title: Alkyne Metathesis with Silica-Supported and Molecular Catalysts at Parts-per-Million Loadings.
abstract: Improvement of the activity, stability, and chemoselectivity of alkyne-metathesis catalysts is necessary before this promising methodology can become a routine method to construct C≡C triple bonds. Herein, we show that grafting of the known molecular catalyst [MesC≡Mo(OtBuF6)3] (1, Mes=2,4,6-trimethylphenyl, OtBuF6=hexafluoro-tert-butoxy) onto partially dehydroxylated silica gave a well-defined silica-supported active alkyne-metathesis catalyst [(≡SiO)Mo(≡CMes)(OtBuF6)2] (1/SiO2-700). Both 1 and 1/SiO2-700showed very high activity, selectivity, and stability in the self-metathesis of a variety of carefully purified alkynes, even at parts-per-million catalyst loadings. Remarkably, the lower turnover frequencies observed for 1/SiO2-700by comparison to 1 do not prevent the achievement of high turnover numbers. We attribute the lower reactivity of 1/SiO2-700to the rigidity of the surface Mo species owing to the strong interaction of the metal site with the silica surface.
authors.affiliation: Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland.
authors.forename: Deven P
authors.initials: DP
authors.lastname: Estes
authors.affiliation: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106, Braunschweig, Germany.
authors.forename: Celine
authors.initials: C
authors.lastname: Bittner
authors.affiliation: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106, Braunschweig, Germany.
authors.forename: Òscar
authors.initials: Ò
authors.lastname: Àrias
authors.affiliation: Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Casey
authors.affiliation: Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland.
authors.forename: Alexey
authors.initials: A
authors.lastname: Fedorov
authors.affiliation: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106, Braunschweig, Germany. m.tamm@tu-bs.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Tamm
authors.affiliation: Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland. ccoperet@ethz.ch.
authors.forename: Christophe
authors.initials: C
authors.lastname: Copéret
keywords: NMR spectroscopy; alkynes; metathesis; molybdenum; supported catalysts