Mononitrosyl tris(thiolate) iron complex [Fe(NO)(SPh)3]- and dinitrosyl iron complex [(EtS)2Fe(NO)2]-: formation pathway of dinitrosyl iron complexes (DNICs) from nitrosylation of biomimetic rubredoxin [Fe(SR)4]2-/1- (R = Ph, Et).

Nitrosylation of the biomimetic reduced- and oxidized-form rubredoxin [Fe(SR) 4 ] 2-/1- (R = Ph, Et) in a 1:1 stoichiometry led to the formation of the extremely air- and light-sensitive mononitrosyl tris(thiolate) iron complexes (MNICs) [Fe(NO)(SR) 3 ] - along with byproducts [SR]- or (RS) 2 . Transformation of [Fe(NO)(SR) 3 ] - into dinitrosyl iron complexes (DNICs) [(RS) 2 Fe(NO) 2 ] - and Roussin's red ester [Fe 2 (μ-SR) 2 (NO) 4 ] occurs rapidly under addition of 1 equiv of NO (g) and [NO] + , respectively. Obviously, the mononitrosyl tris(thiolate) complex [Fe(NO)(SR) 3 ] - acts as an intermediate when the biomimetic oxidized- and reduced-form rubredoxin [Fe(SR) 4 ] 2-/1- exposed to NO (g) were modified to form dinitrosyl iron complexes [(RS) 2 Fe(NO) 2 ] - . Presumably, NO binding to the electron-deficient [Fe ΙΙΙ (SR) 4 ] - and [Fe III (NO)(SR) 3 ] - complexes triggers reductive elimination of dialkyl/diphenyl disulfide, while binding of NO radical to the reduced-form [Fe II (SR) 4 ] 2- induces the thiolate-ligand elimination. Protonation of [Fe(NO)(SEt) 3 ] - yielding [Fe(NO)(SPh) 3 ] - by adding 3 equiv of thiophenol and transformation of [Fe(NO)(SPh) 3 ] - to [Fe(NO)(SEt) 3 ] - in the presence of 3 equiv of [SEt] - , respectively, demonstrated that complexes [Fe(NO)(SPh) 3 ] - and [Fe(NO)(SEt) 3 ] - are chemically interconvertible. Mononitrosyl tris(thiolate) iron complex [Fe(NO)(SPh) 3 ] - and dinitrosyl iron complex [(EtS) 2 Fe(NO) 2 ] - were isolated and characterized by X-ray diffraction. The mean NO bond distances of 1.181(7) A (or 1.191(7) A) in complex [(EtS) 2 Fe(NO) 2 ] - are nearly at the upper end of the 1.178(3)-1.160(6) A for the anionic {Fe(NO) 2 } 9 DNICs, while the mean FeN(O) distances of 1.674(6) A (or 1.679(6) A) exactly fall in the range of 1.695(3)-1.661(4) A for the anionic {Fe(NO) 2 } 9 DNICs.