Iron 1,2-dithiolate complexes

It is not always possible to make a systematic comparison of the effects on the Mossbauer parameters of variations in the ligand and of the overall charge state for a large series of complexes. One of the few cases where this has proved possible is for the 1,2-dithiolate complexes with ligands such as a substituted c/j-ethylene-1,2-dithiolate (I), tetrachlorobenzene-l,2-dithiolate 

The anion [Fe S2C2(CN)2 2] has been shown by X-ray analysis to be dimeric in the soUd state and to have the structure IV. 

Compounds (1-5) are all very similar with one unpaired electron per iron atom, large quadrupole splittings, and a chemical isomer shift compatible with a low-spin Fe(lII) S = 1 configuration. All may therefore be presumed to have the same dimeric structure IV. The quadrupole splittings range from 

2-37 to 3-02 mm s at 77 K and are some of the largest known for this electronic configuration of iron. 

Compounds (6-8) contain the basic structural unit [Fe(py) —S2 2] they have three unpaired electrons and are probably penta-coordinate Fe(IIl) S = i compounds (structure V) similar to the bis-(N,N -dithiocarbamato)-iron(III) halides discussed in the preceding section. Both series show an approximately systematic variation in A with change in the ligand which is not matched by a corresponding variation in the chemical isomer shift, so that it seems unlikely that large changes in delocalisation are occurring. The very small temperature dependence of A in the S = i complexes makes it difficult to determine the electronic level separations. 

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Boese M, Keese MA et al (1997) Inhibition of glutathione reductase by dinitrosyl-iron-dithiolate complex. J Biol Chem 272 21767-21773... 

Four-coordinate, planar iron(II)-dithiolate complexes also exhibit intermediate spin. The first example described was the tetraphenylarsonium salt of the square-planar bis(benzene-l,2-dithiolate)iron(II) dianion, (AsPh4)2[Fe(II)bdt2], which showed 5 = 0.44 mm s and AEq = 1.16 mm s at 4.2 K [157]. The electronic structure of a different salt was explored in depth by DFT calculations, magnetic susceptibility, MCD measurements, far-infra red spectroscopy and applied-field Mossbauer spectroscopy [158]. 

Several studies suggest that LA and DHLA form complexes with metals (Mn2+, Cu2+, Zn2+, Cd2+, and Fe2+/Fe3+) [215-218]. However, in detailed study of the interaction of LA and DHLA with iron ions no formation of iron LA complexes was found [217]. As vicinal dithiol, DHLA must undoubtedly form metal complexes. However, the high prooxidant activity of DHLA makes these complexes, especially with transition metals, highly unstable. Indeed, it was found that the Fe2+-DHLA complex is formed only under anerobic conditions and it is rapidly converted into Fe3+ DHLA complex, which in turn decomposed into Fe2+ and LA [217]. Because of this, the Fe3+/DHLA system may initiate the formation of hydroxyl radicals in the presence of hydrogen peroxide through the Fenton reaction. Lodge et al. [218] proposed that the formation of Cu2+ DHLA complex suppressed LDL oxidation. However, these authors also found that this complex is unstable and may be prooxidative due to the intracomplex reduction of Cu2+ ion. 

Chang and Dolphin [171] reported also that their protoheme-sulfide complexes bind O2 at —45 °C in dimethylacetamide without deterioration of the dioxygen adduct after 1 h. However, Ruf and Wende [172] showed that the visible spectrum of the presumed dioxygen adduct was the same as that of the iron(III)dithiolate complex. 

The oxidation of triphenylphosphine has also been investigated using iron complexes as catalysts [133]. Kinetics of this reaction were studied using [Fe(mnt)2] and [Fe(nmt)3] where mnt " is CM-l,2-dicyanoethylene-l,2-dithiolate. Approximately 1 mol of the iron(IV) complex catalyzed the oxidation of 15 mol of triphenylphosphine compared to about 10 mol of triphenylphosphine for the iron(III) complex. The rate of oxygen uptake in the presence of either complex was found to be proportional to the concentrations of both triphenylphosphine and the iron complex but independent of oxygen pressure. No evidence was obtained for the formation of molecular oxygen complexes. 

Kinetic and equilibrium studies of the reactions of iron(iii) and iron(iv) dithiolate complexes with organic bases have been investigated in acetonitrile solutions. Bis-(c/j-l,2-dicyano-l,2-dithioethylene)iron(iii), [Fe(mnt)2], reacts rapidly with pyridine and triphenylphosphine (B)... 

Several complexes of iron with the 1,1-ethenedithiolates have been isolated. These are mainly tris-Fe(III) complexes with the 1,1-dicyano-2,2-ethylenedithiolate ligand (1). Recently, however, Coucouvanis et al. (262) synthesized a new 1,1-dithiolate ligand (XVIII) from the reac-... 

Very recently, Hammarstrom, Ott, and coworkers found that the catalytic activity was significantly increased (up to 200 TON based on the iron complex) when a diiron complex having a 3,6-dichlorobenzene-1,2-dithiolate ligand (Fig. 10) instead of a benzylazadithiolate ligand was used as a WRC (see ref. [64] in [232]). 

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