Silica-Supported Tungsten Neosilyl Oxo Precatalysts: Impact of the Podality on Activity and Stability in Olefin Metathesis

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• 作者：D. Grekov ; Y. Bouhoute ; K. C. Szeto ; N. Merle ; A. De Mallmann ; F. Lefebvre ; C. Lucas ; I. Del Rosal ; L. Maron ; R. M. Gauvin ; L. Delevoye ; M. Taoufik
• 刊名：Organometallics
• 出版年：2016
• 出版时间：July 11, 2016
• 年：2016
• 卷：35
• 期：13
• 页码：2188-2196
• 全文大小：485K
• 年卷期：0
• ISSN：1520-6041

文摘

In order to establish structure–reactivity relationships in propylene metathesis as a function of the podality of tungsten oxo species bearing neosilyl ligands, we targeted the parent tris alkyl [(≡SiO)WOR₃] and bis alkyl oxo [(≡SiO)₂WOR₂] derivatives prone to carbene formation. Thus, [WO(CH₂SiMe₃)₃Cl] (1) was grafted onto silica dehydroxylated at 700 °C (SiO_2–700), proceeding via W–Cl cleavage to yield well-defined monopodal species [(≡SiO)WO(CH₂SiMe₃)₃] (2a) along with HCl release. On the other hand, the corresponding bipodal species [(≡SiO)₂WO(CH₂SiMe₃)₂] (2b) was obtained on SiO_2–200 by release of both HCl and TMS. The formation of these species were demonstrated by mass balance analysis, elemental analysis, IR, advanced solid-state NMR (1D and 2D ¹H, ¹³C, ²⁹Si, and ¹⁷O), and EXAFS. Furthermore, DFT calculations allowed understanding and rationalizing the experimental results regarding grafting selectivity. Materials 2a and 2b proved to lead to stable and efficient supported tungsten oxo catalysts for propene metathesis under dynamic conditions at 80 °C. The symmetric bipodal precatalyst (expressed as [W(═E)(═CHR)(X)(Y)] (X = Y, E = spectator ligand)) showed somewhat higher activity than the asymmetric (X ≠ Y) counterparts.