Multistep redox properties of 2,2′-bipyridylboronium substituted ferrocenes

A high-yield synthesis and the X-ray crystal structure analysis of the dinuclear complex [FcB(bipy)OC6H4O(bipy)BFc](PF6)2, 6(PF6)2, which consists of two ferrocenyl moieties, two 2,2′-bipyridylboronium substituents and a hydroquinone linker, is described. The compound is perfectly stable toward air and moisture. 6(PF6)2 exhibits a ferrocene-centered two-electron oxidation wave and two separate bipyridylboronium-centered two-electron reduction steps. No oxidation of the hydroquinone spacer takes place in the solvent window. 6(PF6)2 is thus able to accept or deliver up to six electrons. Attempts to connect two [FcB(bipy)] fragments using glycol rather than hydroquinone as the bridging element gave the mononuclear complex [FcB(bipy)O(CH2)2OH]PF6 only. A similar reaction scheme that was applied for the generation of [FcB(bipy)O(CH2)2OH]PF6 was employed to synthesize the diol {1,1′-[HO(CH2)2OB(bipy)]2fc}(PF6)2; fc=[(C5H4)2Fe]. This compound is able to store up to five electrons and may find use as a monomer for the generation of cationic, redox-active polyesters and polyurethanes.