Characterization and Reactivity of Copper(II) and Copper(III) σ-Aryl Intermediates in Aminoquinoline-Directed C–H Functionalization

Over the past decade, numerous reports have focused on the development and applications of Cu-mediated C–H functionalization reactions; however, to date, little is known about the Cu intermediates involved in these transformations. This paper details the observation and characterization of CuII and CuIII intermediates in aminoquinoline-directed C(sp2)–H functionalization of a fluoroarene substrate. An initial C(sp2)–H activation at CuII occurs at room temperature to afford an isolable anionic cyclometalated CuII complex. This complex undergoes single-electron oxidation with ferrocenium or AgI salts under mild conditions (5 min at room temperature) to afford C(sp2)–C(sp2) or C(sp2)–NO2 coupling products. Spectroscopic studies implicate the formation of a transient diamagnetic CuIII-σ-aryl intermediate that undergoes either (i) a second C(sp2)–H activation at CuIII followed by C–C bond-forming reductive elimination or (ii) reaction with a NO2– nucleophile and C(sp2)–NO2 coupling.