Formation of dioxygen complexes of transition metal chelates in oxygen saturated aprotic solvents. Cyclic voltammetric evidence at a micro glassy carbon disk electrode

Abstract

Cyclic voltammetry at a micro electrode of Co(II) salen, Fe(II) salen, electrode generated Fe(II)(acac) 2, Fe(II) (salicylaldehyde) 2, Fe(II) (salicylaldoxime) 2, Fe(II) (bipy) 3, Fe(II) (bipy) 2, Co(II) (bipy) 3, Co(II) (benzacac) 2, and electrode generated Co(acac) 2 in oxygen saturated aprotic solvents show positive shift of the O 2 sigmoidal wave, as well as enhancement of the limiting current in the case of the first five compounds. In the case of Co(II) (bipy) 3 the slope of the sigmoidal wave due to O 2 becomes more positive, while for the other two Co(II) complexes there is no change except a small decrease in the wave height. The data are used to correlate and predict the O 2 binding properties of the chelates in solution. The data for the diketone complexes of Co(II) indicate absence of any direct association, which is in line with the interpretation offered in the literature on the mechanism of their catalytic role in the O 2 oxidation of substrates. The mechanism of the autoxidation of dimethylformamide in the presence of Fe(III) (bipy) 3 and Cu(II) (bipy) 2 is elucidated by the observation that these higher valent compounds are reduced to their next lower oxidation state by DMF.