Although CO homologation has been observed by the coupling between two or more fragments upon insertion of CO into metal-alkyl, 9 -aryl, -hydride, 11 -imide or -boryl bonds, the direct reductive coupling of CO molecules has only been achieved by a very limited number of systems, typically involving low-valent oxophilic-metallic or non-metallic-elements. For example, homogeneous p-15, and d-block compounds have been used to promote CO reductive coupling. Molecular low-valent f-block complexes based on U(III) and Ln(II) metal centers have shown very promising reactivity in the reductive coupling of CO, which can be traced back to their highly reducing character and oxophilic nature. 17 Detailed experimental and computational studies have been performed by Cloke, Green, Maron and coworkers in order to rationalize the CO reductive coupling reactivity by bulky U(III) sandwich complexes.