Amphiphilic Hyperbranched Polyethoxysiloxane: A Self-Templating Assembled Platform to Fabricate Functionalized Mesostructured Silicas for Aqueous Enantioselective Reactions

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• 作者：Kun Zhang ; Juzeng An ; Yanchao Su ; Jueyu Zhang ; Ziyun Wang ; Tanyu Cheng ; Guohua Liu
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：September 2, 2016
• 年：2016
• 卷：6
• 期：9
• 页码：6229-6235
• 全文大小：505K
• 年卷期：0
• ISSN：2155-5435

文摘

Fabrication of amphiphilic mesostructured silica as a heterogeneous catalyst is beneficial to facilitate an aqueous reaction due to its highly dispersed nature in water. In this work, by taking advantage of a self-templating assembled strategy, we construct two types of mesostructured silicas as heterogeneous catalysts, chiral ruthenium/diamine-functionalized and chiral cinchonine-based squaramide-functionalized heterogeneous catalysts, through the use of amphiphilic poly(ethylene glycol) monomethyl ether-modified hyperbranched polyethoxysiloxane as a silica precursor. As presented in the study, the chiral ruthenium/diamine-functionalized catalyst performs an asymmetric transfer hydrogenation of acyclic α-trifluoromethylimines to chiral α-trifluoromethylamines in water, whereas the chiral squaramide-functionalized catalyst enables efficiently asymmetric Michael addition of acetylacetone to nitroalkenes in brine. Both highly catalytic performances are attributed to the combined multifunctionalities of well-defined single-site chiral active species, highly dispersed catalytic centers, and practical phase-transferred function. Furthermore, both catalysts can also be recovered easily and reused repeatedly for at least seven times without loss of catalytic activity. Such a feature makes this self-templating assembly attractive for construction of various heterogeneous catalysts.