Chemical Understanding of Carbide Cluster Metallofullerenes: A Case Study on Sc₂C₂@<i>C</i>_2<i>v</i>(5)–C₈₀ with Complete X-ray Crystallographic Characterizations

Little is known about the chemical properties of carbide cluster metallofullerenes (CCMFs). Here we report the photochemical reaction of a newly assigned CCMF Sc2C2@C2v(5)–C80 with 2-adamantane-2,3-[3H]-diazirine (AdN2, 1), which provides a carbene reagent under irradiation. Five monoadduct isomers (2a–2e), with respective abundances of 20%, 40%, 25%, 5%, and 10%, were isolated and characterized with a combination of experimental techniques including unambiguous single-crystal X-ray crystallography. Results show that the two Sc atoms of the bent Sc2C2 cluster tend to move in most cases, whereas the C2-unit is almost fixed. Accordingly, it is difficult to explain the addition patterns by considering the strain and charge density on the cage with a fixed cluster, and thus a moving cluster may account for the addition patterns. These results show that the situation of CCMFs is more complicated than those in other metallofullerenes. Furthermore, a thermal isomerization process from 2b to 2c was observed, confirming that the most abundant isomer 2b is a kinetically favored adduct. Finally, it is revealed that the electronic and electrochemical properties of pristine Sc2C2@C2v(5)–C80 have been markedly altered by exohedral modification.