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

摘要

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)(S)(3)](-) into dinitrosyl iron complexes (DNICs) [(RS)(2)Fe(NO)(2)](-) and Roussin's red ester [Fe-2(mu-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-III(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)] ielding [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) angstrom (or 1.191(7) angstrom) in complex [(EtS)(2)Fe(NO)(2)](-) are nearly at the upper end of the 1.178(3) - 1.160(6) angstrom for the anionic {Fe(NO)(2)}(9) DNICs, while the mean FeN(O) distances of 1.674(6) angstrom (or1.679(6) angstrom) exactly fall in the range of 1.695(3) - 1.661(4) angstrom for the anionic {Fe(NO)(2)}(9) DNICs.