Oxygen transfer in the oxidation of triphenylphosphine by (bpy)2pyRuO2+

Article abstract of DOI:10.1021/ic50219a029

The oxidation of PPh₃ by (bpy)₂pyRuO²⁺ (bpy is 2,2′-bipyridine) has been studied in acetonitrile solution. The observation of (bpy)₂pyRu^IIO=PPh₃²⁺ as an intermediate demonstrates that the reaction proceeds via an initial redox step (bpy)₂pyRuO²⁺ + PPh₃ → (bpy)₂pyRu^IIO=PPh₃²⁺ which is followed by relatively slow (k(25°C) = 1.15 (±0.10) × 10^-4 s^-1) solvolysis: CH₃CN + (bpy)₂pyRu^IIO=PPh₃²⁺ → (bpy)₂pyRuCH₃CN²⁺ + O=PPh₃. From the results of an ¹⁸O-labeling experiment, oxygen transfer from Ru^IV=O to PPh₃ is quantitative within experimental error. The kinetics of the redox step were studied by stopped-flow spectrometry. The reaction is first order in both reactants with k(26.6°C) = 1.75 ± 0.10 × 10⁵ M^-1 s^-1. Activation parameters were calculated from the temperature dependence of the rate constant, an analysis of which gave ΔH^? = 4.7 ± 0.5 kcal/mol and ΔS^? = -19 ± 3 eu. The probable microscopic details of the reaction are discussed in terms of a 2-equiv step with strong electronic-vibrational coupling between the electron-donor (P) and -acceptor (Ru) sites through Ru-O and O-P stretching vibrations. The possible role of the spin change which occurs in the net reaction is discussed.