Iron complexes polydentate ligands

The importance of connectivity in polydentate ligands has been demonstrated by Dahlenberg.193 The classic QP ligand of Venanzi, P(o-PPh2C6H4)3, containing four phosphorus donor atoms, forms a trigonal bipyramidal complex with iron(II), [FeX(QP)]X (X = Cl, Br, I).194 When flexibility is allowed between the phosphorus donor atoms in P(CH2CH2CH2PMe3)3 a distorted octahedral... 

A large number of polydentate Schiff base ligands have been reported, and of particular interest are the iron(II) complexes of ligands such as (42) (R = H, Ph) because they are low-spin, even though they contain only two diimine units.578 The rate of acid aquation of [Fe(42)]2+ is slow, but this depends on acid concentration. Reaction with hydroxide ion is second order, as is that with cyanide ion. The product of the last reaction is not [Fe(CN)6]4-, but [Fe(CN)4(42)]2 that has only one diimine bound to the metal. Related ligands have been prepared and much of the early work has been reviewed.54615"5464... 

Polynuclear iron(II) and cobalt(III) oximehydrazonates have arisen from the template macrocyclization of the initial nonmacrocyclic tris-complexes with polydentate ligands resulting from the condensation of the corresponding diketones and their monooximes with hydrazine [193]. The tris-complexes formed have... 

A large number of mononuclear iron(II) complexes with polydentate ligands (Fig. 6) have been studied as catalysts in hydroxylation reactions of... 

Several other mononuclear iron(II) complexes bearing picolinate, 2-pyra-zine carboxylate or polydentate ligands have been reported to catalyze the hydroxylation of alkanes by H2O2 (Table III). These complexes show a fair activity in the oxidation of alkane with product yields up to 40% based on H2O2. 

Iron polycations are not as well known as chromium or aluminum polycations because of the lability of ferric complexes. Only a few polycations (dimers, trimers) have been characterized in acidic solutions (pH < 1.5) [39]. [Fe2(OH)2] and [Fc20] dimers are present in organic complexes such as L3(H20)Fe(OH>2-Fc(OH2)L3 and LjFeOFeLs, where the L3 ligand is a tridentate picolinate and L5 a tridentate amine [16,40,41]. Other polydentate ligands, such as proteins, are able to stabilize many polynuclear iron complexes [42-45]. The existence of lire aquo complexes [(H20)4Fe2(0H)2(0H2)4] " and [(H20)5Fe20(0H2)s] is very probable in spite of the lack of structural data. 

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