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Divergent Reactivity of Azides and Diazoalkanes Toward Ferrous Complexes and Isolation of a FeIII Carbene Radical Complex

Zars E, Pick L, Kankanamge A, Gau MR, Carroll PJ, MacMillan SN, Lancaster KM, Meyer K, Mindiola DJ (2025)

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Publication Type: Journal article

Publication year: 2025

Journal

DOI: 10.1021/acs.organomet.4c00471

Abstract

Treatment of [(^tBupyrr2pyr)Fe(OEt2)] (1-OEt2) (^tBupyrr2pyr^2- = 3,5-^tBu2-bis(pyrrolyl)pyridine) with trimethylsilyl azide (N3SiMe3) and subsequent photolysis at 390 nm results in clean formation of [(^tBupyrrpyrpyrrNHSiMe3)Fe] (2) as the result of a nitrene being inserted into a tert-butyl C-H bond of the ^tBupyrr2pyr ligand. Treatment of 1-OEt2 with azidotrimethyltin (N3SnMe3), however, results in isolation of the γ-bound azide adduct ferrous complex, [(^tBupyrr2pyr)Fe(N3SnMe3)] (1-N3SnMe3). When treated with diphenyl diazomethane (Ph2CN2), complex 1-OEt2 converts to the iron carbene complex [(^tBupyrr2pyr)FeCPh2] (1-CPh2), and the X-ray structure revealed a Fe-CPh2 bond length of 1.964(3) Å. A room temperature magnetic moment of 1-CPh2 indicates an S = 2 spin state, consistent with a high-spin Fe^III center antiferromagnetically coupled to a carbene radical anion (CPh2^•-). Zero-field ⁵⁷Fe Mössbauer spectroscopy and Fe K-edge X-ray absorption spectroscopy confirm this assignment. In solution, complex 1-CPh2 rearranges to [{^tBupyrrpyrC(═CPh2)-C(CMe3)═CH-C(CMe3)═N}Fe]2 (3) resulting from carbene insertion into the 1-position of the pyrrolide arm of the ^tBupyrr2pyr ligand and dimerization. Complex 3 possesses two high-spin Fe^II centers according to ⁵⁷Fe Mössbauer spectroscopy, with antiferromagnetic coupling between the spin centers. Monitoring the conversion of 1-CPh2 to 3 by UV-vis spectroscopy reveals this process to be first order in 1-CPh2 with a highly ordered transition state evidenced by activation parameters: ΔS^‡ = −87.6 ± 25.8 J·mol^-1·K^-1 and ΔH^‡ = 63.1 ± 8.3 kJ·mol^-1.

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APA:

Zars, E., Pick, L., Kankanamge, A., Gau, M.R., Carroll, P.J., MacMillan, S.N.,... Mindiola, D.J. (2025). Divergent Reactivity of Azides and Diazoalkanes Toward Ferrous Complexes and Isolation of a FeIII Carbene Radical Complex. Organometallics. https://doi.org/10.1021/acs.organomet.4c00471

MLA:

Zars, Ethan, et al. "Divergent Reactivity of Azides and Diazoalkanes Toward Ferrous Complexes and Isolation of a FeIII Carbene Radical Complex." Organometallics (2025).

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