Synthesis of a vinylene-bridged ferrocene-hydroquinone complex and its unusual structural change originated by proton-coupled electron transfer

The vinylene-bridged ferrocene−hydroquinone complex, 2-(2-ferrocenylvinyl)hydroquinone, 1, underwent 2-electron oxidation and 2-proton elimination by a redox reaction with 1,1‘-dichloroferrocenium hexafluorophosphate as a 1-electron oxidizing agent in methanol to form 3, which includes a novel allene and a quinonoid structure. The quinonoid compound 3 shows interesting proton response to generate a semiquinone−ferrocenium compound 2-1 through proton-coupled intramolecular electron transfer in acetonitrile.