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

Abstract

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 Cu^II and Cu^III intermediates in aminoquinoline-directed C(sp²)-H functionalization of a fluoroarene substrate. An initial C(sp²)-H activation at Cu^II occurs at room temperature to afford an isolable anionic cyclometalated Cu^II complex. This complex undergoes single-electron oxidation with ferrocenium or Ag^I 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 Cu^III-σ-aryl intermediate that undergoes either (i) a second C(sp²)-H activation at Cu^III followed by C-C bond-forming reductive elimination or (ii) reaction with a NO₂^- nucleophile and C(sp²)-NO₂ coupling.