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N‑Heterocylic Carbene-Based Mn Electrocatalyst for Two-Electron CO2 Reduction over Proton Reduction

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journal contribution
posted on 11.04.2016, 00:00 by Kuber Singh Rawat, Arup Mahata, Indrani Choudhuri, Biswarup Pathak
A bifunctional, chelating N-heterocyclic carbene-pyridine (NHC-pyridine) containing Mn­(I) complex [MnBr­(NHC-pyridine)­(CO)3] displays a strong selectivity for CO2 reduction over proton reduction. Interestingly, the two-electron reduction of this complex occurs at a single potential, as opposed to MnBr­(bpy)­(CO)3, which is reduced by two electrons in two separate one-electron reductions. Here, the Gibbs free energy barriers, reduction potentials, rate constants, and pKa values are predicted with theory to understand the one- vs two-electron reduction mechanism. The effects of weak and strong Brønsted acids [HCl, TFE (2,2,2-trifluoroethanol), PhOH, CH3OH, and H2O] are studied to gauge the preference for CO2 vs proton reduction; water is found to be an ideal proton donor that allows for strong CO2 selectivity.