Iron complexes monodentate

Le Caer S, Heninger M, Lemaire J, Boissel P, Maitre P, Mestdagh H. (2004) Structural characterization of selectively prepared cationic iron complexes bearing monodentate and bidentate ether ligands using infrared photodissociation spectroscopy. Chem Phys Lett 273-279. 

Based on the EPR spectral changes of the model iron complexes, Fuji et al have described the importance of a monodentate dianionic catecholate Fe species (32) for the reaction with oxygen rather than (31), (33), (34) [92]. It is noticed that the E/D value is ca 0.30 with a monodentate monoanionic catecholate complex (31), ca 0.20 with a bidentate dianionic catecholate complex (33), and 0.12 with monodentate dianionic catecholate complex (32). Nishida et al. have argued that the bidentate complex (33) is inactive for oxygenation, while the monodentate form (31) which has a vacant site for coordination of oxygen is a reactive species, based on the ESR spectroscopy and molecular orbital considerations [93, 94]. 

Sketch (a) the transition state for a concerted metal atom-assisted 3,9 hydride shift (b) two PNP ligands (c) the ligand used for selective dimerization of butadiene (d) a general structure for molybdenum- and tungsten-based metathesis precatalyst (e) a six-coordinate rathenium precatalyst for metathesis (f) a solid isolated from the reaction between Pd(OAc)j plus PRj (R = o-tolyl) (g) a T-shaped palladium complex and a two-coordinate palladium complex with a monodentate phosphine (h) an iron complex with a seven-membered metallacycle (i) the transition state for metal-catalyzed cyclopropanation (j) a rhodium and a copper precatalyst used in cyclopropanation reactions. 

The photocatalytic oxidation of organic and inorganic compounds and the photo-catalytic production of H202 occurs also at the surface of iron(III)(hydr)oxides. It has been proposed (e.g., Hoffmann, 1990 Faust and Hoffmann, 1986) that the oxidation of S(IV) by 02 in atmospheric water is catalyzed by iron(III)(hydr)oxide particles. It is assumed that the reductant (HSO3) is specifically adsorbed at the surface of an iron(III)(hydr)oxide, forming either a monodentate or a bidentate surface complex ... 

Simple ligands can adsorb on iron oxides to form a variety of surface species including mononuclear monodentate, mononuclear bidentate and binuclear mono or bi-dentate complexes (Fig. 11.2) these complexes may also be protonated. How adsorbed ligands (and cations) are coordinated to the oxide surface can be deduced from adsorption data, particularly from the area/adsorbed species and from coadsorption of protons. Spectroscopic techniques such as FTIR and EXAFS can provide further (often direct) information about the nature of the surfaces species and their mode of coordination. In another approach, the surface species which permit satisfactory modelling of the adsorption data are often assumed to predominate. As, however, the species chosen can depend upon the model being used, this method cannot provide an unequivocal indication of surface speciation confirmation by an experimental (preferably spectroscopic) technique is necessary. 

The purple diamagnetic square planar complexes [Ni S2P(OR)2 2] readily add either monodentate or bidentate bases such as py and substituted pyridines,2040,2049 bipy, phen2040,2050 and N-substituted en2051 to form green paramagnetic derivatives which possess either a cis octahedral structure, [NifS OR bipy],2052 [Ni S2P(OEt)2 2phen],20 [Ni S2P(OEt)2 2-tmed]2054 (281) or a irons octahedral structure, [Ni S2P(OEt)2 2py2].1982 The... 

Binding of the catechol to the enzyme occurs before interaction with dioxygen. So the enzyme-substrate complex can be observed under anaerobic conditions. The ESR spectra of these complexes show the iron to be high-spin Fem with axial distortions. Resonance Raman studies show that the catechol is coordinated to the iron, probably in a monodentate mode, as indicated by... 

NMR studies of porphyrin-containing iron(III) complexes are very many owing to their importance in biological systems. The porphyrin systems are tetradentate dianionic ligands and essentially planar, as reported in Fig. 5.7, and allows easy access of monodentate ligands to both the axial coordination positions [15]. 

In general, these reactions are better characterised with chelated thiolate ligands rather than with monodentate thiolates, although many reactions giving rise to monodentate coordinate thioethers are known. A typical example is shown in Fig. 5-77, in which an iron(n) thiolate is converted to a thioether complex. 

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