Synthesis and characterization of Ni(II) and Cu(II) complexes based on quercetin Schiff base and using them as heterogeneous catalysts in Henry reaction

Quercetin is a dietary flavonoid, which with its specialized structure can form Schiff bases and their metal complexes. Schiff base ligand has been synthesized through the condensation of quercetin and ethanolamine. In this paper, two new metal complexes involving the Schiff base ligand have been prepared by a simple method at room temperature. SBL-Cu and SBL-Ni have been characterized by elemental analysis, ICP, UV-visible, and FT-IR studies. The activity of the synthesized complexes as a heterogeneous catalyst has been assessed in Henry reaction. The complexes have shown high catalytic performance in Henry reaction. However, SBL-Cu had better catalytic activity than SBL-Ni. These catalysts can be recycled and reused five times without a significant reduction in the activity. A series of benzaldehyde derivatives have been applied in the optimized Henry reaction to investigate the effect of the substituent group on the yield of the reaction. As expected, benzaldehydes containing electron-withdrawing group have a higher yield in Henry reaction.