Selective Catalytic Cyclohexene Oxidation Using Titanium-Functionalized Silicone Nanospheres

Synthesis of methyl silicone-substituted nanospheres was accomplished by an emulsion condensation polymerization of methyltrimethoxysilane using conventional stirring. The spheres, ranging from 14 to 20 nm in diameter, are soluble in a variety of organic solvents and exhibit high surface areas for materials in this size regime. Silanol groups on the particles undergo reaction with titanium isopropoxide to give site-isolated, four-coordinate titanium centers, as determined by UV−visible spectroscopy. Grafting of Ti(OiPr)4 onto the spheres yields a material competent in the selective epoxidation of cyclohexene using both cumene and tert-butyl hydroperoxide as oxidants. The nanospheres represent a support material that can be functionalized much like related oxide surfaces to give site-isolated oxidation catalysts with activities and selectivities superior to those of comparable homogeneous systems.