Fluorine-Functionalized NbO-Type {Cu2}-Organic Framework: Enhanced Catalytic Performance on the Cycloaddition Reaction of CO2 with Epoxides and Deacetalization-Knoevenagel Condensation

The high catalytic activity of metal-organic frameworks (MOFs) can be realized by increasing their effective active sites, which prompts us to perform the functionalization on selected linkers by introducing a strong Lewis basic group of fluorine. Herein, the exquisite combination of paddle-wheel [Cu-2(CO2)(4)(H2O)] clusters and meticulously designed fluorine-funtionalized tetratopic 2',3'-difluorop-terphenyl]-3,3 '',5,5 ''-tetracarboxylic acid (F-H(4)ptta) engenders one peculiar nanocaged {Cu-2}-organic framework of {[Cu-2(F-ptta)(H2O)(2)]center dot 5DMF center dot 2H(2)O}(n) (NUC-54), which features two types of nanocaged voids (9.8 x 17.2 angstrom and 10.1 angstrom x 12.4 angstrom) shaped by 12 paddle-wheel [Cu-2(COO)(4)H2O)(2)] secondary building units, leaving a calculated solvent-accessible void volume of 60.6%. Because of the introduction of plentifully Lewis base sites of fluorine groups, activated NUC-54a exhibits excellent catalytic performance on the cycloaddition reaction of CO2 with various epoxides under mild conditions. Moreover, to expand the catalytic scope, the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile were performed using the heterogenous catalyst of NUC-54a. Also, NUC-54a features high recyclability and catalytic stability with excellent catalytic performance in subsequent catalytic tests. Therefore, this work not only puts forward a new solution for developing high-efficiency heterogeneous catalysts, but also enriches the functionalization strategies for nanoporous MOFs.