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Oxidations using dioxoruthenium (VI)-porphyrin complexes ; and studies on some organoruthenium-porphyrin.. Rajapakse, Nimal 1990-01-21

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Oxidations Using Dioxomthenium(VI)-Porphyrin Complexes; and Studies on Some Organommenium-Porphyrin Species. by Nimal Rajapakse B.Sc, University of Sri Lanka, 1979 M.Sc, University of British Columbia, 1985 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 January 1990 © Nimal Rajapakse, 1990. In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver, Canada Date DE-6 (2/88) ii Abstract The oxidation of three alkyl thioethers, phenol and 2-propanol by trans-dioxo ruthenium porphyrin species, and the synthesis, characterization and reactivity of several new ruthenium porphyrin complexes are described in this thesis. The trans-dioxo species Ru(Porp)(0)2 [Porp= the dianions of 5,10,15,20-tetramesitylporphyrin (TMP) and 5,10,15,20-(2,6-dichlorophenyl)porphyrin (OCP)] selectively oxidize diethyl-, di-n-butyl- and decylmethyl- sulfides to the corresponding sulfoxides at room temperature. The reaction is first order in [Ru] and in [thioether]. The second order rate constants for the first O-atom transfer from the Ru(TMP) system are: 7.54xl0'3, 1.23xl0-2 and 1.14x10-* M"1 s"1 respectively for the three thioethers at 20.0 °C. The activation parameters for the O-atom transfer process are also determined: for Et2S, AH*= 58.3 kJ mol"1 and AS*= -86 J K-l mol"1; for nBu2S, AH*= 47.4 kJ mol"1 and AS*= -120 J K-l mol-1; for DecMeS, AH*= 56.5 kJ moH and AS*= -70 J K"l mol"1. A second order rate constant of 7.23xl0"2 M"1 s_1 is measured at 20.0 °C for the oxidation of Et2S by Ru(OCP)(0)2- The intermediates Ru(TMP)(QSEt2)2, Ru(TMP)(OSEt2)(0£Et2) and the final product Ru(TMP)(0£Et2)2,where Q_ and S. refer to O- and S- bonded sulfoxide, are observed by *H nmr, and the last mentioned is isolated and characterized. A mechanism is proposed, based on electrophilic attack of the 0=Ru=0 moiety on :SR2 to form bis-O-bonded species which subsequently isomerizes to bis-S-bonded species via mixed species. The Ru(TMP)(0)2/Et2S/02 system at room temperature is catalytic in complex, but produces only about 5 turnovers due to poisoning of the catalyst by the reaction product. The same system at >65 °C gives higher turnovers, but now porphyrin ligand degradation is observed, perhaps via oxidation by the 0=Ru=0 moiety. The Ru(OCP)(0)2/Et2S/02 system at 100 °C catalytically oxidizes Et2S to Et2SO and Et2SC>2 (in ~ 4:1 ratio) and the porphyrin ligand does not undergo oxidative destruction. iii The Ru(TMP)(0)2 species reacts with phenol via an observed intermediate Ru(TMP)(p-0(H)C6H40H)2 to form Ru(JV0(TMP)(O<^OH)2, a paramagnetic (S=l) complex which is isolated and characterized. The oxidation reaction is first order in both [Ru] and [phenol] with a second order rate constant 6.90x10-2 M'1 s*1 at 20.0 °C. A mechanism based on electrophilic attack by the 0=Ru=0 moiety on the aryl ring followed by proton migration is proposed. This mechanism also explains the formation of some free para-benzoquinone and 1 equivalent of water per Ru. No ortho-benzoquinone is formed in the reaction. Preliminary *H nmr studies reveal that 2-propanol is oxidized to acetone by Ru(TMP)(0)2. A paramagnetic species (S= 1) was isolated as the only porphyrin product but not characterized. A range of novel ruthenium porphyrin complexes is also prepared. The reaction of acetylene with the four-coordinate Ru(TMP) species forms [Ru(TMP)]2(u-C2H2), the first reported organometallic ruthenium porphyrin dimer. The complexes, Ru(TMP)(PhCCPh) and Ru(TMP)(PhCCH), the first 7t-bonded alkyne species in ruthenium porphyrin chemistry, are characterized in solution. The 7t-bonded alkene complexes Ru(TMP)(CH2CH2) OPrOH).(iPrOH) and Ru(TMP)(CH2CH2) are isolated and characterized, while the Ru(TMP)(cyclohexene) complex is characterized in situ. The Ru(TMP)(OSEt2>2 complex is isolated also by the reaction of Ru(TMP)(CH3CN)2 with Et2SO. The Ru(TMP)(L)2 complexes, L= OS_Me2, OS_nPr2 and 0£nBu2 are also prepared via the above method and characterized. Some new Ru(OCP) complexes, (the monocarbonyl, the bis-acetonitrile and the dioxo- species) are also isolated and characterized. iv Contents Page Abstract ii Contents v List of tables viList of figures . viii List of schemes xiAbbreviations xiiAcknowledgements xvi Chapter 1 Chemistry of ruthenium porphyrins 1 1.1 Introduction 2 1.2 Porphyrin as a ligand1.3 Chemical properties of ruthenium porphyrins 4 1.3.1 Ruthenium (0) 5 1.3.2 Ruthenium (I)1.3.3 Ruthenium (TJ)1.3.4 Ruthenium (HI) 14 1.3.5 Ruthenium (TV) 6 1.3.6 Ruthenium (VI) 17 1.4 Catalytic properties of ruthenium porphyrins 11.4.1 Oxygenations using ruthenium porphyrins 17 1.4.2 Decarbonylations using ruthenium porphyrins 21 References- Chapter 1 22 Chapter 2 Experimental 8 2.1 Materials 9 2.1.1 Gases 22.1.2 Solvents 9 V 2.1.3 Reagents 30 2.2 Instrumentation2.3 Techniques 1 2.4 Synthesis and characterization of ruthenium porphyrin complexes 32.5 Oxidation of thioethers to sulfoxides 42 2.5.1 Electronic spectral measurements 42 2.5.2 Nuclear magnetic resonance experiments 42 2.6 Oxidation of phenol 43 2.6.1 Electronic spectral measurements 43 2.6.2 Nuclear magnetic resonance experiments 43 References- Chapter 2 44 Chapter 3 Oxidation of thioethers to sulfoxides 45 3.1 Introduction 6 3.2 Data analysis, results and discussion 47 3.3 Conclusions 7References- Chapter 3 9 Chapter 4 Oxidation of phenol 81 4.1 Introduction 2 4.2 Data analysis, results and discussion 84 4.3 Conclusions 101 References- Chapter 4 3 Chapter 5 Oxidation of 2-propanol 104 5.1 Introduction 105 5.2 Data analysis, results and discussion 106 References- Chapter 5 114 vi Chapter 6 Synthesis, characterization and reactivity of novel ruthenium porphyrin complexes: alkene, alkyne, thioether complexes of Ru(TMP), and CO, bis-CH3CN and dioxo complexes of Ru(OCP) , ...115 6.1 Complexes of Ru(TMP) formed by interactions with alkynes 116 6.1.1 Reaction with acetylene 116.1.2 Alkyne rc-complexes of Ru(TMP) 126 6.2 Alkene complexes of Ru(TMP) 126.3 Sulfoxide complexes of Ru(TMP) 132 6.4 Synthesis and characterization of Ru(OCP) complexes 134 6.4.1 Ru(OCP)(CO) 136.4.2 Ru(OCP)(CH3CN)2 135 6.4.3 Ru(OCP)(0)2 13References- Chapter 6 142 Chapter 7 General conclusions and recommendations for future studies 143 Appendices 147 A Data for UV-visible kinetic studies on oxidation of thioethers 147 A. 1 Oxidation of Et2S by Ru(TMP)(0)2 in benzene solution 147 A.2 Oxidation of DecMeS by Ru(TMP)(0)2 in benzene solution 149 A.3 Oxidation of nBu2S by Ru(TMP)(0)2 in benzene solution 150 A.4 Oxidation of Et2S by Ru(OCP)(0)2 in benzene solution 151 B Data for UV-visible kinetic studies on oxidation of phenol by Ru(TMP)(0)2 in benzene solution 152 C Data for the determination of the molecular weight of Ru[(TMP)]2(u-C2H2) using the Signer method 153 vii List of Tables Table Page 3.1 Pseudo-first order rate constants (kobs) at different diethyl sulfide concentrations 51 3.2 Pseudo-first order rate constants (kobs)at different decylmethyl sulfide concentrations3.3 Second order rate constants (ki) calculated for the oxidation of alkyl thioethers by Ru(TMP)(0)2 at 20.0 °C in benzene 54 3.4 Second order rate constants (ki) at various temperatures and the activation parameters for the oxidation of Et2S, nBu2S and DecMeS by Ru(TMP)(0)2 54 3.5 *H nmr data for Ru(TMP)(0)2, and Et2SO complexes of Ru(TMP) 60 4.1 Pseudo-first order rate constants (k^s) at different phenol concentrations at 20.0 °C in benzene under O2 (1 atm) 84 4.2 -H nmr data for the species observed in the oxidation of phenol by Ru(TMP)(0)2 88 4.3 Temperature dependences of isotropic proton shifts for porphyrin peaks of Ru(TMP)(OC6H4OH)2 in toluene-dg 93 5.1 Room temperature lH nmr data for the porphyrin peaks of known Ru(TMP) species, and unknown species X isolated from the reaction of Ru(TMP)(0)2 with 2-propanol 109 5.2 Temperature depedences of *H nmr shifts for porphyrin peaks of the unknown species X Ill viii List of Figures Figure Page 1.1 Structure of free-base porphyrin 3 1.2 Schematic representation of metal to ligand back-donation of electron density 8 1.3 Schematic representation of metal-olefin electron interaction in olefin Tt-complexes 13 3.1 UV-visible spectral changes observed for the oxidation of Et2S by Ru(TMP)(0)2 at 20.0 °C in (#16 under O2 (1 atm). Inset shows the pseudo-first order plot for the disappearance of Ru(TMP)(0)2 48 3.2 Absorbance at 420 nm vs. time trace for the oxidation of DecMeS by Ru(TMP)(0)2 in benzene at 20.0 °C under O2 (1 atm) and the resulting pseudo-first order plot 50 3.3 Thioether dependence of kobs at 20.0 °C in CgHg for the oxidation of (A): Et2S and (B): DecMeS by Ru(TMP)(0)2 52 3.4 Arrhenius plots for the oxidation of Et2S, nBu2S and DecMeS by Ru(TMP)(0)2 in benzene 55 3.5 Room temperature *H nmr spectrum of Ru(TMP)(0)2 in C6D6 58 3.6 Room temperature JH nmr spectrum of a reaction mixture containing Ru(TMP)(0)2 (initially 5x10-3 M and Et2S (2xl0-2 M) in C6D6 after a 2 h reaction time 59 3.7 Room temperature *H nmr spectrum of in situ Ru(TMP)(OS_Et2)2,5_, in C6D6 61 3.8 Room temperature *H nmr spectrum of an isolated mixture of Ru(TMP)(OSEt2)2,1 and Ru(TMP)(OSEt2)(OSEt2)2,4, in Q£>6 63 3.9 Room temperature lU nmr spectrum of a mixture of Ru(TMP)(OSEt2)2,1, Ru(TMP)(OSEt2)(OSEt2)2,4, and Ru(TMP)(OSEt2)2,5, in C6D6 64 ix 3.10 Room temperature lH nmr spectrum of isolated Ru(TMP)(OSJEt2)2» 5_, in CD2CI2 66 3.11 Room temperature -H nmr spectrum of isolated Ru(TMP)(0£nBu2)2 in CgD^ Inset shows the high-field region of the *H nmr spectrum of isolated Ru(TMP)(OSnPr2)2 67 3.12 Room temperature *H nmr spectrum of a reaction mixture containing Ru(TMP)(0)2 (initially 5x10-3 M and Et2S (5xl0-2 M) under O2 (1 atm at 20 °C) heated for 20 minutes at 35 °C 69 3.13 Room temperature !H nmr spectrum of in situ Ru(TMP)(SEt2)2 in C6E>6 71 3.14 UV-visible spectral changes observed for the oxidation of Et2S by Ru(OCP)(0)2 at 20.0 °C in under 02 (1 atm) 72 3.15 Absorbance at 420 nm vs. time trace for the oxidation of Et2S by Ru(OCP)(0)2 in benzene at 20.0 °C under O2 (1 atm) and the resulting pseudo-first order plot 73 3.16 Room temperature lH nmr spectrum of a reaction mixture containing Ru(OCP)(0)2 (initially -3x10-3 M) and Et2S (2xl0-2 M) under O2 in CoDg after an 8 h reaction time at room temperature 75 3.17 Room temperature *H nmr spectrum of a reaction mixture containing Ru(OCP)(0)2 (initially -2x10-3 M), Et2S (6xl(r2M) and O2 (1 atm at room temperature) in C$>6 after a 12 h reaction time at 100 °C 76 4.1 UV-visible spectral changes observed for the oxidation of phenol at 20.0 °C by Ru(TMP)(0)2 in benzene under O2 (1 atm). Inset shows the ln(Ar Aoo) vs. time plot for the disappearance of Ru(TMP)(0)2 85 4.2 Absorbance at 420 nm vs. time trace for the oxidation of phenol by Ru(TMP)(0)2 in benzene at 20.0 °C under O2 (1 atm) and the resulting pseudo-first order plot 86 4.3 Phenol dependence of k^s at 20.0 °C in benzene under O2 (1 atm) 87 X 4.4 Room temperature *H nmr spectrum of a reaction mixture containing Ru(TMP)(0)2 (-4x10-3 M) and phenol (-2x10-2 M) under O2 (1 atm) in CeDg after a 5 minute reaction time 89 4.5 Room temperature *H nmr spectrum of a reaction mixture containing Ru(TMP)(0)2 (-4xl0-3 M) and phenol (-2x10-2 M) under O2 (1 atm) in C5D6 after a 40 minute reaction time 90 4.6 Room temperature *H nmr spectrum of isolated Ru(TMP)((X^H40H)2 in toluene-dg 92 4.7 Plot of isotropic *H nmr shifts vs. 1/T for the porphyrin peaks of Ru(TMP)(OC6H40H)2 in toluene-dg 94 4.8 Room temperature *H nmr spectrum of a reaction mixture containing Ru(TMP)(0)2 (-4x10-3 M) and phenol (-2x10-2 M) in degassed 97 5.1 Room temperature *H nmr spectra of a reaction mixture containing Ru(TMP)(0>2 (initially -10-3 M) and 2-propanol (-10*2 M) in Q3D6 after (A): 1, (B): 24 and (C): 72 h reaction times 107 5.2 Room temperature -H nmr spectrum of a reaction mixture containing Ru(TMP)(0)2 (initially -3x10-3 M) and 2-propanol (-2.5x10-2 M) in C6D6 after a 72 h reaction time 108 5.3 Room temperature *H nmr spectrum of the product isolated from the reaction of Ru(TMP)(0)2 with 2-propanol 110 5.4 Plot of *H nmr shifts vs. 1/T for the porphyrin peaks of unknown species X in toluene-ds 112 6.1 Room temperature *H nmr spectrum of the in situ product from the reaction of Ru(TMP) with acetylene in C(PG 117 6.2 Proton-decoupled 13C spectrum of the product isolated from the reaction of Ru(TMP) with acetylene in C6D6 119 xi 6.3 13C nmr spectrum (APT) of [Ru(TMP)]2(u-C2H2) in 120 6.4 Gated proton-decoupled 13C spectrum of [Ru(TMP)]2(u-C2H2) in 121 6.5 UV-visible spectrum of [Ru(TMP)]2(u-C2H2) species in under N2 122 6.6 Volume vs. time plot for the determination of molecular weight of [Ru(TMP)]2(|i-C2H2) using the Signer method 124 6.7 Room temperature 2H nmr spectrum of the in situ species Ru(TMP)(PhCCPh) in C^; [RuCTMP)] = 5x10-3 M, [PhCCPh] = 2.5x10-2 M 127 6.8 Room temperature *H nmr spectrum of the in situ species Ru(TMP)(PhCCH) in C6D6; [RuCTMP)] = 5x10-3 M, [PhCCH] = 1.2x10-2 M. 128 6.9 Room temperature lH nmr spectrum of the Ru(TMP)(CH2CH2)(iPrOH).iPrOH complex in C6D6 129 6.10 Room temperature lH nmr spectrum of Ru(TMP)(CH2CH2) in toluene-ds 131 6.11 Room temperature *H nmr spectrum of in situ RufTMPXCgHio) species in the presence of excess cyclohexene in C&D6 133 6.12 Room temperature lH nmr spectrum of Ru(OCP)(CO) in C&>& 136 6.13 Room temperature lH nmr spectrum of Ru(OCP)(CH3CN)2 in 137 6.14 Room temperature lH nmr spectrum of Ru(OCP)(0)2 in CDCI3 138 6.15 UV-visible spectral changes observed for the oxidation of Ru(OCP)(CO) by mCPBA in C6H6 to generate Ru(OCP)(0)2 140 6.16 Room temperature lH nmr spectrum of in situ reaction mixture after the reaction of Ru(OCP)(0)2 with excess P(OCH3)3 in CDCI3 141 xii List of Schemes Scheme Page 1.1 Reactions of [Ru(TPP)]22-; taken from ref.7 6 1.2 Reactions of [Ru(OEP)j2 10 1.3 Reactions of Ru(TMP) 1 1.4 Suggested mechanism for the catalytic oxidation of phosphines 18 1.5 Catalytic cycle for epoxidation of olefins catalyzed by Ru(TMP)(0)2; taken from ref . 69 20 3.1 Proposed mechanism for the oxidation of thioethers by Ru(Porp)(0)2 species. Porp= TMP, OCP 56 4.1 Proposed reaction mechanism for the oxidation of phenol by [(bpy)2(py)RuO]2+ in CH3CN 83 4.2 Proposed mechanistic steps in the oxidation of phenol by Ru(TMP)(0)2 in benzene solution 98 Abbreviations A absorbance A Angstrom unit (IO10 metre) APT attached proton test atm atmosphere bpy 2,2'-bipyridine br broad, in UV-visible or nmr spctroscopies nBu normal butyl °C degree Celsius 13C {*H} proton decoupled carbon-13 cm centimetre cnr1 " wavenumber D or d deuterium DecMeS n-decylmethylsulfide DMSO dimethylsulfoxide e electron Ea activation energy eq. equation Et ethyl Etio 2,7,12,17-tetrametliyl-3,8,13,18-tetraemylrx)iphin dianion FT Fourier transform g gram *H proton AH* activation enthalpy m-H meta proton in aryl ring o-H ortho proton in aryl ring p-H para proton in aryl ring h hour hv light energy Hz Hertz i.r. or IR infra red k kinetic rate constant kobs observed kinetic rate constant K degrees Kelvin L ligand M metal ion m multiplet, in nmr spectroscopy mCPBA meta-chloroperoxybenzoic acid m/e ratio of mass to charge Me methyl mg milligram mL millilitre mmol millimole mol mole nm nanometre (lCr^ metre) nmr or NMR nuclear magnetic resonance OCP mescKetra(2,6-mcMorophenyl)porphinato dianion Ph phenyl PhIO iodosobenzene porp porphinato dianion ppm, or 8 chemical shift in parts per million relative to TMS at 5= 0 Pr propyl group py pyridine q quartet, in nmr specrtoscopy XV R alkyl group ref. reference s second AS* activation entropy sh shoulder, in UV/visible spectroscopy T temperature t triplet, in nmr specrtoscopy THF tetrahydrofuran TMP nxso-terramesitylrxjrphinato dianion TMS tetramethylsilane TPP meso-tetraphenylpcrphinato dianion TTP meso-tetra(r>tolyl)porphinato dianion UY/vis ultra-violet/visible spectroscopy (electronic spectroscopy) w.r.t. with respect to v infrared frequency Xmax wave length of an absorption peak uL microlitre e molar absorptivity (extinction coefficient) Acknowledgements xvi I wish to express my deepest gratitude to Professors D.H. Dolphin and B.R. James for their guidance and encouragement during the course of this work. My thanks are also due to all members of both research groups for their kindness and understanding. Many helpful discussions with Drs. M. Camenzind, T.P. Wijesekera, D. De Silva, V. Karunaratne, Messrs. A. Pacheco and D. Thackray are gratefully acknowledged. The prompt and courteous services provided by NMR, Elemental Analysis, Electronic, Glassblowing and Mechanical shop personnel are deeply appreciated. Finally, I wish to thank my family for their love and support. 1 CHAPTER 1 Chemistry of Ruthenium Porphyrins 2 1.1 Introduction Metalloporphyrin chemistry over the years has developed into a major field of innovative and exciting research. Ruthenium porphyrin chemistry in particular has matured as a vibrant area of investigation thus attracting immense interest. Originally synthesized to serve as models for biologically important compounds such as hemoglobin, myoglobin, chlorophyll, vitamin B-12 and heme-containing oxygenases, peroxidases etc., the metalloporphyrins are now being recognized for their own often unique chemistry. Significant developments in the field of ruthenium porphyrin chemistry, since it's inception nearly two decades ago, will be reviewed in this Chapter which will incorporate also some of the findings of the present work. 1.2 Porphyrin as a Ligand The porphyrin macrocycle is a planar aromatic system containing 9 double bonds, (4n+2)-7t electrons, in conjugation. The four pyrrolic nitrogen atoms (Figure 1.1) define an equatorial plane with four-fold axial symmetry once the two internal protons are removed. The porphyrin dianion thus formed becomes a tetradentate chelating agent. The central cavity having four pyrrolic nitrogen atoms forms coordination compounds with all the transition and lanthanide metals and a number of actinides.1 The porphyrin ligand is a good a-electron donor, but a poor n- acceptor. The meso- and (3-pyrrolic positions of the macrocycle can be substituted with a wide variety of groups thus creating steric and/or electronic effects of choice. Examples of metal-porphyrins, having every d-electron configurations from d° to d10, metal oxidation states of 0 to +VI, spin states S = 0 to 5/2 and metal coordination numbers 4 to 8, can be found in the literature.1 This amply illustrates the versatility and the wide applicability of porphyrin as a ligand. El E2 OEP C2H5 H TPP H C6H5 TTP H 4-MeC6H4 TMP H 2,4,6-Me3C6H2 OCP H 2,6-Cl2C6H3 Figure 1.1 Structure of free-base porphyrin. 4 The porphyrin ligand also serves as a useful probe for spectroscopic characterization of complexes. Nuclear magnetic resonance spectra of the porphyrin reflect the symmetry of the complex and magnetic properties of the central metal. The aromatic ring current associated with the porphyrin exhibits a dramatic up-field shift of resonances due to axially coordinated ligands thus separating them from their usual diamagnetic positions.2,3 Also, being an intensely absorbing chromophore, a porphyrin complex can be studied using electronic spectroscopy to obtain information on oxidation and spin states of the metal and the porphyrin ligand itself. However, there are instances where the porphyrin may act as a non-innocent ligand. The frontier orbitals of the porphyrin and transition metal d-orbitals have similar energies. Therefore, the redox chemistry of the coordinated metal may become entangled with that of the porphyrin ring.4 Also, the pyrrolic nitrogens may be involved in chemical reactions; ligand bridging between the metal and a pyrrolic nitrogen, and migration of a ligand between these two centres, are known.5 1.3 Chemical Properties of Ruthenium Porphyrins Many ruthenium porphyrin complexes have been prepared and characterized, and their chemical properties investigated mainly as models for their biological counterparts. In the early stages of the development of ruthenium porphyrin chemistry, attention was mainly focussed on ruthenium(U) derivatives. However, during the last decade, complexes of other oxidation states of ruthenium have been prepared. In these complexes, ruthenium species with oxidation states 0-VI except V, coordination numbers 4-6 and axial ligation of C-, N-, P-, As-, 0-, S- compounds, including 02, CO, and N2, and halides and hydride have been well documented. The syntheses and chemical properties of ruthenium porphyrin complexes will be discussed below according to the oxidation state of the metal. 5 1.3.1 Rnthp.ninTTifO') Complexes The only Ru(0) porphyrin complexes reported to date are lyRufPorp)] (Porp= OEP, TTP),4 which were prepared by the reduction of the [Ru(Porp)]2 species using Na/K alloy (THF, 30 min) or K metal (THF, several hours) and characterized on the basis of their reactivity A7 These highly reactive species particularly toward electrophiles produce a range of novel organometallic porphyrin complexes; these reactions are summarized in Scheme 1.1. 1.3.2 Rutheniumd) Complexes There is only one report of a Ru(I) porphyrin complex in the literature.2 This species was prepared in situ by the electrochemical reduction of Ru(TPP)L2 complexes (L= tertiaryphosphines, nBuNC) in C6H6/CH3CN (1:1, v:v) solution. The product of one-electron reduction of Ru(U)(TPP)L2 was considered to be Ru(I)(TPP)L2" based on the fact that no esr signal was observed for the porphyrin anion radical.2 However, no further characterization of this species was carried out. 1.3.3 Rutheniumdl) Complexes Ruthenium(II) complexes are by far the largest known class of Ru porphyrin compounds. The Ru(JJ) centre always displays low spin d6, diamagnetic behaviour in these complexes. All general routes available to insert ruthenium metal into porphyrins yield ruthenium(U) carbonyl complexes.3,8"11 These methods include refluxing of free-base porphyrin (H2Porp) with Ru3(CO)12, RuO3.nH20 or [RuCl2(CO)3]2 in a suitable solvent under a CO atmosphere. The Ru(Porp)(CO) species thus formed in solution may be crystallized out following addition of a suitable ligand such as THF OT ROH. Scheme H Reactions of [Ru(TTP)]2-; taken from ref. 7. 7 Being a strong jc-acid, the CO ligand binds rather strongly to the ruthenium(II) centre and renders it unreactive toward other 7t-acids such as 02 and N2. The difficulty encountered in removing the CO ligand has had a marked effect on the development of ruthenium porphyrin chemistry. The first ruthenium porphyrin complex was prepared in 1969,12 and its correct formulation as a Ru(II) carbonyl (see below) was published 2 years later.** Shortly after, structural, spectroscopic and electrochemical studies of such carbonyl species were reported.13,14 The study of chemical properties, however, was confined to the ligand exchange at the sixth axial coordination site trans to the carbonyl group.4,11,15,16 Fleischer et al.12 in 1969 incorrectly concluded using solely i.r. arguments that their new Ru-porphyrin species was Ru(m)(TPP)(Cl)(CO). In 1971, Chow and Cohen8 carefully characterized this species to be Ru(II)(TPP)(CO). This was followed by x-ray crystallographic characterizations of the complex,13,14 of which, the initially reported Ru(TPP)(CO)213 was shown to be in error, the correct formulation being in fact Ru(TPP)(CO)(EtOH).14aThe existence of mono-carbonyl species was further confirmed by the structural characterization of the derived product Ru(TPP)(CO)(py) by Little and Ibers.14b The electrochemical oxidation product of Ru(Porp)(L)(CO), where Porp= OEP, Etio, or TPP, and L= py, CH3CN, THF or vacant, is the Ru(II)porphyrin 7C-cation radical Ru(Porp+-)(CO), whereas when the ruthenium(II)porphyrin was first decarbonylated, electrochemical oxidation now occurred at the metal ion to yield Ru(IH)(Porp) species. The difference in potentials between these two oxidations is approximately 600 mV, with the decarbonylated Ru(II) centre being the one more easily oxidized.4'17 This significant stabilization of Ru(II) by a CO ligand is readily explained in terms of strong rc-back-bonding from the metal to the rc-acceptor CO ligand. This has been confirmed by a resonance Raman study.18 The CD stretching frequencies of Ru(II)(Porp)(CX)) species generally fall within the range 1889-1968 cm-1.15'19 The significant lowering of vco compared to that of free CO (2143 cm-1) is consistent with strong jc-electron back-donation from the d6, low spin Ru(II) to the 7t*-orbitals of CO as depicted in the well known diagram shown in Figure 1.2. Figure 1.2 Schematic representation of metal to ligand back-donation of electron density. The Ru(Porp)(CO) species form six-coordinate Ru(Porp)(CO)(L) complexes upon addition of adequate amounts of L. The binding constants of a large number of L ligands have been c^terrnined and compared to the donor numbers of L and solvent parameters.20" 22 Also studied has been the effect of para-substitution at the phenyl groups of TRP on the reduction potentials for Ru(II)(Porp-+)(CO)L + e > Ru(n)(Porp)(CO)L couples 23 Certain tertiary phosphine ligands (PR3) bind strongly at the vacant site of Ru(Porp)(CO) complexes; neutral oxygen ligands bind weakly, and amine bases occupy an intermediate position.22 This behaviour arises because of strong o-donor and 7C-acceptor capabilities of phosphorus compared to nitrogen, whereas an oxygen-donor cannot act as a 7t-acceptor due to lack of d-orbitals. There are three general procedures for removing the strongly bound CO ligand. (I) Direct substitution of CO by reaction, usually under refluxing conditions, with a suitable ligand L to yield Ru(Porp)(L)2 species; L= more basic tertiary phos-phines 2>8,24"27 isocyanides 25,28,29 nitrosyl,30 or nitrosobenzene.31 (II) Photolytic cleavage of the Ru-CO bond in a coordinating solvent to form Ru(Porp)(Solv)2 species.2'32_37a (Ul) Chemical oxidation of a Ru(Porp)(CO) complex to give Ru(IV) n-oxo binuclear species ,37b>38 Ru(VI)(0)2 species39 or Ru(lTf) complexes.40 Solutions of Ru(Porp)(CH3CN)2 species (Porp= OEP,TPP) in DMA, DMF or pyrrole absorb 1.0 mole of 02/Ru reversibly.35 However, this oxygen adduct was not isolated or well characterized. A kinetic investigation of dioxygen binding to related para-substituted Ru(TPP) systems in DMF suggests that 02 is side-bonded.41 It was also observed that solutions of Ru(OEP)(CH3CN)2 in toluene reacted with dioxygen slowly and irreversibly to form probably the H-oxo binuclear species.35 Solutions of Ru(TMP)(CH3CN)2 upon exposure to air rapidly form Ru(TMP)(0)2 via a detectable Ru(IV)(TMP)(0) intermediate 42 The u,-oxo binuclear species was not formed in this case because of the steric hindrance caused by the ortho-methyl groups in mesitylene units of the porphyrin ring. Major advances in ruthenium porphyrin chemistry were brought about by the preparation of [Ru(Porp)]243 from Ru(Porp)(py)2 (Porp= OEP,TPP), and Ru(TMP)36 from Ru(TMP)(CH3CN)2 using a vacuum pyrolysis procedure. A large number of novel complexes were prepared following the discovery of these species. A summary of such reactions is given in Schemes 1.2 6,31,43-48 13 36,49 10 Scheme 1.2 Reactions of [Ru(OEP)]2. 11 Scheme 1.3 Reactions of RuCTMP). The reactions with R2SO, CH2CH2, CHCH and PhCCR constitute part of this thesis work. 12 The utility of a vacuum pyrolysis procedure was again demonstrated in the preparation of five-coordinate Ru(H)(Porp)(PR)3 complexes, (Porp= OEP.TMP; R= nBu,Ph).50 Such five-ccoidinate, 16-electron species have been suggested as intermediates in catalytic oxidation of phosphines51 and decarbonylation of aldehydes.52,53 The preparation of the 14-electron Ru(TMP) species led to the formation of Ru(TMP)(OEt2)2, which could not be formed via photolysis of Ru(TMP)(CO) in Et20.36 The reactivity of Ru(TMP) is best illustrated by its exposure to 1 atm N2,36 with the resulting formation of the Ru(TMP)(N2)2 complex either in the solid state or in benzene or toluene solution. The i.r. stretching frequency of 2203 cm"1 is the highest observed 54 for any reported dinitrogen complex, other than matrix stabilized species reported by Ozin and Vander Voet.55 Evaporation of solutions of the Ru(TMP)(N2)2 complex in a suitable solvent in a N2 glove-box results in the formation of Ru(TMP)(N2)(Solv) species, Solv= THF, OEt2, DMF or NEt3, the THF species being analyzed crystallographically.49 Prior to this work the Ru(OEP)(THF)(N2) complex had been isolated, but not fully characterized.32 Moreover, Hopf and Whitten had observed, using UV/visible spectroscopy, the binding of N2 and 02 to an 'activated' monolayer assembly of Ru(II)porphyrins.56 Reversible binding of 02 and N2 to sterically protected 'picnic basket' ruthenium porphyrin species has also been demonstrated.373 The species [Ru(Porp)]2 (Porp= OEP,TTP),6 and Ru(TMP) as described in the present work in Section 2.4, form ethylene adducts on exposure to ethylene at 1 atm. Formation of such complexes in solution (eq. 1.1) was mentioned as early as 1979;32 however, these species were not isolated and characterized, until recently.6 Figure 1.3 shows a molecular orbital picture of the electronic interaction between the metal and the olefin ligand. 13 bonding Figure 1.3 Schematic representation of metal-olefin electron interaction in olefin it-complexes. The ethylene complexes of Ru(TMP) were isolated in the present study as RuCTMPXC^C^X'PrOH), solvated with a further isopropanol molecule, and as 'five'-coordinate Ru(TMP)(CH2=CH2)- The Ru(TMP)(cyclohexene) species was characterized only in solution (see Section 6.2). The facile reaction of the ruthenium porphyrin dimers, [Ru(Porp)]2 (Porp= OEP, 1 IF), with neutral carbene precursors led to the formation of Ru(Porp)(=C(H)C2H5) and Ru(Porp)(=C(H)C(0)OCH2CH3).6 Also, a vinylidene complex, Ru(TPP)[=C=C(p-C6H4C1)2], has been prepared by insertion of ruthenium into a free base porphyrin already containing the carbene fragment bridged between two pyrrolic nitrogen atoms.5 A structurally more intriguing carbene-type species has been prepared in the present studies, namely [Ru(TMP)]2(u-C2H2) (eq. 1.2), formed by the reaction of acetylene with Ru(TMP) (see Sections 2.4 and 6.1.1). Only one metalloporphyrin alkyne Tt-complex, Mo(TTP)(PhCCPh) has been reported.57 Other alkynes used in the present work, PhCCPh and PhCCH form the 7t-bonded species in solution (eq. 1.3). RuCTMP) II _ /C"H H-C I RuCTMP) 2 RuCTMP) + HC=CH (1.2) Ru(TMP) +PhC=CR 1.3.4 RutheniumdII) Complexes Ph-C^C-R RuCTMP) R= Ph, H (1.3) All ruthenium (III) porphyrin complexes display paramagnetic behaviour with an S=l/2 spin state which is consistent with a low spin, d5 electronic configuration. There are three general methods for the preparation of Ru(IH) complexes. (1). Chemical oxidation of Ru(H) complexes. Air or bromine oxidation of ruthenium (II) carbonyl complexes in the presence of KCN produces K[Ru(Porp)(CN)2] 8 from which neutral complexes Ru(Porp)(CN)(py) are readily obtained (Porp= OEP.TPP)2'40 (eq 1.4). 15 Air or Br2 py Ru(Porp)(CO) > K[Ru(Porp)(CN)2] > Ru(Porp)(py)(CN) KCN (1.4) Oxidation of Ru(Porp)(00)(PR3) or Ru(Porp)(PR3)2 species with halogens or 02/HX yields the corresponding Ru(m)(Porp) (PR$)(X) species24*58 X2 Ru(II)(OEP)(CO)(PnBu3) > Ru(III)(OEP)PnBu3)(X) CH2C12 (X=Cl,Br) (1.5) X2 or 02/HX Ru(Porp)(PR3)2 > Ru(Porp)(PR3)(X) CH2C12 Porp = OEP; R= Ph, nBu; X= Cl, Br. (1.6) Porp= TPP; R= Ph; X= Br. The complexes Ru(TPP)(L)2 (L= EtOH, THF) in CH2cl2/EtOH (2:1>v:v) are oxidized to Ru(ITJ)(Porp)(OEt)(EtOH) by 02, but in a non-cc>ordinating solvent, such as benzene, [Ru(rV)(OEf)2]20 species is produced.38 Electrochemical oxidation of Ru(IT). The [Ru(III)(Porp)(L)2]+ species is produced by one-electron oxidation of Ru(II)(Porp)(L)2, (L* CO).24*59 The two-electron oxidation of Ru(H)(Porp) (COXSolv) gives the [Ru(III) (Porp"K)(CO)(solv)]+ species.24'60*61 The initial one-electron oxidation of Ru(II)(Porp)(CO)(Solv) species occurs at the porphyrin ring producing the Ru(U)(Porp+-)(CO)(Solv) TC-cation radical species.2*24 However, in the case of Fe(JJ) and Os(U) porphyrin carbonyl complexes, the central metal ion is oxidized in an initial oxidation.17 This unusual behaviour of Ru(JJ)(porp) (CO)(Solv) species is explained in terms of strong 7C-back-bonding from Ru(U) to CO ligand thereby lowering metal d-orbital energy levels below that of porphyrin 7t-orbitals which then become the HOMOs of the system.17 Such a strong influence of axial ligands on metal redox properties helps to explain proposed electron transfer pathways between cytochromes.62 (3). Reduction of nithenium(TV). The homolytic cleavage of a metal-carbon bond in Ru(Porp)(R)2 species (R= alkyl, aryl) produces Ru(UI)(Porp)(R) complexes.63'64 Also, [Ru(OEP)]2(BF4)2 when reacted with CH3CH2MgBr gives Ru(OEP)(CH2CH3).46 1.3.5 RuOV) Complexes The first Ru(IV) porphyrins prepared were the u,-oxo binuclear species [Ru(rV)(OEP)(X)]20 (X=OH, CI, Br, OCOCH3) which were well characterized, including the X-ray crystal structures of the X= CI and OH complexes.37*65,66 All these Ru(IV) complexes display diamagnetic behaviour. Halogen or halogen acid oxidation of [Ru(OEP)]2 yields the paramagnetic (S= 1) complexes Ru(OEP)(X)2, X= Cl.Br.45'46 Also, Br2 oxidation of Ruai)(TTP)(CO) complexes to produce Ru(rV)(TTP)Br2 has been reported 67 These Ru(IV) species readily give organo-metallic derivatives Ru(OEP)(R2) on treatment with the appropriate alkyl- or aryl-lithium reagent. The Ru(TPP)(Br)2 complex has been prepared and structurally characterized.68 17 1.3.6 RutheniumfVD Complexes The oxidation state VI is the highest known for any ruthenium porphyrin. The only compound described so far is RuCTMP)(0)2.39 The analogous species Ru(OCP)(0)2 was synthesized and characterized in the present work (see Sections 2.4 and 6.4.3). Such species can be prepared by chemical oxidation of Ru(Porp)(CO) (Porp= TMP, OCP) using mCPBA or by the reaction of Ru(Porp)(CH3CN)2 with dioxygen (or air). The trans-dioxo ruthenium(VI) TMP species catalyzes oxidation of olefins to epoxides,69,70 and as described in detail in this thesis it also oxidizes thioethers to sulfoxides, phenol to hydroquinone and 2-propanol to acetone. 1.4 Catalytic Properties of Ruthenium Porphyrins Interest in using ruthenium porphyrins as catalysts has been gathering momentum.48,51,53,69-73 In general, two processes have been looked at, but detailed mechanistic studies are lacking. Oxygenation of substrates such as olefins and saturated hydrocarbons,69"73 thioethers,48 and phosphines51 has been reported. Catalytic decarbonylation of aldehydes using ruthenium porphyrins has also been studied.52,53 1.4.1 Oxygenations Using Ruthenium Porphyrins The complex Ru(III)(OEP)(Br)(PPh3) catalytically oxidizes olefins and cyclohexane in the presence of PhIO at 20 °C.72,73 The proposed intermediate species, a porphyrin cation radical, 0=Ru(IV)(OEP+-)(Br), has been isolated and partially characterized.72,73 A higher turnover rate was observed for the related system Ru(TMP)(nBu3P)(Br).71 Selectivities of these complexes toward catalytic hydroxylation and epoxidation reactions exhibit a close similarity to those found for corresponding systems using Fe(UI)-, Cr(IU)-, Os(IJJ)- and Mn(III)- porphyrin catalysts, as well as for Cytochrome P-450 itself.74"79 18 A free-radical mechanism has been proposed74-78 for the oxygenation of saturated hydrocarbons catalyzed by high valent metalloporphyrin oxo species as exemplified in eq. 1.7. I ° OH -C-H+ FeIV(PoTp)+- FeCPorp) • -C-OH + Fem(Porp) (1.7) For olefin epoxidation catalyzed by related systems, several mechanisms have been proposed, including direct attack of the oxygen atom on the C=C double bond,80 involvement of oxo-metallocycles,81 and formation of substrate cationradicals as intermediates.82 The Ru(OEP)(PPh3)2 complex catalyzes the 02-oxidation of added PPh3, possibly via an outer-sphere mechanism51 outlined in Scheme 1.4. +02 Ru(OEP)(PPh3)2 >[Ru(III)(OEP)(PPh3)2]+ + 02" 02- + H+ > H02 2H02 > H202 + 02 H202 +PPh3 > 0=PPh3 + H20 2[Ru(in)(OEP)(PPh3)2]+ + PPh3 + OH—> 2[Ru(II)(OEP)(PPh3)2] + OPPh3 + H+ Scheme 1.4 Suggested mechanism for the catalytic oxidation of phosphines. The step generating the superoxide is thermodynamically unfavorable; 02 + e —> 02", E°= -0.4 V; and the driving force is thought to arise due to the stabilization of superoxide via protonation and subsequent dispropotionation to H202 and 02. Once formed, H202 oxidizes PPh3 to 0=PPh3. The Ru(II) is regenerated via the last step shown in Scheme 1.4 thus completing the catalytic cycle; this involves PPh3 in the presence of OH" acting as a two-equivalent reductant Only trace H+ and OH" are necessary because the complete cycle is catalytic with respect to these species. Selective oxidation of thioethers to sulfoxides is more interesting than oxidation of tertiary phosphines and is also of commercial value.83'84 The catalytic oxidation of added alkyl thioether, decylmethylsulfide (DecMeS) by the Ru(OEP)(DecMeS)2/02 system is also believed to operate via an outer-sphere mechanism,48 similar to the oxidation of phosphines. In principle, any substrate that could be oxidized using H202 may be oxidized by the appropriate six-coordinate Ru(U) porphyrin /02 /H+ system, and a catalytic cycle may be completed if a coreductant (optimally, the substrate itself) is present71 Of major interest is that Ru(TMP)(0)2 oxidizes olefins69'70 without the need of a coreductant, and this system represents the first recognized model for a dioxygenase. A catalytic system consisting of Ru(TMP)(THF)2/02/cyclooctene in benzene solution has afforded 4 equivalents of epoxide in 24 hours at 25 °C. The catalytic cycle suggested for the epoxidation of olefins is given in Scheme 1.5. Groves and co-workers have also studied the cis-trans isomerization of epoxides catalyzed by Ru(Porp)(THF)2 complexes (Porp= TMP, TTP).85 Mechanistic and thermodynamic data on 02-oxygenation processes are relatively rare in the literature. Also, it makes significant economic sense if the cheapest oxygen source, air (and 02) could be used successfully for industrial scale oxidations. Furthermore, the inorganic by-products of classical stoichiometric oxidants such as chromic acid and permanganate are causing increasing environmental problems.71 Scheme 1.5 Catalytic cycle for epoxidation of olefins catalyzed by Ru(TMP)(0)2; taken from ref. 69. 21 Therefore, the oxidation of thioethers, alcohols and phenols catalyzed by the Ru(Porp)(0)2/02 (Porp= TMP.OCP) systems was chosen for investigation as a major part of the present thesis work. The Ru(TMP)(0)2 complex had been synthesized independently in this laboratory by Camenzind86 during the same time period as discovery of the compound in Grove's laboratory.39 Some of the oxidation work to be described in Chapters 3,4 and 5 has been published87 and/or presented at Conferences.88 1.4.2 Decarbonvlations Using Ruthenium Porphyrins As observed initially in this laboratory, catalytic decarbonylation of dimethylformamide (DMF) is effected by Ru(TPP)(CO) under photolysis conditions32 (eq. 1.8). Ru(TPP)(DMF)2 - Ru(TPP)(CO) + HNMe2 hv, DMF, -CO I ^ g) A remarkably efficient purely thermal decarbonylation catalyst system based on Ru(TPP)(PPh3)2 was subsequently discovered.50-53,89 This system in the presence of added nBu3P (phosphine:Ru=10:l), and more surprisingly CO (1 atm) as an initial 'activating' agent, decarbonylates aldehydes with turn-over numbers as high as 2X104 per hour depending on the substrate and conditions. A radical mechanism involving heterolytic or homolytic cleavage of the aldehyde C-H bond to give an acyl radical RCO' was considered most likely. Not readily available in a metalloporphyrin system are the cis-coordination sites required for the familiar, 'classical' decarbonylation mechanism involving concerted oxidative addition of aldehyde RCHO, CO migration, and reductive elimination of RH product. 22 References - Chapter 1 1 Buchler, J.W.; in The Porphyrins, Dolphin, D.; Ed, Academic Press, New York, Vol.1, 1978, p.389. 2. Boschi, T.; Bontempelli, G.; Mazzocchin, G.-A. Inorg. Chim. Acta, 2LL 155 (1979). 3. Tsutsui, M; Ostfeld, D.; Hoffman, L.M. J. Am. Chem. Soc.,9_3_, 1820(1971). 4. Brown, G.M.; Hopf, F.R.; Ferguson, J.A.; Meyer, T.J.; Whitten, D.G. J. Am. Chem. Soc., 25, 5939(1973). 5. Chan, Y.W.; Renner, M.W.; Balch, A.L. Organometallics, 2. 1888(1983). 6. Collman, J.P.; Brothers, P.J.; McElwee-White, L.; Rose, E.; Wright, L.J. J. Am. Chem. Soc.,107, 4570(1985). 7. Collman, J.P.; Brothers, P.J.; McElwee-White, L.; Rose, E. J. Am. Chem. Soc.,107, 6110(1985). 8. Chow, B.C.; Cohen, LA. Bioinorg. Chem.J,, 57(1971). 9. Tsutsui, M.; Ostfeld D.; Francis, J.N.; Hoffman, L.M. J. Coord. Chem., 1, 115(1971). 10. Faller, J.W.; Sibert, J.W. J. Organomet. Chem., 3_I, C5(1971). 11. Eaton, S.S.; Eaton, G.R.; Holm, R.H. J. Organomet. Chem.^2, C52(1971). 12. Reisher, E.B.; Thorp, R.; Venerable, D. J. Chem. Soc., Chem. Commun. 475 (1969). 13. Cullen, D.; Meyer, E., Jr.;Srivastava, T.S.; Tsutsui M. J. Chem. Soc., Chem. Commun. 584(1972). 14. a. Bonnet, J.J.; Eaton, S.S.; Eaton, G.R.; Holm, R.H.; Ibers J.A. J. Am. Chem. Soc., 95, 2141(1973). b. Little R.G.; Ibers, J.A. J. Am. Chem. Soc., 95, 8583(1973). 15. Eaton, S.S.,; Eaton, G.R.; Holm, R.H. J. Organomet. Chem., 29, 179(1972). 23 16. Eaton, S.S.; Eaton, G.R. Inorg. Chem. 16, 72(1977). 17. Brown, G.M.; Hopf, F.R.; Meyer, T.J.; Whitten, D.G. J. Am. Chem. Soc, 22, 5385(1975). 18. Kim, D.; Oliver, S.Y.; Spiro, T.G. Inorg. Chem. 25_, 3993(1986). 19. Ogoshi, H.; Sugimoto, H.; Yoshida, Z.-I. Bull. Chem. Soc. Jpn., 5_L, 2369(1978). 20. Kadish, K.M.; Chang, D. Inorg. Chem., 21, 3614(1982). 21. Kadish, K.M.; Leggett, D.J.; Chang, D. Inorg. Chem., 2L 3618(1982). 22. Barley, M. PhD. Thesis, University of British Columbia, (1983). 23. Malinski, T.; Chang, D.; Bottomley, L.A.; Kadish, K.M. Inorg. Chem. 21. 4218(1982). 24. Barley, M.; Becker, J.Y.; Domazetis, G.; Dolphin, D.; James, B.R. Can. J. Chem., 6i, 2389(1983). 25. Ball, R.G.; Domazetis, G.; Dolphin, D.; James, B.R.; Trotter, J. Inorg. Chem., 20, 1556(1981). 26. Domazetis, G.; James, B.R.; Dolphin, D. Inorg. Chim. Acta, 54, L47(1981). 27. Ariel, S.; Dolphin, D.; Domazetis, G.; James, B.R.; Leung, T.W.; Rettig, S.J.; Trotter, J.; Williams, G.M. Can. J. Chem., 62, 755(1983). 28. Eaton, S.S.; Eaton G.R. Inorg. Chem., 15, 134(1976). 29. Pomposo, R; Carruthers, D.; Stynes, D.V. Inorg. Chem., 21, 4245(1982). 30. Srivastava, T.S.; Hoffman, L.; Tsutsui, M. J. Am. Chem. Soc, <M, 1385(1972). 31. Crotti, C; Sishta, C; Pacheco, A.; James, B.R. Inorg. Chim.Acta, 141. 13(1988). 32. James B.R.; Addison, A.W.; Cairns, M.; Dolphin, D.; Farrell, NJP.; Paulson, D.R.; Walker, S. "Fundamental Research in Homogeneous Catalysis", Tsutsui, M. Ed., Vol. 3, Plenum, New York, p.751(1979). 24 33. Antipas, A.; Buchler, J.W.; Gouterman, M.; Smith, P.D. J. Am. Chem. Soc, 100. 3015(1978). 34. Hopf, F.R.; O'Brien, T.P.; Scheidt, W.R.; Whitten, D.G. J. Am. Chem. Soc., 2L 277(1975). 35. Farrell, N.; Dolphin, D.; James, B.R. J. Am. Chem. Soc., 1QJ), 324(1978). 36. Camenzind, M.J.; James, B.R.; Dolphin, D. J. Chem. Soc., Chem. Commun., 1137(1986). 37. a. Collman, J.P.; Brauman, J.L; Sparapany, J.W.; Ibers, J.A. J. Am. Chem. Soc., 110, 3486(1988). b. Collman, J.P.; Barnes, C.E.; Brothers, P.J.; Collins, T.J.; Ozawa, T.; Gallucci, J.C; Ibers, J.A. J. Am. Chem. Soc., 106, 5151(1984). 38. Sugimoto, H.; Higashi, T.; Mori, M.; Nagano, M.; Yoshida, Z.I.; Ogoshi, H. Bull. Chem. Soc. Jpn., 5JL 822(1982). 39. Groves, J.T.; Quinn, R. Inorg. Chem., 23, 3844(1984). 40. Smith, P.D.; Dolphin, D.; James, B.R. Organomet. Chem., 208, 239(1981). 41. Barringer, L.F.Jr.; Rillema, P.D.; Ham, J.H.,IV. J. Inorg. Biochem., 21, 195 (1984). 42. Groves, J.T.; Ahn, K.-H. Inorg. Chem., 26, 3831(1987). 43. Collman, J.P.; Barnes, C.E.; Collins, T.J.; Brothers, P.J.; Gallucci, J.; Ibers, J.A. J. Am. Chem. Soc., IQ3_, 7030(1981). 44. Collman, J.P.; Prodolliet, J.W.; Leidner, CR. J. Am. Chem. Soc, 108. 2916(1986). 45. Sishta, C; Ke, M.; James, B.R.; Dolphin, D. J. Chem. Soc, Chem. Commun., 787(1986). 46. Sishta, C; Ke, M.; James, B.R.; Dolphin, D.; Ibers, J.A. Manuscript in preparation. 25 47. James, B.R.; Pacheco, A.; Rettig, S.J.; Thorburn, I.S.; Ball, R.G.; Ibers, J.A. J. Mol. Catal., 41, 147(1987). 48. James, B.R.; Pacheco, A.; Rettig, SJ.; Ibers, J.A. Inorg. Chem. 22, 2414(1988). 49. Camenzind, M.J.; James, B.R.; Dolphin, D.; Sparapany, J.W.; Ibers, J.A. Inorg. Chem., 22, 3054(1988). 50. Shista, C; Camenzind, M.J.; James, B.R.; Dolphin, D. Inorg. Chem., 26. 1181(1987). 51. James, B.R.; Mikkelsen, S.R.; Leung, T.W.; Williams, G.M.; Wong, R. Inorg. Chim. Acta, &5, 209(1984). 52. Domazetis, G.; Tarpey, B.; Dolphin, D.; James, B.R. J. Chem. Soc., Chem. Commun., 939(1980). 53. Domazetis, G.; James, B.R.; Tarpey, B.; Dolphin, D. ACS Symp. Ser., 152. 243(1981). 54. Ref. 36 and references therein. 55. Ozin, G.A.; Vander Voet, A. Prog. Inorg. Chem. 19, 105 (1975). 56. Hopf, F.R.; Whitten, D.G. J. Am. Chem. Soc., 98, 7422(1976). 57. De Cian, A.; Colin, J.;Schappacher, M.; Ricard, L.; Weiss, R. J. Am. Chem. Soc., 1Q3_, 1850(1981). 58. James, B.R.; Dolphin. D.; Leung, T.W.; Einstein, F.W.B.; Willis, A.C. Can. J. Chem., 62, 1238(1983). 59. Rillema, D.P.; Nagel, J.K.; Barringer, L.F. Jr.; Meyer, TJ. J. Am. Chem. Soc., 103. 56(1981). 60. Barley, M.; Dolphin, D.; James, B.R. J. Chem. Soc., Chem. Commun., 1499(1984). 61. Barley, M.; Becker, J.Y.; Domazetis, G.; Dolphin, D.; James, B.R. J. Chem. Soc., Chem. Commun., 982(1981). 62. Dolphin, D.; Felton, RM. Acc. Chem. Res.,2, 26(1974). 26 63. Collman, J.P.; McElwee-White, L.; Brothers, PJ.; Rose, E. J, Am. Chem. Soc., 108. 1332(1986). 64. Ke, M.; Rettig, S.J.; James, B.R.; Dolphin, D. J. Chem. Soc., Chem. Commun., 1110(1987). 65. Masuda, H.; Taga, T.; Osaki, K.; Sugimoto, H.; Mori, M.; Ogoshi, H. Bull. Chem. Soc. Jpn. 5£, 3837(1982). 66. Masuda, H.; Taga, T.; Osaki, K.; Sugimoto, H.; Mori, M.; Ogoshi, H. J. Am. Chem. Soc., IQ3, 2199(1981). 67. Rachlewicz, K.; Latos-Grazynski, L. Inorg. Chim. Acta, 144. 213(1988). 68. Ke, M. Ph.D. Thesis, University of British Columbia (1988). 69. Groves, J.T.; Quinn, R. J. Am. Chem. Soc, 107, 5790(1985). 70. Marchon, J. -C; Ramasseul, R. J. Chem. Soc, Chem. Commun., 298(1988). 71. James, B.R. in Fundamental Research in Homogeneous Catalysis, Shilov, A.E., Ed., Vol. 1, Gordon and Beach, New York, p.309(1986). 72. Leung, T.; James, B.R.; Dolphin, D. Inorg. Chim. Acta, 22, 180(1983). 73. Dolphin, D.; James, B.R.; Leung, T. Inorg. Chim. Acta, 22, 25(1983). 74. Groves, J.T.; Haushalter, R.C.; Nakamura, M.; Nemo, T.E.; Evans, B.J. J. Am. Chem. Soc, 10_3_, 2884(1981). 75. Groves, J.T.; Nemo. T.E.; Myers, R.S. J. Am. Chem. Soc, 10.1, 1032(1979). 76. Groves, J.T.;Kruper, W.J. J. Am. Chem. Soc, 101,7613(1979). 77. Hill, C.L.; Schardt, B.C. J. Am. Chem. Soc, 102, 6374(1980). 78. Mansuy, D.; Fontecave, M.; Bartoli, J.F. J. Chem. Soc. Chem. Commun. 253 (1983). 79. Che, C-M.; Chung, W-C. J. Chem. Soc. Chem. Commun. 386(1986). 80. Groves, J.T.; Nemo. T.E. J.Am. Chem. Soc, 105, 5786 and 6243(1983). 81. Collman, J.P.; Kodadek, T.; Raybuck, S.A.; Meunier, B. Proc. Natl. Acad. Sci. USA, 80, 7039(1983). 27 82. Traylor, T.G.; Lee, W.A.; Stynes, D.V. J. Am. Chem. Soc, 1£6_, 755(1984); Tetrahedron, 4Q, 553(1984). 83. a. Rank, W.O.; Nelson, D.C. in Organic Sulfur Compounds, Kharasch, N.; Ed., Pergamon, New York, Vol. 1, Chapter 17 (1964). b. Ledlie, M.A.; Allum, K.G.; Howell, J.V.; Pitkethly, G. J. Chem. Soc. Perkin Trans.1,1734(1976). 84. Riley, D.P.; Correa, P.E. J. Chem. Soc, Chem. Commun., 1097(1986). 85. Groves, J.T.; Ahn, K-H.; Quinn, R. J. Am. Chem. Soc. 110, 4217 (1988). 86. Camenzind, MJ. Unpublished work, October(1984). 87. a. Rajapakse, N.; James, B.R.; Dolphin, D. Catalysis Letters, 2, 219(1989). b. Rajapakse, N.; James, B.R.; Dolphin, D. in New Developments in Selective Oxidations, Centi, G. and Triffiro, F. Eds., Elsivier Science, Amsterdam, 1989 (in press). 88. a. Rajapakse, N.; James, B.R.; Dolphin, D. Proc. 6th Intern. Symp. Homog. Catal., Vancouver, Poster P-23Q988). b. Ke, M-K.; Rajapakse, N., James, B.R., Dolphin, D. 72nd Can. Chem. Conf., Abs. 377, Victoria, B.C.(1989). 89. Belani, R.M.; James, B.R.; Dolphin, D.; Rettig, SJ. Can. J. Chem., 66. 2072(1988). CHAPTER 2 Experimental 2A Materials 2.1.1 Gases Carbon monoxide and dioxygen were supplied by Union Carbide and were used without further purification. Argon (Union Carbide) was passed through a Ridox column (Fisher Scientific) to remove trace dioxygen and subsequently dried using anhydrous CaS04 (Hammond). Acetylene (Matheson) was purified by three freeze-pump-thaw cycles at -130 °C (using an n-pentane/ liquid dinitrogen slush bath) in order to remove carbon monoxide and ethylene impurities. Ethylene (Matheson, CP grade) was dried by passing through an Aquasorb tube (Mallinckrodt) prior to use. 2.1.2 Solvents Solvents such as benzene, dichloromethane, THF, toluene, etc., were obtained from Aldrich, BDH, Eastman or Fisher Chemical Co. as reagent or spectral grades. Benzene was purified by stirring over concentrated H2S04 (100:2, v:v) overnight, washing with distilled water and distilling over CaH2. All other solvents were distilled over CaH2 and stored under Ar or under vacuum. When required, extra-anhydrous solvents were prepared by vacuum transferring the pre-purified solvents over to activated molecular sieves (3A, Fisher) that had been placed in a greaseless Schlenk tube. Deuterated solvents for anaerobic NMR studies were purified by vacuum distillation over to activated molecular sieves. Completely anaerobic conditions were achieved usually after six freeze-pump-thaw cycles. 2.1.3 Reagents Ruthenium in the form of RuCl3.3H20 was obtained on loan from Johnson Matthey Ltd (approximately 40% Ru by weight). Dodecacarbonyltriruthenium(O), Ru3(CO)12, was prepared from the trichloride by a literature procedure.1 Diethylsulfide, di-n-butylsulfide, decylmethylsulfide, phenylacetylene and cyclohexene (Aldrich or Fairfield Chemicals) were passed through Activity I alumina (Fisher) and vacuum distilled prior to use. Dimethylsulfoxide, di-n-propylsulfoxide, di-n-butylsulfoxide, para-benzoquinone and diphenylacetylene were obtained from Aldrich and used without further purification. Phenol (Mallinckrodt) was recrystallized from petroleum ether. 2.2 Instrumentation Electronic absorption spectra were recorded on a Cary 17D, a Perkin Elmer 552A equipped with a thermoelectric temperature controller, or a Hewlett-Packard HP-8452A spectrophotometer. Extinction coefficients are given as log e values in parentheses immediately following the Xmax value for the particular peak. Infra-red spectra were recorded either on a Nicolet 5DX-FT or a Perkin-Elmer 1600 instrument as Nujol mulls on KBr disks. Nuclear magnetic resonance spectra were recorded using Bruker WH-400 (400 MHz) or Varian XL-300 (300 MHz) instruments operating in FT mode. The !H chemical shifts are given as 8 (ppm) values using residual C6Hg at 7.18 ppm, CHC13 at 7.25 ppm or CH3-C6H5 at 2.09 ppm as internal standard (TMS= 0.00 ppm). All *H nmr peaks listed are singlets unless indicated otherwise. Proton-decoupled 13C spectra were recorded using the centre peak of the C6D6 triplet as the standard at 128.0 ppm Elemental analyses were performed by Mr. P. Borda of this department. 2.3 Techniques All air-sensitive materials were handled in a dinitrogen-filled glove-box. Reactions of air-sensitive compounds were performed using standard manipulation techniques with air-tight syringes, flame-sealed tubes or greaseless Schlenk tubes fitted with Kontes valves, special UV-visible cell tonometers, details of which have been described elsewhere.2 The apparatus for the high pressure synthesis of Ru3(CO)12,3 photolytic preparation of Ru(TMP)(CH3CN)2,3and vacuum pyrolysis of Ru(TMP)(CH3CN)2 4 have also been described. Molecular weight detemiination was carried out using the Signer method.5 2.4 Synthesis and Characterization of Ruthenium Porphyrin Complexes The synthesis and characterization of ruthenium porphyrin complexes prepared in this study are described below. The spectroscopic data presented here are in excellent agreement with the reported values in the case of known species: TMPH2, 6 Ru(TMP)(CO),7 Ru(TMP)(CH3CN)2t 8 RuCTMP), 8 Ru(TMP)(N2)2.8 Characterization of new species is discussed in Chapters 3 and 6. TMPHi The free-base porphyrin, TMPH2 was synthesized according to the procedure of Badger et al.9 incorporating modifications by Groves and Nemo.6 Elemental Analysis: % CalculatedCFound) for C^H^N^ TMPHj. C= 85.89(85.28), H= 6.95(7.12), N= 7.16(6.98). NMR ( lH, CD2C12): 8.56 (pyrrole-H,8H), 7.22 (m-H,8H), 2.58 (p-Me,12H), 1.80 (o-Me,24H), -2.54 (N-H,2H). UV-Vis (CH2C12): 418, 512, 546, 590, 645 nm. Ru(TMP)(CO)(iPrOH) Carrx)nyl(2-propanol)tetiamesitylrx)rpr^ was prepared by a modified literature procedure described for the synthesis of Ru(TPP)(CO).10 The free-base porphyrin TMPH2 (0.70 g, 9xl0"4 mol) was heated to reflux in mesitylene (200 mL) under a bubbling stream of CO. To the refluxing solution, Ru3(CO)12 (0.40 g, 6X10"4 mol) was added and the reaction monitored by tic or UV-visible spectroscopy. Another 100 mg of Ru3(CO)12 was added after each 4 hour period until the reaction was completed (14-16 hour total reaction time). The solvent was then removed by rotary evaporation and the crude product was chromatographed on neutral alumina (Activity II) using benzene as the eluent to remove the unreacted TMPH2 and Ru3(CO)12. The product Ru(TMP)(CO) was subsequently eluted with CH2Cl2.The CH2C12 solution was concentrated to ~60 mL, a few drops of 'PrOH was added and the solution stirred. The pure Ru(TMP)(CO)CPrOH) was precipitated by adding hexanes (100 mL); yield 0.54 g, 60% based on TMPH2. Elemental Analysis: % Calculated(Found) for C60H60N4RuO2; Ru(TMP)(CO)('PrOH). C= 74.28(73.51), H= 6.23(6.32), N= 5.77(5.47). NMR (lH, C6D6): 8.80 (pyrrole-H,8H), 7.25 (m-H,4H), 7.10 (m-H,4H), 2.48 (p-Me,12H), 2.19 (o-Me,12H), 1.81 (o-Me,12H); peaks for coordinated 'PrOH; 3.3 (-CH-OH, broad), 0.80 (CH3-, doublet, 6H), 0.4 (-OH,broad). UV-Vis (Toluene): 412, 527 nm. IR (Nujol, KBr): vco = 1937 cm-1. Ru(TMP)(CH±CNh Bis-(acetonitrile)tetramesitylporphinatoruthenium(II), Ru(TMP)(CH3CN)2, was synthesized by the standard photolysis procedure.11 The carbonyl species Ru(TMP)(C0)('PrOH) (0.20 g, 2xl(H mol) was dissolved in a benzene (50 mL) and acetonitrile (30 mL) solvent mixture. This solution was transferred to a glass tube (3 cm diameter, 20 cm length) with a narrow, long neck (1 cm diameter, 20 cm length) fitted with a water cooled condenser and deoxygenated by bubbling Ar via a stainless steel canula for 30 min. The glass container was positioned against a Hanovia Hg vapour lamp (450 W) fitted with a Pyrex water-cooled jacket and photolyzed under Ar purge for a 16 hour period. At this time, a 1 mL aliquot was withdrawn via a syringe and the i.r. spectrum was taken to determine the absence of CO species (vco= 1937 cm-1). The Ru(TMP)(CH3CN)2 was then precipitated by concentrating the reaction mixture by photolyzing for another hour without water cooling. The resulting solid was filtered under Ar, dried and stored in a dinitrogen glove-box; yield 0.14 g, 70%. NMR (iH, CgDg): 8.65 (pyrrole-H,8H), 7.27 (m-H,8H), 2.54 (p-Me,12H), 2.21 (o-Me,24H), -1.32 (CH3CN,6H). UV-Vis (CH2C12): 408, 505 nm. IR (Nujol, KBr): = 2270 cm-1. Ru(TMP) Tetramesitylporphinatoruthenium(II), Ru(TMP), was prepared using a vacuum pyrolysis procedure.8,12 The success of this procedure lies heavily on the preparation of an amorphous powder of Ru(TMP)(CH3CN)2 because the crystalline complex does not lose the CH3CN ligand under the vacuum pyrolysis conditions. A benzene solution (10 mL) of Ru(TMP)(CH3CN)2 (0.06 g, 6xl0"5 mol) was prepared in a Schlenk tube taking care to ensure complete dissolution. This solution was quickly frozen by immersing in a Dewar flask filled with liquid-N2 and evacuated (10"3 torr). A mixture of H20 (40 mL) and acetone (10 mL) was then slowly poured onto liquid-N2 and the system was then allowed to warm-up slowly over a period of 16 hours while being evacuated. The amorphous powder thus formed was pyrolyzed at 220 °C under a vacuum of 2xl0"5 torr for 2 hours. The loss of CH3CN ligand can be easily monitored by the increase in pressure during the process of ligand loss. Once the pressure was decreased to 2xl0-5 torr, the Schlenk was closed, cooled to room temperature and moved to a dinitrogen glove-box. NMR (IH, C6Dg): 8.10 (pyrrole-H,8H), 7.2 (m-H,under CV5H6 peak), 6.90 (m-H, 4H), 2.39 (p-Me,12H), 2.17 (o-Me,12H), 1.17 (o-Me,12H). This brown solid turns red instantly when exposed to dinitrogen giving Ru(TMP)(N2)2.8 NMR (IH, CgDg): 8.80 (pyrrole-H,8H), 7.2 (m-H,under Gs^ peak), 2.48 (p-Me, 12H), 2.05 (o-Me,24H). UV-Vis (CgHg): 412, 516 nm. IR (Nujol, KBr): = 2204 cm-1; a minor peak at 2134 cm-1 was assigned to the mono-N2 species.8 Trans-dioxof tetramesitylporphinato )ruthenium(VI). Ru(TMP)( O )o The Ru(TMP)(CH3CN)2, Ru(TMP)(N2)2 and Ru(TMP) complexes in benzene or toluene solution yield trans-dioxo species Ru(TMP)(0)2 instantaneously upon exposure to dioxygen.8 Formation of two moles of free CH3CN per mole of porphyrin was observed in the case of the bis-acetonitrile precursor. The Ru(TMP)(0)2 species was isolated in near quantitative yield after removal of solvent by evacuation. Elemental Analysis: % Calculated(Found) for C^Hj^RuO^ Ru(TMP)(0)2. C= 73.26(72.85), H= 6.15(5.98), N= 6.10(5.88). NMR(lH, C6D6): 9.01 (pyrrole-H,8H), 7.14 (m-H,8H), 2.45 (p-Me,12H), 1.86 (o-Me,24H). IR (Nujol, KBr): vRu=0 = 820 cm"1. UV-Vis (CgHg): 420, 514, 540(sh) nm. Ru(TMP)(OSMezh Bis-(S-c^emylsulfoxide)tetramesitylrx)rpMnatorum Ru(TMP)(OS_Me2)2» was prepared by the reaction of Ru(TMP)(CH3CN)2 with DMSO. To a solution of Ru(TMP)(CH3CN)2 (10 mg, 10"5 mol) in benzene (2 mL), DMSO (25 uL, 3x10^ mol) was added under an Ar atmosphere and the mixture shaken. The bright orange precipitate that formed was isolated in ~100% yield by evacuating the mixture to dryness. Elemental Analysis: CaculatedCFound) for C60H64N4S2O2RU, Ru(TMP)(OSMe2)2. C= 69.40(69.26), H= 6.21(6.19), N= 5.40(5.45), S= 6.18(6.00). IR (Nujol, KBr): VS=o = 1170 cm"1. Ru(TMP}(QSEt2)2 Bis-(S-methylsulfoxide)tetramesitylporphinatoruthenium(II), Ru(TMP)(OSEt2)2, was prepared by the reaction of Ru(TMP)(0)2 (10 mg, 10'5 mol) in benzene (1.5 mL) with diethylsulfide(10 |iL, 10"4 mol) overnight. The resulting solution was evaporated to dryness and the micro-crystalline product was dried at 80 °C at 10"3 torr for 24h; yield 12 mg, -100%. Elemental Analysis: % Calculated(Found) for C70H78O2N2S2RU; Ru(TMP)(OSEt2)2 •C6H6 C= 71.70(71.50), H= 6.71(6.91), N= 4.78(5.00). NMR (lH, CgDg): 8.68 (pyrrole-H,8H) 7.2 (m-H,8H), 2.52 (p-Me,12H), 2.23 (o-Me, 24H), -1.00 (CH3CH2S,t,12H), -1.46 and -1.80 (-CH2-S, multiplets, 8H) UV-Vis (C6H6): 423(5.43), 510(4.38) nm. IR (Nujol, KBr): Vs=0 = 1165 cm"1. 36 RufTMPHQSiEQk Bis-(S-m-npropylsulfoxid^ RuCIMP)(OSnPr2)2, was prepared by reacting Ru(TMP)(CH3CN)2 (15 mg, 1.5xlO-5 mol) in benzene (3 mL) with excess nPr2SO (50 \iL). The resulting bright-red solution was chromatographed on neutral alumina (Activity U) using hexanes to remove excess sulfoxide, and CH2C12 to elute the red Ru(TMP)(OSnPr2)2 complex. The solvent was removed by evacuation and the product isolated in 80% yield (14 mg). Elemental Analysis: Calculated(Found) for GS8H82N4S2O3RU, Ru(TMP)(OSnPr2)2.H20. C= 69.88(69.64), H= 6.90(6.59), N= 4.79(4.78). (1 mole of H2O per mole of porphyrin was observed by -H nmr). NMR (*H, toiuene-d8) 8.60 (pyrrole-H,8H), 7.23 (m-H,8H), 2.50 (p-Me,12H), 2.10 (o-Me, 24H), -0.20 (CH3,t,12H), -0.43 and -0.70 (p-CH2,m,8H), -1.62 and -1.97 (a-CH2,m,8H). RufTMPHOSnBu^z Bis(S-di-nbutylsulfoxiae)tetramesitylporpWnatoruthenium(IJ), Ru(TMP)(OSnBu2)2, was prepared using a similar procedure used for the preparation of Ru(TMP)(OSnPr2)2-The product was isolated in 75% yield. Elemental Analysis: Calculated(Found) for C72H90N4S2O3RU, Ru(TMP)(OSnBu2)2-H20. C= 70.61(70.81), H= 7.41(7.16), N= 4.57(4.40). (1 mol of H2O per mole of porphyrin was observed by *H nmr). NMR (1H,CGD6) 8.64 (pyrrole-H,8H), 7.23 (m-H,8H), 2.50 (p-Me,12H), 2.22 (o-Me,24H), 0.18 (CH3CH2-,m,20H), -0.40 and -0.60 (P-CH2,m, 8H), -1.56 and -1.78 (a-CH2,m,8H). 37 Ethvlene(2-DroDanol)tetramesitvlDowMnato JPrOH solvate. Ru(TMP) (CHZCHZ) (iPrOH).iPrOH Some Ru(TMP)(N2)2 (8 mg, 8.5xl0"6 mol) was dissolved in THF (1 mL) and subjected to three freeze-pump-thaw cycles. The resulting dark brown solution was then exposed to ethylene (1 atm) for 5 minutes. A color change to bright reddish-brown was observed immediately. At this time, 2-propanol (1 mL) was vacuum transferred into the THF solution. The brown powder which precipitated overnight was filtered under Ar (5 mg, 60% yield). Elemental Analysis: % CalculatedCFound) for C&tf^^RuCh; RuCTMP)(CH2CH2) ('PrOH)2. C= 74.60(73.68), H= 7.04(6.89), N= 5.44(5.40). NMR (*H, C6D6): 8.57 (pyrrole-H,8H), 7.18 (m-H, under C6H6 peak), 7.13 (m-H,4H) EtMene(tetran^sitvlporphinato)mthemum(m Some Ru(TMP)(N2)2 (5 mg, 5.3X10-6 mol) was dissolved in benzene (1 mL) and the solution degassed as described above. The dark-brown solution was exposed to ethylene (1 atm) for 5 min. The resulting reddish-brown solution was evacuated to dryness and the product isolated in -100% yield (~5 mg). 2.46 (p-Me,12H), 2.12 (o-Me,12H), 2.03 (o-Me,12H), -3.11 (CH2CH2,4H) and for 2-propanol (2 moles /porphyrin) 3.4 (-CH, broad), 0.73 (-CH3, doublet), 0.0 (-OH, v. broad). Elemental Analysis: % CalculatedCFound) for C58H56N4RU, Ru(TMP)(CH2CH2). C= 76.54(75.80), H= 6.20(6.40), N= 6.16(6.11). NMR (lH, toluene-dg): 8.44 (pyrrole-H,8H), 7.20 (m-H,4H), 7.10 (m-H,4H), 2.45 (p-Me,12H), 2.16 (o-Me,12H), 1.89 (o-Me,12H), -3.27 (CH2CH2,4H). Bis-( Dara-hvdroquinoxo )tetrarnesiMpoTphinatomthenium(IV). RulTMP VOC^OH)^ Some Ru(TMP)(0)2 (10 mg, 10"5 mol) in benzene (1.5 mL) was stirred with excess phenol (10 mg) under 02 (1 atm) and the reaction monitored by UV-visible spectroscopy. When the starting Ru(TMP)(0)2 was fully consumed, the reaction mixture was chromatographed on neutral alumina (Activity I) using benzene as eluent. The dark-brown band which eluted first was collected and the solvent removed. Yield 10 mg (90%). Elemental Analysis: % CalculatedfFound) for C68H62N4RUO4, Ru(TMP)(OC6H40H)2. C= 74.22(74.55), H= 5.67(5.63), N= 5.09(5.11), 0= 5.82(5.40). NMR(1H, toluene-dg): -30.45 (pyrrole-H,8H), 7.63 (m-H,8H), 3.00 (p-Me,12H), 2.90 (o-Me, 24H), and for coordinated -OC6H4OH, 49.68 and -71.85 (o-H and m-H), -68.19 (-OH). UV-Vis (C6H6): 404, 524 nm. Magnetic Moment: |ieff =3.01 B.M. Bis-f tetramesitvlporpMnatorutheniurn/II) ]^-C1H1 Some Ru(TMP)(N2)2 (8 mg, 8.5x10-6 mol) was dissolved in benzene (1 mL) and degassed by three freeze-pump-thaw cycles. This dark brown solution was exposed to purified acetylene (1 atm) (Section 2.1.1) and shaken. Upon leaving under room light for 16 hours, the solution turned greenish-black. The solvent was then removed by evacuation and the resulting black solid was vacuum-dried for 24 hours at 25°C and 10*3 torr. Yield 8 mg (-100%). Elemental Analysis: % Calculated(Found) for Cii4Hio6N8Ru2, [Ru(TMP)]2( u-C2H2). C= 76.48(76.08), H= 5.97(6.03), N= 6.25(6.38). NMR (IH, C6D6): 10.44 (Ru=CH,2H), 7.92 (pvrrole-H,16H), 7.15 (m-H,8H), 6.92 (m-H,8H), 2.39 (p-Me,24H), 1.91 (o-Me,24H), 1.32 (o-Me,24H). NMR [UCi-rl}, C6D6]: 263.8 (Ru=C), 144.5 ( a-C), 139.1, 138.7, 138.2, 137.3, 128,119.8 (phenyl carbons), 130.6 ( p-C), 23.0 (p-Me), 21.4 and 21.3 (0-CH3). Attached proton test (APT): 263.8,130.6, 128, 23.0, 21.4,21.3 ppm peaks which are either primary (CH3) or tertiary (CH); all other peaks are secondary (CH2) or quaternary (C). The pyrrolic and methyl carbon signals provide proof for the validity of the chosen parameters for the APT experiment. NMR 13C (Gated Decoupled): Peak at 263.8 ppm gives a doublet (262.7,265.0 ppm). Molecular Weight: Calculated(Found) 1790(1561) g/mol. <Carbonvl)tetra-(2.6-dicMorophenvl)poiy^ A sample of OCPH2 was kindly provided by Dr. T. Wijesekera. NMR (1H, CDCI3): 8.68 (pyrrole-H,8H), 7.80 (m-H,d,8H), 7.75 (p-H,t,4H), -2.45 (N-H.2H). UV-Vis (C6H6): 408, 512, 590 nm. The Ru(OCP)(CO) species was prepared by the procedure used to prepare Ru(TMP)(CO)('PrOH), but with minor modifications. The low solubility of Ru(OCP)(CO) compared to Ru(TMP)(CO) species limits the amount of Ru(OCP)(CO) that can be chromatographed in one batch. Chromatography on neutral alumina (Activity I) using benzene as eluent removed unreacted RU3CO12 and OCPH2 as yellow and purple bands respectively. The pure product, Ru(OCP)(CO), was eluted using benzene/CH2Cl2 (1:1, v:v) ahead of a closely trailing black band. A green band stayed at the top of the column. The pure Ru(OCP)(CO) complex was isolated in 50% yield after removal of solvent by rotary evaporation. Elemental Analysis: % Calculated(Found) for C45H20N4CI8RUO, Ru(OCP)(CO). C= 53.13(53.14), H= 2.56(1.98), N= 5.51(5.00). NMR (IH, C6D6): 8.70 (pyrrole-H,8H), 7.36 (m-H,d,4H), 7.25 (m'-H,d,4H), 6.90 (p-H,t,4H). IR (Nujol,KBr): vco= 1946 cm--UV-Vis (G5H6): 408, 528 nm. Mass spectrum (EL m/e): 1018[M+], 990[M+-CO]. Bis-(acetonitrile)tetra-(2.6-dichloronhenvl)porpM Ru(OCP)(CH&Nh Some Ru(OCP)(CO) (50 mg, 5xl0-5 mol) was photolyzed in CH3CN/C6H6 (3:5, v:v) as described earlier for the preparation of Ru(TMP)(CH3CN)2- The product Ru(OCP)(CH3CN)2 was isolated in 80% yield (43 mg). NMR (iH, GsD6): 8.54 (pyrrole-H,8H), 7.42 (m-H,d,8H), 6.9 (p-H,t,4H), -1.44 (CH3CN,6H). UV-Vis (GsHoO: 408, 507 nm. IR (Nujol, KBr): VCN = 2273 cm"1 Trans-dioxo-te.tra(2.6-dichlnrnpheml)porphinatnruthenium(VI). Ru/OCP)(Oh This species can be prepared by two methods. (i). mCPBA oxidation of Ru(OCP)(CO). Some Ru(OCP)(CO) (100 mg, 10"4 mol) was dissolved in CH2C12 (10 mL) and mCPBA (35 mg, 2x10^ mol) was added slowly over a 15 niinute period with continuous stirring. The reaction was monitored by UV-visible spectroscopy until the Soret peak (408 nm) of the starting carbonyl complex had completely disappeared. The resulting mixture was chromatographed on neutral alumina (Activity I) and the solvent removed. Yield 50 mg (50%). (ii). Dioxygen oxidation of Ru(OCP)(CH3CN)2. Ru(OCP)(0)2 was conveniently prepared by exposing solutions (benzene, toluene, CH2CI2) of Ru(OCP)(CH3CN)2 to dioxygen and subsequent removal of the solvent by evacuation. Formation of 2 moles of CH3CN per mole of porphyrin was observed by nmr in in situ preparations. NMR (lH, C6D6): 8.90 (pyrrole-H,8H), 7.85 (m-H,d,8H), 7.75 (p-H,t,4H). UV-Vis (QsHe): 420(5.40), 510(4.10) nm. IR (Nujol.KBr): VR^ = 825 cm"1. Mass spectrum (EI, m/e): 1022[M+], 990[M+-2 O]. Repeated attempts to obtain satisfactory elemental analysis data were unsuccessful, perhaps due to combustion problems. 2.5 Oxidation of Thioethers to Sulfoxides 2.5.1 Electronic Spectral Measurements The solutions of Ru(Porp)(0)2 (Porp= TMP, OCP,-3x10-6 M in C^,3.0 mL) were prepared by adding dioxygen at 1 atm to solutions of either Ru(Porp)(CH3CN)2 or Ru(TMP)(N2)2 and the electronic spectrum recorded from 350-600 nm. The intensity of the newly formed Soret-peak at 420 nm was observed for 15 minutes, in order to determine that the trans-dioxo species was fully formed. The temperature of the cell holder was adjusted to the desired value and maintained to the accuracy of ± 0.1 °C. The thioether was then injected to obtain the desired initial concentration [ (2.5-50)x 10"2 M] using a micro-syringe, and the cell-tonometer was quickly shaken and re positioned in the cell compartment. The reaction was then monitored by one of the following methods. (I) Spectral changes were observed by scanning from 600-350 nm at suitable time intervals pr (II) The change in the intensity of the peak at 420 nm was observed with time. Method (IT) was considered more accurate for obtaining kinetic data since it enables one to read absorbance off the instrument at exact times. The reaction was followed until there was no change in absorbance for about 10 minutes, in order to obtain the Aoo reading. 2.5.2 Nuclear Magnetic Resonance Experiments Some Ru(Porp)(0)2 (Porp= TMP, OCP) in C^Dg or toluene-dg (~5xl0-3 M) was mixed with the appropriate thioether (2-5 uL) and the nmr spectra recorded at different time intervals. Selective decoupling experiments were performed in order to assign the signals for O-and S- bonded sulfoxide complexes. The amounts of free thioether and sulfoxide present were calculated using the integration intensities of the peaks of these species. 2.6 Oxidation of Phenol 2.6.1 Electronic Spectral Measurements Solutions of Ru(TMP)(0)2 (~3xl(h6 M) were prepared as described in section 2.5.1. and the electronic spectrum was recorded from 350-500 nm. A stock solution of phenol (5.58 M in CgHg) was prepared and stored in a refrigerator until use. After addition of phenol (0.04-0.15 M), the reaction was monitored as described in Section 2.5.1. 2.6.2 Nuclear Magnetic Resonance Experiments Some Ru(TMP)(0)2 in G5D6 or toluene-d8 (~5xl0-3 M) was mixed with a 5-10 mole excess of phenol and the reaction followed until all the dioxo-species was fully consumed. In order to determine the amount of water formed during the reaction, the same procedure was followed in extra-dry G5D6 in a sealed nmr rube and the integration intensity of the H2O peak was compared with that of the porphyrin peaks. The above experiments were performed under O2 at 1 atm because O2 is consumed during the reaction. However, to determine that the reaction could be stopped after step 3 (see Section 4.2, eq. 4.7), another experiment was carried out in a sealed tube in the absence of O2. The dissolved O2 in G5D6 that resulted from the preparation of Ru(TMP)(0)2 from Ru(TMP)(CH3CN)2 (Section 2.4) was removed by three freeze-pump-thaw cycles before the addition of phenol. References - Chapter 2 1. Bruce, M.L; Matisons, J.G.; Wallis, R.C.; Patrick, J.M; Skelton, B.W.; White, A.H. J. Chem. Soc., Dalton Trans., 2365(1983). 2. Ke, M. Ph.D. Thesis, University of British Columbia, 1988. 3. Pacheco-Olivella, A. A. M. Sc. Thesis, University of British Columbia, 1986. 4. Sishta, C. M. Sc. Thesis, University of British Columbia, 1986. 5. a. Signer, R. Ann., 478,246(1930). b. Clark, E. P. Ind. Eng. Chem. Anal. Ed., 13, 820(1941). 6. Groves, J.T.; Nemo, T.E. J. Am. Chem. Soc., 105, 6243(1983). 7. Groves, J.T., Quinn, R. Inorg. Chem., 23_ 3844(1984). 8. Camenzind, M.J.; James, B.R.; Dolphin, D. J. Chem. Soc., Chem. Commun., 1137(1986). 9. Badger, G.M.; Jones, R.A.; Laslett, R.L. Aust. J. Chem., 12, 1028(1964). 10. Rillema, DP.; Nagle, J.K.; Baninger, LJ3.; Meyer, T.J. J. Am. Chem. Soc., 1J)3_,56(1981). 11. Antipas, A.; Buchler, J.W.; Gouterman, M.; Smith, P.D. J. Am. Chem. Soc., 1£Q,3015(1978). 12. Camenzind, M.J.; James, B.R.; Dolphin, D.; Sparapany, J.W.; Ibers, J. A. Inorg. Chem., ZL 3054(1988). CHAPTER 3 Oxidation of Thioethers to Sulfoxides 46 3.1 Introduction The selective oxidation of thioethers to sulfoxides is a process of considerable importance.1'3 The sulfoxides which are formed by the partial oxidation of thioethers undergo many synthetically important reactions.3 Also, selective oxidation of waste thioethers (e.g. Me2S) to more valuable sulfoxides is an economically attractive process.2 If the cheap and abundant oxidant dioxygen can be utilized for this oxidation reaction, at relatively mild temperature and pressure conditions, then the process has the potential of becoming extremely useful in industry. All transition metal systems described so far for the oxidation of thioethers have been based on either stoichiometric oxygen atom donors like iodosylbenzene,4'5 metal-oxo reagents such as chromic acid,6 permanganate,7 OsCU7'8 R.UO4 8 or outer-sphere electron transfer systems utilizing Ru(II) 9»10 or Ce(TV) 2 which generate peroxide (from dioxygen) as the oxidizing agent. The peroxide based systems necessarily give sulfoxide/sulfone ratios that parallel those observed for the H2Q2 oxidation of thioethers.11 Investigation of possible oxidation of thioethers to sulfoxides using sterically hindered trans-dioxo ruthenium porphyrins was initiated in the present study in order to establish the kinetics and mechanism of oxidation, to obtain activation parameter data for measured rate constants and to explore the possibility of designing a catalytic system that utilizes dioxygen as the oxo-source. The results obtained in the studies of oxidation of the alkyl thioethers Et2S, nBu2S and DecMeS to corresponding sulfoxides are presented and discussed in this Chapter. All the raw data are tabulated in Appendix A. The basic experimental details rertaining to the results given below have been described in Chapter 2 (Section 2.5). 3.2 Data Analysis. Results and Discussion 47 The reaction of R2S (R= alkyl) with Ru(Porp)(0)2 (Porp= TMP, OCP) in benzene solution can be easily monitored by UV-visible spectroscopy. Figure 3.1 shows initial spectral changes (~first 3 h) observed for the oxidation of Et2S (2.3xlO-2M) by Ru(TMP)(0)2 ("3X10-6 M) in benzene under dioxygen (1 atm) at 20.0 °C, where the reaction product observed is Ru(TMP)(0_SEt2)2> Q_SEt2 being O-bonded sulfoxide (see later). On addition of the thioether, the intensity of the 420 nm Soret peak of the Ru(TMP)(0)2 species begins to decrease gradually, accompanied with a shift of the maximum towards longer wavelength; also, the peak at 514 nm shifts to 508 nm. Isosbestic points are observed at 404, 446, 510, 548 nm. After these initial spectral changes depicted in Figure 3.1, the intensity of the newly formed peak at 423 nm begins to increase slowly (over a period of 16 h) with the resulting loss of isosbestic points. The initial reaction (~3 h) can be monitored conveniently by observing the absorbance change at the 420 nm Soret peak of Ru(TMP)(0)2. This procedure was used to calculate the pseudo-first order rate constants, kobS values, for the disappearance of Ru(TMP)(0)2 by plotting ln(At-Aoo) vs. time according to the following derivation, for the overall reaction: ki Ru(TMP)(0)2 + 2 SR2 > Ru(TMP)(0_SR2)2 1 2 ki being the overall second order rate constant. When [R2S] » [Ru], the reaction is experimentally found to be pseudo-first order in Ru. Therefore, -d[ I ]/dt = kobst I ] d[l]/[l] = -kobsdt m[l jo-ln[l]t = -kobs(0-t) Figure 3.1 UV-Visible spectral changes observed for the oxidation of Et2S by Ru(TMP(0)2 at 20.0 °C in C^rle under O2 (1 atm). Inset shows the pseudo-first order plot for the disappearance of Ru(TMP)(0)2. [Ru]= 3xl0-6 M, [Et2S]= 2.32xl0-2 M. 00 49 [ 1 lo and [ 1 ]t being the concentration of Ru(TMP)(0)2 at time zero and time t respectively. Therefore, ln [ 1 y [ 1 ]0 = -kobs-t If A0, At, and A«, are the initial, at time t and final absorbances of Ru(TMP)(0)2 species respectively, then, [l]ta(ArAeo) [IloOUAo-Aoc) Therefore, ln[ArAoo] = -kobs-t + ln[Ao-Aoo]. Thus, the pseudo-first order rate constant kobs can be calculated from the gradient of the plot of ln[Ar Ax.] against time plotted using least-squares fit. A typical absorbance vs. time trace for the oxidation of DecMeS by Ru(TMP)(0>2 in benzene under dioxygen (1 atm) and the resulting semi-log plot are given in Figure 3.2; the inset of Figure 3.1 shows the corresponding log plot for an experiment involving Et2S. The UV-visible spectral changes and the kobs values determined remain unaffected whether the reaction was carried out under dioxygen or argon. The [thioether] dependence of kobs was investigated by determining the rate constants at various thioether concentrations at 20.0 °C; the data obtained for Et2S and DecMeS are given in Tables 3.1 and 3.2 respectively, and the plots of kobs against [thioether] are given in Figures 3.3. The linear relationships suggest first order dependence of kobs on [thioether]. 50 Time [min.j Figure 3.2 Absorbance at 420 nm vs. time trace for the oxidation of DecMeS by Ru(TMP)(0)2 in Cg^ at 20.0°C under O2 (1 atm) and the resulting pseudo-first order plot [Ru]= 3.4x10-6 M, [DecMeS]= I.llxl0-2M. 51 Table 3.1 Pseudo-first order rate constants Qtobs) at different diethylsulfide concentrations; [Ru]= --4x10-6 M at 20.0° C in benzene.8 [Et2S], 10-2 M kobs, l(Hs-l 0 0 0.309 0.272 1.55 1.25 2.32 1.67 3.10 2.40 4.64 3.50 4.64 3.48b 23.2 17.7 a- under O2 0 atm). b- under Ar (1 atm). Table 3.2 Pseudo-first order rate constants O^obs) at different decylmethylsulfide concentrations; [Ru]= ~4xl0"6 M at 20.0 °C in benzene under O2 (1 arm). [DecMeS], 10*2 M kobs, 10'3 s"1 0 1.11 2.22 0 1.27 3.12 |Et2S| , 10"2M. |DecMeS) ,10"2M. Figure 3.3 Thioether dependence of at 20.0 °C in for the oxidation of (A): Et2S and (B): DecMeS by Ru(TMPXO)2. lRu]= -talO^M. 53 Table 3.3 summarizes second order rate constants (ki) calculated for the oxidation of various thioethers, where kobs= ki [thioether]. A marked increase in the rate of oxidation is observed (Table 3.3) when the alkyl chain length of the thioether is increased. The activation parameters for the ki process were calculated to determine the origin of such an increase by studying the temperature dependence of the reaction rate for the oxidation of the thioethers given in Table 3.3. The data are summarized in Table 3.4. The resulting Arrhenius plots (Ink j vs. 1/T) are given in Figure 3.4; the the activation parameters calculated from the Arrhenius plots are also given in Table 3.4. A mechanism involving electrophilic attack by 0=Ru=0 moiety on :SR2 to form initially bis-O-bonded sulfoxide species, 3_, (Scheme 3.1) is proposed for the oxidation of thioethers by the dioxo-ruthenium porphyrin species, taking into account the results of UV-visible spectroscopic studies described above and the -B. nmr experiments to be discussed below. The bis-O-bonded sulfoxide complex Q) subsequently isomerizes to 5_ via 4. The first order dependence of kobs °n [thioether] and the fact that 2 is not observed by -rl nmr as an intermediate (see below) allow the ki step to be assigned as shown and require that the process 2 —> 1 is fast The increase in rates with increasing alkyl chain length within thioethers is reflected more in AS* than in AH* (Table 3.3). If the O-atom transfer is induced by strong Ru=0 vibrational coupling,1 it might be more efficient in encountering a bulkier substrate. As expected, the process is entropically unfavourable, more so for smaller thioethers. Corresponding data for O-atom transfer from [(bpy)2(py)Ru0]2+ to Me2S are AH*= ~34 kJ mol"1 and AS$= -110 J K"1 mol"1.1 54 A mechanism similar to the one mentioned above has been proposed for the oxidation of Me2S by a related Ru(TV)=0 system, [(bpy)2(py)RuO]2+.1 The O-atom transfer step in this system is also first order in both Ru and thioether, the rate being 150-2000 times faster than those measured at 20 °C in this work. In the above bipyridyl system, the final product [(bpy)2(py)Ru(0£Me2)]2+ undergoes solvolysis in CH3CN to form [(bpy)2(py)Ru (CH3CN)]2+ and Me2SO. However, the Ru(TMP)(0£R2)2 complexes are substitution inert; in fact, they can be prepared by the reaction of Ru(TMP)(CH3CN)2 with R2SO in benzene solution (see below). Table 3.3 Second order rate constants (ki) calculated for the oxidation of alkyl thioethers by Ru(TMP)(0)2 at 20.0 °C in benzene. Thioether DecMeS nBu2S Et2S kiCM-ls-1) 0.114 0.0123 0.00754 Table 3.4 Second order rate constants (ki) at various temperatures and the activation parameters for the oxidation of Et2S, nBu2S and DecMeS by Ru(TMP)(0)2. Thioether T(K) kiCM-ls"1) AH*(kJmoF) AS* (J K*1 mol-1) Et2S 290.15 6.31x10-3 58.3±2.7 -86±9 293.15 7.54x10-3 298.15 12.5x10-3 309.15 30.8x10-3 nBu2S 288.15 8.03x10-3 47.4+2.7 -120+9 293.15 12.3x10-3 303.15 23.4xl0-3 308.15 30.2x10-3 DecMeS 283.15 5.22xl0'2 56.5±1.7 -70±6 293.15 1.14X10'1 303.15 2.71X10'1 Figure 3,4 Arrhenius plots for the oxidation of Et2S, nBu2S and DecMeS by Ru(TMP)(0)2inC6H6. 56 Scheme 3.1 Proposed mechanism for the oxidation of thioethers by Ru(Porp)(0)2 species. Porp= TMP, OCP. 57 As mentioned above, after the initial spectral changes shown in Figure 3.1, the intensity of the newly formed Soret peak at 423 nm increases slowly by AA= -0.02 (16 h) which results in the loss of isosbestic points. These slow spectral changes are attributed to the isomerisation of 3_ to 4 and 5_ (Scheme 3.1), as observed by *H nmr (see below). Therefore, it is concluded that ki>k2»k3 (Scheme 3.1). However, no attempts were made to calculate k2 or k3 because of the close similarity of the UV-visible spectra of 3j 4, and 5_. *H Nuclear magnetic resonance spectroscopic studies were carried out in order to identify the intermediates and the final product The *H nmr spectrum of the starting Ru(TMP)(0)2 (~5xl0"3 M) species in G5D6 is given in Figure 3.5. As soon as the thioether (e.g. Et2S, 2xl0'2 M) is added, the intensity of the peaks due to Ru(TMP)(0)2 begins to decrease, accompanied by the formation of a new porphyrin species (Figure 3.6, pyrrole-H= 8.50 ppm). Associated with this new porphyrin is a set of peaks around -2 ppm, which is the expected chemical shift region for axial ligands containing alkyl groups bound to a Ru(LT) center. This high-field shift of alkyl resonances due the porphyrin ring current is consistent with that observed for other similar ruthenium porphyrin complexes such as Ru(OEP)(DecMeS)2.10 This new porphyrin species is identified (see below) as the bis-O-bonded sulfoxide complex, Ru(TMP)(QSEt2)2,2 (Scheme 3.1). Table 3.5 summarizes lH nmr data for 2. along with those for other species observed. A second new species begins to appear subsequently (pyrrole-H= 8.60 ppm), which is identified as the mixed species, Ru(TMP)(Q_SEt2)(OSEt2), 4 (Figure 3.6, Table 3.5). The Ru(TMP)(0)2 species is almost completely consumed in nearly 2 hours in an experiment where initial concentrations of Ru(TMP)(0)2 and Et2S are 4.4xl0*3 M and 2.0X10*1 M respectively in C5D6 at 25 °C. The reaction mixture contains only 3_ and 4 (in - 2:1 ratio) and no 5_ at this stage. Finally, over a longer period of time (- 36 h) the species 3_ O o-Mc Pyrrole-H Pyrrole-H o-Me C6H6 p-Me Meta-H u • , ! | | I I I I I I I I I I | I I I I I I I I I I I ' ' ' | ' ' ' ' I ' 1 11 | 1 1 11 I 1 ' ' ' I ' ' , 10 8 6 4 2 0 PPM Figure 3.5 Room temperature *H nmr spectrum (300 MHz) of RufTMP)(0)2 in Q£>6, [Ru]= ~5xlO"3M. oo i rTpmirniiiiMimiiiiiimiirmmiTTTr^ nmT| iriT| 111 -O.B r0.B -1.0 -1.? -1.4 -l.B -l.B -2.0 -2.2 PPM ^(CHjCHjh Pyrrole-H' | -O (CHjCHj)jS ^ « 3 ;S(CH2CH3)j Pyrrole-H Ru CHJCHJ C HI k.A "~r r~ r; n—r"T"r -rrp-i-T-rr"'""'_T T~J~1 rri | -1 n~ t i | i Tn-rrTT i J i r T i ^ i i r-i-r~i~t-n-j—r Figure 3.6 Room temperature *H nmr spectrum (300 MHz) of a reaction mixture containing Ru(TMP)(0)2 (initially 5xl0"3M) and Et2S (2xlO-2M) in C6D6 after a 2h reaction time. r- r r-i-T-r-r r-r-n—r VO 60 Table 3.5 -H nmr data8 for Ru(TMP)(0>2. and Et2SO complexes of Ru(TMP). Pcrrphyrin Axial Ligand Complex Pyrrole-H Meta-H p-Me o-Me CH3C -CH2-1 9.01 7.14 2.45 1.86 2 8.50 ~7.2t> 2.50 2.24 -0.80 -1.66(q) 4 8.60 ~7.2*> 2.50 2.30 -0.90 -1.30(m) 2.14 -0.95 -1.58(m) -1.96(q) 5. 8.64 ~7.2b 2.50 2.20 -1.02 -1.44(m) -1.80(m) a- room temperature in C^Dg, all singlets unless mentioned otherwise. b- under residual solvent peak. c- triplet, m- complex multiplet, q- quartet and 4. convert essentially completely to bis-S-bonded species, Ru(TMP)(OS_Et2)2. 5_; an nmr spectrum of which is given in Figure 3.7. The species 2 and 4 can be readily characterized by analyzing the high-field portion of the -H nmr spectrum of a rnixture of these species given in Figure 3.6. Use of selective proton decoupling as well as integration intensities allowed for the peaks labelled as a(CH3) and a(CH2) to be assigned to the bis-O-bonded species, 2- The CH2 protons of the O-bonded Et2SO appear as a quartet (coupled only to adjacent CH3) and thus the theoretically expected magnetic inequivalency is too small to be observed, which is not unprecedented.12 The CH3 protons of 2 appear as the expected triplet a(CH3), while in the mixed species 4, the two types of CH3 groups (from O and S bonded sulfoxides) appear as two partially overlapping triplets b(CH3) and c(CH3), respectively. The CH2 protons of the -T-T-T—i—r-j~i -r-~i—r j-i -i—i—i—i—i-r-i i \ Tt'~\ ~-r T—i—T~Y~>,fT~l r~~'—1—1—1—,~T~r"|—1—'—r "r~ Figure 3.7 Room temperature !H nmr spectrum (300 MHz) of in situ Ru(TMP)(OSEt2)2,5, in QDfr ON 62 O-bonded sulfoxide within the mixed species 4 appear as a quartet b(CH2), while CH2 of the S-bonded sulfoxide appear as two multiplets c(CH2). However, the CH3 signals for the TMP ligand cannot be readily observed in the reaction mixture, because of the presence of overlapping signals for excess Et2S. Therefore, the species 2 and 4. were isolated as a mixture by evacuating the reaction mixture to dryness after 1 had been completely consumed (Figure 3.8). Figure 3.9 shows the -H nmr spectrum of the above mixture after heating at 50 °C under N2 for 45 minutes. The production of 5_ at this time is clearly observed. The CH3 peaks of the TMP ligand can be easily assigned as shown in Figures 3.8 and 3.9. As expected, each of the species 2 and 5_ gives rise to only two CH3 signals which integrate to 2:1 (for o-Me and p-Me respectively) for the TMP ligand resulting from the D4h symmetry and the species 4 contains three magnetically different CH3 groups that integrate to 1:1:1 due to lack of D4h symmetry. It is evident from the *H nmr data that the assumed product of the first O-atom transfer, 2, is not formed in an observable amount If the first two species that initially formed were 2 and 2. only two different methyl signals, one for each of 2 and 2 would be present. In fact, the presence of three methyl signals, as mentioned above, rules out the existence of 2 under these conditions. It might be argued that Z, formally a Ru(TV) species, may not be detectable by ~H nmr because of paramagnetic line-broadening. However, the total integration intensity of the pyrrole peaks of 1,2,4 and 5_ remains constant at all times during the process of converting 1—> 5_ via 2 and 4, excluding the possibility of the existence of 2 as a paramagnetic intermediate in an appreciable amount UV-visible and nmr spectral studies rule out the possibility that the slow step being monitored is the conversion of 2 —> 2- It is interesting and perhaps surprising that in this Ru(VD(0)2 system, the first O-atom transfer step ki (Scheme 3.1) is slower than the second O-atom transfer that generates the detected species 2- If the O-atom transfer occurs via electronic coupling induced by strong Ru=0 vibrational motion,1-13 the findings imply that this C6H6 AJL i i i i i i i i i i r 1 1 I ' 1 ' I | I I I I | I I I I | I I I I | I 7 I 1 | I I I I | I I I I | I I I I | I I I I | I I I I 1 n 6 4 2 0 i i i i 10 n R i. j 0 -2 Figure 3.8 Room terrrperature *H nmr spectrum (300 MHz) of an isolated mixture of Ru(TMP)(Q_SEt2)2,1, and Ru(TMP)(QSEt2)(OSEt2), 4, in -4 4 1 J I 5 - - 3 It C6H6 ;mi|iiii|iiii|iiM|i)ii|iiii|iiii|Hii|iiii|iiii|iiii|iiii|iiii|iiii|"ii|iiiiH _0 8 _10 -1.2 -1.4-1.6 -1.8 -2.0 -2.2 PPM 2.A 5? ^ I. — H20 T I I | I I I I | I I I I I I III |' I | I I I I | I I I I | I I I I | I I I I | 1 I I I I | I I I I | I I I I | I I I I | ' ' I 1 I ' ' ' ' | ' 10 8 6 4 2 0 -2 -4 Figure 3.9 Room temperature iH nmr spectrum (300 MHz) of a mixture of RuCTMP)(QSEt2)2,2, Ru(TMP)(Q_SEt2)(0£Et2), 4, and Ru(TMP)(0£Et2)2,5_, in C6D6. 65 process occurs more readily with 2 than with 1. Groves and Ann14 have formed Ru(IV)(TMP)(0) species in situ by treatment of 1 with a stoichiometric amount of PPI13; here, the phosphine oxide product does not coordinate to the metal and their data imply that 1 is a much more potent oxo-transfer agent than the 5-coordinate Ru(TMP)(0). The role of the trans axial ligand L in LRu(TV)(Porp)(0) species within O-atom transfer is clearly critical, and these systems offer an excellent route into models for biologically important oxo-iron(IV) porphyrins.14'15 In the -H nmr spectrum of the final bis-S-bonded sulfoxide species 5_ (Figure 3.7) the two methylene protons in each ethyl group are seen to be magnetically ^equivalent, as in the free ligand,12 and appear as approximate sextets centered at -1.44 and 1.80 ppm as the AB moiety of an ABX3 system; the CH3 protons approximate as a triplet at -1.02 ppm. The same species was also isolated by another route (see below), via the reaction of Ru(TMP)(CH3CN)2 with Et2SO, and its !H nmr spectrum in CD2CI2 is given in Figure 3.10. The sulfoxide complexes Ru(TMP)(OS.Me2)2, Ru(TMP)(OSnPr2)2 and Ru(TMP)(0£nBu2)2 also were isolated by reacting Ru(TMP)(CH3CN)2 species in benzene solution with the corresponding sulfoxide (Section 2.4). The instantaneous, direct substitution of CH3CN by the sulfoxide to form bis-S-bonded sulfoxide complex was observed by nmr, no O-bonded intermediates were formed during the reaction. The -H nmf spectrum of Ru(TMP)(OS.nBu2)2 complex and the high-field portion of the -H nmr spectrum of the Ru(TMP)(0£.nPr2)2 are given in Figure 3.11. The positions of the porphyrin based peaks are essentially identical in all four bis-sulfoxide complexes isolated (Section 2.4). However, due to the very low solubility of Ru(TMP)(OS_Me2)2 complex in common deuterated solvents no presentable nmr spectra could be recorded; nevertheless, all the anticipated nmr peaks were observed, but as very weak signals. Pyrrole-H Meta-H Ru Pyrrole-H' i / ^2ci2 p-Me o-Me JU A A ii|Mii|iiii|iiii|iiii|iiii|iiii|iiii|iiii|iiii|iiii|iiii|iin|iiii|iiM -1.0 -1.1 -1.4 -1.§ -1.8 -2 0 -2.2 P |H20 r 1 1 11 I 11 ' ' | i ' i i | i i i i ; 10 1 I 1 1 1 1 I 1 1 ' ' I ' ' I I I I I I I I I I I I I I I I I I I I I I I I I I I 4 2 0 -2 PPM Figure 3,10 Room temperature *H nmr spectrum (300 MHz) of isolated Ru(TMP)(0£Et2)2 in CD2CI2. ' ' ' ' I I ' I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I t I I I I I I I I I I I I I I 8 6 4 2 0-2 Figure 3.11 Room ternperature *H nmr spectrum (300 MHz) of isolated Ru(TMP)(OSnBu2)2 in C£>6- ^l shows the hign' field region of the 'H nmr spectrum of isolated Ru(TMP)(OSnPr2)2. 68 In both Ru(TMP)(QS_nPT2)2 and Ru(TMP)(0£nB 112)2 complexes, both the a-methylene and pVmethylene protons of the sulfoxide ligands are seen to be magnetically inequivalent (Figure 3.11). Four separate multiplets are observed for the four a- and {$-methylene protons; integration intensities and selective proton decoupling experiments confirm the assignments given. The examination of molecular models of these complexes reveals that the rotation along Ca-Cp bond is prevented by the presence of the porphyrin ligand thereby rendering otherwise equivalent two P-methylene protons magnetically inequivalent The solubility characteristics of bis-sulfoxide complexes vary widely, depending on the length of the alkyl chains of the sulfoxide. The Ru(TMP)(05.Me2)2 complex precipitates out completely form benzene, toluene, CH2CI2, and acetone solutions as formed either during oxidation of Me2S by Ru(TMP)(0)2 or by the reaction of DMSO with Ru(TMP)(CH3CN)2- The Ru(TMP)(OSEt2)2 complex is only moderately soluble (-2 mg/mL) in benzene or toluene. However, Ru(TMP)(OS,nPT2)2 and Ru(TMP)(OSnBu2)2 complexes dissolve well in these solvents (-10-12 mg/mL). In the presence of a 10-fold excess of Et2S, solutions of I (at -6x10"3 M) under 1 atm O2 at 35 °C catalyze the 02-oxidation to generate selectively the sulfoxide Et2SO, but, after a total turn-over of -8 (after 20 minutes), catalysis is suppressed; at this stage 4 and 5_ are mainly present (Figure 3.12). The catalysis perhaps occurs via 3_, the more labile bis-O-bonded sulfoxides16 being lost with concomitant regeneration of 1. Indeed, Ru(TMP)(L)2 type complexes, where L is a labile ligand (e.g. CH3CN, THF), react with O2 instantaneously to generate Ru(TMP)(0)2 in C^H^ solution at room temperature. However, Groves and Ahn14 have detected the Ru(TV)(TMP)(0) species by lH nmr. Although they describe that the reaction (L= CH3CN) was performed in C^Dfr, their solvent in the Figure referred to was clearly CD2G2 (residual CH2CI2 signal at 5.25 ppm). Of significance, no * -1 -2 fc6H6 9 8 7 2 1 0 ppm Figure 3.12 Room temperature *H nmr spectrum (400 MHz) of a reaction mixture containing RufTMP)(0)2 (~5x 10"3M) and Et2S (5xl0"2M) under O2 (1 atm at 20°Q heated for 20 minutes at 35°C VO 70 Ru(TMP)(SEt2)n» n=l,2, species were formed in the reaction mixture at any time during the reaction of Ru(TMP(0)2 with SEt2- Figure 3.13 shows a !H nmr spectrum of Ru(TMP)(SEt2)2 complex generated in situ by the reaction of Ru(TMP)(CH3CN)2 with excess Et2S. The Ru(TMP)(SEt2)2 species is totally unreactive toward 02 at room temperature in benzene solution over a long period of time (> 24h). This rules out the possibility that the oxidation of Et2S occurs via an outer-sphere mechanism similar to that proposed for the oxidation of phosphines (see Chapter 1, Scheme 1.4). Higher turnovers (-15) are realized for the oxidation of Et2S by Ru(TMP)(0)2 at 65 °C, but now the porphyrin ligand undergoes degradation perhaps via reactivity with the Ru(TMP)(0)2 moiety in an intermolecular process. It was evident that effective oxidation of thioethers using a ruthenium porphyrin/dioxygen system could be made catalytic at elevated temperatures, if a porphyrin ligand that resists oxidative destruction was used. Meso-tetra(2,6-(h^hlorophenyl)porphinatoiron(III)chloride, Fe(OCP)(Cl), which is an efficient catalyst in alkene epoxidation and alkane hydroxylation reactions in the presence of O-atom donors such as PhIO or C6F5IO, has been reported as extremely resistant to oxidative destruction.17 Therefore, Ru(OCP)(0)2 was synthesized in the present work (Section 2.4) in order to investigate the catalytic 02-oxidation of thioethers to sulfoxides. The synthesis and characterization of Ru(OCP)(0)2 species is discussed in Chapters 2 (Section 2.4) and 6 (Section 6.4.3). The electronic spectral changes observed for the oxidation of EtjS (1.55xl0-2 M) by Ru(OCP)(0)2 (4xl0-6 M) in benzene under dioxygen are given in Figure 3.14. The absorbance vs. time trace and the resulting ln(At-Aoo) vs. time plot for the disappearance of Ru(0CP)(0)2 species (420 nm) are given in Figure 3.15. A second-order rate constant, kj= 7.23xl0-2 M"1 s-1 for the oxidation of Et2S at 20.0 °C was calculated. Therefore, Ru(OCP)(0)2 oxidizes Et2S nearly 10 times faster than Ru(TMP)(0)2 (ki= 7.54xl(r3 M"1 Pyrrole-H Meta-H r C6H6 A. Ru Pytrole-H^ T~ / p-Me I i i '» j i i i i I i i i i | I I I i I i i i i | i i i i ; i i i i |--ri i i | i i i i | i1 i I I | i i I i | i i i i | 'i i T 7 J -2 Figure 3,13 Room temperature *H nmr spectrum (300 MHz) of in situ Ru(TMP)(SEt2)2 in CfPe. Figure 3.14 UV-visible spectral changes observed for the oxidation of Et2S by Ru(OCP)(0)2 at 20.0°C in under O2 (1 atm). [Ru]= 4xlO"6M, rEt2S]= 1.55xlO"2M. 73 -J.S-8 c so Time [min.] Figure 3.15 Absorbance at 420 nm vs. time trace for the oxidation of Et2S by Ru(OCP)(0)2 in GsHg at 20.0 °C under O2 (1 atm). [Ru]= 4x10-6 M, [Et2S]= 1.15x10-2 M. 74 s"1; Table 3.3) at 20.0 °C. The introduction of electron-withdrawing CI substituents to the porphyrin ligand decreases the electron density at the ruthenium center thereby making the 0=Ru=0 moiety more electrophilic; such increased electrophilicity presumably accounts for the increased reactivity toward substrates such as thioethers. The Ru(OCP)(0)2/Et2S system too was followed by *H nmr spectroscopy. Figure 3.16 shows a *H nmr spectrum of a reaction mixture containing Ru(OCP)(0)2 (~3xlf>3 M) and Et2S (2xl0-2 M) after an 8 hour reaction time. The principal porphyrin product present at this time is identified as Ru(OCP)(QSEt2)2 (pyrrole-H= 8.30 ppm). Formation of 1.2 equivalents of free sulfoxide per Ru(OCP) is also observed at 5CH3= 0.90 ppm. Compared to the Ru(TMP)(0)2/Et2S system, a major difference observed in this system, in addition to the increase in the rate of formation of the bis-O-bonded species, is the much slower rate of isomerization to form the mixed species (Spynoie-H = 8.40 ppm) and subsequent bis-S-bonded species (8pyn-0ie.H = 8.60 ppm). This observation is in agreement with the explanation given for the driving-force behind such isomerization reactions in related Ru(II) systems. The preference of Ru(II) in an electron rich environment, e.g. [(bpy)2(py)Ru(0_SMe2)]2+ is to form the S-bonded sulfoxide species, thereby reducing the electron density on the metal via Ru —>S 7t-back bonding.90'17-20 The Ru(U) center in Ru(OCP)(0_SR2)2 complex is less rich in electron density than in Ru(TMP)(0_SR2)2 because of the electron withdrawing effect of CI substituents in the OCP ligand compared with the electron releasing effect of CH3 groups in the TMP ligand. Therefore, Ru(TMP)(0_SEt2)2 is expected to isomerize faster compared to Ru(OCP)(QSEt2)2. Figure 3.17 shows the *H nmr spectrum of a reaction mixture that initially contained Ru(OCP)(0)2 (~2xlO-3M) and Et2S (6xlO-2M) under O2 (1 atm at room temperature) heated to 100°C for 12 hours. Two important results are observed here. Firstly, the Ru(OCP) porphyrin species has survived the reaction conditions with no Pyrrole-H C6H6 S-CH JI CH3--CH.SO li TMS ainci^so CH3-CH2-SO-Ru .JL j—r—r—r—r—r 10 -i—i—|—r—i—i—i—|—i—i—i—i—|—i—i—i—r 8 6 -i—i—i—j—i—i—i—i—i—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—i—i—i—i—i—r Figure 3.16 Room ternperature  lU nmr spectrum (300 MHz) of a reaction mixture containing Ru(OCP)(0)2 (initially ~3xl0"3M) and Et2S (2xl0~2M) in Q5D6 after an 8 hour reaction time at room tempetature. JI A ii[iiii|iiii|iiii|iiii|iiii|iiii|i)ii|ir 9 2 90 86 86 02S-CH2-C6H6 iii|iiii|Mii|iiii|iin|iiii|iiii|i,ii|iiii|iiii|ii'i|,iii|iiii|i. i|iiii|iiny»T~ii[111111111 2.6 2 6 2 4 2 i 2 0 18 1.6 14 / 12 PPM iiil|llli|iiii|iiii|iiii|iiii|ini|i -0 8 -1.0 -1.2 -14 -1.6 PPM qi3-CH2-sor I.. ,—i—i i t i i i i i | i i i i i i i i i | 10 8 6 i i i i i i i I i i i i I i i i i I i i i i r' i i i I 4 2 0 r i i i | i i i i [ T i i i I i i -2 Figure 3.17 Room temperature JH nmr spectrum (300 MHz) of a reaction mixture containing Ru(OCP)(0)2 (initially ~2xl0"3M) and Et2S (oxlO-ZM) and O2 (1 atm at room temperature) in C6D6 after a 12 hour reaction time at 100°C. 77 detectable loss due to oxidative destruction and is present as Ru(OCP)(OJSEt2)(0£Et2) and Ru(OCP)(OjSEt2)2- As mentioned above, the Ru(TMP)(0)2/Et2S/02 system completely bleaches out under similar conditions. Secondly, the thioether has been essentially completely oxidized to Et2SO and Et2SC»2 (in a 4:1 ratio). The amount of sulfoxide and sulfone formed accounts for more than 30 turnovers/Ru(OCP). The same reaction carried out at room temperature generates sulfoxide exclusively (Figure 3.16). Therefore, it can be expected that if reacted at a suitable temperature lower than 100 °C the amount of sulfone formed can be reduced if not completely eliminated. 3.3 Conclusions The incorporation of O-atoms into a substrate (thioethers in this case) using O2 as the oxo-source via oxo-ruthenium porphyrin species is demonstrated. A dioxygenase type reactivity, i.e. transfer of both O-atoms to the substrate by Ru(Porp)(0)2 species (Porp= TMP, OCP), is observed. These systems operate via reactive 'M=0' species acting as O-atom donors and do not appear to effect any outer-sphere (022" type) activation of dioxygen. The O-atom transfer reactions are catalytic, but the turnovers are relatively small. The low catalytic activity in both TMP and OCP systems is attributed to the strong coordination of the sulfoxides to the metal center. Incorporation of the electron-withdrawing substituent Cl into the porphyrin ligand increases both the reaction rate and the temperature at which the reaction can be carried out without the degradation of the catalyst. Further studies are necessary using other porphyrins substituted with elecrton-withdrawing, nonoxidizable substituents such as F and Cl (e.g. perfluoro-TPP). The activation parameters determined in this study will be useful in understanding the reaction trends when more data are available for other systems. It is clear that the activation of dioxygen to effect clean O-atom transfer to suitable substrates is now becoming a reality. 78 These processes, when completely understood and improved, appear to have the potential to be successful industrially. References- Chapter 3 1. Rocker, L.; Dobson, J.C; Vining, WJ.; Meyer, TJ. Inorg. Chem., 26,779 (1987). 2. Riley, D.P.; Smith, M.R.; Correa, P.E. J. Am. Chem. Soc., HQ, 177(1988). 3. a. Ranky, W.O.; Nelson, D.C. in Organic Sulfur Compounds; Kharasch, N., Ed.; Pergamon, New York, 1964, Vol. 1, Chapter 17. b. Ledlie, M.A.; Allum, K.G.; Howell, J.V.; Pitkethly, G. J. Chem. Soc. Perkin Trans. 1, 1934(1976). c. Oae, S. in Organic Chemistry of Sulfur, Oae, S., Ed.; Plenum, New York, 1977, Chapter 8 and references therein. 4. Ando, W.; Tajima, R.; Takata, T. Tetrahedron Lett. 23,1685(1982). 5. Takata, T.; Yamazaki, M.; Fujimori, K.; Kim, Y.H.; Oae, S.; Iyangi, T. Chem. Lett., 1441(1980). 6. Szamant, H.H.; Lapinski, R. J. Am. Chem. Soc. 80, 6883(1958). 7. Henbest, H.B.; Khan, S.A. J. Chem. Soc. Chem. Commun., 1036(1968). 8. Djerassi, C; Engle, R.R. J. Am. Chem. Soc., 75* 3838(1953). 9. a. Riley, D.P.; Shumate, R.E. J. Am. Chem. Soc., \Q6, 3179(1984). b. Riley, D.P. Inorg.Chem., 22, 1965(1983). c. Riley, D.P.; Oliver, J.D. Inorg. Chem. 21 1814(1986). 10. James, B.R.; Pacheco, A.; Rettig, S.J.; Ibers, J.A. Inorg. Chem. 27_, 2414(1988). 11. Edwards, J.O. in Peroxide Reaction Mechanisms, Wiley, New York, 1962, Chapter 5, p.96. 12. Kitching, W.; Moore, C.J.; Doddrell, D. Inorg. Chem. £, 541 (1970). 13. Holm, R.H. Chem. Rev. £7_, 1401(1987). 14. Groves, J.T.; Ann, K-H. Inorg. Chem. 26, 3833(1987). 15. Leung, T.; James, B.R.; Dolphin, D. Inorg. Chim. Acta, 7_£, B7, 180(1983). 80 16. Davies, J.A. Adv. Inorg. Chem. Radiochem., 24, 115(1981). 17. Traylor, P.S.; Dolphin, D.; Traylor, T.G. J. Chem. Soc., Chem. Commun. 279(1984). 18. McMillan, R.S.; Mercer, A.; James, B.R.; Trotter, J. J. Chem. Soc. Dalton Trans., 1006(1975). 19. Mercer, A.; Trotter, J. J. Chem. Soc. Dalton Trans., 2480(1975). 20. Davies, A.R.; Einstein, F.W.B.; Farrell, N.P.; James, B.R.; McMillan, R.S. Inorg. Chem., 12, 1965(1978). 81 CHAPTER 4 Qxifatipn of Phenol 82 4J. Introduction There has been a considerable interest in the oxidation of phenols to quinones or hydrcquinones.1*2 Quinones in particular, are valuable intermediates in syntheses of many complex organic molecules.2-3 In the oxidation of phenols to quinones or hydroquinones, a net O-atom transfer occurs and mechanistic details of such oxidative activation of hydrocarbons are of primary importance.2*4 Nevertheless, detailed mechanistic studies on O-atom transfer reactions are rare.2*4 A thorough understanding of the mechanisms of such reactions is a definite prerequisite for the development of catalysts capable of oxidative activation of hydrocarbons preferably using the cheapest and most abundant oxo-source, dioxygen. As a part of their contmuing investigation into evaluating the reactivity of "Ru:^"1"' oxidants, Meyer and co-workers have studied in detail the oxidation of phenol and alkylated phenol derivatives by [(bpy)2(py)RuO]2+ species (abbreviated Ru=0) and the mechanistic steps depicted in Scheme 4.1 have been proposed for the reaction in CH3CN solution.1 These oxo-ruthenium polypyridyl complexes are ideal for mechanistic studies because they are coordinatively well-defined and chemically stable. However, a major drawback of these systems is the inability to generate the 'Ru(TV)=0' moiety via reaction of a ruthenium precursor with dioxygen. The 'Ru=0' moiety in these systems can only be produced from 'Ru(n)-OH2' precursor by electrochemical oxidation or chemical oxidation with an oxidizing agent such as CefTV).5 The ease with which Ru(TMP)(0)2 is generated by the reaction of Ru(TMP)(CH3CN)2 with dioxygen in benzene or toluene solution,6 and the ability of Ru(TMP)(0)2 species to effect O-atom transfer to thioethers7 (Chapter 3), prompted the investigation of the oxidation of phenol by Ru(TMP)(0)2. 83 Ru=0 + ^yOH H H Ru-0-^~^-OH (4.1) Ru-O-^yoH + Ru=0 *~ Ea-o: O + RuOH2 (4.2) Ru- O + CH3CN Ru-NCCH3 + O (4.3) Ru-OH2 + CH3CN Ru.-NCCH3 + H20 (4.4) The overall reaction being, 2Ru=0 + ^~^-QH + 2 CH3CN 2Ru-NCCH3 + C=0 + H20 (4.5) Scheme 4.1 Proposed reaction mechanism for the oxidation of phenol by [(bpy)2(py)RuO]2+ in CH3CN (taken fromref. 1). In this Chapter, the data obtained for the oxidation of phenol by Ru(TMP)(0)2 are presented and the results are discussed. A mechanism for the reaction is proposed and the Ru(TMP)(0)2 system is compared to the [(bpy)2(py)Ru=OJ2+ system in terms of mechanism and reactivity. The raw data are tabulated in Appendix B. The basic experimental details pertaining to the results given below have been described in Chapter 2 (Section 2.6). 42 Data Analysis. Results and Discussion The UV-visible spectral changes observed for the reaction of Ru(TMP)(0)2 (2.5X10"6 M) with phenol (at 3.72xl0-2 M) at 20.0 °C in G5D6 under dioxygen (1 atm) are given in Figure 4.1. The intensity of the 420 nm Soret peak of the Ru(TMP)(0)2 species begins to decrease gradually on addition of phenol (Section 2.6.1), accompanied by the formation of a new peak at 404 nm. Isosbestic points are observed at 411 and 436 nm. The kinetics of this reaction were monitored by following the disappearance of the Ru(TMP)(0)2 species at 420 nm with time (see Section 3.2). The data thus obtained were plotted as described earlier for the oxidation of thioethers (Section 3.2) and the pseudo-first order rate constant for the reaction calculated. A typical absorbance vs. time trace and the resulting ln(At-Aoo) vs. time plot are given in Figure 4.2. The pseudo-first order rate constants, kobs values, calculated for the loss of Ru(TMP)(0)2 are given in Table 4.1 and the first order dependence of kobs on phenol concentration from 3.72xl0-2 to 1.39xl0-1M is shown in Figure 4.3. The second order rate constant ki= 6.90xl0"2 M_1 s_1 at 20.0 °C is calculated from the slope of the line. Table 4.1 Pseudo-first order rate constants (kobs) at different phenol concentrations at 20.0 °C in benzene under O2 (1 atm); [Ru]= -3x10-6 M. [PhOH], 10"2M kobs, lO"3 s"1 0 0 3.72 2.11 9.30 6.34 13.9 9.70 1.0 350 " ~ ' ' " " " " ' " " ' nm 500 Figure 4.1 UV-visible spectral changes observed for the oxidation of phenol at 20.0 °C by Ru(TMP)(0)2 in benzene oo under O2 (1 arm). Inset shows the ln(At-Aoo) vs. time plot for the disappearance of Ru(TMP)(0)2. [Ru]= 2.5x10-6 M, [PhOH]= 3.72x10-2 M. 86 1.2 -Time(s) Figure 4,2 Absorbance at 420 nm vs. time trace for the oxidation of phenol at 20.0 °C by Ru(TMP)(0)2 in benzene under O2 (1 arm) and the resulting pseudo-first order plot [Ru]= 3.7x10-6 M, [PhOH]= 1.39x10-1 M. 87 10-1— — PhOH, IO'2 M. Figure 4.3 Phenol dependence of kobs at 20.0 °C in benzene under Q2 (latm). [Ru]= -3x10"6 M. 88 The oxidation of phenol by Ru(TMP)(0)2 was also followed by *H nmr spectroscopy. The room temperature JH nmr spectrum of a reaction mixture containing Ru(TMP)(0)2 (~4xl0-3 M) and 5 times excess phenol (2xl(r2 M) in G5D6 under O2 (1 atm) after a 5 minute reaction time is given in Figure 4.4. At this time two new porphyrin species are observed, one (a) having diamagnetic peak positions (e.g. pyrrole-H= 8.64 ppm, Table 4.2) and the other (bj having paramagnetic peak positions (e.g. pyrrole-H = -30.45 ppm, Table 4.2). However, during the next 15 minutes, the peaks associated with the new diamagnetic porphyrin species gradually diminished while the paramagnetic product continued to accumulate. All the Ru(TMP)(0)2 is consumed in ~40 minutes (Figure 4.5) and the new porphyrin product b_ is isolated at this time using column chromatography on neutral alumina (Section 2.4). Table 4.2 *H nmr dataa for the species observed in the oxidation of phenol by Ru(TMP)(0)2. Porphyrin Axial Ligandb Complex Pyrrole-H Meta-H p-Me o-Me a 8.64 7.25 1.70 2.50 5.85 5.76 -1.33 h -30.45 7.63 3.00 2.90 49.68 -68.19 -71.85 a- at room temperature in benzene, b- see text for peak assignments. OH > OH "RU^) OH OH 1 = Ru(TMP)(0), O-H O Run O-H h 1. C6H6 a_ \ t. ill 111111111111 1 0 3 i 1111111111111111111II11111111111 2 0 PPM-2 i I I I | II I I | I I I I |I II I|iII I|II i I|II I I|I I I I j I I li | l ll I j l l l I | ll I l | l l II | II I I|I I I I|I I I I | I I I I | 80 60 40 20 0 -20 -40 -6 0 1111 II11111 -80 PPM Figure 4.4 Room temperature *H nmr spectrum (300 MHz) of a reaction mixture containing Ru(TMP)(0)2 (~4xl0"3 M) and phenol (~2xlf>2 M) under O2 (1 atm) in C6D6 after a 5 minute reaction time. O-H O-H b X meta-H p-Me C6H6 UL o-Me CH3CN V m2o |iiii|iiii|iiii|iiii|iiii|mniiii|iiii|iiii|iiii|iiii|iiii|iiii|iiii|iiii[iiii|iiii|iiii|iii 876543210 PPM 1 ' | i ' ' i | i i i i | i i i i | II II | II II | i i i i | i i i i | i i i i | i i i i | i i i i | II i i | i II i | i i i i | i i i i j i i i i | i i i i | 60 40 20 0 -20 -40 -60 -80 PPM -100 Figure 4J5. Room temperature *H nmr spectrum (300 MHz) of a reaction mixture containing Ru(TMP)(0)2 (~4xl0-3 M) and phenol (~2xl0*2 M) under O2 (1 atm) in C^D^ after a 40 minute reaction time. 91 The isolated final porphyrin product analyzes well for Ru(TMP)(OC6H40H)2 (Section 2.4). The calculated magnetic moment using Evan's method,8 |i= 3.01 B.M., accounts for 2 unpaired electrons in the Ru(IV) centre. The -H nmr spectrum (Figure 4.6) is typical of a paramagnetic porphyrin species ; the presence of one o-Me signal indicates porphyrin mirror plane symmetry (D4h) in the complex. The integration intensities of the four rx>rphyrin peaks and the low-field axial ligand peak at 49.68 ppm agree well with the above formulation (with the latter being assigned to either the ortho- or meta- protons). However, the integration intensities of the two high-field signals at -68.19 and -71.85 ppm are smaller than expected for the remaining protons. It was noted that at the nmr acquisition time that was necessary to be used in recording the spectrum of above species (0.25 s), these two peaks initially appeared as negative peaks which required extensive phasing in order to obtain the spectrum given in Figure 4.6. The presence of negative peaks in a *H nmr spectrum is an indication of protons that relaxes slowly with respect to the acquisition time used. Usually, it is necessary for the acquisition time to be at least 5 times larger than the Ti relaxation time for the particular proton(s) in order to obtain accurate integration intensities. Therefore, considering the elemental analysis data and the fact that the product has D4h symmetry, the complex is formulated as Ru(Trvff)(OC^H40H)2. The *H nmr chemical shifts of the Ru(TMP)(OCoH40H)2 species are temperature dependent. Table 4.3 summarizes data obtained at different temperatures and Figure 4.7 shows the plots of isotropic nmr shifts vs. 1/T; the linear variation indicates that the complex exists in a single spin state over the temperature range +70 to -60°C.9,10 The extrapolated intercepts at 1/T= 0 deviate only slightly, if at all, from zero ppm showing the complex conforms well to Curie behaviour. Of note, many other paramagnetic metaUoporphyrins9"12 display non-Curie behaviour, the origin of which is not yet entirely clear.13 92 93 Table 4.3 Temperature dependences of isotropic proton shifts for porphyrin peaks of Ru(TMP)(OC6H40H)2 in toluene-dg.3 Temperatureb Shifts of porphyrin °c 1/T, Meta-H p-Me o-Me Pyrrole-H xlCr3 K"1 obs, iso obs, iso obs.iso obs, iso 70 2.91 7.50, 0.36 2.87, 0.42 2.50, 0.64 -25.35, -34.36 60 3.00 7.52, 0.38 2.89, 0.44 2.62, 0.76 -26.13, -35.13 50 3.10 7.53, 0.39 2.91, 0.46 2.65, 0.79 -26.89, -35.90 40 3.19 7.56, 0.42 2.93, 0.48 2.70, 0.84 -28.02, -37.03 30 3.30 7.59, 0.45 2.96, 0.51 2.76, 0.90 -29.25, -38.26 25 3.35 7.60, 0.46 2.98, 0.53 2.79, 0.93 -29.89, -38.90 9.7 3.53 7.66, 0.52 3.03, 0.58 2.88, 1.02 -31.97, -40.98 -10 3.80 7.44, 0.60 3.12, 0.67 3.04, 1.18 -35.14, -44.15 -20 3.95 7.81, 0.67 3.19, 0.74 3.15, 1.29 -36.88, -45.89 -30 4.11 7.87, 0.73 3.25, 0.80 3.25, 1.39 -38.89, -47.82 -60 4.69 8.13, 0.99 3.49, 1.04 3.69, 1.83 -45.44, -54.45 a- diamagnetic correction based on data for Ru(TMP)(0)2 in C^DQ at room temperature; meta-H= 7.14, p-Me= 2.45, o-Me= 1.86, pyrrole-H= 9.01 ppm; obs= observed chemical shift; iso= isotropic shift= obs- diamagnetic correction, b- temperature deviation= + 0.5 °C. 1/T, 10 3K_1. Figure 4J Plot of isotropic *H nmr shifts vs. 1/T for the porphyrin peaks of Ru(TMP)(OC6H40H)2 in toluene-dg. The isolated solid and the final in situ product of the UV-visible kinetic experiments have the same electronic spectra: Xmax = 404,524 nm. This rules out the possibility that formation of an intermediate is being monitored directly by UV-Visible spectroscopy. The diamagnetic intermediate porphyrin species observed by nmr could be one of the following: +0-H OH A B However, the peaks due to axial ligand of the intermediate species a seen at 5.76 and 5.85 ppm rule out structure A because a ligand of this sort coordinated to RuCTMP) should result in peaks at higher field due to porphyrin ring current effect (for free para-benzoquinone, 8= 5.94 ppm). Moreover, signals for =CH protons of coordinated para-hydroquinone type ligands (as in structure B) are expected to appear in the 8 ~6 ppm region (free para-hydroquinone, =C-H = 6.80 ppm). The peak at 8= -1.33 ppm is assigned to the protons of the two OH groups coordinated to the metal. 96 Another line of evidence for the structure of the intermediate as B_ was obtained by reacting Ru(TMP)(0)2 with phenol in the absence of O2. Under this condition, the same intermediate was formed but in a much larger amount (Figure 4.8), and the species remained as such in a sealed tube. However, as soon as O2 was introduced, the intermediate species reacted to form the final paramagnetic product. In summary, the oxidation of phenol by Ru(TMP)(0)2 in benzene solution proceeds via a detectable intermediate, Ru(n)(TMP)(0(H)CoH40H)2. The reaction is first order in both phenol and Ru(TMP)(0)2. At 20.0 °C, a second order rate constant ki = 6.90xl0-2 M-1 s_1 has been calculated. Based on the evidence presented above the mechanistic steps shown in Scheme 4.2 are suggested for the reaction. The ki and k2 steps appear to occur via electrophilic attack by 'Ru=0' moiety on the aromatic ring. The O-atom transfer to thioethers clearly indicates the electrophilic character of the '0=Ru=0' moiety (Chapter 3). It has also been suggested that the [(bpy)2(py)Ru=0]2+ species reacts via electrophilic attack on the aromatic ring in the oxidation of phenol in CH3CN solution.1 Although the "point of contact" in the electrophilic attack is the 'O' atom in these Ru-oxo systems, the net electron flow occurs to the vacant d-orbitals of the ruthenium centre. As given in eq. 4.6,0=Ru(VI)=0 species reacts with 2 equivalents of phenol in yet unobserved (see Chapter 3 also) reaction steps in which 'Ru(rV)=0' species, that formed after the reaction of Ru(TMP)(0)2 with the first equivalent of phenol, reacts faster than the '0=Ru(VI)=0' species itself with phenol (k2>ki). Only the intermediate B_ is formed in an observable amount. As indicated by the first-order dependences on both the substrate (phenol in this case) and Ru(TMP)(0)2, it is necessary that k2, k3>k4»ki. Therefore, the second order rate constant calculated by UV-visible kinetic studies is assigned to the ki step. C6H6 —« A— | I I I I | I I 10 JLh i i i-1 C6H5" O-H O-H O-H O-H a_ OH f O Ru(l O-H It -OH Ml I a CH3CN |H20 Ax I I I I I I I 8 6 4 | i i i i | i i i i | i i 2 0 PPM Figure 4JI Room temperature ]H nmr spectrum (300 MHz) of a reaction mixture containing Ru(TMP)(0)2 (~4xl0"3 M) and phenol (~2xl0"2 M) in degassed GsD6 under vacuum after a 24 h reaction time. •• Ru • (D Hi A OH H—C I mm RU I H—Q (4.7) OH B (observed intermediate) OH Ru M + HjO (4.s: OH Scheme 4.2 Proposed mechanistic steps in the oxidation of phenol by Ru(TMP)(0)2 in benzene solution. (continued) 99 OH (4.9) II O (4.10) (4.11) Scheme 4*2 Proposed mechanistic steps in the oxidation of phenol by Ru(TMP)(0)2 in benzene solution. (continued from the previous page) As described above, the product of the k3 step, the bis-hydroqumonemtheruum(II) species (B) has been observed as an intermediate by *H nmr. A similar intermediate has been proposed in the oxidation of phenol by the Ru(rV)-bipyridyl system but direct evidence was not obtained.la It is not clear whether B_ reacts directly with C*2 to form b_ (eq. 4.8) or with Ru(TMP)(0)2 (possibly formed in situ by the reaction in eq. 4.9) as shown in eq. 4.10. A reaction similar to eq. 4.10 (eq. 4.2) has also been proposed by Seok and Meyer for the Ru(TV)02+yphenol system.1 Phenol is exclusively oxidized at the para-position by Ru(TMP)(0)2 whereas both para- and ortho-benzoquinone (88% and 12% respectively) are produced in the [(bpy)2(py)RuO]2+ system. This may be due to the sterically hindered nature of the TMP system which prevents the approach of phenol molecule in a direction suitable for oxidation at the ortho- position. The production of about 0.5 equivalents of para-benzoquinone (8CH= 5.94 ppm, Figures 4.5 and 4.8) in the oxidation of phenol by Ru(TMP)(0)2 can be envisioned (eq. 4.11) as being by the oxidation of free para-hydroquinone (generated as in equation 4.9) by Ru(TMP)(0)2- The oxidation of free para-hydroquinone to para-benzoquinone by Ru(TMP)(0)2 in benzene solution has also been observed in this study (see below), and it is also reported that the same oxidation reaction is effected very rapidly by [(bpy)2(py)RuO]2+ in CH3CN (k= 5x10s M"1 s"1 at 25 oQ.1 The Ru(TMP)(p-0(H)C6H40H)2 species could not be prepared by reacting a 5-fold excess of para-hydroquinone with Ru(TMP)(N2)2- However, when the above reaction mixture was exposed to air, para-hydroquinone (8CH= 6.24 ppm and 8OH= 3-40 ppm) was instantaneously oxidized to para-benzoquinone (8CH= 5.94 ppm) and water (8= 0.4 ppm) as evidenced by JH nmr. The only porphyrin product observed was Ru(TMP)(0)2. As a further test for the proposed mechanism, the amount of H2O formed in the reaction was determined by lH nmr. A solution of Ru(TMP)(0)2 (~4xl0-3 M) in extra-dry 101 toluene-ag was mixed with phenol (4xl0*2M) and the reaction was followed with time. Approximately 1.3 equivalents of H2O per mole of porphyrin reacted was observed at -60, -75, and 100% completion of the reaction (i.e. for loss of Ru(TMP)(0)2). The production of 0.5 equivalents of free parabenzoquinone was also observed. As exemplified in eq. 4.11, one equivalent of H2O is formed for each mole of para-benzoquinone produced. When corrected for the amount of H20 formed due to reaction 4.11, -0.8 equivalents of H2O account for that formed in the reaction 4.8 (or 4.10), close to the expected 1:1 stoichiometry. The overall principal reaction can be expressed as eq. 4.12. Ru(TMP)(0)2 + 2G5H5OH + 1/202 > Ru(TMP)(OC6H40H)2 + H20 (4.12) 43. Conclusions The oxidation of phenol by Ru(TMP)(0)2 species proceeds via initial electrophilic attack by the O=Ru=0 moiety on phenol to form a ruthenium(II) bis-para-hydroquinone intermediate which is subsequently oxidized to ruthenium(rV) bis-para-quinoxo species. The production of free para-benzoquinone is observed, but in relatively small amounts. The formation of the ruthenium(TV) product, which is stable toward O2, renders the oxidation process non-catalytic. Although clean O-atom transfer accompanied by C-H activation is demonstrated, this system cannot easily be developed into a catalytic process to oxidize phenol. The oxidation of phenol by Ru(TMP)(0)2 (ki = 6.90xl0"2 M'1 s"1) proceeds nearly 10 times faster than the oxidation of Et2S (ki= 7.54xl0"3 M'1 s*1), the initial electrophilic attack being a common feature in both oxidations. The reactions given in eq. 4.6 (the ki process) and 4.7 are very similar to those suggested for the oxidation of phenol by the [(bpy)2(py)RuO]2+ system. The major difference appears to be the two-electron oxidation of RuO(H)CfiH40H to RuOGjH^O by 102 RuO (eq. 4.2), whereas the analogous intermediate in TMP system, B_, is oxidized to Ru(TMP)(OC6H40H)2 (eq 4.8). Also, the overall stoichiometrics of the oxidation reactions in the two systems are significandy different The bipyridyl system oxidizes 1/2 mole of phenol and forms 1/2 mole of H2O per mole of Ru (eq. 4.5), whereas the TMP system oxidizes 2 moles of phenol and forms 1 mole of H2O per Ru (eq. 4.12). In addition, the TMP system also forms -0.5 equivalents of free para-benzoquinone as shown in eq 4.11. In the TMP system, had reaction 4.8 occurred instead of that found for the bipyridyl system (eq. 4.2), the TMP system could have become catalytic for the oxidation of phenol. 103 References- Chapter 4 1. Seok, W.K.; Meyer, T.J. J. Am. Chem. Soc, UQ, 7358(1988) and references therein. 2. Organic Synthesis by Oxidation with Metal Compounds, Mijs, WJ.; De Jonge, C.R.H.I., Eds.; Plenum, New York, 1986. 3. Evans, D.A.; Hart, D.J.; Koelsch, D.A.; Cain, P.A. Pure Appl. Chem., 51. 1285(1979). 4. Sheldon, R.A.; Kochi, J.K. Metal-Centered Oxidations of Organic Compounds, Academic Press, New York, 1981. 5. Moyer, B.A.; Meyer, TJ. Inorg. Chem. 2Q_, 436(1981). 6. Groves, J.T.; Quinn, RJ. J. Am. Chem. Soc., 10_7_, 5790(1985). 7. a. Rajapakse, N.; James, B.R.; Dolphin, D. Catalysis Letters, 2,219(1989). b. Rajapakse, N.; James, B.R.; Dolphin, D. in New Developments in Selective Oxidations, Centi, G. and Triffiro, F., Eds., Elsivier Science, Amsterdam, 1989(in press). 8. a. Evans, D.F. J. Chem. Soc., 2003(1959). b. Live, D.H.; Chan, S.I. Anal. Chem., 42, 791(1970). 9. Collman, J.P.; Barnes, C.E.; Swepston, P.N.; Ibers, J.A. J. Am. Chem. Soc., 106. 3500(1984). 10. Balch, A.L.; Renner, M.W. J. Am. Chem. Soc, 1PJL 2603(1986). 11. Balch, A.; Chan, Y.W.; La Mar, G.N.; Latos-Grazynski, L. Renner, M.W. Inorg. Chem., 24, 1437(1985). 12. Ke, M. Ph.D. Thesis, University of British Columbia , 1988. 13. La Mar, G.N.; Walker, F.A. in The Porphyrins, D. Dolphin, Ed., Academic, New York, 1979, Vol VI, p. 61. CHAPTER 5 PreUminarv Studies on Oxidation of 2-Propanol to Acetone bv RutTMPVOK 105 5.1 Introduction Stoichiometric and catalytic oxidations of a variety of alcohols by oxo-ruthenium complexes have been observed during the past two decades.1-3 The RuC-4 and RuCU2" systems effect the oxidation of alcohol via a hydride transfer pathway.2'3 These systems become catalytic in the presence of a suitable co-oxidant such as periodate or hypochlorite, but the reactions lack selectivity, with C-C bond cleavage being a common competitive process.4 The polypyridyl mono-oxo complex [(bpy)2(py)RuO]2+ oxidizes a variety of alcohols and mechanistic details of these reactions have been reported;1 oxidation of 2-propanol to acetone also proceeds via a hydride transfer pathway (eq. 5.1).1 CH3 [Ru(TV)=0]2+ + H-C-OH CH3 2+ I Ru-0—H—C-OH CH3 Ru(H)-OH2 + (CH&CO - [Ru(U)-OH]+ + (CH^COrF (5.1) A prehminary JH nmr spectroscopic investigation was carried out in the present study to determine the reactivity of Ru(TMP)(0)2 toward 2-propanol at ambient conditions. A paramagnetic ruthenium porphyrin product was isolated but not characterized. The results of these studies are presented in this Chapter, and some suggestions are made for future experiments to be carried out in order to understand better this reaction which results in oxidation of the alcohol to acetone. 106 5.2 Results and Discussion The reaction of Ru(TMP)(0)2 with 2-propanol is conveniently studied by *H nmr spectroscopy. Figure 5.1 shows the 0 to 10 ppm portion of the lH nmr spectra of a reaction mixture that initially contained Ru(TMP)(0)2, formed in situ from Ru(TMP)(CH3CN)2, (-10"3 M), and 10 times excess 2-propanol (~10"2 M) at room temperature under 1 atmosphere O2 in C5D6 after 1,24, and 72 hour reaction times. Also, the lH nmr spectrum (10 to -14 ppm) of another reaction mixture after all Ru(TMP)(0)2 is consumed [Ru(TMP)(0)2 initially ~3xl0-3 M, 2-propanol 2.5xl0"2 M] is given in Figure 5.2. Figure 5.1 shows the gradual formation of a new porphyrin species, 2£, (see Table 5.1 for peak assignments) accompanied by the disappearance of the Ru(TMP)(0)2 species. The *H nmr spectra of X is typical of a paramagnetic Ru(TMP) species (see Chapter 4 also). The peaks at 7.60, 2.91 and 2.90 ppm are essentially identical to those observed in the paramagnetic species Ru(IV)(TMP)(OC!fjH40H)2 for the meta-H, o-Me and p-Me protons respectively (Chapter 4). The pyrrole-H resonance of X at -11.92 ppm is also typical of a paramagnetic TMP complex. The presence of only one peak each for the meta-H and pyrrole-H is indicative of a TMP species that has D4h symmetry. The production of ~0.5 equivalents of acetone (8= 1.6 ppm) and ~1 equivalent of H2O (8= 0.4 ppm) per Ru is also observed. The new, paramagnetic porphyrin product X is isolated by evacuating the reaction rnixture to dryness after the starting Ru(TMP)(0)2 is fully consumed. In a typical preparation, Ru(TMP)(CH3CN)2 (6 mg, 6xl0"3 mol) in benzene (1 mL) was exposed to 1 atm O2 for 5 minutes and 2-propanol (50 uX, 6X10-4 mol) was added. The mixture was shaken well and left at room temperature for 2 days at which time the solvent was removed by evacuation and the product X_ isolated in nearly quantitative yield. Figure Ll Room temperature *H nmr spectra (300 MHz) of a reaction mixture containing Ru(TMP)(0)2 (initially ~10*3 M) and 2-propanol (-IO*2 M) in C6D6 after (A): 1, (B): 24 and (C): 72 h reaction times. 1= Ru(TMP)(0)2, X= unidentified product 1^1 I I 1 1 I I I I j I I'l I I I I I I j I I I I I I I I I j I I I I I I 1 I 1 j I I I I I I I Mj I I I I ) I I I I M II I | I I I I | I I I I | I I I I y I I I | I I I I M I 1 1 I I I M j M I I | I M I j II I I | I I T I I I M I Figure 5.2 Room temperature *H nmr spectrum (300 MHz) of a reaction mixture containing Ru(TMP)(0)2 (initially ~3xlO"3 M) and 2-propanol (~2.5xl0"2 M) in after a 72 h reaction time. i—» o oo 109 Table 5.1 Room temperature *H nmr dataa for the porphyrin peaks of known RufTMP) species, and unknown species X isolated from the reaction of Ru(TMP)(0)2 with 2-propanol. Complex Pyrrole-H Meta-H o-Me p-Me Unknown X -11.92 7.60 2.91 2.90 Ru(TMP) (OC6H40H)2b -30.45 7.63 2.90 3.00 Ru(TMP) (Br)2c -44.37 13.76 4.41 4.01 Ru(TMP)(0)d -9.46 7.70, 6.95 4.13, 0.97 2.86 a- in toluene-dg; all peaks are singlets and integrate correctiy as assigned, b- see Chapter 4 and Section 2.4 also. c- Sishta, C, Ph.D. Dissertation, University of British Columbia, 1990. d- from ref. 5; data in CD2CI2. The *H nmr spectrum of the isolated species X in toluene-ds is given in Figure 5.3 and the peak positions are tabulated in Table 5.1 along with those for other RufTMP) species for comparison. The *H nmr shifts of the species X are temperature-dependent and Table 5.2 summarizes *H nmr data at different temperatures; Figure 5.4 shows a plot of the *H nmr shifts vs. 1/T. The temperature dependence of the pyrrole-H resonance deviates significantly from Curie behavior compared to that, for example, of Ru(TMP)(OC6H40H)2 111II111111II111111111111111111111111111 [11111111111111111111111111111111111111111111111111111111111 [ 111111111111111 10 8 6 4 2 0 -2 -4 -6 -8 -10 -12 PPM Figure 5.3 Room temperature *H nmr spectrum (300 MHz) in toluene-ds of the product isolated from the reaction of Ru(TMP)(0)2 with 2-propanol. Ill Table 5.2 Temperature dependences of *H nmr shifts for porphyrin peaks of the unknown species X. in toluene-dg.2 Temperature Shifts of porphyrin °c 1/T, X10-3K-1 Meta-H p-Me o-Me Pyrrole-H 60 3.00 7.50 2.83 2.73 -10.90 50 3.10 7.52 2.85 2.77 -11.16 40 3.19 7.54 2.87 2.81 -11.42 30 3.30 7.57 2.89 2.85 -11.67 20 3.41 7.59 2.91 2.90 -11.92 10. 3.53 7.61 2.93 2.93 -12.13 -20 3.95 7.69 3.10 3.10 -12.70 -40 4.29 7.74 3.22 3.22 -13.02 -60 4.69 7.79 3.35 3.12 -13.22 a- temperature deviation = +0.5 °C. (see Chapter 4). Such deviation is common in ruthenium porphyrin chemistry although the reasons for this behavior is not well understood (see Section 4.2 also).6 It is clear from the presence of only one *H nmr signal each for the meta-H and o-Me protons in the spectrum that the new complex X has D4h symmetry. All known RufTMP) complexes, which do not possess porphyrin mirror plane symmetry (D4h), contain only Qy symmetry, and give rise to two signals each for the meta-H and o-Me 112 IO-I el el 4l ol 2, -el -el -iol -12 -14 -16 0.5 ^ • • • ^ meta-H Q p-Me a o-Me O pyrrole-H 1.5 2 2.5 3 3.5 I/T,ICT3K 4.5 Figure 5.4 Temperature dependences of the porphyrin peaks of the unknown species X in toluene-d8. protons [e.g. as in RuCTMPXtXOOfrOH), Ru(TMP)(CH2CH2); Section 2.4], deluding the paramagnetic species Ru(TMP)(0) (Table 5.1). The new, isolated species X shows only one *H nmr signal that can be assigned to an axial ligand; this signal is the broad singlet at ~3.6 ppm at room temperature, and it integrates to about 8 protons per Ru(TMP) (Figure 5.3). The ir spectrum (Nujol/ KBr) shows a weak absoption at 1938 enr1, and no peaks due to RuO-H vibrations. The elemental analysis data (C= 68.87%, H= 5.76% and N= 5.55%) for the product following drying at 70 °C at 10-3 torr for 24 hours do not fit any of the probable products; %C is too low for any Ru(TMP) complex with axial ligands containing carbon. The magnetic moment u= 2.96 B.M., calculated using Evan's method,7 assuming a molecular weight of 1000 g/mol, is indicative of the metal being in a low spin (S=l), Ru(rV) oxidation state. An electrical conductivity measurement and a molecular weight determination are two key experiments to be carried out which might be helpful in identifying this species X. References - Chapter 5 1 Roecker, L; Meyer, TJ. J. Am. Chem. Soc., 10j), 746(1987), and references therein. 2. Lee, D.G.; van den Engh, M. Can. J. Chem., 5JL 2000(1972). 3. Lee, D.G., Spitzer, U.A.; Cleland, J.; Olson, M.E. Can. J. Chem. 54. 2124(1976). 4. a. Schuda, PJ7.; Cichowiz, M.B.; Heimann, M.R. Tetrahedron Lett., 24, 3829(1983). b. Charkraborti, A.K.; Ghatak, U.R. Synthesis, 746(1983). c. Burke, L.D.; Healy, J.F. J. Chem. Soc., Dalton Trans., 1091(1982). d. Carlson, P.H.J. Katsuki, T.; Martin, V.S.; Sharpless, K.B. J. Org. Chem., 46,3936(1981). 5. Groves, J.T.; Ann, K-H. Inorg. Chem., 2£, 3831(1987). 6. La Mar, G.N.; Walker, F.A. in The Porphyrins, D. Dolphin, Ed.; Academic Press, New York, 1979, Vol. VL p.61. 7. a. Evans, D.F. J. Chem. Soc., 2003(1959). b. Live, D.H.; Chan, S.I. Anal. Chem., 42, 791(1970). 115 CHAPTER 6 Synthesis. Characterization and Reactivity of Novel Ruthenium Porphyrin Complexes:  Alkyne. Alkene. Thioether Complexes of RurTMPI. and CO. bis-CH?CN and Dioxo Complexes of Ruf OCP) 116 CHAPTER 6 Synthesis, Characterization and Reactivity of Novel Ruthenium Porohyrin Complexes:  Alkvne. Alkene. Thioether Complexes of RufrMPI and CO. bis-CH^CN and Dioxo Complexes of Ru(OCP) A wide range of novel ruthenium porphyrin complexes has been prepared in this thesis work. The synthesis, characterization and reactivity of these species are discussed in this Chapter. 6.1 Complexes of RufTMP') Formed by Interactions with Alkynes Studies on alkyne interactions with metalloporphyrins are rare in the literature. The only metalloporphyrin alkyne rc-complex reported to date, Mo(TTP)(PhCCPh), has been isolated and characterized by an X-ray structure determination.1 Also, it is reported that [Rh(OEP)h reacts with HCCR (R= H, Ph) to form complexes of the type (OEP)Rh-C(H)=C(R)Rh(OEP).2 The lack of studies on alkyne interactions with ruthenium porphyrins prompted the present investigation in this area. Results obtained for the reactions of RufTMP) species with acetylene, phenylacetylene and diphenylacetylene will be discussed below. 6.1.1 Reaction with Acetylene The Ru(TMP) species in benzene or toluene solution [formed in situ from Ru(TMP)(N2)2)] reacts slowly (16 hours) with acetylene (latm) under room light (much more slowly in the dark) to form a greenish-black complex that was readily isolated following removal of solvent by evacuation; the complex is characterized as [Ru(TMP)]2(H~C2H2). The *H nmr spectrum of the in situ species (Figure 6.1) is significantly different from that expected for a 7t-bonded acetylene complex. The low-field *H nmr signal at 10.44 ppm integrating to a single proton per RufTMP) moiety is typical of Figure fj.H Room ternperarure *H nmr spcctnim (300 MHz) of the in situ product from the reaction of RufTMP) with acetylene in CsDg. 118 a (Porp)Ru-CH- type proton.3 Furthermore, the ^-pyrrolic protons appear at relatively higher field (7.92 ppm) compared to that for other comparable Ru(TI)(TMP) complexes [e.g. in Ru(TMP)(CH2CH2), the pyrrole-H is seen at 8.40 ppm, Section 6.2]. Also, the separation between the two ortho-methyl peaks (0.6 ppm) is much larger than for other five coordinate species [e.g. in Ru(TMP)(CH2CH2), the separation is 0.3 ppm] indicating a "more prominent inequivalency" of the two faces of the porphyrin in the former complex. The low-field 13C resonance at 263.8 ppm (Figure 6.2) is characteristic of a metal carbene complex.4 The results of an nmr attached proton test (APT) experiment suggest that the carbene-type carbon atom contains either one or three protons (Figure 6.3). In a gated proton-decoupled 13C experiment (Figure 6.4) the singlet at 263.8 ppm splits to a doublet confirming that the carbene carbon is in fact coupled to a single proton; the hyperfine splitting present in the doublet is due to long-range proton coupling. Usually, monomeric Ru(U) porphyrin complexes are red or reddish-brown. The greenish-black color of the new species and it's UV-visible spectrum (Figure 6.5) are atypical of a ruthenium (IT) monomeric porphyrin complex. The Soret band has blue-shifted to 400 from the more common 410-420 nm region for Ru(IT)(TMP) complexes. Also, the visible region contains peaks at 502, 530(sh), 615, 670 nm whereas other Ru(U)(TMP) complexes contain only one pronrinent peak and a shoulder in this region (Section 2.4). The above spectral evidence is consistent with the following structure for the new 'acetylene' species: (6.1) I | I I I l I I I I l | l l i l | l i I I | l i r i | i i i i 145 140 135 130 125 120 PPM c Ru mtrnt mm .J • I|MII|IIII|IIII|IIII|IIII|1III|1III|I1II|IIII|IIII|III1|IIII|IIII 75 24 23 22 21 20 PPM mmm* i i i 1 i—i 1 I | 1 1 r-40C 350 I ' ' ' 300 250 200 -i—-i 1 1 1 1 i i 1 | 1 1 r i 1— 150 100 50 —i 1—i 1 1—r-0 PPM Figure 6.2 Proton-decoupled 13C spectrum (75 MHz) of the product isolated from the reaction of RuCTMP) with acetylene in CgDrj; see Section 2.4 for other assignments. 300 250 200 150 —T~ 100 50 PPM Figure 6.3 13C nmr APT srxrctrum (75 MHz) of [Ru(TMP)]2(ji-C2H2) in C6D6-300 250 200 150 100 50 PPM Figured Gated proton-decoupled spectrum (75 MHz) of [RuCTMP)j2(>C2H2) in Q>D6. Figure 6.5 UV-visible spectrum of [Ru(TMP)]20a-C2H2) species in G5H6 under N2. 123 Generally, late-transition metal carbene complexes are formulated as formally neutral carbene fragments bonded to the metal, in this case Ru(U).3 This formulation is consistent with the diamagnetism of the known species Ru(TTP)(CHCH3).3 Therefore, the new 'acetylene' species is also formulated as a Ru(II) complex in accord with it's diamagnetism based on the *H nmr shifts. Formation of the corresponding binuclear complex [Rh(OEP)]2(|i-CRCH) by reaction of [Rh(OEP)]2 with acetylenes (R= H, Ph) has been documented.2 The eight P-pyrrolic protons of the [Ru(TMP)]2(|!-C2H2) complex appear as a singlet in the *H nmr indicating that D4h symmetry is retained in this carbene complex at room temperature. A large barrier to rotation about the metal-carbon bond would not be expected in this complex because either of the symmetry equivalent d^ or orbitals can participate in the it-bonding. Facile axial rotation on the nmr time-scale must result in equivalency of the jJ-pyrrolic protons. As a further confirmation of the proposed structure, the molecular weight of the complex was determined using the Signer method.5 The plot of volume of solution in each arm of the Signer apparatus vs. time is given in Figure 6.6. The molecular weight of the complex was calculated using the formula, Mi = (Mv/mXn^/vj) where M, v and m denote the molecular weight, equilibrium volume and the weight of the standard, and Mj, vj and mj denote those of the complex. The standard used was TMPH2 (molecular weight 783.1 g/mol). The raw data are summarized in Appendix C; the value obtained, 1561 g/mol, agrees reasonably well with the calculated value of 1790 g/mol based on the [Ru(TMP)]2(H-C2H2) formula. Unfortunately, many attempts to grow crystals suitable for an X-ray structure determination were not successful. Figure 6.6 Volume vs. time plot for the determination of molecular weight of [RuCTMPJhCM^H^ using Signer method. 125 In general, crystals of Ru(Porp) species are easily obtained when all six coordination sites of ruthenium are filled. The crystals of "five-coordinate" Ru(Porp) derivatives can be easily grown when the vacant sixth coordination site is filled with a suitable solvent ligand [e.g. Ru(OEP)(CO)(EtOH),6 Ru(TMP)(N2)(THF) 7]. However, even when dissolved in relatively weak donor solvents such as Et2P or THF, the greenish-black binuclear species [Ru(TMP)]2(H-C2H2) slowly (2 days) turns red presumably generating the Ru(TMP)(Solv)2 species. Not surprisingly, on exposure of [Ru(TMP)]2(fx-C2H2) to strongly coordinating ligands such as CO or P(OCH3)3, corresponding reactions occur instantaneously to give bis ligated species. Initial attack by ligand L on the vacant sites of [Ru(TMP)]2(,i-C2H2) and subsequent eurnination of acetylene due to the trans-effect of L, followed by the coordination of another L at the vacant site thus created, are plausible mechanistic steps (eq. 6.2). L <y-H + L L 2 L + CHCH 2L L 2 L (6.2) 126 6.1.2 Alkvne ft-Complexes of RufTMP) In contrast to acetylene itself, diphenylacetylene and phenylacetylene form 1:17C— complexes with RufTMP). The !H nmr spectrum of the in situ complex Ru(TMP)(PhCCPh) is given in Figure 6.7. The coordinated diphenylacetylene ligand gives rise to three -H nmr signals easily assigned to the aryl protons. Clearly, the ortho-protons of the phenyl group have been shifted up-field by a larger amount compared to the meta- and para-protons, perhaps due to a bending of the phenyl groups away from the porphyrin plane. Such a bending is evident in the Mo(TTP)(PhCCPh) molecule, where the C=C-Ph angle is found to be 145° by X-ray crystallography.1 It is also believed that in this complex the acetylenic group is a 4-electron donor to the Mo(U) d4 centre, based on the fact that the Mo-C distance is the shortest known for any Mo-acetylenic complex.1 In Figure 6.7, the absence of any appreciable -H nmr Ime-broadening due to ligand exchange with the excess PhCCPh at room temperature might be an indication of stronger 7t-bonding in the Ru(TMP) (PhCCPh) compared to corresponding alkene complexes, where no signals for the bound ligand are observed in the presence of excess free ligand because of fast exchange (Section 6.2). The in situ RutTMPXCgHsCCH) complex was similarly observed by -H nmr (Figure 6.8). The aryl protons appear as a multiplet at 4.0 ppm and the acetylenic proton appears at -7.40 ppm; the observed up field shift of 8.88 ppm from the free acetylene resonance (1.48 ppm), compares well with the up-field shift 8.42 ppm observed for the protons of ethylene bound to RufTMP) (Section 6.2). 6.2 Alkene Complexes of RufTMP) Two ethylene 7C-complexes, Ru(TMP)(CH2CH2)(iPrOH).iPrOH and Ru(TMP)(CH2CH2) were isolated and characterized in this study. The -H nmr spectrum of the Ru(TMP)(CH2CH2)(iPrOH).iPrOH species is given in Figure 6.9. The coordinated ethylene moiety gives rise to a singlet at -3.11 ppm integrating for one ethylene molecule Figure 6.7 Room temperature *H nmr spectrum (300 MHz) of the in situ species Ru(TMP)(Ph-C=C-Ph) in C^. [RuCTMP)] = 5x10-3 M, [Ph-CsC-Ph] = 1.2x10-2 M. x= Ru(TMP)(CO) impurity. Figure 6.8 Room temperature *H nmr spectrum (300 MHz) of the in situ species Ru(TMP)(Ph-C=C-H) in G5D6. [RuCTMP)] = 5x10*3 M, rph-OC-H] = 1.2x10-2 M. to OO H2C=p=CH2o-Mc „ Pyrrole-H Pyrrole-H D p-Mc O'-MC Hm CHj-C<HXH CHj p-Me V C6H6 H' m JL o'-Me o-Me CH. CH, 1 I I I I | l I l I | I l I l | I l I i | I I I I | i I i i | i i i i | i r 'i i | I I I i | I I I i | i i i i | lilt | I II l | i I I I | > I l 10 8 6 4 2 0 -2 PPU Figure 6.9 Room tempmture *H nmr spectrum (300 MHz) of RufTMP)(CH2CH2)(iPrOH).iPTOH complex QsD6- x= Ru(TMP)(CO) impurity. 130 per RuCTMP). The up-field shift of the ethylene resonance by 8.42 ppm (from 5.31 to -3.11 ppm), due to the porphyrin ring current, compares well with values reported for Ru(Porp)(CH2CH2)(THF) complexes (Porp= OEP, TTP).3 The presence of two moles of iPrOH per mole of RuCTMP) is observed by 1H nmr and this agrees with the elemental analysis data (Section 2.4). There is only one vacant axial site available in the Ru(TMP)(CH2CH2) moiety for iPrOH to a>CTdinate, and hence the other iPrOH molecule is considered to be a solvate. The *H nmr spectrum of the isolated 'five' coordinate, Ru(TMP)(CH2CH2) species is given in Figure 6.10. The nmr spectra of the two ethylene complexes are essentially identical in terms of peak positions for the Ru(TMP)(CH2CH2) moiety, except for the larger separation of the two ortho-methyl peaks of the isopropanol-free species, perhaps due to the greater inequivalency of the two faces of the porphyrin in this system. In the presence of excess ethylene, no coordinated ethylene is observed by nmr, indicating fast exchange on the nmr timescale. The ethylene derivatives can be formulated as either a Ru(TV)-metallocyclopropane (6.3a) or a Ru(JJ)-ethylene it-complex (6.3b). H2C CH2 H2C = CH2 6.3 a 6.3 b The lH nmr shifts for the TMP ligand in the ethylene complexes are typical of those for coordination to diamagnetic Ru(U) and 6.3b is the preferred formulation. The *H nmr spectra of either of the ethylene complexes remain unchanged at -80 °C, indicating a facile rotation of the ethylene moiety around an axis perpendicular to the porphyrin plane. Such a Figure 6.10 Room temperature *H nmr spectrum (300 MHz) of RUCTMPXCH2CH2) in toluene-Dg. x= Ru(TMP)(CO) impurity. 132 low energy barrier to rotation is consistent with the 71-bonded formulation, as the ethylene 71-orbitals can donate electron density in equal probability to the metal d^ or dyZ orbitals. The isolated ethylene complexes can be evacuated to a pressure of 10"3 torr at room temperature for several hours without any loss of ethylene. However, the corresponding cyclohexene complex could not be isolated either by precipitation or by an evacuation procedure (Section 2.4) because of the loss of cyclohexene during the attempted isolation process. However the RufTMPXCoHio) species is readily observed in situ; the *H nmr spectrum (Figure 6.11) is similar to that of Ru(TMP)(CH2CH2) (Figure 6.10). The pyrrolic-H, meta-H and para-Me signals appear at positions identical to those of the ethylene species. However, in the RufTMPXCoHio) species, the ortho-Me appears as a broadened singlet presumably due to relatively slow exchange of bound and excess cyclohexene. &2 Sulfoxide Complexes of RufTMP) The S-bonded sulfoxide complexes of the type RufTMP){OS[(CH2)nCH3]2}2'n=0" 3, were isolated and characterized in this study, the details of which appear in Sections 2.4 and 3.2. These complexes can be prepared either by oxidizing the appropriate thioether by Ru(TMP)(0)2 in which case the final S-bonded sulfoxide complexes are formed via the isomerization of initially O-bonded species (Section 3.2), or by the direct substitution of CH3CN within RufTMP)(CH3CN)2 by the sulfoxide. In the latter reaction, no O-bonded sulfoxide intermediates were observed by nmr and the reaction occurred instantaneously at room temperature. The S-bonded sulfoxide complexes are air-stable in the solid state or in benzene solution. The isomerization of O-bonded sulfoxide to form S-bonded species in the [Ru(U)(bpy)2(py)(OSMe2)]2+ system has been reported.8 The preference of Ruffl) in an electron-rich environment such as the above bipyridyl system, or in the Ru(TMP)(OSR2)2 I I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 10 98765432 10 PPM Figure6.11 Room temperature *H nmr spectrum (300 MHz) of in situ RufTMPXCfiHin) species in the presence of excess cyclohexene in C^Dg. x=Ru(TMP)(CO) impurity. 134 system, is to form the S-bonded sulfoxide species, thereby reducing the electron density on the metal via Ru —>S Tt-back-bonding.9-11 Riley and Oliver12 have concluded that the S-bonded sulfoxide ligand is an excellent rc-acceptor and a weak a-donor when coordinated to a low-spin Ru(U) centre. Even though in Ru(D)(TMP)(OSR2)2 systems, steric interactions probably act against the isomerization from O- to S-bonded species, the electronic driving force appears to play the dominant role in forcing the isomerization to take place. 6A Synthesis and Characterization of RufOCP) Complexes The observed degradation of Ru(TMP)(0)2 during the attempted catalytic reactions at elevated temperatures (Section 3.2) necessitated the preparation of a ruthenium porphyrin species that can be used at higher temperatures for the oxidation of various substrates. It is reported that 5,10,15,20-tetra(2,6-dichlorophenyl)porphinatoiron(IH) chloride [Fe(OCP)(Cl)] is resistant to oxidative destruction and extremely efficient in O-atom transfer to hydrocarbons in the presence of an oxo-source such as PhlO. Therefore, the Ru(OCP)(0)2 species was synthesized via Ru(OCP)(CO) and Ru(OCP)(CH3CN)2 in order to investigate the reactivity within its subsequent O-atom transfer systems. 6A1 Ru(OCP)fCO) The free-base porphyrin OCPH2 was metallated to form Ru(OCP)(CO) using the procedure described in Section 2.4. The metallation proceeds slowly compared to the metallation of TMPH2 under similar conditions. Typically, a 200 mg hatch of TMPH2 can be metallated in 60% isolated yield during a 16 hour reaction in mesitylene (B. Pt 165 °C), whereas it takes ~36 hours to produce a comparable amount of Ru(OCP)(CO). Use of a higher boiling solvent such as decahydronaphthalene (B. Pt 190 °C) may shorten the reation time. Also, the low solubility of Ru(OCP)(CO) in CH2CI2 and CgHg, compared to the Ru(TMP)(CO) species, makes purification by column chromatography more tedious. 135 The *H nmr spectrum of Ru(OCP)(CO) is given in Figure 6.12. The signals for the meta-H protons (Hm and Hm) appear as two doublets at 7.25 and 7.36 ppm indicating the inequivalency of the two faces of the porphyrin. In the case of the more symmetric (D41,) Ru(OCP)(L)2 type complexes the meta-H protons appear as a single doublet (see below). The para-H appears as a triplet regardless of the symmetry of the species. The i J. spectrum of the carbonyl complex shows a strong band at 1946 cnr1 which is assigned to the CO stretching vibration. Elemental analysis and mass spectral data (Section 2.4) also agree with the formulation Ru(OCP)(CO). 6.4.2 Ru(OCP)(CH3CN)2 Photolysis of Ru(OCP)(CO) in a CgHg/Ct^CN solvent mixture as described in Section 2.4, results in the formation of Ru(OCP)(CH3CN)2. The *H nmr spectrum of the isolated complex is given in Figure 6.13. As expected, the meta-H protons now appear as a doublet at 7.40 ppm indicating the D4j, symmetry of the complex. The coordinated CH3CN peak at -1.42 ppm, which integrates for two CH3CN ligands per porphyrin moiety, compares well with the nmr shift for CH3CN in Ru(TMP)(CH3CN)2 at -1.32 ppm. The i.r. band at 2273 cm-1 due to the VCN stretching vibration is also close to the value of VCN= 2270 cm-1 found for Ru(TMP)(CH3CN)2 (Section 2.4). 6.4.3 Ru(OCP)(Q)2 Exposure of Ru(OCP)(CH3CN)2 in benzene solution to 02 or air results in the rapid formation of the new porphyrin species Ru(OCP)(0)2 (Figure 6.14). Two moles of free CH3CN per mole of porphyrin are also formed in the reaction . The same species is produced by the mCPBA oxidation of Ru(OCP)(CO) as described in Secction 2.4. The oxidation of a benzene solution of Ru(OCP)(CO) (~3xl0"6 M) by the addition of increments of mCPBA showed a smooth conversion with isosbestic points at 378, 414, I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 'I ' 10 9 8 7 6 PPM Figure 6.12 Room ternperature *H nmr spectrum (300 MHz) of Ru(OCP)(CO) in CsD^ CH0CN i | i i i i | i i i i | i i i i | i i i i | i i i i | i i i i | ) i i i | i i i i | II II | i ' ' i [ 'I i i I I ' ' ' | ' ' ' ' I 11 1 1 | 1 1 1 10 8 6 4 2 0 -2 -4 PPM Figure 6.13 Room temperature *H nmr spectrum (300 MHz) of Ru(OCP)(CH3CN)2 in C6E>6-Figure 6,14 Room temperature 'H nmr spectrum (300 MHz) of Ru(OCP)(0)2 in CDCI3. Free CH3CN observed at ~1 ppm. £ ?- peak often seen in spectra run in CDCI3. °° 139 432, 488, 576, 569 and 618 nm (Figure 6.15). The ir spectrum of the isolated Ru (OCP) (0)2 species shows a strong band at 825 cm-1 and no peak corresrxmding to that of Ru(OCP)(CO) at 1946 cm'1. The assignment of the ir peak at 825 cnr1 to the Ru=0 vibration is in accord with the analogous data for Ru(TMP)(0)2 (821 cnr1)13 and Os(OEP)(0)2 (825 cm-l).l4 The presence of two chemically available oxo-ligands in the Ru(OCP)(0)2 complex was demonstrated by its reaction with trimethylphosphite. The lH nmr spectrum of the reaction mixture containing Ru(OCP)(0)2 and excess P(OCH3)3 in CDC13 (Figure 6.16) shows resonances for trimethylphosphate (3.78 ppm, Jp_H= 12 Hz), excess P(OCH3)3 (3.53 ppm, JP_H= 12 Hz) and for Ru(OCP)[P(OCH3)3]2. The integration intensities of the peaks confirm the formation of 2 moles of 0=P(OCH3)3 per mole of porphyrin. CHC1, 11 0=P(OCH3) UJ 11111 111111111111 J 8 3 6 11 11111 r i 4 P(OCH3)3 ,—i—i—; | i i i i | i 1 i i | i i i i ; i i i i | i i i i i i i i i | i i M | II i i [ i i i i | i i i i | i i i i | i i i i | i i 9 8 7 6 F» 4 J Figure 6.16 Room temperature !H nmr spectrum (300 MHz) of in situ reaction mixture after the reaction of Ru(OCP)(0)2 with excess P(OCH3)3 in CDC13. 142 References • Chapter 6 1. De Cian, A.; Colin, J.; Schappacher, M.; Ricard, L.; Weiss. R. J. Am. Chem. Soc., 10!, 1850(1981). 2. Setsune J-L; Yoshida, Z-I. J. Chem. Soc. Perkin Trans. 1,983(1982). 3. Collman, JJ3.; Brothers, P.J.; McElWee-White, L.; Rose, E.; Wright, LJ. J.Am. Chem. Soc, JJJ1,4570(1985). 4. Gallop, M.A.; Roper, W.A. Adv. Organomet. Chem. 25, 121(1986). 5. a. Signar, R. Ann.,421, 246(1930). b. Clark, E.P. Ind. Eng., 820(1941). 6. Arial, S.; Dolphin, D.; Domazetis, G.; James, B.R.; Leung, T.W.; Rettig, S.; Trotter, J.; Williams, G.M. Can. J. Chem., 62, 755(1984). 7. Camenzind, M.J.; James, B.R.; Dolphin, D.; Sparapany, J.W.; Ibers, J.A. Inorg. Chem., 22, 3054(1988). 8. Roecker, L.; Dobson, J.C.; Vining, W.J.; Meyer, TJ. Inorg. Chem., 2£, 779 (1987). 9. McMillan, R.S.; Mercer, A.; James, B.R.; Trotter, J. J. Chem. Soc Dalton Trans., 1006(1975). 10. Mercer, A.; Trotter, J. J. Chem. Soc. Dalton Trans., 2480(1975). 11. Davies, A.R.; Einstein, F.W.B.; Farrel, NJ?.; James, B.R.; McMillan, R.S. Inorg. Chem., 12, 1965(1978). 12. Riley, D.P.; Oliver, J.D. Inorg. Chem., 21 1814(1986). 13. Groves, J.T.; Quinn, R. Inorg. Chem., 23^ 384611984} 14. Buchler, J.W.; Smith, P.D. Angew. Chem. Int. Ed. Engl. 13_ 341(1974). 143 CHAPTER 7 General Conclusions and Recommendations for Future Studies 144 11 General Conclusions and Recommendations for Future Studies. In this thesis work, the oxidation of three alkyl thioethers, phenol and 2-propanol by trans-dioxo ruthenium porphyrin species is studied, and several novel ruthenium porphyrin complexes are synthesized and characterized. A dioxygenase-type activity is observed for the oxidation of thioethers by rra>w-Ru(Porp)(0)2 (Porp= TMP, OCP). In the oxidation of Et2S, nBu2S and DecMeS to corresponding sulfoxides by Ru(TMP)(0)2 species in benzene solution, the reaction is found to be first order both in [Ru] and in [thioether]. The second order rate constants and the associated activation parameters for the first O-atom transfer are determined for the three thioethers. The marked increase observed in the rate of oxidation with increasing alkyl chain length within thioethers is reflected more in the AS* than in the AH* value: as expected, for the O-atom transfer process is negative, but less so for the bulkier substrate. A mechanism is proposed, based on electrophilic attack of the 0=Ru=0 moiety on SR2 to form the bis-O-bonded sulfoxide species which isomerizes to bis-S-bonded species via the 'mixed' species. The intermediate formed after the first O-atom transfer in the oxidation of Et2S, namely, Ru(IV)(TMP)(0)(OSEt2) is not observed; however the other intermediates and the final product are characterized by solution *H nmr, and the bis-S-bonded complex is also isolated via two routes and characterized in the solid state. The Ru(TMP)(0)2/Et2S/02 system at room temperature is catalytic in complex, but produces only about 5 turnovers due to poisoning of the catalyst by the reaction product. The same system at >65 °C gives higher turnovers, but now porphyrin ligand degradation is observed, perhaps via oxidation by the 0=Ru=0 moiety. 145 The analogous species, Ru(OCP)(0)2, oxidizes Et2S nearly 10 times faster than Ru(TMP)(0)2 under corresponding conditions at 20.0 °C.The Ru(OCP)(0)2/Et2S/02 system catalytically oxidizes Et2S to EtiSO and Et2S02. Further studies are needed to optimize the reaction conditions for this system. The solvent dependence of the selectivity and the rate of oxidation, and the use of a two-phase solvent system to remove the product sulfoxide as it is formed, are worth studying. The reactivity of other porphyrin ligands containing electron-withdrawing, non-oxidizable substituents such as F and Cl (e.g. perfluoro-TPP) must also be investigated. The activation parameters determined in this study will be useful in understanding the reaction trends when more data are available for other systems. The oxidation of phenol by Ru(TMP)(0)2 is also studied. The reaction is first order both in [Ru] and in [phenol]. A second order rate constant is measured at 20.0 °C. A paramagnetic (S= 1) Ru(IV) porphyrin product, Ru(TMP)(OC6H40H)2, is isolated and characterized. A mechanism for the oxidation is proposed, based on electrophilic attack by the 0=Ru=0 moiety on the aryl ring accompanied by C-H activation. This mechanism also explains the formation of a proposed bis(para-hydroquinone) Ru(U) intermediate, H20 and para-benzoquinone in the reaction. The Ru(TMP)(0)2/phenol/02 system at room temperature does not catalyze formation of the preferred product, para-benzoquinone. This oxidation reaction must be further studied at higher temperatures, using also less-oxidizable porphyrin ligands, to see catalytic activity can be induced. A preh'minary *H nmr study reveals that 2-propanol is oxidized to acetone by Ru (TMP) (0)2- A Ru(TV) species is isolated as the only porphyrin product, but is not characterized. A molecular weight determination and an electrical conductivity measurement are two key experiments to be carried out to identify this novel Ru(IV) porphyrin complex. 146 Several new ruthenium porphyrin species are also prepared and characterized in this thesis work. The reaction of four-coordinate RuCTMP) with acetylene produces the first reported orgahometallic ruthenium porphyrin dimer, [Ru(TMP)]2(^-C2H2). Further attempts are needed to obtain the X-ray crystal structure of this species. Two Jt-bonded alkyne complexes, the first such species to be reported in ruthenium porphyrin chemistry, are characterized in solution. Two ethylene complexes are also isolated and characterized, while a cyclohexene complex is characterized in solution. Four S-bonded sulfoxide complexes of Ru(TMP) are isolated and characterized, and bis-O-bonded and 'mixed' diethylsulfoxide complexes of RuCTMP) and Ru(OCP) are characterized in solution. The range of porphyrin ligands in ruthenium complexes is extended by the synthesis and characterization of three Ru(OCP) complexes, of which Ru(OCP)(0)2 is used in catalytic oxidation of thioethers. Worth noting, and not recorded elsewhere in the thesis, is that two experiments in benzene were made to test the reactivity of RuCTMP) toward 1 atm CH4: there was no evidence of CH4 activation under thermal or photolytic conditions. However, in view of the recent report of the reaction of CH4 with Rh(TMP) to generate Rh(IJJ>hydirde and Rh(III)-methyl species in refluxing benzene (B. Wayland et al., J. Am. Chem. Soc., in press), the reactivity of Ru(TMP) toward CH4 and other saturated hydrocarbons should be studied more thoroughly. 147 Appendices A. Data for UV-visible kinetic studies on oxidation of thioethers. A. 1 Oxidation of Et2S by Ru(TMP)(0)2 in benzene solution. Temperature= 20.0 °C. Temperatures 20.0 °C. Et2S= 2.32x10-2 M. Et2S= 3.09x10-3 M. 1 atm02. 1 atm 02-Time (s) A Time (s) A 0 0.638 480 1.329 780 0.605 1260 1.309 1680 0.570 2340 1.304 3480 0.520 3600 1.293 5580 0.485 5400 1.280 10380 0.440 7440 1.258 oo 0.400 9240 1.242 14040 1.207 oo 0.947 kobs= 1.67xl(H s-1. kobs= 2.72x10-5 s-l. Temperature= 20.0 °C. Temperature= 20.0 °C. Et2S= 1.55x10-2 M. Et2S= 4.64x10-2 M. 1 301102. 1 atm02. Time (s) A Time (s) A 960 1.204 240 1.206 1200 1.191 480 1.180 1440 1.177 720 1.162 1680 1.162 960 1.128 2160 1.130 1200 1.104 2640 1.100 1440 1.085 3120 1.071 1704 1.067 4080 1.020 1920 1.054 5580 0.955 2160 1.041 7320 0.898 2400 1.030 9600 0.844 3186 1.001 11430 0.811 3840 0.984 oo 0.609 oo 0.933 kobs= 1.25x10-4 s-1. kobs= 3.50x10-4 s"1. Temperature^ 20.0 °C. Et2S= 4.64x10-2 M. 1 atm Ar. Temperature= 20.0 °C. Et2S= 2.32x10-1 M. 1 atm02. Time (s) A Time (s) A 540 1.272 60 1.225 720 1,235 180 1.186 840 1.215 300 1.138 960 1.198 540 1.034 1080 1.183 720 0.970 1200 1.170 960 0.912 1380 1.153 1440 0.858 2280 1.092 1800 0.841 2820 1.066 2160 0.831 3600 1.033 oo 0.820 4500 1.004 6480 0.961 oo 0.921 kobs= 3.48X10"4 s"1. kobs= 1.77x10-3 s-1. Temperature= 20.0 °C. Et2S= 3.10x10-2 M. 1 atm02. Time (s) A Temperature= 36.0 °C. Et2S= 9.28x10-2 M. 1 atm02. Time (s) A 90 1.058 60 1.352 150 1.046 120 1.261 240 1.033 240 1.159 420 1.006 360 1.105 600 0.985 480 1.069 1140 0.937 660 1.038 1320 0.925 840 1.011 1620 0.908 1020 0.993 2100 0.884 1260 0.978 2880 0.854 1500 0.972 3720 0.827 oo 0.967 5160 0.790 6300 0.767 10950 0.714 oo 0.690 kobs= 2.40x1a4 s-1. kobs= 2.86x10-3 s"1. Temperature= 25.0 °C. Temperature= 17.0 °C. Et2S= 9.28xl0-2 M. Et2S= 6.16x10-2 M. 1 atmC>2. 1 atm02. Time (s) A Time (s) A 540 1.163 240 1.210 660 1.151 480 1.128 780 1.142 720 1.086 900 1.134 960 1.054 1020 1.129 1200 1.026 1140 1.124 1440 0.998 1320 1.118 1680 0.973 1560 1.112 1920 0.950 1830 1.106 2160 0.929 2160 1.101 2400 0.889 oo 1.091 2880 0.870 3120 0.858 3360 0.842 3600 0.830 3840 0.818 00. 0.703 kobs= 1.16x10-3 s-1. kobs= 3.89x10^ s-1. Oxidation of DecMeS by Ru(TMP)(0)2 in benzene solution. Temperature= 20.0 °C. Temperature= 20.0 °C. DecMeS= I.llxl0-2M. DecMeS= 2.22x10-2 M. 1 atm O2. 1 atm02. Time (s) A Time (s) A 60 1.017 0 1.157 120 1.002 30 1.126 180 0.987 60 1.111 240 0.973 90 1.095 300 0.960 120 1.080 360 0.949 150 1.067 420 0.938 180 1.054 480 0.927 210 1.043 630 0.903 240 1.033 720 0.871 270 1.024 900 0.871 300 1.016 1020 0.860 360 1.002 1200 0.847 420 0.989 1440 0.833 480 0.978 1800 0.818 540 0.969 00 0.793 600 0.961 720 0.949 00 0.928 kobs= 1.27x10-3 s-l. kobs= 3.12x10-3 s-l. Temperatures 10.0 °C. DecMeS= 2.95xl0-2 M. 1 atm02. Temperatures 30.0 °C. DecMeS= 2.95x10-2 M. 1 atm02. Time (s) A Time (s) A 120 1.089 30 1.252 180 1.078 60 1.173 240 1.069 90 1.105 300 1.060 120 1.049 360 1.052 150 1.002 450 1.040 180 0.943 660 1.019 210 0.929 780 1.008 240 0.900 900 0.999 270 0.874 1020 0.992 300 0.855 1140 0.985 360 0.831 1260 0.979 oo 0.799 oo 0.959 kobs= 1.54xl0-3 s"1. kobs= 7.98x10-3 s"1. Oxidation of nBu2S by Ru(TMP)(0)2 in benzene solution. Temperatures 20.0 °C. Temperatures 30.0 °C. nBu2S= 4.64x10-2 M. nBu2S= 9.28x10-2 M. 1 atm02. 1 atm02. Time (s) A Time (s) A 30 1.109 42 1.207 60 1.104 60 1.195 90 1.098 120 1.155 120 1.092 180 1.113 150 1.086 240 1.075 180 1.080 300 1.047 210 1.073 360 1.013 270 1.060 420 0.983 360 1.041 480 0.959 420 1.029 540 0.935 480 1.018 600 0.914 540 1.007 660 0.895 720 0.976 720 0.879 960 0.939 oo 0.779 1200 0.906 1500 0.871 1890 0.834 2160 0.811 2940 0.761 3420 0.739 oo 0.679 kobs= 5.72x10-4 s-1. kobs= 2.17x10-3 s"1. Temperature= 15.0 °C. nBu2S= 9.28xl0-2 M. 1 atm02. Time Cs) A 120 1.293 180 1.270 240 1.247 300 1.217 420 1.172 600 1.102 780 1.047 1020 0.992 1380 0.935 1800 0.888 2580 0.830 3240 0.798 4140 0.768 oo 0.742 kobs= 7.45x10-4 s-1. Temperature= 35.0 °C. nBu2S= 9.28x10-2 M. 1 atm02. Time (s) A 30 1.225 90 1.171 120 1.126 180 1.067 240 1.016 300 0.972 360 0.933 420 0.900 480 0.870 540 0.843 600 0.821 kobs= 2.80x10-3 s-1. A.4 Oxidation of Et2S by Ru(OCP)(0)2 in benzene solution. Tempera ture= 20.0 °C. Et2S= 1.55x10-2 M. 1 atm02. Time (s) A 150. 0.961 180 0.942 240 0.909 360 0.859 420 0.837 480 0.816 540 0.796 600 0.779 720 0.746 960 0.697 1200 0.662 1440 0.635 1980 0.596 2460 0.575 oo 0.543 kobS= 1.12x10-3 s-1. Oxidation of phenol by Ru(TMP)(0)2 in benzene solution. Temperatures 20.0 °C. Phenol= 3.72xl0-2 M. 1 atm02. Time (s) A Temperatures 20.0 °C. Phenols 1.39x10-! M. 1 atm02. Time (s) A 50' 0.623 45 0.800 135 0.544 75 0.715 225 0.501 105 0.657 320 0.451 135 0.612 440 0.408 195 0.556 580 0.372 255 0.525 730 0.344 315 0.508 ~ 0.258 oo 0.485 kobs= 2.11x10-3 s-1. kobs= 9.70x10-3 s-l. Temperatures 20.0 °C. Phenols 9.30x10-2 M. 1 atm02. Time (s) A Temperatures 20.0 °C. Phenol= 3.72x10-2 M. 1 atm02. Time (s) A 60 0.819 50 0.927 120 0.701 135 0.842 180 0.632 220 0.783 240 0.577 305 0.724 360 0.508 390 0.681 oo 0.456 475 0.648 560 0.605 oo 0.428 kobs= 6.34x10-3 s"1. kobs= 1.96x10-3 s-1. Determination of molecular weight of [Ru(TMP)]20J.-C2H2) using the Signer method. Weight of unknown = 7.41 mg. Weight of standard (TMPH2) = 5.63 mg. Molecular weight of standard = 783 g/mol. Time (h) Volume (mL) Standard Unknown 0.0 9.2 8.4 1.0 9.4 8.2 15.5 10.4 7.22.5 10.5 7.1 40.0. 10.6 7.0 63.0 10.6 7.112.0 10.55 7.05 

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