Cinchonine-based organosilica materials as heterogeneous catalysts of enantioselective alkene dihydroxylation

The bridged bis(triethoxysilane) possessing the bis-cinchonine-phthalazine bridging organic unit was synthesized and then subjected to the sol-gel process leading to two hybrid organosilica materials. Both solid materials were characterized by 13C and 29Si CP/MAS NMR, FTIR, SEM, TEM, TGA and gas sorption analyses, and were successfully used as heterogenized ligands in catalysis of enantioselective Sharpless alkene dihydroxylation. The nanostructured material exhibited higher enantioselectivities than the bulk material. For some alkene substrates, the observed enantioselectivities were comparable to the results of homogeneous catalysis. Materials recycling experiments revealed that the nanostructured material can be used at least five times without loss of enantioselectivity.