Multinuclear NMR study of the aggregates between methyllithium and lithium bromide in toluene

A set of high-field, low-temperature NMR experiments has been conducted on various mixtures of (MeLi)-Li-6 and (LiBr)-Li-6 in toluene. All the Li-6 and H-1 signals of the (MeLi)(n)(LiBr)(4-n) aggregates were unambiguously assigned via one- and two-dimensional (HOESY and COSY) experiments. The influence of the MeLi/LiBr ratio on the concentration of these different aggregates in solution was then studied. The data suggest that the populations of the five possible complexes follow an almost purely statistical distribution with the exception of the MeLi(LiBr)(3) species. The later, which was found to be less abundant than expected, is also less favored on the basis of aggregation energies obtained from density functional theory calculations.