School of Chemistry and Chemical Engineering and State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University , Shanghai 200240, China.
Collaborative Innovation Center of Chemical Science and Engineering , Tianjin 300072, China.
J Am Chem Soc. 2017 Sep 27;139(38):13476-13482. doi: 10.1021/jacs.7b06459. Epub 2017 Sep 14.
A key challenge in heterogeneous catalysis is the design and synthesis of heterogeneous catalysts featuring high catalytic activity, selectivity, and recyclability. Here we demonstrate that high-performance heterogeneous asymmetric catalysts can be engineered from a metal-organic framework (MOF) platform by using a ligand design strategy. Three porous chiral MOFs with the framework formula [MnL(HO)] are prepared from enantiopure phosphono-carboxylate ligands of 1,1'-biphenol that are functionalized with 3,5-bis(trifluoromethyl)-, bismethyl-, and bisfluoro-phenyl substituents at the 3,3'-position. For the first time, we show that not only chemical stability but also catalytic activity and stereoselectivity of the MOFs can be tuned by modifying the ligand structures. Particularly, the MOF incorporated with -CF groups on the pore walls exhibits enhanced tolerance to water, weak acid, and base compared with the MOFs with -F and -Me groups. Under both batch and flow reaction systems, the CF-containing MOF demonstrated excellent reactivity, selectivity, and recyclability, affording high yields and enantioselectivities for alkylations of indoles and pyrrole with a range of ketoesters or nitroalkenes. In contrast, the corresponding homogeneous catalysts gave low enantioselectivity in catalyzing the tested reactions.
多相催化面临的一个关键挑战是设计和合成具有高催化活性、选择性和可回收性的多相催化剂。在这里，我们通过配体设计策略证明了可以从金属有机框架（MOF）平台上设计出高性能的多相不对称催化剂。通过使用 3,5-双（三氟甲基）-、双甲基-和双氟苯基取代基在 3,3'-位官能化的手性膦酸羧酸配体，制备了三个具有骨架公式[MnL(HO)]的多孔手性 MOF。我们首次表明，不仅可以通过修饰配体结构来调节 MOF 的化学稳定性，还可以调节其催化活性和立体选择性。特别是，与具有-F 和-Me 基团的 MOF 相比，带有孔壁上-CF 基团的 MOF 对水、弱酸和弱碱的耐受性更强。在分批和流动反应体系中，含 CF 的 MOF 表现出优异的反应性、选择性和可回收性，能够以高收率和对映选择性实现吲哚和吡咯与一系列酮酯或硝基烯烃的烷基化反应。相比之下，相应的均相催化剂在催化测试反应时表现出低的对映选择性。
