Preferential crystallization of (±)-pinenyllithium·TMEDA

Abstract

(±)-Pinenyllithium·TMEDA or (tetramethylethylenediamine-κ2 N,N′)(η3-6,6-dimethyl-2-methylenebicyclo[3.1.1]heptyl)lithium, [Li(C10H15)(C6H16N2)], is readily prepared from β-pinene, butyllithium and TMEDA, and the racemic material preferentially crystallizes even from 96:4 (92% ee) mixtures of (−)- and (+)-β-pinene, respectively. The structure is monomeric, with the geminal-dimethyl bridge of the bicyclic structure shielding one face of the allyl system, restricting the lithium to the opposite face and preventing the Li–allyl–Li aggregation observed with some other allyllithium systems. The symmetry of the allyl system, bond lengths, bond angles and out-of-plane deviations are compared to existing structures. In addition, a much older structure of this complex is compared to this very recent one.