Ligand exchange kinetic stability

If the metals bound in complexes exchange with biological ligands, the dissociation kinetics of these complexes, the ligand-exchange kinetics and the association kinetics with the biological ligands must be considered. Simple dissociation kinetics of complexes are related to their thermodynamic stability constants by the relationship ... 

M2(h-02C-R)4] type binuclear paddle-wheel complexes, where M = V, Nb, Cr, Mo, W, Tc, Re, Ru, Os, Co, Rh, Ir, Pd, Pt, and Cu, are potentially useful for the preparation of analogous linear coordination polymers extending the series. However, the stability of those structures will depend on the magnitude of the formation constants and ligand exchange kinetic constants of each binuclear complex. 

Chelation kinetics Stability constants Ligand exchange... 

The kinetically-stabilized complexes of the cage ligands normally yield redox reagents free of the exchange problems often associated with simple complexes. Indeed, the redox chemistry of the complexes shows a number of unusual features for example, saturated cages of the type mentioned in Chapter 3 are able to stabilize rare (monomeric) octahedral Rh(n) species (d7 electronic configuration) (Harrowfield etal., 1983). In a further study, radiolytical or electrochemical reduction of the Pt(iv) complexes of particular cages has been demonstrated to yield transient complexes of platinum in the unusual 3+ oxidation state (Boucher et al., 1983). 

The chelate ligand in dionato complex 3 is planar and it is particularly stabilized by 71-delocalization. In addition to this thermodynamic stability, the iron center has 17 valence electrons in an octahedron, hence its coordination sphere is kinetically labile. By ligand exchange, the acceptor 41a is coordinated at a vacant site to form species 44 (Scheme 8.18). The function of the center metal is not only to hold the acceptor in proximity to the donor. Additionally, the acceptor is activated by Lewis acidity of the center metal. Subsequently, the nucleophilic carbon atom of the dionato ligand is... 

The results and experience that have accumulated from studies of the exchange reactions of the aminopolycarboxylates of different lanthanides are very useful in the assessment of the kinetic stabilities of the Gd3+ chelates. In the body fluids where the CAs are administered, the Gd3+ chelates are surrounded by various endogenous metal ions and ligands. Some of these metal ions can react with the Gd3+ chelate by displacing Gd3+ in a metal-metal exchange reaction ... 

Despite the kinetic lability of the Ln-X-cr-bonds (even the thermodynamically very stable Ln-OR bond is subject to rapid ligand exchange reactions [49]) organolanthanide compounds are thermally very robust over a wide range of temperature (Fig. 5) [114, 116, 139, 144-151]. Thermal stability is not only favorable in catalytic transformations at elevated temperatures [47], for the support of volatile molecular precursors is of fundamental importance in chemical vapor deposition techniques the sublimation behavior is a criterion of thermal stability and suitability for these processes (Fig. 5). 

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