A Polymer-Coated Rhodium/Diamine-Functionalized Silica for Controllable Reaction Switching in Enantioselective Tandem Reduction–Lactonization of Ethyl 2-Acylarylcarboxylates

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• 作者：Lingyu Kong ; Junwei Zhao ; Tanyu Cheng ; Jingrong Lin ; Guohua Liu
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：April 1, 2016
• 年：2016
• 卷：6
• 期：4
• 页码：2244-2249
• 全文大小：424K
• ISSN：2155-5435

文摘

The design of a smart heterogeneous catalyst for controllable reaction switching is highly desirable in asymmetric catalysis. In this work, by taking advantage of the thermoresponsive behavior of a water-soluble polymer coating and the confined feature of silica nanoparticles, we have constructed a silica material with chiral rhodium/diamine functionality on SiO₂ nanospheres coated with a water-soluble thermoresponsive polymer. The solid-state ¹³C NMR spectrum of the product demonstrated well-defined single-site chiral rhodium active centers within the thermoresponsive polymer, and scanning electron microscopy and transmission electron microscopy revealed its uniformly dispersed morphology. As a smart heterogeneous catalyst, it enables catalyst-based temperature-controlled reaction switching in the enantioselective tandem reduction–lactonization of ethyl 2-acylarylcarboxylates in water. At 40 °C, the catalyst promotes highly enantioselective tandem reduction–lactonization by adopting the extended form of the thermoresponsive polymer coating, whereas at 15 °C the reaction is terminated and the heterogeneous catalyst can be recycled because of its closed form. This feature endows this catalyst with high efficiency and recyclability for the synthesis of chiral phthalides in an environmentally friendly medium.