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Chiral NH functionalities-based discrimination is a key feature of Nature's chemical armory, yet selective binding of biologically active molecules in synthetic systems with high enantioselectivity poses significant challenges. Here we report the assembly of three chiral fluorescent Zn6L6 metallacycles from pyridyl-functionalized Zn(salalen) or Zn(salen) complexes. Each of these metallacycles has a nanoscale hydrophobic cavity decorated with six, three, or zero chiral NH functionalities and packs into a three-dimensional supramolecular porous framework. The binding affinity and enantioselectivity of the metallacycles toward α-hydroxycarboxylic acids, amino acids, small molecule pharamaceuticals (l-dopa, d-penicillamine), and chiral amines increase with the number of chiral NH moieties in the cyclic structure. From single-crystal X-ray diffraction, molecular simulations, and quantum chemical calculations, the chiral recognition and discrimination are attributed to the specific binding of enantiomers in the chiral pockets of the metallacycles. The parent metallacycles are fluorescent with the intensity of emission being linearly related to the enantiomeric composition of the chiral biorelevant guests, which allow them to be utilized in chiral sensing. The fact that manipulation of chiral NH functionalities in metallacycles can control the enantiorecognition of biomolecular complexes would facilitate the design of more effective supramolecular assemblies for enantioselective processes. [ABSTRACT FROM AUTHOR]

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 [Mn2L(H2O)2] 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 -CF3 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 CF3-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. [ABSTRACT FROM AUTHOR]

The modular construction of covalent organic frameworks (COFs) provides a convenient platform for designing high-performance functional materials, but the synthetic control over their chirality has been relatively barely studied. Here we report a multivariate strategy to prepare chiral COFs (CCOFs) with controlled crystallinity and stability for asymmetric catalysis. By crystallizing mixtures of triamines with and without chiral organocatalysts and with a dialdehyde, a family of two- and three-component 2D porous CCOFs that adopt two different stacking modes is prepared. The organocatalysts are periodically appended on the channel walls, and their contents, which can be synthetically tuned using a three-component condensation system, greatly affect the chemical stability and crystallinity of CCOFs. Specially, the ternary CCOFs displayed relatively high crystallinity and stability compared with the binary CCOFs. Under harsh conditions, the ternary CCOFs can serve as efficient heterogeneous catalysts for an asymmetric aminooxylation reaction, an aldol reaction, and the Diels--Alder reaction, with the stereoselectivity and diastereoselectivity rivaling or surpassing the homogeneous analogues. This work not only opens up a new synthetic route toward CCOFs, but also provides tunable control of COF crystallintity and stability and, in turn, the properties. [ABSTRACT FROM AUTHOR]