Theoretical Study of Proton-Coupled Electron Transfer Reaction in Metal-Hydride Complexes^†

Metal-hydride (M-H) complexes are crucial for a variety of catalytic reactions. There have been indications of concerted proton-coupled electron transfer (PCET) reaction recently in several studies involving tungsten hydride complexes covalently connected to pyridyl groups. In this piece of work, we use the density functional theory and nonadiabatic rate theory to study concerted PCET reactions in weakly hydrogen bonded systems. Two dimensional potential energy surfaces of the metal-hydride complexes are first constructed. Wave functions and vibrational energy levels are then obtained, which are used to analyze the transition between each pair of vibronic states and to obtain the total rate constant. It is demonstrated that, because of the hydrogen donor-acceptor distance thermal fluctuations, the concerted PCET reaction and the total reaction rate constant can be significantly enhanced even in the case of weak hydrogen bonding between the proton donor and acceptor.