Restricting shuttling in bis(imidazolium)•••pillar[5]arene rotaxanes using metal coordination

Metal coordination to a series of bis (imidazolium)center dot center dot center dot pillar[5] arene [2]rotaxanes through the formation of metal-carbene bonds facilitates a new strategy to restrict the shuttling motion in [2] rotaxanes. Whereas the pillar[5] arene macrocycle rapidly shuttles along the full length of the bis (imidazolium) rod for the parent [2]rotaxane, Ag(I) coordination to the imidazolium groups through the formation of N-heterocyclic carbenes leads to restricted motion, effectively confining the shuttling motion of the [2] rotaxane. The Ag(I) coordinated [2] rotaxanes can be reacted further, either removing the Ag-carbene species to recreate the parent [2] rotaxane, or reaction with more bulky Pd(II) species to further restrict the shuttling motion through steric inhibition.