The Crystal Structures of the Chiral Alkyllithium Bases [<i>n</i>-BuLi·(−)-Sparteine]₂ and [Et₂O·(<i>i</i>-PrLi)₂·(−)-Sparteine]

The crystal structures of the two chiral alkyllithium bases [n-BuLi·(−)-sparteine]2 (1) and [Et2O·(i-PrLi)2·(−)-sparteine] (2) have been determined. For compound 1, a symmetric dimer is observed in the solid state, with two (−)-sparteine ligands coordinating to the lithium centers. Because of steric reasons, compound 2 crystallizes as an unsymmetric dimer with the four methyl groups pointing away from the sterically demanding (−)-sparteine ligand. Compound 2 contains one four-coordinate lithium center [coordinated to (−)-sparteine] and one three-coordinate lithium center (coordinated to Et2O). As a result of this arrangement, significantly different Li−C distances are found in the central four-membered ring of compound 2.已解析两种手性烷基锂碱的晶体结构：[正丁基锂·(−)-金雀花碱]₂（化合物1）与[二乙基醚·(异丙基锂)₂·(−)-金雀花碱]（化合物2）。对于化合物1，固态下其为对称二聚体结构，两个(−)-金雀花碱配体与锂中心配位结合。受位阻因素影响，化合物2结晶为非对称二聚体，其四组甲基均远离位阻较大的(−)-金雀花碱配体。化合物2包含一个与(−)-金雀花碱配位的四配位锂中心，以及一个与二乙基醚配位的三配位锂中心。该结构排布导致化合物2中心四元环内的锂-碳键长存在显著差异。