Tuning Reactivity of Platinum(II) Complexes

2.2 Mechanism of Ligand Substitution Reactions for Square-planar Complexes
The study of ligand substitution reactions involving coordination compounds has
become an integral part of Inorganic Chemistry. Ligand substitution reaction
mechanisms for transition metal complexes have been categorised by Langford and
Gray 5 into three simple pathways, namely:
i. A dissociative path (D) in which the leaving ligand is lost in the first step.
ii. An associative path (A) in which the entering ligand adds in the first step, producing an
intermediate of increased coordination number.
iii. A concerted path called interchange (I) in which the leaving ligand is moving from the
inner to the outer coordination sphere as the entering group is moving from outer to
inner.
These reaction paths can be summarised according to Equations 2.1–2.3;
D: [L n MX]
A: [L n MX]
I: [L n MX] + Y
-X
+X
+Y
-Y
[L n M]
[L n MXY]
[L n MX]---Y
+Y
-Y
-X
+X
[L n MY]
[L n MY]
where, Y = nucleophile or solvent molecule.
3
[L n MY]---X [L n MY] + X
These reaction paths can also be illustrated as presented in Figure 2.2.
(2.1)
(2.2)
(2.3)