Photocatalytic Oxidative Amine Coupling with 4‑Nitrophenylacetylene-Modified Cu₂O Polyhedra

Compared to using more complicated and expensive metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) for photocatalyzed oxidative amine coupling reactions, simple Cu₂O polyhedral particles functionalized with 4-nitrophenylacetylene (4-NA) are also effective photocatalysts for these reactions. While 4-NA-modified Cu₂O cubes and octahedra are active for benzylamine conversion to N-benzylidenebenzylamine, the functionalized Cu₂O rhombic dodecahedra can achieve a 98% product yield in acetonitrile with 18 h of 370 nm light irradiation under an oxygen-rich atmosphere at room temperature. The functionalized rhombic dodecahedra also give generally high product yields toward diversely substituted benzylamines. Charge carrier and radical scavenging experiments indicate the involvement of photoexcited electrons, holes, and superoxide anion radicals in the oxidative amine coupling reaction. Conjugated molecular functionalization is a good strategy to boost the photocatalytic activity of semiconductor crystals.