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 (=CH 2 ) 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≡CSc 2 ] cluster encapsulated inside a C 80 fullerene cage. The molecular structure of Ce≡CSc 2 @C 80 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.