Mechanochemical Oxidative Coupling of Amine to Azo-based Polymers by Hypervalent Iodine Oxidant

Among porous organic polymers (POPs), azo-linked POPs represent a crucial class of materials, making them the focus of numerous catalytic systems proposed for their synthesis. However, the synthetic process is limited to metal-catalyzed, high-temperature, and liquid-phase reactions. In this study, we employ mechanochemical oxidative metal-free systems to encompass various syntheses of azo-based polymers. Drawing inspiration from the rule of six principle (six or more carbons on an azide group render the organic compound relatively safe), an azo compound featuring significant steric hindrance is obtained using the hypervalent iodine oxidation strategy. Furthermore, during the polymerization process, steric hindrance is enhanced in monomers to effectively prevent explosions resulting from direct contact between hypervalent iodine oxidants and primary amines. Indeed, this approach provides a facile and innovative solid-phase synthesis method for synthesizing azo-based materials. The synthetic strategy of azo-based polymers is tedious and limited to liquid-phase synthesis. In most cases, the explosion is inevitable when hypervalent iodine in direct contacts with primary amines, which further restricts the solid-state synthesis. Inspired by the principle of rule of six, it is feasible to construct azo-based polymers by hypervalent iodine oxidant in ball milling process.image

Automated summary

In this study, various azo-based polymers were synthesized using mechanochemical oxidative metal-free systems. By enhancing steric hindrance, explosions were effectively prevented, and a facile and innovative solid-phase synthesis method was developed.