Hydroboration of phenylmethanimine-borane: synchronicity/nonsynchronicity in a double/single hydrogen transfer reaction

Abstract

Abstract: Hydroboration of phenylmethanimine-borane can take place either according to the intermolecular or intramolecular mechanism. The transition state regions of both reactions, defined by extreme values of reaction forces, were investigated using the Relative Energy Gradient methodology. In the intermolecular reaction, the transfer of both hydrogen atoms takes place simultaneously and the profile of the reaction force constant is characterized by a single minimum. The corresponding graph for the intramolecular mechanism displays two minima, revealing a nonsynchronous reaction in terms of bond breaking, bond formation, and bond transformation. Consequently, the minimum energy path in the vicinity of the intramolecular barrier’s top is flat, which results in a longer lived transition state, as confirmed by Density Functional Theory-based Molecular Dynamics simulations.