A Single-COF Photocatalytic System for One-Pot Oxygen Reduction Coupled Ammoximation of Cyclic Ketones.

Abstract

Photocatalytic oxygen reduction over covalent organic frameworks (COFs) has been extensively studied for H2O2 production, but the in situ utilization of oxygen reduction reaction (ORR) intermediates in chemical synthesis remains underexplored. Herein, two porphyrin-based polyimide COFs, IMCOF-1 and IMCOF-2, are reported as photocatalysts for the one-pot ORR-coupled ammoximation of cyclic ketones using O2 and NH4OAc. Under light irradiation, IMCOF-1 achieves a cyclohexanone oxime formation rate of 18.55 mmol g-1 h-1 and is effective for several other cyclic ketones. Mechanistic investigations reveal that photoinduced electron transfer from the porphyrin units to the electron-deficient imide moieties promotes charge separation and activates O2 at the carbonyl sites. The resulting surface-bound *OOH intermediates are proposed to participate in ammonia oxidation and subsequent NH2OH formation, which then condenses with cyclic ketones to yield the corresponding oximes. In contrast to stepwise systems that first accumulate H2O2 before ammoximation, the present one-pot strategy enables the in situ utilization of oxygen-derived reactive intermediates without requiring substantial bulk H2O2 pre-accumulation, eliminating the need for H2O2 isolation, storage, and transport, thereby improving safety and atom economy while maintaining high selectivity. This work demonstrates the potential of directly harnessing ORR-derived intermediates for the light-driven synthesis of value-added nitrogen-containing chemicals.

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