Coligand role in the NHC nickel catalyzed C–F bond activation: investigations on the insertion of bis(NHC) nickel into the C–F bond of hexafluorobenzene |
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| Authors: | Maximilian W Kuntze-Fechner Hendrik Verplancke Lukas Tendera Martin Diefenbach Ivo Krummenacher Holger Braunschweig Todd B Marder Max C Holthausen Udo Radius |
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| Institution: | Institute for Inorganic Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg Germany.; Institute for Inorganic and Analytical Chemistry, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt Germany.; Institute for Sustainable Chemistry & Catalysis with Boron, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg Germany |
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| Abstract: | The reaction of Ni(Mes2Im)2] (1) (Mes2Im = 1,3-dimesityl-imidazolin-2-ylidene) with polyfluorinated arenes as well as mechanistic investigations concerning the insertion of 1 and Ni(iPr2Im)2] (1ipr) (iPr2Im = 1,3-diisopropyl-imidazolin-2-ylidene) into the C–F bond of C6F6 is reported. The reaction of 1 with different fluoroaromatics leads to formation of the nickel fluoroaryl fluoride complexes trans-Ni(Mes2Im)2(F)(ArF)] (ArF = 4-CF3-C6F42, C6F53, 2,3,5,6-C6F4N 4, 2,3,5,6-C6F4H 5, 2,3,5-C6F3H26, 3,5-C6F2H37) in fair to good yields with the exception of the formation of the pentafluorophenyl complex 3 (less than 20%). Radical species and other diamagnetic side products were detected for the reaction of 1 with C6F6, in line with a radical pathway for the C–F bond activation step using 1. The difluoride complex trans-Ni(Mes2Im)2(F)2] (9), the bis(aryl) complex trans-Ni(Mes2Im)2(C6F5)2] (15), the structurally characterized nickel(i) complex trans-NiI(Mes2Im)2(C6F5)] (11) and the metal radical trans-NiI(Mes2Im)2(F)] (12) were identified. Complex 11, and related NiI(Mes2Im)2(2,3,5,6-C6F4H)] (13) and NiI(Mes2Im)2(2,3,5-C6F3H2)] (14), were synthesized independently by reaction of trans-Ni(Mes2Im)2(F)(ArF)] with PhSiH3. Simple electron transfer from 1 to C6F6 was excluded, as the redox potentials of the reaction partners do not match and Ni(Mes2Im)2]+, which was prepared independently, was not detected. DFT calculations were performed on the insertion of Ni(iPr2Im)2] (1ipr) and Ni(Mes2Im)2] (1) into the C–F bond of C6F6. For 1ipr, concerted and NHC-assisted pathways were identified as having the lowest kinetic barriers, whereas for 1, a radical mechanism with fluoride abstraction and an NHC-assisted pathway are both associated with almost the same kinetic barrier.A combined experimental and theoretical study on the mechanism of the C–F bond activation of C6F6 with Ni(NHC)2] is provided. |
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