Quantum Chemical Analyses of BH 4 - and BH 3 OH - Hydride Transfers to CO 2 in Aqueous Solution with Potentials of Mean Force.

Biomimetic hydride transfer catalysts are a promising route to efficiently convert CO2 into more useful products, but a lack of understanding about their atomic-scale reaction mechanisms slows their development. To this end, we report a computational quantum chemistry study of how aqueous solvation influences CO2 reduction reactions facilitated by sodium borohydride (NaBH4 ) and a partially oxidized derivative (NaBH3 OH). This work compares 0 K reaction barriers from nudged elastic band calculations to free-energy barriers obtained at 300 K using potentials of mean force from umbrella sampling simulations. We show that explicitly treating free energies from reaction pathway sampling has anywhere from a small to a large effect on the reaction-energy profiles for aqueous-phase hydride transfers to CO2 . Sampling along predefined reaction coordinates is thus recommended when it is computationally feasible.