Controlled Exchange of Achiral Linkers with Chiral Linkers in Zr‑Based UiO-68 Metal–Organic Framework

• Published in: Journal of the American Chemical Society Vol. 140; no. 47; pp. 16229 - 16236
• Main Authors: Tan, Chunxia, Han, Xing, Li, Zijian, Liu, Yan, Cui, Yong
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 28.11.2018
• Subjects: alcohols; aldehydes; aminolysis; catalysts; catalytic activity; coordination polymers; crystals; enantioselectivity; epoxidation reactions; epoxides; ligands; nitrogen; sorption; X-ray diffraction
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.8b09606

The development of highly robust heterogeneous catalysts for broad asymmetric reactions has always been a subject of interest, but it remains a synthetic challenge. Here we demonstrated that highly stable metal–organic frameworks (MOFs) with potentially acid-labile chiral catalysts can be synthesized via postsynthetic exchange. Through a one- or two-step ligand exchange, a series of asymmetric metallosalen catalysts with the same or different metal centers are incorporated into a Zr-based UiO-68 MOF to form single- and mixed-M­(salen) linker crystals, which cannot be accomplished by direct solvothermal synthesis. The resulting MOFs have been characterized by a variety of techniques including single-crystal X-ray diffraction, N2 sorption, CD, and SEM/TEM-EDS mapping. The single-M­(salen) linker MOFs are active and efficient catalysts for asymmetric cyanosilylation of aldehydes, ring-opening of epoxides, oxidative kinetic resolution of secondary alcohols, and aminolysis of stilbene oxide, and the mixed-M­(salen) linker variants are active for sequential asymmetric alkene epoxidation/epoxide ring-opening reactions. The chiral MOF catalysts are highly enantioselective and completely heterogeneous and recyclable, making them attractive catalysts for eco-friendly synthesis of fine chemicals. This work not only advances UiO-type MOFs as a new platform for heterogeneous asymmetric catalysis in a variety of syntheses but also provides an attractive strategy for designing robust and versatile heterogeneous catalysts.