Selective synthesis and structural transformation between a molecular ring-in-ring architecture and an abnormal trefoil knot

Abstract

The synthesis of complicated supramolecular architectures and the study of their reversible structural transformations remains a fascinating challenge in the field of supramolecular chemistry. Herein, two types of novel coordination compounds, a non-intertwined ring-in-ring assembly and an abnormal trefoil knot were constructed from a strategically selected Cp*Rh building block and a semi-rigid N,N'-bis(4-pyridylmethyl)diphthalic diimide ligand via coordination-driven self-assembly. Remarkably, the reversible transformation between the abnormal trefoil knot and the ring-in-ring assembly or the corresponding tetranuclear macrocycle could be achieved by the synergistic effects of Ag⁺ ion coordination and alteration of the solvent. Single-crystal X-ray crystallographic data and NMR spectroscopic experiments support the structural assignments.

Scheme 1. Self-assembly of tetranuclear complex 1 and ring-in-ring structure 2.

Fig. 1. Single-crystal X-ray structure of 1′: (a) top view, (b) side view. Most hydrogen atoms, anions, solvent molecules and disordered elements are omitted for clarity (N, blue; O, red; C, gray; Ir, pink).

Fig. 2. Calculated (bottom, blue) and experimental (top, red) ESI-MS spectra (3⁺) of (A) tetranuclear 1 and (B) ring-in-ring complex 2.

Fig. 3. (a) Wireframe, and (b) space-filling representations of the solid-state structure of ring-in-ring complex 2 coloured according to ring; (c) wireframe representation of the solid-state structure of ring-in-ring complex 2 coloured according to atom; (d) wireframe representation of the solid-state structure of ring-in-ring complex 2′ coloured according to atom. Measurements in (c and d) indicate π–π stacking interactions between PDM groups and pyridine moieties and CH⋯π interactions between BiBzIm moieties and phenyl moieties of PDM groups. Hydrogen atoms, anions, solvent molecules and disorder are omitted for clarity (atom colours: N, blue; O, red; C, gray; Rh, orange; Ir, pink).

Fig. 4. Wireframe representation of solid-state structure of 2-pyrene coloured according to (a) atom and (b) ring. Hydrogen atoms, anions, solvent molecules and disorder are omitted for clarity (atom colours: N, blue; O, red; C, gray; Rh, orange).

Scheme 2. Self-assembly of abnormal trefoil knots 3 and 3′.

Fig. 5. Calculated (bottom, blue) and experimental (top, red) ESI-MS spectra of 3.

Fig. 6. Molecular structure of 3′ coloured according to atom: (a) top view; (b) side view. Wireframe representation of (c) right-handed trefoil knot (+3₁) of 3′ and (d) left-handed trefoil knot (−3₁) of 3′. Counteranions and hydrogen atoms are omitted for clarity (atom colours: N, blue; O, red; C, gray; Ag, teal; Rh, orange).

Scheme 3. Schematic representation of supramolecular transformations between tetranuclear macrocycle 1, ring-in-ring complex 2 and abnormal trefoil knot 3 induced by the chemical reactivity of Ag⁺ ions and solvent effects.