Scope and mechanism of the C-H bond activation reactivity within a supramolecular host by an iridium guest: A stepwise ion pair guest dissociation mechanism
Scope and mechanism of the C-H bond activation reactivity within a supramolecular host by an iridium guest: A stepwise ion pair guest dissociation mechanism
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DOI：
10.1021/ja061412w
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发表时间：
2006-08-02
影响因子：
15
通讯作者：
Raymond, Kenneth N.
中科院分区：
文献类型：
--
作者：
Leung, Dennis H.;Bergman, Robert G.;Raymond, Kenneth N.
手性自组装超分子M4 L 6组装体已被证明是一系列能够活化C-H键的反应性单阳离子半夹心铱客体1、3和4的合适主体。在包封后，发生有机基质的选择性C-H键活化。精确的尺寸和形状的选择性观察醛和醚底物的C-H键活化。该反应表现出显着的动力学非对映选择性。热力学研究表明，铱起始材料和产物被主体组装体强烈地结合。封装过程在很大程度上是熵驱动的。动力学研究与水溶性膦陷阱和添加的盐提供了证据的一个独特的逐步机制的客人解离[4子集的Ga 4L 6]。铱客体4首先从主体空腔解离以与主体外部形成离子对。然后，该物质从宿主外部完全解离到本体溶液中。模型离子对中间体，其特征在于直接与H-1 NMR NOESY技术。铱客体解离的速率比观察到的C-H键活化过程的速率慢，表明选择性C-H键活化反应性发生在超分子主体的空腔内。
A chiral self-assembled supramolecular M4L6 assembly has been shown to be a suitable host for a series of reactive monocationic half-sandwich iridium guests 1, 3, and 4 that are capable of activating C-H bonds. Upon encapsulation, selective C-H bond activation of organic substrates occurs. Precise size and shape selectivity are observed in the C-H bond activation of aldehydes and ether substrates. The reactions exhibit significant kinetic diastereoselectivities. Thermodynamic studies have shown that the iridium starting materials and products are bound strongly by the host assembly. The encapsulation process is largely entropy-driven. Kinetic investigations with water-soluble phosphine traps and added salts have provided evidence for a unique stepwise mechanism of guest dissociation for [4 subset of Ga4L6]. Iridium guest 4 first dissociates from the host cavity to form an ion pair with the host exterior. This species then fully dissociates from the host exterior into the bulk solution. Model ion pair intermediates were characterized directly with H-1 NMR NOESY techniques. The rate of iridium guest dissociation is slower than the rate observed for the C-H bond activation processes, indicating that the selective C-H bond activation reactivity occurs within the cavity of the supramolecular host.