A “molecular shuttle” is a mechanically interlocked molecule in which one component moves from one location to another. Such species are interesting for the creation of nanosized molecular machines. Existing examples of molecular shuttles are often based on rotaxanes, in which a macrocycle is threaded on a molecular “axle” with stopper units at both ends. Developing other structures that can be used as molecular shuttles would be useful to allow the creation of more diverse molecular machines.
Susana Ibáñez, Eduardo Peris, Universitat Jaume I, Castellón, Spain, and colleagues have used box-shaped supramolecular organometallic complexes to create such a molecular shuttle. The team used large di-N-heterocyclic carbene ligands (NHCs) and pyrazine to connect iridium centers and build a long, yet narrow box that can serve as a host molecule (pictured below). The complex was synthesized from a quinoxalinophenanthrophenazine-bis-imidazolylidene di-iridium(I) complex and pyrazine in the presence of two equivalents of AgBF4, using CH2Cl2 as the solvent.
The team found that the synthesized “metallobox” can encapsulate different planar guest molecules, such as pyrene, triphenylene, or coronene. For smaller guests, one box can encapsulate two guest molecules. For larger guest molecules such as coronene, the researchers observed a 1:1 stoichiometry. In this type of host-guest complex, the cavity is asymmetrically occupied by the guest molecule, and the researchers observed a dynamic behavior: The guest molecule moves from one side of the cavity to the other, creating a molecular shuttle (pictured at the top). According to the team, it could be possible to fine-tune this dynamic behavior by changing the guest molecule, which can be useful in the development of molecular machines.
- Guest‐shuttling in a Nanosized Metallobox,
Susana Ibáñez, Paula Salvà, Louise N. Dawe, Eduardo Victor Peris,
Angew. Chem. Int. Ed. 2024.