title: C-H Activation on Co,O Sites: Isolated Surface Sites versus Molecular Analogs.
abstract: 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.
authors.affiliation: Department of Chemistry and Applied Biosciences, Eidgenössische Technische Hochschule Zürich , CH-8093 Zürich, Switzerland.
authors.forename: Deven P
authors.initials: DP
authors.lastname: Estes
authors.affiliation: Department of Chemistry and Applied Biosciences, Eidgenössische Technische Hochschule Zürich , CH-8093 Zürich, Switzerland.
authors.forename: Georges
authors.initials: G
authors.lastname: Siddiqi
authors.affiliation: Department of Chemistry and Applied Biosciences, Eidgenössische Technische Hochschule Zürich , CH-8093 Zürich, Switzerland.
authors.forename: Florian
authors.initials: F
authors.lastname: Allouche
authors.affiliation: International Tomography Center, SB RAS , 3A Institutskaya St., Novosibirsk 630090, Russia.|Novosibirsk State University , Pirogova St. 2, Novosibirsk 630090, Russia.
authors.forename: Kirill V
authors.initials: KV
authors.lastname: Kovtunov
authors.affiliation: General Energy Research Department, Paul Scherrer Institute , CH-5232 Villigen, Switzerland.
authors.forename: Olga V
authors.initials: OV
authors.lastname: Safonova
authors.affiliation: National Research Centre "Kurchatov Institute" , 1 Akademika Kurchatova Pl., 123182 Moscow, Russia.
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Trigub
authors.affiliation: International Tomography Center, SB RAS , 3A Institutskaya St., Novosibirsk 630090, Russia.|Novosibirsk State University , Pirogova St. 2, Novosibirsk 630090, Russia.
authors.forename: Igor V
authors.initials: IV
authors.lastname: Koptyug
authors.affiliation: Department of Chemistry and Applied Biosciences, Eidgenössische Technische Hochschule Zürich , CH-8093 Zürich, Switzerland.
authors.forename: Christophe
authors.initials: C
authors.lastname: Copéret