Highly Dispersed Group IV, V Transition Metal Oxide Catalysts from Grafted Metallocalixarenes for Alkene Epoxidation

摘要

Many industrially significant selective oxidation reactions are catalyzed by supported and bulk transition metal oxides. Epoxidation catalysts have largely focused on TiOx supported on or co-condensed with SiO2 [1], and much of the rest of group IV and V have seen relatively little research. Here, metallocalixarenes of titanium, zirconium, hafnium, vanadium, niobium and tantalum (all of groups IV and V) were grafted onto mesoporous silica to yield a family of highly dispersed supported metal oxide catalysts. This series is used to elucidate intrinsic periodic trends in epoxidation reactivity. The calixarene ligand affords steric bulk and multidentate binding to the metal cation, which ensures site-isolation of metal centers during grafting, removing the confounding factor of different extents of metal oxide aggregation during synthesis.