Iron triple bond

At long photolysis times (Scheme 5), the triplet Cp2Fe2(/x-CO)3 loses a CO to give the triplet Cp2Fe2(CO)2. Further photolysis converts this triplet to a doubly bridged singlet, Cp2Fe2(/i-CO)2. These dicarbonyl species are characterized by iron iron triple bonds. ... 

The reactant is adsorbed on the catalyst s surface. As a reactant molecule attaches to the surface of the catalyst, its bonds are weakened and the reaction can proceed more quickly because the bonds are more easily broken (Fig. 13.36). One important step in the reaction mechanism of the Haber process for the synthesis of ammonia is the adsorption of N2 molecules on the iron catalyst and the weakening of the strong N=N triple bond. 

A similar structure for the iron compound would involve quadrivalent iron, which is very improbable, either bivalent or trivalent iron being expected. If NO loses an electron to iron, assuming the triple-bonded 2 structure, the resulting bivalent iron atom, with six d2sp3 bonds and six unshared 3d electrons, will also be in a l2 state, making the compound as a whole diamagnetic. 

Borst et al. <2005CEJ3631> conducted a study on the synthesis of strained bicyclic phosphirane and phosphirene iron-tetracarbonyl complexes (Scheme 11). It was shown that, depending on the ring size of the resulting heterocycle, electrophilic phosphinidene [Ri-PrNP=Fe(CO)4] could be trapped intramolecularly with both double and triple bonds (compounds 146-150). The phosphinidene addition was found to be reversible at room temperature and when using phenylacetylene as solvent, exchange between phenylacetylene and the phosphinidene group took place. Compound 151 was isolated as the dimer, compound 152. 

In terms of models for reduction of triple bonds, a series of isolated iron carbonyl clusters, which nicely show H-atom mobility, provides a... 

The physical conditions to effect a satisfactory extent of reaction are fairly severe, but are needed to overcome the enormous strength of the nitrogen triple bond. The role of the iron is essential chemisorptive adsorption of nitrogen occurs on the surface of the iron, with charge being donated from the N=N bond to the surface of the iron. As a result, less electron density remains between... 

Very cold. Immersing a clean iron surface into liquid nitrogen at 77 K (—196 °C) yields a weak physisorptive bond. The N=N molecule is probably aligned parallel to the metal surface, with electron density donating from the centroid of the triple bond directly to iron atoms on the surface of the metal via a van der Waals type of interaction. The experimental value of A //fadsj is small at about 1.5 kJ mol-1. 

Figure 10.7 During the adsorption of molecular nitrogen onto iron metal, the two nitrogen atoms donate an increment of charge to adjacent atoms of iron on the metal surface, as depicted by the vertical arrows. The N=N triple bond cleaves partially, with a resultant bond order of about 1.5...

As you learned in Chapter 1, aromatic compounds do not react in the same way that compounds with double or triple bonds do. Benzene s stable ring does not usually accept the addition of other atoms. Instead, aromatic compounds undergo substitution reactions. A hydrogen atom or a functional group that is attached to the benzene ring may be replaced by a different functional group. Figure 2.6 shows two possible reactions for benzene. Notice that iron(III) bromide, FeBrs, is used as a catalyst in the substitution reaction. An addition reaction does not occur because the product of this reaction would be less stable than benzene. 

Again several alkyls add—molybdenum, chromium, iron, cobalt, nickel, the alkali metal alkyls and aluminum alkyls react. A tin alkoxide has recently been studied by Russian workers and found to add to acetylenes. Mercury chloride, of course, adds and two cobalt—cobalt bonded compounds add to acetylene. The second is questionable because it dissociates in solution and the reaction may be a radical reaction, one cobalt adding to each end of the triple bond. 

Cyanopentakis(benzyl isonitrile)iron(II) bromide, which represents a new class of iron isonitrile complexes, was investigated in some detail. This complex is diamagnetic and dissociates in nitrobenzene into two univalent-univalent ions as indicated by cryoscopic and conductivity measurements. It exhibits two peaks in the triple bond region of the infrared spectrum one at 2200 cm.—1 assigned to the isonitrile groups and another at 2092 cm.-1 assigned to the cyano group. The structure proof of cyanopentakis (benzyl isonitrile) iron (II) bromide is ... 

An example of an unsaturated hydrocarbon containing a triple bond is acetylene, C2H2. A confined flame of acetylene burning in oxygen is hot enough to melt iron, which makes acetylene a choice fuel for the welding shown in Figure 12.10. 

Another approach for the ring expansion of epoxides uses low-valent iron complexes which open epoxides under reductive conditions, as reported by Hilt et al. [106]. The iron complexes are reduced and after coordination of the epoxide to the iron center an electron transfer initiates the radical-type ring opening of the epoxide. Under formal insertion of an alkene, regioselective formation of tetrahy-drofurans was observed (Scheme 9.46). The reaction is applicable to a broad range of acceptor-substituted alkenes bearing another double or triple bond system in conjugation with the inserted carbon-carbon double bond. 

Bonding of iron to the CO unit is not symmetrical Fe-C and Fe-O bond lengths of 1.8-1.83 and 2.19-2.25 A, respectively, are typical. IR spectra give a typical vc=o of 1586-1605 cm. The acyl carbon resonance appears at 280 ppm in the C NMR spectra but is not always observable at room temperature. Structurally, ) -iminoacyl complexes (124) are strictly analogous to ) -acyl complexes (115), with a C-N bond length intermediate between double and triple bond length (1.21-1.30 A). 

Very recently, a photochemical synthesis of an Fe(VI) compound has been reported by the Wieghardt group. The octahedrally coordinated iron in [(Me3Cy-ac)FeN](PF6)2 has a Fe=N triple bond of 1.57 A as shown by X-ray absorption spectroscopy. Mossbauer spectroscopy in a field of 7 T shows that the iron is diamagnetic and that the sign of A g is positive (Figure 16). 

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