Determination of the Mechanism of Electrocatalytic Water Oxidation by a Dimanganese Tetrakis-Schiff Base Complex: Comparison of Density Functional Theory Calculations with Experiment

Abstract

We have recently reported a new class of tetrakis-Schiff base macrocycles bearing a dimanganese-oxo cluster capable of catalyzing the oxidation of water to O2. Herein we report the applicability of unrestricted density functional theory (DFT) using the B3LYP hybrid functional and the broken symmetry (BS) formalism for the prediction of thermodynamic properties of the proton-coupled electron transfer (PCET) steps involved in the electrocatalytic cycle. We characterize a series of three oxidations of the acetate-bound catalyst [MnII2LAc]+ in acetonitrile solution in terms of standard reduction potentials, and we show that the predicted thermodynamic results are in good agreement with experiment. We further apply this model to the prediction of reaction thermodynamics in the electrocatalytic cycle of the aqua-bound catalyst [MnII2L(OH2)2]2+, and we locate the most energetically favorable pathway for the oxidation of water by this catalyst. We show upon removal of four protons and four electrons that the remaining oxygen atoms approach to a distance of 1.397 Å with the formation of an O–O single bond.