How and Why Do Cluster Size, Charge State, and Ligands Affect the Course of Metal-Mediated Gas-Phase Activation of Methane?

Recent progress in the gas-phase activation of methane is discussed. We demonstrate that cluster size, charge state, and ligands crucially affect both the reactivity and selectivity of metal-mediated bond activation processes. We outline the important role that relativistic effects and spin densities play and discuss the paradigm of two-state reactivity in thermal reactions. State-of-the-art mass-spectrometry based experiments, in conjunction with electronic structure calculations, permit identification of the elementary steps at a strictly molecular level and thus allow to uncover mechanistic features for four types of reactions: (i) metal-mediated dehydrogenation of methane, (ii) ligand-switch processes of the type ML + CH4 M(CH3) + HL, (iii) hydrogen-atom abstraction as the crucial step in the oxidative coupling of methane, and (iv) the mechanism of the challenging CH4CH3OH conversion.