Fluorine-Functionalized NbO-Type {Cu 2 }-Organic Framework: Enhanced Catalytic Performance on the Cycloaddition Reaction of CO 2 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 [Cu2 (CO2 )4 (H2 O)] clusters and meticulously designed fluorine-funtionalized tetratopic 2',3'-difluoro-[ p -terphenyl]-3,3″,5,5″-tetracarboxylic acid (F-H4 ptta) engenders one peculiar nanocaged {Cu2 }-organic framework of {[Cu2 (F-ptta)(H2 O)2 ]·5DMF·2H2 O} n ( NUC-54 ), which features two types of nanocaged voids (9.8 Å × 17.2 Å and 10.1 Å × 12.4 Å) shaped by 12 paddle-wheel [Cu2 (COO)4 H2 O)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.