Alkyne Metathesis with Silica-Supported and Molecular Catalysts at Parts-per-Million Loadings

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• 作者：Deven P. Estes ; Celine Bittner ; Ò ; scar À ; rias ; Martin Casey ; Alexey Fedorov ; Matthias Tamm and Christophe Copé ; ret
• 刊名：Angewandte Chemie
• 出版年：2016
• 出版时间：November 2, 2016
• 年：2016
• 卷：128
• 期：45
• 页码：14166-14170
• 全文大小：2642K
• ISSN：1521-3757

文摘

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(OtBu_F6)₃] (1, Mes=2,4,6-trimethylphenyl, OtBu_F6=hexafluoro-tert-butoxy) onto partially dehydroxylated silica gave a well-defined silica-supported active alkyne-metathesis catalyst [(≡SiO)Mo(≡CMes)(OtBu_F6)₂] (1/SiO_2-700). Both 1 and 1/SiO_2-700 showed 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/SiO_2-700 by comparison to 1 do not prevent the achievement of high turnover numbers. We attribute the lower reactivity of 1/SiO_2-700 to the rigidity of the surface Mo species owing to the strong interaction of the metal site with the silica surface.