Protonation kinetics of anionic intermediates in the electrochemical reduction of triphenylethylene: a disproportionation mechanism

Abstract

The voltammetric behaviour of triphenylethylene (T) in dimethylformamide in the presence of traces of proton donor indicates that the radical anion (T^–˙) is stable, the dianion (T^2–) is rapidly protonated, and the resulting carbanion (TH^–) is a relatively strong base. In the presence of added water, T^–˙ decays via disproportionation followed by protonation of T^2–. This was indicated by both homogeneous and voltammetric kinetics. In fact, in homogeneous conditions, the rate of decay is second-order in [T^–˙], enhanced by water, and inhibited by T. Voltammetric kinetics further support the proposed mechanism showing that, under particular conditions, the reaction is rate-limited by the disproportionation step. Alternative mechanisms can be disregarded on the basis of both kinetic and thermodynamic data.