Endohedral dynamics of push-pull rotor-functionalized cages.

A series of [Pd2L4] coordination cages featuring endohedral functionalities in central backbone positions was synthesized. Although attached via C[double bond, length as m-dash]C double bonds, the substituents behave as molecular rotors. This is explained by their pronounced donor-acceptor character which lowers rotational barriers and allows for electronic control over the spinning rates inside the cage. The dynamic behaviour of the free ligands, assembled cages and host-guest complexes is compared with the aid of NMR experiments, X-ray structure analysis and molecular modelling.