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

摘要

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~(Ⅱ)N~*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 ℃ enabled its characterization with optical, resonance Raman, NMR, and X-ray absorption near-edge spectroscopies, which helped to establish its electronic structure as Cu~(Ⅱ)N~*R Ts (Ts = tosyl group) and not Cu~(Ⅲ)NTs. 3-Sc can initiate tosylamination of cyclohexane, thereby suggesting Cu~(Ⅱ)N~*R Ts cores as viable reactants in oxidation catalysis.