Iron complexes formation

Vanin, A. F., Mordvincev, P. I., Huischildt, S., and Mulsch, A. (1993). The relationship between L-arginine-dependent nitric oxide synthesis, nitrite release and dinitrosyl-iron complex formation by activated macrophages. Biochim. Biophys. Acta 1177, 37-42. 

Ferric iron in solution exists in several forms. The more important forms ass Fe(SO)f. FeSOd+. FE OH), and FeOH2+. The sulfate complexes are greatly favored over the hydroxyl complexes, To illustrate the imponance of iron complex formation, a typical leach solution will be considered in equilibrium with precipitated hydrogen jarosile, having an approximate ftee-sulfate activity of 0.02. The equilibrium is represented by... 

Iron Complex formation with thiocyanate 1.0-30 lron(ll III) can be determined using SF... 

These data from ergosterol and ergosterol-type compounds prove very clearly that approach control in iron-complex formation differs markedly from the one in Diels-Alder cycloadditions. While here all examples investigated so far call for an a-approach of the dienophile to form products like 8 with remarkable regioselectivity, complex formation does at least to some extent take place from the P-side of the molecule. 

Scheme 4-102. Endo selective (T -diene)iron complex formation of a cw-dihydroxycyclohexadiene.

Scheme 4-110. Alkylation of (ri -diene)iron complexes. Formation of c/5-pentadienol ethers by addition of triethylamine.

Compare this reaction with (2) of the oxidising examples, where iron(II) is oxidised to iron(III) in acid solution change of pH, and complex formation by the iron, cause the complexed iron(III) to be reduced.)... 

Ground-state electronic configuration is ls 2s 2p 3s 3p 3i 4s. Manganese compounds are known to exist in oxidation states ranging from —3 to +7 (Table 2). Both the lower and higher oxidation states are stabilized by complex formation. In its lower valence, manganese resembles its first row neighbors chromium and especially iron ia the Periodic Table. Commercially the most important valances are Mn, Mn ", or Mn ". ... 

Interaction of iron(II) chloride with the lithium salt of R4B2NJ (R = Me, Et) gives sandwiches 61 (R = Me, Et) (67ZAAC1, 96MI4), resembling in electronic properties those of ferrocene (99ICA(288)17). The n- rf-) complex stems from the further complex-formation of 61 (R = Me, Et) with mercury(II) salts via the unsubstituted nitrogen atom. 

The synthesis of 1 -benzothiepin 1 -oxide (23) can be achieved via complex formation with tricarbonyl iron, and quantitative oxidation of the coordination compound 22 with 3-chloroperoxy-benzoic acid. Subsequent irradiation at — 50 C provides 23, which crystallized as yellow needles after low-temperature (-40 C) chromatography, and was characterized by 1H NMR spectroscopy at — 30 C23 before loosing sulfur within one hour at 13°C to give naphthalene. 

The lithium enolate 2a (M = Li ) prepared from the iron propanoyl complex 1 reacts with symmetrical ketones to produce the diastercomers 3 and 4 with moderate selectivity for diastereomer 3. The yields of the aldol adducts are poor deprotonation of the substrate ketone is reported to be the dominant reaction pathway45. However, transmetalation of the lithium enolate 2a by treatment with one equivalent of copper cyanide at —40 C generates the copper enolate 2b (M = Cu ) which reacts with symmetrical ketones at — 78 °C to selectively produce diastereomer 3 in good yield. Diastereomeric ratios in excess of 92 8 are reported with efficient stereoselection requiring the addition of exactly one equivalent of copper cyanide at the transmetalation step45. Small amounts of triphcnylphosphane, a common trace impurity remaining from the preparation of these iron-acyl complexes, appear to suppress formation of the copper enolate. Thus, the starting iron complex must be carefully purified. 

Iron, tris(hexafluoroacetylacetone)-structure, 1,65 Iron, tris(oxalato)-chemical actinometer, 1,409 photoreduction, 1,471 relief-image-forming systems, 6,125 Iron, tris(l,10-phenanthroline)-absorptiometry, 1,549 racemization, 1,466 solid state, 1,467 structure, 1, 64 lron(III) chloride amino acid formation prebiotic systems, 6,871 Iron complexes acetonitrile. 4,1210 acetylacetone, 2,371 amidines... 

Unexpectedly, neither direct complexation nor the deoxygenated complexes 95 or 96136,137 were observed in the reaction of diphenylthiirene oxide (18a) with iron nonacarbonyl. Instead, the red organosulfur-iron complex 97138 was isolated12, which required the cleavage of three carbon-sulfur bonds in the thiirene oxide system (see equation 33). The mechanism of the formation of 97 from 18a is as yet a matter of speculation. 

Alkoxy(carbene)iron(0) and amino(carbene)iron(0) complexes usually react with alkynes to give rj4-pyrone iron complexes and furans, respectively [54]. Nevertheless the chemoselective formation of naphthols was reported for alkoxy(carbene)iron(0) complexes with the electron-poor alkyne dimethyl... 

Mono- and polyl dric phenols and enols frequently form characteristically colored complexes with Fe + ions [4, 28, 29]. Here monohydric phenols usually produce reddish-violet colors, while pyrocatechol derivatives yield green chelates [4]. Detection of acetone using Legal s test is based on the formation of an iron complex [4]. The same applies to the thioglycolic acid reaction of the German Pharmacopoeia (DAB 9) [4, 30]. 

The rate of peroxide decomposition and the resultant rate of oxidation are markedly increased by the presence of ions of metals such as iron, copper, manganese, and cobalt [13]. This catalytic decomposition is based on a redox mechanism, as in Figure 15.2. Consequently, it is important to control and limit the amounts of metal impurities in raw rubber. The influence of antioxidants against these rubber poisons depends at least partially on a complex formation (chelation) of the damaging ion. In favor of this theory is the fact that simple chelating agents that have no aging-protective activity, like ethylene diamine tetracetic acid (EDTA), act as copper protectors. 

Experiments with terminal acetylenes, isolation of an intermediate acetal, alkyne hydratation studies, and ab initio calculations provide substantiation of a unified mechanism that rationalizes the reactions in which the complex formation between the alkyne and the iron(III) halides is the activating step (Scheme 12) [27]. 

Abstract Organic syntheses catalyzed by iron complexes have attracted considerable attention because iron is an abundant, inexpensive, and environmentally benign metal. It has been documented that various iron hydride complexes play important roles in catalytic cycles such as hydrogenation, hydrosilylation, hydro-boration, hydrogen generation, and element-element bond formation. This chapter summarizes the recent developments, mainly from 2000 to 2009, of iron catalysts involving hydride ligand(s) and the role of Fe-H species in catalytic cycles. 

Scheme 36 Reaction mechanism of the formation of succinimides catalyzed by iron complexes...

As an alternative method for the C-C bond formation, oligomerization and polymerization reactions of olefins catalyzed by a bis(imino)pyridine iron complex are also well known (Scheme 40) [121-124]. 

In addition to nonheme iron complexes also heme systems are able to catalyze the oxidation of benzene. For example, porphyrin-like phthalocyanine structures were employed to benzene oxidation (see also alkane hydroxylation) [129], Mechanistic investigations of this t3 pe of reactions were carried out amongst others by Nam and coworkers resulting in similar conclusions like in the nonheme case [130], More recently, Sorokin reported a remarkable biological aromatic oxidation, which occurred via formation of benzene oxide and involves an NIH shift. Here, phenol is obtained with a TON of 11 at r.t. with 0.24 mol% of the catalyst. 

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