Functionalized Metal-Free Carbon Nanosphere Catalyst for the Selective C–N Bond Formation under Open-Air Conditions

Abstract

A versatile shape-controlled carbon nanomaterial that can efficiently catalyze the selective C−N coupling reactions under metal-free and open-air conditions was developed by applying Ndoping and KOH activation strategies in candle soot (ANCS). The TEM and elemental mapping results showed the formation of sphereshaped carbon particles as well as the uniform distribution of nitrogen species in the carbon framework. KOH activation enhanced the specific surface area of carbon, whereas N-doping enriched the electron-deficient nature by introducing functional N-based pyrrolic/ graphitic structures in the carbon framework. The synergistic effect of N-doping and KOH activation significantly improved the catalytic efficiency of the carbon catalyst (ANCS), giving a 96% conversion of o-phenylenediamine (OPD) with a good selectivity to 2-phenylbenzimidazole (97%). In contrast, the pristine carbon exhibited very low activity (48% conversion of the OPD and 36% selectivity to 2-phenylbenzimidazole). Besides, the ANCS nanomaterial provided a facile catalytic approach for the homo-and cross-C−N condensation of various aromatic amines and diamines to produce diverse functional imines and benzimidazoles at mild conditions. This work provided promising insights into developing advanced, metal-free carbon-based catalysts for selective C−N coupling reactions to produce valuable drug motifs.