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.