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  • Title: Bis(m-phenylene)-32-crown-10-based cryptands, powerful hosts for paraquat derivatives.
    Author: Huang F, Switek KA, Zakharov LN, Fronczek FR, Slebodnick C, Lam M, Golen JA, Bryant WS, Mason PE, Rheingold AL, Ashraf-Khorassani M, Gibson HW.
    Journal: J Org Chem; 2005 Apr 15; 70(8):3231-41. PubMed ID: 15822986.
    Abstract:
    Four new bis(m-phenylene)-32-crown-10-based cryptands with different third bridges were prepared. Their complexes with paraquat derivatives were studied by proton NMR spectroscopy, mass spectrometry, and X-ray analysis. It was found that these cryptands bind paraquat derivatives very strongly. Specifically, a diester cryptand with a pyridyl nitrogen atom located at a site occupied by either water or a PF(6) anion in analogous complexes exhibited the highest association constant K(a) = 5.0 x 10(6) M(-1) in acetone with paraquat, 9000 times greater than the crown ether system. X-ray structures of this and analogous complexes demonstrate that improved complexation with this host is a consequence of preorganization, adequate ring size for occupation by the guest, and the proper location of the pyridyl N-atom for binding to the beta-pyridinium hydrogens of the paraquat guests. This readily accessible cryptand is one of the most powerful hosts reported for paraquats.
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