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

A versatile shape-controlled\ncarbon nanomaterial that can efficiently\ncatalyze the selective C–N coupling reactions under metal-free\nand open-air conditions was developed by applying N-doping and KOH\nactivation strategies in candle soot (ANCS). The TEM and elemental\nmapping results showed the formation of sphere-shaped carbon particles\nas well as the uniform distribution of nitrogen species in the carbon\nframework. KOH activation enhanced the specific surface area of carbon,\nwhereas N-doping enriched the electron-deficient nature by introducing\nfunctional N-based pyrrolic/graphitic structures in the carbon framework.\nThe synergistic effect of N-doping and KOH activation significantly\nimproved the catalytic efficiency of the carbon catalyst (ANCS), giving\na 96% conversion of <i>o</i>-phenylenediamine (OPD) with\na good selectivity to 2-phenylbenzimidazole (97%). In contrast, the\npristine carbon exhibited very low activity (48% conversion of the\nOPD and 36% selectivity to 2-phenylbenzimidazole). Besides, the ANCS\nnanomaterial provided a facile catalytic approach for the homo- and\ncross-C–N condensation of various aromatic amines and diamines\nto produce diverse functional imines and benzimidazoles at mild conditions.\nThis work provided promising insights into developing advanced, metal-free\ncarbon-based catalysts for selective C–N coupling reactions\nto produce valuable drug motifs.