The study of redox reactions of bisarenechromium complexes by the rotating disk and the rotating ring disk electrode techniques: III. Cathodic reduction of chromium(0) π-complexes and the corresponding arenes in dimethyl sulfoxide solutions

Abstract

The rotating disk (RDE) and the rotating ring-disk (RRDE) electrode techniques have been employed to study the cathodic behavior of eight bisarenechromium complexes and seven corresponding arenes in DMSO solutions. In the first electrochemical step of the process reversible addition of one electron results in anion-radicals, whose formation has been demonstrated for certain arenes and chromium π-complexes by oxidation of these particles on the ring electrode. Substituents on different ligands of bisarenechromium complexes were found to exert pronounced mutual influences. The role of the chromium atom in transfer of electronic effects from one ligand to another is discussed. It was found that a linear correlation exists between the variations in the free energy of the equilibrium “initial compound ▪ anion-radical” (due to coordination of free arene with chromium which is displayed as a shift of the cathodic process half-wave potential Δ E 1 2 CL) and the half-wave potential of the oxidation of the corresponding Cr 0 π-complex to a cation E 1 2 X Δ E 1 2 CL = a + α E 1 2 X At E 1 2 X < −0.3 V, complex formation slows down the cathodic process and at E 1 2 X > −0.3 V the process is facilitated.