Structural investigation of aryllithium clusters in solution I. A 13C and 7Li NMR study of phenyllithium and some methyl-substituted phenyllithium derivatives

Abstract

13C and 7Li NMR spectra of phenyllithium and several methyl subsituted phenyllithium derivatives have been recorded in the presence of known amounts of coordinating solvents such as monodentate diethyl ether and THF and the potentially bidentate TMEDA (tetramethylethylenediamine). The relative amounts of the tetrameric and dimeric aggregates identified in these spectra depend on the donor strength, on the amount and denticity of added donor, and the presence or absence of ortho substituents in the phenyl group. Discrete solvated tetrameric aggregates were formed upon addition of exactly one equivalent of the monodentate donor solvent to an aryllithium compound having no ortho substituents; the addition of either two equivalents or excess of monodentate donor solvent or one equivalent of bidentate donor ligand afforded dimeric species. When one or two methyl substituents were present ortho to the lithium-carbon bond, either a mixture of dimeric and tetrameric species was formed (one methyl group) or the dimeric species was exclusively formed (two methyl groups).