Constructing Crystalline Covalent Organic Frameworks from Chiral Building Blocks

Abstract

Covalent organic frameworks (COFs) represent a new type of crystalline porous materials that are covalently assembled from organic building blocks. Construction of functional COFs is, however, a difficult task because it has to meet simultaneously the requirements for crystallinity and functionality. We report herein a facile strategy for the direct construction of chiral-functionalized COFs from chiral building blocks. The key design is to use the rigid scaffold 4,4'-(1H-benzo[d]imidazole-4,7-diyl)dianiline (2) for attaching a variety of chiral moieties. As a first example, the chiral pyrrolidine-embedded building block (S)-4,4'-(2-(pyrrolidin-2-yl)-1H-benzo[d]imidazole-4,7-diyl)dianiline (3) was accordingly synthesized and applied for the successful construction of two chiral COFs, LZU-72 and LZU-76. Our experimental results further showed that these chiral COFs are structurally robust and highly active as heterogeneous organocatalysts.

Kovalente organische Netzwerke und Käfigverbindungen: Design und Anwendungen von polymeren und diskreten organischen Gerüsten

“…Mastalerz und Mitarbeiter beobachteten in der festen Phase die Bildung von vierfach verzahnten Käfigen, die wahrscheinlich durch attraktive Wechselwirkungen zwischen den lçslichkeitsvermittelnden Hexylketten an den Tr iptycen-Brückenkopfpositionen stabilisiert werden. Chirale Einheiten kçnnen entweder über postsynthetische Modifikationen [185] oder als Substituenten in den Vorstufen [186] eingebaut werden. Der daraus erhaltene Festkçrper ist das erste Beispiel füre in einzelnes porçses organisches Material mit sowohl Mikro-als auch Mesoporen (intrinsisch und extrinsisch).…”

“…[331] Die Aktivitätw ar gegenüber jener des molekularen Cobaltkomplexes um den Faktor 26 erhçht, und auch nach 24 hk onnte keinerlei Zersetzung beobachtet werden. [185] Die direkte Implementierung von chiralen Seitenketten [186] oder intrinsisch chiralen Bausteinen [181,187] führte ebenfalls zu hochaktiven Katalysatoren fürv erschiedene organische Reaktionen. [332] COFs wurden auch als Heterogenmatrices fürc hirale Organokatalysatoren eingesetzt.…”

Porous aromatic framework (PAF-1) as hyperstable platform for enantioselective organocatalysis

“…Among the applications, immobilization of homogeneous catalysts, especially chiral catalysts, on cavity surfaces of the solid porous materials is of great importance. In this field, the latest developments involved enantioselective catalysis based on metal-organic frameworks (MOFs) [1][2][3][4][5][6][7][8][9][10][11][12][13][14], covalent organic frameworks (COFs) [15][16][17][18][19][20][21][22][23][24] and porous organic polymers (POPs) [25][26][27][28][29][30][31][32]. Many advantages of MOFs, COFs and POPs for heterogeneous enantioselective catalysis have been elaborated by scientists.…”

“…Meanwhile, owing to the appropriate size as well as the easy preparation, the proline-type organocatalysts are one of the best candidates to investigate if a new solid material could be used as the platform for enantioselective catalysis. On the other hand, the Aldol reaction is an important reaction which is frequentlyused to investigate the catalytic activity of the catalyst supported by porous materials such as MOFs, COFs and POPs [1][2][3][4][5][6][7][8][9]23,24,32]. Thus in this paper we make an attempt to introduce the chiral catalytically active L-prolinamide unit into the PAF-1 material by stepwise post-synthetic modifications and investigate the catalytic performance of the obtained material for catalyzing the Aldol reaction.…”

Divergent Synthesis of Chiral Covalent Organic Frameworks

“…[5,6] In this context, further construction of COFs with embedded functional moieties [7] still remains challenging:t arget-oriented synthesis has to meet all the requirements of crystallinity,p orosity,a nd functionality.F or example,a lthough promising in asymmetric catalysis and enantioselective recognition/separation, only ah andful of chiral COFs (CCOFs) have been successfully synthesized. [8][9][10][11][12][13][14] In 2016, we targeted at the direct synthesis of as econdaryamine CCOF with ac hiral pyrrolidine building block. [10] However,t he lack of its combinatorial library makes the further high-throughput screening and structure-activity investigation impossible.B ecause our original synthetic route is only suitable for as pecific target, [10] we develop herein an updated strategy to construct aseries of CCOFs for parallel evaluation of their catalytic performance.T his effort may present ag eneral protocol for the bottom-up introduction of designed functionality into COFs.…”