Chirality Transfer in Propeller-Shaped Cyclen―Calcium(II) Complexes: Metal-Coordinating and Ion-Pairing Anion ProtocolsProcedures
Chirality Transfer in Propeller-Shaped Cyclen―Calcium(II) Complexes: Metal-Coordinating and Ion-Pairing Anion ProtocolsProcedures
复制标题
螺旋桨状 Cyclen—钙 (II) 配合物中的手性传递：金属配位和离子对阴离子方案程序
DOI：
10.1002/chem.201204323
复制
发表时间：
2012
期刊：
影响因子：
--
通讯作者：
Satoshi Shinoda
中科院分区：
文献类型：
--
作者：
Hiroshi Ito;Hiroshi Tsukube;Satoshi Shinoda
合成了一系列具有八齿环戊二烯配体的四链Na+和Ca 2+络合物，以产生含有四种不同侧臂组合的络合物（一个三唑并香豆素基团和三个吡啶基团（1），四个吡啶基团（2），一个三唑并香豆素基团和三个喹啉基团（3），以及四个喹啉基团（4））。X射线晶体学分析表明，在用三唑香豆素部分取代一个吡啶基团或用Ca 2+离子取代Na+离子后，这些络合物的立体结构没有发生显著变化，尽管当吡啶基团被喹啉基团取代时，固态络合物的配位数减少。在溶液中，所有的侧臂以螺旋桨状图案排列，以在每个金属络合物中产生Δ和Λ形式的对映异构体对。将叔丁氧羰基（Boc）保护的氨基酸阴离子（即配位手性羧酸根阴离子）添加到环戊二烯-Ca 2+复合物中，通过形成具有相反复合物手性的非对映体三元复合物的1：1混合物，在芳香区诱导圆二色性（CD）信号，而相应的Na+复合物很少显示任何响应。在络合物1-Ca 2+和3-Ca 2+中，通过考虑在两个不同波长处诱导CD信号，即香豆素发色团区域和氮杂芳族区域，有效地遵循了这种手性转移过程。CD信号的符号和强度显著依赖于氮杂芳族部分的性质和外部阴离子的对映体纯度。这些Ca ~（2+）配合物可作为测定手性阴离子对映体过量的有效探针。Cyclen的Ca 2+配合物也通过离子配对机制与非配位的Δ-TRISPHAT阴离子相互作用，实现从阴离子到金属配合物的手性转移;由于与Δ-TRISPHAT阴离子的离子配对作用，1-Ca 2+和3-Ca 2+都在香豆素发色团区域清楚地显示出诱导的CD信号。因此，八齿环戊二烯配体和金属中心的适当组合证明了有效的手性转移。
A series of quadruple‐stranded Na+and Ca2+complexes with octadentate cyclen ligands was synthesized to produce complexes that contained four different side‐arm combinations (one triazolecoumarin group and three pyridine groups (1), four pyridine groups (2), one triazolecoumarin group and three quinoline groups (3), and four quinoline groups (4)). X‐ray crystallographic analysis revealed that no significant changes occurred in the stereostructure of these complexes upon replacing one pyridine group with a triazolecoumarin moiety, or by replacing Na+ions with Ca2+ions, although the coordination number of the complexes in the solid state decreased when pyridine groups were replaced by quinoline groups. In solution, all of the side arms were arranged in a propeller‐like pattern to yield an enantiomer pair ofΔandΛforms in each metal complex. The addition of atert‐butoxycarbonyl (Boc)‐protected amino acid anion, that is, a coordinative chiral carboxylate anion, to the cyclenCa2+complex induced circular dichroism (CD) signals in the aromatic region by forming a 1:1 mixture of diastereomeric ternary complexes with opposite complex chirality, whilst the corresponding Na+complexes rarely showed any response. In complexes1‐Ca2+and3‐Ca2+, this chirality‐transfer process was efficiently followed by considering the induction of the CD signals at two different wavelengths, that is, the coumarin‐chromophore region and the aza‐aromatic region. The sign and intensity of the CD signal were significantly dependent on both the nature of the aza‐aromatic moiety and the enantiomeric purity of the external anion. These Ca2+complexes worked as effective probes for the determination of the enantiomeric excess of the chiral anion. The cyclenCa2+complexes also interacted with the non‐coordinativeΔ‐TRISPHAT anion through an ion‐pairing mechanism to achieve chirality transfer from the anion to the metal complex; both complexes1‐Ca2+and3‐Ca2+clearly showed induced CD signals in the coumarin‐chromophore region, owing to ion‐paring interactions with theΔ‐TRISPHAT anion. Thus, the proper combination of an octadentate cyclen ligand and a metal center demonstrated effective chirality transfer.