Synthesis and post-synthetic modification of tetrazine-based organic frameworks

Porous organic polymers (POPs) have been studied extensively over the past decade. The intrinsic porosity and tunable chemical structures have seen applications in gas storage, separations, and even catalysis. However, a vast majority of the POPs rely on a narrow class of monomeric units and polymerization conditions which limits the diversity of functionality in the polymers, and hence their chemical properties. To get around these issues, a micro- and mesoporous tetrazine-based organic framework with BET surface area of 170 m2/g was synthesized through palladium catalyzed cross-coupling reaction. The structure of the polymer was confirmed by solid-state 13C NMR, ATR-IR and EDX. The 1,2,4,5-tetrazine units on the struts of the framework were active toward inverse electron-demand Diels-Alder reactions, allowing for a post-synthetic introduction of different functionalities into the tetrazine-based organic frameworks (TzOF). The structures of modified polymers were verified by solid-state 13C NMR and ATR-IR. To eliminate the use of transition metals during synthesis, a new class of sulfur-containing tetrazine-based organic framework was designed and synthesized by nucleophilic aromatic substitution reactions. The resulting mesoporous polymer framework, with 3,6-dithio-1,2,4,5-tetrazine unit on the struts, showed BET surface area of 38 m2/g. The structure of the framework was confirmed by ATR-IR and EDX. Post-synthetic modifications of the polymer were also achieved by reacting with dienophiles through inverse electron-demand Diels-Alder reactions. The structures of modified polymers were verified by ATR-IR. These two synthetic methods we have developed for tetrazine-based organic frameworks and their ability to introduce functionality post-synthetically brought additional functionalities to the POP family.