Air and Moisture Stable para - and ortho -Quinodimethane Derivatives Derived from bis - N -Heterocyclic Olefins.

Herein we report the development of a new methodology for the synthesis of various quinodimethane derivatives under two-electron oxidation of --heterocyclic olefins linked by different π-conjugated aromatic spacers. In case of - and -phenylene bridge, we obtained air and moisture stable diimidazolium - and -quinodimethane derivatives. Analogues of the -phenylene spacer such as tetrafluoro--phenylene and -anthracene also led to the corresponding air and moisture stable quinodimethane derivatives. This emphasizes the influence of imidazolium substituents which facilitate the air and moisture stability of the quinodimethane derivatives. Differences were observed for the electron transfer processes: two one-electron vs one two-electron redox transitions between --heterocyclic olefins and diimidazolium-quinodimethanes depending on the employed π-conjugated aromatic spacer. The formation of the π-conjugated radical-cations, transient redox intermediates between --heterocyclic olefins and diimidazolium-quinodimethanes, was addressed by an EPR investigation.