New nitrosyl derivatives of diiron dithiolates related to the active site of the [FeFe]-hydrogenases

Article abstract of DOI:10.1021/ic801542w

Nitrosyl derivatives of diiron dithiolato carbonyls have been prepared starting from the precursor Fe₂(S₂C_nH _2n)(dppv)(CO)₄ (dppv = cis-1,2- bis(diphenylphosphinoethylene). These studies expand the range of substituted diiron(I) dithiolato carbonyl complexes. From [Fe₂(S ₂C₂H₄)(CO)₃(dppv)(NO)]BF ₄ ([1(CO)₃]BF₄), the following compounds were prepared: [1(CO)₂(PMe₃)]BF₄, [1(CO)(dppv)]BF₄, NEt₄[1(CO)(CN)₂], and 1(CO)(CN)(PMe₃). Some of these substitution reactions occur via the addition of 2 equiv of the nucleophile followed by the dissociation of one nucleophile and decarbonylation. Such a double adduct was characterized crystallographically in the case of [Fe₂(S₂C ₂H₄)(CO)₃(dppv)(NO)(PMe₃) ₂]BF₄. This result shows that the addition of two ligands causes scission of the Fe-Fe bond and one Fe-S bond. When cyanide is the nucleophile, nitrosyl migrates away from the Fe(dppv) site, yielding a Fe(CN)₂(NO) derivative. Compounds [1(CO)₃]BF₄, [1(CO)₂(PMe₃)]BF₄, and [1(CO)(dppv)]BF ₄ were also prepared by the addition of NO⁺ to the di-, tri-, and tetrasubstituted precursors. In these cases, the NO⁺ appears to form an initial 36e^- adduct containing terminal Fe-NO, followed by decarbonylation. Several complexes were prepared by the addition of NO to the mixed-valence Fe(I)Fe(II) derivatives. The diiron nitrosyl complexes reduce at mild potentials and in certain cases form weak adducts with CO. IR and EPR spectra of 1(CO)(dppv), generated by low-temperature reduction of [1(CO)(dppv)]BF₄ with Co(C₅Me₅)₂, indicates that the SOMO is located on the FeNO subunit.