Experimental and Theoretical Evidence of the Bidentate Binding Mode of Dichloroacetamido Groups at the Upper Rim of Calix[4]arene Hydrogen-Bonding Anion Receptors

Abstract

Calix[4]arenes in the 1,3-alternate conformation (1-3) and bearing activated amide groups at the upper rim have been synthesized and their anion binding properties studied and compared with conformationally mobile (4) or cone (Ib) receptors having the same binding groups. Association constants determined in CDCl3 show a stronger complexation for Y-shaped carboxylate anions and a higher efficiency for receptors (Ib and 3) bearing dichloroacetamido moieties as hydrogen bonding donor groups. Molecular modeling studies performed on the cone derivative (Ib) and its 1,3-alternate isomer (10) and ab initio calculations on 4-methoxyaniline derivatives (11-13) used as simplified models, reveal that the α,α-dichloroacetamido moieties bind anions in a bidentate fashion using both the N-H and the CHCl2 as hydrogen bonding donor groups. This explains the higher efficiency in carboxylate binding found for Ib and 3 that incorporate the dichloroacetamido binding unit in their structures.

Conformational properties of cyanomethoxy calix[4]arenes

“…. 1 The reaction was carried out under the same conditions described above starting from 1,3-di-O-alkylated compound 1 (2 g, 2.75 mmol) in dry DMF (75 ml) and Cs 2 CO 3 (9 g, 27.5 mmol). Recrystallization from chloroform-methanol gave single crystals of 5(1,2-alt) and a total of 0.23 g (11%).…”

“…The data set for 4(paco) had to be collected at room temperature because the crystals were decomposing upon cooling. One ether group of 4(paco) is disordered over two positions with a ratio of the site occupation factors of 0.51(1)/0.49 (1). The crystal of 5(1,2-alt) was twinned.…”

“…1 H-NMR (400 MHz, C 6 D 6 ) d 1.24 (s, 18H, t-Bu), 3.05 (d, 2H, 2 J = 13.3 Hz, Ar-CH 2 -Ar), 3.14 (s, 4H, -CH 2 -CN), 3.39, 3.47 (2d, 4H, 2 J = 16.8 Hz, Ar-CH 2 -Ar),3.61-3.77 (m, 4H, -CH 2 -CH=CH 2 ), 4.01 (d, 2H, 2 J = 13.2 Hz, Ar-CH 2 -Ar), 4.55-4.77 (m, 4H, CH=CH 2 ), 5.20-5.30 (m, 2H, -CH=CH 2 ), 6.89, 7.08 (2d, 4H, 4 J = 2.3 Hz, ArH), 7.78, 7.95 (2d, 4H, 4 J = 2.7 Hz, ArH). 1 H-NMR (400 MHz, TCE-d 2 ) d 1.30 (s, 18H, t-Bu), 3.05 (d, 2H, 2 J = 13.2 Hz, Ar-CH 2 -Ar), 3.90, 3.94 (2d, 4H, 2 J = 16.2 Hz, Ar-CH 2 -Ar), 4.01, 4.02 (2s, 4H, -CH 2 -CN), 4.09 (m, 4H, -CH 2 -CH=CH 2 ), 4.16 (d, 2H, 2 J = 13.2 Hz, Ar-CH 2 -Ar), 4.77-4.90 (m, 4H, CH=CH 2 ), 5.47 (m, 2H, -CH=CH 2 ), 7.13, 7.21 (2s, 4H, ArH), 8.05 (s, 4H, ArH).…”

Calix[4]arene Anion Receptors Bearing 2,2,2-trifluoroethanol Groups at TheUpperRim

“…Interestingly the {RR -(-SS) racemic mixture (3a) is more efficient in binding than the weso compound (3b) and this is especially true for sterically more demanding anions such as benzoate and phenylalaninate. If we compare the binding properties of receptor 3a toward acetate anion with other difunctionalized calix [4]arene receptors we find that trifluoroethanol is less efficient than other anion binding groups such as urea [15,16], sulfonamide [53] or activated carboxyamides [54][55][56]. However, a comparison with receptors which contain simple alcoholic functions, which show no binding ability towards acetate anion [31], points out the importance of the electrowithdrawing groups CF3 in enhancing the H bonding ability of the OH groups.…”

Calixarene-based anionic receptors

“…Association constants K ass , l mol -1 , of compounds 148-150 with anions (as tetrabutylammonium salts) in methylene chloride at 298 K Conformationally labile calixarenes 151a-151d and 1,3-alternate structures 152a-152c were examined for their receptor properties toward carboxylate ions[105]. The binding constants with PhCOO -in CH 2 Cl 2 were 151, R′ = Pr, R = ClCH 2 (a), Cl 2 CH (b), Cl 3 C (c); R′ = Me, R = Cl 2 CH (d); 152, R = ClCH 2 (a), F 3 C (b), Cl 3 C (c).…”