J Org Chem. 2014 Feb 7;79(3):1032-9. doi: 10.1021/jo402498z.
Crystal structure determination of lithiated N-methylaniline with a variety of ligands, including tetrahydrofuran, methyltetrahydrofuran, trans-2,5-dimethyltetrahydrofuran, dimethoxyethane, tetrahydropyran and N,N-diethylpropionamide, reveals a common Li–N–Li–N four-membered-ring dimeric structure motif. A progression of solvation from tetrasolvated dimer (PhNMeLi·S2)2 through trisolvated dimer to disolvated dimer (PhNMeLi·S)2 was observed by increasing the steric hindrance of the ligand. Solid-state structures of several other lithium N-alkylanilides solvated by tetrahydrofuan are also reported. When the methyl group of N-methylaniline is replaced by an isopropyl or a phenyl group, trisolvated monomers are formed instead of dimers. Interestingly, the solid-state structure of lithiated N-isobutylaniline in tetrahydrofuran is a trisolvated dimer while that of lithium N-neopentylanilide is a disolvated dimer.
用各种配体（包括四氢呋喃、甲基四氢呋喃、反式-2,5-二甲基四氢呋喃、二甲氧基乙烷、四氢吡喃和 N,N-二乙基丙酰胺）对锂离子化 N-甲基苯胺进行晶体结构测定，揭示了一种常见的 Li–N–Li–N 四元环二聚体结构模式。通过增加配体的空间位阻，观察到从四配位二聚体（PhNMeLi·S2）2 到三配位二聚体到二配位二聚体（PhNMeLi·S）2 的溶剂化进展。还报道了几种由四氢呋喃溶剂化的其他锂 N-烷基苯胺的固态结构。当 N-甲基苯胺的甲基被异丙基或苯基取代时，形成三配位单体而不是二聚体。有趣的是，在四氢呋喃中，锂离子化 N-异丁基苯胺的固态结构是三配位二聚体，而锂离子化 N-新戊基苯胺的固态结构是二配位二聚体。
