Low‐temperature sol–gel transformation of methyl silicon precursors to silica‐based hybrid materials

Six new methyl silicon (IV) precursors of the type [MeSi{ONC(R)Ar} 3 ] [when R = Me, Ar = 2‐C 5 H 4 N ( 1 ), 2‐C 4 H 3 O ( 2 ) or 2‐C 4 H 3 S ( 3 ); and when R = H, Ar = 2‐C 5 H 4 N ( 4 ), 2‐C 4 H 3 O ( 5 ) or 2‐C 4 H 3 S ( 6 )] were prepared and structurally characterized by various spectroscopic techniques. Molecular weight measurements and FAB (Fast Atomic Bombardment) mass spectral studies indicated their monomeric nature. 1 H and 13 C{ 1 H} NMR spectral studies suggested the oximate ligands to be monodentate in solution, which was confirmed by 29 Si{ 1 H} NMR signals in the region expected for tetra‐coordinated methylsilicon (IV) derivatives. Thermogravimetric analysis of 1 revealed the complex to be thermally labile, decomposing to a hybrid material of definite composition. Two representative compounds ( 2 and 4 ) were studied as single source molecular precursor for low‐temperature transformation to silica‐based hybrid materials using sol–gel technique. Formation of homogenous methyl‐bonded silica materials (MeSiO 3/2 ) at low sintering temperature was observed. The thermogravimetric analysis of the methylsilica material indicated that silicon‐methyl bond is thermally stable up to a temperature of 400 °C. Reaction of 2 and Al(OPr i ) 3 in equimolar ratio in anhydrous toluene yielded a brown‐colored viscous liquid of the composition [MeSi{ONC(CH 3 )C 4 H 3 O} 3 .Al(OPr i ) 3 ]. Spectroscopic techniques 1 H, 13 C{ 1 H}, 27 Al{ 1 H} and 29 Si{ 1 H} NMR spectra of the viscous product indicated the presence of tetracoordination around both silicon and aluminum atoms. On hydrolysis it yielded methylated aluminosilicate material with high specific surface area (464 m 2 /g). Scanning electron micrography confirmed a regular porous structure with porosity in the nanometric range. Copyright © 2008 John Wiley & Sons, Ltd.