Synthesis and Characterization of U≡C Triple Bonds in Fullerene Compounds

Abstract

Despite decades of efforts, the actinide–carbon triple bond has remained an elusive target, defying synthesis in any isolable compound. Herein, we report the successful synthesis of uranium–carbon triple bonds in carbide-bridged bimetallic [U≡C–Ce] units encapsulated inside the 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.