Issue 33, 2021

C–F bond activation of perfluorinated arenes using NHC-stabilized cobalt half-sandwich complexes

Abstract

A study on the reactivity of NHC cobalt half-sandwich complexes [(η5-C5R15)Co(R22Im)(η2-C2H4)] (R1 = H; R2 = Me 1, iPr 2) and [(η5-C5R15)Co(R22Im)(η2-C2H3{SiMe3})] (R1 = H, R2 = Me 3, iPr 4; R1 = Me, R2 = Me 5, iPr 6) towards selected perfluoroarenes is presented (R2Im = 1,3-di(organyl)-imidazolin-2-ylidene). The reaction with hexafluorobenzene, perfluorotoluene and decafluorobiphenyl at 100 °C led to the isolation of the cobalt(II) complexes [CpCo(iPr2Im)(C6F5)] 7, [CpCo(iPr2Im)(C7F7)] 8, [CpCo(iPr2Im)(C12F9)] 9, [Cp*Co(iPr2Im)(C6F5)] 10, [Cp*Co(iPr2Im)(C7F7)] 11 and [Cp*Co(iPr2Im)(C12F9)] 12 (Cp* = η5-C5{CH3}5), Cp = η5-C5H5). The cobalt(II) fluoride [CpCo(iPr2Im)(F)] was detected as a side product of these reactions. The reaction of [CpCo(R22Im)(η2-C2H4)] (R2 = Me 1, iPr 2) with C6F6 and C7F8 at 60 °C afforded the dinuclear complexes [{CpCo(R22Im)}2(μ-η22-C6F6)] (R2 = Me 13, iPr 14) and [{CpCo(R22Im)}2(μ-η22-C7F8)] (R2 = Me 15, iPr 16). Furthermore, the dinuclear complexes [{CpCo(Me2Im)}2(μ-η22-C10F8)] 17, [{CpCo(iPr2Im)}2(μ-η22-C10F8)] 18 and mononuclear [CpCo(iPr2Im)(η2-C10F8)] 19 were isolated from the reaction of 1 and 2 with octafluoronaphthalene at room temperature. Based on the experimental data a mechanism is proposed for the C–F bond activation of perfluoroarenes with complexes [Cp(*)Co(NHC)(olefin)]. Transfer of [Cp(*)Co(NHC)] to the perfluoroarene, which is limited by the activation barrier to replace the alkene ligand, affords mononuclear cobalt complexes [Cp(*)Co(NHC)(η2-ArF)]. Ligand dismutation at higher temperatures leads to dinuclear complexes [{Cp(*)Co(NHC)}2(μ-η22-ArF)], which are precursors for the formation of the cobalt(II) complexes [Cp(*)Co(NHC)(ArF)] and [Cp(*)Co(NHC)(F)]. One electron oxidative addition prevails in the C–F bond activation step using these cobalt half-sandwich complexes.

Graphical abstract: C–F bond activation of perfluorinated arenes using NHC-stabilized cobalt half-sandwich complexes

Supplementary files

Article information

Article type
Paper
Submitted
17 des 2020
Accepted
12 jan 2021
First published
21 jan 2021

New J. Chem., 2021,45, 14999-15016

C–F bond activation of perfluorinated arenes using NHC-stabilized cobalt half-sandwich complexes

D. Ertler, M. W. Kuntze-Fechner, S. Dürr, K. Lubitz and U. Radius, New J. Chem., 2021, 45, 14999 DOI: 10.1039/D0NJ06137A

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