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.