Role of Ion-Pairs in Br酶nsted Acid Catalysis

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• 作者：Heejae Kim ; Erli Sugiono ; Yuki Nagata ; Manfred Wagner ; Mischa Bonn ; Magnus Rueping ; Johannes Hunger
• 刊名：ACS Catalysis
• 出版年：2015
• 出版时间：November 6, 2015
• 年：2015
• 卷：5
• 期：11
• 页码：6630-6633
• 全文大小：299K
• ISSN：2155-5435

文摘

Phosphoric acids have emerged as efficient organo-catalysts for various reactions. Despite widespread use, details of the reaction intermediates giving rise to stereocontrol have remained elusive. To clarify the nature of the catalyst鈥搒ubstrate interaction, we characterize and quantify catalyst鈥搒ubstrate complex formation by combining dielectric spectroscopy, quantum chemistry, and ¹H NMR spectroscopy. For a series of different solvents, the interaction between substrate and catalyst is dominated by ion-pairing, rather than hydrogen bonding, at ambient conditions. Correlation of ion association with catalytic enantioselectivity provides evidence that close-contact ion-pairing is essential for stereocontrol and that dissociation into free ions dramatically reduces enantioselectivity.