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.