HOST-GUEST COMPLEXATION .17. DESIGN, SYNTHESES, AND COMPLEXATION OF MACROCYCLES CONTAINING PHOSPHORYL, PYRIDINE OXIDE, AND UREA BINDING-SITES

Phosphoryl (P͇O), urea (N2C͇O), pyridine, and pyridine oxide (N→O) groups have been incorporated into the ring systems of macrocyclic polyethers. The association constants of the resulting eight new ligand systems toward Li+, Na+, K+, Rb+, Cs+ and NH4+ picrates in CHCl3 were surveyed, and the free energies of association were estimated. The P͇O complexing sites were covalently bonded through two attached o-totyl groups as in the unit RP(O)(C6H4CH2-o)2, in which different R groups were attached to phosphorus. The resulting unit, written as RPOD. was attached to two ether oxygens (O), which in turn were connected through CH2CH2 or E units to form macrocvcles. Ligand systems C6H5POD(OEOE)2O (9). C6HsPOD(OEOEO)2E (10), o-HO2CC6H4POD(OEOE)2O (11), 0-CH;A>CC6H4POD(OEOE)2O (12), CH3OPOD(OEOE)2O (13), and C6H5POD(OEO)2PODC6H5 (14 and 15, the syn and anti isomers) were synthesized and examined. The urea complexing site was cyclic, CH2(CH2N)2-C͇O (abbreviated to UON), and was bonded through its two nitrogens to E units. The cycle prepared and examined was UON(EOEOE)2O (16). The pyridine and pyridine oxide complexing sites were bonded through CH2groups in their α, α1 positions to comprise the units α-CH2(C5H3N)CH2-α1 and α-CH2(C5H3NO)CH2-α1, respectively, the latter of which was abbreviated as POM. The new cycle prepared and examined was POM(OEOE)2O (18). The patterns of ΔG° values of complexation of these ligand systems were compared to those of 2, 3-naphtho-18-crown-6 (19), 2, 6-pyrido-18-crown-6 (20), and l, 3-benzo-18-crown-5 (21). The results suggest that those ligand systems whose organization of binding sites before and after complexation are the most similar show the highest structural recognition toward the anions. Necessary requirements for high free energies of complexation are : (1) the hosts and guests must possess complimentary structural relationships; (2) the hosts must undergo complexation accompanied by a minimum amount of conformational reorganization. © 1979, American Chemical Society. All rights reserved.