Preparation of mesoporous silica and organosilica nanostructures functionalized with C₂‐symmetric diol and their catalytic performance in diethylzinc addition to aromatic aldehydes

Abstract

In this study, heterogenization of C2‐symmetric (1R,2R)‐1,2‐bis(4‐(3‐(triethoxysilyl)propyl)phenyl)ethane‐1,2‐diol compound and investigation of the effect of structural arrangements of nanocatalysts on catalytic activity were carried out. For this, bissilyl derivative of (1R,2R)‐1,2‐bis(4′‐bromophenyl)‐ethane‐1,2‐diol, named as C2‐BSi, was obtained by 2‐step synthesis. Then, mesoporous silica nanocatalysts C2‐BSi@SBA‐15 and C2‐BSi@MCM‐41 were synthesized by grafting of C2‐BSi onto SBA‐15 and MCM‐41, whereas mesoporous organosilica nanocatalysts C2‐BSi‐MON‐(a) and C2‐BSi‐MON‐(b) were synthesized by co‐condenzation of C2‐BSi and tetraethyl orthosilicate (TEOS). Structure determinations of synthesized organic substances were performed by 1H, 13C NMR, Fourier transform infrared (FT‐IR), polarimeter, and mass analysis, whereas the structural properties of heterogeneous catalysts C2‐BSi@SBA‐15, C2‐BSi@MCM‐41, C2‐BSi‐MON‐(a), and C2‐BSi‐MON‐(b) were determined by FT‐IR, X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), and N2 sorption analyses. The catalytic activities of novel heterogenous materials were tested in the reaction of Ti‐promoted enantioselective diethylzinc addition to aromatic aldehydes. The effects of the structural arrangements of the prepared heterogeneous catalyst on the catalytic activity were examined and compared with the catalytic activity values of their homogeneous analog. According to the results, all catalysts catalyzed the reactions and afforded the corresponding products with high conversion (82–99%) but low enantioselectivity (rac‐7% ee). The conversion values in heterogeneous catalysis were higher than those in homogeneous catalysis. C2‐BSi‐MON‐(a) with the largest pore width stood out as the most effective catalyst (99% conversion, 7% ee). The findings from the catalytic activity experiments confirmed that the structural arrangement of the nanocatalysts has an effect on the performance of the catalysts in the reaction.