Enantiomerically pure polytungstates: Chirality transfer through zirconium coordination centers to nanosized inorganic clusters
Enantiomerically pure polytungstates: Chirality transfer through zirconium coordination centers to nanosized inorganic clusters
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DOI：
10.1002/anie.200500415
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Hill, CL
中科院分区：
文献类型：
--
作者：
Fang, XK;Anderson, TM;Hill, CL
稳定的纳米级对映体纯多氧阴离子可以产生有用的手性材料，从微孔固体和无机药物到均相不对称氧化催化剂。然而，在聚氧乙烯酸酯（POM）体系中，手性在很大程度上尚未被探索。[1]大多数具有手性结构的POM在溶液中经历快速外消旋化，并且外消旋混合物通常在溶液中以及在固态下可见。通常在晶体中，两种对映异构体共存于同一晶胞中，通过晶体学施加的反转中心彼此相关。[2]虽然Pfeiffer效应已被证明与广泛的外消旋POM系统，对映异构体的手性拆分往往是复杂的溶解度，不稳定性和结构相似性。[3，4]已经报道了三种不同的固态对映体纯POM的合成路线。首先，水热合成可以制备具有螺旋特征的固体无机材料。[5]一个例子是磷酸钒络合物，[（CH3）2NH2] K4 [V10O10（H2O）2（OH）4（PO4）7]· 4 H2O，具有Zubieta及其同事的手性互穿双螺旋。[5a]第二，一些聚碳酸酯和手性氨基酸的反应提供手性POM。[6]Kortz等人最近的一项研究表明，基于NMR光谱和X射线研究（Mo和羧酸O原子之间的弱键合，约为2.3），结合的氨基酸在溶液中可能不稳定。[6b]因此，这些复合物的手性很大程度上位于氨基酸部分并不奇怪。第三，抗衡离子可以在确定POM的固态结构中发挥关键作用，并且在某些情况下，导致非手性POM在手性空间群中结晶。[7]有时外消旋本体固体的结晶可导致手性晶体。[8]然而，没有报道手性活性在溶液状态的这种对映体纯POM系统。实现本征手性和构型稳定的POM将提供对映选择性催化性能和增强的生物活性。[9]此外，手性诱导的控制是有效管理和利用手性现象的更大目标的重要组成部分。
Stable, nanometer-sized enantiomerically pure polyoxoanions could lead to useful chiral materials ranging from microporous solids and inorganic pharmaceuticals to catalysts for homogeneous asymmetric oxidation. However, chirality has been largely unexplored in polyoxometalate (POM) systems.[1] Most POMs with chiral structures undergo rapid racemization in solution, and racemic mixtures are usually seen in solution as well as in the solid state. Typically in crystals the two enantiomers coexist in the same unit cell, related to each other by a crystallographically imposed inversion center.[2] Although Pfeiffer effects have been demonstrated with a wide range of racemic POM systems, the chiral resolution of the enantiomers is frequently complicated by their solubility, lability, and structural similarity.[3, 4] Three different synthetic routes to enantiopure POMs in the solid state have been reported. First, hydrothermal synthesis can produce solid inorganic materials with helical characters.[5] One example is the vanadium phosphate complex,[(CH3) 2NH2] K4 [V10O10 (H2O) 2 (OH) 4 (PO4) 7]· 4 H2O, with a chiral interpenetrating double helix of Zubieta and coworkers.[5a] Second, reactions of a few polymolybdates and chiral amino acids afford chiral POMs.[6] A recent study by Kortz et al. demonstrated that the bound amino acids are probably labile in solution, based on NMR spectroscopy and X-ray studies (weak bonding, approximately 2.3, between the Mo and carboxylate O atoms).[6b] Therefore it is not surprising that the chirality of these complexes is largely localized on the amino acid moieties. Third, counterions can play a critical role in determining the solid-state structures of POMs, and, in some cases, cause achiral POMs to crystallize in chiral space groups.[7] Sometimes crystallization of racemic bulk solids can lead to chiral crystals.[8] However, there is no report of chiroptical activity in the solution-state for such enantiopure POM systems. Realization of an intrinsically chiral and configurationally stable POM should afford enantioselective catalytic properties and enhanced biological activities.[9] Furthermore, the control of chiral induction is an important component of the larger goal of effectively managing and utilizing chirogenic phenomena.