l-Prolinamide functionalized mesoporous silicas: Synthesis and catalytic performance in direct aldol reaction

Mesoporous silicas functionalized with the l-prolinamide group in the mesopore were synthesized by co-condensation of silicon precursors with l-prolinamide modified organosilane (PCA) in HOAc–NaOAc buffer solution (pH = 4.4) using block copolymer P123 as a template. The highly ordered 2D hexagonal mesostructure was obtained through one-pot co-condensation of tetraethoxysilane (TEOS), Na2SiO3 and PCA as silicon source. The disordered foam-like mesostructure was also obtained when TEOS and PCA were used as silicon sources. In asymmetric aldol reaction of cyclohexanone with 4-nitrobenzaldehyde, the materials with highly ordered mesostructure exhibit higher enantioslectivity (91% ee) than that with disordered foam-like mesostructure (75% ee), suggesting that the ordered pore structure imparts improved enantioselectivity. The l-prolinamide functionalized materials were also synthesized by grafting PCA onto mesoporous silicas, which showed catalytic efficiencies similar to the materials synthesized by the co-condensation method.

Graphical abstractThe highly ordered 2D hexagonal mesostructure and disordered foam-like mesostruture mesoporous materials functionalized with l-prolinamide were obtained by using different silicon precursors in HAc–NaAc buffer solution. In asymmetric Aldol reaction of cyclohexanone and 4-nitrobenzaldehyde, the materials with ordered mesostructure exhibited higher enantioselectivity (91% ee) than that with disordered foam-like mesostructure (75% ee).Figure optionsDownload full-size imageDownload as PowerPoint slide