Postsynthetic Modification Switches an Achiral Framework to Catalytically Active Homochiral Metal-Organic Porous Materials

Abstract

The postsynthetic modification strategy is adopted to demonstrate for the first time the syntheses of catalytically active chiral MOPMs from a preassambled achiral framework, MIL-101, by attaching L-proline-derived chiral catalytic units to the open metal coordination sites of the host framework. Various characterization techniques (including PXRD, TGA, IR, and N-2 absorption measurements) indicated that the chiral units are successfully incorporated into MIL-101, keeping the parent framework intact. The new chiral MOPMs show remarkable catalytic activities in asymmetric aldol reactions (yield up to 90% and ee up to 80%). It is interesting to note that these heterogeneous catalysts show much higher enantioselectivity than the corresponding chiral catalytic units as homogeneous catalysts. This study demonstrates a simple and efficient route for the generation of catalytically active chiral MOPMs. A variety of chiral catalytic units can be, in principle, incorporated into chemically robust achiral MOPMs with large pores by postmodification and the resulting chiral MOPMs may find useful applications in catalytic asymmetric transformations.