Diimines iron complexes

Scheme 4.12 Reduction chemistry of a-diimine iron complexes.

Electronic and vibrational spectroscopy continues to be important in the characterization of iron complexes of all descriptions. Charge-transfer spectra, particularly of solvatochromic ternary diimine-cyanide complexes, can be useful indicators of solvation, while IR and Raman spectra of certain mixed valence complexes have contributed to the investigation of intramolecular electron transfer. Assignments of metal-ligand vibrations in the far IR for the complexes [Fe(8)3] " " were established by means of Fe/ Fe isotopic substitution. " A review of pressure effects on electronic spectra of coordination complexes includes much information about apparatus and methods and about theoretical aspects, though rather little about specific iron complexes. ... 

Other aspects of solvation have included the use of surfactants (SDS, CTAB, Triton X-100), sometimes in pyridine-containing solution, to solubilize and de-aggregate hemes, i.e., to dissolve them in water (see porphyrin complexes, Section 5.4.3.7.2). An example is provided by the solubilization of an iron-copper diporphyrin to permit a study of its reactions with dioxygen and with carbon monoxide in an aqueous environment. Iron complexes have provided the lipophilic and hydrophilic components in the bifunctional phase transfer catalysts [Fe(diimine)2Cl2]Cl and [EtsBzNJpeCU], respectively. 

Cyanide-bridged complexes involving iron-diimine-cyanide complexes are discussed in Section 5.4.3.5.8. 

There is a brief but eomprehensively referenced section on iron in a review of homoleptie 2,2-bipyridyl eomplexes " iron-terpy (3 pages) and iron-quaterpy (1/2 page) complexes have also been briefly reviewed." Absorption spectra and photochemistry of apprcmriate iron diimine complexes are ineluded in a text on polypyridyl and porphyrin complexes." A review of the applieation of ehiral 2,2 -bipyridines, 1,10-phenanthrolines, and 2,2 6, 2"-terpyridines in homogeneous eatalysis eontains a little material on iron complexes of such ligands." ... 

Fe(gmi)3] in glycol-water and a range of other binary aqueous solvent mixtures. These results, along with further results for AV for base hydrolysis of [Fe(phen)3] " and of [Fe(bipy)3] " in alcohol-water mixtures, have permitted the construction of a scheme combiniim solvent and ligand effects on AF for base hydrolysis of a range of diimine-iron(II) complexes. ... 

Fig. 5. Free energy correlations between the rates of reduction of tris diimine)iron(lII) complexes [cf. Eq. (2) ] and the acid dissociation constants of the di- and monoprotonated free ligands. The lines are drawn with slopes of 1.00. The data are from McBryde (11) and from Table II.

The widespread occurrence of iron ores, coupled with the relative ease of extraction of the metal, has led to its extensive use as a constructional material with the result that the analysis of steels by both classic wet and instrumental methods has been pursued with vigour over many years.3 Iron complexes are themselves widely used as the basis of convenient analytical methods for the detection and estimation of iron down to parts per million. Familiar tests for iron(III) in aqueous solution include the formation of Prussian blue as a result of reaction with [Fe(CN)6]4, and the formation of the intensely red-coloured [Fe(H20)5SCN]2+ on reaction with thiocyanate ion.4 Iron(II) forms particularly stable red tris chelates with a,a -diimines such as 1,10-phenanthroline or 2,2 -bipyridine that have been used extensively in spectrophotometric determinations of iron and in the estimation of various anions.5 In gravimetric estimations, iron(III) can be precipitated as the insoluble 8-hydroxyquinoline or a-nitroso-jS-naphthol complex which is then ignited to Fe203.6 In many situations the levels of free [Fe(H20)6]3+ may be controlled through complex formation by addition of edta. 

Table 8 Absorption maxima, extinction coefficients, stability constants, and standard electrode potentials for selected Tris-(l,4-diimine)iron(II) complexes in water...

Tab. 3.1 H nmr shifts of diimine pyridine ligands 63-65 and iron complexes 66, 67, 69 in CD2CI2 (relative to solvent at d=5.25 ppm).

Diimine Palladium and Imine Pyridine Iron Complexes with Halogenophenyl... 

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