SPHERANDS CONTAINING CYCLIC UREA UNITS

Three new spherands (1-3) and one new hemispher and (4) are reported, all having in common two (CH2)3N2C=0 cyclic urea units, three anisyl units, and one CH2ACH2 unit. In 1, 2, and 3 A = O, S, and C(CO2Et)2, respectively, and these together with the other units provide 18-membered macrorings whose enforced cavities are lined by (roughly) octahedrally arranged heteroatoms. In 4 A = 1,2-C6H4O2 (catechol), and the macroring is 21-membered and is partially preorganized. Crystal structures are reported for 1,1-Na picrate, 2·NaSbF6, 4, and 10·H2O. The association constants (Ka, M-1) and free energies of binding (-ΔG°, kcal mol-1) were determined at 25 °C for Li+, Na+, K+, Rb+, Cs+, NH4+, CH3NH3+, and (CH3)3CNH3+ picrates in CDCl3 saturated with D2O. Peak binding was observed for 1 and 2 with Na+ (19.5 and 19.1 kcal mol-1, respectively), for 3 with Li+ (16.1 kcal mol-1), and for 4 with K+ (12.4 kcal mol-1). The results further illustrate the utility of the principles of complementarity and preorganization. The rates of complexation-decomplexation during CHCl3-water extractions were rapid on the human time scale. The greatest specificity was shown by 2 toward the physiologically important Li+, Na+, and K+ ions: KaNa/KaLi = 250; KaNa/KaK = 10000. © 1990, American Chemical Society. All rights reserved.