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 CuIIand CuIIIintermediates in aminoquinoline-directed C(sp2)–H functionalization of a fluoroarene substrate. An initial C(sp2)–H activation at CuIIoccurs at room temperature to afford an isolable anionic cyclometalated CuIIcomplex. This complex undergoes single-electron oxidation with ferrocenium or AgIsalts under mild conditions (5 min at room temperature) to afford C(sp2)–C(sp2) or C(sp2)–NO2coupling 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 CuIIIfollowed by C–C bond-forming reductive elimination or (ii) reaction with a NO2–nucleophile and C(sp2)–NO2coupling.