Constructing Crystalline Covalent Organic Frameworks From Chiral Building Blocks

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.