The homologous series of 1,1′-ferrocenylenebisdihalophosphanes (C5H4PX2)2Fe (X = F, Cl, Br, I): precursors for the first metallocene bridged bisphosphaalkene

Abstract

A facile synthetic access to the homologous series of 1,1′-ferrocenylene bisdihalophosphanes Fc′(PX₂)₂ (X = F, Cl, Br, I; Fc′ = 1,1′-ferrocenediyl = ferrocenylene = –C₅H₄FeC₅H₄–) is reported. The ³¹P NMR spectroscopic data of this series suggest a similar electronic interaction of the –PX₂ unit with the ferrocene system as in monofunctional ferrocenyldihalophosphanes. Crystal structures for Fc′(PCl₂)₂ and Fc′(PBr₂)₂ reveal that the nature of the halogen atom within the phosphane unit strongly influences the twist angle of the ferrocene system, while leaving the other structural parameters mostly unaffected. Based on these bisdihalophosphanes, a synthetic access to the first metallocene bridged bisphosphaalkene ((C₅H₄PC(t-Bu)OTMS)₂Fe) is reported in which the tert-butyl substituents provide sufficient steric pressure to control the E/Z isomeric ratio which leads to the almost exclusive formation of the most stable Z,Z isomer out of the three possible isomers.