Interaction of alkyllithium compounds with base : Complex formation between ethyllithium and lithium ethoxide in hydrocarbon solvents

Abstract

Freezing point lowering measurements have been carried out upon cyclohexane solutions containing mixtures of ethyllithium and lithium ethoxide. The results demonstrate that lithium ethoxide forms complexes with ethyllithium. The data are explained in terms of an initial coordination of two molecules of lithium ethoxide at two coordination sites of the hexamer. Subsequent attachment of ethoxide is presumed to occur by formation of clusters of lithium ethoxide at each of the two sites of binding to hexamer. The infrared and proton NMR data are consistent with this model. The 7Li nuclear resonance spectra of solutions containing both ethyllithium and lithium ethoxide exhibit only one absorption, which broadens and shifts to higher field with increasing ethoxide concentration. A rapid exchange of lithium nuclei between ethyllithium and lithium ethoxide is indicated. Interaction of lithium ethoxide with ethyllithium does not appear to promote dissociation of the hexamer. In this respect, it differs from amines and ethers.