Electronic Communication in a Series of Novel Multistep Redox Systems

The dinuclear ferrocene complexes {[FcBbipy]2O}(PF6)2, [5](PF6)2, and {[FcBbipy]2C(H)CN}(PF6)2, [7](PF6)2, and the ansa-ferrocenes [1,1‘-fc(Bbipy)2NC6H4OMe](PF6)2, [11](PF6)2, and [1,1‘-fc(Bbipy)2NSiMe3](CO2CF3)2, [13](CO2CF3)2, have been synthesized and characterized by X-ray crystallography and cyclic voltammetry [Fc = (C5H5)Fe(C5H4); fc = (C5H4)2Fe; bipy = 2,2‘-bipyridine]. Electronic communication between the two 2,2‘-bipyridylboronium substituents of each compound was observed, suggesting the reduced radical species to be partially delocalized redox intermediates. The degree of electronic interaction is largely independent from the degree of conformational flexibility of the individual molecule. While charge-transfer processes from the electron-rich ferrocene/1,1‘-ferrocenylene moieties into empty π-orbitals of the electron-poor 2,2‘-bipyridylboronium cations are well apparent in all compounds, no evidence for charge-transfer interactions from the 4-methoxyphenyl substituent to the [Bbipy]+ fragments of [11](PF6)2 could be detected.