Structure and Binding Properties of Four New Oligomeric Cyclophane Esters: 1,4-Xylylene 1,4-Phenylene Diacetates and Dipropionates

Abstract

The X-ray crystal structure determinations of four new oligomeric cyclophane esters are reported. They are: (3a) monomeric 1,4-xylylene (1,4-phenylene)diacetate, P2₁/n (No. 14), a 5·959(5), b 15·795(5), c 8·094(5) Å, β 108·060(5)°, V 724·3(8) ų , Z 2, R₁(2σ) 0·0522, wR₂ 0·125; (3b) monomeric 1,4-xylylene (1,4-phenylene)dipropionate, P2₁/c (No. 14), a 5·878(1), b 14·642(2), c 18·909(2) Å, β 96·00(10)°, V 1618·5(4) ų , Z 4, R₁(2σ) 0·053, wR₂ 0·165; (3c) dimeric 1,4-xylylene (1,4-phenylene)diacetate, P^-1 (No. 2), a 14·633(2), b 17·529(2), c 5·736(1) Å, α 98·30(10), β 90·60(10), γ 95·40(10)°, V 1449·0(4) ų, Z 2, R₁(2σ) 0·057, wR₂ 0·158; (3d) dimeric 1,4-xylylene (1,4-phenylene)dipropionate, P2₁/a (No. 14), a 8·145(1), b 11·379(2), c 17·401(2) Å, β 101·40(10)°, V 1580·9(4) ų, Z 4, R₁(2σ) 0·034, wR₂ 0·095. Monomeric cyclophanes (3a,b) exhibit a well defined cleft, while dimeric (3c,d) adopt a flat conformation devoid of cavities. Binding properties were determined by ¹H n.m.r. titrations in CDCl₃ at T = 296 K. Complexation experiments with quaternary ammonium salts revealed that host (3c) possesses appreciable binding ability toward N-methylpyridinium (–ΔG° = 5·9 kJ mol^-1), tetramethylammonium (–ΔG° = 8·8 kJ mol^-1) and acetylcholine (–ΔG° = 7·5 kJ mol^-1) cations, despite its lack of a preorganized cavity.