From Divalent to Pentavalent Iron Imido Complexes and an Fe(V) Nitride via N-C Bond Cleavage

Keilwerth M, Mao W, Jannuzzi SAV, Grunwald L, Heinemann FW, Scheurer A, Sutter J, Debeer S, Munz D, Meyer K (2022)

Publication Type: Journal article

Publication year: 2022


DOI: 10.1021/jacs.2c09072


As key intermediates in metal-catalyzed nitrogen-transfer chemistry, terminal imido complexes of iron have attracted significant attention for a long time. In search of versatile model compounds, the recently developed second-generation N-anchored tris-NHC chelating ligand tris-[2-(3-mesityl-imidazole-2-ylidene)-methyl]amine (TIMMNMes) was utilized to synthesize and compare two series of mid- to high-valent iron alkyl imido complexes, including a reactive Fe(V) adamantyl imido intermediate en route to an isolable Fe(V) nitrido complex. The chemistry toward the iron adamantyl imides was achieved by reacting the Fe(I) precursor [(TIMMNMes)Fe-I(N-2)]+ (1) with 1-adamantyl azide to yield the corresponding trivalent iron imide. Stepwise chemical reduction and oxidation lead to the isostructural series of low-spin [(TIMMNMes)Fe-(NAd)](0,1+,2+,3+) (2(Ad)-5(Ad)) in oxidation states II to V. The Fe(V) imide [(TIMMNMes)Fe(NAd)](3+) (5(Ad)) is unstable under ambient conditions and converts to the air-stable nitride [(TIMMNMes)Fe-V(N)](2+) (6) via N-C bond cleavage. The stability of the pentavalent imide can be increased by derivatizing the nitride [(TIMMNMes)Fe-IV(N)]+ (7) with an ethyl group using the triethyloxonium salt Et3OPF6. This gives access to the analogous series of ethyl imides [(TIMMNMes)Fe(NEt)](0,1+,2+,3+) (2(Et)-5(Et)), including the stable Fe(V) ethyl imide. Iron imido complexes exist in a manifold of different electronic structures, ultimately controlling their diverse reactivities. Accordingly, these complexes were characterized by single-crystal X-ray diffraction analyses, SQUID magnetization, and electrochemical methods, as well as Fe-57 Mossbauer, IR vibrational, UV/vis electronic absorption, multinuclear NMR, X-band EPR, and X-ray absorption spectroscopy. Our studies are complemented with quantum chemical calculations, thus providing further insight into the electronic structures of all complexes.

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Keilwerth, M., Mao, W., Jannuzzi, S.A.V., Grunwald, L., Heinemann, F.W., Scheurer, A.,... Meyer, K. (2022). From Divalent to Pentavalent Iron Imido Complexes and an Fe(V) Nitride via N-C Bond Cleavage. Journal of the American Chemical Society.


Keilwerth, Martin, et al. "From Divalent to Pentavalent Iron Imido Complexes and an Fe(V) Nitride via N-C Bond Cleavage." Journal of the American Chemical Society (2022).

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