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

Abstract

Little is known about the chemical properties of carbide cluster metallofullerenes (CCMFs). Here we report the photochemical reaction of a newly assigned CCMF Sc₂C₂@<i>C</i>_2<i>v</i>(5)–C₈₀ with 2-adamantane-2,3-[3<i>H</i>]-diazirine (AdN₂, <b>1</b>), which provides a carbene reagent under irradiation. Five monoadduct isomers (<b>2a</b>–<b>2e</b>), 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 <b>2b</b> to <b>2c</b> was observed, confirming that the most abundant isomer <b>2b</b> is a kinetically favored adduct. Finally, it is revealed that the electronic and electrochemical properties of pristine Sc₂C₂@<i>C</i>_2<i>v</i>(5)–C₈₀ have been markedly altered by exohedral modification