Unexpected Mechanistic Variants in the Thermal Gas-Phase Activation of Methane

Abstract

In this review gas-phase studies conducted (mostly) at the Berlin laboratory of the authors are presented. The focus will be on describing mechanistic variants we (and others) came across recently in investigating the thermal activation of methane in the gas phase under idealized conditions. Typical examples include the discussion of those hydrogen-atom-transfer processes that do not follow the well-established conventional pathways in which oxyl radicals play a decisive role. This is the case when the spin is located at a metal center, as in [Al2O2]•+, and the C–H bond cleavage follows a proton-coupled electron-transfer mechanism. Also, examples will be presented in which a high spin density at a bridging oxygen atom can be generated by judicious “doping” of the cluster oxides. Further, the particular role Lewis-acidic sites play in the methane activation by closed-shell metal-oxide ions will be highlighted. Then, aspects of the dissociative adsorption of CH4 on rather small cluster ions will be analyzed...