A flexible-functional-ligand-based metal-organic framework: synthesis, structural characterization and heterogeneous catalytic activity for Knoevenagel condensation

By using the hydrothermal synthesis method, with nickel nitrate as the metal center, 4-[(4-carboxybenzyl)amino]benzoic acid (H 2 L) and 1,4-dimethylimidazol-1-ylbutane (bbi) as the mixed ligands, a porous flexible nickel-based metal-organic framework ( Ni-MOF ) was successfully synthesized. Single-crystal X-ray diffraction reveals that this material possesses a stable two-dimensional network that each Ni(II) center is interconnected with each other through the H 2 L and bbi as bridging ligands. Notably, the uncoordinated amino groups and the Lewis acidic nickel sites together form potential synergistic catalytic active centers. Ni-MOF exhibited excellent heterogeneous catalytic activity for Knoevenagel condensation reaction of benzaldehyde and malononitrile under mild conditions without solvent and at 50 °C, with a conversion rate reaching 100% within 1.5 h. Moreover, Ni-MOF has good substrate compatibility and cycle stability. This work shows that the utilization of multifunctional organic ligands and the introduction of alkali metal ions are beneficial for the construction of porous metal-organic materials with excellent heterogeneous catalytic performance.