[60]Fullerenes with 20- and 21-Membered-Ring Openings

[60]Fullerenes with 20- and 21-Membered-Ring Openings

Author: ChemPlusChem

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.


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