Active-template synthesis of click [2]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 [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 2,20,60,200-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 biterpy [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 H-1 and C-13 NMR and UV-vis spectroscopies, high resolution electrospray ionisation mass spectrometry (HR-ESMS), and elemental analyses. Additionally, H-1 DOSY NMR spectroscopy and GPC analysis were used to provide evidence for the constitution of the self-assembled metallo-supramolecular mechanically-interlocked architectures.