Multidentate ligand, substitution reactions

It had been hoped that the reaction of [MoOaCdien)] with oxine, to yield the known compound [Mo02(OH)2(oxine)], would be amenable to kinetic study, to provide rate and mechanism data pertaining to substitution at octahedral molybdenum(vi). Sadly the proposed investigation proved impossible, as [MoOaCdien)] was found to be extensively hydrolysed in aqueous solution. An understanding of multidentate ligand-replacement reactions is helped by knowledge of dissociation mechanisms for these chelates. Recent studies resulting in kinetic or mechanistic information on the dissociation of amino-carb-... 

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-... 

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 equilibrium between a metal ion, a multidentate ligand and the resulting complex, can be formally represented by the substitution reaction-scheme ... 

With the purpose to design alkoxy bridged dinuclear metal complexes in which the presence of five and six coordinated metal centers is enforced by the ligand in the assembly process, new routes to multidentate ligands were developed. The first method (scheme 8) is based on sequential aromatic Mannich reactions of para-substituted phenols. In this way dinucleating ligand 22, which can bind two metal atoms in chemical or geometrical distinct environments, is accessible. 

Many kinetic investigations have been carried out on substitution reactions of planar Pt(II) complexes. The entering group in these reactions can be either a mono- or multidentate ligand,... 

Reactions of zinc(n) and cobalt(n) complexes of ida, Hida, nta , Eten, and dien with cydta - and Hcydta have been studied. The steric effect of the cyclohexane ring in cydta on the rate of substitution is discussed. Other reports of the replacement of one multidentate ligand by another have appeared for the systems Ni(Hida) + dtpa, Ni(edta-OH) -I- dtpa, and Co(gedta) + (edta-OH) [Hida = A-(2-hydroxyethyl)iminodiacetate, (edta-OH) = lV-(2-hydroxyethyI)ethylenedi-amine-AW A -triacetate, gedta = 2,2 -ethylenedioxybis(ethyIamine)-AAW JV -tetra-acetate). Similar studies of aminopolycarboxylate replacement have appeared for zinc(n), lead(n), and cadmium(n). ... 

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