Amorphous zirconium metal–organic frameworks assembled from mixed porphyrins as solvent-free catalysts for Knoevenagel condensation

Three mixed porphyrins, icpp (1-3), were synthesized via the reactions of 4-formylbenzoic acid and 4-imidazolecarboxaldehyde, and then five amorphous or crystalline Zr-MOFs-SPUZ (1-5) were obtained from icpp (1-3), timp and tcpp, respectively. The catalytic activities of the synthesized porphyrins and MOFs were studied on the Knoevenagel condensation of aldehydes and malononitrile under solvent-free conditions. Among them, amorphous MOF SPUZ-1 showed the highest catalytic activity. Further studies on various aldehydes demonstrated that most reactions were completed with a low catalyst loading (1 mol%) in a short reaction time (5-30 min), and the best result was obtained with the yield of 99.9% within 5 min. Moreover, SPUZ-1 could be recycled 7 times without significant loss of activity.