Chiral 3D Covalent Organic Frameworks for High Performance Liquid Chromatographic Enantioseparation

Abstract

In spite of their great promise for enantioselective processes due to the rich host-guest chemistry, it remains a challenge to construct covalent organic frameworks (COFs) with chiral three-dimensional (3D) structures. Here we report bottom-up synthesis of the first example of 3D chiral COFs by imine condensation of an enantiopure 2-fold symmetric TADDOL-derived tetraaldehyde with a tetrahedral tetra(4-anilyl)methane. After postsynthetic oxidation of imine linkages, the framework is transformed into an amide-linked COF with retention of crystallinity and permanent porosity as well as enhanced chemical stability. The resultant isostructural COFs feature a 4-fold interpenetrated diamondoid open framework with tubular channels decorated with chiral dihydroxy auxiliaries. Both COFs can be used as chiral stationary phases for high performance liquid chromatography to enantioseparate racemic alcohols, and the oxidized COF shows superior separation performance compared to the pristine framework.

Opportunities of Covalent Organic Frameworks for Advanced Applications

“…Cui and co-workers demonstrated the construction of 2D COFs with chiral functionalities embedded into the framework by Schiff base condensation reactions of enantiopure tetraaldehydefunctionalized TADDOL (tetraaryl-1,3-dioxolane-4,5-dimethanols) and 4,4′-diaminodiphenylmethane (Figure 8). [40] The resultant COF material showed high performance in liquid chromatographic enantioseparation. Moreover, due to their ordered microporous structures, obvious size selectivity toward reagents was observed in the COF-based catalyst, given the fact that less than 5% conversions were detected with the CCOF/Ti catalyst in coronenyl transformation which was much lower than the 64% conversion obtained with homogeneous TADDOL/Ti.…”

Covalent Organic Frameworks: Chemical Approaches to Designer Structures and Built‐In Functions

“…The imine‐linked 3D chiral CCOF‐5 (Figure d) has been designed for HPLC separation by condensing chiral tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols with tetra(4‐anilyl)methane . CCOF‐5 can be transformed into the amide‐linked CCOF‐6 by oxidation.…”

Kovalente organische Gerüstverbindungen: chemische Ansätze für Designerstrukturen und integrierte Funktionen

“…Eine wirkungsvolle Methode zum Trennen von Enantiomeren ist die Säulenchromatographie an chiraler Phase. COFs können zu chiralen Gerüsten gestaltet werden, indem chirale Einheiten an die Porenwände gebunden oder chirale Linker eingebaut werden . Chirale (+)‐Diacetyl‐ l ‐weinsäure wurde als funktionelles Zentrum in die Gerüste von CTpPa‐1 (Abbildung b), CTpPa‐2 (Abbildung c) und CTpDB (Abbildung c) eingebaut.…”

“…Das iminverknüpfte dreidimensionale, chirale CCOF‐5 (Abbildung d) wurde für die HPLC‐Trennung synthetisiert, indem chirale Tetraaryl‐1,3‐dioxolan‐4,5‐dimethanole mit Tetra(4‐anilyl)methan kondensiert wurden . CCOF‐5 kann durch Oxidation in das amidverknüpfte CCOF‐6 umgewandelt werden.…”