previous page
synopsis
next page

The Intimate Mechanism for Substitution at Square Planar Complexes

The assiciative pathways utilized in the substitution of one ligand for another at a square planar reaction centre


TYPICAL REACTION COORDINATES

The 1st order dependence of the rate of the reaction on:

  • the concentration of the substrate

  • the concentration entering reagent

    Indicates that these complexes undergo substitution of ligands by a bimolecular mechanism.

    Some important points concerning the "intimate" mechanism

    Profile A applies when the energies of the reactants and products are almost equal, and in which the energies of the transition states are almost equal.

    Profile B is appropriate to a reaction for which the bond breaking is rate determining (d mechanism from the intermediate)

    Profile C depicts the situation when bond forming is rate determining, a situation in which the entering group (Y) lies higher in the trans effect series than the leaving group.

    In a few cases the intermediate is reasonable stable and so lies at lower energy than the products.

    For example;

    A reaction profile for a reaction where a quasi-stable intermediate is formed before the transition state: bond breaking in the five-coordinate intermediate is more important than bond making to form the intermediate