Comparison of the bis(ferrocenylethynyl)phenylmethylium cation with bis(ferrocenylethenyl)methylium analogues

Several new ferrocenylethynyl derivatives, (FcCC)2CHOH, (FcCC)2CH2, (FcCC)2CPhOH have been synthesised from ethynylferrocene. Attempts to synthesise the corresponding bis(ferrocenylethynyl)-stabilised carbocations by hydroxyl or hydride abstraction from the bridging group was unsuccessful for (FcCC)2CHOH and (FcCC)2CH2, respectively. In the case of (FcCC)2CPhOH, the [(FcCC)2CPh]+ cation could be observed by 1H and 13C NMR, and by UV–Vis–NIR spectroscopy, but was too unstable for isolation or prolonged study in solution. The UV–Vis–NIR spectrum of [(FcCC)2CPh]+ is compared to that of the considerably more stable cations, [Fc(CHCH)2CH]+ and [(FcCHCH)2CPh]+.