One-Electron Activation of Water Oxidation Catalysis

Abstract

Rapid water oxidation catalysis is observed following electrochemical oxidation of [Ru^II(tpy)­(bpz)­(OH)]⁺ to [Ru^V(tpy)­(bpz)­(O)]³⁺ in basic solutions with added buffers. Under these conditions, water oxidation is dominated by base-assisted Atom Proton Transfer (APT) and direct reaction with OH^–. More importantly, we report here that the Ru^IVO²⁺ form of the catalyst, produced by 1e^– oxidation of [Ru^II(tpy)­(bpz)­(OH₂)]²⁺ to Ru­(III) followed by disproportionation to [Ru^IV(tpy)­(bpz)­(O)]²⁺ and [Ru^II(tpy)­(bpz)­(OH₂)]²⁺, is also a competent water oxidation catalyst. The rate of water oxidation by [Ru^IV(tpy)­(bpz)­(O)]²⁺ is greatly accelerated with added PO₄^3– with a turnover frequency of 5.4 s^–1 reached at pH 11.6 with 1 M PO₄^3– at an overpotential of only 180 mV