Chirality and Diastereoselection of Δ/Λ-Configured Tetrahedral Zinc Complexes through Enantiopure Schiff Base Complexes: Combined Vibrational Circular Dichroism, Density Functional Theory, 1H NMR, and X-ray Structural Studies
Chirality and Diastereoselection of Δ/Λ-Configured Tetrahedral Zinc Complexes through Enantiopure Schiff Base Complexes: Combined Vibrational Circular Dichroism, Density Functional Theory, 1H NMR, and X-ray Structural Studies
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DOI：
10.1021/ic2009557
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发表时间：
2011-11-21
影响因子：
4.6
通讯作者：
Janiak, Christoph
中科院分区：
文献类型：
--
作者：
Chamayou, Anne-Christine;Luedeke, Steffen;Janiak, Christoph
四配位非平面 Zn(A 布尔 AND B)(2) 配合物的以金属为中心的 Delta/Lambda 手性与双齿对映体纯 (R)-A 布尔 AND B 或 (S)-A 布尔 AND B 席夫碱构建模块的手性相关 [A 布尔 AND B = (R)- 或(S)-N-(1-(4-X-苯基)乙基)水杨醛亚氨基-κ N-2,O，其中 X = OCH3、Cl、Br]。在固态中，(R) 配体手性诱导 A-M 构型，而 (S) 配体手性在结晶时定量给出 A-M 构型，如 X 射线单晶研究推论的那样。通过 H-1 NMR 和振动圆二色性 (VCD) 光谱研究了准四面体锌-席夫碱配合物在 CDCl3 溶液中的非对映选择。 H-1 NMR 中席夫碱 -CH=N- 亚胺质子的两个信号的出现表明 Delta-和 Lambda-非对映异构体均达到平衡，所有三种配体的非对映异构体比例约为 20:80%。 VCD 被证明对金属中心的 Delta/Lambda 手性非常敏感，因为特征带代表两个配体的 C=N 拉伸模式的耦合振动。绝对构型是根据密度泛函理论计算得出的理论 VCD 光谱符号一致来指定的。
The metal-centered Delta/Lambda-chirality of four-coordinated, nonplanar Zn(A boolean AND B)(2) complexes is correlated to the chirality of the bidentate enantiopure (R)-A boolean AND B or (S)-A boolean AND B Schiff base building blocks [A boolean AND B = (R)- or (S)-N-(1-(4-X-phenyl)ethyl)salicylaldiminato-kappa N-2,O with X = OCH3, Cl, Br]. In the solid-state the (R) ligand chirality induces a A-M configuration and the (S) ligand chirality quantitatively gives the A-M configuration upon crystallization as deduced from X-ray single crystal studies. The diastereoselections of the pseudotetrahedral zinc-Schiff base complexes in CDCl3 solution were investigated by H-1 NMR and by vibrational circular dichroism (VCD) spectroscopy. The appearance of two signals for the Schiff-base -CH=N- imine proton in H-1 NMR indicates an equilibrium of both Delta- and Lambda-diastereomers with a diastereomeric ratio of roughly 20:80% for all three ligands. VCD proved to be very sensitive to the metal-centered Delta/Lambda-chirality because of a characteristic band representing coupled vibrations of the two ligand's C=N stretch modes. The absolute configuration was assigned on the basis of agreement in sign with theoretical VCD spectra from Density Functional Theory calculations.