Chirally Functionalized Mesoporous Organosilicas for Chiral Separation and Asymmetric Catalysis

Chiral PMOs (with chiral functionality in the framework) opens up a new avenue for the synthesis of chiral material and may exhibit promising application potentials in the fields of chiral separation and asymmetric catalysis. Recently, we have synthesized spherical (1R,2R)-diaminocyclohexane (DACH) functionalized chiral PMOs and employed as a novel kind of chiral stationary phase for high performance liquid chromatography (HPLC) [1,2]. Several (1R,2R)-diaminocyclohexane and L-tartardiamide functionalized mesoporous organosilicas for asymmetric catalysis have been synthesized and show good to moderate enantioselectivity in transfer hydrogenation of ketones [3-5] and asymmetric epoxidation [6], respectively. Recently, the chiral PMOs with (R)-Binol and (R)-Binap integrated in the mesoporous framework were synthesized using a successive co-condensation and post-synthesis modification method [7]. The catalytic results show that the TOF (43 h-1) of nanospheres with (R)-Binol in the network are much higher than that (1 h-1) of the bulk material in Ti-promoted asymmetric addition of diethylzinc to benzaldehyde. The highest enantioselectivity of 94% could be obtained on the nanospheres for benzaldehyde. Moreover, the chiral PMOs with (R)-Binap in the pore wall (coordination with [RuCl2-(benzene)]2) is an efficient solid catalyst for the asymmetric hydrogenation of β-keto esters with ee as high as 99%, which is among the highest ever reported for the chirally functionalized PMOs in asymmetric catalysis. In summary, the chirally functionalized PMOs with the combination of the rigid nanoporous structure and homogeneously distributed chiral ligands in the pore wall may be potential chiral solids for chiral separation and asymmetric catalysis