A lanthanide-carbon triple bond stabilized within a fullerene cage

Metal-ligand multiple bonds are ubiquitous in coordination and organometallic chemistry. In contrast, lanthanide-carbon multiple bonds are difficult to form. The isolation of complexes containing lanthanide-carbon double bonds with terminal methyl carbene (=CH₂) and lanthanide-carbon triple bonds remains challenging. Here we present the synthesis of a lanthanide-carbon triple bond contained inside an endohedral fullerene cage. More specifically, we report a cerium-carbide [Ce≡CSc₂] cluster encapsulated inside a C₈₀ fullerene cage. The molecular structure of Ce≡CSc₂@C₈₀ and the nature of the Ce≡C triple bond are studied through X-ray crystallography, spectroscopic analyses and quantum chemical calculations. Our data reveal a very short Ce≡C distance of 1.969(7) Å. Chemical bonding analysis suggests that the formation of the Ce≡C bond primarily arises from the stronger bonding affinity between carbon and cerium compared with scandium inside the encapsulated cluster. The fullerene cage plays a crucial role in stabilizing and protecting this trimetallic carbide cluster featuring a Ce≡C triple bond.