Control of Product Distribution and Mechanism by Ligation and Electric Field in the Thermal Activation of Methane

An unexpected mechanistic switch as well as a change of the product distribution in the thermal gas-phase activation of methane have been identified when diatomic [ZnO]^.+ is ligated with acetonitrile. Theoretical studies suggest that a strong metal–carbon attraction in the pristine [ZnO]^.+ species plays an important role in the rebound of the incipient CH₃^. radical to the metal center, thus permitting the competitive generation of CH₃^., OH^., and CH₃OH. This interaction is drastically weakened by a single CH₃CN ligand. As a result, upon ligation the proton-coupled single electron transfer that prevails for [ZnO]^.+/CH₄ switches to the classical hydrogen-atom-transfer process, thus giving rise to the exclusive expulsion of CH₃^.. This ligand effect can be modeled quite well by an oriented external electric field of a negative point charge.