Tridentate chelate

The monoketone bis(2,2, /V,/V -bipyridyl)ketone forms a [CoinL2]+ complex on reaction with [Co(NH3)4(C03)]+ in water.981 As reported for a quite different Co11 complex, the ketone is hydrated to form the gem diol which binds as a monodeprotonated O-donor along with the two pyridine groups in a tridentate chelate, with very little distortion from octahedral observed in the complex. This appears to represent a facile route for this type of inherently poor donor to achieve coordination. Chelated /3-diketonate anions are long-studied examples of O-donor chelates, and continue to be examined. A simple example is the m-[Co(acac)2(NH 3)2]1 (acac = 2,4-pentane-dionate), structurally characterized and utilized to produce molecular mechanics force field parameters for /3-diketones bound to Co111.982... 

The theoretical study of complexes [IrLCl], [cpIrCl]1, and [IrChfPIfvh]1, where L is a tridentate chelating ligand, has resulted in the establishment of criteria for selecting tridentate chelating ligands for the stabilization of hydridoalkyl complexes [(Me)Ir(L)(H)Cl].550... 

Figure 66 Two cofacial tridentate chelators bound to a square planar metal.

Mononuclear Fe(ll) Spin Crossover Compounds of Tridentate Chelating 1,2,4-Triazole Derivatives... 

The coordination properties of two other classes of tridentate chelating... 

Deferasirox is a tridentate chelator with a high affinity for iron and low affinity for other metals, eg, zinc and copper. It is orally active and well absorbed. In the circulation, it binds iron, and the complex is excreted in the bile. Deferasirox was recently approved for the oral treatment of iron overload caused by blood transfusions, a problem in the treatment of thalassemia and myelodysplastic syndrome. 

Tridentate chelation has been established in aqueous solution (see data in Table 2) and in the solid state (see Table 3) for [Co I (L-HisO)J (5) and [Cou(L-HisO)(D-HisO)] (6), in both phases for the bis complexes of Ni , Zn" and Cd11, for numerous complexes of Co111 and Cr111, and is present in the Mov complex [Mo20 (L-HisO)2] (7). 

Although the pK of the cy-amine group for Lys is within the titratable range and that for Arg would probably become so on coordination, the relatively long methylene chains render any tridentate chelation unlikely, and this appears to be the case.10- 4 The shorter methylene side chains in the synthetic diamine-monocarboxylates ornithine, 2,4-diaminobutanoic acid and 2,3-diamino-propionic acid lead to increased tridentate behaviour in that order. 

From potentiometric and spectroscopic studies it is concluded that the main species at neutral pH is a 1 1 tridentate chelate (11) with a log stability constant of ca. — 4. The claim55 that the stability of this species is comparable to that of the Cu(albumin) complex is rather surprising, since for this to occur the involvement of a histidine in the third amino add position is normally required, and furthermore others have concluded that in blood plasma at least the tripeptide is unlikely to compete against other ligands for the available Cu11.56,57 To illustrate the point that such conclusions from blood plasma simulations are only applicable to that medium, Pickart and Thaler58 have shown that in a cell culture medium the tripeptide considerably enhanced Cu uptake into cells and that this was not affected by a 300-fold molar excess of amino adds, including histidine. 

For synthesizing tris-chelates (or bis-tridentate chelates) the ideal source material is RuC13 3 H20 simply because of its availability. Hypophosphite reduction in the presence of the ligand provides a fairly general, rapid synthetic technique. While there will always be questions of purity for compounds prepared by this route, it is a valuable method for the initial synthesis of a compound to determine general properties before exploring other synthetic routes. 

The capping of both termini of three tridentate chelating units with covalent tripods provides highly rigid macrobicyclic receptors (i.e., cryptands), which are ideally suited for investigating variations of crystal-field parameters within isostructural series. Platas et al. (1999) have iso-... 

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