Stable carbonium ions. Part V. Distribution of positive charge in ferrocenylalkylium ions and factors influencing their relative thermodynamic stabilities

Abstract

From pK_R⁺ measurements, evidence relating to the distribution of positive charge in ferrocenylalkylium ions has been obtained. The 1-ferrocenyl-1-methylethylium cation is more stabilised by methyl substitution at the β- than at the 1′-position while substitution at the α-position exerts a destabilising effect. Cation stability is also sensitive to structural deformation of the system caused by interannular bridging. The mixtures of products formed in the reactions of a series of 1-(acetylferrocenyl)-3-phenylallylium cations with sodium methoxide have been analysed. An acetyl substituent reduces the capacity of the ferrocenyl group to delocalise positive charge. A ruthenocenyl group is more effective than a ferrocenyl group in stabilising a carbonium ion.