Asymmetric Hydrophosphonylation of Imines to Construct Highly Stable Covalent Organic Frameworks with Efficient Intrinsic Proton Conductivity

Imine-linked covalent organic frameworks (COFs) have received widespread attention because of their structure features such as high crystallinity and tunable pores. However, the intrinsic reversibility of the imine bond leads to the poor stability of imine-linked COFs under strong acid conditions. Also, their thermal stability is significantly lower than that of many other COFs. Herein, we report for the first time that the reversible imine bonds in the skeleton of COFs can be locked through the asymmetric hydrophosphonylation reaction of phosphite. The functionalized COFs not only retain the crystallinity and porous structure but also exhibit evidently improved chemical and thermal stabilities. In addition, the phosphorous acid groups generated by acidic hydrolysis attached to the skeleton endow the COFs with good intrinsic proton conductivity. Due to the diversity of phosphite derivatives and imine-linked COFs, this work may provide an avenue for extending the COF structures and functions through the asymmetric hydrophosphonylation reaction.