Preparation of Novel Organic-Inorganic Hybrid Materials for Catalysts from Metal-Containing Silsesquioxanes

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Incompletely condensed oligosilsesquioxanes with silanol groups and metal-containing silsesquioxanes have attracted much attention from the viewpoint of discrete, well-defined soluble model compounds of the transition metal-containing siliceous heterogeneous catalysts. In the present work, synthesis synthesis of a series of group 4 metallocene-containing silsesquioxanes with functional silyl or germyl groups have been performed from the viewpoint of the preparation of precursors of organic-inorganic hybrid materials for catalysts. Preparation of porous oxide catalysts utilizing these metal-containing silsesquioxanes was also examined.(1)Preparation_of Microporous Solid Oxides from Various-Metal Containing Silsesquioxane:The controlled calcination of newly-synthesized group 13 elements-containing silsesquioxanes at around 823 K produces Bronsted acidic oxides with high BET surface areas of 330-520 m^2g^<-1> and uniformly-controlled micropores of 5.1Å diameter diameter. Their acidic prop … More erties are greatly affected by the structure of silsesquioxane precursors, and partly controlled by the selection of group 13 elements and counter cations. In particular, oxides from aluminum-bridged silsesquioxanes were found to have high BET surface areas and a large amount of acidic sites. Differences in the dispersion of oxides of group 13 elements in silica matrixes, which are closely related to the structure of precursors, are considered to be one of the reasons of differences in their acidic characters. According to the preliminary study on the cracking of model hydrocarbons such as cumene, these oxides show exceptionally high activity in spite of their **orphous nature.(2)Synthesis of Novel Group 4 Transition Metal-Containing Silsesquioxanes with Functional Groups:Several preparation methods of a series of metallocene-containing silsesquioxanes with alkenylsilyl and trimethylsilyl groups have been explored. Among them, the structures of the complexes Cp_2M[(c-C_5H_9)_7Si_7O_<11>](OSiMe_2CH_2CH=CH_2) [M = Zr or Hf] are unambiguously established by the single-crystal X-ray diffraction analysis. The preliminary examination of the catalytic activity of these metallocene-containing silsesquioxanes towards the epoxidation of cyclohexene by tert-butyl hydroperoxide revealed that titanocene-containing silsesquioxanes show modest catalytic activity. Less