Computational and Experimental Investigations of the Fe(μ-S)/Fe(μ-S) Equilibrium.

Density functional theory (DFT) calculations on FeS(CO)(PMe) for = 0, 1, and 2 reveal that the most electron-rich derivatives ( = 2) exist as diferrous disulfides lacking an S-S bond. The thermal interconversion of the Fe(S) and Fe(S) valence isomers is symmetry-forbidden. Related electron-rich diiron complexes [FeS(CN)(CO)] of an uncertain structure are implicated in the biosynthesis of [FeFe]-hydrogenases. Several efforts to synthesize electron-rich derivatives of Fe(μ-S)(CO) () are described. First, salts of iron persulfido cyanides [Fe(μ-S)(CO)(CN)] and [Fe(μ-S)(CN)(CO)(PPh)] were prepared by the reactions of NaN(tms) with and Fe(μ-S)(CO)(PPh), respectively. Alternative approaches to electron-rich diiron disulfides targeted Fe(μ-S)(CO)(diphosphine). Whereas the preparation of Fe(μ-S)(CO)(dppbz) was straightforward, that of Fe(μ-S)(CO)(dppv) required an indirect route involving the oxidation of Fe(μ-SH)(CO)(dppv) (dppbz = CH-1,2-(PPh), dppv = -CH(PPh)). DFT calculations indicate that the oxidation of Fe(μ-SH)(CO)(dppv) produces singlet diferrous disulfide Fe(μ-S)(CO)(dppv), which is sufficiently long-lived as to be trapped by ethylene. The reaction of and dppv mainly afforded Fe(μ-SCH=CHPPh)(μ-SPPh)(CO), implicating a S-centered reaction.