Oxidation of Organic Substrates with RuIV=O Complexes Formed by Proton-Coupled Electron Transfer

Abstract

We describe our recent progress in mechanistic investigations on substrate oxidation reactions with Ru^IV=O complexes having pyridylamine ligands. The Ru^IV=O complexes are synthesized from the corresponding Ru^II–OH₂ complexes either through a proton-coupled electron-transfer procedure using a cerium(IV) complex as an oxidant or by bulk electrolysis. We have verified the presence of an adduct-formation equilibrium between the Ru^IV=O complex and a substrate in water, which strongly affects the reaction mechanism of the substrate oxidation. We have also shown that the reaction rates of the substrate oxidation in water are independent of the spin states of the Ru^IV centers and of the bond-dissociation enthalpy of the C–H bond of the substrate. Additionally, we have applied the Ru^II–OH₂ complexes as catalysts for photocatalytic substrate oxidations and have observed very efficient catalytic activity. 1 Introduction 2 Formation, Characterization, and Reactivity of Ru^IV=O Complexes by Using a Peroxide as an Oxidant 3 Formation and Characterization of Ru^IV=O Complexes by a Proton-Coupled Electron-Transfer Procedure 4 Catalytic Oxidation of Organic Substrates by Proton-­Coupled Electron-Transfer Oxidation 5 Kinetic Studies on Substrate Oxidations with Ru^IV=O ­Complexes 6 Photocatalytic Oxidation of Organic Substrates 7 Concluding Remarks