Isolation and Characterization of a U≡C Triple Bond in Isolable Fullerene Compounds

Despite decades of efforts, the actinide-carbon triple bond has remained an elusive target, defying isolation in any compound. Herein, we report the successful stabilization of uranium-carbon triple bonds in carbide-bridged bimetallic [U≡C−Ce] units encapsulated inside fullerene cages of C72 and C78. The molecular structures of UCCe@C2n and the nature of the U≡C triple bond were characterized through X-ray crystallography and various spectroscopic analyses, revealing very short uranium-carbon bonds of 1.921(6) and 1.930(6) Å, with the metals existing in their highest oxidation states of +6 and +4 for uranium and cerium, respectively. Quantum-chemical studies further demonstrate that the C2n cages are crucial for stabilizing the [UVI≡C−CeIV] units through covalent and coordinative interactions. This work offers a new fundamental understanding of the elusive uranium-carbon triple bond and informs the design of complexes with similar bonding motifs, opening up new possibilities for creating distinctive molecular compounds and materials.