Kenneth A. Goldsby

Oxidation of nickel(II) bis(salicylaldimine) complexes: Solvent control of the ultimate redox site

Abstract The oxidation of nickel(II) bis(salicylaldimine) complexes has been examined by cyclic voltammetry. The complexes are reversibly oxidized in strong donor solvents, but in weak donor solvents, they are oxidatively polymerized at the electrode surface. A ligand-radical coupling mechanism involving the phenolic portion of the salicylaldimine chelate is proposed, and the solvent dependence is explained in terms of the solvents ability to stabilize the nickel(III) oxidation state relative to ligand-localized oxidation.

Symmetric and Unsymmetric Nickel(II) Schiff Base Complexes; Metal-Localized Versus Ligand-Localized Oxidation

The oxidation of symmetric and unsymmetric nickel(II) Schiff base complexes was examined in acetonitrile by cyclic voltammetry. Unlike nickel(II) bis(salicylaldimine) complexes which undergo oxidative polymerization at the electrode surface, the complexes examined in this study contain at least one β-ketoimine chelate and are irreversibly oxidized at the electrode surface. The mixed chelate complexes are oxidized at potentials midway between those of the symmetric bis(salicylaldimine) and bis(β-ketoimine) complexes, suggesting a metal-localized rather than a ligand-localized oxidation. Oxidation of nickel(II) to nickel(III) followed by rapid intramolecular electron transfer to give reactive ligand-radical species is proposed to explain the irreversible oxidation of the nickel(II) Schiff base complexes.

PH-DEPENDENT METAL-BASED REDOX COUPLES AS MODELS FOR PROTON-COUPLED ELECTRON TRANSFER REACTIONS

Abstract An overview of proton-coupled electron transfer in transition metal–ligand systems known to exhibit pH-dependent metal-based redox potentials is presented. The systems of interest can be thought of as MLH m complexes, where M is a redox-active metal and LH m is a ligand in the inner-coordination sphere containing at least one ionizable hydrogen. The use of pH-dependent redox potentials to determine proton-coupled electron transfer reactions is described, along with some important factors for designing and studying complexes that exhibit this behavior. This chemistry is illustrated by a survey of the common transition metal–ligand systems known to give pH-dependent redox potentials indicative of proton-coupled electron transfer.