C/C Exchange in Activation/Coupling Reaction of Acetylene and Methane Mediated by Os+: A Comparison with Ir+, Pt+, and Au.

The activation and coupling reactions of methane and acetylene mediated by M+ (M = Os, Ir, Pt, and Au) have been comparatively studied at room temperature by the techniques of mass spectrometry in conjunction with theoretical calculations. Studies have shown that Os+ and Ir+ can mediate the activation/coupling reaction of CH4 and C2H2, while Pt+ and Au+ cannot, which could be explained by the number of empty valence orbitals in the metal atom. In addition, there are different competition channels for the reaction mediated by Os+ and Ir+: an expected dehydrogenation and an unexpected C/C exchange. We find that if the rare C/C exchange reaction takes place, there are symmetric carbon atoms in the reaction intermediate and the C/C exchange reaction is favored kinetically. The C/C exchange reaction must be considered, which will affect the yield of the products in the primary reaction. This study shows the molecular-level mechanisms which include the C/C exchange reaction in the activation and coupling reaction of organic compounds mediated by different metals.