Fe–Li Interactions in Ferrocenyllithium Compounds

Intermetallic Fe–Li interactions likely occur during some stereoselective lithiation reactions of ferrocene derivatives. The nature of this interaction was assessed for a ferrocene–methyllithium complex as a model system by coupled-cluster methods [CCSD(T)]. The CCSD(T) calculations predicted an interaction energy of –38.0 kJ mol–1 and an Fe–Li distance of 2.75 A. The abilities of commonly used DFT functionals to describe this interaction were also screened. The best agreement of the structural parameters (energy and Fe–Li distance) with the CCSD(T) results was achieved with the dispersion-corrected TPSS functional. DFT calculations were also used for natural bond orbital analysis of the intramolecular Fe–Li interactions in benzylferrocene ortho-lithiated at the phenyl ring. This dimetallic bond can be explained as a donor–acceptor orbital interaction between the Fe lone pair or the C–Fe bonding electrons with the empty Li orbitals.