| Description |
We studied non-hydrolytic sol-gel reactions to prepare several classes of metallosilicate and phosphosilicate hybrid inorganic-organic materials based on polycondensation reactions between silicon acetate or acetoxysilanes 1RxSi(OC(O)CH3)4-x (1R = Me, Ph; n = 0-2) and phosphoric and phosphonic acid trimethylsilylesters 2RP(O)(OSiMe3)2 (2R = OSiMe3, c-Hex, Ph), metal amides M(N3R2)n (M = Al, Ti; 3R = Me, Et; n = 3, 4) and metal alkoxides M(O4R)n (M = Al, Ti; 4R = i-Pr, t-Bu, SiMe3; n = 3, 4) in aprotic dry solvents. Phosphosilicate xerogels were prepared by the elimination of acetic acid ester from Si(OC(O)CH3)4 and P(O)(OSiMe3)3. The 29Si CPMAS NMR spectra revealed the presence of two types of six-coordinate silicon centers SiO6. The surface area and condensation degree could be controlled by the reaction parameters, such as solvent, temperature, and time. Mixtures of silicon acetate and acetoxysilanes and trimethylsilyl phosphates provided hybrid gels. The presence of alkyl or aryl substituents on Si centers resulted in the absence of SiO6 moieties. Alumosilicate xerogels were prepared by polycondensation reactions between Al(NMe2)3 or Al(Oi-Pr)3 and acetoxysilanes. These elimination reactions led to the formation of Si-O-Al networks and released dimethylacetamide or acetic acid ester and as byproducts, respectively. Non-hydrolytic polycondensation reactions between Ti amides Ti(NR2)4 (R = Me, Et) or Ti alkoxides Ti(OR)4 (R = i-Pr, t-Bu, SiMe3) and acetoxysilanes were employed to prepare titanosilicate xerogels. The acetamide and ester elimination reactions led to Si-O-Ti networks that displayed catalytic activity in epoxidation reactions. Two-step sequential polycondensation procedure was used to prepare metallosilicophosphates. The prepared xerogels were characterized by solid-state 13C, 27Al, 29Si, 31P NMR, IR, surface area analysis, TG/DSC, XANES/EXAFS, and XRD.
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