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, which prevents 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 for probing the accessibility and reactivity of Cu^III–NR/Cu^IIN^•R species. In this paper we report a breakthrough in this field by trapping a transient copper–tosylnitrene species >3–Sc in presence of scandium triflate. Sufficient stability of >3–Sc at −90 °C enabled its characterization with optical, resonance Raman, nuclear magnetic resonance, and x–ray absorption near edge (XANES) spectroscopies, which helped to establish its electronic structure as Cu^IIN^•Ts (Ts = tosyl group) and not Cu^IIINTs. >3–Sc can initiate tosyl–amination of cyclohexane, thereby suggesting Cu^IIN^•Ts cores as viable reactants in oxidation catalysis.