HOST-GUEST COMPLEXATION .15. MACROCYCLIC ACETYLACETONE LIGANDS FOR METAL-CATIONS

Five macroeycles containing 1,5-disubstituted acetylacetone units (AcAc) have been synthesized. Their abilities to complex metal cations in water-dioxane have been compared to those of noncyclic model compounds. The AcAc units were bound together through bridges composed of the following groups: oxa (O), ethylene (E), and 1,3-disubstituted benzene (B). Cycles 0(AcAc0E0E)(E0E0E)0 (7), (OEOAcAcOE)2 (8), and (OEOAcAcOE)3 (9) were prepared by hydrolysis of rings closed by the reactions of CH2[HOCH2C(SCH2)2CH2]2 (2) and appropriate polyethylene glycol ditosylates. Ligand systems O(EACACE)2O (12) and B(CH2AcAcCH2)2B (14) were synthesized in Ca2+ or Mg2+ templated, two-step sequences involving reactions of HAcAcH dianions with either diethylene glycol ditosylate or m-xylyl dibromide, respectively. The preparation of (CH2lsCH2O)3 (17) is also described, in which Is is the 3,5-disubstituted isoxazole unit. Also described are the preparations of O(EACACH)2 (11), B(CH2AcAcH)2 (13), and P(CH2AcAcH)2 (15), in which P is 2,6-disubstituted pyridine. The logarithms of the formation constants (log Krdv) of the salts of (OEOAcAcOE)2 with 11 divalent metal cations and of (OEOAc-AcOE)3 with 3 trivalent cations were 1.8-6.3 units higher valued than for CH3OACACOCH3. The log Kav values for salt formation of O(EAcAcE)2O and B(CH2AeAcCH2)2B with 10 divalent cations were compared with those of O(EAcAcH)2 and B(CH2AcAcH)2, respectively, and with HAcAcH itself. Without exception, O(EAcAcE)2O>>(EAcAcH)2>HAcAcH in values of log Ktav, the maximum difference being 4.3 for Ca2+. Although both B(CH2AcAcCH2)2B and B(CH2AcAcH)2 were better ligands than HAcAcH by 1.8-3.9 in A log values, the difference between B(CH2AcAcCH2)2B and B(CH2-AcAcH)2 varied between +0.9 and -2.2, depending on the ion. The effects on their binding abilities of gathering, orienting, and constraining acetylacetone units in ring systems are discussed. Copyright © 1979, American Chemical Society. All rights reserved.