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Aerobic alcohol and amine oxidations catalyzed by Trans-dioxo(porphyrinato)ruthenium(VI) complexes Dodson, Heather K. 1998

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Aerobic Alcohol and Amine Oxidations Catalyzed by Trans-Dioxo(porphyrinato)ruthenium(VI) Complexes by Heather K. Dobson B.Sc, University of Waterloo, 1996 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We accept this thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA September 1998 © Heather K. Dobson, 1998 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 of CKiWVi The University of British Columbia Vancouver, Canada Date Oct DE-6 (2/88) ABSTRACT The stoichiometric and aerobic catalytic oxidations of amines and benzhydrols by /ran5,-Ru(porp)(0)2 complexes (porp = TMP, OCP, OCP-Clg, see Figure) in benzene under mild conditions are described. Figure: rran5-dioxo(porphyrinato)ruthenium(VI) complexes. TMP, OCP and OCP-Clg are the dianions of meso-tetramesitylporphyrin, meso-tetra(2,6-dichlorophenyl)porphyrin and meso-tetra(2,6-dichlorophenyl)-y3-octachloroporphyrin, respectively. Kinetic data, determined by UV-VIS and ' H - N M R spectroscopic analyses, for the stoichiometric oxidation of /^-substituted benzhydrols indicate that the oxidation mechanism proceeds through the formation of a {Ru-alcohol} adduct (governed by an equilibrium constant K) which subsequently decomposes in a slower step (with rate constant ki) leading to ketone formation. Isotope effects of K H / K D ~ 0.6 and ki H /k i° - 1 5 for a-deuteration of the alcohol indicate that the adduct is formed through hydrogen-bonding interactions probably between the Ru=0 and the a-CH with cleavage of this C-H ii Abstract bond occurring in the rate-determining step. Electron-donating substituents favour alcohol oxidation, as illustrated by a limited linear Hammett relationship of ki with 2rjp for di-/7-substituted benzhydrols. The {Ru-alcohol} adduct formation is essentially isenthalpic, while the ki activation parameters are AHi* = 58 + 10 kJ/mol and ASi* = -120 + 30 J/(mol K). 7ram ,-RuIV(TMP)(alkoxo)2 complexes have been isolated from the stoichiometric oxidation reactions and characterized by 'H-NMR, UV-VIS and IR spectroscopies. Aerobic oxidation of benzhydrols is catalyzed by fra/is-Ru(porp)(0)2 at 50°C in benzene; ketones are the only organic products of the reaction. Water is essential for higher catalytic activity and turnovers of up to 24 (98% conversion) are seen at 50°C after 19 h. Under these conditions, the catalyst activities follow the trend: trans-Ra(OCP-C18)(0)2 > trans-Ru(TMP)(0)2 > trans-Ru(OC?)(0)2. Limited linear Hammett relationships, based on % conversion after 45 h at 50°C, indicate that catalytic oxidation is also favoured by the ^-substitution of electron-donating substituents on the benzhydrols. Catalytic activity is limited by the rate of Ru(VI)-dioxo regeneration. Stoichiometric amine oxidation by trans-Ru(OC?)(0)2 and trans-Ru(TMP)(0)2 studied by UV-VIS spectroscopy gives irreproducible results. The source of the irreproducibility is not determined, though it is not from trace oxygen, the amine, the catalyst, trace acid or water in the system. The reactions, however, are light-sensitive. Aerobic oxidation of amines is catalyzed by trans-Ru(porp)(0)2 at 50°C under 1 atm of air; however, turnovers greater than 3 are only seen after 90 h in biphasic benzene/water systems, a result that contradicts a previous report. i i i TABLE OF CONTENTS ABSTRACT i i TABLE OF CONTENTS iv LIST OF TABLES ix LIST OF FIGURES xiii LIST OF ABBREVIATIONS xviii ACKNOWLEDGMENTS xxii CHAPTER I 1 INTRODUCTION 1 Alcohol Oxidations 1 Non-porphyrin Ruthenium Oxidants 2 Reactions Catalytic in the Presence of N M O (N-methylmorpholine-N-oxide) 2 Reactions Catalytic in the Presence of TBHP (/-Butyl Hydrogen Peroxide) 4 Reactions Catalytic in the Presence of Halogenated Co-oxidants: CIO4", BrCV andI0 4" 4 Using O2 as the Co-oxidant 6 Ruthenium Porphyrin Oxidants 8 Cytochrome P-450: Nature's Oxidant 8 Synthetic Ruthenium Porphyrins 10 Reactions Catalytic in the Presence of Amine N-oxides 12 Catalytic Aerobic Oxidations with Ruthenium Porphyrins 12 Amine Oxidations 14 iv Table of Contents Non-Porphyrin Ruthenium Oxidants 14 Reactions Catalytic in the Presence of N M O , PhIO and Peroxides 14 Aerobic Amine Oxidations 16 Ruthenium Porphyrin Oxidants 17 Goals of this Thesis 21 CHAPTER II 22 EXPERIMENTAL . 22 General 22 Synthesis of Benzhydrol Substrates 28 General Procedure 29 4,4'-Dimethoxybenzhydrol [(p-MeO-C 6H 4) 2CHOH] 29 4,4'-Difluorobenzhydrol [(p-F-C6H4)2CHOH] 30 Benzhydrol [Ph 2CHOH] 30 4-Chlorobenzhydrol [(p-Cl-CeH^PhCHOH] 30 4-Methoxybenzhydrol [0p-MeO-C 6H 4)PhCHOH] 31 4,4'-N,N'-Dimethylaminobenzhydrol [(^Me 2 N-C 6 H4) 2 CHOH] 31 a-Deuterobenzhydrol [Ph 2CDOH] 32 Benzhydrol-O-tf [Ph 2CHOD] 32 Synthesis of Porphyrins 32 General Procedure 32 Meso-Tetramesitylporphyrin [H 2TMP] 33 Meyo-Tetra(2,6-dichlorophenyl)porphyrin [H 2OCP] 33 Synthesis of Ruthenium Porphyrin Complexes 33 Synthesis of Carbonyl(porphyrinato)ruthenium(II) Complexes 33 v Table of Contents Ru(TMP)(CO)..... 34 Ru(OCP)fCO) 35 Synthesis of Carbonyl(meso-tetra(2,6-dichlorophenyl)-^-octachloroporphyrinato)ruthenium(II) [Ru(OCP-Ch)(CO)J 35 Synthesis oflxdxvs-bis(acetonitrile) (meso-tetramesitylporphyrinato)ruthenium (II) 36 Synthesis ofTrans-dioxo(porphyrinato)ruthenium(VI) Complexes 37 Ru(TMP)(0) 2 38 Ru(OCP)(0) 2 38 Ru(OCP-Cl 8)(0) 2 38 Synthesis ofTrsm-bis(alkoxo)(meso-tetramesitylporphyrinato)ruthenium(IV) Complexes 39 Ru(TMP)(OCHPh 2) 2 40 Ru(TMP)(OCH(p-MeO-C 6H 4) 2) 2 40 Ru(TMP)(OCH(p-F-C6H4)2)2 41 CHAPTER III 42 OXIDATION OF ALCOHOLS 42 Introduction 42 Sample Preparation and Data Analysis 42 Stoichiometric Reactions 42 UV-VIS Spectroscopic Experiments 43 ' H - N M R Spectroscopic Experiments 44 Catalytic Aerobic Oxidations 48 Stoichiometric Oxidation of Benzhydrols by *ra#is-Ru(TMP)(0)2 48 Proposed Mechanism for Anaerobic, Stoichiometric Alcohol Oxidation 63 vi Table of Contents Aerobic Oxidation of Benzhydrols Catalyzed by /ra«5-Ru(porp)(0)2 69 Proposed Mechanism of Aerobic Benzhydrol Oxidation Catalyzed by trans-Ru(porp)(0)2 73 Conclusions 82 CHAPTER IV 84 OXIDATION OF AMINES 84 Introduction 84 Sample Preparation and Data Analysis 85 Stoichiometric Reactions 85 Procedure A : Trans-Ru(OC?)(0)2 Oxidant 86 Procedure B: Trans-Ru(YM?)(0)2 Oxidant 86 Catalytic Aerobic Oxidations 87 Stoichiometric Oxidation of Amines with *ra/is-Ru(porp)(0)2 87 Amine Dehydrogenation Catalyzed by *ra#is-Ru(porp)(0)2 Oxidants: Porp = TMP, OCP or OCP-Cl8 97 Conclusions 100 CHAPTER V 102 CONCLUSIONS AND FUTURE WORK 102 General Conclusions 102 Future Work 104 REFERENCES 105 vii Table of Contents APPENDIX A Ill A L C O H O L OXIDATION 111 UV-VIS Spectroscopic Data Ill ' H - N M R Spectroscopic Data 115 APPENDIX B 137 A M I N E OXIDATION 137 UV-VIS Spectroscopic Data ...137 viii LIST OF TABLES Table ILL Conditions for Amine Separation by GC 27 Table H.2. Conditions for Alcohol Separation by GC 28 Table III. 1. K and ki Values for Stoichiometric Benzhydrol Oxidation by trans-Ru(TMP)(0) 2 in benzene 59 Table III.2. Oxidation of Benzhydrols Catalyzed by trans-Ru(TMV)(0)2 69 Table III.3. Oxidation of Benzhydrols by trans-Ru(porp)(0)2: The Effect of Water, Base and the Porphyrin on Alcohol Conversion 70 Table 111.4. % Conversion and Catalyst Turnover for Alcohol Oxidation Catalyzed by *raws-Ru(TMP)(0)2 Under 1 atm of Air at 50°C 73 Table III.5. The Effect of BHT and NEt 3 on Benzhydrol Oxidation 81 Table IV. 1. The Range of kobS Values Determined for Stoichiometric Oxidation of P h 2 C H N H 2 by /rarcs-Ru(OCP)(0)2 95 Table IV.2. Product Yield and Catalyst Turnover after 24 h for Amine Dehydrogenation Catalyzed by /rara-Ru(porp)(0)2 Complexes in Air 99 Table IV.3. Aerobic Dehydrogenation of P h 2 C H N H 2 Catalyzed by Trans-Ru(TMP)(0) 2: The Effect of Neutral and Basic Aqueous/Benzene Biphasic Systems 99 Table A.l. kobs Values for Stoichiometric Oxidation of Ph 2 CHOH at 25°C under 1 atm of N2 in Benzene 112 Table A.2. ko b s Values for Stoichiometric Oxidation of Ph 2 CDOH at 25°C under 1 atm of N2 in Benzene 112 Table A.3. ko b s Values for Stoichiometric Oxidation of (p-MeO-CeH^CHOH at 25°C under 1 atm of N2 in Benzene 113 Table A.4. ko b s Values for Stoichiometric Oxidation of (p-F-C6H4) 2CH0H at 25 °C under 1 atm of N 2 in Benzene 114 ix List of Tables Table A.5. - A.52. Relative Intensity of 'H-NMR Signals of Trans-Ru(TMP)(0)2 as a Function of Time Table A.5. 20°C, [Ph2CHOH] = 0.015 M 115 Table A.6. 20°C, [Ph2CHOH] = 0.053 M 115 Table AJ. 20°C, [Ph2CHOH] = 0.057 M 116 Table A.8. 20°C, [Ph2CHOH] = 0.057 M 116 Table A.9. 20°C, [Ph2CHOH] = 0.21 M 116 Table A.10. 20°C, [Ph2CHOH] = 0.21 M 117 Table A.ll. 20°C, [Ph2CHOH] = 0.20 M 117 Table A.12. 20°C, [Ph2CHOH] = 0.62 M 118 Table A.13. 20°C, [Ph2CHOH] = 0.62 M 118 Table A.14. 20°C, [Ph2CHOH] = 0.61 M 119 Table AAS. 20°C, [Ph2CHOH] = 1.2 M. 119 Table A.16. 20°C, [Ph2CHOH] = 1.2 M 120 Table A.17. 20°C, [Ph2CHOH] = 1.2 M 120 Table A.18. 20°C, [Ph2CHOH] = 1.2 M 121 Table A.19. 20°C, [Ph2CHOH] = 0.20 M, [Ph3CHOH] = 0.41 M 121 Table A.20. 20°C, [Ph2CDOH] = 0.022 M 122 Table A.21. 20°C, [Ph2CDOH] = 0.024 M 122 Table A.22. 20°C, [Ph2CDOH] = 0.40 M 123 Table A.23. 20°C, [Ph2CDOH] = 0.40 M 123 Table A.24. 20°C, [Ph2CDOH] = 0.58 M 124 Table A.2S. 20°C, [Ph2CDOH] = 0.58 M 124 Table A.26. 20°C, [Ph2CDOH] = 0.58 M 125 x List of Tables Table A.27. 20°C, [Ph 2CHOD] = 0.011 M 125 Table A.28. 20°C, [Ph 2CHOD] = 0.093 M 125 TableA.29. 20°C, [Ph 2CHOD] = 0.41 M 126 Table A.30. 20°C, [Ph 2CHOD] = 0.74 M 126 Table A.3L 20°C, [Ph 2CHOD] = 1.1 M 127 Table A.32. 35.5°C, [Ph 2CHOH] = 0.021 M 127 Table A.33. 35.5°C, [Ph 2CHOH] = 0.21 M 128 Table A.34. 35.5°C, [Ph 2CHOH] = 0.20 M 128 Table A.35. 35.5°C, [Ph 2CHOH] = 0.20 M 128 Table A.36. 35.5°C, [Ph 2CHOH] = 0.40 M 129 Table A.37. 35.5°C, [Ph 2CHOH] = 0.40 M 129 Table A.38. 35.5°C, [Ph 2CHOH] = 0.39 M 129 Table A.39. 35.5°C, [Ph 2CHOH] = 0.39 M 130 Table A.40. 50.0°C, [Ph 2CHOH] = 0.021 M 130 Table AM. 50.0°C, [Ph 2CHOH] = 0.10 M 130 Table A.42. 50.0°C, [Ph 2CHOH] = 0.11 M 131 Table A.43. 50.0°C, [Ph 2CHOH] = 0.20 M 131 Table A.44. 50.0°C, [Ph 2CHOH] = 0.21 M 131 Table A.45. 50.0°C, [Ph 2CHOH] = 0.31 M 132 Table A.46. 50.0°C, [Ph 2CHOH] = 0.30 M 132 Table A.47. 50.0°C, [Ph 2CHOH] = 0.30 M 132 Table A.48. 50.0°C, [Ph 2CHOH] = 0.42 M 133 Table A.49. 50.0°C, [Ph 2CHOH] = 0.40 M 133 Table A.50. 50.0°C, [Ph 2CHOH] = 0.40 M 133 xi List of Tables Table A.51. 25°C, [Ph 2CHOH] = 0.71 M , under 1 atm of air 134 Table A.52. 25°C, [Ph 2CHOH] = 0.075 M , under 1 atm of dry 0 2 134 Table A.53. k^s Values for Stoichiometric Oxidation of Ph 2 CHOH under 1 atm of N 2 in Benzene-d6 135 Table A.54. ko b s Values for Stoichiometric Oxidation of Ph 2 CDOH at 20°C under 1 atm of N 2 in Benzene-d6 136 Table A. 55. kobs Values for Stoichiometric Oxidation of Ph 2 CHOD at 20°C under 1 atm of N 2 in Benzene-d6 136 Table B.l. Stoichiometric Oxidation of P h 2 C H N H 2 by /ra«5-Ru(OCP)(0) 2 Under 1 atm Arat23°C 138 Table B.2. Stoichiometric Oxidation of P h 2 C H N H 2 by /rara-Ru(OCP)(0)2 under 1 a tmof0 2 . . . 138 Table B.3. Stoichiometric Oxidation of P h 2 C H N H 2 by trans-Ru(OC?)(0)2 at High Concentrations 139 xii LIST OF FIGURES Figure 1.1. Cyclic tetra-aza and naphthyridine ligands 5 Figure 1.2. Aerobic alcohol oxidation using a tri-component system 7 Figure 1.3. Iron protoporphyrin IX prosthetic group in cytochrome P-450 8 Figure 1.4. Mechanism for substrate oxidation catalyzed by cytochrome P-450; the alternate pathways utilizing (i) an O-atom donor (XO) and (ii) a peroxide are also shown 9 Figure 1.5. rran5-dioxo(porphyrinato)ruthenium(VI) complexes 11 Figure 1.6. Mechanism of amine oxidation with peroxide co-oxidants 15 Figure 1.7. Ruthenium imino ester complexes 19 Figure ILL Anaerobic UV-VIS spectroscopic cell 25 Figure III.l. A typical absorbance versus time plot for stoichiometric benzhydrol oxidation by /r<ms,-Ru(TMP)(0)2. The line, A = A«, + (Ao-A0 0)exp(-kObSt), was fit to the data using non-linear regression analysis, A*, and k^s being variables 44 Figure III. 2. ^ - N M R spectral changes in the o- and p- CH3 signals for the TMP during the stoichiometric oxidation of Ph 2 CHOH by trans-Ru(TMP)(0) 2. ([rrara-Ru(TMPXO) 2]o ~ 5 x 10"4 M and [Ph 2CHOH] = 0.015 M). Peaks identified in regular font correspond to /ra«5-Ru(TMP)(0) 2 with those labeled in italics corresponding to the /ra/7s-Ru(TMP)(OCHPh 2) 2 product 46 Figure III.3. Stoichiometric oxidation of Ph 2 CHOH by frww-Ru(TMP)(0)2 at 20°C followed by monitoring the loss in intensity of its /?-H signal using the alcohol a-CH as an internal standard. The concentration of the Ru(VI)-dioxo species was determined from this ratio. Plots of ln[/ra«5-Ru(TMP)(0) 2] versus time show straight lines, ([trans-Ru(TMP)(0) 2] 0 ~ 5 x IO"4 M , [Ph 2CHOH] = 0.015 M and t i / 2 = 5500 s). Peaks identified with regular font correspond to trans-Ru(TMP)(0) 2 with those labeled in italics corresponding to the /rara-Ru(TMP)(OCHPh 2) 2 product 47 xii i List of Figures Figure 111.4. H-NMR spectral analysis of *ra«s-Ru(TMP)(OCH(/?-MeO-C6H 4) 2) 2 illustrating that the integration of the P-CH3 (TMP) signal and J 9 - O C H 3 (alkoxy) signal is the same, showing that the Ru complex contains two alkoxo ligands 49 Figure 111.5. Linear Curie plots of changes in chemical shift (TMP protons, cf. R(TMP)(MeCN) 2) versus 1/T indicating that the Ru(IV)-bis(alkoxo) species exists in a single spin state over the temperature range of -40 to +20°C ....51 Figure 111.6. Stoichiometric oxidation of Ph 2 CHOH by /rans-Ru(TMP)(0)2 at 25 °C under 1 atm of N 2 followed by UV-VIS spectroscopy over 450-600 nm. Each spectrum represents a 15 min time interval. The corresponding ln(A-Aoo) versus time plot, for absorbance changes at 490 nm, is linear for over 75% of the reaction; [trans-Ru(TMP)(0) 2] ~ 3 x IO"4 M , [Ph 2CHOH] = 0.40 M and t i / 2 = 3090 s 53 Figure 111. 7. Plot of kobs (from UV-VIS spectroscopic data) versus alcohol concentration for the stoichiometric oxidation of (p-MeO-C 6 H4) 2 CHOH by /rara-Ru(TMP)(0) 2 in benzene at 25 °C under 1 atm of N 2 55 Figure 111.8. Plot of kobs (from UV-VIS spectroscopic data) versus alcohol concentration for the stoichiometric oxidation of Ph 2 CHOH and Ph 2 CDOH by /ra«5-Ru(TMP)(0) 2 in benzene at 25°C under 1 atm o f N 2 56 Figure 111.9. Plot of k^s (from UV-VIS spectroscopic data) versus alcohol concentration for the stoichiometric oxidation of (p-F-C 6 H 4 ) 2 C H O H by /ra«s-Ru(TMP)(0) 2 in benzene at 25°C under 1 atm of N 2 57 Figure 111.10. Plot of ko b s (from ' H - N M R spectroscopic data) versus alcohol concentration for the stoichiometric oxidation of Ph 2 CHOH, Ph 2 CDOH and Ph 2 CHOD by trans-Ru(TMP)(0)2 in benzene at 20°C under 1 atm of N 2 62 Figure 111.11. Proposed mechanism for stoichiometric alcohol oxidation by trans-Ru(TMP)(0) 2, Ru = Ru(TMP) 63 Figure 111.12. Hammett plot for stoichiometric benzhydrol oxidation from U V -VIS spectroscopic data 65 Figure 111.13. Ph 2 CHOH oxidation by trans-R\i(TM?)(0)2 from 1 H-NMR spectroscopic data at 35 and 50°C under 1 atm of N 2 in CeD6 67 xiv List of Figures Figure 111.14. Eyring plot for the stoichiometric oxidation of PI12CHOH (0.2 M) with /raws-Ru(TMP)(0)2 under 1 atm N 2 in C 6 D 6 68 Figure 111.15. Correlation of % conversion after 45 h at 50°C with the Hammett factor rjp or 2a p 72 Figure 111.16. Oxidation of Ph 2 CHOH by /ra7«-Ru(TMP)(0) 2 at 25°C under 1 atm of air or 0 2 in C6D6. The loss of trans-Ru(TMP)(0)2 was followed by measuring changes in the fi-H signal intensity using the alcohol a-CH as an internal standard. Reactions were stirred under air or 0 2 to ensure the concentration of 0 2 in solution remained constant; [><ms-Ru(TMP)(0)2] ~ 5 x 10" M and [Ph 2CHOH] = 0.071 - 0.075 M 75 Figure 111.17. 1 H-NMR spectrum obtained during Ph 2 CHOH oxidation under 1 atm of air in benzene at 25°C. Signals corresponding to trans-Ru(TMP)(OCHPh 2) 2 are shown in italics while the trans-Ru(TMP)(0) 2 signals are indicated with a regular font .77 Figure 111.18. ' H - N M R spectra for (p-MeO-C 6 H 4 ) 2 CHOH oxidation by trans-Ru(TMP)(0) 2 in C6D6 under 1 atm of air at 50°C in the presence of NEt 3 ; [rm«5-Ru(TMP)(0) 2] = 4.8 x 10"4 M , [(p-MeO-C 6 H 4 ) 2 C H 0 H ] = 0.075 M and [NEt3] = 0.014 M ; % conversion and [turnover] data after 24 h are: 8% and [13] 79 Figure 111.19. Figure IV.l. 1 H-NMR spectra for (p-MeO-CeH^CHOH oxidation by trans-Ru(TMP)(0) 2 in a biphasic CeD6/H 20 system under 1 atm of air at 50°C in the presence of NEt 3 ; [/raw,y-Ru(TMP)(0)2] = 4.8 x 10"4 M , [0>MeO-C 6H 4) 2CHOH] = 0.072 M and [NEt3] - 0.014 M ; % conversion and [turnover] data after 24 h are: 21% and [31] 79 Plots of absorbance, at 420 nm, versus time for the stoichiometric oxidation of P h 2 C H N H 2 with rrarts-Ru(OCP)(0)2 in dry benzene at 23 °C under Ar. Essentially repeat experiments, run at the same amine concentration, do not show reproducible absorbance changes 88 xv List of Figures Figure IV. 2. Figure IV.3. Figure IV.4. Pseudo first-order plots of ln|A-A«,| versus time for the stoichiometric oxidation of P h 2 C H N H 2 at 23 °C under 1 atm of Ar; [trans-RuCTM?)(0)2] ~ 5 x IO"6 M and [Ph 2CHNH 2] = 0.0025 M 89 Plot of kobs against [Ph2CHNH2] for reactions at 23 °C under 1 atm Ar in dry benzene; non-reproducible results are evident 89 A typical absorbance (at 420 nm) versus time plot for P h 2 C H N H 2 oxidation with fr*am,-Ru(OCP)(0)2 under 1 atm of O2 in dry benzene at 23°C. The line for pseudo first-order kinetics, A = A^, + (A0-Aoo)exp(-kobSt), was fit to the data using non-linear regression analysis; [trans-Ru(OC?)(0)2] = 5.1 x IO - 6 M and [Ph 2CHNH 2] = 1.3 x 10" 3 M .90 Figure IV. 5. Figure IV. 6. Plot of kobs versus [Ph2CHNH2] under O2 and Ar in dry benzene at 23 °C 91 Absorbance changes at 510 nm monitored during the stoichiometric reaction of trans-Ru(OC?)(0)2 with Ph2CHNH2 in CHCI3 under 1 atm of Ar at 23°C; [trans-Ru(OC?)(0)2] ~ 2 x 10"4 M 93 Figure IV. 7. Figure IV.8. Figure IV.9. Figure IV.10. Typical spectral changes observed over 480-570 nm for the oxidation of P h 2 C H N H 2 by fra«s-Ru(OCP)(0)2 under 1 atm of Ar at 23 °C in CHCI3. The reaction was run in the presence of a 200-450 nm filter and the UV-VIS cell was wrapped in A l foil to block out ambient light; [/ra«5-Ru(OCP)(0)2] = 4.9 x 10"4 M and [Ph 2CHNH 2] = 9.7 x 10"3M 93 Absorbance changes at 510 nm during the stoichiometric reaction of trans-Ru(OC?)(0)2 (5 x 10"4 M) with P h 2 C H N H 2 in CHC1 3 under 1 atm of Ar at 23°C. The anaerobic cell was wrapped in A l foil, and a 200-450 nm filter was placed between the source and sample in order to limit the effects of ambient room light and prevent absorbance within the Soret (420 nm) region of the spectrum 94 A ln|A-Aoo| versus time plot based on absorbance data at 510 nm collected at [Ph 2CHNH 2] ~ 0.0097 M for amine dehydrogenation by /rara-Ru(OCP)(0)2 in CHC1 3 94 Absorbance at 508 nm versus time plots for the stoichiometric oxidation of /PrNH 2 by /mra-Ru(TMP)(0) 2 at 23 °C under 1 atm of Ar in dry C 6 H 6 ; [trans-RaCIM?)(0)2] = 3.2-3.5 x 10"4 M and [/PrNH2] = 7.8 x 10"3 M 96 xvi List of Figures Figure IV.ll. Figure A. 1. Figure A. 2. Figure B.L Absorbance at 506 nm versus time plots for the stoichiometric oxidation of rac-Ph(Me)CHNH 2 by trans-Ru(TM?)(0)2 at 23°C under 1 atm of Ar in wet C 6 D 6 ; [trans-Ru(TMP)(0)2] = 1.8-2.8 x 10 - 4 M and [rac-Ph(Me)CHNH2] = 1.4 x IO"2 M 96 Typical absorbance versus time plots for spectral changes at 490 nm measured by UV-VIS spectroscopy for the stoichiometric oxidation of Ph 2 CHOH by /ra«s-Ru(TMP)(0) 2 under 1 atm of N 2 in benzene at 25°C I l l Semilog and Guggenheim plots for the above reaction at [Ph 2CHOH] = 0.211 M . Aoo was determined from a computer fit of the absorbance versus time data (these Aoo values were in agreement with those expected from the known extinction coefficients of the products) I l l Comparison of a ln|A-Aoo| versus time plot (Aoo determined from non-linear regression analysis of an absorbance at 420 nm versus time plot) with a Guggenheim analysis of the absorbance data for the oxidation of Ph 2 CHOH by /ra«s-Ru(OCP)(0) 2 under 1 atm of 0 2 in dry benzene at 23°C 137 xvii LIST OF ABBREVIATIONS % conversioriH % conversionx 5 AH,* ASi* 14- T M C 15- T M C 16- T M C A Aoo A 0 atm BHT bpy br cone, d % conversion of benzhydrol % conversion of a p-X substituted benzhydrol chemical shift extinction coefficient Hammett factor enthalpy of activation wavelength of maximum absorbance Hammett factor entropy of activation 1,4,8,11 -tetramefhyl-1,4,8,11 -tetra-azacyclotetradecane 1.4.8.12- tetramethyl-1,4,8,12-tetra-azacyclopentadecane 1.4.8.13- tetramefhyl-1,4,8,13-tetra-azacyclohexadecane absorbance absorbance at t = oo absorbance at t = 0 s atmosphere(s) 2,6-di(/-butyl)-4-methylphenol bipyridine broad concentrated doublet xviii List of Abbreviations dd doublet of doublets DMSO dimethylsulfoxide expt. experiment(s) eq. equation(s) equiv. equivalent(s) F A B fast atom bombardment FID flame ionization detector GC gas chromatography GC-MS gas chromatography coupled with a mass spectrometer as a detector HPLC high performance liquid chromatography Hz Hertz IR infrared K equilibrium constant ki rate constant for the rate determining step kobs pseudo-first order rate constant L ligand m multiplet M" negative ion parent peak M + positive ion parent peak T W - C P B A w-chloroperbenzoic acid m.p. melting point MeOTPP me50-tetra(3,4,5-trimethoxyphenyl)porphyrin (dianion) xix List of Abbreviations MS mass spectrometry N A D P H nicotinamide adenine dinucleotide phosphate (reduced form) N M O N-methylmorpholine N-oxide N M R nuclear magnetic resonance OAc acetate OCP /weso-tetra(2,6-dicWorophenyl)porphyrin (dianion) OCP-C18 we50-tetra(2,6-dichlorophenyl)-/?-octachloroporphyrin (dianion) OEP yS-octaethylporphyrin (dianion) PhTNTs (4-methylphenyl)sulfonyliminoiodobenzene porp porphyrin dianion R alkyl or aryl group r.t. room temperature rac- racemic Ru Ru(porp) s second(s) or singlet salen bis(salicylaldehyde)efhylenediamine t triplet or time ti/2 half-life TBAP tetra(n-butyl)ammonium perruthenate TBHP /-butylhydrogen peroxide TBPP mes0-tetra(4^butylphenyl)porphyrin (dianion) TLC thin layer chromatography xx List of Abbreviations TMP we50-tetramesitylporphyrin (dianion) TMS tetramethylsilane TPAP tetra(«-propyl)ammonium perruthenate TPP meso-tetraphenylporphyrin (dianion) Ts 4-methylphenylsulfonyl or tosyl UV-VIS ultraviolet-visible X /»-substituent xxi ACKNOWLEDGMENTS Well it has been two years of hard work and I definitely would not have made it without some help. I would like to thank both Liane and Marietta who gave invaluable tips to make life easier in running the N M R spectrometers. Thanks also go to all of the James Gang for aiding me when the research was not going quite as planned! The final copy of my thesis would not have been quite so polished if it had not been for the work of my supervisor, who also deserves commendation for being so patient with my many mistakes. Finally...thanks Craig for keeping me sane!! xxii CHAPTER I INTRODUCTION The oxidation of organic substrates is a fundamental reaction in organic chemistry, whether it is performed on an industrial or laboratory scale.1 At present, however, many reactions commonly use stoichiometric amounts of toxic metal oxidants, high temperatures and are plagued by low selectivities.1 ,2 ,3 Due to environmental demands and the need for efficient, highly selective product formation, performing these reactions catalytically, under mild conditions and using inexpensive oxidants has become a important objective. Since the first use of R u 0 4 as an oxidant in 1953,4 Ru-oxo complexes have gained attention as versatile compounds for the oxidation of a wide range 15 8 of substrates including, olefins, hydrocarbons, sulfides, alcohols and amines. ' " This versatility coupled with the fact that the oxidation reactions can be made catalytic under mild conditions6 has stimulated efforts to develop Ru-oxo complexes as the ideal oxidation catalyst. The following chapter presents a brief review on the application of Ru-oxo complexes to oxidation reactions, focusing on recent developments in alcohol and amine catalytic oxidations. Alcohol Oxidations Ruthenium oxo species are well known for their ability to oxidize primary and secondary alcohols to aldehydes, carboxylic acids and ketones, as is evidenced by their inclusion in several reviews written on oxidation chemistry. ' In most cases Ru-oxo species are the active catalysts although the pre-catalysts may be non-oxo ruthenium 1 Chapter I 2 complexes.8 Often a stoichiometric amount of an oxygen atom donor such as: amine N -oxide, iodosobenzene, peroxide or dioxygen and a 2-equivalent reductant like an aldehyde, is required for catalysis; however, catalytic aerobic oxidation using only pure dioxygen or air as the co-oxidant is also possible. Alcohol oxidations by Ru complexes are discussed in the following sections according to the nature of the Ru complex and the type of co-oxidant used. Non-porphyrin Ruthenium Oxidants Reactions Catalytic in the Presence of NMO (N-methylmorpholine-N-oxide) Some of the best known Ru-oxo complexes involved in alcohol oxidation are the perruthenates, TBAP (tetra-H-butylammonium perruthenate) and its more easily prepared TPAP (tetra-«-propylammonium perruthenate) analogue. In the presence of N M O these [Ru V I I(0)4]" species will oxidize primary and secondary alcohols to aldehydes and ketones without affecting allylic, epoxy, lactone, indole, acetal and ether functionalities. Molecular sieves (4 A) are required to absorb any water present in the reaction mixture. The reactions occur at room temperature (r.t.) and yield a maximum 500 turnovers (moles of substrate consumed per mole of catalyst used).6 Mechanistic studies, in acetonitrile, show the reaction to be first-order in both the catalyst and alcohol and fractional order in N M O . 6 ' 9 The reaction is thought to proceed via the initial formation of a catalyst-substrate complex which then undergoes a rate deteraiining reaction with N M O to yield a second complex which rapidly forms the ketone products. Oxidation of cyclobutanol Chapter I 3 yields mainly cyclobutanone indicating a 2-electron oxidation process occurs in the rate-determining step.6 Two of the oxygen atoms of perruthenate can be replaced with chlorine or nitrogen donors, without the loss of catalytic activity for alcohol oxidation. In addition, the chlorinated complex, [Ru(0)2Cl3]~, will oxidize phosphines, thioethers, alkenes and phenols. These complexes function stoichiometrically as 2- or 4-electron oxidants (with halogen and nitrogen donors, respectively) and will oxidize alcohols to aldehydes or ketones with up to 135 turnovers. The use of chelating nitrogen donors, such as bipyridine, limits the use of the complex to stoichiometric oxidation only. Of note, the majority of the halogenated or nitrated dioxo complexes have trans-oxo ligands. When a carboxylate group is incorporated amongst the ligands a c/s-dioxo orientation is exhibited. These [RuVII(0)2(OCOR)Cl2]" complexes selectively oxidize alcohols to aldehydes and ketones in the presence of double bonds. Oxidation of phosphines and thioethers also occurs.6 Mechanistic studies show conflicting results, indicating a first-order dependence on the catalyst and either fractional or first-order dependence on each of the alcohol and N M O . 9 ' 1 0 Tony et al. have proposed that the varying alcohol dependence results from the pre-association of the catalyst and alcohol.9 A few monooxoruthenium(IV) complexes are known; however, they are poorer oxidants than their corresponding dioxo analogues and will only catalytically oxidize activated benzylic alcohols.6 Chapter I 4 Reactions Catalytic in the Presence ofTBHP (X-Butyl Hydrogen Peroxide) With a three-fold excess of TBHP over the substrate, commercially available RuCl3#nH20 will oxidize secondary alcohols to ketones with up to 550 turnovers at 80°C. n A Ru(III) N,N',N"-trimethyl-l,4,7-triazacyclononane derivative is capable of oxidizing activated allylic and benzylic alcohols to the corresponding aldehydes or ketones at r.t. Secondary aliphatic alcohols are also oxidized though only with 1/10 of the turnovers for the activated alcohols. Mechanistic studies indicate that the oxidation is probably a 2-electron process in that cyclic alcohols were oxidized to cyclic ketones; a 12 Ru-O-O-fBu complex was proposed as the active species. Reactions Catalytic in the Presence of Halogenated Co-oxidants: CIO4, BrOi and IO4 The well-defined R u 0 4 complex will catalytically oxidize a host of substrates in the presence of halogenated co-oxidants. Studies have indicated that the complex is a stoichiometric 5-electron acceptor, forming Ru(III) final products, with hydride transfer proposed as the rate-determining step.6 In the presence of bromate, Ru0 4" will oxidize alcohols to acids and ketones in good yields and turnovers, though the reaction is non-selective and any double bonds present are cleaved.6 The perchlorate salts of several cationic trans-[Ru(L)2(0)2] and trans-[RuL'(0)2J2+ complexes, where L and L' are aromatic, 2- or 4-atom nitrogen donor ligands, respectively, have been studied as stoichiometric oxidants. A large amount of Chapter I 6,13 work has been focused, in particular, on the use of cyclic tetra-aza ligands (Figure 1.1) Tellurato or iodato /rara-Ru(0)2(bpy) complexes will catalyze the formation of aldehydes and ketones from alcohols at r.t, with up to 113 turnovers 14 ;N N; N N / / W \ l \ / N N N / I | \ \ l 1 / N N N N /\ | \ 14-TMC 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane 15-TMC 1,4,8,12-tetramethyl-1,4,8,12-tetra-azacyclopentadecane 16-TMC 1,4,8,13-tetramethyl-1,4,8,13-tetra-azacyclohexadecane 1,8-naphthyridines: R = H, Cl, OMe, NH 2 , N=N-Ph Figure Ll. Cyclic tetra-aza and naphthyridine ligands 6,15 Recently, Boelrijk et al. have shown that the binuclear [{Ru(H20)L2}20] complexes, where L is 1,8-naphthyridine or its derivatives (Figure 1.1), are capable of catalyzing oxidations of primary and secondary alcohols in aqueous solution. With a BrCV co-oxidant, turnovers of 800-900 are achieved at r.t. Unfortunately the selectivity of the system is low as acid, aldehyde and double-bond cleavage products are obtained for the oxidation of allylic alcohols.15 Chapter I 6 Using O2 as the Co-oxidant Air or O 2 is the ideal oxygen source as it is inexpensive, readily available and only generates water as the reduced by-product, in contrast to the previously discussed co-oxidants. Unfortunately, the number of non-porphyrin systems that will catalytically oxidize alcohols using dioxygen as the co-oxidant is limited. One of the first reported was by Tang and co-authors, in 1978, when they determined that RuCb would catalyze ketone formation from secondary alcohols under of 2-3 atm of O 2 at 100°C. The reactions, however, take 95-100 h and do not go to completion, forming olefin side-products in up to 50% yield. A maximum of 44 turnovers is achieved for the oxidation of octan-2-ol.16 Subsequent studies by Matsumoto and Watanabe17 and Drago's group18 indicate that aerobic alcohol oxidation also occurs with R u 0 2 » H 2 0 and the trinuclear ruthenium carboxylate complexes [Ru30(02CR)6L.3]n (R = C H 3 , C2H5; L = H 2 O , PPI13; and n = 0, 1+). In both cases temperatures of 65-70°C are required. Low turnovers of ~ 4 are achieved with Ru02*H20, while 1000 turnovers are possible with the trinuclear ruthenium species under 3 atm of O 2 after 143 h. 7Va«5-dioxoruthenium(VI) complexes with pyridine or T M C ligands will also promote aerobic oxidation of alcohols, though with low turnovers of 12 and 2.8, respectively, at r.t. over 18 h. 6 More recently, it was determined that TPAP would also catalyze the aerobic oxidation of alcohols in 60-99% yield at r.t. in CH 2 C1 2 over 30-60 min. 1 9 ' 2 0 Catalyst concentrations of 5-10 mol% give optimum yields, lower concentrations resulting in deactivation of the catalyst after 10-20 turnovers. Switching the solvent to toluene allows oxidation at a catalyst concentration of 1 mol%; however, the reaction now takes 18 h to reach an equivalent, optimum, Chapter I 7 conversion. As with TPAP oxidations with N M O , 4 A molecular sieves are required to absorb the H2O co-product for the oxidation of secondary alcohols. In contrast, primary alcohols are oxidized to aldehydes in higher yields in the absence of sieves.1 9'2 0 Other non-oxo Ru complexes have also been investigated for aerobic alcohol oxidation. In some tri-component systems, a Co-salen complex acts as the oxygen activating complex while a Ru complex is used to dehydrogenate the alcohol. The two components link the dehydrogenation of the substrate to the reduction of dioxygen to water using a quinone co-catalyst (Figure 1.2). Reaction temperatures range from 20°C with RuCl(OAc)(PPli3)2 to 65-100°C with a binuclear Ru-carbonyl derivative. Turnovers of 70 and up to 200 based on Ru, respectively, are achieved. OH PPh3 Figure 1.2. Aerobic alcohol oxidation using a tri-component system. Chapter I 8 Ruthenium Porphyrin Oxidants Cytochrome P-450: Nature's Oxidant Metalloporphyrins have received attention as oxidation catalysts based on a relation to cytochrome P-450, an enzyme able to catalyze selectively the Cvoxidation of a range of organic compounds under ambient conditions. This monooxygenase enzyme, first isolated from bacteria in 1970, has been found in a wide range of organisms from bacteria to humans, and functions as a catalyst in the oxidation of substrates under aerobic conditions in the presence of an electron source (NADPH). The active oxidation site in cytochrome P-450 is an iron(III) protoporphyrin DC (FePpDC) complex that is bound to the protein through the sulfur atom of a cysteine thiolate residue (Figure I.3). 2 2 a Figure 1.3. Iron protoporphyrin IX prosthetic group in cytochrome P-450.^ Oxygen binds to the metal centre and leads to the formation of the active oxidizing species (PpIX* +)Fe 1^(0), which transfers the oxygen atom to a substrate to regenerate the starting Fe i n(PprX) moiety.2 2 b The substrate itself is not bound directly to the iron cysteine Chapter I centre but is held within the hydrophobic pocket formed by the amino acid residues that surround the active site.2 2 0 The proposed catalytic cycle for substrate oxidation is shown below; however, only the first three steps of the mechanism have been spectroscopically verified while the remaining steps occur too rapidly to be distinguished (Figure 1.4) 22 substrate (PpIX)Fe111 substrate-O (PpIX*+)FeIV substrate H 2 0 2H + X O o22-(PpIX)Fem substrate (PpIX)Fe11 substrate (PpIX)Fem(0-0) 2- substrate (PpIX)Fen(0-0) substrate Figure 1.4. Mechanism for substrate oxidation catalyzed by cytochrome P-450; the alternate pathways utilizing (i) an O-atom donor (XO) and (ii) a peroxide 99 are also shown. Chapter I 10 Synthetic Ruthenium Porphyrins Several metal based porphyrin systems, including Fe, Mn and Ru have been studied in an effort to simulate the activity of cytochrome P-450 in vitro?2 Ruthenium has the distinction of forming metalloporphyrin oxidation catalysts that exhibit true dioxygenase character and transfers both oxygen atoms of O2 to the substrate without the use of additional co-reductants. Fe- and Mn-based systems will also oxidize substrates under 23 O2; however, only in the presence of an electron source such as NaBFLt or ascorbate. Synthetic porphyrins, in contrast to naturally occurring porphyrins such as protoporphyrin IX, are generally substituted at the bridging carbon rather than on the pyrrole rings (octaethylporphyrin, H2OEP, is one exception). Three generations of porphyrin molecules have been described when their use as ligands in Ru porphyrin oxidations are discussed.23 The first generation is we^o-tetraphenylporphyrin (H2TPP) and its alkyl-derivatives. Unfortunately, Ru(TPP) species are unstable under oxidizing conditions and decompose to form the p-oxo 'dimer' [Ru(TPP)(OH)]20. Methyl group substitution at the ortho and para positions on the meso-phenyl rings forms the more stable meso-tetramesitylporphyrin (H 2 TMP), allowing isolation of a trans-dioxorutheniumfVI) (/r<ms-Ru(TMP)(0)2) complex (Figure I.5). 2 4 a The second and third generation of porphyrins have halogenated phenyl substituents and pyrrole rings, respectively.24 Like H2TMP, these porphyrins, such as weso-tetra(2,6-dichlorophenyl)porphyrin (H 2OCP) and /we.«?-tetra(2,6-dichlorophenyl)-/?-octachloroporphyrin (H 2OCP-Clg), form isolable trans-dioxo complexes (Figure I.5).24 Chapter I 11 Interestingly, chlorinating the pyrrole positions of the porphyrin leads to saddle and ruffle distortions of the porphyrin plane in both the free-base and the corresponding Ru(porp)CO complexes. Figure 1.5. rrfln5-dioxo(porphyrinato)ruthenium(VI) complexes. 7rara-dioxo(porphyrinato)ruthenium(VI) complexes (porp = TMP, OCP, OCP-Clg), synthesized from T W - C P B A oxidation of Ru(porp)(CO) complexes, aerobic oxidation of /ram'-Ru(porp)(L)2 complexes (L = M e C N , 5 ' 2 6 THF , 2 7 or N 2 2 8 ) , or oxidation of trans-Ru(porp)(THF)2 with N 2 0 , 2 9 exhibit rich oxidation chemistry. The dioxo complexes will catalytically oxidize olefins to epoxides,5'24 thioethers to sulfoxides,5 tertiary arylphospines, AsPh 3 and SbPh3 to the corresponding oxides,3 0 alcohols to aldehydes and ketones,31'32 Ph 3 CH to P h 3 C 0 H , 3 2 and amines to imines and nitriles.33 The stoichiometric oxidation of phenols to quinones is also possible.24 Chapter I 12 Reactions Catalytic in the Presence of Amine N-oxides The first highly efficient oxidation of alcohols to aldehydes and ketones catalyzed by Ru porphyrin complexes was published by Ohtake et al. in 1991.3 4 Heteroaromatic amine N-oxides are used as the co-oxidants to oxidize primary allylic and benzylic alcohols to aldehydes in 65-90% yield (non-activated alcohols gave only 2% yield of the corresponding aldehyde) at r.t. Catalyst turnovers are within the range of 110-150. Subsequent research by the same authors indicates that the addition of concentrated HBr or HC1 and molecular sieves to the reaction mixture allows even non-activated secondary alcohols to be readily oxidized. 3 5 After 24 h at r.t., ketones are formed selectively in 80-90%o yield, with catalyst turnovers of 160-180. Interestingly, hydroxylation of alkanes, using N-oxide co-oxidants, is also catalyzed by Ru(TMP)(0)2, Ru(TMP)(CO) and Ru(TPP)(CO) with turnovers up to 120000 over a period of 6 h at 40°C (5.6/s). Under these conditions, Ru(TPP)(CO) is actually the best catalyst. The acid is thought to react with the Ru porphyrin precursors to form bromo/chloro species; the acid then, perhaps, accelerates the deoxygenation of the N-oxide co-oxidant by the Ru porphyrins to form the proposed active catalytic species /rara-Ru(porp)(0)(X) (X = C l , Br), although other formulations are feasible.24 Catalytic Aerobic Oxidations with Ruthenium Porphyrins At 50°C under 1 atm of air, fr-<m?-Ru(porp)(0)2, where porp = TMP or OCP, 31 3 2 3 6 catalyze the aerobic oxidation of alcohols to aldehydes and ketones. ' ' Water or K O H (3 M) is essential for the catalytic activity of the complexes in 2-phase aqueous/benzene Chapter I 13 media. Complete conversion occurs for benzylic alcohols after 16 h, showing catalyst turnovers of 200; however, the oxidation of inactivated alcohols is much slower and shows only 8-20% conversion and 16-40 turnovers after 16 h. Both the TMP- and OCP-based complexes are equally active towards alcohol oxidation, though bleaching of the OCP system occurs after 16 h indicating catalyst deactivation. In contrast, the TMP-based system still shows some catalytic activity after 10 days. Kinetic studies for the stoichiometric oxidation of z'PrOH with /ram ,-Ru(TMP)(0)2 (eq. 1.1) indicate that the reaction is first-order in both the catalyst (lO^-lO" 3 M) and substrate (up to 0.3 M). A paramagnetic (S = 1), /ra«s-Ru(TMP)(OCH(CH3)2)2 complex, isolated from the stoichiometric reactions and characterized by N M R , IR, UV-VIS spectroscopies and X -ray crystallography, is proposed to be an intermediate in the aerobic oxidation of the alcohol. Finally, kinetic isotope labeling studies on the stoichiometric reaction show an intramolecular isotope effect of ~ 2 attributed to a-CH bond cleavage which, when combined with an increased rate of reaction in the presence of added base, indicates that hydride transfer is probably the rate-controlling step. Of note, at high concentrations of /PrOH (1-2 M) the kobs vs. [/PrOH] plot levels off, where kobs is the measured pseudo first-order rate constant for loss of /ra«s-Ru(TMP)(0)2 in eq. 1.1. Ru(TMP)(0) 2 + 3/PrOH -> Ru(TMP)(0/Pr) 2 + Me 2 C=0 + 2 H 2 0 (1.1) Chapter I 14 These results were attributed to solvent effects, rather than saturation kinetics, as the oxidation of j'PrOH in the presence of high concentrations of rBuOH (an alcohol inert 31 32 36 to oxidation) had a lower kobs than the oxidation of /PrOH in the absence of rBuOH. ' ' Further work, in this thesis, has attempted to confirm these results and study the effect of changing steric and electronic factors of the substrate on the rate of alcohol oxidation. Amine Oxidations Amine oxidations are important reactions from both synthetic and metabolic perspectives. In living systems, amines are oxidized by a variety of enzymes, including cytochrome P-450, amine oxidase and flavoenzymes.1 Cytochrome P-450, in particular, will catalyze the formation of N-oxides and N-dealkylated or N-dehydrogenated products from amines.37 Understanding the mechanisms of these reactions is important in the metabolism of both naturally occurring amines and xenobiotics.38 Amine oxidations are also important in the synthesis of biologically active compounds, including antibiotics. Because of the versatility of Ru complexes in the catalytic oxidation of a variety of organic substrates, extending their application to amine oxidation was a logical step. Non-Porphyrin Ruthenium Oxidants Reactions Catalytic in the Presence of NMO, PhIO and Peroxides Tertiary amines are oxidatively N-demethylated by Ru catalysts, at r.t., in the presence of peroxides, T B H P 4 0 and H 2 0 2 . 4 1 The reactions are thought to proceed through the formation of an iminium intermediate which is then trapped to give the corresponding Chapter I 15 a-substituted alkylamine (Figure 1.6). In the presence of TBHP (2-3 equiv.), a RuCl 2(PPh 3) 3 catalyst (3 mol%) will oxidize a range of tertiary N-methylanilines to N- f -butyldioxymethylanilines in 80-95% yield. With H 2 0 2 (1.5-4 equiv.), the reactions are performed in MeOH with RuCl 2(PPh 3) 3 or RuCl 3 «nH 2 0 (5 mol%) to yield 55-87% of the tertiary N-methoxymethylanilines. In both systems, treatment of the trapped products with aqueous HC1 results in the formation of N-demethylated amines. R u n / B u O O H R u I V ==0 \ / N - C H 3 H 2 C = N ^ R u i ( O H ) \ f B u O O H N — C H j O O / B u + R u 1 1 + H ^ O Hp2 R u m H 2 0 1— R u v = = 0 \ + ^ N = C H 2 R u ^ O H ) C H 3 O H N — C H 2 O C H 3 + R u m + H 2 0 Figure 1.6. Mechanism of amine oxidation with peroxide co-oxidants 1,41 The same catalyst, RuCl 2(PPh 3) 3 , will oxidize activated secondary amines to imines in 55-98% yield. Both T B H P 4 2 and PhIO 4 3 co-oxidants have been used. In the absence of an activating phenyl ring or double bond, a to the C-H bond being cleaved, oxidation does not occur. Activated primary amines are also oxidized by the catalyst and PhIO, though, in low yields, 15-40%. In these reactions, the imine intermediate is hydrolyzed to give aldehyde and ketone products.43 More recently, Goti and co-workers have determined that the use of TPAP in oxidation reactions may also be extended to include amine substrates. Tertiary Chapter I 16 hydroxylamines are oxidized to nitroenes, in 75-100% yield, using N M O co-oxidant. The reactions occur at r.t., in the presence of 4 A molecular sieves, with 1-5 mol% of the catalyst and a minimum of 1 equiv. of N M O . Under similar reaction conditions, TPAP will oxidize activated secondary amines to imines in 52-95% yield. 4 5 Imine formation by TPAP-catalyzed amine oxidation has recently been applied to the synthesis of pyrrolo[2, l-c][ 1,4]benzodiazepine antibiotics.39 The mild conditions, absence of side-product formation, non-aqueous work up and minimized racemization during the reaction were the main advantages for the use of this method of imine synthesis. Aerobic Amine Oxidations In 1978, Tang et al. first reported that aerobic oxidation of amines was possible using Ru catalysts.16 Under 2-3 atm of 0 2 at 100°C in toluene, RuCl 3«nH 20 oxidizes benzyl- and H-butylamines to the corresponding nitriles and amides with 90-100% conversion. Ketones, N-alkylimines and uncharacterized high boiling compounds are the products of the oxidation of 2-aminoalkanes, in 70% conversion. The reaction is thought to proceed through the formation a Ru(III) hydride species created from /^hydride elimination within a Ru(III) amine complex.1 6 (The first example of /2-hydride elimination from an amine was recently demonstrated within an Ir complex.)46 Aerobic oxidation of benzyl- and w-butylamine is also effected by a RuCl2(PhCH2NH2)2(PPli3)2 catalyst to form the corresponding nitriles at r.t. under 1 atm of 0 2 ; based on a study of these reactions it is proposed that 0 2 oxidizes the Ru(II) to Ru(III), with subsequent dehydrogenation of the amine and regeneration of Ru(II).47 Secondary amines are Chapter I 17 oxidized to imines and imine hydrolysis products by RuCl2(PPh 3) 3 and cis-RuCb(DMS0)4 at 80°C in toluene under a constant flow of 0 2 ; these catalysts are not AQ very active and only oxidize dibenzylamine in 35% conversion. Tertiary amines are stoichiometrically N-demethylated by cationic [Ru(bpy)2(0)(PR3)](C104)2 complexes (bpy = 2,2'-bipyrindine, R = Ph or Et) under an inert atmosphere to form N-methylaniline and formaldehyde;49 the kinetics of the reaction with N,N-dimethylaniline indicate a first-order dependence on both the complex and substrate, and in MeCN a [Ru(bpy)2(PR3)(MeCN)]2+ complex is formed. The reaction is assumed to proceed through the transfer of an oxygen atom from the Ru(IV) complex to the substrate, with the final inclusion of oxygen in the formaldehyde co-product. Under 1 atm of O2 in non-coordinating solvents, the reaction is catalytic with [Ru(OH2)(bpy)2(PPh3)](C104)2; at r.t. with 0.1 mol% of the catalyst, N,N-dimethylaniline is demethylated to form N-methylaniline and formaldehyde exclusively. As the stoichiometric and catalytic reactions generated the same products, it was proposed that the (oxo)ruthenium(IV) complex, formed from the reaction of the Ru(II) precursor with O2, is the active catalyst.49 Ruthenium Porphyrin Oxidants Despite the well known use of Ru porphyrins as oxidants of organic substrates,24 little work has been published on their use in the dehydrogenation of amines. The first example was reported in 1992 by Huang et al. who found that trans-Chapter I 18 dioxo(meso-tetra(3,4,54rimethoxyphenyl^ complexes (trans-Ru(MeOTPP)(0)2) would dehydrogenate diphenylamine 'stoichiometrically' to form a bis(diphenylamido)ruthemum(IV) complex.5 0 This complex is stable in solution, can be purified by column chromatography and recrystallized from CH2CI2 and heptane solvents. The complex was characterized by UV-VIS, IR and 1 H-NMR spectroscopies. Elemental analysis was also performed on the complex, but was not reported. Interestingly, in * 51 * 31 contrast to known paramagnetic dihalogeno- and dialkoxoruthenium(IV) complexes, the bis(diphenylamido) complex is diamagnetic, similar to dialkyl- and diaryl(porphyrinato)ruthenium(IV)52 complexes. The absence of N - H stretches and a band at 1012 cm" in the Ru oxidation state region ' confirms the amido and Ru(IV) nature of the complex.5 0 More recently, Morice et al. have reported the stoichiometric dehydrogenation of TO amino esters by /raHS-dioxoratheruum(VI) picket-fence type porphyrin complexes. In this case, Ru(II) imino ester complexes are isolated in 44-55% yields (Figure 1.7). The reactions are performed in an excess of amino ester at r.t. under an inert atmosphere. The resulting imino ester complexes can be purified by column chromatography and are characterized by IR, UV-VIS and 1 H-NMR spectroscopies, the N M R data indicating two different axial ligands. The presence of the imino ester ligand is confirmed by the presence of a singlet for the N - H proton and one for the a-Me substituent within the alanine methyl ester species, and two doublets (J = 20 Hz, N H and CH) for the 1 38 corresponding glycine methyl ester complex, in the H-NMR data. Chapter I 19 R = CH 3 (alanine) R = H (glycine) R = CH(CH3)2 (valine) R = CH2CH(CH3)2 (leucine) R = CH2Ph (phenylalanine) Ph C F 3 picket-fence type porphyrin Figure 1.7. Ruthenium imino ester complexes. The first dehydrogenation of amines catalyzed by Ru porphyrins was reported by Bailey and James.33 Primary amines of the form RCH2NH2 (R = aryl or alkyl) are quantitatively converted to nitriles at 50°C under 1 atm of air in benzene after 24 h. In contrast, primary, of the type R2CHNH2 (R = aryl), and secondary amines are oxidized to imines in 75-90% yield, whereas R 2 C H N H 2 amines (R = alkyl) form imines only in low yields of 10-20%. With the exception of the synthesis of nitriles, all of the reactions show side-products due to imine hydrolysis. The three dioxo complexes, fraHS-Ru(TMP)(0)2, trans-Ra(OCP)(0)2 and trans-Ru(OCP-Cl%)(0)2, were used in the investigation, with the chlorinated catalysts showing faster rates of reaction and deactivation. A bis(benzylamine) complex, isolated from the /ra«5,-Ru(TMP)(0)2-catalyzed oxidation of benzylamine and characterized by X-ray crystallography, UV-VIS, IR and ' H - N M R spectroscopies, indicates bis(amino)ruthenium(II) complexes are the final Ru products. Chapter I 20 The observation of N - H stretches at 3028 cm"1 and a Ru(II) oxidation state marker 2 6 , 2 7 at 1000 cm in the IR spectrum confirm the presence of the amine ligands. Kinetic and mechanistic details of these reactions are unknown and were sought as a part of this work. Ruthenium porphyrin imido complexes can be synthesized directly from (i) the reaction of PhTNTs ((4-methylphenyl)sulfonyliminoiodobenzene) with Ru(porp)(CO)(MeOH) (porp = TPP or OEP), 5 3 (ii) the reaction of Ru(porp)(Cl)2 (porp = me5,o-tetra(4-r-butylphenyl)porphyrin, TBPP) with j9ara-substituted anilines,54 and (iii) by the bromine oxidation of Ru(porp)(/BuNH2)2 (porp = TPP or MeOTPP). 5 5 In the first case, a bis(tosyl)imidoruthenium(VI) complex was isolated and characterized. The NTs group can be transferred to alkenes to form aziridines and the complex will oxidize benzyl alcohol to benzaldehyde in 95% yield. The Ru(IV) complex Ru(TBPP)(NR) isolated from the second reaction will react with PPI13 to give RN=PPli3 and the bis(phosphine)ruthenium(II) complex. This imido complex is paramagnetic, with a magnetic moment corresponding to two unpaired electrons. In the presence of PhIO, the imido complex will also catalyze the epoxidation of styrene in 25% yield. The third reaction forms diamagnetic fra7w-Ru(porp)(0)(N/Bu) complexes that will react with PPI13 to form 0=PPh 3, ?BuN=PPh3 and Ru(porp)(PPh3)2. The corresponding bis(imido) complexes were not formed, possibly due to hydrolysis to form the more stable oxoimido complexes. Chapter I 21 Goals of this Thesis This thesis is an extension of the work recently done in this laboratory on alcohol 31 33 36 and amine oxidation reactions catalyzed by Ru porphyrin complexes. " ' The goals set for this thesis were: 1. To investigate the kinetics of the stoichiometric oxidation of para-substituted benzhydrols with /rans-Ru(porp)(0)2 oxidants, to help establish the mechanism of alcohol oxidation (porp = TMP, OCP or OCP-Cl 8 ) . 2. As a subsection of goal 1, to determine the role that electronic changes in the alcohol have on the rate of stoichiometric and catalytic oxidations effected by frans-Ru(porp)(0)2. 3. To investigate the mechanism of amine oxidation by /ra«.s-Ru(porp)(0)2. CHAPTER II EXPERIMENTAL General Gases [CO, N 2 , Ar, and 0 2 (99+% pure)] were supplied by Linde Gas, Union Carbide Inc. The Ar used in photolysis was passed through a Ridox column (Fisher Scientific) to remove trace 0 2 . Trace moisture present in Ar and N 2 was removed by passing the gases through a column of CaS04 (Fisher Scientific). The solvents used for synthetic or purification purposes, such as CH 2 C1 2 , benzene, toluene, and C H 3 C N , were supplied by Fisher Scientific as spectroscopic grade. When dry benzene was required, the solvent was dried over Na/benzophenone and stored under N 2 . A l l other solvents, required to be moisture-free, were dried over CaH 2 and stored under N 2 . Decalin, purchased from Aldrich, was used without further purification. Deuterated solvents (C 6 D 6 , CDCI3, C D 3 C N , DMSO-d 6 and D 2 0 , all 99.6+% deuterated) were purchased from Cambridge Isotope Laboratories. When needed to be used under anaerobic conditions, the solvents were degassed using three freeze-pump-thaw cycles or sparged with dry Ar or N 2 for 20-30 min Fine chemicals were purchased either from Fisher Scientific or Aldrich, while RuCl3«3H 20 was obtained on loan from Johnson Matthey Ltd. or Colonial Metals Inc. Dodecacarbonyltriruthenium, Ru3(CO)i2, was prepared according to a published procedure and recrystallized from benzene to yield a bright orange crystalline solid. 5 6 22 Chapter II 23 Pyrrole was distilled from CaH 2 prior to use and stored at 4°C under N 2 . BF3 etherate and MeOH complexes were stored in a vacuum desiccator. Benzhydrols were purified by recrystallization from hexanes and E t 2 0 prior to use. Amines were purified by distillation (under vacuum where necessary) and stored over molecular sieves (5 A , BDH) under N 2 . A l l reactions involving air- or moisture-sensitive reagents were performed under an atmosphere of Ar or N 2 on the bench using standard Schlenk techniques. Reactions were monitored by thin layer chromatography (TLC) using pre-coated, aluminum backed, silica and neutral alumina sheets (Fisher Scientific). Flash chromatographic purification was carried out on silica gel 60 (220-400 mesh ASTM), neutral alumina (activity I), or basic alumina (activity I) purchased from Fisher Scientific. The NMR-spectra were measured on Varian XL-300 (300 MHz), Bruker AC-200E (200 MHz) or Bruker WH-400 (400 MHz) FT spectrometers. Proton chemical shifts are given as 8 in parts per million (ppm) against the residual solvent as the internal standard (7.15 ppm for C 6 H 6 , 7.24 ppm for CHC1 3 and 2.49 ppm for DMSO), relative to TMS. Fluorine chemical shifts are given as 8 referenced to C F 3 C 0 2 H in CeD6 or CDCI3 and were obtained on the Bruker AC-200E (188.31 MHz) spectrometer. The 1 H - N M R chemical shift multiplicities are denoted as follows: Chapter II 24 s: singlet dd: doublet of doublets d: doublet m: multiplet t: triplet br: broad Variable temperature experiments were performed on the Varian XL-300 spectrometer using C6D6 and CDCI3 solvents. The temperature of the probe was allowed to equilibrate for at least 15 min before analysis of a reaction commenced. In anaerobic experiments, a pulse delay of 2 s was incorporated into all of the experiments to ensure complete relaxation of the porphyrin "H resonances. The procedure used to measure the kinetics of alcohol oxidations by ' H - N M R spectroscopy is detailed at the start of Chapter The infrared spectra, over the range of 4000-600 cm"1, were recorded on a ATI Mattson Genesis Series FTIR instrument. Samples were prepared as: (a) a Nujol mull between two KBr plates, or (b) a solid dispersed within a compressed KBr pellet. Only the relevant absorptions are listed. Spectroscopic UV-Visible data were collected on a Hewlett-Packard 8452A Diode-Array Spectrophotometer (resolution 2 nm) equipped with a thermoelectric temperature controller. Extinction coefficients, s, are given in units of M " 1 cm"1 in parentheses following the reported wavelength maximum, A, m a x . Anaerobic kinetic studies followed by UV-VIS were obtained using an anaerobic cell having a 1.0 or 0.1 cm path length III. Chapter II 25 (Figure II. 1). The procedures used in these studies are presented at the beginnings of Chapters III and IV. Kontes \ Valve j i L J 1.0 or 0.1 cm path length quartz cuvet Figure ILL Anaerobic UV-VIS spectroscopic cell. Chapter II 26 Elemental analyses were obtained by Mr. P. Borda of this department. Mass spectral analyses were performed in this department in a facility headed by Dr. G. Eigendorf. A fast atom bombardment (FAB) on thioglycerol and 3-nitrobenzylalcohol matrices method of ionization was used. Melting points were obtained from samples placed between glass plates using a ' Fisher-Johns apparatus. The experimental values were not corrected. Samples were analyzed by gas chromatography on an HP 5891A instrument, using He as the carrier gas, equipped with a hydrogen-flame ionization detector (FID). A l l of the gases were purified with Supelco gas-purifier systems (HC 2-2445). Separation of the sample components was obtained using a medium polarity HP-17 column (cross-linked 50%-Ph-50%-Me silicon capillary column, 25 m in length, 0.32 mm inner diameter, 0.26 pm thick column coating) or a polar Carbowax 20 column (polyethylene glycol stationary phase, 25 m in length, 0.2 mm inner diameter, 0.1 pm thick column coating). Injection volumes of 0.5 - 1 uL were used with sample concentrations of the order of 10" to 10" M . The column head pressure was maintained at 15.5 psi and a split-gas flow rate of ~ 70 mL/min was used to ensure that the sample would not overload the column. A chromosorb W-HP precolumn was used to ensure that all of the metal was removed from the sample before it reached the start of the column. The conditions for separation of the amine and alcohol standards are listed in Table II. 1 and Table II.2, respectively. Calibration curves of concentration versus peak area were measured over four Chapter II 27 concentrations for each of the samples to determine the ratio of substrate/product detector response for each column. Table ILL Conditions for Amine Separation by GC. Substrate/Product [Column]8 Temperature Programb Retention Times (min) Detector Response Ratio (Substrate/Product) Ph 2 CHNH 2 / Ph 2C=NH [Carbowax 20M] 80°C (2 min) 10°C/minto220°C (10 min) 17.38 17.63 0.75/1 Ph 2 CHNH 2 / Ph 2C=NH, Ph 2 CO [HP-17] 150°C (5 min) 2°C/minto 180°C 12.69 13.58 13.10 1/1/1 Ph(Me)CHNH 2/ Ph(Me)C=NH c [Carbowax 20M] 80°C (2 min) 10°C/min to 220°C (10 min) 7.36 8.43 1/1 PhCH 2 NH 2 / benzonitrile [Carbowax 20M] same as above 7.67 7.97 0.6/1 (PhCH 2)NH/ PhCH 2N=CHPh, benzonitrile, PhCHO [Carbowax 20M] 60°C (2 min) 20°C/min to 220°C (10 min) 16.54 17.25 10.32 9.60 2.2/1/1.2/2.3 a Compounds were standards, obtained commercially from Aldrich. Concentrations ranged from 10"2 to 10"1 M in benzene. b Injector and detector ports were maintained at 220°C. 0 Determined by GC-MS. Table II.2. Chapter II Conditions for Alcohol Separation by GC. 28 Substrate/Product [Column]8 Temperature Program5 Retention Times (min) Detector Response Ratio (Substrate/Product) Ph 2CHOH7 Ph 2 CO [HP-17] 0?-MeO-C 6 H 4 ) 2 CHOH/ (p-MeO-C 6H 4) 2CO [HP-17] 0>F-C 6H4) 2CHOH/ ( /7 -F-C 6 H 4 ) 2 CO [HP-17] 0>Cl-C6H4)PhCHOH/ 0f?-Cl-C6H4)PhCO [HP-17] (p-MeO-C 6H 4)PhCHOH/ (p-MeO-C6H4)PhCO [HP-17] 150°C (5 min) 2°C/minto 175°C 150°C(2min) 10°C/min to 220°C (5 min) same as above same as above same as above 13.44 12.99 12.07 15.14 7.25 6.47 9.99 9.39 11.20 11.75 1/1 1/1 1/1 1/1 1/1 a Compounds were standards, obtained commercially from Aldrich or synthesized (see below). Concentrations ranged from 10" to 10" M i n benzene. b Injector and detector ports were always maintained at 220°C. Synthesis of Benzhydrol Substrates Benzhydrol, 4,4'-dimethoxybenzhydrol and 4,4'-difluorobenzhydrol were purchased from Aldrich and recrystallized from hexanes and Et 2 0. The remaining substituted benzhydrols, 4-chlorobenzhydrol, 4-methoxybenzhydrol, 4,4'-N,N'-dimethylaminobenzhydrol and a-deuterobenzhydrol were synthesized as follows. Chapter II 29 General Procedure Dry Et20 (125 mL) was added to a 3-necked round-bottomed flask containing lithium aluminum hydride (500 mg, 12 mmol) under N 2 . The mixture was cooled to 0°C in an ice-bath and the corresponding benzophenone (5 g, 18-27 mmol) in dry E t 2 0 (50 mL) was added drop wise via syringe. The resulting mixture was warmed to r.t. and stirred overnight under N 2 . Analysis by TLC indicated that no starting material remained. The mixture was cooled again to 0°C, and the reaction quenched dropwise with water (50 mL). The aqueous layer was acidified with cone. HC1 and the benzhydrol product extracted with E t 2 0 (2 x 20 mL). The E t 2 0 layers were combined, washed with water and brine and dried over MgS04. Evaporation of the solvent on a rotary evaporator yielded the crude benzhydrol as a pale yellow solid. Recrystallization in hexanes and Et 2 0 yielded the pure substituted benzhydrols as crystalline, white needles. 4,4 '-Dimethoxybenzhydrol f(p-MeO-C6H4)2CHOH] 1 H-NMR (300 MHz, CDCI3, 20°C): 7.24 (d, 4H, o-H); 6.83 (d, 4H, m-H); 5.73 (d, 1H, CH); 3.75 (s, 6tt,p-OMe) 2.04 (d, 1H, OH) Analysis: Calculated: C, 73.74; H , 6.61 Found: C, 73.65; H , 6.57 m.p.: 69-70°C 5 7 Chapter II 4,4 '-Dijluorobenzhydrol [(p-F-CtfJ 2CHOH] ! H - N M R (300 MHz, CDCI3, 20°C): 7.30 (dd, 4H, o-H); 7.01 (t, 4H, m-H); 5.79 (d, 1H, CH); 2.20 (d, 1H, OH) 1 9 F - N M R (188.31 MHz, C 6 D 6 , 20°C): -38.96 (s) Analysis: Calculated: C, 70.89; H, 4.58 Found: C, 71.01; H, 4.55 m.p.: 45-46°C 5 8 Benzhydrol [Ph2CHOH] ' H - N M R (300 MHz, CDCI3, 20°C): 7.33 (m, 10H, phenyl H); 5.95 (d, 1H, CH); 2.29 (d, 1H, OH) Analysis: Calculated: C, 84.75; H , 6.57 Found: C, 84.60; H , 6.53 m.p.: 65-66°C 5 7 4-Chlorobenzhydrol [(^-Cl-C6H4)PhCHOH] Yield: 55% 'H-NMR (200 MHz, CDCI3, 20°C): 7.30 (m, 9H, phenyl H); 5.75 (d, 1H, CH); 2.92 (br d, 1H, OH) Analysis: Calculated: C, 71.54; H, 5.08 m.p. Chapter II Found: C, 71.70; H , 5.06 58-59°C 5 7 31 4-Methoxybenzhydrol [(p-MeO-C6H4)PhCHOHJ Yield: 79% ' H - N M R (200 MHz, CDCI3, 20°C): 7.30 (m, 7H, phenyl H); 6.80 (d, 2H, m-H); 5.70 (d, 1H, CH); 2.25 (br d, 1H,0H) Analysis: Calculated: C, 78.47; H, 6.59 Found: C, 78.30; H, 6.52 m.p.: 64-65°C 4,4'-N,N'-Dimethylaminobenzhydrol [(xy-Me2N-C6H4)2CHOH]i Yield: 52% 1 H-NMR (200 MHz, CDCI3, 20°C): 7.15 (d, 4H, o-H); 6.65 (d, 4H, ra-H); 5.55 (d, 1H, CH); 2.81 (s, 12H, N(CH 3 ) 2 ); 2.35 (br d, 1H, OH) Analysis: Calculated: C, 75.51; H , 8.21; N , 10.37 Found: C, 75.79; H , 8.34; N , 10.42 m.p.: 102-104°C 5 7 This compound was retained by the pre-column in GC analysis and is not listed in Table 2. Conversion and turnovers for catalytic reactions involving this substrate were determined by 'H-NMR analysis (based on o-H and N-Me integration of the benzhydrol and benzophenone species). Chapter II 32 a-Deuterobenzhydrol [Ph2CD0H] This compound was synthesized according to the general procedure listed above, but using lithium aluminum deuteride in place of lithium aluminum hydride. Yield: 55% ' H - N M R (300 MHz, CDCI3, 20°C): 7.33 (m, 10H, phenyl H); 2.19 (s, 1H, OH) Analysis: Calculated: C, 84.28; H , 6.57 Found: C, 84.18; H, 6.53 m.p.: 65-66°C Benzhydrol-O-d [Ph2CHOD] Benzhydrol was heated to reflux in a biphasic CdRsTDiO system for 24 h. The C6H6 layer was dried over Na2S04, and removed under vacuum to yield a pale yellow solid. The compound was purified by sublimation under vacuum to give white needles in 75% yield. Analysis of the product by ' H - N M R indicated 55% incorporation of deuterium. Synthesis of Porphyrins General Procedure The porphyrins H 2 T M P and H 2 OCP were prepared at r.t. in dry CH 2 C1 2 using BF3*MeOH as the catalyst following the procedure determined by Lindsey and Wagner.59 The products were purified by column chromatography through silica gel, and then Chapter II 33 through basic alumina. The product purity was determined by 'H-NMR, UV-VIS spectroscopies, and TLC analysis. The data agree with previously reported analyses.59 Meso-Tetramesitylporphyrin [H2TMPJ Yield: 20% 1 H-NMR (400 MHz, CDCI3, 20°C): 8.59 (s, 8H, yfl-pyrrole); 7.24 (s, 8H, m-U); 2.60 (s, 12H,/?-CH 3); 1.83 (s, 24H, 0-CH3); -2.51 (s, 2H, N-H) UV-VIS (C 6 H 6 ) : 420,514, 550, 590, 648 nm Meso-Tetra(2,6-dichlorophenyl)porphyrin [H2OCP] Yield: 8% ' H - N M R (400 MHz, CDCI3, 20°C): 8.64 (s, 8H, yS-pyrrole); 7.75 (d, 8H, m-H); 7.68(t, 4H,/?-H); -2.54 (s, 2H,N-H) UV-VIS (C 6 H 6 ) : 420, 514, 590, 650, 706 nm Synthesis of Ruthenium Porphyrin Complexes Synthesis of Carbonyl(porphyrinato)ruthenium(II) Complexes [Ru(porp)(CO), porp = TMP or OCP] Ruthenium was inserted into the centre of the porphyrins according to a modified Tsutsui procedure.603 A 200 mL solution of the porphyrin in decalin (0.003 M) was Chapter II 34 heated to reflux in a 3-necked round-bottomed flask equipped with a condenser. The solution was kept under an atmosphere of CO by bubbling the gas through the solution. When the solution had reached reflux, solid Ru3(C0)i2 to generate a 0.005 M solution was added. The reaction was monitored by TLC (toluene eluant on a silica plate) over 4 h. At this time, i f the reaction was incomplete by TLC, additional portions of Ru3(CO)i2 (the same quantity as previously used) were added. When no free-base porphyrin was visible by TLC, the reaction mixture was cooled to r.t. and passed through a column of silica gel using decalin and then toluene as the eluant. Once all of the free-base porphyrin had eluted as a dark purple band, the eluant was changed to 1% MeCN in toluene and the Ru porphyrin complex was eluted as a bright red band. A second purification of the porphyrin complex through basic alumina with a toluene eluant yielded the product in approximately 75% yield. The purities of the complexes were established by 'H-NMR, UV-VIS and TLC analysis, and the data agreed with previously determined results.5 Ru(TMP)(CO) Yield: 70% ' H - N M R (400 MHz, CDC1 3, 20°C): 8.46 (s, 8H, y0-pyrrole); 7.24 (s, 8H, m-H); 2.59 (s, 12H,p-CH 3); 1.86 (br s, 24H, 0-CH3); water is seen as a broad singlet at 8 1.6. UV-VIS (C 6 H 6 ) : 414, 530 nm IR (KBr): v c o = 1940cm"1 Analysis: Calculated: C, 75.22; H , 5.76; N , 6.26 + H 2 0 Found: Chapter II C, 73.76; H , 6.04; N , 5.86 C, 74.14; H, 5.99; N , 5.94 35 Ru(OCP)(CO) Yield: 75% ' H - N M R (400 MHz, CDC1 3, 20°C): 8.50 (s, 8H, yS-pyrrole); 7.75 (br t, 8H, m-H); 7.65 (t, 4H, p-H) UV-VIS (C 6 H 6 ) : 410, 530, 556 (shoulder) nm IR (KBr): v c o = 1950cm"1 M.S. (FAB): [Ru(OCP)(CO)]-, 1053 (M" + CI), 1018 (M"), 990 (M" - CO), 956 (M" -CO - CI) Synthesis of Carbonyl(meso-tetra(2,6-dichlorophenyl)-^-octachloroporphyrinato)ruthenium(II) fRu(OCP-Cls)(CO)J Chlorinating the /2-pyrrole positions of the porphyrin was accomplished using a modified procedure of a published preparation.32 A round-bottomed flask was charged with Ru(OCP)(CO) (100 mg, 0.098 mmol), N-chlorosuccinimide (300 mg, 2.96 mmol) and CH2CI2 (50 mL). The mixture was heated to reflux under air for 24 h and evaporated to dryness. The resulting brown solid was sonnicated in /PrOH, and the mixture filtered to yield a dark purple solid. Further purification by sonnicating the purple solid in MeOH, followed by filtration gave a bright red solid. Yield: 47% Chapter II 36 ' H - N M R (200 MHz, DMSO-d 6 ,20°C): 7.93 (m, m-H andp-H) UV-VIS (CH 2C1 2): 418, 544 nm IR(KBr): v c o = 1965 cm"1 M.S. (FAB): [Ru(OCP-Clg)(CO)]', 1330 ( M ' + Cl), 1266 ( M - CO), 1231 (NT - CO -Cl), 1195 (NT - CO - 2C1), 1162 (M" - CO - 3C1) Synthesis o/Trans-bis(acetonitrile)(meso-tetrantesitylporphyrinato)ruthenium (II) [Ru(TMP)(MeCN) 2] 5 26 32 The title complex was synthesized following a standard photolysis procedure. ' ' During the course of experimentation, however, it was determined that the complex could be synthesized in a Schlenk tube, rather than a photolysis tube. Ru(TMP)(CO) (40 mg, 0.043 mmol) was dissolved in a 3:5 M e C N / C 6 H 6 mixture (HPLC grades, 80 mL) in a Schlenk tube equipped with a condenser. A stainless steel needle (26 gauge) was inserted through a rubber septum into the Schlenk tube, and the solution was purged with dry Ar for 30 min. The solution was irradiated with a 450 W Hanovia-Hg vapour lamp for 7 h. Analysis by 1 H -NMR spectroscopy of a withdrawn sample indicated that no starting material remained. The solvent was removed under vacuum to yield the acetonitrile complex as a dark purple solid. Purity of the complex was determined by 'H-NMR, U V -VIS and IR spectroscopic analysis, and the data agreed with previously determined results.5'2 6'3 2 Chapter II 37 Yield: 80% ' H - N M R (300 MHz, C 6 D 6 , 20°C): 8.65 (s, 8H, p-pyrrole); 7.30 (s, 8H, m-H); 2.55 (s, 12H,p-CH 3); 2.20 (s, 24H, o-CH 3); -1.35 (s, 6H, CH 3 CN) UV-VIS (C 6 H 6 ) : 410, 508 nm IR ( O r ) : v C N = 2270 cm - 1 Synthesis ofTrans-dioxo(porphyrinato)ruthenium(VI) Complexes [Ru(porp)(0)2, porp = TMP, OCP and OCP-Clg] The dioxo complexes were prepared in situ by m-CPBA oxidation of the corresponding Ru(porp)(CO) compounds in benzene or chloroform.5 The excess acids were removed by column chromatography through silica or basic alumina, the dioxo-complex was the first band that eluted. In situ synthesis of trans-Ru(TMP)(0)2 was also S Oft possible by aerobic oxidation of /ram ,-Ru(TMP)(MeCN)2 in benzene. ' Solid trans-Ru(porp)(0)2 complexes were isolated by removing the benzene or chloroform solvents under vacuum to yield dark purple solids (75-98% isolated yield). Analysis of the dioxo complexes by ^ - N M R , UV-VIS, and IR spectroscopies gave data that agreed with those previously reported. ' Chapter II 38 Ru(TMP)(0)2 ' H - N M R (300 MHz, C 6 D 6 , 20°C): 9.02 (s, 8H, /^pyrrole); 7.10 (s, 8H, m-H); 2.42 (s, 12H,/7-CH3); 1.83 (s, 24H, o-CH 3) UV-VIS (C 6 H 6 ) : 422, 516 nm IR (KBr): vRu=o = 820 cm"1 Ru(OCP)(0)2 ' H - N M R (400 MHz, C D C I 3 , 20°C): 8.90 (s, 8H, y3-pyrrole); 7.65 (m, 16H, m-H andp-K) UV-VIS (C 6 H 6 ) : 422, 512, 580 nm IR (KBr): vRu=o = 820 cm"1 Ru(OCP-Cl8)(0)2 'H -NMR (400 MHz, CDC1 3, 20°C): 7.75 (m, m-H andp-U) UV-VIS (CH2CI2): 430, 522 nm IR (KBr): v R u = 0 = 820 cm"1 Chapter II 39 Synthesis ofTrms-bis(alkoxo)(meso-tetramesitylporphyrinato)ruthenium(IV) Complexes [Ru(TMP)(OR)2] A solution of trans-Ru(TM?)(0)2, prepared from Ru(TMP)(CO) (40 mg, 0.044 mmol) and w-CPBA (40 mg, 0.23 mmol) in benzene (10 mL), was purified by column chromatography through basic alumina, and sparged with N 2 for 30 min. Meanwhile, a Schlenk tube containing a substituted benzhydrol (50 mg, 0.2-0.3 mmol) was evacuated and flushed with N 2 . The /rara ,-Ru(TMP)(0)2 solution (8 mL) was transferred to the Schlenk tube using a syringe, and the resulting solution stirred under N 2 for 12 h. A n aliquot, transferred via canula to an N M R tube under N 2 , indicated the absence of any dioxo starting material. Subsequently, the dark brown solution was passed quickly through two pipette columns of basic alumina and evaporated to dryness by blowing N 2 through the solution. A dark purple solid was collected and analyzed by ^ - N M R , U V -VIS, IR, and MS. Extinction coefficients were determined in the presence of a slight excess of the alcohol, the solution concentrations being determined from integration of the o- and p-CYij, protons versus a CH 2 C1 2 internal standard in ' H - N M R spectra. Elemental analysis could not be obtained on the complexes as decomposition of the complexes occurred in solution during elution from the columns. The complexes were unstable in solution under air and regenerated fr7ms-Ru(TMP)(0)2 in the absence of excess alcohol. Chapter II 40 Ru(TMP)(OCHPh2)2 Yield: 50% ' H - N M R (200 MHz, C 6 D 6 ,20°C): 10.81 (d, 8H, m-H); 7.67 (s, 8H, m-H); 4.39 (t, 4H,/?-H); 3.01 (s, 12H, p-CH 3 ) ; 2.83 (s, 24H, o-CH 3); -22.49 (s, 8H, yS-pyrrole) UV-VIS (C 6 H 6 ) : 406 (130000), 522 (15000) nm IR (KBr): v c . N = 1009 cm"1 Ru(IV) oxidation state marker 2 6 ' 2 7 VRU-O = 764 cm"1 (tentative assignment) Ru(TMP)(OCH(p-MeO-C6H4)2)2 Yield: 45% ' H - N M R (200 MHz, C 6 D 6 , 20°C): 9.74 (s, 8H, m-H); 7.58 (s, 8H, m-H); 2.96 (s, 12H,/?-CH 3); 2.85 (s, 24H, o-CH 3); 2.78 (s, 12H,/?-OMe); -24.23 (s, 8H, yfl-pyrrole) UV-VIS (C 6 H 6 ) : 408 (100000), 524 (12000) nm IR (KBr): v c . N = 1010 cm"1 Ru(IV) oxidation state marker 2 6 ' 2 7 VRU-O = 699 cm"1 (tentative assignment) Chapter II 41 Ru(TMP)(OCH(p-F-C6H4)2)2 Yield: 53% ' H - N M R (200 MHz, C 6 D 6 , 20°C): 9.83 (d, 8H, m-H); 7.67 (s, 8H, m-H); 3.01 (s, 12H,p-CH 3); 2.78 (s, 24H, o-CH 3); -24.23 (s, 8H, ^-pyrrole) , 9 F - N M R (188.31 MHz, C 6 D 6 , 20°C): -37.50 (s) UV-VIS (C 6 H 6 ) : 408 (100000), 524 (12000) nm IR (KBr): v c . N = 1009 cm"1 Ru(IV) oxidation state marker 2 6' 2 7 VRU-O = 673 cm"1 (tentative assignment) CHAPTER III OXIDATION OF ALCOHOLS Introduction A variety of Ru complexes can be used to catalyze the conversion of alcohols to aldehydes and ketones; the more recent applications are discussed in Chapter I. The number of non-porphyrin systems that function with O 2 as the oxygen source is limited. Work in this laboratory has shown that tram-Ru(porp)(0)2 complexes (porp = TMP, OCP and OCP-Clg) will catalytically oxidize primary and secondary alcohols to aldehydes and ketones in the presence of water or a base. ' ' The mechanisms of both the stoichiometric and catalytic alcohol oxidations by /ra/w-Ru(porp)(0)2 are not well understood. In order to increase the knowledge of these mechanisms and to evaluate the electronic and steric influence of the alcohol on its reactivity, the kinetics and activity of -^substituted benzhydrols toward oxidation by Ru(VI)-dioxo porphyrin complexes were investigated. Sample Preparation and Data Analysis Stoichiometric Reactions The stoichiometric oxidation of benzhydrol was followed by 'H-NMR and UV-VIS spectroscopies, while that of (/?-MeO-C 6H 4)2CHOH and (p-F-CeFLhCHOH were followed by UV-VIS spectroscopy only. The kinetic data from both ^-NMR and UV-VIS spectroscopic analysis of the reactions are tabulated in Appendix A. 42 Chapter III 43 UV• VIS Spectroscopic Experiments Solid benzhydrol (0.016-1 g, 0.087-5.4 rnmol) was placed in the flask of an anaerobic cell (Figure II. 1, p.25), and the system evacuated and flushed 3 times with N 2 . Meanwhile, a solution of frYws-Ru(TMP)(0)2 (5 x 10"5-7 x 10"4 M), synthesized from m-CPBA oxidation of Ru(TMP)(CO) in benzene and purified by column chromatography through basic alumina, was purged with N 2 for 20 min. Using a syringe, 4 mL of the Ru-solution was transferred to the cuvet of the anaerobic cell and monitored by UV-VIS spectroscopy to determine the Ru concentration. The two components were mixed for 1 min and then the reaction was monitored by UV-VIS spectroscopy over the range of 450-820 nm. The temperature of the sample holder was maintained at 25°C during the course of the reaction and a filter, placed between the light source and sample, was used to prevent 200-450 nm light from reaching the sample. The kinetics of alcohol oxidation were followed, over 3-12 h, by monitoring the changes in absorbance at 490 nm. Pseudo first-order rate constants, kobs, were determined from non-linear regression analysis of absorbance versus time plots (not weighted) where Aoo was a variable (Figure III.l). Values for kobS determined from these plots were verified by comparison with the values obtained from a Guggenheim analysis of the data (see Figure A.2, Appendix A). Chapter III 44 0.58 -i 0.56 -0.54 -E c 0.52 -o o> «* 0.50 -n o> o 0.48 -c n 0.46 -J3 O (0 0.44 -< 0.42 -0.40 -0.38 -0 2000 4000 6000 8000 10000 12000 14000 16000 Time (s) Figure III. 1. A typical absorbance versus time plot for stoichiometric benzhydrol oxidation by trans-RuCTM?)(0)2. The line, A = A*, + (Ao-Aoo)exp(-kobst), was fit to the data using non-linear regression analysis, A« and kobs being variables. H-NMR Spectroscopic Experiments A solution of /ra«s-Ru(TMP)(0)2 (5 x lO^S x 10"3 M) was made by /w-CPBA oxidation of trans-Ru(TMP)(CO) in C 6D 6. The solution was passed through a pipette column of basic alumina to remove any excess acids and purged with N 2 for 20 min. Benzhydrol (1-135 mg, 0.0054-0.73 mmol) was added to an NMR tube that was capped with a septum, and the system evacuated and flushed 3 times with N 2. The N2-saturated /ra«s-Ru(TMP)(0)2 solution (0.5 mL) was added to the alcohol in the NMR tube under Chapter III 45 N2, via syringe, and the resulting solution mixed for 20 s. The reaction was then monitored by ' H - N M R spectroscopy over the next 20 min - 12 h. In experiments run at 35 and 50°C, the ' H - N M R probe was equilibrated at the desired temperature for a minimum of 15 min prior to the start of the experiment. The solution of trans-Ru(TMP)(0)2 and the N M R tube containing the solid alcohol were also heated to the desired temperature prior to the start of the reaction. The kinetics of the stoichiometric benzhydrol oxidation were followed by measuring the loss of /?-H signal intensity of the £rara ,-Ru(TMP)(0)2 oxidant using the intensity of the alcohol a-CH (8 5.50) as an internal standard. Based on this ratio and the known 'practically constant' alcohol concentration, the concentration of trans-Ru(TMP)(0)2 in solution at a given time was calculated. When the ratio of alcohol to Ru was < 30:1 the concentration of trans-Ru(JMP){0)2 could also be determined by comparing the integration of the /J-H signal to that of the alcohol or-CH. However, at alcohol to Ru ratios > 100:1 the error in determining the fi-H integration relative to that of the alcohol or-CH was too large to give an accurate /r<ms-Ru(TMP)(0)2 concentration. At low alcohol concentrations (< 30:1 compared to Ru), kobs values determined from measuring changes in both the intensity and integration of the /?-H signal were the same, 1.7 x 10"4 s"1. The loss of the dioxo-species could not be followed by monitoring changes in the signal intensity of the o- and /?-CH 3 groups of the TMP as, in many cases, these peaks were obscured by the OH signal of the alcohol. In experiments where this was not the case, the same kobs values were obtained for the loss of fra«s-Ru(TMP)(0)2 monitored Chapter III 46 at both the o- or /?-CH 3 and /?-H positions; 1.3 x 10"4 s"1 for the oxidation of Ph 2 CHOH (0.015 M) with /rarts-Ru(TMP)(0)2 ( 'H-NMR spectral changes seen during this reaction are illustrated in Figure III.2 and Figure III.3). The natural logarithm of the [trans-Ru(TMP)(0)2] was plotted against time to determine the value of the pseudo first-order rate constant, kobS (Figure III.3). The oxidation of Ph 2 CDOH was monitored using the intensity of the alcohol OH signal as the internal standard. trans-Ru(TMPXOCHPk2)2 ^«s-Ru(TMP)(0)2 111? II i i ; i • ! 11 ' i r H I i i i M u n i ! II i I I M M n II i " i 1 1 " i |t II I I i ; II II irn I T S i f 3.2 2.8 2.4 2.0 ppm 0 Figure IIL2. 1 H -NMR spectral changes in the o- and p- C H 3 signals for the TMP during the stoichiometric oxidation of Ph 2 CHOH by /ra/«-Ru(TMP)(0) 2 . ([trans-Ru(TMP)(O) 2] 0 ~ 5 x IO"4 M and [Ph 2CHOH] = 0.015 M). Peaks identified in regular font correspond to /rara ,-Ru(TMP)(0)2 with those labeled in italics corresponding to the fra«5-Ru(TMP)(OCHPh2)2 product. Chapter III 47 trans-Ru(TM?)(0)2 m-H (IMP) 18637 s trans-Ru(TMP)(OCHPh2)2 m-H (alkoxo) 18637 s h^tf 15037 s 11437 s wJh^^^ 7837 s 5437 637 s tf*a^*p**> -1.6 _ -1.8 O -2.0 S-2.4 OS a- -2.6 -2.8 -3.0 2000 4000 Time (s) 6000 8000 10000 12000 Figure III.3. Stoichiometric oxidation of Ph 2 CHOH by /ra«s-Ru(TMP)(0) 2 at 20°C followed by monitoring the loss in intensity of its fi-H signal using the alcohol a-CH as an internal standard. The concentration of the Ru(VI)-dioxo species was determined from this ratio. Plots of m[trans-Ru(TMP)(0) 2] versus time show straight lines. ([/ram ,-Ru(TMP)(0)2]o ~ 5 x IO"4 M , [Ph 2CHOH] = 0.015 M and t i / 2 = 5500 s). Peaks identified with regular font correspond to /raw.y-Ru(TMP)(0)2 with those labeled in italics corresponding to the /ram ,-Ru(TMP)(OCHPh 2) 2 product. Chapter III 48 Catalytic Aerobic Oxidations A solution of trans-Ru(porp)(0)2, from /n-CPBA oxidation of Ru(porp)(CO), in benzene or CHCI3 (1-2 mL), was added to a screw-top, 4 dram vial containing the solid alcohol, any additives and a small stir bar. The vial was tightly capped, shaken for 20 s to mix the reagents and placed in a 50°C oil-bath. The reactions were stirred at this temperature under 1 atm of air for 1-7 days and monitored at 24 h intervals by GC or ' H -N M R spectroscopy. The identities of the products were determined by comparison with data for known standards (see Table 11.2, p.28 for GC separation conditions). Percent conversion to products was determined by combining the peak areas for the alcohol and products and normalizing to 100%. From a knowledge of the initial catalyst concentration, calculated from UV-VIS spectroscopic data using known s values,32 and substrate concentration the catalyst turnover during the reaction could also be monitored. In all of the reactions the corresponding benzophenone was the only product of the benzhydrol oxidation. Stoichiometric Oxidation of Benzhydrols by *ra/i,s-Ru(TMP)(0)2 In the absence of air, / ra«5-Ru(TMP)(0)2 oxidizes (p-R-CeFL^CHOH to (p-R-CeFL^CO according to the stoichiometry of eq. 3.1, the Ru(VI) species acting as an overall two-electron oxidant. under in CgD6 l t o ^ O ) 2 + 3 ( ^ R - < ^ C H C H - ^ O C r ^ R - q j L ) ^ +2Hp+(p-R-C^CO (3.1) R-H,F,OVfe lto=Rij(IMP) Chapter III 49 The formation of one equivalent of the corresponding benzophenone is observed by 1 H-NMR spectroscopy when the Ru-dioxo oxidant reacts with an excess of the alcohol under N 2 . Although no precautions were taken to ensure that the benzene was absolutely dry, the water stoichiometry was assumed to be the same as that for the oxidation of 5 32 /PrOH to acetone, in which two equivalents of water were formed. ' Bis(alkoxy)ruthenium(IV) products are obtained from the reactions and are characterized by the 'H-NMR, UV-VIS and IR spectroscopic data (Chapter II). The presence of two alkoxy ligands is confirmed by 1 H -NMR spectral analysis of the /ra«5 ,-Ru(TMP)(OCH(p-MeO-C6H4) 2 )2 complex in which the /?-CH3 protons of TMP and the alkoxo / 7 - O C H 3 protons both integrate to give 12 H-atoms (Figure 111.4). Only one signal is seen for the 0 - C H 3 protons of the TMP ligand, indicating that the Ru(IV) complexes have D4h symmetry. p - M e O (a lkox ide) p - C H 3 ( T M P ) I 100 l .03 3.00 2.80 Figure III.4. 1 H -NMR spectral analysis of /ra«5-Ru(TMP)(OCH(p-MeO-C6H4)2)2 illustrating that the integration of the /?-CH 3 (TMP) signal and y?-OCH3 (alkoxy) signal is the same, showing that the Ru complex contains two alkoxo ligands. Chapter III 50 The bis(alkoxo) complexes show paramagnetic shifts in TMS, CH2CI2 and CeF6 peaks by ' H - or 1 9 F - N M R spectroscopy; however, attempts to verify the number of unpaired electrons by the Evan's method6 0 b yielded values for S ranging from 0.2 to 0.4, depending on the reference signal that was used. A n S = 1 value, indicating 2 unpaired electrons, was expected given the previously reported results for the bis(isopropoxo) 5 31 complex. ' The lower measured magnetic susceptibility for the benzhydrol-based complexes possibly arises from exchange of the alkoxy ligands (see p.51) with slight amounts of excess alcohol in solution, required for stabilization of the complexes (see p.39). This alkoxo ligand exchange, seen as a broadening in the 0-CH3 signal, is still present at low temperatures (-40°C). The paramagnetic nature of the bis(alkoxo) complexes is also evident in the resonance of the /?-H-atoms, found at 8 -22 to -24, in comparison with chemical shifts in the region of 8 8-9 for diamagnetic Ruu(porp)(CO) and /ra/w-RuVI(porp)(0)2 complexes. Similar paramagnetic shifts are noted for other Ru(IV)-bis(alkoxo) porphyrin species ranging from 8 -12 for isopropoxo to 8 -30 for phenoxo ligands. Plots of TMP proton chemical shift against inverse temperature, for /ran5-Ru(TMP)(OCHPh2)2, show straight lines over -40 to +20°C indicating that the species exists in one paramagnetic spin state over this temperature range (Figure III.5). Unfortunately, due to decomposition of the complexes during purification by column chromatography, the compounds were not obtained in a pure enough form for elemental analysis. IR bands at 1010 and 1009 cm"1 are also indicative of a Ru(IV) centre 2 6 ' 2 7 and crystals of the corresponding 2-propoxide, benzoxide and l,3-dichloro-2-propoxide • 31 36 complexes have been isolated and characterized by X-ray crystallography. ' Chapter III 51 10.0 0.0 -10.0 A E a. A -20.0 to < -30.0 -40.0 -50.0 J r ooo-o -o 0.000 0.001 0.002 0.003 1/T (K"1) 0.004 Figure III. 5. Linear Curie plots of changes in chemical shift (TMP protons, cf. Ru(TMP)(MeCN) 2) versus 1/T indicating that the Ru(rV)-bis(alkoxo) species exists in a single spin state over the temperature range of -40 to +20°C. The a-CH and o-CH protons could not be observed by 1 H -NMR spectroscopy in solution at 20°C due to exchange of the ligands with traces of the free alcohol remaining in solution, this causing these signals to broaden into the baseline. Addition of C D 3 O D to a solution of Ru(TMP)(OCH(p-F-C6H4)2)2 confirms that this exchange occurs as all of the signals corresponding to the fluorinated complex disappear within 30 min of mixing. Analysis by 1 9 F - N M R shows the loss of the peak at 5 -37.5 for the fluorinated bis(alkoxo) complex and an increase in the intensity of the alcohol peak at 8 -39.0. Chapter III 52 The kinetics for the stoichiometric oxidation of (jp-F-CeH^CHOH, (p-MeO-C6H4)2CHOH and Ph2CHOH were followed by UV-VIS spectroscopy under pseudo first-order conditions with a minimum 30 equiv. excess of the alcohol over the trans-Ru(TMP)(0)2 oxidant. Plotting the natural logarithm of A-A» against time yields a straight line for over 75% of the reaction, indicating that the reaction is first order in Ru (Figure III.6). (A„ values were obtained from non-linear regression analysis of A versus t plots, see Figure III. 1) Varying the initial concentration of the dioxo complex by a factor of 4 did not affect the value of the observed rate constant at [PhsCHOH] = 0.2 M , confirming this conclusion; at [trans-Ru(TMP)(0)2] = 5 x 10"5 M , kobS = 1.5 x 10"4 s"1 while at [trans-Ru(TM?)(0)2] = 2 x 10"4 M , kobs = 1.6 x 10"4 s"1. Chapter III 53 Figure III.6. Stoichiometric oxidation of Ph 2 CHOH by fra«s-Ru(TMP)(0) 2 at 25°C under 1 atm of N 2 followed by UV-VIS spectroscopy over 450-600 nm. Each spectrum represents a 15 min time interval. The corresponding ln(A-A«,) versus time plot, for absorbance changes at 490 nm, is linear for over 75% of the reaction; [/rara-Ru(TMP)(0)2] ~ 3 x 10"4 M , [Ph 2CHOH] = 0.40 M , and ti/ 2 = 3090 s. Chapter III 54 Plots of the pseudo first-order rate constants, kobS, versus [alcohol] show the reaction rates leveling off at higher alcohol concentrations, indicating saturation kinetics (Figure III.7-Figure III.9). Rate law (eq. 3.2) was fit to the data using non-linear regression analysis and yielded the K and ki values listed in Table III. 1; the K and ki values refer to a pre-equilibrium process, followed by a rate-determining ki step (see Figure III.ll,p.63). _ ,d[Ru(TMP)(0) ; ] = k , K [ R O H ] ( 3 2 ) dt l + K[ROH] 2 Previous studies with stoichiometric /PrOH oxidation by /ra«s-Ru(TMP)(0)2 also showed that the rate of oxidation leveled off at higher alcohol concentrations; however, this was attributed to solvent effects as the addition of the non-oxidizable alcohol /BuOH ([rBuOH] = 0.17 and 0.53 M) to the reaction mixture with [/PrOH] = 0.13 M slowed down the rate of alcohol oxidation by an order of magnitude.32 ,36 Similar results are not obtained with this system, as oxidation of Ph 2 CHOH (0.25 M and 0.54 M) in the presence of the non-oxidizable Ph 3 COH (0.34 M) gave kobs values which fit with the data obtained for Ph 2 CHOH oxidation alone, Figure III.8. A n explanation for the observance of saturation kinetics is the presence of a pre-association step, forming a {Ru-alcohol} adduct, prior to the actual oxidation step. At higher alcohol concentrations when the adduct is completely formed, the rate of oxidation is zero-order in the alcohol. Lower alcohol concentrations will result in partial formation of the {Ru-alcohol} adduct and the Chapter III 55 rate of the reaction will show a dependence on the alcohol concentration. Unfortunately, evidence for the presence of the {Ru-alcohol} adduct was not seen by UV-VIS spectroscopy. 0.00 0.10 0.20 0.30 0.40 0.50 0.60 [(p-MeO-CjH^CHOH] (M) Figure III. 7. Plot of kobS (from UV-VIS spectroscopic data) versus alcohol concentration for the stoichiometric oxidation of (p-MeO-CeH^CHOH by trans-Ru(TMP)(0)2 in benzene at 25°C under 1 atm of N 2 . Error bars indicate the range of kobS values determined from a minimum of three repeat reactions. Instrumental error is within the range of the point size. Chapter III 56 Figure III.8. Plot of kobs (from UV-VIS spectroscopic data) versus alcohol concentration for the stoichiometric oxidation of Ph 2 CHOH and Ph 2 CDOH by trans-Ru(TMP)(0) 2 in benzene at 25°C under 1 atm of N 2 . Error bars indicate the range of kobs values determined from a minimum of three repeat reactions. Instrumental error is within the range of the point size. Chapter III 57 4.5 n 0.0 • 1 1 1 1 1 1 1 1 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 [(p-F-C 6H 4) 2CHOH] (M) Figure III.9. Plot of kobs (from UV-VIS spectroscopic data) versus alcohol concentration for the stoichiometric oxidation of (p-F-C6H4)2CHOH by trans-Ru(TMP)(0) 2 in benzene at 25°C under 1 atm of N 2 . Error bars indicate the range of k^ s values determined from a minimum of three repeat reactions. Instrumental error is within the range of the point size. Chapter III 58 Adduct formation between Ru-oxo species and alcohols has been previously proposed by: Tony et al9 for the TPAP- and [RuV I I(0) 2(OCOR)Cl 2]"- catalyzed oxidation of alcohols in the presence of N M O in MeCN and CH 2 C1 2 , respectively; Behari and co-authors61 for the oxidation of cyclohexanol with R U O 4 2 " in the presence of a Fe(CN)63" co-oxidant; and Bressan et al.62 for the persulfate oxidation of alcohols catalyzed by Ru(II) species. In all three cases, the only evidence for the adduct formation was derived from kinetic data; no spectroscopic evidence for the presence of the adduct was reported. Lee and Congson1 0 have proposed, based on theoretical calculations, that in the stoichiometric oxidation of alcohols by Ru0 4 2 " and Ru0 4 " in 0.3 M NaOH a pre-equilibrium step occurs in which the a-CH bond of the alcohol oxidatively adds to the Ru=0 bond (a 2 + 2 addition) to give a seven-coordinate Ru-hydroxo intermediate. Decomposition of this intermediate then occurs via a rate-determining step, leading to the synthesis of the ketone products. Once again, evidence for this pre-equilibrium step is based solely on kinetic data. As the sterics and rigidity of the porphyrin ligand would hinder formation of a seven-coordinate Ru system, it is likely that the {Ru-alcohol} adduct forms through weak bonding interactions between the Ru=0 bond and the a-CH of the alcohol, similar to the "tight binding" between the alcohol a-CH and an in situ Ru-oxo species, as proposed by Bressen et al. Chapter III 59 Table III. 1. K and ki Values for Stoichiometric Benzhydrol Oxidation by trans-Ru(TMP)(0) 2 in benzene. Alcohol K(M _ 1) kixl04.(s"1) 0>MeO-C 6 H 4 ) 2 CHOH a 0.45 42 (p-F-C 6H4) 2CHOH a 6.5 4.7 Ph 2 CHOH a 1.0 9.4 Ph 2 CDOH a 1.3 0.77 Ph 2 CHOH b 38 2.9 Ph 2 CDOH b 68 0.20 Ph 2 CHOD b 34 2.9 a Followed by UV-VIS spectroscopy at 490 nm, at 25°C under 1 atm N 2 . b Followed by ' H - N M R spectroscopy at 20°C under 1 atm N 2 . * The kinetics of the stoichiometric oxidation of Ph 2 CHOH by /ra«5-Ru(TMP)(0)2 were also followed by 1 H-NMR spectroscopy. The reactions exhibit pseudo first-order kinetics and plots of ln[/rarcs-Ru(TMP)(0)2], determined from intensity changes in the fi-ll signal relative to that of the alcohol a-CH, versus time show straight lines over at least 2 half-lives (Figure III.3, p.47). As with the UV-VIS spectroscopic studies, the reaction exhibits saturation kinetics (Figure III. 10); however, the values of ki and K determined from a non-linear regression fit of eq. 3.2 to a plot of kobs versus [Ph 2CHOH] are significantly different (Table III. 1, cf. Figure III.8, p.56). These differences possibly arise because of some light sensitivity of the reaction. Removal of the 200-450 nm filter from the UV-VIS spectrometer, which allows the sample to absorb light within the Soret region of the spectrum, increases the kobs value for stoichiometric oxidation by a factor of ~ 2 (with the filter at 0.022 M Ph 2 CHOH, kobs = 4.1 x 10"5 s"1, while in the absence of the filter at 0.027 M Ph 2 CHOH, kobs = 1.0 x 10"4 s"1). The ! H - N M R spectroscopic data are considered to pertain only to the thermal reactions. Chapter III 60 Analysis of the spectra collected during the stoichiometric reactions shows three species to be present during the course of the reaction; /ra«s-Ru(TMP)(0)2, trans-Ru(TMP)(OCHPh 2) 2 and Ru(TMP)(0). 2 6 The intermediate Ru-oxo species grows in at the start of the reaction, remains at a low concentrations during the course of the reaction and then disappears at the end of the reaction (Figure III.2, p.46). Once again, no evidence for the presence of a {Ru-substrate} adduct was found, supporting the conclusion that the adduct is probably formed through non-covalent bonds between the Ru=0 and the alcohol a-CH that presumably would not greatly disturb the electronic environment of the porphyrin protons. Media effects of high alcohol concentrations were also investigated by ' H - N M R spectroscopy. The stoichiometric oxidation of benzhydrol (0.19 M) in the presence of Ph 3 COH (0.41 M) gave kobs = 2.7 x 10"4 s"1 which is within 8% of the kobs value determined in the absence of PI13COH (kobs = 2.5 x 10"4 s"1). As kobs typically varied by 10-15% for repeat experiments, this difference is not significant (Figure III. 10). Kinetic isotope effects were investigated by both UV-VIS and ' H - N M R spectroscopies over a range of concentrations. A primary kinetic isotope effect of 12 ± 6 for ki and 0.7 ± 0.7 for K , determined from UV-VIS spectroscopy, is exhibited at the a-C H bond. Similar results are obtained from 1 H -NMR spectroscopy, giving kiH/ki° = 15 ± 1 and K H / K D = 0.6 ± 0.2 for Ph 2 CDOH oxidation. The effect of using the -OD versus -OH alcohol was investigated only by the ' H - N M R spectroscopic kinetics, which showed Chapter III 61 k i 0 H / k i 0 D = 1.0 ± 0.1 and K 0 H / K 0 D = 1.1 ± 0.7, indicating that both the pre-association and rate-determining step are not significantly affected by O-deuteration. Previous work performed on the oxidation of /PrOH indicated a primary kinetic isotope effect of 1.9 + 0.3 with the use of the fully deuterated /PrOD-dg, in the initial first-order stage of the reaction ([/PrOH] < 0.3 M); at higher concentrations ([/PrOH] = 1.7 M), the k H / k D ratio decreased to about 1. 3 2 , 3 6 No isotope effects were noted for /PrOD oxidation. 3 2 , 3 6 Large kinetic isotope effects are typical for cleavage of a-CH bonds in alcohol oxidation by non-porphyrin Ru(IV)-oxo 2 , 6 3 and /ra«s-Ru(VI)-dioxo 1 3 a oxidants, the values ranging from 8 for ethanol1 3 3 up to 50 for benzyl alcohol. 6 3 Chapter III 62 with 0.41 MPhjCOH PhjCHOH 0.00 0.20 0.40 0.60 0.80 [alcohol] (M) 1.00 1.20 ure III. 10. Plot of k^s (from 1 H -NMR spectroscopic data) versus alcohol concentration for the stoichiometric oxidation of P I 1 2 C H O H , Ph 2 CDOH and Ph 2 CHOD by trans-R\i(TM?)(0)2 in benzene at 20°C under 1 atm of N 2 . Error bars indicate the range of k^s values determined from a minimum of three repeat reactions. Instrumental error is within the range of the point size. Chapter III Proposed Mechanism for Anaerobic, Stoichiometric Alcohol Oxidation 63 O Ru II O y1 + OH J , - L / \ " P h H Ph o-Ru O J) 'Ph H "Ph 651" + / I + o H Ru + hydride transfer O Ph Ph fast H + transfer 2 ^ . Ph 2CO OCHPh, alcohol Ru" + 2 H 2 0 I OCHPh, exchange OH O Ru KU Ru™ | \ detected by ' H - N M R OH 1 2 Ph,CHOH H^O Figure 111.11. Proposed mechanism for stoichiometric alcohol oxidation by trans-Ru(TMP)(0)2, Ru = Ru(TMP). Figure III. 11 outlines a proposed mechanism (also considered earlier by members of this group)32'36 for the stoichiometric alcohol oxidations (eq. 3.1, p.48). Saturation kinetics support the presence of a fast pre-equilibrium step forming a {Ru-alcohol} adduct, although no 1 H-NMR nor UV-VIS spectroscopic evidence has been seen for the formation of such a new Ru species. Something akin to hydrogen-bonding between the a-CH and the electrophilic Ru=0 (but perhaps involving a hydride H-atom and an electrophilic O-atom) is thought to occur to form the adduct, followed by subsequent C-H bond breaking in the rate-determining step. The small isotope effect of a-CD on K indicates that deuteration at this site has little effect on the value of AH for adduct formation; the K H / K D value of 0.6 corresponds to only a 1-2 kJ/mol difference for the Chapter III 64 interaction in the presence and absence of a-deuteration. This small change signifies that there is essentially no difference between the bond energies of the Ru=0—D and Ru=0—H moieties in the adduct, supporting the idea of a very weak hydrogen-bonding Ru=0 and alcohol a-CH interaction. Formation of a 'stronger' bond between the Ru=0 and the alcohol a-CH in the pre-equilibrium step would be expected to show a larger difference in AH, resulting in a larger isotope effect on K . Also, the large kinetic isotope effect on k i , seen with P I 1 2 C D O H oxidation, indicates that cleavage of the a-CH bond occurs in the rate-determining step; O-deuteration does not change the value of K or k\. A comparison of the ki values determined from UV-VIS spectroscopy for different benzhydrols indicates that ^-substitution of an electron-donating group on the benzene rings of the alcohol increases the rate of oxidation. With 4,4'-(N,N'-dimethylamino)benzhydroli; (1.0 M , a p = -0.63), complete loss of /ra«s-Ru(TMP)(0)2 occurs within 7 min at r.t. under 1 atm of N 2 , compared with half-lives for trans-Ru(TMP)(0)2 loss (under corresponding conditions with 1.0 M alcohol) of 29 min with 0>F-C 6 H 4 ) 2 CHOH (a p - 0.15), 25 min with Ph 2 CHOH (CTp = 0) and 9 min with (p-MeO-C 6 H 4 ) 2 C H O H (o p = -0.28). A Hammett plot of log(ki X/ki H) against 2<rp for the p-MeO, p-F and p-H substrates shows a linear relationship with a slope p = -1.1 (Figure III. 12), signifying that a transfer of electron density from the alcohol a-CH to the Ru oxidant 5 K and k, values for 0 > M e 2 N - C 6 H 4 )2CHOH oxidation were not included in Table III.l because the alcohol oxidation did not exhibit pseudo first-order spectral changes; plots of ln|A-AK | versus time were not linear. This discrepancy may result from binding of the alcohol to the Ru centre through the N-atom, or from an enhanced light-sensitivity in the reaction. In the absence of water, in solution, (p-Me2N-C6H4)2CHOH is blue in colour. Chapter III 65 occurs in the formation of the transition state.64 These results, in combination with a k i H / k i D ratio of ~ 15 for a-CH bond cleavage, support hydride transfer as the rate-determining step of the oxidation reaction. The rate of stoichiometric oxidation of /PrOH by /ran5,-Ru(TMP)(0)2 was previously found to increase in the presence of added K O H or KO^Bu, adding to the evidence in favour of a hydride transfer mechanism.3 2'3 6 Of note, oxidation via hydrogen atom abstraction from the a-CH bond to form Ru v(TMP)(0)(OH) and an in-cage organic radical Pb^C'-OH, followed by rapid electron transfer to the Ru(V) species and subsequent H + loss from Ph2C=OH+ is also possible. 0.80 T Figure III. 12. Hammett plot for stoichiometric benzhydrol oxidation from UV-VIS spectroscopic data. Formation of the bis(alkoxo) complexes almost certainly occurs through ligand exchange with an intermediate bis(hydroxo) species. Direct evidence for the formation of the Ru(IV)-bis(hydroxo) species in these alcohol systems is not available, though alkoxo ligand exchange with excess alcohol in solution has been observed (see p.51).3 2 Recently Chapter III 66 crystals of Ru(0CP)(0H)2 have been isolated during the preparation of Ru(OCP)(0)2 and analyzed by X-ray crystallography, providing indirect proof for the existence of Ru(TMP)(OH)2 in solution.65 Hydroxo intermediates are also proposed in alcohol oxidations with the non-porphyrin trans-[Ru(0)2L]2+ oxidants (L = 4-N donor macrocycles) where /ra/w-[Ru(0)L(OH2)] 2 + complexes are the final products detected by UV-VIS spectroscopy.133 The stoichiometric oxidation of PIv^CHOH by /ram-Ru(TMP)(0) 2 was followed by ' H - N M R spectroscopy at 35 and 50°C at a variety of alcohol concentrations in an effort to determine the reaction enthalpy for the pre-equilibrium step and the activation parameters for the rate-determining step. At > 0.2 M P I 1 2 C H O H , the reaction exhibits zero-order dependence on the alcohol concentration (Figure in. 13) allowing the values of AHi* and ASi*, 58 ± 10 kJ/mol and -120 ± 30 J/(mol K), respectively, to be determined from an Eyring plot (Figure HI. 14). These values are comparable to the activation parameters (within a first-order kinetic regime in alcohol) measured for the oxidation of iPrOH and benzyl alcohol for both porphyrin (AH*, 45 + 7 and 65 ± 11 kJ/mol; AS* = -167 ± 10 and -70 ± 20 J/(mol K) , respectively)36 and non-porphyrin (AH*, 50 ± 4 and 42 ± 4 kJ/mol; AS* = -117 ± 13 and -109 ± 13 J/(mol K), respectively)13 /ra/«-Ru(VI)-dioxo oxidants. In the current work, first-order dependence on alcohol concentration is seen in the 0.02 M Ph 2 CHOH region, giving kob s values of 2.9 x 10"4 s"1 at 35°C and 1.3 x 10"3 s"1 at 50°C. Using the ki values determined at from a best fit of the data in the [Ph^CHOH] > 0.2 M region, K values of ~ 42 and 57 M " 1 at 35 and 50°C, respectively, can be calculated; Chapter III 67 together with the value of 38 M"1 at 20°C, the data indicate that the formation of the {Ru-alcohol} adduct is essentially isenthalpic. 30 i Figure Ph2CHOH oxidation by /ra^-Ru(TMP)(0)2 from 1 H-NMR spectroscopic data at 35 and 50°C under 1 atm of N 2 in C6D6. Chapter III 68 1/T (1/K) 0.0031 0.0031 0.0032 0.0032 0.0033 0.0033 0.0034 0.0034 0.0035 -11 I 1 1 1 1 I 1 1 1 1 I 1 1 1 ' I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I -12 -12 * -13 * -13 -14 -14 -15 Figure III. 14. Eyring plot for the stoichiometric oxidation of P l^CHOH (0.2 M) with fr<ms-Ru(TMP)(0)2 under 1 atm N 2 in C 6 D 6 . Aerobic Oxidation of Benzhydrols Catalyzed by fra/i$-Ru(porp)(0)2 At 50°C under 1 atm of air in benzene /raws-Ru(porp)(0)2 (porp = TMP, OCP and OCP-Clg) catalyze the conversion of benzhydrols into benzophenones, though only in low turnovers (Table III.2). The addition of water to form a biphasic aqueous/benzene system increases the conversion to ketone products by a factor of 2-6 (Table III.3). In contrast to the results obtained with /PrOH oxidation, 3 2 ' 3 6 the addition of NaOH to the reaction in aqueous benzene does not increase the % conversion of benzhydrol. Alkaline biphasic aqueous/benzene systems show an improved % conversion over straight benzene; however in comparison with neutral aqueous/benzene systems the % conversions are in Chapter III 69 fact lower (Table III.3). The presence of mineral acids, either in concentrated or dilute solution (IN HC1) prevents any oxidation by /raws-Ru(TMP)(0)2 from occurring, almost certainly due to the formation of /ra7w-Ru(TMP)Cl2; 3 2 £rara ,-Ru(porp)Cl2 complexes do not shown catalytic aerobic oxidation activity. 3 2 ' 5 4 Table III.2. Oxidation of Benzhydrols Catalyzed by trans-R\xCTM?)(0)2. Yield (%) and [Turnover]8 Alcohol 45 hb 97 hb Ph 2 CHOH 39 [10] 79 [21] (p-Cl-C 6H4)PhCHOH 22 [6] 63 [17] (p-MeO-C 6H4)PhCHOH 77 [21] 95 [25] (p-MeO-C 6H4) 2CHOH 86 [23] 96 [26] 0?-F-C 6 H 4 )2CHOH 23 [6] 58 [16] 0E?-Me 2N-C 6H4)2CHOH c 47 [131 65 [181 a Reaction conditions: 50°C, 1 mL benzene solvent under 1 atm of air. [trans-Ru(TMP)(0) 2] = 3.8 x IO"3 M , 27 equiv. alcohol. b Determined by GC; see Table 2 (p.28) for separation conditions. 0 Determined by ^ - N M R spectroscopy based on o-H integration of ketone and a-CH integration of alcohol. Chapter III 70 Table III.3. Oxidation of Benzhydrols by trans-Ru(porp)(0)2: The Effect of Water, Base and the Porphyrin on Alcohol Conversion. Yield (%) [Turnover] at -19 h and ~/5 h* Porphyrin1* (solvent) (p-MeO-C6H4)PhCHOH c Ph 2 CHOH c (p-Cl-CettQPhCHOH0 not TMP not measured, measured, not measured, (C 6 H 6 ) 54 [14] 25 [6] 15 [4] TMP 99 [25], 73 [18], 66 [16], (C 6 H 6 /H 2 0) 100 [25] 96 [24] 96[24] TMP 80 [20], 41 [10], 51 [13], ( C 6 H 6 / l N N a 0 H ) 87 [22] 47 [12] 70 [18] OCP 9 [2], 6[1], 8 [2], (C 6 H 6 ) 17 [4] 16 [4] 10 [2] OCP 23 [6], 10 [3], 14 [4], ( C 6 H 6 ^ 2 0 ) 63 [16] 24 [10] 39 [5] OCP-Clg 46 [12], 53 [13], 34 [8], (C 6 H 6 ) 56 [14] 58 [14] 43 [11] OCP-Clg 98 [24], 98 [24], 98 [24], (C 6 H 6 /H 2 0) 98 [25] 99 [25] 98 [25] a Reaction conditions: 50°C, 2 mL benzene solvent under 1 atm of air, biphasic reactions were in a 2:1 ratio by volume of benzene/aqueous phase. b [rra/w-Ru(TMP)(0)2] = 3.8 x 10 - 3 M , [fr-aws-Ru(OCP)(0)2] - 4.6 x IO"4 M , [trans-Ru(OCP-Cl 8)(0) 2] = 2.7 x 10"4 M , 25 equiv. of alcohol. c Determined by GC; see Table 2 (p.28) for separation conditions. Catalyst activity is also affected by the substituents on the porphyrin ligand. Chlorinating the o-positions of the meso-phenyl groups decreases the catalyst activity for oxidation in both benzene and biphasic systems. Substituting chlorine atoms at the j3-Chapter III 71 positions of the porphyrin ring, as in OCP-Clg, provides greater catalytic activity than either the TMP or OCP complexes; the degree of enhanced activity is reduced in biphasic systems (Table 111.3). Catalyst deactivation occurs at 50°C and is evident, in the absence of added water, as insoluble solids are deposited on the sides of the reaction vials after 24 h. In the presence of added water, these deposits are not formed; however, catalyst deactivation still occurs as only 42-50% conversion is noted during the first 20 h after the OCP-Clg based reactions are recharged with additional alcohol. Monitoring the reactions after 120 h by UV-VIS spectroscopy indicates the presence of Ru(porp)(CO), seen as a band at 414, 410 or 418 nm, respectively (porp = TMP, OCP or OCP-Clg). Plotting log(%conversionx/%conversionH), for alcohol oxidation catalyzed by trans-Ru(TMP)(0)2 in benzene at 50°C after 45 h (Table III.2), against the Hammett factor rjp or 2rjp for mono- or di-substituted alcohols, respectively, yields linear plots with slopes of -1.5 and -2.4 when data for ( p - M e 2 N - C 6 H 4 ) 2 C H O H (CTp = -0.63) are excluded. The />-amino-substituted alcohol is not included in the plot because further work indicated that conversion of benzhydrols to benzophenones was inhibited by a factor of ~ 2-7 when a tertiary amine was introduced into the benzene solution (Table III.5, p.80); this indicates that the amino substituent of the alcohol could inhibit the alcohol oxidation. The presence of two singlets for both the N M e 2 and C H protons, attributed to free and N -coordinated alcohol, after 48 h at 50°C supports this conclusion. The negative p values determined from the slopes of the Hammett plots indicate that aerobic oxidation of Chapter III 72 benzhydrols catalyzed by /ra«s-Ru(porp)(0)2 is also favoured by electron-donating substituents. Figure III.IS. Correlation of % conversion after 45 h at 50°C with the Hammett factor CTP or 2a p . Finally, when the catalyst turnovers for the oxidation of benzhydrols at 50°C under 1 atm of air in benzene or biphasic benzene/water systems are compared with those for other alcohols, the following reactivity trends are noted (Table III.4): in the absence of added water, 1° benzylic > 2° alkylic > 2° benzylic alcohols, and in the presence of added water 1° benzylic > 2° benzylic > 2° alkylic alcohols. Chapter III 73 Table III.4. Catalyst Turnover for Alcohol Oxidation Catalyzed by /raras-Ru(TMP)(0)2 Under 1 atm of Air at 50°C. Substrate Product Turnover* Turnoverb (Benzene) (Biphasic System) Benzhydrol Benzophenone 6 18 4-Chlorobenzhydrol 4-Chlorobenzophenone 5 16 4-Methoxybenzhyrdrol 4-Methoxybenzophenone 14 25 Benzyl alcohol 3 2 Benzaldehyde 26 c 32 Isopropanol32 Acetone 6C 10 a Reactions were run in benzene; catalytic turnovers are quoted for reactions after 45 h (when the catalyst is still active). b Reactions were run in a biphasic benzene/water system; catalytic turnovers are quoted for reactions after 19-24 h (when the catalyst is still active). c Reactions were run in benzene; catalytic turnovers are quoted for reactions after 24 h (when the catalyst is still active). Proposed Mechanism of Aerobic Benzhydrol Oxidation Catalyzed by trans-Ru(porp)(0)2 The mechanism shown in eqs. 3.3-3.7 (which has been considered earlier by this group) 3 2 ' 3 6 is proposed for the aerobic oxidation of alcohols catalyzed by trans-Ru(porp)(0)2, where porp = TMP, OCP and OCP-Clg. Evidence for the outlined steps is discussed in the text below. Jfti^ Gfe + 3Ph,CHOH — * ^ ( O C H P h ^ + PhpD + 2H,0 (3.3) Rif(OCHPh2)2 + 2Hp Rdv(OH)2 + 2Ph2CHOH (3.4) Riiv(OH)2^=^ RiF(0) + HP (3.5) 2Rrf\G) *- «M v i (0 )2 + Rtf (3.6) RO1 + 1/20, ~Ru™(0) (3.7) Chapter III 74 A study of the oxidation of Ph 2 CHOH by /ra«s-Ru(TMP)(0) 2 under air in benzene and biphasic water/benzene systems at 25°C using ' H - N M R spectroscopy indicates the following: (i) Ru(IV)-bis(alkoxo) is the major species present in both solutions after 2 h; (ii) under 1 atm of air or dry 0 2 , and in benzene, the reaction exhibits pseudo first-order kinetics (Figure III. 16) for the loss of /rara-Ru(TMP)(0) 2 (in air with [Ph 2CHOH] = 0.071 M , kobs = 4.2 x IO"4 s"1, and in 0 2 with [Ph 2CHOH] = 0.075 M , kobs = 3.4 x 10"4 s"1), the rate of this loss being ~ 2 times faster than noted in the stoichiometric reactions under N 2 at a similar alcohol concentration ([Ph 2CHOH] = 0.057 M , kobs = 1.7 x 10"4 s"1); (iii) after a 24 h reaction, no signals corresponding to the dioxo species are visible in the benzene solution, and under these conditions after 120 h only 3 equiv. of benzophenone are formed; (iv) addition of water prolongs the lifetime of /ra/w-Ru(TMP)(0)2 such that the dioxo species is still visible in solution after 24 h. These data imply that the initial step in the catalytic process is the formation of the Ru(IV)-bis(alkoxo) species during the first 24 h of reaction (eq. 3.3). Reactions run under dry 0 2 or air were stirred at 25°C to ensure that the concentration of 0 2 in solution remained constant; aliquots of solutions were monitored by 1 H-NMR spectroscopy to determine kobs for /rajM-Ru(TMP)(0)2 loss (for the experiments under N 2 no stirring was used). As it was necessary to use a different technique to monitor the reactions under 0 2 or air (vs. N 2 ) , and the kobs values for the reactions under 0 2 or air are similar (indicating no kinetic dependence on 0 2 concentration), the two-fold increase in kobs seen in the presence of 0 2 (vs. N 2 ) is attributed to experimental effects and is not considered to be significant. Of note, pseudo Chapter III 75 first-order kinetics are not observed for loss of /rara ,-Ru(TMP)(0)2 during the oxidation of P I 1 2 C H O H in a biphasic water/benzene system at 25°C under 1 atm of air. -3.5 -4.5 4-2 -5.5 I H Si B -6.5 -7.5 Time (s) 1000 2000 3000 4000 I " 1 1 I 1 1 1 1 I 1 1 1 1 I 1 5000 6000 7000 1 1 1 1 1 1 I 1 1 1 1 I • under dioxygen 0 under air Figure 111.16. Oxidation of Ph 2 CHOH by frw-Ru(TMP)(0)2 at 25°C under 1 atm of air or 0 2 in CeD6. The loss of /m«5-Ru(TMP)(0) 2 was followed by measuring changes in the B-R signal intensity using the alcohol a-CH as an internal standard. Reactions were stirred under air or O 2 to ensure the concentration of O 2 in solution remained constant; [/rcr«5'-Ru(TMP)(0)2] ~ 5 x 10"3 M and [Ph 2CHOH] = 0.071 - 0.075 M . Monitoring the oxidation of Ph 2 CHOH by /rara-Ru(TMP)(0) 2 in C 6 D 6 at 50°C over 5 days, by 1 H-NMR spectroscopy, shows no detectable concentration of dioxo species present in solution after 24 h; only signals for the bis(alkoxo) species are visible. Yet, catalysis still occurs under these conditions as turnovers of 17, 21 and 25 for the oxidation of (p-Cl-C 6H4)PhCHOH, Ph 2 CHOH and (p-MeO-C 6H4)PhCHOH, respectively, are found by GC analysis of reactions run in C6H6 after 97 h (see Table III.2, p.69). Chapter III 76 Presumably, /ram ,-Ru(TMP)(0)2 that has been regenerated in a low, non-detectable, concentration is responsible for the oxidation. When a benzene solution of trans-Ru(TMP)(OCH(p-MeO-C6H4)2)2 is exposed to air at r.t., complete conversion to the dioxo-complex occurs after 1 day; (p-MeO-CeFL^CO is formed as the co-product. However, when a C6D 6 solution of /ra«5 ,-Ru(TMP)(OCH(p-F-C6H 4)2)2 is exposed to air, after 2 days only 50% conversion to the Ru(VI)-dioxo complex has occurred; (p-F-C6H4)2CO is the co-product. This finding, along with the lower catalyst turnover of 17 for (p-Cl-C 6H4)PhCHOH versus 25 for (p-MeO-C 6H4)PhCHOH oxidation, indicates that (i) regeneration of /rans-Ru(TMP)(0)2 is also subject to the electronic effects of the p-substituents with more electron-donating substituents favouring reformation of the dioxo species, and (ii) subsequent to the formation of the Ru(IV)-bis(alkoxo) complexes, the catalytic process is limited by the rate of regeneration of the dioxo species. The Hammett plots shown in Figure III. 15 (p.72) based on % conversion data after 45 h at 50°C probably illustrate, therefore, the electronic effect of changing /j-substitution on the rate of trans-Ru(TMP)(0)2 regeneration during the catalytic process. Previous work has shown that removal of water from the system, by using dry benzene and dry O 2 , 32 completely prevents the formation of the dioxo-complex from /ra«5-Ru(TMP)(0/Pr)2. This result, when combined with point (iv) of above (p.74) and the increase in catalyst turnover in aqueous water/benzene systems (cf. Table UI.3, p.69) indicates that water plays a key role in the regeneration of /raray-Ru(porp)(0)2 from Ru(rV)-bis(alkoxo) complexes. As proposed for the stoichiometric oxidation of alcohols by dioxo-ruthenium species (Figure III. 11, p.63), alkoxo-hydroxo ligand exchange probably occurs to form a Chapter III 77 Ru(IV)-bis(hydroxo) complex (eq. 3.4); this then reacts further through loss of one mole of water to form Ru(porp)(0) (eq. 3.5), which was still detected under the aerobic conditions at 25°C, but only in very low concentrations (Figure III. 17). The generally accepted mechanism, though not fully established, for reformation of trans-Ru(porp)(0)2 • 3 0 from Ru(porp)(0) is via disproportionation of the monooxo species (eq. 3.6). Finally, rapid reaction of the 'bare' Ru(II)(porp)28 with 0 2 regenerates Ru(porp)(0) continuing the catalytic cycle (eq. 3.7). It has also been proposed that water accelerates the disproportionation reaction by increasing the rate of dioxo formation, eq. 3.8. 32 (rans-Ru(TMP)(0) 2 /7 -CH3 trans-Ru(TMP)(OCHPh2)2 p-CH3 3.20 2.80 2.40 Figure III. 17.1 H-NMR spectrum obtained during Ph 2 CHOH oxidation under 1 atm of air in benzene at 25°C. Signals corresponding to /raws-Ru(TMP)(OCHPh2)2 are shown in italics while the /rarts-Ru(TMP)(0)2 signals are indicated with a regular font. Rulw(0) + fl«IV(0)(OH2) Ruvl(0)2 + Ru\OH2) (3.8) Ru = Ru(porp) Evidence for the formation of Ru(II) species in the catalytic reaction was found when benzhydrols were oxidized in benzene under 1 atm of air at 50°C in the presence of Chapter III 78 NEt3 (8 equiv.). The conversion of benzhydrols to benzophenones using a trans-Ru(TMP)(0)2 catalyst is decreased by a factor of 2-7 over the oxidations occurring in the absence of the amine (Table III.5, p.80). Studying the reaction, for (p-MeO-CeFLt^CHOH oxidation in the presence of NEt.3 at 50°C under 1 atm of air in C 6 D 6 , by ' H - N M R spectroscopy shows the lack of any significant concentration of Ru-bis(alkoxo) or -dioxo species after 24 h (Figure III. 18). Presumably, in the absence of significant amounts of water, NEt3 reacts with Ru(TMP) at a faster rate than 0 2 does, and inhibits the regeneration of /r<ms-Ru(TMP)(0)2 via eq. 3.7, most likely by trapping the Ru as the stable /ra»s-Ru(TMP)(NEt3)2 complex, 5 2.44 (/7-CH3) and 2.16 ( 0 - C H 3 ) (evidenced by comparison with data for the Ru(II)-bis(benzylamine) complex, 8 2.35 (/7-CH3) and 2.26 ( 0 - C H 3 ) ) . 3 3 Of interest, when the same reaction is run in a biphasic benzene/water (2:1) system at 50°C under 1 atm of air, the number of catalyst turnovers increases by a factor of 2.5 after 24 h of reaction (Figure III. 19), indicating that water does affect catalytic turnover, possibly by accelerating the regeneration of Ru(IV)-oxo species from Ru(U) complexes (see eqs. 3.9 and 3.10). No significant concentration of trans-RuCJMP)(0)2 is noted in the presence of added water, under these conditions; however, signals corresponding to trans-Ru(JMY){OCYi-(p-McOC^)2)2 are seen while those for trans-Ru(TMP)(NEt 3) 2 are absent (Figure III. 19). Ru\L)2 + 2 H 2 0 Ru\H20)2 + 2 L (3.9) Rull(H20)2 + 1/2 0 2 -> *M I V (0) (H 2 0) + H 2 0 (3.10) L = alcohol or amine, Ru = Ru(porp) Chapter III 79 N-CFJ2-CH 3 of free amine frara-Ru(TMP)(NEt3)2 8 3.00 2.60 2.20 Figure 111.18.1 H-NMR spectra for (p-MeO-CeH^CHOH oxidation by trans-Ru(TMP)(0) 2 in C 6 D 6 under 1 atm of air at 50°C in the presence of NEt 3 ; [ftwtt-Ru(TMP)(0)2] = 4.8 x 10 - 4 M , [0>MeO-C 6H4) 2CHOH] = 0.075 M and [NEt3] = 0.014 M ; % conversion and [turnover] data after 24 h are: 8% and [13]. fram-Ru(TMP)(OCH(p-OMe-C6H4)2)2 N-CHrCHs of free amine 8 3.00 2.60 2.20 Figure 7//.19.'H-NMR spectra for (p-MeO-CeJL^CHOH oxidation by trans-Ru(TMP)(0) 2 in a biphasic C 6 D6/H 2 0 system under 1 atm of air at 50°C in the presence of NEt 3 ; [frw7s-Ru(TMP)(0)2] = 4.8 x IO"4 M , [(p-MeO-C 6 H 4 ) 2 CHOH] = 0.072 M and [NEt3] - 0.014 M ; % conversion and [turnover] data after 24 h are: 21% and [31]. Chapter III 80 Finally, in an attempt to determine whether radical intermediates are formed during alcohol oxidations, BHT (2,6-di(r-butyl)-4-methylphenol) was added to the reactions in benzene. In the presence of 4 equiv. of BHT, based on Ru, the percent conversion of the benzhydrols is generally cut in half after 40 h, although in the (p-F-CeH^CHOH oxidation the conversion actually increased somewhat (Table III.5); however, when BHT is added to a benzene solution of /ra«s-Ru(TMP)(0)2 in the absence of alcohol, loss of the TMP signals for the Ru(VI)-dioxo species occurs after 1 h. at r.t.. Subsequent heating of this solution to 50°C under air results in a decrease in signal intensity for the r-butyl H atoms of BHT and the formation of a large number of alkyl signals in the region of 8 0.7-1.0. These results indicate that the decrease in alcohol conversion in the presence of BHT probably results from the reaction of BHT with trans-Ru(YMP)(0)2, possibly to form a Ru(IV)-bis(phenoxo) complex, rather than through its action as a radical trap. Regeneration of the dioxo species from any such Ru-BHT complex must be slower than that from the bis(alkoxo) complexes (with the exception of /ra«5-Ru(IV)(TMP)(OCH(p-F-C6H4)2)2), thus limiting the catalyst turnover. The fact that /ra«5 ,-Ru(TMP)(0) 2 stoichiometrically oxidizes phenol to form a bis(phenoxo)mthemum(rV) complex and p-hydrobenzoquinone,5'32 implies that a reaction with BHT is not unexpected. Cyclobutanol, cyclopentanol and cyclohexanol are all converted to the corresponding cyclic ketones,36 indicating that long-lived radical species are not formed during the catalytic cycle. Table III.5. Chapter III The Effect of BHT and NEt3 on Benzhydrol Oxidation. 81 Yield (%') and [Turnover]" Alcohol 40 hb 90 hb Ph 2 CHOH 25 [7] 51 [14] + NEt 3 3[1] 6 [2] + BHT 13 [4] 22 [6] G>Cl-C 6H 4)PhCHOH 15 [4] 21 [6] + NEt 3 6 [2] 10 [3] (p-MeO-C 6H4)PhCHOH 54 [15] 77 [21] + NEt 3 7 [2] 10 [3] + BHT 23 [6] 39 [10] ( p - M e O - C 6H4 ) 2 C H O H 85 [23] 95 [25] + NEt 3 42 [11] 36 [10] + BHT 23 [6] 60 [16] (p-F-C 6H4) 2CHOH 15-[4] 32 [9] + NEt 3 6[1] 13 [4] + BHT 22T61 35 [9] a Reaction conditions: 50°C, 1 mL benzene solvent under 1 atm of air. [trans-Ru(TMP)(0) 2] = 1.7 x 10"3 M , 27 equiv. alcohol, [NEt3] = 1.4 x 10"2 M and [BHT] = 6 . 8 x l O - 3 M . b Determined by GC; see Table 2 (p.28) for separation conditions. Chapter III 82 Conclusions The ability of rra«s-Ru(TMP)(0)2 to stoichiometrically oxidize benzhydrols was investigated in an effort to gain insight into the mechanism of the reaction. Intermediates of the type /ra/w-Ru(TMP)(OR)2 were isolated from the stoichiometric reactions and characterized by 1 H-NMR, IR and UV-VIS spectroscopies. Kinetic studies indicate that cleavage of the a-CH bond occurs in the rate-determining step, most likely via hydride transfer to the Ru=0 moiety, though a slow hydrogen-atom transfer followed by a fast 1-electron transfer can not be ruled out. This conclusion is supported by a limited, linear Hammett correlation (p = -1.1) between 2rjp and the stoichiometric rate constants ki determined by UV-VIS spectroscopy for the oxidation ofp-substituted benzhydrols. 7>a«5,-Ru(porp)(0)2 complexes also catalyze the aerobic oxidation of benzhydrols into benzophenones. Studies of the system at 25 and 50°C by ! H - N M R spectroscopy indicate that initially the catalytic process is limited by the rate at which the Ru(IV)-bis(alkoxo) species are formed (the first step in the catalytic cycle). Subsequently, the catalyst turnover is limited by the rate at which the dioxo species can be reformed. Added water is essential for higher catalytic activity and increases the % conversion to ketones by a factor of 2-6 after 45 h at 50°C (Table III.3). The role of water is complex: the water is thought to be involved in accelerating the regeneration of the Ru(VI)-dioxo catalyst through ligand exchange with the Ru(IV)-bis(alkoxo) complexes and by accelerating the reaction of Ru(II) with 0 2 (eqs. 3.4, and 3.8-3.10). Very limited linear Hammett correlation plots between % conversion after 45 h and a p indicate that the conversion of Chapter III 83 benzhydrols to benzophenones in benzene is accelerated in the presence of /7-electron-donating groups. As complete conversion to the bis(alkoxo) complexes occurs within 24 h in the absence of added water, these Hammett plots presumably illustrate the effect of electron-donating groups on the regeneration of /ra«5 ,-Ru(porp)(0)2. Finally, a comparison of catalyst turnover after 24 h at 50°C under 1 atm of air with those of other alcohols shows the following reactivity trend: 1° benzylic > 2° alkylic > 2° benzylic alcohols in the absence of added water, and 1° benzylic > 2° benzylic > 2° alkylic in the presence of added water. CHAPTER IV OXIDATION OF AMINES Introduction Recently, work in this laboratory has extended the use of ?raM.s-Ru(porp)(0)2 oxidants to the catalytic and stoichiometric dehydrogenation of amines (see eqs. 4.1 and 4.2 for the stoichiometric reactions). Ru V I (TMP)(0) 2 + 4 R R ' C H N H 2 -» Ru n (TMP)(RR'CHNH 2 ) 2 + 2 RR'C=NH + 2 H 2 0 (4.1) (R and R' = aryl or alkyl substituents), or Ru V I (TMP)(0) 2 + 3 R C H 2 N H 2 -> Ru"(TMP)(RCH 2 NH 2 ) 2 + R C N + 2 H 2 0 (4.2) This is the first example of Ru-porphyrin catalyzed amine oxidation, though a few stoichiometric oxidations have been investigated also (Chapter I) . 3 8 , 5 0 Understanding the mechanism of this reaction may provide greater knowledge of the metabolism of both naturally occurring amines and xenobiotics.38 In an effort to gain insight into this mechanism, the kinetics of the stoichiometric oxidation of amines by /r<ms-Ru(porp)(0)2 (porp = TMP and OCP) were investigated as part of this thesis work. The catalytic reaction was also examined briefly in an attempt to determine the effect of changing the porphyrin ligand and reaction conditions on the catalyst turnover and % conversion of the amines. 84 Chapter IV 85 Sample Preparation and Data Analysis Stoichiometric Reactions The stoichiometric oxidations of the amines Ph2CHNH2, racemic (rac-)Ph(Me)CHNH 2 and zPrNH 2, by trans-Ru(porp)(0)2 (porp = OCP and TMP) were followed by UV-VIS spectroscopy. Some of the kinetic data amassed during these investigations are listed in Appendix B. 7>ara,-Ru(OCP)(0)2 was synthesized by m-CPBA oxidation of Ru(OCP)(CO) in benzene or CHCI3 and purified, respectively, through a silica or basic alumina column. The corresponding TMP-based oxidant was synthesized through O2 oxidation of /r<ms-Ru(TMP)(MeCN)2 in benzene. Reactions were run at 23°C in an anaerobic, UV-VIS spectroscopic cell (Figure II. 1, p.25) with a 1.0 cm path length, monitored at 420 nm (the Soret maximum for /ra«5-Ru(TMP)(0)2), or a 0.1 cm path length, monitored at 506 for the rac-Ph(Me)CHNH 2 system, 508 for /PrNH 2 or 510 nm for Ph2CHNH2 (the respective a-band absorption maxima for the trans-Ru(ll)-bis(amine) products). The stoichiometric oxidations of amines by /r<my-Ru(porp)(0)2 were examined using several different procedures. Two typical procedures, one for the OCP-based oxidant and the other for the TMP-based oxidant are described below, and any deviations from these procedures are noted, where necessary, in the text. The amines used in all of the experiments were liquid and were purified by distillation (Chapter II). Chapter TV 86 Procedure A: Trans-Ru(OCP)(0)2 Oxidant A freshly columned solution of /ra«5-Ru(OCP)(0)2 was transferred to a 1.0 cm or 0.1 cm path length, anaerobic, UV-VIS spectroscopic cell, the solvent removed in vacuo, and the system then placed under Ar. Meanwhile, a solution of Ph2CHNH-2 in dry solvent (IO'2 M) was purged with Ar for 20-30 min. The solid oxidant was then redissolved in a known amount of dry, Ar-saturated solvent (5-20 mL) and its concentration determined 32 6 by UV-VIS spectroscopy using known 8 values; concentrations were typically 4-8 x 10" M for the 1.0 cm cell and 2-5 x 10"4 M for the 0.1 cm cell. By use of a syringe, the amine solution was transferred to the anaerobic cell and the two solutions mixed for 30 s, prior to the start of analysis. The final amine concentration in the reaction mixture ranged from 0.5-2 x 10"3 M for reactions in the 1.0 cm cell and 0.4-1 x 10"2 M for reactions in the 0.1 cm cell. Procedure B: Trans-Ru(TMP)(0)2 Oxidant Solid /rara-Ru(TMP)(MeCN) 2 (1 mg, 1.1 x 10"3 mmol) was placed in a 0.1 cm anaerobic cell and dissolved in dry benzene. Dioxygen was bubbled through the solution for 10 min and the solution monitored by UV-VIS spectroscopy to ensure complete conversion to the dioxo product. The solvent was removed under vacuum and the solid oxidant placed under an atmosphere of Ar. A solution of /PrNtk (2 mL, 2.6 x 10" M) in dry C 6 H 6 or rac-Ph(Me)CHNH2 (1.5 mL, 1.4 x 10"2 M) in C 6 D 6 under Ar, degassed by 3 freeze-pump-thaw cycles, was transferred to the cell via canula and the two solutions mixed for 60 or 70 s before the reaction was monitored. Chapter TV 87 Catalytic Aerobic Oxidations Solutions of /ra«5-Ru(porp)(0)2 (porp = TMP, OCP and OCP-Clg) in benzene were synthesized by w-CPBA oxidation of the carbonyl precursor and purified through a column of basic alumina. UV-VIS spectroscopy was used to determine the concentration of the oxidant (typically 0.1-1 x 10"3 M) using known s values32 and 20 equiv. of the amine were added to 1 mL of the Ru-dioxo solution in a vial (-15 mL) containing a stir bar. The vials were tightly capped and the solutions stirred at 50°C under 1 atm of air for 24 - 90 h. The solutions were then analyzed by GC and the identities of the products were determined by comparison with data for known standards (see Table II. 1, p.27 for GC separation conditions). Substrate and product concentrations were determined using calibration curves of concentration versus peak area allowing percent conversion and catalyst turnover to be calculated. Stoichiometric Oxidation of Amines with fra#is-Ru(porp)(0)2 Initial investigations into the stoichiometric oxidation of amines commenced using /rans-Ru(0CP)(0)2 oxidant and P h 2 C H N H 2 as substrate. The reaction (eq. 4.1) was monitored in the Soret (420 nm) region of the spectrum at low Ru concentrations (~ 10"6 M) in dry benzene under Ar using a minimum 100 equiv. excess of the amine over 12 h. Spectral changes, monitored at 420 nm, are shown in Figure IV.15 The natural logarithm of A -Aco was plotted against time to determine the pseudo first-order rate constant, kobs, for the reactions; A c was determined from the spectrum at t = 12 h. The slopes of the line 4 Absorbance values at 420 nm for benzene solutions of /raras-Ru(OCP)(0)2 (~ 10"6 M) under Ar or 0 2 , in the absence of added amine, remain essentially constant over 7200 s. Chapter IV 88 for the InjA-Aooj versus time plots determined usually over the first 1500 s, gave kobs values ranging from 2-10 x 10"4 s"1 for a range of amine concentrations from 0.5-8.5 x 10" 3 M (Figure IV.2). Unfortunately, plots of kobS against amine concentration showed non-reproducible results, with ko b s values varying by up to 200% for essentially repeat reactions run at the same amine concentration (Figure IV.3). Comparison of the shapes of the absorbance versus time plots, for spectral changes at 420 nm, also showed that the reactions were not reproducible (Figure IV.l). 1.60 i 1.50 ' 1.40 u S 1.30 1 es 1.20 r La © SB 1.10 | < 1.00 ! 0.90 0.80 0.70 0 2000 4000 — I 1 — 6000 8000 Time (s) [amine] = 0.0025 M expt. 1 [amine] = 0.0025 M expt. 2 [amine] = 0.00061 M 10000 12000 14000 Figure IV.L Plots of absorbance, at 420 nm, versus time for the stoichiometric oxidation of Ph 2CHNH 2 with fra«5-Ru(OCP)(0)2 in dry benzene at 23°C under Ar. Essentially repeat experiments, run at the same amine concentration, do not show reproducible absorbance changes. Chapter IV 89 Figure IV.2. Pseudo first-order plots of ln|A-Aoo| versus time for the stoichiometric oxidation of P h 2 C H N H 2 at 23 °C under 1 atm of Ar; [/ra/w-Ru(TMP)(0)2] ~ 5 x 10"6 M and [Ph 2CHNH 2] = 0.0025 M . 9.0 8.0 7.0 S 5.0 X J 4.0 3.0 + 2.0 1.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 [PhzCHNHz] x 103 (M) Figure IV.3. Plot of kob s against [Ph 2CHNH 2] for reactions at 23 °C under 1 atm Ar in dry benzene; non-reproducible results are evident. Instrumental error is within the size of the points. Chapter TV 90 Because of the possibility that very low concentrations of O2 remaining in the solutions may have played a role in the irreproducibility, the reaction was repeated under an atmosphere of O2. In these case, both the P h 2 C H N H 2 (0.3-1.3 x 10"3 M) and trans-Ru(OCP)(0)2 (~ 10"6M) solutions were purged with dry 0 2 rather than dry Ar. Absorbance data were extracted at 420 nm and non-linear regression analysis of the absorbance versus time plots was used to determine both kobs and A» values (Figure IV.4). These kobs values were compared with those determined from the Guggenheim method of analysis, and excellent agreement was found (see Figure B . l , Appendix B). 1.30 - 1 1.20 1.10 g 1.00 « I 0.90 cn < 0.80 0.70 0.60 0.50 A 1 1 1 1 1 1 0 2000 4000 6000 8000 10000 12000 Time (s) Figure IV.4. A typical absorbance (at 420 nm) versus time plot for Ph2CHNH2 oxidation with /ra«s-Ru(OCP)(0)2 under 1 atm of O2 in dry benzene at 23 °C. The line for pseudo first-order kinetics, A = A» + (Ao-Aoo)exp(-kobst), was fit to the data using non-linear regression analysis; [/ra/w-Ru(OCP)(0)2] = 5.1 x IO"6 M and [Ph 2CHNH 2] = 1.3 x IO"3 M . Chapter TV 91 Plots of kobs against [amine] for the reactions under 1 atm of O 2 (Figure IV.5) again showed a similar scatter of points as for reactions performed under 1 atm of Ar. Similar kobs values were obtained in the presence or absence of O 2 , implying that low concentrations of O 2 remaining in solutions purged with Ar are not the source of the irreproducible results. This finding also indicates that the rate of regeneration of Ru(VI)-dioxo species (for the purposes of a catalytic process) is much slower than that of amine dehydrogenation at 23°C in benzene. 7.0 6.0 5.0 0 2.0 m 1.0 0.0 0.00 0.20 0.40 [Ph2CHNH2] x 103 (M) 0.60 0.80 03 under dioxygen • under argon Figure IV.5. Plot of kobs versus [ P h 2 C F f N H 2 ] under 0 2 and Ar in dry benzene at 23 °C. Instrumental error is within the size of the points. Chapter IV 92 It has been shown previously that low concentrations of fra«s-Ru(OCP-Cl8)(0)2 (< 10"5 M) in neat alkane or alkene catalyze the aerobic oxidation of these compounds via free-radical pathways.32 Perhaps a related stoichiometric reaction is occurring with benzene at low [trans-Ru(OCP)(0)2] thus causing a loss of the oxidant that is not involved in amine oxidation. In an effort to rule out this possibility, the reactions were run at a higher Ru-oxidant concentration. Due to the low solubility of the oxidant in C6H6, the solvent was changed to CHCI3 in order to reach concentrations of 10"4 M . The reactions were run following procedure A under Ar using a 0.1 cm path length cell; the first two reactions attempted did not exhibit typical pseudo first-order absorbance changes at 510 nm with time (Figure rV.6). Because the reaction might be light-sensitive, a filter was placed between the sample and source in order to block out light from 200-450 nm and prevent strong absorbance within the Soret region of the spectrum. The anaerobic cell was also wrapped in A l foil in an attempt to limit the effects from ambient light within the room. Plots of absorbance versus time collected under these conditions (Figure IV.7) now displayed typical pseudo first-order changes (Figure IV.8), and ln|A-Aoo| showed a linear dependence on time over the first 3500 s of the reaction; A*, values were determined after 16 h. Examination of the kobs values at an average amine concentration of 0.097 M shows irreproducibility once again; a range of 0.68-1.3 x 10" s' 1 is found (Table IV. 1). This finding indicates that low Ru-dioxo concentrations are not responsible for the irreproducible pseudo first-order kinetics. However, a comparison of Figure IV.6 and Figure IV.8 shows the reactions do exhibit a light-sensitivity at Ru-dioxo concentrations of l O ^ M . Chapter IV 93 0.39 T Time (s) Figure IV.6. Absorbance changes at 510 nm monitored during the stoichiometric reaction of fraHs-Ru(OCP)(0)2 with P h 2 C H N H 2 in CHC1 3 under 1 atm of Ar at 23°C; [/ra>w-Ru(OCP)(0)2] - 2 x 1 0 ^ M . 0,20 180 4"W 500 510 520 530 540 550 560 570 Wavelength Figure IV. 7. Typical spectral changes observed over 480-570 nm for the oxidation of P h 2 C H N H 2 by /ra«s-Ru(OCP)(0) 2 under 1 atm of Ar at 23°C in CHC1 3 . The reaction was run in the presence of a 200-450 nm filter and the U V -VIS cell was wrapped in A l foil to block out ambient light; [trans-Ru(OCP)(0)2] = 4.9 x 10"4 M and [Ph 2CHNH 2] = 9.7 x 10"3M Chapter TV 94 Figure IV.8. Absorbance changes at 510 nm during the stoichiometric reaction of trans-Ru(OCP)(0) 2 (5 x 10"4 M) with P h 2 C H N H 2 in CHC1 3 under 1 atm of Ar at 23°C. The anaerobic cell was wrapped in A l foil, and a 200-450 nm filter was placed between the source and sample in order to limit the effects of ambient room light and prevent absorbance within the Soret (420 nm) region of the spectrum. Tlme(s) 0 500 1000 1500 2000 2500 3000 3500 4000 Figure IV.9. A ln|A-A«,| versus time plot based on absorbance data at 510 nm collected at [Ph 2CHNH 2] ~ 0.0097 M for amine dehydrogenation by trans-Ru(OCP)(0) 2 in CHC1 3. Chapter IV 95 Table IV. 1. The Range of kobs Values Determined for Stoichiometric Oxidation of P h 2 C H N H 2 by fnms-Ru(OCP)(0)2. [7>a#ts-Ru(OCP)(0)2l x 104 (M)a [Ph2CHNH2l x 103 (M) kobsXlO3^-1) 4.7 9.4 0.68 4.9 9.7 1.3 5.1 10.1 0.98 Reaction conditions: 23°C, 0.1 cm path length anaerobic cell, under 1 atm Ar in CHC1 3; with use of 200-450 nm filter. As both 0 2 and the oxidant concentration were thus ruled out as the source of irreproducibility, a few other possibilities were considered: (i) the amine itself was the source of the problems; (ii) there were traces of residual /w-CPBA leftover from the in situ /ra«5-Ru(OCP)(0) 2 synthesis that affected the results; or (iii) the reactions were extremely water-sensitive. In an effort to rule out (i) and (ii), the stoichiometric oxidation of zPrNH 2 was studied using an oxidant, /ra/w-Ru(TMP)(0)2, synthesized by 0 2 -oxidation of the bis(acetonitrile) complex (see procedure B). A box was used to shield the reactions from ambient light and a 200-450 nm filter prevented strong absorbance in the Soret (420 nm) region of the spectrum. Studying time-resolved absorbance traces for spectral changes at 508 nm showed once again that repeat reactions did not give the same results (Figure IV. 10). Finally, in an effort to rule out water as a source of the problems, wet C6D6 (~ 10"3 M determined by 1 H-NMR spectroscopy) was used as the solvent to study the oxidation of rac-Ph(Me)CHNH2 by /ra«5'-Ru(TMP)(0)2. At this concentration, water is present in a 5-7 fold excess over Ru ([trans-Ru(TM?)(0)2] = 1.8-2.8 x 10"4 M). Even under these conditions, repeat reactions did not show the same spectral changes at 506 nm (Figure IV. 11). Chapter IV 96 Figure IV.10. Absorbance at 508 nm versus time plots for the stoichiometric oxidation of z'PrNH2 by /rcws-Ru(TMP)(0)2 at 23 °C under 1 atm of Ar in dry C 6 H 6 ; [/rans-Ru(TMP)(0)2] = 3.2-3.5 x IO - 4 M and [z'PrNH2] = 7.8 x IO - 3 M . 0.85 0.80 0.75 0.70 a 08 0.65 X ! 0.60 c 09 0.55 < 0.50 0.45 0.40 0.35 0 2000 4000 6000 Time (s) 8000 10000 12000 Figure IV.ll. Absorbance at 506 nm versus time plots for the stoichiometric oxidation of rac-Ph(Me)CHNH 2 by ^a«5 -Ru(TMP)(0) 2 at 23°C under 1 atm of Ar in wet C 6 D 6 ; [/rans-Ru(TMP)(0)2] = 1.8-2.8 x 10"4 M and [rac-Ph(Me)CHNH2] = 1.4 x IO - 2 M . Chapter IV 97 As trace air, low oxidant concentration, the amine, trace acid and water had been ruled out as the source of the problems, and no other possible sources could be thought of, it was concluded that the stoichiometric reaction could not be studied by UV-VIS spectroscopy. At this stage of the studies, Dr. M . Ezhova in this group found that the reaction could be studied successfully by ' H - N M R spectroscopy (at concentrations about 10 times those used in the 0.1 cm path length UV-VIS studies). Thus, further reactions in attempts to study the stoichiometric amine oxidation using fra«5-Ru(porp)(0)2 oxidants were not performed. The success of the N M R spectroscopic studies, where the reaction is monitored in the darkness of the N M R probe, implies perhaps an 'extreme' photosensitivity of the system. Amine Dehydrogenation Catalyzed by 7>fl/w-Ru(porp)(0)2 Complexes in Air; Porp = TMP, OCP or OCP-Cls Previous work in this laboratory has demonstrated that />7ms-Ru(porp)(0)2 catalyzes the dehydrogenation of amines to form imines and imine hydrolysis products, or nitriles. Detailed results had only been compiled for the TMP systems. In an effort to study the effect of chlorinating the porphyrin, the reactions were studied using OCP- and OCP-Clg- as well as the TMP-based Ru-oxidants. Analysis of the results indicates that chlorinating the porphyrin ring has no significant effect on the yield of the dehydrogenated products or catalyst turnover (Table rV.2); more importantly the data show that the reactions are at best marginally catalytic, a result that contrasts with data previously reported.33 Efforts were made to confirm the more substantial catalysis (100% conversion for a 20:1 amine/Ru ratio) by increasing the 7raw,s-Ru(TMP)(0)2 and amine Chapter IV 98 concentrations by a factor of 10, and also stirring the reactions under 0 2 ; however, there were negligible changes in the yield of dehydrogenated products after 24 h. Addition of water or a I N NaOH (aq) solution to form a biphasic benzene/water (2:1) system does have a significant effect on catalyst turnover and the amine % conversion. In the biphasic systems, the catalyst turnover after 90 h at 50°C (Table 1V.3) is increased by a factor of 5 over that for reactions run in benzene alone. Even in biphasic systems, a maximum of 8 turnovers or 39.8% conversion of PI12CHNH2 after 24 h is seen (Table rV.3). The low catalytic activity of trans-Ru(porp)(Q)2 toward amine oxidation in benzene is not unexpected given the effect of NEt3 on benzhydrol oxidation catalyzed by trans-Ru(TMP)(0) 2 (see Table III.5, p.79), i.e. within the difficulty of re-converting the Ru(II)-bis(amine) products to the trans-dioxo species. Previous studies have indicated that /ra/75-Ru(II)(porp)(amine)2 complexes were likely intermediates in the catalytic oxidation process,33 and presumably, in the absence of water, regeneration of the dioxo species from these complexes is slow, thus limiting the catalyst turnover. This finding provides further support for the hypothesis presented in Chapter III that water increases the rate of regeneration of Ru(rV)-oxo species from Ru(II) complexes during the catalytic cycle (see eqs. 3.9 and 3.10, p.78). The reason for the discrepancy between the catalyst activity for amine dehydrogenation found in this thesis and the previously reported results33 could not be elucidated. Chapter IV 99 Table IV.2. Product Yield and Catalyst Turnover after 24 h for Amine Dehydrogenation Catalyzed by /rans-Ru(porp)(0)2 Complexes in Ai r . 3 % Yield [Turnover] with Porphyrin Ligand Amine Product(s) TMP b TMP OCP OCP-Clg P h 2 C H N H 2 Ph 2C=NH not used 7[1] 7[1] Ph(Me)CHNH 2 Ph(Me)C=NH 90 [18] 4[1] 15 [3] 8 [2] P h C H 2 N H 2 PhCN 100 [20] 11 [3] could not be accurately determined0 could not be accurately determined0 (PhCH 2 ) 2 NH PhCH=NCH 2Ph PhCN PhCO 76 [15] 11 13 5 [2] 2 4 7 [2] 2 4 5 [3] 0 7 3 Reaction Conditions: 1 mL of benzene solution containing the oxidant and 20 equiv. of the amine heated to 50°C in a sealed vial under 1 atm of air. [Trans-Ru(TMP)(0) 2] = 4.2 x IO"4 M , [/ra«s-Ru(OCP)(0) 2] = 1.7 x 10"4 M and [trans-Ru(OCP-Cl 8)(0) 2] - 1.8 x 10"4 M . Yield and turnover were determined by GC; see Table II. 1 (p.27) for separation conditions. Results previously determined. 0 Inline signal was to small to give an accurate concentration measurement. Table IV.3. Aerobic Dehydrogenation of P h 2 C H N H 2 Catalyzed by Trans-Ru(TMP)(0) 2: The Effect of Neutral and Basic Aqueous/Benzene Biphasic Systems. Solvent System8 % Yield Ph2C=NH (24 h, 90 h)b % Yield Ph2C=0 (24 h, 90h)b Catalyst Turnover (24 h, 90 hf CeH6 7.6, 3.6, 2, 10.7 4 3 CeHe/water 19.5, 5.2, 5, 52.4 13.8 14 C 6 H 6 / 1N NaOH 29.8, 10, 8, 66 7.1 75 3 Reaction conditions: 2 mL of a benzene solution containing the oxidant and 21 equiv. of amine were sealed in a vial and stirred at 50°C under 1 atm of air. Biphasic systems had aqueous and benzene phases in a 1:2 ratio by volume. [Trans-Ru(TMP)(0) 2] = 1.1 x 10"3 M . b Yield and catalyst turnover were determined by GC on a HP-17 column; see Table II. 1 (p.27) for separation conditions. Chapter IV 100 Conclusions Attempts were made to investigate the kinetics of the stoichiometric dehydrogenation of amines by /ra«s-Ru(porp)(0)2 species in an effort to understand better the mechanism of these reactions. Unfortunately, repeat experiments gave irreproducible results as both kobs values and absorbance traces at 420 nm or 506-510 nm were different for essentially repeat reactions run with the same amine and similar Ru concentrations (Figures IV.3, IV.5 and IV.7-IV.i l ) . Traces of 0 2 remaining in solution, low oxidant concentrations, traces of residual acid from oxidant synthesis, trace water and the amine used were eliminated as the sources of the non-reproducible results; the cause of the problem was not resolved. The reactions, however, did exhibit a light-sensitivity at trans-Ru(OC?)(0)2 concentrations of - 10"4 M (cf. Figure Fv\7 and Figure IV.8), the systems showing pseudo first-order absorbance changes at 510 nm for PI12CHNH2 oxidation with /ra«5-Ru(OCP)(0) 2 in CHC1 3 , only when the ambient room light was blocked out and a 200-450 nm filter was used. Based on this light-sensitivity, and the problems in obtaining similar results with repeat experiments, it was concluded that stoichiometric amine oxidation by trans-R\i(porp)(0)2 should not be studied by UV-VIS spectroscopy. Of note, reactions run under 1 atm of Ar and 1 atm of O2 produced a similar range of kobs values, indicating that, under the reaction conditions, regeneration of the Ru-dioxo complex from the Ru(II)-bis(amino) intermediate is slower than the dehydrogenation of the amine (Figure IV.5). The air-oxidation of amines catalyzed by /ra/7s-Ru(porp)(0)2 with porp = TMP, OCP and OCP-Clg was also investigated in order to determine the effect of chlorinating Chapter W 101 the porphyrin ring on the catalyst turnover and yield of dehydrogenation products. Analysis of the reactions after 24 h at 50°C under 1 atm of air indicates that the type of porphyrin ligand used does not affect the catalyst turnover or amine conversion. In fact only 1-3 catalyst turnovers occurred during this time, a result that contradicts the 15-20 turnovers previously attained (Table IV.2). 3 3 Analysis after 90 h at 50°C did not show improved turnovers, nor did stirring the reactions or running them under 1 atm of O2. Adding water or a I N NaOH (aq) solution to the reaction mixture to create a biphasic system, however, yielded up to a 4-fold increase in catalyst turnover after 24 h and a 5-fold increase after 90 h for the oxidation of PI12CHNH2 catalyzed by zram-Ru(TMP)(0)2 (Table IV.3). These results support the conclusion found with alcohol oxidation that water accelerates the regeneration of the Ru(VI)-dioxo complex from Ru(II) complexes. CHAPTER V CONCLUSIONS AND FUTURE WORK General Conclusions The goals set for this thesis were: 1. To investigate the kinetics of the stoichiometric oxidation of para-substituted benzhydrols with /r<ms-Ru(porp)(0)2 oxidants, in order to help establish the mechanism of alcohol oxidation (porp = TMP, OCP or OCP-Clg). 2. As a subsection of goal 1, to determine the role that electronic changes in the alcohol have on the rates of stoichiometric and catalytic oxidations effected by frara,-Ru(porp)(0)2. 3. To investigate the mechanism of amine oxidation by zraws-Ru(porp)(0)2. Kinetic analysis of the stoichiometric oxidation of benzhydrols by trans-Ru(TMP)(0)2 reveals that the reaction mechanism proceeds through the formation of a {Ru-alcohol} adduct; subsequent cleavage of the alcohol a-CH bond, probably via hydride transfer to the Ru=0 moiety, in a rate-determining step leads to the formation of Ru(IV)-bis(alkoxo) and ketone products. Adduct formation is essentially an isenthalpic process and ki is characterized by AHi* = 58 ± 10 kJ/mol and AS^ = -117 + 30 J/(mol K). Electron-donating substituents favour benzhydrol dehydrogenation. 102 Chapter V J 103 Oxidation of benzhydrols is catalyzed by /raw-Ru(porp)(0)2 under 1 atm of air at 50°C, and water is essential for higher catalyst activity. Up to 24 turnovers (98% conversion) is possible in biphasic water/benzene systems using an OCP-Clg-based catalyst. Catalytic activity shows a dependence on the type of porphyrin, giving the following order of reactivity: OCP-Clg > TMP > OCP. Limited linear Hammett relationships indicate that electron-donating substituents also favour alcohol oxidation. A comparison of catalyst turnovers for various alchols ' at 50°C under 1 atm of air show the following trends: 1° benzylic > 2° alkylic > 2° benzylic alcohols for reactions in benzene, and 1° benzylic > 2° benzylic > 2° alkylic alcohols in biphasic aqueous/benzene systems. Information on the stoichiometric oxidation of amines by trans-Ru(OCP)(0)2 and /ra«s-Ru(TMP)(0)2 could not be obtained as UV-VIS spectroscopic studies of the reaction gave irreproducible results. Trace oxygen, acid, water and the amine are ruled out as the sources of variable experimental results; however, the reactions are light-sensitive. Studies of the aerobic oxidation of amines by /raws-Ru(porp)(0)2 at 50°C indicate that the reactions are catalytic only in biphasic aqueous/benzene systems, giving ~ 15 catalyst turnovers for Ph2CHNH2 oxidation after 90 h; only 3 turnovers occur in the absence of added water. These findings are in a direct contrast to previously reported results,33 but, the source of the discrepancy was not detenriined. Chapter V 104 Future Work As only limited Hammett relationships with ki and % alcohol conversion were obtained, further investigations of the stoichiometric and catalytic oxidation of other m-and ^-substituted benzhydrols are required in order to establish fully the effect of electronic changes in the alcohol on oxidation. Attempts to study the stoichiometric dehydrogenation of amines by trans-Ru(porp)(0)2 by UV-VIS spectroscopy were not successful and further work using ' H -N M R spectroscopy was continued in this group by Dr. M . Ezhova. 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Gupta, Int. J. Chem. Kinet., 1984, 16,195. (62) M . Bressan, L. Forti and F. Ghelfi, J. Mol. Catal, 1993, 79, 85. References 110 (63) L. Roecker and T. J. Meyer, J. Am. Chem. Soc, 1987,109, 746. (64) J. March, Advanced Organic Chemistry, 4 ed., John Wiley and Sons, New York, 1992, p. 278-286. (65) P. Dubourdeaux, M . Taveres, A . Grand, R. Ramasseul and J. -C. Marchon, Inorg. Chim. Acta, 1995, 240, 657. A P P E N D I X A A L C O H O L O X I D A T I O N UV-VIS Spectroscopic Data 0.53 0 1.1 M 2000 4000 6000 Time (s) 8000 10000 12000 Figure A. 1. ln |A - Acol or l n |A t + A t - A t Typical absorbance versus time plots for spectral changes at 490 nm measured by UV-VIS spectroscopy for the stoichiometric oxidation of Ph 2 CHOH by /7ww-Ru(TMP)(0)2 under 1 atm of N 2 in benzene at 25°C. 2000 4000 1 i 1 1 • 1 i 1 Time (s) 6000 8000 10000 12000 kobs = L5 x 10 -4 s"1 kobs = 16 x H T s 14000 16000 1 1 1 I Figure A.2. Semilog and Guggenheim plots for the above reaction at [Ph 2CHOH] = 0.211 M . A * was determined from a computer fit of the absorbance versus time data (these Aoo values were in agreement with those expected from the known extinction coefficients of the products). I l l Appendix A 112 Table A.l. k o b s Values for Stoichiometric Oxidation of Ph 2 CHOH at 25°C under 1 atm of N 2 in Benzene. [7>flAi5-Ru(TMP)(0)2l x 104 (M) [Ph2CHOH] (M) Kb* x 104 (s'V 3.3 0.021 0.38 2.8 0.022 0.46 2.6 0.022 0.39 2.9 0.079 0.76 3.3 0.080 0.72 3.5 0.080 1.1 3.3 0.21 1.9 4.5 0.21 1.5 3.0 0.21 1.5 0.50b 0.20 1.5 2.3 0.40 2.1 1.7 0.40 2.2 2.0 0.40 3.0 2.9 0.60 3.8 3.1 0.60 3.6 3.4 1.1 4.9 0.60c 0.027 1.2 0.55c 0.027 1.1 0.79c 0.027 0.75 3.1d 0.25 2.0 3.6d 0.51 3.1 a Spectral changes were monitored at 490 nm in a 0.1 cm path length cell. A» and kobs were determined from a computer fit of A versus t data; using these A » values gave straight line plots for ln|A-Aoo| against time. kob S values determined from Guggenheim plots were within 5% of the values determined by computer fit. A filter was placed between the sample and source in order to block light from 200 - 450 nm. b Run in a 1.0 cm path length cell with the filter. c Run in a 1.0 cm path length cell with no filter; monitored at 422 nm. d Reactions run in the presence of PI13COH (0.34 M). Appendix A 113 Table A.2. kobs Values for Stoichiometric Oxidation of Ph 2 CDOH at 25°C under 1 atm of N 2 in Benzene. f7ra/i5-Ru(TMP)(0)2l x 104 (M) |Ph2CDOH|(M) ko b sxl04(s-1)a 2.7 0.21 0.15 2.6 0.21 0.13 2.6 0.38 0.30 2.3 0.70 0.36 Spectral changes were monitored at 490 nm in a 0.1 cm path length cell. A«> and kobS were determined from K M S plots of A t versus A t + A t where At = 600-5400 s. Plots of ln|A-Ax,| against time, using an average A*, determined over At = 600-5400 s gave straight lines, kobs values were verified by comparison with those determined from Guggenheim plots. A filter was placed between the sample and source in order to block light from 200 - 450 nm. Table A3. ko b s Values for Stoichiometric Oxidation of (p-MeO-CeH^CHOH at 25°C under 1 atm of N 2 in Benzene. rrrqws-Ru(TMP)(Q)21 x 104 (M) [(p-MeO-QftQiCHOHl (M) k o b s x 104 (s'ijr" 4.1 0.016 0.48 3.7 0.016 0.95 3.6 0.017 0.57 4.3 0.040 0.85 3.1 0.042 0.73 2.9 0.041 0.73 3.3 0.099 2.3 4.4 0.099 1.5 3.0 0.099 1.3 3.4 0.11 2.3 3.4 0.12 2.7 3.0 0.12 2.3 3.5 0.23 3.6 4.2 0.23 3.5 3.2 0.23 3.8 2.9 0.52 8.1 Spectral changes were monitored at 490 nm in a 0.1 cm path length cell. A« and ko b s were determined from a computer fit of A versus t data; using these A*, values gave straight line plots for ln|A-A«,| against time. ko b s values determined from Guggenheim plots were within 5% of the values determined by computer fit. A filter was placed between the sample and source in order to block light from 200 - 450 nm. Appendix A 114 Table A.4. kobs Values for Stoichiometric Oxidation of (p-F-CeFL^CHOH at 25°C under 1 atm of N 2 in Benzene. [Trg#is-Ru(TMP)(0)2l x 104 (M) Kp-F-CfiH^CHOHl (M) kpb, x 104 (g'1)*" 3.0 0.012 0.99 3.4 0.012 0.58 4.7 0.015 1.33 3.3 0.023 1.17 3.0 0.023 0.81 3.0 0.023 0.85 3.3 0.024 1.11 3.2 0.066 0.87 4.5 0.066 0.91 5.2 0.066 0.90 4.0 0.067 1.47 3.1 0.088 1.97 3.6 0.088 1.95 6.5 0.089 1.45 2.9 0.089 2.26 4.0 0.089 1.38 3.8 0.11 1.50 3.7 011 2.19 3.4 0.11 2.02 2.9 0.11 1.85 3.8 0.20 2.65 4.1 0.20 2.24 4.3 0.21 2.44 5.1 0.21 2.36 3.6 , 0.39 3.22 3.8 0.74 4.13 Spectral changes were monitored at 490 nm in a 0.1 cm path length cell. Aoo and kobs were determined from a computer fit of A versus t data; using these A » values gave straight line plots for l n |A - Aoo| against time. k o b S values determined from Guggenheim plots were within 5% of the values determined by computer fit. A filter was placed between the sample and source in order to block light from 200 - 450 nm. Appendix A 115 1 H-NMR Spectroscopic Data The initial concentration of trans-Ru(TMP)(0)2 was determined from UV-VIS spectroscopy by using a known e value. For all the reactions run with [alcohol] > 0.02 M , [trans-Ru(YMP)(0)2] = 5-7 x 10"4 M ; for reactions run with [alcohol] < 0.02 M , [trans-Ru(TMP)(0)2] = 5 x 10"4 M . Unless otherwise mentioned, all of the oxidation reactions were performed under 1 atm of dry N 2 . Table A.S. 20°C, [Ph 2CHOH] = 0.015 M . Time (s) Relative intensity of fi-H of Relative intensity of Ph2CHOH /ra#is-Ru(TMP)(0)2 a-CH x 10 3 637 59.2 0.329 1237 58.6 0.329 1837 59.9 0.351 2437 58.0 0.368 3037 53.8 0.373 3637 55.9 0.392 4237 49.4 0.394 5437 44.6 0.406 6637 36.7 0.404 7837 29.8 0.402 9637 27.4 0.423 11437 20.4 0.416 Table A.6. 20°C, [Ph 2CHGH] = 0.053 M . Time (s) Relative intensity of /?-H of Relative intensity of Ph2CHOH fra/is-Ru(TMP)(0)2 a-CH x 10 3 349 114 0.529 949 103 0.556 1549 93.4 0.558 2149 81.3 0.532 Appendix A 116 Table A. 7. 20°C, [Ph 2CHOH] = 0.057 M . Time (s) Relative intensity of /3-H of fra#is-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 277 118 0.503 877 118 0.562 1477 115 0.621 2077 109 0.647 2677 104 0.667 3277 93.2 0.681 3877 86.4 0.695 Table A.8. 20°C, [Ph 2CHOH] = 0.057 M . Time (s) Relative intensity of /3-H of f/-a/w-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10"3 228 132 0.553 828 126 0.553 1428 122 0.559 2028 116 0.564 2628 106 0.572 3228 97.9 0.585 3828 90.0 0.600 5028 68.7 0.603 6228 49.3 0.589 7428 33.4 0.546 8628 21.1 0.475 9828 14.9 0.421 11028 11.0 0.379 Table A.9. 20°C, [Ph 2CHOH] = 0.21 M . Time (s) Relative intensity of /3-H of *ra#is-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 302 189 1.97 602 178 2.06 902 174 2.19 1202 164 2.27 1502 153 2.37 1802 140 2.39 2102 126 2.16 2702 93.1 1.76 Appendix A 117 Table A.10. 20°C, [Ph 2CHOH] = 0.21 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH fra#is-Ru(TMP)(0)2 a-CH x 10 3 352 115 1.71 652 144 1.94 952 137 2.03 1252 127 2.09 1552 119 2.15 1852 108 2.19 2152 94.3 2.20 2752 70.3 1.85 Table A.ll. 20°C, [Ph 2CHOH] = 0.20 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH fra/is-Ru(TMP)(0)2 a-CH x 10 3 352 90.8 1.23 652 115 1.66 952 114 1.75 1252 109 1.79 1552 105 1.84 1852 101 1.87 2452 96.3 1.99 3052 85.1 2.01 3652 76.2 2.04 4252 63.5 2.08 Appendix A 118 Table A.12. 20°C, [Ph 2CHOH] = 0.62 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH *ra#w-Ru(TMP)(0)2 a-CH x 10 3 302 81.3 3.95 602 77.8 4.27 902 72.8 4.31 1202 65.6 4.34 1502 61.7 4.36 2102 48.9 4.23 2702 40.2 4.09 3302 37.2 4.05 3902 29.6 3.97 4502 23.2 3.93 5102 21.1 3.93 5702 17.8 3.88 Table A.13. 20°C, [Ph 2CHOH] = 0.62 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH *ra#w-Ru(TMP)(0)2 a-CH x 10 3 334 87.2 4.34 634 86.9 4.56 934 84.5 4.69 1234 78.5 4.82 1534 73.6 4.86 2134 65.3 4.97 2734 58.2 5.05 3334 51.2 5.15 3934 42.0 5.16 4534 36.5 5.21 5134 29.4 5.13 5734 23.6 5.07 Appendix A 119 Table A.14. 20°C, [Ph 2CHOH] = 0.61 M . Time (s) Relative intensity of J3-H of fra«5-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 233 84.3 4.64 533 78.4 4.78 833 78.6 4.92 1133 74.0 5.08 1433 71.3 5.18 2033 61.3 5.18 2633 51.0 5.13 3233 43.8 / 5.18 3833 38.7 5.17 4433 29.6 4.98 5033 26.8 5.02 5633 21.2 4.89 6233 17.0 4.78 6833 14.1 4.74 Table A.15. 20°C, [Ph 2CHOH] = 1.2 M . Time (s) Relative intensity of /3-H of fra/is-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x IO"3 269 52.1 7.81 389 51.3 8.18 509 48.2 8.31 629 48.8 8.39 749 45.6 8.58 869 45.4 8.79 1169 41.4 8.69 1469 41.8 8.80 1769 36.0 9.01 2069 33.7 9.04 2369 31.5 9.02 2669 26.3 8.94 3269 25.0 9.03 3869 19.1 9.01 Appendix A 120 Table A.16. 20°C, [Ph 2CHOH] = 1.2 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH fra#is-Ru(TMP)(0)2 a-CH x 10 3 238 62.0 6.86 358 68.7 7.27 658 70.4 7.63 958 67.7 7.90 1258 61.7 7.99 1558 57.2 8.05 1858 55.2 7.97 2158 49.8 8.03 2458 43.0 8.01 3058 38.3 7.97 3658 32.0 7.95 4258 29.6 7.97 4858 24.9 7.79 5458 20.2 7.77 Table AJ 7. 20°C, [Ph 2CHOH] = 1.2M. Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH /ra#is-Ru(TMP)(0)2 a-CH x IO"3 293 44.0 8.41 593 51.2 9.21 893 48.1 9.34 1193 38.6 9.22 1493 36.4 9.42 1793 34.9 9.24 2093 28.4 9.36 Appendix A 121 Table A.18. 20°C, [Ph 2CHOH] = 1.2 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH fra/is-Ru(TMP)(0)2 a-CH x 10 3 334 48.0 6.30 454 49.0 6.56 754 42.9 6.46 1054 37.8 6.48 1354 37.9 6.70 1654 34.7 6.60 1954 33.2 6.58 2254 28.9 6.57 2854 24.4 6.64 3454 19.4 6.63 Table A.19. 20°C, [Ph 2CHOH] = 0.20 M , [Ph 3CHOH] = 0.41 M . Time (s) Relative intensity of y#-H of Relative intensity of Ph2CHOH fra#is-Ru(TMP)(0)2 a-CH x 10"3 445 1.086 0.152 768 1.073 0.149 1040 0.941 0.150 1610 0.668 0.149 2409 0.585 0.148 3210 0.448 0.150 4004 0.361 0.150 4841 0.299 0.150 5637 0.283 0.141 Appendix A 122 Table A.20. 20°C, [Ph 2CDOH] - 0.022 M . Time (s) Relative intensity of /3-H of *ra#M-Ru(TMP)(0)2 Relative intensity of Ph2CDOH O H x 10"3 447 68.6 0.642 4047 65.9 0.622 7647 61.2 0.616 11247 64.3 0.644 14847 61.7 0.644 18447 57.2 0.635 22047 55.6 0.642 25647 54.0 0.641 29247 50.5 0.629 32847 51.8 0.644 36447 47.9 0.639 40047 46.7 0.638 43647 43.1 0.633 47247 40.4 0.629 Table A.21. 20°C, [Ph 2CDOH] = 0.024 M . Time (s) Relative intensity of /3-H of fra/is-Ru(TMP)(0)2 Relative intensity of Ph2CDOH OH x IO"3 3240 45.7 0.329 6840 43.5 0.338 10440 41.2 0.340 14040 40.0 0.343 17640 37.5 0.339 21240 36.7 0.344 24840 34.0 0.338 28440 31.6 0.336 32040 30.7 0.337 35640 29.8 0.332 39240 27.5 0.325 42840 25.6 0.331 46440 24.7 0.329 50040 23.0 0.325 Appendix A 123 Table A.22. 20°C, [Ph 2CDOH] = 0.40 M . Time (s) Relative intensity of fi-H of Relative intensity of Ph2CDOH /ra#is-Ru(TMP)(0)2 O H x 10"3 969 97.8 2.70 4569 97.6 2.83 8169 87.0 2.80 11769 83.5 2.78 15369 74.0 2.84 18969 76.3 2.89 22569 71.7 2.95 26169 66.0 2.97 29769 64.5 2.96 33369 60.9 2.91 36969 53.3 2.96 Table A. 23. 20°C, [Ph 2CDOH] = 0.40 M . Time (s) Relative intensity of /?-H of Relative intensity of Ph2CDOH frans-Ru(TMP)(0)2 OH x 10 3 2007 35.8 1.20 9207 34.1 1.29 12807 32.2 1.27 16407 31.0 1.29 20007 28.4 1.28 23607 27.8 1.29 27207 26.6 1.30 30807 21.5 1.24 34407 21.8 1.26 Appendix A 124 Table A.24. 20°C, [Ph 2CDOH] = 0.58 M . Time (s) Relative intensity of /3-H of *ra#M-Ru(TMP)(0)2 Relative intensity of Ph;CDOH O H x 10"3 395 55.4 2.70 3995 58.3 2.83 7595 53.4 2.80 11195 48.5 2.78 14795 45.9 2.84 18395 43.4 2.89 21995 40.2 2.95 25595 37.1 2.97 29195 34.4 2.96 32795 30.6 2.91 36395 29.7 2.96 38195 28.1 2.96 Table A.25. 20°C, [Ph 2CDOH] = 0.58 M . Time (s) Relative intensity of /3-H of /ra«s-Ru(TMP)(0)2 Relative intensity of Ph2CDOH O H x 10"3 685 56.6 1.74 4285 52.1 1.80 7885 48.6 1.79 11485 46.9 1.80 15085 44.9 1.82 18685 41.3 1.79 22285 38.1 1.79 25885 35.9 1.81 29485 34.8 1.82 33085 31.7 1.80 36685 28.3 1.79 40285 27.1 1.78 43885 26.4 1.80 47485 23.9 1.78 Appendix A 125 Table A.26. 20°C, [Ph 2CDOH] = 0.58 M . Time (s) Relative intensity of /3-H of *ra#w-Ru(TMP)(0)2 Relative intensity of Ph2CDOH O H x IO"3 316 87.1 3.93 3916 82.8 4.01 7516 76.8 3.97 11116 72.0 3.97 14716 66.2 3.96 18316 60.3 3.94 21916 57.0 3.91 25516 53.4 3.93 29116 49.3 3.95 32716 45.6 3.92 Table A.27. 20°C, [Ph 2CHOD] = 0.011 M . Time (s) Relative intensity of >3-H of *ra/w-Ru(TMP)(0)2 Relative intensity of Ph2CHOD a-CH x 10 3 2833 21.3 0.139 3382 24.6 0.139 4228 21.4 0.141 5062 19.7 0.142 Table A.28. 20°C, [Ph 2CHOD] = 0.093 M . Time (s) Relative intensity of /3-H of frans-Ru(TMP)(0)2 Relative intensity of Ph2CHOD a-CH x 10 3 754 70.7 0.505 1054 71.7 0.532 1354 67.6 0.551 1954 63.0 0.594 2554 60.1 0.625 3154 52.4 0.601 3754 48.5 0.535 4354 43.0 0.507 5554 31.0 0.528 6754 20.7 0.616 7954 12.7 0.585 9154 9.63 0.531 10354 6.90 0.475 11554 6.14 0.435 Appendix A 126 Table A.29. 20°C, [Ph 2CHOD] = 0.41 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph 2CHOD /ra«s-Ru(TMP)(0)2 a-CH x 10 3 506 1.68 0.139 981 1.61 0.143 1405 1.21 0.136 1828 1.15 0.137 2245 1.07 0.140 3325 0.648 0.127 3959 0.581 0.136 4543 0.468 0.127 5133 0.376 0.130 5908 0.313 0.130 Table A.30. 20°C, [Ph 2CHOD] = 0.74 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph 2CHOD /ra«5-Ru(TMP)(0)2 a-CH x 10 3 508 2.38 0.152 1292 1.63 0.149 1791 1.42 0.150 2340 1.12 0.149 2922 0.893 0.148 3593 0.771 0.150 4243 0.595 0.150 5264 0.427 0.150 7430 0.228 0.141 Appendix A 127 Table A.31. 20°C, [Ph 2CHOD] = 1.1 M . Time(s) Relative intensity of /3-H of Relative intensity of Ph2CHOD *ra/is-Ru(TMP)(0)2 a-CH x 10 3 643 61.1 7.32 943 57.4 7.41 1243 51.7 7.40 1843 46.0 7.33 2443 37.5 7.18 3043 29.4 7.22 3643 23.8 7.08 4243 23.0 7.23 4843 20.0 7.13 5443 17.9 7.12 6043 16.6 7.18 6643 13.3 7.17 7843 10.7 7.19 Table A.32. 35.5°C, [Ph 2CHOH] = 0.021 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH *ra/w-Ru(TMP)(0)2 a-CH x 10 3 277 94.4 0.445 469 90.5 0.439 661 87.8 0.444 1003 82.9 0.475 1345 76.0 0.489 1687 68.9 0.493 2029 58.2 0.448 2371 52.5 0.427 2713 43.9 0.392 3055 34.9 0.379 Appendix A Table A.33. 35.5°C, [Ph 2CHOH] = 0.21 M . 128 Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH *ra#w-Ru(TMP)(0)2 a-CH x 10 3 256 54.1 1.16 598 45.0 1.27 940 39.8 1.32 1282 32.4 1.32 1624 25.5 1.27 1966 20.1 1.20 Table A.34. 35.5°C, [Ph 2CHOH] = 0.20 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH /ra«s-Ru(TMP)(0)2 a-CH x 10 3 248 62.7 1.29 590 56.6 1.51 932 53.0 1.62 1274 47.3 1.70 1616 38.8 1.75 1958 30.7 1.75 2300 25.4 1.77 2942 13.8 1.71 3584 8.43 1.53 4226 8.41 1.50 Table A.35. 35.5°C, [Ph 2CHOH] = 0.20 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH *ra/is-Ru(TMP)(0)2 a-CH x 10 3 253 81.0 1.27 595 79.9 1.44 937 66.3 1.52 1279 57.0 1.57 1621 41.1 1.49 1963 32.2 1.52 2305 24.5 1.57 2947 14.5 1.40 3589 9.68 1.21 4231 8.03 1.17 Appendix A 129 Table A.36. 35.5°C, [Ph 2CHOH] = 0.40 M . Time (s) Relative intensity of >3-H of fra«5-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 309 62.4 3.20 651 49.5 3.24 993 41.1 3.33 1335 33.6 3.34 1677 26.9 3.33 2019 21.6 3.23 2361 16.5 3.14 3003 11.5 2.95 3645 7.01 2.81 4287 4.03 2.63 Table A.3 7. 35.5°C, [Ph 2CHOH] = 0.40 M . Time (s) Relative intensity of /3-H of fra/is-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 350 144 6.92 542 141 7.32 734 128 7.35 1076 114 7.52 1418 101 7.80 1760 84.6 7.82 2402 59.3 7.84 3044 37.7 7.73 4286 16.2 6.71 5528 6.19 6.04 Table A.38. 35.5°C, [Ph 2CHOH] = 0.39 M . Time (s) Relative intensity of /3-H of fraiis-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH xlO 3 286 106 4.52 628 80.8 4.43 970 65.2 4.47 1312 57.9 4.60 1654 21.3 3.05 Appendix A 130 Table A.39. 35.5°C, [Ph 2CHOH] = 0.39 M . Time (s) Relative intensity of /3-H of fra#w-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 245 77.982 2.88 587 58.917 3 929 51.609 3.15 1271 45.279 3.15 1613 36.22 3.11 1955 25.998 2.96 2297 20.616 2.81 2939 13.86 2.65 3581 9.894 2.5 4223 7.29 2.38 Table A.40. 50.0°C, [Ph 2CHOH] = 0.021 M . Time (s) Relative intensity of /3-H of /ra/w-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 275 125 0.731 446 200 1.36 617 159 1.45 788 125 1.41 959 102 1.34 1130 75.3 1.26 1301 52.9 1.26 Table AM. 50.0°C, [Ph 2CHOH] = 0.10 M . Time (s) Relative intensity of /3-H of fra«*-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 257 104 1.44 398 73.9 1.37 539 60.3 1.45 680 44.0 1.33 821 28.1 1.27 962 15.9 1.32 Appendix A 131 Table A.42. 50.0°C, [Ph 2CHOH] = 0.11 M . Time (s) Relative intensity of /3-H of *ra/is-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 235 73.6 1.17 376 46.4 1.18 517 31.5 1.23 658 22.7 1.15 799 13.8 1.08 940 10.9 1.14 Table A.43. 50.0°C, [Ph 2CHOH] = 0.20 M . Time (s) Relative intensity of /3-H of *ra«s-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 234 60.1 1.10 375 43.1 1.71 516 37.1 1.86 657 26.8 1.81 798 20.5 1.80 939 12.3 1.80 1080 7.73 1.74 1221 5.60 1.68 1362 3.64 1.64 Table A.44. 50.0°C, [Ph 2CHOH] = 0.21 M . Time (s) Relative intensity of /3-H of fra#is-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 260 96.2 3.24 401 66.8 3.22 542 41.7 3.27 683 30.0 3.21 824 23.8 3.17 965 15.2 3.12 1106 12.1 3.02 1247 6.86 2.89 Appendix A 132 Table A.4S. 50.0°C, [Ph 2CHOH] - 0.31 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH *ra#w-Ru(TMP)(0)2 a-CH x 10 3 272 109 7.97 413 68.8 7.10 554 51.3 6.70 695 37.5 6.57 836 31.6 6.58 977 21.4 6.16 1118 18.6 6.24 Table A.46. 50.0°C, [Ph 2CHOH] = 0.30 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH fra/w-Ru(TMP)(0)2 a-CH x 10 3 272 129 1.14 413 98.1 1.11 554 73.4 1.10 695 57.7 1.07 836 46.6 1.05 977 36.9 1.00 1118 27.3 0.993 Table A.47. 50.0°C, [Ph 2CHOH] = 0.30 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH /ra#is-Ru(TMP)(0)2 a-CH x 10 3 335 34.7 0.465 476 18.2 0.430 617 12.1 0.411 758 10.3 0.426 899 8.85 0.398 Appendix A 133 Table A.48. 50.0°C, [Ph 2CHOH] = 0.42 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH /ra#!s-Ru(TMP)(0)2 a-CH x 10 3 355 83.4 1.26 496 96.3 1.44 637 58.0 1.44 778 49.5 1.40 919 26.0 1.40 Table A.49. 50.0°C, [Ph 2CHOH] = 0.40 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH fra/w-Ru(TMP)(0)2 a-CH x 10 3 296 107 1.10 437 89.8 1.11 578 64.6 1.11 719 48.9 1.13 860 40.0 1.10 1001 28.7 1.09 1142 20.2 1.06 Table A.50. 50.0°C, [Ph 2CHOH] = 0.40 M . Time (s) Relative intensity of /3-H of Relative intensity of Ph2CHOH *ra/w-Ru(TMP)(0)2 a-CH x 10 3 312 93.7 1.59 453 71.9 1.57 594 50.3 1.53 735 45.7 1.52 876 26.7 1.50 1017 19.6 1.47 1158 6.74 1.49 Appendix A 134 Table A.51. 25°C, [Ph 2CHOH] = 0.71 M, under 1 atm of air. Time (s) Relative intensity of /3-H of /ra/w-Ru(TMP)fO)2 Relative intensity of Ph2CHOH a-CH x 10 3 788 12.4 0.158 1380 12.5 0.149 1980 9.03 0.155 2530 7.35 0.156 3120 5.25 0.156 3775 5.44 0.148 4230 3.53 0.151 5459 1.73 0.150 6180 1.44 0.150 Table A. 52. 25°C, [Ph 2CHOH] = 0.075 M , under 1 atm of dry 0 2 . Time (s) Relative intensity of fi-H of *ra/w-Ru(TMP)(0)2 Relative intensity of Ph2CHOH a-CH x 10 3 509 5.72 0.022 1152 4.24 0.022 1836 3.34 0.020 2414 2.79 0.021 3019 2.09 0.022 3566 2.19 0.024 4198 1.53 0.022 4813 1.29 0.021 Appendix A 135 Table A. 53. kobs Values for Stoichiometric Oxidation of Ph 2 CHOH under 1 atm of N 2 in Benzene-dg. Temperature (°C) [Ph2CHOH] (M) kobsXlOV 1)* 20.0 0.015 1.2 0.053 1.9 0.057 1.7 0.057 1.5 0.20 2.2 0.21 2.6 0.21 2.8 0.61 2.7 0.62 2.8 0.62 2.7 1.2 3.0 1.2 2.9 1.2 2.5 1.2 3.2 35.5 0.021 2.9 0.20 6.1 0.20 7.0 0.21 5.9 0.39 6.2 0.39 5.5 0.40 5.8 0.40 6.2 50.0 0.021 13 0.10 24 0.11 26 0.20 25 0.21 24 0.30 21 0.30 18 0.30 24 0.40 19 0.40 21 0.42 23 Values were determined from a plot of ln[/raMS-Ru(TMP)(0) 2], determined from the changes in signal intensity of the /3-H-atoms of the TMP ring using the alcohol C H signal intensity as an internal standard, versus time. Plots were linear over at least two half-lives. Appendix A 136 Table A. 54. ko b s Values for Stoichiometric Oxidation of Ph 2 CDOH at 20°C under 1 atm of N 2 in Benzene-d6. [Ph2CDOH](M) k o „ s x 10 4 (s1)8 0.022 0.11 0.024 0.13 0.40 0.18 0.40 0.17 0.58 0.22 0.58 0.18 0.58 0.20 a Values were determined from a plot of ln[/ra«5-Ru(TMP)(0) 2], determined from the changes in signal intensity of the /3-H-atoms of the TMP ring using the alcohol C H signal intensity as an internal standard, versus time. Plots were linear over at least two half-lives. Table A.55. k o b s Values for Stoichiometric Oxidation of Ph 2 CHOD at 20°C under 1 atm of N 2 in Benzene-d6. [Ph2CHOD] (M) k o b s x 10 4 (s 1)a 0.011 0.67 0.093 2.4 0.41 3.1 0.74 3.2 U _2A a Values were determined from a plot of ln|>a«s-Ru(TMP)(0) 2], determined from the changes in signal intensity of the /3-H-atoms of the TMP ring using the alcohol C H signal intensity as an internal standard, versus time. Plots were linear over at least two half lives. APPENDIX B AMINE OXIDATION UV-VIS Spectroscopic Data Time (s) 0 1000 2000 3000 4000 5000 6000 7000 8000 0.0 I 1 1 1 1 I ' 1 1 1 I 1 1 1 1 I 1 1 1 ' I 1 1 ' 1 I ' 1 1 ' 1 ' 1 ' 1 I ' 1 1 ' I -4.0 -1-Figure B.l. Comparison of a ln|A-A«>| versus time plot (A* determined from non-linear regression analysis of an absorbance at 420 nm versus time plot) with a Guggenheim analysis of the absorbance data for the oxidation of Ph 2 CHOH by /ra«s-Ru(OCP)(0) 2 under 1 atm of 0 2 in dry benzene at 23°C. 137 Appendix B 138 Table B.l. Stoichiometric Oxidation of P h 2 C H N H 2 by /ra«s-Ru(OCP)(0) 2 Under 1 atm Arat23°C. [toms-Ru(OCP)(0)2] x 106 (M) [Ph2CHNH2] x 10 3 (M) kotailoV1)' 4.7 0.48 4.4 6.3 0.58 2.1 5.7 0.61 2.9 9.2 1.2 3.6 4.5 1.2 6.3 3.7 1.6 7.4 6.8 1.7 8.3 not measured 2.5 4.9 5.1 2.5 9.8 5.2 2.6 8.5 5.8 3.1 9.3 5.8 5.3 5.0 5.8 8.2 7.6 Spectral changes were monitored at 420 nm for reactions occurring in a 1.0 cm path length cell under 1 atm of Ar at 23°C in dry benzene, kobs was determined from the slope of ln|A - Aoo| versus time plots; Ax, was the absorbance at 420 nm at t = 12 h. Table B.2. Stoichiometric Oxidation of P h 2 C H N H 2 by /ra«5-Ru(OCP)(0) 2 under 1 atm of 0 2 . [frq«s-Ru(OCP)(Q)2] x 106 (M) [Ph2CHNH2] x 103 (M) kpbs x 104 (s"1)' 1.5 0.39 5.47 4.7 0.48 2.24 5.8 0.58 2.33 6.6 0.66 1.62 7.6 0.76 3.26 5.1 1.3 3.4 Spectral changes were monitored at 420 nm for reactions occurring in a 1.0 cm path length cell under 1 atm of 0 2 at 23 °C in dry benzene, kobs and A* were determined from a non-linear regression fit of A = Ax. + (Ao - Aco)exp{-kobst} to the A versus t data. These values for kobs were verified by comparison to those determined from a Guggenheim analysis of the absorbance data. Appendix B 1 3 9 Table B.3. Stoichiometric Oxidation of P h 2 C H N H 2 by /rara-Ru(OCP)(0) 2 at High Concentrations. [fra/is-Ru(OCP)(0)2] x 104 (M) |Ph2CHNH2] x 10 3 (M) k„b s X 104 ( S 1 ) " 4 . 7 9.4 7.3 4 .8 9 .6 2 2 4 . 9 9 .7 16 5.1 10.1 12 Spectral changes were monitored at 5 1 0 nm for reactions occurring in a 1.0 cm path length cell under 1 atm of 0 2 at 23 ° C in CHCI3. kobs was determined from the slope of ln |A - Aoo| versus time plots; A*, was the absorbance at 5 1 0 nm at t = 1 h. The reaction vessel was wrapped in A l foil and a filter was placed between the sample and source in order to block out light from 2 0 0 - 4 5 0 nm. The amount of absorbance versus time data collected for the stoichiometric oxidations of /PrNH 2 and rac-Ph(Me)CHNH2 by /ra«5-Ru(TMP)(0) 2 is too large to be reproduced in this appendix. Please see the plots of absorbance versus time in Chapter IV for a pictorial representation of the spectral changes, at 5 0 6 and 5 0 8 nm respectively, that occurred during the reactions (Figures IV. 10 and TV.l 1). 

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