Synthesis and Catalytic Activity of Group 4 Metallocene Containing Silsesquioxanes Bearing Functionalized Silyl Groups

A series of metallocene-containing silsesquioxanes with alkenylsilyl and trimethylsilyl groups, Cp‘2M[(c-C5H9)7Si7O11](OSiMe2R) (2b−d, 3b−d, 4d, 5d: Cp‘ = Cp (cyclopentadienyl), Cp* (pentamethylcyclopentadienyl); M = Ti, Zr, Hf, R = methyl, vinyl, allyl), have been synthesized. The structures of the complexes Cp2M[(c-C5H9)7Si7O11](OSiMe2CH2CHCH2) (M = Zr (3d), Hf (5d)) have been unambiguously established by single-crystal X-ray diffraction analyses. Silylation or germylation of the zirconocene-containing silsesquioxane monosilanol Cp2Zr[(c-C5H9)7Si7O11](OH) (3a) or its hafnocene derivative Cp2Hf[(c-C5H9)7Si7O11](OH) (5a), which can be prepared by the careful reaction of the silsesquioxane trisilanol (c-C5H9)7Si7O9(OH)3 (1a) with zirconocene dichloride or hafnocene dichloride, yields the new series of metallocene-containing silsesquioxanes Cp2Zr[(c-C5H9)7Si7O11](OSiMe2H) (3e), Cp2Zr[(c-C5H9)7Si7O11](OGeMe3) (3f), and Cp2Hf[(c-C5H9)7Si7O11](OSiMe2H) (5e). The reaction of 3e with 2 equiv of hydrogen chloride results in the formation of the dimethylsilyl-containing silsesquioxane disilanol (c-C5H9)7Si7O9(OH)2(OSiMe2H) (1e), indicating the applicability of metallocene moieties as protecting groups of two adjacent silanol groups. Silsesquioxanes bearing alkenylsilyl groups can be easily converted to derivatives with ethoxysilyl groups, Cp2M[(c-C5H9)7Si7O11][OSiMe2(CH2)3SiMe2(OEt)] (M = Ti (2g), Zr (3g)), by the hydrosilylative reaction. The preliminary examination of the catalytic activity of these metallocene-containing silsesquioxanes toward the epoxidation of cyclohexene by tert-butyl hydroperoxide revealed that titanocene-containing silsesquioxanes (2b−d) show modest catalytic activity. The presence of alkenylsilyl groups has been found to accelerate the reactions, especially in the case of titanium-bridged silsesquioxanes.