Chiral Synthesis of a Mononuclear Nickel(II) Complex Formed from an Achiral Tripodal Amine Ligand: Spontaneous Resolution

A neutral chiral mononuclear Ni(II) complex cis-[Ni(NCS)2(tren)] (1) [tren = tris(2-aminoethyl)amine] has been isolated in a reaction of nickel(II) salt with an achiral ligand tren and NH4SCN in a MeOH−H2O (1:1) mixture. The crystal structure of 1 reveals the encapsulation of Ni(II) ions in a facial {NiN6} coordination environment that includes four nitrogen donors from the tetradentate chelate tren and two nitrogen donors from two cis-NCS (monodentate) ligands. The chirality of 1 arises from symmetry breaking of the cis-(NCS)2-Ni(II) octahedral complex by the tetradentate chelate tren. Compound 1 exhibits both its enantiomers in a DMF solution through a Pfeiffer effect when l- and d-arabinose are used as environment substances. The particular synthesis, described herein, offers total spontaneous resolution, as is evidenced from crystal structure and circular dichroism spectral studies.

中性手性单核Ni(II)配合物顺式-[Ni(NCS)₂(tren)](1) [其中tren即三(2-氨基乙基)胺（tris(2-aminoethyl)amine）]，通过镍(II)盐与非手性配体tren、硫氰酸铵（NH₄SCN）在MeOH−H₂O（1:1）混合溶剂中的反应成功分离得到。配合物1的晶体结构显示，Ni(II)离子处于面式{NiN₆}配位环境中，该环境包含来自四齿螯合配体tren的4个氮供体原子，以及来自2个顺式-NCS（单齿）配体的2个氮供体原子。配合物1的手性源于四齿螯合配体tren打破了顺式-(NCS)₂-Ni(II)八面体配合物的对称性。当以L-阿拉伯糖和D-阿拉伯糖作为手性环境试剂时，配合物1在N,N-二甲基甲酰胺（DMF）溶液中通过普菲弗效应（Pfeiffer effect）展现出其两种对映异构体。本文所述的合成方法可实现完全自发拆分，这一点通过晶体结构与圆二色性（circular dichroism）光谱研究得到了验证。