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

By grafting of TaMe5 (1) on the surface of silica partially dehydroxylated at 500 degrees C (silica(500)), a mixture of ( SiO)TaMe4 (2a; major, 65 +/- 5%) and ( SiO)(2)TaMe3 (2b; minor, 35 +/- 5%) was produced, which has been characterized by microanalysis, IR, and SS NMR (H-1, C-13, H-1-C-13 HETCOR, proton double and triple quantum). After grafting, these surface organometallic compounds are more stable than the precursor TaMe5. 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 degrees 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)TaMe4/( SiO)(2)TaMe3. ( SiO)(2)TaH and ( SiO)(3)Ta exhibit equal reactivities in alkane metathesis and ethylene polymerization in comparison to those in previous reports.