NEW MIXED ORGANIC INORGANIC POLYMERS - HYDROLYSIS AND POLYCONDENSATION OF BIS(TRIMETHOXYSILYL)ORGANOMETALLIC PRECURSORS

A variety of bis(trimethoxysilyl)organometallic precursors, with different structural features, have been obtained in 30-64% yield upon reaction of organic bromides with ClSi(OR)3 (R = Me, Et) in the presence of Mg/THF. The hydrolysis and polycondensation of (MeO)3Si-X-Si(OMe)3 (X = 1,4-C6H4,2,5-C4H2S), (MeO)3Si-C6H4-Si(OMe)2-C6H4-Si(OMe)3, 1,3,5-[Si(OMe)3]3 C6H3, (MeO)3Si-(C=C)nSi(OMe)3 (n = 1, 2), and (MeO)3Si-CH2-CH=CH-CH2-Si(OMe)3, under nucleophilic catalysis by fluoride ion, led quantitatively to new hybrid organic-inorganic silica gels. The derived xerogels were characterized by IR and solid-state C-13 and Si-29 NMR spectroscopy. The silicon-carbon bond was retained within the gel. The major environment of the Si atoms corresponded to a T2:XSi(OR)(OSi)2 Substructure. A higher degree of condensation with a major T3:XSi(OSi)3 was obtained when an excess of fluoride ion was used. In most cases, the gels were amorphous microporous materials with high surface areas (up to 1260 m2 g-1). The latter was shown to be dependent rather on the reaction conditions during gel formation, than on the flexible or rigid-rod-like structure of the organic moiety. The cleavage of the Si-C bond, with elimination of the organic moiety, was achieved upon treatment of the bis(silyl)acetylene-derived gel with MeOH/H2O in the presence of fluoride ion catalyst. Amorphous microporoUS (SiO2)n gel with a surface area of 1055 m2 g-1 was produced.