Between imide, imidyl and nitrene – an imido iron complex in two oxidation states

Reith, Sascha; Demeshko, Serhiy; Battistella, Beatrice; Reckziegel, Alexander; Schneider, Christian; Stoy, Andreas; Lichtenberg, Crispin; Meyer, Franc; Munz, Dominik; Werncke, C. Gunnar

doi:10.1039/d2sc01088g

Cited by 23 publications

(44 citation statements)

References 69 publications

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“…Overall, the Fe-N interactions are reminiscent of imido complexes where a formally iron(IV) complex was described as an iron(III) complex with a nitrenyl radical. [38][39][40][41][42][43][44][45][46][47][48] The amount of radical character on the N is similar to that in tris(phosphino)borane-supported FeNNMe2 complexes studied in detail by Peters. 31 However, in 5a we emphasize that the N radical is not the dominant configuration; rather, 5a can still be viewed as a formally iron(IV) complex with substantial covalency and an iron-nitrogen triple bond, as shown by the presence of two unoccupied orbitals with Fe-N p* character.…”

Section: Mechanistic Evaluation Using Computationssupporting

confidence: 66%

Mechanism of Nitrogen-Carbon Bond Formation From Iron(IV) Disilylhydrazido Intermediates During N2 Reduction

Bhutto

Hooper

Mercado

et al. 2022

Preprint

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We recently reported a reaction sequence that activates C–H bonds in simple arenes as well as the N–N triple bond in N2, delivering the aryl group to N2 to form a new N–C bond. This enables the transformation of abundant feedstocks (arenes and N2) into N-containing organic compounds. The key N–C bond forming step occurs upon partial silylation of N2, which then can accept the aryl fragment. However, the pathway through which reduction, silylation, and migration occurred was unknown. Here we describe synthetic, structural, magnetic, spectroscopic, kinetic, and computational studies that elucidate the steps of this transformation. N2 must be silylated twice at the distal N atom before aryl migration can occur, and sequential silyl radical and silyl cation addition is a kinetically competent pathway to a formally iron(IV) intermediate with an NN(SiMe3)2 ligand. It can be isolated at low temperature. Kinetic studies show its first-order conversion to the migrated product, and DFT calculations indicate a concerted transition state for migration. The electronic structure of the formally iron(IV) intermediate is examined using DFT and CASSCF calculations, which reveal contributions from iron(II) and iron(III) resonance forms with oxidized NNSi2 ligands. The depletion of electron density from the Fe-coordinated N atom makes it electrophilic enough to accept the incoming aryl group. This unprecedented pathway for N–C bond formation offers a method for functionalizing N2 with organometallic chemistry.

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Section: Mechanistic Evaluation Using Computationssupporting

confidence: 66%

Mechanism of Nitrogen-Carbon Bond Formation From Iron(IV) Disilylhydrazido Intermediates During N2 Reduction

Bhutto

Hooper

Mercado

et al. 2022

Preprint

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“…A high-spin three-coordinate Fe imidyl complex 2 was isolated and characterized. 71 Combined magnetic, spectroscopic, and computational (DFT, CASSCF, and CASCI) studies showed that 2 is an S = 2 Fe( iii ) imidyl complex, with an S = 5/2 ground state on Fe that is antiferromagnetically coupled to the imidyl radical on N. The reaction of 1 with AdN 3 afforded the intramolecular C–H amination product 3 , whereas the corresponding Fe imidyl intermediate ( 3′ ) could not be isolated. Quantum mechanical calculations shed light on the divergent reactivity and stability of 2 and 3′ .…”

Section: Discussionmentioning

confidence: 99%

Stabilization of a high-spin three-coordinate Fe(iii) imidyl complex by radical delocalization

Yang¹,

Yu²,

Hsieh³

et al. 2022

Chem. Sci.

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“…Similarly, Fe(II,III) imido complexes have been synthesized by coordinating organic azides at low-valent iron precursors with concomitant release of N 2 . 41−43 Since then, several imido complexes with Fe(II,III) [8][9][10][11][12][13]44 �and fewer with Fe(IV) 2,45,46 �centers have been reported. In contrast, iron imido complexes in oxidation states +V and +VI remain exceedingly rare.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Accordingly, strong σ-donor ligands, such as carbenes, phosphines, and guanidinates, in trigonal, custom-tailored coordination environments have been used to stabilize this class of compounds. ,− Employing these ligands, mononuclear, terminal Fe(IV) ,− and Fe(V) − nitrido complexes have been accessed via dinitrogen fixation or azide photolysis. Similarly, Fe(II,III) imido complexes have been synthesized by coordinating organic azides at low-valent iron precursors with concomitant release of N 2 . − Since then, several imido complexes with Fe(II,III) − , and fewer with Fe(IV) ,, centers have been reported. In contrast, iron imido complexes in oxidation states +V and +VI remain exceedingly rare.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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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)FeI(N2)]+ (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)FeV(N)]2+ (6) via N–C bond cleavage. The stability of the pentavalent imide can be increased by derivatizing the nitride [(TIMMNMes)FeIV(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 57Fe Mössbauer, 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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Between imide, imidyl and nitrene – an imido iron complex in two oxidation states

Abstract: A pair of trigonal imido iron complexes ([Fe(NMes)L2]0,−) in two oxidation states is reported. The anionic complex K{crypt.222}[Fe(NMes)L2] is best described as an iron(ii) imide.

Cited by 23 publications

References 69 publications

Mechanism of Nitrogen-Carbon Bond Formation From Iron(IV) Disilylhydrazido Intermediates During N2 Reduction

Mechanism of Nitrogen-Carbon Bond Formation From Iron(IV) Disilylhydrazido Intermediates During N2 Reduction

Stabilization of a high-spin three-coordinate Fe(iii) imidyl complex by radical delocalization

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

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