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(μ-SEt) 2 Fe(NO) 2 ] - into [2Fe-2S] clusters facilitated by HSCPh 3 /Me 2 S 3 and [Fe(SEt) 4 ] - , respectively, via an intermediate anionic mixed thiolate-sulfide-bridged RRE [(NO) 2 Fe(μ-SEt)(μ-S)Fe(NO) 2 ] - through the reassembling process ([(NO) 2 Fe(SEt) 2 ] - (2)/[(NO) 2 Fe(μ-SEt) 2 Fe(NO) 2 ] - (4) → [(NO) 2 Fe(μ-SEt)(μ-S)Fe(NO) 2 ] - (3-Et) → [(NO) 2 Fe(μ-S) 2 Fe(NO) 2 ] 2- (5)— [(SEt) 2 Fe(μ-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, 1 H 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 HSCPh 3 implicates how the reducing ability of the coordinated thiolates of DNICs modulate the release of sulfide from HSCPh 3 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(μ-SPh)(μ-S)Fe(NO) 2 ] - (3-Ph) via protonation and a bridged-thiolate 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 HSCPh 3 (Me 2 S 3 ) to assemble the [Fe(μ-S) 2 Fe] core but also the Fe source in the biosynthesis of the [2Fe-2S] and [4Fe-4S] iron-sulfur clusters.