Mechanistic Aspects of Gas-Phase Hydrogen-Atom Transfer from Methane to [CO]. plus and [SiO]. plus : Why Do They Differ?

The reactivity of the two diatomic congeneric systems [CO].+ and [SiO].+ towards methane has been investigated by means of mass spectrometry and quantum-chemical calculations. While [CO].+ gives rise to three different reaction channels, [SiO].+ reacts only by hydrogen-atom transfer (HAT) from methane under thermal conditions. A theoretical analysis of the respective HAT processes reveals two distinctly different mechanistic pathways for [CO].+ and [SiO].+, and a comparison to the higher metal oxides of Group 14 emphasizes the particular role of carbon as a second-row p element.