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 1 : [Cu(8H + /14e - )] 1+ ), consisting of Cu I with 2 equiv of the ligand ( cat LH 4 : 1,1'-(4,5-dimethoxy-1,2-phenylene)bis(3-( tert -butyl)urea)), reacted with H + /e - acceptors such as O 2 to generate the deprotonated/oxidized ECPB. The resulting compound, (complex 5 : [Cu(4H + /10e - )] 1+ ), was characterized by X-ray diffraction analysis, nuclear magnetic resonance ( 1 H-NMR), and density functional theory, and it is electronically described as a cuprous bis(benzoquinonediimine) species. The stoichiometric 4H + /4e - reduction of 5 was carried out with H + /e - donors to generate 1 (Cu I and 2 equiv of cat LH 4 ) and the corresponding oxidation products. The 1/5 ECPB system catalyzed the 4H + /4e - reduction of O 2 to H 2 O 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 5 and oxidative deprotonation of 1 , fast disproportionation reactions regenerate complexes 5 and 1 in a stoichiometric fashion to maintain the ECPB equilibrium.