Rotational Control of a Dirhodium-Centered Supramolecular Four-Gear System by Ligand Exchange.

Self-assembled molecular machines have great potential to enable noncovalent regulation of a coupled motion of the building blocks. Herein we report the synthesis and the rotational control of a lantern-type dirhodium complex with circularly arranged four 2,3,6,7,14,15-hexamethyltriptycene carboxylates as gears and two axial ligands as the rate control elements. The rotating rates in solution were markedly affected by the coordination ability and the bulkiness of axial ligands. Notably, the rate changes were closely correlated with the changes in the electronic states of the dirhodium center. Such ligand exchange-based control of rotational motions with color changes would advance stimulus-responsive metallo-molecular multirotors.