Non-innocent Role of the Halide Ligand in the Copper-Catalyzed Olefin Aziridination Reaction

In the context of copper-catalyzed nitrene transfer to olefins, many systems operate upon mixing a CuX salt (X = halide, OTf) and a polydentate N-based ligand, assuming that the X ligand is displaced from the coordination sphere toward a counterion position. Herein, we demonstrated that such general assumption should be in doubt since studies carried out with the well-defined copper­(I) complexes (TTM)­CuCl and [(TTM)­Cu­(NCMe)]­PF6 (TTM = tris­(triazolyl)­methane ligand) demonstrate a dual behavior from a catalytic and mechanistic point of view that exclusively depends on the presence or absence of the chloride ligand bonded to the metal center. When coordinated, the turnover-limiting step corresponds to the formation of the carbon–nitrene bond, whereas in its absence, the highest barrier corresponds to the formation of the copper–nitrene intermediate.