Donor and acceptor properties of the chromium tricarbonyl substituent in benzylic and. homobenzylic anions, cations, and radicals

Both benzylic cations and anions are strongly stabilized by chromium tricar bonyl complexation, while benzylic radicals are largely unaffected. Density functional theory calculations were performed on primary, secondary, and t ertiary benzylic species to explore the effect of substitution on the stabi lizing ability of the chromium tricarbonyl moiety. Complexed 1-indanyl spec ies were also examined to elucidate the effect of conformational restraint. It was found that the strong stabilization of benzylic anions and the slig ht destabilization of benzylic radicals by chromium tricarbonyl are insensi tive to skeletal changes. Chromium-complexed benzylic cations, however, are highly sensitive to changes in the organic framework, with increased subst itution or constriction of conformational mobility eroding the effect of th e metal. 2-Indanyl species were also examined to study the effect of the ch romium tricarbonyl fragment on homobenzylic species. It was found that the metal fragment stabilizes distant anions by field and inductive effects and cations by a direct interaction of the metal with the cationic carbon. Hom obenzylic radicals, however, do not interact with the chromium tricarbonyl moiety and suffer a slight inductive destabilization.