Application of Mesoporous Silica Foam for Immobilization of Salen Complexes in Chiral Intermediates Synthesis

A route to synthesize porous materials with a hierarchical micro/meso/macroscopic pore system was investigated. Meso/macroporous monolithic silica foams with a large pore size could be fabricated from a mixture of monodispersed PMMA beads and SBA-15, -16 sol solutions. The size, bulk shape and density of the mesoporous monolithic foam could be controlled by the container and the heat treatment temperature. Drying at temperatures higher than 300 degrees C resulted in an expansion of the SBA silica sol and its solidification to form the mesoporous foams. In contrast, only a dense silica monolith was obtained after full evaporation of the solvent at room temperature without releasing the foam structure in the monolithic body. A large fraction of macroporosity in three dimensions was formed in the monolith body, and the remaining silica walls exhibited uniform mesoporosity. Hydrolytic and phenolic ring-opening of epoxides were performed successfully using chiral (salen)Co-BF3 complex-immobilized catalysts in the packed bed of a continuous flow system. Very high catalytic activity with desirable enantioselectivity was obtained in asymmetric catalysis.