Facile and Efficient Synthesis of the Surface Tantalum Hydride (SiO)₂Ta^IIIH and Tris-Siloxy Tantalum (SiO)₃Ta^III Starting from Novel Tantalum Surface Species (SiO)TaMe₄ and (SiO)₂TaMe₃

By grafting of TaMe₅ (<b>1</b>) on the surface of silica partially dehydroxylated at 500 °C (silica₅₀₀), a mixture of (SiO)­TaMe₄ (<b>2a</b>; major, 65 ± 5%) and (SiO)₂TaMe₃ (<b>2b</b>; minor, 35 ± 5%) was produced, which has been characterized by microanalysis, IR, and SS NMR (¹H, ¹³C, ¹H–¹³C HETCOR, proton double and triple quantum). After grafting, these surface organometallic compounds are more stable than the precursor TaMe₅. Treatment of <b>2a</b>,<b>b</b> with water and H₂ resulted in the formation of methane in amount of 3.6 ± 0.2 and 3.4 ± 0.2 mol/grafted Ta, respectively. <b>2a</b>,<b>b</b> react with H₂ (800 mbar) to form (SiO)₂TaH. After (SiO)₂TaH was heated to 500 °C under hydrogen or vacuum, [(SiO)₃Ta]­[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)₂TaH and (SiO)₃Ta via the intermediate of the new surface organometallic precursors: (SiO)­TaMe₄/(SiO)₂TaMe₃. (SiO)₂TaH and (SiO)₃Ta exhibit equal reactivities in alkane metathesis and ethylene polymerization in comparison to those in previous reports