A 4H/4e Electron-Coupled-Proton Buffer Based on a Mononuclear Cu Complex.

In this research article, we describe a 4H/4e electron-coupled-proton buffer (ECPB) based on Cu and a redox-active ligand. The protonated/reduced ECPB (complex : ), consisting of Cu with 2 equiv of the ligand (LH: 1,1'-(4,5-dimethoxy-1,2-phenylene)bis(3-(-butyl)urea)), reacted with H/e acceptors such as O to generate the deprotonated/oxidized ECPB. The resulting compound, (complex : ), was characterized by X-ray diffraction analysis, nuclear magnetic resonance (H-NMR), and density functional theory, and it is electronically described as a cuprous bis(benzoquinonediimine) species. The stoichiometric 4H/4e reduction of was carried out with H/e donors to generate (Cu and 2 equiv of LH) and the corresponding oxidation products. The ECPB system catalyzed the 4H/4e reduction of O to HO and the dehydrogenation of organic substrates in a decoupled (oxidations and reductions are separated in time and space) and a coupled fashion (oxidations and reductions coincide in time and space). Mechanistic analysis revealed that upon reductive protonation of and oxidative deprotonation of , fast disproportionation reactions regenerate complexes and in a stoichiometric fashion to maintain the ECPB equilibrium.