A trefoil knot coordinated to two lithium ions: synthesis and structure

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Abstract
The very tight dicopper(I) trefoil knot that contains 1,3-phenylene spacers between the 1,10-phenanthroline subunits could be fully demetallated under drastic conditions (large excess of KCN in refluxing acetonitrile), affording thus the disentangled knotted ligand in almost quantitative yield. This free molecular knot appeared very prompt to protonate or to bind to various ions in order to regenerate the stable “entwined’' conformation. Lithium in particular appeared to be ideal for occupying the tight empty coordinating sites of knot (K-84)p. A new dilithium complex could be obtained almost quantitatively; its surprising stability allowed the determination of its molecular structure both by 1H NMR and X-ray diffraction along with that also determined for its dicopper(I) precursor. Un noeud de trèfle coordine′ à deux ions lithium: synthèse et structure. La de′me′tallation totale du noeud mole′culaire très compact dont les phe′nanthrolines sont ponte′es par des groupes m-phe′nylène peut se faire dans des conditions dures (large excès de KCN dans l'ace′tonitrile à reflux) donnant accès, de manière quasi quantitative, au ligand libre (K-84)p. Ce dernier se caracte′rise par sa forte tendance à se protoner ou à se coordiner à diffe′rents cations de manière à retrouver sa conformation la plus stable. Le lithium en particulier est apparu comme e′tant parfaitement adapte′ pour remplir les sites de coordination vaccant du noeud (K-84)p. Cette affinite′ exceptionnelle a permis d'obtenir de manière quantitative un nouveau complexe dilithium. Grâce à sa surprenante stabilite′ il a e′te′ possible de de′terminer sa structure mole′culaire par RMN, spectrome′trie de masse et diffraction de rayons X.

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