Mechanism of Heterolytic Hydrogen Splitting by Frustrated Lewis Pairs: Comparison of Static and Dynamic Models

Abstract

Free energy surfaces generated via ab initio molecular dynamics simulations for H2 activation reactions with intramolecular frustrated Lewis pairs (FLPs) point to a concerted (single-step) mechanism of H–H bond cleavage. Statistical analysis carried out for a large number of reaction trajectories reveals notable asynchronicity in the development of donor-H and acceptor-H bonds with the latter being in a more advanced phase. These findings are fully consistent with the results of static quantum chemical calculations demonstrating that the previously established mechanistic picture of FLP-mediated heterolytic H2 cleavage remains plausible in a finite temperature dynamic model as well. As a consequence of asynchronicity, the excess kinetic energy released upon H2 cleavage is stored in the form of donor-H bond vibrations, which may influence the mechanism of catalytic hydrogenation.