Using Iron Complexes

The difficulty in removing metal residues from the product induced the search for iron-catalyzed reactions [77]. However, iron complexes can play different roles in catalytic processes  

as ligands for other transition metal catalysts to achieve activation and stereocontrol  

Iron Complexes as Substrates and/or Products in Catalytic Reactions 

The first aspect is illustrated by the synthesis of tricarbonyl(ri4-l,3-diene)iron complexes from pentacarbonyliron in the presence of catalytic amounts of a 1-azabuta- 

---

Use iron complex former (for therapy of iron storage diseases)... 

Better results for the porphyrin complex-catalyzed asymmetric epoxidation of prochiral olefins were achieved by Naruta et al.98 using iron complexes of chiral binaphthalene or bitetralin-linked porphyrin 128 as chiral catalysts. As shown in Scheme 4-45, asymmetric epoxidation of styrene or its analogs provided the product with good ee. Even better results were obtained with substrates bearing electron-withdrawing substituents. 

Method A (using iron complexes) Fe,(CO)12 (0.25 g, 0.5 mmol) and the nitroarene (l.O mmol) in PhH (I0 ml) are stirred for 2 h with TEBA-CI (0.02 g, 0.I mmol) in aqueous NaOH (lM, I0 ml) at room temperature. The organic phase is separated and filtered through silica to give the aniline. 

Cyclometalation reactions using iron complexes have been known for a long time [17-20]. Of special interest for the development of a catalytic reaction under mild conditions are the reports that iron(O) complexes can oxidatively add into the ortho C-H bond of an aromatic imine (Eq. 1), and alkyliron(ll) complexes can cleave an ortho C-H bond with elimination of alkane (Eq. 2) [21, 22]. 

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. 

Scattered examples of incorporation of the two CO groups into organic compounds using iron complexes to afford 1,2-diketones and acyl lactones are known.t Hioi]... 

F. 41 Asymmetric transfer hydrogenation of a [ o hinoyl imine using iron complex 14... 

Darwish, M. Wills, M. Asymmetric catalysis using iron complexes— Ruthenium Lite Catal. Sci. Technol. 2012,2,243-255. 

Table 1 Optimized polymerization results using iron complexes ligated by unsymmetiical bis(imino)pyiidines bearing benzhydryl derivatives (under a pressure of 10 atm)...

Chiral diene—iron tricarbonyl complexes were acylated using aluminum chloride to give acylated diene—iron complexes with high enantiomeric purity (>96% ee). For example, /ra/ j -piperjdene—iron tricarbonyl reacted with acyl haUdes under Friedel-Crafts conditions to give l-acyl-l,3-pentadiene—iron tricarbonyl complex without any racemization. These complexes can be converted to a variety of enantiomericaHy pure tertiary alcohols (180). 

Aminoboranes have been used as ligands in complexes with transition metals (66) in one instance giving a rare example of two-coordinate, non-t/ transition-metal complexes. The molecular stmcture of the iron complex Fe[N(Mes)B(Mes)2]2 where Mes = is shown in Figure 1. The... 

Cyclopentadiene itself has been used as a feedstock for carbon fiber manufacture (76). Cyclopentadiene is also a component of supported metallocene—alumoxane polymerization catalysts in the preparation of syndiotactic polyolefins (77), as a nickel or iron complex in the production of methanol and ethanol from synthesis gas (78), and as Group VIII metal complexes for the production of acetaldehyde from methanol and synthesis gas (79). 

The stmcture of the blue material was not elucidated until 1934, when it was shown to be the iron complex of (67). The new material was christened phthalocyanine [574-93-6] reflecting both its origin from phthaUc anhydride and its beautihil blue color (like cyanine dyes). A year later the stmcture was confirmed by one of the first uses of x-ray crystallography. 

The only nitroso dyes important commercially are the iron complexes of sulfonated l-nitroso-2-naphthol, eg. Cl Acid Green 1 [57813-94-2] (78) (Cl 10020) these inexpensive colorants are used mainly for coloring paper. 

An even more effective homogeneous hydrogenation catalyst is the complex [RhClfPPhsfs] which permits rapid reduction of alkenes, alkynes and other unsaturated compounds in benzene solution at 25°C and 1 atm pressure (p. 1134). The Haber process, which uses iron metal catalysts for the direct synthesis of ammonia from nitrogen and hydrogen at high temperatures and pressures, is a further example (p. 421). 

Discussion. Salicylic acid and iron(III) ions form a deep-coloured complex with a maximum absorption at about 525 nm this complex is used as the basis for the photometric titration of iron(III) ion with standard EDTA solution. At a pH of ca 2.4 the EDTA-iron complex is much more stable (higher stability constant) than the iron-salicylic acid complex. In the titration of an iron-salicylic acid solution with EDTA the iron-salicylic acid colour will therefore gradually disappear as the end point is approached. The spectrophotometric end point at 525 nm is very sharp. 

One of the possible problems of using the complex mixtures is the presence of unwanted materials such as certain metal ions, particularly manganese and iron. In addition, inhibitory compounds such as acetic add may be present All need to be removed before fermentation can proceed. 

Alkylation of the anion 2 with iodomethane or other haloalkanes provides alkyldicarbonyl(t/5-cyclopentadienyl)iron complexes such as 53,0 (see also Houben-Weyl, Vol. 13/9a, p 209). Migratory insertion of carbon monoxide occurs on treatment with phosphanes or phosphites9 -11 (see also Houben-Weyl, Vol. d3/9a, p257) to provide chiral iron-acyl complexes such as 6. This is the most commonly used preparation of racemic chiral iron-acyl complexes. 

Table 9.7 Iron Complexes Used as ATRP Catalysts...

---