Vanadyl tert-Butoxy Orthosilicate, OV[OSi(O t Bu)3]3:  A Model for Isolated Vanadyl Sites on Silica and a Precursor to Vanadia−Silica Xerogels

The single source precursor OV[OSi(O t Bu)3]3 was synthesized in high yield from OVCl3 and HOSi(O t Bu)3. This tri(alkoxy)siloxy complex was characterized by 1H, 13C, 29Si, and 51V NMR, FT-Raman, FT-IR, EXAFS, and UV−vis spectroscopies and by mass spectrometry. In the Raman spectrum of OV[OSi(O t Bu)3]3, VO (1038 cm-1) and V−O (651, 674, and 705 cm-1) vibrations were observed. The 51V NMR shift was observed at −777 ppm and the 29Si NMR resonance appears at −98 ppm. Thermolysis in n-octane at 180 °C resulted in formation of a green gel which upon drying in air formed a xerogel with a surface area of 320 m2 g-1, an average pore size of 140 Å, and a total pore volume of 2.25 cm3 g-1. The calcined xerogel is similar to bulk V2O5 in catalytic performance for propane oxidative dehydrogenation.