Chiral recognition in contact ion-pairs; observation, characterization and analysis
Chiral recognition in contact ion-pairs; observation, characterization and analysis
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DOI：
10.1039/c3sc51096d
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发表时间：
2013-01-01
期刊：
影响因子：
8.4
通讯作者：
Brown, John M.
中科院分区：
文献类型：
--
作者：
Raskatov, Jevgenij A.;Thompson, Amber L.;Brown, John M.
手性离子对在不对称催化中起着越来越重要的作用。为了了解分子识别的来源，研究了一个基于BINAP-Rh（二烯）阳离子和BINOL硼酸盐阴离子的简单模型系统。发现其中一种是能量优先的，并设计了用P-31核磁共振定量差异的方法。对一系列双二萘硼酸盐阴离子的影响是普遍的，并且需要环-1,5-二烯而不是双环七[2.2.1]二烯作为对偶烯组分。母离子对中阳离子的H-1 NMR谱显示出阴离子诱导的一系列化学位移，它们的特异性表明离子对接触的选择性。得到了两种环二烯配合物的x射线结构，并证明了分析单个离子对的优选接触是可能的。而不是涉及特定的pi-pi， CH-pi和CH-O分子间力，在COD的情况下，对一种非对映体的偏好是基于分散力，这种分散力响应于填充dial烯烃的能力，特别是它的sp(3)单元，以最大限度地与凹型萘基片段相互作用。这一解释得到了一种相关NBD复合物分析的支持。
Chiral ion-pairs are playing an increasingly important role in asymmetric catalysis. In order to understand the source of molecular recognition, a simple model system based on a BINAP-Rh(dialkene) cation and a BINOL borate anion was studied for both diastereomeric forms. It was discovered that one of these was energetically preferred and methods for quantifying the difference were devised using P-31 NMR. The effect was general over a series of bis-binaphthyl borate anions, and required cycloocta-1,5-diene rather than bicyclohepta[2.2.1]diene as the dialkene component. The H-1 NMR spectra of the cation in the parent ion pairs showed a range of anion-induced chemical shifts, their specificity implying selectivity in the ion-pair contact. X-ray structures of the two cyclooctadiene complexes were obtained and it proved possible to analyse the preferred contacts of individual ion-pairs. Rather than involving specific pi-pi, CH-pi and CH-O intermolecular forces, the preference for one diastereomer in the COD case is based on dispersion forces that respond to the ability to pack the dialkene, and particularly its sp(3) units, for maximum interaction with a concave naphthyl fragment. This interpretation is supported by analysis of one related NBD complex.