Cu-Catalyzed aromatic C–H imidation with N-fluorobenzenesulfonimide: mechanistic details and predictive models

The LCuBr-catalyzed C–H imidation of arenes by N-fluorobenzenesulfonimide (NFSI), previously reported by us, utilizes an inexpensive catalyst and is applicable to a broad scope of complex arenes. The computational and experimental study reported here shows that the mechanism of the reaction is comprised of two parts: (1) generation of the active dinuclear Cu(II)–Cu(II) catalyst; and (2) the catalytic cycle for the C–H bond imidation of arenes. Computations show that the LCu(I)Br complex used in experiments is not an active catalyst. Instead, upon reacting with NFSI it converts to an active dinuclear Cu(II)–Cu(II) catalyst that is detected using HRMS techniques. The catalytic cycle starting from the Cu(II)–Cu(II) dinuclear complex proceeds via (a) one-electron oxidation of the active catalyst by NFSI to generate an imidyl radical and dinuclear Cu(II)–Cu(III) intermediate, (b) turnover-limiting single-electron-transfer (SET1) from the arene to the imidyl radical, (c) fast C–N bond formation with an imidyl anion and an aryl radical cation, (d) reduction of the Cu(II)–Cu(III) dinuclear intermediate by the aryl radical to regenerate the active catalyst and produce an aryl-cation intermediate, and (e) deprotonation and rearomatization of the arene ring to form the imidated product. The calculated KIE for the turnover-limiting SET1 step reproduces its experimentally observed value. A simple predictive tool was developed and experimentally validated to determine the regiochemical outcome for a given substrate. We demonstrated that the pre-reaction LCuX complexes, where X = Cl, Br and I, show a similar reactivity pattern as these complexes convert to the same catalytically active dinuclear Cu(II)–Cu(II) species.