Synthesis of ferrocene derivatives with π-extended conjugation

Abstract

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 l-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(l-ferrocenyl-2-( p-phenylethenyl)-1,3-butadiyne, both as centrosymmetric structures.