New Nitrosyl Derivatives of Diiron Dithiolates Related to the Active Site of the [FeFe]-Hydrogenases

Nitrosyl derivatives of diiron dithiolato carbonyls have been prepared starting from the precursor Fe-2(S2CnH2n)(dPPV)(CO)(4) (dppv = cis-1,2-bis(diphenylhosphinoethylene). These studies expand the range of substituted diiron(l) dithiolato carbonyl complexes. From [Fe-2(S2C2H4)(CO)(3)(dppv)(NO)]BF4 ([1(CO)(3)]BF4), the following compounds were prepared: [1(CO)(2)(PMe3)]BF4, [1(CO)(dppv)]BF4, NE4[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 decarbortylation. Such a double adduct was characterized crystallographically in the case of [Fe-2(S2C2H4)(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)]BF4 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 decarbortylation. 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.