Syntheses and Crystal Structures of Phenyl-Lithium Derivatives

Although organolithium compounds have been studied and applied for ∼100 years, only few crystal structures of pure, unsolvated organolithium compounds have been reported so far. Therefore, several phenyl-lithium derivatives were synthesized by lithium-halogen exchange reactions, yielding fairly soluble polymers in the cases of 4- and 2-methylphenyl-lithium ( p-TolLi and o-TolLi). Their crystal structures have been determined by X-ray powder diffraction. Remarkably, o-TolLi crystallizes in the noncentrosymmetric space group P2₁2₁2₁ with two independent monomers, whereas the crystal structure of p-TolLi is described in spacegroup P2₁/ a. In contrast, no polymer of 5- m-XyLi (3,5-dimethyl-phenyl-lithium) could be observed, but single crystals of a [(5- m-XyLi)₃(MTBE)₃LiBr] adduct were isolated (MTBE = methyl- tert-butylether). This gives hints on the nature of lithium-halogen exchange reactions. Steric and electronic effects of the phenyl-lithium substitution are further discussed in conjunction with related compounds.