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

Direct experimental determination of redox properties of superoxo (O 2 .− ) and peroxo (O 2 2− ) embedded in dicopper complexes bearing an unsymmetrical binucleating ligand was achieved using cryo‐electrochemistry and cryo‐spectroelectrochemistry in dichloromethane. Cyclic voltammetry for dicopper(I) ( 1 + ) oxidation to a Cu I Cu II mixed‐valent species ( 1 2+ ) 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  2 2+ at E 0 =0.11 V (vs. SCE) with a small inner sphere electron‐transfer reorganization energy, λ i =0.54 eV, determined from variable temperature electrochemical impedance spectroscopy. The data suggest that the O 2 .− /O 2 2− redox process occurs directly on the O 2 ‐derived core.