Strukturänderungen sterisch und elektronisch aktivierter Ketenderivate bei der elektrochemischen und chemischen Oxidation

Abstract

Substituents at C-12 distinctively influence the electron-transfer behavior of dibenzoheptafulvenes 1 as demonstrated by cyclovoltammetry and by chemical oxidation. Oxidation of the bisdimethylamino compound 1a to the dication 1a^2⊕ occurs in two one-electron steps. In contrast to this the formation of dication 1b^2⊕ from ketene dithioacetal 1b exhibits a single two-electron wave. The electron-transfer processes are accompanied by significant structural reorganization. This follows from the shape of the cyclovoltammograms. Spectroscopic properties of the radical cation 1a^⊙⊕ and the dication 1a^2⊕ are monitored by UV/VIS-spectroelectrochemical measurements. Chemical oxidation of 1a by iodine/Cu^II in methanol leads to anthracenes 5, 6 and methyl formate 7. The mechanism of formation is shortly addressed.