58740-82-2Relevant articles and documents
Synthesis of new chiral Mn(iii)-salen complexes as recoverable and reusable homogeneous catalysts for the asymmetric epoxidation of styrenes and chromenes
Chaudhary, Pooja,Damodaran, Krishna K.,Singh, Surendra,Yadav, Geeta Devi
, p. 1308 - 1318 (2022/02/07)
New chiral Mn(iii)-salen complexes 1a-e and 2a-e were synthesized from the reaction of C2-symmetric chiral salen ligands and Mn(CH3COO)2·4H2O under an inert atmosphere followed by aerobic oxidation. These complexes were obtained in 91-96% yields and characterized by HRMS, FT-IR, UV-visible spectroscopy, TGA, and elemental analysis. The chiral Mn(iii)-salen complexes 1a-e and 2a-e were evaluated in the asymmetric epoxidation of styrene using NaOCl as an oxidant in ethyl acetate as a green solvent. The chiral Mn(iii)-salen complexes 1b and 2b (2 mol%) catalyzed the asymmetric epoxidation of substituted styrenes and chromenes to afford the corresponding epoxides in 95-98% yields with 29-88% ee's. The catalysts 1b and 2b were recovered and reused for up to 2 and 3 runs, respectively, in the asymmetric epoxidation of styrene, and the yield of styrene oxide gradually decreased but the ee was consistent.
Design and Assembly of Chiral Coordination Cages for Asymmetric Sequential Reactions
Jiao, Jingjing,Tan, Chunxia,Li, Zijian,Liu, Yan,Han, Xing,Cui, Yong
supporting information, p. 2251 - 2259 (2018/02/19)
Supramolecular nanoreactors featuring multiple catalytically active sites are of great importance, especially for asymmetric catalysis, and are yet challenging to construct. Here we report the design and assembly of five chiral single- and mixed-linker tetrahedral coordination cages using six dicarboxylate ligands derived-from enantiopure Mn(salen), Cr(salen) and/or Fe(salen) as linear linkers and four Cp3Zr3 clusters as three-connected vertices. The formation of these cages was confirmed by a variety of techniques including single-crystal and powder X-ray diffraction, inductively coupled plasma optical emission spectrometer, quadrupole-time-of-flight mass spectrometry and energy dispersive X-ray spectrometry. The cages feature a nanoscale hydrophobic cavity decorated with the same or different catalytically active sites, and the mixed-linker cage bearing Mn(salen) and Cr(salen) species is shown to be an efficient supramolecular catalyst for sequential asymmetric alkene epoxidation/epoxide ring-opening reactions with up to 99.9% ee. The cage catalyst demonstrates improved activity and enantioselectivity over the free catalysts owing to stabilization of catalytically active metallosalen units and concentration of reactants within the cavity. Manipulation of catalytic organic linkers in cages can control the activities and selectivities, which may provide new opportunities for the design and assembly of novel functional supramolecular architectures.
Controlled Exchange of Achiral Linkers with Chiral Linkers in Zr-Based UiO-68 Metal-Organic Framework
Tan, Chunxia,Han, Xing,Li, Zijian,Liu, Yan,Cui, Yong
supporting information, p. 16229 - 16236 (2018/11/27)
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.
