Dinuclear iron complexes Fe2

DNICs are spontaneously [128] formed in aqueous media using a simple Fe(II) salt, S-nitrosothiol and thiol, with a ratio of Fe2+/RSH of 1 20. NO is transferred quantitatively from the sulfur atom in the RSNO to the iron. The complete mechanism is yet to be fully determined. A 1 2 ratio results in the formation of an EPR silent yellow dinuclear iron complex ([Fe2(RS)2(NO)4]. At the higherer ratio, the green paramagnetic, mononuclear dinitrosyl predominates. The reaction is very straightforward at pH 7.8, under an inert atmosphere and in water. Under anaerobic conditions the stability of this compound is enhanced, however, in the presence of air and hydrogen peroxide, it readily decomposes to give the dinuclear complex [126] which is similar in structure to the Roussin red salt, as shown in Scheme 5.5. 

Ziegler and co-workers reported DFT with self-consistent reaction field calculations on multielectron redox reactions for dinuclear iron complexes [Fe2(CO)6(/x2-PR2)2]° (R=CH3, CF3). They did calculations on all three oxidation states for the complexes to construct energy profiles for the addition of two electrons to the = 0 oxidation state. It was found that inclusion of solvent and/or ion pairing effects was necessary to predict the experimentally observed disproportionation reaction of the singly reduced complex. It was also found that CO ligands are important in the deloealization of added electron density due to reduction. Interestingly, the authors also conclude that ion pairing with the anionic complexes should be modeled to produce the most realistic calculations. 

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