Cages Covalently Interlocked

As if making a molecular cage weren’t enough of a synthetic challenge, chemists at the University of Liverpool, in England, have one-upped themselves by mechanically bonding two such cage molecules together into a triply interlocked structure (Nat. Chem., DOI: 10.1038/nchem.739). Using so-called dynamic covalent chemistry with an acid catalyst, a team led by Andrew I. Cooper created the interlaced tetrahedral cages via a cycloimination reaction that combines 20 precursor molecules—eight trialdehyde nodes and 12 vicinal diamine linkers—in a one-step process. To make such mechanically interlocked molecules, including catenanes, Borromean rings, and Trefoil knots, chemists have typically needed to tie pieces of the molecule together using coordination chemistry or ionic templates. Cooper’s group, however, does it all via hydrogen bonding and π-π stacking interactions, which provide a template for the covalent bonding. The work demonstrates that “interlocked species can be thermodynamically more stable than the corresponding monomeric structures,” the researchers note. “Indeed, a remarkable level of complexity emerges from rather simple starting materials and procedures.”