Preparation, Properties, and ESCA Characterization of Vanadium Surface Compounds on Silicagel. III

Conveniently available transition metal hexamethyldisilazanes (M‐HMDS) are described as novel surface reacting agents in SiOM type surface compound formation on silicagel. Secondary reaction products SiOSiMe 3 and SiN(SiMe 3 ) 2 confer “silanized” (hydrophobic) environments which can be removed at 300–400°C. Reactivity of MN linkages with surface silanols and strained siloxanes can be manipulated by coordinating ligands L (also as solvents) in the molecule. Three legged vanadium(III) surface compounds were obtained directly by thermal activation of V[N(SiMe 3 ) 2 ] 3 on SiO 2 in neutral or reducing atmospheres. Detailed course of the reaction were monitored by ESCA and Reflectance Spectroscopy. Impregnation from benzene (0.40–0.45 wt. % V) and subsequent heating to 400–800°C (for 1 hr) gave optimized products. The optimized (SiO) 3 V from V(HMDS) 3 was found to have identical spectral, chemical, and catalytical properties as the oxidation/reduction products from NH 4 VO 3 etc. from aq. impregnations including chemiluminescence with O 2 at 20°C. This is the first reported example of such remarkable surface product correspondence by different mechanistic pathways and its utility in structural elucidation is emphasized. Importance of chemiluminescence as most sensitive indicator of identical surface states is discussed as well as attempts to produce “naked” two legged V II /SiO 2 and V III /SiO 2 .