Understanding coordination equilibria in solution and gel-phase [2]rotaxanes

Abstract

This paper describes the use of the copper(I)-catalysed azide–alkyne cycloaddition reaction in an active metal template methodology for the synthesis of [2]rotaxanes both in solution and on polymer resins. The use of TentaGel resin beads has allowed the rotaxane functionalised solid supports to be characterized by ¹H HR MAS NMR. Whereas previous research in the assembly of interlocked architectures on surfaces are complicated by the concurrent attachment of large proportions of non-interlocked byproducts, in this example over 80% of the functionalization is the desired interlocked rotaxane. The inclusion of zinc metalloporphyrins in the structure of the [2]rotaxane thread allowed the position of the macrocycle to be ‘switched’ upon the addition of competing base, removal of the metal or appropriate choice of solvent. Investigations into the pseudocooperative effect the mechanical bond has on the metalloporphyrin-macrocycle coordination equilibrium were performed and the associated effective molarity in this [2]rotaxane was calculated to be 120 mM.