Engineering Redox-Active Metal Sites into Covalent Organic Frameworks for Efficient Photocatalytic Activation and Aerobic Oxidation of C(sp³)─H Bonds

Partial oxidation of alkanes with green O₂ source for valuable oxygenated products is one of the most challenging tasks in chemistry due to the difficulty of the activation of both inert C(sp³)─H bonds and unreactive O₂ molecules. Taking advantage of the structural designability of covalent organic frameworks (COFs) for incorporating diverse functional groups and embedding redox-active Fe/Cu ions into a bipyridine-based COF (BPY-COF), metalated COFs (M@COFs; M = Fe, Cu) with open coordinative metal sites are obtained as heterogeneous photocatalysts for the activation and aerobic oxidation of alkanes under mild conditions. Photoinduced activation of the C(sp³)-H bonds is achieved via hydrogen atom transfer (HAT) by chlorine radicals (Cl•), which are generated via ligand-to-metal charge transfer (LMCT) between the metal centers in the M@COFs and chlorine ions; and the M@COFs with good photoelectric performance can activate O₂ via photoinduced electron transfer (PET). Through dynamic matching of the photoinduced C-H bond and oxygen activation processes, a highly efficient partial oxidation transformation of alkanes is achieved. This study paves the way for the application of multifunctional COF materials in energy and chemical feedstock-related fields.