Multiple threading of a triple-calix[6]arene host

Abstract

The synthesis of the triple-calix[6]arene derivative 6 in which three calix[6]arene macrocycles are linked to a central 1,3,5-trimethylbenzene moiety is reported. Derivative 6 is able to give multiple-threading processes in the presence of dialkylammonium axles. The formation of pseudo[2]rotaxane, pseudo[3]rotaxane, and pseudo[4]rotaxane by threading one, two, and three, respectively, calix-wheels of 6 has been studied by 1D and 2D NMR, DOSY, and ESI-FT-ICR MS/MS experiments. The use of a directional alkylbenzylammonium axle led to the stereoselective formation of endo-alkyl pseudo[n]rotaxane stereoisomers.

Keywords: calixarene; multiple-threading; pseudo[n]rotaxane; stereoisomers.

Figure 1

Sketch of the currently known prototypical examples of handcuff-derived architectures.

Figure 2

Chemical drawing of the known bis-calix[6]arene 1 and its handcuff pseudorotaxane architectures 3²⁺ and 5²⁺ previously reported. Structure of the triple-calix[6]arene host 6 studied in the present work.

Scheme 1

Synthesis of triple-calix[6]arene host 6.

Scheme 2

Formation of the 7⁺6, (7⁺)₂6, (7⁺)₃6 pseudorotaxane architectures by multiple-threading of 6 with 7⁺ as TFPB⁻ salt.

Figure 3

(Bottom) Portion of the ESI-FT-ICR mass spectrum of 7⁺6. (Top a–c) Significant portions of: (a) ¹H NMR spectrum of 6 (CDCl₃, 298 K, 600 MHz); (b) ¹H NMR spectrum of a 1:1 mixture of 6 and 7⁺·TFPB⁻ (CDCl₃, 298 K, 600 MHz); (c) DOSY spectra of 6 (black line) and a 1:1 mixture of 6 and 7⁺·TFPB⁻ (red line). Inset: structures of the triple-calix[6]arene 6 and 7⁺6 pseudo[2]rotaxane obtained by molecular mechanics calculations.

Figure 4

¹H NMR titration of 6 with 7⁺·TFPB^– (CDCl₃ , 298 K, 600 MHz). Significant portions of the ¹H NMR spectra of: (a) 6; (b) 1:1, (c) 1:2, (d) 1:3, (e) 1:4, (f) 1:5 and (g) 1:6 mixture of 6 and 7⁺·TFPB⁻. Marked: red diamond = 7⁺6; purple circle = (7⁺)₂6; green triangle = (7⁺)₃6.

Figure 5

ESI-FT-ICR-MS and HR-ESI-FT-ICR-CID mass spectrum of (7⁺)₂6.

Figure 6

Different views of the minimized structures of (7⁺)₃6 obtained by molecular mechanics calculations.

Scheme 3

Formation of the 4⁺6, (4⁺)₂6, (4⁺)₃6 pseudorotaxane architectures by multiple-threading of 6 with 4⁺ as TFPB⁻ salt.

Figure 7

(a–d) ¹H NMR titration of 6 with 4⁺·TFPB⁻ (CDCl₃, 298 K, 600 MHz). Significant portions of the ¹H NMR spectra of: (a) 6; (b) 1:1, (c) 1:2, (d) 1:3, mixture of 6 and 4⁺·TFPB^–. (e) HR-ESI-FT-ICR mass spectrum of 4⁺6. (f) HR-ESI-FT-ICR-CID mass spectrum of (4⁺)₂6.

Figure 8

Different views of the minimized structures of (4⁺)₃6 obtained by molecular mechanics calculations.

Figure 9

(Top) Possible endo-benzyl and endo-alkyl stereoisomers obtainable by directional threading of calix[6]arene-wheel with alkylbenzylammonium axles. (Bottom) Sketch of the possible pseudo[4]rotaxane stereoisomers obtainable by triple-threading of 6 with 8⁺.

Figure 10

(Left) HR-ESI-FT-ICR mass spectrum of 8⁺6. (Right) HR-ESI-FT-ICR-CID mass spectrum of (8⁺)₂6.

Figure 11

(a–d) ¹H NMR titration of 6 with 8⁺·TFPB⁻ (CDCl₃ , 298 K, 600 MHz). Significant portions of the ¹H NMR spectra of: (a) 6; (b) 1:1, (c) 1:2, (d) 1:3, mixture of 6 and 8⁺·TFPB⁻. (Top) Formation of the 8⁺6, (8⁺)₂6, (8⁺)₃6 pseudorotaxane architectures (sketch) by multiple-threading of 6 with 8⁺ as TFPB⁻ salt.