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 Cu II and Cu III intermediates in aminoquinoline-directed C(sp 2 )-H functionalization of a fluoroarene substrate. An initial C(sp 2 )-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(sp 2 )-C(sp 2 ) or C(sp 2 )-NO 2 coupling products. Spectroscopic studies implicate the formation of a transient diamagnetic Cu III -σ-aryl intermediate that undergoes either (i) a second C(sp 2 )-H activation at Cu III followed by C-C bond-forming reductive elimination or (ii) reaction with a NO 2 - nucleophile and C(sp 2 )-NO 2 coupling.