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Kinetics and mechanism of hydrogenolysis of a ruthenium(II) acyl complex

University of British Columbia

This thesis describes the results of kinetic investigations into the hydrogenolysis of the ruthenium-acyl complex dicarbonylchloro-(norbornenoyDbis(triphenylphosphine)ruthenium(II ),RuCl(CO⋅C₇H₉) (CO) ₂-(PPh₃)₂. 2. N,N-Dimethylacetamide (DMA) and toluene solutions of 2 react with one mole equivalent of H₂ to give HRuCl(CO)₂(PPh₃)₂, 3, and the unsaturated aldehyde product C₇H₉CHO, 4. The subsequent, relatively slow hydrogenation of 4 by a further mole of H₂ to give the saturated aldehyde C₇H₁₁-CHO, 5, was found to be catalyzed by 3. A detailed kinetic study on the hydrogenolysis of 2 in DMA solvent revealed a first-order rate dependence on [Ru][sub Total] an inverse dependence on added [PPh₃], and a first- to zero-order dependence on H₂pressure. The following mechanism is proposed to account for these observations: [See Thesis for Diagram] Values of k₁ and k₋₁/k₂ have been evaluated at 65°C (k₁ = 4.6±0.5x10⁻⁵ s⁻¹ k₋₁/k₂ = 1.7±0.2) and the activation enthalpy and entropy for the k₁ step determined (ΔH[sup ‡] = 69±7 kJmole⁻¹, Δs‡ = -126+13 JK⁻¹ mole⁻¹). New, and as yet incompletely characterized, ruthenium complexes of stoichiometry "RuCl(C₆H₉)(PPh₃)₂”, 6, HRuCl(C₆H₈)(C₆H₉)(PPh₃)₂-benzene solvate", 7, and RuCl₂(C₆H₈)(PPh₃)₂, 8, have been synthesized by the reactions of 1,4-cyclohexadiene (C₆H₈) with HRuCl(PPh₃)₃⋅C₆H₆ (complexes 6 and 7), and RuCl₂ (PPh₃)₃ (complex 8), respectively. Reactions of 6, 7, and 8 in DMA with H₂ and with CO were investigated, and the organic and inorganic products identified: [See Thesis for Diagram]

Text

2010-06-20

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http://hdl.handle.net/2429/25895

Chemistry

University of British Columbia

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