Old dog, new tricks: DFT insights into the hydrolysis of NH3BH3 by Hoveyda-Grubbs catalysts

The Grubbs catalyst, a classic catalyst used for the metathesis of alkenes, was first used for the hydrolysis of ammonia borane. A density functional theory study was carried out to explore the mechanism by which the Hoveyda-Grubbs catalyst facilitates the hydrolysis of ammonia borane, producing three equivalents of H₂ through detailed mechanistic pathways. Whether the dissociation of chloride anions occurs or not has a crucial influence on the reaction mechanism. The computational results indicate that upon the dissociation of chloride anions, the coordination of ammonia borane with the catalyst is capable of forming a stable intermediate. Subsequently, this intermediate undergoes the nucleophilic attack of H₂O and the activation process of the O–H bond, eventually generating H₂. All three hydrogen generation cycles exhibit a similar catalytic mechanism. Through energy decomposition analysis (EDA), an independent gradient model based on the Hirshfeld partition method (IGMH), and Fukui functions, the energy sources of competing transition states, reaction sites, and intermolecular interaction forces are investigated.