Reductive disproportionation of carbon dioxide to carbonate and squarate products using a mixed-sandwich U(III) complex

The mixed-sandwich U(III) complexes [U(eta-(C8H6SiPr3)-Pr-i-1,4}(2))(eta-Cp-R)(THF)] (R = Me-5, Me4H) react with CO2 to give free CO and the U(IV) carbonate products [U(eta-C8H6{Si-i Pr-3-1,4}(2))(eta-Cp-R)](2)(mu-eta(1): eta(2)-CO3)]; the latter has been structurally characterised for R = Me4H; a 25% molar excess of the U(III) reductant gives a mixture of the carbonate and squarate [U(eta-C8H6{Si-i Pr-3-1,4}(2))(eta-C5Me4H)] 2(mu-eta(2):eta(2)-C4O4) products the first synthesis of an oxocarbon from a CO2 carbon source.