title: Bis(oxofluorenediyl)oxacyclophanes: synthesis, crystal structure and complexation with paraquat in the gas phase.
abstract: The first three representatives of the new family of oxacyclophanes incorporating two 2,7-dioxyfluorenone fragments, connected by [-CH(2)CH(2)O-](m) spacers (m=2-4), have been synthesized. The yield of the smallest oxacyclophane (m=2) is considerably higher with respect to the larger ones (m=3 and m=4), which are formed in comparable yields. Molecular modeling and NMR spectra analysis of the model compounds suggest that an essential difference in oxacyclophanes yields is caused by formation of quasi-cyclic intermediates, which are preorganized for macrocyclization owing to intramolecular pi-pi stacking interactions between the fluorenone units. The solid-state structures of these oxacyclophanes exhibit intra- and intermolecular pi-pi stacking interactions that dictate their rectangular shape in the fluorenone backbone and crystal packing of the molecules with the parallel or T-shape arrangement. The crystal packing in all cases is also sustained by weak C--HO hydrogen bonds. FAB mass spectral analysis of mixtures of the larger oxacyclophanes (m=3 and m=4) and a paraquat moiety revealed peaks corresponding to the loss of one and two PF(6) (-) counterions from the 1:1 complexes formed. However, no signals were observed for complexes of the paraquat moiety with the smaller oxacyclophane (m=2). Computer molecular modeling of complexes revealed a pseudorotaxane-like incorporation of the paraquat unit, sandwiched within a macrocyclic cavity between the almost parallel-aligned fluorenone rings of the larger oxacyclophanes (m=3 and m=4). In contrast to this, only external complexes of the smallest oxacyclophane (m=2) with a paraquat unit have been found in the energy window of 10 kcal mol(-1).
authors.affiliation: Department of Fine Organic Synthesis, A. V. Bogatsky Physico-Chemical Institute, National Academy of Sciences of Ukraine, Lustdorfskaya doroga 86, 65080 Odessa, Ukraine. ngl@farlep.net
authors.forename: Nikolay G
authors.initials: NG
authors.lastname: Lukyanenko
authors.forename: Tatiana I
authors.initials: TI
authors.lastname: Kirichenko
authors.forename: Alexander Yu
authors.initials: AY
authors.lastname: Lyapunov
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Mazepa
authors.forename: Yurii A
authors.initials: YA
authors.lastname: Simonov
authors.forename: Marina S
authors.initials: MS
authors.lastname: Fonari
authors.forename: Mark M
authors.initials: MM
authors.lastname: Botoshansky