A series of uranium(III) mixed-sandwich complexes of the type [U(COT^TIPS2)(Cp^EMe4)] (Cp^EMe4 = EC₄Me₄, E is N, P or As, and COT^TIPS2 = C₈H₆{1,4-SiⁱPr₃}), 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 CO₂ afford the structurally characterised carbamate and phosphacarbonate complexes [U(COT^TIPS2)]₂(μ-O)(μ-η¹:η¹-O₂CEC₄Me₄)₂ (E = N and P respectively), arising from CO₂ reduction and insertion.