A CRYSTALLOGRAPHIC AND COMPUTATIONAL STUDY OF A DIETHYL-ETHER COMPLEXOF FLUORENYLLITHIUM

The structure of a diethyl ether (DEE) complex of fluorenyllithium, [L i(C13H9)(DEE)(2)], was investigated by X-ray crystallography and quant um chemical calculations. In the crystal structure, the lithium cation interacts in an eta(2)-arrangement with the fluorenyl anion at distan ces of 2.26 and 2.31 Angstrom away from C9 and C10. In contrast to the uncomplexed ion pair where recent calculations revealed that Lif is s ituated over the five-membered ring, calculations at the B3LYP/6-31+G( d)/B3LYP/6-31G(d) level show that for the DEE-coordinated complex, the optimal structure resembles the X-ray structure. Since the eta(2)-arr angement is the global minimum in both the solid state and gas phase, it was concluded that crystal packing is not the main factor that caus es the lithium cation to change position when going from the uncomplex ed to the DEE-complexed fluorenyllithium. A comparison with the smalle r water-coordinated complex indicates that intramolecular steric inter actions within,the DEE-coordinated complex lead to an eta(2)-arrangeme nt instead.