Multidentate ligands, substitution

Complex Formation Involving Unsubstituted Metal Ions Multidentate Ligand Substitution... 

Further reports on the kinetics of multidentate-ligand substitution have appeared and it has been shown that the reaction of Ni + with (1) involves an initial and rate-determining bond formation to a pyridine nitrogen. Rate... 

Alternatively, bi- or multidentate ligands can also be used for support. As an additional benefit, the latter offer greater stability for the coordinatively bound metal center against leaching through ligand dissociation and substitution reactions. The first, somewhat remarkable, approach to this is shown in Figure 42.11, based on numerous examples of the support of bidentate phosphines on polymers [1-5]. 

The kinetics and mechanisms of substitution reactions of metal complexes are discussed with emphasis on factors affecting the reactions of chelates and multidentate ligands. Evidence for associative mechanisms is reviewed. The substitution behavior of copper(III) and nickel(III) complexes is presented. Factors affecting the formation and dissociation rates of chelates are considered along with proton-transfer and nucleophilic substitution reactions of metal peptide complexes. The rate constants for the replacement of tripeptides from copper(II) by triethylene-... 

It has been tacitally assumed in this discussion that the second-order formation rate constants measure the simple water substitution process. Although this must apply when unidentate ligands replace coordinated water, a composite process could describe the replacement by multidentate ligands. However, consideration of rate constants for successive formation and dissociation processes suggests that the overall rate of complex formation with flexible bidentate (and probably multidentate) ligands such as diamines, dipyridyl, glycine is probably determined by the rate of expulsion of the first water molecule from the metal aqua ion (56, 80, cf. 3 and 84). 

The reaction is coupled to an indicator color change which is much faster than the metal substitution step. L refers to the multidentate ligands which were employed to avoid multiple relaxations r is the relaxation time. 

The study of supramolecular complexes of metal cations is really nothing more than the coordination chemistry of relatively labile (i.e. ligand substitution is relatively rapid under ambient conditions) metal ions and relatively elaborate, usually chelating or multidentate ligands (see Section 1.5) T It is therefore worth spending a little time reviewing some basics of coordination chemistry before looking at specific supramolecular systems. Experts read no further ... 

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