Oxidative Substitution of Organocopper(II) by a Carbon-Centered Radical

Copper-catalyzed coupling reactions of alkyl halides are believed to prominently involve copper­(II) species and alkyl radicals as pivotal intermediates, with their exact interaction mechanism being the subject of considerable debate. In this study, a visible light-responsive fluoroalkylcopper­(III) complex, [(terpy)­Cu­(CF3)2(CH2CO2 t Bu)] Trans-1, was designed to explore the mechanism. Upon exposure to blue LED irradiation, Trans-1 undergoes copper–carbon bond homolysis, generating Cu­(II) species and carbon-centered radicals, where the carbon-centered radical then recombines with the Cu­(II) intermediate, resulting in the formation of Cis-1, the Cis isomer of Trans-1. Beyond this, a well-defined fluoroalkylcopper­(II) intermediate ligated with a sterically hindered ligand was isolated and underwent full characterization and electronic structure studies. The collective experimental, computational, and spectroscopic findings in this work strongly suggest that organocopper­(II) engages with carbon-centered radicals via an “oxidative substitution” mechanism, which is likely the operational pathway for copper-catalyzed C–H bond trifluoromethylation reactions.