Different routes for preparing mesoporous organosilicas containing the Tröger's base and their textural and catalytic applications

Abstract

Organosilica materials with different contents of Tr¿oger¿s base (TB) as builder moieties have been synthesized from previously synthesized bis-trialkoxysilylated Tr¿oger¿s base. Three well-nanostructured hybrid mesoporous materials were prepared through different approachs: (a) anchoring the TB on a preformed silica SBA-15 material by postsynthesis grafting, (b) incorporating the TB fragments into the rigid and ordered periodic mesoporous organosilica (PMO) with hexagonal structure (HMS) by self-assembling process, and (c) using anion fluoride as catalyst for a sol gel synthesis process in the absence of structural directing agents (SDAs), at neutral pH and low synthesis temperature, to introduce the TB units into the walls of high surface orderless mesoporous materials with flexible structure. The degree of long-range ordering of the materials was determined from X-ray diffraction and transmission electron microscopy and the texture of the various samples were analyzed by nitrogen sorption volumetry. The composition of the materials was determined by elemental analyses and thermogravimetry, and the integrity, topology and structuration level of the Tr¿oges base units were characterized by 13C NMR and 29Si MAS NMR spectroscopy. The materials were used as basic organocatalysts in Knoevenagel reaction. The disordered mesoporous hybrid materials show the highest catalytic activity due to the appropriate combination of high accessibility and structural flexibility. These mesoporous organosilica materials are stable upon recycling.