Dual activity of durable chiral hydroxyl-rich MOF for asymmetric catalytic reactions

Abstract

The quest to prepare of asymmetric heterogeneous catalysts with both effective Brønsted acid sites (BASs) and Lewis acid sites is very significant challenge. Herein, we report the construction of a chiral metal-organic framework with two kinds of catalytic active sites (Lewis acid/Brønsted acid). It contains coordinative unsaturation metal centers and chiral functional groups that have cooperation in the catalytic activity. In the synthesized CMOF, the chiral decoration of metal node was performed through the practical method: anions exchange hypothesis (post-synthetic exchange). For this aim, the elimination of framework fluorides happened by using the enantiopure auxiliary anions (L-(+)-tartrate anion (tart−)) that led to a chiral cationic MOF with eventual chemical formula [Cr3tart(H2O)2O(bdc)3]. XRD, BET, 1H NMR, SEM and EDX were employed to characterize of the present CMIL. Despite the chiral tartrate anions generate a chiral environment, they have main role in the activating of epoxide ring due to hydrogen-bonding interaction. Experiments show that the enantiopure tartrate-functionalized MIL-101(Cr) as a green asymmetric catalyst has the considerable performance in the enantioselective reactions due to chiral modified surface without remarkable loss in activity.