Structures and relative energies of polylithiated benzenes.

The geometries of dilithiobenzene, trilithiobenzene, tetralithiobenzene, pentalithiobenzene, and hexalithiobenzene were optimized at the B3LYP/6-311+G** level. The lowest energy structures can be understood in terms of maximizing the electrostatic interactions between carbanions and lithium cations. In particular, in-plane lithium cations bridging ortho dianions is a geometric arrangement that is repeatedly found, as epitomized in the star-shaped D6h hexalithiobenzene structure 11a. Disproportionation reactions involving phenyllithium leading to polylithiated benzenes are exothermic, suggesting that it may be posible to prepare highly lithiated aromatic species.