Direct Determination of Electron-Transfer Properties of Dicopper-Bound Reduced Dioxygen Species by a Cryo-Spectroelectrochemical Approach

摘要

Direct experimental determination of redox properties of superoxo (O2^•−) and peroxo (O2²⁻) embedded in dicopper complexes bearing an unsymmetrical binucleating ligand was achieved using cryo-electrochemistry and cryospectroelectrochemistry in dichloromethane. Cyclic voltammetry for dicopper(I) (>1⁺) oxidation to a Cu^ICu^II mixed-valent species (>1²⁺) under inert atmosphere at 193 K reveals slow heterogeneous electron-transfer kinetics, indicative of a large reorganization energy. Oxygenation of the dicuprous complex >1⁺ gives the bridged peroxo dicopper(II) species >3⁺, which is reversibly oxidized to the superoxo complex >2²⁺ at E⁰=0.11 V (vs. SCE) with a small inner sphere electron-transfer reorganization energy, λi=0.54 eV, determined from variable temperature electrochemical impedance spectroscopy. The data suggest that the O2^•−/O2²⁻ redox process occurs directly on the O2-derived core.