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

The LCuBr-catalyzed C-H imidation of arenes by -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-Cu catalyst; and (2) the catalytic cycle for the C-H bond imidation of arenes. Computations show that the LCuBr complex used in experiments is not an active catalyst. Instead, upon reacting with NFSI it converts to an active dinuclear Cu-Cu catalyst that is detected using HRMS techniques. The catalytic cycle starting from the Cu-Cu dinuclear complex proceeds (a) one-electron oxidation of the active catalyst by NFSI to generate an imidyl radical and dinuclear Cu-Cu intermediate, (b) turnover-limiting single-electron-transfer () 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-Cu 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 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-Cu species.