The reaction of [W(dNAr)(dCHtBu)(CH 2 tBu) 2 ] (1; Ar ) 2,6-iPrC 6 H 3 ) with a silica partially dehydroxylated at 700 °C, SiO 2-(700) , giVes syn-[(tSiO)W(dNAr)(dCHtBu)(CH 2 tBu)] (2) as a major surface species, which was fully characterized by mass balance analysis, IR, NMR, EXAFS, and DFT periodic calculations. Similarly, complex 1 reacts with [(c-C 5 H 9 ) 7 Si 7 O 12 -SiOH] to giVe [(SiO)W(dNAr)(dCHtBu)(CH 2 tBu)] (2m), which shows similar spectroscopic properties. Surface complex 2 is a highly actiVe propene metathesis catalyst, which can achieVe a TON of 16 000 within 100 h, with only a slow deactiVation.

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