Thesis (Ph. D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 189-204).

Thesis (Ph.D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 189-204) Also available in print.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

One microfiche--`Data from crystal structures solved by the author`--in pocket Bibliography: leaves 214-225

Thesis (M. Sc.)--York University, 2001. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 77-83). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ66415.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

This thesis work reports developments in the coordination chemistry of ruthenium porphyrin complexes, both in terms of the synthesis and chemistry of new compounds, as well as the study of the solution chemistry of some previously reported complexes. The synthesis, characterization and chemistry of ten new Ru(porp) coordination complexes in the oxidation states Ru[superscript]Ⅲ and Ru[superscript]Ⅳ containing halide (Br, CI) and other axial ligands (pyridine, CH₃CN, NH₃ and SbF₆) are described in this thesis. Some additional ten Ru(porp) complexes have been studied in situ. Measurement of the rate constants for forward and reverse reactions and the corresponding equilibrium constant by 'H NMR and UV/visible spectroscopy for the dissociation of PPh₃ ligand from Ru(OEP)L(PPh₃) (OEP is the octaethylporphyrinato dianion; L = CO, PPh₃) in C₇D₈ to generate the previously reported five-coordinate Ru(OEP)L complexes allowed for an estimation of the Ru-P bond strength (64 ± 9 kJ mol⁻¹) in these complexes. A study of PPh₃ dissociation from Ru(OEP)CO(PPh₃) in C₇D₈ and in CDC1₃ indicates that solvation effects play a major role, with CDC1₃ being more capable than C₇D₈ of solvating the Ru(OEP)CO complex. The presence of trace H₂0 in these systems was a major problem, and the coordination of H₂0 to Ru(OEP)L complexes to generate the in situ Ru(OEP)L(H₂0) complexes (L = CO, PPh₃) is described. The formation of Ru(OEP)L(H₂0) and the observed difference in the solvation of Ru(OEP)CO by C₇H₈ and CHC1₃ indicate that truly Five-coordinate species may not exist in solution. The outer-sphere oxidation of Ru [superscript]Ⅳ(OEP)PPh₃ by 0₂ to give [Ru [superscript]Ⅳ(OEP)OH]₂0 was shown to occur only in the presence of H₂0. Mechanistic studies on the previously reported reaction of HCI with [Ru(OEP)]₂ to generate Ru^(OEP)Cl₂ (C. Sishta, M.Sc.Thesis, University of British Columbia, 1986) show that solvent plays a major role in directing this oxidation reaction. A reaction stoichiometry of 4:1 between HCI and [Ru(OEP)]₂ in C₆D₆ or C₇D₈ showed that HCI itself was the oxidant and not trace Cl₂ in HCI, as thought previously. A range of HX acids having pK[subscript]a, values in the range 38 to less than -10 (HX = H₂, MeOH, H₂0, H₂S, CH₃COOH, C₆H₅COOH, HF, CF₃COOH, HN0₃, HBF₄, HCI. HBr, and HSbF₆) were tested for reactivity with [Ru(OEP)]₂in C₆D₆; the data showed that a strong acid (pK[subscript]a < ca. 0) was necessary to initiate reactivity. The complex Ru[superscript]Ⅳ(OEP)(SbF₆)₂ was generated in situ by reacting HSbF₆ with [Ru(OEP)]₂. In CH₂C1₂, a 1:1 stoichiometric reaction between HCI and [Ru(OEP)]₂ was observed, instantly fanning a mixture of products, tentatively formulated as Rura(OEP)H and [Ru[superscript]Ⅲ(OEP)]₂CHCl₂ based on spectroscopic data. The species proved impossible to separate. These same products were formed slowly by the reaction of [Ru(OEP)]₂ with CH₂C1₂ in the absence of HCI, and kinetic studies suggest that a direct reaction of [Ru(OEP)]₂ with CH₂C1₂ is likely, rather than reaction of [Ru(OEP)]₂ with impurities in CH₂C1₂. The product mixture generated Ru(OEP)Cl₂ upon further reaction with HCI, both in the absence and in the presence of air. The complex Ru[superscript]Ⅳ(OEP)(BF₄)₂ was generated in situ by an analogous reaction of aqueous HBF₄ with the product mixture. The required hydrogen-containing co-product from the reaction of HX (X = Br, CI) with [Ru(OEP)|₂ in C₇D₈ or CH₂C1₂ was not detected, but was shown not to be H₂. Oxidation of Ru(porp)(CH₃CN)₂ and Ru(OEP)py₂ (py = pyridine; porp = OEP, TMP (the dianion of tetramesitylporphyrin)) by gaseous HX (X = Br, CI) in the absence of air yielded Ru[superscript]Ⅳ(porp)X₂ complexes. The new compound Ru(TMP)Br₂ was synthesized by this method using the bis(acetonitrile) precursor, and was characterized by spectroscopy; the chloride analogue Ru(TMP)Cl₂ was generated in situ. The magnetic properties (susceptibility and moment) of Ru(OEP)Br₂ from 6 to 300 K are unlike those reported for ruthenium(IV) non-porphyrin complexes, and reveal a significant contribution from temperature-independent paramagnetism. The reaction of Ru(OEP)X₂ (X = Br, CI) with NH₃ gave the complexes Ru[superscript]Ⅲ(OEP)X(NH₃), which upon acidification under an inert atmosphere yielded the Rum(OEP)X compounds. These Ru111 complexes were characterized by spectroscopic techniques, and the solution chemistry of the five-coordinate species Ru(OEP)X was developed: the Ru[superscript]Ⅲ(OEP)X(CH₃CN) species were also characterized. Solvation of the five-coordinate species Ru(OEP)X (X = Br, CI) was observed in coordinating solvents to form the six-coordinate species Ru(OEP)X(solvent) (solvent = py, CH₃CN and MeOH). Estimates of the equilibrium constants for the association of these ligands to Ru(OEP)X were obtained from UV/visible titration experiments in CH₂C1₂. Similarly, the equilibrium constant for the association of Br to Ru(OEP)Br to generate in situ (n-Bu)₄N⁺[Ru[superscript]Ⅲ(OEP)Br⁺₂]", was measured. Disappointingly, the complexes Ru(OEP)X were shown not to catalyze the oxidation of organic substrates such as cyclohexene. Electrochemical and spectroelectrochemical studies of the complexes Ru(OEP)X₂ and Ru(OEP)X (X = Br, CI) showed that the Ru[superscript]Ⅳ/Ru[superscript]Ⅲ couple occurred at 480-460 mV and 950-870 mV vs. NHE, respectively, and that the probable reductant for the reaction of Ru(OEP)X₂ with NH₃ was NH₃ itself. A facile reduction of Ru(OEP)(SbF₆)₂ gave the complex Ru[superscript]Ⅲ(OEP)SbF₆, by a probable homolysis of the Ru-F bond. The outer-sphere oxidation of Ru(OEP)py₂ by air in the presence of HX acids gave the isolated or in situ characterized complexes [Ruin(OEP)py₂]+ X" (X = CI, Br, F, BF₄). Similar oxidation of Ru(OEP)(CH₃CN)₂ formed [Ru(OEP)(CH₃CN)₂]+ Br-. Electrochenucal studies showed that 0₂ in acidic media was capable of oxidizing the Ru(OEP)(solvent)₂ complexes (solvent = py, CH₃CN) to the Ru[superscript]Ⅲ complexes, presumably generating H0₂ . / Science, Faculty of / Chemistry, Department of / Graduate

Interaction of metalloporphyrins, particularly of the iron subgroup, with gas molecules such as 0₂ and CO, remains of considerable interest in terms of comparison with natural heme protein systems. This thesis describes studies on ruthenium(II) porphyrin complexes, the second row analogues of the heme systems. Toluene solutions of the bis(acetonitrile) complex RuOEP(CH₃CN) ₂, (OEP = the dianion of octaethylporphyrin) with or without excess acetonitrile present, are irreversibly oxidized by 0₂ at 30°C. However, with CO, the complex undergoes a clean reaction to give RuOEP(CO)(CH₃CN) with several isosbestic points observed in the UV/VIS spectrum. The kinetic dependence on the CO pressure and acetonitrile concentration are consistent with a dissociative mechanism: [Chemical Reaction I] The kinetic rate constants, k-₁, k-₂ and k-₁/k₂ and the overall equilibrium constant were determined at 30°C in toluene. The Ru0EP(P(n-Bu) ₃) ₂ complex, in toluene, is completely unreactive toward 0₂ at 30°C over a period of several days; although again a monocarbonyl is formed under a CO atmosphere. In the presence of excess P(n-Bu) ₃, under CO, an equilibrium mixture of RuOEP(P(n-Bu) ₃) ₂ and RuOEP(CO)(P(n-Bu) ₃) is formed. The equilibrium constant K for reaction (II) and the thermodynamic parameters AH (3.7 Kcal/mole) and ΔS (10.3 e.u.) are determined along with the rate constants for the dissociative mechanism (cf. Equation I). The low ΔH value implies comparable bond [Chemical Reaction II] strengths between ruthenium and the two ligands P(n-Bu) ₃ and CO. The k -₁/k₂ values for the acetonitrile and phosphine systems are thought to relate to the structure of the five-coordinate intermediate, RuOEP(L); the data suggest the ruthenium is probably more in the porphyrin plane than out of plane, al least compared to analogous iron systems. The major difference between the acetonitrile and phosphine systems is in the k₂value which varies by 10⁵ , partially due to the difference in ir-acidity of the two axial ligands. Toluene solutions of RuOEP(CH₃CN) ₂ bind N₂ and C₂H₄ very weakly. However, due to the extreme photo- and oxygen-sensitivity of the products, no consistent kinetic data could be obtained. Solutions of RuOEP(py) ₂ in neat pyridine, formed in situ from the bis(acetonitrile) complex in pyridine, are completely unreactive toward CO. Even toluene solutions with small amounts of pyridine react only partially (~15% in three days at 25°C) to give the monocarbonyl. Upon dissolving the RuOEP(CH₃CN) ₂ complex in DMA, DMF and THF, the species formed seem to be RuOEP(CH₃CN)(solvent). These species react with CO at 30°C in a two step reaction, an instantaneous part followed by a much slower one; the reactions appear to involve the rapid formation of one monocarbonyl followed by decomposition to the expected monocarbonyl, RuOEP(CO)(solvent). Decarbonylation of the amide solvent to give an amine ligand may be involved in the fast reaction. Judging by the reaction with CO (non-first-order in ruthenium) there are possibly two species present when RuOEP(CH₃CN) ₂ is dissolved in pyrrole, RuOEP(pyrrole)₂ and RuOEP(CH₃CN)(pyrrole), which react at different rates. / Science, Faculty of / Chemistry, Department of / Graduate

The thesis describes a study of the catalytic hydrogenation of an olefinic substrate by the complex hydridochlorobis(triphenylphosphine) ruthenium(II) and an investigation of the complex in the solid state and in solution. The visible spectra of the complex, (HRuCl(PPh₃)₂)₂, at a series of concentrations showed that Beer's law is not obeyed, and that in solution a dissociative equilibrium exists: (1) (HRuCl(PPh₃)₂)₂ K ⇆ (2HRuCl(PPh₃)₂ The complex in N,N-dimethylacetamide solution was found to be an effective catalyst for the homogeneous hydrogenation of hex-l-ene. A detailed kinetic study on this system revealed a mechanism involving initial formation of a σ-alkyl intermediate which then reacts with molecular hydrogen to produce the saturated product and regenerate the catalyst: (2) HRuCl(PPh₃)₂ + olefin k₁ ⇆ k₋₁ RuCl(PPh₃)₂(alkyl) (3) HRuCl(PPh₃)₂(alkyl) + H₂ k₂→ HRuCl(PPh₃)₂ + alkane. The mechanism is quite different from that reported for the same catalyst system but using acrylamide as substrate, thereby showing that the nature of the substrate can have a pronounced affect on the course of hydrogenation. Addition of triphenylphosphine and lithium chloride to the (HRuCl(PPh₃)₂)₂- hex-l-ene system were found to decrease and increase the rate of hydrogenation, retrospectively. The added phosphine likely competes with the olefinic substrate for a coordination site; the role of the chloride ion is more uncertain, but a more active catalyst containing more than one chloride ligand is the most obvious rationale. To enhance the solubility of this hydridophosphine type catalyst the tri-p-tolylphosphine analogue of the triphenylphosphine complex was prepared; the variable temperature ¹H and ³¹P{¹H}-solution n.m.r. of the (HRuCl(P(p-tolyl)₃)₂)₂ complex showed the presence of both monomer and fluxional dimer. Addition of dimethyl maleate to the complex in order to obtain a Ru-alkyl species (equation (2)) gave very complex spectra which could not be interpreted in terms of a single species, but there was some evidence for a hydrido(olefin) species rather than an alkyl. An x-ray analysis of the p-tolyl complex confirmed the expected chloro-bridged dimeric structure of these hydridochlorobis(phosphine) species. There is a square pyramidal coordination geometry about each ruthenium atom, and two such centres share a basal edge, but the molecule has no symmetry as a result of the small hydride ligands allowing distortion. / Science, Faculty of / Chemistry, Department of / Graduate

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy