Quantum Chemical Analyses of BH4- and BH3 OH- Hydride Transfers to CO2 in Aqueous Solution with Potentials of Mean Force

Abstract

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.

Keywords: carbon dioxide; density functional theory; hydride transfer; molecular dynamics; umbrella sampling.