Molecular Structure of Fluorenyllithium,

The orange precipitate obtained after the well-known preparation of fluorenyllithium was recrystallized from a solution of benzene or toluene in order to get orange-red crystals which were of sufficient quality for X-ray diffraction. By this procedure we succeeded in redetermining the molecular structure of a donor-free unsubstituted fluorenyllithium compound, which might be the smallest alkali-metal compound containing a donor-free cyclopentadienyl-like ligand within an annelated ring system to date. The description of the bonding situation is based on ab initio calculations as well as on a comparison with analogous compounds.