Thermal restructuring of silica-grafted -CrO₂Cl and -VOCl ₂ species

The volatile molecular precursors CrO₂Cl₂ and VOCl₃ were grafted to thermally dehydrated silica in order to obtain site-isolated, monopodal SiO-MO_xCl_y-1 species (M = V, Cr). Thermal restructuring under dynamic vacuum was investigated up to 450°C with different spectroscopic techniques (viz., NMR, UV-Vis, IR, Raman and XPS). During this thermal restructuring, VOCl₃ or CrO₂Cl ₂ is partially eliminated from the surface, whilst the remaining surface species become multiply bound to the silica surface. This restructuring increases both the chemical and thermal stability of these materials, and has significant consequences for their performance as heterogeneous catalysts.