Lewis Acid Trapping of an Elusive Copper–Tosylnitrene Intermediate Using Scandium Triflate

High-valent copper–nitrene intermediates have long been proposed to play a role in copper-catalyzed aziridination and amination reactions. However, such intermediates have eluded detection for decades, preventing the unambiguous assignments of mechanisms. Moreover, the electronic structure of the proposed copper–nitrene intermediates has also been controversially discussed in the literature. These mechanistic questions and controversy have provided tremendous motivation to probe the accessibility and reactivity of Cu^III–NR/Cu^IIN^•R species. In this paper, we report a breakthrough in this field that was achieved by trapping a transient copper–tosylnitrene species, 3-Sc, in the presence of scandium triflate. The sufficient stability of 3-Sc at −90 °C enabled its characterization with optical, resonance Raman, NMR, and X-ray absorption near-edge spectroscopies, which helped to establish its electronic structure as Cu^IIN^•Ts (Ts = tosyl group) and not Cu^IIINTs. 3-Sc can initiate tosylamination of cyclohexane, thereby suggesting Cu^IIN^•Ts cores as viable reactants in oxidation catalysis.