Electrochemistry of the sterically hindered imidazolidine zwitterion and its paramagnetic derivative

To investigate the redox properties of the stable paramagnetic anion 4,4,5,5-tetramethyl-2-oxoimidazolidine-3-oxide-1-olate (1−) and 4,4,5,5-tetramethyl-1,2-dioxoimidazolidin-1-ium-3-olate (zwitterions 2) we used the combined cyclic voltammetry and ESR method. It was found that the electrochemical reduction of the zwitterion in CH3CN (−0.35 V) occurred reversibly and gave 1−. When the cathode potential increased further to −0.95 V, anion 1− was irreversibly reduced to 4,4,5,5-tetramethyl-2-oxoimidazolidine-1,3-diolate (32−), which comproportionated with 2 and was again converted into 1−. It was also found that treatment of the zwitterion with a sevenfold excess of KOH led to its complete disappearance and formation of 1−. Under these conditions, 1− underwent reversible one-electron reduction (−0.55 V) and irreversible oxidation; the latter process occurred when low potentials were applied (∼0.05 V).