Facile access to polymer supported zinc–salen complex: highly efficient heterogeneous catalyst for synthesizing hydantoins, thiohydantoins and Schiff bases in aqueous medium

The synthesis of polymer supported zinc–salen complex (PS-Zn–salen) is described. The mononuclear zinc(II)–salen complex was characterized by Fourier-transform NMR spectroscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrophotometry (FT-IR), thermogravimetric analysis, scanning electron microscopy, surface area and pore size distribution by Brunauer–Emmett–Teller. The synthesized PS-Zn–salen complex used as a recyclable heterogeneous catalyst for the efficient synthesis of hydantoins, thiohydantoins and Schiff bases in an aqueous medium. The isolated yields of hydantoins, thiohydantoins and Schiff bases achieved up to 89, 95 and 94%, respectively. In spite of conventional heterogeneous catalysts, current PS-Zn–salen complex shows thermal stability up to 280 °C. Moreover, the catalyst could be recovered easily by simple filtration and reused for next run with slightly declining its activity up to six successive runs. The FT-IR spectrum of recycle catalyst after 6th run confirmed that the catalyst was stable during the course of a reaction. The leaching of metal from the PS-Zn–salen is negligible, which was confirmed by AAS and hot filtration test.