The Redox Behavior of Transition Metal Complexes with Soft Ligands

Abstract

Recent electrochemical investigations of binary mesityl compounds of the early transition metals and of a series of nickel(0) complexes illustrate the influence of the nature and oxidation state of the central atom and of the ligands on the redox behavior. On the basis of macrocyclic nickel(II) complexes, the effects of ring size and unsaturation of the ligand on the redox potential and on the site of electron addition [one-electron reduction of nickel(II) or of the ligand] are demonstrated. The electrochemical data may be used for an explanation or even for a prediction of the course of chemical reactions. A remarkable process is the nucleophilic substitution of unsaturated organic substrates (maleic acid anhydride, quinones) within the coordination sphere of nickel(0) which yields a radical anion.