Iron-based systems

In many respects the apparently analogous reduction of nitroarenes with triruthenium dodecacarbonyl under basic phase-transfer conditions is superior to that of the iron carbonyl-mediated reductions. However, the difference in the dependence of the two processes on the concentration of the aqueous sodium hydroxide and the pressure of the carbon monoxide suggests that they may proceed by different mechanisms. Although the iron-based system is most effective under dilute alkaline conditions in the absence of carbon monoxide, the use of 5M sodium hydroxide is critical for the ruthenium-based system, which also requires an atmosphere of carbon monoxide [11]. The ruthenium-based reduction has been extended to the... 

Oxidation of Oximes A different type of N-oxidation reaction involves the direct oxidation of oximes to nitro compounds. Although a variety of oxidizing agents have been described for this reaction, the use of non-heme iron-based systems is rather limited. In this context, the oxidation of the oxime group in tetrahydro-4H-pyrido[ 1,2-a]pyrimidines was carried out at room temperature in the presence of 50 mol% of Clayfen [K10 montmorillonite-supported iron(III) nitrate] (Scheme 3.45) [147]. Under these conditions the corresponding nitro derivatives were obtained in 32-35% yield. 1SN mass studies revealed that the reaction involved the direct oxidation of the hydroxyimino group. 

The conversion of thiols into disulfides (oxidative S—S coupling) is an important reaction in synthetic organic chemistry and many stoichiometric and catalytic metal reagents have been reported as oxidants for this transformation. However, there are only few reports on the oxidation of thiols using iron-based systems. 

K. R. and Collins, T.J. (1998) Designing ligands to achieve robust oxidation catalysts. Iron based systems. Coord. Chem. Rev., 174, 361. 

Although the [ Fe(HBpz3)(hfacac) 20] system is quite intriguing, it is unclear whether ferrous decomposition products are responsible for the observed chemistry, particularly in light of the reported reactivity properties of several less well characterized mononuclear nonheme iron systems that are capable of hydroxylating aromatic compounds (22-26). The relationship between the chemistry of these iron-based systems, such as 4 and the Gif (and modified Gif) systems (15-18) is currently unclear. 

As with ruthenium, iron belongs to the group 8 series of elements and can similarly take various oxidation states (—2 to +4), among which Fe(II), Fe-(I), and Fe(0) species have been reported to be active in Kharasch addition reactions.33 For metal-catalyzed living radical polymerizations, several Fe(II) and Fe-(I) complexes have thus far been employed and proved more active than the Ru(II) counterparts in most cases (Figure 2). The iron-based systems are attractive due to the low price and the nontoxic nature of iron. 

The use of Cp or Cp -based ligands is also beneficial for the iron-based systems in controlling radical polymerization. For instance, FeCpI(CO)2 (Fe-3, X = I) induced a living radical polymerization of styrene in conjunction with an iodide initiator [(CH.s C-(C02C2H5)I] in the presence of Ti(Oi-Pr)4 to give very narrow MWDs (MJMn =1.1) and controlled molecular weights.72 The rate was increased with the use of the corresponding bromide, while the MWD was narrowed by replacement of Cp with Cp. 73 A faster and controlled polymerization was possible with dinuclear Fe(I) complexes (Fe-5 and Fe-6) in the absence of metal alkoxides. 

E. A. Duban, K. P. Bryliakov, E. P. Talsi, The active intermediates of non-heme-iron-based systems for catalytic alkene epoxidation with H2Q2/CH3COOH, Eur.. Inorg. Chem. (2007) 852. 

Czv-Symmetric Catalysts. Syndiotactic polymers have been formed using metallocene catalysts where the polymer chain end controls the syndiospecificity of olefin insertion. Resconi has shown that Cp 2MCl2 (M = Zr. Hf) derived catalysts produce predominantly syndiotactic poly(l-butene) with an approximate 2 kcal/mol preference for syndiotactic versus isotactic dyad formation." At —20 °C. Cp 2HfCl2/MAO produces poly(l-butene) with 77% rr triads. Pellecchia had reported that the diimine-ligated nickel complex 30 forms moderately syndiotactic polypropylene at —78 °C when activated with MAO ([rr] = 0.80)." " Olefin insertion was shown to proceed by a 1.2-addition mechanism." in contrast to the related iron-based systems which insert propylene with 2.1-regiochemistry. ... 

Experimental investigations of the thermodynamic properties Cr-Fe-Nb alloys have not been reported. Thermodynamic data for liquid, ferrite and austenite of some iron-based systems were optimized by [1998Mie] in order to give a more accurate representation of phase equilibria between these phases in multieomponent steels. But for the Cr-Fe-Nb system, the auflior has noted fliat a eareM examination of the system is necessary in order to get a reliable prediction of die partitioning tendency of niobium. 

Zup] Zupp, R.R., Stevenson, D.A., The Influence of Vanadium on the Activity of Carbon in the Fe-C-V System at 1000°C Correlation of the Influence of Substitutional Solutes on the Activity Coefficient of Carbon in Iron base Systems , Trans. AIME, 236, 1316-1323 (1966) (Thermodyn., Theory, 35)... 

Fe—Cr. The Fe—Cr phase diagram. Fig. 3.1-106, is the prototype of the case of an iron-based system with an a-phase stabilizing component. Chromium is the most important alloying element of corrosion resistant, ferritic stainless steels and ferritic heat-resistant steels. If a-Fe—Cr alloys are quenched from above 1105 K and subsequently annealed, they decompose according to a metastable miscibility gap shown in Fig. 3.1-107. This decomposition reaction can cause severe embrittlement which is called 475 C-embrittlement in ferritic chromium steels. Embrittlement can also occur upon formation of the a phase. 

A wide range of acrylates with various side chains have been polymerized using ATRP to obtain well-de ned functional polymers, e.g., ATRP of 2-hydroxyethyl acrylate, glycidyl acrylate, and tert-butyl acrylate (yielding well-de ned poly(acrylic acid) on hydrolysis). Among several transition metal catalysts, viz., copper, ruthenium, and iron-based systems, which have been successfully used for the controlled ATRP of acrylates, copper appears to be superior in producing well-de ned polyacrylates with low polydispersities. 

In this paragraph, we will discuss catalytic systems in which an iron compound is the only catalyst, that is we will not consider those systems in which an iron compound is used as a cocatalyst in what is considered to be a palladium- or rhodium-based eatalytic system. These last systems have already been discussed in paragraphs 6.3.1. and 6.5.2. Synthetic applications of iron-based systems for the carbonylation (Chapter 3) and reduction (Chapter 4) of nitroarenes have already been described. 

Our aim in this paper is to demonstrate the applicability of the method to the study of low-dimensional magnetic systems and for this purpose we have chosen iron-based systems. The reason of this choice is double. On the one hand, iron-based systems have been widely investigated through both all electron ab initio methods and semiempirical methods so that we can compare our results. On the other hand, it is an element of great current interest maybe it is also the most studied magnetic element experimentally and it is not completely understood so far in many respects. 

Kiihn and coworkers [19] extended the MTO catalytic system to ketone substrates. Benzoic acid additive was needed to activate the ketones, a strategy that was first developed by Zhang and coworkers [20] in their investigation of olefination of unactivated ketones using an iron-based catalyst In contrast to the -selectivity observed for the iron-based system, MTO-catalyzed olefination of ketones favored Z-olefin products (Scheme 4). Up to 89/11 Z/ selectivity... 

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