Insights into the role of zirconium in proline functionalized metal-organic frameworks attaining high enantio- and diastereoselectivity
Insights into the role of zirconium in proline functionalized metal-organic frameworks attaining high enantio- and diastereoselectivity
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DOI：
10.1016/j.jcat.2019.07.003
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发表时间：
2019-09
影响因子：
7.3
通讯作者：
K. Nguyen;Christel Kutzscher;S. Ehrling;I. Senkovska;V. Bon;M. de Oliveira;T. Gutmann;G. Buntkowsky;S. Kaskel
中科院分区：
文献类型：
--
作者：
K. Nguyen;Christel Kutzscher;S. Ehrling;I. Senkovska;V. Bon;M. de Oliveira;T. Gutmann;G. Buntkowsky;S. Kaskel
通过手性单羧酸l -脯氨酸与Zr6O6(OH)2(TDC)4(HCOO)2（DUT-67, TDC = 2,5-噻吩二羧酸酯）的合成后功能化，得到了含8-连接zr6簇的手性锆基催化剂DUT-67- pro。DUT-67-Pro的13C和15n固态MAS和DNP NMR研究证实了l -脯氨酸在多孔框架中的整合。手性MOF催化剂在低温（298 K）条件下对环己酮与4-硝基苯甲醛的不对称醛加成反应表现出优异的催化活性，并具有前所未有的syn-（S，S）产物选择性（产率 = 95%,ee= 96%）。使用分子zr6簇模型化合物进行的比较催化研究表明，与已建立的l-脯氨酸有机催化相比，zr6片段负责这种逆非对映选择性，并提出了解释zr6簇介导的同步选择性的机制。掩盖骨架簇中残留的酸性活性位点是实现高对映体选择性的关键前提。基于DUT-67-Pro的纯多相催化体系稳定性高，可多次循环使用。
A chiral zirconium-based catalyst, DUT-67-Pro containing 8-connected Zr6-clusters is obtained by post synthetic functionalization of Zr6O6(OH)2(TDC)4(HCOO)2(DUT-67, TDC = 2,5-thiophenedicarboxylate) with the chiral monocarboxylic acid,L-proline.13C and15N solid state MAS and DNP NMR studies of DUT-67-Pro confirm the integration ofL-proline into the porous framework. The chiral MOF catalyst exhibits an excellent catalytic activity at low temperature (298 K) with an unprecedentedsyn-(S,S)-product selectivity in an asymmetric aldol addition reaction of cyclohexanone to 4-nitrobenzaldehyde (yield = 95%,ee= 96%). Comparative catalytic studies using a molecular Zr6-cluster model compound indicate the Zr6-moiety to be responsible for this inverse diastereoselectivity compared to well-establishedL-proline organocatalysis and a mechanism is proposed to explain the Zr6-cluster-mediatedsyn-selectivity. Masking residual acidic active sites in the cluster of the framework was found to be a key prerequisite to achieve the high enantioselectivity. The purely heterogeneous catalytic system based on DUT-67-Pro is highly stable and can be recycled several times.