Brønsted Acid Catalysis-Structural Preferences and Mobility in Imine/Phosphoric Acid Complexes.
Brønsted Acid Catalysis-Structural Preferences and Mobility in Imine/Phosphoric Acid Complexes.
复制标题
布朗斯特酸催化结构的偏好和亚胺/磷酸复合物中的迁移率。
DOI：
10.1021/jacs.6b09244
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发表时间：
2016-12-14
影响因子：
15
通讯作者：
Gschwind RM
中科院分区：
文献类型：
--
作者：
Greindl J;Hioe J;Sorgenfrei N;Morana F;Gschwind RM
尽管对映体选择性的Brnsted酸催化取得了巨大的成功，但关于底物/催化剂络合物在溶液中的结构和活化方式的实验数据非常少见。本文首次以核磁共振数据为基础，以理论计算为基础，对亚胺/溴酸络合物的结构进行了详细的研究。研究了手性Brnsted酸催化剂R-TRIP(3，3′-bis(2，4，6-triisopropylphenyl)-1，1′-binaphthyl-2，2′-diyl(磷酸二氢)与六种芳香亚胺的反应。对于每个被研究的体系，都观察到一个E-亚胺/R-TRIP络合物和一个Z-亚胺/R-TRIP络合物。每个配合物都由两个结构组成，它们在核磁共振时间尺度上交换很快，即总共发现了四个结构。两种已鉴定的E-亚胺/R-Trip结构都具有较强的氢键，但亚胺相对于催化剂的取向不同。交换通过倾斜络合物内部的亚胺来进行，从而交换构成氢键的氧。所有被研究的Z-亚胺/R-TRIP络合物都有类似的情况。这里，通过亚胺的旋转打开了一条额外的交换路径。对于所有研究的亚胺/R-Trip络合物，四个核心结构都被高度保存。因此，这些核心结构与芳香亚胺的电子密度和取代基调制无关。总体而言，本研究表明二元亚胺/Trip络合物的绝对结构空间较大，四个核心结构的变化较小。高迁移率被认为是为了促进反应活性，而核心结构的保留以及广泛的π-π和CH−π相互作用导致了对不同底物的高对映选择性和耐受性。
Despite the huge success of enantioselective Brønsted acid catalysis, experimental data about structures and activation modes of substrate/catalyst complexes in solution are very rare. Here, for the first time, detailed insights into the structures of imine/Brønsted acid catalyst complexes are presented on the basis of NMR data and underpinned by theoretical calculations. The chiral Brønsted acid catalyst R-TRIP (3,3′-bis(2,4,6-triisopropylphenyl)-1,1′-binaphthyl-2,2′-diyl hydrogen phosphate) was investigated together with six aromatic imines. For each investigated system, an E-imine/R-TRIP complex and a Z-imine/R-TRIP complex were observed. Each of these complexes consists of two structures, which are in fast exchange on the NMR time scale; i.e., overall four structures were found. Both identified E-imine/R-TRIP structures feature a strong hydrogen bond but differ in the orientation of the imine relative to the catalyst. The exchange occurs by tilting the imine inside the complex and thereby switching the oxygen that constitutes the hydrogen bond. A similar situation is observed for all investigated Z-imine/R-TRIP complexes. Here, an additional exchange pathway is opened via rotation of the imine. For all investigated imine/R-TRIP complexes, the four core structures are highly preserved. Thus, these core structures are independent of electron density and substituent modulations of the aromatic imines. Overall, this study reveals that the absolute structural space of binary imine/TRIP complexes is large and the variations of the four core structures are small. The high mobility is supposed to promote reactivity, while the preservation of the core structures in conjunction with extensive π–π and CH−π interactions leads to high enantioselectivities and tolerance of different substrates.