Iron(III)–salen complex on a polymer scaffold as heterogeneous catalyst for synthesis of benzimidazoles

Abstract

Benzimidazoles are important bioactive compounds with diverse applications in the medicinal, industrial, as well as agrochemical fields. In this study, an iron–salen complex on a polymer scaffold was synthesized and characterized, and its performance assessed as a heterogeneous catalyst for synthesis of benzimidazoles. Formation of the metal complex was well confirmed by Fourier-transform infrared spectroscopy (FT-IR) analysis, and the surface morphology and elemental composition was verified by scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The surface area and pore size distribution were determined by Brunauer–Emmett–Teller analysis, and the high thermal stability of the catalyst was revealed by thermogravimetric analysis. Its general potential for synthesis of benzimidazoles from o-phenylenediamine with aldehydes containing various electron-withdrawing and electron-donating substituents was confirmed. The effects of different solvents, catalyst loadings, temperatures, and reaction durations were also studied. The present protocol is found to be beneficial in terms of excellent yield, adequate reaction time, and simple workup. Also, hot filtration tests confirmed that the catalyst was truly heterogeneous and could be readily recycled and reused several times, making this protocol attractive, commercial, and environmentally friendly.