Development of functionality of metal complexes based on proton-coupled electron transfer

Abstract

Proton-coupled electron transfer (PCET), in which a proton and an electron are directed to respective accepting sites separately, is a fundamental process as observed in many kinds of redox reactions including biological and chemical processes. PCET oxidation of Ru(II)-aqua complexes has been applied for the formation of Ru(IV)-oxo, Ru(III)-hydroxo, and novel Ru(III)-oxyl complexes as reactive species in oxidation reactions of organic substrates and mechanistic insights into the reactions are gained on the basis of kinetic analysis. Ru(III)-pterin complexes without oxo ligands can accept hydrogen from O–H and C–H bonds of substrates and the reactivity and transition states of hydrogen-atom transfer reactions are revealed to be controlled by the proton acceptability and electron acceptability of the hydrogen acceptors; this is also valid for Ru(IV)-oxo complexes. Intramolecular PCET also enables to establish novel molecular bistability to regulate the direction of electron transfer and to create unprecedented electronic structures of metal complexes.