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

Abstract

The new complex ( i PrO) 2Ta[OSi(O t Bu) 3] 3 ( 1) was prepared via silanolysis of Ta(O i Pr) 5 with ( t BuO) 3SiOH 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 Ta 2O 5 ⋅ 6SiO 2 and Ta 2O 5 ⋅ 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, high-surface-area (ca. 450 m 2 g −1) xerogels (Ta 2O 5 ⋅ 6SiO 2) that are amorphous up to approximately 1100 °C. A more silica-rich tantala–silica material (Ta 2O 5 ⋅ 18SiO 2) was prepared via a solution-phase co-thermolytic route with 1 and HOSi(O t Bu) 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.