W-oxo Adamantylidenes: Stable Molecular Precursors for Efficient Silica-Supported Metathesis Catalysts

Abstract

Tungsten oxo adamantylidenes (=Ad) are a new class of readily accessible alkylidenes, that opens the possibility to evaluate a broader class of molecular and supported olefin metathesis catalysts. In this context, W(O)(=Ad)X2, with X=pyrrolide and perfluoro-tert-butoxide, were grafted on partially dehydroxylated silica, to generate the corresponding silica-supported tungsten oxo adamantylidenes. The high thermal stability of the molecular perfluoro-tert-butoxide complex, that exists as a dimer in the solid state, even enables its grafting through sublimation. Evaluation of their catalytic activities toward olefin metathesis using standardized protocols show that these supported species display high activity toward internal and terminal olefins. In particular, avoiding the use of solvent during grafting of the highly electrophilic perfluoro-tert-butoxide compounds, that can bind to the W center, enable to generate significantly more active catalysts.