Tantalum–Polyhedral Oligosilsesquioxane Complexes as Structural Models and Functional Catalysts for Epoxidation

Tantalum-based supported catalysts have been shown to be very selective for epoxidations with aqueous hydrogen peroxide. To gain information relative to the active site on the surface, access to molecular complexes that mimic the active site of the catalyst on the surface is of great interest. In this contribution, several new Ta-polyhedral oligosilsesquioxane (POSS) complexes with POSS ligands are used to model silica-bound Ta sites and are shown to be active as epoxidation catalysts. Notably, a Ta-POSS complex modified by germanoxy ligands and possessing a dinuclear Ta(μ-O)(μ-OH)Ta core is observed to be very efficient for the epoxidation of cyclooctene using aqueous hydrogen peroxide.