Construction of porphyrin-based photocatalyst comprising pyridinium ionic liquid moiety for the metal-free visible light-assisted N-arylation of amines: facile approach to afford drug intermediates

Abstract

Herein, a pyridinium-based ionic liquid-functionalized porphyrin (PBILFPc) photocatalyst was successfully synthesized and characterized using various techniques, such as ¹H NMR, HR-MS, FT-IR, SEM, and XPS. The surface area of the photocatalyst was calculated using the BET method and found to be 125.882 m² g⁻¹. The successful formation of the porphyrin was supported by the extremely shielded inner NH-protons at −2.61 δ ppm. The energy band gap and Hammett acidity were determined to be 1.42 eV and 0.64, respectively, using UV-Vis spectroscopy. Subsequently, PBILFPc was employed as a proficient photocatalyst for the arylation of various N-heterocycles with inactivated/activated aryl halides. The photocatalytic cross-coupling was achieved under metal/base/ligand-free conditions in a laboratory-made photoreactor under the exposure of 5 W white LED light and ambient conditions. Similarly, this protocol was also appropriate for a variety of N-heterocycles, offering N-substituted aryl/alkyl derivatives in appreciable yields (71% to 91%). The photocatalytic activity of PBILFPc was supported by its low energy band gap, promoting the absorption of radiation in the visible region and leading to the formation of excitons (holes and electrons). Moreover, the presence of Brønsted acidic groups together with excitons enhanced its photocatalytic activity at room temperature. This protocol afforded the synthesis of moieties analogous to clotrimazole using the optimized parameters. Furthermore, after the reaction, the reused PBILFPc photocatalyst was found to be active and afforded a reasonable yield (82%) even after six runs. Thus, this sustainable metal/base/ligand-free PBILFPc photocatalytic route in a homemade photoreactor under visible light will motivate investigators to study the synthesis of medicinally vital scaffolds and other intermediates.