Electrochemistry and oxygenation kinetics of tetradentate Schiff base manganese(II) complexes

The electrochemistry and oxygenation kinetics of a series of Mn(II) complexes containing ligands derived from substituted salicylaldehyde and linear diamines have been studied. Complexes prepared from ethylenediamine produce cyclic voltammograms with a quasi-reversible Mn(II)-Mn(III) couple and oxygenation reactions which are first-order in both complex and O₂, indicating formation of an Mn(III)-O⁻₂ species as the slow step in the reaction. The case of oxidation/oxygenation increases with increasing electron-donating ability of substituents on the salicyladehyde rings. Complexes with from six to 10 methylene groups in the diamine precursor produce highly irreversible voltammograms and oxygenation data which can not be interpreted in terms of a simple mechanism. Polymerization of the complexes is advanced as an explanation for these effects.