The electroreduction of heptaphenyltropylium ion to the free radical in acetonitrile

The reduction of heptaphenyltropylium ion (HPT⁺) in acetonitrile solutions containing 0.1 M tetra-n-butylammonium perchlorate at a platinum electrode was studied by cyclic voltammetry and controlled potential coulometry. A reversible wave for the production of the free radical at ?1.20 V vs. SCE was observed. The radical was stable on the voltammetric time scale (～ seconds) but decayed slowly. The production of a dimeric species involving coupling via the phenyl groups and reducible at about ?1.9 V is proposed.