Ligand substitution, kinetic control

One of the most fundamental questions when dealing with the activation of dioxygen by transition metal complexes is whether the process is controlled kinetically by ligand substitution or by electron transfer. A model system that involved the binding of dioxygen to a macrocyclic hexamethylcyclam Co(II) complex to form the correspond-... 

Kinetically inert square-planar complexes are found by d8 low-spin ions, particularly Pt2+. Ligand substitution is associative and correlated with the ease of forming a five coordinate transition state (or intermediate). Substitution is much faster with Ni2+ where five-coordinate complexes such as [Ni(CN)5]3- are more stable than for Pt. For a given metal, the rate of substitution is controlled by ... 

Ligand substitution is thus kinetically faster than antissfe gauche isomerization. Another example of kinetic control in ligand substitution at a dimolybdenum center is seen in the following. Hexane solutions of 1 -MogBrglCHgSiMe (MiM) react... 

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