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The well-defined single-site silica-supported tungsten complex [([triple bond, length as m-dash]Si-O-)W(Me) 5 ], 1 , is an excellent precatalyst for alkane metathesis. The unique structure of 1 allows the synthesis of unprecedented tungsten hydrido methyl surface complexes via a controlled hydrogenolysis. Specifically, in the presence of molecular hydrogen, 1 is quickly transformed at -78 °C into a partially alkylated tungsten hydride, 4 , as characterized by 1 H solid-state NMR and IR spectroscopies. Species 4 , upon warming to 150 °C, displays the highest catalytic activity for propane metathesis yet reported. DFT calculations using model systems support the formation of [([triple bond, length as m-dash]Si-O-)WH 3 (Me) 2 ], as the predominant species at -78 °C following several elementary steps of hydrogen addition (by σ-bond metathesis or α-hydrogen transfer). Rearrangement of 4 occuring between -78 °C and room temperature leads to the formation of an unique methylidene tungsten hydride [([triple bond, length as m-dash]Si-O-)WH 3 ([double bond, length as m-dash]CH 2 )], as determined by solid-state 1 H and 13 C NMR spectroscopies and supported by DFT. Thus for the first time, a coordination sphere that incorporates both carbene and hydride functionalities has been observed.

chemical science

Controlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides