Generation of triarylamine radical cations through reaction of Triarylamines with Cu(II) in acetonitrile : A kinetic investigation of the electron-transfer reaction

Abstract

Triphenylamine derivatives react with Cu(2+) in acetonitrile to give radical cations. which Subsequently Undergo dimerization to provide tetraphenylbenzidine derivatives. Kinetic aspects of radical cation formation were examined by stopped-flow spectrophotometry. A broad range of triphenylamine derivatives Were studied, and the driving force for the electron-transfer reaction ranged from +3.67 to -8.56 kcal M(-1) with rate constants varying from 1.09 x 10(2) to 2.15 x 10(5) M(-1) s(-1) for these systems. Reorganization energy for the electron-transfer reaction was estimated using experimentally determined activation parameters. Filling of the rate data to the Marcus equation using different values of the electronic coupling matrix element H(el) provided a good fit with H(el) = 100 cm(-1) suggesting that electron transfer in the TPA/Cu(2+) system conforms to the Marcus-type electron transfer. Furthermore, the high reorganization obtained from these Studies is consistent with significant bond cleavage in the transition state, and a mechanism consistent with the experimental data is proposed.