Journal
NANO RESEARCH
Volume 14, Issue 2, Pages 466-472Publisher
TSINGHUA UNIV PRESS
DOI: 10.1007/s12274-020-2905-7
Keywords
metal-organic frameworks; metal phosphonate; Lewis acid; asymmetric catalysis; hydrogenation reaction
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Funding
- National Natural Science Foundation of China [91956124, 21875136, 21620102001, 91856204, 21978058, 21676094]
- National Key Basic Research Program of China [2016YFA0203400]
- Key Project of Basic Research of Shanghai [17JC1403100, 18JC1413200, 19JC1412600]
- Shanghai Rising-Star Program [19QA1404300]
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Metal-organic frameworks (MOFs) have shown great potential in heterogeneous catalysis, and the enantioselectivities of chiral MOF (CMOF) catalysts can be significantly enhanced by designing metals and ligands, resulting in improved chiral catalytic reactions.
Metal-organic frameworks (MOFs) have achieved great success in the field of heterogeneous catalysis, however, it's still challenging to design MOF catalysts with enhanced selectivity. Here, we demonstrated a combination strategy of metal design and ligand design on the enantioselectivity-that is the enantioselectivities of chiral MOF (CMOF) catalysts could be significantly enhanced by the rational choice of metal ions with higher electronegativities and introducing sterically demanding groups into the ligands. Four isostructural Ca-, Sr- and Zn-based CMOFs were prepared from enantiopure phosphono-carboxylate ligands of 1,1 '-biphenol that are functionalized with 2,4,6-trimethyl- and 2,4,6-trifluoro-phenyl groups at the 3,3'-position. The uniformly distributed metal phosphonates along the channels could act as Lewis acids and catalyze the asymmetric transfer hydrogenation of heteroaromatic imines (benzoxazines and quinolines). Particularly, the Ca-based MOF 1 with 2,4,6-trimethyl groups at the substituents exhibited enhanced catalytic performance, affording the highest enantioselectivity (up to 97%). It is also the first report of the heterogeneous catalyst with chiral non-noble metal phosphonate active sites for asymmetric transfer hydrogenation reactions with Hantzsch ester as the hydrogen source. The catalyst design strategy demonstrated here is expected to develop new types of chiral materials for asymmetric catalysis and other chiral applications.
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