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O₂-oxidations catalyzed by trans-dioxoporphyrinatoruthenium(VI) species Cheng, Stephen Yau Sang 1996

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02-Oxidations Catalyzed by rra«s-Dioxoporphyrinatomtherrium(Vt) Species by Stephen Yau Sang Cheng B.Sc, University of British Columbia, 1992 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We accept this thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA July 1996 © Stephen Y. S. Cheng, 1996. 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 Ctf£j*fi Tfi-«/ The University of British Columbia Vancouver, Canada Date S^Y^t V{ DE-6 (2/88) Abstract Some /raw5-RuVI(porp)(0)2 complexes [porp = TMP (1), TDCPP (2), TDCPP-C18 (3)] were synthesized and used to oxidize, both stoichiometrically and (in the presence of air/02) catalytically, a variety of organic compounds in benzene under relatively mild conditions. Ru(porp) (The Z labels apply to all the pyrrole positions; the ^ X/Y labels apply to all the phenyl groups) X = Y = Me; Z = H TMP X = C1; Y = Z = H TDCPP X = Z = C1; Y = H TDCPP-C18 The kinetic data (measured by stopped-flow) for the stoichiometric oxidation of EAr3 substrates (E = P, As, Sb) by (1) to give initially RuIV(TMP)(0)(OEAr3) suggest that the O-atom transfer mechanism, governed by a ki second-order rate constant, involves electrophilic attack of a Ru=0 moiety on the lone-pair of electrons on the E-atom. For a kx series of P(p-X-C6H4)3 substrates, the ki values do not give a linear Hammett plot Oogj^ vs. a); however, the plot of AH* versus o is linear, and shows that a more electron-releasing para substituent gives a more favourable, lower value AH*. The AS* values correlate linearly with the molecular masses of the phosphines, with bulkier substrates giving rise to more favourable, less negative AS* values, an indication that the O-atom transfers are strongly vibrationally coupled. In subsequent stages of the mechanism, the OEAr3 ligand dissociates from the Ru(IV) intermediate to form RuIY(TMP)(0), which then disproportionates to (1) and Run(TMP), and excess EAr3 reacts with the latter to form Run(TMP)(EAr3) species. Under 1 atm air or O2, the oxidation of EAr3 substrates becomes catalytic; approximately 1 turnover h"1 is obtained for the oxidation of PPh3 at ambient conditions. The oxidative dehydrogenation of'PrOH by (1) follows the indicated stoichiometry: (1) + 3 TrOH -> RuTV(TMP)(0'Pr)2 + acetone + 2 H20 The Ru(IV) product was characterized crystallographically. Species (1) can also oxidize other primary or secondary alcohols (e.g. benzyl alcohol, 1-PrOH, l,3-dichloro-2-propanol, 1-phenylethanol, etc.) to the corresponding aldehydes or ketones. The activation parameters for the stoichiometric oxidation of PrOH and benzyl alcohol are: AH* = 45 ± 7 and 65 ± 11 kJmol"1, and AS = -167 ± 10 and -70 ± 20 Jmol^K"1, respectively. A small kinetic isotope effect of kH/kD -1.9 observed for the stoichiometric oxidation of "PrOH at 18 °C is attributed to cleavage of the alcohol a-C-H bond in the rate-determining step. Exposure of Rurv(TMP)(0'Pr)2 to moist air in benzene solution regenerates (1), and thus the catalytic 02-oxidation of PrOH becomes viable. Complexes (1), (2) and (3) are all active catalysts for the aerobic, selective oxidation of alcohols to aldehydes or ketones at room temperature or 50 °C under 1 atm air. The activities of the catalysts followed the order (1) > (3)» (2) for the oxidation of benzyl alcohol to benzaldehyde: in a 2-phase benzene/3.0 M aq. KOH system, (1) gave 2000 turnovers in 13 d at 50°C, iii and (3) gave 1200 turnovers in 15 d. While (1) was not very efficient in oxidizing 1-phenylethanol to acetophenone, giving only a few turnovers before being deactivated, (3) produced 140 turnovers in 60 h under the same 2-phase conditions. Complex (3) does not effectively catalyze the oxidation of alkenes and alkanes in benzene under 1 atm O2 at 50 °C; however, at 35 - 90 °C under 1 atm O2, (3) (at low concentrations of ~10"5 M, but not at 10"3 M) does catalyze the oxidation of neat cyclohexene, c/s-cyclooctene and methylcyclohexane via free-radical pathways. Hydroperoxides are present in the reaction solutions, and the addition of the radical inhibitor BHT (2,6-ditertbutyl-4-methylphenol) stops the oxidations. Approximately 60000 turnovers were realized in 26 h (and after 55 h, 120000 turnovers, 80% total conversion) for the oxidation of cyclooctene, and the reaction was > 80% selective for epoxide formation; cyclohexene yielded only ~ 3 % epoxide, the main products being cyclohexene-2-ol and cyclohexene-2-one. The oxidation of methylcyclohexane yielded mainly 1 -methylcyclohexanol and 2-, 3- and 4-methylcyclohexanones, with smaller amounts of the corresponding 2-, 3- and 4-methylcyclohexanols. The reaction of HO Ac' acids (CF3COOH and CHCl2COOH) with (1) yields paramagnetic RuIV(TMP)(OAc')2 species. For the bis(CF3COO) complex, a u,eff value of 2.5 pB is consistent with a Ru(IV) S = 1 spin state, and the linear dependence of the 1H-chemical shifts of the TMP ligand with inverse temperature shows that a single spin state exists from -60 to +25 °C . The reaction of phenol with (1) studied in preliminary work earlier in this laboratory was shown to give the following products: a paramagnetic, S = 1 Ru(IV)-TMP iv species, 0.5 equivalents ofp-benzoquinone and 1.3 equivalents of H20. The Ru(IV) product was proposed to be Rurv(TMP)(/?-OC6H40H)2; however, the data from the present thesis work favour the formulation as RuIV(TMP)(OC6H5)2, while /?-hydroquinone is formed via O-atom insertion at the para position of the phenol. Species (1) oxidizes the /7-hydroquinone formed to give ^-benzoquinone (and presumably H20); the oxidation of /j-hydroquinone itself is demonstrated in separate experiments (without phenol) to be catalytic, and under 1 atm 02 at -20 °C, ~ 200 turnovers are obtained after 22 h. The 02-oxidation of N, N-dimethylaniline to />-hydroxy-iV,iV-dimethylaniline by (1) in wet benzene is also catalytic, but less than 10 total turnovers are achieved at 50 °C under 1 atm air. Table of Contents Page Abstract ii Table of Contents vList of Figures xiList of Tables x List of Abbreviations xxi Acknowledgements xxiv Chapter 1 Ruthenium Complexes as Oxidants for Organic 1 Compounds 1 Introduction 2 1.1 Using 02 as a Terminal Oxidant: Nature's Cytochrome 2 P-450 1.1.1 Metalloporphyrins as P-450 Models 7 1.2 Ruthenium(VIII) Complexes 9 1.3 Ruthenium(VII) Complexes 11 1.4 Ruthenium(VI) Complexes 2 1.4.1 Ruthenium(VI) Porphyrin Complexes 12 1.4.2 Ruthenium(VI) Non-Porphyrin Complexes 18 1.5 Ruthenium( V) Complexes 21 1.6 Ruthenium(IV) Complexes 2 1.7 Ruthenium(in) Complexes 26 1.8 Ruthenium(II) Complexes 7 1.9 Aims and Scope of this Thesis 29 vi References for Chapter 1 32 Chapter 2 Experimental Methods 37 2.1 Materials 38 2.1.1 Gases2.1.2 Solvents and Reagents 3 8 2.2 Instrumentation and General Experimental Procedures 40 2.2.1 UV-Visible Spectroscopy 40 2.2.2 Stopped-flow Kinetic Studies 41 2.2.3 Infrared Spectrophotometer 43 2.2.4 FT-NMR Instruments 42.2.5 Gas Chromatography Experiments 44 2.2.6 Elemental Analyses, X-ray Crystallography and 46 Mass Spectral Analyses 2.3 Techniques 46 2.4 Synthesis and Characterization of Starting Compounds 46 References for Chapter 2 55 Chapter 3 Mechanism of Aerobic Oxidation of EAr3 56 (E = P, As, Sb) 3.1 Introduction 57 3.1.1 Aims of Phosphine Oxidation in Current Work 58 3.2 Sample Preparation and Data Analysis 5 9 3.2.1 Sample Preparation 59 3.2.1 Data Analysis 61 vii 3.3 Overview of the Mechanism of Tertiaryarylphosphine 63 Oxidation 3.3.1 O-atom Transfer 68 3.3.2 Disproportionate of Ru^CTMPXO) 81 3.4 Run(TMP)(L) Species and Catalytic Aerobic Oxidation 95 of Phosphines 3.4.1 Run(TMP)(L) Species 95 3.4.2 Catalytic Aerobic Oxidation of Phosphines 99 3.5 Conclusions 10References for Chapter 3 110 Chapter 4 Catalytic Aerobic Oxidation of Alcohols and Alkanes 112 4.1 Introduction 113 4.1.1 Scope of Alcohol Oxidations in Current Work 114 4.2 Sample Preparation and Data Analysis 114 4.2.1 Sample Preparation 114.2.2 Data Acquisition and Analysis 117 4.3 Stoichiometric Oxidation of Alcohols by Oxoruthenium 120 Species 4.3.1 Bis(alkoxo)porphyrinatoruthenium(IV) Species 120 4.3.2 Mechanism of Alcohol Oxidation by 129 RuVI(TMP)(0)2 4.3.3 Aerobic Oxidations of Alcohols to Aldehydes 141 and Ketones 4.4 Aerobic Oxidation of Tertiary Alkanes Catalyzed by 151 RuVI(porp)(0)2 Species viii 4.5 Conclusions 154 References for Chapter 4 5 Chapter 5 Reactivities of Ru(TDCPP-Clg) Species 157 5.1 Introduction 158 5.1.1 Ru-Perhalogenated Porphyrins: Aims and Scope 159 5.2 Sample Preparation and Data Analysis 160 5.2.1 Sample Preparation in Catalysis Studies 160 5.2.2 Preparation of/ra«5-RuVI(TDCPP-Cl8)(0)2 163 5.2.3 Data Acquisition and Analysis 166 5.3 Catalytic Aerobic Oxidation of Alcohols 167 5.4 Oxidation of Alkenes 171 5.5 Oxidation of Alkanes 177 5.6 Conclusions 185 References for Chapter 5 7 Chapter 6 Preliminary Work: Reactions of Ru^(TMP)(0)2 with 189 HX acids and Oxidation of Phenol and N,N-Dimethylaniline 6.1 Introduction 190 6.2 Experimental: Sample Preparation and Data Analysis 191 6.3 RuIV(TMP)(X)2 Species 197 6.4 Oxidation of Phenol by Ru^(TMP)(0)2 210 6.4.1 Oxidation of Phenol 216.4.2 Kinetic Studies 220 ix 6.5 Oxidation of A^JV-Dimethylaniline by Ruvl(TMP)(0)2 225 6.6 Conclusions 233 References for Chapter 6 5 Chapter 7 Conclusion and Recommendations for Future Work 236 7.1 General Conclusions 237 7.2 Recommendations for Future Work 239 Appendix A Kinetic Data for the Oxidation of EAr3 241 Appendix B Mathematical Derivation for the Equation Reflecting 257 the Observed lst-Order Absorbance-Time Changes in the Oxidation of PPh3 by RuVI(TMP)(0)2 Appendix C Oxidation of Alcohols and Alkanes: Kinetic and 259 Catalysis Data Appendix D Supplementary Data for the Crystallographic 276 Structures of RuIV(TMP)(OR)2 Complexes D.l Ru^TMPXO'Pr^ 276 D.2 Ru^CTMPXOCHCC^Cl),), 284 Appendix E Catalytic Oxidation of Alcohols, Alkenes and Alkanes 293 by Ru(TDCPP-Clg) Species: Catalysis Data E. 1 Oxidation of Benzyl Alcohol at 50 °C Under 1 atm air. 293 E.2 Oxidation of Alkenes under 1 Atm 02 294 E.3 Oxidation of Alkanes 295 E.4 GCMS Data for the Cyclohexene Oxidation 296 E.5 GCMS Data for the Cyclooctene Oxidation 300 E.6 GCMS Data for the Methylclohexane Oxidation 304 Appendix F Kinetic Data for the Oxidation of Phenol by 310 RuVI(TMP)(0)2 Appendix G Oxidation of N, N-Dimethylaniline by Ruvl(TMP)(0)2: 313 GCMS Data xi List of Figures Figure Page 1.1 Molecular orbital (MO) diagram for O2 in its ground state 4 1.2 Illustration of Fe-Protoporphyrin-IX in Cytochrome P-450 5 1.3 Mechanism of Cytochrome P-450 oxidation 6 1.4 Structures of dianions of some free base porphyrins 8 1.5 Various 02-oxidations catalyzed by RuVI(TMP)(0)2 13 1.6 Schematic representation of a chiral RuVI(por*)(0)2 species 15 1.7 Illustration of several macrocyclic tetraaza and dioxadiaza 19 ligands 1.8 Schematic representations of two Ru-oxo polypyridyl 23 complexes 1.9 Catalytic cycle of a triple component ruthenium(II)- 30 /quinone/cobalt system for the aerobic oxidation of alcohols 2.1 Diagram of the sample handling unit of the Applied 42 Photophysic stopped-flow spectrophotometer 3.1 Mechanism of oxidation of P(p-X-C6H4)3, AsPh3 and SbPh3 by 65 RuVI(TMP)(0)2 3.2 Room temperature UV-visible/time traces for the oxidation of 67 PPh3 by RuVI(TMP)(0)2 in benzene in the presence of 0=PPh3 3.3 Plot of kobs versus [PPh3] for the initial O-atom transfer to PPh3 71 from RuVI(TMP)(0)2 3.4 Eyring Plots for the determination of AHi* and ASi* 72 of the initial O-atom transfer reaction Hammett plot for logr- values for the ki step at 20 °C 3.6 Modified Hammett plot, AHi* versus CT, for the initial O-atom 77 transfer reaction for P(p-X-C6H4)3 systems 3.7 Plot of molecular mass of P(/?-X-C6H4)3 and related substrates 78 versus AS2* 3.8 Plot of [PPh3] versus kobs (slower 2nd reaction) at various 82 concentrations of 0=PPh3 in benzne at 20 °C 39a „, „ 1 [0=PPh3] nnn,t „ , . , 84 Plot of versus rppn j at 20 °C (slower 2nd reaction) 3.9b „, , 1 [OPPh3l „ „ 85 Plot of i— versus 7^7—per}—TTTTVT for the kinetic data of kobs [P(p-OMe-C6H4) 3J the Soret shift from 430 to 412 nm (slower 2nd reaction) 3.9c „ 1 [OPPh3J „ „ , 85 Plot of \— versus rT)/ \, n U N n for the kinetic data of the kobs [P(p-Me-C6H4)3] Soret shift from 430 to 412 nm (slower 2nd reaction) 39d 1 [OPPh3] Plot of ;— versus rn, cri;N1 for the kinetic data of the kobs [Pt>-F-C6H4)3] Soret shift from 430 to 412 nm (slower 2nd reaction) 86 3.9e „, „ 1 [OPPbJ , „ , 86 Plot of ;— versus m, Lr,run for the kinetic data of the kobs [P{/?-Cl-C6H4)3] Soret shift from 430 to 412 nm (slower 2nd reaction) 3.9f „ 1 [OPPh3] „ , 87 Plot of 1— versus rri/ ™ 1^ TT \ i for the kinetic data of the kobs [P(p-CF3-C6H4)3] Soret shift from 430 to 412 nm (slower 2nd reaction) 3.10 Plot of kobs versus [PPh3] for the kinetic data of the Soret shift 88 from 430 to 412 nm at 20.5 °C (slower 2nd reaction) 3 11 [PPh3l 89 Plots of ^— versus [PPh3] for slower 2nd reaction Kobs 3.12 Eyring plots derived from the temperature dependence data for 90 the slower 2nd reaction for the PPh3 system 3.13 Room temperature ^-NMR (200 MHz) spectra of 97 Run(TMP)(PPh3) in benzene-c/6 xiii 3.14 Variable-temperature lR and "P^HJ-NMR (300 MHz) > 98 spectra of Run(TMP)(PPh3) in toluene-o?8 3.15 !H-NMR (300 MHz) spectrum of Run(TMP)(AsPh3) in 102 benzene-fife exposed to air for ~ 2 min at 25 °C 3.16a Catalytic oxidation of PPh3 in the presence of RuVI(TMP)(0)2 105 under 1 atm air or 02 in benzene-afe at 24 °C 3.16b Catalytic oxidation of ^(p-F-CoVUh m tne presence of 106 Ruvl(TMP)(0)2 under 1 atm air or 02 in benzene-fife at 24 °C 3.16c Catalytic oxidation of P(p-OMe-C6H4)3 in the presence of 107 RuVI(TMP)(0)2 under 1 atm 02 in benzene-fife at 24 °C 3.16d Catalytic oxidation of P(p-Cl-C6H4)3 in the presence of 108 RuVI(TMP)(0)2 under 1 atm 02 in benzene-fife at 24 °C 4.1 The kinetics of the stoichiometric oxidation of 'PrOH by 118 RuVI(TMP)(0)2 in benzene-fife under 1 atm Ar at 18.2 °C followed by JH-NMR spectroscopy (300 MHz) 4.2 Room temperature 'H-NMR (300 MHz) spectra of 122 RuIV(TMP)(0'Pr)2 in benzene-fife with and without the presence excess TrOH 4.3 ORTEP diagram of RuIV(TMP)(0/Pr)2 124 4.4 ORTEP diagram of RuIV(TMP)(OCH(CH2Cl)2)2 125 4.5 Pseudo-1 st-order rate constant, kobs, as a function of excess 131 "PrOH concentration in benzene-ofe under 1 atm Ar at 18.2 °C 4.6 Pseudo-1 st-order rate constant, k^s, as a function of [benzyl 132 alcohol] at various temperatures in benzene-fife under 1 atm Ar 4.7 Eyring plots for the stoichiometric oxidation of 'PrOH by 139 RuVI(TMP)(0)2 under 1 atm Ar in benzene-fife 4.8 Eyring plots for the stoichiometric oxidation of benzyl alcohol 140 by RuVI(TMP)(0)2 under 1 atm Ar in benzene-fife 4.9 Mechanism of alkene epoxidation catalyzed by RuVI(TMP)(0)2 145 xiv 4.10 Plot of daily turnovers versus [benzyl alcohol] for the aerobic 149 oxidation of benzyl alcohol catalyzed by RuVI(TMP)(0)2 at 50 °C in benzene 4.11 Plot of total turnovers versus time for the aerobic oxidation 150 of benzyl alcohol catalyzed by RuVI(TMP)(0)2 at 50 °C 4.12 Plots of total turnovers versus time for the aerobic oxidations 153 of Ph3CH and adamantane catalyzed by RuVI(porp)(0)2 species at 24 °C in benzene 5.1 Experimental setup for the oxidations of neat cyclohexene, 162 cyclooctene and methylcyclohexane under 1 atm 02 5.2 Mass spectrum (EI) of RuIV(TDCPP-Cl8)(Cl)2 165 5.3 Progress of the aerobic oxidation of benzyl alcohol to 168 benzaldehyde catalyzed by RuVI(TDCPP-Clg)(0)2 in benzene at 50 °C 5.4 Progress of the aerobic oxidation of R, S-1 -phenylethanol to 169 acetophenone catalyzed by RuYI(TDCPP-Clg)(0)2 in benzene at 50 °C 5.5 Diagram illustrating a radical-chain mechanism proposed for 174 the autoxidation of alkenes 5.6 Progress of the 02-oxidation of neat cyclooctene under 1 atm 176 02 at 93 °C catalyzed by RuVI(TDCPP-Cl8)(0)2 5.7 Diagram showing a radical-chain mechanism for the 02- 178 oxidation of alkanes via peroxide decomposition catalyzed by Fe-porphyrin species 5.8 Aerobic oxidation of Ph3CH to Ph3COH catalyzed by 185 RuVI(TDCPP-Cl8)(0)2 in benzene at 24 °C 6.1 Mass spectrum of RuIV(TMP)(CF3COO)2 (FAB ionization 194 in a 3-nitrobenzylalcohol matrix) 6.2 UV-visible spectra recorded on monitoring the reaction of 195 RuIV(TMP)(0)2 with phenol in benzene under 1 atm 02 to form RuIY(TMP)(OC6H5)2 XV f 6.3 Mass spectra of solid residue isolated from the reaction of 196 RuVI(TMP)(0)2 with iV.iV-dimethylaniline in benzene-^ under 1 atm air 6.4 UV-visible spectra of RuVI(TMP)(0)2 in benzene at 25 °C 198 acquired after the addition of CF3COOH and CHCl2COOH 6.5 !H-NMR (300 MHz) spectrum of RuIV(TMP)(CF3COO)2 in 201 toluene-ds at -57.1 °C under air 6.6 XH-NMR (300 MHz) spectrum of RuIV(TMP)(CHCl2COO)2 202 in toluene-dg at 17.3 °C in vacuo 6.7 Inverse temperature plot, 'H-chemical shifts (300 MHz) versus 204 T\ for RuIV(TMP)(CF3COO)2 in toluene-ofe 6.8 Inverse temperature plot, 'H-chemical shifts (300 MHz) versus 205 T\ for RuIV(TMP)(CHCl2COO)2 in toluene-^ 6.9 Infrared spectra of free CF3COOH and RuIV(TMP)(CF3COO)2 207 obtained as Nujol mulls in KBr plates 6.10 Infrared spectra of free CHCl2COOH and 208 RuIV(TMP)(CHCl2COO)2 obtained as Nujol mulls in KBr plates 6.11 Mass spectrum (EI ionization) of Rurv(TMP)(OC6H5)2 212 6.12 ^-NMR spectrum (400 MHz, C6D6) for the metathesis 213 reaction of RuIV(TMP)('OPr)2 with /?-hydroquinone under Ar 6.13 'H-NMR spectrum (200 MHz) acquired after 2 min for the 216 reaction between RuVI(TMP)(0)2 and /?-hydroquinone (1:2) in benzene-di, under 1 atm air 6.14 Illustration showing the proposed phenol oxidation mechanism 218 based on the reversible interconversion of RuIV(TMP)(0) to RuIV(TMP)(OH)2 and phenol metathesis reactions 6.15 Plots of kobs versus [phenol] (0.1 -1 M) for the oxidation of 221 phenol by RuVI(TMP)(0)2 in benzene under 1 atm air at various temperatures xvi 6.16 Plot of kobs versus [phenol] (0.01 - 0.1 M) for the oxidation of 221 phenol by RuYI(TMP)(0)2 in benzene at 20 °C under 1 atm air 6.17 Log(kobs) versus log[phenol] plot for the oxidation of phenol 223 at various temperatures 6.18 Arrhenius plot, ln(A) versus T1, for the parameter A for the 224 reaction between RuVI(TMP)(0)2 and phenol 6.19 Illustration of the proposed scheme for the oxidation of N,N- 226 dimethylaniline catalyzed by RuVI(TMP)(0)2 under 1 atm air 6.20 'H-NMR (200 MHz) spectra for the reaction 228 "RuVI(TMP)(0)2 + 4 /V.N-dimethylaniline" in benzene-fife at 25 °C under 1 atm air 6.21 ^-NMR (200 MHz) spectra monitoring the reaction 229 "RuVI(TMP)(0)2 + 10 iV^-dimethylaniline" in benzene-fife at 25 °C under 1 atm Ar A. 1 Absorbance-time traces monitored at 422 nm by 241 stopped-flow spectrophotometry for the reaction of RuVI(TMP)(0)2 with PPh3 A.2 Semilog and Guggenheim plots for [PPh3] = 4.05 x 10'3 M 241 trace in Figure A. 1 A. 3 Absorbance-time traces monitored at 430 nm by stopped-flow 242 spectrophotometry for the loss of the intermediate RuVI(TMP)(0)(0=PPh3) A.4 Semilog and Guggenheim plots for [PPh3] = 3.83 x 10"3 M, 242 [0=PPh3] - 3.93 X 10"3 M trace in Figure A.3 A. 5 Absorbance-time traces monitored at 412 nm by stopped-flow 243 spectrophotometry for the appearance of the product Run(TMP)(PPh3) A. 6 Semilog and Guggenheim plots for [PPh3] = 3.83 x 10"3 M, 243 [0=PPh3] = 3.93 X 10"3 M trace in Figure A.5 D. 1 ORTEP plot of Rutv(TMP)(0'Pr)2 (sideway view) along 276 the porphyrin plane xvii D.1.2 Stereoview of RuIV(TMP)(0'Pr)2 276 D.2.1 PLUTO plot showing the partial structure of 284 RuIY(TMP)(OCH(CH2Cl)2)2 D. 2.2 Stereoview of RuIV(TMP)(OCH(CH2Cl)2)2 285 E. 4.1 GC trace for the run in Table E.2.2 for the oxidation of neat 296 cyclohexene E.4.2 Low resolution mass spectra (EI) for the various 297 products from the cyclohexene oxidation E.5.1 GC trace for the run in Table E.2.1 for the oxidation of neat 300 c/s-cyclooctene E. 5.2 Low resolution mass spectra (EI) for the various 3 01 products from the cyclooctene oxidation E.5.3 Known fragmentation patterns for cyclooctene oxide and 303 cz's-7-oxabicyclo [4,3,0] -nonane E.6.1 GC trace for the run in Table E.3.1 for the oxidation 304 of neat methylcyclohexane E.6.2 Low resolution mass spectra (EI) for the various 305 products from the methylcyclohexane oxidation G. 1 GC trace of the benzene solution of RuVI(TMP)(0)2 with 313 added N,iV-dimethylaniline used for GCMS analysis G.2 Mass spectrum of analyte at 2:23 in the GC trace in Figure G. 1 314 G.3 Mass spectrum of analyte at 4:15 in the GC trace in Figure G. 1 314 xviii List of Tables Page 2.1 Optimum conditions of GC runs used throughout this thesis 45 work for the separation of mixtures of compounds 3.1 Second-order rate constants, ki, for the initial O-atom transfer 70 from RuVI(TMP)(0)2 to various phosphines, AsPh3 and SbPh3 substrates in benzene 3.2 Activation parameters, AHi* and ASi*, for the initial O-atom 73 transfer from RuVI(TMP)(0)2 to P(/>-X-C6H4)3, AsPh3 and SbPh3 substrates. 3.3 Values of j2, dissociation of OPPh3 from 89 Ru^TMPXOXOPPh;,) 3.4 k.2 93 Values of, , ^ i/2 obtained from the kinetic data for the K2K4JS.3 spectral change of the Soret maximum from 430 to 412 nm 3.5 !H and 31P{'H}-NMR data for various Run(TMP)(L) species 100 3.6 Total turnovers for various phosphines catalytically 104 oxidized in benzene-fife at 24 °C under 1 atm 02 in the presence of RuVI(TMP)(0)2 4.1 ^-NMR data for /rfirra-RuIV(TMP)(OR)2 species 127 4.2 Selected pseudo-1 st-order rate constants, kobs, for the 134 stoichiometric oxidation of'PrOH to acetone by RuVI(TMP)(0)2 in benzene-fife 4.3 2nd-order rate constants, k2, for the stoichiometric oxidations 138 of 'PrOH and benzyl alcohol in benzene-fife by RuVI(TMP)(0)2 4.4 Catalytic activity of RuVI(porp)(0)2 [porp=TMP or TDCPP] 148 towards 02-oxidation of'PrOH and benzyl alcohol in benzene 5.1 Oxidation of neat alkenes catalyzed in the presence of 173 Run(TDCPP-Cl8)(CO) or RuVI(TDCPP-Cl8)(0)2 under 1 atm 02 xix 5.2 Oxidation of methylcyclohexane in the presence of 180 Run(TDCPP-Clg)(CO) or RuYI(TDCPP-Cl8)(0)2 under 1 atm 02 6.1 IR absorption frequencies for some Ru-porphyrin complexes in 200 the 1000 cm"1 region 6.2 Observed variable temperature ^-NMR chemical shifts for 206 some RuIV(TMP)(X)2 species 6.3 . Values for the parameter A for the oxidation of phenol by 223 RuYI(TMP)(0)2 derived from the expression kobs = A.[phenol]3/2 6.4 Oxidation of W-dimethylaniline catalyzed by Ru^(TMP)(0)2 232 under 1 atm air in benzene XX List of Abbreviations [X] concentration of species X A or Abs absorbance A angstrom unit (10"10 m) ABN azobis(2-methylpropionitrile); common radical initiator Ar aryl group (or argon) BHT 2,6-ditertbutyl-4-methylphenol bpy 2,2'-bipyridine dcbpy 6,6'-dichloro-2,2'-bipyridine d day (unit of time) e extinction coefficient in UV-visible spectra EI electron impact exp(x) natural base e raised to the power of x FAB fast atom bombardment FED flame ionization detector FT Fourier Transform GC gas chrotomatography GCMS tandem gas chrotomatography-mass spectrometry h Planck's constant, 6.626 x 10"34 J s (or hour) H2TDCPP /weso-tetra(2,6-dichlorophenyl)porphyrin FLTMP /weso-tetramesitylporphyrin Int area of integration in 'H-NMR spectrum K Kelvin k„ kinetic rate constant for nth elementary step kb Boltzman's constant, 1.38x10'23 J K"1 kn/ko kinetic isotope effect kobs pseudo-first order rate constant In natural logarithm log base ten logarithm xxi M molarity m multiplet, as used in the description of NMR resonances ivf parent ion (mass spectrometry) TM-CPBA meto-chloroperbenzoic acid m-H/w'-H /we/a-proton M.W. molecular weight Bohr Magneton P-eff effective magnetic susceptibility mg milligram MO molecular orbital (m)mol (milli)mole V infrared frequency nm nanometer o-Me o/Y/20-Methyl group OEP dianion of 2,3,7,8,12,13,17,18-octaethylporphryin 7C* antibonding 71-molecular orbital P-450 cyctochrome P-450 enzyme system p-n para-proton p-Me para-Methyl group Ph phenyl group ppm parts per million qvib vibrational partition function R alkyl group (or Ideal gas constant) Ru ruthenium porphyrin a Hammett factor s second (unit of time) S spin quantum number t triplet, as in the description of NMR resonances %T percent transmittance, as used in IR spectroscopy T temperature xxii TDCPP dianion of /weso-tetra(2,6-dicrilorophenyl)porphyrin TDCPP-Clg dianion of /weso-tetra(2,6-dichlorophenyl)-/?-octachloroporphyrin terpy terpyridine THF tetrahydrofuran TLC thin layer chromatography TMP dianion of /weso-tetramesitylporphyrin TMS tetramethylsilane TPFPP dianion of /weso-tetra(pentafluorophenyi)porphyrin TPFPP-Clg dianion of /weso-tetra(pentafluorophenyl)-/?-octachloroporphyrin TPP dianion of /weso-tetraphenylporphyrin TRIZMA® HC1 tris(hydroxymethyl)aminomethane hydrochloride (Sigma Chemicals) UBC University of British Columbia VT variable temperature W Watt Xn mole fraction of nth species xxiii Acknowledgments This is perhaps the most difficult section to write; perhaps I am not used to committing myself in writing. Clearly, thesis writing is not possible without readily available resources. I have to say that UBC and NSERC have treated me well in the last four years in the form of a scholarship. Without some luck, my work would not have gone as smoothly as it had in the last few years; success is 100% hard work, but luck is the catalyst. To acknowledge specific names would do injustice to those I do not mention. Everyone around me has contributed to this thesis, either though his/her spiritual support or helpful comments/suggestions. (Those who deserve to have a bigger share of my thanks will find it in some other form!)...If this page does not make any sense, probably it is because BRJ has not edited this page (and I am quite happy that there is ONE page in this thesis that did not undergo any editing); nonetheless, this thesis appears that much more presentable than it was when it was first completed is due in no small part to my supervisor... THANKS !!! xxiv Chapter 1 Chapter 1 Ruthenium Complexes as Oxidants for Organic Compounds 1 References on p. 32 Chapter 1 1 Introduction The oxidation of organic functional groups plays an important role in the synthesis of organic compounds in the laboratory and industry.1 Classical stoichiometric oxidants, such as permanganate and dichromate, used for oxidizing organics are disfavoured because of growing environmental concerns over the disposal of such ecologically harmful metal wastes.2 High-valent oxoruthenium complexes are competent oxidants, the classic example being RuOu, which found its place in laboratory syntheses in the 1950s.3 (RuCv is not implied to be environmentally benign.) In this chapter, advances in the last few years pertaining to the development of the oxidation chemistry of ruthenium complexes will be discussed, with particular focus on, but not limited to, alkane hydroxylations. The subject is vast, and this is by no means a complete review; there are several recent reviews on oxoruthenium complexes.4 The work in the present thesis, which pertains to the catalytic oxidations effected by ruthenium porphyrin species, will be incorporated in the discussion of such recent work where appropriate. Some of the material in this thesis has been published5 or presented in conference proceedings.6 1.1 Using O2 as a Terminal Oxidant: Nature's Cytochrome P-450 The ideal oxidant satisfies the following criteria: i) economically affordable; ii) naturally abundant; iii) produces clean reaction by-products; iv) high reactivity and v) high selectivity under relatively mild conditions. Usually, only some of these conditions can be satisfied at the expense of others. In recent years, the use of molecular oxygen as an alternative to currently used oxidants has led to intense research.7 Already, O2 satisfies 2 References on p. 32 Chapter 1 the first three criteria out of the five (02 from air would be more inexpensive than pure 02); however, 02 exists in a paramagnetic triplet ground state (see Figure 1.1), and thus the reaction of 02 with diamagnetic organic molecules is invariably slowed down in overcoming this spin-forbidden barrier. If any reaction with 02 proceeds, it usually operates via a radical (paramagnetic) pathway. Free-radical reactions are usually undesired as they give to little regio- and enantio-selectivity. Strong oxidants such as Ru04, Os04 and Mn04" are high-valent, diamagnetic oxometal species capable of oxidizing a variety of organic substrates.1'8 The active centre in the ubiquitous cytochrome P-450 enzyme (from now on referred to as P-450), found in abundance in the mamallian liver, as well as among many other living organisms, is believed to oxidize substrates via a high-valent oxoiron porphyrin intermediate (see Figures 1.2 and 1.3).9 This Fe=0 moiety is generated by the reductive activation of 02 (Eq. 1.1), in which one O-atom is reduced to H20, while the other O-atom is used for oxidation (Figure 1.3). RH + 02 + 2FT + 2e' — ROH + H20 (1.1) Nature's P-450 system perhaps represents the optimal conditions for the oxidation of organic substrates. The mechanism of the O-atom transfer with a P-450 oxidation is generally accepted to occur via the "oxygen rebound mechanism", depicted in Figure 1.3.9,10 The hydrophobic hydrocarbon substrate occupies a binding site in the protein cavity adjacent to the iron centre11 and is oxidized as the iron is activated to a high valence. In hydrocarbon hydroxylation a hydrogen atom is thought to be abstracted, and the OH group bound to the Fe-centre is then transferred to, and recombines with, the 3 References on p. 32 Chapter 1 hydrocarbon fragment (R*) before it leaves the protein cavity, hence oxygen rebound. Perhaps a synthetic metalloporphyrin system mimicking the active centre in P-450 may become practical, hence affording the use of O2 (with appropriate reductants) as a clean and inexpensive oxidant without the need of the protein in a natural enzyme. V^N-/a2s ENERGY ^^t-\CT*ls Figure 1.1 Molecular orbital (MO) diagram for 02 in its ground state. Note that the energy levels are not drawn to scale, and the diagram shows only the relative energies of the orbitals. The ground state electronic configuration is a 3E state. Two unpaired electrons occupy the highest occupied molecular orbitals (HOMO), a pair of degenerate of n -antibonding orbitals. 4 References on p. 32 Chapter 1 S = thiolate RS from the cysteine residue of cytochrome P-450 protein Figure 1.2 The active centre of cytochrome P-450 enzymes is an iron protoporphyrin-IX moiety. The 5th coordination site is occupied by a sulfur-bound thiolate from a cysteine amino acid residue of the P-450 protein. 5 References on p. 32 Chapter 1 ~Fe~"" = iron protoporphyrin-LX moiety Figure 1.3 Mechanism of the catalytic cycle of the cytochrome P-450 enzyme. The oxidizing species is written as an oxoiron(IV) porphyrin radical-cation species, which is favoured in model studies.9'10 Two equivalents of reductant are not required if an O-atom donor is used; this bypasses the full P-450 cycle and proceeds via what is known as the shunt pathway. 6 References on p. 32 Chapter 1 1.1.1 Metalloporphyrins as P-450 Models Generally, synthetic porphyrins fall into three classes or generations when it comes to the description of metalloporphyrin oxidation catalysts (see Figure 1.4).12 The first generation metalloporphyrin catalysts are TPP* derivatives (OEPt derivatives also have been used). Such porphyrins are susceptible to destruction under the oxidizing conditions that exist in the reaction medium, or to deactivation to the thermodynamically more stable p-oxo-dinuclear species;13 however, the steric bulk present in TMP^ prevents the formation of p-oxo-diruthenium species, and a derived monomeric trans-RuVI(IMP)(0)2 species exhibits a rich array of oxidation chemistry (see Section 1.4.1). The second generation metalloporphyrin catalysts, with the addition of halogens on the /weso-phenyl group for improved stability, are improvements over the first-generation type, and the steric bulk of the 2- and 6- chloro groups of TDCPP5 also prevents the formation of p-oxo-dinuclear ruthenium species. To go one step further, the third generation metalloporphyrins have the yff-pyrrolic positions halogenated as well. One can envision the steric repulsion amongst the halogens, especially at the /2-pyrrole positions, and the porphyrin adopts a saddle-shaped conformation to relieve such stress. Crystallographic analyses on some such metalloporphyrins show that they adopt saddle-shaped structures;14 these results are complemented by theoretical studies which favour a non-planar conformation for such highly halogenated metalloporphyrins.15 t TPP = dianion of /weso-tetraphenylporphyin (see Figure 1.4). f OEP = dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin. ? TMP = dianion of /neso-tetramesitylporphyrin (see Figure 1.4). 5 TDCPP = dianion of we5o-tetra(2,6-dichlorophenyl)porphyrin (see Figure 1.4). 7 References on p. 32 Chapter 1 C 1st Generation Porphyrins 2nd Generation Porphyrins 3rd Generation Porphyrins A, B, C, Z = H (TPP) B,C,Z = H; A -CI (TDCPP) B,C = H; A,Z = C1 /weso-TetraPhenylPorphyrin we50-Tetra(2,6- (TDCPP-Clg) DiChloroPhenyl)Porphyrin A, C = Me; B, Z = H (TMP) AB,C = F; Z = CI meso- A,B,C = F; Z = H (TPFPP) (TPFPP-Clg) TetraMesitylPorphyrin meso-Tetra(PentaFluoroPhenyl)- A,B,C = F; Z = F Porphyrin (TPFPP-F8) A,B,C = F;Z = Br (TPFPP-Br8) Figure 1.4. Abbreviations and names of some dianions of free-base porphyrins that are based on the tetraphenylporphyrin family mentioned in this chapter and the rest of this thesis. A systematic nomenclature has been developed for porphyrins, but the above abbreviations (or ones similar to those used by other authors) are more convenient. g References on p. 32 Chapter 1 Experimentally, the extensive halogenation appears to increase the stability, and above all the reactivity of the metalloporphyrin catalysts.16 Ruthenium, periodically analogous with iron, was a natural choice in the extension of iron porphyrin chemistry. The active species carrying out the P-450 oxidation is generally accepted to be an extremely unstable and reactive, high-valent oxoiron moiety.9'10 By switching to ruthenium, it was hoped the chemistry could be "slowed down" to allow for mechanistic studies.2'13 Also, the wide range of oxidation states available, as high as 8+, makes ruthenium a potentially powerful oxidant (see Sections 1.2 to 1.8). To date, a number of oxidations carried out by ruthenium porphyrins has been discovered and investigated (examples from References 2,5,6,7,22-25,27-30,32,34,38,51,53,55,59 are discussed in the following sections) but the oxidation chemistry of ruthenium non-porphyrin species is also very rich (examples from References 3,4,17-20,39-50,52,57,61). 1.2 Ruthenium(VHI) Complexes The highest attainable oxidation state for ruthenium is +8. The most well-known and perhaps the only well-defined ruthenium(VIII) complex is RuO/t.1'3 The potential of Ru04 as a laboratory reagent for organic synthesis was not realized until the 1950s,3 even though the compound had been discovered early in the turn of the century. In the laboratory, Ru04 finds wide use in the oxidation of secondary alcohols to ketones,1'3'4'17 but the oxidation of primary alcohols almost always over-oxidizes the aldehyde product to the carboxylic acid, diminishing the value of this reagent in this respect. Perhaps Ru04 is 9 References on p. 32 Chapter 1 of greater importance in the field of carbohydrate chemistry, where the selective oxidation of the hydroxyl groups in carbohydrates to carbonyl groups without oxidizing the other protected groups is possible.1 Lee and Van den Engh performed mechanistic studies on the stoichiometric oxidation of alcohols by Ru04, 17 and found that two different rate-limiting steps govern the overall rate of the reaction at different pH ranges. At very high acidities, carbenium-ion formation was rate-determining, but at lower acidities (1 to 6 M perchloric acid) hydride abstraction was the slow step. The stoichiometric alcohol oxidation by RuC»4 is represented in Eq. 1.2, and the process can be made catalytic if the tetraoxide is regenerated (Eq. 1.3). Ru04 + 2RR1CH2OH — Ru02-2H20 + 2 RRiCO (1.2) Ru02»2H20 + 2NaI04 — Ru04 + 2NaI03 + 2 H20 (1.3) Hence, instead of using the tetraoxide stoichiometrically, in the presence of excess oxidizing agents such as hypochlorite or periodate, Ru04 can be regenerated catalytically, a definite advantage over using a large, stoichiometric amount of the tetraoxide. Ru04 can also be formed from lower-valent ruthenium species, such as RuCl3#nH20.18 More recently, Ru04 generated in situ has been used in the hydroxylation of saturated hydrocarbons.18 The stoichiometric oxidation of cis and *ra«s-pinane with a RuCl3 / NaI04 / (CC14 / CH3CN / H20) system showed some interesting mechanistic insights. In summary, the bond-breaking in the saturated hydrocarbons was observed mainly to occur at tertiary C-H bonds and was proposed to occur via a two-electron hydride transfer pathway. Of greater interest is that the analysis of the numerous products 10 References on p. 32 Chapter 1 from the oxidation of the pinanes by the in situ RuGu indicated that an unprecedented methyl (1°) C-H cleavage occurred. 1.3 Ruthenium(VII) Complexes The perruthenate ion, RuOY, is the only well-defined oxoruthenium(VlI) complex. Lee and Congson have also carried out some mechanistic studies on the oxidation of alcohols by RuOV,19 and invoked a free-radical mechanism, as the oxidation of cyclobutanol cleaved the C-C bond and yielded mainly butanoic acid rather than cyclobutanone. More recently, the same group investigated the oxygen-atom transfer properties of the perruthenate ion to sulfides;20 here, the active oxidizing species was proposed to be a five-coordinate oxoruthenium(VII) species formed by coordination sphere expansion (Eq. 1.4). OH C\ X> OH- -O I £> O O- O O-The oxidation of the thioether substrate was proposed to occur via either direct O-atom transfer or attack of the S lone pair on an empty 7i*-orbital of Ru=0, followed by the release of the S=0 moiety. Both mechanisms have been considered for other O-atom transfer reactions;21'29 however, kinetic and mechanistic data are generally lacking in ruthenium oxidation chemistry, and the O-atom chemistry is not fully understood. ll References on p. 32 Chapter 1 1.4 Ruthenium(VI) Complexes Many oxoruthenium(VI) complexes are competent oxidation reagents or catalysts. Examples from both non-porphyrin and porphyrin work are numerous, with the latter emerging in recent years. These complexes contain high-valent ruthenium-oxo moieties capable of oxygen-atom transfer or C-H bond cleavage. 1.4.1 Ruthenium(VI) Porphyrin Complexes The first dioxoporphyrinatoruthenium(VI) complex, fraws-RuVI(TMP)(0)2, was discovered independently by Grove's group22 and this group at UBC.23 The RuVI(TMP)(0)2 complex can be formed by the /weto-chloroperbenzoic acid (/w-CPBA) oxidation of Run(TMP)(CO), or by the aerobic oxidation of Run(TMP)(L)2 ( L = MeCN,24 THF,25 N2 or vacant26). More recently, RuVI(TMP)(0)2 was reported to be generated by oxidizing Run(TMP)(THF)2 with N20.27 The use of TMP as a ligand, with its methyl substituents on the 2- and 6- positions on the meso-phenyl groups, prevents dimerization of the porphyrin complex to p-oxo-dinuclear ruthenium(IV) species, which are generally regarded as catalytically inactive, thermodynamic sinks.2b'13 The use of TMP for catalytic systems was thus an improvement over the use of unhindered Ru(TPP) species. The RuYI(TMP)(0)2 complex is a versatile, stoichiometric and 02-catalytic oxidant (see Figure 1.5).2b Both of the oxygen atoms in RuVI(TMP)(0)2 can be used for the oxidation of substrates, hence this shows that the dioxo species exhibits genuine dioxygenase-type activity. Under air or O2 at mild conditions, the following oxidations catalyzed by RuIY(TMP)(0)2 take place: alkenes25'28c or steroids28a'b to corresponding 12 References on p. 32 Chapter 1 rt«n(MeCN)2 OEAr3 EAr3 /f«n(EAr3) « Ruvi(0)2 O2 / benzene Ph,C Ruw(0) Ru™(Q) aldehyde/ketone J?«IV(OR)2 JRM11(OSR2)2 Ru = Ru(TMP) unit Figure 1.5. Various oxidations carried out by Ruvl(TMP)(0)2 in benzene or toluene; the processes become catalytic in the presence of excess substrate under 1 atm air or 02. The intermediates and/or products, where indicated, are identified based on spectroscopic or structural evidence. Higher temperatures usually speed up the rate of catalysis; however, the porphyrin decomposes faster under such conditions than at room temperature. 13 References on p. 32 Chapter 1 epoxides, thioethers to sulfoxides,29 tertiaryarylphosphines,5b'6a'24't AsPh35b'6a,t and SbPh35b'6a,t to the corresponding oxides, alcohols to aldehydes or ketones,5a,6a,t and the tertiary alkane Ph3CH to Ph3COH.f Stoichiometrically, RuVI(TMP)(0)2 hydroxylates activated mono-substituted aromatic rings, such as phenol29a'b and jV,A/-dimethylaniline to /?-hydroquinone and /?-hydroxy-7Vr,A'-dimethylaniline, respectively.* Prior to this thesis work, mechanistic details and a kinetic database were generally lacking on the RuVI(TMP)(0)2 oxidation chemistry, and the present work has sought to study such systems in more detail, as well as to develop catalytic CVoxidation systems based on the dioxo complex. Recently, a catalytic system based on RuVI(TMP)(0)2 using pyridine-A'-oxide was developed,30 with remarkable activity towards the hydroxylation of secondary and tertiary alkanes. For adamantane, up to 14000 turnovers (giving primarily 1-adamantanol) were realized at ambient conditions. Water inhibited the catalytic activity of the system; however, trace anhydrous acid (HC1 or HBr) enhanced the rates of catalysis. Treatment of a benzene solution of RuYI(TMP)(0)2 with HC1 (gaseous or aqueous) has been suggested to produce the complex RuIV(TMP)(Cl)2,30'31'¥ and the active catalytic species in the above system was proposed to be RuVI(TMP)(0)(Cl)+.30 Of note, Run(TMP)(CO) was an active catalyst precursor, and even Run(TPP)(CO) was shown to be effective in hydroxylations. In fact Run(TPP)(CO) was the most effective catalyst precursor, oxidizing adamantane to 1-adamantanol and adamantane-1,3-diol, with a trace of 2-adamantanone (68 : 25 : 1), the total turnover being 120000 after heating for 6 h at 80 °C in benzene. ' Present work to be discussed in later chapters. * The reaction of HX acids with RuVI(TMP)(0)2 will be discussed in Chapter 6. 14 References on p. 32 Chapter 1 The first chiral picket-fence trans-R.un(poT*)(0)2 complex was synthesized recently (por* = chiral porphyrin ligand, see Figure 1.6),32 and some chiral recognition was observed in the stoichiometric oxidation of R- and S-phosphine mixtures. For the a,P,a,P isomer of the dioxoruthenium porphyrin, the oxidation of R- and S-P(CH2Ph)(Ph)(Me) showed that the i?-enantiomer was oxidized more selectively to the phosphine oxide (R.S = 2.4); however, the phosphorus binding-preference in the final Ru(II)-product,33 Run(por*)(phosphine)2, was the ^-configuration about phosphorus (S.R = 2.3 preference of binding to Ru). Figure 1.6. The first chiral picket-fence dioxoporphyrinatoruthenium(VI) species. The ot,P,oc,P and oc,a,P,P isomers are shown above. 15 References on p. 32 Chapter 1 Some RuVI(porp)(0)2 species (where porp = TPP-xf and OEP,34 the non-sterically hindered porphyrins) have been prepared without the expected formation of the inactive p-oxo-dinuclear ruthenium(IV) species.2b'13 The Run(porp)(CO)(MeOH) precursors were oxidized by /w-CPBA in EtOH/CH2Cl2, which resulted in the formation of the corresponding dioxo species. A coordinating solvent such as EtOH appears to be crucial in preventing the formation of the p-oxo-diruthenium species. Of note, the dioxo species were reported to be capable of oxidizing stoichiometrically the tertiary alkanes adamantane and methylcyclohexane to the corresponding tertiary alcohols with yields of approximately 20% based on the metal complex. Ethylbenzene was also oxidized to 1-phenylethanol and acetophenone. Epoxidations of alkenes were also reported in the studies.34 In all these cases, it appears that the dioxo species eventually do form p-oxo-dinuclear ruthenium(IV) species, thought to be due to contamination by water. The fact that these dioxo species also oxidized alcohols leads one to question the true identity of the Ru-product in the alkene oxidation reactions; RuIV(TPP)(0)«EtOH or RuIV(TPP)(OH)2«EtOH was proposed as the Ru-product based solely on 'H-NMR spectroscopy in a CD3CD2OD/CDCl3 solvent system. Studies carried out in this thesis work show that a bis(alkoxo)ruthenium(IV) species is the inorganic product of alcohol oxidation with the RuVI(TMP)(0)2 species,5"'63 and that excess alcohol can exchange rapidly with the alkoxo ligands. It seems likely that RuIV(porp)(OR)2 [R = CD3 or CD2CD3)] species are formed in the conditions noted above. TPP-x = dianion of weso-tetra(para-substituted-phenyl)porphyrin (see Figure 1.4). 16 References on p. 32 Chapter 1 A most exciting breakthrough in ruthenium porphyrin oxidation chemistry came about with the use of halogenated porphyrins, commencing with /ra«5-RuVI(TDCPP)(0)2, which was shown to be a much more robust catalyst than the TMP analogue;29 an iron-TDCPP system had been demonstrated earlier to epoxidize alkenes efficiently using O-atom donors.35 The RuVI(TDCPP)(0)2 species exhibits very much the same chemistry described in Figure 1.5,29'* generally with higher reactivity than the TMP analogue due to the increased electronegativity on the /weso-phenyl rings. Recently, iron, chromium and manganese complexes of TPFPP5 were reported to catalyze the aerobic oxidation of light alkanes, such as isobutane and propane under 02 pressures < 1000 psi at temperatures reaching 150 °C.36 Further halogenation of the eight /^-pyrrole positions lying on the porphyrin plane led to some remarkably reactive species. The use of Fem(TPFPP-Br8)(Cl)^ as a catalyst precursor afforded a system that oxidized isobutane to ferf-butanol with turnovers of about 13000, again under 1000 psi 02 but now the reaction proceeds at room temperature. Of note, there has been some debate as to whether a genuine oxoiron species is involved,36 or whether free-radical hydroperoxide decomposition is responsible for the actual oxidation.163'37 On the ruthenium front, very little work has been done on such perhalogenated Ru-porphyrins, except for the recent synthetic/structural studies with TPFPP-Clg systems,14 and the work to be described in Chapter 5 on the aerobic oxidation of alcohols, alkenes and tertiary alkanes catalyzed by some Ru(TDCPP-Clg) species. Present work to be discussed in later chapters. TPFPP = dianion of weTO-tetra(2,3,4,5,6-pentafluorophenyl)porphyrin (see Figure 1.4). Refer to figure 1.4 for the abbreviations for these 3rd generation porphyrins. 17 References on p. 32 Chapter 1 The 6+ formal oxidation state is the highest observed to date for ruthenium in any ruthenium porphyrin complex, although a Ru(VT) porphyrin-radical-cation has been formed in the oxidation of RuVI(porp)(0)2, porp = TMP or OEP, by phenoxathin hexachloroantimonate(V).38 A g-value of 2.002 observed in the ESR spectrum taken at 77 K, a blue-shifted Soret band and a broad Q-band are suggestive of the formation of a porphyrin radical-cation. The oxidation of diphenylsulfide and several alkenes by these radical-cation species implied that they are stronger oxidants than the non-radical Ru(VI) counterparts. The removal of one electron from the porphyrin ligand likely increased the electrophilicity of the Ru-oxo moieties, and hence, their reactivities as well.38 1.4.2 Ruthenium(VI) Non-porphyrin Complexes A group of /raws-dioxomthenium(VI) complexes based on tetradentate tetraaza N-donor macrocycles and tetradentate dioxadiaza N- and O-donor ligands has been extensively studied in recent years.39 These tetradentate ligands (some are shown in Figure 1.7) behave similarly to porphyrin ligands in their binding mode and the ligand binding geometry forces the two oxo ligands to a trans configuration. These high-valent dioxoruthenium(VI) complexes can oxidize stoichiometrically alcohols to the corresponding ketones or aldehydes in CH2Cl2,39b'd'e and under air, some of these systems become marginally catalytic (2 to 3 turns) at ambient conditions.39d'e Alkenes are also oxidized exclusively to epoxides.398 Of note, large kinetic isotope effects (kH/kD about 20) were observed in the stoichiometric oxidation of alcohols by these Ru(VI) complexes, in contrast with the findings on the alcohol oxidations by RuVI(TMP)(0)2 in the present 18 References on p. 32 Chapter 1 thesis (Chapter 4). The dioxoruthenium non-porphyrin species are also capable of oxidizing C-H bonds in alkanes.39c The oxidation of some aromatic hydrocarbons showed the following reactivity trend: toluene < ethylbenzene < cumene, the oxidized products being benzaldehyde, acetophenone and 2-phenyl-isopropanol, respectively. A two-electron hydride or one-electron H-atom abstraction pathway was proposed as a possible mechanistic step. Kinetic isotope effects of kH/kD > 10 were observed in these alkane oxidations, indicating that C-H bond-breaking is the rate-determining step. Mes | | JVle -N N-A^,#'-dimethyl-6,7,8,9,10,ll,17,18-octahydro-5//-dibenzo[e«]-[ 1,4,8,12]dioxadiazacyclopentadecine Mev | | jVIe i—N N—1 N N—' Me Me 1,4,8,11-tetramethyl-1,4,8,11 -tetraazacyclotetradecane meso-2,3,7,11,12-pentamethyl-3,7,11,17-tetraazabicyclo [11.3.1]-heptadeca-1 (17), 13,15-triene Figure 1.7. Several examples of tetradentate macrocyclic tetraaza and dioxadiaza N- and N-/0-donor macrocyclic ligands, analogous to porphyrins, that have been used in the synthesis of dioxoruthenium(VI) complexes 19 References on p. 32 Chapter 1 Perhaps the most notable non-porphyrin oxoruthenium(VI) complex is the ruthenate ion, Ru(0)3(OH)22". Once thought to be the tetrahedral RUO42" anion, the ruthenate ion is now known to be trigonal pyramidal from crystallographic studies.40 The ruthenate ion finds use in the oxidation of alcohols to carboxylic acids or ketones, and the system becomes catalytic in the presence of oxidizing agents such as persulfate.43 Mechanistic studies by Lee and Congson19 suggest that a two-electron hydride transfer mechanism is operating in the oxidation of alcohols, which is different from the one-electron H-atom abstraction mediated by perruthenate noted in Section 1.3. Recently, barium ruthenate has been successfully applied to the stoichiometric oxidation of alkanes at room temperature with remarkable reactivity.41 Acetic acid enhanced the reactivity of the reagent toward the hydroxylation of alkanes,413 and the tertiary alkanes adamantane and methylcyclohexane were oxidized in CH2CI2 in the presence of acetic acid to the corresponding tertiary alcohols within 2 h, with yields reaching 95 and 42%, respectively. For «-hexane, the oxidation occurred mainly at the secondary C-H bonds, forming 2- and 3-hexanone, with yields reaching 20% and 16%, respectively. The oxidation of cyclohexane yielded 60% cyclohexanone exclusively; no cyclohexanol was observed. The addition of Lewis acids such as ZnCb and FeCl3 reduced the reaction time dramatically to a few minutes, in contrast to a few hours. Cyclohexane was now oxidized to cyclohexanone with the same yield in about 5 min, with some trace cyclohexanol being detected. In another study,41b trifluoroacetic acid was used instead of acetic acid, and such a change resulted in a very reactive system capable of oxidizing the light alkanes ethane and propane to acetic acid (40% yield) and acetone (65%), 20 References on p. 32 Chapter 1 respectively. Benzene was also hydroxylated to /?ara-benzoquinone with a 20% yield. Dioxoruthenium(VI) acetato species were proposed to be the active oxidizing species, the reactivities of which were possibly further enhanced by the presence of Lewis acids. Of interest, the effect of the acids seems to be similar to that of HC1 and HBr in the Ru(porp)/pyridine-iV-oxide systems30 mentioned earlier in Section 1.4.1, although the role of the acids in either systems is unknown. 1.5 Ruthenium(V) Complexes Oxoruthenium(V) complexes are rare. Griffith and co-workers characterized crystallographically the product from the reaction of [Ru04][N"Pr4] and 2-hydroxy-2-ethylbutyric acid as [Ruv(0)(02COCEt2)2][N"Pr4].42 This oxoruthenium(V) complex is a mild stoichiometric oxidant that can oxidize primary alcohols to aldehydes and secondary alcohols to ketones. Excess 7V-methylmorpholine-7V-oxide can be used as the primary O-atom source, and the system can produce up to 25 turnovers at room temperature. Che and co-workers have demonstrated recently that [Ruv(L)(0)][C104]2 (L = anion of [2-hydroxy-2-(2-pyridyl)ethyl]bis[2-(2-pyridyl)ethyl]amine) was an oxidant strong enough to oxidize cyclohexane to cyclohexanone (60% yield) in acetonitrile.43 Other tertiary alkanes, such as adamantane and methylcyclohexane were oxidized exclusively to the corresponding tertiary alcohols with yields of 60% and 43%, respectively. A kinetic isotope effect kH/kD of 5.3 was observed for the oxidation of cyclohexane, suggesting C-H bond cleavage as the rate-determining step. 21 References on p. 32 Chapter 1 1.6 Ruthenium(IV) Complexes Meyer's group, and a few others, have worked extensively with cis-Ru(bpy)2)(py)(0)2+ (bpy = 2,2'-bipyridine, py = pyridine) and similar polypyridine complexes, and have studied alkene epoxidation,44 alcohol,45 phenol46 and para-hydroquinone47 oxidations, as well as O-atom transfer reactions to thioethers48 and phosphines.49 This type of Ru-complexes is shown in Figure 1.8. These stoichiometric oxidations usually were carried out in acetonitrile or acetonitrile/water solvent systems. As kinetic and mechanistic studies on Ru-oxo oxidations are rather sparse, the results for the oxidation of alcohols by RuIV(bpy)2(py)(0)2+ are particularly relevant with respect to the oxidation of alcohols by RuVI(TMP)(0)2 described in this thesis. Although the Ru-atoms are in different formal oxidation states, 4+ and 6+, respectively, both oxidations are proposed to occur via a two-electron, hydride transfer pathway. Roecker and Meyer458 observed an unusually large kinetic isotope effect (kH/kD = 50) for the oxidation of benzyl alcohol, and a kn/ko value of 18 for 'PrOH. The stoichiometric oxidation of 'PrOH in benzene by RuYI(TMP)(0)2 has a much lower value of kH/kD = 1.9 for the a-C-H bond cleavage. The discussion of this subject will be presented later in Chapter 4. Che and co-workers have varied the Ru(bpy)2(py)(0)2+ theme and replaced the polypyridine ligands with substituted polypyridines. Generally the chemistry that can be accomplished (alkene epoxidation, alcohol oxidation, etc.) by these complexes is not much different from that of their unsubstituted analogues.50 One interesting find was that Ruiv(terpy)(dcbpy)(0)2+ (terpy = 2,2':6',2"-terpyridine, dcbpy = 6,6'-dichloro-2,2'-bypyridine) (see Figure 1.8) also was capable of oxidizing stoichiometrically alkanes in 22 References on p. 32 Chapter 1 acetonitrile at room temperature. Adamantane was oxidized to 1-adamantanol with a 28% yield after 4 h, while ethylbenzene was oxidized to 70% acetophenone and 31% 1-phenylethanol in the same amount of time. The presence of the electron-withdrawing 6 and 6' CI groups likely enhances the reactivity of the Ru=0 moiety. cw-RUlV(bipy)2(py)(0)2+ 2+ Ruiv(terpy)(dcbpy)(0) 2+ Figure 1.8. Two examples of monooxoruthenium(IV) polypyridyl complexes. These complexes have been used to oxidize stoichiometrically a variety of organic substrates (phosphines, thioethers, alcohols, alkenes). 23 References on p. 32 Chapter 1 Earlier work in this laboratory led to the discovery of RuIV(OEP'+)(0)(Br) (OEP*+ = OEP porphyrin radical-cation) formed from the reaction of Ru(OEP)(Br)(PPh3) and PhlO.51 The Ru(OEP'+)(0)(Br) was proposed as such based on ESR evidence for a porphyrin radical-cation, as well as the stoichiometry of O-atom transfer to PPh3. Of particular importance is that this oxoruthenium(IV) moiety is isoelectronic with the proposed active Fe^-O intermediate in the P-450 system, and thus for the first time a ruthenium model of the oxoiron(IV) protoporphyrin-IX radical-cation species was available. The oxidation of cyclohexane with this oxoruthenium(IV) species was marginally catalytic on using PhlO as an oxidant, producing cyclohexanol, cyclohexanone and cyclohexylbromide in a 1:8:9 ratio, the total turnover being 1.7 based on the metalloporphyrin. The other often quoted oxoruthenium(IV) porphyrin species is Rurv(TMP)(0), a proposed intermediate in various catalytic oxidations: epoxidation of alkenes,25'28 oxidative dehydrogenation of alcohols5"'63 and oxidations of tertiaryarylphosphines,5b'6a'24 AsPh35b'6a and SbPh3.5b'6a Equally important, RuIV(TMP)(0) is the proposed intermediate in the formation of RuVI(TMP)(0)2 from the aerobic oxidation of Run(TMP)(L)2 (L = MeCN,24 THF,25 N2 or vacant26), which is believed to proceed via Eqs. 1.5 and 1.6 [Ru = Ru(TMP)]. -L +Ru\h)2 -2L Ru\h)2 + 02 — Ru(L)02 —- (L)Ru(0-0)Ru(L) —2Ruw(0) (1.5) -L + 2L 2^(0)— Ru\L)2 + ^(O), (1.6) 24 References on p. 32 Chapter 1 The monooxo Ru(IV)-species has yet to be isolated, but 'H-resonances assignable to RuIV(TMP)(0) can be observed in situ by 'H-NMR spectroscopy in benzene-ofe during the oxidations of tertiaryarylphosphines,5b'6a'24 AsPh35b'6" and SbPh3.5b'6a The Ru^TMPXO) species is paramagnetic and exhibits shifted 'H-resonances (relative to those, for example, of diamagnetic Ru(II) species) for the TMP ligand characteristic of such Ru(rVr)-porphyrin 24,27,31 species. In non-porphyrin work, monooxoruthenium(IV) species have been shown to undergo proton-coupled equilibria with H20 in solution to form the trans-bis(hydroxo)ruthenium(IV) species.52 This type of equilibrium is likely to occur for RuIV(TMP)(0) species (Eq. 1.7), and such a reaction has been invoked to account for the catalytic aerobic oxidation of alcohols. 5a'6a The bis(hydroxo) species depicted in Eq. 1.7 RuIV(TMP)(0) + H20 — RuIV(TMP)(0)(OH2) — RuIV(TMP)(OH)2 (1.7) has been reported by two group s.29ab'53 Preliminary work in this laboratory, reported in 1990 on the oxidation of'PrOH, led to the isolation of a complex, which was proposed to be RuIV(TMP)(OH)2 29a'b based mainly on the non-detection of any axial ligand protons by H-NMR spectroscopy. In 1993, the same RuIV(TMP)(OH)2 was reported to be isolated from the m-CPBA oxidation of Run(TMP)(CO) in EtOH/CH2Cl2, with the mention of unpublished crystallographic data on the complex.53 The isolation of RuIY(TMP)(OTJr)2 in the oxidation of'PrOH by RuVI(TMP)(0)2 in benzene,5"'6" and the subsequent detailed study and understanding of such alcohol oxidations (Chapter 4) strongly refute the proposal of the isolation of RuIV(TMP)(OH)2. Indeed, the work described in Chapter 4 shows that the axial alkoxo ligands of RuIV(TMP)(OR)2 species exchange rapidly with 25 References on p. 32 Chapter 1 excess alcohol in solution; therefore, the bis(hydroxo) species, though possibly existing as part of the equilibria of Eq. 1.7, would not be the favoured species when excess alcohol is present. Of interest, the supposed "Rurv(TMP)(OH)2" reported by Che and co-workers53 was reported to be slightly more effective than RuVI(TMP)(0)2 for the epoxidation of norborene. Although this author believes that RuIY(TMP)(OH)2 has not been successfully isolated under the above-mentioned conditions, recently the RuIV(TDCPP)(OH)2 analogue was characterized crystallographically, and a Ru-0 bond distance of 1.78 A was observed,54 which is extremely short for a Ru-0 bond length for this class of Ru(IV) complexes (1.892 or 1.905 A for RuIV(TMP)(OR)2, where R = 'Pr5a'55 or l,3-dichloro-2-propyl,55 respectively) and 1.944 A in [RuIY(TPP)(p-OC6H4Me)2]0.13a A high degree of 7i-backbonding seems to be shortening the Ru-0 bond to almost a Ru-oxo double bond,54 which is typically ca. 1.73 (Ru^) to 1.78 (Ru™) A in various dioxo- and oxoruthenium i 4c 56 complexes. ' 1.7 Ruthenium(III) Complexes A RuCl3»nH20 or Run(Cl)2(PPh)3 / aldehyde system was recently employed to effect the catalytic 02-hydroxylation of alkanes under relatively mild conditions.57 Aldehydes are known to form peracids in the presence of 02,58 and once formed the peracid can oxidize low-valent ruthenium(II or III) to higher-valent oxoruthenium species. In these systems, elemental iron was more effective as a catalyst precursor than the ruthenium complexes, and under 1 atm 02, some saturated hydrocarbons (cyclohexane, methylcyclohexane, adamantane, cyclooctane, »-decane and ethylbenzene) were oxidized 26 References on p. 32 Chapter 1 at the secondary and tertiary positions to the corresponding ketones and tertiary alcohols. For the RuCl3»nH20/heptanal/acetic acid/CH2Cl2 system, cyclooctane was oxidized to cyclooctanone and cyclooctanol (3:1) over a period of 15 h, the total turnover being 8.4 based on the starting ruthenium. 1.8 Ruthenium(Il) Complexes Work conducted in this laboratory throughout the 1980s led to the discovery of the production of hydrogen peroxide from FT and 02 mediated by a ruthenium(II) porphyrin species (Eqs. 1.8 and 1.10).59 In the presence of a reductant, the Ru(II) species is regenerated (Eq. 1.12), making the production of H202 catalytic. The in situ generated H202 then can oxidize organic substrates that are present in solution. Phosphines were studied first with this system, but the chemistry can be applied to the oxidation of thioethers. The overall reaction is catalytic in Run(OEP)(PR3)2, FT and OFT. The following mechanism was proposed (Eqs. 1.8 to 1.12): Ru(OEP)(PR3)2 + 02 — Ru(OEP)(PR3)2+ + 02" (1.8) H20 — FT + OFT (1.902- + ft — H02 — \ H202 + \ 02 (1.10) H202 + PR3 —* H20 + OPR3 (1.11) 2 Ru(OEP)(PR3)2+ + PR3 + OFT —- 2 Ru(OEP)(PR3)2 + OPR3 + Ff (1.12) For any substrate that can be oxidized by H202, the system can, in principle utilize 02 as oxidant within the above scheme. As mentioned, a reductant is necessary to regenerate 27 References on p. 32 Chapter 1 the Ru(II)-catalyst (Eq. 1.12), and for an "optimum" system this reductant is preferably the substrate itself. The same basic mechanism applies to the oxidation of thioethers, namely, superoxide is first generated by an outer sphere electron transfer (Eq. 1.8), followed by the generation of H2O2 (Eq. 1.10), which then subsequently oxidizes the thioether to sulfoxide. Visible light from a tungsten source was necessary to assist in driving equilibria 1.8 and 1.10 to the product side.593 Initial turnovers were close to 360 h"1, with total turnovers of about 10000. Slowly, the catalytically less active Run(OEP)(SR2)(OSR2) species containing S-bound sulfoxide was formed. The oxidation of primary or secondary alcohols to the corresponding aldehydes or ketones is in essence a dehydrogenation reaction (Eq 1.13). RCH2OH —- RCHO + {H2} (1.13) RROO + {H2} —- RRCH2OH (1.14) The hydrogen, {H2}, that is liberated in Eq. 1.13 may or may not be transferred to a hydrogen acceptor R'R"C=0 (Eq. 1.14). The liberation of free H2 in a dehydrogenation reaction is an endothermic process, e.g. for 'PrOH, AH = + 66.5 kJ^mol"1 at 327 °C.60 In the aerobic oxidative-dehydrogenation of alcohols to aldehydes/ketones and H20, the end hydrogen acceptor is 02 and the overall reaction becomes exothermic. It is not necessary to use O2 as the hydrogen acceptor; for example, an imine or a ketone can accept the hydrogen from the substrate. The use of O2 as acceptor is generally referred to as oxidation, while the use of other acceptors is usually referred to as transfer hydrogenation. Transfer hydrogenation is more generally concerned with the use of a hydrogen source other than H2 to effect hydrogenation, and the focus is on reducing the unsaturated 28 References on p. 32 Chapter 1 substrate, not the oxidized hydrogen source. In the last few years, Backvall and co workers have developed ruthenium(II)-based systems for dehydrogenating alcohols by transfer hydrogenation.61 Imines, ketones and O2 have been used as hydrogen acceptors. With O2, an elaborate catalytic system involving three components was employed (see Figure 1.9).61a Secondary alcohols, which are more difficult to oxidize than benzyl alcohol, were oxidized to the corresponding ketones with high yields. Overall, most alcohols gave turnovers around 30 to 40 h"1 at 100 °C. Of note, the reactions were more efficient under a low 02 partial pressure, ca. 0.6 -1.5% in 1 atm N2, than those under higher 02 partial pressures, and this was thought to be due to the sensitivity of the Ru(II)-catalytic precursor to O2. When both the hydrogenated product and oxidized hydrogen source are valuable chemicals, this kind of transfer hydrogenation can be an extremely useful process. 1.9 Aims and Scope of this Thesis A general overview has been presented and the diverse chemistry of Ru oxidation reagents and catalysts is very much apparent. The aims of this thesis work were two-fold. The foremost interest in the current research focussed on the use of dioxoruthenium(VT) porphyrin complexes as 02-oxidation catalysts for the oxidation of organic substrates. Secondly, the continual need for detailed kinetic and mechanistic studies was recognized, as they may further the understanding of such oxidation reactions. As the discussion of each individual subject is at hand, the particular aims and scope (as well as success and failure!) will be explored more clearly. Chapter 2 summarizes the general experimental 29 References on p. 32 Chapter 1 Figure 1.9. Ruthenium-based, aerobic, triple catalytic system for the Ovoxidation of alcohols to aldehydes and ketones. The ruthenium complex {Ru} dehydrogenates the alcohol. Regeneration of the ruthenium catalyst is accomplished by the bulky benzoquinone. A cobalt Schiff base complex is responsible for regenerating the benzoquinone from the reduced /?ara-hydroquinone. O2, is the sole terminal oxidant that oxidizes the reduced cobalt complex, {CoL}red (Ref. 61a). 30 References on p. 32 Chapter 1 procedures, and preparation and characterization of starting materials. Chapters 3 and 4 present kinetic and mechanistic studies on the stoichiometric and catalytic oxidations of phosphines and alcohols, respectively. Chapter 5 introduces work concerning the O2-oxidation of alcohols and neat hydrocarbons catalyzed by ruthenium perhalogenated porphyrins. Chapter 6 includes some preliminary work on the reactions of RuVI(TMP)(0)2 with HX acids, mono-substituted aromatics and /?-hydroquinone. Finally, Chapter 7 presents the overall conclusions of the entire thesis work, and suggests research topics that need further study. 31 References on p. 32 Chapter 1 References 1 a) A. H. Haines, Methods for Oxidation of Organic Compounds, Academic Press, Toronto, 1988. b) M. Hudlicky, Oxidations in Organic Chemistry, American Chemical Society, Washington, DC, 1990. 2 a) B. R. James, Fundamental Research in Homogeneous Catalysis, ed. A. E. Shilov, Plenum Press, Vol 1, 1986, p. 309. b) T. Mlodnicka and B. R. James, in Metalloporphyrins Catalyzed Oxidations, eds. F. Montanari and L. Casella, Kluwer Academic Publishers, Dordrecht, 1994, p. 121. 3 R. R. Engle and C. Djerassi, J. Am. Chem. Soc, 75, 3838 (1953). 4 a) W. P. Griffith, Chem. Soc. Rev., 21, 179 (1992) b) W. P. Griffith, Trans. Met. Chem., 15, 251 (1990) c) C.-M. Che and V. W.-W. Yam, Adv. Inorg. Chem., 39, 233 (1992) 5 a) S. Y. S. Cheng, N. Rajapakse, S. J. Rettig and B. R. James, J. Chem. Soc, Chem. Commun., 2669 (1994). b) S. Y. S. Cheng and B. R. James, J. Mol. Cat., in press. 6 a) S. Y. S. Cheng and B. R. James, Proc. of the 78th Can. Chem. Conf, Guelph, Canada, 1995, Abstract IN-447. b) S. Y. S. Cheng and B. R. James, Poster Presentation at the 15th Annual BC Inorganic Research Colloquim, Victoria, Canada, June 18-20, 1993. 7 a) Metalloporphyrin Catalyzed Oxidations, eds. F. Montanari and L. Casella, Kluwer Academic Publishers, Dordrecht, 1994. b) Metalloporphyrins in Catalytic Oxidations, ed. R. A. Sheldon, Marcel Dekker, New York, 1994. c) B. Meunier, Chem. Rev., 92, 1411 (1992). d) T. Mukaiyama and T. Yamada, Bull. Chem. Soc. Jpn., 68, 17 (1995). 8 R. Stewart, Oxidation Mechanisms, W. A. Benjamin, Inc., New York, 1965. 9 a) Cytochrome P-450, eds. T. Omura, Y. Ishimura and Y. Fujii-Kuriyama, Tokyo, 2nd Ed, 1993, Chapter 2. b) N. Rajapakse, M. Sc. Dissertation, University of British Columbia, Vancouver, Canada, 1985. 10 J. T. Groves, J. Chem. Ed., 62, 928 (1985). 32 References on p. 32 Chapter 1 11 T. L. Poulos, B. C. Finzel, I. C. Gunzalus, Wagner and J. Kraut, J. Biol. Chem., 260, 16122 (1985). 12 Reference 7b, p. 113. 13 a) J. P. Collman, C. E. Barnes, P. J. Collins, T. Owaza, J. C. Galluci and J. A. Ibers, J. Am. Chem. Soc, 106, 5151 (1984). b) H. Masuda, T. Tagu, K. Osaki, H. Suzimoto, M. Mori and H. Ogoshi, J. Am. Chem. Soc, 103, 2199 (1981). 14 a) E. R. Birnbaum, W. P. Schaefer, J. A. Labinger, J. E. Bercaw and H. B. Gray, Inorg. Chem., 34, 1751 (1995). b) D. Mandon, P. Ochsenbein, J. Fischer, R. Weiss, K. Jayaraj, R. N. Austin, A. Gold, P. S. White, O. Brigaud, P. Battioni and D. Mansuy, Inorg. Chem., 31, 2044 (1992). 15 a) T. Takeuchi, H. B. Gray and W. A. Goddard III, J. Am. Chem. Soc, 116, 9730 (1994). b) P. Ochsenbein, K. Ayougou, D. Mandon, J Fischer, R. Weiss, R. N. Austin, K. Jayaraj, A. Gold, J. Terner and J. Fajer, Angew. Chem. Int. Ed. Engl., 33, 348 (1994). 16 a) M. W. Grinstaff, M. G. Hill, J. A. Labinger and H. B. Gray, Science, 264, 1311 (1994). b) J. E. Lyons and P. E. Ellis,' Catal. Lett, 8, 45 (1991). c) P. E. Ellis and J. E. Lyons, Coord. Chem. Rev., 105, 181 (1990). d) J. E. Lyons and P. E. Ellis, Catal. Lett, 3, 389 (1989). e) J. F. Bartoli, O. Grigaud, P. Battioni and D. Mansuy, J. Chem. Soc, Chem. Commun., 440 (1991). f) A. M. d'A. R. Gonsalves, R. A. W. Johnstone, M. M. Pereira, J. Shaw and A. J. F. doN. Sobral, Tetrahedron Lett., 23, 1355 (1991). 17 D. G. Lee and M. Van den Engh, Can. J. Chem., 50, 2000 (1972). 18 J. -L. Coudret and B. Waegell, Inorg. Chim. Acta, 222, 115 (1994). 19 D. G. Lee and L. N. Congson, Can. J. Chem., 68, 1774 (1990). 20 D. G. Lee and H. Gai, Can. J. Chem., 73, 49 (1995). 21 R. H. Holm, Chem. Rev., 87, 1401 (1987). 22 T. J. Groves and R. Quinn, Inorg. Chem., 23, 3844 (1984). 33 References on p. 32 Chapter 1 23 M. J. Camenzind, B. R. James and D. Dolphin, unpublished work, Oct. 1984. 24 J. T. Groves and K.-H. Ahn, Inorg. Chem., 26, 3833 (1987). 25 J. T. Groves and R. Quinn, J. Am. Chem. Soc., 107, 5790 (1985). 26 M. J. Camenzind, B. R. James and D. Dolphin, J. Chem. Soc, Chem. Commun., 1137 (1986). 27 J. T. Groves and J. S. Roman, J. Am. Chem. Soc, 117, 5594 (1995). 28 a) M. Tavares, R. Ramasseul, J.-C. Marchon, B. Bachet, C. Brassy and J.-P. Mornon, J. Chem. Soc. Perkin Trans. 2, 1321 (1992). b) J.-C. Marchon and R. Ramasseul, J. Chem. Soc, Chem. Commun., 298 (1988). c) B. Scharbert, E. Zeisberger and E. Paulus, J. Organometallic Chem., 493, 143 (1995). 29 a) N. Rajapakse, B. R. James and D. Dolphin, Stud. Surf. Sci. Catal, 55, 109 (1990). b) N. Rajapakse, PhD Dissertation, University of British Columbia, 1990. c) N. Rajapakse, B. R. James and D. Dolphin, Catal. Lett., 2, 219 (1989). 30 a) H. Ohtake, T. Higuchi and M. Hirobe, Heterocycles, 40, 867 (1995). b) H. Ohtake, T. Higuchi and M. Hirobe, J. Am. Chem. Soc, 114, 10660 (1992). 31 a) C. S. Alexander, Ph. D. Dissertation, University of British Columbia, 1995. b) C. Sishta, Ph. D. Dissertation, University of British Columbia, 1990. 32 P. Le Maux, H. Bahri and G. Simonneaux, J. Chem. Soc, Chem. Commun., 1287 (1994). 33 C. Sishta, M. J. Camenzind and B. R. James, Inorg. Chem., 26, 1181 (1987). 34 a) C.-M. Che and W. H. Leung, J. Chem. Soc. Dalton Trans., 2932 (1991). b) W. H. Leung and C.-M. Che, J. Am. Chem. Soc, 111, 8812 (1989). 35 P. S. Traylor, D. Dolphin and T. G. Traylor, J. Chem. Soc, Chem. Commun., 279 (1984). 36 P. E. Ellis and J. E. Lyons, J. Chem. Soc, Chem. Commun., 1189 (1989); 1315 (1989). 37 J. A. Labinger, Catal. Lett., 26, 95 (1994). 34 References on p. 32 Chapter 1 38 Y. Tokita, K. Yamaguchi, Y. Watanabe and I. Morishima, Inorg. Chem., 32, 329 (1993). 39 a) C.-M. Che, C.-K. Li, W.-T. Tang and W.-Y. Yu, J. Chem. Soc. Dalton Trans., 3153 (1992). b) C.-M. Che, W.-T. Tang, W.-O. Lee, K.-Y. Wong and T.-C. Yu, J. Chem. Soc. Dalton Trans., 1551 (1992). c) C.-M. Che, W.-T. Tang, K.-Y. Wong and C.-K. Li, J. Chem. Soc. Dalton Trans., 3277 (1991). d) C.-M. Che, T.-F. Lai and K.-Y. Wong, Inorg. Chem., 26, 2289 (1987). e) K.-W. Wong, C.-M. Che and F. C. Anson, Inorg. Chem., 26, 737 (1986). 40 M. O. Elout, W. G. Haije and W. J. A. Maaskant, Inorg. Chem., 27, 10 (1988). 41 a) T.-C. Lau and C.-K. Mak, J. Chem. Soc. Chem. Commun., 766 (1993); b) 943 (1995). 42 A. C. Dengel, W. P. Griffith, C. A. O'Mahoney and D. J. Williams, J. Chem. Soc, Chem. Commun., 1720(1989). 43 C.-M. Che, C. Ho and T.-C. Lau, J. Chem. Soc. Dalton Trans., 1259 (1991). 44 L. K. Stultz, R. A. Binstead, M. S. Reynolds and T. J. Meyer, J. Am. Chem. Soc, 117, 2520 (1995). 45 a) L. Roecker and T. J. Meyer, J. Am. Chem. Soc, 109, 746 (1987). b) J. G. Muller, J. H. Acquaye and K. J. Takeuchi, Inorg. Chem., 31, 4552 (1992). 46 W. K. Soek and T. J. Meyer, J. Am. Chem. Soc, 110, 7358 (1988). 47 R. A. Binstead, M. E. McGuire, A. Dovletoglou, W. K. Soek, L. Roecker and T. J. Meyer, J. Am. Chem. Soc, 114, 173 (1992). 48 a) L. Roecker, L. J. C. Dobson, W. J. Vining and T. J. Meyer, Inorg. Chem., 26, 779 (1987). b) J. H. Acquaye, J. G. Muller and K. J. Takeuchi, Inorg. Chem., 32, 160 (1993). 49 a) A. Dovletoglou and T. J. Meyer, J. Am. Chem. Soc, 116, 215 (1994). b) B. A. Moyer, B. K. Sipe and T. J. Meyer, Inorg. Chem., 20, 1475 (1981). 50 C.-M. Che, C. Ho and T.-C. Lau, J. Chem. Soc. Dalton Trans., 1901 (1991) 51 T. Leung, B. R. James and D. Dolphin, Inorg. Chim. Acta, 19, 180 (1983). 35 References on p. 32 Chapter 1 52 C.-M. Che, W.-T. Tang, W.-T. Wong and T.-F. Lai, J. Am. Chem. Soc, 111, 9048 (1989). 53 W.-H. Leung, C.-M. Che, C.-H. Yeung and C.-K. Poon, Polyhedron, 12, 2331 (1993). 54 P. Dubourdeaux, M. Taveres, A. Grand, R. Ramasseul and J.-C. Marchon, Inorg. Chim. Acta, 240, 657 (1995). 55 This thesis, Chapter 4. 56 J. M. Mayer, Inorg. Chem., 27, 3899 (1988). 57 S.-I. Murahashi, Y. Oda and T. Naota, J. Am. Chem. Soc, 114, 7913 (1992). 58 R. A. Sheldon and J. Kochi, Metal-Catalyzed Oxidations of Organic Compounds, Academic Press, Toronto, p. 25, 1981. 59 a) A. Pacheco, Ph. D. Dissertation, University of British Columbia, 1993. b) A. Pacheco, B. R. James and S. J. Rettig, Inorg. Chem., 34, 3477 (1995). c) BR. James, A. Pacheco, S. J. Rettig and J. A. Ibers, Inorg. Chem., 27, 2414 (1988). d) B. R. James, S. R. Mikkelsen, T. W. Leung, G. M. Williams and R. Wong, Inorg. Chim. Acta, 85, 209 (1984). e) BR. James, T. W. Leung, F. W. B. Einstein and A. W. Willis, Can. J. Chem., 62, 1238 (1984). 60 Kirk-Othmer Concise Encyclopedia of Chemical Technology, ed. M. Grayson, D. Eckroth, E. Graber, A. Klingsberg and P. M. Siegel, John Wiley and Sons, Toronto, 1985, p. 13. 61 a) G.-Z. Wang, U. Andreasson and J.-E. Backvall, J. Chem. Soc, Chem. Commun., 1037 (1994). b) G.-Z. Wang and J.-E. Backvall, J. Chem. Soc, Chem. Commun., 980 (1992). c) G.-Z. Wang and J.-E. Backvall, J. Chem. Soc, Chem. Commun., 337 (1992). d) J.-E. Backvall, R. L. Chowdhury and U. Karlsson, J. Chem. Soc, Chem. Commun., 473 (1991). e) R. L. Chowdhury and U. Karlsson, J. Chem. Soc, Chem. Commun., 1063 (1991). 36 References on p. 32 Chapter 2 CHAPTER 2 Experimental Methods 37 References on p. 55 Chapter 2 2.1 Materials 2.1.1 Gases CO, Ar, N2 and 02 (99.99+ % pure) were supplied by Linde Gas (Union Carbide Inc.) and used without further purification. The Ar gas used for photolysis was passed through a Ridox column (Fisher Scientific) to remove any trace 02. Trace moisture present in the gases was removed by passing the gases over activated 5 A molecular sieves (BDH). 2.1.2 Solvents and Reagents Common organic solvents, such as benzene, toluene, CH2C12 and CHCU, were supplied by Fischer Scientific as reagent or spectroscopic grade. Benzene or toluene, if required to be moisture-free, was dried over sodiunVbenzophenone and stored under N2. Other solvents were dried over CaH2 (BDH) and stored under N2. Mesitylene (Aldrich) was used without further purification. Deuterated solvents used for NMR studies (D20, benzene-ok, toluene-dg, CD2C12 and CDCI3, all 99.6+% deuterated) were purchased from MSD ISOTOPES or ISOTEC Inc. When needed to be used under anaerobic conditions, these deuterated solvents were dried over ground molecular sieves (5 A, BDH). Subsequently, three to five freeze-pump-thaw cycles were applied to remove the air. 'PrOD-dg was purchased from Aldrich. 'PrOD-^i was obtained by mixing 1 mL of'PrOH in 100 mL of D20, with subsequent distillation of the isopropanol-afi. Any co-distilled D20 was removed by the addition of 38 References on p. 55 Chapter 2 molecular sieves (5 A, BDH). The absence of the -OH functional group in the 'PrOD-di was confirmed by 'H-NMR spectroscopy. Ruthenium was obtained as RuCi3#3H20 on loan from Johnson Matthey Ltd. and Colonial Metals Inc. Ru3(CO)i2 was prepared from RuCl3»3H20 by a literature method.1 Pyrrole (Aldrich) was distilled prior to use. BF3 (50 % weight) in MeOH was supplied by Aldrich and was stored in a vacuum desiccator. Mesitaldehyde and 2,6-dichlorobenzaldehyde were obtained from Aldrich. P(p-X-C6H4)3 compounds (X = H, Me, OMe, F, Cl and CF3) (Strem Chemicals) were recrystallized from EtOH prior to use. Triphenylphosphine oxide (Aldrich, 99% pure) was purified by column chromatography (Activity I neutral alumina), with the impurities first eluted with benzene, and the phosphine oxide subsequently eluted with acetone. The purities of the phosphines and phosphine oxide were determined by TLC analysis and *H and 31P{XH}-NMR spectroscopies. AsPh3 and SbPha (Eastman) were purified by recrystallization from EtOH. MeOH, EtOH, 1-PrOH, 'PrOH and benzyl alcohol were spectroscopic grade reagents obtained from Fischer Scientific, while -R.S-l-phenylethanol and 1,3-dichloropropan-2-ol were purchased from Eastman. All the alcohols were dried over molecular sieves (5 A, BDH) and were used without further purification. Ph3CH and adamantane were from BDH and Aldrich, respectively. The purities of these two alkanes were verified on a gas chromatograph. PI13COH was from Eastman, while 1-adamantanol, 2-adamantanol and 2-adamantanone were from Aldrich. These alcohols and ketone were employed as standards for GC experiments. Methylcyclohexane (Eastman) was found by 39 References on p. 55 Chapter 2 GC analysis to contain no other impurities. 1-Methylcyclohexanol, 2-methylcyclohexanol, 2-methylcyclohexanone, 3-methylcyclohexanone and 4-methylcyclohexanone were purchased from Eastman, and were used as GC standards. Cyclohexene, c/s-cyclooctene (herein referred to simply as cyclooctene), cyclohexene-oxide and cyclooctene-oxide were obtained from Eastman. The alkenes were pre-purified by first passing down neutral alumina (Activity I) before being distilled. Cyclohexene was pure by GC analysis. GC analysis of the distilled cyclooctene showed another compound (~ 4%), presumably an isomer of cyclooctene, to be present; the distilled substrate was used without further purification. Cyclohexene-oxide and cyclooctene-oxide were used as standards without further purification. iV,A/-Dimethylaniline (Eastman) was passed down a silica column before being atmospherically distilled. Phenol (BDH) was recrystallized twice from petroleum ether before use. p-Hydroquinone and /^-benzoquinone (Aldrich) were used as received. 2.2. Instrumentation and General Experimental Procedures 2.2.1 UV-Visible Spectroscopy UV-visible spectroscopic data were obtained with a Perkin Elmer 5 52A UV-Visible Spectrometer or a Hewlett-Packard HP 8452A Diode-Array Spectrophotometer, both equipped with thermoelectric temperature controllers. It should be noted that wavelength readings from the HP 8452A instrument are approximately 2 nm higher than those from the Perkin Elmer 552A instrument; all reported readings within this thesis 40 References on p. 55 Chapter 2 correlate to those from the HP 8452A instrument.* Extinction coefficients, 8, are given in units of M^cm"1 in parentheses immediately following the reported wavelength maxima, X-2.2.2 Stopped-flow Kinetic Studies A stopped-flow apparatus capable of achieving mixing within 1 to 2 ms was manufactured by Applied Photophysics Inc., and was used, for example, to study reactions of /raw5-RuVI(TMP)(0)2 with EAr3-type substrates (E = P, As, Sb). The apparatus was equipped with a monochrometer, and both the in-slit and out-slit widths were set to 0.25 mm. The light source was a 150 W Xe arc lamp. Anaerobic conditions for the instrument, when required, were achieved by bubbling N2 or Ar into the cooling water. In addition, TRIZMA® hydrochloride (Sigma) and sodium thiosulfite were added to the water to remove dissolved 02 on the surface of the Teflon coils. Data acquisition was computer controlled by an Archimedes 410/1 computer; the software was supplied by Applied Photophysics and was custom-made for the stopped-flow apparatus. Figure 2.1 shows a diagram of the sample handling section of stopped-flow apparatus. The syringes that contain the sample solutions are called the "drive syringes". An electronic trigger releases the 5 atm N2 pressure to force the drive platform upwards, pushing the drive syringes in the same direction. The samples were mixed rapidly and at the same time the computer acquired 400 data points within a preset time interval (5 ms to 1000 s intervals are possible). * The UV-visible spectrum of aqueous KMn04 (Mallinckrodt) obtained on the HP 8452A instrument shows absorption maxima at 508, 526 and 546 nm. 41 References on p.55 Chapter 2 Fill syringes Figure 2.1. The diagram showing the various parts of the sample-handling section on the stopped-flow apparatus. Benzene solutions of RuVI(TMP)(0)2 were loaded into the left fill-syringe via a disposal syringe from the top, while benzene solutions of ¥(p-X-C(£U)i, AsPh3 and SbPh3 were filled on the right. The drive platform is controlled electronically via a trigger, which starts and stops a flow of pressurized N2 gas (~ 5 atm). The mixing chamber and observation window lie in perpendicular to the sample handling unit are not shown in the diagram. 42 References on p. 55 Chapter 2 Isothermal conditions were maintained within the sample-handling compartment with the use of a thermoelectric temperature controller. The operating range of the stopped-flow apparatus itself was between 5 and 50 °C. Temperatures outside this range tend to make the drive syringe pistons either too loose or too stiff, respectively. In the course of these studies, the temperatures of the cooling source were set typically at 10, 20, 30 or 40 °C, and the exact temperatures were obtained from the digital readout at the sample compartment of the stopped-flow apparatus. 2.2.3 Infrared Spectrophotometer Infrared spectra were taken on an ATI Mattson Genesis Series FTIR instrument.* The samples were prepared by one of three methods: 1) a Nujol mull sandwiched between KBr plates (referred herein as "Nujol, KBr"), 2) solid compound dispersed within a compressed KBr pellet or 3) dissolved in a solvent and then coated and dried on the surface of a KBr plate (both 2 and 3 will be referred from now as "KBr"). 2.2.4 FT-NMR Instruments Solution NMR spectra were obtained on a Bruker AC-200E (200 MHz) or a Varian XL-300 (300 MHz) instrument in FT modes. Proton chemical shifts are given as 8 in parts per million (ppm) with reference to the solvent residual [CeHg at 7.15, CHCI3 at 7.24 or CHj-CeHs at 2.09] as the internal standard, relative to TMS. ^P^Hj-NMR chemical shifts are given as 8 referenced to aq. H3PO4 in a particular solvent. 19F-NMR The IR spectrum of a polystyrene film shows absorption at vc=c = 1600 cm"1. 43 References on p.SS Chapter 2 chemical shifts are given as 8 referenced to CF3COOH in a particular solvent. The reported 'H-NMR chemical shifts are singlets unless indicated otherwise (d = doublet; t = triplet; m = multiplet). The Varian XL-300 instrument was equipped with a variable-temperature unit, making VT-NMR experiments possible. Toluene-dg was used as the solvent in all the VT-NMR studies. Typically the temperature at the NMR probe was lowered at 20 °C intervals, and thermal equilibration was allowed to proceed for 10 min before data acquisition began. 2.2.5 Gas Chromatography Experiments Gas chromatograms were obtained on an HP 5891A instrument, equipped with an HP17 column (cross-linked 50%-Ph-50%-Me Silicone capillary column, 25 m length, 0.32 mm diameter, 0.26 pm thick column coating) and a hydrogen-flame ionization detector (FID). The carrier gas was He, and all gases used were purified by a Supelco gas purifier system (HC 2-2445). The column conditions and temperature programs are listed in Table 2.1 for the elution of various known standards. Sample injection volumes were typically 1 to 2 pL of solution, with typical solute concentrations between 10"2 to 10"1 M, although concentrations in the order of 10"3 M presented no difficulties. A split-gas flow rate of ~ 70 mL/min was employed, so that the injected sample would not overload the column. 44 References on p.55 Chapter 2 Table 2.1. Conditions for the separation of compound mixtures by gas chromatography. Substrate/products0 Temperature Column Head Pressure (kPa) Retention times (min) benzyl alcohol/benzaldehyde 150 °C 45 3.6; 3.2 #,S-l-phenylefhanol/6 110 °C 40 7.2 acetophenone 8.1 Ph3CH / Ph3COH 220 °C 45 13.9 24.5 adamantane/1 -adamantanol 120 °C for 6 min, then 20 °C min"1 until 200 °C 45 4.9 9.4 cz's-cyclooctene/ 90 °C for 4 min, 45 . 4.0 cyclooctene oxide then 10 °C min'1 until 140 °C 9.4 methylcyclohexane/ 50 °C for 5 min, then 45 3.8 1 -methylcyclohexanol, 10 °C min"1 until 9.3 2-methylcyclohexanone, 200 °C 11.4 3 -methylcyclohexanone, 11.6 4-methylcyclohexanonec 11.8 A/^-dimethylaniline 100 °C for 2 min., then 10°C min"1 until 200°C 45 6.82 ° These compounds were standards, obtained commercially, and were not further purified. Typically, 10"2 to 10"1 M solute was dissolved in benzene, and 1 to 2 pL were injected into the injection port, which was always set to 220 °C. The split injection flow rate was appoximately 70 mL/min. b A racemic mixture was used. 0 CH2CI2 was used as a solvent. 45 References on p. 55 Chapter 2 2.2.6 Elemental Analyses, X-ray Crystallography and Mass Spectral Analyses Elemental analyses were obtained by Mr. P. Borda of this department. X-ray crystallographic structures were determined in this department by Dr. S. Rettig with a Ragaku X-ray Diffractometer, the X-ray source being Cu-Ka or Mo-Ka radiation. Mass spectral analyses were obtained in this department in a facility headed by Dr. G. Eigendorf. Both electron impact and fast atom bombardment (on thioglycerol and 3-nitrobenzylalcohol matrices) methods of ionization were used. 2.3 Techniques A N2-filled glove-box was used to handle air-sensitive compounds. Standard Schlenk techniques were used to carry out air-sensitive reactions and solvent transfers. Flame-sealed tubes attached to vacuum lines were used to prepared anaerobic NMR samples. These standard vacuum techniques2 and the photolysis procedure to prepare Run(TMP)(MeCN)2 have been described elsewhere.2'3,7 2.4 Synthesis and Characterization of Starting Compounds The Ru-porphyrin complexes prepared during the course of this thesis are described below. Where known, the spectroscopic data are in excellent agreement with those from prior studies in this laboratory. Many new porphyrin species were observed in situ, their description will be presented later in the appropriate sections, where their reactivities will also be described in detail. 46 References on p. 55 Chapter 2 H2TMP H2TMP, the free-base porphyrin weso-tetramesitylporphyrin, was made by a procedure reported by Groves and Nemo,4 which was a modification of the Rothemund synthesis.5 The purity of the product was determined by UV-visible and 'H-NMR spectroscopies and TLC analysis. The data are in good agreement with those previously reported.11 Molecular formula (M.W.) C56H54N4 (783.07) NMR (1H, C6D6, 25 °C) 8.56 Opyrrole-H, 8H), 7.22 (w-H, 8H), 2.58 (p-Me, 12H), 1.80 (o-Me, 24H), -2.54 (N-H, 2H) UV-Visible (CH2C12) 422, 516, 550 nm Ru"(TMP)(CO) Carbonyl(tetramesitylporphyrinato)ruthenium(II), Run(TMP)(CO), was prepared by a modification of a procedure that has been used to synthesize Run(TPP)(CO).6 H2TMP (500 mg, 0.063 mmol) was added to 200 mL mesitylene, and the solution was refluxed under a bubbling stream of CO gas. Ru3(CO)i2 (300 mg, 0.047 mmol) was added in 18 aliquots during the next 6 h. The solution was heated for a total of-24 h, and during this time the reaction was monitored by TLC. At the end of 24 h, the mixture was rotary evaporated to remove the mesitylene, and the product was chromatographed on alumina (neutral Activity I). Unreacted TMPH2 and Ru3(CO)i2 were eluted first with benzene as purple and yellow bands, respectively. Run(TMP)(CO) was subsequently eluted with 1:1 benzene/CH2Cl2 as a red-orange band. Purity was assessed by TLC analysis and UV-47 References on p. 55 Chapter 2 visible and 'H-NMR spectroscopies. Yield 0.30 g, 60 %. The data are in good agreement with those previously reported.11 Molecular formula (M.W.) RUC57H52N4O (910.13) NMR(1H, C6D6, 25 °C) 8.79 Opyrrole-H, 8H), 7.25 (/n-H, 4H), 7.10 (m-H, 4H), 2.48 (p-Me, 12H), 2.20 (o-Me, 12H), 1.83 (o-Me, 12H) UV-Visible(CH2Cl2) 414, 532 nm IR (KBr) vco= 1943 cm-1 Ru"(TMP)(MeCN)2 7>a«5-bis(acetonitrile)(tetramesitylporphyrinato)ruthenium(II), Run(TMP)(MeCN)2, was prepared from Run(TMP)(CO) by a standard photolysis procedure described elsewhere.2'3'7 Run(TMP)(CO) (0.10 g, 0.11 mmol) was dissolved in a 5:3 benzene/acetonitrile mixture (80 mL) and the solution was transferred to a glass tube (3 cm wide, 20 cm long) with a narrow neck (1 cm wide, 20 cm long). A water-cooled condenser was fitted over this narrow neck, and the opening was covered with a rubber septum.2,11 A stainless steel needle was inserted into the solution through the rubber septum and the solution was purged with Ar for 30 min before it was irradiated with a 450 W Hanovia Hg-vapour lamp for 24 h. After this time a solution sample withdrawn from the mixture showed no remaining Run(TMP)(CO) in the IR spectrum (vCo = 1943 cm"1). The remaining solvent was removed by continuing the Ar-purging without water-cooling. After about 1 h, all the solvent was removed, and the solid was isolated and dried under 48 References on p. 55 Chapter 2 vacuum for 24 h. Yield 0.08 g, 80%. The data are in good agreement with those previously reported.11 Molecular formula (M.W.) RuC60H5gN6 (964.23) NMR CH, C6D6, 25 °C) 8.65 Opyrrole-H, 8H), 7.27 (m-U, 8H), 2.54 (p-Me, 12H), 2.21 (o-Me, 24H), -1.32 (MeCN, 6H) Analysis, Calculated Found UV-Visible (CeHe) IR (Nujol, KBr) C, 74.74; H, 6.06; N, 8.72 C, 74.80; H, 6.16; N, 8.56 410, 506 nm vCN = 2270 cm"1 Ruvl(TMP)(0)2 Ruvl(TMP)(0)2, ^a«5-dioxo(tetramesitylporphyrinato)ruthenium(VI), can be synthesized by the oxidation of Run(TMP)(CO) with /neta-chloroperbenzoic acid (m-CPBA),8 or by the aerobic oxidation of Run(TMP)(N2)2,9 Run(TMP),9 or Run(TMP)(MeCN)2.n In this thesis, RuVI(TMP)(0)2 was produced in situ either by the /w-CPBA oxidation of Run(TMP)(CO), or by the aerobic oxidation of Run(TMP)(MeCN)2 in benzene or benzene-fife Two mole equivalents of MeCN were observed by ^-NMR spectroscopy upon the formation of RuVI(TMP)(0)2 when the bis(acetonitrile) complex was used as the dioxo-precursor. Evacuation of the resulting solution gave a quantitative yield of the dioxo complex with no trace of the acetonitrile. The data are in good agreement with those previously reported.11 Molecular formula (M.W.) RuC56H52N402 (914.12) 49 References on p. 55 Chapter 2 NMR (JH, C6D6, 25 °C) 9.01 (/?-pyrrole-H, 8H), 7.10 (m-H, 8H), 2.45 (p-Me, 12H), 1.86 (o-Me, 24H) UV-Visible (CeHe) 422 (280,000 M'W1), 516 (22,000)nm IR (Nujol, KBr) vRu=0 = 821 cm"1 H2TDCPP The free-base porphyrin H2TDCPP, /we50-tetra(2,6-dichlorophenyl)porphyrin, was synthesized by a literature procedure10 reported for the synthesis of H2TMP. The modifications to the original literature preparation are described below. 2,6-Dichlorobenzaldehyde (10.0 g, 0.058 mol), pyrrole (4.0 mL, 0.058 mol) and chloranil (4.0 g, 0.0016 mol) were added in the above order to 1 L CH2C12, which had been dried, distilled and N2-purged. When all the aldehyde had dissolved, BF3-MeOH (50 % weight BF3 in MeOH) (1.3 mL, 0.014 mol) was added via a syringe to the solution, which was then stirred magnetically at about 25 °C for 10 min. Then NEt3 (2.0 mL, 0.014 mol) was added to quench the BF3 catalyst. The resulting solution was rotary evaporated and the black tarry solid was chromatographed on a silica column (BDH 70-230 mesh). The porphyrin was eluted first with benzene as a red-purple band, although substantial amounts of dark green and violet compounds contaminated the porphyrin. MeOH (100 mL) was added to the crude porphyrin, and the solution was left sitting overnight. The purple precipitate of H2TDCPP was collected and chromatographed again on a silica column (BDH 70-230 mesh). This time, the dark green and violet impurities that remained in the 50 References on p. 55 Chapter 2 precipitate were retained on the silica column. Yield 0.20 g, 1.6 %. The data are in good agreement with those previously reported.11. Molecular formula (M.W.) C44H22N4C18 (890.30) NMR (1H, CDC13, 25 °C) 8.68 (^pyrrole-H, 8H), 7.80 (m-U, d, 8H), 7.75 (p-U, t, 4H), -2.45 (N-H, 2H) UV-Visible (CgFL) 420, 514, 592 nm Ru"(TDCPP)(CO) Run(TDCPP)(CO), carbonyl(tetra(2,6-dichlorophenyl)porphyrinato)ruthenium(II), was prepared by the same method as that used for the preparation of Run(TMP)(CO) described above. H2TDCPP (160 mg, 0.18 mmol) was added to a 500 mL 3-necked flask containing mesitylene (200 mL), and the solution was refluxed under a bubbling stream of CO for 48 h. Ru3(CO)i2 (200 mg, 0.31 mmol) was added in 5 mg aliquots over this 48 h period, and the reaction was monitored by TLC. The mixture was then rotary evaporated to remove the mesitylene and the product was chromatographed on a neutral Activity I alumina column. Unreacted FLTDCPP and Ru3(CO)i2 were eluted first with benzene as purple and yellow bands, respectively, and Run(TDCPP)(CO) was subsequently eluted as a red-orange band with 1:1 benzene/CH2Cl2. The purity of the compound was assessed by TLC analysis and UV-visible and ^-NMR spectroscopies. Yield 80 mg, 50%. The data are in good agreement with those previously reported.11 Molecular formula (M.W.) RuC45H2oN4Cl80 (1017.37) 51 References on p. 55 Chapter 2 NMR OH, C6D6, 25 °C) 8.70 (yS-pyrrole-H, 8H), 7.36 (/w-H,d, 4H), 7.25 (m'-H, d, 4H), 6.90 (p-K, t, 4H) UV-Visible (CgHe) 412, 532 nm IR (Nujol, KBr) vCo - 1951 cm' -i Ruv,(TDCPP)(0)2 This species can be prepared either by the aerobic oxidation of Run(TDCPP)(MeCN)2 or by the /w-CPBA oxidation of Run(TDCPP)(CO), in benzene.11 RuVI(TDCPP)(0)2 was prepared via the latter route by mixing Run(TDCPP)(CO) (40 mg, 0.04 mmol) and w-CPBA (120 mg, 0.12 mmol) in benzene (10 mL). After 15 min, the complete conversion to RuVI(TDCPP)(0)2 was verified by UV-visible spectroscopy and the product was purified with on a silica column (BDH 70-230 mesh), with the dioxo species eluted first with benzene. A dark brown band remained unmoved on the column. The complex was pure by TLC analysis and UV-visible and ^-NMR spectroscopies, and the solid was stored in a vacuum desiccator. Yield 20 mg, 50 %. The data are in good agreement with those previously reported.11 Molecular formula (M.W.) RuC44H2oN402Cl8 (1021.36) NMR (1H, C6D6, 25 °C) 8.90 (pyrrole-H, 8H), 7.85 (m-U, d, 8H), 7.75 (p-H, t, 4H) UV-Visible (CeHe) 420 (255,000 M^cm'1), 514 (14,000) nm IR (Nujol, KBr) vRu=o = 822 cm"1 52 References on p. 55 Chapter 2 Run(TDCPP-Cl8)(CO) Run(TDCPP-Cl8)(CO), carbonyl(/^octachloro(/we5o-tetra[2,6-dichlorophenyl])-porphyrinato)mthenium(II) was prepared by Dr. L. Xie from Dr. D. Dolphin's group in a collaborative venture with this laboratory. Run(TDCPP)(CO) (100 mg, 0.1 mmol) that has been prepared by the previously mentioned method (H2TDCPP was provided by Dolphin's group) was suspended in MeOH (50 mL). A'-Chlorosuccinimide (300 mg) was then added to the MeOH suspension, and the resulting mixture was refluxed in air for 18 h. After this time, the solid Run(TDCPP-Cl8)(CO) that had precipitated was filtered-off and washed with a small amount of MeOH. The filtrate was green and the solid that remained was dark purple. Yield 82 mg, 64%. Molecular formula (M.W.) RuC45H,2N4OCli6 (1292.93) NMR ('H, DMSO-^e, 25 °C) 7.50 (p-K, d, 4H), 7.64 (m-H, t, 8H) UV-Visible (CH2C12/C6H6 1:20) 418 (205,000 M1 cm"1), 540 (17,000) nm IR (KBr) vco= 1965 cm"1 Analysis, Calculated C, 41.80; H, 0.94; N, 4.33 Found , 41.79; H, 1.05; N, 4.15 Mass Spec. (EI) [Ru(TDCPP-Cl8)]+, 1266 amu; loss of CO ligand RuVi(TDCPP-Cl8)(0)2 The w-CPBA oxidation of Run(TDCPP-Cl8)(CO) in benzene or CH2C12 yielded RuVI(TDCPP-Cl8)(0)2. Only sufficient dioxo complex (< 5 mg) was made immediately prior to use as needed. Approximately 10 equivalents of /w-CPBA were added to a suspension.of Run(TDCPP-Cl8)(CO) in CH2C12 or benzene, as the carbonyl compound is 53 References on p. 55 Chapter 2 not very soluble either of the two solvents, and the mixture was stirred rigorously. At the end of 5 min, the completion of the reaction was confirmed by UV-visible spectroscopy. The resulting solution was chromatographed on a silica column (BDH 70- 230 mesh), using either benzene or CH2CI2 as the eluent; with CH2C12 some TH-CPBA could be eluted as well, as the colourless peracid followed very closely the yellow-brown dioxo complex as they were eluted down the column. With benzene as the eluent, the /w-CPBA was retained by the silica; however, the dioxo complex (A^ 430 nm) in the eluent was converted to a new Ru(porp) species characterized by a Soret maximum at 422 and a Q-band at 518 nm. This porphyrin species with A™,X 422 nm can be readily converted back to the dioxo species, almost quantitatively, by the addition of m-CPBA. The transformation of the dioxo complex to this unknown porphyrin species was slower in CH2C12 (~ 2 h). Thus, the choice of the eluent was important for the preparation of a pure sample of the dioxo species. Even in the solid state, the dioxo species degraded substantially overnight in air, evidenced by the loss of VR„=O intensity in the YR spectrum. Presumably, RuVI(TDCPP-Clg)(0)2 reacts with impurities in the solvent, or even with the solvent itself, to give the species with A™>x 422 nm. Molecular formula (M.W.) RuC44Hi2N402Cli6 (1296.92) UV-Visible (CeHe) 430 (200,000 M"1 cm-1), 516 (16,000) nm IR (KBr) vRu=o = 827 cm"1 Analysis, Calculated C, 40.75; H, 0.93; N, 4.32 Found C, 41.95; H, 1.0 ; N, 4.04 Mass Spec. (EI and FAB) [Ru(TDCPP-Clg)]+, 1266 amu; loss of 2 O-ligands 54 References on p. 55 Chapter 2 References 1 a) J. L. Dawes and J. D. Holmes, Inorg. Nucl. Chem. Lett., 7, 847 (1971). b) A. Mantovani and S. Cenini, Inorg. Syn., 16, 47 (1976). 2 C. Alexander, Ph.D. Dissertation, University of British Columbia, 1995. 3 M. Ke, Ph. D. Dissertation, University of British Columbia, 1988. 4 J. T. Groves and T. E. Nemo, J. Am. Chem. Soc, 105, 6243 (1983). 5 G. M. Badger, R. A. Jones and R. L. Laslett, Aust. J. Chem., 17, 1028 (1964). 6 D. P. Rillema, J. K. Nagle, L. F. Barringer and T. J. Meyer, J. Am. Chem. Soc, 103, 56(1981). 7 A. Antipas, J. W. Buchler, M. Gouterman and P. D. Smith, J. Am. Chem. Soc, 100, 3015 (1978). 8 J. T. Groves and R. Quinn, Inorg. Chem., 23, 3844 (1984). 9 M. J. Camenzind, B. R. James and D. Dolphin, J. Chem. Soc, Chem. Commun., 1137(1986). 10 J. S. Lindsey, K. A. MacCrum, J. S. Tyhonas and Y.-Y. Chuang, J. Org. Chem., 59, 579 (1994). 11 N. Rajapakse, B. R. James and D. Dolphin, Stud. Surf. Sci. Catal., 55, 109, (1990). 55 References on p. 55 Chapter 3 Chapter 3 Mechanism of Aerobic Oxidation of EAr3 (E = P, As, Sb) 56 References on p. 110 Chapter 3 3.1 Introduction Phosphines are readily oxidized to phosphine oxides. In fact, phosphines are O2-sensitive, the tertiaryarylphosphines being air-stable only in the solid state1 and somewhat air-oxidizable in solution.f Phosphines are easily oxidized and they can serve as useful test substrates for oxidation studies; a transition-metal complex to be used as an (Voxidation catalyst can be tested initially for the oxidation of phosphines. Moreover, the oxidation by oxometal species is a relatively simple process, an oxygen-atom transfer to the phosphorus atom, compared to other organic oxidations which might involve breakage or formation of more than one bond.2 An oxygen-atom transfer generally is defined as a reaction of the type represented in Eq. 3.1. This is the simplest DnO + Am D(n"2) + A(m+2)0 (3.1) representation where DnO is the O-atom donor and Am is the acceptor. The O-atom does not change in its oxidation state, while the donor's and acceptor's oxidation states change by -2 and +2, respectively. For example, the O-atom transfer reaction of interest between oxoruthenium species and PPh3 involves only cleavage of the Ru=0 bond and formation of the 0=P bond, unlike alcohol or alkane oxidations where O-H and C-H bonds are also involved. As a result, mechanistic studies can be carried out more easily when phosphines are used as test-substrates. In addition, the oxidation of phosphines by an oxometal species is likely to proceed via an intermediate in which the phosphine oxide product is bound to the metal before dissociating into solution.3a'b Rate constants for such ' PPh3 and Pip-X-CetUh are slightly air-sensitive in solution. These phosphines (in benzene solutions at ~10"2 M) under 1 atm air at room temperature are oxidized to approximately 5% of the corresponding phosphine oxide in 24 h. AsPh3 and SbPh3 are not oxidized to their respective oxides under the same conditions. 57 References on p. 110 Chapter 3 dissociation reactions of phosphine oxide may be of value in the design of homogeneous catalysts that make use of hemi-labile chelating ligands, similar to the phosphine-ether bidentate type ligands used in some homogeneous catalysis systems.4 The oxidizable nature of phosphines allows one to determine the stoichiometry of an O-atom transfer reaction with an oxometal species, and the number of active oxo-moieties can be readily determined, thus providing a useful diagnostic tool. 3.1.1 Aims of Phosphine Oxidation in Current Work Previous studies in this laboratory on the 02-oxidation of thioethers catalyzed by zraw5-RuVI(TMP)(0)2 (1) [from now on simply referred to as RuVI(TMP)(0)2] led to interesting observations.5 Thioethers with longer alkyl chain lengths were more rapidly oxidized, the faster rates being due to more favourable AS* values for the longer chain thioethers. One mechanistic suggestion was that the O-atom transfer from oxoruthenium species to the sulfur was induced via strong Ru=0 vibrational coupling,30 and for the case of the Ru=0 moiety on the porphyrin a bulkier substrate was considered to be entropically more favourable.5 Tertiaryarylphosphines can be easily handled in the solid state as well as in solution. In addition, a whole range of P(p-X-C6H4)3 compounds are available commercially, allowing for kinetic studies of the O-atom transfer from RuVI(TMP)(0)2 to give a direct comparison with the earlier thioether oxidations. Also an earlier study on the same RuYI(TMP)(0)2/PPh3 system implied that the phosphine oxide was non-coordinating;6 however, the kinetic studies in the present work showed the presence of 58 References on p. 110 Chapter 3 OPPh3 to be important in the overall reaction. The compounds PPh3, AsPh3 and SbPh3 were oxidized stoichiometrically by (1), and the rate constants and activation parameters were obtained. The para substituent on the phenyl group within a series of P(p-X-C6FL03 [X = OMe, Me, H, F, CI and CF3] was systematically varied so that electronic effects were also studied. 3.2 Sample Preparation and Data Analysis 3.2.1 Sample Preparation Freshly distilled benzene was used to prepare the phosphine, arsine and stibine substrate solutions. The stopped-flow spectrophotometer was prepared for anaerobic conditions as described in Section 2.2.2. The sample solutions were purged with Ar and dried over molecular sieves (5 A), but samples treated in this manner gave the same kinetic data as samples that were simply prepared with freshly distilled benzene without subsequent Ar purging. The procedure required for anaerobic sample handling is time-consuming, and thus all the stopped-flow kinetic runs were performed aerobically. Solutions of RuVI(TMP)(0)2 were prepared by aerobically oxidizing Run(TMP)(MeCN)2 in freshly distilled benzene or by adding solid RuVI(TMP)(0)2 directly (Chapter 2). Complete conversion to the dioxo species from the bis(MeCN) precursor was ensured by monitoring the UV-visible spectrum from 350 to 650 nm, and the resulting concentrations in the dioxo species, determined spectrophotometrically (Chapter 2), were of the order of 10'6 M. Solutions of P(p-X-CeH4)3, AsPh3 and SbPh3 were prepared by dissolving appropriate weights of the compound in freshly distilled benzene, with 59 References on p. 110 Chapter 3 concentrations typically ~10"3 M ([SbPh3] ~ 10"4 M). Solutions of Pf/J-X-CeFLOs containing OPPh3 were prepared in the same way, with the appropriate weights of OPPh3 added as well ([OPPh3] ~ If/3 M). The above solutions [(1) and substrate] were filled into the stopped-flow apparatus via disposal 2.5 mL syringes (Aldrich). Isothermal conditions were maintained by a water-cooled temperature controller, with the temperature at the sample compartment maintained at ± 0.1 °C for the temperature range between 5 °C and 45 °C. A computer was triggered electronically to acquire the data immediately after the porphyrin and substrate solutions were mixed. The absorbances were monitored at wavelengths of 422, 430 and 412 nm, which correspond to the loss of the dioxo species, loss of an intermediate and appearance of the product, respectively (see Figure 3.2, p. 67). For the catalyzed C«2-oxidations, benzene-fife solutions containing ~10'4 M (1) were prepared, and their concentrations were determined by UV-visible spectroscopy from the known extinction coefficient of (1) (Chapter 2). P(p-X-C6H4)3 [X = OMe, H, F, Cl] stock solutions were prepared by dissolving appropriate weights of the phosphines in 1.00 mL benzene-fife. All catalysis experiments were carried out in NMR tubes by adding 0.40 mL solution of (1) first. Then the NMR tubes were capped with rubber septa and secured with Parafilm. Appropriate volumes of the phosphine stock solutions subsequently were added with a 250 pL syringe (Unimetrics), so that the final concentrations of the phosphines were 0.014 and 0.027 M for the experiments under 1 atm O2. An O2 atmosphere (1 atm) in these NMR tubes was created by bubbling a stream of 02 with a stainless steel needle into the benzene-fife solutions for 10 min. The catalytic oxidations of 60 References on p. 110 Chapter 3 PPh3 and P(p-F-C6H4)3 were also studied under 1 atm air. Blank solutions with the same phosphine concentrations but containing no species (1) were prepared and purged with 0*2 (or left under 1 atm air), so that the contributions from the autoxidation could be taken into account in the calculation of the total turnover numbers. All of the NMR samples were kept at room temperature, 24 ± 2°C, for the duration of the experiment. 3.2.2 Data Analysis Absorbance-time data for each phosphine oxidation run were transferred to an IBM-compatible computer as an ASCII text file. Sigma Plot for Windows on an IBM PC was used to function fit the data as a first-order exponential decay of the form represented by Eq. 3.2, of which the derivation can be found in Appendix B. A = (A) - AX))exp(-k0bst) + Ax,, where t = time (seconds) and A = absorbance (3.2) The parameters Ao, kobS and A*, (A> = initial absorbance, kobs = observed pseudo-lst-order rate constant and A*, = absorbance at completion of reaction) were determined by the function-fitting program in Sigma Plot. Values twice the standard errors of regression were taken to be the error estimates for the individual rate constants. Pseudo-first-order rate constants, kobs, obtained from function fitting were compared to kobs values obtained by the Guggenheim method7 and semi-log analysis (where Ao and A* were known), and the results from all three cases were in perfect agreement (see Appendix A). The raw data from the stopped-flow experiments, if in numerical form (400 data points for each absorbance-time trace), would be too voluminous to list in the present thesis. Hence, the kinetic data for the oxidations of all the substrates are tabulated in Appendix A as pseudo-61 References on p. 110 Chapter 3 first-order rate constants for the corresponding absorbance-time traces. Samples of the actual PPh3 oxidation absorbance-time traces are shown in Appendix A. At the outset of the kinetic studies on the stoichiometric oxidation of PPh3 by (1), a fast (10"2 to 10"1 s) phase, followed by a slow phase(101 to 102 s), in the overall reaction was observed. In the presence of excess PPh3, the slow kinetic phase exhibited non-first-order behaviour in (1): kobs varied as [(1)] was adjusted and exponential-decay, absorbance-time traces were not observed. The addition of excess OPPh3 alleviated the above two problems. For the fast kinetic phase, the kinetic data exhibited first-order behaviour in (1), with and without added excess OPPh3. Evidently, OPPh3 plays an important role in the slow phase of the reaction between PPh3 and (1). For the stoichiometric oxidation of the phosphine series, P(p-X-C6H4)3, excess OPPh3 was added when the slow kinetic phase was monitored (see Table 3.4). For the catalytic aerobic oxidation experiments, the ratios of oxide product to phosphine substrate in every NMR sample (including the blank solution systems) were determined from integration areas on the NMR spectra. The autoxidation contributions to the overall conversion of phosphine to the phosphine oxide within the sample solutions were taken to be equal to that of the appropriate blank solutions, and the percentages due to the blanks were subtracted from the percentages in the samples to ensure an accurate determination of the turnover numbers. For PPh3, P(p-OMe-CoFl4)3 and Vlp-CX-C^U)*, integrations in the 31P{1H}-NMR spectra were used. A pulse delay of 1.0 s was implemented initially. These relative integrations then were compared to the spectrum obtained immediately afterwards with a pulse delay of 4.0 s when the ratio of the 62 References on p. 110 Chapter 3 integration areas varied by approximately 7%. The process was repeated with the implementation of a 8.0 s pulse delay. No further change in the integration intensities was observed, indicating that a pulse delay of 8.0 s was sufficient to allow the 31P nuclei to relax and allow for consistent integrations. For Vip-V-C^U)^ the integration areas on the 19F-NMR spectra were used to determine the product/reactant ratios. Pulse delay experiments were performed similarly to the 31P{1H}-NMR experiments, and it was found that the product/reactant ratios were independent of pulse delay times. Of note, 19F-NMR spectroscopy has the convenience of a more rapid data acquisition over that of 3,P{1H}-NMR spectroscopy. 3.3 Overview of the Mechanism of Tertiaryarylphosphine Oxidation The first mention in the literature of the oxidation of PPh3 by RuVI(TMP)(0)2 (1) was in 1987 by Groves and Ann.6 The experiment involved a stoichiometric "H-NMR titration which monitored the conversion of (1) first to RuIV(TMP)(0) and OPPh3, and then to Run(TMP)(PPh3) and 2 OPPh3, as one and three equivalents of PPh3 were added, respectively. A successive O-atom transfer mechanism was implied in the report. Of note, the experiment was described to have taken place in benzene-^, although examination of the 'H-NMR spectrum indicated that the experiment most likely took place in CD2CI2, as indicated by the solvent residual peak at 5 ~ 5.3 ppm,8 whereas the solvent residual for benzene-^is at 8 ~ 7.15. The results from the stoichiometric titrations implied a non-coordinating OPPh3, with no possible role of the phosphine oxide in the oxidation mechanism. The simple stepwise O-atom transfers suggested by the "H-NMR titrations 63 References on p. 110 Chapter 3 were found to be an inadequate description once kinetic studies were undertaken in this laboratory. The mechanism of phosphine oxidation is presented first (see Figure 3.1), and the supporting data will be presented in the upcoming sections. This choice of presentation is for the benefit of the reader, as the mechanism involves several interrelated steps. The mechanism is summarized in Eqs. 3.3 to 3.6 [Ru = Ru(TMP), L = PPh3]. Step 1: Initial O-atom Transfer: Jfoi^Ofc + L Ru™(0)(OL) (3.3) Step 2: OL Dissociation: /?«IV(0)(OL) Ruw(0) + OL (3.4) Step 3: Disproportionate 2Ru™(0) - " Run + Ru^O^ (3.5) Step 4: Ligation of L: Run + L Ru\h) (3.6) The oxidation mechanism in Figure 3.1 equally applies to the other phosphines within the series P(p-X-C6H4)3 [X = OMe, Me, F, Cl and CF3]. When AsPh3 and SbPh3 were used as substrates, only their initial O-atom transfer reactions with (1) (Step 1) were monitored. Step 1 involves the O-atom transfer from RuVI(TMP)(0)2 to PPh3. This fast step, the fast kinetic phase referred to in Section 3.2.2, is first-order in (1) and PPh3, and zero-order in OPPh3. Step 2 is the reversible dissociation of the OPPh3 product from the intermediate species, RuIV(TMP)(0)(OPPh3) (2), to form RuIV(TMP)(0) (3). Step 3 is the disproportionate of (3) to (1) and Run(TMP) (4). In Step 4, PPh3 readily coordinates to (4) to form Run(TMP)(PPh3) (5). Species (1) formed from the disproportionate in Step 3 can oxidize PPh3, and the cycle repeats to oxidize 2 equivalents of phosphine with complete formation of (5). 64 References on p. 110 Chapter 3 Oxygen-atom Transfer followed by Disproportionation —Ryn-L f<5) ki O-atom transfer faster step +L,k4 —Run— + —Ru^— (2) reversible k2 dissociation of phosphine oxide —RuIV— (3) O Disproportionation (4) ^-(1) + 0=L Regeneration of Catalyst (see Section 3.4) + L *P b=o: + L y a series of steps L = L*, used to denote an exchange process (1) Figure 3.1. Mechanism of oxidation of P(p-X-C6H4)3, AsPh3 and SbPh3 by RuVI(TMP)(0)2 (1). The overall reaction involves the transfer of the O-atom from (1) followed by the disproportionation of RuIV(TMP)(0). Under air or 02 the process becomes catalytic, but the catalysis occurs at a much slower time-scale (see Section 3.4). 65 References on p. 110 Chapter 3 Steps 2, 3 and 4 were observed as an isosbestic set of UV-visible spectra, referred to in Section 3.2.2 as the slow kinetic phase, with the Soret maximum shifting from 430 to 412 nm. Figure 3.2 shows UV-visible/time traces of a benzene solution, initially containing (1) (5 x 10"6 M). In the presence of 0.1 M OPPhj, addition of 10 equivalents of PPh3 rapidly shifted the 422 nm Soret band [characteristic of (1)] to 430 nm (Step 1). Within the next few minutes, the spectrum's 430 nm Soret maximum shifted to 412 nm (Steps 2, 3 and 4), corresponding to that of (5) (see Section 3.4). Addition of only 1 equivalent of PPh3, again in the presence of 0.1 M OPPh3. shifted the Soret band to 430 nm, and then there was no further change in the position of the Soret maximum. As Groves and Ann's 'H-NMR studies6 suggested that (3) was formed on the addition of 1 equivalent of PPh3 to (1), it is reasonable to assign the 430 nm Soret band to RuIV(TMP)(0)(OL) (2) with the OPPh3 still coordinated to Ru. Isosbestic points at 382, 420, 484 and 538 nm for the second spectral change [(2) to (5)] are consistent with no other intermediates being formed in any significant quantity during the conversion to the product. The experiment involving the addition of 1 equivalent of PPh3 to (1) (~10'3 M) in benzene-fife under vacuum, similar to that performed by Groves and Ahn,6 gave a 1H-NMR spectrum that showed 'H-resonances corresponding to those of free OPPh3 and RuIV(TMP)(0) (3). The UV-visible spectrum of the same sample had absorption maxima at 424 and 518 nm. These results further support the assignment of the species with A™,* 430 nm as RuIV(TMP)(0)(OPPh3) (2) (with coordinated OPPh3). Of note, species (3) in the benzene-fife solution had decomposed when the sample was analyzed again by !H-NMR and UV-visible spectroscopies after 24 h. 66 References on p. 110 Chapter 3 16 T 350 J RuVI(TMP)(0)2 (1) Fast O-atom transfer step; appearance of intermediate at 430 nm RuIV(TMP)(0)(OPPh3) (2) Dissociation of OPPh3, di sproporti onati on, followed by L ligation; 1 slower step; loss of intermediate at 430 nm 400 450 500 Wavelength (nm) 550 600 Figure 3.2. UV-visible/time traces monitoring the conversion from RuVI(TMP)(0)2 (1) (422 nm) to Run(TMP)(PPh3) (5) (412 nm). In the presence of -0.1 M OPPh3, addition of 10 equivalents of PPh3 forms an intermediate at 430 nm before proceeding to form the product (5) at 412 nm. Total time < 5 min. Isosbestic points can be seen clearly at 382, 420, 484 and 538 nm. [(1)] = 5 x 10'6 M in benzene at room temperature under 1 atm air. XmaX(e, IVT'cm'1) values for (5) in benzene: 412(230,000) and 504(20,000) nm. 67 References on p. 110 Chapter 3 The rate expressions derived from the proposed mechanism in Figure 3.1 are represented in Eqs. 3.7 and 3.8 (see Appendix B for their derivation). O-atom transfer: rate = --^^ = -^^ = ki[(l)][L] (3.7) OL dissociation followed by disproportionation: ratp= dJi2yi=d[(5yi = k2k4K31/2rLir(2)l raie " dt dt k.2[OL] + (ki+k4)K31/2[L] Under 02 or air, the oxidation becomes catalytic. The rate-determining step is the regeneration of the catalyst, and the catalysis occurs on a much slower time-scale. The catalysis will be discussed in Section 3.4 after the mechanism of phosphine oxidation by RuVI(TMP)(0)2 has been discussed in detail. 3.3.1 Oxygen-atom Transfer In the present study, the fast UV-visible spectral change from 422 to 430 nm (Figure 3.2) corresponds to the initial O-atom transfer step that forms (2) as the phosphine adds to the oxo ligand. The slower, second spectral change from 430 to 412 nm, resulting in the formation of the final product (5), was inhibited by added excess OPPh3 (Section 3.3.2). This suggests that the phosphine oxide product initially formed in fact remains coordinated to the metal centre, and that the OPPh3 can reversibly coordinate and dissociate. Thus, the O-atom transfer reaction between (1) and PPh3 is thought to result initially in the formation of RuIY(TMP)(0)(OPPh3) (2). Of note, no evidence from XH or 3IP{1H}-NMR experiments was found to support the existence of a bound phosphine t The kobs values were the same for monitoring the loss of (2) or production of (5) at 430 and 412 nm, respectively (see Appendix A). 68 References on p. 110 Chapter 3 oxide species in the absence of added excess OPPh3 (Section 3.4 and Ref. 6), and unfortunately similar NMR experiments in the presence of ~0.1 M OPPh3 are not feasible; however, that phosphine oxides bind at axial positions of Ru(II) and Ru(IV) centres within an equatorial N4-ligand set as observed in other systems,3a'b and that OPPh3 slows the rate of reaction in the present system, suggest strongly the formulation of the intermediate species (2) as RuIV(TMP)(0)(OPPh3). Furthermore, that RuIV(TMP)(0) (3) absorbs differently in the UV-visible spectrum (see Section 3.3) supports the formulation of (2) as RuIV(TMP)(0)(OPPh3). Plots of kobs (observed pseudo-first-order rate constant for the initial O-atom transfer) versus [L] are linear throughout the concentration range studied (5 x 10"5 to 4 x 10"3 M for the case of PPh3). Figure 3.3 shows the kinetic data for PPh3. The values for the second-order rate constants, ki, are given in Table 3.1 for the oxidation of all the substrates. The activation parameters for the O-atom transfer reaction to PPh3 are AHi* = 18 ± 1.4 kJ moi"1 and ASi* = -94 ± 5 J mo^K"1 (Table 3.2), calculated from the slopes of the Eyring plotst (Figure 3.4). The AHi* value is lower than that for the thioether oxidations (AH* ~ 50 kJ moi"1),5 suggesting that PPh3 is perhaps a better nucleophile than thioethers. The ASi* values are comparable, showing that both coupling reactions are unfavourable in terms of activation entropy. No trend was found for AHi* on going from PPh3 to AsPh3 to SbPh3 (Table 3.2). AHi* increases by 50% on going from PPh3 to AsPh3. On the other hand, the AHi* value for SbPh3 is about half that for the PPh3 system. AHi* is the key factor governing the ki t Eyring Equation: ln ^r- = (- -pr) ^ + (+ ln ^ ). See Ref. 20. 69 References on p. 110 Chapter 3 Table 3.1. Second-order rate constants, ki, for the initial O-atom transfer from RuVI(TMP)(0)2 (1) to various phosphines, AsPh3 and SbPh3 substrates in benzene. Substrate ki xlO^MV at 10, 20 30, and 40°C, respectively P(/?-X-C6H4)3 8.14 + 0.08 X = OMe 10.9 + 0.02 14.8 + 0.02 19.2 + 0.02 X = Me 4.29 + 0.07 5.88 + 0.07 7.69 + 0.18 10.0 + 0.3 X = H 3.95 + 0.14 5.7 ±0.3 7.18 + 0.14 9.38 + 0.15 X = F 7.62 + 0.13 10.6 + 0.02 14.2 + 0.2 18.1+0.4 X = C1 9.17 + 0.11 12.8 + 0.2 16.9 + 0.2 22.3 ± 0.03 X = CF3 6.38 + 0.17 9.10 + 0.3 12.7 + 0.3 16.6 + 0.4 (dichloro)(triphenylphosphine)(tris(2- 0.945 ± 0.02 pyridyl)phosphine-A')ruthenium(II) 1.38 + 0.04 2.00 + 0.08 2.87 + 0.08 AsPh3 0.0623 ± 0.0007 0.0940 ± 0.0006 0.147 + 0.001 0.212 + 0.001 SbPh3(10, 15, 20,and25°C) 285 + 30 303 +35 325 +30 362 + 35 70 References on p. 110 Chapter 3 0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045 [PPh3] (Molar) Figure 3.3. Plot of kobs, pseudo-first-order rate constant, as a function of [PPh3] in benzene. kobs corresponds to the rate constant for the initial O-atom transfer from RuVI(TMP)(0)2 (1) to PPh3. Inset shows the data at 20 °C at a lower value of [PPh3]. [(1)] = 4.2 x 10"6 M (1.6 x 10-6 M for the data in the inset). A tabulation of kobs values can be found in Appendix A for all the different substrates listed in Table 3.1. 71 References on p. 110 Chapter 3 Figure 3.4. Eyring plots, ln(!jf) versus ^, and Tln(^f) versus T. From the slopes of these lines the activation parameters, AFT.* and ASi*, are derived, respectively. 72 References on p. 110 Chapter 3 Table 3.2. Activation parameters, AHf and ASr, for the initial O-atom transfer from RuVI(TMP)(0)2 (1) to phosphine, arsine and stibine substrates. Substrates AHi* (kJ moi1) and ASi* (J moi"1 K"1), respectively P(p-X-C6H4)3 18 + 1 X=OMe -87 ±5 X = Me 18± 1 -92 ±5 X = H 18 ± 1.4 -94 ±5 X = F 18.9 + 1 -84 ±4 X = C1 19.4 ± 1.6 -81+5 X = CF3 21 + 1.4 -78 + 5 (dichloro)(triphenylphosphine)(tris(2- 25.7+1 pyridyl)phosphine-AOruthenium(II) -78 ±5 AsPh3 28.7 + 1 -90 + 3 SbPh3 10.2 ±2 -85 ± 10 73 References on p. 110 Chapter 3 values for the oxidations of PPh3, AsPh3 and SbPh3 by (1), as the ASi* values are similar in all three cases. The following are some periodic trends within the series EPh3 (E = P, As, Sb):9 1) a donor strength decreases in the order P > As > Sb; 2) steric effects due to E increases in the order P < As < Sb; 3) steric effects due to the Ph groups decreases in the order P > As > Sb. That such effects should contribute to the activation enthalpy seems feasible, but no firm conclusions can be drawn based on the current data. An attempted Hammett correlation plot for the kt values for the P(p-X-CeH4)3 substrates versus a values10 is shown in Figure 3.5. The non-linearity observed is usually considered to indicate a change in the reaction mechanism,11 but this would seem unlikely for this series of phosphine substrates. Hammett analysis is a type of linear free energy relationship, where the activation free energy, AG*, is being correlated with the para substituent. More precisely (and especially in this case) the correlation is between the purely electronic effect brought about by a change in the para substituent on the P-atom, and the numerical value, o. A conventional Hammett plot of logj^ versus a can be linear only if the change in the para substituent results in one of the following three scenarios: 1) AHi* = constant, implying that A(ASi*) oc a; 2) ASi* = constant, implying that A(AHi*) oc a; 3) A(AH!*) oc A(ASi*) oc a. As a non-linear Hammett plot is observed for the present systems, the logical alternative is to look at how the activation parameters, AHi* and ASi*, are affected by the para substituents. Consideration of the different contributions of AHi* and ASi* (Table 3.2) suggests that the change in the values might indeed be independent of one another, and hence the phosphine systems fit none of the above three situations. The AHi* values do increase 74 References on p. 110 Chapter 3 • OMe 0.4 -r 0 35 4-0.3 --0.25 0.2 -• 0.15 --0.1 0.05 Me • -+ -0.2 • F H / • CI • CF3 -0.4 0.2 0.4 0.6 a (Hammett factor) Figure 3.5. Hammett plot for logr- values for the ki step at 20 °C (a values taken fromRef. 10).* * A supervisory member of my Ph.D. committee, M. Tanner, has suggested that the p-substituent effects are small, and that the Hammett plot may be horizontal. 75 References on p. 110 Chapter 3 with increasing electron-withdrawing groups (see Figure 3.6 for the modified Hammett plot). If one considers an electrophilic attack of a Ru=0 moiety of (1) on the lone-pair of electrons on P(p-X-C6H4)3, then withdrawal of electron density from phosphorus by X should tend to increase AHi*. In terms of ASi*, no correlation can be seen with a, although ASi* generally becomes more favourable, i.e. less negative, as the mass of the phosphine, arsine or stibine substrates increases (see Figure 3.7). An earlier suggestion has been made that if the O-atom transfers are induced via strong Ru=0 vibrational coupling,3 the effect is perhaps reflected in a more favourable activation entropy with bulkier substrates.5 To test the effect of the mass of the phosphine on ASi*, the complex (dichloro)(triphenyl-phosphine)(tris[2-pyridyl]phosphine-iV)ruthenium(II) (Eq. 3.9) was used as an oxidizable phosphine substrate, as the phosphorus on the coordinated tris(2-pyridyl)phosphine ligand can be oxidized to the phosphine oxide. The identities of the two species in Eq. 3.9 are known from prior work carried out in this laboratory.12 O (3.9) ph3p"; 76 References on p. 110 Chapter 3 24 -j 23 -22 -16 -15 -14 -13 --0.4 -0.2 0.0 0.2 0.4 0.6 a (Hammett factor) Figure 3.6. Modified Hammett plot, AHi* versus o. 77 References on p. 110 Chapter 3 Molecular Mass of P(p-X-C6H4)3 and Related Substrates (gram moi ) -75 H 1 1 1 1 1 ASx* moi1 KY 650 750 {P(2-pyridyl)3}(PPh3)(Cl)2Ru Figure 3.7. Plot of molecular mass of P(p-X-C6Fi4)3 and related substrates versus ASi*. 78 References on p. 110 Chapter 3 The value of ASi* perhaps reaches some limiting value as the mass is increased; this is not surprising as the coupling reaction between (1) and L is expected to be entropically unfavourable. The tris(2-pyridyl)phosphine complex is very different structurally from the EPh3-type substrates, and within this set an almost linear trend is established. Intuitively, one may envision this quantum mechanically in terms of the vibrational energy levels of the transition state becoming closer together as the mass becomes larger* A non-linear Hammett plot has been observed for the oxidation of p- and m-substituted styrenes by Ruvl(porp)(0)2 (porp = OEP and TPP).13 The non-linearity was ascribed to a shift in the electron density on the alkene C=C double bond, as the substituent on the phenyl ring varied from electron-withdrawing (NO2) to electron-releasing (OMe) groups, and this was suggested to lead to a change in the electronic structure of the transition state. Of note, the Hammett plot was concaving upwards, with the unsubstituted styrene at the minimum of the plot. If there was some change in the electronic structure in the C=C bond, this would not necessarily occur when the substituent was H, although this was invoked in order to explain the observed experimental results. A look at the activation parameters would be more insightful in this case. T Vibrational Entropy <x In qvib, where the vibrational partition function, q,* = [1 - exp(- )]"' for a simple harmonic oscillator (Ref. 21). The vibrational frequency, v « u,"1/2, where \x = reduced mass. As the mass of phosphine substrate increases, the reduced mass also increases, leading to an decrease in the vibrational energy gaps, and hence a greater number of vibrational levels. A greater number of vibrational levels leads to an increase in vibrational entropy in the transition state; the macromolecules in the present system are, of course, much more complicated than the species considered in the Transition State Theory. 79 References on p. 110 Chapter 3 Vip-X-C^U)?, compounds, compared to other substrates such as alkenes or thioethers, yield the largest span of molecular mass differences, and thus this effect is perhaps the most pronounced for this series. The rates of O-atom transfer from RuVI(TMP)(0)2 to phosphines are clearly governed by both AHi* and ASi*: AHi* becomes more favourable as the electron density around phosphorus increases, while ASi* is more favourable with more massive substituents. The increased bulk at the para position should not increase any steric hindrance,14 and should have minimum effects on the activation parameters in terms of steric considerations. The O-atom transfer is probably similar to the process in thioether oxidations, and occurs via strong Ru=0 vibrational coupling, with a more massive phosphine giving rise to a more favourable AS i1 via a larger vibrational entropy. In terms of the actual mode of O-atom transfer, the phosphine could initially coordinate to Ru, followed by O-atom transfer to the phosphorus; however, the steric constraint presented by the TMP ligand makes this unlikely. The redox process could conceivably involve two successive one-electron transfers; this would be difficult to distinguish mechanistically from a single two-electron O-atom transfer pathway, although rates arising from single-electron transfers would perhaps be more likely to adhere to a Hammett correlation. The non-Hammett behaviour of this system, as well as the strong AS* dependence on the substrate mass, are consistent with a single two-electron O-atom transfer pathway. 80 References on p. 110 Chapter 3 3.3.2 Disproportionation of Ru1 (TMP)(0) Figure 3.2 shows that two separate processes occur on different time-scales. The shift in the Soret maximum from 422 to 430 nm has been discussed, and corresponds to the O-atom transfer to form RuIV(TMP)(0)(OPPh3) (2). The shift of the Soret maximum from 430 to 412 nm occurs on a slower time-scale and is thought to correspond to the dissociation of OPPh3 from (2), followed by a disproportionation equilibrium driven to the product side by the formation of the stable Run(TMP)(PPh3) (5) (see Figure 3.1). The disproportionation reaction mechanism was summarized previously in Eqs. 3.3 to 3.6, with the resulting rate equation given in Eq. 3.8. In agreement with this mechanism for the slower second step, the rate is first-order in [(2)], first- to zero-order in [PPh3], and shows an inverse dependence on [OPPh3] (see Figure 3.8). The analysis of the kinetic data will be considered later. An alternative simpler, but less favoured, mechanism can be proposed for the second step by assuming that the second UV-visible spectral change corresponds to a second O-atom transfer starting with dissociation of OL from (2), followed by oxidation of L by (3), and ending with the formation of (5) via rapid PPh3 ligation, Eq. 3.10 (jn = rate constants). A steady state approximation applied to the series of reactions in Eq. 3.10 yields the rate law shown in Eq. 3.11 which is of the same form as Eq. 3.8. +L / -OL fast *. Ru\L) (5) (3.10) ibs ; j.2[OL]+j3[L] (3.11) 81 References on p. 110 Chapter 3 0.00138M OPPh.3 0.00271M 0.00399M 0 0.001 0.002 0.003 0.004 0.005 [PPh3] (Molar) Figure 3.8. Plots of kobs (2nd slower UV-visible spectral change from 430 to 412 nm) versus [PPh3] at various [OPPh3] values in benzene at 20 °C. [(lfeai = 4.2 xlO"6M. 82 References on p. 110 Chapter 3 Rearrangement of Eq. 3.11 to the form represented by Eq. 3.12 facilitates the J-2 analysis of the kinetic data to yield values for j2 and • . Figure 3.9a shows the plot of Kobs J2 J2J3 [L] v ' 1 [OL] j.2 1 T— versus rT-, for L = PPh3 at 20 °C, with the slope giving r~r and the y-intercept —. Kobs LM J?)3 J2 (Figures 3.9b to f show similar plots for the other P(p-X-C6H4)3 substrates). The y-intercept is near 0, hence the value obtained for J2 is unreliable. It is possible to obtain j2 by a different method. As [L] is increased, j3[L] > j.2[OL], and eventually j.2[OL] becomes negligible. In essence, the rate-determining step is now the dissociation of the OL ligand. 1.3 x 10"5 M OL was present (instead of ~10"3 M in typical experiments as described in Section 3.2.1) in order to minimize the competition by the j.2[OL] term. The expected saturation kinetics are observed with the values of kobs leveling-off as [L] increases to nearly 0.05 M (Figure 3.10). Rearrangement of Eq. 3.12 to the form represented in Eq. 3.13 allows the value of r- to be determined from the slope of the plot J2 of versus [L] (Figure 3.11). The values of j2 are obtained under various Kobs ^ = ~ [L] + ^constant, for fixed [OL] (3.13) Kobs J2 J2j3 temperatures (Table 3.3), and the following activation parameters may be obtained (Figure 3.12): AHj2 = 39 ± 13 kJ mol"1 and As/2 = -85 ±40 J mol"1K"1; however, the Eyring plots are unsatisfactory (see below). 83 References on p. 110 Chapter 3 8 T 7 + 6 + 5 + (s) 4 + 3 + 2 + 1 + + + 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 [PPh3] Figure 3.9a. Plot of r~ versus^^^r1 for the kinetic data of the Soret shift from 6 kobS [PPh3] 430 to 412 nm at 20 °C, corresponding to the slower 2nd step in the overall reaction between RuVI(TMP)(0)2 (1) and PPh3. The kobs values are pseudo-first-order rate constants under the conditions of added excess PPh3 and OPPh3. [(1)]^ = 4.2 x 10-6 M. kobs values for all P(p-X-C6H4)3 substrates are tabulated in Appendix A. 84 References on p. 110 Chapter 3 10 15 FOPPh3] 20 25 30 [P(p-OMe-C6H4)3] Figure 3.9b. Plot of 7^~~ versus 7^7—7^T~~^77TT for the kinetic data of the Soret shift 6 kobs [PO-OMe-CeFLO 3] from 430 to 412 nm (see also Appendix A). 120 -100 -• 80 i<s> 60" 40 20 + 0 10 °C + + 0 10 20 30 fOPPh3l [P(/>-Me-C6H4)3] 40 50 Figure 3.9c. Plot of r~ versus m/ ^TUT^L \ i for the kinetic data of the Soret shift 6 kobs [P(p-Me-C6H4)3] from 430 to 412 nm (see also Appendix A). 85 References on p. 110 Chapter 3 30 -• 25 -• 20 - • 10 -• 5 " 0 --0 + 10 [OPPh3l [Pi>F-C6H4)3] 15 20 Figure 3.9d. Plot of ir— versus ro/^*^] for the kinetic data of the Soret shift 6 kobs [P">-F-C6H4)3] from 430 to 412 nm (see also Appendix A). 40 35 30 25 -• 1 20 -• ;<s>i5--10 •• 5 o -• + + 10 15 •lOPPhal [P(p-Cl-C6H4)3] 20 25 10 °C 40 °C •H 30 Figure 3.9e. Plot of r~ versus rrt/ ^^T^vl \ -, for the kinetic data of the Soret shift 6 kobs [P^-Cl-CeFLOs] from 430 to 412 nm (see also Appendix A). 86 References on p. 110 Chapter 3 10 20 [OPPh3l [P(p-CF3-C6H4)3] 20 °C 30 40 Figure 3.9f. Plot of r— versus vnr ^J^I^IT \ ^ for the kinetic data of the Soret shift 6 kobs [P(p-CF3-C6H4)3] from 430 to 412 nm (see also Appendix A). 87 References on p. 110 Chapter 3 18 " 16 " 14 " 12 " 10 kobs 8 <*V-4 " 2" 0 0 0.01 0.02 0.03 0.04 0.05 [PPh3] (Molar) Figure 3.10. Plot of kobs versus [PPh3] for the kinetic data of the Soret shift from 430 to 412 nm at 20.5 °C, corresponding to the slower 2nd step in the overall reaction between RuYI(TMP)(0)2 (1) and PPh3. The kobs values are pseudo-first-order rate constants under the conditions of added excess PPh3 and OPPh3. The kobs values at other temperatures are tabulated in Appendix A. [OPPh3] = 1.3 x 10"5 M, [(l)]^ = 2 x 10"6 M 88 References on p. 110 Chapter 3 Table 3.3. Values of j2, dissociation of OPPh3 from Rulv(TMP)(0)(OPPh3). Temperature (°C) j2 (s"1) 11.2 18.7 + 1 20.5 22.7 ± 1 30.1 55.7 ±9 40.1 82 + 25 89 References on p. 110 Chapter 3 j2 1 j2 Figure 3.12. Eyring plots, ln(y-) versus j , and Tln(^ ) versus T. From the slopes of these lines the activation parameters, AHj2 and ASj2, are derived. 90 References on p. 110 Chapter 3 The large negative ASj2 value would thus correspond to the loss of OPPh3, a dissociation reaction. This is unusual, but could be ascribed in part to solvent effects, perhaps due to some solvation of the transition state, if its geometry approximates that of RuIY(TMP)(0). As written, this second O-atom transfer follows the dissociation of OL from (2), while the coordination of OL inhibits the O-atom transfer. This is contrary to the mechanism suggested for thioether oxidations by (l),5 where RuIY(TMP)(0)(OSR2) is considered more active than (1) as an O-atom transfer agent (see later). The disproportionation mechanism (Eqs. 3.3 to 3.6) is favoured for the phosphine oxidation reaction as explained below. First, the disproportionation of Rurv(TMP)(0) to Run(TMP) and RuVI(TMP)(0)2, although not directly established, presents a "consistent" explanation for the RuVI(TMP)(0)2 oxidation chemistry demonstrated for a range of different systems studied. The 02-oxidation of alkenes catalyzed by (1) has been proposed to involve a disproportionation process15'16 as depicted below. RuVI(TMP)(0)2 + alkene - RuIV(TMP)(0) + epoxide 2 Ru^TMPXO) =5==S5 Run(TMP) + RuVI(TMP)(0)2 The generation of RuVI(TMP)(0)2 from Run(TMP)(MeCN)2 upon exposure to air5'6 also has been suggested to occur via the disproportionation of RuIV(TMP)(0). In addition, the catalytic 02-dehydrogenation of primary and secondary alcohols to aldehydes and ketones, respectively (Chapter 4), is proposed to involve this disproportionation reaction. According to the disproportionation mechanism, the pseudo-first-order rate constant, koDS, assumes the form represented in Eq. 3.8, and the observed saturation 91 References on p. 110 Chapter 3 kinetics yield not j2 (the OL dissociation rate constant), but rather the combination of rate k2lC4 constants, k' = ^ +^, where k2 alone represents the OL dissociation rate constant (see Appendix B). The Eyring plots in Figure 3.12 are performed on k', and the observed AS* value of -85 J mor'K"1 is probably not meaningful. The Eyring equation applied to k' is not expected to yield a linear plot, and the scatter of the data in Figure 3.12 suggests that the Eyring plots are probably non-linear. The dissociation of OL from RuIV(TMP)(0)(OL) is a necessity within the disproportionation mechanism, as a vacant site is required for the disproportionation of RuIV(TMP)(0) to take place.16 k.2 The slope from the plot in Figure 3.9a gives the value of k" = IC2IC4K3 1/2 AT 20 °C for the PPh3 system [the values at other temperatures, as well as those for other P(/?-X-C6H4)3 systems, are listed in Table 3.4]. Excess OPPh3 was used throughout each study, as the dominant oxide present would then be OPPh3 regardless of the phosphine substrate. The inhibition of the rates of reaction by OPPh3 in all the P(p-X-C6H4)3 systems (see data in Appendix A and the linear r~ versus [JJ^^QFL^] plots, Figures 3.9b to 3.9f) implies that the k2 and L2 steps involve a rapid replacement of OPQj-X-CelUh by excess OPPh3, and hence the reversible dissociation and coordination reactions involve mainly OPPh3. K3 is independent of the phosphine substrate as well. Thus, the smaller the value k-2 of iC2k4K31/'2' larger the relative value of IQ. From Table 3.4, the relative rate of binding of L to Ru(II) follows the order: CI > F > CF3 ~ OMe > H ~ CH3 at 10 °C. 92 References on p. 110 Chapter 3 Table 3.4. Values of, , v 1/2 obtained from the kinetic data for the spectral change K2K4IV3 of the Soret maximum from 430 to 412 nm. P(p-X-C6H4)3, X= k.2 k2k4K31/2 "at 10, 20 30 and 40°C OMe 1.52 + 0.2 0.92 ± 0.07 0.63+0.08 0.48 ±0.08 Me 2.25 + 0.17 1.27 + 0.1 1.05 + 0.06 0.846 + 0.07 H 2.16 + 0.2 1.62 + 0.09 1.26 + 0.1 1.06 + 0.1 F 1.38 + 0.06 0.864 + 0.06 0.628 ± 0.06 0.536 + 0.05 Cl 1.12 + 0.1 0.69 + 0.06 0.52 + 0.054 0.38 ±0.045 CF3 1.48 + 0.3 0.94 ±0.14 0.444 ± 0.09 0.31 ±0.07 0 k2, k-2 and K3 are considered to be the same for every reaction (see text). Excess OPPh3 was used in every study to allow for a comparison of kj between different phosphine systems. 93 References on p. 110 Chapter 3 The orders are slightly different at other temperatures: Cl > F > OMe > CF3 > CH3 > H at 20 °C, CF3 > Cl > F > OMe > CH3 > H at 30 °C, and CF3 > Cl > OMe > F > CH3 > H at 40 °C. The data suggest that the electron-rich groups tend to give the smaller relative IQ values. Perhaps the electron-rich Ru(II)-centre favours rc-acceptor ligands; for example S-bound sulfoxides are generally favoured over O-bound sulfoxides in Ru(JJ)-complexes.5'17 A more electron-deficient phosphine may act as a better 7t-acceptor. The coordination of L to Ru(II) may well be the driving force for the effective disproportionation of Ru^TMP^O). In hindsight, the two-stage oxidation of thioethers may follow the same mechanism as the phosphines, via disproportionation, rather than via two successive O-atom transfers.5 The time-scale of the O-atom transfer from (1) to aliphatic thioethers is of the order of hours, and any RuIV(TMP)(0) that may have formed should have rapidly disproportionated. The scheme represented in Eq. 3.14 [Ru = Ru(TMP), S = SEt2; O and S imply oxygen- and sulfur-bonding sulfoxides, respectively] is the mechanism of thioether + SEt2 + SEt2 *"VI(°)2 lbw~ *"IV(0)(QS) IST* *"n(QS)2 — i?«n(OS)(OS) — *«n(OS)2 (3.14) (1) (6) (7) (8) (9) oxidation proposed in Reference 5. More careful examination of the data in Reference 5 shows that the formulation of species (7) as the bis(0-bonded sulfoxide) complex may be incorrect. In Reference 5a, the 'H-NMR spectrum of Run(TMP)(SEt2)2, produced in situ from the reaction of Run(TMP)(MeCN)2 and excess SEt2, is found to be identical to that assigned to (7). This also possibly suggests that the formulation for species (8) as written in Eq. 3.14 is also incorrect, and it might be the Run(TMP)(SEt2)(OSEt2) species. This 94 References on p. 110 Chapter 3 chemistry would be consistent with the labile nature of an O-bound Et2SO ligand in the Ru(TMP) system.5 A plausible route to these Ru(II) thioether and S-bound sulfoxide species is from the disproportionation of RuIV(TMP)(0) to Run(TMP) and (1), followed by rapid ligation of thioether and sulfoxide to the Ru(II)-centre. 3.4 Ru"(TMP)(L) Species and Catalytic Aerobic Oxidation of Phosphines 3.4.1 Ru"(TMP)(L) Species Stoichiometric 'H-NMR titrations (see Section 3.3) performed by Groves and Ahn6 showed Run(TMP)(PPh3) (5) along with 2 equivalents of OPPh3, to be the products of the reaction between RuVI(TMP)(0)2 (1) and 3 equivalents of PPh3. It was assumed initially that perhaps the bis(phosphine) complex, Run(TMP)(PPh3)2, would form if more than 3 equivalents of PPh3 were added to (1), as Run(TMP)(PnBu3)2 and Run(OEP)(PPh3)2 have been synthesized previously in this laboratory;18 however, 1H and ^P^HJ-NMR experiments showed that only (5) was formed even when more than 3 equivalents of PPh3 reacted with (1). Figure 3.13 shows the ^-NMR spectrum of (5), the product from the reaction of (1) with 3 equivalents of PPh3 in benzene-^. That two distinct ortho-Me ^-resonances are observed is indicative of (5) possessing C4v symmetry.5 Of note, addition of 1 equivalent of PPh3 to Run(TMP)(MeCN)2 yields a product giving a ^-NMR spectrum identical to that of (5), with production of free MeCN. This rules out the possibility that OPPh3 coordinates to the Ru-centre [as Run(TMP)(L)(OL) also exhibits C4v symmetry] when (5) is produced via PPh3 oxidation by (1), where 2 equivalents of OPPh3 is produced. 95 References on p. 110 Chapter 3 Thus, the formulation of (5) as the mono-phosphine complex Run(TMP)(PPh3) is correct. Also shown in Figure 3.13 is the 'H-NMR spectrum of the same benzene-fife solution at room temperature containing (5), formed via the reaction between (1) and 30 of equivalents PPh3. The two ^-NMR spectra for the systems containing no excess PPh3 and excess PPh3 are generally the same, except that the ortho-Me protons of TMP were exchanged broadened and the signals of the coordinated PPh3 protons had disappeared for the system containing the excess PPh3. Most likely, rapid PPh3 exchange via nucleophilic attack at the Ru centre is causing the broadening of the ortho-Me protons signals. The ligand exchange process of (5) with excess PPh3 was verified in variable temperature 'H and ^PjTiJ-NMR studies. Figure 3.14 shows the !H and 31P{TiJ-NMR spectra in benzene-fife of (5) formed from the reaction of (1) with 60 equivalents PPh3. At 10 °C, the ortho-Me signals were exchange broadened, and the signals of the PPh3 protons disappeared. At -78 °C, 'H-resonances due to the two inequivalent ortho-Me groups, as well as 'H -resonances for the protons on the coordinated PPh3, were detected, as the ligand exchange rate at the lower temperature was decreased. Also at -78 °C, the 31P{1H}-resonance for the coordinated PPh3 was observed (Figure 3.14). These results clearly suggest that a five-coordinate mono-phosphine complex is favoured. That no other Run(TMP) species can be detected in these NMR studies indicates that the bis(phosphine) species is present only in a trace amount needed to effect phosphine ligand exchange, 96 References on p. 110 Chapter o r-r-i o 'r»5 E a a. .<=> -e "3 w E oc" cfl (3D cd —' * 3 Vi[ o E-H fa s WD 97 References on p. 110 Chapter 3 l toluene 'H-NMR spectra Coordinated PPh3 9.0 8.0 7.0 6.0 5.0 4.0 Chemical Shift (ppm) Me p-Me toluene 3.0 2.0 10 °C -40 °C -78 °C 10 °c Free PPh3 Coordinated PPfc te  PPh3 I Fro Free OPPh, 45 35 25 15 Chemical shift (ppm) MP{'H}-NMR spectra Figure 3.14. Variable-temperature !H and 31P{1H}-NMR (300 MHz) spectra of Run(TMP)(PPh3) (5) (5 x 10"4 M) containing excess PPh3 (3 x 10"2 M) in toluene-dg. Species (5) was formed by reacting (1) with 60 equivalents of PPh3, and free OPPh3 is observed in the 31P{'H}-NMR spectra. The partial 31P{lH}-NMR spectrum at 10 °C shows only OPPh3; the signal due to the coordinated PPh3 is not observed. 98 References on p. 110 Chapter 3 which would make the ortho-Me protons become equivalent (Eq. 3.15 [Ru = Ru(TMP)]). The UV-visible spectrum of (5) (Figure 3.2) did not change when more Ru\L) + V ==== Run(V)(L) ===== Rua(L*) + L (3.15) phosphine was added (up to ~0.1 M), a strong indication that there is no significant amount of Run(TMP)(PPh3)2 in solution, if any. Run(TMP)(L) [L = PO-X-CeFLOs, X = OMe, Me, F, CI and CF3] species can also be formed from the reaction of (1) with 3 equivalents of L, and the NMR data obtained for these species produced in situ are tabulated in Table 3.5. The reaction of (1) with 3 equivalents of EPh3 (E = As and Sb) also afforded the Run(TMP)(EPh3) species. The 'H-NMR spectra of the solutions containing excess phosphine L show the same exchange broadening of the ortho-Me protons and non-detection of the coordinated ligand phenyl protons, as observed for the PPh3 system, showing that the phosphines within the P(p-X-CeH4)3 series do not form complexes of the type Run(TMP)(L)2. It seems that only stronger rj-donor phosphines such as P"Bu3 can form the Run(TMP)(P"Bu3)2 complex in solution; however, the second P"Bu3 ligand within the complex can be removed at 270 °C under a vacuum of ~ 10"5 torr.18 3.4.2 Catalytic Aerobic Oxidation of Phosphines Ruw(TMP)(0), RuVI(TMP)(0)2 and Run(TMP)(L) were observed in benzene-^ solutions of Run(TMP)(L) (initially made from (1) + 3 L) [L = P(p-X-C6H4)3, AsPh3 and SbPh3] when these solutions were exposed to air for approximately 2 min. Free L was not observed during the reaction, and within 10 min OL and (1) were the only species in 99 References on p. 110 Chapter 3 Table 3.5. "H and 31P{"H}-NMR data for various Run(TMP)(L) species (L = substituted phosphine, AsPh3 or SbPh3). Run(TMP)(L)° Hp Chemical shifts,6'" 8 Mea Hm Ho Hp 31P{-H) L = PPh3 8.42 2.41 2.18, 1.40 6.32 4.80 6.44 35.3^ L = P(p-OMe-C6H4)3 8.45 2.41 2.32, 1.41 6.07 4.88 - -L = P->-Me-C6H4)3 8.45 2.43 2.23, 1.70 6.25 4.86 - 29.6d L = V(p-F-C6n4)3 8.38 2.43 2.23, 1.29 6.10 4.64 N/A 31.7 L = P(p-Cl-C6H4)3 8.37 2.43 2.23, 1.28 6.39 4.57 N/A 35.1* L = P->-CF3-C6H4)3 8.37 2.43 2.19, 1.20 6.65 4.69 N/A 29.5 L = AsPh3 8.28 2.38 1.92, 1.78 6.54 5.35 6.67 N/A L = SbPh3 8.55 2.38 2.25, 1.55 6.38 5.18 6.52 N/A Run(TMP)(P"Bu3)e 8.45 2.63 2.47, 1.72 N/A 53.09 Run(TMP)(P"Bu3)2e 8.43 2.48 2.4/ N/A -0.38 a Run(TMP)(L) species produced in situ from the reaction between RuVI(TMP)(0)2 and 3 equivalents of L. b lH relative to TMS; 31P{ JH} relative to H3P04(aq); 200 MHz machine at 25 °C in benzene-tfk unless indicated otherwise. 0 Legend: Porphyrin protons (singlets) Me0, 2 sets of 12 inequivalent H X = P, As, Sb Me„ 12 H; Hp, 8 H Hme,a, around 7 ppm region, buried beneath solvent, L and OL protons Ligand Protons (multiplets) He, 6 H; Hm, 6 H; Hp, 3 H d Temperature at -68 °C in toluene-dg on a 300 MHz instrument. e Reference 18. f Singlet for the ortho-Ms "H-resonance is indicative of the complex possessing Z)4h symmetry. 100 References on p. 110 Chapter 3 solution. Figure 3.15 shows the ^-NMR spectrum of a benzene-ofe solution of Run(TMP)(AsPh3) [formed from (1) reacting with 3 AsPh3], which has been exposed to air for approximately 2 min. Other substrate systems generally give the same type of XH-NMR spectrum under the corresponding conditions: namely, Rurv(TMP)(0), RuVI(TMP)(0)2 and Run(TMP)(L) are observed. For the spectrum of the AsPh3 system shown in Figure 3.15, an unassigned upheld ^-resonance at 8 ~ -8 ppm that is not present in the spectra of the other systems is observed. This broad signal disappeared in the spectrum that was acquired after a total time of ~ 4 min of exposure to air. This unassigned 8 value could result from a species formed from the binding of OAsPh3 to Ru^fTMPXO). If RuIV(TMP)(0)(OAsPh3) is indeed present, the ligand binding is expected to be weak, and the 'H-chemical shifts of RuIV(TMP)(0) moiety generally might not be perturbed to a great extent; nonetheless, the perturbation on the yff-pyrrole-H signal might be large enough to be detected. The yS-pyrrole-H signals of the paramagnetic RuIV(porp)5'19't species are very sensitive to the environment about the ruthenium and might possible discriminate between Ru^TMPXO) and RuIV(TMP)(0)(OAsPh3). As the exposure of Run(TMP)(L) species to air in solution regenerates RuVI(TMP)(0)2 (1), oxidizing L catalytically with 02 is clearly viable. Initial qualitative f The ^pyrrole protons within RuIY(TMP)(OR)2 (R = Me, CgHj, 'Pr, Et) species exhibit very different chemical shifts (-21.8, -30.45, -11.95, -17.6 ppm, respectively), while the Mepflrfland Meortho 'H-chemical shifts differ by ~ 0.3 ppm. See Chapter 4. 101 References on p. 110 Chapter 3 102 References on p. 110 Chapter 3 experiments showed that PPh3 can be 02-oxidized using (1) as the catalyst, with total turnovers of approximately 20 at the end of 24 h at room temperature under 1 atm air. The turnover frequency of about 1 h"1 (exclusive of the initial 2 equivalents of phosphine oxide formed from the stoichiometric reaction) is low considering that the O-atom transfer and disproportionation steps to form Run(TMP)(PPh3) (5) are complete within a few minutes. The relatively slow regeneration of (1) from (5) most likely is initiated via 02 attack at the vacant axial site in (5) (Figure 3.1), and the excess PPh3 competes against this 02-binding. Catalysis studies were done on various phosphine systems under 1.0 atm O2 and/or air (Table 3.6 and Figs. 3.16a to d). The catalytic activity of (1) generally is higher under 1 atm O2, but the turnovers obtained are not too much greater than those obtained under 1 atm air, especially during the initial 24 h of the catalytic runs. The diffusion of O2 from the gas phase into the benzene-fife solutions within the NMR tubes to replenish the consumed 02 is expected to be slow and dependent upon various factors, and thus no firm conclusions regarding the effect of O2 on the rate of catalysis can be drawn from the current data; indeed diffusion may be rate-limiting. There is generally little effect of the concentration of phosphine on the catalytic activity, especially when the experimental errors are taken into consideration. A possible exception might be the P(p-Cl-C6H4)3 system, which gave higher turnovers at a higher value of [phosphine]. Again, the 02-diffusion problem precludes any discussion regarding the effect of [phosphine], as the key step in the catalytic process, that of the regeneration of (1), must depend on both phosphine and O2 binding to (5). 103 References on p. 110 Chapter 3 Table 3.6. Total turnovers of various phosphines catalytically oxidized at 24 °C in benzene-^ under 1 atm 02 in the presence of Ru^(TMP)(Q)2 (1). Substrate (Molar) ([RuVI(TMP)(0)2] in parentheses) Time (hours) Blank contributions (% of initial L) Turnovers based on RuVI(TMP)(0)2a PPh3 64 excess; 0.0147 M (2.3 x IO"4 M) 64 excess; 0.0147 M*(2.0 x IO-4 M) 128 excess; 0.0257 M (2.3 x 10"4 M) 22 3.5 31 ±3 22 3.0 21+3 22 5.0 36 + 5 128 excess; 0.0257 M 6 (2.0 x 10'4 M) 22 5.5 14 + 3 P(p-F-C6H4)3 175 excess; 0.0148 M (8.5 x IO"5 M) 19 0.8 9 + 2 48 1.4 82 + 4 62 2.3 96 + 5 350 excess; 0.0274 M (7.8 x 10"5 M) 19 1.3 14 + 2 48 2.7 80 + 3 62 4.2 112 + 6 155 excess; 0.0278 M6 (1.8 x IO-4 M) 22 1.5 11+2 49 3.4 27 + 3 70 7.6 40 + 4 310 excess; 0.0515 M6 (1.7 x 10"4 M) 22 3.0 13+2 49 7.0 32 + 3 70 15.0 40 + 4 P(p-OMe-C6H4)3 166 excess; 0.0144 M (8.7 x IO-5 M) 19.75 1.7 24 + 3 48.75 4.2 131 ± 10 60 5.6 166 + 12 332 excess; 0.0272 M (8.2 x 10"5 M) 19.75 3.4 19 + 2 48.75 8.5 180+15 60 11.5 190 + 20 P(p-Cl-C6H4)3 180 excess; 0.0150 M (8.3 x IO'5 M) 20 1.4 7+1 48 3.0 64 + 5 62.5 4.0 71+6 360 excess; 0.0275 M (7.6 x 10'5 M) 20 2.4 15+2 48 5.9 110 + 10 62.5 6.2 115 + 10 " Autoxidation by 02 has been taken into account in these reported turnover numbers. Refer to Section 3.2.2 on the quantification of OL and L. b Experiment done under 1 atm air (-0.20 atm 02) 104 References on p. 110 Chapter 3 40 -i 0 5 10 15 20 25 Time (hours) Figure 3.16a. Catalytic oxidation of PPh3 in the presence of Ru (TMP)(0)2 (~ 2 x 10"4 M) under 1 atm air or 02 in benzene-afe at 24 °C. Linear dependences are assumed, based on related systems-see Figs. 3.16b to d. 105 References on p. 110 Chapter 3 120 H 100 H Total 80 -| Turnovers 60 40 H 20 V(p-F-C6R4)3 0 i Legend 0.0274 M 350 excess 1 atm 02 0.0148 M 175 excess 1 atm 02 0.0274 M 350 excess 1 atm air 0.148 M 175 excess 1 atm air if 10 20 "i 1 r-30 40 50 Time (hours) 60 70 80 Figure 3.16b. Catalytic oxidation of P(p-F-C6H4)3 in the presence of RuVI(TMP)(0)2 (1) under 1 atm air and 02 in benzene-£& at 24 °C. [(1)] ~ 2 x 10"4 M for experiments under 1 atm air and ~ 8 x 10"5 M under 1 atm 02. 106 References on p. 110 Chapter 3 200 H 150 Total Turnovers -JQQ J 50 H P(p-OMe-C6H4)3 1 atm 02 o 4 1 1 1 r-0 10 20 30 40 Time (hours) 50 0.0272 M 332 excess X 0.0144 M j 166 excess 60 70 Figure 3.16c. Catalytic oxidation of P(p-OMe-C6H4)3 in the presence of RuVI(TMP)(0)2 (~ 8 x 10"5 M) under 1 atm 02 in benzene-de at 24 °C. 107 References on p. 110 Chapter 3 140 -i 120 H 100 P(p-Cl-C6H4)3 1 atm O2 i 0.0275 M 360 excess Total Turnovers 80 60 0.0150 M 180 excess 40 H 20 H 0 -W 1 1 1 r— 0 10 20 30 40 Time (hours) 50 60 70 Figure 3.16d. Catalytic oxidation of P(p-Cl-C6H4)3 in the presence of RuVI(TMP)(0)2 (~ 8 x 10"5 M) under 1 atm 02 in benzene-^ at 24 °C. 108 References on p. 110 Chapter 3 3.5. Conclusions This chapter presented some kinetic data for the O-atom transfer from trans-RuVI(TMP)(0)2 to tertiaryarylphosphines, AsPh3 and SbPh3. The increasing AHi* for the O-atom transfer upon withdrawing electron density around phosphorus suggests that the Ru-oxo moieties are electrophilic in nature, and that the reaction proceeds via an electrophilic attack of the Ru=0 moieties on the lone pair of phosphorus. Alternatively, a nucleophilic attack of the phosphorus lone pair on the empty Ru=0 7r*-orbital, with the phosphorus atom coordinating to Ru, as suggested for O-atom transfer reactions with organic sulfides within non-porphyrin Ru=0 systems,22 is also a possibility, but unlikely due to the steric constraints presented by the mesityl groups on TMP. Furthermore, the O-atom transfer appears to occur via strong Ru=0 vibrational coupling, as reflected in the trend found for ASi*. In contrast to the conclusions drawn for the thioether oxidations,5 a successive two O-atom transfer mechanism is not favoured for the phosphine systems. Rather, an initial O-atom transfer from RuVI(TMP)(0)2, followed by a disproportionation reaction of the Ru(IV) formed to generate Ru(II) and Ru(VI), is favoured. This type of disproportionation is more consistent in explaining Ru(TMP) oxidation chemistry in general, for example, in alkene13'14 and alcohol oxidations (Chapter 4). Indeed, the thioether oxidations may also proceed via the same disproportionation mechanism as that for the phosphine oxidations; the reported kinetic data5 could equally well be rationalized in terms of the disproportionation mechanism, as discussed in Section 3.3.2. 109 References on p. 110 Chapter 3 References 1 R. A. Sheldon and J. K. Kochi, Metal-Catalyzed Oxidations of Organic Compounds, Academic Press, Toronto, 1981, p. 395. 2 R. H. Holm, Chem. Rev., 87, 1401 (1987). 3 a) B. A. Moyer, B. K. Sipe and T. J. Meyer, Inorg. Chem., 20, 1475 (1981). b) A. Dovletoglou and T. J. Meyer, J. Am. Chem. Soc, 116, 215 (1994). c) L. Roecker, J. C. Dobson, W. J. Vinning and T. J. Meyer, Inorg. Chem., 26, 779 (1987). 4 E. Lindner and M. Haustein, Coord. Chem. Rev., in press. 5 a) N. Rajapakse, Ph. D. Dissertation, University of British Columbia, 1990. b) N. Rajapakse, B. R. James and D. Dolphin, Stud. Surf. Sci. Catal., 55, 109 (1990). 6 J. T. Groves and K.-H. Ahn, Inorg. Chem., 26, 3831 (1987). 7 B. Borderie, D. Lavalire, G. Levy and J. C. Michaeu, J. Chem. Ed., 67, 459 (1990). 8 DeuteratedNMR Solvents-Handy Reference Data, Merck and Co., Quebec, Canada, 1992. 9 F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 5th edition, John Wiley and Sons, Toronto, 1988, p. 432. 10 CD. Johnson, The Hammett Equation, Cambridge University Press, Chapter 1, 1973. 11 P. R. Wells, Chem. Rev., 62, 171 (1962). 12 R. Schutte, Ph. D. Dissertation, University of British Columbia, 1995. 13 C. Ho, W.-H. Leung and C.-M. Che, J. Chem. Soc, Dalton Trans., 2933 (1991). 14 a) C. A. Tolman, Chem. Rev., 77, 313 (1977). b) P. B. Dias, M. E. Minas de Piedale and J. A. Martinho Simoes, Coord. Chem. Rev., 135/136, 737 (1994). 15 J. T. Groves and R. Quinn, J. Am. Chem. Soc, 107, 5790 (1985). 110 References on p. 110 Chapter 3 16 J. T. Groves and J. S. Roman, J. Am. Chem. Soc, 117, 5594 (1995). 17 a) D. T. T. Yapp, J. Jaswal, S. J. Rettig, B. R. James and K. A. Skov, Inorg. Chim. Acta., 177, 199 (1990). b) D. T. T. Yapp, J. Jaswal, S. J. Rettig, B. R. James and K. A. Skov, J. Chem. Soc, Chem. Commun., 1528 (1992). 18 C. Sishta, M. J. Camenzind, B. R. James and D. Dolphin, Inorg. Chem., 26, 1181 (1987). 19 S. Y. S. Cheng, N. Rajapakse, S. J. Rettig and B. R. James, J. Chem. Soc, Chem. Commun., 2669 (1994). 20 H. E. Avery, Basic Reaction Kinetics and Mechanisms, Macmillan Education, London, 1974, p. 66. 21 G. M. Barrow, Physical Chemistry, 4th Edition, McGraw-Hill, Toronto, 1979, p. 228. 22 D. G. Lee and H. Gai, Can. J. Chem., 73, 49 (1995). Ill References on p. 110 Chapter 4 Chapter 4 Catalytic Aerobic Oxidation of Alcohols and Alkanes 112 References on p. 155 Chapter 4 4.1 Introduction The recent developments in the use of ruthenium complexes in the oxidation of saturated hydrocarbons were discussed in Chapter 1. Most of the complexes discussed were represented by examples from non-porphyrin oxoruthenium species.1 Attention is now turned to the discussion of the oxidation of alcohols and alkanes catalyzed by dioxoruthenium(VI) complexes containing porphyrin ligands that were studied in the present thesis. Work carried out as a part of this thesis led to the development of a ruthenium porphyrin-based system exhibiting remarkable activity for the catalytic aerobic oxidation of alcohols. The complexes RuVI(porp)(0)2 [porp = TMP (la) and TDCPP (lb)] catalyzed the aerobic oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones, respectively, under mild conditions. An intermediate in the oxidation of'PrOH to acetone was identified to be a bis(alkoxo)ruthenium(IV) species, Rurv(TMP)(0'Pr)2 (2a), which was characterized crystallographically.2 To the best of the author's knowledge, this represents the first structurally characterized, monomeric alkoxo complex of ruthenium porphyrins; the results clarify earlier proposals by this group3 and others4 that the intermediate was possibly the bis(hydroxo) species, RuIV(TMP)(OH)2. The ability of some dioxoruthenium porphyrins5 similar to (la) and non-porphyrin oxoruthenium species6 to hydroxylate tertiary alkanes stoichiometrically prompted further studies on (la) and (lb) in their abilities to oxidize alkanes. Species (la) catalyzes the aerobic oxidation of Ph3CH to Ph3COH, while species (lb) [but not (la)] also catalyzes the aerobic oxidation of adamantane to 1-adamantanol, although the rates were slow and 113 References on p. 155 Chapter 4 the overall turnovers were low. The question regarding whether (la) or (lb) can oxidize alkanes; either stiochiometrically or catalytically, has been raised,3b and the catalytic aerobic oxidation of the above tertiary alkanes clearly answers that question, as well as demonstrating some significant chemistry within these ruthenium porphyrin systems. 4.1.1 Scope of Alcohol Oxidations in Current Work As mentioned, the nature of the intermediate in the stoichiometric oxidation of 'PrOH by RuVI(TMP)(0)2 (la), tentatively proposed in previous studies to be RuIY(TMP)(OH)2,3'4 was unresolved, and it was the initial goal to establish its identity. Also, it was hoped that a better understanding of the oxidation mechanism could be realized through kinetic studies and deuterium-isotope labeling experiments. Furthermore, in the initial thesis work the RuVI(TMP)(0)/PrOH system was found to be marginally catalytic under 1 atm air (Section 4.3), and thus a considerable effort was devoted to enhance the lifetime and reactivity of the catalyst. 4.2 Sample Preparation and Data Analysis 4.2.1 Sample Preparation The kinetics for the stoichiometric oxidation of'PrOH and benzyl alcohol were followed by ^-NMR spectroscopy. In typical experiments, solutions of (la) (made from the aerobic oxidation of Run(TMP)(MeCN)2, Chapter 2), 1 to 5 x 10"4 M in benzene-^ (0.30 to 0.40 mL), were purged with Ar for 30 min. During this time, the NMR probe was preset at the desired temperature, between 18 and 35 °C. At the end of this time, 114 References on p. 155 Chapter 4 'PrOH or benzyl alcohol, dried over molecular sieves (5 A, BDH), was injected (1 to 5 pL) into the benzene-^ solution, with resulting concentrations of the alcohol between 10"2 and IO"1 M. The catalytic aerobic oxidations of'PrOH and benzyl alcohol were generally carried out at 24 or 50 °C (± 2) under 1 atm air. Typical solutions of (la) 10"4 to 10"3 M in benzene-^ (0.40 mL) were prepared, and the alcohols were added via syringe (Unimetrics), with resulting concentrations between 10"2 and 10"1 M. The conversions of the alcohols to the ketone or aldehyde were monitored periodically (usually between 24 h intervals) by "H-NMR spectroscopy, with the relative amounts of the reactant to product determined from the integration intensities of Me2CHOH ('PrOH), Me^CO (acetone), PI1CH2OH (benzyl alcohol) and PhCHO (benzaldehyde) at 3.68, 1.58, 4.31 and 9.62 ppm, respectively. In gas chromatography experiments, the aerobic oxidations of benzyl alcohol and 1-phenylethanol were carried out at 50 °C under 1 atm air. Benzene solutions (0.40 mL) of (la) or (lb) [see Chapter 2 for the preparation of (la) or (b)] in the concentration range between 10"6 and 10"4 M were prepared in screw-capped glass vials. The caps were lined with Teflon tape to ensure that the benzene did not evaporate. The vials then were immersed in an oil-bath, which was maintained at a temperature of 50 ± 2 °C. At the end of approximately every 24 h, a sample (1 to 2 pL) of the solution was withdrawn and analyzed by a gas chromatograph to determine the total turnover number. The retention times of the various substrates and the column conditions of the GC runs are tabulated in Section 2.2.5, Table 2.1. 115 References on p. 155 Chapter 4 For the above catalysis studies, the deuterated and non-deuterated benzene solvents were not dried and were used directly from the bottle. The concentration of F£20 in benzene-fife directly from the bottle that has not been pre-dried was determined to be approximately 4 x 10"3 M from the 'H-NMR spectra using MeCN as the standard. The concentration of H20 in benzene directly from the bottle was assumed to be of the same order of magnitude as in benzene-fife. H20 saturated benzene-fife (with H20/benzene-fife as a two-phase system) was found to have a water concentration of 1.0 x 10"2 M in the organic phase. In both the NMR and GC catalysis experiments, no additional water, 50 pL water, or 50 pL 3.0 M aqueous KOH was added to the benzene or benzene-fife solutions. The catalytic hydroxylations of Ph3CH by (la) and Ph3CH and adamantane by (lb) were studied in benzene solutions at 24 ± 2 °C under 1 atm air in the same type of vials that were used for the catalytic oxidation of alcohols. Complex (la) [1.2 x 10"4 M in 0.40 mL benzene generated from the bis(acetonitrile) precursor] was prepared and 50 pL 0.026 M Ph3CH in benzene solution was added to the solution of (la). The resulting excess of alkane over (la) was 29-fold. Complex (lb) (2.4 x 10"4 M in benzene) was prepared by the /n-CPBA oxidation of Run(TDCPP)(CO) (Chapter 2). 25 pL of 0.10 M adamantane in benzene was added to 0.40 mL of benzene solution containing (lb), giving rise to a 26-fold excess of alkane over (lb). 25 pL of 0.074 M Ph3CH in benzene was added to 0.40 mL benzene solution containing (lb), giving rise to a 19.4-fold excess of alkane over (lb). X-ray quality crystals of RuIV(TMP)(0'Pr)2 (2a) and RuIV(TMP)(0'CH(CH2Cl)2)2 (2b) were obtained from concentrated benzene-fife solutions that were used for 'H-NMR 116 References on p. 155 Chapter 4 analyses of the stoichiometric oxidations of the 'PrOH and l,3-dichloro-2-propanol substrates. Extended evacuation of these solutions to dryness at ambient temperatures yielded crystals suitable for X-ray diffraction. 4.2.2 Data Acquisition and Analysis The kinetics of the stoichiometric oxidations of'PrOH and benzyl alcohol under 1 atm Ar were followed by the integrations of the para-methyl protons of (la) and the product Ru^TMPXO'Pr^ (2a) or RuIY(TMP)(OCH2Ph)2 (2c), respectively. The combined integrations of (la) and (2a) or (2c) were normalized to 100%, since no porphyrin intermediates* were observed by NMR, ESR or UV-visible spectroscopies. The natural logarithm of the mole fraction of (la), lnfJGa), was plotted versus time. For the 'PrOH oxidations, the half-lives were 3 to 4 h in typical experiments, and it was practical to follow only one of the reactions for more than three half-lives to establish first-order dependence in (la) (see Figure 4.1). Subsequent reactions, where the concentrations for both (la) and 'PrOH or benzyl alcohol were systematically varied (Appendix C), were monitored only for 1 to 2 h. Of note, !H-NMR spectroscopy, rather than UV-visible spectroscopy, was chosen as the method to follow the kinetics for the stoichiometric oxidation of alcohols, because the concentration of (la) in UV-visible experiments is ~ 10"6 M. The alcohol oxidations become catalytic in the presence of 02, and removing 02 ' i) Species (la) and (2a) were the only ones observed in solution during the reaction, as monitored by 'H-NMR spectroscopy, ii) A frozen benzene-cfe solution of "(la) + 'PrOH" under Ar at 110 K showed no ESR signals (see later), iii) Previous work (Ref. 3) followed the conversion of (la) to (2a) by UV-visible spectroscopy in benzene, and the set of spectra showed isosbestic points, suggesting that (la) and (2a) are the dominant species in solution. 117 References on p. 155 Chapter 4 Time (s) Chemical Shift, ppm Figure 4.1. The kinetics of the stoichiometric oxidation of 'PrOH by RuVI(TMP)(0)2, (la), in benzene-c/e under 1 atm Ar at 18.2 °C followed by XH-NMR spectroscopy (300 MHz) in the 2 to 3 ppm region. Inset shows the plot of lnCYia) versus time (Xu = mole fraction of starting porphyrin (la) = Intp.Me{Ru(vi))/[InVMe(Ru(vi)) + 1/3 Intp+0-Me(Ru(iv))]), the slope of which gives the pseudo-first -order rate constant, kob9. [(la)] = 4.0 x IO-4 M; ['PrOH] = 0.0568 M. 118 References on p. 155 Chapter 4 to the extent that it becomes less than 10"6 M, such that (la) does not regenerate, is not feasible. The catalytic oxidations of 'PrOH and benzyl alcohol were followed by "H-NMR spectroscopy and GC analysis, with results in agreement. The products of oxidation were solely acetone and benzaldehyde, respectively; benzaldehyde was not further oxidized to benzoic acid under the conditions described in Section 4.2.1. In both ^-NMR and GC experiments, the identities of the products were determined with the use of known standards. The combined integrations of the alcohols and products were normalized to 100%, and subsequently the percentage conversions were calculated. Knowledge of the initial ratios of substrates to the catalyst (la) or (lb) allowed the catalytic turnovers to be determined as the reactions progressed. The catalytic hydroxylations of adamantane to 1-adamantanol and PI13CH to Ph3COH by (la) and (lb) in benzene were followed by GC analysis. The retention times of the solutes were determined from authentic samples of the starting alkanes and alcohol products (Chapter 2, Table 2.1). The response factors of adamantane and 1-adamantanol to the FID detector were proportional to the molar concentrations of the analyte. The same also applies to the Ph3CH/Ph3COH, benzyl alcohol/benzaldehyde and 1-phenylethanol/acetophenone systems. In the GC analyses, the starting alkanes and tertiary alcohol products accounted for all the organics present, and thus the conversions were calculated based on the relative intensity of the alkane and alcohol signals. The kinetic data for the stoichiometric oxidation of'PrOH and benzyl alcohol by (la) are tabulated in Appendix C. The data from the catalytic oxidation of benzyl alcohol 119 References on p. 155 Chapter 4 are also tabulated in Appendix C. The alkane hydroxylation data can also be found in Appendix C. The supplementary data for the crystal structures of (2a) and (2b) are given in Appendix D. 4.3 Stoichiometric Oxidation of Alcohols by Oxoruthenium Species Kinetic and mechanistic studies on the stoichiometric oxidation of alcohols by monooxoruthenium(IV) and dioxoruthenium(VI) complexes have been reported, mainly by the groups of Meyer,7 Lee,8 Griffith1 and Che6a'9'15. Nonetheless, further detailed kinetic and mechanistic studies on the oxidation of alcohols by oxoruthenium complexes are invaluable in order to understand better such oxidations in general; this can aid in the design of better oxidation catalysts. Further, the Ru-porphyrin catalysts reported in this thesis are the first to utilize effectively 02 as the oxidant in alcohol oxidations. 4.3.1 Bis(aIkoxo)porphyrinatoruthenium(IV) Species The kinetic studies on the stoichiometric oxidation of'PrOH to acetone and benzyl alcohol to benzaldehyde by (la) were studied, and the proposed mechanism will be discussed in the next section. The metalloporphyrin products in these alcohol oxidations were the corresponding bis(alkoxo) species, RuIV(TMP)(OR)2 [R = 'Pr (2a) or CH2Ph (2c)]. For the stoichiometric oxidation of'PrOH by (la), the Ru-porphyrin product proposed from preliminary work in this laboratory was RuIV(TMP)(OH)2, the underlying reason being mainly the non-detection of axial 'PrO ligand protons by 'H-NMR 120 References on p. 155 Chapter 4 spectroscopy.3 This proposal now seems incorrect. Previously in this laboratory,33 (2a) was prepared following the scheme represented in Eq. 4.1 (not balanced). 1) Ambient temp., Ru^(TMP)(0)2 + xs 'PrOH —^4h Ru^TMPXO'POa + acetone (4.1) 2) rotary evap. (la) (2a) In the earlier work,3" the removal of solvent and excess 'PrOH by rotary evaporation gave a compound, the elemental analysis (C 68.87; H 5.76; N 5.55%) corresponding neither to that calculated for RuIY(TMP)(0'Pr)2 (C 74.45; H 6.65; N 5.60%)3a nor RuIV(TMP)(OH)2 (C 73.42; H 5.94; N 6.12%); however, the non-detection of the axial ligand protons and magnetic susceptibility measurement3 (peff = 2.96 p,B; S = 1) favoured the formulation of (2a) as RuIV(TMP)(OH)2 at the time. In the present thesis work, the preparation of (2a) in an NMR tube from which the solvent and excess 'PrOH were removed completely under vacuum overnight gave a "H-NMR spectrum that showed the chemical shifts for the axial 'PrO ligand protons (Figure 4.2). Heating the sample (> 100 °C) under vacuum to remove the solvent and 'PrOH led to decomposition of the complex, while pumping under vacuum at a lower temperature was not always effective in removing all of the 'PrOH (see also Section 4.3.3). A satisfactory elemental analysis of (2a) still is not obtained, presumably due to the above-mentioned difficulties; however, the fact that the axial ligands were alkoxo, and not hydroxo, was shown unambiguously through the X-ray structural analyses of (2a) and its bis(l,3-dichloro-2-propoxo) analogue (2b). Thus, the earlier incorrect proposals from this group3 and others4 that RuIV(TMP)(OH)2 existed in the presence of excess alcohol were clarified. 121 References on p. 155 Chapter 4 o in a <w so 0) >- , Ol n o on w o vi O <a o o O </-> o o r-~' o oo s a S u <u -a h s WO 122 References on p. 155 Chapter 4 Of note, the TDCPP analogue, RuIV(TDCPP)(OH)2, recently has been characterized crystallographically (see Section 4.3.3). X-ray analyses of (2a) and (2b) revealed structures with inversion centres, with the Ru-atom being essentially octahedral, sitting in the centre of the porphyrin plane with coordinated axial 'PrO or l,3-dichloro-2-propoxo ligands (Figures 4.3 and 4.4). The tetramesityl groups on the porphyrin ring are perpendicular to the porphyrin plane and the Ru(TMP) moiety essentially has the same dimensions as those found in Run(TMP)(MeCN)2.3 There are no significant non-bonding interactions between the axial alkoxo ligand and the porphyrin in either (2a) or (2b) less than 3.6 A (see Appendix D). The crystal structures of (2a) and (2b), even though exhibiting disorder about the axial ligands due to high thermal motion, unambiguously show the complexes to contain axial alkoxo ligands. In terms of the Ru-0 distances, 1.892(3) A in (2a) and 1.905(6) A in (2b), these values lie within the range found for similar Ru(IV)-porphyrin complexes [1.929(9) A within RuIV(TMP)(OEt)2t and 1.944 A within the coordinated /?ara-cresol for [RuIY(TPP)(p-OC6H4Me)]20,10 although the latter is a Ru(IV) diamagnetic species]. On the other hand, the average Ru(III)-0 bond length for the coordinated ethanol/ethoxo in Ruffl(OEP)(OEt)(EtOH) is longer at 2.019 A.11 The marginally longer Ru-0 bond length in (2b) over that in (2a) is presumably due to the inductive electron-withdrawing effect of the two chlorine atoms, which reduces the extent of 7i-backbonding from the oxygen to the ruthenium. Such backbonding is evident in the large Ru-O-C bond angles ' The axial ligand was unidentified due to severe disorder in the axial ligands, but the axial ligand was most likely ethoxo. See Reference 4. 123 References on p. 155 Chapter 4 Figure 4.3. The structure of RuIV(TMP)(0/Pr)2 (2a) (H-atoms omitted for clarity). Selected bond lengths (A) and angles (°): Ru-O(l) 1.892(3), av. Ru-N 2.033, 0(1)-C(29a) 1.18(3), 0(1)-C(29) 1.34(1), C(29)-C(31) 1.55(2), C(29a)-C(31) 1.47(3), C(29)-C(30) 1.56(1), C(29a)-C(30) 1.66(3); Ru-0(1)-C(29) 139.7(5), Ru-0(1)-C(29a) 155(1), 0(1)-C(29)-C(31) 103(1), O(l)-C(29)-C(30) 100(1), O(l)-C(29a)-C(30) 101(1), 0(1)-C(29a)-C(31) 117(2). At the Ru, all c/s-angles are 90 ± 1.2°. Additional crystallographic data can be found in Appendix D. 124 References on p. 155 Chapter 4 Figure 4.4. The structure of RuIY(TMP)(OCH(CH2Cl)2)2 (2b) (H-atoms omitted for clarity). Selected bond lengths (A) and angles (°). Ru-O(l) 1.905(6), Ru-N(av.) 2.036; Ru-0(1)-C(29) 146(1), Ru-0(1)-C(29a) 150(2). Additional crystallographic data can be found in Appendix D. 125 References on p. 155 Chapter 4 of 139.7 and 155° in (2a) and 146 and 151° in (2b), and in both complexes the bond angles deviate significantly from the ideal value of a sp3 hybrid expected at the O-atom of the alkoxo ligand. Unfortunately, the disorder problem precludes any direct comparison between the bond angles of (2a) and (2b), and masks the information pertaining to the difference in degree of backbonding as a result of the two chlorines. The ability of RuVI(TMP)(0)2 (la) to oxidize alcohols was tested with some primary and secondary alcohols, and the spectroscopic evidence suggests that the Ru-porphyrin intermediates are the corresponding bis(alkoxo) species, RuIV(TMP)(OR)2 (see later, Table 4.1). The products of the stoichiometric oxidation of these alcohols are aldehydes or ketones, and the reactions are most likely general for any primary or secondary alcohol, although the methanal and ethanal products from the oxidations of MeOH and EtOH, respectively, are not identified by 'H-NMR spectroscopy, as the characteristic aldehyde ]H-resonances for the two aldehyde products are not observed. The non-detection of the methanal and ethanal products is likely due to polymer formation, which is known to occur with these aldehydes,11 and as the stoichiometrics of the 'PrOH and benzyl alcohol oxidations have been established (see Section 4.3.2), no further attempts were made to detect the methanal and ethanal products. The 'H-NMR chemical shifts of various RuIV(TMP)(OR)2 species are reported in Table 4.1. These RuIV(TMP)(OR)2 species [R = Me, Et, 'Pr, 1-Pr, PhCH2, (CH2C1)2CH, PhCH(Me)] were observed in situ in benzene-afe under 1 atm Ar in ^-NMR studies when the corresponding primary and secondary alcohols were oxidized by (la) to the aldehyde and ketone, respectively. The data for these RuIV(TMP)(OR)2 species are entirely consistent with Ru(IV) species possessing £)4h symmetry, as all known RuIV(TMP)(X)2 126 References on p. 155 Chapter 4 Table 4.1 'H-NMR data" for /ra/75-RuIY(TMP)(OR)2 species. OR* = meta-H0 para-Mt ortho-Med pyrrole-H O'Pr (2a)e 7.52 2.85 2.90 -11.95 1,3-dichloropropoxo (2b) 7.69 not observed^ -28.8 OMe 7.40 2.93 2.70 -21.8 OEt* 7.40 2.85 2.76 -17.6 1-PrO 7.49 2.78 2.93 -16.4 benzoxo (2c) 7.48 2.74 2.92 -20.6 1-phenylethoxo* 7.66, 7.60 2.91,2.83 3.00, 2.96 -19.4 phenoxo'* 7.63 3.00 2.90 -30.5 para-OC6a4OB'k 7.63 3.00 2.90 -30.45 ° Chemical shifts, 5 ppm, in benzene-ak relative to TMS at -25 °C. * These bis(alkoxo) species are typically generated in situ by the addition of corresponding excess alcohol (1.0 x 10"2 M) to (la) (~ 5.0 x 10"4 M) under 1 atm Ar in benzene-^. Excess alcohol is present, which generally leads to exchange broadening and non-observance of axial ligand protons. Extended heating under (~ 100 °C) vacuum can remove all the alcohol, but this leads to decomposition of the complex as well (see text). Axial ligand "H-chernical shifts are reported if observed. c Single meta-H peak indicates a £>4h symmetry about the porphyrin plane. d Single meta-Me peak indicates a £>4h symmetry about the porphyrin plane. e Axial ligand protons observed after removal of excess 'PrOH: -OCH, 2H, -14.22; CH(CH3)2, 12 H, -15.2. f The 'H-chemical shifts for the free alcohol are in the - 3 ppm range and overlap with those for the bis(alkoxo) complex. g Ligand protons observed after removal of excess EtOH: -OCEb, 4H, -7.48; -CH3, 6H, -12.90. * Racemic 1-phenylethanol was used, leading to a mixture of 3 isomers: a 1:1 enantiomeric mixture of Ru(TMP)(OR*)(OR*) and Ru(TMP)(OR5)(ORs) accounts for 50%; Ru(TMP)(ORs)(OR/?) accounts for the other 50%. Two sets of axial ligand *H-chemical shifts, unassigned, are observed (excess alcohol not removed) in the NMR spectra of the solution containing the above set of compounds: -18.9 and -18.4; 7.91 and 8.02; 15.2 and 13.9. ' Generated in situ in benzene-^ under 1 atm Ar from "(2a) + excess phenol" (see text). Axial ligand protons (excess phenol not removed): para-H, 2H, -71.9; ortho-H, 4H, -68.2; meta-H, 4 H, 49.7. j Axial ligand protons: para-OU, 2H, -71.85; ortho-H, 4H, -68.19; meta-H, 4 H, 49.68 (Ref. 3). * The bis(p-hydroquinoxo) complex has been incorrectly assigned as such (Ref. 3) and is in fact the bis(phenoxo) complex (see Section 6.4.1). 127 References on p. 155 Chapter 4 species belonging to the D4h point group exhibit single meta-H and ortho-Me signals.3'4'12 Previously in this laboratory, the ^-chemical shifts for the bis(isopropoxo) and bis(phenoxo) species have been measured between -60 and +60 °C.3a The isotropic 1H-chemical shifts for the TMP ligand within these paramagnetic Ru(IV) species, and also within other paramagnetic RuIV(TMP)(X)2 species4'12 (X = Cl and Br), vary with inverse temperature, showing the existence of a single spin state over this temperature range. The paramagnetic nature of the RuIV(TMP)(OR)2 complexes suggests bonding similar to that found in Ru(porp)(X)2 species (X = Cl, Br), which accommodate two unpaired electrons in a closely spaced t2g set (with either dxy or d^yz being lowest in energy).12 Among the complexes listed in Table 4.1, only the protons of the axial EtO, 'PrO, 1-phenylethoxo, and phenoxo ligands within the RuIV(TMP)(OR)2 species are observed by ^-NMR spectroscopy. In general, the alkoxo ligands exchange readily with the corresponding alcohol in solution, leading to line-broadening in the 'H-NMR spectra and undetectable axial ligand chemical shifts, although the 1-phenylethoxo and phenoxo ligands could be detected even in the presence of the corresponding alcohols. The increased steric bulk of the 1-phenylethoxo ligand perhaps slows the rate of exchange, while for the phenoxo ligands, the slow exchange may be due to steric as well as possible electronic effects of the aromatic ring. The exchangeability of the 'PrO ligands was used to prepare the bis(phenoxo) analogue in situ. Phenol (~ 50-fold excess) was added to an Ar-purged benzene-ofe solution of (2a) (~ 5 x 10"4 M). Within the time required to acquire a ^-NMR spectrum (-15 min), quantitative axial ligand exchange, with the liberation of free 'PrOH, was observed, with no trace of (2a). Of note, the product from the above-128 References on p. 155 Chapter 4 mentioned phenol exchange shows ^-resonances nearly identical to those of a complex previously proposed to be Rurv(TMP)(p-OC6H40H)2 (Table 4.1);3 the significance of this will be discussed in Chapter 6. The exchange of the 'PrO ligands with alcohol in solution was observed readily when (2a) (~ 10"6 M) was dissolved in benzene containing ~10'3 M EtOH or MeOH; almost instantaneous shifts (within seconds) of the Soret band of (2a) from 412 to 408 and 406 nm were observed, respectively, indicating formation of the different RuIV(TMP)(OR)2 species in solution. The UV-visible data for these RuIV(TMP)(OR)2 species in benzene are [Wnm (e/lO^MW1)]: R = 'Pr, 412 (240), 522(29.0); R = Et, 408(230), 520(25.4); R = Me, 406(200), 520(26.7). 4.3.2 Mechanism of Alcohol Oxidation by RuVI(TMP)(0)2 Previous work in this laboratory,3 in addition to the knowledge from the crystallographic structure of the metalloporphyrin product (2a) from the 'PrOH oxidation, allow the overall stoichiometry of the oxidation reaction to be established (Eq. 4.2). One equivalent of acetone and two equivalents of water33 were observed by ^-NMR spectroscopy upon complete formation of (2a). The oxidation of benzyl alcohol presumably follows the same stoichiometry as that for 'PrOH; again, one equivalent of benzaldehyde was observed by 'H-NMR spectroscopy, although no special precautions were taken to remove all the water from the system, and the water stoichiometry was assumed to be the same as in Eq. 4.2. Thus (la) RuVI(TMP)(0)2 + 3 'PrOH (la) RuIV(TMP)(0'Pr)2 + 2 H20 + Me2C=0 (4.2) (2a) 129 References on p. 155 Chapter 4 in reaction 4.2 is an overall two-electron oxidant, similar to other oxoruthenium(VI or IV) complexes.5"9'13'15 The kinetics of PrOH oxidation by (la) under 1 atm Ar showed a first-order dependence in (la) (see Figure 4.1 in Section 4.2.2). The first-order dependence was also assured, as the kinetics monitored for ['PrOH] = 0.218 M were independent of [(la)] (2.0 vs. 4.0 x 10"4 M; see Appendix C). Under pseudo-first-order conditions at about 18 °C, the 'PrOH dependence is first-order at ['PrOH] values below 0.3 M (Figures 4.5). In this linear range, the use of'PrOD-cfe showed that a kinetic isotope effect of 1.9 ± 0.3 is exhibited at the a-C-H bond, while the use of'PrOD gave no kinetic isotope effect. The kobs versus ['PrOH] plot for the oxidation of PrOH by (la) tends to level-off at ['PrOH] values beyond 0.4 M (see later); that is, the oxidation of'PrOH by (la) exhibits saturation kinetics as the concentration of'PrOH increases. The oxidation of benzyl alcohol by (la) is more rapid; the concentration range studied (Figure 4.6) is lower than that for 'PrOH, and there is no obvious fall-off of kobs from a first-order dependence on [benzyl alcohol]. Regarding the non-linear kobs versus ['PrOH] plot (Figure 4.5), the phenomenon is likely due to solvent effects. Addition of an inert alcohol, fBuOH, to simulate the high 'PrOH content, slows the rate of oxidation of'PrOH by (la). At 18.2 °C with [TPrOH] = 0.130 M, the kobs value for the 'PrOH oxidation is (4.2 ± 0.5) x 10"5 s"1. At the same value of ['PrOH], but with [fBuOH] = 0.177 and 0.530 M, kobs = (9.2 ± 0.7) x 10"6 s"1 and (3.6 ± 0.5) x 10"6 s"1, respectively. Hence, it seems very likely that the levelling-off of the kobs values as the 'PrOH content increases is attributed to some solvent effect. 130 References on p. 155 Chapter 4 0.0002 - -0.00018 --0.00016 --0.00014 0.00012 + (s1) 0.0001 + 0.5 1.5 ['PrOH] (Molar) Figure 4.5. Pseudo-first-order rate constant, kobs, as a function of excess 'PrOH concentration in benzene-ok under 1 atm Ar at 18.2 °C. A kinetic isotope effect of kn/ko = 1.9 ± 0.3 was observed at low concentrations of alcohol (< 0.3 M). The kobs values for both 'PrOH and 'PrOD-dg at higher [alcohol] values level-off at about 1.3 x 10" See Appendix C for a list of the raw data. v4 g-l 131 References on p. 155 Chapter 4 0.0025 T [benzyl alcohol] (Molar) Figure 4.6. Pseudo-first-order rate constant, kobs, as a function of [benzyl alcohol] at various temperatures in benzene-^ under 1 atm Ar. The following mechanism [Eqs. 4.3 and 4.4; Ru = Ru(TMP)] for the oxidation of alcohols by (la) is favoured by the experimental evidence, which will be further presented after the introduction of the mechanism. 132 References on p. 155 Chapter 4 hydride transfer 0=/?KVI=0 •P=RuV}—OH (4.3) proton transfer/fast /?uIV(OH)2 alcohol exchange fli#IV(OH)2 + 2 'PrOH Ru^iOPrh + 2H20 (4.4) A hydride transfer pathway seems appropriate (Eq. 4.3) because the addition of KOH/'PrOH and KO'Bu/'PrOH increases the rate of oxidation (see Table 4.2). The electrophilic Ru=0 moiety (Chapter 3) would favour attack of the a-C-H bond of the 'PrO over that of'PrOH. In the presence of base, (la) attacks the a-C-H bond of an alkoxide, followed by stepwise hydride and proton transfers to the oxo ligands to generate Ruw(TMP)(OH)2 (Eqs 4.5, 4.6; B" = OH" or 'BuO"). B + 'PrOH HB + 'PrO" (4.5) 0=Ruvl =0 ^ H hydride transfer i)=RuVL—OH (4.6) HB proton transfer /toIV(OH)2 + B" 133 References on p. 155 Chapter 4 Table 4.2. Selected pseudo-first-order rate constants, koDS for the stoichiometric oxidation of 'PrOH to acetone by RuVI(TMP)(0)2 (la). ['PrOH]a(M) KOH/PrOH* KO'Bu/'PrOH pseudo-lst-order rate constant, kobs (s1) 0.0568c - (1.87 ± 0.1) x 10"5 0.131c - (4.21 +0.5) x 10"5 0.0408 4x 106MKOH (0.9 ± 0.2) x 10"4 0.0408 2x 105MKOH (1.2 ± 0.2) x 10"4 0.0816 4x 10"6MKOH (1.1 ±0.2)x 10"4 0.130 1.2 x 10-4MKO'Bu (5.4 ± 0.8) x 10"4 0.130 1.6 x 10"3MKO'Bu (5.6 ± 0.8) x 10"3 * [RuVI(TMP)(0)2] = 10-4 to 103 M in benzene-dfe at 18.2 °C under 1 atm Ar. * Various solutions of'PrOH with dissolved KOH or KOfBu were prepared and injected into the benzene-afe solutions, and the [base] values refer to those in the diluted solutions. The approximately constant rate of oxidation, apparently independent of the concentrations of KOH and 'PrOH, is likely due to the insolubility of KOH in benzene such that a saturation concentration has been reached. Hence, a maximum increase of rate is reached. c See Figure 4.5 for the kobs versus ['PrOH] plot and Appendix C for the raw data. That KOH or KO'Bu accelerated the rate of oxidation suggests bond cleavage by the Ru=0 moiety at the a-C-H bond (Eq. 4.5). At lower ['PrOH] values where the k^s versus ['PrOH] plots are linear, the kn/kn ratio is approximately 1.9. The oxidation of 'PrOH by (la), based on the observed kinetic isotope effect, also seems reasonably consistent with the cleavage of the alcohol a-C-H bond by a Ru=0 moiety as the initial oxidation step (Eq. 4.3), although the isotope effect of 1.9 is clearly very small, especially considering that a kH/kD value is expected to be -6.9, if VC-H and VC-D zero point energies are the only factors under consideration. In non-porphyrin systems, the oxidations of alcohols by oxoruthenium(IV)7a'9'13 and ^*a«5-dioxoruthenium(VI)15b complexes have been observed to give kinetic isotope effects larger than the theoretical value of 6.9, including 134 References on p. 155 Chapter 4 kH/kD values as high as 50 and 18 for the oxidations of benzyl alcohol and 'PrOH, respectively.73 The data for the 'PrOH oxidation at 18.2 °C (Figure 4.5) show that the kobs versus [alcohol] plots for 'PrOH and 'PrOD-dg both level-off at approximately the same value of kobs ~ 1.3 x 10'4 s"1, which means that the under such conditions, the kH/kD ratio is approximately 1.0. The levelling-off of the kobs values has been shown to be an artifact resulting from a solvent effect at the high 'PrOH concentration (see earlier). It is not known why the oxidation of'PrOH by (la) exhibits such a small kinetic isotope effect if a-C-H bond cleavage is involved, or why the kH/kD values becomes ~ 1.0 at higher 'PrOH concentrations. One interpretation of the findings is that significant solvent effects (perhaps due to the alcohol content itself), in addition to direct a-C-H bond cleavage by the Ru=0 moiety, may be involved in the oxidation reaction. An alternative explanation for the levelling-off of the kobs values (saturation kinetics) is the operation of a preassociation step, forming a {Ru-alcohol} adduct prior to the actual oxidation step, which has been invoked in alcohol oxidations by non-porphyrin oxoruthenium(IV) species.73 Roecker and Meyer studied the stoichiometric oxidation of some alcohols using RuIV(bpy)2(py)(0)2+ as the oxidant in MeCN solutions, and they observed non-linear kobs versus [benzyl alcohol] plots which were attributed to a preassociation step;73 however, a linear plot was observed once the solution ionic strength in MeCN was rendered constant by the addition of 0.10 M TEAP or when the reaction took place in H20. Neither the RuVI(TMP)(0)2 nor RuIV(byp)2(py)(0)2+ 73 system shows any spectroscopic evidence for the formation of a preassociation complex in the respective oxidation reactions. Hence, the observed levelling-off of the k^s values, at least in the 135 References on p. 155 Chapter 4 RuVI(TMP)(0)2 system, is considered due mainly to a solvent effect caused by high 'PrOH concentrations used. As for the formation of the bis(alkoxo) product (2a), a likely path is via a metathesis reaction of'PrOH with RuIV(TMP)(OH)2 (Eq. 4.4). There is no evidence for the existence of RuIY(TMP)(OH)2, nor is there any direct proof regarding the rapid exchange of the hydroxo ligands with the alcohol in solution to form (2a), although rapid alcohol exchange with the axial alkoxo ligands within the Rurv(TMP)(OR)2 species has been observed (Section 4.3.1); it is feasible that the formation of RuIV(TMP)(OH)2 is disfavoured over that of (2a) in the presence of excess 'PrOH. There is indirect support that RuIV(TMP)(OH)2 exists in solution, as the bis(hydroxo) analogue of TDCPP, RuIV(TDCPP)(OH)2, has been characterized crystallographically recently;14 of interest the complex was isolated from a toluene filtrate solution (that had been left standing at -25 °C) obtained during the preparation of Ruvl(TDCPP)(0)2. The stoichiometric oxidations of alcohols by some non-porphyrin *ra«s-dioxomthenium(VI) species have been shown, based on UV-visible data, to form oxo(aquo)ruthenium(IV) species.15b These Ru(IV) species also have been suggested to isomerize to the bis(hydroxo)-Ru(IV) species via proton migration.15 Of note, ^-resonances assignable to RuIV(TMP)(0) were detected in the 02-oxidation ofp-hydroquinone to p-benzoquinone catalyzed by (la) (Section 6.4.1). As for the present RuVI(TMP)(0)2/'PrOH system, ^-resonances corresponding to RuIV(TMP)(0) or RuIV(TMP)(0)(OH2) were not detected; the only observable 1U-resonances in the 'PrOH system corresponding to Ru(TMP) species are those assignable to (la) and (2a). Although RuIV(TMP)(0) has not been detected in the 'PrOH system (but 136 References on p. 155 Chapter 4 as RuIV(TMP)(0) has been detected in the /?-hydroquinone system), it can still be envisaged that the initial hydride transfer (Eq. 4.3) yields RuIV(TMP)(0), while the RuIY(TMP)(OH)2 could form subsequently via reaction of RuIV(TMP)(0) and H20 similar to that proposed in the Ru(IV) non-porphyrin systems15 (see also Section 4.4.3 regarding the role of H20 in a RuVI(TMP)(0)2/alkene oxidation system). The slopes of the lines in Figures 4.5 and 4.6 give the second-order rate constants, k2, for the stoichiometric oxidation of'PrOH and benzyl alcohol by (la) (Table 4.3). The Eyring plots derived for these k2 values, Figures 4.7 and 4.8, give the following activation parameters: AH2* = 45 ± 7 and 65 ± 11 kJ mol"1, and AS2* = -167 ± 10 and -70 ± 20 J mof'K"1 for 'PrOH and benzyl alcohol, respectively, a marked difference being noted. The rates of alcohol oxidations in the Ruvl(TMP)(0)2 system are limited by large and negative AS2* values, and that benzyl alcohol is oxidized approximately 10 times faster than 'PrOH is due entirely to a more favourable AS2*; indeed, the relative AH2* values favour oxidation of 'PrOH. In comparison, the activation parameters for the oxidation of 'PrOH and benzyl alcohol by RuIV(bpy)2(py)(0)2+ in MeCN are AH* = +33.5 and +24.2 kJ mol"1, and AS* = -176 and -160 J mol"1 K"1, respectively;73 although the AS* values are large and negative, as in the RuVI(TMP)(0)2 systems, the AH* term is the major factor affecting the differences in the rate constants. An alternative mechanism for the stoichiometric 'PrOH oxidation by (la) involves oxidative addition of the alcohol a-C-H bond across the Ru=0 moiety of (la), leading to an organoruthenium intermediate (as proposed for a Ru0327alcohol system),8 although the lack of cis sites at the Ru makes this unlikely. The Ru=0 moiety of (la) could perhaps 137 References onp, 155 Chapter 4 abstract a hydrogen atom from the a-C-H bond to form Ruv(TMP)(0)(OH) and an in-cage organic radical Me2C"-OH; a single-electron transfer from Me2C*-OH to Ruv(TMP)(0)(OH), followed by loss of H" from Me2C=OH+, will give the same products as those shown in Eq. 4.3. This hydrogen abstraction path is disfavoured somewhat as no ESR signals due to either an organic radical and/or a Ru(V) paramagnetic species were observed at 110 K in a frozen benzene solution of (la) and 'PrOH; however, as the organic radical and Ru(V) species might be unable to escape from each other in a solvent cage in the frozen environment, an electron transfer from the radical to the Ru(V) species may have occurred prior to the attempted detection of the radicals by ESR spectroscopy, and thus the hydrogen abstraction mechanism cannot be ruled out completely. Table 4.3. Second-order rate constants, k2, for the stoichiometric oxidations of'PrOH and benzyl alcohol in benzene-de by RuVI(TMP)(0)2 (la). Temperature (Kelvin) [for benzyl alcohol] PrOH k2 (M1 s"1)" benzyl alcohol 291.4 3.8 x 10"4 2.6 x 10"3 [291.2] 301.7 7.4 x 10"46 7.6 x 10"3 [302.7] 308.7 1.05 x lO-3* 1.4 x 10"2 T307.7] ° The kinetics were monitored by ^-NMR spectroscopy in benzene-afe under 1 atm Ar. b These k2 values were derived from a single kobs value determined at ['PrOH] = 0.161 and 0.174 M at 301.7 and 308.7 K, respectively. These [PrOH] values are well within the linear region of the kobs versus [alcohol] plots (Figures 4.5 and 4.6), and hence are deemed reliable in the calculation of k2. 138 References on p. 155 Chapter 4 Figure 4.7. Eyring plots for the stoichiometric oxidation of'PrOH by RuVI(TMP)(0)2 under 1 atm Ar in benzene-^. 139 References on p. 155 Chapter 4 Figure 4.8. Eyring plots for the stoichiometric oxidation of benzyl alcohol by Ruvl(TMP)(0)2 under 1 atm Ar in benzene-ok. 140 References on p. 155 Chapter 4 4.3.3 Aerobic Oxidations of Alcohols to Aldehydes and Ketones The implication for (la) to function catalytically in the aerobic oxidation of alcohols was noticed in 'H-NMR experiments where excess 'PrOH was added to a vacuum-degassed sample of (la) [generated in situ in benzene-ak from the aerobic oxidation Run(TMP)(MeCN)2 (3)]. Complete conversion of (la) to (2a) and the formation of one equivalent of acetone after about 24 h under vacuum, in accordance with Eq. 4.2, were observed by 'H-NMR spectroscopy. After an additional 48 h, the same sample was analyzed again by 'H-NMR spectroscopy, and 'H-resonances characteristic of species (3) (-10%) were detected (j0-pyrrole-H, 8.65; o-Me, 2.21; p-Me, 2.54; MeCN. -1.32 ppm). At the end of 2 weeks, when no further noticeable changes were observed in the 'H-NMR spectrum of the sample, greater than 90% of (2a) was converted to (3). Also, almost two, instead of the original one, equivalents of acetone were detected. This regeneration of (3), coupled with the fact that (3) under air or 02 can reform (la) (Chapter 2), suggests that the 02-oxidation of alcohols can be catalyzed by (la). The mechanism for the aerobic oxidation of alcohols catalyzed by (la) is proposed to follow the pathways represented in Eqs. 4.7 to 4.11 [Ru = Ru(TMP)], and the evidence suggesting the operation of these pathways will be presented below. Rua(MeCN)2 (3) 1/2 O Rul\0) + 2 MeCN (4) (4.7) 2 MeCN *. ««n(MeCN)2 + /?«VI(0)2 (3) (la) (4.8) 2 Rul\0) (4) Jto^Ofc + 3 'PrOH (la) Ruw(0^r)2 + Me2C=0 + 2 H20 (4.9) (2a) 141 References on p. 155 Chapter 4 RtT'(0'Pr)2 + 2H20 (2a) ^(0^2 + 2'PrOH (4.10) /fc*IV(OH)2 Rul\0) + H20 (4) (4.11) The formation of Run(TMP)(MeCN)2 (3), as well as the production of an additional equivalent of acetone in vacuum, observed in the previously mentioned !H-NMR experiment, can be accommodated by the proposed catalytic mechanism (Eqs. 4.7 to 4.11). In the absence of 02, Eq. 4.7 is removed from the scheme for the catalytic oxidation, and the 1/2 equivalent of Run(TMP) formed from the disproportionation of 1 equivalent of (4) can no longer regenerate (la). Thus only 1/2 equivalent of (la) oxidizes the excess 'PrOH, and in the next cycle the 1/2 equivalent of (4) disproportionates to reform only 1/4 equivalent of (la), and so forth. All the cycles added together as an infinite sum* would yield exactly one additional equivalent of acetone and one equivalent of Run(TMP) [which is coordinated readily by MeCN to form (3)]; the net, overall reaction is given in Eq. 4.12, Ru = Ru(TMP). Evidence for reaction 4.10 can be inferred from the following experiment, where an isolated sample of (2a) dissolved in benzene-afe and exposed to air regenerated (la), with acetone forming concurrently, as monitored by 'H-NMR spectroscopy. Moisture was crucial in the regeneration of (la), as (2a) dissolved in benzene-afe containing dry 02 gave no reaction. During the regeneration of (la), no free 'PrOH was observed at any f 2 + (2)2 + (2)3+ •=2(—T)= !> Reference 27-Jto^Ofc + 2 'PrOH + 2MeCN /?«n(MeCN)2 +2Me2C=0 + 2H20 (4.12) 142 References on p. 155 Chapter 4 time [-30 min for complete regeneration of (la)]. Of note, the complete removal of 'PrOH from (2a) was a problem (mentioned earlier in Section 4.3.1), and as high as 10 equivalents of acetone have been observed on one occasion when a sample of (2a) was exposed to air. Typically less 'PrOH is present, although usually more (3 to 6 equivalents) than the expected two equivalents of acetone are formed. The slightly excess 'PrOH was not observed in the 'H-NMR spectrum, presumably due to the rapid exchange of the axial alkoxo ligands with the alcohol (Section 4.3.1). Because water is crucial in the regeneration of the active catalyst (la) from (2a), H20 is proposed to exchange with the axial alkoxo ligands of (2a) to form RuIV(TMP)(OH)2, followed by conversion to RuIV(TMP)(0) (4) (Eqs. 4.10 and 4.11, respectively). Species (4) then disproportionates (cf. Eq. 4.8) to (la) and Run(TMP). The pathways shown in Eqs. 4.7 and 4.8, although not fully established, generally represent the accepted mechanism16 for generating (la) from the aerobic oxidation of Run(TMP)(L)2 species (L = THF,17 MeCN,18 N2 or vacant19), with the disproportionation of (4) to (la) and Run(TMP) (cf. Eq. 4.8) occurring via attack of the Ru=0 moiety on the vacant site of another molecule of (4).20 In addition, (4) is also the supposed intermediate in the catalytic epoxidation of alkenes by (la).17'20'21 Of note, a recent study showed that the addition of water promoted the catalytic 02-oxidation of alkenes by (la).21 No explanation was offered by the authors; however, noting the above observations in the present 'PrOH system, two possible proposals may explain the H20 effect. The rate-determining step in the epoxidation of alkenes catalyzed by (la) appears to be the dissociation of the epoxide product from 143 References on p. 155 Chapter 4 Ru (TMP)(0)(epoxide) (Figure 4.9), as the catalysis is independent of alkene concentration and O2 partial pressures.17 Hence, water could displace the epoxide from the Ru-centre and speed up the disproportionation of (4) to (la) and Run(TMP). The lack of a trans or cis site leaves a seven-coordinate associative mechanism as the only possibility for a water-assisted dissociation of epoxide, but considering the steric constraints presented by the TMP mesityl groups, an associative mechanism is unlikely. Another potential role of water might be its participation in the disproportionation reaction shown in Eq. 4.12 [Ru = Ru(TMP)]. Such reactions (and their reverse reactions) are suggested to be proton-coupled, electron transfer processes (the FT coming from H20) in the non-porphyrin oxoruthenium(III, IV, V, VI) systems,71''15 based on electrochemical studies. If H20 can speed up the disproportionation of (4), the rates of epoxidation will also be increased. The results for the aerobic oxidation of'PrOH and benzyl alcohol catalyzed by (la) and (lb) are tabulated in Table 4.4. Complex (la) is a far more effective catalyst than (lb) for the oxidation of benzyl alcohol. This was initially surprising as (lb) is generally more reactive than (la) due to the presence of the electron-withdrawing Cl-groups on the TDCPP ligand.3 That (lb) is less reactive than (la) is due to the former being more susceptible to deactivation during the catalysis, to form the inactive Run(TDCPP)(CO) species, as evidenced by the appearance of UV-visible and IR absorption bands characteristic of the carbonyl complex (Chapter 2). Species (la) is also deactivated, as /?«1V(0) + /?i#lv(0)(OH2) (4) Ru\OU2) + ^(0)2 (la) (4.13) 144 References on p. 155 Chapter 4 well as decomposed, but more slowly (see later); the formation of Run(TMP)(CO) is a problem not only in alcohol oxidations, but also in epoxidations of alkenes.17'21 Ruthenium(II) is known to have a strong affinity for CO and other rc-acid ligands (e.g. S-bound is favoured over O-bound sulfoxides),3'22'23 where rc-backbonding stabilizes the Ru(II) centre. Decarbonylation of carbonyl-containing organic compounds by Ru-porphyrins is not without precedent; for example, earlier work from this laboratory showed Ru(TPP)(phosphine)2 species to be competent catalysts in the thermal decarbonylation of aldehydes.23 X — RUII— / ^- 1/2 02 Figure 4.9. Mechanism of alkene epoxidation catalyzed by RuVI(TMP)(0)2. The dissociation of the epoxide from the Ru(IV) centre is interpreted as being the rate-determining step, as the rate of catalysis is the insensitive to the alkene concentration and O2 partial pressure (Ref. 17). 145 References on p. 155 Chapter 4 The data in Table 4.4 show that (la) is a far more effective catalyst for oxidizing benzyl alcohol than 'PrOH. The aerobic oxidation of 1-phenylethanol to acetophenone catalyzed by (la) and (lb) also was studied briefly, and as with 'PrOH, only a few total turnovers were achieved at room temperature (~ 20 °C); carbonylation of the catalyst to Run(porp)(CO) (porp = TMP and TDCPP) within 24 h was the main deactivation pathway, as evidenced by ^-NMR and UV-visible spectroscopies. Benzyl alcohol is an order of magnitude more reactive than 'PrOH and, under the optimum conditions, a total turnover of 2000 was achieved in a period of 13 d. The presence of water which created a two-phase system enhanced the rates of catalysis, and the addition of 3.0 M aqueous KOH increased, at least for benzyl alcohol, the turnovers even further (Figure 4.10). Of note, the turnover numbers were independent on the O2 partial pressure (1 atm air versus 1 atm 02; see Table 4.4). Figure 4.10 shows the turnovers in the initial 24 h as a function of [benzyl alcohol], while Figure 4.11 shows the progress of the aerobic oxidation of benzyl alcohol catalyzed by (la) as a function of time. The daily turnovers in Figure 4.10 show that an upper limit in the effectiveness of the catalyst (in terms of turnover numbers) is reached beyond certain [benzyl alcohol] values (> 0.2 M); therefore, it is plausible that the rate-limiting step in the catalysis, when [benzyl alcohol] values are below 0.2 M, is the alcohol oxidation step (Eq. 4.9). As the [benzyl alcohol] values increase, the turnovers per day versus [benzyl alcohol] plots level-off, and one of the processes (Eqs. 4.7, 4.8, 4.10 or 4.11) involving the regeneration of (la) may become the rate-limiting step in the catalytic cycle. The generation of (la) from Ru(II)-porphyrin species,16 when exposed to air or 02, 146 References on p. 155 Chapter 4 is known to occur rapidly (usually within minutes, see also Chapter 3); therefore, the rate-limiting step is likely reaction 4.10 or 4.11. Figure 4.11 shows that the activity of the system slowly degrades over time and, as mentioned earlier, the catalyst becomes carbonylated to Run(TMP)(CO) at 24 °C; the aldehyde or ketone product is presumably decarbonylated, but this was not checked experimentally. At 50 °C, the Ru(TMP)(OR)2 species in the 'PrOH and benzyl alcohol systems also decompose, as evidenced by the disappearance of the 'H-resonances in the NMR spectrum characteristic of the TMP ligand; the relative contributions from carbonylation of versus destruction of Ru(TMP) species are not known, although at 24 °C deactivation to Run(TMP)(CO), as evidenced by 'H-NMR spectroscopy, was the primary deactivation pathway. It is not obvious from the data or graphs, but an important point is that the presence of aqueous KOH extended the catalytic activity of (la) to over 10 d and, although the addition of H20 increased the turnover numbers, the catalyst did not survive for more than 4 d in typical experiments. A finding relevant to this is that substantial decomposition of (la) occurs in a benzene solution under 1 atm air overnight,* with the instability thought to be due to the presence of trace acid impurities.3 In direct support of this postulation, addition of-25 pL 3.0 M aqueous KOH to -5 x 10"6 M benzene solution of (la), again in air, led to the preservation of the 422 nm Soret band of (la) overnight, while solutions of (la) without added base lost this characteristic Soret band (a new band appears at 414 nm). x At room temperature under 1 atm air, a substantial portion of (la) (~ 10"6 M) decomposes in the benzene solution overnight. Under the same conditions (lb) converts to Run(TDCPP)(CO) in solution, as well as in the solid state, via an unknown process (see Chapter 5). 147 References on p. 155 Chapter 4 Table 4.4. Catalytic activity of Ru"(porp)(0)2 [porp = TMP (la) and TDCPP (lb) towards Q2-oxidation of 'PrOH and benzyl alcohol under mild conditions in benzene. [(la)or(lb)]fl [alcohol] turnovers total turnovers; 3.0 M KOH(aq), (M) (M) within 1st % conversion H20, or NONE1 24 h* [time]c (la) 20 °C PrOH 4.0x10^ 0.033 1.5 ±0.1 - NONE 50 °C 7.0 xlO'6 0.242 6.0 ±0.5 - NONE 2.0 x 10"4* 0.0325 10.6 ± 1 - H20 2.0 x IO"4' 0.0325 6.3 ±0.5 - D20 20 °C PhCH2OH 2.0 x IO"46 0.0242 30 ±2.5 - NONE 0.0484 . 40 ±3 - NONE 0.121 50 ±4 - NONE 50 °C 1.5xl0^e/ 0.0242 24 ±2 - NONE 1.5 xlO"4* 0.0242 28 ±2 - NONE 1.5 xlO"4' 0.0483 42 ±3 - NONE 2.35 x IO"46 0.121 50 ±4 122; 77% (67.5 h) NONE 8.33 x 10"5 0.00083 5.5 ±0.4 - H20 8.33 x 10"5 0.00167 14 + 1 - H20 8.33 x IO"5 0.0321 28 ±5 - H20 2.1 x IO"4 0.0321 34 ±3 - H20 2.0 x IO"4 0.121 77 ±6 - H20 8.33 x IO"5 0.138 72 ±6 - H20 2.0 xlO"4 0.362 137 ±9 - H20 7.5 x 10"5 0.362 101 ±8 - H20 7.5 x IO"5 0.725 113 + 9 - H20 2.63 x 10"5 0.121 111 ±9 440; 9.5% (259 h) KOH 2.63 x IO"5 0.241 274 ± 22 950; 10% (234 h) KOH 2.63 x IO"5 0.483 297 ± 25 1860; 10%(334h) KOH 2.63 x 10"5 0.876 272 ± 22 2000; 5.3% (308h) KOH (lb) 50 °C PhCH2OH 9.0 x IO"5 0.121 10 + 1 complete loss of H20 9.0 x 10"5 0.242 18 + 1.5 catalytic activity H20 2.19 x IO"4 0.0966 15 + 1.2 after about KOH 2.19 x 10^ 0.387 20 + 1.6 2d KOH " In benzene, under 1 atm air, followed by GC analysis, unless otherwise indicated. 6 Turnovers are typically obtained during a period between 18 to 25 h and are normalized to 24 h. c At 50 °C, (la) decomposes gradually and the systems loses its catalytic activity. d Benzene directly out of the bottle contains H20 at a concentration of the order of 10"3 M, and "JVeWZT' means that no further H20 has been added. Addition of H20 (or KOHaq) to benzene creates a 2-phase system, with the benzene phase containing H20 at ~10"2 M (Section 4.2.1). e Followed by 'H-NMR spectroscopy in benzene-d6- / Under 1 atm 02. 148 References on p. 155 Chapter 4 350 T [benzyl alcohol] (Molar) Figure 4.10. Daily turnovers versus [benzyl alcohol] for the aerobic oxidation of benzyl alcohol catalyzed by RuVI(TMP)(0)2 (la) at 50 °C. [(la)] ~ 10"4 M in benzene (see also Table 4.4). 149 References on p. 155 Chapter 4 2000 j 1800 + 1600 + 1400 + 1200 + Total TwnoverslOOO f 0.8791VL* 0.483M ^.^--m 0.242M 0.121M 50 100 150 200 250 Time (hours) 300 350 ure 4.11. Total turnovers versus time for the aerobic oxidation of benzyl alcohol (concentrations indicated) catalyzed by Ru^TMPXO^ (la) at 50 °C. [(la)] = 2.63 x 10"5 M in benzene (see also Table 4.4). 150 References on p. 155 Chapter 4 Of note, a recent report on the use of the same catalysts, namely RuVI(porp)(0)2 species (porp = TMP and TDCPP), using pyridine-iV-oxides as oxidants, demonstrated efficient catalytic activity for the oxidation of alcohols, with total turnovers for the conversion of benzyl alcohol to benzaldehyde being -140 (80 % yield).24 The oxidation of adamantane in the same RuVI(TMP)(0)2/pyridine-Ar-oxide system was more impressive; up to 14000 total turnovers were realized. Active species other than RuVI(porp)(0)2 must account for such high activities, as the studies described in Section 4.4 show that the dioxo species are only barely able to oxidize the more active alkanes adamantane and Ph3CH. Acids such as HC1 and HBr were present in the pyridine-N-oxide system, and were essential for the enhanced reactivity, and RuVI(TMP)(0)(X)+ species (X = Cl, Br) have been suggested to be the active oxidant;23 the coordination of the pyridine-Ar-oxide to the ruthenium centre may play a role in the system's high catalytic reactivity. In addition, a Ru-porphyrin catalyzed decomposition of pyridine-TV-oxide to generate perhaps an O-atom, and thus initiate a possible radical-chain reaction, might lead to such high activities. 4.4 Aerobic Oxidation of Tertiary Alkanes Catalyzed by RuVI(porp)(0)2 Species At 24 °C under 1 atm air in benzene, (la) catalyzes the aerobic oxidation of Ph3CH to Ph3COH, while (lb), but not (la), can also catalyze the aerobic oxidation of adamantane to 1-adamantanol; however, the reactions are sluggish (< 1 turnover per day). As the dioxoruthenium(VI) species are subject to degradation, particularly (la), kinetic studies were deemed to be impractical, and no kinetics studies were undertaken on 151 References on p. 155 Chapter 4 these alkane systems. In 'H-NMR studies in benzene-^6, 'H-resonances corresponding to (la) (~10"3 M) can still be detected after 24 h (i.e. not all of (la) at this higher concentration has decomposed after this time, see end of Section 4.3.3); 'H-resonances corresponding to RuIV(TMP)(0) (see Section 3.4.2) also can be observed [~ 5 % of the total Ru]. The progress of the catalyses is shown in Figure 4.12. The presence of electron-withdrawing Cl-groups makes (lb) more reactive, and almost four times the turnovers are achieved for the Ph3CH oxidation catalyzed by (lb) over that by (la). The addition of 2,6-ditertbutyl-4-methylphenol (BHT, 0.01 M)f to the RuYI(TMP)(0)2/Ph3CH system does not inhibit the oxidation, and thus the oxidation most likely is due to direct attack of the tertiary C-H bond by the Ru=0 moiety. The mechanism of oxidation is proposed to occur via Eq. 4.14 [Ru = Ru(TMP) or Ru(TDCPP)]; whether the reaction in Eq. 4.14 proceeds via an 0=Ruvl=0 + R-H ^ 0=/?M(OH)'R* ^ 0=Ruw + R-OH (4.14) H-atom abstraction followed by electron transfer is unknown. For example, oxidation of alkanes by Fe(TMP)(Cl)(0) species has been proposed occur via a hydride transfer pathway,25 while oxidations by non-porphyrin oxoruthenium species have been proposed to undergo a homolytic H-atom abstraction pathway.6b For the RuVI(TMP)(0)2 system, a homolytic cleavage of the tertiary C-H bond by a Ru=0 moiety to initiate the alkane oxidation reaction, with the *OH being transferred to the R* fragment within a solvent cage, is consistent with the results in Chapter 5, where the catalytic oxidation of hydrocarbons occurs via radical-chain pathways, possibly initiated by a homolytic C-H 1 The addition of BHT (~ 0.01 M) to RuVI(TMP)(0)2 (~ 10"6 M) in benzene, under 1 atm air, gave no reaction, as evidenced by UV-visible spectroscopy. 152 References on p. 155 Chapter 4 16 X 0 10 20 30 40 50 Time (days) 3.5 T Time (days) Figure 4.12. Total turnovers versus time for the aerobic oxidations of a) Ph3CH and b) adamantane catalyzed by RuVI(porp)(0)2 [porp = TMP (la) and TDCPP (lb)] at 24 ± 2 °C in benzene. a) TMP: [(la)] = 1.2 x IO"4 M; [Ph3CH] = 2.89 x 10"3 M TDCPP: [(lb)]-2.4 x 10"4M; [Ph3CH] = 4.64 x IO"3 M b) [(lb)] = 2.4 x IO-4 M; [adamantane] = 6.28 x 10° M. 153 References on p. 155 Chapter 4 bond cleavage by Ru=0 moieties. Eq. 4.14 corresponds to the oxygen-rebound mechanism26 proposed for the ubiquitous cytochrome P-450 enzyme, where the *OH group is transferred to the R* fragment before the substrate leaves the protein cavity. 4.5 Conclusion The description and plausible mechanism of an efficient catalytic aerobic system based on /raw5-dioxoporphyrinatoruthenium(VI) species, capable of oxidizing benzyl alcohol, 'PrOH and 1-phenylethanol to the corresponding aldehydes and ketones, have been presented. The initiation of the oxidation via a hydride transfer from the alcohol a-C-H bond was proposed. At 50 °C under 1 atm air, benzyl alcohol was oxidized selectively to benzaldehyde with daily turnovers up to 300 d"1, and total turnovers reaching 2000 in 13 d. This is among the most efficient of Ru-based catalyst systems for the aerobic oxidation of alcohols.1 The RuVI(porp)(0)2 species (porp = TMP and TDCPP) can also catalyze the aerobic oxidations, although slowly, of Ph3CH to Ph3COH and adamantane to 1-adamantanol under 1 atm air at 24 °C. 154 References on p. 155 Chapter 4 References 1 W. P. Griffith, Chem. Soc. Rev., 21, 179 (1992). 2 a) S. Y. S. Cheng, N. Rajapakse, S. J. Rettig and B. R. James, J. Chem. Soc, Chem. Commun., 2669 (1994). b) S. Y. S. Cheng and B. R. James, Proc. of the 78th Can. Chem. Conf, Guelph, Canada, 1995, Abstract IN-447. 3 a) N. Rajapakse, Ph. D. Dissertation, University of British Columbia, 1990. b) N. Rajapakse, B. R. James and D. Dolphin, Stud. Surf. Sci. Catal, 55, 105 (1990) . 4 W.-H. Leung, C.-M. Che, C.-H. Yeung and C.-K. Poon, Polyhedron, 12, 2331 (1993). 5 a) C.-M. Che and W. H. Leung, J. Chem. Soc. Dalton Trans., 2932 (1991). b) W. H. Leung and C.-M. Che, J. Am. Chem. Soc, 111, 8812 (1989). 6 a) C.-M. Che, C. Ho and T.-C. Lau, J. Chem. Soc. Dalton Trans., 1259 (1991). b) M. S. Thompson and T. J. Meyer, J. Am. Chem. Soc, 104, 5070( 1982). 7 a) L. Roecker and T. J. Meyer, J. Am. Chem. Soc, 109, 746 (1987). b) M. S. Thompson and T. J. Meyer, J. Am. Chem. Soc, 104, 4106 (1982). 8 D. G. Lee and L. N. Congson, Can. J. Chem., 68, 1774 (1990). 9 C.-M. Che, W.-T. Tang, W.-O. Lee, K.-Y. Wong and T.-C. Lau, J. Chem. Soc Dalton Trans., 1551 (1992). 10 J. P. Collman, C. E. Barnes, P. J. Brothers, T. J. Collins, T. Ozawa, J. C. Galluci and J. A. Ibers, J. Am. Chem. Soc, 106, 5151 (1984). 11 R. J. Fessenden and J. S. Fessenden, Organic Chemistry, 3rd Edition, Brookes/Cole, Monterey, 1986, p: 523-524. 12 a) C. Sishta, M. Ke, B. R. James and D. Dolphin, J. Chem. Soc, Chem. Commun., 787 (1987). b) M. Ke, C. Sishta, B. R. James and D. Dolphin, Inorg. Chem., 30, 4776 (1991) . c) C. S. Alexander, Ph. D. Dissertation, University of British Columbia, 1995. 13 J. G. Muller, J. H. Acquaye and K. J. Takeuchi, Inorg. Chem., 31, 4552 (1992). 155 References on p. 155 Chapter 4 14 P. Dubourdeaux, M.Taveres, A. Grand, R. Ramasseul and J.-C. Marchon, Inorg. Chim. Acta., 240, 657 (1995). 15 a) C.-M. Che, W.-T. Tang, W.-T. Wong and T.-F. Lai, J. Am. Chem. Soc, 111, 9048 (1989). b) C.-K. Li, C.-M. Che, W.-F. Tong and T.-F. Lai, J. Chem. Soc. Dalton Trans., 813 (1992). 16 T. Mlodnicka and B. R. James, in Metalloporphyrins Catalyzed Oxidations, eds. F. Montanari and L. Casella, Kluwer Academic Publishers, Dordrecht, 1994, p. 121. 17 J. T. Groves and R. Quinn, J. Am. Chem. Soc, 107, 5790 (1985). 18 J. T. Groves and K.-H. Ahn, Inorg. Chem., 26, 3833 (1987). 19 M. J. Camezind, B. R. James and D. Dolphin, J. Chem. Soc, Chem. Commun., 1137(1986). 20 J. T. Groves and J. S. Roman, J. Am. Chem. Soc, 111, 5594 (1995). 21 B. Scharbert, E. Zeisberger and E. Paulus, J. Organometdllic Chem., 493, 143 (1995). 22 a) D. T. T. Yapp, J. Jaswal, S. J. Rettig, B. R. James and K. A. Skov, Inorg. Chim. Acta., Ill, 199 (1990). b) D. T. T. Yapp, J. Jaswal, S. J. Rettig, B. R. James and K. A. Skov, J. Chem. Soc, Chem. Commun., 1528 (1992). 23 G. Domazetis, B. Tarpey, D. Dolphin and B. R. James, J. Chem. Soc, Chem. Commun., 939 (1980). 24 a) H. Ohtake, T. Higuchi and M. Hirobe, Heterocycles, 40, 867 (1995). b) H. Ohtake, T. Higuchi and M. Hirobe, J. Am. Chem. Soc, 114, 10660 (1992). 25 J. T. Groves and T. E. Nemo, J. Am. Chem. Soc, 105, 6243 (1983). 26 J. T. Groves, J. Chem. Ed, 62, 928 (1985). 27 J. F. Hurley, Intermediate Calculus, Saunders College, Philadelphia, 1980, p. 682. 156 References on p. 155 Chapter 5 Chapter 5 Reactivities of Ru(TDCPP-CI8) Species 157 References on p. 187 Chapter 5 5.1 Introduction The development of metalloporphyrins as catalysts in 02-oxidations of organic compounds, a particular aim being the oxidation of light alkanes, entered a new stage with the introduction of the so-called third-generation porphyrins (See Section 1.4.1). The methodology behind the development of this class of compounds is based on the extensive halogenation of the TPP ligand at its ^-pyrrole positions and on the /weso-phenyl rings to stabilize the porphyrin against oxidative destruction in the oxidizing medium of the reaction mixture. Furthermore, the saddle shape conformation1 for these extensively halogenated metalloporphyrins favours monomelic structures and prevents their "dimerization" to p-oxo-dinuclear species,2 a cause for catalyst deactivation. Adding to these properties a very reactive oxometal moiety due to the addition of electron-withdrawing halogen groups (if the systems indeed generate M=0 moieties as the active catalytic centres), a potentially powerful reagent is thus available for oxidizing organic compounds. Of particular significance is the work of Lyons and Ellis on the 02-oxidation of light alkanes catalyzed by Fe(porp) species [porp = octa-/?-fluoro, chloro and bromo-tetra(pentafluorophenyl)porphyrins] under mild conditions; for example, total turnovers for an isobutane system exceeded 10000 moi"1.3 One of the aims of the present thesis is to extend the periodic analogy of Fe to Ru and examine the reactivity of similar Ru-porphyrins of the third generation. One difficulty is the insertion of ruthenium into the free-base porphyrins having a large number of electron-withdrawing halogens. Collaboration with Dolphin and Xie led to successful preparation of one of the first 158 References on p. 187 Chapter S perhalogenated Ru-porphyrin complexes, Run(TDCPP-Clg)(CO) (TDCPP-C18 = dianion of octa->S-chloro-tetra(2,6-dichlorophenyl)porphyrin], whose reactivity is the subject of this chapter. 5.1.1 Ru-Perhalogenated Porphyrins: Aims and Scope Although a wide range of transition metals across the periodic table has been inserted into free-base porphyrins, the metallation of the highly-halogenated third-generation porphyrins, to the best of the author's knowledge, has been limited until very recently to the first row transition metals.4 Metalloporphyrins of such type, particularly iron porphyrins, have been shown to exhibit high activity in the hydroxylation of alkanes.3 Only recently have there been reports on the second row (Ru) congeners,5'* although no catalysis studies on these Ru-porphyrins are yet reported. The metallation of Ru into these highly-halogenated porphyrins is non-trivial. The common procedure of Ru-insertion is to reflux Ru3(CO)i2 and the free-base porphyrin (eg. TPP) in a high-boiling organic solvent, such as mesitylene6 under 1 atm CO for extended periods of time, or more recently, heating Ru(DMF)63+ and water-soluble free-base porphyrins in DMF.7 Initial attempts in this thesis work to metallate H2TPFPP (which contains twenty F-groups, and does not have any yff-pyrrole-halo groups) via the Ru3(CO)i2 route [see Chapter 2 regarding the preparation of Run(porp)(CO), where porp = TMP and TDCPP] gave low yields of Run(TPFPP)(CO) (<10% approximated by spectrophotometry and TLC), and the application of the Ru3(CO)i2 route to other highly-* Work described in the present thesis was being carried out when the papers of Ref. 5 appeared in the literature. 159 References on p. 187 Chapter 5 halogenated porphyrins was assumed to be similarly difficult. Recently, Murahashi et al.8 reported the reaction of Ru3(CO)i2 and H2TPFPP in decalin to give Run(TPFPP)(CO) in a 49% yield; this solvent was also used in the preparation of Run(TDCPP)(CO) by Dubourdeaux et al9 Also, Birnbaum et al.5 reported the insertion of ruthenium into H2TPFPP-Clg, the reaction involving heating Ru3(CO)i2 and the free-base porphyrin in refluxing perfluorobenzene to form Run(TPFPP-Clg)(CO).5 Clearly, the choice of the solvent for the Ru3(CO)i2 route is critical for the successful preparation of Ru-porphyrins containing a large number of electron-withdrawing groups. Again, at the time when the current research was in progress, the reports of Birnbaum etal.5 were unpublished, and an alternative route to obtain the highly-chlorinated Ru-porphyrin, Run(TDCPP-Cl8)(CO), (1), was discovered in a collaborative effort with Dolphin and Xie (Chapter 2). Following the successful preparation of (1), /ra«5-RuVI(TDCPP-Clg)(0)2, (2), was obtained from the /w-CPBA oxidation of (1). (1) and (2) were tested as catalyst precursors in the 02-oxidations of alcohols, alkenes and alkanes. 5.2 Sample Preparation and Data Analysis 5.2.1 Sample Preparation in Catalysis Studies The catalytic 02-dehydrogenations of benzyl alcohol and 1-phenylethanol (up to 0.58 M) were studied at 50 °C in benzene under 1 atm air using an experimental procedure similar to that outlined in Section 4.2.1. Concentrations of (2) were 10'5 - 10"4 M in benzene, these being determined spectrophotometrically using the extinction coefficient of the complex (Chapter 2). The aerobic oxidation of Ph3CH (~10'2 M) to Ph3COH catalyzed by (2) (~10"4 M) in benzene also follows the same setup as that 160 References on p. 187 Chapter 5 described in Section 4.2.1. The 02-oxidations of neat c/'s-cyclooctene (referred to as cyclooctene), cyclohexene and methylcyclohexane were studied under 1 atm O2. The 1 atm O2 environment created by the continual purge of O2 into the neat hydrocarbons resulted in some solvent losses in the cyclohexene and methylcyclohexane systems, and the experimental setup shown in Figure 5.1 was employed to minimize the evaporation of the hydrocarbons. The reactions were done in a 25 mL, three-neck, conical flask topped with a water-cooled (10 °C) condenser, although under such an experimental setup, -20% losses of methylcyclohexane and cyclohexene were still observed over the time of the experiment,* typically < 24 h. Alkane or alkene (5 mL) was added into the flask, and subsequently -0.5 mg (1) or (2) was added into the hydrocarbons. A 25 uL aliquot of the neat hydrocarbon containing the Ru-porphyrin was diluted in 1 mL benzene, and the diluted concentration of (1) or (2) was determined spectrophotometrically in the benzene solution; typical concentrations of the Ru-porphyrin in the original neat hydrocarbons, where significant catalysis occurred (see Sections 5.4 and 5.5), were calculated to be - 3 x 10'5 M. The reaction vessel was submerged into an oil-bath heated by an electric hot plate, with the desired temperature (35 to 100 °C) maintained within ± 1 °C. 02 was introduced into the solution through a stainless steel needle, with the gas continually purging through the solution at -5 mL min"1. Physical changes were observed approximately 1 h after the cyclooctene system was heated to 93 °C. The darker brown colour of the alkene solutions due to the presence * The 20% losses in volumes were assumed to contain mostly methylcyclohexane and cyclohexene, as they are the most volatile component in the respective systems. 161 References on p. 187 Chapter 5 10 °c cooling water /o2 Stainless steel needle Neat Alkane/Alkene with Dissolved Ru-porphyrin Electrically heated oil-bath Figure 5.1. Experimental setup for the oxidations of neat cyclohexene, cyclooctene and methylcyclohexane under 1 atm O2. The constant purge of O2 necessitated the use of a water-cooled condenser. -20% losses of cyclohexene or methylcyclohexane (see text) were observed over a period of-24 h. 162 References on p. 187 Chapter 5 of (2) turned greenish-yellow after this time; however, a Soret absorption, although gradually disappearing as the reaction progressed, was still observed at 422 nm at this time. Of note, the Soret XmaX for (2) is at 430 nm; however, (2) reacts with the neat cyclooctene almost immediately at room temperature, and the resulting Ru-porphyrin species absorbs at 422 nm. At the end of 24 h, < 30% of the intensity of the Soret maximum at 422 nm remained, indicating that a substantial amount of the Ru-porphyrin had decomposed. After 55 h, a very small (< 5%) Soret absorption was still observed in the cyclooctene system, but a large UV-visible absorption, presumably due to the organic products (starting from ~ 420 nm and rising steeply below this wavelength), made an accurate determination of the amount of intact porphyrin difficult. The methylcyclohexane system showed no oxidation after 2 h of heating at 90 °C; however, the solution became bleached after 24 h, when no Soret absorbances were evident. 5.2.2 Preparation of <ra«s-RuVT(TDCPP-Cl8)(0)2 That /raw5-RuYI(TDCPP-Clg)(0)2(2) contains two oxo ligands is shown by its ability to oxidize 2 equivalents of P^-F-CeUt^ to the corresponding phosphine oxide in CDCI3 under 1 atm Ar, as observed by 19F-NMR spectroscopy.* The IR absorption due to VRU=O within (2) is observed at 827 cm"1 (solid KBr), in agreement with values for other ?raw5-RuVI(porp)(0)2 species (porp = TMP,10 TDCPP,11 OEP and TPP12), whose vRu=o values range between 820 and 823 cm"1. Hence a trans geometry for the oxo ligands in (2) 1 5 equivalents of POJ-F-QJLOS (2.5 x 10"3M) were added to a CD2C12 solution of (2) (5.0 x 10"4M) under 1 atm Ar, and the amount of oxide product was determined from integrations on the 19F-NMR spectrum (acquired ~ 30 min after the addition of the phosphine): OPip-F-CetUh and Pip-F-CetUh at 8 = -30.7 and -36.4, respectively (see also Chapter 3). 163 References on p. 187 Chapter 5 seems reasonable. Purification of (2) by column chromatography (activity I neutral alumina) using benzene as the eluent gives a product with Soret and Q-bands at 430 and 516 nm, respectively (Chapter 2); however, when species (2) is left in benzene, within 1 h the Soret maximum shifts to 422 (e ~ 150,000 M"1 cm"1) and the Q-band to 518 nm (e ~ 14,000 M"1 cm"1). Using CH2CI2 as the eluent leads to the same Soret and Q-band shifts, although the time for the transformation is typically longer (~ 2 h) than that in benzene. The loss of the dioxo ligands in these solution species is certain, as the Soret shift from 430 to 422 nm is accompanied by the loss of the 827 cm"1 absorption band in the IR spectrum of a recovered solid sample. Of note, the addition of ~ 10 equivalents of m-CPB A to the benzene solution containing the unknown Ru(porp) species with A™,x 422 nm regenerates almost quantatively (2). Addition of 0.50 mL HCl-saturated benzene solution to a fresh benzene solution of (2) (~ 4 x 10"6 M, 5.00 mL), within 1 min, yielded a new species which absorbed at 424 and 528 nm, with e values of 140,000 and 14,000 M^cm"1, respectively. The reaction of HC1 with RuVI(porp)(0)2 species, which will be discussed in Chapter 6, gives RuIV(porp)(Cl)2 products. The benzene solution was pumped to dryness, and the solid that remained was analyzed by mass spectrometry (Figure 5.2); the mass peak at 1336 amu corresponds to the parent peak for [RuIV(TDCPP-Clg)(Cl)2]+, which suggests that the bis(chloro) species was present in the solid. This reaction of (2) with HC1 gives further indirect evidence that (2) is the dioxo species. 164 References on p. 187 Chapter 5 Chapter 5 The identity of the Ru(TDCPP-Clg) species with a Soret maximum at 422 nm is unknown. Most likely the sixteen Cl-groups on the porphyrin makes the Ru=0 moieties within (2) extremely reactive, and (2) perhaps react with any trace impurities in the solvents* presumably to form reduced, lower-valent Ru-species. When a solution (benzene or CH2CI2) of (2) is left standing for 1 week in air, the Soret maximum shifts further to 418 nm, and at this time an IR absorption due to Vco can be observed at 1965 cm"1. Even more remarkable is that a solid sample of (2) left exposed to air for 1 month shows the presence of an IR stretch at vco = 1965 cm"1. 5.2.3 Data Acquisition and Analysis The progress of all the catalytic oxidations (alcohol and hydrocarbon systems) was monitored by GC analysis. The procedure and methodology have been described already in Sections 2.2.5 and 4.2.2. Known standards, when available, were used to identify the oxidation products (Chapter 2). In addition, GC-MS analyses were employed to ascertain the identities of some of the products from the neat cyclohexene, cyclooctene and methylcyclohexane systems, where known standards were unavailable for all of the oxidation products. The GC-MS data are compiled in Appendix E, as are the raw data from the GC analyses for the catalysis studies on these neat hydrocarbons systems. ' The benzene and CH2CI2 eluents used were HPLC grade solvents from Fisher, and were used without further purification. 166 References on p. 187 Chapter 5 5.3 Catalytic Aerobic Oxidation of Alcohols RuVI(TDCPP-Cl8)(0)2 (2) was tested as a catalyst for the aerobic oxidation of alcohols. In Chapter 4, the aerobic oxidation of alcohols in benzene catalyzed by the RuVI(porp)(0)2 species (porp = TMP and TDCPP) was discussed, and the TDCPP analogue was more susceptible to deactivation via decarbonylation pathways (total loss of catalytic activity within 24 h). The activity of (2) is of the same order of magnitude as that of RuVI(TMP)(0)2 (Chapter 4); this is surprising as the reactivity of (2) had been thought to resemble that of the TDCPP analogue, also highly chlorinated, and (2) was expected to be similarly susceptible to deactivation. That (2) does not lose catalytic activity as rapidly as RuVI(TDCPP)(0)2 under similar conditions suggests perhaps that the highly distorted and sterically crowded environment about the ruthenium prevents decarbonylation of the aldehyde or ketone products (Chapter 4); however, inspection of the 1-phenylethanol system after ~ 7 d shows the presence of Run(TDCPP-Cl8)(CO), as evidenced by the presence of Vco at 1965 cm"1 in the IR spectrum. The aerobic oxidations of benzyl alcohol and 1-phenylethanol catalyzed by (2) are shown in Figures 5.3 and 5.4. About 1200 turnovers are obtained for benzyl alcohol after 15 d; no benzoic acid is detected under the conditions described below. The conditions used in this system are the optimum ones found for the Ru(TMP)/benzyl alcohol system: addition of 3.0 M aqueous KOH (50 pL) to benzene (0.40 mL) and moderate reaction conditons (1 atm air at 50 °C). Of interest, the unknown species with a characteristic Xmax 422 nm described in Section 5.2.2 gives almost the same turnover numbers as those by (2) (see later). 167 References on p. 187 Chapter 5 Time (hours) 1400 - • 1200 • • 1000 - -| 800 - • o 1600 1400 + 200 + 0 (b) [(2)] = 3.5x 10"5M 0 Figure 5.3. £.580M 0.290M • • • + + 100 200 300 Time (hours) 400 500 Aerobic oxidation of benzyl alcohol to benzaldehyde catalyzed by RuYI(TDCPP-Clg)(0)2 (2) under 1 atm air in benzene at 50 °C (2-phase system containing 0.40 mL benzene/50 uL 3.0 M aqueous KOH, see text). The unknown Ru-porphyrin species with characteristic Soret absorption at 422nm (a) exhibits almost the same activity as (2) (b). 168 References on p. 187 Chapter 5 0 50 100 150 200 Time (hours) Figure 5.4. Aerobic oxidation of R, S- 1-phenylethanol to acetophenone catalyzed by Ru VI(TDCPP-Clg)(0)2 (2) under 1 atm air in benzene at 50 °C (2-phase system containing 0.40 mL benzene/50 pL 3.0 M aqueous KOH, see text). [(2)] = 2.1 x 10-*M 169 References on p. 187 Chapter 5 Addition of the common radical inhibitor, 2,6-ditertbutyl-4-methylphenol (BHT, 0.1 M) to the benzyl alcohol system did not hinder the oxidation, thus ruling out the operation of a radical-chain mechanism. The selective oxidation of benzyl alcohol to benzaldehyde without further conversion to benzoic acid also strongly suggests a mechanism not involving free-radicals. The catalytic process most likely is analogous to that of the RuVI(TMP)(0)2 system, which has been fully discussed in Section 4.3.3, and is summarized again in Eqs. 5.1 through 5.4 [Ru = Ru(TDCPP-Clg)]. ^(0)2 + 3RR'CHOH » Jta^COCHRR'fc + RR'CO + 2 H20 (5.1) /?iiIV(OCHRR')2 + 2H20 Ruw(OH)2 + 2 RR'CHOH (5.2) /^(OFfy ^"^(O) + H20 (5.32Ruw(0) ~Run + Ru^iOh (5.4) Of note, the addition of 10 pL of benzyl alcohol (1 x 10"2 M) to (2) (3.0 x 10"6 M in benzene under air), after -30 min, gives a Ru-species which absorbs at 422 and 518 nm; this spectral change is the same, and occurs on the same timescale, as that observed with (2) alone in benzene solution (see earlier). If the present system exhibits chemistry similar to that of the TMP system (Chapter 4), the Ru-product in the benzyl alcohol reaction is expected to be RuIY(TDCPP-Clg)(OCH2Ph)2. That the unknown Ru(TDCPP-Clg) species with A™* 422 nm formed from (2) alone in benzene exhibits almost the same reactivity as that of (2) implies that it is an equally effective catalyst precursor, presumably exhibiting similar chemistry as (2) (Eqs. 5.1 to 5.4); this suggests that the ^ 422 nm 170 References on p. 187 Chapter 5 species is similar in nature to Ru™(0), RuTY/(L)2 or J?«n(L')2 species (L, L' = ligands that are labile or exchangeable with water or alcohol; see Chapter 4). The catalytic activity of (2) is vastly superior to that of RuVI(TDCPP)(0)2 and is comparable to that of RuIV(TMP)(0)2 for the aerobic oxidation of benzyl alcohol. In addition, (2) gives -130 turnovers for the catalytic aerobic oxidation of 1-phenylethanol to acetophenone, while RuVI(porp)(0)2 species (porp = TMP or TDCPP) give only a few turnovers before being deactivated completely (Chapter 4). Hence, (2) might offer a greater potential as an alcohol oxidation catalyst, and possibly is more useful for a greater range of alcohol substrates. 5.4 Oxidation of Alkenes The 02-oxidations of cyclohexene and c/'s-cyclooctene catalyzed by (2) give total turnovers of the order of 105 when the neat alkenes are used without any solvent. The epoxide is the main product ih the cyclooctene oxidation; however, cyclohexene-2-ol and cyclohexene-2-one, allylic C-H bond cleavage compounds, are the main products in the cyclohexene oxidation. Table 5.1 lists the results from the oxidation of cyclohexene and cyclooctene catalyzed by (1) and (2). The addition of BHT (either 0.01 or 0.1 M) completely inhibits oxidation in both alkene systems, and both active systems test positive (Kl/starch) for the presence of organic peroxides. The BHT experiment and the predominant production of allylic C-H bond cleavage products within the cyclohexene system suggest a free-radical oxidation mechanism. It is clear from blank studies at higher temperatures that (1) and (2) are necessary in these alkene oxidations, and a reasonable 171 References on p. 187 Chapter 5 conclusion is that the Ru-porphyrins are involved in the decomposition of organic peroxides to propagate a radical-chain process at a lower temperature (see later, Figure 5.7). The Ovoxidations of alkenes using radical initiators have been well-studied,13 and the reactions generally follow the mechanism outlined in Figure 5.5. Two main propagating pathways, addition of R02* to alkenes (Eq. 5.7) and H-abstraction from alkenes by R02* (Eq. 5.9), are identified within this mechanism, with the former leading to epoxides as products (Eq. 5.8). Clearly, for every equivalent of epoxide formed, one equivalent of alkoxyl radical must be accounted for (Eqs. 5.8, 5.10, 5.11 and possibly 5.12); therefore, the maximum yield of epoxide should never exceed 50%, if addition is the only epoxide yielding path. Mayo mentioned the possibility of an alkoxyl radical giving directly an epoxide (Eq. 5.12);13c however, how such a reaction can proceed was not indicated in the report and the actual mechanism for such an epoxide forming route is not obvious. The yields of the various products in the cyclohexene system are consistent with radical pathways in operation; however, the cyclooctene system gives as high as 87% cyclooctene-oxide among the products (see also Figure 5.6), which is far higher than the expected maximum of 50% based on an addition pathway alone. Cyclooctene is known to be an unusual substrate in autoxidation studies in that it is not as autoxidizable compared to its cyclohexene, cyclopentene and cycloheptene homologues.13b A most intriguing, and still unexplained, observation by de Roch and Balaceanu was that the autoxidation of cyclooctene at 106 °C in the presence of 172 References on p. 187 Chapter 5 Table 5.1. Oxidation of alkenes catalyzed by Run(TDCPP-Cl8)(CO) (1) and RuYI(TDCPP-Cl8)(0)2 (2) under 1 atm 02. Substrate Products (% of starting alkene) Total Products [% Distribution of oxidation products] (% of starting alkene) 0" OH d 6 o d OOH e,f 6 OO +other dimers" Blank 24 h 0.012 [2.8] 0.16 [37] 0.23 [54] 0.0032 [0.74] 0.023 [5.4] 0.42 ±0.1 [(l)f = 3.15 x 10"5M 23 h 1.05 [3.6] 13.4 [45] 12.8 [43] 0.031 [1.0] 2.1 [7.0] 29.6 ± 1 [92000 turnovers]5 a o o d -C=0, -OH and -OOF/containing and rearrangement products6 Blank 23 hc [(2)] = 5.0 x 10'5M 26 h 8.2 [73] 35.8 [87] 3.1 [27] 5.4 [13] 11.3 ± 1 41.2±4 [63000 turnovers]*'7 " Reaction conditions: 5 mL neat alkene under 1 atm 02; 35 ± 1 °C for cyclohexene and 93 ± 1 °C for cyclooctene, unless indicated otherwise. * Similar conversion were obtained in qualitative studies under the same conditions using (2) as the catalyst. Again, cyclohexene-2-ol and cyclohexene-2-one were the major products. c 110± 1 °C d Identification of product from the correlation of retention times with known standards, as well as by GC-MS (Appendix E). e Formulation of product identity based on GC-MS only (Appendix E). f Presence of hydroperoxides suggested from a positive Kl/starch test result. * Turnovers based on [neat cyclohexene] = 9.86 M. * Turnovers based on [neat cyclooctene] = 7.69 M. ' Progress of this reaction beyond 26 h is shown in Figure 5.6. 173 References on p. 187 Chapter 5 Initiation RH " R* + H* (5.5) Peroxide R* + O2 R02* (5.6) formation O2R ADDITION RCV + / \ /—\ (5?) & ox formation 02R O Epoxide >—( — /-A + RO' (5.8) rirmatrnn / \ / \ ABSTRACTION RO? + JJ—/ \ R02H + /~\ (5.9) Fates of RO* RO* \ ROH + / \ (510) H RQ RO* + /~\ — /~\ (5-11) » Q " (5.12) Figure 5.5. Radical-chain mechanism proposed for the oxidation of alkenes (Ref. 13). Chain propagation proceeds through either an ADDITION or ABSTRACTION pathway. 174 References on p. 187 Chapter 5 cobalt(II) stearate gave over 70% yield in the epoxide.14 At about the same time, Van Sickle et al. conducted similar experiments (ABN-initiated autoxidation) and found that only 40% cyclooctene-oxide was obtained at 70 °C;13b the high epoxide yield observed by de Roch and Balaceanu was viewed with skepticism. The present cyclooctene system using (2) as the catalyst yields 87 % epoxide among the oxidation products after 26 h; there is no doubt that a > 50 % yield of epoxide is generated. Approximately 60000 turnovers per day are realized at 93 °C when (2) is added to the cyclooctene, and the catalytic activity does not decrease much as the reaction proceeds (see Figure 5.6). As < 30% of the starting Ru-porphyrin remains in the cyclooctene system after 24 h (Section 5.2.1), the almost linear turnover versus time plot suggests that Ru-porphyrin species are not solely responsible for the catalytic activity (see Section 5.5 later). Worth noting is that the reaction involving cyclooctene and (2) is relatively clean and that the epoxide content among the products remains almost constant throughout the reaction (Figure 5.6). Autoxidation at 93 °C in the absence of (2) is negligible (< 0.4 % product after 24 h), but at 110 °C some 11 % cyclooctene autoxidation is evident (blank study, Table 5.1); the amount of epoxide obtained at 110 °C (blank study) is 73 ± 4 % of the total products, which is close to the distribution seen when (2) is present as a catalyst at 93 °C. Earlier work by Mayo's group on the ABN-initiated autoxidation of cyclohexene at 60 °C (closed system initially under ~5 atm 02) achieved a 6.15 % overall conversion in 13.5 h; among the products observed were cyclohexene-2-peroxide (80.4 %), cyclohexene-2-ol (7.0 %), cyclohexene-2-one (4.7 %), cyclohexene-oxide (0.9 %) and 175 References on p. 187 Chapter 5 dimers (7.0 %).13b In comparison, the present cyclohexene system catalyzed by (1) shows a higher activity (30 vs. 6 % conversion) at a lower temperature (35 vs. 60 °C) and pressure (1 vs. 5 atm O2). Thus, (1) and (2) are effective catalyst precursors, and are even more effective than some free-radical initiators (e.g. ABN) in promoting the free-radical propagated 02-oxidation of cyclohexene and cyclooctene. At lower temperatures (24 and 50 °C) under 1 atm air in benzene solvent [~10"2 M alkene, ~ 5 x 10"4 M (1) or (2)], (1) is completely inactive as a catalyst, while (2) shows marginal activity in the epoxidation of cyclohexene and cyclooctene. Under such 90% T Time (hours) Figure 5.6. 02-oxidation of cyclooctene under 1 atm 02 at 93 ± 1 °C catalyzed by Ru^TDCPP-Clg)^ (2). [(2)] = 5.0 x 10'5 M. Excess of alkene to (2) corresponds to 150000 : 1. 176 References on p. 187 Chapter 5 conditions, approximately 1 turnover per day is realized (total turnovers -10) for either alkene when (2) is employed as the catalyst, and the turnovers obtained are invariant with temperature. Under 1 atm 02 at 35 °C, (2) (3.5 x 10"5 M in benzene) also gives only 1 turnover after 16 h for the oxidation of cyclohexene (1.5 x 10"2 M) to cyclohexene-oxide. The Soret intensity at 422 nm has not changed when the solution is inspected after 24 h, unlike in the reactions involving the neat cyclooctene, indicating that the Ru-porphyrin remains intact in the reaction medium. The oxidation of both cyclohexene and cyclooctene, at dilute concentrations in benzene, produces exclusively the corresponding epoxides, a direct contrast with the neat alkene systems. An O-atom transfer mechanism, suggested by the specificity for epoxide formation, is most likely in operation in the case where the alkenes are dilute in the benzene solutions. 5.5 Oxidation of Alkanes Lyons and Ellis have suggested that their isobutane and propane oxidations (~ 13000 turnovers for isobutane) catalyzed by Fe(TPFPP-Br8)(Cl) occur via a high-valent oxoiron intermediate, with the Fe=0 moiety attacking the hydrocarbon C-H bonds.3 Recent work by Grinstaff et al.,15 however, demonstrated that the oxidations involve the decomposition of organic peroxides by Fe-porphyrins via a radical-chain mechanism (Figure 5.7). The inhibition of any oxidation in the presence of 0.01 M BHT, as well as the >99% selectivity for the tertiary C-H bond, led to the conclusion that the main reaction pathway was a free-radical one.15 Also, computer simulation studies based on free-radical 177 References on p. 187 Chapter 5 propagation of oxidation via Fe(porp) decomposition of hydroperoxides closely accounted for the actual experimental observations.16 ROH —M— = metalloporphyrin Figure 5.7. Radical-chain mechanism for the oxidation of alkanes via peroxide decomposition catalyzed by Fe-porphyrin species. Adapted from Ref 15. Ru(TDCPP-Clg) species can be considered to undergo similar chemistry, catalyzing the decomposition of hydroperoxides. 178 References on p. 187 Chapter 5 In the present study, (1) and (2) are also effective in initiating the 02-oxidation of methylcyclohexane at 90 °C via a radical-chain pathway, likely via a mechanism similar to the one proposed by Grinstaff et al. (Figure 5.7).15 The results for the methylcyclohexane oxidation catalyzed by (1) and (2) are listed in Table 5.2. A blank study conducted at 100 °C under 1 atm 02 shows that the autoxidation gives only 0.67% oxidized products, which are distributed between 57 % 1-methylcyclohexanol, 26% secondary alcohols and 17% ketones. The selectivity for oxidation at the tertiary C-H bond over secondary ones normalized on a per bond basis* is approximately 12.4 for the autoxidation within the the blank solution. When (1) or (2) is present, a similar tertiary bond selectivity of 13 ± 3 (average of the three runs involving (1) and (2) in Table 5.2) is observed. Hence, the presence of (1) or (2) does not have any effect on the selectivity of oxidation, and the role of Ru-porphyrin species in the oxidation likely involves the catalytic decomposition of organic peroxides, similar to that of Fe-porphyrins in the scheme shown in Figure 5.7. Although the systems containing (1) or (2) give the same distribution of products as that in the blank, the Ru-porphyrin species are clearly effective in promoting oxidation of the methylcyclohexane by about 10-fold (Table 5.2). Of note, when BHT (0.01 M) was added, (1) and (2) were completely ineffective in promoting the autoxidation of methylcyclohexane, this result being consistent with a free-radical mechanism. + S30 products * no. 3° CH bond = 1; no. 2° CH bonds = 10; bond selectivity = £ 2„ products * 10-179 References on p. 187 Chapter 5 u .12 £Pi £ -S o 1/3 CO go i * CO c • S 15 co o O o €^ o o .22 o ^ •3 s •a ts 8X> o -t> O o t/3 o o u 60 CO CD o NO > o o o P o +1 +1 t-i +1 t- CN -4—* 00 VI o o CN o o 60 60 1 1 CO 1 CO L-> > o 1—1 O e +1 e •4-> ON 3 o ON' o o o m o ON v> 1—' CN til NO NO o ON vi CN IT) ON ON r-1. o r"1. o ON CN NO vi CN ^ NO CN O ,—, o „ r<-> OO V) NO ° oo' o „ o o CN • ! NO1 V> o1 o CN d oo" m V) d CN CN V> m ^ d ^ oo" rfr °\ vi o m »/-) CQ CN i-f o CN X! II J= i 1 V) CN r-NO NO V> ,__, , , ON i , m 00 <—' CN VI ON d NO d NO d vi o ON C«1 00 V) vi d d r_1 r_• NO o ON ON r- 00 NO V) vi d d 1 1 d i i ON , , ON O vi vf p-J" NO cW ' v> II J3 i—i v> CN <N <u 3 co CD t_ T3 CD 15 3 -S -*-* CD J2 P O o o O e CD c CD CD X> CD u o CX <a e O ox O CN O c o O a, > T3 co ii co CO O w CL I; CO s CO RJ CO «J co" T3 c5 t3 O U o +1 CN ON U o 3 CO CO <U 6 a o a> O P o 18 J3 "u fc o o <o s o o o p o o X «J C O (U I-; Cu « ^a. to 00 'S r~ s a" cd CD £ 3° IT '+-> co 0) 1 8 6 ^ S « o § c 3 C 1—1 O CX o CX u- T3 - cn ° £ a .2 o to -H « o o 15 <u <u • o > c -co 4> O B _ „ 3 PM H 180 References on p. 187 Chapter S As a further test for catalytic activity, RuVI(TMP)(0)2 (1.5 x 10'4 M) was added to neat methylcyclohexane, and the solution heated at 93 °C under 1 atm 02. At the end of 16 h, approximately 3.6 % of oxidation products were present, with product distribution (52 % 1-methylcyclohexanol, 9 % secondary alcohols, 34 % ketones and 5 % other products) similar to that shown for systems containing (1) or (2) (see Table 5.2). An important observation is that after 16 h the brown colour due to RuVI(TMP)(0)2 was completely bleached, and a small amount of black residue was present in the solution. In an attempt to increase the amount of the black residue formed, 5 mg RuVI(TMP)(0)2 (10"3 M) was added to 5 mL methylcyclohexane and the procedure was repeated; however, almost no oxidation occurred after 16 h, and the oxidation products accounted for approximately 0.1% of the total organics (~ 8 turnovers), an amount even less than that for the blank study (Table 5.2). Also in this case, by visual inspection the colour of RuVI(TMP)(0)2 was still present and no black residue was formed. A similar experiment, performed by adding 5 mg (1) (10"3 M) to 5 mL methylcyclohexane under corresponding conditions, also showed negligible oxidation after 16 h. These "ineffective oxidation" experiments involving RuVI(TMP)(0)2 and (1) correspond to porphyrin concentrations of approximately 10"3 M, while experiments that generated oxidation products have porphyrin concentrations that are 1 to 2 orders of magnitude more dilute. The reduced forms of the Ru-porphyrins, when present at higher concentrations, may react with the hydroperoxides to form Ru(porp)(0)2 species,6 rather than decomposing them according to the scheme in Figure 5.7, and thus the radical-chain does not propagate (see below). 181 References on p. 187 Chapter 5 Ru(TMP) species are known to decompose hydroperoxides. Hansen studied the decomposition of cyclohexyl hydroperoxide catalyzed by Ru(porp) species (porp = TMP, TDCPP and TPP),17 and the following results are particularly relevant to the present TDCPP-Clg system: i) the Run(porp)(CO) precursors are initially oxidized to the corresponding RuVI(porp)(0)2 species by the cyclohexyl hydroperoxide; ii) the decomposition rate of the cyclohexyl hydroperoxide is almost linear for about 120 min, although ~ 90 % of the Ru(TDCPP) species are destroyed in about 30 min; iii) the use of the radical scavenger, galvinoxyl, slows the rate of decomposition of hydroperoxides to 54% that of the reaction without any added radical scavenger; and iv) ESR studies show that the system contains ESR-active species which give rise to g-values of 2.0023 and 2.35, with the latter suggested to belong to a Ru non-porphyrin species. In the present TDCPP-Clg system, an almost linear rate in the cyclooctene oxidation was observed (Figure 5.6), although > 70% of the Ru(TDCPP-Clg) species had been destroyed in the first 24 h. This result suggests that Ru-porphyrin species are not solely responsible for the catalytic oxidation within the neat hydrocarbon systems; complementing this proposal are Hansen's studies,17 which suggest that Ru non-porphyrin species are responsible, at least partly, for the decomposition of cyclohexyl hydroperoxide. Dioxoruthenium(VI) porphyrin species may act as initiators for oxidation via a radical-chain pathway (Eqs. 5.13 and 5.14, [Ru = Ru(porp)]) by initially producing R' (and thus RO2') radicals; in Chapter 4, the oxidation of tertiary alkanes by RuVI(TMP)(0)2 was Ruv\0)2 RH {/?II(0)(OH)}{R-} (5.13) {/?«(0)(OH)}{R-} RU(0)(OH) + (R' fast ROV) (5.14) 182 References on p. 187 Chapter 5 discussed, and a homolytic C-H cleavage was proposed as a possible mechanism (Eq. 5.13). When the Ru(porp) (porp = TDCPP-Clg and TMP) concentrations are ~ 10"3 M, which are ineffective in initiating any oxidation, the hydroperoxides formed (Eq. 5.14) may not be decomposed according to the scheme in Figure 5.7, but rather, the reduced Ru(porp) species react with the hydroperoxides preferentially to give the corresponding dioxo complexes.6'17 When the Ru(porp) concentrations are lower (10'4 to 10'5), the systems become effective, operating via radical-chain pathways, for the oxidation of methylcyclohexane and cyclooctene; in these active systems, the destruction of the Ru(porp) species is noted. Hence, it is feasible that Ru non-porphyrin,17 decomposition products, not Ru(TDCPP-Clg) species, are responsible for mediating the radical-chain pathways depicted in Figure 5.7. As the Ru(porp) species are clearly destroyed during the oxidations, the usefulness of the porphyrin ligands is questionable (see below). The black residue mentioned above is most likely RuC>2, but this as yet is unsubstantiated; demetallation of Ru-porphyrin species to give Ru02 under oxidizing conditions has been demonstrated in this laboratory.18 It is difficult to increase the amount of Ru-porphyrin to give more decomposition product as the metalloporphyrin itself, when present at a higher concentration, inhibits the oxidation (and the demetallation seems to occur as the oxidation progresses). Of note, the essentially insoluble RuCl3»3H20 (5 mg, -20 pmol, in 5 mL methylcyclohexane at 90 °C under 1 atm 02 for 20 h) gives approximately 2% oxidation products for the methylcyclohexane system [35 % 1-methylcyclohexanol, 5.4 % secondary alcohols, 29.3 % ketones and 30.3% other products; cf. Table 5.2]. It is plausible that some RUCI3 is oxidized to Ru02 under the 183 References on p. 187 Chapter 5 above conditions, and the dioxide in turn can catalyze the generation and decomposition of hydroperoxides similar to a recently used RuCl3/aldehyde/saturated hydrocarbon 02-oxidation system, where the formation of high-valent Ru-oxo species was invoked.19 In this thesis work, RuCl3»3H20 and Ru02#2H20, although essentially insoluble in neat cyclooctene, were also found to be effective in catalyzing the oxidition of the alkene: after 16 h at 92 °C, the RuCl3»3H20 system gave an 8% conversion (with 72% epoxide formation), while the Ru02#2H20 system gave a 16% conversion; after 56 h, the latter system showed almost 80% conversion (with 86% epoxide formation). At room temperature (24 °C) under 1 atm air, the aerobic oxidation of Ph3CH to Ph3COH in benzene catalyzed by (2) is similar to that catalyzed by RuVI(porp)(0)2 species (porp = TMP and TDCPP) (Section 4.4). Figure 5.8 shows the progress of the aerobic oxidation of Ph3CH catalyzed by (2). The catalytic activity is marginal, and at the end of 20 d three turnovers are realized. As BHT (0.01 M) does not inhibit the oxidation, the mechanism most likely does not involve hydroperoxide decomposition, and is presumably similar to that described for the TMP and TDCPP systems (Chapter 4). 184 References on p. 187 Chapter 5 5.6 Conclusions That Ru(TDCPP-Clg) species can catalyze 02-oxidations of hydrocarbons via a radical-chain propagation pathway is clearly demonstrated in this chapter; however, the Ru-porphyrin species are completely destroyed in the methylcyclohexane system, as the colour of the Ru-porphyrin is completely bleached. For the neat cyclooctene system ~ 70% of the initial porphyrin most certainly disappears after 24 h. Among the oxidations discussed in this chapter, the oxidation of alcohols to aldehydes or ketones in benzene catalyzed by (2) appears to be the only efficient oxidation 185 References on p. 187 Chapter 5 that proceeds via a high-valent oxoruthenium species. The Ru(TMP and TDCPP) systems were well-studied (Chapter 4) and the activity of Ruv,(TDCPP-Cl8)(0)2 resembled that of the TMP analogue. The exclusive production of benzaldehyde from benzyl alcohol without further oxidation to benzoic acid, as well as the fact that BHT has no effect on the catalysis, suggest a process not involving a radical-chain pathway. The higher activity of (2), over that of the TMP and TDCPP analogues (Chapter 4), in catalyzing the aerobic oxidation of 1-phenylethanol suggests that (2) may be potentially more useful in the oxidation of other alcohols. 186 References on p. 187 Chapter 5 References 1 P. Ochsenbein, K Ayougou, D. Mandon, J. Fischer, R. Weiss, R. N. Austin, K. Jayaraj, A. Gold, J. Terner and J. Fajer, Angew. Chem. Int. Ed. Engl. 33, 348 (1994). 2 a) J. P. Collman, C. E. Barnes, P. J. Collins, T. Owaza, J. C. Galluci and J. A. Ibers, J. Am. Chem. Soc, 106, 5151 (1984). b) H. Masuda, T. Tagu, K. Osaki, H. Suzimoto, M. Mori and H. Ogoshi, J. Am. Chem. Soc, 103, 2199 (1981). 3 a) J. E. Lyons and P. E. Ellis, Catal. Lett., 8, 45 (1991). b) P. E. Ellis and J. E. Lyons, Coord. Chem. Rev., 105, 181 (1990). c) J. E. Lyons and P. E. Ellis, Catal. Lett., 3, 389 (1989). 4 T. P. Wijesekera and D. Dolphin, in Metalloporphyrins in Catalytic Oxidations, ed. R. A. Sheldon, Marcel Dekker, Inc., New York, p. 218, 1994. 5 a) E. R. Birnbaum, W. P. Schaefer, J. A. Labinger, J. E. Bercaw and H. B. Gray, Inorg. Chem., 34, 1751 (1995). b) E. R. Birnbaum, J. A. Hodge, M. W. Grinstaff, W. S. Schaefer, L. Herding, J. A. Labinger, J. E. Bercaw and H. B. Gray, Inorg. Chem., 34, 3625 (1995). 6 N. Rajapakse, B. R. James and D. Dolphin, Stud. Surf. Sci. Catal, 55, 109 (1990). 7 C. J. Ware, M. Sc. Thesis, University of British Columbia, 1994. 8 S.-I. Murahashi, T. Naota and N. Komiya, Tetrahedron Lett, 36, 8059 (1995). 9 P. Dubourdeaux, M. Taveres, A. Grand, R. Ramasseul and J.-C. Marchon, Inorg. Chim. Acta., 240, 657 (1995). 10 J. T. Groves and R. Quinn, Inorg. Chem., 23, 3844 (1984). 11 N. Rajapakse, Ph.D. Dissertation, University of British Columbia, 1990. 12 a) C.-M. Che and W. H. Leung, J. Chem. Soc. Dalton Trans., 2932 (1991). b) W. H. Leung and C.-M. Che, J. Am. Chem. Soc, 111, 8812 (1989). 13 a) F. R. Mayo, Acc. Chem. Research, 1, 193 (1968). b) D. E. Van Sickle, F. R. Mayo and R. M. Arluck, J. Am. Chem. Soc, 87, 4824 (1965). c) F. R. Mayo, J. Am. Chem. Soc, 80, 2497 (1958). 14 I. S. de Roch and J. C. Balaceanu, Bull. Soc. Chim. Fr., 1393 (1964). 187 References on p. 187 Chapter 5 15 M. W. Grinstaff, M. G. Hill, J. A. Labinger and H. B. Gray, Science, 264, 1311 (1994). 16 J. A. Labinger, Catal. Lett., 26, 95 (1994). 17 a) C. B. Hansen, Ph.D. Dissertation, Utrecht University, Netherlands, 1991. b) C. B. Hansen, F. P. W. Agterberg, A. M. C. van Eijndhoven and W. Drenth, J. Mol. Cat., 102,117(1995). 18 B. R. James, S. R. Mikkelsen, T. W. Leung, G. W. Williams and R. Wong, Inorg. Chim. Acta, 85, 209 (1984). 19 S.-I. Murahashi, Y. Oda and T. Naota, J. Am. Chem. Soc, 114, 7913 (1992). 188 References on p. 187 Chapter 6 Chapter 6 Preliminary Work: Reactions of Ru^CTMPKO^ with HX Acids and Oxidation of Phenol and A^-Dimethylaniline 189 References on p. 235 Chapter 6 6.1 Introduction The formation of RuIV(TMP)(X)2 species (X = Cl, CF3COO and CHCl2COO) from the reaction represented in Eq. 6.1 (reaction not balanced) [Ru - Ru(TMP)] was /fo^(0)2 + excess HX benzen- RuW(X)2 (6.1) discovered in the course of this thesis work. The effects of acids and bases on the rates of oxidation of alcohols (Chapter 4) were examined, and the above-mentioned acids were found to react with RuVI(TMP)(0)2 (1) instead of giving a possible rate enhancement effect, as observed for the BaRuOs/HOAc1 and Ru(porp)/pyridine-JV-oxide2 systems used for the hydroxylation of hydrocarbons. Some preliminary data on the characterization of these RuIV(TMP)(X)2 species are discussed in this chapter; they are unexpected products and are characterized mainly in situ. Preliminary studies have been carried out earlier in this laboratory on the stoichiometric oxidation of phenol by (1), and the Ru-porphyrin product was thought to be a bis(hydroquinoxo)ruthenium(IV) species.3 The mechanism represented in Eqs. 6.2 to 6.4 was proposed based on the evidence available at the time [Ru = Ru(TMP)]. fli^O), + C6H5OH -£T5w /f«IY(0)(p-HOC6H4OH) (6.2) (1) (2) /?aIV(p-HOC6H40H)(0) +C6H5OH TasT" ^VHOCerLjOH^ (6.3) (2) (3) 1 fast /?«V-HOC6H40H)2 + JO2 /?«IV0?-OC6H4OH)2 + H2O (6.4) (3) (4) 190 References on p. 235 Chapter 6 While the intermediate (2) [or the analogous RuIV(TMP)(0)] was not observed, *H-resonances characteristic of Run(TMP) and Ru^TMP) species, tentatively formulated as (3) and (4) in Eq. 6.4, respectively, were observed under anaerobic conditions in an approximately 2:3 ratio.3a Under 1 atm O2 or air, only 'H-resonances due to the paramagnetic RuIV(TMP) species (4) were detected. This phenol system is re-examined, and compared to the chemistry of Ru(TMP) species within the phosphine and alcohol systems (Chapters 3 and 4). The use of TV.JV-dimethylaniline as a mono-substituted aromatic substrate seemed a logical step in testing the reactivity of (1), and preliminary work showed that (1) oxidizes iV,iV-dimethylaniline to /?-hydroxy-A/,./V-dimethylaniline both stoichiometrically, and in the presence of air, catalytically. 6.2 Experimental: Sample Preparation and Data Analysis The reactions of (1) with FfX acids (X = CI, CF3COO and CHCl2COO) were studied in situ by 'H-NMR, ESR and UV-visible spectroscopies. RuIY(TMP)(CF3COO)2 (5) was isolated and subjected to mass (by FAB ionization) and elemental analyses. Run(TMP)(MeCN)2 (10 mg, 0.01 mmol) was dissolved in air in 5 mL benzene until the aerobic oxidation to (1) was complete (< 30 min). Subsequently CF3COOH (10 pX, 0.13 mmol) was added, when an instantaneous darkening (from brown to dark green) of the solution was observed. After 10 min the solvent and excess acid were removed by pumping under vacuum, and the solid (5) that remained was dried at 100 °C under vacuum for a further 24 h. RuIV(TMP)(CHCl2COO)2 (6) was prepared in situ in benzene 191 References on p. 235 Chapter 6 (1 mL) in an NMR tube by adding CHC12C00H (1 pL, 0.012 mmol) to (1) (formed from the aerobic oxidation of Run(TMP)(MeCN)2, 0.001 mmol), when an instaneous darkening of the solution was observed. After 10 min, the solvent and excess acid were removed under vacuum at room temperature for 12 h. Toluene-dg (1 mL) was then vacuum transferred to the NMR tube containing (6), which was used in ^-NMR experiments (see later, Figures 6.6, 6.8 and Table 6.2). A sample of (5) for NMR studies was prepared in the same way as that for (6); however, the solvent and excess CF3COOH were removed with heat (100 °C) under vacuum, instead of at room temperature. This sample did not exhibit any characteristic TMP 'H-resonances, implying that compound (5) had decomposed. Subsequently, (5) was prepared in situ by adding CF3COOH (1 pL, 0.013 mmol) to (1) (from bis(MeCN) precursor, 0.001 mmol) in toluene-dg (1 mL) under 1 atm air, and the excess acid was not removed. Attempts to purify compound (5) by column chromatography were unsuccessful, as the compound moved down the column in streaks using either benzene or CH2C12 as the eluent. Elemental analysis of (5), compared with the theoretical formulation as RuIV(TMP)(CF3COO)2, gave the following data: Analysis, calculated for CeoHs^CvFgRu C, 65.03; H, 4.73; N, 5.06 Found C, 57.21; H, 4.92; N, 5.13. Mass spectral analysis of (5) (FAB ionization in a 3-nitrobenzylalcohol matrix) showed the following ion mass peaks: [Ru(TMP)(CF3COO)2]+ at 1108, [Ru(TMP)(CF3COO)f at 995 and [Ru(TMP)]+ at 822 amu (see Figure 6.1). A frozen benzene solution of (5) at 110 K did not show any ESR signals, suggesting that Ru(III) or Ru(V) species are absent. The kinetics of the stoichiometric oxidation of phenol by (1) in benzene were monitored by UV-visible spectroscopy, using an HP 8452A Diode-Array instrument for 192 References on p. 235 Chapter 6 experiments involving [phenol] < 0.1 M and a stopped-flow spectrophotometer for [phenol] values between 0.1 and 1.0 M. The experimental setup, sample preparations and data analysis for the phosphine oxidations have been described in Sections 2.2.2 and 3.2, and these procedures are equally applicable to the phenol oxidation kinetics monitored on the stopped-flow instrument. For the kinetic experiments using the HP 8452A instrument, phenol solutions (1.00 mL) of the appropriate concentrations (0.001 to 0.1 M) were prepared in benzene and added to a UV-visible quartz cell (1 cm path-length), which were then equilibrated thermally at 20 + 1°C. After 10 min, appropriate volumes of a benzene solution containing (1) (~10"3 M) were added to the cell to arrive at diluted concentrations of ~ IO"6 M, and the kinetics were monitored over the 340 - 650 nm range. Figure 6.2 shows a typical isosbestic set of spectra acquired during a kinetic run (0.0943 M phenol; (1) 5 x IO"6 M; 1 atm 02 at 20 °C). The values of the pseudo-first-order rate constants, kobs, were derived from the absorbance changes at the Soret maximum for (1) at 422 nm for all the kinetic experiments. The kinetic data and kobs values are tabulated in Appendix F. The reaction of (1) with A^N-dimethylaniline under 1 atm air or 1 atm Ar was studied in situ by 'H-NMR spectroscopy. The Ru-porphyrin product from the reaction of (1) with A^N-dimethylaniline in benzene-di; under air was isolated by pumping off the solvent (see also Section 6.5), and the solid that remained was analyzed by mass spectrometry (Figure 6.3). The data from the mass spectrum suggest a mixture of compounds to be present (see later, Section 6.5). The catalytic oxidation of N,N-dimethylaniline in benzene employed the same procedure as that used for the alcohol oxidations, which has been described previously in Sections 4.2 and 5.2. 193 References on p. 235 Chapter Chapter 6 Chapter 6 100—1 3-Nitrobenzylalcohol Matrix 100 t i V r \ 200 i—i—i——i—r^l—i—(-1—i i .1 '| "i 300 400 500 600 1 I Relative intensity i ' i1 r i j i T-700 800 [Ru(CO) + 2H]+ [Eu]+/ 882 / [&y(U)]+ il 1003 fML2)]+ 912 | ^|019 ' 1 I 1 1 1 1 I 1200 1300 100—i T 100 4 Thioglycerol Matrix i 300 I 400 1 I 1 1 ' 1 I ' '" 500 600 100-0—' [Ru]+ [Ru(CO) + 2H]+ 882 700 ^0L0^+rRu(L2)+H]+ ,1020 too 900 1000 Ai s . i*f *t 'i* r t | i—r • i • i-1000 1100 I 1 1 1 1 I 1200 1300 M/Z Figure 6.3 Mass spectra of solid sample isolated from the reaction between RuVI(TMP)(0)2 and /V-dirnethylaniline in benzene-ak under 1 atm air. The results suggest a mixture of Run(TMP)(/?-NMe2-C6H4-X) species, where X = H (Ll) and OH (L2), to be present. (FAB ionization of the compound supported in (a) 3-nitrobenzylalcohol and (b) thioglycerol matrices). See also Section 6.5. 196 References on p. 235 Chapter 6 6.3 RuIV(TMP)(X)2 Species RuIY(TMP)(X)2 species (X = Cl and Br) have been synthesized and characterized previously in this laboratory.4 The preparation of these compounds follows the scheme represented in Eq. 6.5 [Ru = Ru(TMP) and X = Cl or Br]. The presence of air or 02 has /?«n(MeCN)2 + excess HXanhydrom/benzene 1 WCC» RuIV(X)2 (6.5) been noted to accelerate the rate of the reaction as depicted in Eq. 6.5, if the air or 02 is introduced into the system after the FIX has been added.4b Recently the formation of RuIV(TMP)(Cl)2, via the reaction of RuVI(TMP)(0)2 (1) with anhydrous HC1 in benzene, was reported,2 and it was found independently during the course of this thesis work that exposure of a benzene solution of (1) to gaseous HC1 or 12 M aqueous HC1 gives RuIV(TMP)(Cl)2 quantitatively, the reaction being complete within a few minutes at room temperature, as evidenced by 'H-NMR and UV-visible spectroscopies. Furthermore, the addition of the strong organic acids, CF3COOH and CHCl2COOH, to benzene solutions of (1) produces rapid changes in the UV-visible spectra (Figure 6.4); the expected products are bis(substituted-acetato)-Ru(IV) complexes (see below). Of note, the oxidation products in the reactions between (1) and HX, presumably derived from the acids themselves, are presently unknown; one way to balance reaction 6.1 is to consider H202 as the oxidation product [Eq. 6.6; /?«=Ru(TMP)], but this is unlikely chemically. ^11^(0)2 (1) + 2 HX • Ruw(X)2 + H202 (6.6) 197 References on p. 235 Chapter 6 0.18T 402 nm 0.16" 0.14-• (b) CHCl2COOH added Figure 6.4. 350 400 450 500 550 600 650 Wavelength (nm) UV-visible spectra of RuVI(TMP)(0)2, (1), in 1 mL benzene at 25 °C followed by the addition of 5 pL (a) CF3COOH and (b) CHCl2COOH. [(1)] = 6.4 x 10"7 M in (a) and 1.1 x 10"6 M in (b). 198 References on p. 235 Chapter 6 The 1000 cm"1 region in the IR spectra of Ru(TMP) complexes contains what is known as the "oxidation state marker", the name arising from the strong IR signal which varies depending upon the oxidation state of the ruthenium centre. This property has been used by other workers5'6 to demonstrate a change in the oxidation state of the Ru within Ru-porphyrin complexes; however, the IR database has been somewhat limited to a few complexes. Earlier work carried out in this laboratory led to the preparation of a variety of alkoxo (Chapter 4), alkyl and haloruthenium(IV and III)4 TMP complexes, and thus a larger number of complexes has become available and firmer comparisons may be drawn (Table 6.1, see also Figures 6.9 and 6.10 later). The TR data from Table 6.1 are consistent with assigning an oxidation state of 4+ for the Ru-centre in the proposed bis(acetato)ruthenium(IV) species. A sample of (5), generated in situ from the reaction of (1) and excess CF3COOH in benzene-c/6 for 'H-NMR experiments, exhibits a solution magnetic susceptibility value of peff = 2.5 pB measured by the Evan's method.7 The peff value suggests a Ru(IV) S = 1 spin state. The ^-NMR spectrum of (5) in toluene-c/8 is shown in Figure 6.5 and that of the CHCI2COO analogue, RuIY(TMP)(CHCl2COO)2 (6), in Figure 6.6. Single w-H and o-Me 'H-resonances of the TMP ligand in (5) and (6) are indicative of these species possessing Z)4h symmetry,3'4 and coordination of two acetate ligands would give the observed single w-H and o-Me ^-resonances. The 19F-NMR spectrum of (5) (Figure 6.5 inset) clearly indicates the presence of coordinated CF3COO at 5 25.4. The upfield-shifted /2-pyrrole 'H-resonances at -61.10 for (5) and -63.33 ppm for (6) at -290 K are reminiscent of those of the paramagnetic RuIV(TMP)(X)2 (X = Br4a and Cl4b) complexes. 199 References on p. 235 Chapter 6 Table 6.1. IR absorption frequencies for some Ru(TMP) complexes in the 1000 cm" region. Ru(TMP) species IR Absorption Frequency0 (cm1) Reported Source Run(TMP)(PPh3) 1000* Groves etal.5 Run(TMP)(MeCN)2 1001(1003)* this thesis (Groves et al.5) Run(TPP)(NH2T3u)2 1000 Huang etal.6a Run[(MeO)i2TPP](NH2'Bu)2 c 1004 Huang etal.60 Rura(TMP)(NH3)(Cl) d 1005 this thesis Rum(TMP)(NH3)(Br) d 1004 this thesis RuIV(TMP)(0) 1011* Groves etal.5 Ru^CTMPXO'POz 1010 this thesis RuIV(TMP)(OEt)2 1010(1011) this thesis (Leung et al.6b) Ru^fTMPXCl)/6 1007 this thesis Ru^TMPXMe)/ 1007 this thesis RuIV(TMP)(Ph)2rf 1007 this thesis RuIV(TMP)(CF3COO)2 1011 this thesis Ru^TMPXCHC^COO)/ 1011 this thesis RuIV[(MeO)i2TPP](0)(NH2'Bu) c 1016 Huangef a/.6c RuIV(TPP)(0)(NH2'Bu) 1016 Huang et al.6c RuVI(TMP)(0)2 1019* Groves etal.5 RuVI(TPP)(0)2 1017 Leunge/a/.6a RuVI[(MeO)12TPP](0)2c 1019 Huang etal.6a " IR spectra in this thesis are obtained in Nujol mulls in KBr plates, unless indicated otherwise. IR spectra reported by other workers are in Nujol mulls, unless indicated otherwise. * Solution IR in benzene. 0 (MeO)i2TPP = dianion of /weso-tetra(3,4,5-MeO-phenyl)porphyrin. d These compounds were prepared by Dr. C. S. Alexander (Ref. 4b) of this laboratory. e Prepared by the reaction of (1) with HCl(g). f IR spectrum obtained from a benzene solution, which was dried on a KBr plate, initially containing (1) and added CHCl2COOH (see Section 2.2.3). 200 References on p. 235 Chapter 6 202 References on p. 235 Chapter 6 Ru^TMP) paramagnetic species4 delocalize the spin density to the empty 4e(7i*) orbitals on the porphyrin through Ru(dxz,yz) -> porpfjr*) charge transfer.8 This interaction is reflected in the inverse temperature dependence of the 'H-chemical shifts within the TMP ligand, with the y9-pyrrole ^-resonances within RuIV(TMP) species varying most noticeably with temperature.3'4 The 'H-chemical shifts of the TMP ligand in (5) and (6) vary with inverse temperature (see Figures 6.7 and 6.8), suggestive of a single spin state for (5) and (6) over the observed temperature range. Of interest, the m-H and o-Me ^-resonances are more strongly temperature-dependent, as well as being much more downfield-shifted than those of the analogous RuIV(TMP)(X)2 complexes (X = Cl, Br; Table 6.2). In contrast, the 'H-resonances of the TMP ligand in RuIV(TMP)(OR)2 species (R = C6H5 and *Pr)3 are relatively temperature-insensitive except those for the /^-pyrrole hydrogens. The CO stretching frequencies for the acetate groups within (5) and (6) show that the coordinated acetates have vco values shifted to lower wavenumbers than those of the corresponding free acids. In (5), vCo = 1670 cm"1 with a weaker shoulder at 1709 cm"1, while for the free acid Vco = 1783 cm"1 (Figure 6.9). In (6), Vco = 1648 cm"1 with a weaker shoulder at 1667 cm*1, while for the free acid vco = 1732 cm"1 (Figure 6.10). An acetate ligand is expected to give two vCo absorptions (vc=o and vC-o), and the difference between the two reflects its bonding mode within the complex. For example, the difference between the two vCo absorptions for the free CH3COO" ion is 144 cm'1, and a coordinated CH3COO" is considered to be V-monodentate if the difference between the 203 References on p. 235 Chapter 6 40 Figure 6.7. Inverse temperature plot, 'H-chemical shifts (300 MHz) versus T1 for RuIY(TMP)(CF3COO)2 (5) in toluene-dg (same sample as for Figure 6.5). 204 References on p. 235 Chapter 6 Figure 6.8. Inverse temperature plot, 'H-chemical shifts (300 MHz) versus T1 for RuIY(TMP)(CHCl2COO)2 (6) in toluene-d8 (same sample as for Figure 6.6) 205 References on p. 235 Chapter 6 Table 6.2. Observed variable temperature 'H-NMR chemical shifts" for selected Rurv(TMP)(X)2 species. RuIV(TMP)(X)2 X = Temp. (Kf /2-pyrrole H meta-H* ortho-Mth para-Me Ct* 223.55 -79.75 14.44 4.41 4.71 274.65 -59.35 12.82 3.93 4.19 291.15 -55.42 12.50 3.83 4.07 Brfc 204 -63.29 16.20 5.37 4.93 243 -54.22 14.69 4.84 4.40 303 -43.24 13.15 4.27 3.88 0'Prc 213.15 -13.22 7.79 3.12 3.35 253.15 -12.70 7.69 3.10 3.10 293.15 -11.92 7.59 2.90 2.91 213.15 -45.44 8.13 3.69 3.49 253.15 -36.88 7.87 3.15 3.19 298.15 -29.89 7.60 2.79 2.98 CF3COOe 216.05 -76.44 32.62 10.82 4.93 (5) 236.25 -73.30 27.27 8.92 4.58 256.65 -69.61 23.13 7.55 4.29 277.15 -64.53 21.33 - 4.12 292.45 -61.10 20.25 6.72 4.00 CHCl2COtf 215.95 _ 25.46 8.09 4.67 (6) 236.15 -81.41 22.40 - 4.37 256.15 -74.20 20.77 6.66 4.16 276.25 -67.38 19.55 6.36 4.02 290.45 -63.33 18.79 6.16 3.92 " In toluene-fifo; data acquired on a 300 MHz instrument. b Selected data for X = Br and CI from Ref. 4a and 4b, respectively. c Selected data from Ref. 3 a. d This species is shown in the present thesis work to contain OCoHs axial ligands, rather than/7-OC6H4OH ligands (see Section 6.4.1). e [(5)] = 1.0 x 10"3 M in situ, [CF3COOH] = 1.5 x 10"2 M, in toluene-dg under 1 atm air (see Section 6.2). f [(6)] = 1.0 x 10"3 M in situ, under vacuum without any excess acid (see Section 6.2). * Uncertainty in T = ± 0.5 K. * Single ^-resonance indicates £>4h symmetry for these Ru(TMP) species. 206 References on p. 235 Chapter 6 50 40 % T 30 20 %T 50 40 30 20 10 T V •1 (a) I.' I1 • 1783 cm"' Free CF3COOH i I 1800 1600 1400 1200 1000 800 ^11 ,". ;i .1 ' I 's (b) / t rJ 7 ty / 1709 \ 1670 Coordinated CF3COO A I 1 :'J r .1 V 1011 "Oxidation State Marker" 1800 1600 1400 1200 1000 80cT Wavenumber (cm1) Figure 6.9. Infrared spectra of (a) free CF3COOH and (b) RiT (TMP)(CF3COO)2 (5), obtained as Nujol mulls in KBr plates. 207 References on p. 235 Chapter 6 60 %T 50 40 A i (a) \ ^ 1 iM/ .-1 1732 cm" Free CHCl2COOH 2000 1500 70 65 %T 60 55 (b) Free CHCl2COOH J I 1732 V I I 1667 1648 Coordinated CHCl2COO 1000 .' II! 11 '. II I I ion ' Oxidation State Marker" il ! 2000 1800 1600 1400 1200 1000 800 Wavenumber (cm1) Figure 6.10. Infrared spectra of (a) free CHCl2COOH and (b) RuIV(TMP)(CHCl2COO)2 (6), obtained as Nujol mulls in KBr plates. 208 References on p. 235 Chapter 6 two Vco absorptions is lower than that of the free acetate, and r|2-bidendate if the difference is larger.9 Ru(CH3COO)2(CO)2(PPh3)2, with V-acetate ligands, has vCo absorptions at 1613 and 1315 cm"1, corresponding to a difference of 289 cm"1; RuCl(CH3COO)(CO)(PPh3)2, with one r|2-acetate, has vco absorptions at 1507 and 1465 cm"1, corresponding to a difference of 42 cm"1.9 Hence, a large difference between the two Vco absorptions relative to that of the free acetate is indicative of V-monodentate binding mode for the acetate, and vice versa. Consideration of the steric constraints presented by the TMP ligand and the expected six-coordinate Ru(IV) centre in (5) and (6) imply the presence of r\ ^acetates; however, the IR data for (5) and (6) suggest ri2-acetates, as differences between the vco absorptions (main peak and shoulder) are 39 and 19 cm"1, respectively. Nevertheless, an r|2-binding mode would require both complexes to contain the unlikely, eight-coordinate ruthenium centres. The solution magnetic susceptibility, MS, IR, XH and 19F-NMR data all support the formulation of (5) as RuIV(TMP)(CF3COO)2. The elemental analysis of (5) gives agreeable values for H and N (Section 6.2); however, the extremely low C content, which cannot be explained, is not consistent with solvated acid, solvent or water, or the presence of axial ligands other than CF3COO. The poor elemental analysis is likely due to decomposition of (5) when the excess acid and solvent are removed with heat. Nonetheless, all the spectroscopic data point to the formulation of RuIY(TMP)(X)2 (X = CF3COO and CHCl2COO) for the Ru-porphyrin products from the reactions between (1) and HX acids. 209 References on p. 235 Chapter 6 6.4 Oxidation of Phenol by Ruw(TMP)(0)2 6.4.1 Stoichiometric Oxidation of Phenol The stoichiometric and catalytic oxidations of phosphines (Chapter 3) and alcohols (Chapter 4) have been discussed, and a key step in both systems is believed to involve the disproportionation of RuIV(TMP)(0) to RuVI(TMP)(0)2 (1) and Run(TMP). Also the reaction of RuIV(TMP)(0) and H20 to give RuIV(TMP)(OH)2 (herein referred to as the reaction involving the "conversion to a bis(hydroxo) species"), followed by alcohol metathesis to form RuIY(TMP)(OR)2 species, is implicated from the reaction conditions required for the catalyzed 02-oxidation of alcohols (Chapter 4). That RuIV(TMP)(0) prefers to react via disproportionation or conversion to a bis(hydroxo) species, rather than acting as an O-atom transfer agent is suggested in both the phosphine and alcohol systems; therefore, the initially proposed phenol oxidation mechanism (Eqs. 6.2 to 6.4)3 was re examined in this thesis work. In fact, experimental results now disfavour the successive two-step oxidation mechanism presented in Eqs. 6.2 to 6.4. Previous work in this laboratory showed that the reaction between (1) and phenol under 1 atm air gives 1 equivalent of a paramagnetic RuIV(TMP) species, tentatively formulated from ^-NMR data as Ru^TMP^-OCeF^OH);, (4), 0.5 equivalent of p-benzoquinone and 1.3 equivalents of H20 [Eq. 6.7, Ru = Ru(TMP)];3 however, the expected reaction stoichiometry according to the proposed mechanism (Eqs. 6.2 to 6.4) is shown in Eq. 6.8. Ru^Oh + xs C6H5OH -SIT.. Ru"'(p-OC6H40H)2 + 0.5 /?-OC6H40 + 1.3 H20 (6.7) (!) <*) t. (1) + 2 C6H5OH + \o2 (4) + H20 (6.8) 210 References on p. 235 Chapter 6 The successive two-step oxidation mechanism (Eqs. 6.2 to 6.4) can account for the formation of the suggested Ru-porphyrin product (4), but cannot adequately explain the formation of the /?-benzoquinone. Moreover, the data from the present thesis work, particularly the mass spectrum of (4) (Figure 6.11), show it to contain axial OCeH5, rather than /^-OCeFLjOH, ligands, and thus (4) is more favourably formulated as RuIV(TMP)(OC6H5)2. In addition, the metathesis reaction between RuJV(TMP)(0'Pr)2 and phenol (50-fold excess) in benzene-^ under 1 atm Ar gives a product with an in situ 1H-NMR spectrum identical to that obtained for isolated (4).* A small amount of product assignable to Rurv(TMP)(p-OC6H4OH)2 is formed from the metathesis reaction between p-hydroquinone (1.5 x 10"3 M) and RuIV(TMP)(0'Pr)2 (1 x 10"3 M) in benzene-</6; the *H-chemical shifts (/?-pyrrole-H, -34.7; o-Me, 2.99; p-Me, 3.04; m-U, 7.55; axial ligand, 14.4, -21.6, -23.8) (Figure 6.12) of the new compound are distinctively different from those of (4)} Hence, (4) is now considered to be Rurv(TMP)(OC6H5)2. Of note, the preliminary work carried out in this laboratory33 included the attempted purification of (4) by column chromatography, and the isolated compound gave elemental analysis data (C, 74.55; H,5.63; N, 5.11; 0, 5.40) which agreed with those calculated for Ru^TMP)^-OC6H40H)2 (C68H62N4RUO4; C, 74.22; H, 5.67; N, 5.09; 0,5.82); those calculated for RuIY(TMP)(OC6H5)2 (CegHedS^uOz) are: C, 76.45; H, 5.85; N, 5.24; O, 3.00. f 1H-NMRdatafor(4)inbenzene-rf6: >3-pyrrole-H, -30.5; m-H, 7.60; o-Me, 2.90; p-Me, 3.00; axial ligand, 49.7, -68.2, -71.9 (Chapter 4, Table 4.1). t Of note, almost no p-hydroquinone is detected (Fig. 6.12), but some p-benzoquinone and (1) can be seen. /?-Hydroquinone is likely oxidized by (1), which can be reformed from the reaction of RuIY(TMP)(0'Pr)2 with H20 (Chapter 4). Although the metathesis reaction is not complete, the 'H-signals assignable to RuIY(TMP)(p-OC6H4OH)2 clearly show that (4) is not the bis(hydroquinoxo) species. 211 References on p. 235 Chapter 6 A o 5\ t8 5?V EC U • O . 1 8 L8 5x-J-3 © 11..i|i• i Mi• • 111• M• • • • •'• I |• • • • |• • • • I 8 1 t | ,\ 8" 8 8 8 R 8 8 ! 8 8 2 ot8 8 8 R 8 8 ? 8 8 2 »* E 3 3 > v 0> c o <U on 2 c £ S - ° o ^ X « H. § a o D. B <u +-» s o o c o N •a o o G &> J3 03 6 to O <U > io.j a-*5 —i " H 2 vo v u 3 M) 212 References on p. 235 Chapter > o •8 tu o o o © e CL & u 5 o o r-' p 00 oo .2 •a o 3 << j- oj H T3 ffi SB fS s en 213 References on p. 235 Chapter 6 In the present thesis work, attempts to purifry (4) by the reported column chromatography procedure33 were unsuccessful in removing the />-benzoquinone product, and hence, elemental analysis was not obtained for (4); however, the 'H-NMR data, the metathesis reaction and the mass spectral data all suggest (4) to be the bis(phenoxo) complex. The good elemental analysis determined for the supposed RuIV(TMP)(p-OC6H40H)2, particularly the oxygen content, was probably fortuitous, and might have resulted from /7-benzoquinone impurity; the compound could have been RuIY(TMP)(OC6H5)2,2H20, which would give an elemental analysis (C68H66N4RUO4; C, 73.96; H, 6.02; N, 5.07; O, 5.79) equally agreeable with that reported earlier.33 The phenol oxidation mechanism needs to be reconsidered to account for the formation of the bis(phenoxo) species (4), as well as the production of /?-benzoquinone. The observed /?-benzoquinone is undoubtly formed via the oxidation of p-hydroquinone, which is initially produced from the oxidation of phenol by (1) via reaction 6.2. That (1) oxidizes, in fact catalytically under O2, />-hydroquinone to p-benzoquinone in benzene is demonstrated in separate experiments. Under 1 atm O2 with fc-hydroquinone] = 1.5 x 10"3 M and [(1)] = 5.5 x 10"5 M, 8 equivalents of p-benzoquinone were produced in 20 min (0.4 turnover min"1). Under 1 atm O2 with [>-hydroquinone] = 1.5 x 10"3 M and [(1)] = 5.5 x 10"6 M, 200 equivalents of /?-benzoquinone were produced when the benzene solution was analyzed by GC after 22 h. Of note, no noticeable continuation of the catalysis was observed in the solution after 22 h, possibly due to the deactivation or decomposition of (1) via some unknown pathway. Species (1) clearly catalyzed the 02-oxidation of/j-hydroquinone, as no 214 References on p. 235 Chapter 6 /?-benzoquinone was formed in the absence of (1) under corresponding conditions. The C»2-oxidation of /?-hydroquinone catalyzed by (1) is likely initiated by the reaction represented in Eq. 6.9 [Ru = Ru(TMP)], and RuIV(TMP)(0) can then regenerate (1) via disproportionation (Chapters 3 and 4). ^^(0)2 + P-HOC6H4OH - Ru™(0) + /J-OC6H4O + H20 (6.9) The reaction between (1) andp-hydroquinone (-1:2 ratio) under 1 atm air at room temperature was monitored by XH-NMR spectroscopy, and after approximately 2 min, the spectrum showed that mainly (1) was present (Figure 6.13). RuIV(TMP)(0) and a Ru(II) species, possibly Run(TMP)0-HOC6H40H)2 (~ 10%),f can also be detected. At this time no free /?-hydroquinone was present in the benzene-^ solution, implying that the oxidation of hydroquinone by (1) is rapid; furthermore, the - 90% reconversion to (1) suggests that the disproportionation of RuIV(TMP)(0) [and the aerobic oxidation of the Ru(II) species to (1)] is also fast (Chapter 3). No special precautions were taken to dry the benzene-ok solvent, and as such the H20 stoichiometry in Eq. 6.9 cannot be determined, although 1 equivalent of H20 is expected to be present by mass balance. The mechanism for the stoichiometric oxidation of /»-hydroquinone by (1) cannot be determined from the current preliminary data; a hydride transfer mechanism analogous to that suggested for the alcohol oxidation (Chapter 4) is plausible, although two successive one-electron transfer/deprotonation steps can equally apply. f A /J-pyrrole-H signal at 8.5 ppm shows that a Run(TMP) species is present in solution; however, the 'H-NMR data (Ref. 3a) for a Run(TMP) species proposed as the bis^-HOCeKtOH) complex are different: y8^pyrrole-H, 8.64; o-Me, 2.50; p-Me, 1.70. As only the ^pyrrole signal at 8.5 ppm can be clearly observed, and the other signals are presumably buried beneath those of (1), the identity of the Run(TMP) species is unclear. After 10 min, only (1) and p-benzoquinone are present. 215 References on p. 235 Chapter 6 216 References on p. 235 Chapter 6 The production of 0.5 equivalent of/^-benzoquinone, which cannot be explained by the scheme in Eqs. 6.2 to 6.4, provides a key insight into the phenol oxidation mechanism. The /?-benzoquinone was observed by both 'H-NMR spectroscopy3* and in this thesis work by gas chromatography experiments ([(1)] = 2.0 x 10"3 M and [phenol] = 5 and 8-fold excesses in the respective studies). Attempts to detect the intermediate /7-hydroquinone by GC analysis were unsuccessful. The ti/2 value for the reaction between phenol and (1) under NMR experimental conditions (~ 10"2 M and 10*3 M, respectively) is approximately 16 min (estimated from kobs = 0.069 IVrV1 X 0.01 M = 0.00069 s"1),3 while the ti/2 value for the reaction between /?-hydroquinone (~ 10'3 M) and (1) is approximately 0.1 min (a rough estimate of ti/2 of - 0.08 min is made using 5 ti/2 = 1 turnover = 0.4 min). That no /?-hydroquinone is detected by GC is certainly a consequence of the faster reaction of (1) with /?-hydroquinone than with phenol, and any /?-hydroquinone produced from the initial oxidation of phenol will be oxidized at a faster rate by any species (1) that remains in solution. In essence (1), a 2-electron oxidant, oxidizes phenol to p-benzoquinone via the /?-hydroquinone intermediate, which is a 4-electron process; this explains the formation of 0.5 equivalent of/?-benzoquinone for every equivalent of (1). A proposed mechanism for the oxidation of phenol involving the RuIV(TMP)(0)/RuIV(TMP)(OH)2 interconversion, the chemistry of which is consistent within that of the Ru(TMP)/alcohol systems (Chapter 4), is outlined in Figure 6.14; 217 References on p. 235 Chapter 6 Figure 6.14. Phenol oxidation mechanism based on the reversible interconversion of RuIV(TMP)(0) to a bis(hydroxo) species and phenol metathesis reactions. The reaction of (1) and phenol produces /?-hydroquinone, which is further oxidized to /^-benzoquinone at a faster rate compared to the rate of the phenol oxidation. Disproportionation of RuIV(TMP)(0) to (1) and Run(TMP) is a competing pathway, and under anaerobic conditions, some Ru(II)-species can be detected (see text). 218 References on p. 235 Chapter 6 according to the scheme, the overall reaction should produce 0.5 equivalent ofp-benzoquinone and 1.5 equivalents of H20 [Eq. 6.10; Ru = Ru(TMP)]. The stoichiometry of reaction 6.10 closely accounts for the experimentally observed 0.5 quinone and 1.3 H20.3 ^(0)2 (1) + | C6H5OH /fci^OCsH^ + \ p-OCsFLO +1 H20 (6.10) A Ru-porphyrin species formulated from ^-NMR data as Run(Tlvff )(p-HOC6H40H)2 (3) has been observed in the reaction between (1) and excess phenol under anaerobic conditions;33 however, (3) only accounted for ~ 40% of the reaction products, with the other -60% being (4). The large percentage of (4) was explained within the successive two-step oxidation mechanism (Eqs. 6.2 to 6.4), with * trace 02 being the cause for the formation of (4).3A This is now considered unlikely considering that the concentration of (1) was 4 x 10"3 M,3a and even with only one freeze-pump-thaw cycle the system should not have contained enough dissolved 02 to give rise to the large amount of observed (4). Furthermore, the fact that (4) is the bis(phenoxo) complex, not the bis(p-hydroquinoxo) complex as proposed initially, invalidates the above "trace 02" explanation. The reaction of (1) and phenol under anaerobic conditions was repeated in this thesis work, and the formation of (4) was always observed in excess of 90%, with (3) accounting for < 10% of the inorganic products. That (4) is produced even in the absence of 02 is inconsistent with the formerly suggested mechanism (Eqs. 6.2 to 6.4). The production of (4) via the bis(hydroxo) species, within the present mechanism (Figure 6.14), is expected to occur if H20 is present, and to inhibit the conversion to the bis(hydroxo) species is impossible, as the 219 References on p. 235 Chapter 6 oxidation reaction produces H20. Even under initially dry conditions, the conversion to the bis(hydroxo) species can occur once some FJ20 forms, and subsequently (4) is produced via the metathesis reaction with RuIV(TMP)(OH)2. Under anaerobic conditions, the disproportionation of 2 RuIV(TMP)(0) to (1) and Run(TMP), followed by ligation of p-hydroquinone and/or phenol to the Ru(II) centre provides a plausible explanation to account for the formation of the Ru(II) species (3). As the disporportionation pathway accounts for < 10% of the loss of RuIV(TMP)(0) (see above), its contribution to the reformation of (1) is insignificant; therefore, disproportionation is not considered to be one of the main reactions followed by the kinetics monitored for the loss of (1) (see Section 6.4.2) 6.4.2 Kinetic Studies When (1) (4 x 10"3 M) reacted with phenol (2 x 10"2 M) in benzene-<i6 under 1 atm air or 02, no other intermediates were observed in the !H-NMR spectrum of the solution en route to the product (4).3a The kinetic data in the present thesis work for the stoichiometric oxidation of phenol by (1) under 1 atm air at various temperatures are shown in Figure 6.15. The reaction is first-order in (1), as demonstrated by a linear semilog plot (inset of Figure 6.2); this first-order dependence is also confirmed, as the same kobs values are obtained with varying amounts of initial (1) at the same [phenol] value of 0.0381 M (see Figure 6.16 and Appendix F). The kinetic data are independent of 02 partial pressure, as kinetics obtained under 1 atm 02 or air were identical. Also, purging the solutions with N2 for 10 min did not affect the kinetics (Appendix F). 220 References on p. 235 Chapter 6 0.90 T [phenol] (M) Figure 6.15. Plots of kobs versus [phenol] for the oxidation of phenol by RuVI(TMP)(0)2 (1) in benzene under 1 atm air at various temperatures. [(1)] ~ IO"6 M. kobs values are tabulated in Appendix F. Kinetic data were obtained on a stopped-flow spectrophotometer. i+ Stopped-flow data [phenol] (M) Figure 6.16. Plot of kobs versus [phenol] for the oxidation of phenol by RuVI(TMP)(0)2 in benzene at 20.0 °C under 1 atm air, except for the point labelled "1 atm 02". [(1)] ~ IO"6 M. The raw data are listed in Appendix F. Kinetic data were obtained on the HP 8452A Diode-Array instrument, except for the point indicated as "Stopped-flow data". 221 References on p. 235 Chapter 6 The non-linearity in the plots of kobs versus [phenol] can be seen readily, illustrating a non-first-order dependence in phenol. Earlier preliminary work in this laboratory was carried out at a lower [phenol] region (up to 0.14 M) and less data were obtained.3 The kinetic experiments were repeated in this thesis work at the lower [phenol] region (see Figure 6.16), and while the kobs values obtained at [phenol] = 0.0381 M agreed reasonably well with that obtained in the preliminary work, the other data from the earlier work clearly do not agree with those obtained in the present studies. This reason for this non-agreement is not known, but only the new curved-dependence data will be considered in the following discussion. The log(kobs) versus log[phenol] plots are linear with slopes averaging 1.51 ± 0.09 (Figure 6.17), which suggest a 3/2 order dependence in phenol. A log-log plot is generally somewhat misleading, as a reaction with kobs going from 1st- to 2nd-order kinetics with increasing added reagent (cf. Figure 6.15) might exhibit an average apparent order of 3/2; however, the plot for the data at 20 °C (Figure 6.17) is linear over 2 orders of magnitude of [phenol] values. The linearity of a log-log plot for a 1st- to 2nd-order dependence system is unlikely to extend over such a large concentration range (0.01 to 1.0 M), and hence the kobs expression may indeed take the form kobs= A.[phenol]3/2 (see Table 6.3). The curvature in the kobs versus [phenol] plots could possibly be ascribed to "solvent effects", as the [phenol] corresponds to ~ 10% mole fraction for the case of the highest concentration used; however, the curvature is considered to be real as the non-linearity starts at [phenol] values as low as ~ 0.04 M for the data at 20 °C. 222 References on p. 235 Chapter 6 Table 6.3. Values for the parameter A for the oxidation of phenol by (1), derived from the expression kobs = A.[phenol]3/2. The activation energy, AE*, is also calculated from the values of A from the Arrhenius plot (Figure 6.18). Temperature A (lvr3V) 10.2 °C 0.362 ±0.03 15.0 °C 0.425 + 0.03 20.0 °C 0.583 ±0.04 30.5 °C 0.98 ±0.07 AE* = 39 ± 2 kJ mol"1 precollision factor" = (5.1 ± 0.3) x 106 s"1 Calculated at every temperature and then averaged. 223 References on p. 235 Chapter 6 0.0033 1 ln(A) 0.0034 T 0.0035 1 0.2 --0 ---0.2 --T1 -0.4 - -<Kl>-0.6--0.8 ---1 ---1.2 --Figure 6.18. Arrhenius plot, ln(A) versus T"1, for the parameter A for the reaction between (1) and phenol. The values for A are listed in Table 6.3. According to the mechanism proposed in Figure 6.14, the following reaction pathways [Eqs. 6.11 to 6.15; ^i#=Ru(TMP)] are expected to play a role in the rate law for the phenol oxidation reaction. Rum(0)2 + C6H5OH -A* ^Miy(O)0?-HOC6H4OH) (6.11) k2 /?«IV(0)(p-HOC6H40H) ===gj-== Rul\0) + p-HOCeFLOH ^(0)2 + /7-HOC6H40H Ruw(0) + /?-OC6H40 + H20 Ruw(0) + H20 =^ Ru™(OH)2 +C6H5OH/-H20 /?KIV(OH)2 /?«IV(OH)(OC6H5) +C6H5QH ^11^(006^)2 C6H5OH/+H20 -H20 (6.12) (6.13) (6.14) (6.15) The [(1)] values were ~ 10"3 M in 'H-NMR and GC studies (see earlier, Section 6.4.1), and the oxidation by (1) of the /?-hydroquinone formed (~ 10'3 M) was shown to be 224 References on p. 235 Chapter 6 faster than that of phenol (~10"2M). In the kinetic studies, the [(1)] values were three orders of magnitude lower (-10"6 M), while [phenol] values were higher (0.01 to 1 M); therefore, the rate of oxidation of the /7-hydroquinone formed (~ 10"6 M) might not have been faster than that of phenol. In addition, the reversible coordination and recoordination reactions of/?-hydroquinone (Eq. 6.12) may contribute to the overall rate law, as similar reactions with OPPh3 are found to be significant within the phosphine systems (Chapter 3). Clearly, more work is necessary to arrive at a rate law which can accommodate the experimental data, namely the curvature in the kobs versus [phenol] plots. The Arrhenius plot (Figure 6.18) for the parameter A gives an activation energy, AE*, of 39 ± 2 kJ moi"1 and a precollision factor of (5.1 ± 0.3) x 106 s"1. The paramter A is presumably comprised of various rate constants and equilibrium constants for the reaction pathways (Eqs. 6.11 to 6.15), but they are still useful for indicating the general ease of the phenol oxidation reaction. The AE1 value is similar to the AH* value of 45 kJ moi"1 (which corresponds to AE* ~ 48 kJ moi"1) for the 'PrOH oxidation by (1) (Chapter 4), implying perhaps that cleavage of the aromatic C-H bond requires approximately the same energy as that for the a-C-H bond in 'PrOH. 6.5 02-Oxidation of Av\-Dimethylaniline Catalyzed by Ru^TMPKO^ Following the oxidation of phenol, other mono-substituted aromatics (N,N-dimethylaniline, methoxybenzene, toluene, chlorobenzene, bromobenzene and nitrobenzene) were tested as potential substrates. Only A^,A/-dimethylaniline, which contains the electron releasing NMe2 group, was oxidized by (1). Under 1 atm air the 225 References on p. 235 Chapter 6 oxidation of A/,A/-dimethylaniline is catalytic, producing a hydroxy-A^-dimethylaniline, as shown by GC-MS analysis (Appendix G), and the oxidation presumably occurs at the para position based on analogy with the phenol system (Section 6.4.1). Figure 6.19 shows the proposed scheme for the oxidation reaction. Ru^TMP)(0)2 (1) ^^-NMe2 | ^HO RuIV(TMP)(0) NMe2 H2O (2a) + H2O Ru™(TMP)(OH)2 ^ " Ru^(TMP)(0-(f~yNMe2)2 +2H2O \=/ (4a) + 2N Ru^TMP) — 2N - Run(TMP)(N)2 (7) N = X-^Qr-NMQ2, where X = OH and/or H d denotes a disproportionation reaction Figure 6.19. Proposed scheme for the oxidation of A^JV-dimethylaniline catalyzed by RuYI(TMP)(0)2 (1) under 1 atm air. Trace H20 was present, as the benzene-d6 was not dried; in any case FJ20 is generated during formation of (4a) from (1). 226 References on p. 235 Chapter 6 Figure 6.20 shows the 'H-NMR spectra recorded on monitoring the reaction between (1) and Af-dimethylaniline (1:4) in benzene-fife under 1 atm air. After 1 min, Ru^TMPXO) was not detected, but 'H-resonances for the TMP ligand characteristic of those within a bis(alkoxo)-Ru(IV) species, (4a), were seen (o-Me, 2.99; p-Me, 2.90; m-H 7.60; yS-pyrrole-H, -22 ppm) (see Chapter 4, Table 4.1), and these are assigned to Rutv(TMP)(/?-OC6H4NMe2)2. Of note, the axial /?-OC6H4NMe2 ligand protons within (4a) are not detected by 'H-NMR spectroscopy, while those of the OCeHs ligands within the analogous complex (4) (Table 4.1) are clearly detectable. The reason for the non-detection of the /7-OC6H4NMe2 ligands is not substantiated; however, one factor for the non-detection of the alkoxo ligand protons by 'H-NMR spectroscopy can be the rapid exchange of the alkoxo ligands with excess alcohol in solution (Section 4.3.1). The amount of species (4a) increases over time (Figure 6.20) and, unlike in the reaction between (1) and phenol, 'H-NMR signals corresponding to Ru(II) species (7) and a Ru(TMP)(CO) species (D) were observed as well after 30 min. After a total of 60 min, the benzene-fife solvent was removed under vacuum, and the solid residue was analyzed by mass spectrometry (Figure 6.3). Species (7) is thought to be a mixture of Run(TMP)(p-NMe2C6H4X)2 species (where X = H or OH). The mass spectral data in Figure 6.3 suggest that Ru(TMP) species containing either one NMe2C6H5 or one /?-NMe2C6H40H ligand are present, with mass peaks at 1003 and 1019 amu, respectively. In solution, (7) is likely a six-coordinate, bis(amine)ruthenium(II) species, rather than the five-coordinate complex suggested from the mass spectra. The sixth ligand is perhaps labile and readily dissociates when (7) is 227 References on p. 235 Chapter 6 benzene 4a N // 4a 1 minute 4a 4a N 5 minutes Legend: Ru = Ru(TMP) N =NMe2C6H5 1 =^(0)2 4a = RuIV(p-OC6H4NMe2)2 7 =Rjjn(N)2 D = "Run(C0)" see text U = Organic product 1 accompanying the formation of D Porphyrin 'H-resonances at 25 °C ppm 4a 7 D -22 8.30 8.36 8.66 Hn 7.60 - -2.99 2.18 2.08 1.88 1.85 1.67 Me,, 2.90 - 2.41 4a 4a 4a i 30 minutes 11.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 -22.0 ppm Figure 6.20. JH-NMR (200 MHz) spectra for the reaction "RuVI(TMP)(0)2 + 4 A^iV-dimethylaniline" in benzene-fife at 25 °C under 1 atm air. [(1)] = 2.0 x 10"3 M. 228 References on p. 235 Chapter 6 I benzene 1 minute N N • I • ' ' • I 1 9.0 8.0 . I i i i i 1 i • ' • I 7.0 6.0 S.O 4.0 PPM benzene J 3.0 2.0 N 10 minutes N 2a 2a u • i • 1.0 2a(p-pyrrole-H) ' I 1 ' ' ' 1 ' 9.0 8.0 1 I • 1 ' • I 7.0 6.0 5.0 PPM ' I 1 ' ' ' I 1 ' ' ' 1 1 ' ' • 1 I ' 1 4.0 3.0 2.0 -6.0 -8.0 benzene N 20 minutes N 2a 4a • i • • ' • i • • ' • i » • • • i • • • ' i v • • • i • • • • i • ' • • i • t.O •.0 7.0 6.0 S.S 4.0 S.O (.0 2a(P-pynole-H) i i"" -o.o -a.o Figure 6.21. 'H-NMR (200 MHz) spectra monitoring the reaction "RuVI(TMP)(0)2 + 10 tyN-dimethylaniline" in benzene-* at 25 °C under 1 atm argon. [(1)] = 1.0 x 10"3 M. Refer to the legend in Fig. 6.20 for the identities of the observed Ru(TMP) species. 2a = RuIV(TMP)(0). 229 References on p. 235 Chapter 6 ionized by the fast atom bombardment ionization method in the MS experiment. In a separate experiment, Run(TMP)(MeCN)2 was added to a benzene-ak solution containing excess AfN-dimethylaniline (aniline:Ru = 10:1), and ^-resonances corresponding to a new Ru(II) species were assumed to be those of Run(TMP)(HMe2C6H5)2 (yS-pyrrole-H, 8.34; o-Me, 2.05; p-Me, 2.45 ppm; axial ligand protons were not observed, presumably due to rapid exchange of the ligands with free A/,7V-dimethylaniline); the data support the suggestion of (7) (/"-pyrrole-FL ~ 8.3 ppm; see Figure 6.20) as species containing coordinated NMe2C6H5 and/or />-NMe2C6H40H ligands. The 'H-NMR data for (7) in Figure 6.20 (at 30 min) show more than one set of o-Me "H-resonances, which can result from three different coordination environments about the Ru(II) centre where two dimethylaniline, one hydroxy-dimethylaniline and one dimethylaniline, and two hydroxy-dimethylaniline, ligands are present, respectively. The solid residue that had been subjected to mass analysis was also analyzed by IR spectroscopy, and a band at 1942 cm"1 is assignable to a Run(TMP)(CO) species (D) (vco = 1943 cm"1, Chapter 2); however, the ^-NMR signals assignable to (D) in Figure 6.20 do not correspond well (except for the yS-pyrrole ^-signal) to those of Run(TMP)(CO) itself (/i-pyrrole-H, 8.79; o-Me, 2.20, 1.83; p-Me, 2.48 ppm; Chapter 2). Nonetheless, the mass spectrum (Figure 6.3) of the solid sample, which also contains (D), shows a mass peak centred around 912 amu, consistent with the presence of a Run(TMP)(CO) species (MW = 910 g moi"1). Accompanying the formation of (D) is an organic product (U), which exhibits ^-NMR signals in the 5.5 to 6 ppm region (Figure 6.20). The identities of (D) and (U) are not known. 230 References on p. 235 Chapter 6 Of note, the reaction between (1) and N-dimethylaniline under 1 atm Ar, unlike the reaction under 1 atm air, produced some RuIV(TMP)(0) after 10 min; Ru^TMP)^-OCeH4NMe2)2 (4a) was not observed at this time, and was only seen after about 20 min (Figure 6.21). Also, the 'H-resonance at 8.66 ppm attributable to the ^-pyrrole-H of the TMP ligand within (D) was observed after 20 min. Unlike the reaction under 1 atm air, the reaction under Ar, after ~ 40 min, showed decomposition of the Ru-porphyrin species in the benzene-afe solution, as suggested by the disappearance of the characteristic TMP ^-NMR signals for all the species in solution. The natures of the Run(TMP)(CO) formation and Ru(TMP) decomposition reactions are not known. The 'H-NMR spectra (Figure 6.21) for the reaction under Ar showed that RuIV(TMP)(0) was first detected, followed by (4a). For the reaction under air (Figure 6.20), 'Ff -resonances corresponding to (7) appear after those for (4a). This chronological order in which the Ru-porphyrin species are detected supports the mechanism presented in Figure 6.19. Of note, the formation of the Ru(II) species (7) (Figure 6.20) provides a potential pathway for regenerating RuVI(TMP)(0)2 under air or O2, the criterion being that the axial aniline ligands are labile. Indeed, the oxidation of NMe2C6H5 to /?-NMe2C6H40H by (1) is catalytic in air, although only marginally with less than 10 total turnovers (Table 6.4). Of note, the oxidation of phenol to p-hydroquinone by (1) is not catalytic, as the product RuIY(TMP)(OC6H5)2 (4) does not regenerate (1) under air in wet benzene. 231 References on p. 235 Chapter 6 Table 6.4. Aerobic oxidation of N, N-dimethylarriline catalyzed by Ru (TMP)(0)2 (1) under 1 atm air in benzene. Reaction Conditions Time (hours) % conversion to /»-hydroxy-A^A^-dimethylaniline* [total turnovers] 24 °C [(l)] = 3.3xlO"3M [aniline] = 0.0158 M H20 added" 28.5 47% [2.5] [(l)] = 3.3xl0"3M [aniline] = 0.0316 M H20 added" 29.0 33% [3.1] [(I)] = 3.3xl0-3M [aniline] = 0.0316 M NO H20 added" 29.0 19.7% [2.1] 50 °C [(1)] = 7.4 x IO-4 M [aniline] = 0.0316 M H20 added" 18.0 12.7% [5.4] [(l)] = 3.0x lO^M [aniline] = 0.0316 M H20 added" 18.5 36.5 8.4% [9.1] 8.8% [9.4] [(I)] = 7.4xl0-4M [aniline] = 0.0631 M H20 added" 18.5 8.6% [7.3] [(l)] = 7.4x lO^M [aniline] = 0.126 M H20 added" 18.5 4.9% [8.4] " 50 u.L H20 was added to 0.50 mL benzene solutions, otherwise benzene (HPLC grade) was used directly. * An hydroxy-AA,A/-dimethylaniline is suggested from GCMS analysis (Appendix G), and incorporation of the O-atom at the para position is based on analogy with the phenol system (see text). 232 References on p. 235 Chapter 6 6.6 Conclusions A reaction between RuYI(TMP)(0)2 (1) and strong organic acids (CF3COOH, CHCI2COOH) was discovered and the Ru products are bis(acetato)ruthenium(IV) type species. Such reactions are of interest because acids have been observed to enhance the reactivity within systems used for the stoichiometric and catalytic hydroxylation of alkanes.1'2 The oxidation product from the reaction between (1) and HX, when identified, will reveal the nature of the reaction. The preliminary study conducted earlier in this laboratory on the oxidation of phenol3 by (1) was re-examined in this thesis. A new mechanism is proposed consistent with the oxidation chemistry of (1) discovered within the phosphine and alcohol systems (Chapters 3 and 4); RuIV(TMP)(0) is no longer considered to be an active oxidant. Rather, a RuIV(TMP)(0)/RuIV(TMP)(OH)2 interconversion, and disproportionation of 2 equivalents of RuIV(TMP)(0) to Run(TMP) and RuVI(TMP)(0)2, are considered to be the significant reaction pathways for Ruw(TMP)(0). Kinetic studies for the phenol system reveal a non-first-order (between first and second) dependence on the phenol, which cannot be satisfactorily accommodated within the formerly successive two-step oxidation3 or the current single O-atom oxidation and RuIV(TMP)(0)/RuIV(TMP)(OH)2 interconversion mechanisms. Preliminary work on the oxidation of AyV-dimethylaniline suggests the process to be similar to the phenol oxidation. GC-MS analysis suggests the product from the oxidation reaction to be a hydroxy-N, N-dimethylaniline; a larger scale reaction should be carried out so that the organic product could be isolated and its identity confirmed. Unlike the phenol system, the A^A'-dimethylaniline system is catalytic (< 10 233 References on p. 235 Chapter 6 total turnovers) under 1 atm air in benzene; however, the catalytic activity of (1) is lost, involving decomposition of Ru(TMP) species and formation of a Run(TMP)(CO) species, of which the natures are unknown at this time. 234 References on p. 235 Chapter 6 References 1 T.-C. Lau and C.-K. Mak, J. Chem. Soc, Chem. Commun., 766 (1993); 943 (1995). 2 a) H. Ohtake, T. Higuchi and M. Hirobe, Heterocycles, 40, 867 (1995). b) H. Ohtake, T. Higuchi and M. Hirobe, J. Am. Chem. Soc, 114, 10660 (1992). 3 a) N. Rajapakse, Ph.D. Dissertation, University of British Columbia, 1990. b) N. Rajapakse, B. R. James and D. Dolphin, Stud. Surf. Sci. Catal, 55, 109 (1990). 4 a) C. Sishta, Ph.D. Disseratation, University of British Columbia, 1990. b) C. S. Alexander, Ph.D. Dissertation, University of British Columbia, 1995. 5 J. T. Groves and K.-H. Ahn, Inorg. Chem., 26, 3833 (1987). 6 a) W. H. Leung and C.-M. Che, J. Am. Chem. Soc, 111, 8812 (1989). b) W.-H. Leung, C.-M. Che, C.-H. Yeung and C.-K. Poon, Polyhedron, 12, 2331 (1993). c) J.-S. Huang, C.-M. Che and C.-K. Poon, J. Chem. Soc, Chem. Commun., 161 (1992). 7 a) D. F. Evans, J. Chem. Soc, 2003 (1959). b) D. H. Live and S. I. Chan, Anal. Chem., 42, 791 (1970). 8 G. N. La Mar and F. A. Walker, in The Porphyrins, ed. D. Dolphin, Volume 4, Academic Press, New York, Chapter 2, 1979. 9 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 3rd Ed., John Wiley and Sons, Toronto, 1978, p. 232. 235 References on p. 235 Chapter 7 Conclusion and Recommendations for Future Work 236 Chapter 7 7.1 General Conclusions The stoichiometric and catalytic 02-oxidations of a variety of organic substrates (phosphines, alcohols, alkenes and alkanes) effected by fra«5-RuYI(porp)(0)2 species (porp = TMP, TDCPP and TDCPP-Cl8)t were presented in the preceding chapters. The preparation of the Ru(TDCPP-Clg) species was a collaborative joint effort with Xie from Dolphin's group. The kinetic data for the oxidation of EAr3 substrates (E = P, As, Sb) by RuVI(TMP)(0)2 (1) in benzene reveal a characteristic two-phase reaction, with the faster stage occurring on a timescale ~ 10'2 s and the slower ~ 101 s. The faster reaction is considered to be an O-atom transfer involving the electrophilic attack of a Ru=0 moiety of (1) on the lone pair of electrons on the E-atom, to form initially RuIY(TMP)(0)(OEAr3). A plot of AHi* (but not logr* ) for the O-atom transfer versus the Hammett factor CT was close to linear, suggesting that a more electron-withdrawing para substituent gives a more favourable, lower value AHi*. The ASi* values for the O-atom transfer reactions correlate with the substrate molecular masses, with bulkier substrates giving more favourable, less negative ASi* values, an indication that the O-atom transfers occur via strong Ru=0 vibrational coupling. The slower stage of the reaction of (1) with EAr3 is thought to involve the dissociation of OEAr3 from RuIV(TMP)(0)(OEAr3) to form RuIV(TMP)(0), which then disproportionates to (1) and Run(TMP); EAr3 readily coordinates to the latter species to form the 5-coordinate + TMP, TDCPP and TDCPP-C18 = dianions of mero-tetramesityl, /nero-tetta(2,6-dicMorophenyl) porphyrins and meTO-tetra(2,6-cuchlorophenyl)-y3K)ctachloroporphyrin, respectively. 237 Chapter 7 Run(TMP)(EAr3) product. The oxidation of EAr3 becomes catalytic under air or O2, and preliminary data show that the catalysis is slow compared to the stoichiometric reaction; approximately 1 turnover h"1 is obtained for the PPh3 system at ambient conditions. The paramagnetic Ru(IV) species formed from the reaction of (1) with 'PrOH was formulated as RuIY(TMP)(OH)2 in previous preliminary work in this laboratory; it is now reformulated as RuIV(TMP)(0'Pr)2 from crystallographic and spectroscopic studies in the present thesis work. The oxidation of the alcohol is proposed to involve an initial cleavage of the a-C-H with transfer of a hydride to a Ru=0 moiety. The oxidation of 'PrOH to acetone by (1), under air in wet benzene, is catalytic, and (1) can also oxidize benzyl alcohol to benzaldehyde (without further oxidation to benzoic acid); in a benzene/3.0 M aq. KOH 2-phase system, 2000 equivalents of benzaldehyde are produced in ~ 13 d at 50 °C. Species (1) can also oxidize Ph3CH to Ph3COH catalytically under air. RuVI(TDCPP)(0)2 is slightly more reactive and can also oxidize adamantane to 1-adamantanol, although both systems give only a few total turnovers. That these dioxo complexes use solely 02 as the oxidant for these alkane systems demonstrates some remarkable chemistry. For the first time, Ru(TDCPP-Clg) species are prepared and used as catalyst precursors for the 02-oxidation of alcohols, alkenes and alkanes. The oxidation of benzyl alcohol catalyzed by RuVI(TDCPP-Clg)(0)2 is about as effective as that by (1) under corresponding conditions, and the mechanism is presumably the same. The oxidations of neat cyclohexene, cz's-cyclooctene and methylcyclohexane operate via free-radical 238 Chapter 7 pathways to give turnovers of ~ 105, probably based on hydroperoxide formation and decomposition mediated by Ru(TDCPP-Clg) species. The reactions of (1) with HX acids (X = Cl, CF3COO, CHCl2COO) are found to give RuIV(TMP)(X)2 products, as established by NMR and IR spectroscopies and mass spectrometry. The bis(acetato)ruthenium(IV) species are similar to the paramagnetic bis(halo)ruthenium(IV) complexes that have been characterized previously in this laboratory. The stoichiometric oxidation of phenol by (1) in benzene was proposed from previous preliminary work in this laboratory to form Ru™(TMP)(p-OCoH40H)2. The present data favour the formulation of the Ru(IV) product as RuIY(TMP)(OC6H5)2; furthermore, the reaction mechanism is proposed to involve a RuIV(TMP)(0)/RuIV(TMP)(OH)2 interconversion, followed by phenol metathesis with the bis(hydroxo) species. The RuIV(TMP)(0) intermediate is not considered to be an active oxidant; the species either undergoes the disproportionation or interconversion pathways (see above). Species (1), under air, also catalytically oxidizes JV^A'-dimethylaniline, presumably to /?-HOCeH4NMe2 (see Section 7.2); however, less than 10 total turnovers are obtained in 1 d. 7.2 Recommendations for Future Work A wide area of 02-oxidation chemistry mediated by Ru(porp) species was opened up in this thesis work. The potential of these Ru-porphyrin species, particularly the TDCPP-Clg type, as 02-oxidation catalysts has yet to be determined. The 02-oxidation of 239 Chapter 7 a wider variety of substrates (alkenes and alkanes) catalyzed by the Ru(TDCPP-Clg) species deserves greater study to establish the scope of the usage of such metalloporphyrins. The following experiments are suggested as starting points in answering some questions raised in Chapter 6. Although the reaction of (1) with HX acids undoubtedly gives Rurv(TMP)(X)2 species, the reaction mechanism is not understood; furthermore, the product from the HX species is not known. Stoichiometric titration studies are obviously needed to elucidate the nature of these reactions. The scheme proposed in Chapter 6 for the oxidation of phenol by (1) is consistent with the experimental observations, as well as with the chemistry of Ru(TMP) species within the phosphine and alcohol systems; however, the mechanism does not accommodate satisfactorily the observed kinetic data, which show a non-first-order (-1.5) dependence on phenol. An initial step would be to acquire more kinetic data over lower [phenol] values (< 10"2 M) to determine whether the non-first-order dependence is valid over a greater concentration range. The GCMS data show that the O-atom is incorporated into the substrate during the oxidation of N, A^-dimethylaniline by (1); the product is presumably /7-HOC6H4NMe2, and that the oxidation occurs at the para position is based on analogy with the phenol system. More direct identification of the oxidation product is necessary, and a larger scale reaction, followed by product separation, would be one way to confirm that /?-HOC6H4NMe2 is formed. 240 Appendix A Appendix A. Kinetic Data for the Oxidation of EAr3. Abs A Q I 0.6 0.7 4- 4.05xl0"3M 0.00 0.02 —r— H— 0.04 0.06 Time (s) 0.08 0.10 Fi2ure A.l. Absorbance-time traces monitored at 422 nm by stopped-flow spectrophotometry for the reaction of Ruvl(TMP)(0)2 (4.2 x 10" M in benzene) and PPh3. l^AfA,*,) or -2 5 + Figure A.2. Semilog and Guggenheim plots for [PPh3] = 4.05 x 10'3 M trace in Figure A.l above, where A< = absorbance at time t, A» = final absorbance, and At = 0.0075 s. Slope = kobs = 216 ± 1.7, 220 ± 1.7 and 227 ± 2 by semilog, Guggenheim and curve-fitting analyses, respectively. 241 Appendix A 2 4 6 8 10 Time (s) Figure A.3. Absorbance-time traces monitored at 430 nm by stopped-flow spectrophotometry for the loss of the intermediate Ru^TMPXOXOPPlb) via further reaction with PPh3 (3.9 x 10° M) (initial [Ruvl(TMP)(0)2] = 4.2 x 10"5 M in benzene). Time (s) 0 0.5 1 1.5 2 2.5 3 -1 " • -1.5 ln(At-A„) or -2 ln(At-AAt) -2.5 -3 -3.5 Figure A.4. Semilog and Guggenheim plots for [PPh3] = 3.83 x 10'3 M, [OPPh3] = 3.93 x 10'3 M trace in Figure A.3 above. At = absorbance at time t, A*, = final absorbance, and At = 1.0 s. Slope = k'ob, = 0.686 ± 0.01, 0.739 ± 0.01 and 0.713 ± 0.008 by semilog, Guggenheim and curve-fitting analyses, respectively. 242 Appendix A Time (s) Figure A.5. Absorbance-time traces monitored at 412 nm by stopped-flow spectrophotometry for the accumulation of the product Run(TMP)(PPh3) (initial [RuY1(TMP)(0)2] = 4.2 x 10'6 M in benzene). [PPh3] = 3.9x 10° M. lnCAt-A.) -1.5 f or ln(At -2.5 - • -3 -3^5 A" -4.5 Guggenheim Figure A.6. Semilog and Guggenheim plots for [PPh3] = 3.83 x 10*"* M, [OPPh3] = 3.93 x 10"3 M trace in Figure A.5 above. At = absorbance at time t, A* = final absorbance, and At = 1.0 s. Slope = k'ob, = 0.693 ± 0.011, 0.809 ± 0.02 and 0.748 ± 0.009 by semilog, Guggenheim and curve-fitting analyses, respectively. 243 Appendix A Table A. 1.1. Pseudo-1 st-order rate constants for the oxidation of PPh3 by Ruw(TMP)(Q)2 (1). [(Di fpphji [opphii k,*, (s1)" k'ob, (S-y (10 3 M) (IO-3 M) (O-atom transfer) (Slower 2nd reaction) 20.0 °C 1.59 x 10'6M 0.985 4.05 35.2 ±0.2 0.101 10.002 [0.0961] 1.00 2.75 38.3 ±0.3 0.18610.003 [0.183] 1.01 1.40 36.110.2 0.274 10.004 [0.274] 1.04 - 37.210.2 -1.95 4.01 69.710.5 0.298 10.005 [0.286] 1.99 2.72 76.410.5 0.38910.6 [0.352] 2.03 1.39 74.7 10.6 0.613 ±0.009 [0.571] 2.07 - 74.5 10.6 -2.90 3.97 1091 1 0.374 10.007 2.95 2.70 1161 1 0.57510.009 3.01 1.37 1371 1 0.71210.01 3.07 - 1371 1 -3.83 3.93 153 1 1.4 0.495 10.008 3.90 2.67 15611.5 0.662 10.009 3.97 1.36 1581 1.5 1.1710.03 4.05 - 1481 1.4 -0.0501 _ 2.9010.02 -0.0501 1.43 2.83 10.02 -0.119 - 6.23 10.03 -6.35 10.05 0.169 9.35 10.6 -10.4410.8 0.985 4.05 52.010.4 0.14210.004 1.00 2.75 - 0.242 10.005 1.01 1.40 - 0.34010.005 1.04 - - -1.95 4.01 8610.7 0.32010.005 1.99 2.72 - 0.43810.007 2.03 1.39 - .0.752 10.008 2.07 - 103 1 1 -2.90 3.97 - 0.493 10.007 2.95 2.70 - 0.685 10.009 3.01 1.37 1801 1.5 1.1010.02 3.07 - 161 1 1.2 -3.83 3.93 22712 0.713 10.008 3.90 2.67 22912 0.937 1 10.009 3.97 1.36 245 12 1.2710.02 4.05 - 227 12 -244 Appendix A Table A. 1.1 continued... , . . KD1 iTPhjl [OPPtbl kob, (s1)" k'ob, (S-y (10"3 M) (10-3M) (O-atom transfer) (Slower 2nd reaction) 30.7 °C 0.985 4.05 62.6 ±0.5 0.179 ±0.003 4.2 x 10"6 M 1.00 2.75 80.5 ±0.9 0.337 ±0.005 1.01 1.40 74.6 ±0.7 0.475 ± 0.008 1.04 _ 71.9 ±0.7 -1.95 4.01 143 ± 1 0.498 ± 0.006 1.99 2.72 147 ± 1 0.642 ± 0.007 2.03 1.39 144 ± 1 0.946 ±0.01 2.07 _ 144 ± 1 -2.90 3.97 218 ±2 0.808 ±0.01 2.95 2.70 223 ±2 0.935 ±0.02 3.01 1.37 217 ± 2 1.33 ±0.02 3.07 . 207 ± 2 -3.83 3.93 274 ±2 1.18 ±0.03 3.90 2.67 286 ±3 1.31 ±0.03 3.97 1.36 273 ±3 1.88 ±0.04 4.05 - -40.2 °C 0.985 4.05 94.7 ±0.8 0.207 ± 0.006 4.2 x lO-5 M 1.00 • 2.75 102 ± 1 0.367 ±0.008 1.01 1.40 98.0 ±0.9 0.470 ±0.008 1.04 _ - -1.95 4.01 182 ±2 0.549 ±0.009 1.99 2.72 187 ±2 0.682 ±0.01 2.03 1.39 181 ±2 0.847 ±0.01 2.07 - - -2.90 3.97 268 ±2 0.892 ±0.02 2.95 2.70 280 ±3 1.04 ±0.02 3.01 1.37 275 ±2 1.42 ±0.03 3.07 - - -3.83 3.93 - 1.14 ±0.02 3.90 2.67 - - 1.28 ±0.02 3.97 1.36 380 ±4 1.67 ±0.03 4.05 - - -' Monitored at 422 nm for the loss of (1). * Monitored at 430 nm for the loss of Rulv(TMP)(0)(OPPh3). Values in [] were obtained at 412 nm for the appearance of the product RuD(TMP)(PPh3). 245 Appendix A Table A. 1.2. Pseudo-1 st-order rate constants for the oxidation of PPh3 by 11.2 °C 20.5 °C 30.1 °C 40.1 °C [PPh3lfl (M) k'ob, (sT (Slower 2nd reaction) 0.0184 14.97 ±0.5 15.13 ±0.4 15.13 ±0.5 0.0323 18.56 ±0.4 16.97 ±0.4 16.93 ±0.3 0.0462 17.64 ±0.2 16.58 ±0.2 0.0114 10.09 ±0.4 0.0323 15.42 ±0.5 0.0462 17.25 ±0.6 17.43 ±0.7 0.0184 15.21 ±0.3 16.94 ±0.4 16.97 ±0.4 0.0323 22.37 ±0.3 22.81 ±0.4 23.46 ±0.4 0.0462 27.4 ±0.5 28.79 ±0.7 28.79 ±0.6 0.0162 16.86 ±0.6 17.98 ±0.4 17.0 ±0.5 0.0323 32.32 ±0.6 29.77 ±0.4 31.9 ± 0.8 0.0462 35.5 ±0.6' 35.63 ±0.8 " [OPPh3] = 1.3 x 10'5 M in all the runs. [(1)] = 2 x 10"6 M. * Monitored at 412 nm for the appearance of the product RuD(TMP)(PPh3). 246 Appendix A Table A.2. Pseudo-1 st-order rate constants for the oxidation of P^-MeO-CeRt^ (L) by Ruv,(TMP)(0)2 (1). KD1 l(L)] (1Q-4M) [OPPh,l (IP-3 M) (O-atom transfer) (Slower 2nd reaction) 10.1 °C 2.5 x 10* M 1.07 2.12 4.21 8.25 1.16 1.18 2.30 2.35 3.44 3.50 2.90 1.48 2.89 1.47 2.88 1.47 8.60 ± 0.07 8.62 ±0.07 8.65 ±0.07 16.8 ±0.15 16.9 ±0.15 16.9 ±0.2 33.7 ±0.3 33.6 ±0.4 33.2 ±0.3 67.8 ±0.6 68.3 ±0.6 66.8 ±0.7 0.0248 ±0.0005 0.0365 ±0.0007 0.0503 ±0.001 0.0770 ±0.001 0.0749 ± 0.002 0.113 ±0.003 20.4 °C 1.07 2.12 4.21 8.25 1.16 1.18 2.30 2.35 3.44 3.50 2.90 1.48 2.89 1.47 2.88 1.47 12.2 ±0.1 12.7 ±0.1 12.6 ±0.1 22.9 ±0.2 22.8 ±0.2 22.8 ±0.2 45.3 ±0.4 45.4 ±0.4 45.8 ±0.4 89.2 ±0.9 89.0 ±0.9 91.1 ± 1 0.0391 ±0.0008 0.0625 ±0.001 0.0732 ± 0.002 0.108 ±0.003 0.101 ±0.003 0.164 ±0.005 247 Appendix A Table A.2 continued. [(1)1 I(L)1 [OPPM kob.ts1)" k'ob. (•')* (lO^M) (IO"3 M) (O-atom transfer) (Slower 2nd reaction) 30.1 °C 1.07 - 17.3 ±0.2 -17.0 ±0.2 17.4 ±0.2 2.5 x 10"* M 2.12 30.3 ±0.4 -30.4 ±0.5 31.0±0.4 4.21 - 45.3 ±0.6 -45.4 ±0.7 45.8 ±0.6 8.25 - 89.2 ± 1 -89.0 ± 1 91.1 ± 1 1.16 2.90 - 0.0549 ±0.0009 1.18 1.48 - 0.0773 ±0.001 2.30 2.89 - 0.0988 ± 0.002 2.35 1.47 - 0.140 ±0.003 3.44 2.88 - 0.142 ±0.003 3.50 1.47 - 0.202 ± 0.004 39.9 °C 1.07 _ 23.3 ±0.3 -21.9±0.4 21.7 ±0.3 2.12 - 38.8 ±0.4 -40.3 ± 0.6 38.5 ±0.5 4.21 - 78.7 ±0.9 -78.8 ±0.7 78.5 ±0.8 8.25 - 160 ± 1.4 -160 ±1.7 159 ± 1.5 -1.16 2.90 - 0.0728 ±0.001 1.18 1.48 - 0.0961 ±0.001 2.30 2.89 - 0.129 ±0.002 2.35 1.47 - 0.177 ± 0.003 3.44 2.88 - 0.194 ±0.004 3.50 1.47 - 0.270 ± 0.006 " Monitored at 422 nm for the loss of (1). * Monitored at 430 nm for the loss of RuIY(TMP)(0)(OPPh3). 248 Appendix A Table A.3. Pseudo-1 st-order rate constants for the oxidation of P(p-Me-C<£Uh (L) by Ruw(TMP)(Q)2 (1). ((1)1 [(L)j (10"4 M) [OPPh,] (IO-3 M) kob. (i-'r (O-atom transfer) k'ob. (sV (Slower 2nd reaction) 10.1 °C 2.5 x HTM 10.3 °C 2.05 4.08 8.08 12.0 1.02 1.04 1.52 1.55 2.53 2.58 4.89 2.49 4.88 2.49 4.86 2.48 8.25 ±0.09 8.52 ±0.1 8.22 ±0.08 17.1 ±0.2 17.2 ±0.2 17.2 ±0.2 35.3 ±0.3 35.3 ±0.3 34.1 ±0.4 53.8 ±0.6 53.0 ±0.5 53.0 ±0.6 0.00906 ±0.0001 0.0154 ±0.0003 0.0133 ±0.0002 0.0245 ± 0.0003 0.0250 ± 0.0004 0.0404 ± 0.0006 20.4 °C 2.05 4.08 8.08 12.0 1.02 1.04 1.52 1.55 2.53 2.58 4.89 2.49 4.88 2.49 4.86 2.48 12.3 ±0.1 12.2 ±0.1 12.2 ±0.14 24.2 ±0.3 24.1 ±0.3 24.6 ±0.2 47.7 ±0.5 49.7 ±0.5 48.1 ±0.4 71.7 ±0.9 72.4 ±0.7 70.7 ±0.9 0.0152 ±0.0002 0.0249 ± 0.0004 0.0202 ± 0.0003 0.0343 ±0.0005 0.0339 ±0.0005 0.0631 ±0.0008 249 Appendix A Table A3 continued.. [(1)1 l(L)l [OPPh,] kob, (s1) k'ob. (s1/ (10"4 M) (i<r3 M) (O-atom transfer) (Slower 2nd reaction) 30.1 °C 2.05 - 16.2 ±0.2 -16.3 ±0.2 16.4 ±0.16 2.5 x lO^M 4.08 - 32.2 ±0.5 -31.8 ±0.4 32.0 ±0.5 8.08 - 66.2 ±0.8 -65.1 ±0.9 66.0 ±0.8 12.0 - 93.2 ±1 -95.7 ± 1 99.8 ± 1 30.0 °C 1.02 4.89 - 0.0185 ±0.0003 1.04 2.49 - .0.0322 ± 0.0005 1.52 4.88 - 0.0254 ±0.0004 1.55 2.49 - 0.0433 ± 0.0007 2.53 4.86 - 0.0447 ± 0.0005 2.58 2.48 - 0.0718 ±0.0009 39.9 °C 2.05 _ 21.4 ±0.3 -22.1 ±0.3 21.6 ±0.35 4.08 - 38.3 ±0.5 -37.3 ±0.45 39.3 ±0.5 8.08 - 81.9±0.8 -81.7 ± 0.9 81.0 ± 1 12.0 - 130 ± 1.5 -129 ± 1.7 126 ± 2 1.04 2.49 - 0.0384 ± 0.0004 1.55 2.49 - 0.0510 ±0.0006 2.58 2.48 - 0.0862 ± 0.0009 1.02 4.89 - 0.0228 ± 0.0003 1.52 4.88 - 0.0300 ± 0.0004 2.53 4.86 - 0.0547 ±0.0007 " Monitored at 422 nm for the loss of (1). * Monitored at 430 nm for the loss of Rutv(TMP)(0)(OPPh3). 250 Appendix A Table A.4. Pseudo-1 st-order rate constants for the oxidation of ?{p-?-C^U)i (L) by Ru (TMP)(Q)2 (1). [(1)1 l(L)l [OPPhjl kob. (s1) k'ob. (sY (lO^M) (10 3 M) (O-atom transfer) (Slower 2nd reaction) 9.9 °C 0.609 - 4.84 ±0.03 -1.7 x lO^M 1.21 - 10.6 ±0.07 -2.40 - 18.5 ±0.1 -4.71 - 36.2 ±0.2 -10.3 °C 1.57 2.72 - 0.0396 ± 0.0004 1.60 1.38 - 0.0808 ± 0.002 2.34 2.70 - 0.0592 ± 0.0006 2.39 1.38 - 0.100 ±0.001 3.11 2.69 - 0.0783 ± 0.0007 3.17 1.37 - 0.143 ±0.001 20.4 °C 0.609 - 6.96 ±0.05 -1.21 - 13.3 ±0.1 -2.40 - 26.0 ±0.2 -4.71 - 49.8 ±0.4 -1.57 2.72 - 0.0596 ±0.0006 1.60 1.38 - 0.104 ±0.001 2.34 2.70 - 0.0873 ± 0.0007 2.39 1.38 - 0.141 ±0.002 3.11 2.69 - 0.124 ±0.001 3.17 1.37 - 0.187 ±0.002 30.1 °C 0.609 - 9.26 ±0.08 -1.21 - 17.6 ±0.1 -2.40 - 33.3 ±0.2 -4.71 - 65.0 ±0.5 -1.57 2.72 - 0.0788 ± 0.0008 1.60 1.38 - 0.134 ±0.001 2.34 2.70 - 0.128 ±0.001 2.39 1.38 - 0.185 ±0.002 3.11 2.69 - 0.152 ±0.001 3.17 1.37 - . 0.243 ± 0.002 39.9 °C 0.609 - 12.3 ±0.09 -1.21 - 23.3 ±0.2 -2.40 - 44.0 ±0.4 -4.71 - 81.4±0.7 -1.57 2.72 - 0.0914 ±0.0008 1.60 1.38 - 0.145 ±0.001 2.34 2.70 - 0.135 ±0.001 2.39 1.38 - 0.203 ± 0.002 3.11 2.69 - 0.173 ±0.002 3.17 1.37 0.272 ± 0.003 4 Monitored at 422 nm for the loss of (1). * Monitored at 430 nm for the loss of Rurv(TMP)(0)(OPPh3). • 251 Appendix A Table A.5. Pseudo-1 st-order rate constants for the oxidation of P(p-Cl-C£h)i (L) by Ruvl(TMP)(0)2 (1). KDl 1(L)1 (lO^M) [OPPh,] (IP"3 M) kob. (s'l)a (O-atom transfer) k'ob. (• V (Slower 2nd reaction) 9.8 °C 2.5 x 1(T M 10.3 °C 1.00 1.98 2.94 4.81 1.25 1.27 1.86 1.90 2.47 2.52 3.59 1.83 3.57 1.82 3.55 1.81 9.72 ±0.05 9.90 ± 0.04 9.44 ±0.05 17.8 ±0.1 18.0 ±0.1 17.9 ±0.1 27.0 ±0.2 26.9 ±0.2 27.1 ±0.2 44.2 ±0.3 43.4 ±0.4 43.0 ±0.4 0.0277 ±0.0003 0.0457 ± 0.0005 0.0427 ±0.0005 0.0625 ±0.0007 0.0492 ± 0.0006 0.0998 ±0.001 20.2 °C 20.3 °C 1.00 1.98 2.94 4.81 1.25 1.27 1.86 1.90 2.47 2.52 3.59 1.83 3.57 1.82 3.55 1.81 15.8 ± 0.1 14.8 ±0.1 15.0 ± 0.1 26.1 ±0.2 26.0 ±0.3 24.8 ±0.2 36.5 ±0.4 37.1 ±0.3 37.4 ±0.4 61.5 ±0.5 61.5 ±0.6 60.0 ± 0.6 0.0429 ±0.0005 0.0680 ± 0.0008 0.0542 ± 0.0006 0.0899 ±0.001 0.0770 ± 0.0009 0.121 ±0.002 252 Appendix A Table A.5 continued.. Id)] I(L)1 (lO^M) [OPPh,] (IO3 M) ko0, (••')• (O-atom transfer) k'.„. (s1)* (Slower 2nd reaction) 30.4 °C 2.5 x 10* M 30.0 °C 1.00 1.98 2.94 4.81 1.25 1.27 1.86 1.90 2.47 2.52 3.59 1.83 3.57 1.82 3.55 1.81 18.210.1 18.3 ±0.2 17.9 ±0.2 34.4 ± 0.3 34.4 ±0.4 34.0 ±0.4 50.5 ±0.6 49.2 ±0.5 48.1 ±0.5 79.4 ±0.7 82.5 ±0.8 78.4 ±0.8 0.0562 ± 0.0007 0.0888 ±0.001 0.0812 ±0.0009 0.115 ±0.001 0.107 ±0.001 0.172 ±0.002 39.9°C 40.0 °C 1.00 1.98 2.94 4.81 1.25 1.27 1.86 1.90 2.47 2.52 3.59 1.83 3.57 1.82 3.55 1.81 23.9 ±0.3 24.5 ±0.2 24.7 ±0.2 43.8 ±0.4 43.3 ±0.5 43.3 ±0.4 66.8 ±0.6 68.6 ±0.6 64.3 ±0.7 105 ± 1 106 ± 1 106 ± 1 0.0715 ±0.001 0.112 ±0.002 0.109 ±0.002 0.147 ±0.003 0.137 ±0.002 0.186 ±0.003 " Monitored at 422 nm for the loss of (1). * Monitored at 430 nm for the loss of RuIY(TMP)(0)(OPPh3). 253 Appendix A Table A.6. Pseudo-1 st-order rate constants for the oxidation of P(p-CF3-C6l-Lt)3 (L) by Ruvl(TMP)(Q)2 (1). [(1)1 I(L)1 [OPPtaj] kob. (s1) k'0b, (»•')* (lO^M) (103 M) (O-atom transfer) (Slower 2nd reaction) 10.1 °c 1.33 4.11 9.05 ± 0.04 0.0194 ±0.0003 4.4 x lO^M 1.35 2.10 9.24 ±0.04 0.0299 ± 0.0005 1.98 4.10 12.6 ±0.05 0.0354 ±0.0004 2.02 2.09 13.5 ±0.06 0.0513 ±0.0006 2.63 4.07 17.7 ±0.1 0.0464 ± 0.0005 2.68 2.08 16.6 ±0.1 0.0670 ± 0.0009 20.3 °C 1.33 4.11 12.9 ±0.1 0.0310 ±0.0005 1.35 2.10 13.4 ±0.1 0.0501 ±0.0006 1.98 4.10 19.4 ±0.1 0.0512 ±0.0007 2.02 2.09 17.2 ±0.1 0.0707 ± 0.0007 2.63 4.07 25.1 ±0.2 0.0675 ±0.0008 2.68 2.08 24.8 ±0.2 0.119 ±0.001 30.0 °C 1.33 4.11 17.1 ±0.1 0.0543 ± 0.0006 1.35 2.10 17.6 ±0.1 0.0732 ± 0.0007 1.98 4.10 27.0 ±0.3 0.0795 ±0.0009 2.02 2.09 25.8 ±0.2 0.102 ±0.001 2.63 4.07 34:6 ±0.3 0.105 ±0.001 2.68 2.08 34.3 ±0.4 0.140 ±0.0016 39.9 °C 1.33 4.11 23.9 ±0.2 0.0764 ±0.001 1.35 2.10 24.0 ±0.2 0.0997 ±0.001 1.98 4.10 34.4 ±0.3 0.114±0.001 2.02 2.09 33.8 ±0.4 0.148 ±0.0013 2.63 4.07 44.0 ±0.4 0.150 ±0.0017 2.68 2.08 42.9 ±0.3 0.191 ±0.002 " Monitored at 422 nm for the loss of (1). * Monitored at 430 nm for the loss of Rutv(TMP)(0)(OPPh3). 254 Appendix A Table A. 7. Pseudo-1 st-order rate constants for the oxidation of [P(2-pyridyl)3](PPh3)(Cl)2Ru (L) by Ru^CTMPXO); (1) [(DI [(D) (10's M) kob. (s-1)4 (O-atom transfer) 10.4 °C 1.5 x lO^M 20.3 °C 30.0 °C 39.9 °C 2.19 0.205 ± 0.005 0.248 ± 0.006 4.38 0.513 ±0.01 0.508 ± 0.009 6.58 0.664 ±0.01 0.665 ±0.01 8.77 0.886 ±0.012 0.925 ±0.014 11.0 1.04 ±0.02 1.05 ±0.016 2.19 0.383 ± 0.008 0.403 ± 0.009 4.38 0.677 ±0.01 0.687 ±0.01 6.58 0.982 ±0.02 0.984 ±0.02 8.77 ' 1.27 ±0.02 1.26 ±0.02 11.0 1.55 ±0.03 1.52 ±0.03 2.19 0.571 ±0.01 0.576 ±0.009 4.38 0.960 ±0.013 0.940 ±0.01 6.58 1.35 ±0.02 1.31 ±0.03 8.77 1.77 ±0.04 2.02 ±0.04 11.0 2.31 ±0.05 2.19 ±0.04 2.19 0.828 ±0.01 0.826 ±0.01 4.38 1.36 ±0.02 1.39 ±0.03 6.58 1.96 ±0.04 2.03 ±0.04 8.77 2.62 ±0.05 2.66 ±0.05 11.0 3.22 ±0.06 3.28 ±0.08 " Monitored at 422 nm for the loss of (1). 255 Appendix A Table A.8. Pseudo-lst-order rate constants for the oxidation of AsPh3 and SbPh3, (L), by Ruyi(TMP)(0)2 (1). [(1)1 [AsPhj] (10J M) kob. (••')• (O-atom transfer) 9.9 °C 1.48 0.928 1 0.008 1.06 ±0.01 -2.3 x 10"6 M 2.91 1.75 ±0.01 1.78 ±0.006 1.8410.014 4.36 2.68 ±0.01 2.69 ±0.014 2.7710.03 5.61 3.29 ±0.016 3.49 ±0.02 3.6810.03 19.8 °C 1.48 1.30 ±0.01 1.32 ±0.01 -2.91 2.60 ±0.01 2.69 ±0.014 2.75 10.017 4.36 4.10 ±0.022 4.10 ±0.015 3.9610.03 5.61 5.32 ±0.03 5.43 ±0.03 5.2610.09 75.0 69.0 ±0.4 66.4 ±0.5 -30.1 °C 1.48 2.21 ±0.01 2.21 ±0.02 2.33 10.01 2.91 4.07 ± 0.02 4.06 ± 0.02 4.3510.03 4.36 6.55 ±0.05 6.13 ±0.04 6.4710.03 5.61 8.19 ±0.04 8.26 ±0.03 8.54 10.06 39.9 °C 1.48 3.06 ±0.02 3.20 ±0.02 2.9910.02 2.91 6.02 ±0.07 6.21 ±0.03 6.2410.04 4.36 9.06 ± 0.06 9.08±0.08 9.5410.09 5.61 12.1 ±0.1 11.8 ±0.1 11.9 ±0.1 KD1 [SbPh3j (IO"4 M) kob. (s-y (O-atom transfer) 9.7 °C 1.14 423 ± 10 3.0 x lO^M 2.19 3.17 4.08 647 ± 30. 820 ± 40 • 1216 ±100 14.5 °C 1.14 2.19 3.17 4.08 445 ± 30 673 ± 50 872 ± 70 1300 ±120 20.3 °C 1.14 2.19 3.17 4.08 464 ± 40 700160 -933 ±85 14101130 25.4 °C 1.14 2.19 3.17 4.08 713 160 1080 1 100 15701 150 * Monitored at 422 nm for the loss of (1). * Monitored at 430 nm for the appearance of Rurv(TMP)(0)(OSbPh3). 256 Appendix B Appendix B. Mathematical Derivation for the Equation Reflecting the Observed lst-Order Absorbance-Time Changes in the Oxidation of PPh3 by Ru^fTMPXOJa B.l O-atom Transfer (Faster Kinetic Phase) The O-atom transfer is a simple (1) - (2) reaction. If the reaction follows first-order kinetic behaviour, the absorbance contributions due to (1) and (2) are the following: a = aoexp(-kob,t); b = b„ - bcoexp(-kob5t), where a^ = initial absorbance of (1), bo = final absorbance due to complete formation of (2), kobs = pseudo-1 st-order rate constant and t = time. Thus the absorbance observed at any time, t, is Abs = a + b = (ao - boo)exp(-kobst) + b». A semilog plot of ln(Abs - b*) versus t should give a straight line with slope = -kobs in the case where ao > boo- When ao < br the absorbances are rising, and In | Abs - bco I should be used instead. (Slower Kinetic Phase) (B.l) (B.2) (B.3) (B4) B.2. Dissociation of OL Followed by Disproportionation The following mechanism was proposed in Chapter 3. (2) ===== (3) + OL 2(3) J*^ (l) + (4) (1) + L k. , (2) (4) + L let r (5) 257 Appendix B Only (2) and (5) were observed in 'H-NMR studies during this stage of the reaction [(1) has been completely consumed in the faster O-atom transfer reaction]. The observed rate expression is represented by Eq. B.5. -^jp = M(2)] - M0L][(3)] - k,[L][(l)] = = k4[L][(4)] (B.5) [(1)] = [(4)] = K31/2[(3)], as the only source of (1) is via the disproportionation reaction, Eq. B.2. Upon substitution of (1) and (4) by K31/2[(3)] into Eq. B.5, we obtain Eqs. B.6, 3.7 and B.8. k2[(2)] - k_2[OL][(3)] - k,K3,/2[L][(3)] - k4K31/2[L][(3)] = 0 (B.6) [<3» = MOLl + k.Ka^rLl + k-JC,^] [(2)] (B7) k K 1/2 = MOL] + k,K31/2[L] + k4K31/U] C(2)1 (B 8) Thus, the rate expression (Eq. B.5) becomes Eq. B.9. krml+ k.2k2[0L] dt ' -k2[(2)] + k.2[OL] + k,K3"2[L] + k4K31/2[L] [(2)] + kik2K31/2rL] MOL] + k!K3"2[L] + k4K3ty2[L] [(2)] = -k'«"»t(2)], where • (B.9) k2k4K3'/2rL] k'obs = ie2[OL] + (ki+k4)K31/2[L] 'n ^e Presence °^excess [L] and [OL]. As only (2) and (5) are present in any significant quantities, the relationship between the observed rate and absorbance changes follows the same derivation as in the previous section. 258 Appendix C Appendix C. Oxidation of Alcohols and Alkanes by Ru (TMP)(0)2 C.l Kinetic Data for the Stoichiometric Oxidation of Alcohols under 1 atm Ar. Table C.l.l. ['PrOH] = 0.0435 M in benzene-*. [Ru^(TMP)(0)2] = 4.0 x 10"4 M. Temperature " 18.2 °C. Time (s) Integration of p- and o-Me groups of RuIV(TMP)(0/Pr)2 (Arbitrary Units) Integration of o-Me of Ruvl(TMP)(0)2 (Arbitrary Units) 0 0 100 2115 82.2 208.2 3825 80.8 138.0 5395 49.9 60.7 8955 55.0 57.1 11130 91.2 88.4 14280 90.0 64.7 18075 126.8 73.5 21315 120.6 47.6 25350 135.4 46.8 28360 73.2 23.4 kobs 2.0 x 10"5 s"1 Table C.l.2. ['PrOH] = 0.0568 M in benzene-*. [Ruvl(TMP)(0)2] = 4.0 x IO"4 M. Temperature = 18.2 °C. Time (s) Integration of p- and o-Me groups of Ru,v(TMP)(0'Pr)2 (Arbitrary Units) Integration of p-Me of Ru%a(TMP)(0)2 (Arbitrary Units) 0 0 100 1340 12.9 109.8 3600 14.2 79.76 4620 23.9 76.0 8380 30.4 54.56 11785 46.2 62.7 14700 50.4 56.3 17575 44.3 35.6 68610 200 17 kobs = 1.9 x 10"5 s'1 259 Appendix C Table C.1.3. ['PrOH] = 0.131 M in benzene-^. [Ruvl(TMP)(0)2] = 4.0 x 10"4 M. Temperature = 18.2 °C. Time (s) Integration of p- and o-Me groups of RuIV(TMP)(0'Pr)2 (Arbitrary Units) Integration of p-Me of Ru'q(TMP)(0)2 (Arbitrary Units) 0 0 100 1805 65.1 163.4 3560 93.6 200.4 5025 67.4 87.3 8640 91.6 64.6 10860 130.9 96.5 13980 107.2 58.2 17925 131.1 58.6 21120 128.4 41.1 25110 136.9 40.2 kobs 4.2 x lO-5 s"1 Table C.1.4. ['PrOH] = 0.174 M in benzene-^. [Ru^(TMP)(0)2] = 3.8 x 10"4 M Temperature = 18.2 °C. Time (s) Integration of Integration of p-Me of p- and o-Me groups of Ruv1(TMP)(0)2 RuIV(TMP)(0'Pr)2 (Arbitrary Units) (Arbitrary Units) 0 0 10 930 3.9 7.95 1795 6.0 9.0 koh, = 8.0 x 10'5 s'1 Table C.1.5. ['PrOH] = 0.435 M in benzene-^. [Ru^(TMP)(0)2] = 3.8 x 10"4 M. Temperature = 18.2 °C. Time (s) Integration of p- and o-Me groups of RuIV(TMP)(OPr)2 (Arbitrary Units) Integration of p-Me of Ruvl(TMP)(0)2 (Arbitrary Units) 0 540 1200 2340 3540 0 2.45 3.1 7.0 7.7 kobs = 10 5.2 . 5.1 6.3 4.55 1.2 x 10-V 260 Appendix C Table C.1.6. ['PrOH] = 0.435 M in benzene-afe. [RuVI(TMP)(0)2] = 5.2 x 10"4 M Temperature = 18.2 °C Time (s) Integration of para and ortho-Mt's of RuIV(TMP)(0'Pr)2 Integration of para-Mt of Ru^fTMPXOk (Arbitrary Units) 0 0 10 600 3.6 6.15 1260 5.1 • 5.9 2280 7.4 6.5 3240 8.2 6.3 5280 51 1^ = 1.2 x 10-V 36 Table C.1.7. ['PrOH] = 0.871 M in benzene-^. [Ruv,I(TMP)(0)2] = 5.2 x 10"4 M. Temperature =18.2 °C. Time (s) Integration of p- and o-Me groups of RuIV(TMP)(0'Pr)2 Integration of p-Me of Ruvl(TMP)(0)2 (Arbitrary Units) 0 0 10 900 1.35 5.15 1800 1.3 5.25 2700 4.72 2.25 3600 3.2 6.3 4500 5.15 lc^ = 1.37 xlO-V 5.6 Table C.1.8. ['PrOH] = 0.161 M in benzene-fife. [Ru^TMPXO^] = 4.0 x 10-4 M Temperature = 28.5 °C. Time (s) Integration of p- and o-Me groups of Ru,v(TMP)(0'Pr)2 (Arbitrary Units) Integration of p-Me of Ru^TMPXOfc (Arbitrary Units) 0 540 1155 1750 2910 4230 0 4.1 4.1 7.1 7.7 11.0 10 8.1 6.0 7.0 6.1 7.0 ie*,=i.2o xio-y 261 Appendix C Table C.1.9. ['PrOH] = 0.174 M in benzene-*. [Ru^fTMPXOfc] = 4.0 x 10 M. Temperature = 35.5 °C. Time (s) Integration of p- and o-Me groups of Ru,v(TMP)(0'Pr)2 Integration of p-Me of Ru^fTMPXOk (Arbitrary Units) 0 0 10 850 1.75 4.2 1320 3.8 4.3 1920 4.3 5.0 3440 5.3 5.0 4320 5.4 kobs = 1.82 xlO-V 3.8 Table C.1.10. [T>rOH] = 0.218 M in benzene-*. [Ruv,(TMP)(0)2] = 4.0 x 10 M. Temperature = 18.2 °C. Mole Fraction of Ru^CTMPXOV 0 1 750 0.912 2485 0.832 4285 0.698 kobs = 8.0 xlO'V jr=Integrationp.Me(Ru(vi))/[lntegration/,.MefRu(vi))-r 3 ""S5"l"»''/>. 1.9 were converted to mole fractions to derive kob, (see Chapter 4) + \ Integrationp.o-MeCRuav))] The data from Table C. 1.1 Table C.1.11. ['PrOH] = 0.218 M in benzene-*. [Ru^TMPXO^] = 2.0 x IO-4 M. Temperature = 18.2 °C. Time (s) Mole Fraction of Ru^fTMPKOk 0 1 1040 0.922 2660 0.846 4200 0.80 kobs = 7.8 x lQ-y 262 Appendix C Table C.1.12. ['PrOH] = 0.218 M in benzene-*. [RuYI(TMP)(0)2] = 4.0 x 10"4 M. Temperature = 18.2 °C. Time (s) Mole Fraction of RuVI(TMP)(0)2 0 4665 6005 7555 1 0.584 0.586 0.495 Us = 9.2 x 10-V Table C.1.13. ['PrOD-*] = Temperature 1.74 M in benzene-*. [RuVI(TMP)(0)2] = 4.0 x 10"4 M. = 18.0 °C. Time (s) Mole Fraction of Ruvl(TMP)(0)2 0 780 1680 2580 3480 4380 1 0.89 0.806 0.7865 0.77 0.741 kobs = 1.3 x 10-V Table C.l. 14. [PrOD-*] = Temperature 0.327 M in benzene-*. rRu^(TMP)(0)2] = 4.0 x 10"4 M. = 18.0°C. Time (s) Mole Fraction of Ruvl(TMP)(0)2 0 720 1320 2280 2940 4800 1 0.87 0.865 0.84 0.81 0.763 kobs = 6.66 x 10-5 s"1 263 Appendix C Table C.1.15. ['PrOD-*] = 0.131 M in benzene-*. [RuY1(TMP)(0)2] = 4.0 x IO"4 M. Temperature = 18.0 °C. , Time (s) Mole Fraction of Ru^(TMP)(0)2 0 1 600 . 0.935 1200 • 0.922 . 1800 0.933 3000 0.911 4920 0.878 kobs = 3.1 x 1Q-V Table C.l.16. ['PrOH] = 0.0408 M in benzene-*. [KOH] = 4 x 10*6 M. [Ruvl(TMP)(0)2l = 4.0 x IO-4 M. Temperature = 18.2 °C. Time (s) Mole Fraction of RuVI(TMP)(0)2 0 1 600 0.818 1530 0.813 2550 0.733 4530 0.614 8250 0.56 kobs = 9.0 x 10-y Table C.l.17. ['PrOH] = 0.0408 M in benzene-*. [KOH] = 2 x 10"5 M. ^_ [Ruv1(TMP)(Q)2l = 4.0 x IO-4 M. Temperature = 18.2 °C. Time (s) Mole Fraction of Ruvl(TMP)(0)j 0 210 810 2910 3510 4410 koi ibs 1 1 0.889 0.793 0.699 0.700 0.594 1.2 x 10-V 264 \ Appendix C Table C.1.18. ['PrOH] = 0.0816 M in benzene-^. [KOH] = 4 x 10"6 M. rRuv"1(TMP)(Q)2] = 4.0 x 10"4 M. Temperature = 18.2 °C. Time (s) Mole Fraction of Ru^TMPXO): 0 1 900 0.90 2820 0.75 6600 0.6kobs=l.lx1Q-4s-Table C.1.19. ['PrOH] = 0.130 M in benzene-^. [KO'Bu] = 1.2 x 10-4 M. [Ruvl(TMP)(0)2l = 2 0 x 10"4 M. Temperature = 18.2 °C. Time (s) Mole Fraction of RuVI(TMP)(0)2 0 1 150 0.90 450 0.75 750 0.68 ^ = 5.4 x 1Q-4 s-Table C.1.20. ['PrOH] = 0.130 M in benzene-fife [KO'Bu] = 1.6 x 10'3 M. [Ruvl(TMP)(0)2] = 4.0 x 10'4 M. Temperature = 18.2 °C. Time(s) Mole Fraction of RuVI(TMP)(0)2 _ , . 360 0.133 kobs = 5J3 x!0'3s'' 265 Appendix C Table C.1.21. ['PrOH] = 0.130 M in benzene-*. ['BuOH] = 0.177 M. [Ruv'(TMP)(0)21 = 4.0 x IO-4 M. Temperature = 18.2 °C. Time (s) Mole Fraction of Ru^(TMP)(0)2 0 810 2850 5010 1 0.99 0.97 0.95 kobs = 9.2xl0^s-1 Table C.1.22. ['PrOH] = 0.130 M in benzene-*. ['BuOH] = 0.530 M. fRuvVTMPVO)9l = 4.0 x IO-4 M. Temperature = 18.2 °C. Time (s) Mole Fraction of Ruv,(TMP)(0)2 0 2520 4500 10000 1 0.99 0.98 0.96 kobs = 3.6 x io-y Table C.l.23. [Benzyl alcohol] = [RuVI(TMP)(0)2] = 0.193 M in benzene-*. = 2.0 x 10"4 M. Temperature = 18.0 °C. Time (s) Mole Fraction of Ruvl(TMP)(0)2 0 510 1290 2010 2610 3630 1 0.717 0.555 0.335 0.299 0.154 kobs = 5.06 xlQ-V 266 Appendix C Table C.1.24. [Benzyl alcohol] = 0.129 M in benzene-fife. rRuvl(TMP)(0)2] = 3.0 x 10"4 M. Temperature = 18.0 °C. Time (s) Mole Fraction of Ruvl(TMP)(0)2 0 300 900 1800 2460 3000 1 0.852 0.719 0.509 0.432 0.359 kohs = 3.57xl0-4s-' Table C.1.25. [Benzyl alcohol] = rRuVI(TMP)(0)2] = 0.0966 M in benzene-fife. = 3 0 x 10'4 M. Temperature = 18.2 °C. Time (s) Mole Fraction of RuN'(TMP)(0)2 0 720 1320 2100 2700 3480 1 0.856 0.726 0.609 0.575 0.434 kobs = 2.28 x 10-V Table C.1.26. [Benzyl alcohol] = rRuvl(TMP)(0)2] = 0.193 M in benzene-fife. = 3.0 x 10"4 M. Temperature = 29.5 °C. Time (s) Mole Fraction of Ru^TMPXO): 0 300 600 900 1200 1 0.613 0.451 0.275 0.15 ^ = 1.47 xlO-V 267 Appendix C Table C.l.27. [Benzyl alcohol] = 0.0966 M in benzene-*. rRuv'(TMP)(Q)21 = 3.0 x IO-4 M. Temperature = 29.5 °C. Time (s) Mole Fraction of Ruv,(TMP)(0)2 0 300 720 1200 1620 2100 1 0.768 0.616 0.401 0.425 0.274 1^ = 7.41 x 10-V Table C.1.28. [Benzyl alcohol] = [Ruv,(TMP)(0)2] = 0.161 M in benzene-*. = 3 0 x IO-4 M. Temperature = 34.5 °C. Time (s) Mole Fraction of Ru"(TMP)(0)2 0 270 615 900 1 0.486 0.277 0?164 kobs = 2.26 x 10V Table C.l.29. [Benzyl alcohol] = [Ru%a(TMP)(0)2] 0.0966 M in benzene-*. = 3 0 x IO"4 M. Temperature = 34.5 °C. Time (s) Mole Fraction of RuVI(TMP)(0)2 0 360 720 990 1260 1 0.545 0.427 0.410 0.286 kobs = 1.37 xl0V 268 Appendix C Table C.1.30. [Benzyl alcohol] = 0.0322 M in benzene-^. rRu%n(TMP)(Q)2l = 3.0 x 10"4 M. Temperature = 34.5 °C. Time(s) Mole Fraction of Ruvl(TMP)(0)2 0 > 300 0 811 600 0626 900 0511200 0-40 kntw-7.52xlQ-4s-1 269 Appendix C C.2 Data for the Catalytic Oxidation of Alcohols in Benzene at 50 °C under 1 Atm Air. Table C2.1. [Benzyl alcohol] = 0.121 M; [Ru^TMPXO^] = 2.56 x 10° M 30 pL 3.0 M aqueous KOH. Blank benzyl alcohol contains 0.174% benzaldehyde. Time (h) Amount of Benzaldehyde Amount of Benzyl alcohol (Arbitrary Units)" (Arbitrary Units)" 17.25 2466 128990 2146 846941.75 166 8935 282790 5250 1134067,5 10358 219070 10012 1793891.5 5580 81365 6148 84881 115.5 8372 103440 12503 15409141 6663 76489 5085 58015423 62989 6097 65081 191.5 2340 22020 2698 26863 234.5 4674 44081 4832 44437 259 1894 17512 2519 25095 " Second set of values in correspond to data from a second GC run for the same sample. 270 Appendix C Table C2.2. [Benzyl alcohol] = 0.242 M; [Ruv,(TMP)(0)2] = 2.56 x 10'5 M 30 uL 3.0 M aqueous KOH. Blank benzyl alcohol contains 0.174% benzaldehyde. . Time (h) Amount of Benzaldehyde (Arbitrary Units)" Amount of Benzyl alcohol (Arbitrary Units)" 17.25 5210 220470 5318 221710 41.75 10570 275790 11035 273770 67.75 22708 424950 7206 130280 91.75 12923 188880 6204 83797 116 29382 392590 23962 323130 141.5 11163 129500 11865 136620 166.25 15965 166030 13078 139400 191.5 6943 65093 8241 78154 234.5 2908 24787 2453 21542 ° See footnote a for Table C.l. 1. 271 Appendix C Table C2.3. [Benzyl alcohol] = 0.483 M, [RuVI(TMP)(0)2] = 2.56 x 10'5 M 30 pL 3.0 M aqueous KOH. Blank benzyl alcohol contains 0.174% benzaldehyde. ' Time (h) Amount of Benzaldehyde (Arbitrary Units)" Amount of Benzyl alcohol (Arbitrary Units)" 17.75 6356 468220 7991 605370 41.75 17669 727430 16266 693480 67.75 13809 387560 16923 500590 91.75 23066 499500 24948 568720 116.5 40029 722480 16708 311130 141.5 20428 311660 21472 332190 166.5 20531 281680 5493 77760 191.75 3120 39047 2847 35490 234.75 5127 54642 5061 54414 259.5 3589 37622 4308 47706 283.15 4032 40980 2878 27753 307.75 12039 105910 10812 96041 334 8293 74321 7894 67489 * See footnote a for Table C.2.1. 272 Appendix C Table C2.4. [Benzyl alcohol] = 0.878 M; [RuY1(TMP)(0)2] = 2.56 x 10'5 M 30 uL 3.0 M aqueous KOH. Blank benzyl alcohol contains 0.174% benzaldehyde. . Time (h) Amount of Benzaldehyde (Arbitrary Units)" Amount of Benzyl alcohol (Arbitrary Units)" 18 7986 991370 6211 869580 41.75 13053 970480 15489 1156000 67.75 11232 582850 11727 719600 91.75 22805 1012100 22861 1031700 116.75 17076 652320 18004 724730 141.75 26168 842020 14971 470820 166.5 5424 150490 2499 71781 192 3136 76891 2056 55694 235 3558 77071 3171 70126 259.75 4462 88628 4819 99322 283.5 2827 53784 3038 55869 308 12391 214570 13183 231900 334 10445 190150 " See footnote a for Table C.2.1. 273 Appendix C C.3 Data for the Catalytic Oxidation of Alkanes in Benzene at 24 °C under 1 Atm Air. Table C.3.1. [Ph3CH] = 2.89 x 10'3 M; [Ru^TMPXO^I = 1.2 x W4 M Time (h) Percentage conversion of Ph3CH to Ph3COH (%) 0 0 20 1.51 45 2.07 93 3.33 118.5 3.98 142 4.30 166.5 5.12 191 5.22 215.5 6.29 244 6.68 262 6.96 287.5 6.87 360 7.88 410 8.80 505 9.86 1150 13.93 Table C.3.2. [Adamantane] = 6.28 x 10"3 M; [Ruvl(TDCPP)(0)2] = 2.39 x 10"4 M Time (h) Percentage conversion of adamantane to 1-adamantanol (%) 0 0 19.5 0.44 43.5 1.13 67.25 2.11 93 3.42 117 4.30 145.5 4.38 166.5 4.96 189 5.37 213 6.20 262 6.48 312 8.82 407 10.21 274 Appendix C Table C.3.3. [Ph3CH] = 4.64 x lO"3 M, [Ru\TOCPP)(0)2] = 2.39 x 10"4 M Time (h) Percentage conversion of Ph3CH to Ph3COH (%) 0 0 20 2.21 44 3.57 68 6.09 93 7.74 117 9.38 146 11.31 164 12.33 190 14.25 212.5 15.57 261 18.43 312 23.92 407.5 31.36 481.5 38.56 1150 67.01 275 Appendix D Appendix Table D.l.l. Experimental Details. A. Crystal Data Empirical Formula Formula Weight Crystal Color, Habit Crystal Dimensions Crystal System Lattice Type No. of Reflections Used for Unit Cell Determination (20 range) Omega Scan Peak Width at Half-height Lattice Parameters Space Group Z value Dcalc Fooo u(CuKa) C62H06N4O2RU 1000.30 black, irregular 0.15x0.25 x0.32 mm tetragonal I-centered 25 (35.7- 53.8°) 0.380 a = 27.967(1) A c= 1.4.274(2) A V= 11164(1) A3 I4i/a (#88) 8 1.190 gem'3 4208 26.13 cm"1 Diffractometer Radiation Take-off Angle Detector Aperture Crystal to Detector Distance Temperature Scan Type B. Intensity Measurements Rigaku AFC6S CuKa(X= 1.54178 A) graphite monochromated 6.0° 6.0 mm horizontal 6.0 min vertical 285 mm 21.0 °C ©-26 277 Appendix D Scan Rate Scan Width 29max No. of Reflections Measured 16.0°/min (in co) (up to 9 scans) (0.89 + 0.20 tan 0)° 155.5° Total 5676 Unique: 5448 (R*, = 0.020) Corrections Lorentz-polarization Absorption (trans, factors: 0.779- 1.000) Secondary Extinction (coefficient: 3.2(4) x 10'8) Structure Solution Refinement Function Minimized Least Squares Weights p-factor Anomalous Dispersion No. Observations (I > 3.00o(I)) No. Variables Reflection/Parameter Ratio Residuals: R, Rw Goodness of Fit Indicator Max Shift/Error in Final Cycle Maximum peak in Final Diff. Map Minimum peak in Final Diff. Map C Structure Solution and Refinement Patterson Methods (DIRDIF92 PATTY) Full-matrix least-squares Ico(^0|-^)2 \/c\Fo) = 4Fo2/o\F02) 0.000 All non-hydrogen atoms 3417 318 10.75 0.043; 0.044 2.34 0.001 0.42 e* A"3 -0.32 e' A"3 278 Appendix D Table D.1.2. Atomic Coordinates and Beq. atom B leg- OCC. Ru(l) 0(1) N(l) N(2) C(l) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(H) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C(20) C(21) C(22) C(23) C(24) C(25) C(26) C(27) C(28) C(29) C(29a) C(30) C(31) 0.2500 0.1975(1) 0.2059(1) 0.2604(1) 0.1827(2) 0.1562(2) 0.1636(2) 0.1951(1) 0.2113(1) 0.2416(1) 0.2583(2) 0.2868(2) 0.2885(2) 0.3148(2) 0.1980(2) 0.2266(2) 0.2153(2) 0.1774(2) 0.1498(2) 0.1590(2) 0,2699(2) 0.1662(2) 0.1274(2) 0.3419(2) 0.3895(3) 0.4117(3) 0.3895(4) 0.3433(4) 0.3186(3) 0.4152(2) 0.4153(4) 0.2672(3) 0.1679(4) 0.158(1) 0.1602(4) 0.1191(3) 0.2500 0.2814(1) 0.1987(1) 0.2096(1) 0.1999(2) 0.1562(2) 0.1295(2) 0.1559(1) 0.1399(1) 0.1650(1) 0,1486(1) 0.1827(2) 0.2214(1) 0.2634(2) 0.0900(1) 0.0519(2) 0.0063(2) -0.0023(2) 0.0356(2) 0.0824(2) 0.0595(2) -0.0526(2) 0.1225(2) 0.2679(2) 0.2531(2) 0.2558(3) 0.2710(3) 0.2850(2) 0.2837(2) 0.2345(3) 0.2732(3) 0.2988(3) 0.2763(4) 0.2972(9) 0.3300(5) 0.2644(4) 0.2500 0.3064(3) 0.1968(2) 0.3663(2) 0.1111(3) 0.0999(4) 0.1765(4) 0.2375(3) 0.3245(3) 0.3831(3) 0.4722(3) 0.5084(3) 0.4424(3) 0.4530(3) 0.3557(3) 0.3280(3) 0.3581(3) 0.4170(4) 0.4442(3) 0.4140(3) 0.2669(4) 0.4491(4) . 0.4442(4) 0.5447(4) 0.5497(5 0.6377(6) 0.7152(6) 0.7088(5) 0.6227(5) 0.4670(6) 0.8103(6) 0.6198(5) 0.379(1) 0.309(2) 0.4065(9) 0.333(1) 3.80(1) 6.9(1) 4.17(8) 4.09(8) 5.0(1) 6.1(1) 58(1) 4.4(1) 4.3(1) 4.3(1) 4.8(1) 51(1) 45(1) 5.0(1) 4.3(1) 4.5(1) 5.0(1) 5.4(1) 5.6(1) 4.9(1) 60(1) 8.2(2) 7.2(2) 5.9(1) 7.5(2) 10.1(2) 116(3) 10.9(3) 8.2(2) 10.6(3) 18.6(4) 11.7(3) 11.6(4) 9.0(6) 25.0(6) 22.1(5) 0.50 0.70 0.30 Beq = 8/37t2[t7„(flo*)2 + U22(bb*)2 + U3i(cc*f + 2Vl2aa*bb*cosy+ 2U&a*cc*cosB+ 2Unbb*cc*cosa] 279 Appendix D Table D.1.3. Bond Lengths (A).fl atom atom distance atom atom distance Ru(l) 0(1) 1.892(3) Ru(l) N(l) 2.038(3) Ru(l) N(2) 2.029(3) 0(1) C(29) 1.34(1) 0(1) C(29a) 1.18(3) N(l) C(l) 1.385(5) N(l) C(4) 1.366(5) N(2) C(6) 1.375(5) N(2) C(9) 1.380(5) C(l) C(2) 1.437(6) C(l) C(10)* 1.377(6) C(2) C(3) 1.341(6) C(3) C(4) 1.441(5) C(4) C(5) 1.396(5) C(5) C(6) 1.384(5) C(5) C(ll 1.511(5) C(6) C(7) 1.431(5) C(7) C(8) 1.346(6) C(8) C(9) 1.436(6) C(9) C(10) 1.394(6) C(10) C(20) 1.517(6) C(il) C(12) 1.389(5) C(ll C(16) 1.387(6) C(12) C(13) 1.384(5) C(12) C(17) 1.508(6) C(13) C(14) 1.373(6) C(14) C(15) 1.368(6) C(14) C(18) 1.511(6) C(15) C(16) 1.401(6) C(16) C(19) 1.493(6) C(20) C(21) 1.396(8) C(20) C(25) 1.364(8) C(21) C(22) 1.403(8) C(21) C(26) 1.476(9) C(22) C(23) 1.34(1) C(23) C(24) 1-35(1) C(23) C(27) 1 539(g) C(24) C(25) 1.410(8) C(25) C(28) 1 499(g) C(29) C(30) 156(1) C(29) C(31) 155(2) C(29a) C(30) 1.66(3) C(29a) C(31) 1.47(3) "Here and elsewhere in D.l, * refers to symmetry operation: 1/2-x, 1/2-y, 1/2-z. 280 Appendix D Table D.1.4. Bond Angles (°). atom atom atom angle 0(1) Ru(l) 0(1)* 180.0 0(1) Ru(l) N(l)* 89.0(1) 0(1) Ru(l) N(2)* 88.8(2) N(l) Ru(l) N(2) 90.0(1) N(2) Ru(l) N(2)* 180.0 Ru(l) 0(1) C(29a) 155(1) Ru(l) N(l) C(4) 126.4(3) Ru(l) N(2) C(6) 126.3(3) C(6) N(2) C(9) 107.2(3) N(l) C(l) C(10)* 125.4(4) C(l) C(2) C(3) 107.6(4) N(l) C(4) C(3) 109.1(4) C(3) C(4) C(5) 124.9(4) C(4) C(5) C(ll) 118.6(4) N(2) C(6) C(5) 126.2(4) C(5) C(6) C(7) 125.0(4) C(7) C(8) C(9) 107.5(4) N(2) C(9) C(10) 125.9(4) C(l)* C(10) C(9) 125.7(4) C(9) C(10) , C(20) 115.3(4) C(5) C(ll) C(16) 120.8(4) C(ll) C(12) C(13) 119.1(4) C(13) C(12) C(17) 119.5(4) C(13) CO 4) C(15) 118.3(4) C(15) C(14) C(18) 121.2(5) C(ll) C(16) C(15) 118.3(4) C(15) C(16) C(19) 120.2(5) C(10) C(20) C(25) 119.6(5) C(20) C(21) C(22) 117.0(7) C(22) C(21) C(26) 121.2(7) C(22) C(23) C(24) 118.7(8) C(24) C(23) C(27) 119(1) C(20) C(25) C(24) 119.1(7) C(24) C(25) C(28) 119.1(8) 0(1) C(29) C(31) 103(1) 0(1) C(29a) C(30) 101(1) C(30) C(29a) C(31) 100(1) atom atom atom angle 0(1) Ru(l) N(l) 91.0(1) 0(1) Ru(l) N(2) 91.2(2) N(l) Ru(l) N(l)* 180.0 N(l) Ru(l) N(2)* 90.0(1) Ru(l) 0(1) C(29) 139.7(5) Ru(D N(l) C(l) 126.6(3) C(l) N(l) C(4) 107.0(3) Ru(I) N(2) C(9) 126.4(3) N(l) C(l) C(2) 108.7(4) C(2) C(l) C(10)* 125.9(4) C(2) C(3) C(4) 107.6(4) N(l) C(4) C(5) 126.0(4) C(4) C(5) C(6) 125.0(4) C(6) C(5) C(ll) 116.3(4) N(2) C(6) C(7) 108.8(4) C(6) C(7) C(8) 107.8(4) N(2) C(9) C(8) 108.6(4) C(8) C(9) C(10) 125.6(4) C(l)* C(10) C(20) 119.0(4) C(5) C(ll) C(12) 118.8(4) G(12) C(ll) C(16) 120.3(4) C(ll) C(12) C(17) 121.4(4) C(12) C(13) C(14) 121.9(4) C(13) C(14) C(18) 120.5(5) C(14) C(15) C(16) 122.1(5) C(ll) C(16) C(19) 121.6(4) C(10) C(20) C(21) 119.7(6) C(21) C(20) C(25) 120.6(6) C(20) C(21) • C(26) 121.8(6) C(21) C(22) C(23) 123.4(8) C(22) C(23) C(27) 121(1) C(23) C(24) C(25) 121.2(9) C(20) C(25) C(28) 121.7(6) 0(1) C(29) C(30) 100(1) C(30) C(29) C(31) 101.0(8) 0(1) C(29a) C(31) 117(2) 281 Appendix Table D.1.5. Least-Square Planes. Plane number 1 Plane number 2 Atoms defining plane Distance N(l)" -0.003(3) C(l) 0.005(5) C(2) -0.002(5) C(3) -0.003(5) C(4) 0.004(4) Additional Atoms Distance Ru(l) 0.039 C(5) 0.005 C(10)* 0.005 Plane number 4 Atoms defining plane Distance N(l) -0.008(3) N(2) -0.005(3) C(l) 0.006(5) C(2) 0.007(5) C(3) 0.004(5) C(4) 0.002(4) C(5) -0.002(4) C(6) 0.001(4) C(7) 0.002(4) C(8) -0.001(5) C(9) -0.003(4) C(10) 0.014(5) Additional Atoms Distance Ru(l) 0.022 0(1) -1.867 C(H) 0.097 C(20) -0.021 Plane number 6 Atoms defining plane Distance C(ll) -0.001(4) C(12) 0.008(4) C(13) -0.011(4) CO 4) 0.003(4) C(15) 0.006(5) C(16) -0.006(4) Additional Atoms Distance C(5) 0.054 C(17) 0.053 C(18) -0.007 C(19) -0.029 Plane number 3 Atoms defining plane Distance N(2) -0.001(3) C(6) 0.002(4) C(7) -0.001(4) c(8) 0:000(5) C(9) 0.001(4) Additional Atoms Distance Ru(l) 0.031 C(5) -0.004 C(10) 0.022 Plane number 7 Atoms defining Atoms defining plane Distance plane Distance N(l) -0.001(3) C(20) 0.001(4) N(2) 0.000(3) C(21) -0.004(5) C(4) 0.004(4) C(22) 0.005(7) C(5) -0.003(4) C(23) -0.001(8) C(6) 0.002(4) C(24) -0.003(7) Additional C(25) 0.001(6) Atoms Distance Additional Ru(l) 0.034 atoms Distance C(10) -0.084 C(26) -0.041 Plane number 5 C(27) 0.004 C(28) -0.025 Atoms defining plane Distance N(l)* 0.023(4) N(2) -0.002(3) C(l)* -0.002(3) C(9) 0.003(4) C(10) 0.000(5) Additional Atoms Distance Ru(l) -0.008 282 Appendix D Table D.1.5. Least-Square Planes (continued). Summary plane mean deviation 72 1 0.0046 22.5 2 0.0032 3.0 3 0.0010 0.4 4 0.0019 1.6 5 0.0019 1.3 6 0.0059 13.8 7 0.0025 1.2 plane 5 Dihedral angles between planes (°) 1 2 3 4 2 0.35 3 0.18 0.33 4 0.22 0.36 0.04 1 13 1.25 1.31 1.35 6 86 94 86.63 86.95 86.97 86.74 7 94 15 93 97 93.97 93.93 95.22 81.61 Table D.1.6. Non-bonded Contacts out to 3. atom atom distance ADC C(7) C(14) 3.511(6) 4 C(8) C(15) 3.515(6) 4 C(7) H(2) 2.89 4 C(13) H(9) 2.94 4 C(14) H(5) 2.87 4 C(15) H(3) 2.96 44411 H(l) H(34) 2.50 45507 H(4) H(15) 2.55 4 atom atom distance ADC C(7) C(l 5) •3.530(6) 4 C(13) C(l 7) 3.552(7) 4 C(13) H(3) 2.78 44411 C(14) H(3) 2.68 44411 C(l 5) H(4) 2.93 44411 C(16) H(4) 2.98 44411 H(2) H(7) 2.56 44411 H(6) H(24) 2.36 45067 283 Appendix D Appendix D 285 Table D.2.1. Experimental Details. A. Empirical Formula Formula Weight Crystal Color, Habit Crystal Dimensions Crystal System Lattice Type No. of Reflections Used for Unit Cell Determination (29 range) Omega Scan Peak Width at Half-height Lattice Parameters Space Group Z value DM|c Fooo p(MoKa) Appendix D Crystal Data C62H02CI4O2N4RU 1138.08 dark-brown prism, prism 0.40 x 0.40 x 0.40 mm tetragonal I-centered 25 (20.1 -27.1°) 0.39° a = 29.334(2) A c= 13.517(6) A V= 11630(4) A3 I4,/a(#88) 8 1.300 gem'3 4720.00 4.98 cm"' Diffractometer Radiation Detector Aperture Crystal to Detector Distance Temperature Scan Type . Intensity Measurements Rigaku AFC6S MoKa(X = 0.71069 A) graphite monochromated Take-off Angle 6.0° 6.0 mm horizontal 6.0 mm vertical 285 mm 21.0 °C ©-29 286 Appendix D Scan Rate Scan Width 20max No. of Reflections Measured Corrections 16.0° min-1 (in ©) (up to 9 scans) (1.37+ 0.35 tan G)° 55.1° Total: 7249 Unique: 6984 (R*, = 0.034) Lorentz-polarization Absorption (trans, factors: 0.933 - 1.000) Structure Solution C. Structure Solution and Refinement Patterson Methods (DIRDIF92 PATTY) Refinement Full-matrix least-squares Function Minimized Lco(|F0| - |FC|)2 Least Squares Weights Vc2(Fo) = 4F02/c\Fo2) p-factor 0.008 Anomalous Dispersion All non-hydrogen atoms No. Observations (I > 3.00a(I)) 2421 No. Variables 376 Reflection/Parameter Ratio 6.44 Residuals: R, R« 0.051; 0.046 Goodness of Fit Indicator 2.62 Max Shift/Error in Final Cycle 0.03 Maximum peak in Final Diff. Map 0.75 e'A3 Minimum peak in Final Diff. Map -0.41 e"A-3 287 Appendix D Table D.2.2. Atomic Coordinates and B*,. atom Ru(D Cl(l) Cl(la) Cl(2) Cl(2a) 0(1) N(l) N(2) C(l) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(ll) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C(20) C(21) C(22) C(23) C(24) C(25) =0(26) C(27) C(28) C(29) C(29a) C(30) C(30a) C(31) C(31a) Beq 0.2500 0.4133(3) 0.4034(9) 0.3415(2) 0.3487(6) 0.2998(2) 0.2386(2) 0.2923(2) 0.2109(2) 0.2109(2) 0.2386(2) 0.2559(2) 0.2856(2) 0.3021(2) 0.3327(2) 0.3397(3) 0.3146(2) 0.3133(2) 0.2993(2) 0.3365(3) 0.3463(2) 0.3210(3) 0.2848(3) 0.2734(2) 0.3655(3) 0.3324(3) 0.2330(3) 0.3397(4) 0.3181(4) 0.3428(4) 0.3864(-D) 0.4080(3) 0.383 i-(4) 0.2689(4) 0.4151(4) 0.4085(3) 0.3269(9) 0.340(2) 0.366(1) 0.375(2) 0.318(1) 0.334(2) 0.2500 0.2522(2) 0.2128(7) 0.1637(2) 0.1449(6) 0.2206(2) 0.2897(2) 0.2990(2) 0.2795(2) 0.3170(2) 0.3492(2) 0.3323(2) 0.3563(2) 0.3403(2) 0.3646(2) 0.3382(3) 0.2969(2) 0.2611(2) 0.4035(2) 0.4096(2) 0.4538(3) 0.4909(2) 0.4836(2) 0.4400(2) 0.3704(3) 0.5384(2) 0.4350(2) 0.2654(2) 0.2820(3) 0.2843(3) 0.2710(4) 0.2554(3) 0.2521(3) 0.2966(3) 0.2750(3) 0.2338(4) 0.222(1) 0.202(2) 0.2439(9) 0.201(3) 0.171(1) 0.216(2) Z/3n2[Un(aa*f + U22{bb*f + Ui3{cc*Y + 2U23bb*cc*cosa] 0.7500 0.6392(8) 0.703(1) 0.4757(6) 0.601(2) 0,6859(5) 0.6296(3) 0.8060(4) 0.5500(5) 0.4832(5) 0.5210(5) 0.6140(5) 0.6740(5) 0.7635(5) 0.8278(6) 0.9081(6) 0.8957(5) 0.9626(5) 0.6412(5) 0.5783(5) 0.5462(5) 0.5762(6) 0.6379(5) 0.6724(5) 0.5446(6) 0.5401(6) . 0.7382(6) 1.0588(7) 1.1419(7) 1.2306(7) 1.2347(9) 1.1540(10) 1.0622(8) 1.1396(7) 1.3306(8) 0.9746(9) 0.623(3) 0.689(3) 0.628(4) 0.638(5) 0.556(3) 0.496(7) 2U]2aa*bb*cosy BtJ1 occ. 5.02(2) 0.50 21.4(3) 0.68 20.0(7) 0.32 17.6(3) 0.68 21.3(8) 0.32 8.6(2) 54(1) 5.7(1) 60(2) 7.1(2) 7.1(2) 5.6(2) 5.6(2) 5.8(2) 7.4(2) 8.1(2) 6.1(2) 6.3(2) 5.3(2) 6.3(2) 66(2) 6.5(2) 6.4(2) 5.5(2) 9.1(3) 9.3(2) 7.9(2) 7.1(3) 8.3(3) 10.4(3) 10.7(4) 9.9(3) 9.5(3) 12.9(4) 16.3(4) 12.7(4) 13.8(10) 0.68 11(1) 0.32 30(1) 0.68 20(2) 0.32 25(1) 0.68 29(3) 0.32 f 2Uuaa*cc*'cos B+ 288 Appendix D Table D.2.3. Bond Lengths (A). atom atom distance Ru(l) 0(1) 1.905(6) Ru(l) N(2) 2.042(5) Cl(l) C(30a) 1.87(8) Cl(la) C(30a) 1.25(4)* Cl(2) C(31a) 1.58(5) 0(1) C(29a) 1.29(5) N(l) C(l) 1.381(7) N(2) C(6) 1.373(7) C(l) C(2) 1.425(8) C(2) C(3) 1.346(8) C(4) C(5) 1.383(8) C(5) C(ll) 1.509(8) C(7) C(8) 1.350(8) C(9) C(10) 1.387(8) C(ll) C(12) 1.393(8) C(12) C(13) 1.397(8) C(13) C(14) 1.379(9) C(14) C(18) 1.513(9) C(16) C(19) 1.491(8) C(20) C(25) 1.35(1) C(21) C(26) 1.51(1) C(23) C(24) 1.34(1) C(24) C(25) 1.44(1) C(29a) C(30) 1.66(5) C(29) C(30) 1.31(4) C(29) C(31). 1.77(5) Here and elsewhere in D.2, * Denotes symmetry atom atom distance Ru(l) N(l) . 2.029(4) Cl(l) C(30) 1.42(4) Cl(la) C(30) 1.75(5) Cl(2) C(31) 1.30(3) Cl(2a) C(30a) 1.89(7) 0(1) C(29) 1.16(3) N(l) C(4) 1.365(7) N(2) C(9) 1.379(7) C(l) C(10)* 1.394(8) C(3) C(4) 1.445(8) C(5) C(6) 1.384(8) C(6) C(7) 1.439(8) C(8) C(9) 1.427(8) C(10) C(20) 1.519(9) C(ll) C(16) 1.378(8) C(12) C(17) 1.501(9) C(14) C(15) 1.366(9) C(15) C(16) 1.399(8) C(20) C(21) 1.38(1) C(21) C(22) 1.40(1) C(22) C(23) 1.34(1) C(23) C(27) 1.55(1) C(25) C(28) 1.49(1) C(29a) C(30a) 1.25(7) C(29) C(30a) 157(4) C(29) C(31a) 1.74(9) operation: 1/2-x, 1/2-y, 3/2-z. 289 Appendix D Table D.2.4. Bond Angles (°). atom atom atom angle 0(1) Ru(l) 0(1)* 180.0 0(1) Ru(l) N(l)* 88.8(2) 0(1) Ru(l) N(2)* 88.8(2) N(l) Ru(l) N(2) 89.7(2) N(2) Ru(l) N(2)* 180.0 Ru(l) 0(1) C(29) 146(1) Ru(l) N(l) C(4) 125.9(4) Ru(l) N(2) C(6) 126.4(4) C(6) N(2) C(9) 107.9(5) N(l) C(l) C(10)* 125.4(6) C(l) C(2) C(3) 107.6(6) N(l) C(4) C(3) 108.5(6) C(3) C(4) C(5) 123.8(6) C(4) C(5) C(H) 117.7(6) N(2) C(6) C(5) 126.3(6) C(5) C(6) C(7) 125.3(6) C(7) C(S) C(9) 108.3(6) N(2) C(9) C(10) 126.4(6) C(l)* C(10) C(9) 125.4(6) C(9) C(10) C(20) 118.7(6) C(5) C(ll) C(l 6) 118.4(6) C(ll) C(12) C(13) 118.0(7) C(13) C(l 2) C(l 7) 119.9(7) C(13) C(l 4) C(l 5) 118.2(7) CO 5) C(14) C(18) 121.0(8) C(ll) C(16) COS) 118.4(6) C(15) C(16) CO 9) 118.7(7) C(10) C(20) C(25) 119.5(9) C(20) C(21) C(22) 118.4(9) C(22) C(21) C(26) 119(1) C(22) C(23) C(24) 121(1) C(24) C(23) C(27) 116(1) C(20) C(25) C(24) 119(1) C(24) C(25) C(28) 117(1) 0(1) C(29) C(30) 125(3) 0(1) C(29) C(31) 104(2) C(30) C(29) C(31) 124(2) Cl(l) C(30) C(29) 160(3) Cl(l) C(30a) C(29a) 117(4) Cl(la) C(30a) C(29a) 98(5) Cl(2) C(31) C(29) 119(3) Cl(2) C(31a) C(29) 106(4) atom atom atom angle 0(1) Ru(l) NO) 91.2(2) 0(1) Ru(l) N(2) 91.2(2) N(l) Ru(l) N(l)* 180.0 N(l) Ru(l) N(2)* 90.3(2) Ru(l) 0(1) C(29a) 150(2) Ru(l) N(l) CO) 126.7(4) CO) N(l) C(4) 107.4(5) Ru(l) N(2) C(9) 125.7(4) N(l) C(l) C(2) 109.0(6) C(2) CO) C(10)* 125.6(6) C(2) C(3) C(4) 107.5(6) N(l) C(4) C(5) 127.7(6) C(4) C(5) C(6) 124.0(6) C(6) C(5) C(H) 118.3(6) N(2) C(6) C(7) 108.4(6) C(6) C(7) C(8) 107.2(6) N(2) C(9) C(8) 108.1(6) C(8). C(9) C(10) 125.4(6) cor C(10) C(20) 115.8(6) C(5) C(H) C(12) 120.4(6) C(12) C(ll) C(16) 121.2(6) C(ll) C(12) C(17) 122.0(7) C(12) C(13) CO 4) 122.0(7) C(13) C(14) CO 8) 120.8(8) CO 4) CO 5) C(16) 122.2(7) C(ll) C(16) C(19) 122.9(6) C(10) C(20) C(21) 119.5(8) C(21) C(20) - C(25) 121.0(9) C(20) C(21) C(26) 121.6(8) C(21) C(22) C(23) .121(1) C(22) C(23) C(27) 122(1) C(23) C(24) C(25) 119(1) C(20) C(25) C(28) 123.0(10) 0(1) C(29a) C(30a) 139(5) 0(1) C(29) C(30a) 120(4) 0(1) C(29) C(31a) 142(3) Cl(l) C(30) C(29a) 121(4) Cl(la) C(30) C(29) 109(3) Cl(l) C(30a) C(29) 102(4) Cl(la) C(30a) C(29) 124(4) Cl(2a) C(31) C(29) 98(3) 290 Appendix D Table D.2.5. Least-Square Planes. Plane number 1 Atoms defining plane Distance Ru(l) 0.004 N(l) 0.019 N(2) 0.022 C(l) 0.012 C(2) -0.022 C(3) -0.019 C(4) -0.003 C(5) 0.005 C(6) 0.013 C(7) 0.011 C(8) -0.013 C(9) -0.008 C(10) -0.022 Additional Atoms Distance 0(1) 1.906 C(29a) 3.025 C(29) 2.901 C(30) 3.501 C(30a) 4.182 C(31) . 3.750 C(31a) 3.928 H(27) 2.560 Plane number 4 Plane number 5 Atoms Atoms defining Distance defining Distance plane plane Ru(l) -0.010 Ru(l) -0.007 NO) 0.013 N(l)* -0.003 N(2) 0.007 N(2) 0.013 C(4) -0.007 CO)* 0.012 C(5) -0.003 C(9) -0.007 C(6) 0.000 C(10) -0.009 Additional Additional atoms Distance atoms Distance C(5) -0.002 C(5) -0.027 C(10) -0.048 C(10) -0.009 Plane number 2 Atoms defining plane Distance N(l) 0.000(5) CO) 0.003(7) C(2) -0.005(7) C(3) 0.005(7) C(4) -0.002(6) Additional Atoms Distance Ru(l) -0.053 C(5) 0.005 C(10) -0.113 Plane number 3 Atoms defining plane Distance N(2) 0.005(5) C(6) -0.009(6) C(7) 0.007(7) C(8) -0.002(8) C(9) -0.005(7) Additional Atoms Distance Ru(l) -0.033 C(5) -0.035 C(10) -0-009 Plane number 6 Plane number 7 Atoms Atoms defining Distance defining Distance plane plane C(ll) -0.003(6) C(20) -0.002(7) C(12) 0.003(6) C(21) 0.004(8) C(13) -0.004(7) C(22) -0.001(9) C(14) 0.003(6) C(23) -0.01(1) C(15) -0.004(6) C(24) 0.007(9) CO 6) 0.004(6) C(25) -0.002(8) Additional Additional atoms Distance atoms Distance C(5) -0.069 C(10) -0.043 CO 7) 0.014 C(26) -0.010 C(18) -0:006 C(27) 0.048 C(19) -0.028 C(28) -0.014 291 Appendix D Table D.2.5. Least-Square Planes (continued). Summary plane mean deviation 1 0.0135 0.0 2 0.0029 1.1 3 0.0056 4.2 4 0.0067 0.0 5 0.0084 0.0 6 0.0034 1.6 7 0.0036 1.1 Dihedral angles between planes nlanp 1 2 3 4 L/lul Iw 2 1.09 3 0.83 1.72 4 0.22 0.92 1.04 0.76 5 0.55 1.63 0.52 6 87.11 87.60 86.28 87,30 7 92.84 91.93 92.87 92.75 86.72 93.19 83.87 Table D.2.6. Non-bonded Contacts out to 3.60 A. atom atom distance ADC atom atom distance ADC Cl(la) C(24) 3.44(2) 54616 C(2) C(13) 3.592(9) 45412 C(3) C(14) 3.524(9) 45412 C(3) C(13) 3.581(9) 45412 Cl(l) H(26) 2 96 45615 Cl(l) H(17) -3.03 45615 Cl(la) H(4) 3.24 54616 Cl(2a) H(4) 3.15 54616 n\A\ Hm 2.67 3 C(13) H(2) 2.99 3 uW n^, C(14) H(6) 2.90 45412 C(15) H(13) 2.82 45412 C(15) H(2) 2.91 3 C(27) H(21) 2.90 45715 H(5) H(18) 2.55 55403 H(6) H(13) 2.38 45412 H(ll) H(18) 2.26 55403 worn W2G\ 2 38 55713 H(21) H(22) 2.09 54716 atom C(2) atom C(13) C(3) C(13) Cl(l) H(17) Cl(2a) H(4) C(14) H(2) C(15) H(13) C(27) H(21) H(6) H(13) H(20) H(20) 292 Appendix E Appendix E. Oxidation of Alcohols, Alkenes and Alkanes by Ru(TDCPP-Cl8) Species. E.l. Oxidation of benzyl alcohol at 50 °C under 1 atm air. Table E.l. [Ruvl(TDCPP-Cl8)(0)2] = 3.5 x 10"5 M A alcohol] = 0.290 M Time (h) Conversion to Time (h) benzaldehyde (%) 0 0 0 24 1.06 24 47.5 2.28 47.5 74.25 3.95 74.25 92.5 4.31 92.5 116.5 5.85 116.5 140.5 6.08 140.5 244 7.36 166.5 289.5 7.90 188 360 8.65 216.5 412 9.74 294 263 313 384 benzyl alcohol] = 0 580 M Conversion to benzaldehyde (%) 0 0.627 1.74 2.60 3.33 3.71 4.34 4.90 4.72 5.20 5.66 5.74 6.29 6.90 [422 nm species] = 1.9 x 10-5 M = 0.0242 M 0.12,1 M [benzyl alcohol] Time (h) 0.242 M 0483 M Conversion to Conversion to benzaldehyde (%) 0 0 0 24 2.7733 1.9161 49.5 4.8985 2.81385 101 6.7525 4.4155 119.75 7.5445 5.1305 144.25 8.377 5.634 168.75 7.9495 6.169 Time (h) 0 24.5 50 101.25 119.75 144.5 169 194 219 242.5 288.75 312 337 360.5 benzaldehyde (%) 0 0.86 1.53 2.61 2.99 3.22 3.56 3.90 4.15 4.62 5.04 5.38 5.74 5.80 0 0.48 0.96 1.66 1.85 1.88 2.54 2.85 3.06 3.49 3.97 3.95 4.50 4.52 293 Appendix E E.2. Oxidation of Alkenes under 1 Atm 02. Table E.2.1. Oxidation of cyclohexene at 35 °C [RuD(TDCPP-Cl8)(C0)] = 3.1x10" M. Substance present" Blank 23 h at 35 °C (arbitrary units cyclohexene* 16098000 cyclohexene-oxide 2427 cyclohexene-2-ol 31695 cyclohexene-2-one 46473 cyclohexene-peroxides 638 dimers 4604 Ruu(TDCPP-Cl8)(CO) heated for 23 h (arbitrary units) 200640 3755 47629 45773 1089 7414 See Section t.^t laier IUI me mnimiwuu,. v. v..~ , " the 20% loss due to evaporation has NOT been taken into account in this reported value; i.e. the amount of cyclohexene is increased by 20% prior to the calculation of percentage conversion (see Chapter 5). Table E.2.2. Oxidation of m-cyclooctene at 93 °C. [RuVI(TDCPP-Cl«)(0)2] = 5.0 x 10'5 M. Values in parentheses are those for the blank cyclooctene system at 110 °C heated for 23 h. TIME (h) Amount of cyclooctene (Arbitary units) Amount of epoxide Amount of other products* 601640 73218 14661 26 {23} 185130 {2517200, 1697400}° 112940 {232670; 166060} 32 279330 226300 40074 55 26106 50896 13165 16954 {102897; , 49390) 8 Two sets of data are given, which correspond to 2 GC runs of the same sample. * See Section E.5 later for the identification of the other products by GCMS analysis. 294 Appendix E E.3. Oxidation of Alkanes. Table E.3.1. Oxidation of methylcyclohexane under 1 atm 02. RuD(TDCPP-CU(CO) (1); Ru%a(TDCPP-Clg)(Q)2 (2) Blank [(l)] = 3.1xlO"sM [(2)]=l.lxlO"'M [(2)] - 3.1x10" M Substance present methylcyclohexane* v OH 6 24 h at 100 °C 6460500 19985 9044 1643 v OH . OH .OH & 6. $ C7H14O3 Mixture of ring-opened acids and/or peroxides 20 h at 93 °C 3206100 88347 21819 15232 17.5 h at 93 °C 22.5 h at 100 °C 3000 1353 5900 36750 14679 12142 27272 1324900 16673 5428 3257 7010 2945 3357 8451 347380 17588 2821 2761 7368 2846 5104 9441 r 1 • See Section E.6 later for the identification of the substances present by GCMS analysis. ' * The 20% loss due to evaporation has NOT been taken into account in this reported value; i.e. the amount of methylcyclohexane is increased by 20% prior to the calculation of percentage conversion (see Chapter 5). Table E.3.2. Oxidation of Ph3CH catalyzed by RuY1(TDCPP-Cl8)(0)2 at 24 °C under 1 atm air in penzene. imi yii^i Time (h) Turnovers per mole of initial porphyrin 0 0 26 0.895 45.5 1.21 75.5 1.42 96 1.56 148.5 1.69 484 3.07 295 Appendix E E.4. GCMS Data for the Cyclohexene Oxidation. 3:51 Relative intensity 0:00 9:01 8:00 10:50 12:17 _ 15:39 14:35 5:00 10:00 15:00 17:38 ! 18:06 21:16 20:00 Retention time (min) Figure E.4.1.. GC trace for the run in Table E.2.2 for the oxidation of cyclohexene. Table E.4.1. Retention times and identity of substances from the GCMS analysis. Retention Time Substance Retention Substance (min) Time (min) 3:51 cyclohexene 14:35 cyclohexene-peroxide 8:00 cyclohexene-oxide 15:39 Dimeric product 9:01 cyclohexene-2-ol 17:38 DIMER 10:50 cyclohexene-2-one 18:06 DIMER 12:17 cyclohexene-3-one 21:16 DIMER 296 Appendix E Figure E.4.2. Low Resolution Mass Spectra for the various products indicated in Figure E.4.1. Relative intensity 55 69 28 42 _au u. 1 LUI 83 o: 98 8:00 20 40 60 80 100 120 M/z 140 160 180 200 Relative intensity 170 55 28 41 JLiiL. 98 83 20 40 60 80 OH 100 120 M/z 9:01 "140 160 180 200 Relative intensity 24 20 39 40 68 55 +iiJi. 60 81 80 96 10:50 100 120 140 M/z 297 Appendix E Figure E.4.2. continued... Relative intensity 28 39 55 68 96 81 12:17 20 40 60 80 100 120 140 M/z Relative intensity 68 55 44 28 96 81 86 114 20 40 60 80 100 M/z OOH 14:35 TJo " 140" Relative 81 -28 41 53 i 6f„ , 1,1 1 105 115117 133 154 40 60 80 lOO 120 140 15:39 Dimeric Product ,162 • , ._ 160 180 200 220 24<> 260 55o~ M/z 298 Appendix E Figure E.4.2. continued... Relative intensity 20 160 Relative intensity 21) 137 81 67 55 Ii Ii 95 123 96 109 JX 1+ 139 151 _1_ 80 100 120 140 17:38 Dimeric Product 180 200 220 M/z 240 260 280 139 81 95 55 68 ""'I', il""'-' "I 96 109 ,1.1,1, 123 L L 137 151 60 80 100 120 140 18:06 Dimeric Product 231 loO 220~ 240 260 280 M/z 299 E.5. GCMS Data for the Cyclooctene Oxidation. Appendix E Relative intensity 1:38 7:26 12:29 9:56 9:51 | , 14:44 ll 0:00 20:00 5:00 10:00 15:00 Retention time (min) Figure E.5.1. GC trace for the run in Table E.2.1 for the oxidation of cyclooctene. Table E.5.1. Retention times and identity of substances from the GCMS analysis. Retention Time Substance Retention Substance (min) Time (min) 1:38 cyclooctene 11:52 unknown, possible dimer 7:26 cyclooctene-oxide 12:29 cis-1-oxabicyclo[4,3,0]-nonane 9:51 unknown 14:44 unknown 9:56 unknown 300 Appendix E Figure E.5.2. Mass spectra for the various products indicated in Figure E.5.1. 155 Relative intensity Relative intensity 26 100 120 140 160 M/z 98 Unknown; possible dimer 11:52 180 181 197 i 1 i 140 160 180 301 83 Appendix E Relative intensity 70 28 55 41 !., .!1 P 12.29 126 93 108 131 20 40 60 80 100 M/z 120 140 160 180 Relative intensity 28 81 68 53 39 20 40 60 95 j L 124 106 Unknown product 14:44 80 100 M/z 120 140 160 180 302 55 Appendix E Relative intensity 41 2? O 6? 03 97 111 126 i i i i I I'I i i i i i i I i i i i i ' i i ' ' i i 111 1111 11 i i 0 10 20 30 40 50 60 70 80 90 100 110 120 130140 M/z 83 Relative intensity 41 11111111 M 11111111 0 20 40 60 .M/z 67 o 12b 97 93,. I, 108 I I I I' I * 111' I I I I I I I I I I » I I I'I 80 100 120 r i i i | i i i i | 140 Figure E.5.3. Known fragmentation patterns for cyclooctene-oxide and m-7-oxabicyclo[4,3,0]-nonane. 303 Appendix E E.6. GCMS Data for the Methylcyclohexane Oxidation. Relative intensity 18 16 14 12 10 8 6 4 2 °l— 0:00 |3:30 4:47 7:02 7:51 12:05 11:04 , 2:00 4:00 6:00 8:00 10:00 12:00 Retention time (min) 14:00 16:00 18:00 Figure E.6.1. GC trace for the run in Table E.3.1 for the oxidation of methylcyclohexane. Retention Time Substance Retention Substance (min) Time (min) 4:47 methylcyclohexane 7:47" (2,3 and 4)-7:51 methylcyclohexanone 7:55" 7:02 1 -methylcyclohexanol 10:30 11:04 l-ol-(2,3 and 4)-ones 11:11 7:36" (2,3 and 4)- 12:05 Peroxide and/or acid 7:43" methylcyclohexanol " These retention times were not shown on the above chromatogram due to the lack of space 304 Appendix E Figure E.6.2. Low resolution mass spectra for the various products indicated in Figure E.6.1. 1 171 Relative intensity 99 7:02 OH 43 58 81 114 29 _L fO 40 60 80 100 M/z Tio 140160 180 Relative intensity 68 81 96 57 43 28 •II i 20 40 7:36 ii4 60 80 100 120 140 160 180 M/z 305 Appendix E Relative intensity 41 29 _JL 20 40 Figure E.6.2. continued.. |96 71 81 57 60 80 113 100 M/z OH ^ -OH 7:43 120 140 160 180 306 Appendix E 307 Appendix E Figure E.5.2. continued. Relative intensity 28 55 43 69 184 112 97 128 20 40 60 80 100 120 M/z cr OH 10:50 140 160 180 98 169 Relative intensity 55 42 11:04 128 80 29 -I r-20 40 60 80 100 120 140 160 180 M/z 308 Appendix E Figure E.5.2. continued.. Relative intensity 41 29 i 20 40 56 69 60 98 83 114 80 OH 128 11:11 100 120 M/z 140 160 180 143 Relative intensity 20 27 4TT 58 JJ L 60 84 73 80 98 111 126 C7H1203 12:05 144 AW 120 140 145_ 160 M/z 180 309 Appendix F Appendix F. Kinetics Data for the Oxidation of Phenol by Ruv,(TMP)(0)2. Table F.l. Pseudo-first-order rate constants, kobs, for the oxidation of phenol by Ruvl(TMP)(0)2 (1) (5.0 x 10-6 M) in benzene under 1 atm air, unless indicated otherwise. Data acquired on stopped-flow instrument. 283.4 K 288.2 K 293.2 K 303.6 K [phenol] (M) k„b5 (s1) (errors < 5% from linear regression of semilog plots) 0.0973 8.66xl0"3 1.40xlQ-2 1.45xl0"2 2.58 x 10' 0.257 4.30 x 10'2 5.95 x IO-2 7.50 x IO-2 (7.25 x IO"2)" (7.67 x IO"2)* 1.37 x 10"1 0.301 5.36 x 10"2 7.70 x IO'2 9.40 x 10'2 1.82 x 10'1 0.467 1.07 x IO-1 1.56 x IO-1 1.93 x 10'1 3.40 x 10'1 0.989 2.98 x 10"' 3.86x 10° 5.12 x 10"1 8.30 x 10'1 " Solutions purged with N2 for 10 min. * [(l)] = 3.0x 10'6M. Table F.2. Absorbance-time data for the oxidation of phenol by Ruvl(TMP)(0)2 (1) in benzene under 1 atm air at 293.2 K, unless indicated otherwise. Ill L/ Vi ii^VUV UIIUl [(l)] = 4.5x 10'6M [phenol] = 0.0102 M Time (s) Absorbance" „1 A Ml... _W- _»v — " — • — 5 ______ [(l)] = 5.2x 10'7M [phenol] = 0.0292 M Time (s) Absorbance" [(l)] = 5.2x 10^M [phenol] = 0.0292 M Time (s) Absorbance" 30 1.195 20 0.139 20 " 1.408 750 1.070 140 0.120 140 1.360 1470 0.932 260 0.103 260 1.286 2190 0.811 380 0.093 380 1.195 2910 0.721 500 0.084 500 1.108 3630 0.656 620 0.079 620 1.027 4350 0.609 740 0.074 740 0.959 5070 0.577 860 0.071 860 0.904 5790 0.554 980 0.069 980 0.862 6510 0.539 1100 0.067 1100 0.828 7230 0.527 1220 0,066 1220 0.801 00 0.50 00 0.062 00 0.70 kobs = 4.8 x 10 V kobs = 2.7 x 10-V kobs = 2.0 x lO'V " Absorbance at 422 nm, monitored for the loss of (1). 310 Appendix F Table F.2. continued. [(l)] = 4.0x lO^M [(1)] = 2.5 x lO^M [(1)] = = l.Ox 10"5M [phenol] = 0.0381 M [phenol] = 0.0381 M [phenol] = 0.0381 M (monitored at 518 nm) Time (s) Absorbance" Time (s) Absorbance" Time (s) Absorbance 20 1.099 20 0.630 20 0.236 80 1.006 140 0.510 140 0.220 140 0.920 260 0.425 260 0.209 200 0.844 380 0.367 380 0.201 260 0.777 500 0.325 500 0.197 320 0.719 620 0.298 620 0.193 380 0.670 740 0.280 740 0.191 440 0.629 860 0.267 860 0.190 oo 0.42 980 0.260 980 0.189 1100 0.255 1100 0.189 1220 0.251 oo 0.185 oo 0.24 kobs = 2.85 x 10'3 s"1 kobs 3.15 x 10"V kobs 3.43 x lO-3 s'1 [(!)] = 3.6x 10'6M [(!)] = = 3.8x lO^M [(1)] ' = 4.7xT0"*M [phenol] = 0.0547 M [phenol] = 0.0381 M [phenol] = 0.0381 M Time (s) Absorbance" Time (s) Absorbance" Time (s) Absorbance" 20 0.909 20 0.980 10 1.219 140 0.668 140 0.693 100 0.880 260 0.537 260 0.531 190 0.691 380 0.468 380 0.450 280 0.615 500 0.435 500 0.410 370 - 0.588 620 0.418 620 0.390 460 0.579 740 0.411 740 0.380 550 0.576-860 0.408 860 0.376 640 0.576 980 0.406 980 0.374 730 0.577 1100 0.406 1100 0.374 oo 0.575 oo 0.40 1220 0.373 00 0.37 kobs = 6.03 x 10'3 s° kobs — 6.0 x lO'V kobs = 1.19 x 10-V ' Absorbance at 422 nm, monitored for the loss of (1). 311 Appendix F Table F.2. continued [(1)] = [phenol] Time (s) 4x 10"6M = 0.0943 M Absorbance" [(l)] = 5x lO^M [phenol] = 0.0943 M 1 atm 02 Time (s) Absorbance" [(l)] = 5x lO^M [phenol] = 0.0943 M 1 atmN2 Time (s) Absorbance" 10 1.341 10 1.404 10 1.395 50 1.128 58 1.230 58 1.058 90 0.935 106 1.034 106 0.858 130 0.815 154 0.913 154 0.755 170 0.745 202 0.846 202 0.693 210 0.705 250 0.812 250 0.665 250 0.684 298 0.795 298 0.654 290 0.671 346 0.787 346 0.648 330 0.665 394 0.783 394 0.645 610 0.659 442 0.781 442 0.641 cc 0.65 490 0.780 490 0.641 oo 0.78 oo 0.64 kobs = 1.41 x 10"1 s"1 . kobs 1.40 x 10'' s'1 kobs = 141 x 10"' s'1 " Absorbance at 422 nm, monitored for the loss of (1). 312 Appendix G Appendix G. Oxidation of A^-dimethylaniline by Ru^TMPHOh in benzene. Relative intensity 112:23 0:00 1:00 4:15 2:00 3:00 4:00 5:00 6:00 Retention time (min) 7:00 8:00 9:00 Figure G.l. GC trace of a benzene solution containing RuVI(TMP)(0)2 with N.JV-dimethylaniline added. The sample with analytes corresponding to the retention times of 2:23 and 4:15 minutes were subjected to MS analysis (Figures G.2 and 3). 313 Appendix G Relative intensity 77 51 42 28 63 105 91 k L J L 120 NMej 20 40 60 80 100 120 140 160 180 M/z Figure G.2. Mass spectrum of analyte at 2:23 in the GC trace in Figure G. 1. 106 Relative intensity [M-2H]+ 135 51 20 28 38 40 66 'ill . 60 77 80 94 100 liO 140 160 181 180 M/z Figure G.3. Mass spectrum of analyte at 4.15 in the GC trace in Figure G. 1 314 

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