Iron complex binuclear

A number of binuclear iron complexes have also been isolated (with a neutral base attached to each metal in an axial position). The iron complexes undergo net two-electron redox reactions with dioxygen to yield products containing two identical low-spin Fe(n) metal sites superoxide or peroxide are simultaneously generated. Remarkably, the reaction can be partially reversed by removal of 02 from the system by, for example, flushing with N2 in a mixed aqueous solvent at 0°C. 

A suitable model for the oxygen carrier protein hemerythrin is [Fe2(Et-HPTB)(OBz)](BF4)2 (Et-HPTB = AWAT,iV -tetrakis[(N-ethyl-2-benzimidazolyl)methyl]-2-hydroxy-l,3-diaminopropane, OBz = benzoate). It can mimic the formation of a binuclear peroxo iron complex in the natural system (101). The measured value of -12.8 cm3 mol1 for the activation volume of the oxidation reaction together with the negative value of the activation entropy confirm the highly structured nature of the transition state. 

The binuclear iron complexes (317) have been found to undergo a thermal rearrangement to afford the complexes (318), which were evidently formed via a metathesis between Si—Si and Fe—Fe bonds in (317). A similar rearrangement has been observed in a disilyl-bridged bis(cyclopentadienyl)tetracarbonyldiruthenium complex. Unprecedented and stable in — rf J7 -pentafulvadiene)dimthenium complexes (320) have been prepared" from a two-electron oxidation of frani -l,2-bis(mthenocenyl)ethylenes (319), and dimethyl analogues have been similarly obtained from trans- and cM-l,2-dimethyl-l,2-bis(ruthenocenyl)ethylenes. 

Table I. Comparison of Structural and Spectroscopic Parameters of Binuclear Iron Complexes...

There is currently a paucity of structural data for binuclear iron complexes in other oxidation states. Wieghardt et al. have reported the structure of the only triply bridged diferrous complex thus far, [(Me3tacnFe)20H(OAc)2] (7,8). Its structure is closely related to that of the corresponding difertic complex, with Fe-p.-OH bond lengths of 1.99 A and an Fe Fe separation of 3.4 A. The two metal centers are antiferrcMnagnetically coupled with a J value of -13 cm . ... 

A multiple-path mechanism has been elaborated for dissociation of the mono- and binuclear tris(hydroxamato)-iron(III) complexes with dihydroxamate ligands in aqueous solution. " Iron removal by edta from mono-, bi-, and trinuclear complexes with model desferrioxamine-related siderophores containing one, two, or three tris-hydroxamate units generally follows first-order kinetics though biphasic kinetics were reported for iron removal from one of the binuclear complexes. The kinetic results were interpreted in terms of discrete intrastrand ferrioxamine-type structures for the di-iron and tri-iron complexes of (288). " Reactivities for dissociation, by dissociative activation mechanisms, of a selection of bidentate and hexadentate hydroxamates have been compared with those of oxinates and salicylates. ... 

Reaction of Fe3(CO)12 with 3-pentyn-l-ol gives the hydrido cluster 4, formed by coupling of an allenylidene unit with a coordinated carbonyl ligand and methoxy group. In contrast, reaction with the isomeric alkyne 2-methyl-3-butyn-2-ol affords a binuclear iron complex.18 Treatment of Fe3(p3-S)2(CO)9 with Me3NO affords the vinylferrocene complex 5, whereas the similar reaction with Fe3(p3-Te)2(CO)9 gives no cluster products.19... 

Gritsenko, O.N., Nesterenko, G. N., and Shteinman, A.A. (1995) Effect of substituents in the ligand on oxidation of alkanes by binuclear oxo-bridged iron complexes, Izv. Akad. Nauk, Ser. Khim. 12, 2518-2520. 

A wide variety of synthetic binuclear iron complexes (39) bridged by sulfide, disulfide and/or thiolate groups are known. They have proven to be good models for the two-iron ferredoxin proteins, as demonstrated by comparisons of structure and properties. Early attempts to isolate two-iron complexes by direct reaction of a monothiol with FeCl3, NaSH and NaOMe afforded only four-iron products suggesting that a particularly high stability is associated with the tetrameric... 

High yields of the moisture-sensitive tris(chelates) Fe(ArNNNAr)3 have been obtained by shaking anhydrous iron(III) chloride with silver(I) triazen-ides in dry ether at room temperature (18). Silver triazenides also react with the iron complexes FeX(CsH5)L2 [L = PPhj, P(OMe)j, P(OPh>3, or CO] via unstable binuclear species (C5H5)LFe(ArNNNAr)AgX to give the chelate triazenide complexes Fe(ArNNNAr)(C5H5)L (13). The complexes... 

Some preparations of iron exchanged into zeolite H-MFI by vapor-phase FeCL are known to be active and selective catalysts for the reduction of NO, with hydrocarbons or ammonia in the presence of excess oxygen and water vapor (45,46). The active centers in Fe/MFI are assumed to be binuclear, oxygen-bridged iron complexes, as follows from H2-TPR, CO-TPR, and ESR data (45,47) and EXAFS and XANES results (48,49). These complexes are structurally similar to the binuclear iron centers in methane monooxygenase enzymes that are employed by methanotrophic bacteria in utilization of methane as their primary energy source (50). It is believed that molecular oxygen reacts with these centers to form peroxide as the initial step in this chemistry (50). 

Previous syntheses of tricarbonyl( /-diene)iron complexes have relied mainly on the reaction of Fe(CO)s, Fc3(CO)i2, or Fc2(CO)9 with the free diene. The use of the first two carbonyls suffers from the prolonged reflux times and/or ultraviolet irradiation necessary to obtain reaction and the consequent low yields and mixtures of complexes obtained with heat- and ultraviolet-sensitive dienes. The latter reagent, although utilized at lower temperatures, may react with polyenes (n > 3) to give mixtures containing, in addition to the expected product, binuclear derivatives containing a metal—metal bond.2... 

Treatment of 2,2,4,4-tetramethyl-3-thietanone with diiron nonacarbonyl gives the binuclear iron complex 381. 2,2-Dimethyl-3-thietanone undergoes oxidative dimerization to 382 on treatment with potassium ferricyanide. Methylene-3-thietanones such as 359 add chlorine from thionyl chloride to the carbon-carbon double bond. 2,2,4,4-tetramethyl-3-thietanone is converted to the 3-thione in 14% yield by treatment with hydrogen sulfide-hydrogen chloride. Electrochemical reduction of the thione produces radical anions. 

The binuclear iron complex (C8H8)Fe2(CO)6 had been expected from the reaction, but the chair conformation (XXXV), which was subsequently found for this substance, was entirely unexpected (65j 66j 67). In this complex, each end of the cyclooctatetraene ligand behaves as a butadiene-type (n = 4) ligand, and bond distance measurements indicate very little tt-tt interaction between the two halves of the ring. The proton NMR spectrum of the complex in solution exhibits two resonances of equal intensity, while the infrared spectrum is very similar to the spectrum of butadiene-iron tricarbonyl and similar diene complexes (105). 

The mononuclear cobalt complexes are stable and are able to be isolated in both 2+ and 3+ oxidation states. Cyclic voltammetric studies reveal reversible waves for both Co " 2+ and Co + i reduction couples. These redox couples are shifted anodically as the ligand substituents are changed from methyl to phenyl. Electrolytic and cyclic voltammetric studies before and after electrolysis support the idea that the integrity of the complexes is maintained during electrolytic cycles of the 2+/3+ oxidation states. The IpJIpa values of the Co + 2+ couple for the binuclear cobalt complexes are identical to those observed for the oxidation of the analogous iron complex. Attempts to produce the binuclear cobalt(III) species by exhaustive electrolysis have been limited by adsorption of the cobalt(III) complexes on the electrode surface [186, 187],... 

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