A practical synthesis of ethynylferrocene from ferrocene carboxaldehyde: Structure of 1,4-diferrocenyl-1,3-butadiyne

Ethynylferrocene was satisfactoryly obtained by a Wittig reaction between ferrocene carboxaldehyde and chloromethylentriph-enylphosphonium ylid to give an E/Z mixture of 2-chloro-1-ferrocenylethene. Both isomers were isolated pure by chemical methods. Reaction of the isomers mixture with n-butyllithium allowed ethynylferrocene to be obtained in good yield. The method was applied in one pot giving the ethynylferrocene and ( E/Z)-1,4-diferrocenyl-but-1-en-3-yne as a secondary product. Oxidative coupling to 1,4-diferrocenyl-1,3-butadiyne has been carried out in quantitative yields. A single-crystal analysis of the diyne was carried out, but the compound is unreactive in solid state.