Kinetics Ligand exchange reaction

Hering, J. G. and Morel, F. M. M. (1990). Kinetics of trace metal complexation ligand-exchange reactions, Environ. Sci. Technol., 24, 242-252. 

The kinetics of various ligand exchange reactions have been studied by the conductometric methods. 

Kinetic studies of ligand exchange reactions seek to elucidate the mecha-... 

Octahedral six-coordination is especially favoured by the low-spin d6 configuration. This can be understood in terms of simple CFSE considerations. For M(III) (M = Co, Rh, Ir) and Pt(IV), hardly any complexes other than octahedral ones are known. These complexes are kinetically fairly inert, in the sense that they undergo ligand exchange reactions slowly. For this reason, much of our knowledge of kinetics and mechanism in transition element chemistry has come from studies of low-spin d6 octahedral complexes (see Sections 9.4 and 9.5). 

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). 

Scheme VII classifies potential spectator ligands according to their ligation mode. Ansa, doubly charged A-type ligands, have been prominent in catalytic investigations up to now and are usually employed in a neutral, heteroleptic form. The additional Ln-R moiety directs the catalytic reactivity in a nonspectator manner Due to its kinetic lability, the Ln-R bond is accessible to ligand exchange reactions, as shown in ansa-cyclopentadienyl-supported catalysts for hydrogenation and polymerization reactions [83]. Biphenol or binaphthol ligands [175], the latter of which was recently successfully applied (e.g. in...

The appropriateness of this speciation calculation from the kinetics standpoint can be assessed by considering the associative ligand-exchange reaction (cf. Eq. 2.12) ... 

Stability constants are not always the best predictive tool for measuring the ease and the extent of chemical reactions involving complexes nor their stability with time, because their kinetic behavior can often be even more crucial. For example, when ligand exchange reactions of ML (e.g., [FeEDTA]) with other metal ions (e.g., Zn2+ or Ca2+) are ki-netically slow, they do not significantly influence ligand speciation. Another typical example of the thermodynamics vs kinetics competition is the fact that the degradability of some metal complexes (e.g., metal-NTA) is related to their kinetic lability, rather than to their thermodynamic stability constants. Kinetic rather than thermodynamic data are then used to classify metal complexes as labile, quasi-labile, slowly labile, and inert (or stable). See Section 3.2.6. 

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