Synthesis, molecular structure, and binding properties of a hemispherand incorporating a phosphoryl hard donor group
(1998) Chemistry: A European Journal — Vol. 4, n° 1, p. 100-106 (1998)
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- Phosphahemispherand 3 was synthesized in 63 % yield from its macrocyclic precursor 2 and 1,3-propanediol ditosylate in the presence of NaH in THF. Host 3 exhibited temperature-dependent H-1, Cl-13 and P-31 NMR spectra owing to conformational exchange throughout the molecular framework. Exo and endo conformers are in equilibrium in solution, and the energy barrier between the two forms is 61 kJ mol(-1). Two exo conformers, with the P=O bond directed away from the macrocyclic cavity, were predominant at low temperature. The major form was assigned to the C-s symmetry exo conformation, The minor exo form was assigned to the asymmetric conformation that has one methoxy group on each face of the macroring. The energy barrier for interconversion between the two exo forms is 56 kJ mol(-1). The binding energies of alkali metal and ammonium cations to 2 and 3 wore measured by the picrate extraction technique, The highest K-a values were obtained for the complexes of 3 with K+ and Rb+. The conformational changes observed upon complexation were examined by NMR spectroscopy and X-ray analysis and are discussed in terms of pre organization, The formation of 1:1 complexes was only observed with the endo conformer.
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Delangle, P., Declercq, J.-P., Dutasta, JP., & Tinant, B. (1998). Synthesis, molecular structure, and binding properties of a hemispherand incorporating a phosphoryl hard donor group. Chemistry: A European Journal, 4(1), 100-106. https://doi.org/10.1002/(SICI)1521-3765(199801)4:1<100::AID-CHEM100>3.0.CO;2-5 (Original work published 1998)