Abstract
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.