62044-68-2Relevant academic research and scientific papers
Grafted Ta-calixarenes: Tunable, selective catalysts for direct olefin epoxidation with aqueous hydrogen peroxide
Morlanes, Natalia,Notestein, Justin M.
, p. 191 - 201 (2011/02/21)
Supported Ta(V) oxide catalysts were prepared by grafting calixarene-Ta(V) and TaX5 complexes on SiO2 at coverages less than 0.25 Ta nm-2. Thermogravimetric and elemental analyses and UV-visible spectroscopy indicate that catalysts consist of isolated, 1:1 Ta:ligand surface sites. Catalysts obtained by this one-pot procedure were studied in cyclohexene and cyclooctene epoxidation with H2O2. In sharp contrast with bare oxides, calixarene-containing catalysts had initial cyclohexene direct epoxidation turnover rates of 3.9 ± 0.1 × 10-2 s -1 unaffected by surface density, demonstrating single-site character. Calixarene-containing catalysts were up to 3× more active than the corresponding TaCl5-based catalysts at high surface densities and were also up to 95% selective to direct (non-radical) cyclohexene epoxidation versus 5-based catalysts or only ～20% selectivity for grafted calixarene-Ti(IV) catalysts. Capping silanols with octanol reduced epoxide hydrolysis from >50% to 2O2 and demonstrate that a surface ligand on an otherwise traditionally prepared supported oxide can selectively direct oxidation down mechanistically distinct pathways.
Pentabenzyltantalum: Straightforward synthesis, x-ray structure, and application in the synthesis of [O2N]TaBn3-type and [O3N]TaBn2-type complexes
Groysman, Stanislav,Goldberg, Israel,Kol, Moshe,Goldschmidt, Zeev
, p. 3793 - 3795 (2008/10/08)
The direct reaction between tantalum pentachloride and benzylmagnesium chloride leads to pentabenzyltantalum, previously prepared by a two-step synthesis. The X-ray structure of pentabenzyltantalum reveals a square-pyramidal geometry. Pentabenzyltantalum was found to be an efficient starting material for the preparation of amine-phenolate complexes via toluene elimination reactions. Thus, its reactions with amine bis(phenolate) and amine tris(phenolate) ligand precursors gave the tribenzyltantalum and dibenzyltantalum complexes, respectively, in quantitative yields.
