Anionic Mixed Thiolate-Sulfide-Bridged Roussin's Red Esters [(NO)2Fe(μ-SR)(μ-S)Fe(NO)2]- (R = Et, Me, Ph): A Key Intermediate for Transformation of Dinitrosyl Iron Complexes (DNICs) to [2Fe-2S] Clusters

Transformations of dinitrosyl iron complex (DNIC) [(NO)(2)Fe(SEt)(2)](-) and the anionic Roussin's red ester (RRE) [(NO)(2)Fe(mu-SEt)(2)Fe(NO)(2)](-) into [2Fe-2S] clusters facilitated by HSCPh3/Me2S3 and [Fe(SEt)(4)](-), respectively, via an intermediate anionic mixed thiolate-sulfide-bridged RRE [(NO)(2)Fe(mu-SEt)(mu-S)Fe(NO)(2)](-) through the reassembling process ([(NO)(2)Fe(SEt)(2)](-) (2)/[(NO)(2)Fe(mu-SEt)(2)Fe(NO)(2)](-) (4) -> [(NO)(2)Fe(mu-SEt)(mu-S)Fe(NO)(2)](-) (3-Et) -> [(NO)(2)Fe(mu-S)(2)Fe(NO)(2)](2-) (5) -> [(SEt)(2)Fe(mu-S)(2)Fe(SEt)(2)](2-) (1)) were demonstrated. The anionic mixed thiolate-sulfide-bridged RRE 3-Et was characterized by IR, UV-vis, electron paramagnetic resonance, H-1 NMR, cyclic voltammetry, and single-crystal X-ray diffraction. In contrast to the nucleophilicity displayed by complex 2, the inertness of [(NO)(2)Fe(SPh)(2)](-) toward HSCPh3 implicates how the reducing ability of the coordinated thiolates of DNICs modulate the release of sulfide from HSCPh3 via reduction and the conversion of DNICs into the anionic mixed sulfide-thiolate-bridged complex. The reversible interconversion between complex 3-Et and complex [(NO)(2)Fe(mu-SPh)(mu-S)Fe(NO)(2)](-) (3-Ph) via protonation and a bridged-thio late exchange reaction, respectively, demonstrates that the [{Fe(NO)(2)}(9)-{Fe(NO)(2)}(9)] motif displays a preference for the stronger electron-donating alkylthiolate-bridged ligand over the phenylthiolate-bridged ligand. This study may signify that the anionic mixed thiolate-sulfide bridged RREs act as a key intermediate in the transformation of DNICs into [2Fe-2S] clusters. Also, the thiolate-coordinate DNICs serve as not only the thiolate/electron carrier activating the incorporation of sulfide of HSCPh3 (Me2S3) to assemble the [Fe(mu-S)2Fe] core but also the Fe source in the biosynthesis of the [2Fe-2S] and [4Fe-4S] iron sulfur clusters.