Functionalized Endohedral Metallofullerene Materials

Typically, endohedral metallofullerenes are produced in an electric arc by evaporating composite carbon rods filled with atomic or molecular elements that later end up inside the carbon cages. However, the yield of endohedral metallofullerenes is rather low, less than 1%, and their formation mechanism is unknown. Furthermore, no particular rules are applied on the selection of the carbon cage that will be formed and on the nature of the element that ultimately will be encapsulated. 

Since then, several studies on the chemical reactivity of endohedral metallofullerenes have been performed in order to understand their basic chemical properties. The endohedral metallofullerenes Gd C82 [137], La2 C80, and Sc2 C84 [138] showed similar behavior towards disilirane, forming the corresponding adducts via C-Si bonds. Also, similar functionalization of La C82 was achieved with digermirane [ 139,140]. However, when diphenyldiazomethane was added to La C82 an exohedral adduct was formed via C-C bonds [ 140,141 ]. This organic functionalization of endohedral metallofullerenes opened the way to chemically tune the electronic properties of the so-produced materials, the degree of charge transfer, and ultimately their electronic properties. 

The first Diels-Alder cycloaddition on endohedral metallofullerenes was recently reported. Sc3N C80 endohedral metallofullerene was reacted with the diene precursor 6,7-dimethoxyisochroman-3-one to yield the corresponding adduct [ 142 ], while its structure was also verified by X-ray diffraction measurements [143]. 

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