A Bio-inspired Cu₄ O₄ Cubane: Effective Molecular Catalysts for Electrocatalytic Water Oxidation in Aqueous Solution

Inspired by the cubic Mn₄ CaO₅ cluster of natural oxygen-evolving complex in Photosystem II, tetrametallic molecular water oxidation catalysts, especially M₄ O₄ cubane-like clusters (M=transition metals), have aroused great interest in developing highly active and robust catalysts for water oxidation. Among these M₄ O₄ clusters, however, copper-based molecular catalysts are poorly understood. Now, bio-inspired Cu₄ O₄ cubanes are presented as effective molecular catalysts for electrocatalytic water oxidation in aqueous solution (pH 12). The exceptional catalytic activity is manifested with a turnover frequency (TOF) of 267 s^-1 for [(L_Gly -Cu)₄ ] at 1.70 V and 105 s^-1 for [(L_Glu -Cu)₄ ] at 1.56 V. Electrochemical and spectroscopic study revealed a successive two-electron transfer process in the Cu₄ O₄ cubanes to form high-valent Cu^III and Cu^III O^. intermediates during the catalysis.