Reusable cobalt-copper catalyzed cross-coupling of (hetero)aryl halides with primary amides under air: investigating a new Co0/CoII-based catalytic cycle

Abstract

We report an efficient ligand-free cobalt-copper catalyzed cross-coupling reaction of aryl halides with primary amides, and also investigate a new Co0/CoII-based catalytic cycle for this transformation. This reaction successfully couples a wide range of aryl and heteroaryl halides (including chlorides, bromides, and iodides) with various aryl, heteroaryl, and aliphatic primary amides in air under solvent-minimized conditions. This cost-effective method efficiently produces the desired cross-coupling products (N-arylamides) in good to excellent yields, showcasing a broad substrate scope (51 examples) and tolerance to many sensitive functional groups (including heterocycles). This protocol requires no conventional work-up and can be performed without the need for strict inert conditions. The established method is also suitable for gram-scale synthesis. Importantly, the catalyst is environmentally benign, inexpensive, and can be reused several times with insignificant loss of catalytic activity. A series of experiments, including UV spectroscopy, Transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), and cyclic voltammetry (CV) were carried out to determine the oxidation state of the active catalytic species, and a radical clock experiment using a radical probe was conducted to examine the reaction mechanism. The experiments support the proposed novel mechanism and eliminating the possibility of a radical-based pathway.