Pentabenzylcyclopentadienides of Lithium

(Pentabenzylcyclopentadienyl)lithium (Li(η5-C5Bz5)) has been prepared by lithiation of pentabenzylcyclopentadiene with tert-butyllithium in toluene or benzene. This compound, which is the nonisolated starting material for most of the known pentabenzylcyclopentadienides, has been characterized by NMR and mass spectroscopy. The molecular structure of the benzene adduct of dimeric Li(η5-C5Bz5) has been determined by X-ray diffraction studies. A triple-decker-like structure, (η5-C5Bz5)Li(η5-C5Bz5)Li(η2-C6H6), results. The reaction of Li(η5-C5Bz5) with Al(η5-C5Me5) leads to Al(η5-C5Bz5) and Li(η5-C5Me5), with [Li(η5-C5Bz5)2][Al(η5-C5Me5)2] as a side product. The molecular structure of the last-named compound consists of the separated sandwich ions [Li(η5-C5Bz5)2]- and [Al(η5-C5Me5)2]+.