Mechanistic Studies of the Rhodium-Catalyzed Direct C–H Amination Reaction Using Azides as the Nitrogen Source

Direct C–H amination of arenes offers a straightforward route to aniline compounds without necessitating aryl (pseudo)­halides as the starting materials. The recent development in this area, in particular in the metal-mediated transformations, is significant with regard to substrate scope and reaction conditions. Described herein are the mechanistic details on the Rh-catalyzed direct C–H amination reaction using organic azides as the amino source. The most important two stages were investigated especially in detail: (i) the formation of metal nitrenoid species and its subsequent insertion into a rhodacycle intermediate, and (ii) the regeneration of catalyst with concomitant release of products. It was revealed that a stepwise pathway involving a key Rh­(V)–nitrenoid species that subsequently undergoes amido insertion is favored over a concerted C–N bond formation pathway. DFT calculations and kinetic studies suggest that the rate-limiting step in the current C–H amination reaction is more closely related to the formation of Rh–nitrenoid intermediate rather than the presupposed C–H activation process. The present study provides mechanistic details of the direct C–H amination reaction, which bears both aspects of the inner- and outer-sphere paths within a catalytic cycle.