Functionalization of a chiral Zr(IV)-based metal-organic framework for rapid and mild catalysis

Post-synthetic functionalization of robust metal-organic frameworks (MOFs) with chiral functional groups is a useful approach to endow the structures with chirality and rich functionality for wide areas of applications. Herein, MOF-808 containing 1,3,5-benzene tricarboxylate (BTC3−) as the linker and formate as the modulator was selected for a two-step post-functionalization. Through the post-synthetic exchange (PSE) in the first stage, some formate modulators were replaced with D-histidine to prepare CMOF-808. The incorporation of D-histidine in MOF-808 caused chirality induction in the framework and created a unique platform for chemical modification. Then, via the post-synthetic modification (PSM) in the second step, the amino acid was functionalized with propyl sulfonic acid groups to produce CMOF-808-SO3H. The prepared CMOF-808-SO3H was characterized by powder X-ray diffraction (PXRD), FT-IR, nuclear magnetic resonance (NMR), field emission scanning electron microscopy (FE-SEM), elemental analysis, circular dichroism (CD) spectroscopy, thermogravimetric analysis, N2 adsorption-desorption isotherms, and temperature-programmed desorption of NH3 (NH3-TPD). As a heterogeneous acid catalyst, CMOF-808-SO3H was used for the methanolysis of styrene oxide and the acetalization of benzaldehyde with alcohols. By using methanol for these acid-catalyzed reactions, high conversion (≥ 99%) and excellent selectivity were obtained within 5 min at room temperature. The catalyst maintained its activity after recycling and displayed structural stability during the reaction. High catalytic performance of CMOF-808-SO3H could be ascribed to its promoted acidity (743.3 μmol/g) compared to the original MOF-808 with 245.7 μmol/g acidic content. In brief, this work contributes to the rapidly expanding field of chiral MOF-based catalysis.