含硼酸的有机催化剂的氢键活化作用的NMR定量,The Journal of Organic Chemistry

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含硼酸的有机催化剂的氢键活化作用的NMR定量
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2018-12-05 00:00:00 , DOI: 10.1021/acs.joc.8b02389
Kayla M. Diemoz ₁ , Annaliese K. Franz ₁

Affiliation

使用三乙基氧化膦（TEPO）的³¹ P NMR结合实验已对66种有机催化剂的氢键活化进行了定量。通过各种空间和电子修饰，对包括苯酚，二醇，硅烷醇，羧酸，硼酸和磷酸在内的各种结构类别进行了检查，以了解其结构和次要作用如何促进氢键合能力和催化作用。哈米特地块表现出较高的相关性的Δδ ³¹ P NMR移位到哈米特参数，建立TEPO的结合来预测电子趋势的能力。在与Friedel-Crafts加成反应中的催化活性相关时，数据表明³¹ P NMR位移与催化活性的相关性好于pK _a值。对硼酸进行了研究，³¹ P NMR结合实验预测了强大的氢键结合能力，并证实了其催化活性，从而在所研究的所有有机催化剂的弗里德尔-克拉夫茨添加中观察到了最大的速率增强。详细的研究支持硼酸活化是通过氢键相互作用而不是与路易斯酸性硼中心配位而进行的。使用³¹ P NMR光谱法可为设计和应用新型有机催化剂和超分子合成子提供量化和预测氢键结合能力的简单而快速的工具。

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NMR Quantification of Hydrogen-Bond-Activating Effects for Organocatalysts including Boronic Acids

The hydrogen-bonding activation for 66 organocatalysts has been quantified using a ³¹P NMR binding experiment with triethylphosphine oxide (TEPO). Diverse structural classes, including phenols, diols, silanols, carboxylic acids, boronic acids, and phosphoric acids, were examined with a variety of steric and electronic modifications to understand how the structure and secondary effects contribute to hydrogen-bonding ability and catalysis. Hammett plots demonstrate high correlation for the Δδ ³¹P NMR shift to Hammett parameters, establishing the ability of TEPO binding to predict electronic trends. Upon correlation to catalytic activity in a Friedel–Crafts addition reaction, data demonstrate that ³¹P NMR shifts correlate to catalytic activity better than pK_a values. Boronic acids were investigated, and ³¹P NMR binding experiments predicted strong hydrogen-bonding ability, for which catalytic activity was confirmed, resulting in the greatest rate enhancement observed in the Friedel–Crafts addition of all organocatalysts studied. A detailed investigation supports that boronic acid activation proceeds through hydrogen-bonding interactions and not coordination with the Lewis acidic boron center. Using ³¹P NMR spectroscopy offers a simple and rapid tool to quantify and predict hydrogen-bonding abilities for the design and applications of new organocatalysts and supramolecular synthons.

更新日期：2018-12-05

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