The Reactivity Patterns of Low-Coordinate Iron−Hydride Complexes

Abstract

Abstract:We report a survey of the reactivity of the first isolable iron-hydride complexes with a coordination number less than 5. The high-spin iron(II) complexes [( -diketiminate)Fe(µ-H)] 2 react rapidly with representative cyanide, isocyanide, alkyne, N 2, alkene, diazene, azide, CO2, carbodiimide, and Brønsted acid containing substrates. The reaction outcomes fall into three categories: (1) addition of Fe-H across a multiple bond of the substrate, (2) reductive elimination of H 2 to form iron(I) products, and (3) protonation of the hydride to form iron(II) products. The products include imide, isocyanide, vinyl, alkyl, azide, triazenido, benzo[c]cinnoline, amidinate, formate, and hydroxo complexes. These results expand the range of known bond transformations at iron complexes. Additionally, they give insight into the elementary transformations that may be possible at the iron-molybdenum cofactor of nitrogenases, which may have hydride ligands on high-spin, low-coordinate metal atoms.

Effects of Ligand Halogenation on the Electron Localization, Geometry and Spin State of Low‐Coordinate (β‐Diketiminato)iron Complexes

“…The doublet spin states of each complex optimized to a pseudo‐square‐planar geometry. This is consistent with the square‐planar [L Me, i Pr Fe(CN t Bu) 2 ] having a doublet spin state as determined by EPR spectroscopy . The quartet spin states of each complex optimized to a tetrahedral geometry consistent with the S = 3/2 spin state of 8 , supporting the magnetic susceptibility results shown above and indicating that 8 indeed has an S = 3/2 ground state.…”

Effects of Ligand Halogenation on the Electron Localization, Geometry and Spin State of Low‐Coordinate (β‐Diketiminato)iron Complexes

“…The doublet spin states of each complex optimized to a pseudo‐square‐planar geometry. This is consistent with the square‐planar [L Me, i Pr Fe(CN t Bu) 2 ] having a doublet spin state as determined by EPR spectroscopy . The quartet spin states of each complex optimized to a tetrahedral geometry consistent with the S = 3/2 spin state of 8 , supporting the magnetic susceptibility results shown above and indicating that 8 indeed has an S = 3/2 ground state.…”

Electronic Structure of Four-Coordinate Iron(I) Complex Supported by a Bis(phosphaethenyl)pyridine Ligand

“…The magnetic moment of 2 ranged from 3.5 to 4.2 μ B at 5−300 K, demonstrating an S = 3/2 ground state. The Mössbauer isomer shift of δ = 0.59 mm/s (Δ E Q = 2.68 mm/s) was clearly smaller than that of 1 and relatively closer to the values hitherto reported for four-coordinate Fe(I) complexes with high-spin states (0.41−0.46 mm/s). , Actually, the observed isomer shift was consistent with the calculated value for a model compound of 2 with a high-spin Fe(I) center (0.64 mm/s, vide infra).…”

Isolation of chloride- and hydride-bridged tri-iron and -zinc clusters in a tris(β-oxo-δ-diimine) cyclophane ligand

“…Unlike the reported result for monometallic βdiketiminatoiron(II) complexes, we do not observe transmetalation and adventitious formation of iron-alkyl species. 17,45 A total of ten resonances are observed in 1 H-NMR spectra of 3, consistent with the expected retention of C 3v molecular symmetry ( Figure S12).…”

Effects of Ligand Halogenation on the Electron Localization, Geometry and Spin State of Low‐Coordinate (β‐Diketiminato)iron Complexes

“…The doublet spin states of each complex optimized to a pseudo‐square‐planar geometry. This is consistent with the square‐planar [L Me, i Pr Fe(CN t Bu) 2 ] having a doublet spin state as determined by EPR spectroscopy . The quartet spin states of each complex optimized to a tetrahedral geometry consistent with the S = 3/2 spin state of 8 , supporting the magnetic susceptibility results shown above and indicating that 8 indeed has an S = 3/2 ground state.…”

Electronic Structure of Four-Coordinate Iron(I) Complex Supported by a Bis(phosphaethenyl)pyridine Ligand

“…The magnetic moment of 2 ranged from 3.5 to 4.2 μ B at 5−300 K, demonstrating an S = 3/2 ground state. The Mössbauer isomer shift of δ = 0.59 mm/s (Δ E Q = 2.68 mm/s) was clearly smaller than that of 1 and relatively closer to the values hitherto reported for four-coordinate Fe(I) complexes with high-spin states (0.41−0.46 mm/s). , Actually, the observed isomer shift was consistent with the calculated value for a model compound of 2 with a high-spin Fe(I) center (0.64 mm/s, vide infra).…”

Isolation of chloride- and hydride-bridged tri-iron and -zinc clusters in a tris(β-oxo-δ-diimine) cyclophane ligand

“…Unlike the reported result for monometallic βdiketiminatoiron(II) complexes, we do not observe transmetalation and adventitious formation of iron-alkyl species. 17,45 A total of ten resonances are observed in 1 H-NMR spectra of 3, consistent with the expected retention of C 3v molecular symmetry ( Figure S12).…”

Effects of Ligand Halogenation on the Electron Localization, Geometry and Spin State of Low‐Coordinate (β‐Diketiminato)iron Complexes

“…The doublet spin states of each complex optimized to a pseudo‐square‐planar geometry. This is consistent with the square‐planar [L Me, i Pr Fe(CN t Bu) 2 ] having a doublet spin state as determined by EPR spectroscopy . The quartet spin states of each complex optimized to a tetrahedral geometry consistent with the S = 3/2 spin state of 8 , supporting the magnetic susceptibility results shown above and indicating that 8 indeed has an S = 3/2 ground state.…”

Electronic Structure of Four-Coordinate Iron(I) Complex Supported by a Bis(phosphaethenyl)pyridine Ligand

“…The magnetic moment of 2 ranged from 3.5 to 4.2 μ B at 5−300 K, demonstrating an S = 3/2 ground state. The Mössbauer isomer shift of δ = 0.59 mm/s (Δ E Q = 2.68 mm/s) was clearly smaller than that of 1 and relatively closer to the values hitherto reported for four-coordinate Fe(I) complexes with high-spin states (0.41−0.46 mm/s). , Actually, the observed isomer shift was consistent with the calculated value for a model compound of 2 with a high-spin Fe(I) center (0.64 mm/s, vide infra).…”

Isolation of chloride- and hydride-bridged tri-iron and -zinc clusters in a tris(β-oxo-δ-diimine) cyclophane ligand

“…Unlike the reported result for monometallic βdiketiminatoiron(II) complexes, we do not observe transmetalation and adventitious formation of iron-alkyl species. 17,45 A total of ten resonances are observed in 1 H-NMR spectra of 3, consistent with the expected retention of C 3v molecular symmetry ( Figure S12).…”