Synthesis of the Bis(iron) Carbene Complex [Cp*(dppe)FeC(OMe)CHCHC(OMe)Fe(dppe)Cp*][PF₆]₂:  A Binuclear Organometallic Compound with a Low-Spin ↔ High-Spin Interconversion

Abstract

The new diiron μ-bis(carbene) complex [Cp*(dppe)FeC(OCH3)-CHCHC−(OCH3)Fe(dppe)Cp*][PF6]2 (4) [Cp* = pentamethylcyclopentadienyl, dppe = ethylenebis(diphenylphosphine)] was obtained by double deprotonation of [Cp*(dppe)FeC(OCH3)CH2CH2C(OCH3)Fe(dppe)Cp*]·2[PF6] (2) with KOBut followed by a two-electron oxidation with 2 equiv of ferrocenium (80%). On the basis of the multinuclear NMR spectroscopy the complex 4 appeared as diamagnetic in solution. Temperature-dependent magnetic susceptibility measurements with a microcrystalline sample of 4 showed antiferromagnetic behavior. Isotropic spin-only models of the data derived magnetic exchange coupling constants of J = − 27.4 cm-1. Variable-temperature Mössbauer spectroscopy allowed the observation of both the singlet and triplet spin isomers and their interconversion. The time scale for the spin flipping is larger than 10-6 s, suggesting the existence of a thermal barrier between the two spin states.

Preparation and Characterization of the Triflate Complex [Cp*(dppe)FeOSO2CF3]: A Convenient Access to Labile Five‐ and Six‐Coordinate Iron(I) and Iron(II) Complexes

“…The Mössbauer parameters depend on several factors including the oxidation and the spin states, the atoms coordinated at the Mössbauer nucleus, and the coordination numbers , . In the present case, only the comparison of IS and QS between the iron(II) with oxygen ligands 4 , 12 , and 14 makes sense.…”

“…The line broadening (Γ) are in line with the value observed for half sandwich iron complexes, except in the case of the five‐coordinated complex 5(PF 6 ) . Probably, relaxation phenomenon due to the magnetic properties of this complex (S = 1) is at the origin of the broad lines …”

1,2-Diethynylbenzene-Bridged [Cp*(dppe)Fe]n+ Units: Effect of Steric Hindrance on the Chemical and Physical Properties

“…1.1 mm/s). 42 57 Fe Mossbauer spectroscopy is a powerful means for studying mixed-valent (MV) species in the solid state. Indeed, direct observation of the iron nuclei provides the evaluation of the electron-transfer rate between the redox-active centers of heterovalent derivatives relative to the acquisition time of the technique.…”

Magnetic perturbation of the redox potentials of localized and delocalized mixed-valence complexes

“…The detailed synthesis and the properties of these compounds have already been presented elsewhere [43][44][45][46][47][48][49][50][51][52][53][54]. The oneelectron oxidized complexes present a mixed-valence character and as monoradicals they are paramagnetic.…”