Effect of chiral cavities associated with molecularly imprinted platinum centers on the selectivity of ligand-exchange reactions at platinum
Effect of chiral cavities associated with molecularly imprinted platinum centers on the selectivity of ligand-exchange reactions at platinum
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DOI：
10.1021/ja000462c
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发表时间：
2000-07-05
影响因子：
15
通讯作者：
Gagné, MR
中科院分区：
文献类型：
--
作者：
Brunkan, NM;Gagné, MR
将金属间化合物（乙烯基dppe）Pt[（R）-Bu 2BINOL]（1）与乙二醇二甲基丙烯酸酯共聚，制备了分子印迹聚合物（MIP）P1。通过用HCl或过量的α，α，α-三氟-间甲酚、BINOL或Br 2BINOL处理从P1中除去手性印迹配体（R）-Bu 2BINOL，得到聚合物P2-P5。从P1中释放的印迹配体的量与裂解剂的空间体积成反比，表明在MIP中存在具有不同辅助性的Pt位点的分布。将P3（含有被（R）-Bu 2BINOL形空腔包围的Pt（OAr）（2）中心）暴露于rac-BINOL（一种印迹配体类似物）导致印迹对映体通过配体交换优先重新结合。两个聚集体的选择性和反应的程度（在MIP中的总Pt位点的百分比，参与再结合）增加与再结合时间和温度，高达69%ee和58%Pt位点反弹，分别。观察到选择性和反应性之间的正线性相关。开放的，容易获得的Pt位点被认为是选择性低于非反应性位点，因为它们相关的手性空腔是不太明确的，因此不太能够基于形状的对映体歧视。P3中最小反应性位点的动力学选择性通过rac-BINOL然后rac-Br 2BINOL的顺序再结合来评估。反弹BINOL回收89- 94%ee.All数据表明，手性空腔（外层）与这些MIP中的活性Pt中心是负责化学计量配体交换反应中观察到的选择性在金属中心的MIP中的最低反应性Pt网站的8至20%。
The metallomonomer (vinyl dppe)Pt[(R)-Bu2BINOL] (1) was copolymerized with ethylene glycol dimethacrylate to produce the molecularly imprinted polymer (MIP) P1. The chiral imprinting ligand (R)-Bu2BINOL was removed from P1 by treatment with HCl or an excess of alpha,alpha,alpha-trifluoro-m-cresol, BINOL, or Br2BINOL, giving polymers P2-P5. The amount of imprinting ligand released from P1 varied inversely with the steric bulk of the cleaving agent, indicating that a distribution of Pt sites with different accessibilities exists in the MIP. Exposure of P3 (containing Pt(OAr)(2) centers surrounded by (R)-Bu2BINOL-shaped cavities) to rac-BINOL, an imprinting ligand analogue, led to preferential rebinding of the imprinted enantiomer via ligand exchange. Both aggregate selectivity and extent of reaction (percent of the total Pt sites in the MIP that participated in rebinding) increased with rebinding time and with temperature, up to 69% ee and 58% Pt sites rebound, respectively. A positive linear correlation between selectivity and reactivity was observed. Open, easily accessible Pt sites were proposed to be less selective than unreactive sites because their associated chiral cavities are less well-defined and therefore less capable of shape-based enantiodiscrimination. The kinetic selectivity of the least reactive sites in P3 was assessed by sequential rebinding of rac-BINOL and then rac-Br2BINOL. Rebound BINOL was recovered from 8 to 20% of the least reactive Pt sites accessible in the MIP in 89-94% ee. All data indicate that chiral cavities (outer sphere) associated with the reactive Pt centers in these MIPs are responsible for the selectivities observed for stoichiometric ligand-exchange reactions at the metal center.