Bifunctional {Pb₁₀K₂}–Organic Framework for High Catalytic Activity in Cycloaddition of CO₂ with Epoxides and Knoevenagel Condensation

Abstract

Seeking strategies to enhance the chemical stability of metal–organic framework (MOF) materials has become a focus for practical applications, which prompts us to carry out the exploratory self-assembly of microporous heterometallic MOFs by introducing alkali metal ions. Herein, the exquisite combination of scarcely reported S-shaped [Pb10K2(μ2-OH)2(COO)24] clusters and 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H6TDP) ligands under solvothermal conditions generated a highly robust microporous framework of {(Me2NH2)2[Pb5K(TDP)2(μ2-OH)]·4DMF·6H2O}n (NUC-45) with one-dimensional (1D) open channels along the a-axis. Thanks to the excellent confined pore environments, such as large surface area, rich Lewis acid sites including Pb2+ and K+, plentiful Lewis base sites including the μ2-OH group and Npyridine atom, and open channels, activated NUC-45a exhibits excellent catalytic performance in the cycloaddition of CO2 with various epoxides under mild conditions. Moreover, NUC-45a, as a heterogeneous catalyst, shows a high catalytic activity for Knoevenagel condensation of aldehydes and malononitrile with high catalytic stability and recyclability. Meanwhile, both reactions have a high turnover number and turnover frequency. This work shows that the use of multifunctional organic ligands and the introduction of alkali metal ions are conducive to the construction of porous cluster-based metal–organic materials with excellent heterogeneous catalysis.