Stable carbonium ions. Part I. 2-Ferrocenylnorbornan-2-yl cation

Abstract

The 2-ferrocenylnorbornan-2-yl cation is formed quantitatively on treatment of either 2-ferrocenylnorborn-2-ene or the 2-ferrocenylnorbornan-2-ol epimers with protic acids. The cation, which may also be generated under aprotic conditions by abstraction of hydroxide from the norbornanols using triphenylmethyl tetrafluoroborate, undergoes proton elimination in preference to addition reactions, shows no tendency towards skeletal or hydride-shift rearrangement, but is reversibly converted into a new species in strongly acidic media (>80% H₂SO₄ aq.). The ¹H n.m.r. and electronic spectra of the cation and of methylferrocenyl analogues are discussed.