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

• Published in: Journal of the American Chemical Society 2022-09, Vol.144 (37), p.16905-16915
• Main Authors: Wu, Tong, Rajabimoghadam, Khashayar, Puri, Ankita, Hebert, David D., Qiu, Yi Lin, Eichelberger, Sidney, Siegler, Maxime A., Swart, Marcel, Hendrich, Michael P., Garcia-Bosch, Isaac
• Format: Article
• Language: English
• Subjects: Copper - chemistry; Electrons; Ligands; Oxidation-Reduction; Protons; Urea
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.2c05454

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 CuI with 2 equiv of the ligand (catLH4: 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: [Cu­(4H+/10e–)]1+ ), was characterized by X-ray diffraction analysis, nuclear magnetic resonance (1H-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 (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 of 5 and oxidative deprotonation of 1, fast disproportionation reactions regenerate complexes 5 and 1 in a stoichiometric fashion to maintain the ECPB equilibrium.