A unique lithium halide complex, [(LiBr)2·3HMPA·toluene]: synthesis from reaction of solid NH4Br with BunLi in HMPA (hexamethylphosphoramide)/toluene media, crystal structure showing two Li–Br units linked by three µ2-HMPA ligands, and detection of 7Li ⋯31P coupling in solutions of the complex

Abstract

Reaction of solid NH₄Br with BuⁿLi and HMPA (hexamethylphosphoramide)(1 : 1 : 2 ratio) in toluene produces (LiBr)₂·3HMPA·toluene, (1), shown by X-ray crystallography to contain (LiBr)₂·3HMPA molecules whose two terminal Li–Br units are linked by three µ₂-HMPA ligands and with toluene molecules lying between these units in the lattice; in arene solutions, the (LiBr)₂·3HMPA units remain intact, giving rise in ⁷Li n.m.r. spectra to 1 : 3 : 3 : 1 quartets caused by through-bond (OP) coupling of each ⁷Li nucleus to three ³¹P(HMPA) centres.