Thermolytic conversion of a bis(alkoxy)tris(siloxy)tantalum(V) single-source molecular precursor to catalytic tantala-silica materials

The new complex ((PrO)-Pr-i)(2)Ta[OSi((OBu)-Bu-t)(3)](3) (1) was prepared via silanolysis of Ta((OPr)-Pr-i)(5) with ((BuO)-Bu-t)(3)SiOH and is a useful structural and spectroscopic (NMR, FTIR) model of Ta(V) on silica. The complex was also used to prepare tantalum-containing silica materials, via the thermolytic Molecular precursor method (yielding Ta2O5 . 6SiO(2) and Ta2O5 . 18SiO(2)) or by grafting 1 onto mesoporous SBA-15 silica (yielding a surface-supported tantala species, TaSBA-15). The Solution phase thermolysis of 1 in nonpolar media afforded homogeneous, hi-h-surface-area (ca. 450 m(2) g(-1)) xerogels (Ta2O5 . 6SiO(2)) that are amorphous up to approximately 1100degreesC. A more silica-rich tantala-silica material (Ta2O5 . 18SiO(2)) was prepared via a solution-phase co-thermolytic route with 1 and HOSi((OBu)-Bu-t)(3), to yield a material with a Si/Ta ratio of 9/1. It was demonstrated that tantala-silica materials are active as catalysts for cyclohexene oxidation. (C) 2004 Elsevier Inc. All rights reserved.