REACTIONS OF COORDINATED LIGANDS

This chapter reviews the reactions of transition metal-bound aromatic heterocycles, focusing on the ways in which metal coordination affects the reactivity of the bound heterocycle in comparison to that of the free ligand. The coordination of a ligand to a metal ion has long been known to alter its chemical properties. The coordination of a ligand to a transition metal perturbs both the d-orbitals of the metal and the molecular orbitals of the ligand via a combination of electronic and steric effects, and these interactions can significantly alter the reactivity of the bound ligand relative to its free counterpart. The coordination to a metal ion also introduces steric constraints that are not present in the free ligand. Consequently, ligand atoms adjacent to the metal ion are sterically hindered and reactivity at these sites may be reduced or indeed totally eliminated. © 1993, Academic Press Inc.