Electrochemical Investigations of the Complexes Resulting from the Acid-Promoted Deoxygenation and Dimerization of (N,N′-Ethylenebis(salicylideneaminato))oxovanadium(IV)

Electrochemical confirmation that (N,N′-ethylenebis(saiicylideneaminato))oxovanadium(IV), VO(salen), reacts with trifluoromethanesulfonic acid (CF₃SO₃H) or triphenylmethyl tetrafluoroborate (Ph₃C(BF₄)) to form a deoxygenated complex, V^IV(salen)²⁺, and μ-oxodinuclear complex, [(salen)VOV(salen)]X₂, (X = CF₃SO₃⁻ or BF₄ ⁻) is presented. Cyclic voltammograms of VO(salen) in the presence of CF₃SO₃H or Ph₃C(BF₄) exhibit reversible waves with formal potentials near 0.5 and 0.8 V (vs Ag/AgCl). The cathodic wave at 0.5 V is argued to arise from the combined reduction of V(salen)²⁺ and the μ-oxo dimeric complex and the wave at 0.8 V from the oxidation of the V(salen)²⁺ complex. The diffusion coefficients of these three complexes in acetonitrile were determined. The dimerization of VO(salen) is initiated by deoxygenation of the V=O center by H⁺ or Ph₃C⁺ to produce V(salen)²⁺ which enters into an equilibrium with a second VO(salen) complex to produce the μ-oxo dimer. The kinetics of the second order dimerization reaction were monitored, and the equilibrium contant for the formation of the μ-oxo dimer in acetonitrile was evaluated as 0.7 mM⁻¹.