Opening up the Valence Shell: A T‐Shaped Iron(I) Metalloradical and Its Potential for Atom Abstraction

Ott, Jonas; Wadepohl, Hubert; Gade, Lutz H.

doi:10.1002/anie.202003118

Cited by 31 publications

(55 citation statements)

References 46 publications

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“…5 Our group has recently described the synthesis of a T-shaped iron(I) compound (1) bearing a carbazole-based PNP pincer-type ligand 6 and a first study probing its reactivity. 7 A notable feature is the relative inertness of complex 1 toward coordination of simple σ-donor ligands such as ethers and alkylamines. This apparent inertness is a consequence of the shielding of the Kohn−Sham LUMO, which is orientated orthogonally to the FeNP 2 -plane, by the bulky tert-butyl substituents at the phosphorus atoms.…”

Section: ■ Introductionmentioning

confidence: 99%

Metalloradical Reactivity, Charge Transfer, and Atom Abstractions in a T-Shaped Iron(I) Complex

2021

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A study of the reactivity of a T-shaped iron(I) complex supported by a carbazole-based PNP pincer ligand (1) has established its strongly reducing character and propensity to bind small molecules with concomitant transfer of charge and spin density. Metalloradical reactivity was observed in the reaction with the stable radical 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) yielding the corresponding Fe II hydroxylaminato complex 2. Complex 1 reacted rapidly and selectively with two molecules of carbon monoxide to give the corresponding low-spin dicarbonyl complex 3. When reacted with phenylacetylene, the alkyne complex 4 was isolated in which the alkyne was found to bind side-on as an η 2 -ligand, which adopts radical anion character as a result of charge transfer from the metal center. Reaction with diphenyl diazomethane generated an adduct 5 in which the diazoalkane also appears to be partially reduced and acquires radical character. Upon exposure to carbon dioxide, oxygen atom abstraction was observed, ultimately leading to the isolation of the monocarbonyl iron(I) complex 6 and a dinuclear carboxylato ferrous complex 7. Furthermore, reaction with chalcogen atom transfer reagents resulted in the formation of the corresponding dinuclear ferrous chalcogenido compounds (E = S (8), Se (9)), which were found to display strong antiferromagnetic coupling (8,

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Section: ■ Introductionmentioning

confidence: 99%

Metalloradical Reactivity, Charge Transfer, and Atom Abstractions in a T-Shaped Iron(I) Complex

2021

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“…However, especially in the activation of small molecules, these compounds are promising research objects. In contrast to PNP pincer chemistry of iron, − cobalt, ,− and manganese, , chromium compounds of this class of spectator ligand are basically limited to the examples provided by the Fryzuk group. − …”

Section: Introductionmentioning

confidence: 99%

Single or Paired? Structure and Reactivity of PNP-Chromium(II) Hydrides

et al. 2020

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The preparation and reactivity of a range of novel paramagnetic chromium(II) complexes supported by a carbazole-based PNP pincer ligand is reported. Deprotonation of the ligand precursors R(PNP)H (1 R ) and subsequent reaction with chromium(II) chloride led to the formation of square-planar chlorido complexes R(PNP)CrCl (2 R ). Further reaction with various alkylating agents resulted in the isolation of chromium alkyl complexes R(PNP)CrR′ (3 R -R′) which were then hydrogenated to yield two rare examples of paramagnetic chromium(II) hydrides 4 i Pr and 4 t Bu . Both compounds were characterized by X-ray diffraction and paramagnetic NMR spectroscopy supported by a comprehensive DFT-supported assignment of the resonances. While the di(tert-butyl)phosphino PNP substituted complex 4 t Bu was found to exhibit a monomeric square-planar molecular structure, its isopropyl-substituted analog 4 i Pr forms a dimer, also indicated by a strong antiferromagnetic coupling of the chromium centers. The pronounced reactivity of these compounds toward CX double bonds was demonstrated by reaction with benzophenone, N,N′-dicyclohexylcarbodiimide, and carbon dioxide, which gave the corresponding insertion products. The alkoxido complex 5 i Pr , the amidinato complex 6 i Pr , and the formato compound 7 t Bu were also characterized by X-ray diffraction.

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“…[ 3 , 4 ] At the same time, there is a growing interest in the detection and analysis of paramagnetic intermediates in catalytic reaction cycles, particularly for the first‐row transition metals, where the reactive molecular fragments tend to be either directly bonded, or otherwise in close proximity to the metal. [ 5 , 6 , 7 , 8 , 9 , 10 , 11 ] Other areas of current interest are single‐molecule magnets (SMMs),[ 12 , 13 , 14 , 15 ] contrast agents in magnetic resonance imaging (MRI),[ 16 , 17 , 18 ] and pseudocontact shift (PCS) probes in structural biology. [ 19 , 20 , 21 , 22 ] Several recent studies used magneto‐structural correlations derived by multireference ab initio methods to refine chemical structures using paramagnetic NMR shifts.…”

Section: Introductionmentioning

confidence: 99%

Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts

et al. 2021

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We report an experimental observation of 31 P NMR resonances shifted by over 10 000 ppm (meaning percent range, and a new record for solutions), and similar 1 H chemical shifts, in an intermediate-spin square planar ferrous complex [ tBu (PNP)Fe-H], where PNP is a carbazole-based pincer ligand. Using a combination of electronic structure theory, nuclear magnetic resonance, magnetometry, and terahertz electron paramagnetic resonance, the influence of magnetic anisotropy and zero-field splitting on the paramagnetic shift and relaxation enhancement is investigated. Detailed spin dynamics simulations indicate that, even with relatively slow electron spin relaxation (T 1 % 10 À11 s), it remains possible to observe NMR signals of directly metal-bonded atoms because pronounced rhombicity in the electron zero-field splitting reduces nuclear paramagnetic relaxation enhancement.

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Opening up the Valence Shell: A T‐Shaped Iron(I) Metalloradical and Its Potential for Atom Abstraction

Cited by 31 publications

References 46 publications

Metalloradical Reactivity, Charge Transfer, and Atom Abstractions in a T-Shaped Iron(I) Complex

Metalloradical Reactivity, Charge Transfer, and Atom Abstractions in a T-Shaped Iron(I) Complex

Single or Paired? Structure and Reactivity of PNP-Chromium(II) Hydrides

Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts

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