Active-template synthesis of “click” rotaxane ligands: self-assembly of mechanically interlocked metallo-supramolecular dimers, macrocycles and oligomers†
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 rotaxanes by interlocking an exo-alcohol functionalised macrocycle and functionalised triphenylmethyl stoppers. These 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-(rotaxane). At high dilution the bi-terpy rotaxane ligand forms a rotaxane metallo-macrocycle, in the presence of Fe(II) ions. Conversely, at high concentration self-assembly of the bi-terpy rotaxane ligand with Fe(II) ions results in the generation of a metallo-supramolecular poly-rotaxane oligomer. The 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.