The development of bioinspired copper complexes for CO₂ activation and hydration

Here, we report a thioether-modified pyridine-2,6-dicarboxamide copper complex, [Cu(L)], 1 and its hydroxide-bridged dimer form, 2 exhibit different mechanisms of CO₂ activation. The incorporation of a thioether moiety enhances the stabilization of the Cu(I) state and improves the redox reversibility of the complex for CO₂ activation. While 1 monomer shows no direct reactivity toward CO₂ in its resting state, the µ-OH dimer 2 reacts with CO₂ to form a bicarbonate species, mimicking the nucleophilic CO₂ hydration observed in Zn-containing carbonic anhydrases. In comparison, upon reduction, 1 forms a CO₂-bound intermediate, revealing a redox-triggered pathway distinct from that of 2. Under electrochemical conditions, both complexes exhibit irreversible Cu(II/I) reduction in the presence of CO₂, wherein an initial electron-transfer (E) step is followed by a chemical (C) transformation involving transient Cu-CO₂ (EC-type) adduct formation. Overall, these findings demonstrate that the incorporation of soft sulfur donors equips copper complexes to mediate CO₂ reactivity, providing a new direction toward the design of copper-based catalysts for CO₂ conversion.