A 4H+/4e− electron-coupled-proton buffer (ECPB) based on Cu and redox-active ligand was synthesized and characterized. The protonated/reduced ECPBs (complex 1: [tBu-MeOCu(8H+/14e−)]1+), consisting of CuI with 2 equiv of the ligands (tBu-MeOLH4: 1,1'-(4,5-dimethoxy-1,2-phenylene)bis(3-(tert-butyl)urea)), reacted with H+/e− acceptors such as O2 to generate the deprotonated/oxidized ECPB. The resulting compound, (complex 5: [tBu-MeOCu (4H+/10e−)]1+), was characterized by X-ray diffraction analysis, 1H-NMR and DFT, 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 (CuI and 2 equiv of catLH4) and the corresponding oxidation products. The 1/ 5 ECPB system catalyzed the 4H+/4e− reduction of O2 to H2O 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 5 and oxidative protonation of 1, fast disproportionation reactions regenerate complexes 5 and 1 in a stoichiometric fashion to maintain the ECPB equilibrium. Currently, we have prepared Cu-phenylenediamine-based ECPBs with BDFEs (bond dissociation free energy) ranging from 63.5 kcal/mol to 71.0 kcal/mol. The 4H+/4e− reactivity of these ECPBs was studied by reacting them with PCET reagents with known BDFE values.

4H+/4e- electron-coupled-proton buffers based on mononuclear Cu complexes

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