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 CH and CH, 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.