Macrocyclic ligands, complexation

Lindoy, L. F. The Chemistry of Macrocyclic Ligand Complexes Cambridge University Press Cambridge, UK, 1989. 

What is different about macrocyclic ligand complexes ... 

Chelate ring formation may be rate-limiting for polydentate (and especially macrocyclic) ligand complexes. Further, the rates of formation of macrocyclic complexes are sometimes somewhat slower than occur for related open-chain polydentate ligand systems. The additional steric constraints in the cyclic ligand case may restrict the mechanistic pathways available relative to the open-chain case and may even alter the location of the rate-determining step. Indeed, the rate-determining step is not necessarily restricted to the formation of the first or second metal-macrocycle bond but may occur later in the coordination sequence. 

The redox chemistry of macrocyclic ligand complexes has received much attention. There are several reasons for this. 

Selected other metal ion systems. There have been a number of investigations of the reduction of iron macrocyclic ligand complexes. In one such study, the Fe(n) complex [FeL(CH3CN)2]2+ [where L = (292)] was shown to exhibit three reduction waves in acetonitrile (Rakowski Busch, 1973). Controlled-potential electrolysis at the first reduction plateau (—1.2 V) led to isolation of [FeL]+ for which the esr spectrum is typical of a low-spin Fe(i) system. The quasi-reversible Fe(i)/Fe(n) couple occurs at —0.69 V versus Ag/AgN03. 

As mentioned previously, a large number of redox reactions involving macrocyclic ligand complexes have resulted in discrete changes in the unsaturation pattern of a variety of macrocyclic systems. Chemical, electrochemical, and catalytic reactions have been widely used to change the level of unsaturation in such systems. Although the mechanisms of the majority of such transformations are not well understood, it is clear that the reactions tend to proceed via prior change in the oxidation state of the central metal ion. 

Oxidative dehydrogenations of many macrocyclic ligand complexes have now been documented. Typically, these reactions involve conversion of coordinated secondary amines to imine groups. 

The chemistry of macrocyclic ligand complexes/Leonard F. Lindoy. p. cm. 

G. A. Melson, ed. Coordination Chemistry of Macrocyclic Compounds, Plenum, NY 1979 contains several chapters in which the template effect is utilised J. F. Lindoy, The Chemistry of Macrocyclic Ligand Complexes, Cambridge 1989. 

Other aza-donor macrocyclic ligand complexes of manganese(II) have been synthesized using metal template procedures." ... 

Halo-alkenes are common pollutants. Therefore, there is an ongoing study on plausible approaches to the dehalogenation of halo-alkanes. One of these approaches involves their electrocatalytic reduction. NinL2 + (L = a tetraaza macrocyclic ligand) complexes were proposed as plausible electrocatalysts (150). A pulse radiolytic study on the mechanism and kinetics of the reaction ... 

Macrocyclic and maeropolycyclic (cryptate) effects designate the greater thermodynamic stability of macrocyclic ligand complexes compared to nonmacrocyclic analogs. 

L. F. Lindoy, "The Chemistry of Macrocyclic Ligand Complexes", Cambridge University Press, 1989. 

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