C–H Activation on Co,O Sites: Isolated Surface Sites versus Molecular Analogs Deven P. Estes Georges Siddiqi Florian Allouche Kirill V. Kovtunov Olga V. Safonova Alexander L. Trigub Igor V. Koptyug Christophe Copéret 10.1021/jacs.6b08705.s003 https://acs.figshare.com/articles/journal_contribution/C_H_Activation_on_Co_O_Sites_Isolated_Surface_Sites_versus_Molecular_Analogs/4212765 The activation and conversion of hydrocarbons is one of the most important challenges in chemistry. Transition-metal ions (V, Cr, Fe, Co, etc.) isolated on silica surfaces are known to catalyze such processes. The mechanisms of these processes are currently unknown but are thought to involve C–H activation as the rate-determining step. Here, we synthesize well-defined Co­(II) ions on a silica surface using a metal siloxide precursor followed by thermal treatment under vacuum at 500 °C. We show that these isolated Co­(II) sites are catalysts for a number of hydrocarbon conversion reactions, such as the dehydrogenation of propane, the hydrogenation of propene, and the trimerization of terminal alkynes. We then investigate the mechanisms of these processes using kinetics, kinetic isotope effects, isotopic labeling experiments, parahydrogen induced polarization (PHIP) NMR, and comparison with a molecular analog. The data are consistent with all of these reactions occurring by a common mechanism, involving heterolytic C–H or H–H activation via a 1,2 addition across a Co–O bond. 2016-10-21 00:00:00 Isolated Surface Sites mechanism PHIP silica surface isotope effects activation Molecular Analogs metal siloxide precursor Transition-metal ions silica surfaces Co NMR terminal alkynes rate-determining step hydrocarbon conversion reactions