Substitution reactions in square planar complexes

Substitution Reactions in Square Planar Complexes 538 Thermodynamic and Kinetic Stability 547 Kinetics of Octahedral Substitution 548 Mechanisms of Redox Reactions 557... 

Associative mechanism for substitution reactions in square planar complexes. Sites above or below the plane are inherently readily accessible to incoming ligands. 

Eighteen-electron complexes react more slowly than similar complexes with either more or less electrons. The eighteen-electron rule explains why some reactions are associative and others dissociative. Complexes in which the metal has sixteen or less valence electrons tend to react by associative mechanisms, since the metal has vacant low-energy orbitals which can be used to form a bond with the entering ligand. This orbital can accept an electron pair from an entering ligand and provide a path for associative substitution. Substitution reactions in square planar complexes illustrate this point, reaction (40). 

Substitution reactions in square planar complexes take place via associative mechanisms. In the kinetic trans effect, a series can be constructed in which species are put in order of their ability to labilize ligands trans to themselves. Using this series, high-purity square planar isomers can be readily synthesized. The trans-directing ability of a ligand is also directly related to its polarizability. 

Figure 1 A ligand substitution reaction in square planar complex showing two possible isomeric products.

The knowledge of trans effect while carrying out substitution reactions in square planar complexes has provided two interesting applications ... 

FACTORS AFFECTING THE RATE OF SUBSTITUTION REACTIONS IN SQUARE PLANAR COMPLEXES... 

The observed rate of substitution reactions in square planar complexes is the result of multifaceted interplay between several factors. The effect of some such factors is summarized in Table 1. 

Solvent The identification of solvent path for the substitution reactions in square planar complexes has increased the importance of solvent effect on the rate. The solvents with greater coordinating abfiity show faster rates of substitution reactions. The observed rate constants for some of the popular solvents vary as ROH < H2O < CH3NO2 < (CH3)2S0... 

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