Synthesis and application of tin triflate-containing MCM-41 as heterogeneous Lewis acid catalysts for the Mukaiyama aldol reaction at room temperature

Sn-containing MCM-41 (Sn-MCM-41) with different tin content was prepared by hydrothermal synthesis then treated with triflic acid to form tin triflate within the silica framework (SnOTf-MCM-41). XRD and UV–visible measurements revealed that SnOTf-MCM-41 have highly ordered mesoporous structures with tetrahedrally-coordinated Sn species. Moreover, results from FT-IR analysis revealed that triflate ligands are selectively coordinated with Sn⁴⁺ species in the mesoporous silica frameworks. SnOTf-MCM-41, as Lewis acid catalysts, promoted the Mukaiyama aldol reaction of benzaldehyde with 1-trimethylsiloxycyclohexene at room temperature and had greater catalytic activity than untreated Sn-MCM-41. Taking into account results from in situ FT-IR experiments using pyridine as probe molecule, the enhanced catalytic performance after triflic acid treatment was attributed to an increase in the number of acid sites, because of appearance of water tolerance by the formation of metal triflate species. In addition, the SnOTf-MCM-41 catalyst was reusable at least three times in the Mukaiyama aldol reaction.