Han Jeehwan, Kim Seongwoo, Lee Mi Sun, Kim Min, Jeong Nakcheol
Department of Chemistry, Korea University.
Department of Chemistry and BK21Plus Research Team, Chungbuk National University.
J Vis Exp. 2020 Jan 17(155). doi: 10.3791/60624.
Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of the reaction site in metal-organic framework (MOF)-based catalysts in an enantioselective catalytic reaction system. Therefore, a method of validating the reaction site of MOF-based catalysts is necessary to investigate this issue. Substrate size discrimination by pore size was accomplished by comparing the substrate size versus the reaction rate in two different types of carbonyl-ene reactions with two kinds of MOFs. The MOF catalysts were used to compare the performance of the two reaction types (Zn-mediated stoichiometric and Ti-catalyzed carbonyl-ene reactions) in two different media. Using the proposed method, it was observed that the entire MOF crystal participated in the reaction, and the interior of the crystal pore played an important role in exerting chiral control when the reaction was stoichiometric. Homogeneity of the chiral environment of MOF catalysts was established by the size control method for a particle used in the Zn-mediated stoichiometric reaction system. The protocol proposed for the catalytic reaction revealed that the reaction mainly occurred on the catalyst surface regardless of the substrate size, which reveals the actual reaction sites in MOF-based heterogeneous catalysts. This method for reaction site validation of MOF catalysts suggests various considerations for developing heterogeneous enantioselective MOF catalysts.
在对映选择性催化反应体系中，基于金属有机框架（MOF）的催化剂反应位点的孔径大小以及手性环境的均一性对底物大小的辨别作用，是该反应位点验证过程中的重要问题。因此，有必要采用一种方法来验证基于MOF的催化剂的反应位点，以研究这一问题。通过比较两种不同类型的羰基烯反应中底物大小与反应速率，利用两种MOF实现了基于孔径的底物大小辨别。使用MOF催化剂比较了两种不同介质中两种反应类型（锌介导的化学计量反应和钛催化的羰基烯反应）的性能。采用所提出的方法观察到，当反应为化学计量反应时，整个MOF晶体都参与了反应，并且晶体孔内部在施加手性控制方面发挥了重要作用。通过锌介导的化学计量反应体系中所用颗粒的尺寸控制方法，确定了MOF催化剂手性环境的均一性。所提出的催化反应方案表明，无论底物大小如何，反应主要发生在催化剂表面，这揭示了基于MOF的多相催化剂中的实际反应位点。这种用于MOF催化剂反应位点验证的方法为开发多相对映选择性MOF催化剂提供了各种考虑因素。
