Concomitant Carboxylate and Oxalate Formation From the Activation of CO₂ by a Thorium(III) Complex

Improving our comprehension of diverse CO₂ activation pathways is of vital importance for the widespread future utilization of this abundant greenhouse gas. CO₂ activation by uranium(III) complexes is now relatively well understood, with oxo/carbonate formation predominating as CO₂ is readily reduced to CO, but isolated thorium(III) CO₂ activation is unprecedented. We show that the thorium(III) complex, [Th(Cp'')₃ ] (1, Cp''={C₅ H₃ (SiMe₃ )₂ -1,3}), reacts with CO₂ to give the mixed oxalate-carboxylate thorium(IV) complex [{Th(Cp'')₂ [κ² -O₂ C{C₅ H₃ -3,3'-(SiMe₃ )₂ }]}₂ (μ-κ² :κ² -C₂ O₄ )] (3). The concomitant formation of oxalate and carboxylate is unique for CO₂ activation, as in previous examples either reduction or insertion is favored to yield a single product. Therefore, thorium(III) CO₂ activation can differ from better understood uranium(III) chemistry.