Controlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides
Samantaray, Manoja K.
Hoffman, Adam S.
Widdifield, Cory M.
Gates, Bruce C.
KAUST DepartmentKAUST Catalysis Center (KCC)
Permanent link to this recordhttp://hdl.handle.net/10754/583970
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AbstractThe 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 1H 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–)WH3(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–)WH3([double bond, length as m-dash]CH2)], as determined by solid-state 1H and 13C NMR spectroscopies and supported by DFT. Thus for the first time, a coordination sphere that incorporates both carbene and hydride functionalities has been observed.
CitationControlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides 2016 Chem. Sci.
PublisherRoyal Society of Chemistry (RSC)