Tri-site Synergistic Cu(I)/Cu(II)─N Single-Atom Catalysts for Additive-Free CO₂ Conversion

As the highly stable and abundant carbon source in nature, the activation and conversion of CO₂ into high-value chemicals is highly desirable yet challenging. The development of Cu(I)/Cu(II)─N tri-site synergistic single-atom catalysts (TS-SACs) with remarkable CO₂ activation and conversion performance is presented, eliminating the need for external additives in cascade reactions. Under mild conditions (40 °C, atmospheric CO₂), the catalyst achieves high yields (up to 99%) of valuable 2-oxazolidinones from CO₂ and propargylamine. Notably, the catalyst demonstrates easy recovery, short reaction times, and excellent tolerance toward various functional groups. Supported by operando techniques and density functional theory calculations, it is elucidated that the spatially proximal Cu(I)/Cu(II)─N sites facilitate the coupling of multiple chemical transformations. This surpasses the performance of supported isolated Cu(I) or Cu(II) catalysts and traditional organic base-assisted cascade processes. These Cu(I)/Cu(II)─N tri-site synergistic atom active sites not only enable the co-activation of CO₂ at the Cu(II)─N pair and alkyne at the Cu(I) site but also induce a di-metal locking geometric effect that accelerates the ring closure of cyclic carbamate intermediates. The work overcomes the limitations of single metal sites and paves the way for designing multisite catalysts for CO₂ activation, especially for consecutive activation, tandem, or cascade reactions.