Electro-organic chemistry. Part 2. Structure and anodic peak potential relationships. Cyclophanes. Cyclic voltammetric studies of cation-radical formation and reactions

Abstract

The peak potentials for a series of cyclophanes were measured and compared with those of model compounds. Measurements were performed by cyclic voltammetry in acetonitrile–tetrabutylammonium perchlorate. Cyclic voltammetry revealed that the first electron-transfer step was not reversible and that the rate of electron transfer dominated. Peak potentials measured at 250 mV s^–1 were used for comparison. Compared with xylene the anodic peak potentials were lowered as follows: [2.2]meta-(ΔO₁ 0.75 V), [2.2]para-(0.51 V), and [2,2]meta-, para-cyclophanes (0.29 V). Electron-withdrawing substituents increased the potential of one-electron abstraction from the opposite benzene ring for [2.2]para- and [2.2]metapara-cyclophane reflecting π-π interactions. 5,13-Dialkyl[2.2]metacyclophane had an anomalously low peak potential with ΔO₁ almost 1 V. Other dialkyl derivatives showed no such anomaly indicating the dependence on the position of substitution. Homologous compounds were found to be less anomalous. The geometrical isomers of [2.2](2,7)naphthalenophane behaved differently and the trans-isomer showed two oxidation peaks instead of one with lower O₁ than for the cis-isomer. The possible involvement of a transannular cation-radical from [2.2]metacyclophane is suggested for electrophilic and photolytic reactions as well as for reactions with metal salts.