Development of Asymmetric Reactions Catalyzed by Metal-Encapsulated Chiral Polysiloxane Gels

将分子催化剂固载于固体载体上是有机合成中实现环境友好反应过程的重要途径。我们最近发现金属包裹的聚硅氧烷凝胶（[M]@Si-O）是由Ru和Pt催化的羧酰胺与聚甲基氢硅氧烷（PMHS）的脱氧还原形成的，并且凝胶中的催化剂物种通过添加氢硅烷对羧酰胺的脱氧还原仍然具有活性。本研究的目的是开发实用的立体和化学选择性的有机转化过程中使用的催化剂固定的有机凝胶。在过渡金属配合物存在下，以二元醇和二烯为桥连试剂，合成了Ru和Pt包封的聚硅氧烷凝胶（M@Si）。三钌羰基簇包覆的聚硅氧烷凝胶（[Ru_3]@Si-EG或[Ru_3]@Si-BP）与乙二醇或双酚交联，对烯烃异构化反应具有催化活性。烯丙基醚或高烯丙基醚的双键异构化，然后用本方法水解，提供了一种实用的方法，烯丙基醚和高烯丙基醚的脱保护。以1，5-己二烯为交联剂的Pt/Si-C_6（[Pt]@Si-C_6）凝胶作为催化剂，对硝基芳烃的硝基选择性还原反应具有良好的催化活性。该程序适用于以克为单位生产苯胺。在这两种情况下，通过简单的萃取将产物与凝胶催化剂分离，并且在产物中检测不到催化剂物质。

Immobilization of molecular catalysts on solid supports is an important approach in organic synthesis directed towards environmentally benign reaction processes. We have recently found that the metal-encapsulated polysiloxane gels ([M]@Si-O) are formed by Ru and Pt-catalyzed deoxygenative reduction of carboxamides with polymethylhydrosiloxanes (PMHSs) and catalyst species in the gels are still active towards deoxygenative reduction of carboxamides by addition of hydrosilanes. The purpose of this research is development of practical processes for stereo- and chemoselective organic transformations using catalyst-immobilized organogels. Ru and Pt-encapsulated polysiloxane gels (M@Si) were synthesized by treatment of PMHS with diols and dienes as a bridging reagent in the presence of transition metal complexes having dehydrogenative silylation or hydrosilylation activity. Triruthenium carbonyl cluster-encapsulated polysiloxane gels cross-linking with ethylene glycol or biphenol ([Ru_3]@Si-EG or ([Ru_3]@Si-BP) showed catalytic activity towards isomerization of alkenes. Double bond isomerization of allyl or homoallyl ethers using the present method followed by hydrolysis provided a practical method for deprotection of allyl and homoallyl ethers. Pt-encapsulated polysiloxane gel cross-linking with 1,5-hexadiene ([Pt]@Si-C_6) acted as efficient and reusable catalysts for nitro-selective reduction of functionalized nitroarenes. This procedure was applicable to production of anilines in gram-quantities. In these two cases, the product is separated from the gel catalyst by simple extraction, and catalyst species is not detectable in the product.