Facile and Efficient Synthesis of the Surface Tantalum Hydride (≡SiO) 2 Ta III H and Tris-Siloxy Tantalum (≡SiO) 3 Ta III Starting from Novel Tantalum Surface Species (≡SiO)TaMe 4 and (≡SiO) 2 TaMe 3

By grafting of TaMe 5 ( 1 ) on the surface of silica partially dehydroxylated at 500 °C (silica 500 ), a mixture of (≡SiO)TaMe 4 ( 2a; major, 65 ± 5%) and (≡SiO) 2 TaMe 3 ( 2b; minor, 35 ± 5%) was produced, which has been characterized by microanalysis, IR, and SS NMR ( 1 H, 13 C, 1 H– 13 C HETCOR, proton double and triple quantum). After grafting, these surface organometallic compounds are more stable than the precursor TaMe 5 . Treatment of 2a, b with water and H 2 resulted in the formation of methane in amount of 3.6 ± 0.2 and 3.4 ± 0.2 mol/grafted Ta, respectively. 2a, b react with H 2 (800 mbar) to form (≡SiO) 2 TaH. After (≡SiO) 2 TaH was heated to 500 °C under hydrogen or vacuum, [(≡SiO) 3 Ta][≡SiH] was produced, and the structure was confirmed by IR, NMR, and EXAFS. Considering the difficulty of the previous preparation method, these syntheses represent a facile and convenient way to prepare tantalum surface species (≡SiO) 2 TaH and (≡SiO) 3 Ta via the intermediate of the new surface organometallic precursors: (≡SiO)TaMe 4 /(≡SiO) 2 TaMe 3 . (≡SiO) 2 TaH and (≡SiO) 3 Ta exhibit equal reactivities in alkane metathesis and ethylene polymerization in comparison to those in previous reports.