Hydrogen bonding in anion recognition: A family of versatile, nonpreorganized neutral and acyclic receptors
Article
Kavallieratos, K, Bertao, CM, Crabtree, RH. (1999). Hydrogen bonding in anion recognition: A family of versatile, nonpreorganized neutral and acyclic receptors
. JOURNAL OF ORGANIC CHEMISTRY, 64(5), 1675-1683. 10.1021/jo982382l
Kavallieratos, K, Bertao, CM, Crabtree, RH. (1999). Hydrogen bonding in anion recognition: A family of versatile, nonpreorganized neutral and acyclic receptors
. JOURNAL OF ORGANIC CHEMISTRY, 64(5), 1675-1683. 10.1021/jo982382l
The diamides and disulfonamides m-C6H4(CONHAr)2 (Ar = Ph, 1; p-n- BuC6H4, 2, 2,4,6-Me3C6H2, 3), m-C6H4(SO2NHPh)2, 4, and 2,6- C6H3N(CONHPh)2, 5, readily synthesized on a multigram scale, bind strongly to halides and acetate in organic solvents with K(a)'s as high as 6.1 x 104 (NMR spectroscopy). The binding stoichiometry is 1:1 in solution for all cases except for the 4·F- and 4·OAc- complexes, where both 1:1 and 1:2 binding stoichiometries were found. The association constants in CD2Cl2 (1H NMR) follow the trend Cl- > Br- > I- for all the receptors. F- and OAc- binding may be stronger or weaker than Cl- depending on the nature of the receptor. The presence of the pyridine nitrogen in 5 and of the more rigid amide in 1-3 and 5 vs the less rigid sulfonamide structure in 4 increases selectivity for smaller anions. The enthalpy and entropy of formation for 2·Cl- were ΔH = -31 kJ/mol, ΔS = -23 J/(mol·K) (VT-NMR). The X-ray structure of [PPh4]2[1·Br][Br]·CH2Cl2, shows 1:1 complexation of Br- via two N-H···Br- hydrogen bonds and a syn-syn nonplanar binding conformation for 1. Solution hydrogen bonding was confirmed by FT-IR and NMR spectroscopy. The receptor conformation changes on complexation. Trends in structure/binding relationships show receptor flexibility is an important factor in anion recognition.
