Triply Threaded [4]Rotaxanes

Abstract

[4]Rotaxanes featuring three axles threaded through a single ring have been prepared through active metal template synthesis. Nickel-catalyzed sp(3)-sp(3) homocouplings of alkyl bromide "half-threads" through 37- and 38-membered 2,2':6',2″-terpyridyl macrocycles generate triply threaded [4]rotaxanes in up to 11% yield. An analogous 39-membered macrocycle produced no rotaxane products under similar conditions. The constitutions of the [4]rotaxanes were determined by NMR spectroscopy and mass spectrometry. Doubly threaded [3]rotaxanes were also obtained from the reactions but no [2]rotaxanes were isolated, suggesting that upon demetalation the axle of a singly threaded rotaxane can slip through a macrocycle that is sufficiently large to accommodate three threads.