Isolation and Structure Analysis of Neohexyllithium Generated by Ether Cleavage: Primary and Secondary Coordination in Alkyllithium Aggregates

Ether cleavage of THF at low temperature affords halide-free neohexyllithium in a two-step reaction via insertion of in situ formed ethylene into the C-Li bond of tert-butyllithium. The crystal structure analysis reveals the formation of tetrameric THF-solvated aggregates in the solid state. The neohexyl ligands adopt a staggered arrangement with respect to the tetrahedral lithium core, in contrast to the eclipsed conformation generally observed in unsolvated species. The different conformations in these oligomers can be rationalized readily by distinguishing between primary and secondary cation coordination.