Selective imidazolidine ring opening during complex formation of iron(III), copper(II), and zinc(II) with a multidentate ligand obtained from 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine.
Selective imidazolidine ring opening during complex formation of iron(III), copper(II), and zinc(II) with a multidentate ligand obtained from 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine.
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DOI：
10.1021/ic9914037
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发表时间：
2000-07
影响因子：
4.6
通讯作者：
M. Boča;P. Baran;R. Boča;H. Fuess,;G. Kickelbick;W. Linert;F. Renz;I. Svoboda,
中科院分区：
文献类型：
--
作者：
M. Boča;P. Baran;R. Boča;H. Fuess,;G. Kickelbick;W. Linert;F. Renz;I. Svoboda,
2-吡啶甲醛N-氧化物与三乙烯四胺的缩合反应生成了带有两个咪唑烷环的产物，固体X射线结构分析和核磁共振溶液光谱都证明了这一点。这种配体L1与铜(II)形成络合物时发生开环反应，生成[CuL2]2+，其中L2作为五齿配体，只含有一个咪唑烷环。在与锌(II)和铁(III)配位时，两个环都被打开，形成了具有六齿L3配体的[ZnL3]2+和[FeL3]3+。[ZnL3]2+从DMSO溶液中重结晶，生成了配合物[ZnL1(DMSO)2]2+，其中L1以四齿配体的形式存在。因此，X射线结构分析证实，L1、L2和L3是具有两个、一个或没有咪唑烷环的结构异构体。分子内环的形成是N(氨基)基团亲核加成到亲电sp2杂化的-HC Delta+=N位的结果。由于对属于咪唑烷环的SP3杂化碳原子没有螯合作用，所以在与铜(II)、锌(II)和铁(III)形成络合物时，容易观察到开环。
The condensation of 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine yields a product with two imidazolidine rings, as proven by a solid-state X-ray structure analysis as well as by NMR solution spectra. This ligand, L1, undergoes a ring-opening reaction on complex formation with Cu(II), yielding [CuL2]2+ where L2 functions as a pentadentate ligand, containing only one imidazolidine ring. On complexation with Zn(II) and Fe(III), both rings are opened and the complexes [ZnL3]2+ and [FeL3]3+ with a hexadentate L3 ligand are formed. The recrystallization of [ZnL3]2+ from DMSO solution results in the complex [ZnL1(DMSO)2]2+ in which L1 behaves as a tetradentate ligand. Thus L1, L2, and L3 are structural isomers with two, one, or no imidazolidine rings, as confirmed by X-ray structure analyses. The intramolecular ring formation is the result of the nucleophilic addition of the N(amino) group to the electrophilic sp2-hybridized -HC delta+=N site. Owing to the absence of the chelate effect on the sp3-hybridized carbon atom belonging to the imidazolidine ring, the ring opening is facilitated and readily observed upon complex formation with Cu(II), Zn(II), and Fe(III).