Solid-state and solution structures of hetero-aggregates formed between nBuLi and NCN pincer aryl lithium.

The reaction of NCNLi pincers (NCN = 2,6-(R(2)NCH(2))(2)C(6)H(3), R = Me (), Et ()) with various equivalents of nBuLi in non-polar solvent results in the generation of novel mixed alkyl-aryl organolithium hetero-aggregates. The identification (variable temperature (1)H, (13)C, (7)Li and 2D NMR spectroscopy and X-ray crystallography) of multiple, equilibrating mixed-aggregates that form in these reactions has been achieved. Fluxional processes in the parent NCNLi dimeric homo-aggregates were re-evaluated and Li-N bond rupture was found to be in operation, a prerequisite towards further aggregation chemistry. The crystallized aggregates, with the formula (2).nBuLi or (2).nBuLi, shows one amine arm from each NCNLi fragment stabilizing a nBuLi dimer. The core of the aggregates exhibit a roughly cubic Li(4)C(4) configuration with each aryl carbanion eta(3) coordinated to Li(3) triangular faces. Dissolution of microcrystalline powders of (2).nBuLi or (2).nBuLi regenerates the observed equilibria. Based on the NMR data, the remaining mixed aggregates are proposed to have the formula .nBuLi and .nBuLi, respectively; the solution structure is again based on a Li(4)C(4) cluster. The relative concentration of the constituents in these equilibria was found to vary depending on the steric size of the amine groups. In the case of , the predominant species is the (2).nBuLi aggregate while for , the dimer (2) is favoured.