Stable carbocations. Part 12. Generation, observation, and properties of ferrocenyl-stabilised vinyl cations

Abstract

A series of stable ferrocenylvinyl cations has been prepared by protonation of alkynylferrocenes in trifluoroacetic acid, and their structural and chemical properties have been investigated by spectroscopic means. Their stability towards nucleophilic addition is enhanced by alkyl substitution in the ferrocene rings and by steric shielding of the reaction centre. For cations bearing a vinyl β-substituent, torsional isomerisation by rotation around the ring–C⁺ bond has been studied by ¹H n.m.r. spectroscopy.