HOST-GUEST COMPLEXATION .18. EFFECTS ON CATION BINDING OF CONVERGENT LIGAND SITES APPENDED TO MACROCYCLIC POLYETHERS

Syntheses are reported for 16 new macrocyclic polyether ligand systems which contain potentially convergent side chains containing additional binding sites. The free energies of association of these systems in CDCI3 at 25 °C with Li+. Na+, K+, Rb+, Cs+, NH4+, CH3NH3+, and t-BuNH3+ picrates were determined. The structures of these hosts are indicated by the following abbreviations: E is CH2CH2; D is 1, 1ʹ-dinaphthyl attached to two macroring oxygens at its 2, 2ʹ positions and to two substituents at its 3, 3ʹ positions; T is 1, 1ʹ-bitetralyl attached to two macroring oxygens at its 2, 2ʹ positions and to two substituents in its 3, 3ʹ positions; Ur is the cyclic urea unit, N(CH2)3(CO)NCH3; Py is α-pvridvl; Bz is C6H5CH2. The hosts prepared and examined were (CH3)2D(OEOEO)2E (3),(OCH)2D(OEOEO)2E (5), (CH3O2C)2D(OEOEO)2E (6), (H02C)2- D(OEOEO)2E (7), (CH3CO)2D(OEOEO)2E (9), (UrCH2)2D(OEOEO),E (11), [(EtO)2OPCH2]2D(OEOEO)2E (12), [(EtO)2OPCH2]2D(OEOEO)20 (13), (PySCH2)2D(OEOEO)2E (14), (PyCH2OCH2)2D(OEOEO)2E (15), [(EtO)2- 0PCH2]2T(0E0E)20 (20), w-(BzOCH->)2E(OEOEO)2E (22), trans«i-(BzOCH2)2E(OEOEO)2E (23), cis-(o-ClC6H4)2- E(OEOEO)2E (24), frani-(o-ClC6H4)2E(OEOEO)2E (25), and E(OEOEOCH2)2E(OEOEO)2E (26). Noncyclic model compounds were also prepared: (CH3)2D(OEOEOCH3)2 (1) and [(EtO)2OPCH2]2D(OCH3)2 (17). The free energies of association (—ΔG°) of these compounds with various picrate salts were compared with one another and with those of known hosts, D(OEOEO)2D (2). 2, 3-naphtho-18-crown-6 (21), and dicyclohexyl-18-crown-6. The highest (—ΔG°) value (kcal/mol) observed involved [(EtO)2OPCH2]2D(OEOEO)2E (12) and Na+ (12.4), and the lowest, (CH3)2D(OEOEOCH3)2 (1) and t-BUNH3+ (3.38), as complexing partners. The —ΔG°av of association (kcal/mol) with Li+. Na+, K+, Rb+, Cs+, and NH4+ picrates allowed the hosts to be ranked as general ligand systems. Values of —Δ(—ΔG°)max (the difference in free energies of the best and poorest bound of these six picrate salts) allowed the ligand systems to be graded with regard to ion selectivity. Values of [formula ommitted] allowed the ligand systems to be judged with regard to their capacity for structural recognition of NH4+ vs. r-BuNH3+ ions. With respect to all three parameters, the [(EtO)2OPCH2]2D(OEOEO)2E (12) system ranked the highest. The location, binding, and steric properties of the two P→O oxygens in this ligand system appear responsible for its superior properties. © 1979, American Chemical Society. All rights reserved.