Stereoselective Recognition of Vicinal Diamines with a Zn(II) Complex

Zn(II) complex of L (N,N‘-bis(2-pyridylmethyl)-N,N‘-dimethyl-trans-1,2-diaminocyclohexane) binds chiral vicinal
diamines (1,2-diphenylethylenediamine (dpen) and 1,2-diaminocyclohexane (dach)) stereoselectively. Crystallographic studies reveal that the ternary complex has the C2
symmetric cis-α topology. 1H NMR shows that the R,R form
of the tetradentate zinc complex binds rapidly and reversibly
to the R,R form of the diamine over the S,S form with a
streoselectivity of about 5:1. Although the diamine exchange
rate is rapid it is slower than the NMR time scale, and distinct
signals for the diastereomeric complexes are observed when
racemic mixtures of the host and guest molecules are mixed.
Origin of stereoselectivity is discussed in terms of steric
effects.

配体L（N,N'-双(2-吡啶甲基)-N,N'-二甲基-反式-1,2-环己二胺）的锌(II)配合物可立体选择性地结合手性邻位二胺：1,2-二苯基乙二胺（dpen）与1,2-环己二胺（dach）。晶体学研究显示，该三元配合物具有C2对称的顺式-α拓扑结构。氢核磁共振波谱（1H NMR）测试表明，相较于S,S构型的二胺，该四齿锌配合物的R,R构型可快速、可逆地结合R,R构型的二胺，立体选择性比例约为5:1。尽管二胺的交换速率较快，但仍慢于核磁共振时间尺度，因此当主体与客体分子的外消旋混合物混合时，可观测到非对映异构配合物的特征信号。本研究从位阻效应角度探讨了该立体选择性的起源。