Chiral modular n-butyllithium aggregates: nbuli complexes with anisyl fencholates.

Chiral, enantiopure aggregates are formed spontaneously by mixing solutions of n-butyllithium with anisyl fenchols. X-ray crystal analyses reveal the structures of these aggregates with different ortho substituents in the anisyl moieties (X), X = H (1-H), SiMe3 (2-H), tBu (3-H) SiMe2(tBu) (4-H) and Me (5-H). While the complex of 1-BuLi shows a 3:1 composition, 2-BuLi, 3-BuLi and 4-BuLi yield 2:2 stoichiometries. The aggregate 5-BuLi crystallizes with a 2:4 composition and hence is a derivative of hexameric n-butyllithium, in which two trans-situated nBuLi molecules are substituted by lithium fencholate moieties. The variety in the synthesized chiral nBuLi aggregates demonstrates the high propensity of anisyl fencholates to chirally modify nBuLi. Variations in the modular ligand structures by alterations of the ortho-substituents (X) enable tunings of compositions and also of enantioselectivities in nBuLi additions to benzaldehyde.