Hydrolysis silsesquioxane synthesis

The self-organization of polysilanols in the presence of other hydrogen bond acceptors has been studied by several groups.512-516 Several other publications have dealt with the stepwise synthesis of siloxane and siloxanol chains.450,517-522 Recent work on fully condensed siloxane rings and silsesquioxane cages involves the non-aqueous hydrolysis of chlorosilanes - as well as mechanistic and structural studies. 

On the basis of all the information collected from this MS study, it is possible to propose a mechanism for the formation of silsesquioxane a7bi (Fig. 9.10). Silsesquioxanes with learly stages of the synthesis and react very quickly to form more condensed species. It is assumed that the very reactive a1 bi will not be formed again by hydrolysis reactions of more condensed species this means that the reactions in which albi takes part are effectively irreversible and that the compound will only be available for the reactions in the early stages of the synthesis. Silsesquioxanes with 2react with each other to form the more condensed silsesquioxanes with 4[Pg.226]

The reaction between the silsesquioxane HgSigOn and acetone in the presence of Co2(CO)8, and pyridine gives, after a six-week period for crystallization, a 35% yield of 27 (equation 9). This presumably occurs via initial formation of the octa-substituted (/-Pr( ))sSix( >i2 followed by partial hydrolysis of just two of the substituents to give the diol 27, which should be of use in the synthesis of polymeric silsesquioxanes119. 

An interesting new approach in this area has been reported with the synthesis of novel polymeric zirconocene-silsesquioxanes (4.15) with R=cyclohexyl [42, 43]. The condensation of zirconocene derivatives with polyhedral silsesquioxanes led to amorphous polymers in high yields ( 90%) that were characterized by NMR spectroscopy and elemental analysis. These high molecular weight (M =14,000) materials exhibited high thermal stability (to ca. 475-515 °C) and, surprisingly, 4.15 a was found to be stable to both air and hydrolysis. 

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