Abstract
Reaction of [PPN][Fe(CO)3(NO)] and S8 in a 1:1 molar ratio in THF proceeded to give the dinitrosyl iron complex [PPN][S5Fe(NO)2] (1) and the known [PPN]2[S5Fe(μ-S)2FeS5] (2). Nitrosylatin of complex 2 in THF shows that cluster 2 is converted into the dinitrosyl iron complex 1 identified by IR, UV-vis, and X-ray diffraction analysis. A THF solution of dinitrosyl iron complex 1 can be transformed back to the [2Fe-2S] cluster 2 in the presence of NO-acceptor reagent [(C4H8O)Fe(S,S-C6H4)2]–(3) (or [Fe(S2CN(Et)2)2]) under photolysis. This result demonstrates a successful biomimetic reaction cycle (Scheme 2) on degradation and reassembly of the [2Fe-2S] cluster [S5Fe(μ-S)2FeS5]2– relevant to the biological cycle (Scheme 1) of the nitric oxide-modified and repair of the ferredoxin [2Fe-2S] cluster by cysteine desulfurase and L-cysteine in vitro. This study implicates that NO-acceptor [(C4H8O)Fe(S,S-C6H4)2]– is required in promoting transformation of dinitrosyl iron complex 1 into cluster 2 under photolysis. Apparent differences were found in the efficiency of transnitrosylation in two NO acceptors, [(C4H8O)Fe(S,S-C6H4)2]– (photolysis, at λ = 352 nm) and [Fe(S2CN(Et)2)2] (no photolysis needed). For the electronic structure of {Fe(NO)2} core, EPR, magnetic susceptibility measurement, and Fe K-/L-edge XAS spectroscopy of complex 1 lead to a description of {Fe+1(•NO)2}9. The water soluble DNIC complex [K-18-crown-6-ether][ S5Fe(NO)2](5) was also synthesized and characterized by IR, UV/vis, X-ray diffraction analysis. NO-transfer from [PPN][(NO)Fe(S,S-C6H2-3,6-Cl,Cl)2] to [PPN][(C4H8O)Fe(S,S-C6H4)2] (3),presumably via associative mechanism, was observed in THF at ambient temperature.