Density Functional Theory Prediction of the Electrocatalytic Mechanism of Proton Reduction by a Dicobalt Tetrakis(Schiff Base) Macrocycle.

A dicobalt tetrakis(Schiff base) macrocycle has recently been reported to electrochemically catalyze the reduction of H+ to H2 in an acetonitrile solution. Density functional theory (DFT) calculations using the ωB97X-D functional are shown to produce structural and thermodynamic results in good agreement with the experimental data. A mechanistic model based on thermodynamics is developed that incorporates electrochemical and magnetic details of the complex, accounting for electron-spin reorganization of the metal center after redox steps. The model is validated through a comparison of the predicted electrochemical potentials with the irreversible cyclic voltammogram of [Co2LAc]+, which shows redox-coupled spin-crossover (RCSCO) behavior for the CoII/III transitions. Using our model, we predict the thermodynamically favored mechanism of H2 evolution by [Co2L]2+ to be one of heterolytic proton attack on a [CoII2L(μ-H)]+ species. Understanding the electronic details and thermodynamically preferred mechanism of this catalyst will aid in improving its efficiency and the future design of bimetallic Co-based H+ electrocatalysts. Also, this work will assist in the future DFT modeling of bimetallic RCSCO complexes.