Engineering Homochiral Metal‐Organic Frameworks for Heterogeneous Asymmetric Catalysis and Enantioselective Separation

Abstract

Owing to the potential applications in technological areas such as gas storage, catalysis, separation, sensing and nonlinear optics, tremendous efforts have been devoted to the development of porous metal-organic frameworks (MOFs) over the past ten years. Homochiral porous MOFs are particularly attractive candidates as heterogeneous asymmetric catalysts and enantioselective adsorbents and separators for production of optically active organic compounds due to the lack of homochiral inorganic porous materials such as zeolites. In this review, we summarize the recent research progress in homochiral MOF materials, including their synthetic strategy, distinctive structural features and latest advances in asymmetric heterogeneous catalysis and enantioselective separation.

Engineering chiral porous metal-organic frameworks for enantioselective adsorption and separation

“…The present MOF represents a new generation of chiral porous solid that is capable of chiral separation of a variety of racemic amines. The success may result from a combination of the chiral channels with amphiphilic channel interior lined with chiral -OH auxiliaries, which may govern the intermolecular interactions between the host and amines favouring enantioselectivity during the adsorption process 43,44,51 . Unfortunately, attempts to get the single crystal of the inclusion adduct were unsuccessful.…”

“…Many artificial porous organic and hybrid hosts have been developed for chiral recognition and resolution of organic molecules, such as alcohols in a solid state, but there are few examples of enantioselective inclusion of amines 8,43,44 . In 1995, Mallouk et al 49 pioneered optical resolution of amine (1,2-diaminocyclohexane, 85% ee) through intercalation by a layered phosphate with an optically active building block.…”

“…For a MOF to act an enantioselective selector, it should possess multiple chiral recognition sites that can work synergistically to induce selective recognition and binding of analytes and to exert stereocontrol. However, it is challenging to create the selectivity essential for separation of stereoselectively different forms of compounds 43,44 .…”

“…An important challenge associated with chiral MOFs as enantioselective adsorbents is how to create the driving force efficiently to discriminate two opposite enantiomers in an inclusion process 43,44 . Chiral recognition generally relies on a minimum of three simultaneous interactions between the selector and analyte-the so-called three-point rule 3,44 . At least one of these interactions must be stereoselective to form diastereomeric complexes and enable chiral separation.…”

Homochiral metal-organic framework [Zn2(d-Cam)2(4,4′-bpy)]nfor high-resolution gas chromatographic separations

“…To date, a large number of chiral MOFs have been synthesized [23][24][25][26][27][28][29][30][31][32][33], which can be suitable as chiral stationary phases (CSPs) because of its excellent chiral recognition ability and thermal and mechanical stability [34,35]. However, only a few chiral MOFs have been used as CSPs in gas chromatography (GC) for separation of racemic compounds [36][37][38][39].…”