Activation of carbon dioxide by new mixed sandwich uranium( iii ) complexes incorporating cyclooctatetraenyl and pyrrolide, phospholide, or arsolide ligands

A series of uranium( iii ) mixed-sandwich complexes of the type [U(COT TIPS2 )(Cp EMe4 )] (Cp EMe4 = EC 4 Me 4 , E is N, P or As, and COT TIPS2 = C 8 H 6 {1,4-Si i Pr 3 }), featuring a heterocyclic five membered ring, have been synthesised and their X-ray crystal structures determined. The redox properties of these complexes have been assessed using cyclic voltammetry and the results compared to the purely carbocyclic mixed-sandwich analogues. The reactions of [U(COT TIPS2 )(Cp NMe4 )] and [U(COT TIPS2 )(Cp PMe4 )] with CO 2 afford the structurally characterised carbamate and phosphacarbonate complexes [U(COT TIPS2 )] 2 (μ-O)(μ-η 1 :η 1 -O 2 CEC 4 Me 4 ) 2 (E = N and P respectively), arising from CO 2 reduction and insertion.