Chiral Organic Ion Pair Catalysts Assembled Through a Hydrogen-Bonding Network
Chiral Organic Ion Pair Catalysts Assembled Through a Hydrogen-Bonding Network
复制标题
DOI：
10.1126/science.1176758
复制
发表时间：
2009-10
期刊：
影响因子：
56.9
通讯作者：
D. Uraguchi;Y. Ueki;T. Ooi
中科院分区：
文献类型：
--
作者：
D. Uraguchi;Y. Ueki;T. Ooi
催化组装有机化学中使用的大多数不对称催化剂是通过手性配体与一个或多个金属离子的结合来组装的。Uraguchi等人（第120页，8月27日在线发表）表明，在不存在金属的情况下，高选择性催化剂可以通过氢键从小分子的小集合中组装。在固态下，催化剂包含与两个苯酚分子结合的中心手性鳞阳离子，所述两个苯酚分子又结合电荷补偿苯氧离子。在溶液中，恶唑酮衍生物似乎能够取代酚盐结合，促使其立体选择性地加成到广泛的酯中。一小簇氢键分子充当高选择性不对称催化剂。开发用于不对称有机转化的结构离散的手性超分子催化剂的研究取得了有限的成功。在这里，我们报告说，一个手性tetraaminophosphonium阳离子，两个酚，和一个苯氧阴离子出现自组装成一个催化活性的超分子结构，通过分子间氢键。所得分子组装体的结构通过X射线衍射分析在固态下确定。此外，在溶液中，该络合物促进酰基阴离子等价物与具有广泛底物范围的α，β-不饱和酯替代物的高度立体选择性缀合加成。催化剂的所有结构组分协同参与立体控制事件。
Catalytic Assembly Most asymmetric catalysts employed in organic chemistry are assembled through binding of chiral ligands to one or more metal ions. Uraguchi et al. (p. 120, published online 27 August) show that a highly selective catalyst can assemble through hydrogen bonding from a small collection of small molecules in the absence of metals. In the solid state, the catalyst comprises a central chiral phosphonium cation bound to two phenol molecules, which in turn bind a charge-compensating phenoxide ion. In solution, an oxazolone derivative appears to be able to bind in place of the phenoxide, spurring its stereoselective addition to a broad range of esters. A small cluster of hydrogen-bonded molecules acts as a highly selective asymmetric catalyst. Research to develop structurally discrete, chiral supramolecular catalysts for asymmetric organic transformations has met with limited success. Here, we report that a chiral tetraaminophosphonium cation, two phenols, and a phenoxide anion appear to self-assemble into a catalytically active supramolecular architecture through intermolecular hydrogen bonding. The structure of the resulting molecular assembly was determined in the solid state by means of x-ray diffraction analysis. Furthermore, in solution the complex promotes a highly stereoselective conjugate addition of acyl anion equivalents to α,β-unsaturated ester surrogates with a broad substrate scope. All structural components of the catalyst cooperatively participate in the stereocontrolling event.