Impact of the α-Ferrocenyl Group on the Solvolytic Reactivity – Electrofugality – of Ferrocenylphenylmethyl Cations

The electron-donating effect of the ferrocenyl group in -position to the reaction center on S(N)1 solvolytic reactivity has been quantified by determining the electrofugalities (E-f) of a series of ferrocenyl-X-phenylmethyl cations according to the LFER equation: logk = s(f)(E-f + N-f). Due to highly stabilized transition state, the E-f values are about eight units higher than those of the corresponding benzhydryl cations. Impact of the phenyl group in ferrocenylphenylmethyl derivatives on stabilization of the positive charge is somewhat leveled by the ferrocenyl group, so the rate effect of the substituents on the phenyl ring is suppressed, causing narrow range of E-f parameters and small absolute values of the (+) constant. Calculations at B2PLYP-D3/may-cc-pVTZ level of theory showed that the positive charge in ferrocenylphenylmethyl cation is largely shifted from the phenyl to ferrocenyl moiety, and that the substituents on the phenyl ring have small impact on its stability.