Well-Defined Supported Mononuclear Tungsten Oxo Species as Olefin Metathesis Pre-Catalysts

[WOCl4] was grafted on silica dehydroxylated at 200 degrees C, and the structure of the surface species was elucidated by a combination of spectroscopic and theoretical methods, demonstrating the formation of [( SiO)(2)WOCl2] (1a) as the major species accompanied by minor monopodal species [( SiO)WOCl3] (1b). Most noteworthy, EXAFS and O-17 NMR combined to DFT calculations helped elucidate the structure of the surface species. Alkylation was performed using SnMe4, affording methyl species that were also precisely characterized. The alkylated species achieved excellent performances in isobutene metathesis to 2,3-dimethylbutene.