External-stimulus-triggered conformational inversion of mechanically self-locked pseudo[1]catenane and gemini-catenanes based on A1/A2-alkyne-azide-difunctionalized pillar[5]arenes

Abstract

Herein, we report a methodology for constructing mechanically self-locked molecules (MSMs) through the efficient intramolecular copper(i)-catalyzed alkyne-azide cycloaddition (CuAAC) of self-threaded A1/A2-azido-propargyl-difunctionalized pillar[5]arenes. The obtained monomeric "pseudo[1]catenane" and dimeric "gemini-catenane" were isolated and fully characterized using mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy, and X-ray crystallography. Upon investigation by ¹H NMR spectroscopy in chloroform, the observed motion for the threaded ring in the pseudo[1]catenane was reversibly controlled by the temperature, as demonstrated by variable-temperature ¹H NMR studies. Two gemini-catenane stereoisomers were also isolated in which the two pillar[5]arene moieties threaded by two decyl chains were aligned in different topologies. Furthermore, the conformational inversion of pseudo[1]catenane and the gemini-catenanes triggered by solvents and guests was investigated and probed using ¹H NMR spectroscopy, isothermal titration calorimetry, and single-crystal X-ray analysis.

Scheme 1. Synthesis of a self-locked pseudo[1]catenane (Pillar-3M) and a gemini-catenane (Pillar-3D1-2) via the copper(i)-catalyzed alkyne–azide 1,3-dipolar cycloaddition (CuAAC) reaction.

Fig. 1. ¹H NMR spectra (600 MHz, CDCl₃, 298 K) of (a) pseudo[1]catenane Pillar-3M, and gemini-catenanes (b) Pillar-3D1, and (c) Pillar-3D2.

Fig. 2. Different views of the X-ray single-crystal structure of the Pillar-3D1gemini-catenane, in (a) CDCl₃ and (b) CD₂Cl₂. Red, grey/green/light blue, and purple represent oxygen, carbon, and nitrogen, respectively. Hydrogen atoms are omitted for clarity.

Fig. 3. ¹H NMR spectra (600 MHz, CDCl₃, 298 K) of Pillar-3M (a) immediately after preparation, (b) after 24 h, and (c) after 48 h.

Fig. 4. Variable-temperature ¹H NMR spectra (600 MHz, CDCl₃) of the Pillar-3Mpseudo[1]catenane.

Fig. 5. ¹H NMR spectra (600 MHz, CDCl₃, 298 K) of (a) the Pillar-3Mpseudo[1]catenane at a concentration of 25 mM, and (b) and (c) Pillar-3M (25 mM) in the presence of the adiponitrile guest G at concentrations of (b) 7.5 mM and (c) 25 mM.

Fig. 6. ¹H NMR spectra (600 MHz, CDCl₃, 298 K) of the Pillar-3D1gemini-catenane (10 mM) in the presence of different concentrations of the adiponitrile guest G.