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

Abstract

Density functional the ory ( DFT) calculations on Fe 2 S 2 (CO) 6−2n (PMe 3 ) 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 II 2 (S) 2 and Fe I 2 (S 2 ) valence isomers is symmetry-forbidden. Related electron-rich diiron complexes [Fe 2 S 2 (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 Fe 2 (μ-S 2 )(CO) 6 (1) are described. First, salts of iron persulfido cyanides [Fe 2 (μ-S 2 )(CO) 5 (CN)] − and [Fe 2 (μ-S 2 )(CN)-(CO) 4 (PPh 3 )] − were prepared by the reactions of NaN(tms) 2 with 1 and Fe 2 (μ-S 2 )(CO) 5 (PPh 3 ), respectively. Alternative approaches to electron-rich diiron disulfides targeted Fe 2 (μ-S 2 )(CO) 4 (diphosphine). Whereas the preparation of Fe 2 (μ-S 2 )(CO) 4 (dppbz) was straightforward, that of Fe 2 (μ-S 2 )(CO) 4 (dppv) required an indirect route involving the oxidation of Fe 2 (μ-SH) 2 (CO) 4 (dppv) (dppbz = C 6 H 4 -1,2-(PPh 2 ) 2 , dppv = cis-C 2 H 2 (PPh 2 ) 2 ). DFT calculations indicate that the oxidation of Fe 2 (μ-SH) 2 (CO) 4 (dppv) produces singlet diferrous disulfide Fe 2 (μ-S) 2 (CO) 4 (dppv), which is sufficiently longlived as to be trapped by ethylene. The reaction of 1 and dppv mainly afforded Fe 2 (μ-SCH=CHPPh 2 )(μ-SPPh 2 )(CO) 5 , implicating a S-centered reaction.

Synthesis and Dynamics of Ferrous Polychalcogenides [Fe(Ex)(CN)2(CO)2]2– (E = S, Se, or Te)

“…A further incentive is our search for new platform complexes that might be useful in elucidating the biochemistry of Fe–CN–CO–S complexes, which are related to the biosynthesis of the [FeFe]-hydrogenases − as well as the artificial maturation of the [NiFe]-hydrogenases . A well-characterized Fe–S x –CO–CN complex is [Fe 2 (μ-S 2 )­(CN)­(CO) 5 ] − , which we recently prepared from Fe 2 (μ-S 2 )­(CO) 6 …”

“…11 A well-characterized Fe−S x −CO−CN complex is [Fe 2 (μ-S 2 )(CN)(CO) 5 ] − , which we recently prepared from Fe 2 (μ-S 2 )(CO) 6 . 12 This paper focuses on the oxidative addition of S−S bonds to [Fe(CN) 2 (CO) 3 ] 2− . 13 This Fe(0) precursor complex is known to be susceptible to oxidative addition, e.g., by H + and Me + .…”

Challenges in the Synthesis of Active Site Mimics for [NiFe]-Hydrogenases

“…Materials and methods used herein have recently been described . Ni­(N2S2 555 ) was prepared according to the literature method. , The crude N 2 S 2 H 2 was not distilled, but Ni­(N2S2 555 ) was purified.…”

Final Stages in the Biosynthesis of the [FeFe]‐Hydrogenase Active Site

“…The preceding experiments establish the mutual compatibility of the FmocNHCH 2 and iron(I) carbonyl groups but show that cyanide ligands must be installed before forming the S‐CH 2 NHFmoc linkages. A revised route toward [ 1 ] 2− started with the monocyanide [K(18‐crown‐6)][Fe 2 (S 2 )(CN)(CO) 5 ] [21] . This persulfide was treated with two equiv.…”

“…A revised route toward [1] 2À started with the monocyanide [K(18-crown-6)][Fe 2 (S 2 )(CN)-(CO) 5 ]. [21] This persulfide was treated with two equiv. of LiBHEt 3 , and the reduced species was alkylated with two equiv.…”