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A Two-Coordinate Iron(II) Imido Complex with NHC Ligation: Synthesis, Characterization, and Its Diversified Reactivity of Nitrene Transfer and C–H Bond Activation

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Schnegg,  Alexander
Research Department DeBeer, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Bill,  Eckhard
Research Department DeBeer, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Ye,  Shengfa
Research Group Ye, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Citation

Cheng, J., Liu, J., Leng, X., Lohmiller, T., Schnegg, A., Bill, E., et al. (2019). A Two-Coordinate Iron(II) Imido Complex with NHC Ligation: Synthesis, Characterization, and Its Diversified Reactivity of Nitrene Transfer and C–H Bond Activation. Inorganic Chemistry, 58(11), 7634-7644. doi:10.1021/acs.inorgchem.9b01147.


Cite as: http://hdl.handle.net/21.11116/0000-0004-7AA4-A
Abstract
Iron terminal imido species are typically implicated as reaction intermediates in iron-catalyzed transformations. While a large body of work has been devoted to mid- and high-valent iron imidos, to date the chemistry of iron(II) imidos has remained largely unexplored due to the difficulty in accessing them. Herein, we present a study on the two-coordinate iron(II) imido complex [(IPr)Fe(NArTrip)] (3; IPr = 1,3-bis(2′,6′-diisopropylphenyl)imidazol-2-ylidene; ArTrip = 2,6-bis(2′,4′,6′-triisopropylphenyl)phenyl) prepared from the reaction of an iron(0) complex with the bulky azide ArTripN3. Spectroscopic investigations in combination with DFT calculations established a high-spin S = 2 ground spin state for 3, consistent with its long Fe–N multiple bond of 1.715(2) Å revealed by X-ray diffraction analysis. Complex 3 exhibits unusual activity of nitrene transfer and C–H bond activation in comparison to the reported iron imido complexes. Specifically, the reactions of 3 with CH2═CHArCF3, an electron-deficient alkene, and CO, a strong π acid, readily afford nitrene transfer products, ArCF3CH═CHNHArTrip and ArTripNCO, respectively, yet no similar reaction occurs when 3 is treated with electron-rich alkenes and PMe3. Moreover, 3 is inert toward the weak C(sp3)–H bonds in 1,4-cyclohexadiene, THF, and toluene, whereas it can cleave the stronger C(sp)–H bond in p-trifluoromethylphenylacetylene to form an iron(II) amido alkynyl complex. Interestingly, intramolecular C(sp3)–H bond functionalization was observed by adding (p-Tol)2CN2 to 3. The unique reactivity of 3 is attributed to its low-coordinate nature and the high negative charge population on the imido N atom, which render its iron–imido unit nucleophilic in nature.