Characterization and Reactivity of Copper(II) and Copper(III) σ-Aryl Intermediates in Aminoquinoline-Directed C–H Functionalization
Isaac M. Blythe, Jingtong Xu, J. Scott O'Dell, Jeff W. Kampf, Miriam A. Bowring, Melanie S. Sanford
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(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.