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The construction of an appropriate support for a single atom catalyst plays an important role in delivering a high catalytic performance. However, most reported host materials suffer the drawbacks of low photostability and limited visible light absorption. Herein, we report a porous organic cage as a high-quality support for single metal atoms by a facile stepwise nucleophilic substitution approach. Thanks to its intrinsic advantages of extended visible light absorption, suppressed charge recombination, and improved electron transfer, the obtained single Co atoms anchored organic cage (CoP@POC) demonstrates a prominent photocatalytic efficiency for oxidation of amines into imines in visible light. An excellent reaction conversion and selectivity up to 99%, associated with a turnover frequency (TOF) of 1389 h–1 and 22 989 mmol g–1 h–1 are achieved based on organic cage and single Co atoms, respectively, which outperforms most reported photocatalysts. Moreover, a negligible conversion decrease in 5 repeating cycles and no photobleaching after the reaction was detected, implying a remarkable photostability of CoP@POC.

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The preparation of imines has drawn increasing attention as they are fundamental intermediates in the production of pharmaceuticals, agricultures, and fine chemicals. Nevertheless, current approaches for imines synthesis mainly focus on thermally driven reactions which always involve the consumption of high price noble metal catalysts, expensive ligands, strong base, and harsh reaction conditions. Herein, we demonstrate single atom nickel anchored on polymeric carbon nitride (Ni-SA@PCN) in Ni−N 4 structure for visible light-promoted crossed coupling between aromatic alcohols and aliphatic amines. As expected, the Ni atoms dispersed carbon nitride demonstrates an obviously improved charge separation and transfer as reflected in UV−vis, fluorescence intensity and lifetime, photocurrent density, and electrochemical impedance characterizations. More impressively, the density functional theory (DFT) calculations also reveals that the presence of Ni atoms can dramatically accelerate the absorption of reactive substrates on the surface of PCN. The decreased absorption energy from −0.51 to −3.35 eV, associated with increased OO bond length from 1.226 to 1.371 Å indicates a huge advantage of single Ni atom on oxygen activation. As a result, the obtained Ni-SA@PCN photocatalyst shows a prominent catalytic efficiency in imines formation with a reaction conversion of 73% and selectivity of >99%. Lastly, the photocatalytic reactions displays an excellent compatibility with various imines being achieved with high yield.