This journal is © The Royal Society of Chemistry 2014 Chem. Commun., 2014, 50, 2857--2860 | 2857 Cite this: Chem. Commun., 2014, 50, 2857 Self-assembly formation of mechanically interlocked [2]- and [3]catenanes using lanthanide ion [Eu(III)] templation and ring closing metathesis reactions† Christophe Lincheneau, Bernard Jean-Denis and Thorfinnur Gunnlaugsson* The formation of interlocked lanthanide-based catenanes using Eu(III)-directed synthesis is described (catenation being achieved via a ring-closing metathesis reaction); the self-assembly formation of the supramolecular structures was analysed by HRMS, NMR and luminescent spectroscopies. The development of mechanically interlocked molecules such as catenanes and rotaxanes using metal ion directed self-assembly templating is now a well-established synthetic strategy in supramo- lecular chemistry. 1–3 While d-metal ions are commonly used in such synthesis, Beer et al. have recently also demonstrated the use of anions in such self-assembly. 4 The templating ions can be employed as an integrated part of the resulting self-assembly structure or be removed after its formation by competitive extraction/displacement, changing their oxidation states, chemical reactions, etc. 5 Many examples of such elegantly designed systems have been reported by leading scientists in this field, including those of Sauvage et al., 5 Stoddart et al. 6 and Leigh et al. 7 All have demonstrated the use of d-metal ion directed synthesis of interlocked molecules. 8,9 In contrast, the use of lanthanide ions (f-metal ions) in the formation of such interlocked molecules has remained relatively unexplored to date. To the best of our knowledge, only a few examples of this kind exist, including those of Beer, Faulkner, and coworkers 10 who used lanthanide ions for the formation of [2]rotaxanes and Loeb et al., 11 who developed interlocked MOF structures. However, the formation of lanthanide template [n]catenanes has not yet been reported. Over the last few years we have developed many examples of the use of lanthanide ions in directing the synthesis of supramolecular architectures. 12 These include the formation of self-assembled gels and Langmuir–Blodget films, 13 chiral luminescent bundles (termed the ‘‘Trinity Sliotar’’) 14 and triple-stranded dimetallic helicates. 15 Of these, the bundles were formed by the self-assembly of three chiral pyridyl di-amide ligands (PDA) using ions such as Eu(III). We envisaged that such PDA ligands could also provide a structural platform for the development of [3]catenanes, where the three rings would be ‘all’ interlocked around a single metal ion, and not in a linear ‘chain’ fashion, as demonstrated by Sauvage et al. 5c and recently by Rowan et al. 16 Our synthetic strategy is shown schematically in Fig. 1, where by using PDA ligands containing polyethoxy spacers and terminal alkene groups, the initial self-assembly with the lanthanide (1 : 3 Ln : L) would result in preorganization of the alkene groups in a manner that could facilitate their catenation or ‘closing’ by ‘triple clipping’ of adjacent alkenes using a ring-closing metathesis (RCM) reaction. Here we present, to the best of our knowledge, the first examples of Ln-based [2]- and [3]catenanes, the formation and structures of which were elucidated in solution using UV-vis, luminescence and NMR spectroscopy and HRMS. The synthetic strategy chosen for this approach is shown schematically in Scheme 1. Having unsuccessfully explored a large number of ligand structures related to L1 (Scheme 1) as candidates for the catenation process, results from MM2 force field calcula- tions (see ESI†) indicated that the [3]catenane catÁLnÁL2 3 could be formed upon a RCM reaction of LnÁL1 3 , which was derived from the PDA ligand L1.‡ The synthesis of L1 (see ESI†) was achieved by reacting 2,6-pyridinedicarboxylic acid chloride (1) with 3-(2-(2-(2- aminoethoxy)ethoxy)ethoxy)propen-1-ene (2) 17 (see ESI†). L1 was isolated in 48% yield as a yellow oil after a series of acid–base extractions and flash column chromatographic purification. The 1 H-NMR analysis (400 MHz, CDCl 3 ) of L1 confirmed its successful Fig. 1 The synthetic strategy for the Ln-directed synthesis of [3]catenane, involving 1 : 3 (M : L) self-assembly formation between the L1 (in different colours for clarity) and Ln(III), yielding LnÁL1 3 , and catenation by ‘triple clipping’ to give catÁLnÁL2 3 . School of Chemistry and Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland. E-mail: gunnlaut@tcd.ie; Tel: +353 1 896 3459 † Electronic supplementary information (ESI) available: Synthesis and character- isation; Fig. S1–S20. See DOI: 10.1039/c3cc49640f Received 19th December 2013, Accepted 22nd January 2014 DOI: 10.1039/c3cc49640f www.rsc.org/chemcomm ChemComm COMMUNICATION Published on 23 January 2014. Downloaded by Trinity College Dublin on 26/01/2015 15:20:49. View Article Online View Journal | View Issue