resulted. Thus, trifluoromethylation using free-base porphyrin (45a) resulted in a similar product distribution as was obtained for Cu(II) porphyrin 45c. Zn(II) porphyrin 45b is more soluble than 45c and 45d in D M F at 70 °C. Thus, Zn(II) porphyrin 45b seems to be the best choice of the four tested porphyrins. However, even with this 45b as the starting material, 10 % of it was recovered. This implies that 45b may not be completely soluble under the reaction conditions. ry(49) Ph C F 3 Ph 47 48 Scheme 2-4. Trifluoromethylation of P-tettabromo-^-fo-porphyrins by metathesis of CF3-Cd*/CuBr/HMPA. i)70 °C, N 2 , 5 h, ii)removal of solvents, iii)filtration, iv)conc. H 2 S 0 4 , v)10 % aq. N a H C 0 3 * C F 3 - C d = (CF3)2Cd + CF 3 CdBr . 75 Table 2-2. Trifluoromethylation by metathesis using M T P P B r 4 (45)a. Porphyrin M Product (%)b 45a 2 H + 45c(67), 46a(l), 47a(4), 48a(0) 45b Zn(II) 45b(10), 46a(2), 47a(8), 48a(l 1) 45c Cu(II) 45c(73), 46a(2), 47a(5), 48a(0) 45d Ni(II) 45d(86), 46a(l), 47a(2), 48a(0) a Porphyrin 0.16 mmol/CuBr 4 mmol /CF 3 -Cd 4 m m o l / H M P A 4 mL, 70 °C, 5 h, under N 2 . b Isolated yields are reported. Partially brominated and partially trifluoromethylated porphyrins are not shown in the table because isolation was not possible. P-Tetrakis-trifluoromethyl porphyrin was produced in 11 % yield. This result represents a significant improvement from that observed in the pyrolysis method. However, the yield was still low. Since significant amounts of partially brominated and partially trifluoromethylated porphyrins (49b) were obtained, the reaction may be slow and long reaction times may be needed. Usually, trifluoromethylation of halogenated aromatic compounds by metathesis under the same reaction conditions gives moderate yields (e.g. 76 % for the conversion of on^o-iodotoluene to on$o-tjifluoromethyltoluene)133 j n thi s W O r k , trifluoromethylation is required to occur in a sterically hindered region (P-pyrrolic positions are located between two phenyl groups and adjacent to each other) and the reaction may thus be slower than usual trifluoromethylation using simple substrates such as iodotoluene. Consequendy, either longer reaction times or higher reaction temperatures may be necessary in order to facilitate trifluoromethylation with the same molar ratio of the reactants. Thus, optimization using Zn(TPPBr 4) (45b) in metathesis induced trifluoromethylation at different reaction times and temperatures was investigated. 76 (2) Optimisation of the yieldfor B4etrakis(trifluoromethyl)-meso-tetraphenylporphyrin As described in the previous section, trifluoromethylation of Zn(TPPBr 4) (45b) under the conditions shown in Scheme 2-4 showed significant amounts of partially brominated and tnfluoromethylated porphyrins, presumably due to steric hindrance. The first part of this section describes investigations concerning the effects of reaction times upon the yield of P-tettakis(tiifluoromemyl)-OTWo-tetJraphenylporphyrin by the metathesis methodology. The reaction time was extended to 88 h with all other reaction conditions shown in Scheme 2-4 remaining constant. During the reaction, changes in the UV-visible spectrum were monitored. As shown in Figure 2-1, the spectrum of an aliquot of the reaction mixture diluted in CH 2 C1 2 changed considerably with time. The Soret band (430 nm) of 48b (trace A in Figure 2-1) had shifted to 448 nm and a maximum of a broad Q band was at about 700 nm after 4 h (trace C). After 48 h, the Soret and the maximum of the broad Q band was seen to have gradually blue-shifted and settled at 438 nm and 660 nm, respectively (trace F). There was a large shoulder around 460 nm. There was no change after 48 h (trace F (48 h), G (68 h), and H (88 h)). Trace I in Figure 2-1 is the spectrum of the required product Zn(TPP(CF3)4)(48b) in CH 2Cl2 and trace J is 48b in CHjCL^ containing ~1 % (v/v) H M P A . Spectrum J has maxima at 448 nm and 724 nm, with a large broad shoulder at 462 nm, which is attributed to the presence of H M P A by comparison to the spectrum F, G, and H. After 88 h, the reaction mixture was subjected to an acidic work-up (TFA-CH^CL) to effect demetallation of the products. Analysis by F A B mass spectrometry indicated that the product mixture contained several perfluoroalkylporphyrins as shown in Table 2-3. The mass of compound 50a is different from that of H 2 TPP(CF 3 ) 3 (47a) by 50, which agrees with the mass of - C F 2 - (= 50.0). It is conjectured that the presence of compounds 50a, 51a, 52a, 53a, 54a, and 55a originates from the 77 00 CO T 1 1 1 r 350 400 450 500 550 600 650 700 750 800 Wavelength/nm Figure 2-1. UV-visible spectra during trifluoromethylation of 45b at 70 °C. A: 45b, B: 15 min, C: 4 h, D: 20 h, E: 25 h, F: 48 h, G: 68 h, H: 88 h, I: 48b, J: 48b + H M P A . . 78 introduction of extended perfluoroalkyl chains into the porphyrin (see eq.(1.3) and (1.4), p.37). Similarly, a mass difference of 50 is seen among 48a, 52a, 54a, and 55a and between 50a and 51a. The structure of 52a is shown below but the regiochemistry of porphyrins 50a, 51a, 53a, 54a, and 55a is uncertain. Table 2-3. Products obtained by the reaction at 70 °C for 88 h Products Mass(obsd)a) Mass(calcd for) Relative Intensity H 2 TPP(CF 3 ) 3 (47a) 820 818.7(C 4 7H 2 7F 9N 4) 24 H 2 TPP(CF 3 ) 4 (48a) 888 886.7(C 4 8H 2 6F 1 2N 4) 80 50a 870 868.8(C 4 8 H 2 7 F n N 4 ) 37 51a 920 918.8(C 4 9H 2 7F 1 3N 4) 36 H 2 TPP(CF 2 CF 3 ) (CF 3 ) 3 (52a) 938 936.8(C 4 9H 2 6F 1 4N 4) 100 53a 970 968.8(C 5 0H 2 7F 1 5N 4) 21 54a 988 986.8(C 5 0H 2 6F 1 6N 4) 81 55a 1038 1036.8(C 5 1H 2 6F 1 8N 4) 21 Low resolution F A B mass spectrometry. Separation of the perfluoroalkylated porphyrins was attempted. A patient and agonizing search for a suitable solvent system for T L C analysis found a solvent system to separate these porphyrins as shown in Table 2-4. The major products 48a, 52a, and 54a could be separated on a silica gel chromatographic plate using benzene/cyclohexane/acetone= 6/3.5/0.5 (Table 2-4). Due to the small amounts present, products 50a, 51a, 53a, and 55a could not be clearly seen on the T L C plate. After 48a and 52a were isolated, a weakly colored (orange) band was left near the top of the column. This colored band could not be flushed out with polar solvents such as M e O H or acetone. Unfortunately, 54a could not be isolated. Presumably, it decomposed on the 79 silica gel column during the chromatographic separation of 48a and 52a. Isolated 48a and 52a were identified by ' H and 1 9 F N M R spectroscopy, EI mass spectrometry, and elemental analysis. Table 2-4. R f values for metal-free perfluoroalkylated porphyrins Solvent System CH2Cl2:hexane C6H6:cyclohexane:acetone =3:7 =6:3.5:0.5 Porphyrin 46a 0.57a) -47a 0.29 -48a 0.09 0.38 52a 0.09 0.27 54a 0.09 0.18b) a)Mixture of regioisomers. b ) Smears. The yield of the required porphyrin H 2 TPP(CF 3 ) 4 (48a) was 13 % (Table 2-5). This result was similar to that obtained by trifluoromethylation at 70 °C and 5 h (see Table 2-2) but the yield of H 2 TPP(CF 2 CF 3 ) (CF 3 ) 3 (52a) was 22 % (Table 2-5). This product was not obtained after the reaction of 5 h duration. Since partially brominated and partially trifluoromethylated porphyrins were not detected in the product mixture by F A B mass spectrometry, the reaction time (88 h) was evidently long enough to allow complete exchange of the bromine by nucleophiles. However, it seems that exchange of - B r and —CF 3 groups is slow and the C F 3 nucleophile is lost due to extension of perfluoroalkyl anions (eq.(1.3) and (1.4), p.37). Thus, nucleophilic attack by oligomerized perfluoroalkyl anions rather than the trifluoromethyl anion is increased, giving porphyrins with oligomerized perfluoroalkyl groups. In summary, extension of the reaction time to 70 °C facilitated exchange of - B r with perfluoroalkyl groups but the product distribution was found to be complex due to extension of the perfluoroalkyl chain. 133 Separation and purification of the complex mixture of 80 P-trifluoroalkylated porphyrin products were found to be extremely difficult and not wholly successful despite intense efforts. Reactions were also run at higher temperatures in order to investigate the effect of temperature on the product distribution and yield. Figure 2-2 shows the UV-visible spectra observed for trifluoromethylation at 110 °C under otherwise identical conditions to those shown in Table 2-2. In this reaction, the peak of the Soret band of 45b was observed at 448 nm at 15 min (trace B). The spectra remained unchanged between l h (C) and 2 h (D). At 4 h (E), a split of the Soret band was observed. At 6 h (F), the Soret was a single band at 434 nm and there was little change in the spectra afterwards (8h (G) and 21 h (H). Unlike the case for the reaction at 70 °C, the shoulder around 460 nm is not prominent after reaction completion (compare Figure 2-1, H to Figure 2-2, H). The final position of the Soret band was 4 nm shorter than that of the reaction at 70 °C and the final U V -visible spectrum seems quite different to traces I and J. EI mass spectrometry of the final reaction mixture contained neither partially brominated porphyrins nor the porphyrins with extended perfluoroalkyl chains. The product mixture contained only bis-, tris-, and tetrakis-trifluoromethyl Zn(II) porphyrins (46b, 47b, and 48b). After demetallation, the porphyrin mixture was purified by column chromatography on silica gel to give the isolated products H 2 TPP(CF 3 ) 2 (46a) (13 %), H 2 TPP(CF 3 ) 3 (47a) (12 %), and H 2 TPP(CF 3 ) 4 (48a) (17 %). Dehalogenation of halogenated aromatic compounds in D M F is known. 187 The reaction was also run at 90 °C and isolation of the final products in free-base form was performed. Isolated products of the several reactions with different temperatures and times are summarized in Table 2-5. Figure 2-2. UV-visible spectra during trifluoromethylation of 45b at 110 °C. A: 45b, B: 15 min, C: 1 h, D: 2 h, E: 4 h, F: 6 h, G: 8 h, H: 21 h, I: 48b, J: 48b + H M P A . 82 At low reaction temperatures, extension of perfluoroalkyl chains occurs giving significant amounts of H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a). At high reaction temperatures the yields of P-bis- and P-teis(trifluorometliyl)porphyrin (46a and 47a) increase and 52a is not isolated. As shown in Table 2-5, the several-hour reactions at 90 °C resulted in the best yields of the required P-tetrakis(difluoromethyl)porphyrin (48a). Table 2-5. Isolated P-perfluoroalkyl-^gJo-tetraphenylporphyrins. Isolated porphyrin(%) Temp.(°C) Time (h) 46a 47a 48a 52a 70 88 5.6 13 22 90 7 9 21 38 10 5 11 24 42 8 110 21 13 12 17 8 16 13 20 In summary, the pyrolysis method was not appropriate for the effective trifluoromethylation of P-octabromo- and P-tetrabromo-/»wo-tetraphenylporphyrins. Only complex mixtures and low yields of P-tiifluoromemyl-w^o-tettaphenylporphyrins were obtained using P-octabromo-w^-tetraphenylporphyrin as a starting material. The reactions using P-tetrabromo metalloporphyrins yielded P~bis- or P-tris (trifluoromethyl) -meso-tetraphenylporphyrins as major products and P-tettalds(tjifluoromethyl)porphyrin was obtained in very low yields. The reaction conditions, especially the high temperature (150 °C), were found to be too severe for multiple trifluoromethylation using P-octabromo or P-tetrabromoporphyrins and reductive debromination seemed to dominate under these conditions. Trifluoromethylation by C F 3 C u generated by the metathesis of tofluoromethylcadrnium and CuBr can be performed under relatively milder reaction conditions. However, the highest 83 temperature reported for this reaction (70 °C)133 Was not sufficiently high for effective multiple trifluoromethylation of p-tettabromo-wwo-tetjraphenylporphyrins. Longer reaction times at 70 °C increased the yields of higher fluorinated alkyl species, which attack the brominated p-pyrrolic positions to yield porphyrins with extended perfluoroalkyl chains such as 50a - 55a. Reactions at 110 °C did not give such porphyrins but higher yields of porphyrins 46 and 47 were obtained due to reductive debromination. Thus, the yields of P-tettalds(ttifluoromethyl)porphyrin 48 were maximized for the reaction at 90 °C for 5 h. The UV-visible spectra obtained during trifluoromethylation via the metathesis method showed significant red-shifts of the peaks in the early stage of the reactions (Figure 2-1 and Figure 2-2), and for the reaction at 110 °C red-shifts were followed by blue-shifts of the peaks (Figure 2-2). It is known that porphyrin plane distortion induces red-shifts of UV/visible absorption bands (see Chapter 1, section D./.b.).144-147 Steric interaction between the adjacent pyrrolic P-substituents was analyzed by computer modeling. Figure 2-3 shows geometry optimized 3,4-dibromopyrrole and 3,4-bis(trifluoromethyl)pyrrole (2,5-hydrogens were omitted) by molecular mechanics.188 According to the calculation, the — C F 3 groups are closer to the pyrrole ring than the —Br groups and the van der Waals radius of —CF 3 is much larger than that of —Br. The distance between the two —Br centers (3.645 A) is comparable to the sum of the two - B r vdw radii (3.90 A). O n the other hand, the C-C distance between the two - C F 3 groups (3.273 A) is much smaller than the sum of the two - C F 3 vdW radii (5.66 A). Since rotation of the —CF 3 presumably occurs, steric interaction between the two —CF 3 groups may be seriously large. Keeping this in mind, the author attempted to rationalize the unique shifts of peaks of the U V -visible spectra during trifluoromethylation (Scheme 2-5). In the early stage of the reactions, the partially brominated and trifluoromethylated porphyrins such as mono-trifluoromethylated 84 v d W ( B r ) = 1.95 A C - F = 1.492 A v d W ( F ) = 1.35 A . w d W (CF3) = 2.83 A Figure 2-3. 3,4-Dibromopyrrole and 3,4-bis(trifluoromethyl)pyrrole modeled by H y p e r C h e m . 1 8 9 The van der Waals (vdW) radii o f B r and F were obtained from ref.123 and the v d W o f C F 3 was calculated from the C - F bond length and the v d W (F). 85 86 ZnTPPBr 3 (CF 3 ) or bis-tofluoromethylated ZnTPPBr 2 (CF 3 ) 2 may be produced fairly easily but introduction of the bulky - C F 3 groups presumably forces the macrocycle to distort to some degree. Macrocycle distortion will cause red-shifts of the absorption bands in the UV-visible spectrum. 144-147 j t j s conjectured that a problem starts after introduction of the second —CF 3 group. Since the steric interaction between the adjacent - C F 3 groups on a pyrrole is severe as shown in Figure 2-3, introduction of the third and the fourth - C F 3 should be much more difficult (slower) than that of the first two. The measures taken in order to overcome this steric encumberance were to extend the reaction time and to raise the reaction temperature. For extended reaction times at 70 °C, more of the extended perfluoroalkyl chains are introduced onto the porphyrins and complete trifluoromethylation is hampered by extension of perfluoroalkyl chain. O n the other hand, at 110 °C reductive debromination prevents effective trifluoromethylation. The reactions at 90 °C gave the best yield (-40%) of Zn(TPP(CF 3) 4) (48b) of the three temperatures. However, difficult chromatographic purification was still required in order to obtain pure P-tetraltis(rjifluorometliyl)-OTtfj'o-teteaphenylporphyrin (48a). Nevertheless, the optimized trifluoromethylation reaction produces the required porphyrin 48a in a sufficient yield to continue further studies. The yield of required 48a could also be improved by increasing the amount and concentration of C F 3 C u but the effect of molar ratio of the reactant on the product yield was not investigated. In the demetallation process following trifluoromethylation, CuBr must be completely removed. This is because treatment of the product mixtures containing 48a with acid in the presence of CuBr gives an unidentified orange compound. As shown in Figure 2-4, a broad Soret-band-like peak appeared at 420 nm and no Q bands were observed in the UV-visible spectrum of this orange compound. This phenomenon was checked with pure 48a in the 350 450 550 650 750 850 950 Wavelength (nm) Figure 2-4. UV-visible spectra of the orange compound (dark line) and H2TPP(CF3)4( 8a) (narrow line). 88 presence of CuBr in acidic (TFA) CH 2 C1 2 and indeed the orange compound was obtained. Porphyrin 48a seems to be reduced to the orange compound by the electron produced by the presence of CuBr in acidic conditions, thus causing a significant decrease of the final product yield. This phenomenon was also observed with H 2 TPP(CF 2 CF 3 ) (CF 3 ) 3 (52a). This phenomenon can be avoided by careful removal of CuBr (for example tofluoromemylporphyrins in metallated forms are very soluble in acetone, CH 2 C1 2 , or CHC1 3 but CuBr is not. Thus after the reaction, dried product mixtures were dissolved in acetone and CuBr could be filtered off before demetallation. Although further investigation to study the mechanism of reduction was not attempted since the orange compound could not be identified, sensitivity of these porphyrins to reducing reagents will also be shown in section AJ. and B.5.a.(2). 2. Methylation (3-Methyl-wwo-tetraphenylporphyrins were required in order to compare the electronic and structural effects of these porphyrins with the trifluoromethyl analogues. Methylation of P-tettabromo-^j-o-tettaphenylporphyrin Zn(II) complex (45b) was performed by Cu(I) assisted methylation involving the use of C H 3 L i and Cu(I) halide. 1^9 As shown in Scheme 2-6, 45b was treated with an excess of Li(CH 3 ) 2 Cu at 32 - 33 °C for 24 h, which was formed by the reaction of C H 3 L i and CuBr at - 80 °C in ether. Oligomerization as observed for trifluoromethylation of P-tetrabromoporphyrin by metathesis did not occur in this case. After the coupling reaction, the remaining bromo substituents were removed by reflux in D M F in the presence of CuBr under air for 2 h. Since the major purpose was to obtain P-methylporphyrins but not to analyze the methylation reaction products, brominated sites were eliminated in order to simplify separation of P-methylporphyrins. Formation of p-methyl-^jo-tetraphenylporphyrins (57b - 59b) was confirmed by EI mass spectrometry. The solubility of the Zn(II) complexes of ZnTPP (2b) 58b 59b iii, iv T 2a (32 %), 56a (0.5 %), 57a (19 %), 58a (17 %), 59a (15 %) Scheme 2-6. Methylation of 45b. i) E t 2 0 , 32 °C, 24 h, ii)CuBr, D M F , reflux, 2 h, iii)TFA, reflux, 1.5 h, iv)10 % aq. N a H C 0 3 . a = 2 H + , b = Zn(II) 90 p-methylporphyrins (ZnTPP(CH 3 ) 2 (57b), ZnTPP(CH 3 ) 3 (58b), ZnTPP(CH 3 ) 4 (59b)  was low in CHC1 3 , CH 2 C1 2 and benzene, while the free-bases showed moderate solubility in those solvents. Thus, separation by chromatography on silica gel was performed with the metal-free porphyrins (H 2 TPP(CH 3 ) 2 (57a), H 2 TPP(CH 3 ) 3 (58a), H 2 TPP(CH 3 ) 4 (59a). The isolated yields are shown in Scheme 2-6. p-Mono(methyl)-w^-tetraphenylporphyrin (H 2TPP(CH 3)) (56a) and H 2 T P P (2a) were also obtained in 0.5 % and 32 % yield, respectively. As found for trifluoromethylation products, P-bis(methyl)-OTtfj-o-tetraphenylporphyrin (57a) is formed as a mixture of regioisomers which were not separated. In summary, methylation of the P-tetrabromo-wwo-tetraphenylporphyrin zinc complex by C H 3 L i and CuBr (Li(CH3)2Cu) was achieved. The required P-tetramethyl-w^o-tetraphenylporphyrins (59a) were obtained in 15 % yield. The yield was low but since the amount of isolated 59a was sufficient for analysis to compare with P-tetrakis(trifluoromethyl)-OTtfjo-tetraphenylporphyrin (48a), this reaction was not optimized. Two other P-methyl porphyrins (57a and 58a) were also obtained, which enabled a study of a series of compounds. 3. Metallation MetaUation of H 2 TPP(CF 3 ) 4 (48a) with Zn(H)/Co(H)/Fe(Iir) is described to give the corresponding complexes. The Zn(II) and Co(II) complexes were to be used in electrochemical studies and in the study of axial ligand binding by spectrophotometric titration. Zn(TPP(CF 3) 4) (48b) was synthesized by trifluoromethylation of Zn(TPPBr 4) (45b) as described in the previous section. However, pure p-tettalds(trifluorometJiyl)-OTtfj"o-tetJ:aphenylporphyrin could only be obtained by chromatography of the free-base 48a. Thus, complex 48b was subsequently obtained by re-metallation of 48a. The Fe(III) complex is important for models for 91 cytochromes P-450s since the enzymes contain protoporphyrin IX Fe(III) complex in the functional site. a. Synthesis of Zn(II) and Co(II) complex of 48 Insertion of Zn(II) and Co(II) into 48a was found to be straightforward. As shown in Scheme 2-7, 2.5-3 eq. (excess amount of metal salts were used to ensure complete metallation) of C F 3 Ph MTPP(CF 3) 4 98 %, 48b: M = Zn(ll) 96 %, 48e: M = Co(ll) Scheme 2-7. Insertion of Zn(II) and Co(II) into H 2 T P P ( C F 3 ) 4 (48a). i)Zn(OAc) 2 .2H 2 0 or CoCl 2 , M e O H - C H C l , a solution of Zn(OAc) 2 -2H 2 0 (or CoCL) dissolved in M e O H were added to a CHC1 3 solution of free-base porphyrin (48a). For the reaction with the Zn(II) salt, the color of the brown suspension of the free-base porphyrin instantly changed to bright green at room temperature upon addition of Zn(OAc) 2 dissolved in M e O H . The color change was easily observed by U V -visible spectroscopy (UV-visible spectra will be shown later in this chapter). For the reaction with the Co(II) salt, formation of the complex was observed by a color change from brown to bright green upon heating the mixture on a steam bath. Since the ligand was known to be pure, purification required only removal of excess metal salts which was easily done by washing the CHC1 3 solution of the complexes with water and drying over anhydrous Na 2 S0 4 . The yields for 92 48b and 48e were 98 and 96 %, respectively. Formation of 48b and 48e was confirmed by elemental analysis, mass spectrometry, and J H and 1 9 F N M R spectroscopy. b. Synthesis ofFe(III) complexes of 48 and 52 Usually, Fe(III) complexes of porphyrins are made by insertion of Fe(II) into the macrocycle followed by aerobic autoxidation of Fe(II) to Fe(III). 6 9 Typically the reactions are conducted using FeBr2i9o or FeCl 2i9i in dry T H F , FeS0 4 -7H 2 0 (saturated aqueous solution)69,163 m a c e u c acid/pyridine, or Fe(OAc) 2 (Fe powder in hot acetic acid) 6 9 in acetic acid. The insertion reaction must be initially performed under Ar or N 2 , followed by exposure of the reaction mixture to air after the Fe(II) insertion, thus allowing oxidation to Fe(III). In some cases Fe(0) (from Fe(CO)5) can also be inserted to give Fe(III) complexes.I63,192 As shown in path A of Scheme 2-8(a), all of these routes were attempted but synthesis of the Fe(III) complex of 48a proved to be unsuccessful. In each case when the free-base porphyrin (48a) was mixed with the Fe(II) or Fe(0) reagent, the solution (initially brown due to free base 48a) became orange, and showed a broad single band at 418-420 nm in the UV-visible spectrum in CH 2 C1 2 . This spectrum was identical to the one obtained from 48a + CuBr under acidic conditions (chapter 2 section A . / . , Figure 2-4). The same spectrum was obtained when the free-base (48a) was treated with aqueous L-ascorbic acid (we employed this reducing reagent since ascorbic acid is a well-known reducing reagent for the reduction of transition metal cations such as Fe(III)l 9 3). Assuming that the orange compound was a reduced form of the free-base 48a by reaction with Fe(0), Fe(II), ascorbic acid, or Cu(I), the orange compound was treated with an oxidizing reagent such as dilute H 2O 2(5-10 %) in CH 2 C1 2 but the UV-visible spectrum of the orange compound did not return to that of the free-base. Thus, it was found that 48a is very 93 Orange compound (b) Ph Br Ph-< /FeOIIJ^-Ph Scheme 2-8. Synthesis o f F e C T P P ( C F 3 ) 4 ) C l (48f) and F e ( T P P B r 4 ) C l (45e). i ) F e C l 2 , T H F , reflux, 2 h(Ar) , 2 h(air); Fe, H O A c , 100°C, 2 h(Ar) , 2 h(air); or F e ( C O ) 5 , 1 2 , 60°C, 5 h(Ar),rt, 12 h(air), i i ) L i N ( S i M e 3 ) 2 , T H F , r.L, A r , i i i ) F e C l 2 , 50°C, 5 min(Ar) , r.t., 2 h(air), iv)neutral alumina ch roma tog raphy-CHCl 3 , v)6 M aq. H C 1 , v i ) T H F - 2 0 % aq. K O H , r . t , 2 h, air. 94 sensitive to reduction to give an unidentified orange compound which is not itself easily oxidized. For comparative purpose, a Fe(III) complex was prepared using H 2 T P P B r 4 (45a) but the free-base 45a did not suffer reduction under these conditions. In order to facilitate the insertion of Fe(II), and avoid the irreversible reduction of 48a, path B of Scheme 2-8(a) was followed; firstly the N - H protons of the free-base were deprotonated by treatment with lithium bis(tjtimethylsilyl)amide (LiN(SiMe3)2) to yield the lithium complex of the porphyrin (60), 1 9 4 then this was reacted with F e C ^ . ^ 3 This method successfully gave the final product, Fe(TPP(CF 3) 4)Cl (48f), in 56 % yield after purification. The rationale for why reduction of the porphyrin did not occur in this case is probably due to a change of the reduction potential of the macrocycle by replacement of H + with L i + . The first ionization energies of H and I i are 13.60 eV and 5.32 eV respectively,!9^ ancj ^ u s H + should be more electron-withdrawing than L i + and the reduction potential of the macrocycle should decrease (harder to reduce) by replacement of H + with L i + . In the purification process (step iv in Scheme 2-8(a)), the p-oxo dimer (61) was formed on the neutral alumina chromatographic column. The p-oxo dimer was then converted to 48f by washing 61 in CH 2 C1 2 with 6 M HC1. Compound 61 can also be produced by treatment of 48f with an alkali solution (step vi in Scheme 2-8(a). Similarly, Fe(TPP(CF 3) 3(CF 2CF 3))Cl (52c) (not shown in Scheme 2-8) was obtained in 76 % yield after purification. As shown in Scheme 2-8(b), for 45a, in addition to the reported F e C l 2 / T H F method^ 9!, Fe(OAc) 2in acetic acid also worked well to prepare Fe(TPPBr 4)Cl (45e) in 92 % yield. Compounds 48f, 52c, and 61 were characterized using EI mass spectrometry and ' H and 1 9 F N M R spectroscopy. The ' H N M R spectrum of 48f and 52c showed a broad singlet at 77 ppm and a broad multiplet at 74 ppm respectively, which are similar chemical shifts to that of 74 ppm observed for the P-pyrrolic protons of Fe(TPPBr 4)Cl (45e) and 95 that of 79 ppm observed for Fe(TPP)Cl (2d). These large downfield chemical shifts of the P-pyrrolic protons are indicative of high spin (S=5/2) Fe(III) porphyrins.191,196 Thus, with compounds Fe(TPP(CF 3) 4)Cl (48f) and Fe(TPP(CF 3) 3(CF 2CF 3))Cl (52c) in hand analysis and comparison studies could be continued. 4. Summary To conclude, P-trifluoromethyl and P-methyl porphyrins have been prepared from p-tetrabromo-porphyrin. Zn(TPP(CF 3) 4) (48b) and Co(TPP(CF 3) 4) (48e). Preparation of the Fe(III) complex of P-tetrakis(trifluoromethyl)- and P-tiis(tjifluoromemyl)(pentafluoroethyl)-porphyrins was found to be more problematic, but eventually Fe(TPP(CF 3) 4)Cl (48f) and Fe(TPP(CF 3) 3(CF 2CF 3))Cl (52c) could be obtained in moderate yields. Further research into the synthesis of these compounds must focus on increasing the yields. For the trifluoromethylation reaction, the effect of molar ratio of the reactants may be investigated. For methylation, palladium-catalyzed cross coupling reaction may be a useful alternative method.197,198 phe yield of the Fe(III) complex of P-tetrakis(trifluoromethyl)-porphyrin (481) may be improved indirecdy by understanding the mechanism of reduction of the free-base porphyrin, which was the major problem in preparation of the complex. B. Analysis of P-trifluoromethyl-weso-tetraphenylporphyrins As described in Chapter I, the porphyrin macrocycle shows characteristic UV-visible, N M R spectroscopic, and redox properties due to the 7t-conjugated electron system. The strong electron-withdrawing effect of the —CF 3 group introduced onto the macrocycle affects the electronic property of the macrocycle. Thus, the first point of investigation is the electronic 96 structures of the novel P-teifluoromethylporphyrins. One of the main objects of section B is to describe the investigation regarding this point by the UV-visible, N M R spectroscopy, cyclic voltammetry, and X-ray crystallography. Since —CF 3 is also a bulky group, the second point of investigation is a structural change of the macrocycle imposed by introduction of —CF 3 groups. In order to achieve this goal the steric effect of - C F 3 groups on the macrocycle, the X-ray crystal structure of a p-tettakis(trifluoromethyl)porphyrinato Zn(II) (Zn(TPP(CF3)4) (48b), see Scheme 2-7) is examined and compared with those of a P-tetramethylporphyrinato Zn(II) (Zn(TPP(CH 3) 4) (59b), Scheme 2-6), a p-tetrabromoporphyrinato Zn(II) (Zn(TPPBr4) (45b), Scheme 2-1), and other reported metalloporphyrins such as Zn(TPP) (2b) (Figure 1-8). Rationalization of characteristic UV-visible and N M R spectra of P-trifluoromethylporphyrins in terms of the steric effect as well as the electronic effect of —CF 3 was also attempted. Our tliird point of investigation is the electron-deficiency of the novel P-trifluoromethylporphyrins. Electron-deficiency and affinity can be discussed in terms of the redox properties of the macrocycles, although the pure electronic effect of substituents can be hampered by a structural change of the macrocycle as discussed in Chapter I, section D.Zb. Accordingly, in order to assess the electron-deficiency of P-tetrakis(tri.fluoromethyl)porphyrin from view points other than the macrocycle redox properties, determination of the piC, for the first deprotonation of pyrrolic N - H of p-tettalds(trifluoromethyl)porphyrin and determination of the stability constants for pyridine and imidazole binding to the central Co(II) of p-tettalds(tiifluoromethyl)porphyrin Co(II) complex by spectrophotometric titration were performed. The reason that Co(II) complex was chosen as the porphyrin system and pyridine 97 and imidazole as ligands is that homologous systems have been studied using a few electron-deficient porphyrins. The resulting evaluation of electron-deficiency of P-tettakis(tofluoromemyl)-porphyrin can be easily done by comparing this system with other reported electron-deficient porphyrin systems. Details of the analysis are described in the following sections. /. UV-visible spectra of synthesized novelporphyrins The main purpose of this section is to analyze the electton-withdrawing effect of trifluoromethyl groups on the electronic structure of the novel p-trifluoromethyl-w^o-tettaphenylporphyrins. The three synthetic porphyrins, P-bis-, tris-, tetrakis(trifluoromethyl)porphyrins (H 2 TPP(CF 3 ) 2 (46a), H 2 TPP(CF 3 ) 3 (47a), and H 2 TPP(CF 3 ) 4 (48a) see Chapter II, section A) are the subject of the investigation. The first part of this section concerns the UV-visible spectra of the novel P-trifluoromethylporphyrins in the free-base form. The UV-visible spectra of these are compared with those of H 2 T P P (2a) (Figure 1-8), H 2 T P P B r 4 (45a)(Scheme 2-1), and P-methylporphyrins (56a-59a) (Scheme 2-6) and the similarity of the spectra of H 2 TPP(CF 3 ) 3 (47a), H 2 TPP(CF 3 ) 4 (48a) and p-tris(trifluoromethyl)(pentafluoroethyl)porphyrin (H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a), p.78) to that of bacteriochlorin (64) (p. 108) is to be discussed. The second part of the section describes the concentration effect on the UV-visible spectral change of H 2 TPP(CF 3 ) 4 (48a) and H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a), since there is a concern that electron-deficient porphyrins may have high tendency to aggregate (see Chapter I, section D J.b.). In the second part of the section the UV-visible spectra of the Zn(II), Co(II), and Fe(III) P-tettakis(trifluoromethyl)porphyrins are compared with known metalloporphyrins and the some 98 tendencies commonly observed through the novel P-tettakis(trifluoromemyl)metaUoporphyrins are described. a. Free-base porphyrins (1) UV-visible spectra in CH2Cl2 In this section UV-visible spectra of the free-base porphyrins in one of the most common solvents for porphyrins, CH 2 C1 2 , are shown and effects of - C F 3 groups on the electronic and steric properties of the porphyrin macrocycle are discussed. UV-visible absorption maxima of free-base P-substituted ^j-o-tetraphenylporphyrins together with reported electron-deficient porphyrins are summarized in Table 2-6. All porphyrins except for H 2 (CF 3 ) 4 P (16a, n=l) (Figure 1-8, p. 11) are «?«o-tetraphenylporphyrins. As observed along with introduction of other electron-withdrawing groups onto H 2 T P P (2a) (Figure 1-8) (e.g. 2a -> H 2 T P P B r 4 (45a)(Scheme 2-1) or 2a H 2 TPP(CN) 4 (32a, x=4)185 (Figure 1-20, p.51)), large red-shifts of absorption maxima were observed for the series of p-trifluoromethylporphyrins H 2 TPP(CF 3 ) 2 (46a), H 2 TPP(CF 3 ) 3 (47a), H 2 TPP(CF 3 ) 4 (48a) (Scheme 2-2) and H 2 TPP(CF 3 ) , (CF 2 CF 3 ) (52a) (p.78). O n the other hand, the series of P-methylporphyrins H 2 TPP(CH 3 ) 2 (57a), H 2 TPP(CH 3 ) 3 (58a), and H 2 TPP(CH 3 ) 4 (59a) (Scheme 2-6) showed insignificant red-shifts from that of H 2 T P P (2a). These observations indicate that the electronic structures of P-tjrifluoromethylporphyrins were significantly changed from that of 2a but those of P-methylporphyrins were not. Interestingly, OTWO-tettalds(tofluoromemyl)porphyrin39 (H 2(CF 3) 4P (16a, n=l)) (Figure 1-12, p.29) shows blue-shifts of the Soret and of the two of the four Q bands in spite of having four - C F 3 groups. Thus, 99 CO C J T3 a a! HO a a o •d fi" o co HO O a o I o U \6 CN 3 os H a cu in O GO a >, o O PH C N OO cn, SO T f S O C O ON o C N m m o C N T f m cn T f m O N S O oo' T f S O C N «8 PH E SO P O 0 0 -^H T f , cn, rn. so ^ m oo so m so so r-m S O so so S O O so m c<S, o ON m T f C N cn, o in m cn CN T f ^ CN cn oo 0 0 cn cn^ C/3 o CN so 0 0 cn, o oo m CN cn T £ , CN CN 0 0 so cn T f , oo m T f r- CN rn, m. oc? S O 1 T f m 0 0 so cn. co, cn^ cn^ S O 0 0 [-- T f CN OO 0 0 SO so in m p f i t so so so CN O Q . 0 0 0 0 m T f o S O O N ON cn^ cn. cn. t-- so so t - - 0 0 T f m in in C N CN CN T f T f cn CN m m m ON cn CN T f so m in S O o CD, o CN in o T f ON T f m m S O cn T f T f CN T f ON CN in 5 T f so T—< cn cn < cn so so S O so T l - -4 T f U U U U U cN eg cN cN CN E ffi DH u u u u u E NO u r e . -c- so PH Pw y> y «4 00 T * £ £ £ $ CN CN (N CN I I I X u PQ PH PH PH CN m PH u CN PH C J , <*-> PH C J , PH CN E ^ 00 C \ i f) , IT) IO, CN f i ""cn '"""c^i E E E cj, cj, cj, PH PH PH £ £ £ (N CN CN E E X T P so" o ON cn cn, ON so ON T f T f CN S O so r~-oo1 S O ON cn^ T f , cn. cn in C N 0 0 so m m so R so^  C N ' ON CN cn^ m cn oo' T f T f C N m m in oc? C N o cn^ T f , o cn m m m Os so so Xoo'i 0 0 o in. in. Xoo'i in ocT T f ON T f 420(: <-n o T f CN U CN U CN U CN U CN U E" a? X X u u u u C J II c so y. CN CN CN in in in CN 5 U E cn II x T f cn, C J , PH cN E 0 0 o cn m T f T f U E u T f II x T f rn, T C J , PH CN E CD n Pi o o CN ij-! cu C N cn l+H <u PH •5-in oo CU Pi C N <u Pi G u CU O u a o u 100 the positions of electton-withdrawing groups or the symmetry of the porphyrin and strong electron-withdrawal of the substituents affect the electronic structure of the macrocycle. U V -visible spectra of H 2 TPP(CF 3 ) 2 (46a), H 2 TPP(CF 3 ) 3 (47a), and H 2 TPP(CF 3 ) 4 (48a) in CH 2 C1 2 at room temperature are shown in Figure 2-5. For comparison, UV-visible spectra of H 2 T P P B r 4 (45a) and (3-methylporphyrins (H 2 TPP(CH 3 ) 2 (57a), H 2 TPP(CH 3 ) 3 (58a), H 2 T P P ( C H 3 ) 4 (59a)  are shown in Figure 2-6 and Figure 2-7 respectively (also see Figure 1-14, p.39 for the spectrum of H 2 T P P (2a). The spectral pattern observed for H 2 TPP(CF,) 2 (46a) is very similar to that of H 2 T P P B r 4 (45a). This is reasonable from the view point of the inductive effect of the B-substituents; the inductive effect of four - B r groups (4ap = 0.92)(see Table 1-3, p.31) is approximately the same as that of two - C F 3 groups (2ap = 1.08). The spectral pattern of the P-methylporphyrins (Figure 2-7) shows little change from that of Ff 2TPP (2a) (Figure 1-14), indicating that P-methylporphyrins have similar electronic structures to that of 2a. O n the other hand, the patterns of the spectra of P-trifluoromediylporphyrins dramatically change as the number of —CF 3 groups increases (Figure 2-5). In Chapter I, section D. / .b , it was discussed that UV-visible spectra of porphyrins are possibly affected by the electronic and steric effects of substituents on the macrocycle. Takeuchi et al)-^ analyzed each effect on the H O M O s and the L U M O s of a series of octa p-substituted /^^-tettalds(perfluoromediyl)-porphyrinato Zn(II) (Zn(TPFPPX 8), X = H , F, CI, Br, CH 3 ) by semiempirical A M I calculations. In the theoretical study, it was found that the H O M O - L U M O (71-71*) gap did not change appreciably if the structure of the macrocycle was kept planar and only X (i.e. electronic effect) is varied. (Zn(TPFPPF 8) (12b) was an exception, which showed a significandy larger gap. The rationale for this is extremely strong electton-withdrawing effect of F according to Takeuchi et al\ 44) t although the H O M O and L U M O vary from a Zn(II) porphyrin to another in the series. O n the 101 Figure 2-5. UV-visible spectra of P-ttifluorormemyl-^j-o-tetaphenylporphyrm (a) 46a, (b) 47a, and (c) 48a in CH2C12. The narrow lines show ten times magnification of the corresponding regions of the thick lines. Figure 2-6. UV-visible spectra of P-tettabromo-^j-o-tetraphenylporphyrin (45a) in CH2C12. The narrow line shows ten times magnification of the corresponding regions of the thick line. Figure 2-7. UV-visible spectra of P-memyl-^j-o-tetraphenylporphyrins,(a) 57a, (b) 58a, and (c) 59a in CH2C12. The narrow lines show ten times magnification of the corresponding regions of the thick lines. 104 other hand, if the macrocycle distortion was the variable in each Zn(II) porphyrin, significant gap contraction occurred along with macrocycle distortion. Thus, theoretically the pure electronic effect causes littie change and the steric effect (macrocycle distortion) should red-shift absorption maxima in UV-visible spectra. There was no implication that electton-withdrawing effects cause red-shifts in UV-visible spectra. The theoretical study by Takeuchi et al. demonstrated that the red-shifts observed in UV-visible spectra can be attributed mainly to the macrocycle distortion. The estimated gap contraction by macrocycle distortion was a range of 0.1 — 0.2 eV, which corresponds to 24 — 48 nm red-shifts of the lowest energy Q band.144 X Ar x X = H (4b) = Br (8b) = F (12b) = CI (62) = CH3 (63) H 2 TPP(CF 3 ) 3 (47a) and H 2 TPP(CF 3 ) 4 (48a) show two broad Q bands (also a shoulder at around 620 nm for 48a) and the red-shifts of the lowest energy Q band of 47a and 48a from the that of FLTPP (2a) are 89 nm and 186 nm, respectively. These values are extremely large compared to 24 - 48 nm obtained for Zn^TPFPPBrg) (8b) whose macrocycle is severely distorted^Ol and thus it is unlikely that the large red-shifts of 47a and 48a were caused by macrocycle distortion only. Furthermore, the red-shift of the lowest energy Q band of H 2 T P P B r 4 (45a) for that of H 2 T P P (2a) is 40 nm but the macrocycle of 45a is known to be planar by X-ray crystal structure analysis.202 These results suggest that electton-withdrawing effects of substituents should be involved in order to account for the red-shifts of 45a, 47a, and 48a. 105 The second unusual feature in the UV-visible spectra of 47 a and 48a is the order of the intensity of the Q bands; the Q band at the longer wavelength has a higher intensity which is reversed in the spectra of 2a, 45a, H 2 TPP(CF 3 ) 2 (46a), and p-methylporphyrins (H 2 TPP(CH 3 ) 2 (57a), H 2 TPP(CH 3 ) 3 (58a), and H 2 T P P ( C H 3 ) 4 (59a). Only the spectrum of H 2 TPP(CN) 4 (34a, x=4 ) 2 0 0 (Table 2-6) mimics those of H 2 TPP(CF 3 ) 3 (47a) and H 2 TPP(CF 3 ) 4 (48a). In the spectrum of 48a, the Soret band is split into two bands. The split of the Soret band becomes more prominent in a presumably more electron-deficient porphyrin, H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a) (Figure 2-8). A similar spktting of the Soret band observed for 48a and 52a can be observed for H 2 TPP(CN) 4 (34a, x=4) (Table 2-6) as well. The difference between P-tofluoromedaylporphyrins (47a, 48a and 52a) and 34a (x=4) is that the Q bands of 34a (x=4) are resolved into four unlike the very broad ones observed for 47a, 48a, or 52a. The band widths at the half intensity of the lowest energy Q bands are extremely broad; 94 and 122 nm for those of 47a and 48a compared to 26 nm of H 2 T P P (2a) (Figure 1-14) and 56 nm of H 2 T P P B r 4 (45a). The unusually broad Q bands are possibly caused by a hindered rotation of - C F 3 groups that may induce a change of the conformation of substituents (-CF 3 and phenyl groups) and lead to a fluctuation of electronic transitions. The details of the steric interaction and the conformation of - C F 3 and phenyl groups are discussed in section B.4.(3) for the analysis of an X-ray crystal structure of Zn(TPP(CF 3) 4) (48b).The unusual Q bands and the split of the Soret band are not observed for meso- tettakis(trifluoromethyl)porphyrin (H 2(CF 3) 4P) (16a (n=l))3 9(Figure 1-8, p.ll) . Other noticeable results for p-perfluoroalkylporphyrins are the low extinction coefficients of the Soret bands (1 - 3 x 105 M'cm"1) compared to the general range for porphyrins!^ a n c j a sirnilar low extinction coefficient is seen in H 2 (CF 3 ) 4 P (16a, n=l). Presumably, rotation of - C F 3 groups 106 causes a fluctuation o f electronic transitions and leads to the broad absorption wi th low intensities. 300 400 500 600 700 800 900 1000 Wavelength (nm) Figure 2-8. U V - v i s i b l e spectra o f 52a i n C H 2 C 1 2 . The narrow line shows ten times magnification o f the corresponding regions o f the thick line. 107 The unusual spectral pattern, especially in terms of the pattern of the Q bands, of 47a, 48a and 52a is similar to that of the UV-visible spectrum of P-tetrahyckoporphyrin (bacteriochlorin) (64) (Figure 2-9). Thus, porphyrin 47a, 48a, and 52a may have a similar electronic structure to that of bacteriochlorin (64), although the Q bands of H 2 TPP(CF 3 ) 3 (47a), H 2 TPP(CF 3 ) 4 (48a) and H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a) are not as intense and sharp as those of 64. As shown in Scheme 2-9(a), bacterichlorin (64) is only allowed to take one 187T-electron conjugated pathway (shown by the dotted line in the structure). The unique spectral pattern of 64, for example, compared to that of H 2 T P P (2a)(Figure 1-14, p.39), is due to the distorted electronic pathway.203 The distorted electronic pathway of 64 also results in the H O M O -L U M O gap contraction and thus leads to the red-shift of the low energy Q band.!42,204,205 \ rationale for the possibly similar electronic pathway of P-trifluoromethylporphyrins to that of 64 is that the reduced electron density of the pyrrolic P-C-C bonds where —CF 3 groups reside may be disadvantageous for the conjugated 1871-electron path. As discussed in Chapter I, section DJ.c, there are two possible tautomers for H 2 T P P (2a) in terms of the 187X-electron pathway or the location of N - H protons (see Figure 1-25, p.59) and the two tautomers are indistinguishable at room temperature, leading to an averaged derealization of the two electronic pathways. Unlike the case in 2a, the electronic pathways in P-trifluoromethylporphyrins 47a, 48a, and 52a may be distorted as in bacteriochlorin (64) due to the strong electron-withdrawing substituents on the P-position of the pyrroles in the antipodal positions. These may result in the structure shown in Scheme 2-9(b). In order to assess the electronic pathway of trifluoromethylated porphyrins, a H N M R experiments to determine the location of N H protons were attempted through which the electronic pathway could be R = H: H 2TPP(CF 3) 3 (47a) R = CF 3 : H 2TPP(CF 3) 4 (48a) R = CF 2 CF 3 :H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a) Scheme 2-9. (a) 187T-electron pathway of bacteriochlorin (64) and (b) the possible electronic pathway of P-ttifluoromethylporphyrins. 109 determined. The results of the N M R experiments are shown later (p. 116). In summary, red-shifts in the UV-visible spectra of the P-tafluoromethylporphyrins are possibly caused by macrocycle distortion as well as electronic effects. As shown in Table 2-6, as the number of the perfluoroalkyl moieties increases (2a —» 46a —» 47a —» 48a —> 52a), the absorption maxima in the spectra progressively shift to longer wavelengths. The observed red-shifts were unusually large for the effect of macrocycle distortion alone. The strong electron-withdrawing effect of —CF 3 groups on the pyrrolic P-positions of antipodal pyrroles may be affecting the electronic structure that is probably similar to that of bacteriochlorin and results in the unusual UV-visible spectra of the P-trifluoromethylporphyrins. (2) Absorbance vs. concentration of 48a According to Ono etal^Z a s discussed in Chapter I, section D.i .b. , it seems that electron-deficient porphyrins have some tendency to aggregate. Since p-trifluoromethylporphyrins are extremely electron-deficient, aggregation of P-trifluoromethylporphyrins might occur. There are also reports that sphtting of the Soret band is occasionally accompanied by porphyrin dimerization.206,207 As shown in Figure 2-5, the Soret bands of H 2 TPP(CF 3 ) 4 (48a) and H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a) split. This may be an indication of aggregation of porphyrins. In order to examine aggregation of P-trifluoromethylporphyrins, the behavior of Ff 2TPP(CF 3) 4 (48a) and H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a) in solution was investigated by UV-visible spectroscopy. Aggregation of porphyrins is often detected in the concentration range, 10"4 - 10"7 M.^69 As this concentration range is suitable for UV-visible spectroscopy, the spectral changes with concentration for 48a and 52a in CH 2 C1 2 and benzene were investigated. 110 Figure 2-10 shows the UV-visible spectral change of 48a in CH 2C1 2 and absorbance vs. concentration plot over the concentration range 5.90xl0~7to 2.95xl0~4M. Perfect linear correlation between absorbance and concentration at five different wavelengths was obtained with coefficients of correlation close to 1.208 j t should be noted that usually absorbance 1.5 is the upper limit for analysis of Beer's law. The plot of the data at 620 nm, however, proves the linear relationship of the concentration and the absorbance. Figure 2-11 shows that a similar result obtained for 52a in CH 2C1 2. The same experiments using 48a in benzene in the similar concentration range also showed the linear correlation between absorbance and concentration (data not shown). These results show that the structures of 48a and 52a are retained in solution in a range of concentrations (5.90 x 10~7 - 2.95 x 10~4 M). Since non-linear spectral changes were not detected in this concentration range, it was presumed that P-trifluoromethylporphyrins (48a and 52a) are monomelic in solution in the range of the concentration for the UV-visible spectroscopy. b. UV-visible spectra of metalloporphyrins Figure 2-12 shows the UV-visible spectra of Zn(TPP(CF 3 ) 4 ) (48b) and C o ( T P P ( C F 3 ) 4 ) (48e) in CH 2C1 2. For comparison, the spectrum Zn (TPP) (2b) is also shown with that of 48b. Although the absorption bands are broad, the Soret bands do not split. As shown in Table 2-7, the absorption maxima of Zn(TPP(CF 3 ) 4 ) (48b) were red-shifted and the extinction coefficients were decreased compared to those of Zn (TPP) (2b). O n the other hand, the positions of absorption maxima and extinction coefficients of Z n ( T P P ( C H 3 ) 4 ) (59b) are similar to those of Zn (TPP) (2a). Thus, electronic and structural deviations of the macrocycle in 59b may be very small from those of Zn (TPP) (2a). The red-shift of the Q band is 114 nm from that of 2b to 48b. As described in the discussion of the UV-visible spectra of I l l (a) Concentration X 104 (M) Figure 2-10. (a) UV-visible spectral change of H 2 T P P ( C F 3 ) 4 (48a) over the concentration range from 5.90 X 10"7 to 2.95 x 10"4 M in C H 2 C 1 2 at room temperature. (b) Absorbance vs. concentration plot at 444 (O), 463 (•), 580 (•) , 620 (•) and 832 nm (A). 112 Concentration X 104 (M) Figure 2-11. (a) UV-visible spectral change of H 2 TPP(CF 3 )3 (CF 2 CF 3 ) (52a) over the concentration range from 9.87 X 10"7 to 2.47 x 10"4 M in C H 2 C 1 2 at room temperature. (b) Absorbance vs. concentration plot at 444 (O), 468 (•), 586 (•) , 628 (•) and 844 nm (A). 113 Figure 2-12. UV-visible spectra (thick lines) of Zn(TPP(CF3)4) (48b) and CoCrPP(CF3)4) (48e) in CH2C12. The narrow line is Zn(TPP) (2b). 114 P-trifluoromethyl porphyrin free-bases, red-shifts caused by a large macrocycle distortion is at best 24 — 48 nm according to calculations by Takeuchi et al}^ Therefore, the large red-shift of the Q band in 48b must be attributed to both the steric and electronic effects. Table 2-1. UV-visible absorption maxima of metalloporphyrins. Porphyrin A,max (nm)(log s) Zn(TPP) (2b) 419 (5.83), 548 (4.36), 582 (3.41) Zn(TPP(CF 3) 4) (48b) 442 (5.37), 662 (4.31) Zn(TPP(CH 3) 4) (62b) 420 (5.63), 551 (4.26), 584sh(3.66) Co(TPP(CF 3) 4) (48e) 440 (5.06), 636 (4.32) Fe(TPPBr 4)Cl (45e) 433 (5.02), 520 (4.11), 591 (3.81), 700 (3.56) Fe(TPP(CF 3) 4)Cl (48f) 452 (4.76), 618 (4.12) Fe(TPP(CF 3) 3(CF 2CF 3))Cl (52c) 459 (4.62), 624 (4.00) (FeTPP(CF 3) 4) 2Q (61) 435 (1.00)* 700 (0.27)* ( )* : relative intensity A rationale for explaining why the Soret bands of Zn(TPP(CF 3) 4) (48b) and Co(TPP(CF 3) 4) (48e) do not split is that the postulated distorted electronic pathway (Scheme 2-9) may be disturbed by metallation. However, the macrocycles seem be forced to take an unusual electronic structure even in the presence of a central metal. For instance the Soret band of 48b is not completely symmetric, indicating an overlap of two bands, and the pattern of the Q bands are significandy different from that of Zn(TPP) (2b). Figure 2-13 shows the UV-visible spectra of hemins (Fe(III)Cl complex) Fe(TPPBr 4)Cl (45e), Fe(TPP(CF 3) 4)Cl (48f), and FeCTPP(CF 3) 3(CF 2CF 3))Cl (52c). The absorption maxima and extinction coefficients are also listed in Table 2-7. The Soret bands of 48f and 52c red-shift from that of 45e and the intensities of the absorption bands progressively decrease as the number of perfluoroalkyl moieties increases. The p,-oxodimer Fe(III) complex (61) showed very broad UV-visible bands and a low ratio of intensity of the Soret to the Q band (Soret/Q 45e 48f 52c 12 300 400 500 600 700 800 900 1000 Wavelength (nm) Figure 2-13. UV-visible spectra of [FeTPP(CF 3) 4]Cl (48f)(—), [FeTPP(CF 3)3(CF 2CF 3)]Cl (52c)(—), [FeTPPBr 4]Cl (45e)( —) in CH 2 C1 2 . 116 band intensities = 3.7) compared to Soret/Q band intensities = 6.6 of the u,-oxo dimer Fe(III) complex of 45 ( (FeTPPBr 4 ) 2 0) . 1 9 2 In summary, the UV-visible spectra of metalloporphyrins of 48 and 52 show red-shifted and very broad absorption bands with decreased extinction coefficients compared to those of metalloporphyrins of H 2 T P P (2a), H 2 T P P B r 4 (45a), and H 2 TPP(CH 3 ) 4 (59a). This is a pattern similar to that observed for the corresponding free-base species. The presence of the electron-withdrawing and steric effect of trifluoromethyl groups (see Chapter II, section B.4.b.(3) for the discussion of the sizes of —CF 3 and —CH 3 groups) may lead to the characteritic UV-visible absorption bands of these novel P-tiifluoromethylmetaUoporphyrins. 2. NMR spectroscopy As discussed in Chapter I, section D . i . c , electronic effects of a P-substituent on the porphyrin macrocycle can affect the 1871-electron pathway, or the location of N H protons of the porphyrin macrocycle, while very unusual UV-visible spectra of P-trifluoromethylporphyrins were obtained. EspeciaUy, the UV-visible spectra of H 2 TPP(CF 3 ) 3 (47a), H 2 TPP(CF 3 ) 4 (48a), and H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a) showed a similarity to that of bacteriochlorin (64), indicating these P-trifluoromethylporphyrins have a similar electronic structure to that of 64. The major purpose of this section is to determine the electronic structure of p-trifluoromethylporphyrins by N M R spectroscopy. The analysis of the positions of N - H protons was achieved by inference through ' H C O S Y or lH homonuclear decoupling experiments. The second part of this section describes an unusual chemical shift of P-pyrrolic protons of p-tetrakis(trifluoromethyl)-meso-tetraphenylporphyrin (48a). 117 a. Determination of electronic pathway of B-trifluoromethylporphyrins. As shown in Figure 1-25, the N - H tautomerism accompanies the tautomerism of the 187T-electron pathways of the macrocycle. Tautomerism is generally fast on the N M R time scale at room temperature and we cannot assign the N - H protons on specific pyrroles. 1 6 6 However, when the temperature is lowered the tautomerism is slowed. For example, the : H N M R showed two resolved lines for the two kinds of pyrrolic P-protons (H A and H B in Figure 1-25) of H 2 T P P (2a) below 220 K.174 Electronic effects of substituents on the macrocycle are also known to affect the tautomerism of a macrocycle (see Chapter I, section D.J?.C). According to a low temperature N M R study,1 187t-electton pathway of the porphyrin tends to avoid a pyrrolic Cp-Cp bond where an electron-withdrawing substituent resides because of the reduced electron density. It may be worth mentioning the *H N M R of H 2 T P P B r 4 (45a) reported by Crossley etal.^^ in which a long-range coupling between N - H and pyrrolic p-H was observed. Figure 2-14 shows the ' H N M R spectra of 45a obtained by the author. The doublet of pyrrolic P -H with a coupling constant of 1.4 Hz is due to the long-range coupling between N - H and pyrrolic P -H which is decoupled by irradiation at N - H (the doublet of P -H can be observed by a 200MHz spectrophotometer as well). Long range H-H couplings (i.e. over four or more bonds) are sometimes observed in a planar zig-zag orientation (the structure is shown below) and an approximate representation of theoretical calculations for a 4 / H i . H 2 coupling in unstrained systems is given by (2.1): ^C^ o % 1 . H 2 = cos2(j)1 + cos2(|)2-0.7 (2.1) H C hr where (j^  and <)>2 are the H - C ' - C ^ - C 3 and C 1 - C 2 - C 3 - H 2 dihedral angles in the coupling 1 ; 1 1 j 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 j 1 1 1 r 8.6 8.4 8.2 8.0 7.8 Chemical shift (ppm) (b) I Chemical shift (ppm) Figure 2-14. 400MHz *H nmr spectra of H2TPPBr4 (45a) in CDC1 3 at room temperature, (a) Normal spectrum. 4J(NH-pH)=1.4 Hz. (b) Decoupled at -NH (-2.88ppm). 119 H c x aromatics cyclohexanes meta equatorial-equatorial 4 / = 2 - 3 H z 4 / = l - 2 H z pathways.209 The examples of such long-range couplings are shown below. 2 ^ The commonest example of a long-range coupling is the meta 4J coupling of 2 — 3 Hz in aromatics. Long-range couplings are also observed in saturated systems such as the equatorial-equatorial coupling (1 — 2 Hz) in cyclohexanes and even a 5 / coupling can be observed for H 4 and H 8 in quinoline. Pyrroles are planar aromatic systems and have such zig-zag orientations between N - H and P-H and thus observing a 4J coupling of ~1 Hz between N - H and p - H coupling is reasonable. In porphyrin 45a the N - H - P - H coupling can be observed at room temperature (see ' H N M R spectrum of H 2 T P P (2a) at room temperature (Figure 1-23) for comparison). Thus, the N - H localization tells us that the macrocycle has a specific 187t-electron pathway as shown in Figure 2-14. Using H 2 TPP(CF 3 ) 3 (47a), which resulted in a bacteriochlorin-type UV-visible spectrum, determination of the positions of N - H protons was attempted. Figure 2-15 shows the 400 M H z lH N M R spectrum of 47a. The reason porphyrin 47a was used was that H 5 (see the structure of 47a in Figure 2-15) could be a good probe to determine the electronic pathway for the analysis of correlation between pyrrolic P -H and N - H protons. The spectrum shows the N - H protons (two broad singlets at -1.73 and -1.86 ppm), meta+para-phenyl-H (7.66 - 7.81 ppm), ortho-phenyl-H (8.11 - 8.24 ppm), and pyrrolic P -H (8.30 - 8.77 ppm). It is easy to assign H 5 because it appeared as a singlet and other pyrrolic P-Hs (H 1 , H 2 , H 3 , and H 4 ) appeared (a) CHCL U H5 Ph H1 47a i r 10 9 _ i r i i r 3 2 1 "i r 6 5 4 Chemical shift (ppm) 0 -1 (b) »./>-phenyl-H(12H) I I I I 1 1 I 1 » — i 1 1 9.0 8.8 8.6 8.4 8.2 8.0 7.8 7.6 -1.7 -1.9 Chemical shift (ppm) Figure 2-15. 400 M H z J H N M R spectra of H 2 T P P ( C F 3 ) 3 (47a) in CDC1 3 at room temperature.(a) Full spectrum and (b) expansion of the peaks. Peaks labeled with * are impurities. 121 Figure 2-16. 400 M H z C O S Y spectra of H 2 T P P ( C F 3 ) 3 (47a). (a) Full spectrum and (b) expansion of one of the circled areas. 122 as doublets due to coupling to adjacent protons; H - H 2 and H 3 -H* . Assignment of each of H , H 2 , H 3 and H 4 was not attempted, since it was unnecessary for determination of the electronic pathway. Unlike the case of H 2 T P P B r 4 (45a), the 400 M H z ] H N M R of H 2 TPP(CF 3 ) 3 (47a) did not show the fine splitting of pyrrolic (5-H signals. However, the coupling connectivity between pyrrolic P -H and the N - H protons was observed by a C O S Y experiment at room temperature, as indicated by the dotted circles in Figure 2-16(a). Expansion of the correlation (Figure 2-16(b)) clearly showed that the N - H protons are not coupled to H 5 but to H , H 2 , H 3 , and H 4 . By the experiment it can be concluded that locations of the N - H protons are assigned on the pyrroles not substituted by —CF 3 groups and thus at room temperature the porphyrin preferably takes the electronic structure shown in the box in Figure 2-17. During the course of the N M R Ph C F 3 V - N H i W C F 3 P h - - P h F 3 C -H P h H Ph Figure 2-17. 187t-electeon pathway of H 2 TPP(CF 3 ) 3 (47a). experiments, it was also discovered that N - H protons of H 2 TPP(CF 3 ) 3 (47a) can exchange easily with residual water. The observation is shown in Figure 2-18(a) and (b). In the presence of trace water (Figure 2-18(a)), the signals from water and N - H protons are broad. In the absence of water (Figure 2-18(b)), on the other hand, the spectra showed two N - H proton signals clearly. In addition to this observation, intensities of H 1 , H 2 , H 3 , and H 4 signals dropped significantly and peak widths were obviously greater compared to those observed in Figure 2-18(a). In contrast, such significant changes were not observed for H 5 and o-phenyl-H signals. The 123 C H C L (a) H 5 8.60 8 .40 8 .20 H 2 0 8.00 (PP m ) N H """I' r i "i—i—i—i—[—i—[—r-I—[—i—i—r~r i I i i i i (b) 5 4 3 2 1 Chemical shift (ppm) H 5 o-phenyl-H r H ^ H ^ H 4 ^ inwtHimiii*iiimin*i 30 8.60 8.40 8.20 8.00 (PP m ) N H ».i>mw>i< s*— niiirtiiMil II>II|IHI#IH iimUwi>i'i UNI i'mfim n Df'tlt« I 11 ' 1 I 1 8 7 4 3 2 1 Chemical shift (ppm) 0 n^ - 1 -' i 1 ' ' 1 i -1 -2 -3 Figure 2-18. 200 MHz !H NMR spectra of H2TPP(CF3)3 (47a) (a) in the presence of and (b) in the absence of residual water in CDC1 3 . Inner traces are expansion of the region of pyrrolic P -H and or^o-phenyl-H. Designation for pyrrolic P-Hs was given in Figure 2-15. 124 change from Figure 2-18 (a) to (b) evidently confirms the electronic pathway of H 2 TPP(CF 3 ) 3 (47a) as shown in Figure 2-17. The coupling connectivity between the N-H and the P-H protons in P-tettakis(trifluoromemyl)porphyrin H 2 TPP(CF 3 ) 4 (48a) seems not as strong as that of 47a. Unlike the P-H signal of H 2 T P P B r 4 (45a)(doublet, see Figure 2-14), the P-H signal of 48a was a sharp singlet and the coupling connectivity could not be observed by a C O S Y experiment either. However, there was a slight increase of the absolute intensity of P-H upon irradiation at N-H (-1.42 ppm) and the intensity of o-phenyl-H and w+/)-phenyl-H signals was unchanged. Although a clear evidence for the connectivity between N-H and P-H protons for 48a was not obtained, this is also a phenomenon expected from the porphyrin having an electronic structure as shown in Figure 2-17 deft). A coupling through bonds is transmitted via the bonding electrons.209 Accordingly, it should be harder to transmit the coupling if the density of bonding electrons is lowered. Although the orientation of the N-H and P-H in the pyrroles may satisfy the criterion for a long-range coupling (planar zig-zag orientation), a possible reason for not observing a spurting of the P-H signals due to long-range couplings between the N-Hr and P-Hr may be the lower electron density of the macrocycle induced by the strong electton-withdrawing effect of the —CF 3 groups. Analysis of the electronic pathway of P-ttimethylporphyrin H 2 TPP(CH 3 ) 3 (58a) was also attempted. However, any information that suggests the porphyrin takes a specific electronic pathway could not be obtained. As shown in Figure 2-19, the N-H signals are quite broad even in the absence of water, indicating N - H tautomerization at room temperature. 125 10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 Chemical shift (ppm) 0) • = H',H2,H3,H4 «?+/)-phenyl-H(12H) o-phenyl-H(8H) •CH 3O ~ C 3 P (3H) (6H) 8.6 8.4 8.2 8.0 7.8 Chemical shift (ppm) T—r-ft 1 1 i 1 . 1 1 . 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 . 1 , 1 1 7.6 3.0 2.8 2.6 2.4 2.2 2.0 Figure 2-19. 400 M H z lH N M R spectra of H 2 T P P ( C H 3 ) 3 (58a) in CDC1 3 at room temperature, (a) Full spectrum, (b) Expansion of the selected peaks. Peaks labeled with * are impurities. 126 These observations for P-trifluoromethyl and P-methylporphyrins by N M R spectroscopy suggested that in order to observe the coupling connectivity between the N - H and the P~H, a porphyrin may have to satisfy at least the following conditions: (1) the porphyrin has substituents on the antipodal pyrroles and (2) the substituents are moderately electron-withdrawing. The ' H N M R experiments showed that at room temperature the 187T—electronic pathways for P-tris- and P-tettaltis(teifluoromethyl)porphyrins (47a and 48a) are fixed so that they avoid the paths where —CF 3 groups reside because of the reduced electron density. This result is similar to those obtained for p-mono-substituted wwo-tetraphenylporphyrins17^ (Chapter I, section D.3.) but it has to be emphasized that one of the N - H tautomers can be locked at room temperature presumably due to the strong electron-withdrawing effects of —CF 3 groups. O n the other hand, a H N M R spectra of P-tjimethylporphyrin H 2 TPP(CH 3 ) 3 (58a) suggested that tautomerization of the N - H protons or the electronic pathways occur as is the case of H 2 T P P (2a). The results obtained by the N M R studies for P-trifluoromethyl- and p-metliyl-porphyrins agree with the prediction made by the UV-visible spectra of these porphyrins in terms of the electronic structures. b. Unusual 'H NMR chemical shiftfor pyrrolic ^ -protons ofH2TPP(CF3)4 (48a) The chemical shift for the pyrrolic p - H of H 2 TPP(CF 3 ) 4 (48a) appears at fairly high field compared to those of other wwo-tetraphenylporphyrin derivatives such as H 2 T P P B r 4 (45a) or H 2 TPP(CH 3 ) 4 (59a). This part of the N M R section is a discussion of the possible origin of this unique chemical shift for the pyrrolic P-protons of H 2 TPP(CF 3 ) 4 (48a). Figure 2-20 shows the 200 M H z ' H N M R of H 2 T P P (2a) and P-tetrasubstituted-^j-o-tetraphenylporphyrins H 2 T P P B r 4 (45a), H 2 TPP(CF 3 ) 4 (48a), and H 2 TPP(CH 3 ) 4 (59a) in Q D 6 . The porphyrin 48a is the B - H (a) o-phenyl-H m,p-phenyl-H N H chem. shift (ppm) -2.13 9 . 0 8 . 8 8 . 8 8 . 4 8 . 2 8 . 0 7 . 8 7.6 7.4 7.2 m,p-ph.eny\-H (b) B - H o-phenyl-H -2.69 9 . 0 8 . 8 8 . 6 8 . 4 8 . 2 8 . 0 7 . 8 7 . 6 7 . 4 7 . 2 (c) <?-phenyl-H ' ,1 p - H /», />-phenyl-H Mir**-*? -1.42 J . O 8 . 8 8 . 6 8 . 4 8 . 2 8 . 0 7 . 8 7 . 6 7 . 4 7 . 2 (d) « , /> -phenyl -H o-phenyl-H -2.72 9 . 0 8 . 8 8 . 6 8 . 4 8 . 2 8 . 0 7 . 8 7 . 6 7 . 4 7 . 2 Chemica l Shift (ppm) Figure 2-20.200 M H z lH N M R spectra o f (a) H 2 T P P (2a), (b) H 2 T P P B r 4 (45a), (c) H 2 T P P ( C F 3 ) 4 (48a) and (d) H 2 T P P ( C H 3 ) 4 (59a) in C 6 D 6 a t r o o m temperature * is 1 3 C satellite o f benzene. 128 most soluble in benzene but unfortunately is sparingly soluble in CHC1 3 in neutral conditions. Accordingly, the comparison of the N M R spectra was performed in C 6 D 6 . (Porphyrin 48a is also very soluble in T F A and the N M R spectra of related porphyrins in T F A - d will be shown later in this section.) The concentrations of porphyrin 45a, H 2 TPP(CF 3 ) 4 (48a), and Ff2TPP(CH3)4 (59a) were set to 0.0025 - 0.003 M (~ 1 mg porphyrin/0.5 m L QDg). The concentration of H 2 T P P (2a) was 0.0065 M . Porphyrin 48a is very different from other porphyrins in terms of the chemical shift of pyrrolic (3-protons and N - H protons. Al l the porphyrins (2a, 45a, 48a, and 59a) have phenyl groups on the wwo-positions of the macrocycle and the chemical shifts for phenyl protons appear at similar chemical shifts. This indicates that the environment of phenyl substituents is independent of the macrocycle structures, although there might be some interactions between P-substituents and ort/w-phenyl-Hs. Two possibilities were considered for the unusual chemical shift of pyrrolic P-proton signal of 48a. The first possibility is a deterioration of ring current due to a macrocycle distortion and strong electron-witiidrawing effect. The P-pyrrolic protons are deshielded and the N H protons are shielded due to the ring current effect of the macrocycle (Chapter I, section DJ.a. for the ring current and chemical shifts). The —CF 3 group is a strongly election-withdrawing and bulky substituent. Accordingly, the macrocycle in 48a is expected be electron-deficient and distorted (see Chapter II, section B.4.b.(3) for steric interaction between substituents and a macrocycle distortion of Zn(TPP(CF 3) 4) (48a). Consequendy, the smooth ring current is possibly hampered by the electronic and the steric effects of the - C F 3 groups and deshielding and shielding effects will be weakened. Appearances of the pyrrolic P-proton signal at the higher field (ca. 0.9 ppm shift from that of H 2 T P P (2a) and of the N H proton signal at the lower field (ca. 0.6 ppm shift from that of 2a) are explained by this hypothesis. 129 The second possibility is an aggregation. As shown by Ono et alX^^ (Chapter I, section D.i.b.), P-pyrrolic protons shift to the higher field when the porphyrins aggregate. Aggregation of porphyrin 48a and H 2 TPP(CF 3 )3 (CF 2 CF 3 ) (52a) has already been investigated using UV-visible spectroscopy for a concentration range of K T 7 - 1 ( T 4 M and the monomer form of the porphyrins was suggested. Since the concentration of 48a for the N M R spectrum shown in Figure 2-20 was much higher than those examined in the UV-visible spectroscopy, the possibility of aggregation was investigated. At 0.00045 M , 0.001 M , and 0.002 M (0.9 mg/0.5 mL was the maximum concentration) the chemical shift of p-pyrrolic protons of 48a appeared always at 8.00 ppm. It should be noted that 0.00045 M is nearly equal to the maximum of the concentration range investigated by the UV-visible spectroscopy. This means the structure of porphyrin 48a is unchanged and presumably exists as monomers in the concentration of IO - 7 — 2 x 10 3 M in benzene. Thus, the large highfield chemical shift of pyrrolic P-protons and lowfield chemical shift of N H protons of H 2 TPP(CF 3 ) 4 (48a) are probably due to a macrocycle distortion. In fact, a large downfield shift of N H (that appears at -0.5 ppm) of P-octabromo-^jo-tetrakis(perfluorophenyl)porphyrin (I^ TPFPPBrg)(8a)(Figure 1-8, p.11) from that (-2.76 ppm) of H2TPP(2a), was explained by a severe macrocycle distortion of 8a.^6 The unusual chemical shift of pyrrolic P-protons of 48a was also observed in deuterated ttifluoroacetic acid (TFA-d). Comparison of the ' H N M R spectrum of 48a with H 2 T P P B r 4 (45a) and H 2 TPP(CH 3 ) 4 (59a) is shown in Figure 2-21.* Figure 2-21 (a) shows the spectrum of 48a in T F A - d . The assignment of the signals was done by comparing the peak integrations. The pyrrolic UV-visible spectra of diacids of 48a and 59a are shown in appendix B (P.233). 130 B-H(4H) /»,/)-phenyl-H(12H) 1 • i — i • | i — i I—• | . I I i 1 . 1 1 • 1 1 1 1 . | — i 1 1 1 1 1 , , , 1 , — r -9 . 4 0 9 . 2 0 9 . 0 0 8 . 8 0 8 . 6 0 8 . 4 0 8 . 2 0 8 . 0 0 Chemical shift (ppm) Figure 2-21. 400 M H z *H N M R spectra of diacid of (a) H 2 T P P ( C F 3 ) 4 (48a), (b) H 2 T P P B r 4 (45a) and (c) H 2 T P P ( C H 3 ) 4 (59a) in T F A - d at room temperature. 131 P -H for 48a appeared at 8.28 ppm as a sharp singlet and the chemical shift was about 0.5 ppm higher than those for pyrrolic P -H of 45a (Figure 2-21 (b)) and 59a (Figure 2-21 (c)), indicating that there are macrocycle distortions and electron-withdrawing effects of - C F 3 groups in 48a. A n interesting observation in the N M R spectra of these porphyrins in T F A - d is that porphyrin 45a and 59a showed splitting of the o-phenyl-H signal into two peaks with equal area but 48a showed only one peak for c-phenyl-H. It is known that protonation of the macrocycle of ^jo-tetraarylporphyrins causes severe macrocycle distortion into a saddle shape and the distortion accompanies rotation of the meso-atyl groups along the C-C axis between the porphyrin macrocycle and the aryl groups.^1-0,211 Modes of distortion of the macrocycle upon protonation are shown in Figure 2-22. The structures in the figure were created by HyperChem.188 T n m e diacid form of D 4 h porphyrins such as Ff 2TPP (2a), all o-phenyl-Hs are equivalent (Figure 2-22(a)), which has been observed by X-ray crystal crystallography^l 0,211 a n c j ! H N M R in TFA-d.212 Since the pyrrole rings are alternately tilted up and down to the average plane of the macrocycle, in the case of D 2 h porphyrins such as H 2 T P P B r 4 (45a) or H 2 TPP(CH 3 ) 4 (59a), a distorted porphyrin macrocycle should have two different faces regarding the average plane of the macrocycle (Figure 2-22 (b)) and it is reasonable for D 2 h porphyrins to have two kinds of non-equivalent o-phenyl-Hs and to show two peaks in the N M R spectra. However, this analysis does not fit to the N M R spectrum of H 2 TPP(CF 3 ) 4 (48a) in T F A - d which shows only one broad singlet for o-phenyl-Hs. A rationale for this observation may be rotation of - C F 3 groups. One piece of information regarding rotation of - C F 3 groups is that the 1 9 F N M R spectrum of H 2 TPP(CF 3 ) 4 (48a) shows a sharp singlet at room temperature. The steric interaction between the meso-phenyl groups and - C F 3 groups on the pyrrolic P-positions was found to be significant (see Chapter II, section B.4.b.(3)). Thus, rotation of - C F 3 possibly 132 Figure 2-22. Structures of (a) [ H 4 T P P ] 2 + and (b) [H 2 TPP(CH 3 ) 4 ] 2 + . Molecular structures were created by HyperChem geometry optimization (MM+). 1 8 9 133 induces rotation of meso-phenyl groups along the C-C axis between the macrocycle and the phenyl groups. As a result of the continuous conformation change, o-phenyl-Hs may lose non-equivalency and show one peak in the N M R spectrum in spite of the mode of distortion in the D a porphyrin upon protonation. Unlike the cases of the free-base and diacid form of H 2 TPP(CF 3 ) 4 (48a), the N M R spectrum of Zn(TPP(CF 3) 4) (48b) in CDC1 3 at room temperature showed a pyrrolic p-H signal shifted the most downfield (8.43 ppm) compared to other two chemical shifts of o-phenyl-H at 8.07 ppm and ^ - p h e n y l - H at 7.76 ppm (Table 2-8). The electron-deficiency of 48a may be relaxed by metallation with Zn(II) and the ring current may be increased. O n the other hand, other Zn(II) porphyrins in the table did not show significant change in chemical shift of the pyrrolic P-H from those of corresponding free-base porphyrins. Table 2-8. Chemical shift values of zinc P-tetrasubstituted /^o-tettaphenylporphyrins porphyrin ' H (ppm) P-H o-phenyl-H #?,/>-phenyl-H solvent Zn(TPP(CF 3) 4) (48b) 8.43 (s, 4H) 8.07 (m, 8H) 7.70 (m, 12H) CDC1 3 H 2 TPP(CF 3 ) 4 (48a) 8.00 (s, 4H) 8.11 (m, 8H) 7.45 (m, 12H) Q D 6 Zn(TPP(CH 3) 4) (59b) 8.65 (s, 4H) 8.06 (m, 8H) 7.75 (m, 12H) CD 2 C1 2 H 2 TPP(CH 3 ) 4 (59a) 8.44 (s, 4H) 8.07 (m, 8H) 7.71 (m, 12H) CDC1 3 Zn(TPPBr 4) (45b) 8.61 (s, 4H) 8.02 (m, 8H) 7.80 (m, 12H) D M S O - d 6 H 2 T P P B r 4 (45a) 8.68 (d, 4H) 8.18 (m, 8H) 7.78 (m, 12H) CDC1 3 Zn(TPP) (2b) 8.90 (s, 4H) 8.08 (m, 8H) 7.73 (m, 12H) CDC1 3 H 2 T P P (2a) 8.86 (s, 4H) 8.22 (m, 8H) 7.75 (m, 12H) CDC1 3 In summary, ] H N M R experiments using H 2 TPP(CF 3 ) 3 (47a) and H 2 TPP(CF 3 ) 4 (48a) showed that the positions of the N - H protons were locked at room temperature due to —CF 3 groups on the antipodal pyrroles. The positions of the N - H protons in the P-Oifluoromethylporphyrins indicate that the 187t-electronic pathway of the macrocycle avoids positions where —CF 3 groups reside. Positions of the N - H protons in P-trimethylporphyrin H 2 TPP(CH 3 ) 3 (58a) were not resolved by the N M R experiment at room temperature, 134 presumably due to exchange of the two possible N - H tautomers. Thus, for a locked N - H tautomer or 187t-electton pathway, strong electxon-withdrawing effects by substituents will be required. The analysis by the N M R experiments concerning the electronic structure of the macrocycle agrees with the prediction deduced from the UV-visible spectroscopic data that P-trifluoromethylporphyrins may have a fixed 187t-electron pathway similar to that of bacteriochlorin. The unusual chemical shift of the pyrrolic P-proton signal is characteristic of H 2 TPP(CF 3 ) 4 (48a) and is possibly caused by the electton-withdrawing and steric effects of —CF 3 groups. 3. Redox potentials As discussed in Chapter I section D . Z b , electron-withdrawing substituents positively shift the reduction and the oxidation potentials of the porphyrin macrocycle and thus comparison of the redox potentials enables us to estimate the electron-deficiency of porphyrins. So far, we have seen the dramatically different characteristics of P-t^fluoromethyl-^Jo-tettaphenylporphyrins from those of wwo-tettaphenylporphyrin, p-tettabromo-^ro-tettaphenylporphyrin, and P-methyl-^j-o-tetraphenylporphyrins in their UV-visible and N M R spectra. The effects of the strongly electton-withdrawing - C F 3 groups were analyzed qualitatively by those methods. This section describes direct quantitative analysis and comparison of electronic properties of P-trifluoromethylporphyrins with those of other related porphyrin systems such as Wcvo-tetraphenylporphyrn or p-methylporphyrins based on their results obtained from cyclic voltammetry. The purpose of this section is to estimate electron-deficiency of P-trifluoromethylporphyrins and to show some supporting evidence that agrees with those 135 analyses in the previous sections regarding the 187t-electron pathway of the porphyrins. This section is separated into three parts. The first part describes comparison of the ring redox potentials of free-base P-tofluoromemylporphyrins with those of other ^j"o-tetraphenylporphyrin derivatives and how the redox potentials changes as the number of — C F 3 group increases. The second part focuses on comparison of the redox potentials of P-tettasubstimted-^j'O-tettaphenylporphyrinato Zn(II) complexes in order to investigate the electronic effects of substituents on the porphyrins with the same symmetry, D 2 h , as that of Zn(rPP(CF3)4) (48b) (Scheme 2-7). In this comparison, the redox potential of p-tettakis(tofluoromemyl)porphyrinato Zn(II) is investigated with other Zn(II) complexes of selected electron-deficient porphyrins. In the first and second parts, the electronic structure of p-teifluoromethylporphyrins is discussed by comparing the H O M O - L U M O gap of the macrocycles with those of ^jo-tetraphenylporphyrins. As discussed in Chapter I, section D.Za.(2), the first oxidation and reduction of a porphyrin ring correspond to the formation of a 7t-cation radical and a 7t-anion radical.149,150 Strictly speaking, the difference between the potentials to form Tt-cation and 71-anion radicals is not exacdy the H O M O - L U M O gap, but the theoretical H O M O - L U M O gap agrees with the difference between the first oxidation and the reduction potentials. 149,150 j n m e final section, the redox potentials of the cytochrome P-450 models, P-trifluoromethylporphyrinato Fe(III) chloride complexes are compared with those of Fe(III) complexes of other electron-deficient porphyrins to assess their electron-deficiency and possibility as oxidation catalysts. 136 a. Free-base P-trifluoromethyl-meso-tetraphenylporphyrins Redox potentials of free-base porphyrins were measured under the same conditions; in CH 2 C1 2 and with supporting electrolyte, tetrabutylammonium hexafluorophosphate (TBAPFg). The standard potentials were obtained by the use of an internal reference; ferrocene/ferrocenium couple.213 The experimental details are described in Chpater III. Cyclic voltammograms of H 2 TPP(CF 3 ) 2 (46a) and H 2 TPP(CF 3 ) 3 (47a) are shown in Figure 2-23. Porphyrin 46a showed the two reduction reactions and two oxidation reactions, but the two reduction processes were not resolved well and the second oxidation process was not a one-electron process. Porphyrin 47a showed two well-resolved, one-electron reduction and one-electron oxidation reactions. Figure 2-24 shows the cyclic voltammograms of H 2 TPP(CF 3 ) 4 (48a) at various scan rates. At any scan rate two clean reversible one-electron oxidations were observed. The reduction processes differed in that the one-electron process was always irreversible for the first electron. The electrochemical behavior of H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a) was similar to that of 48a. The reason for the irreversible reduction process is not known. The electrochemical reduction may result in a similar change of the macrocycle ring to that observed in the chemical reductions. Such a change led to decomposition of porphyrin 48a and 52a (see Chapter II, section A.l.c.(2), and section A.3.b.). For comparison, the cyclic voltammograms of (3-methylporphyrins (H 2 TPP(CH 3 ) 2 (57a), H 2 TPP(CH 3 ) 3 (58a), H 2 TPP(CH 3 ) 4 (59a) are shown in Figure 2-25. The three P-methylporphyrins showed two one-electron reduction and two one-electron oxidation processes. In addition, porphyrin 58a and 59a showed a third one-electron oxidation process Figure 2-23. Cyclic voltammograms of (a) H 2 T P P ( C F 3 ) 2 (46a) and (b) H 2 T P P ( C F 3 ) 3 (47a). Solvent: CH 2 C1 2 , [porphyrin]^ 1 x 10 " 3 M , Supporting electrolyte: [TBAPF 6] = 1 x 10 1 M , Scan rate: 0.05 V / s . White arrows indicate ferrocene/ferrocenium coupling; 0.46 V vs. SCE. 138 2.0 1.0 0.0 -1.0 -2.0 Potential (V vs. SCE) Figure 2-24. Cyclic voltammograms of H 2 T P P ( C F 3 ) 4 (48a) at different scan rates. Solvent: CH 2 C1 2 , [porphyrin]=5 x IO 4 , Supporting electrolyte: [TBAPF 6 ] = 1 x 10 1 M . (a) X 10 pA 2.0 1.0 0.0 -1.0 -2.0 Potential (V vs. SCE) Figure 2-25. Cyclic voltammograms of (a) H 2 T P P ( C H 3 ) 2 (57a), (b) H 2 T P P ( C H 3 ) 3 (58a), and (c) H 2 T P P ( C H 3 ) 4 (59a). Solvent: CH 2 C1 2 , [porphyrin]=1 x 10 3 M , Supporting electrolyte: [TBAPF 6]=1 x 10 _ 1 M . Scan rate: 0.05 V / s . White arrows indicate ferrocene/ferrocinium coupling: 0.46 V vs. SCE. 140 that was not observed for H 2 T P P (2a) (see Figure 1-17, p.45). Since the methyl substituents are electron-releasing, the macrocycles are more electron-rich and easier to oxidize. Such a rationale explains the increased difficulty in their reductions. The redox potentials of (3-trifluoromethyl-and (3-methylporphyrins together with those of H 2 T P P (2a) and H 2 TPP(CN) X (32a, x = 2-4) 1 6 1 are summarized in Table 2-9. The redox potentials of H 2 T P P (2a) by this work show good agreement with the reported literature values. 1 3 0' Thus, the cyclic voltammetry system employed was reliable. Table 2-9. Redox potentials of p-substituted ^?gjQ-tetraphenylporphyrins in C H 2 C l 2 . a „ , . Potential (V vs. S C E ) b £ - ( 3 ) E - ( 2 ) E ° ; 2 ( l ) Eff 2(l) Eff2(2) AE 1 / 2 (1) C H 2 T P P (2a)d H 2 T P P (2a)c'f - 1.34 1.01 -1.22 -1.56 2.23 - 1.35e 1.02f -1.20f -1.55f 2.22 H 2 TPP(CF 3 ) 2 (46a)d H2TPP(CF3)3(47a)d H 2 TPP(CF 3 ) 4 (48a)d - - 1.09 -0.97 -1.28 2.06 - 1.22 1.02 -0.61 -0.77 1.63 - 1.30 0.95 -0.47 - 1.42 H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a)d H 2 TPP(CH 3 ) 2 (57a)d H 2 TPP(CH 3 ) 3 (58a)d H2TPP(CH3)4(59a)d - 1.25 0.93 -0.27 - 1.20 - 1.13 0.94 -1.28 -1.60 2.22 1.46 1.03 0.88 -1.29 -1.59 2.17 1.40 0.94 0.81 -1.30 -1.60 2.12 H 2 TPP(CN) 2 (32a, x=2)e - 1.41 1.32 -0.71 -1.01 2.03 H 2 TPP(CN) 3 (32a, x=3)c - 1.54 1.36 -0.50 -0.61 1.86 H 2 TPP(CN) 4 (32a, x=4)e - - 1.43 -0.23 - 1.66 "Experimental conditions: [porphyrin] = 0.5 mM; [TBAPFJ = 0.1 M ; scan rate = 0.05 V / s ; reference electrode = A g wire. Potentials were determined by referencing to the internal standard of ferrocene/ferrocenium redox couple (0.46 V vs. SCE, CH 2 Cl 2 2i3) . b E,° 2 (n)and E,r/2(n) are n th oxidation and reduction potential respectively. (E p c +E p a )/2 are reported, where E p c and E p a are the cathodic and anodic peak potentials, respectively . c AE 1 / 2(1) = E ° / 2 ( l ) - E,rc/2(1); H O M O -L U M O gap. dThis work. c R e £ 1 6 1 . f Re£156. The reduction potentials of the p-tiifluoromethylporphyrins (H 2 TPP(CF 3 ) 2 (46a), H 2 TPP(CF 3 ) 3 (47a), H 2 TPP(CF 3 ) 4 (48a), and H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a)  are higher than that of H 2 T P P (2a). The positively shifted reduction potentials are due to the strong electron-withdrawing effect of - C F 3 groups. A similar phenomenon is observed for a series of 141 p-cyanoporphyrins (32a, x = 2-4). 1^ 1 The reduction potentials of these porphyrins are higher than those of P-trifluoromethylporphyrins, indicating the difference in electron-witEdrawing strength between - C F 3 and - C N groups. Electrochemical studies regarding P-substituted /W^o-tetraarylporphyrins showed the first reduction potential of the macrocycle linearly changes with the electronic effect of a substituent and it does not depend on the structure of the macrocycle. 1°1-165 implies that the electronic effects of pyrrolic P-substituents should be reflected in the difference in the first reduction potentials. The changes in the first reduction potentials from 2a to 48a and to 32a (x = 4) are 0.75 V and 0.99 V, respectively and the difference between 48a and 32a is 0.24 V. Similar analysis concerning the first reduction potentials of 46a and 32a (x = 2) and 47a and 32a (x = 3) results in 0.26 V and 0.11 V, respectively for the differences between P-trifluoromethyl- and —methylporphyrins. Thus, it is estimated that the difference in the electron-withdrawing strength between —CF 3 and —CN groups causes approximately a 0.2 V difference in the first reduction potential. O n the other hand, the oxidation potentials of P-trifluoromethylporphyrins 46a, 47a, 48a, and 52a are more or less same as those of 2a, while those of P-cyanoporphyrins (32a, x = 2-4) are obviously higher than those of 2a. As discussed in Chapter I, section D.2.£.(2), oxidation of the macrocycle is sensitive to distortion of the macrocycle. Thus, it is probable that the electron-withdrawing effects of —CF 3 groups are offset by macrocycle distortion caused by the steric interaction between the P-trifluoromethyl groups and the meso-pehnyl groups (We will discuss the macrocycle distortion in detail in the analysis of an X-ray crystal structure of Zn(TPP(CF 3) 4) (48b) in section B.4.b(3)). A n estimation of the first oxidation potential of H 2 TPP(CF 3 ) 4 (48a) barring macrocycle distortion would be approximately 0.2 V higher (i.e. ~ 1.15 V) according to the analysis concerning the first reduction potentials. 142 A n interesting observation is the H O M O - L U M O gap (AE 1 / 2(1) difference between the first oxidation and the first reduction potentials, Table 2-9). This progressively decreases as the number of —CF 3 groups increases even when the offset of oxidation potentials is considered. A similar phenomenon is also observed in a series of P-cyanoporphyrins (32a, x = 2-4). 161 O n the other hand, such H O M O - L U M O gap contraction is not observed for a series of p-methylporphyrins (H 2 TPP(CH 3 ) 2 (57a), H 2 TPP(CH 3 ) 3 (58a), H 2 TPP(CH 3 ) 4 (59a). Figure 2-26 shows the plots of the first redox potentials of p-ttifluoromethylporphyrins (46a, 47a, and 48a) and P-methylporphyrins (57a, 58a, 59a) against the number (n) of the pyrrolic P-substituents (-CF 3 or —CH3). The plot ofthe first oxidation potentials of P-trifluoromethylporphyrins (•) has a maximum at n = 2. In contrast, the first reduction potential (o) increases almost linearly. It seems to fit a sigmoid curve better. Further discussion on this is not possible because the potentials for n = 1 is not available for now. The deviation of the oxidation potential at n = 4 from the predicted linearity (dotted line) made by the points at n = 0 and n = 2 is 0.22 V. This value may be reflecting distortion of the macrocycle in 48a. Even if we consider the effect of a presumed macrocycle distortion, the difference between the first oxidation and reduction potentials (i.e. the H O M O - L U M O gap) obviously decreases as the number of —CF 3 groups increases. The first oxidation (•) and reduction (o) potentials of p-methylporphyrins, on the other hand, change linearly as the number of methyl groups increases and the H O M O - L U M O gap parallels. These observations imply that the H O M O - L U M O gap contraction for a series of P-trifluoromethyl- and P-cycanoporphyrins is due to strong electron-withdrawing effects of —CF 3 and —CN groups. This phenomenon can be also rationalized by the unique electronic Figure 2-26. Redox potentials of (a) H2TPP(CF3)X (x = 0 (2a), 2 (46a), 3 (47a), and 4 (48a) and (b) H2TPP(CH3)X (x = 0 (2a), 2 (57a), 3 (58a), and 4 (59a). Symbols in the graphs indicate diferent electrode reactions; • : 1 st oxidation and O : 1st reduction. 144 structure of P-tiifluoromethylporphyrins as shown in the analysis of UV-visible and N M R spectra. Figure 2-27 shows the energy level diagram for H O M O s and L U M O s of the four generic metalloporphyrin classes.205 According to this diagram, as the macrocycle is reduced the H O M O - L U M O gap progressively contracts. The gap of bacteriochlorin, in which the 1871-electron pathway is fixed due to the reduced pyrroles in antipodal positions, displays about 60 % of resonance compared to that of a porphyrin. P-Trifluoromethylporphyrins have a bacterichlorin-type fixed 18TC-electron pathway (see Figure 2-16) and the distorted electronic pathway probably leads to the narrow H O M O - L U M O gap for which strong electron-withdrawing groups must reside on the pyrrolic P-positions of pyrroles in antipodal positions. b. Zn(II) porphyrins Many of the electrochemical studies of porphyrins have shown the redox potentials of Zn(II) porphyrins. Thus investigation of Zn(II) porphyrin redox properties is advantageous for comparison with those of other porphyrin macrocycles. In this section the redox potentials of p-tetralds(tofluorometJiyl)-^j-o-tetj:aphenylporphyrinato Zn(II) (Zn(TPP(CF3)4)) (48b) are reported and compared with those of other selected Zn(II) porphyrin systems. Figure 2-28(a) shows the cyclic voltammogram of Zn(TPP(CF 3) 4) (48b) in CH 2 C1 2 . Unlike the cyclic voltammetry of the corresponding free-base, two one-electron oxidations and clean two one-electron reductions were observed. Under the same condition, redox potentials of Zn(TPP) (2b), Zn(TPPBr 4) (45b), and Zn(TPP(CH 3) 4) (59b) were also measured and the redox potentials of these porphyrins are summarized in Table 2-10 with those of other electron-deficient porphyrins reported in the literature. In Figure 2-28(b), the first oxidation and the first reduction potentials of P-tetrasubstituted ^.ro-tetaphenylporphyrins including Zn(TPP(CN) 4) (32b, x = 4) were plotted against the 4o~p value (Table 1-3 in Chapter I, section BJ.b.(l) for o~p values for each 145 > >. 00 O -8 r -9 --10 -11 -12 — L U M 0 ( T T * ) •••H- H O M O ( T C ) Porphyrin Chlorin Isobacterio-chlorin Bacterio-chlorin Zn complexes Figure 2-27. Energy level diagram for H O M O s and L U M O s of the four generic porphyrin classes. Adapted from ref.205. 146 (a) 2.0 1.0 0.0 -1.0 -2.0 Potential (V vs. S C E ) (b) 2 4 a Figure 2-28. (a) Cycl ic vol tammogram o f Z n ( T P P ( C F 3 ) 4 ) (48b). Solvent: C H 2 C 1 2 , [48b] = 1 x 10 " 3 M , [ T B A P F 6 ] = 1 x 10 _ 1 M , scan rate: 50 m V / s . T h e white arrow indicates ferrocene/ferrocenium couple, (b) 4 a vs. 1st oxidation ( • ) and 1st reduction (O) potentials o f P-tettasubstituted /mo-tettaphenylporphyrinato Zn(II) (Zn(TPP) (2b), Z n C T P P ( C N ) 4 ) (34b, x=4), Z n ( T P P B r 4 ) (45b), Z n C T P P ( C F 3 ) 4 ) (48b). 147 Table 2-10. Redox potentials of |3-substituted ^ao-teteaphenylporphyrin Zn(II) complexes in CH 2 C1 2 . Porphyrin Potential (V vs. SCE) a E,°; 2(2) Ev d 2 (l) E$(2) AE 1 / 2(1) Zn(TPP) (2b)b 1.12 0.80 -1.40 - 2.20 Zn(TPP) (2b)c 1.11 0.78 -1.39 -1.84 2.17 Zn(TPFPP) (4b)b Zn(TPFPP) (4b)d 1.64 1.38 -0.99 -1.36 2.37 1.58 1.37 -0.95 -1.37 2.32 Zn(TPFPPBr 8) (8b)d Zn(TPPBr 4) (45b)b 1.53 1.57 -0.48 -0.76 2.03 1.10 0.93 -1.08 -1.30 2.01 Zn(TPPBr 4) (45b)c 1.14 0.90 -1.09 -1.36 1.99 Zn(TPPBr 8) (7b)c 1.11 0.85 -0.85 -1.10 1.70 Zn(TPP(CF 3) 4) (48b)b 1.24 0.92 -0.58 -0.81 1.50 Zn((CF3)4P) (16b)e - 1.44 -0.71 - 2.15 Zn(TPP(CH 3) 4) (59b)b Zn(TPP(CN) 4) (32a)f 0.83 0.71 -1.50 - 2.21 - .1.11 -0.44 - 1.55 Z n C T D C P P ^ O ^ , ) (15b)g - - 0.16 - -a E ° / 2 (n)and E " 2 (n) are n th oxidation and reduction potential respectively. AE 1 / 2(1)= E,°;2 (1)- E\% (1); H O M O - L U M O gap. b This work. Experimental conditions: [porphyrin]: 0.5 or 1 mM; [TBAPF6]:0.1 M ; scan rate: 0.05 V / s ; reference electrode: A g wire. Potentials were determined by the internal standard of ferrocene/ferrocenium redox couple (0.46 V vs. SCE, C H ^ h ) . 2 1 3 c Ref.164. d Ref.214 Values are vs Ag .AgCl . c Ref.39. In benzonitrile.f Ref.161. 8 Ref.37. group). Since each of Zn(TPPBr 4) (45b), Zn(TPP(CF 3) 4) (48b), Zn(TPP(CH 3) 4) (59b), Zn(TPP(CN) 4) (32b, x = 4) contains four (3-substituents, 4a p values were used instead of ap values. As shown in the figure, the first oxidation potentials of Zn(TPP(CH 3) 4) (59b), Zn(TPP)(2b), Zn(TPPBr 4) (45b) and Zn(TPP(CN) 4) (32b, x = 4) are on a slightly curved line. However, the oxidation potential for 48b is slightly lower than the line by about 0.2 V , which is similar to the deviation of Figure 2-26(a). The plots of the first reduction potentials show an interesting result. Previous studies^°2-164 s h o w e d that reduction potentials linearly changed as the number of bromines on the P-pyrrolic positions increased. Thus we can expect that change in the first reduction potential of porphyrins is proportional to the sum of the rjp values of the substituents. However, as shown in Figure 2-28(b), the plot of the reduction potentials against 148 the CTp values in the series of (3-tetrasubstituted /#£ro-tettaphenylporphyrinato Zn(II) shows a gentle sigmoid curve. The oxidation potentials, except for that of - C F 3 , may also fit a sigmoid curve, but the change in the oxidation potentials is too small to argue this point. Unfortunately, the number of the data shown in Figure 2-28(b) is limited but the plots show that both oxidation and reduction potentials are leveling off at higher 4cjp values and leading to a fixed and narrow H O M O - L U M O gap. This indicates that the electronic structure of the macrocycle converges into a bacteriochlorin-type structure due to strong electron-withdrawing effects of substituents on the antipodal pyrroles. O n the other hand, at lower 4a p values (i.e. for Zn(TPP(CH 3) 4) (59a) the H O M O - L U M O gap is as wide as that of Zn(TPP) (2a). This result matches the observations of P-trifluoromethylporphyrins by the UV-visible and N M R spectroscopies. In order to compare P-tetealds(tiifluoromethyl)porphyrinato Zn(II) with other Zn(II) porphyrins in Table 2-10, the first oxidation and the first reduction potentials are plotted in Figure 2-29. As shown in Chapter I, the reduction potential reflects the electron-deficiency. Thus, a high reduction potential of a porphyrin indicates that the porphyrin is electron-deficient. This simple analysis ranks Zn(TPP(CF 3) 4) (48b) as an electron-deficient porphyrin. It seems more electron-deficient than porphyrin Zn(TPFPP) (4b) (see Figure 1-8, p i 1) and Zn(TPPBr 8) (7b), and as electron-deficient as Zn(TPFPPBr 8) (8b). This latter macrocycle is well known in the third generation porphyrin catalysts (see Chapter I, section B.Zd). For better robustness as an oxidation catalyst, a higher oxidation potential is desired, but the oxidation potential of Zn(TPP(CF 3) 4) (48b) is the same as that of Zn(TPP) (2b). Thus, the high reduction potential of 48b may be a good indication that it may be advantageous to activate a central metal in porphyrin catalysts. Metal complexes such as Fe(III) or Mn(III) porphyrins may give a small 149 L U M P of ZnTPP V H O M O of ZnTPP V ZnTPP (2b) • ZnTPPBr 4 (45b) p h ^ . : z h ^ P h sr x -fh Br ZnTPPBr 8 (7b)b ZnTPFPP (4b) ZnTPFPPBr 8 (8b)c?h • ZnTPP(CF 3 ) 4 (48b) Ph-F 3 C ZnTPP(CH 3 ) 4 (59b) ZnTPP(CN) 4 (34b) • Zn(CF3)4P (16b)e t\l02 tfC>2 \ f 0 2 N-CN Ph o ZnTDGPPQSlO^g (15b/ - v _ N y Ar—( ^Zh(ll) >-C 6H 3CI 2(=Ar) -1 0 1 Potential (V)a Figure 2-29. The H O M O (•: 1st oxidation)-LUMO (O: 1st reduction) gap of P-substituted mro-arylporphyrin Zn(II) complexes.3 Potentials are in vs. S C E for 2b, 4b, 7b, 15b, 16b, 34b, 45b, 48b, and 59b and in vs. A g / A g C l for 8b and 12b. Data were measured in C H 2 C 1 2 except for 16b, which was measured in benzonitrile. b Ref.75.c Ref.214. d Ref.161. e R e £ 3 9 . f Ref.37. 150 gain in the oxidation potential. This would be an unsatisfactory result for a robust oxidation catalyst. The high reduction and the low oxidation potential of Zn(TPP(CF 3) 4) (48b) result in a narrow H O M O - L U M O gap. In Figure 2-29, the numbers between the oxidation and the reduction show the H O M O - L U M O gaps for various Zn(II) porphyrins in volts while the two dotted lines are the H O M O and the L U M O of Zn(TPP) (2a). Obviously, the H O M O - L U M O gaps of 48b and Zn(TPP(CN) 4) (32b, x = 4) are narrower than those of other electron-deficient porphyrins. Since the H O M O - L U M O gaps of Zn((CF3)4P) (16b, n = 1) (Figure 1-8, p.l l) , Zn(TPPBr 4) (45b), and Zn(TPP(CH,) 4) (59b) are close to that of 2a, it is obvious that both symmetry and strong electton-witlidrawing substituents are required for the narrow H O M O -L U M O gap. The reason for this, as explained for the free-base porphyrins, is that the macrocycles of 48b and 32b (x = 4) presumably have the bacteriochlorin-like fixed 187t-electron, pathway. In addition to the distorted electronic pathway of the macrocycle, offset of the oxidation potential by the macrocycle distortioni44-146 m a v a j s o contribute to the narrow H O M O - L U M O gap of 48b. In summary, the electron-withdrawing effects of —CF 3 groups on the pyrrolic P-positions increased the reduction potentials of P-trifluoromethylporphyrins almost linearly as the number of —CF 3 groups increased. The first oxidation potential did not gain much from that of /Wwo-tetraphenylporphyrin and a linear increase of the potential with the number of —CF 3 groups was not obtained due to the offset by a presumed macrocycle distortion. Narrowing of the H O M O - L U M O gap was observed as the number of —CF 3 groups increased. This is presumably because the macrocycle is forced to take a distorted 1871-electton pathway just like that of 151 bacteriocMorin by the strong electton-withdrawing effect of —CF 3 groups on the antipodal pyrroles. P-Tettakis(trifluoromethyl)porphyrin (48) may be as electron-deficient as the porphyrins appeared in the tliird generation porphyrin catalysts such as P-octabromo-#?£ro-tetrakis(perfluorophenyl)porphyrin (TPFPPIkg) (8) (Figure 1-8, p.11) but the oxidation potential of 48 seems to be insufficient for a robust oxidation catalyst. c. Fe(III) porphyrins In the past, redox potentials of Fe porphyrins were used to discuss the activity and the stability of the porphyrins as oxidation catalysts.45,73 j n this section redox potentials of Fe(III) complexes of P-trifluoromethylporphyrins (Fe(TPP(CF3)4)Cl (48f) and Fe(TPP(CF 3 ) 3 (CF 2 CF 3 )Cl (52c)  measured by cyclic voltammetry are reported and they are compared with those of other selected Fe(IIF) porphyrins. Table 2-11 summarizes the redox potentials of Fe(IIi) porphyrin chloride complexes. Cyclic voltammetry measurements with known porphyrins, Fe(TPP)Cl (2d) (Figure 1-8, p.l l) and Fe(TPPBr 4)Cl (45e) (Scheme 2-8) showed that the measured values were close to the reported values. The first reduction potentials (Fe(III/II) couple) for 48f and 52c shifted positively about 0.3 - 0.4 V from that of 2d and are as the same as that of the wwo-tetrakis(heptafluoropropyl)porphyrinato Fe(III) chloride (Fe((C3F7)4P)Cl) (16d) (Figure 1-8). The Fe(III/II) couples of 48f and 52c are ranked between the values of the second generation catalyst, Fe(TPFPP)Cl (4d) (Figure 1-8) and the third generation catalyst, Fe(TPFPPBr 8)Cl (8d) (Figure 1-8). Thus, redox tuning of the Fe(III) in 48f and 52c seems to be successful for modelling P-450 compounds. However, the first oxidation potentials of 48f and 52c are the same level of as that of 2d. This may imply that these porphyrins will not perform as robust oxidation catalyts. The reason for the low oxidation potentials in 48f and 52c must be the macrocycle distortion as discussed in the previous sections. 152 c/5 a o co M . o u <u o u a o PH e-o a CU PH a CU +H O a x o -a PH CN C4 H CN o PH PH PH PH PH < < PL, PH QH PH PH PH PH PH PH PH PH PH PH <! <^  CQ <1 <I <J <1 j u X # C J PH z a z ^ £ 5 ? PH C J PH 2 0 2 u C J ^ u ^ 5 ? £ ?P SH PI U PH C J oo cq vo O rn O (N so Cs ro to CN o d d so oo Tt-o o CO O t • T-H (M o o d d o CN 00 C O S O H H (S| t— m CN m m m C O O so m so in co so T3 u pT PH •d m U PP (3^ oo PH C J , PH 00 SO u CN m U PH C J CN PH C J , m PH cy PH cu PH 1) PH PH PH PH < < EE o z C J PH EE PH PH E O CN CN T-H C7i O C \ C \ cn oo T-H o o o o o CN CN T h T"H O T-H m "2; so T-H o P o o d ° d d m oo ^ h VH p d P cn oo T 3 \ - ' CN £ j s m "d -— so p? c j ^ PH PH" PH PH 00 CN O T-H O C N CN d z C J PH cn z cj HH PH m S O ^ 3 00 d cn m > JJ o u II •d 0 P7 & PH •d go, U PQ PH PH PH T3 o y 1 C J 1 PH ' PH C J m T-H CN cu PH 153 However, as shown in Table 2-11 the first oxidation potential of one of the third generation porphyrin catalysts, Fe(TDCPPCl 8 )Cl (lOd) (Figure 1-8), is even lower than that of Fe(TPP)Cl (2d) (Figure 1-8). It is not easy to predict the catalytic activity of 48f and 52c from the redox properties alone. Accordingly, actual oxidation reactions have to be run to investigate the efficacy of these Fe(III) porphyrins as catalysts. 4. Crystal structures In this section, the X-ray crystal structures of Zn(II) complexes of P-tetrasubstituted ^-teteaphenylporphyrins (Zn(TPPBr4) (45b), Zn(TPP(CF 3) 4) (48b) and Zn(TPP(CH 3) 4) (59b) are reported. These X-ray crystal structures are very important not only to elucidate the structures of the macrocycles but also to support discussions presented for the UV-visible, N M R spectroscopic and electrochemical studies of the p-trifluoromethylporphyrins. These discussions suggested a fixed 187t-electron pathway (Figure 2-16) and the macrocycle distortion as dominant electronic and structural characteristics. O f specific interest are the steric effects of - C F 3 groups. Therefore, in the second part of this section analysis of distortion of the macrocycle of Zn(TPP(CF 3) 4) (48b) is focused. a. Preparation of the crystals and crystallographic data. Zn(TPP(CF 3) 4) (48b) was crystallized as Zn(TPP(CF 3) 4)-(EtOH) 3 (48b-(EtOH)3) from a mixture of E t O H and CHC1 3 . In addition to X-ray crystallography, the crystals were analyzed by *H and 1 9 F N M R solution spectroscopy and elemental analysis. The 200 M H z ' H N M R spectrum of 48b-(EtOH)3 in CDC1 3 showed that E t O H signals shifted to the higher field than those of the normal E t O H in CDC1 3 at room temperature, suggesting a shielding effect by porphyrin. Attempts to crystallize out Zn(TPPBr 4) (45b) and Zn(TPP(CH 3) 4) (59b) from the same solvent system failed due to their low solubility in E t O H / C H C 1 3 . Accordingly, porphyrin 154 45b was crystallized as Zn(TPPBr 4)• (MeOH)• (DMF) to give the solvate 45b-(MeOH)-(DMF) by slow diffusion of M e O H into the D M F solution. The compound 59b was crystallized as Zn(TPP(CH 3 ) 4 )-(THF) 1 6 -(CHCl 3 ) 0 4 (59b-CTHF)16-(CHCl3)04) by slow evaporation from C H C L / T H F . These single crystals were analyzed by *H N M R solution spectroscopy and elemental analysis as well as by X-ray crystallography. Table 2-12 shows crystallographic data. The three Zn(II) porphyrins showed square pyramidal coordination for the central Zn(II) atoms. In the crystal structure of 45b-(MeOH)-(DMF) and 48b-(EtOH)3, a M e O H molecule and a E t O H molecule are coordinated to Zn(II) atoms, respectively. In 59b-(THF)16-(CHCl3)04, T H F coordinated to Zn(II) and disordered structure was observed for the axial T H F . In addition, two different solvents, T H F and CHC1 3 appear to occupy the same volume 60 % and 40 % of the time respectively. Details of the structures of these complexes are described in the following section. Table 2-12. Crystallographic data for 45b-(MeOH)-(DMF), 48b-(EtOH)3, and 59b-fTHF)1,6-(CHCl3)ft4 45b-(MeOH)-(DMF) 48b-(EtOH), 59b-CrHF)1/;(CHCl,)o, Empirical formula C 4 8 H , 5 B r 4 N 5 0 2 Z n C 5 4 H 4 2 F 1 2 N 4 0 3 Z n C54.80r^49.2oN4Zn01.6 0Cl F.W. 1098.83 1088.31 897.34 space group P 1 p T P2,/n a, A 12.257(2) 12.0428(11) 13.585(1) b , A 13.4377(8) 13.275(2) 18.182(1) c , A 14.387(1) 16.909(2) 18.065(2) <x,° 83.819(2) 96.951(5) !V 71.227(2) 108.124(2) 93.274(3) Y,° 73.575(3) 107.354(2) v , A 3 2151.7(3) 2383.2(5) 4454.9(6) z 2 2 4 D c a k (g/cm3) 1.70 1.52 1.34 u. (Mo-Ka) (cm-1) 43.42 6.13 6.70 T (°C) -100 ± 1 -93 ± 1 -100 ± 1 No. of observations 6086 5823 2621 R(F) 0.058 0.099 0.129 0.089 0.091 0.155 155 b. Structure details O R T E P views (in 30 % probability ellipsoid) of the crystal structures are shown in Figure 2-30-45b, Figure 2-30-48b, and Figure 2-30-59b. Each figure shows the top view and the side view. Solvent molecules for the top views and meso-phenyl groups and part of the solvent molecules for the side views were omitted for clarity. Selected bond lengths and bond angles for the shown structures are summarized in Table 2-13. Structural data for Zn(TPP)(H 2 0) (2a-(H20))216 a r e also listed in the table for comparison. Some designations used in Table 2-13 are shown in the molecular diagram in Scheme 2-10. R = H (2b) = Br (45b) = C F 3 (48b) = C H 3 (59b) Scheme 2-10. Atom designations used in Table 2-13. (1) Core si%e, Zn displacement, and axial coordination Coordination around Zn(II) in complexes 45b(MeOH)-(DMF), 48b-(EtOH)3, and 59b-(THF)16-(CHCl3)04 is penta-coordinate square pyramidal. This structure is common for Zn(II) porphyrins.2! ^  In complexes 45b, 48b, and 59b, the Zn(II) atoms are displaced by 0.277, 0.325, and 0.234 A from the least-square plane through the four porphyrin nitrogen atoms (N 4 plane), respectively. These values are larger than the 0.173 A reported for Zn(TPP)-(H 20) (2a-(H20)).216 The macrocycle core sizes (N—Cr, where Ct is the centroid of the four nitrogen atoms. Table 2-13 for the details.) of Zn(TBBBr 4) (45b), Zn(TPP(CF 3) 4) (48b), 156 Figure 2-30-45b. X-ray crystal structures of 45b- (MeOH)- (DMF). The axial ligand and the solvent molecule for the top view and the meso-xphenyl groups for the side view were omitted for clarity. Figure 2-30-48b. X-ray crystal structures of 48b- (EtOH) 3 . The axial ligand and the solvent molecules for the top view and the meso-phenjl groups and solvent molecules for the side view were omitted for clarity. 158 Figure 2-30-59b. X-ray crystal structures of 59b- (THF), 6- (CHC13)0 4 . The axial ligand and the solvent molecules for the top view and the meso-phenyl groups and solvent molecules for the side view were omitted for clarity. 159 Table 2-13. Core size, selected bond lengths and bond angles. Selected bonds" Zn(TPPBr 4) (45b) ZnCrPP(CF3)4) (48b) Zn(TPP(CH 3) 4) (59b) Zn(TPP) b (2b) N—Ct, N ' C f Core sized (A) N1 Ct 2.097 2.105 2.076 N3 Ct 2.090 2.108 2.076 2.043 N2 Ct 2.012 1.976 2.013 N4 Ct 2.006 1.949 2.010 Bond length (A) Zn -O 2.108(MeOH) 2.110(EtOH) 2.182(THF) 2.228(H2Q) Zn-N, Z n - N , c Zn1-N1, Zn1-N3 2.121,2.109 2.130,2.108 2.091, 2.092 2.050 Znl-N2, Znl -N4 2.030, 2.021 2.008, 1.997 2.024, 2.020 N-Ca, N ' - C a ' c N1-C1, N1-C4 1.371, 1.374 1.379, 1.378 1.356, 1.385 1.374,1.369 N3-C11,N3-C14 1.383, 1.371 1.365, 1.374 1.375, 1.384 N2-C6, N2-C9 1.372,1.369 1.382,1.380 1.380,1.380 N4-C16, N4-C19 1.365,1.375 1.384,1.378 1.379,1.368 CcrCp, C a ' - C p ' c C1-C2, C4-C3 1.451, 1.449 1.462, 1.445 1.453, 1.447 1.441,1.443 C11-C12, C14-C13 1.448, 1.446 1.439, 1.459 1.468, 1.454 C6-C7, C9-C8 1.445,1.450 1.445,1.445 1.454,1.449 C16-C17, C19-C18 1.449,1.439 1.446, 1.464 1.443,1.470 Cp-Cp, Cp' -Cp' c C2-C3, C12-C13 1.357, 1.344 1.371, 1.366 1.382, 1.369 1.341 C7-C8, C17-C18 1.342,1.346 1.335,1.337 1.337,1.358 C1-C20, C4-C5 1.408, 1.411 1.424, 1.404 1.428, 1.417 C11-C10, C14-C15 1.411, 1.405 1.445, 1.414 1.408, 1.423 1.405 C19-C20, C6-C5 1.405,1.400 1.386,1.401 1.394,1.394 C9-C10,C16-C15 1.395,1.405 1.407,1.392 1.391,1.374 Selected angles3 Bond anj ?les 0 N-Zn-N, N'-Zn-N' N1-Zn1-N3 163.9 166.8 165.9 170.3 N2-Znl-N4 165.4 156.8 168.1 CcrN-Ca, Ca'-N-Ca"-' C1-N1-C4,C11-N3-C14 108.5, 107.8 108.2, 108.1 105.2, 106.6 106.8 C6-N2-C9, C16-N4-C19 107.1,106.2 106.3,107.4 106.9,108.0 (continued) 160 Table 2-13 (continued) Selected angles" Zn(TPPBr 4) (45b) Zn(TPP(CF 3) 4) (48b) ZnCTPP(CH 3) 4) (59b) Zn(TPP) b (2b) Bond an gles 0 CyCVA/, C p ' - C a ' - N ' e C2-C1-N1, C3-C4-N1 108.7, 107.9 108.7, 108.1 111.9, 110.9 C12-C11-N3, C13-C14-N3 108.0, 108.5 109.4, 108.1 109.8, 109.8 109.3 C7-C6-N2, C8-C9-N2 108.9,109.2 109.1,109.3 109.1,108.6 C17-C16-N4, C18-C19-N4 110.0,109.8 108.3,108.5 108.9,108.6 CorCp-Cp, C a ' - C p ' - C p ' c C1-C2-C3, C4-C3-C2 106.8, 108.1 106.2, 108.1 105.6, 106.3 C11-C12-C13, C14-C13-C12 107.9, 107.6 106.8, 107.2 106.4, 107.2 107.5 C6-C7-C8, C9-C8-C7 107.8,107.0 107.7,107.5 107.1,108.3 C16-C17-C18, C19-C18-C17 106.7,107.3 108.6,106.9 107.9,106.6 CcrCmeso~Cpby CQ?-Cmeso-Cph0^ C1-C20-CpU, C4-C5-Cph1 119.1, 118.6 121.0, 117.6 119.3, 117.7 C11-C10-Chh2,C14-C15-Chhi 118.3, 118.6 118.3, 121.8 118.4, 117.2 117.2 C19-C20-C p h 4, C6-C5-C p h l 115.4,116.4 114.7,117.4 115.7,115.8 C9-C10-C n h 2 , C16-C15-C o h 3 116.3,116.0 117.8,113.2 115.4,117.3 Ca-Cmeso-Ca'6 C1-C20-C19, C4-C5-C6 125.5,124.8 124.3,124.5 124.9,126.5 N.A. C9-C10-C11,C14-C15-C16 125.4,125.4 123.7,125.0 126.2,125.5 C a - C p - R e * C1-C2-R 129.5 128.6 129.6 C4-C3-R 128.7 124.2 129.5 C11-C12-R 129.6 125.7 127.6 C14-C13-R 129.6 129.3 128.3 a See Figure 2-30-45b, 48b and 59b for atom designations. b Ref. 216. c Ct is the centroid of the four nitrogens. d Calculated using d — [^(x^xj2 + b2(yx-y^)2 +c2(^J-^2)2 + 2bc-cosa{yrj^)(^-t^) + 2ca-cosR(^-^)(xrx^) +2ab-cosy{xrx^){yrj2)]i/2 , where d is the distance between coordinates (xuji, Ki) a n d (xi,j2, e S e e Scheme 2-10 for N , N' , C a , C a ' , Cp, Cp', Cmta, and C p h designations. f Cph,: C21 for 45b, C25 for 48b and 59b, C p h 2 : C27 for 45b and C31 for 48b and 59b, C p h 3 : C33 for 45b and C37 for 48b and 59b, C p h 4 : C39 for 45b and C43 for 48b and 59b. 8 R: Br for 45b, C F 3 for 48b, and C H 3 for 59b. and Zn(TPP(CH 3) 4) (59b) in the direction of P-substituted pyrroles (values in this direction are reported in italic in Table 2-13; N- • -Ct (average) = 2.048, 2.106, and 2.076K respectively) are obviously larger than those in the direction of non-substituted pyrroles (N'-Ct (average) = 2.009, 1.962, and 2.012 A respectively) and the core sizes in the direction of non-161 substituted pyrroles of 45b, 48b, and 59b are smaller than that ( C t - N (2.043 A)) of the macrocycle in Zn(TPP)-(H 20) (2a-(H20)).216 The largest Zn(II) displacement from the N 4 plane in 48b may be due to the smallest N---Ct values in the direction of non-substituted Although the axial ligands for the complexes in Table 2-13 are different, the donor atom in all cases is oxygen. Thus, comparison of Z n - O distance may provide a rough measurement for the electron-deficiency of the porphyrins. The Z n - O distances of 45b-(MeOH) (2.108 A) and 48b-(EtOH) (2.110 A) are significandy shorter than the 2.228 A of Zn(TPP)-(H 20) (2a-(H20))216 or the 2.226 A of Zn(OETPP)-(MeOH) (30)147 (see p.43 for 30) and comparable to the 2.092 A of Z n f T P P F ^ t H p ) (12b-(H20))41 (Figure 1-8, p . l l for 12b), indicating electron-deficiency of the macrocycles of 45b and 48a. (2) Effects of antipodal B-substitution Antipodally P-substituted porphyrins show unique structural profiles. Firsdy, Z n - N distances (or the core sizes) are longer in the direction of P-substituted pyrroles (see Table 2-13) than in the direction non-substituted pyrrole. In the reported structural studies of antipodally substituted porphyrins such as Ni(TPP(CN) 4)-(L) 2 (L=py or l-Melm) (63),219.220 (Fe(TPPBr 4)) 20 (64)192, or Fe(TPPBr 4)Cl (45e),19 similar differences in Z n - N distances between the p-substituted and non-substituted directions were observed. The bond weakening pyrroles. 162 of Z n - N in the P-substituted direction due to electron-wimdrawing effects of the substituents is the rationale for such observations.1^1,219 However, a recent review 2 ^ Q f crystal structures of antipodally P-substituted /^.ro-arylporphyrins suggested there are considerable distortions of the macrocycle cavity due to both electronic and steric effects of the substituents. As shown in Figure 2-31, due to the steric interaction between the P-substituents (R and R) or R and meso-phenyl groups, the phenyl groups are pushed away from the R groups. The macrocycle expands in the direction of the P-substituted pyrroles and contracts in the direction of the non-substituted pyrroles. The analysis shown in Figure 2-31 is essential to rationalize a similar observation regarding the Z n - N distances in Zn(TPP(CH 3) 4) (59b) (Table 2-13) which cannot be explained by the electronic effects of electron-releasing —CH 3 groups. The steric interaction of the substituents seems to be reflected on the longer Cp-Cp lengths (C2-C3 > C7-C8, Table 2-13) in Zn<TPP(CF3)4) (48b) and Zn(TPP(CH 3) 4) (59b) due to the repulsion between the bulky pyrrolic P-substituents; the effective van der Waals radius of the - C F 3 group is 2.2 A 126 and that of - C H , group is 1.8 A^ 2 6. The C2-C3 and C12-C13 lengths in 48b and 59b are significantly longer than those in Zn(TPP) (2a). In contrast, significant differences in Cp-Cp (C2-C3 vs. C7-C8) bond lengths were not observed for Zn(TPPBr 4) (45b). The van der Waals radius of Br (1.95 A ) ^ 2 3 is nearly as large as that of - C H 3 , but the Cp-Br bond length in 45b (1.87 A, not shown in Table 2-13) is much longer than that of Cp-CH 3 in Zn(TPP(CH 3) 4) (59b) (1.54 A). The difference is due to the longer Cp-Br lengths. This reduces Br-Br contacts. The Ca-Cims-Cph angles (Table 2-13) show the steric interaction between meso-phenyl groups and the pyrrolic P~ substituents; wider angles were observed in the direction of the P-substituted pyrroles. Comparison of Cp-Cp lengths in various antipodally P-substituted porphyrins is summarized in N ~ W Steric interaction Figure 2-31. Schematic illustration of the steric effects of antipodal (5-substituents and meso-phenyl groups on the macrocycle of P-tetrasubstituted OT^o-tetraphenylporphyrin. 164 Table 2-14. In the metalloporphyrins of P-tetrabromo-^Jo-phenylporphyrins 45b and 45e, the difference between the two Cp-Cp lengths is not obvious. The longer Cp-Cp bonds in the direction of P-substituted pyrroles in 59b and 63 suggest that the bond elongation was caused by either steric or electron-withdrawing effects. In Zn(TPP(CF3)4) (48b), it is likely that elongation of Cp-Cp bonds occurs due to both effects. The electron-withdrawing effect of —CF3 group Table 2-14. Cp-Cp bond lengths in antipodally P-tetrasubstituted ^?gjQ-tetraphenylporphyrins. Cp-Cp length (A) Porphyrins P-substituted P-non-substitued Reference direction direction Zn(TPPBr 4) (45b) 1.35 1.34 fFe(TPPBr4)]Cl (45e) 1.36 1.35 b Zn(TPP(CF 3) 4) (48b) 1.37 1.34 Zn(TPP(CH 3) 4) (59b) 1.38 1.35 Ni(TPP(CN) 4) (63) 1.37 1.34 c-d Zn(TPP) (2b) - 134 e a This work. b Ref.191.c Ref.219. d Ref.220.e Ref.216. presumably leads to a low electron density of the bonds between the pyrrolic P-carbons where the substituents are attached. This Cp-Cp elongation in 48b may direct the 187t-electron to avoid resonance through those double bonds. (3) Macrocycle distortion Investigation of macrocycle distortion of P-teti:altis(tjifluoromethyl)porphyrin is important in order to rationalize the UV-visible, N M R spectra, and electrochemical data of the porphyrin. Here, distortion of the macrocycle of Zn(TPP(CF 3) 4) (48b) is compared with that of Zn(TPPBr 4) (45b) and Zn(TPP(CH 3) 4) (59b) and then the mechanism of the distortion is analyzed. 165 Figure 2-32 shows the degree of distortion in the macrocycles of 45b, 48b, and 59b. The numbers in the porphyrin structures indicates the deviation (in 0.01 A) of each atom from the N 4 mean plane. We can imagine the N 4 plane to be on the page of the figure for the porphyrin structures in the left column. The atoms with positive values are above the page in the porphyrin structures, while atoms with negative values are below the page. The figures beside the porphyrin structures show the skeletal deviations of the 24 core atoms of the macrocycles from the N 4 mean plane. As indicated in Figure 2-32(a), (b), and (c), for all the three macrocycles, pyrrole rings are alternately up and down relative to the N 4 mean plane and thus the macrocycles are saddle-distorted (for general modes of porphyrin distortion refer to the references. 18,145) -ph e averages of the absolute values of pyrrolic P-carbon displacements are 0.40, 0.79, and 0.52 A in 45b, 48b, and 59b, respectively. Distortion of the macrocycle observed in 45b and 59b is very similar to that in Z n f T P P F ^ t H p ) (12b-(H20))41(see Figure 1-8, p. 11 for 12b) which showed the saddle distortion and the average value, 0.49 A, of pyrrolic P-carbon displacement. In fact, crystal structures of a four-coordinate Zn(TPPBr 4) (45b) shows a planar porphyrin macrocycle.221 Thus, it is very likely that the distortion of Zn(TPPBr 4) (45b), Zn(TPP(CH 3) 4) (59b), and Zn(TPPF 8) (12b) is due to the five-coordinate Zn(II), which is displaced by 0.23-0.28 A from the N 4 plane. The 0.79 A displacement of pyrrolic P-carbons on average in Zn(TPP(CF 3) 4) (48b) is obviously larger and this indicates the severe distortion of the macrocycle itself. Comparison of the rms (root-mean-square) values (Figure 2-32), which are the average deviations of the 24 core atoms from their least squares plane, also shows the severe distortion in the macrocycle of 48b. The van der Waals (vdW) radius of fluorine is 1.35 -1.47 A 1 2 3 ' 1 2 6 , which is close to 1.1-1.3 A of hydrogen. 1 2 3 However, the size of - C F 3 is estimated to be 2 . 2 A . 1 2 6 . T h e vdW radius of - C F 3 is estimated as 2.69-2.81 A 166 (a) ZnCTPPBr 4) (b) ZnCTPP(CF 3) 4) (c) ZnCTPP(CH 3) 4) Figure 2-32. Perpendicular atomic displacements of Z n porphyrins (a) 45b, (b) 48b, and (c) 59b, relative to the N 4 mean plane. The numbers in the porphyrin structures on the left column are the distances in 0.01 A units. The figures on the right column display the skeletal deviations of 24 core atoms of the porphyrins from the N 4 mean plane. • indicates the pyrrolic P-carbons bearing substituents. The rms values show the average deviation of the 24 core atoms from their least squares plane. 167 from the crystallographic data of 48b; the vdW radius of —CF 3 = 1.34 A(average C-F distance) +(1.35 to 1.47 A) (vdW of F). Thus, it is probable that - C F 3 is much larger than - C H 3 (vdW = 1.8 - 2.0 A)123,126 a n ( j s t e r i c interactions among substituents are expected. As observed in the top view in Figure 2-30-48b, two meso-phenyl groups (C25-C30 and C31-C36) seem to be extremely twisted due to the steric interaction with-CF 3 groups. The average of the torsion angle made by C^(C26 or C30)-C25-C5-C a(C4 or C6) is 54.4° and similarly 52.1° for the other extremely twisted phenyl ring (C31-C36). Interestingly, two other phenyl rings (C37-C42 and C43-C48) are almost orthogonal to the best plane of the porphyrin macrocycle (the corresponding torsion angles are 85.2 and 80.2°, respectively). Instead; the compensation for it seems to be made by pushing the - C F 3 groups away from these phenyl groups (C37-C42 and C43-C48). SmaU C4-C3-R (R=C22) and C11-C12-R (R=C23) angles (see Table 2-13) are indications of the interaction between the phenyl groups (C37-C42 and C43-C48) and the - C F 3 groups that eventually forces the two phenyl rings (C25-C30 and C31 and C36) to rotate. This structural relationship is clearly shown in Figure 2-33(b), which is a part of the crystal structure of Zn(TPP(CF 3) 4) (48b) projected from the direction indicated by the arrow in the stick model of the top view of the molecule (Figure 2-33(a)). The steric interaction between the phenyl (C43-C48) and - C F 3 (F1-F3) determines the orientation of the - C F 3 so that no F of F1-F3 is pointing at the face of the phenyl ring. This orientation makes the F3 point at the adjacent - C F 3 (F4-F6), which orients so that F3 points between F4 and F5. Similarly the orientation of the - C F 3 (F4-F6) shifts the position of the phenyl ring (C25-C30) to minimize the steric interaction. In addition, the negative interactions between the 7t-cloud of the phenyl rings and the - C F 3 groups may be the driving force for the severe distortion of the macrocycle. A n electrostatic repulsion between the electronegative fluorine and the 7t-electrons is k n o w n . 2 2 2 The distance from the center 168 Figure 2-33. Orientations of phenyl and CF 3 groups in 48b. (b) shows a projection of a part of the crystal structure, 48b shown by stick model (a), from the direction indicated by the arrow. 169 of the carbon atom to the plane of the adjacent phenyl ring would be approximately 3 A, if it were not for steric interactions. Since the half thickness of benzene is 1.85 A 1 2 3 and the vdW radius of —CF 3 is at least 2.2 A^ 2 ", a strong electronic repulsion between these two groups is expected. The average torsion angles made by the C o r t h o -C p h-C O T„„-C a are 68.4, 78.2, 76.8, and 72.9° in Zn(TPPBr 4) (45b) and 75.9, 67.6, 71.5, and 71.3° in Zn(TPP(CH 3) 4) (59b) and none of the phenyl groups in 45b and 59b is severely twisted. Figure 2-34(b) shows the orientations of phenyl and C H 3 groups featured in a part of the crystal structure of 59b. There is no such strong interaction between the phenyl and C H 3 groups as that observed in Zn(TPP(CF 3) 4) (48b). (4) Orientation of the axial ligand A n interesting feature of the crystal structure of 48b-(EtOH)3 is the orientation of E t O H molecules to the macrocycle distortion. As shown in Figure 2-30-45b and Figure 2-30-59b, in 45b-(MeOH)-(DMF) and 59b-fTHF)j.6-(CHCl3)a4 axial ligands are coordinated to Zn(II) on top of the bow-like shape created along the direction of antipodal P-substitution (Scheme 2-11(a)). O n the other hand, in 48b-(EtOH)3 (Figure 2-30-48b) an ethanol is coordinated to Zn(II) in the bow-like shape along the direction with - C F 3 groups (Scheme 2-11 (b)). Interestingly, as shown in Figure 2-30-48b, the axial ethanol is hydrogen bonded to the second ethanol (HI 02 (1.90 A)), whose methylene hydrogen (H32) has a non-bonding contact with F9 (H32 F9 (2.71 A)). The third ethanol (not shown in the figure) is also hydrogen-bonded to the second ethanol (03 H31 (2.03 A), where 03 is the oxygen atom in the third ethanol and H31 is hydroxyl hydrogen of the second ethanol). There were also many other H F nonbonding contacts within 3 A between solvent ethanols, P-pyrrolic hydrogen, or phenyl ring hydrogen and 170 Figure 2-34. Orientations of phenyl and C H 3 groups in 59b. (b) shows a projection of a part of the crystal structure, 59b shown by stick model (a), from the direction indicated by the arrow. 171 =porphyrin macrocycle L (a) (b) Scheme 2-11. Schematic representations of macrocycle distortion and axial coordination in (a)Zn(TPPBr4)(45b)• (MeOH) and Zn(TPP(CH3)4)(59b)-(THF) and in (b) Zn(rPP(CF3)4) (48b) • (EtOH). - C F 3 moieties across the different porphyrin units. Intermolecular 5 + c_p 5 - a n d 5 " C - H 8 + bond dipole interactions or C-H—F-C hydrogen bonding is known.126 Unfortunately, these non-bonded contacts are so complicated in this porphyrin system that they cannot be pictured in an appropriate way. In summary, crystal structure analysis of three zinc complexes of P-teteasubstitued meso-tetraphenylporphyrins showed elongated macrocycle cavities due to the substituents on the pyrrolic P-positions of antipodal pyrroles. Elongation of the macrocycle was reflected in different Z n - N distances (or core sizes) in the directions of P-substituted pyrroles and of non-substituted pyrroles. The Cp-Cp bonds in the P-substituted direction can also be stretched due to the strong election-withdrawing and/or steric effect of the P-substituents. The structure analysis also revealed slightly distorted macrocycles of Zn(TPPBr 4) (45b) and Zn(TPP(CH 3) 4) (59b) and very distorted macrocycle of Zn(TPP(CF 3) 4) (48b). These observations support the results obtained in UV-visible spectroscopy and electrochemistry. Electron-deficiency is reflected on the shortening of Z n - O distances in 45b-(MeOH) and 48b-(EtOH). A n interesting result to be noted R=Br, C H 3 L = M e O H , T H F 172 is that axial ethanol as well as one of the two solvated ethanols are found in a pocket created by -C F 3 groups and the macrocycle distortion. This could be due to the high affinity of - C F 3 moieties to the hydrocarbon moieties for ethanol and may be an advantageous property for hydrocarbon oxidation using the Fe(III) complex of this porphyrin as a catalyst. 5. Spectrophotometric titration In Chapter II, section B.3., the electron-deficiency of fi-tnQuoiomethyl-meso-tetraphenylporphyrins was evaluated by the analysis of redox potentials measured by cyclic voltammetry. In section B.Za. describing N M R spectroscopy experiments of (3-tos(trifluoromethyl)porphyrin H 2 TPP(CF 3 ) 3 (47a), it was shown that exchange of N H protons of the porphyrins with the proton of residual water easily occurs. This phenomenon may be related to the lower pK, value for the first deprotonation of the free-base porphyrin compared to non-electron-deficient porphyrins such as H 2 T P P (2a) (Figure 1-8, p.ll) . Given this, it became essential to estimate the piC, of P-trifluoromethylporphyrins. In the first part of this section, spectrophotometric titrations of the free-base of p-tetrakis (trifluoromethyl) -meso-tetraphenylporphyrin (H 2 TPP(CF 3 ) 4 (48a)  with D B U and E t 3 N in CH 2 C1 2 are shown. In the second part, spectrophotometric titrations of Co(TPP(CF 3) 4) (48e) with pyridine (Py) and imidazole (lm) are shown. There are a few reports of determination of Py and lm binding constants of Co(II) porphyrins. 177-180 These include some electron-deficient porphyrins. Comparison of the binding constants with other electron-deficient porphyrin systems was allowed by analysis of the titrations using 48e. Thus, this section provides additional information regarding the electron-deficiency of P-tetralds^fluoromethy^-OTWO-tettaphenylporphyrin. 173 a. Titration of 48a with strong organic bases in CH2C/2 (1) Titration with DBU Figure 2-35 shows the results of the spectrophotometric titration of 48a with D B U in CH 2 C1 2 . Figure 2-35(a) shows an isosbestic spectral change for the first deprotonation. The arrows indicate the direction of the change of the absorption peaks. The color of the solution changed from golden-yellow for the free-base to weak orange for the first deprotonated species. This colorimetric change stopped at [DBU] = 4.5 x 10"2M. After the first deprotonation, the second deprotonation was attempted using neat D B U (Figure 2-35 (b)). The further colormetric change was observed, but the spectral change did not stop for the second end point. Assuming that the spectrum at [DBU] = 4.5 - 5.4 x 10 2 M is that of the porphyrin monoanion, the pK difference between H 2 P (P stands for porphyrin dianion) and DBUH +(protonated DBU) was determined (see Experimental section in Chapter TV). The results were analyzed based on the absorbance change at 463 and 513 nm (s™' =9.34 x 104, s™~ =3.22x 104, S ^ J =8.78 x 103, and e M 3 =3.72 x 10 4M "'xm"') ). The logarithmic analysis of the first colorimetric change gave a straight line with a slope of 1.1 and the intercept of 2.9 as the pK value for the reaction, H 2 P + D B U <^ H F + D B U H + (Figure 2-36). The pXis indeed the difference between the pK\.nv (pK, of H 2 TPP(CF 3 ) 4 ) and p K D B U (pK, of DBU) (see Chapter IV, Section C, Spectrophotometric titrations.); pK = ApiC, = p.KH 2p - p X D B U . The pK^ of D B U in M e C N was determined as 24223,224 a n d ^ in H 2 0 was estimated as 1 4 . 2 2 3 Unfortunately, the pK, of D B U in CH 2 C1 2 is not known. Thus, we can only compare the acidity of porphyrins by using D B U as an anchor. Woller and DiMagno determined the pi<Q difference (ApiCj between electron-deficient porphyrins H 2 T P P F 8 (12a), H 2 T P F P P F 8 (13a) (Figure 1-8, p.l l) and D B U in CH 2 C1 2 by the same method and found that the N H in 12a and 13a were less acidic than protonated D B U by 3.9 and 300 400 500 600 700 800 900 1000 Wavelength (nm) Figure 2-35. UV-visible spectral change in titration of H 2 T P P ( C F 3 ) 4 (48a) with D B U in CH 2 C1 2 . [48a] = 1.24 x 10"5 M . (a) The first deprotonation at [DBU] = 0 - 5.4 x 10 _ 2 M. N o spectral change between 4.5 x 10"2 and 5.4 x 10"2 M . (b) The spectral change at [DBU] = 5.4 x 10"2 ~ 1.5 M . 1 Log([H2P]/[HP-]) = 1.1 x log ( p B U H + ] / [ D B U ] ) + 2.9 -2 H 1 1 : 1 -4 -3 -2 -1 log [H2P]/[HP-] Figure 2-36. Logarithmic analysis of the spectral data for the addition of D B U to H 2 T P P ( C F 3 ) 4 (48a) in CH 2 C1 2 . pK = pKH2V-pKmv; pKmv and pKDm are pKa of 48a and D B U H + , respectively. 176 0.2 units respectively and 12a was at least 1000 times more acidic than H 2 T P P (2a) (pK, for 2a > 19).36 The ApK, of 2.9 for 48a proves that this porphyrin is indeed an electron-deficient porphyrin. (2) Titration with Et3N A similar titration was performed on 48a in CH 2 C1 2 with taethylamine. Figure 2-37 shows the UV-visible spectral change for the titration. The spectral change occurred isobestically but in a different way from the titration with D B U . No further spectral change occurred after [taethylamine] == 1.43 x 10 1 M . The final spectrum has only one broad band at 420 nm (s = 7.45 x 104 M _ 1 cm _ 1). The color of the final compound was orange. This orange color slowly fades away in CH 2 C1 2 solution at room temperature. When 6 x l O ^ M of H 2 TPP(CF 3 ) 4 was treated with 0.29 M of taethylamine in CH 2 C1 2 , the initial peak intensity at 420 nm of the orange compound dropped to 40% in a few days at room temperature and no other new peaks were observed. The UV-visible spectrum of the orange compound was the same as that in Figure 2-4; the porphyrin is presumably reduced by E t 3 N . b. Titration of Co(TPP(CF})4) (48e) with pyridine and imidazole Binding constants for pyridine (Py) and imidazole (Im) coordination to Co(TPP(CF 3) 4) (48e) were also measured in CH 2 C1 2 by spectrophotometric titration. The UV-visible spectra given in Figure 2-38 show the change for the first step of pyridine addition to 48e. The spectral change showed six isobestic points and is very similar to the change for the first pyridine coordination to Co(TPP(CN) 4) in C H 2 C 1 2 . ^ 9 The second coordination was very slow and thus titration was not possible, though spectral changes occurred with isobestic points. This result is shown in Figure 2-39. When 40,000 eq. of pyridine was 0.7 350 450 550 650 750 850 950 Wavelength (nm) Figure 2-37. UV-visible spectral change in titration of H2TPP(CF3)4(8a) with E t 3 N in CH2C12. [48a] = 5.74 g 10 "6 M . [Et 3N] = 0 - 4.30 x 10 4 M . 178 0.0 H 1 1 1 1 350 400 450 500 550 Wavelength (nm) Figure 2-38. Ti trat ion o f C o C T P P ( C F 3 ) 4 ) (48e)(8.60 x 10 ~6 M ) i n C H 2 C l 2 w i t h pyridine at 25.0 °C: spectral change at (a) 350 - 850 n m and (b) the Soret band region during the transition between 4- and 5-coordinate cobalt, [Py] =0 - 2.76 x 10 " 3 M . 350 450 550 650 750 850 Wavelength (nm) Figure 2-39. Spectral changes in the pyridine addition to Co(TPP(CF 3) 4)- (Py) (48e- (Py)) (8.60 x 10 "6 M) in C H 2 C 1 2 at 25.0 °C. [Py] = 2.76 x 10 "3 - 3.40 x 10 4 180 added to the Co (II) porphyrin, a slow change of the spectrum with time was noticeable. It took about 15 days at 25 °C for the reaction to reach the equilibrium. Similarly, a slow second ligand addition reaction was observed using imidazole at 25 °C. For Co(TPP(CN) 4), CofTPPFg), and Co(TPFPPF 8) such a slow reaction for the second ligand addition was not reported and the binding constants (X, and K^) were given.179,180 -p^e reason for the slow reaction might be the sterically very crowded porphyrin peripheral of Co(TPP(CF 3) 4) (48e). It was shown in the analysis of the crystal structure of Zn(TPP(CF 3) 4) (48b) that macrocycle distortion occurs due to the interaction between the phenyl rings and - C F 3 groups. Coordination of first Py (or lm) to four coordinate 48e may result in a similar structure that was observed for Zn(TPP(CF 3) 4)-(EtOH) 3 (48b-(EtOH)3) (Figure 2-30-48b) with Co(II) deviated from the N 4 plane. As discussed in section B.4., the severely saddle-distorted macrocycle of 48b-(EtOH) is a necessary structure to minimize the interaction between the phenyl and — C F 3 groups. The second axial coordination to the five-coordinate Co(II) complex would have to by necessity move the Co(II) into the centroid of the four pyrrolic nitrogens. The two axial nitrogens and the change from the five-coordinate to the six-coordinate complex may also require rearrangement of the peripheral substituents. Since the steric interaction among the peripheral substituents is severe in the P-tetraltis(trifluoromethyl)-wwo-tetiaphenylporphyrin ligand (chapter II, section B.4.), fast change from the five- to six-coordinate complex may be encumbered. The reason that the logJ<C2 for Co(T((?-OCH3)PP) (43) 1^ 8 w a s n o t g i v e n may be a too weak binding of the second ligand. Thus in order to observe binding of the second ligand, an electron-deficient and planar macrocycle ligand is necessary. I 181 Figure 2-40. Logarithmic analysis of the spectral data for the addition of pyridine to Co(TPP(CF3)4)(48e) in CH 2 C1 2 . The pyridine addition step was monitored at 440 nm. A 0 , A, and Ay are absorbances without pyridine, at each titration point, and at the final point, respectively. 182 Logarithmic analysis (Hill's plot) 2 2- 5 of the spectrophotometric data for the first pyridine addition is shown in Figure 2-40. The analysis gave a binding constant of log iC, = 4.2. A similar experiment with imidazole gave log iC, = 7.5. These results are listed in Table 2-15 with reported Table 2-15. Binding constants of Co(II) porphyrins for base binding in in CH^CLj. Porphyrin Base log Kx log K2 Reference Co(rPP(CF 3) 4) (48e) Py 4.2 - a Im 7.5 - a CoCl>-OCH 3)PP) (43) Py 2.68 - 158 Im 3.15 - 158 1-Melmb 3.37 - 158 Co(TPP(CN) 4) (34c) Py 4.2 -0.35 179 CofTPPFg) (12h) Py 4.3 -0.08 180 Co(TPFPPF 8) (14h) Py 5.9 1.03 180 1-Melmb 6.8 1.76 180 a This work. b 1-Memylimidazole. values of other Co(II) porphyrins. Porphyrin 48e has a similar binding constant for the first binding of Py to those of 34c and 12h (see p.62 for the structures) and the value for 48e is larger than that of 43. Thus, the result proves the electron-deficiency of the P-tetrakis(trifluoromethyl)-OTWO-tetraphenylporphyrin ligand. The increment from the log for Py to that for Im of 48e, 43, and 14h correlates with basicity of the ligands (pJQ values; Py: 5.22, Im: 6.65, and l-Melm: 7.06)158 hut the increase for 48e seems to be large compared to those for 43 and 14h. A rationale for this phenomenon is that the smaller axial base (Im) is preferable for binding to sterically hindered 48e. 6. Summary P-Trifluoromethylporphyrins H 2 TPP(CF 3 ) 3 (47a), H 2 TPP(CF 3 ) 4 (48a), H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a) showed bacteriocHorin-like UV-visible spectra that suggest fixed 187t-electron pathways of these porphyrins (section B./.). The J H N M R experiments using 47a 183 suggested that the porphyrin preferably takes the fixed 187t-electron pathway (section B.2). The analysis of the H O M O - L U M O gaps of P-ttifluoromethylporphyrins obtained by cyclic voltammetry also suggested that the tautomerism of the two electronic pathways of /^jtf-tettaphenylporphyrin is shifted into one, like that of bacteriochlorin, due to the strong electron-withdrawing effect of the —CF 3 groups (section B.J). The steric effect of the —CF 3 groups was shown by the analysis of an X-ray crystal structure of Zn(TPP(CF 3) 4) (48b) (section B.4). The estimated van der Waals radius of - C F 3 from the crystallographic data is 2.7 A and the steric interaction between the meso phenyl groups and the bulky —CF 3 groups seems to be the driving force of a severe saddle distortion of the macrocycle. The steric effect of the —CF 3 groups in the P-tetealris(tofluoromediyl)porphyrin ligand possibly correlates with the large red-shifts and broadening of the UV-visible absorption bands, the unusual ' H N M R chemical shift for the pyrrolic P-protons, the non-linear increase of the first oxidation potentials, and the slow base binding to the Co(II) complex. Comparison of the reduction potentials, the pKa value for the first deprotonation of the N H protons, and the binding constant of Py and lm to Co(TPP(CF 3) 4) (48e) with those of other electron-deficient porphyrin systems proved that the P-tettalds(tjifluoromethyl)porphyrin ligand is electron-deficient. The Fe(II/III) reduction potentials of Fe(TPP(CF 3) 4)Cl (481) and Fe(TPP(CF 3 ) 3 (CF 2 CF 3 )Cl (52c) were tuned in the ideal range for an oxidation catalyst; between those of the second and the third generation porphyrin catalysts such as Fe(TPFPP)Cl (4d) and Fe(TPFPPBr 8)Cl (8d). Thus, the catalytic activities of 48f and 52c were investigated in order to assess the usefulness of these complexes as oxidation catalysts. 184 C. Catalytic oxidation of cyclohexane and cyclohexene As reviewed in the first chapter, some electron-deficiency is necessary to improve the catalytic activity and the robustness of metalloporphyrins. In order to investigate the usefulness of the Fe(III) complexes of P-oifluoromethyl-OTMo-tetj:aphenylporphyrins Fe(TPP(CF 3) 4)Cl (481) and Fe(TPP(CF3)3(CF 2CF 3)Cl (52c) as oxidation catalysts, hydroxylation of cyclohexane and epoxidation of cyclohexene in CH 2 C1 2 was examined. As discussed briefly in Chapter I, section A . Z d , detailed reaction conditions for catalytic oxidation in the studies of porphyrin catalysts are diverse. Although we have to keep this point in mind, the performance of 48f and 52c was compared with that of one of the best porphyrin catalysts F e ^ D C P P C k j C l (10d)226 (third generation porphyrin catalyst) under the same reaction conditions. In a catalytic oxidation of cyclohexane, to a CH 2 C1 2 solution containing 1 eq. of the porphyrin catalyst and 5,000 eq. of cyclohexane, 200 eq. of PhIO were added during the first 1 h. The reaction was performed in a vial at 24 °C for 4 h. The solutions of 48f and 52c are green but both solutions turned orange instantiy when the first 50 eq. of PhIO was added and the orange color gradually faded away during the reaction. The solution of 45e was greenish yellow at the beginning of the reaction and it was bleached gradually too. The solution containing lOd was green and the color was almost maintained during the reaction. After the reaction, the liquid phase of the reaction mixture was analyzed by gas chromatography. The results are summarized in Table 2-16. Since the amount of substrate used is a large excess, normally the yield of the product is given based on consumed oxidant; (peak area of cyclohexanoi)/(peak area of Phi) x 100 is reported in Table 2-16. 185 Table 2-16. Oxidation of cyclohexane and cyclohexene using Fe(III) porphyrins and iodosylbenzene in C H 2 C l 2 . a . cyclohexanol cyclohexene oxide y S t Yield (%)b turnover1 Yield (%)b turnover' Fe(TPP(CF 3) 4)Cl (481) 7 5 62 77 Fe(TPP(CF 3) 3(CF 2CF 3))Cl (52c) 9 6 61 61 Fe(TPPBr 4)Cl (45e) 5 4 68 82 Fe(TDCPPCl 8 )Cl (lOd) 44 86 89 109 a Reaction conditions: CH2C12 = 500 pL, catalyst = 1x10^ mmol, cyclohexane = 5 x 10 _ 1 mmol, cyclohexene = 1 mmol, PhIO = 2 x 10 ~2 mmol. For hydroxylation; temp. = 24 °C, t = 4 h. For epoxidation; temp. = 30 °C, t = 2 h. b Based on PhIO consumed . c Product (mmol)/catalyst (mmol). Although we cannot direcdy compare these data with the literature values such as those shown in Chapter I, there was a clear difference between the yields with p-trifluoromethylporphyrins Fe(TPP(CF 3) 4)Cl (48f) and Fe(TPP(CF 3) 3(CF 2CF 3))Cl (52c) and the third generation catalyst, Fe(TDCPPCl 8 )Cl (lOd). Fe(III) porphyrins 48f and 52c are not good oxidation catalysts at least under these conditions. The Fe(III) complex 45e was also found to be ineffective for hydroxylation of cyclohexane. Bleaching of the solutions containing 45e, 48f, and 52c implies that these porphyrins may be decomposing during the reaction. Epoxidation of cyclohexene was performed under the same conditions except for the amount of the substrate. The yields of the epoxide from cyclohexene were much higher than those for hydroxylation but the result shows that catalysts 48f and 52c are not as effective as P-halogenated porphyrins. The solutions of 48f and 52c were not completely bleached during the reactions but the color of the porphyrins faded away gradually. Since a supply of 48f and 52c was not enough, thorough examination of hydroxylation and epoxidation could not be performed. However, the preliminary tests regarding catalytic oxidation 186 showed the instability and the ineffectiveness of 48f and 52c compared to one of the best porphyrin catalysts lOd. Potential reasons for these results are: The first oxidation potentials (ring oxidation) of 48f and 52c are about the same as that of Fe(TPP)Cl (2d) (see Table 2-12). Oxidation of 48f and 52c is as easy as that of 2d. The macrocycles are destabilized by severe distortion caused by the steric or the electronic interaction between the peripheral substituents. Thus, the electron-withdrawing effect of - C F 3 groups does not contribute to improve robustness of the macrocycle. Although Fe(III) porphyrins 48f and 52c have four bulky perfluoroalkyl groups but there are still (3-hydrogens and twenty phenyl-hydrogens. Thus, more protection of the macrocycle may be required for robustness. As observed in the crystal structure of ZnTPP (CF 3) 4 (48b), meso-xphenyl rings are extremely tilted by the steric or the electronic interactions with - C F 3 groups. This may facilitate the formation of the p,-oxo dimer. In fact, the u-oxo dimer (61) is easily formed from 48f (Scheme 2-8, p.93). Ligands 48 and 52 presumably take a bacteriochlorin-type electronic structure. The macrocycles should be redox sensitive due to the small H O M O - L U M O gap; the low first oxidation and the high first reduction potentials. Thus, this may trigger a decomposition of the macrocycles. As discussed in this Chapter, P-tafluoromethylporphyrins are electron-deficient and introduction of the - C F 3 groups on the pyrrolic P-positions of antipodal pyrroles leads to the 187 unusual electronic properties and the structure of the macrocycle. However, this seems to be not advantageous for an activity as oxidation catalysts. 188 C H A P T E R III Conclusions and Future Work A . Conclusions In these studies towards the synthesis of novel electron-deficient porphyrins, based on the structure of ^jo-tetraphenylporphyrin, - C F 3 groups were introduced onto the pyrrolic P-positions of the macrocycle using P-bromo-^wo-tetraphenylporphyrins and the agent in-situ generated C F 3 C u . Trifluoromethylation at the pyrrolic P-position of ^.ro-tettaphenylporphyrin was difficult due to the steric bulkiness of the —CF 3 group. Therefore, the maximum number of —CF 3 groups added to the porphyrin was four. Partially introduced —CF 3 groups at the antipodal pyrrolic P-positions not only made the macrocycle electron-deficient but also directed the 187t-electron pathway of the porphyrin macrocycle to take one similar to that of bacteriochlorin. The unique electronic structure of the P-tofluoromethylporphyrins resulted in red-shifted bacteriochlorin-like UV-visible spectra. The unique electronic pathway in the novel porphyrins was proved by the locked positions of N - H protons determined by ' H N M R spectroscopy. The analysis of the redox potentials of P-tofluoromethylporphyrins showed a progressive decrease of the H O M O - L U M O gap along with the antipodal trifluoromethylation. This was also an indication of the bacteriochlorin-like distorted 187t-electronic pathway. Redox potentials also enabled approximate comparison of the electron-deficiency of P-trifluoromethylporphyrins with other electron-deficient porphyrin systems. However, the comparison has to be done carefully because in the conclusion of this work, the electronic structure of the novel p-teifluoromethylporphyrins is different and thereby 189 the redox potentials may change. The electron-deficiency of p-tettalds(mfluoromethyl)porphyrin was evaluated to be the same as the reported electron-deficient porphyrins such as P-octafluoro-/wwo-tettaphenylporphyrtn (TPPFg) or P-teteacycano-/W£ro-teteaphenylporphyrin (TPP(CN)4) by the determination of the pXa and the axial base binding constants to Co(II) porphyrin. The - C F 3 groups on the pyrrolic P-positions also exhibited a large impact on the structure of the macrocycle as a result of steric interactions between - C F 3 and - C F 3 groups and between - C F 3 and phenyl groups. The macrocycle of P-tetrakis (trifluoromethyl) -meso-tetraphenylporphyrin is distorted into a saddle shape. The van der Waals radius of the - C F 3 group obtained from HyperChem and the X-ray crystal analysis is 2.7 —2.8 A, which is large enough for steric interaction between the substituents to lead to such macrocycle distortion. Fe(III) complexes of P-trifluoromethylporphyrins showed a well-tuned Fe(III/Il) redox couple which was comparable to those of good porphyrin catalysts such as the second and the third generation porphyrin catalysts. However, it was found that Fe(III) complexes of P-tofluoromethylporphyrins were not superior catalysts to the third generation porphyrin catalyst Fe(TDCPPCl 8 )Cl in oxidation of cyclohexane and cyclohexene. Stability of the catalysts seems to be the problem. The unique electronic structure of the P-trifluoromethylporphyrins could be disadvantageous for a stable macrocycle system. B. Future work Studies of redox properties of the macrocycle in a series of porphyrins bearing strong electron-withdrawing groups such as —CN or —NO z have been reported37>161 but the detailed electronic structures and spectroscopic properties have not been reported in the literature. 190 Although redox properties of some series of P-brominated zwo-tettaphenylporphyrins have been extensively studied by Kadish et « / ,162-164 a unique electronic structure of the macrocycle like the system observed in this work has not emerged in the series of brominated porphyrins probably because the —Br group is mildly electron-withdrawing. One way to continue these investigations regarding the electronic structures of the macrocycle may be to extend the series of P-trifluoromethyl-^j'o-tetophenylporphyrins. This would allow us to see the change in spectroscopic and electrochemical data through which we could determine the electronic structure ofthe macrocycle. However, the synthesis of highly P-trifluoromethylated porphyrins is challenging and may not be productive because P-pyrrolic positions are not suitable for smooth introduction of —CF 3 groups. In addition, separation becomes more difficult as the number of perfluoroalkyl moieties increases. Thus, the details of effects of extremely strong electron-withdrawing substituents on the electronic structure of the macrocycle may be investigated by P-cyano or p-nitroporphyrins. P-Nitration of a ^wo-tetraarylporphyrin is fully controllable by the method recently devised by Palacio et affl and allows access to P-mono- to P-octanitroporphyrins. Although trifluoromethylation on the pyrrolic P-position of the macrocycle is difficult, a different porphyrin system may be synthesized to achieve high-performance porphyrin catalysts. A potential porphyrin candidate is shown in Scheme 3-1. The first measure Groves et al. took to achieve some improvement from Fe(TPP)Cl (Figure 1 -8) was to introduce the steric bulk on the periphery of the macrocycle and Fe(TMP)Cl (Figure 1-8) appeared.98 This porphyrin, (Fe(TMP)Cl), is not likely to be a good catalyst for oxidations. The meso- and pyrrolic 191 P-positions are protected by the bulky mesityl groups but methyl groups in the mesityl groups are exposed to the exterior. These are problematic for robustness of the catalyst. If a metal complex of w<?.ro-tetealds(2,6-dibromophenyl)porphyrin (65) and C F 3 C u are used, T M P -analogous OT^o-tettakis(2,6-bis(tofluorometiiyl)phenyl)porphyrin (66)(Scheme 3-1 (a)) may be obtained. The synthesis of 66a was attempted by Lindsey et al. by condensation of pyrrole and 2,6-bis(tofluoromediyl)benzaldehyde67 but was unsuccessful, presumably due to the steric hindrance of the two —CF 3 groups on the benzaldehyde, preventing cyclization with pyrrole. In the porphyrin, the o^o-positions of the meso-phenyl groups are not hindered and thus introduction of the —CF 3 groups there may not be as difficult as that of the pyrrolic p-positions. A geometry optimized molecular structure of 66a by HyperChem (Scheme 3-1 (a) and (b)) shows a planar macrocycle and four orthogonal meso-aryl groups to the macrocycle. The —CF 3 groups are more stable and bulkier than the —CH 3 groups (Chapter I, section B.J.b). Thus, it is expected that the —CF 3 groups may protect the macrocycle effectively. The distance from the macrocycle to the edge of the ortho-CP ^  groups (Scheme 3-1 (c)) is approximately 5 A. This distance also suggests that formation of the p-oxo dimer would be unlikely. Finally the meso-2,6-bis(trifluoromethyl)phenyl groups are electron-withdrawing and they can keep the macrocycle electron-deficient. One problem for this future work may lie in the synthesis of porphyrin 65, which is a known compound synthesized by condensation of pyrrole and 2,6-dibromobenzaldehyde.67 However, 2,6-dibromobenzaldehyde is not manufactured right now. Thus, we need to synthesize 2,6-dibromobenzaldehyde in order to obtain porphyrin 65. Attempts towards the synthesis of P-octolds(ttifluoromethyl)-^j"o-arylporphyrins may not be an appropriate direction for improvement of the catalytic activity of porphyrin catalysts. The Scheme 3-1. wwo-Tettakis(2,6-bis(rjifluoromemyl)phenyl)porphyrin (66). (a) A possible synthetic route for 66. (b) A computer model o f 66a. (c) A side view o f the computer m o d e l . 1 8 9 193 eight —CF 3 groups on the pyrrolic p-positions promise a high electron-deficiency of the macrocycle, but too much electronegativity may lead to stable Mn(II) or Fe(II) porphyrins, which are inactive as monooxygenase systems, as shown by Grinstaff ^«/ . (Fe(II ) (TPFPPBr 8 ) ) 1 07 a n c j BartoH eral ( M n ^ t T D C P P f N O ^ ) . 4 7 Therefore, super electron-deficiency is not an ultimate solution for a perfect cyctochrome P-450 mimic. The ultimate goal for P-450 model compounds may be to let metalloporphyrins utilize molecular 0 2 (or air) as a source of oxidant to form the oxo Fe(IV) porphyrin 7t-cation radical, the key intermediate in the P-450 catalytic cycle. 2^ 4^ As reviewed in Chapter I, two electrons and two protons are required in order to form the intermediate from Fe(III) porphyrin and 0 2 and to reduce one of the oxygen atoms of 0 2 to water. Thus, mimicking the P-450 cycle with only 0 2 and synthetic Fe(III) seems very difficult. However, the oxo Fe(TV) porphyrin 7i-cation radical can be also formed via the shunt path (see Figure 1-5) using an oxygen atom transfer reagent. Although there are variety of " O " transfer reagents such as NaOCl , PhIO, peroxides, and peroxy acids, the use of these reagents generates by-products (NaCl, Phi, etc.). A n exception is hydrogen peroxide. Although hydrogen peroxide is more costiy than molecular 0 2 , it is a competitive source of oxygen atoms with molecular 0 2 . since it is a clean and environmentally friendly oxidant. 2 2 7 A n ideal reaction of Fe(III) porphyrin and hydrogen peroxide for catalytic oxidations is shown in Scheme 3-2(a) (Path A), where heterolytic O - O bond cleavage of Fe(III)-0-0-H occurs to form the oxo Fe(IV) porphyrin 7T-cation radical. For this type of cleavage, polarization of the O - O bond is necessary.53 As shown in Scheme 3-2(b), the - C F 3 groups on the ortho-positions of the meso-aryl groups might help polarization of the O - O bond 194 via the hydrogen bonding. Formation of p-peroxoclimer (Scheme 3-2(a), Path B) should be ruled out due to the bulky —CF 3 groups. The ortho-CP\ groups might play the following important roles in catalytic oxidations; (1) protection of the macrocycle by their steric and electron-withdrawing effects, (2) formation oxo Fe(TV) porphyrin Tt-cation radical by the use of H 2 O z via an intramolecular interaction, and (3)activation of the active intermediate by electron-withdrawing effects. Therefore, investigation of metal (such as Fe(III) or Mn(III)) complexes of porphyrin 66 may provide new insights for the development of cyctochrome P-450 model compounds. X M + H (a) Fe(lll) H,0 2^2 Fe(lll) Path B porphyrin dianion x = anion (Cl", OH", etc.) PFe(lll): PFe(lll) Path .4 •H,0 2x O Fe(IV) O Fe(IV) (b) -FUO \ _ Scheme 3-2. Formation of oxo Fe(IV) porphyrin 7t-cation radical from Fe(III) porphyrin and hydrogen peroxide, (a) Reaction pathways, (b) Mode of activation of the O - O bond. 195 C H A P T E R IV E x p e r i m e n t a l A . Chemicals All chemicals for synthesis were purchased from Sigma-Aldrich fine chemicals, Across Chemicals, or Fisher Scientific. If necessary, chemicals were purified by published procedures.2 2^ Deuterated solvents for N M R measurements were purchased from Cambridge Isotope Laboratories or Aldrich. Chlorinated solvents were filtered using N-alurnina (activity I) to remove trace acid (HC1 or DC1). Column chromatography was performed using 70 - 230 or 230 - 400 mesh silica gel (Merck). Analytical thin-layer chromatography was performed using pre-coated silica gel aluminum plates which contains a fluorescent indicator (GF 254 Merck). B . Instrumentation UV-visible spectra were recorded on a Varian Cary 50 scan UV-visible spectrophotometer or a Hewlett-Packard 8452A diode array spectrophotometer. N M R spectra were recorded on Bruker AC-200, WH-400, or Avance 300 spectrometers. Cyclic voltammetry measurements were performed on a Pine Instrument Company bipotentiostat model AFCBP1 and Pine Chem Sweep Voltammetry software for Windows v. 2.00. The cyclic voltammetric experiments were performed using an electrochemical cell as shown in Figure 4 -1 . 2 2 9 X-ray crystallographic data were collected on a Rigaku/ADSC C C D . A Hewlett-Packard G C HP-17 was used to detect oxidation products. This G C utilizes a phenyl methyl silicone (50 % crosslinked, 25 m x 0.32 mm x 0.26 um (length x tubing inner diameter x film thickness)) capillary column, and a flame ionization detector, and helium was used as a carrier gas. 9 0 ° Figure 4-1. Electrochemical cell and electrodes (a. Pt working electrode, b. A g reference electrode, c. Pt counter electrode). 197 C. Procedures Cyclic voltammetry. CH 2 C1 2 and P h C N were distilled and degassed by three cycles of the freeze-pump-thaw method and dried over activated molecular sieves 4A. A sample solution for a measurement was prepared by the following procedure. Ar was introduced from gas inlet E (see Figure 4-1 for designations A - E and a - c). The electrochemical cell was dried using a heat gun. Electrodes a, b, C were also dried using a heat gun and placed in A, B, C of the cell, respectively, so that the electrodes did not contact each other and were then cooled under a slow Ar stream. For a typical measurement, porphyrin typically (0.015 - 0.03 mmol), and T B A P F 6 (0.3 mmol) were weighed and transferred to the cell through D. Dry solvent (3 mL) was then introduced into the cell through D. The solution was bubbled with Ar for a few minutes, and then D was closed with a glass stopper. The connections at A, B, C, and D were secured with parafilm. A n Ar balloon was put on E and the stopcock was then opened. Porphyrin was dissolved completely using a sonicator. The cell was connected to the potentiostat and voltammograms were recorded without stirring the solution. In order to standardize the potentials, ferrocene (0.005 mmol) was added to the solution from D. Voltammograms were recorded again under the same conditions. Addition of ferrocene did not affect the redox potentials of porphyrins. Spectrophotometric titrations. (Titration of H2TPP(CF3)4 (48a) with DBU and Et^SS). Titrations were performed by the following procedure. The concentration of 48a was set to 9.66 x 10 - 3 m M while varying the concentration of D B U within the range of 0-2.1 x 10 2 M . The color change was noted immediately upon addition of D B U to the solution containing the porphyrin. Solutions were made up in H P L C grade CH 2 C1 2 and the UV-visible spectrum of each batch was recorded. The same procedure was followed for the spectrophotometric titration using E t 3 N . 198 The pKa for the first deprotonation of H 2 TPP(CF 3 ) 4 (48a) was determined by the following analysis. According to the Lambert-Beer law,2^0 m e following equations, (4.1) and (4.2) can be written with the assumption that only the porphyrin species contributes to the absorbance at the -^463 — £463'Q-I2P-^~'~ ^463'CHP-'^ (4-1) -A-513 — £5lVQ-I2P'^~'~ ( 4 - 2 ) selected wavelengths, where A 4 6 3 and A 5 1 3 are the total absorbances, s ^ 3 , S ™ 3 , s " 2 3 , and S™~are the extinction coefficients of the free-base porphyrin (H 2P; P2~ = dianion of 48a) and the porphyrin mono anion (HP -), C H 2 P and C,.n,- are the concentrations of H 2 P and HP" at 463 and 513 nm, respectively, and / is the cell path length, 1 cm. Given the molar extinction coefficients and absorbances, the concentrations of the free-base and the mono anion are determined by the following equations (4.3) and (4.4). HP- * HP- A &463 -"513 &513 -"-463 p r j -|-yi J J I J J 1J t u j /A |H21 J - H 2 p H p _ H 2 p H p . ( 4 . 3 ) FC513 FC463 FC463 FC513 E H 2 P A - E H 2 P A Vnl J P H 2 P P H P - o H 2 P p H P " V*' V ^463 B513 ""B513 B463 Also, the relationships between concentrations of protonated D B U ( D B U H + ) , H P , initial D B U , and D B U at each titration point are written as (4.5) and (4.6). P B U H + ] = [HP"! (4.5) P B U ] = p B U ] 0 - p B U H + ] (4.6) 199 The equilibrium constants KH2P and i<CDBU for deprotonation of H 2 P and D B U H + are written as (4.7) and (4.8). H 2 P ^ H P + H + KH2P = ] (4.7) D B U H + - D B U + H + KDBU = p B U P T ] 1 (4-8) The equilibrium constant for the H 2 P - D B U reaction can be rearranged as (4.9). H 2 P + D B U ^ H P ' + D B U H + K = ^ ^ B U ] 1 ^ = W * D B U (4-9') Logarithm of both sides of (4.9) gives: |H,P1 P B U H + ] ^ S = P I C + L O G W (4-9) Analysis of titration data using (4.3) - (4.6) and (4.9") should give a straight line with the slope of 1 and the intercept of pK. PK=pKH2P-pKDm=ApKt (4.10) (Spectrophotometric titration of 48e with pyridine and imidazole). CH 2 C1 2 and pyridine were distilled and degassed by three freeze-pump-thaw cycles, and dried over activated molecular sieves (4A). 200 A CH 2 C1 2 solution of Co(rPP(CF3)4) (48e) (8.60 x 10"3 mM) in a 1 cm path length cuvette was titrated with a pyridine solution (0 - 3.4 x 10 - 1 M) prepared in CH 2 C1 2 . Titration was performed in a N 2 glove bag. After each injection of the titer, the cuvette was tighdy capped with a Teflon top to take out to UV-visible spectral measurements. In order to make sure that the reaction reached equikbrium, the UV-visible spectrum was monitored for 20 min after each titration. For higher concentrations of pyridine, neat pyridine was used. The concentrations of the species in the cuvette were corrected with the volume of the added titer. The same procedure was followed for the titration using imidazole. For higher concentrations of imidazole, solid was direcdy added to the cuvette. The binding constant was determined according to the following analysis.22^ The binding constant is written as (4.11). K [CoPB] CoP + B ^ C o P B , K - ^ p j . p j j (4.11) CoP: four-coordinate Co(TPP(CF3)4) (48e), B: pyridine or imidazole, CoPB: five-coordinate Co(II) porphyrin pyridine complex. The mass balance regarding Co complexes is written as (4.12). [CoP] + [CoPB] = [CoP]0 (4.12) [CoP], [CoPB], and [CoP]o: concentrations of CoP and CoPB during the titration and the initial concentration of CoP, respectively. From (4.11) and (4.12), (4.13) is obtained. [CoP]0 K P ] + 1 = [ C o P ] ( 4- 1 3) According to the Lambert-Beer law, 201 A 0 = e [CoP] 0 , /= lcm (4.14) A F = s'[CoPB] f = £'[CoP]0 (4.15) A = s [CoP] + e'[CoP-B] (4.16) Ao, Af, and A: the absorbances initially and finally, and during the titration, respectively, at the monitored wavelength. 8 and £': the extinction coefficients of CoP and CoPB at the wavelength. [CoPBJf: the final concentration of CoPB. From (4.14), (4.15), and (4.16), (4.17) is obtained. [CoP] A - A f ^ A / ) Substitution of (4.13) into (4.17), rearranging and taking the log of the resultant equation gives (4.18). L 0 G ( A ^ ) = 1 ° 8 ^ + L 0 G [ B ] ( 4 - 1 8 ) The concentration of B is obtained from (4.19). [B] = [B] tot - [CoPB] = [B] tot - ([CoP]0 - [CoP]) = [B] to t - [ C o P ] 0 - ^ (4.19) [B]tot: the total concentration of the base. VA' Thus, the plot of log [B] vs. log ^ ^ J should give a straight line with the slope equal to 1. The y intercept is the log K value. 202 Gas chromatography. For the analysis of cyclohexane oxidation, a typical temperature program was 40 °C (3 min) -» 20 ° C / m i n -» 220 °C (10 min). Injection temp, and FID temp.: 220 °C. Retention times for CH 2 C1 2 , cyclohexane, cyclohexanol, and iodobenzene were 1.02, 1.23, 5.36, and 7.40 min, respectively. For the analysis of cyclohexene oxidation, the program was 25 °C (3 min) — 20 ° C / m i n — 220 °C(10min). Injection temp.: 180 °C. FID temp.: 220 °C. Retention times for CH 2 C1 2 , cyclohexene, cyclohexene oxide, and iodobenzene were 1.25, 1.80, 6.48, and 7.48 min, respectively. D. Preparation of materials 5,10,15,20-Tetraphenylporphyrin (H2TPP) (2a). The porphyrin was synthesized by a published procedure. 6 4 UV-vis (Ct^CL): A,m a x (nm) 418 (Soret), 514, 549, 590, 646. 'H N M R (CDC13): 8 -2.76 (s, 2H, NH) , 7.75 (m, 12H, phenylp- and m-H), 8.22 (m, 8H, phenyl o-H), 8.86 (s, 8H, pyrr-P-H); (QD^: -2.13 (s, 2H, NH) , 7.44 (m, 12H, phenyl p- and m-H), 8.10 (m, 8H, phenyl o-H), 8.91 (s, 8H, pyrr-P-H). The spectroscopic characteristics of this compound compare well to those reported in the literature.64 5,10,15,20-Tetraphenylporphyrinatozinc(I) (Zn(TPP) (2b). The porphyrin was synthesized by a published procedure. 6 8 UV-vis (CH^L): A,m a x (nm) 419 (Soret), 548, 582. *H N M R (CDCI3): 5 7.73 (m, 12H, phenyl p- and m-H), 8.08 (m, 8H, phenyl o-H), 8.90 (s, 8H, pyrr-P-H). The spectroscopic characteristics of this compound compare well to those reported in the literature.-3"6 Chloro(5,10,15,20-tetraphenylporphyrinato)iron(I) (Fe(TPP)Cl) (2d). Metallation using FeCl 2 and oxidation to the Fe(III) complex were achieved by a published procedure. 6 9 203 ' H N M R (CDCL): 8 5.11 (s, 4H, phenyl o-H), 6.39 (s, 4H, phenyl p-H), 7.98 (s, 4H, phenyl o-H), 12.17 (s, 4H, phenyl m-H), 13.32 (s, 4H, phenyl m-H), 79.46 (s, 8H, pyrr-p-H). The spectroscopic characteristics of this compound compare well to those reported in the literature.2 3! 5,10,15,20-Tetrakis(perfluorophenyl)porphyrin (H2TPFPP) (4a). The porphyrin was synthesized by a published procedure 2 3 2 . UV-vis (CH2OJ: Xmxi (nm) 410 (Soret), 505, 535, 582, 635. ' H N M R (CDC13): 8 -2.50 (s, 2H, N H ) , 8.80 (s, 8H, pyrr-p-H). 1 9 F N M R (CDC13),: 5 (vs. CFCI3) -137.0 (d, 2F, aryl o-F), -151.7 (t, IF, arylp-¥), -161.8 (m, 2F, aryl m-F). The spectroscopic characteristics of this compound compare well to those reported in the literature. 2 3 3 5,10,15,20-Tetrakis(perfluorophenyl)porphyrinatozinc(I) (Zn(TPFPP) (4b). Zn(II) was inserted into 4a by a published procedure using Z n ( O A c ) 2 - 2 H 2 0 6 8 . UV-vis (CF^CL): \nax (nm) 414 (Soret), 544. ' H N M R (CDC13): 5 9.17 (s, 8H, pyrr-p-H). , 9 F N M R (CDC13): 8 (vs. CFC13) -138.5 (d, 2F, aryl o-F), -154.8 (t, IF, arylp-F), -163.7 (m, 2F, aryl m-F). The spectroscopic characteristics of this compound compare well to those reported in the literature.78>234 7,8,17,18-Tetabromo-5,10,15,20-tetraphenylporphyrin (H2TPPBr4) (45a). The porphyrin was synthesized by published proceduresl85,186 except for the purification process. Analytically pure porphyrin was obtained by the following procedure. Crude product (100 mg) was dissolved completely in hot chloroform (30 mL) and silica gel (30 mL — 15 g, 70 - 230 mesh) was mixed into the solution. The solvent was removed at room temperature in a fume hood. The color of the porphyrin-adsorbed silica gel was brown. The brown silica gel was loaded on top of silica gel (2 x 20 cm) wet with benzene/hexane 50:50 (v/v) and the impurities (mainly H 2 TPPBr 3 ) were eluted with the solvent of the same composition. The main brown fraction was 204 coUected with 100 % benzene. UV-vis ( C F L A ) : ^(nm) 436 (Soret), 534, 616, 686. ln N M R (CDC13): 5 -2.83 (s, 2H, NH) , 7.78 (m, 12H, phenyl p- and m-H), 8.18 (m, 8H, phenyl o-H), 8.68 (d, 4H, pyrr-p-H); (QD^: 8 -2.69 (s, 2H, NH) , 7.50 (m, 12H, phenyl p- and m-H), 8.04 (m, 8H, phenyl o-H), 8.54 (d, 4H, pyrr-p-H); (CF 3 C0 2 D): 8 8.37 (m, 12H, phenyl p- and m-H), 8.68 (m, 4H, phenyl. o-H), 8.92 (m, 4H, phenyl o-H), 8.75 (s, 4H, pyrr-p-H). The spectroscopic characteristics of this compound compare well to those reported in the Uterature. 185,186 2,3,12,13-Tetrabromo-5,10,15,20-tetraphenylporphyrinatozinc(II) (Zn(TPPBr 4 ))(45b). Zn(II) was inserted into 45a by a published procedure using Z n ( O A c ) 2 - 2 H 2 0 . 6 8 LR-MS (EI, 300 °C): M + (m/z)= 993 , calcd. for C 4 4 H 2 4 B r 4 N 4 B r : 993.6888. UV-vis (CH.CL): X m a x (nm) 430 (Soret), 560, 598. ] H N M R (DMSO-d,): 8 8.61 (s, 4H, pyrr-P-H), 8.02 (m, 8H, phenyl-o-H), 7.80 (m, 12H, phenyl-/? and m-H). The spectroscopic characteristics of this compound compare well to those reported in the literature.2-^ 2,3,12,13-Tetrabromo-5,10,15,20-tetraphenylporphyrinatocopper(II) (Cu(TPPBr 4))(45c). Cu(II) was inserted into 45a by a published procedure using C u ( O A c ) 2 - H 2 0 . 6 8 LR-MS (EI, 300 °C): M + (m/z)= 991 , calcd. for C^H^Br.N.Cu: 991.8828. UV-vis (CHjCL): A,m a x (nm) 426 (Soret), 553, 586. The spectroscopic characteristics of this compound compare well to those reported in the literature.2-3^ 2,3,12,13-Tetrabromo-5,10,15,20-tetraphenylporphyrinatonickel(II) (Ni(TPPBr 4 ))(45d). Ni(Ii) was inserted into 45a by a published procedure using N i C l 2 . 6 8 L R -MS (EI, 300 °C): M + (m/z)= 987, calcd. for C^H^Br.N.Ni : 987.0528. UV-vis (CH.CL): 205 Xmax (nm) 428 (Soret), 544, 538. The spectroscopic characteristics of this compound compare well to those reported in the literature.235 Chloro(2,3,12,13-Tetrabfomo-5,10,15,20-tetraphenylpotphyrinato)iron(III) (Fe(TPPBr 4 )Cl ) (45e). Insertion of Fe(II) and formation and purification of this Fe(IIi) complex were achieved by published procedures^,! 90 UV-vis (CHjCy: (nm) 433 (Soret), 520, 591, 714. ' H N M R (CDC13): 5 4.77 (s, 4H, phenyl o-H) 6.59 (s, 4H, phenylp-H), 7.41 (s, 4H, phenyl o-H), 12.46 (s, 4H, phenyl m-H), 13.19 (s, 4H, phenyl m-H), 79.49 (s, 4H, pyrr43-H). The spectroscopic characteristics of this compound compare well to those reported in the literature.191 2,3,7,8,12,13,17,18-Octabromo-5,10,15,20-tettaphenylporphyrinatocopper(II) (Cu(TPPBt 8 ) ) (7c). The porphyrin was synthesized by a published procedure.^. LR-MS (EI, 300 °C): M + (m/z) = 1307, calcd. for C ^ H ^ B r ^ C u : 1307.4908. UV-vis (CPECy: ^ ( n m ) 365, 448 (sh), 466 (Soret), 581, 625. The spectroscopic characteristics of this compound compare well to those reported in the literature.75 Sodium trifluoromethylacetate ( C F 3 C 0 2 N a ) . N a O H aqueous solution (0.75 M) was slowly added to a solution of trifluoroacetic acid, 99 % (5.76 mL (75 mmol) in 100 mL H 2 0 ) . This solution was stirred and the p H monitored. As the p H of the solution approached 5-6 , the N a O H solution to be added was diluted to about 0.1 M and further added to the solution of p H 5-6. Near p H 7 more diluted N a O H solution was used to adjust the p H at 7.0. The neutralized solution was transferred to a 500-mL round-bottomed flask and most of the water was removed 206 by a rotary evaporator. A hygroscopic white solid was obtained. The wet solid was transferred to a vial and dried under in vacuo at 100 °C overnight. The product was kept in a desiccator. Trifluoromethylcadmium (CF3CdBr + (CF3)2Cd)). This reagent was synthesized by the published procedure. 139 Trifluoromethylcadmium reagent was obtained as ca. 1 M solution of trifluoromethyl anion in D M F . 1 9 F N M R (DMSO-d,): 5 (vs. CFCL) -33.2 (CF 3CdBr), and -33.9. These chemical shifts agree with the reported values.139 ((CF3)2Cd), each of which was accompanied by the satellite peaks by i n C d and 1 1 3 C d . J( , , 3 Cd- 1 9 F): CF 3 CdBr, 370.9; (CF 3) 2Cd, 423.7 Hz. J ( m C d - , 9 F ) : CF 3 CdBr, 355.9; (CF 3) 2Cd, 404.8 Hz. The concentration of CF 3" was determined by the ratio of the peak integration to the internal reference, 3-fluorotoluene. The spectroscopic characteristics of this compound compare well to those reported in the literature. 139 P-Trifluoromethyl-weso-tetraphenylporphyrins. (Pyrolysis of CFjCO^a) A one-neck 100 mL round-bottom flask equipped with a N 2 inlet was charged with C F 3 C 0 2 N a (2.70 g, 19.8 mmol), Cul (1.52 g, 8.00 mmol), Zn(TPPBr 4) (45b) (0.500 g, 0.503 mmol), dry D M F (15 mL) and toluene (5.5 mL). The flask was equipped with a distillation apparutus and toluene was removed during the first one hour at 120 °C under a N 2 stream. The reaction mixture was then heated up to 150 °C. C0 2(g) generation started at about 145 °C. The mixture was allowed to cool after 1 h and D M F was removed by a rotary evaporator. CH 2 C1 2 (50 mL) was added to the green product and the resulting solution was passed through a short silica gel column to remove the inorganic salts. The volume of CH 2 Cl 2 was reduced to about 10 mL, T F A (4 mL) was added and the mixture was refluxed for 1 h. The brown solution was diluted to ~100 m L with CH 2 C1 2 and washed with the same amount of water 3 times. Silica gel T L C of the free-base 207 porphyrin mixture showed three distinctive spots for H 2 TPP(CF 3 ) 2 (46a), H 2 TPP(CF 3 ) 3 (47a), and H 2 TPP(CF 3 ) 4 (48a) (Rf = 0.58, 0.47, and 0.09, respectively. CH2Cl2:hexane=5:5 (v/v)). In addition to these three spots, some less intensive spots were observed between 47a and 48a. Compound 46a, 47a, and 48a were separated by silica gel column, by changing the composition of solvent mixture gradually (CH 2Cl 2/hexane = 30/70 -» 50/50 -» 70/30 — benzene (100)). Since the solubility of 48a was low in this solvent system, the mixture of 46a, 47a, and 48a was pre-adsorbed on a minimal amount of silica gel before column chromatography. The solvents were removed from each fraction to yield 46a (60 mg, 16%), 47a (120 mg, 29%), and 48a (11 mg.2.5%). (Metathesis of trifluoromethylcadmium) A typical example of this reactions is shown below. As shown in chapter II, reaction temperatures and times were varied. Trifluoromethylcadmium reagent (14 mL, ca.l M) and dry H M P A (14 mL) were transferred to a two-neck 100 mL round-bottom flask and the mixture was cooled down to 0 °C and stirred for 3 min under N 2 . To this brown solution CuBr (1 g, 7 mmol) was added and the mixture was stirred until the CuBr was dissolved at room temperature. Zn(TPPBr 4) (45b) (0.5 g, 0.5 mmol) was then added and the mixture was heated at 90 °C for 7 h under N 2 . After the mixture was cooled to room temperature, D M F was removed by a rotary evaporator at 100 °C and small amount of H M P A was removed at 2 - 3 mmHg at 100 °C. H M P A could not be removed completely. Trifluoromethylated porphyrins were extracted with petroleum ether (35-60) until the green color of the petroleum ether became weak. The resultant residue which remained after the petroleum-ether extraction was dissolved in minimum amount of CH 2 C1 2 and approximately the same volume of silica gel (230 - 400 mesh) was added to adsorb the impurities and porphyrin products. After drying the pre-adsorbed silica gel for several hours at room temperature, it was 208 packed in a short column without additional silica gel and washed with benzene. Only the green porphyrin products were extracted and the brown impurities remained on the silica gel phase. The green benzene solution was then combined with the petroleum-ether extracts. Volatile solvents were removed in vacuo, H M P A * was distilled off at 100 - 110 °C at 2 - 3 mmHg. The product was dissolved in CH 2 C1 2 and filtered. CH 2 C1 2 (50 mL) and T F A (10 mL) were added to the green solid and the mixture was refluxed over a steam bath for 30 min until the color became dark orange. The mixture was diluted with CH 2 C1 2 , washed with 4M HC1, distilled water, and 10 % aq. N a H C 0 3 . CH 2 C1 2 , was removed and the free-base mixture was dissolved in a miriimum amount of benzene and adsorbed on silica gel (230 - 400 mesh, same volume as the benzene solution). After drying at room temperature in the fume hood, the pre-adsorbed silica gel was loaded on top of a wet silica gel bed prepared using 5 x volume to the amount used for pre-adsorption and chromatographed with CH 2Cl 2/hexane (30/70 (v/v) -»• 50/50) to isolate H 2 TPP(CF 3 ) 2 (46a) (34 mg, 9 %) and H 2 TPP(CF 3 ) 3 (47a) (86 mg, 21 %). The remaining porphyrins on the column were washed with benzene/acetone (90/10 (v/v)). The solvents were removed and the porphyrins were dissolved in benzene and pre-adsorbed on a minimum amount of silica gel (230 — 400 mesh). Pre-absorbed silica gel was place on top of a wet silica gel bed prepared using 7 — 8 x volume of silica gel to the amount used for pre-adsorption and flush-chromatographed with benzene/cyclohexane/acetone (20/80/2 (v/v/v) ->• 50/50/2 -* 90/0/10)). Yield; H 2 TPP(CF 3 ) 4 (48a) (140 mg, 38 %), H 2 TPP(CF 3 ) 3 (CF 2 CF 3 ) (52a) (47 mg, 10%), 54a (trace). * Caution ! H M P A is a carcinogen and highly toxic. Distillation must be performed with an apparatus equipped with double traps in a fume hood. 209 46a showed a single mass corresponding to P-bis(trifluoromethyl)-w^o-tetraphenylporphyrin by mass spectroscopy. However, ' H N M R of 46a did not show a clear spectrum corresponding to a specific regioisomer. Two very close bands that could not be separated were recognized by T L C analysis of 46a on a silica gel plate using CH 2Cl 2/hexane (10/90(v/v)) as a solvent. 1 9 F N M R of 46a showed two singlets whose chemical shifts were very close. Thus, 46a could be a mixture of regioisomers, 46a' and 46a" (p.71). The mixture of the regioisomers was used throughout the experiments (e.g. UV-vis spectroscopy and cyclic voltammetry). As for 47a, the structure of the porphyrin was confirmed by the following analysis. There are seven possible regioisomers for p-tris(trifluoromemyl)-^j'o-tetraphenylporphyrin in terms of the occupancy of the eight pyrrolic P-positions by three - C F 3 groups (Figure 4-2). ! H N M R of 47a (Figure 2-15, p.120) showed one singlet and four doublets (AB quartet) for the five pyrrolic P-protons. Four structures, 47-3, 47-4, 47-5, and 47-6 are ruled out because the ' H N M R spectra of these compounds would have to consist of three singlets and two doublets. 47-0, 47-1 and 47-2 are expected to show one singlet and four doublets. However, for 47-1 and 47-2, in order to satisfy the result of the ! H C O S Y spectrum (Figure 2-16, p.121), the positions of the N - H protons must be as shown in 47-1' and 47-2' (box in Figure 4-2). It is known that such tautomers are not stable due to penetration of each proton into the van der Waals sphere of the other and a N - H tautomer with two inner protons on transannular nitrogens is the most probable. 141 Thus, 47-1 and 47-2 should be also ruled out, and 47-0 is the only possible structure for the synthesized p-tris(trifluoromemyl)-^j'0-te1raphenylporphyrin. In other words, the copper assisted trifluoromethylation occurs regiospecifically at the brominated sites, and side reactions such as rearrangement of - C F 3 groups are unlikely. 210 Figure 4-2. Possible isomers for P-ttis(tofluoromemyl)-wwo-tetraphenylporphyrin. Double bonds, N , and N - H were omitted for for clarity. N and N - H are shown in 47-1' and 47-2'. 211 Physical data of 46a, 47a, 48a, 52a, and 54a P-Bis(trifluoromethyl)-5,10,15,20-tetraphenylporphyrin (H2TPP(CF3)2  (46a): L R -MS (EI, 250 °C): M + (m/z) = 750, calcd for Q H ^ F . N , : 750.7448. UV-vis (CH.CL): A . m a x (nm) (logs) 424 (5.49), 524 (4.19), 601 (3.62), 661 (3.86). 1 9 F N M R (CDCL): 5 (vs. CFCL) -52.7 (s), -52.8 (s). 7,847-Tris(trifluofomethyl)-5,10)15,20-tetfaphenylporphytin(H2TPP(CF3)) (47a): LR-MS (EI, 250 °C): M + (m/z) = 818, calcd for C 4 7 H 2 7 F 9 N 4 : 818.7418. UV-vis (CHjCL): ^max (nm) Gogs) 440 (5.29), 550 (3.94), 590sh (3.51), 735 (4.13). ' H N M R (CDC13): 8 -1.73 (s,lH, NH) , -1.85 (s,lH, NH) , 7.77 (m, 12H, phenyl-;* and m-H), 8.17 (m, 8H, phenyl-o-H), 8.70 and 8.57, 8.61 and 8.31 (2 A B q, JAB=5.06, 5.11 Hz, 4H, pyrr-p-H), 8.76 (s, 1H, pyrr-P-H). 1 9 F N M R (CDC13): 8 (vs. CFC13) -49.1 (m, 6F), -53.1 (s, 3F). C H N anal.(%), calcd for C 4 7 H 2 7 F 9 N 4 : C, 68.95; H , 3.32; N , 6.84, found: C, 68.71; H , 3.38; N , 6.54. 7,8^748-Tetrakis(trifluoromethyl)-5,10,15,20-tetraphenylporphyrin (H2TPP(CF3)4  (48a): LR-MS (EI, 250 °C): M + (m/z)= 887, calcd for C 4 8 H 2 6 F 1 2 N 4 : 886.7388. UV-vis (CH.CL): A.m a x (nm) dog s) 444(5.04), 463 (4.96), 580(3.81), 620sh (3.38), 832(4.23); (QFLJ: ^max (nm) doge) 446 (5.11), 466 (5.03), 577 (3.94), 616sh (3.48), 822 (4.32). ' H N M R (QD^: 8 -1.42(s, 2H, NH) , 7.45 (m, 12H, phenyl-/* and p-H), 8.00 (s, 4H, pyrr-p-H), 8.11 (m, 4H, phenyl-o-H), 8.13 (m, 4H, phenyl-o-H); (CF 3 C0 2 D): 8 8.16 (m, 12H, phenyl-^ and p-H), 8.28 (s, 4H, pyrr-P-H), 8.55 (s, 8H, phenyl-o-H). . 1 9 F N M R (QD^),: 8 (itr. CFC13) -49.6 (s). C H N anal.(%), calcd for C 4 8 H 2 6 F 1 2 N 4 : C, 65.02; H , 2.96; N , 6.32, found: C, 65.00; H , 2.86; N , 6.17. 212 7,8,17-Tris(trifluoromethyl)-18-^  (H2TPP(CF3)3(CF2CF3)) (52a): LR-MS (EI, 250 °C): M + (m/z)= 936, calcd for C 4 9 H 2 6 F 1 4 N 4 : 936.7458. UV-vis (CH^l,): X m a x (nm) (log s) 444(5.03), 468(5.01), 586(3.90), 628(3.55), 844 (4.36). 5 H N M R (QD^: 5 -1.27 (s, IH , NH), -1.03 (s, IH , NH) , 7.44 (m, 12H, phenyl m and p-H), 7.92 (d, I H , pyrr-P-H), 7.96 (d, IH , pyrr-P-H), 8.03 (m, 8H, phenyl o-H), 8.22 (br d (maybe overlapped two doublets), 2H, pyrr-P-H), in addition to these porphyrin peaks there were two sharp peaks at 1.40 (s, 2H) and 1.60 (s, 2H). These peaks diminish when D 2 0 is added. So possibly these peaks are due to water. A residual water peak also appears at 0.4 ppm as usual case for the ' H N M R spectrum for C 6 D 6 . , 9 F N M R (QD,),: 6 (vs. CFC13) -47.7 (m, 3F), -49.6 (m, 6F), -82.3 (m, 3F), -98.2 (m, 2F). C H N anal.(%), calcd for C 4 9 H 2 6 F 1 4 N 4 -0 .75C 6 H 6 : C, 53.18; H , 2.43; N , 5.64, found: C, 53.25; H , 2.54; N , 5.42. 54a: LR-MS (+LSIMS): M + (m/z) = 987, calcd. for C 5 0 H 2 6 F 1 6 N 4 : 986.7528. UV-vis (CF^CL): Xm i L X (nm) 444, 486, 588, 648. Color observation (in solid): 46a; purple, 47a; brown, 48a and 52a; golden brown in solid. 48a and 52a are tangerine in color in CH 2 C1 2 containing T F A (0.5 %). 2,3,12,13-Tetakis(trifluofomethyl)-5,10,15,20-tetiaphenylporphyrmatozinc(I) (Zn(TPP(CF3)4  (48b). Zn(OAc) 2 -2H 2 0 (37 mg, 0.17 mmol) in M e O H (10 mL) was added to a brown suspension of H 2 TPP(CF 3 ) 4 (48a) (50 mg, 0.056 mmol) in CHCl 3 (10mL) at room temperature. The color instandy changed to a bright green and solids were completely dissolved. The mixture was stirred for 30 min at room temperature, then CHC1 3 (100 mL) was added and the mixture was then washed with water (2 x 100 mL). The volume of the green CHC1 3 solution was reduced in vacuo and dried over anhydrous Na 2 S0 4 . Filtration and removal of the solvent 213 gave a green powder of 48b. The yield was 52 mg (98 %). UV-Vis (CHjCL): kmm (nm) (log e) 442 (5.37), 662 (4.31). I H N M R (CDC13): 8 7.70 (m, 12H, phenyl-w and p-H), 8.07 (m, 8H, phenyl-o-H), 8.43 (s, 4H, pyrr-p-H). 1 9 F N M R (CDC13): 5 (vs. CFC13) -48.3. C H N anal.(%), calcd for C ^ H ^ F ^ N . Z n : C, 60.68; H , 2.55; N , 5.90, found: C, 60.60; H , 2.56; N , 5.75. 2,3,12,13-Tettalds(trifluofomethyl)-5,10,15,20-tetraphenylpotphyfinatocobalt(II) (Co(TPP(CF 3 ) 4 ) (48e). H 2 TPP(CF 3 ) 4 (48a) (50 mg, 0.056 mmol) and CHCl 3 (10mL) were placed in a 50 mL-round-bottomed flask. CoCl 2 (22 mg, 0.17 mmol) in M e O H ( l O m L ) was added to the brown suspension in the flask and the mixture was refluxed for 30 min. The color of the solution changed from brown to bright green. The green solution was diluted with CHC1 3 (100 mL) and washed with water (2 x 100 mL). The amount of the green CHC1 3 solution was reduced in vacuo and dried over anhydrous Na 2 S0 4 . Filtration and removal of the solvent gave a green powder of 48e. The yield was 51 mg (96 %). HR-MS (EI, 220 °C): M + (m/z) = 943.11455 (100%), calcd for C 4 8 H 2 4 F 1 2 N 4 C o : 943.11413. UV-Vis (CPLjjL): Xmax (nm) (log s) 440(5.06), 636 (4.32). ' H N M R (CDC13): 8 9.55 (m, 12H, phenyl-/*? and p-H), 13.57 (bs, 8H, phenyl-o-H), 15.41 (bs, 4H, pyrr-p-H). 1 9 F N M R (CDC13): 8 (vs. CFCL) -54.3. C H N anal.(%), calcd for C 4 8 H 2 4 F 1 2 N 4 C o : C, 61.09; H , 2.56; N , 5.94, found: C, 61.41; H , 2.62; N , 5.78. Chloro(2,3,12,13-tetiakis(trifluoromethyl)-5,10,15,20-tettaphenylporphyrinato)iton(III) (Fe(TPP(CF 3 ) 4 )Cl ) (48f). H 2 TPP(CF 3 ) 4 (48a) (45.3 mg, 0.0511 mmol) and lithum bis(trimethylsilyl)amide (122.2 mg, 0.730 mmol) were dissolved in dry T H F (4.5 mL) at room temperature under N 2 . The color of the solution became dark orange. The solution was stirred for 5 min in a septum-sealed flask. Under an N 2 atmosphere anhydrous FeCl 2 (87.2 mg, 0.692 mmol) was added to the solution. The mixture was then warmed at 50°C. 214 The color of the solution gradually changed to dark green in 3 min. The solution was stirred under N 2 at room temperature for 2 h. The color further changed to brighter green. T L C using an alumina plate (CH 2Cl 2/petroleum ether = 50/50(v/v)) showed a weak brown spot moving fastest and a major green band smearing from the origin. After the solvent was removed from the reaction mixture, the product was dissolved in CH 2Cl 2/petroleum ether (50/50 (v/v)(10 mL) and was chromatographed on an acidic alumina column. The green color of the compound turned brown on the column. The first fraction was identified as the u—oxodimer (Fe(TPP(CF 3) 4] 20 (61) from mass spectrometry. The slow moving green fraction was washed with acetone and combined with the Li-oxodimer (61). The solvent was removed, the product was dissolved in CH 2 C1 2 (50 mL) and washed with cold 6 M HC1 (50 mL) until the organic phase turned bright green. The CH 2 C1 2 phase was collected and dried over anhydrous Na 2 S0 4 . Filtration and removal of the solvent gave a dark blue powder of 48f (31.0mg, 62.3%). Fe((TPP(CF 3) 4)Cl (48f): LR-MS (+LSIMS): M + (m/z) = 940, calcd. for C 4 8 H 2 4 F 1 2 N 4 F e : 940.5728. UV-Vis (CH 2CL): A . m a x (nm) (log 8) 452(4.76), 618(4.12). ' H N M R (CDCL): 5 4.04 (s, 4H, phenyl-^-H), 6.5 - 3.5 (bs, 8H, phenyl-o-H), 14.52 (s, 8H, phenyl-w-H), 77.15 (bs, pyrr-p-H, 4H). 1 9 F N M R (CDC13): 8 (vs. CFCL) 0.05 (s). [Fe(TPP(CF 3) 4] 20 (61): LR-MS (+LSIMS): M + (m/z) = 1897 (93 %), 940 (100%), calcd. for C % H 4 8 F 2 4 N 8 O F e 2 : 1897.145. UV-Vis (CH.CL): ?Vax (nm) (relative intensity) 435 (1.0), 700 (0.3). ' H N M R (CDC13): 8 6.55 (bs, 8H, phenyl-H), 7.36 (bs, 8H, phenyl-H), 7.72 - 8.12 (m, 24H, phenyl-H), 11.52 (bs, 4H, pyrr-p-H), 12.19 (bs, 4H, pyrr-p-H). , 9 F N M R (CDCL): 8 (vs. CFC13) -46.8 (s. 12F),-45.2 (s, 12F). Chloro(23,12-tris(trifluoromethyl)-13-pentafluoroethyl-5,10,15,20-tetraphenylporphyrinato)iron(III) (Fe (TPP(CF 3 ) 3 (CF 2 CF 3 ) )C l ) (52c). This porphyrin was synthesized in a similar method as for the synthesis of Fe((TPP(CF 3) 4)Cl (48f). The yield was 215 42mg(76% based on 50 mg of 52a). LR-MS (+LSIMS): M + (m/z) = 940, calcd. for C ^ H ^ N . F e : 940.5728. UV-Vis (CH.CL): A.M A X (nm) (log e) 452(4.76), 618(4.12). ' H N M R (CDCL): 5 3.10 (m, 4H, phenyl-^-H), 4.80 (bs, 8H, phenyl-o-H), 14.75 (s, 2H, phenyl-w-H), 15.22 (s, 6H, phenyl-^-H), 73.52 (bs, 1H, pyrr-p-H), 74.65 (bs, 3H, pyrr-p-H). 1 9 F N M R (CDC13): 5 (vs. CFC13) -66.3 (s, 3F), -13.8 (b, 2F), -6.2 (s, 3F), 1.1 (s, 3F), 14.5 (s, 3F). P-Methyl-meso-tetraphenylporphyrins. CuBr (l.OOg ,7 mmol) and C H 3 L i ( 1 0 m L of 1.4 M solution in Et 20,14 mmol) were mixed at -80 °C under N 2 in a flame-dried 50-mL one-neck round-bottomed flask with a stopcock side arm that was sealed with a rubber septum. The mixture was stirred at -80°C under N 2 until the CuBr was dissolved completely. Zn(TPPBr 4) (45b) (233 mg , 0.235 mmol) was added under a N 2 stream to the solution. The color of the mixture became green instandy. The solution was kept in an oil bath at 32°C. A small amount of mixture was withdrawn with a syringe to monitor the UV-Vis spectrum of the mixture during the reaction. The solids that built up at the edge of the solution were dissolved using a sonicator. The reaction was run for 24 h. There was no difference in UV-Vis spectra between 6 and 24 h. After the reaction was complete, dilute HC1 (5 mL) was carefully added. 100 mL of CH 2 C1 2 was added and the solution was washed with H 2 0 (100 mL). A red powder of the mixture of Zn(II) porphyrins was obtained by removing CH 2 C1 2 . In order to remove the —Br groups remaining on the pyrolic P-positions, the Zn(II) porphyrins were refluxed in D M F (not dried) in the presence of CuBr for 2 h. After this reaction was complete, D M F was evaporated. Zn(II) porphyrins were dissolved in CH 2 C1 2 and CuBr was removed by filtration. A red powder was obtained by removing CH 2 C1 2 . Since the product was poorly soluble in common organic solvents and a T L C investigation did not give a satisfactory result, the Zn(II) porphyrins were then demetallated. The red powder (140 mg) was then dissolved in T F A (3 mL) and refluxed for 216 1.5 h. Demetallation was complete as confirmed by disappearance of the Soret peak at 416 nm. The resultant green mixture gave a broad Soret band at 446 nm and a Q band at 656 nm in CH 2 C1 2 The mixture was cooled down to room temperature and diluted with CHC1 3 (100 mL). The green solution was washed with H z O (2 x 100 mL), with 7.5 % aq. N a H C 0 3 (1 x 100 mL), and with H 2 0 (1 x 100 mL). The amount of the CHC1 3 solution was reduced to ca.5 mL. Free-base porphyrins were mixed with approximately the same amount of silica gel (70 - 230 mesh). The silica gel was dried in air at room temperature in the fume hood. The porphyrin-preadsorbed silica gel was placed on the top of the silica gel column prepared in CHC1 3 . Two fractions were obtained from the column chromatography with CHC1 3 . Each fraction contained two compounds. The compounds in the first fraction were chromatographed on a silica gel column with CH 2C1 2/petroleum ether and the separation yielded H 2 TPP(CH 3 ) (56a) (less than 0.5 mg) and H 2 TPP(CH 3 ) 2 (57 a) (29 mg, 19 %). The remaining mixture was chromatographed on a silica gel column with CH 2 C1 2 containing 2 vol% of acetone and the separation yielded H 2 TPP(CH 3 ) 3 (58a) (26 mg, 17 %) and H 2 TPP(CH 3 ) 4 (59a) (24 mg, 15 %). Physical data of 56a, 57a, 58a, and 59a p-Methyl-5,10,15,20-tettaphenylporphyrin (H2TPP(CH3)) (56a): LR-MS (EI, 250 °C): M + (m/z) = 628, calcd. for C 4 5 H 3 2 N 4 : 628.7778. UV-vis (CH^CL): (nm) 417 (Soret), 514, 548, 588, 644. p-Dimethyl-5,10,15,20-tettaphenylporphyrin (H 2TPP(CH 3) 2) (57a): LR-MS (EI, 250 °C): M + (m/z)= 642, calcd. for C 4 6 H 3 4 N 4 : 642.8048. UV-vis (CH.Ch): X m a x (nm) (log e) 418 (5.69), 514 (4.35), 546 (3.76), 587 (3.87), 640 (3.75). 217 2,3,12-Trimethyl-5,10,15,20-tetfaphenylporphyrin (H2TPP(CH3)3  (58a): LR-MS (EI, 250 °C): M + (m/z) = 656, calcd. for C 4 7 H 3 4 N 4 : 656.8318. UV-vis (CH 2CL): X m a x (nm) (log e) 419 (5.60), 516 (4.29), 584 (3.66), 644 (3.24). ' H N M R (CDCL): 5 -2.67 (s, 1H, NH), -2.94 (s, 1H, NH) , 2.42 (s, 3H, -CH 3 ) , 2.44 (s, 3H, -CH 3 ) , 2.59 (s, 3H, -CH 3 ) , 7.70 (m, 12H, phenyl-/* and p-H), 8.06 (m, 6H, phenyl-o-H), 8.17 (m, 2H, phenyl-o-H), 8.63, 8.56 (ABq, 2H, pyrr-p-H), 8.54 (m, 2H, pyrr-P-H), 8.59 (s, 1H, pyrr-p-H). C H N anal.(%), calcd for C 4 7 H 3 6 N 4 -0 .5H 2 O: C, 84.78; H , 5.68; N , 8.41, found: C, 84.79; H , 5.43; N , 8.48. 2,3,12,13-Tetramethyl-5,10,15,20-tetraphenylporphyrin (H2TPP(CH3)4  (59a): LR-MS (EI, 250 °C): M + (m/z) = 670, calcd. for C 4 8 H 3 8 N 4 : 670.8588. UV-vis (CH 2CL): Xm3X (nm) 420 (Soret), 520, 588, 640. ] H N M R (CDCL): 5 -2.77 (s, 2H, NH), 2.39 (s, 12H, -CH 3 ) , 7.71 (m, 12H, phenyl-/* and p-H), 8.07 (m, 8H, phenyl-o-H), 8.44 (s, 4H, pyrr-P-H); (QD 6 ): 5 2.38 (s, 12H, -CH 3 ) , 7.40 (m, 12H, phenyl-/* and p-H), 7.97 (m, 8H, phenyl-o-H), 8.75 (s, 4H, pyrr-P-H); (CF 3 CO z D): 8 2.57 (s, 12H, -CH 3 ) , 8.40 (m, 12H, phenyl-/* and p-H), 8.66 (s, 4H, phenyl-o-H), 9.01 (s, 4H, phenyl-o-H), 8.80 (s, 4H, pyrr-p-H). C H N anal.(%), calcd for C^H^N.-O.SCHCL,: C, 79.73; H , 5.31; N , 7.67, found: C, 79.35; H , 5.31; N , 7.41. Color obsevations: 57a, 58a, and 59a were purple in the solid phase and green in CH 2 C1 2 containing 0.5 % T F A . 2,3,12,13-Tetramethyl-5,10,15,20-tetraphenylporphyrinatozinc(I) (Zn(TPP(CH3)4) (59b). Zn(TPP(CH 3) 4) (59a) (20 mg, 0.030 mmol) was dissolved in CHCl 3 (20mL) . Zn(OAc) 2 -2H 2 0 (20 mg, 0.091 mmol) was dissolved in M e O H (10 mL) and added to the CHC1 3 solution of porphyrin. The mixture was refluxed for 1 h. The color of the solution changed from 218 purple to red. After the solvents were removed by a rotary evaporator, the product was dissolved in CHCI3 (60 mL) and washed with water (3 x 60 mL). The solution was dried using anhydrous Na 3 S0 4 . Filtration and evaporation of the CHC1 3 solution yielded a red powder of 59b (18 mg, 80%). LR-MS (EI): M + (m/z) = 732, calcd. for C 4 8 H 3 , N 4 Z n : 732.7718 (63.929 ("Zn) for Zn). UV-vis (CHjCh): Xmax (nm) 420 (5.63), 534sh (3.99), 551 (4.26), 587sh (3.64). ' H N M R (CDC13): 8 2.34 (s, 12H, -CH 3 ) , 7.75 (m, 12H, phenyl-**? and.p-H), 8.06 (m, 8H, phenyl-o-H), 8.65 (s, 4H, pyrr-P-H). Crystals for X-ray crystalography. Zn(TPPBr4) • (MeOH) • (DMF). Zn(TPPBr 4) (45b) was completely dissolved in hot D M F and the solution was cooled to room temperature. The same volume of M e O H was layered on top of the porphyrin solution. After a period of 1 — 2 days shiny chip crystals were obtained. ' H N M R could not be measured in CDC1 3 because of the low solubility of the crystals. ' H N M R (DMSO-d^: 8 2.75 (s, 3H, D M F (-CH,)), 2.89 (s, 3H, D M F (-CHj)), 3.22 (d, 3H, M e O H (-CH3)), 4.08 (q, IH , M e O H (-OH)), 7.78 (m, 12H, phenyl-^ and p-H), 7.99 (s, IH , D M F (-CHO)), 8.02 (m, 8H, phenyl-o-H), 8.60 (s, 4H, pyrr-P-H). C H N anal.(%), calcd for C 4 8 H 3 5 B r 4 N 5 0 2 Z n (45b-(MeOH)-(DMF)): C, 52.47; H , 3.21; N , 6.37, found: 52.32; H , 3.17; N , 6.02. Zn(TPP(CF3)4(EtOH)3. Zn(TPP(CF 3) 4) (48b) was dissolved in C H C l 3 / E t O H (50/50 (v/v)) at room temperature. After period of two weeks, purple prism crystals were obtained by slow evaporation of the solvents at room temperature. H N M R ( C D C y : 8 0:34 (t, 3H, E t O H (-OH)), 0.73 (t, 9H, E t O H (-CH,)), 2.94 (m, 6H, E t O H (-CH2-)), 7.70 (m, 12H, 19 phenyl-*? and p-H), 8.08 (m, 8H, phenyl-o-H), 8.37 (s, 4H, pyrr-p-H). F N M R (CDC13): 8 (vs. CFC13) -48.36. UV-vis ( C H 2 C y X m a x (nm) (log e): 444(5.42), 598sh (3.82), 664(4.34). C H N 219 anal.(%), calcd for C 5 4 H 4 2 F 1 2 N 4 Z n 0 3 (48b-(EtOH)3), C, 59.60; H , 3.89; N , 5.15, found: C, 60.00; H , 3.64; N , 5.02. Zn(TPP(CH3)4)(THF)16-(CHCl3)04. ZnCTPP(CH 3) 4) (59b) was dissolved in C H C 1 3 / T H F (50/50 (v/v)) at room temperature. After a period of a week, red needle crystals were obtained by slow evaporation of the solvents at room temperature. *H N M R (CDjCL): 5 I. 76 (m, T H F ) , 2,37 (s, H 2 0 ) , 3.56 (m, THF) , 7.32 (s, CHC1 3), 7.75 (m, 12H, phenyl-/* and p-H), 8.06 (m, 8H, phenyl-o-H), 8.65 (s, 4H, pyrr-p-H). C H N anal.(%), calcd for C 5 4 8 H 4 9 2 C 1 1 2 N 4 0 , 6 Z n (59b-(THF)16-(CHCl3)04), C, 73.35; H , 5.53; N , 6.24, found: C, 73.15; H , 5.60; N , 6.06. 220 REFERENCES 1) Nomenclature of tetrapyrroles; Recommendations of IUPAC-IUB Joint Commision on Biochemical Nomenclature Eur. J. Chem. 1988, 178, 277. 2) Bonnett, R. 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Acta Part A 1997, 53, 2109. APPENDICES A. UV-visible spectra of diacids of 48a and 59a < 0 300 400 500 600 700 800 900 1000 a CO 2.5E+05 2.0E+05 1.5E+05 1.0E+05 5.0E+04 4 0.0E+00 -I 1 1 1 1 1 1—^—H 300 400 500 600 700 800 900 1000 Wavelength (nm) Figure A-l. UV-visible spectra of freebase porphyrins, H 2 T P P ( C F 3 ) 4 (48a) and H 2 T P P ( C H 3 ) 4 (59a) in C H 2 C 1 2 and their diacids in C H 2 C 1 2 containing 0.5 %(v) T F A . The Q bands are shown in five times magnification. 234 B. Crystallographic Data Table B-l-a. Atomic coordinates and B„ for Zn(TPP(CF 3) 4)-(EtOH) 3 atom X y z K Z n © 0.40652(4) 0.45182(3) 0.27515(2) 2.105(9) F(l) -0.0024(2) 0.6348(2) 0.17616(14) 5.05(7) F(2) 0.1343(2) 0.7873(2) 0.25687(13) 4.76(7) F(3) 0.0886(2) 0.7600(2) 0.12336(12) 4.59(7) F(4) 0.0857(2) 0.6128(2) 0.01207(12) 4.21(6) F(5) 0.2337(2) 0.7615(2) 0.02916(12) 4.45(6) F(6) 0.2514(2) 0.6072(2) -0.00580(1) 3.80(6) F(7) 0.5928(2) 0.1348(2) 0.19573(11) 4.27(6) F(8) 0.6770(2) 0.0913(2) 0.31178(13) 4.28(6) F(9) 0.4803(2) 0.0155(2) 0.23892(13) 4.55(6) F(10) 0.3258(3) 0.0129(2) 0.35462(14) 5.28(7) F(l l ) 0.4561(2) 0.1002(2) 0.48003(12) 4.25(6) F(12) 0.5179(2) 0.0247(2) 0.39364(15) 5.72(8) 0(1) 0.2500(3) 0.3304(2) 0.17867(15) 3.47(7) 0(2) 0.1471(4) 0.1289(3) . 0.1850(2) 8.52(12) 0(3) -0.0946(6) 0.0432(6) 0.1786(5) 17.6(3) N © 0.3575(3) 0.5874(2) 0.24406(15) 2.20(7) N(2) 0.5318(3) 0.4892(2) 0.21806(15) 2.16(7) N(3) 0.4884(2) 0.3448(2) 0.33033(15) 1.86(6) N(4) 0.3399(2) 0.4618(2) 0.36900(14) 2.04(6) C © 0.2669(3) 0.6174(3) 0.2632(2) 2.13(8) C(2) 0.2081(3) 0.6642(3) 0.1953(2) 2.40(8) C(3) 0.2633(3) 0.6573(3) 0.1361(2) 2.47(8) C(4) 0.3642(3) 0.6183(3) 0.1702(2) 2.11(8) C(5) 0.4671(3) 0.6248(3) 0.1460(2) 2.15(8) C(6) 0.5511(3) 0.5719(3) 0.1758(2) 2.13(8) C(7) 0.6700(3) 0.5931(3) 0.1655(2) 2.78(9) C(8) 0.7205(3) 0.5242(3) 0.1999(2) 2.88(9) C(9) 0.6330(3) 0.4561(3) 0.2308(2) 2.20(8) C(10) 0.6454(3) 0.3656(3) 0.2631(2) 2.25(8) C(ll ) 0.5600(3) 0.3027(3) 0.2980(2) 2.04(8) C(12) 0.5460(3) 0.1964(3) 0.3140(2) 2.22(8) C(13) 0.4765(3) 0.1810(3) 0.3648(2) 2.18(8) C(14) 0.4393(3) 0.2754(3) 0.3749(2) 1.96(8) C(15) 0.3732(3) 0.3039(3) 0.4245(2) 1.78(7) C(16) 0.3394(3) 0.3954(3) 0.4261(2) 2.01(8) C(17) 0.2878(3) 0.4319(3) 0.4858(2) 2.49(8) C(18) 0.2550(3) 0.5155(3) 0.4642(2) 2.77(9) (continued) 235 Table B-l-a (continued) atom X y z C(19) 0.2818(3) 0.5319(3) 0.3870(2) 2.06(8) C(20) 0.2427(3) 0.6006(3) 0.3387(2) 2.18(8) C(21) 0.1079(4) 0.7096(3) 0.1883(2) 3.27(10) C(22) 0.2101(4) 0.6614(3) 0.0437(2) 3.26(10) C(23) 0.5764(4) 0.1102(3) 0.2673(2) 3.07(10) C(24) 0.4430(4) 0.0796(3) 0.3977(2) 3.16(10) C(25) 0.4989(3) 0.7049(3) 0.0941(2) 2.24(8) C(26) 0.5115(3) 0.8111(3) 0.1200(2) 2.75(9) C(27) 0.5424(4) 0.8870(3) 0.0731(2) 3.45(10) C(28) 0.5577(4) 0.8543(3) -0.0023(2) 3.35(10) C(29) 0.5462(4) 0.7497(3) -0.0297(2) 3.12(10) C(30) 0.5171(3) 0.6737(3) 0.0178(2) 2.69(9) C(31) 0.7586(3) 0.3389(3) 0.2678(2) 2.41(8) C(32) 0.7922(4) 0.3252(3) 0.1960(2) 3.37(10) C(33) 0.9020(4) 0.3082(4) 0.2033(2) 4.34(12) C(34) 0.9799(4) 0.3025(4) 0.2804(3) 4.26(12) C(35) 0.9455(4) 0.3125(3) 0.3518(2) 3.42(10) C(36) 0.8361(3) 0.3308(3) 0.3448(2) 2.64(9) C(37) 0.3268(3) 0.2326(3) 0.4786(2) 2.22(8) C(38) 0.2116(3) 0.1517(3) 0.4429(2) 2.85(9) C(39) 0.1627(4) 0.0876(3) 0.4918(3) 4.26(12) C(40) 0.2295(5) 0.1089(4) 0.5784(3) 4.91(14) C(41) 0.3432(5) 0.1917(4) 0.6161(2) 4.70(13) C(42) 0.3923(4) 0.2548(3) 0.5662(2) 3.48(10) C(43) 0.1717(3) 0.6601(3) 0.3729(2) 2.49(9) C(44) 0.0479(4) 0.6083(3) 0.3607(2) 3.37(10) C(45) -0.0117(4) 0.6642(4) 0.3981(3) 4.57(13) C(46) 0.0512(5) 0.7673(5) 0.4467(3) 5.19(15) C(47) 0.1739(5) 0.8170(4) 0.4596(2) 5.00(13) C(48) 0.2353(4) 0.7654(3) 0.4231(2) 3.76(10) C(49) 0.1611(3) 0.3458(3) 0.1053(2) 317(9) C(50) 0.2063(4) 0.3502(4) 0.0323(2) 4.58(12) C(51) 0.1920(10) 0.0529(7) 0.1521(5) 13.4(3) C(52) 0.1820(14) 0.0259(12) 0.0790(8) 21.2(7) C(53) -0.1280(8) -0.0194(10) 0.2344(6) 14.0(4) C(54) -0.0855(10) .-0.1019(7) 0.2312(7) 16.8(4) Equivalent temperature factor: Btq = 3 7 t 2 (U„(aa*) 2 + U22(bb*)2 + U33(cc*)z + 2(712aa*bb*cosY + 2L/13aa*cc*cos|3 + 2L/23bb*cc*cosa) [Refer to the end of Table B-3-b for the parameters.] 236 Table B-l-b. Anisot ropic displacement parameters for Z n ( T P P ( C F 3 ) 4 ) ' ( E t O H ) 3 . atom Un rj3  u„ Ui3 ua Z n © 0.0361(3) 0.0268(2) 0.0254(2) 0.0155(2) 0.0156(2) 0.0129(2) F © 0.0400(15) 0.088(2) 0.078(2) 0.0266(15) 0.0281(13) 0.0414(15) F(2) 0.090(2) 0.070(2) 0.0491(13) 0.062(2) 0.0283(14) 0.0210(12) F(3) 0.076(2) 0.087(2) 0.0524(13) 0.062(2) 0.0358(13) 0.0464(13) F(4) 0.0395(15) 0.080(2) 0.0386(12) 0.0219(14) 0.0074(11) 0.0246(12) F(5) 0.073(2) 0.067(2) 0.0491(13) 0.0390(14) 0.0249(13) 0.0416(12) F(6) 0.0579(15) 0.067(2) 0.0270(10) 0.0314(13) 0.0150(11) 0.0170(10) F(7) 0.105(2) 0.0460(15) 0.0390(11) 0.0425(14) 0.0449(13) 0.0198(10) F(8) 0.077(2) 0.057(2) 0.0610(14) 0.0496(14) 0.0385(14) 0.0281(12) F(9) 0.077(2) 0.0292(14) 0.0729(15) 0.0187(14) 0.0379(15) 0.0077(12) F(10) 0.079(2) 0.0362(15) 0.074(2) 0.0003(15) 0.031(2) 0.0186(13) F ( l l ) 0.083(2) 0.065(2) 0.0502(13) 0.0473(15) 0.0420(13) 0.0448(12) F(12) 0.127(2) 0.066(2) 0.099(2) 0.075(2) 0.084(2) 0.064(2) O ( l ) 0.045(2) 0.039(2) 0.0336(14) 0.0048(15) 0.0036(13) 0.0121(12) 0(2) 0.113(3) 0.045(3) 0.129(3) 0.002(2) 0.018(3) 0.028(2) 0(3) 0.203(7) 0.207(7) 0.317(8) 0.089(6) 0.121(6) 0.160(7) N(l) 0.042(2) 0.028(2) 0.0274(14) 0.0200(15) 0.0206(14) 0.0155(12) N(2) 0.040(2) 0.026(2) 0.0287(14) 0.0202(15) 0.0176(14) 0.0162(13) N(3) 0.029(2) 0.024(2) 0.0267(14) 0.0136(14) 0.0154(13) 0.0159(12) N(4) 0.036(2) 0.027(2) 0.0245(14) 0.0192(15) 0.0143(14) 0.0152(12) C © 0.031(2) 0.027(2) 0.029(2) 0.015(2) 0.012(2) 0.0121(15) C(2) 0.038(2) 0.036(2) 0.032(2) 0.023(2) 0.018(2) 0.021(2) C(3) 0.041(2) 0.036(2) 0.026(2) 0.020(2) 0.015(2) 0.018(2) C(4) 0.042(2) 0.021(2) 0.025(2) 0.015(2) 0.015(2) 0.0133(15) C(5) 0.034(2) 0.024(2) 0.027(2) 0.012(2) 0.012(2) 0.0134(15) C(6) 0.036(2) 0.028(2) 0.027(2) 0.015(2) 0.017(2) 0.0148(15) C(7) 0.037(2) 0.038(2) 0.043(2) 0.015(2) 0.025(2) 0.024(2) C(8) 0.031(2) 0.050(3) 0.046(2) 0.023(2) 0.023(2) 0.030(2) C(9) 0.035(2) 0.030(2) 0.024(2) 0.014(2) 0.013(2) 0.0135(15) C(10) 0.036(2) 0.030(2) 0.028(2) 0.017(2) 0.016(2) 0.0138(15) C ( l l ) 0.031(2) 0.031(2) 0.023(2) 0.017(2) 0.012(2) 0.0133(15) C(12) 0.040(2) 0.023(2) 0.032(2) 0.019(2) 0.018(2) 0.0129(15) C(13) 0.036(2) 0.027(2) 0.027(2) 0.016(2) 0.012(2) 0.0174(15) C(14) 0.035(2) 0.022(2) 0.021(2) 0.011(2) 0.012(2) 0.0137(14) C(15) 0.027(2) 0.023(2) 0.022(2) 0.011(2) 0.0096(15) 0.0124(14) C(16) 0.028(2) 0.027(2) 0.022(2) 0.009(2) 0.011(2) 0.0098(15) C(17) 0.038(2) 0.038(2) 0.028(2) 0.019(2) 0.016(2) 0.013(2) C(18) 0.053(3) 0.036(2) 0.028(2) 0.023(2) 0.022(2) 0.011(2) C(19) 0.031(2) 0.023(2) 0.023(2) 0.009(2) 0.011(2) 0.0040(14) C(20) 0.035(2) 0.025(2) 0.029(2) 0.015(2) 0.016(2) 0.0108(15) C(21) 0.055(3) 0.052(3) 0.034(2) 0.033(2) 0.020(2) 0.022(2) C(22) 0.039(3) 0.051(3) 0.039(2) 0.021(2) 0.013(2) 0.022(2) C(23) 0.056(3) 0.033(3) 0.039(2) 0.022(2) 0.023(2) 0.016(2) C(24) 0.057(3) 0.033(3) 0.051(2) 0.027(2) 0.033(2) 0.021(2) (continued) 237 Table B-l-b. (continued) atom ua rj33 L712 u„ ua C(25) 0.034(2) 0.031(2) 0.025(2) 0.016(2) 0.010(2) 0.0150(15) C(26) 0.055(3) 0.028(2) 0.034(2) 0.024(2) 0.020(2) 0.015(2) C(27) 0.070(3) 0.030(2) 0.044(2) 0.027(2) 0.025(2) 0.020(2) C(28) 0.064(3) 0.038(3) 0.039(2) 0.024(2) 0.024(2) 0.028(2) C(29) 0.055(3) 0.043(3) 0.035(2) 0.025(2) 0.025(2) 0.021(2) C(30) 0.054(3) 0.030(2) 0.031(2) 0.024(2) 0.023(2) 0.015(2) C(31) 0.038(2) 0.034(2) 0.031(2) 0.019(2) 0.019(2) 0.018(2) C(32) 0.055(3) 0.069(3) 0.030(2) 0.042(2) 0.025(2) 0.029(2) C(33) 0.067(3) 0.089(4) 0.052(3) 0.054(3) 0.044(3) 0.041(2) C(34) 0.056(3) 0.076(3) 0.068(3) 0.049(3) 0.041(3) 0.040(3) C(35) 0.049(3) 0.047(3) 0.046(2) 0.028(2) 0.017(2) 0.027(2) C(36) 0.036(2) 0.037(2) 0.035(2) 0.017(2) 0.017(2) 0.018(2) C(37) 0.035(2) 0.030(2) 0.032(2) 0.017(2) 0.019(2) 0.018(2) C(38) 0.038(2) 0.033(2) 0.043(2) 0.014(2) 0.018(2) 0.017(2) C(39) 0.056(3) 0.040(3) 0.090(3) 0.020(2) 0.050(3) 0.033(2) C(40) 0.102(4) 0.055(3) 0.076(3) 0.041(3) 0.072(3) 0.045(3) C(41) 0.101(4) 0.058(3) 0.038(2) 0.034(3) 0.038(3) 0.028(2) C(42) 0.064(3) 0.035(2) 0.031(2) 0.013(2) 0.015(2) 0.016(2) C(43) 0.047(3) 0.033(2) 0.027(2) 0.024(2) 0.018(2) 0.016(2) C(44) 0.048(3) 0.051(3) 0.050(2) 0.029(2) 0.029(2) 0.024(2) C(45) 0.074(3) 0.071(4) 0.064(3) 0.047(3) 0.043(3) 0.038(3) C(46) 0.114(5) 0.093(4) 0.048(3) 0.087(4) 0.050(3) 0.038(3) C(47) 0.099(4) 0.056(3) 0.045(3) 0.051(3) 0.019(3) 0.003(2) C(48) 0.064(3) 0.041(3) 0.042(2) 0.028(2) 0.015(2) 0.007(2) C(49) 0.034(2) 0.043(3) 0.039(2) 0.015(2) 0.007(2) 0.008(2) C(50) 0.072(3) 0.076(4) 0.037(2) 0.036(3) 0.022(2) 0.021(2) C(51) 0.243(11) 0.110(7) 0.119(6) 0.109(8) -0.021(6) 0.017(6) C(52) 0.46(2) 0.32(2) 0.280(12) 0.28(2) 0.29(2) 0.229(14) C(53) 0.166(9) 0.228(12) 0.193(8) 0.070(8) 0.115(7) 0.114(8) C(54) 0.287(13) 0.110(7) 0.363(13) 0.146(9) 0.199(11) 0.074(8) The general temperature factor expression: exp(-27l2(a*2£V2 + b*2U22k2 + c*2Uj + 2a*b*[/ 1 2M + 2a*c*[/13/>/ + 2b*c*U23>fe/ [Refer to the end of Table B-3-b for parameters.] 238 Table B-2-a. Atomic coordinates and B„ for Zn(TPPBr 4)-(MeOH>pMF) atom x y_ z ffeq Br© 0.58180(4) -0.04914(3) 0.69092(3) 1.875(8) Br(2) 0.53182(4) -0.28795(3) 0.74241(3) 2.238(8) Br(3) 0.72294(5) -0.43406(3) -0.07081(3) 3.16(1) Br(4) 0.68507(4) -0.17764(3) -0.11018(3) 2.351(9) Z n ® 0.74243(3) -0.26443(3) 0.29861(3) 0.925(7) O(l) 0.9292(2) -0.3092(2) 0.2706(2) 1.84(5) 0(2) 0.9950(3) -0.4945(3) 0.3487(3) 4.26(9) N © 0.6918(2) -0.2356(2) 0.4507(2) 0.97(5) N(2) 0.7148(2) -0.4077(2) 0.3328(2) 0.99(5) N(3) 0.7404(3) -0.2803(2) 0.1550(2) 1.13(6) N(4) 0.7244(3) -0.1109(2) 0.2710(2) 1.05(5) N(5) 1.0279(3) -0.6695(3) 0.3602(3) 3.14(9) C © 0.6800(3) -0.1434(2) 0.4904(2) 0.98(6) C(2) 0.6312(3) -0.1512(2) 0.5963(2) 1.11(6) C(3) 0.6151(3) -0.2480(3) 0.6173(2) 1.15(6) C(4) 0.6568(3) -0.3030(2) 0.5260(2) 0.84(6) C(5) 0.6689(3) -0.4089(2) 0.5139(2) 0.99(6) C(6) 0.6999(3) -0.4559(2) 0.4234(2) 0.95(6) C(7) 0.7228(3) -0.5660(2) 0.4117(3) 1.25(7) C(8) 0.7493(3) -0.5831(2) 0.3158(3) 1.35(7) C(9) 0.7437(3) -0.4831(2) 0.2656(2) 0.97(6) C(10) 0.7598(3) -0.4684(2) 0.1650(3) 1.28(7) C(l l ) 0.7470(3) -0.3717(3) 0.1150(2) 1.21(7) C(12) 0.7347(3) -0.3479(3) 0.0177(3) 1.61(7) C(13) 0.7220(3) -0.2456(3) 0.0008(3) 1.52(7) C(14) 0.7313(3) -0.2030(3) 0.0852(2) 1.12(6) C(15) 0.7386(3) -0.1024(2) 0.0951(3) 1.28(7) C(16) 0.7412(3) -0.0631(2) 0.1808(3) 1.25(7) C(17) 0.7598(4) 0.0378(3) 0.1855(3) 1.78(8) C(18) 0.7536(3) 0.0495(3) 0.2790(3) 1.52(7) C(19) 0.7291(3) -0.0423(2) 0.3331(3) 1.19(7) C(20) 0.7082(3) -0.0561(2) 0.4349(2) 1.05(6) C(21) 0.6585(3) -0.4795(2) 0.6026(2) 0.94(6) C(22) 0.7444(3) -0.4985(3) 0.6507(3) 1.35(7) C(23) 0.7353(4) -0.5599(3) 0.7349(3) 1.81(8) C(24) 0.6404(4) -0.6046(3) 0.7719(3) 1.75(7) C(25) 0.5561(3) -0.5885(3) 0.7234(3) 1.67(7) C(26) 0.5650(3) -0.5263(3) 0.6385(3) 1.25(7) C(27) 0.7910(3) -0.5649(3) 0.1069(3) 1.40(7) C(28) 0.7039(4) -0.6128(3) 0.1091(3) 2.23(8) • C(29) 0.7328(4) -0.7001(3) 0.0536(3) 2.81(9) C(30) 0.8487(5) -0.7402(3) -0.0030(3) 3.1(1) C(31) 0.9364(4) -0.6944(3) -0.0061(3) 2.92(9) C(32) 0.9075(4) -0.6062(3) 0.0505(3) 2.10(8) (continued) 239 Table B-2-a. (continued) atom X y z C(33) 0.7473(4) -0.0301(3) 0.0077(3) 1.64(7) C(34) 0.8540(4) -0.0412(3) -0.0688(3) 2.36(9) C(35) 0.8596(5) 0.0228(3) -0.1512(3) 3.0(1) C(36) 0.7586(6) 0.0984(4) -0.1574(3) 3.7(1) C(37) 0.6541(5) 0.1117(3) -0.0823(4) 3.2(1) C(38) 0.6477(4) 0.0485(3) . 0.0021(3) 2.44(9) C(39) 0.7183(3) 0.0311(2) 0.4860(2) 1.12(6) C(40) 0.6320(3) 0.1252(3) 0.5007(3) 1.62(7) C(41) 0.6417(4) 0.2044(3) 0.5494(3) 1.83(8) C(42) 0.7399(4) 0.1913(3) 0.5816(3) 1.89(8) C(43) 0.8271(4) 0.0987(3) 0.5663(3) 1.99(8) C(44) 0.8170(3) 0.0178(3) 0.5185(3) 1.56(7) C(45) 0.9928(4) -0.2383(3) 0.2765(4) 3.2(1) C(46) 1.0115(4) -0.5789(4) 0.3124(4) 3.5(1) C(47) 1.0232(4) -0.6752(4) 0.4616(4) 3.6(1) C(48) 1.0378(6) -0.7651(5) 0.3164(5) 5.6(2) Equivalent temperature factor: g Btq = -7t 2(U„(aa*) 2+ U22(bb*)2+ U3)(cc*)2 + 2fJ12aa*bb*cosy + 2rj13aa*cc*cosp + 2fJ23bb*cc*cosa) 240 Table B-2-b. Anisotropic displacement parameters for Zn(TPPBr 4)-(MeOH)-(DMF) atom ^22 U 3 3 Un C713 u* B r ® 0.0403(2) 0.0150(2) 0.0120(2) -0.0079(2) -0.0010(2) -0.0041(1) Br(2) 0.0444(2) 0.0194(2) 0.0130(2) -0.0126(2) 0.0061(2) -0.0009(1) Br(3) 0.0841(4) 0.0252(2) 0.0243(2) -0.0213(2) -0.0284(2) -0.0013(2) Br(4) 0.0524(3) 0.0255(2) 0.0177(2) -0.0111(2) -0.0198(2) 0.0036(2) Z n ® 0.0184(2) 0.0076(2) 0.0099(2) -0.0046(2) -0.0047(2) 0.0011(1) O(l) 0.016(1) 0.018(1) 0.032(2) -0.004(1) -0.004(1) 0.004(1) 0(2) 0.039(2) 0.038(2) 0.102(3) -0.023(2) -0.046(2) 0.035(2) N ® 0.016(1) 0.009(1) 0.011(1) -0.004(1) -0.004(1) 0.002(1) N(2) 0.016(1) 0.010(1) 0.012(1) -0.004(1) -0.004(1) 0.000(1) N(3) 0.023(2) 0.010(1) 0.011(1) -0.007(1) -0.006(1) 0.000(1) N(4) 0.020(1) 0.009(1) 0.009(1) -0.002(1) -0.005(1) 0.000(1) N(5) 0.025(2) 0.030(2) 0.053(3) -0.003(2) -0.005(2) 0.010(2) C(I) 0.015(2) 0.011(1) 0.013(2) -0.004(1) -0.005(1) -0.001(1) C(2) 0.019(2) 0.011(1) 0.015(2) -0.007(1) -0.006(1) 0.001(1) C(3) 0.016(2) 0.015(2) 0.012(2) -0.006(1) -0.001(1) 0.001(1) C(4) 0.012(2) 0.012(1) 0.008(2) -0.003(1) -0.004(1) 0.003(1) C(5) 0.014(2) 0.012(2) 0.015(2) -0.007(1) -0.008(1) 0.004(1) C(6) 0.013(2) 0.009(1) 0.015(2) -0.004(1) -0.006(1) 0.002(1) C(7) 0.019(2) 0.011(1) 0.018(2) -0.005(1) -0.006(1) 0.003(1) C(8) 0.026(2) 0.008(1) 0.015(2) -0.004(1) -0.005(1) 0.000(1) C(9) 0.015(2) 0.007(1) 0.015(2) -0.006(1) -0.004(1) 0.000(1) C(10) 0.021(2) 0.012(2) 0.014(2) -0.006(1) -0.002(1) -0.004(1) C(ll) 0.019(2) 0.014(2) 0.013(2) -0.007(1) -0.002(1) -0.004(1) C(12) 0.030(2) 0.019(2) 0.015(2) -0.009(2) -0.007(2) -0.003(1) C(13) 0.027(2) 0.020(2) 0.010(2) -0.008(2) -0.004(1) 0.001(1) C(14) 0.019(2) 0.014(2) 0.008(2) -0.004(1) -0.002(1) 0.000(1) C(15) 0.022(2) 0.011(2) 0.012(2) -0.002(1) -0.003(1) 0.001(1) C(16) 0.023(2) 0.010(1) 0.013(2) -0.003(1) -0.004(1) 0.002(1) C(17) 0.040(2) 0.012(2) 0.017(2) -0.008(2) -0.010(2) 0.005(1) C(18) 0.032(2) 0.011(2) 0.016(2) -0.008(2) -0.007(2) 0.000(1) C(19) 0.024(2) 0.008(1) 0.016(2) -0.005(1) -0.009(1) 0.000(1) C(20) 0.017(2) 0.008(1) 0.015(2) -0.001(1) -0.006(1) -0.001(1) C(21) 0.017(2) 0.008(1) 0.009(2) -0.001(1) -0.003(1) -0.001(1) C(22) 0.019(2) 0.016(2) 0.018(2) -0.004(1) -0.009(1) 0.000(1) C(23) 0.032(2) 0.020(2) 0.018(2) 0.002(2) -0.015(2) -0.002(1) C(24) 0.038(2) 0.014(2) 0.007(2) -0.001(2) -0.003(2) 0.002(1) C(25) 0.026(2) 0.014(2) 0.021(2) -0.008(2) -0.002(2) 0.004(1) C(26) 0.017(2) 0.013(2) 0.018(2) -0.002(1) -0.008(1) -0.001(1) C(27) 0.028(2) 0.010(1) 0.012(2) -0.006(2) -0.002(1) -0.001(1) C(28) 0.037(2) 0.024(2) 0.019(2) -0.017(2) 0.007(2) -0.009(2) C(29) 0.054(3) 0.027(2) 0.025(2) -0.026(2) 0.004(2) -0.009(2) C(30) 0.071(3) 0.019(2) 0.021(2) -0.011(2) -0.001(2) -0.009(2) C(31) 0.040(3) 0.028(2) 0.029(2) 0.004(2) 0.001(2) -0.012(2) C(32) 0.029(2) 0.024(2) 0.022(2) -0.006(2) 0.000(2) -0.006(2) (continued) 241 Table B-2-b, (continues) atom Un r j 1 3 ^23 C(33) 0.043(2) 0.013(2) 0.008(2) -0.010(2) -0.009(2) 0.003(1) C(34) 0.041(2) 0.026(2) 0.022(2) -0.011(2) -0.007(2) 0.000(2) C(35) 0.067(3) 0.033(2) 0.016(2) -0.026(2) -0.003(2) 0.003(2) C(36) 0.103(5) 0.028(2) 0.022(2) -0.028(3) -0.028(3) 0.012(2) C(37) 0.069(3) 0.022(2) 0.032(3) -0.005(2) -0.029(3) 0.010(2) C(38) 0.047(3) 0.021(2) 0.023(2) -0.003(2) -0.014(2) 0.002(2) C(39) 0.022(2) 0.013(1) 0.010(2) -0.007(1) -0.004(1) 0.001(1) C(40) 0.029(2) 0.015(2) 0.021(2) -0.008(2) -0.011(2) 0.001(1) C(41) 0.036(2) 0.009(2) 0.023(2) -0.004(2) -0.009(2) -0.003(1) C(42) 0.037(2) 0.019(2) 0.022(2) -0.015(2) -0.010(2) -0.004(1) C(43) 0.027(2) 0.031(2) 0.025(2) -0.012(2) -0.013(2) -0.003(2) C(44) 0.019(2) 0.019(2) 0.021(2) -0.002(2) -0.008(2) 0.000(1) C(45) 0.031(2) 0.030(2) 0.067(4) -0.014(2) -0.018(2) 0.001(2) C(46) 0.027(2) 0.049(3) 0.063(4) -0.017(2) -0.023(2) 0.027(3) C(47) 0.035(3) 0.039(3) 0.056(3) -0.008(2) -0.014(2) 0.024(2) C(48) 0.072(4) 0.049(3) 0.072(5) -0.006(3) -0.004(4) -0.010(3) The general temperature factor expression: e x p ^ T i ^ a * 2 ^ / 2 + b*2U22k2 + c*2U3/ + 2a*b*t / 1 2 M + 2a*c*rj13/,/+ 2b*c*L723/fe/ 242 Table B-3-a. Atomic coordinates and B„ for Zn(TPP(CH 3) 4)-(THF) 1 6-(CHCl 3), atom X y z Z n © 0.26812(5) 0.12829(4) 0.87154(5) 1.19(1) CI© 0.1904(4) 0.0949(3) 0.3699(3) 6.7(1) Cl(2) 0.2592(4) 0.2290(3) 0.4358(4) 5.2(1) Cl(3) 0.3791(7) 0.1530(5) 0.3397(5) 8.0(2) 0(1) 0.2693(4) 0.2483(2) 0.8706(3) 2.6(1) 0(2) 0.2858(7) 0.0902(5) 0.3694(6) 4.4(2) N © 0.2283(3) 0.1139(3) 0.7589(3) 1.3(1) N(2) 0.1244(3) 0.1180(3) 0.8938(3) 1.1(1) N(3) 0.3076(3) 0.1145(3) 0.9843(3) 1.2(1) N(4) 0.4112(3) 0.1155(3) 0.8494(3) 1.2(1) C © 0.2890(4) 0.1004(3) 0.7035(3) 1.1(1) C(2) 0.2343(5) 0.0816(3) 0.6346(4) 1.3(1) C(3) 0.1361(4) 0.0900(3) 0.6487(4) 1.3(1) C(4) 0.1338(4) 0.1099(3) 0.7262(3) 1.2(1) C(5) 0.0496(4) 0.1254(4) 0.7663(3) 1.2(1) C(6) 0.0462(4) 0.1300(4) 0.8431(3) 1.3(1) C(7) -0.0423(4) 0.1432(4) 0.8827(3) 1.5(1) C(8) -0.0170(4) 0.1370(4) 0.9550(3) 1.5(1) C(9) 0.0874(4) 0.1209(4) 0.9633(3) 1.3(1) C(10) 0.1415(4) 0.1099(3) 1.0302(3) 1.3(1) C(l l ) 0.2443(4) 0.1001(3) 1.0393(3) 1.1(1) C(12) 0.3009(5) 0.0792(3) 1.1077(4) 1.5(1) C(13) 0.3983(4) 0.0868(3) 1.0936(3) 1.2(1) C(14) 0.4021(4) 0.1093(3) 1.0166(3) 1.1(1) C(15) 0.4875(4) 0.1221(3) 0.9763(3) 1.2(1) C(16) 0.4898(4) 0.1239(4) 0.9004(3) 1.3(1) C(17) 0.5789(4) 0.1321(4) 0.8613(3) 1.6(1) C(18) 0.5542(4) 0.1272(4) 0.7875(3) 1.6(1) C(19) 0.4468(4) 0.1167(4) 0.7801(3) 1.3(1) C(20) 0.3938(4) 0.1069(3) 0.7125(3) 1.4(1) C(21) 0.2714(5) 0.0547(4) 0.5623(4) 2.2(2) C(22) 0.0455(5) 0.0720(4) 0.5890(4) 2.2(2) C(23) 0.2626(5) 0.0461(4) 1.1761(4) 2.5(2) C(24) 0.4834(5) 0.0682(4) 1.1484(4) 1.8(2) C(25) -0.0471(4) 0.1397(4) 0.7222(4) 1.3(1) C(26) -0.0647(5) 0.2056(4) 0.6863(4) 2.0(2) C(27) -0.1513(5) 0.2175(4) 0.6438(4) 2.7(2) C(28) -0.2223(5) 0.1636(4) 0.6392(4) 2.6(2) C(29) -0.2081(5) 0.0976(4) 0.6766(4) 2.6(2) C(30) -0.1208(5) 0.0857(4) 0.7183(4) 2.0(2) C(31) 0.0832(4) 0.1127(3) 1.0982(3) 1.3(1) C(32) 0.0164(4) 0.0577(4) 1.1144(4) 1.6(2) C(33) -0.0348(4) 0.0621(4) 1.1801(4) 1.8(2) C(34) -0.0198(5) 0.1210(5) 1.2279(4) 2.4(2) (continued) Table B-3-a. (continued) atom X y z C(35) 0.0428(5) 0.1770(4) 1.2097(4) 2.3(2) C(36) . 0.0942(4) 0.1731(4) 1.1463(4) 2.0(2) C(37) 0.5829(4) 0.1344(4) 1.0205(3) 1.2(1) C(38) 0.5990(4) 0.1982(4) 1.0577(4) 1.7(1) C(39) 0.6882(5) 0.2116(4) 1.0990(4) 2.5(2) C(40) 0.7608(4) 0.1581(4) 1.1019(4) 2.4(2) C(41) 0.7452(5) 0.0937(4) 1.0639(4) 2.2(2) C(42) 0.6576(4) 0.0812(4) 1.0220(4) 1.8(2) C(43) 0.4534(4) 0.1069(3) 0.6453(3) 1.1(1) C(44) 0.5153(4) 0.0479(4) 0.6294(4) 1.7(1) C(45) 0.5665(4) 0.0476(4) 0.5668(4) 2.1(2) C(46) 0.5632(5) 0.1059(5) 0.5197(4) 2.3(2) C(47) 0.5047(5) 0.1660(4) 0.5340(4) 2.2(2) C(48) 0.4504(4) 0.1663(4) 0.5973(4) 1.7(1) C(49A) 0.3495(8) 0.2900(6) 0.9008(7) 0.6(2) C(50) 0.3115(6) 0.3694(5) 0.9017(4) 3.6(2) C(51) 0.2362(6) 0.3695(5) 0.8364(5) 3.7(2) C(52A) 0.226(1) 0.292(1) 0.813(1) 3.8(4) C(53) 0.166(1) 0.1741(9) 0.4080(8) 4.3(3) C(54) 0.255(2) 0.220(1) 0.378(2) 8.6(5) C(55) 0.320(2) 0.162(1) 0.360(1) 5.8(4) C(56) 0.249(3) 0.185(2) 0.354(2) 7.5(6) C(49B) 0.314(2) 0.288(2) 0.925(2) 7.5(6) C(52B) 0.186(1) 0.2938(8) 0.8415(9) 2.4(3) Equivalent temperature factor: Btq = 3 7 i 2 (U„(aa*) 2 + U 2 2(bb*) 2 + U33(cc*)2 + 2L712aa*bb*cosy + 2C713aa*cc*cosP + ,bb*cc*cosa) 244 Table B-3-b. Anisotropic displacement parameters for Zn(TPP(CH 3) 4)'(THF) 1 f/(CHCi 3), atom ^33 Uu u„ u23 Z n © 0.0077(3) 0.0205(4) 0.0171(4) 0.0000(4) 0.0008(2) -0.0007(5) O(l) 0.031(2) 0.023(2) 0.042(3) 0.002(3) -0.012(2) -0.001(3) N © 0.010(3) 0.022(3) 0.018(3) -0.004(2) 0.004(2) 0.003(2) N(2) 0.009(2) 0.018(3) 0.014(3) -0.001(2) -0.002(2) -0.001(2) N(3) 0.005(2) 0.016(3) 0.024(3) -0.001(2) 0.000(2) -0.001(2) N(4) 0.016(3) 0.017(3) 0.013(3) -0.001(2) 0.000(2) -0.002(2) C © 0.010(3) 0.019(4) 0.013(3) 0.002(2) 0.002(3) 0.002(3) C(2) 0.013(3) 0.020(3) 0.018(4) 0.003(3) 0.000(2) -0.005(4) C(3) 0.014(3) 0.017(4) 0.020(4) 0.001(3) -0.001(3) 0.003(3) C(4) 0.011(3) 0.022(4) 0.013(3) -0.003(2) -0.003(3) 0.005(3) C(5) 0.012(3) 0.013(3) 0.019(3) -0.005(3) -0.003(2) 0.004(3) C(6) 0.014(3) 0.019(3) 0.017(3) -0.001(3) 0.000(2) -0.003(3) C(7) 0.008(3) 0.028(4) 0.019(4) -0.001(3) -0.002(3) -0.003(3) C(8) 0.008(3) 0.027(4) 0.024(4) -0.003(3) 0.007(2) 0.001(3) C(9) 0.016(3) 0.016(4) 0.016(3) 0.002(3) 0.003(3) 0.001(3) C(10) 0.011(3) 0.015(4) 0.023(4) -0.001(2) 0.005(3) 0.004(3) C(l l ) 0.012(3) 0.012(3) 0.019(4) 0.000(2) 0.003(3) 0.001(3) C(12) 0.021(3) 0.021(4) 0.015(4) 0.000(3) 0.006(3) -0.001(3) C(13) 0.016(3) 0.015(3) 0.016(4) -0.004(3) -0.001(3) -0.002(3) C(14) 0.016(3) 0.013(4) 0.014(3) 0.002(2) -0.003(3) -0.005(3) C(15) 0.010(3) 0.013(3) 0.024(4) 0.001(3) -0.001(3) 0.002(3) C(16) 0.012(3) 0.018(3) 0.017(3) -0.002(3) -0.003(2) -0.004(3) C(17) 0.007(3) 0.025(4) 0.028(4) -0.002(3) 0.000(3) -0.007(3) C(18) 0.010(3) 0.032(4) 0.021(3) -0.002(3) 0.002(2) -0.005(4) C(19) 0.008(3) 0.028(4) 0.016(3) 0.003(3) 0.004(2) 0.002(3) C(20) 0.015(3) 0.021(4) 0.018(4) 0.004(3) -0.001(3) 0.001(3) C(21) 0.019(4) 0.039(5) 0.026(4) 0.003(3) 0.005(3) 0.001(3) C(22) 0.021(4) 0.024(4) 0.039(5) 0.008(3) 0.024(3) 0.004(3) C(23) 0.024(4) 0.047(5) 0.026(4) 0.011(3) 0.007(3) 0.007(4) C(24) 0.016(4) 0.019(4) 0.035(4) -0.001(3) 0.002(3) 0.010(3) C(25) 0.009(3) 0.023(4) 0.017(4) 0.001(3) -0.002(3) 0.003(3) C(26) 0.020(4) 0.023(4) 0.034(4) -0.003(3) -0.008(3) 0.004(3) C(27) 0.035(4) 0.024(4) 0.040(5) 0.001(3) -0.017(3) 0.006(4) C(28) 0.019(4) 0.036(5) 0.041(5) 0.006(3) -0.012(3) -0.004(4) C(29) 0.017(4) 0.038(5) 0.044(5) -0.005(3) -0.004(3) 0.007(4) C(30) 0.015(4) 0.028(4) 0.033(5) -0.004(3) -0.005(3) 0.015(4) C(31) 0.008(3) 0.022(4) 0.020(4) 0.004(2) -0.001(3) 0.002(3) C(32) 0.013(3) 0.023(4) 0.025(4) -0.002(3) 0.003(3) 0.002(3) C(33) 0.014(3) 0.030(4) 0.024(4) 0.002(3) 0.004(3) 0.014(3) C(34) 0.020(4) 0.047(5) 0.027(4) 0.006(3) 0.013(3) -0.004(4) C(35) 0.030(4) 0.034(5) 0.023(4) 0.003(3) 0.001(3) -0.007(3) C(36) 0.021(4) 0.025(4) 0.030(4) -0.003(3) 0.005(3) -0.007(3) C(37) 0.006(3) 0.020(4) 0.019(3) .-0.004(3) 0.001(2) -0.002(3) C(38) 0.017(3) 0.021(4) 0.026(4) 0.003(3) -0.001(3) -0.004(3) (continued) 245 Table B-3-b. (continued) atom Uu Un r j 1 2 L713 f j 2 3 C(39) 0.028(4) 0.023(4) 0.043(5) -0.006(3) -0.007(3) -0.006(4) C(40) 0.011(3) 0.037(4) 0.040(5) -0.001(3) -0.014(3) -0.003(4) (41 C 0.019(4) 0.020(4) 0.044(5) 0.006(3) -0.011(3) -0.001(4) C(42) 0.021(4) 0.014(4) 0.033(4) 0.003(3) -0.006(3) -0.003(3) C(43) 0.009(3) 0.021(4) 0.013(3) -0.001(2) 0.003(3) -0.001(3) C(44) 0.019(3) 0.025(4) 0.019(4) 0.004(3) -0.002(3) -0.002(3) C(45) 0.012(3) 0.038(5) 0.030(4) 0.002(3) 0.000(3) -0.007(4) C(46) 0.017(4) 0.059(6) 0.012(4) -0.003(3) 0.007(3) -0.007(4) C(47) 0.024(4) 0.037(5) 0.023(4) -0.011(3) 0.001(3) 0.015(4) C(48) 0.017(3) 0.024(4) 0.023(4) 0.003(3) -0.001(3) -0.002(3) C(50) 0.060(5) 0.025(4) 0.052(5) -0.008(4) 0.021(4) -0.006(5) C(51) 0.047(5) 0.025(4) 0.071(6) 0.005(4) 0.012(4) 0.010(5) The general temperature factor expression: exr3(-2n\a*zUuh2 + b^U^k2 + c* 2 r j 3 3 / + 2a*b*Unhk + 2a*c*l713<W + 2b*c*fJ 2 3 £/ Parameters: a, b, c, a, (3, y; lattice constants (refer to Table 2-12) a*, b*, c*; reciprocal lattice parameters2^8 

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