Dynamic control of circumrotation of a [2]catenane by acid‐base switching

Abstract Dynamic control of the motion in a catenane remains a big challenge as it requires precise design and sophisticated well‐organized structures. This paper reports the design and synthesis of a donor‐acceptor [2]catenane through mechanical interlocking, employing a crown ether featuring two dibenzylammonium salts on its side arms as the host and a cyclobis(paraquat‐p‐phenylene) (CBPQT ⋅ 4PF6) ring as the guest molecule. By addition of external acid or base, the catenane can form self‐complexed or decomplexed compounds to alter the cavity size of the crown ether ring, consequently affecting circumrotation rate of CBPQT ⋅ 4PF6 ring of the catenane. This study offers insights for the design and exploration of artificial molecular machines with intricate cascading responsive mechanisms.


1．General information
Instrument: 1 H NMR and 13 C NMR data were recorded on a Bruker ADVANCE NEO 600 MHz testing at 298 K, and variable temperature NMR were recorded on a Bruker ADVANCE NEO 400 MHz.The chemical shifts (δ) for both 1 H and 13 C NMR are recorded in parts per million, with TMS serving as the internal standard.High resolution mass spectral data were obtained on Thermo Scientific Q Exactive.UV-vis absorption spectra were tested using a Lambda 950 spectrometer (PerkinElmer, Germany).
Reagent and materials: All reactions were achieved under an argon atmosphere unless otherwise indicated.All reagents were purchased from Energy Chemical or Bide Pharmatech and were used as received without further purification.Analytical thin-layer chromatography (TLC) was performed on Nuotai silica gel F254 plates and viewed under UV light.

Synthesis of 5
A solution was prepared by dissolving 6 (3.50 g, 4.70 mmol) in dry THF (15 mL), and the solution was slowly added to a flask containing LiAlH4 (0.72 g, 18.80 mmol) at 0 ℃, and the reaction was maintained at 0 ℃ for more than 4 h.After the reaction was finished, ethyl acetate was slowly added at 0 ℃ until no bubbles were produced, and then 1 M HCl and CH2Cl2 were added at 0 ℃, stirring until there is no residue on the wall of the bottle, and the aqueous phase was extracted with CH2Cl2 for three times, and the organic phases were collected and dried with anhydrous Na2SO4, and then the solvent was evaporated and recrystallized with the solvent of CH3OH to get compound 5 as a light yellow solid (2.47 g, yield: 77%).

Synthesis of 4
5 (2.00 g, 1.45 mmol) and PCC (2.50 g, 5.81 mmol) were dissolved in CH2Cl2 (40 mL) and stirred at r.t. for more than 4 h.Then the filtrate was collected by vacuum filtration and the solvent was evaporated, which was separated by column chromatography [V(ethyl acetate):V(dichloromethane)=2:1] to obtain compound 4 as a white solid (1.41 g, yield: 71%).

Synthesis of 3
4 (1.90 g, 2.78 mmol) and benzylamine (1.19 g, 11.10 mmol) were dissolved in dry PhCH3 (20 mL) stirring at 120 ℃ for 12 h.After the reaction, the solvent was evaporated and the 5 mL CH3OH and 1 mL THF were added to dissolve rude product.Then NaBH4 (0.63 g, 16.65 mmol) was added several times in a small amount at 0 ℃, and the reaction was maintained at 0 ℃ for more than 4 h.After the reaction was finished, distilled water and 1 M HCl were slowly added at 0 ℃ until no bubbles were produced, and the solvent was stirred for 30 min.Then the aqueous phase was extracted with CH2Cl2 for 3 times, and the organic phases were collected and dried with anhydrous Na2SO4, and the solvent was removed to get compound 3 as a light yellow oil (2.07 g, yield: 86%).

Synthesis of 2
3 (2.89g, 3.33 mmol), Et3N (1.35 g, 13.32 mmol) and (Boc)2O (2.91 g, 13.32 mmol) were dissolved in dry THF (20 mL) stirring at 0 ℃ for 12 h.After the reaction, the solvent was evaporated and the CH2Cl2 was added to dissolve rude product, which was washed by distilled water twice, and then washed with saturated aqueous NaCl twice.The organic phase was collected and dried with anhydrous Na2SO4 and separated by column chromatography [V(ethyl acetate):V(dichloromethane)=1:4] to obtain compound 2 as a light yellow oil (2.67 g, yield: 75%).

Figure S19 .
Figure S19.(a) Schematic representation the change of the cavity of crown ether 3 by acid-base switching, (b) 1 H NMR spectra (600 MHz, 298 K, CDCl3) of 11.53 x10 -6 M compound 3, (c) the solution obtained after addition of 3.0 equiv. of TFA to part (b), (d) the solution obtained after addition of 4.0 equiv. of TEA to part (c).

Figure S29 .
Figure S29.(a) Scheme representation the change of the cavity of catenane by acid-base switching, (b) 1 H NMR spectra (600 MHz, 298 K, CD3CN) of 7.52 x10 -6 M 1-H2•6PF6, (c) the solution obtained after addition of 3.0 equiv. of TEA to part (b), (d) the solution obtained after addition of 6.0 equiv. of TFA to part (c).