Fractal Features of the Catalytic Performances of Bimodal Mesoporous Silica‐Supported Organocatalysts Derived from Bipyridine‐Proline for Asymmetric Aldol Reaction

Abstract

The three bipyridine-proline chiral ligands (Z) with different structural units as highly active species were successfully introduced on Zn-modified bimodal mesoporous silicas (BMMs). The representative heterogeneous catalysts (ZZnBMMs-n) containing different molar ratios of Z/Zn (5, 20, 50, 100, 200%) were prepared, and their catalytic performances were evaluated in the asymmetric aldol reactions between p-nitrobenzaldehyde and cyclohexanone, showing the satisfactory activities (yields) and good stereoselectivity (dr and ee). Meanwhile, their microstructural features and physicochemical properties were characterized by various methods. Particularly, the fractal evolution, the pair distance distribution function, and the Porod plots of the ZZnBMMs catalysts were demonstrated by SAXS analysis. The results revealed that the interfacial layer thickness and their mass fractal (D m ) value gradually increased with the enhanced molar ratios of Z/Zn, along with the decrease of pore size and densification of volume, suggesting the successful Z-grafting into the mesoporous channels of Zn-modified matrixes. The essential relationships between the fractal features and their catalytic performance (yield, dr and ee) were explored, showing the larger the D m values, the better catalytic performance. Besides, the uniform distributions of Zn and S elements in ZZnBMMs catalysts and the formation of enamine-imine intermediates during the asymmetric aldol reactions were confirmed.

Dispersion Performances of Naphthalimides Doped in Dual Temperature- and pH-Sensitive Poly (N-Isopropylacrylamide-co-acrylic Acid) Shell Assembled with Vinyl-Modified Mesoporous SiO2 Core for Fluorescence Cell Imaging

“…Figure S3B,C illustrated N 2 adsorption–desorption isotherms and the corresponding pore size distribution profiles of all related samples. As shown in Figure S3B , the isotherms of M-BMMs ( Figure S3B (b) ) and PAN@BMMs ( Figure S3B (c) to (h) ) were apparently identified as type IV isotherms with H1 type hysteresis loops, similar to a typical feature of BMMs ( Figure S3B (a) ), implying the presence of the uniform mesopores [ 42 ]. Meanwhile, BMMs ( Figure S3B (a) ) exhibited the bimodal mesopore distributions: the first one was centered at 3.12 nm, and the broader second one was about 40.1 nm.…”