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

将分子催化剂固定在固体载体上是有机合成中面向环境友好反应的重要途径。我们最近发现，金属包覆的聚硅氧烷凝胶([M]@Si-O)是由Ru和Pt催化的羧胺与聚甲基氢硅氧烷(PMHSs)脱氧还原形成的，凝胶中的催化剂物种对加氢硅烷脱氧还原羧胺仍然具有活性。这项研究的目的是开发使用催化剂固定的有机凝胶进行立体和化学选择性有机转化的实用工艺。在具有脱氢硅化或硅氢化活性的过渡金属络合物存在下，用二元醇和二烯烃作为桥联剂与PMHS反应，合成了Ru和Pt包覆的聚硅氧烷凝胶(M@Si)。以乙二醇或联苯酚([Ru3]@Si-EG或[Ru3]@Si-BP)为交联剂的聚硅氧烷凝胶具有催化烯烃异构化的活性。用本方法对烯丙基醚或高烯丙基醚进行双键异构化，然后进行水解，为烯丙基醚和高烯丙基醚的脱保护提供了一种实用的方法。以1，5-己二烯为交联剂的铂包覆聚硅氧烷凝胶([Pt]@Si-C6)是一种高效、可重复使用的硝基选择还原功能化硝基芳烃催化剂。该方法适用于克量苯胺的生产。在这两种情况下，通过简单的萃取将产物从凝胶催化剂中分离出来，并且在产物中没有检测到催化剂种类。

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.