Cu-Catalyzed aromatic C-H imidation with N-fluorobenzenesulfonimide: mechanistic details and predictive models.
نویسندگان
چکیده
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 CuII-CuII catalyst; and (2) the catalytic cycle for the C-H bond imidation of arenes. Computations show that the LCuIBr complex used in experiments is not an active catalyst. Instead, upon reacting with NFSI it converts to an active dinuclear CuII-CuII catalyst that is detected using HRMS techniques. The catalytic cycle starting from the CuII-CuII dinuclear complex proceeds via (a) one-electron oxidation of the active catalyst by NFSI to generate an imidyl radical and dinuclear CuII-CuIII 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 CuII-CuIII 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 CuII-CuII species.
منابع مشابه
Cu-Catalyzed aromatic C–H imidation with N-fluorobenzenesulfonimide: mechanistic details and predictive models† †Electronic supplementary information (ESI) available: (1) CuIBr oxidation by NFSI; (2) details of the Br/F exchange process; (3) bimetallic oxidation of LCuIX (where X = F, Br, Cl, and I) by NFSI; (4) conformational analysis of the oxidation of D3-N-3F; (5) NBO analysis of the Cu2F2 dimer; (6) analysis of electronic states along the catalytic cycle; (7) energy scan for the deprotonation step; (8) isotope effect calculation; (9) calculation procedure to predict regioselectivity for C–H imidation; (10) kinetic profiles of product formation of pre-catalysts; (11) characterization data, 1H and 13C NMR spectra; (12) observation of the proposed intermediate D3-N-3F; (13) energies and Cartesian coordinates. See DOI: 10.1039/c6sc04145k Click here for additional data file.
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ورودعنوان ژورنال:
- Chemical science
دوره 8 2 شماره
صفحات -
تاریخ انتشار 2017