Synthetic Methods to Ferrocenomesogens containing a Pendent Ferrocenyl Group

Ferrocene behaves much like a three dimensional arene and is useful for incorporating a metal atom into a molecule that requires a certain degree of structural rigidity such as a liquid crystal.1 The ferrocenyl unit is not only useful for modifying the shape of a molecule; in addition the metal atom with its large electron density can be used to modify the physical properties such as colour, polarisability and magnetism. Following the publication in 1976 of the first examples of ferrocene derivatives with liquid-crystalline properties (type A) 2and more notably since 1988 when the first liquid crystals based on a disubstituted ferrocene were synthesized (type B),3 there has been a growing interest in these compounds amongst chemists. The majority of ferrocenyl-containing liquid crystals or ferrocenomesogens (as we have named them) prepared so far belong to one of the structural types A, B or C. Although the synthesis of derivatives with interesting new shapes continue to be exciting, a systematic approach to structure-liquid crystal activity which will allow meaningful predictions has become necessary.