Super-Stabilization of π-Conjugated Cations by Annelation to Bicyclic Frameworks

Abstract

As exemplified by the synthesis of the extraordinarily stable tropylium ion, the annelation of cyclic π-conjugated cations with rigid σ-framework, bicyclo[2.2.2]octene, has been found to be an effective method for creation of unusually stable cationic π-conjugated systems. By using this method, detailed X-ray crystallographic studies have been conducted for the monomeric radical-cation salts of hydrocarbons such as cyclooctatetraene and a series of benzenoid condensed aromatics and of sulfur containing compounds such as thiophene, dithiins, and oligothiophenes. Some of these species can be further oxidized to dications, and also undergo intriguing rearrangements to cationic species with novel structures. The results are well interpreted by the use of theoretical calculations. 32