Abstract:

Epoxides are crucial intermediates in fine chemical production, but existing synthesis processes suffer from issues such as pollution, long process flows, or safety risks. Linking molecular oxygen activation and olefin epoxidation through active hydrocarbons as a bridge is a feasible pathway; this method typically involves effective C-H dehydrogenation to form active free radicals, which then couple with molecular oxygen to achieve subsequent selective oxidation. However, the design of catalysts capable of efficiently regulating the oxidative activation of C-H bonds to generate key intermediates for olefin epoxidation remains challenging. Herein, we designed a metal porphyrin-based COF catalyst (Ru-COF-TPD) and, using air as the oxidant, constructed a catalytic system for olefin epoxidation via the oxidation relay of adamantane. Ru-COF-TPD features highly dispersed metal atoms, excellent stability, and tunable pore sizes. Under an air atmosphere, it can activate the C-H bonds of adamantane to in-situ generate peroxy species and regulate active oxygen transfer, thereby enabling selective olefin epoxidation. It achieves 83% conversion for 1-butylene with 81% selectivity to the corresponding epoxide, and exhibits good activity towards various olefins. After the reaction, the metal sites remain dispersed, indicating good structural stability of the catalyst. This tandem system is an endothermic and disordered, following a pseudo-first-order model with an apparent activation energy of 108.08 kJ/mol. It was further found that Ru-COF-TPD generates carbon-centered radicals by activating the C-H bonds of adamantane, which then combine with oxygen to form peroxy radicals, and regulates the epoxidation process high-valence Ru=O intermediates. The catalytic system established in this study is safe, economical, and efficient, providing a lab-scale protocol for olefin oxidation with air.

Key words: Air oxidation, Porphyrin-based COF, Adamantane C-H activation, Relay catalysis, Olefins epoxidation