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‘ 2 M[(c-C 5 H 9 ) 7 Si 7 O 11 ](OSiMe 2 R) ( 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 Cp 2 M[(c-C 5 H 9 ) 7 Si 7 O 11 ](OSiMe 2 CH 2 CH CH 2 ) (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 Cp 2 Zr[(c-C 5 H 9 ) 7 Si 7 O 11 ](OH) ( 3a ) or its hafnocene derivative Cp 2 Hf[(c-C 5 H 9 ) 7 Si 7 O 11 ](OH) ( 5a ), which can be prepared by the careful reaction of the silsesquioxane trisilanol (c-C 5 H 9 ) 7 Si 7 O 9 (OH) 3 ( 1a ) with zirconocene dichloride or hafnocene dichloride, yields the new series of metallocene-containing silsesquioxanes Cp 2 Zr[(c-C 5 H 9 ) 7 Si 7 O 11 ](OSiMe 2 H) ( 3e ), Cp 2 Zr[(c-C 5 H 9 ) 7 Si 7 O 11 ](OGeMe 3 ) ( 3f ), and Cp 2 Hf[(c-C 5 H 9 ) 7 Si 7 O 11 ](OSiMe 2 H) ( 5e ). The reaction of 3e with 2 equiv of hydrogen chloride results in the formation of the dimethylsilyl-containing silsesquioxane disilanol (c-C 5 H 9 ) 7 Si 7 O 9 (OH) 2 (OSiMe 2 H) ( 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, Cp 2 M[(c-C 5 H 9 ) 7 Si 7 O 11 ][OSiMe 2 (CH 2 ) 3 SiMe 2 (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.