Cobalt Porphyrin-Catalysed Synthesis of Azobenzenes by Dehydrogenative Coupling of Anilines

Abstract

The demand for azobenzenes has exponentially grown due to their wide range of applications in textile, medical, and dye industries. Here we report a procedure to synthesise azobenzenes by the dehydrogenative coupling of anilines in the presence of CoII(TPP) (TPP=dianion of tetraphenyl porphyrin) catalyst and 4-nitrophenyl azide oxidant species. Differently substituted azobenzenes were obtained in yields up to 72 % together with 4-nitrophenyl amine, which is the stoichiometric by-product of the process. The procedure displayed a good sustainability due to the almost quantitative recovery of pure 4-nitrophenyl amine that can be transformed again into the desired azide to pave the way for an efficient circular process. Experimental data supported the occurrence of a radical mechanism mediated by putative nitrene radical cobalt intermediate.