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.