LED-Light Induced Novel Additive/Base/Metal Free Brønsted Acid Functionalized Porphyrin to Afford N-Arylated Benzimidazole

A convenient method for the C–N bond formation via Brønsted acid functionalized porphyrin (BAFPc) catalyzed reaction of aryl halides with benzimidazole was achieved. In this work, novel BAFPc photocatalyst bearing sulfonic acid functionality, was synthesized, and characterized using ¹H NMR, ¹³C NMR, FT-IR, BET, and elemental analysis by SEM/EDAX. The proton level by Hammett acidity function (H₀ = 0.923) and energy band gap (Eg = 1.26 eV) were determined by UV–Visible spectrophotometer. The present metal-free environmental benign route afforded C–N coupling under irradiation of LED-light in lab-made photoreactor in absence of strong base/additive at normal conditions. The photocatalytic reaction was found to be suitable with a variety of aryl halides, (X = Cl, Br) comprising activating and deactivating groups, offering the N-arylated products under given conditions affording satisfactory yield (60 and 58%). Further, this methodology can also be predominantly employed for the construction of C–N derivatives of different heterocycles under optimized conditions with good to admirable yields (49–67%). Moreover, the optimized protocol exhibited competence for C–N coupling of benzyl chloride and benzimidazole to afford drug intermediates like Chlormidazole with good yield (62%). Furthermore, BAFPc, was recycled for 6 times using model reaction supporting heterogeneous and environmental benign protocol.

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