Open [60]Fullerenes can be promising nanomaterials for use in molecular storage and delivery. Guest molecules such as H₂ or He are commonly used in this kind of chemistry. For the encapsulation of larger guest molecules into the [60]fullerene cavity, a larger opening is required. However, so far, openings with a ring-atom count of 20 or more are still somewhat rare.

Yasujiro Murata, Kyoto University, Japan, and colleagues have synthesized a [60]fullerene with a 20-membered-ring opening (pictured above on the left), which allows guest molecules such as H₂, N₂, and CH₃OH to be encapsulated. The desired product was prepared from a suitable open fullerene precursor via a reaction with 4,5-dimethyl-1,2-phenylenediamine in o-dichlorobenzene (ODCB) at 180 °C. The structure of the product was determined by X-ray diffraction analysis, and the team found that the cavities contained water and dinitrogen molecules. Heating in a methanol solution allowed them to remove these guests and encapsulate methanol.

The researchers also prepared a derivative with a 21-membered-ring opening (pictured above on the right) via a reductive decarbonylation of the [60]fullerene with the 20-membered-ring opening, using tris(dimethylamino)methane (TDAM) as a single-electron reductant in the presence of water. In this reaction, one of the carbon atoms was moved out of the [60]fullerene skeleton to form an N,N-dimethylamide group. The product allows argon encapsulation at –30 °C with an occupation level of up to 52 %.

When the encapsulated argon atom is released by elevating the temperature, the methyl group of the N,N-dimethylamide moves into the opening, i.e., the system shows undergoes self-inclusion. This effect could be used, e.g., to construct molecular machines or to realize physical protection/deprotection systems that do not require chemical transformations.

• Construction of a 21‐Membered‐Ring Orifice on [60]Fullerene,
  Yoshifumi Hashikawa, Shumpei Sadai, Yasujiro Murata,
  ChemPlusChem 2023.
  https://doi.org/10.1002/cplu.202300225