Iron complexes with diimines

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

The steric environment for iron complexes with tridentate pyridine-bis(imine) ligands is similar to that for the Ni diimine complexes, except that the two metal-bound halogen atoms, which are presumably transformed into a polymerization site upon activation, are located in the plane perpendicular to the Fe-N3 plane (9, Figure 6.2), while they are in the Ni-N2 plane of the square planar Ni complexesIn the iron complex-catalyzed polymerizations, the propylene monomer is inserted in a highly regioregular 2,1 -fashion and exclusively yields 1 -propenyl chain ends. The polypropylene that is produced is prevailingly isotactic (up to 67% mmmm at —20 C 69% mm at 0 °C) irrespective... 

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. 

The first example of a helical complex with pre-determined chirality was the dinuclear complex [Fe2(rdt)3], where rdtFl2 is the fungal iron chelator rhodotorulic acid, (15), a dihydroxamate siderophore. Several more helical and chiral Fe " " and Fe complexes are documented in the diimine and in the hydroxamate and catechol sections. A doubly looped ( bow tie ) complex has been constructed with the aid of a tris-terimine ligand (Section 5.4.3.5.7). 

The frequent occurrence of thiocyanate in spin cross-over complexes is documented, in Section 5.4.1.4 above and in connection with diimine and with triazole ligands in Sections 5.4.3.5.9 and 5.4.3.6.3 below, while complex formation with iron(III) appears in Section 5.4.5.1.4. 

Figure 9-37. The oxidation of an iron(n) diimine complex with cerium(iv) results in an oxygen atom transfer to give a complex of the hydroxyimine tautomer of amide 9.22,...

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. 

Complexes with other Bidentate 1,4-Diimines. The thermodynamic stability of the five-membered iron(II) 1,4-diimine chelate ring in low-spin complexes is illustrated by the facile autoxidation of saturated amine complexes to the corresponding colored 1,4-diimine complexes. The first example of this oxidative dehydrogenation is shown in equation (14), and the more recently studied " reaction (15) is known to involve iron(III) species and radical intermediates. Interestingly, the complex [Fe(CN)4(HN=CHCH=NH)] can be obtained by oxidizing [Fe(CN)4(en)] , whereas the tris-ligand complex of this smallest diimine ligand has yet to be prepared. 

With complete exclusion of air, fra i -[FeCl2(H20)4] reacts with acetylacetone to form hydrated bis(2,4-pentanedionato)iron(II). The complex is coordinatively unsaturated and forms an interesting tetrameric structure [Fe4(acac)g] in which two asymmetric triply oxygen bridged dimers (32) are linked by rather long Fe-C bonds (2.785 A, 33). [Fe(acac)2] forms simple hexacoordinate adducts in reaction with a variety of bases, for example, heterocyclic diimines snch as bipyridines. Complexes formed by iron(II) with other /3-diketonates are polymeric and highly air sensitive. Iron(III), however, forms a series of stable highly colored... 

---