Fan Y, Ren Y, Li J, Yue C, Jiang H. Enhanced Activity and Enantioselectivity of Henry Reaction by the Postsynthetic Reduction Modification for a Chiral Cu(salen)-Based Metal-Organic Framework.
Inorg Chem 2018;
57:11986-11994. [PMID:
30199236 DOI:
10.1021/acs.inorgchem.8b01551]
[Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Metal-organic frameworks (MOFs) imbedded privileged molecular catalysts are of particular interest due to their higher catalytic activities derived from the MOFs pore/channel confinement effect, improved lifetime through eliminating intermolecular deactivation pathway, and the recyclability based on their heterogeneity. In this work, a 3D chiral metallosalen-based MOF [Cd2(Cu(salen))(DMF)3]·DMF·3H2O (1) with a 1D open channel was synthesized and characterized by single-crystal X-ray diffraction and other physicochemical methods. Upon postsynthetic reduction modification with NaBH4, the conversion from imino to amino group on salen cores of 1 generates the reduction product 2 with a more flexible chiral group and more alkaline backbone, meanwhile still maintaining the original porous framework. 2 can be used as an efficient heterogeneous catalyst for the asymmetric Henry reaction with broad substrate applicability and exhibits higher activity and enantioselectivity (ee up to 98%) compared with the unreduced 1. Note that 2 can accelerate the Henry reaction of pyridine-2-carboxaldehyde possessing a potential coordination atom with excellent ee value; however, the homogeneous counterpart does not. In addition, the bulky aldehydes show a decrease in activity but almost the same enantioselectivity with an increase in the molecular size of substrates as a result of the chiral confinement effect of 2, indicating the size-dependent selectivity. To the best of our knowledge, this is the highest enantioselectivity for asymmetric Henry reaction catalyzed by MOF-based catalysts.
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