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

Abstract

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.