The study of redox reactions of bisarenechromium complexes by the rotating disk and the rotating ring-disk electrode techniques : II. Electrochemical reduction of benzalacetophenone and bis(benzalacetophenone)chromium

Abstract

The processes of electrochemical reduction of free benzalacetophenone and its symmetrical π-complex with chromium in DMSO show two ( e - + e -) and three ( e - + e - + 2 e -), respectively, cathodic waves on the polarization curves. π-Coordination with the chromium atom exerts little influence on the mechanism of the process in the region of the first cathodic wave potentials. In both cases reversible transfer of one electron is followed by dimerization of the primary products of the electrode reaction, i.e. anion-radicals (AR). AR and the products of their dimerization were detected directly by the rotating ring-disk electrode technique. The reactivity of bis(benzalacetophenone)chromium in the reaction ▪ is approximately an order of magnitude lower than that of free benzalacetophenone in a similar reaction: ▪ Accordingly, the half-wave potential of the former reaction is shifted towards a more negative value and the equilibrium constant decreases: log( K c/ K L) = -0.9 ± 0.3. The effect of coordination on the kinetics of AR dimerization is noticeably less. The rate constant of complex AR dimerization, k d C = (1.5 ± 0.7) × 10 4