A Bio-inspired Cu4O4 Cubane: Effective Molecular Catalysts for Electrocatalytic Water Oxidation in Aqueous Solution

Inspired by the cubic Mn4CaO5 cluster of natural oxygen-evolving complex in Photosystem II, tetrametallic molecular water oxidation catalysts, especially M4O4 cubane-like clusters (M=transition metals), have aroused great interest in developing highly active and robust catalysts for water oxidation. Among these M4O4 clusters, however, copper-based molecular catalysts are poorly understood. Now, bio-inspired Cu4O4 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 (CuO center dot)-O-III intermediates during the catalysis.