Cubic siloxane molecules

Materials related to polysiloxanes are silsesquioxanes (Scheme 1) (2). These cubic siloxane molecules have been produced with a number of functional species such as styrene and methacrylate moieties protruding from one corner of the structure (3, 4). Classic free radical polymerization of these molecules has been shown to produce an inorganic / organic hybrid homopolymer. Furthermore, cubes have been synthesized with pendant silyl hydrido and silanolate moieties which can be used for further functionalization (5). 

The products of the reactions of silanetriols with gallium [41] and indium alkyls [42] are very similar to those obtained from aluminum alkyls described above. The interest in Ga containing siloxanes stems from the known catalytic activity of Ga-doped zeolites in the dehydrogenation reactions of alkanes. The reactions of silanetriols 15 and 16 with GaMej or InMes in refluxing hexane/1,4-dioxane lead to the cubic Ga/In siloxanes [RSi03M-THF]4 (M = Ga 38, 39 In 40, 41), respectively. In the resulting products, the Ga and In centers are coordinated to a dioxane solvent molecule These compounds have a very similar structure to that of aluminosiloxanes 30-33 shown in Scheme 7. 

The crystal structure of 1 is shown in Fig. 1 the atom labeling is omitted for clarity. The molecule contains a cubic SigOi2 framework with a 4-(trimethylsilylethynyl)phenyl substituent bound to each of the silicon atoms. The silicon atoms of the siloxane cage are approximately tetrahedrally coordinated. The whole molecule shows C symmetry. In contrast to the solid state, 1 shows perfect Of, symmetry in solution, which was verified by NMR spectroscopy. 

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