1,1′-Biferrocenylenes-The More Redox Stable Ferrocenes! New Derivatives, Corrected NMR Assignments, Redox Behavior, and Spectroelectrochemistry

Following an improved protocol, several monosubstituted 1,1'-biferrocenylenes (BFDs) were prepared as a mixture of alpha and beta constitutional isomers. The isomers were separated and their structures assigned from H-1-H-1-COSY and H-1-H-1-ROESY NMR data, resulting in a correction of earlier erroneous assignments. Both redox stages (BFD0/BFD+ and BFD+/BFD2+) were examined by cyclic voltammetry. The reactivity of the parent BFD+ versus that of ferrocenium (Fc(+)) in aqueous solution was evaluated by UV vis spectroscopy, suggesting that ferrocene should be replaced by BFD derivatives for redox applications in aqueous media due to their more than 1000-fold higher kinetic stability. Electronic transitions of monoalkylated BFD+ derivatives were measured by thin-layer spectroelectrochemistry, revealing unperturbed mixed-valence class III systems independent of alpha or beta substitution.