Nested nanostructures direct fullerene functionalization

For years, chemists have been kicking around plenty of ideas for adding groups to soccer ball–shaped C₆₀. Some of the work has led to functionalized fullerenes that have applications in solar cells, for example. The challenge is that most syntheses produce a multitude of isomers that have to be painstakingly separated. Max von Delius’s group at Ulm University had been trying to make bis-adducts of C₆₀—fullerenes with substituents added in just two locations—by surrounding the buckyballs with nanohoops. Xavi Ribas’s group at the University of Girona was working on a similar strategy with nanocages. When the chemists saw each other’s work during a scientific meeting, they decided to combine their efforts. Together, their teams made a molecular matryoshka, named for the Russian nesting dolls (Nat. Chem. 2021, DOI: 10.1038/s41557-021-00658-6). The supramolecular structure features a buckyball surrounded by a nanohoop, which is encased in a cage (shown). The structure limits reagents’ access to the fullerene. A cyclopropanation reaction produced a single isomer of a bis-adduct in 90% yield. The same reaction with naked buckyballs gives more than a dozen isomers. The authors suggest that the strategy could be used generally for making bis-adducts of buckyballs, although they note that streamlined reagents work better with the assembly than bulky ones.