Solvent-controlled oxidation-state switching in a CuA-type dicopper complex

Controlling oxidation states and metal-metal bonding in bimetallic complexes is central to understanding electron-transfer processes in both biological and synthetic systems. Here we report a dicopper platform supported by a fluxional multiquelating ligand that enables reversible modulation of oxidation states and Cu-Cu interactions through solvent coordination. The dicopper complex 1·X (X = BF4, B(ArF)4) features a [Cu1+·Cu1+] core with structural and electronic characteristics reminiscent of the reduced biological CuA site. Reversible single-electron oxidation generates the mixed-valence complex 4·X, which displays a shortened Cu···Cu distance and spectroscopic signatures consistent with a Robin-Day class III system. In coordinating solvents such as acetonitrile, the mixedvalence state converts to the localized [Cu2+·Cu1+] complex 3·X, whereas removal of the coordinating solvent restores the delocalized state. Structural, spectroscopic, electrochemical, and computational studies support this reversible solvent-driven redox interconversion. These findings provide an unprecedented example of solvent-controlled cleavage and formation of a formal metal-metal bond, coupled to reversible oxidationstate switching, in a dicopper system.