Synthesis of ferrocene derivatives with pi-extended conjugation

Synthesis of (E)-1-ferrocenyl-2-(p-iodophenyl)ethene was carried out by means of the Wittig reaction between the p-iodobenzyl triphenylphosphonium ylid and the ferrocene carboxaldehyde, satisfactory as a mixture of E/Z isomers. Isomerization Z --> E was induced by iodine-NBS in quantitative yield. The X-ray molecular structure of this (E)-isomer indicates that the molecules are linked by charge transfer complexation between the iodine atom and the cyclopentadiene ring. The conjugation of the molecule of 1-ferrocenyl-2-(p-iodophenyl)ethene was expanded to the (Z,Z)- and(E, E)-1,4-di[1-ferrocenyl-2- (p-iodophenyl)ethenyl]biphenyl and to the (Z,Z)- and (E,E)-1,4-di(1-ferrocenyl-2-(p-phenylethenyl)-1,3-butadiyne, both as centrosymmetric structures.