An Unsaturated Coordination Cu ₁ O ₂ Moiety Toward Efficient Aromatic C─H Bond Selective Oxidation

ABSTRACT The enrichment of electron density at the active site contributes to a higher charge‐transfer efficiency with oxidants, thus promoting the catalytic oxidation performance of single‐atom catalysts (SACs). Herein, we adopt a facile thermal reduction approach to cleave a weaker Cu─O bond of Cu 1 O 3 configuration on SiO 2 support (Cu 1 O 3 /SiO 2 ), generating a unique unsaturated coordination Cu 1 O 2 motif with enriched electron density (Cu 1 O 2 /SiO 2 ). Density functional theory (DFT) calculations reveal that the enriched electron density enhances the charge transfer between Cu 1 O 2 sites and adsorbed H 2 O 2 molecules, leading to H 2 O 2 gaining more electron. As a result, the sufficient charge transfer elongates the O─O bond in H 2 O 2 , thereby lowering the activation barrier for generating reactive oxygen species, as supported by transition state (TS) analysis. These species drive the selective oxidation of benzene to phenol. Kinetic studies reveal a substantially lowered activation energy barrier for H 2 O 2 activation over Cu 1 O 2 /SiO 2 compared to Cu 1 O 3 /SiO 2 (37.9 vs. 65.1 kJ mol −1 ). Remarkably, Cu 1 O 2 /SiO 2 achieves a 2.2‐fold enhancement in catalytic activity relative to its precursor. This study, integrating DFT and TS analyses with experimental kinetics, offers critical insights for the rational design of low‐coordinated SACs for selective oxidation applications.