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Computational and Experimental Investigations of the Fe₂(μ-S₂)/Fe₂(μ-S)₂ Equilibrium.

ABSTRACT: Density functional theory (DFT) calculations on Fe₂S₂(CO)_6-2n(PMe₃)_2n for n = 0, 1, and 2 reveal that the most electron-rich derivatives (n = 2) exist as diferrous disulfides lacking an S-S bond. The thermal interconversion of the Fe^II₂(S)₂ and Fe^I₂(S₂) valence isomers is symmetry-forbidden. Related electron-rich diiron complexes [Fe₂S₂(CN)₂(CO)₄]^2- of an uncertain structure are implicated in the biosynthesis of [FeFe]-hydrogenases. Several efforts to synthesize electron-rich derivatives of Fe₂(μ-S₂)(CO)₆ (1) are described. First, salts of iron persulfido cyanides [Fe₂(μ-S₂)(CO)₅(CN)]^- and [Fe₂(μ-S₂)(CN)(CO)₄(PPh₃)]^- were prepared by the reactions of NaN(tms)₂ with 1 and Fe₂(μ-S₂)(CO)₅(PPh₃), respectively. Alternative approaches to electron-rich diiron disulfides targeted Fe₂(μ-S₂)(CO)₄(diphosphine). Whereas the preparation of Fe₂(μ-S₂)(CO)₄(dppbz) was straightforward, that of Fe₂(μ-S₂)(CO)₄(dppv) required an indirect route involving the oxidation of Fe₂(μ-SH)₂(CO)₄(dppv) (dppbz = C₆H₄-1,2-(PPh₂)₂, dppv = cis-C₂H₂(PPh₂)₂). DFT calculations indicate that the oxidation of Fe₂(μ-SH)₂(CO)₄(dppv) produces singlet diferrous disulfide Fe₂(μ-S)₂(CO)₄(dppv), which is sufficiently long-lived as to be trapped by ethylene. The reaction of 1 and dppv mainly afforded Fe₂(μ-SCH=CHPPh₂)(μ-SPPh₂)(CO)₅, implicating a S-centered reaction.

SUBMITTER: Arrigoni F

PROVIDER: S-EPMC8100967 | biostudies-literature | 2021 Mar

REPOSITORIES: biostudies-literature

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Computational and Experimental Investigations of the Fe2(μ-S2)/Fe2(μ-S)2 Equilibrium.

Arrigoni Federica F Zampella Giuseppe G Zhang Fanjun F Kagalwala Husain N HN Li Qian-Li QL Woods Toby J TJ Rauchfuss Thomas B TB

Inorganic chemistry 20210302 6

Density functional theory (DFT) calculations on Fe2S2(CO)6-2n(PMe3)2n for n = 0, 1, and 2 reveal that the most electron-rich derivatives (n = 2) exist as diferrous disulfides lacking an S-S bond. The thermal interconversion of the FeII2(S)2 and FeI2(S2) valence isomers is symmetry-forbidden. Related electron-rich diiron complexes [Fe2S<su ...[more]

PMID: 33650855

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Project description:The mixed-valence triiron complexes [Fe3(CO)7-x (PPh3) x (μ-edt)2] (x = 0-2; edt = SCH2CH2S) and [Fe3(CO)5(κ2-diphosphine)(μ-edt)2] (diphosphine = dppv, dppe, dppb, dppn) have been prepared and structurally characterized. All adopt an anti arrangement of the dithiolate bridges, and PPh3 substitution occurs at the apical positions of the outer iron atoms, while the diphosphine complexes exist only in the dibasal form in both the solid state and solution. The carbonyl on the central iron atom is semibridging, and this leads to a rotated structure between the bridged diiron center. IR studies reveal that all complexes are inert to protonation by HBF4·Et2O, but addition of acid to the pentacarbonyl complexes results in one-electron oxidation to yield the moderately stable cations [Fe3(CO)5(PPh3)2(μ-edt)2]+ and [Fe3(CO)5(κ2-diphosphine)(μ-edt)2]+, species which also result upon oxidation by [Cp2Fe][PF6]. The electrochemistry of the formally Fe(I)-Fe(II)-Fe(I) complexes has been investigated. Each undergoes a quasi-reversible oxidation, the potential of which is sensitive to phosphine substitution, generally occurring between 0.15 and 0.50 V, although [Fe3(CO)5(PPh3)2(μ-edt)2] is oxidized at -0.05 V. Reduction of all complexes is irreversible and is again sensitive to phosphine substitution, varying between -1.47 V for [Fe3(CO)7(μ-edt)2] and around -1.7 V for phosphine-substituted complexes. In their one-electron-reduced states, all complexes are catalysts for the reduction of protons to hydrogen, the catalytic overpotential being increased upon successive phosphine substitution. In comparison to the diiron complex [Fe2(CO)6(μ-edt)], [Fe3(CO)7(μ-edt)2] catalyzes proton reduction at 0.36 V less negative potentials. Electronic structure calculations have been carried out in order to fully elucidate the nature of the oxidation and reduction processes. In all complexes, the HOMO comprises an iron-iron bonding orbital localized between the two iron atoms not ligated by the semibridging carbonyl, while the LUMO is highly delocalized in nature and is antibonding between both pairs of iron atoms but also contains an antibonding dithiolate interaction.

Dataset Information

Computational and Experimental Investigations of the Fe₂(μ-S₂)/Fe₂(μ-S)₂ Equilibrium.

Publications

Computational and Experimental Investigations of the Fe<sub>2</sub>(μ-S<sub>2</sub>)/Fe<sub>2</sub>(μ-S)<sub>2</sub> Equilibrium.

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