Threading-Followed-by-Shrinking Protocol for the Synthesis of a [2]Rotaxane Incorporating a Pd(II)−Salophen Moiety

This communication describes a new protocol for the construction of [2]rotaxanes:  “threading-followed-by-shrinking”. This approach involves the threading of a rodlike unit through a crown ether-like macrocycle and then shrinking the size of the macrocycle's cavity through coordination of a transition-metal ion by a salophen moiety in the macrocycle. The self-assembly of the macrocycle and a thread, followed by addition of palladium acetate, afforded the [2]rotaxane, which contains a palladium(II)−salophen moiety, after counterion exchange. This [2]rotaxane was characterized fully by NMR and IR spectroscopic, mass spectrometric, and elemental and X-ray crystallographic analyses.