Active-template synthesis of "click" [2]rotaxane ligands: Self-assembly of mechanically interlocked metallo-supramolecular dimers, macrocycles and oligomers

Abstract

Due to potential applications in the biological and material sciences there is considerable interest in the development of mechanically interlocked ligands (MILs). The mild functional-group tolerant copper(i)-catalysed azide-alkyne cycloaddition active-metal-template (CuAAC-AMT) method has been exploited to generate mono- and bi-functionalised [2]rotaxanes by interlocking an exo-alcohol functionalised macrocycle and functionalised triphenylmethyl stoppers. These [2]rotaxanes were post-synthetically conjugated to either one or two 2,2′,6′,2′′-terpyridine (terpy) coordinating units to generate mechanically interlocked "super" ligands. Addition of Fe(ii) ions to the mono-terpy ligand leads to the formation of a metallo-bis-([2]rotaxane). At high dilution the bi-terpy [2]rotaxane ligand forms a [2]rotaxane metallo-macrocycle, in the presence of Fe(ii) ions. Conversely, at high concentration self-assembly of the bi-terpy [2]rotaxane ligand with Fe(ii) ions results in the generation of a metallo-supramolecular poly-[2]rotaxane oligomer. The [2]rotaxane ligands and corresponding Fe(ii) complexes have been characterised with 1H and 13C NMR and UV-vis spectroscopies, high resolution electrospray ionisation mass spectrometry (HR-ESMS), and elemental analyses. Additionally, 1H DOSY NMR spectroscopy and GPC analysis were used to provide evidence for the constitution of the self-assembled metallo-supramolecular mechanically-interlocked architectures. This journal is