A Thiazole-Linked Dithiophenedione-Functionalized Covalent Organic Framework for Photocatalytic Oxidative Dehydrogenation Reactions

A large number of catalysts have been developed to carry out oxidative dehydrogenative coupling reactions. However, the majority of catalysts are homogeneous transition metals that only work at very high temperatures. The heterogeneous modifications of these systems also have some limitations, including but not limited to metal nanoparticle sintering, metal leaching during multiple catalytic runs, and nanoparticle size control during recycling. Here, we present a metal-free catalyst, a covalent organic framework (COF), that serves as a promising photocatalyst to carry out the targeted dehydrogenative coupling at room temperature. The COF, Th-DHTD, was synthesized by a postsynthetic modification of an imine-linked COF, Im-DHTD, using sulfur (S8) to incorporate a thiazole linkage into the COF backbone via a bond-locking strategy. Encouragingly, this postmodification maintains crystallinity, increases porosity, and improves the base stability of the COF. Using this COF at very low loading, we have synthesized a series of quinazolinone and benzothiadiazine-1,1-dioxide in high yields under visible light excitation. The unprecedented ease of oxidative reactions, coupled with exceptionally low catalyst loading, mild operational conditions, and remarkable recyclability of the COF over multiple cycles, establishes a benchmark for this class of reactions, surpassing prior limitations and expanding the scope of catalytic efficiency and sustainability.