Computational study of H2 generation from BH3 and BH3− with HO˙ radical

Abstract

Hydrogen formation via reactions involving boron hydrides has attracted increasing attention due to its relevance to clean energy and radical chemistry. In this study, density functional theory at the M06-2X/6-311++G(d,p) level, combined with transition state theory (TST) including Wigner tunneling corrections, is employed to investigate the mechanisms and kinetics of hydrogen generation from reactions of neutral BH₃ and anionic BH₃⁻ with hydroxyl radicals (HO˙) in both the gas phase and aqueous solution. The results reveal reaction pathways involving stabilized pre-reactive intermediates followed by hydrogen transfer steps, with stronger donor acceptor interactions in the anionic system facilitating H–H bond formation. Kinetic analysis shows pronounced temperature dependence and tunneling effects. In the gas phase, a negative temperature dependence is observed, arising from a dominant pre-equilibrium associated with a strongly stabilized intermediate. In aqueous solution, the overall kinetics are governed by the combined effects of pH-dependent speciation, diffusion, and temperature. These findings provide key insights into the mechanisms of hydrogen formation from boron hydrides and identify the critical factors controlling reactivity in both gas and liquid environments.