Expanding the Diversity of Linkages in Covalent Organic Frameworks Through Staudinger Cycloaddition: Synthesis of Cis-β-Lactam and Cis-β-Thiolactam COFs

The strategic incorporation of diverse functional groups into covalent organic frameworks (COFs) can expand their use across various applications. Here, a novel application of the Staudinger cycloaddition is presented to synthesize crystalline cis-β-lactam substituted COFs from two-parent, 1,3,6,8-tetraphenylpyrene-based, imine-linked COFs. The resulting cis-β-lactam-linked COFs are microporous and show excellent chemical stability across a broad range of pH levels and excellent thermal stability up to 443–556 °C. These cis-β-lactam COFs are then converted into their thiolactam analogs using Lawesson's reagent. The resulting thionated β-lactam COFs are found to be capable of Hg²⁺ capture with capacities up to 7.8 × 10² mg g⁻¹ and are reusable, retaining a removal efficiency of up to 64% over four cycles. This is the first time that the Staudinger cycloaddition reaction has been used to functionalize COFs, this new route to heteroatom substituted COFs opens potential applications such as heavy metal ion capture.