Template-driven construction of [8]-imidazolium macrocycles

Abstract

Tetrakisimidazolium macrocycles have been widely used in supramolecular chemistry due to their inherently cationic nature and sizable cavity. However, [n]-imidazolium macrocycles (n > 4) are rather undeveloped. Reported here is a controllable synthetic strategy for [n]-imidazolium (n = 8) macrocycles, which involves the formation of metal–carbene templates, a double [2 + 2] photocycloaddition and the subsequent removal of metal ions. Two octakisimidazolium macrocycles H₈-2a(PF₆)₈ and H₈-2b(PF₆)₈ were prepared from linear tetrakisimidazolium salts H₄-1a(PF₆)₄ and H₄-1b(PF₆)₄. More significantly, the present work not only further verified the strategy of metal–carbene templated photochemical [2 + 2] cycloaddition for the construction of novel polyimidazolium macrocycles, but also offers a new synthetic approach for the preparation of functional acceptors for molecule recognition.