The Importance of Length and Flexibility of Macrocycle-Containing Molecular Translocators for the Synthesis of Improbable [2]Rotaxanes.

This work reports on the use of molecular translocators to capture a dibenzo-24-crown-8 (DB24C8) and then release it onto targeted molecular axles to afford, after removal of the translocator, [2]rotaxanes that do not hold any template site. Various translocators were studied and successfully aided the synthesis, with more or less efficacy, of [2]rotaxanes of different lengths. During the releasing step, the DB24C8 macrocycle shuttles along the thread, and the localization of the macrocycle might be driven by steric repulsion on the translocator part and/or electronic attraction of the targeted part of the axle to be encircled, which depends on both the nature of the translocator and the targeted thread to be encircled.