Extremely Electron-Poor Bis(diarylmethylium)-Substituted Ferrocenes and the First Peroxoferrocenophane

We have prepared and studied extremely electron-poor, deeply colored dicationic 1,1'-bis(diarylmethylium)-substituted ferrocenes [(eta(5)-C5H4-CAr2)(2)Fe](2+) with various aryl substituents as their [B{C6H3(CF3)(2)-3,5}(4)](-) salts. Due to the strong acceptor substitution, the redox potential for the ferrocene-based oxidation of the anisyl- or 2-methylanisyl-substituted congeners 1b(2+) and 1c(2+) is close to or even surpasses that of the second oxidation of parent ferrocene, i.e. the Cp2Fe+/2+ couple. The strongly Lewis-acidic character of these complexes is manifest through strong interactions with donor solvents, which lead to a significant reduction of the intensities of the charge-transfer bands in their electronic spectra and to solvatochromism. The reduced forms of the complexes tend to dimerize or oligomerize as revealed by EPR spectroscopy. Direduced 1b selectively reacts with molecular oxygen to form a peroxo-bis(diarylmethyl)[4]ferrocenophane, which was also characterized by X-ray crystallography.