title: Bis(m-phenylene)-32-crown-10-based cryptands, powerful hosts for paraquat derivatives.
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.
authors.affiliation: Department of Chemistry, Virginia Polytechnic Institute & State University, Blacksburg, VA 24061, USA.
authors.forename: Feihe
authors.initials: F
authors.lastname: Huang
authors.forename: Karen A
authors.initials: KA
authors.lastname: Switek
authors.forename: Lev N
authors.initials: LN
authors.lastname: Zakharov
authors.forename: Frank R
authors.initials: FR
authors.lastname: Fronczek
authors.forename: Carla
authors.initials: C
authors.lastname: Slebodnick
authors.forename: Matthew
authors.initials: M
authors.lastname: Lam
authors.forename: James A
authors.initials: JA
authors.lastname: Golen
authors.forename: William S
authors.initials: WS
authors.lastname: Bryant
authors.forename: Philip E
authors.initials: PE
authors.lastname: Mason
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.forename: Mehdi
authors.initials: M
authors.lastname: Ashraf-Khorassani
authors.forename: Harry W
authors.initials: HW
authors.lastname: Gibson
mesh_terms: D018360:Crystallography, X-Ray; D004988:Ethers, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008968:Molecular Conformation; D015394:Molecular Structure; D010269:Paraquat / Q000031:analogs & derivatives* / Q000737:chemistry*; D012545:Schiff Bases / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D004988:Ethers, Cyclic; D012545:Schiff Bases; C444241:cryptand; D010269:Paraquat